脉冲功率晶闸管反向恢复特性

为建立有效的晶闸管模型来仿真晶闸管关断时过电压,减小晶闸管过压损坏的概率,以最大通流150 kA、耐压5.2 kV的脉冲晶闸管为研究对象,将其前置于脉冲形成单元回路中作为大功率开关使用,记录放电过程中晶闸管两端电压及电流。实验数据表明：恢复过程中的电流下降率、反向恢复电荷、反向恢复电流峰值随通态电流峰值的增大而增大,晶闸管关断时间随通态电流峰值的增大而减小。此外,在关断过程中,当电流下降率在-50~1000 A/s时,电流下降率与电流峰值为线性关系。因此,在大脉冲电流条件下,推导反向恢复过程参数与通态电流参数的关系时电流下降率可用与电流峰值的线性关系代替。基于Matlab仿真平台,建立了具有反向恢复过程的脉冲晶闸管模型。该模型仿真得到的晶闸管反向恢复电流峰值与实测结果较为吻合,反向恢复电压尚待进一步修正。     

带陡化间隙的触发真空开关触发源研制

针对主电极间距20 mm以上的沿面击穿型多棒极触发真空开关（TVS）,研制了开关触发源。触发源利用脉冲变压器产生脉冲高压输出,在脉冲变压器高压侧并联小容值电容并在电容后串联陡化间隙。陡化间隙的加入可以使触发源输出不受触发沿面金属蒸气沉积的影响。通过调节间隙击穿电压也可以提高电容充电电压及储存能量,从而增加TVS触发沿面被击穿时注入到其中的触发能量。使用该触发源对TVS进行导通实验,结果表明,加入陡化间隙后的触发源输出能量大幅提高且不受触发沿面金属蒸气沉积的影响,能够实现TVS的100%可靠导通。     

辐射成像系统模拟软件NUCRPD的研发与应用

在辐射成像系统的设计研发中,经常需要计算系统的各项物理性能指标。为了提升产品研发的效率,同方威视联合清华大学,基于蒙特卡罗程序包Geant4,研发了国内首套具有自主知识产权的辐射成像系统模拟软件NucRPD(NUCTECH Radiography Performance Design Tools),其能够快速、精确地模拟系统的各项性能指标。该软件对常用的一些辐射成像系统进行了参数化建模,用户通过修改软件界面上的少量参数,就可以快速建立各类辐射成像系统的几何体、源项、物理模型和统计量,然后在服务器上以并行计算方式完成模拟计算,能在较短的时间内模拟出系统的性能指标,并给出直观的图形帮助用户深入理解模拟结果。NucRPD的模拟结果经过了大量的实验验证,其剂量场分布和物理指标等模拟结果和实验结果符合得很好。NucRPD已经应用于同方威视辐射成像系统产品的设计研发,在产品的物理指标优化和辐射防护优化中发挥了重要作用。     

改进型低阻类膜片加载同轴渡越时间振荡器

采用2.5维粒子模拟软件对改进型低阻类膜片加载同轴渡越时间振荡器进行了研究。研究结果表明：提取腔工作于类模场时,具有较高的束波互作用效率;引入渐变型输出波导,提高了提取腔内微波向外耦合输出的能力;通过加载感性支撑杆,一方面对金属膜片起支撑固定作用,另一方面可以及时将膜片上的感应电荷导流至接地外筒、从而降低间隙附近的空间电荷效应,以增加可提取的束动能。经优化设计,该结构在二极管电压为530 kV,二极管电流为12.9 kA、外加导引磁场为0.5 T的条件下,输出微波功率2.74 GW,微波频率7.76 GHz,束波功率转换效率达40%。     

Proteomic Insights into Cardiac Fibrosis: From Pathophysiological Mechanisms to Therapeutic Opportunities

Cardiac fibrosis is a common pathophysiologic process in nearly all forms of heart disease which refers to excessive deposition of extracellular matrix proteins by cardiac fibroblasts. Activated fibroblasts are the central cellular effectors in cardiac fibrosis, and fibrotic remodelling can cause several cardiac dysfunctions either by reducing the ejection fraction due to a stiffened myocardial matrix, or by impairing electric conductance. Recently, there is a rising focus on the proteomic studies of cardiac fibrosis for pathogenesis elucidation and potential biomarker mining. This paper summarizes the current knowledge of molecular mechanisms underlying cardiac fibrosis, discusses the potential of imaging and circulating biomarkers available to recognize different phenotypes of this lesion, reviews the currently available and potential future therapies that allow individualized management in reversing progressive fibrosis, as well as the recent progress on proteomic studies of cardiac fibrosis. Proteomic approaches using clinical specimens and animal models can provide the ability to track pathological changes and new insights into the mechanisms underlining cardiac fibrosis. Furthermore, spatial and cell-type resolved quantitative proteomic analysis may also serve as a minimally invasive method for diagnosing cardiac fibrosis and allowing for the initiation of prophylactic treatment.     

