Chemical Bonding State of Chlorine on Ag{100} as Determined by Angle-Resolved Secondary Ion Mass Spectrometry

The power of the angle-resolved ion desorption technique for straightforward characterization of surfaces is demonstrated. The structural sensitivity of secondary ion desorption has led to a successful application of angle-resolved ion sputtering yield measurements to the determination of the Cl chemical bonding structure on the Ag {100} surface. Angular distributions of the sputtered Cl^? ions show that chlorine dissociates at the surface to yield a bonding state of atomic form at the room temperature. Both the polar and the azimuthal angle dependencies of the sputter intensity for Ag⁺ and Cl^? ions reveal that the Cl adatom is chemi-sorbed high above the topmost substrate layer of Ag atoms. At all Cl exposures, the Ag-Cl bond is oriented along the <100> azimuth with the adsorbate occupying a C₄ symmetry site, not an a-top, a bridge, or a high symmetry site. Shadow-cone enhanced ion desorption spectra show that die geometrical structure of the Cl chemisorbed surface changes slightly as the exposure is increased.     

Ultrasonic phased array controller for hyperthermia applications

Multiple and mechanically scanned ultrasound transducer systems have demonstrated the efficacy of using ultrasound to produce deep localized hyperthermia. The use of ultrasonic phased arrays has been proposed as an alternative to these systems. A phased array offers a more flexible approach to heating tumours in that the size, shape, and position of its focal region can be altered during the course of treatment in order to achieve the desired temperature distribution. This added flexibility comes at the cost of increased complexity of the hardware necessary to drive the transducer because each element requires its own amplifer with both phase and amplitude control. In order for phased arrays with large numbers of elements to be feasible for hyperthermia applications, the complexity of this circuitry must be minimized. This paper describes a circuit design which simplifies the electronics required to control a phased array transducer system for hyperthermia applications. The design is capable of controlling virtually any type of phased array transducer operating at frequencies less than 2 MHz. The system performance was verified through beam profile measurements using a 48-element tapered phased array transducer.     

Multiple solutions of a boundary-value problem in enzyme kinetics

In some immobilized enzyme systems the steady state of substrate concentration may suddenly change from a low profile to a high profile or vice versa when the physical parameters of the systems pass through certain critical values. This phenomenon is due to the transition from a unique solution to multiple solutions (or vice versa) of the enzyme reaction equation. This problem is studied by considering two physical parameters which represent the internal reaction mechanism and the external influence on the boundary of the reaction-diffusion medium. Both analytical and numerical results for the problem are presented. The analytical results include some sufficient conditions for the existence of multiple steady-state solutions as well as a unique solution. Various numerical results of the problem including time-dependent solutions and their convergence to steady-state solutions are given.     

Orbital relaxation in the Rydberg series of the He atom

The orbital behavior of both the singlet and triplet Rydberg series for 1sns configurations of the He atom has been investigated using one- and two-configuration Hartree–Fock wave functions. The core orbital within the triplet series changes negligibly; however, a contract trend is noticeable as the Rydberg orbital penetrates more into the core region, which is in contrast to that found in the 1s²ns ²S Rydberg series of Li atom. Although some properties of the whole atom can be calculated, the core relaxation of the singlet series can not be drawn without ambiguity because a two-configuration correlated wave function has to be used, and thus the orbital picture is lost.     

Numerical solutions for some coupled systems of nonlinear boundary value problems

Summary In the well-known Volterra-Lotka model concerning two competing species with diffusion, the densities of the species are governed by a coupled system of reaction diffusion equations. The aim of this paper is to present an iterative scheme for the steady state solutions of a finite difference system which corresponds to the coupled nonlinear boundary value problems. This iterative scheme is based on the method of upper-lower solutions which leads to two monotone sequences from some uncoupled linear systems. It is shown that each of the two sequences converges to a nontrivial solution of the discrete equations. The model under consideration may have one, two or three nonzero solutions and each of these solutions can be computed by a suitable choice of initial iteration. Numerical results are given for these solutions under both the Dirichlet boundary condition and the mixed type boundary condition.     

The Hybrid Type Natural Orbitals for Excited States

Under certain circumstance, natural orbitals of excited states have quite unusual hybrid behavior, which is drastically different from that of the familiar cononical orbitals, and gives ambiguous results for the one-electron properties. We show that a simple 2×2 density matrix obtained from a multiconfiguration self-consistent-field calculation is sufficient to reveal the NO behavior in this situation.     

基于近红外光谱技术与化学计量学的绿茶无损鉴别方法研究

该文利用近红外光谱技术结合化学计量学方法开发了不同品种绿茶的无损鉴别方法。通过近红外光谱技术得到了8个品种绿茶样品的近红外光谱,比较了单一以及优化组合光谱预处理方法对光谱的影响,利用无监督的主成分分析(PCA)与有监督的线性判别分析方法(LDA)分别构建了茶叶品种鉴别模型。结果表明：对比单一预处理方法,优化组合预处理具有更优的鉴别准确性。标准正态变量变换预处理消除了茶叶样品大小不均造成的光谱散射影响,一阶导数预处理实现了变动背景的消除,减少了基线漂移的影响,突出了图谱中的有效信息,采用二者相结合的预处理方式并结合无监督的主成分分析法可实现较为准确的绿茶样品种类鉴别分析,准确率达75.0%。此外,采用有监督的线性判别分析方法处理原始光谱数据,可达到100%的鉴别准确率,但该方法需提供类别的先验知识。因此,采用近红外光谱技术和化学计量学相结合的手段可实现不同品种绿茶的快速无损鉴别。     

Photo‐physical Properties of N‐methyl‐3,4‐fulleropyrrolidine and Its Derivatives: A DFT and TD‐DFT Investigation

A series of N‐methyl‐3,4‐fulleropyrrolidine (NMFP) derivatives were designed by selecting different π‐conjugated linkers and electron‐donating groups as D‐π‐A and D‐A systems. The optimised structures and photo‐physical properties of NMFP and its derivatives have been determined using density functional theory (DFT) and time‐dependent density functional theory (TD‐DFT) methods with the B3LYP functional and the 6‐31G basis set. According to the computation analysis, both the π‐conjugated linkers and the electron‐donating groups can influence the electronic and photo‐physical properties of the NMFP derivatives. Our calculated results demonstrated that the electron‐donating groups, with significant electron‐donating ability, had the tendency to increase the highest occupied molecular orbital (HOMO) energy. The π‐conjugated linkers with lower resonance energy decreased the lowest occupied molecular orbital (LUMO) energy and caused a significant decrease in the energy gap (E_g) between the E_HOMO and E_LUMO. A Natural Bond Orbital (NBO) analysis examines the effect of the electron‐donating group, π conjugated linker, and electron‐withdrawing group for these NMFP derivatives. For the NMFP derivatives, a projected density of state (PDOS) analysis demonstrated that the electron density of HOMO and LUMO are concentrated on the electron‐donating group and the π‐conjugated linker, respectively. A TD‐DFT/B3LYP calculation was performed to calculate the electronic absorption spectra of these NMFP derivatives. Both the electron‐donating group and the π‐conjugated linker contribute to the major absorption peaks, which are assigned as HOMO to LUMO transitions and are red‐shifted relative to those of non‐substituted NMFP.