基于信息检索课的大学生信息检索行为调查研究

信息检索课程的系统化讲授,对于大学生优化信息检索行为,提高信息检索使用效率具有不容忽视的教学辅助作用。立足问卷调查形成的一系列相关数据,探讨大学生信息检索行为存在问题,最终在课程教学中提出优化大学生信息检索的对策：明确信息检索目的,提升实施效果;有效提升检索行为实施频率,增强综合质量;使得信息获取多元发展,优化成效凸显。     

混凝土坝裂缝变形的不确定性分析模型

混凝土坝裂缝的发生和发展受到不确定因素影响。将大坝系统及其安全监控看作一个受诸多因素影响的不确定性系统,结合裂缝实测资料,应用近似推理模型和信息分配法,建立了裂缝变形的不确定性分析模型。     

基于正交设计的黄池沟退水道弯道体型优化的数值模拟分析

为探求黄池沟退水道弯道的合理体型,采用正交设计与数值模拟相结合的方法研究了体型参数对弯道水流的影响。选取弯道宽度、弯道曲率半径、纵向坡度3个主要影响参数按正交试验设计,确定了9组正交试验方案,利用经水工模型试验结果验证的数学模型对正交试验方案进行模拟,分析了体型参数对弯道及下游陡坡段横向水位差的影响。结果表明,3个体型参数影响作用由大到小依次为纵向坡度、弯道宽度和弯道曲率半径;坡度为显著影响因素,且平坡最佳,弯道曲率半径和弯道宽度影响不显著,据此推荐合理体型参数为坡度取0,弯道宽度和弯道曲率半径采用原设计值。     

全桥拓朴隔离式开关电源主变压器磁设计

全桥拓朴结构的隔离式开关电源能在较小的尺寸下实现较高的功率变换,是高功率密度电源的重要电路结构,其高频主变压器磁心一般选择低损耗功率锰锌软磁铁氧体材料,其设计对电源的尺寸、性能有显著影响.磁设计的目的是用尽可能小的磁心传输尽可能高的功率,但受到两个限制性条件的制约,即磁心的发热和磁饱和.在散热充分的情况下,限制性条件就是磁饱和了.磁心参数设计多采用AP值公式,但目前的几个计算公式都存在一些缺点,要么计算不够准确,要么计算过于复杂不便工程应用.从全桥变压器基本原理出发,将一个工作周期分成了四个时间段.根据各时段的电流大小、方向所对应的磁工作状态,推演了磁心参数计算公式,并用一个实例进行了验证.     

离子束增强沉积氮化硅膜及TiAl抗高温氧化性能的改善

用离子束增强沉积（ＩＢＥＤ）方法在金属间化合物ＴｉＡｌ上合成厚度为０．５，１，和２μｍ的氮化硅薄膜。所形成的薄膜为非晶态，膜与基底间存在混合的过渡区，膜与基底结合紧密用ＡＥＳ，ＸＲＤ和ＸＰＳ研究薄膜的组成和结构，高温循环氧化结果表明，经沉积膜的ＴｉＡｌ试样的抗氧化性能显著提高其中沉积０．５μｍ薄膜的试样表现出极好的抗循环氧化性能由ＳＥＭ及ＥＤＳ分析得出，良好的高温稳定性能、高的膜／基底结合力和形成富Ａｌ２Ｏ３和硅化物的保护层是提高ＴｉＡｌ抗高温氧化性能的主要因素．     

黄河内蒙古段干流沉积物中砷含量及形态研究

为探明黄河内蒙古段沉积物中砷含量及形态分布特征,采集黄河内蒙古段干流柱状沉积物,采用HNO4-H2SO4-HCl O4法消解沉积物样品,提取沉积物中吸附型砷(A-As)、铝型砷(Al-As)、铁型砷(Fe-As)、钙型砷(CaAs)、包蔽型砷(O-As)5种形态砷,并采用氢化物发生原子荧光分光光度法测定砷含量。结果表明:黄河内蒙古段干流柱状沉积物中砷含量为7.123~16.661 mg/kg,平均为9.292 mg/kg;从整体上看,左岸沉积物砷含量高于右岸,随深度增加砷含量呈下降趋势,从上游至下游砷含量在黑柳子段出现高值;黄河内蒙古段沉积物中砷以Ca-As为主,O-As次之;随着深度的增加,总体上,Ca-As含量略有升高,A-As和O-As含量有所下降,Al-As和Fe-As含量基本不变。     

积石峡水电站溢洪道堰闸段工程中锚索测力计的应用

文章简述了积石峡水电站溢洪道堰闸段锚索测力计的设计布置、率定检验、安装方法及张拉过程中对测力计的观测等方面,以加强锚索测力计在锚索张拉施工过程中的质量控制。     

Mice deficient for 5-lipoxygenase, but not leukocyte-type 12-lipoxygenase, display altered immune responses during infection with Schistosoma mansoni

