bluuebunny/crossref_metadata_2025 huggingface dataset:
COMPUTABLE STRONGLY ERGODIC RATES OF CONVERGENCE FOR CONTINUOUS-TIME MARKOV CHAINS
Authors: LIU YUANYUAN , ZHANG HANJUN , ZHAO YIQIANG
Published: October 2008

In this paper, we investigate computable lower bounds for the best strongly ergodic rate of convergence of the transient probability distribution to the stationary distribution for stochastically monotone continuous-time Markov chains and reversible continuous-time Markov chains, using a drift function and the expectation of the first hitting time on some state. We apply these results to birth–death processes, branching processes and population processes.
A NOTE ON THE HU–HWANG–WANG CONJECTURE FOR GROUP TESTING
Authors: LEU MING-GUANG
Published: October 2008

Hu et al. [“A boundary problem for group testing”, SIAM J. Algebraic Discrete Meth.2 (1981), 81–87] conjectured that the minimax test number to find d defectives in 3d items is 3d−1, a surprisingly difficult combinatorial problem about which very little is known. In this article we state three more conjectures and prove that they are all equivalent to the conjecture of Hu et al. Notably, as a byproduct, we also obtain an interesting upper bound for M(d,n).
MISSILE CONTROL DESIGN BASED ON THE LINEAR MULTIPLE SLIDING MODE RECURSIVE METHOD
Authors: SHI Y. J. , MA G. F.
Published: October 2008

To ensure that the elevator of a cruise missile is operating within the design specification in high-attitude flight, we present a design method for the construction of a sliding mode recursive variable structure controller. In this design method, a target sliding mode surface is first designed without considering the engineering specification of the elevator. Secondly, by using this specification, the critical state is solved. Then, the transitional sliding mode surfaces are designed recursively by using the critical state of the previous sliding mode surface so that the state will move smoothly from one transitional sliding mode surface to the next until the target sliding mode surface. This design method is based on linear sliding mode variable structure theory. Thus, the controller obtained is simple in structure and practical. Furthermore, the elevator will operate within the engineering specification. The simulation results show the effectiveness of the proposed method.
Broad frequency tidal dynamics simulated by a high‐resolution global ocean tide model forced by ephemerides
Authors: Weis P. , Thomas M. , Sündermann J.
Published: October 2008

Traditionally, global ocean tide models are forced by individual partial tides resulting from a decomposition of the complete lunisolar tidal potential in Fourier components. Implicitly, this approach neglects nonlinear interactions between partial tides. This can be partly compensated by a superposition of a selection of partial tides. In order to ensure the full dynamics, the Tidal Model forced by Ephemerides (TiME) incorporates the tidal potential of second degree calculated online from analytical ephemerides and utilizes the classical shallow‐water equations with a horizontal resolution of 5 min globally. Interactions between partial tides generate shallow‐water tides which are shown to form in extended shelf areas where they develop the highest amplitudes. However, as they propagate into the open ocean, they should be regarded as a global phenomenon. Simulations with TiME confirm that M4 is particularly pronounced in the Atlantic and suggest further areas of strong energy fluxes in the southern Pacific. MN4 is strongest in the Atlantic and MS4, 2SM2, and MK3 mainly spread out into the Indian Ocean.
For how long will the current grand maximum of solar activity persist?
Authors: Abreu J. A. , Beer J. , Steinhilber F. , Tobias S. M. , Weiss N. O.
Published: October 2008

Understanding the Sun's magnetic activity is important because of its impact on the Earth's environment. The sunspot record since 1610 shows irregular 11‐year cycles of activity; they are modulated on longer timescales and were interrupted by the Maunder minimum in the 17th century. Future behavior cannot easily be predicted – even in the short‐term. Recent activity has been abnormally high for at least 8 cycles: is this grand maximum likely to terminate soon or even to be followed by another (Maunder‐like) grand minimum? To answer these questions we use, as a measure of the Sun's open magnetic field, a composite record of the solar modulation function Φ, reconstructed principally from the proxy record of cosmogenic 10Be abundances in the GRIP icecore from Greenland. This Φ record extends back for almost 10,000 years, showing many grand maxima and grand minima (defined as intervals when Φ is within the top or bottom 20% of a Gaussian distribution). We carry out a statistical analysis of this record and calculate the life expectancy of the current grand maximum. We find that it is only expected to last for a further 15–36 years, with the more reliable methods yielding shorter expectancies, and we therefore predict a decline in solar activity within the next two or three cycles. We are not able, however, to predict the level of the ensuing minimum.
On the need for bias correction of regional climate change projections of temperature and precipitation
Authors: Christensen Jens H. , Boberg Fredrik , Christensen Ole B. , Lucas‐Picher Philippe
Published: October 2008

Within the framework of the European project ENSEMBLES (ensembles‐based predictions of climate changes and their impacts) we explore the systematic bias in simulated monthly mean temperature and precipitation for an ensemble of thirteen regional climate models (RCMs). The models have been forced with the European Centre for Medium Range Weather Forecasting Reanalysis (ERA40) and are compared to a new high resolution gridded observational data set. We find that each model has a distinct systematic bias relating both temperature and precipitation bias to the observed mean. By excluding the twenty‐five percent warmest and wettest months, respectively, we find that a derived second‐order fit from the remaining months can be used to estimate the values of the excluded months. We demonstrate that the common assumption of bias cancellation (invariance) in climate change projections can have significant limitations when temperatures in the warmest months exceed 4–6 °C above present day conditions.
Interaction between kinetic ballooning perturbation and thin current sheet: Quasi‐electrostatic field, local onset, and global characteristics
Authors: Liu W. W. , Liang J. , Donovan E. F.
Published: October 2008

