Extraordinary behaviour of the Y1?xPrxBa2Cu3O7?δ system

Investigations of Ygt;1–gt;xgt; gt;Mgt; gt;xgt; gt;Bagt;2gt;Cugt;3gt;Ogt;7–gt;g src="/content/g552326622313098/xxlarge948.gif" alt="delta" align="BASELINE" BORDER="0">gt; gt; (M=Ce, Th)gt;cgt;-axis oriented thin film specimens show that the rate of depression ofgt;Tgt; gt; gt;cgt; gt; withgt;xgt; is larger for M=Th, than for M=Ce and Pr, and suggest that Ce, like Th, is tetravalent in this compound. Hall effect measurements on Ygt;1–gt;xgt; gt;Prgt; gt;xgt; gt;Bagt;2gt;Cugt;3gt;Ogt;7–gt;g src="/content/g552326622313098/xxlarge948.gif" alt="delta" align="BASELINE" BORDER="0">gt; gt; single crystals reveal agt;Tgt; gt;2gt; dependence of the cotangent of the Hall angle in the normal state and a g src="/content/g552326622313098/xxlarge8220.gif" alt="ldquo" align="MIDDLE" BORDER="0">negative Hall anomalyg src="/content/g552326622313098/xxlarge8221.gif" alt="rdquo" align="MIDDLE" BORDER="0"> belowgt;Tgt; gt; gt;cgt; gt; in the superconducting state, in agreement with recent reports. Our research shows that the depth, g src="/content/g552326622313098/xxlarge916.gif" alt="Delta" align="BASELINE" BORDER="0">, of the negative Hall signal scales withgt;T/Tgt; gt; gt;cgt; gt; and that the maximum value of g src="/content/g552326622313098/xxlarge916.gif" alt="Delta" align="BASELINE" BORDER="0"> decreases linearly withgt;xgt; and vanishes atgt;xgt;g src="/content/g552326622313098/xxlarge8776.gif" alt="ap" align="MIDDLE" BORDER="0">0.24. Magnetoresistance measurements on Ygt;1–gt;xgt; gt;Prgt; gt;xgt; gt;Bagt;2gt;Cugt;3gt;Ogt;7–gt;g src="/content/g552326622313098/xxlarge948.gif" alt="delta" align="BASELINE" BORDER="0">gt; gt; single crystals indicate that the irreversibility linegt;H(Tgt; gt;*gt;) obeys a universal scaling relation characterized by angt;mgt;=3/2 power law neargt;Tgt; gt;cgt;, with a crossover to a more rapid temperature dependence of belowgt;T/Tgt; gt; gt;cgt; gt;g src="/content/g552326622313098/xxlarge8776.gif" alt="ap" align="MIDDLE" BORDER="0">0.6, similar to that observed for polycrystalline specimens.     

基于太赫兹布拉格光纤的表面生物传感器

空心布拉格光纤在传感领域应用极为广泛。本文提出了一种基于带有缺陷层的太赫 兹(terahertz,THz)空心布拉格光纤的表面生物传感器,并对该传感器在太赫兹频段的细菌种类检测性能进行 分析。在太赫兹布拉格光纤中,高折射率光敏树脂层和低折射率空气层以纤芯为中心周期性 排列,在纤芯内壁沉积分析物引入缺陷模式。本文对提出的传感器性能进行了数值研究。仿 真结果表明,该传感器有很高的纤芯功率比,限制损耗在0.3 THz和0.45 TH z频 段有损耗峰,能得到可识别的特征频率,此特征频率用于细菌种类检测。当频率大于0.7 TH z时,该传感器可实现厚度无关的表面生物传感。本文所提出的基于太赫兹空心布拉格光纤 的 表面生物传感器可用于检测细菌种类,在微生物检测方面有很大的应用潜力。     

