Increasing Wave Number Research Articles

Pattern dynamics of the Bénard-Marangoni instability in a medium aspect ratio container

This study is an experimental work devoted to Bénard-Marangoni instability in a medium vessel. The free surface deformation is visualised by interferometry and the free surface temperature field by infrared thermography. These two techniques are complementary, since each method provides specific information, which may allow the detection of peculiar phenomena such as the spatial resonance, which is a situation in which the interfacial deformation does not conform to the flow pattern. The influences of the aspect ratio, Rayleigh, Biot and Prandtl numbers, are considered. More dynamics are induced by increasing the Biot number. Conversely, increasing the Prandtl number reduces the dynamics. The deformation magnitude and the wavenumber increase as functions of the gradient of temperature. Two behaviours of the deformation, as a function of Prandtl and Biot numbers, were observed, depending on the value of the applied gradient of temperature. The obtained results are discussed with previous experimental, theoretical and numerical studies. Results of other authors were confirmed concerning the evolution as functions of the gradient of temperature and the aspect ratio and new results were obtained concerning the behaviour of the pattern as functions of Pr and Biot numbers.

Stability of vortex flow in a modulated channel

Linear stability analysis of a fully developed two-dimensional periodic steady flow in a spatially modulated symmetric channel is investigated numerically. Both walls are sinusoidally modulated. The modulation amplitude is assumed to be small. The base steady flow is calculated using a regular perturbation expansion of the flow field coupled to a variable-step finite-difference scheme. The disturbance flow equations are derived within the framework of Floquet theory and solved using a two-point boundary value method. The implemented procedure is simple, direct, and very efficient. The accuracy of this method is established. The influence of geometric parameters on the threshold for the onset of instability is systematically investigated. It is established that the critical Reynolds number for the onset of hydrodynamic instability decreases as the wall modulation amplitude or wave number increases. Modulated channel flow is characterized by the formation of a recirculation region or vortices beneath the modulation crest as the Reynolds number exceeds a certain critical threshold. The relation between the thresholds for the onset of instability and vortex flow is examined over a wide range of geometric parameters. Vortex flow effects on the conditions for the onset of instability are systematically investigated. The parameter regime of stable vortex flow is established. It is found that the parameter regime of stable vortex flow increases significantly with the wall modulation wave number for small wave numbers. This increase become less pronounced as the wave number is further increased.

Exchange-Correlation Effects on Low-Dimensional Plasmons in an Array of Metallic Quantum Wires

We investigate low-dimensional plasmons (PL’s) in an array of metallic quantum wires. By developing a self-consistent local-field-correction (LFC) theory for treatment of the PL’s in the wire array, we take account of both the intrawire exchange-correlation (XC) effect and the interwire correlation effect. By comparing the results involving the LFC with those in the random-phase approximation, we examine the XC effect on the energy distribution and the energy-loss intensity of all the PL modes in an array of a finite number of wires. Our theoretical scheme is applied to an array of Au-atom wires on the Si(557) surface. The XC effect is found to play a significant role because of strong one-dimensional confinement, though a high effective density of the electron system is suggestive of the free-electron-gas character. With an increase in wave number q, the XC effect operates to lower the mode energy increasingly, and to start the decline of the energy-loss intensity at smaller q values. In a smaller q range of qd\\lesssim1, where d denotes the interwire separation, the interwire interaction has the mode energies separated from one another to form an energy distribution of considerable width. Our results of the XC effect and the effect of the interwire interaction yield general insights into the PL’s in a variety of wire arrays.

Characteristics of the JRA-25 Dataset from the Viewpoint of Global Energetics

In this study, the global circulation represented by JRA-25 is examined from the viewpoint of global energetics, compared with ERA-40 and NCEP/NCAR reanalysis. Although the peak and slope of the spectrum for JRA-25 are consistent with those of the other datasets, the magnitude of energy or energy conversion is generally ERA-40 > JRA-25 > NCEP. For short waves, a rapid decrease of amplitude with increasing wave number is shown for NCEP/NCAR reanalysis and ERA-40. The energy conversion from zonal available potential energy to zonal kinetic energy, caused by zonal-mean meridional circulation, is the largest for JRA-25, which is the result of a large amount of cancellation of the local conversion term in the Hadley cell.

