bluuebunny/crossref_metadata_2025 huggingface dataset:
Multimission empirical ocean tide modeling for shallow waters and polar seas
Authors: Cheng Yongcun , Andersen Ole Baltazar
Published: August 2011

A new global ocean tide model named DTU10 (developed at Technical University of Denmark) representing all major diurnal and semidiurnal tidal constituents is proposed based on an empirical correction to the global tide model FES2004 (Finite Element Solutions), with residual tides determined using the response method. The improvements are achieved by introducing 4 years of TOPEX–Jason 1 interleaved mission into existing 18 years (1993–2010) of primary joint TOPEX, Jason 1, and Jason 2 mission time series. Hereby the spatial distribution of observations are doubled and satellite altimetry should be able to recover twice the spatial variations of the tidal signal which is particularly important in shallow waters where the spatial scale of the tidal signal is scaled down. Outside the ±66° parallel combined Envisat, GEOSAT Follow‐On, and ERS‐2, data sets have been included to solve for the tides up to the ±82° parallel. A new approach to removing the annual sea level variations prior to estimating the residual tides significantly improved tidal determination of diurnal constituents from the Sun‐synchronous satellites (e.g., ERS‐2 and Envisat) in the polar seas. Extensive evaluations with six tide gauge sets show that the new tide model fits the tide gauge measurements favorably to other state of the art global ocean tide models in both the deep and shallow waters, especially in the Arctic Ocean and the Southern Ocean. One example is a comparison with 207 tide gauge data in the East Asian marginal seas where the root‐mean‐square agreement improved by 35.12%, 22.61%, 27.07%, and 22.65% (M2, S2, K1, and O1) for the DTU10 tide model compared with the FES2004 tide model. A similar comparison in the Arctic Ocean with 151 gauge data improved by 9.93%, 0.34%, 7.46%, and 9.52% for the M2, S2, K1, and O1 constituents, respectively.
Interactive response surface approaches using computationally intensive models for multiobjective planning of lake water quality remediation
Authors: Castelletti A. , Antenucci J. P. , Limosani D. , Quach Thi X. , Soncini‐Sessa R.
Published: August 2011

Recent work has demonstrated the utility of interactive response surfaces in integrating decision making and complex process‐based modeling of environmental systems. Specifically, we focus on problems that require computationally expensive dynamic models where a limited number of simulations are possible and so traditional meta‐modeling might be not an option for the optimization process. Within this constraint, the interactive global response surface method aims to develop a complete picture of how the system responds to a planning decision on the basis of a restricted number of simulations. The interactive local response surface method utilizes the current best alternative to determine improvements on the basis of relatively small changes in the current decision. We outline the use of both methods to a real example of remediation in a water supply reservoir, demonstrating the key advantages and disadvantages of each method and describe a new, interactive cascade approach that provides an improved solution to the problem.
CREB and ChREBP oppositely regulate SIRT1 expression in response to energy availability
Authors: Noriega Lilia G , Feige Jérôme N , Canto Carles , Yamamoto Hiroyasu , Yu Jiujiu , Herman Mark A , Mataki Chikage , Kahn Barbara B , Auwerx Johan
Published: August 2011

The nicotinamide adenine dinucleotide (NAD+)‐dependent deacetylase SIRT1 is a major metabolic regulator activated by energy stresses such as fasting or calorie restriction. SIRT1 activation during fasting not only relies on the increase in the NAD+/NADH ratio caused by energy deprivation but also involves an upregulation of SIRT1 mRNA and protein levels in various metabolic tissues. We demonstrate that SIRT1 expression is controlled systemically by the activation of the cyclic AMP response‐element‐binding protein upon low nutrient availability. Conversely, in the absence of energetic stress, the carbohydrate response‐element‐binding protein represses the expression of SIRT1. Altogether, these results demonstrate that SIRT1 expression is tightly controlled at the transcriptional level by nutrient availability and further underscore that SIRT1 is a crucial metabolic checkpoint connecting the energetic status with transcriptional programmes.
The transcription factor Krox20 is an E3 ligase that sumoylates its Nab coregulators
Authors: García‐Gutiérrez Pablo , Juárez‐Vicente Francisco , Gallardo‐Chamizo Francisco , Charnay Patrick , García‐Domínguez Mario
Published: August 2011

Covalent attachment of small ubiquitin‐like modifier (SUMO) to proteins regulates many processes in the eukaryotic cell. This reaction is similar to ubiquitination and usually requires an E3 ligase for substrate modification. However, only a few SUMO ligases have been described so far, which frequently facilitate sumoylation by bringing together the SUMO‐conjugating enzyme Ubc9 and the target protein. Ubc9 is an interaction partner of the transcription factor Krox20, a key regulator of hindbrain development. Here, we show that Krox20 functions as a SUMO ligase for its coregulators—the Nab proteins—and that Nab sumoylation negatively modulates Krox20 transcriptional activity in vivo.
Drosophila syndecan regulates tracheal cell migration by stabilizing Robo levels
Authors: Schulz Joachim G , Ceulemans Helga , Caussinus Emmanuel , Baietti Maria F , Affolter Markus , Hassan Bassem A , David Guido
Published: August 2011

