bluuebunny/crossref_metadata_2025 huggingface dataset:
Interactions between urban water policy, residential irrigation, and plant & bird diversity in the Fresno-Clovis Metro Area
Authors: Özgöc-Çağlar Derya , Katti Madhusudan , Reid Seth , Schleder Bradley , Bushoven John , Jones Andrew , Delcore Henry
Published: August 2011

Background/Question/Methods:

Ecological theory has begun to incorporate humans as part of coupled socio-ecological systems. Modern urban development provides an excellent laboratory to examine the interplay among socio-ecological relationships. Urban land and water management decisions result from dynamic interactions between institutional, individual and ecological factors. Landscaping and irrigation at any particular residence, for example, is a product of geography, hydrology, soil, and other local environmental conditions, the homeowners’ cultural preferences, socioeconomic status, identity construction, neighborhood dynamics, as well as zoning laws, market conditions, city policies, and county/state/federal government regulations. Since land and water management are key determinants of habitat for other species, urban biodiversity is strongly driven by the outcome of interactions between these variables. This study addresses the significance of water as a key variable in the Fresno-Clovis Metropolitan Area (FCMA), shaping current patterns of landscape and water use, at a time when the city of Fresno is installing meters as a regulatory tool to conserve water. We combine data from a citizen science bird monitoring project, field surveys of trees, and mail surveys of residents to address interactions among key components of the urban socioecological system.

Results/Conclusions:

We present results of multivariate analyses of bird and tree surveys to show that neighborhood income and irrigation levels interact to influence species diversity of both taxa. Data from the Fresno Bird Count found that bird species richness and functional group diversity are both strongly correlated with residential irrigation and neighborhood income levels. Tree species diversity shows a similar pattern. We examine these results to test and develop several theoretical models explaining outdoor water use behaviors, with the aim of assessing the resilience of such behaviors with the introduction of water metering in Fresno, and the resilience of urban plant and bird communities to resulting changes in water use in the landscape. We argue that socioeconomic status results from a complex interplay of cultural, economic, structural, and social-psychological factors, influencing institutional policies regarding the governance of water resources, and in turn impacts biodiversity within the urban landscape through spatial and temporal variations in water usage. This study is part of a long-term research project that examines the impacts of human water usage and water use policies on biodiversity within an urban environment.
ONS Open Melting Point Collection
Authors: Bradley Jean-Claude , Lang Andrew , Williams Antony , Curtin Evan
Published: August 2011

This book represents a PDF version of Dataset ONSMP029 (2706 unique compounds, 7413 measurements) from a project to collect and curate melting points made available as Open Data. This particular collection was selected from the application of a threshold to favor the likelihood of reliability. Specifically, the entire range of averaged values for a data point was set to 0.01 C to 5 C, with at least two different measurements within this range. Measurements were pooled and processed from the following sources: Alfa Aesar, MDPI, Bergstrom, PhysProp, DrugBank, Bell, Oxford MSDS, Hughes, Griffiths and the Chemical Information Validation Spreadsheet. Links to all the information sources and web services are available from the Open Melting Point Resource page: http://onswebservices.wikispaces.com/meltingpoint
Association of Variations in TPH1 and HTR2B with Gestational Weight Gain and Measures of Obesity
Authors: Kwak Soo Heon , Park Byoung Lae , Kim Hail , German Michael S. , Go Min Jin , Jung Hye Seung , Koo Bo Kyong , Cho Young Min , Choi Sung Hee , Cho Yoon Shin , Shin Hyoung Doo , Jang Hak C. , Park Kyong Soo
Published: August 2011

Serotonin is involved in appetite regulation and energy homeostasis. Recently, it has been reported that 5‐hydroxytryptamine receptor 2B (Htr2b) and tryptophan hydroxylase 1 (Tph1) play major role in β‐cell proliferation in mouse during pregnancy. We investigated the genetic association of HTR2B and TPH1 with risk of gestational diabetes mellitus (GDM) and measures of obesity, in 869 Korean GDM women and carefully selected 632 nondiabetic control subjects. Six single‐nucleotide polymorphisms (SNPs) in HTR2B and ten SNPs in TPH1 were selected for genotyping according to their tagging status. Genetic variants in HTR2B and TPH1 were not associated with the risk of GDM. In GDM women, SNPs of TPH1 were significantly associated with weight gain during pregnancy. In nondiabetic controls, SNPs of TPH1 were associated with waist circumference and BMI. We also found that a variant of TPH1 (rs623580) was associated with BMI in a genome‐wide association study comprised of 8,842 subjects. Although genetic variants in HTR2B and TPH1 were not associated with risk of GDM, we found significant association of these variants with measures of obesity. However, further replication studies in a different population are required to confirm our findings.
Large Size Cells in the Visceral Adipose Depot Predict Insulin Resistance in the Canine Model
Authors: Kabir Morvarid , Stefanovski Darko , Hsu Isabel R. , Iyer Malini , Woolcott Orison O. , Zheng Dan , Catalano Karyn J. , Chiu Jenny D. , Kim Stella P. , Harrison Lisa N. , Ionut Viorica , Lottati Maya , Bergman Richard N. , Richey Joyce M.
Published: August 2011