Correlation among electronic polarizability, optical basicity and interaction parameter of Bi 2O 3–B 2O 3 glasses

For optical basicity and electronic polarizability, the previous studies basically concentrate on the wavelength range of the visible light region. However, heavy metal oxides glasses have a reputation of being good materials for infrared region. In this study, new data of the average electronic polarizability of the oxide ion α O 2 - , optical basicity Λ and Yamashita–Kurosawa's interaction parameter A of Bi 2O 3–B 2O 3 glasses have been calculated in a wavelength range from 404.66 to 1083.03 nm. The present investigation suggests that both α O 2 - and Λ increase gradually with increasing wave number, and A decreases with increasing wave number. Furthermore, close correlations are studied among α O 2 - , Λ, A and refractive index n in this paper. Particularly, it has been found that a quantitative relationship between electronic polarizability and optical basicity is observed in a wavelength range from 404.66 to 1083.03 nm. Our present study extends over a wide range of α O 2 - , Λ and A values.

Numerical studies for the linear growth of resistive wall modes generated by plasma flows in a slab model

The resistive wall mode generated by plasma-wall relative rotations is studied numerically in a slab model with a compressible plasma flow parallel to the magnetic field. The linear growth of the mode is investigated with different parameters in numerical simulations. The critical plasma flow velocities for the instability are calculated as the wave number of the mode and other parameters vary. It is found that in the long wavelength regime, the critical velocity is in the range of the sound speed cs, as predicted in theory. In the short wavelength regime however, the critical velocity increases to a level of Alfvén velocity VA and a second stable region is found. This region eventually merges with the first stable region as the wave number increases and stabilizes the mode. The growth rate of the mode decreases with the wave number of the mode and the plasma viscosity. The critical wave number for the instability is also calculated as the plasma velocity changes.

Superluminal Behaviour of Modified Bessel Waves

Much experimental evidence of superluminal phenomena has been availableby electromagnetic wave propagation experiments, with the resultsshowing that the phase time describes the barrier traversal time.Based on the extrapolated phase time approach and numerical methods, weshow that, in contrast to the ordinary Bessel waves of real argument,the group velocities of modified Bessel waves are superluminal. Weobtain the following results. The group velocities increase with theincrease of propagation distance, which is similar to the evanescentplane-wave cases. For large wave numbers, the group velocities fall offas the wave numbers increase, which is similar to the evanescentplane-wave cases. For small wave numbers, the group velocities increasewith the increase of wave numbers, this is different from the evanescentplane-wave cases.

Nonlinear backward stimulated Raman scattering from electron beam acoustic modes in the kinetic regime

The backward stimulated Raman scattering (BSRS) of a laser from electron beam acoustic modes (BAM) in the presence of self-consistent non-Maxwellian velocity distributions is examined by linear theory and particle-in-cell (PIC) simulations in one and two dimensions (1D and 2D). The BAM evolve from Langmuir waves (LW) as electron trapping modifies the distribution to a non-Maxwellian form that exhibits a beam component. Linear dispersion relations using the nonlinearly modified distribution from simulations are solved for the electrostatic modes involved in the parametric coupling. Results from linear analysis agree well with electrostatic spectra from simulations. It is shown that the intersection of the Stokes root with BAM (instead of LW) determines the matching conditions for BSRS at a nonlinear stage. As the frequency of the unstable Stokes mode decreases with increasing wave number, the damping rate and the phase velocity of BAM decreases with the phase velocity of the Stokes mode, providing a self-consistently evolving plasma linear response that favors continuation of the nonlinear frequency shift. Coincident with the emergence of BAM is a rapid increase in BSRS reflectivity. The details of the wave-particle interaction region in the electron velocity distribution determine the growth/damping rate of these electrostatic modes and the nonlinear frequency shift; in modeling this behavior, the use of sufficiently large numbers of particles in the simulations is crucial. Both the reflectivity scaling with laser intensity and the spectral features from simulations are discussed and are consistent with recent Trident experiments.

