bluuebunny/crossref_metadata_2025_split huggingface dataset:
Temperature effects on the UV–Vis electronic spectrum of trans‐stilbene
Authors: Kwasniewski S. P. , François J. P. , Deleuze M. S. 
Published: August 2002

AbstractThe ultraviolet (UV)–Visible absorption spectrum of trans‐stilbene (tS) is computed at different temperatures by coupling molecular dynamics (MD) simulations with the classical MM3 force field to ZINDO/S‐CIS calculations of vertical excitation energies and transition dipole moments. The selection of a large number of structures along the MD trajectories enables a consistent treatment of temperature effects in the vacuum, whereas the ZINDO/S‐CIS calculations permit a reliable treatment of electron correlation and relaxation, taking account of multistate interactions in the final state. Thermal motions are found to alter very differently the width and shape of bands. Structural alterations such as the stretching and the torsion of the vinyl single and double bonds very strongly influence the appearance of the first valence state, pertaining to the highest occupied and lowest unoccupied molecular orbital (HOMO–LUMO) transition. At temperatures less than 400 K, these are found to yield a merely Gaussian and very pronounced thermal broadening of the related band (A), up to nearly 30 nm, together with a minor blue shift of its maximum λmax. In contrast, a red shift by several nanometers occurs due to thermal motions for the remaining three valence bands. As can be expected, the broadening intensifies at higher temperatures, and for the A‐band, becomes markedly asymmetric when T exceeds 400 K. The combination of MD(MM3) and ZINDO/S‐CIS computations enables also consistent calculations of hot bands, which are forbidden by symmetry at 0 K. © 2001 John Wiley & Sons, Inc. Int J Quantum Chem, 2001
Magnetoresistance effect, Runge–Lenz vector, and the torque vector due to anisotropy of electron orbits in cubic lattices submitted to the action of a constant magnetic field
Authors: Olszewski S. , Baszczak M. 
Published: August 2002

AbstractParameters due to an anisotropic character of the electron orbits in cubic metals submitted to the action of an external magnetic field are calculated. These parameters are, in the first step, a nonzero value of the metal magnetoresistance and—in the second step—the nonvanishing electron torque vector and the Runge–Lenz vector. Both these vectors depend on the electron angular momentum in the crystal lattices, which is also examined together with the radius of curvature of the electron orbits. The calculation of magnetoresistance is specified to the case of the body‐centered cubic lattice of metallic iron for which a comparison of the theory with the experimental data for magnetoresistance is also presented. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002
Theoretical study of the internal rotational barriers in nitrobenzene, 2‐nitrotoluene, 2‐nitrophenol, and 2‐nitroaniline
Authors: Chen P. C. , Chen S. C. 
Published: August 2002

AbstractThe molecular geometries and internal rotational barriers of the nitro group of nitrobenzene (NB), 2‐nitrotoluene (2‐NT), 2‐nitroaniline (2‐NA), and 2‐nitrophenol (2‐NP) were calculated by five different types of density functional theory (DFT) methods with three different levels of basis sets. Analysis of the torsional angles of the nitro, methyl, amino, and hydroxyl groups indicate that NB, 2‐NA, and 2‐NP are planar molecules, but 2‐NT is not a planar molecule. Internal rotational barriers of the nitro group were calculated as V2 barriers, and the NO2 torsional potentials for each molecule were given. The values of the V2 barriers depend on the DFT methods and basis sets. The average values of the V2 barriers for NB, 2‐NT, 2‐NA, and 2‐NP are 6.47 kcal/mol, 3.00 kcal/mol, 10.20 kcal/mol, and 13.26 kcal/mol, respectively. © 2001 John Wiley & Sons, Inc. Int J Quant Chem 83: 332–337, 2001
Sum‐frequency generation first hyperpolarizability from time‐dependent Hartree–Fock method
Authors: Quinet Olivier , Champagne Benoît 
Published: August 2002

