bluuebunny/crossref_metadata_2025 huggingface dataset:
Geological evidence of paleotsunamis at Torre degli Inglesi (northeast Sicily)
Authors: Pantosti D. , Barbano M. S. , Smedile A. , De Martini P. M. , Tigano G.
Published: March 2008

Two layers of fine sand of marine origin occur in a sequence of organic rich colluvia in an archaeological excavation at Torre degli Inglesi, on Capo Peloro, northeast Sicily. Stratigraphic and micropaleontologic analyses support the hypothesis that these layers are related to deposition due to paleotsunami waves. Their ages are constrained both with radiocarbon and archaeological datings. The age of the oldest layer is coincident with the 17 A.D. earthquake that hit Reggio Calabria but for which no tsunami was previously reported. The age of the youngest layer can be only constrained in the range 3rd–19th century and is tentatively associated to the 6 Feb. 1783 event.
Space geodetic investigation of the coseismic and postseismic deformation due to the 2003 Mw7.2 Altai earthquake: Implications for the local lithospheric rheology
Authors: Barbot Sylvain , Hamiel Yariv , Fialko Yuri
Published: March 2008

We use Envisat Advanced Synthetic Aperture Radar data and SPOT optical imagery to investigate the coseismic and postseismic deformation due to the 27 September 2003, Mw7.2 Altai earthquake, which occurred in the Chuya Basin near the Russia‐China‐Mongolia border. On the basis of the synthetic aperture radar (SAR) and SPOT data, we determined the rupture location and developed a coseismic slip model for the Altai earthquake. The inferred rupture location is in a good agreement with field observations, and the geodetic moment from our slip model is consistent with the seismic moment determined from the teleseismic data. While the epicentral area of the Altai earthquake is not optimal for radar interferometry (in particular, due to temporal decorrelation), we were able to detect a transient signal over a time period of 3 years following the earthquake. The signal is robust in that it allows us to discriminate among several commonly assumed mechanisms of postseismic relaxation. We find that the postearthquake interferometric SAR data do not warrant poroelastic rebound in the upper crust. The observed deformation also disagrees with linear viscoelastic relaxation in the upper mantle or lower crust, giving rise to a lower bound on the dynamic viscosity of the lower crust of the order of 1019 Pa s. The data can be explained in terms of fault slip within the seismogenic zone, on the periphery of areas with high coseismic slip. Most of the postseismic deformation can be explained in terms of seismic moment release in aftershocks; some shallow slip may have also occurred aseismically. Therefore the observed postseismic deformation due to the Altai earthquake is qualitatively different from deformation due to other similarly sized earthquakes, in particular, the Landers and Hector Mine earthquakes in the Mojave desert, southern California. The observed variations in the deformation pattern may be indicative of different rheologic structure of the continental lithosphere in different tectonically active areas.
Simple power law for transport ratio with bimodal distributions of coarse sediments under waves
Authors: Calantoni Joseph , Thaxton Christopher S.
Published: March 2008

Morphodynamic models of coastal evolution require relatively simple parameterizations of sediment transport for application over larger scales. Here we present a transport parameterization for bimodal distributions of coarse quartz grains using simulations from a discrete particle model for sheet flow and near sheet flow conditions. The discrete particle model simulates the simplest one‐dimensional fluid using a turbulent eddy viscosity determined from a mixing length coupled to particle motions. The motions of individual sand grains are simulated using spherical elements. Newton’s second law in translational and rotational forms is solved for every particle in the domain as determined by both grain‐grain and grain‐fluid interactions. The forcing from idealized monochromatic waves is accomplished by specifying a spatially constant, time varying horizontal pressure gradient acting on the simulation domain. Consequently, the time series of the free‐stream fluid acceleration and velocity are also fixed. Simulations cover a range of wave forcing, diameter ratios for the large and small grains in the bimodal size distribution, and mass ratios of large to small grains in the simulation domain, for a total of 243 unique simulation conditions. The simulation results are successfully parameterized with a simple power law that allows for the prediction of the transport rates of each size fraction in the bimodal distribution. The simple power law determined from simulations provides favorable predictions of transport rates for each size fraction when applied to available laboratory data for sheet flow with bimodal size distributions. It is important to note that rapid vertical kinematic sorting of grains by size is explicitly simulated with the model and thus implicitly captured by the power law. Discussion focuses on practical application of the power law.
Modeling the influence of wave‐enhanced turbulence in a shallow tide‐ and wind‐driven water column
Authors: Jones Nicole L. , Monismith Stephen G.
Published: March 2008

The ability of one‐dimensional hydrodynamic models to reproduce dissipation of turbulent kinetic energy and velocity profiles for conditions of whitecapping waves in a shallow water, tide‐ and wind‐forced environment was assessed. The models were forced with the conditions experienced during a month‐long field experiment in a shallow estuarine embayment, and the results were compared with the observed dissipation and mean velocity profiles. Three turbulence models were assessed: the k‐ω model and two k‐l models, with different prescribed bilinear relationships for the turbulent length scale, l. The k‐ω turbulence model was found to best replicate the measured decay of dissipation with depth with a surface roughness length, z0s = 1.3Hs, and wave energy parameter, α = 60. The k‐l model achieved equally as good reproduction of the observations as the k‐ω model when the proportionality constant in the prescribed linear length scale relationship for the upper half of the water column was modified from the traditionally employed von Karman's constant, κ = 0.4, to 0.25. The model results show that the whitecapping waves often supplied the dominant source of turbulent kinetic energy over the majority of the water column in the shallow, tide‐ and wind‐forced system.
Aerosol properties over the SAFARI‐2000 area retrieved from ATSR‐2
Authors: Robles‐Gonzalez C. , de Leeuw G.
Published: March 2008

