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Abstract  Another hybrid conjugate gradient algorithm is subject to analysis. The parameter β k is computed as a convex combination of $$ \beta ^{{HS}}_{k} $$ (Hestenes-Stiefel) and $$ \beta ^{{DY}}_{k} $$ (Dai-Yuan) algorithms, i.e. $$ \beta ^{C}_{k} = {\left( {1 - \theta _{k} } \right)}\beta ^{{HS}}_{k} \theta _{k} \beta ^{{DY}}_{k} $$. The parameter θ k in the convex combination is computed in such a way so that the direction corresponding to the conjugate gradient algorithm to be the Newton direction and the pair (s k , y k ) to satisfy the quasi-Newton equation $$ \nabla ^{2} f{\left( {x_{{k 1}} } \right)}s_{k} = y_{k} $$, where $$ s_{k} = x_{{k 1}} - x_{k} $$ and $$ y_{k} = g_{{k 1}} - g_{k} $$. The algorithm uses the standard Wolfe line search conditions. Numerical comparisons with conjugate gradient algorithms show that this hybrid computational scheme outperforms the Hestenes-Stiefel and the Dai-Yuan conjugate gradient algorithms as well as the hybrid conjugate gradient algorithms of Dai and Yuan. A set of 750 unconstrained optimization problems are used, some of them from the CUTE library. [ABSTRACT FROM AUTHOR]

In this work, the mesomorphic, morphologic, thermotropic, thermooptical, and thermodynamical properties of 4-(octyloxy)-N-(4-hexylphenyl)-2-hydroxybenzalimine thermotropic liquid crystalline compound, which was synthesized by our group, have been studied in detail. This compound displays smectic C and nematic mesophases. These mesophases are enantiotropic and exhibit specific confocal and schlieren textures, respectively. Thermotropic, thermooptical, and thermodynamical properties of the compound at direct and reverse phase transitions between smectic C and nematic mesophases and also between nematic mesophase and isotropic liquid have been investigated. The peculiarities of the bistable heterophase regions of these phase transitions have been studied. [ABSTRACT FROM AUTHOR]

This paper presents an analysis of diffraction effects taking place at different Schlieren diffracting elements. Two types of diffraction effects are prominent in the Schlieren schemes. One is diffraction of direct light (source image) at the Schlieren element, which limits the sensitivity and resolution of Schlieren systems. The second type is the diffraction of light deflected from the test object at the Schlieren-diffracting element. This second type of diffraction degrades the quality of Schlieren results. Experimental results showing the effect of diffraction of light deflected from the test object at a phase knife-edge, corner of a square phase aperture and an optical fiber tip as Schlieren diffracting elements have been presented and discussed. [ABSTRACT FROM AUTHOR]

We present a novel approach for examining the complex feeding behavior of a filter feeder at a previously unexploited scale. A Daphnia lives in a viscous environment and thus creates a feeding current with a distinct laminar inflow and a repetitive pulsed outflow. We propose that by treating the feeding apparatus as a black box, and using the pulsed outflow current as a surrogate to the inside working of the apparatus, we can calculate feeding rate in near real time. The structure of the outflow is interpreted as a direct representation of the organism’s response to its environment. Therefore, we examine how the work performed by an organism’s feeding apparatus is altered according to environmental factors and metabolic demands. Our approach is an integration of optical (Schlieren system) and electrochemical (chronoamperometry) techniques that allow for real time visualization and temporal analysis of flow systems, respectively. As electrochemistry requires a tracer chemical, we employed low dopamine concentrations (≤ 1mM), and tested the effect of dopamine on the heart rate and swimming of Daphnia. It appears that dopamine free in solution at concentrations below 10 mM has no adverse effects on the organism, and all observed differences in Daphnia feeding behavior were due to environmental or metabolic factors. The feeding nature of daphnids in the presence or absence of food, and differences between the sexes is reported. Our results indicate that in the absence of food a Daphnia has a strict and repetitive feeding behavior with short delays between pumping actions. However, in the presence of food this behavior becomes complex, with increased delays between pumps, perhaps designed to maximize feeding efficiency. Our observations demonstrate that males have a higher appendage beat frequency than females under identical conditions. We hypothesize that the difference may be dictated by metabolic demand, as a male spends more time actively seeking a mate. The application of electrochemistry to the study of Daphnia feeding behavior is an improvement over current methods for its near real time quantification of behavioral response, its versatile application under varying environmental conditions and its extreme sensitivity to changes in the organism’s feeding behavior. This technique is a valuable addition to the current tools available for studying Daphnia feeding behavior and will allow us to learn more about the interactions of an organism with its environment. [ABSTRACT FROM AUTHOR]

