有源相控阵可靠性分析及设计

基于有源相控阵原理和特点,对有源相控阵可靠性特征展开了分析。在同等复杂度下,采用可靠性表决模型和全串联模型对可靠性特征进行了对比分析,给出了有源相控阵表决模型设计的工程经验参数,并利用氮化镓器件对有源相控阵高可靠性设计进行了展望。     

Process capability study of laser assisted micro milling of a hard-to-machine material

Laser assisted micro milling (LAMM) is capable of generating three-dimensional micro scale features in hard-to-machine materials. This paper compares the process capability of LAMM with conventional micro milling of a hardened tool steel. In particular, the potential advantages of LAMM over micro milling with respect to cutting forces, tool wear, material removal rate, burr formation and surface roughness are investigated when micro milling hardened A2 tool steel (62 HRC). The results show that LAMM has significant advantages over micro milling, especially in terms of cutting forces, material removal rate and tool wear. The average reduction in the resultant cutting force is found to be up to 69% with laser assist. In addition, tool wear is found to be substantially less with laser assist even when the material removal rates are increased by a factor of six over the tool manufacturer recommended cutting conditions.     

改善典型硝胺类易燃易爆材料引燃性能研究

通过针对典型硝胺类易燃易爆材料黑索今(RDX)和奥克托今(HMX)的引燃性能实验,研究了掺混碳黑和反应体系的封闭对上述药剂引燃特性的影响规律。研究表明,碳黑对硝胺类易燃易爆材料的激光吸收率有重要影响;反应体系的密封可以有效提高激光引燃感度,缩短激光引燃延迟时间,改善硝胺类易燃易爆材料的激光引燃性能。     

Size distributions of manure particles released under simulated rainfall

Manure and animal waste deposited on cropland and grazing lands serve as a source of microorganisms, some of which may be pathogenic. These microorganisms are released along with particles of dissolved manure during rainfall events. Relatively little if anything is known about the amounts and sizes of manure particles released during rainfall, that subsequently may serve as carriers, abode, and nutritional source for microorganisms. The objective of this work was to obtain and present the first experimental data on sizes of bovine manure particles released to runoff during simulated rainfall and leached through soil during subsequent infiltration. Experiments were conducted using 200 cm long boxes containing turfgrass soil sod; the boxes were designed so that rates of manure dissolution and subsequent infiltration and runoff could be monitored independently. Dairy manure was applied on the upper portion of boxes. Simulated rainfall (ca. 32.4 mm h(-1)) was applied for 90 min on boxes with stands of either live or dead grass. Electrical conductivity, turbidity, and particle size distributions obtained from laser diffractometry were determined in manure runoff and soil leachate samples. Turbidity of leachates and manure runoff samples decreased exponentially. Turbidity of manure runoff samples was on average 20% less than turbidity of soil leachate samples. Turbidity of leachate samples from boxes with dead grass was on average 30% less than from boxes with live grass. Particle size distributions in manure runoff and leachate suspensions remained remarkably stable after 15 min of runoff initiation, although the turbidity continued to decrease. Particles had the median diameter of 3.8 microm, and 90% of particles were between 0.6 and 17.8 microm. The particle size distributions were not affected by the grass status. Because manure particles are known to affect transport and retention of microbial pathogens in soil, more information needs to be collected about the concurrent release of pathogens and manure particles during rainfall events.     

珠江三角洲大暴雨的多普勒特征及形成机制

利用广州CINRAD-SA新一代多普勒天气雷达资料,结合天气形势分析,研究了华南地区夏季短时大暴雨的发生、发展过程,特别是中小尺度系统引发短时大暴雨不同发展阶段的多普勒特征以及辐合强度与短时大暴雨的关系,并对短时大暴雨的发展机制进行了初步探讨.通过分析发现,短时大暴雨产生于低空强盛西南气流等有利条件下,近地层雨区附近的气旋式扰动有利于激发对流,抽吸作用、局地锋生对对流的维持和加强起到了十分重要的作用.在短时大暴雨发生初期及发展旺盛期,大多数都伴有逆风区、辐合带等多普勒特征,中气旋更是与高强度降水、地面强风等剧烈天气密切相关.     

基于风廓线雷达的广州边界层局地回流指数廓线对污染物浓度的影响

利用2016—2019年广州增城风廓线雷达资料、地面气象站资料及附近广州九龙镇污染物浓度数据,研究了广州边界层局地回流指数R廓线对污染物浓度变化的影响,并综合分析了造成污染日或污染过程的R廓线及其阈值.结果表明,污染物浓度变化与局地回流指数R呈负相关及负滞后相关,负相关系数随高度的升高而下降.污染物NO₂浓度变化与局地回流指数R的负相关性最高,污染物O₃浓度变化与局地回流指数R的负相关性最低.不同季节、不同污染物浓度与局地回流指数R的负相关性有差异.当局地回流指数R（平均）<0.3的厚度大于400 m或至少3个高度层（每层高度差60 m）R<0.28时,发生复合型污染过程的可能性增大,同时可能出现超过7 d的长时间污染过程.     

