Wavelength Ratio Research Articles

Elastic properties of rock salt ScN thin films investigated by laser ultrasound

Elastic moduli of scandium nitride (ScN) films are determined using a laser-based experimental method working with surface acoustic waves (SAWs). ScN, a semiconductor material with promising potential for various applications, crystallizes in the cubic rock salt (rs) structure. We investigate two samples of high-crystallinity ScN(111) films with thicknesses ∼200 and ∼300 nm, grown on Si(111) substrates by pulsed DC-magnetron co-sputtering and a sample with a fiber-textured ScN film (∼800 nm) on Si(001). From the shape evolution of laser-generated acoustic pulses, SAW dispersion curves were obtained in a frequency range of 50–500 MHz. In order to take advantage of the anisotropy of the film and substrate materials, measurements were performed for 10–15 SAW wavevector directions, which could be defined with a precision of 0.2°. Using perturbation theory with respect to the ratio of film thickness and SAW wavelength, two combinations of the three independent elastic constants of the high-crystallinity rs ScN films could be extracted from the measurement data. The surface roughness of the ScN films is accounted for with a simple model. Complete sets of the three elastic moduli were inferred in two different ways: (i) SAW dispersion data for the third sample were included in the extraction procedure; and (ii) the bulk modulus is set equal to a theoretical literature value. The extracted values for the three elastic constants are at variance with published theoretical results for single-crystal ScN. Possible reasons for these discrepancies are discussed.

Electromagnetic scattering by curved surfaces and calculation of radiation force: Lattice Boltzmann simulations

This study aims to investigate the effectiveness of the lattice Boltzmann method (LBM) in studying the scattering of electromagnetic waves by curved and complex surfaces. The computation of Maxwell’s equations is done by solving for a pair of distribution functions, which evolve based on a two-step process of collision and streaming. LBM bypasses the need for expansion via vector spherical harmonics and thus is amenable to scatterers with complex geometries. We have employed LBM to compute the scattering width and radiation force for perfect electrically conducting and dielectric cylinders of circular and elliptical cross sections. Both smooth and corrugated surfaces are studied, and the results are compared against known analytical and numerical solutions from other methods. To ensure the broad applicability of the method, we have explored a wide range of parameter space—the dielectric constant and particle size to the wavelength ratio spanning Rayleigh, Mie, and geometrical optics regimes. Our simulations have successfully reproduced well-known analytical and numerical solutions, confirming the accuracy and reliability of the LBM for scattering calculations by complex-shaped objects.

Mathematical modeling of electroosmotically driven peristaltic propulsion due to transverse deflections of two periodically deformable curved tubes of unequal wavelengths

The present study aims to investigate the viscid fluid propulsion due to the electroosmosis and transverse deflections of the sinusoidally deformable tubes of unequal wavelengths in the presence of electro-kinetic forces. This situation is estimated from the physical model of physiological fluid flow through a tubular structure in which an artificial flexible tube is being inserted. In this model, both peristaltically deforming tubes are taken in a curved configuration. The flow-governing momentum equations are simplified by the approximation of the long wavelength as compared to the outer tube's radius, whereas the Debye–Hückel approximation is used to simplify the equations that govern the electric potential distribution. Here, the authors have used the DSolve command in the scientific computing software MATHEMATICA 14 to obtain the expressions for electric potential and axial velocity of viscid fluid. In this work, the authors have analyzed the impact of various controlling parameters, such as the electro-physical parameters, curvature parameter, radius ratio, wavelength ratio, and amplitude ratios, on the various flow quantities graphically during the transport of viscid fluid through a curved endoscope. Here, contour plots are also drawn to visualize the streamlines and to observe the impacts of the control parameters on fluid trapping. During the analysis of the results, a noteworthy outcome extracted from the present model is that an increment in electro-physical parameters, such as Helmholtz–Smoluchowski velocity and the Debye–Hückel parameter, are responsible for enhancement in the shear stress at the inner tube's wall and the axial velocity under the influence of electro-kinetic forces. This is because of the electric double layer (EDL) thickness, which gets reduced on strengthening the Debye–Hückel parameter. This reduced EDL thickness is responsible for the enhancement in the axial velocity of the transporting viscid fluid. The present model also suggests that the axial velocity of viscid fluid can be reduced by enhancing the ratio of wavelengths of waves that travel down the walls of the outer curved tube and the inner curved tube. The above-mentioned results can play a significant role in developing and advancing the endoscopes that will be useful in many biomedical processes, such as gastroscopy, colonoscopy, and laparoscopy.

