#flow birefringence
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The Science Manuscripts of S. Sunkavally. Page 241.
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fibermarts · 8 months ago
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Get To Know About the Fiber Optic Circulators In Details
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An optical circulator operates similarly to a microwave circulator. It is a multiport gadget with three or more ports. Lightwave is barred from traveling from one port to the port before it, but it can travel with the least amount of loss from one consecutive port to the next.
Telecom systems were the first to employ optical circulators. Nonetheless, they are also employed in the sensing and imaging domains due to the readily available affordability and high-performance circulators.
Optical circulator applications
  
Add-Drop Multiplexing
  
Fiber Sensors
  
Bidirectional Pumping
  
Bidirectional Signal Transmission Systems
  
Coupling In-Line Chromatic Dispersion Compensation Devices
Telecom systems were the first to employ optical circulators to boost the transmission capacity of their networks. In a bidirectional transmission system, the capacity may be readily quadrupled by utilizing a Fiber Circulator. 
Strong tools for removing optical signals from a reflecting device are optical circulators. A reflective erbium-doped fiber amplifier (EDFA), may be used in conjunction with a mirror to doubly pass an optical element to boost efficiency.
Optical circulator types
Polarization-dependent circulator
Only works with a certain polarization condition of light. Polarization-dependent circulators have limited uses, such as optical sensing and free-space communications between satellites, because conventional optical fibers cannot preserve the polarization state of light due to birefringence generated by fiber imperfection.
Polarization-independent circulator
It is independent of a light's polarization state in terms of functionality. It is often employed in telecom networks using fiber optics.
The functionality
Full circulator: Light travels through every port in a full circle, returning light from the last port to the opening port.
Quasi-circulator:  Light flows through each port in turn, but at the last port, it loses energy and is unable to return to the source.
For the majority of applications, just a quasi-circulator is needed.
Principles of Optical Circulator Working
An optical circulator is built using two primary design concepts.
Type I, the most used at the moment, involves splitting and recombining polarization beams.
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Faraday effect-driven non-reciprocal polarization rotation
Type II (unpopular because of poor performance and manufacturing issues):
Unbalanced field conversion
Reversible phase transition
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tenderlysharpmidain · 2 years ago
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natural lighting flowing fabric on Kodak portra 800 film:: nature photography natural lighting on Kodak portra 800 film:: colors birefringence on Kodak portra 800 film:: smoke sculputure on Kodak portra 800 film --chaos 60
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juniperpublishersajop · 2 years ago
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Investigation of Extensional Flow Behavior of Polyethylene Melts through Birefringence by using Extrusion Cross-slot Die
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Abstract
Flow parameters of polymers melt under steady state condition in shear are required to assess flow behaviour of the molten material in the die or downstream operations. Very often this is not sufficient to have a full understanding of the polymer processability, and additional information of flow response in extension is also needed. In this paper, the extensional properties of two molten polyethylene have been investigated by measuring stress response when a high extensional deformation is applied in a cross-slot die. Flow induced birefringence analysis and stress-optical rule are applied to determine rheological properties. Two polyethylene’s with similar rheology in shear but different molecular structure (HDPE and LLDPE) are analysed. Very interestingly, this approach appears capable of capturing differences in extensional flow that are not detectable using other conventional analytical methods.
Keywords: Flow Birefringence; Stress Optical Rule; Extensional Flow; Extensional Rheometry; Viscoelasticity
Introduction
Viscoelastic responses in shear and extensional regime of polymer melts are of paramount importance as they dominate most of the processing of polymers in the molten state [1]. Therefore, in industrial field, knowledge of rheology of polymers plays a central role in designing and understanding many processing operations: extrusion, blow molding, cast-blow extrusion, injection molding [2,3]. Specifically, extensional flow al high strain rate (ε ̇) is easily encountered in many industrial processes and there is increasing demand for generating more information about it [4]. It is usually more difficult to characterise properties of extensional flow than for simple shear. This kind of flow is commonly achieved with rheometers designed to uniaxially stretch the material. They typically include filament stretching [5] and dual wind-up stretching device [6]. However, true steady-state flow conditions are quite often difficult or impossible to reach because unlimited deformation is theoretically required [7], whereas elongational test is prone to sample inhomogeneity (due to localized necking) and rupture [8,9]. Gravity and non-isothermal condition on the sample, if the test is not carried out in climatic chamber or in thermostatic fluid, conspire to add limitation with these approaches. In many cases, when materials need to be tested at relative high temperature and broad strain rate close to effective industrial processing conditions, conventional lab-scale approaches in extensional flow with existing stretching rheometers are not capable to fully provide the required information. Low melt strength or sagging of molten materials promote premature deformation of the specimen, forcing to carrying out test at lower temperatures and it is not representative of real process conditions. This can limit the usage of conventional devices and methods. Therefore, there are relatively few data available for extensional flow [10] and especially for low viscosity molten polymers, measurements are very often overlooked and sometimes results are an over-simplification of real behavior.
For these reasons, full characterization of true steady state value for extensional stress response over a broad range strain rates is still an open topic in the field of polymer melts. In this scenario, cross-slot die, and rheo-optical approach appear to be a valid tool to get insight into rheology of complex flow and mimic and capture more closely extensional flow typically encountered in industrial operations [11,12]. Specifically, rheo-optical method offers potential to explore and evaluate the spatial-temporal evolution of the stress response of polymer melts [13]. It is an elegant and non-invasive way to generate extensional flow in controlled environment and confined geometries (the cross-slot die), it is well suited for polymer melts with poor melt strength, and/or non-homogeneous deformation at relatively high Henky strain or in case of not-achievement of a robust steady state [14]. Lastly, extensional flow can be sustained indefinitely in long run. This is possible through the connection of flow cell to a couple of extruders that provide a continuous feed of molten polymers up to relatively high flow rate. Thanks to the execution of the test in confined geometries, the method is insensitive to problems of melt yielding and high fluidity that, on the contrary, could make problematic the use of current rheometers operating in “not confined” environment. The specific geometry of the crossslot used in these experiments provides, for material transiting close to the stagnation point, high planar extensional flow that propagates along the entire plane of symmetry toward the outlet, which results in high level of extensional rate. Flow induced birefringence measurement (FIB) is used to evaluate interaction of the light with the polymer melt flow. Moreover the birefringence property is related to the stress distribution, polymer chains orientation and stretching with respect to stress directions.
