Ultrasound Attenuation in Biological Tissue Predicted by the Modified Doublet Mechanics Model

Experimental results have shown that in the megahertz frequency range the relationship between the acoustic attenuation coefficient in soft tissues and frequency is nearly linear. The classical continuum mechanics （CCM）, which assumes that the materiaJ is uniform and continuous, faJls to explain this relationship particularly in the high megahertz range. Doublet mechanics （DM） is a new elastic theory which takes the discrete nature of material into account. The current DM theory however does not consider the loss. We revise the doublet mechanics （DM） theory by including the loss term, and cMculate the attenuation of a soft tissue as a function of frequency using the modified the DM theory （MDM）. The MDM can now well explain the nearly linear relationship between the acoustic attenuation coefficient in soft tissues and frequency.     

Droplet model for sound absorption in fluids near the critical point

The dynamic droplet model of critical fluids is applied to understanding critical fluid sound absorption. The resonance frequency of an oscillating droplet is used to explain the scaling on frequency and temperature observed in sound absorption data.     

位相共轭镜耦合到染料激光器中的频移现象

本文建议了一个测量位相共轭镜耦合到染料激光器后,当波长自扫描时,BaTiO_3晶体内的运动光栅的多普勒频移的方法,实验结果表明,多普勒频移Δf<0.2Hz.进一步的分析显示,多普勒频移不能解释朝长波方向扫描的波长自扫描现象.     

非晶态快离子导体电导特性的低频弛豫理论

结合快离子导体玻璃的结构特点和倪嘉陵(Ngai)的低能激发、弛豫、耗散统一理论,依据非Markov方程探讨了快离子的输运特点,导出了非晶态快离子导体电导的频率-温度依赖关系。理论方法与现有快离子导体电导理论不同,结果表明与实验数据符合较好,理论能较好地描述低温下电导的色散现象。色散的程度与表征物质内部结构差异的参数——红外发散指数n有关。 关键词：     

High frequency optogalvanic signals and CO2 laser stabilisation

The normal optogalvanic effect used in the stabilisation of CO₂ lasers decreases in amplitude with increase in frequency and disappears at 2–3 kHz. We show that there is also a high frequency optogalvanic effect in CO₂-N₂-He-Xe laser gas mixtures up to ～ 100 kHz, explain its origin and use it to frequency stabilise a laser with long term (hours) frequency drift of < 50 kHz and frequency re-settability of < 100 kHz.     

非晶态快离子导体电导特性的低频弛豫理论

结合快离子导体玻璃的结构特点和倪嘉陵(Ngai) 的低能激发、弛豫、耗散统一理论, 依据非Markov 方程探讨了快离子的输运特点, 导出了非晶态快离子导体电导的频率一温度依赖关系. 理论方法与现有快离子导体电导理论不同, 结果表明与实验数据符合较好, 理论能较好地描述低温下电导的色散现象. 色散的程度与表征物质内部结构差异的参数— 红外发散指数n有关. 关键词：     

半导体激光器塞曼调制稳频的实验对比研究

首先阐述了实现半导体激光器外调制锁频方案的必要性,并针对一种利用塞曼效应进行外调制稳频的实验方案,详细地阐述了其基本思想和实验原理,以及这种稳频方案相对于一般的内调制饱和吸收稳频技术在实验上的差异.本文给出的具体实验参数和实验结果表明,这种方案相对于其他方案可以获得同等好的锁频质量.不仅如此,本文还给出了塞曼调制稳频和电流调制稳频的锁定频率输出的监视对比情况,从对比结果中,我们可以清楚地看到塞曼调制稳频使得激光器锁定频率无调制输出的优越特性.     

基于不动点理论的多系统兼容接收机频点选择问题的研究与遗传算法实现

基于不动点理论研究了多系统兼容接收机的频点选择问题,并引入遗传算法解决了这一问题.将Banach不动点理论引入频点空间,提出并证明了频点空间中频点集的遗传进化过程反映了频点空间呈现出的一种不动点物理特性;经过频点空间算子的足够多次的反复遗传进化作用,频点空间中的任一迭代序列源频点集都将最终收敛于唯一不动点目标频点集,而该不动点目标频点集中的目标频点即为该频点选择问题的最优解.完成了遗传算法应用于频点选择问题的理论研究与实现.仿真结果表明,该算法能够有效地解决多系统兼容接收机的频点选择问题. 关键词： 多系统 接收机 遗传算法 不动点     

铷原子频标中的微波功率频移

根据我们的测量，在铷原子频标中微波功率频移系数总是正的。已有的关于微波功率频移的解释无法解释此现象。本文从微波场引起交流Ｚｅｅｍａｎ效应的观点出发，解释了这一现象。     

On the frequency-dependence of the impedance of n- and p-type gallium arsenide electrodes

The impedance of n- and p-type GaAs electrodes has been studied as a function of applied voltage and of frequency. Simple frequency laws were found to exist for the series capacitance and resistance. To explain these laws, a distribution of time constants has been assumed, associated with dielectric relaxation phenomena in the double-layer at the semiconductor/electrolyte interface. This distribution was found to be independent of the distance from the crystal surface for n-type samples but to depend upon it for p-type specimens. An investigation on the role of the applied voltage in these frequency laws yielded additional evidence for the mathematical model which was originally introduced in a previous paper in order to explain similar laws observed at CdSe, CdS and TiO₂ electrodes. The frequency-dispersion of the p-type samples was found to be strongly influenced by an appropriate pretreatment of the surface, in contrast with the behaviour of the n-type specimens. In both cases, the experimental results indicate that the source of the frequency dispersion has to be sought in structural irregularities of the depletion region of the electrode. The possibility of determining the flat-band potential from frequency-dependent impedance data is discussed.     