AbstractA general time‐dependent Hartree–Fock scheme has been implemented using the 2n+1 rule in order to evaluate the sum frequency generation first hyperpolarizability. It has been applied to estimate the second‐order nonlinear optical response of p‐nitroaniline with one fixed frequency in the ultraviolet (UV) domain and one tunable infrared frequency. This scheme has also been employed to determine the antisymmetric isotropic component of the first hyperpolarizability of chiral molecules including helicenes. © 2001 John Wiley & Sons, Inc. Int J Quantum Chem, 2001
Quantization of the ab initio nonadiabatic coupling matrix: The C2H molecule as a case study
Authors: Baer Michael , Mebel Alexander M. 
Published: August 2002

AbstractThe observation that, for a given sub‐Hilbert space, diabatic potentials, just like adiabatic potentials, have to be single‐valued in configuration space led to the unavoidable conclusion that the relevant nonadiabatic coupling matrix (i.e., the matrix that contains the vectorial electronic nonadiabatic coupling terms) has to be quantized along any contour in configuration space. In the present article this statement is tested with respect to the three (excited) states of the C2H molecule, i.e., the 22A′, 32A′, and 42A′ states. For this purpose ab initio electronic nonadiabatic coupling matrices were calculated along various contours surrounding the relevant conical intersections (one conical intersection between the 22A′ and 32A′ states and two conical intersections between the 32A′ and 42A′ states). Employing the line‐integral technique it was shown that as long as the contour that surrounds the (2,3) conical intersection is close enough to the CI and avoids the two (3,4) conical intersections, the 2×2 nonadiabatic coupling matrices are quantized. However they fail to be quantized for contours that also surround one or two of the other conical intersections. In this case one is obliged to employ the three‐state nonadiabatic coupling matrix. Doing that, it was shown that it is the 3×3 matrices that satisfy the quantization condition. © 2001 John Wiley & Sons, Inc. Int J Quantum Chem, 2001
A mass spectrometric study of Al2O3‐SiO2 melts using a Knudsen cell
Authors: Björkvall Johan , Stolyarova Valentina L. 
Published: August 2002

AbstractThe thermodynamic activities of SiO2 in Al2O3‐SiO2 liquid slags were measured by the high‐temperature Knudsen cell mass spectromeric method in the present work. The measurements were carried out in the temperature range 1863–2169 K. Tungsten crucibles were used to hold the slags. The system was calibrated using a CaF2 standard. The mass spectra obtained for pure SiO2 were in agreement with earlier data. The activities of silica, measured in the present work at 2150 K, show a slight negative deviation at very low alumina mole fractions which changed to a positive deviation at higher alumina contents. The activity values are in reasonable agreement with the assessment carried out by Hillert et al. The results were analysed on the basis of a slag model developed earlier at KTH, Stockholm. The present results are found to be compatible with the phase diagram proposed by Klug et al. Copyright © 2001 John Wiley & Sons, Ltd.
Study of bradykinin metabolism in human and rat plasma by liquid chromatography with inductively coupled plasma mass spectrometry and orthogonal acceleration time‐of‐flight mass spectrometry
Authors: Marshall Peter , Heudi Olivier , Mckeown Stephen , Amour Augustin , Abou‐Shakra Fadi 
Published: August 2002

AbstractBradykinin is a small peptide that acts mainly as a hormone by activating specific receptors that confer protection against the development of hypertension. The efficacy of bradykinin is influenced by the activities of various kininases present in plasma and blood. In this study, both human and rat plasma were incubated with a labelled form of bradykinin (at 4 and 12.5 µM), that will be referred to as bromobradykinin. The metabolic fate of bromobradykinin was monitored by liquid chromatography coupled to an orthogonal acceleration time‐of‐flight mass spectrometer (oaTOF). Quantification measurements of the bromine‐containing metabolites were performed on‐line, via flow splitting, by inductively coupled plasma mass spectrometry (ICPMS). The data obtained highlighted that the mechanism(s) of bradykinin metabolism in human and rat plasma are different, with the metabolism of bradykinin in rat plasma being much more aggressive than that observed in human plasma. In addition to the known bradykinin metabolites, e.g. [1,5], [1,7] from ACE, [1,8] from carboxypeptidase and [2,9] from aminopeptidase activity, we have identified the presence of new bradykinin metabolites in both human and rat plasma. These have been identified as fragment [5], the amino acid phenylalanine, which was present in both the human and rat plasma and the fragments [2,8] and [4,8] in rat plasma. To our knowledge it is the first time that these fragments have been recorded in human and rat plasma. The occurrence of these new fragments provides evidence for the presence of potentially new enzymes and mechanisms of bradykinin metabolism.The method described here provides a powerful technique for monitoring the activity of the many kininases involved in bradykinin metabolism such as ACE (angiotensin I converting enzyme), carboxypeptidase N and aminopeptidase P. In addition, this procedure could be used as a screening assay for selecting and monitoring the actions of inhibitors of the enzymes implicated in bradykinin metabolism directly in plasma or serum. Copyright © 2002 John Wiley & Sons, Ltd.
Pyrolysis‐gas chromatography/mass spectrometry of fractions separated from a low‐temperature coal tar: an attempt to develop a general method for characterising structures and compositions of heavy hydrocarbon liquids
Authors: Islas C. A. , Suelves I. , Carter J. F. , Li W. , Morgan T. J. , Herod A. A. , Kandiyoti R. 
Published: August 2002

