"光子"与"光子学"

19世纪末普朗克在推导黑体辐射公式的过程中,假定物体在发射和吸收辐射时能量是不连续的,是呈现与辐射频率v成正比例的最小能量单位ε=hv的整数倍变化的,这个能量元ε称为能量子．普朗克所提出的“能量子”假说,冲破了经典物理学中的一切自然过程都是连续的这一原理,标志着人类对客观世界物     

谈"速度"与"速率"

一 高教出版社出版的中专《物理》教材(王银明主编1999年版)第40页中有这样一道题: 2-3-1关于匀速运动的特点,下列说法中正确的是: A.运动轨迹是直线 B.运动方向不变 C.运动速率不变 D.运动速度是常量     

物理"海马"、数学"海马"与生物"海马"

在C60-TCNQ(一种有机分子名称的缩写)和纯的TCNQ有机分子薄膜中,文章作者得到了一种形似海洋中生存的动物海马的图案结构,取名为"海马"分形结构.这种"海马"图案在旋转180度时具有近似的对称性,但是不同于简单的二维反转对称.在数学中用复变函数的多项式,通过Julia对复杂空间中函数的纯粹数学映射(即z→z2 c,其中c=-0.74543 0.1130i),也能模拟出相似的"海马"图案.对于"海马"分形,文章作者提出如下的一种形成机制,即:在薄膜形成初期过程中,中性分子或团簇中存在部分荷电粒子,由于库仑排斥作用,成核和生长过程中会形成对称性破缺,最终形成"海马"状分形."海马"的有趣图案,加深了人们对自然与科学统一的认识,激发了人们对自然本源的探索激情.     

"验证机械能守恒定律"实验中的"八项注意"

验证机械能守恒定律这个实验,是高中物理实验中十分重要的实验,因为它是“打点计时器的使用“、“长度的测量“、“运动学规律“、“能量的不同形式及其转化“等的综合应用,对培养学生动手能力,分析判断能力,综合能力都十分有益,并且在近几年来的高考中也时常出现本实验中的题目.为能够顺利完成并熟练掌握本实验,笔者总结出“八项注意“,望能引起注意.……     

浅议"对称"

世界是丰富多彩、千差万别的．但众多的物理大师们却说：一切事物规律都是“对称的”．在物理思想中，对称性像基石似的重要．各种事物都具有对称性，它常表现在两个方面，一是体现在物理规律中的对称性；如伽利略相对原理；爱因斯坦相对论；宇称原理等．另一个是体现在数学形态上的对称性．如镜像对称；旋转对称等．本文将浅议一下物理学中的对称．     

网络"建筑学"

复杂网络系统普遍地存在于自然界与人类社会中，对它们的研究也具有广泛而重要的意义．我们如何来认识和区分晶格、Internet和一个生态食物链?它们又是如何演化的?在这些网络背后，是否隐藏着某种无形的组织原理?近年来，借助强大的计算工具，人们对网络的认识发生了巨大的改变，文章以小世界、集团化和无标度等新的概念为中心，介绍了其中的研究进展．     

正确理解"电势能"

在“电势能”的教学中，本人结合多年来教学经验，在教学内容的编排和教学方法上作了一些探讨。     

浅说"混沌"

以单摆的强迫阻尼运动、罗伦兹系统及Ｌｏｇｉｓｔｉｃ映射为例,解说了混沌运动地主要特征,并介绍了混沌理论建立与与发展过程中的一些史话。     

"三步曲"巧解"有界磁场"粒子偏转运动

通过整合"有界磁场"带电粒子运动轨迹中的弦角关系以及溯源它的动量变化,找出"3个关系"来处理粒子运动的相关问题,可以省去轨迹圆绘图的烦扰.     

