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Background-oriented schlieren (BOS)methods suited for large-scale and in-flight testing are presented with special emphasis on the detection and tracing of blade tip vortices in situ. Retroreffective recording and photogrammetric epipolar analysis for the computation of the vortices' spatial coordinates in the wind tunnel are described. Feasibility and fidelity of reference-free BOS in conjunction with natural formation backgrounds and related evaluation methods are discussed, additionally, illustrating their simplicity and robustness. Results of successful image acquisition from a chaser aircraft are presented allowing vortex wakes to be identified at a wide range of flight attitudes, including complex maneuvers. [ABSTRACT FROM AUTHOR]

Abstract: A non-scanning 3D-CT technique using a multi-directional quantitative schlieren system, is proposed to obtain instantaneous density distributions of unsteady premixed flames. This “schlieren 3D-CT” is based on (i)simultaneous acquisition of schlieren images taken from numerous directions, (ii) reproduction of projection images from the schlieren images, and (iii) 3D-CT reconstruction of the projections by an appropriate algorithm. In this paper, 3D-CT reconstruction of an axisymmetric steady flame is made with a single-directional quantitative schlieren system. Also combined reconstruction of density and light-emission-intensity distributions of non- axisymmetric steady flame is made. These investigations are conducted as a preliminary research relevant to a massive system having 20 schlieren systems, suitable for the observation of high speed turbulent flames. [Copyright &y& Elsevier]

A high-speed digital streak camera designed for simultaneous high-resolution color photography and focusing schlieren imaging is described. The camera uses a computer-controlled galvanometer scanner to achieve synchroballistic imaging through a narrow slit. Full color 20 megapixel images of a rocket sled moving at 480 m/s and of projectiles fired at around 400 m/s were captured, with high-resolution schlieren imaging in the latter cases, using conventional photographic flash illumination. The streak camera can achieve a line rate for streak imaging of up to 2.4 million lines/s. [ABSTRACT FROM AUTHOR]

Background: For the design and characterization of ultrasonic particle manipulation devices the pressure field in the fluid cavity is of great interest. The schlieren method provides an optical tool for the visualization of such pressure fields. Due to its purely optical nature this experimental method has got some unique advantages compared to methods like particle tracking. Results: A vertical schlieren setup and an investigation with the same of a mm-sized chamber used to agglomerate particles are presented here. The schlieren images show a two-dimensional representation of the whole pressure distribution recorded simultaneously with a good resolution in time. The gained description of the pressure field is shown to be in agreement with a numerical simulation. Thermal effects as well as streaming effects are shown. Conclusions: The results show the great potential of schlieren visualization to investigate ultrasonic particle manipulation devices. Visualized are pressure fields, acoustic streaming, temperature effects and effects caused by fluid volumes of different density. [ABSTRACT FROM AUTHOR]

High-speed schlieren visualization at 20,000 fps was performed to investigate the transient penetration depth of helium gas jets into air at 8 different pressure ratios. The injection pressure investigated was between 1.5 and 40 bar. The pressure in the mixing chamber was varied between 1.0 and 4.0 bar. The different pressure ratios were chosen to examine subsonic and underexpanded jets. To investigate the density dependence of the process, cryo injections were performed at injection temperatures of 224, 198 and 173 K at different pressure ratios. Using the image processing technique for detecting the jet tip penetration distance, presented in this article, it can be shown that for a given injector the jet penetration behavior is the same for the same pressure ratio. A new self-similar model was developed, to describe the influence of the injection and chamber gas density on the jet penetration behavior more accurately. The model was verified with the experimental data sets presented in this paper and with literature data. [ABSTRACT FROM AUTHOR]

A new variant of the background oriented schlieren technique is presented. Using a laser to generate a speckle reference pattern, several shortcomings of the conventional technique can be overcome. The arrangement decouples the achievable sensitivity from the placement constraint on the reference screen, facilitating the design of compact, high-sensitivity configurations. A new dual-pass imaging mode is introduced which further improves system performance and permits focusing on the target scene. Examples are presented that confirm the theoretical predictions. [ABSTRACT FROM AUTHOR]

The process of the impulse outflow of a gas jet occurring due to the discharge inside the discharge chamber is studied experimentally. The flow was investigated by means of the schlieren-visualization and the Particle Image Velocimetry optical techniques. During the study, impulse jet parameter variations were obtained. A number of features were revealed of the impulse outflow from the discharge chamber, such as formation of a second vortex ring, reduction of the vortex ring circulation during the outflow, and formation of vortices in front of the main vortex ring. [ABSTRACT FROM AUTHOR]

A new method is proposed for polarization modulation of random electromagnetic beams. The changes in the spectral degree and the state of polarization of such after their passage through the gradient-index (GRIN) waveguide lens system are investigated while the parameters of the system are adjusted. It is demonstrated that passage through the GRIN waveguide lens system can lead to more complex changes in the beam's polarization than its free-space propagation. [ABSTRACT FROM AUTHOR]

