bluuebunny/crossref_metadata_2025 huggingface dataset:
Transition metal azolates from metallocenes. Part 1: Dimetallic and trimetallic cyclopentadienyl nickel pyrazolates, synthesis and structural studies
Authors: Rettig Steven J. , Storr Alan , Summers David A. , Thompson Robert C. , Trotter James
Published: May 2006

The reactions of nickelocene with pyrazoles in benzene solution have resulted in the isolation of either dimeric compounds, [CpNi(μ-pz′)]2, (room temperature conditions) or trimetallic complexes, [CpNi(μ-pz″)2]2Ni, (elevated temperature conditions). Both dimeric and trimetallic species were obtained as red crystalline materials and X-ray structural investigations are reported for representative samples of each type. Structural features are interpreted and compared with similar, previously reported, nickel pyrazolate structures. Crystals of [CpNi(3,5-diMepz)]2 (C20H24N4Ni2), 1, are orthorhombic, a = 15.204(1), b = 17.967(2), c = 6.9786(9) Å, Z = 4, space group Ama2; those of [CpNi(4-NO2-3,5-diMepz)]2 (C20H22N6Ni2O2), 5, are orthorhombic, a = 17.145(3), b = 17.738(1), c = 7.006(1) Å, Z = 4, space group P212121; those of [CpNi(3,5-F6diMepz)]2 (C20H12F12N4Ni2), 6, are orthorhombic, a = 18.7134(8), b = 15.619(2), c = 7.7263(9) Å, Z = 4, space group Pnma; those of [CpNi(3,5-diMepz)2]2Ni (C30H38N8Ni3), 7, are triclinic, a = 10.078(2), b = 16.134(2), c = 9.992(1) Å, α = 91.586(10)°, β = 111.050(9)°, γ = 86.95(1)°, Z = 2, space group [Formula: see text]; and those of [CpNi(4-Cl-3,5-diMepz)2]2Ni (C30H34Cl4N8Ni3), 10, are monoclinic, a = 10.2201(7), b = 16.174(1), c = 10.7207(9) Å, β = 108.193(5)°, Z = 2, space group P21/a. The structures were solved by direct (dimetallic species) or Patterson (trimetallic complexes) methods and were refined by full-matrix least-squares procedures to R = 0.035, 0.032, 0.058, 0.032, and 0.033 (Rw = 0.021, 0.026, 0.053, 0.028, and 0.032) for 1157, 1894, 1642, 4499, and 2113 reflections with I ≥ 3σ(F2), respectively. Keywords: crystal structures, nickel, nickelocene, pyrazolates, cyclopentadienyl.
Far-UV laser flash photolysis in solution. A time-resolved spectroscopic study of the chemistry of 1,1-dimethyl-1,3-(1-sila)-butadiene
Authors: Kerst Corinna , Byloos Martin , Leigh William J.
Published: May 2006

Laser flash photolysis (193 nm) of 1,1-dimethyl-(1-sila)cyclobut-2-ene in hexane solution leads to the formation of a transient species [Formula: see text] assigned to 1,1-dimethyl-1,3-(1-sila)butadiene on the basis of its UV absorption spectrum (λmax = 312 nm), and reactivity toward methanol (kMeOH = (3.6 ± 0.1) × 109 M−1 s−1; kH/kD = 1.3 ± 0.1), ethanol (kEtOH = (2.41 ± 0.06) × 109 M−1 s−1), tert-butanol (kBuOH = (1.8 ± 0.1) × 109 M−1 s−1; kH/kD = 1.5 ± 0.1), and oxygen [Formula: see text]. Experiments using isooctane and acetonitrile as solvent are also described. In acetonitrile, the lifetime of the silene is shortened considerably compared to hydrocarbon solvents, presumably due to quenching by adventitious water. In isooctane, under conditions of low excitation intensity, the siladiene decays with clean pseudo-first-order kinetics and a maximum lifetime of ~ 5 μs at 23 °C. The decay rate constant varies only slightly with temperature over the 20–60 °C range, leading to Arrhenius activation parameters of Ea = 0.5 ± 0.2 kcal/mol and log A = 5.7 ± 0.2. While steady state irradiation experiments suggest that in the absence of silene traps the predominant fate of the silabutadiene is thermal ring closure to regenerate the precursor, it is concluded that the rate constants and activation parameters for decay of the siladiene measured by flash photolysis represent a composite of those due to thermal electrocyclic ring closure (with Ea > ~3 kcal/mol) and reaction with adventitious quenchers (probably water, with Ea < 0). The measured Arrhenius parameters for reaction of the siladiene with methanol in isooctane (Ea = −2.6 ± 0.3 kcal/mol and log A = 7.6 ± 0.3) are consistent with this proposal. The potential and limitations of the use of 193-nm laser excitation for flash photolysis studies in solution are discussed. Keywords: far-UV, silene, flash photolysis, kinetics, electrocyclic.
Theoretical study on naphthyl-phenylacetylenes for second-order nonlinear optical applications
Authors: Rao B.V.V.S.N. Prabhakara , Dube D.C. , Tewari D.P. , Mathur S.C. , Banerjee M.
Published: May 2006