Here we identify a new role for Syndecan (Sdc), the only transmembrane heparan sulphate proteoglycan in Drosophila, in tracheal development. Sdc is required cell autonomously for efficient directed migration and fusion of dorsal branch cells, but not for dorsal branch formation per se. The cytoplasmic domain of Sdc is dispensable, indicating that Sdc does not transduce a signal by itself. Although the branch‐specific phenotype of sdc mutants resembles those seen in the absence of Slit/Robo2 signalling, genetic interaction experiments indicate that Sdc also helps to suppress Slit/Robo2 signalling. We conclude that Sdc cell autonomously regulates Slit/Robo2 signalling in tracheal cells to guarantee ordered directional migration and branch fusion.
Sir2 histone deacetylase prevents programmed cell death caused by sustained activation of the Hog1 stress‐activated protein kinase
Authors: Vendrell Alexandre , Martínez‐Pastor Mar , González‐Novo Alberto , Pascual‐Ahuir Amparo , Sinclair David A , Proft Markus , Posas Francesc
Published: August 2011

Exposure of yeast to high osmolarity induces a transient activation of the Hog1 stress‐activated protein kinase (SAPK), which is required for cell survival under these conditions. However, sustained activation of the SAPK results in a severe growth defect. We found that prolonged SAPK activation leads to cell death, which is not observed in nma111 cells, by causing accumulation of reactive oxygen species (ROS). Mutations of the SCFCDC4 ubiquitin ligase complex suppress cell death by preventing the degradation of Msn2 and Msn4 transcription factors. Accumulation of Msn2 and Msn4 leads to the induction of PNC1, which is an activator of the Sir2 histone acetylase. Sir2 is involved in protection against Hog1‐induced cell death and can suppress Hog1‐induced ROS accumulation. Therefore, cell death seems to be dictated by the balance of ROS induced by Hog1 and the protective effect of Sir2.
Lac operator repeats generate a traceable fragile site in mammalian cells
Authors: Jacome Ariana , Fernandez‐Capetillo Oscar
Published: August 2011

One limitation for the study of chromosomal fragile sites is that they must be studied on metaphase spreads, after the breakage. We show here that bacterial lac operator (lacO) repeats are prone to spontaneous breakage, which when combined with a fluorescent lac repressor (lacR) has allowed us to track a fragile site through the cell cycle. By using this system, we show that Plk1‐interacting checkpoint helicase (PICH) is already present at fragile sites during interphase, suggesting roles for this helicase beyond mitosis. In addition, we report that the oncogene Myc promotes the formation of anaphase bridges and micronuclei containing fragile‐site sequences.
Heparanase enhances nerve-growth-factor-induced PC12 cell neuritogenesis via the p38 MAPK pathway
Authors: Cui Hengxiang , Shao Chenghao , Liu Qin , Yu Wenjie , Fang Jianping , Yu Weishi , Ali Amjad , Ding Kan
Published: August 2011

Heparanase is involved in the cleavage of the HS (heparan sulfate) chain of HSPGs (HS proteoglycans) and hence participates in remodelling of the ECM (extracellular matrix) and BM (basement membrane). In the present study we have shown that NGF (nerve growth factor) promoted nuclear enrichment of EGR1 (early growth response 1), a transcription factor for heparanase, and markedly induced heparanase expression in rat adrenal pheochromocytoma (PC12) cells. K252a, an antagonist of the NGF receptor TrkA (tyrosine kinase receptor A), decreased heparanase protein expression induced by NGF in PC12 cells. Suramin, a heparanase inhibitor, decreased heparanase in PC12 cells and blocked NGF-induced PC12 neuritogenesis. Stable overexpression of heparanase activated p38 MAPK (mitogen-activated protein kinase) by phosphorylation and enhanced the neurite outgrowth induced by NGF, whereas knock down of heparanase impaired this process. However, overexpression of latent pro-heparanase with a Y156A mutation still led to enhanced NGF-induced neurite outgrowth and increased p38 MAPK phosphorylation. Inhibition of p38 MAPK by SB203580 suppressed the promotion of NGF-induced neuritogenesis by the wild-type and mutant heparanase. The impaired differentiation by knock down of heparanase could be restored by transfection of wild-type or mutant heparanase in PC12 cells. The results of the present study suggest that heparanase, at least in the non-enzymatic form, may promote NGF-induced neuritogenesis via the p38 MAPK pathway.
Key functions for gap junctions in skin and hearing
Authors: Scott Claire A. , Kelsell David P.
Published: August 2011

Cx (connexin) proteins are components of gap junctions which are aqueous pores that allow intercellular exchange of ions and small molecules. Mutations in Cx genes are linked to a range of human disorders. In the present review we discuss mutations in β-Cx genes encoding Cx26, Cx30, Cx30.3 and Cx31 which lead to skin disease and deafness. Functional studies with Cx proteins have given insights into disease-associated mechanisms and non-gap junctional roles for Cx proteins.
Anti-carcinogenic action of curcumin by activation of antioxidant defence system and inhibition of NF-κB signalling in lymphoma-bearing mice
Authors: Das Laxmidhar , Vinayak Manjula
Published: August 2011

