邮票上的物理学史⑨--牛顿

"牛顿由于发现了万有引力定律而创立了科学的天文学,由于进行了光的分解而创立了科学的光学,由于建立了二项式定律和无穷理论而创立了科学的数学,由于认识了力的本性而创立了科学的力学."恩格斯的这段话很好地总结了牛顿的科学业绩.为了纪念牛顿在科学上的伟大建树,许多国家发行了多枚一套的邮票.     

物理实验开放式教学初探

网上预约实验实现了各校区资源共享、教学内容有弹性满足了不同层次学生的需求，开放式教学增强了教师的责任心，激发了学生学习的主动性和积极性，提高了实验教学质量，充分利用了实验室的资源，取得了较好的效果。     

自由落体实验的改进

针对教材中自由落体实验操作的不稳定性,改进了实验,增强了实验操作的稳定性,提高了实验的精确度,减少了实验次数,节省了时间,提高了课堂效率.     

双波段扫描辐射计的研制

介绍了一种新型小视场、高精度的双波段扫描辐射计。描述了系统的特点,分析了系统的总体方案。介绍了系统的工作原理,对系统的NETD进行了估算,对其探测器的选择、光学系统设计、调制系统设计、扫描机构设计、信号处理等方案进行了详细论述,对系统的标定和测量原理进行了分析,并给出了相应的计算公式。给出了系统的检测结果。     

大统一理论:回顾与展望

本文系统地讨论了大统一理论的来龙去脉。回顾了大统一理论的发展历史,讨论了其发展现状及存在问题,指出了进一步发展的方向。本文重点介绍了SU(5)和SO(10)两个模型,讨论了Higgs场、规范等级、渐近自由、重正化等问题。文章进而讨论了一些有趣问题,比如提供了对宇宙重子起源的解释、计算了质子衰变寿命、论述了B-L是否守恒以及讨论了中子和中微子可能有的振荡现象等。     

大统一理论:回顾与展望

本文系统地讨论了大统一理论的来龙去脉。回顾了大统一理论的发展历史,讨论了其发展现状及存在问题,指出了进一步发展的方向。本文重点介绍了SU(5)和SO(10)两个模型,讨论了Higgs场、规范等级、渐近自由、重正化等问题。文章进而讨论了一些有趣问题,比如提供了对宇宙重子起源的解释、计算了质子衰变寿命、论述了B-L是否守恒以及讨论了中子和中微子可能有的振荡现象等。     

La/酸化膨润土吸附剂的表征与除磷性能

以酸化改性膨润土为载体,采用浸泡法制备了稀土La掺杂的La/酸化膨润土吸附剂.通过XRD和FTIR对其结构进行了表征,探讨了膨润土的改性机理,研究了该吸附剂对废水的除磷性能.结果表明：酸化过程洗掉了膨润土中的杂质和氧化铝,稀土镧的掺杂在膨润土层间及表面引入了一定数量的羟基化合物,改善了膨润土的层间结构并生成了新的La-O-Si键,实现了La与膨润土的复合,提高了膨润土的吸附性能.     

地磁场测量实验教学设备的改造、替代及软件选取

介绍了周期幅值法测量地磁场的实验方法,指出了原实验设备存在的问题,同时提出了实验设备的改造方案,并详细介绍了如何软选取件模块.该工作降低了实验教学的维护成本,节约了因等待维护耗费的大量时间,保证了实验教学的顺利进行.     

