bluuebunny/crossref_metadata_2025 huggingface dataset:
Implementation and evaluation of MPI‐based parallel MD program
Authors: Trobec R. , Šterk M. , Praprotnik M. , Janežič D.
Published: August 2002

The message‐passing interface (MPI)‐based object‐oriented particle–particle interactions (PPI) library is implemented and evaluated. The library can be used in the n‐particle simulation algorithm designed for a ring of p interconnected processors. The parallel simulation is scalable with the number of processors, and has the time requirement proportional to n2/p if n/p is large enough, which guarantees optimal speedup. In a certain range of problem sizes, the speedup becomes superlinear because enough cache memory is available in the system. The library is used in a simple way by any potential user, even with no deep programming knowledge. Different simulations using particles can be implemented on a wide spectrum of different computer platforms. The main purpose of this article is to test the PPI library on well‐known methods, e.g., the parallel molecular dynamics (MD) simulation of the monoatomic system by the second‐order leapfrog Verlet algorithm. The performances of the parallel simulation program implemented with the proposed library are competitive with a custom‐designed simulation code. Also, the implementation of the split integration symplectic method, based on the analytical calculation of the harmonic part of the particle interactions, is shown, and its expected performances are predicted. © 2001 John Wiley & Sons, Inc. Int J Quant Chem 84: 23–31, 2001
Potential energy surfaces in hybrid quantum mechanical/molecular mechanical methods
Authors: Tokmachev A. M. , Tchougréeff A. L.
Published: August 2002

The problem of conjunction between quantum and classical parts in hybrid quantum mechanical/molecular mechanical methods is considered. The form of the junction is deduced with use of the perturbation expansion on the assumption that the wave function underlying molecular mechanics is of the antisymmetrized product of strictly localized geminals type. The renormalization of the potential energy surfaces of the combined system due to interaction between quantum and classical subsystems is represented as a sum of contributions with transparent physical sense. © 2001 John Wiley & Sons, Inc. Int J Quant Chem 84: 39–47, 2001
Effective Hamiltonian approach to catalytic activity of transition metal complexes
Authors: Tokmachev A. M. , Tchougréeff A. L. , Misurkin I. A.
Published: August 2002

The application of an effective electron Hamiltonian approach to the description of the electronic structure of transition metal complexes with chemically active ligands is analyzed. This approach is implemented in a computational code. The evolution of the electronic structure along a path of isomerization of quadricyclane to norbornadiene in the coordination sphere of Co‐tetraphenylporphyrin is considered. In addition, the electronic states of atomic oxygen coordinated to transition metal oxides and metal porphyrins are studied. © 2001 John Wiley & Sons, Inc. Int J Quant Chem 84: 99–109, 2001
Theoretical study of MgO(001) surfaces: Pure, doped with Fe, Ca, and Al, and with and without adsorbed water
Authors: Almeida A. L. , Martins J. B. L. , Longo E. , Furtado N. C. , Taft C. A. , Sambrano J. R. , Lester W. A.
Published: August 2002

Ab initio calculations of large cluster models have been performed in order to study water adsorption at the five‐fold coordinated adsorption site on pure Mg(001) and MgO(001) surfaces doped with Fe, Ca, and Al. The geometric parameters of the adsorbed water molecule have been optimized preparatory to analysis of binding energies, charge transfer, preferential sites of interaction, and bonding distances. We have used Mulliken population analysis methods in order to analyze charge distributions and the direction of charge transfer. We have also investigated energy gaps, HOMO energies, and SCF orbital energies as well as the acid‐base properties of our cluster model. Numerical results are compared, where possible, with experiment and interpreted in the framework of various analytical models. © 2001 John Wiley & Sons, Inc. Int J Quant Chem, 2001
Theoretical studies on field‐induced superconductivity in molecular crystals
Authors: Nagao Hidemi , Kitagawa Yasutaka , Kawakami Takashi , Yoshimoto Takashi , Saito Hiroaki , Yamaguchi Kizashi
Published: August 2002

We investigate superconductivity of molecular crystals induced by charge injection by using a two‐band model based on the Green function techniques. Expressions of transition temperature for several phases derived from the model are summarized. The model is applied to a model of CuO2 plane for copper oxides, anthracene, oligothiophene, and C60 crystals and phase diagrams of the crystals are presented. It is important that the band structure of crystals is described by a two‐ or multiband model for realization of high‐Tc superconductivity. © 2001 John Wiley & Sons, Inc. Int J Quantum Chem, 2001
Study of molecular orbitals in momentum space
Authors: Errea L. F. , Macías A. , Méndez L. , Riera A. , Pons B. , Sevila I.
Published: August 2002

Molecular orbitals are presented in configuration and momentum representations. We propose to minimize large oscillations present in calculated momentum wavefunctions by cancelling position factor phases. We illustrate the distortion introduced by different electron translation factors and show continuum states and dynamical wavefunctions in momentum coordinates. © 2001 John Wiley & Sons, Inc. Int J Quantum Chem, 2001
Determination of the disulfide bond pattern of a novel C‐type lectin from snake venom by mass spectrometry
Authors: Zeng Rong , Xu Qiang , Shao Xiao‐Xia , Wang Ke‐Yi , Xia Qi‐Chang
Published: August 2002

