Controlling anisotropic nanoparticle growth through plasmon excitation

Inorganic nanoparticles exhibit size-dependent properties that are of interest for applications ranging from biosensing and catalysis to optics and data storage. They are readily available in a wide variety of discrete compositions and sizes. Shape-selective synthesis strategies now also yield shapes other than nanospheres, such as anisotropic metal nanostructures with interesting optical properties. Here we demonstrate that the previously described photoinduced method for converting silver nanospheres into triangular silver nanocrystals--so-called nanoprisms--can be extended to synthesize relatively monodisperse nanoprisms with desired edge lengths in the 30-120 nm range. The particle growth process is controlled using dual-beam illumination of the nanoparticles, and appears to be driven by surface plasmon excitations. We find that, depending on the illumination wavelengths chosen, the plasmon excitations lead either to fusion of nanoprisms in an edge-selective manner or to the growth of the nanoprisms until they reach their light-controlled final size.     

Neurotrophin-evoked rapid excitation through TrkB receptors.

Neurotrophins are a family of structurally related proteins that regulate the survival, differentiation and maintenance of function of different populations of peripheral and central neurons. They are also essential for modulating activity-dependent neuronal plasticity. Here we show that neurotrophins elicit action potentials in central neurons. Even at low concentrations, brain-derived neurotrophic factor (BDNF) excited neurons in the hippocampus, cortex and cerebellum. We found that BDNF and neurotrophin-4/5 depolarized neurons just as rapidly as the neurotransmitter glutamate, even at a more than thousand-fold lower concentration. Neurotrophin-3 produced much smaller responses, and nerve growth factor was ineffective. The neurotrophin-induced depolarization resulted from the activation of a sodium ion conductance which was reversibly blocked by K-252a, a protein kinase blocker which prefers tyrosine kinase Trk receptors. Our results demonstrate a very rapid excitatory action of neurotrophins, placing them among the most potent endogenous neuro-excitants in the mammalian central nervous system described so far.     

Formation of massive black holes through runaway collisions in dense young star clusters

A luminous X-ray source is associated with MGG 11--a cluster of young stars approximately 200 pc from the centre of the starburst galaxy M 82 (refs 1, 2). The properties of this source are best explained by invoking a black hole with a mass of at least 350 solar masses (350 M(o)), which is intermediate between stellar-mass and supermassive black holes. A nearby but somewhat more massive cluster (MGG 9) shows no evidence of such an intermediate-mass black hole, raising the issue of just what physical characteristics of the clusters can account for this difference. Here we report numerical simulations of the evolution and motion of stars within the clusters, where stars are allowed to merge with each other. We find that for MGG 11 dynamical friction leads to the massive stars sinking rapidly to the centre of the cluster, where they participate in a runaway collision. This produces a star of 800-3,000 M(o) which ultimately collapses to a black hole of intermediate mass. No such runaway occurs in the cluster MGG 9, because the larger cluster radius leads to a mass segregation timescale a factor of five longer than for MGG 11.     

Vibrational properties of uracil

1 Introduction Spectroscopic behavior of biological macromole- cules, such as the nucleic acid (NA) bases, contained in non-interacting environments or their solvation, may help us clarify the role of these molecules in biological systems. There are many …     

Hit-and-run planetary collisions

Terrestrial planet formation is believed to have concluded in our Solar System with about 10 million to 100 million years of giant impacts, where hundreds of Moon- to Mars-sized planetary embryos acquired random velocities through gravitational encounters and resonances with one another and with Jupiter. This led to planet-crossing orbits and collisions that produced the four terrestrial planets, the Moon and asteroids. But here we show that colliding planets do not simply merge, as is commonly assumed. In many cases, the smaller planet escapes from the collision highly deformed, spun up, depressurized from equilibrium, stripped of its outer layers, and sometimes pulled apart into a chain of diverse objects. Remnants of these 'hit-and-run' collisions are predicted to be common among remnant planet-forming populations, and thus to be relevant to asteroid formation and meteorite petrogenesis.     

