bluuebunny/crossref_metadata_2025 huggingface dataset:
Psychoendokrinologie der Angst
Authors: Ehlert Ulrike
Published: July 2006

Zusammenfassung. Ätiologie, Symptomatik und Verlauf von Angststörungen sind multikausal zu erklären. Ein Teilaspekt der psychobiologischen Erklärungsansätze von Angststörungen sind endokrine Auffälligkeiten, anhand derer bestimmte Unterformen pathologischer Angst charakterisiert werden können. Vor allem die Hypothalamus-Hypophysen-Nebennierenrinde-Achse und das sympathiko-adrenomedulläre System werden im Zusammenhang mit Emotionsregulation und pathologischer Angst untersucht. Beide Hormonsysteme spielen bei der Anpassung an individuelle Belastungssituationen eine bedeutende Rolle und beeinflussen die psychobiologische Anpassung an angstauslösende Situationen nachhaltig. In dieser Überblicksarbeit werden endokrine Dysregulationen der o.g. Hormonsysteme für verschiedene Unterformen von Angststörungen aufgezeigt und bzgl. ihrer ätiologischen Bedeutsamkeit, auch unter Berücksichtigung genetischer Befunde, diskutiert. Darüber hinaus werden erste therapeutische Ansätze, bei denen psychoendokrinologische Methoden genutzt werden, aufgezeigt.
Kann web-basierte Stressprävention erfolgreich sein?
Authors: Hänggi Yves
Published: July 2006

Zusammenfassung. Theoretischer Hintergrund: In den vergangenen Jahren wurden unterschiedliche Präventionsprogramme zur Stressbewältigung durchgeführt und untersucht. Internet basierte Ansätze wurden bisher selten evaluiert. Fragestellung: Wie charakterisiert sich die Benutzergruppe des web-basierten Online-Elterntrainings zur Bewältigung von Familienstress (OET)? Wie hoch ist der Dropout? Wie ist dessen kurz- und langfristige Wirksamkeit zu beurteilen? Methode: Im Mai und Juni 2003 haben 198 Personen am OET teilgenommen. 77 bzw. 142 Personen beteiligten sich an der Evaluation der kurz- und langfristigen Effekte (Kontrollgruppendesign). Ergebnisse: Die Resultate zeigen, dass a) sich vorwiegend Mütter mit eher jüngeren Kindern für das OET interessiert haben, b) die Niederschwelligkeit des Angebots die Dropoutrate erhöht haben dürfte und c) das OET positive Effekte zeigte. Schlussfolgerungen: Das Internet hat sich als Methode zur Stressprävention bei Eltern bewährt.
Prädiktoren von lebenslanger Delinquenz
Authors: Seiffge-Krenke Inge , Roth Marcus , von Irmer Jörg
Published: July 2006

Zusammenfassung. Theoretischer Hintergrund: Die Unterscheidung zwischen jugendgebundener und persistierender Delinquenz ist von theoretischer und praktischer Relevanz. Fragestellung: Relevante Merkmale für persistierende Delinquenz sollen identifiziert werden. Methode: Frühe Delinquenz, belastende Lebensereignisse, Copingstile und Persönlichkeitsvariablen wurden an 241 männlichen Straftätern untersucht. Ergebnisse: Straftäter mit langen Haftstrafen unterschieden sich von solchen mit kürzerer Haftdauer in der Persönlichkeitsstruktur sowie dem Bewältigungsverhalten. Früheres aggressives, antisoziales Verhalten leistete keinen substanziellen Anteil zur Gruppentrennung, während das Ausmaß schwerer familiärer Belastungen und maladaptive Copingstile substanzielle Beiträge leisteten. Schlussfolgerungen: Interventionsansätze sollten verstärkt den Zusammenhang zwischen maladaptiven Copingstilen und schweren Belastungen berücksichtigen.
Chronische Kopfschmerzen und Stress bei Kindern
Authors: Saile Helmut , Scalla Pascale
Published: July 2006

Zusammenfassung. Theoretischer Hintergrund: Zur Untersuchung von Stress bei Kindern mit chronischen Kopfschmerzen werden Differenzierungen aus dem transaktionalen Stressmodell hinsichtlich Stressereignisse, Stresserleben sowie Stressverarbeitung genutzt. Fragestellung: Unterscheiden sich Kinder mit und ohne chronische Kopfschmerzen hinsichtlich Stresswahrnehmung und -verarbeitung? Welchen Stellenwert hat Stress für die Verarbeitung chronischer Kopfschmerzen? Methode: Untersucht wurden 70 Kinder mit chronischen Kopfschmerzen sowie 83 Kinder einer Kontrollgruppe mit standardisierten Instrumenten zur Erfassung von Kopfschmerzen und Stress. Ergebnisse: Kinder mit chronischen Kopfschmerzen zeigen eine ausgeprägtere psychische Stresssymptomatik und ungünstigere Stressverarbeitung als Kinder ohne Kopfschmerzen. Schmerzbedingte Hilflosigkeitskognitionen, schmerzbedingte Depression sowie schmerzbedingtes Rückzugsverhalten sind abhängig von der Intensität der Kopfschmerzen, der Anzahl erlebter Stressereignisse, dem Stresserleben sowie der Stressverarbeitung. Schlussfolgerungen: Alle drei Differenzierungen aus dem transaktionalen Stressmodell sind an der Kopfschmerzverarbeitung beteiligt.
Affektregulatorische Funktion der Binge-Episode bei Bulimia nervosa und Binge Eating Störung
Authors: Schöttke Henning , Eversmann Julia , Wiedl Karl H.
Published: July 2006

