Effects of Reflector on Intensity of Thermal Neutrons Emitted from Moderator for Pulsed Neutron Source

Intensity of the thermal neutrons emitted from the moderator with a reflector was calculated to study the effects on the intensity caused by a macroscopic total neutron cross section and an average logarithmic energy loss of the reflector materials.

A reflector with a large macroscopic total neutron cross section produced higher thermal neutron intensity than that with a small cross section if they had the same average logarithmic energy loss. Among the reflectors with the same total macroscopic neutron cross section, the thermal neutron intensity was not changed by decreasing the average logarithmic energy loss to a range less than about 0.1 but above this value the intensity was weakened. From this result it was found that a large macroscopic total cross section and a small average logarithmic energy loss are preferable characteristics for reflector materials.

As actual reflector materials, three reflector materials were examined, namely beryllium, graphite and lead, which are now considered to be candidates. The lead reflector was effective for the moderator with a large emission-surface and the beryllium reflector for the moderator with a small one. This result indicates that the moderator size is important for choosing the best reflector material to produce the highest beam intensity.     

γFe2O3的选择性催化还原脱硝性能及其对NH3和NO的表面吸附行为研究

采用γFe2O3纳米粉末制备选择性催化还原(selective catalysis reduction,SCR)脱硝催化剂,通过XRD、BET对催化剂进行表征,并对此催化剂的低温SCR脱硝性能在一固定床反应器中进行考察;此外通过原位红外漫反射光谱法(diffuse reflectance infrared Fourier transform spectroscopy, DRIFTS)研究了反应物在催化剂表面的吸附活化。结果表明,实验所采用的Fe2O3为纯γ相,具有较高的热稳定性和脱硝效率。DRIFTS实验研究表明,NH3主要吸附到γFe2O3催化剂表面 L 酸位形成吸附态的 NH3,在小于270℃时有部分NH3吸附到B酸位生成NH4+;O2的存在能促进吸附到L 酸位上的 NH3发生脱氢反应生成 NH2,并能够大大促进NO在催化剂表面吸附生成硝酸盐和吸附态的NO2,从而促进低温下的SCR反应。在90~360℃的温度区间内可能遵循两种反应途径,主要反应是吸附在L酸位的NH3脱氢生成NH2,然后和气态的NO反应生成N2和H2O;在低于240℃时,可能存在另外一种反应途径,中间产物 NO2(NH4+)2与NO反应生成N2、H2O和H+。     

黄色喷印墨水的配制和试用

对黄色喷印墨水进行了多次制备试验,对产品各组分在喷印墨水中的性能和作用进行了深入探讨,并在此基础上对多种配方进行了选优,找出了黄色喷印墨水的较佳配方,几次试用的结果证实了该配方良好的实用性.     

固相萃取光谱法测定水及肉制品中痕量亚硝酸钠

采用固相萃取光谱法对亚硝酸钠进行定量分析。首先确定分析波长为472.5 nm,随后优化衍生化反应的条件：pH 4.74、衍生化时间15 min、衍生化试剂亚硝酸钠-对氨基苯磺酸-1-萘酚物质的量比1∶3∶3。富集条件：富集膜种类为尼龙膜,过膜体积为10 mL。在0.002～0.030 mg/L质量浓度范围,吸光度y与质量浓度x之间呈二次函数关系,y=－268.76x2＋14.55x＋0.03,R2=0.999,检出限为1.29 μg/L。将该方法用于自来水中亚硝酸钠的检测,加标回收率在91.3%～114.0%之间,相对标准偏差在4.21%～7.90%之间;用于培根亚硝酸钠的检测,检测结果与离子色谱检测结果相符,平行实验的相对标准偏差分别为8.51%、9.98%。本研究为测定亚硝酸钠提供了一种具有较高的灵敏度和选择性,以及较理想的准确度和精密度的新型快速检测方法。     

反光板对提高热管真空管热性能的研究

提出了对带反光板的吸热体接收太阳辐射量的分析方法，并对三种有渐开线反光板且吸热体形状不同的热管真空管和一种无反光板的热管真空管进行了对比实验。结果表明：渐开线反光板可大幅度提高热管真空管的热性能，而且其吸热体的形状对热性能提高的幅度有影响。     

Comparative study of various correlations in estimating hourly diffuse fraction of global solar radiation

Proper design and performance predictions of solar energy systems require accurate information on the availability of solar radiation. The diffuse-to-global solar radiation correlation, originally developed by Liu and Jordan, has been extensively used as the technique providing accurate results, although it is latitude dependent. Thus, in the present study, empirical correlations of this type were developed to establish a relationship between the hourly diffuse fraction (k_d) and the hourly clearness index (k_t) using hourly global and diffuse irradiation measurements on a horizontal surface performed at Athalassa, Cyprus. The proposed correlations were compared against 10 models available in the literature in terms of the widely used statistical indicators, rmse, mbe and t test. From this analysis, it can be concluded that the proposed yearly correlation predicts diffuse values accurately, whereas all candidate models examined appear to be location-independent for diffuse irradiation predictions.     

基于实数编码遗传算法的赋形反射面天线设计

为了使星载天线的远场方向图与服务区的形状相匹配,并在服务区内获得高的增益和好的交叉极化隔离度,采用改进的实数编码遗传算法对其进行了优化设计。在优化过程中,以主极化增益和交叉极化隔离度作为优化目标,参考目标规划法来构造适应度函数;在群体选择的基础上采用差分进化方式、内插/外推和基因交换3种方法相结合来产生新个体,并采用自适应变异概率,来保证新一代染色体模式的多样性。最后以一个工作在Ku频段的赋形反射面天线为例,对其形状进行了优化设计。数值仿真结果表明,不仅天线的方向图与服务区形状匹配度很高,而且主极化增益和交叉极化隔离度都满足特定的设计要求,充分验证了所提算法的可行性和有效性。     

双曲率反射面天线数据处理方法探索

以某雷达双曲率反射面天线为对象,介绍了大型曲面天线常用的精度测量方法,这些方法存在测量点拟合和设计坐标系与测试坐标系的转换关系等难点,数据处理关系复杂,利用统一基准、编程、数据转换等方法求出测量点对应的设计坐标值,通过与测试值比较得出工作面的均方根误差值,实现面精度测量和计算,解决了数据处理难点问题.     

Effects of nanostructured back reflectors on the external quantum efficiency in thin film solar cells

Hydrogenated amorphous Si ( α-Si:H) is a promising material for photovoltaic applications due to its low cost, high abundance, long lifetime, and non-toxicity. We demonstrate a device designed to investigate the effect of nanostructured back reflectors on quantum efficiency in photovoltaic devices. We adopt a superstrate configuration so that we may use conventional industrial light trapping strategies for thin film solar cells as a reference for comparison. We controlled the nanostructure parameters via a wafer-scale self-assembly technique and systematically studied the relation between nanostructure size and photocurrent generation. The gain/loss transition at short wavelengths showed red-shifts with decreasing nanostructure scale. In the infrared region the nanostructured back reflector shows large photocurrent enhancement with a modified feature scale. This device geometry is a useful archetype for investigating absorption enhancement by nanostructures.     

980nm高功率垂直腔面发射激光列阵的单元结构优化

为了提高980 nm垂直腔面发射激光器(VCSEL)列阵的整体性能,对列阵单元器件的分布布拉格反射镜(DBR)的反射率进行了优化.分析了DBR的反射率与阈值电流,输出功率及转换效率之间的关系,在维持较低阈值电流的前提下适当调节了N-DBR的反射率,使单元器件斜率效率得到了有效提高,进而改善了VCSEL列阵的整体输出特性...