bluuebunny/crossref_metadata_2025 huggingface dataset:
Variations of the Hawaiian hot spot activity revealed by variations in the magma production rate
Authors: Vidal V. , Bonneville A.
Published: March 2004

In order to evaluate the activity of the Hawaiian hot spot, we calculate both the magma production rate, associated with volcanism, and the rate of swell formation, characteristic of the plume behavior. Both computations are made along the Emperor‐Hawaii track. Depth anomaly is calculated by correcting the 2′ bathymetry grid of Smith and Sandwell [1997] from thermal subsidence. A new filtering method is then used to separate the topography associated with volcanism and the swell surrounding the hot spot chain. The volume of magma includes the compensating root underlying the volcanoes, computed assuming either an Airy compensation (local) or a flexural root (regional) associated with the volcanic load. Next, the volume corresponding to the swell is calculated between the swell amplitude map and the zero value of the depth anomaly. Temporal variations of both volumes are then computed by the means of 1° × 10° windows translated along the hot spot track. Both volume fluxes are correlated through time and present (1) a general increase in amplitude for the last 30 Ma, indicating an increase in hot spot activity, and (2) short‐wavelength oscillations with a 5 m.y. period, which may reflect the presence of solitary waves in the plume conduit. Contrary to the swell volume flux, the magma production rate estimation is not dependent on the subsidence model and is still valid for the older part of the chain. It is thus the most relevant parameter to describe the temporal variation of the Hawaiian hot spot behavior.
Images of crustal variations in the intermountain west
Authors: Gilbert Hersh J. , Sheehan Anne F.
Published: March 2004

We develop a map of crustal thickness variations across the Great Basin, Colorado Plateau, Rocky Mountain, and Great Plains Provinces of the western United States using common conversion point stacking of teleseismic receiver functions. Below the Rocky Mountains and High Plains in Colorado we find the thickest crust in the region at 45–50 km thick. Beneath the Basin and Range, thinner, between 30 and 40 km, crust is found. Thin, 30 km thick, crust is present in the northern portion of Nevada and Utah despite elevations similar to those farther south. Crustal thickness across the Colorado Plateau can be characterized as a broad transitional region between the thin crust of Basin and Range to the thicker crust of the Rocky Mountains. The impedance contrast across the Mohorovicic discontinuity decreases below the Colorado Plateau, as converted arrivals recorded in this region appear weak compared to surrounding areas. Variations in VP/VS across the region indicate higher values along the western boundary of the Basin and Range, in the Rocky Mountains, and in the western Great Plains. We are not able to characterize VP/VS in the Colorado Plateau. We find that crustal thickness does not closely correlate with surface topography within each region or across the region as a whole. Differences in crustal thickness in each tectonic province indicate the need for a mantle component to support the high elevations across the western United States.
Real‐time forecasting at weekly timescales of the SST and SLA of the Ligurian Sea with a satellite‐based ocean forecasting (SOFT) system
Authors: Álvarez A. , Orfila A. , Tintoré J.
Published: March 2004

Satellites are the only systems able to provide continuous information on the spatiotemporal variability of vast areas of the ocean. Relatively long‐term time series of satellite data are nowadays available. These spatiotemporal time series of satellite observations can be employed to build empirical models, called satellite‐based ocean forecasting (SOFT) systems, to forecast certain aspects of future ocean states. SOFT systems can predict satellite‐observed fields at different timescales. The forecast skill of SOFT systems forecasting the sea surface temperature (SST) at monthly timescales has been extensively explored in previous works. In this work we study the performance of two SOFT systems forecasting, respectively, the SST and sea level anomaly (SLA) at weekly timescales, that is, providing forecasts of the weekly averaged SST and SLA fields with 1 week in advance. The SOFT systems were implemented in the Ligurian Sea (Western Mediterranean Sea). Predictions from the SOFT systems are compared with observations and with the predictions obtained from persistence models. Results indicate that the SOFT system forecasting the SST field is always superior in terms of predictability to persistence. Minimum prediction errors in the SST are obtained during winter and spring seasons. On the other hand, the biggest differences between the performance of SOFT and persistence models are found during summer and autumn. These changes in the predictability are explained on the basis of the particular variability of the SST field in the Ligurian Sea. Concerning the SLA field, no improvements with respect to persistence have been found for the SOFT system forecasting the SLA field.
Phase structure functions for ionospheric radio sounding: Dependence on irregularity scale
Authors: Zabotin N. A. , Wright J. W.
Published: March 2004

Because the ionospheric plasma drifts, radio sounding signals encounter different irregularities of electron density, even at only slightly different times, causing temporal phase variations; these may be characterized conveniently by the structure function. We have proposed in several recent publications a new irregularity diagnostic method based on this effect, and it is now useful to consider the range of irregularity scales affecting the observed phase fluctuations. We show, in particular, that for the two‐dimensional irregularity power spectrum index 2 < ν < 3 (quite typical for the ionosphere) the phase structure function value at the smallest available lag (0.01 s) is sensitive to irregularities in a broad range of scales, between several meters and several kilometers.
On the generalization of Snell's law
Authors: Coleman C. J.
Published: March 2004