The disulfide bond pattern of Trimeresurus stejnegeri lectin (TSL), a new member of the C‐type lectin family, was determined by mass spectrometry. Four intrachain disulfide bonds of TSL, Cys3‐Cys14, Cys31‐Cys131, Cys38‐Cys133 and Cys106‐Cys123, and two interchain linkages, Cys2‐Cys2 and Cys86‐Cys86, were determined. Three strategies were used in this work. One intrachain (Cys106‐Cys123) and one interchain (Cys86‐Cys86) disulfide linkages were detected by standard MS methods. The disulfide bonds Cys2‐Cys2 and Cys3‐Cys14 were analyzed using a modified partial reduction procedure and MS/MS. The last two disulfide bonds were characterized by a MS/MS/MS technique. The strategies developed in this work could be applied more generally to detection of disulfide bond patterns. Copyright © 2001 John Wiley & Sons, Ltd.
Identification of substituted sites on MUC5AC mucin motif peptides after enzymatic O‐glycosylation combining β‐elimination and fixed‐charge derivatization
Authors: Czeszak X. , Ricart G. , Tetaert D. , Michalski J. C. , Lemoine J.
Published: August 2002

A strategy for determination of O‐glycosylation site(s) in glycopeptides has been developed using model compounds obtained by enzymatic glycosylation (by human GaNTase‐T2 isoform) on peptides derived from the human MUC5AC mucin tandem repeat motif. The β‐elimination‐addition reaction (using dimethylamine and concomitantly ethanethiol) on the formerly glycosylated sites through a Michael‐type condensation produced efficient deglycosylation with appropriate chemical modification. After N‐terminal derivatization by a phosphonium group, peptide sequencing was then carried out by nanospray tandem mass spectrometry experiments. The highly predictable fragmentation pathways of these fixed‐charge phosphonium derivatives enable straightforward recognition of glycosylation site(s) based on the mass increment of +44 Da for originally glycosylated threonine compared to the mass of fragments containing nonglycosylated residues. Copyright © 2001 John Wiley & Sons, Ltd.
Evidence for an aryl migration during the electron impact induced fragmentation of substituted aryloxymethylquinoxalines
Authors: Starke I. , Sarodnick G. , Ovcharenko V. V. , Pihlaja K. , Kleinpeter E.
Published: August 2002

The electron impact (EI) mass spectra of 34 differently substituted 2‐phenoxymethyl‐, 2‐naphthyloxymethyl‐, 2‐pyridinyloxymethyl‐ and 2‐chinolinyloxymethylquinoxalines were recorded. The fragmentation patterns were examined by metastable ion analysis and exact mass measurements, employing finally also selective deuterium labelling. The inclusion of the substituted aryl ring moiety appears to be important for the fragmentation of the aryloxymethylquinoxalines. A molecular ion rearrangement is proposed for the observed loss of OH· and CHO· radicals. The influence of the different substituents on the aryl ring moiety on the rearrangement in the gas phase and on the resulting fragmentation was investigated. Copyright © 2001 John Wiley & Sons, Ltd.
Post‐source decay time‐of‐flight study of fragmentation mechanisms of protonated synthetic polymers under matrix‐assisted laser desorption/ionization conditions
Authors: Fournier I. , Marie A. , Lesage D. , Bolbach G. , Fournier F. , Tabet J. C.
Published: August 2002

Post‐source decay (PSD) of three different nylon oligomers desorbed under matrix‐assisted laser desorption/ionization (MALDI) conditions was studied and their fragmentation pathways were investigated. The fragmentation of the protonated oligomers is very similar to that of peptides. The bn+, yn+ and zn+ series of ions were observed in abundance in the PSD spectrum. The end groups and the length of the spacer in the repeating unit influence the fragmentation of the different polyamides and the relative abundances of the product ions. Competitive dehydration and deamination reactions were observed, and depend on the nature of the end groups and the repeating units. The PSD spectra are very similar to collision‐induced dissociation (CID) spectra obtained under low‐energy conditions, implying that the selected precursor ions possess similar average internal energies. All the peaks observed in the PSD spectrum can be rationalized by reasonable fragmentation mechanisms. Copyright © 2002 John Wiley & Sons, Ltd.
Highly robust stainless steel tips as microelectrospray emitters
Authors: Ishihama Yasushi , Katayama Hiroyuki , Asakawa Naoki , Oda Yoshiya
Published: August 2002

Tapered stainless steel spray tips for sheathless microelectrospray ionization (µESI) have been developed. The fabrication procedure for the tapered stainless steel tips was optimized using an electropolishing technique followed by removal of the burr. Using the tip as the µESI emitter, a stable ESI spray was obtained at a flow rate of 20 nL/min. The sensitivity of the µESI system was almost two orders greater than that of the conventional ion spray system. The tip was highly stable, and was successfully used for over 1000 h. Moreover, these stainless steel tips were suitable for use with sheathless capillary electrophoresis/mass spectrometry (CE/MS) and capillary liquid chromatography/mass spectrometry (LC/MS) for routine analysis in proteomic and pharmaceutical applications. Copyright © 2002 John Wiley & Sons, Ltd.
Electrospray ionization mass spectrometric studies of phosphorus oxychloride directed synthesis of homo‐oligopeptide ester libraries
Authors: Zhou Ning , Lu Kui , Liu Yan , Chen Yi , Tang Guo , Cao Shu‐Xia , Qu Ling‐Bo , Zhao Yu‐Fen
Published: August 2002