The aerosol optical depth (AOD) at three wavelengths has been retrieved from the radiance measured at the top of the atmosphere (TOA) by the ATSR‐2 (Along Track Scanning Radiometer) during the SAFARI‐2000 (Southern African Regional Science Initiative) dry season field campaign from 1 August to 30 September 2000. Two aerosol types were implemented in the ATSR‐2 retrieval algorithm: a highly absorbing aerosol that is mainly due to biomass burning and a less absorbing mixture of biomass burning, anthropogenic and biogenic aerosols. The mixing ratio of these two aerosol types was determined by comparison of the two modeled aerosol types with the ATSR‐2 measured signal. The accuracy of the AOD values determined from the ATSR‐2 data is 0.08 ± 0.06 for August and 0.14 ± 0.13 for September, as determined from comparison with various AERONET Sun photometers located in the area. In August 2000, the highly absorbing aerosol was the major aerosol component retrieved over the North‐Western part of the SAFARI‐2000 area. AOD values of up to 0.8 and Ångström coefficients of up to 2.1 were observed. Further to the South, the less absorbing type dominated with AOD values of up to 0.3 over the central SAFARI‐2000 area. During September the meteorological situation changed and the high absorbing aerosols were observed further South, due to advective transport of aerosol over a wider area. AOD values were up to 1 with Ångström coefficients similar to those in August. Low absorbing aerosols were observed over a relatively small area. Over the Namibian and Kalahari deserts dust emissions caused high AOD values of up to 0.75 during both months.
Dual‐beam measurements of gravity waves over Arecibo: Reevaluation of wave structure, dynamics, and momentum fluxes
Authors: Fritts David C. , Janches Diego
Published: March 2008

A previous study by Zhou and Morton (2006) employed dual‐beam incoherent scatter radar measurements of radial velocities at the Arecibo Observatory to study the structure, dynamics, and momentum fluxes of gravity waves in the mesosphere and lower thermosphere for ∼8 h on 28 July 2001. Because of erroneous assumptions about wave character and inferences of the relationship between radial velocities, however, the advertised results of this previous study are largely in error. The purposes of the present study are both to point out these errors to help avoid such pitfalls in the future and to provide a new interpretation of these data, which represent a very interesting case study of gravity wave dynamics at these altitudes. Specific findings of the present study (largely in contradiction to the previous analysis) include (1) the ∼15‐min oscillation was apparently a large‐amplitude Doppler‐ducted gravity wave structure propagating at one or two maxima of the westward large‐scale wind present during the event; (2) the gravity wave exhibited a deep and coherent vertical phase structure, except between the two westward wind maxima at later times, entirely inconsistent with proximity to a critical level; (3) the dominant motions within the gravity wavefield were vertical velocities up to ∼10 m s–1, except for inferred horizontal motions where the vertical motions changed phase and above and below the vertical velocity maxima, as dictated by the continuity equation; (4) there were likely no regions of dynamical instability accompanying these ducted wave motions; and (5) momentum fluxes due to this wave motion were small, despite its very large amplitude.
Predicting the response of seven Asian glaciers to future climate scenarios using a simple linear glacier model
Authors: Ren Diandong , Karoly David J.
Published: March 2008

Observations from seven Central Asian glaciers (35–55°N; 70–95°E) are used, together with regional temperature data, to infer uncertain parameters for a simple linear model of the glacier length variations. The glacier model is based on first order glacier dynamics and requires the knowledge of reference states of forcing and glacier perturbation magnitude. An adjoint‐based variational method is used to optimally determine the glacier reference states in 1900 and the uncertain glacier model parameters. The simple glacier model is then used to estimate the glacier length variations until 2060 using regional temperature projections from an ensemble of climate model simulations for a future climate change scenario (SRES A2). For the period 2000–2060, all glaciers are projected to experience substantial further shrinkage, especially those with gentle slopes (e.g., Glacier Chogo Lungma retreats ∼4 km). Although nearly one‐third of the year 2000 length will be reduced for some small glaciers, the existence of the glaciers studied here is not threatened by year 2060. The differences between the individual glacier responses are large. No straightforward relationship is found between glacier size and the projected fractional change of its length.
Water vapor, cloud liquid water paths, and rain rates over northern high latitude open seas
Authors: Zuidema Paquita , Joyce Robert
Published: March 2008

