Extinction Angle Research Articles

Hydrogenation-induced change of magneto optical Kerr effect in Pd/Fe bilayers

The hydrogenation induced change of magneto-optical Kerr effect (MOKE) was studied in n ML Pd/30 ML Fe bilayers on Al2O3(0001). With the increasing of Pd thickness from 3 ML to 60 ML, the MOKE extinction angle was gradually shifted by 0.6° and the enhancement of Kerr intensity reached 35%–40% after exposure to 1 atm hydrogen. The reversibility of this significant change was demonstrated by cyclic desorption and reabsorption of hydrogen. This study reveals the sensitive MO response in the combination of a magnetic Fe thin film with a highly hydrogenated Pd capping layer.

Precipitation of rutile and ilmenite needles in garnet: Implications for extreme metamorphic conditions in the Acadian Orogen, U.S.A.

We report the discovery of oriented needles of rutile and ilmenite in garnet crystals from granulite facies metapelitic rocks of the Merrimack synclinorium, Connecticut, and present a precipitation model for their origin. The rocks were strongly metamorphosed and deformed during the Devonian Acadian orogeny. The needles are primarily elongated parallel to in garnet. Rutile has anomalous extinction angles as great as ~35° (cf. Griffin et al. 1971). Rutile and ilmenite needles are typically a few hundred nanometers to several micrometers in diameter and are several tens of micrometers to nearly a millimeter long. Other oxide inclusions that may be present include submicrometer- to micrometer-scale twinned rutile bicrystals, as well as srilankite and a crichtonite group mineral. Some garnet cores have unusual, box-shaped quartz inclusions, which coexist with Ti±Fe oxide needles and commonly contain micrometer-scale rods of F-OH-Cl apatite. Negative garnet crystal “pores” are also widespread. Ti±Fe oxide needles are restricted to garnet core regions; rims have a distinctly different inclusion population dominated by granulite facies minerals including sillimanite, spinel, cordierite, and K-feldspar. Consequently, the garnet core regions represent an earlier, distinct period of growth relative to the rims. Garnet cores contain ~25–35% pyrope, and a host of minor and trace constituents including TiO2 (0.07–0.6 wt%), Cr2O3 (0.01–0.10 wt%), Na2O (0.01–0.03 wt%), P2O5 (0.01–0.09 wt%), and ZrO2 (up to ~150 ppm). Na2O and ZrO2 correlate positively with TiO2. Titanium zoning is preserved in some garnets; zoning profiles and two-dimensional chemical mapping show that Ti and, to a lesser degree, Cr are depleted around Ti±Fe oxide inclusions. Therefore, we conclude that the needles are precipitates that formed from Ti-bearing garnet during exhumation and cooling. Garnet contained sufficient Ti to form precipitates; no Ti source external to garnet was necessary. Titanium-bearing garnets that contain oriented Ti±Fe oxide needles are known primarily from ultrahigh-pressure metamorphic rocks, mantle peridotites and pyroxenites, and high-pressure granulites. Thus, the presence of needle-bearing garnets in Connecticut strongly suggests that a previously unrecognized domain of extreme pressure and/or temperature metamorphism exists in the Acadian orogen.

Rheophysical Properties of Fluorinated Nonionic Micellar Phases

Micellar phases can be used as templates for the preparation of mesoporous silica materials. Fluorinated and hydrogenated surfactants can provide a large variety of well-defined micellar structures: spherical and cylindrical micelles as well as more complex structures such as lamellar or sponge phases can be formed in various thermodynamic conditions. However, the preparation of ordered mesoporous materials from these organized media is not always successful for a reason not known at the moment. It thus seems of the highest importance to properly characterize the micellar solution prior to the addition of the silica precursor during the material synthesis. In this paper, we describe some rheophysical properties of the micellar phase L(1) prepared with a fluorinated surfactant, the formula of which is C(7)F(15)C(2)H(4)(OC(2)H(4))(8)OH, labeled as R(F)(7)(EO)(8). This surfactant forms micelles in water, and the direct micellar phases have been characterized in a wide range of temperatures and surfactant concentrations. The rheological properties of the L(1) phase have also been studied as a function of temperature and concentration. Under steady and dynamic flow conditions, the solutions behave like Newtonian or shear thinning fluids depending on the temperature and surfactant concentration. A crossover between G' and G" is observed in the solution at the concentration of 20 wt % and at the temperature of 10 °C, suggesting the presence of long entangled micelles in solution at this temperature. When subjected to the action of a shearing device, the 20 wt % solution becomes optically anisotropic and shows flow birefringence, but the average orientation of the micelles quantified by the extinction angle χ shows an unexpected behavior when the shear rate is gradually increased.