The ground state dipole moments (μg), excited state dipole moments (μe), linear polarizabilities (α), first hyperpolarizabilities (β), and absorption maxima [Formula: see text] of a new series of 6,4′-disubstituted 2-naphthylphenylacetylenes have been calculated using the finite field – MNDO (Modified Neglect of Diatomic Overlap) technique and studied for second-order nonlinear optical (NLO) applications. Among all the molecules studied here, the strongest and the weakest electron donor/acceptor pairs [N(CH3)2/NO2] and [CH3/CN] exhibit the largest and the smallest βμ (projection of β on the axis of the μ) of 46.3 × 10−30 esu and 10.2 × 10−30 esu, respectively. The coefficients of the power law that describes the dependence of α and β on the number of conjugated bonds (n) were calculated for [NH2/NO2]n=1–5 and [NH2/CN]n=1–5 molecules. For β, exponents of 0.36 and 0.31 were obtained for [NH2/NO2]n=1–5 and [NH2/CN]n=1–5 molecules, respectively, and for α, an exponent of 0.37 was obtained for both series of molecules. A comparison is made between naphthylphenylacetylenes and diphenylacetylenes on the basis of their hyperpolarizabilities. Keywords: nonlinear optics, organic molecules, hyperpolarizabilities.
Lanthanide catalysts for the hetero Diels–Alder reaction: effect of ligand structure and acidity
Authors: Spino Claude , Clouston Laurel L. , Berg David J.
Published: May 2006

A series of yttrium, ytterbium, and lanthanum hexa-or heptacoordinate complexes were prepared and their catalytic activities tested in the hetero Diels–Alder reaction between crotonaldehyde and ethyl vinyl ether. It was found that a pKa below 7 of the ligand was necessary but not sufficient for catalytic activity. It was determined that the ligand should possess a perfluoromethyl-β-diketonate functionality. Other factors such as bite angle and hinging motion may also play a determining role. Keywords: lanthanide, catalyst, hetero Dielsis–Alder, yttrium, ytterbium, lanthanum.
Near-infrared spectra of Ba(NO2)2•X2O (X = H,D) at 10 K. A local-mode approach
Authors: Walker Ian M. , McCarthy Paul J.
Published: May 2006

The fundamental and overtone vibrational spectra of Ba(NO2)2•X2O (X=H,D) have been interpreted using the local mode model. The calculated parameters are consistent with the structure, which has one strong hydrogen bond and one weak bifurcated hydrogen bond. Evidence for Fermi resonance between stretch and bend features having similar energies is discussed. Evidence for the breakdown of the simple Morse oscillator model, which was quite successful for [Formula: see text] hydrogen bonds, is also presented. Keywords: overtone, spectra, near-infrared, hydrates, local-mode model.
Peptide models XX. Aromatic side-chain–backbone interaction in phenylalanine-containing diamide model system. A systematic search for the identification of all the ab initio conformers of N-formyl-L-phenylalanine-amide
Authors: Perczel András , Farkas Ödön , Csizmadia Imre G. , Császar Attila G.
Published: May 2006

Phenylalanine is the simplest among the four natural amino acid residues that have aromatic side chains. The ab initio conformational analysis performed at the RHF/3-21G level on a phenylalanine-containing diamide model system (N-Formyl-L-Phe-NH2) revealed 19 different structures. Single-point energy calculations were performed using RHF/6-31+G* and DFT(B3LYP)/6-311++G** levels for all conformers. The inverse (γL) and the normal (γD) gamma turn, the extended (βL), the left-handed helical [Formula: see text], and the inverse polyproline II [Formula: see text] backbone conformers each have three (g+, a, and g−) side-chain (χ1,) rotamers. The [Formula: see text] and the [Formula: see text] type main-chain conformers have only two side-chain orientations, respectively. No minima have been found for the conformational building unit of the right-handed helical [Formula: see text] and for the polyproline II [Formula: see text] structures. The present ab initio conformational analysis for For-L-Phe-NH2 is a unique example in which a systematic and complete conformational set was established for a diamide system with an aromatic side chain. Analytic vibrational frequency calculations were established for all stationary points found as minima on the potential energy surface. These data may be used in the future as reference conformers in more detailed vibrational and (or) chemical shielding calculations or during the structural analysis of peptides and proteins by X-ray or NMR techniques. Keywords: ab initio peptide conformers, all RHF/3-21G structures of For-L-Phe-NH2, backbone – side-chain interaction in phenylalanine-containing peptide models.
The chemistry of thujone. XX. New enantioselective syntheses of Ambrox and epi-Ambrox
Authors: Kutney James P. , Cirera Carles
Published: May 2006

The development of a new synthetic approach to (−)-Ambrox® (37) and epi-Ambrox® (29) using thujone (1) as a chiral synthon, is presented. Thujone (1), a readily available starting material obtained from Western red cedar, can be efficiently converted to β-cyperone (2) and the latter is then chemically elaborated to the key intermediate, the enone 6. A carbonyl transposition of 6 to enone 9 also allows a formal synthesis of (−)-Polywood® (18). Keywords: thujone, β-cyperone, (−)-Ambrox®, epi-Ambrox®, synthesis.
Spiro-fused 2-alkoxy-2-amino-Δ3-1,3,4-oxadiazolines. Synthesis and thermolysis to corresponding aminooxycarbenes
Authors: Couture Philippe , Warkentin John
Published: May 2006

Δ3-1,3,4-Oxadiazolines spiro-fused at C2 to C2 to oxazolidines (12) or to C2 of tetrahydro-1,3-oxazines (13) were synthesized. The oxadiazolines undergo thermolysis in benzene at 90 °C with first-order rate constants of (1.6–50) × 10−5 s−1. The dependence of these rate constants on the nature of the substituents present on the oxadiazoline ring is consistent with a mechanism involving a carbonyl ylide intermediate. Substituents on N of the oxazolidine or tetrahydro-1,3-oxazine moieties play a major role in determining the fragmentation pathways. Oxadiazolines with N-carbonyl groups (12c–j, 13d,e) afford essentially quantitative yields of the corresponding aminooxycarbenes, while other fragmentation reactions compete with carbene generation in the case of oxadiazolines with N-methyl (12b, 13c) or N-sulfonyl (12k) groups. Keywords: nucleophilic carbene, aminooxycarbene, oxadiazoline, oxazolidin-2-ylidene, carbonyl ylide.
Chemistry of cyclic aminooxycarbenes
Authors: Couture Philippe , Warkentin John
Published: May 2006

