#dipole selection rules

[dat-physics-gal]

Explain to me dipole selection rules please I beg

Okay, so for a transition between energy eigenstates, there needs to be an exchange of a photon with the correct energy. I'm assuming you know that.

Since photons are waves of the electromagnetic field, they impose an electric moment on charged particles, which in a vast majority of cases can be modeled as a simple dipole moment.

Now here's where the quantum mechanics starts: The dipole moment is expressed as a linear operator, which when applied to the wave function of a particular state gives you back the eigenvalue for the dipole moment of that state. However, since we want to describe the transition between states, and the operator only applies to the ket of the wave function, the bra and the ket which it is nestled in between are of the different states, aka the starting and the final electron state.

The operator applies to the starting state ket, which can then be completed on the left with the final state bra, and then integrated over to obtain the transition dipole moment integral.

This integral will tell you the expectation value for the transition. For the selection rules, you don't actually have to precisely calculate this integral, you just have to find out whether or not it is zero, because if it is, that means you have an impossible transition on your hands.

Depending on your representation, the dipole operator as well as the wave functions will look different, as will the space you integrate over.

So first, find which representation (spatial, spherical, momentum space, etc.) you are working with, how the dipole operator looks for that representation, and then pick the two states you want to see if a dipole transition exists between them.

The tricky part is usually to get the wave function representation right, and then to leverage the symmetries of that function to determine if the value of the integral is zero or not. The representation that i find most common for tasks like this is this one, which separates the wave function into a radial and two angular parts. It is also already conveniently expressed in terms of 3 quantum numbers, that being the main quantum number n, the orbital angular momentum number l, and the magnetic quantum number m.

I am afraid you'll have to learn the quirks and symmetries of the generalized Laguerre polynomials as well as the spherical harmonics, in order to make statements about the transition dipole moment integral. However, once you get a feel for their symmetries and remember in what special cases integrals vanish (like integrating an odd function over a symmetric interval, etc.) you will be able to derive the selection rules.

I know this wasn't a simple and easy answer, but, well, this is quantum mechanics, to be fair. Hope that helped anyway.

[ionthevoid]

I'm taking hormones, doing dark magic, and emitting photons that violate electric dipole selection rules. Call that a forbidden transition.

[enetarch-quantum-physics]

Topics to study for Quantum Physics

Calculus

Taylor Series

Sequences of Functions

Transcendental Equations

Differential Equations

Linear Algebra

Separation of Variables

Scalars

Vectors

Matrixes

Operators

Basis

Vector Operators

Inner Products

Identity Matrix

Unitary Matrix

Unitary Operators

Evolution Operator

Transformation

Rotational Matrix

Eigen Values

Coefficients

Linear Combinations

Matrix Elements

Delta Sequences

Vectors

Basics

Derivatives

Cartesian

Polar Coordinates

Cylindrical

Spherical

LaPlacian

Generalized Coordinate Systems

Waves

Components of Equations

Versions of the equation

Amplitudes

Time Dependent

Time Independent

Position Dependent

Complex Waves

Standing Waves

Nodes

AntiNodes

Traveling Waves

Plane Waves

Incident

Transmission

Reflection

Boundary Conditions

Probability

Probability

Probability Densities

Statistical Interpretation

Discrete Variables

Continuous Variables

Normalization

Probability Distribution

Conservation of Probability

Continuum Limit

Classical Mechanics

Position

Momentum

Center of Mass

Reduce Mass

Action Principle

Elastic and Inelastic Collisions

Physical State

Waves vs Particles

Probability Waves

Quantum Physics

Schroedinger Equation

Uncertainty Principle

Complex Conjugates

Continuity Equation

Quantization Rules

Heisenburg's Uncertianty Principle

Schroedinger Equation

TISE

Seperation from Time

Stationary States

Infinite Square Well

Harmonic Oscillator

Free Particle

Kronecker Delta Functions

Delta Function Potentials

Bound States

Finite Square Well

Scattering States

Incident Particles

Reflected Particles

Transmitted Particles

Motion

Quantum States

Group Velocity

Phase Velocity

Probabilities from Inner Products

Born Interpretation

Hilbert Space

Observables

Operators

Hermitian Operators

Determinate States

Degenerate States

Non-Degenerate States

n-Fold Degenerate States

Symetric States

State Function

State of the System

Eigen States

Eigen States of Position

Eigen States of Momentum

Eigen States of Zero Uncertainty

Eigen Energies

Eigen Energy Values

Eigen Energy States

Eigen Functions

Required properties

Eigen Energy States

Quantification

Negative Energy

Eigen Value Equations

Energy Gaps

Band Gaps

Atomic Spectra

Discrete Spectra

Continuous Spectra

Generalized Statistical Interpretation

Atomic Energy States

Sommerfels Model

The correspondence Principle

Wave Packet

Minimum Uncertainty

Energy Time Uncertainty

Bases of Hilbert Space

Fermi Dirac Notation

Changing Bases

Coordinate Systems

Cartesian

Cylindrical

Spherical - radii, azmithal, angle

Angular Equation

Radial Equation

Hydrogen Atom

Radial Wave Equation

Spectrum of Hydrogen

Angular Momentum

Total Angular Momentum

Orbital Angular Momentum

Angular Momentum Cones

Spin

Spin 1/2

Spin Orbital Interaction Energy

Electron in a Magnetic Field

ElectroMagnetic Interactions

Minimal Coupling

Orbital magnetic dipole moments

Two particle systems

Bosons

Fermions

Exchange Forces

Symmetry

Atoms

Helium

Periodic Table

Solids

Free Electron Gas

Band Structure

Transformations

Transformation in Space

Translation Operator

Translational Symmetry

Conservation Laws

Conservation of Probability

Parity

Parity In 1D

Parity In 2D

Parity In 3D

Even Parity

Odd Parity

Parity selection rules

Rotational Symmetry

Rotations about the z-axis

Rotations in 3D

Degeneracy

Selection rules for Scalars

Translations in time

Time Dependent Equations

Time Translation Invariance

Reflection Symmetry

Periodicity

Stern Gerlach experiment

Dynamic Variables

Kets, Bras and Operators

Multiplication

Measurements

Simultaneous measurements

Compatible Observable

Incompatible Observable

Transformation Matrix

Unitary Equivalent Observable

Position and Momentum Measurements

Wave Functions in Position and Momentum Space

Position space wave functions

momentum operator in position basis

Momentum Space wave functions

Wave Packets

Localized Wave Packets

Gaussian Wave Packets

Motion of Wave Packets

Potentials

Zero Potential

Potential Wells

Potentials in 1D

Potentials in 2D

Potentials in 3D

Linear Potential

Rectangular Potentials

Step Potentials

Central Potential

Bound States

UnBound States

Scattering States

Tunneling

Double Well

Square Barrier

Infinite Square Well Potential

Simple Harmonic Oscillator Potential

Binding Potentials

Non Binding Potentials

Forbidden domains

Forbidden regions

Quantum corral

Classically Allowed Regions

Classically Forbidden Regions

Regions

Landau Levels

Quantum Hall Effect

Molecular Binding

Quantum Numbers

Magnetic

Withal

Principle

Transformations

Gauge Transformations

Commutators

Commuting Operators

Non-Commuting Operators

Commutator Relations of Angular Momentum

Pauli Exclusion Principle

Orbitals

Multiplets

Excited States

Ground State

Spherical Bessel equations

Spherical Bessel Functions

Orthonormal

Orthogonal

Orthogonality

Polarized and UnPolarized Beams

Ladder Operators

Raising and Lowering Operators

Spherical harmonics

Isotropic Harmonic Oscillator

Coulomb Potential

Identical particles

Distinguishable particles

Expectation Values

Ehrenfests Theorem

Simple Harmonic Oscillator

Euler Lagrange Equations

Principle of Least Time

Principle of Least Action

Hamilton's Equation

Hamiltonian Equation

Classical Mechanics

Transition States

Selection Rules

Coherent State

Hydrogen Atom

Electron orbital velocity

principal quantum number

Spectroscopic Notation

=====

Common Equations

Energy (E) .. KE + V

Kinetic Energy (KE) .. KE = 1/2 m v^2

Potential Energy (V)

Momentum (p) is mass times velocity

Force equals mass times acceleration (f = m a)

Newtons' Law of Motion

Wave Length (λ) .. λ = h / p

Wave number (k) ..

k = 2 PI / λ

= p / h-bar

Frequency (f) .. f = 1 / period

Period (T) .. T = 1 / frequency

Density (λ) .. mass / volume

Reduced Mass (m) .. m = (m1 m2) / (m1 + m2)

Angular momentum (L)

Waves (w) ..

w = A sin (kx - wt + o)

w = A exp (i (kx - wt) ) + B exp (-i (kx - wt) )

Angular Frequency (w) ..

w = 2 PI f

= E / h-bar

Schroedinger's Equation

-p^2 [d/dx]^2 w (x, t) + V (x) w (x, t) = i h-bar [d/dt] w(x, t)

-p^2 [d/dx]^2 w (x) T (t) + V (x) w (x) T (t) = i h-bar [d/dt] w(x) T (t)

Time Dependent Schroedinger Equation

[ -p^2 [d/dx]^2 w (x) + V (x) w (x) ] / w (x) = i h-bar [d/dt] T (t) / T (t)

E w (x) = -p^2 [d/dx]^2 w (x) + V (x) w (x)

E i h-bar T (t) = [d/dt] T (t)

TISE - Time Independent

H w = E w

H w = -p^2 [d/dx]^2 w (x) + V (x) w (x)

H = -p^2 [d/dx]^2 + V (x)

-p^2 [d/dx]^2 w (x) + V (x) w (x) = E w (x)

Conversions

Energy / wave length ..

E = h f

E [n] = n h f

= (h-bar k[n])^2 / 2m

= (h-bar n PI)^2 / 2m

= sqr (p^2 c^2 + m^2 c^4)

Kinetic Energy (KE)

KE = 1/2 m v^2

= p^2 / 2m

Momentum (p)

p = h / λ

= sqr (2 m K)

= E / c

= h f / c

Angular momentum ..

p = n h / r, n = [1 .. oo] integers

Wave Length ..

λ = h / p

= h r / n (h / 2 PI)

= 2 PI r / n

= h / sqr (2 m K)

Constants

Planks constant (h)

Rydberg's constant (R)

Avogadro's number (Na)

Planks reduced constant (h-bar) .. h-bar = h / 2 PI

Speed of light (c)

electron mass (me)

proton mass (mp)

Boltzmann's constant (K)

Coulomb's constant

Bohr radius

Electron Volts to Jules

Meter Scale

Gravitational Constant is 6.7e-11 m^3 / kg s^2

History of Experiments

Light

Interference

Diffraction

Diffraction Gratings

Black body radiation

Planks formula

Compton Effect

Photo Electric Effect

Heisenberg's Microscope

Rutherford Planetary Model

Bohr Atom

de Broglie Waves

Double slit experiment

Light

Electrons

Casmir Effect

Pair Production

Superposition

Schroedinger's Cat

EPR Paradox

Examples

Tossing a ball into the air

Stability of the Atom

2 Beads on a wire

Plane Pendulum

Wave Like Behavior of Electrons

Constrained movement between two concentric impermeable spheres

Rigid Rod

Rigid Rotator

Spring Oscillator

Balls rolling down Hill

Balls Tossed in Air

Multiple Pullys and Weights

Particle in a Box

Particle in a Circle

Experiments

Particle in a Tube

Particle in a 2D Box

Particle in a 3D Box

Simple Harmonic Oscillator

Scattering Experiments

Diffraction Experiments

Stern Gerlach Experiment

Rayleigh Scattering

Ramsauer Effect

Davisson–Germer experiment

Theorems

Cauchy Schwarz inequality

Fourier Transformation

Inverse Fourier Transformation

Integration by Parts

Terminology

Levi Civita symbol

Laplace Runge Lenz vector

[studychemistrytopics]

Infrared Absorption Spectrum of Molecules

Some specific features required for a molecule to show the infrared absorptions spectrum. Therefore an electric dipole moment of the molecule must change during the vibration. This is the selection rule for infrared spectroscopy.

For an example of an ‘infrared-active’ molecule, a heteronuclear diatomic molecule. The dipole moment of such a molecule changes as the bond expands and contracts.

For an example of an ‘infrared-inactive’ molecule is a homonuclear diatomic molecule because its dipole moment remains zero no matter how long the chemical bond.

Electromagnetic spectrum of Infrared region are not infinitely narrow and there are several factors that contribute to the broadening.

For gases, the Doppler effect, in which radiation is shifted in frequency when the radiation source is moving towards or away from the observer, is a factor.

There is also the broadening of bands due to the collisions between molecules.

Another source of line broadening is the finite lifetime of the states involved in the transition. From quantum mechanics, when the Schrodinger equation is solved for a system that is changing with time, the energy states of the system do not have precisely defined energies and this leads to lifetime broadening.