The anode region of an argon high intensity arc with a superimposed cold flow has been investigated experimentally. Three-dimensional electron temperature and electron density distributions have been obtained with a laser Thomson scattering system, and the flow fields have been observed with a high speed Schlieren system. The transition from a steady mode to a takeover mode and finally to a restrike mode has been clearly identified. During the transition, the flow field becomes turbulent and the electron temperature and the electron density values in the major anode attachments increase significantly. Starting from a takeover mode, extended anode boundary layers have been found, which have high electron temperatures and low electron densities, indicating their non-equilibrium nature. In a restrike mode, the restrike behaviour has been found to be initiated by flow instabilities, which bring high electron temperature clouds into the extended anode boundary layer and encourage the electron overheating instabilities. Finally, together with the anode burn patterns, the experimental results are applied to plasma spray torches and a takeover mode is suggested as the favourable operation mode. [ABSTRACT FROM AUTHOR]

Abstract   We observed a profile of nonequilibrium superfluid-normal (SN) interface of 4He near a vertical wall. A glass, brass or copper wall was used. The SN interface was produced by cooling liquid 4He in a bath from the bottom, where liquid 4He was pumped through a flow impedance in order to cool down the liquid. Superfluid (Normal fluid) occupied the lower (upper) part of the bath. The SN interface was visualized by three methods: simple visualization, shadowgraphy and schlieren method. The interface touched a vertical glass wall at almost 90. A large hollow was observed near a brass wall which had intermediate thermal conductivity. Downward flow was observed on a copper wall due to the very good thermal conductivity of the wall. Various types of interface profile were observed depending on the thermal conductivity of the wall used. [ABSTRACT FROM AUTHOR]

Abstract  Three-dimensional density information of a double free air jet was acquired using optical tomography. The projections of the density field were measured using the background oriented schlieren method (BOS). Preceding the free jet measurements, the sensitivity, accuracy and resolution of the BOS method were investigated. The sensitivity depends mostly on the focal length of the lens used, the relative position of the object between camera and background and the smallest detectable shift in the image plane. The accuracy was found to be sufficiently high to apply a tomographic reconstruction process. The resolution is determined by the transfer function of the BOS-method. It is not constant and depends on the size of the interrogation windows used for the cross-correlation-algorithm. The reconstruction of the free jet was computed, using filtered back projection. The reconstructed 3D density field shows with good resolution the typical diamond structure of the density distribution in under-expanded free jets. [ABSTRACT FROM AUTHOR]

Abstract  Experiments to demonstrate the use of the background-oriented schlieren (BOS) technique in hypersonic impulse facilities are reported. BOS uses a simple optical set-up consisting of a structured background pattern, an electronic camera with a high shutter speed and a high intensity light source. The visualization technique is demonstrated in a small reflected shock tunnel with a Mach 4 conical nozzle, nozzle supply pressure of 2.2 MPa and nozzle supply enthalpy of 1.8 MJ/kg. A 20� sharp circular cone and a model of the MUSES-C re-entry body were tested. Images captured were processed using PIV-style image analysis to visualize variations in the density field. The shock angle on the cone measured from the BOS images agreed with theoretical calculations to within 0.5�. Shock standoff distances could be measured from the BOS image for the re-entry body. Preliminary experiments are also reported in higher enthalpy facilities where flow luminosity can interfere with imaging of the background pattern. [ABSTRACT FROM AUTHOR]

Experiments to demonstrate the use of the background-oriented schlieren (BOS) technique in hypersonic impulse facilities are reported. BOS uses a simple optical set-up consisting of a structured background pattern, an electronic camera with a high shutter speed and a high intensity light source. The visualization technique is demonstrated in a small reflected shock tunnel with a Mach 4 conical nozzle, nozzle supply pressure of 2.2 MPa and nozzle supply enthalpy of 1.8 MJ/kg. A 20° sharp circular cone and a model of the MUSES-C re-entry body were tested. Images captured were processed using PIV-style image analysis to visualize variations in the density field. The shock angle on the cone measured from the BOS images agreed with theoretical calculations to within 0.5°. Shock standoff distances could be measured from the BOS image for the re-entry body. Preliminary experiments are also reported in higher enthalpy facilities where flow luminosity can interfere with imaging of the background pattern. [ABSTRACT FROM AUTHOR]