Stresses in the melt stream were evaluated and quantified from flow-induced-birefringence (FIB) pattern along the centerline using the stress optical rule (SOR). It is well known that there exists, under a wide variety of conditions, a constant in the ratio of birefringence n and stress σ and is expressed as:
Where SOC is the stress optical coefficient for the polymers under analysis. It is given in unit of Pa-1. For the work presented in this paper a SOC of 1,80 x 10-9 Pa-1 is used for HDPE and LLDPE, which is in good agreement with the range given in literature for PE from 1,2 to 2,4 x10-9 Pa-1 [15,16]. Stress-optical rule has been found to remain linear in a wide stress range [17] and SOC weakly dependent on temperature [17,18]. The main goal of this paper is to investigate if melt flow induced stress birefringence can capture and well allow distinction of the behavior in extensional flow of the two polymers, otherwise not distinguishable with conventional rheological techniques. At the same time, we want to verify how sensitive the method is to capture differences in behaviour due to branching.
Materials and Experimental Setups
Materials
Materials used in this paper are a linear HDPE (Eraclene ML70U) and LLPDE (Clearflex CLD0) produced by Versalis, both with a very similar melt flow index. The first one is designed for extrusion application, whereas the second one is more suitable for injection moulding and film processes. They have very different degree of branching but despite this different molecular structure and application, still exhibit similar shear viscosity (Table 1).
Material Characterization in Shear Flow
The viscoelastic behaviour of two polyethylene samples has been evaluated in shear capillary experiment and by dynamic analysis. Results are reported in Table 1 and in Figure 1 (Master Curves). The grades have been selected because have very similar shear viscosity and master curve but very different degree of branching. It must be pointed out that both PE’s grades, neither elongational viscosity test nor fiber melt spinning measurements can be performed, due to the very low melt strength and sagging of the polymers at high temperature. Oscillating shear capillary rheometry (OSCAR) [19] has been also used to assess the complex rheology of LLDPE and of HDPE. The behaviour of the elastic modulus was measured at 190 °C for a shear cycle of period p=180s and amplitude . The elastic shear modulus reaches almost the same low shear rate value of 0.12 MPa for both PE but shows a plateau only for the HDPE up to 200 s-1 while for the LLDPE it keeps constantly decreasing within the same range of shear. It is also important to report that the shear viscosity modulus V(γ ̇) for both samples is perfectly superimposable.The elastic shear modulus behaviour can give some explanation to the industrial evidence on why the LLDPE is not suitable for extrusion production due to the inconsistency of its melt strength, also providing an explanation on why those polymers are not suitable for the same transformation process. Unfortunately, this approach requires a dedicated instrument with a very time-consuming experimental approach. In this work we have investigated the extensional viscosity at high ε ̇ rate of strain to fully access the rheological response of both material in many industrial processes.
Experimental Set Up
Equipment used for flow induced birefringence (from now on named as FIB) experiments is called “GEMINA”. It was designed and manufactured by Isotattica [20]. It basically consists of a couple of extruders and a patent pending cross-slot die including an optical bench for flow visualization.
Single screw extruders
To obtain a continuous flow of molten polymer to be delivered to the cross-slot die, the two independent-controlled extruders are coupled with the cross-slot apparatus. Each extruder is equipped with a 30 mm barrel/screw diameter and a L/D ratio of 25. Each of them is heated by three electrically powered zones on the barrel, a fourth one on the flange and a fifth one on die. It is powered by a 4 kW electric motor with a drive gear and electronic speed controller. Experiments are carried out at three different melt temperatures: 160, 190 and 220 °C, the extents of this range has been chosen in order to reproduce typical situations of use in machining processes. Pellets of polymers are feed in the hopper and molten polymer is transported along the extruder into the die. Setting temperatures from hopper to the die are selected in such way to get an effective temperature of the molten polymers as indicated above. Flow visualization experiments were performed after waiting for a certain time (15 min) for extruder parameters stabilization. Typical data collected for each run are as follows: flow rate, video and picture capturing for subsequent sequencing and processing via FIB. The range of flow rate used for experiments is from 20 cm3/min up to 290 cm3/min (i.e. from 16 s-1 to 225 s-1 in terms of apparent shear rates near inlet flow passageway).
Cross-slot die
A modular cross-slot die is fitted at the extruders exit from when the molten polymers flow. The cross-slot geometry provides four perpendicular, intersecting coplanar channels (width 4 mm, channel depth 8 mm), rounded at intersection point (Figure 2). The flow involves two opposed inlet streams which lies on the same axis meeting at a planar stagnation point and then exit orthogonally. It has a pair of stress-free transparent viewing windows (borosilicate glass) that allows a light beam to pass through the midsection of flow field and orthogonal analyzer before being captured using a digital video camera. The entire die is heated with electric heaters deeply inserted in the die, then connected with two independent temperature probe and controlled by the two zones 5B of the extruder panel control. The die is also equipped with 4 thread holes, in the passageway between adapters and cross die, for inserting melt pressure transducer or temperature probe (flush mounted). The two molten polymers are extruded with controlled flow rate and temperature in opposite directions towards the centre along the opposing collinear flow channels. By impinging these two fluids, flow induced stress birefringence is generated, allowing visualization and mapping of stress fringes, that correspond to a locus of constant value of principal stress differences PSD. Largestrain extensional flow deformations, preferred alignments and stagnation flow are generated along the inlet-outlet symmetry plane of the collinear channels and then analysed via flow-induced birefringence.
