bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of chloride substitution on electromechanical responses in the pulmonary artery of Dahl normotensive and hypertensive rats
Authors: Bieger Detlef , Duggan Jennifer A , Tabrizchi Reza
Published: March 2004

We have investigated the in vitro interaction between chloride ions and endothelium as revealed by alterations in vascular contractility and smooth muscle cell membrane potential in isolated pulmonary arteries from Dahl salt‐resistant normotensive and salt‐sensitive hypertensive rats.

Exposure to nitro‐L‐arginine methyl ester (L‐NAME) of tissues from normotensive but not hypertensive rats augmented contractions to cirazoline. While chloride removal did not alter cirazoline‐induced contractions, it completely abolished the augmentation by L‐NAME in normotensive rats. However, in hypertensive rats, removal of chloride ions significantly attenuated contractions elicited by cirazoline, and L‐NAME effectively reversed this inhibition.

Methacholine‐induced endothelium‐dependent relaxations of the same magnitude were evident in both normotensive and hypertensive rats. However, basal cyclic GMP levels were found to be significantly higher (7.8‐fold) in blood vessels of normotensive rats compared to hypertensive rats.

The resting membrane potential in pulmonary arteries of hypertensive rats (−52.1±1.04 mV) revealed a significant hyperpolarisation when compared with that of normotensive rats (−46.4±1.58 mV). Cirazoline did not produce a significant depolarisation in blood vessels of either normotensive or hypertensive rats. Perfusion with chloride‐free solution resulted in a modest but significant hyperpolarisation (−8.0 mV) in the blood vessels of hypertensive but not in normotensive rats.

We conclude that salt‐dependent hypertension in Dahl rats is accompanied by functional and biochemical changes in low‐pressure blood vessels. These changes can, in part, be attributed to impairment in the basal, but not methacholine‐stimulated, release of nitric oxide, and to altered chloride ion handling.

British Journal of Pharmacology (2004) 141, 1068–1076. doi:10.1038/sj.bjp.0705703
Nociceptin inhibits airway microvascular leakage induced by HCl intra‐oesophageal instillation
Authors: Rouget Céline , Cui Yong Yao , D'Agostino Bruno , Faisy Christophe , Naline Emmanuel , Bardou Marc , Advenier Charles
Published: March 2004

Gastro‐oesophageal acid reflux may cause airway responses such as cough, bronchoconstriction and inflammation in asthmatic patients. Our previous results suggest that microvascular leakage induced, in the guinea‐pig airways, by intra‐oesophageal hydrochloric acid (HCl) infusion was mainly dependent on the release of tachykinins. Nociceptin, an endogenous ligand of the opioid receptor NOP, has been shown to inhibit bronchoconstriction and cough in guinea‐pig or cat by inhibiting tachykinin release.

The purpose of this study was to investigate the effects of nociceptin on the intra‐oesophageal HCl‐induced airway microvascular leakage evaluated by Evans blue dye extravasation measurement in anaesthetised guinea‐pigs pretreated with propranolol, atropine and phosphoramidon.

Infusion of intra‐oesophageal HCl led to a significant increase in plasma extravasation in the main bronchi and trachea. This increase was abolished when animals underwent a bilateral vagotomy.

Airway microvascular leakage was inhibited by nociceptin (3–30 μg kg−1 i.v.) in a dose‐dependent manner (maximal inhibition at the dose of 30 μg kg−1: 19.76±1.13 vs 90.92±14.00 ng mg−1 tissue for nociceptin and HCl infusion, respectively, in the main bronchi, P<0.01). The NOP receptor agonist [Arg14,Lys15]N/OFQ mimicked the inhibitory effect of nociceptin, but at a 10‐fold lower dose (3 μg kg−1 i.v). The NOP receptor antagonist J‐113397 had no effect on plasma protein extravasation by itself, but was able to block the inhibitory effect of nociceptin.

Morphine (1 mg kg−1) had a similar inhibitory effect as that of nociceptin. Naloxone pretreatment abolished the effect of morphine, but was enable to block the inhibitory effect of nociceptin.

Under similar conditions, nociceptin, in the previous range of concentration, was unable to counteract the airway microvascular leakage induced by substance P (SP).

These results suggest that airway plasma extravasation induced by intra‐oesophageal HCl instillation might be inhibited by specific stimulation of the NOP receptor with nociceptin. Nociceptin is likely to act at a pre‐junctional level, by inhibiting tachykinin release, since it was unable to prevent SP‐induced airway plasma extravasation.

British Journal of Pharmacology (2004) 141, 1077–1083. doi:10.1038/sj.bjp.0705704
Muscarinic M3 receptor‐dependent regulation of airway smooth muscle contractile phenotype
Authors: Gosens Reinoud , Bromhaar Mechteld M Grootte , Tonkes Annet , Schaafsma Dedmer , Zaagsma Johan , Nelemans S Adriaan , Meurs Herman
Published: March 2004

Airway smooth muscle (ASM) cells are known to switch from a contractile to a proliferative and synthetic phenotype in culture in response to serum and growth factors. Phenotype switching in response to contractile agonists, however, is poorly characterised, despite the possible relationship between ASM phenotype and airway remodelling in asthma.

To investigate the effects of muscarinic receptor stimulation on ASM phenotype, we used organ‐cultured bovine tracheal smooth muscle (BTSM) strips, in which contractile responsiveness, contractile protein expression and proliferation were measured after pretreatment with methacholine.