There is a relationship between the lifetime of an excited state and the bandwidth of the absorption band associated with the transition to the excited state, and this is a consequence of the Heisenberg Uncertainty Principle. This relationship demonstrates that the shorter the lifetime of a state, then the less well defined it is its energy.

[toppersexam]

GATE Life Science Question Paper, Exam Pattern, Mock Test, MCQ

GATE Life Science Question Paper, Exam Pattern, Mock Test, MCQ The Graduate Aptitude Test in Engineering is an examination that primarily tests the comprehensive understanding of various undergraduate subjects in engineering and science for admission into the Masters Program of institutes as well as jobs at Public Sector Companies. GATE Life Science Question Paper and MCQs Buy the question bank or online quiz of GATE Life Science Exam Going through the GATE Life Science Exam Question Bank is a must for aspirants to both understand the exam structure as well as be well prepared to attempt the exam. The first step towards both preparation as well as revision is to practice from GATE Life Science Exam with the help of Question Bank or Online quiz. We will provide you the questions with detailed answer. GATE Life Science Question Paper and MCQs : Available Now GATE Life Science Mock Test Crack GATE Life Science Recruitment exam with the help of online mock test Series or Free Mock Test. 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Structure and bonding: Ionic and covalent bonding, MO and VB approaches for diatomic molecules, VSEPR theory and shape of molecules, hybridization, resonance, dipole moment, structure parameters such as bond length, bond angle and bond energy, hydrogen bonding and van der Waals interactions. Ionic solids, ionic radii and lattice energy (Born‐Haber cycle). HSAB principle. s.p. and d Block Elements: Oxides, halides and hydrides of alkali, alkaline earth metals, B, Al, Si, N, P, and S. General characteristics of 3d elements. Coordination complexes: valence bond and crystal field theory, color, geometry, magnetic properties and isomerism. Chemical Equilibria: Colligative properties of solutions, ionic equilibria in solution, solubility product, common ion effect, hydrolysis of salts, pH, buffer and their applications. Equilibrium constants (Kc, Kp and Kx) for homogeneous reactions. 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Ecology and Environment: Ecosystems – types, dynamics, degradation, ecological succession; food chains and energy flow; vegetation types of the world, pollution and global warming, speciation and extinction, conservation strategies, cryopreservation, phytoremediation. 3. Microbiology Historical Perspective: Discovery of microbial world; Landmark discoveries relevant to the field of microbiology; Controversy over spontaneous generation; Role of microorganisms in transformation of organic matter and in the causation of diseases. Methods in Microbiology: Pure culture techniques; Theory and practice of sterilization; Principles of microbial nutrition; Enrichment culture techniques for isolation of microorganisms; Light-, phase contrast- and electron-microscopy. Microbial Taxonomy and Diversity: Bacteria, Archea and their broad classification; Eukaryotic microbes: Yeasts, molds and protozoa; Viruses and their classification; Molecular approaches to microbial taxonomy. 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Microbial Metabolism: Energetics: redox reactions and electron carriers; An overview of metabolism; Glycolysis; Pentose-phosphate pathway; Entner-Doudoroff pathway; Glyoxalate pathway; The citric acid cycle; Fermentation; Aerobic and anaerobic respiration; Chemolithotrophy; Photosynthesis; Calvin cycle; Biosynthetic pathway for fatty acids synthesis; Common regulatory mechanisms in synthesis of amino acids; Regulation of major metabolic pathways. Microbial Diseases and Host Pathogen Interaction: Normal microbiota; Classification of infectious diseases; Reservoirs of infection; Nosocomial infection; Emerging infectious diseases; Mechanism of microbial pathogenicity; Nonspecific defense of host; Antigens and antibodies; Humoral and cell mediated immunity; Vaccines; Immune deficiency; Human diseases caused by viruses, bacteria, and pathogenic fungi. Chemotherapy/Antibiotics: General characteristics of antimicrobial drugs; Antibiotics: Classification, mode of action and resistance; Antifungal and antiviral drugs. Microbial Genetics: Types of mutation; UV and chemical mutagens; Selection of mutants; Ames test for mutagenesis; Bacterial genetic system: transformation, conjugation, transduction, recombination, plasmids, transposons; DNA repair; Regulation of gene expression: repression and induction; Operon model; Bacterial genome with special reference to E.coli; Phage λ and its life cycle; RNA phages; RNA viruses; Retroviruses; Basic concept of microbial genomics. Microbial Ecology: Microbial interactions; Carbon, sulphur and nitrogen cycles; Soil microorganisms associated with vascular plants. 4. Zoology Animal world: Animal diversity, distribution, systematics and classification of animals, phylogenetic relationships. Evolution: Origin and history of life on earth, theories of evolution, natural selection, adaptation, speciation. Genetics: Basic Principles of inheritance, molecular basis of heredity, sex determination and sex-linked characteristics, cytoplasmic inheritance, linkage, recombination and mapping of genes in eukaryotes, population genetics. Biochemistry and Molecular Biology: Nucleic acids, proteins, lipids and carbohydrates; replication, transcription and translation; regulation of gene expression, organization of genome, Kreb’s cycle, glycolysis, enzyme catalysis, hormones and their actions, vitamins Cell Biology: Structure of cell, cellular organelles and their structure and function, cell cycle, cell division, chromosomes and chromatin structure. Gene expression in Eukaryotes : Eukaryotic gene organization and expression (Basic principles of signal transduction). Animal Anatomy and Physiology: Comparative physiology, the respiratory system, circulatory system, digestive system, the nervous system, the excretory system, the endocrine system, the reproductive system, the skeletal system, osmoregulation. Parasitology and Immunology: Nature of parasite, host-parasite relation, protozoan and helminthic parasites, the immune response, cellular and humoral immune response, evolution of the immune system. Development Biology: Embryonic development, cellular differentiation, organogenesis, metamorphosis, genetic basis of development, stem cells. Ecology: The ecosystem, habitats, the food chain, population dynamics, species diversity, zoogerography, biogeochemical cycles, conservation biology. Animal Behaviour: Types of behaviours, courtship, mating and territoriality, instinct, learning and memory, social behaviour across the animal taxa, communication, pheromones, evolution of animal behaviour. GATE 2021 LX Exam Pattern Duration : 180 Mint Negative Mark : 0.66 SectionNo. of QuestionsMarksMarks/QuestionsTotal Marks General Aptitude5 55 51 25 10 Technical, Engineering, Mathematics25 3025 301 225 60 Total65  100

[montdigital1]

Is titanium magnetic

Is Titanium Magnetic An implant worth considering? What does it do? How is it different from similar medical implants? Is it safe?

In a nutshell, titanium is relatively weakly magnetized (compared to much stronger non-magnetic materials) when an external magnetic field is applied to it. It exhibits the Lenz effect but to a much lesser extent than other alloys. However, it does have the potential to provide a higher level of magnetic field than other metallic alloys.

Is this enough to suggest that this metal is capable of producing an implanted magnetic field? Let us imagine that a bar of metal is placed just a few millimeters from the titanium implant. If the titanium has no moving magnets, the surrounding metals will push on the implant, causing the insertion to move away. If the implant is moving with a high level of magnetic force, the metal will push back against the moving magnet, forcing the implant back into the proper location.

Is it likely that such high magnetic fields can be maintained over long periods of time? There are some alloys that are more efficient at generating such forces, but this efficiency comes at a price. Since nickel is quite a costly metal, and because nickel itself is also rather inert, the efficient alloys are too expensive to use. The best alternative is to use an alloy with a low density, but with sufficient magnetic property for MRI applications: gold, lead, ruthenium, and nickel alloys are the most common choice.

Is there a way to maintain the strong attraction between the titanium and the other metallic alloys? Is there a way to directly apply an externally applied magnetic fields to the surface of the titanium? Several experiments show that the surface of titanium can be effectively probed using a strong magnetic field; it is shown that a localized strong current produces a strong magnetic field inside the titanium. However, these experiments did not address the effect of the magnetic field on the implant, or the way in which the implant and the titanium are being held together. These experiments therefore cannot rule out the idea that the surface of the titanium is maintained by a magnetic force, but they do indicate that a strong external magnetic field can be used to keep the titanium stable during surgery.

Is it possible to design new metallic materials that have similar properties to the nickel-titanium or ruthenium alloys? Materials having similar electrical and magnetic properties are likely to exist, but these properties may be different from those of nickel and other metallic alloys. This is why it is important to investigate the properties of alloys before selecting one for implantation. For instance, some of these alloys may have a dipole moment, where the dipole moment of one piece is opposite that of the other piece. If such a property is found, then it would be possible to fabricate a metal with similar properties using only one alloy instead of two. The same will hold true for other magnetic properties.

Theoretically, one could use a single metal to create a magnetic field by applying only a very strong external field, which is in the form of a direct current, between the two metals. Such a technique could apply a paramagnetic material to any kind of metal, including stainless steel and titanium. In order to construct a paramagnetic object, a series of dipoles would need to be arranged in a way that creates a small permanent magnetic field in a conductive piece of metal. It should be noted that the construction of such a device would involve strong current passing through the pieces in the circuit.

Is there a relationship between the strength of the intrinsic magnetic field and the level of magnetic susceptibility of the object? It is believed that the intrinsic field is proportional to the total size of the object and its weight. In such a case, the smaller the object, the lesser the susceptibility towards developing a permeable field. On the other hand, larger objects have high values of magnetic susceptibility and this leads to the conclusion that metallic objects with high magnitudes of magnetism tend to reduce the permeability of a field. This is the main idea behind why titanium is such a good conductor. Is titanium magnetic

[friedaromo186-blog]

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[raymondmccullers]

New high-energy-density physics research provides insights about the universe

Researchers have applied physics theory and calculations to predict the presence of two new phenomena — interspecies radiative transition (IRT) and the breakdown of the dipole selection rule — in the transport of radiation in atoms and molecules under high-energy-density (HED) conditions. The research enhances an understanding of HED science and could lead to more information about how stars and other astrophysical objects evolve in the universe. New high-energy-density physics research provides insights about the universe syndicated from https://triviaqaweb.blogspot.com/

[chhatramani]

New high-energy-density physics research provides insights about the universe Latest Science News -- ScienceDaily New high-energy-density physics research provides insights about the universe #EngineeringCy Researchers have applied physics theory and calculations to predict the presence of two new phenomena -- interspecies radiative transition (IRT) and the breakdown of the dipole selection rule -- in the transport of radiation in atoms and molecules under high-energy-density (HED) conditions.

[fumpkins]

New high-energy-density physics research provides insights about the universe

Atoms and molecules behave very differently at extreme temperatures and pressures. Although such extreme matter doesn’t exist naturally on the earth, it exists in abundance in the universe, especially in the deep interiors of planets and stars. Understanding how atoms react under high-pressure conditions—a field known as high-energy-density physics (HEDP)–gives scientists valuable insights into the fields of planetary science, astrophysics, fusion energy, and national security.

One important question in the field of HED science is how matter under high-pressure conditions might emit or absorb radiation in ways that are different from our traditional understanding.

In a paper published in Nature Communications, Suxing Hu, a distinguished scientist and group leader of the HEDP Theory Group at the University of Rochester Laboratory for Laser Energetics (LLE), together with colleagues from the LLE and France, has applied physics theory and calculations to predict the presence of two new phenomena—interspecies radiative transition (IRT) and the breakdown of dipole selection rule—in the transport of radiation in atoms and molecules under HEDP conditions. The research enhances an understanding of HEDP and could lead to more information about how stars and other astrophysical objects evolve in the universe.

WHAT IS INTERSPECIES RADIATIVE TRANSITION (IRT)?

Radiative transition is a physics process happening inside atoms and molecules, in which their electron or electrons can “jump” from different energy levels by either radiating/emitting or absorbing a photon. Scientists find that, for matter in our everyday life, such radiative transitions mostly happen within each individual atom or molecule; the electron does its jumping between energy levels belonging to the single atom or molecule, and the jumping does not typically occur between different atoms and molecules.

However, Hu and his colleagues predict that when atoms and molecules are placed under HED conditions, and are squeezed so tightly that they become very close to each other, radiative transitions can involve neighboring atoms and molecules.

“Namely, the electrons can now jump from one atom’s energy levels to those of other neighboring atoms,” Hu says.

WHAT IS THE DIPOLE SELECTION RULE?

Electrons inside an atom have specific symmetries. For example, “s-wave electrons” are always spherically symmetric, meaning they look like a ball, with the nucleus located in the atomic center; “p-wave electrons,” on the other hand, look like dumbbells. D-waves and other electron states have more complicated shapes. Radiative transitions will mostly occur when the electron jumping follows the so-called dipole selection rule, in which the jumping electron changes its shape from s-wave to p-wave, from p-wave to d-wave, etc.

Under normal, non-extreme conditions, Hu says, “one hardly sees electrons jumping among the same shapes, from s-wave to s-wave and from p-wave to p-wave, by emitting or absorbing photons.”