Silymarin Protects against Acute Liver Injury Induced by Acetaminophen by Downregulating the Expression and Activity of the CYP2E1 Enzyme

Previous studies have shown that silymarin protects against various types of drug-induced liver injury, but whether the protective mechanism of silymarin against acetaminophen-induced liver injury is related to the CYP2E1 enzyme remains unclear. In this study, we investigated the effect of silymarin on the activity and expression of CYP2E1 in vitro and in vivo. The results of in vitro studies showed that silymarin not only inhibited the activity of CYP2E1 in human and rat liver microsomes but also reduced the expression of CYP2E1 in HepG2 cells. In vivo studies showed that silymarin pretreatment significantly reduced the conversion of chlorzoxazone to its metabolite 6-OH-CLX and significantly increased the t_1/2, area under the curve (AUC) and mean residence time (MRT) of chlorzoxazone. In addition, silymarin pretreatment significantly inhibited the upregulation of Cyp2e1 expression, reduced the production of 3-cysteinylacetaminophen trifluoroacetic acid salt (APAP-CYS), and restored the liver glutathione level. The results of our study show that silymarin plays an important protective role in the early stage of acetaminophen-induced acute liver injury by reducing the activity and expression of CYP2E1, reducing the generation of toxic metabolites, and alleviating liver injury.     

Thermally activated delayed fluorescence with dual-emission and pressure-induced bidirectional shifting: cooperative effects of intramolecular and intermolecular energy transfer

Different from the conventional piezochromic materials with a mono-redshift of single emission, our well-designed molecule demonstrates a sensitive turn-on and color-tunable piezochromic luminescence in response to the hydrostatic pressure. The molecule PXZ-W-SOF possesses dual-emission and pressure-induced bidirectional shifting characteristics. On the basis of in-depth experimental studies, on one hand, it is confirmed that the origin of the dual-emission behavior is the intramolecular charge transfer, namely thermally activated delayed fluorescence (TADF), and the intermolecular excimer; on the other hand, the emission of the excimer exhibits three-step variations with increasing pressure, which is mainly attributed to the molecular structure and its crystal packing state. The remarkable color change of PXZ-W-SOF from sky-blue to green to deep-blue during the whole process of boosting and releasing pressure is a result of intramolecular and intermolecular energy-transfer interactions. The PXZ-W-SOF molecular model is an extremely rare example of highly sensitive fluorescence tuning driven by TADF and excimer conversion under mechanical stimulation, thus providing a novel mechanism for the field of piezochromism. The unique molecular design also offers a new idea for rare deep-blue and ultraviolet TADF materials.

A high-contrast luminescent material exhibits dual-emission and pressure-induced bidirectional shifting, originating from the cooperative effects of TADF and excimers. It provides a novel mechanism for the piezochromic behavior.     

An unusual autocatalysis with an air-stable Pd complex to promote enantioselective synthesis of Si-stereogenic enynes

Given the powerful potential of chiral-at-silicon chemistry, enantioselective synthesis of Si-stereogenic centers has attracted substantial research interest in recent years. However, the catalytic asymmetric synthesis of Si-stereogenic organosilicon compounds remains an appealing venture and is a challenging subject because of the difficulty in achieving high reactivity and stereoselectivity for “silicon-center” transformations. Herein, we disclose a highly enantioselective palladium-catalyzed hydrosilylation of 1,3-diynes with dihydrosilanes, which enables the facile preparation of Si-stereogenic enynes and an enyne-linked chiral polymer (polyenyne) in good yields and excellent ees (up to >99%) by desymmetrization. The unusual stereoselectivity in this reaction is achieved by precisely controlling the steric hindrance and electronic effect of the newly developed chiral ligands, resulting in a wide range of chiral silanes and a Si-containing polymer bearing a Si-stereogenic center which is otherwise difficult to access. The key to the high enantioselectivity relies on catalyst aggregation-induced non-covalent interaction, which exerts a remarkably positive influence on the Si–H bond activation and enhancement of enantioselectivity, in which the palladium/P-ligand complex was proved to be air-stable and moisture-insensitive in this reaction.

A highly enantioselective palladium-catalyzed hydrosilylation of 1,3-diynes with dihydrosilanes was established for the facile preparation of Si-stereogenic enynes and an enyne-linked chiral polymer (polyenyne) in good yields with excellent ees.     

低阻无箔渡越辐射振荡器励磁系统

为开展L波段低阻无箔渡越辐射高功率微波发生器的单次实验,设计了一种满足需要的电容器储能脉冲磁场系统。系统储能电容5.4 mF,设计的螺线管线圈长45 cm,其理论电感和电阻值分别为42 mH和0.66 。基于该设计,绕制了磁场线圈并搭建了实验平台,线圈实际电感和电阻值分别为40 mH和0.61 。目击靶实验进一步证实了励磁系统产生的导引磁场能够较好地约束电子束。