Limit induced bifurcation due to converter transformer tap and DC controller limit

The limit induced bifurcation (LIB) in AC/DC power system caused by converter transformer tap and extinction angle limit under the control mode of constant current in rectifier and constant voltage in inverter is studied in this paper. The reason why the singularity induced bifurcation does not occur while the hard limit encounters is analyzed. The transformer ratio should be larger than a critical value while LIB occurs and the formulas for critical value of LIB in defferent types are derived in this paper. The sensitivities of critical value to parameters are calcaulated, from which some bifurcation points are eliminated and the stable region is augmented. And, the effects of field voltage limit on critical value and stable region are discussed. Finally, a mechanism of limit induced bifurcation is proposed. The increase of reactive power consumed in converter transformer and the decrease of the reactive power compensation in converter AC bus and the transform of control mode result in the system destabilization due to the lack of reactive power.

An experimental study on the effects of injection-molding types for the birefringence distribution in polycarbonate discs

Even though injection molding technology has been developed for many years, it is still needed to study the effect of processing conditions on the final properties of injection-molded parts for producing precision products in optical field. The optical anisotropy, i.e., birefringence, is a significant factor which affects the function of many optical components. In the present study, we have focused on the effects of packing and compression processes on the birefringence structure remaining in the disc by examining the gap-wise distribution of birefringence and extinction angle. As a result, two extra birefringence and extinction peaks near the center in thickness direction showed the effect of packing pressure, which came from the extra flow during packing stage. Furthermore, more uniform birefringence distribution was found in injection/compression case than in conventional injection-molded case. Depending on the process condition, even the reversal flow was found from the distribution of extinction angle in injection/compression case. Finally, graphical representation technique of optical refractive indicatrix was suggested to show the difference of final birefringence structure for different process types.

Generation and dynamics of quadratic birefringent spatial gap solitons

A method is proposed to generate and study the dynamics of spatial light solitons in a birefringent medium with quadratic nonlinearity. Although no analytical expression for propagating solitons has been obtained, our numerical simulations show the existence of stable localized spatial solitons in the frequency forbidden band gap of the medium. The dynamics of these objects is quite rich and manifests for instance elastic reflections, or inelastic collisions where two solitons merge and propagate as a single solitary wave. We derive the dynamics of the slowly varying envelopes of the three fields (second harmonic pump and two-component signal) and study this new system theoretically. We show that it does present a threshold for nonlinear supratransmission that can be calculated from a series expansion approach with a very high accuracy. Specific physical implications of our theoretical predictions are illustrated on LiGaTe${}_{2}$ (LGT) crystals. Once irradiated by a cw laser beam of $10 \ensuremath{\mu}$m wavelength, at an incidence beyond the extinction angle, such crystals will transmit light, in the form of spatial solitons generated in the nonlinear regime above the nonlinear supratransmission threshold.

Densification behavior and microstructure of carbon/carbon composites prepared by chemical vapor infiltration from xylene at temperatures between 900 and 1250 °C

Carbon/carbon composites were prepared by film boiling chemical vapor infiltration from xylene pyrolysis. Their densification behaviors such as the mass gain, the deposition rate and the density profile were investigated. The microstructure was studied by polarized light microscopy and characterized quantitatively with average extinction angle (Ae). Results showed that, under the particular experimental equipment and process, the initial deposition rate and the average Ae of pyrocarbon (PyC) increased with the increasing deposition temperature ( T d). The structural transition of PyC from rough laminar (RL) to smooth laminar along both the axial and radial directions of the composites was retarded as T d increased from 900 to 1100 °C; PyC was deposited by the heterogeneous nucleation and growth. The homogeneous nucleation was generated producing isotropic PyC at the bottom of the composites for 1200–1250 °C deposition. The matrix produced at 1100–1250 °C was dominated by RL PyC, and the composites with high average density and uniform RL matrix were rapidly produced for T d around 1100 °C.