However, as Hu and his colleagues found, when materials are squeezed so tightly into the exotic HED state, the dipole selection rule is often broken down.

“Under such extreme conditions found in the center of stars and classes of laboratory fusion experiments, non-dipole x-ray emissions and absorptions can occur, which was never imagined before,” Hu says.

USING SUPERCOMPUTERS TO STUDY HEDP

The researchers used supercomputers at both the University of Rochester’s Center for Integrated Research Computing (CIRC) and at the LLE to conduct their calculations.

“Thanks to the tremendous advances in high-energy laser and pulsed-power technologies, ‘bringing stars to the Earth’ has become reality for the past decade or two,” Hu says.

Hu and his colleagues performed their research using the density-functional theory (DFT) calculation, which offers a quantum mechanical description of the bonds between atoms and molecules in complex systems. The DFT method was first described in the 1960s, and was the subject of the 1998 Nobel Prize in Chemistry. DFT calculations have been continually improved since. One such improvement to enable DFT calculations to involve core electrons was made by Valentin Karasev, a scientist at the LLE and a co-author of the paper.

The results indicate there are new emission/absorption lines appearing in the x-ray spectra of these extreme matter systems, which are from the previously-unknown channels of IRT and the breakdown of dipole selection rule.

Hu and Philip Nilson, a senior scientist at the LLE and co-author of the paper, are currently planning future experiments that will involve testing these new theoretical predictions at the OMEGA laser facility at the LLE. The facility lets users create exotic HED conditions in nanosecond timescales, allowing scientists to probe the unique behaviors of matters at extreme conditions.

“If proved to be true by experiments, these new discoveries will profoundly change how radiation transport is currently treated in exotic HED materials,” Hu says. “These DFT-predicted new emission and absorption channels have never been considered so far in textbooks.”

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This research is based upon work supported by the United States Department of Energy National Nuclear Security Administration and the New York State Energy Research and Development Authority. The work is partially supported by the National Science Foundation.

The LLE was established at the University in 1970 and is the largest US DOE university-based research program in the nation. As a nationally funded facility, supported by the National Nuclear Security Administration as part of its Stockpile Stewardship Program, the LLE conducts implosion and other experiments to explore fusion as a future source of energy, to develop new laser and materials technologies, and to conduct research and develop technology related to HED phenomena.

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300+ TOP BIOCHEMISTRY Interview Questions and Answers

BioChemistry Interview Questions for freshers experienced :-

1. Give the example for electrophilic substitution reaction. The species, which accepts the electrons, are called Electrophilles (or) Electrophilic reagents. When the atom (or) group of atoms present in the organic compound is replaced by another atom (or) group of atoms (electrophilic) is called electrophilic substitution reaction. 2. What is addition reaction? When atoms (or) group of atoms are added, to form more saturated compound it is called addition reaction. 3. How do you define free radical addition reaction? Give an example. When unsaturated compounds undergo addition reactions with free radicals, it is called free radical addition reaction. Ex; CH3-CH = CH2+HBr-----------> CH3-CH2-CH2Br 4. What is nucleophilic addition reaction? When the attacking species during the addition reaction is Nucleophilic, it is nucleophilic addition reaction. Ex; Acetaldehyde cynohydrin 5. What is electrophilic addition reaction? When the attacking species during the addition reaction is Electrophile, it is called electrophilic addition reaction. Ex; (+) (-) (+) (-) (+) (-) CH2Br-CH2BràH2C-CH2+BrBr-àH2C=CH2+Br2- 6. What are the favorable conditions for formation of cat ions? Low Ionisational potential Lesser Charge More atomic size of atoms forms cations easily Ions having Inert gases configuration formed easily 7. What are the favorable conditions for formation of Anions? High Electron affinity Small size Less charge of an atoms form anion more easily 8. Define lattice energy. The energy released when one mole of ionic crystal is formed by the combination of the corresponding gaseous (+ve) and (-ve) ions brought from infinite distance is called lattice energy. 9. What happens if Lattice energy increases? The Strength of ionic bond Stability of the Ionic compound Ease of formation of the Ionic bond Increases 10. What is Sublimation energy? The amount of energy required to convert one mole of solid substance to vapor state is called Sublimation energy

