“PPAS” X-RAY ABSORPTION SPECTROSCOPY IN LASER-PRODUCED ALUMINUM PLASMA

We have developed and successfully demonstrated the "point projection absorption spectroscopy (hereafter abbreviated to PPAS)" technique to record keV X-ray absorption spectra in the coronal region of laser produced aluminum plasma which provides spatial information in the corona. Absorption spectrum of the Al Ⅻ 1s²-1s2p resonant line for time delays up to 250, 500 and 750 ps after the peak of the incident laser pulse have been observed. Analysis of an absorption spectrum should allow a high spatial resolution (< 25μm) history of the absorbing ion population density to be determined. The 1-D hydro-code JB19 has been used to simulate the experiment and the predictions are compared to the observations. Such comparison can be useful in validating parts of the codes used for gain prediction on recombination X-ray laser transitions.     

INVESTIGATION OF ULTRASONIC RELAXATION ABSORPTION IN MOLECULAR CRYSTALS

The general formulation of ultrasonic absorption in a relaxation medium is discussed in thispaper.By taking account of transitions between all neighbouring energy levels of internal oscilla-tors a new calculation of ultrasonic absorption coefficients in molecular crystals is given.Ultrasonicabsorption coefficents for crytalline naphthalene are estimatd for different temperatures in termsof improved theory.Good agreement is found between the predicted values and experimental resultson the temperature dependence of the absorption coefficient.     

INVESTIGATION OF BONDING IN NANO—SiO2 BY Si L2，3 X—RAY ABSORPTION NEAR—EDGE STRUCTURE SPECTROSCOPY

The Si L2,3 X-ray absorption near-edge structure(XANES) can be used to probe the local structure around Si and derive electronic information of the unoccupied s- and d-like partial density of states in nano-size SiO2.We present Si L2,3-edge for three different size silicates acquired by total electron yield(TEY) at the photoemission atation of Beijing Synchrotron Radiation Facility (BSRF).The Si L2,3-edge spectra are interpreted based on ab initio full multiple-scattering(MS) calculation.The Si L2,3-edge of nano-size materials has XANES similar to that of α-quartz.The similarities between the Si L2,3-edge shapes attest to a common molecular-orbital picture of their Si-O bonding and the same coordination state.However,a considerable broadening of Si L2,3-edge XANES spectra as decrease of particle size is also an indicative of polyhedral distortions.     

INVESTIGATION OF THE MECHANISM OF SOUND ABSORPTION BY THE BORIC ACID RELAXATION IN SEA WATER

The dependencies of the relaxation frequency and the maximum absorption per wavelength ofboric acid relaxation on B(OH)_3 and NaHCO_3 concentrations were obtained by the cylindrical resona-tor method.The experimental results may be explained by an apparent one-step process:Theory and experimental results show that the effects of calcium on the relaxation parameters of boricacid relaxation can be interpreted by a coupled-reaction system,which is equivalent to that apparentone-step process,including all the ion association reactions.     

STRESS ANALYSIS IN CUBIC BORON NITRIDE FILMS BY X-RAY DIFFRACTION USING sin2 ψ METHOD

The boron nitride (BN) films containing cubic boron nitride (c-BN) and hexagonal boron nitride (h-BN) were prepared by radio frequency a ssisted thermal filament chemical vapor deposition. The stress and strain in BN films were investigated by X-ray diffraction analysis using the sin² ψ method. The results showed that both c-BN and h-BN in the same film have similar values of elastic strain, however, the compressive stress in c-BN is much greater than that in h-BN for the same film. Both stress and strain gradually decre ased with the increase of substrate temperature (T_s). The effective stress in the films calculated by the effective stress model increased with the increase of T_s. Furthermore, the dependence of effective stress in the films on T_s was also investigated.     

EDGE REYNOLDS STRESS STRUCTURE OF LOWER HYBRID WAVE INJECTION IN THE HL—1M PLASMA

The radial profiles of electrostatic Reynolds stress,plasma poloidal rotations,radial and poloidal electric fields have been measured in the plasma boundary region on the HL-1M tokamak using a multi-array of Mach/Langmuir probes.During experiments of lower hybrid wave current drive,the variations in LHW drive power xill cause changes in the edge electric field,poloidal rotation veloity and Reynolds stress.The results indicate that sheared poloidal flow can be generated in the edge plasma due to radially varied Reynolds stress.     

“TIME ARROW” IN WAVE-PACKET EVOLUTION

Availability of short, femtosecond laser pulses has recently made feasible the probing of phases in an atomic or molecular wave-packet (superposition of energy eigenstates). With short duration excitations the initial form of the wave-packet is an essentially real doorway state, and this develops phases for each of its component amplitudes as it evolves. It is suggested that these phases are hallmarks of a time arrow and irreversibility that are inherent in the quantum mechanical processes of preparation and evolution. To display the non-triviality of the result, we show under what conditions it would not hold; to discuss its truth, we consider some apparent contradictions. We propose that (in time-reversal invariant systems) the preparation of initially complex wave-packets needs finite times to complete, i.e., is not instantaneous.     

STRESS ANALYSIS IN CUBIC BORON NITRIDE FILMS BY X-RAY DIFFRACTION USING sin2 ψ METHOD

The boron nitride (BN) films containing cubic boron nitride (c-BN) and hexagonal boron nitride (h-BN) were prepared by radio frequency a ssisted thermal filament chemical vapor deposition. The stress and strain in BN films were investigated by X-ray diffraction analysis using the sin² ψ method. The results showed that both c-BN and h-BN in the same film have similar values of elastic strain, however, the compressive stress in c-BN is much greater than that in h-BN for the same film. Both stress and strain gradually decre ased with the increase of substrate temperature (T_s). The effective stress in the films calculated by the effective stress model increased with the increase of T_s. Furthermore, the dependence of effective stress in the films on T_s was also investigated.     