Data from the Special Sensor Microwave Imager (SSMI; years 1987–2006), Advanced Microwave Scanning Radiometer, and a surface‐based radiometer at Barrow, Alaska are examined for insights into the behavior of water vapor, cloud liquid water and rainrates over the northern high latitude seas. We evaluated two separate sets of retrievals, and achieved the best results through combining one that contained explicit monthly mean sea ice fractions with the Wentz V6 water vapor path (WVP), cloud liquid water path (LWP), and rainrate (RR) retrievals. The water vapor path retrieval shows no sensitivity to a proxy for sub‐pixel sea ice presence, while the liquid water path retrievals are sensitive to sea ice presence during summertime but otherwise the Wentz internal sea‐ice screening appears effective. The rainrate retrieval is highly sensitive to any sea ice during all seasons. The seasonal cycle and 1987–2006 time trends are examined. The WVP annual cycle has an amplitude of ∼1 cm at all locations, approximately double a broad winter minimum, with a July maximum phasing that is consistent with a continental influence. Little change occurs between January and April in WVP and LWP. The springtime LWP increase usually occurs in tandem with the WVP increase and slightly lags the falltime WVP decrease. The maximum lag occurs over the northern Pacific, where the maximum LWP occurs in August, one month later than over the northern Atlantic, and is correlated to an August precipitation maximum. The strongest SSMI‐derived trend is an increase in wintertime moisture south of Greenland, with wintertime LWP increases in the Labrador Sea. North of the Bering Strait, where much of the recent summer and autumn sea ice loss has occurred, the autumn WVP and LWP increased from 1989 to 2001 with a subsequent LWP decrease in recent years. The recent decline appears linked to a decrease in cyclone activity. Winter and spring LWP increases from 2002 to the present are noted in the surface‐based data set from Barrow, Alaska. Over the Barents Sea, where much of the recent winter sea ice loss has occurred, winter WVP and LWP have increased over the past decade. A comparison to National Center for Atmospheric Research Community Atmospheric Model Version 3.5 values finds modeled WVPs are slightly underestimated but the amplitude of the annual cycle is similar to that observed. Modeled winter LWPs slightly exceed those measured while the modeled summer LWPs exceed by a factor of two those observed (which are more likely to be positively biased also). The modeled rainrates are similar to retrieved values in the north Pacific, and exceed retrieved values by approximately a factor of 2 in the northeast Atlantic.
Spatial analysis of the intra‐annual variation of precipitation isotope ratios and its climatological corollaries
Authors: Bowen Gabriel J.
Published: March 2008

Intra‐annual variation in the stable isotope ratios of precipitation imparts a time‐dependent isotopic signal to continental hydrological and ecological systems. This variation is forced by seasonal climate cycles, with temperature and precipitation intensity each driving isotopic seasonality in different parts of the globe. In order to better characterize and understand the isotopic seasonality of precipitation and to advance applications such as the inversion of isotope/climate relationships for paleoclimate seasonality reconstruction, these relationships are analyzed using a database of precipitation isotope ratio observations and gridded maps. The results confirm the overwhelming dominance of temperature‐ and precipitation amount–related isotopic seasonality within specific, well‐defined geographic zones and indicate that these zones encompass most of Earth's continental land surface. Analysis of global maps of precipitation isotopic seasonality, however, indicates spatially patterned variation in isotope/climate relationships, including patterns related to continentality in temperature‐dominated regions and meridional trends in amount‐dominated areas. These features reflect more complex climatological controls on isotope seasonality and suggest limitations and opportunities for paleoclimate reconstruction using isotopic archives.
Hot spots and hot moments of carbon and nitrogen dynamics in a semiarid riparian zone
Authors: Harms Tamara K. , Grimm Nancy B.
Published: March 2008

Riparian ecosystems are characterized by spatial and temporal heterogeneity in physical and biological attributes, with consequences for nutrient cycling. We investigated the responses of carbon (C) and nitrogen (N) cycling processes to the hydrogeomorphic template in the riparian zone of the San Pedro River, Arizona, a large (catchment area ∼11,500 km2), free‐flowing, semiarid river. Over an annual period we documented spatial and temporal patterns in soil, shallow groundwater, and stream nutrient chemistry as well as rates of N‐transforming processes in soils of the surface (0–17 cm) and region of seasonal saturation (RoSS). A hot moment of N retention and removal was indicated by elevated rates of microbial processes during the summer monsoon season. At the same time, elevated C was observed in soil microbial biomass for both surface soils and soils in the RoSS. Analyses of C‐use profiles for soil microbes, coupled with trends in stream and shallow‐groundwater chemistry, further suggest that this hot moment of N removal was fueled by newly available, labile organic material. In a spatial context, patchiness in soil resources, microbial biomass, and potential denitrification were best explained by variation in microtopography; low‐elevation landscape positions were hot spots of resource availability and microbial activity. Vertical heterogeneity also corresponded with variation in the factors influencing N transformation rates. Organic matter was more frequently a significant factor explaining N transformation rates in RoSS soils whereas soil water content was more often important in surface soils. Together, these patterns suggest that understanding the points on the hydrogeomorphic template, both in space and in time, that bring together water and labile organic matter will lead to greater predictive capability regarding C and N cycling in semiarid river‐riparian corridors.
Three‐dimensional simulation of liquid drop dynamics within unsaturated vertical Hele‐Shaw cells
Authors: Huang Hai , Meakin Paul
Published: March 2008