Ambient desorption/ionization mass-spectrometry (ADI-MS) has shown tremendous potential for the direct analysis of materials in the open atmosphere. Unfortunately, processes governing analyte desorption and transport into the mass spectrometer, which ultimately limit sampling reproducibility and quantification, have not been investigated for most ADI-MS sources. For plasma-based ADI-MS sources, such studies are further complicated because the discharge support gas is optically transparent. Here, two methods were employed to probe these otherwise invisible phenomena. Specifically, schlieren imaging and infrared (IR) thermography were utilized to visualize plasma-gas flow and heat transfer, respectively, from a pin-to-capillary geometry flowing atmospheric-pressure afterglow (FAPA) ambient ionization source. The influence of operating conditions was investigated, including plasma-gas flow rate and source capillary diameter. Interactions of the desorption/ionization beam with a sample probe or a sample surface before it is captured by a mock mass spectrometer interface were also explored. These experiments showed that schlieren imaging is a viable means for visualization of the plasma transport gas, and that coupling with IR thermography yields information on gas and temperature distributions. Schlieren images revealed that the existence of a discharge can alter by up to 8 cm the location where the flowing afterglow transitions from laminar to turbulent flow. Addition of a sample-introduction probe into the plasma gas perturbed the width of the gas beam by 1.5 cm. Additionally, helium impinging on a surface expanded rapidly, unless an interface was present to capture the gas, while local heating was confined to a small area (＜1 cm2), based on 75% of the maximum temperature, compared to background. [ABSTRACT FROM AUTHOR]

The uncertainties in design variables are unavoidable in the optimal design of electromagnetic devices, and there is an imperative demand to find a robust design, which is insensitive to the uncertainties and remains within the feasible region of constraints even perturbed by the uncertainties. In this paper, a gradient-based worst case optimization (G-WCO) algorithm is proposed in a limited uncertainty set to increase the numerical efficiency based on the worst case optimization (WCO) algorithm. Through applications to the robust optimal design of TEAM 22, the performances of the proposed G-WCO, conventional WCO, and multiobjective optimization approach using gradient index (GI) are compared. [ABSTRACT FROM AUTHOR]

Plasma jet arrays are considered a viable means to enhance the scale of a downstream surface treatment beyond that possible using a single plasma jet. Of paramount importance in many processing applications is the uniformity of the plasma exposure on the substrate, which can be compromised when multiple plasma jets are arranged in close proximity due to their interaction. This contribution explores a dielectric barrier plasma jet array consisting of multiple individually ballasted jets. It is shown that capacitive ballasting is a promising technique to allow simultaneous operation of the plasma plumes without the losses associated with resistive ballasting. The interaction between adjacent plasma plumes and the background gas is investigated with Schlieren imaging; it is shown that the strong repulsive force between each plasma plume causes a divergence in propagation trajectory and a reduction in the laminar flow length with significant ramifications for any downstream surface treatment. [ABSTRACT FROM AUTHOR]

This work presents a study of acoustic oscillations generated and the wave structure associated with supersonic flow past wall mounted 3D open cavities of varying length-to-width (L/W) ratio. Experiments were conducted to investigate the acoustic signature generated by the cavities at freestream Mach number of 1-7. The effect of L/W ratio of the cavity on the dominant modes of the acoustic signature registered on different walls of the cavities is investigated for an L/W range of 0-83-4. Shift in the dominant acoustic mode is observed as L/W ratio changes from 3 to 4. Statistical analysis of pressure data showed existence of acoustic waves and spreading of acoustic energy over different modes with change in cavity width. Time averaged schlieren visualisation indicated variation of shock and shear layer structure in the mainstream for the different cavities. Acoustic waves generated by the presence of the cavity and the dynamic behaviour of the shear layer were observed during instantaneous shadowgraph visualisation. Numerical simulation was done to make a prior assessment of the flow structure and the results are in good agreement with those from experiments. Ratio of mass exchange between cavity and mainflow and the cavity volume was observed to have profound effect on the magnitude of pressure oscillations generated by the cavities. [ABSTRACT FROM AUTHOR]

An optical lensed fiber for detecting respiration condition in the vicinity of nose has been proposed and been demonstrated to work as a breath sensor. For simple preparation and larger sensing area, a piece of about quarter-pitch of an optical gradient index fiber (GIF) tip was spliced to the end of a single mode fiber. The sensing principle is based on the change of back reflection intensity caused by attachment of water molecules on the GIF tip during respiration. The experimental results showed that this breath sensor operated with a good sensitivity and a real-time respiration monitor was presented. In terms of the tiny size and light weight, the optical lensed fiber breath sensor is potential for the application of monitoring breathing condition in hospital and in home care. © 2012 Wiley Periodicals, Inc. Microwave Opt Technol Lett 55:450-454, 2012; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.27322 [ABSTRACT FROM AUTHOR]

The background-oriented schlieren (BOS) technique has not yet been used in the visualization of fuel spray in automotive research despite its great promise. To investigate the potential of this technique, the density distribution of a cross section of the spray was obtained by applying a filtered back projection (FBP) to the BOS results. Using the density distribution, the penetration lengths of the liquid and vapor phases of the fuel were measured and compared with the results of Mie scattering and shadowgraph images. The results show that the BOS technique is applicable for measuring the liquid and vapor penetration lengths simultaneously. Furthermore, the analysis of the back-projected density distribution revealed that the BOS technique is capable of visualizing the difference in the transient change in the density distribution due to changes in the injection pressure and the fuel volatility. [ABSTRACT FROM AUTHOR]

