黄土公路隧道预支护施工技术研究

针对目前黄土公路隧道设计与施工的现状以及存在的问题,结合在建古浪隧道实体工程,分析了小导管注浆超前支护施工技术的要点,利用ANSYS程序建立三维实体模型分析预支护技术对开挖围岩的稳定性影响及围岩和支护结构在施工过程中的受力变化情况.结果表明,超前支护可以提高围岩自稳自承的能力,减小围岩的收敛变形.     

使命与转型——云计算时代与信息设计

云计算将会给明天我们所处的信息时代带来什么样的新气象?在时代发展的机遇和挑战中,信息设计应该担负什么样的社会使命、体现何种文化功用?我们认为,无论是云计算产业的宏观规划还是产业链的软实力突破,都需要对设计有足够的重视。在提升硬件的同时,未来IT产业的关键更在于提升中国的文化软实力。不掌握设计,我们就不可能参与到软实力竞争的核心。信息设计的发展是决定我国云计算产业链条能否由低端制造向非物质盈利跨越的关键一步。     

海岸带生态健康评价方法综述

生态健康是指人与环境关系的健康,是测度人的生产生活环境及其赖以生存的生命支持系统的代谢过程和服务功能完好程度的系统指标,包括人体和人群的生理和心理生态健康、人居物理环境、生物环境和代谢环境的健康及产业和区域生态服务功能的健康.文章综述了海岸带生态健康评价的主要方法.这些方法不仅可用于海岸带的生态健康评价,同样可用于其他生态系统的健康评价.     

换热器内随温度变化的黏度对两流体(火积)的影响

以橄榄油为例来研究黏度固定和黏度为温度函数的情况下黏性热效应对顺流换热器内两流体相似文献   

Ia型超新星测距揭示宇宙的命运——2011年诺贝尔物理学奖简介

2011年度诺贝尔物理学奖授予了在天体物理研究领域取得杰出成就的美国科学家索尔·波尔马特、拥有美国和澳大利亚双重国籍的科学家布赖恩·施密特以及美国科学家亚当·里斯。他们通过Ia型超新星测距发现宇宙的膨胀是加速的,从而揭示了暗能量的存在。笔者将对人类认识宇宙的过程、Ia型超新星与宇宙加速膨胀、暗能量以及Ia型超新星研究中存在的问题做全面的介绍,并介绍中国学者在该领域的研究进展。文章的最后做了展望。     

High-frequency, scaled graphene transistors on diamond-like carbon

Owing to its high carrier mobility and saturation velocity, graphene has attracted enormous attention in recent years. In particular, high-performance graphene transistors for radio-frequency (r.f.) applications are of great interest. Synthesis of large-scale graphene sheets of high quality and at low cost has been demonstrated using chemical vapour deposition (CVD) methods. However, very few studies have been performed on the scaling behaviour of transistors made from CVD graphene for r.f. applications, which hold great potential for commercialization. Here we report the systematic study of top-gated CVD-graphene r.f. transistors with gate lengths scaled down to 40 nm, the shortest gate length demonstrated on graphene r.f. devices. The CVD graphene was grown on copper film and transferred to a wafer of diamond-like carbon. Cut-off frequencies as high as 155 GHz have been obtained for the 40-nm transistors, and the cut-off frequency was found to scale as 1/(gate length). Furthermore, we studied graphene r.f. transistors at cryogenic temperatures. Unlike conventional semiconductor devices where low-temperature performance is hampered by carrier freeze-out effects, the r.f. performance of our graphene devices exhibits little temperature dependence down to 4.3 K, providing a much larger operation window than is available for conventional devices.     

Molecular regulation of sexual preference revealed by genetic studies of 5-HT in the brains of male mice

Although the question of to whom a male directs his mating attempts is a critical one in social interactions, little is known about the molecular and cellular mechanisms controlling mammalian sexual preference. Here we report that the neurotransmitter 5-hydroxytryptamine (5-HT) is required for male sexual preference. Wild-type male mice preferred females over males, but males lacking central serotonergic neurons lost sexual preference although they were not generally defective in olfaction or in pheromone sensing. A role for 5-HT was demonstrated by the phenotype of mice lacking tryptophan hydroxylase 2 (Tph2), which is required for the first step of 5-HT synthesis in the brain. Thirty-five minutes after the injection of the intermediate 5-hydroxytryptophan (5-HTP), which circumvented Tph2 to restore 5-HT to the wild-type level, adult Tph2 knockout mice also preferred females over males. These results indicate that 5-HT and serotonergic neurons in the adult brain regulate mammalian sexual preference.     

Tumour hypoxia promotes tolerance and angiogenesis via CCL28 and T(reg) cells

Although immune mechanisms can suppress tumour growth, tumours establish potent, overlapping mechanisms that mediate immune evasion. Emerging evidence suggests a link between angiogenesis and the tolerance of tumours to immune mechanisms. Hypoxia, a condition that is known to drive angiogenesis in tumours, results in the release of damage-associated pattern molecules, which can trigger the rejection of tumours by the immune system. Thus, the counter-activation of tolerance mechanisms at the site of tumour hypoxia would be a crucial condition for maintaining the immunological escape of tumours. However, a direct link between tumour hypoxia and tolerance through the recruitment of regulatory cells has not been established. We proposed that tumour hypoxia induces the expression of chemotactic factors that promote tolerance. Here we show that tumour hypoxia promotes the recruitment of regulatory T (T(reg)) cells through induction of expression of the chemokine CC-chemokine ligand 28 (CCL28), which, in turn, promotes tumour tolerance and angiogenesis. Thus, peripheral immune tolerance and angiogenesis programs are closely connected and cooperate to sustain tumour growth.     

Spin-orbit-coupled Bose-Einstein condensates

Spin-orbit (SO) coupling--the interaction between a quantum particle's spin and its momentum--is ubiquitous in physical systems. In condensed matter systems, SO coupling is crucial for the spin-Hall effect and topological insulators; it contributes to the electronic properties of materials such as GaAs, and is important for spintronic devices. Quantum many-body systems of ultracold atoms can be precisely controlled experimentally, and would therefore seem to provide an ideal platform on which to study SO coupling. Although an atom's intrinsic SO coupling affects its electronic structure, it does not lead to coupling between the spin and the centre-of-mass motion of the atom. Here, we engineer SO coupling (with equal Rashba and Dresselhaus strengths) in a neutral atomic Bose-Einstein condensate by dressing two atomic spin states with a pair of lasers. Such coupling has not been realized previously for ultracold atomic gases, or indeed any bosonic system. Furthermore, in the presence of the laser coupling, the interactions between the two dressed atomic spin states are modified, driving a quantum phase transition from a spatially spin-mixed state (lasers off) to a phase-separated state (above a critical laser intensity). We develop a many-body theory that provides quantitative agreement with the observed location of the transition. The engineered SO coupling--equally applicable for bosons and fermions--sets the stage for the realization of topological insulators in fermionic neutral atom systems.     

基于锥模型的非单调自适应信赖域算法

基于锥模型,结合提出的新的自适应技术,建立了一个求解无约束最优化问题的非单调自适应信赖域算法.当试探步不被接受时,采用非单调线搜索,减少了计算量.充分利用包含当前迭代点信息的新的自适应策略调节信赖域半径.在适当的条件下,证明了算法的全局收敛性和Q-二阶收敛性.数值试验表明该算法是有效的.