超声清洗装置空化噪声谱分析法空化噪声级测量

空化强度是用以衡量液体介质中空化活动的剧烈程度,同时空化效应在超声清洗中起关键作用,因此,测量超声清洗槽中的空化强度便可了解其中空化活动的情况.当发生空化时,液体介质中会产生成分复杂空化噪声,对空化噪声谱进行分析和计算得到空化噪声级,据此可判断空化强度.实验测得结果表明:超声清洗装置内稳态空化分布广泛、均匀,瞬态空化分...     

Ultrafast proton transfer dynamics of 2-(2'-hydroxyphenyl)benzoxazole dye in different solvents

The excited-state intramolecular proton transfer of 2-(2-hydroxyphenyl)benzoxazole dye in different solvents is investigated using ultrafast femtosecond transient absorption spectroscopy combined with quantum chemical calculations.Conformational conversion from the syn-enol configuration to the keto configuration is proposed as the mechanism of excited-state intramolecular proton transfer.The duration of excited-state intramolecular proton transfer is measured to range from 50 fs to 200 fs in different solvents.This time is strongly dependent on the calculated energy gap between the N-S;and T-S;structures in the S;state.Along the proton transfer reaction coordinate,the vibrational relaxation process on the S;state potential surface is observed.The duration of the vibrational relaxation process is determined to be from8.7 ps to 35 ps dependent on the excess vibrational energy.     

Thermodynamic Irreversibility Analysis of Dual-Skin Chest-Freezer

In this work, a transient analysis of a dual-skin chest-freezer refrigeration system, operating with R290, is studied numerically with the purpose of performing the characterization of the system through the second law of thermodynamics. A mathematical model which accounts for refrigerant mass distribution inside the system is used. In addition, this work addresses the calculation of entropy generation and exergy destruction for characterizing the system performance during its operations. In order to validate the model, a comparison with measured experimental data is performed for both pull-down and on-off operations. The characterization of the system through the second law of thermodynamics is conducted using two different methods. One consists of a direct calculation of the entropy generation rate and the second one in the calculation of exergy destruction rate. The equivalence of these two methods is used as an indicative of the “correctness” of the performed calculations. The model results agree near 97% with the experimental data used in the comparisons. Entropy generation and exergy destruction results along time for the whole system and in its individual components are characterized with the second law. These results are very useful for improving refrigeration system design.     

HfO2基铁电场效应晶体管读写电路的单粒子翻转效应模拟

使用器件-电路仿真方法搭建了氧化铪基铁电场效应晶体管读写电路,研究了单粒子入射铁电场效应晶体管存储单元和外围灵敏放大器敏感节点后读写数据的变化情况,分析了读写数据波动的内在机制.结果表明:高能粒子入射该读写电路中的铁电存储单元漏极时,处于"0"状态的存储单元产生的电子空穴对在器件内部堆积,使得栅极的电场强度和铁电极化增大,而处于"1"状态的存储单元由于源极的电荷注入作用使得输出的瞬态脉冲电压信号有较大波动;高能粒子入射放大器灵敏节点时,产生的收集电流使处于读"0"状态的放大器开启,导致输出数据波动,但是其波动时间仅为0.4 ns,数据没有发生单粒子翻转能正常读出.两束高能粒子时间间隔0.5 ns先后作用铁电存储单元漏极,比单束高能粒子产生更大的输出数据信号波动,读写"1"状态的最终输出电压差变小.     

基于激光瞬态特性的气体浓度光纤传感器

报道了一种基于掺铒光纤激光器瞬态特性的新型气体浓度传感器.用光纤环全反镜和光纤Bragg光栅(FBG)构成F-P线形腔，通过调节光栅的反射波长，使激光激射波长落在C₂H₂的一个较强的吸收峰1531.56 nm.激光激射延迟时间与激光器谐振腔损耗密切相关，气体浓度的改变将引起谐振腔损耗的改变，通过测量激光激射延迟时间可以获得气体的浓度.该装置分辨率及灵敏度由抽运光脉冲的高功率电平和低功率电平决定，传感器的动态测量范围由抽运光高功率电平决定.当高功率和低功率电平分别为25 mW和5.9 mW时,该传感器的灵敏度和分辨率分别为100 ppm/μs和20 ppm.     

一种火炸药瞬态光谱测试的精确定位

介绍一种火炸药在瞬态光辐射参测量中的精确定位以及绝对光谱亮度参数的数据处理。     

Influence of carrier correlations on the excitonic optical response including disorder and microcavity effects

A model study of the characteristic signatures of carrier-correlation effects on the excitonic differential absorption spectra in semiconductors is presented. Using an effectively one-dimensional tight-binding system Coulomb-induced carrier-correlations up to third-order in the optical field are treated without additional approximations. To illustrate the influence of the different many-body contributions excitonic differential absorption spectra are computed for various polarizations and pump-probe time delays. The simultaneous influence of energetic disorder and correlations on the differential absorption spectra is discussed. Also presented are numerical results for the case when the semiconductor system is placed inside a microcavity in the strong-coupling regime. It is shown that the correlations induce characteristic signatures in the normal mode spectra. Received 22 January 1999     

Effects of a modulation of the pump-polarization in a degenerate pump/probe experiment

The effects of the pump-polarization in a degenerate pump/probe experiment are analyzed. It is shown that modulating the pump polarization from linear to circular induces a modulation in the probe absorption change that allows to separate various contributions that are mixed in the signal. An experimental demonstration is carried out in a laser dye (Coumarin 500). Received: 21 July 1998 / Revised: 28 October 1998 / Accepted: 20 November 1998