开孔泡沫金属动态力学性能及能量特性

泡沫金属材料在防护吸能领域有着重要的应用前景,深入研究泡沫金属及其相关结构的冲击力学性能十分必要。通过Φ50 mm的分离式霍普金森杆(split Hopkinson pressure bar, SHPB)装置对开孔泡沫金属Fe、Ni、Fe-Ni合金(50 mm×10 mm)进行动态冲击试验。试验分析了应变和应变率对其力学性能及吸能特性的影响,通过对其峰值应力、波动应力、理想吸能效率等参数的对比分析多种冲击速度下不同泡沫金属材料的抗压强度与吸能性,为建筑、航天等工程的使用提供理论基础。研究结果表明：高冲击速度下峰值应力增大且Fe-Ni合金抗压强度最高,不同材料泡沫金属均存在波动应力且压密阶段时间各不相同。应变率介于600～1 150时泡沫金属Ni吸能性最优,该区间外Fe-Ni合金更优。当应变率大于1 000时,Fe-Ni合金理想吸能效率增幅较大,相较于700时提高了48%、为最优理想吸能材料。     

量子通信实用化现状分析与探讨

量子密钥分发和量子隐形传态不断取得的新突破,使量子通信实用化问题日益成为关注的焦点。本文简析了量子通信研究的发展历程,并对量子通信的实用化现状进行了概括：实用化量子密钥分发技术已近在眼前,但量子隐形传态的实用化仍尚需时日。针对认识和理解量子通信时的典型误区,本文做了简要澄清。根据量子通信实用化发展态势,为我国量子通信的发展提出了4点对策和建议     

Control of a key transition from prostrate to erect growth in rice domestication

The transition from the prostrate growth of ancestral wild rice (O. rufipogon Griff.) to the erect growth of Oryza sativa cultivars was one of the most critical events in rice domestication. This evolutionary step importantly improved plant architecture and increased grain yield. Here we find that prostrate growth of wild rice from Yuanjiang County in China is controlled by a semi-dominant gene, PROG1 (PROSTRATE GROWTH 1), on chromosome 7 that encodes a single Cys(2)-His(2) zinc-finger protein. prog1 variants identified in O. sativa disrupt the prog1 function and inactivate prog1 expression, leading to erect growth, greater grain number and higher grain yield in cultivated rice. Sequence comparison shows that 182 varieties of cultivated rice, including 87 indica and 95 japonica cultivars from 17 countries, carry identical mutations in the prog1 coding region that may have become fixed during rice domestication.     

Germline-specific dgcr8 knockout in zebrafish using a BACK approach

Zebrafish is an important model to study developmental biology and human diseases. However, an effective approach to achieve spatial and temporal gene knockout in zebrafish has not been well established. In this study, we have developed a new approach, namely bacterial artificial chromosome-rescue-based knockout (BACK), to achieve conditional gene knockout in zebrafish using the Cre/loxP system. We have successfully deleted the DiGeorge syndrome critical region gene 8 (dgcr8) in zebrafish germ line and demonstrated that the maternal-zygotic dgcr8 (MZdgcr8) embryos exhibit MZdicer-like phenotypes with morphological defects which could be rescued by miR-430, indicating that canonical microRNAs play critical role in early development. Our findings establish that Cre/loxP-mediated tissue-specific gene knockout could be achieved using this BACK strategy and that canonical microRNAs play important roles in early embryonic development in zebrafish.     

DPSIR model-based evaluation index system for geographic national conditions

Establishing a reasonable evaluation index system is the basis and premise for the scientific evaluation of geographic national conditions. By analyzing the DPSIR model and its correlation and relation with the evaluation index system, the indexes for geographic national conditions were selected from the aspects of resources, ecology, environment, economy, society, etc to build an evaluation index system for geographic national conditions that consists of three hierarchies: index, criterion, and target levels. Furthermore, the index system was analyzed in terms of index integrity, low overlapping of elements, non-existence of isolated indexes, hierarchy of index system, etc., for the purpose of demonstrating that the DPSIR model-based evaluation index system for geographic national conditions meets the principles of index system establishment.     

时滞控制系统变结构控制器的一种等效设计方法

本文对时滞控制系统的变结构控制器提出了一种等效的设计方法。此方法因只需对相应的无时滞控制系统进行变结构控制器设计,所以不仅简化了变结构控制器本身的设计,而且也相应的简化了切换面的设计。同时,还给出了这种等效方法的时滞范围及系统数值仿真,仿真结果表明此方法的可行性及其效果的优良性。     

用数字波束形成技术测量干扰环境中目标的方向

本文讨论了在干扰环境中利用数字波束形成技术确定目标方向的方法,给出了计算机模拟结果。测量目标角度是基于单脉冲技术中的和差波束的方法。由于各路接收机幅相误差和算法本身的影响,差波束指向零点将产生漂移且零深不够理想,影响了测角精度。本文提出了在差波束的理想指向零点方向用正交化算法产生一零点的办法来校正零点漂移和加深零深,又不影响差方向图的其它性能,从而为用数字波束形成技术精密测角提出了一条路径。另外,本文给出了为消除主瓣干扰而对和差方向图影响的模拟结果。