bluuebunny/crossref_metadata_2025 huggingface dataset:
Inferring spatial distribution of the radially integrated transmissivity from pumping tests in heterogeneous confined aquifers
Authors: Copty Nadim K. , Trinchero Paolo , Sanchez‐Vila Xavier
Published: May 2011

Hydrologists routinely analyze pumping test data using conventional interpretation methods that are based on the assumption of homogeneity and that, consequently, yield single estimates of representative flow parameters. However, natural subsurface formations are intrinsically heterogeneous, and hence, the flow parameters influencing the drawdown vary as the cone of depression expands in time. In this paper a novel procedure for the analysis of pumping tests in heterogeneous confined aquifers is developed. We assume that a given heterogeneous aquifer can be represented by a homogeneous system whose flow parameters evolve in time as the pumping test progresses. At any point in time, the interpreted flow parameters are estimated using the ratio of the drawdown and its derivative observed at that particular time. The procedure is repeated for all times, yielding time‐dependent estimates of transmissivity Ti(t) and storativity, Si(t). Based on the analysis of the sensitivity of drawdown to inhomogeneities in the T field, the time‐dependent interpreted transmissivity values are found to be a good estimate of Tg(r), the geometric mean of the transmissivity values encompassed within a progressively increasing radius r from the well. The procedure is illustrated for Gaussian heterogeneous fields with ln(T) variances up to a value of 2. The impact of the separation distance between the pumping well and observation point on data interpretation is discussed. The results show that information about the spatial variability of the transmissivity field can be inferred from time‐drawdown data collected at a single observation point.
Antagonistic regulation of EMT by TIF1γ and Smad4 in mammary epithelial cells
Authors: Hesling Cédric , Fattet Laurent , Teyre Guillaume , Jury Delphine , Gonzalo Philippe , Lopez Jonathan , Vanbelle Christophe , Morel Anne‐Pierre , Gillet Germain , Mikaelian Ivan , Rimokh Ruth
Published: May 2011

TGF‐β is a potent inducer of epithelial‐to‐mesenchymal transition (EMT), a process involved in tumour invasion. TIF1γ participates in TGF‐β signalling. To understand the role of TIF1γ in TGF‐β signalling and its requirement for EMT, we analysed the TGF‐β1 response of human mammary epithelial cell lines. A strong EMT increase was observed in TIF1γ‐silenced cells after TGF‐β1 treatment, whereas Smad4 inactivation completely blocked this process. Accordingly, the functions of several TIF1γ target genes can be linked to EMT, as shown by microarray analysis. As a negative regulator of Smad4, TIF1γ could be crucial for the regulation of TGF‐β signalling. Furthermore, TIF1γ binds to and represses the plasminogen activator inhibitor 1 promoter, demonstrating a direct role of TIF1γ in TGF‐β‐dependent gene expression. This study shows the molecular relationship between TIF1γ and Smad4 in TGF‐β signalling and EMT.
Hypobaric hypoxia preconditioning attenuates acute lung injury during high-altitude exposure in rats via up-regulating heat-shock protein 70
Authors: Lin Hung-Jung , Wang Chia-Ti , Niu Ko-Chi , Gao Chungjin , Li Zhuo , Lin Mao-Tsun , Chang Ching-Ping
Published: May 2011

HHP (hypobaric hypoxia preconditioning) induces the overexpression of HSP70 (heat-shock protein 70), as well as tolerance to cerebral ischaemia. In the present study, we hypothesized that HHP would protect against HAE (high-altitude exposure)-induced acute lung injury and oedema via promoting the expression of HSP70 in lungs prior to the onset of HAE. At 2 weeks after the start of HHP, animals were exposed to a simulated HAE of 6000 m in a hypobaric chamber for 24 h. Immediately after being returned to ambient pressure, the non-HHP animals had higher scores of alveolar oedema, neutrophil infiltration and haemorrhage, acute pleurisy (e.g. increased exudate volume, increased numbers of polymorphonuclear cells and increased lung myeloperoxidase activity), increased pro-inflammatory cytokines [e.g. TNF-α (tumour necrosis factor-α), IL (interleukin)-1β and IL-6], and increased cellular ischaemia (i.e. glutamate and lactate/pyruvate ratio) and oxidative damage [glycerol, NOx (combined nitrate+nitrite) and 2,3-dihydroxybenzoic acid] markers in the BALF (bronchoalveolar fluid). HHP, in addition to inducing overexpression of HSP70 in the lungs, significantly attenuated HAE-induced pulmonary oedema, inflammation, and ischaemic and oxidative damage in the lungs. The beneficial effects of HHP in preventing the occurrence of HAE-induced pulmonary oedema, inflammation, and ischaemic and oxidative damage was reduced significantly by pretreatment with a neutralizing anti-HSP70 antibody. In conclusion, HHP may attenuate the occurrence of pulmonary oedema, inflammation, and ischaemic and oxidative damage caused by HAE in part via up-regulating HSP70 in the lungs.
Spatial dependence of output pulse delay in a niobium nitride nanowire superconducting single-photon detector
Authors: O’Connor J. A. , Tanner M. G. , Natarajan C. M. , Buller G. S. , Warburton R. J. , Miki S. , Wang Z. , Nam S. W. , Hadfield R. H.
Published: May 2011

