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The Luneburg lens is a powerful imaging device, exhibiting aberration free focusing for parallel rays incident from any direction. However, its advantages are offset by a focal surface that is spherical and thus difficult to integrate with standard planar detector and emitter arrays. Using the recently developed technique of transformation optics, it is possible to transform the curved focal surface to a flat plane while maintaining the perfect focusing behavior of the Luneburg over a wide field of view. Here we apply these techniques to a lesser-known refractive Luneburg lens and implement the design with a metamaterial composed of a semi-crystalline distribution of holes drilled in a dielectric. In addition, we investigate the aberrations introduced by various approximations made in the implementation of the lens. The resulting design approach has improved mechanical strength with small aberrations and is ideally suited to implementation at infrared and visible wavelengths. [ABSTRACT FROM AUTHOR]

Abstract: There are not many studies on DDT with no obstacles and the initiation of DDT near the end of a closed tube. Therefore in the present study we experimentally investigate the mechanism of the combustion wave transition to a detonation wave when there are no obstacles. In particular, we show that a local explosion near the tube wall is necessary for the initiation of a detonation. Parameters that we varied are the wall configuration, distance between the ignition point and the wall, and initial filling pressure. The combustion waves and the compression waves are visualized using the Schlieren optical system. From the results, we found it is necessary for the combustion wave to reach four walls so that the detonation could be initiated by the local explosion. In the conditions of the present experiment, we exhibited that the local explosion did not occur in the vicinity of a single wall and four orthogonal walls; instead, the local explosion occurred in a situation with five orthogonal walls. The time of the local explosion and the detonation initiation is 2.6±1.1 and 2.0±0.1 times the characteristic time for the combustion wave to propagate hemispherically from an ignitor and reach the four walls. [ABSTRACT FROM AUTHOR]

The dynamic characteristics and stability of moving functionally graded material thin rectangle plate were investigated. Based on Voigt model, the material properties are assumed to vary continuously through their thickness according to a power-law distribution of the volume fractions of the plate constituents. The differential equations of motion of the moving FGM rectangle plate are derived by the Kirchhoff thin-plate theory. Then the equations are discretized by the differential quadrature method, and the dimensionless complex frequencies of a moving FGM rectangle plate with two opposite edges simply supported and other two edges clamped, and one edge clamped and three edges simpiy supported are calculated. The effects of the gradient index, aspect ratio, and dimensionless moving speed, on the transverse vibration and stability of the moving FGM rectangle plate are analyzed. [ABSTRACT FROM AUTHOR]

The applicability of the particle image velocimetry (PIV) and the background-oriented schlieren (BOS) techniques in the high-enthalpy shock tunnel Göttingen of the German Aerospace Center, DLR is demonstrated. As a part of this feasibility study two different experiments are performed. The velocity field past a wedge in a Mach 6 flow at a total specific enthalpy of 1.5 MJ/kg is determined by means of PIV and the results are compared to numerical predictions. The BOS technique is applied to investigate the density field in the shock layer of a sphere at 12 and 22 MJ/kg total specific enthalpies. Using a ray tracer method, the BOS results are compared to the data obtained by corresponding numerical computations. [ABSTRACT FROM AUTHOR]

Schlieren imaging is a method for visualizing differences in refractive index as caused by pressure or temperature non-uniformities within a medium, or as caused by the mixing of two fluids. It is an inexpensive yet powerful and straightforward tool for sensitive and high-resolution visualization of otherwise invisible phenomena. In this article, application of the method to liquid membranes, sonar pulses and microscopic gas flows is used to illustrate its usefulness and versatility in physics education and research. [ABSTRACT FROM AUTHOR]

To prevent damage caused by accidental overpressure inside a closed duct (e.g. jet engine) safety valves are introduced. The present study experimentally investigates the dynamic opening of such valves by employing a door at the end of a shock tube driven section. The door is hung on an axis and is free to rotate, thereby opening the tube. The evolved flow and wave pattern due to a collision of an incident shock wave with the door, causing the door opening, is studied by employing a high speed schlieren system and recording pressures at different places inside the tube as well as on the rotating door. Analyzing this data sheds light on the air flow evolution and the behavior of the opening door. In the present work, emphasis is given to understanding the complex, unsteady flow developed behind the transmitted shock wave as it diffracts over the opening door. It is shown that both the door inertia and the shock wave strength influence the opening dynamic evolution, but not in the proportions that might be expected. [ABSTRACT FROM AUTHOR]

