Electromagnetic Spectrum Control Programs

The radio frequency spectrum is becoming increasingly saturated and polluted due to intensified use and unnecessary radiations and is being taxed severely to meet man's communications-electronics needs. Additional corrective measures are necessary-improved standards, increased concern for conservation of the resource, greater emphasis on intersystems compatibility, increased research, better educational and training programs, and the inclusion of economic and social values in evaluating the uses to which the spectrum should be put.     

An imaging telescope for soft gamma ray astronomy

A telescope capable of producing images of the gamma ray sky in the energy range 0.2–20 MeV with an angular resolution of a few tenths of a degree is presented. This capability is achieved by means of a large array of Sodium Iodide position sensitive elements together with a coded imaging mask. The expected performance, derived from calculations and preliminary laboratory tests, is described.     

电阻点焊质量控制系统的研究

分析了利用动态电极压力监控点焊质量的原理，利用压电石英力传感器、负荷放大器及其外围电路，建立了动态电极压点焊质量控制系统。介绍了控制系统硬件结构和控制软件设计。实验结果表明，采用该控制系统能够有效地控制焊点质量。     

点焊质量控制方法的研究

利用光栅位移传感器和压电石英力传感器 ,建立了热膨胀位移和动态电极压力点焊质量微机监控系统 ,并对这两种监控方法的控制原理、控制性能和控制效果进行了分析比较。试验结果表明 ,此类单参数质量控制系统能够实现点焊过程质量监控 ,并具有自适应特性 ,可用于构造多参数点焊质量控制系统     

线切割放电加工助航空客户飞得更高

过去20年里线切割的切割速度几乎增加了5倍,粗加工的直线切割速度可达600mm2/min;对大多数复杂型腔的加工速度较慢,但也可达到约350mm2/min。通过优化粗加工和精加工的策略,变质层几乎为零,同时没有材料或微观结构的变化,放电脉冲的控制特别是脉冲的持续时间和频率是达到最小损伤的关键因素。     

The Use of Environmental Stress in Conjunction with Simulation Testing

Large-scale vehicle simulations in which human subjects are exposed to realistic environmental profiles are well within the engineering state-of-the-art. The Boeing Multiple-Stress Laboratory is capable of exposing subjects to heat, noise, vibration, and altitude, while measuring their performance and physiology. Data have been obtained on simulations relative to fixed-wing aircraft, helicopters, and three-stage boosters. Exposure periods have ranged from a minimum of 9 minutes to a maximum of 6 hours. Boeing experience, in the past 4 years, has evidenced that a facility of this type can provide an effective bridge between analytical studies and the operational situation. Inherently flexible, such a facility can support a wide variety of development programs.     

公路隔离网专用焊机微机控制系统研制

介绍了公路隔离网专用焊机微机控制系统的功能、系统的硬件结构和软件设计。控制系统具有手动、半自动、全自动等工作方式，可自动补偿网压波动对焊接电流的影响。批量生产应用表明：控制系统操作方便，性能可靠，焊接质量稳定。     

Extragalactic γ-ray astronomy

Space Science Reviews - Extragalactic γ-ray astronomy is in its infancy. In this paper a review is presented of the γ-ray emission of the few individual objects observed to date and some...     

高职学校教学质量保障系统与教学评价体系研究

本文通过对教学质量的再认识,分析了当前影响高校教学质量的因素,构建了高校教学质量保障系统,制定了高职教学评价指标体系。     

Type-III radio bursts and their interpretation

The observations of type-III solar radio bursts are briefly reviewed to set requirements on a model for their interpretation. The most important of these requirements is that the source must be an electron stream which is in a state of continuous quasilinear relaxation and which initially must have a nearly monotonically decreasing velocity distribution. The problem of constructing a model is broken into three parts: (1) The plasma wave source which depends on the interaction of the electron stream with electron plasma waves. (2) The radiation source which depends on the interaction of plasma waves and transverse electromagnetic waves or in a magnetized plasma the ordinary and extraordinary modes of magnetoionic theory. (3) The propagation of radiation between the source and the observer which depends on the transmission of radiation through a scattering refracting absorbing magnetized plasma.Progress on a model for the plasma wave source is reviewed and it is concluded that no existing models are adequate. The equations which would lead to an adequate model are written down, but not solved. These include, in addition to collisional damping, Landau damping both by the exciting stream and the background plasma, and spontaneous and induced processes for a three-dimensional distribution of plasma waves. Possible limitations to a quasilinear approach such as pile-up of plasma waves and nonlinear effects are considered. Processes which affect the gross structure of the source such as electron trajectories in coronal streamers and electron scattering by inhomogeneities are reviewed.Progress on the radiation source is considered both in the absence and presence of a magnetic field. At high frequencies (e.g., 80 MHz) observations of radiation near the fundamental and second harmonic of the plasma frequency allow a unique determination of source size and the energy density in plasma waves within the uncertainties of geometry by source ray tracing. This determination is extremely critical because the fundamental must be amplified and thus production of the fundamental is effectively a much more highly nonlinear process than production of the second harmonic. At low frequencies (e.g., 500 kHz) the second harmonic is shown to be dominant because amplification of the fundamental becomes an inefficient process.Calculations of scattering of radiation in a random medium are reviewed. It is concluded that these are adequate at high and low frequencies, but have not been carried out properly at intermediate frequencies where amplification of the fundamental may still be present. It is shown in particular that when scattering is taken into account at high frequencies all observations can be explained by isotropic emission near the second harmonic. At low frequencies the nature of the scatterers is determined by source occultations unlike the case at high frequencies where these are free parameters. This fact allows the possibility of determining true source sizes at low frequencies by subtracting out the contribution due to scattering. A mechanism for producing the possibly observed linear or highly elliptical polarization of type-III bursts, which must be imposed far from the source due to Faraday rotation, is reviewed.Finally, the questions of what remains to be done and what we can hope to obtain upon completion of this work are briefly considered.The National Center for Atmospheric Research is sponsored by the National Science Foundation.