By means of Noether's theorem, it is shown that there is a large class of complicated refractive media for which there exists a Snell like law. Furthermore, a ray path through such a medium is shown to be related to one through an appropriate plane stratified medium. As a consequence, it is possible to find analytic expressions for the ray trajectories through a large subclass of such media.
Seismic investigations of the O'Higgins Seamount Group and Juan Fernández Ridge: Aseismic ridge emplacement and lithosphere hydration
Authors: Kopp H. , Flueh E. R. , Papenberg C. , Klaeschen D.
Published: March 2004

The O'Higgins Seamount Group is a cluster of volcanic domes located 120 km west of the central Chilean Trench on the crest of the Juan Fernández Ridge. This aseismic hot spot track is subducting under South America triggering a belt of intraslab earthquake hypocenters extending about 700 km inland. The Juan Fernández Ridge marks the southern boundary of a shallow subduction segment. Subduction of oceanic basement relief has been suggested as a cause for the “flat” slab segments characterizing the Andean trench system. The Juan Fernández Ridge, however, shows only moderate crustal thickening, inadequate to cause significant buoyancy. In 2001, wide‐angle seismic data were collected along two perpendicular profiles crossing the O'Higgins Group. We present tomographic images of the volcanic edifices and adjacent outer rise‐trench environment, which indicate a magmatic origin of the seamounts dominated by extrusive processes. High‐resolution bathymetric data yield a detailed image of a network of syngenetic structures reactivated in the outer rise setting. A pervasive fault pattern restricted to the hot spot modified lithosphere coincides with anomalous low upper mantle velocities gained from a tomographic inversion of seismic mantle phases. Reduced uppermost mantle velocities are solely found underneath the Juan Fernández Ridge and may indicate mineral alterations. Enhanced buoyancy due to crustal and upper mantle hydration may contribute an additional mechanism for shallow subduction, which prevails to the north after the southward migration of the Juan Fernández Ridge.
Experimental study of flash flood surges down a rough sloping channel
Authors: Chanson H.
Published: March 2004

Flood waves resulting from flash floods and natural dam overtopping have been responsible for numerous losses. In the present study, surging waters down a flat stepped waterway (θ = 3.4°) were investigated in a 24 m long chute. Wave front propagation data were successfully compared with Hunt's [1982, 1984] theory. Visual observations highlighted strong aeration of the leading edge. Instantaneous distributions of void fractions showed a marked change in shape for (t − ts)* ∼ 1.3, which may be caused by some major differences between the wave leading edge and the flow behind, including nonhydrostatic pressure distributions, plug‐slug flow regime, and different boundary friction regime. Practically, the results quantified the large amount of entrained air (i.e., “white waters”) at the wave front, which in turn, reduces buoyancy and could affect sediment motion at the leading edge because the sediment relative density is inversely proportional to the entrained air content.
Stochastic determination of three‐dimensional capture zones for a fully penetrating well
Authors: Lessoff S. C. , Indelman P.
Published: March 2004

A stochastic methodology is used to investigate transport of a conservative solute by steady flow to a fully penetrating pumping well in a three‐dimensional heterogeneous formation. The spatially variable hydraulic conductivity is modeled as a stationary random function of anisotropic two‐point covariance. Although mean transport is radial, heterogeneity produces three‐dimensional velocity fluctuations which are shown to affect solute recovery and the capture zone distribution. Expressions accurate to the first order in log conductivity variance σY2 are derived for travel time variance, capture zone extent, and solute recovery under the following simplifying assumptions: (1) the vertical integral scale of conductivity is much less than the horizontal integral scale, (2) the depth of the formation is much greater than the vertical integral scale of conductivity, (3) the well bore diameter is much smaller than the horizontal scale of conductivity, (4) longitudinal and lateral local dispersion are negligible while the effect of transverse dispersion is examined. Travel time variance στ2 for transport in convergent flow in a three‐dimensional aquifer is shown to be greater than στ2 in either constant mean flow in a three‐dimensional formation or radially convergent flow in a heterogeneous two‐dimensional medium. Transverse dispersion between layers in a sedimentary formation is found to increase mixing between flow paths leading to a marginal reduction in travel time variance. Because of negative correlation between mass flux and travel time, solute retrieval at the well occurs earlier from a constant flux solute source than from an instantaneous plume. The relationship between initial plume length and relative plume spreading is illustrated for simple plume geometries.
Numerical modeling of carbon dioxide in unsaturated soils due to deep subsurface leakage
Authors: Altevogt Andrew S. , Celia Michael A.
Published: March 2004

A two‐dimensional numerical model was utilized to explore the flux mechanisms governing CO2 transport in the vadose zone. The simulations were set up to approximately correspond to a site of natural CO2 leakage at Mammoth Mountain, California. The mass fraction gradient driving force, responsible for diffusive and slip fluxes, was determined to lead to less plume spreading than advection alone. Density‐driven flow of CO2 led to significantly greater spreading of the plume and greater storage of CO2 within the vadose zone than if density contrasts were not accounted for. Exposure assessment simulations indicate that for the conditions of interest there may be no physically realistic domain that would lead to CO2 levels below the criteria for human health impacts (sub 10%) in surface soils for the leakage rate present at Mammoth Mountain.
Strategy as a ‘Project’: overcoming dualisms in the strategy debate
Authors: Knights David , Mueller Frank
Published: March 2004

