bluuebunny/crossref_metadata_2025 huggingface dataset:
Crustal seismic anisotropy in central Tibet: Implications for deformational style and flow in the crust
Authors: Ozacar A. Arda , Zandt George
Published: November 2004

Receiver functions obtained at INDEPTH III stations located near the Bangong‐Nujiang suture in central Tibet display a weak Moho signal and strong P to S conversions within the first 5 s that vary systematically with back‐azimuth. A single station with representative azimuthal variations located at the sharp onset of strong SKS splitting, is modeled for both dipping layers and seismic anisotropy by using a global minimization technique. Inversion results indicate strong anisotropy (>10%) near the surface and in the middle crust separated by a south‐dipping (∼25°) layer, possibly related to the earlier phase of crustal shortening. Near‐surface anisotropy has a fabric dipping steeply southward and trending WNW‐ESE that correlates with the suture and younger strike‐slip faults. In contrast, mid‐crustal anisotropy occurs in a low‐velocity zone and has a fabric dipping gently (∼18°) northward that might be related to a well‐developed near‐horizontal rock fabric induced by crustal flow.
On the validity of the Millionshchikov quasi‐normality hypothesis for open‐ocean deep convection
Authors: Losch Martin
Published: November 2004

Data from numerical simulations of free convection in the ocean with rotation are used to explore the validity of the Millionshchikov quasi‐normality hypothesis. The parameterizations of fourth‐order moments according to a universal model proposed by Gryanik et al. are found to be far more accurate than their corresponding Gaussian parameterizations, which are based on the Millionshchikov hypothesis. The universal model is marginally improved by fitting the model parameters to the data. The present results extend previous results that discuss shallow convection in the planetary boundary layer to rotationally controlled deep convection.
Similarity and scaling in creep and load relaxation of single‐crystal halite (NaCl)
Authors: Stone Donald S. , Plookphol Thawatchai , Cooper Reid F.
Published: November 2004

This work explores the physical basis for Hart's mechanical equation of state in high‐temperature plasticity. The experiments seek to identify a possible microstructural basis for the “hardness” parameters associated with load relaxation curves. The experiments also seek to examine the microstructural basis for scaling in load relaxation data and to explore the relationship between creep and load relaxation. Constant stress creep and load relaxation tests were conducted on [100] oriented single crystals of halite at 700°C and stresses between 0.6 and 3 MPa. Load relaxation tests were performed at 400°C up to a stress level of 13 MPa. After testing, specimens were sectioned, and dislocation densities and subgrain size distributions were measured. Results at 700°C reveal that distributions of subgrain size in crystals crept at different stress levels are similar to each other; that is, they have the same shape but different average subgrain sizes depending on stress level. Hardness curves obtained from load relaxation experiments at different levels of work hardening were found to correspond to different average subgrain size. Load relaxation data from 700°C and 400°C belong to a single‐parameter family of curves, with hardness curves translating onto each other with a scaling slope m = 0.33 ± 0.05. Subgrain size distributions generated in creep are statistically identical to those from load relaxation. The hardness parameter, σ*, specified as the (apparent) high‐strain rate limit of stress in the load relaxation data, is approximately 50Gb/DI, where G is the shear modulus, b is the Burgers vector, and DI is the mean intercept subgrain diameter. During creep under constant stress the subgrain size evolves until a steady value is approached. The experimental data lend credence to Hart's interpretation that load relaxation data represent (nearly) constant “structure” with subgrain size playing the role of the structural variable.
Single‐crystal elasticity of fayalite to 12 GPa
Authors: Speziale Sergio , Duffy Thomas S. , Angel Ross J.
Published: November 2004

Single‐crystal elastic constants of a natural Fe‐rich olivine (Fe0.94Mn0.06)2SiO4 were determined by Brillouin scattering to 12.1 GPa. The aggregate bulk modulus, shear modulus, and their pressure derivatives are KS0 = 136.3 (2) GPa, G0 = 51.2 (2) GPa, (∂KS/∂P)T0 = 4.9 (1), (∂G/∂P)0 = 1.8 (1), and (∂2G/∂P2)0 = −0.11 (1) GPa−1. The numbers in parentheses are 1σ uncertainties on the last digit. Our results demonstrate that both the bulk and the shear moduli of fayalite depend on the Fe/(Fe + Mg) ratio at both ambient and high pressures. The pressure derivative of the bulk modulus is very sensitive to the Fe content of olivine, while the pressure dependences of the shear modulus of Mg‐rich and Fe‐rich compositions are comparable. The longitudinal (C11, C22, C33) and the off‐diagonal (C12, C13, C23) moduli of fayalite show a nearly linear dependence on pressure along the whole experimental pressure range. However, the shear constants C44 and C55 show a strongly nonlinear dependence on pressure starting at P > 5 GPa, more than 2 GPa above the extrapolated room temperature stability limit of fayalite. The behavior of the shear constants could be a precursor of the high‐pressure amorphization of fayalite observed at 30 to 40 GPa. C44 is the modulus that shows the strongest tendency to soften with pressure, in disagreement with previous suggestions that C55 softening could trigger the structural transition of olivine to the high‐pressure γ‐Fe2SiO4. Softening of C44 and C55 is compatible with a diffusionless mechanism of the structural α‐ to γ‐Fe2SiO4 transition.
Falcarindiol impairs the expression of inducible nitric oxide synthase by abrogating the activation of IKK and JAK in rat primary astrocytes
Authors: Shiao Young‐Ji , Lin Yun‐Lian , Sun Ya‐Hui , Chi Chih‐Wen , Chen Chieh‐Fu , Wang Chuen‐Neu
Published: November 2004

The effects of falcarindiol on the expression of inducible nitric oxide synthase (iNOS) induced by lipopolysaccharide/interferon‐γ (LPS/IFN‐γ) in rat primary astrocytes were investigated. The molecular mechanisms underlying falcarindiol that confers its effect on iNOS expression were also elucidated.