BIOCHEMISTRY Interview Questions 11. What can you calculate by selecting Born-Haber cycle? Born-Haber cycle is useful for calculation of lattice energy, heat of reaction and electron affinity. 12. How can energy change in the formation of NACL be determined? With the help of Born Haber’s cycle 13. What is the relation between reaction taking place in one of the several stages and the total amount of energy liberated in the reaction? The relation between reaction taking place in one of the several stages and the total amount of energy liberated in the reaction is same. 14. Define limiting radius. The ratio between the radius of cation and the radius of anion is called Limiting radius. 15. What is Co-ordination number? The number of appositively charged ions surrounded a particular ion in an ionic crystal lattice is called co- ordination number 16. What is structure of Nacl and give the co-ordination number of Nacl? The structure of Nacl is face centered Cubic and Co- ordination number of Nacl is 6 17. What is the structure of cscl and give the co-ordination number of Cscl? The structure of cscl is Body Centered Cubic and the Co- ordination number of CsCl is 8 18. Ionic compound does not show the property of space isomerism, Give the reason? Ionic bond is Electrostatic. It is non directional, so Ionic compounds does not show the property of Space Isomerism 19. In double bond, how many sigma and Pi bonds are present in it? Double bond = 1 Sigma bond and one Pi bond Among sigma and Pi bonds which is the stronger one Sigma bond is Stronger than pi bond 20. Define polar covalent bond The covalent bond formed by the unequal sharing of electrons between the two atoms is called polar covalent bond. 21. What is dipole? In polar covalent molecule, one atom gets positive charge and the other one gets negative charge hence called dipole. 22. Covalent bond is directional therefore which covalent property is shown? Space Isomerism 23. Which theory explains the paramagnetic nature of oxygen? Who proposed it? Molecular orbital theory, proposed by Hunds and Mulliken 24. Define co-ordination covalent bond. Co-ordination covalent bond is formed by the mutual sharing of pair of electrons between two atoms contributed by only one of the combining atoms. 25. What does one Debye equals? 10-18 e.s.u – Cm 26. If a polar molecule has a charge of 4.8 * 10^ (-10) and internuclear distance is 1A then what is its dipole moment? 4.8 * 10-10 e.s.u * 1A0 4.8 * 10-10 * 10-8 4.8 * 10-18 e.s.u – Cm = 4.8 Debye Give the mathematical expression to calculate or measure the percentage of ionic Character. % of Ionic Character = (Observed dipole moment / Dipole moment of 100% ionic bond)*100 27. Who proposed VSEPR theory? What does it explain? VSEPR theory was proposed by Sedgwick and Powell. It explains the shapes of polyatomic molecules. 28. In water molecule the bond angle decreases from 109.28 to 104.5, why this does happens? The repulsion between lone pair and lone pair electrons In NH3 molecule, the bond angle decreases from 109.28 to 107.3 why does it happen. The more repulsion between lone pair and bond pair 29. Define Hybridization. The distribution of electrons into Hybrid orbitals is as per the Paulis Exclusion principle and the Hunds rule of Maximum Multiplicity. According to which rule the distribution of electrons into hybrid orbital takes place. The distribution of electrons into Hybrid orbitals is as per the Paulis Exclusion principle and the Hunds rule of Maximum Multiplicity. 30. What is the shape of molecules SF6 and IF7? SF6 is Octahedral IF7 is pentagonal Bipyramidal Give the reason why the water molecule has high Boiling point and melting points. Due to the presence of Hydrogen bond in water molecule 31. What are the units of bond length? The intermolecular distance between the bonded atoms in a molecule is called bond length and the units are Angstrom units (A0) 32. What is the order of C-H bond length in C2H6 and C2H4 and C2H2? c2h6>c2h4 >c2h2 33. Define bond angle. The angle between the lines joining the nuclei of the bonded atom with a central atom is called bond angle. 34. Define bond energy. The amount of energy released when one mole of bonds are formed between the corresponding gaseous atoms is called Bond energy. 35. Define the phenomenon resonance. When a molecule is represented by two or more nearly equal structures, which differ in the arrangement of electrons, then the molecule is said to exhibit resonance. 36. Which group of elements is called alkaline earth metals? 1st A group because the oxides and hydrides are alkaline in nature Among 1A group elements why the element lithium is the most powerful, reducing agent in equivalent state Due to its low sublimation and hydration energy 37. What is the property of Alkaline earth metal Ions? Lithium 38. Which metal is more metallic in nature among 1A group elements? Francium 39. Which element in 1A group does not form peroxides? Lithium 40. Which property among the following generally increases from top to bottom in a group 1A? Electropositive, Density, Basic nature, classical reactivity Electropositive, Density, Basic nature, classical reactivity, and solubility generally increase from top to bottom from lithium to caesium. 41. Which property among the following generally decreases from top to bottom in a group 1A? Electropositive, Density, Basic nature, classical reactivity Electro affinity, electro negativity, Ionisational potential, melting and boiling points decreases from top to bottom in a group 1A from lithium to caesium 42. Alkaline metals when dissolved in ammonium (NH3) act as better conductor and better reducing agent what is the reason behind it? Due to formation of solvated or Ammoniated electrons 43. Which element in 1A group is lighter than water? Lithium, Sodium, and potassium 44. What are the raw materials used for the precipitation of Na2Co3 by Solvay ammonium Process? Sodium Chloride, limestone and ammonia 45. Give the chemical formula for Borax. (Na2) B4 (O7) .10(H2) O 46. Give the formula for Peral Ash. The formula for Peral Ash is K2CO3. 47. What are the compounds used for extraction of Gold and Silver? NaCN and KCN 48. Which is the most Abundant Alkaline earth element? Calcium 49. Which is the least abundant Alkaline earth element? Radium 50. What is the Chemical formula for Epsom salt? MgSO4. 7H20 51. Why the 2A group elements are called Alkaline earth elements? The elements occur in earth and the oxides of these metals are basic in nature hence the name alkaline earth metals. 52. Give the formula for baking soda. The formula for baking soda is NaHCO3. 53. What is the name for magnesium per chlorate and what is its formula? Magnesium per chlorate is called Anhydrone {mg (ClO4)2} 54. Bleaching powder is obtained when cl2 is passes through. Dry Slake lime CaOCl2+H2OCa (OH) 2+Cl2 55. What is the ratio of slaked lime and sand in mortar? Ratio is 1:3 56. Which elements are present in Electron? Electron consist of 95 % mg, 5% Zn 57. Which are the most abundant metal and third abundant element in the earth crust? Aluminium (Al) (7.28%) 58. What is inert pair effect? The reluctances of ns electrons in the participation of bond formation is called inert pair effect 59. What is the process, by which Aluminium is refined? By Hoope’s process 60. Which process is used in welding the gaps in railway tracks? Gold Schmidt’s alumino thermi process 61. What does Ammonal contain? For what purpose it is used. It is a mixture of ammonium nitrate and aluminium powder is called ammonal, which is used as an explosive in Bombs. 62. What is Thermite mixture? A mixture of Fe2O3 and ammonium powder in 3:1 ratio is called Thermite mixture. 63. What are hydrides of boron called? Boranes 64. Which Univalent element cannot form Alums and why? Lithium (Li+) does not produce alums because of its very small size. 65. How do we prepare Diborane? The Diborane (B2H6) is prepared by the reduction of BCl3 with aluminium hydride B2H6+3AlCl3+3LiCl4 BCl3+3LiAlH4 66. What is Banana bond? Diborane contains how many banana bonds In Diborane B-H-B, bridge, which is formed by the sharing of two electrons, is called banana bond or Tau bond Diborane contains two banana bonds. 67. Give the formula of Borax. Borax is chemically called as. Borax Na2B4O7 10H2O is chemically called as hydrated sodium tetra borate 68. Garnet is the ore of which element. Give its chemical formula. Garnet is Silicate ore of Aluminium (MgFe) 3 AlSi3O2. 69. How do you call fifth, ‘A’ group elements collectively? Pnicogens Name the family of fifth ‘A’ group elements. Nitrogen Family 70. Which is the most reactive element in Nitrogen family? Phosphorous 71. How much amount of energy is required to break the Triple bond in nitrogen molecule? 225 Kcal/mole or 945.4 KJ/mole 72. How many sigma and pi bonds are present in nitrogen formula? Each nitrogen molecule contain one sigma and 2 Pi bonds 73. What are the important sources of Phosphorus? Sources of Phosphorous are Phosphate rocks • Flourapatite {2Ca3 (PO4)2 CaF2} • Phosphorite {Ca3 (PO4)2} 74. Name two elements, which are Non-metallic in nature in 5th A group? Nitrogen and Phosphorous 75. What is Allotropy? Nitric acid Negative oxidation states of nitrogen are because. Higher Electro negativity 76. What is the molecular formula, Structure, and bond angle of Phosphorous? P4- Phosphorous molecule (Tetra atomic) Structure- Tetrahedral Bond angle – (60 degrees) 77. What is the Anhydride of N2O5? Nitric acid 78. Why nitrogen cannot form penta halides? Because of the absence of d-orbital in its valency shells Ortho Phosphoric acid is. Give oxidation no of phosphorous in it. H3PO4-ortho phosphoric acid Oxidation state of phosphorous is +5 79. What is the Super phosphate of lime? Ca (H2Po4)2 caSO4. 2H2O. Super phosphate of lime is also called as Calcium super Phosphate Sixth group elements are called as. Chalcogens (ore forming elements) 80. What is the other name of sulphur? Brimstone Sulphur molecule exists as. S8 molecule (octa atomic) 81. Which is element exhibit allotrope in the 6thA group? Sulphur 82. Which is the most stable sulphur at room temperature? Rhombic Sulphur 83. Which oxo acids of sulphur contain S-S bonds? Thio acids Thio sulphuric acid is. What are the nature of acid and how many OH? Groups are present in it. Thio Sulphuric acid is H2S2O3 H2S2O7 is. Oxidation state of sulphur in it is. H2S2O7 is Di (or) pyro Sulphuric acid and oxidation state of Sulphur is +6 Oil of Vitriol and king of chemicals is called. H2SO4 Sulphuric acid 84. What is the formula of Hypo in Oxidation state of sulphur? The formula of Sodium Thio Sulphate is Na2S2O3. H2O is called as hypo Oxidation state of Sulphur in it is +6 0r -2 85. How many elements are there in 3d-series of first transition series? Ten elements from Sc (Z=21) to Zn (z=30) or {Sc –scandium to Zn (zinc)} 86. In 3d-series, which two elements exhibit an anomalous configuration? Chromium Cr(Z=24) = 4s1 3 d5 Copper(Cu)(Z=29)= 4s1 3 d10 In transition series the element with maximum Ionization energy is. Zinc – due to stable electronic configuration 86. What is the element in third series the element with maximum oxidation state? Mn – manganese -+7-oxidation state 87. Why FE3+ ion is more stable than Fe2+ ion is? Because of stable, half filled 3 d5 electronic configurations in fe3+ Magnetic property exhibited by which of the following element? Fe, Co, Ni Ferro magnetic 88. Why the transition metal ions or compounds exhibit color? Due to incomplete partially filled d- orbitals 89. In which oxidation state chromium exhibit different color? Chromium is Blue in +2 states, Green in +3 states and Yellow in +6 state. 90. The bond formed between the transition metal ion and ligand is? Co-ordination covalent bond Transitional metal Ions can form complex compounds by. By accepting the lone pair of electrons from ligand 91. Define Ionic product of water. What is its value? The product concentrations H+ and OH- in pure water are in aqueous solutions at a given temperature is known as Ionic Product of water. Its value is 1.0 * 10-14 moles2 / litre2. 92. What is PH? What are the units of PH? PH is the negative logarithm of the hydrogen Ion Concentration express4ed in moles/liter of aqueous solution. PH of buffer solution is calculated by. Henderson’s equation Name the best indicator Phenolphthalein, PH range 8.3 to 10.0 Chemical kinetics deals with study of. Rates and mechanisms of chemical and Biochemical reactions 93. What does Thermodynamics helps in predicting? Predicting the feasibility of reaction and does not indicate the rate of chemical reaction 94. What does the expression –dc/dt indicates? Rate of reaction can be expressed as –dc/dt where dc is small decreasing concentration in time dt seconds, (-) sign indicates that the concentration decreases with time. For every 10 degrees rise of temperature, the rate of reaction is generally. Doubled 94. Which equation gives the relation between specific rate (k) and Temperature? Arrhenius equation K = Ae-E a / R T In some reactions, Rate of reaction is directly proportional to. Concentration of catalyst Catalyst used in Bio-Chemical reactions is called. Enzymes Reactions catalyzed by light are called as. Photo catalyzed or Photosensitised reactions Define order of reaction The order of reaction is the number of moles whose concentrations determine the rate of a reaction at a given temperature Give the integrated equation for first order reaction. K = (2.303 / t) * log (a / a-x) Rate equation of first order reaction is. dx/dt = K * (a-x) where ‘a’ is the initial concentration of reactants ‘x’ is the amount reacted in time t seconds 95. What is Threshold energy? The minimum amount of energy required for the reaction to takes place is called threshold energy. 96. What is activation energy? The difference between Threshold energy and average energy of the molecules is called activation energy. Ina chemical reaction lowers the rate of reaction the greater will be. The activation energy 97. How do you define the molecularity of a reaction? The number of species participating in the slowest step of the reaction is called molecularity of the reaction. Define Equilibrium state The chemical reaction at one time the rate of forward and backward reaction becomes equal that state is called Equilibrium state. In a chemical equilibrium, the following properties remain unchanged with time. Pressure, Temperature, density, color Pressure, Temperature, density, color 98. Who proposed law of mass action? What does it states? Laws of mass action were proposed by Gulberg and Waage. The rate of chemical reaction is directly proportional to the product of the active masses of the reactants (molar concentrations of the reactants) 99. What is Kc? Kc is the equilibrium constants when the concentrations are expressed in moles/litre Kc = product of concentrate ions of products / product of concentrate ions of reactants Mole fraction of the gas X total pressure gives. Partial pressure of a gas 100. The expression q=delta (E)-W is? What does it states? 1st law of thermodynamics may be represented as q= E-W According to this law the energy can neither be created nor destroyed, but can be converted into one form to another. 101. What is Internal energy? Every substance poses definite amount of energy called internal energy or intrinsic energy (E). Property of Enthalpy depends on. Enthalpy is an extensive property, which depends on the amount of substance. For example - mass and volumes 102. How can you determine the reaction, taking place at constant pressure delta (H)? The difference of Enthalpy’s of products and reactants H=Hp-Hr Define heat of Combustion The amount of heat liberated when one mole of any substance is completely burnt in oxygen is called heat of combustion H is negative for heat of combustion. Define standard feat of formation The amount of heat liberated of absorbed when one mole of compound is formed in its standard state from its elements in their standard state is called standard heat of formation ( Hf *) 103. What does Hess law states? Hess law states that the heat of reaction is same whether the reaction takes place in one or several states. Therefore Q=Q1+Q2+Q3+… Hess law is useful to calculate. Heat of reactions Lattice energy of ionic solids can be calculated by using. Hess law- Q = S+1/2 D +I.E-Ea-U 104. What is the lattice energy of Nacl? -796.69k.j 105. Which branch of science deals with the transformation of chemical energy into electrical energy and vice versa? Electrochemistry 106. In electronic conductors, what is the reason for flow of current? Reason for flow of current is that moment of free electrons from higher negative potential to a lower positive potential region. 107. What is Galvanic cell? A Galvanic cell or voltaic cell or electrochemical cell is a system in which a spontaneous chemical oxidation- reduction occurs and generates electrical energy. 108. Which electrode acts as reference electrode and gives its potential value? Standard hydrogen electrode was taken as reference electrode whose potential is assumed zero. Nelsons equation for any cell reaction is given by. E = Eo + (2.303RT /nF) log / 109. To calculate the e.m.f of the cell when does the nelsons equation is use? The Nernst equation is useful to calculate the e.m.f of the cell when the concentrations of solution are different from unity. 