The internal state of a gas of particles with spin

A Hamiltonian theory of motion for particles with internal structure, based on a dynamical bracket algebra, serves to define a generalized phase space for axially symmetric particles. Hydrodynamics of a gas of particles are explored through Liouville's and Boltzmann's equations and the equilibrium distribution function is obtained. Some modification of the pressure and density are necessary because of the spin and for a cold Fermi gas in thermal equilibrium they are shown explicitly.This work is based on a Ph.D. thesis of Y. Feldman submitted to Tel Aviv University in 1979.     

传统白光LED与远程荧光粉白光LED的发光性能比较

研究了传统白光LED与蓝光激发的球冠形远程荧光粉白光LED在不同电流、不同热沉温度下的发光性能,并对其机理差异展开了探讨。实验结果表明：随热沉温度和驱动电流的上升,传统白光LED的量子效率和电光转换效率急剧下降,并导致其Y/B比（Yellow/Blue Ratio）下降,相关色温上升。而在远程荧光粉白光LED中,其量子效率、光转换效率和相关色温在相同实验条件下变化幅度都较小。由光强空间分布和Y/B比空间分布可知,远程荧光粉白光LED的光强分布呈类似蝠翼分布,且Y/B比空间均匀性远大于传统白光LED。     

Quantum state tomography with array detectors

I propose a method for measuring the quantum state of an optical field that occupies a mode having a complicated spatial structure. The technique uses array detectors and a single, plane-wave local oscillator beam. The advantage of using array detectors is that the local oscillator is not mode matched to the field being measured, yet the deleterious effects of this mismatch on the effective detection efficiency are greatly reduced compared to using single detectors. Indeed, when the spatial mode of the signal field is describable by a real function, the effective mode-matching efficiency is unity.     

几何活性原子态的计算

通过广义的Laguerre类型轨道,在组态相互作用框架内,发展了一套从头计算程序,来研究原子中的电子结构.应用该程序,通过计算能量最小值,求出最优波函数.利用优化波函数的单电子密度分布和角双电子密度的最可几分布,研究了处于最低激发态的Be,B,C,N,O,Ne原子的sαpβ组态的几何活性原子态GAAS(geometricallyactive atomic state).结果显示,作为原子波函数的内禀性质,双电子密度最可几角分布的角度与通常由分子杂化轨道理论解释的相关原子的分子的结合键角近似相等.     

Modeling the cw lasing regime for diode-pumped solid state lasers

In terms of a system of balance equations, we propose a model for describing the operation of lasers based on solid-state quasi-three-level active media in the cw lasing regime with longitudinal pumping by emission from diode lasers, taking into account the spatial distribution of the pump and lasing light beams. We model the operation of lasers based on the active crystals Yb³⁺:NaLa(MoO₄)₂ and Yb³⁺:YVO₄, taking into account the proposed spatial distribution function of the intensity and the emission spectrum of the pump. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 1, pp. 55–60, January–February, 2007.     

Effect of heat release distribution on combustion oscillation

This paper describes the effect of flame position and its spatial variation on prediction accuracy of combustion oscillation in a dry low emission (DLE) combustor. A one-dimensional linear model has been developed. The flame is usually treated as fixed and located at a single axial plane in conventional analysis. However, in practice, the flame position varies during operation. A new flame model considering this variation by a spatial distribution function has been developed. Variation of flame position is empirically measured by using UV images of OH radicals in the oscillating flame. A triangular distribution function is introduced into the flame model because it is similar to the experimentally obtained distribution function. A ‘top-hat’ distribution is also considered to test the influence of distribution shape on the result. Numerical results are compared with experimental data. The triangular flame model shows better prediction of the stability boundaries of combustion oscillation compared with the simple flame sheet model. The results of the top-hat flame model differ from those of the experiment. It is found that consideration of the spatial distribution yields good results for the DLE combustor.     

Collective state in a bose gas of interacting interwell excitons

Experiments associated with direct observations of a collective state in a gas of interacting interwell excitons in GaAs/AlGaAs double quantum wells are discussed. The structures constitute Schottky photodiodes. In a metallic gate, circular windows of various sizes (diameters of 2 to 20 μm) are etched by means of electronic-beam lithography. Through these windows, the photoluminescence of interwell and intrawell excitons is excited and detected. A microscopic device allows the observation of the spatial structure of luminescence with a resolution of 1 μm through the windows of a sample placed in superfluid helium. Using optical interference filters, the spatial structure of the luminescence is analyzed selectively in the spectrum for interwell and intrawell excitons under the same experimental conditions. It is found that the photoluminescence of interwell excitons under certain conditions exhibits an axisymmetric spatial structure: along the perimeter of the windows through which the photoluminescence is observed, a regular ring pattern of equidistant bright spots of the luminescence of interwell excitons appears. This structure appears only above the photoexcitation power threshold and the number of equidistant bright spots in the ring increases with the pumping power. At high pumping powers, the structure of distinct periodic luminescence spots is smeared. At a fixed pumping power, the phenomenon exhibits explicit critical temperature dependence: the structure of regularly located luminescence spots is smeared at T > 4 K. Axisymmetric spatial configurations of equidistant luminescence spots are observed in windows of the diameters 2, 5, and 10 μm. For intrawell excitons, the spatial structure of luminescence is not observed under similar experimental conditions: the luminescence of intrawell excitons is spatially uniform in all the windows under investigation. The effect is a result of the collective behavior of interacting interwell excitons.     