NF-κB (nuclear factor κB) plays a significant role in inflammation, immunity, cell proliferation, apoptosis and malignancy. ROS (reactive oxygen species) are among the most important regulating factors of NF-κB. Intracellular ROS are mainly regulated by an endogenous antioxidant defence system. Any disruption of redox balance leads to oxidative stress, which causes a number of pathological conditions including inflammation and malignancy. Increased metabolic activity in cancerous cells leads to oxidative stress, which is further enhanced due to depletion of the endogenous antioxidant defence system. However, the activation and signalling of NF-κB are reported to be inhibited by overexpression and induced activity of antioxidant enzymes. Therefore the present study focuses on the correlation between the endogenous antioxidant defence system, ROS and NF-κB activation during lymphoma growth in mice. The study highlights the anti-carcinogenic role of curcumin by modulation of NF-κB activation and oxidative stress via the endogenous antioxidant defence system. Oxidative stress was monitored by lipid peroxidation, protein carbonylation and antioxidant enzyme activity. NF-κB-mediated signalling was tested by DNA-binding activity. The results reflect that intracellular production of H2O2 in oxidative tumour micro-environment regulates NF-κB activation. Curcumin inhibits oxidative state in the liver of lymphoma-bearing mice by enhancing the transcription and activities of antioxidant enzymes, which in turn modulate activation of NF-κB, leading to a decrease in lymphoma growth. Morphological changes as well as cell proliferation and cell survival assays confirmed reduced lymphoma growth. Thus curcumin contributes to cancer prevention by disrupting the vicious cycle of constant ROS production, responsible for a high oxidative micro-environment for tumour growth.
Nucleated polymerization with secondary pathways. II. Determination of self-consistent solutions to growth processes described by non-linear master equations
Authors: Cohen Samuel I. A. , Vendruscolo Michele , Dobson Christopher M. , Knowles Tuomas P. J.
Published: August 2011

Nucleated polymerisation processes are involved in many growth phenomena in nature, including the formation of cytoskeletal filaments and the assembly of sickle hemoglobin and amyloid fibrils. Closed form rate equations have, however, been challenging to derive for these growth phenomena in cases where secondary nucleation processes are active, a difficulty exemplified by the highly non-linear nature of the equation systems that describe monomer dependent secondary nucleation pathways. We explore here the use of fixed point analysis to provide self-consistent solutions to such growth problems. We present iterative solutions and discuss their convergence behaviour. We establish a range of closed form results for linear growth processes, including the scaling behaviours of the maximum growth rate and of the reaction end-point. We further show that a self-consistent approach applied to the master equation of filamentous growth allows the determination of the evolution of the shape of the length distribution including the mean, the standard deviation, and the mode. Our results highlight the power of fixed-point approaches in finding closed form self-consistent solutions to growth problems characterised by the highly non-linear master equations.
Nucleated polymerization with secondary pathways. III. Equilibrium behavior and oligomer populations
Authors: Cohen Samuel I. A. , Vendruscolo Michele , Dobson Christopher M. , Knowles Tuomas P. J.
Published: August 2011

We explore the long-time behavior and equilibrium properties of a system of linear filaments growing through nucleated polymerisation. We show that the length distribution for breakable filaments evolves through two well defined limiting cases: first, a steady state distribution determined by the balance of breakage and elongation is reached; upon monomer depletion at the end of the growth phase, an equilibrium length distribution biased towards smaller filament fragments emerges. We furthermore compute the time evolution of the concentration of small oligomeric filament fragments. For frangible filaments, oligomers are present both at early times and at equilibrium, whereas in the absence of fragmentation, oligomers are only present in significant quantities at the beginning of the polymerisation reaction. Finally, we discuss the significance of these results for the biological consequences of filamentous protein aggregation.
Analytical solutions of the microscopic two-band theory for the temperature dependence of the upper critical fields of pure MgB2 compared with experimental data
Authors: Palistrant M. , Surdu A. , Ursu V. , Petrenko P. , Sidorenko A.
Published: August 2011

Major theoretical results from the microscopic two-band theory for the temperature dependence of the upper critical fields Hc2(ab) and Hc2(c) in pure two-band systems such as MgB2 are presented. Analytical solutions for the upper critical fields near the superconducting transition temperature and near zero temperature are transformed for direct comparison with experimental data. The temperature variations of Hc2(ab) and Hc2(c) for textured MgB2 films near the superconducting transition temperature are measured and compared with the theory. The results of this theoretical approach are also compared with previously published experimental data. The theory and experimental data are in good agreement.
Effect of magnetoelastic interactions on the formation of spiral magnetic structures in frustrated non-Heisenberg magnets
Authors: Fridman Yu. A. , Gorelikov G. A.
Published: August 2011

The spectra of coupled magnetoelastic waves in highly anisotropic non-Heisenberg frustrated magnets with S = 1 are obtained in the mean field approximation. An analysis of the elementary excitation spectra shows that, besides uniform phases (ferromagnetic and quadrupole), spatially-modulated magnetic structures such as magnetic spirals can develop in these systems. The points at which phase transitions into the spiral phase occur are determined. It is shown that magnetoelastic interactions cause significant changes in the size of the region where spiral structures exist.
Magnetic field-induced rotation of the plane of polarization of light in the antiferromagnetic ferroborate TbFe3(BO3)4
Authors: Bedarev V. A. , Pashchenko M. I. , Bludov A. N. , Gnatchenko S. L. , Bezmaternykh L. N. , Temerov V. L.
Published: August 2011

The magnetic field dependences of the rotation of the plane of polarization of light and the magnetization in single crystals of the ferroborate TbFe3(BO3)4 are studied. The main contribution to the magnetic field-induced rotation of the plane of polarization is found to be from the magnetic subsystem of the terbium ions.
Effect of magnetic fields on magnetic phase separation in anion-deficient manganite La0.70Sr0.30MnO2.85
Authors: Trukhanov S. V. , Trukhanov A. V. , Szymczak H.
Published: August 2011

