环形激光陀螺仪机械抖动参数的优化设计

在简要介绍了动态锁区形成原理后 ,通过对 RL G基本输入输出关系的推导得出了动态锁区的宽度表达式。基于减小动态锁区影响的目的 ,建立了相应的优化模型。优化结果表明 :适当增大抖动深度对减小动态锁区的影响是必要的 ,但当抖动深度增大到一定程度后 ,再增大抖动深度对减小动态锁区没有明显的效果 ,而根据优化结果进行局部调整却可能得到很好的偏频效果。     

Early stages of laser graphitization of diamond

A mechanism for photographitization of a free diamond surface is proposed. The quantum-kinetic rate of this process is determined. The graphitization rate is close to zero if the activation energy of the graphitization process is taken as being equal to the binding energy of a carbon atom with the surface (i.e. equal to the sublimation energy of a carbon atom). On the contrary, if the activation energy is close to the energy of C–C bonds, the graphitization process may occur at a noticeable rate and be observed under ‘relatively smooth’ experimental conditions. The temperature rise leads to a considerable increase in the graphitization rates. Preliminary experimental data on the low-rate laser ablation of diamond are presented to support the proposed model of photographitization. An early stage of laser-induced graphitization in the bulk of diamond is also considered. It is found that the nucleation of a ‘tiny graphite drop’ is possible in the bulk of the diamond inside the focal area of a laser beam; the ‘graphite drop’ growth causing the appearance of mechanical stresses in the surrounding regions. The maximum size of the graphite drop is determined, which, when exceeded, leads to mechanical damage of the sample and to a change in the mechanism of laser graphitization. An evident mechanical criterion for laser-induced damage of diamond is proposed. Received: 2 October 2002 / Accepted: 5 October 2002 / Published online: 29 January 2003 RID="*" ID="*"Corresponding author. E-mail: stvn@stankin.ru     

粉末颗粒气力加注特性实验研究

粉末发动机是以粉末颗粒为燃料的新型发动机,具有多次起动和推力调节的功能.粉末加注是粉末发动机实验组织过程中的重要环节.本研究通过搭建粉末供应系统开展粉末气力加注实验,研究对比了集粉箱加注位置、流化气量对粉末气力加注特性的影响.考虑了供粉过程中储箱内粉末堆积密度的动态变化,并建立了相应的计算方法,同时还采用控制系统理论揭示了储箱内粉末堆积密度的变化规律.结果表明:在相同条件下,较大的流化气量有利于加注过程稳定,但集粉箱加注率较低;气力加注方式下集粉箱内的粉末堆积密度大于储箱内初始堆积密度;采用较小的流化气量与集粉箱壁面切向加注方式有利于提高粉末粒径分布均匀性;集粉箱壁面切向加注方式下,流化气量较小时储箱内粉末的堆积密度是先增大后减小,且堆积密度最终值小于初始值,而流化气量较大时,储箱内粉末的堆积密度是先增大后减小再增大后减小,且堆积密度最终值大于初始值;储箱内粉末堆积密度的动态变化过程类似于欠阻尼二阶系统,流化气量较小时系统阻尼系数较小,而流化气量较大时系统阻尼系数较大,且是一个变阻尼过程.     

Microscopic derivation of non-Markovian thermalization of a Brownian particle

In this paper, the first microscopic approach to Brownian motion is developed in the case where the mass density of the suspending bath is of the same order of magnitude as that of the Brownian (B) particle. Starting from an extended Boltzmann equation, which describes correctly the interaction with the fluid, we derive systematically via multiple-time-scale analysis a reduced equation controlling the thermalization of the B particle, i.e., the relaxation toward the Maxwell distribution in velocity space. In contradistinction to the Fokker-Planck equation, the derived new evolution equation is nonlocal both in time and in velocity space, owing to correlated recollision events between the fluid and particle B. In the long-time limit, it describes a non-Markovian generalized Ornstein-Uhlenbeck process. However, in spite of this complex dynamical behavior, the Stokes-Einstein law relating the friction and diffusion coefficients is shown to remain valid. A microscopic expression for the friction coefficient is derived, which acquires the form of the Stokes law in the limit where the meanfree path in the gas is small compared to the radius of particle B.Knowing the interest of Matthieu Ernst in the subtle and fundamental problems of kinetic theory, we have the pleasure to dedicate this study to him.     

