Nonlocal Models of Cosmic Acceleration

I review a class of nonlocally modified gravity models which were proposed to explain the current phase of cosmic acceleration without dark energy. Among the topics considered are deriving causal and conserved field equations, adjusting the model to make it support a given expansion history, why these models do not require an elaborate screening mechanism to evade solar system tests, degrees of freedom and kinetic stability, and the negative verdict of structure formation. Although these simple models are not consistent with data on the growth of cosmic structures many of their features are likely to carry over to more complicated models which are in better agreement with the data.     

The Effect of the Ion Assistance Energy on the Electrical Resistivity of Carbon Films Prepared by Pulsed Plasma Deposition in a Nitrogen Atmosphere

Physics of the Solid State - Thin carbon films prepared by pulsed plasma ion-assisted deposition of graphite in an atmosphere of a mixture of argon and nitrogen are studied. The results of...     

脉冲等离子体推力器等离子体羽流的光谱研究

脉冲等离子体推力器(pulsed plasma thruster, PPT)具有体积小、重量轻、比冲高等优点,特别适合作为执行微小卫星轨道转移、阻力补偿和姿态控制等任务的推进系统。为了深入理解PPT推力产生的机理,本文对采用具有张角的舌型极板的尾部馈送式PPT等离子体羽流开展了时空分辨光谱诊断研究。通过对光谱数据的分析发现： 等离子体羽流的主要成分为C,F,C+,F+,C2+,还含有少量的由于极板烧蚀产生的Cu+和Cu2+;等离子体在放电通道内的分布不均匀,通道中心的等离子体浓度最大,靠近阳极板的等离子浓度要明显大于靠近阴极板的等离子体浓度;在不同位置处等离子体成分也具有较大差别,F+和中性粒子主要分布在靠近阳极侧的区域;通过对各个分立谱线进行多普勒线性拟合,得到了放电通道内等离子体温度信息;以中轴线靠近工质的观测点为例,对该点在整个放电过程中不同时刻的谱线进行分析,得到了该点等离子体的具体演化过程,发现在放电的不同阶段羽流成分及各组分所占比例差别较大。     

Diagnostics of Pulsed Discharge Plasma in Electrolyte

Two experimental methods are applied to determine electron temperature: the method of calculating temperature from the slope of the continuum's relative intensity, and the Boltzmann plot of the relative line intensity of oxygen OII, in a pulsed discharge in an electrolyte (PDE). Electron density is determined using the electron impact widths of magnesium ionic lines.     

Emission Spectrum and Resistivity of Low Power Plasma Weld Arcs

Emission spectra from plasma arc welds were observed under a variety of current, voltage, polarity, and standoffs. If reverse polarity (welding torch positive) welds are struck below 50 amperes most of the power is deposited at the electrode rather than the workpiece because of low carrier density within the arc. Straight polarity, on the other hand, suffers no such limitation because of electrons created in the pilot arc used to start the weld process.     

Beat Wave Generation of Plasma Waves for Particle Acceleration

The space-time evolution of beat wave generation is studied analytically and numerically. Electromagnetic cascading, collisional damping and relativistic frequency shift of the beat plasmon are taken into account in the model. In particular, detuning and dispersion effects are investigated. The achievable plasmon amplitude depends strongly on the collisional damping. At low electron temperatures, the induced beat wave follows the laser pulse and decays rapidly behind it. At high electron temperatures, amplitude modulation appears and an intense slowly decaying plasmon wake can be excited. The wake formation is controllable by varying the pulse length or by detuning the driver slightly off resonance. The amount of electromagnetic cascading is proportional to the plasmon amplitude and the propagation distance of the pulse. The EM spectra offer excellent diagnostics for beat wave experiments, because plasmon amplitude variations are directly reflected in them.     

Spectroscopic Diagnostics of Atmospheric Argon Microwave Plasma Based on an Inductive Coupling Window-Rectangular Resonator

We present a novel microwave plasma source based on an inductive coupling window-rectangular resonator. A definite volume of atmospheric argon microwave plasma is excited in the source under the input of several kilowatts of microwave power operating at 2.45 0Hz. The excitation temperature and electron temperature of the argon plasma are separately researched by using Boltzmann plot and line-to continuum intensity ratio of Ar I spectral lines. Its electron density is inferred from the Stark broadening of the Hβ line at 486.13nm.     

Collective Acceleration of Ions in a Pulsed Magnetic Field of a Conical Spiral

The collective acceleration of laser plasma ions in a magnetic field generated by a powerful fast-growing current pulse in a low-inductive conical spiral is studied. The velocity of ions for a number of elements which significantly differ in atomic weight are obtained on the basis of collector measurements. The maximum velocity of both light (lithium) and heavy (lead) ions exceed the value of 108 cm/s; for ions of lead, the corresponding energy amounts to a value of ∼1 MeV. A mathematical model of ion acceleration is proposed and simulation results are compared with the experiment.     

Resistivity of an Infinite Three Dimensional Stationary Random Electric Conductor

The aim of this paper is to prove that the resistivity of an infinite stationary random medium can be computed from one realization. This is accomplished through the application of the pointwise degree 2 ergodic theorem for divergence-free stationary random fields (see [4]).     