A series of oxazolidin-2-ylidenes and one tetrahydro-1,3-oxazin-2-ylidene, generated by thermolysis of Δ3-1,3,4-oxadiazolines in benzene at 90 °C, were intercepted by insertion into the OH bond of phenols. In two cases the initial products rearranged to N-(2-aryloxyethyl)-N-methylformamides. The activation energy for rotation about the amide CN bond of those ultimate products was measured as 20.4 kcal/mol. The aminooxycarbenes reacted with two equivalents of methyl or phenyl isocyanate to give spiro-fused hydantoins. Major products from the reactions of the N-carbonyl carbenes with dimethyl acetylenedicarboxylate or with methyl propiolate were 2-oxazolines resulting from apparent acyl transfers from N to C in the proposed dipolar intermediates; minor products of 1:2 (carbene:trap) stoichiometry were also observed. Keywords: nucleophilic carbene, aminooxycarbene, oxadiazoline, amide rotation, oxazolidine.
1997 Noranda Award Lecture Chemical applications of electron–matter interactions: from probing low-temperature industrial plasmas and atmospheric chemistry of "environment-safe" Freon substitutes to enhancing novel surface reactions on metals and semiconductors
Authors: Leung K.T.
Published: May 2006

Since the discovery of the electron by Sir Joseph John Thomson a century ago, the limitless applications of the electron in chemistry have been both profound and fun. We present recent results from two of our experiments that involve such applications of the electron beam in the study of new aspects of gas-phase chemical physics and of surface chemistry. In particular, our precise measurements of momentum-transfer-resolved "absolute" excitation transition probabilities of the low-lying transitions in "environment-safe" Freon substitutes using a high-energy electron beam are finding applications in the modelling of low-temperature industrial plasma and atmospheric processes. The use of low-energy electrons as a powerful in situ means to activate and to probe "novel" surface reactions, including oxide and carbide formation and CO oxidation, has been demonstrated on Cu(100) and Si(111) surfaces. These experiments further illustrate the value and the enormous potential of technological payoffs of electron-based fundamental research. Keywords: electron scattering and interactions, surface chemistry.
Correlation between the electron solvation time and the solvent dielectric relaxation times τ2 and τL1 in liquid alcohols and water: towards a universal concept of electron solvation?
Authors: Jay-Gerin Jean-Paul
Published: May 2006

A simple model of electron solvation in polar liquids is presented, in which we attempt to link the electron solvation time τs to τ2, the time for reorientation of monomeric molecules, and to τL1, the longitudinal dielectric relaxation time of the solvent. It is shown that this model, which is suggested by the so-called hybrid model of electron solvation previously described for methanol, can satisfactorily account for electron solvation in all polar liquids, including linear alcohols (methanol to decanol), 1,2-ethanediol, H2O, and D2O, for which data are available from the literature. A close similarity is indeed obtained between our calculated values of τs and those measured experimentally. The observation of such a correlation supports a universal concept of electron solvation. Keywords: polar liquids, electron solvation time, solvent dielectric relaxation times, universal concept of electron solvation.
Solubility of anthracene in binary alcohol + alkoxyalcohol solvent mixtures. Comparison of observed versus predicted values based upon Mobile Order theory
Authors: McHale Mary E.R. , Coym Karen S. , Roy Lindsay E. , Hernández Carmen E. , Acree Jr. William E.
Published: May 2006

Experimental solubilities are reported for anthracene dissolved in eight binary mixtures containing 2-isopropoxyethanol with 1-propanol, 2-propanol, 1-butanol, 2-butanol, 1-pentanol, 2-pentanol, 3-methyl-1-butanol, and 1-octanol at 25 °C. Results of these measurements, along with previously published solubility data for anthracene in binary alcohol + alkoxyalcohol (2-methoxyethanol, 2-ethoxyethanol, 2-propoxyethanol, 2-butoxyethanol, 3-methoxy-1-butanol) solvent mixtures, are used to test the limitations and applications of expressions derived from Mobile Order theory. For the 50 different binary solvent systems considered, the derived expressions were found to provide reasonably accurate predictions for the observed anthracene solubility behavior, with the average absolute deviation between measured and predicted values being on the order of 3% or less. A single numerical value of Keq = 5000 cm3 mol−1 was assumed for all self-association and cross-association hydrogen-bond stability constants. Keywords: anthracene solubilities, alcohol solvents, solubility predictions, hydrogen-bonding, model.
Thermodynamics of mixtures containing the CO and OH groups. I. Estimation of the DISQUAC interchange coefficients for 1-alkanol + n-alkanone systems
Authors: González Juan Antonio
Published: May 2006

1-Alkanol + n-alkanone mixtures are treated in terms of the DISQUAC group contribution model, reporting the interaction parameters for hydroxyl–carbonyl contacts. The quasichemical interchange coefficients are independent of the compounds in the mixture; the dispersive interchange coefficients depend on the intramolecular environment of the hydroxyl and (or) carbonyl groups. Mixtures of a given 1-alkanol with isomeric ketones are characterized by the same first dispersive interaction parameter, which is constant from 2-pentanone. This type of system, when including an alcohol up to 1-pentanol, needs different dispersive enthalpic parameters depending on the symmetry of the ketone. In this case, such parameters are constant from 2-pentanone or 3-pentanone. A detailed comparison is presented between DISQUAC results and data available in the literature on vapour–liquid equilibria, VLE (including azeotropic data), molar Gibbs energies, GE, molar excess enthalpies, HE, solid–liquid equilibria, SLE, natural logarithms of activity coefficients, In [Formula: see text] and partial molar excess enthalpies at infinite dilution,[Formula: see text]. For 54 systems, the mean relative standard deviation in pressure is 0.018; for 61 systems, this magnitude in the case of the HE is 0.059. It is noteworthy that the model yields good predictions over a very wide range of temperature for VLE and SLE. HE is also reasonably well represented at different temperatures. Larger discrepancies are encountered, as usual, for partial molar quantities at infinite dilution. Keywords: liquids, mixtures, thermodynamic properties, group contributions.
Influence of adsorption of organic compounds and surface heterogeneity on the hydrogen evolution reaction
Authors: Lasia Andrzej
Published: May 2006