A three‐dimensional, multiphase fluid flow model with volume of fluid‐interface tracking was developed and applied to study the multiphase dynamics of moving liquid drops of different sizes within vertical Hele‐Shaw cells. The simulated moving velocities are significantly different from those obtained from a first‐order analytical approximation, based on simple force‐balance concepts. The simulation results also indicate that the moving drops can exhibit a variety of shapes and that the transition among these different shapes is largely determined by the moving velocities. More important, there is a transition from a linear moving regime at small capillary numbers, in which the capillary number scales linearly with the Bond number, to a nonlinear moving regime at large capillary numbers, in which the moving drop releases a train of droplets from its trailing edge. The train of droplets forms a variety of patterns at different moving velocities.
Parent–Offspring Conflict in Mate Preferences
Authors: Buunk Abraham P. , Park Justin H. , Dubbs Shelli L.
Published: March 2008

Prevailing evolutionary approaches to human mating have largely ignored the fact that mating decisions are heavily influenced by parents and other kin. This is significant because parents and children often have conflicting mate preferences. We provide a brief review of how parents have influenced their children's mating behavior across cultures and throughout history. Then, by drawing on evolutionary reasoning, we offer a hypothesis for why parents and offspring may have conflicting interests with respect to mate preferences. Specifically, parents may have a relatively stronger preference for children's mates with characteristics suggesting high parental investment and cooperation with the ingroup, whereas children may have a relatively stronger preference for mates with characteristics signaling heritable fitness. We review past research consistent with this hypothesis, and we report new results from an empirical study consisting of 768 participants from a variety of cultures that provided clear support for the hypothesis.
Suppression of cytotoxic and proliferative xenogeneic T‐cell responses by transgenic expression of indoleamine 2,3‐dioxygenase
Authors: Wee Janet Lye‐Keng , Christiansen Dale , Li Yu‐Qin , Boyle William , Sandrin Mauro S
Published: March 2008

Tryptophan catabolism initiated by the enzyme indoleamine 2,3‐dioxygenase (IDO) has been postulated to be a natural regulatory mechanism for T cells. In this study, we generated a pig endothelial cell line expressing full‐length human IDO (P‐HuIDO) to serve as a simple model of a cellular xenogeneic graft. Splenocytes from mice primed to P‐HuIDO cells were found to be as responsive to secondary stimulation as splenocytes from mice primed to parental cells. However, in T‐cell proliferation assays using P‐HuIDO cells as stimulators, a significant inhibition of both naive and memory xenogeneic proliferative responses was noted. Furthermore, the production of interferon‐γ and cytotoxic T lymphocyte function were also affected. When severe combined immunodeficiency mice were grafted with P‐HuIDO cells, then challenged with primed splenocytes from BALB/c mice, cellular infiltration to the graft was delayed. Our findings suggest that transgenic expression of IDO in xenografts contributes to prolonged graft survival.
Functional differentiation within the monkey cortex as revealed by near-infrared spectroscopy
Authors: Ardestani Allen , Darvas Felix , Steinbrink Jens , Toga Arthur , Fuster Joaquin
Published: March 2008

The role of prefrontal cortex in working memory (WM) is well established. However, questions remain regarding the topography and “domain-specific differentiation” of different types of information processing in the cortex. While it has been theorized that dorsolateral (DPFC) and ventrolateral (VPFC) prefrontal cortex preferentially process spatial and object WM, respectively, both electrophysiological evidence in the monkey and neuroimaging in the human have largely failed to demonstrate such regional differentiation. In this study we use near-infrared spectroscopy (NIRS) to detect functional changes, across relatively large cortical cell populations, simultaneously from prefrontal and posterior parietal cortices. Imaging data were recorded from a Rhesus macaque performing two types of WM tasks: a spatial task in which the animal had to retain the spatial position of a visual stimulus, and a non-spatial task where he had to retain its color (red or green) during a 20s delay. During performance of the spatial WM task, cerebral activation trends were found in which DPFC exhibited stronger activation than did the VPFC, and posterior parietal cortex maintained higher delay activation than did frontal regions. These differences were less pronounced during performance of the non-spatial task. Additionally, incorrect trials generally elicited lower activations during the delay period than did trials ending with a correct response. Furthermore, NIRS data collected during the performance of a haptic WM task also appear to exhibit inter-regional differences in delay activation. The data thus suggest the presence of preferential cognitive processing between and within posterior and frontal cortical regions.
Integrated Collaboration across Distributed Sites: The Perils of Process and the Promise of Practice
Authors: David Gary C , Chand Donald , Newell Sue , Resende-Santos João
Published: March 2008

In an era where a strategic command of global resources is becoming a requisite for success, firms are struggling to successfully unify their onshore and offshore sites. The literature on global virtual teams generally frames the impediments to coordination and collaboration based on divergent nationally based cultural attributes, language barriers, and the limitations of information and communication technologies. Drawing on world-systems theory, this paper argues for a decrease in the importance afforded to national boundaries and individual sites, and a re-orientation to the social dynamics across sites regardless of nationality. By changing the unit of analysis to the organization as a world system and focusing on emergent practices, this paper provides new insights regarding globally distributed collaborative work and identifies how to manage global relations to overcome structural impediments, to develop positive social relations, and achieve collaboration.
Electron attachment to Ni(PF3)4 and Pt(PF3)4
Authors: Friedman Jeffrey F. , Miller Thomas M. , Friedman-Schaffer Jessica K. , Viggiano A. A. , Rekha G. K. , Stevens Amy E.
Published: March 2008

