近海边高空光学湍流的探空测量与模式比较

 用自行研制的探空仪测量了近海边高空湍流廓线。探空气球携带微温传感器以4 m·s-1速度上升至20 km测量大气湍流,微温传感器附加在59型气象探空仪上,可同时测量垂直空间分辨率为30 m的气压、温度和湿度以及折射率结构常数。运用Tatarskii公式计算了高空湍流外尺度,分析了边界层湍流和自由大气层湍流特征。与AFGL AMOS模式、Hufnagel模式以及北京天文台兴隆站的探空拟合曲线进行的比较发现,海边测量的高空湍流强度比其它模式大2个量级,折射率结构常数随高度从表面层较大值以近似相同的递减率缓慢地减小,对流层顶附近没有出现较强的湍流区,外尺度测量值小于30 m,并得到外尺度的拟合曲线。     

Phase prediction of the response of choked nozzles to entropy and acoustic disturbances

The development and transmission of sound through the exit of an aero-engine combustor is often investigated by modelling the complex geometry as a convergent-divergent nozzle. However, these analytical acoustic predictions are usually limited to the compact case, where the length of the nozzle is insignificant compared to the wavelength of the flow perturbations, or to cases where the variation of the mean velocity through the nozzle may be treated as linear or piece-wise linear. Considering terms up to first order in frequency for the conservation of mass, momentum and energy, this paper investigates an alternative approach by deriving effective lengths for the passage of the flow perturbations through a supercritical convergent-divergent nozzle. The effects due to the presence of a normal shock wave are also studied using a linearised form of the Rankine-Hugoniot relations. The analyses lead to predictions for the phase and magnitude of the transmitted acoustic waves from finite-length nozzles, and are valid for low non-dimensional frequencies. It has been found that these predictions agree well with the numerical results from inviscid simulations.     

旁路耦合电弧焊温度场模拟及验证

针对旁路耦合电弧焊的特点, 建立了一种适于用旁路耦合电弧焊的复合热源模型. 利用该热源模型对不同焊接参数下的旁路耦合电弧焊温度场进行了数值分析, 得到了总电流相同时不同旁路电流下的焊缝熔深、母材温度和特征点焊接热循环曲线的模拟结果, 分析了旁路耦合电弧焊焊接参数对母材热输入的影响, 并将特征点热循环曲线的模拟结果与相同条件下的试验结果进行了比较. 结果表明, 焊接总电流相同时母材热输入随着旁路电流的增加而降低, 且越靠近焊缝母材热输入的降幅越大, 特征点焊接热循环曲线的模拟结果与试验结果基本一致, 旁路耦合电弧焊温度场模型是合理的, 所建立的热源模型能够正确反映焊接参数与母材热输入之间的关系.     

Self-filtering unstable resonator: An approximate analytical model with comparison to computed and XeCl laser experimental results

Approximate analytical solutions for the lowest-order transverse mode of empty self-filtering unstable resonator have been deduced for magnification M 》 1, and compared with some experimental measurements on an X-ray preionized XeCl discharge laser.     

Further studies on the dual-resonance nonlinear filter model of cochlear frequency selectivity: responses to tones

A number of phenomenological models that simulate the response of the basilar membrane motion can reproduce a range of complex features observed in animal measurements over different sites along its cochlea. The present report shows a detailed analysis of the responses to tones of an improved model based on a dual-resonance nonlinear filter. The improvement consists in adding a third path formed by a linear gain and an all-pass filter. This improvement allows the model to reproduce the gain and phase plateaus observed empirically at frequencies above the best frequency. The middle ear was simulated by using a digital filter based on the empirical impulse response of the chinchilla stapes. The improved algorithm is evaluated against observations of basilar membrane responses to tones at seven different sites along the chinchilla cochlear partition. This is the first time that a whole set of animal observations using the same technique has been available in one species for modeling. The resulting model was able to simulate amplitude and phase responses to tones from basal to apical sites. Linear regression across the optimized parameters for seven different sites was used to generate a complete filterbank.     

Behavior near the focal points of asymptotic solutions to the Cauchy problem for the linearized shallow water equations with initial localized perturbations

We study the behavior of the wave part of asymptotic solutions to the Cauchy problem for linearized shallow water equations with initial perturbations localized near the origin. The global representation for these solutions based on the generalized Maslov canonical operator was given earlier. The asymptotic solutions are also localized in the neighborhood of certain curves (fronts). The simplification of general formulas and the behavior of asymptotic solutions in a neighborhood of the regular part of fronts was also given earlier. Here the behavior of asymptotic solutions in a neighborhood of the focal point of the fronts is discussed in detail and the proof of formulas announced earlier for the wave equation is given. This paper can be regarded as a continuation of the paper in Russiian Journal of Mathematical Physics 15 (2), 192–221 (2008). In memoriam V.A. Borovikov     

Models,predictions, and experimental measurements of far-infrared NH3-laser dynamics and comparisons with the Lorenz-Haken model

Dynamics of the intensity and optical field amplitude of a coherently pumped far-infrared NH₃-laser are measured and characterized. The experimental findings in certain parameter ranges closely follow the dynamics of the Lorenz model and its generalization for laser systems. Similarities and some specific differences are found in geometrical or statistical characterizations of the attractors. The experimental results are also consistent with the results of a model of optically pumped three-level lasers which takes into account the presence of a multiplicity of velocity groups as well as three-level coherence effects. For a certain region in parameter space, this far more complex model with a much larger phase space produces results similar to the dynamics of the Lorenz model. The model also provides explanations of differences between the experimental results and results from the Lorenz model.     