Long‐term methacholine pretreatment (8 days) decreased maximal contraction and sensitivity to methacholine as well as to histamine and KCl. This decrease was dose‐dependent (pEC50=5.2±0.1). Pretreatment with the highest concentration of methacholine applied (100 μM) could suppress maximal histamine‐induced contraction to 8±1% of control. In addition, contractile protein expression (myosin, actin) was downregulated two‐fold. No concomitant increase in proliferative capacity was observed.

The M3/M2 muscarinic receptor antagonist DAU 5884 (0.1 μM) completely inhibited the observed decrease in contractility. In contrast, the M2/M3 muscarinic receptor antagonist gallamine (10 μM) was ineffective, demonstrating that M2 receptors were not involved.

Pretreatment (8 days) with 60 mM KCl could mimick the strong decreases in contractility. This was completely prevented by pretreatment with verapamil (1 μM).

Regulation of contractility was not affected by protein kinase C inhibition, whereas inhibitors of phosphatidyl inositol 3‐kinase and p42/p44 mitogen activated protein kinase were partially effective.

These results show that long‐term methacholine pretreatment (8 days) induces an M3 receptor‐dependent decrease in BTSM contractility without increased proliferative capacity.

British Journal of Pharmacology (2004) 141, 943–950. doi:10.1038/sj.bjp.0705709
Anti‐inflammatory effect of diosmectite in hapten‐induced colitis in the rat
Authors: González Raquel , Sánchez de Medina Fermin , Martínez‐Augustin Olga , Nieto Ana , Gálvez Julio , Risco Severiano , Zarzuelo Antonio
Published: March 2004

Diosmectite is a natural silicate effectively used in the treatment of infectious diarrhoea. Its antidiarrhoeal properties involve adsorption of toxins and bacteria and modifications of the rheological characteristics of gastrointestinal mucus. Hence, the aim of this study was to test the intestinal anti‐inflammatory activity of diosmectite.

Diosmectite (500 mg kg−1 day−1, p.o.) was administered as a post‐treatment to rats with chronic trinitrobenzene sulphonic acid colitis. Colonic status was checked 1 and 2 weeks after colitis induction by macroscopic, histological and biochemical examination.

Diosmectite post‐treatment resulted in amelioration of the morphological signs (intestinal weight, macroscopic damage, necrosed area, histology) and biochemical markers (myeloperoxidase activity, glutathione levels, MUC2 expression, inducible nitric oxide synthase and interleukin‐1β (IL‐1β) and leukotriene B4 synthesis), as well as in the reduction of the severity of diarrhoea. The effect of the clay was comparable to that of sulphasalazine (50 mg kg−1 day−1).

Diosmectite exhibited a dose‐dependent capacity to adsorb proteins in vitro as well as a dose‐dependent inhibitory effect on the basolateral secretion of IL‐8 by lipopolysaccharide (LPS)‐stimulated HT29 cells.

Diosmectite had a dose‐dependent inhibitory effect on IL‐1β production by LPS‐stimulated THP‐1 cells.

The effect of diosmectite on MUC2 was post‐transcriptional, since mRNA levels were unaffected. However, diosmectite is able to upregulate MUC2 mRNA levels in HT29‐MTX cells.

Diosmectite has anti‐inflammatory activity administered as a post‐treatment. Possible mechanisms include adsorption of luminal antigens, increase of colonic mucin levels and possibly a direct modulatory action of cytokine production by mucosal cells.

British Journal of Pharmacology (2004) 141, 951–960. doi:10.1038/sj.bjp.0705710
Strategie risk and competitive advantage: an integrative perspective
Authors: Fiegenbaum Avi , Thomas Howard
Published: March 2004

Abstract The purpose of this paper is to investigate the important relationship between risk taking and competitive advantage. Over the last two decades, a range of theoretical frameworks, drawn from behavioral decision theory, agency theory and strategic management have examined organizational risk‐return trade‐offs. This paper develops a model for the strategic management of risk. A dynamic model of competitive strategy linking risk and competition is presented, in which strategic reference points and risk attitudes are endogenously determined and influence risk/return performance. Following Shapira's (1995) arguments that good managers take high risk but are able to reduce it over time, we highlight the relevance of managing risk taking to achieve competitive advantage and then show how risk‐seeking organizations can strategically achieve sustainable high returns at low risk.
Achieving results in an after modern context: thoughts on the role of strategizing and organizing
Authors: Løwendahl Bente R. , Revang Øivind
Published: March 2004

Abstract In the after modern context, firms have to combine two sets of scarce resources: Competencies and customers. Demanding customers and competent employees enable firms to deliver more services, a higher degree of customization, and more co‐specialized interaction between supplier and customer. Major managerial challenges result, as neither customers nor knowledge workers accept standardized solutions. Yet there are still possibilities for improved value creation through processes of strategizing and organizing.
Theoretical study of the H2 reaction with a Pt4 (111) cluster
Authors: Cruz A. , Bertin V. , Poulain E. , Benitez J. I. , Castillo S.
Published: March 2004