Optical bench
The flow birefringence measurements are performed using an optical bench as shown schematically in Figure 3. From top to the bottom, it consists of light source (white light), polarizer, two quarter wave plate (the cross-slot die is placed between them), analyser, extension tube with camera lens, and digital video camera. Firstly, the light beam passes the polarizer and quarter wave pate, enter through glass windows the melt stream which rotates its polarization state, then exit through the other glass window, quarter wave plate and analyser before reaching video camera. With this arrangement polarization of light is circular (circular polariscope in dark or bright field), isoclinic extinction bands (loci of points where principal stresses directions are constant) are not visible, leaving only stress-related isochromatic fringes (loci of points where the difference of principal normal stresses is constant). The optical parts are designed for fast assembly on a stand, are mechanically independent and moveable in all three dimensions for precise tuning of each component. Additionally, said stand, after competition of runs, can be moved away from die housing and extruders. With white light, coloured bands are observed, they are called “isochromatic fringes”. Firstly, fringe tracking and fringe order assignment are done. Considering that each isochromatic fringe with same colour carries the same light retardation and corresponds to a constant value of principal stress difference, the latter can be quantified through the stress optical rule.
The most important relation that allows us to calculate the PSD is given below:
Here N is the fringe order, l is the wavelength of light, d the channel depth. Combining stress optical rule (Equation 1) and Equation 2 it is possible to calculate the PSD by determining birefringence in molten flow on each isochromatic fringe.
Results and Discussion
Elongational flow/FIB
In the symmetry plane inlet-outlet along the centreline, at steady state regime, polymer flow experiences a constant extension rate ε̇. It can be estimated by the formula:
Where Vavg is the average velocity in the passageway and w the channel width. In this area flow approaches fully developed planar stretching flow. The steady state elongational viscosity is calculated from tensile stress (σstd is the PSD-principal stress difference between X-extensional and y-compressional axes, determined by FIB analysis) and the steady state strain rate ε̇ (Equation 4):
The evolution of the fringes as function of flow rate indicates a progressive increase of level of anisotropy between inlet and outlet channels (Figure 4). The isochromatic fringes of the birefringence are used to determine the principal stress difference in steadystate condition: each fringe carries a fixed stress contribution and through fringe sequencing and assignment of fringe order along the exit symmetry plane (fringe counting technique) is possible to determine PSD. An increase on concentration of isochromatic fringes is observed at high flow rate, mainly located along the exit symmetry plane where stretching flow is supposed to be fully developed. Quantitative representation of stress build-up versus extension rate is well illustrated in Figure 5. The graph corresponds to steady state conditions of fringe patterns. It is observed that the difference in stress between HDPE and LLDPE is maintained throughout the extended range of extension rate investigated. For both materials, the level of stress anisotropy between inlet and outlet channel flow increases as flowrates increase. The difference in stress concentration leads finally to a different evolution of extensional viscosity vs extension rate (Figure 6). The effect of difference in structure between HDPE and LLDPE is also well illustrated in Figure 7 & 8. The differences in fringe numbers sequencing made at same level of extensional rate are representative of the polymer type. LLDPE (short chain branching) shows the lower level on center-line stress fringes on comparison to HDPE (extensive branching), thus indicating for the former a lower stress concentration localized in the area of outlet symmetry plane.
As explained above, the configuration of the optical train used for the evaluations (circular polarization) is such as to examine isochromatic fringes. We have mentioned that with a different optical setup (linear polarization in dark field) is possible to also evaluate the isocline bands, loci of points where principal stresses directions are constant. With this configuration the initial field is dark, the principal stresses on melt produce a pattern of coloured fringes that vary with loading (isochromatic), on the same time some dark bands remain fixed with stress (isoclines); by rotating the polariser and analyser together, the coloured fringes do not vary (isochromatic) while the dark fringes change (clearly detectable isoclines). It has been made an exploratory survey and it has provided an interesting mapping of their distribution (Figure 9). Isoclinic fringes of HDPE are practically superimposable to those of LLDPE, an indicator that materials express a similar spatial orientation of stresses. There are some points which remain dark during simultaneous rotation, they are called singular points (S1 and S2) where both principal stresses are equal and hence σ1 = σ2 or σ1 – σ2 = 0. If σ1 = σ2 they represent fringe order 0 (black colour) in isochromatic evaluation. Isoclinic fringes allow, through a subsequent graphic elaboration, to determine the so-called isostatics which are the trajectories of the stresses. However, this issue is not the subject of this investigation, it will be addressed in future studies.
Summary and Conclusion
The cross-slot device coupled with two extruders allows measurement of steady-state planar extensional viscosity in a broad strain rate regime through stress birefringence. Specifically, the properties of two polyethylenes under extensional flow have been assessed by using this non-invasive rheo-optical approach. This analysis show how steady-state extensional flow can be evaluated through cross-slot measurement and how different branching in the molecular structure has an impact on stress in elongational flow. The PSD at different level of strain rate was captured using flow-induced birefringence. The PSD pattern developed from an initial near-Newtonian response (slow flow, quasi symmetric pattern between inlet and outlet) to gradually increasing level of asymmetry between inlet and outlet flow as the flow rate increases (stretching flow). It has been experimentally verified that these two materials show a difference in extensional viscosity, and the presence of long chain branches in the molecular morphology in HDPE affects the stress in extensional flow. On the other hand, LLDPE shows a lower extensional viscosity. The advantage of this method lies in the possibility to replicate the same temperature of industrial process and extensional optical device has confined geometry that allows the testing on molten polymers that, due their poor melt strength, sagging, localized necking at test temperature, cannot be otherwise tested in free-surface devices (not-confined geometries) like current commercial stretching rheometers.