AbstractA low‐temperature coal tar has been fractionated by column chromatography into acetonitrile, pyridine and 1‐methyl‐2‐pyrrolidinone‐ (NMP) solubles. The tar and its fractions have been examined by pyrolysis‐gas chromatography/mass spectrometry (GC/MS). Fractionation by planar chromatography was also carried out for purposes of comparison. Molecular masses of the fractions were estimated by size‐exclusion chromatography (SEC), and bulk structural characterisation was carried out by 13C‐NMR and UV‐fluorescence spectrometry. SEC showed that the fractions shifted to progressively shorter elution times (higher apparent masses) with diminishing solubility, i.e. from acetonitrile to NMP solubles. UV‐fluorescence spectra showed parallel shifts to longer wavelengths and lower fluorescence quantum yields, indicating increasing sizes of aromatic ring systems and increasingly complex molecules. GC/MS analysis of the tar showed alkanes from C10 to C32 and extensive series of alkylated aromatics, phenols, indenes, naphthalenes, phenanthrenes and fluoranthenes. Pyrolysis‐GC/MS results for the acetonitrile solubles closely resembled the data for the tar sample, with extensive series of alkylated benzenes, phenols and naphthalenes as well as alkanes from C16 to C28. The pyridine‐soluble fraction showed no significant aromatic pyrolysis products and only relatively weak signals for alkanes between C16 and C27. The NMP‐soluble fraction showed even less overall signal, with no significant aromatic components and weak signals for alkanes between C21 and C25, even though 13C‐NMR analyses showed that approximately half of the carbon detected was aromatic. The aliphatics are assumed to provide bridging structures between polycyclic aromatic (PCA) ring systems. Copyright © 2002 John Wiley & Sons, Ltd.
Gas chromatography/mass spectrometric assay of endogenous cellular lipid peroxidation products: quantitative analysis of 9‐ and 10‐hydroxystearic acids
Authors: Bertucci C. , Hudaib M. , Boga C. , Calonghi N. , Cappadone C. , Masotti L. 
Published: August 2002

AbstractA sensitive, specific, accurate and reproducible gas chromatography/mass spectrometry method was developed for the assay of 9‐ and 10‐hydroxystearic acids in samples obtained as cell extracts. The preparation of the samples required specific procedures to allow the analysis of both the free and the conjugated hydroxy acids as the corresponding methyl esters. The quantification used propyl‐paraben as the internal standard and monitoring of a specific fragment of each isomeric hydroxy acid methyl ester, and allowed quantification of the conjugate and the free fractions of both 9‐ and 10‐hydroxystearic acids. This method is suitable for identification and quantification (LOQ 1.8 and 4.4 ng, respectively) of these important metabolites of lipid peroxidation. In particular the development of an assay for the free 9‐hydroxystearic acid methyl ester makes the method a reliable analytical tool for investigations of the role of this metabolite in the mechanisms of tumour cell proliferation. Copyright © 2002 John Wiley & Sons, Ltd.
Application to routine analysis of a method to determine multiclass pesticide residues in fresh vegetables by gas chromatography/tandem mass spectrometry
Authors: Vidal J. L. Martínez , Arrebola F. J. , Mateu‐Sánchez M. 
Published: August 2002