Zusammenfassung. Theoretischer Hintergrund: Die Rolle der Affektregulation bei der Aufrechterhaltung bulimischer Essanfälle und kompensatorischer Verhaltensweisen ist geprägt durch ein heterogenes Forschungsfeld. Der Vergleich dieser affektregulatorischer Funktionen zwischen bulimischen Patientinnen und Patientinnen mit einer Binge Eating Disorder (BED) fehlt weitgehend. Fragestellung: Die Studie untersucht die Frage, ob ein Essanfall zu einer Zunahme negativer Affekte führt, und ob diese Zunahme durch das Abführen wieder reduziert wird. Zusätzlich wird untersucht, inwieweit die Zunahme der negativen Affekte für die bulimischen Patienten spezifisch ist. Methode: Die differentielle Affektskala wird in einem problemanalytischen Explorationssetting zu Essanfällen und Episoden des Erbrechens bei 27 stationär behandelten bulimischen Patientinnen und 21 Patientinnen mit BED eingesetzt. Ergebnisse: Die bulimischen Patientinnen berichten im Vergleich zu den BED Patientinnen nach einem Essanfall eine Zunahme von Scham, Schuld, Ekel und Verachtung bei gleichzeitiger Reduktion von Interesse. Die BED Patientinnen berichten nur einen Anstieg von Schuld. Für die bulimischen Patientinnen reduziert das Erbrechen die erlebte Angst und den Ekel und führt außerdem zu einer Zunahme an Freude.
Earthquake nucleation on dip‐slip faults with depth‐dependent frictional properties
Authors: Zhang Chuanli , Oglesby David D. , Xu Guanshui
Published: July 2006

Previous research has indicated that for dip‐slip faults embedded in a half‐space, the nonvertical, asymmetric fault geometry can have a significant effect on the seismic nucleation process. Using quasi‐static simulation methods and a slip‐weakening friction law, we investigate the coupled effects of asymmetric fault geometry and depth‐dependent frictional properties on seismic nucleation on dip‐slip faults. As a first‐order approximation to the depth‐dependent parameters in the Earth, we assume that the normal stress tapers to a small value near the free surface, and we assume that the drop in frictional coefficient decreases with depth. We find that these depth‐dependent properties have an important effect on the nucleation process of these faults: Compared to models with homogeneous frictional properties, the nucleation point moves down dip, the time to unstable slip nucleation decreases, and the amount of preseismic surface slip increases significantly. However, these effects do not dominate the effects of the asymmetric dipping geometry of these faults on the nucleation process: thrust faults nucleate farther up dip than normal faults and nucleate earlier as well. Normal faults have a larger amount of preseismic surface slip than thrust faults. The results indicate that both geometrical and frictional heterogeneity can have important effects on nucleation and that both sources of complexity must be taken into account to produce accurate models of the seismic nucleation process.
Flow, hydrography, turbulent mixing, and dissipation at Fieberling Guyot examined with a primitive equation model
Authors: Lavelle J. W.
Published: July 2006

The extensive set of measurements previously taken at Fieberling Guyot provides a backdrop for model results on flow, hydrography, turbulent mixing, and derivative variables. A z‐level primitive equation model driven at subinertial and superinertial tidal frequencies allows the nonlinear interaction of free and topographically trapped motions to jointly determine model outcomes. Model residual flows, mean hydrographic features, topographic amplification of oscillatory currents, turbulent dissipation (ɛ) and vertical diffusivity (KV) profiles are all examined in the light of the observations. Azimuthal residual flows are toroidal above the summit with maximum speed ∼20 cm s−1. Diurnal flow over the summit is intensified by a factor >20. Downward vertical flow as a time‐mean (〈w〉t) occurs from ∼150 m above the summit apex to summit rim depth, with radially inward flow above the apex and radial outward flow below. Upward 〈w〉t rings the summit at larger r. The existence of the observed cold dome is shown to depend on 〈w〉t in the summit circulation cell. Vertical current shear is concentrated in a 150 m thick cap above the summit, accounting for a domed distribution of ɛ and KV with maxima of ∼10−7 W kg−1 and ∼30 cm2 s−1, respectively. Profiles most like the observations of KV are obtained with a subgrid‐scale parameterization in which the turbulent Prandtl number (Pr) depends on the shear Richardson number (Ri).
Upwelling off Yangtze River estuary in summer
Authors: Lü Xingang , Qiao Fangli , Xia Changshui , Zhu Jianrong , Yuan Yeli
Published: July 2006

The mechanisms of upwelling off the Yangtze River estuary (YRE) and in the adjacent waters in boreal summer are studied using numerical modeling. First, the persistent feature of this phenomenon is confirmed using cruise observations, satellite sea surface temperature (SST), and SST climatologic data. Then, the MASNUM (Marine Science and Numerical Modeling) wave‐tide‐circulation coupled numerical model is employed to simulate the upwelling patterns. On the basis of the simulation, a set of numerical experiments are designed to explore the main mechanisms inducing the upwelling. The results suggest that tidal mixing plays a predominant role in inducing the upwelling. In offshore waters, strong tidal mixing results in considerable horizontal density gradient across tidal fronts. Upwelling is induced as a branch of the secondary circulation, which is stimulated by the cross‐frontal density gradient. Topography also exerts profound influences on upwelling by steering bottom currents to ascend upward and regulating tidal fronts in both location and intensity. Besides the tides and topography, other dynamical factors also alter the strength of upwelling locally. The Yangtze River discharge (YRD) and Taiwan Warm Current (TWC) account partly for the upwelling off the YRE and near Zhoushan Islands, respectively. The influence of wind on upwelling is small. In the coastal waters near Zhoushan Islands, the wind forcing exerts negative influences on upwelling by weakening the encroachment of TWC onto the continental shelf, which may exceed the positive effects of Ekman pumping.
Single scattering parameters of randomly oriented snow particles at microwave frequencies
Authors: Kim Min‐Jeong
Published: July 2006