Abstract: This experimental study addresses the re-initiation mechanism of detonation waves following the Mach reflection of a shock–flame complex. The detonation diffraction around a cylinder is used to reproducibly generate the shock–flame complex of interest. The experiments are performed in methane–oxygen. We use a novel experimental technique of coupling a two-in-line-spark flash system with a double-frame camera in order to obtain microsecond time resolution permitting accurate schlieren velocimetry. The first series of experiments compares the non-reactive sequence of shock reflections with the reflection over a rough wall under identical conditions. It was found that the hot reaction products generated along the rough wall are entrained by the wall jet into a large vortex structure behind the Mach stem. The second series of experiments performed in more sensitive mixtures addressed the sequence of events leading to the detonation establishment along the Mach and transverse waves. Following ignition and jet entrainment, a detonation first appears along the Mach stem while the transverse wave remains non-reactive. The structure of the unburned tongue however indicates local instabilities and hot spot formation, leading to the rapid reaction of this gas. Numerical simulations are also reported, confirming the sequence of ignition events obtained experimentally. [Copyright &y& Elsevier]

Abstract: High-intensity focused ultrasound (HIFU) is widely used in cancer therapies, and it is hoped that its noninvasiveness will allow it to be applied to other clinical domains. Because HIFU is percutaneously delivered in the treatment of the liver, breast and uterus, there is a problem with the ultrasound beam being deflected or attenuated during its travel. In contrast, the intracorporeal use of an HIFU device provides an obstacle-free path, but the focal length is limited because of size constraints. In this paper, we propose the use of an intracorporeal device equipped with an acoustic mirror or lens to allow the ultrasound energy delivered through the abdominal wall to be reflected or focused in the body. The insertion of such a device into the body requires a small incision, but the proposed concept can help to safely control the HIFU focal point in the treatment of deep-seated organs. Moreover, safety is ensured because the device is electrically isolated. We have developed an experimental setup where the intracorporeal device is robotically positioned in front of an HIFU transducer. In preliminary experiments, the focused ultrasound energy was reflected using a metal plate, and the planar ultrasound waves were focused using an acrylic biconcave lens, with Schlieren imaging used for visualisation, and the results demonstrated the proof of concept. [Copyright &y& Elsevier]

A simple method of generating polygonal gas interfaces is proposed by using the soap film technique. Thin pins are used as angular vertexes to connect the adjacent sides of polygonal soap films in order to avoid the pressure singularities around the vertexes caused by the surface tension. As a demonstration, three polygonal interfaces (i.e., square, equilateral triangle and diamond) are created in the test section of a shock tube. Experiments are then carried out for a planar shock wave (Mach number about 1.2) interacting with air/SF polygonal interfaces. Numerical simulations are also performed to validate the proposed method of the interface formation. Wave systems and interface structures can be clearly identified in experimental schlieren images and agree well with the numerical results. It is also indicated that the presences of thin pins and fine chamfers only have limited effects on the interface evolution and can be ignored at the very early stage. Experimental and numerical results about the movement of the distorted interface, the width and height of the interface structures are further compared and good agreement is achieved. It is then concluded that the polygonal interface formed by the proposed method is applicable for the Richtmyer-Meshkov instability study. [ABSTRACT FROM AUTHOR]

In a Mach 3.8 wind tunnel, both instantaneous and time-averaged flow structures of different scales around a blunt double-cone with or without supersonic film cooling were visualized via nano-tracer planar laser scattering (NPLS), which has a high spatiotemporal resolution. Three experimental cases with different injection mass flux rates were carried out. Many typical flow structures were clearly shown, such as shock waves, expansion fans, shear layers, mixing layers, and turbulent boundary layers. The analysis of two NPLS images with an interval of 5 μs revealed the temporal evolution characteristics of flow structures. With matched pressures, the laminar length of the mixing layer was longer than that in the case with a larger mass flux rate, but the full covered region was shorter. Structures like K-H (Kelvin-Helmholtz) vortices were clearly seen in both flows. Without injection, the flow was similar to the supersonic flow over a backwardfacing step, and the structures were relatively simpler, and there was a longer laminar region. Large scale structures such as hairpin vortices were visualized. In addition, the results were compared in part with the schlieren images captured by others under similar conditions [ABSTRACT FROM AUTHOR]

Laboratory experiments have been performed to investigate the interaction of internal waves with a pycnocline. An oscillating cylinder generated internal wave beams, which were observed using the synthetic schlieren technique. Internal waves incident on the pycnocline layer excited higher-frequency modes. In the absence of shear, a discrete spectrum of harmonic modes was generated due to nonlinear effects. These harmonic modes might play a role in the formation of internal solitary waves which have been observed in ocean pycnoclines. With shear, a continuous spectrum of excited modes was found. [ABSTRACT FROM AUTHOR]

The mechanism behind cavity-induced pressure oscillations in supersonic flows past a deep rectangular cavity is not well understood despite several investigations having been carried out. In particular, the process by which the pressure wave is generated and the path of the pressure wave propagating inside the cavity remains unclear. In the present study, the pressure waves around a deep rectangular cavity over which nitrogen gas flows at a Mach number of 1.7 are visualized using the schlieren method. The length of the cavity is 14.0 mm. The depths of the cavity are selected as 20.0 and 11.7 mm, corresponding to length-to-depth ratios of 0.70 and 1.2, respectively. The pressure waves propagating inside as well as outside the cavity have been successfully visualized using a high-speed camera, and the propagation pattern of these waves is found to be different from that previously predicted by numerical simulation and from those expected in previous oscillation models. In addition, the pressure oscillation near the trailing edge of the cavity is also measured using semiconductor-type pressure transducers simultaneously with the capture of the schlieren images. As a result, the relationship between the shear-layer motion, pressure-wave generation, and pressure oscillation at the trailing edge of the cavity is clarified experimentally. [ABSTRACT FROM AUTHOR]

