压铸镁合金AZ91表面化学镀Ni P合金研究

研究了压铸镁合金AZ91的表面化学镀镍磷合金的工艺，利用X射线衍射(XRD)、扫描电镜SEM)、能谱(XPS)及极化曲线的测量等方法，探讨了镁合金表面化学镀Ni P层的组织、相、成分及其耐蚀性，结果显示，镁合金化学镀Ni-P合金镀层在350 ℃热处理后成晶态，镀层成分为NiP、Ni₂P等.化学镀Ni-P合金镀层在3.5% NaCl中的极化曲线存在明显的钝化区，且钝化区呈直线均匀，耐蚀性较好.     

射频功率HBT自加热效应及补偿方法

从器件I-V特性的角度,表征了射频功率异质结双极晶体管(HBT)的自加热效应。研究了器件热阻、工作电压、电流增益、发射结价带不连续性(ΔEV)等诸多因素对器件I-V特性的影响。进而研究了为补偿自加热效应所加镇流电阻对热稳定性的改善情况,给出了器件热稳定所需最小镇流电阻(REmin)与这些因素的关系。结果表明,HBT的REmin要小于同质结双极晶体管(BJT)的REmin,因此,射频功率HBT将有更大的输出功率、功率增益和功率附加效率(PAE)。     

不确定广义系统的鲁棒脉冲耗散控制

本文在状态空间下, 基于线性矩阵不等式(LMI)的方法, 研究了一类不确定广义系统在允许的不确定性下的脉冲耗散控制问题, 并且通过解线性矩阵不等式得到了此类不确定广义系统对于允许的不确定性的鲁棒脉冲耗散状态反馈控制器和输出反馈控制器, 最后通过数值算例验证了定理的可行性.     

基于段流行度的移动流媒体代理服务器缓存算法

提出了一种基于段流行度的移动流媒体代理服务器缓存算法P2CAS2M2(proxy caching algorithm based on segment popularity for mobile streaming media),根据移动流媒体对象段的流行度,实现了代理服务器缓存的接纳和替换,使移动流媒体对象在代理服务器中缓存的数据量和其流行度成正比,并且根据客户平均访问时间动态决定该对象缓存窗口大小。仿真结果表明,对于代理服务器缓存大小的变化,P2CAS2M2比A2LS(adaptive and lazy segmentation algorithm)具有更好的适应性,在缓存空间相同的情况下,能够得到更大的被缓存流媒体对象的平均数,更小的被延迟的初始请求率,降低了启动延时,而字节命中率接近甚至超过A2LS。     

关于小型蓄冷复合空调系统节能潜力的探讨

小型蓄冷复合空调器同普通空调器相比,节约了能源和费用,经济性能更高.从小型蓄冷复合空调系统的节能机理、节能效果进行比较与分析.     

移动对等网络中自私节点的检测和激励机制

由于其自身资源等客观因素的限制以及主观态度的影响,移动对等网络中的节点常常表现出自私性,因此,检测并激励自私节点合作成为当前重要的研究内容通过允许节点自由表达其主观转发态度,实现对自私节点的检测.即在路由选择时,不仅考虑到链路质量和节点能量等因素决定的路径的客观转发概率,而且考虑到路径上节点自私性影响下的主观转发概率,以选择出综合转发概率最高的路径,从而减轻自私节点的影响.当节点自私度过重时,设计了一个基于惩罚机制的激励合作模型以鼓励节点参与合作.根据节点自私行为的危害程度,对其采取相应的惩罚措施.节点之间的监控机制和严格的惩罚机制保证了防策略性的实现.模拟实验结果表明,该检测和激励机制不仅能够在节点能量受限和理性自私的情况下寻找到合适的路由,而且能够激励过于自私的节点积极参与网络活动.     

Sonocatalytic damage of bovine serum albumin (BSA) under ultrasonic irradiation by mixed TiO2/SiO2 powder

BACKGROUND: In order to effectively damage some biomolecules under ultrasonic irradiation, a mixed TiO₂/SiO₂ powder with high catalytic activity and selectivity was used as a sonocatalyst. RESULTS: The mixed TiO₂/SiO₂ powder heat treated at 450 °C for 30 min was adopted as a sonocatalyst and the damage to BSA molecules under ultrasonic irradiation was assessed. In addition, the effects of such variables as molar ratio of TiO₂ and SiO₂, treatment temperature and time, ultrasonic irradiation time, catalyst amount, solution acidity, ionic nature and strength, ultrasonic irradiation power and D₂O concentration on the damage to BSA molecules were studied by means of UV‐visible and fluorescence spectra. The results showed that the degree of damage was aggravated by an increase in ultrasonic irradiation time, catalyst amount, solution acidity, ultrasonic irradiation power and D₂O concentration, but was reduced by an increase in ionic strength. CONCLUSION: The results indicated that the mixed TiO₂/SiO₂ powder displayed higher activity and selectivity compared with nano‐sized TiO₂ and SiO₂ powders during the sonocatalytic damage of BSA. The extent of the damage decreased in the order TiO₂/SiO₂ > nano‐sized TiO₂ > nano‐sized SiO₂. These results are of great significance for applying sonocatalytic methods to treat tumours. Copyright © 2008 Society of Chemical Industry     

Study of high-pressure and high-temperature behaviors and α-to-β phase transition of forsterite by first-principles and quasi-harmonic Debye model

The high-pressure and/or high-temperature behavior and α/β phase transition of forsterite (Mg₂SiO₄) were investigated by first principle calculations: local density approximation (LDA), generalized gradient approximation (GGA) and the quasi-harmonic Debye model in consideration of the temperature effect. At zero pressure and zero temperature, the calculated values of lattice parameters and elastic constants are well concordant with experimental data. The calculated values of cell volume at different pressures and temperatures are compatible with experiments. The results calculated by LDA are more concordant with the experimental results than those by GGA for describing Mg₂SiO₄ crystals. The boundaries of the P-T plots for α/β phase transition are calculated to be 0.00779 GPa/K by LDA and 0.00772 GPa/K by GGA, suggesting the upper and lower limits of the phase boundary for α/β forsterite. At temperature of less than 1000 K, the calculated results agree reasonably with experimental ones. Thus, the present results indicate that combination of first-principles and quasi-harmonic Debye model is an efficient approach to simulate the behavior of minerals at high pressure and/or high temperature.     

光透过率法测量煤粉平均粒径

文中详细介绍了利用光透过率法测量煤粉颗粒比表面积平均直径的原理和测量装置，给出了实际测量数据，取得了与筛分法一致的结果，使用普通的光电测量装置，本法测量极限误差一般可小于２％ 。     

Electron trapping of laser-induced carriers in Er-doped SnO2 thin films

In order to investigate optically excited electronic transport in Er-doped SnO₂, thin films are excited with the fourth harmonic of an Nd:YAG laser (266 nm) at low temperature, yielding conductivity decay when the illumination is removed. Inspection of these electrical characteristics aims knowledge for electroluminescent devices operation. Based on a proposed model where trapping defects present thermally activated cross section, the capture barrier is evaluated as 140, 108, 100 and 148 meV for doped SnO₂ thin films with 0.0, 0.05, 0.10 and 4.0 at% of Er, respectively. The undoped film has vacancy levels as dominating, whereas for doped films, there are two distinct trapping centers: Er³⁺ substitutional at Sn⁴⁺ lattice sites and Er³⁺ located at grain boundary.