Turbulence characteristics from minisodar data

Vertical profiles of atmospheric turbulence characteristics, including spatial and temporal longitudinal and transverse velocity structure functions, velocity structure characteristics, and turbulent kinetic energy dissipation rates retrieved from time series of vertical profiles of the wind velocity vector measured with a minisodar operating at a frequency of 4900 Hz are presented. It is established that the structure functions first increase with the separation distance between the observation points and then are saturated; moreover, the longitudinal structure function is much greater than the transverse one, which is in agreement with the data available from the literature. The velocity structure characteristic is well described by the z^−2/3 altitude dependence predicted theoretically. Calculated values of the turbulent energy dissipation rate are in agreement with the data available from the literature.     

Transverse-longitudinal coherence function of a sound field for line-of-sight propagation in a turbulent atmosphere

Using the narrow-angle and Markov approximations, a formula for the transverse-longitudinal coherence function of a sound field propagating in a turbulent atmosphere with temperature and wind velocity fluctuations is derived. This function, which applies to observation points that are arbitrarily located in space, generalizes the transverse coherence function (coherence when the observation points are in a plane perpendicular to the sound propagation path), which has been studied extensively. The new result is expressed in terms of the transverse coherence function and the extinction coefficient of the mean sound field. The transverse-longitudinal coherence function of a plane sound wave is then calculated and studied in detail for the Gaussian and von Kármán spectra of temperature and wind velocity fluctuations. It is shown, for relatively small propagation distances, that the magnitude of the coherence function decreases in the longitudinal direction but remains almost constant in the transverse direction. On the other hand, for moderate and large propagation distances, the magnitude of the coherence decreases faster in the transverse direction than in the longitudinal. For some parameters of the problem, the coherence function has relatively large local maxima and minima as the transverse and longitudinal coordinates are varied. With small modifications, many results obtained in the paper can be applied to studies of electromagnetic wave propagation in a turbulent atmosphere.     

Heating of gadolinium plasma ions by the ion cyclotron resonance method

Resonance rf heating of gadolinium plasma ions is calculated in the configuration when an electric field travels along a permanent magnetic field and simultaneously rotates in the direction normal to the latter. Two model functions are taken as initial ion distribution functions over longitudinal velocities: one is a linear function of the velocity in the low velocity range and the other is a shifted semi-Maxwellian function. The ion transverse velocity distribution function is calculated under the assumption that the initial “transverse” distribution function is Maxwellian with a temperature of 5 eV. Ion fluxes toward collector plates are calculated by integrating the total distribution function over the allowed ranges of longitudinal and transverse velocities and transverse coordinates of the guiding center of the ions before the collector. The calculation is performed as applied to the ¹⁵⁷Gd target isotope and its two nearest neighbors. The effect of the longitudinal temperature on the width of the heating efficiency resonance line and of the longitudinal magnetic field on the ion heating selectivity is studied. Also, the influence of the longitudinal wavenumber of the warming traveling electric field on the selectivity of an ion cyclotron resonance reactor is investigated. The heating efficiency is estimated from the frequency dependence of the fraction of ions heated to an energy above a given value.     

The impact of Martian aerosols on the retrieval of temperature profiles from PFS measurements

Our purpose was a qualitative assessment of the impact of dust and water ice aerosols on the retrieved temperature profiles and the retrieval process itself in the Martian atmosphere. It aims to quantify the related uncertainties in the atmospheric temperature profiles derived from radiance measurements of the Planetary Fourier Spectrometer (PFS), currently operating on the Mars Express orbiter. In this study the effects of aerosol opacities on simulated data and retrieved temperature profiles were also investigated.From the analysis of the model atmosphere including dust and water ice with different size distributions it results that the dust component affects weighting functions and brightness temperatures less than water ice. A similar situation is also observed when different vertical distributions are considered. Unlike dust, water ice with different sizes of crystals evidently influences weighting functions and brightness temperatures. The impact of the considered water ice vertical distributions on brightness temperatures is noticeable only near 840 cm⁻¹.Considering different dust opacities, the largest differences—5 K maximum—between retrieved temperature profiles were observed close to the surface, regardless assumptions on a size distribution or the refractive indices. Contrary to dust, the different sizes of water ice particles assumed during retrieval stronger affected the retrieved temperature profiles than water ice opacities. Moreover, the differences in the retrieved temperature profiles were amplified while wrong optical properties for dust as well as for water ice aerosol were assumed instead of the nominal case. This means that the wrong assumption can induce an additional source of the retrieval error and lead to unreasonable temperature profiles. In the cases of expected heavily loads water ice crystals, their size distribution in the Martian atmosphere should be known from other observations before the retrieval of the temperature profile is attempted.For the analyzed examples of real PFS measurements the impact of different dust vertical distributions on the retrieval of temperature profile is prominent only in layers close to the surface. However, these differences remain comparable with retrieval errors. All influences of dust on weighting functions, brightness temperatures and during retrieval can be neglected if the noise equivalent radiance (NER) of PFS is taken into account.     