AbstractThe use of gas chromatography/tandem mass spectrometry (GC/MS/MS) applied to determine multiple pesticide residues in fresh vegetables has been thoroughly studied. A single injection method to detect, confirm and quantify 54 multiclass pesticides has been developed and applied in a routine analysis laboratory. The proposed method consists of a rapid extraction of 15 g of vegetable sample with dichloromethane. An additional clean‐up step is not necessary even when injecting 10 µL of extract. Instead the gas chromatograph was fitted with a carbofrit inserted into the glass liner and a guard column. In addition, the detection mode chosen (MS/MS) provides additional selectivity. The method has been validated and applied to 1300 samples in a routine laboratory following specified quality criteria. The recovery efficiencies obtained for all the pesticides ranged between 70.2 and 110.8% at two different fortification levels. The relative standard deviation for quantification (RSD) was lower than 16.7% for all the compounds. Important experimental parameters, such as the conditioning of carbofrit, overload of the analytical column, and cleanliness of the ion trap, were evaluated for their influence on the performance of the method. Copyright © 2002 John Wiley & Sons, Ltd.
A review of genetic differences between limited and extensively passaged human cytomegalovirus strains
Authors: Prichard M. N. , Penfold M. E. T. , Duke G. M. , Spaete R. R. , Kemble G. W. 
Published: August 2002

AbstractThe complete genetic content of human cytomegalovirus (HCMV) has been difficult to determine, since most strains studied in the laboratory have been extensively passaged in human fibroblast cultures which can change the genetic content as well as the biological properties of the virus. Approximately 13 kb of novel DNA sequences located near the right edge of the unique long (UL) component of the genome has been discovered in Toledo, clinical isolates and certain stocks of Towne. This region of novel sequence, designated the UL/b′ region, encodes several interesting proteins including vCXC‐1, a potent IL‐8 homologue, and UL144, a member of the TNF receptor family. This region is missing from the prototypic laboratory variants of Towne and AD169. In contrast to Toledo and other low passage isolates which have relatively small repeats bracketing the UL component, the Towne and AD169 laboratory variants contain large (>10 kb) b/b′ repeats. The large size of these repeats in AD169 and Towne appear to have arisen as compensation for the loss of sequences from the UL/b′ region that existed in less passaged variants of these strains. Consequently, many of the haploid genes at the left edge of the prototypic wild‐type (wt) UL component are diploid in AD169 and Towne. We hypothesise that this plasticity of the genome at the right edge of the UL component results from extensive passage and adaptation to replication in fibroblasts in vitro. Further work will be required to understand the complete genetic content of wt HCMV. Copyright © 2001 John Wiley & Sons, Ltd.
Global optimization for robust control synthesis based on the Matrix Product Eigenvalue Problem
Authors: Yamada Yuji , Hara Shinji 
Published: August 2002

AbstractIn this paper, we propose a new formulation for a class of optimization problems which occur in general robust control synthesis, called the Matrix Product Eigenvalue Problem (MPEP):Minimize the maximum eigenvalue of the product of two block‐diagonal positive‐definite symmetric matrices under convex constraints. This optimization class falls between methods of guaranteed low complexity such as the linear matrix inequality (LMI) optimization and methods known to be NP‐hard such as the bilinear matrix inequality (BMI) formulation, while still addressing most robust control synthesis problems involving BMIs encountered in applications.The objective of this paper is to provide an algorithm to find a global solution within any specified tolerance ε for the MPEP. We show that a finite number of LMI problems suffice to find the global solution and analyse its computational complexity in terms of the iteration number. We prove that the worst‐case iteration number grows no faster than a polynomial of the inverse of the tolerance given a fixed size of the block‐diagonal matrices in the eigenvalue condition. Copyright 2001 © John Wiley & Sons, Ltd.
Constrained robust sampled‐data control for nonlinear uncertain systems
Authors: Hu Li‐Sheng , Cao Yong‐Yan , Shao Hui‐He 
Published: August 2002

