bluuebunny/crossref_metadata_2025_split huggingface dataset:
Evolution of defect states in doped polythiophene: A study based on the method of simulated annealing
Authors: Chaudhury Pinaki , Bhattacharyya S. P. 
Published: January 2003

AbstractA modified Su–Schrieffer–Heeger Hamiltonian‐based model is used to compute the electronic and geometric structures of fairly long polythiophene (PT) chains, neutral as well as doped. The geometry optimization is carried out by the simulated annealing method. Both Metropolis and Glauber functions are used for sampling. It is shown that a bipolaron can be structurally represented by a fragment of the PT chain containing 14 thiophene units. As a series of bipolaronic defects are introduced in a long PT chain (50–100 rings), the highest occupied molecular orbital (HOMO)–lowest unoccupied molecular orbital (LUMO) gap energy (Δ) becomes vanishingly small, a feature not present in the PT chains of similar sizes containing polaronic defects. The Fermi energy level (EF) also moves into the valency band and nonzero density of states at ϵ = EF are created. Once again, this feature is shown to be missing in PT chains containing polaronic defects. Implications of these findings are analyzed. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2003
Cracking the genetic code(s) with a modular determinative degree: An algebraic approach
Authors: Négadi Tidjani 
Published: January 2003

AbstractWe introduce a new “modular” (compositional and positional) determinative degree for the four bases U, C, A, and G to define a “Dinucleotide charge number” for the dinucleotides, which discriminates between the two octets of dinucleotides: M1 and M2. These two components are exchanged under a transformation, which, we show, implements the Rumer symmetry. We invoke also the base “size index” of Rosen as a complementary determinative degree for the third‐base component of a codon. Next, we define the address functions for the 64 codons (amino acids), which are functions only of the composition and position of these codons in the genetic table. With these ingredients, we build an algebraic classification of the amino acids in the genetic code and some of its nonstandard versions as a preliminary application. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2003
Origin of cis preference among the three isomers of 1,4‐difluorobutadiene
Authors: Hu Hai‐Rong , Gong Mao‐Chu , Tian Anmin , Wong Ning‐Bew 
Published: January 2003

AbstractThe slight energy differences among the three isomers of 1,4‐difluorobutadiene have been investigated by Gaussian‐3 (G3) theory. The computational results suggest that the Gaussian‐3–Becke's three‐parameter functional (G3B3) theoretical estimates are in good agreement with experimental data. Mulliken population analysis also has been performed to interpret the anomalous equilibrium relationship among these three isomers. Wire mesh contours of the highest occupied molecular orbital (HOMO) orbitals of these isomers help to illustrate the cis effect visually. Natural bond orbital (NBO) analysis indicates that the origin of cis preference among the three isomers may lie in the configurational orientation and the n‐π conjugative interaction between fluorine atom and CC double bond. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2003
Improving the accuracy of ab initio methods with summation approximants and singularity analysis
Authors: Goodson David Z. 
Published: January 2003

AbstractThe accuracy of Møller–Plesset (MP) perturbation theory and coupled‐cluster (CC) theory can be significantly improved, at essentially no increase in computational cost, by using summation approximants that model the way in which these theories converge to the full configuration interaction limit. Approximants for MP4 and CCSD(T) are presented, their size scaling is analyzed, and the functional analysis of the MP energy, on which the MP4 approximant is based, is discussed. The MP approximants are shown to have a form that is appropriate for describing resonance energies. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2003
N‐band Hubbard models II: Cooperative mechanisms of electron–phonon, electron correlation, and many‐band effects toward high‐Tc superconductors
Authors: Yamaguchi Kizashi , Yamaki Daisuke , Kitagawa Yasutaka , Takahata Masahiro , Kawakami Takashi , Ohsaku Tadafumi , Nagao Hidemi 
Published: January 2003