光波前向散射闪烁相关法测量光传播路径横向风速廓线

光传播路径横向风速风向的准确测量,对于科学研究和工程应用都具有重要意义。哈特曼传感器用来接收光波大气传输前向散射的波前和光强信息,提出利用哈特曼传感器接收的前向散射光强闪烁相关信息,实现路径横向风速廓线测量的方法。理论推导给出了光传播路径上横向风速分段反演的公式。根据不同的子孔径间距路径权重函数的差异,针对不同子孔径间距对路径不同位置的敏感性,分析了如何合理的选取光传播路径横向风速廓线的权重函数。利用哈特曼传感器开展了水平1 000 m光传输路径横向风速的探测实验。初步研究结果表明,哈特曼传感器测量的路径横向平均风速与接收端附近的风速计测量的结果具有较好的一致性;得到的两段路径横向风速的分布在随时间的变化趋势上一致性较好,特殊的下垫面布局使得靠近光源的第一段路径与靠近探测器的第二段路径的平均横向风速分别为1.273和0.952 m·s-1。将第二段横向风速与路径横向平均风速的测量结果进行了相关性分析,具有一致的变化趋势,两者的相关系数达0.86。     

Calculation of the ion transverse velocity distribution function under ion cyclotron resonance heating

The ion transverse velocity distribution functions and the fraction η of ions heated above a certain energy W ₁ are calculated as applied to the ion cyclotron resonance heating method of isotope separation. It is assumed that the longitudinal ion velocity distribution in a plasma source is nonequilibrium. Under high heating temperatures, the averaged ion transverse velocity distribution becomes essentially nonequilibrium and exhibits two maxima. The ion heating efficiency η is calculated for W ₁=40 eV and various values of the parameter p=λ/L, where λ is the wavelength of the electric field of an antenna and L is the heating zone extension. The relative contributions of the time-of-flight and Doppler broadenings are evaluated.     

Analysis of structure function equations up to the seventh order

We examine balances of structure function equations up to the seventh order N = 7 for longitudinal, mixed and transverse components. Similarly, we examine the traces of the structure function equations, which are of interest because they contain invariant scaling parameters. The trace equations are found to be qualitatively similar to the individual component's equations. In the even-order equations, the source terms proportional to the correlation between velocity increments and the pseudo-dissipation tensor are significant, while for odd N, source terms proportional to the correlation of velocity increments and pressure gradients are dominant. Regarding the component equations, one finds under the inertial range assumptions as many equations as unknown structure functions for even N, i.e. can solve for them as function of the source terms. On the other hand, there are more structure functions than equations for odd N under the inertial range assumptions. Similarly, there are not enough linearly independent equations in the viscous range r → 0 for orders N > 3.     

Condensation-induced kinematics and dynamics of cyclones, hurricanes and tornadoes

A universal equation is obtained for air pressure and wind velocity in cyclones, hurricanes and tornadoes as dependent on the distance from the center of the considered wind pattern driven by water vapor condensation. The obtained theoretical estimates of the horizontal profiles of air pressure and wind velocity, eye and wind wall radius in hurricanes and tornadoes and maximum values of the radial, tangential and vertical velocity components are in good agreement with empirical evidence.     

Numerical simulation of transitional flow on a wind turbine airfoil with RANS-based transition model

This paper presents a numerical investigation of transitional flow on the wind turbine airfoil DU91-W2-250 with chord-based Reynolds number Re_c = 1.0 × 10⁶. The Reynolds-averaged Navier–Stokes based transition model using laminar kinetic energy concept, namely the k ? k_L ? ω model, is employed to resolve the boundary layer transition. Some ambiguities for this model are discussed and it is further implemented into OpenFOAM-2.1.1. The k ? k_L ? ω model is first validated through the chosen wind turbine airfoil at the angle of attack (AoA) of 6.24° against wind tunnel measurement, where lift and drag coefficients, surface pressure distribution and transition location are compared. In order to reveal the transitional flow on the airfoil, the mean boundary layer profiles in three zones, namely the laminar, transitional and fully turbulent regimes, are investigated. Observation of flow at the transition location identifies the laminar separation bubble. The AoA effect on boundary layer transition over wind turbine airfoil is also studied. Increasing the AoA from ?3° to 10°, the laminar separation bubble moves upstream and reduces in size, which is in close agreement with wind tunnel measurement.     

