bluuebunny/crossref_metadata_2025 huggingface dataset:
2D shape optimization of turbine blades
Authors: Montrone F. , Wever U. , Zheng Q.
Published: January 2004

In this paper, we present methods to optimize the efficiency of turbine blades. The profile of a turbine blade is parameterized by curves, its parameters form the variables of a nonlinear optimization problem. Because of the very expensive function evaluation, gradient based optimization methods are preferred. In order to provide gradient information for the optimization method, the fluid sensitivities have to be considered. Theoretical properties and implementation aspects for the sensitivity equation are discussed. Constraints guarantee the requirements for casting, machining, and cooling of the blades.
Cavity detection by the electric method: The 3‐dimensional case
Authors: Ang D.D. , Mennicken R. , Thanh D.N. , Trong D.D.
Published: January 2004

In this paper the authors prove a uniqueness theorem for the electric detection of cavities in a three dimensional solid from Cauchy data measured on the surface. The cavities, finite in number, are assumed to be insulating. The surfaces of the cavities are assumed to be smooth on the complement of a set that is, in some sense, negligible.
Mammalian Fertilization: From Sperm Factor to Phospholipase Cζ
Authors: Kurokawa Manabu , Sato Ken‐ichi , Fissore Rafael A
Published: January 2004

Abstract In mammalian eggs, the fertilizing sperm evokes intracellular Ca2+ ([Ca2+]i) oscillations that are essential for initiation of egg activation and embryonic development. Although the exact mechanism leading to initiation of [Ca2+]i oscillations still remains unclear, accumulating studies suggest that a presently unknown substance, termed sperm factor (SF), is delivered from the fertilizing sperm into the ooplasm and triggers [Ca2+]i oscillations. Based on findings showing that production of inositol 1,4,5‐trisphosphate (IP3) underlies the generation of [Ca2+]i oscillations, it has been suggested that SF functions either as a phospholipase C (PLC), an enzyme that catalyzes the generation of IP3, or as an activator of a PLC(s) pre‐existing in the egg. This review discusses the role of SF as the molecule responsible for the production of IP3 and the initiator of [Ca2+]i oscillations in mammalian fertilization, with particular emphasis on the possible involvement of egg‐ and sperm‐derived PLCs, including PLCζ, a novel sperm specific PLC.
Subcellular distribution of the inositol 1,4,5‐trisphosphate receptors: functional relevance and molecular determinants
Authors: Vermassen Elke , Parys Jan B. , Mauger Jean‐Pierre
Published: January 2004

Abstract The inositol 1,4,5‐trisphosphate receptor (IP3R) is an intracellular Ca2+ channel that is for the largest part expressed in the endoplasmic reticulum. Its precise subcellular localization is an important factor for the correct initiation and propagation of Ca2+ signals. The relative position of the IP3Rs, and thus of the IP3‐sensitive Ca2+ stores, to mitochondria, nucleus or plasma membrane determines in many cases the physiological consequences of IP3‐induced Ca2+ release. Most cell types express more than one IP3R isoform and their subcellular distribution is cell‐type dependent. Moreover, it was recently demonstrated that depending on the physiological status of the cell redistribution of IP3Rs and/or of IP3‐sensitive Ca2+ stores could occur. This indicates that the cell must be able to regulate not only IP3R expression but also its distribution. The various proteins potentially determining IP3R localization and redistribution will therefore be discussed.
Verarbeitung von personbeschreibender Information als Textverstehen
Authors: Krolak-Schwerdt Sabine , Wintermantel Margret
Published: January 2004

Zusammenfassung. Der vorliegende Beitrag stellt einen Bezug zwischen der Forschung zur sozialen Kognition und zum Textverstehen her, indem argumentiert wird, dass Theorien und Methoden der Textverarbeitung sich in besonderem Maße dazu eignen, den Prozess der Verarbeitung von Personinformationen zu verstehen. Zunächst wird gezeigt, dass Forschung zu Gedächtnis- und Eindrucksbildungsprozessen über Personen fast durchgängig sprachliches Material verwendet, das aus einer listenförmigen Aneinanderreihung von Aussagen über Personmerkmale besteht. Forschung auf dem Gebiet des Textverstehens zeigt dagegen, dass die sprachlichen Mittel der Aussagenverknüpfung grundlegend für die Verarbeitung sind, denn durch Sie werden die Einzelaussagen zueinander in Beziehung gesetzt und hierarchisch geordnet. Es wird argumentiert, dass die Analyse der Eindrucks- und Urteilsbildung aus Textbeschreibungen einen besseren Zugang zu Prozessen der sozialen Informationsverarbeitung gestattet, weil dieser der Komplexität von Beziehungen zwischen Merkmalen und deren kognitiver Repräsentation Rechnung trägt. Für einen adäquateren theoretischen Rahmen sind die vorherrschenden Netzwerkmodelle zur Repräsentation von Personinformationen mit Ansätzen des Textverstehens zu verbinden, die über assoziative Verbindungsstärken hinaus qualitative Spezifikationen von Aussagenverknüpfungen zulassen.
Die Genese akademischer Selbstkonzepte:
Authors: Möller Jens , Köller Olaf
Published: January 2004

