bluuebunny/crossref_metadata_2025_split huggingface dataset:
Analytic evaluation of two‐center STO electron repulsion integrals via ellipsoidal expansion
Authors: Harris Frank E. 
Published: August 2002

AbstractExtant analytic methods for evaluating two‐center electron repulsion integrals in a Slater‐type orbital (STO) basis using ellipsoidal coordinates and the Neumann expansion of 1/r12 have problems of numerical stability that are analyzed in detail using computer‐assisted algebraic techniques. Some of these problems can be eliminated by use of procedures known in this field 40 years ago but seemingly forgotten now. Others can be removed by use of a formulation suitable for small values of the STO screening parameter. A recent attempt at such a formulation is corrected and extended in a way permitting its practical use. The main functions encountered in the integrations over the ellipsoidal coordinate of the range 1 … ∞ are Bessel functions or generalizations thereof, as pointed out here for the first time. This fact is used to motivate the derivation of recurrence relations additional to those previously known. Novel techniques were devised for using these recurrence relations, thereby providing new ways of calculating the quantities that enter the ellipsoidal expansion. The convergence rate of this expansion and the numerical characteristics of several computational strategies are reported in enough detail to identify the ranges where various schemes can be used. This information shows that recent discussions of the “convergence characteristics of [the] ellipsoidal coordinate expansion” are in fact not that, but are instead discussions of an inability to make accurate calculations of the individual terms of the expansion. It is also seen that the parameter range suitable for use of Kotani's well‐known recursive scheme is more limited than seems generally believed. The procedures discussed in this work are capable of yielding accurate two‐center electron repulsion integrals by the ellipsoidal expansion method for all reasonable STO screening parameters, and have been implemented in illustrative public‐domain computer programs. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002
Hybrid molecular mechanics: For effective crystal field method for modeling potential energy surfaces of transition metal complexes
Authors: Darhovskii M. B. , Razumov M. G. , Pletnev I. V. , Tchougréeff A. L. 
Published: August 2002

AbstractThe effective crystal field (ECF) methodology previously developed for description of the electronic structure of transition metal complexes (TMCs) is combined with molecular mechanics (MM) formalism. In this way, a new method for calculations of potential energy surfaces of the Werner‐type TMC is developed. It is based on a combined quantum mechanics (QM)–MM approach with the ECF method taking part of the QM and advanced MM package MMPC developed for the metal ion complex computations and based on the CHARMM organic force field. The MM region consists of ligand atoms and metal ion coordination sphere, leaving out effects of d‐shell, while the QM region is limited to metal ion d‐shell. Crystal field matrix for the d‐shell is calculated with use of the local ECF method. It is shown that the procedure proposed reproduces with considerable accuracy geometry characteristics of values of the Fe(II) complexes with both mono‐ and polydentate ligands. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002
Ionization potentials within semiempirical antisymmetrized product of strictly localized geminals approach
Authors: Tokmachev A. M. , Tchougréeff A. L. , Misurkin I. A. 
Published: August 2002

AbstractThe APSLG‐MINDO/3 method is evolved to reproduce the vertical ionization potentials for organic molecules. Two different schemes—one allowing for adjustment of the local electronic structure to the hole in each configuration and another one with a fixed local electronic structure—are developed and implemented. These methods are applied to a series of normal hydrocarbons. The possibility of localization of a hole in the polyethylene cation is discussed. Vertical ionization potentials are also obtained for a set of organic molecules with heteroatoms. Their values together with degeneracy of ionized states are compared with the data of photoelectron spectroscopy. © 2001 John Wiley & Sons, Inc. Int J Quantum Chem, 2001
Numerical solution of a two‐dimensional time‐independent Schrödinger equation by using symplectic schemes
Authors: Liu Xue‐Shen , Su Li‐Wei , Liu Xiao‐Yan , Ding Pei‐Zhu 
Published: August 2002

