小径薄壁管射线透照布置方法

小径薄壁管广泛用于工艺管道中，在对其进行无损探伤时，一般采用双壁双影椭圆成像法和双壁重叠成像法，针对小径薄壁管对接焊缝透照成像的特殊要求，具体介绍双壁双影椭圆成像法的透照布置方法。     

热辐射的破坏准则和池火灾的破坏半径

热辐射破坏是发生在开放气环境中的池火灾的主要破坏机理。本文讨论了热辐射的破坏准则，提出预测池火灾破坏半径的方法，进行了数值模拟计算，分而和时纳了池火灾的基本规律     

池火灾热辐射的数值研究

通过列举储罐火灾事故,提出对池火灾进行研究的重要性。介绍目前池火灾国内外的研究现状及发展情况,描述池火灾燃烧特征和模型。应用化学流体力学基本定律,建立了描述池火灾过程的基本控制方程组,并根据适当的条件选择辐射模型。建立物理模型,做出合理假设,确定初始和边界条件,对池火灾热辐射过程进行数值模拟,得出火焰周围入射热流密度分布图,计算出相邻两罐之间的最小安全距离,应用于工程实际中,给防火间距的制定提供理论依据,计算结果定性合理。     

Effect of 450 MHz Microwave Modulated with 217 Hz on Human EEG in Rest

Summary This study focuses on discrimination of changes, produced by low-level microwave exposure in intensity and time variability of the human EEG at rest. The power spectral density (PSD) method and nonlinear scaling analysis of the length distribution of low variability periods (LDLVP) were selected for analysis of the EEG signal. During the study, 19 healthy volunteers were exposed to a microwave (450 MHz) of 217 Hz frequency on-off modulation. The field power density at the scalp was 0.16 mW/cm². The experimental protocol consisted of ten cycles of repetitive microwave exposure. Signals from frontal, temporal, parietal and occipital EEG channels on EEG theta, alpha and beta rhythms were analysed. Exposure to microwave causes average increase of EEG activity. LDLVP analysis discriminated significant effect in time variability for 2 subjects (11%). PSD method detected significant changes in intensity for 4 subjects (21%). The effect of low-level microwave exposure is stronger on EEG beta rhythm in temporal and parietal regions of the human brain.     

A Parallel Study of SAR Levels in Head Tissues for Three Antennas Used in Cellular Telephones: Monopole, Helix and Patch

Summary This paper is a comparative study of several antennas commonly used in cellular telephones. These include a monopole, a helix-monopole and a patch antenna. Each one of these structures is modeled and numerically tested using finite-difference time-domain simulation and human models based on magnetic-resonance images, which allow for inclusion of details of the human body in the simulation. The testing procedure involves antenna simulation in the proximity of the human head. The behavior of each antenna is evaluated for variable distances from the head geometry (0, 1, 2, 4, 8 and 16 mm). Continuous waveform, representative of the sources used in mobile telephones, (250 mW, 1.8 GHz) is used as the form of the antenna excitation. The simulation outputs used as measures for this comparative study include transmitting and receiving antenna characteristics and the specific absorption rate (SAR). The SAR levels for the head tissues are calculated for and with accordance to the two currently accepted standards: Federal Communications Commission (FCC) and International Commission on Non-Ionizing Radiation Protection (ICNIRP). The computed SAR levels within each of the considered tissues vary for the three antennas under investigation and are within the determined health safety standards. Results suggest that the patch antenna may be the structure of choice when considering safety standards, as its radiation yields the lowest local SAR in the head tissues.     