Analysis and control of self-excited induction generator-converter systems for battery charging applications

A method has been developed for the analysis of operation of self-excited induction generators (SEIGs) supplying battery charging loads through three-phase semi-converters by representing the battery circuit as equivalent resistance and reactance in the equivalent circuit of these generators. Such equivalent values are functions of the dc charging voltage and current and the control angle set in the converter. The solution for this circuit has been carried out using the genetic algorithm technique instead of using higher-order polynomials for the loop or nodal equations of the circuit. Apart from the conventional phase angle control, other firing control schemes namely negative firing angle control, extinction angle control and symmetrical angle control have been considered for the operation of the converter. The relative performance of these control schemes, for the various modes of operation of SEIG-converter systems such as constant and variable speed, has been brought out. Experimental results obtained on a three-phase SEIG charging suitable batteries through an IGBT-based semi-converter, controlled with all these schemes, confirm the usefulness of the proposed system and the validity of its analysis.

OPTICAL ANOMALY IN IRIDESCENT ANDRADITE FROM THE SIERRA MADRE MOUNTAINS, SONORA, MEXICO

Detailed investigations of the optical anomalies, surface and internal lamellar textures in a crystal of iridescent andradite from Sonora, Mexico, were made by optical polarizing microscope, electron-probe micro-analyzer (EPMA) and back-scattered electron imaging (BEI). The average chemical composition measured by EPMA is Adr 79 Grs 21 in the {112} sector and Adr 95 Grs 5 in the {110} sector. There is a pronounced chemical sector zoning in the {112} sector. In a (110) thin section, the {112} sectors exhibit a much stronger optical anomaly, with an extinction angle 40° inclined to the [113] direction, whereas the {110} sector is almost isotropic. The andradite is optically biaxial with a 2 V x of 86°– 88°. The principal optical direction X nearly coincides with the growth direction [112]. The Z direction is inclined to the axis [220], Y is inclined to the axis [001], and both rotate up to 10° around the axes. The optic axial plane is parallel to the plane of symmetry m . The symmetry determined optically is triclinic.

사출 및 사출/압축 성형품 내에서의 복굴절 구조 변화에 관한 연구

It is still needed to study the effect of process conditions on the final properties of injection-molded parts for producing precision optical products. Especially, the optical anisotropy, i.e., birefringence, is a significant factor to affect the function of many optical components. In the present study we have focused on the effect of holding and compression processes on the birefringence remaining in the transparent disc by examining the gap-wise distribution of birefringence and extinction angle. As a result, two extra birefringence and extinction peaks near the center in thickness direction showed the effect of holding pressure, which came from the flow in packing stage. However, more uniform birefringence distribution than injection-only cases could be found in injection/compression cases. Depends on the process condition even the flow reversal could be found from the distribution of extinction angle. Finally, graphical representation of optical indicatrix was added for better understanding the final structure of injection-only and injection/compression cases.

Densification and microstructure of carbon/carbon composites prepared by chemical vapor infiltration using ethanol as precursor

Chemical vapor infiltration of carbon fiber felts with uniform initial bulk density of 0.47 g·cm−3 was investigated at the ethanol partial pressures of 5–20 kPa, as well as the temperatures of 1050, 1100, 1150 and 1200°C. Ethanol, diluted by nitrogen, was employed as the precursor of pyrolytic carbon. Polarized light microscopy (PLM), scanning electron microscopy and X-ray diffraction were adopted to study the texture of pyrolytic carbon deposited at various temperatures. A change from medium- to high-textured pyrolytic carbon was observed in the sample infiltrated at 1050°C. Whereas, homogeneous high-textured pyrolytic carbons were deposited at the temperatures of 1100, 1150 and 1200°C. Extinction angles of 19°–21° were determined for different regions in the samples densified at the temperatures ranging from 1100 to 1200°C. Scanning electron microscopy of the fracture surface after bending test indicated that the prepared carbon/carbon composite samples exhibited a pseudo-plastic fracture behavior. In addition, fracture behavior of the carbon/carbon samples was obviously effected by their infiltration temperature. The fracture mode of C/C composites was transformed from shearing failure to tensile breakage with increasing infiltration temperature. Results of this study show that ethanol is a promising carbon source to synthesize carbon/carbon composites with homogeneously high-textured pyrolytic carbon over a wide range of temperatures (from 1100 to 1200°C).