AbstractDiscoveries of superconductivity of MgB2 by Akimitsu et al. and high‐Tc cupurate superconductors by Bednorz and Muller have raised great interest for elucidation of the superconducting mechanism from both experimental and theoretical grounds. The transition temperature (Tc) was found to be 40 K for MgB2, while the very high‐Tc over 130 K was reported for doped copper oxides with layer structures. A crucial role of the electron–phonon (EP) interaction was pointed out as a common mechanism of the superconductivity of both materials. However, such high‐Tc superconductivity may indicate the possibility of cooperative mechanism of the EP interaction with others such as electron correlation (EC) and multiband (MB) effects discussed in part I (Int J Quantum Chem 1990, 37, 167) of this series. Here, as a continuation of part I, theoretical backgrounds are briefly described to select active orbital space for superconductivity and elucidate the nature of EP, EC, and MB effects for cooperative mechanisms. Next, molecular orbital calculations of MgmBn and cage‐type carbon cluster are carried out to elucidate contributions of the EP interaction using McMillan equation. The relative contributions of the EP and EC interactions are also discussed in relation to the screening of the Coulomb repulsion. Pair binding energies are calculated for cage‐type carbon clusters. Finally, the cooperative mechanisms of the EP, EC, and MB effects are discussed to realize the high‐Tc superconductivity in molecule‐based materials such as cage compounds and nanotubes. Several possible candidates are proposed on both experimental and theoretical grounds. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2003
Molecular similarity of potential endocrine disruptors: Structural index control of pharmacological clustering
Authors: King James W. , Molnar Stephen P. 
Published: January 2003

AbstractA series of 37 substituted indoles for which estrogen receptor binding data had been reported were studied from a quantitative structure–activity relationship (QSAR) viewpoint. The structures were represented by an established unitary mathematical index, the molecular transform (FTm), whose derivation is entirely from the geometry‐optimized structure. Data clusters were generated by a primary numerically descending sort of the structure indices and a concurrent secondary numerically descending sort of the binding data. Reversal of numerical descent of the latter served to generate the cluster boundaries. Analysis within and across the clusters permitted a definitive and detailed picture of the influence of substituents and substituent positions on the molecule, and their effect on the biodata, and suggested the structure of a molecule of greater binding ability than any in the database. The relationship of the electronic and charge nature of the molecules to their binding ability was considered. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2003
Ab initio fragment orbital‐based theory
Authors: Das G. P. , Yeates A. T. , Dudis D. S. 
Published: January 2003

AbstractA new formulation of ab initio theory is presented that treats a large molecule in terms of wave functions of its constituent molecular subunits (to be called fragments). The method aims to achieve near conventional ab initio accuracy but using a truncated set of fragment orbitals with a consequent drastic reduction of computing time and storage requirement. Illustrative calculations are presented for the molecule amino‐nitro‐stilbene. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2003
Charge exchange in C6++ H (1s) collisions at low energies
Authors: Saha Bidhan C. 
Published: January 2003

AbstractThe low‐energy single electron capture cross‐sections by C6+from H atoms have been evaluated employing the semiclassical, impact parameter, close‐coupling method based on a molecular expansion augmented with the plane‐wave translation factor. Using the method of Bates and Carson, the exact Born–Oppenheimer eigenfunctions and eigenvalues are calculated. Eight‐state coupled equations are solved to obtain transition probabilities and thereby evaluate capture cross‐sections. Our calculated capture cross‐sections agree well with other theoretical and experimental results. At these energies it is found that the capture into then= 4 manifold of the C5+remains the main contributor to the charge exchange process. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2003
Influence of hydrogen bonding on the properties of water molecules adsorbed in zeolite frameworks
Authors: Larin A. V. , Trubnikov D. N. , Vercauteren D. P. 
Published: January 2003

AbstractThree hydrated aluminosilicate frameworks—LiABW, NaNAT, and BaEDI—are partly optimized with the periodic Hartree–Fock CRYSTAL95 code. In particular, we optimized the positions of the adsorbed water molecules including the positions of the framework cations (ABW, NAT) or part of the framework atomic positions (ABW). This allowed us to compare cation–water clusters in the gas and adsorbed states and discuss the influence of hydrogen bonding to the framework oxygen atoms or to the neighbor water molecules on the atomic properties (quadrupole coupling constant, anisotropy of electric field gradient) of the adsorbed water molecules. The LiBIK structure obtained from X‐ray diffraction is also considered to illustrate the hydrogen bonds occurring between adsorbed water molecules. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2003
The shortest disjunctive normal form of a random Boolean function
Authors: Pippenger Nicholas 
Published: January 2003