The Cs symmetry reaction of the H2 molecule on a Pt4 (111) clusters, has been studied using ab initio multiconfiguration self-consistent field plus extensive multireference configuration interaction variational and perturbative calculations. The H2 interaction by the vertex and by the base of a tetrahedral Pt4 cluster were studied in ground and excited triplet and singlet states (closed and open shells), where the reaction curves are obtained through many avoided crossings. The Pt4 cluster captures and activates the hydrogen molecule; it shows a similar behavior compared with other Ptn (n=1,2,3) systems. The Pt4 cluster in their lowest five open and closed shell electronic states: B23, B21, A11 3A1, A11, respectively, may capture and dissociate the H2 molecule without activation barriers for the hydrogen molecule vertex approach. For the threefolded site reaction, i.e., by the base, the situation is different, the hydrogen adsorption presents some barriers. The potential energy minima occur outside and inside the cluster, with strong activation of the H–H bond. In all cases studied, the Pt4 cluster does not absorb the hydrogen molecule.
A rotational study of laser ablated thiourea
Authors: Lesarri Alberto , Mata Santiago , Blanco Susana , López Juan C. , Alonso José L.
Published: March 2004

A laser ablation device in combination with a molecular beam Fourier-transform microwave spectrometer has allowed the observation of the rotational spectrum of solid thiourea for the first time. The sensitivity reached in the experiment allowed the observation of the isotopomers S34, C13, and N15 in their natural abundance. The spectrum of D4-thiourea was also analyzed from an enriched sample. The complicated hyperfine structure arising from the presence of two N14 quadrupolar nuclei has been fully resolved and analyzed. The substitution rs structure has been derived from the experimental moments of inertia. Thiourea in gas phase presents a planar heavy atom skeleton. Experimental inertial defect values and high-level ab initio calculations reveal that the amino groups hydrogen atoms lie out-of-plane with a C2 symmetry configuration and are involved in large amplitude inversion motions.
Existence of Gibbs state for continuous gas with many-body interaction
Authors: Kutoviy O. V. , Rebenko A. L.
Published: March 2004

A continuous infinite system of point particles interacting via finite-range many-body potentials of superstable type is considered in the framework of classical statistical mechanics. We prove that for any temperature and chemical activity there exists at least one Gibbs state.
Variational approach to the problem of the energy spectrum of surface electrons over a liquid helium film
Authors: Sokolov S. S.
Published: March 2004

The energies of the first two subbands are calculated, within a variational approach, for electrons localized over the surface of a liquid helium film covering a solid substrate. The results are obtained for arbitrary value of the dielectric constant of the solid substrate, covering both the limit of a substrate with a dielectric constant close to unity (such as a rare gas solid) and a metal. The results for the subband energies in the case of a metallic substrate are compared with those obtained previously by a different method by Gabovich, Ilchenko, and Pashitskiı̆. The agreement is rather good, supporting the applicability of the variational method for calculating the energy spectrum of surface electrons in a wide range of substrate parameters.
Magnetic phase diagram of the manganites Bi1−xSrxMnO3
Authors: Mantytskaya O. S. , Troyanchuk I. O. , Chobot A. N. , Szymczak H.
Published: March 2004

An experimental study of the crystal structure and the magnetic and elastic properties of the manganites Bi1−xSrxMnO3 is carried out. The following phase transformations are found: ferromagnet (x<0.15)–spin glass (0.15⩽x⩽0.25)–charge-ordered antiferromagnet (0.35⩽x⩽0.8). The ferromagnetic state corresponds to ordering of the orbitals of the Mn3+ ions. It is assumed that the orbitally disordered phase is not realized in the Bi1−xSrxMnO3 system in the concentration interval 0.15⩽x⩽0.35. Samples with 0.25⩽x⩽0.8 undergo a first-order transition of the crystal structure, attributed to ordering of the Mn3+ and Mn4+ ions in the ratios 1:1 (x⩽0.6) and 1:3 (x⩾0.7). The antiferromagnetic charge-ordered and spin glass phases coexist in samples with 0.25<x<0.35, possibly because of the martensitic character of the charge order–disorder phase transformation. A hypothetical magnetic phase diagram is constructed.
On the quantum oscillations of the sound attenuation coefficient in layered conductors
Authors: Kirichenko O. V. , Peschansky V. G. , Krstovska D.
Published: March 2004

The attenuation of a transverse sound wave in a layered conductor with a quasi-two-dimensional dispersion relation of the charge carriers in a quantizing magnetic field is considered. The oscillatory dependence of the sound attenuation coefficient on the inverse magnetic field is analyzed, and the role of Joule losses in the absorption of energy from the sound wave by electrons is ascertained for different orientations of the magnetic field with respect to the plane of the layers.
Thermoelectric effects in layered conductors in magnetic field
Authors: Galbova O. , Ivanovski G. , Krstovska D.
Published: March 2004

The magnetic-field dependence of the thermopower in layered conductors with a quasi-two-dimensional electron energy spectrum of arbitrary form is investigated theoretically. It is shown that the dependence of the thermopower on the magnitude and orientation of the magnetic field with respect to the layers contains detailed information about the velocity distribution of the charge carriers on the Fermi surface.
Phase transitions in the magnetoelastic crystals CsDy1−xGdx(MoO4)2
Authors: Zvyagina G. A. , Fil’ V. D. , Kharchenko Yu. N. , Nesterenko N. M.
Published: March 2004