We present observation of plasma waves in the current sheet across multiple THEMIS satellites in a substorm event on March 5, 2008. It is shown that the arrival of a kinetic ballooning perturbation interacts with the local current sheet to generate a quasi‐electrostatic wave a few minutes before local onset, consistent with the prediction that the current sheet thins after the passage of a rarefaction wave. The propagation speed of current disruption front is found to be ∼100 km/s, about a tenth of the fast mode speed. The observed pattern of interaction was constant across radial distances between 10 and 20 RE in the event reported. It is further proposed that the presence of the quasi‐electrostatic field may change the local stability condition and induce local current disruption.
Energetic electron precipitation during substorm injection events: High‐latitude fluxes and an unexpected midlatitude signature
Authors: Clilverd Mark A. , Rodger Craig J. , Brundell James , Bähr John , Cobbett Neil , Moffat‐Griffin Tracy , Kavanagh Andrew J. , Seppälä Annika , Thomson Neil. R. , Friedel Reiner H. W. , Menk Frederick W.
Published: October 2008

Geosynchronous Los Alamos National Laboratory (LANL‐97A) satellite particle data, riometer data, and radio wave data recorded at high geomagnetic latitudes in the region south of Australia and New Zealand are used to perform the first complete modeling study of the effect of substorm electron precipitation fluxes on low‐frequency radio wave propagation conditions associated with dispersionless substorm injection events. We find that the precipitated electron energy spectrum is consistent with an e‐folding energy of 50 keV for energies <400 keV but also contains higher fluxes of electrons from 400 to 2000 keV. To reproduce the peak subionospheric radio wave absorption signatures seen at Casey (Australian Antarctic Division), and the peak riometer absorption observed at Macquarie Island, requires the precipitation of 50–90% of the peak fluxes observed by LANL‐97A. Additionally, there is a concurrent and previously unreported substorm signature at L < 2.8, observed as a substorm‐associated phase advance on radio waves propagating between Australia and New Zealand. Two mechanisms are discussed to explain the phase advances. We find that the most likely mechanism is the triggering of wave‐induced electron precipitation caused by waves enhanced in the plasmasphere during the substorm and that either plasmaspheric hiss waves or electromagnetic ion cyclotron waves are a potential source capable of precipitating the type of high‐energy electron spectrum required. However, the presence of these waves at such low L shells has not been confirmed in this study.
Modified “Rankine‐Hugoniot” shock fitting technique: Simultaneous solution for shock normal and speed
Authors: Koval A. , Szabo A.
Published: October 2008

We introduce a modification of the nonlinear least squares fitting technique of Viñas and Scudder and Szabo (VSSz) with simultaneous determination of the shock normal direction (θ and ϕ) and propagation speed (VS). Similar to the 2D case of the VSSz technique, the uniqueness of the solution can still be graphically demonstrated in the 3D space of the unknown variables. The modified technique is validated through the analysis of synthetic shocks and is also applied to an interplanetary shock observed by Wind. Our technique provides self‐consistent 3D confidence regions for the parameters while the VSSz technique assumes the independence of the VS confidence interval from θ and ϕ. The 3D confidence region is highly dependent on VS resulting in θ and ϕ joint confidence regions that are generally significantly larger and oriented differently than those obtained by the VSSz technique. This also leads to significantly larger confidence intervals for the individual parameters determined by our modified technique. While the best fit values provided by the two techniques are usually close to each other, we also demonstrate the advantage of the VS best fit value determination with our technique in the case when a small density jump is combined with significant density fluctuations. The agreement between the best fit solutions of the techniques can also be used as a test for the correctness of the chosen upstream and downstream intervals.
Oblique proton fire hose instability in the expanding solar wind: Hybrid simulations
Authors: Hellinger Petr , Trávníček Pavel M.
Published: October 2008

Oblique fire hose instability is investigated using hybrid simulations for proton betas of the order of one and for proton parallel temperatures sufficiently greater than the perpendicular ones. The simulations confirm previous simulation results showing that this instability has self‐destructing properties and efficiently reduces the proton temperature anisotropy. A parametric study using one‐dimensional standard hybrid simulations shows that stronger changes in the temperature anisotropy and stronger wave emissions appear for larger initial temperature anisotropies. An ideal, slow plasma expansion, modeled by a two‐dimensional hybrid expanding box simulation, leads to a generation of proton temperature anisotropy. The anisotropy leads first to destabilization of the dominant parallel fire hose, which interacts mainly with minor supra‐Alfvénic protons, whereas the evolution of core protons is determined by expansion. Consequently, the effective anisotropy is only slightly reduced and the system eventually becomes unstable with respect to the oblique fire hose instability. The oblique fire hose strongly scatters the protons and removes the anisotropy disrupting the parallel fire hose. An important portion of the fluctuating wave energy is dissipated to protons, and only long wavelength waves remain in the system. The system with low wave activity then develops again larger temperature anisotropies, and the evolution repeats itself. It is concluded that both parallel and oblique proton fire hose instabilities constrain the proton temperature anisotropy in the expanding solar wind, with the latter one constituting a final frontier for the anisotropy. These results give a possible explanation of some apparent discrepancies between observations and linear predictions. In addition, a simple bounded anisotropy model is developed to include some of the kinetic effects of the fire hose instabilities in fluid models.
Predicted impacts of climate and land use change on surface ozone in the Houston, Texas, area
Authors: Jiang Xiaoyan , Wiedinmyer Christine , Chen Fei , Yang Zong‐Liang , Lo Jeff Chun‐Fung
Published: October 2008