Understanding of Various Type of Unambiguous Discrimination in View of Coherence Distribution

Unambiguous quantum state discrimination is a strategy where the conclusive result can always be trusted. This strategy is very important, since it can be used for various quantum information protocols, including quantum key distribution. However, in the view of quantumness, it is not clear what is going on in performing unambiguous quantum state discrimination. To answer the question, we investigate coherence distribution when unambiguous discrimination is performed by generalized measurement. Specially, we study coherence distribution in three cases, which consist of unambiguous quantum state discrimination, sequential quantum state discrimination, and assisted optimal discrimination, which are considered to be a family of unambiguous quantum state discrimination. In this investigation, we show that the structure of generalized measurements performing various types of unambiguous quantum state discrimination can be understood in terms of coherence distribution. Our result is not limited to the discrimination of two pure quantum states, but it is extended to the discrimination of two mixed states.     

Structure and properties of detonation waves of heterogeneous explosives from the point of view of the hot spots mechanism

It is assumed that the chemical reaction of a detonation transformation, that is, burning, arises first in separate hot spots originated by the explosive compression behind or within the detonation wave front due to heterogeneity of charges, instability of the detonation wave, etc. Then the burning spreads around into the bulk of the explosive and is completed in the Chapman–Jouguet plane, where the detonation product velocity relative to the detonation front is equal to the sound velocity. A simple analytical method proposed early by the authors is used to calculate the expression for the detonation transformation time, from which it follows that there are at least two nondimensional numbers defining the possibility of the realization of the mechanism mentioned above. The first one is the Frank-Kamenetskii number, that is, the relation of the characteristic time of the cooling of the hot spot to the adiabatic induction period at some characteristic temperature of the hot spot. The hot spot mechanism is realized if the Frank-Kamenetskii number is greater than the critical one that determines the minimum possible size of hot spots capable of ignition. The second number is the relation of the detonation transformation time in the presence of hot spots to the reaction time in accordance with classical mechanism. The hot spot mechanism at detonation is realized if this number is less than unity. By means of the numbers proposed, some interpretations of available experimental data concerning the detonation process are given.     

电子小提琴与常规小提琴的无线载波传输演示

小提琴可分解成拉弦系统和共振箱系统．在拉弦系统中,弦的振动被变为电声信号,以电磁波的形式发射到空中．在共振箱系统中,由调频接收器接收信号,经电声转换后驱动共鸣箱发声．改装后的电子小提琴可用于物理实验演示教学及小提琴弦振动和共鸣箱的频谱分析．     

Study of influences of laser power fluctuation on thermogram of the material

The effects of the laser beam instability on the temperature of the material are studied in this paper. The fluctuation of the temperature not only relates to the laser beam instability, but also correlates with the thermal conductivity, the thermal diffusivity, the emissivity, the laser–solid interaction time, and the laser spot diameter. The temperature fluctuation of the aluminum, the polymethylmethacrylate, the epoxylite, and the low carbon steel is measured by the infrared thermal imagers (HWRX··) to determine validity of the theory prediction. It is found that the theoretical prediction is in good agreement with the experimental results. Besides, the maximum amplitude of the temperature fluctuation is calculated and how to control the temperature fluctuation is discussed. The results show that the temperature fluctuation in the laser–solid interaction is of importance in practice.     

Prediction of the performance of an algorithm for the detection of small targets in infrared images

Detection of small targets in infrared (IR) images is important in IR image processing. For the prediction of performance of a detection algorithm, it is necessary to calculate the probability of detection and probability of false alarm. A method is developed to calculate the probabilities in this paper. The detection is divided into two parts: the first part, which is called pre-detection, is to find out candidates for targets in a single frame of an image; and the second part is to localize the target in multiple frames of the image. Under some assumptions, the pre-detection probability, the false detection probability of single frame, detection probability and false alarm probability are derived. The algorithm for the detection of small target in IR image, which is used for the derivation of the probabilities, is contrast threshold detection based on background prediction, and a pipeline filter is used for multiframe image processing. The results show the relationship of the probabilities to the contrast of target to background, SNR, and contrast threshold.     

