A redox switch in angiotensinogen modulates angiotensin release

Blood pressure is critically controlled by angiotensins, which are vasopressor peptides specifically released by the enzyme renin from the tail of angiotensinogen-a non-inhibitory member of the serpin family of protease inhibitors. Although angiotensinogen has long been regarded as a passive substrate, the crystal structures solved here to 2.1?? resolution show that the angiotensin cleavage site is inaccessibly buried in its amino-terminal tail. The conformational rearrangement that makes this site accessible for proteolysis is revealed in our 4.4?? structure of the complex of human angiotensinogen with renin. The co-ordinated changes involved are seen to be critically linked by a conserved but labile disulphide bridge. Here we show that the reduced unbridged form of angiotensinogen is present in the circulation in a near 40:60 ratio with the oxidized sulphydryl-bridged form, which preferentially interacts with receptor-bound renin. We propose that this redox-responsive transition of angiotensinogen to a form that will more effectively release angiotensin at a cellular level contributes to the modulation of blood pressure. Specifically, we demonstrate the oxidative switch of angiotensinogen to its more active sulphydryl-bridged form in the maternal circulation in pre-eclampsia-the hypertensive crisis of pregnancy that threatens the health and survival of both mother and child.     

一种新的单/多密钥交换协议

文章提出一种新的无散列函数单/多密钥交换协议;该协议同Diffie-Hellm an协议一样都是建立在离散对数问题上的,具有较好的安全性;该协议具有身份认证功能,可以避免Diffie-Hellm an协议中存在的漏洞——中间人攻击,而且它既可以进行单密钥交换又可以进行多密钥交换。     

高功率因数 220V/10A 电力系统直流操作开关电源

为了满足未来电力系统对直流操作电源的要求，给出了一种具有高功率因数的用于电力系统的新型直流操作开关电源的设计和实现。通过对高频开关电源几种常见拓扑结构的比较和分析，设计的开关电源模块输入级采用了升压变换器来校正功率因数，ＤＣ／ＤＣ变换采用高可靠性的双管正激电路和电流型控制。电源系统采用无主均流控制方式，真正实现Ｎ＋１冗余运行，并以８０３１单片机控制ＲＳ４８５串行接口构成智能监控，使该电源系统具备新一代直流操作电源系统的所有功能。文中给出了系统较详细的设计过程，分析了影响开关电源性能的各种因素及解决方法。     

一种新型的基于软件无线电交换网络结构的设计

高速的多DSP并行处理技术是软件无线电关键技术之一．近年来，为了解决这一难题，提出了多种设计方案．该文以基于交换网络结构的方案作为研究重点，在此基础上提出一种改进型的交换网络结构，研究了该种结构核心器件——适配器的设计，在该新型结构上实现TCP／IP协议．最后，分析该新型结构的性能，并与最初的交换网络结构做了比较．     

Intracellular Ca indicator Quin-2 inhibits Ca2+ inflow via Na/Ca exchange in squid axon

Until recently, intracellular free calcium has been amenable to measurement and investigation only in cells large enough to permit either microinjection of a suitable Ca sensor such as a aequorin or arsenazo III or insertion of a Ca-sensitive microelectrode. This constraint on cell size was removed by the development of the fluorescent Ca2+ -sensitive dye Quin-2 and its acetoxymethyl ester, which can be introduced into a wide range of cell types. A major requirement of any intracellular Ca2+ indicator is that it should not disturb intracellular Ca2+ homeostasis and Quin-2 is generally considered to be satisfactory in this respect. We now report that injection of Quin-2 into squid (Loligo forbesi) axons can almost completely abolish one component of Ca2+ entry--intracellular Na+ (Nai)-dependent Ca2+ inflow, which occurs via Na/Ca exchange. Mixtures of Ca and Quin-2 that buffer an ionized Ca2+ at close to physiological concentrations also block Nai-dependent Ca2+ influx but these same mixtures fail to block the extracellular Na+ (Na0)-dependent extrusion of Ca2+, showing that Quin-2 acts specifically on Ca2+ inflow.     

