Use Of Longer Wavelengths Research Articles

Comparative analysis of viscous dissipation effects on Prandtl fluid including contraction and relaxation phenomena

AbstractThis paper investigates the effects of magnetohydrodynamics and heat transfer on the peristaltic transport of Prandtl fluid in a vertical endoscopic tube. The reduction of the complexity of the equations governing the flow of Prandtl fluid entails the use of long wavelength and low Reynolds number approximations. These complex equations for the pressure gradient and velocity profile are handled analytically using the perturbation technique with convective boundary conditions, and the temperature and concentration profiles are carefully solved for the exact solution. The frictional forces and pressure rise are also simulated with numerical integration. The resulting formulas for velocity, temperature, concentration, pressure rise, and pressure gradient are graphed using the MATLAB and MATHMATICA software, and the effects of all the different physical parameters are investigated and assessed. The streamlines with five distinct wave types are sketched at the conclusion to show the phenomenon of trapping. It is investigated that the velocity profile rises due to buoyancy forces and falls due to the influence of magnetic forces.

Experimental phasing opportunities for macromolecular crystallography at very long wavelengths

Despite recent advances in cryo-electron microscopy and artificial intelligence-based model predictions, a significant fraction of structure determinations by macromolecular crystallography still requires experimental phasing, usually by means of single-wavelength anomalous diffraction (SAD) techniques. Most synchrotron beamlines provide highly brilliant beams of X-rays of between 0.7 and 2 Å wavelength. Use of longer wavelengths to access the absorption edges of biologically important lighter atoms such as calcium, potassium, chlorine, sulfur and phosphorus for native-SAD phasing is attractive but technically highly challenging. The long-wavelength beamline I23 at Diamond Light Source overcomes these limitations and extends the accessible wavelength range to λ = 5.9 Å. Here we report 22 macromolecular structures solved in this extended wavelength range, using anomalous scattering from a range of elements which demonstrate the routine feasibility of lighter atom phasing. We suggest that, in light of its advantages, long-wavelength crystallography is a compelling option for experimental phasing.

Opportunities in the use of Very Cold Neutrons in reflectometry techniques

Reflectometry techniques are especially suited for time-of-flight measurements. The use of longer wavelengths does not modify the physics probed during a reflectivity measurement. Besides, reflectometry measurements are not affected by effects such as multiple scattering or absorption. The use of longer wavelengths would permit to achieve instrumental gains. Indeed, in the scattering plane, the phase space can be used more efficiently by a geometrical factor proportional to λ 2 provided by a simple increase of the incidence angles on the sample (for a given Q range). Perpendicular to the scattering plane, the neutron flux can be increased by a factor proportional to λ due to the increased critical angle of optics used for focusing in this direction. However, to comply with a given pulse structure of the neutron source would either require to proportionally decrease the instrument length or to drop neutron frames. Both options are viable depending on the scientific goals and we show that the flux penalties are actually minimal. However, owing to the fact that the performances of reflectometry instrumentation at ESS are expected to be extremely high, it is questionable if it is worth investing in Very Cold Neutrons (VCN) production for this specific technique the more so as the implementation will not be optimal for extrinsic reasons. On the other hand, implementing VCN on sources such as CANS where the flux is intrinsically limited may be worth the investment since (i) such sources could probably be designed to use VCN in an optimal way, (ii) the construction and handling of VCN sources would be much easier as radiative heating would be reduced by several orders of magnitude, in the range of hundreds of watts.

Transmissive-detected laser speckle contrast imaging for blood flow monitoring in thick tissue: from Monte Carlo simulation to experimental demonstration

Laser speckle contrast imaging (LSCI) is a powerful tool to monitor blood flow distribution and has been widely used in studies of microcirculation, both for animal and clinical applications. Conventionally, LSCI usually works on reflective-detected mode. However, it could provide promising temporal and spatial resolution for in vivo applications only with the assistance of various tissue windows, otherwise, the overlarge superficial static speckle would extremely limit its contrast and resolution. Here, we systematically investigated the capability of transmissive-detected LSCI (TR-LSCI) for blood flow monitoring in thick tissue. Using Monte Carlo simulation, we theoretically compared the performance of transmissive and reflective detection. It was found that the reflective-detected mode was better when the target layer was at the very surface, but the imaging quality would rapidly decrease with imaging depth, while the transmissive-detected mode could obtain a much stronger signal-to-background ratio (SBR) for thick tissue. We further proved by tissue phantom, animal, and human experiments that in a certain thickness of tissue, TR-LSCI showed remarkably better performance for thick-tissue imaging, and the imaging quality would be further improved if the use of longer wavelengths of near-infrared light. Therefore, both theoretical and experimental results demonstrate that TR-LSCI is capable of obtaining thick-tissue blood flow information and holds great potential in the field of microcirculation research.