Adipocyte size plays a key role in the development of insulin resistance. We examined longitudinal changes in adipocyte size and distribution in visceral (VIS) and subcutaneous (SQ) fat during obesity‐induced insulin resistance and after treatment with CB‐1 receptor antagonist, rimonabant (RIM) in canines. We also examined whether adipocyte size and/or distribution is predictive of insulin resistance. Adipocyte morphology was assessed by direct microscopy and analysis of digital images in previously studied animals 6 weeks after high‐fat diet (HFD) and 16 weeks of HFD + placebo (PL; n = 8) or HFD + RIM (1.25 mg/kg/day; n = 11). At 6 weeks, mean adipocyte diameter increased in both depots with a bimodal pattern only in VIS. Sixteen weeks of HFD+PL resulted in four normally distributed cell populations in VIS and a bimodal pattern in SQ. Multilevel mixed‐effects linear regression with random‐effects model of repeated measures showed that size combined with share of adipocytes >75 µm in VIS only was related to hepatic insulin resistance. VIS adipocytes >75 µm were predictive of whole body and hepatic insulin resistance. In contrast, there was no predictive power of SQ adipocytes >75 µm regarding insulin resistance. RIM prevented the formation of large cells, normalizing to pre‐fat status in both depots. The appearance of hypertrophic adipocytes in VIS is a critical predictor of insulin resistance, supporting the deleterious effects of increased VIS adiposity in the pathogenesis of insulin resistance.
Overexpression of a cytosolic pyrophosphatase (TgPPase) reveals a regulatory role of PPi in glycolysis for Toxoplasma gondii
Authors: Pace Douglas A. , Fang Jianmin , Cintron Roxana , Docampo Melissa D. , Moreno Silvia N. J.
Published: August 2011

PPi is a critical element of cellular metabolism as both an energy donor and as an allosteric regulator of several metabolic pathways. The apicomplexan parasite Toxoplasma gondii uses PPi in place of ATP as an energy donor in at least two reactions: the glycolytic PPi-dependent PFK (phosphofructokinase) and V-H+-PPase [vacuolar H+-translocating PPase (pyrophosphatase)]. In the present study, we report the cloning, expression and characterization of cytosolic TgPPase (T. gondii soluble PPase). Amino acid sequence alignment and phylogenetic analysis indicates that the gene encodes a family I soluble PPase. Overexpression of the enzyme in extracellular tachyzoites led to a 6-fold decrease in the cytosolic concentration of PPi relative to wild-type strain RH tachyzoites. Unexpectedly, this subsequent reduction in PPi was associated with a higher glycolytic flux in the overexpressing mutants, as evidenced by higher rates of proton and lactate extrusion. In addition to elevated glycolytic flux, TgPPase-overexpressing tachyzoites also possessed higher ATP concentrations relative to wild-type RH parasites. These results implicate PPi as having a significant regulatory role in glycolysis and, potentially, other downstream processes that regulate growth and cell division.
Full wave effects on the lower hybrid wave spectrum and driven current profile in tokamak plasmas
Authors: Shiraiwa S. , Ko J. , Meneghini O. , Parker R. , Schmidt A. E. , Scott S. , Greenwald M. , Hubbard A. E. , Hughes J. , Ma Y. , Podpaly Y. , Rice J. E. , Wallace G. , Wilson J. R. , Wolfe S. M. , C-Mod Group Alcator
Published: August 2011

A numerical modeling of current profile modification by lower hybrid current drive (LHCD) using a fullwave/Fokker-Planck simulation code is presented. A MHD stable LHCD discharge on Alcator C-Mod was analyzed, and the current profile from full wave simulations was found to show better agreement with the experiment than a ray-tracing code. Comparison of full wave and ray-tracing simulation shows that, although ray-tracing can reproduce the stochastic wave spectrum broadening, the full wave calculation predicts even wider spectrum broadening, and the wave spectrum fills all of the kinematically allowed domain. This is the first demonstration of LHCD current profile modeling using a full wave simulation code in a multi-pass absorption regime, showing the clear impact of full wave effects on the LHCD driven current profile.
Rheo–small-angle neutron scattering at the National Institute of Standards and Technology Center for Neutron Research
Authors: Porcar L. , Pozzo D. , Langenbucher G. , Moyer J. , Butler P. D.
Published: August 2011

We describe the design and operation of a modified commercial rheometer to simultaneously perform rheological measurements and structural studies by small angle neutron scattering (SANS). The apparatus uses a Couette geometry shear cell allowing two of the three scattering planes to be observed by performing experiments in either the radial or tangential geometries. The device enables small angle neutron scattering patterns to be obtained simultaneously with a wide variety of rheological measurements such as stress/strain flow curves, oscillatory deformations, and creep, recovery and relaxation tests, from −20 °C to 150 °C, for samples with viscosities varying by several orders of magnitude. We give a brief report of recent experiments performed on a dispersion of acicular nanoparticles and biopolymer network under stress demonstrating the utility of such measurements. This device has been developed at the National Institute of Standards and Technology's Center for Neutron Research (NCNR) and made available to the complex fluids community as part of the standard sample environment equipment.
Low frequency noise due to magnetic inhomogeneities in submicron FeCoB/MgO/FeCoB magnetic tunnel junctions
Authors: Herranz D. , Gomez-Ibarlucea A. , Schäfers M. , Lara A. , Reiss G. , Aliev F. G.
Published: August 2011