Abstract This paper is concerned to challenge a selection of the strategy literature on the basis that it tends to follow one or other side of a polarity between a subjective and an objective approach. There is a tendency here for strategy analysis to collapse into subjectivism (e.g. a reification of personalities) or objectivism (e.g. structural determinism) respectively. In seeking to avoid the worst excesses of dualism, we focus on strategy as a project in which numerous stakeholders make demands and serve to condition its development. A notion of strategy as a perennially unfinished project allows us to see how it is in a continuous process of self‐formation and reconstruction. As a project, strategy may appear in different discursive configurations depending on which of the stakeholders (e.g. managers, shareholders, competitors, suppliers, intermediaries, the financial community, consultants, regulators, and customers) a corporation is focused on impressing or placating. For example, managers might embrace a core competence narrative or cost‐cutting practices in order to maintain or enhance stock market ratings in the financial community. At the same time, strategy is invariably focused on securing the support or loyalty of its customers. This may involve heavy resources being directed towards advertising and brand imaging as well as service quality as part of a strategy of constituting the subjectivity of the (actual or prospective) customer. All this takes place within the framework of constraints laid down by regulators that leave corporate decision‐makers limited room for manoeuvre. The paper draws on a limited number of empirical vignettes through which to illustrate our arguments concerning this approach to strategy as a project.
Strategy viewed from a management fashion perspective
Authors: Clark Timothy
Published: March 2004

Abstract This article argues for the greater inclusion of external agents within strategy research. Drawing on the emergent management fashion literature, it conceives of these as a group of actors operating within a management fashion‐setting arena. The outputs of this community dominate conceptions of what are deemed legitimate strategic actions. They thus have a critical, if presently neglected, impact on the nature strategy. The roles of the members of the management fashion‐setting community are described and three promising areas of research outlined.
Strategy after modernism: recovering practice
Authors: Whittington Richard
Published: March 2004

Abstract This article identifies an opportunity for European researchers to develop a more practice‐sensitive research programme for strategy ‘after modernism’. Strategy's intellectual lock‐in on modernist detachment and economic theory can now be relaxed. Strategy can draw also on the rich resources of sociology to engage more directly with strategy as a social practice. This article outlines elements of a double agenda for strategy research after modernism: first, a sociological agenda concerned with understanding strategy's elites, its skills and its technologies, and their implications for society as a whole; second, a managerial agenda, turning this sociological understanding to practical advantage in terms of how managers become strategists, how strategy skills are acquired and how strategy technologies can be better designed and used. The article considers implications for research methods and the Mintzbergian tradition in strategy.
Bowling along: strategic management and social capital
Authors: Starkey Ken , Tempest Sue
Published: March 2004

Abstract This paper argues that social capital is an under‐examined but central contributing factor to effective strategic management. In an economy where capitalizing upon knowledge is becoming more important, social capital provides the basis for firms to leverage their existing knowledge resources, and to renew and refresh their knowledge base. We suggest that context is a crucial factor in developing our understanding of how social capital does or does not manifest itself. We argue that the context for much current strategic thinking is a growing ‘Americanization’. We suggest that the current variant of the American system of management is characterized by values and practices ‐ unrestrained pursuit of self‐interest, market fundamentalism, minimal state, low taxation ‐ that are at odds with the development of social capital and explore the implications of the social capital argument for European strategic management.
Thinking and acting strategically: New challenges for interrogating strategy
Authors: Wilson David C. , Jarzabkowski Paula
Published: March 2004

Abstract This paper takes a critical and evaluative stance toward micro‐activity‐based approaches to understanding strategy. It argues that such approaches bring with them important theoretical and empirical challenges. The paper argues against a tendency to reductionism without equal emphasis to the contextual influences that bound micro‐strategising. Finally, the paper argues for a more international and comparative approach to micro‐strategy studies than has currently been the case.
Rethinking strategy: contemporary perspectives and debates
Authors: Ezzamel Mahmoud , Willmott Hugh
Published: March 2004

Abstract This paper seeks to clarify and illustrate the distinctive contribution of Foucauldian discursive analysis to the study of strategy. We distinguish it from other forms of analysis before applying it to interpret a fragment of empirical material drawn from a longitudinal study of a global retailing company. In conclusion, the paradox of undertaking discursive analysis is discussed.
Crisis in strategy: fragmentation, integration or synthesis
Authors: Volberda Henk W.
Published: March 2004