控制环量设计涡轮的实验研究

采用控制环量方法设计了一单级涡轮。该方法打破了传统的设计规律,为验证该方法的可靠性进行了模型试验。在宽广的范围内测定了总特性;在设计点附近作了沿叶高效率分布及动叶进、出口速度三角形的测定。本文给出了主要试验结果并作了简要分析。结果表明基本上达到了设计要求,控制环量设计的主要特征得到了验证,该方法基本可行。     

体内(in Vivo)NMR研究

本文综述了体内(in Vivo)核磁共振波谱技术的目前概况,简要介绍了这一技术的基本原理。对空间定位技术进行了重点评述,并给出了分类表。同时讨论了化学位移对空间定位精确的影响,介绍了提高定位精确度的实验方法。列举了空间定位波谱技术在生命科学研究中的应用,给出了大量的参考文献。     

A new method of ultrasound color flow mapping

Conventional ultrasound color flow mapping systems estimate and visualize only the axial velocity component. To obtain the transverse velocity component a modification of a multiple-beam method is proposed. The new two-dimensional color flow mapping system has a small size and consists of three transducers. The central transducer is an appodized and focused phased array. The other transducers are unfocused probes. Three transducers act as receivers and the central transducer operates as a transmitter. All receivers acquire rf scan lines that are then processed to estimate three axial velocity components using an autocorrelation method. These estimates are then combined to estimate the transverse velocity component, taking into account the geometric relationships among three transducers. Two algorithms for transverse velocity estimation are proposed. The first uses the Doppler angle estimate for calculation of the transverse velocity component. The other algorithm calculates the transverse velocity component directly from the axial components. The accuracy of the flow velocity estimators is estimated by simulations. Analysis of accuracy allows choosing the more effective algorithm for two-dimensional velocity estimation, which is insensitive to variations of the Doppler angle.     

磁驱动准等熵压缩下单晶氟化锂的光学特性

以"阳"加速器和PTS装置为驱动源,开了展单晶氟化锂(LiF,通光方向[100])窗口材料在准等熵压缩下的光学特性实验研究。应用全光纤激光多普勒探针系统(DPS,激光波长1550nm)同时测量了Ly12铝材料电极加窗和未加窗的后界面速度历史,结合窗口材料修正方法获取了单晶氟化锂窗口材料在实验条件下折射率随密度的变化和界面粒子速度修正因子。每次实验可获取窗口材料样品的连续加载历史数据,进而处理得到LiF窗口材料在近50GPa准等熵压力范围内的修正因子。结合拟合的线性关系,进一步处理获得了在实验过程中折射率随密度的变化。将这些实验结果与D.E.Fratanduono,Y.Ma,B.J.Jensen的对应数据比较,其中与光子多普勒测速系统(PDV,1550nm)测量结果基本相符,不确定度与多次冲击实验得到的结果相当。     

Approximation of the Boltzmann equation by discrete velocity models

Two convergence results related to the approximation of the Boltzmann equation by discrete velocity models are presented. First we construct a sequence of deterministic discrete velocity models and prove convergence (as the number of discrete velocities tends to infinity) of their solutions to the solution of a spatially homogeneous Boltzmann equation. Second we introduce a sequence of Markov jump processes (interpreted as random discrete velocity models) and prove convergence (as the intensity of jumps tends to infinity) of these processes to the solution of a deterministic discrete velocity model.     

一种超快时间分辨速度干涉仪的设计和理论研究

在单发、超快时间分辨的测量技术中,线性啁啾脉冲和光谱仪的结合使用是一种常见方法.本文以成像型光谱仪为记录系统,利用线性啁啾脉冲的频-时对应关系,设计了一种应用于自由面速度超快测量的速度干涉仪.理论研究了其工作原理和适用范围,该速度干涉仪可以实现皮秒量级的时间分辨,且速度灵敏度可调、易调,大大拓宽了速度干涉仪的应用范围.数值模拟了系统的测速过程,结果表明,重建速度信号与给定物体速度符合得很好,进一步验证了系统的可行性.     

Temperature Dependence of Retrograde Velocity of Vacuum Arcs in Magnetic Fields

Retrograde velocity of vacuum arcs in transverse magnetic fields is known to depend on, among other things, the magnetic induction, the arc current, the electrode spacing, the cathode material, and the cathode surface condition, and was also found to depend on the cathode temperature. Using the optical method, the retrograde velocity was measured as a function of the cathode temperature with copper, aluminum, and stainless steel as cathode materials. The optical measurement shows that by increasing the cathode temperature, the arc velocity decreases. It appears that with the increase in the cathode temperature, the decrease of the arc velocity is related to the increase of the cathode crater radius. The experimentally measured temperature dependence of the retrograde velocity of vacuum arcs can be explained by the ion jet model for retrograde motion of vacuum arcs [10]. The relative decrease of retrograde velocity as a function of the cathode temperature calculated according to this model agrees quantitatively with the reported measurements.     

