Vacuum Polarization Tensor for QED in the Light Front Gauge

The use of light front coordinates in quantum field theories (QFT) always brought some problems and controversies. In this work we explore some aspects of its formalism with respect to the employment of dimensional regularization in the computation of the photon’s self-energy at the one-loop level and how the fermion propagator has an important role in the outcoming results.     

The effects of sample preparation methods on the variability of the electrospray ionization response for model drug compounds

A post-column infusion system was developed in order to analyze suppression of electrospray ionization (ESI) tandem mass spectrometry response in the presence of endogenous plasma interferences. By enabling direct detection of these interfering components, this experimental system was used to analyze the ability of several common extraction procedures to remove endogenous plasma components that cause changes in the ESI response of model drug substances. Methyl-t-butyl ether (MTBE) liquid-liquid, Oasis and Empore solid-phase, and acetonitrile (ACN) protein precipitation sample preparation methods were tested using the post-column infusion system. In all cases, ACN protein precipitation samples showed the greatest amount of ESI response suppression while liquid-liquid extracts demonstrated the least. In addition, the three test compounds, phenacetin, caffeine, and a representative Merck compound, demonstrated that ESI response suppression is compound dependent. Suppression was greatest with caffeine, the most polar analyte, and the smallest for the Merck compound, the least polar analyte. Copyright 1999 John Wiley & Sons, Ltd.     

Gamma-ray spectroscopy with relativistic exotic heavy-ions

Feasibility of gamma-ray spectroscopy at relativistic energies with exotic heavy-ions and new generation of germanium detectors (segmented Clover) is discussed. An experiment with such detector array and radioactive is discussed.     

Percolative transport in the vicinity of charge-order ferromagnetic transition in a hole-doped manganite

We report measurements of non-linear charge transport in epitaxial (La_1−x Pr _x )_0.7Ca_0.3MnO₃ thin films fabricated on (100) oriented SrTiO₃ single crystals by pulsed laser deposition. The end members of this series, namely Pr_0.7Ca_0.3MnO₃ and La_0.7Ca_0.3MnO₃ are canonical charge-ordered (CO) and ferromagnetic manganites, respectively. The onset of the CO state in Pr_0.7Ca_0.3MnO₃ is manifested by a pronounced insulating behavior below ∼ 200 K. The CO state remains stable even when a large (∼ 2×10⁵ V/cm) electric field is applied across the thin film samples. However, on substitution of Pr with La, a crossover from the highly resistive CO state to a state of metallic character is observed at relatively low electric fields. The current-voltage characteristics of the samples at low temperatures show hysteretic and history dependent effects. The electric field driven charge transport in the system is modelled on the basis of an inhomogeneous medium consisting of ferromagnetic metallic clusters dispersed in a CO background.     

Zweig's rule violation,SU(3) character of the decay of the new particles,and pole dominance picture

The decays ψ′ → ψππ and ψ → ω? are studied in the framework of Zweig Rule violation via SU(4) pole dominance. The SU(3) character of the decay of the ψ is discussed in the same model. Using results of the purely hadronic decays, the cascade transition rates ψ′ → ?_c + γ and ?_carψ + γ are calculated and compared to recent experimental data.     

Effects in polarography attributable to specific adsorption of depolarizers

Summary Some effects in polarography produced by specific adsorption of the oxidised form of the depolarizer are discussed. It is suggested that this adsorption may lead to maxima in d.c. polarography when the depolarizer concentration is small and the solution has a high electrical conductivity. In normal pulse polarography specific adsorption of the oxidised form of the depolarizer may produce a maximum on the polarographic wave which is not basically due to streaming of the solution. Specific adsorption also leads to an increase in sensitivity in a.c. polarography and in R.F. polarography it produces asymmetry in the wave. Experimental results for lead ion in HClO₄ solutions containing varying amounts of Br^– ion suggest that as the concentration of Br^– increases, although the adsorbed species is probably at first PbBr⁺, eventually undissooiated PbBr₂ is strongly adsorbed.

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Zusammenfassung Die Wirkung der spezifischen Adsorption der oxydierten Form des Depolarisators auf polarographische Bestimmungen wird erörtert. Diese Adsorption kann bei der Gleichstrompolarographie Maxima verursachen, wenn die Depolarisationskonzentration niedrig ist und die Lösung eine hohe elektrische Leitfähigkeit besitzt. Bei der normalen Pulspolarographie kann die spezifische Adsorption der oxydierten Form des Depolarisators auch ein Maximum verursachen, daß grundsätzlich nicht von einer Strömung der Lösung herrührt. Bei der Wechselstrompolarographie führt die spezifische Adsorption auch zu einer Zunahme der Empfindlichkeit und bei der Radiofrequenzpolarographie wird eine Asymmetrie der Stufen hervorgerufen. Versuche mit Bleiionen in perchlorsauren Lösungen mit verschiedenen Gehalten an Bromid zeigten, daß bei steigenden Br^–-Konzentrationen anfangs wahrscheinlich PbBr⁺, schließlich jedoch undissoziiertes PbBr₂ stark adsorbiert wird.