An experimental study has been made of thermal electron attachment to the transition-metal trifluorophosphine complexes Ni(PF3)4 and Pt(PF3)4 using a flowing-afterglow Langmuir-probe apparatus. Both complexes are efficient at electron attachment, although the rate constants are somewhat less than collisional. The rate constant for electron attachment to Ni(PF3)4 is 1.9×10−7cm3s−1 at room temperature, about a factor of 2 less than collisional. The activation energy is 39±5meV for the attachment reaction. The rate constant for electron attachment to Pt(PF3)4 is 5.4×10−8cm3s−1 at room temperature, and the activation energy is 84±8meV. For both complexes, a PF3 ligand is lost on electron attachment, and only the M(PF3)3− ion is observed in the negative-ion mass spectrum. Density functional calculations were carried out on Ni(PF3)4 and various fragments in order to describe the thermochemistry of the attachment reaction.
The energetics of tetrahydrocarbazole aromatization over Pd(111): A computational analysis
Authors: Crawford P. , Burch R. , Hardacre C. , Hindle K. T. , Hu P. , Rooney D. W.
Published: March 2008

The carbazole moiety is a component of many important pharmaceuticals including anticancer and anti-HIV agents and is commonly utilized in the production of modern polymeric materials with novel photophysical and electronic properties. Simple carbazoles are generally produced via the aromatization of the respective tetrahydrocarbazole (THCZ). In this work, density functional theory calculations are used to model the reaction pathway of tetrahydrocarbazole aromatization over Pd(111). The geometry of each of the intermediate surface species has been determined and how each structure interacts with the metal surface addressed. The reaction energies and barriers of each of the elementary surface reactions have also been calculated, and a detailed analysis of the energetic trends performed. Our calculations have shown that the surface intermediates remain fixed to the surface via the aromatic ring in a manner similar to that of THCZ. Moreover, the aliphatic ring becomes progressively more planer with the dissociation of each subsequent hydrogen atom. Analysis of the reaction energy profile has revealed that the trend in reaction barriers is determined by the two factors: (i) the strength of the dissociating ring-H bond and (ii) the subsequent gain in energy due to the geometric relaxation of the aliphatic ring.
Influence of inductance variation on performance of a permanent magnet claw pole soft magnetic composite motor
Authors: Guo Youguang , Zhu Jian Guo , Lin Zhi Wei , Lu Haiyan , Wang Xiaolin , Chen Jiaxin
Published: March 2008

Winding inductance is an important parameter in determining the performance of electrical machines, particularly those with large inductance variation. This paper investigates the influence of winding inductance variation on the performance of a three-phase three-stack claw pole permanent magnet motor with soft magnetic composite (SMC) stator by using an improved phase variable model. The winding inductances of the machine are computed by using a modified incremental energy method, based on three-dimensional nonlinear time-stepping magnetic field finite element analyses. The inductance computation and performance simulation are verified by the experimental results of an SMC claw pole motor prototype.
Finding reaction paths using the potential energy as reaction coordinate
Authors: Aguilar-Mogas Antoni , Giménez Xavier , Bofill Josep Maria
Published: March 2008

The intrinsic reaction coordinate curve (IRC), normally proposed as a representation of a reaction path, is parametrized as a function of the potential energy rather than the arc-length. This change in the parametrization of the curve implies that the values of the energy of the potential energy surface points, where the IRC curve is located, play the role of reaction coordinate. We use Carathéodory’s relation to derive in a rigorous manner the proposed parametrization of the IRC path. Since this Carathéodory’s relation is the basis of the theory of calculus of variations, then this fact permits to reformulate the IRC model from this mathematical theory. In this mathematical theory, the character of the variational solution (either maximum or minimum) is given through the Weierstrass E-function. As proposed by Crehuet and Bofill [J. Chem. Phys. 122, 234105 (2005)], we use the minimization of the Weierstrass E-function, as a function of the potential energy, to locate an IRC path between two minima from an arbitrary curve on the potential energy surface, and then join these two minima. We also prove, from the analysis of the Weierstrass E-function, the mathematical bases for the algorithms proposed to locate the IRC path. The proposed algorithm is applied to a set of examples. Finally, the algorithm is used to locate a discontinuous, or broken, IRC path, namely, when the path connects two first order saddle points through a valley-ridged inflection point.
Magnetic and transport properties of the room-temperature ferrimagnetic semiconductor Fe1.5Ti0.5O3±δ: Influence of oxygen stoichiometry
Authors: Ndilimabaka Hervé , Dumont Yves , Popova Elena , Desfonds Pascal , Jomard François , Keller Niels , Basletic Mario , Bouzehouane Karim , Bibes Manuel , Godlewski Marek
Published: March 2008