Estimating ice water content for winter storms from millimeter-wavelength radar measurements using a synthesis of polarimetric and dual-frequency radar observations

Abstract The potential of millimeter-wavelength radar-based Ice Water Content (IWC) estimation is demonstrated using a Ka-band Scanning Polarimetric Radar (KASPR) for the U.S northeast coast winter storms. Two IWC relations for Ka-band polarimetric radar measurements are proposed: one that uses a combination of the radar reflectivity Z and the estimated total number concentration of snow particles Nt and the other based on the joint use of Z, specific differential phase KDP, and the degree of riming frim. A key element of the algorithms is to obtain the “Rayleigh-equivalent” value of Z measured at Ka band, i.e., the corresponding Z at longer radar wavelength for which Rayleigh scattering takes place. This is achieved via polarimetric retrieval of the mean volume diameter Dm and incorporating the relationship between the dual wavelength ratio DWRS/Ka and Dm. Those techniques allow for retrievals from single millimeter-wavelength radar measurements and do not necessarily require the DWR measurements, if the DWR-Dm relation and Rayleigh assumption for Ka-band KDP are valid. Comparison between the quasi-vertical profile product obtained from KASPR and the columnar vertical profile product generated from the nearby WSR-88D S-band radar measurements demonstrates that the DWRS/Ka can be estimated from the two close radars without the need for collocated radar beams and synchronized antenna scanning and can be used for determining the “Rayleigh-equivalent” value of Z. The performance of the suggested techniques is evaluated for seven winter storms using surface disdrometer and snow accumulation measurements.

Deriving Vegetation Indices for 3D Canopy Chlorophyll Content Mapping Using Radiative Transfer Modelling

Leaf chlorophyll content is a major indicator of plant health and productivity. Optical remote sensing estimation of chlorophyll limits its retrievals to two-dimensional (2D) estimates, not allowing examination of its distribution within the canopy, although it exhibits large variation across the vertical profile. Multispectral and hyperspectral Terrestrial Laser Scanning (TLS) instruments can produce three-dimensional (3D) chlorophyll estimates but are not widely available. Thus, in this study, 14 chlorophyll vegetation indices were developed using six wavelengths employed in commercial TLS instruments (532 nm, 670 nm, 808 nm, 785 nm, 1064 nm, and 1550 nm). For this, 200 simulations were carried out using the novel bidirectional mode in the Discrete Anisotropic Radiative Transfer (DART) model and a realistic forest stand. The results showed that the Green Normalized Difference Vegetation Index (GNDVI) of the 532 nm and either the 808 nm or the 785 nm wavelengths were highly correlated to the chlorophyll content (R2 = 0.74). The Chlorophyll Index (CI) and Green Simple Ratio (GSR) of the same wavelengths also displayed good correlation (R2 = 0.73). This study was a step towards canopy 3D chlorophyll retrieval using commercial TLS instruments, but methods to couple the data from the different instruments still need to be developed.

Evolution of tooth surface morphology and tribological properties of helical gears during mixed lubrication sliding wear

In mixed lubrication, the interplay of lubricant flows, solid asperity contact, and material wear between tooth surfaces creates complex and unpredictable contact states on tooth surface. To comprehensively understand the interaction between the lubrication and wear characteristics of the rough tooth surfaces of helical gears, this study established a mixed lubrication sliding wear calculation model for helical gears based on the mixed elastohydrodynamic lubrication model and Archard’s model. Specifically, the study aimed to examine the effects of surface topography features on average film thickness, contact area ratio, and accumulated wear at the meshing point. The findings demonstrated that the texture and power spectral density distributions of a non-Gaussian reconstructed surface closely resembled those of the actual ground surface. Furthermore, for non-Gaussian rough surfaces, a larger wavelength ratio enhanced microwedge motion, which increased film thickness and reduced wear. Additionally, a negatively skewed surface demonstrated better lubrication performance compared to both positively skewed and Gaussian surfaces. This improved performance is evident in the smaller contact area ratio and lower accumulated wear value of the negatively skewed surface.