Falcarindiol abrogated the LPS/IFN‐γ‐mediated induction of iNOS by about 80%. Falcarindiol attenuated the induction of iNOS in a concentration‐dependent manner.

The inhibitory effect of falcarindiol on iNOS induction was attributable to decrease in the protein content and the mRNA level of iNOS.

Treatment with 50 μM of falcarindiol for 30 min decreased LPS/IFN‐γ‐induced nuclear factor‐κB (NF‐κB) activation by 32%.

Treatment with 50 μM of falcarindiol for 60 min diminished the LPS/IFN‐γ‐mediated activation of IκB kinase‐α (IKK‐α) and IKK‐β by 28.2 and 29.7%, respectively.

Falcarindiol modulated the nuclear translocation of signal transducer and activator of transcription 1 (Stat1) in a time‐dependent manner. Falcarindiol (50 μM) decreased the tyrosine phosphorylation of janus kinase 1 (JAK1) by 84.8% at 5 min. Falcarindiol also abrogated the tyrosine phoshorylation of JAK2 by 82.3% at 10 min.

The present study demonstrates that falcarindiol attenuated the activation of IKK and JAK contributing to the blockade of activation of NF‐κB and Stat1, thereby leading to the suppression of iNOS expression.

British Journal of Pharmacology (2005) 144, 42–51. doi:10.1038/sj.bjp.0706022
Deoxycholic acid inhibits pacemaker currents by activating ATP‐dependent K+ channels through prostaglandin E2 in interstitial cells of Cajal from the murine small intestine
Authors: Jun Jae Yeoul , Choi Seok , Chang In‐Youb , Yoon Cha Kyung , Jeong Hye‐Gwang , Kong In Deok , So Insuk , Kim Ki Whan , You Ho Jin
Published: November 2004

We investigated the role of deoxycholic acid in pacemaker currents using whole‐cell patch‐clamp techniques at 30°C in cultured interstitial cells of Cajal (ICC) from murine small intestine.

The treatment of ICC with deoxycholic acid resulted in a decrease in the frequency and amplitude of pacemaker currents and increases in resting outward currents. Also, under current clamping, deoxycholic acid produced the hyperpolarization of membrane potential and decreased the amplitude of the pacemaker potentials.

These observed effects of deoxycholic acid on pacemaker currents and pacemaker potentials were completely suppressed by glibenclamide, an ATP‐sensitive K+ channel blocker.

NS‐398, a specific cyclooxygenase‐2 (COX‐2) inhibitor, significantly inhibited the deoxycholic acid‐induced effects. The treatment with prostaglandin E2 (PGE2) led to a decrease in the amplitude and frequency of pacemaker currents and to an increase in resting outward currents, and these observed effects of PGE2 were blocked by glibenclamide.

We next examined the role of deoxycholic acid in the production of PGE2 in ICC, and found that deoxycholic acid increased PGE2 production through the induction of COX‐2 enzyme activity and its gene expression.

The results suggest that deoxycholic acid inhibits the pacemaker currents of ICC by activating ATP‐sensitive K+ channels through the production of PGE2.

British Journal of Pharmacology (2005) 144, 242–251. doi:10.1038/sj.bjp.0706074
Marketing Translation Services Internationally: Exploiting it to Achieve a Smart Network
Authors: Holland Christopher P , Shaw Duncan R , Westwood JB , Harris Ian
Published: November 2004

An organization operates within a network of relationships with economic partners. The translation services market provides rich examples of networks in practice that connect a diverse range of customers who require translation services to a global array of translators ranging from individual experts through to organized groups. This paper examines the marketing strategy of a global translation company, Thebigword. In the case of Thebigword, the network is constructed around shared information systems that encapsulate and define the nature of relationships with both business customers and thousands of individual translators worldwide. The marketing problem for Thebigword is that it must be able to sense and react to changes and requests from large business customers around the world, whether this is a change to their website, or a request for a new document translation. In the financial services market, the request for translation services may also be very time sensitive. The focus of the paper is on how Thebigword has used information systems to create a smart business network that defines marketing channels along the key dimensions of target market, business processes, IT architectures and systems, and network intelligence. A range of business examples is presented that illustrate how the marketing and information technology concepts fit together, including that of an international bank and an airline company. The case also provides technology examples of portal technology, web services and e-procurement.
Long range interactions on wires: A reciprocal space based formalism
Authors: Mináry Peter , Morrone Joseph A. , Yarne Dawn A. , Tuckerman Mark E. , Martyna Glenn J.
Published: November 2004