Based on the data of ultrasonic studies and on the temperature behavior of the absorption spectra, a study of the phase diagram of the crystals CsDy1−xGdx(MoO4)2 is made and the structural distortions occurring as a result of the pseudo-Jahn–Teller effect are discussed. It is shown that in the presence of impurities there are several lines of phase transitions on the x–T phase diagram. It is established that one of the phase transitions these found is essentially of a magnetoelastic origin.
Oscillations of the elastic superstructure formed by a lattice of screw dislocations
Authors: Kosevich A. M.
Published: March 2004

The equations of small oscillations of a dislocation lattice formed by a periodic system of parallel rectilinear screw dislocations are formulated. The stability of such a lattice is discussed, and it is shown that it brings about a corresponding spontaneous twisting of a crystalline sample. The long-wavelength collective oscillations of an isotropic elastic medium containing a dislocation lattice are described, among which are some which resemble plasma oscillations in a system of electric charges. The dispersion relations are obtained for five branches of oscillations, corresponding to the five degrees of freedom of the system under study (three degrees of freedom for displacements of the medium and two corresponding to bending oscillations of the dislocations). The possibility of observing the resonance frequency in the oscillation spectrum near the analog of the plasma frequency is pointed out.
The determination of all syzygies for the dependent polynomial invariants of the Riemann tensor. I. Pure Ricci and pure Weyl invariants
Authors: Lim A. E. K. , Carminati J.
Published: March 2004

In this paper, we shall consider all pure Ricci and pure Weyl scalar invariants of any degree, in a four-dimensional Lorentzian space. We present a general graph-theoretic based reduction algorithm which decomposes, using syzygies, any pure invariant in terms of the independent base invariants {r1,r2,r3} or {w1,w2} [E. Zakhary and J. Carminati, J. Math. Phys. 42, 1474 (2001)].
Decoherence in a two-particle model
Authors: Dürr Detlef , Figari Rodolfo , Teta Alessandro
Published: March 2004

We consider a simple one-dimensional quantum system consisting of a heavy and a light particle interacting via a point interaction. The initial state is chosen to be a product state, with the heavy particle described by a coherent superposition of two spatially separated wave packets with opposite momentum and the light particle localized in the region between the two wave packets. We characterize the asymptotic dynamics of the system in the limit of small mass ratio, with an explicit control of the error. We derive the corresponding reduced density matrix for the heavy particle and explicitly compute the (partial) decoherence effect for the heavy particle induced by the presence of the light one for a particular set up of the parameters.
Spectral properties of a short-range impurity in a quantum dot
Authors: Brüning J. , Geyler V. , Lobanov I.
Published: March 2004

The spectral properties of the quantum mechanical system consisting of a quantum dot with a short-range attractive impurity inside the dot are studied in the zero-range limit. The Green function of the system is obtained in an explicit form. In the case of a spherically symmetric quantum dot, the dependence of the spectrum on the impurity position and strength of the impurity potential is analyzed in detail. The recovering of the confinement potential of the dot from the spectroscopy data is proven; the consequences of the hidden symmetry breaking by the impurity are considered. The effect of the positional disorder is analyzed.
Disentangling density and temperature effects in the viscous slowing down of glassforming liquids
Authors: Tarjus G. , Kivelson D. , Mossa S. , Alba-Simionesco C.
Published: March 2004

We present a consistent picture of the respective role of density (ρ) and temperature (T) in the viscous slowing down of glassforming liquids and polymers. Specifically, based in part upon a new analysis of simulation and experimental data on liquid ortho-terphenyl, we conclude that a zeroth-order description of the approach to the glass transition (in the range of experimentally accessible pressures) should be formulated in terms of a temperature-driven super-Arrhenius activated behavior rather than a density-driven congestion or jamming phenomenon. The density plays a role at a quantitative level, but its effect on the viscosity and the α-relaxation time can be simply described via a single parameter, an effective interaction energy that is characteristic of the high-T liquid regime; as a result, ρ does not affect the “fragility” of the glassforming system.
Quantum-mechanical scattering in exterior domains with impenetrable periodic boundaries and short-range potentials
Authors: Sáenz A. W.
Published: March 2004

We study the scattering of a nonrelativistic particle in an exterior domain (=open connected subset) Ω⊂Rν(ν⩾2) containing a half-space and contained in another half-space, and having an impenetrable periodic boundary ∂Ω. “Impenetrable” means that (generalized) homogeneous Dirichlet conditions are imposed on ∂Ω. We prove the existence and completeness of the wave operators W±=limt→±∞ exp(itH1)P exp(−itH0) corresponding to the scattering of a nonrelativistic particle in Ω by the combined effect of the boundary and a short-range potential present in Ω. Here H0=−Δ is the negative distributional Laplacian in the Hilbert space H0=L2(Rν), H1=−ΔD(Ω)+V, ΔD(Ω) being the Dirichlet Laplacian in the Hilbert space H=L2(Ω), V an operator of multiplication in ℋ by a bounded measurable function V(x) on Ω having the periodicity of the boundary, and P:H0→H an identification operator. The operators W± model the quantum-mechanical scattering of low-energy atoms by crystal surfaces, with V modeling the interaction between the incident particles and the surface atoms. This interaction is idealized by assuming that V(x) depends solely on xν when xν>a, a being a sufficiently large positive constant, and xν the component of x∈Rν directed perpendicularly to the surfaces of the above two half-spaces. Under this and other hypotheses on Ω and V stated precisely in the paper, we prove that W± exist as partially isometric operators whose initial sets have a transparent physical meaning. Moreover, we prove the following: (a) Ran W±=Hscatt; and (b) W± are asymptotically complete, in the sense that H=Hscatt⊕Hsurf. Here Hscatt and Hsurf are suitably defined subspaces of scattering and surface states of ℋ. These results are proved by using direct-integral techniques, asymptotic methods from the theory of ODEs, and methods analogous to those of Lyford. The present paper generalizes an earlier one by the author for the case V=0.
The investigation of spin–orbit effect for the F(2P)+HD reaction
Authors: Zhang Yan , Xie Ting-Xian , Han Ke-Li , Zhang John Z. H.
Published: March 2004