AbstractThis paper gives a new upper bound for the average length ℓ(n) of the shortest disjunctive normal form for a random Boolean function of n arguments, as well as new proofs of two old results related to this quantity. We consider a random Boolean function of n arguments to be uniformly distributed over all 2 such functions. (This is equivalent to considering each entry in the truth‐table to be 0 or 1 independently and with equal probabilities.) We measure the length of a disjunctive normal form by the number of terms. (Measuring it by the number of literals would simply introduce a factor of n into all our asymptotic results.) We give a short proof using martingales of Nigmatullin's result that almost all Boolean functions have the length of their shortest disjunctive normal form asymptotic to the average length ℓ(n). We also give a short information‐theoretic proof of Kuznetsov's lower bound ℓ(n) ≥ (1 + o(1)) 2n/log n log log n. (Here log denotes the logarithm to base 2.) Our main result is a new upper bound ℓ(n) ≤ (1 + o(1)) H(n) 2n/log n log log n, where H(n) is a function that oscillates between 1.38826 … and 1.54169 … . The best previous upper bound, due to Korshunov, had a similar form, but with a function oscillating between 1.581411 … and 2.621132 … . The main ideas in our new bound are (1) the use of Rödl's “nibble” technique for solving packing and covering problems, (2) the use of correlation inequalities due to Harris and Janson to bound the effects of weakly dependent random variables, and (3) the solution of an optimization problem that determines the sizes of “nibbles” and larger “bites” to be taken at various stages of the construction. © 2003 Wiley Periodicals, Inc. Random Struct. Alg., 22: 161–186, 2003
Simple analysis of graph tests for linearity and PCP
Authors: Håstad Johan , Wigderson Avi 
Published: January 2003

AbstractWe give a simple analysis of the PCP with low amortized query complexity of Samorodnitsky and Trevisan [16]. The analysis also applies to the linearity testing over finite fields, giving a better estimate of the acceptance probability in terms of the distance of the tested function to the closest linear function. © 2003 Wiley Periodicals, Inc. Random Struct. Alg., 22: 139–160, 2003
Minors in graphs of large girth
Authors: Kühn Daniela , Osthus Deryk 
Published: January 2003

AbstractWe show that for every odd integer g ≥ 5 there exists a constant c such that every graph of minimum degree r and girth at least g contains a minor of minimum degree at least cr(g+1)/4. This is best possible up to the value of the constant c for g = 5, 7, and 11. More generally, a well‐known conjecture about the minimal order of graphs of given minimum degree and large girth would imply that our result gives the correct order of magnitude for all odd values of g. The case g = 5 of our result implies Hadwiger's conjecture for C4‐free graphs of sufficiently large chromatic number. © 2003 Wiley Periodicals, Inc. Random Struct. Alg., 22: 213–225, 2003
Random channel assignment in the plane
Authors: McDiarmid Colin 
Published: January 2003

AbstractIn the model for random radio channel assignment considered here, points corresponding to transmitters are thrown down independently at random in the plane, and we must assign a radio channel to each point but avoid interference. In the most basic version of the model, we assume that there is a threshold d such that, in order to avoid interference, points within distance less than d must be assigned distinct channels. Thus we wish to color the nodes of a corresponding scaled unit disk graph. We consider the first n random points, and we are interested in particular in the behavior of the ratio of the chromatic number to the clique number. We show that, as n → ∞, in probability this ratio tends to 1 in the “sparse” case [when d = d(n) is such that the average degree grows more slowly than ln n] and tends to $2\sqrt{3}/\pi$ ∼ 1.103 in the “dense” case (when the average degree grows faster than ln n). We also consider related graph invariants, and the more general channel assignment model when assignments must satisfy “frequency‐distance” constraints. © 2003 Wiley Periodicals, Inc. Random Struct. Alg., 22: 187–212, 2003
Joint multi‐user detection and intersymbol interference cancellation for WCDMA satellite UMTS
Authors: da Silva Mário Marques , Correia Américo M. C. 
Published: January 2003