The onset of Mach reflection or regular reflection at the vertices of a converging polygonal shock wave was investigated experimentally in a horizontal annular shock tube. The converging shock waves were visualized by schlieren optics. Two different types of polygonal shock convergence patterns were observed. We compared the behavior during the focusing process for triangular and square-shaped shocks. It is shown that once a triangular shaped shock is formed, the corners in the converging shock will undergo regular reflection and consequently the shape will remain unaltered during the focusing process. A square-shaped shock suffers Mach reflections at the corners and hence a reconfiguring process takes place; the converging shock wave alternates between a square and an octagon formation during the focusing process. [ABSTRACT FROM AUTHOR]

We report the use of optical coherence tomography (OCT) for noninvasive measurement of the refractive index profile of a crystalline lens of a fisheye. The approach exploits the fact that OCT provides a direct measurement of the optical path of the light traveled through the medium. The gradient refractive index profile for the crystalline lens was retrieved by iterative fitting of the optical path calculated by the ray tracing method with that experimentally measured using OCT. The estimated error in refractive index is approximately 1%. The measured gradient refractive index and Matthiessen’s ratio (ratio of focal length to lens radius) are in good agreement with the previously reported values. [ABSTRACT FROM AUTHOR]

Within the framework of boundary diffraction wave theory it has been shown that the first bright fringe on either side of the central dark fringe of the phase knife-edge Fresnel diffraction pattern could be broadened to cover the whole field of view. Broadening of the first diffraction fringe, instead of conventionally modifying the spatial frequency spectrum, enhances the sensitivity of the Schlieren system. The use of phase knife-edge as viewing diaphragm in Schlieren diffraction interferometry not only enhances the fringe contrast but also avoids the loss in phase information as it lets through light from all parts of the test object and its thin interfacing makes the method suitable even for studying weak disturbances. [ABSTRACT FROM AUTHOR]

In this work, spark plug and corona discharge of 3–20 ms in duration have been used for ignition of stoichiometric and lean fuel methane/air mixtures. Comparison of spark plug and corona ignition abilities shows that corona discharge allows more efficient ignition with less discharge energy. It is proved experimentally that corona ignition provides faster combustion due to larger discharge volume, generation of turbulence around the discharge electrodes promoting combustion and assistance to the flame front propagation through the combustion chamber. In our experimental conditions corona allows ignition and flame propagation regime in quiescent extremely lean fuel mixture of equivalence ratio 0.52 that cannot be realized using more powerful spark. [ABSTRACT FROM AUTHOR]

A flow pattern characterization of electrohydrodynamically (EHD) induced flow phenomena of a stratified dielectric fluid situated in an ac corona discharge field is conducted by a Schlieren optical system. A high voltage application to a needle-plate electrode arrangement in gas-phase normally initiates a conductive type EHD gas flow. Although the EHD gas flow motion initiated from the corona discharge electrode has been well known as corona wind, no comprehensive study has been conducted for an EHD fluid flow motion of the stratified dielectric liquid that is exposed to the gas-phase ac corona discharge. The experimentally observed result clearly presents the liquid-phase EHD flow phenomenon induced from the gas-phase EHD flow via an interfacial momentum transfer. The flow phenomenon is also discussed in terms of the gas-phase EHD number under the reduced gas pressure (reduced interfacial momentum transfer) conditions. [ABSTRACT FROM AUTHOR]

The article discusses the application of optical imaging techniques to hypersonic facilities. Examples of experimental measurements are also provided. Traditional Schlieren and shadowgraph techniques remain as inexpensive and easy-to-use flow visualization techniques. Planar laser induced fluorescence has been used to visualize complex flows and to measure quantities as temperature and velocity.

The mechanisms of formation of hanging discontinuities, vortex dipoles, and vortex arrays in the wave wake behind a cylinder moving at a constant velocity in a stratified fluid are investigated using various schlieren methods. The existence of discontinuities is attributable to the distortion of the internal-wave phase pattern in the shear flow and to the varying stratification and subsequent interaction of the waves with the appearing nonuniformities. Hanging discontinuities and vortex systems are low-velocity analogs of shock waves. An analysis of the internal-wave pattern indicates that the values of the normal velocity component differ on the upper and lower edges of the discontinuities. A regime diagram for flows of this kind is given. [ABSTRACT FROM AUTHOR]