A study on the best irradiation dose of X-ray for Hep-2 cells by Fourier transform infrared spectroscopy

Fourier transform infrared spectroscopy (FTIR) was employed to study the human epidermis larynx carcinoma cell lines (Hep-2) which were irradiated by different doses of X-ray.The results show that (1) the irradiation of X-ray damages the structure of the CH3 groups of the thymine in DNA,which restrains the reproduction of Hep-2 cells effectively,(2) the 8 Gy dose of X-ray irradiation changes the framework and the relative contents of some proteins,lipids and the nucleic acid molecules intercellular in the greatest degree,and (3) the 8 Gy dose of X-ray irradiation is the best irradiation dose for lowering the degree of the cancerization of Hep-2 cells according to the criteria for the degree of the cancerization reported recently.Meanwhile,the apoptosis of these cells were detected by using flow cytometry (FCM) primarily.It shows that the apoptotic ratio of the Hep-2 cells depends on the irradiation dose to some extent,but is not linearly.And the apoptotic ratio of the 12 Gy dose group is the maximum (20.36%),but the apoptotic ratios of the 2 to 8 Gy dose groups change little.     

Modification to first-order Born approximation for improved prediction of scattered sound from weakly scattering objects

When deriving the Fourier diffraction theorem based on the first-order Born approximation,the difference between wave number of the scattering object and that of the surrounding medium is ignored,causing substantial errors in sound scattering prediction.This paper modifies the Born approximation by taking into account the amplitude and phase changes between the scattering object and the water due to the wave number difference.By changing the radius and center position of the sampling circle in the Fourier domain,accuracy of the predicted sound scattering is improved.With the modified Born approximation,the computed far-field directional pattern of the scattered sound from a circular cylinder is in good agreement with the rigorous solution.Numerical calculations for several objects with different shapes are used to show applicability and effectiveness of the proposed method.     

Study on the radiation problem caused by electron beam loss in accelerator tubes

The beam dynamic code PARMELA was used to simulate the transportation process of accelerating electrons in S-band SW linacs with different energies of 2.5, 6 and 20 MeV. The results indicated that in the ideal condition, the percentage of electron beam loss was 50% in accelerator tubes. Also we calculated the spectrum, the location and angular distribution of the lost electrons. Calculation performed by Monte Carlo code MCNP demonstrated that the radiation distribution of lost electrons was nearly uniform along the tube axis, the angular distributions of the radiation dose rates of the three tubes were similar, and the highest leaking dose was at the angle of 160° with respect to the axis. The lower the energy of the accelerator, the higher the radiation relative leakage. For the 2.5 MeV accelerator, the maximum dose rate reached 5% of the main dose and the one on the head of the electron gun was 1%, both of which did not meet the eligible protection requirement for accelerators. We adopted different shielding designs for different accelerators. The simulated result showed that the shielded radiation leaking dose rates fulfilled the requirement.     

Fiber Modal Index Measurements Based on Fiber Gratings

A novel method based on fiber gratings for measuring the effective indices of fiber modes is proposed. The effective index difference between the core mode and a cladding mode was obtained by analyzing the interference fringe of a pair of cascaded long-period fiber gratings. In order to extract the core mode index from the measured index difference, an index matching oil immersion method is proposed. By analyzing the interaction between the cladding mode and the oil applied on the cladding surface, the mode order and the effective index of the involved cladding mode might be calculated. Experimental results about the interference fringe shifts induced by the oil index and the oil-applied length are also presented.     

Factors affecting the spectrum of an electromagnetic light wave on scattering from a semisoft boundary medium

The spectrum of an electromagnetic light wave on scattering from a semisoft boundary medium is discussed within the accuracy of the first-order Born approximation. It is shown that spectral shifts and spectral switches are affected both by the polarization of the incident light wave and by the characters of the scat-tering medium. Moreover, numerical results show that the direction at which the spectral switch occurs is governed by the characters of the scattering medium, whereas the magnitude of the spectral switch is affected by the polarization of the incident light wave.     

Temperature Sensitivity Control and Mechanical Stress Effect of Boron-Doped Long-Period Fiber Gratings

We will present in this work the quantitative analysis of the relationship between the doping concentrations of GeO 2 and B 2 O 3 in the core and cladding regions and the temperature sensitivity of the resonance wavelength shift in long-period fiber gratings (LPFGs). Based on this analysis, the temperature sensitivity was suppressed and enhanced to 0.002 nm/°C and 0.28 nm/°C, respectively. We will also discuss the effect of the residual mechanical stress on the optical and mechanical properties of LPFGs. In particular, we will present the measurement results of the dependence of the refractive index change and mechanical strength on the residual mechanical stress in the boron-doped fibers with depressed clad and matched clad.     