Zusammenfassung. Akademische Selbstkonzepte gelten als wichtige Einflussgrößen leistungsthematischen Verhaltens. Im Bereich der Pädagogischen Psychologie ist ihre Genese insbesondere im Zusammenhang mit dem Bezugsrahmenmodell (Internal/External frame of reference model; kurz: I/E-Modell, Marsh, 1986 ) diskutiert worden. Das Modell postuliert im Kern positive Auswirkungen von Schulleistungen auf das akademische Selbstkonzept im selben Fach als Folge sozialer oder externaler (E) Vergleiche und negative Auswirkungen dieser Fachleistungen auf das akademische Selbstkonzept in einem anderen Fach als Folge dimensionaler oder internaler (I) Vergleiche. Der Überblick über die bisherige Forschung weist die Gültigkeit des I/E-Modells mit einer Vielzahl von quer- und längsschnittlichen Studien in verschiedenen Altersgruppen, Ländern und Schulsystemen nach. Experimentelle Studien untermauern die Annahmen zu den Auswirkungen dimensionaler Vergleiche.
Warum Brainstorming in Gruppen Kreativität vermindert:
Authors: Stroebe Wolfgang , Nijstad Bernard A.
Published: January 2004

Zusammenfassung. Dass Brainstorming in Gruppen die Kreativität erhöht gilt als Binsenwahrheit. Dennoch hat eine Vielzahl von Untersuchungen gezeigt, dass in Brainstorminggruppen viel weniger und auch weniger gute Ideen erzeugt werden als individuell. Dieser Artikel berichtet die Ergebnisse von zwei Forschungsprogrammen, in denen mögliche Ursachen dieser Leistungseinbußen und die ihnen zugrunde liegenden kognitiven Prozesse identifiziert wurden. In den frühen Untersuchungen identifizierten Diehl und Stroebe (1987 , 1991 ) Produktionsblockierung als Hauptursache. Um zu erklären, warum die Gruppenmitglieder die aufgrund des “Turn-taking“ entstehenden Wartezeiten nicht produktiv nützen können, entwickelten Nijstad, Stroebe und Lodewijkx (2002 , in Druck ) eine kognitive Theorie der Ideengenerierung (SIAM: Seach for Ideas in Associative Memory). Nach dieser Theorie beruht die Produktion von Ideen auf einem zwei-Phasenprozess, in dem eine Phase der Wissensaktivierung von einer Phase der Ideengenerierung gefolgt wird. In beiden Phasen wird der kognitive Prozess durch die Wartezeiten behindert, wobei sich die mangelnde Vorhersagbarkeit der Wartezeiten vor allem auf die erste Phase, die Dauer der Wartezeiten hingegen auf die zweite Phase auswirkt. Zwei Untersuchungen bestätigen diese Vorhersagen. Im letzten Teil des Artikels werden Vorhersagen der SIAM-Theorie über Bedingungen geprüft, unter denen die Darbietung von Ideen, bei gleichzeitiger Ausschaltung der Blockierung (z.B. elektronisches Brainstorming), die Ideengenerierung stimulieren können.
Seasonal and interannual variability in algal biomass and primary production in the Mediterranean Sea, as derived from 4 years of SeaWiFS observations
Authors: Bosc E. , Bricaud A. , Antoine D.
Published: January 2004

Because the Mediterranean has been subject for several decades to increasing anthropogenic influences, monitoring algal biomass and primary production on a long‐term basis is required to detect possible modifications in the biogeochemical equilibrium of the basin. This work was initiated thanks to a 4‐year‐long time series of SeaWiFS observations. Seasonal variations of algal biomass (estimated using a previously developed regional algorithm) and primary production were analyzed for the various regions, and compared with those estimated using the CZCS sensor (1978–1986). Also, interannual variations could be assessed for the first time. The seasonal cycles of algal biomass generally reveal a maximum in winter or spring, and a minimum in summer. Some conspicuous differences with CZCS observations (e.g., in the Northwest Basin, reduction of the deep convection zone, earlier start of the spring bloom, quasi‐absence of the vernal bloom) likely result from environmental changes. Interannual variations in algal biomass are noticeable all over the basin, including in the very oligotrophic waters of the Eastern Basin. The seasonal evolution of primary production is predominantly influenced by that of algal biomass in the Western Basin (with, in particular, a spring maximum). In the Eastern Basin, the seasonal courses of PAR and biomass tend to compensate each other, and primary production varies weakly along the year. The annual values computed over the 1998–2001 period for the Western Basin (163 ± 7 gC m−2 yr−1) and the Eastern Basin (121 ± 5 gC m−2 yr−1) are lower (by 17 and 12%, respectively) than those previously derived (using the same light‐photosynthesis model) from CZCS data.
Photochemistry and nature of organic matter in Arctic and Antarctic snow
Authors: Grannas Amanda M. , Shepson Paul B. , Filley Timothy R.
Published: January 2004

It has been shown that sunlit snowpacks are photochemically active, producing a number of species that can significantly impact the overlying atmosphere. Here we investigate the origin of the flux of low molecular weight carbonyl compounds (formaldehyde and acetaldehyde) from sunlit snow obtained from both Arctic (Alert, Canada, and Summit, Greenland) and Antarctic (South Pole) sources. In addition, efforts to characterize the potential snow‐phase organic matter (SPOM) precursors were undertaken. Using chemically characterized SPOM, we find that formaldehyde and acetaldehyde are produced upon irradiation, and that production is enhanced with the addition of nitrate (a precursor to OH radicals). SPOM from both Alert and Summit is found to be derived from a variety of sources, including vascular plants. This indicates deposition of atmospheric particulate matter containing vascular tissue to high‐altitude Arctic snow. These findings open a potential window for a rich record of variations in terrestrial vegetation‐derived aerosol signals that could be preserved in ice cores.
Westward propagating twin gyres in the equatorial Indian Ocean
Authors: Reddy P. Rahul Chand , Salvekar P. S. , Deo A. A. , Ganer D. W.
Published: January 2004