Cavitation plays an important role in fuel atomization mechanisms, but the physics of cavitation and its impact on spray formation and injector efficiency are not well documented yet. Experimental investigations are required to support the development and the validation of numerical models and the design of tomorrow's injectors, in the context of pollutant and fuel consumption reduction. The complexity of modern injectors and the extreme conditions of injection do not facilitate experimental investigations. In this paper, experiments are conducted in a simplified geometry. The model nozzle consists of a transparent 2D micro-channel supplied with a test oil (ISO 4113). Three different optical techniques are proposed to investigate the channel flow, with the pressure drop between upstream and downstream chambers as a parameter. A shadowgraph-like imaging technique allows the observation of cavitation inception and vapor cavities development throughout the channel. The technique also reveals the presence of density gradients (pressure or temperature) in the channel flow. However, this additional information is balanced by difficulties in image interpretation, which are discussed in the paper. In addition, a combination of Schlieren technique and interferometric imaging is used to measure the density fields inside the channel. The three techniques results are carefully analyzed and confronted. These results reveal a wealth of information on the flow, with pressure waves generated by bubble collapses, turbulence in the wake of vapor cavities and bubble survival in flow regions of high pressure. Our results also show that cavitation inception is located in the shear layers between the recirculation zones and the main flow, relatively far from the inlet corner, where the pressure is minimum in average. To explain this behavior, we propose a scenario of cavitation inception based on the occurrence and the growing of instabilities in the shear layers. [ABSTRACT FROM AUTHOR]

This paper deals with the initiation mechanism of a negative nanosecond pulsed discharge in supercritical (SC) carbon dioxide that was examined in detail using Schlieren and photomultiplier techniques. A negative pulsed voltage with a rise time of about 90 ns and half-width of 410 ns was applied to the point electrode. The experimental results show that: 1) The negative primary streamer was of a form quite different than that of a positive one: a bushlike negative streamer and a filamentlike positive streamer; 2) a drastic change in the density dependence of streamer initiation voltage appeared around the subcritical phase in the characteristics for streamer initiation voltage versus medium density; and 3) a shock wave of speed 1–1.5 Mach began growth following a delay of around 50 ns from the streamer initiation. It was predicted from the analysis of the experimental results that the drastic change in the streamer initiation voltage versus medium density characteristics may be due to a transition between the two types of generation mechanisms of the initial electron: electron detachment from negative ions in the gas phase and field electron emission from the point electrode in the SC and liquid phases. The shock wave was presumed to be caused by thermal relaxation of the vibrational energy in carbon dioxide molecules in a decay process of the primary streamer. [ABSTRACT FROM PUBLISHER]

A spark-induced hot gas jet of a gas turbine combustor igniter has been investigated using high-speed schlieren, stereo, and stereoscopic shadowgraph imaging visualization techniques. The schlieren images show that the spark-induced local high pressure generates a spherical shockwave. The energy released by the spark initiation combines with the igniter tip geometry to produce a hot gas jet. The hot gas front velocity was obtained from the high-speed schlieren images. The results have shown that the input voltage does not have much effect on the propagation speed of the hot gas front. It was observed that each spark had caused the erosion of some melted tiny metal bits flying off the igniter tip. The 3D velocity vectors of the flying off metal bits are calculated by a stereo reconstruction and evaluation algorithm. It has been found that the amount and velocity distributions of the eroded metal bits are very different even at a fixed input voltage to the igniter, which contrasts with the quite consistent hot gas jet development. The 3D structures of the interaction boundary between hot gas and ambient air are reconstructed for the first time using a stereoscopic shadowgraph technique. [ABSTRACT FROM AUTHOR]

The laminar diffusion flame response to external acoustic excitation is investigated at low frequencies. Two typical responses are observed: the flame oscillates either at the same or half the excitation frequency. The flame and vortex dynamics of the two typical cases are visualized by high-speed schlieren and stereo images. A “vortex merging” phenomenon is observed and is responsible for the flame flickering frequency reduction to half. The 3D flame structures in the two cases are reconstructed based on stereo images. The 3D flame topology shows great variances from different view angles, which indicates the necessity of 3D visualization. [ABSTRACT FROM AUTHOR]

To reveal the inner mechanism of gas explosion dynamic behavior affected by gas equivalent concentration, a high speed Schlieren image system and flow field measurement technology was applied to record the gas explosion flame propagation and flame structure transition. The results show that a flame front structure transition occurs, followed by a flame accelerating propagation process. The laminar to turbulence transition was the essential cause of the flame structure changes. The laminar flame propagation behavior was influenced mainly by gas expansion and fore-compressive wave effect, while the turbulent flame speed mostly depended on turbulence intensity, which also played an important role in peak value of the explosive pressure and flame speed. On the condition that the laminar-turbulent transition was easier to form, the conclusion was drawn that, the lowest CH4 concentration for maximum overpressure can be obtained, which was the essential reason why the ideal explosive concentration differs under different test conditions. [ABSTRACT FROM AUTHOR]

The electric-field-driven liquid crystal lens (ELC) induces the lens effect by the spatially non-uniform distribution of the refractive index. A scheme to analyse the performance of the ELC lens for the lights of various incident angles is devised by the calculation of the phase through the ELC lens and the determination of light ray directions from these phases. The calculated results show that the ELC lens changes the incident light of the plane wave into a focused wave and the focal distance becomes shorter for larger incident angles. [ABSTRACT FROM AUTHOR]