Abstract: We have calculated the band structures of (M: Na, K, Rb, and Cs) using the density-functional theory with the generalized gradient corrected local density approximation. They are indirect semiconductors with the calculated gaps from 0.45 to 0.89 eV, the gaps becoming wider with the promotion to the heavier encapsulated guest alkali atoms. These are comparable to the calculated gap of 0.65 eV of crystalline Si with the diamond structure. [Copyright &y& Elsevier]

To study the characteristics of plasma evolution produced by metal bridge foil exploding, the experimental device of bridge foil exploding was established, and the bridge exploding experiments were conducted. Based on schlieren photography technique, the double pulse light source plasma evolution measuring system was used to observe the bridge foil exploding flow field. The schlieren pictures at different times were obtained. The shape and evolution of plasma flow field were analyzed, and the characteristic parameters of the plasma and shock wave were derived. [ABSTRACT FROM AUTHOR]

The flow over a missile-shaped configuration is investigated by means of Schlieren visualization in short-duration facility producing free stream Mach numbers of 5.75 and 8. This visualization technique is demonstrated with a 41° full apex angle blunt cone missile-shaped body mounted with and without cavity. Experiments are carried out with air as the test gas to visualize the flow field. The experimental results show a strong intensity variation in the deflection of light in a flow field, due to the flow compressibility. Shock stand-off distance measured with the Schlieren method is in good agreement with theory and computational fluid dynamic study for both the configurations. Magnitude of the shock oscillation for a cavity model may be greater than the case of a model without cavity. The picture of visualization shows that there is an outgoing and incoming flow closer to the cavity. Cavity flow oscillation was found to subside to steady flow with a decrease in the free stream Mach number. [ABSTRACT FROM AUTHOR]

Copyright of Boletin de Geologia is the property of Universidad Industrial de Santander and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Results of numerical and experimental modeling of a supersonic flow (M = 4.85) around a model of a streamwise-aligned cylinder with a cellular-porous insert permeable for the gas on the frontal face of the cylinder are described. Experimental data on the influence of the pore structure and the length of the porous cylindrical insert on the model drag, pressure on the frontal face of the cylinder, and flow pattern are obtained. Numerical modeling includes solving Favre-averaged Navier-Stokes equations, which describe the motion of a viscous compressible heat-conducting gas. The system is supplemented with a source term taking into account the drag of the porous body within the framework of the continuum model of filtration. Data on pressure and velocity fields inside the porous body are obtained in calculations, and the shape of an effective pointed body whose drag is equal to the drag of the model considered is determined. The calculated results are compared with the measured data and schlieren visualization of the flow field. [ABSTRACT FROM AUTHOR]

blue diode-pumped Pr:YLF laser with emission at visible wavelengths is presented that employs a suitably coated GRIN-lens as the output coupler. The GRIN-lens element combines the functionality of focusing and reflecting the laser beam. In this way the usual curved output coupler is replaced and the laser resonator consists entirely of planar elements. This is of relevance for large volume-low cost production. The experimental results presented here indicate that the use of the GRIN-lens element as the output coupler does not lead to significantly increased round-trip losses for the solid-state laser. [ABSTRACT FROM AUTHOR]

Three esters of maltose (A1-A3) with 4-(4-(alkoxybenzoyloxy)phenoxy) -6-oxohexanoic acid (b1-b3) side-arms have been synthesised. All the maltose derivatives were laevo-rotationary, unlike their parent cores. The side arm b1 did not display liquid crystalline (LC) properties, and b2 and b3 displayed thermotropic nematic LC properties. The star-shaped compound (SSC) A1 with b1 side-arms did not display a mesomorphic phase. Unlike the nematic schlieren texture provided by side-arms b2 and b3, the star-shaped liquid crystals (SSLC) A2 and A3 displayed Grandjean and oily texture in the cholesteric phase. The results suggest that the LC properties of the side-arms have an important influence on the formation of LC properties in an SSC, and that the maltose core is important in determining the mesomorphic phase type. In other words, the SSC displayed LC properties only when the side-arms were also LC, and the maltose core induced a cholesteric phase in the SSLC with nematic side-arms. The mesomorphic regions for A2 and A3 were 39.1 and 53.7°C during the heating cycle and 63.8 and 107.0°C during the cooling cycle, respectively. The longer terminal chain rendered the mesomorphic region broader. [ABSTRACT FROM AUTHOR]