Additionally, high strain steady-state limit can also be reached in long stable extrusion run. According to our findings, this approach is capable to detect and differentiate extensional rheology of different polymers that would not otherwise be captured with other techniques Cross slot die and rheo-optical analysis does have some limitations. At high stress values, fringes stratification become very high and the sequencing and counting may be more demanding. The PSD patterns for HDPE show a higher level of stress vs LLDPE at same strain rate, and it is observed that sequence of patterns of HDPE is always approximately two levels of fringe orders more forward than the LDPE compared at same level on central extension rate. The difference in growing number of fringes for HDPE versus LLDPE ultimately lead to a different extensional viscosity response. It should be remembered that these two materials have very similar shear viscosity and mater curve, despite significant different degree of branching is present. On the same time the differentiation observed in extensional viscosity is in good qualitative agreement with mechanical behaviour - elastic shear modulus under shear flow - performed via-OSCAR technique. Results obtained with these two techniques corroborate the explanation of the different evidence of extensional behaviour of these two polyethylenes. This also reflected in the industrial field: HDPE is more suitable for extrusion than LLDPE.
The design of the die inevitably leads to a compromise in relation to channel dimension and aspect ratio. Ideally twodimensional flow is desirable, even if an increase in branching enhance localized three-dimensional flow with stress pattern increasingly asymmetric. In conclusion, it has been shown that rheo-optical approach with flow induced birefringence analysis can be used for mapping and measuring properties of melts in extension along the plane of the outlet channels, or simultaneously shear properties in the inlet channels as well, depending on geometry of die, thus providing to be a very useful and intriguing tool to capture the smallest differences in flow behaviour and assess polymer performances. This methodology can become an indicator of rarely observed phenomenon that are not made manifest with conventional approaches and/or non-fully predict with simulation. It can be seen as a complementary approach to current extensional rheometers, towards which it strengthens the measuring range, provides kinematically steady extensional flow, exceeds their limits in maximum allowable testing temperature and applicable extension rate. The connection of the rheooptical die with extruders also guarantees a constant support of homogeneous molten material to the flow cell and above all a long and stable test duration. Lastly, this kind of lay out (cross-slot die and extruder coupling) makes this equipment quite innovative among the available equipment for industrial rheology. It can be used with the purpose of quality control, polymer and compounds design, R&D and optimization in tooling designing.
Future Works
Rheo-optic analysis with cross-slot die coupled with extruders is certainly a field of investigation still to be fully exploited. Further tests with polymers different from each other or belonging to the same monomeric identity but different molecular architecture are to be encouraged, making the most of the potential of the flow-induced birefringence. New potential field of study is certainly the evaluation of isoclines, in parallel to birefringence analysis of isochromatic. Isotropic points appearing in low fringe order zones are often either overlooked or entirely missed in conventional rheo-optical analysis. Vice versa, isoclines and especially their processing into isostatics, could provide complementary information to understand the stress trajectories in flowing materials. This will be the subject of a future work.
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wingcrystal · 2 years ago
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Brief Introduction of Calcite
Calcite is a kind of calcium carbonate mineral, and it is the most common natural calcium carbonate. Therefore, calcite is a widely distributed mineral. Calcite has a variety of crystal shapes, and their aggregates can be clusters of crystals, granular, massive, fibrous, stalactite, earthy and so on. Many square fragments can be obtained by knocking calcite, hence the name calcite.
Basic introduction of calcite
Calcite is a kind of calcium carbonate mineral, and it is the most common natural calcium carbonate. Therefore, calcite is a widely distributed mineral. Calcite has a variety of crystal shapes, and their aggregates can be clusters of crystals, granular, massive, fibrous, stalactite, earthy and so on. Many square fragments can be obtained by knocking calcite, hence the name“Fang Jie”in Chinese. The color of calcite varies with the impurities it contains, such as light yellow, light red, brown black and so on when it contains iron and manganese. But it is usually white or colorless. Colorless and transparent calcite, also known as Iceland spar, has a wonderful feature, that is, through it, objects can be seen in double images. Therefore, Iceland spar is an important optical material. Calcite is the main mineral of limestone and marble, which has many uses in production and life. We know that limestone can form caves, in which stalactites, stalagmites and white marble are actually made of calcite. Calcite often contains isomorphic substitutes such as Mn, Fe, Zn, Mg, Pb, Sr, Ba, Co and TR. When they reach a certain amount, they can form manganese calcite, iron calcite, zinc calcite, magnesium calcite and other varieties. In addition, brucite, dolomite, iron hydroxide, oxide, sulfide, quartz and other mechanical inclusions are also common in crystals. Tripartite crystal system; Common intact crystals. There are various forms, with more than 600 different forms. Mainly in the form of parallel columns and parallel plates, and various rhombohedral or complex triangular polyhedron. Calcite often forms contact twin, and more often it forms flake twin. The orientation of flake twin grain on cleavage plane is different from that of dolomite. In nature, the appearance of flake twin grain can be used to explain that calcite has been subjected to geological stress after its formation.
Use of calcite
Calcite has various crystal shapes, and the main mineral of limestone, marble and beautiful stalactite is calcite. Travertine can be deposited in spring water, and it is often a secondary mineral in igneous rocks. In almond caves of basalt flow, calcite is often filled into veins in cracks of sedimentary rocks, or it is produced in the form of shells or rocks through biological action.
Iceland spar is often used as a polarizing prism because of its birefringence. If it is cut into columns in a certain way, it can be used as a prism of a microscope to detect the optical properties of minerals. Its quality requirements must be: colorless and transparent, without bubbles or cracks inside, without twins or distortion, more than 0.5 inch (12.5mm) cubic meters. Calcite is generally used as industrial raw materials such as chemicals and cement. Calcite is used as flux in metallurgical industry, and it is used to produce cement and lime in construction industry. Also used in plastics, paper, toothpaste. Used as a filling additive in food. When calcite is added in glass production, the glass will become translucent, which is especially suitable for making glass lampshades.
Calcite is found in limestone mountain and widely exists in limestone and metamorphic rock deposits in Tertiary and Quaternary. Calcite is a rock-forming ore of the earth, occupying more than 40% of the total crust, with no less than 200 kinds. Representative producing areas are China, Mexico, Britain, France, the United States and Germany. All countries in the world have mines. Calcite can be divided into large Calcite and small Calcite, and Iceland spar. Calcite in China is mainly distributed in Guangxi, Jiangxi and Hunan. Calcite in Guangxi is famous for its high whiteness and less acid-insoluble substances in the domestic market. Calcite is also found in the northeast of North China, but it is often accompanied by dolomite. The whiteness is generally below 94, and the acid insoluble matter is too high.