AbstractSymplectic schemes are extended to the solution of a two‐dimensional time‐independent Schrödinger equation. The Schrödinger equation is first transformed into a Hamiltonian canonical equation and then the numerical method is developed to solve the numerical solution of the two‐dimensional time‐independent Schrödinger equation. This called the symplectic scheme–matrix eigenvalue method (SSMEM). This method is applied to calculations of the two‐dimensional harmonic oscillator and the two‐dimensional Henon–Heils potential. It is shown that the numerical results of the two‐dimensional harmonic oscillator by using the SSMEM tend to the exact ones monotonically with decreasing space step length and the numerical eigenvalues of the two‐dimensional Henon–Heils potential by using the SSMEM are lower than those by using the Gaussian basis set method. © 2001 John Wiley & Sons, Inc. Int J Quant Chem 83: 303–309, 2001
Model systems for rod‐like polyheteroarylethynylenes
Authors: Göller Andreas , Klemm E. , Egbe D. A. M. 
Published: August 2002

AbstractB3LYP density functional theory (DFT) and MM3 molecular mechanics/dynamics are used to model the flexibility of the building blocks of poly(phenyleneethynylene)s, which are rod‐like segmented polymers usually assumed to be strongly rigid, with well‐defined, highly fluorescent fragments and beneficial material properties like electroluminescence and large nonlinear optical hyperpolarizabilities. Whereas the DFT‐calculated torsional barriers of the building block molecules 2,2′‐bipyridine and some tolane derivatives give insight into weak intramolecular effects in these molecules, the much less detailed MM3 barriers are nevertheless of sufficient quality to use MM3 for polymer modeling. From MM3 molecular dynamics gas phase and water box simulations at different temperatures, insight into the time‐dependent behavior of the model compounds was obtained as well as the conditions at which cis–trans isomerizations occur. It turns out that these formally rigid polymers are quite flexible and do not at all possess strictly coplanar aryl rings over time, significantly decreasing the effective conjugation length. © 2001 John Wiley & Sons, Inc. Int J Quant Chem 84: 86–98, 2001
BSSE‐free description of the formamide dimers
Authors: Bende A. , Vibók Á. , Halász G. J. , Suhai S. 
Published: August 2002

AbstractThe different configurations (linear, zig‐zag, and cyclic) of formamide dimers have been studied at the level of both Hartree–Fock (HF) and second order Møller–Plesset perturbation theory (MP2). The widely used a posteriori Boys–Bernardi “counterpoise” (CP) correction scheme has been compared with our a priori methods utilizing the “chemical Hamiltonian approach” (CHA). The appropriate interaction energies have been calculated in six different basis sets (6‐31G, 6‐31G**, DZV, DZP, TZV, and cc‐pVDZ). © 2001 John Wiley & Sons, Inc. Int J Quant Chem, 2001
Theoretical study of AlC3+
Authors: Redondo Pilar , Largo Antonio , García Flor , Barrientos Carmen 
Published: August 2002

AbstractA theoretical study of the AlC3+species has been carried out. Predictions have been made for some of the molecular properties (geometries, dipole moments, and harmonic vibrational frequencies) which could help in their possible experimental detection. In addition, a topological analysis of the electron density and its associated Laplacian has also been carried out. The global ground state is predicted to be a linear species with1Σ electronic state, but a rhombic four‐membered ring (1A1) lies close in energy. It seems that both isomers could be accessible to experimental detection. © 2001 John Wiley & Sons, Inc. Int J Quantum Chem, 2001
Ionization and protonation of MgC3: A theoretical study
Authors: Barrientos Carmen , Redondo Pilar , Largo Antonio 
Published: August 2002