We report on the position-dependent variation in output pulse timing across a superconducting single-photon detector. Our device consists of a single niobium nitride nanowire meander (100 nm width, 4 nm film thickness, 2 mm length). We use a confocal microscope configuration (full width at half maximum-spot size 1.3 μm at 1550 nm wavelength) and a femtosecond laser to study local variations in detection efficiency and output pulse timing. Pulse delays of up to 50 ps across the device correlate to local detection efficiency and resistance variations. This study indicates an underlying mechanism for timing jitter in superconducting nanowire devices.
Edge energy transport barrier and turbulence in the I-mode regime on Alcator C-Mod
Authors: Hubbard A. E. , Whyte D. G. , Churchill R. M. , Cziegler I. , Dominguez A. , Golfinopoulos T. , Hughes J. W. , Rice J. E. , Bespamyatnov I. , Greenwald M. J. , Howard N. , Lipschultz B. , Marmar E. S. , Reinke M. L. , Rowan W. L. , Terry J. L. ,   Alcator C-Mod Group
Published: May 2011

We report extended studies of the I-mode regime [Whyte et al., Nucl. Fusion 50, 105005 (2010)] obtained in the Alcator C-Mod tokamak [Marmar et al., Fusion Sci. Technol. 51(3), 3261 (2007)]. This regime, usually accessed with unfavorable ion B × ∇B drift, features an edge thermal transport barrier without a strong particle transport barrier. Steady I-modes have now been obtained with favorable B × ∇B drift, by using specific plasma shapes, as well as with unfavorable drift over a wider range of shapes and plasma parameters. With favorable drift, power thresholds are close to the standard scaling for L–H transitions, while with unfavorable drift they are ∼ 1.5–3 times higher, increasing with Ip. Global energy confinement in both drift configurations is comparable to H-mode scalings, while density profiles and impurity confinement are close to those in L-mode. Transport analysis of the edge region shows a decrease in edge χeff, by typically a factor of 3, between L- and I-mode. The decrease correlates with a drop in mid-frequency fluctuations (f ∼ 50–150 kHz) observed on both density and magnetics diagnostics. Edge fluctuations at higher frequencies often increase above L-mode levels, peaking at f ∼ 250 kHz. This weakly coherent mode is clearest and has narrowest width (Δf/f ∼ 0.45) at low q95 and high Tped, up to 1 keV. The Er well in I-mode is intermediate between L- and H-mode and is dominated by the diamagnetic contribution in the impurity radial force balance, without the Vpol shear typical of H-modes.
Global minimum structures and structural phase diagrams of modified Morse clusters: 11 ≤ N ≤ 30
Authors: Wu Jing , Cheng Longjiu
Published: May 2011

The energetically favored structures of clusters are determined by the interactions among particles. Using the modified Morse pair potential, which has two parameters that can freely control the interactions at the minimum, short range, and long range, we systematically investigated how the interactions determines the global minimum structures of clusters and gave the structural phase diagram at 0 K for each cluster size at the range 11 ≤ N ≤ 30. Compared to the Morse potential, a number of new structures are found, and some of them are unexpected. The global minimum structures of modified Morse clusters can act as structural bank, which will be helpful in the optimization of certain real clusters.
Simulation and theory of a model for tetrahedral colloidal particles
Authors: Munaó G. , Costa D. , Sciortino F. , Caccamo C.
Published: May 2011

We study the thermodynamic and structural properties of a five-site tetrahedral molecular model by means of different Monte Carlo simulation techniques, and the reference interaction site model (RISM) theory of molecular fluids. Simulations and theory signal the onset, at sufficiently low temperatures, of two different tetrahedral molecular arrangements, with a more open topology progressively giving place to a fully bonded one, as the temperature decreases. The RISM theory reproduces the splitting of the static structure factor at low temperatures, a feature intimately related to the onset of the tetrahedral ordering. Less accurate predictions are obtained for the liquid-vapor coexistence and the short-range correlations.
Theoretical efficiency of solar thermoelectric energy generators
Authors: Chen Gang
Published: May 2011

This paper investigates the theoretical efficiency of solar thermoelectric generators (STEGs). A model is established including thermal concentration in addition to optical concentration. Based on the model, the maximum efficiency of STEGs is a product of the opto-thermal efficiency and the device efficiency. The device efficiency increases but the opto-thermal efficiency decreases with increasing hot side temperature, leading to an optimal hot-side temperature that maximizes the STEG efficiency. For a given optical concentration ratio, this optimal hot-side temperature depends on the thermoelectric materials’ nondimensional figure-or-merit, the optical properties of wavelength-selective surface and the efficiency of the optical system. Operating in an evacuated environment, STEGs can have attractive efficiency with little or no optical concentration working in the low temperature range (150–250 °C) for which Bi2Te3-based materials are suitable.
Superconducting quantum interference device as a near-quantum-limited amplifier for the axion dark-matter experiment
Authors: Kinion D. , Clarke John
Published: May 2011

We characterized a microstrip superconducting quantum interference device amplifier (MSA) as a function of frequency and temperature. At 40 mK, with optimal current and flux biases, the maximum gain of 20.4 dB was at 620 MHz; the bandwidth was 21 MHz. The minimum noise temperature TN=48±5 mK occurred at 612 MHz, slightly below the frequency of maximum gain. This value of TN is within a factor of 1.6 of the quantum limit TQ=hf/kB (f is frequency) for a linear, phase-preserving amplifier. Incorporating the MSA into the axion detector at the University of Washington will increase the scan rate by two to three orders of magnitude.
An approximate κ state solutions of the Dirac equation for the generalized Morse potential under spin and pseudospin symmetry
Authors: Ikhdair Sameer M.
Published: May 2011

