七年级电功及电功率的学习

关于电功及电功率的教材,在与学习苏联电力化的物理原理有关的知识范围中,占有重要的地位。这些概念的理解、关于它们的量度单位的清楚的观念以及进行有关的简单计算的技能应该是综合技术教育的必要组成部分。可惜,在七年级的物理教科书中,这个学习材料的叙述是形式的、干燥的、很简单的,并且从     

超声波及其应用

超声就是普通的弹性介质的机械扳动,这种振动以一定的速度传播并且具有一定的能量。超声波——是介质的互相更替的稠密和稀疏。超声的传播速度与介质的弹性和介质的密度有关。超声波的波长,也和普通的声波一样,决定于两相隣的稠密或稀疏之间的距离。超声频率的下限     

大气的激光监测

在人口稠密的工业区,大气污染已成为严重的问题,研究污染物以及它们和大气组分的反应已成为迫切的需要了.为了预示与日俱增的污染源对环境的影响和采取及时而有效的措施,需要建立大气的数学模型.这些模型的发展、完善和与之相关的连续监测,要求具有广泛的监测功能. 地球上的生命不仅直接或间接地受近地面的大气组分的影响,而且还受到平流层及平流层以上的大气组分的影响.要用合理的成本来恰当地监测这广阔的区域,为此激光监测是唯一可能提供这种功能的技术. 一、大气遥感技术的特点 激光器的发现促进了人们对物质的非线性特性的研究,以及关…     

开放教学资源下新的教学方式的探讨与尝试

网络时代信息是开放的、共享的和丰富的.网络时代的学习有其自身的特点.作为教育者,我们应该从教学的各个环节作出相应的改变,使我们的教学更加适应时代的发展,从而达到"授之以渔"的教育境界.基于这样的认识,我们在双语物理课的教学中有步骤地指导学生借助互联网上公开的、丰富的信息和学习资源进行课程的学习和课题研究.结果表明这种尝试极大地提高了学生的自我学习的能力和学习兴趣,起到了事半功倍的作用,弥补了课堂教学的不足.     

一种基于迈斯纳效应的超导电机的驱动力的计算

超导体的迈斯纳效应是超导体的特有的性质之一,超导驱动的电机正是利用超导体的这个性质而设计的一种新型电机,由于驱动原理与传统的电机有很大的不同,这种电机的驱动力的计算一直是这种超导电机设计中要解决的主要问题,针对一种结构的电机,利用理论分析和数值计算的方法计算了一种基于超导体迈斯纳效应的超导电机驱动力的大小,为这种电机的设计提供了主要依据。     

寂静地震与地震预测的物理问题

寂静地震是指发生了缓慢的位错、但几乎不辐射地震波的“地震” .在目前的地震预测的物理学研究中 ,通常是通过计算历史上曾经发生过的地震所引起的应力变化 ,或者通过研究地震活动的统计性质或“图像动力学” ,来推测一个断层带上发生地震的危险性 .寂静地震的信息的缺失 ,形成了地震预测的物理学研究中的一个很大的“盲区” ,而在相当程度上 ,解决地震预测的物理问题的主要困难和可能的突破的希望 ,也许就在于此 .寂静地震的研究目前还很不深入 .关于寂静地震的性质 ,文章作者提出两个猜想 :(1)寂静地震的频度 ,满足类似于GR定律的幂律分布 ;(2 )最大的寂静地震的地震矩 ,与“可见”的最大地震的地震矩相当 .     

物理学和天文学

历史上，物理学和天文学的发展是密切联系的。它们在整个现代科学的发展和技术的发达上起到了先锋的作用。物理学的基本规律和天文学提供的广亵的实验室构成了理想的科学发展的基础。20世纪的一系列科学上的重要突破正是这种优良结合的产物。今天，天文学和物理学又共同面对着更新的前测问题，并一道酝酿着新的科学上的重大进展。它们所取得的每一个进展也必然伴随着技术的创新和提高，也不断更新着人类的认识和文明。     

时间,计时标准和原子时钟

一、时间和它的标准问题在这星球土发展、生存和繁衍的人类,他们起始有时间观念恐怕不比有空间的观念来得迟。这种时间观念存在的表现有时是非常自然的。人是生存在三维空间里的,但是人类思维的发展是动的,辩证地开展的,是四维空间的。人类对于时间的感觉,是从因时而异的物质变化而觉察得的。最简单的物质的变化是一种物体的运动。不要以为颐和园门前的铜狮是     

基于低维相变薄膜的显示器件光学性质的研究

采用传输矩阵模型研究了基于低维相变薄膜的显示器件的光学特性与器件结构的关系。显示器件的类型有反射型和透射型,器件结构的关键参数包括Ge_2Sb_2Te_5(GST)层的厚度、ITO层的厚度、GST层的晶态与非晶态的变化。结果表明:对于反射型器件,ITO层的厚度对器件的反射光谱影响较大,可以通过改变ITO层的厚度达到改变器件颜色的效果;GST层的厚度为12 nm时,GST的晶态与非晶态的变化使器件有最好的颜色对比度且消耗较低的电功率。对于透射型器件,通过使用超薄的GST薄膜,器件的透明度可以保持很高,器件的透明度在GST的厚度超过几纳米后迅速下降。     

赝标Goldstone玻色子的手征拉氏量的 Gasser-Leutwyler系数

基于我们提出的参数化的完全穿衣服的夸克传播子,我们预言了未知的赝标Goldstone玻色子的手征拉氏量的Gasser-Leutwyler系数Li。预言的G-L系的数值与在文献中广泛应用的经验值和其他许多具有QCD特征的理论模型所预言的值一致。说明参数化的夸克传播子的适用性和可靠性。     

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.