Two new series of Schiff base thermotropic liquid crystals, 6-methoxy-2-(2-hydroxy-4-alkanoyloxybenzylidenamino)benzothiazoles and 6-ethoxy-2-(2-hydroxy-4-alkanoyloxybenzylidenamino)benzothiazoles, comprising different terminal groups, a methoxyl and ethoxyl group, respectively, were synthesized. Structural elucidation was carried out using elemental analysis and spectroscopic techniques such as Fourier transform infrared (FTIR), 1H and 13C nuclear magnetic resources (NMR), and mass spectrometry. The mesomorphic properties and thermal stabilities of the title compounds were studied by using differential scanning calorimetry, optical polarizing microscopy, and thermogravimetric analysis. No liquid-crystal phases were observed for the short-chain members (n = 2 and 3) in both series, and the remaining members all exhibited nematic phase with Schlieren or marble-like textures. Effects of the lateral hydroxyl group, terminal group, and the length of the terminal alkanoyloxy chain on the mesomorphic properties are discussed. Structure-property relationships were established upon comparison with other structurally related compounds. [ABSTRACT FROM AUTHOR]

motion of a vortex ring in a stratified fluid is accompanied by associated disturbances which, in the schlieren visualization in the field of a horizontal density gradient, have the shape of a symmetric four-petal configuration. The criterion of the existence of the disturbances is the Froude number Fr based on the motion velocity and the vertical vortex size. On the range Fr > 1, the disturbances are stable with respect to the variation of themotion regime and the distortion of the vortex shape. For Fr < 1 the disturbances disappear. Computer processing of the schlieren photographs showed that the experimental spatial dependences of the disturbance amplitude are close to the functions describing the distribution of the vertical velocity component in the inviscid flow past a sphere. [ABSTRACT FROM AUTHOR]

Short pulsed laser-induced single acoustic wave generation, propagation, interaction within a water-filled internal channel are experimentally and numerically studied. A large-area, short-duration, single-plane acoustic wave was generated by the thermoelastic interaction of a homogenized nanosecond pulsed laser beam with a liquid–solid interface and propagated at the speed of sound in water. Laser flash Schlieren photography was used to visualize the transient interaction of the plane acoustic wave in various internal channel structures ((a) sudden expansion and contraction channels, (b) bifurcating channels, (c) gradual contraction wall channels and (d) a cylinder). Fairly good agreement between the experimental results and numerical simulation is observed. [ABSTRACT FROM AUTHOR]

Supersonic flow over a tapered body of revolution has been investigated both experimentally and numerically. The experimental study consisted of a series of wind tunnel tests on an ogive-cylinder body. Static pressure distributions on the body surfaces at several longitudinal cross sections, as well as the boundary layer profiles at various angles of attack have been measured. Further, the flow around the model was visualized using Schlieren technique. Tests with a natural development of the boundary layer and with tripping were also carried out. All tests were conducted in the trisonic wind tunnel of Qadr Research Center. Our results show that artificial boundary layer tripping has minor effect on the static surface pressure distribution (depending on its diameter and installation location), while the changes in total pressure around the body were significant. Tripping the boundary layer increased its thickness, changed its profile particularly near the body surface. Two oblique shock waves were formed in the front and behind the trip wire. In this study, using multi-block grid, the thin layer Navier-Stokes (TLNS) equations were solved around the above models. Also patched method was used near the interfaces. Good agreements were achieved when the numerical results were compared with the corresponding experimental data. [ABSTRACT FROM AUTHOR]

This work describes an optical device for the simultaneous recording of shadowgrams and schlieren images, and some results are presented concerning its applications to the study of plasma assisted flow control in airfoil models. This approach offers many advantages in comparison to other methods, specially because the use of tracer particles (like smoke in wind tunnels) is not required for the experiments, thus avoiding contaminations in the electric discharges or air flows. Besides, while schlieren images reveal the refractive index gradients in the area of study, shadowgrams detect the second order spatial derivatives of the refractive indexes. Therefore, the simultaneous recording of these different images may give interesting information about the phenomena under study. In this paper, these images were used to confirm the existence of vortex structures in the flow induced by corona discharges on airfoil models. These structures are a possible explanation for the effects of drag reduction and lift force increasing, which have been reported in experiments of plasma assisted Aerodynamics. [ABSTRACT FROM AUTHOR]

Abstract: Schlieren visualization of ultrasound wave fields is a relative fast and inexpensive way to analyze different transducer characteristics. The spatial filtering in the Fourier plane offers an interesting possibility for image processing. Especially for comparatively low-frequency ultrasound wave fields around 1 MHz the requirements on the quality of the optical components and the filtering in the Fourier plane increases because of decreasing distances between the different orders and the difficulty to influence each of them separately. In this contribution a new method is introduced to realize the necessary spatial filtering. A Digital Micromirror Device (DMD) is used as a adjustable filter for the amplitudes in the Fourier plane without influencing the phase information simultaneously. Using different filters (e.g. knife-edge cutoff or low-pass filter) sequentially and applying methods of information fusion the quality of the sound field visualization can be improved significantly. With this setup the interpretation of different phenomena (e.g. sound interaction with solid boundaries) is possible. The experimental setup and first interesting results will be presented. [Copyright &y& Elsevier]

