bluuebunny/crossref_metadata_2025 huggingface dataset:
A study of land surface processes using land surface models over the Little River Experimental Watershed, Georgia
Authors: Sahoo Alok K. , Dirmeyer Paul A. , Houser Paul R. , Kafatos Menas
Published: October 2008

Three different land surface models (Hydrological improvements to the Simplified version of the Simple Biosphere model (HySSiB), Noah model, and Community Land Model (CLM)) were simulated on the NASA Goddard Space Flight Center's Land Information System platform at 1‐km resolution over the Little River Experimental Watershed, Georgia, and the simulated results were analyzed to address the local‐scale land‐atmosphere processes. All the three models simulated the soil moisture in space and time realistically. The Noah model produced higher soil moisture whereas the CLM got lower soil moisture with many dry down phases. CLM and HySSiB models were oversensitive to the atmospheric events. Different vertical discretizations of the model layers affected the soil moisture results in all the three models. The arithmetic model ensemble mean soil moisture performed reasonably well even at individual in‐situ measurement sites. We found that different model schemes partitioned the incoming water and energy differently and hence produced different results for the water and energy budget parameters. In CLM, the energy and water budget parameters were very closely connected to the soil moisture (e.g., evaporation, latent, and sensible heat) change. HySSiB produced very high surface runoff and very low subsurface runoff. The Noah model did not produce much surface and subsurface runoff resulting in high surface soil moisture. We did not find much variability in Noah latent heat, sensible heat, and ground heat fluxes. From soil moisture data assimilation point of view, the mean bias removed Noah soil moisture was found to be better than other data sets.
A Bayesian approach to electric field and E‐region neutral wind estimation with the Poker Flat Advanced Modular Incoherent Scatter Radar
Authors: Heinselman Craig J. , Nicolls Michael J.
Published: October 2008

In this paper, we describe an approach for computing vector electric fields in the F region and neutral winds in the E region from incoherent scatter radar (ISR) measurements, applicable especially for Advanced Modular Incoherent Scatter Radar (AMISR) systems, namely, the Poker Flat Incoherent Scatter Radar (PFISR). PFISR is a 128‐panel (upgraded from 96 panels in September 2007) AMISR system installed at the Poker Flat Research Range near Fairbanks, Alaska. The pulse‐to‐pulse steering capabilities of AMISR support the measurement of line‐of‐sight velocities in multiple look directions essentially simultaneously. This capability in turn allows electric fields and neutral winds to be resolved with minimal assumptions regarding time stationarity of the medium. The multibeamforming capability also allows additional flexibility in the estimation of those parameters, for which experiment planning can become very important. The approach described herein is ideally suited for such planning, is appropriate for the overdetermined problem characteristic of AMISR measurements, and allows in a simple way for the inclusion of appropriate a priori information such as the assumption of negligible parallel electric fields and negligible vertical neutral winds. We present some case studies from the PFISR that demonstrate some of the new capabilities.
Spectral variability of the Martian high latitude surfaces
Authors: Poulet F. , Langevin Y. , Boubin G. , Jouglet D. , Bibring J.‐P. , Gondet B.
Published: October 2008

We report the surface distributions of some minerals in the high latitude (>50°) regions of Mars using the OMEGA/MEx observations in the near‐infrared wavelength domains (1–2.5 μm). Mafic minerals (pyroxene and olivine) are observed in the low albedo terrains. The identification of these minerals is consistent with the presence of volcanic features identified by geologic mappings. Water‐bearing minerals identified on the basis of the 1.9 μm band cover the surfaces of latitudes larger than 60°. The presence of this hydration is likely the result of diffusive exchange of water between the sub‐surface ice, the pore space of the regolith and the atmosphere, rather than chemically bound water resulting from hydrous alteration during the formation of the minerals. These observations will allow for comprehensive, coordinated analyses of data from the orbital and Phoenix platforms.
Conservation of open solar magnetic flux and the floor in the heliospheric magnetic field
Authors: Owens M. J. , Crooker N. U. , Schwadron N. A. , Horbury T. S. , Yashiro S. , Xie H. , St. Cyr O. C. , Gopalswamy N.
Published: October 2008

The near‐Earth heliospheric magnetic field intensity, |B|, exhibits a strong solar cycle variation, but returns to the same “floor” value each solar minimum. The current minimum, however, has seen |B| drop below previous minima, bringing in to question the existence of a floor, or at the very least requiring a re‐assessment of its value. In this study we assume heliospheric flux consists of a constant open flux component and a time‐varying contribution from CMEs. In this scenario, the true floor is |B| with zero CME contribution. Using observed CME rates over the solar cycle, we estimate the “no‐CME” |B| floor at ∼4.0 ± 0.3 nT, lower than previous floor estimates and below |B| observed this solar minimum. We speculate that the drop in |B| observed this minimum may be due to a persistently lower CME rate than the previous minimum, though there are large uncertainties in the supporting observational data.
Aging of biomass burning aerosols over West Africa: Aircraft measurements of chemical composition, microphysical properties, and emission ratios
Authors: Capes G. , Johnson B. , McFiggans G. , Williams P. I. , Haywood J. , Coe H.
Published: October 2008

