Experimental study of the stack geometric parameters effect on the resonance frequency of a standing wave thermoacoustic refrigerator

Thermoacoustic refrigeration is an emerging technology that makes use of acoustic power to pump heat. The resonance frequency is important for the performance of thermoacoustic refrigerators, as it affects the temperature difference across the stack. This paper aims to optimize the performance of thermoacoustic refrigerators by experimentally investigating the effect of the stack geometric parameters (i.e. stack position, stack length, and the stack size) on the resonance frequency of a standing wave loudspeaker driven thermoacoustic refrigerator. Celcor Ceramic stacks of normalized positions of 0.764, 1.05, 1.43, and 1.72, normalized lengths of 0.076, 0.114, 0.153, and 0.191, and two porosities of 0.8 and 0.85 are used. The clarification of the relationship between the stack geometric parameters and the resonance frequency of the thermoacoustic refrigerator is presented. Moreover, the coefficient of performance of the thermoacoustic refrigerator is observed to increase at the resonance frequency of each stack configuration.     

电动振动台台面加速度失真度的分析

通过对影响电动振动台失真度因素的定性分析，得出影响失真度的理论依据，提出降低电动振动台台面加速度失真度的措施，供设计电动振动台及使用电动振动台者参考。     

运用盐充法测量双壳贝类的壳腔体积

以长牡蛎（Crassostreagigas）和紫贻贝（Mytilusedulis）为例,研究了以食盐为填充物（盐充法）测量贝类壳腔体积的测量方法,并运用“水容法”进行验证。对两种贝类的测量结果表明,两种方法测得的壳腔容积结果相近,均无显著性差异（P〉0．05）。但运用盐充法测量牡蛎壳腔体积是水容法效率的8．4倍,测量贻贝壳腔体积的效率是水容法的6．2倍。由此可见,运用盐充法测量双壳类的壳腔体积具有操作简便和高效的特点,可广泛应用于贝类生理、生态和环境科学等领域的研究中。     

污水再生过程中消毒副产物前体物转化规律

采用大孔吸附树脂将污水中的消毒副产物(DBP)前体物分离为亲水性物质(HPI)、强疏水性物质(HPO)和弱疏水性物质(TPI)这3个组分,通过三维荧光光谱、傅里叶红外光谱和核磁共振对再生水处理各沿程前体物进行表征,并测定各沿程出水的消毒副产物生成势(DBPFP).结果表明,生活污水中DBPs前体物主要组分为腐殖质和脂肪烃,以HPI为主.一级处理(沉淀)基于HPO与水互斥的物理性能对疏水性腐殖质有较好的去除效果,腐殖质的去除会导致含碳消毒副产物生成势(CDBPFP)的降低.此外由于DON/DOC的增加,含氮消毒副产物生成势(N-DBPFP)有所增加.二级处理(生物处理)对腐殖质和脂类均有较好的去除效果,但会产生大量疏水性的溶解性微生物产物(SMP),因此生物处理后DBPs前体物主要表现为疏水性.SMP的累积会导致C-DBPFP和N-DBPFP的大幅增加.深度处理(滤布滤池)能截留部分腐殖质和疏水性的SMP,因此前体物HPO占比减少,HPI占比增加.深度处理可以通过对SMP的去除来降低C-DBPFP和N-DBPFP.     

Policy, personal dispositions and the evaluation of aircraft noise

In this paper, we hypothesize and test the ideas that (1) people’s subjectivity in relation to aircraft noise is shaped by the policy discourse, (2) this results in a limited number of frames towards aircraft noise, (3) the frames inform people how to think and feel about aircraft noise and (4) the distribution of the frames in the population is dependent on structural variables related to the individual. To reveal subjects’ frames of aircraft noise a latent class model is estimated based on survey data gathered among a sample of 250 residents living near Amsterdam Airport Schiphol, a major international airport in the Netherlands. In line with expectations, the results show that there are four evaluative frames of aircraft noise, three of which are strongly linked to the policy discourse. The frames are associated with fitting levels of annoyance response. In turn, frame membership is influenced by two structural variables, namely aircraft noise exposure and noise sensitivity. The results indicate that social factors operate discursively in the explanation of subjective reaction to noise, while psychological factors operate within a traditional cause-and-effect model. The paper concludes with several policy implications.     

Major brain lesions by intrauterine herpes simplex virus infection: MRI contribution

The majority of neonatal Herpes Simplex Virus (HSV) infections are acquired at birth as a consequence of direct fetal contact with the infected birth canal or through an ascending infection after premature rupture of the amniotic membranes. Intrauterine transmission of HSV infection from mother to the fetus is rare; in only 5% of the cases it occurs from haematogenous transplacental dissemination. We present a case of transplacental intrauterine HSV infection after a primary maternal HSV infection in the first trimester of pregnancy. The diagnosis was assessed by viral culture and serologic tests. Ultrasound imaging revealed fetal brain damage in the third trimester. Finally, the MRI showed the devastating extensiveness of the HSV infection, which was beyond the expectation based on the ultrasound images. Copyright © 2007 John Wiley & Sons, Ltd.     

Inhibition of rhythmic neural spiking by noise: the occurrence of a minimum in activity with increasing noise

The effects of noise on neuronal dynamical systems are of much current interest. Here, we investigate noise-induced changes in the rhythmic firing activity of single Hodgkin–Huxley neurons. With additive input current, there is, in the absence of noise, a critical mean value μ = μ _c above which sustained periodic firing occurs. With initial conditions as resting values, for a range of values of the mean μ near the critical value, we have found that the firing rate is greatly reduced by noise, even of quite small amplitudes. Furthermore, the firing rate may undergo a pronounced minimum as the noise increases. This behavior has the opposite character to stochastic resonance and coherence resonance. We found that these phenomena occurred even when the initial conditions were chosen randomly or when the noise was switched on at a random time, indicating the robustness of the results. We also examined the effects of conductance-based noise on Hodgkin–Huxley neurons and obtained similar results, leading to the conclusion that the phenomena occur across a wide range of neuronal dynamical systems. Further, these phenomena will occur in diverse applications where a stable limit cycle coexists with a stable focus.