In this paper, we employ the time-dependent quantum wave packet method to study the reaction of F(2P3/2, 2P1/2) with HD on the Alexander–Stark–Werner potential energy surface. The reaction probabilities and total integral cross sections of the spin–orbit ground and excited states for the two possible products of the system are calculated. Because the reaction channel of the excited spin–orbit state is closed at the resonance energy, the resonance feature does not appear in the reaction probabilities and cross section for the F(2P1/2)+HD(v=j=0)→HF+D reaction, in contrast with that found for the ground spin–orbit state. We also compare the average cross sections of the two possible products with the experimental measurement. The resonance peak in the present average cross section for the HF+D product is slightly larger than the experimental result, but much smaller than that of the single-state calculations on the potential energy surface of Stark and Werner. It seems that the spin–orbit coupling would play a relatively important role in this reaction. Moreover, the isotope effects of the ground and excited spin–orbit states and the reactivity of the two product channels from the excited spin–orbit state are presented.
Second-order Møller–Plesset perturbation theory without basis set superposition error.  II. Open-shell systems
Authors: Salvador P. , Mayer I.
Published: March 2004

The basis set superposition error-free second-order Møller–Plesset perturbation theory of intermolecular interactions, based on the “chemical Hamiltonian approach,” which has been introduced in Part I, is applied here to open-shell systems by using a new, effective computer realization. The results of the numerical examples considered (CH4…HO, NO…HF) showed again the perfect performance of the method. Striking agreement has again been found with the results of the a posteriori counterpoise correction (CP) scheme in the case of large, well-balanced basis sets, which is also in agreement with a most recent formal theoretical analysis. The difficulties of the CP correction in open-shell systems are also discussed.
A state-specific approach to multireference coupled electron-pair approximation like methods: Development and applications
Authors: Chattopadhyay Sudip , Pahari Dola , Mukherjee Debashis , Mahapatra Uttam Sinha
Published: March 2004

The traditional multireference (MR) coupled-cluster (CC) methods based on the effective Hamiltonian are often beset by the problem of intruder states, and are not suitable for studying potential energy surface (PES) involving real or avoided curve crossing. State-specific MR-based approaches obviate this limitation. The state-specific MRCC (SS-MRCC) method developed some years ago [Mahapatra et al., J. Chem. Phys. 110, 6171 (1999)] can handle quasidegeneracy of varying degrees over a wide range of PES, including regions of real or avoided curve-crossing. Motivated by its success, we have suggested and explored in this paper a suite of physically motivated coupled electron-pair approximations (SS-MRCEPA) like methods, which are designed to capture the essential strength of the parent SS-MRCC method without significant sacrificing its accuracy. These SS-MRCEPA theories, like their CC counterparts, are based on complete active space, treat all the reference functions on the same footing and provide a description of potentially uniform precision of PES of states with varying MR character. The combining coefficients of the reference functions are self-consistently determined along with the cluster amplitudes themselves. The newly developed SS-MRCEPA methods are size-extensive, and are also size-consistent with localized orbitals. Among the various versions, there are two which are invariant with respect to the restricted rotations among doubly occupied and active orbitals separately. Similarity of performance of this latter and the noninvariant versions at the crossing points of the degenerate orbitals imply that the all the methods presented are rather robust with respect to the rotations among degenerate orbitals. Illustrative numerical applications are presented for PES of the ground state of a number of difficult test cases such as the model H4, H8 problems, the insertion of Be into H2, and Li2, where intruders exist and for a state of a molecule such as CH2, with pronounced MR character. Results obtained with SS-MRCEPA methods are found to be comparable in accuracy to the parent SS-MRCC and FCI/large scale CI results throughout the PES, which indicates the efficacy of our SS-MRCEPA methods over a wide range of geometries, despite their neglect of a host of complicated nonlinear terms, even when the traditional MR-based methods based on effective Hamiltonians fail due to intruders.
Ab initio molecular dynamics simulations of local structure of supercooled Ni
Authors: Jakse Noël , Pasturel Alain
Published: March 2004

We report results of first-principles molecular dynamics simulations for stable and undercooled nickel liquids. The calculated structure factors as a function of temperature are discussed with respect to recent experimental measurements. In addition, structural analysis using bonding orientational order and three-dimensional pair analysis techniques have been performed in detail and the effect of undercooling on the microstructure has been analyzed. More particularly, we show the importance of fivefold symmetry local structures.
Double excitations within time-dependent density functional theory linear response
Authors: Maitra Neepa T. , Zhang Fan , Cave Robert J. , Burke Kieron
Published: March 2004