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Sprue in a sample of polypropylene (PP)
Processing: Polypropylene is injected into a mould via this inlet or 'sprue' Applications: Polypropylene has good resistance to chemicals and to fatigue.  It is widely used in food packaging in the form of rigid tubs, lids and screw-tops as well as in flexible films. [...] Technique: Cross-polarised light microscopy Length bar: 10 mm Further information: The colours in the image are the result of birefringence and relate to the residual strain in the polypropylene.   The pattern of strain is indicative of the flow of material during the injection process and highlighting the injection point or 'sprue' from which all the material flows radially into the mould.  The molecules are aligned parallel to the direction of flow. Contributor: J A Curran Organisation: Department of Materials Science and Metallurgy, University of Cambridge 
Source.
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musicmakesyousmart · 5 years ago
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advancednavigation · 2 years ago
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Outright Novices' Manual for Fiber Optic Sensors
What are fiber optic sensors?
The focal characteristic of all fiber optic sensors is that they depend upon a couple of optical properties, similar to compel, stage, state of polarization and recurrence, to be changed by measurands. Measurands could be pressure, temperature, electromagnetic field or evacuation.
All fiber optic sensors have an optical part that is distinguishing these property changes. For most sensors, this part is the optical fiber itself or a non-fiber optical part.
Fiber optic sensors with optical fiber as sensor part are assigned "inalienable fiber sensor" and sensors with a non-optical fiber distinguishing part are grouped "outward fiber sensor".
1. Characteristic Fiber Sensors
In the normal fiber sensor, outside measurands, for instance, pressure, vibration, temperature team up with optical fiber part and cause fiber bending, fiber distortion and a change of the refractive record of the identifying fiber.
Because of the refractive record change, lights that development through the fiber are influenced fittingly. The movements in light properties, for instance, light power, light recurrence and light stage are then perceived. The size of measurands communicating with the fiber can not altogether firmly established.
2. Superfluous Fiber Sensors
Birefringent valuable stone, power cloak or small film shields are most often used as sensor parts in unessential fiber sensors. Ordinarily they are facilitated into the optical way.
Right when the external power helps out the recognizing part, the light properties are changed as well. The sensor has light source, optical way and photo identifier parts. The size of measurands is distinguished like inalienable fiber sensors.
The Purposes of Fiber Optic Sensor
Wide Locale Recognizing and Checking
Due to optical fiber's impervious to electromagnetic field, Fiber Optic Gyrator have a significant conceivable there. They are by and large used in temperature recognizing in building, spillage seeing along oil pipelines, and so on.
The recently referenced applications are called wide locale recognizing or noticing. The name infers that the distinguishing covers a wide locale. Around here, fiber sensors are parcel into two classes: spread sensor and semi scattered sensor.
1. Coursed Sensor
Coursed sensors sense measurands continuouly over the entire length of the fiber. The principal decides is that Fiber Optic Gyroscope ought to be incredibly fragile to measurands.
A standard delineation of flowed sensors is a temperature sensor utilizing Raman disseminating influence in optical strands. Another model is OTDR (Optical Time Region Reflectometer) which distinguishes signal appearance in the whole length of an optical way.
2. Semi Appropriated Sensor
Semi appropriated sensors use discrete sensor parts that are meticulously coordinated in the fiber association. This sort expecting sensor ought to be little size, insignificant cost and high trustworthiness.
High Mindfulness Assessments
Another district for fiber sensors is the high responsiveness assessment applications. This sort of sensors typically utilize light impedance's extremely high mindfulness property.
Different interferometric fiber sensors have been used for assessment of temperature, strain, vibration, and so on. The fiber optic whirligig is one normal outline of this kind of uses.
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Inertial Navigation Systems
Autonomous Underwater Vehicle
GPS Compass
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shreeramenterprise · 2 years ago
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SPECTRAL DOMAIN OCT
Optical coherence tomography (OCT) was first developed by Fujimoto's group at MIT about 10 years ago and the method has since matured into an important clinical imaging modality. The success of OCT in making such a rapid transition from research and development into the clinical setting is not surprising given the numerous advantages that it offers clinicians. (i) Quality images—OCT has demonstrated the ability to render images with 0.5 m resolution . (ii) Flexibility—the light fluence level required for OCT imaging is low enough that OCT can be used in sensitive tissue locales, such as the eye . Further, OCT probes are typically optical fiber-based, and they may be made to be sufficiently small and pliable to operate within the gastrointestinal (GI) tract  and major blood vessels . (iii) Additional functionality—while a basic OCT imaging method is able to render depth-resolved structural images of the target, more sophisticated OCT imaging strategies can provide additional functional information, such as flow (through Doppler OCT) tissue structural arrangement (through birefringence OCT) and the spatial distribution of specific contrast agents (through molecular contrast OCT)
Since the invention of OCT, the method has been extensively applied in ophthalmology settings. The popularity of the method lies in its ability to perform high-resolution cross-sectional imaging and analysis of structural changes in the eye during disease progression. For example, OCT is excellent at rendering a depth-resolved profile of macular hole disease progression which generally involves a thinning or detachment of the retina and is difficult to assess with  face imaging methods . OCT has also been proven useful for ophthalmology applications  where structural information provides an indirect measure of physiologically relevant information that is useful for disease diagnosis. OCT's applications to image other parts of the human body include endoscopic GI tract imaging for tumor detection  monitoring and risk assessing of vulnerable lipid plaques in the vascular system , monitoring intracoronary stenting , and tracking structural weakness associated with tooth decay. OCT's applications in bioscience endeavors include tracking cardiac development in chick embryos  studying gastrulation in mouse embryos  and imaging neural morphology in Xenopus laevis
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https://www.labmedicasystems.com/mediworks-fc-162.php?c=12
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ptc-stress · 2 years ago
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Optical Lens Residual Stress Analysis
During the assembly process of the optical lens, when the lens is fixed by the fixing component, poor fixing often occurs, resulting in residual stress and poor optical imaging and changes in optical characteristics. Therefore, how to observe the internal residual stress of the optical lens is a very important and urgent problem in the optoelectronics industry.