Periovular granuloma formation during Schistosoma mansoni infection is a complex, multifaceted immunologic response. Products of arachidonic acid metabolism have been shown to contribute to this response through studies in which general inhibitors of lipoxygenase function reduce granulomatous inflammation. To determine which lipoxygenases are important for granuloma development in schistosomiasis, wild type mice or mice deficient for 5-lipoxygenase (5-LO) or "leukocyte-type" 12-lipoxygenase (12-LO) were infected with S. mansoni and studied for responses to schistosome eggs and egg antigens. At the acute stage of infection, when granuloma formation is usually maximal, 5-LO deficient mice developed smaller granulomas around liver-deposited schistosome eggs compared with wild type or 12-LO deficient mice. 5-LO mice also displayed less antibody-mediated (5 h) and cell-mediated, delayed-type (24 h) hypersensitivity to schistosome egg antigens than did the other two infection groups. In an attempt to determine possible mechanisms for the reduced inflammatory responses, we also measured hepatic mRNA levels of cytokines that have been shown to influence granuloma size (IL-4, IL-10, and IFN-gamma). The mRNA levels for IL-10 were significantly lower in 5-LO-deficient mice, but SEA-stimulated spleen cells did not demonstrate a significant difference in IL-10 production between wild type and 5-LO mice. These data suggest that 5-LO plays a role in host responses to schistosomiasis via a mechanism that cannot be explained solely by changes in expression of these cytokines.     

NRP/B, a novel nuclear matrix protein, associates with p110(RB) and is involved in neuronal differentiation

The nuclear matrix is defined as the insoluble framework of the nucleus and has been implicated in the regulation of gene expression, the cell cycle, and nuclear structural integrity via linkage to intermediate filaments of the cytoskeleton. We have discovered a novel nuclear matrix protein, NRP/B (nuclear restricted protein/brain), which contains two major structural elements: a BTB domain-like structure in the predicted NH2 terminus, and a "kelch motif" in the predicted COOH-terminal domain. NRP/B mRNA (5.5 kb) is predominantly expressed in human fetal and adult brain with minor expression in kidney and pancreas. During mouse embryogenesis, NRP/B mRNA expression is upregulated in the nervous system. The NRP/B protein is expressed in rat primary hippocampal neurons, but not in primary astrocytes. NRP/B expression was upregulated during the differentiation of murine Neuro 2A and human SH-SY5Y neuroblastoma cells. Overexpression of NRP/B in these cells augmented neuronal process formation. Treatment with antisense NRP/B oligodeoxynucleotides inhibited the neurite development of rat primary hippocampal neurons as well as the neuronal process formation during neuronal differentiation of PC-12 cells. Since the hypophosphorylated form of retinoblastoma protein (p110(RB)) is found to be associated with the nuclear matrix and overexpression of p110(RB) induces neuronal differentiation, we investigated whether NRP/B is associated with p110(RB). Both in vivo and in vitro experiments demonstrate that NRP/B can be phosphorylated and can bind to the functionally active hypophosphorylated form of the p110(RB) during neuronal differentiation of SH-SY5Y neuroblastoma cells induced by retinoic acid. Our studies indicate that NRP/B is a novel nuclear matrix protein, specifically expressed in primary neurons, that interacts with p110(RB) and participates in the regulation of neuronal process formation.     

Isoseparation curves: a mechanism for optimizing off-axis dose homogeneity of intact breast irradiation

The purpose of this paper is to determine whether using off-axis isoseparation curves to optimize the collimator rotation angle improves dose homogeneity. Eleven intact breast irradiation patients underwent computerized tomography (CT) treatment planning with 1 cm abutting slices. Central plane treatment planning, using 6 MV photons, tissue inhomogeneity corrections, and isocentric opposed tangent treatment fields, was performed. Collimators were rotated to match chest wall slope through the use of a beam's-eye-view setting. Patient separations were measured from the apex of the breast to the posterior field border on each axial CT slice. Sagittal-plane isoseparation curves were constructed from these measurements. Using these curves, the collimator rotation that minimized off-axis separation differences was determined. A comparison of off-axis dose inhomogeneity was performed for patients with a > or =10 degrees difference between this optimized collimator angle and the angle determined by chest wall slope. These comparative treatment plans differed only with respect to collimator angle rotation. The mean optimal collimator rotation angle differed significantly from the mean rotation angle which matched the chest wall slope (5.4 degrees vs. 11 degrees, respectively, P < 0.001). Four of the 11 patients had rotation angle differences of 10 degrees. In these patients, the optimization of collimator angle reduced the percentage of breast volume to "that" received > or =110% of the prescribed dose. For the patient with the largest breast size to the patient with the smallest breast size the decreases were, respectively, 5% (15% to 10%), 3% (24% to 21%), 1% (4% to 3%), and 1% (0.9% to 0%). The mean reduction in dose inhomogeneity was greatest in the inferior breast quadrants. At 6 cm and 4 cm off axis, the mean reductions in the percentages of the breast tissue to "that" received 110% of the prescribed dose were respectively 15.1% and 5.3 %. Optimizing the collimator angle through the use of isoseparation curves decreases dose inhomogeneity. The greatest improvements are in the inferior quadrants of the intact breast. The improved dose homogeneity may have clinical relevance in the treatment of patients with large breast sizes.