Abstract  The background-oriented schlieren (BOS) flow visualization method has the potential for large-scale flow imaging outside the laboratory by using natural backgrounds instead of the artificial patterns normally used indoors. The natural surroundings of an outdoor test site can sometimes be used as such a background, subject to criteria of fine scale, randomness and contrast that are developed here. Some natural backgrounds are more appropriate than others for a given application. Backgrounds used here to visualize both high- and low-speed schlieren disturbances include a sunlit cornfield and a backlit grove of trees. A range of image post-processing methods is considered for qualitative BOS. It is found that high sensitivity and a broad measuring range are in conflict here, much as they are in traditional schlieren instruments. Applications of natural-BOS include explosive characterization, firearms and artillery testing, chemical and natural-gas leak detection, and related phenomena. [ABSTRACT FROM AUTHOR]

The principle of the background oriented schlieren (BOS) method and its chief areas of applications are considered. An algorithm that generates background patterns and the features in the adaptation of the parameters of the patterns to the conditions of a particular experiment are presented. The influence of the basic parameters of the particular plant on the method is investigated by means of computer simulation as well as experimentally. [ABSTRACT FROM AUTHOR]

This article aims to develop a method for the detection and segmentation of a cytoplast and nucleus from a cervix smear image. First, the technique of equalization method with Gaussian filter is adopted to eliminate noise in the image. Second, a new edge enhancement technique is proposed to work out the coarseness of each pixel, which is later used as a determining characteristic of reinforced object images. A two-group object enhancement technique is then used to reinforce this object according to rough pixels. Third, the proposed detector enhances the gradients of the edges of the cytoplast and nucleus while suppressing the noise gradients, and then specifies the pixels with higher gradients as possible edge pixels. Finally, it picks out the two longest closed curves constructed by part of the edge pixels. Detection and segmentation performance of the proposed method is later compared with seed region growing feature extraction and level set method using 10 cervix smear images as example. Besides comparing the contour segment of the cytoplast and nucleus obtained by using different methods, we also compare the quality of the segmentation results. Experimental results show that the proposed detector demonstrates an impressive performance. © 2009 Wiley Periodicals, Inc. Int J Imaging Syst Technol, 19, 260–270, 2009 [ABSTRACT FROM AUTHOR]

This paper analyzes the transient response of the dynamic stress intensity factor for an interfacial crack of a functionally graded piezoelectric material (FGPM) coated on the surface of a homogeneous piezoelectric substrate. Different from previous analyses, this study mainly considers a realistic situation when electromechanical loadings are suddenly applied at the material surface. Obtained results are compared with those when the crack surfaces are directly loaded by the same impacts. By using the integral transform method, the problem is reduced to solving two singular integral equations. It is found that dynamic stress intensity factors are significantly amplified and reduced depending on the negative and positive gradient for electromechanical impacts at the material surface. Positive or negative electric impact also decreases or increases the overshoot of the dynamic stress intensity factor. It is suggested that designing an FGPM with a positive gradient index is safer than a negative gradient index. [ABSTRACT FROM AUTHOR]

Abstract  The dual bell nozzle is a concept of altitude adaptive nozzles. The flow adapts to the altitude by separation at the wall inflection at low altitude, and full flowing at high altitude. To understand the phenomenology of the flow by the transition from sea-level mode to high altitude mode, a series of tests have been made at the cold flow test bench P6.2 at DLR Lampoldshausen. A dual bell nozzle have been successively shorten and driven in the same conditions for each length. Hence it was possible to observe the flow in the vicinity of the wall inflection using Schlieren optics. Furthermore this study yields the influence of the length ratio between basis and extension on the transition conditions. [ABSTRACT FROM AUTHOR]

Turbulent flame speeds of a premixed synthetic natural gas mixture were measured using a jet flow apparatus over a range of pressures to 0·8 MPa at an equivalence ratio of 0·9. The method adopted was the 'flame angle' technique, using schlieren imaging to obtain the flame vertex angle from the peak density gradient. Image analysis techniques were developed to reduce interpretation errors and to give information on the velocity and combined gradient distribution local to the flame front. [ABSTRACT FROM AUTHOR]