The hydrogen evolution reaction on rough or porous surfaces often leads to low Tafel slopes that cannot be explained in terms of the Volmer–Heyrovsky–Tafel mechanism. In addition, adsorption of organic compounds and ions causes an increase in the Tafel slopes. To explain such behavior, a concept of distribution of adsorption energies on heterogeneous surfaces, leading to a distributed kinetics, was studied. Simulations of the dependence of the current and the surface coverage by adsorbed hydrogen on overpotential are presented for different values of the kinetic parameters in the absence and presence of the adsorbed foreign substances. These results were compared with those obtained using the Frumkin/Temkin adsorption isotherm. It was found that for some kinetic parameters and a flat distribution of adsorption energies, low Tafel slopes, similar to those observed experimentally, are obtained. Keywords: hydrogen evolution, adsorption, heterogeneous surfaces, distributed kinetics, Frumkin/Temkin isotherm.
SERS studies of monoprotonated pyrazine (pyrazinium) cations adsorbed onto positively charged silver electrodes
Authors: Brolo A.G. , Irish D.E.
Published: May 2006

The surface-enhanced Raman scattering (SERS) spectra of monoprotonated pyrazine cations adsorbed on silver electrodes have been measured. The molecular orientation of the pyrazinium cation is dependent on the electrode potential. At potentials more positive than −170 mV the monoprotonated pyrazine is adsorbed end-on. However, the spectral features suggest a flat orientation as the potential becomes more negative than −300 mV. Monoprotonated pyrazine cations with both orientations can coexist at potentials between these limits. The adsorption of the positive ion to a positively charged electrode is mediated by specifically adsorbed bromide ions. Keywords: SERS; monoprotonated pyrazine cation, silver electrode, pyrazinium.
Response of the EQCM to specific adsorption on gold electrodes: adsorption of pyridine and benzene
Authors: Zilberman Galit , Tsionsky Vladimir , Gileadi Eliezer
Published: May 2006

The electrochemical quartz crystal microbalance (EQCM) is used to study adsorption of pyridine and benzene on gold. The most important result observed is that thefrequencyincreaseswhentheorganicmoleculeisadsorbed, namely, the total mass of the species rigidly adsorbed is reduced as a result of adsorption. This is consistent with the accepted idea that electrosorption is a replacement reaction, in which a number of water molecules are replaced from the interface for each organic molecule adsorbed. However, this is the first time, to the best of our knowledge, that it has been observed experimentally. If the number of water molecules desorbed to make place for one molecule of pyridine is larger than 4.4, a decrease in mass should be observed. When independent data on the dependence of surface coverage on potential is available, this number can be estimated. In the case of pyridine, the EQCM data best fit the adsorption results if each molecule is assumed to replace 10–12 water molecules. In the case of benzene a similar calculation could not be performed since there are no adsorption data collected under comparable experimental conditions. Nevertheless, a positive shift of frequency is observed, indicating that this number must be >4.4. Keywords: electrochemical quartz crystal microbalance, electrical double layer, gold, pyridine, benzene.
Hydrous Ir oxide films: the mechanism of the anodic prepeak reaction
Authors: Birss V.I. , Bock C , Elzanowska H.
Published: May 2006

The origin and significance of the anodic prepeak (peak A0), seen in cyclic voltammetric studies of hydrous Ir oxide films in acidic solution just prior to the large Ir(III)/(IV) redox peaks (A1/C1), has been examined in this work. By also studying only very thin films, a corresponding cathodic feature (peak C0) has also been identified. The pH dependence of the A0/C0 peaks, assumed to also depict the Ir(III)/(IV) process, has been examined in sulfuric acid solutions, indicating that a ca. −80 mV shift per pH unit applies to this reaction. By also taking into consideration the measured in situ mass changes as the potential is scanned through the A0/C0 peaks, it is shown that these peaks are associated with a greater involvement of anions and more extensive water exchange than is the reaction in the main A1/C1 peaks. Other results also indicate that the film sites that react in the A0/C0 peaks are located deep within the oxide film, likely near the Ir – oxide film interface. Keywords: Ir oxide, hydrous oxide films, cyclic voltammetry, quartz crystal microbalance (QCMB), prepeak, pH dependence, electrochemistry.
Thermodynamic properties of ternary mixtures containing nitrobenzene
Authors: Sharma V.K. , Kalra Khem Chand , Katoch A.
Published: May 2006

Molar excess volumes, [Formula: see text], and molar excess enthalpies, [Formula: see text], of nitrobenzene (i) + benzene (j) + cyclohexane (k), nitrobenzene (i) + benzene (j) + n-hexane (k), and nitrobenzene (i) + benzene (j) + n-heptane (k) ternary mixtures have been determined dilatometrically and calorimetrically as a function of composition at 298.15 K. The data have been analyzed in terms of (i) the graph-theoretical approach and (ii) Flory's Theory. It has been observed that [Formula: see text], data calculated by graph theoretical as well as Flory's approach compare well with their corresponding experimental values. Keywords: molar excess volumes, molar excess enthalpies, specific interactions, molar volume interaction parameter, molar interaction enthalpy parameter.
Selective aromatic chlorination of activated arenes with sodium chlorite, (salen)manganese(III) complex, and alumina in dichloromethane
Authors: Hirano Masao , Yakabe Shigetaka , Monobe Hiroyuki , Morimoto Takashi
Published: May 2006