佛山春季两次典型臭氧污染过程分析

近地层臭氧污染与气象条件密切相关,为了解珠三角地区春季臭氧（O₃）污染的气象成因,选取了2020年4月9日和28日佛山地区春季两次典型O₃污染过程进行对比分析.结果表明：（1）小风、低湿和高温是造成佛山春季O₃污染发生的气象成因.（2）两次过程各站点O₃峰值浓度大致出现在16:00—18:00,较年均统计偏晚1 h左右,最高气温明显低于夏、秋季;大多数站点日变化以单峰型为主,部分站点受局地风场和城市下风向传输影响呈现“倒U型”和“双峰型”.（3）垂直探测分析表明,4月9日O₃污染过程主要由局地反应生成,垂直方向下沉气流主导,污染主要积聚在1000 m以下的近地面层;28日受局地生成和垂直交换作用影响,O₃污染自下而上扩展,且早间残留层下传影响显著.（4）与长距离和高层输送相比,短途和低层传输对局地O₃污染发生的作用更为明显（输送频率可达60%以上）.春季佛山地区O₃污染的主要传输源为珠三角东部和南部地区,污染防控...     

激光光散射在混凝研究中的应用评述

混凝研究的理论与实践近三十年来得到长足的发展，很大的原因在于现代检测技术与手段的大力运用，激光光散射为其中得力的方法之一。本文对其基本操作原理作了简要介绍，并对测定过程中存在的若干问题作了探讨。然后就其在混凝领域中诸层次的研究现状与发展趋势进行了若干概括。本文试图阐明其应用于混凝领域的研究所具有的巨大潜力及困难与局限所在，以期将来更大的进展     

The application of ground penetrating radar attenuation tomography in a vadose zone infiltration experiment

Cross-borehole ground penetrating radar (XBGPR) is used in monitoring a long-term vadose zone infiltration experiment at a test site in Socorro, NM in order to examine contaminant transport in the vadose zone. XBGPR attenuation tomography is conducted in order to test the ability of using images of electromagnetic attenuation for hydrogeologic investigations. The results of four pre-infiltration attenuation inversions shows standard deviations below 0.1 Np/m, and demonstrate the consistency of the XBGPR tomography technique for making time-lapse observations. Correlation to the core records indicates that XBGPR attenuation tomograms provide high-resolution images of clay distribution in the vadose zone. Water infiltration at the ground surface was initiated in February 1999 at a constant rate of 2.7 cm/day, and continued at this rate throughout the data collection experiment. Time-lapse attenuation tomograms show that attenuation increases by approximately 0.3 Np/m during the water infiltration, and indicate a snowplow effect may be occurring where salts are dissolved by the water and concentrated at the front of the plume. Seasonal temperature changes may also cause changes in electromagnetic attenuation images, and masking the evidence of water infiltration. Thus caution must be taken when using time-lapse attenuation images to interpret the movement of a water plume during a long-term experiment as temperature changes.     

基于地基遥感资料的厦门市污染边界层特征分析

城市大气边界层是影响城市环境气象的重要研究对象,本研究利用新型地基遥感数据针对城市颗粒物污染过程开展边界层特征分析,旨在利用风廓线雷达和微波辐射计等高时空分辨率的遥感数据探讨边界层内大气运动、温湿条件的变化与近地面污染累积的关系.结果表明:厦门地区颗粒物污染过程中,边界层内弱风层厚度较地面风速而言更能够代表边界层内扩散条件的变化,可以更好地表征和预测近地面污染的变化;在局地累积的污染过程中,边界层内存在较厚的弱风层,同时2 km以下的风场有明显的风向转变特征,导致边界层内不存在有效的传输和扩散,另外,污染时边界层垂直温差可以在一定程度上反映干季的垂直扩散条件,0～3 km温差与PM_(2.5)浓度有着密切的联系;冷空气过程有将上游污染物向本地区输送的可能,城市边界层在东北大风的条件下伴随着显著的垂直下沉运动,有利于上空污染向下扩散.多源地基遥感数据联合分析能够进一步解释城市边界层内气象条件对于城市大气污染变化的影响,集合各设备的探测优势开展城市宜居和污染气象条件研究具有较高的科学性和可行性.