THE SU(6) “UNITARY ENERGY BAND” STRUCTURE IN THE TRIBARYON SYSTEM

A picture of the tribaryon system is proposed based on the papers [1—3]. It is considered that proton, neutron and A hyperon from the basic particles of SU(3) group and form the basic particles of SU(6) group on account for spin. It turns out that there exist "unitary energy band" structure in the tribaryon system. From the mass formula of T₃³ breaking, one can find that the SU(6) symmetry gives the mass relations between different spin levels of the same strangeness analog states. Finally, simple calculations are made and tbere is no discrepancy between tbe results and the experimental data.     

以“ 做”促“ 思”

物理解题是有些学生很头痛的问题, 这些学生拿到一道题目有的无从下手, 有的瞎做一气, 有的思路正 确动手做了就错, 有的只能做出一半 …… 怎样才能让这些学生找到正确的思路呢? 如何帮助这些学生更好地解决 问题, 养成良好的解题习惯呢?     

从“教学”到“导学”

1大学生学习方式的现状及不足 中国地质大学刘杰,庞岚所作的有关调查显示：在约1500名被调查学生中,课程经常需要重修的占13．89％,偶尔重修和重修课程没超过两门的学生有28．29％和27．93％,这三项加在一起是70．11％．照此推算,全校大约超过70％的学生都有重修课程的经历．大学生目前学习的状况不容乐观．究其原因,学生们主要把它归结为自身的学习兴趣或对专业的兴趣等方面．但相关的调查结果显示,学生对学习的精力投入不足才是主要原因,包括不上课、不做作业、课余不学习、没有学习计划以及没有养成良好的学习习惯等．     

CALCULATION OF THE ELASTIC-SCATTERING CROSS-SECTION OF ENERGETIC ELECTRON BY 40Ca NUCLEUS IN CONSIDERATION OF THE INFLUENCE OF“PION CONDENSATION”

Using Migdal's theoretical results of "pion Condensation", the influence of "π condensation" on the distribution of charge of N=Z nucleus is determined. The elastic-scattering differential cross-section of energetic electron by ⁴⁰Ca nucleus is also calculated. The results of our calculations agree better with the experimental data.     

四、“光学”和“原子结构”

光学一、教材的系统和重点本编内容可分为光度学、几何光学和物理光学三部分。所谓光度学,是指从事光流的测量以及测定光现象中的定量特性的知识。课本中则只阐述了一些简单光度量的概念。在几何光学中,是从观察光在两种媒质界面上的光现象开始,再分开来研究反射现象和折射现象中存在的规律以至光路控制的原理和光学仪器。     

光速的“不变”和“变”

光速不变原理是狭义相对论的重要物理基础,也是整个现代物理学中具有重大影响的基本原理之一．对光速不变原理的深入讨论和进一步的实验验证,无疑将产生广泛而深远的影响．自然科学是相对真理,光速不变原理当然也不例外,即一方面它包含有绝对真理的成份,因而它确能具有广泛的适用范围．但同时它又是相对的、近似的、有条件的．因此,对光速不变原理的正确性的简单否定或绝对化,都是不对的．一、光速的不变性光迹不变原理?...     

始于“集邮”,终于“思想”

物理学研究虽然要从研究一个个自然现象,进行知识点"集邮"开始,但追求的是"思维经济",追求利用简单的规律来描述复杂的世界。学习物理虽亦始于"集邮"但不能终于"集邮",而要重视思维方式的训练与建构。     

用GeoGebra模拟“月相”和“人像”

利用GeoGebra的3D视图功能解决从不同视角观察被平行光照射的球体问题.     

A STUDY OF RAMAN SCATTERING AND INFRARED ABSORPTION SPECTRUM IN A NEW SERIES OF MERCURY-BASED HIGH-Tc SUPERCONDUCTOR (Hg,Mo)Sr2(Y1-xCax)Cu2O6+δ

Lattice vibrations of the (Hg,Mo)Sr₂(Y_1-xCa_x)Cu₂O_6+δ—a new series of mercury-based high-T_c superconductor are analyzed with the aid ofgroup theory. The vibrations of species are given. They are 4A_1g+ B_1g+ 5E_g+ 7A_2u + B_2u+ 8E_u. The 4A_1g, B_1g and 5E_g modes are Ramma active, the 6A_2u and 7E_u are infrared active. Phonon vibration characteristics of the samples are studied using Raman scattering and infrared absorption spectra. The experimental results show that the typical phonon vibrational modes appear mainly at 145, 320, 440, 578, 592 and 645cm^-1, The intensities of the 145, 320, 440, 578 and 645 peaks decrease with increasing Ca content x and the position of 645 peak moves to higher wavenumber slightly. In this article, the phonan modes are assigned and their variation behavior with increasing Ca content x are discussed.     

物理学中的“场”和“理想模型”

一物理学中＂场＂的概念桌子、黑板、房、树木……都是由分子、原子组成的,而分子、原子又是由电子、质子、中子等基本粒子组成的.这些实物都是物质.物质是客观存在的,能作用于我们的感觉器官而引起感觉的东西.在我们周围的物质世界里,