Theory of Electrorotation of Clustered Colloidal Particles

When a colloidal suspension is exposed to a strong rotating electric field, an aggregation of the suspended particles is induced to appear. In such clusters, the separation between the suspended particles is so close that one could not neglect the multiple image effect on the electrorotation (ER) spectrum. Since so far the exact multiple image method exists in two dimensions only, rather than in three dimensions, we investigate the ER spectrum of the clustered colloidal particles in two dimensions, in which many cylindrical particles are randomly distributed in a sheet cluster. We report the dependence of the ER spectrum on the material parameters. It is shown that the multiple image method predicts two characteristic frequencies, at which the rotation speed reaches maximum. To this end, the multiple image method is numerically demonstrated to be in good agreement with the known Maxwell-Garnett approximation.     

像增强器的荧光屏亮度均匀性测试的校正法研究

像增强器荧光屏亮度均匀性参数是判断其性能好坏的一个重要技术指标。设计了一种测试系统来测试它的亮度均匀性参数。该系统利用标定过的具有均匀亮度的荧光屏(裸屏),以标准像增强器的图像作为标准来校正面源电子枪。由于校正后的面源电子枪仍然存在误差,所以具有均匀亮度的荧光屏(裸屏)的图像不可能是完全均匀的,呈现边缘暗中间亮。分析其图像的亮度曲线,建立校正函数,改变校正函数中的调节系数,直到计算机上显示出图像均匀为止,这时可得出系数确定的校正函数。首先利用校正后的电子枪轰击待测荧光屏,采集其图像,以确定的校正函数对其进行修正,然后观察由计算机显示出的图像是否均匀,从而判断待测荧光屏的均匀性。     

太赫兹波光谱特性分析

目前太赫兹技术的研究主要集中在它的产生、探测机理研究上。由于太赫兹波处于微波和可见光之间的频率范围,已有的微波和光波理论是否能适用于太赫兹波或者具有某些共同的特性仍需实验验证。通过实验分析验证了太赫兹波在空气介质中在垂直于传播方向的平面内场振幅是服从高斯函数分布的,测量给出了太赫兹波的能量分布图。根据测试数据推导出太赫兹波在空气介质中能量衰减公式,利用法布里-珀罗(F-P)干涉仪原理设计出太赫兹波长仪,对美国Corehent公司SIFIR-50THz太赫兹激光器发射的1～3THz波长进行了测量。讨论分析了远场发射角、光束入射角度、机械振动、温度波动和折射率n波动等相关因素对测量精度的影响。     

Effect of dielectrophoretic force in the self-assembly process of electrosprayed nanoparticles

In this work the effect of the dielectrophoretic force (DEP) in the self-assembly process of nanoparticles electrosprayed onto a substrate, is examined. DEP force is originated by the electric field created by the electrospray gun and by the distortion of the field created by the effective dipole of each nanoparticle. It is also shown that the modulus of this force is large when the distance between particles is few times its diameter, provided the medium is wet and the electric field is not switched off.The directional nature of DEP In this wet phase, is shown to chain nanoparticles aligned with the main electric field direction. Although there is a repulsive force between chains in the orthogonal direction to the field, it is minimum when the beads align with the voids in the nearby chains.DEP is a dominant force in the close distances of nanoparticles compared to double layer, van der Waals, electrophoretic retardation, weight and buoyancy.     

Some properties of the dissipative model of strain-gradient plasticity

A theoretical and computational investigation is carried out of a dissipative model of rate-independent strain-gradient plasticity and its regularisation. It is shown that the flow relation, when expressed in terms of the Cauchy stress, is necessarily global. The most convenient approach to formulating the flow relation is through the use of a dissipation function. It is shown, however, that the task of obtaining the dual version, in the form of a normality relation, is a complex one. A numerical investigation of problems in two space dimensions casts further light on the response using the dissipative theory in situations of non-proportional loading. The elastic gap, a feature reported in recent investigations, is observed in situations in which passivation has been imposed. The computational study indicates that the gap may be regarded as an efficient path between a load-deformation response corresponding to micro-free boundary conditions, and that corresponding to micro-hard boundary conditions, in which plastic strains are set equal to zero on all or part of the boundary.     