Multi-objective optimization of a non-uniform sinusoidal mini-channel heat sink by coupling genetic algorithm and CFD model

Wavy mini-channel heat sinks (MCHS) can disrupt the development of the thermal boundary layer, resulting in superior performance compared to straight MCHS. For complete utilization of the coolant, this study proposed and optimized a non-uniform sinusoidal MCHS with varying wavelength or varying amplitude along the flow direction. The optimization for five design variables was accomplished through a multi-objective genetic algorithm, where the thermal resistance θ or the pressure drop Δp were defined as two objectives. The computational fluid dynamics (CFD) software was employed to solve all direct problems encountered during the evolutionary process. Compared to the straight MCHS with different channel widths, the optimal designs achieved reductions of 27.74 % in θ or 59.51 % in Δp. Simultaneously, all the optimal values of the wavelength ratio and amplitude ratio indicate that enhancing the heat transfer performance downstream is more efficient. It was observed that among the five design variables, the number of wave cycles is the most relevant parameter with a Spearman’s correlation up to 0.983. Subsequently, a multiple-criteria decision-making approach was employed to ascertain the best compromise solution to balance the two objectives. Although the θ of the best compromise solution could be higher by 38.57 % than that of the lowest θ solution, the Δp presents a more substantial reduction of 92.45 % after the trade-off. Compared to the straight MCHS with the same Δp, the best compromise solution with varying wavelength reduces the θ and the standard temperature deviation by 26.20 % and 76.98 % respectively, while lowering the average base temperature by 3.07 K. Therefore, the optimal non-uniform wavy MCHS, along with the optimization approach presented, is meaningful for practical applications.

Effects of serration angle on noise reduction mechanism of trailing edge serration

This study investigates the effects of serration angle on the three-dimensional flow field and noise reduction mechanism of a NACA6512-63 airfoil using large eddy simulation (LES) and spectral proper orthogonal decomposition (SPOD) techniques. The serration angle is defined as the ratio of serration wavelength (λ) to serration amplitude (h). The mean flow field analysis on suction side of serration reveals the outward flow towards the serration edges and the downwash flow between the valleys that generate the counter-rotating vortex pair. This flow alteration changes the serration effective angle of the serration, consequently affecting the noise reduction performance. Additionally, by comparing the general solution of Lyu’s semi-analytical equation with the SPOD mode results, the noise reduction mechanism is examined, and the frequency range in which noise reduction occurs is analyzed. The linearly distributed multipole-like pressure patterns, similar to those in the semi-analytical solution, are observed in the low-frequency range for all three cases, with the λ/h = 0.3 case exhibiting the most effective noise reduction. The findings suggest that the local deviation of the turbulence axis, caused by the strong outward flow near the serration edges, can hinder the formation of the optimal pressure field distribution required for effective noise reduction.

Investigating Flow-Induced Vibration by Regarding the Alignment of Flow Modes and Structural Modes

In this work, a modal matching approach is developed to investigate the impact of the spatial correlation of wall pressure fluctuations on structural vibration and its role in suppressing flow-induced vibration in aircraft. The modal matching method defines the wavelength ratio between the convection wave and the flexural wave to capture the spatial characteristics of both the flow mode and the structural mode. In comparison to conventional methods such as the finite element method and analytical method, the proposed modal matching approach allows for obtaining the vibration response in the spatial–wavenumber domain. To validate the spatial correlation effect on structural vibrations obtained with the modal matching approach, a wind tunnel test was conducted to measure flow-induced vibrations. The calculated spatial–wavenumber data for flow-induced vibrations reveal that the crests and troughs of the vibration velocity alternate periodically as the wavelength of the wall pressure fluctuations changes. At the resonance frequency, a vibration velocity trough can be observed when the spatial correlation of wall pressure fluctuations aligns with the structural mode. Additionally, the concept of resonance independence of flow-induced vibrations is introduced to describe the phenomenon where the most severe structural vibration, determined by the matching value between the aerodynamic mode and the structural mode, does not always occur at the resonance frequency. The modal matching approach effectively suppresses structural vibration by utilizing the spatial correlation of wall pressure fluctuations, offering a new perspective on controlling flow-induced vibrations.