Enhanced Gertsenshtein effect in type-II superconductors

Previously published calculations show that gravitational waves propagate inside superconductors with a phase velocity reduction of ∼300 times and a wavenumber increase of ∼300 times. This result has major significance for the propagation of gravitational waves. It is shown here that one important consequence may be regarded as a considerably enhanced Gertsenshtein effect for very-high-frequency gravitational waves within type-II superconductors. This arises because type-II superconductors do not always completely expel large magnetic fields; above their lower critical field they allow vortices of magnetic flux to channel the magnetic field through the material. Within these vortices, the superconducting order parameter reduces to zero and so the material has properties approaching those of normal material or non-superconductor. Varying the applied magnetic field varies the proportion of material that is normal, which consequently affects the propagation speed of very-high-frequency gravitational waves through a type-II superconductor.

Viscous Damping of Non-Adiabatic MHD Waves in an Unbounded Solar Coronal Plasma

The damping of MHD waves in solar coronal magnetic field is studied taking into account thermal conduction and compressive viscosity as dissipative mechanisms. We consider viscous homogeneous unbounded solar coronal plasma permeated by a uniform magnetic field. A general fifth-order dispersion relation for MHD waves has been derived and solved numerically for different solar coronal regimes. The dispersion relation results three wave modes: slow, fast, and thermal modes. Damping time and damping per periods for slow- and fast-mode waves determined from dispersion relation show that the slow-mode waves are heavily damped in comparison with fast-mode waves in prominences, prominence–corona transition regions (PCTR), and corona. In PCTRs and coronal active regions, wave instabilities appear for considered heating mechanisms. For same heating mechanisms in different prominences the behavior of damping time and damping per period changes significantly from small to large wavenumbers. In all PCTRs and corona, damping time always decreases linearly with increase in wavenumber indicate sharp damping of slow- and fast-mode waves.

Single-crystal growth of mercury indium telluride (MIT) by vertical Bridgman method (VB)

The photoelectronic single crystals of mercury indium telluride (MIT) have been successfully grown by vertical Bridgman method (VB) at the optimized growth conditions. The energy band gap of MIT was authenticated to be 0.73 eV. The crystal was determined through the X-ray diffraction to be defect zinc-blende structure with the space group F 4 ¯ 3 m . The infrared transmittance of the crystal in the region from 400 to 4000 cm −1 was determined by FT-IR to be 50–55%, which decreases gradually with the increase of wavenumber due to the lattice absorption and free carriers absorption.

Effects of compressibility on the magneto-Rayleigh-Taylor instability in Z-pinch implosions with sheared axial flows

A linear analysis of the ideal magnetohydrodynamic (MHD) stability of the compressible Z-pinch plasma with axial flow is presented. Comparing with results of incompressible models, compressibility can reduce the growth rate of the magneto-Rayleigh-Taylor (MRT)/Kelvin-Helmholtz (KH) instability and allow sheared axial flows to mitigate the MRT instability far more effectively. The effect of magnetic field, which cannot be detected in an incompressible model, is also investigated. The result indicates that the mitigation effect of magnetic field on the MRT instability becomes significant as the perturbation wave-number increases. Therefore, with the cooperation of sheared axial flow, magnetic field, and plasma compressibility, the stability of the Z-pinch plasma is improved remarkably. In addition, the analysis also suggests that in an early stage of the implosion, because the plasma temperature is relatively low, the compressible model is much more suitable than the incompressible one based on the framework of MHD theory.

Manipulation of gravitational waves for communications applications using superconductors

Previously published calculations claim that gravitational waves propagate inside superconductors with a phase velocity reduction of ∼300 times and a wavenumber increase of ∼300 times. Subsequent claims that this result is not credible appear to be either not tenable or not complete. This result has major consequences for the design of instruments to generate and detect gravitational waves, in particular high-frequency gravitational waves (HFGWs) having wavelengths on the same order as the dimensions of typical superconductive components. It is generally assumed that in free space the velocity of an HFGW is the same as that of light and so the free space wavelength of an HFGW at 3 GHz will be ∼10 cm. Inside a superconductor, the corresponding 3 GHz HFGW wavelength will therefore be ∼300 μm. The present paper will discuss the technical consequences of this surprising result. In particular, such a large mismatch in HFGW propagation impedance inevitably results in large Fresnel reflections from superconductor-air interfaces. This will cause a number of design problems in equipment proposed for HFGW generation and detection. For example, the superconductor thickness used in HFGW detectors will be critical. It may also be possible with care to exploit the result to obtain HFGW resonators and focusing reflectors.