Supply power factor and load current harmonic performance improvement of three phase AC voltage controller

AC voltage controllers as power converters used in many application between power ranges from few watts up to fractions of megawatts, such as light dimmers, induction motor soft starter, industrial heating and cycloconverters. Overall efficiency of power system controlled by some advanced methods in power converters is very important which covers supply and load power factor, harmonic distortion at both supply and load side. One of these advanced methods that is best used is the conventional controller, with phase angle control (PAC) of thyristors and it is a known method in contolling AC voltage applied to specific loads. However, these controllers are found to create some problems whose main problems are introduction of high level low order harmonics in current at the load and supply side, poor supply power factor and also low efficiency. This paper presents a proposed three phase AC voltage contoller scheme which allows the application of extinction angle control (EAC) to overcome these problems. Also, a comparison is given between proposed and conventional controllers on the basis of simulation under this viewpoints. The improvements are obtained in terms of high supply power factor, low harmonic content in the load current and high efficiency by proposed controller on comparing to conventional controllers. Key words: AC voltage controller, soft starter, thyristor, power factor, harmonic.

Extinction and small angle scattering by thin plate crystals

In the framework of the physical optics method, we performed a numerical study of the energy and polarization characteristics of the optical radiation, transmitted through the semitransparent plate crystal. It is found that the dependence of the energy characteristic of the field, scattered in the near-forward direction, on the particle physical parameters is most substantial for the scattering angle not exceeding 4 degrees, and for IR wavelengths. It is shown that for certain combinations of the particle physical parameters, the off-diagonal elements of the extinction matrix and scattering matrix differ from the first elements of the respective matrices within 1 order of magnitude.

Deposition of pyrolytic carbon using ethanol as precursor in chemical vapor infiltration

Using ethanol as the precursor of pyrolytic carbon,chemical vapor infiltration of a carbon fiber felt with an initial bulk density of 0.47g/cm3 was performed at the temperature of 1125°C and the pressure of 20kPa,resulting in a bulk density of 1.67g/cm3 after densification of 114h.Extinction angles from 19.5° to 20.5° for various regions in the densified sample are determined,which correspond to a high-textured carbon,leading to flexure strength of 137MPa.Analysis of 2D texture distribution suggests that ethanol is a promising carbon source to synthesize carbon-carbon composites with homogeneously high-textured pyrolytic carbon.

Magneto-optic Faraday effect in maghemite nanoparticles/silica matrix nanocomposites prepared by the Sol–Gel method

Bulk monolithic samples of γ-Fe 2O 3/SiO 2 composites with different iron oxide/silica ratios have been prepared by the sol–gel technique. Iron oxide nanoparticles are obtained in-situ during heat treatment of samples and silica matrix consolidation. Preparation method was previously optimized to minimize the percentage of antiferromagnetic α-Fe 2O 3 and parallelepipeds of roughly 2×5×12 mm 3, with good mechanical stability, are obtained. RT magnetization curves show a non-hysteretic behavior. Thus, magnetization measurements have been well fitted to an expression that combines the Langevin equation with an additional linear term, indicating that some of the nanoparticles are still superparamagnetic as confirmed by X-ray diffraction and electron microscopy measurements. Zero field cooled /field cooled experiments show curves with slightly different shapes, depending on the size and shape distribution of nanoparticles for a given composition. Magneto-optical Faraday effect measurements show that the Faraday rotation is proportional to magnetization of the samples, as expected. As a demonstration of their sensing possibilities, the relative intensity of polarized light, measured at 5° from the extinction angle, was plotted versus applied magnetic field.