With the assistance of phosphorus oxychloride, α‐amino acids were assembled into homo‐peptides, which were analyzed by electrospray ionization mass spectrometry (ESI‐MS) and multistage electrospray ionization mass spectrometry (ESI‐MS/MS). On quenching with water or various alcohols, the reaction mixtures yielded the corresponding peptides or peptide esters, respectively. This paper reports a simple method to synthesize the homo‐oligo‐peptide‐ester conjugated library by phosphorus oxychloride activation. Copyright © 2002 John Wiley & Sons, Ltd.
Does thermal degradation occur in laser spray ionization?
Authors: Hiraoka K. , Asakawa Y. , Ueda K. , Hori A. , Sakai T. , Okazaki S. , Nakamura M.
Published: August 2002

A laser spray interface for use in liquid chromatography/mass spectrometry (LC/MS) has been investigated with respect to the degradation of the thermally labile compounds, ribostamycin, acetylcholine chloride, and cholesterol 3‐sulfate sodium salt. It was confirmed that few fragment ions were formed when the laser beam was focused at the center of the stainless steel capillary, i.e., no wall heating. When the laser beam was slightly off‐center, the sample ions suffered from thermal degradation by the heated wall of the stainless steel capillary to give fragment ions, which would be useful for the structural elucidation of the sample molecules. Copyright © 2002 John Wiley & Sons, Ltd.
Experimentation and modelling of HTTP over satellite channels
Authors: Kruse Hans , Allman Mark , Griner Jim , Tran Diepchi
Published: August 2002

This paper investigates the performance of various versions of the hyper text transfer protocol (HTTP) over a geosynchronous satellite link. Both HTTP/1.0, the currently popular form of the protocol, and HTTP/1.1, the recently standardized form of HTTP, are studied. Next, we quantify the impact of a moderate bit‐error rate on the performance of HTTP. Finally, we expand the mathematical model of HTTP presented in Heidemann, Obraczka and Touch (IEEE/ACM Transactions on Networking 1997; 5:616–630) to encompasses a wider range of HTTP behaviour. We show this model accurately predicts HTTP throughput by comparing it with HTTP transfers made over a satellite channel. Published in 2001 by John Wiley & Sons, Ltd.
An architecture for Internet service via broadband satellite networks
Authors: Bharadwaj Vijay G. , Baras John S. , Butts Norman P.
Published: August 2002

High bandwidth satellites offer the promise of a rapidly deployable communications infrastructure with a natural support for mobility. However, many widely used versions of the Transmission Control Protocol perform poorly over satellite links, and this presents an obstacle to the deployment of such systems. We present an architecture that overcomes these problems and allows easy integration of heterogeneous networks into the larger Internet. We also present some results from our initial implementation, which uses TCP connection splitting to improve TCP performance over satellite links. Copyright © 2001 John Wiley & Sons, Ltd.
Understanding nature of science as progressive transitions in heuristic principles
Authors: Niaz Mansoor
Published: August 2002

This study has the following objectives: (a) understand nature of science as progressive transitions in heuristic principles as conceptualized by Schwab (1962); (b) reformulate Smith and Scharmann's characterization of nature of science (Smith & Scharmann, 1999) in the light of evidence from history and philosophy of science; and (c) provide a rationale for the inclusion of three more characteristics of nature of science, to the original five suggested by Smith and Scharmann. It is concluded that nature of science manifests in the different topics of the science curriculum as heuristic principles. Science education, by emphasizing not only the empirical nature of science but also the underlying heuristic principles, can facilitate conceptual understanding. © 2001 John Wiley & Sons, Inc. Sci Ed 85:684–690, 2001.
Beyond Interpretation: Initial Evaluation and Technique in Short‐Term Dynamic Psychotherapy. Part I
Authors: Malan David
Published: August 2002

The present article begins by describing the two basic questions in Short‐Term Dynamic Psychotherpy, namely what are the techniques that maximize success, and how may suitable patients be recognized? A consideration of work at the Tavistock Clinic leads to the conclusion that purely interpretative techniques, whether of short‐ or long‐term therapy, are inadequate. In the author's view, Davanloo has developed a technique that largely overcomes these limitations. This is illustrated by an initial interview of great length and complexity, which therefore needs to be divided into two parts. The second part follows. At the end of the second part the practical and theoretical consequences of Davanloo's work will be considered.
Interfacial phenomena and microstructural evolution during superplastic deformation
Authors: Kashyap B. P.
Published: August 2002

Certain polycrystalline materials of fine equiaxed grains of size <10µm exhibit tensile ductility of several hundred to a few thousand per cent, called superplasticity, at intermediate strain rates and high temperatures. Experimental and theoretical results on mechanisms for superplastic deformation and concurrent microstructural evolution are reviewed to understand the role of grain boundary phenomena towards enhancement of grain growth and cavitation, etc. Grain boundary sliding (GBS) dominates superplastic flow, the extent of which varies between the grain and interphase boundaries in two‐phase alloys. Accommodation to GBS is provided by diffusional and dislocation mechanisms, which are manifested in the form of grain boundary migration (GBM), grain rotation and grain switching events. Although GBS helps in retaining the initial equiaxed grain shape of superplastic materials, the accommodation processes accelerate grain growth. In the lack of other accommodation processes the cavities are formed, being more pronounced at the boundaries of maximum sliding. The ppm‐level impurities present in superplastic materials do not influence the sliding and flow characteristics under typical superplastic conditions but they do promote cavitation and limit the ductility. The presence of precipitate or hard particles in quasi‐single‐phase superplastic materials inhibits GBM but provides sites for cavitation. Such materials exhibit more dislocation activities than anticipated for accommodation of GBS. The nature of microstructural changes noted during superplastic deformation supports the operation of cooperative GBS, in addition to a large variety of combinations between sliding and accommodation processes. Copyright © 2001 John Wiley & Sons, Ltd.
Deformation microstructures and selected examples of their recrystallization
Authors: Hughes D. A.
Published: August 2002