To develop a generally applicable fast and accurate parameterization method for computations of single scattering parameters at microwave frequencies requires a thorough knowledge of how the ice particle shape affects the scattering parameters. This study computes single scattering parameters (scattering cross sections (Csca), absorption cross sections (Cabs), and asymmetry factors) of various nonspherical snow particles using the discrete dipole approximation (DDA) method and the T‐matrix method to examine the sensitivity of scattering parameters to snow particles at frequencies between 95 GHz and 340 GHz. Results show that Csca/πreff2, Cabs/πreff2, and asymmetry factors of complex particles at a fixed size parameter x = 2πreff/λ do not depend on the specific particle shapes when x is less than about 2.5. Here λ is the wavelength and reff is the radius of equal‐volume ice spheres. The Mie theory may be used to compute the single scattering parameters of randomly oriented snow particles if radius of equal‐volume ice spheres reff is known over this range. On the other hand, when x > 2.5, scattering parameters of nonspherical particles are sensitive to the particle shapes because they are in an anomalous diffraction regime. In this regime, particles have a smaller projected area for a given volume so that the “unfavorable” interference effect grows, resulting in smaller minimum values of scattering cross sections and asymmetry factors. Single scattering parameters averaged over a Gamma size distribution show that scattering coefficients are sensitive to shapes and that differences are larger than 10% when πDm/λ; the size parameter of the median mass diameter (Dm) is greater than 1. Single scattering albedo values do not show significant differences over most size parameter ranges considered in this study. Asymmetry factors are sensitive to particle shapes when πDm/λ is greater than 2.
An endobiont‐bearing allogromiid from the Santa Barbara Basin: Implications for the early diversification of foraminifera
Authors: Bernhard Joan M. , Habura Andrea , Bowser Samuel S.
Published: July 2006

Our current understanding of paleoecology and paleoceanography is largely based on the superb Phanerozoic fossil record of foraminiferan protists. The early history of the group is unresolved, however, because basal foraminiferans (allogromiids) are unmineralized and thus fossilize poorly. Molecular‐clock studies date foraminiferal origins to the Neoproterozoic, but the deep sea, one of Earth's most extensive habitats and presently hosting a significant fraction of basal foraminiferal diversity, was probably anoxic at that time and, until now, anaerobic allogromiids were unknown. Molecular, cell, and ecological analyses reveal the presence of a previously unknown allogromiid inhabiting anoxic, sulfidic deep‐sea sediments (Santa Barbara Basin, California). The fact that the new foraminifer harbors prokaryotic endobionts implicates symbiogenesis as a driving force in early foraminiferal diversification.
Parameterization of the main ionospheric trough in the European sector
Authors: Pryse S. E. , Kersley L. , Malan D. , Bishop G. J.
Published: July 2006

Measurements of total electron content, obtained by monitoring satellite transmissions at stations in the United Kingdom during a period of 12 months, have been used to characterize the structure and dynamics of the main ionospheric trough in terms of a set of defined parameters. The primary aim of the investigation was to represent the position and shape of the trough in such a way that the experimental observations can be used for direct comparison and validation of ionospheric models.
Future global tropospheric ozone changes and impact on European air quality
Authors: Szopa S. , Hauglustaine D. A. , Vautard R. , Menut L.
Published: July 2006

A global chemistry climate model is used in conjunction with a regional chemistry‐transport model dedicated to air quality studies to investigate the impact of anthropogenic emission changes, under several scenarios, on western European summertime surface O3 levels in 2030. The implementation of presently decided emission control legislation in the individual countries worldwide leads to a geographically heterogeneous impact on summertime surface O3 levels over Europe. A decrease of the averaged O3 mixing ratio reaching −3 ppbv is predicted in southern areas whereas an increase reaching up 4 ppbv is calculated in northwestern Europe. The benefit of European emission control measures is found to be significantly counterbalanced by increasing global O3 levels and subsequent long range transport since both are of the same magnitude (up to 4 ppbv) but opposite in sign. However, the net effect of both global and European emission changes is a significant decrease of O3 extreme episodes during summertime.
On coastal ocean embedded modeling
Authors: Auclair Francis , Estournel Claude , Marsaleix Patrick , Pairaud Ivane
Published: July 2006

The initialization and forcing of embedded coastal ocean models is shown to raise several serious difficulties, however, surprisingly enough, very little attention is paid by coastal modelers to resulting dynamical discrepancies introduced over both short and long time scales. A modular and “Knowledge accumulating” approach for coastal ocean embedded modeling is proposed based on a variational approach. The extrapolation situations mostly associated to bathymetry constraints are discussed and are shown to be of great importance for any embedded coastal model. A well adapted extrapolation scheme is proposed. Two variational constraints are more particularly shown to lead to important improvements of the downscaling: the mass balance is satisfied in a dynamically coherent way based on Green's theorem and an optimal scheme is presented to extrapolate both the temperature and the salinity in the deepest regions where no data is available.
A tomographic image of upper crustal structure using P and S wave seismic refraction data in the southern granulite terrain (SGT), India
Authors: Rajendra Prasad B. , Behera Laxmidhar , Rao P. Koteswara
Published: July 2006

