锁相检测式二维小角度测量装置

介绍了一种新型的二维小角度检测装置。由于该装置采用了光电自准直结构,以高灵敏度的四象限硅光电探测器作为检测元件,采用交流调制,锁相放大的方法对信号进行了处理,所以有效地消除了直流漂移的影响,提高了稳定性和测试精度。分析了光斑的形状和大小对测试结果的影响,研制了专门的标定装置。首先由高精度的光电自准直仪标定测量角度与输出信号的关系,并将相关数据存入单片机,然后由软件拟合出关系曲线。测量时,既可自动显示角度的大小,同时也可以与计算机相连。该测试系统结构小巧,具有较高的测量精度。     

New terahertz dispersive device for single-shot spectral measurements of terahertz pulse

A new terahertz dispersive device designed for single-shot spectral measurements of broadband terahertz pulses is proposed. With two-dimensional quasi-randomly distributed element design, the device exhibits approximately the dispersive property of single-order diffraction in far field. Its far-field diffraction pattern is experimentally verified employing a continuous terahertz source centered at 2.52 THz and a pyroelectric focal-plane-array camera, which is in good agreement with the numerical result. The device provides a new approach for direct single-shot spectral measurements of broadband terahertz waves.     

Variable temperature system using vortex tube cooling and fiber optic temperature measurement for low temperature magic angle spinning NMR

We describe the construction and operation of a variable temperature (VT) system for a high field fast magic angle spinning (MAS) probe. The probe is used in NMR investigations of biological macromolecules, where stable setting and continuous measurement of the temperature over periods of several days are required in order to prevent sample overheating and degradation. The VT system described is used at and below room temperature. A vortex tube is used to provide cooling in the temperature range of -20 to 20 degrees C, while a liquid nitrogen-cooled heat exchanger is used below -20 degrees C. Using this arrangement, the lowest temperature that is practically achievable is -140 degrees C. Measurement of the air temperature near the spinning rotor is accomplished using a fiber optic thermometer that utilizes the temperature dependence of the absorption edge of GaAs. The absorption edge of GaAs also has a magnetic field dependence that we have measured and corrected for. This dependence was calibrated at several field strengths using the well-known temperature dependence of the (1)H chemical shift difference of the protons in methanol.     

Experimental study of the relationships between the spectral emissivity of brass and the temperature in the oxidizing environment

Effect of surface oxidization on the spectral emissivity of brass is studied over the temperature range from 800 to 1070 K at the wavelength of 1.5 μm. The temperature of brass surface is measured by averaging the two R-type platinum–rhodium thermocouples. The radiant energy emitted by the brass surface is received by an InGaAs photodiode detector. Two kinds of relationships between the spectral emissivity and the temperature are investigated in the oxidizing environment at the elevated temperature. One is the variation of spectral emissivity with the heating-duration time at the given temperature. The other is the variation of spectral emissivity with the temperature at the given heating-duration time. The interference effect of radiation coming from the brass surface and coming from the oxidization film is discussed when the oxidation film on the surface is grown. The resonant structures of spectral emissivity are observed during the whole heating period, in particular at the early stage of heating duration. The analytic formula of spectral emissivity versus the temperature is derived at the heating-duration time of 30, 60, 90, 120, 150, 180, 210, 240, 270 and 300 min, respectively. The conclusion is obtained that coefficients of analytic expressions between the spectral emissivity and the temperature are different from each other for the experimental results obtained at the different heating-duration time, though the polynomial functional form is suitable to fit all the measurements obtained in the present work.     

"神舟"号飞船的微重力测量

航天器在太空自由漂移时出现失重状态．当存在各种干扰力时，呈现微重力状态．失重状态使得物体各部分之间不产生压力作用或者形变作用，对此开展的研究称之为微重力科学．微重力用微重力加速度的值度量．准稳态加速度来自大气阻力、潮汐力、太阳辐射压等，分析得到“神舟”号飞船的准稳态加速度在10^-7g0以下．瞬变加速度和振动加速度可用石英挠性加速度计检测．“神舟”号飞船的微重力测量仪器具有三轴检测、守时、统计分析、依照预先注入的指令准实时传送微重力统计数据或原始数据的能力．该仪器带宽为(0．06—100)Hz，分辨率5μg0，量程(-10— 10)mg0，沿飞行轴线还有一个放大为(-150— 150)mg0的量程．该仪器对“神舟一号”到“神舟五号”各艘飞船轨道运行段实施全过程连续监测，准实时提供了飞船各种动作发生的时刻及引起的加速度量值，为飞船飞行控制、有效载荷动作监测和空间微重力科学实验分析提供了有效服务。     

Microwave cavity perturbation technique: Part III: Applications

The resonant cavity perturbation method as described in the preceding two parts of this series is applied to study the electrodynamical properties of different materials in the microwave and millimeter wave spectral range. We briefly discuss the relevant uncertainties which are asociated with the different measurement techniques and we find that employing the amplitude technique it is possible to measure both the width and frequency to nearly the same precision. We then demonstrate the broad range of applicability of this technique by showing results obtained on several different materials, ranging from an insulator to a superconductor. The performance limitations of this technique are discussed in detail.     

Protective measurement and quantum reality

It is shown that from the expectation values of obervables, which can be measured for a single system using protective measurements, the linear structure, inner product, and observables in the Hilbert space can be reconstructed. A universal method of measuring the wave function of a single particle using its gravitational field is given. Protective measurement is generalized to the measurement of a degenerate state and to many particle systems. The question of whether the wave function is real is examined, and an argument of Einstein in favor of the ensemble interpretation of quantum theory is refuted.     

Gauge-invariant treatment of the exponential decay of an unstable atomic state

Summary By using a self-consistent projection-operator method, developed recently by the present author, a gauge-invariant Markovian treatment of the spontaneous decay of an unstable atomic state is presented. Without ignoring retardation and electron-spin effects a gauge-invariant result for the probability amplitude of finding the atom in the unstable state is obtained.     

Forecasting of precipitation occurrence in long-range trajectory climatology

Summary A procedure to include a way for forecasting the precipitation occurrence in the air mass trajectory computation for climatological studies in order to compute the wet deposition of airborne pollutants is presented. It is based on a technique proposed by Moscoet al., Riv. Meteorol. Aeronaut.,33, 229 (1973). Its performance is tested comparing the forescen occurrence of either precipitation or no precipitationversus the actual one for two stations, Parma and Vipiteno, for a period of four years. In more than 80% of the cases the forecasting was correct.     

Measurement: It ain't over till it's over

Elby (1993) has raised certain problems that appear to be devastating for modal interpretations of quantum mechanics, but do not arise for Bohm's pilot wave theory. Here I show that the features Elby identifies as objectionable in my version of the modal interpretation have their counterpart in Bohm's theory. To the extent that Bohm's theory works as a no collapse solution to the measurement problem - and I think it does - so does my modal interpretation.