One of the fastest methods of localizing edges in images is based on small gradient kernels, such as Sobel, Prewitt, and Roberts. Although small gradient kernels provide a fast way of computing the gradients, they have little control over noise, edge location, and edge orientation. They are known to be only sensitive to step edges and fail to detect smooth boundaries, On the other hand, large kernels provide superior noise suppression characteristics, but they suffer from wide response area around edges. They cause edges of neighboring objects to merge due to their wide support. Problems associated with large gradient kernels prevent their widespread usage. This paper presents a fuzzy topology-based method to facilitate the use of larger gradient kernels. The new method effectively limits the response area around the edge and prevents neighboring objects to affect each other. Synthetic images are used to show the superior noise suppression properties and response characteristics to both step and ramp edges. Natural images are also used to assess the performance of the newly proposed topological gradient estimation qualitatively. [ABSTRACT FROM AUTHOR]

Abstract  The background oriented schlieren method (BOS) allows for accurate flow measurements with a simple experimental configuration. To estimate per-pixel displacement vectors between two images, BOS systems traditionally borrow window-based algorithms from particle image velocimetry. In this paper, we evaluate the performance of more recent optical flow methods in BOS settings. We also analyze the impact of different background patterns, suggesting the use of a pattern with detail at many scales. Experiments with both synthetic and real datasets show that the performance of BOS systems can be significantly improved through a combination of optical flow algorithms and multiscale background. [ABSTRACT FROM AUTHOR]

Abstract: Very rich premixed outward propagating spherical flames of n-heptane (ϕ =3.5) and iso-octane (ϕ =3.9) spherical flames were experimentally investigated under microgravity conditions at 420K and initial pressures of up to 30bar. Inert gases with significantly different molecular weights were used as diluents leading to mixtures with varying effective Lewis numbers. The experimental setup consisted of a spherical closed pressurized vessel that enabled optical access. The experiments were performed in a drop tower under microgravity conditions to prevent the influence of buoyancy on the expanding flames. A Schlieren measurement technique combined with a high-speed CCD camera was used to track the expanding flames. During the entire experiment, the flames were laminar and smooth with no wrinkles due to combustion instabilities observed. This allowed for accurate measurements of the propagation speed and its dependence on stretch, which was then compared to theoretical predictions based a hydrodynamic model for relatively thin flames. The experimental and theoretical results show good agreement with each other. Investigation of such rich mixtures that are close to the upper flammability limit has not been reported before. [Copyright &y& Elsevier]

A series of experiments in a wind tunnel using optoelectronic instruments has been carried out. Flow in a 2D ultrasonic nozzle was investigated. Experimental results were obtained using three methods – the shadow method, the schlieren method and holographic interferometry, which are compared with the classical method of measuring pressure and the results of numerical calculations. [ABSTRACT FROM AUTHOR]

The wavefields of bounded acoustic beams and pulses reflected from water-loaded plates are fully modeled with the phase advance technique. The wavefield produced at the source is propagated at any incidence angle using phase-shift modeling that incorporates the full analytic solution for the acoustic reflectivity at the interface. This approach provides for the ready visualization of both the stationary monofrequency beam wavefield and animation of the temporally bounded pulse. The model images are reminiscent of the classic Schlieren photographs that first illustrated the nonspecular behavior of the reflected beams incident near critical angles. Various phenomena such as the lateral displacement and the null zone at the Rayleigh critical angle are recreated. A new approximation for this shift agrees well with that of the peak energy of the reflected beam. Similar effects are observed during the reflection of a bounded pulse. Although more computationally costly than existing analytic approximations, the phase advance technique can facilitate the interpretation of reflectivity measurements obtained in laboratory experiments. In particular, the full visualization allows for a better understanding of the behavior of reflected waves at any angle of incidence. [ABSTRACT FROM AUTHOR]

In the Ordovician time, the transform margin of the Gornyi Altai region consisted of two bathymetric stages: (1) shelf and upper parts of continental slope; (2) foothills and lower parts of continental slope. The first stage includes the shallow-water facies complexes (terrigenous and terrigenous-carbonate schlieren and variegated flyschoid), while the second stage is composed of deep-water (black shale terrigenous) and subflysch gray (carbonate terrigenous) complexes. Model series of the facies complexes established in our work should be taken into account during the geodynamic analysis of fold zones. [ABSTRACT FROM AUTHOR]

Experimental investigations on interference and diffraction phenomenon occurring in a folding mirror schlieren diffraction interferometer have been presented. It is shown that the well-known Lloyd mirror interferometer can easily be converted into a folding mirror schlieren diffraction interferometer. Various intermediate stages occur as the basic two-beam interference pattern in Lloyd mirror interferometer is transformed into a schlieren diffraction pattern. Study of these intermediate stages gives a good insight in understanding the transition behaviour between the fundamental phenomenon of interference and diffraction taking place as the mirror-edge approaches the Airy disk. [ABSTRACT FROM AUTHOR]

