A heat-driven thermoacoustic cryocooler capable of reaching below liquid hydrogen temperature

A "double-gas acoustic amplifier" is introduced to couple a thermoacoustic heat engine and a two-stage pulse tube cooler in this paper. Compared with previous acoustic amplifiers, this new acoustic amplifier maintains the function of amplification for pressure amplitude. In particular, the novel acoustic amplifier with a reservoir makes it possible to install an acoustic transparent but gas blocking elastic membrane between the engine and the cooler. Thus, the engine can use nitrogen as the working gas to work at low frequency; and meanwhile, the cooler can still use helium as the working gas to maintain its high performance. With this new amplifier, the cooling temperature of a two-stage pulse tube cooler driven by an energy-focused thermoacoustic engine reached 18.7 K.     

试论国外施工风险管理及对策

在集团公司“走出去”战略的指导下，施工企业积极开拓国外市场，承揽了多个施工项目。如何在复杂多变的国际市场中防范和控制工程施工风险是每个施工企业非常关注的问题。文章重点就国外施工的常见风险及应对策略做了概述。     

带执行器节点的无线传感器网络密钥预分配策略

针对带执行器节点的无线传感器网络的安全通信问题,提出了一种新的密钥预分配方案.充分利用执行器节点具有能量充足、存储器资源丰富、较强计算和通信能力等特点,构建一棵以Sink为根节点、执行器节点为分支节点、传感器节点为叶子节点的密钥管理树,实现集中式和分布式密钥管理的安全通信机制.该分配策略包括三个阶段:初始化阶段、共享密钥发现阶段和安全路径建立阶段.重点论述如何构建密钥管理树,以实现通信的安全认证.讨论了添加或删除网络节点时的密钥管理自适应能力.     

Morphology and contact mechanics influence adhesive characteristics of Dung Beetle’s bristle and Gecko’s setae

Geckos (Gekko gecko) use their hairy setae to adhere on various solid surfaces and dung beetles (Copris ochus Motschulsky) use their hairy bristles to anti-adhere in sticky environments. We study why two hairy systems express a conflict in functions by using SEM, histological approaches and functional experiments. Adhesion models and various parameters were collected and analyzed. Based on the morphological data and functional experimental results carried out by natural and denatured gecko setae and beetle bristles, we first demonstrated that the stiffness along the hair is 1000 to 30000 times that perpendicular to the hair. This stiffness difference is the key factor leading to the two hairy systems’ functional differences. Slope of gecko setae reduces contact stiffness, increases contact points and real contact area that results in amazing adhesive abilities. On the other hand, stiff bristles in a beetle have higher contact stiffness, which reduces the real contact area and decreases the adhesion between two contact surfaces. Deformation of gecko setae destroys the hierarchical structure, increases the contact stiffness and results in a decrease of adhesion forces. Similarly, deformation of beetle bristles destroys the erect structure of the hair, interconnects the separated bristles and thus decreases the anti-adhesive functions. These observations inspire us in designing anti-adhesive and adhesive biomimetic systems.     

多层次灰色评价法在员工绩效考评中的应用

针对企业员工绩效考评问题，通过建立员工绩效考评指标体系，采用层次分析法（AHP）确定了各层评价指标的权重；应用定性与定量相结合的分析方法，给出了员工绩效考评的多层次灰色评价方法和实际的算例；在具体实例中的应用表明，采用该评价方法切实可行。     

Gene flow from transgenic oilseed rape (Brassica napus L.) to cruciferous weeds under mentor pollen inducement