110. Define the Phenomenon catenation. Which element has maximum Catenation ability? Carbon has maximum catenation ability. The self-linkage of the atoms of elements to produce long chains is called catenation. Name the first synthetic organic compound. Who proposed it and from which compound? The first synthetic organic compound is Urea. It was prepared by Wohler from ammonium cynate. NH4CNO……………………NH2-CO-NH2 Name the 1st synthetic organic compound that was prepared from its Elements is. Acetic acid What is function group? An atom or group of atoms, which determine the characteristic properties of the Substance it, is called functional group. Give the type of functional group, General formula, and the suffix for Methanoic acid (or) formic acid. Type of functional group is Alkonic acids or Carboxylic acids. The general formula is R-CooH and functional group –COOH. Suffic is –Oic acid. What is Isomerism? Compounds with same molecular formula but different properties are called Isomers and the phenomenon is called Isomerism. What is optical Isomerism? Which compounds exhibit optical Isomerism? Isomers, which differ in the rotation of the plane polarized light, are called Optical Isomerism. How can we calculate the number of possible optical Isomers for a given Compound? 2n-Where n is the number of asymmetric carbon atoms. What is racemic mixture? Why it is optically inactive? Optical Isomers of a substance that are mirror images of each other are called Enantiomers (or) Enantimorphs. Ex: d and L – Lactic acid Optical Isomers of a substance that are not mirror images of each other are called Diastereomers. Ex: d-Tartaric and meso –Tartaric acids What are dextrorotary compounds and Levi rotary compounds? Compounds that rotate the plane polarized light to the right are called Dextro rotatory compounds and that rotate the plane polarized light to the left are called Leavo rotatory. What are enantimorphs and diastereomers ? Optical Isomers of a substance that are mirror images of each other are called Enantiomers (or) Enantimorphs. Ex: d and L – Lactic acid Optical Isomers of a substance that are not mirror images of each other are called Diastereomers. Ex: d-Tartaric and meso –Tartaric acids Define Geometrical Isomerism. Isomers, which differ in the orientation of groups around the double bounded carbon atoms, are called geometrical Isomers. It is also called as Cis-Trans Isomerism. How do you call the Geometrical Isomerism, similar groups are present on same Side? Cis-Isomer In the Geometrical Isomerism, if the similar groups are present on opposite Side is called as. Trans-Isomer Which form of isomers of a substance is more stable? Trans -Isomer of a substance is more stable than Cis-Isomer. Why ethylene undergoes electrophilic addition reactions? Ethylene is unsaturated Hydrocarbon. Due to the presence of loosely bound pi electrons between two carbon atoms ethylene CH2=CH2 is more reactive towards addition reactions. What is markownikoff’s rule? In addition, of hydrogen halides to the unsymmetrical alkens, Hydrogen is added to the carbon atom containing more number of hydrogen atoms and halide is added to the carbon atoms containing lesser number of hydrogen atoms. Ex; CH2-CHBr-CH3àCH3-CH=CH2+HBr-- Iso Prophyl Bromide What is kararch effect? In the addition of the hydrogen, halide to unsaturated alkenes in the presence of peroxides the halide adds to the carbon atom linked to more number of hydrogen atoms and hydrogen adds to the carbon atom linked to lesser number of hydrogen atoms. This is called Peroxide effect (or) Kharasch effect. CH3-CH2-CH2BRàCH3-CH=CH2+HBr- N Prophyl bromide Ethylene on ozonolysis gives. Formaldehyde Ex; àCH2=CH2+O3 2HXH0+H2O2 What is saytzeff’s rule? The formation Alkenes by the dehydration of alcohols (using concentrated H2SO4) the hydrogen atom will be removed (to remove as water) from the adjacent carbon atom linked to the less number of hydrogen atoms. Example: In the dehydration of Butane – 2Ol 2Butane is formed CH3-CH=CH-CH3+H2Oàconcentrated H2SO4àCh3-CH2-CH-CH3 But2-ene Which type of reactions did Acetylene undergoes? Acetylene undergoes both additions as well as substitution reactions Name the vinyl halide that reacts with hydrogen halides and the product Formed is. Vinyl chloride is a vinyl halide Vinyl chloride again reacts with hydrogen halide and produce Ethylidine chloride CH3-CHCl2àCH2=CHCl + HCl Polymers of vinyl chloride are. Polymers of Vinyl chloride are called PVC and it is used as plastic. Aromatic compounds generally undergo which type of reactions Electrophilic substitution reactions Lucas reagent is a mixture of________. Anhydrous ZnCl2 and concentrated HCl Aldehydes and ketones are known as. Carbonyl compounds Aldehydes (CH3Cho) and vinyl alcohol (CH2=CHOH) are? Tautomers Give examples of Tautomers. Ketone (CH3CoCh3) and Enolporm What is Hoffman degradation method? Benz amide on treatment with bromide and Caustic potash produce aniline C6H5NH2+2KBr+2H2O+K2CO3àC6H5CoNH2+Br2+4KOH Aldehydes and ketones characteristically undergo which reactions Aldehydes and ketones characteristically undergo nucleophilic addition reactions. On what structural level of the enzyme (primary, secondary, tertiary, or quaternary) does the enzyme-substrate interaction depend? The substrate binds to the enzyme in the activation centers. These are specific three-dimensional sites and thus they depend on the protein tertiary and quaternary structures. The primary and secondary structures however condition the other structures and so they are equally important. What is the activation center of an enzyme? Is it the key or the lock of the lock and key model? The activation center is a region of the enzyme produced by its spatial conformation to which the substrate binds. In the lock and key model, the activation center is the lock and the substrate is the key. Why can it be said that the enzymatic action is highly specific? The enzymatic action is highly specific because only specific substrates of one enzyme bind to the activation center of that enzyme. Each enzyme generally catalyzes only a specific chemical reaction. What happen to a denaturated enzyme regarding its functionality? How that result can be explained with the help of the lock and key model? According to the lock and key model, the enzyme functionality depends entirely on the integrity of the activation center, a molecular region with specific spatial characteristics. After the denaturation the spatial conformation of the protein is modified, the activation center is destroyed and the enzyme loses its catalytic activity. What are the main factors that alter the speed of enzymatic reactions? The main factors that change the speed of enzymatic reactions are temperature, pH and substrate concentration (quantity). How does the substrate concentration affect the speed of enzymatic reactions? Initially as substrate concentration increases the speed of the reaction increases, this happens because free activation centers of the enzyme bind to free substrates. Once all activation centers of the available enzymes become bound to their substrates new increments of the substrate concentration will have no effect in the speed of the reaction. How does temperature affect the action of enzymes upon their substrates? There are defined temperature ranges under which enzymes operate. There is a specific temperature-level where the enzymes have maximum efficiency. Therefore, temperature variations affect enzymatic activity and the speed of the reactions they catalyze. In addition, as proteins, enzymes can be denaturated under extreme temperatures. Concerning enzymatic reactions how different, are the graphic curve of the variation of the speed of a reaction as function of substrate concentration and the curve of variation of the speed of a reaction as function of temperature? The curve of variation of speed of the enzymatic reaction as function of growing substrate concentration is a growing curves until the point where it stabilizes due to the saturation of the activation centers of the enzymes. The curve of variation of speed of the enzymatic reaction as function of growing temperature has a crescent portion, reaches a peak (the optimum temperature) then it decreases, and reaches zero in the point of inactivity of the enzymes by denaturation. How is the cooling of organs and tissues for medical transplantations associated with the effect of temperature upon enzymatic reactions? The molecular degradation during the decomposition of organs and tissues is catalyzed by enzymes. The cooling to adequate temperatures of some organs and tissues destined to transplantation reduces that enzyme activity and thus lessens the natural decomposition process. By the same rational the cooling reduces the metabolic work of cells and prevents that, they degrade their own structures to obtain energy. Elevation of temperature later revert denaturation of enzymes and the organs and tissues also preserved by other specific techniques may be grafted into the receptors. Does pH affect the enzyme activity? The concentration of hydrogen ions in solution affects the enzyme activity. Each enzyme has maximal efficiency under an optimum pH. Since pH is one of the factors for the denaturation of proteins, if an enzyme is submitted to a pH level under which, it is denaturated there will be no enzymatic activity. Do enzymes act better under acid or basic pH? Most enzymes act in pH between 6 and 8, a range that corresponds to the general acidic level of cells and blood. There are enzymes however, that act only under very acid or very basic pH. Therefore, enzyme activity depends on a pH interval. In the stomach, for example, the gastric juice has a very low pH, around 2, and there the enzyme pepsin acts intensively digesting proteins. In the duodenum, pancreatic secretions increase the pH of the enteric juice for the action of other digestive enzymes, for example, trypsin. Since pepsin is a gastric enzyme does it, has acid or basic optimum pH? What happen to pepsin when it passes to the duodenum? Pepsin acts within the stomach so its optimum pH is around 2, an acid pH. When the enzyme passes to the duodenum, it meets a higher pH and its enzyme activity ends. What are enzyme cofactors? Some enzymes need other associated molecules to work. These molecules are called enzyme cofactors and they can be, for example, organic ions, like mineral salts, or organic molecules. Inactive enzymes for not being bound to their cofactors are called apoenzymes. Active enzymes bound to their cofactors are called holoenzymes. What is the relation between vitamins and enzyme cofactors? Many vitamins are enzyme cofactors that cannot be synthesized by the organism and must be obtained from the diet. What are allosteric enzymes? Allosteric enzymes are those that have more activation center and to which other substances called allosteric regulators bind. Allosteric regulators can be allosteric inhibitors or allosteric activators. The interaction between an allosteric enzyme and the allosteric inhibitor disallows the binding of the substrate to the enzyme. The interaction between the allosteric enzyme and the allosteric activator allows the binding of the substrate to the enzyme and sometimes increases the affinity of the enzyme for the substrate. This regulatory phenomenon of the enzyme activity is called allosterism. Enzyme Activity: allosteric enzymes What are zymogens? Zymogens, or proenzymes, are enzymes secreted in inactive form. Under certain conditions, a zymogen shifts to the active form of the enzyme. Zymogen secretions in general happen because the enzyme activity can harm the secretory tissue. For example, the pepsinogen secreted by the stomach becomes active under acid pH turning into the enzyme pepsin. Other well-known zymogens are trypsinogen and chymotrypsinogen. Enzymes are secreted by the exocrine pancreas and respectively trypsin and chymotrypsin. What are nucleic acids? What is the historic origin of this name? DNA and RNA, the nucleic acids, are the molecules responsible for the hereditary information that commands the protein synthesis in the living beings. The name “nucleic” derives from the fact that they were discovered (by the Swiss biochemist Friedrich Miescher, in 1869) within the cell nucleus. In that time, it was not known that those substances contained the hereditary information. Of what units are, nucleic acids constituted. What are the chemical entities that compose that unit? Nucleic acids are formed by sequences of nucleotides. Nucleotides are constituted by one molecule of sugar (ribose in DNA and deoxyribose in RNA) bound to one molecule of phosphate and to one nitrogen-containing base (adenine, uracil, cytosine, or guanine, in RNA, and adenine, thymine, cytosine, and guanine, in DNA). Nucleic Acid Review - Image Diversity: nucleotide structure nitrogen-containing bases What are pentoses? To what organic group do pentoses belong? Are nucleotides formed of only one type of pentose? Pentoses are carbohydrates made of five carbons. Deoxyribose is the pentose that constitutes DNA nucleotides and ribose is the pentose that is part of RNA nucleotides. Into which two groups can the nitrogen-containing bases that form DNA and RNA be classified? What is the criterion used in that classification? The nitrogen-containing bases that form DNA and RNA are classified as pyrimidine and purine bases. By the analysis of the structural formulas of those nitrogen-containing bases, it is possible to realize that three of them, cytosine, thymine and uracil, have only one nitrogenized carbon ring. The others, adenine and guanine, have two nitrogenized associated carbon rings. Nucleic Acid Review - Image Diversity: pyrimidine bases purine bases Concerning the nitrogen-containing bases that participate in nucleotides what is the difference between DNA and RNA. In DNA, nucleotides can be formed of adenine (A), thymine (T), cytosine (C) or guanine (G). In RNA, nucleotides can also contain adenine (A), cytosine (C) or guanine (G), however, instead of thymine (T) there is uracil (U). Which are the nucleotides “portions” that bind in the formation of nucleic acids? What is meant by the 5’ and 3’ extremities of nucleic acids? The phosphate group of one nucleotide binds to the pentose of the other nucleotide and so on to make the polynucleotide chain. Each extremity of a DNA or RNA chain can be distinguished from the other extremity according to their terminal chemical entity. The phosphate-ended extremity is called 5’-extremity and the pentose-ended extremity is called 3’-extremity. So DNA or RNA chains can be run along the 5’-3’ way or along the 3’-5’ way. These ways are important in several biological functions of DNA and RNA since some reactions specifically occur following one way or the other way. Bacteria are prokaryotic cells, i.e., they do not have membrane-delimited nucleus. Eukaryotes have cells with delimited nucleus. Where in these types of cells can DNA are found? In eukaryotic cells, DNA is found within the cell nucleus. In prokaryotic cells, DNA is found dispersed in the cytosol, the fluid space inside the cell. Other DNA molecules can also be found within mitochondria and chloroplasts, specialized organelles of eukaryotic cells. Who were James Watson, Francis Crik and Maurice Wilkins? Watson (North American), Crick (British) and Wilkins (New Zealander) were the discoverers of the molecular structure of DNA, the double helix made of two polynucleotide chains paired by their nitrogen-containing bases. They won the Nobel Prize of Medicine in 1962 for the discovery. Nucleic Acid Review - Image Diversity: Watson and Crick According to the Watson - Crick Model how many polynucleotide chains does a DNA molecule has? The DNA molecule is formed by two polynucleotide chains bound in antiparallel mode (5’-3’ to 3’-5’) and forming a helical structure. Nucleic Acid Review - Image Diversity: DNA double helix What is the rule for the pairing of nitrogen-containing bases in the DNA molecule and in the RNA? Is this last question appropriate? The rule for the pairing of nitrogen-containing bases of the polynucleotide chains that form the DNA molecule is pyrimidine base binds to purine base, under the condition that thymine (T) binds to adenine (A), and cytosine (C) binds to guanine (G). In RNA, there is no binding between nitrogen-containing bases. That is because RNA is formed of only one polynucleotide chain; differently, DNA is formed of two chains. It is not correct so to question about base pairing in RNA. Nucleic Acid Review - Image Diversity: DNA base paring What is the numeric relation between pyrimidine and purine bases in the DNA molecule? Is that relation valid in RNA molecules? The DNA molecule is made of two bound polynucleotide chains that form a helical structure (the double helix). The binding of the two chains is between their nitrogen-containing bases and it always obey the following rules: adenine (A), a purine base, binds with thymine (T), a pyrimidine base, and guanine (G), a purine base, binds to cytosine (C), a pyrimidine base. Therefore in one molecule of DNA there will be same number of adenine (A) and thymine (T) and same number of cytosine (C) and guanine (G). The quantities of purine and of pyrimidine bases so will also be the same in a 50% proportion for each type. The relation A = T and C = G, or A/T = C/G = 1, is called Chargaff’s relation and the pairing rules described above are known as Chargaff’s rules. In RNA, there are not two nucleotide chains. RNA is a simple chain molecule and there is no necessary proportionality of nitrogen-containing bases to form it. Which type of chemical bond maintains the pairing of each chain in the DNA molecule? To form the DNA molecule, purine bases bind to pyrimidine bases by intermolecular bonds called hydrogen bonds. Hydrogen bonds occur when there is hydrogen near one of these electronegative elements: fluorine, oxygen, or nitrogen. In such conditions hydrogen looks like having, lost electron for those elements and a very strong polarization is created. The highly positive hydrogen attracts pairs of electrons of other molecules making a hydrogen bond. What is the completing sequence of nitrogen-containing bases for an AGCCGTTAAC fragment of a DNA chain? TCGGCAATTG What is the name of the DNA duplication process? What is the main enzyme that participates in it? The process of copying, or duplication, of the DNA molecule