Spectral properties of Dirac operators with singular potentials

We investigate the spectral properties of Dirac operators with singular potentials which are constructed by means of a cut-off procedure. We prove the invariance of the essential spectrum, establish norm resolvent convergence of the cut-off operators, and prove spectral gap formulas.     

Application of Multivariate Calibration Techniques to HPLC Data for Quantitative Analysis of a Binary Mixture of Hydrochlorathiazide and Losartan in Tablets

New multivariate approaches have been applied to high-performance liquid chromatography (HPLC) with multiwavelength photodiode-array (PDA) detection. Multivariate calibration techniques such as partial least squares (PLS), principal component regression (PCR), classical least squares (CLS), and inverse least squares (ILS) was subjected to HPLC data for simultaneous quantitative analysis of synthetic binary mixtures and a commercial tablet formulation containing hydrochlorothiazide (HCT) and losartan potassium (LST). The combined use of HPLC and multivariate calibrations has been denoted HPLC–CLS, HPLC–ILS, HPLC–PCR, and HPLC–PLS. Successful chromatographic separation of the two active compounds and enalapril maleate, used as internal standard (IS), was accomplished by means of a 4.6 mm i.d. × 250 mm, 5 m particle, Waters Symmetry C₁₈ reversed-phase column and a mobile phase consisting of 60:40 acetate buffer (0.2 M, pH 4.8)–acetonitrile (v/v, 60:40). HPLC data based on the ratio of analyte peak areas to IS peak area were obtained by PDA detection at five-wavelengths (250, 255, 260, 265, and 270 nm). The HPLC–CLS, HPLC–ILS, HPLC–PCR, and HPLC–PLS calibration plots for hydrochlorothiazide and losartan potassium were constructed separately by using the peak-area ratios corresponding to the concentrations of each active compound. The HPLC multivariate calibrations obtained were tested for different synthetic mixtures containing HCT and LST in the presence of the IS. These multivariate chromatographic methods were also applied to a commercial pharmaceutical dosage form containing HCT and LST. The results obtained from the multivariate calibrations were compared with those obtained by use of another, classical HPLC method using single-wavelength detection.Revised: 29 September 2004 and 4 January 2005     

Linear-scaling implementation of molecular electronic self-consistent field theory

A linear-scaling implementation of Hartree-Fock and Kohn-Sham self-consistent field (SCF) theories is presented and illustrated with applications to molecules consisting of more than 1000 atoms. The diagonalization bottleneck of traditional SCF methods is avoided by carrying out a minimization of the Roothaan-Hall (RH) energy function and solving the Newton equations using the preconditioned conjugate-gradient (PCG) method. For rapid PCG convergence, the Lowdin orthogonal atomic orbital basis is used. The resulting linear-scaling trust-region Roothaan-Hall (LS-TRRH) method works by the introduction of a level-shift parameter in the RH Newton equations. A great advantage of the LS-TRRH method is that the optimal level shift can be determined at no extra cost, ensuring fast and robust convergence of both the SCF iterations and the level-shifted Newton equations. For density averaging, the authors use the trust-region density-subspace minimization (TRDSM) method, which, unlike the traditional direct inversion in the iterative subspace (DIIS) scheme, is firmly based on the principle of energy minimization. When combined with a linear-scaling evaluation of the Fock/Kohn-Sham matrix (including a boxed fitting of the electron density), LS-TRRH and TRDSM methods constitute the linear-scaling trust-region SCF (LS-TRSCF) method. The LS-TRSCF method compares favorably with the traditional SCF/DIIS scheme, converging smoothly and reliably in cases where the latter method fails. In one case where the LS-TRSCF method converges smoothly to a minimum, the SCF/DIIS method converges to a saddle point.     

