Cr-Nb系机械合金化及其热压过程中的X射线衍射分析

讨论了X射线衍射测试技术在Cr-Nb系元素机械合金化及随后的热压工艺的物相衍变过程中的应用,包括晶粒细化引起的峰形宽化、不同热压温度对Cr2Nb相形成量的对比.通过X射线衍射测试技术及应用EVA、TOPAS P软件包可以直观地进行分析,在合金相中发现了一种新的Cr2Nb相态.     

部件冷却对二元俯仰矢量排气系统红外特征抑制实验

实验测试了采用中心锥气膜冷却和喷管冲击-气膜冷却的二元俯仰（2D-CD）矢量排气系统,在几何偏转0,10,20°三种角度下,壁面温度和红外辐射特征分布,并与未冷却状态进行了对比分析。结果表明:前密后疏的气膜孔排布形式可有效减小热侧面高温区域大小。中心锥冷却时,密流比为0.8条件下壁面冷却效率达45%~63%,排气系统尾向±10°范围内红外辐射强度下降20%;但是由于冷气流注入,导致下游壁面（隔热屏、喷管）温度升高,在30°探测方向上红外辐射强度上升15%。喷管冷却时,收敛段（密流比为0.25）冷却效率达19%~33%,扩张段（密流比为0.65）冷却效率达75.5%~83.5%,侧壁段（密流比为0.65）冷却效率达78%~90%,导致在排气系统尾向15°~75°范围内,红外辐射强度下降30%以上,最大降幅达80%（几何偏转20°,宽边探测面30°探测方向）。      

脉冲激光辐射下VO_2薄膜的光限幅性能

采用反应溅射和后续退火工艺,在石英衬底上制备具有热致相变特性的VO_2薄膜,并对薄膜的光学性能进行表征。研究发现:在弱光辐射下,随着温度的改变,薄膜的透射率在可见及近红外光区会发生显著变化,具有良好的相变光开关特性;在强光辐射下,制备的VO_2薄膜同样具有良好的红外光调制深度;当脉冲激光波长为1064 nm时,随着脉冲能量的逐渐增强,薄膜的表面反射率逐渐降低,光限幅性能呈现出先升高再降低的趋势,其透射率最低可降至7%,薄膜的脉冲激光损伤阈值约为50 mJ/cm~2。     

O相合金Ti2AlNb的超塑性研究进展

以O相为基础的Ti2AlNb合金具有高的比强度、比刚度以及良好的高温蠕变性能和抗氧化性能,己经成为最具潜力的航空航天高温结构材料.在其实用化进程中,超塑成形是该材料成形加工形成制件的理想工艺.本文综述了Ti2AlNb基合金材料超塑性研究的最新进展,对其超塑变形中的组织特征和变形机制进行了详细讨论.最后,展望了Ti2AlNb基合金超塑性加工未来的发展趋势.     

A low dose pre-irradiation induces radio- and heat-resistance via HDM2 and NO radicals,and is associated with p53 functioning

The aim of this work was to clarify the effect of low dose pre-irradiation on radio- and heat-sensitivity. Wild-type (wt) p53 and mutated (m) p53 cells derived from the human lung cancer H1299 cell line were used. The parental H1299 cell line is p53-null. Cellular sensitivities were determined with a colony-forming assay. When wtp53 cells were exposed to a low dose X-irradiation, induction of radio- and heat-resistance was observed only in the absence of RITA (an inhibitor of p53-HDM2 interactions), aminoguanidine (an iNOS inhibitor) and c-PTIO (an NO radical scavenger). In contrast, the induced radio- and heat-resistance was not observed under similar conditions in mp53 cells. Moreover, heat-resistance as well as radio-resistance developed when wtp53 cells were treated with ISDN (an NO generating agent) alone. These findings suggest that NO radicals are an initiator of radio- and heat-resistance, and function through the activation of HDM2 and the depression of p53 accumulation.     

