The effects of air temperature and humidity on the acoustic design of voice alarm systems on underground stations

Sound attenuation of air due to climatic conditions is often assumed to be constant and/or negligible in the electro acoustic design of voice alarm (VA) systems. However, air attenuation variations can be significant in large underground spaces and particularly as the frequency increases to the mid to high frequencies which are the most relevant to speech intelligibility. This investigation evaluates and quantifies the impact of the variability of the most influential climatic parameters, air temperature and relative humidity, on the performance of VA systems in underground stations. Computer simulations were employed to predict the effect of varying these climatic parameters on key performance metrics. Results demonstrated a significant increase in the values of reverberation time parameters with both temperature and humidity, at frequencies critical for speech intelligibility. Consequently the values of speech intelligibility related metrics decreased with rising temperatures and humidity. Hence, the study shows how ignoring temperature and humidity effects can lead to calculation errors in the design of VA systems. These errors could cause over-specification of the absorption required of surface materials, and the inaccurate prediction of acoustic and speech intelligibility related parameters.     

炉内管道泄漏声检测与定位系统的研究现状

电站锅炉管道泄漏的声检测与定位系统,已经越来越广泛地应用于电站锅炉。该系统主要利用声学技术检测炉内管道的泄漏状态,并利用多传声器定位机理对泄漏点进行定位,有效地减少了由管道泄漏引起的非计划停炉,这对电站锅炉来说意义尤为重要。本文分析了炉内管道泄漏声检测与定位系统的关键技术,介绍了该系统的发展概况及应用现状,并提出了改进方向。     

Comparison and application of the experimental methods for multi-layer prediction of acoustical properties of noise control materials in standing wave-duct systems

A comparison among the existing experimental methods used for measuring and predicting acoustical properties, such as absorption ratio and transmission loss, of noise control materials was accomplished in this paper. Four methods for absorption ratio and five methods for transmission loss, which can be generalized as standing wave ratio method, two-cavity method and two-load method, were performed in a special standing wave-duct with two configurations of two- and four-microphone holders and compared with the theoretical expressions in the literature. Conclusions were drawn that the standing wave ratio method with two and four-microphones was more reliable, faster, and easier to use for measuring absorption ratio and transmission loss, respectively. The two-cavity and two- load methods, which may be used to predict acoustical properties of an exceedingly thick sample or a multi-layered treatment consisting of variant materials, have different conditions of using limits. The two-cavity method, especially, can be easily conducted and is suitable for the materials with properties of symmetry and reciprocity. The two-load method, however, is more cumbersome to apply, due to the fact of its complex calibration and measurement procedure. Furthermore, some prediction examples for a set of multi-layered treatments of materials were executed by a newly proposed approach, so-called experimental hybrid multi-layer prediction. In view of applications, the works done in this paper may be directly applied in standing wave-duct systems or other noise control configurations to measure, predict and/or optimize their in situ designs.     

The development and evaluation of Freeze-Fracture/Cytoplasmic maceration for the SEM to investigate algal ultrastructure

Freeze-fracture/cytoplasmic maceration (FF/CM) to expose chloroplast ultrastructure for the SEM was developed for the green alga Enteromorpha intestinalis (Linnaeus) Link, and the results were compared with conventional TEM preparation. Preliminary investigations showed that the method used for higher plants was inadequate to expose algal chloroplast membrane detail, but, by decreasing the molarity of the buffer during maceration to make it more hypotonic relative to the tissue, sufficient cytoplasmic extraction was accomplished in 7 days using osmium tetroxide at a lower concentration than suggested in previous work. Post-maceration in tannic acid was omitted from the processing after the preliminary study to assess its effects on the final images, and consequently preparation time was shortened drammatically and now compares favourably with the time take to prepare material for the TEM. Ultrastructural integrity is preserved and is consistent with normal TEM preparations.     

声学立靶弹着点测试数学模型与误差分析

本文根据空气动力学理论和超音速弹丸的激波特性，建立了在使用L型立靶基础上正向射击和任意角度射击时的数学模型，并进行了误差分析，提出了减小误差的修正方法。     

The carrier contribution to the elastic constants in III-V, ternary and quaternary materials in the presence of light waves: Simplified theory, relative comparison and a suggestion for experimental determination

In this paper, we have studied the electronic contribution to the elastic constants for III-V, ternary and quaternary materials in the presence of light waves on the basis of newly formulated electron statistics. It has been found taking n-InAs, n-InSb, n-Hg_1−xCd_xTe and n-In_1−xGa_xAs_yP_1−y lattice matched to InP, as examples that the elastic constants increase with increasing electron concentration, intensity and wavelength in various manners. The strong dependence of the elastic constants on both the light intensity and wavelength reflects the direct signature of the light waves which is in contrast as compared with the corresponding bulk specimens in the absence of photo-excitation. The well-known results for degenerate wide gap materials in the absence of light waves have been obtained as a special case under certain limiting conditions and this compatibility is the indirect test of our generalized formalism. In this context, we have suggested the experimental method of determining the carrier contribution to the elastic constants for materials having arbitrary carrier energy spectra and our results find six important applications in the regime of photon-assisted transport in modern optoelectronic devices.     

The order with respect to oxygen and the activation energy for the burning of an anthracitic char in O2 in a fluidised bed, as measured using a rapid analyser for CO and CO2

Measurements of the oxidation of a coal char in a fluidised bed have the advantages that the rates of heat and mass transfer to and from a reacting particle are large and characterised well. However, problems have arisen from a combination of the slow, but typical, response–time (4 s) of the analysers for CO and CO₂ and the slow mixing of gases when filling a fairly large fluidised bed. The resulting time constant for the sampling system was 8 s and comparable to the time for combustion at 900 °C or above. The purpose of this work was to measure the kinetics of oxidation of a char in a smaller fluidised bed (with a shorter mixing time) using an analyser for CO and CO₂ with a response time as low as 0.1 s. The result is that the oxidation of an anthracitic char is now found to be first order in O₂ between 700 and 900 °C; at 900 °C the order previously measured was almost zero. The activation energy is now measured here to be 145 ± 25 kJ/mol, in agreement with some early work.