Reconstruction of an acoustically sound-soft obstacle from one incident field and the far-field pattern

The problem considered is that of determining the shape of aplane acoustically sound-soft obstacle from the knowledge ofthe far-field pattern for one time-harmonic incident field.An iterative procedure is proposed based on two boundary integralsrepresenting the incident field and the far-field pattern, respectively.Numerical examples are included which show that the proceduregives accurate numerical approximations in relatively few iterations.     

Compressibility and Volume Effects of Mixing of 1-Propanol with Heavy Water

Speed of sound and density of 1-propanol + heavy water were measured in the whole concentration range at temperatures from 293 to 313 K. Isentropic compressibility was calculated from the Laplace formula. The partial molar volume of 1-propanol reaches a minimum at the mole fraction of 1-propanol x ₁ 0.03. At the same concentration, the compressibility isotherms intersect one another. These features of the investigated system are similar to those of 1-propanol + H₂O, that points to essential similarity of the two mixtures. A clathrate-like structure was suggested to explain the experimental results for dilute solutions of the alcohol. Somewhat more pronounced hydrophobic hydration in D₂O than in H₂O is manifested by an effect similar to that resulting from the elongation of the alcohol molecule.     

Density and Speed of Sound for Binary Mixtures of a Cyclic Ether with a Butanol Isomer

Densities and speeds of sound of the binary mixtures 1,3-dioxolane + 1-butanol, 1,3-dioxolane + 2-butanol, 1,4-dioxane + 1-butanol, and 1,4-dioxane + 2-butanol have been measured at 25 and 40°C. The excess molar volumes and excess isentropic compressibility coefficients were calculated from experimental data and fitted to a Redlich–Kister polynomial function. Results were analyzed in terms of molecular interactions and compared with literature data.     

Sound velocity in different reacting thermal plasma systems

In most cases the energy dissipated in plasma jets used either,for heating or spraying is varied by changing the are current, the total gas floc+rate, and composition. However, when doing so, conditions are reached where the plasma jet may become supersonic. To predict such conditions or to characterize supersonic plasma jets the knowledge of the sound velocitya is mandatory The goal of this paper is to calculatea versus plasma forming gas composition, temperature, and pressure. Rigorous calculation would imply the knowledge of the chemical reaction kinetics, sound velocity depending strongly on this. Unfortunately such kinetics are generally lolknown for plasma jet floras and the only possibility is to determine the equilibrium sound velocitya calculated through the isentropic coefficient T. This coefficient has been calculated taking into account the dissociation and ionization reactions at equilibrium for temperatures ranging from 300 to 25,000 K and pressures between 0.1 and 1 Mpa for Ar, H₂, He, Ar-He, Ar-H₂, O₂, N₂, air, .steam, and methane.a often called the frozen sound velocity, was also calculated using (ratio of specific heats) instead of .     

Digital sound broadcasting: Satellites or Terrestrial Networks?

When European laboratories decided to develop a digital sound broadcasting system (DSB), they specified three main conditions to fulfil:

• quality improvement up to the level of ‘CD’ sound, even in difficult reception conditions (mobile vehicles, etc)
• additional significant digital data transmissions in order to transform sound broadcasting into a really new service
• the possibility of a common system for satellite and terrestrial transmissions.

It is on these bases that the European project ‘Eureka 147’ defined the system called DAB (digital audio broadcasting). In 1992, the ITU Conference WARC 92 allocated 40 MHz to DSB in the L-band in the configuration of complementary terrestrial and satellite networks; nevertheless, the present state of technical possibilities makes such mixed networks almost unfeasible and the lack of available spectrum in VHF bands led a significant number of countries to envisage L-band for T-DAB. The situation could turn to a competition between terrestrial and satellite networks, especially because the bandwidth in L-band is not that large! France belongs to the countries facing this problem. L-band alone is intended to be used by T-DAB, and broadcasters taking part in the work of ‘Club DAB’ estimated that 20 MHz would be a minimum to ensure the success of T-DAB introduction. It is half of the DSB band. Splitting this band into two parts has already been decided by CEPT, but in the proportion of 1/3 for T-DAB. This organization intends to arrange a European planning meeting for T-DAB in July 1995, and, shortly after, several countries are ready to start the implementation of the terrestrial networks. At the same time, international broadcasters wonder whether satellite transmission could present an alternative to HF.     

Thermodynamic properties of peptide solutions: 7. Partial molar isentropic pressure coefficients of some dipeptides in aqueous solution

The partial molar isentropic pressure coefficients at infinite dilution, K _S,2 ^o , have been determined for a number of dipeptides in aqueous solution at 25°C. For a series of dipeptides of sequence gly-X, where X is an amino acid with a neutral side chain, the K _S,2 ^o values are all more negative than that for diglycine. The results are discussed in terms of the hydration of the side chains. There are significant differences in the K _S,2 ^o values for sequence isomeric dipeptides. These differences can be rationalized in terms of the mutual interactions between the side chain and the ionic end groups in the dipeptides. Possible relationships between K _S,2 ^o and V ₂ ^o , the partial molar volume at infinite dilution, were investigated. For the dipeptides of sequence gly-X there is an interesting linear relationship between K _S,2 ^o /V ₂ ^o and V ₂ ^o .     

基于微分干涉仪的新型光纤声传感器

基于微分干涉仪原理，建立了一套新型光纤声传感器系统。对该系统进行了理论分析，建立了系统的数学模型，推导并分析了干涉仪的输出信号，并以宽频信号做声源进行了实验研究。实验结果与理论分析相吻合，解决了目前双干涉仪线性范围窄的问题，简化了信号处理电路，可使用低相干光源，并且系统不受外界缓变因素的影响，对宽频声源定位的误差小于1％。     

智能手机中的SIM卡密码管理

随着移动多媒体时代的到来,拥有强大娱乐商务功能的智能手机越来越受到消费者的青睐。文中简要介绍一种新的智能手机平台Qtopia、Qtopia中独特的信号与槽机制、SIM(用户识别模块)卡中密码的种类以及Qtopia如何采用AT指令来管理SIM卡密码,并阐述了实际智能手机项目中SIM卡密码管理程序的实现思路。     

基于校园网络的一卡通系统设计

从建设数字化校园。实现校园一卡通的要求出发，探讨了校园一卡通系统的总体设计方案，并对校园宽带环境下的一卡通系统的具体结构和功能进行了详细的阐述。提出了将一卡通系统建设成为信息资源数字化，通信传输网络化，用户终端智能化。管理结算自动化的数字化系统的可行方法。     

音响设备开发使用中应进退取舍有据

设备中能量的流向、转换出现异常,是影响系统设备可靠性、稳定性的常见问题,对音响设备开发使用中如何进退取舍进行了定性的分析与探讨。