Generation of a red-green-blue laser by stimulated Raman scattering of ethanol.

In this paper, we report an efficient red-green-blue (RGB) laser based on the stimulated Raman scattering (SRS) of ethanol. The wavelengths of the three-color laser are 631, 532, and 447 nm, respectively, and the gamut space that can cover is 116% of the Rec. 2020 standard gamut in the CIE1976 color space. The maximum output energy of the RGB laser was 595.9 µJ under the total pump energy of 1.56 mJ, which corresponds to an optical conversion efficiency of 38.2%. By adjusting the energy ratio of different wavelengths, a white laser output with a maximum output energy of 544.8 µJ is achieved, corresponding to a conversion efficiency of 34.9%. To the best of our knowledge, this is the first time that an RGB laser has been realized based on liquid SRS. It provides a simple, practical route for efficiently obtaining RGB and white lasers, which may find important applications in many fields like laser display, atmospheric monitoring, and medical beauty.

URANS Prediction of the Hydrodynamic Interactions of Two Ship-like Floating Structures in Regular Waves

A side-by-side configuration of floating structures is commonly used in ocean exploration practices, such as offshore vessels for loading and offloading, floating cranes, and offshore floating wind turbines. Computational Fluid Dynamics (CFD) method is current practice for the analysis of hydrodynamic interactions of the side-by-side vessels. The purpose of this study is yo carry out a benchmark study of CFD method applied for the above analysis. URANS CFD method was applied utilizing a k-ε turbulence model and a volume of fluid (VOF) method to capture the free surface. Different ratios of wave length to vessel’s length and different gaps between between the vessels were considered in the study. Simulation results show that the wave length to vessel’s length ratio /L affects significantly the wave pattern around the vessels and inside the gap. For the shorter waves, the gap influences the wave pattern both inside and outside the gap. Further, the pressure distribution on the keel surface of the vessels is asymmetric about the vertical center plane along the vessel, which resulted in roll motion eventhough the vessel is in head seas. Roll motion was observed in all gap variations considered. Amplitude modulation was observed in the heave and pitch motions, while generation of side-band frequency components were observed in the roll motion, which indicate a non-linear fluid-structure interaction.

SPH study of scale effects of perforated caissons

The hydrodynamic characteristics of perforated caissons are significantly influenced by the viscous fluid motion near the perforations on the front wall. Consequently, models designed in accordance with the Froude similarity suffer from the scale effects. To investigate the scale effects, a Smoothed Particle Hydrodynamics (SPH) model is established, in which fluid motion is governed by the continuity and Navier-Stokes equations, and the solid boundaries are represented by the dynamic boundary particles. The convergence and reliability of the SPH model are examined by employing it to replicate two laboratory experiments. Subsequently, the SPH model is applied to the study of interactions between regular waves and perforated caissons with different length scales, porosities, and chamber length to wavelength ratios. This enables an analysis of the scale effects on the vorticity and velocity fields, wave reflection, and wave force. The findings indicate that a scaled-down model tends to underestimate flow field intensity and wave force amplitude, while overestimate the wave reflection coefficient.

Dual-emissive BT-CP-TD covalent organic polymers for detecting furacillin, white light emission and information encryption

Recently, luminescent covalent organic polymers (LCOPs) are garnering more and more attention owing to their excellent emissive properties. However, the precise control of LCOPs’ luminescence behaviors remains a formidable challenge. Here, a dual-emissive CP-(BTxTD100-x) COP which was composited of CP, BT and TD (x is the added molar ratio of BT to total feed aldehyde) were synthesized by Knoevenagel condensation reaction between 1,3,5-tri(4-cyano-methylbenzene) benzene (CP) and 2,7-dibenzaldehyde-benthiadiazole (BT)/1,4-bis(4-aldehyde phenyl)benzene (TD). The luminescent behaviors of CP-(BTxTD100-x) COP could be precisely tuned by the ratio of CP, BT and TD as well as excitation wavelength. The CP-(BT33TD67) COP emitted white light (0.3012, 0.3207) when excited at 310 nm. A ratiometric fluorescence sensor was developed for detecting furacillin using CP-(BT33TD67) COP, showing a detection limit of 8.23 ng mL−1. Based on the excitation-depending behaviors of CP-(BT33TD67) COP, combined with CP-(BT100TD0) COP, a kind of security and information encryption image in the form of a quick response was designed. The discoveries provide a new idea for the design of dual-emission LCOPs by regulating the ratio of monomers and excitation wavelengths. The findings also extend the potential applications of dual-emission LCOPs.

