中立型差分方程解的半环项数的估计

考虑中立型差分方程Δ(xn+pnxn- l) +qnxn- k=0 ,　 n=0 ,1 ,2 ,… ,其中 { pn} ,{ qn}为非负实数列 ,qn>0 .k,l为非负整数 k>l,本文给出其任一解的正、负半环的项数的若干上界估计 .     

Exploring the mobility of mobile phone users

Mobile phone datasets allow for the analysis of human behavior on an unprecedented scale. The social network, temporal dynamics and mobile behavior of mobile phone users have often been analyzed independently from each other using mobile phone datasets. In this article, we explore the connections between various features of human behavior extracted from a large mobile phone dataset. Our observations are based on the analysis of communication data of 100,000 anonymized and randomly chosen individuals in a dataset of communications in Portugal. We show that clustering and principal component analysis allow for a significant dimension reduction with limited loss of information. The most important features are related to geographical location. In particular, we observe that most people spend most of their time at only a few locations. With the help of clustering methods, we then robustly identify home and office locations and compare the results with official census data. Finally, we analyze the geographic spread of users’ frequent locations and show that commuting distances can be reasonably well explained by a gravity model.     

Instabilität einer von unten erwärmten Flüssigkeitsschicht bei gleichzeitiger Berücksichtigung von Oberflächenspannung und Auftriebskraft

Combined effects of surface tension and buoyancy force on the thermal instability in a horizontal liquid film heated from below, which is bounded by a rigid wall and a free surface, are considered under a generalized boundary condition for the temperature disturbance at the free surface, which is introduced by consideration of the continuity of heat flow through the free surface to a gas above the liquid film. The results show that the critical Rayleigh number varies with the Marangoni number and with the Nusselt number.

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Die Arbeit ist während eines Aufenthaltes als Dozentenstipendiat der Alexander-von-Humboldt-Stiftung bei Herrn Prof. Dr.H. Görtler im Institut für Angewandte Mathematik der Albert-Ludwigs-Universität, Freiburg i. Br. entstanden.     

Addition of alkynyl anions to aldimines containing α-hydrogens: a novel synthesis of β-aminoacetylenes

Alkynylboranes (or alkynylborates), prepared $\text{in situ}$ from lithium acetylide and BF₃ · Et₂O, added to aldimines containing α-hydrogens to afford β-aminoacetylenes in good yields.     

On a cubic cyclic field with discriminant 1632

Let K be the cubic subfield of a field of the 163rd root of unity. It is proved that the class number of K is 4. Moreover its Hilbert class field is given explicitly. also a system of the fundamental units is obtained.     

Hydromagnetische Stabilität laminarer Grenzschicht an einer längsangeströmten ebenen Platte

Summary The purpose of the paper is to consider the stability for wavelike disturbances in the steady, twodimensional, laminar boundary layer of a magnetic field, which is applied uniformly normal to the flat plate. The results show that the critical Reynolds number (R _c ^* ) increases remarkably with the characteristic parameter (). The increase of the critical Reynolds number depends not only on the shape parameter of the velocity distribution in the boundary layer but also on the peculiarity of the velocity profile. It is also found that the boundary layer holds itself laminar all over the flat plate, when the magnetic parameterN is greater than 1.25×10^–7, then a reduction of the skin-frictin drag might be expeced.     

爆炸地震效应的时频分析

以一个爆炸地震地运动信号的测试结果为例,分别应用传统Fourier变换、短时Fourier变换(STFT)、连续小波变换(CWT)和离散小波变换(DWT)进行了对比分析,讨论了爆炸地震效应的时频分布问题。结果表明,小波变换方法可以更好地给出爆炸地震效应的细节信息。在频率值较高的频带上,地震能量可能较小,但振动的峰值强度却仍较大。     

硫代磷酸三正辛酯的合成及其摩擦学性能研究

合成了一统代及四硫代磷酸三正辛酯，用电感耦合等离子体原子发射光谱仪、质谱仪和傅立叶转换红外光谱仪等表征了所合成的一硫代及四硫代磷酸三正辛酯的组成和结构，并在四球摩擦磨损试验机上考察了其在液体石蜡中的摩擦学性能；用扫描电子显微镜和X射线光电子能谱仪对钢球磨痕表面进行了分析表征。结果表明：所合成的一硫代磷酸酯具有比二烷基二硫代磷酸锌更优异的摩擦学性能，可以显著提高液体石蜡的承载能力和抗磨能力，并能在适当浓度和较高载荷（≥400N）下改善液体石蜡的减摩性能；而活性元素含量较高的四硫代磷酸酯对液体石蜡的极压、抗磨和减摩性能的影响不大，这可能是由于其导致腐蚀磨损所致，磨损表面分析结果表明，含添加剂的石蜡油在摩擦过程中发生腐蚀磨损，主要形成了由物理吸附膜和摩擦化学反应膜组成的复合膜。     

科里教授和逆合成分析法

伊莱亚斯·科里(E.J.Corey)是一位造诣很深的有机合成大师。瑞典皇家科学院授予这位哈佛大学的教授1990年诺贝尔化学奖,以表彰他创立了有机合成的理论和方法。科里1928年出生于美国,1948年获得了学士学位,在随后的三年中,他以优异的学习成绩、杰出的科研素质和创造性的研究论文从美国的著名高等学府麻省理工学院获得了博士学位,当时他年仅23岁。