There are many atomic scale systems in materials, chemistry, and biology that can be effectively modeled as finite in two of the physical spatial dimensions and periodically replicated in the third including nanoscale metallic and semiconducting wires, carbon nanotubes, and DNA. However, it is difficult to design techniques to treat long range forces in these systems without truncation or recourse to slowly convergent supercells or computationally inefficient Poisson solvers. In this paper, a rigorous reciprocal space based formalism which permits long range forces on wires to be evaluated simply and easily via a small modification of existing methods for three dimensional periodicity is derived. The formalism is applied to determine long range interactions both between point particles using an Ewald-like approach and the continuous charge distributions that appear in electronic structure calculations. In this way, both empirical force field calculations and, for example, plane-wave based density functional theory computations on wires can be performed easily. The methodology is tested on model and realistic systems including a lithium doped carbon nanotube.
Absolute electron-impact total ionization cross sections of chlorofluoromethanes
Authors: Martı́nez Roberto , Sierra Borja , Redondo Carolina , Rayo Marı́a N. Sánchez , Castaño Fernando
Published: November 2004

An experimental study is reported on the electron-impact total ionization cross sections (TICSs) of CCl4, CCl3F, CCl2F2, and CClF3 molecules. The kinetic energy of the colliding electrons was in the 10–85 eV range. TICSs were obtained as the sum of the partial ionization cross sections of all fragment ions, measured and identified in a linear double focusing time-of-flight mass spectrometer. The resulting TICS profiles—as a function of the electron-impact energy—have been compared both with those computed by ab initio and (semi)empirical methods and with the available experimental data. The computational methods used include the binary-encounter-Bethe (BEB) modified to include atoms with principal quantum numbers n⩾3, the Deutsch and Märk (DM) formalism, and the modified additivity rule (MAR). It is concluded that both modified BEB and DM methods fit the experimental TICS for (CF4), CClF3, CCl2F2, CCl3F, and CCl4 to a high accuracy, in contrast with the poor accord of the MAR method. A discussion on the factors influencing the discrepancies of the fittings is presented.
Growth of nanocrystalline MoO3 on Au(111) studied by in situ scanning tunneling microscopy
Authors: Biener Monika M. , Biener Juergen , Schalek Richard , Friend Cynthia M.
Published: November 2004

The growth of nanocrystalline MoO3 islands on Au(111) using physical vapor deposition of Mo has been studied by scanning tunneling microscopy and low energy electron diffraction. The growth conditions affect the shape and distribution of the MoO3 nanostructures, providing a means of preparing materials with different percentages of edge sites that may have different chemical and physical properties than atoms in the interior of the nanostructures. MoO3 islands were prepared by physical vapor deposition of Mo and subsequent oxidation by NO2 exposure at temperatures between 450 K and 600 K. They exhibit a crystalline structure with a c(4×2) periodicity relative to unreconstructed Au(111). While the atomic-scale structure is identical to that of MoO3 islands prepared by chemical vapor deposition, we demonstrate that the distribution of MoO3 islands on the Au(111) surface reflects the distribution of Mo clusters prior to oxidation although the growth of MoO3 involves long-range mass transport via volatile MoO3 precursor species. The island morphology is kinetically controlled at 450 K, whereas an equilibrium shape is approached at higher preparation temperatures or after prolonged annealing at the elevated temperature. Mo deposition at or above 525 K leads to the formation of a Mo-Au surface alloy as indicated by the observation of embedded MoO3 islands after oxidation by NO2. Au vacancy islands, formed when Mo and Au dealloy to produce vacancies, are observed for these growth conditions.
Two-photon state selection and angular momentum polarization probed by velocity map imaging: Application to H atom photofragment angular distributions from the photodissociation of two-photon state selected HCl and HBr
Authors: Manzhos Sergei , Romanescu Constantin , Loock Hans-Peter , Underwood Jonathan G.
Published: November 2004

A formalism for calculating the angular momentum polarization of an atom or a molecule following two-photon excitation of a J-selected state is presented. This formalism is used to interpret the H atom photofragment angular distributions from single-photon dissociation of two-photon rovibronically state selected HCl and HBr prepared via a Q-branch transition. By comparison of the angular distributions measured using the velocity map imaging technique with the theoretical model it is shown that single-photon dissociation of two-photon prepared states can be used for pathway identification, allowing for the identification of the virtual state symmetry in the two-photon absorption and/or the symmetry of the dissociative state. It is also shown that under conditions of excitation with circularly polarized light, or for excitation via non-Q-branch transitions with linearly polarized light the angular momentum polarization is independent of the dynamics of the two-photon transition and analytically computable.
Stability of smectic phases in the Gay–Berne model
Authors: de Miguel Enrique , Martı́n del Rı́o Elvira , Blas Felipe J.
Published: November 2004