Abstract The strategy field is replete with competing prescriptions and directives with regard to successful performance. Although integration should be pursued more vigorously from an academic standpoint, in this paper it is argued that real progress in the strategy field requires synthesis. Attempts at integration often lead to theoretical frameworks that are relatively disconnected from urgent problems in strategic management. In escaping this fragmentation‐integration dilemma, several avenues for strategy synthesis are provided. Synthesis does not attempt to develop a single paradigm consisting of universal concepts and laws covering the entire strategic management field. Instead it is anchored in a few clusters of strategic management problems: drawing firm boundaries, developing dynamic capabilities, and finding viable strategy configurations. They are essential future directions in strategy synthesis.
Sizing of microdrops
Authors: Lee Irwin T. , Fan Sewan , Halyo Valerie , Kim Peter C. , Lee Eric R. , Perl Martin L. , Rogers Howard
Published: March 2004

Several techniques for determining the size of small fluid microdrops with diameters ranging from 5 to 30 μm have been developed and evaluated using an automated variation on the Millikan oil drop experiment. The average diameter of a large sample of monodisperse fluid drops was determined by measuring their terminal velocity in air, or if charged, their motion under the influence of an electric field, as well as by measurement of the magnitude of their Brownian motion. The diameter of individual drops was determined optically, by direct observation using an imaging system based on a charge-coupled-device camera. The technique used to analyze the image data is based on a best-fit technique taking the point spread function of the lens into account, and yields results accurate to 1% (based on a single image) without the need for any calibration. By combining this technique with terminal velocity measurements, the density of the fluid can be determined to similar accuracy.
Comment on “The nucleation behavior of supercooled water vapor in helium” [J. Chem. Phys. 117, 5647 (2002)]
Authors: Labetski D. G. , Holten V. , van Dongen M. E. H.
Published: March 2004

In a recent paper Peeters et al. published new experimental data on nucleation rates of water in the temperature range of 200–235 K. They reported about a drastic change in the nucleation rate at 207 K. An error in their experimental procedure has been found. The data of Peeters et al. have been reinterpreted. The jump in nucleation rate disappears and the corrected nucleation rate data are in good agreement with data found by Wölk and Strey with a different experimental facility.
Influence of sequence correlations on the adsorption of random heteropolymers onto homogeneous planar surfaces
Authors: Polotsky Alexey , Schmid Friederike , Degenhard Andreas
Published: March 2004

Using a reference system approach, we develop an analytical theory for the adsorption of random heteropolymers with exponentially decaying and/or oscillating sequence correlations on planar homogeneous surfaces. We obtain a simple equation for the adsorption-desorption transition line. This result as well as the validity of the reference system approach is tested by a comparison with numerical lattice calculations.
Simulation of polymer–polymer interdiffusion using the dynamic lattice liquid model
Authors: Polanowski Piotr , Pakula Tadeusz
Published: March 2004

In this paper, we present computer simulation results concerning interdiffusion of fully compatible components in symmetric binary (AB) polymer mixtures in solutions. The simulation is performed in two dimensions using the algorithm based on the dynamic lattice liquid model. The solvent molecules are taken into account explicitly. The evolution of the concentration profiles in time at an interface is studied for chain lengths N=2,4,8,16 for three polymer concentrations φ=0.1,0.5,0.9. The tracer diffusion coefficients for polymer chains and for the solvent are obtained by monitoring the mean square displacements of their center of mass. The relationships between coefficients of interdiffusion and self-diffusion are tested.
Influence of diffusion on the kinetics of excited-state association–dissociation reactions: Comparison of theory and simulation
Authors: Popov Alexander V. , Agmon Noam , Gopich Irina V. , Szabo Attila
Published: March 2004

Several recent theories of the kinetics of diffusion influenced excited-state association–dissociation reactions are tested against accurate Brownian dynamics simulation results for a wide range of parameters. The theories include the relaxation time approximation (RTA), multiparticle kernel decoupling approximations and the so-called kinetic theory. In the irreversible limit, none of these theories reduce to the Smoluchowski result. For the pseudo-first-order target problem, we show how the RTA can be modified so that the resulting formalism does reduce correctly in the irreversible limit. We call this the unified Smoluchowski approximation, because it unites modern theories of reversible reactions with Smoluchowski’s theory of irreversible reactions.
Liquid stability in a model for ortho-terphenyl
Authors: La Nave E. , Mossa S. , Sciortino F. , Tartaglia P.
Published: March 2004

We report an extensive study of the phase diagram of a simple model for ortho-terphenyl, focusing on the limits of stability of the liquid state. Reported data extend previous studies of the same model to both lower and higher densities and to higher temperatures. We estimate the location of the homogeneous liquid–gas nucleation line and of the spinodal locus. Within the potential energy landscape formalism, we calculate the distributions of depth, number, and shape of the potential energy minima and show that the statistical properties of the landscape are consistent with a Gaussian distribution of minima over a wide range of volumes. We report the volume dependence of the parameters entering in the Gaussian distribution (amplitude, average energy, variance). We finally evaluate the locus where the configurational entropy vanishes, the so-called Kauzmann line, and discuss the relative location of the spinodal and Kauzmann loci.
Radiative decay of nonstationary system
Authors: Banerjee Sumana , Gangopadhyay Gautam
Published: March 2004