By using an improved approximation scheme to deal with the centrifugal (pseudo-centrifugal) term, we solve the Dirac equation for the generalized Morse potential with arbitrary spin-orbit quantum number κ. In the presence of spin and pseudospin symmetry, the analytic bound state energy eigenvalues and the associated upper- and lower-spinor components of two Dirac particles are found by using the basic concepts of the Nikiforov-Uvarov method. We study the special cases when κ = ±1 (\documentclass[12pt]{minimal}\begin{document}$l= \widetilde{l}=0,$\end{document}l=l̃=0, s-wave), the non-relativistic limit and the limit when α becomes zero (Kratzer potential model). The present solutions are compared with those obtained by other methods.
Electronic structure, chemical bonding features, and electron charge density of the double-cubane single crystal [Sb7S8Br2](AlCl4)3
Authors: Reshak Ali H. , Kamarudin H. , Auluck S. , Minofar B. , Kityk I. V.
Published: May 2011

The present calculations were performed using all-electron full potential linearized augmented plane wave method based on the density functional theory. We have optimized the structure of the double-cubane single crystal [Sb7S8Br2](AlCl4)3, starting with the x-ray diffraction data Zhang et al., [J. Am. Chem. Soc. 131, 9896 (2009)], by minimization of the forces (1 mRy/au) acting on the atoms, keeping the lattice parameters fixed at the experimental values. Our calculations show that [Sb7S8Br2](AlCl4)3 possesses a wide indirect energy band gap of about 1.6 eV (2.03 eV) using local density approximation (Engel–Vosko generalized gradient approximation) exchange correlation potentials. To describe the bonding properties we have evaluated the electronic charge space density contour in four planes-namely (001), (110), (100), and (010) which show that this compound possesses a considerable anisotropy. The contour plot shows partial ionic and strong covalent bonding between S–Sb, Al–Cl, S–Br, S–S, Cl–Cl, and Sb–Br atoms.
Nonlinear vibration energy harvester using diamagnetic levitation
Authors: Liu L. , Yuan F. G.
Published: May 2011

This letter proposes a nonlinear vibration energy harvester based on stabilized magnetic levitation using diamagnetic. Restoring forces induced by the magnetic field in harvesting vibration energy is employed instead of the forces introduced by conventional mechanical suspensions; therefore dissipation of vibration energy into heat through mechanical suspensions is eliminated. The core of the design consists of two spiral coils made of diamagnetic materials, which serve dual purposes: providing nonlinear restoring force and harnessing eddy current to power external circuits. From the theoretical analysis presented, the proposed harvester has the potential to provide wideband power outputs in low frequency range.
Broad-band and high-temperature ultrasonic transducer fabricated using a Pb(In1/2Nb1/2)-Pb(Mg1/3Nb2/3)-PbTiO3 single crystal/epoxy 1–3 composite
Authors: Zhou Dan , Cheung Kwok Fung , Lam Kwok Ho , Chen Yan , Chiu Yat Ching , Dai Jiyan , Chan Helen Lai Wa , Luo Haosu
Published: May 2011

In this paper, 1–3 composites based on Pb(In1/2Nb1/2)-Pb(Mg1/3Nb2/3)-PbTiO3 (PIMNT) single crystal and high-temperature epoxy were fabricated with various volume fractions of PIMNT single crystal ranging from 0.4 to 0.9. The electrical properties were studied as functions of PIMNT volume fraction and temperature, and it revealed that the nature of ultrahigh electromechanical coupling coefficient (0.82–0.93) and low acoustic impedance (17–19 MRayl) of the composites can be retained within a wide temperature range from room temperature to 185 °C. Single element ultrasonic transducer using the PIMNT 1–3 composite was fabricated and characterized as a function of temperature. It was found that the transducer can still work normally at high temperatures, such as 165 °C, possessing a bandwidth of 95% and insertion loss of –27 dB.
Tunnelling under a conical intersection: Application to the product vibrational state distributions in the UV photodissociation of phenols
Authors: Dixon Richard N. , Oliver Thomas A. A. , Ashfold Michael N. R.
Published: May 2011

When phenol is photoexcited to its S1 (11ππ*) state at wavelengths in the range 257.403 ≤ λphot ≤ 275.133 nm the O−H bond dissociates to yield an H atom and a phenoxyl co-product, with the available energy shared between translation and well characterised product vibration. It is accepted that dissociation is enabled by transfer to an S2 (11πσ*) state, for which the potential energy surface (PES) is repulsive in the O−H stretch coordinate, RO–H. This S2 PES is cut by the S1 PES near RO–H = 1.2 Å and by the S0 ground state PES near RO−H = 2.1 Å, to give two conical intersections (CIs). These have each been invoked—both in theoretical studies and in the interpretation of experimental vibrational activity—but with considerable controversy. This paper revisits the dynamic mechanisms that underlie the photodissociation of phenol and substituted phenols in the light of symmetry restrictions arising from torsional tunnelling degeneracy, which has been neglected hitherto. This places tighter symmetry constraints on the dynamics around the two CIs. The non-rigid molecular symmetry group G4 necessitates vibronic interactions by a2 modes to enable coupling at the inner, higher energy (S1/S2) CI, or by b1 modes at the outer, lower energy (S2/S0) CI. The experimental data following excitation through many vibronic levels of the S1 state of phenol and substituted phenols demonstrate the effective role of the ν16a (a2) ring torsional mode in enabling O–H bond fission. This requires tunnelling under the S1/S2 CI, with a hindering barrier of ∼5000 cm−1 and with the associated geometric phase effect. Quantum dynamic calculations using new ab initio PESs provide quantitative justification for this conclusion. The fates of other excited S1 modes are also rationalised, revealing both spectator modes and intramolecular vibrational redistribution between modes. A common feature in many cases is the observation of an extended, odd-number only, progression in product mode ν16a (i.e., the parent mode which enables S1/S2 tunnelling), which we explain as a Franck-Condon consequence of a major change in the active vibration frequency. These comprehensive results serve to confirm the hypothesis that O−H fission following excitation to the S1 state involves tunnelling under the S1/S2 CI—in accord with conclusions reached from a recent correlation of the excited state lifetimes of phenol (and many substituted phenols) with the corresponding vertical energy gaps between their S1 and S2 PESs.
Soft and hybrid-doped Pb(Zr,Ti)O3 ceramics under stress, electric field, and temperature loading
Authors: Suchanicz J. , Kim-Ngan N.-T. , Konieczny K. , Jankowska-Sumara I. , Balogh A. G.
Published: May 2011

