bluuebunny/crossref_metadata_2025 huggingface dataset:
The Vanishing problem of the string class with degree 3
Authors: Kuribayashi Katsuhiko , Yamaguchi Toshihiro
Published: April 2009

Let ξbe anSO(n)-bundle over a simple connected manifoldMwith a spin structureQ → M. The string class is an obstruction to h1 the structure groupLSpin(n)of the loop group bundleLQ → LMto the universal central extension ofLSpain(n)by the circle. We prove that the string class vanishes if and only if 1/2 the first Pontrjagin clsss of values whenMis a compact simply connected homogeneous space of rank one, a simpiy connected 4 dimensional manifold or a finite product space of those manifolds. This result is deduced by using the Eclesberg spectral sequence converging to the modpcohomology ofLMwhoseE2-term to the Hochschild homology of the modpcohomology algebra ofM. The key to the consideration is existence of a morphism of algebras, which is injective below degree 3, from an important graded commutator algebra into the Hochschild homology of a certain graded commutative algebra.
Continuous nilpotents on topological spaces
Authors: Sullivan R. P. , Rubinstein J. H.
Published: April 2009

K. D. Magill has investigated the semigroup generated by the idempotent continuous mappings of a topological space into itself and examined whether this semigroup determines the space to within homeomorphism. By analogy with this (and related work of Bridget Bos Baird) we now consider the semigroup generated by nilpotent continuous partial mappings of a space into itself.
Democrat, Republican, or None of the Above? The Role of Religiosity in Muslim American Party Identification
Authors: Barreto Matt A. , Bozonelos Dino N.
Published: April 2009

The role of religiosity as an important predictor of partisan identification has been well researched over the years, with most of our understanding of religion focused on Christianity. However, it is not clear that religiosity operates equally for the partisan identification of non-Christian religious groups. One of the most discussed religious minority groups in the United States today is Muslim-Americans. Numbering between 2.3 million and 7 million, Muslim-Americans have been the focus of considerable debate regarding religion and American political inclusion. We argue that religiosity does influence Muslim-American party identification, however not in the same manner as with other groups. While the two major political parties encourage religiosity among Protestants, Jews, and Catholics, they are either silent or opposed to religiosity among Muslims within their parties. Thus, religiosity among Muslim-Americans may not necessarily lead to partisan identification with either Republicans or Democrats. Rather, high levels of religiosity, coupled with perceptions of discrimination against Muslims, may lead many to oppose both major political parties and instead identify with “none of the above.” This is not to say that Muslim-Americans reject civic engagement or political participation in the United States, but rather the two political parties have not carved out a space to welcome Islam, as they have for Christianity and Judaism. We examine new data from the 2007 Muslim-American Public Opinion Survey to assess the predictors of partisan identification among Muslims in the United States.
The Congressional Representation of Muslim-American Constituents
Authors: Martin Shane
Published: April 2009

Legislators' responsiveness to constituency preferences is an accepted cornerstone of American representative democracy. Focusing on key domestic anti-terrorism votes during the 109th Congress, this study explores whether or not the presence of Muslim-Americans in a district influenced House members' roll-call behavior. We apply and test two competing theories of representation: the congruence theory and the minority backlash hypothesis. Using original data on Muslim-American constituency size, our analysis indicates little evidence of a representational backlash and some evidence that both Democratic and Republican members are positively responsive in their roll-call behavior to the presence of Muslim voters in their districts.
Americans' Views of Muslims and Mormons: A Social Identity Theory Approach
Authors: Penning James M.
Published: April 2009

Although American society is religiously pluralistic, not all religious groups enjoy equal levels of public approval and support. Indeed, America has a history of viewing members of nontraditional religious groups with considerable distrust and suspicion. Two religious groups in particular — Muslims and Mormons — have come under fire in recent years, though not necessarily for the same reasons. Muslims and Mormons have frequently been viewed as outside the mainstream of American culture and, perhaps for that reason, have suffered from discrimination, threats, and violence. This article examines Americans' views of these two important and rapidly growing groups, using social identity theory as the primary vehicle of analysis. The theory proves useful in helping us explain variance in Americans' views of these two groups. While a variety of social, political and religious variables help to explain Americans' views of Muslims and Mormons, religious variables have the greatest impact.
The pacemaker of major climate shifts
Authors: Wang Geli , Swanson Kyle L. , Tsonis Anastasios A.
Published: April 2009

Models and data suggest that the interplay of major climate modes may result in climate shifts. More specifically it has been shown that when the network of North Atlantic Oscillation (NAO), Pacific Decadal Oscillation (PDO), El Nino/Southern Oscillation (ENSO) and North Pacific Index (NPI) synchronizes, an increase in the coupling between these oscillations destroys the synchronous state and leads the climate system to a new state. These shifts are associated with significant changes in global temperature trend and in ENSO variability. Here we probe the details of this network's dynamics to investigate if a certain oscillation is the culprit in these shifts. From a total of 12 synchronization events observed in three climate simulations and in observations we find that the instigator of these shifts is NAO. Without exception only when NAO's coupling with the Pacific increases a shift will occur. Our results suggest a dynamical sequence of events in the evolution of climate shifts which is consistent with recent independent empirical and modeling studies.
Trends in joint quantiles of temperature and precipitation in Europe since 1901 and projected for 2100
Authors: Beniston Martin
Published: April 2009