AbstractIn industrial process control, computer control, which makes the closed‐loop system a sampled‐data one containing both continuous‐ and discrete‐time signals, is widely used. In contrast with traditional approximation methods, sampled‐data synthesis, a direct digital controller design procedure without approximation, has received increasing attention during the past few years. However, many of the existing results cannot be applied to sampled‐data control design for the uncertain systems. In this paper, a result of robust asymptotic stability of sampled‐data systems with constraints on the state is presented based on a result on practical stability for these systems. Then the robust sampled‐data control for a class of uncertain nonlinear systems with constraints on the output is developed. The problem is formulated from vehicle steering control with constraint on the side slip angle of body. The result is described by some matrix inequalities which could be solved by an iterative algorithm based on the linear matrix inequality technique. Finally, a numerical example is presented to demonstrate the result. Copyright © 2002 John Wiley & Sons, Ltd.
A new approach for estimating controllable and recoverable regions for systems with state and control constraints
Authors: Yfoulis C. A. , Muir A. , Wellstead P. E. 
Published: August 2002

AbstractIn this paper the problem of estimating controllable and recoverable regions for classes of nonlinear systems in the presence of uncertainties, state and control constraints is considered. A new computational technique is proposed based upon a ray‐gridding idea in contrast to the usual gridding techniques. The new technique is also based on the positive invariance principle and the use of piecewise linear (PL) Lyapunov functions to generate polytopic approximations to the controllable/recoverable region with arbitrary accuracy. Various types of stabilizing controllers achieving certain trade‐offs between robustness, performance and safety, while respecting state and control constraints, can be easily generated. The technique allows the approximation of nonlinear systems viapiecewise linear uncertainmodels which reduces the conservatism associated withlinear uncertainmodels. Copyright © 2002 John Wiley & Sons, Ltd.
Generalization of the Nyquist robust stability margin and its application to systems with real affine parametric uncertainties
Authors: Baab Charles T. , Cockburn Juan C. , Latchman Haniph A. , Crisalle Oscar D. 
Published: August 2002

AbstractThe critical direction theory for analysing the robust stability of uncertain feedback systems is generalized to include the case of non‐convex critical value sets, hence making the approach applicable for a much larger class of relevant systems. A redefinition of the critical perturbation radius is introduced, leading to the formulation of a Nyquist robust stability measure that preserves all the properties of the previous theory. The generalized theory is applied to the case of rational systems with an affine uncertainty structure where the uncertain parameters belong to a real rectangular polytope. Necessary and sufficient conditions for robust stability are developed in terms of the feasibility of a tractable linear‐equality problem subject to a set of linear inequalities, leading ultimately to a computable Nyquist robust stability margin. A systematic and numerically tractable algorithm is proposed for computing the critical perturbation radius needed for the calculation of the stability margin, and the approach is illustrated via examples. Copyright © 2001 John Wiley & Sons, Ltd.
Bilateral parallel force/position teleoperation control
Authors: Hashtrudi‐Zaad Keyvan , Salcudean Septimiu E. 
Published: August 2002

AbstractThe extension of parallel force/position control to teleoperation systems is considered in this article. In the proposed four‐channel bilateral controller, higher priority is granted to position control at the master side and to force control at the slave side. The primary goal of this control architecture is the enhancement of force and position tracking performance in the presence of uncertainties in the system and environment. The stability and performance of the proposed controller is investigated by analyzing the three decoupled single‐degree‐of‐freedom systems obtained from decoupling and projecting the closed‐loop system dynamics onto the slave task‐space orthogonal directions. Experimental results demonstrate significant improvement in transparency. © 2002 Wiley Periodicals, Inc.
Robust tracking control of mobile robots in the presence of uncertainties in the dynamical model
Authors: Corradini M. L. , Orlando G. 
Published: August 2002

AbstractIn this article, the robust trajectory tracking problem for the dynamical model of a wheeled mobile robot has been solved using sliding mode control. The presence of bounded uncertainties (parameter variations and input disturbances) has been considered. The control policy makes use of two nonlinear sliding surfaces, able to ensure the robust asymptotic vanishing of the three tracking errors. The control law has been tested by simulation. The reported results show the effectiveness of the proposed control law. © 2001 John Wiley & Sons, Inc.