     

Dispersive liquid–liquid microextraction based on solidification of floating organic droplet for the determination of triazine and triazoles in mineral water samples

A simple, rapid, and sensitive method for the determination of atrazine, simazine, cyproconazole, tebuconazole, and epoxiconazole in mineral water employing the dispersive liquid–liquid microextraction with solidification of a floating organic drop with determination by liquid chromatography tandem mass spectrometry has been developed. A mixed solution of 250 μL 1‐dodecanol and 1250 μL methanol was injected rapidly into 10 mL aqueous solution (pH 7.0) with 2% w/v NaCl. After centrifugation for 5 min at 2000 rpm, the organic solvent droplets floated on the surface of the aqueous solution and the floating solvent solidified. The method limits of detection were between 3.75 and 37.5 ng/L and limits of quantification were between 12.5 and 125 ng/L. The recoveries ranged from 70 to 118% for repeatability and between 76 and 95% for intermediate precision with a relative standard deviation from 2 to 18% for all compounds. Low matrix effect was observed. The proposed method can be successfully applied in routine analysis for determination of pesticide residues in mineral water samples, allowing for monitoring of triazine and triazoles at levels below the regulatory limits set by international and national legislations.     

Hydrogen and Methane Production, Energy Recovery, and Organic Matter Removal from Effluents in a Two-Stage Fermentative Process

This study evaluates the potential for using different effluents for simultaneous H₂ and CH₄ production in a two-stage batch fermentation process with mixed microflora. An appreciable amount of H₂ was produced from parboiled rice wastewater (23.9?mL g^?1 chemical oxygen demand [COD]) and vinasse (20.8?mL g^?1 COD), while other effluents supported CH₄ generation. The amount of CH₄ produced was minimum for sewage (46.3?mL g^?1 COD), followed by parboiled rice wastewater (115.5?mL g^?1 COD) and glycerol (180.1?mL g^?1 COD). The maximum amount of CH₄ was observed for vinasse (255.4?mL g^?1 COD). The total energy recovery from vinasse (10.4?kJ g^?1 COD) corresponded to the maximum COD reduction (74.7?%), followed by glycerol (70.38?%, 7.20?kJ g^?1 COD), parboiled rice wastewater (63.91?%, 4.92?kJ g^?1 COD), and sewage (51.11?%, 1.85?kJ g^?1 COD). The relatively high performance of vinasse in such comparisons could be attributed to the elevated concentrations of macronutrients contained in raw vinasse. The observations are based on kinetic parameters of H₂ and CH₄ production and global energy recovery of the process. These observations collectively suggest that organic-rich effluents can be deployed for energy recovery with sequential generation of H₂ and CH₄.     

The diffusion coefficient of Cd2+ ion in different ionic media measured by pulse polarography

The voltammetric reduction behaviors of 12 chlorinated benzenes have been examined in dimethylsulfoxide. Accurate and reproducible reduction potentials were obtained for overlapping reduction peaks by using interrupted sweep voltammetry. Controlled-potential electrolysis and subsequent gas chromatographic product analysis were performed to verify the reduction pathways predicted by the voltammetric reduction potentials.     

Growth and characterization of ferromagnetic MnAs films on different semiconductor substrates

MnAs thin films were grown by metalorganic vapour-phase epitaxy (MOVPE) on GaAs(0 0 1), Si(0 0 1) and oxidised silicon substrates. All films are crystalline and contain only the ferromagnetic α-MnAs phase. X-ray diffraction (XRD) and atomic force microscopy (AFM) measurements show that films on GaAs(0 0 1) have strong preferential orientation, developing elongated grains parallel to [1 –1 0] GaAs while films on bare and oxidised Si are polycrystalline with irregular-shaped, randomly oriented grains. Magneto-optic Kerr effect (MOKE) measurements show good magnetic properties for films on GaAs, such as strong in-plane anisotropy and squareness of the hysteresis loop in the easy direction. A Curie temperature of 340 K, remarkably higher than the bulk material (315 K), was found for a 65 nm thick film on GaAs. Films grown on bare and oxidised silicon wafers had lower Curie temperature and were magnetically isotropic.