This study assesses the changes in the exceedances of joint extremes of temperature and precipitation quantiles for a number of sites in Europe. The combination of cool/dry, cool/wet, warm/dry and warm/wet modes reveals a systematic change at all locations investigated in the course of the 20th century, with significant declines in the frequency of occurrence of the “cold” modes and a sharp rise in that of the “warm” modes. The changing behavior of these four modes is also accompanied by changes in the particular conditions of temperature and precipitation associated with each mode; for example, the average amount of precipitation during cool/wet events decreases while that during warm/wet events increases, even though mean precipitation at most locations shows no significant trend. In a “greenhouse climate”, the “cool” modes are almost totally absent by 2100 whereas the warm/dry and warm/wet modes pursue the progression already observed in the 20th century.
Progressive strain localization in a major strike‐slip fault exhumed from midseismogenic depths: Structural observations from the Salzach‐Ennstal‐Mariazell‐Puchberg fault system, Austria
Authors: Frost Erik , Dolan James , Sammis Charles , Hacker Brad , Cole Joshua , Ratschbacher Lothar
Published: April 2009

Analysis of a strike‐slip fault exhumed from midseismogenic depths reveals that the fault experienced progressive strain localization toward a high‐strain fault core. We focus on the Ennstal segment of the 400‐km‐long Salzach‐Ennstal‐Mariazell‐Puchberg (SEMP) strike‐slip fault system in the Eastern Alps, which accommodated ∼60 km of left lateral displacement during Oligo‐Miocene time. Macroscopic and microscopic observations reveal a zoned fault featuring a high‐strain core at least 10 m wide within a fault zone that is at least 150 m wide. Grain‐size distribution analysis shows how the Ennstal segment of the SEMP evolved. Our data reveal a 10‐m‐wide high‐strain fault core (characterized by a power law relationship of grain sizes, D2 ≈ 2.0) bordered by a 54‐m‐wide “transition zone” where the largest and smallest grains are characterized by two power law relationships (D2 ≈ 2.0 and 1.6, respectively). This zone is in turn bordered by a region with grain sizes that show a single low‐strain power law relationship of D2 ≈ 1.6. We interpret these relationships to be the result of concentrated shear overprinting an initial low‐strain, power law grain‐size distribution before strain localized to the core. This is consistent with the theory that faults mature by smoothing geometrical complexities, forming a highly localized, high‐strain fault core. The data do not support the idea that damage forms primarily in response to dynamic stresses during seismic rupture, although they do suggest that this mechanism may operate within tens of meters of the fault once it has developed its zoned structure.
Viscosity of the asthenosphere from glacial isostatic adjustment and subduction dynamics at the northern Cascadia subduction zone, British Columbia, Canada
Authors: James Thomas S. , Gowan Evan J. , Wada Ikuko , Wang Kelin
Published: April 2009

Late glacial sea level curves located in the Cascadia subduction zone (CSZ) fore arc in southwestern British Columbia show that glacial isostatic adjustment (GIA) was rapid when the Cordilleran Ice Sheet collapsed in the late Pleistocene. GIA modeling with a linear Maxwell rheology indicates that the observations can be equally well fit across a wide range of asthenospheric thicknesses, provided that the asthenospheric viscosity is varied from 3 × 1018 Pa s for a thin (140 km) asthenosphere to 4 × 1019 Pa s for a thick (380 km) asthenosphere. Present‐day vertical crustal motion predicted by the GIA models shows rates of a few tenths of a millimeter per year, consistent with previous analyses. The model viscosities largely pertain to the viscosity of the oceanic mantle beneath the subducting Juan de Fuca slab but include a contribution from the mantle wedge above the slab. For comparison, effective viscosities for the upper mantle due to the tectonic regime (subduction) were computed using the strain rates and temperatures of an independent geodynamic model of the CSZ with a wet olivine power law rheology. The effective viscosities agree well with GIA model viscosities of 1019 Pa s or less, corresponding to an asthenosphere of 100 or 200 km thickness. The agreement suggests a significant role for power law flow in the GIA response. Regardless of the microphysical mechanisms responsible for the GIA response, the viscosity values inferred from GIA can be applied to studies of the megathrust earthquake cycle because both processes take place on comparable time scales.
Vertical cascade structure of the atmosphere and multifractal dropsonde outages
Authors: Lovejoy S. , Tuck A. F. , Hovde S. J. , Schertzer D.
Published: April 2009