We report on room temperature low frequency noise due to magnetic inhomogeneities/domain walls (MI/DWs) in elliptic submicron FeCoB/MgO/FeCoB magnetic tunnel junctions with an area between 0.0245 and 0.0675 μm2. In the smaller area junctions we found an unexpected random telegraph noise (RTN1), deeply in the parallel state, possibly due to stray field induced MI/DWs in the hard layer. The second noise source (RTN2) is observed in the antiparallel state for the largest junctions. Strong asymmetry of RTN2 and of related resistance steps with current indicate spin torque acting on the MI/DWs in the soft layer at current densities below 5 × 105 A/cm2.
Constitutive modeling of shock response of polytetrafluoroethylene
Authors: Resnyansky A. D. , Bourne N. K. , Millett J. C. F. , Brown E. N.
Published: August 2011

Polytetrafluoroethylene (PTFE) is a polymer with a simple atomic structure that shows complex behavior under pressure and demonstrates a highly variable metastable phase structure in shock waves with amorphous and crystalline components. In turn, the crystalline component has four known phases with the high-pressure transition of the crystalline domain from crystalline phase IV at ambient through phase II to III. At the same time, as has been recently studied using spectrometry, the crystalline region nucleates from the amorphous one with load. Stress and velocity shock-wave profiles acquired recently with embedded gauges demonstrate features that may be related to the impedance mismatch between the phase domains subjected to such transitions resulting in variations of mechanical and thermophysical characteristics. We consider the inter-phase non-equilibrium and the amorphous-to-crystalline and inter-crystalline transitions that are associated with the high pressure and temperature transformations under shock wave loading as possible candidates for the analysis. The present work utilizes a multi-phase constitutive model that considers strength effects to describe the observed response under shock loading of the PTFE material. Experimental plate impact shock-wave histories are compared with calculated profiles using kinetics describing the transitions. The study demonstrates that the inter-phase pressure non-equilibrium of the state parameters plays the key role in the delay of the shock wave attenuation. At the same time, the forward transition associated with the crystallization might be responsible for the velocity spike in the experimental velocity profiles at high impact velocity and the modulus variation at low impact velocity. On the other hand, an accelerated attenuation of the velocity in the rarefaction wave is associated with another transition resulting in the residual crystallinity change during unloading.
Barrier height dependence of Fano factor and 1/f noise effect on InGaP based Schottky barrier diode
Authors: Mangal Sutanu , Ghelfi P. , Bogoni A. , Banerji P.
Published: August 2011

We report a study on flicker noise reduction in the space charge limitation region of a Zn-Pd/n-In0.49Ga0.51P Schottky barrier diode (SBD). A suitable model has been suggested to explain the barrier height dependence of the Fano factor. The reduction of Fano factor with barrier height has been experimentally investigated from I-V characteristics and noise power density measurements. Finally a comparative study was made with the theoretically obtained value of the Fano factor. Another important parameter, known as the Hooge parameter, of InGaP SBD has also been calculated as a function of temperature.
Oxygen diffusion in c-axis oriented Y1Ba2Cu3O7−δ thin films
Authors: Mori Zon , Doi Toshiya , Hakuraku Yoshinori
Published: August 2011

Optimizing oxygen content is one of the most essential factors with practical ramifications for the production of Y1Ba2Cu3O7–δ (YBCO) superconductors. In this study, oxygen diffusion was studied using homogeneous c-axis oriented YBCO thin films prepared via the pulsed laser deposition method. The oxygen diffusion process was examined by applying the one-dimensional diffusion model. The diffusion coefficient of oxygen and the activation energy were determined. This will facilitate the optimization of oxygenation in the production of thin films for YBCO superconductors.
Relations between light emission and electron density and temperature fluctuations in a helium plasma
Authors: Ma Shuiliang , Howard John , Thapar Nandika
Published: August 2011

The relations between three atomic lines, He I 667.8 nm (31D → 21P), 706.5 nm (33S → 23P), and 728.1 nm (31S → 21P), and the underlying fluctuations in a helium plasma are investigated for the quantitative interpretation of optical observations in plasma fluctuation measurements. Frequency dependent fluctuation amplitude ratios and phase delays between the line emission fluctuation and the electron density and temperature fluctuations are calculated based on a quasi-static collisional-radiative model and a linear approximation technique. For frequencies up to the upper limit of practical interest (<1 MHz), the fluctuation amplitude ratios and phase delays are similar to those directly evaluated by the quasi-static model. It is found that the difference between the results from the linear approximation technique and from the quasi-static model is due to the absence of metastable fluctuations. Contributions of the 21S and 23S metastable fluctuations to the three helium line emission fluctuations are analyzed. The linearity between fluctuations in the line emission and in the electron density and temperature is valid for fluctuation levels higher than 10%.
Conservation equations and calculation of mean flows in gyrokinetics
Authors: Abiteboul J. , Garbet X. , Grandgirard V. , Allfrey S. J. , Ghendrih Ph. , Latu G. , Sarazin Y. , Strugarek A.
Published: August 2011

Conservation equations are derived for the gyrocenter toroidal momentum density and the polarization field. These equations are derived from the gyrokinetic model as it is implemented in simulation codes. In view of predicting the toroidal rotation in future fusion devices such as ITER, where external momentum input will be small, accurate simulations of momentum transport are crucial. The evolution equation for gyrocenter toroidal momentum density involves the divergence of the off-diagonal components of the Reynolds and generalized Maxwell stress, while the source term is the radial current of gyrocenters. The time evolution of the polarization field is the opposite of the gyrocenter current. Hence, an evolution equation for the total momentum density, i.e., the sum of gyrocenter and polarization field toroidal momentum density can be written. The force balance equation and the toroidal momentum conservation equations have been numerically tested with the gysela code. They are satisfied with a high level of accuracy.
Atomistic study of nanotwins in NiTi shape memory alloys
Authors: Zhong Yuan , Gall Ken , Zhu Ting
Published: August 2011