We present a detailed computer simulation study of the phase behavior of the Gay–Berne liquid crystal model with molecular anisotropy parameter κ=4.4. According to previous investigations: (i) this model exhibits isotropic (I), smectic-A (Sm-A), and smectic-B (Sm-B) phases at low pressures, with an additional nematic (N) phase between the I and Sm-A phases at sufficiently high pressures; (ii) the range of stability of the Sm-A phase turns out to be essentially constant when varying the pressure, whereas other investigations seem to suggest a pressure-dependent Sm-A range; and (iii) the range of stability of the Sm-B phase remains unknown, as its stability with respect to the crystal phase has not been previously considered. The results reported here do show that the Sm-A phase is stable over a limited pressure range, and so it does not extend to arbitrarily low or high pressures. This is in keeping with previous investigations of the effect of molecular elongation on the phase behavior of Gay–Berne models. A detailed study of the melting transition at various pressures shows that the low-temperature crystalline phase melts into an isotropic liquid at very low pressures, and into a nematic liquid at very high pressures. At intermediate pressures, the crystal melts into a Sm-A liquid and no intermediate Sm-B phase is observed. On the basis of this and previous investigations, the reported Sm-B phase for Gay–Berne models appears to be a molecular solid rather than a smectic liquid phase.
Dynamics of glass-forming liquids. IX. Structural versus dielectric relaxation in monohydroxy alcohols
Authors: Wang Li-Min , Richert Ranko
Published: November 2004

The prominent Debye-type but non-Arrhenius dielectric relaxation is a feature common to many monohydroxy alcohols in their liquid state. Although this exponential process is often considered to reflect the primary structural relaxation, only a faster, smaller, and nonexponential relaxation peak correlates with viscous flow and mechanical relaxation. We provide dielectric relaxation data for 2-methyl-1-butanol, 2-ethyl-1-hexanol, and 3,7-dimethyl-1-octanol across ten decades in time. Based on these and previous results, we show that there exists a variety of dielectric to mechanical relaxation time ratios in the viscous regime, but a universal value of 100 for that ratio appears to evolve in the high temperature limit. The temperature dependence for both the relaxation time and strength of the Debye peak differs from the typical behavior of structural dynamics in terms of the α process. The implications of these findings for rationalizing the Debye-type dielectric process of hydrogen-bonded liquids are discussed.
Stationary molecular wave packets at nonequilibrium nuclear configurations
Authors: Chang Bo Y. , Lee Sungyul , Sola Ignacio R.
Published: November 2004

We study different schemes that allow laser controlled adiabatic manipulation of the bond in diatomic molecules by using sequences of nonresonant time-delayed chirped pulses. The schemes rely on adiabatic passage of the vibrational wave packet by laser-induced potential shaping from the ground electronic state to a laser-stabilized dissociative electronic state by two-photon absorption. The degree of control that is possible over the position (bond length) and width (bond spread) of the vibrational wave packet is compared for the different schemes. The dynamics is analyzed detailing the role of the different control knobs and the conditions that allow or break the adiabatic passage.
Effect of end-group sticking energy on the properties of polymer brushes: Comparing experiment and theory
Authors: Titmuss S. , Briscoe W. H. , Dunlop I. E. , Sakellariou G. , Hadjichristidis N. , Klein J.
Published: November 2004

Using surface force balance measurements we have established that polystyrene chains bearing three zwitterionic groups have a higher end-group sticking energy than equivalent chains bearing a single zwitterionic group. In a good solvent, polystyrene chains end-functionalized with three zwitterionic groups form brushes of a higher surface coverage than those bearing a single zwitterion. The increase in surface coverage is slow compared with the initial formation of the brush. Measurements of the refractive index allow us to directly quantify the variation of surface coverage, permitting comparison with models for the kinetics of brush formation based on scaling theory and an analytical self-consistent field. We find qualitative support for associating the kinetic barrier with the energy required for an incoming chain to stretch as it penetrates the existing brush.
Correlation energy extrapolation by intrinsic scaling. II. The water and the nitrogen molecule
Authors: Bytautas Laimutis , Ruedenberg Klaus
Published: November 2004

The extrapolation method for determining benchmark quality full configuration-interaction energies described in preceding paper [L. Bytautas and K. Ruedenberg, J. Chem. Phys. 121, 10905 (2004)] is applied to the molecules H2O and N2. As in the neon atom case, discussed in preceding paper [L. Bytautas and K. Ruedenberg, J. Chem. Phys. 121, 10905 (2004)] remarkably accurate scaling relations are found to exist between the correlation energy contributions from various excitation levels of the configuration-interaction approach, considered as functions of the size of the correlating orbital space. The method for extrapolating a sequence of smaller configuration-interaction calculations to the full configuration-interaction energy and for constructing compact accurate configuration-interaction wave functions is also found to be effective for these molecules. The results are compared with accurate ab initio methods, such as many-body perturbation theory, coupled-cluster theory, as well as with variational calculations wherever possible.
Structure and dynamics in a monolayer of dipolar spheres
Authors: Duncan Peter D. , Camp Philip J.
Published: November 2004

The structure and dynamics in a monolayer of dipolar soft spheres have been investigated using molecular dynamics simulations. This is a basic model of colloidal ferrofluid monolayers, and other magnetic liquids in planar geometries, which can exhibit self-assembled chainlike aggregates due to strong dipole-dipole interactions. The effects of such chaining on the structure, single-particle translational and rotational motions, and the collective rotational motions are examined. The signatures of aggregation in the various structural and dynamical functions considered in this study could prove useful in experimental investigations of strongly dipolar materials.
Inhibition of CO oxidation on RuO2(110) by adsorbed H2O molecules
Authors: Paulus U. A. , Wang Y. , Kim S. H. , Geng P. , Wintterlin J. , Jacobi K. , Ertl G.
Published: November 2004