We present a 2‐D tomographic P and S wave velocity (Vp and Vs) image with Vp/Vs ratios along N‐S trending 220 km long deep seismic profile acquired in 2005, which traverses across major shear and tectonically disturbed zones in southern granulite terrain (SGT), India. The 2‐D velocity model constrained down to maximum 8 km depth shows velocity anomalies (>0.2 km/s) beneath major shear zones with good spatial resolution (>0.05 km/s). The presence of high Vp (6.3–6.5 km/s), Vs (3.5–3.8 km/s), Vp/Vs (>1.75) and Poisson's ratio (0.25–0.29) indicate significant compositional changes of rocks at shallow depths (0.5 to 8 km) reveal rapid crustal exhumation of mid to lower crustal rocks. This crustal exhumation could be responsible due to Pan‐African tectonothermal activity during Neoproterozoic period.
Geomagnetic modulation of clouds effects in the Southern Hemisphere Magnetic Anomaly through lower atmosphere cosmic ray effects
Authors: Vieira Luis Eduardo Antunes , da Silva Ligia Alves
Published: July 2006

The study of the physical processes that drive the variability of the Earth's climate system is one of the most fascinating and challenging topics of research today. Perhaps the largest uncertainties in our ability to predict climate change are the cloud formation process and the interaction of clouds with radiation. Here we show that in the southern Pacific Ocean cloud effects on the net radiative flux in the atmosphere are related to the intensity of the Earth's magnetic field through lower atmosphere cosmic ray effects. In the inner region of the Southern Hemisphere Magnetic Anomaly (SHMA) it is observed a cooling effect of approximately 18 W/m2 while in the outer region it is observed a heating effect of approximately 20 W/m2. The variability in the inner region of the SHMA of the net radiative flux is correlated to galactic cosmic rays (GCRs) flux observed in Huancayo, Peru (r = 0.73). It is also observed in the correlation map that the correlation increases in the inner region of the SHMA. The geomagnetic modulation of cloud effects in the net radiative flux in the atmosphere in the SHMA is, therefore, unambiguously due to GCRs and/or highly energetic solar proton particles effects.
The tropopause inversion layer in models and analyses
Authors: Birner T. , Sankey D. , Shepherd T. G.
Published: July 2006

Recent high‐resolution radiosonde climatologies have revealed a tropopause inversion layer (TIL) in the extratropics: temperature strongly increases just above a sharp local cold point tropopause. Here, it is asked to what extent a TIL exists in current general circulation models (GCMs) and meteorological analyses. Only a weak hint of a TIL exists in NCEP/NCAR reanalysis data. In contrast, the Canadian Middle Atmosphere Model (CMAM), a comprehensive GCM, exhibits a TIL of realistic strength. However, in data assimilation mode CMAM exhibits a much weaker TIL, especially in the Southern Hemisphere where only coarse satellite data are available. The discrepancy between the analyses and the GCM is thus hypothesized to be mainly due to data assimilation acting to smooth the observed strong curvature in temperature around the tropopause. This is confirmed in the reanalysis where the stratification around the tropopause exhibits a strong discontinuity at the start of the satellite era.
Generalized Ornstein-Uhlenbeck processes
Authors: Bezuglyy V. , Mehlig B. , Wilkinson M. , Nakamura K. , Arvedson E.
Published: July 2006

We solve a physically significant extension of a classic problem in the theory of diffusion, namely the Ornstein-Uhlenbeck process [Ornstein and Uhlenbeck, Phys. Rev. 36, 823 (1930)]. Our generalized Ornstein-Uhlenbeck systems include a force which depends upon the position of the particle, as well as upon time. They exhibit anomalous diffusion at short times, and non-Maxwellian velocity distributions in equilibrium. Two approaches are used. Some statistics are obtained from a closed-form expression for the propagator of the Fokker-Planck equation for the case where the particle is initially at rest. In the general case we use spectral decomposition of a Fokker-Planck equation, employing nonlinear creation and annihilation operators to generate the spectrum which consists of two staggered ladders.
Calculation of origin-independent optical rotation tensor components in approximate time-dependent density functional theory
Authors: Krykunov Mykhaylo , Autschbach Jochen
Published: July 2006

We outline an implementation of the origin-independent optical rotation tensor, which includes electric dipole-magnetic dipole and electric dipole-electric quadrupole polarizability. The method is based on approximate time-dependent density functional theory. We utilize time-periodic magnetic-field-dependent basis functions as well as a modified velocity-gauge formulation of dynamic polarizability tensors in order to obtain a gauge-origin independence. To ensure gauge-origin independence of the results within a given numerical accuracy, density fit coefficient derivatives are employed. A damping constant has been introduced into the linear response equations to treat both resonance and nonresonance regions of optical activity. We present calculations for trans-2,3-dimethyloxirane and derivatives thereof as well as calculations for androst-4,17-dien-3-one. In the Appendix, we derive the equivalence between the common-gauge origin and gauge-including atomic orbitals formulations for the optical rotation tensor in time-dependent DFT.
Origin of the enhanced performance in poly(3-hexylthiophene): [6,6]-phenyl C61-butyric acid methyl ester solar cells upon slow drying of the active layer
Authors: Mihailetchi Valentin D. , Xie Hangxing , de Boer Bert , Popescu Lacramioara M. , Hummelen Jan C. , Blom Paul W. M. , Koster L. Jan Anton
Published: July 2006