Resonance scattering of canonical elastic shells in absorbing fluid medium

Resonance scattering of elastic spherical shell and cylindrical shell while the surrounding fluid medium has absorption is studied. The normal mode solution derived using exact elastic theory and the separation of variables is still applicable. However, the scattering form function has to be modified for the absorbing medium, otherwise the unreasonable result would be obtained. The backscattering form function in the absorbing medium is redefined, and the form function of elastic spherical and cylindrical shell with vacuum or solid matter filled is calculated in various absorption conditions. The results show that the absorption of surrounding fluid leads to notable attenuation of the coincidence resonances in the mid-frequency, but it has a little influence on the low-frequency resonance scattering induced by the filler inside the shell.     

Exploitation of the Fiber Capacity in Optical Networks Using Time, Frequency, and Space Division Multiple Accesses

In this work we investigate how to obtain very high capacity transmissions in optical networks taking into account the limitations due to the physical channel. We consider both the case in which all the users are connected by a star coupler and the case in which the users are directly connected by the network topology. As a reference, we consider a ring network and a Shuffle Multihop Network (SMN). The use of optical systems to implement high-capacity networks is numerically investi gated by means of numerical simulations taking into consideration the channel limitations due to the chromatic dispersion, the Kerr effect, and the amplified spontaneous emission (ASE) noise of the optical amplifiers. In our model, we consider that the signal, during the routing process that is performed at the user position, undergoes only an attenuation. We suppose the use of intensity modulated signals and receivers with direct detection. Packet switching and digital transmission are assumed with soliton and conventional nonreturn to zero signals. Both wave length and time division multiple accesses are considered. The results show that, in the case of the Time Division Multiple Access (TDMA) technique, the use of a star coupler to connect the users reduces the capacity of a network with respect to the case in which a direct connection of the users is used. This is due to the strong power fluctuations that are present during the signal propagation and to the large quantity of accumulated ASE noise. On the other hand, the use of a star coupler shows the advantage to being easily reconfigurable. The Wavelength Divison Multiple Access (WDMA) technique permits us to achieve higher capacities with respect to the TDMA. This is due to the fact that in the propagation conditions, due to the presence of a star coupler, high bit rate signals are strongly degraded. On the other hand, several low bit rate signals operating at different wavelengths can propagate with a low power level, avoiding strong degradation due to the Four Wave Mixing (FWM) effect. Among the topologies considered in this work, the SMN is the one that generally permits us to reach the highest throughput because in the SMN the signal hops in a limited number of Network Interface Units (NIUs) before reaching the final destination.     

Time domain finite volume method for the transient response and natural characteristics of structural-acoustic coupling in an enclosed cavity

A time domain finite volume method（TDFVM）based on wave theory is developed to analyze the transient response and natural characteristics of structural-acoustic coupling problems in an enclosed cavity.In the present method,the elastic dynamic equations and acoustic equation in heterogeneous medium are solved in solid domains and fluid domains respectively.The structural-acoustic coupling is implemented according to the continuity condition of the particle velocity along the normal direction and the normal traction equilibrium condition on the interface.Several numerical examples are presented to validate the effectiveness and accuracy of the present TDFVM.Then the effects of water depth on the acoustic and vibration characteristics and the natural characteristics of a structural-acoustic coupling system are analyzed.The numerical results show that the increase of water depth leads to a stronger coupling between the water and structure and the decrease of natural frequencies of coupling system,The computational cost and memory of this method are small and it can be applicable to structural-acoustic coupling problems in the heterogeneous fluid.     

Influences of SiO2 protective layers and annealing on the laser-induced damage threshold of Ta2O5 films

Ta2O5 films are prepared on BK7 substrates with conventional electron beam evaporation deposition.The effects of SiO2 protective layers and annealing on the laser-induced damage threshold (LIDT) of the films are investigated.The results show that SiO2 protective layers exert little influence on the electric field intensity(EFI)distribution,microstructure and microdefect density but increase the absorption slightly.Annealing iS effective on decreasing the microdefect density and the absorption of the films.Both SiO2 protective layers and annealing are beneficial to the damage resistance of the films and the latter is more effective to improve the LIDT.Moreover,the maximal LIDT of Ta2O5 films is achieved by the combination of SiO2 protective layers and annealing.