This paper investigates the physical and chemical characteristics of biomass burning aerosol over West Africa using data from the UK Facility for Airborne Atmospheric Measurements aircraft. Measurements of biomass burning aerosol were made during the Dust and Biomass‐burning Experiment (DABEX) and Dust Outflow and Deposition to the Ocean (DODO) field experiments in January and February 2006. Layers of aged biomass burning aerosols were observed throughout the region, and fresh biomass burning aerosols were encountered during the penetration of smoke plumes at low altitudes. Vertical profiles of aerosol properties across the region are shown. Measurements from an Aerodyne Quadrupole Aerosol Mass Spectrometer (Q‐AMS) show changes in chemical composition between fresh and aged biomass burning aerosols, over a region spanning thousands of kilometers. These data represent the first time that continental‐scale variability in biomass burning aerosol composition has been observed. However, an almost linear relationship between organic aerosol mass concentration and carbon monoxide concentration was observed across the region. A net carbon loss occurs over the aerosol lifetime in the region owing to a combination of chemical processing and repartitioning of organic mass to the gas phase. Evolution of the number size distribution was observed, with coagulation concluded to be the dominant process involved, a finding supported by coagulation box modeling. Regional‐scale emission ratios for organic (0.041) and black carbon (0.0072) with respect to CO have been estimated over West Africa, one of the largest sources of biomass burning globally. Biomass burning emissions from the West African Sahel are poorly represented in the literature, and these results represent important continental‐scale emissions. They are in good agreement with literature values from other regions.
AMMA dust experiment: An overview of measurements performed during the dry season special observation period (SOP0) at the Banizoumbou (Niger) supersite
Authors: Rajot Jean Louis , Formenti Paola , Alfaro Stéphane , Desboeufs Karine , Chevaillier Servanne , Chatenet Bernadette , Gaudichet Annie , Journet Emilie , Marticorena Béatrice , Triquet Sylvain , Maman Aliko , Mouget Nicolas , Zakou Alfari
Published: October 2008

In the frame of the African Monsoon Multidisciplinary Analysis–Special Observation Period 0 (AMMA SOP0) field campaign, a sophisticated instrumental setup specially designed for documenting the characteristics of aerosols in the surface boundary layer has been operated for 1 month (13 January to 13 February 2006) at the Banizoumbou supersite in Niger. The analysis of the long‐term routine sunphotometer measurements shows that the intensive measurements were performed during a transition phase between a period when biomass burning aerosols are present in the atmospheric column and another when mineral dust is clearly predominant. On the basis of ground‐level observations, three types of events can be defined. (1) Type B events are those corresponding to advection of Biomass burning plumes from southern Sahel. They represent only 3% of the measurement period. (2) Type D events are those during which mineral dust concentrations are larger than 200 μg m−3. They represent 35% of the measuring time, and coincide with advection of mineral dust from distant sources to the measurement site. The composition of the dust differs significantly from one episode to the other, depending on the trajectory of air mass that transported it. (3) Type L events are those that can be explained by occurrence of local erosion and that are of short duration. During them, the aerosol size distribution is dominated by a coarser mode (9 μm) than during the events of the D type dominated by a finer mode (4.5 μm). Elemental analysis also shows that mineral dust is relatively rich in Fe and poor in Ca, which is typical of the Sahelian aerosols.
A European daily high‐resolution gridded data set of surface temperature and precipitation for 1950–2006
Authors: Haylock M. R. , Hofstra N. , Klein Tank A. M. G. , Klok E. J. , Jones P. D. , New M.
Published: October 2008

We present a European land‐only daily high‐resolution gridded data set for precipitation and minimum, maximum, and mean surface temperature for the period 1950–2006. This data set improves on previous products in its spatial resolution and extent, time period, number of contributing stations, and attention to finding the most appropriate method for spatial interpolation of daily climate observations. The gridded data are delivered on four spatial resolutions to match the grids used in previous products as well as many of the rotated pole Regional Climate Models (RCMs) currently in use. Each data set has been designed to provide the best estimate of grid box averages rather than point values to enable direct comparison with RCMs. We employ a three‐step process of interpolation, by first interpolating the monthly precipitation totals and monthly mean temperature using three‐dimensional thin‐plate splines, then interpolating the daily anomalies using indicator and universal kriging for precipitation and kriging with an external drift for temperature, then combining the monthly and daily estimates. Interpolation uncertainty is quantified by the provision of daily standard errors for every grid square. The daily uncertainty averaged across the entire region is shown to be largely dependent on the season and number of contributing observations. We examine the effect that interpolation has on the magnitude of the extremes in the observations by calculating areal reduction factors for daily maximum temperature and precipitation events with return periods up to 10 years.
Nonstationary influence of the North Atlantic Oscillation on European precipitation
Authors: Vicente‐Serrano Sergio M. , López‐Moreno Juan I.
Published: October 2008