The origin of the enhanced performance of bulk heterojunction solar cells based on slowly dried films of poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl C61-butyric acid methyl ester is investigated, combining charge transport measurements with numerical device simulations. Slow drying leads to a 33-fold enhancement of the hole mobility up to 5.0×10−7m2V−1s−1 in the P3HT phase of the blend, thereby balancing the transport of electrons and holes in the blend. The resulting reduction of space-charge accumulation enables the use of thick films (∼300nm), absorbing most of the incoming photons, without losses in the fill factor and short-circuit current of the device.
Translocation of a proteinlike chain through a finite channel
Authors: Sun Tingting , Zhang Linxi , Su Jiaye
Published: July 2006

We use the pruned-enriched-Rosenbluth method and the modified orientation-dependent monomer-monomer interaction model to study the translocation of a proteinlike chain through a finite channel. The mean-square radius of gyration per bond ⟨S2⟩∕N and shape factor ⟨δ*⟩ of proteinlike chains with different secondary structures transporting through a finite channel with different channel radii R=1, 2, 3, 4, and 20 are investigated in the translocation. The average Helmholtz free energy per bond A∕N and the mechanical force f are also presented. A∕N remains unchanged when X0<0 and X0>1, and decreases monotonously when 0.5<X0<0.1. Here X0=X∕N≡2X∕L,X is the position of the first monomer, N is chain length, and L is channel length. No free energy barrier is found in our calculation. f is negative and has a plateaulike behavior. The plateau becomes narrow and the value of f increases as R increases. The total energy per bond ⟨U⟩∕N is also calculated in the process of translocation. An energy barrier is shown. The proteinlike chains must cross this energy barrier when they escape from the channel. The position of the maximum of ⟨U⟩∕N depends on the secondary structures and the channel radius. We also discuss the average contact energy per bond ⟨U⟩c∕N, the average α-helical energy per bond ⟨U⟩h∕N, and the average β-sheet energy per bond ⟨U⟩b∕N.
Adsorption geometry and core excitation spectra of three phenylpropene isomers on Cu(111)
Authors: Kolczewski C. , Williams F. J. , Cropley R. L. , Vaughan O. P. H. , Urquhart A. J. , Tikhov M. S. , Lambert R. M. , Hermann K.
Published: July 2006

Theoretical C 1s near edge x-ray absorption fine structure (NEXAFS) spectra for the C9H10 isomers trans-methylstyrene, α-methylstyrene, and allylbenzene in gas phase and adsorbed at Cu(111) surfaces have been obtained from density functional theory calculations where adsorbate geometries were determined by corresponding total energy optimizations. The three species show characteristic differences in widths and peak shapes of the lowest C 1s→π* transitions which are explained by different coupling of the π-electron system of the C6 ring with that of the side chain in the molecules as well as by the existence of nonequivalent carbon centers. The adsorbed molecules bind only weakly with the substrate which makes the use of theoretical NEXAFS spectra of the oriented free molecules meaningful for an interpretation of experimental angle-resolved NEXAFS spectra of the adsorbate systems obtained in this work. However, a detailed quantitative account of relative peak intensities requires theoretical angle-resolved NEXAFS spectra of the complete adsorbate systems which have been evaluated within the surface cluster approach. The comparison with experiment yields almost perfect agreement and confirms the reliability of the calculated equilibrium geometries of the adsorbates. This can help to explain observed differences in the catalytic epoxidation of the three molecules on Cu(111) based on purely geometric considerations.
The effect of protein dielectric coefficient on the ionic selectivity of a calcium channel
Authors: Boda Dezső , Valiskó Mónika , Eisenberg Bob , Nonner Wolfgang , Henderson Douglas , Gillespie Dirk
Published: July 2006

Calcium-selective ion channels are known to have carboxylate-rich selectivity filters, a common motif that is primarily responsible for their high Ca2+ affinity. Different Ca2+ affinities ranging from micromolar (the L-type Ca channel) to millimolar (the ryanodine receptor channel) are closely related to the different physiological functions of these channels. To understand the physical mechanism for this range of affinities given similar amino acids in their selectivity filters, we use grand canonical Monte Carlo simulations to assess the binding of monovalent and divalent ions in the selectivity filter of a model Ca channel. We use a reduced model where the electolyte is modeled by hard-sphere ions embedded in a continuum dielectric solvent, while the interior of protein surrounding the channel is allowed to have a dielectric coefficient different from that of the electrolyte. The induced charges that appear on the protein/lumen interface are calculated by the induced charge computation method [Boda et al., Phys. Rev. E 69, 046702 (2004)]. It is shown that decreasing the dielectric coefficient of the protein attracts more cations into the pore because the protein’s carboxyl groups induce negative charges on the dielectric boundary. As the density of the hard-sphere ions increases in the filter, Ca2+ is absorbed into the filter with higher probability than Na+ because Ca2+ provides twice the charge to neutralize the negative charge of the pore (both structural carboxylate oxygens and induced charges) than Na+ while occupying about the same space (the charge/space competition mechanism). As a result, Ca2+ affinity is improved an order of magnitude by decreasing the protein dielectric coefficient from 80 to 5. Our results indicate that adjusting the dielectric properties of the protein surrounding the permeation pathway is a possible way for evolution to regulate the Ca2+ affinity of the common four-carboxylate motif.
Nematic-fluid structure in wall-field geometry. II. The direct correlation function
Authors: Sokolovska T. G. , Sokolovskii R. O. , Patey G. N.
Published: July 2006