Spectrally Resolved Characterization of Thermally Induced Underwater Turbulence Using a Broadband White-Light Interrogator

To allow for reliable wireless optical links in realistic underwater environments, we study the dependence of turbulence-induced fading on the wavelength using a laser-based white-light interrogator in emulated realistic conditions. We experimentally show that the scintillation index decreases significantly with the increase of wavelength. The results are verified for longer distances using a Monte Carlo simulation. We numerically and experimentally demonstrate that the use of longer wavelengths lowers the bit error ratio by as much as three orders of magnitude. We conclude that using green light is more reliable in turbulent channels than blue. The correlation between different wavelengths under turbulence is studied, which was made possible by the use of the laser-based white-light interrogator.

Efficient Use of Low-Bandgap GaAs/GaSb to Convert More than 50% of Solar Radiation into Electrical Energy: A Numerical Approach

A recent trend in photovoltaic technology is to aim to enhance the conversion efficiency of this energy harvesting technique. Although multijunction solar cells offer high efficiency, factors such as fabrication cost, cost per watt of energy produced, etc. limit their application. An alternative approach based on a lower-bandgap GaAs/GaSb dual-junction solar cell is proposed herein. For efficient use of longer wavelengths of the solar spectrum, a model for a simple antireflection coating (ARC)-less GaAs/GaSb dual-junction cell with a double back-surface field layer was optimized. The model was simulated using the Silvaco ATLAS technology computer-aided design (TCAD) tool and validated based on parameters such as the quantum efficiency, photogeneration rate, and spectral response. The model predicts conversion efficiency of 54%, better than some reported experimental results.

Comparison of second harmonic microscopy images of collagen-based ocular tissues with 800 and 1045 nm.

Second harmonic generation (SHG) imaging is a well-suited multiphoton technique allowing visualization of biological tissues mainly composed of collagen with submicron resolution. Despite its inherent confocal properties, imaging of deeper layers within thick samples has still some limitations. Although the use of longer wavelengths might help to overcome this, the dependence between SHG signals and wavelength is still under discussion. We report here on the dependence with wavelength of SHG signals from collagen-based ocular tissues. The quality of SHG images for two commonly used excitation wavelengths (800 and 1045 nm) is studied. The analysis of the collagen structural information reveals that the information provided by both wavelengths is similar. It was also found that, independently of the depth location, 1045-nm SHG images presented always lower signal levels than those acquired with 800 nm. However, the contrast of the former images was higher, what may improve the visualization of certain features of interest.

Wavelength dependence of the efficiency of photocatalytic processes for water treatment

The main objective of this work is to present a novel approach to evaluate quantitatively the action spectra and energy efficiency for chemical oxidation and bacterial inactivation of photocatalytic processes using monochromatic LED sources. Two different catalysts with different absorption spectra (TiO2 and iron citrate complex) were used. In all cases, it was confirmed a direct relationship between the absorption spectrum of the catalyst and the spectral dependence of the photonic efficiency. The best alternative for TiO2 processes in terms of energy consumption when using artificial lighting is the use of 365nm. In contrast, for iron complexes it seems more economically feasible the use of longer wavelengths close to the visible range, because the lower absorption of the complex is counterbalanced by the higher energy efficiency of the LED devices. This can be obviously extrapolated to the use of sunlight, where the use of iron-based photocatalytic processes can harvest a higher fraction of the available light. Predictions of the process efficiency under solar irradiation based on the action spectra determined with LED at laboratory scale have been successfully validated by experimental data. The methodology proposed in this work could be easily extrapolated to other wavelength ranges required by novel catalysts or efficient short wavelength monochromatic LED sources available in the future.