SiO2 改性ZrO2 气凝胶高温稳定性

以ZrOCl2·8H2O 为锆源,以环氧丙烷( PO) 为凝胶促进剂制备ZrO2 凝胶,将ZrO2 凝胶置于正硅
酸乙酯乙醇溶液中老化,再结合高温超临界干燥工艺制备了SiO2 改性ZrO2 气凝胶。通过对比ZrO2 气凝胶和
SiO2 改性ZrO2 气凝胶高温结构转变讨论了SiO2 改性对ZrO2 气凝胶高温结构的影响。采用FT-IR、XRD、SEM
和TEM 等分析手段对样品进行高温结构表征。结果表明:采用正硅酸乙酯乙醇溶液老化ZrO2 凝胶后,在ZrO2
凝胶粒子表面形成了一层SiO2 包裹层,这层SiO2 包裹层显著抑制了ZrO2 的扩散、成核和生长过程,高温稳定
性得以显著提高。     

一种适用于情报图像处理的图像集分类算法

无人机情报处理系统是无人机地面控制系统的重要组成部分之一,主要负责对无人机侦察载荷下传的侦察情报进行处理,从复杂的情报中获得直观的情报产品并传递给上级和友邻单位。对于搭载光电载荷的无人机情报处理当前仍以依靠人力鉴别为主。介绍一种基于快速近似最近邻( FLANN) 搜索特征的K 近邻用分类决策,可去除背景信息对分类性能的影响;为了进一步提高算法的运行速度及减少算法的内存开销,采用特征选择的方式分别减少测试图像和训练图像集的特征数目,并尝试同时减少测试图像和训练图像集中的特征数目平衡分类正确率与分类时间之间的矛盾。该算法保留了原始NBNN 算法的优点,无需参数学习的过程,实验结果验证了算法的正确性和有效性。     

Variability of foF2 in the African equatorial ionosphere

This paper presents the impact of diurnal, seasonal and solar activity effects on the variability of ionospheric foF2 in the African equatorial latitude. Three African ionospheric stations; Dakar (14.8°N, 17.4°W, dip: 11.4°N), Ouagadougou (12.4°N, 1.5°W, dip: 2.8°N) and Djibouti (11.5°N, 42.8°E, dip: 7.2°N) were considered for the investigation. The overall aim is to provide African inputs that will be of assistance at improving existing forecasting models. The diurnal analysis revealed that the ionospheric critical frequency (foF2) is more susceptible to variability during the night-time than the day-time, with two peaks in the range; 18–38% during post-sunset hours and 35–55% during post-midnight hours. The seasonal and solar activity analyses showed a post-sunset September Equinox maximum and June Solstice maximum of foF2 variability in all the stations for all seasons. At all the stations, foF2 variability was high for low solar activity year. Overall, we concluded that equatorial foF2 variability increases with decreasing solar activity during night-time.     

Behavior of the equivalent slab thickness over three European stations

The total electron content (TEC) derived from the global positioning system (GPS) and the F2-layer peak electron density obtained from Digisonde data have been used to study the diurnal, seasonal and solar activity variations of the ionospheric equivalent slab thickness (τ) over three European stations located at Pruhonice (50.0°N, 15.0°E), Ebro (40.8°N, 0.5°E) and El Arenosillo (37.1°N, 353.3°E). The diurnal variation of the τ is characterized by daytime values lower than nighttime ones for all seasons at low solar activity while daytime values larger than nighttime characterizes the diurnal variation for summer at high solar activity. A double peak is noticeable at dusk and at dawn, better expressed for winter at low solar activity. The seasonal variations of τ depend on local time and solar activity, the daytime values of τ increases from winter to summer whereas nighttime values of τ show the opposite. The effect of the solar activity on τ depends on local time and season, there being very sensitive for winter nighttime values of τ. The results of this study are compared with those presented by other authors.     

Comparative study of foF2 measurements with IRI-2007 model predictions during extended solar minimum

The unusually deep and extended solar minimum of cycle 23/24 made it very difficult to predict the solar indices 1 or 2 years into the future. Most of the predictions were proven wrong by the actual observed indices. IRI gets its solar, magnetic, and ionospheric indices from an indices file that is updated twice a year. In recent years, due to the unusual solar minimum, predictions had to be corrected downward with every new indices update. In this paper we analyse how much the uncertainties in the predictability of solar activity indices affect the IRI outcome and how the IRI values calculated with predicted and observed indices compared to the actual measurements. Monthly median values of F2 layer critical frequency (foF2) derived from the ionosonde measurements at the mid-latitude ionospheric station Juliusruh were compared with the International Reference Ionosphere (IRI-2007) model predictions. The analysis found that IRI provides reliable results that compare well with actual measurements, when the definite (observed and adjusted) indices of solar activity are used, while IRI values based on earlier predictions of these indices noticeably overestimated the measurements during the solar minimum. One of the principal objectives of this paper is to direct attention of IRI users to update their solar activity indices files regularly. Use of an older index file can lead to serious IRI overestimations of F-region electron density during the recent extended solar minimum.