Symmetric anti-eigenvalue and symmetric anti-eigenvector

The idea of symmetric anti-eigenvalue and symmetric anti-eigenvector of a bounded linear operator T on a Hilbert space H is introduced. The structure of symmetric anti-eigenvectors of a self-adjoint and certain classes of normal operators is found in terms of eigenvectors. The Kantorovich inequality for self-adjoint operators and bounds for symmetric anti-eigenvalues for certain classes of normal operators are also discussed.     

Electrochemical behavior of ascorbic acid at a 2,2'-[3,6-Dioxa-1,8-octanediylbis(nitriloethylidyne)]-bis-hydroquinone carbon paste electrode

Electrocatalytic oxidation of ascorbic acid (AA) at a carbon paste electrode, chemically modified 2,2'-[3,6-dioxa-1,8-octanediylbis(nitriloethylidyne)]-bis-hydroquinone, was thoroughly investigated. The results of cyclic voltammetry, double potential-step chronoamperometry, linear sweep voltammetry and differential pulse voltammetry (DPV) studies were used for the prediction of the mechanism of electrochemical oxidation of AA mediated with 2,2'-[3,6-dioxa-1,8-octanediylbis(nitriloethylidyne)]-bis-hydroquinone at the surface of the modified electrode. The diffusion coefficient (D = 2.45 x 10(-5) cm(2) s(-1)) and the kinetic parameters such as the electron transfer coefficient (alpha = 0.34) were also determined. The results of DPV using the 2,2'-[3,6-dioxa-1,8-octanediylbis(nitriloethylidyne)]-bis-hydroquinone-modified electrode were applied in a highly sensitive determination of AA in drug samples. A linear range of 3.0 x 10(-6) - 1.2 x 10(-4) M and the detection limit (3sigma) 3.8 x 10(-7) M were obtained for DPV determination of AA in buffered pH 7.00 solutions (0.1 M phosphate buffer).     

Selective monotetrahydropyranylation of symmetrical diols using P2O5/SiO2 under solvent-free conditions and their depyranylation

Selective protection of one of the hydroxyl group in 1, n-symmetrical diols is achieved by P2O5/SiO2-catalyzed reaction of the diol with dihydropyran under solvent-free conditions at room temperature. This selective protection is simple and it occurred under economically cheap conditions in high yield. The deprotected diol is simply obtained by refluxing of this compound in methanol using the same catalyst without any byproduct formation or additional purifications.     

A microscopic theory of muon capture in nuclei

The muon capture rates are calculated for a series of nuclei, using the Hartree-Fock randomphase approximation, and compared with experiment. The recoil term, the binding energy of the muon and finite size effects are calculated in detail. In a schematic model, the validity of the assumption M²_V = M²_A = M²_P is studied, and found to hold reasonably well even for nuclei as heavy as ²⁰⁸Pb.     

Domain Patterns in the Microwave-Induced Zero-Resistance State

It has been proposed that the microwave-induced “zero-resistance” phenomenon, observed in a GaAs two-dimensional electron system at low temperatures in moderate magnetic fields, results from a state with multiple domains, in which a large local electric field E(r) is oriented in different directions. We explore here the questions of what may determine the domain arrangement in a given sample, what do the domains look like in representative cases, and what may be the consequences of domain-wall localization on the macroscopic dc conductance. We consider both effects of sample boundaries and effects of disorder, in a simple model, which has a constant Hall conductivity, and is characterized by a Lyapunov functional.     

Incorporation of nitrogen into amorphous-hydrogenated carbon (diamond-like) films

Nitrogen-doped amorphous hydrogenated carbon films (a-C:H) were prepared by mixing nitrogen gas and benzene during dc plasma discharge deposition. The growth rate of the film decreases strongly with increasing nitrogen content in the mixture. The nitrogen concentration in the films was determined by nuclear reaction analysis (NRA) and Auger electron spectroscopy (AES) using suitable calibration samples. The results of AES measurements are generally consistent with NRA values. Nitrogen incorporation in the a-C:H films shows pronounced doping effects as reflected in their optical and electrical properties.Dedicated to Professor J. P. F. Sellschop for his 60^th birthday     

A new PVC-activated charcoal fiber coated on silver wire; application in determination of n-alkanes in the headspace of soil samples by SPME-GC.

In this study, a new solid phase microextraction (SPME) fiber based on activated charcoal and polyvinyl chloride (PVC) coated on silver wire is presented. This fiber is very mechanically and thermally stable. Unlike commercial fiber, which is coated on fused silica, this fiber has a metallic base to which the coating adheres very strongly. On the other hand, producing this fiber is very fast, and can be completed in less than 30 min. This compares favorably with the time to make a fiber based on fused silica, which may last several days, due to many steps, such as conditioning in HCl, drying, deactivation, impregnation with a binder and coating. Also, this fiber is stable up to 250 degrees C. It has been successfully used for the analysis of n-alkanes in the gaseous phase and headspace of soil samples after optimization of the experimental parameters by capillary gas chromatography. The relatively high capacity of the sorbent allows 20-30% of the analytes to be transferred to a separative system during first extraction.     

Characterization of a high efficiency, ultrashort pulse shaper incorporating a reflective 4096-element spatial light modulator

We demonstrate pulse shaping via arbitrary phase modulation with a reflective, 1 × 4096 element, liquid crystal spatial light modulator (SLM). The unique construction of this device provides a very high efficiency when the device is used for phase modulation only in a prism based pulse shaper, namely 85%. We also present a single shot characterization of the SLM in the spatial domain and a single shot characterization of the pulse shaper in the spectral domain. These characterization methods provide a detailed picture of how the SLM modifies the spectral phase of an ultrashort pulse.