A novel graphite/phenolic resin bipolar plate modified by doping carbon fibers for the application of proton exchange membrane fuel cells

In this study, the carbon fibers treated by three methods were selected as a reinforcement to investigate the influence on the properties of composite bipolar plates. The properties and microstructure of the composite bipolar plate were characterized by the four-point probe, universal test machine, contact angle tester and scanning electron microscopy. The optimum treatment methods and the fiber content were analysed. The results showed that the carbon fibers treated by Fenton reagent for 2 ​h exhibited the best performance, which could improve the electrical conductivity and the flexural strength for composite bipolar plate. Besides, the optimal content content of carbon fibers treated by Fenton reagent was 4%. The maximum power density of the PEMFC with the composite bipolar plates could reach 662.75 ​mW ​cm⁻² in H₂-air conditions. Therefore, the phenolic resin/graphite composite bipolar plate modified by doping carbon fibers was a promising candidate for bipolar plate materials for PEMFC.     

Scalable synthesis of A2S3 （A=Sb, Bi） submicro/nanowires using their powders via solvothermal proceeding

One-dimensional (1D) nanostructural materials of semiconductors are being widely studied due to their unusual opto-electronic properties and potential im-plementation as nanodevices[1―6]. The nanowires of A2S3 (A=Sb, Bi) are one of the most interesting 1…     

基于贝叶斯纳什均衡的政府补贴福利分析——以垂直不完全竞争市场为例

【目的】基于贝叶斯纳什均衡理论研究了垂直不完全竞争市场中政府补贴的福利影响。【方法】采用了比较预期福利的方法。【结果】在Asker所建立的框架下分析了政府补贴对最终消费者福利和社会总福利的影响,得到了社会总福利的增量超过政府补贴投入的充分条件。【结论】推广了Asker的一些结果。
     

Computed tomography of the acoustic nonlinearity parameter B／A for biological tissues via difference frequency wave from a parametric array in reflection mode

Based on the finite amplitude insert-substitution method, a novel technique to reconstruct the acoustic nonlinear parameter B/A tomography for biological tissues in reflection mode via the difference frequency wave generated by a parametric array is developed in this paper. An experimental system is established, and the beam pattern of the difference frequency wave is measured and compared with that excited directly from a transmitter at the same frequency. B/A tomography for several biological tissues including normal and pathological tissues, is experimentally obtained with satisfying quality. Results indicate that B/A imaging using this mode may become a novel modality in ultrasonic diagnosis.     

A simple and novel synthetic route to prepare anatase TiO_2 nanopowders from natural ilmenite via the H_3PO_4/NH_3 process

A simple and novel technique for the preparation of anatase TiO_2 nanopowders using natural ilmenite(FeTiO_3) as the starting material is reported. Digesting ilmenite with concentrated H_3PO_4 under refluxing conditions yields a white α-titanium bismonohydrogen orthophosphate monohydrate(TOP), Ti(HPO_4)_2·H_2O, which can be easily isolated via gravity separation from unreacted ilmenite. The addition of ammonia to the separated TOP followed by calcination at 500°C completes the preparation of anatase TiO_2. Calcination at temperatures above 800°C converts the anatase form of TiO_2 to the stable rutile phase. The removal of iron from ilmenite during the commercial production of synthetic TiO_2 is problematic and environmentally unfriendly. In the present study, the removal of iron was found to be markedly simple due to the high solubility of iron phosphate species in concentrated H_3PO_4 with the precipitation of TOP. The titanium content of the prepared samples on metal basis with silica and phosphorous as major impurities was over 90%. Prepared TiO_2 samples were characterized using X-ray fluorescence, Fourier-transform infrared spectroscopy, Raman spectroscopy, ultraviolet –visible diffuse reflectance spectroscopy, high-resolution transmission electron microscopy, and X-ray diffraction analyses. The photocatalytic potentials of the commercial and as-prepared TiO_2 samples were assessed by the photodegradation of rhodamine B dye.