Catalytic CO oxidation on the RuO2(110) surface was studied at 300 K by scanning tunneling microscopy (STM), high-resolution electron-energy-loss spectroscopy (HREELS), and thermal desorption spectroscopy (TDS). Upon repeatedly exposing the surface to several 10 L of CO and O2 at 300 K, STM shows that unreactive features accumulate with each CO and O2 titration run. HREELS and TDS show formation of increasing amounts of H2O, retarded formation of O-cus atoms and incomplete removal of CO-bridge molecules during O2 dosing, and a changing ratio of single- and double-bonded CO-bridge molecules. It is concluded that H2O (presumably from the residual gas) is accumulating at the Ru-cus sites thus blocking them, so that the dissociative adsorption of oxygen is prevented and the CO oxidation reaction is suppressed. Some 10% CO- bridge remains on the surface even during oxygen exposure. Consistent with this interpretation, deactivation of the surface is suppressed at 350 K, at the onset of H2O desorption.
Diffusion in the presence of periodically spaced permeable membranes
Authors: Dudko Olga K. , Berezhkovskii Alexander M. , Weiss George H.
Published: November 2004

The diffusion of molecules in biological tissues and some other microheterogeneous systems is affected by the presence of permeable barriers. This leads to the slowdown of diffusion at long times as compared to barrier-free diffusion. At short times the effect of barriers is weak. In consequence, the diffusion coefficient D(t) decreases as a function of time. We derive an exact solution for the Laplace transform of D(t) for diffusion in a space separated into layers by equally spaced, parallel identical planes of arbitrary permeability. Additionally, we give an approximation to D(t) which is reasonably accurate over the whole range of the partition permeability from zero (the case of isolated layers) to infinity (the case of no barriers).
Vibrational and electronic excitations of H2O on thymine films induced by low-energy electrons
Authors: Cho W. , Michaud M. , Sanche L.
Published: November 2004

We investigated vibrational and electronic excitations of 0.1-layer up to 2.4-layer film of H2O deposited on a 1.4-layer film of thymine condensed on Ar at a temperature of 18 K using high-resolution electron-energy loss (EEL) spectroscopy at the incident energy of 12 eV. The spectral contribution originating essentially from the H2O overlayer is obtained by separating the measured contribution from the underlying film of thymine, considering the electron beam attenuation in the H2O overlayer. The vibrational EEL spectrum of submonolayer amount of H2O on thymine, which excepts for small energy shift of the vibrational bands, is found to compare in intensity to that of the same amount of H2O deposited directly on the argon. The electronic energy-loss intensity near 8.6 eV, which is attributed to the excitation of B13,1 states of H2O in condensed phase, is observed to decrease by a factor of about 3 by the presence of the underlying film of thymine. This indicates that the corresponding cross section for excitation the B13,1 states of H2O by the electron impact is reduced significantly by the close proximity of the thymine molecules.
Lifetime of reactive scattering resonances: Q-matrix analysis and angular momentum dependence for the F+H2 reaction by the hyperquantization algorithm
Authors: Aquilanti Vincenzo , Cavalli Simonetta , Simoni Andrea , Aguilar Antonio , Lucas Josep Maria , De Fazio Dario
Published: November 2004

We report a study on the behavior with total angular momentum J of several resonances occurring at collision energies below or slightly above the reaction barrier in the F+H2→HF+H reaction. Resonance positions and widths are extracted from exact time-independent quantum mechanical calculations using the hyperquantization algorithm and Smith’s Q-matrix formalism which exploits complete S-matrix information. The results confirm previous work but provide much greater insight. Identification of quasi-bound states responsible for the resonances based on adiabatic models for the long-range atom–molecule interactions both in the entrance and exit channels, is successful except for the feature occurring at the lowest energy, which is found to overlap with an exit-channel resonance for J∼7. The two features are analyzed as overlapping resonances and their excellent Lorentzian fits, with well-behaved J-dependences of positions and widths, support the interpretation of the low-energy feature as a resonance to be associated to the triatomic transition state of the reaction. Resonance role on the reactive observables (integral cross sections and angular distributions) is investigated. The mechanism leading to forward scattering in the reactive differential cross section is commented, while the effects on rate constants, as well as the sensitivity of the resonance pattern to modification of the potential energy surface, are fully discussed elsewhere.
Distributions of angular anisotropy and kinetic energy of products from the photodissociation of methanol at 157 nm
Authors: Lee Shih-Huang , Lee Hsin-I. , Lee Yuan T.
Published: November 2004

We investigated distributions of angular-anisotropy parameter β and kinetic energy of fragments after photodissociation of methanol using time-of-flight (TOF) mass spectrometry. Fragments, in particular CH3O and CO, were successfully detected using tunable radiation from a synchrotron for photoionization. Following O–H bond fission, a CH3O fragment with internal energy greater than 104 kJ mol−1 dissociates to CH2O+H. Elimination of two H2 accompanies formation of CO. The 〈β〉 value of hydroxyl hydrogen is −0.26 whereas that of methyl hydrogen is zero. H2 has two distinct components in TOF spectra; these rapid and slow components have 〈β〉 values −0.30 and −0.18, respectively. The CH3+OH dissociation exhibits a highly anisotropic angular distribution with 〈β〉=−0.75. The β values of fragments from CD3OH photolysis are addressed. From measurements of angular-anisotropy parameters of various fragments, we surmise that the transition dipole moment μ is almost perpendicular to the C–O–H plane and that n−3px (2 1A″) is the major photoexcited state at 157 nm.
Boundary homogenization for trapping by patchy surfaces
Authors: Berezhkovskii Alexander M. , Makhnovskii Yurii A. , Monine Michael I. , Zitserman Vladimir Yu. , Shvartsman Stanislav Y.
Published: November 2004