We use 220 atmospheric profiles from state‐of‐the‐art dropsondes to test the predictions of multiplicative cascade models of the atmosphere on the horizontal velocity, pressure, temperature, log potential temperature, log equivalent potential temperature, air density, humidity, and vertical sonde velocity. We found that the predictions were accurately verified (to within ±1 to ±2% over 10 m to 1 km for the statistical moments up to second order); the effective outer cascade scale Leffwas in the range 1–30 km. In order to perform the analyses and to correctly interpret the results, we needed to overcome technical difficulties caused by the sonde's highly intermittent sampling. This intermittency is the result of both data outages and variable sonde fall speeds; we (surprisingly) found that the outages also had a cascade structure. The wide‐range scaling of the sampling rate implies a variable sonde resolution, so that interpolation onto regular grids should generally be avoided (e.g., it would give rise to serious artifacts in estimating the corresponding spectra). In earlier studies, before the cascade nature of the outages was understood, interpolation was avoided by studying the fluctuations using all the pairs of measurement points; this was adequate for fluctuation scaling exponents in the range 0 ≤ H ≤ 1. However, determining the cascade structure involves systematically degrading the resolution of fluxes (not fluctuations) so that the variable resolution and their attendant biases could not be avoided. We therefore developed a new method of estimating the fluxes and theoretically determined the corrections necessary to estimate the unbiased exponents. The resulting sonde cascade picture was given further support by (much more straightforward) analysis of uniformly sampled vertical cross sections of the atmosphere obtained from airborne lidar. Using the turbulent fluxes obtained from these various sources, we determined the corresponding cascade regimes and the corresponding exponents as well as the small deviations from the theoretical behavior. In addition to the fluxes, we also studied the fluctuations. To do this we generalized the data point pair method (restricted to nonconservation parameters 0 ≤ H ≤ 1) to data triplets (extending the method to 0 ≤ H ≤ 2). The resulting fluctuations were analyzed using (generalized) structure functions. We found that while the scaling of the fluxes often broke down at scales greater than about 1 km, the scaling of the fluctuations extended over the entire range 10 m to 10 km.
Experimental study on rainfall interception over an outdoor urban‐scale model
Authors: Nakayoshi Makoto , Moriwaki Ryo , Kawai Toru , Kanda Manabu
Published: April 2009

Rainfall interception (RI) over an outdoor urban‐scale model was investigated from the perspectives of water and energy balance. On average, RI was 6% of the gross rainfall and smaller than typical values in forests. No correlation was found between RI and gross rainfall or rainfall duration unlike the correlations found in forests. Most RI occurred in the first several hours of rainfall, and then RI rapidly decreased with time during a rainfall event. RI was dependent on the saturation deficit at the beginning of the rainfall event. The latent heat for RI was approximately balanced by heat conduction from the concrete surfaces. Differences in the canopy structure are considered as possible reasons for the different behaviors of RI between the present site and forests. Accordingly, three aspects of the canopy structure, i.e., effective wet surface area, efficiency for scalar transfer, and canopy heat capacity, are discussed.
Short‐term variations of Mercury's Na exosphere observed with very high spectral resolution
Authors: Leblanc F. , Doressoundiram A. , Schneider N. , Massetti S. , Wedlund M. , López Ariste A. , Barbieri C. , Mangano V. , Cremonese G.
Published: April 2009

Short time variations of Mercury's exosphere cannot be tracked easily from ground based observatories because of the difficulty of distinguishing them from Earth atmospheric effects. On July 13th 2008, using THEMIS solar telescope, we were able to simultaneously measure brightness, Doppler shift and width of the exospheric sodium D2 emission line during half a day with a resolving power of ∼370,000. Mercury's exosphere displayed an emission brightness peak in the Northern hemisphere which vanished in few hours and a more persistent Southern Hemispheric peak. The bulk Doppler shift of the exosphere suggests a period of strong escape from Mercury. The global changes of the Doppler shift and of the Doppler width suggest that a cloud of sodium atoms ejected before or at the beginning of our sequence of observations passed through THEMIS field of view moving anti‐sunward. A preferentially southern ejection of sodium atoms leading to the observed persistent southern emission peak is consistent with the orientation of the Interplanetary Magnetic Field during that period.
The intracellular interactions of the L1 family of cell adhesion molecules
Authors: Herron Lissa R. , Hill Maria , Davey Fleur , Gunn-Moore Frank J.
Published: April 2009

The L1 family of CAMs (cell adhesion molecules) has long aroused the interest of researchers, but primarily the extracellular interactions of these proteins have been elucidated. More recently, attention has turned to the intracellular signalling potentiated by transmembrane proteins and the cytoplasmic proteins with which they can interact. The present review brings up to date the current body of published knowledge for the intracellular interactions of L1-CAM family proteins and the potential importance of these interactions for the mechanisms of L1-CAM action.
Orientation effects in 2-2 piezocomposites based on (1−x)Pb(A1/3Nb2/3)O3−xPbTiO3 single crystals (A=Mg or Zn)
Authors: Topolov V. Yu. , Krivoruchko A. V.
Published: April 2009

Volume fraction and orientation dependences of piezoelectric coefficients and hydrostatic piezoelectric response of 2-2 parallel-connected composites with two piezoactive components are analyzed. These composites comprise relaxor-ferroelectric (1−x)Pb(A1/3Nb2/3)O3−xPbTiO3 single crystals (A=Mg or Zn) and polyvinylidene fluoride, and different variants of poling directions of these layers are considered. It is shown how the orientation of the main crystallographic axes and the anisotropy of the electromechanical properties of the single crystal influence maxima of effective piezoelectric coefficients and other parameters of the composites. Advantages of the piezocomposites based on the [011] poled single crystals are discussed.
Complex permittivity and permeability of iron-based composite absorbers measured by cavity perturbation method in X-band frequency range
Authors: Yang R. B. , Tsay C. Y. , Hung D. S. , Liang W. F. , Yao Y. D. , Lin C. K.
Published: April 2009