AbstractA theoretical study of the MgC3+ and MgC3H+ species has been carried out. Predictions for their geometries and vibrational frequencies have been made at both second‐order Møller–Plesset (MP2) and B3LYP levels, whereas electronic energies have been computed at G2 and coupled cluster single and double excitation model augmented with a noniterative triple excitation conection (CCSD(T)) levels. The predicted global minimum for MgC3+ is a rhombic structure (2A1 electronic state), whereas a T‐shaped structure and an open‐chain isomer lie about 10 and 12 kcal/mol, respectively, higher in energy. In the case of MgC3H+ the predicted global minimum is also a four‐membered ring obtained upon protonation of the most stable neutral isomer. Low ionization potentials and high proton affinities are generally obtained, especially for the most stable MgC3+ isomer. The estimated values at the CCSD(T) level for the predicted global minimum are 7.20 eV [ionization potential (IP)] and 256.5 kcal/mol [proton affinities (PA)]. Therefore, if present in the interstellar medium, MgC3 should be easily ionized and would react quite easily to give the protonated species. © 2002 John Wiley & Sons, Inc. Int J Quantum Chem, 2001
Molecular structure of fulvic acids by electrospray with quadrupole time‐of‐flight mass spectrometry
Authors: Plancque Gabriel , Amekraz Badia , Moulin Valérie , Toulhoat Pierre , Moulin Christophe 
Published: August 2002

AbstractCharacterisation of the molecular structure of aquatic fulvic acids (FA) has been performed using a quadrupole time‐of‐flight (Q‐TOF) mass spectrometer equipped with an electrospray ionisation interface. Molecular masses centred around 450 Da and sinusoidal spectral distributions have been obtained for all fulvic acids. Tandem mass spectrometry (MS/MS) experiments showed losses of 18 Da (H2O) and 44 Da (CO2), and possible molecular structures were determined for the first time to our knowledge. A methodology is reported for evaluating the average elemental composition of FA from high‐resolution mass spectra by processing post‐acquisition data calculations using molecular size distributions and atomic compositions of ions. The results are found to be consistent with elemental analysis data. Copyright © 2001 John Wiley & Sons, Ltd.
Matrix‐ and surface‐assisted laser desorption/ionization time‐of‐flight mass spectrometry of dibromocalix[4]crown ether
Authors: Kang Weekyung , Kim Junghwan , Paek Kyungsoo , Shin Kuan Soo 
Published: August 2002

AbstractLaser desorption/ionization mass spectrometry (LDI‐MS) has been investigated for dibromocalix[4]crown ether, a compound known to undergo prompt dissociation in excited electronic states. As a result of direct absorption by the analyte, a considerable proportion of fragment ions were observed in the UV matrix‐assisted LDI mass spectrum. This would make it difficult to study host‐guest complexation by this crown ether using matrix‐assisted laser desorption/ionization (MALDI) mass spectrometry. However, the molecular ion peak is largely dominant without the debrominated ions in the LDI mass spectrum obtained using visible laser radiation with a graphite plate as a photon‐absorbing material. This mass spectrum shows good signal‐to‐noise ratio, with a high spot‐to‐spot reproducibility, reflecting homogeneous sample distribution on the graphite plate. This study suggests that use of a visible laser for LDI with a graphite plate could provide advantages for macromolecules with general transparency within the visible region. Copyright © 2001 John Wiley & Sons, Ltd.
Determination of the disulfide bond pattern of the endogenous and recombinant angiogenesis inhibitor endostatin by mass spectrometry
Authors: John Harald , Forssmann Wolf‐Georg 
Published: August 2002

AbstractEndostatin, a C‐terminal fragment of collagen XVIII, is a promising protein drug which is in development for cancer therapy due to its anti‐angiogenic activity. Although several endogenous molecular forms of human endostatin differing in their N‐terminal length and their post‐translational modifications (18.5–22 kDa) have been discovered, only one recombinant form of 20 kDa is used in clinical trials. This protein, recombinantly expressed inPichia pastoris, contains four cysteines forming two disulfide bonds (Cys1‐Cys4 and Cys2‐Cys3). In contrast, there are conflicting data about the disulfide pattern of endogenous material. This report presents the disulfide analyses of both the endogenous circulating endostatins isolated from human hemofiltrate and the recombinant protein. The determination of the disulfide pattern was performed by Edman degradation, matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry (MALDI‐TOFMS) and electrospray ionization ion trap mass spectrometry (ESI‐ITMS) performed in the off‐line nanospray mode. All native and recombinant endostatins exhibited a Cys1‐Cys4 (Cys162‐Cys302) and Cys2‐Cys3 (Cys264‐Cys294) linkage. For a clear discussion of fragmented disulfide‐bridged peptide chains obtained from MSnexperiments, a modified general nomenclature is proposed. Copyright © 2001 John Wiley & Sons, Ltd.
Unusual MSn fragmentation patterns of 2,4‐dinitrophenylhydrazine and its propanone derivative
Authors: Kölliker Stephan , Oehme Michael , Merz Leo 
Published: August 2002