The reaction of alkyl phenyl ethers with sodium chlorite in dichloromethane in the presence of a (salen)manganese(III) complex and alumina preloaded with a small amount of water afforded monochlorination products with unusually high para selectivities under mild conditions. The NaClO2-based biphasic system can also be successfully used for the regioselective monochlorination of substituted anisoles and polymethoxybenzenes. Keywords: aromatic chlorination, alkyl aryl ethers, sodium chlorite, (salen)manganese(III) complex, alumina.
BIOPHYSICAL AND PHENOMENOLOGICAL MODELS OF MULTIPLE SPIKE INTERACTIONS IN SPIKE-TIMING DEPENDENT PLASTICITY
Authors: BADOUAL MATHILDE , ZOU QUAN , DAVISON ANDREW P. , RUDOLPH MICHAEL , BAL THIERRY , FRÉGNAC YVES , DESTEXHE ALAIN
Published: May 2006

Spike-timing dependent plasticity (STDP) is a form of associative synaptic modification which depends on the respective timing of pre- and post-synaptic spikes. The biophysical mechanisms underlying this form of plasticity are currently not known. We present here a biophysical model which captures the characteristics of STDP, such as its frequency dependency, and the effects of spike pair or spike triplet interactions. We also make links with other well-known plasticity rules. A simplified phenomenological model is also derived, which should be useful for fast numerical simulation and analytical investigation of the impact of STDP at the network level.
SPATIO-TEMPORAL MODELING AND ANALYSIS OF fMRI DATA USING NARX NEURAL NETWORK
Authors: LUO HUAIEN , PUTHUSSERYPADY SADASIVAN
Published: May 2006

This paper presents spatio-temporal modeling and analysis methods to fMRI data. Based on the nonlinear autoregressive with exogenous inputs (NARX) model realized by the Bayesian radial basis function (RBF) neural networks, two methods (NARX-1 and NARX-2) are proposed to capture the unknown complex dynamics of the brain activities. Simulation results on both synthetic and real fMRI data clearly show that the proposed schemes outperform the conventional t-test method in detecting the activated regions of the brain.
WIGHTMAN FUNCTION AND CASIMIR DENSITIES FOR ROBIN PLATES IN THE FULLING–RINDLER VACUUM
Authors: SAHARIAN A. A. , AVAGYAN R. M. , DAVTYAN R. S.
Published: May 2006

Wightman function, the vacuum expectation values of the field square and the energy–momentum tensor are investigated for a massive scalar field with an arbitrary curvature coupling parameter in the region between two infinite parallel plates moving by uniform proper acceleration. We assume that the field is prepared in the Fulling–Rindler vacuum state and satisfies Robin boundary conditions on the plates. The mode–summation method is used with a combination of a variant of the generalized Abel–Plana formula. This allows to extract manifestly the contributions to the expectation values due to a single boundary and to present the second plate-induced parts in terms of exponentially convergent integrals. Various limiting cases are investigated. The vacuum forces acting on the boundaries are presented as a sum of the self-action and "interaction" terms. The first one contains well-known surface divergences and needs a further renormalization. The "interaction" forces between the plates are investigated as functions of the proper accelerations and coefficients in the boundary conditions. We show that there is a region in the space of these parameters in which the "interaction" forces are repulsive for small distances and attractive for large distances.
THE PEREMPTORY INFLUENCE OF A UNIFORM BACKGROUND FOR TRAPPING NEUTRAL FERMIONS WITH AN INVERSELY LINEAR POTENTIAL
Authors: DE CASTRO ANTONIO S.
Published: May 2006

The problem of neutral fermions subject to an inversely linear potential is revisited. It is shown that an infinite set of bound-state solutions can be found on the condition that the fermion is embedded in an additional uniform background potential. An apparent paradox concerning the uncertainty principle is solved by introducing the concept of effective Compton wavelength.
A STUDY OF SCHISTOSOME TRANSMISSION DYNAMICS AND ITS CONTROL
Authors: DAS PRASENJIT , MUKHERJEE DEBASIS , SARKAR A. K.
Published: May 2006

This article concentrates on the study of delay effect on a model of schistosomiasis transmission with control measures such as predation or harvesting and chemotherapy. In the presence of predation or harvesting and chemotherapy, system admits multiple endemic equilibria. Mathematical analysis shows that they are opposite in nature regarding stability. One may observe switching phenomena for the unstable equilibrium by incorporating delay. The disease may be highly endemic if there is no control measure, which is obvious from the model analysis. Results obtained in this paper are also verified through numerical simulations.
EXTREMAL PRINCIPLES WITH SPECIAL EMPHASIS ON EXERGY AND ASCENDENCY — THE MODERN APPROACH IN THEORETICAL ECOLOGY
Authors: RAY SANTANU
Published: May 2006

Extremal principles or ecological orientors or goal functions are the most modern approach in theoretical ecology. There are many such principles proposed by different theoretical ecologists. In this paper, the most important extremal principles are discussed based on their theoretical backgrounds. Two widely accepted goal functions, i.e. exergy and ascendency are optimized and treated in a quantitative manner in an aquatic ecosystem model of planktonic and fish systems for their appropriateness. In the model varied body sizes of phytoplankton and zooplankton are considered. Parameter values varied according to the allometric principle with the body sizes. For self-organization of the model system two goal functions predict different results, however both are realistic.
Secular Trends in Deaths From Cardiovascular Diseases
Authors: Gerber Yariv , Jacobsen Steven J. , Frye Robert L. , Weston Susan A. , Killian Jill M. , Roger Véronique L.
Published: May 2006

Background—

Although age-adjusted cardiovascular disease (CVD) mortality has declined over the past decades, controversies remain about whether this trend was similar across locations of death and disease categories and about the existence of age and sex disparities.