A reduced‐gravity (1‐layer) model forced by daily climatological winds simulates twin, anticyclonic gyres, which propagate westward on either side of the equator. The gyres form at the beginning of both the Southwest Monsoon and the Northeast monsoon in the equatorial eastern Indian Ocean, and subsequently propagate across the basin. Their existence is supported by velocity observations taken during WOCE in 1995 and by TOPEX/Poseidon sea‐level observations during 1993. They are also present in the ECCO model/data product. They form at the front of a Rossby‐wave packet generated by the reflection of the equatorial jet (EJ) from the eastern boundary of the basin. They are likely either Rossby solitons or result from the nonlinear interaction between the EJ and the Rossby‐wave front.
Scarp‐bounded benches in Gorgonum Chaos, Mars: Formed beneath an ice‐covered lake?
Authors: Howard Alan D. , Moore Jeffrey M.
Published: January 2004

Level, bench‐like platforms edged with scarps facing the interior of the Martian Gorgonum Chaos basin may have formed in conjunction with an ancient ice‐covered lake. These benches, however, lack the typical features of shorelines associated with wave and current transport and erosion, such as crescentic embayments, spits, barrier islands, and wave‐cut cliffs. Rather, the basin‐facing platform edges are commonly rounded and cumulate in planform, often evenly encircling buttes protruding above the level of the benches. The benches are postulated to have been formed by outward growth in a quiescent environment, possibly by deformative lateral flow of sediment below the ice‐water interface in a perennially frozen lake due to the weight of the ice overburden.
Fram Strait sea ice outflow
Authors: Kwok R. , Cunningham G. F. , Pang S. S.
Published: January 2004

We summarize 24 years (1978–2002) of ice export estimates and examine, over a 9‐year record, the associated variability in the time‐varying upward‐looking sonar (ULS) thickness distributions of the Fram Strait. A more thorough assessment of the PMW (passive microwave) ice motion with 5 years of synthetic aperture radar (SAR) observations shows the uncertainties to be consistent with that found by Kwok and Rothrock [1999], giving greater confidence to the record of ice flux calculations. Interesting details of the cross‐strait motion profiles and ice cover characteristics revealed by high‐resolution SAR imagery are discussed. The average annual ice area flux over the period is 866,000 km2/yr. Between the 1980s and 1990s, the decadal difference in the net exported ice area is ∼400,000 km2, approximately half the annual average. Except for the years with extreme negative NAO, correlation of winter ice area export with the NAO index remains high (R2 = 0.62). With thickness estimates from ULS moorings, we estimate the average annual ice volume flux (8 years) to be ∼2218 km3/yr (∼0.07 Sv). Over the ∼9‐year ULS ice thickness data set, there is an overall decrease of 0.45 m in the mean ice thickness over the entire time series and a decrease of 0.23 m over the winter months (December through March). Correspondingly, the mode of the MY ice thickness exhibits an overall decrease of 0.55 m and a winter decrease of 0.42 m. These are significant trends. Whether these trends are indicative of the thickness trends of the Arctic Ocean is examined, as the time‐varying behavior of the monthly ULS thickness distributions can be related not only to the seasonal cycle in the basal growth and melt, but also to the magnitude and pattern of ice motion in the Arctic Ocean, and the proximity of the ULS moorings to the ice edge.
Circulation during winter and northerly storm events in southern Lake Michigan
Authors: Rao Y. R. , McCormick M. J. , Murthy C. R.
Published: January 2004

Moored observations of winds, currents, and temperature made off the southeastern Lake Michigan shore during 1998 to 2000 winter‐spring periods are studied to describe the mean winter circulation and episodic circulation during northerly storms in Lake Michigan. Late winter‐spring sediment plumes in southeastern Lake Michigan were attributed to these episodic circulation features. The winter‐spring currents in southeastern Lake Michigan are quite depth independent, and the mean currents flow predominantly alongshore and toward the north. The observed currents show the signature of a forced two‐gyre circulation in the southeastern basin. The interannual variability of mean and fluctuating currents is mainly due to the variability of prevailing wind‐forcing. The intermittent episodic circulation influenced by northerly storms causes significant asymmetry to the mean circulation. During northerly storm episodes, the mean current speeds increased significantly, and the currents within 10 km of shore followed the surface wind stress, while farther offshore the circulation was oppositely directed. During these episodes it is also observed that the combination of directly wind‐forced currents and northward propagating vorticity wave generates significant offshore transport in this region.
Statistical analysis of lightning current parameters: Measurements at Morro do Cachimbo Station
Authors: Visacro Silvério , Soares Amilton , Schroeder Marco Aurélio O. , Cherchiglia Luiz C. L. , de Sousa Vander José
Published: January 2004

Most of the available data concerning lightning current parameters were obtained by means of measurements made in temperate regions in the Northern Hemisphere. Considering the influence of regional aspects on such parameters, the need for references concerning lightning protection practices specifically in tropical zones requires dedicated data. An experimental investigation program has been carried on in Brazil since 1971 in order to provide data for characterization of local lightning current parameters. The authors of the present work are involved in that research. With such purpose, they have evaluated a significant amount of data, obtained by means of measurements taken at an instrumented tower located at “Morro do Cachimbo” Station, in Southeastern Brazil. The lightning current wave registers correspond to 157 strokes, which were measured during 13 years at the station. In this paper, the authors present a statistical evaluation of measured current waves, with particular interest in front wave parameters. The considered parameters (peak current, front duration and front steepness) are compared with those traditionally presented in literature. The cumulative frequency distributions and the correlation coefficients between parameters were determined. One main result was derived from this work, concerning the negative downward discharges: the median (and average) value of current peak measured at tower basis was found to be around 50% and 30% higher, respectively for the first and subsequent strokes, than the usual Berger references measured at tower top.
Asian dust storm events of spring 2001 and associated pollutants observed in New England by the Atmospheric Investigation, Regional Modeling, Analysis and Prediction (AIRMAP) monitoring network
Authors: DeBell Linsey J. , Vozzella Marcy , Talbot Robert W. , Dibb Jack E.
Published: January 2004