We investigated the influence of uniaxial pressure (0–1000 bars) applied parallelly or perpendicularly to the ac or dc electric field (in a one-dimensional or two-dimensional manner) on dielectric and ferroelectric properties of selected soft and hybrid-doped PZT ceramics (1 mol. % Gd, 1 mol. % La and 1 mol. % (La+Fe)-doped Pb(Zr0.54Ti0.46) O3). Applying uniaxial pressure leads to a reduction of the peak intensity of the electric permittivity (ɛ), of the frequency dispersion, and of the dielectric hysteresis. The peak intensity of ɛ becomes diffused and shifts to a higher temperatures with increasing pressure. Simultaneous application of uniaxial pressure and dc electric field (perpendicular to each other) in the poling process implies in improvement of the ferroelectric properties, indicating a new possibility for poling materials with a high coercive field and/or high electric conductivity. It was also found that simultaneous application of uniaxial pressure and dc electric field (perpendicular to each other) allowed observation of the space charge in the depolarization process. The electrostrictive coefficient Q11 and differential permittivity were evaluated from obtained data. Our results show that applying uniaxial pressure induces similar effects as increasing the Ti-ion concentration in the PZT system. We interpreted our results based on the Cochran soft-mode and domain switching processes under the action of pressure.
The infrared spectra of BF3+ and BF2OH+ trapped in solid neon
Authors: Jacox Marilyn E. , Thompson Warren E.
Published: May 2011

Observations on a Ne:BF3 = 400:1 mixture into which a trace of normal or isotopically enriched water had been introduced, codeposited at 4.3 K with a beam of neon atoms that had been excited in a microwave discharge, demonstrate that a pair of absorptions at 1662 cm−1 and 1722 cm−1 that were previously assigned to the two boron-isotopic species of BF3+ should be reassigned to a BF2 stretching fundamental of BF2OH+. The OH stretching fundamental of that product was identified for the first time at 3240 cm−1. The degenerate BF3 stretching fundamental of 11BF3+ appears at an unusually high frequency, 1790 cm−1, consistent with strong pseudo-Jahn-Teller interaction of that ground-state fundamental with the $\tilde{\rm B}$B̃2E′ electronic state, as predicted by theory. The recent availability of detailed ab initio and density functional calculations of the vibrational fundamentals of BF2− and BF3− facilitates assignment of the infrared absorptions of those two products.
An experimentally validated and parameterized periodic unit-cell reconstruction of open-cell foams
Authors: De Jaeger P. , T’Joen C. , Huisseune H. , Ameel B. , De Paepe M.
Published: May 2011

The physical behavior of open-cell foams depends on their microscopic structure. An open-cell geometrical model is proposed, which can serve as the basis for a future macroscopic analysis. The strut geometry is of particular interest, as it is reported to have substantial influence on the occurring thermo-hydraulic and mechanical phenomena. Axial strut size variation, as well as the porosity dependence of shape is quantified and included in a geometrical model. The foam is generated by placing the struts on an elongated tetrakaidecahedron. The required input parameters for the model are two cell dimensions, corresponding to the mean transverse and conjugate diameters of the ellipse encompassing a cell, and the strut cross-sectional surface area at its midpoint between two nodes. The foam geometry is generated iteratively, as porosity is used as validation. A high resolution micro-computed tomography scan is performed to measure the three parameters, the resulting porosity and surface-to-volume ratio. This allows to validate the model. The predictions are found to be within measurement accuracy. A numerical implementation of the model in the preprocessor of a commercial CFD package is demonstrated.
Determination of hole effective mass in SiO2 and SiC conduction band offset using Fowler–Nordheim tunneling characteristics across metal-oxide-semiconductor structures after applying oxide field corrections
Authors: Kumar Chanana Ravi
Published: May 2011

Fowler–Nordheim electron and hole tunneling characteristics across 4H-SiC MOS diodes are studied. Their slope constants are used to determine the hole effective mass in the thermal SiO2 and the 4H-SiC conduction band offset. The hole effective mass in the SiO2 is found to be 0.58 m, where m is the free electron mass. The 4H-SiC conduction band offset is found to be 2.78 eV. The average oxide fields used in the carrier tunneling characteristics are formulated. It is found that anode and cathode field corrections by the flatband voltage are critical in the evaluation of the above tunneling parameters.
Nuclear spin dependence of the reaction of ${\rm H}_3^+$H3+ with H2. I. Kinetics and modeling
Authors: Crabtree Kyle N. , Tom Brian A. , McCall Benjamin J.
Published: May 2011