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In 1853, Maxwell proposed the law of stress optics, proposing that when a material is stressed, its optical refractive index will change. This law establishes the theoretical basis for photoelastic stress analysis. Transparent materials are widely used, such as panels, optical lens industries. In its production, assembly and operation process, it will inevitably cause residual stress, thereby reducing the quality of the product. To change this phenomenon, we must first measure its stress. The photoelastic experiment method is the most suitable method to measure the global stress. When the finished optical lens is cracked or damaged in use, from the viewpoint of material science, this phenomenon means that the total stress value of the optical lens in the damaged area exceeds the physical strength value of the material itself. The residual stress in injection molded products is mainly caused by two reasons: one is the molecular alignment caused by the flow residual stress in the filling stage; the other is the thermal residual stress caused by uneven shrinkage in the cooling stage. The flow residual stress is mainly caused by the high shear rate during the plastic filling flow, and the cooling and demolding void point after filling is continuously released or frozen. Thermal residual stress is generated by uneven shrinkage and density changes after the high temperature plastic material is cooled to the glass transition temperature. To solve the problem of product damage in use, we should start from how to increase the physical strength of the material and how to reduce the stress value of the finished product. The stress on optical lenses can usually be divided into internal stress and external stress according to the source. Birefringence occurs when transparent plastic and glass optical lenses are stressed. At this time, the incident polarized light will be divided into a fast beam and a slow beam, and the relative distance of the speed difference is called the phase difference or retardation. In a monochromatic photoelastic fringe, the thick line represents the point where the principal stress direction is parallel to the polarized light. Therefore, the phase difference between the two beams of light is an integer wavelength, resulting in bright and dark fringes in the light field, and the fringes in the light field can be observed. The denser the fringes, the greater the stress, that is, the place where the stress is concentrated, and where the failure of the material first begins. The sparser the fringes, the smaller the residual stress. Because the composition of plastics is a long-chain polymer, generally there will be some residual stress left in the product during the molding process, especially in the injection molding process. During injection, the high shear rate, fast cooling, small feed gate and other factors will cause the residual stress of the injection product to be relatively serious. Therefore, it is inevitable that plastics will be stressed in the processing process (different types of plastics have different stress levels). The direction of the effort is how to reduce the residual stress of plastic products.
In the following figures (a) and (b), a qualitative Polariscope is used to observe the transparent plastic optical lens, from which the sensitivity of different plastics to molding stress can be known. (c)(d)(e) are the stress observation images of the glass material optical lens. (c) is the image taken by the optical lens without any external force, which is evenly distributed; (d) is the image taken after the optical lens is equipped with a fixing ring. When irradiated by polarized light, the stress distribution presents a circular arc distribution; (e) is the stress distribution diagram obtained by fixing the four-point screw of the optical lens.
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After research, we found that using a Polariscope to observe the residual stress of optical lenses is a relatively simple qualitative observation method, which enables optical lenses to be assembled on the production line to quickly obtain stress distribution information, and can quickly adjust the setting of molding parameters and reduce the number of finished products. residual stress and reduce the possibility of product damage.
https://www.ptc-stress.com/optical-lens-residual-stress-analysis/
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TSRNOSS. Page 241. Sorry about the break in continuity, but my files got jumbled, and this came up instead of 109, which latter is probably lurking somewhere in those files. I'll get around to finding it.
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siva3155 · 5 years ago
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300+ TOP ENGINEERING GEOLOGY Lab Viva Questions and Answers
ENGINEERING GEOLOGY Lab Viva Questions :-
1. The shape of the Earth is: Geoid 2. Age of the Earth is 4.6 billion years 3. Sial and Sima are separated by Conrad discontinuity 4. Morhorovicic discontinuity is found between Crust and Mantle 5. Mantle and Core are separated by Gutenberg discontinuity
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GEOLOGY Viva Questions 6. The term ‘NiFe’ refers to Core of the Earth 7. The plastic layer of the mantle is called Asthenosphere 8. The composition of Sial is Granitic to grano dioritic 9. The composition of Sima is Basaltic 10. The polar and equatorial diameter of the Earth is 12,713 km and 12,756 km Geomorphology : 11. The process of disintegration and decomposition is called Weathering 12. The process of Erosion includes Disintegration 13. Frost action takes place due to Freezing of water 14. Which minerals are highly susceptible to chemical weathering Ferromagnesian Minerals 15. Which are characteristic functions of the geomorphic agents Erosion, Transportation and Depositional works 16. William Morris Devis has recognised the stages involves in a cycle of river erosion are Initial stage, Youth stage, Mature stage and Old stage 17. In which stage of erosional cycle maximum changes occur Mature stage 18. Waterfalls and Gorges are characteristic features of the river in Initial stage 19. Pot holes are formed generally by Abrassion or Corrosion 20. Chemical erosion by river water is known as Corrosion 21. The transportation by Creeping and Rolling is known as Traction 22. The plain land produced by the river action is Peneplain 23. Deltas are formed in Old Stage of the River 24. The transportation through lifts and falls of materials is known as Saltation 25. Which type of drainage pattern develops in folded or tilted beds Trellis pattern 26. Canyon is A deep valley with steep near vertical sides 27. Pass is An opening between the Mountains 28. Aeolian topography is created by the geological action of Wind 29. Yardang topography associated with Wind action 30. Which instrument is used to measure the wind velocity Anemometer 31. Loess is Homogeneous and unstratified deposit of silt 32. A Crescent shaped dune with two tapering arms is known as Barchan 33. Wind ripples are generally formed by Saltation movement of sand grains 34. A normal sand-dune is characterised by Gentle windward and Steeper leeward sides 35. Blow-outs are Broad shallow depression in desserts 36. When one wing of a Barchan is missing, then it is known as Seif 37. The space between the dunes is known as Gassis 38. Chinook is a local hot wind which flows mostly in USA and Canada 39. Which abrasion is more effective in rounding the sand grains Wind abrasion 40. “Lag-Gravel” is The coarse sediments left behind where wind has removes the finer grain sizes 41. Glaciers are formed by Compaction and Re-crystallisation of snow 42. Ne’ve’ or Flrn are Granular ice mass 43. The polar glaciers are Below the freezing point throughout the year 44. The Karst topography developed due to the action of Groundwater 45. Which process is mainly responsible for development of the Karst topography Chemical Process 46. The columns of limestone that hang from the ceiling downwards are known as Stalactites 47. Stalagmites are Rising up vertically from the floor of the cavern 48. Blind valleys are found in Karst topography 49. Drip-stones are Columns formed by joining of Stalactite and Stalagmite 50. ‘Terra rossa’ is Residual red soil occurring on limestone in Karst region 51. The difference between lake and basin is Lakes commonly occur above the mean-sea level while basins have their bottoms below the water table. 