Path-averaged differential meter of atmospheric turbulence parameters

A path-averaged differential meter of the structure constant of the atmospheric refractive index, C _n ², has been developed and tested. The results of a model numerical experiment on measuring C _n ² and the horizontal component of average wind velocity transverse to the path are reported.     

Second wind of the Dulong-Petit law at a quantum critical point

Renewed interest in ³He physics has been stimulated by experimental observation of non-Fermi-liquid behavior of dense ³He films at low temperatures. Abnormal behavior of the specific heat C(T) of two-dimensional liquid ³He is demonstrated in the occurrence of a T-independent term in C(T). To uncover the origin of this phenomenon, we have considered the group velocity of transverse zero sound propagating in a strongly correlated Fermi liquid. For the first time, it is shown that if two-dimensional liquid ³He is located in the vicinity of the quantum critical point associated with a divergent quasiparticle effective mass, the group velocity depends strongly on temperature and vanishes as T is lowered toward zero. The predicted vigorous dependence of the group velocity can be detected in experimental measurements on liquid ³He films. We have demonstrated that the contribution to the specific heat coming from the boson part of the free energy due to the transverse zero-sound mode follows the Dulong-Petit Law. In the case of two-dimensional liquid ³He, the specific heat becomes independent of temperature at some characteristic temperature of a few millikelvins.     

梯度倾斜相关测量水平C_n~2和横向风速廓线的理论与仿真研究

根据Rytov近似以及泰勒湍流冻结假设,推导出以不同距离的前向散射光为信标的水平路径上梯度倾斜角的相关表达式.基于该表达式,在理论上提出了计算湍流强度与横向风速的新方法,并通过数值仿真对该方法进行了初步验证.结果表明,在5%高斯误差情况下,大气折射结构常数和风速的计算结果与理论真值在整体变化上具有较好的一致性,线性相关系数分别能达到0.8与0.9.该方法能够得到不同湍流与风速条件下的湍流强度廓线以及风速廓线,为反演大气湍流强度以及风速提供了一种新思路.     

Bose–Einstein study of position–momentum correlations of charged pions in hadronic Z0 decays

A study of Bose–Einstein correlations in pairs of identically charged pions produced in e⁺e^- annihilations at the Z⁰ peak has been performed for the first time assuming a non-static emitting source. The results are based on the high statistics data obtained with the OPAL detector at LEP. The correlation functions have been analyzed in intervals of the average pair transverse momentum and of the pair rapidity, in order to study possible correlations between the pion production points and their momenta (position–momentum correlations). The Yano–Koonin and the Bertsch–Pratt parameterizations have been fitted to the measured correlation functions to estimate the geometrical parameters of the source as well as the velocity of the source elements with respect to the overall centre-of-mass frame. The source rapidity is found to scale approximately with the pair rapidity, and both the longitudinal and transverse source dimensions are found to decrease for increasing average pair transverse momenta.     

White-light spectral interferometric technique to measure a nonlinear phase function of a thin-film structure

We present a new two-step white-light spectral interferometric technique to measure a nonlinear phase function of a thin-film structure. The technique is based on recording of channeled spectra at the output of a Michelson interferometer and their processing by using a windowed Fourier transform to retrieve the phase functions. First, the phase function including the effect of a thin-film structure is retrieved. Second, the structure is replaced by a reference sample of known phase change on reflection and the corresponding phase function is retrieved. From the two functions, the nonlinear phase function of the thin-film structure is obtained. The feasibility of this simple method is confirmed in processing the experimental data for a SiO₂ thin film on a Si wafer of known optical constants. Four samples of the thin film are used and their thicknesses are determined. The thicknesses obtained are compared with those resulting from reflectometric measurements, and a good agreement is confirmed.     