AbstractDuring the structural elucidation of carbonyl‐2,4‐dinitrophenylhydrazone derivatives in the low‐ng range by multiple mass spectrometry combined with high performance liquid chromatography (HPLC/MSn) some fragments were detected which were difficult to explain by ordinary fragmentation rules. Atmospheric pressure chemical ionization in the negative ion mode was applied. The ion formation was studied by labelling the parent compounds with D, 13C and 15N and recording the MS/MS, MS3 and MS4 spectra. This allowed an investigation of the detailed fragmentation of 2,4‐dinitrophenylhydrazine and its propanone derivative as well as the structures of the MS2 and MS3 product ions. A highly reactive product ion was found which undergoes unexpected reactions inside the ion trap of an HPLC/MSn system. In addition, reactions of MSn fragments with solvents or species generated in situ in the ion source and/or the ion trap were observed. It is demonstrated that unusual fragments in the MS/MS or MSn spectra of a compound may be formed by such reactions and that the eluent used for HPLC might have an influence on the observed fragmentation even if the mass spectrum itself is completely free from adducts. Copyright © 2001 John Wiley & Sons, Ltd.
Mass spectrometric analysis of cyclofenil and its metabolites in human urine
Authors: Myung Seung‐Woon , Min Hye‐Ki , Kim Dong‐Hyun , Kim Myungsoo , Cha SuJin , Yoo Eun‐Ah , Yim Yong‐Hyeon 
Published: August 2002

AbstractUsing gas chromatography/electron impact‐mass spectrometry (GC/EI‐MS) and high performance liquid chromatography with atmospheric pressure chemical ionization tandem mass spectrometry (HPLC/APCI‐MS/MS), the structures of cyclofenil metabolites in human urine have been assigned. The hydroxyl metabolites liberated from the glucuronide conjugates after acid hydrolysis were characterized as the trimethylsilyl (O‐TMS) derivatives using GC/MS. The conjugate glucuronide forms were detected without hydrolysis by HPLC/MS. Cyclofenil was not observed in urine. Tentative structures for the two metabolites are proposed. Copyright © 2002 John Wiley & Sons, Ltd.
The hyporheic zone: Linking groundwater and surface water—understanding the paradigm
Authors: Biksey Thomas M. , Gross Elisa D. 
Published: August 2002

AbstractThe hyporheic zone, the transition region between groundwater and surface water, represents an important
interface between terrestrial and aquatic ecosystems. When groundwater combines with surface water in this zone,
the characteristics of each are blended and new gradients are established, especially for contaminants. Therefore,
the hyporheic zone is important in considering the “big ecological picture” as the hydrologic continuum
connecting groundwater and surface water. The importance is reflected by the current focus of this zone in
ecological risk assessments conducted under the Resource Conservation and Recovery Act (RCRA),
Comprehensive Environmental Response, Compensation and Liability Act (CERCLA), and Clean Water Act
(CWA) programs. A variety of tools can be used to measure, analyze, and predict the physical, chemical,
and biological processes that occur within the hyporheic zone. Directly measuring the flux of water across the
interface between groundwater and surface water determines whether surface water enters the streambed at
downwelling zones or groundwater discharges from the streambed in upwelling zones. In addition to direct
measurements of the flux of water, several states have developed models to characterize the interaction of
groundwater and surface water. The variability in physical and chemical characteristics between upwelling and
downwelling zones influences the local ecology within the zone. The study of the species within the hyporheic zone
includes ecological surveys and ecotoxicological investigations. The evolving study of the hyporheic zone will
necessitate an increase in basic research into hydraulic considerations, an identification of regional
representative sites with contaminated hyporheic zones, and a better understanding of the ecology of the species
within the zone. © 2001 John Wiley & Sons, Inc.
Linear time computation of feasible regions for robust compensators
Authors: Fadali M. Sami , LaForge Laurence E. 
Published: August 2002