不同湍流模型对热等离子体射流模拟的影响

本文应用大气压等离子体射流传热与流动的三维数学模型,在相同初始条件下,计算得到了采用不同湍流模型时氩等离子体射流对称轴线上的温度、速度及空气质量分数分布,并与文献中同等条件下的实验结果进行了比较,结果表明采用标准κ-ε模型和Realizableκ-ε模型时与实验结果相差较大,而采用RNGκ-ε湍流模型时模拟结果与实验数...     

纳秒脉冲等离子体合成射流激励器的流场特性分析

采用一台高重频、快上升沿纳秒脉冲电源作为激励源,对典型的双电极合成射流激励器进行放电,通过粒子图像测速法（particle image velocimetry,PIV）测量放电实验中激励器稳定流场特性以及发展速度.分析实验结果发现,随着重复频率的提高,合成射流的平均发展速度也随之增大,1 kHz时的平均速度最高达到28.28 m/s,并在单脉冲能量远低于微秒脉冲的情况下,实现了更快的稳态流场控制,表明高重复频率下,更多次数的脉冲放电可提高激励总能量,有效地弥补纳秒脉冲单脉冲输出能量不足的缺点.而且频率越高,流场发展速度越快,说明高重频工作模式会对输出总能量有补偿作用.      

Nonlinear Effects Related to the Simultaneous Excitation of Three Instabiities in Magnetized Plasma

Experimental results are presented on the nonlinear effects related to the simultaneous excitation of three low‐frequency instabilities in the magnetized plasma column of a Q‐machine, namely the potential relaxation instability, the electrostatic ion‐cyclotron instability and the Kelvin‐Helmholtz instability. The influence of electron drift and magnetic field intensity on appearance, dynamics and mutual interaction of these instabilities was investigated (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Optimization of Electric Thrust Based on Pulse Arc Plasma Using Pulsed Magnetic Field

Russian Physics Journal - Based on the results of a numerical simulation, a possibility in principle is shown to achieve an effective magneto-induction correction of high-gradient plasma expansion...     

面向产品状态的工装建模技术研究

为了在工艺装备设计过程中,提前考虑后续制造、使用、维护的相关需求,确保工艺装备在使用过程中对武器装备状态更改的及时响应;在分析工装生命周期特点的基础上,总结了面向产品状态工装模型的要求,提出了面向产品状态工装模型的定义,着重指出了工装模型与产品模型的关联关系;最后介绍了面向产品状态工装模型响应武器装备状态改变的实现方法。     

Propagation of Plasma Generated by Intense Pulsed Ion Beam Irradiation

Taking the calculation results based on the established two-dimensional ablation model of the intense-pulsed-ionbeam （IPIB） irradiation process as initial conditions, we build a two-dimensional hydrodynamic ejection model of plasma produced by an IPIB-irradiated metal titanium target into ambient gas. We obtain the conclusions that shock waves generate when the background pressure is around 133 mTorr and also obtain the plume splitting phenomenon that has been observed in the experiments.     

SILEX-1装置上等离子体尾场加速电子初步实验

激光等离子体加速电子机制可以产生准单能的高能电子束, 近年来成为国际上的研究热点. 中国工程物理研究院激光装置已经能够达到286TW的输出功率, 为国内在该领域的研究提供了实验条件. 文章介绍了在SILEX-1装置上开展的激光等离子体加速电子的初步实验, 并对测得结果进行讨论, 为下一步实验的进行提供了准备条件.     

Continuing Studies of Plasma Erosion Switches for Power Conditioning on Multiterawatt Pulsed Power Accelerators

Recent PITHON experiments with plasma erosion switches (PES) have extended the range of operation of the switches by about 50 percent, in terms of closed time and charge passing through the switch. The quantity of charge passed through the switch has been increased to as much as 35 mC. Currents as large as 1 MA and voltages as great as 1.8 MV have been switched off to be diverted to a downstream load. The impedance of the erosion switch can be described as having three stages: 1) essentially zero impedance, 2) a transitional opening phase, and 3) an impedance which is very large (greater than 5 ?) in comparson with the subohm downstream load. Current diagnostics, consisting of Rogowski coils and segmented shunts, have been successfully developed to monitor the current which propagates to the load region. These monitors have measured rise times as short as 38 ns and slew rates as great as 1014 A/s at the load. With wire array loads, the pulse conditioning of the switch has been observed to reduce the magnitude of the current losses in the feed which are present when no switch is used. Correlations have been made between the switch closed time, voltage, current, and power with the feed inductance and the generator power injected into the magnetic insulated transmission line (MITL).     

Numerical Simulation on Expansion Process of Ablation Plasma Induced by Intense Pulsed Ion Beam

We present a one-dimensional time-dependent numerical model for the expansion process of ablation plasma induced by intense pulsed ion beam （IPIB）. The evolutions of density, velocity, temperature, and pressure of the ablation plasma of the aluminium target are obtained. The numerical results are well in agreement with the relative experimental data. It is shown that the expansion process of ablation plasma induced by IPIB includes strongly nonlinear effects and that shock waves appear during the propagation of the ablation plasma.     

试论研究性学习的三种模式

研究性学习,是指学生在教师的指导下,在学科领域、跨学科领域或社会生活中,选择研究课题,以独立或小组合作的方式进行探索性、研究性的学习;是学生通过亲身实践,学会对大量信息的收集、分析和判断的学习;是学生以类似于科学研究的方式主动地获取知识,应用知识解决问题的学习.