Transformation of space coordinates can be used as a convenient tool for producing a controlled electromagnetic field pattern. In this paper, using a conformal transformation, the design procedure of a lens antenna with high gain and low sidelobes is presented which can be realized by isotropic graded refractive index (GRIN) materials. Applying proper simplifying techniques, the designed lens can be made by non-resonant metamaterials or non-magnetic dielectrics having wide frequency band and low loss. A graded photonic crystal (GPC) operating in metamaterial regime is used for this purpose. By placing the lens in a horn antenna, a highly directive beam is achieved. It is also shown that by lateral displacement of the lens medium, the beam direction can be controlled to some extent. A multibeam antenna in which each beam can be controlled independently is also presented. Simulation results are used to justify the design approach. [ABSTRACT FROM PUBLISHER]

The current standard used for the characterization of ultrasonic transducers is the hydrophonic technique, which is able to measure the acoustic pressure profile. This technique allows a quantitative analysis, but is marred by several problems. A scan of the region of interest is a time-consuming operation, especially when measuring a long acoustic beam. Furthermore, a hydrophone placed near the radiating surface is certainly an impediment to the free propagation of the field. Off-axis measurements can be inaccurate because of the angular response of the hydrophone. These problems, together with the costs, have encouraged the search for an alternative quick and inexpensive test system. The well-known Schlieren technique allows a real-time visualization of the whole pressure range of the transducers, but to display the entire beam emitted by the transducers it is necessary to use very large-diameter lenses, with focal lengths of several meters. Such systems are very cumbersome and difficult to use. The system developed in this paper allows the imaging of an acoustic beam up to 200 mm in length, but the system is compact, being only about 1 m long and 0.30 m wide. A similar system based on the classic Schlieren effect would be several meters long, with lenses of 200 mm in diameter. Finally, the system can reconstruct the section of the beam at any height, using an acoustic tomography technique, and can also implement a quantitative analysis. Because it uses only commercial components, the developed and fabricated ultrasonic beam analyzer is a very low-cost imaging system. The goal of this work is to create a compact, low-cost system based on this technique to test a wide range of ultrasonic transducers up to 40 MHz and above. [ABSTRACT FROM AUTHOR]

The feasibility of using high-power light-emitting diodes (LED) as a light source for high frame rate schlieren imaging is investigated. Continuous sequences of high-intensity light pulses are achieved by overdriving the LED with current pulses up to a factor of ten beyond its specifications. In comparison to commonly used pulsed light sources such as gas discharge lamps and pulsed lasers, the pulsed LED has several attractive advantages: the pulse-to-pulse intensity variation is on the same order of magnitude as the detector (camera) noise permitting quantitative intensity measurements. The LED's narrow emission bandwidth reduces chromatic abberations, yet it is spectrally wide enough to prevent the appearance of speckle and diffraction effects in the images. Most importantly, the essentially lag-free light emission within tens of nanoseconds of the applied current pulse allows the LED to be operated at varying frequencies (i.e., asynchronously), which generally is not possible with neither lasers nor discharge lamps. The pulsed LED source, driven by a simple driver circuit, is demonstrated on two schlieren imaging setups. The first configuration visualizes the temporal evolution of shock structures and sound waves of an under-expanded jet that is impinging on a rigid surface at frame rates of 500 kHz to 1 MHz. In a second application, long sequences of several thousand high-resolution images are acquired on a free jet at a frame rate of 1 kHz. The low-intensity fluctuation and large sample number allow a reliable computation of two-point correlation data from the image sequences. [ABSTRACT FROM AUTHOR]

Two new homologous series consisting of central azo and ester linkage and methyl groups at the central as well as terminal benzene rings are synthesized and their mesomorphic properties are studied. Between these two series; Series I has lateral methyl group on terminal benzene ring where as series II has lateral methyl groups at central as well as terminal benzene cores. All the homologues of series I and II are mesogenic in nature; series I exhibits nematic phase from C1 to C14 members whereas C16 member shows smectic C mesophase alongwith nematic mesophase on the other hand all the members of series II are nematogenic in nature. The nematic phase of the series I and II shows marble/schlieren texture and the smectic phase shows schlieren texture of smectic C variety. The mesomorphic properties of both the series are compared with each other and also with other structurally related series to evaluate the effect of lateral methyl group at central as well as terminal benzene core on mesomorphism. [ABSTRACT FROM AUTHOR]

A method is presented for improving the brilliance of laser-produced soft x-ray sources that are based on pulsed gas jets as the targets. The conversion efficiency of laser energy into soft x-ray radiation is enhanced by locally increasing the particle density of the target species. This is achieved by applying a small background pressure to the supersonic flow emanating from a nozzle. In this manner, a supersonic jet with a so-called barrel shock system is formed. On passing the shocks, particles become locally concentrated, forming highdensity regions that are used as the targets. An estimate of possible increases in particle densities is provided. The jet flow is then analyzed experimentally by Schlieren imaging, thus visualizing the spatial shock structure. Additionally, a quantitative measurement of the gas density is made using a Hartmann-Shack wavefront sensor. The beneficial effect of the applied background gas on plasma generation is clearly more prominent than its absorbing effect on the photons originating from the plasma. This is shown for a nitrogen target with helium as the background gas. A plasma, generated behind the barrel shock in the nitrogen jet, emits monochromatic photons at a wavelength of 2.88 nm. The peak brilliance of the source is increased by an order of magnitude, resulting in 3.15×1016 photons (mm2 mrad2 s)-1. [ABSTRACT FROM AUTHOR]