The chemical reaction \documentclass[12pt]{minimal}\begin{document}${\rm H}_3^+$\end{document}H3+ + H2 → H2 + \documentclass[12pt]{minimal}\begin{document}${\rm H}_3^+$\end{document}H3+ is the simplest bimolecular reaction involving a polyatomic, yet is complex enough that exact quantum mechanical calculations to adequately model its dynamics are still unfeasible. In particular, the branching fractions for the “identity,” “proton hop,” and “hydrogen exchange” reaction pathways are unknown, and to date, experimental measurements of this process have been limited. In this work, the nuclear-spin-dependent steady-state kinetics of the \documentclass[12pt]{minimal}\begin{document}${\rm H}_3^+$\end{document}H3+ + H2 reaction is examined in detail, and employed to generate models of the ortho:para ratio of \documentclass[12pt]{minimal}\begin{document}${\rm H}_3^+$\end{document}H3+ formed in plasmas of varying ortho:para H2 ratios. One model is based entirely on nuclear spin statistics, and is appropriate for temperatures high enough to populate a large number of \documentclass[12pt]{minimal}\begin{document}${\rm H}_3^+$\end{document}H3+ rotational states. Efforts are made to include the influence of three-body collisions in this model by deriving nuclear spin product branching fractions for the \documentclass[12pt]{minimal}\begin{document}${\rm H}_5^+$\end{document}H5+ + H2 reaction. Another model, based on rate coefficients calculated using a microcanonical statistical approach, is appropriate for lower-temperature plasmas in which energetic considerations begin to compete with the nuclear spin branching fractions. These models serve as a theoretical framework for interpreting the results of laboratory studies on the reaction of \documentclass[12pt]{minimal}\begin{document}${\rm H}_3^+$\end{document}H3+ with H2.
Dynamics of cis isomers in highly sensitive amino-azobenzene monolayers: The effect of slow relaxation on photo-induced anisotropy
Authors: Yi Youngwoo , Fang Guanjiu , Maclennan Joseph E. , Clark Noel A. , Dahdah Joseph , Furtak Thomas E. , Kim Kyoungsik , Farrow Matthew J. , Korblova Eva , Walba David M.
Published: May 2011

The initial development of photoinduced anisotropy in highly photosensitive monolayers of an aminoazobenzene molecule (dMR, a derivative of o-methyl red) that are initially randomized using circularly polarized light is found to be significantly slower than in monolayers randomized by thermal relaxation. We propose that this is a direct consequence of the slow thermal relaxation of isomers from the cis to the trans state and suggest that such considerations are important in designing even more sensitive photoactive monolayers and in understanding their photodynamics.
Improved luminescence and thermal stability of semipolar (11-22) InGaN quantum dots
Authors: Das A. , Dimitrakopulos G. P. , Kotsar Y. , Lotsari A. , Kehagias Th. , Komninou Ph. , Monroy E.
Published: May 2011

Semipolar (11-22)-oriented InGaN/GaN quantum dots (QDs) emitting in the 380–620 nm spectral range were synthesized by plasma-assisted molecular-beam epitaxy. The influence of the growth temperature on the properties of InGaN QDs has been investigated by photoluminescence and transmission electron microscopy. Growth temperatures low enough to prevent indium desorption provide a favorable environment to semipolar plane (11-22) to enhance the internal quantum efficiency of InGaN/GaN nanostructures.
Molecular density functional theory of solvation: From polar solvents to water
Authors: Zhao Shuangliang , Ramirez Rosa , Vuilleumier Rodolphe , Borgis Daniel
Published: May 2011

A classical density functional theory approach to solvation in molecular solvent is presented. The solvation properties of an arbitrary solute in a given solvent, both described by a molecular force field, can be obtained by minimization of a position and orientation-dependent free-energy density functional. In the homogeneous reference fluid approximation, limited to two-body correlations, the unknown excess term of the functional approximated by the angular-dependent direct correlation function of the pure solvent. We show that this function can be extracted from a preliminary MD simulation of the pure solvent by computing the angular-dependent pair distribution function and solving subsequently the molecular Ornstein-Zernike equation using a discrete angular representation. The corresponding functional can then be minimized in the presence of an arbitrary solute on a three-dimensional cubic grid for positions and Gauss-Legendre angular grid for orientations to provide the solvation structure and free-energy. This two-step procedure is proved to be much more efficient than direct molecular dynamics simulations combined to thermodynamic integration schemes. The approach is shown to be relevant and accurate for prototype polar solvents such as the Stockmayer solvent or acetonitrile. For water, although correct for neutral or moderately charged solute, it tends to underestimate the tetrahedral solvation structure around H-bonded solutes, such as spherical ions. This can be corrected by introducing suitable three-body correlation terms that restore both an accurate hydration structure and a satisfactory energetics.
Thermal decomposition mechanisms of methylamine, ethylamine, and 1-propylamine on Si(100)-2 × 1 surface
Authors: Cho Jieun , Choi Cheol Ho
Published: May 2011

The thermal decomposition reactions of methylamine, ethylamine, and 1-propylamine absorbed on Si(100)-2 × 1 surface were theoretically investigated. Eight decomposition channels were found leading to desorption products of imine, H2, alkyl cyanide, ammonia, aziridine, alkene, azetidine, and cyclopropane, which supports the experimental assignments. Our mechanistic studies strongly suggest that the alkyl cyanide (hydrogen cyanide in the case of methylamine) channel is coupled with the hydrogen desorption step. The β-hydrogen of ethylamine and 1-propylamine was found to undergo additional decomposition reactions producing aziridine and alkene, which were classified as γ- and β-eliminations, respectively. It was also found that the γ-hydrogen of 1-propylamine undergoes azetidine and cyclopropane producing decompositions, which were classified as δ- and γ-eliminations. In general, γ- and δ-hydrogen involved decomposition reactions are kinetically less favorable than β-hydrogen involved ones. Consequently, it is expected that the thermal decompositions of the primary alkyl amines with longer alkyl chains would not add additional favorable decomposition channels. Except alkyl cyanide and ammonia desorption channels, the decompositions occur in a concerted fashion.
Band gap formation in graphene by in-situ doping
Authors: Park Jeongho , Mitchel W. C. , Brown Gail J. , Elhamri Said , Grazulis Lawrence , Smith Howard E. , Pacley Shanee D. , Boeckl John J. , Eyink Kurt G. , Mou Shin , Tomich David H. , Hoelscher John E.
Published: May 2011