The temperature dependence of the specific magnetic moment of anion-deficient manganite La0.70Sr0.30MnO2.85 is measured in external magnetic fields of 0–140 kOe, with the prehistory taken into account. The inhomogeneous magnetic state is a cluster spin glass and is the result of a redistribution of oxygen vacancies. Increasing the external magnetic field initially (H < 10 kOe) leads to breakup of the ferromagnetic clusters, and then (H ≥ 10 kOe) to a transition of the antiferromagnetic matrix into a ferromagnetic state and an increase in the degree of polarization of the local manganese spins. The freezing temperature for the magnetic moments varies as Tf = 65–6H0.21, while the temperature at which the ZFC- and FC-curves diverge varies at Trev = 250–90H0.11. The cause of and mechanism for the magnetic phase separation are discussed.
Optics of semiconductors with a linear electron spectrum
Authors: Falkovsky L. A.
Published: August 2011

The temperature and carrier concentration dependences of the frequency dispersion of the dielectric constant of graphene and 3D semiconductors with a narrow band gap are examined at frequencies above the carrier relaxation frequency but well below the conduction band width. The linearity of the electronic spectrum over a wide range of energies, which is a general features of these materials, leads to an anomalously high dielectric constant of the 3D semiconductors, and when they are doped, to a logarithmic singularity in the real part of the dielectric function at the absorption threshold. For graphene, the optical transmission is determined by the fine structure constant of quantum electrodynamics, and is independent of any properties of graphene, itself.
Andreev-reflection spectroscopy of ferromagnets: The impact of Fermi surface mismatch
Authors: Tuuli Elina , Gloos Kurt
Published: August 2011

We have investigated point contacts between superconductors (Nb, AuIn2) and normal metals (ferromagnetic Co, nonmagnetic Cu). The observed Andreev-reflection spectra are analyzed using a modified BTK theory including spin polarization effects. This results in a polarization of Co that agrees with observations by others, but lifetime effects describe the spectra equally well. On the other hand, the spectra with nonmagnetic Cu can be described well by a spin-polarization model. The discrepancy between the polarization and lifetime interpretations poses a dilemma which can be resolved by considering normal reflection at those interfaces owing to Fermi surface mismatch. Our data suggest that Andreev reflection at Nb-Co contacts gives the correct magnetic polarization of Co only when lifetime effects and intrinsic normal reflection are included.
The study for the incipient solvation process of NaCl in water: The observation of the NaCl–(H2O)n (n = 1, 2, and 3) complexes using Fourier-transform microwave spectroscopy
Authors: Mizoguchi Asao , Ohshima Yasuhiro , Endo Yasuki
Published: August 2011

Pure rotational spectra of the sodium chloride-water complexes, NaCl–(H2O)n (n = 1, 2, and 3), in the vibronic ground state have been observed by a Fourier- transform microwave spectrometer coupled with a laser ablation source. The 37Cl-isotopic species and a few deuterated species have also been observed. From the analyses of the spectra, the rotational constants, the centrifugal distortion constants, and the nuclear quadrupole coupling constants of the Na and Cl nuclei were determined precisely for all the species. The molecular structures of NaCl–(H2O)n were determined using the rotational constants and the molecular symmetry. The charge distributions around Na and Cl nuclei in NaCl are dramatically changed by the complex formation with H2O. Prominent dependences of the bond lengths r(Na–Cl) on the number of H2O were also observed. By a comparison with results of theoretical studies, it is shown that the structure of NaCl–(H2O)3 is approaching to that of the contact ion-pair, which is considered to be an intermediate species in the incipient solvation process.
Irreversibility and pinching in deterministic particle separation
Authors: Luo Mingxiang , Sweeney Francis , Risbud Sumedh R. , Drazer German , Frechette Joelle
Published: August 2011

We investigate the settling of spherical particles through a pinching gap created by a cylindrical obstacle and a vertical wall. These macroscopic experiments capture the essence of pinched-flow-fractionation in microfluidics and highlight its deterministic nature. In the absence of pinching, we observe asymmetric trajectories consistent with a hard-core model of particle-obstacle repulsion that leads to separative lateral displacement. Then, we show that pinching promotes the onset of these short-range repulsion forces, amplifying the relative separation in the outgoing trajectory of different-size particles. Inertia effects, however, tend to reduce such relative separation and lead to a more complex behavior.
Air stability of TiO2/PbS colloidal nanoparticle solar cells and its impact on power efficiency
Authors: Zhai Guangmei , Bezryadina Anna , Breeze Alison J. , Zhang Daoli , Alers Glenn B. , Carter Sue A.
Published: August 2011

The short-term (less than 1 hour) exposure of TiO2/PbS quantum dot photovoltaics to air increases the open circuit voltage (Voc) and fill factor (FF) while slightly decreasing the short circuit current density (Jsc), leading to a power conversion efficiency above 4% and a peak external quantum efficiency over 80% for 1.1 eV PbS. The resulting Jsc, Voc, and FF under 100 mW/cm2 AM1.5 are 18.6 mA/cm2, 0.517 V, and 42% for 1.1 eV PbS and 8.03 mA/cm2, 0.655 V, and 35% for 1.7 eV PbS, respectively. Long-term air exposures result in much lower conductivities. Furthermore, short-term air exposure effects are fully reversible upon removal from air, and longer-term effects are mostly reversible through soaking in 1,2-ethanedithiol.
Tunnel spin injection and the conductivity of ferromagnet-superconductor heterostructures with zero bias
Authors: Rudenko E. M. , Korotash I. V. , Shlapak Yu. V. , Kudryavtsev Y. V. , Krakovny A. A. , Dyakin M. V.
Published: August 2011

