气垫导轨在刚体转动惯量测定实验中的应用

本文介绍了一种测量刚体转动惯量的新方法。即把气垫导轨和刚体转动仪结合起来来测量刚体的转动惯量,使传统的气垫导轨实验和刚体转动惯量测定实验得以更新,提高了实验测量的精度,拓展了实验内容。     

GaAsN/AlAs/AlGaAs double barrier quantum wells grown by molecular beam epitaxy as an alternative to infrared absorption below 4 μm

In this work, we report on the design, growth and characterization of GaAsN/AlAs/AlGaAs double barrier quantum well infrared detectors to achieve intraband absorption below 4 μm. Due to the high effective mass of N-dilute alloys, it is common for these N-containing double barrier quantum well structures to have more than one bound state within the quantum well, enabling the possibility of achieving multispectral absorption from these confined levels to the quasi-bound. Based on a transfer matrix calculation we will study the influence of the potential parameters, in particular the well width and the introduction of a GaAs spacer layer in between the N-well and the AlAs barriers. We will compare the case in which there are two confined levels with the case in which only one level is bound, like in the conventional AlGaAs/AlAs/GaAs structures. On the basis of the simulation, we have grown and characterized some N-containing double barrier detectors. Moreover, an optimization of the post-growth annealing treatments of the GaAsN quantum well structures has also been performed. Finally, room temperature absorption measurements of both as-grown and annealed samples are presented and analyzed.     

A fast method to measure the thickness of removed layer from etching of SSNTD based on EDXRF

Solid state nuclear track detectors are commonly used for measurements of concentrations of radon gas and/or radon progeny. All these measurements depend critically on the thickness of the removed layer during etching. However, the thickness of removed layer calculated using the etching period does not necessarily provide a sufficiently accurate measure of the thickness. For example, the bulk etch rate depends on the strength of stirring during etching for the LR 115 detector. We propose here to measure the thickness of the removed layer by using energy-dispersive X-ray fluorescence spectrometry. In the present work, a reference silver nitrate pellet is placed beneath the LR 115 detector, and the fluorescence X-ray intensity for silver is then measured. We have found a linear relationship between the X-ray intensity and the thickness of the removed layer for LR 115 detector. This provides a fast method to measure the thickness of removed layer from etching of LR 115 detector. However, this method was found to be inapplicable for the CR-39 detector. Therefore, alternative methods have yet to be explored for the CR-39 detector.     

一种简易云雾室的制作

本文利用自制云雾室把微观粒子的运动转化为宏观现象，从而供实验观察和研究。     

Resonance method for IR sensing

A highly sensitive method for infrared radiation detection based on thermal resonance in an active bolometer is set forth. An active bolometer is a self-oscillating system consisting of an IR-sensitive cell in a feedback circuit of an adjustable proportional controller. The analysis of an active bolometer autonomous (dark) dynamics reveals that with a generalized gain factor A variation the system evolves from relaxation type towards oscillating and self-oscillating type. When A=A_c, where A_c is a critical value of the generalized gain factor A, the steady state loses stability through self-excited thermal oscillations. The resonance in a system weakly perturbed by IR radiation modulated at self-oscillation frequency q₀[1+exp(iω_ct)] is considered. It is shown that in a small precritical vicinity =(A−A_c)/A_c of the gain factor the amplitude of forced thermal oscillations is proportional to q₀/A_c. The D^* calculation reveals that the detection power of a passive (A=0) bolometer increases with feedback introduction by a factor of 1/||. The detection powers of feasible versions of an active bolometer are compared.     

Surface morphologies of anthracene single crystals grown from vapor phase

The morphologies and lattice structures of anthracene single crystals grown from the vapor phase were investigated using optical microscopy, phase contrast microscopy, atomic force microscopy (AFM), and X-ray diffraction analysis. Common morphologies with hexagonal large planes were observed irrespective of crystal size. The observation of certain surface morphologies with a phase contrast microscopy revealed that the spiral steps originated from screw dislocations present on the (0 0 1) planes. Moreover, the center and edge of the (0 0 1) planes had large curvatures, similar to hills. Resultantly, quarter-monolayer (ML) steps were observed on the large and flat planes between both hills.     

Indoor radon measurements in dwellings of four Saudi Arabian cities

An indoor radon survey of a total of 269 dwellings, with one dosimeter per house, distributed in four Saudi Arabian cities was carried out. The objective of this survey was to carry out indoor radon measurements of two cities in the Eastern Province, Khafji and Hafr Al-Batin and to compare this with two cities in the Western Province, Al-Madina and Taif. The survey provides additional information about indoor radon concentrations in Saudi Arabia. The results of the survey in these cities showed that the overall minimum, maximum and average radon concentration were 7,137 and 30 Bqm⁻³, respectively. The lowest average radon concentration (20 Bqm⁻³) was found in Hafr Al-Batin, while the highest average concentration was found in Khafji (40 Bqm⁻³).     

Uniformity in radon exhalation from construction materials using can technique

The uniformity in radon exhalation rates for 46 tiles of granite, marble and ceramic used as construction materials were determined using “Can Technique” employing CR-39 nuclear track detectors (NTDs). On each tile, two sealed cans, each enclosing one NTD fixed at the center of the tile surface area covered by the can, were mounted at two different locations of each individual tiles. The track production rates on the NTDs representing radon exhalation rates were measured. The radon exhalation rates from the surface of individual tiles showed uniform exhalations within the calculated uncertainties of the measured values. This makes Can Technique an alternative simple method to measure radon exhalation rates. Calibration required to convert track production rates into radon exhalation rates for the used can and NTD was done using an active technique. The correlation between the measurements by the two techniques shows a good linear correlation coefficient (0.83).     

High resolution staring arrays answering compact MW and LW applications

This paper overviews the electro-optical and thermal performances of different types of infrared detectors manufactured by Sofradir. The detector’s fabrication processes and detector’s performance are shortly described. New staring arrays are more compact and offer system solutions required by infrared market. Special attention is directed to some reliability advantages of new dewar design. Finally, the development trends for highest resolution infrared detector are discussed. The paper presented there appears in Infrared Photoelectronics, edited by Antoni Rogalski, Eustace L. Dereniak, Fiodor F. Sizov, Proc. SPIE Vol. 5957, 59570U (2005).     

线性规划的符号跟踪算法

分析了只含一个约束条件的线性规划最优基变量的特征，将其运用到搜寻含m个约束条件的线性规划的最优基变量，从而提出了线性规划的符号跟踪算法，为线性规划求解提供了新途径。