Application of acoustic feedback to target detection in a waveguide: experimental demonstration at the ultrasonic scale

People are familiar with the acoustic feedback phenomenon, which results in a loud sound that is heard when a musician plays an electric instrument directly into a speaker. Acoustic feedback occurs when a source and a receiver are connected both acoustically through the propagation medium and electrically through an amplifier, such that the amplified received signal is continuously re-emitted by the source. The acoustic feedback can be initiated from a continuous sine wave. When the emitter and the receiver are in phase, resonance is obtained, which appears to be highly sensitive to any fluctuation of the propagation medium. Another procedure consists in initiating the acoustic feedback from a continuous loop of ambient noise. It then generates an unstable self-sustained feedback oscillator (SFO) that is tested here as a method for monitoring temperature fluctuations of a shallow-water oceanic environment. The goal of the present study is to reproduce and study the SFO at the laboratory scale in an ultrasonic waveguide. The experimental results demonstrate the potential applications of the SFO for the detection of a target in the framework of the acoustic-barrier problem in shallow-water acoustics.     

A comparison of a theoretical model for quasi-statically and dynamically induced environmental vibration from trains with measurements

This paper presents comparisons between a theoretical ground vibration model and measured data at three sites. The model, which is briefly outlined here, encompasses both the quasi-static and dynamic mechanisms of excitation. The vertical dynamics of a number of vehicles travelling at a constant speed on an infinite track are coupled to a semi-analytical model for a three-dimensional layered ground. This model is also used to demonstrate the roles of the two components of vibration at different frequencies and for train speeds below and above the lowest ground wave speed. It is found that, in most practical cases, the dynamic component gives rise to the higher level of vibration.     

Sound propagation in the ear canal and coupling to the eardrum, with measurements on model systems

A theoretical model of sound propagation in the ear canal is described, which takes into account both the complicated geometry of real ear canals and the distributed acoustical load presented by the eardrum. The geometry of the ear canal enters the theory in the form of a cross-sectional area function relative to a curved axis that follows the center of the ear canal. The tympanic membrane forms part of the ear canal wall and absorbs acoustical energy over its surface. Its motion leads to a driving term that must be added to the horn equation describing the pressure distribution in the ear canal. The sound field within the canal is assumed to be effectively one dimensional, depending only on longitudinal position along the canal. Experiments using model ear canals of uniform cross section were performed to test the ability of the theory to handle distributed loads. Sound-pressure distributions within each model canal were measured using a probe microphone. The behavior of the eardrum was simulated using either a distributed, locally reacting impedance or a mechanically driven piston. The agreement between theory and experiment is good up to a nominal upper frequency limit at which the ratio of canal width to wavelength is 0.25. It is estimated that the theory is applicable in ear canals of cats for frequencies at least as high as 25 kHz and in human ear canals to at least 15 kHz.     

New type of exact solutions to the generalized Ashkin-Teller model and anisotropic Ising model with spin 3/2

The generalized Ashkin-Teller model involving both biquadratic and bilinear interactions between the Ising subsystems (α and s) and equivalent to the anisotropic Ising model with spin 3/2 is considered. For a certain magnitude of the opposite-sign bilinear interactions along the horizontal and vertical axes of a square lattice, the exact analytic solution is obtained that describes the phase transition between the disordered (〈α 〉=〈s〉=〈αs〉=0) and the correlated ordered (〈s〉 ≠0 and 〈α〉=〈s〉=0) states.     

Interlaboratory comparison of size and surface charge measurements on nanoparticles prior to biological impact assessment

The International Alliance for NanoEHS Harmonization (IANH) organises interlaboratory comparisons of methods used to study the potential biological impacts of nanomaterials. The aim of IANH is to identify and reduce or remove sources of variability and irreproducibility in existing protocols. Here, we present results of the first IANH round robin studies into methods to assess the size and surface charge of suspended nanoparticles. The test materials used (suspensions of gold, silica, polystyrene, and ceria nanoparticles, with [primary] particles sizes between 10?nm and 80?nm) were first analysed in repeatability conditions to assess the possible contribution of between-sample heterogeneity to the between-laboratory variability. Reproducibility of the selected methods was investigated in an interlaboratory comparison between ten different laboratories in the USA and Europe. Robust statistical analysis was used to evaluate within- and between-laboratory variability. It is shown that, if detailed shipping, measurement, and reporting protocols are followed, measurement of the hydrodynamic particle diameter of nanoparticles in predispersed monomodal suspensions using the dynamic light scattering method is reproducible. On the other hand, measurements of more polydisperse suspensions of nanoparticle aggregates or agglomerates were not reproducible between laboratories. Ultrasonication, which is commonly used to prepare dispersions before cell exposures, was observed to further increase variability. The variability of the zeta potential values, which were also measured, indicates the need to define better surface charge test protocols and to identify sources of variability.     