This paper analyzes the changing role of the North Atlantic Oscillation (NAO) in European precipitation in relation to interdecadal shifts in the atmospheric dynamic over the North Atlantic region. For this purpose, moving window correlations between precipitation and NAO have been related to the interdecadal variability of atmospheric pressure patterns. Analyses have been replicated using observed climate data for the twentieth century, paleoclimate reconstructions since 1785, and physically modeled climate by AOGCMs (CGCM3.1(T63), 20C3M). Results evidence that nonstationary relationship of the NAO across Europe is linked to interdecadal shifts in the location of the positions of the NAO pressure centers, which have been occurred at least since the last 2 centuries. Such displacement of the pressure NAO centers points to possible existence of different NAO patterns, which may help to explain why studies relating NAO to European climate behavior have not shown systematically strong correlations in the course of the twentieth century. A general trend toward a strengthening of the NAO‐precipitation relationship over most of Europe has been detected for the twentieth century.
Determination of transport properties from flowing fluid temperature logging in unsaturated fractured rocks: Theory and semi‐analytical solution
Authors: Mukhopadhyay Sumit , Tsang Yvonne W.
Published: October 2008

Flowing fluid temperature logging (FFTL) has recently been proposed as a method to locate flowing fractures. We argue that FFTL, backed up by data from high‐precision distributed temperature sensors, can be a useful tool in locating flowing fractures and in estimating the transport properties of unsaturated fractured rocks. We have developed the theoretical background needed to analyze data from FFTL. In this article, we present a simplified conceptualization of FFTL in unsaturated fractured rock and develop a semi‐analytical solution for spatial and temporal variations of pressure and temperature inside a borehole in response to an applied perturbation (pumping of air from the borehole). We compare the semi‐analytical solution with predictions from the TOUGH2 numerical simulator. On the basis of the semi‐analytical solution, we propose a method to estimate the permeability of the fracture continuum surrounding the borehole. Using this proposed method, we estimated the effective fracture continuum permeability of the unsaturated rock hosting the Drift Scale Test (DST) at Yucca Mountain, Nevada. Our estimate compares well with previous independent estimates for fracture permeability of the DST host rock. The conceptual model of FFTL presented in this article is based on the assumptions of single‐phase flow, convection‐only heat transfer, and negligible change in system state of the rock formation. In a sequel article, we extend the conceptual model to evaluate some of these assumptions. In that paper, we also perform inverse modeling of FFTL data to estimate, in addition to permeability, other transport parameters (such as porosity and thermal conductivity) of unsaturated fractured rocks.
Defining, Identifying, and Evaluating Clinical Trials of Stuttering Treatments: A Tutorial for Clinicians
Authors: Onslow Mark , Jones Mark , O’Brian Sue , Menzies Ross , Packman Ann
Published: October 2008

Purpose

To develop a method for clinicians to evaluate stuttering treatment efficacy research with very little burden of work.

Method

The clinical trial is the most fundamental, clinically interpretable, and useful output unit of stuttering treatment research. We define a clinical trial of a stuttering treatment and specify 3 levels of clinical trials evidence. We use this taxonomy to identify and evaluate clinical trials of stuttering treatment. Our taxonomy draws on 2 fundamental principles of clinical trials used to evaluate health care: randomization and effect size.

Results

Published clinical trials of stuttering treatments were identified and allocated to 1 of 3 levels of evidence.

Conclusions

We outline a 3-step, semi-automated, Internet-based method to identify the publication of a report of stuttering treatment efficacy. For a report identified as such, a 10-item checklist is applied to verify its status as a clinical trial and to allocate it to 1 of 3 levels of clinical trials evidence. The present taxonomy reduces the burden of work of a 136-item checklist in an existing taxonomy.
Molecular hydrogen adsorbed on benzene: Insights from a quantum Monte Carlo study
Authors: Beaudet Todd D. , Casula Michele , Kim Jeongnim , Sorella Sandro , Martin Richard M.
Published: October 2008

We present a quantum Monte Carlo study of the hydrogen-benzene system where binding is very weak. We demonstrate that the binding is well described at both variational Monte Carlo (VMC) and diffusion Monte Carlo (DMC) levels by a Jastrow correlated single determinant geminal wave function with an optimized compact basis set that includes diffuse orbitals. Agreement between VMC and fixed-node DMC binding energies is found to be within 0.18mhartree, suggesting that the calculations are well converged with respect to the basis. Essentially the same binding is also found in independent DMC calculations using a different trial wave function of a more conventional Slater–Jastrow form, supporting our conclusion that the binding energy is accurate and includes all effects of correlation. We compare with previous calculations, and we discuss the physical mechanisms of the interaction, the role of diffuse basis functions, and the charge redistribution in the bond.
Continuity of the nucleation of bulk and surface phases
Authors: Sear Richard P.
Published: October 2008

Nucleation of a new bulk phase is almost always heterogeneous: It occurs at a surface. Nucleation of a new surface phase also occurs at a surface of course. We study nucleation in an Ising model with both bulk and surface (prewetting) transitions. We find no clear distinction between nucleation of the bulk and surface phases. As the bulk transition is crossed, the phase that is nucleating changes from being a new surface phase to being a new bulk phase. However, neither the nucleation rate nor the nucleus itself changes discontinuously. It appears that because the nucleus is only approximately two spins high, it is oblivious to the fact that on one side of the bulk transition it will grow to form a thick wetting layer, while on the other side it will grow to form a bulk phase of limitless thickness. The phase diagram of hard spheres at a hard wall is analogous to that of our model. Therefore, we suggest that the nucleation of the crystal phase of hard spheres at a hard wall may also be indistinguishable from that associated with a prefreezing surface transition.
Excess entropy scaling of transport properties of Lennard-Jones chains
Authors: Goel Teena , Patra Chandra Nath , Mukherjee Tulsi , Chakravarty Charusita
Published: October 2008