Measurement of small spin-spin splittings in the presence of chemical exchange: case of deuteriated water

A new implementation of a described data processing for measuring small scalar coupling constant J is proposed. It is applied particularly to situations where the coupling constant is around the linewidth at half-height, and in the presence of chemical exchange. This modified data processing uses only a simple "one-pulse" experiment instead of a series of spin echoes experiments required by the previous processing. The FID recorded in the one pulse experiment is used by a reconstitution program to generate a set of signals, which are analyzed in the time domain to obtain a spectrum where the scalar coupling constant is apparently multiplied by n+1, where n is positive. The new processing is tested with simulated spectra. The coupling constant between proton and deuterium is measured in the proton spectrum of a solution of 80% of D(2)O and 20% of H(2)O. It was found to be J=1.54+/-0.01 Hz.     

Comparison of the Parameters of the Exergoeconomic Environmental Analysis of Two Combined Cycles of Three Pressure Levels with and without Postcombustion

Nowadays, in Mexico, most of the installed electricity generation capacity corresponds to combined cycles, representing 37.1%. For this reason, it is important to maintain these cycles in good operating conditions, with the least environmental impacts. An exergoeconomic and environmental analysis is realized to compare the operation of the combined cycle, with and without postcombustion, with the comparison of exergoeconomic and environmental indicators. With the productive structure of the energy system, the process of formation of the final products and the residues are identified, and an allocation criterion is also used to impute the formation cost of residue to the productive components related to its formation. This criterion considers the irreversibilities generated in each productive component that participates in the formation of a residue. The compositions of pollutant gases emitted are obtained, and their environmental impact is determined. The unit exergoeconomic cost of the power output in the gas turbine is lower in the combined cycle with postcombustion, indicating greater efficiency in the process of obtaining this energy stream, and the environmental indicators of global warming, smog formation and acid rain formation are higher in the combined cycle with postcombustion, these differences being 5.22%, 5.53% and 5.30%, respectively.     

Characterization of size effect of natural convection in melting process of phase change material in square cavity

The accelerating effect of natural convection on the melting of phase change material(PCM) has been extensively demonstrated. However, such an influence is directly dependent on the size and shape of domain in which phase change happens, and how to quantitatively describe such an influence is still challenging. On the other hand, the simulation of natural convection process is considerably difficult, involving complex fluid flow in a region changing with time, and is typically not operable in practice. To overcome these obstacles, the present study aims to quantitatively investigate the size effect of natural convection in the melting process of PCM paraffin filled in a square latent heat storage system through experiment and simulation, and ultimately a correlation equation to represent its contribution is proposed. Firstly, the paraffin melting experiment is conducted to validate the two-dimensional finite element model based on the enthalpy method.Subsequently, a comprehensive investigation is performed numerically for various domain sizes. The results show that the melting behavior of paraffin is dominated by the thermal convection. When the melting time exceeds 50 s, a whirlpoor flow caused by natural convection appears in the upper liquid phase region close to the heating wall, and then its influencing range gradually increases to accelerate the melting of paraffin. However, its intensity gradually decreases as the distance between the melting front and the heating wall increases. Besides, it is found that the correlation between the total melting time and the domain size approximately exhibits a power law. When the domain size is less than 2 mm, the accelerating effect of natural convection becomes very weak and can be ignored in practice. Moreover, in order to simplify the complex calculation of natural convection, the equivalent thermal conductivity concept is proposed to include the contribution of natural convection to the total melting time, and an empirical correlation is given for engineering applications.     

A phase-field study of the aluminizing of nickel

A quantitative phase-field approach for multiphase systems that is based upon CALPHAD free energies is used to model the aluminization of nickel wires, wherein vapour-phase alloying is used to deposit Al on the surface of the Ni wire and then the wire is annealed so that to remove all Al gradients and achieve a homogenous Ni-Al alloy. Both processes are modelled and numerical results are compared with experiments. It is found that the kinetics of both processes is controlled by bulk diffusion. During aluminization at 1273 K, formation and growth of intermetallics, Ni₂Al₃ NiAl and Ni₃Al, are strongly dependent on the Al content in the vapour phase. Ni₂Al₃ growth is very fast compared with NiAl and Ni₃Al. It is also found that an intermediate Al content in the vapour phase is preferable for aluminization, since the Ni₂Al₃ coating thickness is difficult to control. Ni₂Al₃ is found to disappear in a few minutes during homogenization at 1373 K. Thereafter, the NiAl phase, in which the composition is highly non-uniform after aluminization, continues growing until the supersaturation in this phase vanishes. Then, NiAl coating disappears concomitantly with the growth of Ni₃Al, which disappears thereafter. Finally, the Al concentration profile in Ni(Al) homogenizes.