We report the formation of band gaps in as-grown stacks of epitaxial graphene with opposite doping. Control of in-situ doping during carbon source molecular beam epitaxy growth on SiC was achieved by using different carbon sources. Doping heterostructures were grown by stacking n-type material from a C60 source on p-type material from a graphite filament source. Activation energies for the resistivity and carrier concentration indicated band gaps up to 200 meV. A photoconductivity threshold was observed in the range of the electrical activation energies. Band gap formation is attributed to electric fields induced by spatially separated ionized dopants of opposite charge.
Trap-limited and percolation conduction mechanisms in amorphous oxide semiconductor thin film transistors
Authors: Lee Sungsik , Ghaffarzadeh Khashayar , Nathan Arokia , Robertson John , Jeon Sanghun , Kim Changjung , Song I-Hun , Chung U-In
Published: May 2011

The electron conduction mechanism in the above-threshold regime in amorphous oxide semiconductor thin film transistors is shown to be controlled by percolation and trap-limited conduction. The band tail state slope controls the field effect mobility, while the average spatial coherence length and potential fluctuation control percolation conduction. In these limits, the field effect mobility is found to follow a power law, from which a universal mobility versus carrier concentration dependence is extracted.
Adsorption properties versus oxidation states of rutile TiO2(110)
Authors: Martinez Umberto , Hammer Bjørk
Published: May 2011

Using density functional theory we have studied the adsorption properties of different atoms and molecules deposited on a stoichiometric, reduced, and oxidized rutile TiO2(110) surface. Depending on the oxidation state of the surface, electrons can flow from or to the substrate and, therefore, negatively or positively charged species are expected. In particular, we have found that a charge transfer process from or to the surface always occurs for highly electronegative or highly electropositive species, respectively. For atoms or molecules with intermediate electron affinity, the direction of the charge flow depends on the oxidation state of the rutile surface and on the adsorption site. Generally, the charging effect leads to more stable complexes. However, the increase in the binding energy of the adsorbates is highly dependent on the electronic states of the surface prior to the adsorption event. In this work we have analyzed in details these mechanisms and we have also established a direct correlation between the enhanced binding energy of the adsorbates and the induced gap states.
Proton conduction in hydrous glasses of the join CaAl2Si2O8–CaMgSi2O6: An impedance and infrared spectroscopic study
Authors: Fanara Sara , Behrens Harald
Published: May 2011

Hydrous silicate glasses with compositions along the join diopside–anorthite (An, CaAl2Si2O8)–(Di, CaMgSi2O6) containing up to 3 wt. % H2O were synthesized at temperatures 1523–1723 K and pressures of 200 MPa in an internally heated gas pressure vessel. The water content of the glasses was analyzed by Karl-Fischer titration. Infrared microspectroscopy was used to test the homogeneity of the water distribution and to measure the concentrations of OH groups and H2O molecules before and after conductivity measurements. The electrical conductivity was measured by impedance spectroscopy at temperature up to 685 K. A positive correlation between water content and conductivity was observed for An100 from 0 to 1.8 wt. % H2O, for An50Di50 (in mol. %) from 1.5 to 2.8 wt. % H2O, and for Di100 from 0 to 1.2 wt. % H2O. At same water content of ∼1.2 wt. %, the conductivity was three orders of magnitude higher in Di100 than in the other two glasses, emphasizing the importance of non-bridging oxygens on the transport of hydrous charge carriers. Consistent with findings in literature, we conclude that protons are the predominant mobile charge carriers in alkali-free hydrous silicate glasses. Conductivity data were evaluated in terms of proton diffusivity by the Nernst-Einstein equation. The obtained diffusion coefficients range from 10−17 m2/s for An50Di50 with 1.50 wt. % of H2O at 596 K to 10−12 m2/s for An50Di50 with 2.77 wt. % of H2O at 685 K.
High-sensitivity and wide-directivity ultrasound detection using high Q polymer microring resonators
Authors: Ling Tao , Chen Sung-Liang , Guo L. Jay
Published: May 2011

Small size ultrahigh Q polymer microrings working at near visible wavelength have been experimentally demonstrated as ultralow noise ultrasound detectors with wide directivity at high frequencies (>20 MHz). By combining a resist reflow and a low bias continuous etching and passivation process in mold fabrication, imprinted polymer microrings with drastically improved sidewall smoothness were obtained. An ultralow noise-equivalent pressure of 21.4 Pa over 1–75 MHz range has been achieved using a fabricated detector of 60 μm diameter. The device’s wide acceptance angle with high sensitivity considerably benefits ultrasound-related imaging.
Strain in Si doped GaN and the Fermi level effect
Authors: Xie Jinqiao , Mita Seiji , Rice Anthony , Tweedie James , Hussey Lindsay , Collazo Ramón , Sitar Zlatko
Published: May 2011