Atomistic simulations are performed to study the structure and geometrical limit of nanoscale twins in NiTi shape memory alloys. We analyze compound twins as narrow as ∼1 nm, involving a few atomic layers. A novel nanotwinned structure is found, forming through the martensitic transformation of sublattices. We predict the temperatures of phase transformation, which are consistent with experimental measurements. The results provide an atomistic basis for further study of nanometer length scale effects on the martensitic phase transformation and shape memory behavior.
Heat operator with pure soliton potential: Properties of Jost and dual Jost solutions
Authors: Boiti M. , Pempinelli F. , Pogrebkov A. K.
Published: August 2011

Properties of Jost and dual Jost solutions of the heat equation, Φ(x, k) and Ψ(x, k), in the case of a pure solitonic potential are studied in detail. We describe their analytical properties on the spectral parameter k and their asymptotic behavior on the x-plane and we show that the values of e−qxΦ(x, k) and the residues of eqxΨ(x, k) at special discrete values of k are bounded functions of x in a polygonal region of the q-plane. Correspondingly, we deduce that the extended version L(q) of the heat operator with a pure solitonic potential has left and right annihilators for q belonging to these polygonal regions.
Modeling the first stages of Cu precipitation in α-Fe using a hybrid atomistic kinetic Monte Carlo approach
Authors: Castin N. , Pascuet M. I. , Malerba L.
Published: August 2011

We simulate the coherent stage of Cu precipitation in α-Fe with an atomistic kinetic Monte Carlo (AKMC) model. The vacancy migration energy as a function of the local chemical environment is provided on-the-fly by a neural network, trained with high precision on values calculated with the nudged elastic band method, using a suitable interatomic potential. To speed up the simulation, however, we modify the standard AKMC algorithm by treating large Cu clusters as objects, similarly to object kinetic Monte Carlo approaches. Seamless matching between the fully atomistic and the coarse-grained approach is achieved again by using a neural network, that provides all stability and mobility parameters for large Cu clusters, after training on atomistically informed results. The resulting hybrid algorithm allows long thermal annealing experiments to be simulated, within a reasonable CPU time. The results obtained are in very good agreement with several series of experimental data available from the literature, spanning over different conditions of temperature and alloy composition. We deduce from these results and relevant parametric studies that the mobility of Cu clusters containing one vacancy plays a central role in the precipitation mechanism.
Dependence of fast-ion transport on the nature of the turbulence in the Large Plasma Device
Authors: Zhou Shu , Heidbrink W. W. , Boehmer H. , McWilliams R. , Carter T. A. , Vincena S. , Tripathi S. K. P.
Published: August 2011

Strong turbulent waves (δn/n ∼0.5, f ∼5-40 kHz) are observed in the upgraded Large Plasma Device [W. Gekelman, H. Pfister, Z. Lucky, J. Bamber, D. Leneman, and J. Maggs, Rev. Sci. Instrum. 62, 2875 (1991)] on density gradients produced by an annular obstacle. Energetic lithium ions (Efast/Ti≥300, ρfast/ρs~10) orbit through the turbulent region. Scans with a collimated analyzer and with probes give detailed profiles of the fast ion spatial distribution and of the fluctuating wave fields. The characteristics of the fluctuations are modified by changing the plasma species from helium to neon and by modifying the bias on the obstacle. Different spatial structure sizes (Ls) and correlation lengths (Lcorr) of the wave potential fields alter the fast ion transport. The effects of electrostatic fluctuations are reduced due to gyro-averaging, which explains the difference in the fast-ion transport. A transition from super-diffusive to sub-diffusive transport is observed when the fast ion interacts with the waves for most of a wave period, which agrees with theoretical predictions.
Cylindrical and spherical electron acoustic solitary waves with nonextensive hot electrons
Authors: Pakzad Hamid Reza
Published: August 2011

Nonlinear propagation of cylindrical and spherical electron-acoustic solitons in an unmagnetized plasma consisting cold electron fluid, hot electrons obeying a nonextensive distribution and stationary ions, are investigated. For this purpose, the standard reductive perturbation method is employed to derive the cylindrical/spherical Korteweg-de-Vries equation, which governs the dynamics of electron-acoustic solitons. The effects of nonplanar geometry and nonextensive hot electrons on the behavior of cylindrical and spherical electron acoustic solitons are also studied by numerical simulations.
Hybrid (particle in cell-fluid) simulation of ion-acoustic soliton generation including super-thermal and trapped electrons
Authors: Nopoush M. , Abbasi H.
Published: August 2011