Excess-entropy scaling relationships for diffusivity and viscosity of Lennard-Jones chain fluids are tested using molecular dynamics simulations for chain sizes that are sufficiently small that chain entanglement effects are insignificant. The thermodynamic excess entropy Se is estimated using self-associating fluid theory (SAFT). A structural measure of the entropy S2 is also computed from the monomer-monomer pair correlation function, gm(r). The thermodynamic and structural estimators for the excess entropy are shown to be very strongly correlated. The dimensionless center-of-mass diffusivities, Dcm*, obtained by dividing the diffusivities by suitable macroscopic reduction parameters, are shown to conform to the excess entropy scaling relationship, Dcm*=Anexp(αnSe), where the scaling parameters depend on the chain length n. The exponential parameter αn varies as −(1∕n) while An varies approximately as n−0.5. The scaled viscosities obey a similar relationship with scaling parameters Bn and βn where βn varies as 1∕n and Bn shows an approximate n0.6 dependence. In accordance with the Stokes–Einstein law, for a given chain length, αn=−βn within statistical error. The excess entropy scaling parameters associated with the transport properties therefore display a simple dependence on chain length.
Binary crystals in two-dimensional two-component Yukawa mixtures
Authors: Assoud Lahcen , Messina René , Löwen Hartmut
Published: October 2008

The zero-temperature phase diagram of binary mixtures of like-charge particles interacting via a screened Coulomb pair potential is calculated as a function of composition and charge ratio. The potential energy obtained by a Lekner summation is minimized among a variety of candidate two-dimensional crystals. A wealth of different stable crystal structures is identified including A, B, AB2, A2B, and AB4 structures [A (B) particles correspond to large (small) charge.] Their elementary cells consist of triangular, square, or rhombic lattices of the A particles with a basis comprising various structures of A and B particles. For small charge asymmetry there are no intermediate crystals besides the pure A and B triangular crystals. The predicted structures are detectable in experiments on confined mixtures of like-charge colloids or dusty plasma sheets.
Torsional potentials and full-dimensional simulation of electronic absorption and fluorescence spectra of para-phenylene oligomers using the semiempirical self-consistent charge density-functional tight binding approach
Authors: Lukeš Vladimír , Šolc Roland , Barbatti Mario , Elstner Marcus , Lischka Hans , Kauffmann Harald-Friedrich
Published: October 2008

A systematic study on the structural properties of para-phenylene oligomers based on the self-consistent charge density-functional tight binding approach (SCC-DFTB) and its time-dependent (TD) version is presented. Our goal is to investigate the applicability of DFTB for the present class of compounds and to use its computational efficiency for on-the-fly dynamics calculations and to perform in this way simulations of absorption and fluorescence spectra. For this purpose geometry optimizations have been performed for the ground state and for the electronically lowest excited state of oligomers containing two to seven aromatic rings. The torsional potential curves have been computed for para-biphenyl and para-terphenyl in the ground and lowest excited state. Agreement with previously computed DFT results is quite encouraging and DFTB seems to be well suited for the treatment of the class of conjugated π systems investigated in this work. The intrachain vibrational broadening of absorption and emission spectra computed from dynamics simulations are presented and compared with experimental spectra.
Selective passive shielding and the Faraday bracelet
Authors: Bidinosti C. P. , Hayden M. E.
Published: October 2008

We describe a general approach for the design of passive conducting structures that preferentially shield the ac magnetic field produced by a specific coil geometry. We demonstrate the utility of selective passive shielding with the Faraday bracelet, an open-access shield for saddle-shaped rf coils. Our data also corroborate the poorly known fact that effective shielding can occur when the ratio of shield thickness to skin depth is much less than unity.
Molecular simulation of cooperative hydrodynamic effects in motion of a periodic array of spheres between parallel walls
Authors: Kohale Swapnil C. , Khare Rajesh
Published: October 2008

We use molecular dynamics simulations to investigate the cooperative hydrodynamic interactions involved in the collective translation of a periodic array of spheres in a fluid which is confined between two atomistic surfaces. In particular, we study a spherical particle that is moving with a constant velocity parallel to the two confining surfaces. This central sphere along with its periodic images forms the translating two dimensional periodic grid. The cooperative hydrodynamic effects between neighboring spheres in the grid are determined by monitoring the friction force experienced by the spheres that are moving through an atomistic solvent. The dependence of the hydrodynamic cooperativity on the grid spacing is quantified by running simulations in systems with different sizes of the periodic box. Our results show a clear evidence of hydrodynamic cooperation between the spherical particles for grid spacing of 90σ and larger, where σ is the solvent molecular diameter. These cooperative interactions lead to a reduced value of the friction force experienced by these spheres as opposed to the case for a single sphere moving in an infinite quiescent fluid. The simulated friction force values are compared with the recent continuum mechanics predictions [Bhattacharya, J. Chem. Phys. 128, 074709 (2008)] for the same problem of the motion of a periodic grid of particles through a confined fluid. The simulated values of friction force were found to follow the same qualitative trend as the continuum results but the continuum predictions were consistently larger than the simulation results by approximately 22%. We attribute this difference to the fluid slip at the surface of the spherical particle, as measured in the simulations.
Electromagnetic field distribution calculation in solenoidal inductively coupled plasma using finite difference method
Authors: Li W. P. , Liu Y. , Long Q. , Chen D. H. , Chen Y. M.
Published: October 2008