ОПТИМАЛЬНОЕ РАЗМЕЩЕНИЕ АНТЕННЫХ ЭЛЕМЕНТОВ ШИРОКОДИАПАЗОННОГО АДАПТИВНОГО КОМПЕНСАТОРА ПОМЕХ В ДЕКАМЕТРОВЫХ ЛИНИЯХ РАДИОСВЯЗИ МЧС РОССИИ

The analysis of adaptive spatial interference compensation methods converging to the optimal Wiener solution with accuracy up to a constant multiplier is carried out. 
 A mathematical apparatus is presented for calculating the gain in noise immunity of decameter radio communication lines due to the use of an adaptive interference compensator from two spaced antenna emitters. The results of modeling the calculation of the dependence of the normalized gain in noise immunity on the ratio of antenna element spacing and wavelength are presented. Proposals are formulated for the optimal spatial placement of emitters in terms of gain in noise immunity at a given direction to a useful signal in the interests of increasing the efficiency of signal reception in decameter communication lines of the EMERCOM of Russia.

Fenton reaction in the process of “Laser + Fe” mode excited plasma for Rhodamine B degradation

The spectral emission of laser-induced plasma in water has a broadband continuum containing ultraviolet light, which can be used as a novel light source for the degradation of organic compounds. We studied the degradation process of the organic dye Rhodamine B (RhB) using plasma light source excited by the “Laser + Fe” mode. Spectral analysis and reaction kinetics modelling were used to study the degradation mechanism. The degradation process using this light source could be divided into two stages. The initial stage was mainly photocatalytic degradation, where ultraviolet light broke the chemical bond of RhB, and then RhB was degraded by the strong oxidising ability of ·OH. As the iron and hydrogen ion concentrations increased, the synergistic effect of photocatalysis and the Fenton reaction further enhanced the degradation rate in the later stage. The plasma excited by the “Laser + Fe” mode achieved photodegradation by effectively enhancing the ultraviolet wavelength ratio of the emission spectrum and triggered the Fenton reaction to achieve rapid organic matter degradation. Our findings indicate that the participation of the Fenton reaction can increase the degradation rate by approximately 10 times. Besides, the impact of pH on degradation efficiency demonstrates that both acidic and alkaline environments have better degradation effects than neutral conditions; this is because acidic environments can enhance the Fenton reaction, while alkaline environments can provide more ·OH.

Dual-Emissive Iridium(III) Complexes and Their Applications in Biological Sensing and Imaging.

Phosphorescent iridium(III) complexes are widely recognized for their unique properties in the excited triplet state, making them crucial for various applications including biological sensing and imaging. Most of these complexes display single phosphorescence emission from the lowest-lying triplet state after undergoing highly efficient intersystem crossing (ISC) and ultrafast internal conversion (IC) processes. However, in cases where these excited-state processes are restricted, the less common phenomenon of dual emission has been observed. This dual emission phenomenon presents an opportunity for developing biological probes and imaging agents with multiple emission bands of different wavelengths. Compared to intensity-based biosensing, where the existence and concentration of an analyte are indicated by the brightness of the probe, the emission profile response involves modifications in emission color. This enables quantification by utilizing the intensity ratio of different wavelengths, which is self-calibrating and unaffected by the probe concentration and excitation laser power. Moreover, dual-emissive probes have the potential to demonstrate distinct responses to multiple analytes at separate wavelengths, providing orthogonal detection capabilities. In this concept, we focus on iridium(III) complexes displaying fluorescence-phosphorescence or phosphorescence-phosphorescence dual emission, along with their applications as biological probes for sensing and imaging.