When a finite quantum system, say a fluorescent molecule is attached to a bulk surface and excited by a short laser pulse, the decay dynamics of the system is modulated by the surface and the signal is enhanced due to the bulk surface. We have considered the decay dynamics of a model of displaced distorted molecule whose excited potential surface is coupled to a continuum and then this first continuum is in turn coupled to a second continuum. In the short time scale there is a coherent exchange of energy between the system molecule and the first continuum states. In the long time scale the energy of the whole system plus first continuum drains out to the final continuum states. A dendrimer nanocomposite with the gold surface [O. Varnavski, R. G. Ispasoiu, L. Balogh, D. Tomalia, T. Goodson, III, J. Chem. Phys. 114, 1962 (2001)] shows an enhanced light emission. This can be qualitatively understood from the model we proposed here. We have numerically studied the various potential parameters of the molecule which can affect the signal. When the potential surfaces are flat, the band structure of the first continuum states along with its initial excitation has some nontrivial effect on the profile of the radiative decay.
Path integral Monte Carlo approach for weakly bound van der Waals complexes with rotations: Algorithm and benchmark calculations
Authors: Blinov Nicholas , Song XiaoGeng , Roy Pierre-Nicholas
Published: March 2004

A path integral Monte Carlo technique suitable for the treatment of doped helium clusters with inclusion of the rotational degrees of freedom of the dopant is introduced. The extrapolation of the results to the limit of infinite Trotter number is discussed in detail. Benchmark calculations for small weakly bound HeN4–OCS clusters are presented. The Monte Carlo results are compared with those of basis set calculations for the He–OCS dimer. A technique to analyze the orientational imaginary time correlation function is suggested. It allows one to obtain information regarding the effective rotational constant for a doped helium cluster based on a model for the rotational Hamiltonian. The renormalization of the effective rotational constant for HeN4–OCS clusters derived from the orientational imaginary time correlation function is in good agreement with experimental results.
First principles calculations of electronic structures and metal mobility of NaxSi46 and NaxSi34 clathrates
Authors: Conesa J. C. , Tablero C. , Wahnón P.
Published: March 2004

Energetics, geometry, electronic band structures, and charge transfer for NaxSi46 and NaxSi34 clathrates with different degrees of cavity filling by sodium, and the mobility of the Na atom inside the different cavities are studied using first principles density functional calculations within the generalized gradient approximation. The stabilization of the clathrate lattice and the cell volume variation upon the inclusion of Na (which appears to move easily in the larger cavities of NaxSi34, thus justifying the experimental observations) are discussed in connection with the onset of the repulsion between Na and Si for distances shorter than ∼3.4 Å. For all degrees of filling of the different cavities examined we find that the electron population of the s orbitals in the partially ionized Na atoms increases with a decrease in the size of the cavity, and that the Na states contribute significantly to the density of states at the Fermi level and thus influence the properties of these compounds.
Quality of contracted Gaussian-type function basis sets
Authors: Tatewaki Hiroshi , Koga Toshikatsu , Shimazaki Tsuyoshi , Yamamoto Shigeyoshi
Published: March 2004

The valence quality of contracted (C) Gaussian-type function (GTF) basis sets in molecular calculations is discussed for the first- through fourth-row atoms. The split-valence basis sets derived from minimal-type CGTF sets are compared with those derived from primitive (P) GTF sets. Using F, Cl, Br, and I atoms and their homonuclear diatomics as test species, we find that the split-valence CGTF sets have almost the same quality as PGTF sets with larger s and p expansion terms: For example, the (53/5), (533/53), (5333/533/5), and (53 333/5333/53) CGTF sets correspond approximately to the [9/5], [15/9], [19/15/5], and [22/18/7] PGTF sets for the first- to fourth-row atoms, respectively, where the slash separates the s, p, and d symmetries. For the main group atoms of the four rows, we recommend using the above-mentioned CGTFs or larger.
Theoretical investigation of ground and excited states of the methylene amidogene radical (H2CN)
Authors: Eisfeld Wolfgang
Published: March 2004

The excited states and the absorption spectrum of the methylene amidogene radical are studied by high-level ab initio calculations. The multireference configuration interaction method was used in combination with different basis sets and basis set extrapolation to compute equilibrium geometries, harmonic frequencies, and excitation energies of the four lowest doublet electronic states of the title species. Potential curves and transition dipole moment functions were determined along the normal mode coordinates of the electronic ground state. These functions were employed to determine vibronic absorption spectra. The intensities of dipole forbidden but vibronically allowed transitions were calculated by explicitly evaluating integrals over the vibrational wave functions and the transition dipole functions of the involved electronic states. By this method the oscillator strengths of the dipole allowed A12←2B2 and the dipole forbidden B12←2B2 bands were computed. It turns out that the dipole forbidden transition is two orders of magnitude weaker than the dipole allowed one. The 0–0 excitation energies are found to be 30 256 cm−1 for the B12 state and 34 646 cm−1 for the A12 state. From the combined results of the excitation energies and oscillator strengths it is concluded that the experimentally observed peaks must be due to the A12 state, in contradiction to earlier assignments.
Relativistic all-electron two-component self-consistent density functional calculations including one-electron scalar and spin–orbit effects
Authors: Peralta Juan E. , Scuseria Gustavo E.
Published: March 2004