Near-infrared laser annealing of Ge layers epitaxially grown on Si for high-performance photonic devices

Near-infrared laser annealing of Ge epitaxial layers on Si is studied as a postgrowth annealing process to reduce the density of threading dislocations (TDs) in Ge. Laser annealing is performed using an exposure of 1.07-μm-laser light with the power density as large as 8 kW/cm2 and the duration as short as 10 ms. The TD density is successfully reduced from 6 × 108 to 2 × 108 cm−2 in a 600-nm-thick Ge layer grown by ultrahigh-vacuum chemical vapor deposition on Si. Vertical pin photodetectors of laser-annealed Ge show a significant reduction of dark leakage current as small as 20 mA/cm2 with a high photodetection efficiency. The short annealing time is effective to prevent the dopant diffusion in Ge together with the Ge-Si intermixing at the interface, being applicable to the annealing even after the formation of pin junctions in Ge. In terms of the reduction of thermal budget, the use of longer wavelength up to ∼1.6 μm has potential applications to preferential annealing of Ge layers on a Si platform due to the strong optical absorption in Ge despite the high optical transparency in Si.

Vibration mode shapes visualization in industrial environment by real-time time-averaged phase-stepped electronic speckle pattern interferometry at 10.6 μ m and shearography at 532 nm

We present our investigations on two interferometric methods suitable for industrial conditions dedicated to the visualization of vibration modes of aeronautic blades. First, we consider long-wave infrared (LWIR) electronic speckle pattern interferometry (ESPI). The use of long wavelength allows measuring larger amplitudes of vibrations compared with what can be achieved with visible light. Also longer wavelengths allow lower sensitivity to external perturbations. Second, shearography at 532 nm is used as an alternative to LWIR ESPI. Both methods are used in time-averaged mode with the use of phase-stepping. This allows transforming Bessel fringes, typical to time averaging, into phase values that provide higher contrast and improve the visualization of vibration mode shapes. Laboratory experimental results with both techniques allowed comparison of techniques, leading to selection of shearography. Finally a vibration test on electrodynamic shaker is performed in an industrial environment and mode shapes are obtained with good quality by shearography.

Parametric generation and characterization of femtosecond mid-infrared pulses in ZnGeP2.

Ultrafast mid-infrared (IR) coherent radiation plays an important role in strong-field physics, wherein the use of longer wavelengths has reduced the optical intensities needed to drive light-matter interactions by orders of magnitude in comparison to near-IR radiation. Optimizing parametric interactions for generation and characterization of mid-IR pulses is an enabling step for those applications. We report on the production of >50 µJ femtosecond pulses centered at 5 µm in a two-stage optical parametric amplifier (OPA) based on ZnGeP2, a high-performance optical material in this spectral region. The OPA is pumped by an ultrafast 2-µm source. Amplified pulses have been characterized by parametric upconversion, enabling the use of standard silicon detectors. A numerical model of the system has been developed and tested to control dispersion, group-velocity mismatch, and off-axis parametric fluorescence. The source architecture is suitable for production of mJ-level mid-IR ultrafast pulses without the use of chirped-pulse amplification, where convenient pumping could be realized directly by mid-IR laser sources based on materials such as Cr:ZnSe or Cr:ZnS.

Structure determination by multiple-wavelength anomalous dispersion (MAD) at the PrLIIIedge

The use of longer X-ray wavelengths in macromolecular crystallography has grown significantly over the past few years. The main reason for this increased use of longer wavelengths has been to utilize the anomalous signal from sulfur, providing a means for the experimental phasing of native proteins. Here, another possible application of longer X-ray wavelengths is presented: MAD at the L(III) edges of various lanthanide compounds. A first experiment at the L(III) edge of Pr was conducted on HZB MX beamline BL14.2 and resulted in the successful structure determination of the C-terminal domain of a spliceosomal protein. This experiment demonstrates that L(III) edges of lanthanides constitute potentially attractive targets for long-wavelength MAD experiments.

Structure determination by multiple-wavelength anomalous dispersion (MAD) at the Pr LIIIedge

The use of longer X-ray wavelengths in macromolecular crystallography has grown significantly over the past few years. The main reason for this increased use of longer wavelengths has been to utilize the anomalous signal from sulfur, providing a means for the experimental phasing of native proteins. Here, another possible application of longer X-ray wavelengths is presented: MAD at the L(III) edges of various lanthanide compounds. A first experiment at the L(III) edge of Pr was conducted on HZB MX beamline BL14.2 and resulted in the successful structure determination of the C-terminal domain of a spliceosomal protein. This experiment demonstrates that L(III) edges of lanthanides constitute potentially attractive targets for long-wavelength MAD experiments.

