Should particle trajectories comply with the transverse momentum distribution?

The momentum distributions associated with both the wave function of a particle behind a grating and the corresponding Bohmian trajectories are investigated and compared. Near the grating, it is observed that the former does not depend on the distance from the grating, while the latter changes with this distance. However, as one moves further apart from the grating, in the far field, both distributions become identical.     

Experimental design methodologies to optimize monobutyltin chloride determination by hydride generation gas phase molecular absorption spectrometry

A hydride generation gas phase molecular absorption spectrometry (HG-GPMAS) method for the determination of butyltin compound is optimized by experimental design. This method is based on the conversion of the butyltin chloride into gaseous monobutyltin hydride by adding a sodium tetrahydroborate (III) solution. The hydride generated is collected in a liquid nitrogen cryogenic trap. This is revolatilized, driven to the quartz flow cell and measured with GPMAS with diode array detection. A Plackett-Burmann design is used for the study of the factors that influence the absorption signal. The optimization of the parameters affecting the production and collection of the monobutyltin hydride is achieved using a central composite design. Partial least square (PLS), multiple linear regression (MLR) and univariate calibration are applied to the spectra obtained. The quality parameters (detection limits and precision) for the butyltin chloride are reported. An interference study is made.     

A magnetic resonance device designed via global optimization techniques

In this paper we are concerned with the design of a small low-cost, low-field multipolar magnet for Magnetic Resonance Imaging with a high field uniformity. By introducing appropriate variables, the considered design problem is converted into a global optimization one. This latter problem is solved by means of a new derivative free global optimization method which is a distributed multi-start type algorithm controlled by means of a simulated annealing criterion. In particular, the proposed method employs, as local search engine, a derivative free procedure. Under reasonable assumptions, we prove that this local algorithm is attracted by global minimum points. Additionally, we show that the simulated annealing strategy is able to produce a suitable starting point in a finite number of steps with probability one.This work was supported by CNR/MIUR Research Program Metodi e sistemi di supporto alle decisioni, Rome, Italy.Mathematics Subject Classification (1991):65K05, 62K05, 90C56     

Oxidative dissolution of chalcopyrite by Acidithiobacillus ferrooxidans analyzed by electrochemical impedance spectroscopy and atomic force microscopy

The microbiological leaching of chalcopyrite (CuFeS(2)) is of great interest because of its potential application to many CuFeS(2)-rich ore materials. However, the efficiency of the microbiological process is very limited because this mineral is one of the most refractory to bacterial attack. Knowledge of bacterial role during chalcopyrite oxidation is very important in order to improve the efficiency of bioleaching operation. The oxidative dissolution of a massive chalcopyrite electrode by Acidithiobacillus ferrooxidans was evaluated by electrochemical impedance spectroscopy (EIS) and atomic force microscopy (AFM). A massive chalcopyrite electrode was utilized in a Tait-type electrochemical cell in acid medium for different immersion times in the presence or absence of bacterium. The differences observed in the impedance diagrams were correlated with the adhesion process of bacteria on the mineral surface.     

Oxygen vacancies on TiO2 (110) from first principles calculations

We have carried out a systematic study of oxygen vacancy formation on the TiO2 (110) surface by means of plane-wave pseudopotential density-functional theory calculations. We have used models with the mean number of vacancies per surface unit cell being theta=0.25 and theta=0.5. The study comprises several kind of vacancies within the outermost layers of the surface. The use of a suitable set of technical parameter is often essential in order to get accurate results. We find that the presence of bridging vacancies is energetically favored in accordance to experimental data, although the formation of sub-bridging vacancies might be possible at moderate temperatures. Surprisingly, the spin state of the vacancy has little influence on the results. Atomic displacements are also analyzed and found to be strongly dependent on the particular arrangement of vacancies.     