This paper studies the effects of climate change under future A1B scenario and land use change on surface ozone (O3) in the greater Houston, Texas, area. We applied the Weather Research and Forecasting Model with Chemistry (WRF/Chem) to the Houston area for August of current (2001–2003) and future (2051–2053) years. The model was forced by downscaled 6‐hourly Community Climate System Model (CCSM) version 3 outputs. High‐resolution current year land use data from National Land Cover Database (NLCDF) and future year land use distribution based on projected population density for the Houston area were used in the WRF/Chem model coupled with an Urban Canopy Model (UCM). Our simulations show that there is generally a 2°C increase in near‐surface temperature over much of the modeling domain due to future climate and land use changes. In the urban area, the effect of climate change alone accounts for an increase of 2.6 ppb in daily maximum 8‐h O3 concentrations, and a 62% increase of urban land use area exerts more influence than does climate change. The combined effect of the two factors on O3 concentrations can be up to 6.2 ppb. The impacts of climate and land use change on O3 concentrations differ across the various areas of the domain. The increase in extreme O3 days can be up to 4–5 days in August, in which land use contributes to 2–3 days' increase. Additional sensitivity experiments show that the effect of future anthropogenic emissions change is on the same order of those induced by climate and land use change on extreme O3 days.
A Bayesian approach to snow water equivalent reconstruction
Authors: Durand Michael , Molotch Noah P. , Margulis Steven A.
Published: October 2008

Snow water equivalent (SWE) reconstruction methods have previously been used to characterize seasonal SWE accumulation using mass and energy balance models and time series of remotely sensed snow‐covered area (SCA). Recognizing that the spatial signature of the seasonal SWE accumulation is an integration of a series of snowfall events, we have formulated a Bayesian SWE reconstruction that combines time series of remote sensing estimates of SCA with a land surface model to estimate storm‐specific snowfall distribution with a retrospective data assimilation scheme. The analysis is identical in form to the ensemble Kalman filter or ensemble Kalman smoother. A snow depletion curve is used to relate SCA and SWE. We perform a series of synthetic tests to assess how much information concerning snowfall accumulation patterns can be extracted from a time series of SCA measurements taken during the ablation season. The posterior estimate of SWE calculated via our method effectively recovers the true SWE: the mean and standard deviation of the SWE estimate error improve by 86% and by 78%, respectively, over the prior for pixels with vegetation fraction less than 90%. The sensitivity of the method to climatic and physiographic variables and input errors is investigated. The technique shows promise for future work in characterizing spatial patterns of snowfall over mountainous regions.
Model assessment of the observed relationship between El Niño and the northern East Asian summer monsoon using the Community Climate System Model Community Atmosphere Model‐Community Land Model version 3 (CAM‐CLM3)
Authors: Lee Eungul , Chase Thomas N. , Lawrence Peter J. , Rajagopalan Balaji
Published: October 2008

Plausibility and reproducibility of the relationship and physical mechanisms proposed between the northern East Asian summer monsoon (NEASM) and El Niño are verified and illuminated using the Community Climate System Model (CCSM) with the Community Atmosphere Model–Community Land Model version 3 (CAM‐CLM3). The climate responses over East Asia and western North Pacific to El Niño are simulated in the CCSM3 using dynamic atmosphere and land with prescribed climatological and El Niño sea surface temperature (SST) anomalies. A significantly intensified NEASM is simulated for the El Niño experiments, which validates the positive correlation between NEASM precipitation and El Niño found in recent observational analysis. Analysis of lower level wind vector and vorticity in the model experiments elucidates the physical mechanism behind the positive correlation between NEASM precipitation and El Niño, and shows that the western North Pacific anticyclone plays an important role in the connection between the NEASM and the tropical SST anomalies.
Extinction, refraction, and delay in the atmosphere
Authors: Rapp‐Arrarás Ígor , Domingo‐Santos Juan M.
Published: October 2008

This paper establishes that absolute optical air mass and hydrostatic atmospheric delay of electromagnetic waves are proportional magnitudes, and, consequently, their respective obliquity ratios are identical dimensionless quantities. This means that a potential source for developing new models for relative optical air mass can be found in the formulae for the atmospheric delay in electromagnetic signals (and vice versa). In this respect, for estimating relative optical air mass, we demonstrate that Herring's (1992) family of mapping functions for modeling atmospheric delay is more accurate than functional forms devised expressly for the purpose, such as that of Kasten (1965).
Sea breeze simulation over the Malay Peninsula in an intermonsoon period
Authors: Joseph B. , Bhatt B. C. , Koh T. Y. , Chen S.
Published: October 2008