The giant spin blocking of tunnel currents discovered by us (Low. Temp. Phys. 36, 186 (2010)) is investigated theoretically and experimentally in ferromagnet F (Co2CrAl)- insulator I- superconductor S (Pb) heterostructures with a wide range of specific resistances (10−7–10−4 Ω · cm2). The magnitude of this effect is found to depend on the specific resistance of the junction in the normal state and on recombination spin depolarization. A theoretical model which provides an adequate description of the tunnelling of spin-polarized electrons in F-I-S junctions is proposed. It is found that the normalized conductivity σFS of an F-I-S tunnel junction can be considerably lower than the fundamental normalized conductivity σNS of an N-I-S junction (where N is a normal metal). The proposed model is used to estimate the degree of spin polarization p of films of the ferromagnetic semimetal Co2CrAl (Heusler alloy) with B2- and L21-type crystal structures, which is close to 1 (p ≈ 0.97). The temperature dependence σFS(T) of a Co2CrAl-I-Pb F-I-S tunnel junction is studied experimentally. A theoretical model is proposed which provides an adequate description of the temperature behavior of the normalized conductivity σFS(T) with features of spin-polarized tunnelling taken into account.
Electric field-induced deformation behavior in mixed Bi0.5Na0.5TiO3 and Bi0.5(Na0.75K0.25)0.5TiO3-BiAlO3
Authors: Lee Dae Su , Lim Dong Hwan , Kim Min Soo , Kim Kwang Ho , Jeong Soon Jong
Published: August 2011

In this study, a method in which an electric field-induced phase transition in bismuth-based ceramics is used at a relatively low field of 40 kV/cm is proposed. This study investigated the electrical properties and electric field-induced strain of Bi0.5Na0.5TiO3 (BNT) single particle-added Bi0.5(Na0.75K0.25)0.5TiO3-BiAlO3 (BNKT-BA) ceramics. Strains of 0.27% and 0.29%, for 0.94BNKT-0.06BA with 10% BNT and 0.93BNKT-0.07BA with 20% BNT, were observed, respectively. These strains were attributed to the transition from non-polar to ferroelectric phases in BNKT-BA small grains with ferroelectric BNT large grains during external electric field execution.
The identification of a solvated electron pair in the gaseous clusters of Na−(H2O)n and Li−(H2O)n
Authors: Zhang Han , Liu Zhi-Feng
Published: August 2011

By first principles calculations, we explore the possibility that Na−(H2O)n and Li−(H2O)n clusters, which have been measured previously by photoelectron experiments, could serve as gas-phase molecular models for the solvation of two electrons. Such models would capture the electron-electron interaction in a solution environment, which is missed in the well-known anionic water clusters \documentclass[12pt]{minimal}\begin{document}$({\rm H}_{2}{\rm O})^- _n$\end{document}(H2O)n−. Our results show that by n = 10, the two loosely bound s electrons in Li−(H2O)n are indeed detached from lithium, and they could exist in either the singlet (spin-paring) or the triplet (spin-coupling) state. In contrast, the two electrons would prefer to stay on the sodium atom in Na−(H2O)n and on the surface of the cluster. The formation of a solvated electron pair and the variation in solvation structures make these two cluster series interesting subjects for further experimental investigation.
Deuteration effects in the thermal conductivity of molecular glasses
Authors: Krivchikov A. I. , Bermejo F. J. , Sharapova I. V. , Korolyuk O. A. , Romantsova O. O.
Published: August 2011

The thermal conductivity κ(T) of pure deuterated ethanol has been measured at the equilibrium vapor pressure of its orientationally-ordered crystal form (T = 2 K − Tm), orientational glass, and glass state (T = 2 K − Tg, Tg is the glass transition temperature) solid phases. The temperature dependence of the conductivity is well described by the sum of two contributions, κ(T) = κI(T) + κII(T), where κI(T) accounts for heat transport by acoustic phonons and κII(T), for heat transfer by localized high-frequency excitations. The thermal conductivities of deuterated and hydrogenated ethanols are compared in the different phases. The mechanisms of phonon scattering in the glasses are analyzed. In these glasses the effect of complete deuteration shows up in the κII(T) term.
IR spectroscopy of ethanol in nitrogen cryomatrices with different concentration ratios
Authors: Aldiyarov A. , Aryutkina M. , Drobyshev A. , Kurnosov V.
Published: August 2011

Thin films of cryovacuum condensates of ethanol-nitrogen mixtures formed by co-condensation of gas mixtures with different concentrations on a cooled metal substrate are studied by IR spectrometry. The condensation temperature was Tc = 16 K and the pressure of the gaseous phase during cryodeposition was P = 10−5 Torr. The ethanol concentration in nitrogen was varied from 0.5 to 10% and the film thickness, from 1 to 30 μm. Measurements were made in the range from 400 to 4200 cm−1. An analysis of the IR spectra and a comparison with published data shows that ethanol monomers and dimers are present in the nitrogen matrix. This is indicated by an absorption band at a frequency of 3658 cm−1 owing to vibrations of O–H bonds of ethanol monomers and dimers. The local minima of this band at 3645 and 3658 cm−1 are related to the existence of two conformational states of the ethanol molecule: anti (3658 cm−1) and gauche (3645 cm−1). In addition, the presence of ethanol dimers and monomers in the matrix leads to the appearance of absorption bands at 1259 and 1276 cm−1 attributable to deformation vibrations δ(COH) of the anti- and gauche-isomers, respectively, as well as bands corresponding to a combination of ν(CCO) valence vibrations and rotational oscillations of the methyl group r(CH3) attributable to anti-dimers (ν = 1090 cm−1) and anti-monomers (ν = 1095 cm−1). Local minima within 3000–3600 cm−1 also indicate the presence of cyclical dimers, trimers, and tetramers, as well as hexamers in the matrix. A broad band over 3250–3330 cm−1 indicates that large polyaggregates, with ethanol molecules in a hydrogen-bond state (multimer), exist in the matrix.
A method for treating the passage of a charged hard sphere ion as it passes through a sharp dielectric boundary
Authors: Boda Dezső , Henderson Douglas , Eisenberg Bob , Gillespie Dirk
Published: August 2011