Modeling and analysis of 3D mixed lubrication in marine cam–tappet pair

During the operation of the marine cam–tappet pair, affected by periodic dynamic load, transient velocity, and micromorphology, it usually operates in a mixed lubrication state. Under extreme operational conditions, contact is likely to occur at the asperity of the interface, leading to problems such as stress concentration and dry contact. Considering the transient dynamics and three-dimensional roughness of cam–tappet pair, a mixed-elastohydrodynamic lubrication model is developed in this article, while the effects of surface waviness on the lubrication state are also investigated. The results show that the film thickness can be increased by 0.098 μm, and the coefficient of friction can be reduced by 10.6% when the wavelength ratio ranges from 1/6 to 6. However, when the amplitude exceeds 0.6 μm, the coefficient of friction may reach 0.10. Under conditions of low speed and high load, the film thickness decreases and contact load ratio increases. And about 30% reduction in film thickness is achieved on cam–tappet pair, potentially leading to increased wear or scuffing failure.

Surface corrugations induce helical near-surface flows and transport in microfluidic channels

We study theoretically and experimentally pressure-driven flow between a flat wall and a parallel corrugated wall, a design used widely in microfluidics for low-Reynolds-number mixing and particle separation. In contrast to previous work, which focuses on recirculating helicoidal flows along the microfluidic channel that result from its confining lateral walls, we study the three-dimensional pressure and flow fields and trajectories of tracer particles at the scale of each corrugation. Employing a perturbation approach for small surface roughness, we find that anisotropic pressure gradients generated by the surface corrugations, which are tilted with respect to the applied pressure gradient, drive transverse flows. We measure experimentally the flow fields using particle image velocimetry and quantify the effect of the ratio of the surface wavelength to the channel height on the transverse flows. Further, we track tracer particles moving near the surface structures and observe three-dimensional skewed helical trajectories. Projecting the helical motion to two dimensions reveals oscillatory near-surface motion with an overall drift along the surface corrugations, reminiscent of earlier experimental observations and independent of the secondary helical flows that are induced by confining lateral walls. Finally, we quantify the hydrodynamically induced drift transverse to the mean flow direction as a function of distance to the surface and the wavelength of the surface corrugations.

Corrugation characteristics effect of channel on heat transfer and pressure Drop: Experimental study

Four sinusoidal wavy channels were examined experimentally under turbulent flow conditions of air to clarify the potentials of such configuration in terms of heat transfer and hydrodynamic performance. The subjected heat flux on these wavy walls (sinusoidal wavy plates) were (500, 750, and 1000) W /m2. The ratio of corrugation wavelength (λ) to corrugation amplitude (a) had a range of (5.7–12.6), and the four wavy channels are scrutinized at zero angles (0°) of phase shift. According to the applied range of Reynolds number which is (1.932 × 103–3.286 × 103) and duct entrance dimension, the supplied inlet velocities were (0.3––0.67) m/s. The collected outcomes of the tested wavy sections showed a gained in heat transfer coefficient of (11–39 %) compared to the conventional duct, this increase is originally came out due to the occurred gained of the enhancement factors which is (1.1–1.4). regarding the pressure drop, the acquired decay of the wavy channels is (17–45 %) compared to the conventional channels. Also the results showed the corrugation angle 54.5° is the best in terms of thermal performance factor TPF at Re ≈ 3300 with appreciable high pressure drop, while the corrugation angle of 32.5° has a poor TPF at Re ≈ 1950.

The Influence of Non-Gaussian Roughness and Spectral Properties on Mixed Lubrication for Heavily Loaded Counterformal Contacts

The impact of non-Gaussian height distribution and spectral properties on the lubrication performance of counterformal (point) contacts is quantitatively studied (film parameter, Λ, and asperity load ratio, La) by developing a mixed lubrication model. The Weibull height distribution function and power spectral density (PSD) are used to generate artificial surface topographies (non-Gaussian and Gaussian, isotropic), as these surface topographies are found in many tribological components. The set of variables needed to parametrize and their effect on mixed lubrication is discussed, including the shape parameter, the autocorrelation length, the wavelength ratio, and the Hurst coefficient. It is revealed that a rough surface with a lower shape parameter exhibits higher hydrodynamic lift. The spectral properties (the autocorrelation length and the wavelength ratio) of rough surfaces significantly affect the film parameter and the hydrodynamic and asperity pressures. The film parameter is slightly influenced by the Hurst coefficient.