74% Slope efficiency from a diode-pumped Yb3+:LiNbO3:MgO laser crystal

An optimization of the laser action performance from a diode-pumped Yb³⁺-doped LiNbO₃:MgO crystal has been carried out. In this sense, efficient laser action at 1.06 m when pumping with a fiber-coupled laser diode at 980 nm has been demonstrated, achieving laser slope efficiencies as high as 74%. The influence of output mirror transmittance on both pumping threshold and laser slope efficiency has been investigated, and the parameters of relevance in laser dynamics (emission cross section and optical losses) have been determined. Under the experimental conditions leading to maximum slope efficiency, the pump power at threshold was 300mW, and the pump-to-laser conversion efficiency was 40%. PACS 42.55.Xi; 42.55.Rz; 42.60.Lh     

Recent Reviews. 67

Reviews are listed in order of appearance in the sources indicated. In multidisciplinary review journals, only those reviews which fall within the scope of this Journal are included. Sources are listed alphabetically in three categories: regularly issued review journals and series volumes, contributed volumes, and other monographs. Titles are numbered serially, and these numbers are used for reference in the index. Major English-language sources of critical reviews are covered. Encyclopedic treatises, annual surveys such as Specialist Periodical Reports, and compilations of symposia proceedings are omitted. This installment of Recent Reviews covers principally the middle part of the 2002 literature. Previous installment: J. Org. Chem. 2002, 67(20), 7169-74. SUPPORTING INFORMATION AVAILABLE: A file containing this Recent Review compilation in Microsoft Word and the data in rtf format. This material is available free of charge via the Internet at http://pubs.acs.org.     

Antioxidant activity of o-bisphenols: the role of intramolecular hydrogen bonding

A kinetic and thermodynamic investigation on the antioxidant activity of 2,2'-methylenebis(6-tert-butyl-4-methylphenol) (2), 2,2'-ethylidenebis(4,6-di-tert-butylphenol) (3), and 4,4'-methylenebis(2,6-di-tert-butylphenol) (4) are reported. EPR studies of the equilibration between 3 or 4 and a reference phenol, and the corresponding phenoxyl radicals, allowed us to determine the O-H bond dissociation enthalpy (BDE) of the O-H bond as 81.2 and 81.1 kcal/mol in 3 and 4, respectively. Despite this similarity, the absolute rate constants for the reaction with peroxyl radicals, determined by autoxidation studies under controlled conditions, indicate that the o-bisphenols 2 and 3 behave as excellent antioxidants while the p-bisphenol 4 is less effective by a factor of 64 and 22, respectively. FT-IR spectroscopy and product studies suggest that the very good antioxidant activity of the o-bisphenols largely arises from both the reduced steric crowding about the hydroxyl group and the stabilization of the aroxyl radical due to the formation of an intramolecular hydrogen bond between the residual OH and the oxygen radical center.     

Analysis by gas chromatography-mass spectrometry of the essential oil from the aerial parts of Pimpinella junoniae Ceb. & Ort., gathered in La Gomera, Canary Islands, Spain

The essential oil from the aerial parts of Pimpinella junoniae Ceb. & Ort., growing in La Gomera, Canary Islands, Spain, was studied by gas chromatography and gas chromatography-mass spectrometry, and 43 constituents were identified. The major components were found to be alpha-zingiberene (20.6%), alpha-pinene (17.9%), (E)-beta-farnesene (9.3%), ar-curcumene (7.4%), beta-phellandrene (7.0%), beta-bisabolene (6.1%) and epoxypseudoisoeugenyl 2-methylbutyrate (6.0%). The decomposition product of epoxypseudoisoeugenol derivatives, 5-methoxy-2-methylbenzofuran (5.7%), moderate amounts of other arylpropanoids with the pseudoisoeugenol skeleton (total percentage, 5.2%) and other compounds such as beta-sesquiphellandrene (3.0%), cis-beta-guaiene (1.5%), alpha-phellandrene (1.5%) and alpha-bisabolol (1.3%), were also found.     

Multiresolution Analysis and Radon Measures on a Locally Compact Abelian Group

A multiresolution analysis is defined in a class of locally compact abelian groups G. It is shown that the spaces of integrable functions and the complex Radon measures M(G) admit a simple characterization in terms of this multiresolution analysis.