We analyze trapping of diffusing particles by nonoverlapping partially absorbing disks randomly located on a reflecting surface, the problem that arises in many branches of chemical and biological physics. We approach the problem by replacing the heterogeneous boundary condition on the patchy surface by the homogenized partially absorbing boundary condition, which is uniform over the surface. The latter can be used to analyze any problem (internal and external, steady state, and time dependent) in which diffusing particles are trapped by the surface. Our main result is an expression for the effective trapping rate of the homogenized boundary as a function of the fraction of the surface covered by the disks, the disk radius and trapping efficiency, and the particle diffusion constant. We demonstrate excellent accuracy of this expression by testing it against the results of Brownian dynamics simulations.
Theoretical model of interfacial polymerization
Authors: Yashin Victor V. , Balazs Anna C.
Published: November 2004

We present a theoretical description for the creation of a thin polymeric layer through the interfacial polymerization of two immiscible, low molecular weight liquids. The theory specifically takes into account the effects of polydispersity on the formation of the polymer film at the liquid-liquid interface. Consequently, we can describe the structure of the growing film and the molecular weight distribution of the resultant polymer chains. We focus on a model system where alternating AB copolymers are formed at the interface between phase-separated, low molecular weight species A and B. It is assumed that any A(B) unit can reversibly attach to any available B(A) unit or B(A)-ended chain. The formation of the copolymer layer is described by a system of reaction-diffusion equations, which detail the chemical evolution and diffusive dynamics of the polydisperse mixture of AB copolymers around the interface, and the evolution of the interface itself. Using this model, we determine the effects of the chemical reaction rates and the initial conditions on the kinetics of forming the AB copolymer layer and the structure of this film.
The rotational spectrum and dynamical structure of LiOH and LiOD: A combined laboratory and ab initio study
Authors: Higgins Kelly J. , Freund Samuel M. , Klemperer William , Apponi Aldo J. , Ziurys Lucy M.
Published: November 2004

Millimeter wave rotational spectroscopy and ab initio calculations are used to explore the potential energy surface of LiOH and LiOD with particular emphasis on the bending states and bending potential. New measurements extend the observed rotational lines to J=7←6 for LiOH and J=8←7 for LiOD for all bending vibrational states up to (0330). Rotation-vibration energy levels, geometric expectation values, and dipole moments are calculated using extensive high-level ab initio three-dimensional potential energy and dipole moment surfaces. Agreement between calculation and experiment is superb, with predicted Bv values typically within 0.3%, D values within 0.2%, ql values within 0.7%, and dipole moments within 0.9% of experiment. Shifts in Bv values with vibration and isotopic substitution are also well predicted. A combined theoretical and experimental structural analysis establishes the linear equilibrium structure with re(Li–O)=1.5776(4) Å and re(O–H)=0.949(2) Å. Predicted fundamental vibrational frequencies are v1=923.2, v2=318.3, and v3=3829.8 cm−1 for LiOH and v1=912.9, v2=245.8, and v3=2824.2 cm−1 for LiOD. The molecule is extremely nonrigid with respect to angular deformation; the calculated deviation from linearity for the vibrationally averaged structure is 19.0° in the (000) state and 41.9° in the (0330) state. The calculation not only predicts, in agreement with previous work [P. R. Bunker, P. Jensen, A. Karpfen, and H. Lischka, J. Mol. Spectrosc. 135, 89 (1989)], a change from a linear to a bent minimum energy configuration at elongated Li–O distances, but also a similar change from linear to bent at elongated O–H distances.
The matrix-isolated molecular complexes CO/XF (X=Cl,Br,I) and the molecular structure of FC(O)Br
Authors: Garcı́a Plácido , Willner Helge , Oberhammer Heinz , Francisco Joseph S.
Published: November 2004

FC(O)Br has been synthesized, and its IR spectrum in the gas phase and isolated in an Ar matrix, as well as, its Raman spectrum in the solid state at −196 °C has been analyzed. Its molecular structure has been determined and its UV has been measured. FC(O)Br and FC(O)Cl has been photodissociated in an argon matrix at 17 K with a 193 nm laser. The photolysis produces CO and XF which recombine to form CO/XF complexes. The formation of complexes are followed by the shift of the normal vibration modes with respect to CO and XF isolated in argon matrix. In the case of FC(O)Br, three isomers are identified, OC⋯BrF, OC⋯FBr, and CO⋯BrF, whereas for FC(O)Cl only one isomer is observed, OC⋯ClF. High level quantum chemical calculations are used to help the assignment of the different isomers.
Electron spectroscopy and scanning tunneling microscopy study of quasi-two-dimensional freezing at the liquid/vapor interface of Ga-Bi alloys
Authors: Issanin A. , Turchanin A. , Freyland W.
Published: November 2004