This study presents a characteristic intermonsoon weather situation over the Malay Peninsula. The Coupled Ocean/Atmosphere Mesoscale Prediction System (COAMPS) is used to investigate the mesoscale details of the simulated sea breeze circulations over the Malay Peninsula on 23 April 2002. The occurrence of sea breeze collisions occurring in the inland region of the southern Malay Peninsula is noted. On the peninsula‐scale, convection was first initiated along the low‐level convergence line that became established along the west coastal region of the Malay Peninsula in the early afternoon. Deep clouds that led to thunderstorms developed in the northwestern part of the Malay Peninsula after the sea breeze encountered the mountain wave induced under the ambient easterlies above the mountain ridge line. The convective activity was further enhanced over the central Malay Peninsula because of the interaction between sea breeze front and gap winds from the mountains. This case study suggests that the Malay Peninsula is a potentially fertile ground for many dynamically interesting case studies of land–sea breeze circulations.
Estradiol after Cardiac Arrest and Cardiopulmonary Resuscitation is Neuroprotective and Mediated through Estrogen Receptor-β
Authors: Noppens Ruediger R , Kofler Julia , Grafe Marjorie R , Hurn Patricia D , Traystman Richard J
Published: October 2008

We evaluated long-term administration of estrogen after cardiac arrest and cardiopulmonary resuscitation (CA/CPR) on neurohistopathological and behavioral outcome. We also examined the effect of estrogen receptor (ER) stimulation using ER-α agonist propyl pyrazole triol (PPT) and ER-θ agonist diarylpropionitrile (DPN) on neuronal survival after CA/CPR to determine whether possible neuroprotective effects of estrogen are ER-mediated. Male C57Bl/6 mice underwent 10 mins of CA/CPR and 3-day survival. In protocol 1, intravenous injection of vehicle (NaCl 0.9%) and 0.5 or 2.5 µg 17β-estradiol (E2 loading dose) was performed followed by subcutaneous implants containing vehicle (oil) or E2 (12.6 µg), according to a treatment group. In experimental protocol 2, mice were injected (intravenously) with the ER-α agonist PPT or ER-θ agonist DPN followed by Alzet pump implants (subcutaneously) containing PPT (200 µg) or DPN (800 µg). Long-term E2 administration reduced neuronal injury in the striatum after administration of either loading dose (41%±19%, 35%±26% of injured neurons), as compared with vehicle (68%±7%, P< 0.01), with no effect in the hippocampal CA1 field. In protocol 2, treatment with ER-θ agonist DPN reduced neuronal injury in the striatum (51%±13% injured neurons) as compared with ER-α agonist PPT (68%±10%) and vehicle (69%±11%; P < 0.01). Estrogen receptor-θ agonist DPN reduced neuronal injury in the hippocampal CA1 field (29%±22% injured neurons) as compared with ER-α agonist PPT treatment (62%±33%; P < 0.05). Injury was not different in hippocampal CA1 between vehicle and ER-α agonist-treated animals. We conclude that long-term E2 administration after CA/CPR is neuroprotective and that this effect is most likely mediated via ER-β.
Energy-consistent small-core pseudopotentials for 3d-transition metals adapted to quantum Monte Carlo calculations
Authors: Burkatzki M. , Filippi Claudia , Dolg M.
Published: October 2008

We extend our recently published set of energy-consistent scalar-relativistic Hartree–Fock pseudopotentials by the 3d-transition metal elements, scandium through zinc. The pseudopotentials do not exhibit a singularity at the nucleus and are therefore suitable for quantum Monte Carlo (QMC) calculations. The pseudopotentials and the accompanying basis sets (VnZ with n=T,Q) are given in standard Gaussian representation and their parameter sets are presented. Coupled cluster, configuration interaction, and QMC studies are carried out for the scandium and titanium atoms and their oxides, demonstrating the good performance of the pseudopotentials. Even though the choice of pseudopotential form is motivated by QMC, these pseudopotentials can also be employed in other quantum chemical approaches.
Intermixing and chemical structure at the interface between n-GaN and V-based contacts
Authors: Pookpanratana S. , France R. , Bär M. , Weinhardt L. , Fuchs O. , Blum M. , Yang W. , Denlinger J. D. , Moustakas T. D. , Heske C.
Published: October 2008

The interface between n-type GaN and V-based contacts was characterized by soft x-ray spectroscopy. We have investigated the chemical interface structure before and after a rapid thermal annealing (RTA) step, which is crucial for the formation of an Ohmic contact. X-ray photoelectron and x-ray excited Auger electron spectra suggest that RTA induces an accumulation of metallic Ga at the surface. Using x-ray emission spectroscopy, we find that the probed nitrogen atoms are in a VN-like environment, indicating that vanadium interacts with nitrogen atoms from the GaN to form VN.
Horizontal molecular orientation in vacuum-deposited organic amorphous films of hole and electron transport materials
Authors: Yokoyama Daisuke , Sakaguchi Akio , Suzuki Michio , Adachi Chihaya
Published: October 2008

Using wide-range variable angle spectroscopic ellipsometry, the authors demonstrate large optical uniaxial anisotropy of vacuum-deposited organic amorphous films of hole and electron transport materials having long or planar molecular structures. The ordinary refractive indices and extinction coefficients were higher than the extraordinary ones, revealing that the molecules in the amorphous films are horizontally oriented. The horizontal orientation requires significant modifications in the understanding of both the electrical and optical characteristics of amorphous films when we use materials having long or planar molecular structures.
An explicit algorithm for fully flexible unit cell simulation with recursive thermostat chains
Authors: Jung Kwangsub , Cho Maenghyo
Published: October 2008