The elements that are needed to describe a deformation structure—grains, grain boundaries, macroscale banding within crystals, cell blocks, geometrically necessary boundaries and incidental dislocation boundaries (cell boundaries)—are presented and described for fcc metals and alloys of medium to high stacking fault energy. Pertinent to this quantitative description are the local orientations, structural morphology, different boundary misorientations and spacings as a function of strain and deformation conditions. Three specific examples are given in which particular aspects of the deformation structure are shown to direct the recrystallization behavior. Copyright © 2001 John Wiley & Sons, Ltd; first published by Risø National Laboratory.
Two‐band photoluminescence spectra from nanometre Si particle‐embedded Si oxide films
Authors: Ma S. Y.
Published: August 2002

Nanometre Si particle (NSP)‐embedded Si oxide films were deposited on p‐type Si substrates by the r.f. magnetron sputtering technique using Si and SiO2 composite sputtering targets. All samples were annealed in a nitrogen ambient at 600° for 30 min. X‐ray photoelectron spectroscopy and optical absorption measurements were performed on the samples. The sizes of the NSPs were increased by increasing the relative area of the Si wafer in the co‐sputtering target. The photoluminescence spectra of all the samples exhibited two bands with their peaks located at 370 nm (3.4 eV) in the ultraviolet spectral range and 650–665 nm (1.9 eV) in the orange–red spectral range. The experimental results indicate that there are two types of photoexcitation processes in the NSP‐embedded Si oxide films: one for the orange–red band occurring in the NSPs and the other for the ultraviolet band occurring in the SiO2 layers. Copyright © 2001 John Wiley & Sons, Ltd.
Electron effective attenuation lengths for applications in Auger electron spectroscopy and x‐ray photoelectron spectroscopy
Authors: Powell C. J. , Jablonski A.
Published: August 2002

The electron effective attenuation length (EAL) can be defined for the measurement of overlayer film thicknesses (the most common application) and for the measurement of the depth of a thin marker layer by Auger electron spectroscopy (AES) and x‐ray photoelectron spectroscopy (XPS). For each of these applications, a local EAL can be defined for a narrow range of thicknesses or depths and a practical EAL can be defined for specified larger ranges of thicknesses or depths. We show the results of illustrative calculations of these different EALs for XPS of Si 2p3/2 photoelectrons with Mg Kα x‐rays, and point out situations where numerical differences occur. We compare practical EALs (with the overlayer film definition) for Si 2s, Si 2p3/2, Au 4s and Au 4f7/2 photoelectrons that were obtained from Monte Carlo simulations and from an analytical expression derived from solution of the Boltzmann equation within the transport approximation. The average of the percentage deviations between the EALs from the two approaches for various overlayer thicknesses and emission angles was 5.28%. This average percentage deviation was considered to be acceptably small and justifies the use of the more approximate analytical expression in calculations of practical EALs for the measurement of overlayer thicknesses by AES and XPS. This computational approach is much faster than Monte Carlo simulations. We report calculations of practical EALs for the principal photoelectron and Auger electron lines of Si, Cu, Ag and W. For overlayer thicknesses of practical relevance, the practical EALs do not change appreciably with film thickness for electron emission angles (with respect to the surface normal) of <60°. Under these conditions, average practical EALs can be used to determine overlayer film thicknesses. For emission angles of >60°, the practical EALs generally change rapidly with film thickness and emission angle and, for these conditions, an EAL should be determined for the particular conditions. We have compared our practical EALs for photoelectron and Auger electron lines of Si, Cu, Ag and W with similar EALs derived from Monte Carlo simulations by Cumpson and Seah. At an emission angle of 45°, we find a root‐mean‐square deviation of 1.6% between the EALs from the two approaches. Published in 2002 John Wiley & Sons, Ltd.
Monte Carlo simulation of x‐ray generation and energy dissipation in a W/Cu target for optimum design of a high‐power x‐ray source
Authors: Araki K. , Yoshioka A. , Shimizu R. , Nagatomi T. , Takahashi S. , Nihei Y.
Published: August 2002

Monte Carlo simulation of x‐ray generation by electron impact was applied to a W/Cu target (tungsten W film on a copper substrate) to find the optimum conditions for a high‐power x‐ray source. To assess the performance of the high‐power x‐ray source, we propose using:

The total intensity of continuous x‐rays emitted from the target, $I_{E_{0}} = \int\limits_{\lambda_{\min}}^{\infty}{i_{E_{0}} (\lambda)}\,\hbox{d}\lambda$, where i(λ) is a spectrum of continuous x‐rays emitted from the target under bombardment of an electron beam of primary energy E0.

The cooling efficiency of the W/Cu target, which is

where $\left({\hbox{d} E\over \hbox{d} z}\right)_{j}$ and σj are the in‐depth energy dissipation in a target of element j and the thermal conductivity of element j, respectively, in the W/Cu target with tungsten film thickness ΔW.