NMR velocimetry of falling liquid films

First results on NMR velocimetry of falling liquid films are presented. A film of average thickness 1 mm and width 40 mm is sustained by a continuous flow of silicon oil over a vertical plate made from PMMA. The spatial distribution of velocities is measured using a double spin--echo imaging pulse sequence supplemented by a bipolar velocity encoding gradient. Spin density and velocity images as well as two-dimensional velocity maps of different situations, i.e., undisturbed and disturbed falling film flow, are discussed. Experimental and theoretical velocity data for undisturbed film flow are compared.     

On the velocity of propagation of a signal in nonlinear optical media

The maximum velocity of propagation of a signal, which is defined as the velocity of propagation of the wave front, is considered for electromagnetic waves in nonlinear media. It is shown that the magnitude of velocity is determined to a considerable extent on the form of the constitutive equation defining the relation between the polarization of the medium with the radiation field strength. In the noninertial nonlinearity model, this velocity may be smaller (in media with self-focusing nonlinearity) or larger (defocusing nonlinearity) than the velocity of light in vacuum. For real nonlinear media, for which the inertia of their response is taken into account, the wave front velocity coincides with the velocity of light in vacuum.     

入射速度对长杆弹垂直侵彻行为的影响规律

 以长杆弹垂直侵彻半无限厚靶板为研究对象,分析了弹体最大侵彻深度与入射速度的关系,研究了弹体入射速度对侵彻最大深度的影响规律。研究表明：靶板的强度和界面效应使弹体在侵彻过程中存在一个临界速度,当入射速度大于临界速度时,弹体的侵彻才能通过开坑阶段进入准稳定阶段,它是造成当入射速度较小时侵彻深度随入射速度的提高而几乎不变或缓慢增加的主要原因;准稳定侵彻过程中弹体速度和侵彻速度基本不变,并且两者存在线性关系,这种关系只与弹体和靶板的材料性能有关,是造成当入射速度较大时侵彻深度随入射速度的提高呈快速线性增大的主要原因。     

Atomistic simulation of the 60∘ dislocation mobility in silicon crystal

Dislocation velocity and mobility are studied via molecular dynamics simulation for a 60^∘ dislocation dipole in silicon crystal. The atomic interactions are described using the Stillinger–Weber potential and the external stress is applied by means of the Parrinello–Rahman algorithm. It is found that the dislocation begins to move when the applied stress is larger than the Peierls stress, and the calculated Peierls stress decreases as the temperature increases, which is in agreement with the Peierls–Nabarro model. The dislocation velocity at relatively low temperature is insensitive to variation of temperature. In fact, the velocity increases monotonically as the stress increases, and eventually approaches its plateau velocity which is about 2900 m/s. At higher temperature, however, the velocity no longer increases monotonically as the stress increases and the plateau velocity decreases as the temperature increases. In general, the dislocation velocity decreases as the temperature increases, which is consistent with the phonon drag model.     

Particular features of a Vavilov-Cherenkov-like phenomenon with emission of surface plasmons

We consider a phenomenon of the Vavilov-Cherenkov type that can be observed in a space with a metal-dielectric boundary that well reflects light. An electron that initially uniformly moves at a constant velocity near this boundary creates surface plasmon-polaritons the phase velocity of which is lower than the electron velocity. The momentum of a photon in the created plasmon-polariton is calculated. This momentum may be almost as high as the doubled initial electron momentum. The velocity of the electron that created the photon in the plasmon-polariton may also become almost zero. We show that, at a nonzero temperature, this process has a nonzero probability.