Between 18 April and 13 May 2001, three statistically extreme dust aerosol events were observed across the entire northeastern United States. High levels of bulk aerosol water‐soluble Ca2+ (range = 42–482 pptv) and PM2.5 elemental Ca (range = 19–156 pptv) were observed simultaneously at Atmospheric Investigation, Regional Modeling, Analysis and Prediction (AIRMAP) and Interagency Monitoring of Protected Visual Environments (IMPROVE) stations. On the basis of Ca2+ concentrations, the average bulk dust concentration for all events across all four AIRMAP stations was estimated to be 7.4 μg/m3. There was no evidence of dust outbreaks in North America large enough to explain these events. However, in April 2001, massive dust storms occurred in the Tarim Pendi basin and in the Gobi deserts of southern Mongolia and China. Comparison of elemental ratios of AIRMAP samples to previously reported Asian dust aerosol samples showed that all AIRMAP samples had a chemical composition similar to Asian dust transported over long distances. Within the dust plumes, strong correlations were observed between absorption, scattering, and CO, indicative of an anthropogenic contribution including elemental carbon and SO42− aerosols. Aerosol NO3− was also highly elevated during event days, most likely due to uptake of HNO3 by the dust during transport. A comparison of dust plumes sampled by AIRMAP to those sampled off the Asian coast during the TRACE‐P airborne mission and on the U.S. west coast, strongly suggested entrainment of additional pollutants (e.g., CO, aerosol NO3−, and SO42−) as the dust plumes were transported over North America.
Atmospheric sounding by global navigation satellite system radio occultation: An analysis of the negative refractivity bias using CHAMP observations
Authors: Beyerle G. , Wickert J. , Schmidt T. , Reigber C.
Published: January 2004

Validation studies of current GPS radio occultation experiments using meteorological analyses consistently report on a negative refractivity bias in the lower troposphere. End‐to‐end simulations including the GPS receiver's signal tracking process suggest that receiver‐induced phase deviations contribute to this observed bias. We propose a heuristic retrieval algorithm based on the canonical transform and the sliding spectral technique, which seems less susceptible to tracking phase errors than the canonical transform method. The approach is described using simulated profiles and validated on the basis of 4221 CHAMP occultations recorded between 14 May and 10 June 2001. Compared to the canonical transform results, the heuristic method results in a significantly smaller tropospheric refractivity bias at low latitudes at the expense of a reduced vertical resolution.
The use of rituximab, anti‐CD20 monoclonal antibody, in pediatric transplantation
Authors: Pescovitz Mark D.
Published: January 2004

Abstract:  Rituximab, chimeric anti‐human CD20, is approved for treatment of B‐cell lymphoma in adults. It is being used experimentally in other various immune related disease such as immune thrombocytopenic purpura, myasthenia gravis, and rheumatoid arthritis. In transplant recipients it is used for treatment of post‐transplant lymphoproliferative disease, and prevention and treatment of acute rejection. There are few data on its use in children. This paper reviews the use of rituximab in these disease states and provides hypotheses for its mode of action.
Surface nuclear spin relaxation of Hg199
Authors: Romalis M. V. , Lin L.
Published: January 2004

We report the results of a detailed study of surface relaxation of Hg199 nuclear spins in paraffin coated cells. From measurements of the magnetic field and temperature dependence of the spin relaxation rates we determine the correlation time for magnetic fluctuations and the surface adsorption energy. The data indicate that surface relaxation is caused by dipolar coupling to paramagnetic sites on the surface. We also observe changes in the spin relaxation rate caused by ultraviolet radiation resonant with the 254 nm transition in Hg.
An ab initio theoretical prediction:  An antiaromatic ring π-dihydrogen bond accompanied by two secondary interactions in a “wheel with a pair of pedals” shaped complex FH⋯C4H4⋯HF
Authors: Wu Di , Li Zhi-Ru , Hao Xi-Yun , Jalbout A. F. , Adamowicz L. , Li Ru-Jiao , Sun Chia-Chung
Published: January 2004

By the counterpoise-correlated potential energy surface method (interaction energy optimization), the structure of the π H-bond complex FH⋯C4H4⋯HF has been obtained at the second-order Møller–Plesset perturbation theory (MP2/aug-cc-pVDZ) level. Intermolecular interaction energy of the complex is calculated to be −7.8 kcal/mol at the coupled-cluster theory with single, double substitutions and perturbatively linked triple excitations CCSD (T)/aug-cc-pVDZ level. The optimized structure is a “wheel with a pair of pedals” shaped (1|1) structure in which both HF molecules almost lie on either vertical line passing through the middle-point of the C=C bond on either side of the horizontal plane of the C4 ring for cyclobutadiene. In the structure, an antiaromatic ring π-dihydrogen bond is found, in which the proton acceptor is antiaromatic 4 electron and 4 center π bond and the donors are both acidic H atoms of HF molecules. In accompanying with the π-dihydrogen bond, two secondary interactions are exposed. The first is a repulsive interaction between an H atom of HF and a near pair of H atoms of C4H4 ring. The second is the double π-type H bond between two lone pairs on a F atom and a far pair of H atoms.
Theoretical analysis of electron transport through organic molecules
Authors: Tomfohr John , Sankey Otto F.
Published: January 2004