On three-dimensional instability of a traveling magnetic field driven flow in a cylindrical container

Three-dimensional instability and patterns of an axisymmetric flow of electrically conducting liquid in a cylindrical enclosure driven by an axial traveling magnetic field (TMF) is studied. The attention is focused on the TMF of a large axial wavenumber or large frequency, which leads to a formation of the skin layer near the sidewall. It is shown that the flow intensity grows with the increase of the TMF wavenumber from small to a moderate value and decreases with further increase of the wavenumber. Similar dependence of the flow intensity on the growing TMF frequency is observed. The critical amplitude of the electromagnetic forcing, which corresponds to a transition from axisymmetric to three-dimensional flow state, sharply decreases with the increase of the TMF wavenumber or frequency from a small value. After reaching a minimum it slowly increases with the further increase of the wavenumber or frequency.

Side Chain Dependence of Intensity and Wavenumber Position of Amide I‘ in IR and Visible Raman Spectra of XA and AX Dipeptides

A series of AX and XA dipeptides in D2O have been investigated by FTIR, isotropic, and anisotropic Raman spectroscopy at acidic, neutral, and alkaline pD, to probe the influence of amino acid side chains on the amide I' band. We obtained a set of spectral parameters for each peptide, including intensities, wavenumbers, half-widths, and dipole moments, and found that these amide I' parameters are indeed dependent on the side chain. Side chains with similar characteristic properties were found to have similar effects on the amide I'. For example, dipeptides with aliphatic side chains were found to exhibit a downshift of the amide I' wavenumber, while those containing polar side chains experienced an increase in wavenumber. The N-terminal charge causes a substantial upshift of amide I', whereas the C-terminal charge causes a moderate decrease of the transition dipole moment. Density functional theory (DFT) calculations on the investigated dipeptides in vacuo yielded different correlations between theoretically and experimentally obtained wavenumbers for aliphatic/aromatic and polar/charged side chains, respectively. This might be indicative of a role of the hydration shell in transferring side chain-backbone interactions. For Raman bands, we found a correlation between amide I' depolarization ratio and wavenumber which reflects that some side chains (valine, histidine) have a significant influence on the Raman tensor. Altogether, the obtained data are of utmost importance for utilizing amide I as a tool for secondary structure analysis of polypeptides and proteins and providing an experimental basis for theoretical modeling of this important backbone mode. This is demonstrated by a rather accurate modeling for the amide I' band profiles of the IR, isotropic Raman, and anisotropic Raman spectra of the beta-amyloid fragment Abeta(1-82).

Kinetics of microphase separation in interpenetrated polymer networks in solution

We present here a theoretical study of the early kinetics of the microphase separation in crosslinked polymer blends, made of two incompatible polymers A and B, dissolved in a common good solvent. Use is made of an extended blob model used previously for the investigation of the static properties of such a transition. We are interested in the variation of the relaxation rate, tau(q), versus the wave number q, in the vicinity of the spinodal temperature. We first show that kinetics is entirely dominated by local motions, which are of Rouse type. Slow motions are absent, because of the permanent presence of crosslinks. Second, we find that the characteristic frequency, omega (q) = tau(q)(-1), increases with increasing wave number q according to a sixth power law, that is omega (q) approximately q6 phi(-9/4), where phi is the overall monomer volume fraction. Therefore, the swelling of strands due to the excluded-volume forces leads to a renormalization of the characteristic frequency by a multiplicative factor scaling as phi(-9/4). The main conclusion is that the presence of a good solvent necessitates relaxation rates less important than those relative to crosslinked mixtures in the molten state.

1154 変形物体による推進力の数値的研究(J04-2 生物の運動機能/バイオミメティクスとバイオメカニクス/バイオロボティクスとバイオメカトロニクス(2),J04 生物の運動機能/バイオミメティクスとバイオメカニクス/バイオロボティクスとバイオメカトロニクス)

Fish swimming can be very interested in high efficiency mechanisms of unsteady motion. It is hard to capture the details containing such complex properties because the direct experiment is so difficult. In order to investigate the mechanism of the fish swimming, an arbitrary Lagrangian-Eulerian method based on finite difference method is applied to solve the flow field around swimming fish. The flow around periodic bending flat plate and airfoil are computed. As the results of this investigation, efficiency of deformation plate and airfoil were estimate. It was clear seen that longitudinal vortex was generate at both side of undulated plate. And the efficiency increased with increasing wave number.

