双色激光场中激光强度和脉宽对线性多原子分子离子电离的影响

利用强激光场电离和离解分子来研究分子激发态的波包结构是强场物理的重要研究方向。利用短时指数传播子对称分割法和快速傅里叶变换技术。数值求解了一维含时Schr（oe）dinger方程，探讨了双色激光场中激光的基波和谐波强度之间的不同配比以及脉宽对线性多原子分子离子电离的影响。理论计算结果表明：基波和谐波的相对相位为π时，尽管随着激光的基波和谐波强度之间配比的变化，电离几率随原子间距变化的趋势基本保持不变，但在一定的激光基波强度下(1．2×10^13～1．2×10^15W／cm^2)，激光基波强度的变化可以明显

Sphaerotilus natans: description of the morphology, growth and systematics of [Translation from: Schr. Ver. Zellstoff u. Pap.-Chem. u. -Ing., 26, 20-37, 1956]

The morphology, increase and systematica of Sphaerotilus natans is studied and culture methods examined.

"Ein schwarzer Mann sorgt für rote Köpfe". Ein Gespräch mit Bernhard Schär und André Holenstein

Das Zeichen der Berner Zunft der Tuchhändler sorgte in der Bundeshauptstadt für Diskussionen: Es zeigt einen «Mohren» mit wulstigen Lippen und fliehender Stirn. Zwei junge Stadträte haben sich beschwert und eine Debatte vor allem unter Historikern ausgelöst. Ist der «Mohr» rassistisch oder harmloser Zeuge seiner Zeit? Es diskutieren der Historiker Bernhard Schär und André Holenstein.

Sepher Schimmusch Tehillim oder Gebrauch der Psalme zum leiblichen Wohl der Menschen : ein Fragment aus der praktischen Kabbala ; nebst einem Ausz. aus einigen andern kabbalistischen Schr.

uebers. von Gottfried Selig

The ENIGMA Consortium: Large-scale collaborative analyses of neuroimaging and genetic data

The Enhancing NeuroImaging Genetics through Meta-Analysis (ENIGMA) Consortium is a collaborative network of researchers working together on a range of large-scale studies that integrate data from 70 institutions worldwide. Organized into Working Groups that tackle questions in neuroscience, genetics, and medicine, ENIGMA studies have analyzed neuroimaging data from over 12,826 subjects. In addition, data from 12,171 individuals were provided by the CHARGE consortium for replication of findings, in a total of 24,997 subjects. By meta-analyzing results from many sites, ENIGMA has detected factors that affect the brain that no individual site could detect on its own, and that require larger numbers of subjects than any individual neuroimaging study has currently collected. ENIGMA's first project was a genome-wide association study identifying common variants in the genome associated with hippocampal volume or intracranial volume. Continuing work is exploring genetic associations with subcortical volumes (ENIGMA2) and white matter microstructure (ENIGMA-DTI). Working groups also focus on understanding how schizophrenia, bipolar illness, major depression and attention deficit/hyperactivity disorder (ADHD) affect the brain. We review the current progress of the ENIGMA Consortium, along with challenges and unexpected discoveries made on the way.

非传播孤立波及其相互作用的数值模拟

通过数值求解由Miles导出的目前公认的非传播孤立波的控制方程——一个带复共轭项的非线性立方Schr〖AKo¨〗dinger方程,对非传播孤立波进行研究.讨论了Miles方程中的线性阻尼系数α的值,模拟了两个非传播孤立波的相互作用,数值模拟表明,两个波的作用模式依赖于系统的参数,对不同的初始扰动及其演化的计算表明,只有适当的初始扰动才能形成单个稳定的非传播孤立波,否则扰动可能消失或发展成多个孤立波.

The forward problem for the electromagnetic Helmholtz equation

157 p.

超短激光脉冲在不同色散参量光子晶体光纤中传输的数值模拟

为了使得数值模拟更为精确, 采用广义非线性薛定谔方程(GNSE)描述超短激光脉冲在光子晶体光纤中的传输演化过程, 并利用二阶分步傅里叶方法通过求解方程, 数值计算了相同脉宽和能量的超短脉冲在不同色散参量的光子晶体光纤中非线性传输和超连续谱的产生。比较了超短脉冲在光纤不同色散区传输时, 高阶色散和非线性效应对超连续谱的产生以及对脉冲波形演化的影响。结果表明, 相对于超短脉冲中心波长位于光子晶体光纤的正常和反常色散区, 可以相应获得短波波段和长波波段的超连续谱输出, 当超短脉冲中心波长位于零色散波长点时, 通