In this work, a spectrophotometric methodology for the determination of metoclopramide in pharmaceutical preparations is proposed. The approach was based on the reaction of metoclopramide with Folin–Ciocalteu reagent and was implemented on a sequential injection analysis automated flow system. An in-line mixing chamber was used to promote reaction zone homogenization, to increase reaction time, and to attenuate the high refractive index gradient generated by the utilization of concentrated solutions, thus enabling the minimization of the Schlieren effect. Linear calibration plots for metoclopramide concentrations up to 100 mg L-1 were obtained, with good precision (RSD<3%, n=10). The detection limit was 2.0 mg L-1 and the quantification limit was 6.8 mg L-1. [ABSTRACT FROM AUTHOR]

Simulations are combined with laboratory measurements to show the important role of shock waves in a popular physics demonstration, the ‘ping pong cannon.’ The simulation and measurements confirm a developing shock wave that reflects from the end of the closed tube and approaching ball and the eventual formation of a transient localized pressure build-up near the exit tape barrier. This 2 atm burst of pressure peaks within a few microseconds of the ball's arrival, resulting from the combination of near ambient gas density and shock heating to about 1200 K. Pulsed schlieren images beyond the exit confirm the sequence of internally reflected shock waves and the intense, hot air pressure pulse that explosively removes the exit tape just prior to the ball arrival. [ABSTRACT FROM AUTHOR]

Six series of a family of non-symmetric dimers, the α-(4-cyanobiphenyl-4′-yloxy)-ω-(4-n-alkylanilinebenzylidene-4′-oxy)alkanes, have been prepared. In three of the series, the number of methylene groups in the flexible alkyl spacer has been varied from 3 to 12 while the terminal alkyl chain is held constant at either 2, 6 or 10. In the remaining series, the effect of increasing the terminal chain length has been studied by holding the spacer length constant at 3, 4 or 5 methylene units while varying the length of the terminal chain from 0 to 10 carbon atoms. The phase behaviour and transitional properties of these series have been investigated using optical microscopy and differential scanning calorimetry, while the structures of the mesophases have been studied using X-ray diffraction on both powder and aligned samples. This study has revealed novel phase behaviour involving intercalated smectic phases stabilized by the mixed mesogenic group interaction. We have identified the first examples of intercalated smectic C, smectic I, crystal B and crystal J phases and have assigned the layer stacking sequences in the crystal B phases. An extension to the current nomenclature used to describe smectic phases is proposed in order to include these new structural modifications such that, for example, SAc , refers to the intercalated smectic A phase. The specific interaction between the two unlike groups has a much smaller influence on the nematic-isotropic transition temperatures than it has on the structures of the smectic phases. Quantitative estimates of the nematic-isotropic transition temperatures based on the Marcelja-Luckhurst theory provide further evidence for a specific interaction between the unlike mesogenic groups. Finally, the thermal behaviour of binary mixtures of the analogous symmetric dimers is also found to be governed by the mixed core interaction and intercalated smectic phases are observed in these mixtures. [ABSTRACT FROM AUTHOR]

The thermodynamic response of matter heated with intense ion beams was analyzed using the schlieren technique. The energy deposition zone and the propagation of the thermal wave were visualized in the experiment. Fused quartz has been chosen as a target to investigate the phenomena in a material with high yield point. The temperature in the ion beam heated region was estimated using the schlieren data and by analysis of the material changes after irradiation. [ABSTRACT FROM AUTHOR]

Groundwater seeps are known to occur in Eckernförde Bay, Baltic Sea. Their discharge rate and dispersion were investigated with a new schlieren technique application, which is able to visualize heterogeneous water parcels with density anomalies down to Δ σt = 0.049 on the scale of millimeters. With the use of an inverted funnel, discharged fluids can be captured and the outflow velocity can be determined. Overall, 46 stations could be categorized by three different cases: active vent sites, seep-influenced sites, and non-seep sites. New seep locations were discovered, even at shallow near-shore sites, lacking prominent sediment depression, which indicate submarine springs. The detection of numerous seeps was possible and the groundwater-influenced area was defined to be approximately 6.3 km2. Flow rates of between 0.05 and 0.71 l m−2 min−1 were measured. A single focused fluid plume, which was not disturbed by the funnel was recorded and revealed a flux of 59.6 ± 20 ml cm−2 min−1 and it was calculated that this single focused plume would be strong enough to produce a flow rate through the funnel of 1.32 ± 0.44 l m−2 min−1. The effect of different seep-meter funnel sizes is discussed. [ABSTRACT FROM AUTHOR]

In this article, the local unconstrained and the constrained optimization problems in the Heisenberg group are investigated. The framework on which we work is given by the class of weakly H-convex functions recently introduced in the literature. This geometric notion of convexity, that is strictly related to the stratified structure of the group and has not an analogous in a Euclidean setting, requires a condition of convexity to be satisfied at the points of the horizontal planes. We find second-order sufficient conditions for a local extremum in both the unconstrained and the constrained optimization problems exploiting the weak H-convexity and the geometric behaviour of the horizontal planes in . [ABSTRACT FROM AUTHOR]