Methods and Results—

We examined CVD mortality trends in Olmsted County, Minnesota, between 1979 and 2003 using the categories defined by the American Heart Association, including coronary heart disease (CHD), non-CHD diseases of the heart, and noncardiac circulatory diseases. Data on demographics, cause, and location of death of all 6378 residents who died of CVD were analyzed. Although decreases in the age-adjusted rates occurred in all groups, the magnitude of the decline varied widely. Lesser annual declines were noted in out-of-hospital than in-hospital deaths (1.8% versus 4.8%;
P
<0.001), in older than in younger persons (1.5% at age ≥85 years versus 3.9% for those ≤74 years of age;
P
<0.001), and in women relative to men (2.5% versus 3.3%;
P
=0.007). Furthermore, although CHD showed a marked annual decrease (3.3%), more modest decrements were found for non-CHD diseases of the heart (2.1%) and noncardiac circulatory diseases (2.4%) (
P
=0.02 and
P
=0.04 for the comparison with CHD decline, respectively).

Conclusions—

Over the past 25 years, CVD mortality declined markedly in the community, but there were large disparities in the magnitude of the decline, resulting in a shift in the distribution toward out-of-hospital and non-CHD deaths. Further reduction in CVD mortality will require strategies directed at elderly persons and women, in whom out-of-hospital rates have improved only minimally.
Chemokine CXCL10 Promotes Atherogenesis by Modulating the Local Balance of Effector and Regulatory T Cells
Authors: Heller Eric A. , Liu Emerson , Tager Andrew M. , Yuan Qian , Lin Alexander Y. , Ahluwalia Neil , Jones Krister , Koehn Stephanie L. , Lok Vincent M. , Aikawa Elena , Moore Kathryn J. , Luster Andrew D. , Gerszten Robert E.
Published: May 2006

Background—

Studies to define the overall contribution of lymphocytes to lesion formation in atherosclerosis-susceptible mice have demonstrated relatively subtle effects; the use of lymphocyte-deficient mice, however, compromises both the effector and regulatory arms of the immune system. Here, we tested the hypothesis that deletion of CXCL10 (IP-10), a chemokine specific for effector T cells that has been localized within atherosclerotic lesions, would significantly inhibit atherogenesis.

Methods and Results—

Compound deficient
Apoe
−/−
/
Cxcl10
−/−
mice fed a Western-style diet for either 6 or 12 weeks demonstrated significant reductions in atherogenesis as compared with
Apoe
−/−
controls, as assessed by both aortic en face and cross-sectional analyses. Immunohistochemical studies revealed a decrease in the accumulation of CD4
+
T cells, whereas quantitative polymerase chain reaction analysis of lesion-rich aortic arches demonstrated a marked reduction in mRNA for CXCR3, the CXCL10 chemokine receptor. Although overall T-cell accumulation was diminished significantly, we found evidence to suggest that regulatory T-cell (T
reg
) numbers and activity were enhanced, as assessed by increased message for the T
reg
-specific marker Foxp3, as well as increases in immunostaining for the T
reg
-associated cytokines interleukin-10 and transforming growth factor-β1. We also documented naturally occurring T
reg
cells in human atherosclerotic lesions.

Conclusions—

We provide novel evidence for a functional role for the effector T-cell chemoattractant CXCL10 in atherosclerotic lesion formation by modulating the local balance of the effector and regulatory arms of the immune system.
Incremental Analysis Updates Initialization Technique Applied to 10-km MM5 and MM5 3DVAR
Authors: Lee Mi-Seon , Kuo Ying-Hwa , Barker Dale M. , Lim Eunha
Published: May 2006

An incremental analysis updates (IAU) technique is implemented for 3-h updates of the fifth-generation Pennsylvania State University–NCAR Mesoscale Model (MM5) three-dimensional variational data assimilation (3DVAR) and model system with a 10-km resolution to remove spurious gravity waves. By gradually incorporating analysis increments, IAU affects only the removal of high frequencies, leaving the waves related to diurnal processes. IAU appears to be efficient in reducing the moisture spinup problem in the MM5 3DVAR cycling system. The advantage of the IAU is the most significant in improving precipitation forecasts. Rapid update cycle (RUC) with 1- and 2-h intervals in conjunction with the IAU indicates a rapid minimization and less spinup and -down problems because of greater balancing between the moisture and dynamic variables. Impact studies are performed on a heavy rainfall case that occurred in the Korean Peninsula. Verification results with a 3-h cycling system are presented on operational environments.
Surface In Situ Observations within the Outflow of Forward-Flank Downdrafts of Supercell Thunderstorms
Authors: Shabbott Christopher J. , Markowski Paul M.
Published: May 2006

In the long-standing conceptual model of a supercell thunderstorm, the forward-flank downdraft (FFD) and its associated negative buoyancy originate from precipitation loading and the latent chilling of air due to the melting and evaporation of precipitation. The horizontal buoyancy gradient within the outflow of the FFD has been identified as an important source of low-level, streamwise vorticity in three-dimensional numerical simulations of supercells. These simulations have demonstrated that the formation of low-level mesocyclones is critically dependent on the baroclinic generation of horizontal vorticity within the FFD outflow.