An experimental investigation was conducted to determine the flow characteristics of shallow swept cavities at a free-stream Mach number of 2. The investigation described herein focused on obtaining information on both time-averaged and time-dependent flow features. The data consisted of steady and unsteady pressure measurements as well as some surface oil and schlieren flow visualisation. The effective length-to-depth ratios l/d of cavities investigated ranged between 5·65 and 8 for shallow 'open' cavities and between 11·31 and 16 for 'closed' cavities. The cavity sweep angles were 0°, 15° and 45°. The results of the swept cavities, when compared to the datum cases of the straight (0°) cavities, showed some distinct differences. With regard to time-averaged flow characteristics, in an open swept cavity (5·65 < l/d < 8), the flow displayed quasi-open flow behaviour, distorted by the spanwise cross flow within the cavity. In the case of the closed swept cavity (11·31 < l/d < 16), flow features resembling the 'closed' to 'transitional closed' cavity flow types were seen to exist simultaneously across the span. Unsteady pressure data indicated that for an open cavity at 15° sweep angle, the discrete frequencies observed were similar to those of a straight open cavity. In contrast to this, at 45° sweep angle, the frequencies were broadband with no discrete frequency across the cavity length. For the closed cavity, the frequencies were all broadband irrespective of the sweep angle. The investigation also showed that the influence of the sweep angle on the pressure drag of the cavity strongly depends on the type of cavity flow: a sweep angle increase from 0° to 45° approximately doubled the pressure drag for an open cavity, while it led to a drag reduction of about 37% for the closed cavity. [ABSTRACT FROM AUTHOR]

The ability to dynamically shape the spatial intensity profile of an incident laser beam enables new ways to modify and structure surfaces through pulsed laser processing. Here we describe a method to generate doughnut-shaped beams from an input Gaussian source using a tunable acoustic gradient index (TAG) lens. The TAG lens is capable of modulating between focused beams and annular rings of variable size, using sinusoidal driving frequencies. Laser micromachining is accomplished by synchronizing the TAG lens to a 355 nm pulsed nanosecond laser. Results in polyimide demonstrate the ability to generate adjacent surface features with different shapes and sizes. [ABSTRACT FROM AUTHOR]

Surface-induced exo-energetic inelastic transitions among atomic Zeeman states in a magnetic field (“van der Waals – Zeeman” transitions) are useable as tuneable beam splitters. A transversally coherent atom beam impinging a pair of opposite surfaces (e.g. 2 edges of a slit or of an ensemble of periodic slits) gives rise to two coherently diffracted wave packets. Within the wave packet overlap, non-localised interference fringes of the Young-slit type are predicted. From the diffraction pattern observed in the Fraunhofer regime (Schlieren image), detailed information about the transition amplitude on a scale of a few nanometers should be derived. [ABSTRACT FROM AUTHOR]

A novel, diaphragmless shock tube (DFST) has been developed for use in high temperature chemical kinetic studies. The design of the apparatus is presented along with performance data that demonstrate the range and reproducibility of reaction conditions that can be generated. The ability to obtain data in the fall off region, confined to much narrower pressure ranges than can be obtained with a conventional shock tube is shown, and results from laser schlieren densitometry experiments on the unimolecular dissociation of phenyl iodide (P2=57±9 and 122±7 torr, T2=1250–1804 K) are presented. These are compared with results similar to those that would be obtained from a classical shock tube and the implications for extrapolation by theoretical methods are discussed. Finally, the use of the DFST with an online mass spectrometer to create reproducible experiments that can be signal averaged to improve signal/noise and the quality of mass peaks is demonstrated; something that is not possible with a conventional shock tube where each experiment has to be considered unique. [ABSTRACT FROM AUTHOR]

Turbulent flame acceleration process has been studied in a two-dimensional valveless pulsed detonation combustor (PDC) using Schlieren flow visualization, ionization probes, and companion high-frequency pressure instrumentation. Experiments were conducted using near stoichiometric propane-air mixtures in a 76.2 mm × 76.2 mm, 1.68 m long modular detonation tube with the windowed combustor under multicyclic conditions within the PDC operating in a valveless mode. The effect of the presence of the obstacle was investigated at various stages of the flame acceleration process in aerodynamically confined environment. Amplification of the leading shock waves through the interaction of the obstacle enhances the flame acceleration process owing to the reduction of post-shock induction time and the hydrodynamic instabilities at the baroclinic interface. The internal configuration of the combustor including the obstacle plays a major role of the flame acceleration due to the shock amplification pattern. Sequences of schlieren images also show the flow drifting and blowdown processes confirming that the gasdynamic valves are successfully operative in the valveless PDC. [ABSTRACT FROM AUTHOR]