We have implemented a Gaussian basis-set two-component self-consistent field method based on the fourth-order nuclear-only Douglas–Kroll–Hess approximation. Two-electron spin–orbit effects are included using Boettger’s screened-nuclear spin–orbit approximation [Phys. Rev. B 62, 7809 (2000)]. In our two-component approach, the spin–orbit interaction is taken into account in a variational fashion employing a generalized Kohm–Sham scheme which allows one to work with hybrid density functionals. For open-shell systems we adopt the noncollinear spin-density approximation. Results are presented for equilibrium bond lengths, harmonic vibrational frequencies, and bond dissociation energies with local spin-density, generalized gradient approximation, and hybrid functionals in a set of benchmark molecules.
Theoretical study of Ng–NiN2 (Ng=Ar,Ne,He)
Authors: Ono Yuriko , Taketsugu Tetsuya
Published: March 2004

It is shown that NiN2 and noble gas atoms, Ar, Ne, and He, combine with the binding energy of 11.52, 4.06, and 7.37 kcal/mol, respectively, by the multireference perturbational (CASPT2) method. By the density functional theory calculations using MPWPW91 functionals, the Ni–N–N bending frequency in NiN2 and Ar–NiN2 is estimated as 310.7 and 358.7 cm−1, respectively, the latter of which is in good agreement with the corresponding experimental frequency, 357.0 cm−1, determined for NiN2 isolated in solid argon.
Performance of the general-model-space state-universal coupled-cluster method
Authors: Li Xiangzhu , Paldus Josef
Published: March 2004

The capabilities of the recently developed multireference, general-model-space (GMS), state-universal (SU) coupled-cluster (CC) method have been extended in order to enable the handling of any excited state that represents a single (S) or a double (D) excitation relative to the ground state. A series of calculations concerning the ground and excited states of the CH+, HF, F2, H2O, NH2, and CH2 molecules were carried out so as to assess the performance of the GMS SU CCSD method. For diatomics we have computed the entire potential energy curves, while for triatomics we have focused on vertical excitation energies. We demonstrate how a systematic enlargement of the model space enables a consideration of a larger and larger number of excited states. A comparison of the CC and full configuration interaction or large-scale CI results enables an assessment of the accuracy and reliability of the GMS SU CCSD method within a given basis set. In all cases very good results have been obtained, including highly excited states and those having a doubly-excited character.
Quantum study of the N+N2 exchange reaction: State-to-state reaction probabilities, initial state selected probabilities, Feshbach resonances, and product distributions
Authors: Wang Dunyou , Huo Winifred M. , Dateo Christopher E. , Schwenke David W. , Stallcop James R.
Published: March 2004

We report a detailed three-dimensional time-dependent quantum dynamics study of the state-to-state N+N2 exchange scattering in the 2.1–3.2 eV range using a recently developed ab initio potential energy surface (PES). The reactive flux arrives at the dividing surface in the asymptotic product region in a series of six packets, instead of a single packet. Further study shows that these features arise from the “Lake Eyring” region of the PES, a region with a shallow well between two transition states. Trappings due to Feshbach resonances are found to be the major cause of the time delay. A detailed analysis of the Feshbach resonance features is carried out using an L2 calculation of the metastable states in the “Lake Eyring” region. Strong resonance features are found in the state-to-state and initial state selected reaction probabilities. The metastable states with bending motions and/or bending coupled with stretching motions are found to be the predominant source of the resonance structure. Initial state selected reaction probabilities further indicate that the lifetimes of the metastable states with bending motions in the “Lake Eyring” region are longer than those of states with stretching motions and thus dominate the reactive resonances. Resonance structures are also visible in some of the integral cross sections and should provide a means for future experimental observation of the resonance behavior. A study of the final rotational distributions shows that, for the energy range studied here, the final products are distributed toward high-rotational states. Final vibrational distributions at the temperatures 2000 and 10 000 K are also reported.
Time-dependent wave packet study on trans-cis isomerization of HONO
Authors: Richter Falk , Rosmus Pavel , Gatti Fabien , Meyer Hans-Dieter
Published: March 2004

Using a full six-dimensional ab initio potential energy surface and nuclear motion Hamiltonian, time-dependent computations were performed for the cis-trans isomerization of HONO. The multiconfiguration time-dependent Hartree method was used to propagate the six-dimensional wave packets. The initial excitations were chosen to be excitations of the local stretch modes and the HON local bend mode. The energy redistribution within 2 to 5 ps in the energy region of the OH stretching modes in both isomers was analyzed. The Fourier transformed frequency domain spectra were attributed to the eigenstates calculated previously by the time-independent variational approach. The results are also compared with classical trajectory computations of Thomson et al. [J. Chem. Phys. 118, 1673 (2003)] on empirical surfaces. In agreement with matrix experiments, the cis→trans isomerization was found to be much faster than the opposite interconversion. The intramolecular dynamics were found to be very complex involving numerous weakly excited delocalized eigenstates and anharmonic resonances. Particularly in the cis-isomer, the excitation of the HON bending local mode leads to fast energy redistribution in cis-trans delocalized modes. Neither the excitation of the OH stretching local mode in the cis nor in the trans form produces a fast isomerization, in agreement with the strongly localized characters of the corresponding eigenstates calculated variationally by Richter et al. [J. Chem. Phys. 120, 1306 (2004)] and the gas phase spectra of HONO.
Size and persistence length of molecular bottle-brushes by Monte Carlo simulations
Authors: Elli Stefano , Ganazzoli Fabio , Timoshenko Edward G. , Kuznetsov Yuri A. , Connolly Ronan
Published: March 2004