C20离子团簇在氧化物中穿行时库仑爆炸过程的理论研究

研究了C20团簇在几种金属氧化物(Al2O3,SiO2)中穿行时发生的库仑爆炸过程.采用线性介电响应理论,并结合Mermin形式的介电函数,得到了团簇中各组成离子的空间感应势,其中组成团簇中各组成离子的电荷分布情况由Brandt-Kitagawa有效电荷理论模型来描述.通过求解运动方程得到离子团结构随时间的演化过程,并采用Monte Carlo方法模拟了爆炸过程中的多重散射现象.我们发现,尾流效应使团簇的空间结构和电荷分布呈现非对称性.     

Violation of the Porod law in a freely cooling granular gas in one dimension

We study a model of freely cooling inelastic granular gas in one dimension, with a restitution coefficient which approaches the elastic limit below a relative velocity scale delta. While at early times (tdelta;{-1}) it exhibits a new fluctuation-dominated phase ordering state. We find distinct scaling behavior for the (i) density distribution function, (ii) occupied and empty gap distribution functions, (iii) the density structure function, and (iv) the velocity structure function, as compared to the completely inelastic sticky gas. The spatial structure functions (iii) and (iv) violate the Porod law. Within a mean-field approximation, the exponents describing the structure functions are related to those describing the spatial gap distribution functions.     

Distribution and morphometric studies of flagellar sensilla in Emphorini bees (Hymenoptera, Apoidea)

The tribe Emphorini is a group of pollen-collecting solitary bees with a geographical distribution restricted to the western hemisphere. Most of the Emphorini bees collect Page 10 linepollen from a few specific plant families and display specialized behaviors for constructing their nests. Insect sensilla are the basic structural and functional units of cuticle receptors, serving mainly mechano- and chemo-receptor functions. The external morphology of the antennal sensilla has been well characterized in species of different families of Apoidea, however there is scarce information about this issue in solitary bees of the family Apidae. For a better understanding of the association between the external sensory system and several types of behaviors which emerged along the evolutionary history of bees, it is important to characterize the antennal receptors in several representative species of this tribe. The distribution of the antennal sensilla on the dorsal flagella of 18 taxa was studied in insects of both sexes, using light and scanning electron microscopy. There were six types of sensilla and setae on the antennae, which were identified as sensilla placodea, trichodea, basiconica, coeloconica, coelocapitular and ampullacea. The sensilla trichodea were classified into subtypes, A, B, C-D. Sensilla subtype A were the most abundant sensilla and were distributed over the entire antennae, while sensilla placodea and sensilla trichodea type B, showed a restricted distribution on specific areas of the flagella. We have recognized four patterns of spatial distribution of setae on dorsal flagella. Species having setae on the distal part of the flagellomeres tended to contain a low density of sensilla trichodea type A. Females showed a higher number of sensilla subtypes B and C-D than males; instead sensilla trichodea A were more abundant in males. No significant difference was found in the number of sensilla placodea, ampullacea, coeloconica and coelocapitular. Sensilla basiconica were found only in females. Our results showed that gustative and tactile sensilla were more abundant in female bees, as well as, olfactory receptors predominate in the antennal system of males. The possible coevolution of flagellar sensilla in males and females of solitary bees is discussed in light of previous reports. Patterns of distribution of setae determine the relative abundance of the types of sensilla in the flagellum.     

Equation of state for pure fluids at critical temperature

In this paper, we employ the concept of probability for creating a cavity with diameter d in fluid along with the perturbation and variation approach, and develop an equation of state (EOS) for a hard sphere (HS) and Lennard– Jones (LJ) fluids. A suitable axiomatic form for surface tension S(r) is assumed for the pure fluid, with r as a variable. The function S(r) has an arbitrary parameter m. S(r) = A + B(d/r)/[1 + m(d/r)]. We use the condition in terms of radial distribution function G(λd, η) containing the self-consistent parameter λ and the condition of continuity at r = d/2 to determine A and B. A different EOS can be obtained with a suitable choice of m and the EOS has a lower root-mean-square deviation than that of Barker–Henderson BH2 for LJ fluids.     