We present a theoretical study of electron transport through a variety of organic molecules. The analysis uses the Landauer formalism in combination with complex bandstructure and projected densities of states calculations to reveal the main aspects of coherent electronic transport through alkanes, benzene-dithiol, and phenylene-ethynylene oligomers. We examine the dependence of the current on molecule length, the effects of molecule-molecule interactions from film packing, differences in contact geometry, and the influence of phenyl ring rotation on the conductances of phenylene-ethynylene oligomers such as 1,4-bis-phenylethynyl-benzene.
Improved LeRoy–Bernstein near-dissociation expansion formula, and prospect for photoassociation spectroscopy
Authors: Comparat Daniel
Published: January 2004

NDE (Near-dissociation expansion) including LeRoy–Bernstein formulas are improved by taking into account the multipole expansion coefficients and the nonasymptotic part of the potential curve. The theory is tested with the Rydberg–Klein–Rees (RKR) potential curve of the Cs2(0g−{6s+6p3/2}) state. Results indicate that the formula could be used to improve the determination of the asymptotic coefficient (within a 1% accuracy) and to extract relativistic correction from photoassociation spectra of long-range potential curve of diatomic molecules.
Dynamic light scattering in liquid and supercooled diphenylmethane
Authors: Rubio J. E. F. , Baonza V. G. , Taravillo M. , Núñez J. , Cáceres M.
Published: January 2004

We use a dynamic light scattering technique to measure both polarized (VV) and depolarized (VH) spectra of liquid diphenylmethane (DPM) between 288 and 362 K, covering both normal and supercooled liquid ranges. Our results allow extracting information on structural relaxation processes, rotational motions, rotation–translation couplings, and molecular reorientation phenomena in liquid DPM. The VV spectra are modeled according to the microscopic theory of Wang [J. Chem. Phys. 70, 3796 (1979)], which assumes that a structural relaxation process dominates the spectrum. We find that the relaxation time of the structural relaxation in DPM follows an Arrhenius behavior. The Rayleigh dip was observed in the VH spectra, which are described using the Andersen–Pecora [J. Chem. Phys. 54, 2584 (1971)] theory. Our results are discussed in terms of the rotation–translation coupling parameter, which we find independent of temperature over the experimental range. The collective reorientation time also follows an Arrhenius behavior with temperature. Finally, we calculate the hydrodynamic volumes for the reorientation process from geometric molecular models in two hydrodynamic limits: slip and stick boundary conditions. Our results suggest that the DMP molecule reorientates in quasi-slipping conditions in the bulk liquid.
Ion mobilities and microscopic dynamics in liquid (Li,K)Cl
Authors: Morgan Ben , Madden Paul A.
Published: January 2004

The dynamical properties of ionic melts formed from mixtures of LiCl and KCl have been studied across the full composition range in computer simulations of sufficient length to enable reliable values for such collective transport coefficients as the viscosity, conductivity, and internal mobilities to be determined reliably. Interest centers on the nontrivial concentration dependence exhibited by these transport coefficients, which agrees well with that observed experimentally, and in relating this to the strength of the association between an ion and its first coordination shell. The relationships between the various transport coefficients, such as those between the diffusion coefficient and the viscosity (Stokes–Einstein) and the conductivity (Nernst–Einstein) also exhibit composition dependences that reflect this association. The connection between the internal mobility and two measures of the coordination shell dynamics (the cage relaxation time and the self-exchange velocity) is explored; it is shown that the self-exchange velocity follows the composition and temperature dependence of the internal mobility very well. Finally, it is shown that allowing for anion polarization in the interaction model increases the mobility of all species without changing the structure of the melt discernibly, with the largest effect being found for the Li+ ion.
Bead–bead interaction parameters in dissipative particle dynamics: Relation to bead-size, solubility parameter, and surface tension
Authors: Maiti Amitesh , McGrother Simon
Published: January 2004

Dissipative particle dynamics (DPD) is a mesoscale modeling method for simulating equilibrium and dynamical properties of polymers in solution. The basic idea has been around for several decades in the form of bead-spring models. A few years ago, Groot and Warren [J. Chem. Phys. 107, 4423 (1997)] established an important link between DPD and the Flory–Huggins χ-parameter theory for polymer solutions. We revisit the Groot–Warren theory and investigate the DPD interaction parameters as a function of bead size. In particular, we show a consistent scheme of computing the interfacial tension in a segregated binary mixture. Results for three systems chosen for illustration are in excellent agreement with experimental results. This opens the door for determining DPD interactions using interfacial tension as a fitting parameter.
Low temperature electron transfer in strongly condensed phase
Authors: Ankerhold Joachim , Lehle Hartwig
Published: January 2004

Electron transfer coupled to a collective vibronic degree of freedom is studied in strongly condensed phase and at lower temperatures where quantum fluctuations are essential. Based on an exact representation of the reduced density matrix of the electronic+reaction coordinate compound in terms of path integrals, recent findings on the overdamped limit in quantum dissipative systems are employed. This allows us to give a consistent generalization of the well-known Zusman equations to the quantum domain. Detailed conditions for the range of validity are specified. Using the Wigner transform these results are also extended to the quantum dynamics in full phase space. As an important application electronic transfer rates are derived that comprise adiabatic and nonadiabatic processes in the low temperature regime including nuclear tunneling. Accurate agreement with precise quantum Monte Carlo data is observed.
Electron and nuclear dynamics of molecular clusters in ultraintense laser fields. II. Electron dynamics and outer ionization of the nanoplasma
Authors: Last Isidore , Jortner Joshua
Published: January 2004