Single-chain simulations of densely branched comb polymers, or “molecular bottle-brushes” with side-chains attached to every (or every second) backbone monomer, were carried out by off-lattice Monte Carlo technique. A coarse-grained model, described by hard spheres connected by harmonic springs, was employed. Backbone lengths of up to 100 units were considered, and compared with the corresponding linear chains. The backbone molecular size was investigated as a function of its length at fixed arm size, and as a function of the arm size at fixed backbone length. The apparent swelling exponents obtained by a power-law fit were found to be larger than those for the corresponding linear polymers, indicative of stiffening of the comb backbone. The probability distribution function for the backbone end-to-end distance was also investigated for different backbone lengths and arm sizes. Analysis of this function yielded the critical exponents, which revealed an increase in the swelling exponent consistent with values found from the molecular size. The apparent persistence length of the backbone was also determined, and was found to increase with increasing branching density. Finally, the static structure factors of the whole bottle-brushes and of their backbones are discussed, which provides another consistent estimate of the swelling exponents.
Thermodynamic stability and kinetic foldability of a lattice protein model
Authors: Li Jie , Wang Jun , Zhang Jian , Wang Wei
Published: March 2004

By using serial mutations, i.e., a residue replaced by 19 kinds of naturally occurring residues, the stability of native conformation and folding behavior of mutated sequences are studied. The 3×3×3 lattice protein model with two kinds of interaction potentials between the residues, namely the original Miyazawa and Jernigan (MJ) potentials and the modified MJ potentials (MMJ), is used. Effects of various sites in the mutated sequences on the stability and foldability are characterized through the Z-score and the folding time. It is found that the sites can be divided into three types, namely the hydrophobic-type (H-type), the hydrophilic-type (P-type) and the neutral-type (N-type). These three types of sites relate to the hydrophobic core, the hydrophilic surface and the parts between them. The stability of the native conformation for the serial mutated sequences increases (or decreases) as the increasing in the hydrophobicity of the mutated residues for the H-type sites (or the P-type sites), while varies randomly for the N-type sites. However, the foldability of the mutated sequences is not always consistent with the thermodynamic stability, and their relationship depends on the site types. Since the hydrophobic tendency of the MJ potentials is strong, the ratio between the number of the H-type sites and the number of the P-type sites is found to be 1:2. Differently, for the MJJ potentials it is found that such a ratio is about 1:1 which is relevant to that of real proteins. This suggests that the modification of the MJ potentials is rational in the aspect of thermodynamic stability. The folding of model proteins with the MMJ potentials is fast. However, the relationship between the foldability and the thermodynamic stability of the mutated sequences is complex.
Non-Born–Oppenheimer study of positronic molecular systems: e+LiH
Authors: Bubin Sergiy , Adamowicz Ludwik
Published: March 2004

Very accurate non-Born–Oppenheimer variational calculations of the ground state of e+LiH have been performed using explicitly correlated Gaussian functions with preexponential factors dependent on powers of the internuclear distance. In order to determine the positron detachment energy of e+LiH and the dissociation energy corresponding to the e+LiH fragmentation into HPs and Li+ we also calculated non-BO energies of HPs, LiH, and Li+. For all the systems the calculations provided the lowest ever-reported variational upper-bounds to the ground state energies. Annihilation rates of HPs and e+LiH were also computed. The dissociation energy of e+LiH into HPs and Li+ was determined to be 0.036 548 hartree.
An ab initio study of tunneling splittings in the water dimer
Authors: Watanabe Yumiko , Taketsugu Tetsuya , Wales David J.
Published: March 2004

Tunneling splittings in the water dimer have been determined by the semiclassical WKB method, based on pathways characterized at the computational level of second-order Møller–Plesset (MP2) theory with basis sets of aug-cc-pVTZ quality. This calculation takes into account all three acceptor tunneling, donor–acceptor interchange, and bifurcation tunneling rearrangements of the water dimer. The tunneling splittings were evaluated as 7.73 cm−1 (large splitting) and 0.42 cm−1 (small splitting), which are in good agreement with the corresponding experimental values of 11.18 cm−1 and 0.70 cm−1, respectively.
Phase dilemma in density matrix functional theory
Authors: Pernal Katarzyna , Cioslowski Jerzy
Published: March 2004

