民机噪声适航合格审定试验中地面影响研究

在民用飞机噪声适航合格审定试验中,传声器布置在地面上1.2 m处,测得的噪声包含地面影响。该文提出了一种分析地面对民机噪声适航合格审定试验中有效感觉噪声级影响的方法,并以ARJ21-700飞机噪声适航合格审定试验为例,对地面对飞越噪声的影响进行了计算和分析。在对飞行试验中飞机自由场声压级理论计算方法进行分析的基础上,通过飞越噪声测量点处布置的倒置传声器装置测量结果,计算了该测量点处的自由场声压级。随后,对满足"CCAR-36部"的不同地面声阻抗对噪声的影响进行了计算,分析了地面条件对噪声适航合格审定中有效感觉噪声级的影响。结果表明,地面声阻抗对噪声适航合格审定结果有明显影响,该方法可以为民用飞机噪声适航合格审定试验提供一种分析测量点地面的声学处理对噪声评定结果影响的手段。     

A minimal energy tracking method for non-radially symmetric solutions of coupled nonlinear Schrödinger equations

We aim at developing methods to track minimal energy solutions of time-independent m-component coupled discrete nonlinear Schrödinger (DNLS) equations. We first propose a method to find energy minimizers of the 1-component DNLS equation and use it as the initial point of the m-component DNLS equations in a continuation scheme. We then show that the change of local optimality occurs only at the bifurcation points. The fact leads to a minimal energy tracking method that guides the choice of bifurcation branch corresponding to the minimal energy solution curve. By combining all these techniques with a parameter-switching scheme, we successfully compute a non-radially symmetric energy minimizer that can not be computed by existing numerical schemes straightforwardly.     

声子之间的相互作用对量子线中极化子性质的影响

研究了量子线中弱耦合极化子的性质。采用线性组合算符和微扰法导出量子线中弱耦合极化子的基态能量。在计及电子在反冲效应中发射和吸收不同波矢的声子之间的相互作用时,讨论了量子线的受限强度﹑电子-LO声子耦合强度和声子之间相互作用对量子线中弱耦合极化子的基态能量的影响。数值计算结果表明：量子线中弱耦合极化子的基态能量 随量子线的受限强度 的增大而增大, 表现出了量子线的量子尺寸效应。     

A Contour Method on Cayley Trees

We consider finite-range lattice models on Cayley trees with two basic properties: the existence of only a finite number of ground states and with a Peierls type condition. We define the notion of a contour for the model on the Cayley tree. By a contour argument we show the existence of s different (where s is the number of ground states) Gibbs measures. Dedicated to N.N. Ganikhodjaev on the occasion of his 60th birthday. The work supported by NATO Reintegration Grant: FEL.RIG.980771.     

西安地铁二号线沿线地裂缝特征、危害及对策

地裂缝是西安地区典型的地质灾害,对该地区的各类工程建筑、交通设施、城市生命线工程及土地资源造成威胁,尤其是对拟建的西安地铁二号线的施工与安全运营影响更大。本文首先介绍了西安地裂缝的基本特征,然后阐述了西安地铁二号线穿越地裂缝的基本情况。根据实际观测数据及地表累计活动量确定了地铁二号线穿越的各条地裂缝在不同时间段的活动速率及地裂缝活动的影响范围,在此基础上提出了针对地裂缝灾害的防治措施。     

Time series analysis for ground penetrating radar (GPR) asphalt thickness profile

Time series obtained from the waveform profiles of the ground penetrating radar (GPR) thickness of the asphaltic concrete layers of in–service pavement holds a key to the understanding of thickness variation and the presence of cavities within and below the pavement surface. In this paper, the fundamental techniques of time series modelling—(i) identification, (ii) estimation and (iii) diagnostics—are applied to the GPR thickness profile of three types of pavement—(a) fully–designed (b) partially–designed and (c) compositely designed pavement. Actual applications are made using data from in–service pavement in the state of Kansas. The main purpose of this study is to investigate the mechanism that drives the data and to compare the model errors and statistics of the thickness profiles of different types of flexible pavement. In the present study, the time series is replaced by a distance scale, but the name time series is retained.     

The relation between structure and reactivity in five-membered heteroaromatic compounds—II: CNDO/2 calculations on azolium cations and on the zwitterions resulting from their deprotonation

Olofson's group and Norris and Henry have reported proton exchange rates for a variety of azolium cations in aqueous solution. They found that ring protons in positions located α- to pyrrole-type N atoms exchange much faster than those located β- to such nitrogens, and that addition of pyridine-type nitrogen to the ring also caused a large increase in rate of exchange. This report describes the results of CNDO/2 calculations on azolium cations representative of those studied experimentally, and on the zwitterions resulting from the deprotonation of these cations. The calculated vapor-phase energies of deprotonation are in agreement with the structure-reactivity trends summarized above, but the calculated effect of added nitrogen is unexpectedly small relative to the effect of interchanging α- and β- pyrrole-type N atoms. The calculated charge distributions and one- and two-atom contributions to the calculated energies of deprotonation are analyzed in terms of classical organic mechanisms for transmission of substituent effects. The results of this analysis suggest that the relative reactivities of isomeric tetrazolium cations are determined primarily by coulombic effects, but that relative reactivities of isomeric positions in the imidazolium and pyrazolium series are apparently determined primarily by inductive and hybridization effects. π-Electron resonance (contributions from carbenoid resonance forms) is apparently not of overriding importance. When nitrogen is added to the ring in an α-position relative to the CH group undergoing exchange, the resulting increase in CH acidity seems to be due to inductive and hybridization effects, partially offset by a coulombic effect due to the negative charge on the added nitrogen. If classical σ-inductive and hybridization effects from an added β-nitrogen are at all influential, they seem much less so than from an added α-nitrogen; thus according to CNDO/2 these effects alone apparently cannot explain the observed large rate increase due to added β-nitrogen. The possible importance of solvent effects, delocalization of the added negative charge into the σ-framework and coulombic effects due to the added nitrogen are discussed.     

Classical ground states in one dimension

We give conditions on an interaction sufficient to guarantee that in one dimension it yield a periodic ground state with one or two particles per unit cell.Research supported in part by NSF Grant MCS 81-01596-A01.     

Novel structure and electronic property of Sin (21n30) clusters

Using first-principles simulated annealing generalized gradient approximation density functional calculations based on norm-conserving pseudopotentials, we have investigated the geometric and electronic structures of low-energy silicon clusters (Si_n, n=21–30). We have obtained new low-energy structures not reported previously. Our calculations suggest that the lowest energy structures are spherical ones including core atoms whose number increases with the cluster size. The trend of the binding energy as well as that of the energy difference between the highest occupied and the lowest unoccupied molecular orbitals is studied as a function of the cluster size and the number of core atoms.     

青藏高原清水河多年冻土区铁路路基沉降变形特征研究

通过埋设在青藏铁路路基中两个断面内的6条沉降观测管3 a来的地基沉降变形资料,研究了高原多年冻土区铁路路基的沉降变形特征,分析了填筑铁路路基对下伏多年冻土融化变形的影响。研究表明,由于受到填筑路基时赋存在路基填料内的热量的影响,铁路路基下伏多年冻土上限在施工初期会有一个明显的下移沉降,铁路路基也随之有一个较大幅度的工后下沉变动,随着时间的推移,路基下降速率会逐渐下降,但在短时间内不会停止下来,而且由于太阳辐射和路基边坡形状的影响,路基向阳面与背阴面的变形有较大的差别,且在近南北向展布的路基上表现最为明显。