Small-signal analysis of two cascaded semiconductor optical amplifiers in a counterpropagating configuration

In this work, we present a small-signal analysis which reveals its usefulness to explain the evolution of the optical frequency responses obtained at the outputs of two-cascaded semiconductor optical amplifiers (SOAs) used in a counterpropagating configuration (TC-SOA-CC). To obtained these responses, the TC-SOA-CC configuration has been implemented on an electric simulator and we have used for each SOA a multisection rate equation based model. This model permits us to study both the static and dynamic behavior of the TC-SOA-CC optical outputs in the context of bidirectional transmission. Thanks to this model, we can also obtain the evolution of the carrier lifetimes in each SOA in order to determinate their influence on the optical frequency responses. The small-signal responses derived from our small-signal analysis are given as a function of the intrinsic parameters and for each specific situation for the value of the average injected optical power. This small-signal analysis is used to comment the behavior of the frequency responses obtained by simulation at the TC-SOA-CC optical outputs. Thanks to our small-signal analysis, we explain why for such a configuration, the features of the frequency responses obtained at the SOAs optical outputs can change from a low-pass, to a high-pass, and/or to a band-pass form by varying the average injected optical powers in the SOAs.     

Fourier and Wavelet Transform Analysis of Pressure Signals during Explosive Boiling

The transient pressure in a liquid-pool during explosive boiling of acetone is measured by a micro-pressure-measuring system. The Fast Fourier transform and continuous wavelet transform methods are applied to investigate the frequency characteristics. The results show that the dominant frequency of the explosive boiling is 0-2 MHz, and the bubble cluster formed by numerous tiny bubbles departs twice. Analysis and discussions are also conducted to explain the bubble evolution during the explosive boiling.     

Hot luminescence in polyacetylene

We propose that the unusual frequency dependent lineshapes observed in Raman scattering experiments on polyacetylene are due to hot luminescence in very long polyene chains. Employing a generalized equation of motion technique we find that a photoexcited polyene is unstable with respect to a variety of symmetry lowering distortions which vary as a function of the frequency of the exciting radiation. Radiative decay during this relaxation is observably strong in the inelastically scattered photon spectrum and would explain the dominant observed lineshape variations.     

Effects of word frequency, contextual diversity, and semantic distinctiveness on spoken word recognition

The relative abilities of word frequency, contextual diversity, and semantic distinctiveness to predict accuracy of spoken word recognition in noise were compared using two data sets. Word frequency is the number of times a word appears in a corpus of text. Contextual diversity is the number of different documents in which the word appears in that corpus. Semantic distinctiveness takes into account the number of different semantic contexts in which the word appears. Semantic distinctiveness and contextual diversity were both able to explain variance above and beyond that explained by word frequency, which by itself explained little unique variance.     

Frequency locking by external force from a dynamical system with strange nonchaotic attractor

Usually, phase synchronization is studied in chaotic systems driven by either periodic force or chaotic force. In the present work, we consider frequency locking in chaotic Rössler oscillator by a special driving force from a dynamical system with a strange nonchaotic attractor. In this case, a transition from generalized marginal synchronization to frequency locking is observed. We investigate the bifurcation of the dynamical system and explain why generalized marginal synchronization can occur in this model.     

InSb磁电阻在交变磁场下的特性研究

利用数字示波器,通过观察李萨如图形,在弱交变磁场信号下,验证了InSb磁电阻的倍频效应;通过改变信号源的频率,得到了李萨如图形随频率的变化规律。从李萨如图形的变化规律可以发现,随信号源频率的升高,磁电阻的交流分量减小;与信号源的相位差趋于-π。通过对不同励磁频率下,励磁电流、磁电阻的变化规律的研究分析,解释了李萨如图形随频率变化的原因。     

Submillimeter Wave ESR Measurement for Cr3+ in Ruby Crystal Using a Gyrotron as a Radiation Source

Fine structure constant of ruby has been measured using an ESR spectrometer with a pulse magnetic for high fields and a gyrotron as a radiation source in a millimeter to submillimeter wave range. The measurement was carried out at room temperature. The Zeeman energy in this frequency range is large enough compared with the fine structure constant. The higher order term in the effective spin Hamiltonian can explain the dependence of fine structure constant on the frequency. The observed fine structure constants depend on the field intensity.     

平行光路方向运动的光栅多普勒效应及其在测微小位移中的应用

研究了光栅平行光路运动时产生的光的多普勒效应,用实验进行了验证,并将该原理应用到对微小位移量的检测中. 对原理进行了拓展,得到光栅以任意角度运动产生光的频移的普适公式.     

Surface helicon waves in the Faraday geometry: Do they exist?

A number of authors have investigated magnetoplasma surface waves in semiconductors in an attempt to explain the low frequency surface modes observed by Baibakov and Datsko. We show that none of the explanations suggested to date gives a satisfactory account of the experimental observations.     

The influence of anharmonic potentials in calculations of planar channeling radiation from GeV positrons

The frequency of radiation from planar channeled positrons in the GeV region is discussed for realistic planar potentials when the dipolarity condition is not satisfied. It is found that there is a critical beam momentum at which the maximum radiated frequency is practically the same for all channeled positrons. For this momentum a sharp peak in the calculated composite spectrum is to be expected and this could explain the sharp peaking observed in a recent CERn experiment for 5 GeV/c positrons.