The present paper is devoted to the simulation of the nonlinear disintegration of a localized perturbation into an ion-acoustic soliton in a plasma. Recently, this problem was studied by a simple model [H. Abbasi et al., Plasma Phys. Controlled Fusion 50, 095007 (2008)]. The main assumptions were (i) in the electron velocity distribution function (DF), the ion-acoustic soliton velocity was neglected in comparison to the electron thermal velocity, (ii) on the ion-acoustic evolution time-scale, the electron velocity DF was assumed to be stationary, and (iii) the calculation was restricted to the small amplitude case. In order to generalize the model, one has to consider the evolution of the electron velocity DF for finite amplitudes. For this purpose, a one dimensional electrostatic hybrid code, particle in cell (PIC)-fluid, was designed. It simulates the electrons dynamics by the PIC method and the cold ions dynamics by the fluid equations. The plasma contains a population of super-thermal electrons and, therefore, a Lorentzian (kappa) velocity DF is used to model the high energy tail in the electron velocity DF. Electron trapping is included in the simulation in view of their nonlinear resonant interaction with the localized perturbation. A Gaussian initial perturbation is used to model the localized perturbation. The influence of both the trapped and the super-thermal electrons on this process is studied and compared with the previous model.
Effect of electron spin-spin exchange interaction on spin precession in coupled quantum well
Authors: Ito Tetsu , Shichi Wataru , Ichida Masao , Gotoh Hideki , Kamada Hidehiko , Ando Hiroaki
Published: August 2011

Electron spin-spin interaction in an asymmetric coupled quantum well (CQW) was investigated through electron spin-precession measurements. Precession (Larmor) frequencies from electrons localized in two CQWs were measured by means of polarization- and time-resolved photoluminescence measurements under a high magnetic field. At a low excitation power density, the Larmor frequency of the CQW was same as that of a single quantum well. The Larmor frequency of electron spin in one well was shifted to that in the other well as the excitation power density was increased. These experimental results are quantitatively explained by an exchange interaction between electrons localized in the two wells.
Imploding and exploding shocks in negative ion degenerate plasmas
Authors: Hussain S. , Akhtar N.
Published: August 2011

Imploding and exploding shocks are studied in nonplanar geometries for negative ion degenerate plasma. Deformed Korteweg de Vries Burgers (DKdVB) equation is derived by using reductive perturbation method. Two level finite difference scheme is used for numerical analysis of DKdVB. It is observed that compressive and rarefactive shocks are observed depending on the value of quantum parameter. The effects of temperature, kinematic viscosity, mass ratio of negative to positive ions and quantum parameter on diverging and converging shocks are presented.
Diagnosis of the ion density in two discharge modes generated in atmospheric pressure argon with pin-to-plate dielectric barrier geometry
Authors: Qi Bing , Huang Jianjun , Qiu Yunming , Liu Ying , Liu Lijun
Published: August 2011

In this study, the ion densities of an ac dielectric barrier discharge (DBD) (that is, a pin-to-plate DBD) as a function of the applied frequency in argon have been studied by means of the plasma radiation. The pin-to-plate DBD shows the characteristic of radiation oscillations with a low-frequency wave hidden in a high-frequency wave to form a mosaic structure, which reveals the coexistence of two discharge modes in the ac barrier discharge, i.e., the streamer mode and the corona mode. According to the oscillation frequencies, the ion densities are calculated. The results show that the ion density in streamer discharge is higher than that in corona discharge for about 1–2 magnitude orders.
On the evolution of spherical gas interfaces accelerated by a planar shock wave
Authors: Zhai Zhigang , Si Ting , Luo Xisheng , Yang Jiming
Published: August 2011

The interaction of a planar shock wave with a spherical gas interface (SF6 or helium) surrounded by air is studied experimentally and numerically. By means of the high-speed schlieren photography with high time resolutions and the numerical method VAS2D, the detailed flow field structures including the evolution of interfaces and the development of wave patterns are obtained. The sequences of schlieren frames of SF6 show that the refracted shock wave converges inside the volume and causes the shock focusing within the bubble interface, resulting in an outward jet. The SF6 jet is different from the krypton jet studied because of the difference in their acoustic impedances. The pressure perturbation plays an important role in the jet formation. Quantitative data of the evolving interface length, height, and vortex spacing as well as the displacements of the interface and the jet are acquired and compared. The generation and distribution of vorticity are also analyzed numerically and are found to be the dominant factors for the interface deformation and the resulting turbulent mixing. Furthermore, the velocities of the interfaces and shock waves obtained from the x-t diagrams in the experimental and numerical photographs are compared with those predicted from one-dimensional gasdynamics. In this way, the air contaminations of both gases are re-evaluated and it is shown that the contamination by air inside the helium bubble is significant while it has just small influence in the SF6 case, which confirms the findings in literatures.
Control of spin configuration in half-metallic La0.7Sr0.3MnO3 nano-structures
Authors: Rhensius J. , Vaz C. A. F. , Bisig A. , Schweitzer S. , Heidler J. , Körner H. S. , Locatelli A. , Niño M. A. , Weigand M. , Méchin L. , Gaucher F. , Goering E. , Heyderman L. J. , Kläui M.
Published: August 2011

We investigate the interplay between the governing magnetic energy terms in patterned La0.7Sr0.3MnO3 (LSMO) elements by direct high-resolution x-ray magnetic microscopy as a function of temperature and geometrical parameters. We show that the magnetic configurations evolve from multidomain to flux-closure states (favored by the shape anisotropy) with decreasing element size, with a thickness-dependent crossover at the micrometer scale. The flux-closure states are stable against thermal excitations up to near the Curie temperature. Our results demonstrate control of the spin state in LSMO elements by judicious choice of the geometry, which is key for spintronics applications requiring high spin-polarizations and robust magnetic states.
Theory of plasmonic near-field enhanced absorption in solar cells
Authors: Lagos N. , Sigalas M. M. , Lidorikis E.
Published: August 2011