is called replication. The enzyme that participates in the formation of a new DNA chain is the DNA polymerase. There are also other important enzymes in the replication process, the helicase, the gyrase and the ligase. Nucleic Acid Review - Image Diversity: DNA replication Why is not it correct to assert that DNA self-replicates? DNA is not completely autonomous in its duplication process because the replication does not occur without enzymatic activity. Therefore, it is not entirely correct to assert that DNA self-replicates. How do the two complementary nucleotide chains of the DNA facilitate the replication process of the molecule? The fact that the DNA molecule is made of two polynucleotide chains whose nitrogen-containing bases form hydrogen bonds facilitates the duplication of the molecule. During the DNA replication, the binding of the two chains is broken and each of them serves as template for the formation of a new nucleotide sequence along it, with the help of the enzyme DNA polymerase and obeying the pairing rule A-T, C-G. At the end of the process two double helix of DNA are produced, each made of an original template chain and of a new synthesized polynucleotide chain. What are the chemical bonds of the DNA molecule that are broken for the replication process to occur? During the DNA replication, process hydrogen bonds between nitrogen-containing bases of the polynucleotide chains are broken. Because of DNA replication, two DNA molecules come to existence. Why is not it correct to assert that two “new” DNA molecules are created? What is the name given to the process concerning that fact? During replication each chain of the DNA molecule act pairing new nucleotides and after the process, two newly formed chains made with the union of these nucleotides appear. Then two DNA molecules are created, each with one chain from the original molecule and one newly chain formed by new nucleotides. Thus, it is not entirely correct to assert that the replication produces two new molecules of DNA. It is better to affirm that two new half-molecules are created. For this phenomenon DNA, replication is called semi conservative replication. Does DNA replication occur in cell division? Yes. DNA replication occurs in mitosis as well in meiosis. One characteristic of the DNA molecule is its replication capability. What are the consequences of failures during DNA replication? Ideally, a DNA molecule should replicate in a perfect way. Sometimes however failures in the duplication occur, with alteration (deletion, addition, or substitution) of one or more nucleotides in the molecule. Those mistakes, or mutations, therefore make changes in the protein synthesis process too. For example, the production of an important protein for cells or tissues may be suppressed new utile or inutile proteins can be created, etc. The mistake in the DNA duplication and the resulting production of altered genetic material are some of the main creative forces for the biological evolution and the diversity of species. Mistakes may happen during every copying process. The same is true for DNA replication. Are there correction systems in cells that try to fix those mistakes? Under which situation are the mistakes carried only by the individual owner of the cell which the mistake has occurred and in which situation are they transmitted to other individuals The cell is equipped with an enzymatic system that tries to fix mistakes of the DNA replication process. This system however is not completely efficient. DNA replication mistakes are kept in the original individual where the failure occurred when the phenomenon affects somatic cells. If a replication mistake occurs in the formation of a germline cell (e.g., in gametes) the DNA alteration may be transmitted to the offspring of the individual. Where can RNA are found within cells? In the eukaryote cell nucleus, RNA can be found dispersed in the nuclear fluid, along with DNA, and as the main constituent of the nucleolus. In cytosol (in eukaryotes or in bacteria) RNA molecules can be found free, as structural constituent of ribosomes (organelles specialized in protein synthesis) or even associated to them in the process of making proteins. Mitochondria and chloroplasts also have their own DNA and RNA. Does RNA molecule have two polynucleotide chains likewise DNA? Only DNA has two polynucleotide chains. RNA is formed just by one polynucleotide chain. Nucleic Acid Review - Image Diversity: RNA molecule How the production of RNA called? What is the enzyme that catalyzes the process? The making of RNA from information contained in DNA is called transcription. The enzyme that catalyzes the process is the RNA polymerase. What are similarities and differences between the transcription process and the replication processes? A DNA polynucleotide chain serves as template in replication (DNA duplication) as well in transcription (RNA formation). In both processes, the pairing of the two-polynucleotide chains of the original DNA molecule is broken by the breaking of hydrogen bonds for the chains to be exposed as templates. The reaction is catalyzed by specific enzymes in transcription and in replication. In replication, the enzyme DNA polymerase catalyzes the formation of a new polynucleotide chain using free nucleotides in solution and putting them in the new chain according to the DNA template exposed and to the rule A-T, C-G. In transcription, the enzyme RNApolymerase makes a new polynucletide chain according to the DNA template exposed obeying, however, the rule A-U, C-G. In replication, the original template DNA chain is kept bound by hydrogen bonds to the newly formed DNA chain and a new DNA molecule is then created. In transcription the association between the template DNA chain and the newly formed RNA is undid and RNA constituted of only one polynucleotide chain is liberated. What are the three main types of RNA? What is meant by heterogeneous RNA? Messenger RNA, or mRNA, transfer RNA, or tRNA, and ribosomal RNA, or rRNA, are the three main types of RNA. The newly formed RNA molecule, a precursor of mRNA, is called heterogeneous RNA (hnRNA). The heterogeneous RNA bears portions called introns and portions called exons. The hnRNA is processed in many chemical steps, introns are removed, and mRNA is created formed only of exons, the biologically active nucleotide sequences. Concerning their biological function what is the difference between DNA and RNA? DNA is the source of information for RNA production (transcription) and thus for protein synthesis. DNA is still the basis of heredity due to its replication capability. The messenger RNA is the template for protein synthesis (translation). In this process, tRNA and rRNA also participate since the first carries amino acids for the polypeptide chain formation and the second is a structural constituent of ribosomes (the organelles where proteins are made). Is there any situation in which DNA is made based on a RNA template? What is the enzyme involved? The process in which DNA is synthesized having as template a RNA chain is called reverse transcription. In cells infected by retroviruses (RNA viruses, like the AIDS or SARS viruses) reverse transcription occurs and DNA is made from information contained in the viral RNA. Viral RNA within the host cell produces DNA with the help of an enzyme called reverse transcriptase. Based on that DNA the host cell then make viral proteins, new virus are assembled and viral replication occurs. Nucleic Acid Review - Image Diversity: reverse transcription Do the phosphate and the pentose groups give homogeneity or heterogeneity to the nucleic acid chains? Supported by that which of those groups is expected to participate in the highly diverse and heterogeneous genetic coding, i.e., which of those groups is the basis of the information for protein production? The phosphate and the pentose groups are the same in every nucleotide that forms the nucleic acid and so they give homogeneity to the molecule. The nitrogen-containing bases however can vary among adenine, thymine, cytosine, guanine (in DNA), and uracil (in RNA). These variations provide the heterogeneity of the nucleic acid molecule. Homogeneous portions of a molecule seldom would store any information, by the same reason that a sequence of the same letter of the alphabet cannot make many words with different meanings. The nitrogen containing bases, on the other hand, because they are different (four different types for RNA or DNA), can make different sequences and combinations that allow the diversity of the genetic code. What is the primary structure of a protein? What is the importance of the primary structure? The primary protein structure is the linear sequence of amino acids that form the molecule. The primary structure is the basis of the protein identity. Modification of only one amino acid of the primary structure creates a different protein. This different protein can be inactive or even can have other biological function. Protein Structure Review - Image Diversity: protein primary structure What is the secondary structure of a protein? The secondary protein structure is generated by the manner its amino acids interact through intermolecular bond. These interactions create a spatial conformation of the polypeptide filament. The two most studied secondary conformations of proteins are the alpha helix and the beta-sheet. Protein Structure Review - Image Diversity: protein secondary structure What is the difference between the alpha helix and the beta-sheet protein conformations? Alpha helix and beta-sheet conformations are the two main types of secondary structure of a protein molecule. According to the primary protein structure, its secondary structure can be of one type or other. In the alpha-helix structure, the polypeptide curls longitudinally by the action of hydrogen bonds forming a spiral, or helix. In the beta-sheet conformation, the protein is more distended and the hydrogen bonds form a zig-zag-shaped protein structure called B-strand. Many assembled beta-strands make a beta-sheet. What is the tertiary structure of a protein? What are the main types of tertiary structure? The tertiary protein structure is a spatial conformation additional to the secondary structure in which the alpha helix or the beta-sheet folds up itself. The forces that keep the tertiary structure generally are interactions between the –R groups of the amino acids and between other parts of the protein and water molecules of the solution. The main types of tertiary structure of proteins are the globular proteins and the fibrous proteins. Protein Structure Review - Image Diversity: protein tertiary structure What is the quaternary structure of a protein? Do all proteins have quaternary structure? The quaternary protein structure is the spatial conformation due to interactions among polypeptide chains that form the protein. Only those proteins made of two or more polypeptide chains have quaternary structure. Insulin (two chains), hemoglobin (four chains), and the immunoglobulins (antibodies, four chains) are some examples of protein having quaternary structure. Protein Structure Review - Image Diversity: protein quaternary structure What is protein denaturizing? Is there any change in the primary structure when a protein is denaturized? Secondary, tertiary, and quaternary structures of proteins are spatial structures. Denaturizing is modification in any of these spatial structures that makes the protein deficient or biologically inactive. After denaturizing, the primary protein structure is not affected. Protein Structure Review - Image Diversity: denaturized protein How can denaturizing be classified regarding its reversibility? Protein denaturizing can be a reversible or an irreversible process, i.e., it can be possible or impossible to make the protein regain its original spatial conformation. What are some factors that can lead to protein denaturizing? Protein denaturizing can be caused by temperature variation, pH change, and changes in the concentration of surrounding solutes and by other processes. Most proteins are denatured after certain elevation of temperature or when in very acid or very basic solutions. This is one of the main reasons, why it is necessary for the organisms to keep adequate temperature and stable pH. Is it expected a change in the primary, in the secondary or in the tertiary structure of a protein to produce more functional consequences? Any change of the protein structure is relevant if it alters its biological activity. Changes in the primary protein structure are more important because they are modifications in the composition of the molecule and such composition determines all other structures of the protein. In sickle cell anemia, a hereditary disease, there is substitution of one amino acid by other in one of the four-polypeptide chains of hemoglobin. In this case, are all of the structural levels of the protein modified? In sickle cell disease, there is change in the primary protein structure of one of the polypeptide chains that form hemoglobin: the amino acid glutamic acid is substituted by the amino acid valine in the ? chain. The spatial conformation of the molecule in addition is also affected and modified by this primary “mistake” and the modification creates a different (sickle) shape of the red blood cells. Modified, sickled, red blood cells sometimes aggregate and obstruct the peripheral circulation causing tissue hypoxia and the pain crisis typical of sickle cell anemia. What is the difference between essential and natural amino acids? Essential amino acids are those that the organism is not able to synthesize and that need to be ingested by the individual. Natural amino acids are those that are produced by the organism. There are living species that produce every amino acid they need, for example, the bacteria Escherichia coli that does not have essential amino acids. Other species, like humans, need to obtain essential amino acids from the diet. Among the twenty different known amino acids that form proteins, humans can make twelve of them and the remaining eight needs to be taken from the proteins they ingest with food. The essential amino acids for humans are phenylalanine, histidine, isoleucine, lysine, methionine, threonine, tryptophane and valine. What are respectively some remarkable functions of myosin, CD4, albumin, keratin, immunoglobulin, reverse transcriptase, hemoglobin, and insulin? Myosin is a protein that associated to actin produces the muscular contraction. CD4 is a membrane protein of some lymphocytes, the cells that are infected by HIV. Albumin is an energy storage protein and an important regulator of the blood osmolarity. Keratin is a protein with structural function present in the epidermis and skin appendages of vertebrates. Immunoglobulins are the antibodies, specific proteins that attack and inactivate strange agents that enter the body. Reverse transcriptase is the enzyme responsible for the transcription of RNA and formation of DNA in the life cycle of retroviruses. Hemoglobin is the protein that carries oxygen from the lungs to the cells. Insulin is a hormone secreted by the pancreas that participates in the metabolism of glucose. What are catalysts? Catalysts are substances that reduce the activation energy of a chemical reaction, facilitating it or making it energetically viable. The catalyst increases the speed of the chemical reaction. What amount of catalyst is consumed in the reaction it catalyzes? Catalysts are not consumed in the reactions they catalyze. Is there difference between the initial and the final energy levels in catalyzed and non-catalyzed reactions? The catalysis does not alter the energetic state of reagents and products of a chemical reaction. Only the energy necessary for the reaction to occur, i.e., the activation energy, is altered. Enzyme Activity: activation energy graphic What are enzymes? What is the importance of enzymes for the living beings? Enzymes are proteins that are catalysts of chemical reactions. From Chemistry, it is known that catalysts are non-consumable substances that reduce the activation energy necessary for a chemical reaction to occur. Enzymes are highly specific to the reactions they catalyze. They are of vital importance for life because most part of chemical reaction of the cells and tissues are catalyzed by enzymes. Without enzymatic action, those reactions would not occur or would not happen in the required speed for the biological processes in which they participate. What is meant by substrates of enzymatic reactions? Substrates are reagent molecules upon which enzymes act. The enzyme has spatial binding sites for the attachment of its substrate. These sites are called activation centers of the enzyme. Substrates bind to theses centers forming the enzyme-substrate complex. Enzyme Activity: enzyme-substrate complex What are the main theoretical models that try to explain the formation of the enzyme-substrate complex? There are two main models that explain the formation of the enzyme-substrate complex the lock and key model and the induced fit model. In the lock and key model, the enzyme has a region with specific spatial conformation for the binding of the substrate. In the induced fit model, the binding of the substrate induces a change in the spatial configuration of the enzyme for the substrate to fit. Enzyme Activity: lock and key model induced fit model How does the formation of the enzyme-substrate complex explain the reduction of the activation energy of chemical reactions? The enzyme possibly works as a test tube within which reagents meet to form products. With the facilitation of the meeting provided by enzymes it is easier for collisions between reagents to occur and thus the activation energy of the chemical reaction is reduced. This is one of the explanatory hypotheses. Read the full article

