Kinetic Approach to Long time Behavior of Linearized Fast Diffusion Equations

We show that the rate of convergence towards the self-similar solution of certain linearized versions of the fast diffusion equation can be related to the number of moments of the initial datum that are equal to the moments of the self-similar solution at a fixed time. As a consequence, we find an improved rate of convergence to self-similarity in terms of a Fourier based distance between two solutions. The results are based on the asymptotic equivalence of a collisional kinetic model of Boltzmann type with a linear Fokker-Planck equation with nonconstant coefficients, and make use of methods first applied to the reckoning of the rate of convergence towards equilibrium for the spatially homogeneous Boltzmann equation for Maxwell molecules.     

Estimation of the production frequencies for manufacturing systems

Email: dimitri.lefebvre{at}utbm.fr This work deals with the production frequencies estimation formanufacturing systems by measurement of the buffers content.The considered systems are modelled by continuous Petri nets.The estimation problem has exact and approximated solutionsthat are described. In the case of approximated solutions, theestimation error is also valued. At last, when the set of solutionscontains several elements, the Petri net evolution equationis completed to give one unique solution.     

Ruggedized digital holographic data storage with fast access

Recent investigations in holographic mass memory systems have produced proof-of-concept demonstrations that have highlighted their potential for providing unprecedented capacity, data transfer rates and fast random access performance (Heanue et al. 1994; Hong et al. 1995; Psaltis and Mok 1995; Bernal et al. 1996; McMichael et al. 1996). The exploratory nature of most such investigations has been largely confined to benchtop experiments which have ignored the practical constraints of packaging and environmental concerns. We have embarked on an effort to demonstrate the holographic mass memory concept by developing a compact prototype system geared for avionics and similar applications which demand the following features (mostly interdependent factors): (1) solid state design (no moving parts), (2) fast data seek time, (3) robust with respect to environmental factors (temperature, vibration, shock). In this paper, we report on the development and demonstration of two systems, one with 100 MB and the other with more than 1 GB of storage capacity. Both systems feature solid state design with the addressing mechanism realized with acoustooptic deflectors that are capable of better than 50 sec data seek time. Since the basic designs for the two systems are similar, we describe only the larger system in detail. The operation of the smaller system has been demonstrated in various environments including hand-held operation and thermal/mechanical shock; a photograph of the smaller system is provided, as well as actual digital data retrieved from the same system.     

Low-frequency molecular dynamics studied by spin-lock field cycling imaging

Spin-lock adiabatic field cycling imaging (SLOAFI) relaxometry was shown to be a useful technique for obtaining a fast study of spin-lattice relaxation dispersion in the rotating frame. The aim of the present article is to describe some technical aspects of the experiment in more detail, while showing simple examples that can be compared with laboratory frame relaxation. We also present here a general discussion of the equations for an off-resonance experiment used to analyze low-frequency molecular dynamics.     

Calculation of transient dynamic stress intensity factors at bimaterial interface cracks using a SBFEM-based frequency-domain approach

A frequency-domain approach based on the semi-analytical scaled boundary finite element method (SBFEM) was developed to calculate dynamic stress intensity factors (DSIFs) at bimaterial interface cracks subjected to transient loading. Because the stress solutions of the SBFEM in the frequency domain are analytical in the radial direction, and the complex stress singularity at the bimaterial interface crack tip is explicitly represented in the stress solutions, the mixed-mode DSIFs were calculated directly by definition. The complex frequency-response functions of DSIFs were then used by the fast Fourier transform (FFT) and the inverse FFT to calculate time histories of DSIFs. A benchmark example was modelled. Good results were obtained by modelling the example with a small number of degrees of freedom due to the semi-analytical nature of the SBFEM. Supported by the Scientific Research Foundation for the Returned Overseas Chinese Scholars, Ministry of Education of China (Grant No. J20050924) and the Australian Research Council Discovery Project (Grant No. DP0452681)     

Fast Room Temperature Detection of State of Circular Polarization of Terahertz Radiation

We report on a room temperature detector which allows to determine and monitor the state of polarization of terahertz radiation with picosecond temporal resolution. The detector is based on the circular photogalvanic effect recently observed in GaAs/AlGaAs quantum wells. The circular photogalvanic effect yields in response to elliptically polarized radiation a current signal proportional to the degree of circular polarization. The peak current signal occurs in unbiased samples for circular polarization, vanishes at linear polarization and changes sign by switching the helicity from right-handed to left-handed. The detector consists of a (113)A MBE grown pGaAs/AlGaAs multiple quantum well structure. The response has been measured in the wavelength range between 76 m and 280 m at normal incidence of the radiation on the sample.     

Relativistic second-harmonic generation in a laser-produced plasma

Summary In this paper the relativistic second-harmonic generation of a high-power laser radiation in a laser-produced plasma has been studied theoretically in the presence of a self-generated magnetic field. The relativistic Vlasov equation has been employed for the nonlinear response of the electrons in the hot magnetized plasma. It is observed that the power conversion efficiency of the generated second harmonic wave is much higher for relativistic calculations than that for nonrelativistic calculations. To speed up publication, the authors of this paper have agreed to not receive the proofs for correction.     

快中子在Li核上的弹性散射微分截面

用伴随粒子飞行时间法测量了14.7MeV中子在⁶Li和⁷Li核上的弹性散射截面,并用蒙特卡罗方法对中子在样品中的通量衰减、多次散射作了修正.本文工作与他人工作以及理论数据作了比较.给出了截面的勒让德系数;截面实验点总误差在10%到15%之间,其中统计误差为1%-5%.     

新型超快速三角波脉冲电路的研究

本文讨论了一种新型三角波脉冲发生器,此脉冲发生器是由雪崩晶体管作为开关器件,产生出的三角波脉冲半宽度为3.5ns,上升时间最快达2ns,幅值为±1300V,电路的延迟时间为8.3us。     

Synthesis of 1-lyso-2-palmitoyl-rac-glycero-3-phosphocholine and its regioisomers and structural elucidation by NMR spectroscopy and FAB tandem mass spectrometry

Three regioisomers of a naturally occurring lysophosphatidylcholine were chemically synthesized from glycerol. The phosphocholine moiety of the molecule was introduced by sequentially reacting with ethylene chlorophosphite, bromine, water, and trimethyl amine. Removal of a silyl protecting group of the hydroxyl group in the glycerol backbone was achieved without any accompanying acyl migration in the final stage of the synthesis by using NBS in a dimethyl sulfoxide-water cosolvent system. Structures of all regioisomers were compared by NMR spectroscopy and FAB tandem mass spectrometry.