Quantitative spectrally resolved imaging through a spectrograph

A grating spectrograph can be used for spectrally selective two-dimensional imaging if it is operated with a broad entrance slit. The resulting intensity distribution in its exit plane is a one-dimensional convolution of the spatial and spectral distributions of incident light. We present a dedicated deconvolution filter to reconstruct the spatial image from the spectrograph output. The algorithm is illustrated on Raman imaging of an underexpanded dry air jet. Recorded Raman images correspond to density maps convolved with the Raman spectrum of air; the latter essentially acts as a blurring function for the density map. The deconvolution filter combines the individual images recorded in the O2 and N2 Raman bands into a single image of relative air density.     

Light-induced drift of neon under optical excitation from a metastable state

A running light wave, resonant with the neon transition 1s₅-2p₂, has been found out to affect the spatial distribution of neon atoms in a positive discharge column. The effect has shown an antisymmetric dependence (typical of the light-induced drift) on the tuning out of the radiation frequency relatively the absorption line centre, as well as on the direction of the light wave vector.     

Mapping the B1 field distribution with nonideal gradients in a high-resolution NMR spectrometer

To understand the behavior of many NMR experiments, it is important to determine the spatial distribution of the B1 field. In this paper, we show how this distribution can be mapped independently of spin density, coil responsiveness, and nonlinearities of the B0 field gradients. As a by-product we obtain a map of the (possibly nonlinear) spatial variation of the B0 field gradients used in the imaging procedure.     

Insights into a spatially embedded social network from a large-scale snowball sample

Much research has been conducted to obtain insights into the basic laws governing human travel behaviour. While the traditional travel survey has been for a long time the main source of travel data, recent approaches to use GPS data, mobile phone data, or the circulation of bank notes as a proxy for human travel behaviour are promising. The present study proposes a further source of such proxy-data: the social network. We collect data using an innovative snowball sampling technique to obtain details on the structure of a leisure-contacts network. We analyse the network with respect to its topology, the individuals’ characteristics, and its spatial structure. We further show that a multiplication of the functions describing the spatial distribution of leisure contacts and the frequency of physical contacts results in a trip distribution that is consistent with data from the Swiss travel survey.     

Spatial structure of a collisionally inhomogeneous Bose-Einstein condensate

The spatial structure of a collisionally inhomogeneous Bose-Einstein condensate (BEC) in an optical lattice is studied. A spatially dependent current with an explicit analytic expression is found in the case with a spatially dependent BEC phase. The oscillating amplitude of the current can be adjusted by a Feshbach resonance, and the intensity of the current depends heavily on the initial and boundary conditions. Increasing the oscillating amplitude of the current can force the system to pass from a single-periodic spatial structure into a very complex state. But in the case with a constant phase, the spatially dependent current disappears and the Melnikov chaotic criterion is obtained via a perturbative analysis in the presence of a weak optical lattice potential. Numerical simulations show that a strong optical lattice potential can lead BEC atoms to a state with a chaotic spatial distribution via a quasiperiodic route.     

Features of the electronic structure of the intermetallic Co3Ti in an atomically disordered state

Using a method based on incorporating statistics into the theory of multiple scattering via the distribution function of atoms on lattices, the electronic structure of the intermetallic Co₃Ti is calculated for both complete atomic order and complete disorder. An unusual feature of the electronic structure of this intermetallic when it is disordered in the solid state is identified. Possible consequences of this behavior are analyzed. Fiz. Tverd. Tela (St. Petersburg) 39, 809–810 (May 1996)     

Electric-field distribution in a quantum superlattice with an injecting contact: Exact solution

A very simple model describing steady-state electron transport along a quantum superlattice of a finite length taking into account an arbitrary electrical characteristic of the injecting contact is considered. In the singleminiband approximation, exact formulas for the spatial distribution of the electric field in the superlattice are derived for different types of contact. Conditions under which the field is uniform are identified. Analytical expressions for the current–voltage characteristics are obtained. In the context of the developed theory, the possibility of attaining uniform-field conditions in a diode structure with a natural silicon-carbide superlattice is discussed.     

Angular- and spatial-dependent intensity behaviour for a prototype laterally inhomogeneous sample studied with an ES200B spectrometer

An investigation into the surface area sampled in an ESCA experiment for a laterally inhomogeneous sample is described. The experiments use a special sample with gold “islands” in a polymeric matrix machined to the normal dimensions as encountered when using an ES200B spectrometer. The spatial distribution of the X-rays is not symmetrical about the anode and the effective area of acceptance into the analyzer changes with the electron take-off angle.