复合泡沫填充管的高g值冲击防护特性

目的 为避免或减小高gt;ggt;值冲击对弹内轻质元器件的破坏,应加强对轻质元器件缓冲防护结构的研究。方法 基于新型复合泡沫和通孔泡沫铝的2种泡沫填充管,通过万能试验机和落锤冲击系统研究了2种泡沫填充管的静动态力学特性,并运用数值模拟方法研究高gt;ggt;值冲击下等质量的泡沫填充管与夹芯管的加速度缓冲效果和吸能机制。结果 数值模拟所得结构变形和落锤加速度与实验结果较为一致,验证了数值模拟方法的可靠性。复合泡沫平台应力具有显著的应变率效应,其填充管压溃载荷平稳且高于泡沫铝填充管,比泡沫铝填充管体现出更优异的高过载防护性能。等质量的泡沫夹芯管的抗冲击性能优于填充管,2种泡沫填充而成的夹芯管具有相似的高过载防护性能,泡沫材料压缩行为对夹芯管压溃载荷特征的影响低于填充管。结论 所得结果对轻质元器件的高gt;ggt;值缓冲防护有较强的指导意义。     

Production of perovskite-like La1−xCaxMnO3+δ ferromagnetic thin films by electrochemical reduction

Ferromagnetic and perovskite-like thin films (<1g src="/content/g5h62026068581x8/xxlarge956.gif" alt="mgr" align="MIDDLE" BORDER="0"&gt;m) of La1–xCaxMnO3+g src="/content/g5h62026068581x8/xxlarge948.gif" alt="delta" align="BASELINE" BORDER="0"&gt; have been routinely prepared by heat treatment of an amorphous La–Ca–Mn precursor. The precursor was electrodeposited cathodically in the absence of oxygen and water onto polished silver substrates from a nonaqueous solution of the components' nitrates. Analysis by X-ray diffraction and SQUID magnetometry shows these materials exhibit the appropriate structural and magnetic phases indicative of colossal magnetoresistance.     

Isochoric p-ρ-T Measurements on 1,1-Difluoroethane (R152a) from 158 to 400 K and 1,1,1-Trifluoroethane (R143a) from 166 to 400 K at Pressures to 35 MPa

The gt;pgt;-g src="/content/h51h437771l84g21/xxlarge961.gif" alt="rgr" align="MIDDLE" BORDER="0"&gt;-gt;Tgt; relationships have been measured for 1,1-difluoroethane (R152a) and 1,1,1-trifluoroethane (R143a) by an isochoric method with gravimetric determinations of the amount of substance. Temperatures ranged from 158 to 400 K for R152a and from 166 to 400 K for R143a, while pressures were up to 35 MPa. Measurements were conducted on compressed liquid samples. Determinations of saturated liquid densities were made by extrapolating each isochore to the vapor pressure, and determining the temperature and density at the intersection. Published gt;pgt;-g src="/content/h51h437771l84g21/xxlarge961.gif" alt="rgr" align="MIDDLE" BORDER="0"&gt;-gt;Tgt; data are in good agreement with this study. For the gt;pgt;-g src="/content/h51h437771l84g21/xxlarge961.gif" alt="rgr" align="MIDDLE" BORDER="0"&gt;-gt;Tgt; apparatus, the uncertainty of the temperature is ±0.03 K, and for pressure it is ±0.01% at gt;pgt;&gt;3 MPa and ±0.05% at gt;pgt;&#60;3 MPa. The principal source of uncertainty is the cell volume (g src="/content/h51h437771l84g21/xxlarge8764.gif" alt="sim" align="MIDDLE" BORDER="0"&gt;28.5 cmgt;3gt;), which has a standard uncertainty of ±0.003 cmgt;3gt;. When all components of experimental uncertainty are considered, the expanded relative uncertainty (with a coverage factor gt;kgt;=2 and thus a two-standard deviation estimate) of the density measurements is estimated to be ±0.05%.     