The high-speed combustible gas ignited by a hot gas jet, which is induced by shock focusing, was experimentally investigated. By use of the separation mode of shock tube, the test section of a single shock tube is split into two parts, which provide the high-speed flow of combustible gas and pilot flame of hot gas jet, respectively. In the interface of two parts of test sections the flame of jet was formed and spread to the high-speed combustible gas. Two kinds of the ignitions, 3-D “line-flame ignition” and 2-D “plane-flame ignition”, were investigated. In the condition of 3-D “line-flame ignition” of combustion, thicker hot gas jet than pure air jet, was observed in schlieren photos. In the condition of 2-D “plane-flame ignition” of combustion, the delay time of ignition and the angle of flame front in schlieren photos were measured, from which the velocity of flame propagation in the high-speed combustible gas is estimated in the range of 30–90m/s and the delay time of ignition is estimated in the range of 0.12–0.29ms. [ABSTRACT FROM AUTHOR]

A new technique is presented for the formation of annular plasmas on a metal surface with a high-power laser using a combination of axicon and converging lenses. The annular plasma formed on a titanium target in a chamber of hydrogen gas was investigated using schlieren imaging and Mach Zehnder interferometry. Expansion of the plasma was shown to be anisotropic with velocities of ∼103–104 m/s. Electron densities of 1018 cm-3 were measured with radial profiles that confirm the presence of a hollow structure. The interferometric observations also show the presence of an inward shock wave traveling to the center of the annular plasma, which compresses the background neutrals, reaching a density around 18 times initial gas density, at 95 ns after the initial annular plasma is produced. [ABSTRACT FROM AUTHOR]

The dynamics of relaxation and transformation of the structure of convective flows of a weakly stratified liquid are investigated by optical methods in the case of uniform lateral heating. The experiments were carried out for different (small ( S = 0.22%) and high (6.5%) basic-salinity values, for which the main parameters of the medium (the thermal expansion coefficient, the saline compression coefficient, the kinematic viscosity, the thermal diffusivity, and the salt diffusion coefficient) differ somewhat. It is shown that the dependence of the structure parameters on the properties of the medium is weak, which justifies the possibility of extrapolating the data of bench experiments on highly stratified liquids to weakly stratified natural systems, such as the atmosphere and the hydrosphere. It is shown that, over a wide range of the experimental parameters, the length and height of the convective cells vary at a constant rate. [ABSTRACT FROM AUTHOR]

The correspondence between the linear integral transform and the ray-transfer matrix of a first-order optical system is used to evaluate the transmittance function of gradient-index (GRIN) human lens regarded as a quadratic phase transformer. The size of the GRIN crystalline lens has been considered for redefining the effective transmittance function by the pupil function. The role that the GRIN nature of the human lens plays in the retinal image quality using the point spread function (PSF) is commented on. The simulation results show that the effective radius of the output face of the lens decreases with increasing thickness and that it is higher for flat end surfaces than for curved end faces. On the other hand, the simulation results also show, for small pupil sizes, that the GRIN nature of the human lens is a retinal image degradation source producing the spread of the PSF and that the curved end surfaces of the lens constitute a retinal image quality improve factor contributing to the narrowing of the PSF. [ABSTRACT FROM AUTHOR]

Ultrasonic transducers uniformly poled have been used for clinical diagnostic applications, and usually medical imaging use focused beams that present a short depth of ultrasonic field. With ultrasonic transducers that produce limited diffraction beams (Bessel transducers), high-resolution images can be achieved over a large depth of field compared with the focused beams. In this paper we use the Schlieren method in order to obtain a 2-dimensional image of the acoustic field. By assuming axi-symmetrical proprieties of the field, we develop a fast algorithm that allows as reconstructing the 3-dimensional field of acoustical power. We compare its diffraction field with one emitted by a piston-like transducer with the same diameter and excited with the same frequency. We see that the diffraction effect in the last transducer produces a power spread greater than the Bessel one. [ABSTRACT FROM AUTHOR]

This article reports on the three-dimensional projection display used with polarized eyeglasses. It consists of polymer-dispersed liquid crystal light valves that modulate the illuminated light based on light scattering, and a Schlieren projection system. The basic configuration of a full-color 3-D projection system and the structure and operating principle of the polymer-dispersed liquid crystal light valve have been described.