In the implicit solvent models of electrolytes (such as the primitive model (PM)), the ions are modeled as point charges in the centers of spheres (hard spheres in the case of the PM). The surfaces of the spheres are not polarizable which makes these models appropriate to use in computer simulations of electrolyte systems where these ions do not leave their host dielectrics. The same assumption makes them inappropriate in simulations where these ions cross dielectric boundaries because the interaction energy of the point charge with the polarization charge induced on the dielectric boundary diverges. In this paper, we propose a procedure to treat the passage of such ions through dielectric interfaces with an interpolation method. Inspired by the “bubble ion” model (in which the ion's surface is polarizable), we define a space-dependent effective dielectric coefficient, \documentclass[12pt]{minimal}\begin{document}$\epsilon _{\mathrm{eff}}(\mathbf {r})$\end{document}ε eff (r), for the ion that overlaps with the dielectric boundary. Then, we replace the “bubble ion” with a point charge that has an effective charge \documentclass[12pt]{minimal}\begin{document}$q/\epsilon _{\mathrm{eff}}(\mathbf {r})$\end{document}q/ε eff (r) and remove the portion of the dielectric boundary where the ion overlaps with it. We implement the interpolation procedure using the induced charge computation method [D. Boda, D. Gillespie, W. Nonner, D. Henderson, and B. Eisenberg, Phys. Rev. E 69, 046702 (2004)]. We analyze the various energy terms using a spherical ion passing through an infinite flat dielectric boundary as an example.
Molecular dynamics studies to understand the mechanism of heat accommodation in homogeneous condensing flow of carbon dioxide
Authors: Kumar Rakesh , Li Zheng , van Duin Adri , Levin Deborah
Published: August 2011

Using molecular dynamics (MD), we have studied the mechanism of heat accommodation between carbon dioxide clusters and monomers for temperatures and cluster size conditions that exist in homogeneous condensing supersonic expansion plumes. The work was motivated by our meso-scale direct simulation Monte Carlo and Bhatnagar-Gross-Krook based condensation simulations where we found that the heat accommodation model plays a key role in the near-field of the nozzle expansion particularly as the degree of condensation increases [R. Kumar, Z. Li, and D. Levin, Phys. Fluids 23, 052001 (2011)]. The heat released by nucleation and condensation and the heat removed by cluster evaporation can be transferred or removed from either the kinetic or translational modes of the carbon dioxide monomers. The molecular dynamics results show that the time required for gas-cluster interactions to establish an equilibrium from an initial state of non-equilibrium is less than the time step used in meso-scale analyses [R. Kumar, Z. Li, and D. Levin, Phys. Fluids 23, 052001 (2011)]. Therefore, the good agreement obtained between the measured cluster and gas number density and gas temperature profiles with the meso-scale modeling using the second energy exchange mechanism is not fortuitous but is physically based. Our MD simulations also showed that a dynamic equilibrium is established by the gas-cluster interactions in which condensation and evaporation processes take place constantly to and from a cluster.
The mean reaction force: A method to study the influence of the environment on reaction mechanisms
Authors: Vöhringer-Martinez Esteban , Toro-Labbé Alejandro
Published: August 2011

The mean reaction force is introduced as the negative derivative of the free energy along a predefined reaction path. In analogy to the reaction force, this descriptor allows detailed characterization of different processes of the reaction mechanism and the assignment of electronic and structural free energy contributions to activation barriers. Due to its free energy dependence, the mean reaction force represents a new tool to study the influence of the environment on the reaction mechanism. Moreover, it enables the separation of catalytic effects in structural and electronic components responsible for the free energy barrier reduction of a reaction. To validate the method, the intramolecular proton transfer in tryptophan was studied in the gas phase, in aqueous solution and at the vacuum-water interface employing molecular dynamics simulation in combination with ab initio calculations and the quantum molecular/molecular mechanics (QM/MM) methodology. The obtained results were compared to static vacuum and continuum calculations. The mean reaction force distinguishes structural rearrangements as the dominant free energy component to reach the transition state from the neutral form, whereas electronic reorganization predominates the activation of the zwitterion in aqueous solution. In addition, it identifies the origin of the reduction of the activation barrier for desolvated functional groups at the water-vacuum interface as the absence of hydrogen bonds which stabilize charge delocalized species.
Molecular dynamics simulation of liquid trimethylphosphine
Authors: Costa Luciano T. , Malaspina Thaciana , Fileti Eudes E. , Ribeiro Mauro C. C.
Published: August 2011