Despite the implied dynamical importance of the FFD outflow in the evolution of supercell thunderstorms, only a very limited number of thermodynamic observations have been obtained within FFD outflow. The range of thermodynamic conditions within FFD outflow is not well known, nor is it known whether any systematic relationship exists between the thermodynamic characteristics of FFD outflow and the intensity of low-level mesocyclones and/or tornadogenesis. In this paper, in situ observations obtained at the ground by a mobile mesonet within FFD outflow are used to investigate whether any relationship exists between the thermodynamic characteristics of the outflow and low-level mesocyclogenesis and/or tornadogenesis. The data were obtained within both tornadic and nontornadic supercells (12 cases total) during the Verification of the Origins of Rotation in Tornadoes Experiment (VORTEX) from 1994 to 1995, and in smaller field campaigns during the 1997–99 period.
Virtue, Character and Situation
Authors: Webber Jonathan
Published: May 2006

Philosophers have recently argued that traditional discussions of virtue and character presuppose an account of behaviour that experimental psychology has shown to be false. Behaviour does not issue from global traits such as prudence, temperance, courage or fairness, they claim, but from local traits such as sailing-in-rough-weather-with-friends-courage and office-party-temperance. The data employed provides evidence for this view only if we understand it in the light of a behaviourist construal of traits in terms of stimulus and response, rather than in the light of the more traditional construal in terms of inner events such as inclinations. More recent experiments have shown this traditional conception to have greater explanatory and predictive power than its behaviourist rival. So we should retain the traditional conception, and hence reject the proposed alteration to our understanding of behaviour. This discussion has further implications for future philosophical investigations of character and virtue.
Correction of scaling mismatches in oligonucleotide microarray data
Authors: Barenco Martino , Stark Jaroslav , Brewer Daniel , Tomescu Daniela , Callard Robin , Hubank Michael
Published: May 2006

Background

Gene expression microarray data is notoriously subject to high signal variability. Moreover, unavoidable variation in the concentration of transcripts applied to microarrays may result in poor scaling of the summarized data which can hamper analytical interpretations. This is especially relevant in a systems biology context, where systematic biases in the signals of particular genes can have severe effects on subsequent analyses. Conventionally it would be necessary to replace the mismatched arrays, but individual time points cannot be rerun and inserted because of experimental variability. It would therefore be necessary to repeat the whole time series experiment, which is both impractical and expensive.

Results

We explain how scaling mismatches occur in data summarized by the popular MAS5 (GCOS; Affymetrix) algorithm, and propose a simple recursive algorithm to correct them. Its principle is to identify a set of constant genes and to use this set to rescale the microarray signals. We study the properties of the algorithm using artificially generated data and apply it to experimental data. We show that the set of constant genes it generates can be used to rescale data from other experiments, provided that the underlying system is similar to the original. We also demonstrate, using a simple example, that the method can successfully correct existing imbalancesin the data.

Conclusion

The set of constant genes obtained for a given experiment can be applied to other experiments, provided the systems studied are sufficiently similar. This type of rescaling is especially relevant in systems biology applications using microarray data.
Derivation of species-specific hybridization-like knowledge out of cross-species hybridization results
Authors: Bar-Or Carmiya , Bar-Eyal Meira , Gal Tali Z , Kapulnik Yoram , Czosnek Henryk , Koltai Hinanit
Published: May 2006

Background

One of the approaches for conducting genomics research in organisms without extant microarray platforms is to profile their expression patterns by using Cross-Species Hybridization (CSH). Several different studies using spotted microarray and CSH produced contradicting conclusions in the ability of CSH to reflect biological processes described by species-specific hybridization (SSH).

Results

We used a tomato-spotted cDNA microarray to examine the ability of CSH to reflect SSH data. Potato RNA was hybridized to spotted cDNA tomato and potato microarrays to generate CSH and SSH data, respectively. Difficulties arose in obtaining transcriptomic data from CSH that reflected those obtained from SSH. Nevertheless, once the data was filtered for those corresponding to matching probe sets, by restricting proper cutoffs of probe homology, the CSH transcriptome data showed improved reflection of those of the SSH.

Conclusions

This study evaluated the relative performance of CSH compared to SSH, and proposes methods to ensure that CSH closely reflects the biological process analyzed by SSH.
Radiosensitizers in cervical cancer. Cisplatin and beyond
Authors: Candelaria Myrna , Garcia-Arias Alicia , Cetina Lucely , Dueñas-Gonzalez Alfonso
Published: May 2006

Cervical cancer continues to be a significant health burden worldwide. Globally, the majority of cancers are locally advanced at diagnosis; hence, radiation remains the most frequently used therapeutical modality. Currently, the value of adding cisplatin or cisplatin-based chemotherapy to radiation for treatment of locally advanced cervical cancer is strongly supported by randomized studies and meta-analyses. Nevertheless, despite these significant achievements, therapeutic results are far from optimal; thus, novel therapies need to be assayed. A strategy currently being investigated is the use of newer radiosensitizers alone or in combination with platinum compounds. In the present work, we present preclinical information on known and newer cytotoxic agents as radiosensitizers on cervical cancer models, as well as the clinical information emanating from early phase trials that incorporate them to the cervical cancer management. In addition, we present the perspectives on the combined approach of radiation therapy and molecular target-based drugs with proven radiosensitizing capacity.
Influence of metabolic network structure and function on enzyme evolution
Authors: Vitkup Dennis , Kharchenko Peter , Wagner Andreas
Published: May 2006

Background

Most studies of molecular evolution are focused on individual genes and proteins. However, understanding the design principles and evolutionary properties of molecular networks requires a system-wide perspective. In the present work we connect molecular evolution on the gene level with system properties of a cellular metabolic network. In contrast to protein interaction networks, where several previous studies investigated the molecular evolution of proteins, metabolic networks have a relatively well-defined global function. The ability to consider fluxes in a metabolic network allows us to relate the functional role of each enzyme in a network to its rate of evolution.