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Design and Comparison of Terahertz Graphene Antenna: Ordinary dipole, Fractal dipole, Spiral, Bow-tie and Log-periodic - Juniper Publishers

Juniper Publishers - Open Access Journal of Engineering Technology

Abstract

This paper investigated several configurations of terahertz graphene antenna. Five structures: Ordinary dipole, Fractal dipole, Spiral, Bow-tie and Log-periodic antenna have been investigated and graphene is the main substance while a thin layer of SiO2 as a bed was used. The fractal dipole and round spiral antenna in the terahertz band and comparison of these structures for the first time has been considered. Designed antenna are credited, exploiting proper full-wave numerical simulations while using time domain simulations. According to simulation results, designed round spiral and log-periodic antennas show adaptive behavior on wide range of frequencies and confirms wideband operation. Also, antenna is compared regarding on board sizes and the absorption cross section. The radiation efficiency is above 85% for all antennas. The results of this study can offer design insight and give vision to researchers, selecting appropriate structure with specific features and applications (Figure 1).

Keywords: Terahertz antenna; Graphene; Log-periodic; Dipole; Bow-tie; Fractal

    Introduction

In recent years, Nano technology has provided novel solutions for engineering society. So, fabrication of electronic devices for specific application are realized and appropriately discussed. In any effort to increase sustainability and energy efficiency, neither productivity nor quality should suffer – quite the opposite should be the case. Increased sustainability and efficiency can only be achieved through the use of reliable and modern technology. Graphene based devices outperform silicon products, regarding higher operational frequency, design efficiency and even fewer losses. So, researchers hope, graphene will pavethe way to new era of high frequency-high efficiency electronics and optical devices. As a two-dimensional substance, Graphene shows transparent structure with hexagonal shape, has attracted a lot of attention due to its excellent physical, electrical and optical properties [1]. Starting with transparency, Graphene has constantly extended its range of properties in recent years. Nowadays this 2-D substance meets a growing range of requirements, from excellence electrical properties and simple control of charge careers to reliable frequency response. Extensive research and investigations have begun and continue to design, description and implementation of graphene-based Nano devices. Long and highlighted list of these researches is existing. For instance, ultra-high-speed transistor [2], transparent solar cells [3], meta-materials [4] and graphene plasmonics [5-6] are among most known fields. Regarding increasing demand for high speed operation and powerful processing, the need of design and fabrication of high frequency antennas is rising. On the other hand, one of the functional features of graphene is the ability to operate in high frequencies, which can be used in wireless communications and terahertz band [7]. Due to comparable depth of penetration with wavelength and increasing losses, we cannot increase operation frequency via dimension reduction. Since in a few micro-meter structure, the microwave rules are not entirely true in this area, so concept like PEC which exploits in microwave analysis is not compatible in the new shrinked domain, but still a half-wavelength antenna with 1 micro-meter long works at frequency about 150THz. This phenomena is justifiable, exploiting effective wavelength concept, which states antenna design can be transferred to optical frequencies with linear effective wavelength substituting [8]. The planar antenna which are placed on the substrate are mainly different from microwave antenna, because they tend to radiate in the sub bed medium and power division of each medium varies approximately as [9]. Basic research of planar structure of graphene antenna are studied in [10,11]. Graphene-based Nano patch and different shape of such antenna have been studied in [12,13] and [14] respectively. These antennas radiate, harvesting the graphene capability of supporting Surface Plasmon Polaritons (SPPs) which is comprehensively presented in [15,16]. In addition, propagation of SPP waves on doped graphene is analyzed, studied and proved [17-19].

In this work, to exploit the fascinating potential of this transparent material, five famous types of antenna are designed and simulated which graphene is main substance in these structures. We consider an ordinary dipole antenna with L as length and was width, with two separate graphene arms, as basic design for other antennas. All of presented configurations lay on a thin layer of SiO2 as substrate. Return Loss, Bandwidth, Absorption Cross Section, Directivity and Radiation Efficiency are numerically simulated and analyzed. The remainder of this paper is organized as follows. In section 2, the expression used to model the electric conductivity of graphene is presented. In section 3, the ordinary dipole antenna has been analyzed and design of other configurations is obtained based on the approximate length and exact width of ordinary dipole antenna. In next sub-section, the fractal dipole antenna has been designed and analyzed. The other sub-sections are design and analysis of spiral, bow-tie and log-periodic structures. In the section 4, the comparison of these structures has been presented and finally the paper has been concluded.

    Modeling of Graphene Conductivity

The conductivity of graphene, an allotrope of carbon in the form of a two-dimensional material, includes two parts, interband and intraband transitions. Since we are working on lower terahertz frequencies, intraband transition is considered solely [20] which is modeled using Kubo formula [16]. So, we assume that in low frequencies in terahertz band, intraband is just represented graphene conductivity. By harvesting random phase approximate method, surface conductivity of graphene with the time harmonic dependency of exp (jωt) can be descript in local form [13]:

Where e is the electron charge, kB is the Boltzman constant, ℏ is the reduced Planck’s constant, τ is the transport relaxation time, T is the temperature and μc is the chemical potential. In this work, we use T=300K (ambient temperature) and τ =1ps. These values are considered to as real as possible graphene parameters. The real and imaginary parts of intraband conductivity are depicted in Figure 2.

The chemical potential of graphene can be controlled using gate voltage. In all sections, μc is considered equal to 0.3eV. To developing a reliable library to simulate graphene, a combination of Drude model and surface conductivity can be used to determine the plasma frequency as follows:

A detailed description is represented in Appendix A.

    Simulation and Analysis

Five configurations that mentioned above is depicted in Figure 3. In this section, these structures will be analyzed and simulated at low frequency of terahertz band. Graphene with a thickness of 0.34nm is used in these structures and the results, exploiting time domain simulations has been achieved using CST Studio ver. 2016.

Ordinary dipoles

To avoid conjugate impedance matching, a half wavelength dipole antenna can be fabricated, resonates and shows pure real impedance. Antenna theory states that a normal half-wavelength dipole antenna possess 73+i42.5 ohm as impedance. If we assume the length of antenna about 0.48λ, bite smaller than λ/2, imaginary part will be set to zero. Usually dipole antenna is fabricated using conductive wires, but as we use graphene plates, design is similar to micro-strip antenna, where graphene plates plays roles of conducting wires. There is a gap between graphene plates, which antenna feeds through this gap. The feed can be a THz continuous –wave (CW) photo mixer placed in the middle of the patch. In order to model photo mixer [21,22], a current source is used to simulate antenna. To loss reduction, matching between supply and antenna is very significant. The geometrical shape of planar ordinary dipole is shown in Figure 3(a). As small as possible, if targeted gap changes, matched impedance changes accordingly. Regarding fabrication considerations, we assume gap width 5μm. Also designed antenna possess L=225μm and W =11μm. A standard principle states that an antenna can be designed wideband if occupied volume increased [23]. Based on our results, this is true while variations of bandwidth were small. The return loss for different width values are shown in Figure 4.

For W=11μm, directivity is obtained about 2.51dBi and radiation efficiency is achieved about 90%. These values are relatively constant for different width. In addition, bandwidth is obtained equal to 0.201THz. With shrinking ordinary dipole width, resonant frequency increase and antenna operates in second resonant frequency. This is clearly shown in Figure 4. For design of directive antenna, we can add a ground plate to bottom of substrate and be sure that the thickness of substrate is selected properly. This guarantees that the reflected waves from ground plate adds in-phase with the radiated waves.

Fractal dipoles

One of the nature inspired methods for bandwidth boosting, is fractal antennas design. Its features include low area, but unlimited circumference. Here we construct the proposed fractal dipole antenna by dividing each ordinary dipole antenna arm into three equal parts and creating a Koch curve with a 60° angle. The geometrical structure is depicted in Figure 3(b) while length of this antenna can be described by equation (3).

Where n is number of iterations and h states the initial length value. Regarding to the antenna width of 11μm and initial length value of 220μm, high numbers of repetitions cannot be achieved, and the shape of the antenna is achieved using single repetition.

By repeating on the ordinary dipole antenna, it was observed that the resonant frequency replaced, and this replacement was considerably tending to higher frequencies while has more bandwidth, and the resonant frequency for the fractalized ordinary dipole antenna was discussed, about 1.6terahertz was obtained and depicted in Figure 5.

By increasing the length of the antenna, the resonant frequency can be reduced. Designed fractal antenna has 390μm length to resonate at the frequency of designed ordinary dipole. The fractal dipole shape for planar antenna creates sharp points and sharp points, which does not work well for distribution of the current on the antenna surface. To solve this problem, we can use the technique of rounding the sharp points, which results in rounding is the frequency shift, changes of matched impedance and radiation at higher frequencies.

Spirals

Spiral antennas with circular structure whose obvious characteristic are independent of frequency, due to their circular structure, usually have high bandwidth and circular polarization. The geometry of these antennas is shown in Figure 3(c). The important point in designing these antennas is attention to the relation D=λ /π, where D is the diameter of the large circle of the antenna and λ is the desired resonant wavelength.

The outer radius of antenna determines the lowest frequency of operation and usually approximated to occur when the wavelength is equal to the circumferences of largest circle in antenna [24]:

And the highest frequency in the round spiral antenna’s operating band occurs when the innermost radius of the spiral is equal to λ /4. The highest frequency can be determined from the inner radius [24]:

Designed antenna has D =145μm and the width of the graphene sheets is 11μm. The simulation results show that this structure exhibits good frequency independent behavior, which results is high bandwidth.

Bow-ties

Another frequency independent configuration which the basic feature of their structures is dependence on the bow and not the antenna’s length, is the bow-tie antenna. Easy design and broadband impedance are other features of this configuration. The structure of this terahertz graphene antenna is slightly different from its microwave model and its geometric shape is shown in Figure 3(d).

The results show that the increase in the angle θ leads to that the behavior independent of frequency of this configuration more apparent. Bow-tie structure is simulated with angles of 3, 15 and 45 degrees, W=11μm, L=225μm and the return loss is shown in Figure 6.

By circling the corners of the structure of this antenna, it can also improve the current distribution and thus achieve better radiation.

Log-periodics

The geometric structure of the log-periodic tooth planar antenna is shown in Figure 3(e). This structure is chosen in such a way that electrical properties are repeated with wavelength logarithms and the teeth of this antenna make it suitable for the distribution of current. If the values of β1 and β2 are chosen such that β1+β2=90˚, the antenna becomes self-complementary [25]. The ratio of the circles of the log-periodic tooth planar antenna is a constant number that gives the structure period:

In the designed antenna, the physical parameters appeared in Figure 3(e) are optimized as follows:

τ =1.96, Rn=169.3μm, β1=60˚, β2=30˚

The antenna radiates when the length of each arc An, is equal to λeff/2 which length of each arcs can be calculated as below:

    Comparison

The return loss of the five antennas discussed is shown in Figure 7 and the designed frequency is 0.834THz. Spiral, bowtie and log-periodic antennas as expected, shown independent frequency behavior which can be seen well in Figure 7. The bandwidth of the ordinary dipole antenna is 0.2 terahertz. By changing the geometric structure of the antenna, the bandwidth has reached to 2.7terahertz, which corresponds to the logperiodic antenna.

In order to study the performance of these terahertz graphene antenna, it is interesting to investigate the absorption cross section of these graphene patches with plane wave normal incident as shown in Figure 7. The meaning of high absorption is that the excitation of SPPs on the antenna surface is good and it does not necessarily, but it can radiate at these frequencies. The calculated absorption cross section of five configurations is depicted in Figure 8.

In lower frequencies of terahertz band, the absorption cross section of fractal dipole antenna is low, therefor the characteristics of the fractal dipole antenna at designed frequency compare to the ordinary dipole expected that it will not improve, but at higher frequencies, about 3.8THz, where the absorption cross section of fractalized dipole is much better than the ordinary dipole, the fractalized antenna features are expected to be improved. This analysis can also be done for the spiral antenna at designed frequency and expected that this structure has better parameters at higher frequencies. A remarkable point in comparing these configurations is the significant peak of absorption cross section in the log-periodic structure and the fractalized dipole antenna at the frequencies of about 1THz and 3.8THz respectively. This fact indicates the better excitation of the SPPs on the surface of these configurations.

The highest directivity between these five famous structures is 3.08dBi, which is related to the log-periodic antenna. As shown in Figure 9, all antennas except the spiral have null at angles of 0 and 180 degrees. The antennas discussed, do not have a narrow beam, so the concept of reconfigurable for these graphene antennas which can be obtained by applying the gate voltage, does not make sense. The polarization of the spiral antenna is also elliptic, while four other antennas have linear polarization.

Regarding to comparison of board sizes, the log-periodic antenna occupies the largest size of the board which is approximately 6 times larger than ordinary dipole and after that is the bow-tie, fractalized dipole, spiral and ordinary dipole respectively.

According to results, the log-periodic antenna has better features in terms of directivity and bandwidth compared to the spiral antenna and less matched impedance, but in contrast, it has more occupied volumes. Comparison of these five configurations with consideration of important parameters is presented in Table 1.

    Conclusion

Five different types of antenna were studied, analyzed and simulated. Ordinary dipole, fractalized dipole, spiral, bow-tie and log-periodic configurations are compared in terms of bandwidth, absorption cross section, directivity and finally board sizes. It was shown that by decreasing the width of the ordinary dipole antenna, the resonant frequency shifted towards higher frequencies and the antenna radiates at its second frequency resonance. It has been presented that fractalized ordinary dipole antenna has the frequency shift to higher frequencies and in lower frequencies of terahertz band, the SPPs cannot excite well in this configuration. It was observed that at lower frequencies of the terahertz band, as the bow angle increases from zero to 45 degrees, the behavior of independent of frequency becomes more apparent. The designed spiral and log-periodic antennas shown a good bandwidth and among these antennas, the log-periodic configuration has the best features in terms of bandwidth, absorption cross section and directivity. The calculated radiation efficiency for ordinary dipole, fractal dipole, spiral, bow-tie and log-periodic structures was 90%, 89%, 98%, 96% and 86% respectively.

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[optromix]

Raman spectroscopy vs. FTIR process spectroscopy

Raman spectroscopy is a method of molecular process spectroscopy based on the interaction of light with matter. It allows getting data about the material structure or its characteristics, and in this regard, it is similar to the method of FTIR spectroscopy. Raman process spectroscopy is based on the study of scattered light, while IR spectroscopy is based on the absorption of the light. Raman spectroscopy provides information about intramolecular and intermolecular vibrations and helps to get a more complete data of the reaction. 