A cavity perturbation resonance technique is used to determine the complex permittivity and permeability of iron-based composite absorbers prepared by mixing various weight percentages of carbonyl iron powder with epoxy as the matrix. The complex permittivity (ε′-jε″) and permeability (μ′-jμ″) are measured around X-band (7–12.5 GHz for permittivity and 7.5–14 GHz for permeability) by the cavity perturbation resonance technique and the results are compared with those obtained by the transmission/reflection method. Experimental results show that the average differences of real parts of permittivity (ε′) and real and imaginary parts of permeability (μ′ and μ″) measured by these two techniques are less than 10%. The differences in ε″, however, is apparently higher than the others. As a general trend, the difference increases with increasing weight percentage of carbonyl iron.
Startup process in the Richtmyer–Meshkov instability
Authors: Lombardini M. , Pullin D. I.
Published: April 2009

An analytical model for the initial growth period of the planar Richtmyer–Meshkov instability is presented for the case of a reflected shock, which corresponds in general to light-to-heavy interactions. The model captures the main features of the interfacial perturbation growth before the regime with linear growth in time is attained. The analysis provides a characteristic time scale τ for the startup phase of the instability, expressed explicitly as a function of the perturbation wavenumber k, the algebraic transmitted and reflected shock speeds US1<0 and US2>0 (defined in the frame of the accelerated interface), and the postshock Atwood number A+: τ=[(1−A+)∕US2+(1+A+)∕(−US1)]∕(2k). Results are compared with computations obtained from two-dimensional highly resolved numerical simulations over a wide range of incident shock strengths S and preshock Atwood ratios A. An interesting observation shows that, within this model, the amplitude of small perturbations across a light-to-heavy interface evolves quadratically in time (and not linearly) in the limit A→1−.
Formation and electron-ion recombination of N4+ following photoionization in near-atmospheric pressure N2
Authors: Adams S. F. , DeJoseph C. A. , Williamson J. M.
Published: April 2009

The time dependent behavior of molecular nitrogen ions has been investigated following pulsed photoionization of near atmospheric pressure N2 using multiphoton laser techniques and kinetic modeling. Multiple fluorescence bands, some unreported previously, with various temporal behaviors were observed after ultraviolet laser photoionization of N2(X Σ1g). The initial N2 ionization was generated via resonance-enhanced multiphoton ionization with focused radiation in the 275–290 nm range, where several resonant transitions are accessible. The observed optical fluorescence bands appeared to be unique to the near-atmospheric pressure N2 condition and were shown by the evidence in this work to be the result of collisional formation and recombination of N4+. Measured time dependent fluorescence spectra during and after pulsed laser photoionization of N2, together with a coupled rate equation model, allowed for the determination of the absolute densities of N2+ and N4+ as these species evolved.
Reference interaction site model investigation of homonuclear hard dumbbells under simple fluid theory closures: Comparison with Monte Carlo simulations
Authors: Munaò G. , Costa D. , Caccamo C.
Published: April 2009

We revisit the thermodynamic and structural properties of fluids of homonuclear hard dumbbells in the framework provided by the reference interaction site model (RISM) theory of molecular fluids. Besides the previously investigated Percus–Yevick (PY) approximation, we test the accuracy of other closures to the RISM equations, imported from the theory of simple fluids; specifically, we study the hypernetted chain (HNC), the modified HNC (MHNC) and, less extensively, the Verlet approximations. We implement our approach for models characterized by several different elongations, up to the case of tangent diatomics, and investigate the whole fluid density range. The theoretical predictions are assessed against Monte Carlo simulations, either available from literature or newly generated by us. The HNC and PY equations of state, calculated via different routes, share on the whole the same level of accuracy. The MHNC is applied by enforcing an internal thermodynamic consistency constraint, leading to good predictions for the equation of state as the elongation of the dumbbell increases. As for the radial distribution function, the MHNC appears superior to other theories, especially for tangent diatomics in the high density limit; the PY approximation is better than the HNC and Verlet closures in the high density or elongation regime. Our structural analysis is supplemented by an accurate inversion procedure to reconstruct from Monte Carlo data and RISM the “exact” direct correlation function. In agreement with such calculations and consistent with the forecast of rigorous diagrammatic analysis, all theories predict the occurrence in the direct correlation function of a first cusp inside the dumbbell core and (with the obvious exception of the PY) of a second cusp outside; the cusps’ heights are also qualitatively well reproduced by the theories, except at high densities.
Mechanical and electronic properties of vanadium oxide nanotubes
Authors: Sipos B. , Duchamp M. , Magrez A. , Forró L. , Barišić N. , Kis A. , Seo J. W. , Bieri F. , Krumeich F. , Nesper R. , Patzke G. R.
Published: April 2009

Vanadium oxide nanotubes with a diameter of 20–100 nm and an aspect ratio of 50–100 were synthesized by hydrothermal method. Young’s modulus of 20–80 GPa was obtained by bending measurements of individual nanotubes using an atomic force microscope. Electrical resistivity and thermopower measurements on a large assembly of nanotubes determined the characteristic energies required to put a charge into a polaronic site (ΔEg=0.20 eV) and to extract and propagate the polaron between neighboring sites (ΔEp=0.09 eV).
Topological methods for exploring low-density states in biomolecular folding pathways
Authors: Yao Yuan , Sun Jian , Huang Xuhui , Bowman Gregory R. , Singh Gurjeet , Lesnick Michael , Guibas Leonidas J. , Pande Vijay S. , Carlsson Gunnar
Published: April 2009