The electromagnetic field (both E and B fields) is calculated for a solenoidal inductively coupled plasma (ICP) discharge. The model is based on two-dimensional cylindrical coordinates, and the finite difference method is used for solving Maxwell equations in both the radial and axial directions. Through one-turn coil measurements, assuming that the electrical conductivity has a constant value in each cross section of the discharge tube, the calculated E and B fields rise sharply near the tube wall. The nonuniform radial distributions imply that the skin effect plays a significant role in the energy balance of the stable ICP. Damped distributions in the axial direction show that the magnetic flux gradually dissipates into the surrounding space. A finite difference calculation allows prediction of the electrical conductivity and plasma permeability, and the induction coil voltage and plasma current can be calculated, which are verified for correctness.
Two-dimensional electron gas based actuation of piezoelectric AlGaN/GaN microelectromechanical resonators
Authors: Brueckner K. , Niebelschuetz F. , Tonisch K. , Michael S. , Dadgar A. , Krost A. , Cimalla V. , Ambacher O. , Stephan R. , Hein M. A.
Published: October 2008

Free-standing piezoelectric AlGaN/GaN beam resonators have been prepared on silicon substrates. The two-dimensional electron gas at the interface of the III/V heterostructure has been employed to act as back electrode for the piezoelectric active layer. The fundamental mode as well as higher order resonant modes of flexural vibration has been excited piezoelectrically and analyzed using optical laser–Doppler vibrometry. The experimental investigations were carried out under normal ambient conditions. The specific piezoelectric actuation scheme is described and the dependence of the measured resonant frequencies between 0.2 and 8.1 MHz on geometry and material parameters is investigated.
10
ℏ
superconducting quantum interference device amplifier for acoustic gravitational wave detectors
Authors: Falferi P. , Bonaldi M. , Cerdonio M. , Mezzena R. , Prodi G. A. , Vinante A. , Vitale S.
Published: October 2008

From measurements of additive and back action noise, we estimate the noise temperature of a two-stage superconducting quantum interference device (SQUID) amplifier developed for the acoustic wide-band gravitational wave detectors of the next generation. The minimum noise temperature evaluated at 8.9 kHz and T≤0.3 K is about 4 μK and corresponds to 10 times the quantum-limited noise temperature. As the high-Q electrical resonator used for the back action noise measurements behaves in many respects like the input load constituted by an acoustic gravitational wave detector, this SQUID amplifier is expected to keep the same noise performance once installed on the detector.
Experimental and numerical simulation of three-dimensional gravity currents on smooth and rough bottom
Authors: La Rocca Michele , Adduce Claudia , Sciortino Giampiero , Pinzon Allen Bateman
Published: October 2008

The dynamics of a three-dimensional gravity current is investigated by both laboratory experiments and numerical simulations. The experiments take place in a rectangular tank, which is divided into two square reservoirs with a wall containing a sliding gate of width b. The two reservoirs are filled to the same height H, one with salt water and the other with fresh water. The gravity current starts its evolution as soon as the sliding gate is manually opened. Experiments are conducted with either smooth or rough surface on the bottom of the tank. The bottom roughness is created by gluing sediment material of different diameters to the surface. Five diameter values for the surface roughness and two salinity conditions for the fluid are investigated. The mathematical model is based on shallow-water theory together with the single-layer approximation, so that the model is strictly hyperbolic and can be put into conservative form. Consequently, a finite-volume-based numerical algorithm can be applied. The Godunov formulation is used together with Roe’s approximate Riemann solver. Comparisons between the numerical and experimental results show satisfactory agreement. The behavior of the gravity current is quite unusual and cannot be interpreted using the usual model framework adopted for two-dimensional and axisymmetric gravity currents. Two main phases are apparent in the gravity current evolution; during the first phase the front velocity increases, and during the second phase the front velocity decreases and the dimensionless results, relative to the different densities, collapse onto the same curve. A systematic discrepancy is seen between the numerical and experimental results, mainly during the first phase of the gravity current evolution. This discrepancy is attributed to the limits of the mathematical formulation, in particular, the neglect of entrainment in the mathematical model. An interesting result arises from the influence of the bottom surface roughness; it both reduces the front velocity during the second phase of motion and attenuates the differences between the experimental and numerical front velocities during the first phase of motion.
Atomistic study of temperature dependence of interaction between screw dislocation and nanosized bcc Cu precipitate in bcc Fe
Authors: Shim Jae-Hyeok , Kim Dong-Ik , Jung Woo-Sang , Cho Young Whan , Hong Kyung Tae , Wirth Brian D.
Published: October 2008

