高频地波雷达频谱监测系统的前端电路设计

利用超外差式接收和直接数字合成(DDS)技术设计了高频地波雷达频谱监测系统的前端电路．该电路能够根据雷达探测距离的远近选择相对应的噪声信号接收频段,为后续的数据采集与处理提供噪声电平数据．实验证明：本系统的跳频本振信号信噪比(SNR)优于60dB;对输入信号具有60dB左右的增益和1μV的灵敏度,满足了武汉大学研制的下一代高频地波海态监测雷达对频谱监测的需要．     

准周期链状聚合物电子谱及特征

研究了链状聚合物的长短键结构呈准周期排列的电子谱。利用紧束缚近似和转移矩阵方法通过理论证明和计算表明：这种准周期排列聚合物的电子谱,当长短键长度相差很小时,具有类似于金属晶体的能带结构;相差很大时,具有无序系统一维能级结构;而对于一般情形,其电子谱与上两者均异,形成所谓的类Cantor集。这3类不同的谱结构反映在链状聚合物的宏观物理性质上也将有所不同,它无疑会影响聚合物的稳定性及相关(超)导电性能,深入研究这方面问题将有助于对有机超导的认识。     

On Fučik Spectra and Periodic Solutions

In this paper, we continue extending the theory of boundary-value problems to ordinary differential equations and inclusions with discontinuous right-hand side. To this end, we construct a new version of the method of shifts along trajectories. We compare the results obtained by the new approach and those obtained by the method of Fuik spectra.     

Synthesis, Characterization and Thermal Decomposition of Hydroxylammonium Uranyl Acetate

The synthesis of hydroxylammonium uranyl acetate is described. The identity of the synthesized compound was confirmed by chemical and infrared analysis. The intermediates and final products of the thermal decomposition were identified by means of thermogravimetric analysis, differential thermal analysis and X-ray diffraction. The thermal decomposition of hydroxylammonium uranyl acetate involves several steps. Two of them are due to decomposition of this compound to UO₂ via UO₂(CH₃COO)₂, and the third to the partial oxidation of UO₂ to UO₃ and the formation of U₂O₈ in the solid state at higher temperature.This revised version was published online in November 2005 with corrections to the Cover Date.     

Production of high quality shocks for equation of state experiments

In this paper we describe the quality requirements that a shock wave must fulfil to make equation of state (EOS) measurements possible: planarity, no-preheating and stationarity of the shock. Experimental measurements have been performed at the Max Planck Institut für Quantenoptik (Garching). We also present simple analytical models that allow to verify shock stationarity and absence of preheating. Received 17 June 2002 Published online 21 January 2003 RID="a" ID="a"e-mail: batani@mib.infn.it RID="b" ID="b"Present address: Pro-beam, Behrinsta?e 6, 85152 Planegg b. München, Germany. RID="c" ID="c"UMR 7605     

A novel electron scattering apparatus combining a laser photoelectron source and a triply differentially pumped supersonic beam target: characterization and results for the resonance

A novel electron scattering apparatus for high resolution studies of angle-differential elastic and inelastic electron scattering from atoms and molecules in the gas phase is described and its performance characterized. It combines a laser photoelectron source, a triply differentially pumped collimated supersonic beam target (half angle 0.015 rad, background to beam density ratio < 0.01), and several electron multipliers for simultaneous detection of elastically scattered electrons and metastable atoms (or molecules) due to inelastic scattering. In detailed test measurements of the yield for the production of metastable He^*(2³S₁) atoms around its threshold, the dependence of the overall energy width on various experimental parameters has been investigated. So far a resolution down to 7 meV (FWHM) has been obtained. Under such conditions we have investigated the profile of the He^- (1 s 2 s ^{2 2} S _1/2 ) resonance at the scattering angles 22 ^° , 45 ^° , and 90 ^° . From a consistent fit of the measured profiles by resonant scattering theory we determine a new value for the resonance energy ( E _r = 19.365(1) eV) and an accurate resonance width ( Γ = 11.2(5) meV). These results are consistent with the previously recommended values. Received 23 July 2002 Published online 29 October 2002 RID="a" ID="a"e-mail: hotop@physik.uni-kl.de RID="b" ID="b"Permanent address: Department of Physics and Astronomy, Drake University, Des Moines, IA 50311, USA.     

Theoretical total ionization cross-sections of CH x,CF x,SiH x,SiF x ( ) and CCl 4 targets by electron impact

Total ionization cross-sections of electron impact are calculated for the molecular targets CH_x, CF_x, SiH_x, SiF_x (x = 1-4) and CCl₄ at incident energies 20-3 000 eV. The calculation is based on Complex Scattering Potential approach, as developed by us recently. This leads to total inelastic cross-sections, from which the total ionization cross-sections are extracted by reasonable physical arguments. Extensive comparisons are made here with the previous theoretical and experimental data. The present results are satisfactory except for the CF_x and SiF_x (x = 1-3) radicals, for which the experimental data are lower than most of the theories by more than 50%. Received 23 May 2002 / Received in final form 24 October 2002 Published online 21 January 2003 RID="a" ID="a"e-mail: knjoshipura@yahoo.com     

On Transfer Operators for Continued Fractions with Restricted Digits

For any non-empty subset I of the natural numbers, let _I denotethose numbers in the unit interval whose continued fractiondigits all lie in I. Define the corresponding transfer operator for , where Re (rß) = _I is the abscissa of convergence of the series . When acting on a certain Hilbert space H_I, rß, weshow that the operator L_I, rß is conjugate to an integraloperator K_I, rß. If furthermore rß is real,then K_I, rß is selfadjoint, so that L_I, rß: H_I, rß H_I, rß has purely real spectrum.It is proved that L_I, rß also has purely real spectrumwhen acting on various Hilbert or Banach spaces of holomorphicfunctions, on the nuclear space C [0, 1], and on the Fréchetspace C [0, 1]. The analytic properties of the map rß L_I, rßare investigated. For certain alphabets I of an arithmetic nature(for example, I = primes, I = squares, I an arithmetic progression,I the set of sums of two squares it is shown that rß L_I, rß admits an analytic continuation beyond thehalf-plane Re rß > _I. 2000 Mathematics SubjectClassification 37D35, 37D20, 30B70.     

First-Order Necessary Conditions of Optimality for Strongly Monotone Nonlinear Control Problems

Necessary conditions for the optimality of a pair (y*, u*) with respect to the cost functional g(y) + h(u) subject to AyBu + f are given in terms of generalized gradients. Here, g is locally Lipschitz, h is convex, A is a maximal strongly monotone operator, and B is linear. Two examples of applications of our necessary conditions to nonlinear partial differential equations of elliptic type are presented.     

On the Pseudospectra of Multidimensional Integral Operators with Homogeneous Kernels of Degree -n

We study the limit behavior of the spectral characteristics of truncated multidimensional integral operators whose kernels are homogeneous of degree –n and invariant under the rotation group SO(n). We prove that the limit of the -pseudospectra of the truncated operators K as 0 is equal to the union of the -pseudospectra of the original operator K and the transposed operator .