Through the combination of the recursive multiple thermostat (RMT) Nosé–Poincaré and Parrinello–Rahman methods, the recursive multiple thermostat chained fully flexible unit cell (RMT-NσT) molecular dynamics method is proposed for isothermal-isobaric simulation. The RMT method is known to have the advantage of achieving the ergodicity that is required for canonical sampling of the harmonic oscillator. Thus, an explicit time integration algorithm is developed for RMT-NσT. We examine the ergodicity for various parameters of RMT-NσT using bulk and thin film structures with different numbers of copper atoms and thicknesses in various environments. Through the numerical simulations, we conclude that the RMT-NσT method is advantageous in the cases of lower temperatures.
The use and characterization of a backilluminated charge-coupled device in investigations of pulsed x-ray and radiation sources
Authors: Fullagar Wilfred , Uhlig Jens , Walczak Monika , Canton Sophie , Sundström Villy
Published: October 2008

Examinations of bremsstrahlung and energetic electron beams from a novel laser plasma source motivate and assist characterization of a backthinned, backilluminated direct detection x-ray charge-coupled device (CCD), a topology that is uncommon in hard x-ray work. Behavior toward pseudomonochromatic (F55e) and multichromatic (A241m) sources is briefly reviewed under optimized noise conditions. Results collectively establish the previously unknown functional depth structure. Several modes of usage are illustrated in ∼4–20 keV x-ray laser plasma source investigations, where the significance of the characterization is briefly discussed. The spectral redistribution associated with this CCD topology is unfavorable, yet appropriate analysis ensures that sufficient spectral information remains for quantitative determination of broadband x-ray flux and spectra in essentially single laser shot measurements. The energy dependence of nascent electron cloud radii in silicon is determined using broadband x-rays from the laser plasma source, turning the narrow depletion depth to advantage. Finally, the characterization is used to quantify recent x-ray spectral explorations of the water jet laser plasma source operating under aspirator vacuum. These results will have key value for establishment of laboratory based ultrafast extended x-ray absorption fine structure experiments using microbolometric detectors.
Fluid phase behavior of a model colloid-polymer mixture: Influence of polymer size and interaction strength
Authors: Rosch Thomas W. , Errington Jeffrey R.
Published: October 2008

We examine how the fluid-fluid phase behavior of a model colloid-polymer mixture evolves with variation of polymer size and/or interaction strength. Polymer-polymer interactions are approximated through Gaussian-core potentials while colloid-colloid and colloid-polymer interactions are assumed purely hard. Grand canonical transition matrix Monte Carlo simulation is used to construct binary liquid-liquid phase diagrams for a wide range of polymer sizes and interaction strengths. Overall, our results indicate that independently decreasing the polymer size or increasing the strength of repulsion between polymers have similar effects; these variations lead to an increase in the critical colloid concentration and decrease in the critical polymer concentration. An examination of the phase diagrams collected in this study reduced by their critical reservoir polymer concentration and critical colloid concentration reveals a single common phase envelope that is quantitatively similar to that for common models used to describe simple fluids. Finally, evaluation of the osmotic second virial coefficient in the vicinity of the critical point suggests that this quantity cannot be used as a reliable predictor for the conditions under which colloid-polymer mixtures phase separate.
Magnetic field effect on the hydrogen desorption and recombination reaction in disproportionated Sm–Co-type alloys
Authors: Rivoirard S. , Lyubina J. , Beaugnon E. , Gutfeisch O.
Published: October 2008

This paper reports on a unique approach to influence the hydrogen desorption and recombination reaction in hydrogen disproportionated SmCo-type alloys upon heating in vacuum (HDDR process) by applying magnetic fields up to 4.1T. The recombination reaction is affected strongly by the magnetic field. More specifically, hydrogen desorption is shifted to higher temperatures when the field is increased. This influence of magnetic field on the equilibrium of the HDDR reaction is qualitatively explained by its effect on the respective phase stability. It is related to the contribution of the magnetic energy term to the total Gibbs free energy of the reactants.
Microstructure and optical properties of Eu3+ activated YV1−xPxO4 phosphors
Authors: Pan Guohui , Song Hongwei , Dai Qilin , Qin Ruifei , Bai Xue , Dong Biao , Fan Libo , Wang Fang
Published: October 2008

Microstructure and spectroscopic properties of YV1−xPxO4:2 mol % Eu3+ (x=0, 0.05, 0.5, 0.95, and 1) powders derived from solid state reaction method were systematically reinvestigated by various spectroscopic techniques such as x-ray diffraction, Fourier transform infrared, excitation and emission spectra, and particularly by frequency-selective excitation techniques. The present results further show the evolutions of local environment surrounding both cations and anion groups with composition, which yielded systematic changes in spectroscopic properties. At least three symmetry sites were identified by laser-selective excitation to be present in the mixed yttrium vanadate/phosphate compounds due to chemical disorder in microstructure based on the random distribution of VO4 and PO4 tetrahedrons. Luminescence dynamics under site-selective excitation indicates that luminescence lifetime of D50 level of Eu3+ ions decreased in going from YPO4 to YVO4 host mainly due to the enhanced electronic dipole transitions. The Ω2 and Ω4 Judd–Ofelt intensity parameters for Eu3+ were determined from the emission spectra and also indicated different local environments experienced by Eu3+ due to the significant changes in ligand polarizability.
Flow past an oscillating circular cylinder in a channel with an upstream splitter plate
Authors: Celik Bayram , Akdag Unal , Gunes Sibel , Beskok Ali
Published: October 2008