Application of the Heisenberg model with cubic anisotropy to phase transitions on surfaces

The paramagnetic to ferromagnetic transition of the two-dimensional Heisenberg model with cubic anisotropy exhibits different behavior depending upon whether the anisotropy favors the faces or the corners of a cube. In the former case the transition must be first order, whereas in the latter it can be continuous with Ising exponents. Applications of the results to the (2 × 2) transitions observed in O/Ni(111) and CF₄/graphite and the (2 × 1) transitions observed in O/Ir(111) and N₂/graphite are discussed.     

Fluctuation kinetics of the hopping fluorescence quenching in disordered solid solutions: A theoretical model and experimental evidence

Fluctuation kinetics of the hopping fluorescence quenching in disordered solid solutions is investigated for the first time. Measurements were made in the chelated complexes of rare-earth ions [Y_1−xTb_x(pyca)₃(H₂O)₂]nH₂O used as chromophore. The Tb³⁺ ions and the OH^--ions of unbounded water molecules appear as fluorescent donors and randomly distributed acceptors, respectively, with the dipole-dipole interaction between them. The measured fluctuation kinetics is the kinetics of the Förster type but with larger decay amplitude. It begins almost immediately after the initial static stage of quenching, and lasts for the entire interval of measurements leaving no room at all for the well-known exponential kinetics with constant rate. Proposed theoretical explanation of the phenomenon is based on the solution of the closed many-particle integral equation for the observable kinetics of hopping fluorescence quenching. The methods for determination of the energy transfer microparameters by the measured fluorescence quenching kinetics are discussed.     

Far-infrared reflection measurements on nitromethane and the relevance of the plasmon model

An attempt to repeat the experiments of Ascarelli, in which direct evidence was claimed for the existence of the dipolar plasmon, previously introduced theoretically by Lobo et al., is reported. Similar results for pure nitromethane are indeed observed but those are shown to arise principally from interface effects and to be consistent with the optical constants of the liquid which themselves reveal no immediate evidence for the plasmon.     

Application of computer vision and laser interferometer to the inspection of line scale

In the paper machine vision, laser interferometer and coordinate measuring machine (CMM) are combined to develop a vision inspection system. The measurement capability of the developed system is investigated by measuring the distances between the lines on a standard line scale. The vision camera is used to replace the probe of the CMM to take the images of the interested lines on a line scale at two different positions. Meanwhile, the displacement of the CCD camera is measured using laser interferometer. Using subpixel edge localization and outlier-excluding least-squares regression, the distance between two interested lines is computed under an image plane coordinate system. By adding the displacement of the CCD camera measured using laser interferometer, the line space can be determined. Experiments have been performed repeatedly to measure the line space on the 1.00 and 300.0 mm line scales. Results indicate that the measured data only have a little fluctuation and are close to those obtained by the NML (National Measurement Laboratory, Taiwan).     

Neutron scattering and compressibility measurements for the study of hydration effects on polymeric aqueous solutions

Summary The present paper reports the results of compressibility and incoherent quasi-elastic neutron scattering measurements performed on polymeric systems and on their aqueous solutions. From the compressibility data, the temperature evolution of the polymer hydration number can be derived. On the other hand, neutron data show that the translational diffusion coefficientD _T turns out to be higher in the case of ethylene glycol + water, with respect to that of pure, suggesting that the water molecules act as a ?structure breaker? of the intermolecular connectivity existing into the pure. Furthermore the dynamical properties of the H₂O molecules in the presence of poly(ethylene glycol) deeply differ from those in the bulk, and show that we are in the presence of entangled water. Paper presented at the I International Conference on Scaling Concepts and Complex Fluids, Copanello, Italy, July 4–8, 1994.     

A comparison of the effectiveness of GaAs surface passivation with sodium and ammonium sulfide solutions

To explore the possibility of improving the effectiveness of chemical and electronic passivation, a study has been made of the properties of GaAs surface treated with solutions of inorganic sulfides [Na₂S and (NH₄)₂S] in various amphiprotic solvents (water, alcohols). X-ray photoelectron and photoluminescence spectroscopy shows that the efficiency of both chemical and of electronic passivation of GaAs surface increases with decreasing dielectric permittivity of the solvent. The degree of this increase reached with solutions of the sulfide of a strong base (Na₂S) is larger than that of a weak-base sulfide [(NH₄)₂S]. Fiz. Tverd. Tela (St. Petersburg) 39, 63–66 (January 1997)