52. Dhands are Small lakes of Aeolian origin 53. A narrow strip of water joining the two water bodies is called Strait 54. The ocean which is between Africa and Australia Indian Ocean Crystallography & Mineralogy : 55. The faces, edges and solid angles have a definite relationship with each other. This relationship is expressed by Euler’s formula 56. Euler’s formula is F+A = E+2 57. Centre of symmetry is Repetition is with respect to a point 58. Axis of Symmetry Repetition is with respect to a line 59. Plane of Symmetry Repetition is with respect to a plane 60. Which instrument is used to measure the interfacial-angle of crystals Goniometer 61. Which crystal system is having maximum of classes Hexagonal system 62. In which crystal system majority of minerals crystallises Monoclinic system 63. The Isometric system is characterised by 4 axes of 3 fold symmetry 64. What is the normal interfacial angle in dodecahedron form of cubic system 600 65. Gyroidal class belongs to Isometric system 66. The cleavages in twinned crystals are In different directions 67. Butterfly twinning is seen in Gypsum 68. Pericline twin is found in Plagioclase 69. The degree of transparency of a mineral is known as Diaphaneity 70. Give an example of a mineral in which cleavage is absent Quartz, Corundum 71. Hardness of human nail varies between 1.5 to 2.5 72. Hardness is which kind of property Anisotropic (A mineral may show different values in different directions.) 73. The tendency of a crystallized mineral to break along certain directions yielding more or less smooth, plane surface is Cleavage 74. The behaviour of a mineral towards the forces that tend to destroy it is called Tenacity 75. A Mineral is Naturally occurring inorganic substance with definite chemical composition 76. The external appearance of a Mineral is known as Habit/ Form 77. The powered form of a mineral is Streak 78. Shining property of a Mineral is Lustre 79. Form in which neither a crystal face nor a cleavage is seen in Amorphous 80. Quartz shows which lustre Vitreous 81. Which mineral shows silky lustre Asbestos, Gypsum 82. Mica is Flexible and elastic 83. Kyanite shows which form Bladed 84. Structure or form which depicts leaf like sheets is Lamellar 85. Muscovite mica shows which structure Foliated 86. Which form resembles human kidney Reniform 87. chromite shows which type of structure Granular 88. Colour changing phenomenon which involves oxidation is Tarnish (A phenomenon of change of original colours of minerals to some secondary colours at its surface due to oxidation at the surface) 89. Diamond shows which type of lustre Adamantine 90. Streak is an important diagnostic property of Coloured minerals 91. Generally which minerals give streak Coloured and opaque 92. Hardness of a mineral depends upon Chemical composition and atomic constitution 93. The scale of hardness is Mohs (It was in 1822 that Austrian mineralogist F. Mohs proposed a relative, broadly quantitative “scale of hardness” of minerals assigning values between 1 to 10) 94. Which mineral group is abundantly found in the Earth’s crust Feldspar group (Second abundant is Silicate or Quartz group) 95. Feldspar is found majority in which kind of rock Igneous rocks 96. Acicular habit shown in Natrolite 97. Violet colour of Amethyst is due to MnO2 98. The mineral which can be cut and powdered are known as Sectile 99. Opaque minerals indicate their origin from a Rapidly cooled silicate melt 100. Orpiment and Realgar are Sulphides of Arsenic Optical Mineralogy : 101. In natural light, the elctro-magnetic vibrations are: Always perpendicular to the direction of light-wave prorogation 102. Refractive index depends upon Nature of the substance and Kind of light used 103. The refractive index of Canada balsam is 1.54 104. Plane polarised light can be produced by Nicol prism, Reflections, Absorption 105. Backe-line method is used to determine the Refractive index 106. Which property determines the colour Wavelength 107. The wavelength varies from slightly more than …. at the red end to about …. at the violet end 7000 Å and 4000 Å respecively 108. The isotropic substance has A single refractive index 109. Double refraction phenomenon shown by Anisotropic substance 110. The angle between the reflected and refracted ray is 900, stated by Brewster’s law 111. Which crystal systems are optically uniaxial Hexagonal and Tetragonal 112. Which crystal systems have two optic axis Orthorhombic, Monoclinic and Triclinic 113. Uniaxial crystal are positive if Ordinary ray has the greater velocity than the Extraordinary ray 114. The difference between the maximum and minimum indices of a particular mineral is known as Birefringence 115. What is the birefringence of Quartz mineral 0.009 116. Birefringence is used to determine Thickness of section 117. Bereck compensator is an optical device which is made up of Calcite 118. The order of interference colour is determined by Quartz plate 119. A Polaroid is a Light filter 120. Biaxial minerals show Symmetrical extinction 121. Complete extinction occurs only when the section is Perpendicular to optic symmetry 122. Which is also known as Glimmer plate Gypsum plate 123. Amorphous substance are Anisotropic 124. Orthoclase is distinguished from Quartz in thin section by Low refractive index, Type of twinning and Negative sign 125. The Michael-Levy method is used to determine the extinction angle of Plagioclase 126. Which plate is generally used to determine the optical sign of plagioclase Selenite plate 127. The Orthopyroxenes show interference colour of 1st order 128. Which type of extinction is often shown by Quartz mineral Wavy 129. Calcite is characterised by Rhombohedral cleavage, low interference colour and optically negative character 130. Calcite and Magnesite can be distinguished from one another in thin section Magnesite is never twinned GEOLOGY Lab Viva Questions and Answers Pdf Download :: Read the full article
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Liquid crystals (LCs) are matter in a state which has properties between those of conventional liquids and those of solid crystals For instance, a liquid crystal may flow like a liquid, but its molecules may be oriented in a crystal-like way. There are many different types of liquid-crystal phases, which can be distinguished by their different opticalproperties (such as birefringence). When viewed under a microscope using a polarized light source, different liquid crystal phases will appear to have distinct textures. The contrasting areas in the textures correspond to domains where the liquid-crystal molecules are oriented in different directions. Within a domain, however, the molecules are well ordered. LC materials may not always be in a liquid-crystal phase (just as water may turn into ice or steam).