Structural and dynamical properties of liquid trimethylphosphine (TMP), (CH3)3P, as a function of temperature is investigated by molecular dynamics (MD) simulations. The force field used in the MD simulations, which has been proposed from molecular mechanics and quantum chemistry calculations, is able to reproduce the experimental density of liquid TMP at room temperature. Equilibrium structure is investigated by the usual radial distribution function, g(r), and also in the reciprocal space by the static structure factor, S(k). On the basis of center of mass distances, liquid TMP behaves like a simple liquid of almost spherical particles, but orientational correlation due to dipole–dipole interactions is revealed at short-range distances. Single particle and collective dynamics are investigated by several time correlation functions. At high temperatures, diffusion and reorientation occur at the same time range as relaxation of the liquid structure. Decoupling of these dynamic properties starts below ca. 220 K, when rattling dynamics of a given TMP molecules due to the cage effect of neighbouring molecules becomes important.
Ab initio calculations of the reaction pathways for methane decomposition over the Cu (111) surface
Authors: Gajewski Grzegorz , Pao Chun-Wei
Published: August 2011

Growth of large-area, few-layer graphene has been reported recently through the catalytic decomposition of methane (CH4) over a Cu surface at high temperature. In this study, we used ab initio calculations to investigate the minimum energy pathways of successive dehydrogenation reactions of CH4 over the Cu (111) surface. The geometries and energies of all the reaction intermediates and transition states were identified using the climbing image nudged elastic band method. The activation barriers for CH4 decomposition over this Cu surface are much lower than those in the gas phase; furthermore, analysis of electron density differences revealed significant degrees of charge transfer between the adsorbates and the Cu atoms along the reaction path; these features reveal the role of Cu as the catalytic material for graphene growth. All the dehydrogenation reactions are endothermic, except for carbon dimer (C2) formation, which is, therefore, the most critical step for subsequent graphene growth, in particular, on Cu (111) surface.
The air-broadened, near-infrared CO2 line shape in the spectrally isolated regime: Evidence of simultaneous Dicke narrowing and speed dependence
Authors: Long David A. , Bielska Katarzyna , Lisak Daniel , Havey Daniel K. , Okumura Mitchio , Miller Charles E. , Hodges Joseph T.
Published: August 2011

Frequency-stabilized cavity ring-down spectroscopy (FS-CRDS) was employed to measure air-broadened CO2 line shape parameters for transitions near 1.6 μm over a pressure range of 6.7–33 kPa. The high sensitivity of FS-CRDS allowed for the first measurements in this wavelength range of air-broadened line shape parameters on samples with CO2 mixing ratios near those of the atmosphere. The measured air-broadening parameters show several percent deviations (0.9%–2.7%) from values found in the HITRAN 2008 database. Spectra were fit with a variety of models including the Voigt, Galatry, Nelkin-Ghatak, and speed-dependent Nelkin-Ghatak line profiles. Clear evidence of line narrowing was observed, which if unaccounted for can lead to several percent biases. Furthermore, it was observed that only the speed-dependent Nelkin-Ghatak line profile was able to model the spectra to within the instrumental noise level because of the concurrent effects of collisional narrowing and speed dependence of collisional broadening and shifting.
Hole mobility enhancement of pentacene organic field-effect transistors using 4,4′,4″-tris[3-methylphenyl(phenyl)amino] triphenylamine as a hole injection interlayer
Authors: Yu Xinge , Yu Junsheng , Zhou Jianlin , Huang Jiang , Jiang Yadong
Published: August 2011

Organic field-effect transistors (OFETs) were prepared and analyzed by inserting various thickness of 4,4′,4″-tris[3-methylphenyl(phenyl)amino] triphenylamine (m-MTDATA) between pentacene and gold electrodes as a hole injection layer. These OFETs showed a significant enhancement of hole mobility comparing to the corresponding single layer device. The interfacial morphologies of pentacene and pentacene/m-MTDATA contact were characterized by atomic force microscopy. The hole mobility improvement of OFETs was attributed to an intermediate energy level formed between pentacene and gold heterojunction when inserting an ultrathin m-MTDATA layer, leading to a remarkable reduction of contact resistance at the metal-organic interface.
Rotational spectrum of asymmetric top molecules in combined static and laser fields
Authors: Omiste J. J. , González-Férez R. , Schmelcher P.
Published: August 2011

We examine the impact of the combination of a static electric field and a non-resonant linearly polarized laser field on an asymmetric top molecule. Within the rigid rotor approximation, we analyze the symmetries of the Hamiltonian for all possible field configurations. For each irreducible representation, the Schrödinger equation is solved by a basis set expansion in terms of a linear combination of symmetric top eigenfunctions respecting the corresponding symmetries, which allows us to distinguish avoided crossings from genuine ones. Using the fluorobenzene and pyridazine molecules as prototypes, the rotational spectra and properties are analyzed for experimentally accessible static field strengths and laser intensities. Results for energy shifts, orientation, alignment, and hybridization of the angular motion are presented as the field parameters are varied. We demonstrate that a proper selection of the fields gives rise to a constrained rotational motion in three Euler angles, the wave function being oriented along the electrostatic field direction, and aligned in other two angles.
Structural homogeneity and low-temperature micromechanical properties of ultrafine-grained AZ31 magnesium alloy
Authors: Estrin Y. Z. , Fomenko L. S. , Lubenets S. V. , Rusakova A. V.
Published: August 2011

The degree of microstructural homogeneity of ultrafine-grained (UFG) AZ31 magnesium alloy produced by a special thermomechanical process including four cycles of equal-channel angular pressing (ECAP, route Bc) is studied by the microindentation method. The defect structure of the UFG alloy is quite homogeneous. Texture owing to ECAP showed up as a lower average microhardness measured in a plane perpendicular to the extrusion axis than that measured in a plane containing that axis, and in a slight dependence of the microhardness on the location of the indent on the billet surface. The microhardness of the initial coarse-grained alloy is close to that of the UFG samples measured in a plane perpendicular to the extrusion axis. Tensile deformation of the samples over a wide temperature range of 4.2–295 K increased the microhardness in the region of the neck by more than 30%. The temperature dependence of the microhardness over 77–295 K is indicative of thermally activated plastic deformation in AZ31 alloy. The mechanism for deformation of the alloy appears to be interactions between dislocations and local defects of impurity origin.
A practical integral equation for the structure and thermodynamics of hard sphere Coulomb fluids
Authors: Zwanikken Jos W. , Jha Prateek K. , de la Cruz Monica Olvera
Published: August 2011