Effect of free-carrier absorption on the threshold current density of GaAs∕(Al,Ga)As quantum-cascade lasers

Ga As ∕ Al 0.33 Ga 0.67 As quantum-cascade lasers with plasmon-assisted waveguides exhibit a decreasing threshold current density jth with increasing wave number ν0 of the laser line, which changes as a function of the injector doping density. We have developed an analytical approach based on the effective dielectric tensor component for the p-polarized light emitted from a quantum-cascade laser, which explains the observed dependence of jth(ν0) in terms of losses due to free-carrier absorption predominantly in the doped waveguides αWG(ν0). A contribution to the losses by free-carrier absorption in the quantum-cascade structure itself and subsequently to jth can be neglected except for very high injector doping densities. The calculated values for αWG(ν0) are in good agreement with the experimental data. Our approach quantitatively predicts the observed decrease of jth from 17to7kAcm−2 with increasing ν0 between 900 and 1100cm−1. In addition to achieving a direct physical insight into the influence of free-carrier absorption on the laser performance, the proposed analytical approach provides a simple tool for the determination of the waveguide losses for any quantum-cascade laser without adopting a numerical solver.

Unstable density stratification of miscible fluids in a vertical Hele-Shaw cell: influence of variable viscosity on the linear stability

The influence of viscosity variations on the density-driven instability of two miscible fluids in a vertical Hele-Shaw cell is investigated by means of a linear stability analysis. Dispersion relations are presented for different Rayleigh numbers, viscosity ratios and interfacial thickness parameters of the base concentration profile. The analysis employs the three-dimensional Stokes equations, and the results are compared with those obtained from the variable density and viscosity Hele-Shaw equations. While the growth rate does not depend on which of the two fluids is the more viscous, the maxima of the eigenfunctions are always seen to shift towards the less viscous fluid. For every parameter combination, the dominant instability mode is found to be three-dimensional. With increasing viscosity ratio, the instability is uniformly damped. For a fixed viscosity ratio, both the growth rate and the most unstable wavenumber increase monotonically with the Rayleigh number, until they asymptotically reach a plateau.Surprising findings are obtained regarding the effects of varying the interface thickness. At higher viscosity ratios the largest growth rates and unstable wavenumbers are observed for intermediate thicknesses. This demonstrates that for variable viscosities thicker interfaces can be more unstable than their thinner counterparts, in contrast to the constant viscosity case. The reason behind this behaviour can be traced to the influence of the gap width on the vertical extent of the perturbation eigenfunctions. For thick interfaces, the eigenfunction can reside almost entirely within the interfacial region. In that way, the perturbation maximum is free to shift towards the less viscous fluid, i.e. into a locally more unstable environment. In contrast, for thin interfaces, the eigenfunction is forced to extend far into the viscous fluid, which leads to an overall stabilization. While the Hele-Shaw analysis also captures this ‘optimal’ growth for intermediate interface thicknesses, the growth rates differ substantially from those obtained from the full Stokes equations. Compared to the Hele-Shaw results, growth rates obtained from the modified Brinkman equation are seen to yield better quantitative agreement with the Stokes results.

Impurities in CdZnTe crystal grown by vertical Bridgman method

The impurity segregation in CdZnTe grown by vertical Bridgman method and its corresponding effects on the crystal optical and electrical properties have been studied in detail. Inductively coupled plasma mass spectrometry reveals that impurities Al and Ga with segregation coefficient larger than one centralize in the first-to-freeze portion of the ingot, while impurities Li, Na, Mn, and Cu with segregation coefficient less than one enrich in the last-to-freeze portion of the ingot. At the same time, all impurities enrich in the grain boundaries. Hall measurement indicates that there exists an approximate linear monotonously increasing relationship between the free-carrier density and the sum of all the impurities concentration, which leads to an increase in the infrared transmission with the increase of wave number within the impurity enriching portions caused by the free carrier absorption. It is also found that the resistivity decreases with the concentration of Li, Na, and Cu, but increases with the concentration of Al, Mn, and Ga. An annealing processing is adopted to extract the impurities and therefore improve the crystal properties.