Fe 1.5 Ti 0.5 O 3 ± δ epitaxial thin films have been grown on α-Al2O3 (0001) substrates by pulsed laser deposition technique. The samples are both ferrimagnetic and semiconducting beyond room temperature. Oxygen pressure (PO2) during the deposition appears to be a critical parameter in promoting high temperature long range magnetic order and semiconducting properties. For all oxygen pressures, Fe1.5Ti0.5O3±δ thin films are single phase with twin epitaxy. High dc conductivity and low magnetization are obtained at low PO2, whereas high saturation magnetization and low conductivity stand for high PO2. Oxygen vacancies and∕or change of iron valence state are pointed out to be responsible of these properties. Superexchange mechanism via oxygen bonds seems rather to dominate the magnetic properties especially for high PO2, whereas for low PO2 a double exchange mechanism might occur. Fe1.5Ti0.5O3±δ appears thus to be an interesting material for high temperature spintronics applications.
Temperature dependence of half-metallic hybridization gaps
Authors: Skomski Ralph
Published: March 2008

The temperature dependence of the spin polarization of half-metallic ferromagnets is investigated by model calculations. Emphasis is on changes in the density of states, especially on the closure of the hybridization gap. The Stoner-type calculation yields a simple one-electron expression for the gap as a function of temperature and a corresponding transition temperature T*, above which the spin polarization is drastically reduced. The small parameter determining the finite-temperature breakdown of the spin splitting is the width of the hybridization gap relative to other bandwidth parameters. The model predictions are consistent with the experiment and with first-principles electronic structure calculations, and we argue that such band-structure effects are not limited to specific materials but rather widespread in hybridization-gap half-metals.
A concept of homeomorphic defect for defining mostly conjugate dynamical systems
Authors: Skufca Joseph D. , Bollt Erik M.
Published: March 2008

A centerpiece of dynamical systems is comparison by an equivalence relationship called topological conjugacy. We present details of how a method to produce conjugacy functions based on a functional fixed point iteration scheme can be generalized to compare dynamical systems that are not conjugate. When applied to nonconjugate dynamical systems, we show that the fixed-point iteration scheme still has a limit point, which is a function we now call a “commuter”—a nonhomeomorphic change of coordinates translating between dissimilar systems. This translation is natural to the concepts of dynamical systems in that it matches the systems within the language of their orbit structures, meaning that orbits must be matched to orbits by some commuter function. We introduce methods to compare nonequivalent systems by quantifying how much the commuter function fails to be a homeomorphism, an approach that gives more respect to the dynamics than the traditional comparisons based on normed linear spaces, such as L2. Our discussion addresses a fundamental issue—how does one make principled statements of the degree to which a “toy model” might be representative of a more complicated system?
Zero kinetic energy photoelectron spectroscopy of tetracene using laser desorption for vaporization
Authors: Zhang Jie , Pei Linsen , Kong Wei
Published: March 2008

Far infrared (FIR) spectroscopy of polycyclic aromatic hydrocarbons is of particular interest to astrophysics since vibrational modes in this range are representative of the molecular size and shape. This information is hence important for identification of chemical compositions and for modeling of the IR spectrum observed in the outer space. In this work, we report neutral and cation FIR spectroscopy of tetracene vaporized from a laser desorption source. Results from two-color resonantly enhanced multiphoton ionization and two-color zero kinetic energy photoelectron spectroscopy will be presented. Several skeletal vibrational modes of the first electronically excited state of the neutral species and those of the cation are assigned, with the aid of ab initio and density functional calculations. The adiabatic ionization potential is determined to be 55918±7cm−1. Interestingly, all observed vibrational modes can be rationalized based on a simple Hückle calculation, i.e., by observing the addition or elimination of nodal planes due to electronic excitation and/or ionization. Limited by the Franck–Condon principle and the rigidity of the molecular frame of tetracene, only IR forbidden modes are observed in this work.
Fast precessional reversal in perpendicular composite patterned media
Authors: Livshitz B. , Choi R. , Inomata A. , Bertram H. N. , Lomakin V.
Published: March 2008

Magnetization reversal mechanisms in composite exchange-coupled dual-layer (composite) patterned media are allowed in the regime of precessional reversal, which is characterized by substantially reduced reversal fields. An important property of precessional reversal in composite patterned media is that it can occur for recording field rise times of more than an order larger than those in patterned media comprising homogeneous elements. These longer rise times can be allowed by realistic recording systems even for materials with ultrahigh coercivity. The reversal field and rise times required for precessional reversal can be controlled by varying the soft layer parameters and coupling strength between the layers.
Influence of demagnetization coil configuration on residual field in an extremely magnetically shielded room: Model and measurements
Authors: Knappe-Grueneberg Silvia , Schnabel Allard , Wuebbeler Gerd , Burghoff Martin
Published: March 2008

The Berlin magnetically shielded room 2 (BMSR-2) features a magnetic residual field below 500pT and a field gradient level less than 0.5pT∕mm, which are needed for very sensitive human biomagnetic recordings or low field NMR. Nevertheless, below 15Hz, signals are compromised by an additional noise contribution due to vibration forced sensor movements in the field gradient. Due to extreme shielding, the residual field and its homogeneity are determined mainly by the demagnetization results of the mumetal shells. Eight different demagnetization coil configurations can be realized, each results in a characteristic field pattern. The spatial dc flux density inside BMSR-2 is measured with a movable superconducting quantum interference device system with an accuracy better than 50pT. Residual field and field distribution of the current-driven coils fit well to an air-core coil model, if the high permeable core and the return lines outside of the shells are neglected. Finally, we homogenize the residual field by selecting a proper coil configuration.
A study of the Fermi–Pasta–Ulam problem in dimension two
Authors: Benettin Giancarlo , Gradenigo Giacomo
Published: March 2008