An explicit expression for the wall-nematic direct correlation function (DCF) is obtained for any orientation of the wall with respect to an external orienting field. It is found that inside the surface of the wall, the DCF rapidly tends to a function of the nematogen orientation and depends only on parameters of the bulk fluid. We suggest that the wall-nematic DCF can be used as an ansatz for the colloid-nematic DCF in dilute nematic colloids. The reliability of this ansatz is investigated at different field strengths in both isotropic and nematic regions. Our calculations for spherical colloidal particles show that this approximation is valid for colloidal particles that are large, but well within the physically realistic size range. The ansatz could also be applied to nonspherical colloidal particles.
Ferromagnetism in Fe-implanted a-plane ZnO films
Authors: Wu P. , Saraf G. , Lu Y. , Hill D. H. , Gateau R. , Wielunski L. , Bartynski R. A. , Arena D. A. , Dvorak J. , Moodenbaugh A. , Siegrist T. , Raley J. A. , Yeo Yung Kee
Published: July 2006

Fe ions of dose 5×1016cm−2 were implanted at 200keV into a-plane ZnO epitaxial films. The epitaxial quality of the postannealed samples was verified by x-ray diffraction ω-rocking curves and φ scans, whereas x-ray absorption spectroscopy identified the presence of both Fe2+ and Fe3+ ions, as well as changes in their relative concentration during postannealing. Superconducting quantum interference device measurements show that the as-implanted and postannealed films are ferromagnetic at room temperature. The saturation magnetization reduces during annealing possibly due to the decrease in the number of oxygen vacancies.
Quasiperiodic attractors, Borel summability and the Bryuno condition for strongly dissipative systems
Authors: Gentile Guido , Bartuccelli Michele V. , Deane Jonathan H. B.
Published: July 2006

We consider a class of ordinary differential equations describing one-dimensional analytic systems with a quasiperiodic forcing term and in the presence of damping. In the limit of large damping, under some generic nondegeneracy condition on the force, there are quasiperiodic solutions which have the same frequency vector as the forcing term. We prove that such solutions are Borel summable at the origin when the frequency vector is either any one-dimensional number or a two-dimensional vector such that the ratio of its components is an irrational number of constant type. In the first case the proof given simplifies that provided in a previous work of ours. We also show that in any dimension d, for the existence of a quasiperiodic solution with the same frequency vector as the forcing term, the standard Diophantine condition can be weakened into the Bryuno condition. In all cases, under a suitable positivity condition, the quasiperiodic solution is proved to describe a local attractor.
Self-consistent field study of the alignment by an electric field of a cylindrical phase of block copolymer
Authors: Lin Chin-Yet , Schick M.
Published: July 2006

Self-consistent field theory is applied to a film of cylindrical-forming block copolymer subject to a surface field which tends to align the cylinders parallel to electrical plates, and to an external electric field tending to align them perpendicular to the plates. The Maxwell equations and self-consistent field equations are solved exactly, numerically, in real space. By comparing the free energies of different configurations, we show that for weak surface fields, the phase of cylinders parallel to the plates makes a direct transition to a phase in which the cylinders are aligned with the field throughout the sample. For stronger surface fields, there is an intermediate phase in which cylinders in the interior of the film, aligned with the field, terminate near the plates. For surface fields which favor the minority block, there is a boundary layer of hexagonal symmetry at the plates in which the monomers favored by the surface field occupy a larger area than they would if the cylinders extended to the surface.
The stress tensor of a molecular system: An exercise in statistical mechanics
Authors: Morante S. , Rossi G. C. , Testa M.
Published: July 2006

We prove that conservation of the stress tensor is a consequence of the invariance of the partition function under canonical diffeomorphisms. From this observation a simple and general derivation of the formula which gives the local expression of the stress tensor of a molecular system in terms of its microscopic degrees of freedom readily follows. The derivation is valid in the canonical as well as the microcanonical ensemble. It works both in the classical and in the quantum mechanical settings and for arbitrary boundary conditions. In particular, if periodic boundary conditions are assigned to the system, the usual minimal-image prescription is naturally born out for mathematical consistency. An interesting outcome of our general analysis is that only in the case of a short-range interaction potential a truly local formula for the stress tensor can exist.
Anodic aluminum oxide membrane bonded on a silicon wafer for carbon nanotube field emitter arrays
Authors: Jung Hyun Young , Jung Sung Mi , Gu Geun Hoi , Suh Jung Sang
Published: July 2006

We have developed a method to bond a very thin anodic aluminum oxide membrane (400nm thick) on a Si wafer. Furthermore, we were able to fabricate well-ordered carbon nanotube (CNT) arrays on the membrane at a very high temperature—above 1000°C—without deformation. The CNT arrays fabricated at 800°C exhibited long-term stability and uniform emission. Their current density was higher than 1mA∕cm2; such a density might be required for flat panel displays. When the tip of the CNTs was modified from an open shape to a closed shape by exposure to acetylene gas, the turn-on voltage decreased significantly and the enhancement factor increased significantly.
Low friction lubrication between amorphous walls: Unraveling the contributions of surface roughness and in-plane disorder
Authors: Jabbarzadeh A. , Harrowell Peter , Tanner R. I.
Published: July 2006

Using molecular dynamics simulations, we show that dodecane films confined between amorphous surfaces at 300K retain liquid-like behavior down to film thicknesses of at least 1.8nm and possibly smaller. This is in stark contrast to the behavior of films confined between crystalline surfaces which show an abrupt transition to a very high viscosity state at a film thickness of 4nm. We show that it is the small increase in surface roughness in going from crystalline to amorphous walls, rather than the in-plane disorder, that is responsible for disrupting the crystalline bridges found in the crystal-confined films. The main consequences of the in-plane disorder are the removal of the orientational pinning of the local domain alignment and the reduction of the critical thickness at which the transition to film rigidity appears.
Unimolecular processes in CH2OH below the dissociation barrier: O–H stretch overtone excitation and dissociation
Authors: Wei Jie , Karpichev Boris , Reisler Hanna
Published: July 2006