A remarkably simple exact analytical solution is obtained for the electromagnetic field distribution across infinite metamaterial-containing composites with any arbitrary periodic variation of complex effective permittivity and permeability for the case of constant impedance across the structure. Arbitrary temporal dispersion and losses are allowed and the model is generally applicable to different inhomogeneous and anisotropic media simultaneously containing positive and negative refractive index constituents, as long as the effective medium approximation remains valid. The analytical solution is validated by a dispersive numerical model of lossy metamaterials that uses a transmission line matrix method based on Z-transforms, where a close agreement between the analytic and numerical results is obtained. [ABSTRACT FROM AUTHOR]

By means of the falling soap film tunnel and the Schlieren optical method, the Marangoni convection were observed directly in the immediate interfacial neighborhood during the desorption process of acetone from the falling soap film. Moreover, the hydraulic characteristics of the falling soap film tunnel, the acetone concentration, the surface tension of the soap liquid and the mass transfer has been investigated in details through the experimental or theoretical method. [ABSTRACT FROM AUTHOR]

In pathology, histological examination of the 'gold standard' to diagnose various diseases. It has contributed significantly toward identifying the abnormalities in tissues and cells, but has inherent drawbacks when used for fast and accurate diagnosis. These limitations include the lack of in vivo observation in real time and sampling errors due to limited number and area coverage of tissue sections. Its diagnostic yield also varies depending on the ability of the physician and the effectiveness of any image guidance technique that may be used for tissue screening during excisional biopsy. In order to overcome these current limitations of histology-based diagnostics, there are significant needs for either complementary or alternative imaging techniques which perform non-destructive, high resolution, and rapid tissue screening. Optical coherence tomography (OCT) is an emerging imaging modality which allows real-time cross-sectional imaging with high resolutions that approach those of histology. OCT could be a very promising technique which has the potential to be used as an adjunct to histological tissue observation when it is not practical to take specimens for histological processing, when large areas of tissue need investigating, or when rapid microscopic imaging is needed. This review will describe the use of OCT as an image guidance tool for fast tissue screening and directed histological tissue sectioning in pathology. [ABSTRACT FROM AUTHOR]

Abstract: The application of High-speed schlieren technology in flow field evolvement diagnosis of laser induced LSD wave is presented. Schlieren technology is improved to investigate the fast and self-luminescent flow field evolvement. Nanosecond magnitude and suitable light exposure could be obtained at the same time. The time sequence is designed and the time interval between high speed camera, strobo and laser is controlled. The clear flow field evolvement picture is appropriately processed to get the position and velocity information. The results show that the focusing angle and the inducer exert great influence on the evolvement of LSD wave. This work could provide the reference and convenient condition for the next research. [Copyright &y& Elsevier]

Mixing of jets is crucial for optimal performance of many industrial applications and there is a need to optimize both nozzle geometry and flow conditions. The present study reports the influence of buoyancy and perforation on mixing between a jet and its environment. Optical techniques are ideal for the study of jet mixing due to their non-intrusive and inertia free properties. The present study gives an account of mixing between helium jet and the ambient fluid using a combination of color schlieren deflectometry and radial tomographic mathematics. Four different perforation sizes have been used and the experiments are performed for Reynolds numbers 21-676 and Richardson numbers 3.27-0.0015. Color schlieren images show distinct influence of perforation and flow conditions (Richardson number). Oxygen concentration and jet width quantify effectiveness of jet mixing. Buoyancy plays an important role in mixing at high Richardson number. Perforation improves jet mixing i.e. there is about 120% increase in jet width and the size of perforation plays an important role. [ABSTRACT FROM AUTHOR]

The background oriented schlieren (BOS) technique is one of the visualization techniques that enable the quantitative measurement of density information in the flow field with very simple experimental setup. BOS requires only a background and a digital still camera and it can realize the quantitative measurement of density. In this report we propose the colored grid background image for BOS technique (CGBOS). The experiments were carried out in the 0.6 m x 0.6 m test section of supersonic wind tunnel at JAXA-ISAS. The measurement setup consisted of metal halide ramps, a colored grid background image and a digital still camera. A colored grid pattern was used as background image and density gradient in vertical and horizontal direction was obtained. The measurement result and prospect of CGBOS technique are reported. [ABSTRACT FROM AUTHOR]

Sedimentation velocity runs were carried out on two standard polystyrene polymers and their 1:1 mixture in an analytical ultracentrifuge as a function of polymer concentration. Schlieren optics was used for the detection and self-developed VelXLS data analysis program was used for the evaluation of sedimentation data. The generated mean molecular weight for the single component polymer solutions using VelXLS program was similar as the values from dynamic light scattering. The molecular weight distributions from VelXLS also matched with the distributions generated by using interference optics and VelXLAI data analysis program. The sedimentation coefficient was observed to have a concentration dependency as the sedimentation coefficient values shifted to lower values as a function of polymer concentration. The relative amount of polymer fractions in a polymer mixture detected by the analysis programs was also compared. VelXLS program led to the computation of better detection of the amount of polymer fractions, thus, indicating the application potential of VelXLS program for the colloid characterization. [ABSTRACT FROM PUBLISHER]