Lubricated optical rheometer for the study of two-dimensional complex flows of polymer melts

We describe a novel optical cross-slot channel rheometer generating two-dimensional and isothermal complex flows of polymer melts. This is made possible by lubricating the channel front and back viewing windows. Flow-induced birefringence and particle tracking velocimetry are reviewed and used to investigate the cross-slot flow of a low density polyethylene melt involving mixed shear and planar extensional deformations. This new device solves the issue of end effects in flow birefringence experiments where no variations of the optical properties along the light path are expected. It greatly facilitates the interpretation of stress field data by providing reliable measurements of the polymer melt extinction angle χ and retardation δ , with a spatial resolution of one tenth of a millimeter. At the same time, it offers an enhanced temperature control and an increased optical accuracy due to an improved laser beam shaping. The capabilities and performances of this unique type of lubricated rheometer are discussed in detail and compared with previous approaches.

Automatic control of high-voltage DC power transmission on the basis of self-organizing regulators with extrapolation

Automatic control of high-voltage DC transmission is considered. The methods of regulation in rectification and inverter modes, measurements, and forecasting for such systems are described. The use of the algorithm of the self-organizing regulator with extrapolation (SORE) for forecasting the extinction angle in a thyristor is proposed.

Viscosity and Structural Alteration of a Coarse-Grained Model of Polystyrene under Steady Shear Flow Studied by Reverse Nonequilibrium Molecular Dynamics

The reverse nonequilibrium molecular dynamics (RNEMD) method is implemented to predict the viscosity of a coarse-grained model of short-chain polystyrene. The coarse-grained model has been derived to reproduce the structure of polystyrene. It is therefore not a generic model, but polymer-specific. Here, its performance for dynamical quantities is tested. The zero-shear viscosity is compared with experimental data. The pronounced difference can be mainly attributed to the inherent dynamic properties of the coarse-grained model. The qualitative results are compared to previous results calculated via conventional nonequilibrium molecular dynamics (NEMD) and more generic polymer models, and the agreement is reasonable. The structural alterations under shear are investigated by characterizing the molecular deformation and birefringence extinction angle.

Chalcedony (a crystalline variety of silica): Biogenic origin in electric organs from living Psammobatis extenta (family Rajidae)

The electric organs of electric fish have been used extensively for the study of peripheral cholinergic synapses. Aluminum and silicon have been observed in the electrocytes of Psammobatis extenta, a fish belonging to the family Rajidae, using a combination of scanning electron microscopy and X-ray spectrometry. Based on this evidence, the presence of silica minerals has been documented by means of mineralogical techniques. Electric organ cryostat sections and subcellular fractions were observed using a Leica DMLP mineralogical microscope. The shape, size and color, among other properties, were analyzed in plane-polarized light, while birefringence and the extinction angle, which allow for mineral identification, were observed through crossed-polarized illumination. The distribution of chalcedony, an oxide silicon mineral, in the sections and all the fractions of the electric organ was recorded. X-ray diffraction analysis of the electric organ segments showed a similar result, with a low-quartz variety. Chalcedony precipitation occurred at a specific pH (7–8) and oxidation potential (Eh; 0.0 to −0.2). This observation supports the important role played by pH and Eh conditions in silica precipitation in electrocytes, as has been reported in geological environments. It is possible that silica formation and silica degradation in electric organs are also related to the enzymes, silicatein and silicase, that direct the polymerization and depolymerization of amorphous silica in sponges. Carbonic anhydrases (silicase) are involved in physiological pH regulation. Crystallization of chalcedony via spiral growth from a partially polymerized fluid is consistent with processes known to occur in organic systems. This is the first time that a biogenically produced crystalline mineral phase (i.e., chalcedony) has been observed in the electrocytes and cholinergic nerves from living electric fish.

Measurement of the extinction angle about laminar pyrocarbons by image analysis in reflection polarized light

A new technique, including optical imaging and data processing, was presented for measuring of the extinction angle of pyrocarbons deposited around carbon fibers. The experiment was performed using a rotating analyzer in the reflection polarized light microscope coupled with a digital imaging camera. The special specifications for adjusting each part in the optical arrangement were detailed. The principle of the proposed method was discussed from the crystal grain distribution of pyrocarbons and the extinction property of graphite. The researched C/C composites respectively contain smooth laminar, rough laminar and dark laminar pyrocarbons. The digital images were captured at intervals of 1°. The extinction curves were plotted by fitting the sampled pixel values, and the extinction angles were obtained corresponding to the lowest point of these curves. The correlation between the experimental results and the observation by eyes in PLM is consistent with Bourrat's conclusion.