Both Raman and FTIR spectroscopy gives a spectral characteristic of molecular vibrations (the “molecular imprint”) and are used to identify substances. Herewith, Raman spectroscopy can provide additional information on low-frequency modes and vibrations, which indicate the features of the crystal lattice and molecular structure. 

Raman spectroscopy is used to monitor crystallization processes, mechanisms and reaction kinetics. In combination with analytical tools, this data allows better understanding and optimizing the response. 

The principle of Raman process spectroscopy is based on the interaction of light with molecules in a gas, liquid or solid, while the vast majority of photons are scattered, having the same energy as the incident photons. The Raman effect is widely applied in various fields, from medical diagnostics to materials science and reaction analysis. The Raman effect allows studying the vibration characteristics of the molecule, giving information about how it is arranged and how it interacts with other molecules.

In contrast to Fourier-transform infrared spectroscopy, Raman process spectroscopy demonstrates changes in the polarizability of molecular bonds. The interaction of light with a molecule can cause deformation of its electronic cloud. This deformation is called a change in polarizability. Under certain energy transitions, accompanied by changes in the polarizability of molecular bonds, active Raman modes arise.  

It should be noted that since the Raman effect is weak, the optical components of the Raman spectrometer should be specially optimized and well-adjusted. In addition, since organic molecules may cause fluorescence under the influence of short-wave radiation, monochromatic sources with a long wavelength are commonly used, such as solid-state diode lasers that emit light at a wavelength of 785 nm.  

Raman spectroscopy is used in industry for solving various problems, including:

Study of crystallization processes;

Identification of polymorphic forms;

Study of polymerization reactions;

Study of the reactions of hydrogenation;

Chemical synthesis;

Biocatalysis and enzymatic catalysis;

Chemical processes in the flow;

Monitoring of biological processes;

Study of synthesis reactions.

Although the methods of FTIR and Raman process spectroscopy are interchangeable in many cases and complement each other well, there are differences that should be considered when choosing one method or another in practice. Most molecules with symmetry can be identified both in the infrared and Raman spectra. A special case is represented by molecules with the center of inversion. 

If the molecule has an inversion center, then the Raman scattering bands and the IR bands will be mutually exclusive, that is, the link will be active either in the Raman or in the IR spectrum. There is a general rule: functional groups with strong changes in the dipole moment are clearly visible in the IR spectrum, whereas functional groups with weak changes or with a high degree of symmetry are better seen in the Raman spectra.

Raman spectroscopy is recommended in the following cases:

if it is required to examine carbon bonds in aliphatic and aromatic rings;

if it is necessary to identify bonds that are difficult to see in the IR spectra (for example, O–O, S–H, C=S, N=N, C=C, etc.);

if the study of particles in solution is carried out, for example in the study of polymorphism;

if low-frequency modes are studied (e.g. in inorganic oxides); 

to study reactions in the water environment;

if it is easier and safer to observe the reaction through a viewing window (for example, catalytic reactions under high pressure, polymerization);

to study the low-frequency vibrations of the crystal lattice;

to determine the beginning and end of the reaction, to study the stability of the product in two-phase and colloidal reactions.

FTIR spectroscopy is recommended in the following cases:

for the study of liquid-phase reactions;

if the reactants, reagents, solvents and other components, involved in the reaction, fluoresce;

if connections with strong dipole moment change are important (for example, C=O, O–H, N=O);

if the reagents and the reactants have a low concentration;

if the solvent bands appear strongly in the Raman spectrum and can suppress the signal of the main components;

if the intermediate reaction products are active in the IR spectrum.

Raman spectroscopy has many advantages. Since visible-light lasers are used in Raman spectrometers, flexible fiber optic cables made from quartz glass fibers can be used to excite a sample and collect scattered radiation. If necessary, these fiber cables can be quite long. 

Since visible light is used, samples can be placed in glass or quartz containers. Therefore, a Raman spectroscopy probe can be put into the reaction medium or Raman spectra can be recorded through a window, for example, in an external sampling loop or in a flow cell during studying chemical reactions. The latter method eliminates the possibility of sample contamination. 

Since quartz or high-quality sapphire can be used as a window material, Raman spectra of catalytic reactions can be observed in high-pressure cells. During the study of catalysts, the operative process spectroscopy using the Raman effect is useful for studying in situ reactions on catalytic surfaces in real-time. 

Another advantage of the Raman process spectroscopy is that hydroxyl bonds are not very active in the Raman spectrum, and therefore, this sensing technique is suitable for aqueous media. Raman spectroscopy is considered to be non-destructive, although laser radiation may affect some samples. It is necessary to consider how specific a sample may tend to fluorescence when choosing this method. Raman spectroscopy scattering is a weak effect, and fluorescence can suppress the signal, making it difficult to obtain high-quality data. This problem can be easily solved using an excitation source with a longer wavelength.

As for the analysis of reactions, Raman process spectroscopy is sensitive to many functional groups but it is particularly effective in obtaining information about the molecular structure. The Raman spectrum uniquely defines molecules. Since Raman spectroscopy is based on the polarizability of bonds and is capable to measure low frequencies, the process spectroscopy is sensitive to lattice vibrations, which provide information about polymorphs. FTIR process spectroscopy is less informative there. This makes it possible to use Raman spectroscopy with great efficiency in the study of crystallization and other complex processes. 

A modern compact Raman spectrometer consists of several main components, including a laser, which serves as a source of molecule excitation for inducing Raman scattering. Usually, modern Raman spectrometers use solid-state laser systems with wavelengths of 532, 785, 830 and 1064 nm. Lasers with shorter wavelengths have a larger scattering area, so the signal is ultimately more powerful, but fluorescence occurs more often at such lengths. 

Fiber optic cables are used to transmit laser energy. Band-pass or edge filters are used to eliminate Rayleigh and anti-Stokes scattering, and the remaining light that has undergone Stokes scattering is transmitted to the dispersion element — usually a holographic grating. 

The following types of Raman spectroscopy techniques are identified:

Resonance Raman scattering spectroscopy, where the frequency of the laser radiation is selected in accordance with the electronic transitions in the molecule or crystal, which correspond to the excited electronic states. This approach allows for obtaining high scattering intensity in the absence of unwanted fluorescent interference, the frequency of which is lower than the frequency of exciting radiation.

Coherent anti-Stokes Raman spectroscopy. This method requires the use of two lasers, one of which has a fixed and the other a variable generation frequency. A spectrum of resonant Raman scattering is achieved by varying the frequency of the tunable laser.

Surface-enhanced Raman scattering spectroscopy, in particular, for the study of biomolecules imparted to nanoparticles of noble metals.

Tip-enhanced Raman scattering spectroscopy is a special type of surface-enhanced Raman spectroscopy, in which the SPM probe is applied to amplify the signal.

Optical Tweezers Raman Spectroscopy is used to study individual particles, as well as biochemical processes in cells captured by optical tweezers - a device that allows for manipulating microscopic objects using laser light.

If you would like to obtain an optical fiber product, you should choose Optromix company. Optromix is a provider of top quality special fibers and broad spectra optical fiber solutions. The company delivers the best quality special fibers and fiber cables, fiber optic bundles, spectroscopy fiber optic probes, probe couplers and accessories for process spectroscopy to clients. If you have any questions, please contact us at info@optromix.com

[lovelikenoother712]

In spectroscopy, a forbidden mechanism (forbidden transition or forbidden line) is a spectral line associated with absorption or emission of photons by atomic nuclei, atoms, or molecules which undergo a transition that is not allowed by a particular selection rule but is allowed if the approximation associated with that rule is not made.[1] For example, in a situation where, according to usual approximations (such as the electric dipole approximation for the interaction with light), the process cannot happen, but at a higher level of approximation (e.g. magnetic dipole, or electric quadrupole) the process is allowed but at a much lower rate.

[sciencebulletin]

New high-energy-density physics research provides insights about the universe

Atoms and molecules behave very differently at extreme temperatures and pressures. Although such extreme matter doesn't exist naturally on the earth, it exists in abundance in the universe, especially in the deep interiors of planets and stars. Understanding how atoms react under high-pressure conditions—a field known as high-energy-density physics (HEDP)—gives scientists valuable insights into the fields of planetary science, astrophysics, fusion energy, and national security. One important question in the field of HED science is how matter under high-pressure conditions might emit or absorb radiation in ways that are different from our traditional understanding. In a paper published in Nature Communications, Suxing Hu, a distinguished scientist and group leader of the HEDP Theory Group at the University of Rochester Laboratory for Laser Energetics (LLE), together with colleagues from the LLE and France, has applied physics theory and calculations to predict the presence of two new phenomena—interspecies radiative transition (IRT) and the breakdown of dipole selection rule—in the transport of radiation in atoms and molecules under HEDP conditions. The research enhances an understanding of HEDP and could lead to more information about how stars and other astrophysical objects evolve in the universe. What Is Interspecies Radiative Transition (Irt)? Radiative transition is a physics process happening inside atoms and molecules, in which their electron or electrons can "jump" from different energy levels by either radiating/emitting or absorbing a photon. Scientists find that, for matter in our everyday life, such radiative transitions mostly happen within each individual atom or molecule; the electron does its jumping between energy levels belonging to the single atom or molecule, and the jumping does not typically occur between different atoms and molecules. However, Hu and his colleagues predict that when atoms and molecules are placed under HED conditions, and are squeezed so tightly that they become very close to each other, radiative transitions can involve neighboring atoms and molecules. "Namely, the electrons can now jump from one atom's energy levels to those of other neighboring atoms," Hu says. What Is The Dipole Selection Rule? Electrons inside an atom have specific symmetries. For example, "s-wave electrons" are always spherically symmetric, meaning they look like a ball, with the nucleus located in the atomic center; "p-wave electrons," on the other hand, look like dumbbells. D-waves and other electron states have more complicated shapes. Radiative transitions will mostly occur when the electron jumping follows the so-called dipole selection rule, in which the jumping electron changes its shape from s-wave to p-wave, from p-wave to d-wave, etc. Under normal, non-extreme conditions, Hu says, "one hardly sees electrons jumping among the same shapes, from s-wave to s-wave and from p-wave to p-wave, by emitting or absorbing photons." However, as Hu and his colleagues found, when materials are squeezed so tightly into the exotic HED state, the dipole selection rule is often broken down. "Under such extreme conditions found in the center of stars and classes of laboratory fusion experiments, non-dipole X-ray emissions and absorptions can occur, which was never imagined before," Hu says. Using Supercomputers To Study Hedp The researchers used supercomputers at both the University of Rochester's Center for Integrated Research Computing (CIRC) and at the LLE to conduct their calculations. "Thanks to the tremendous advances in high-energy laser and pulsed-power technologies, 'bringing stars to the Earth' has become reality for the past decade or two," Hu says. Hu and his colleagues performed their research using the density-functional theory (DFT) calculation, which offers a quantum mechanical description of the bonds between atoms and molecules in complex systems. The DFT method was first described in the 1960s, and was the subject of the 1998 Nobel Prize in Chemistry. DFT calculations have been continually improved since. One such improvement to enable DFT calculations to involve core electrons was made by Valentin Karasev, a scientist at the LLE and a co-author of the paper. The results indicate there are new emission/absorption lines appearing in the X-ray spectra of these extreme matter systems, which are from the previously-unknown channels of IRT and the breakdown of dipole selection rule. Hu and Philip Nilson, a senior scientist at the LLE and co-author of the paper, are currently planning future experiments that will involve testing these new theoretical predictions at the OMEGA laser facility at the LLE. The facility lets users create exotic HED conditions in nanosecond timescales, allowing scientists to probe the unique behaviors of matters at extreme conditions. "If proved to be true by experiments, these new discoveries will profoundly change how radiation transport is currently treated in exotic HED materials," Hu says. "These DFT-predicted new emission and absorption channels have never been considered so far in textbooks." Provided by University of Rochester More information: S. X. Hu et al. Interspecies radiative transition in warm and superdense plasma mixtures. Nature Communications (2020). DOI: 10.1038/s41467-020-15916-3 Image Credit: CC0 Public Domain Read the full article

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New high-energy-density physics research provides insights about the universe

https://ift.tt/2j9hSdV have applied physics theory and calculations to predict the presence of two new phenomena -- interspecies radiative transition (IRT) and the breakdown of the dipole selection rule -- in the transport of radiation in atoms and molecules under high-energy-density (HED) conditions. The research enhances an understanding of HED science and could lead to more information about how stars and other astrophysical objects evolve in the universe. from Latest Science News -- ScienceDaily https://ift.tt/2zoKoRX April 24, 2020 at 09:36AM Researchers have applied physics theory and calculations to predict the presence of two new phenomena -- interspecies radiative transition (IRT) and the breakdown of the dipole selection rule -- in the transport of radiation in atoms and molecules under high-energy-density (HED) conditions. The research enhances an understanding of HED science and could lead to more information about how stars and other astrophysical objects evolve in the universe. from Blogger https://ift.tt/3bDIRpB