Both I and γ were obtained from Monte Carlo calculations for different tungsten film thicknesses by varying the incidence angle of the electron beam and the take‐off angle of the x‐rays according to the primary energy levels of the electron beam. Copyright © 2002 John Wiley & Sons, Ltd.
Experimental estimation of surface excitation parameter for surface analysis
Authors: Gergely G. , Menyhard M. , Gurban S. , Sulyok A. , Toth J. , Varga D. , Tougaard S.
Published: August 2002

The surface excitation produced by impinging or escaping electrons is a competitive process to elastic backscattering. It affects the intensity of Auger and XPS peaks and is characterized by the surface excitation parameter Pse. This appears in the surface loss peak I(Epls), and possibly a surface plasmon. In our work Pse is defined as the ratio of the probability to create a surface plasmon/elastic scattering and is deduced from the integrated surface loss peak and elastic peak, respectively. Our procedure is based on reflection electron energy loss spectroscopy and elastic peak electron spectroscopy spectra and Kλi spectra (K is the inelastic scattering cross‐section and λi is the inelastic mean free path), determined using Tougaard's method. The normalized Kλi curves are fitted to the spectrum at E = 5 keV (primary energy) and EL = Epl1 (volume plasmon), approximated with the Lorentzian type three‐parameter formula of Tougaard. For E>Epl1, the normalized curves are overlapping and Pse is deduced from the integrated difference spectra fitted with the Tougaard cross‐sections. The procedure was applied on materials exhibiting surface and volume plasmons: III–V semiconductors (GaAs, InSb) and In and Sb metals. The REELS experiments were carried out with an ESA 31 HSA spectrometer covering the E = 0.2–5 keV energy range. Copyright © 2002 John Wiley & Sons, Ltd.
Estimating the number needed to treat (NNT) index when the data are subject to error
Authors: Walter S. D. , Irwig L.
Published: August 2002

The number needed to treat (NNT) index has been proposed as a clinically useful measure to assess the results of randomized trials and other clinical studies. In its usual form, NNT indicates the expected number of patients who must be treated with an experimental therapy in order to prevent one adverse event, compared to the expected event rates under the control therapy. It can be formulated as a function of the proportions of patients who respond to treatment by more than a certain amount, the clinically important difference. We may also wish to evaluate two group studies comparing treatment and control responses, and to consider net benefit from treatment (by also allowing for individuals who deteriorate as well as those who respond positively). In this paper, we investigate the effect on NNT caused by measurement errors in continuous outcome measures. Such errors can lead to bias in the estimated proportions of subjects with clinically important responses, and hence bias the associated values of NNT. General expressions for the bias are derived, and enumerated for typical scenarios. For many situations, reliability of 80 per cent or more in the observations is required to restrict the bias to tolerable levels. Copyright © 2001 John Wiley & Sons, Ltd.
Role of conventional radiology in the diagnosis and staging of gastrointestinal tract neoplasms
Authors: Gourtsoyiannis Nick , Grammatikakis John , Prassopoulos Panos
Published: August 2002

Preoperative diagnosis and staging of primary gastrointestinal (GI) neoplasms are challenges for both clinicians and radiologists. Barium studies are very sensitive in disclosing primary malignancies, even at an early stage. Radiologic signs depend on the evolutional stage of the disease and its appearance on gross pathology. A neoplasm may be manifested on barium studies by a wide spectrum of findings, including mucosal abnormalities, mass presence, ulcerative lesions, submucosal infiltration, and lumen stenosis. Advanced disease can be accurately diagnosed, whereas early cancer should be differentiated from other neoplastic or inflammatory disorders by meticulous analysis of radiologic findings. The extent of GI involvement and multiplicity of the lesions can be assessed on barium studies. In the staging of GI neoplasms, barium studies are of little value. Skeletal survey by conventional radiographs and chest plain films can reveal distant metastases in a short time and with low cost, although they are not that sensitive to the detection of early or subtle lesions. The exact role of conventional radiology in the imaging workup of GI malignancies depends on local expertise and availability of other diagnostic techniques and modalities. Semin. Surg. Oncol. 20:91–108, 2001. © 2001 Wiley‐Liss, Inc.
Web dynamics
Authors: Levene Mark , Poulovassilis Alexandra
Published: August 2002

The global usage and continuing exponential growth of the World Wide Web poses a host of challenges to the research community. In particular, there is an urgent need to understand and manage the dynamics of the Web, in order to develop new techniques that will make the Web tractable. MARK LEVENE and ALEXANDRA POULOVASSILIS provide an overview of recent statistics relating to the size of the Web graph and its growth. They then briefly review some of the key areas relating to Web dynamics with reference to the recent literature. Finally, they summarise the talks given in a recent workshop devoted to Web dynamics, which was held in the beginning of January 2001 at the University of London. Copyright © 2001 John Wiley & Sons, Ltd.
Models for character animation
Authors: Collins Gordon , Hilton Adrian
Published: August 2002

GORDON COLLINS and ADRIAN HILTON present a reviewof methods for the constructionand deformation of charactermodels. They consider both stateof the art research and common practice. In particular they review applications, data capture methods, manual model construction, polygonal, parametricand implicit surface representations, basic geometric deformations, free form deformations, subdivision surfaces, displacement map schemes and physical deformation. Copyright © 2001 John Wiley & Sons, Ltd.
L‐type calcium channels reduce ROS generation in cerebellar granule cells following kainate exposure
Authors: Leski Michael L. , Hassinger Linda C. , Valentine Stacey L. , Baer Jesse D. , Coyle Joseph T.
Published: August 2002