Ab initio study of anharmonicity in high pressure Cmca-4 metallic hydrogen

Hydrogen is the only atom for which the Schr odinger equation is solvable. Consisting only of a proton and an electron, hydrogen is the lightest element and, nevertheless, is far from being simple. Under ambient conditions, it forms diatomic molecules H2 in gas phase, but di erent temperature and pressures lead to a complex phase diagram, which is not completely known yet. Solid hydrogen was rst documented in 1899 [1] and was found to be isolating. At higher pressures, however, hydrogen can be metallized. In 1935 Wigner and Huntington predicted that the metallization pressure would be 25 GPa [2], where molecules would disociate to form a monoatomic metal, as alkali metals that lie below hydrogen in the periodic table. The prediction of the metallization pressure turned out to be wrong: metallic hydrogen has not been found yet, even under a pressure as high as 320 GPa. Nevertheless, extrapolations based on optical measurements suggest that a metallic phase may be attained at 450 GPa [3]. The interest of material scientist in metallic hydrogen can be attributed, at least to a great extent, to Ashcroft, who in 1968 suggested that such a system could be a hightemperature superconductor [4]. The temperature at which this material would exhibit a transition from a superconducting to a non-superconducting state (Tc) was estimated to be around room temperature. The implications of such a statement are very interesting in the eld of astrophysics: in planets that contain a big quantity of hydrogen and whose temperature is below Tc, superconducting hydrogen may be found, specially at the center, where the gravitational pressure is high. This might be the case of Jupiter, whose proportion of hydrogen is about 90%. There are also speculations suggesting that the high magnetic eld of Jupiter is due to persistent currents related to the superconducting phase [5]. Metallization and superconductivity of hydrogen has puzzled scientists for decades, and the community is trying to answer several questions. For instance, what is the structure of hydrogen at very high pressures? Or a more general one: what is the maximum Tc a phonon-mediated superconductor can have [6]? A great experimental e ort has been carried out pursuing metallic hydrogen and trying to answer the questions above; however, the characterization of solid phases of hydrogen is a hard task. Achieving the high pressures needed to get the sought phases requires advanced technologies. Diamond anvil cells (DAC) are commonly used devices. These devices consist of two diamonds with a tip of small area; for this reason, when a force is applied, the pressure exerted is very big. This pressure is uniaxial, but it can be turned into hydrostatic pressure using transmitting media. Nowadays, this method makes it possible to reach pressures higher than 300 GPa, but even at this pressure hydrogen does not show metallic properties. A recently developed technique that is an improvement of DAC can reach pressures as high as 600 GPa [7], so it is a promising step forward in high pressure physics. Another drawback is that the electronic density of the structures is so low that X-ray di raction patterns have low resolution. For these reasons, ab initio studies are an important source of knowledge in this eld, within their limitations. When treating hydrogen, there are many subtleties in the calculations: as the atoms are so light, the ions forming the crystalline lattice have signi cant displacements even when temperatures are very low, and even at T=0 K, due to Heisenberg's uncertainty principle. Thus, the energy corresponding to this zero-point (ZP) motion is signi cant and has to be included in an accurate determination of the most stable phase. This has been done including ZP vibrational energies within the harmonic approximation for a range of pressures and at T=0 K, giving rise to a series of structures that are stable in their respective pressure ranges [8]. Very recently, a treatment of the phases of hydrogen that includes anharmonicity in ZP energies has suggested that relative stability of the phases may change with respect to the calculations within the harmonic approximation [9]. Many of the proposed structures for solid hydrogen have been investigated. Particularly, the Cmca-4 structure, which was found to be the stable one from 385-490 GPa [8], is metallic. Calculations for this structure, within the harmonic approximation for the ionic motion, predict a Tc up to 242 K at 450 GPa [10]. Nonetheless, due to the big ionic displacements, the harmonic approximation may not su ce to describe correctly the system. The aim of this work is to apply a recently developed method to treat anharmonicity, the stochastic self-consistent harmonic approximation (SSCHA) [11], to Cmca-4 metallic hydrogen. This way, we will be able to study the e ects of anharmonicity in the phonon spectrum and to try to understand the changes it may provoque in the value of Tc. The work is structured as follows. First we present the theoretical basis of the calculations: Density Functional Theory (DFT) for the electronic calculations, phonons in the harmonic approximation and the SSCHA. Then we apply these methods to Cmca-4 hydrogen and we discuss the results obtained. In the last chapter we draw some conclusions and propose possible future work.

高功率激光系统中B积分的研究

通过对非线性薛定谔方程的求解,数值模拟了高功率激光系统中钕玻璃的B积分传输规律,并理论分析了B积分对光脉冲的波形和频谱的影响,详细介绍了几种消除B积分影响的方法。这对高功率激光系统中光放大有一定指导意义。

非均匀交换各向异性铁磁介质的非线性表面自旋波

利用Landau Lifshitz方程 ,研究了具有非均匀交换各向异性的半无限大铁磁体的非线性表面自旋波理论。导出了部分钉扎纯交换铁磁介质的磁化强度所满足的边界条件和非线性表面自旋波的色散关系 ,并获得了自旋波振幅沿z方向驻波的一维非线性Schr dinger方程和包络振幅沿平面传播的二维非线性Schr dinger方程 ,结果表明铁磁体磁化强度的包络振幅随时空变化的性质是由二维非线性Schr dinger方程决定的。因此预言铁磁介质的表面非线性激发应是二维孤波的形式。对于弱非线性表面自旋波 ,对非线性Schr dinger方程存在孤子形式解的可能性作了讨论 .