Results

Our results, based on the yeast metabolic network, demonstrate that important evolutionary processes, such as the fixation of single nucleotide mutations, gene duplications, and gene deletions, are influenced by the structure and function of the network. Specifically, central and highly connected enzymes evolve more slowly than less connected enzymes. Also, enzymes carrying high metabolic fluxes under natural biological conditions experience higher evolutionary constraints. Genes encoding enzymes with high connectivity and high metabolic flux have higher chances to retain duplicates in evolution. In contrast to protein interaction networks, highly connected enzymes are no more likely to be essential compared to less connected enzymes.

Conclusion

The presented analysis of evolutionary constraints, gene duplication, and essentiality demonstrates that the structure and function of a metabolic network shapes the evolution of its enzymes. Our results underscore the need for systems-based approaches in studies of molecular evolution.
Interpreting Disparate Responses to Cancer Therapy: The Role of Human Population Genetics
Authors: Maitland Michael L. , DiRienzo Anna , Ratain Mark J.
Published: May 2006

Increasingly, investigators are recognizing differences in tumor biology, drug metabolism, toxicity, and therapeutic response among different patient populations receiving anticancer agents. These observations provide exciting opportunities to identify the factors most important for predicting individual variability in pharmacologically relevant phenotypes and consequently for personalizing the delivery of cancer therapy. Although pharmacogenomic differences may explain some of these disparities, rigorous investigation of both genetic and nongenetic differences is important to identify the variables most important for optimal selection and dosing of treatment for an individual patient. For example, pharmacogenetic tests currently used in cancer therapy, such as genotyping UGT1A1 to reduce the incidence of severe toxicity of irinotecan and sequencing epidermal growth factor receptor from tumors to identify somatic mutations conferring sensitivity to tyrosine kinase inhibitors, were developed without initial identification of interpopulation differences. Although interpopulation variability in toxicity and efficacy of these agents has been observed, the basis for these population differences remains only partially explained. Here, we review concepts of human population genetics to inform interpretations of disparate drug effects of cancer therapy across patient populations. Understanding these principles will help investigators better design clinical trials to identify the variables most relevant to subsequent individualization of a cancer therapy.
Ethnic Differences in Response to Epidermal Growth Factor Receptor Tyrosine Kinase Inhibitors
Authors: Calvo Emiliano , Baselga José
Published: May 2006

The identification of somatic mutations in the tyrosine kinase domain of the epidermal growth factor receptor (EGFR) in non–small-cell lung cancer (NSCLC) and their correlation with response to EGFR inhibitors has become an important event in the fields of cancer genetics and therapeutics. The initial observation of a higher response to gefitinib and erlotinib in patients of Asian origin was followed by the discovery that they harbor more frequent EGFR mutations in NSCLC; this raises the issue of ethnic diversity in the pathogenesis of given tumors. In a similar fashion, amplification of the closely related HER2 gene, which could also have implications for the treatment of NSCLC, is also more frequent in East Asian patients. On the other hand, EGFR gene amplification may be more prevalent in Western populations. The implication of these findings is that ethnicity may indicate different genetic backgrounds in common tumors that may influence clinical outcome and response to therapy. Therefore, in clinical trials with tyrosine kinase inhibitors and other molecular-targeted therapies, the inclusion of a global population appears to be required.
Thermal and Ferroelectric Properties of Chiral Liquid-Crystalline Polytartrate
Authors: Ujiie Seiji , Iimura Kazuyoshi
Published: May 2006

Chiral liquid-crystalline polytartrate (LCPTT) with 2R,3R-(+)-tartrate moiety in the skeletal main chain and two mesogenic pendant groups in the repeating unit was prepared. Thermal and ferroelectric properties of LCPTT were dependent on those of the chiral structure. LCPTT exhibited cholesteric and smectic C* phases. The mode value of the spontaneous polarization was 5 mC/m2.
Samarium Diiodide-Promoted Reductive Coupling of Imines
Authors: Imamoto Tsuneo , Nishimura Seijiro
Published: May 2006

Aromatic aldimines are reductively coupled to 1,2-diamines by treatment with samarium diiodide. Cross-coupling of aromatic ketimines with ketones to 2-aminoalcohols is also promoted by the same reagent.
Diphosphonium Salts as Effective Reagents for Stereoselective Synthesis of 1,2-cis-Ribofuranosides
Authors: Mukaiyama Teruaki , Suda Shinji
Published: May 2006

1,2-cis-Ribofuranosides are stereoselectively synthesized in high yields directly from 1-hydroxy sugars and alcohols or trimethylsilylated nucleophiles by the use of diphosphonium salts as a condensation reagent.
Synthesis, Structures, and Magnetic Properties of Novel Binuclear and Mononuclear Manganese(II) Complexes with 2,6-Bis[N-(2-pyridylethyl)iminomethyl]-4-methylphenol
Authors: Mikuriya Masahiro , Fujii Toshinori , Kamisawa Satoru , Kawasaki Yasushi , Tokii Tadashi , Oshio Hiroki
Published: May 2006

Binuclear and mononuclear manganese(II) complexes with 2,6-bis[N-(2-pyridylethyl)iminomethyl]-4-methylphenol (HL), [Mn2(L)(CH3COO)2(NCS)] and [Mn(HL)(NCS)2(H2O)], have been prepared and characterized by X-ray structure analyses, magnetic susceptibilities (80–300 K), and EPR spectrum.