Using high resolution x-ray diffraction and Hall effect measurements, we found that the tensile strain caused by dislocation inclination in Si doped GaN became immeasurable when carbon codoping was used to compensate the free carriers. This result suggested that the tensile strain is related to free carrier concentration instead of Si concentration. Such an effect could be explained by the Fermi level effect on the surface-mediated dislocation climb governed by Ga vacancies, whose concentration is strongly influenced by the Fermi level position. This phenomenon is possibly similar to the well-known Fermi level effect in GaAs and GaP systems.
Simultaneous measurement of temperature and emissivity of lunar regolith simulant using dual-channel millimeter-wave radiometry
Authors: McCloy J. S. , Sundaram S. K. , Matyas J. , Woskov P. P.
Published: May 2011

Millimeter wave (MMW) radiometry can be used for simultaneous measurement of emissivity and temperature of materials under extreme environments (high temperature, pressure, and corrosive environments). The state-of-the-art dual channel MMW passive radiometer with active interferometric capabilities at 137 GHz described here allows for radiometric measurements of sample temperature and emissivity up to at least 1600 °C with simultaneous measurement of sample surface dynamics. These capabilities have been used to demonstrate dynamic measurement of melting of powders of simulated lunar regolith and static measurement of emissivity of solid samples. The paper presents the theoretical background and basis for the dual-receiver system, describes the hardware in detail, and demonstrates the data analysis. Post-experiment analysis of emissivity versus temperature allows further extraction from the radiometric data of millimeter wave viewing beam coupling factors, which provide corroboratory evidence to the interferometric data of the process dynamics observed. These results show the promise of the MMW system for extracting quantitative and qualitative process parameters for industrial processes and access to real-time dynamics of materials behavior in extreme environments.
Landau theory description of observed isotropic to anisotropic phase transition in mixed clay gels
Authors: Pujala Ravi Kumar , Pawar Nisha , Bohidar H. B.
Published: May 2011

A characteristic new cooperative dehydration transition, in 1:1 Laponite-MMT cogel, was observed at Tc ≈ 60 °C, a temperature at which the storage modulus (G′) and depolarization ratio (Dp) showed sharp increase, and the isotropic cogel turned into an anisotropic one. The dehydration dynamics could be described through power-law relations: G′ ∼ (Tc – T)−γ and Dp ∼ (Tc – T)−β with γ ≈ β = 0.40 ± 0.05. The x-ray diffraction data revealed that the crystallite size decreased from 17 nm (at 20 °C) to 10 nm (at 80 °C) implying loss of free and inter-planar water. When this cogel was spontaneously cooled below Tc, it exhibited much larger storage modulii values which implied the existence of several metastable states in this system. This phase transition could be modeled through Landau theory, where the depolarization ratio was used as experimental order parameter (ψ). This parameter was found to scale with temperature, as ψ ∼ (Tc – T)−α, with power-law exponent α = 0.40 ± 0.05; interestingly, we found α ≈ β ≈ γ.
Time-resolved spectroscopic diagnostic of laser-induced plasma on germanium targets
Authors: Camacho J. J. , Diaz L. , Poyato J. M. L.
Published: May 2011

Time-resolved optical emission measurements have been made in laser-induced plasma plumes following CO2 pulsed-laser (10.591 μm, 64 ns and intensity from 0.27 to 4.9 GW cm−2) irradiation of germanium targets. The temporal behavior of Ge atoms and ionized excited species Ge3+, Ge2+, and Ge+ is reported. The results show a faster decay of the continuum emission and Ge3+, Ge2+ ionic species than in the case of Ge+ and neutral Ge atoms. The velocity distributions for Ge3+, Ge2+, Ge+, and Ge species are obtained from time-of-flight measurements. Electron density in the laser-induced plasma was estimated from the analysis of spectral data at various times from the CO2 laser pulse incidence. From the intensity decay with the delay time for Ge+, Ge2+, and Ge3+, we estimated the three-body electron-ion recombination rate constants for these species.
Field- and current-induced domain-wall motion in permalloy nanowires with magnetic soft spots
Authors: Vogel Andreas , Wintz Sebastian , Gerhardt Theo , Bocklage Lars , Strache Thomas , Im Mi-Young , Fischer Peter , Fassbender Jürgen , McCord Jeffrey , Meier Guido
Published: May 2011

We study field- and current-induced domain-wall motion in permalloy nanowires containing a square-shaped magnetically softened region. Implantation of chromium ions is used to induce pinning sites via a local reduction in the saturation magnetization. Micromagnetic simulations, magnetic transmission soft x-ray microscopy, and electrical measurements are employed to characterize the pinning potential which significantly differs for transverse and vortex walls. Reliable domain-wall depinning from a so-called magnetic soft spot by single current pulses is observed. This demonstrates the suitability of these pinning sites for applications.
Far-infrared and terahertz lasing based upon resonant and interband tunneling in InAs/GaSb heterostructures
Authors: Zhang W.-D. , Woolard D. L.
Published: May 2011

A far-infrared lasing device based upon conduction-band to heavy-hole level interband transitions within a double-barrier broken-gap structure is presented. The upper conduction-band level is populated by resonant tunneling electron injection, and the lower heavy-hole state is depopulated by ultrafast valence-band electron interband tunneling. Significant optical gain exceeding 103 cm−1 for operation in the frequency range 1.9–3.4 THz is predicted from a Kane multiband model based study of an unoptimized structure.
Primitive chain network simulations for asymmetric star polymers
Authors: Masubuchi Yuichi , Yaoita Takatoshi , Matsumiya Yumi , Watanabe Hiroshi
Published: May 2011