We have studied the interfacial characteristics of Ga-rich liquid Ga-Bi alloys at various compositions and temperatures up to 300 °C by different electron spectroscopies under ultrahigh vacuum conditions. In particular, the thickness and thickness profiles of Bi-rich wetting and surface freezing films have been measured. It is found that at the surface freezing transition the Bi film thickness jumps from ∼5 Å to macroscopic values of over 100 Å. This distinct behavior is discussed in comparison with the results in Ga-Pb. In addition, we report first scanning tunneling microscopy observations of the surface structure of a solidified Ga0.989Bi0.011 alloy after passing a surface freezing transition. The topology at room temperature is characterized by extended, atomically flat Bi terraces covered by nanosized triangular two-dimensional Bi islands.
Short-time Fourier transform analysis of ab initio molecular dynamics simulation: Collision reaction between NH4+(NH3)2 and NH3
Authors: Yamauchi Yusuke , Nakai Hiromi , Okada Yoshiki
Published: November 2004

An analyzing technique of the ab initio molecular dynamics simulation is proposed with the use of short-time Fourier transform (ST-FT). The ST-FT analysis demonstrates the dynamical change of the vibrational states in the simulated system. Numerical assessments are preformed for the collision reaction of the ammonia cluster ion NH4+(NH3)2 with the ammonia monomer NH3. Spectrogram obtained by the ST-FT method, which corresponds to the time evolution of vibrational power spectra, clarifies the relationship between the vibrational states and the reaction channels such as nonreactive collision, substitution, and incorporation.
Friction and diffusion of a Brownian particle in a mesoscopic solvent
Authors: Lee Song Hi , Kapral Raymond
Published: November 2004

The friction and diffusion coefficients of a massive Brownian particle in a mesoscopic solvent are computed from the force and the velocity autocorrelation functions. The mesoscopic solvent is described in terms of free streaming of the solvent molecules, interrupted at discrete time intervals by multiparticle collisions that conserve mass, momentum, and energy. The Brownian particle interacts with the solvent molecules through repulsive Lennard-Jones forces. The decays of the force and velocity autocorrelation functions are analyzed in the microcanonical ensemble as a function of the number N of solvent molecules and Brownian particle mass and diameter. The simulations are carried out for large system sizes and long times to assess the N dependence of the friction coefficient. The decay rates of these correlations are confirmed to vary as N−1 in accord with earlier predictions. Hydrodynamic effects on the velocity autocorrelation function and diffusion coefficient are studied as a function of Brownian particle mass and diameter.
Effect of encaged aromatic guests on the shape and connectivity of molecular cavity in crystalline polystyrene evaluated by molecular simulations
Authors: Tamai Yoshinori , Fukuda Mitsuhiro
Published: November 2004

The δ form of crystalline syndiotactic polystyrene is a clathrate molecular compound in which various aromatic molecules are encaged. We have investigated the size, shape, and connectivity of the molecular cavity in the crystal using a molecular dynamics simulation. The effects of the guest species on the cavity structure were investigated in detail. In order to systematically vary the guest structure, various aromatic guests, e.g., benzene, toluene, p-xylene, m-xylene, o and mesitylene were examined. The interstitial spaces between the guests and the polymer chains were analyzed by cluster analysis of the free volumes. The individual cavity volumes into which the guests are clathrated were also evaluated. It was found that the guest molecules can greatly affect not only the cavity size and shape but also the connectivity of the cavities. The transport of small molecules in the crystal is discussed in connection with the cavity structure.
Nucleation free energy of pore formation in an amphiphilic bilayer studied by molecular dynamics simulations
Authors: Tolpekina T. V. , den Otter W. K. , Briels W. J.
Published: November 2004

The formation of a pore in a membrane requires a considerable rearrangement of the amphiphilic molecules about to form the bilayer edge surrounding the pore, and hence is accompanied by a steep increase of the free energy. Recent rupture and conductance experiments suggest that this reshuffling process is also responsible for a small energy barrier that stabilizes “prepores” with diameters of less than 1 nm, rendering both the opening and closing of pores an activated process. We use the potential of mean constraint force method to study this free energy profile, as a function of pore radius, in a coarse grained bilayer model. The calculations show that the free energy rises by (15–20) kT during pore opening, making it an extremely rare nucleation event. Although we do not observe a barrier to pore closure, the results do make the existence of such a barrier plausible. For larger pores we find a smooth transition to Litster’s model, from which a line tension coefficient of about 3.7×10−11 J m−1 is deduced.
The vaporization rate of ice at temperatures near its melting point
Authors: Sadtchenko Vlad , Brindza M. , Chonde M. , Palmore B. , Eom R.
Published: November 2004

The first study of free vaporization kinetics of ice at temperatures near its melting point is reported. The experimental approach employed is based on a unique combination of thermal desorption spectroscopy, microcalorimetry, and time-of-flight mass spectrometry, making it possible to overcome challenges associated with the introduction of volatile solids into a high vacuum environment. Measurements of the vaporization rate of polycrystalline ice demonstrate that the vaporization kinetics deviate dramatically from those predicted by a simple mobile precursor mechanism. The vaporization rate follows Arrhenius behavior from −40 to 0 °C with an effective activation energy of 50±4 kJ/mol, which is significantly higher than the value predicted by the simple mobile precursor mechanism. Extrapolation of earlier measurements conducted below −40 °C yields a value of approximately 0.02 at 0 °C for the vaporization coefficient αv. In contrast, experimentally determined vaporization coefficient is found to be 0.7±0.3 and shows a weak dependence on temperature up to the bulk melting point. The role of possible surface phase transitions in the mechanisms of release and uptake of H2O and other chemical species by ice surfaces is discussed.
Polydisperse hard spheres at a hard wall
Authors: Buzzacchi Matteo , Pagonabarraga Ignacio , Wilding Nigel B.
Published: November 2004