A closure for the Ornstein-Zernike equation is presented, applicable for fluids of charged, hard spheres. From an exact, but intractable closure, we derive the radial distribution function of nonlinearized Debye-Hückel theory by subsequent approximations, and use the information to formulate a new closure by an extension of the mean spherical approximation. The radial distribution functions of the new closure, coined Debye-Hückel-extended mean spherical approximation, are in excellent agreement with those resulting from the hyper-netted chain approximation and molecular dynamics simulations, in the regime where the latter are applicable, except for moderately dilute systems at low temperatures where the structure agrees at most qualitatively. The method is numerically more efficient, and more important, convergent in the entire temperature-density plane. We demonstrate that the method is accurate under many conditions for the determination of the structural and thermodynamic properties of homogeneous, symmetric hard-sphere Coulomb systems, and estimate it to be a valuable basis for the formulation of density functional theories for inhomogeneous or highly asymmetric systems.
Use of an AC electric field in galvanotactic on/off switching of the motion of a microstructure blotted by Serratia marcescens
Authors: Tran Trung-Hieu , Hyung Kim Dal , Kim Jihoon , Jun Kim Min , Byun Doyoung
Published: August 2011

In this study, we manipulated the swimming direction of bacteria and controlled the switching off movement by using dc and ac galvanotaxis. The microstructures blotted by Serratia marcescens could be spontaneously manipulated and switched off at the desired position. The optimum ac frequency for switching off the microstructural motion was 7 Hz. We built a mathematical model to analyze and understand the oscillating motion of microstructure.
On the role of Al doping in La0.7Ca0.3MnO3: A magnetic Compton scattering study
Authors: Ahuja B. L. , Tiwari Shailja , Dashora Alpa , Mund H. S. , Sahariya Jagrati , Phase D. M. , Choudhary R. J. , Banerjee A. , Itou M. , Sakurai Y.
Published: August 2011

Spin and orbital magnetic moments in hole doped manganite La0.7Ca0.3Mn1−xAlxO3 (x = 0, 0.02, and 0.06) have been scrutinized using experimental spin momentum densities. An analysis of magnetic Compton profiles shows that the spin moment of Mn 3d has a major contribution towards the total spin moment and its contribution decreases as we increase the concentration of Al. The present experiment along with magnetization data predict orbital moment of −0.29 ± 0.03 μB/f.u. in the parent compound (x = 0), which almost disappears on substitution of Al. The results are explained on the basis of imbalance in Mn3+ and Mn4+ charge ratio in these compounds.
Field-effect modulation of conductance in VO2 nanobeam transistors with HfO2 as the gate dielectric
Authors: Sengupta Shamashis , Wang Kevin , Liu Kai , Bhat Ajay K. , Dhara Sajal , Wu Junqiao , Deshmukh Mandar M.
Published: August 2011

We study field-effect transistors realized from VO2 nanobeams with HfO2 as the gate dielectric. When heated up from low to high temperatures, VO2 undergoes an insulator-to-metal transition. We observe a change in conductance (∼6%) of our devices induced by gate voltage when the system is in the insulating phase. The response is reversible and hysteretic, and the area of hysteresis loop becomes larger as the rate of gate sweep is slowed down. A phase lag exists between the response of the conductance and the gate voltage. This indicates the existence of a memory of the system and we discuss its possible origins.
Transport of a soft cargo on a nanoscale ratchet
Authors: Sekeroglu Koray , Gurkan Umut A. , Demirci Utkan , Demirel Melik C.
Published: August 2011

Surface ratchets can guide droplet transport for microfluidic systems. Here, we demonstrated the actuation of microgels encapsulated in droplets using a unidirectional nanotextured surface, which moves droplets with low vibration amplitudes by a ratcheting mechanism. The nanofilm carries droplets along the ratchets with minimal drop shape deformation to move the encapsulated soft cargo, i.e., microscale hydrogels. The tilted nanorods of the nanofilm produce unidirectional wetting, thereby enabling droplet motion in a single direction. Maximum droplet translation speed on the nanofilm was determined to be 3.5 mm/s, which offers a pathway towards high throughput microgel assembly applications to build complex constructs.
Electrically pumped near-ultraviolet lasing from ZnO/MgO core/shell nanowires
Authors: Liu C. Y. , Xu H. Y. , Ma J. G. , Li X. H. , Zhang X. T. , Liu Y. C. , Mu R.
Published: August 2011

Electrically pumped near-ultraviolet lasing was achieved in a metal/insulator/semiconductor laser diode based on ZnO/MgO core/shell nanowires. The nanowire diode shows higher emission intensity at relatively low operating current density compared with the planar device. The improved efficiency is attributed to enhanced exciton oscillator strength and superior carrier transport properties of single-crystalline ZnO nanowires, and effective surface passivation by MgO coating. Random laser action was confirmed by the calculation of quality factor and the real-time changes of lasing spectra. The results reveal that the MgO coating serves as electron blocking, hole supplying and surface passivation layer for the nanowire heterostructure.