We explore electron dynamics in molecular (CD4)1061 clusters and elemental Xen (n=249–2171) clusters, responding to ultraintense (intensity I=1016–1019 W cm−2) laser fields. Molecular dynamics simulations (including magnetic field and relativistic effects) and analyses of high-energy electron dynamics and nuclear ion dynamics in a cluster interacting with a Gaussian shaped laser field (frequency 0.35 fs−1, photon energy 1.44 eV, phase 0, temporal width 25 fs) elucidated the time dependence of inner ionization, the formation of a nanoplasma of unbound electrons within the cluster or its vicinity, and of outer ionization. We determined the cluster size and the laser intensity dependence of these three sequential-parallel electronic processes. The characteristic times for cluster inner ionization (τii) and for outer ionization (τoi) fall in the femtosecond time domain, i.e., τii=2–9 fs and τoi=4–15 fs for (CD4)1061, τii=7–30 fs and τoi=5–13 fs for Xen (n=479,1061), with both τii and τoi decreasing with increasing I, in accord with the barrier suppression ionization mechanism for inner ionization of the constituents and the cluster barrier suppression ionization mechanism for outer ionization. The positive delay times ΔτOI between outer and inner ionization (e.g., ΔτOI=6.5 fs for Xen at I=1016 W cm−2 and ΔτOI=0.2 fs for (CD4)1061 at I=1019 W cm−2) demonstrate that the outer/inner ionization processes are sequential. For (CD4)1061, τii<τoi, as appropriate for sequential outer/inner ionization dynamics, while for Xen clusters τii>τoi, reflecting on the energetic hierarchy in the ionization of the Xe atoms. Quasiresonance contributions to the outer ionization of the nanoplasma were established, as manifested in the temporal oscillations in the inner/outer ionization levels, and in the center of mass of the nanoplasma electrons. The formation characteristics, dynamics, and response of the nanoplasma in molecular or elemental clusters were addressed. The nanoplasma is positively charged, with a high-average electron density [ρP=(2–3)1022 cm−3], being characterized by high-average electron energies εav (e.g., in Xe1061 clusters εav=54 eV at I=1016 W cm−2 and εav=0.56–0.37 keV at I=1018 W cm−2, with εav∝I1/2). Beyond the cluster boundary the average electron energy markedly increases, reaching electron energies in the range of 1.2–40 keV for outer ionization of Xen (n=249–2171) clusters. The nanoplasma exhibits spatial inhomogeneity and angular anisotropy induced by the laser field. Femtosecond time scales are predicted for the nanoplasma production (rise times 7–3 fs), for the decay (decay times ∼5 fs), and for the persistence time (30–10 fs) of a transient nanoplasma at I=1017–1018 W cm−2. At lower intensities of I=1016 W cm−2 a persistent nanoplasma with a “long” lifetime of >50 fs will prevail.
Franck–Condon simulation of the single vibronic level emission spectra of HSiF and DSiF including anharmonicity
Authors: Mok Daniel K. W. , Lee Edmond P. F. , Chau Foo-tim , Dyke John M.
Published: January 2004

Potential energy functions (PEFs) of the X̃ 1A′ and Ã 1A″ states of HSiF have been computed using the coupled-cluster single-double plus perturbative triple excitations and complete-active-space self-consistent-field multireference internally contracted configuration interaction methods, respectively, employing augmented correlation-consistent polarized-valence quadruple-zeta basis sets. For both electronic states of HSiF and DSiF, anharmonic vibrational wavefunctions and energies of all three modes have been calculated variationally with the ab initio PEFs and using Watson’s Hamiltonian for nonlinear molecules. Franck–Condon factors between the two electronic states, allowing for Duschinsky rotation, were computed using the calculated anharmonic vibrational wavefunctions. These Franck–Condon factors were used to simulate the single vibronic level (SVL) emission spectra recently reported by Hostutler et al. in J. Chem. Phys. 114, 10728 (2001). Excellent agreement between the simulated and observed spectra was obtained for the Ã 1A″(1,0,0)→X̃ 1A′ SVL emission of HSiF. Discrepancies between the simulated and observed spectra of the Ã 1A″(0,1,0) and (1,1,0) SVL emissions of HSiF have been found. These are most likely, partly due to experimental deficiencies and, partly to inadequacies in the ab initio levels of theory employed in the calculation of the PEFs. Based on the computed Franck–Condon factors, minor revisions of previous vibrational assignments are suggested. The calculated anharmonic wave functions of higher vibrational levels of the X̃ 1A′ state show strong mixings between the three vibrational modes of HSi stretching, bending, and SiF stretching.
Theory of time-resolved photoelectron imaging. Comparison of a density functional with a time-dependent density functional approach
Authors: Suzuki Yoshi-ichi , Seideman Tamar , Stener Mauro
Published: January 2004