A transversely oscillating circular cylinder confined in a channel has the potential to promote mixing and heat transfer at moderate Reynolds number flows. In the present study, simulation results for flow past a circular cylinder subjected to forced cross-flow oscillations in a straight channel with an upstream splitter plate are presented in a wide range of cylinder oscillation frequencies, including the subharmonic, superharmonic, and primary lock-in regimes. Simulations are performed at Re=100, with cylinder oscillation amplitude of 0.4 diameters and a blockage ratio of 1/3. A spectral element algorithm based on the arbitrary Lagrangian Eulerian formulation is utilized. The numerical method exhibits spectral accuracy and allows large mesh deformation in the computational domain without mesh refinements. The main objective of this study is systematic investigations of the cylinder oscillation on the vortex shedding mechanism, downstream vortex patterns, and forces exerted on the cylinder.
Multidimensional instability of electron-acoustic solitary waves in a magnetized plasma with vortexlike electron distribution
Authors: Anowar M. G. M. , Mamun A. A.
Published: October 2008

The basic features of obliquely propagating electron-acoustic (EA) solitary waves and their multidimensional instability in a magnetized plasma containing cold electrons, hot electrons obeying a vortexlike distribution, and stationary ions have been theoretically investigated by the reductive perturbation method and small-k perturbation expansion technique. The combined effects of external magnetic field (obliqueness) and trapped electron distribution, which are found to significantly modify the basic properties (amplitude and width) of small but finite-amplitude EA solitary waves, are explicitly examined. It is also found that the instability criterion and the growth rate are significantly modified by the external magnetic field and the propagation directions of both the nonlinear waves and their perturbation modes. The implications of our results in space plasmas are briefly discussed.
Molecular dynamics nanoindentation simulation of an energetic material
Authors: Chen Yi-Chun , Nomura Ken-ichi , Kalia Rajiv K. , Nakano Aiichiro , Vashishta Priya
Published: October 2008

Molecular dynamics simulation approach is used to study nanoindentation of the (100) crystal surface of cyclotrimethylenetrintramine (RDX) by a diamond indenter. The indenter and substrate atoms interact via reactive force fields. Nanoindentation causes significant heating of the RDX substrate in the proximity of the indenter, resulting in the release of molecular fragments and subsequent “walking” motion of these molecules on the indenter surfaces.
Revisiting the separation dependent surface enhanced Raman scattering
Authors: Liu Y.-J. , Zhang Z.-Y. , Zhao Q. , Zhao Y.-P.
Published: October 2008

Surface-enhanced Raman scattering intensity versus the separation of 100 nm diameter Au nanopost array on Si substrate was investigated. The relative Raman peak intensity per nanopost at different Raman modes rapidly decreases in a similar manner with the increase in the separation. This experimental result agrees well with the localized electric field enhancement calculation by three dimensional finite-difference time-domain method. The Raman peak intensity is mainly due to the edge enhancement of the nanopost through the coupling effect, and the nonenhancement contribution from the top of the nanopost also plays an important role.
Converse magnetoelectric coupling in multilayer capacitors
Authors: Israel C. , Kar-Narayan S. , Mathur N. D.
Published: October 2008

We report electrically induced changes of 20% in both the remnant magnetization and the coercive field of a magnetoelectric heterostructure. This heterostructure is an industrially produced multilayer capacitor comprising Ni-based magnetostrictive electrodes sandwiching a BaTiO3-based dielectric that is ferroelectric and therefore piezoelectric. Both magnetization and strain are shown to be hysteretic with applied electric field. These inexpensive capacitors might find use as electrically controlled ferromagnets.
Ultrashort-pulse laser calligraphy
Authors: Yang Weijia , Kazansky Peter G. , Shimotsuma Yasuhiko , Sakakura Masaaki , Miura Kiyotaka , Hirao Kazuyuki
Published: October 2008

Control of structural modifications inside silica glass by changing the front tilt of an ultrashort pulse is demonstrated, achieving a calligraphic style of laser writing. The phenomena of anisotropic bubble formation at the boundary of an irradiated region and modification transition from microscopic bubbles formation to self-assembled form birefringence are observed, and the physical mechanisms are discussed. The results provide the comprehensive evidence that the light beam with centrosymmetric intensity distribution can produce noncentrosymmetric material modifications.
Quantum confinement effect in ZnO thin films grown by pulsed laser deposition
Authors: Nie J. C. , Yang J. Y. , Piao Y. , Li H. , Sun Y. , Xue Q. M. , Xiong C. M. , Dou R. F. , Tu Q. Y.
Published: October 2008

High quality crystalline nanostructured ZnO thin films were fabricated by pulsed laser deposition on (0001) sapphire substrates. The films were investigated by x-ray diffraction, scanning electron microscopy, and optical absorption spectroscopy. The exciton peak energy from absorption spectra was used to determine the band gap energy Eg, which was found to increase systematically with the decrease in the mean grain size and ranged from 3.388to3.647eV. This is consistent with the quantum confinement model and, up until now, not observed in a convincing manner in the ZnO thin films.
Resistance switching properties of sol-gel derived La0.67Ca0.33MnO3 thin films on F-doped SnO2 conducting glass
Authors: Zhang Ting , Su Zhaohui , Chen Hongju , Ding Linghong , Zhang Weifeng
Published: October 2008