Continuing the previous work on the same subject, we study here different two-dimensional Fermi–Pasta–Ulam (FPU)-like models, namely, planar models with a triangular cell, molecular-type potential and different boundary conditions, and perform on them both traditional FPU-like numerical experiments, i.e., experiments in which energy is initially concentrated on a small subset of normal modes, and other experiments, in which we test the time scale for the decay of a large fluctuation when all modes are excited almost to the same extent. For each experiment, we observe the behavior of the different two-dimensional systems and also make an accurate comparison with the behavior of a one-dimensional model with an identical potential. We assume the thermodynamic point of view and try to understand the behavior of the system for large n (the number of degrees of freedom) at fixed specific energy ε=E∕n. As a result, it turns out that: (i) The difference between dimension one and two, if n is large, is substantial. In particular (making reference to FPU-like initial conditions) the “one-dimensional scenario,” in which the dynamics is dominated for a long time scale by a weakly chaotic metastable situation, in dimension two is absent; moreover in dimension two, for large n, the time scale for energy sharing among normal modes is drastically shorter than in dimension one. (ii) The boundary conditions in dimension two play a relevant role. Indeed, models with fixed or open boundary conditions give fast equipartition, on a rather short time scale of order ε−1, while a periodic model gives longer equilibrium times (although much shorter than in dimension one).
Voltage-limitation-free analytical single-electron transistor model incorporating the effects of spin-degenerate discrete energy states
Authors: Pruvost Benjamin , Mizuta Hiroshi , Oda Shunri
Published: March 2008

A physically based analytical single-electron transistor (SET) model is proposed. This model virtually shows no voltage limitation in the scope of the orthodox theory, which makes it particularly suitable for hybrid simulation where the SET is biased by a current source. The model is verified against Monte Carlo simulation with excellent agreement and compared to existing models. It is found that our model is valid and accurate whatever the drain voltage and faster than reported models on the whole. A way to integrate into the model the effects of spin-degenerate quantum energy level discreteness, in the case of a silicon-based SET, is also introduced and observed quantum mechanical effects, such as negative differential conductance, are discussed.
Light-induced programming of Si nanocrystal flash memories
Authors: de Sousa J. S. , Farias G. A. , Leburton J.-P.
Published: March 2008

We show theoretically that it is possible to achieve much faster programming performances in nanocrystal flash memory devices by means of a light-induced mechanism that inverts the direction of charge transfer between nanocrystals and device substrate in comparison to conventional voltage-induced programming. Our method is based on the self-consistent solutions of Hartree and Poisson equation for both electrons and holes with open boundary conditions.
Characterization of superparamagnetic Fe3O4 nanoparticles by fluxgate magnetorelaxometry for use in biomedical applications
Authors: Ludwig F. , Heim E. , Schilling M. , Enpuku K.
Published: March 2008

We have investigated the magnetorelaxometry (MRX) of various Fe3O4 nanoparticle suspensions utilizing a differential fluxgate setup. To estimate the distribution of the hydrodynamic size of the magnetic nanoparticles (MNPs) with organic shell, the cluster moment superposition model is applied. On a sample series of MNPs from the same batch diluted in water-glycerine mixtures of varying viscosity, it is demonstrated that the model is suited for the estimation of the distribution of the hydrodynamic size of MNPs and clusters. Since a MRX measurement lasts only a few seconds, it is also highly suited to study the aggregation kinetics. This is demonstrated on MNPs with silica shell suspended in 5% phosphate-buffered saline solution.
Effect of introducing gettering sites and subsequent Au diffusion on the thermal conductivity and the free carrier concentration in n-type 4H-SiC
Authors: Kazan M. , Ottaviani L. , Moussaed E. , Nader R. , Masri P.
Published: March 2008

We report on the application of introducing gettering sites by helium implantation prior to an annealing and subsequent gold diffusion as an approach to control the thermal conductivity and the charge carrier concentration in n-type 4H-SiC. Rutherford backscattering spectroscopy showed high diffusion of gold impurities to the introduced gettering sites which implied a success in introducing gettering sites. Data obtained from the measurements of the specific heat, thermal diffusivity, and room temperature density were used to deduce the thermal conductivity of the samples investigated. The thermal conductivity modeling showed that introducing gettering sites can increase the thermal conductivity in n-type 4H-SiC due to the reduction of phonon-impurity scattering. Raman measurements showed the presence of the desired defects introduted by ion implantation at 20°C. The analysis of the Fourier transform infrared reflectivity showed that the gettering sites can act as majority carrier traps and reduce the recombination process.
Inertial consistent subgrid model for large-eddy simulation based on the lattice Boltzmann method
Authors: Dong Yu-Hong , Sagaut Pierre , Marie Simon
Published: March 2008