Time-resolved photoelectron differential cross sections are computed within a quantum dynamical theory that combines a formally exact solution of the nuclear dynamics with density functional theory (DFT)-based approximations of the electronic dynamics. Various observables of time-resolved photoelectron imaging techniques are computed at the Kohn–Sham and at the time-dependent DFT levels. Comparison of the results serves to assess the reliability of the former method and hence its usefulness as an economic approach for time-domain photoelectron cross section calculations, that is applicable to complex polyatomic systems. Analysis of the matrix elements that contain the electronic dynamics provides insight into a previously unexplored aspect of femtosecond-resolved photoelectron imaging.
A theory ofnonverticaltriplet energy transfer in terms of accurate potential energy surfaces: The transfer reaction from π,π* triplet donors to 1,3,5,7-cyclooctatetraene
Authors: Frutos Luis Manuel , Castaño Obis , Andrés José Luis , Merchán Manuela , Acuña A. Ulises
Published: January 2004

Triplet energy transfer (TET) from aromatic donors to 1,3,5,7-cyclooctatetraene (COT) is an extreme case of “nonvertical” behavior, where the transfer rate for low-energy donors is considerably faster than that predicted for a thermally activated (Arrhenius) process. To explain the anomalous TET of COT and other molecules, a new theoretical model based on transition state theory for nonadiabatic processes is proposed here, which makes use of the adiabatic potential energy surfaces (PES) of reactants and products, as computed from high-level quantum mechanical methods, and a nonadiabatic transfer rate constant. It is shown that the rate of transfer depends on a geometrical distortion parameter γ=(2g2/κ1)1/2 in which g stands for the norm of the energy gradient in the PES of the acceptor triplet state and κ1 is a combination of vibrational force constants of the ground-state acceptor in the gradient direction. The application of the model to existing experimental data for the triplet energy transfer reaction to COT from a series of π,π* triplet donors, provides a detailed interpretation of the parameters that determine the transfer rate constant. In addition, the model shows that the observed decrease of the acceptor electronic excitation energy is due to thermal activation of C=C bond stretchings and C–C bond torsions, which collectively change the ground-state COT bent conformation (D2d) toward a planar triplet state (D8h).
Photochemistry in the charge transfer and neutral excited states of HCl in Xe and Kr matrices
Authors: Berghof V. , Gudipati M. S. , Schwentner N.
Published: January 2004

HCl-doped Xe and Kr films are irradiated with wavelength dispersed synchrotron radiation in the wavelength range from 200 to 130 nm. The growth of H, Cl, Xe2H+, XeH2, HXeCl, Kr2H+, and HKrCl as well as the decomposition of HCl are recorded by a combination of UV, VIS, and IR spectroscopy. A turnover in the formation of Xe2H+ and Kr2H+ by a predominant two-step reaction on neutral surfaces at low energies to a one-step formation on ionic surfaces is determined at 172 and 155 nm in Xe and Kr, respectively. A potential energy diagram for neutral and ionic states is derived that is consistent with a DIIS calculation, with new UV fluorescence bands from Xe+HCl− centers, with the turnover energies and with a deconvolution of the absorption spectra in neutral and ionic contributions. The cage exit of charged as well as of neutral H, the latter via a harpoon reaction, is discussed for the ionic surfaces. The self-limitation of HCl decomposition on the neutral surfaces due to absorption by H and Cl fragments is treated quantatively. Dissociation efficiencies φe, together with absolute absorption cross sections σH and σCl of the fragments, are derived. σH and σCl are of the order of 10−16 cm2 compared to 10−18 cm2 for σHCl. Dissociation is accompanied by many excitation cycles of the fragments, which leads to light-induced migration of H and recombination. φe therefore represents a product of the cage exit probability φ that was treated theoretically and the survival probability concerning geminate and nongeminate recombination.
CASSCF and CASPT2 studies on the structures, transition energies, and dipole moments of ground and excited states for azulene
Authors: Murakami Akinori , Kobayashi Takao , Goldberg Alexander , Nakamura Shinichiro
Published: January 2004

The electronic structure of azulene molecule has been studied. We have obtained the optimized structures of ground and singlet excited states by using the complete active space self-consistent-field (CASSCF) method, and calculated vertical and 0–0 transition energies between the ground and excited states with second-order Møller–Plesset perturbation theory (CASPT2). The CASPT2 calculations indicate that the bond-equalized C2v structure is more stable than the bond-alternating Cs structure in the ground state. For a physical understanding of electronic structure change from C2v to Cs, we have performed the CASSCF calculations of Duschinsky matrix describing mixing of the b2 vibrational mode between the ground (1A1) and the first excited (1B2) states based on the Kekulé-crossing model. The CASPT2 0–0 transition energies are in fairly good agreement with experimental results within 0.1–0.3 eV. The CASSCF oscillator strengths between the ground and excited states are calculated and compared with experimental data. Furthermore, we have calculated the CASPT2 dipole moments of ground and excited states, which show good agreement with experimental values.
Indirect adsorbate–adsorbate interactions mediated through the surface electronic structure of the Si(100) surface
Authors: Widjaja Yuniarto , Musgrave Charles B.
Published: January 2004

Indirect adsorbate–adsorbate interactions between adsorbed ammonia (NH3) molecules on the Si(100) surface are investigated using density functional theory. Two different nonlocal effects mediated through the surface electronic structure are observed: “poisoning” and hydrogen bonding. We find that adsorbed NH3 “poisons” adsorption of NH3 on neighboring Si dimers on the same side of the dimer row whereas neighboring NH2(a) groups favor this configuration. Adsorption of NH3 involves charge transfer to the surface that localizes on neighboring Si dimer atoms, preventing adsorption of NH3 at these sites. These indirect interactions are similar to Friedel-type interactions observed on metal surfaces with an estimated range of less than 7.8 Å on the Si(100) surface. These interactions may be manipulated to construct local ordering of the adsorbates on the surface.
A study of the mode-selective trans–cis isomerization in HONO using ab initio methodology
Authors: Richter Falk , Hochlaf Majdi , Rosmus Pavel , Gatti Fabien , Meyer Hans-Dieter
Published: January 2004

