Tight-binding description of Landau levels of graphite in tilted magnetic fields

The electronic structure of Bernal-stacked graphite subject to tilted magnetic fields is studied theoretically. The minimal nearest-neighbor tight-binding model with the Peierls substitution is employed to describe the structure of Landau levels. We show that, while the orbital effect of the in-plane component of the magnetic field is negligible for massive Dirac fermions in the vicinity of the K point of the graphite Brillouin zone, at the H point it leads to the experimentally observable splitting of Landau levels, which grows approximately linearly with the in-plane field intensity.     

Atomic imaging and direct phase retrieval using anomalous surface x-ray diffraction

The application of multi-wavelength anomalous diffraction to thin films, interfaces and surface structures is presented. The method directly determines the amplitudes and phases of the complex surface structure factors from surface x-ray diffraction data, measured at three different energies around the absorption edge of one of the elements present in the film. Thereby, one is able to directly Fourier transform the data, which immediately provides meaningful and unambiguous electron-density distributions. These serve as a starting point for subsequent structural refinement. The robustness of the algorithm was evaluated on simulated data as a proof of principle. The experimental limitations and their effect on the method will be discussed as well as stability tests for the algorithm, such as the positions of the anomalous scatterers and the interfacial roughness. It will be shown that the method can be applied to real structures. The algorithm was tested on real data from a thin film of SrTiO(3) grown on NdGaO(3)(110).     

Helium, neon and argon diffraction from Ru(0001)

We present an experimental and theoretical study of He, Ne and Ar diffraction from the Ru(0001) surface. Close-coupling calculations were performed to estimate the corrugation function and the potential well depth in the atom-surface interaction in all three cases. DFT (density functional theory) calculations, including van der Waals dispersion forces, were used to validate the close-coupling results and to further analyze the experimental results. Our DFT calculations indicate that, in the incident energy range 20-150?meV, anticorrugating effects are present in the case of He and Ar diffraction, whereas normal corrugation is observed with Ne beams.     

Slippage and nanorheology of thin liquid polymer films

Thin liquid films on surfaces are part of our everyday life; they serve, e.g.,?as coatings or lubricants. The stability of a thin layer is governed by interfacial forces, described by the effective interface potential, and has been subject of many studies in recent decades. In recent years, the dynamics of thin liquid films has come into focus since results on the reduction of the glass transition temperature raised new questions on the behavior of especially polymeric liquids in confined geometries. The new focus was fired by theoretical models that proposed significant implication of the boundary condition at the solid/liquid interface on the dynamics of dewetting and the form of a liquid front. Our study reflects these recent developments and adds new experimental data to corroborate the theoretical models. To probe the solid/liquid boundary condition experimentally, different methods are possible, each bearing advantages and disadvantages, which will be discussed. Studying liquid flow on a variety of different substrates entails a view on the direct implications of the substrate. The experimental focus of this study is the variation of the polymer chain length; the results demonstrate that inter-chain entanglements and in particular their density close to the interface, originating from non-bulk conformations, govern the liquid slip of a polymer.     

奇妙的非晶态金属

在日常生活中,人们所接触的材料不外乎两类,即晶态材料和非晶态材料。形象地说,如果材料中的原子排列像被检阅的士兵方阵那样有序,该材料就是晶态材料;如果原子排列像集市的人群那样杂乱无章,那么这种材料就是非晶态材料。在我们接触的物质中,食盐、钻石等都属于晶态材料,而木材、纺     

正交各向异性粘弹性接触应力分析

本文利用拟静态粘弹性和线弹性的对应原理，通过Ｓｃｈａｐｅｒｙ数值反演做Ｌｏｐｌａｃｅ逆变换，由正交各向异性线弹性接触应力解获正交各向异性粘弹性接触应力的数值解．     

电磁振动给料机复合材料板弹簧疲劳性能实验分析

本文设计了一种复合材料层合板弯曲疲劳实验系统,对复合材料层合板弯曲疲劳时的模量损伤参数进行了研究。对玻璃/酚醛环氧复合材料板弹簧的弯曲疲劳性能进行了实验研究,得到了复合材料板弹簧的载荷—寿命曲线。     

结合高斯定理的应用,提高学生分析问题的能力

在讲解高斯定理的应用时,我认为引进下面的习题作为例题进行详细分析,或用来作为作业课供学生讨论用的练习题,对于提高学生分析具体问题的能力、加深对高斯定理内容的理解,并应用于求解D与E是很有益的. 习题:如图-1所示,一带电行Q的金属球壳沉浸在无限大的真空(ε0)与介电常数为ε的介质中,球的上半部为空气,下半部为介质,求: (1)球壳外各区域中任意点之D; (2)球壳外各区域中任意点之E; (3)球壳外各区域中任意点之电位V; (4)球面上各区域的自由面电荷密度的分布; (5)用拉普拉斯方程求解V,以验证(3)的结果.首先作如下的具体分析: (1)这里…     

消息与动态

<正> 世界先进的高速气体轴承高速气体浮环轴承,主要用于手表、精密仪器等磨削和钻削加工.目前,在世界上,最先进的高速气体轴承的转速每分钟为20万转,线速每秒钟为20米.国内外专家把实现转速每分钟30万转和线速每秒钟30米,视为高速气体轴承研究