The alien gene flow between genetically modified glyphosate-resistant rapeseed variety Q3 (Brassica napus L.) and four cruciferous weeds was studied under mentor pollen inducement. The results showed that when Thlaspi arvense L., Capsella bursa-pastoris (L.) Medic, Cardamine hirsute L. and Rorippa palustris (L.) Besser were pollinated with mentor pollen, the mixed Q3 and the weed, pollen grains aggregated largely and germinated quickly, and the numbers of pollen tubes penetrating into the style and the ovary were greatly increased as compared with corresponding self-pollination groups. Twenty four to forty eight hours after pollination, several pollen tubes were observed to penetrate into the ovule via micropyle in each mentor combination. However, when the mentor progenies were analyzed by PCR, all of them showed negative for the Q3 herbicide-resistant gene. Collectively, these results indicated that crossing between T. arvense, C. bursa-pastoris, C. hirsuta, R. palustris (as female) and Q3 (as male) was highly incompatible and the herbicide-resistant gene could not flow from Q3 to these four weeds.     

Water-vapor source shift of Xinjiang region during the recent twenty years

The aim of this paper is to investigate the climate water-vapor sources of Xinjiang region and their shifts during the past 20 years. First, the principle and steps are roughly regulated to seek the water-vapor sources. Second, the climate stationary water-vapor transport in troposphere is calculated to distinguish where the water vapor comes from by ERA-40 reanalysis. In addition, the collocation between the transport and the atmospheric column water vapor content is analyzed. The results show that the major vapor comes from the west side of Xinjiang for mid-month of seasons, apart from July while the water vapor comes from the north or northwest direction. The water vapor sources are different for different seasons, for example, the Caspian Sea and Mediterranean are the sources in January and April, the North Atlantic and the Arctic sea in July, and the Black Sea and Caspian Sea in October, respectively. In recent ten years more water vapor above Xinjiang comes from the high latitudes and the Arctic sea with global warming, and less from Mediterranean in comparison with the case of 1973—1986. In fact, the air over subtropics becomes dry and the anomalous water vapor transport direction turns to west or southwest during 1987—2000. By contrast, the air over middle and high latitudes is warmer and wetter than 14 years ago.     

Sinorhizobium meliloti nifA gene exerts a pleiotropic effect on nodulation through the enhanced plant defense response

Sinorhizobium meliloti nifA gene is required for the expression of a bunch of nif and fix genes. Here, we report its pleiotropic effects on the nodule formation. Compared with wild type strain, nifA mutant sig- nificantly reduced nodule suppression rate in split-root system. The plants inoculated with mutant strain produced lower amount of daidzein and less necrotic cells on their roots. In addition, the defense genes failed to be evoked by nifA mutant at the early nodulation stage. These findings indicated that host defense response was one of the mechanisms mediated by nifA gene to regulate nodule formation during symbiosis. Even though nifA mutant could increase the number of nodules in host plant, it synthesized lower Nod factors than wild type. This suggested that nifA gene mediated multiple and diverse instances in nodulation formation.     

脉冲功率开关RSD的高dⅠ／dt特性研究

基于等离子体双极漂移模型，得到了超高速大功率半导体开关反向开关晶体管（RSD）的dⅠ／dt耐量解析表达式，分析了RSD的主放电回路模型，在此基础上讨论了影响RSD的dⅠ／dt特性的因素，dⅠ／dt随预充电荷总量的增加、通过p基区的电子扩散时间和p基区电子寿命的缩短而增大，随主放电回路电压的上升和电感的减小而增大．RSD的dⅠ／dt耐量可达1×10^5A·μs^-1，远高于普通晶闸管，可应用于短脉冲大电流领域．     

基于ASPEN PLUS平台的生物质气化模拟

基于ASPEN PLUS软件的Gibbs自由能最小化法,并利用RGIBBS反应器的限制平衡法修正,建立了生物质气化模型.模拟花生壳气化和木粉气化,发现模拟值和实验值符合良好.对气化两个重要影响因素(空气当量系数和床温)作了灵敏度分析,发现产气组分主要受床温影响,燃气热值和气化效率主要受空气当量系数影响.模拟分析了气化剂温度对产气组分和气化效率的影响,结果表明:基于ASPEN PLUS平台的生物质气化模型能准确地模拟实际气化过程,具有较好的可靠性和适用性.