夹层梁的振动分析

通过对夹层梁的单元分析,建立了位移基本方程,对于多种边界条件的夹层梁,得出了相应的振动特征方程,并且讨论了梁的受迫振动。     

振动力学的专题精选

本书是《系统的稳定性、振动和控制》系列丛书A系列的第11卷。振动力学是非线性动力学和非线性振荡理论中新发展起来的一个分支，此书反映近几年来在振动力学的数学工具和在一起应用问题解这两方面所得到的主要成果。     

QD-QW结构中的振动本征模

使用连续介质模型研究了量子点-量子阱结构中的振动本征模.对不同阱宽的ZnSeQD-QW结构计算并取得了具体结果.发现该结构中界面声子的本征频率依赖于阱的宽度.角量子数越小的界面模能量越依赖于阱的宽度.     

生物液膜振荡器中的振动共振

通过数值模拟的方法研究了生物液膜振荡器在高、低两种不同频率信号作用下的振动共振现象。结果表明：体系线性响应随高频信号振幅的变化发生了多重振动共振,且低频信号的频率越低,系统的多重振动共振强度越大。体系线性响应随高频信号频率的变化可以发生高频频率依赖的多重振动共振,体系对大振幅低频信号的放大程度要比小振幅低频信号大;低频信号频率越低,系统的高频频率依赖的多重振动共振强度越大。通过负反馈机制可以有效调节体系多重振动共振峰的个数和高频频率依赖的多重振动共振的强度。当低频信号的频率等于高频信号的频率时,体系可以发生类频率共振强化的振动共振。     

Ag13振动性质研究

应用动力学矩阵对角化方法，计算了Ａｇ１３振动基频，讨论了其振动特性．在计算Ａｇ１３的动力学矩阵时，采用了根据嵌入原子法的物理图象而建立起来的半经验模型势．     

有限的一维复式晶格的振动模谱

以一维复式晶格模型为例,介绍有限晶格振动模的理论研究方法.分析了有限晶格振动模谱与无限晶格振动模谱的异同,发现边界晶格的构型能影响振动模谱,导致在振动模谱中出现带隙模或虚模.     

驱动两能级系统中的振动共振

考虑了一个两能级系统在高频驱动力作用下对一个低频驱动的隧穿响应,通过数值求解系统的动力学方程发现,当高频驱动力的幅度取某些特殊值时,隧穿响应将出现一系列离散的共振峰.在高频近似下得到了系统的有效动力学方程,从而分析得到了系统出现振动共振的条件,它很好地吻合了数值分析的结果.     

GaAs—AlAs准晶超晶格振动特性研究

研究了人工晶体GaAs-AlAs准晶超晶格的振动特性,并与GaAs-AlAs的周期超晶格、一维准晶链的振动特性作了比较,对态密度作了进一步约化,所得结果与实验所测喇曼谱符合得很好。     

深度非弹性散射实验数据中坡密子圈效应研究（英文）

采用来自坡密子圈方程的衍射标度效应,研究最新实验数据中的坡密子圈效应。用质量因子的方法分析最新的HERA实验数据,得到了饱和指数λ=0.208,该指数与理论预言相一致。为了直观的显示衍射标度效应,绘制了散射截面为标度变量的图形。观察图形可知无论是单举还是衍射的实验数据都几乎位于一条曲线上。结果证明了最新的HERA实验中存在坡密子圈效应。     

3-乙基戊烷分子振动与构象分析

通过正交坐标计算与红外和拉曼光谱的对比分析,确定3—乙基戊烷分子可以很多种空间构象存在,其中存在量最大的是3种空间构象：Cs,C1,C3,并通过分子力学和量子力学半经验方法的计算,得到这3种稳定构象的相对能量。     

齿谐波励磁的混合励磁永磁同步发电机

将电机中固有的齿谐波磁场在转子绕组中感应的齿谐波电动势应用于混合励磁永磁同步电机的励磁中,不仅可以提高材料的利用率,而且便于实现电机的无刷化。该文分析了齿谐波磁场的产生机理及它在转子绕组中感应齿谐波电动势的情况,在此基础上提出了一种新型的基于齿谐波磁场励磁的混合励磁永磁同步发电机。为了验证齿谐波励磁的混合励磁的可行性,试制了一台齿谐波励磁的混合励磁永磁同步发电机。实验结果表明:齿谐波磁场在转子绕组中感应的齿谐波电动势可以用于实现混合励磁永磁同步电机气隙磁场的调节。