The structural properties of polydisperse hard spheres in the presence of a hard wall are investigated via Monte Carlo simulation and density functional theory (DFT). Attention is focused on the local density distribution ρ(σ,z), measuring the number density of particles of diameter σ at a distance z from the wall. Estimates of ρ(σ,z) are obtained for bulk volume fractions ηb=0.2 and ηb=0.4, and for two choices of the bulk parent distribution: a top-hat form, which we study for degrees of polydispersity δ=11.5% and δ=40.4%, and a truncated Schulz form having δ=40.7%. Excellent overall agreement is found between the DFT and simulation results, particularly at ηb=0.2. A detailed analysis of ρ(σ,z) confirms the presence of oscillatory size segregation effects, as observed in a previous DFT study [I. Pagonabarraga, M. E. Cates, and G. J. Ackland, Phys. Rev. Lett. 84, 911 (2000)]. For large δ, the character of these oscillation is observed to depend strongly on the shape of the parent distribution. In the vicinity of the wall, attractive σ-dependent depletion interactions are found to greatly enhance the density of the largest particles. The local degree of polydispersity δ(z) is suppressed in this region, while further from the wall it exhibits oscillations.
Statistical evaporation of rotating clusters. IV. Alignment effects in the dissociation of nonspherical clusters
Authors: Parneix P. , Calvo F.
Published: November 2004

Unimolecular evaporation in rotating, nonspherical atomic clusters is investigated using phase space theory in its orbiting transition state version. The distributions of the total kinetic energy release εtr and the rotational angular momentum Jr are calculated for oblate top and prolate top main products with an arbitrary degree of deformation. The orientation of the angular momentum of the product cluster with respect to the cluster symmetry axis has also been obtained. This statistical approach is tested in the case of the small eight-atom Lennard-Jones cluster, for which comparison with extensive molecular dynamics simulations is presented. The role of the cluster shape has been systematically studied for larger, model clusters in the harmonic approximation for the vibrational densities of states. We find that the type of deformation (prolate versus oblate) plays little role on the distributions and averages of εtr and Jr except at low initial angular momentum. However, alignment effects between the product angular momentum and the symmetry axis are found to be significant, and maximum at some degree of oblateness. The effects of deformation on the rotational cooling and heating effects are also illustrated.
Density functional calculation of the electronic absorption spectrum of Cu+ and Ag+ aqua ions
Authors: Bernasconi Leonardo , Blumberger Jochen , Sprik Michiel , Vuilleumier Rodolphe
Published: November 2004

The UV absorption of aqueous Cu+ and Ag+ has been studied using Time Dependent Density Functional Theory (TDDFT) response techniques. The TDDFT electronic spectrum was computed from finite temperature dynamical trajectories in solution generated using the Density Functional Theory (DFT) based Ab Initio Molecular Dynamics (AIMD) method. The absorption of the two ions is shown to arise from similar excitation mechanisms, namely transitions from d orbitals localized on the metal center to a rather delocalized state originating from hybridization of the metal s orbital to the conduction band edge of the solvent. The ions differ in the way the spectral profile builds up as a consequence of solvent thermal motion. The Cu+ absorption is widely modulated, both in transition energies and intensities by fluctuations in the coordination environment which is characterized by the formation of strong coordination bonds to two water molecules in an approximately linear geometry. Though, on average, absorption intensities are typical of symmetry forbidden transitions of metal ions in the solid state, occasionally very short (<100 fs) bursts in intensity are observed, associated with anomalous Cu–H interactions. Absorption by the Ag+ complex is in comparison relatively stable in time, and can be interpreted in terms of the energy splitting of the metal 4d manifold in an average crystal field corresponding to a fourfold coordination in a distorted tetrahedral arrangement. Whereas the spectral profile of the Ag+ aqua ion is in good agreement with experiment, the overall position of the band is underestimated by 2 eV in the BLYP approximation to DFT. The discrepancy with experiment is reduced to 1.3 eV when a hybrid functional (PBE0) is used. The remaining inaccuracy of TDDFT in this situation is related to the delocalized character of the target state in d→s transitions.
Phase behavior of ionic fluids in slitlike pores: A density functional approach for the restricted primitive model
Authors: Pizio O. , Patrykiejew A. , Sokołowski S.
Published: November 2004

We present a density functional theory of nonuniform ionic fluids. This theory is based on the application of the electrostatic contribution to the free energy functional arising from mean spherical approximation for a bulk restricted primitive model and from the energy route bulk equation of state. In order to employ this functional we define a reference fluid and additional averaged densities, according to the approach introduced by Gillespie, Nonner and Eisenberg [J. Phys.: Condens. Matter 14, 12129 (2002)]. In the case of bulk systems the proposed theory reduces to the mean spherical approximation equation of state, arising from the energy route and thus it predicts the first-order phase transition. We use this theory to investigate the effects of confinement on the liquid–vapor equilibria. Two cases are considered, namely an electrolyte confined to the pore with uncharged walls and with charged walls. The dependence of the capillary evaporation diagrams on the pore width and on the electrostatic potential is determined.