The OH-stretch overtone spectroscopy and dynamics of the hydroxymethyl radical, CH2OH, are reported in the region of the second and third overtones, which is above the thermochemical threshold to dissociation to H+CH2O (D0=9600cm−1). The second overtone spectrum at 10484cm−1 is obtained by double resonance IR-UV resonance enhanced multiphoton ionization (REMPI) spectroscopy via the 3pz electronic state. It is rotationally resolved with a linewidth of 0.4cm−1 and displays properties of local-mode vibration. No dissociation products are observed. The third overtone spectra of CH2OH and CD2OH are observed at ∼13600cm−1 by monitoring H-atom photofragments while scanning the excitation laser frequency. No double resonance REMPI spectrum is detected, and no D fragments are produced. The spectra of both isotope analogs can be simulated with a linewidth of 1.3cm−1, indicating dissociation via tunneling. By treating the tunneling as one dimensional and using the calculated imaginary frequency, the barrier to dissociation is estimated at about 15200cm−1, in good agreement with theoretical estimations. The Birge-Sponer plot is linear for OH-stretch vibrations 1ν1–4ν1, demonstrating behavior of a one-dimensional Morse oscillator. The anharmonicity parameter derived from the plot is similar to the values obtained for other small OH containing molecules. Isomerization to methoxy does not contribute to the predissociation signal and the mechanism appears to be direct O–H fission via tunneling. CH2OH presents a unique example in which the reaction coordinate is excited directly and leads to predissociation via tunneling while preserving the local-mode character of the stretch vibration.
Dynamics of radiation induced isomerization for HCN–CNH
Authors: Na Kyungsun , Jung Christof , Reichl L. E.
Published: July 2006

We have analyzed the dynamics underlying the use of sequential radiation pulses to control the isomerization between the HCN and the CNH molecules. The appearance of avoided crossings among Floquet eigenphases as the molecule interacts with the radiation pulses is the key to understanding the isomerization dynamics, both in the adiabatic and nonadiabatic regimes. We find that small detunings of the incident pulses can have a significant effect on the outcome of the isomerization process for the model we consider.
Energy pooling in multiple ionization and Coulomb explosion of clusters by nanosecond-long, megawatt laser pulses
Authors: Sharma P. , Vatsa R. K. , Kulshreshtha S. K. , Jha J. , Mathur D. , Krishnamurthy M.
Published: July 2006

We report the results of experiments that establish the possibility of bringing about multiple ionization and Coulomb explosion of molecular clusters with nanosecond laser pulses at intensities as small as 109Wcm−2. We demonstrate several new facets of the laser-cluster interaction in the low-intensity, long-pulse domain: (i) The choice of laser wavelength for a given cluster species is very crucial. (ii) Excited electronic states play a very important role in the ionization dynamics. (iii) When field ionization is insignificant and ponderomotive energies are very small, it is energy pooling rather than inverse bremsstrahlung that determines how clusters absorb energy from the optical field.
A molecular dynamics simulation study of buckyballs in water: Atomistic versus coarse-grained models of C60
Authors: Choudhury Niharendu
Published: July 2006

A simple coarse-grained water-C60 model potential is proposed to study the solvation behavior of C60 in water. Extensive molecular dynamics simulations are performed to compare the hydration behavior of the coarse-grained C60 with that of its atomistic counterpart. In the coarse-grained description, we model the C60 as a spherical solute and its interaction with water is represented by a simple two-body central potential as obtained from a coarse graining of the interactions of a water molecule with all the atoms of the C60. On the other hand, the atomistic model takes into account a discrete nature of all the atoms of C60 explicitly. Molecular dynamics simulations are carried out in an isothermal-isobaric ensemble at normal temperature and pressure. Various spatial and orientational correlations of the water around the two model C60s are compared. The coarse-grained model is shown to reproduce the hydration behavior of the C60 quite well. The simplicity and the computational economy of the coarse-grained model will allow for simulations of self-assembly processes of a much larger system over a longer period of time.
Light emission at 5V from a polymer device with a millimeter-sized interelectrode gap
Authors: Shin Joon-Ho , Dzwilewski Andrzej , Iwasiewicz Agnieszka , Xiao Steven , Fransson Åke , Ankah Genesis Ngwa , Edman Ludvig
Published: July 2006

We report the onset of electrochemical doping and subsequent visible light emission at 5V and 360K from a planar light-emitting electrochemical cell with a 1mm interelectrode gap containing poly[2-methoxy-5-(2′-ethyl-hexyloxy)-1, 4-phenylenevinylene] (MEH-PPV), poly(ethylene oxide) (PEO), and XCF3SO3 (X=K,Li) as the active material. We rationalize the unprecedented low turn-on voltage of such wide-gap light-emitting electrochemical cells by demonstrating that the active material contains a mixture of crystalline PEO+XCF3SO3 domains and amorphous MEH-PPV domains at room temperature, but that the crystalline domains have melted at 360K resulting in a significant increase in the ionic conductivity.
Implantation assisted copper diffusion: A different approach for the preparation of CuInS2∕In2S3 p-n junction
Authors: Wilson K. C. , Sebastian Tina , John Teny Theresa , Sudha Kartha C. , Vijayakumar K. P. , Magudapathi P. , Nair K. G. M.
Published: July 2006