Cerebellar granule cells (CGC) deprived of serum or trophic factors develop sensitivity to kainate neurotoxicity that is mediated by the α‐amino‐3‐hydroxy‐5‐methyl‐isoxazole proprionic acid (AMPA) subtypes of glutamate receptors (GluR). The L‐type voltage‐gated calcium channel (L‐type VGCC) blocker nifedipine increases the potency of kainate 50‐fold. Thus, one goal of this laboratory is to determine the underlying protective mechanism triggered by calcium influx through this channel. The cell‐permeable heavy metal chelator N,N,N′,N′‐tetrakis(2‐pyridylmethyl)ethylenediamine effected complete protection against kainate treatment in the presence of nifedipine, as did the iron chelator deferoxamine. The chelatable heavy metal pool decreased ∼70% immediately following treatment with kainate, but did not change following kainate/nifedipine treatment. Tetramethylrhhodamine ethyl ester (TMRE) fluorescence, an indicator of mitochondrial membrane potential, decreased ∼70% following kainate treatment but displayed a more modest decrease (∼15%) when CGC were treated with kainate/nifedipine. Reactive oxygen species (ROS) formation decreased in CGC immediately following kainate treatment but was slightly elevated following kainate/nifedipine treatment. Electron microscopic examinations of the CGC indicated severe swelling and distortion of mitochondria immediately following kainate/nifedipine treatment and the appearance of mitochondrial herniations, whorls, and bridges 2 h later, features that were rarely observed following kainate treatment. These results support the hypothesis that calcium entry through L‐type VGCCs protects CGC during kainate treatment by lowering the chelatable heavy metal pool and the mitochondrial membrane potential, thereby mitigating the formation of ROS. Synapse 43:30–41, 2002. © 2001 Wiley‐Liss, Inc.
Entopeduncular lesions facilitate and thalamic lesions depress spontaneous and drug‐evoked motor behavior in the hemiparkinsonian rat
Authors: Olds M.E. , Jacques D.B. , Kopyov O.
Published: August 2002

Pallidotomy is a neurosurgical procedure designed to ameliorate the akinesia and bradykinesia associated with Parkinson's disease. In the present study, the effects of pallidal‐like lesions on motor behavior in the hemiparkinsonian rat were compared to the effects of lesions in the ventrolateral thalamus, a target of entopeduncular projections feeding motor‐related information to motor cortex. Six aspects of spontaneous and evoked behavior induced by amphetamine and apomorphine in the hemiparkinsonian rat with either bilateral electrolytic entopeduncular lesions or bilateral electrolytic ventrolateral thalamic lesions were measured for 60 min. Saline or amphetamine, 5 mg/kg, or apomorphine, 0.3 mg/kg, were administered IP 5 min before the tests. The results show that on all measures except time spent resting the hemiparkinsonian rats with the entopeduncular lesions were more active than the hemiparkinsonian rats with the thalamic lesions. The asymmetrical rotation responses to dopamine receptor stimulation evoked by amphetamine and apomorphine were influenced by the general effect on gross motor behavior, as shown by the response being very large in the entopeduncular group and very small in the thalamic group. These results are consistent with current thinking about the functional organization of the basal ganglia according to which damage of the entopeduncular nucleus reduces its inhibitory control of the thalamic motor regions, thereby promoting thalamic facilitation of motor cortex, and damage to the thalamic motor regions has the opposite effect. These effects of the lesions translate, respectively, into hyperactivity and hypoactivity without blocking the asymmetrical rotation response of the hemiparkinsonian rat. Synapse 40:215–224, 2001. © 2001 Wiley‐Liss, Inc.
Homocysteine modifies development of neurulation and dorsal root ganglia in chick embryos
Authors: Epeldegui Marta , Peña‐Melian Angel , Varela‐Moreiras Gregorio , Pérez‐Miguelsanz Julia
Published: August 2002

Background

The formation of the neural tube (neurulation) involves two mechanisms: primary and secondary neurulation. In chicks, there is also an overlap zone, where both mechanisms work together. Homocysteine (Hcy) may have an important teratogenic role in neural tube defects (NTD) when folic acid levels are considered normal. Recently, Hcy capability to generate NTD and modify neural crest cell migration has been demonstrated in chick embryos. This study was aimed to evaluate the effects of Hcy on neurulation and the development of the dorsal root ganglia (DRG).

Methods

Chick embryos were treated with L‐Hcy thiolactone 20 μmol to produce the highest rate of survival with embryos carrying neural tube defect (NTD) in the spine. Embryos at stages (st) 3–10 were treated and harvested at st 18–23. Only externally normal embryos or those carrying spinal NTD embryos were considered.

Results

Histological sections of Hcy‐treated embryos showed: open spina bifida (39% of embryos), more than one tube forming the spinal cord (26%), disorganized spinal cord (26%), always affecting lumbosacral regions, probably in the overlap zone. Additionally, 32% of embryos had small and continuous DRG, associated with a slimmed roof plate. Three‐dimensional reconstruction showed unsegmented DRG until the C8 ganglion level. There was a 75% reduction of C3 DRG cells in treated embryos in comparison to untreated ganglia.

