粉末注射成形充模流动的数值模拟

论文将粉末注射成形喂料在薄壁模腔中的流动视为二维流动,以流变学的基本方程为基础,建立了从动量方程、连续方程和热传递方程得到的描述粉末注射成形充模流动的数学模型。在无滑移边界的条件下,推导了喂料熔体流导率的计算公式和压力场的控制方程,得到的压力场控制方程是一非线性椭圆偏微分方程,从而可用Galerkin方法进行数值求解,使模型的数值求解成为可能,为进一步对粉末注射成形进行计算机模拟和数值分析奠定了数学基础。     

半导体三极管的统一小信号跨导模型

本文为晶体管引入小信号跨导模型，从而使晶体管的小信号模型与场效应管的小信号模型取得一致，低频模型与高频模型获得统一，电路的分析和设计得到简化，缩短了半导体三极管电路的教学和学习过程。     

Transport in open quantum systems: comparing classical and quantum phase space dynamics

Transport in open quantum systems is of great interest. We show that the discrete states of an open quantum system may be classified into three distinct groups, dependent upon the manner in which they influence transport when connected to an external environment. A first class of states is current-carrying states, which are naturally strongly connected to the environment. A second class of states is discrete, but stable and isolated, and thought to be the pointer states of decoherence theory. Finally, we identify backscattered states, which do not propagate through the system.     

Investigation of electrical transport characteristics of nanoscale stacks fabricated on thin graphite layer

We investigated the electrical transport characteristics of nanoscale stacks of thin graphite layer fabricated using focused ion beam (FIB) three dimensional (3D) etching. By varying the stack height, we fabricated nanostacks with the dimensions of W = 1 μm, L = 1 μm, H = 100 nm and W = 1 μm, L = 1 μm, H = 200 nm. The nanostack contains lot of elementary junctions between the graphene layers with interlayer distance of 0.34 nm (along c-axis). We observed a typical semiconducting characteristic until 50 K and a metallic behavior below 50 K for all the fabricated nanostacks, which was well agreed with an identical c-axis characteristics of graphite. From I-V characteristics, we found an ohmic-like characteristic at 300 K for both low and high current biasing; however at low temperature, this behavior was turned into nonlinear characteristics when it was highly biased. The temperature dependent differential conductance measurements for the fabricated stacks were carried out and found that at 300 K, the stack showed larger conductance rather than at any other lower temperatures. However, the stack with 100 nm height showed larger conduction values of 36.3 mS and 16.95 mS for 300 K and 20 K respectively, which are comparatively smaller values of stack with 200 nm height. We also studied conductance fluctuations of nanostacks experimentally and the fluctuations are appearing on increasingly fine when the temperature goes down; however the amplitude of fluctuation is suppressed at low temperature.     

两种温度下斯里兰卡橄榄贮藏特性的比较研究

探讨了斯里兰卡橄榄在常温和低温下的贮藏效果。分别在室温(25oC)和低温(9℃±1)贮藏。跟踪测定果实的呼吸强度、电导率、过氧化物酶活性、维生素C含量的变化和腐烂率、失水率。结果表明斯里兰卡橄榄属典型呼吸高峰型果实,低温可有效降低呼吸强度和延迟呼吸高峰的出现;两种温度下的电导率和过氧化物酶活性均随贮藏时间的延长而变大,但在低温条件下变化速度较慢;低温条件下维生素C的损失较小;两种温度下失水率均较低,表明蒸腾作用较弱;低温条件下的腐烂率远低于常温贮藏条件下。低温可明显改善斯里兰卡橄榄的贮藏性,延长斯里兰卡橄榄的贮藏寿命。     

新型导电有机纤维粉的制备与性能研究

采用自制的银活化液对聚酯短切纤维粉进行敏化、活化处理后,以化学镀的方法在该纤维表面镀银,制备具有低电阻率的有机导电纤维粉.研究了化学镀银过程中,纤维粉表面镀银层的形成和变化过程,扫描电镜观察了镀银层的形貌变化,EDAX能谱和X射线衍射(XRD)分析了不同反应时间镀银层的银含量和组成.结果表明:纤维粉镀银后,其镀银层的结构致密,银的平均晶粒尺寸约为0.452nm,且分布均匀,有金属光泽;镀层中银的质量分数最高为84.81%.对镀银纤维粉的电性能测试表明,一定时间内.该镀银纤维的室温电阻率随着时间的延长而显著降低,其最低室温电阻率为5.85×10-4Ω·cm,该镀银纤维粉显示了优良的导电性.     

Synthesis,characterisation and performance of piezo-resistive cementitious nanocomposites

Smart material reinforced non-destructive structural health monitoring technique has been evolving as the most predominated route for assessing the performance of the civil structures. In the present study, multiwalled nanotubes (MWNT) were suitably incorporated into the cement matrix, which act as actively embedded sensor for monitoring real-time flaws in structures. Initially, the stable homogenous MWNT dispersion was prepared by using ionic surfactant technique with high-intensity ultrasonic agitation process. Since, a suitable and adequate synthesis procedure to incorporate MWNT in cement matrix is essential, but complicated, the role of amplitude and frequency of sonication on dispersion of nanotubes was categorically evaluated. Further, this paper focuses to find out the effect of surfactant on MWNT dispersion by using the UV Visible spectroscopy and by evaluating the effective hydro-dynamic diameter. Based on micromechanics based analytical model, the influence of the interface layer thickness and geometrical configuration of nanotubes on the electrical conductivity of cement nano-composite are also analyzed. Further, the electrical conductivity of MWNT incorporated cement system, as developed in the present study, is measured using four probe method. Piezo-resistivity of the oven dried samples is measured to evaluate the change in potential drop under cyclic loading regime. It is found that the efficiency of the piezo-resistive strain sensors greatly depends on synthesis process and the circuit system. Appropriately proportioned and properly synthesized MWNTs incorporated in cement matrix were capable of providing consistent and steady response under the variable external stress. Thus, the material can be used as embedded sensor for health monitoring and identifying initiation of any damage in reinforced concrete structure.     

密封铅蓄电池的电导与容量的关系

采用不同的方法对不同型式的铅蓄电池内阻测试结果表明 :荷电态高于 50 %的密封铅蓄电池 ,其内阻或电导值基本不变 ,只是在 50 %以下时才会迅速下降。对多组密封铅蓄电池统计数据证实 :失效前的铅蓄电池容量和电导之间并不存在相关关系 ,因而用密封铅蓄电池的电导值去推测电池放电容量是欠妥的     

Interactions of Molecules with Metallic Quantum Wires

Can you imagine how to detect a single molecule? Techniques, such as fluorescent spectroscopy and scanning probe microscopy have become available for us to probe single molecules. Described in this article is a simple approach based on atomically thin metallic wires. The interactions of even a single molecule with the wire may cause a large change in the conductance and mechanical properties of the wire and can thus be used to detect single molecules.     

金属膜材料后向反射1.06微米激光实验测试与分析

金属膜在光学应用中作用各异,用1.06 μm激光从不同入射角对5种镀金属薄膜材料作了相关后向反射实验,反射率的起伏与入射角和偏振性能有关,同时做了具体的理论分析.