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apshalt8hack-blog · 7 years ago
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Airborne For PC
Tap here to turn on desktop notifications to get the news sent straight to you. The paper seeks to address the need to consider issues regarding professionalism in computer forensics in order to allow the discipline to develop and to ensure the credibility of the discipline from the differing perspectives of practitioners, the criminal justice system and in the eyes of the public. There is a need to examine and develop professionalism in computer forensics in order to promote the discipline and maintain the credibility of the discipline.
cadmium-manganese-telluride crystal that exhibits both the Pockels and Faraday effects is used to produce a Poynting-vector sensor for signals in the microwave regime. This multi-birefringent crystal can independently measure either electric or magnetic fields through control of the polarization of the optical probe beam. After obtaining all the relevant electric and magnetic field components, a map of the Poynting vector along a 50-Omega microstrip was experimentally determined without the need for any further transformational calculations. The results demonstrate that this sensor can be used for near-field mapping of the Poynting vector. Utilizing both amplitude and phase information from the fields in the microwave signal, it was confirmed for the case of an open-terminated microstrip that no energy flowed to the load, while for a microstrip with a matched termination, the energy flowed consistently along the transmission line.
These are not usually tested by us (because there are so many), so please use them at your own cheats gamer surveyanswer and enter for a chance to win $ video is queuequeuewatch next video is to make money in asphalt 8 ibesubscribedunsubscribe2, to watch this again later?Sign in to add this video to a to report the video?Sign in to report inappropriate in to make your opinion 't like this video?Sign in to make your opinion interactive transcript could not be is available when the video has been feature is not available right now.
The Kepler mission monitors > 100,000 stellar targets using 42 2200 1024 pixel CCDs. Bandwidth constraints prevent the downlink of all 96 million pixels per 30-minute cadence, so the Kepler spacecraft downlinks a specified collection of pixels for each target. These pixels are selected by considering the object brightness, background and the signal-to-noise of each pixel, and are optimized to maximize the signal-to-noise ratio of the target. This paper describes pixel selection, creation of spacecraft apertures that efficiently capture selected pixels, and aperture assignment to a target. Diagnostic apertures, short-cadence targets and custom specified shapes are discussed.
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shogoyamashita · 8 years ago
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Shogo Yamashita
‒ CV (curriculum vitae)
http://yamasy.com/publications/
‒ Research Plan
Tittle: Human-Computer Interaction in Underwater  Keywords: Underwater Entertainment, Virtual Reality  
We introduced a surround-screen swimming pool filled with transparent tracer particles for water flow visualization. The particles enable interactions in underwater entertainment by tracing the water flows by a camera. Moreover, swimming training users can see his/her swimming form displayed on the bottom with visualized water flows caused by strokes in the swimming pool.   The transparent tracer particles have a flat shape. For this reason, the tracking system sometimes loses the visualized particles when they are vertical since they look very thin from the camera for tracking. Moreover, the width and height constantly change. This shift in size reduces the stability of blob detection since we can not define the threshold for blob size. To avoid this issue, we have to invent ball shaped tracer particles. In addition, the flat shaped tracer particles become recognizable when they reflect light from the background. Water absorptive polymer used for growing plants are ball shape and becomes quite transparent in water without reflection. With some stress on the surface, the plastic also shows the characteristic of photoelasticity. We suspect water absorptive polymer showing photoelasticity by default without stress can solve the issue.
‒ Social Issues and the Research
Although swimming is considered to be one of the best exercises to maintain our health, swimming in a pool is normally monotonous; thus, maintaining its motivation is sometimes difficult. AquaCAVE is a computer-augmented swimming pool with rear-projection acrylic walls that surround a swimmer, providing a CAVE-like immersive stereoscopic projection environment. The system can also provide swimming training with projections such as record lines or swimming forms.
‒ GCL Plan in 2017
A surround-screen swimming pool can realize various forms of underwater entertainment and enable enhanced swimming training with supplemental visual information during underwater activities. However, one of the big challenges for such an augmented swimming pool is user interaction because the surround screen and water can make existing position-tracking methods unusable. we propose a water flow visualization method with transparent tracer particles to enhance interactivity. We used an optical property of clear plastics called birefringence that provides vivid colors on transparent tracer particles when they are between two circular polarization sheets. Tracing objects using cameras in front of a complex background is not a stable method, but this technology enables visible tracer particles on a simple and dark background. For underwater entertainment, the water flow tracing works as a user interface because the transparent tracer particles do not stop users from viewing the images on the screen. For enhanced swimming training, swimmers can view visualized water flow caused by strokes in the augmented swimming pool.
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tombadger · 8 years ago
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(via Flow Birefringence of Milling Yellow - YouTube)
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