For branched polymers, the curvilinear motion of the branch point along the backbone is a significant relaxation source but details of this motion have not been well understood. This study conducts multi-chain sliplink simulations to examine effects of the spatial fluctuation and curvilinear hopping of the branch point on the viscoelastic relaxation. The simulation is based on the primitive chain network model that allows the spatial fluctuations of sliplink and branch point and the chain sliding along the backbone according to the subchain tension, chemical potential gradients, drag force against medium, and random force. The sliplinks are created and/or disrupted through the motion of chain ends. The curvilinear hopping of the branch point along the backbone is allowed to occur when all sliplinks on a branched arm are lost. The simulations considering the fluctuation and the hopping of the branch point described well the viscoelastic data for symmetric and asymmetric star polymers with a parameter set common to the linear polymer. On the other hand, the simulations without the branch point motion predicted unreasonably slow relaxation for asymmetric star polymers. For asymmetric star polymers, further tests with and without the branch point hopping revealed that the hopping is much less important compared to the branch point fluctuation when the lengths of the short and long backbone arms are not very different and the waiting time for the branch point hopping (time for removal of all sliplinks on the short arm) is larger than the backbone relaxation time. Although this waiting time changes with the hopping condition, the above results suggest a significance of the branch point fluctuation in the actual relaxation of branch polymers.
Polymorphic transformation mechanism of η and η′ in single crystalline Cu6Sn5
Authors: Li M. Y. , Zhang Z. H. , Kim J. M.
Published: May 2011

Polymorphic transformation mechanism of η and η′ in single crystalline Cu6Sn5 has been investigated in this study. η phase exists at room temperature in the quenched specimens and transforms to η′ phase under aging at 150 °C for 40 d. The nucleation and growth of η′ phase is observed by field emission scanning electron microscope and surface reconstruction of polymorphic transformation is confirmed by both x-ray diffractometer and differential scanning calorimetry analysis. The results show that the volumetric strain energy is the dominant reason for occurring polymorphic transformation rather than order-disorder transition of η and η′ phases.
Fast electrical switching of spin injection in nonlocal spin transport devices
Authors: Fuhrer A. , Alvarado S. F. , Salis G. , Allenspach R.
Published: May 2011

We present spin-injection experiments in a nonlocal spin transport device where spin is injected from a ferromagnetic FeCo electrode into a GaAs epilayer. The magnetization of the injection contact is switched by Oersted fields generated by alternating current pulses. This enables fast and offset-free measurements of nonlocal spin signals. Due to a negligible time-averaged electron spin polarization, dynamic nuclear polarization effects are small and Hanle curves measured down to T=3 K can be fit very accurately by drift-diffusion theory if a small constant Overhauser field BN=0.4 mT is accounted for.
Electronic tuning of magnetic permeability in Co2Z hexaferrite toward high frequency electromagnetic device miniaturization
Authors: Chen Yajie , Daigle Andrew , Fitchorov Trifon , Hu Bolin , Geiler Michael , Geiler Anton , Vittoria C. , Harris V. G.
Published: May 2011

The magnetic and magnetostriction properties of Z-type cobalt-doped barium hexaferrite with perpendicular c-axis crystallographic texture are presented. The hexaferrite was utilized as a component in Co2Z/lead magnesium niobate-lead titanate multiferroic heterostructures whose tunability of permeability with electric field in terms of ferromagnetic resonance shift was supported by experiments and theoretical calculation. A permeability change of 16% was measured by an induced magnetic field of 38 Oe under the application of 6 kV/cm of electric field. These findings lay the foundation for the application of Z-type hexaferrites in tunable rf and microwave devices valued for sending, receiving, and manipulating electromagnetic signals.
Reconstruction of a scanned topographic image distorted by the creep effect of a Z scanner in atomic force microscopy
Authors: Han Cheolsu , Chung Chung Choo
Published: May 2011

We analyzed the illusory slopes of scanned images caused by the creep of a Z scanner in an atomic force microscope (AFM) operated in constant-force mode. A method to reconstruct a real topographic image using two scanned images was also developed. In atomic force microscopy, scanned images are distorted by undesirable effects such as creep, hysteresis of the Z scanner, and sample tilt. In contrast to other undesirable effects, the illusory slope that appears in the slow scanning direction of an AFM scan is highly related to the creep effect of the Z scanner. In the controller for a Z scanner, a position-sensitive detector is utilized to maintain a user-defined set-point or force between a tip and a sample surface. This serves to eliminate undesirable effects. The position-sensitive detector that detects the deflection of the cantilever is used to precisely measure the topography of a sample. In the conventional constant-force mode of an atomic force microscope, the amplitude of a control signal is used to construct a scanned image. However, the control signal contains not only the topography data of the sample, but also undesirable effects. Consequently, the scanned image includes the illusory slope due to the creep effect of the Z scanner. In an automatic scanning process, which requires fast scanning and high repeatability, an atomic force microscope must scan the sample surface immediately after a fast approach operation has been completed. As such, the scanned image is badly distorted by a rapid change in the early stages of the creep effect. In this paper, a new method to obtain the tilt angle of a sample and the creep factor of the Z scanner using only two scanned images with no special tools is proposed. The two scanned images can be obtained by scanning the same area of a sample in two different slow scanning directions. We can then reconstruct a real topographic image based on the scanned image, in which both the creep effect of the Z scanner and the slope effect of the sample have been eliminated. The slope effect of the sample should be eliminated so as to avoid further distortion after removal of the creep effect. The creep effect can be removed from the scanned image using the proposed method, and a real topographic image can subsequently be efficiently reconstructed.