Porous structures can be used to avoid flame transmissions as it is done in flame arresters or breathing devices of explosion protected equipment. A detailed examination of the different flame transmission behaviours of different porous structures is performed using several methods of laser diagnostics. The flow behaviour is analysed using a Schlieren technique and the flame transmission itself is examined using laser induced fluorescence of OH radicals. [ABSTRACT FROM AUTHOR]

The paper is focused on measurement techniques of gradient-index elements particularly useful for slightly inhomogeneous glasses from small laboratory melts. A construction of the measurement cuvette and dependence of the refractive index of an immersion liquid on its parameters is discussed. The dependence of the refractive index of α-bromonaphtalene on temperature for λ= 0.6328 &miro;m is described. A measuring method of the refractive index profile of gradient-index elements is presented. [ABSTRACT FROM AUTHOR]

Abstract  This paper describes application of a background oriented schlieren technique in order to obtain quantitative measurements of shock waves from explosions by processing high speed digital video recordings. The technique is illustrated by an analysis of two explosions, a high explosive test and a hydrogen gas explosion test. The visualization of the shock front is utilized to calculate the shock Mach number, leading to a predicted shock front pressure. For high explosives the method agreed quite well with a standard curve for side-on shock pressures. In the case of the gas explosion test we can also show that the shock front is non-spherical. It should be possible to develop this technique to investigate external blast waves and external explosions from vented gas explosions in more details. [ABSTRACT FROM AUTHOR]

Under the circumstance of a Gaussian control field, the cold atomic medium with electromagnetically induced transparency (EIT) turns out to be the special medium with the quadratic index distribution which is controllable online. In our study, the optical system occupies a portion of the EIT medium which acts as an imaging device. With the help of the Collins formula, the analytic expression for the spatial distribution of the probe field in the cold atomic medium is obtained as well as the location of the imaging. The methods for improving the visibility of the imaging are proposed in this paper. Moreover, we also show that the shapes of the images on the output are strongly influenced by the intensity of the control field, which provides a potential optical processing method. [ABSTRACT FROM AUTHOR]

Abstract-This paper presents a methodology for analyzing multimodal and multiperspective systems for person surveillance. Using an experimental testbed consisting of two color and two infrared cameras, we can accurately register the color and infrared imagery for any general scene configuration, expanding the scope of multispectral analysis beyond the specialized long-range surveillance experiments of previous approaches to more general scene configurations common to unimodal approaches. We design an algorithmic framework for detecting people in a scene that can be generalized to include color, infrared, and/or disparity features. Using a combination of a histogram of oriented gradient (HOG) feature-based support vector machine and size/depth-based constraints, we create a probabilistic score for evaluating the presence of people. Using this framework, we train person detectors using color stereo and infrared stereo features as well as tetravision-based detectors that combine the detector outputs from separately trained color stereo and infrared stereo-based detectors. Additionally, we incorporate the trifocal tensor in order to combine the color and infrared features in a unified detection framework and use these trained detectors for an experimental evaluation of video sequences captured with our designed testbed. Our evaluation definitively demonstrates the performance gains achievable when using the trifocal framework to combine color and infrared features in a unified framework. Both of the trifocal setups outperform their unimodal equivalents, as well as the tetravision-based analysis. Our experiments also demonstrate how the trained detector generalizes well to different scenes and can provide robust input to an additional tracking framework. [ABSTRACT FROM AUTHOR]

Copyright of Geodesy & Cartography (1392-1541) is the property of Vilnius Gediminas Technical University and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

We examined the relationship between bat species activity and composition and the extent of forest cover and urbanization in and adjacent to 11 U.S. National Park Service, National Capital Region Parks in Maryland, Virginia, West Virginia, and Washington, D.C., from 2003-2004, using mist nets, harp traps, acoustical detectors, and visual observations in a variety of habitats. Our efforts included 363 trap nights across 74 sites along with acoustical sampling at 362 sites. We captured 383 bats and identified 6,380 echolocation passes of 6 species. Both overall and species-specific activities were affected more by forest fragmentation within parks than by urbanization adjacent to parks. With an ability to exploit anthropogenic structures for day-roosts, big brown bats (Eptesicus fuscus) were the most ubiquitous and probably the most abundant species in NCR Parks, particularly in forested, urban parks. Northern myotis (Myotis septentrionalis), and to a lesser extent, little brown myotis (Myotis lucifugus) were more prevalent in forested, rural parks of the Ridge and Valley and Blue Ridge than in eastern, less forested urban parks of the Piedmont and Coastal Plain physiographic provinces. Retention of larger, residual forest tracts and day-roosting habitat (i.e., trees and snags) would be beneficial to most species, as urban expansion continues throughout the region. [ABSTRACT FROM AUTHOR]