AbstractIn this work we present two different intersymbol interference (ISI) cancellation systems, namely the commutation signaling (CS) and orthogonal code‐division transmit diversity (O‐CDTD) in combination with satellite path diversity, which leads to a high diversity order. The ISI is due to the use of satellite path diversity (in order to introduce multipath diversity artificially). This work combines the proposed ISI cancellation systems with subtractive multi‐user detectors—a variation of the conventional parallel interference cancellation (PIC) and successive interference cancellation (SIC) for the downlink channel of S‐UMTS. The blind detection is also considered without knowledge of spreading sequences or the channel state information (CSI) of the interfering users with a noise whitening matched filter (NWMF) that combats the MAI through the whitening of the interfering power spectrum, also with and without the ISI cancellation systems—CS and O‐CDTD. It is shown that the proposed PIC is a very promising detector to be used for the downlink of S‐UMTS, especially when combined with CS or O‐CDTD, the NWMF being efficient only when we consider jointly any of the proposed ISI cancellation systems for low number of interfering users. Copyright © 2003 John Wiley & Sons, Ltd.
The pervasiveness of evolution in GRUMPS software
Authors: Evans Huw , Atkinson Malcolm , Brown Margaret , Cargill Julie , Crease Murray , Draper Steve , Gray Phil , Thomas Richard 
Published: January 2003

AbstractThis paper describes the evolution of the design and implementation of a distributed run‐time system that itself is designed to support the evolution of the topology and implementation of an executing, distributed system. The three different versions of the run‐time architecture that have been designed and implemented are presented, together with how each architecture addresses the problems of topological and functional evolution. In addition, the reasons for the rapid evolution of the design and implementation of the architecture are also described.From the lessons learned in both evolving the design of the architecture and in trying to provide a run‐time system that can support run‐time evolution, this paper discusses two generally applicable observations: evolution happens all the time, and it is not possible to anticipate how systems will evolve as designs; and large, run‐time systems do not follow a predictable path. In addition to this, rapid prototyping has proved to be extremely useful in the production of the three architectures; this kind of prototyping has been made much easier by designing the core set of Java abstractions in terms of interfaces; and building an architecture that allows as many decisions as possible to be made at run‐time which has produced a support system that is more responsive to the user as well as the distributed environment in which it is executing. Copyright © 2003 John Wiley & Sons, Ltd.
Noradrenergic modulation of ephedrine‐induced hypophagia
Authors: Wellman Paul J. , Miller Dennis K. , Ho Dao H. 
Published: January 2003

AbstractThe hypophagic action of the sympathomimetic amine ephedrine (EPH) in the rat may reflect actions on central dopaminergic (DA) and noradrenergic (NE) systems. EPH indirectly facilitates DA and NE activity and acts as a partial agonist at α1‐adrenergic receptors. Two approaches were used to assess the possible contribution of NE and DA pathways to EPH‐induced hypophagia. In the first, regression analyses of published archival data were computed to characterize the relation between the hypophagic potency values of (−)‐(EPH) and related sympathomimetic drugs, including (+)‐amphetamine, aminorex, mazindol, and phentermine (data derived from Blosser JC et al., 1987) and the most potent action of these drugs on facilitating NE activity or DA activity in rat brain (data derived from Rothman RB et al., 2001). In the NE analyses, the ED50 values for these drugs for the inhibition of eating in rats were significantly related (r = 0.91, P = 0.03) to the potency of each drug in facilitating NE activity (either release or inhibition of [3H]NE reuptake), whereas in the DA analyses the correlation between ED50 values and DA activity for these drugs was also significant (r = 0.98, P = 0.003). The regression analyses are thus supportive of a role for NE or DA in the hypophagic capacity of EPH. Although an earlier study noted that administration of the putative DA antagonist pimozide in rats attenuated EPH hypophagia, pimozide exerts similar potency in antagonizing DA receptors and α1‐adrenergic receptors. To clarify the role of α1‐adrenoceptors in EPH‐induced hypophagia, adult male rats were pretreated with the α1‐adrenergic receptor antagonist prazosin (0.0.5 and 2 mg/kg) prior to the administration of (−)‐EPH (0, 5, 10, or 20 mg/kg, IP). Prazosin pretreatment at 2.0 mg/kg significantly attenuated the hypophagia, but not the hypodipsia, induced by administration of 10 mg/kg and by 20 mg/kg (−)‐EPH. Collectively, these results confirm a critical contribution of of α1‐adrenoceptors to the hypophagic action of (−)‐EPH in rats. Synapse 48:18–24, 2003. © 2003 Wiley‐Liss, Inc.
Performance prediction of networked information systems via Petri nets and queuing nets
Authors: Shin Insub , Levis Alexander H. 
Published: January 2003