This article reports on the analysis of the performance of the three-dimensional image projector with polarized glasses which consists of polymer-dispersed liquid-crystal light valves and a Schlieren optical system. Quantitative analyses show that sufficient extinction ratio is almost the same as the light valve and the proposed display achieves small cross talk of less than 1%.

Calamitic liquid crystalline amides 1–3 were synthesized and their thermodynamic behaviors were investigated. Bent-rod shaped compound 1 exhibited a usual smectic C phase. On the other hand, in the case of straight-rod compound 2, two kinds of smectic C phases (SmC x and SmC y ) were observed above the crystal phase. Although SmC y phase belonged to general smectic C phases, SmC x phase exhibited very sharp lines in its schlieren textures. As the packing model of smectic C x phase, a lateral linear arrangement of the molecules was proposed to explain the difference between these smectic C phases. Additionally, in the case of 3 which has a flexible spacer between its amide group and straight rodlike core, the molecules generated the highly ordered smectic C (3a, SmC x ) and a chiral cubic phase (3b). [ABSTRACT FROM AUTHOR]

While larval sea lampreys exist as eyeless filter feeders for several years, they transform into free-swimming juveniles (transformers) that attach parasitically to prey fish as they develop sexual maturity. This study examines lamprey lens development and optics and, since the lens is often the only refractive component of an aquatic eye, the data also provide an indication of visual ability during transformer and adult periods of life. Seven adult sea lampreys (0.40–0.55 m) and eight transformers (0.15–0.18 m) were sacrificed, the eyes removed and lenses dissected, measured, and placed in an automated laser scanning instrument. Back vertex focal length (spherical aberration) was measured for 14 beam positions across each lens by using a digital camera to record the position of the refracted beam. Transformer lenses exhibit positive spherical aberration, with average focal lengths varying from about 2.40 mm near the lens center and 1.06 mm at the lens periphery. On the other hand, the lenses from adults are largely corrected for spherical aberration, with average focal lengths varying from 2.19 mm to 2.44 mm. This result indicates that the younger lenses do not have a gradient refractive index necessary to mitigate the aberration and that further study of this model may reveal the relation between lens embryology and the development of such a gradient. [ABSTRACT FROM AUTHOR]

Recent theoretical and numerical investigations predict that localized nonlinear effects in the overlapping region of an incoming and reflected internal wave beam can radiate higher-harmonic beams. We present the first set of experimental visualizations, obtained using the digital Schlieren method, that confirm the existence of radiated higher-harmonic beams. For arrangements in which the angle of propagation of the second harmonic exceeds the slope angle, radiated beams are visualized. When the propagation angle of the second harmonic deceeds the slope angle no radiated beams are detected, as the associated density gradient perturbations are too weak for the experimental method. The case of a critical slope is also reported. [ABSTRACT FROM AUTHOR]

Presents information on a classroom demonstration of natural convection using an overhead projector. Discussion of the principle of schlieren which is applied in the demonstration; Guidelines for optical tuning for the demonstration; Significance of the demonstration to student learning of natural convection.

The Schlieren pulsed method uses short-term lighting triggered by an acoustic pulse. This allows for an observation of elastic deformation fields in pulsed regime and for an evaluation of the evolution of the pulse in the interior of homogenous and heterogeneous media. In this paper we apply the Schlieren pulsed method to determine the conditions of the change from simple to multiple scattering. An ultrasound transducer put in water emits a wide-band pulse. The pulse goes through a region of parallel cylindrical wires, uniformly spaced and perpendicular to the acoustic beam. Varying the width of the zone of the scatterer cylinders, it is possible to optically observe the transmitted acoustic field and to calculate the transmission coefficient. By studying the behavior of this coefficient in function of the medium width, we obtained the zone in which the transition between simple and multiple scattering happens. [ABSTRACT FROM AUTHOR]

Multilayer gradient InAs1 – xSbx/.../InAs1 – x – ySbxPy/n-InAs structures emitting in a wavelength range of 6 to 9 μm during injection, extraction, and optical pumping were studied. © 2005 Pleiades Publishing, Inc. [ABSTRACT FROM AUTHOR]

Abstract: Laminar burning velocities are presented for benzene, toluene, ethylbenzene, m-xylene, and n-propylbenzene. The data have been acquired at elevated temperature (450K) and pressure (304kPa) over the equivalence ratio range 0.80? ? ?1.4. High speed schlieren visualization, used to monitor flame growth following ignition, provides a direct determination of the laminar flame speed. The data are corrected for flame stretch to yield the unstretched laminar burning velocities and burned gas Markstein lengths. The data show benzene to be the fastest, followed by ethylbenzene> n-propylbenzene>toluene> m-xylene. Iso-octane results are also presented for comparison to the literature. Flame front perturbations are observed, particularly under fuel-rich conditions, due to hydrodynamic and preferential mass diffusion instabilities. The kinetic factors responsible for the changes in the laminar burning velocities upon alkyl substitution of the aromatic ring are discussed. [Copyright &y& Elsevier]