Characterization of transient intermediate or transition states is crucial for the description of biomolecular folding pathways, which is, however, difficult in both experiments and computer simulations. Such transient states are typically of low population in simulation samples. Even for simple systems such as RNA hairpins, recently there are mounting debates over the existence of multiple intermediate states. In this paper, we develop a computational approach to explore the relatively low populated transition or intermediate states in biomolecular folding pathways, based on a topological data analysis tool, MAPPER, with simulation data from large-scale distributed computing. The method is inspired by the classical Morse theory in mathematics which characterizes the topology of high-dimensional shapes via some functional level sets. In this paper we exploit a conditional density filter which enables us to focus on the structures on pathways, followed by clustering analysis on its level sets, which helps separate low populated intermediates from high populated folded/unfolded structures. A successful application of this method is given on a motivating example, a RNA hairpin with GCAA tetraloop, where we are able to provide structural evidence from computer simulations on the multiple intermediate states and exhibit different pictures about unfolding and refolding pathways. The method is effective in dealing with high degree of heterogeneity in distribution, capturing structural features in multiple pathways, and being less sensitive to the distance metric than nonlinear dimensionality reduction or geometric embedding methods. The methodology described in this paper admits various implementations or extensions to incorporate more information and adapt to different settings, which thus provides a systematic tool to explore the low-density intermediate states in complex biomolecular folding systems.
Streaming current and streaming potential for particle covered surfaces: Virial expansion and simulations
Authors: Sadlej Krzysztof , Wajnryb Eligiusz , Bławzdziewicz Jerzy , Ekiel-Jeżewska Maria L. , Adamczyk Zbigniew
Published: April 2009

Streaming potential changes induced by deposition of particles at solid/liquid interfaces are considered theoretically. The solution is obtained in terms of a virial expansion of the streaming potential up to the third order of the surface coverage of particles, assumed to be distributed according to the hard sphere equilibrium distribution function. Theoretical methods, including the idea of cluster expansion, are adopted from statistical physics. In the cluster expansion, two-body and three-body hydrodynamic interactions are evaluated with a high precision using the multipole method. The multipole expansion algorithm is also used to perform numerical simulations of the streaming potential, valid for the entire surface coverage range met in practice. Results of our calculations are in good agreement with the experimental data for spherical latex particles adsorbed on a mica surface.
Perturbative total energy evaluation in self-consistent field Iterations: Tests on molecular systems
Authors: Zhang Yu Adam , Wang Yan Alexander
Published: April 2009

The corrected Hohenberg–Kohn–Sham and corrected Harris total energy functionals recently proposed [B. Zhou and Y. A. Wang, J. Chem. Phys. 128, 084101 (2008)] have been generalized to the Hartree–Fock method. We have tested the functionals on a few molecular systems and found them to be very useful in accelerating the convergence of the total energy during a self-consistent field process.
Investigation of morphology of an enneadic particle system confined onto a spherical surface through Monte Carlo simulation
Authors: Shew Chwen-Yang
Published: April 2009

The morphology of an enneadic particle system confined to a spherical surface is investigated through Monte Carlo simulation. The model assumes nine hard spheres adsorbed onto a spherical surface of the same diameter. In addition to hard core repulsion, these nine particles interact through Coulomb repulsion or Lennard-Jones potential. At a low enough temperature, the ordered structure of the enneadic particle system exhibits a symmetric arrangement corresponding to the D3h point group and is similar to hexagonal close packing. The nine particles can be divided into three groups, and each group occupies an equilateral triangle along with the same principle axis. The top and bottom triangles form the mirror image and the middle triangle of a different size rotates 60° from the other two triangles. This symmetry is independent of interaction potentials but the two interaction potentials deform the ordered structure in a slightly different way. From the analysis of monomers of inertia, we notice that Coulombic particles compress the ordered morphology to an oblate shape, whereas Lennard-Jones particles display an elongated prolate morphology. By use of the analysis of a simple model, we find that these fine structures tend to lower the total energy of the system. Moreover, the calculation based on the temperature dependent heat capacity of many noninteracting enneadic clusters suggests that large interaction strengths are essential to sustain the highly symmetric ordered structure.
Using stochastic models calibrated from nanosecond nonequilibrium simulations to approximate mesoscale information
Authors: Calderon Christopher P. , Janosi Lorant , Kosztin Ioan
Published: April 2009

We demonstrate how the surrogate process approximation (SPA) method can be used to compute both the potential of mean force along a reaction coordinate and the associated diffusion coefficient using a relatively small number (10–20) of bidirectional nonequilibrium trajectories coming from a complex system. Our method provides confidence bands which take the variability of the initial configuration of the high-dimensional system, continuous nature of the work paths, and thermal fluctuations into account. Maximum-likelihood-type methods are used to estimate a stochastic differential equation (SDE) approximating the dynamics. For each observed time series, we estimate a new SDE resulting in a collection of SPA models. The physical significance of the collection of SPA models is discussed and methods for exploiting information in the population of estimated SPA models are demonstrated and suggested. Molecular dynamics simulations of potassium ion dynamics inside a gramicidin A channel are used to demonstrate the methodology, although SPA-type modeling has also proven useful in analyzing single-molecule experimental time series [J. Phys. Chem. B 113, 118 (2009)].
Near-field imaging of coupled photonic-crystal microcavities
Authors: Vignolini Silvia , Intonti Francesca , Zani Margherita , Riboli Francesco , Wiersma Diederik S. , Li Lianhe H. , Balet Laurent , Francardi Marco , Gerardino Annamaria , Fiore Andrea , Gurioli Massimo
Published: April 2009