We derive analytical expressions for the absorption enhancement expected when dilute suspensions of small metallic nanoparticles are inserted inside an organic semiconductor. A comparison with accurate numerical simulations shows excellent agreement for a wide range of volume filling ratios and even in the case of mixing different types of metals. These results are invaluable tools in optimizing the absorption performance of plasmonic thin-film organic solar cells.
Quantifying cooperative intermolecular interactions for improved carbon dioxide capture materials
Authors: de Lange Katrina M. , Lane Joseph R.
Published: August 2011

We have optimized the geometry and calculated interaction energies for over 100 different complexes of CO2 with various combinations of electron accepting (Lewis acid) and electron donating (Lewis base) molecules. We have used the recently developed explicitly correlated coupled cluster singles doubles and perturbative triples [CCSD(T)-F12] methods and the associated VXZ-F12 (where X = D,T,Q) basis sets. We observe only modest changes in the geometric parameters of CO2 upon complexation, which suggests that the geometry of CO2 adsorbed in a nanoporous material should be similar to that of CO2 in gas phase. When CO2 forms a complex with two Lewis acids via the two electron rich terminal oxygen atoms, the interaction energy is less than twice what would be expected for the same complex involving a single Lewis acid. We consider a series of complexes that exhibit simultaneous CO2-Lewis acid and CO2-Lewis base intermolecular interactions, with total interaction energies spanning 14.1–105.9 kJ mol−1. For these cooperative complexes, we find that the total interaction energy is greater than the sum of the interaction energies of the constituent complexes. Furthermore, the intermolecular distances of the cooperative complexes are contracted as compared to the constituent complexes. We suggest that metal-organic-framework or similar nanoporous materials could be designed with adsorption sites specifically tailored for CO2 to allow cooperative intermolecular interactions, facilitating enhanced CO2 adsorption.
Quantum crossover in moderately damped epitaxial NbN/MgO/NbN junctions with low critical current density
Authors: Longobardi Luigi , Massarotti Davide , Rotoli Giacomo , Stornaiuolo Daniela , Papari Gianpaolo , Kawakami Akira , Piero Pepe Giovanni , Barone Antonio , Tafuri Francesco
Published: August 2011

High quality epitaxial NbN/MgO/NbN Josephson junctions have been realized with MgO barriers up to a thickness of d = 1 nm. The junction properties coherently scale with the size of barrier, and low critical current densities down to 3 A/cm2 have been achieved for larger barriers. In this limit, junctions exhibit macroscopic quantum phenomena for temperatures lower than 90 mK. Measurements and junction parameters support the notion of a possible use of these devices for multiphoton quantum experiments, taking advantage of the fast non equilibrium electron-phonon relaxation times of NbN.
Microfocus infrared ellipsometry characterization of air-exposed graphene flakes
Authors: Weber J. W. , Hinrichs K. , Gensch M. , van de Sanden M. C. M. , Oates T. W. H.
Published: August 2011

Graphene and ultrathin graphite flakes prepared by exfoliation were characterized by microfocus synchrotron infrared mapping ellipsometry. The dielectric function of graphene in a dry-air atmosphere is determined and compared to that of ultrathin graphite, bulk graphite, and gold. The imaginary part of graphene is revealed to be about an order of magnitude higher than that of graphite and comparable to that of gold. Comparing the conductivity to an optical model considering intraband transitions, we discuss the critical effects of environmental exposure, relevant for real-world applications.
Functional electroless gold Ohmic contacts in light emitting diodes
Authors: Chen P. Y. , Wong H. C. , Hu S. F. , Huang C. Y. , Liu R. S.
Published: August 2011

Conducting gold pads on light-emitting diodes chips are synthesized by electroless chemical deposition and exhibit no color difference, reliable ability of wire bonding, and high electrical conductivity. A plating electrolyte with a long life time and high stability is developed. The hardness of pads formed by electroless plating is three times softer than those formed by evaporation and the force gauge of the p- and n-pads yields of approximately 55 g. The mechanism of electroless gold plating is elucidated and the functions of chemical reagents are explained using the proposed model. The industrial application of electroless gold plating is feasible.
Effect of interparticle interactions and size dispersion in magnetic nanoparticle assemblies: A static and dynamic study
Authors: Sung Lee Ji , Tan Reasmey P. , Hua Wu Jun , Keun Kim Young
Published: August 2011

Interparticle interactions in magnetic nanoparticles are studied by dc and ac magnetization measurements. For non-interacting nanoparticles, while the anisotropy constant of the nanoparticles Keff = 1.6 × 105 erg/cm3 is accurately determined by fitting zero-field-cooled and field-cooled measurements, we show that Keff values deduced only from time relaxation measurements must require simultaneous adjustments of the complex susceptibility by taking into account the size distribution of nanoparticles. This leads to Keff = 1.7 × 105 erg/cm3 in agreement with dc measurements. For interacting nanoparticles, comparisons with theoretical models show that energies due to magnetic dipolar interactions can only be predicted for weak and moderate interactions.
Improving the spectral response of amorphous Se photodetectors using organic semiconductors
Authors: Campbell I. H.
Published: August 2011