Conclusion

Hcy teratogenicity in avian embryos affected the neural tube in the overlap zone, secondary neurulation and the cervical DRG. Teratology 65:171–179, 2002. © 2002 Wiley‐Liss, Inc.
Placental transfer of vigabatrin (γ‐vinyl GABA) and its effect on concentration of amino acids in the embryo of TO mice
Authors: Abdulrazzaq Yousef M. , Padmanabhan R. , Bastaki Salim M.A. , Ibrahim Ahmed , Bener Abdulbari
Published: August 2002

Background

The mechanism of the teratogenicity of vigabatrin (VGB) is unknown. The objectives of this study were to determine the placental transfer of VGB and to evaluate the effect of VGB on maternal, placental, and fetal concentrations of amino acids.

Methods

A single dose of 400 mg/kg VGB in physiological saline was administered intraperitoneally to a group of Theiler outbred (TO) mice on gestational day (GD) 10. The controls received a proportionate volume of saline. Maternal blood samples, embryos, and placentas were collected at 3.5, 6.0, and 9.0 hr after treatment and their total amino acid concentrations determined in an ion‐exchange amino acid analyzer.

Results

At 3.5 hr, there was a decrease in concentrations of some amino acids in the blood, placenta, and embryos of VGB‐treated mice, but the decrease in methionine was most marked. γ‐aminobutyric acid (GABA) was significantly higher in the VGB group in both the embryos and the placentas at 3.5 hr but at 6.0 and 9.0 hr the differences were not significant. Vigabatrin levels were higher in the placenta than in the embryo at 3.5 hr, but at 6.0 hr there was an overlap of the VGB peak with that of tryptophan with very much lower levels than at 3.5 hr. At 9.0 hr, there was no vigabatrin peak in either the placenta or the embryo.

Conclusions

Maternal exposure to VGB results in peak levels of the drug after 3.5 hr in the placenta and embryo. Methionine concentration is most severely affected in VGB‐treated mothers, placentas, and fetuses. We speculate that this deficiency could be a possible mechanism for the teratogenic effects of vigabatrin. Teratology 63:127–133, 2001. © 2001 Wiley‐Liss, Inc.
A population‐based study of coarctation of the aorta: Comparisons of infants with and without associated ventricular septal defect
Authors: Wollins Dana Swartzberg , Ferencz Charlotte , Boughman Joann A. , Loffredo Christopher A.
Published: August 2002

Background

Coarctation of the aorta (CoA) is a congenital cardiovascular malformation (CCVM) sometimes associated with ventricular septal defect (VSD). Although the phenotypic association is well documented, little research exists on the epidemiological features distinguishing CoA with and without VSD.

Methods

The Baltimore–Washington Infant Study (1981–1989), a population‐based study of CCVM, evaluated 126 infants with “pure” CoA (free of associated cardiac defects) and 67 infants with CoA and VSD (COA/VSD) in comparison to 3,572 controls.

Results

The proportion of infants with associated extracardiac anomalies was greater among CoA/VSD than among pure CoA (31% versus 11%). Infants with CoA/VSD were twice as likely as those with pure CoA to be born small for gestational age (23% versus 12%, respectively, compared with 6% of controls). All‐cause mortality during the first year of life was higher in CoA/VSD than in pure CoA (21% vs. 7%). Multiple logistic regression models revealed that family history of CCVM was associated with pure CoA (adjusted case‐control odds ratio [OR] = 4.6; 99% confidence interval [CI] = 1.5–13.9) and with CoA/VSD (OR = 5.9, CI = 1.2–23.5); maternal history of organic solvent exposures early in pregnancy was also associated with pure CoA (OR = 3.2, CI = 1.0–10.2) and with CoA/VSD (OR = 3.7, CI 0.9–14.9). Additional risk factors, including maternal epilepsy (OR = 5.3, CI = 0.9–30.6), and use of macrodantin (OR = 6.7, CI = 1.4–31.8) were associated only with pure CoA.

Conclusions

These findings highlight possible genetic and environmental differences between pure CoA and CoA/VSD and may stimulate further investigations of the etiology of CoA. Teratology 64:229–236, 2001. © 2001 Wiley‐Liss, Inc.
Derivative Ruination in the 1990s: Les Apparences sont Trompeuses
Authors: Sanders Thomas B.
Published: August 2002

A spectacular financial revolution spanning 20 years created new securities deriving from other securities, which trade in volumes of trillions of dollars in markets, now thought to be the largest and more important in the world. Known as swaps, swaptions, index futures, puttable bonds, collateralized mortgage obligations, stripped bonds, options, and futures, among other exotic names, these financial contracts were designed as a means of laying off risk involving conventional business transactions. This article details massive abuses in the proper use of these insurance products, which resulted in billions of dollars of speculation losses suffered by Procter & Gamble, Gibson Greeting Cards, Orange County California, Metallgesellschaft AG, various‐public employees' retirement funds—and which brought down one of Europe's oldest merchant banks, Barings PLC. © 2001 John Wiley & Sons, Inc.
Analysis of hierarchical cellular networks with mobile base stations
Authors: Cui Wei , Bassiouni Mostafa A.
Published: August 2002