We report by means of near-field microscopy on the coupling between two adjacent photonic crystal microcavities. Clear-cut experimental evidence of the spatial delocalization of coupled-cavity optical modes is obtained by imaging the electromagnetic local density of states. We also demonstrate that it is possible to design photonic structures with selective coupling between different modes having orthogonal spatial extensions
Griffiths phase and charge ordering in electron-doped La0.9Ce0.1MnO3 films
Authors: Eom T. W. , Hyun Y. H. , Park J. S. , Lee Y. P. , Prokhorov V. G. , Flis V. S. , Svetchnikov V. L.
Published: April 2009

Microstructural, magnetic, and transport properties of as-deposited La0.9Ce0.1MnO3 films prepared by pulse laser deposition have been investigated. The high-resolution electron-microscopy study reveals that films have a high c-oriented texture with a negligible quantity of CeO2 inclusions. The observed Griffiths-type magnetic behavior above the Curie point and the partial transition of the film into the antiferromagnetic state with decreasing temperature are attributed to the microstructural peculiarities.
Optimal replica exchange method combined with Tsallis weight sampling
Authors: Kim Jaegil , Straub John E.
Published: April 2009

A unified framework integrating the generalized ensemble sampling associated with the Tsallis weight [C. Tsallis, J. Stat. Phys. 52, 479 (1988)] and the replica exchange method (REM) has been proposed to accelerate the convergence of the conventional temperature REM (t-REM). Using the effective temperature formulation of the Tsallis weight sampling, it is shown that the average acceptance probability for configurational swaps between neighboring replicas in the combination of Tsallis weight sampling and REM (Tsallis-REM) is directly proportional to an overlap integral of the energy distributions of neighboring replicas as in the t-REM. Based on this observation, we suggest a robust method to select optimal Tsallis parameters in the conventional parametrization scheme and present new parametrization schemes for the Tsallis-REM, which significantly improves the acceptance of configurational swaps by systematically modulating energy overlaps between neighboring replicas. The distinguished feature of our method is that all relevant parameters in the Tsallis-REM are automatically determined from the equilibrium phase simulation using the t-REM. The overall performance of our method is explicitly demonstrated for various simulation conditions for the Lennard-Jones 31 atom clusters, exhibiting a double-funneled energy landscape.
Quasimonoenergetic electron acceleration in the self-modulated laser wakefield regime
Authors: Hidding B. , Geissler M. , Pretzler G. , Amthor K.-U. , Schwoerer H. , Karsch S. , Veisz L. , Schmid K. , Sauerbrey R.
Published: April 2009

Details on the generation of (multiple) quasimonoenergetic electron bunches in the self-modulated laser wakefield acceleration (SMLWFA) regime are presented. This type of laser-plasma interaction can result in pronounced longitudinal laser pulse fragmentation, dependent on plasma density and laser intensity. It is shown by experiments and particle-in-cell simulations that these laser pulse fragments can be powerful enough to trigger nonlinear plasma wave breaking, injection, and acceleration of electrons to quasimonoenergetic energies. With high plasma densities, self-modulation is promoted, and the advantages of SMLWFA such as especially high accelerating fields and short electron bunches (<5 fs) can be harvested. In addition, more than one quasimonoenergetic electron bunch can be created, with a temporal spacing between each bunch of only few tens of femtoseconds, again governed by plasma density.
Direct numerical simulation of the near-field dynamics of annular gas-liquid two-phase jets
Authors: Siamas George A. , Jiang Xi , Wrobel Luiz C.
Published: April 2009

Direct numerical simulation has been used to examine the near-field dynamics of annular gas-liquid two-phase jets. Based on an Eulerian approach with mixed fluid treatment, combined with an adapted volume of fluid method and a continuum surface force model, a mathematical formulation for the flow system is presented. The swirl introduced at the jet nozzle exit is based on analytical inflow conditions. Highly accurate numerical methods have been utilized for the solution of the compressible, unsteady, Navier–Stokes equations. Two computational cases of gas-liquid two-phase jets including swirling and nonswirling cases have been performed to investigate the effects of swirl on the flow field. In both cases the flow is more vortical at the downstream locations. The swirling motion enhances both the flow instability resulting in a larger liquid spatial dispersion and the mixing resulting in a more homogeneous flow field with more evenly distributed vorticity at the downstream locations. In the annular nonswirling case, a geometrical recirculation zone adjacent to the jet nozzle exit was observed. It was identified that the swirling motion is responsible for the development of a central recirculation zone, and the geometrical recirculation zone can be overwhelmed by the central recirculation zone leading to the presence of the central recirculation region only in the swirling gas-liquid case. Results from a swirling gas jet simulation were also included to examine the effect of the liquid sheet on the flow physics. The swirling gas jet developed a central recirculation region, but it did not develop a precessing vortex core as the swirling gas-liquid two-phase jet. The results indicate that a precessing vortex core can exist at relatively low swirl numbers in the gas-liquid two-phase flow. It was established that the liquid greatly affects the precession and the swirl number alone is an insufficient criterion for the development of a precessing vortex core.
Nonradiative decay of the lowest excited singlet state of 2-aminopyridine is considerably faster than the radiative decay
Authors: Zhang Feng , Ai Yue-Jie , Luo Yi , Fang Wei-Hai
Published: April 2009