The electric-pulse-induced resistance switching of the Au–La0.67Ca0.33MnO3(LCMO)-FTO (fluorine-doped tin oxide) heterostructures was studied by electrochemical workstation. A distinct current-voltage characteristic of the device with pronounced reproducible nonlinearity, asymmetry, and hysteresis was observed at room temperature. The current-voltage characteristics suggest a Poole–Frenkel and space-charge-limited current type mechanism controlled by Au/LCMO interface traps. The resistance switching behavior shows obvious multilevel resistance switching. The present results suggest a possible application of Ag-LCMO-FTO system as multilevel memory devices.
Human domain antibodies to conserved sterically restricted regions on gp120 as exceptionally potent cross-reactive HIV-1 neutralizers
Authors: Chen Weizao , Zhu Zhongyu , Feng Yang , Dimitrov Dimiter S.
Published: October 2008

The antibody access to some conserved structures on the HIV-1 envelope glycoprotein (Env) is sterically restricted. We have hypothesized that the smallest independently folded antibody fragments (domains) could exhibit exceptionally potent and broadly cross-reactive neutralizing activity by targeting hidden conserved epitopes that are not accessible by larger antibodies. To test this hypothesis, we constructed a large (size 2.5 × 10
10
), highly diversified library of human antibody variable domains (domain antibodies) and used it for selection of binders to conserved Env structures by panning sequentially against Envs from different isolates. The highest affinity binder, m36, neutralized all tested HIV-1 isolates from clades A– D with an activity on average higher than that of C34, a peptide similar to the fusion inhibitor T20, which is in clinical use, and that of m9, which exhibits a neutralizing activity superior to known potent cross-reactive antibodies. Large-size fusion proteins of m36 exhibited diminished neutralizing activity but preincubation of virions with soluble CD4 restored it, suggesting that m36 epitope is sterically restricted and induced by CD4 (CD4i). M36 bound to gp120-CD4 complexes better than to gp120 alone and competed with CD4i antibodies. M36 is the only reported representative of a promising class of potent, broadly cross-reactive HIV-1 inhibitors based on human domain antibodies. It has potential for prevention and therapy and as an agent for exploration of the closely guarded conserved Env structures with implications for design of small molecule inhibitors and elucidation of mechanisms of virus entry and evasion of immune responses.
A second wave of
Sonic hedgehog
expression during the development of the bat limb
Authors: Hockman Dorit , Cretekos Chris J. , Mason Mandy K. , Behringer Richard R. , Jacobs David S. , Illing Nicola
Published: October 2008

Sonic hedgehog
(
Shh
) plays an integral role in both the anterior-posterior (A-P) patterning and expansion of developing vertebrate limbs through a feedback loop involving
Fgfs
,
Bmps
, and
Gremlin
. In bat limbs A-P patterning and the size of the digital field are unique. The posterior digits of the forelimb are elongated and joined by tissue, whereas the thumb is short. The hindlimb digits often are uniform in length. Here, we reveal novel expression patterns for
Shh
and its target,
Patched 1
(
Ptc1
), during limb development in two bat species. Early
Shh
expression in the zone of polarizing activity is wider in the bat forelimb than in the mouse forelimb, correlating with the reported expansion of
Fgf8
expression in the apical ectodermal ridge and the early loss of symmetry in the bat forelimb. Later in limb development,
Shh
and
Ptc1
expression is reinitiated in the interdigital tissue.
Shh
is graded along the A-P axis in forelimb and is expressed uniformly at a lower level across the hindlimb interdigital tissue. We also show that the reported
Fgf8
expression in the interdigital tissue precedes the expression of
Shh.
We propose that the reinitiation of
Shh
and
Fgf8
expression in bat limbs reactivates the
Shh-Fgf
feedback loop in the interdigital tissue of stage 16 bat embryos. The cell survival and proliferation signals provided by the
Shh-Fgf
signaling loop probably contribute to the lengthening of the posterior forelimb digits, the survival of the forelimb interdigital webbing, and the extension of the hindlimb digits to a uniform length.
Angiopoietin-2 is associated with decreased endothelial nitric oxide and poor clinical outcome in severe falciparum malaria
Authors: Yeo Tsin W. , Lampah Daniel A. , Gitawati Retno , Tjitra Emiliana , Kenangalem Enny , Piera Kim , Price Ric N. , Duffull Stephen B. , Celermajer David S. , Anstey Nicholas M.
Published: October 2008

Adherence of parasitized erythrocytes to activated endothelium causes microvascular obstruction, tissue ischemia, and clinical complications in severe malaria (SM); however, the mechanisms leading to endothelial activation remain unclear. The angiogenic factors, angiopoietin-2 (Ang-2) and vascular endothelial growth factor (VEGF) are modulators of endothelial activation, with Ang-2 release from Weibel–Palade bodies (WPBs) being regulated by endothelial nitric oxide (NO). We explored the relationships between endothelial NO bioavailability, Ang-2, VEGF, tissue perfusion, and clinical outcomes in SM. We measured plasma Ang-2 and VEGF, together with biomarkers of severity from 146 adults with and without SM, in parallel with longitudinal measures of endothelial function by using reactive hyperemia peripheral arterial tonometry (a measure of endothelial NO bioavailability). Regression was used to relate concentrations of Ang-2/VEGF with malaria disease severity, biomarkers of perfusion, endothelial activation, and parasite biomass. The longitudinal relationship between Ang-2 and endothelial function was assessed by using a mixed-effects model. Ang-2 concentrations were elevated in SM and associated with increased venous lactate, plasma intercellular cell adhesion molecule-1 concentrations, parasite biomass, and mortality. In contrast, VEGF concentrations were inversely associated with these biomarkers. Ang-2 concentrations were significantly better predictors of death than venous lactate (P= 0.03). Recovery of endothelial function was associated with falling concentrations of Ang-2. Ang-2 release from endothelial cells with reduced NO bioavailability is likely to contribute to endothelial activation, sequestered parasite biomass, impaired perfusion, and poor outcome in severe falciparum malaria. Agents that improve endothelial NO, reduce WPB exocytosis, and/or antagonize Ang-2 may have therapeutic roles in SM.
Wnt-mediated self-renewal of neural stem/progenitor cells
Authors: Kalani M. Yashar S. , Cheshier Samuel H. , Cord Branden J. , Bababeygy Simon R. , Vogel Hannes , Weissman Irving L. , Palmer Theo D. , Nusse Roel
Published: October 2008