For closed-shell systems, a particular parametrization of coefficients in a configuration interaction (CI) expansion provides a convenient formulation for the search over electronic wave functions constrained by a set of natural orbitals (NOs) and the corresponding occupation numbers that are invoked in every variational construction of the density matrix functional (DMF) Vee(Γ) for the electron–electron repulsion energy. It produces an explicit expression for Vee in terms of the Coulomb and exchange integrals over NOs, and an idempotent matrix ω, diagonal elements of which equal the occupation numbers. At the same time, it reveals a very serious bottleneck affecting any rigorous approach to the DMF theory, namely the phase dilemma that stems from the necessity to carry out minimization over a large number of possible combinations of CI coefficient signs. While underscoring its lack of variational nature, a simple approximation for the phase factor products provides a strict derivation for the recently proposed Kollmar–Hess functional.
A theoretical model of the photoabsorption spectra of carbon buckyonions
Authors: Ruiz A. , Bretón J. , Gomez Llorente J. M.
Published: March 2004

A theoretical model has been developed to predict the photoabsorption spectra of spherical carbon buckyonions in the region dominated by the π-plasmon feature. This model makes use of the microscopic electronic structure of the system, which is provided by an effective Hückel one-electron model. The important screening effects are treated within the random phase approximation, whose form is an extension to the dynamic case of the one derived in a previous work [S. Iglesias-Groth, et al., J. Chem. Phys. 118, 7103 (2003)] for the static polarizabilities of these species. A systematic analysis as a function of the buckyonion size is performed. We compare the spectra obtained in this way with those derived from a different representation of the electron motion, namely a two-dimensional spherical electron gas, and from a classical dielectric model.
Surface/interface electronic structure in C60 anchored aminothiolate self-assembled monolayer: An approach to molecular electronics
Authors: Patnaik Archita , Setoyama Hiroyuki , Ueno Nobuo
Published: March 2004

Electronic structure in self-assembled monolayers (SAMs) of C60 anchored 11-amino–1-undecane thiol (C60-11-AUT) on Au(111) was studied by means of ultraviolet photoelectron spectroscopy and hybrid density functional theory calculations. Valence band features of the molecular conformation revealed the interface electronic structure to be dominated by σ(S–Au), localized at the thiolate anchor to Au. Formation of a localized covalent bond as a result of hybridization between N Pz orbital of –NH2 group of the thiolate SAM and the π level of C60 resulted in a symmetry change from Ih in C60 to C1 in C60-11-AUT SAM. Appearance of low, but finite amplitude surface electronic states of bonded C60, much beyond the Fermi level, ruled out Au–C60 end group contact. The band gap Eg of the SAM, determined to be 2.7 eV, was drastically reduced from the insulating alkanethiol SAMs (∼8.0 eV) and fell intermediate between the C60 ground state (N electrons, 1.6 eV) and C60 solid (N±1 electrons, 3.7 eV).
Water’s polyamorphic transitions and amorphization of ice under pressure
Authors: Johari G. P. , Andersson Ove
Published: March 2004

Transformations of water’s high density amorph (HDA) to low density amorph (LDA) and of LDA’s to cubic ice (Ic) have been studied by in situ thermal conductivity κ measurements at high pressures. The HDA to LDA transformation is unobservable at p of 0.07 GPa, indicating that, for a fixed heating rate, an increase in pressure increases the temperature of HDA to LDA transformation and decreases that of LDA to ice Ic, causing thereby the two transformations to merge, and HDA appears to convert directly to ice Ic. Thus either LDA forms but converts extremely rapidly to ice Ic, or LDA does not form. At a fixed p and T, in the range of pressure amorphization of hexagonal ice, κ continues to decrease with time. Therefore, the amorphization of ice Ih is kinetically controlled. When HDA at 1 GPa was heated from 130 to 157 K and densified to very HDA, its κ increased by 3%. Our findings and a scrutiny of earlier reports show that a reversible transition between HDA and LDA does not occur at ∼135 K and ∼0.2 GPa. Since there is no unique HDA, it is difficult to justify the conjecture for a second critical point for water.
Electric field effects on photoinduced electron transfer processes of methylene-linked compounds of pyrene and N,N-dimethylaniline in a polymer film
Authors: Tsushima Minoru , Ohta Nobuhiro
Published: March 2004

Time-resolved measurements of the electric-field-induced change in fluorescence intensity have been made for methylene-linked compounds of pyrene and N,N-dimethylaniline (DMA) doped in a polymer film. The lifetime of the fluorescence emitted from the locally excited state of pyrene chromophore becomes shorter in the presence of electric field (F), when the dopant concentration is high. The lifetime of the excipelx fluorescence resulting from the photoinduced electron transfer (PIET) from DMA to the excited state of pyrene chromophore between different molecules also becomes shorter in the presence of F. Based on the simulation of the electric field effect on fluorescence decay, the mechanism of intermolecular PIET between DMA and pyrene chromophore in a polymer film is discussed.
The role of polymer spacers in specific adhesion
Authors: Moreira André G. , Marques Carlos M.
Published: March 2004

We study the role of flexible spacers in specific adhesion from the point of view of polymer reaction–diffusion theory. By assuming that the interactions between complementary adhesion moieties occur on a length scale much smaller than the size of the polymer spacer, we describe in detail binding and rupture between two opposing surfaces. Predictions are given for the physical properties of interest such as the time evolution of bond density and the ranges of attraction and unbinding. We also discuss the dynamic crossover between reversible and irreversible bridging.