Ab initio calculations reveal that radiative lifetime of the lowest excited singlet state of 2-aminopyridine molecule should be around 20 ns, consistent with the molecules of the same type but is about one order of magnitude larger than the claimed experimental fluorescent lifetime in recent years. An S1/S0 conical intersection close to the S1 state has been located, which could be the possible nonradiative channel that is responsible for the fast decay observed in the experiment.
Locating an atmospheric contamination source using slow manifolds
Authors: Tang Wenbo , Haller George , Baik Jong-Jin , Ryu Young-Hee
Published: April 2009

Finite-size particle motion in fluids obeys the Maxey–Riley equations, which become singular in the limit of infinitesimally small particle size. Because of this singularity, finding the source of a dispersed set of small particles is a numerically ill-posed problem that leads to exponential blowup. Here we use recent results on the existence of a slow manifold in the Maxey–Riley equations to overcome this difficulty in source inversion. Specifically, we locate the source of particles by projecting their dispersed positions on a time-varying slow manifold, and by advecting them on the manifold in backward time. We use this technique to locate the source of a hypothetical anthrax release in an unsteady three-dimensional atmospheric wind field in an urban street canyon.
Bulk photonic metamaterial with hyperbolic dispersion
Authors: Noginov M. A. , Barnakov Yu. A. , Zhu G. , Tumkur T. , Li H. , Narimanov E. E.
Published: April 2009

We have demonstrated the thickest bulk photonic metamaterial reported in the literature based on an Ag-filled alumina membrane. The material is highly anisotropic with hyperbolic dispersion at λ>0.84 μm. The refraction of light in the direction expected of isotropic media with n<1 has been experimentally demonstrated at λ=632.8 nm. This makes the material potentially suitable for a variety of applications ranging from subdiffraction imaging to optical cloaking.
X-ray- and electron-induced infrared emission spectroscopy
Authors: Rosenberg R. A. , Abu Haija M. , Watkins S. P.
Published: April 2009

We demonstrate the use of Fourier transform infrared (IR) spectroscopy for midinfrared emission measurements following x-ray or electron excitation. Spectra from an InAs low band-gap semiconductor film, which emits in the IR from 3000 to 3400 cm−1, are presented. There is good agreement between the present results and previously published laser-excited spectra. Using focused beams, it should be possible to perform sub-diffraction-limited IR imaging. In addition, simultaneous structural and electronic analysis could be performed using the x-ray or electron excitation probes.
Structural, dielectric, and optical properties of yttrium calcium borate glasses
Authors: Santos Cristiane N. , De Sousa Meneses Domingos , Echegut Patrick , Neuville Daniel R. , Hernandes Antonio C. , Ibanez Alain
Published: April 2009

Structural and optical properties of stable glasses in the Y2O3–CaO–B2O3 system, containing the same Y/Ca ratio as the YCa4O(BO3)3 (YCOB) crystal, were determined from Raman and reflectance infrared spectroscopy. Changes in optical functions with composition are associated with an increase in the number of non-bridging oxygen and to calcium/yttrium oxides content. Refractive indexes values (from 1.597 to 1.627 at λ=2 μm) are in good agreement with those of the YCOB crystal, an indication that these glasses are potential candidates for optical applications due to their ease of shaping as large bulk samples or fibers.
Can a double stranded DNA be unzipped by pulling a single strand?: Phases of adsorbed DNA
Authors: Kapri Rajeev
Published: April 2009

We study the unzipping of a double stranded DNA (dsDNA) by applying an external force on a single strand while leaving the other strand free. We find that the dsDNA can be unzipped to two single strands if the external force exceeds a critical value. We obtain the phase diagram, which is found to be different from the phase diagram of unzipping by pulling both the strands in opposite directions. In the presence of an attractive surface near DNA, the phase diagram gets modified drastically and shows richer surprises including a critical end point and a triple point.
A generalization of the Kullback–Leibler divergence and its properties
Authors: Yamano Takuya
Published: April 2009

A generalized Kullback–Leibler relative entropy is introduced starting with the symmetric Jackson derivative of the generalized overlap between two probability distributions. The generalization retains much of the structure possessed by the original formulation. We present the fundamental properties including positivity, metricity, concavity, bounds, and stability. In addition, a connection to shift information and behavior under Liouville dynamics are discussed.
Anisotropy graded FePt–TiO2 nanocomposite thin films with small grain size
Authors: Zhou Tie-Jun , Lim Boon Chow , Liu Bo
Published: April 2009