The article focuses on the experimental realization of the plane discontinuity breakdown during pulsed ionization of a flow region bordered by the surface of a shock in a channel. The images of the discharge plasma during a self-localization of the front of a plane shock were obtained with the Schlieren patterns. The experimental realization of the plane discontinuity breakdown is confirmed by the Schlieren images showing features of time dependent gas dynamic flow after the discharge action.

Abstract  The “synthetic schlieren” method has been used to measure the amplitude of internal waves that are two-dimensional and axisymmetric. Here it is adapted to reconstruct fully three-dimensional perturbations. This non-intrusive technique, which uses inverse tomography methods, shows accurate results when a sufficient number of perspectives taken from the same experiment are provided to the inversion code. We demonstrate the effectiveness of the wavefield reconstruction from three idealized disturbances in the form of a Gaussian function, a Gaussian multiplied in amplitude by a sine function and a sinusoidal plane wave with an elliptical envelope. The consequences of noisy data input are also investigated. [ABSTRACT FROM AUTHOR]

This paper deals with air bubbles rising in purified water in the range of equivalent diameters where surface oscillations appear on the interface. The shape of the bubbles including these capillary distortions is recorded by taking a large number of high speed pictures for each spiraling or zigzagging bubble trajectory. In analogy with surface harmonics, the oscillations are indicated as (2,0) axisymmetric and with wavelength equal to the distance from pole to pole and (2,2) nonaxisymmetric and with wavelength equal to one-half of the length of the equator. In the second series of experiments, the phenomena in the wakes of rising bubbles are made visible by using Schlieren optics, which are applicable because a temperature gradient is applied to the water. The frequencies of vortex shedding correspond to the (2,0) mode of surface oscillation, whereas in other works reported in the literature, they correspond to twice the frequency of the spiraling or zigzagging bubble paths. By measurements and by analysis, it is shown here that the latter is due to contamination of surfactants. [ABSTRACT FROM AUTHOR]

Three methods are analyzed for the design of ocean observing systems to monitor the meridional overturning circulation (MOC) in the North Atlantic. Specifically, a continuous monitoring array to monitor the MOC at 1000 m at different latitudes is “deployed” into a numerical model. The authors compare array design methods guided by (i) physical intuition (heuristic array design), (ii) sequential optimization, and (iii) global optimization. The global optimization technique can recover the true global solution for the analyzed array design, while gradient-based optimization would be prone to misconverge. Both global optimization and heuristic array design yield considerably improved results over sequential array design. Global optimization always outperforms the heuristic array design in terms of minimizing the root-mean-square error. However, whether the results are physically meaningful is not guaranteed; the apparent success might merely represent a solution in which misfits compensate for each other accidentally. Testing the solution gained from global optimization in an independent dataset can provide crucial information about the solution’s robustness. [ABSTRACT FROM AUTHOR]

In the present study, a temperature gradient system was designed with the aim of carrying out the tensile and fatigue test of thin-walled cylindrical alloyed steel (30CrMnSi). The tensile test under different temperatures was first carried out to obtain the static mechanical parameters. And then a three-dimensional (3D) finite element model was constructed to further study the deformation behavior under temperature gradient by the finite element analysis (FEA). The FE result was in good agreement with that of the experiment. Following this, the tensile fatigue test was performed under cooled air and no-cooled air to investigate the influence of the temperature gradient on fatigue life-time, respectively. The influence of cooled air under the lower nominal stress on fatigue life was not obvious than that of higher nominal stress. Finally, the scanning electron microscopy (SEM) was employed to investigate the fracture mechanism. The microstructure revealed that the fracture first occurred at the zone where there was a lower temperature. [ABSTRACT FROM AUTHOR]

In this work, a new contour detection method is studied for detecting brain tumor regions based on their gradient magnitude information. Gradient magnitude data, an edge detection method, is generated from the brain slice image intensity or perceived brightness information. Contour map of the brain tumor is generated by using the gradient magnitude differences of the template masks (cropped from brain slice tumor image) and the sample masks (traverses the image) raw pixel and perceived brightness (luminance) date. Then these differences are averaged and normalized to produce edge profiles of the brain tumor region contours. This data is used by the remote surgical devices for removing the tumor area. [ABSTRACT FROM AUTHOR]