Heat transfer phenomena, which frequently involve convection, are usually described through a convective heat-transfer coefficient h. Precise measurement of h is difficult, since calculation requires knowledge of the temperature gradient between the solid surface and the fluid measured, possibly, without disturbing the thermal layer. Optical techniques are powerful tools in experimental analysis because of their non-disturbing nature. In this paper, natural convection heat transfer in vertical channels is investigated by applying two different optical techniques, namely, schlieren and holographic interferometry Experiments were conducted at DITEC, University of Genova (Italy) and at the Energetic Department of the University of L'Aquila (Italy) on the same test section. The obtained results are discussed and compared. [ABSTRACT FROM AUTHOR]

In this paper, streamer discharges in dielectric liquids which have various molecular structures, such as a double bond or a triple bond in the molecular formula, are observed in detail for positive point polarity under the application of an impulse voltage to the point electrode. As test liquids, four straight-chain hydrocarbon liquids—n-hexane, n-heptane, n-octane, and n-decane—are selected and in addition the influence of a double or triple bond included in their molecular formula on the propagation of positive streamers is investigated in detail by simultaneously using a high-speed schlieren method and an LED current measurement system. Some differences in the mean propagation velocity and the propagation shape of positive streamers are evident. Their shape is mainly filamentary in test liquids including a double or triple bond. Also, positive streamer propagation is promoted in these liquids. It is thought that this is due to the effect of π bonds which have smaller bond energies than σ bonds. © 2004 Wiley Periodicals, Inc. Electr Eng Jpn, 149(1): 15–21, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.10366 [ABSTRACT FROM AUTHOR]

We explicitly compute the constrained quasiconvexification of the integrand associated with the square of the gradient of the state in a typical optimal design problem in which a volume constraint is enforced. [ABSTRACT FROM AUTHOR]

The flow pattern around a carbon particle (∼ 3.5 mm in diameter) during the supercritical water oxidation (SCWO) process (25 MPa, 723 K, 3.6 wt % O2 concentration) was visualized for the first time by the use of Schlieren optics and a SCWO reactor equipped with transparent sapphire windows. To link Schlieren images with flow fields, computational fluid dynamics (CFD) simulations were executed, assuming temperature-dependent density of supercritical water and heat of a surface reaction, and then the obtained density fields around the particle were numerically converted to Schlieren images. Numerically obtained Schlieren images agreed well with observed images, confirming that the CFD simulation was able to predict the flow field in SCWO processes. Such a combined approach of CFD and flow visualization revealed that, in SCWO of solid substances with a fast reaction rate, the heat of surface reaction increased the temperature of the fluid and induced an upward flow from the particle with higher fluid temperature than that of the surroundings. Such flow can increase reaction rates by enhancing the mass transfer of O2 to solids. Therefore, a flow field in SCWO is an important factor controlling the progress of reaction and it can be reasonably predicted by CFD simulations. [ABSTRACT FROM AUTHOR]

The computer simulation study for color-schlieren is to provide a new method for validations between experiment and theory, which can get colorschlieren image from the computational flow field data. This paper gives a brief description about the theory of method, technical way, algorithm, key problem that has been solved, the computational results and the future development direction. [ABSTRACT FROM AUTHOR]

In the past decade color has been developed as an effective cue for object recognition and image indexing. The initial draw of color was how easily object signatures could be captured and compared. Simple histograms of colors radiated from an object proved to be a stable representation of many objects without requiring complex geometric processing to address object pose. While recognition/indexing should depend only on colors intrinsic to object reflectance, a color signature computed from raw image colors is highly sensitive to the color and pose (direction) of incident illumination. Several methods have explored illumination-color invariants, and most of the recent invariants to illumination color and pose employ some form of chromacity representations based on the ratios of image color values or their combinations. This paper presents a comprehensive framework for logarithmic chromacities for the interpretation of image color change due to illumination pose and color. A log-chromacity space is developed from spectral (color) derivatives of logarithmic image irradiance, called spectral gradients, to achieve invariance to global illumination color and pose. In this space, the multiplicative influence of illumination color and pose on image irradiance become additive effects, and this facilitates the analysis of illumination color and pose. A representation from spatial derivatives of spectral gradients, called spectral–spatial gradients is also developed to additionally provide invariance to local variation of illumination color within an image. Experimental results are presented to demonstrate the efficacy of the proposed descriptors. [Copyright &y& Elsevier]