The interaction of a shock train with a normal suction slot is presented. It was found that when the pressure in the suction slot is smaller or equal to the static pressure of the incoming supersonic flow, the pressure gradient across the primary shock is sufficient to push some part of the near wall boundary layer through the suction slot. Due to the suction stabilized primary shock foot, the back pressure of the shock train can be increased until the shock train gradually changes into a single normal shock. During the experiments, the total pressure and therewith the Reynolds number of the flow were varied. The structure and pressure recovery within the shock train is analysed by means of Schlieren images and wall pressure measurements. Because the boundary layer is most important for the formation of a shock train, it has been measured by a Pitot probe. Additionally, computational fluid dynamics is used to investigate the shock boundary-layer interaction. Based on the experimental and numerical results, a simplified flow model is derived which explains the phenomenology of the transition of a shock train into a single shock and derives distinct criteria to maintain a suction enhanced normal shock. This flow model also yields the required suction mass flow in order to obtain a single normal shock in a viscous nozzle flow. Furthermore, it allows computation of the total pressure losses across a normal shock under the influence of boundary-layer suction. [ABSTRACT FROM AUTHOR]

A noncontact bubble manipulation by an optically induced local surface tension gradient is described in this paper. In microfluidic devices, the effects of interfacial phenomena become dominant with decreasing of the length scale. An appropriate control of the local gradient of the interfacial properties can provide a powerful method for bubble handling in the microfluidic system. Here, the photothermal technique is used to induce the gradient in surface tension around a microbubble. The thermocapillary force around the bubble is induced and controlled by local laser focusing. The bubble in a microchannel filled with silicone oil with varied viscosity was examined to verify experimentally the optical manipulation method of bubbles based on the photothermal Marangoni effect. As a result, three applications of bubble manipulation by using photothermal Marangoni effect are obtained: detachment from channel wall, trapping in liquid phase, and transportation in the channel. Additionally, minimum optical power for the manipulation was evaluated. The effects of bubble size, liquid viscosity, and irradiated optical power on the manipulation characteristics can be summarized by a dimensionless number that is a ratio of the thermocapillary force to viscous drag force for the bubble. [ABSTRACT FROM AUTHOR]

The stability of and the laminar-turbulent transition in a plane subsonic helium microjet flowing out into the atmosphere is studied experimentally. The microjet experiences both natural perturbations and controlled periodic acoustic effects. The averaged and instantaneous flow fields are visualized using the Schlieren method and particle tracking method. The pulsation parameters of the mass flow rate are measured, and data for nonlinear interaction between the perturbations at the laminar-turbulent transition in the microstructure are obtained by bispectral analysis. [ABSTRACT FROM AUTHOR]

Many practical combustion systems such as residential gas burners contain dense groupings or clusters of jet flames with sufficiently small spacing between them, which causes flame interaction. The interaction effect, due in part to Oxygen deficiency in the interstitial space between the flames, causes the spreading of flames, which may merge together to form larger group flames. This interactive effect is studied analytically by revisiting the laminar isolated flame theory for 2D jets, for which similarity solutions are readily available in compressible form, and symmetrical interaction zones can be observed. Flame characteristics were studied by obtaining analytical expressions for flame specific parameters such as height and width, lift-off height and blow-off velocity, air entrainment and mixing layer growth. The theory for multiple interacting jets describes an approximate criterion for interburner spacing at which flame interaction and group flame formation are first observed. The analytical framework presented in this paper presented in this paper produced results which were compared with experimental measurements. The experimental apparatus allowed the interburner spacing to be varied from 7.87 mm to 50.8 mm, and measurements of flame height, width, lift-off height and group-flame formation under interactive modes. Images of the evolving flow field were taken and Schlieren images of the multiple 2D jets were also recorded using a digital camera. [ABSTRACT FROM AUTHOR]

A new type of gradient-index (GRIN) metamaterial (MTM), composed of a dielectric post array (DPA), is proposed for millimeter-wave applications to achieve wideband, low-reflection characteristics, and low sensitivity to the polarization of the incident wave. The design concept is different from that followed in GRIN, in which a systemic phase-shifting (PS) strategy is used for flat lens synthesis. The performance of the proposed lens has been numerically examined, and its focusing property has been investigated. The behavior of refraction index of the lens material has also been retrieved to see how it is compared with that of GRIN design. [ABSTRACT FROM AUTHOR]

In this work, an improvement of a previously-published human eye model with aging is presented. The previous eye model showed the overestimated performance of an averaged MTF at low spatial frequencies at all ages. Since that model had rotationally symmetrical corneal surfaces, these have been modeled to resemble an astigmatic element according to the recent experimental published data and have been included to produce a more accurate eye model. The gradient refractive index (GRIN) profile proposed for the crystalline lens has not been modified to test its robustness. Further, a tilt and decentration of the lens, and only a decentration for the iris, have been permitted in order to fit the average performance of the new eye model with aging. The results demonstrate that the GRIN profile for the crystalline lens fits the model well, since the decentration and/or tilt of the lens and the iris are sufficient free parameters to simulate the performance of the retinal image quality of an emmetropic human eye with aging, having an average astigmatic cornea. [ABSTRACT FROM AUTHOR]