Molecular dynamics simulations of the interaction between a screw dislocation and a 3.5 nm diameter bcc Cu precipitate in bcc Fe have been performed in the twinning and antitwinning direction between 10 and 400 K. The results indicate a significant temperature dependence in the antitwinning direction, whereby the screw dislocation bypasses the Cu precipitate by Orowan looping below 200 K, but shears the precipitate above 300 K. The transition in interaction mechanism is caused by a screw dislocation assisted martensitic transformation of the Cu precipitate, which significantly diminishes above 300 K. The screw dislocation shears the precipitate at all temperatures between 10 and 400 K in the twinning direction. Thus, transformation of the precipitate induces additional precipitate strengthening below 200 K in the antitwinning direction, which drastically decreases with increasing temperature above 300 K.
Phase and photoelectrochemical behavior of solution-processed Fe2O3 nanocrystals for oxidation of water under solar light
Authors: Borse Pramod H. , Jun Hwichan , Choi Sun Hee , Hong Suk Joon , Lee Jae Sung
Published: October 2008

Monodispersed iron-oxide nanocrystals of controlled sizes (5–16nm) were prepared by the thermal decomposition of iron-oleate complex to fabricate photoanode films for photoelectrochemical oxidation of water under simulated solar light. The smallest 5nm particles were made mostly of γ-Fe2O3, but other sizes showed mixed phases with Fe3O4, whose fraction increased with size. Size-dependent photoanodic currents were also observed, showing maximum photocurrent density for 12nm particles. The high photocurrents were attributed to the lowered electron-hole recombination rates for the nanocrystals with the sizes comparable to the hole diffusion length.
Quasi-transverse electromagnetic modes supported by a graphene parallel-plate waveguide
Authors: Hanson George W.
Published: October 2008

A model is developed for a parallel-plate waveguide formed by graphene. The graphene is represented by an infinitesimally thin, local two-sided surface characterized by a surface conductivity obtained from the Kubo formula. Maxwell’s equations are solved for the model fields guided by the graphene layers. It is shown that despite the extreme thinness of its walls, a graphene parallel-plate waveguide can guide quasi-transverse electromagnetic modes with attenuation similar to structures composed of metals, while providing some control over propagation characteristics via the charge density or chemical potential. Given the interest in developing graphene electronics, such waveguides may be of interest in future applications.
Electrical instability in vanadyl-phthalocyanine thin-film transistors
Authors: Wang Lijuan , Liu Guojun , Zhu Feng , Pan Feng , Yan Donghang
Published: October 2008

We investigated the electrical instability of vanadyl-phthalocyanine (VOPc) thin-film transistors (TFTs) at various temperatures. The results demonstrate a slow threshold voltage shift in the bias stress process and a rapid recovery after the removal of bias stress, which indicates that a slower degradation process occurs in the on state while a faster removal in the off state of VOPc TFTs. The shift of threshold voltage comes from traps generated at the organic/dielectrics interface. Additionally, a relaxation time of 107 s was obtained at room temperature according to the stretched exponential model, which is comparable to a-Si:H TFTs. Therefore, VOPc TFTs are suitable to be applied in flat panel displays.
Reversal of cocaine addiction by environmental enrichment
Authors: Solinas Marcello , Chauvet Claudia , Thiriet Nathalie , El Rawas Rana , Jaber Mohamed
Published: October 2008

Environmental conditions can dramatically influence the behavioral and neurochemical effects of drugs of abuse. For example, stress increases the reinforcing effects of drugs and plays an important role in determining the vulnerability to develop drug addiction. On the other hand, positive conditions, such as environmental enrichment, can reduce the reinforcing effects of psychostimulants and may provide protection against the development of drug addiction. However, whether environmental enrichment can be used to “treat” drug addiction has not been investigated. In this study, we first exposed mice to drugs and induced addiction-related behaviors and only afterward exposed them to enriched environments. We found that 30 days of environmental enrichment completely eliminates behavioral sensitization and conditioned place preference to cocaine. In addition, housing mice in enriched environments after the development of conditioned place preference prevents cocaine-induced reinstatement of conditioned place preference and reduces activation of the brain circuitry involved in cocaine-induced reinstatement. Altogether, these results demonstrate that environmental enrichment can eliminate already established addiction-related behaviors in mice and suggest that environmental stimulation may be a fundamental factor in facilitating abstinence and preventing relapse to cocaine addiction.
A double dissociation revealing bidirectional competition between striatum and hippocampus during learning
Authors: Lee Anni S. , Duman Ronald S. , Pittenger Christopher
Published: October 2008

The multiple memory systems framework proposes that distinct circuits process and store different sorts of information; for example, spatial information is processed by a circuit that includes the hippocampus, whereas certain forms of instrumental conditioning depend on the striatum. Disruption of hippocampal function can enhance striatum-dependent learning in some paradigms, which has been interpreted as evidence that these systems can compete with one another in an intact animal. However, it remains unclear whether such competition can occur in the opposite direction, as suggested by the multiple memory systems framework, or is unidirectional. We addressed this question using lesions and genetic manipulations in mice. Impairment of dorsal striatal function with either excitotoxic lesions or transgenic inhibition of the transcription factor cAMP response element-binding protein, which disrupts striatal synaptic plasticity, impaired striatum-dependent cued learning but enhanced hippocampus-dependent spatial learning. Conversely, excitotoxic lesions of the dorsal hippocampus disrupted spatial learning and enhanced cued learning. This double dissociation demonstrates bidirectional competition that constitutes strong evidence for the parallel operation of distinct memory systems.
Urea denaturation by stronger dispersion interactions with proteins than water implies a 2-stage unfolding
Authors: Hua Lan , Zhou Ruhong , Thirumalai D. , Berne B. J.
Published: October 2008