We demonstrate a heterojunction amorphous Se (a-Se)/organic semiconductor photodetector that extends the long wavelength spectral response of pure a-Se devices from a cutoff of about 500 nm to 1000 nm. We show that a-Se/organic interfaces behave similarly to organic/organic interfaces in terms of energy level alignments and organic exciton dissociation. Due to the large ionization potential of a-Se (5.7 eV), organic materials with similarly large ionization potentials are required for hole injection into a-Se and possible avalanche multiplication.
Quantum molecular dynamic simulations of warm dense carbon monoxide
Authors: Zhang Yujuan , Wang Cong , Li Dafang , Zhang Ping
Published: August 2011

Using quantum molecular dynamic simulations, we have studied the thermophysical properties of warm dense carbon monoxide under extreme conditions. The principal Hugoniot pressure up to 286 GPa, which is derived from the equation of state, is calculated and compared with available experimental and theoretical data. The chemical decomposition of carbon monoxide has been predicted at 8 GPa by means of pair correlation function and the charge density distribution. Based on Kubo-Greenwood formula, the dc electrical conductivity and the optical reflectivity are determined, and the nonmetal-metal transition for shock compressed carbon monoxide is observed around 40 GPa.
Direct observation of surface plasmon far field for regular surface ripple formation by femtosecond laser pulse irradiation of gold nanostructures on silicon substrates
Authors: Obara Go , Tanaka Yuto , Nedyalkov Nikolay N. , Terakawa Mitsuhiro , Obara Minoru
Published: August 2011

We have directly observed the interference ripple pattern between surface plasmon far field by gold nanosphere and the incident laser on silicon substrate. We explained the ripple formation using three-dimensional finite-difference time-domain simulation method. Nanosphere is an origin for regular ripple formation due to Mie scattering. We present a new method to control the plasmonic far-field pattern using an arbitrary gold nanostructure on the silicon substrate. Previously, the formed ripples were not regular but wavy because they were formed incoherently through the self organization process originating from the random surface roughness. The ripple structure was well controlled coherently.
Competitive roles of elastic and magnetic interactions in twin boundary behaviors of magnetic shape memory alloys
Authors: Jin Yongmei M.
Published: August 2011

Domain microstructure evolutions under applied magnetic field in magnetic shape memory alloys are investigated by phase field micromagnetic microelastic modeling. The computer simulations reveal respective roles of elastic interaction, magnetic interaction, and their competition in the coupled magnetic and elastic domain processes. It is observed that different relative strengths of elastic interaction with respect to magnetic interaction lead to different domain evolution pathways and different twin boundary behaviors, including field-induced twin boundary displacement, deformation, and annihilation. Distinct twin boundary behaviors driven by magnetic field from that driven by mechanical stress are discussed.
On-a-chip surface plasmon tweezers
Authors: Wong H. M. K. , Righini M. , Gates J. C. , Smith P. G. R. , Pruneri V. , Quidant R.
Published: August 2011

We report on an integrated optical trapping platform operated by simple fiber coupling. The system consists of a dielectric channel optical waveguide decorated with an array of gold micro-pads. Through a suitable engineering of the waveguide mode, we achieve light coupling to the surface plasmon resonance of the gold pads that act as individual plasmonic traps. We demonstrate parallel trapping of both micrometer size polystyrene beads and yeast cells at predetermined locations on the chip with only 20 mW total incident laser power.
Communication: Iteration-free, weighted histogram analysis method in terms of intensive variables
Authors: Kim Jaegil , Keyes Thomas , Straub John E.
Published: August 2011

We present an iteration-free weighted histogram method in terms of intensive variables that directly determines the inverse statistical temperature, βS = ∂S/∂E, with S the microcanonical entropy. The method eliminates iterative evaluations of the partition functions intrinsic to the conventional approach and leads to a dramatic acceleration of the posterior analysis of combining statistically independent simulations with no loss in accuracy. The synergistic combination of the method with generalized ensemble weights provides insights into the nature of the underlying phase transitions via signatures in βS characteristic of finite size systems. The versatility and accuracy of the method is illustrated for the Ising and Potts models.
Collective plasmon modes in a compositionally asymmetric nanoparticle dimer
Authors: Chen Fuyi , Alemu Negash , Johnston Roy L.
Published: August 2011

The plasmon coupling phenomenon of heterodimers composed of silver, gold and copper nanoparticles of 60 nm in size and spherical in shape were studied theoretically within the scattered field formulation framework. In-phase dipole coupled σ-modes were observed for the Ag-Au and Ag-Cu heterodimers, and an antiphase dipole coupled π-mode was observed for the Ag-Au heterodimer. These observations agree well with the plasmon hybridization theory. However, quadrupole coupled modes dominate the high energy wavelength range from 357-443 nm in the scattering cross section of the D=60 nm Ag-Au and Ag-Cu heterodimer. We demonstrate for the first time that collective plasmon modes in a compositionally asymmetric nanoparticle dimer have to be predicted from the dipole-dipole approximation of plasmon hybridization theory together with the interband transition effect of the constitutive metals and the retardation effect of the nanoparticle size.
Resonant exciton-phonon coupling in ZnO nanorods at room temperature
Authors: Chakraborty Soumee , Dhara S. , Ravindran T. R. , Pal S. Sarkar , Kamruddin M. , Tyagi A. K.
Published: August 2011