In this work we have uncovered a role for Wnt signaling as an important regulator of stem cell self-renewal in the developing brain. We identified Wnt-responsive cells in the subventricular zone of the developing E14.5 mouse brain. Responding cell populations were enriched for self-renewing stem cells in primary culture, suggesting that Wnt signaling is a hallmark of self-renewing activity in vivo. We also tested whether Wnt signals directly influence neural stem cells. Using inhibitors of the Wnt pathway, we found that Wnt signaling is required for the efficient cloning and expansion of single-cell derived populations that are able to generate new stem cells as well as neurons, astrocytes, and oligodendrocytes. The addition of exogenous Wnt3a protein enhances clonal outgrowth, demonstrating not only a critical role for the Wnt pathway for the regulation of neurogenesis but also its use for the expansion of neural stem cells in cell culture and in tissue engineering.
Staged assembly of histone gene expression machinery at subnuclear foci in the abbreviated cell cycle of human embryonic stem cells
Authors: Ghule Prachi N. , Dominski Zbigniew , Yang Xiao-cui , Marzluff William F. , Becker Klaus A. , Harper J. Wade , Lian Jane B. , Stein Janet L. , van Wijnen Andre J. , Stein Gary S.
Published: October 2008

Human embryonic stem (hES) cells have an abbreviated G
1
phase of the cell cycle. How cells expedite G
1
events that are required for the initiation of S phase has not been resolved. One key regulatory pathway that controls G
1
/S-phase transition is the cyclin E/CDK2-dependent activation of the coactivator protein nuclear protein, ataxia–telangiectasia locus/histone nuclear factor-P (p220
NPAT
/HiNF-P) complex that induces histone gene transcription. In this study, we use the subnuclear organization of factors controlling histone gene expression to define mechanistic differences in the G
1
phase of hES and somatic cells using in situ immunofluorescence microscopy and fluorescence in situ hybridization (FISH). We show that histone gene expression is supported by the staged assembly and modification of a unique subnuclear structure that coordinates initiation and processing of transcripts originating from histone gene loci. Our results demonstrate that regulatory complexes that mediate transcriptional initiation (e.g., p220
NPAT
) and 3′-end processing (e.g., Lsm10, Lsm11, and SLBP) of histone gene transcripts colocalize at histone gene loci in dedicated subnuclear foci (histone locus bodies) that are distinct from Cajal bodies. Although appearance of CDK2-phosphorylated p220
NPAT
in these domains occurs at the time of S-phase entry, histone locus bodies are formed ≈1 to 2 h before S phase in embryonic cells but 6 h before S phase in somatic cells. These temporal differences in the formation of histone locus bodies suggest that the G
1
phase of the cell cycle in hES cells is abbreviated in part by contraction of late G
1
.
Human papillomavirus in the placenta and umbilical cord blood
Authors: SARKOLA MARJA E. , GRÉNMAN SEIJA E. , RINTALA MARJUT A.M. , SYRJÄNEN KARI J. , SYRJÄNEN STINA M.
Published: October 2008

Objective. To analyze human papillomavirus (HPV) DNA in umbilical cord blood and in placenta, including its cellular localization. Design. Longitudinal prospective study. Setting. Maternity Unit of Turku University Hospital, and MediCity, University of Turku. Samples. Placental and cord blood samples obtained at delivery from 315 mothers and 311 neonates included in the Finnish HPV Family Study. Methods. HPV testing by nested PCR and sequencing. Tyramide amplified in situ hybridization (ISH) for viral DNA localization in placenta. Correlation to mother's and neonate's oral and genital HPV status and maternal demographic data. Main outcome measures. Detection and cellular localization of HPV DNA. Results. HPV DNA was detected in 4.2 and 3.5% of placenta and cord blood samples, respectively, including HPV types 16, 6, 83 and 39. In placenta, HPV6 and 16 DNA was localized in syncytiotrophoblasts. Abnormal cytology increased the risk of HPV+ placenta and cord blood. History of genital warts was the only independent predictor of cord blood HPV in multivariate analysis (adjusted OR=4.0, 95% CI: 1.09–14.54, p = 0.036). HPV DNA in cord blood increased the risk of genital (OR=4.0, 95% CI: 1.08–14.83, p = 0.048) and oral (OR=4.4, 95% CI: 1.17–16.14, p = 0.039) HPV DNA carriage of the neonate. HPV+ placenta increased the risk of oral HPV of the neonate (OR=8.6, 95% CI: 2.73–27.13, p = 0.0001). Delivery mode did not predict HPV status of the neonate. Conclusions. HPV DNA is detected in placental trophoblasts and umbilical cord blood. The presence of HPV DNA at these sites increases the risk of a neonate testing HPV‐positive at birth.