We describe the design of finite-size linear-phase separable kernels for differentiation of discrete multidimensional signals. The problem is formulated as an optimization of the rotation-invariance of the gradient operator, which results in a simultaneous constraint on a set of one-dimensional low-pass prefilter and differentiator filters up to the desired order. We also develop extensions of this formulation to both higher dimensions and higher order directional derivatives. We develop a numerical procedure for optimizing the constraint, and demonstrate its use in constructing a set of example filters. The resulting filters are significantly more accurate than those commonly used in the image and multidimensional signal processing literature. [ABSTRACT FROM AUTHOR]

A technique of interference comparative analysis of the shape of wavefronts that can be applied to incoherent light beams is proposed. The difference in the shape of the wavefronts of the incoherent light beams under study is visualized by using the moire pattern appearing upon superposition in real time of the lateral-shear interferograms or their photographs. The possibility of producing the interference pattern that visualizes the difference in the shape of the wavefronts of incoherent beams with an enhanced measurement sensitivity is shown. The results of experimental testing of this technique in visualization of the difference between the shapes of the wavefronts of two light beams emitted by different lasers are presented. © 2004 MAIK “Nauka / Interperiodica”. [ABSTRACT FROM AUTHOR]

Focuses on the development of a theory concerning the effective linear and nonlinear optical properties of composite media by considering the dielectric anisotropy of the nonlinear graded particles. Model of the effective linear dialectric constant; Application of the nonlinear anisotropic differential effective dipole approximation in a nonlinear metal-dielectric composite; Role of the presence of gradation in the radial dialectric constant in enhancing the optical nonlinearity.

An expression is obtained for effective buoyancy per unit volume in inviscid anelastic flow with surrounding horizontal density variations. Effective buoyancy is defined here as the statically forced part of the locally nonhydrostatic, upward pressure-gradient force because this is the part of the net vertical force that is both absolute (i.e., independent of an arbitrary base state) and dependent solely on variations in the specific weight of the air-hydrometeor mixture. For the case where the domain is the half space z > 0 above flat ground, effective buoyancy β(x) at a given field point x is given by β(x) = &inf;[SUP∞,SUB-∞] &inf;[SUP∞,SUB-∞] &inf;[SUP∞,SUB-∞] [g ˆ∇[SUP2,SUBh]ρ[SUBT](xcirc;)]/4π&verbar; x - ○&verbar; ) d○ dŷ d&zcirc; where gρ[SUBT] is the total weight of air and hydrometeors per unit volume, the ○ ≡ (○, ŷ, &zcirc;) are source points, is the horizontal Laplacian with respect to ○, and &∇circ;[SUB2,SUBH]ρ[SUBT] ((○, ŷ, &zcirc;). [ABSTRACT FROM AUTHOR]

The radiation equilibrium temperature field in a gradient index semitransparent absorbing-emitting gray medium is analyzed. The medium is bounded by two semitransparent specular surfaces and possesses a refractive index varying spatially or dependent on temperature. By discretizing the medium into many sublayers and adopting a linear refractive index approximation for each sublayer, the curved ray tracing technique is developed to solve the radiation transfer in medium. The temperature field at radiation equilibrium is obtained based on the energy conservation. The influences of refractive index distribution and optical thickness on the temperature field as well as the coupled effect of temperature and refractive index are examined. The results display the significant influences of gradient index on radiation transfer and the temperature distribution. [ABSTRACT FROM AUTHOR]

Proposes an imaging interferometer with two long gradient-index lenses and a charge coupled device sensor array for application to an optical coherence tomography system that can observe the subsurface structure of internal organs through a small hole in the body. Image of lines obtained using the phase shifting method and a test pattern as a sample; Lateral resolution obtained; Axial resolution measurement.

Two numerical methods for solving the radiative heat transfer in a gradient index semitransparent slab are compared. The slab is discretized into many sublayers. The constant refractive index assumption in a sublayer and the ray splitting and tracing technique are used in the first method, and the linear approximation of refractive index in a sublayer and the curved ray tracing technique are adopted in the second method. The heat transfer at radiative equilibrium and coupled radiation-conduction are involved in the comparison. The results of the two methods show good agreement, but their calculating efficiencies are found to be quite different. [ABSTRACT FROM AUTHOR]