AbstractWe introduce an application of computational geometry, including figures of merit standard in the analysis of algorithms, to the design of robust control systems. With respect to system transfer function magnitude, we show how to compute feasible regions for compensators whose plant transfer function is the ratio of uncertain interval polynomials. Our solution sweeps the Minkowski quotient set of the corresponding Kharitonov rectangles. Enumerating the winding numbers of Minkowski sum convolution curves, we obtain optimal, linear time algorithms that eliminate three factors from the execution inefficiency of traditional gridding approaches. We illustrate with examples pertinent to quantitative feedback theory (QFT). Copyright © 2001 John Wiley & Sons, Ltd.
Normal form representation of control systems
Authors: Cheng Daizhan , Martin Clyde F. 
Published: August 2002

AbstractThis paper is to investigate the normal form representation of control systems. First, as numerical tools we develop an algorithm for normal form expression and the matrix representation of the Lie derivative of a linear vector field over homogeneous vector fields. The concept of normal form is modified. Necessary and sufficient conditions for a linear transformation to maintain the Brunowsky canonical form are obtained. It is then shown that the shift term can always be linearized up to any degree. Based on this fact, linearization procedure is proposed and the related algorithms are presented. Least square linear approximations are proposed for non‐linearizable systems. Finally, the method is applied to the ball and beam example.The efforts are focused on the numerical and computer realization of linearization process. Copyright © 2002 John Wiley & Sons, Ltd.
A path following control for unicycle robots
Authors: Díaz del Río F. , Jiménez G. , Sevillano J. L. , Vicente S. , Civit Balcells A. 
Published: August 2002

AbstractIn this work we present a new path following control for unicycle robots that is applicable for almost all the possible desired paths and whose analysis is very straightforward. First we select the path following method that consists of two steps: choosing a “projection” that relates the actual posture to the desired path and imposing a “motion exigency” to ensure that the robot advances. A “projection” that considers all the error coordinates is selected and closed equations are obtained for it. The uniqueness projection is carefully analyzed and a necessary and sufficient condition is also presented. This condition shows that a slight bound on the curvature derivative of desired paths must be imposed to preserve uniqueness. It is remarkable that the selected path following is applicable for paths containing zero‐radius turns, a problem that has never been resolved as far as we know. In addition, an asymptotically stable control law is found using the closed form equation of the proposed path following and the second Lyapunov method. Finally, we show the behavior of the path following and the control law through several simulated and experimental results, using a computerized wheelchair built at our research facility. © 2001 John Wiley & Sons, Inc.
Perfect position/force tracking of robots with dynamical terminal sliding mode control
Authors: Parra‐Vega V. , Rodríguez‐Angeles A. , Hirzinger G. 
Published: August 2002

AbstractAccording to a given performance criteria, perfect tracking is defined as the performance of zero tracking error in finite time. It is evident that robotic systems, in particular those that carry out compliant task, can benefit from this performance since perfect tracking of contact forces endows one or many constrained robot manipulators to interact dexterously with the environment. In this article, a dynamical terminal sliding mode controller that guarantees tracking in finite‐time of position and force errors is proposed. The controller renders a dynamic sliding mode for all time and since the equilibrium of the dynamic sliding surface is driven by terminal attractors in the position and force controlled subspaces, robust finite‐time convergence for both tracking errors arises. The controller is continuous; thus chattering is not an issue and the sliding mode condition as well the invariance property are explicitly verified. Surprisingly, the structure of the controller is similar with respect to the infinite‐time tracking case, i.e., the asymptotic stability case, and the advantage becomes more evident because terminal stability properties are obtained with the same Lyapunov function of the asymptotic stability case by using more elaborate error manifolds instead of a more complicated control structure. A simulation study shows the expected perfect tracking and a discussion is presented. © 2001 John Wiley & Sons, Inc.