The mechanism of denaturation of proteins by urea is explored by using all-atom microseconds molecular dynamics simulations of hen lysozyme generated on BlueGene/L. Accumulation of urea around lysozyme shows that water molecules are expelled from the first hydration shell of the protein. We observe a 2-stage penetration of the protein, with urea penetrating the hydrophobic core before water, forming a “dry globule.” The direct dispersion interaction between urea and the protein backbone and side chains is stronger than for water, which gives rise to the intrusion of urea into the protein interior and to urea's preferential binding to all regions of the protein. This is augmented by preferential hydrogen bond formation between the urea carbonyl and the backbone amides that contributes to the breaking of intrabackbone hydrogen bonds. Our study supports the “direct interaction mechanism” whereby urea has a stronger dispersion interaction with protein than water.
Distinct populations of tumor-initiating cells derived from a tumor generated by rat mammary cancer stem cells
Authors: Zucchi I. , Astigiano S. , Bertalot G. , Sanzone S. , Cocola C. , Pelucchi P. , Bertoli G. , Stehling M. , Barbieri O. , Albertini A. , Schöler H. R. , Neel B. G. , Reinbold R. A. , Dulbecco R.
Published: October 2008

Tumors derived from rat LA7 cancer stem cells (CSCs) contain a hierarchy of cells with different capacities to generate self-renewing spheres and tubules serially
ex vivo
and to evoke tumors
in vivo
. We isolated two morphologically distinct cell types with distinct tumorigenic potential from LA7-evoked tumors: cells with polygonal morphology that are characterized by expression of p21/
WAF1
and p63 and display hallmarks of CSCs and elongated epithelial cells, which generate tumors with far less heterogeneity than LA7 CSCs. Serial transplantation of elongated epithelial cells results in progressive loss of tumorigenic potential; tumor heterogeneity; CD44, E-cadherin, and epithelial cytokeratin expression and increased α-smooth muscle actin I and vimentin expression. In contrast, serial transplantation of LA7 CSCs can be performed indefinitely and results in tumors that maintain their heterogeneity, consistent with self-renewal and multilineage differentiation potential. Collectively, our data show that polygonal cells are CSCs, whereas epithelial elongated cells are lineage-committed progenitors with tumorigenic potential, and suggest that tumor progenitors, although lacking indefinite self-renewal potential, nevertheless may make a substantial contribution to tumor development. Because LA7 cells can switch between conditions that favor maintenance of pure CSCs vs. differentiation into other tumor cell types, this cell system provides the opportunity to study factors that influence CSC self-renewal and differentiation. One factor,
p63
, was identified as a key gene regulating the transition between CSCs and early progenitor cells.
The tumor suppressor activity of IKKα in stratified epithelia is exerted in part via the TGF-β antiproliferative pathway
Authors: Marinari Barbara , Moretti Francesca , Botti Elisabetta , Giustizieri Maria Laura , Descargues Pascal , Giunta Alessandro , Stolfi Carmine , Ballaro Costanza , Papoutsaki Marina , Alemà Stefano , Monteleone Giovanni , Chimenti Sergio , Karin Michael , Costanzo Antonio
Published: October 2008

The transforming growth factor type β-1 (TGF-β) signaling pathway is a major tumor suppressor during early carcinogenesis, and its growth-suppressive activity is commonly lost during early tumor progression. IκB kinase α (IKKα) also acts as a tumor suppressor in stratified epithelia, and its expression and nuclear localization are progressively down-regulated during malignant progression of squamous cell carcinoma (SCC) and acquisition of an invasive phenotype. A critical role for IKKα in TGF-β signaling in stratified epithelia was identified recently during normal keratinocyte differentiation, and both IKKα and components of the TGF-β signaling pathway are required for induction of antiproliferative Myc antagonists in such cells. We now describe that the interaction between IKKα and the TGF-β signaling pathway is also important in a subset of SCCs. In SCCs that are unable to shuttle IKKα to the nucleus, defective TGF-β-induced growth arrest was rescued by introduction of a constitutively nuclear IKKα variant. These results suggest that the tumor-suppressive activity of IKKα in stratified epithelia may be exerted in part via the TGF-β signaling pathway.
Short stature, smoking habits and birth outcome in international adoptees in Sweden
Authors: EKÉUS CECILIA , LINDBLAD FRANK , HJERN ANDERS
Published: October 2008