In this paper, we develop and evaluate a hierarchical cellular architecture for totally mobile wireless networks (TMWNs). Extensive performance tests were conducted to evaluate the performance of a two‐tier system and compare its throughput, handoff blocking rate and new call success rate with those obtained by a one‐tier model. Our tests have shown that when the total number of channels is kept the same, the two‐tier system outperformed the one‐tier counterpart under all load conditions. Under the constraint of equal power consumption, the two‐tier system still achieved improvement over the one‐tier system, especially at light and medium load levels. The improvement of the two‐tier system over the one‐tier system was observed to diminish as the degree of randomness in the mobility model is reduced; scenarios where the one‐tier system outperforms the two‐tier system are given. Load balancing schemes based on the concept of reversible handoffs are introduced and their performance improvements are analyzed. Comparison results on the percentage of terminal coverage are presented. An analytical model to compute the new call and handoff blocking probabilities in TMWN is given and evaluated. The model extends the Markov chain approach previously used in hierarchical architectures with stationary base stations and uses a corrected derivation for the handoff blocking probability. Copyright © 2002 John Wiley & Sons, Ltd.
Use of data permutation to reduce the peak‐to‐average power ratio of an OFDM signal
Authors: Jayalath A. D. S. , Tellambura C.
Published: August 2002

A set of fixed permutations is used in this paper to reduce the peak‐to‐average power ratio (PAR) of an orthogonal frequency division multiplexing (OFDM) signal. For this technique, K − 1 interleavers are used to produce K − 1 permuted sequences from the same information sequence. The peak powers of the permuted sequences and the original information sequence are computed using K inverse discrete Fourier transforms; the sequence with the lowest PAR is chosen for transmission. Before the optimization process begins the identity of each interleaver is embedded into the data frame as side information (SI). SI which is critical to the receiver operation, is coded using a simple forward error correction code in order to increase its reliability. An adaptive approach is proposed for the reduction of this technique's complexity. Furthermore, theoretical expressions are derived for the complementary cumulative distribution function of the PAR and for the average number of permutations required by the adaptive approach. Computer simulations are performed for finding the PAR reduction capability of several types of interleavers. It is subsequently found that random interleavers and odd–even symmetric interleavers are performing equally well in reducing the PAR. Results are also presented for the out of band radiation and the bit error rate performance of interleaved OFDM (IOFDM) and conventional OFDM in an additive white Gaussian noise channel. IOFDM also has less adjacent channel interference than that of conventional OFDM. Copyright © 2002 John Wiley & Sons, Ltd.
Long‐term proximity relationships in a captive social group of western lowland gorillas (Gorilla gorilla gorilla)
Authors: Nakamichi Masayuki , Kato Eiko
Published: August 2002

To visualize long‐term social relationships among 12 gorillas in a captive breeding group at the San Diego Wild Animal Park, San Diego, CA, the multidimensional scaling (MDS) procedure was applied to proximity (within 5 m) values collected in five different periods over 2.5 years. The resulting two‐dimensional representations clearly show that in samples taken during this 2.5‐year period, the silverback male was surrounded by five adult females, while three infant or young juvenile females, gathered in a body, remained between the silverback male and adult females. Some adult females maintained proximity to the silverback male more frequently than other adult females throughout the five periods. Unlike mountain gorillas in the wild, females with dependent offspring did not tend to stay near the silverback male more frequently than other females, and related females did not tend to spend more time near each other than non‐related females. Three older juvenile or young adult males were plotted the furthest from the silverback male, with gradual changes with increasing age. The usefulness of the MDS procedure, which can be used to visualize easily and clearly the social relationships among individuals, is discussed from the viewpoint of the management of breeding groups of captive gorillas. Zoo Biol 20:197–209, 2001. © 2001 Wiley‐Liss, Inc.
A Formal Definition of Time in LOTOS
Authors: Léonard Luc , Leduc Guy
Published: August 2002

Enhanced Timed-LOTOS, denoted ET-LOTOS, is an extension of LOTOS that allows the modelling of real-time behaviours. It covers all the aspects of full LOTOS, including data types, it supports both a dense and a discrete time domain and can manipulate time values as any other data values. A tutorial on ET-LOTOS, showing many application examples, has already been published [LéL97]. The present paper adds to it by providing an in-depth presentation of its theoretical aspects. The complete semantics is given and explained, and its properties are studied. In particular, we prove that the semantics is consistent and that strong bisimulation is a congruence. This requires to deal carefully with the presence of negative premises in the operational semantics, which are necessary to express urgency. ET-LOTOS is also shown to be a conservative extension of LOTOS for guarded processes, and is the basis of the timed extension of LOTOS currently developed by ISO [ISO98]. To our knowledge, this is the first in-depth study of a language that combines data types and real-time behaviours.
Efficacy of Diagnosis of Mechanical Cholestasis by MagneticResonance Cholangiography
Authors: Urban Michael , Holzer Brigitte , Sebesta Christian , Schmid Leopold , Schiessel Rudolf , Hruby Walter , Rosen Harald R.
Published: August 2002

The aims of this study were to evaluatethe effectiveness of magnetic resonance cholangiography (MRC) indiagnosing patients with cholestasis and to compare these results tothose obtained with endoscopic retrograde cholangiopancreaticography(ERCP). From January 1996 to December 1998 a total of 85consecutive patients who were candidates for ERCP because of asuspected diagnosis of mechanical cholestasis were included in thisstudy. All patients underwent MRC and consecutive ERCP 24 to 48 hourslater. The sensitivity for detecting common bile duct stones was 93%,specificity 74%, positive predictive value 89%, and negativepredictive value 82%. For the determination of tumorous bile ductstenosis the sensitivity and specificity were both 100%. MRC might bean ideal method for evaluating patients with unclear laboratory orultrasonography findings before laparoscopic cholecystectomy, therebyavoiding unnecessary invasive diagnostic tests with possible harmfulcomplications.