Copper indium sulfide thin films were prepared using copper diffusion into argon ion implanted In2S3 thin films. A comparative study of copper diffusion in pristine and ion implanted In2S3 samples was also performed. It was found that copper indium sulfide formation was much better in argon implanted samples compared to that in unimplanted samples. Copper diffusion in implanted samples enabled us to prepare an In2S3∕CuInS2 solar cell. The fill factor of the cell prepared was 30.2% and the efficiency was 0.34%.
Diffusion and clustering of substitutional Mn in (Ga,Mn)As
Authors: Raebiger Hannes , Ganchenkova Maria , von Boehm Juhani
Published: July 2006

The Ga vacancy mediated microstructure evolution of (Ga,Mn)As during growth and postgrowth annealing is studied using a multiscale approach. The migration barriers for the Ga vacancies and substitutional Mn together with their interactions are calculated using first principles, and temporal evolution at temperatures 200–350°C is studied using lattice kinetic Monte Carlo simulations. We show that at the typical growth and annealing temperatures (i) Ga vacancies provide an efficient diffusion transport for Mn and (ii) in 10–20h the diffusion of Mn promotes the formation of clusters. Clustering reduces the Curie temperature, and explains its decrease during long-term annealing.
GaN ultraviolet avalanche photodiodes with optical gain greater than 1000 grown on GaN substrates by metal-organic chemical vapor deposition
Authors: Limb J. B. , Yoo D. , Ryou J. H. , Lee W. , Shen S. C. , Dupuis R. D. , Reed M. L. , Collins C. J. , Wraback M. , Hanser D. , Preble E. , Williams N. M. , Evans K.
Published: July 2006

We report the performance of GaN p-i-n ultraviolet avalanche photodiodes grown on bulk GaN substrates by metal-organic chemical vapor deposition. The low dislocation density in the devices enables low reverse-bias dark currents prior to avalanche breakdown for ∼30μm diameter mesa photodetectors. The photoresponse is relatively independent of the bias voltage prior to the onset of avalanche gain which occurs at an electric field of ∼2.8MV∕cm. The magnitude of the reverse-bias breakdown voltage shows a positive temperature coefficient of ∼0.05V∕K, confirming that the avalanche breakdown mechanism dominates. With ultraviolet illumination at λ∼360nm, devices with mesa diameters of ∼50μm achieve stable maximum optical gains greater than 1000. To the best of our knowledge, this is the highest optical gain achieved for GaN-based avalanche photodiodes and the largest area III-N avalance photodetectors yet reported.
White-light-emitting CdSe quantum dots synthesized at room temperature
Authors: Jose Rajan , Zhelev Zhivko , Bakalova Rumiana , Baba Yoshinobu , Ishikawa Mitsuru
Published: July 2006

White-light-emitting CdSe quantum dots (QDs) were synthesized at room temperature (RT, ∼23°C) using an organometallic colloidal growth process. These QDs are characterized by high and reproducible quantum yields (ΦPL∼0.4) as well as by unusual spectral broadening [full width at half maximum (FWHM) ∼150nm) despite of their observed size monodispersity. Surface functionalization of these quantum dots using mercaptosuccinic acid made them soluble in water. A change of color together with an enhancement in ΦPL was observed upon surface functionalization.
Thermal relaxation time and heat distribution in pulsed InGaAs quantum dot lasers
Authors: Chan P. K. L. , Pipe K. P. , Mi Z. , Yang J. , Bhattacharya P. , Lüerßen D.
Published: July 2006

Using a charge coupled device-based thermoreflectance technique, we achieve a high-resolution (∼700nm) cross-sectional temperature profile of a semiconductor laser. This two-dimensional profile allows us to identify separate heat sources due to contact heating and nonradiative recombination in the active region. By adapting the technique to pulsed operation and varying the laser’s duty cycle, we measure the thermal relaxation time constant. We also quantitatively determine the heat transfer from device-internal heat sources and demonstrate both the large effect of lateral heat spreading and the distinction between a laser’s top surface temperature and its active region temperature.
Room-temperature Coulomb blockade effect in silicon quantum dots in silicon nitride films
Authors: Cho Chang-Hee , Kim Baek-Hyun , Park Seong-Ju
Published: July 2006

A room-temperature Coulomb blockade effect was observed in silicon quantum dots (Si QDs) spontaneously grown in a silicon nitride film. The metal-insulator-metal device containing the Si QDs showed a clear Coulomb staircase and differential conductance peaks at room temperature. The size distribution of the Si QDs determined by high-resolution transmission electron microscopy suggests that the measured single electron addition energy of 67meV can be attributed to the charging energy of 63meV of the Si QDs with the largest diameter of 4.7nm among the various-sized Si QDs.
Thermal stress evolution in embedded Cu/low-k dielectric composite features
Authors: Murray Conal E. , Goldsmith Charles C. , Shaw Thomas M. , Doyle James P. , Noyan I. C.
Published: July 2006

To determine the effect of low-modulus materials on the thermal stress evolution within interconnect metallization, thermal and residual stresses in copper features, embedded in an organosilicate glass (SiCOH) on a silicon substrate, were measured by x-ray diffraction as a function of temperature and calculated using finite element modeling. The elastic response of the structures was dictated by the thermal expansion mismatch between copper and silicon, the copper and SiCOH elastic moduli, and the composite geometry. The presence of a low-modulus layer between the features and underlying substrate plays a major role in the elastic stress relaxation generated during thermal cycling.