Objective. To investigate short stature and smoking habits as risk factors for birth outcome in international adoptees in comparison with non‐adopted mothers. Design. Prospective cohort study. Setting. Nationwide study in Sweden. Population. Two study groups were identified from mothers who were born 1968–1979 and gave birth during 1982–2001 – 3,610 mother‐child dyads with a mother adopted from a non‐European country and 336,992 mother‐child dyads with a mother born in Sweden. Method. Register study. Outcome measures. Pre‐eclampsia, instrumental delivery, preterm delivery, small for gestational age (SGA), Apgar score, cephalhematoma and perinatal mortality and birth weight. Results. Short stature and smoking were more common in international adoptees compared with non‐adopted, odds ratios (ORs) 29.07 (95% C.I.: 25.29–33.42) and 1.39 (1.27–1.52), respectively. International adoptees had a slightly increased risk for instrumental delivery (OR: 1.42; 1.32–1.54) and preterm delivery (<37 weeks) (OR: 1.39; 1.24–1.56) and there was a slightly increased risk for SGA (OR: 1.24; 1.01–1.52) in their offspring. However, when we adjusted for maternal height, preterm delivery was the only outcome that remained statistically significant. Adjustment for smoking habits had marginal effects on all outcomes. Conclusion. The short stature of international adoptees increased their risk for delivery and birth complications in a predictable manner, but otherwise outcomes were very similar to the general population. No special obstetric monitoring is indicated by adoption status in itself.
Sonic Hedgehog signaling impairs ionizing radiation–induced checkpoint activation and induces genomic instability
Authors: Leonard Jennifer M. , Ye Hong , Wetmore Cynthia , Karnitz Larry M.
Published: October 2008

The Sonic Hedgehog (Shh) pathway plays important roles in embryogenesis, stem cell maintenance, tissue repair, and tumorigenesis. Haploinsufficiency of Patched-1, a gene that encodes a repressor of the Shh pathway, dysregulates the Shh pathway and increases genomic instability and the development of spontaneous and ionizing radiation (IR)–induced tumors by an unknown mechanism. Here we show that Ptc1+/− mice have a defect in the IR-induced activation of the ATR–Chk1 checkpoint signaling pathway. Likewise, transient expression of Gli1, a downstream target of Shh signaling, disrupts Chk1 activation in human cells by preventing the interaction of Chk1 with Claspin, a Chk1 adaptor protein that is required for Chk1 activation. These results suggest that inappropriate Shh pathway activation promotes tumorigenesis by disabling a key signaling pathway that helps maintain genomic stability and inhibits tumorigenesis.
Segregation and activation of myosin IIB creates a rear in migrating cells
Authors: Vicente-Manzanares Miguel , Koach Margaret A. , Whitmore Leanna , Lamers Marcelo L. , Horwitz Alan F.
Published: October 2008

We have found that MLC-dependent activation of myosin IIB in migrating cells is required to form an extended rear, which coincides with increased directional migration. Activated myosin IIB localizes prominently at the cell rear and produces large, stable actin filament bundles and adhesions, which locally inhibit protrusion and define the morphology of the tail. Myosin IIA forms de novo filaments away from the myosin IIB–enriched center and back to form regions that support protrusion. The positioning and dynamics of myosin IIA and IIB depend on the self-assembly regions in their coiled-coil C terminus. COS7 and B16 melanoma cells lack myosin IIA and IIB, respectively; and show isoform-specific front-back polarity in migrating cells. These studies demonstrate the role of MLC activation and myosin isoforms in creating a cell rear, the segregation of isoforms during filament assembly and their differential effects on adhesion and protrusion, and a key role for the noncontractile region of the isoforms in determining their localization and function.
Familial pulmonary alveolar proteinosis caused by mutations in CSF2RA
Authors: Suzuki Takuji , Sakagami Takuro , Rubin Bruce K. , Nogee Lawrence M. , Wood Robert E. , Zimmerman Sarah L. , Smolarek Teresa , Dishop Megan K. , Wert Susan E. , Whitsett Jeffrey A. , Grabowski Gregory , Carey Brenna C. , Stevens Carrie , van der Loo Johannes C.M. , Trapnell Bruce C.
Published: October 2008

Primary pulmonary alveolar proteinosis (PAP) is a rare syndrome characterized by accumulation of surfactant in the lungs that is presumed to be mediated by disruption of granulocyte/macrophage colony-stimulating factor (GM-CSF) signaling based on studies in genetically modified mice. The effects of GM-CSF are mediated by heterologous receptors composed of GM-CSF binding (GM-CSF-Rα) and nonbinding affinity-enhancing (GM-CSF-Rβ) subunits. We describe PAP, failure to thrive, and increased GM-CSF levels in two sisters aged 6 and 8 yr with abnormalities of both GM-CSF-Rα–encoding alleles (CSF2RA). One was a 1.6-Mb deletion in the pseudoautosomal region of one maternal X chromosome encompassing CSF2RA. The other, a point mutation in the paternal X chromosome allele encoding a G174R substitution, altered an N-linked glycosylation site within the cytokine binding domain and glycosylation of GM-CSF-Rα, severely reducing GM-CSF binding, receptor signaling, and GM-CSF–dependent functions in primary myeloid cells. Transfection of cloned cDNAs faithfully reproduced the signaling defect at physiological GM-CSF concentrations. Interestingly, at high GM-CSF concentrations similar to those observed in the index patient, signaling was partially rescued, thereby providing a molecular explanation for the slow progression of disease in these children. These results establish that GM-CSF signaling is critical for surfactant homeostasis in humans and demonstrate that mutations in CSF2RA cause familial PAP.