基于最大信噪比测量两相流速度

为了克服噪声对信号的影响,提出一种利用最大信噪比和相关法测量两相流速度的方法.基于最大信噪比的信号分离方法是一种盲源信号分离方法,该算法利用统计独立信号完全分离时信噪比最大作为分离准则,它具有非常低的计算复杂度.这里首先利用盲源信号分离方法分别提取出上游和下游两相流信号,并据此求出两相流信号的相关函数曲线,由此求出信号的渡越时间,最后给出仿真实验的处理结果.实验结果表明该方法能够满足两相流速度的测量要求.     

Elimination of environmental noise in interferometric wavelength shift demodulation for dynamic fiber Bragg grating sensor array

We present a novel reference compensation method for eliminating environmental noise in interferometric wavelength shift demodulation for dynamic fiber Bragg grating (FBG) sensors. By employing a shielded wavelength-division-multiplexed reference FBG in the system, the environmental noise is measured from the reference channel, and then subtracted from the demodulation result of each sensor channel. An approximate 40 dB reduction of the environmental noise has been experimentally achieved over a frequency range from 20 Hz to 2 kHz. This method is also suitable for the elimination of broadband environmental noise. The corresponding FBG sensor array system proposed in this paper has shown a wavelength resolution of .     

Optimization for high precision Shack-Hartmann wavefront sensor

A comprehensive noise model about digital camera which is a main component of SHWFS is constructed, including the readout noise, the photon shot noise, the quantization noise and the response un-uniformity. Based on the noise model, the spot centroid errors caused by each kind of noise are analyzed, respectively. And then the synthetic error from all the noise is calculated. The result demonstrates that the limit of the spot centroid accuracy is 1% pixels. At last, the crossing error caused by the high order diffraction spots is analyzed. It is approximately proportional to the secondary spots number. So the structure of the microlens array must be optimized together with the digital camera when designing SHWFS.     

1/f noise and slow relaxations in glasses

Recently we have shown that slow relaxations in the electron glass system can be understood in terms of the spectrum of a matrix describing the relaxation of the system close to a metastable state. The model focused on the electron glass system, but its generality was demonstrated on various other examples. Here, we study the noise spectrum in the same framework. We obtain a remarkable relation between the spectrum of relaxation rates λ described by the distribution function P (λ) ～ 1/λ and the 1/f noise in the fluctuating occupancies of the localized electronic sites. This noise can be observed using local capacitance measurements. We confirm our analytic results using numerics, and also show how the Onsager symmetry is fulfilled in the system.     

Numerical study on reduction of the elevated structure noise by surface absorption on plate girders

With the aim to propose a reasonable and effective countermeasure for the elevated structure noise, the sound field radiated by a steel plate girder, which is the main source of the elevated structure noise, have been theoretically analysed. In the present study, steel plate girders are modelled as infinitely long elastic plate strips placed in parallel and numerical examples on the sound field radiated by the steel plate girders are shown. In the analysis of the radiated sound field, the equivalent source method is employed. Effect of the surface absorption on the sound field radiated by the girders is discussed through numerical examples. The results show that the surface absorption is effective for reduction of the radiated sound field, especially in the area that increase of sound pressure due to reflection by adjacent plate girders is observed. Furthermore, to design for reasonable countermeasure, variation of the noise reduction effect due to changing the pattern of surface absorption area on plate girders is classified.     

Study on the effect of sound duration on the annoyance of helicopter noise by applying a technique of time compression and expansion of sound signals

The number of helicopter operations has rapidly increased during the last 20 years in Japan. Helicopter noise sounds different from other aircraft; the waveform of the sound pressure is impulsive and the signal duration is relatively long. The Environmental Agency of Japan implemented new guidelines for evaluating noise exposure around small airports, including heliports, in 1990. This study was executed in connection with the development of provisional guidelines. Psychoacoustic experiments were carried out to identify an evaluation index for helicopter noise. In order to examine the effect of duration independently, we not only used original sound recordings, but also synthesized sound signals. The durations of these sound signals were time compressed or expanded without degrading the quality of the original sound recording. The test results show that the effect of duration is significant, and that the A-weighted sound exposure level is a better index than the maximum A-weighted sound pressure level for the evaluation of helicopter noise.     

Weighted oscillator strengths and lifetimes for the S XIV spectrum

The weighted oscillator strengths gf and the lifetimes for S XIV presented in this work have been calculated in a multiconfigurational Hartree–Fock relativistic approach. In this calculation, the electrostatic parameters were optimized by a least-squares procedure in order to improve the adjustment to experimental energy levels. This method produces gf values that are in better agreement with observed line intensities and lifetime values closer to the experimentally determined ones. In this work we presented all the experimentally known electric dipole S XIV spectral lines. Published in Zhurnal Prikladnoi Spektroskopii, Vol. 76, No. 3, pp. 473–476, 2009.     

Evaluation of the acoustic performance of classrooms in public schools

This paper presents the results of an evaluation of acoustic comfort of classrooms built according to a standard design. Three constructive designs located in the metropolitan area of Curitiba (Brazil) have been evaluated, two schools built under each of these three designs, in a total of six schools. The acoustic quality of the classrooms have been analyzed based on measurements of the reverberation time, sound pressure level inside and outside the classrooms, and sound insulation. Measurements of ambient noise (external and internal) followed the Brazilian Standards NBR 10151 and NBR 10152. Measurement of reverberation time and sound insulation followed the international Standards ISO 140-4, ISO 140-5, ISO 717-1, and ISO 3382. Results (sound insulation and reverberation time) have been compared with reference values found in the Brazilian Standard NBR 1279, and in the Standards ANSI S12.60 and DIN 18041. Results reveal poor acoustical quality of the surveyed classrooms, for all 3 constructive designs studied. The surveyed designs do not meet the guidelines of either the Brazilian Standards or of the International Standards employed as references.     

Noise exposure of workers of the construction sector

Noise is one of the most highly found physical contaminants in the construction sector. The most negative effects caused by noise exposure are related to the hearing system and may produce professional deafness or even permanent deafness. As these effects have a very important influence on people’s health and well-being, it is necessary to assess the noise exposure and to develop mechanisms for studying and proposing preventive solutions.This work has studied the noise levels which the workers of the construction sector are exposed to. A number of representative measurements have been carried out using a sound level meter and a dosimeter to collect data from workers devoted to different tasks in the construction process. Analysis of the most important levels and indexes have been done with those data, and afterwards, they have been compared with the limits imposed by the different current regulations.     

惠东县乡镇学龄前儿童血铅水平分析

为了解惠东县乡镇3～6岁儿童血铅水平。采取随机与特定结合的方法,于2 0 0 4年1 0月～1 1月对惠东县5个乡镇的790名3～6岁儿童进行了血铅水平测定。检测采用全国统一的BH -2 1 0 0钨舟原子吸收仪及随机专用试剂进行。所有操作均严格按照要求进行。结果表明,惠东县乡镇3～6岁儿童血铅水平为(70 70±2 4 89) μg/L达到我国近年来5 2个调查结果所示的普通市区儿童血铅水平70～90 μg/L的下限。其中高于国际儿童铅中毒标准占9 6%。儿童的血铅水平存在明显的区域差异,制鞋工业乡镇较高。同时儿童血铅水平存在着性别差异。男童较女童偏高。提示不能忽视乡镇儿童铅污染情况,尤其是制鞋工业乡镇的儿童高血铅水平应引起有关部门重视。