Within the adiabatic approximation, time-dependent density functional theory yields only single excitations. Near states of double excitation character, the exact exchange–correlation kernel has a strong dependence on frequency. We derive the exact frequency-dependent kernel when a double excitation mixes with a single excitation, well separated from the other excitations, in the limit that the electron–electron interaction is weak. Building on this, we construct a nonempirical approximation for the general case, and illustrate our results on a simple model.
Calculating potentials of mean force from steered molecular dynamics simulations
Authors: Park Sanghyun , Schulten Klaus
Published: March 2004

Steered molecular dynamics (SMD) permits efficient investigations of molecular processes by focusing on selected degrees of freedom. We explain how one can, in the framework of SMD, employ Jarzynski’s equality (also known as the nonequilibrium work relation) to calculate potentials of mean force (PMF). We outline the theory that serves this purpose and connects nonequilibrium processes (such as SMD simulations) with equilibrium properties (such as the PMF). We review the derivation of Jarzynski’s equality, generalize it to isobaric–isothermal processes, and discuss its implications in relation to the second law of thermodynamics and computer simulations. In the relevant regime of steering by means of stiff springs, we demonstrate that the work on the system is Gaussian-distributed regardless of the speed of the process simulated. In this case, the cumulant expansion of Jarzynski’s equality can be safely terminated at second order. We illustrate the PMF calculation method for an exemplary simulation and demonstrate the Gaussian nature of the resulting work distribution.
Mixtures of lattice polymers with structured monomers
Authors: Buta Dorel , Freed Karl F.
Published: March 2004

The influence of monomer structure on the thermodynamic properties of lattice model polymer blends is investigated through Monte Carlo computations. The model of lattice polymers with monomer structure has been used extensively in the context of the lattice cluster theory (LCT), a thermodynamic theory for polymer mixtures in the liquid state. The Monte Carlo computations provide the first unequivocal test of the accuracy of the LCT predictions for binary mixtures of polymers with structured monomers. Four types of monomer structures are analyzed, corresponding to to the monomers of polyethylene, polypropylene, polyethylethylene, and polyisobutylene (PIB). Most computations use chains with M=12 and 24 beads and the total volume fraction of the beads is φ=0.6. Both structurally symmetric and asymmetric blends are investigated. For the symmetric case, the predictions of the LCT for the energies of mixing and the liquid–liquid coexistence curves are in qualitative agreement with the Monte Carlo computations, except for the PIB/PIB symmetric blend. For structurally asymmetric blends, the LCT does not capture contributions to the energy of mixing arising solely from structural differences between the components. Computational estimates of the nonideal entropy of mixing indicate that the LCT also underestimates the entropic cost of mixing chains with different structures, thus explaining some discrepancies between the theoretical and the Monte Carlo liquid–liquid coexistence curves.
Emergence of multiple tori structures in a single polyelectrolyte chain
Authors: Sakaue Takahiro
Published: March 2004

We investigated the collapsed structure of a weakly charged wormlike chain under a moderate concentration of 1:1 electrolyte solution. By assuming a torus as a grand state, we found that the size of a torus is determined by the balance between surface energy and electrostatic energy, which leads to a finite torus thickness almost independent of the chain contour length. Owing to this unique characteristic, a long charged wormlike chain forms multiple tori structure as a collapsed product, which is never seen with a neutral wormlike chain. These features were confirmed by a Monte Carlo simulation.
A reoptimization of the five-site water potential (TIP5P) for use with Ewald sums
Authors: Rick Steven W.
Published: March 2004

The five-site transferable interaction potential (TIP5P) for water [M. W. Mahoney and W. L. Jorgensen, J. Chem. Phys. 112, 8910 (2000)] is most accurate at reproducing experimental data when used with a simple spherical cutoff for the long-ranged electrostatic interactions. When used with other methods for treating long-ranged interactions, the model is considerably less accurate. With small modifications, a new TIP5P-like potential can be made which is very accurate for liquid water when used with Ewald sums, a more physical and increasingly more commonly used method for treating long-ranged electrostatic interactions. The new model demonstrates a density maximum near 4 °C, like the TIP5P model, and otherwise is similar to the TIP5P model for thermodynamic, dielectric, and dynamical properties of liquid water over a range of temperatures and densities. An analysis of this and other commonly used water models reveals how the quadrupole moment of a model can influence the dielectric response of liquid water.
Continuum singularities of a mean-field theory of collisions
Authors: Giraud B. G. , Weiguny A.
Published: March 2004

Consider a complex energy z for an N-particle Hamiltonian H and let χ be any wave packet accounting for any channel flux. The time-independent mean-field (TIMF) approximation of the inhomogeneous, linear equation (z−H)|Ψ〉=|χ〉 consists of replacing Ψ by a product or Slater determinant φ of single-particle states φi. This results, under the Schwinger variational principle, in self-consistent TIMF equations (ηi−hi)|φi〉=|χi〉 in single-particle space. The method is a generalization of the Hartree–Fock (HF) replacement of the N-body homogeneous linear equation (E−H)|Ψ〉=0 by single-particle HF diagonalizations (ei−hi)|φi〉=0. We show how, despite strong nonlinearities in this mean-field method, threshold singularities of the inhomogeneous TIMF equations are linked to solutions of the homogeneous HF equations.
Quantum indistinguishability from general representations of SU(2n)
Authors: Harrison J. M. , Robbins J. M.
Published: March 2004

