Simulation and statistical retrieval for inhomogeneous nonisothermal atmospheric precipitation

A numerical approach is developed to treat the thermal radiative transfer theory applicable to inhomogeneous (stratified), nonisothermal layers composed of different spherical Mie scatterers. Calculations are performed to obtain the microwave brightness temperatures at 19.35, 22.235, 37, and 85.5 GHz in the presence of atmospheric precipitation with a top ice crystal layer or inhomogeneous structure. These frequencies are applicable to the SSM/I microwave imager which will be flown within the next year. Surface emissions from various underlying media, including calm and rough ocean, sea ice, snowpack, soil, and vegetation are taken into account. Functional relationships between emitted thermal radiation from atmospheric precipitation and rainfall parameters are discussed. By using a statistical regression technique (the D-matrix method), the geophysical parameters, rain rates, and emissivity from the underlying surfaces, etc., are retrieved from simulated data. The error analysis is discussed.     

Search for acoustic effects from extensive atmospheric showers in Baikal

The search for acoustic effects from showers by means of hydrophones was realized in a trigger scheme of recording sound files when atmospheric showers were detected by the scintillation installation. A method of peaks and noncoincidences was proposed to search for weak sound sources. The algorithm of the method is amplitude independent. Processing of a great body of data (obtained for different geometries, different noise background during three expeditions to Baikal) allows one to indicate the closely analogous phenomena at the instant of time of expected sound signals from showers. In spite of their low power, the effects appear in the different hydrophones and have similar time distributions, which points to the detection of the acoustic effects. The text was submitted by the authors in English.     

Application of an acoustic noise removal method to aircraft-based atmospheric temperature measurements

An acoustic noise removal method is used to reject engine acoustical disturbances from aircraft-based atmospheric temperature measurements. Removal of engine noise from atmospheric temperature measurements allows a larger wave number range to be fit while quantifying the magnitude of atmospheric temperature turbulence. The larger wave number range was found to result in a more statistically certain spectral slope estimate, with up to a 50% reduction in the standard deviation of measured spectral slopes. The noise removal technique was found to break down under conditions of weak atmospheric temperature turbulence where the engine acoustical disturbance can be several orders of magnitude larger than atmospheric temperature turbulence.     

Enhancement of high-frequency acoustic cavitation effects by a low-frequency stimulation

The cavitation effects given by a high-frequency pulsed ultrasound field are studied with and without the stimulation of a low-frequency field. Sonoluminescence intensity and subharmonic one-half intensity of the high-frequency field are measured. The stimulation gives a sharp rise of both subharmonic and sonoluminescence intensities.     

Modeling of atmospheric propagation of acoustic gravity waves generated by different surface sources

A model of acoustic gravity wave propagation is developed and a numerical algorithm for solving the corresponding hydrodynamics equations is elaborated. Behavior of the waves in the upper atmospheric layers is studied in relation to the parameters of the ground-based sources.     

体育馆声学设计探讨

本文分析了我国综合性体育馆共同的体形特征及其所导致的运用建筑声学时的出现的若干问题，探讨了有关的声学标准，并以工程实践为例，说明必须依靠建筑声学设计和电声设计的结合，才能作好体育馆的声学设计。     

体育馆声学设计探讨

本文分析了我国综合性体育馆共同的体形特征及其所导致的运用建筑本学时出现的若干问题，探讨了有关的声学标准，并以工程实践为例，说明必须依靠建筑产学设计和电声设计的结合，才能作好体育馆的声学设计．     

Electrocortical effects of MDMA are potentiated by acoustic stimulation in rats

Background  

3,4-Methylenedioxymethamphetamine (MDMA; ecstasy) is known for its toxicological, psychopathological and abuse potential. Some environmental conditions, e.g. acoustic stimulation typical of the "rave scene" can influence the toxicity of this drug.     