Vibronic and optoelectronic properties, along with detailed studies of exciton-phonon coupling at room temperature (RT) for random and aligned ZnO nanorods are reported. Excitation energy dependent Raman studies are performed for detailed analysis of multi-phonon processes in the nanorods. We report here the origin of coupling between free exciton and its associated phonon replicas, including its higher order modes, in the photoluminescence spectra at RT. Resonance of excitonic electron and resonating first order zone center LO phonon, invoked strongly by Frolich interaction, are made responsible for the observed phenomenon.
Nucleotide pyrophosphatase employs a P-loop-like motif to enhance catalytic power and NDP/NTP discrimination
Authors: Pécsi Ildikó , Szabó Judit E. , Adams Scott D. , Simon István , Sellers James R. , Vértessy Beáta G. , Tóth Judit
Published: August 2011

We investigated the potential (d)NDP/(d)NTP discrimination mechanisms in nucleotide pyrophosphatases. Here, we report that dUTPase, an essential nucleotide pyrophosphatase, uses a C-terminal P-loop-like sequence in a unique mechanism for substrate discrimination and efficient hydrolysis. Our spectroscopy and transient kinetics results on human dUTPase mutants combined with previous structural studies indicate that (
i
) H-bond interactions between the γ-phosphate and the P-loop-like motif V promote the catalytically competent conformation of the reaction center at the α-phosphate group; (
ii
) these interactions accelerate the chemical step of the kinetic cycle and that (
iii
) hydrolysis occurs very slowly or not at all in the absence of the γ-phosphate—motif V interactions, i.e., in dUDP, dUDP.BeFx, or in the motif V-deleted mutant. The physiological role of dUTPase is to set cellular dUTP∶dTTP ratios and prevent injurious uracil incorporation into DNA. Based upon comparison with related pyrophosphate generating (d)NTPases, we propose that the unusual use of a P-loop-like motif enables dUTPases to achieve efficient catalysis of dUTP hydrolysis and efficient discrimination against dUDP at the same time. These specifics might have been advantageous on the appearance of uracil-DNA repair. The similarities and differences between dUTPase motif V and the P-loop (or Walker A sequence) commonly featured by ATP- and GTPases offer insight into functional adaptation to various nucleotide hydrolysis tasks.
Carbon debt of Conservation Reserve Program (CRP) grasslands converted to bioenergy production
Authors: Gelfand Ilya , Zenone Terenzio , Jasrotia Poonam , Chen Jiquan , Hamilton Stephen K. , Robertson G. Philip
Published: August 2011

Over 13 million ha of former cropland are enrolled in the US Conservation Reserve Program (CRP), providing well-recognized biodiversity, water quality, and carbon (C) sequestration benefits that could be lost on conversion back to agricultural production. Here we provide measurements of the greenhouse gas consequences of converting CRP land to continuous corn, corn–soybean, or perennial grass for biofuel production. No-till soybeans preceded the annual crops and created an initial carbon debt of 10.6 Mg CO
2
equivalents (CO
2
e)·ha
−1
that included agronomic inputs, changes in C stocks, altered N
2
O and CH
4
fluxes, and foregone C sequestration less a fossil fuel offset credit. Total debt, which includes future debt created by additional changes in soil C stocks and the loss of substantial future soil C sequestration, can be constrained to 68 Mg CO
2
e·ha
−1
if subsequent crops are under permanent no-till management. If tilled, however, total debt triples to 222 Mg CO
2
e·ha
−1
on account of further soil C loss. Projected C debt repayment periods under no-till management range from 29 to 40 y for corn–soybean and continuous corn, respectively. Under conventional tillage repayment periods are three times longer, from 89 to 123 y, respectively. Alternatively, the direct use of existing CRP grasslands for cellulosic feedstock production would avoid C debt entirely and provide modest climate change mitigation immediately. Incentives for permanent no till and especially permission to harvest CRP biomass for cellulosic biofuel would help to blunt the climate impact of future CRP conversion.
Catalysis by dihydrofolate reductase and other enzymes arises from electrostatic preorganization, not conformational motions
Authors: Adamczyk Andrew J. , Cao Jie , Kamerlin Shina C. L. , Warshel Arieh
Published: August 2011

The proposal that enzymatic catalysis is due to conformational fluctuations has been previously promoted by means of
indirect
considerations. However, recent works have focused on cases where the relevant motions have components toward distinct conformational regions, whose population could be manipulated by mutations. In particular, a recent work has claimed to provide
direct
experimental evidence for a dynamical contribution to catalysis in dihydrofolate reductase, where blocking a relevant conformational coordinate was related to the suppression of the motion toward the occluded conformation. The present work utilizes computer simulations to elucidate the true molecular basis for the experimentally observed effect. We start by reproducing the trend in the measured change in catalysis upon mutations (which was assumed to arise as a result of a “dynamical knockout” caused by the mutations). This analysis is performed by calculating the change in the corresponding activation barriers without the need to invoke dynamical effects. We then generate the catalytic landscape of the enzyme and demonstrate that motions in the conformational space do not help drive catalysis. We also discuss the role of flexibility and conformational dynamics in catalysis, once again demonstrating that their role is negligible and that the largest contribution to catalysis arises from electrostatic preorganization. Finally, we point out that the changes in the reaction potential surface modify the reorganization free energy (which includes entropic effects), and such changes in the surface also alter the corresponding motion. However, this motion is never the
reason
for catalysis, but rather simply a reflection of the shape of the reaction potential surface.