A treatment of the spin-statistics relation in nonrelativistic quantum mechanics due to Berry and Robbins [Proc. R. Soc. London Ser. A 453, 1771–1790 (1997)] is generalized within a group-theoretical framework. The construction of Berry and Robbins is reformulated in terms of certain locally flat vector bundles over n-particle configuration space. It is shown how families of such bundles can be constructed from irreducible representations of the group SU(2n). The construction of Berry and Robbins, which leads to a definite connection between spin and statistics (the physically correct connection), is shown to correspond to the completely symmetric representations. The spin-statistics connection is typically broken for general SU(2n) representations, which may admit, for a given value of spin, both Bose and Fermi statistics, as well as parastatistics. The determination of the allowed values of the spin and statistics reduces to the decomposition of certain zero-weight representations of a (generalized) Weyl group of SU(2n). A formula for this decomposition is obtained using the Littlewood–Richardson theorem for the decomposition of representations of U(m+n) into representations of U(m)×U(n).
Homotopy structure of 5d vacua
Authors: Park Eun Kyung , Kwon Pyung Seong
Published: March 2004

It is shown that flat zero-energy solutions (vacua) of the 5d Kaluza–Klein theory admit a nontrivial homotopy structure generated by certain Kaluza–Klein excitations. These vacua consist of an infinite set of homotopically different space–times denoted by M5(n), among which M5(0) and M5(1) are especially identified as M4×S1 and M5, the vacuum states of the 5d Kaluza–Klein theory and the 5d general relativity, respectively (where Mk represents the k-dimensional Minkowski space).
Symmetries of the energy-momentum tensor of cylindrically symmetric static space–times
Authors: Sharif M.
Published: March 2004

We investigate matter symmetries of cylindrically symmetric static space–times. These are classified for both cases when the energy-momentum tensor is nondegenerate and also when it is degenerate. It is found that the nondegenerate energy-momentum tensor gives either three, four, five, six, seven or ten independent matter collineations in which three are isometries and the rest are proper. The worth mentioning cases are those where we obtain the group of matter collineations finite dimensional, even the energy-momentum tensor is degenerate. These are either three, four, five or ten. Some examples are constructed satisfying the constraints on the energy-momentum tensor.
On solvable potentials related to SO(2,2). II. Natanzon potentials
Authors: Baran S. A. , Kerimov G. A.
Published: March 2004

General Natanzon potentials related to the SO(2,2) group are studied. The S-matrices for systems under consideration are related to intertwining operators between Weyl equivalent most degenerate principal series representations of SO(2,2).
Supersymmetric field-theoretic models on a supermanifold
Authors: Franco Daniel H. T. , Polito Caio M. M.
Published: March 2004

We propose the extension of some structural aspects that have successfully been applied in the development of the theory of quantum fields propagating on a general space–time manifold so as to include superfield models on a supermanifold. We only deal with the limited class of supermanifolds which admit the existence of a smooth body manifold structure. Our considerations are based on the Catenacci–Reina–Teofillatto–Bryant approach to supermanifolds. In particular, we show that the class of supermanifolds constructed by Bonora–Pasti–Tonin satisfies the criteria which guarantee that a supermanifold admits a Hausdorff body manifold. This construction is the closest to the physicist’s intuitive view of superspace as a manifold with some anticommuting coordinates, where the odd sector is topologically trivial. The paper also contains a new construction of superdistributions and useful results on the wavefront set of such objects. Moreover, a generalization of the spectral condition is formulated using the notion of the wavefront set of superdistributions, which is equivalent to the requirement that all of the component fields satisfy, on the body manifold, a microlocal spectral condition proposed by Brunetti–Fredenhagen–Köhler.
Bound states in coupled guides. II. Three dimensions
Authors: Linton C. M. , Ratcliffe K.
Published: March 2004

We compute bound-state energies in two three-dimensional coupled waveguides, each obtained from the two-dimensional configuration considered in paper I [J. Math. Phys. 45, 1359–1379 (2004)] by rotating the geometry about a different axis. The first geometry consists of two concentric circular cylindrical waveguides coupled by a finite length gap along the axis of the inner cylinder, and the second is a pair of planar layers coupled laterally by a circular hole. We have also extended the theory for this latter case to include the possibility of multiple circular windows. Both problems are formulated using a mode-matching technique, and in the cylindrical guide case the same residue calculus theory as used in paper I is employed to find the bound-state energies. For the coupled planar layers we proceed differently, computing the zeros of a matrix derived from the matching analysis directly.
Laminar Flows Past Oblate Spheroids of Various Thicknesses
Authors: Rimon Yermiyahu , Lugt Hans J.
Published: March 2004

The effect of high surface curvature of bodies on a surrounding laminar flow field is studied by means of steady axisymmetric flows past oblate spheroids of various thicknesses. For vanishing Reynolds number the Oberbeck solution is discussed. For nonzero Reynolds numbers Re ≤ 100 a numerical program is used which was recently developed by Rimon. The numerical stability of this finite-difference scheme deteriorates rapidly as the oblate spheroids become very thin. For Reynolds numbers 0 and 10 two different types of flows are observed, depending on the thickness of the body: for spherelike oblate spheroids the surface pressure has a maximum at the stagnation point, whereas for disklike bodies this maximum moves toward the edge with decreasing thickness. However, for Re = 100 the maximum pressure is always at the stagnation point, no matter how thin the body is. In the limiting case of the infinitely thin disk the edge becomes a singular body point. Although this limit could not be examined for nonzero Reynolds numbers with the numerical scheme used, the trend in the behavior of the solutions as the thickness decreases is discussed. From a previous analysis of the nature of possible solutions near a singular point, it appears from the numerical results that for Re = 100 the flow is regular at the edge. Since for Re = 0 the solution is weakly singular (pressure and vorticity are infinite at the singular body point), a change in the flow characteristics must occur between Re = 0 and Re = 100.
Instability of Three-Layer Viscous Stratified Flow
Authors: Li Chin-Hsiu
Published: March 2004