Ab initio calculations on the six-dimensional cis–trans double minimum potential energy surface of the electronic ground state of the HONO molecule were performed using a coupled cluster approach. An analytic fit to the data points was established. The interconversion barrier was calculated to be 4105 cm−1. The nuclear motion problem was solved variationally using a full six-dimensional Hamiltonian in internal coordinates. The eigenstates up to about 3650 cm−1 were tentatively assigned by harmonic quantum numbers. The assignment was based on the mean values of the internal coordinates of the six-dimensional eigenfunctions and on a comparison of the eigenenergies with those calculated by second-order perturbation theory from a full quartic force field in dimensionless normal coordinates. In cold matrices the trans- and the cis-OH ν1 stretching modes and the first trans- and cis-NO 2ν2 stretching overtones lead to isomerization. In the isolated molecule these modes (J=0) were found to be entirely localized. However, several overtones of the ν4 ONO bending and ν5 N–O stretching, which are close in energy to the OH stretch and combined with the torsional mode, were found to be strongly cis–trans delocalized.
Charge transfer mechanism in hybrid bulk heterojunction composites
Authors: Kucur Erol , Riegler Jürgen , Urban Gerald A. , Nann Thomas
Published: January 2004

Charge transfer mechanisms of several conducting polymers and polymer/CdSe nanocrystal composites (hybrid bulk heterojunction composites) were investigated by means of cyclic voltammetry. Potential application of these composites in hybrid light-emitting diodes was discussed. It was found that charge transfer is observed in most of the composites, used so far, but was relatively slow or incomplete. The PVPy/CdSe nanocrystal composite showed promising results, and is favorable for use in electroluminescent devices.
Attraction-driven disorder in a hard-core colloidal monolayer
Authors: Huerta Adrian , Naumis Gerardo G. , Wasan Darsh T. , Henderson Douglas , Trokhymchuk Andrij
Published: January 2004

Monte Carlo simulation techniques were employed to explore the effect of short-range attraction on the orientational ordering in a two-dimensional assembly of monodisperse spherical particles. We find that if the range of square-well attraction is approximately 15% of the particle diameter, the dense attractive fluid shows the same ordering behavior as the same density fluid composed of purely repulsive hard spheres. Fluids with an attraction range larger than 15% show an enhanced tendency to crystallization, while disorder occurs for fluids with an attractive range shorter than 15% of the particle diameter. A possible link with the existence of “repulsive” and “attractive” states in dense colloidal systems is discussed.
Adsorption and order formation of colloidal nanoparticles on a substrate: A Brownian dynamics study
Authors: Miyahara Minoru , Watanabe Satoshi , Gotoh Yoshiaki , Higashitani Ko
Published: January 2004

Adsorption process and order formation of electrostatically stabilized colloidal particles with a radius of 50 nm onto a planar surface with countercharge are examined. We perform Brownian dynamics simulations with a new three-dimensional cell model, in which the particle–particle and particle–substrate interactions are modeled based on the DLVO theory. The simulations yield the following results: (1) a larger bulk concentration would be required for larger κa to reach order formation to compensate for the decrease in the bulk potential; (2) the phase transition from a disordered to an ordered structure of the adsorbed particles on the substrate is considered to be of the Kirkwood–Alder type of transition through the examination of the two-dimensional pressure of the adsorbed particles; (3) the adsorbed particles are found to form a hexagonally ordered array, only if what we call “one-directional average force” acting on an adsorbed particle exceeds a critical value, which is independent of the ionic strength, or the interaction potentials. The critical value of the one-directional average force is interpreted as the force needed to keep an ordered structure by localizing adsorbed particles at fixed positions. In addition, the critical force is used to develop a new model to estimate the surface coverage at the order–disorder transition and it is demonstrated that the new model gives better estimation than other models previously reported.
The dissociation adiabaticity parameter and the strong field dissociation of HCl+
Authors: Paci Jeffrey T. , Wardlaw David M.
Published: January 2004

In earlier work on H2+ [J. T. Paci and D. M. Wardlaw, J. Chem. Phys. 119, 7824 (2003)], we showed how a dissociation adiabaticity parameter, γDv≡(Dv/2Upm)1/2 (Dv is the dissociation energy from vibrational state v and Upm is the molecular ion system’s ponderomotive energy), proposed by Walsh et al. [T. D. G. Walsh, L. Strach, and S. L. Chin, J. Phys. B 31, 4853 (1998)], can be modified and be a useful indicator of the strong field dissociation regime for a homonuclear diatomic. In the case of H2+, the new adiabaticity parameter, γmol, indicates when a dissociation process can be most easily described as multiphoton above-threshold dissociation (γmol>1) and when it is better described using barrier-suppressed dissociation (γmol<1). In the case of a heteronuclear diatomic like HCl+, different electronic states can lead to different dissociation product channels to which are ascribed different γmol values. We show for a wide range of laser wavelengths and intensities that this adiabaticity parameter successfully predicts the type of dissociation dynamics (multiphoton above-threshold dissociation versus barrier-suppressed dissociation) on each electronic potential curve. We also discover that the dynamics in one electronic state can influence the dynamics in another at the same laser wavelengths and intensities, overriding the predictive capability of an adiabaticity parameter defined for a particular electronic state. Reasonable physical explanations are provided for these overriding cases.