The recently introduced inertial-range (IR) consistent Smagorinsky model and the classical Smagorinsky model are applied to the large-eddy simulation (LES) of decaying homogeneous isotropic turbulence based on the lattice Boltzmann method (LBM), which is implemented using the 19-velocity D3Q19 lattice model. The objectives of this study are to examine the effectiveness of the LES-LBM technique for study of turbulence and to extend and validate the efficiency of the inertial-range consistent Smagorinsky model for lattice Boltzmann fluid dynamics. The LES-LBM results are compared with the direct numerical simulation data as well as experimental data. The time evolution of the kinetic energy and the decay exponents of the dissipation rate, the velocity derivative skewness, and instantaneous energy spectra are analyzed. The dependency of behavior of the model coefficients on the ratio of grid width Δ and the Kolmogorov scale η is examined numerically. The results demonstrate that the LES-LBM in conjunction with the IR consistent Smagorinsky model can be used to simulate turbulence more satisfactorily than the standard Smagorinsky model.
Enhanced ferroelectric properties of predominantly (100)-oriented CaBi4Ti4O15 thin films on Pt∕Ti∕SiO2∕Si substrates
Authors: Yan Jing , Hu Guangda , Liu Zongming , Fan Suhua , Zhou Ying , Yang Changhong , Wu Weibing
Published: March 2008

Predominantly (100)-oriented CaBi4Ti4O15 (CBTi) films were fabricated on Pt (111)∕Ti∕SiO2∕Si substrates using a metal organic decomposition method at annealing temperatures ranging from 600to800°C. The growth mode of the predominantly (100)-oriented CBTi films fabricated by the sequential layer annealing method was discussed based on the structure evolution with the annealing temperature. The remanent polarization and coercive field of the CBTi film annealed at 750°C are 38.1μC∕cm2 and 216kV∕cm, respectively. No fatigue can be observed after 109 switching cycles. The remanent polarization of the purely a-axis-oriented CBTi film should be higher than 50μC∕cm2.
Dielectric function of warm dense gold
Authors: Ping Y. , Hanson D. , Koslow I. , Ogitsu T. , Prendergast D. , Schwegler E. , Collins G. , Ng A.
Published: March 2008

Single-state measurements of the broadband (450–800nm) dielectric function of gold using a supercontinuum probe are reviewed. These measurements have demonstrated the first evidence of the existence of band structure in ultrathin gold foils isochorically heated by a femtosecond laser pulse to energy densities of 106–107J∕kg. The Drude component of the dielectric function increases with energy density while the interband component shows both enhancement and redshift. Ab initio molecular-dynamics calculations based on thermalized electrons cannot reproduce the experimental results, suggesting a non-Fermi distribution of excited electrons.
Conformational landscape of the HIV-V3 hairpin loop from all-atom free-energy simulations
Authors: Verma Abhinav , Wenzel Wolfgang
Published: March 2008

Small beta hairpins have many distinct biological functions, including their involvement in chemokine and viral receptor recognition. The relevance of structural similarities between different hairpin loops with near homologous sequences is not yet understood, calling for the development of methods for de novo hairpin structure prediction and simulation. De novo folding of beta strands is more difficult than that of helical proteins because of nonlocal hydrogen bonding patterns that connect amino acids that are distant in the amino acid sequence and there is a large variety of possible hydrogen bond patterns. Here we use a greedy version of the basin hopping technique with our free-energy forcefield PFF02 to reproducibly and predictively fold the hairpin structure of a HIV-V3 loop. We performed 20 independent basin hopping runs for 500cycles corresponding to 7.4×107 energy evaluations each. The lowest energy structure found in the simulation has a backbone root mean square deviation (bRMSD) of only 2.04Å to the native conformation. The lowest 9 out of the 20 simulations converged to conformations deviating less than 2.5Å bRMSD from native.
Mechanism for blob generation in the TORPEX toroidal plasma
Authors: Furno I. , Labit B. , Fasoli A. , Poli F. M. , Ricci P. , Theiler C. , Brunner S. , Diallo A. , Graves J. P. , Podestà M. , Müller S. H.
Published: March 2008

The mechanism for blob generation is detailed in the toroidal magnetized plasma of the TORPEX device [Fasoli et al., Phys. Plasmas 13, 055902 (2006)] using an experimental configuration, which features a plasma region dominated by a coherent wave and a region on the low field side characterized by the propagation of blobs. Predictions from linearized 2D drift-reduced Braginskii equations are compared with experimental data, revealing the interchange nature of the coherent wave. The dynamics of blob formation is investigated using time-resolved measurements of two-dimensional profiles of electron density, temperature, plasma potential and E×B velocity. Blobs form from radially elongated structures associated with the interchange wave. When a blob is generated, the following sequence of events is observed: 1) A decrease of local pressure gradient length provides an increase of the interchange mode drive; 2) in response, the interchange mode increases in amplitude and expands in the radial direction forming a radially elongated structure from the wave crest; 3) the elongated structure is convected by the E×B flow and is eventually sheared off, forming a blob on the low field side. The dependence of the blob amplitude upon the minimum pressure radial scale length before the blob ejection is also investigated.