Effect of Incident Light Wavelength and Corneal Edema on Light Scattering and Penetration: Laboratory Study of Human Corneas

The outcome of ultrashort pulse laser surgery of the cornea is strongly influenced by the light scattering properties of the tissue, for which little data are available. The purpose of the present study is to provide quantitative values for light scattering and its relation to the degree of edema. An experimental optical measuring setup based on confocal geometry was used to measure the unscattered and scattered fractions of light transmitted by eye bank corneas presenting various degrees of edema. From these measurements, the effective light penetration depth in the cornea was calculated as a function of wavelength. Corneal transparency depends on the pathological state of the cornea and on wavelength. It may be predicted as a function of corneal thickness, ie, the degree of edema. In healthy and edematous cornea, the percentage of scattered light decreases with increasing wavelength. The total penetration depths at the wavelengths of ~1050 nm (which is used in typical clinical systems) and 1650 nm (which is recommended for future devices) are comparable; however, the former is limited by scattering, which degrades the laser beam quality, whereas the latter is only limited by optical absorption, which may be compensated for. The use of longer wavelengths should help improve the surgical outcome in ultrashort pulse laser surgery of the cornea when working on pathological tissue. A wavelength of approximately 1650 nm appears to be a good compromise, as it allows for reduced light scattering while keeping optical absorption reasonably low.

Update of endovenous laser therapy and the latest application studies

Abstract Endovenous laser therapy (ELT) has been applied in clinical practice as a therapy for truncal vein incompetence for about 10 years. One characteristic of ELT is the broad spectrum of different treatment protocols using a variety of laser systems and different forms of endovenous application. The principles behind the way ELT is carried out and the clinical results are described in detail in the following article. Despite good clinical results with effective, relatively pain-free occlusion of incompetent truncal veins, undesired side effects have been observed such as ecchymosis, phlebitis and recanalization. These can mainly be traced to thermal lesions in the vein wall concentrated in certain spots with transmural ablations of the tissue and perforations. In recent years systematic experimental investigations and the analysis of clinical results have increased understanding of the connection between endovenous laser application and clinical results. This has led to a continuous development and optimization of ELT. Particularly the use of longer wavelengths and radially irradiating optical fibers, together with endovenous laser irradiation with continuous pull-back of the optical fiber seem to have had a positive influence on the side effects. As a result ELT treatment is coming closer to the goal of standardizing an effective method for the treatment of varicose veins. Further controlled studies are required to compare optimized ELT treatment protocols with not only other endothermal modes of treatment but also with conventional open surgery.

Incorporation of N in high N‐content GaAsN films investigated by Raman scattering

AbstractHigh N‐content GaAs1–x Nx films (0 ≤ x ≤ 0.055) grown GaAs (001) substrates by MOVPE were investigated using micro‐Raman spectroscopy. The nitrogen local vibration mode (N‐LVM) which was clearly observed at around 468 ‐ 475 cm‐1 is used as a tool to examine the N incorporation. No change in the local environment of N is observed for the high N‐containing films with N contents up to x = 0.055. The use of 514.5 nm‐line Ar+ laser as the light source gives a linear dependence of the N contents determined by Raman spectroscopy (xRaman) on the N contents determined by the high resolution X‐ray diffraction (xXRD) for xXRD ≤ 0.055, providing a realizable calibration method to determine N content in the high N‐content GaAs1‐x Nx films. On the other hand, the use of longer wavelength (632.8 nm‐line He‐Ne laser) gives a best coincidence for only the lower N contents (x < 0.02). Since, the use of longer wavelength requires the thicker film owing to a thicker optical penetration depth. Thus, in our case, a deviation from the linear behavior for higher N contents, xXRD ≥ 0.02, is not due to the N‐related reasons, but this is the results of the additional Raman scattering intensity of GaAs‐LO from the substrate. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

The use of softer X-rays in the structure elucidation of microporous materials

Microporous materials, such as zeolites and aluminophosphates, have many applications as molecular sieves and shape-selective catalysts. This is due to their three-dimensional frameworks, which contain regular pores and channels, to their high acidity, arising from Brønsted and Lewis acid active sites, and to the incorporation of transition metal atoms into framework sites. This review firstly provides an introduction into the nature and properties of these materials, and their important applications; the difficulties in their full characterization and possible methods of elucidating their structures are then outlined; finally, methods of characterization, utilizing 'softer X-rays' are introduced. The first method is the determination of low concentrations of transition metals, incorporated into the frameworks using single crystal anomalous dispersion crystallography; synchrotron radiation is used to tune to the absorption edge of the metal atom in question, in order to change its signal relative to that of the rest of the structure, thereby allowing the pinpointing of its positions and the determination of its concentration at each site in the framework. Secondly, the use of longer wavelengths in powder diffraction studies is described, which, by stretching out the powder pattern, thereby reduces the overlapping of the diffraction peaks, thus allowing the structure to be solved by conventional direct methods. Finally, the use of X-ray absorption spectroscopy to determine the metal incorporation and the nature of coordination at the metal atom sites, in Mn silicalite-1 and FAPO-36, are described.

