A comparison of total reaction cross section models used in particle and heavy ion transport codes

Understanding the interactions and propagations of high energy protons and heavy ions are essential when trying to estimate the biological effects of Galactic Cosmic Rays (GCR) and Solar Particle Events (SPE) on personnel in space. To be able to calculate the shielding properties of different materials and radiation risks, particle and heavy ion transport codes are needed. In all particle and heavy ion transport codes, the probability function that a projectile particle will collide within a certain distance x in the matter depends on the total reaction cross sections, and the calculated partial fragmentation cross sections scale with the total reaction cross sections. It is therefore crucial that accurate total reaction cross section models are used in the transport calculations. In this paper, different models for calculating nucleon–nucleus and nucleus–nucleus total reaction cross sections are compared with each other and with measurements. The uncertainties in the calculations with the different models are discussed, as well as their overall performances with respect to the available experimental data. Finally, a new compilation of experimental data is briefly presented.     

加力燃烧室NOx排放生成规律试验分析

实现航空发动机大推力通常采用加力燃烧室设计,燃烧室进气温度升高会同步导致排放尾气中NO_x浓度提高.采用典型加力燃烧室主稳定器的V型结构试验件,测试加力燃烧前后(进口600 ℃,出口600~1 200 ℃)燃烧室排放断面的NO_x浓度分布,通过相同流场4种试验工况的NO_x生成浓度组分和氧含量变化分析,验证了加力燃烧室NO_x生成以热力型NO为主的"高温、富氧、贫油"燃烧特性.结果表明加力燃烧室燃烧过程中消耗的氧含量大多贡献于CO₂增量,在800~1 000 ℃燃气排放温度范围内,不完全燃烧产物CO对NO的热力生成有明显抑制作用.     

舷外雷达有源诱饵在舰艇反导中的运用研究

阐述了舷外雷达有源诱饵的干扰机理,并对影响干扰效果的诱饵有效雷达截面积理论计算公式进行了推导,从中找出了影响诱饵有效雷达截面积大小的因素,通过对其中诱饵有效辐射功率和诱饵距反舰导弹距离因素的分析,提出了舰艇使用舷外雷达有源诱饵防御反舰导弹时,在发射时机、布放位置和干扰方位上应采取的措施。     

并列双发三维非对称多S弯喷管参数化设计方法

形成了一套基于CFD计算评价的并列双发三维非对称多S弯喷管参数化设计方法,并初步证明了该方法的正确性和可行性.多S弯中心线在Z向偏心度为0时:第一S弯Y向偏心度、长度都最小,第二S弯Y向偏心度、长度都最大,第三S弯Y向偏心度、长度分别介于前两个S弯对应参数之间,各S弯都采用进口缓慢转弯,出口快速转弯的规律,以利于抑制背风侧分离和涡.剖面在各S弯上都采用进口快速收缩缓慢转弯,出口缓慢收缩快速转弯的规律,且宽高比与侧边倾角在进出口变化速率相同,且侧边倾角只分布在第一S弯上,以利于稳定流场和增加隐身性能.合流器采用楔底宽高比约束,其值应不超过0.26.      

Response of photosynthetic systems to salinity stress in the desert cyanobacterium Scytonema javanicum

The present study investigated the physiological and biochemical characteristics of Scytonema javanicum, a pioneer species isolated from desert biological crusts, under salinity stress. Pigment analysis showed that salinity decreased chlorophyll a and phycocyanin content, while low salinity increased carotenoid concentration and high salinity decreased carotenoid concentration. Salinity also inhibited CO₂ assimilation rate and photosynthetic oxygen evolution in this cyanobacterium. Chlorophyll a fluorescence transient parameters (φPo, φEo, ψO, RC/ABS, RC/CS, PI_ABS, and PI_CS) were decreased under salt stress, while dVo/dto(Mo), Vj and φDo were increased. The decrease of ETRmax and Yield and the change of chlorophyll a fluorescence transients showed that salt stress had an important influence on photosynthesis. These results indicated that the effects of salinity stress on photosynthesis in S. javanicum may depend on the inhibition of electron transport and the inactivation of the reaction centers, but this inhibition may occur in the electron transport pathway at the PSII donor and acceptor sites.     

三角网格曲面模型快速分层算法

提出一种三角网格曲面模型快速分层算法,该算法基于R*-tree建立三角网格动态空间索引结构,依据索引结构数据结点的分布状况计算各层截平面的位置;采用深度优先遍历方法获取与截平面相交的三角面片集合,并计算该集合中各面片与截平面的交线,将交线首尾相连,生成截面轮廓线,实现三角网格曲面模型的快速分层;实例证明该算法可对各种复杂三角网格曲面模型进行分层,算法准确、稳定,运行效率高.     

苏通长江大桥主梁断面三分力系数的雷诺数效应

以苏通长江大桥为研究背景,研发了一套测压装置,通过测压法对苏通长江大桥施工状态主梁断面三分力系数进行了现场实测研究,并把现场实测所得结果与风洞试验结果进行了对比,研究了雷诺数对三分力系数的影响。结果表明：雷诺数对阻力系数影响较大,现场实测值比风洞试验所得值小约15％,对升力系数及力矩系数影响较小。因此,针对特大桥梁,在利用风洞实验获取三分力系数时应尽量使雷诺数接近实际情况,否则结果可能偏于保守。     

方形截面飞行器上仰机动对滚转特性影响的数值模拟

飞行器从中小迎角至大迎角范围内,由于背风区流动分离形态的演化,静态气动特性特别是横侧向气动特性也随迎角显著变化,可能诱发复杂的滚转运动。但飞行器一般是上仰机动时,才从平飞状态快速拉起至大迎角,此机动过程对横侧向气动特性和滚转运动可能产生较大影响。本文发展了刚体动力学方程和Navier-Stokes方程的松耦合求解技术,并通过数值模拟航天飞机脱落碎片的六自由度运动轨迹进行了验证。针对背风区涡流形态及横侧向气动特性复杂的方形截面飞行器,数值模拟研究了其不同迎角下的静态滚转气动特性、自由滚转运动特性,以及上仰机动时不同拉起速率对滚转运动特性的影响。结果表明,对于此飞行器,静态时存在临界迎角约为13°,当迎角小于临界迎角时,滚转方向是静不稳定的,诱发快速滚转运动;当迎角大于临界迎角时,滚转方向是静稳定的,其滚转运动是收敛的。但上仰机动时,滚转运动的形态还与拉起速率相关,即使拉起的终止迎角大于临界迎角,如果拉起速率较慢,也可能出现快速滚转运动。     

薄壁泡沫塑料模成型工艺参数的研究

针对大型薄壁件消失模精铸的特点，对消失模的成型工艺进行了大量试验。结果表明，成型工艺与模样密度相互制约，预发泡工艺可影响模样的密度，一定的模样密度又制约了其成型发泡工艺。对不同密度要求的模样，应采用不同的成型工艺。     

大直径液氧煤油发动机燃烧室结构和隔板型式对声学特性的影响

随着火箭发射任务轨道高度和载荷质量的提高,发动机推力和燃烧室直径增大,使燃烧室固有声学振型越发复杂.燃烧室收敛段、抗脉动隔板及其结构型式会显著影响燃烧室的声学特性,进而改变发动机的燃烧不稳定性裕度.为了研究燃烧室结构和隔板型式对声学特性的影响,建立了燃烧室声学有限元模型,并通过单喷嘴声学实验验证了仿真模型的准确性.研究...