AbstractAn approach is presented for generating a performance prediction model so that both qualitative (logical correctness) and quantitative (timeliness) properties of a real‐time system can be evaluated. The architecture of a system is layered into a functional layer and a physical one. Both architectural layers are developed as executable models: the executable functional model is a Petri net and the executable physical model is a queuing net. The two‐layered executable models are then connected to develop a performance prediction model. A message‐passing pattern is generated from the Petri net using a state space analysis technique. Then, the queuing net model processes these messages preserving the pattern. Once the network delays are obtained from the queuing model, their values are inserted back into the Petri net model. Since the communication service demands are isolated from the executable functional model, the communications network can be specified independently at any preferred level of detail. This enables the executable functional model to be invariant with respect to the executable physical model resulting in additional flexibility in designing a large‐scale information system. This property, together with the synthesis technique, enables both formal and simulation methods to be used together, when each one utilizes a different self‐contained commercial‐off‐the‐shelf software application. © 2002 Wiley Periodicals, Inc. Syst Eng 6: 1–18, 2003
A Model of System Coherence
Authors: Aslaksen Erik W. 
Published: January 2003

AbstractModeling of system behavior is an important part of the systems engineering methodology. One characteristic of system behavior that is common to a large class of systems is coherence, and we propose a simple model of coherent behavior, which at the same time gives an operational definition of system coherence. Results of simulation of system behavior obtained using this model are presented, and they display all the features normally associated with cooperative behavior. This indicates that with the proposed definition, coherence could become a useful system parameter. © 2002 Wiley Periodicals, Inc. Syst Eng 6, 19–27, 2003
Using objected‐oriented and UML tools for hardware design: A case study
Authors: Bahill Terry , Daniels Jesse 
Published: January 2003

AbstractThis paper argues for the adoption of object‐oriented design and UML tools for nonsoftware designs, i.e., systems, hardware and algorithms: This is a controversial position. It presents a case study, the design of a heating, ventilation, and air conditioning system, using UML tools. This case study also shows the incremental elaboration used to progress from the requirements model, to the analysis model, to the design model, etc. The paper finally discusses some difficulties that must be overcome in order to apply UML tools to system designs. © 2002 Wiley Periodicals, Inc. Syst Eng 6: 28–48, 2003.
On customer value and improvement in product development processes
Authors: Browning Tyson R. 
Published: January 2003

AbstractIn an effort to improve company operations and their results, more firms are applying the principles of “Lean”—not only to manufacturing but also to systems engineering processes. Too often, however, this is done with a shallow understanding of Lean and/or without a systems view, in which case Lean creates new problems and tensions and may not deliver expected results. Lean is not about just minimizing cost, cycle time, or waste. Lean is about maximizing value. In systems engineering or product development (PD), maximizing value may require doing more activities, not fewer. Since a process is a kind of system, a systems view and systems engineering principles are helpful. As the value of a system is more than the value of its individual components, the value of a process is more than the value of its individual activities. Value is driven not only by the presence of necessary (value‐adding) activities in the PD process but also by the way those activities work together to ensure that they use and produce the right work products, services, and information at the right time. This paper discusses how value is added in PD through work on activities and the production of deliverables. It integrates findings from several streams of research and provides bases upon which to build improved value models. It shows how the concept of Lean can broaden from asking “What wasteful activities can we stop doing?” to include insights from asking “What helpful activities can we start doing, and when?” © 2003 Wiley Periodicals, Inc. Syst Eng 6: 49–61, 2003. DOI 10.1002/sys.10034