Dispersion simulation of a wind tunnel experiment with Lagrangian particle models

Summary A particle model LAMDA suitable for dealing with the atmospheric dispersion is presented. The reliability of the model is tested comparing the results of its simulations to the wind tunnel measurements by Khurshudyanet al. (1981). Two versions of the model, both based on the Langevin equation and askewed distribution of the vertical wind velocity fluctuations, are considered. To develop the second version of the model we derived a proper scheme to produce skewed distributions of particle velocities consistent with the observed first and second moments of turbulent fluctuating velocities, with their horizontal and vertical derivatives, and their cross-correlations. The 2D geometry of the obstacle (in the wind tunnel experiment considered) allowed some simplifications. Due to the lack of some input data (such as the vertical profiles of crosswind standard deviation of wind velocity fluctuations and of the Lagrangian time scales) we looked for three different parametrizations. It was found that particular combinations of measured and parametrized data could give rise to critical vertical regions in which the derived scheme for the generation of random vertical velocity fluctuations cannot be applied. The best vertical distributions of the Lagrangian time scales (third parametrization) were estimated by fitting simple formulations for the average plume height and lateral variances to the measured data. The main results of this work were the model performance in simulating dispersion in shear flow over flat terrain, and its sensivity to the shape of the crosscorrelation term .     

A comparative study of muonium states in crystalline and amorphous hydrogenated silicon

A study of muons implanted into amorphous hydrogenated silicon (a-Si: H), using both transverse and longitudinal field μSR, is presented. Particular use is made of the muon repolarization curves in longitudinal fields. By comparison with the results of similar measurements on polycrystalline silicon, both the diamagnetic and Mu^* fractions are found to be substantially increased. We postulate that weak strained bonds in the amorphous structure are responsible. Little evidence has been found from longitudinal field measurements for isotropic muonium Mu', and a transverse field experiment on a-Si: D suggests that this state might not exist in the amorphous material.     

Acoustic sounding of the thermal and velocity structure characteristics with allowance for the turbulent attenuation

A method of simultaneous acoustic sounding of vertical profiles of the thermal and velocity structure parameters with allowance for the turbulent sound attenuation is suggested in the present work. A closed iterative algorithm that implements the suggested method is described, and results of its application for processing of measurements with the Zvuk-2 three-component Doppler sodar are given. It is demonstrated that the thermal, velocity, and acoustic refractive index structure characteristics obtained are in good agreement with the data available from the literature. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 84–90, November, 2008.     

Spin–lattice relaxation phenomena in the magnetic state of a suggested Weyl semimetal CeAlGe

ABSTRACT

In this work, we report the results of DC susceptibility, AC susceptibility and related technique, resistivity, transverse and longitudinal magnetoresistance and heat capacity on polycrystalline magnetic semimetal CeAlGe. This compound undergoes antiferromagnetic type ordering around 5.2 K (T¹). Under the application of external magnetic fields, parallel alignment of magnetic moments is favoured above 0.5?T. At low field and temperature, frequency and AC field amplitude response of AC susceptibility indicate the presence of spin–lattice relaxation phenomena. The observation of spin–lattice interaction suggests the presence of the Rashba–Dresselhaus spin–orbit interaction which is associated with inversion and time-reversal symmetry breaking. Additionally, the presence of negative and asymmetric longitudinal magnetoresistance indicates anomalous velocity contribution to the magnetoresistance due to the Rashba–Dresselhaus spin–orbit interaction which is further studied by heat capacity.     

An analytical dispersion model for sources in the surface layer

Summary A two-dimensional model, based on an analytical solution of the diffusion equation in a shear flow, is validated by comparison with cross-wind integrated concentrations of Prairie-Grass experiment. The wind velocity and eddy diffusivity power law profiles, defined respectively by exponent α and β, are determined by fitting log-linear profiles using both Businger and Dyer flux-profile relationships. They result to depend on the vertical plume spread which is a function both of the stability and of the distance from the source. The model, with Dyer's parametrization, fits the data quite well, except for very unstable conditions. Paper presented at the 1^o Congresso del Gruppo Nazionale per la Fisica dell'Atmosfera e dell'Oceano, June 19–22, 1984, Rome.     

Solutions of the Maxwell equations and photon wave functions

Properties of six-component electromagnetic field solutions of a matrix form of the Maxwell equations, analogous to the four-component solutions of the Dirac equation, are described. It is shown that the six-component equation, including sources, is invariant under Lorentz transformations. Complete sets of eigenfunctions of the Hamiltonian for the electromagnetic fields, which may be interpreted as photon wave functions, are given both for plane waves and for angular-momentum eigenstates. Rotationally invariant projection operators are used to identify transverse or longitudinal electric and magnetic fields. For plane waves, the velocity transformed transverse wave functions are also transverse, and the velocity transformed longitudinal wave functions include both longitudinal and transverse components. A suitable sum over these eigenfunctions provides a Green function for the matrix Maxwell equation, which can be expressed in the same covariant form as the Green function for the Dirac equation. Radiation from a dipole source and from a Dirac atomic transition current are calculated to illustrate applications of the Maxwell Green function.