面向Oracle 11g的语义查询集成平台

在VOEditor本体可视化编辑器的基础上,结合本体的相关知识,采用Oracle 11g和其他推理引擎的语义技术,开发一个基于语义的信息查询集成平台原型系统,介绍其体系结构、主要查询机制、实现技术及初步使用情况。结果表明,该系统能对知识库进行不同程度的推理查询,并能支持大型的语义应用。     

基于IEEE 802.11无线局域网的VoIP性能分析

对无线局域网的两种标准IEEE 802.11b和IEEE 802.11g的差异进行了研究,后者在前者的基础上采用了正交频分复用(OFDM)技术,通过设计一个针对这两种标准的无线局域网上的VoIP性能测试的试验,使用Chariot网络工具进行仿真,对延迟、抖动、丢包率进行对比分析,结果表明IEEE 802.11g标准比IEEE 802.11b标准具有明显的性能优势.     

Automatic Registration of Multi‐Projector Domes Using a Single Uncalibrated Camera

In this paper we present a novel technique for easily calibrating multiple casually aligned projectors on spherical domes using a single uncalibrated camera. Using the prior knowledge of the display surface being a dome, we can estimate the camera intrinsic and extrinsic parameters and the projector to display surface correspondences automatically using a set of images. These images include the image of the dome itself and a projected pattern from each projector. Using these correspondences we can register images from the multiple projectors on the dome. Further, we can register displays which are not entirely visible in a single camera view using multiple pan and tilted views of an uncalibrated camera making our method suitable for displays of different size and resolution. We can register images from any arbitrary viewpoint making it appropriate for a single head‐tracked user in a 3D visualization system. Also, we can use several cartographic mapping techniques to register images in a manner that is appropriate for multi‐user visualization. Domes are known to produce a tremendous sense of immersion and presence in visualization systems. Yet, till date, there exists no easy way to register multiple projectors on a dome to create a high‐resolution realistic visualizations. To the best of our knowledge, this is the first method that can achieve accurate geometric registration of multiple projectors on a dome simply and automatically using a single uncalibrated camera.     

Chemical correlates of α-tocopherol (Vitamin E) alteredMalacosoma disstria herbivory inFraxinus pennsylvanica var.Subintegerrinia,green ash

The antioxidant g src="/content/r16002605483g385/xxlarge945.gif" alt="agr" align="BASELINE" BORDER="0"&gt;-tocopherol (vitamin E), applied in a basal trunk band to the green ash tree,gt;Fraxinus pennsylvanicagt; var.gt;subintergerriniagt;, elicited an alteration of foliar feeding bygt;Malacosoma disstriagt; larvae (Lepidoptera: Lasiocampidae). The bioassayed effects were dependent on the dosage of elicitor, the time after elicitation, and the position in the tree. Leaves for chemical analysis were collected from trees receiving two dosages and at two intervals after elicitation. Compounds in the ethyl acetate extractables from the ash tree leaves were separated by TLC and HPLC. TLC separations showed differences in the nonhydrolyzed extractables attributable to elicitor dosage and time after elicitation. TLC-resolved differences were also evident among acid-hydrolyzed samples. HPLC-resolved profiles revealed eight peaks in the nonhydrolyzed extractables that were quantitatively negatively correlated with larval feeding preference between elicited versus control foliage on at least one of the two sampling dates. Results from this study and other investigations reported in the literature indicate that the antioxidantgt;g src="/content/r16002605483g385/xxlarge945.gif" alt="agr" align="BASELINE" BORDER="0"&gt;gt;-tocopherol (vitamin E) can function as an environmental-stress elicitor of alterable defensive chemistry in green ash and other plants.     

电信牌照的无形资产内涵及价值测度研究

电信牌照属于企业重要的无形资产,其内涵是由电信业务经营权、无线频段使用权和通信标准经营权组成的权利集合。在分析电信牌照资产获利能力及收益来源的基础上,综合采取净现值法和实物期权法对中国电信市场三张3G牌照的价值进行了评估测度。最后,基于测度结果围绕我国电信产业未来发展提出了政策建议。