We reported the fabrication of (001)-textured FePt–TiO2 nanocomposite thin films composed of isolated grains of size of 5.3±1.1 nm. Anisotropy graded FePt–TiO2 thin films with hard layer thickness of 10 nm and soft layer thickness ranging from 0 to 8 nm were also prepared by cosputtering FePt and TiO2 at different substrate temperature. An exchange-coupled composite effect was demonstrated at a soft layer thickness of more than 3 nm.
Lattice thermal conductivity of nanostructured thermoelectric materials based on PbTe
Authors: Koh Yee Kan , Vineis C. J. , Calawa S. D. , Walsh M. P. , Cahill David G.
Published: April 2009

We report the through-thickness lattice thermal conductivity Λl of (PbTe)1−x/(PbSe)x nanodot superlattices (NDSLs) over a wide range of periods 5 nm≤h≤50 nm, compositions 0.15≤x≤0.25, growth temperatures 550 K≤Tg≤620 K, and growth rates 1 μm h−1≤R≤4 μm h−1. All of our measurements approach Λl of bulk homogenous PbTe1−xSex alloys with the same average composition. For 5 nm≤h≤50 nm, Λl is independent of h; a result we attribute to short mean-free paths of phonons in PbTe and small acoustic impedance mismatch between PbTe/PbSe. We alloyed the PbTe layers of four NDSLs with SnTe up to a mole fraction y=18%; Λl is reduced by <25%.
Photoreflectance study of the energy gap and spin-orbit splitting in InNAs alloys
Authors: Kudrawiec R. , Misiewicz J. , Zhuang Q. , Godenir A. M. R. , Krier A.
Published: April 2009

Photoreflectance spectroscopy has been applied to study the energy gap and the spin-orbit splitting in InNAs alloys with the nitrogen concentration changing from 0% to 0.88%. It has been observed that the energy gap of InNAs decreases with the increase in nitrogen concentration (about 60 meV per 1% of nitrogen) but the spin-orbit splitting almost does not change. It shows that nitrogen atoms in InNAs alloys influence mainly the conduction band, i.e., shift this band toward the valence band. The bowing parameter for the energy gap and spin-orbit splitting has been determined to be 7.3±0.6 and −0.7±0.4 eV, respectively.
Crystal structure and optical properties of silver nanorings
Authors: Zhou Li , Fu Xiao-Feng , Yu Liao , Zhang Xian , Yu Xue-Feng , Hao Zhong-Hua
Published: April 2009

We report the polyol synthesis and crystal structure characterization of silver nanorings, which have perfect circular shape, smooth surface, and elliptical wire cross-section. The characterization results show that the silver nanorings have well-defined crystal of singly twinned along the whole ring. The spatial distribution of the scattering of a silver nanoring with slanted incidence reveals the unique focus effect of the nanoring, and the focus scattering varies with the incident wavelength. The silver nanorings with perfect geometry and well-defined crystal have potential applications in nanoscaled photonics, plasmonic devices, and optical manipulation.
Ultrashort-period lateral composition modulation in TlInGaAsN/TlInP structures
Authors: Ishimaru Manabu , Tanaka Yuusuke , Hasegawa Shigehiko , Asahi Hajime , Sato Kazuhisa , Konno Toyohiko J.
Published: April 2009

We prepared TlInGaAsN/TlInP quantum well structures using gas source molecular-beam epitaxy and characterized them by means of transmission electron microscopy and scanning transmission electron microscopy. It was found that naturally formed vertical quantum wells, so-called lateral composition modulation (LCM), with a periodicity of ∼1 nm are formed in TlInGaAsN layers. We discuss their formation process using a simple kinetic Ising model for layer-by-layer growth, and point out that the formation of ultrashort-period LCM is a universal phenomenon in most of epitaxially grown III-V semiconductor alloys.
Large plasticity and tensile necking of Zr-based bulk-metallic-glass-matrix composites synthesized by the Bridgman solidification
Authors: Qiao J. W. , Wang S. , Zhang Y. , Liaw P. K. , Chen G. L.
Published: April 2009

The microstructures of the in situ bulk-metallic-glass-matrix composites are usually controlled by changing the alloy compositions. In this paper, Zr-based bulk-metallic-glass-matrix composites containing dendrites with a fixed composition of Zr37.5Ti32.2Nb7.2Cu6.1Be17.0 are synthesized by the Bridgman solidification. The sizes and volume fractions of dendrites in the composites are controlled by adjusting the withdrawal velocities. A linear relationship between the spanning lengths of individual dendrites and the withdrawal velocities is established. Large plasticity and tensile necking can be obtained by only controlling the cooling condition.
Manipulation and trapping of semiconducting ZnO nanoparticles into nanogap electrodes by dielectrophoresis technique
Authors: Kumar Sanjeev , Seo Young-Kyo , Kim Gil-Ho
Published: April 2009

The assembly of ZnO nanoparticles into nanogap electrodes using ac dielectrophoresis (DEP) process is reported. DEP parameters such as frequency, voltage, and time were optimized to assemble minimum number of nanoparticles into nanogap electrodes. Frequency variation study revealed that positive DEP is active at frequencies less than 500 kHz; whereas negative DEP starts dominating at 1 MHz. The fabricated device exhibited a nonlinear I-V characteristic and under ultraviolet (UV) illumination a remarkable change in conductivity of one order of magnitude was observed. The results show the potential for realizing future optoelectronic devices such as miniaturized UV sensor.