An investigation was carried out with the aim of reconstructing the gradient index (GRIN) profile of human crystalline lenses ex-vivo using optical coherence tomography (OCT) imaging with an optimization technique and to study the dependence of the GRIN profile with age. Cross-sectional images of nine isolated human crystalline lenses with ages ranging from 6 to 72 (post-mortem time 1 to 4 days) were obtained using a custom-made OCT system. Lenses were extracted from whole cadaver globes and placed in a measurement chamber filled with preservation medium (DMEM). Lenses were imaged with the anterior surface up and then flipped over and imaged again, to obtain posterior lens surface profiles both undistorted and distorted by the refraction through the anterior crystalline lens and GRIN. The GRIN distribution of the lens was described with three variables by means of power function, with variables being the nucleus and surface index, and a power coefficient that describes the decay of the refractive index from the nucleus to the surface. An optimization method was used to search for the parameters that produced the best match of the distorted posterior surface. The distorted surface was simulated with accuracy around the resolution of the OCT system (under 15 µm). The reconstructed refractive index values ranged from 1.356 to 1.388 for the surface, and from 1.396 to 1.434 for the nucleus. The power coefficient ranged between 3 and 18. The power coefficient increased significantly with age, at a rate of 0.24 per year. Optical coherence tomography allowed optical, non-invasive measurement of the 2D gradient index profile of the isolated human crystalline lens ex vivo. The age-dependent variation of the changes is consistent with previous data using magnetic resonance imaging, and the progressive formation of a refractive index plateau. [ABSTRACT FROM AUTHOR]

The aim of the work is the presentation of operating principle and properties of multimode interference structure devices made in gradient index technology by K+ and Na+ ion exchange method from the point of view of optical sensor design. Numerical analysis was performed using beam propagation method. Analyzed sensor structures are covered by nanolayers whose refractive index higher than the multimode interference section index is the reason for the concentration of wave propagation energy in the sensor layer area and its vicinity. Modifications of external propagation conditions change the refractive index and extinction coefficient of a sensor layer. The variation of optical properties leads to the modification of waveguiding conditions in the multimode interference coupler. [ABSTRACT FROM AUTHOR]

Guderley's self-similarity solution r = r0(1 - t/t0)α for strong converging cylindrical shocks is investigated experimentally for three different gases with adiabatic exponents γ = 1.13; 1.40; and 1.66 and various values of the initial Mach number. Corresponding values of the similarity exponent α which determines the strength of shock convergence are obtained for each gas thus giving the variation of α with γ. Schlieren imaging with multiple exposure technique is used to track the propagation of a single shock front during convergence. The present experimental results are compared with previous experimental, numerical, and theoretical investigations. [ABSTRACT FROM AUTHOR]

There is an important need for simple methods to visualize and measure whole-field airflow patterns in the HVAC field. The background-oriented schlieren (BOS) method is presented here as an answer to this need—a simple and effective method for visualizing refractive HVAC flowfields in situ. The equipment required is simple, portable, inexpensive, and readily available, thus superseding some previous approaches, including lens-and-grid schlieren techniques that require large fixed installations. For BOS a custom random-dot background pattern is used, and imaging is done by a consumer-grade digital single-lens-reflex (SLR) camera. After covering the principles of BOS, examples are shown of visualized airjets and plumes from heating vents and registers, a space-heater, a teakettle, and a human thermal plume and cough. BOS images of candle plumes are also used to explore several different visualization approaches, equipment arrangements, and image color scales. While current results are purely-qualitative visualizations, quantitative temperature measurements can also be made in certain cases where the flow is approximately two dimensional. Finally, BOS lends itself well to certain HVAC chores, such as the diagnosis of commercial kitchen ventilation airflows. [ABSTRACT FROM AUTHOR]

Mangroves are an assemblage of salt-tolerant woody hydrophytes that are the foundational species along tropical and subtropical coastlines, estuaries, lagoons and rivers. Once covering 75% of the world's tropical and subtropical coastlines, mangrove forests have been declining rapidly throughout the world in the last few decades. Monitoring and modelling mangrove forest growth are critical for their conservation. Salinity is one of the primary limiting factors for mangrove forest growth. In this letter, we report the potential of using hyperspectral remotely sensed data collected in the field for monitoring the photosynthesis rate of red (Rhizophora mangle) and white (Laguncularia racemosa) mangroves with regard to salinity gradient. Using photochemical reflectance index (PRI) as proxy for photosynthetic rate, PRI for both species are strongly related to salinity gradient, indicating the potential of monitoring mangrove forest growth on a regional scale using hyperspectral remote sensing. [ABSTRACT FROM AUTHOR]

Mach wave radiation is one of the better understood sources of jet noise. However, the exact conditions of its onset are difficult to determine and the literature to date typically explores Mach wave radiation well above its onset conditions. In order to determine the conditions for the onset of Mach wave radiation and to explore its behaviour during onset and beyond, three ideally expanded jets with Mach numbers Mj = 0.9, 1.3 and 1.65 and stagnation temperature ratios ranging over To/T∞ = 1.0–2.5 (acoustic Mach number 0.83–2.10) were used. Data are collected using a far-field microphone array, schlieren imaging and streamwise two-component particle image velocimetry. Using arc filament plasma actuators to force the jet provides an unprecedented tool for detailed examination of Mach wave radiation. The response of the jet to various forcing parameters (combinations of one azimuthal mode m = 0, 1 and 3 and one Strouhal number StDF = 0.09–3.0) is explored. Phase-averaged schlieren images clearly show the onset and evolution of Mach wave radiation in response to both changes in the jet operating conditions and forcing parameters. It is observed that Mach wave radiation is initiated as a coalescing of the near-field hydrodynamic pressure fluctuations in the immediate vicinity of the large-scale structures. As the jet exit velocity increases, the hydrodynamic pressure fluctuations coalesce, first into a curved wavefront, then flatten into the conical wavefronts commonly associated with Mach wave radiation. The results show that the largest and most coherent structures (e.g. forcing with m = 0 and StDF ~ 0.3) produce the strongest Mach wave radiation. Conversely, Mach wave radiation is weakest when the structures are the least coherent (e.g. forcing with m = 3 and StDF > 1.5). [ABSTRACT FROM PUBLISHER]