Instability of plane Couette flow of three superposed layers of fluids of different viscosity between two horizontal planes is investigated. It is found that there are two modes of disturbance dominated, respectively, by the two interfaces. The flow is found to be unstable in the zero-order approximation of wavenumber α for certain values of the depth and viscosity ratios. This is owing to a sort of resonance which prevails when a free wave at the lower interface forces a free wave at the upper interface. As is known from results previously obtained, the existence of a single surface of viscosity discontinuity will cause instability. The presence of an additional surface of discontinuity may or may not be stabilizing, depending upon the values of the depth and viscosity ratios at the additional interface.
Turbulent Hydrodynamic Line Stretching: Consequences of Isotropy
Authors: Cocke W. J.
Published: March 2004

A Lagrangian formalism for treating the stretching of material line and surface elements convected with a turbulent fluid is developed, and consequences of statistical isotropy for the distribution function of the components of a tensor are derived. Incompressibility and isotropy are then used to prove rigorously that the expectation value of the logarithmic change of the length of a line element (and area of a surface element) is greater than zero. A connection between the distribution function of the velocity shear tensor and that of the symmetric time-development tensor used in the Lagrangian formalism is shown.
High-Temperature Viscosity Ratios for Hydrogen, Helium, Argon, and Nitrogen
Authors: Guevara F. A. , McInteer B. B. , Wageman W. E.
Published: March 2004

The temperature dependency of the coefficient of viscosity relative to its value at 283°K has been determined for hydrogen, helium, argon, and nitrogen at atmospheric pressure. The method used is a variation of the usual capillary viscometry scheme in that no attempt is made to obtain absolute viscosity values. The measurements provide the ratio of the viscosity of a gas at temperature T to its viscosity at the reference temperature, 283°K. The value of T ranges from 1100°K to 2150°K and is measured by a disappearing filament pyrometer. In this relative method there is cancellation of most noncontrolled experimental variables so that the measurements are of high reproducibility, ±0.1%, and apparently accuracy, ±0.4%, is limited only by the uncertainties in the international temperature scale in the optical pyrometer range. These results are higher by 3%-8% compared with the results of previous workers. However, extrapolation of lower-temperature viscosity measurements by Kestin and Leidenfrost, and more recently by DiPippo, gives excellent agreement with the values reported here.
Flow Field of a Sonic Jet Exhausting Counter to a Low-Density Supersonic Airstream
Authors: Cassanova Robert A. , Wu Ying-Chu Lin
Published: March 2004

The flow field of a sonic jet exhausting counter to a supersonic airstream has been investigated theoretically and experimentally. An inviscid analysis shows the shock layer thickness and the position of the outer and inner shocks to be a function of free stream Mach number, jet reservior pressure, free stream Pitot pressure, and orifice size. The predicted inner shock position agrees with previous data in the continuum. The experiments were conducted in a Mach 3 low-density wind tunnel at free stream Re/l == 2.9 to 31.5 per cm and p0i/p′0∞ 10 to 104. The experimental results in the transition regime show the orifice to outer shock distance is greater than the predicted inviscid value.
Flow Field behind a Shock Wave in a Low-Pressure Test Gas
Authors: Hubbard Edward W. , de Boer P. C. T.
Published: March 2004

A study is made of the two-dimensional flow field resulting from boundary-layer growth in the driven gas of a shock tube. Attention is given to circular as well as to rectangular shock tubes. Formulas that describe the axial and transverse velocity components near the shock front are developed and are evaluated numerically. The properties of the two-dimensional flow field are discussed. It is found that the flow is nearly one-dimensional at distances greater than a tube radius from the shock front. In the region near the shock front, averaging of the perturbations gives results identical to those of Mirels' quasi-one-dimensional theory. An approximate description of the entire flow field can be obtained by taking the average velocity provided by Mirels' theory, and by superimposing the two-dimensional flow pattern stretched axially so as to conform to the prescribed average. The details of the flow field provided in the present paper can, therefore, be considered a complement to Mirels' work.
Kinetic-Theoretical Studies of the Shock Wave Structure
Authors: Muraoka Katsunori , Murakami Terutosi , Ikui Takefumi
Published: March 2004

The one-dimensional, steady, neutral shock wave structure was theoretically investigated by expanding the distribution function of the Boltzmann equation in terms of the Hermite polynomials, where the downstream equilibrium distribution function is taken to be the weighting function. The resulting nonlinear coupled differential equations were numerically integrated and various thermodynamic variables were calculated; reasonable results were obtained for low (where Navier-Stokes approximations are thought to be correct) and high (where Mott-Smith treatment was seen to be appropriate) Mach numbers. The thermodynamic background of the present treatment is thoroughly discussed and criticism of various other theoretical methods is made.