卤化氢共振增强多光子电离光谱

测定了卤化氢(HCl, HBr 和HI) (2+1)共振增强多光子电离(REMPI)光谱, 采用模拟计算法分析推导出转动常数、谱带源以及Ω态振动谱带的同位素位移值. 得到的HCl数据同Green等人用常规分析法所推导的结果极为吻合. 得出8条振动谱带,其中包括V(¹∑⁺)态, E(¹∑⁺)的v'=4态以及HBr的5个新谱带, 此外还推导出HI的E态v'=1的4个振动谱带光谱参数. 观测了V和E态之间因同类相互作用而产生的不规则能级间距、转动参数和同位素位移. 讨论了HCl和HBr的E态和V态振动谱带中的转动谱线序列O和S对Q的强度比变化,提出了双光子激发机理.     

Gold nanoparticle included graphene oxide modified electrode: Picomole detection of metal ions in seawater by stripping voltammetry

We obtained a gold nanomaterial/graphene oxide-modified glassy carbon electrode and characterized it using transmission electron microscope, scanning electron microscope, cyclic voltammetry (CV), and X-ray photoelectron spectroscopy techniques. A response of the electrode using square wave anodic stripping voltammetry for Pb²⁺, Cu²⁺, and Hg²⁺ was found linear in the range from 1 × 10^–7 to 1 × 10^–11 M. The detection limits of Pb²⁺, Cu²⁺ and Hg²⁺ were 0.14, 0.5 and 1.2 pM, respectively. The method was applied to the simultaneous determination of Pb²⁺, Cu²⁺ and Hg²⁺ in seawater samples from a coastal region of Anatolia, and the results corresponded well with the values obtained by inductively coupled plasma-optical emission spectroscopy.     

In vitro immunosuppressive activity of tacrolimus dihydrodiol precursors obtained by chemical oxidation and identification of a new metabolite of SDZ-RAD by electrospray and electrospray-linked scan mass spectrometry

Different tacrolimus epoxides and dihydrodiol epoxides arising from the chemical oxidation of the parent drug are described. Open-chain tautomeric forms involving the lactone function were identified for the tacrolimus epoxides. Moreover, the identification by electrospray and electrospray linked scan mass spectrometry of an SDZ-RAD C16-C27 O-demethyl 17, 18-19, 20-21, 22 tris-epoxide new metabolite isolated from pig liver microsomes is reported. The in vitro immunosuppressive activity, using mixed lymphocyte reactions of the two macrolide reported oxidation compounds are discussed.     

HyperLab: A new concept in gamma-ray spectrum analysis

HyperLab is a new Ge gamma-ray analysis code for MS Windows, developed using object-oriented design. The novel feature of the program is the extensive use of relational database technology, which allows the efficient storage and handling of any digital data encountered in gamma-ray spectroscopy. While preserving the main concept of the predecessors (HYPERMET and its derivatives) for semi-automatic analysis of multichannel pulse-height spectra, the substantially reshaped basic routines vastly improved the stability and reliability of peak fitting. New features include the fitting of peaks with high energy tail, as well as library-directed Graphical Isotope Identification. Procedures for efficiency, nonlinearity, etc. calibrations are now highly automated. By exploiting all the benefits of MS Windows technology (point-and-click simplicity in task executions, intelligent mouse pointer, etc.) HyperLab is a versatile and user-friendly tool which the discriminating spectroscopist will find of great value.     

The competition between crystallization and demixing in polymer blends. IV. Detection of composition inhomogeneities around growing spherulites

In polymer blends of an amorphous and a semicrystalline component, the crystallization kinetics and the resulting morphology are heavily determined by the diffusion ability of the whole chains and by the dwelling site of the amorphous polymer. Depending on the relative rates of spherulite growth and chain diffusion, radial composition profiles around the growing spherulites and a gradual increase of the melt bulk composition can develop. The resulting change in composition, particularly at the crystallization front, causes a corresponding temporal variation of the spherulite growth rate. In the present article, two experimental techniques are introduced to prove the existence and to determine the course of these concentration profiles. They are based on the composition dependences of the spherulite growth rate and the number density of primary nuclei. Their efficiency is demonstrated by measurements on PVDF/PEA blends. The blend composition at the crystal growth front was found to change by absolute 25%, and the width of the profile can amount to up to 70 μm. © 1996 John Wiley & Sons, Inc.