A strategy for the broad range detection of compounds with affinity for nucleic acids

A nucleic acid based optical biosensing strategy for the broad range detection of compounds with affinity for nucleic acids is described. The strategy attempts to use the chemical and structural information contained in the DNA helix as a sensing element per se. Detection is based on measuring changes in the fluorescence signal intensity of ToPro-3 complexed with nucleic acids. ToPro-3 is a cationic, planar aromatic fluorescent nucleic acid dye that binds to DNA by intercalation. The fluorescence of the dye is environment dependent and is greatly enhanced upon intercalation. ToPro-3 has a long excitation wavelength of 642 nm with emission occurring at 661 nm. At these wavelengths, spectral interference from organic compounds is dramatically reduced. The sensor is capable of detecting known intercalating and groove binding compounds over a broad range of binding affinities. Detection limits of 200, 20, 95 and 1 nM were obtained for EtBr, DAPI, PI and TOTO1, respectively. The ability of the assay to detect the known mutagens bisbenzidine, 1,2,4-benzenetriamine and proflavin, as well as of unknown compounds in natural product extracts was also investigated. Furthermore, the use of longer wavelengths allows the implementation of solid-state instrumentation which allows stable DC operation, reduces electronic noise and simplifies miniaturization, all of which increase portability. This scheme provides a flexible strategy for detecting compounds with affinity for DNA that can be used in a wide range of application areas. Approaches for expanding the informational content of the scheme are discussed.

Two-fiber laser Doppler velocimetry in blood: Monte Carlo simulation in three dimensions

Laser Doppler velocimetry in blood when fiber-optic catheters are used is limited by the effects of multiple scattering and flow disturbance produced by the catheter. To minimize the effects of flow disturbances, the system should be designed to project the velocity-sensing region as far as possible from the surface of the catheter. Because of multiple scattering, determining the region of sensitivity requires the use of transport theory. We present numerical results of Monte Carlo simulations of the spatial Doppler sensitivity field of a two-fiber velocimeter. The simulations show that a peak of sensitivity can be projected approximately 0.5 mm from the fiber tips (at 685 nm); the use of longer wavelengths would increase this distance somewhat. The generation of such a peak requires overlapping the partially spatially coherent propagation regions of the two fibers, which in turn depends strongly on the relative orientation of the fibers, even though much of the scattered light is diffuse.

BVRI main-sequence photometry of the globular cluster M4

view Abstract Citations (41) References (75) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS BVRI main-sequence photometry of the globular cluster M 4. Alcaino, G. ; Liller, W. Abstract BV and RI photographic photometry is presented of 1421 and 189 stars in the intermediate metallicity globular cluster M4 (NGC 6121). The investigation includes the first results of RI main-sequence photometry of a globular cluster. The use of longer wavelengths and longer color baselines provides the potential for improved isochrone fittings and emphasizes the need for calculations of RI synthetic isochrones for comparison with observations. The position of the main sequence turnoff was found to lie at V = 16.6 and B - V = 0.80. A comparison of the present BV observations with CCD data from the literature showed excellent agreement between the two fiducial main sequences. For the cluster a distance modulus of 21.52 was derived, and reddening was determined to be near 0.44. The properties of the color magnitude and color-color diagrams in the longer wavelength bands are discussed in detail. A fold-out map is provided which shows the positions of the stars. Publication: The Astrophysical Journal Supplement Series Pub Date: September 1984 DOI: 10.1086/190975 Bibcode: 1984ApJS...56...19A Keywords: Astronomical Photometry; Globular Clusters; Main Sequence Stars; Stellar Color; Stellar Evolution; Stellar Magnitude; Astrometry; Astronomical Maps; Color-Color Diagram; Hertzsprung-Russell Diagram; Interstellar Extinction; Stellar Composition; Ubv Spectra; Astronomy full text sources ADS | data products SIMBAD (86) GCPD (1)