时间反演聚焦经颅磁声电刺激仿真与实验研究*

无创脑神经调控技术是生物医学领域的研究热点,经颅磁声电刺激是利用静磁场和声场的耦合而产生的感应电场作用于神经组织,对大脑的目标位置进行刺激和调控的一项技术。颅骨的存在使超声在传播过程中发生相位畸变和幅值衰减,聚焦区域偏离,难以实现精准聚焦。该文基于时间反演法,模拟颅内点声源发射脉冲以及超声传播过程,计算各个阵元接收到的时间差,按照后到先发的原则发射脉冲进行聚焦刺激。与传统相控阵聚焦相比,焦点偏移现象基本得到解决,焦域横向、纵向分辨率均有所提高,提高了声束聚焦精度和感应电场峰值。通过搭建实验平台,将两种聚焦方法所测得的声场归一化处理,验证了时间反演法能补偿焦点偏移,并通过实验证实了超声换能器声场和产生感应电场分布存在较高的一致性。基于真实颅脑结构的虚拟点源时间反演聚焦可以实现无创、精准、灵活的经颅磁声电刺激,有助于推动精准神经调控技术的发展。     

On collisionless damping of ion acoustic waves

Exact theoretical treatments show that the damping of ion acoustic waves in collisionless plasmas does not vanish when the derivative of the undisturbed distribution function at the phase velocity equals zero.     

On the theory of acoustic self-induced transparency

The effect of coherent interaction of a sound pulse of longitudinal polarization with an electron-nuclear spin system in an external constant magnetic field under the conditions of a “forbidden” transition is investigated. The parameters of the stationary electron-nuclear sound pulse are determined.     

On the acoustic vaporization of micrometer-sized droplets

This paper examines the vaporization of individual dodecafluoropentane droplets by the application of single ultrasonic tone bursts. High speed video microscopy was used to monitor droplets in a flow tube, while a focused, single element transducer operating at 3, 4, or 10 MHz was aimed at the intersection of the acoustical and optical beams. A highly dilute droplet emulsion was injected, and individual droplets were positioned in the two foci. Phase transitions of droplets were produced by rarefactional pressures as low as 4 MPa at 3 MHz using single, 3.25 micros tone bursts. During acoustic irradiation, droplets showed dipole-type oscillations along the acoustic axis (average amplitude 1.3 microm, independent of droplet diameter which ranged from 5 to 27 microm). The onset of vaporization was monitored as either spot-like, within the droplet, or homogeneous, throughout the droplet's imaged cross section. Spot-like centers of nucleation were observed solely along the axis lying parallel to the direction of oscillation and centered on the droplet. Smaller droplets required more acoustic intensity for vaporization than larger droplets, which is consistent with other experiments on emulsions.     

On the availability of atmospheric optical communication lines

Dependence of the probability of “blocking” (unavailability) of an atmospheric optical communication line (AOCL), caused by light scattering by fogs and precipitation, on the length of this line was studied based on an analysis of the statistical data on the meteorological visibility range (MVR). Averaged over several years, this dependence is approximately linear for many geographical locations. It is assumed that the linearity takes place in a wide interval (from kilometers to tens of meters) of the AOCL length. This assumption is confirmed by an analysis of statistical data on the MVR for one of the Moscow airports. The dependence was found to become significantly nonlinear on the averaging over long-term data for separate months of a year. Based on the analysis of the MVR statistics, AOCL unavailability estimates are suggested. It is expedient to consider a value of no less than 0.1% as a reasonable estimate of the annual average unavailability even for short (several hundred meters) lines. It is concluded that, in the general case, an increase of the optical transmitter power even by dozens of times does not result in a significant increase of the AOCL availability.     

On observing acoustic backscattering from salinity turbulence

It has been hypothesized that at sufficiently high levels of oceanic salinity turbulence it should be possible to observe acoustic backscattering. However, there have been limited in situ measurements to confirm this hypothesis. Using an autonomous underwater vehicle equipped with upward and downward looking 1.2 MHz acoustic Doppler current profilers and with turbulence and fine scale sensors, measurements were performed in a region of intense turbulence and a strong salinity gradient. The approach taken was to correlate variations in the backscattered acoustic intensity, I, with a theoretical acoustic backscattering cross section per volume for salinity turbulence, σ(s), to obtain an estimated scattering cross section per volume, σ(e). Results indicated that of order 50% of the observed region was characterized by salinity turbulence induced backscattering.     

On the Coriolis effect in acoustic waveguides

Rotation of an elastic medium gives rise to a shift of frequency of its acoustic modes, i.e., the time-period vibrations that exist in it. This frequency shift is investigated by applying perturbation theory in the regime of small ratios of the rotation velocity and the frequency of the acoustic mode. In an expansion of the relative frequency shift in powers of this ratio, upper bounds are derived for the first-order and the second-order terms. The derivation of the theoretical upper bounds of the first-order term is presented for linear vibration modes as well as for stable nonlinear vibrations with periodic time dependence that can be represented by a Fourier series.