0.1～3000MHz射频电磁环境时间变化规律及其与人群作息时间关系的研究

利用自动连续监测仪器对在成都市城区选定的监测点位开展了持续数日的测量,获取了测点的长时间监测数据,通过对监测数据的分析,研究了0.1~3000MHz射频电磁环境随时间变化的规律及其与人群作息时间的关系,并对电磁环境人工手动监测的适宜时间段进行了分析。     

Brain myelination in rats treated with ionizing radiation in utero

Abstract

Effects of ionizing radiation on brain myelination and some physical development parameters were studied in laboratory rats (Fisher F‐344 inbred strain). Rats were treated with three different doses of radiation (150 rad, 15 rad, and 6.8 rad) delivered on the 20th day of prenatal life. Exposure to 150 rad reduced body, brain, ovary, kidney, heart and spleen weights. Prenatal exposure to 150 rad of radiation reduced the cerebral cortex weight by 22 percent at 30 days of age, and 20 percent at 52 days of age which caused a reduction in cerebral cortex myelin content by 20 and 23 percent at the ages of 30 and 52 days respectively. This dose did not affect the myelin content of the cerebellum or the brain stem, or the myelin concentration (mg myelin/g brain tissue) of the cerebral cortex, cerebellum, and the brain stem. The cerebral cortex weight of the 15 rad treated rats was reduced at the age of 30 days. Exposure to 15 rad, and 6.8 rad did not affect either the myelin content or the myelin concentration of these brain areas.     

太阳风暴对短波电子装备性能的影响及应对措施

目的掌握太阳风暴对短波电子装备性能的影响及应对措施,为系统设计提供参考。方法分析太阳风暴的表现形式,并从作用距离、目标检测、定位精度等方面给出太阳风暴对短波超视距雷达、短波通信等装备的影响。结果电离层SID、电离层暴可造成短波通信中断,短波通信可用频段变窄。电离层强吸收可降低天波超视距雷达作用距离和目标定位精度,电子浓度、电离层虚高快速变化影响超视距雷达检测性能和定位精度,负相电离层暴使天波超视距雷达可用频段严重变窄。地球磁暴期间,电磁场突变产生的强电压和电流有可能烧毁用于天、地波超视距雷达的电子设备。电离层非规则现象对超视距雷达有严重影响。结论太阳风暴对电子装备性能有利有弊,要分别对待。系统设计时应充分考虑太阳风暴的影响,在出现太阳风暴时,采取针对性措施降低其影响。     

铝合金-丁腈橡胶航空带垫卡箍典型环境损伤研究

目的研究典型环境对丁腈橡胶-铝合金带垫卡箍的损伤效应。方法通过模拟铝合金-丁腈橡胶航空带垫卡箍使用时的装配结构和应力状态,应用GJB 150A—2009中的湿热和太阳辐射两种典型老化环境,采用宏观形貌观察、卡箍保持力测试和橡胶衬垫拉伸性能测试方法,结合扫描电子显微镜和傅里叶红外光谱技术,分析带垫卡箍的性能劣化过程。结果带垫卡箍在湿热和太阳辐射环境中老化50 d后,卡箍橡胶衬垫表面出现大量微孔缺陷,拉伸性能大幅降低,导致卡箍保持力分别下降了35%和51%。结论带垫卡箍在模拟装配状态下进行湿热和太阳辐射环境暴露实验,卡箍橡胶衬垫内部结构由致密逐渐变得疏松,部分碳碳双键发生氧化交联反应,并在一定程度上提高了聚合物的交联密度,材料硬度提高,回弹性能减弱,橡胶衬垫对芯轴的包裹能力降低,导致卡箍保持力性能降低。     

无线电引信电磁辐射能量耦合路径研究

目的为了确定外界电磁能量究竟如何进入到引信电路内部,针对无线电引信的电磁能量耦合路径进行系统研究。方法通过对多种引信进行不同形式的连续波、强电磁脉冲电磁辐照效应试验,对比引信天线、孔缝、弹体、电源模块等部位的能量耦合可能性。分析连续波、强电磁脉冲电磁环境对无线电引信作用的耦合规律。结果确定了电磁信号类型和引信接地结构是影响电磁能量耦合通道的关键因素,揭示了前门耦合是连续波电磁辐射环境的最主要方式。结论弹体或引信前端与电路共地的金属部件是强电磁脉冲辐射环境的主要能量路径,从而为无线电引信抗电磁性能加固的实施提供了有益参考。