bluuebunny/crossref_metadata_2025 huggingface dataset:
In vivo biochemistry: quantifying ion and metabolite levels in individual cells or cultures of yeast
Authors: Bermejo Clara , Ewald Jennifer C. , Lanquar Viviane , Jones Alexander M. , Frommer Wolf B.
Published: July 2011

Over the past decade, we have learned that cellular processes, including signalling and metabolism, are highly compartmentalized, and that relevant changes in metabolic state can occur at sub-second timescales. Moreover, we have learned that individual cells in populations, or as part of a tissue, exist in different states. If we want to understand metabolic processes and signalling better, it will be necessary to measure biochemical and biophysical responses of individual cells with high temporal and spatial resolution. Fluorescence imaging has revolutionized all aspects of biology since it has the potential to provide information on the cellular and subcellular distribution of ions and metabolites with sub-second time resolution. In the present review we summarize recent progress in quantifying ions and metabolites in populations of yeast cells as well as in individual yeast cells with the help of quantitative fluorescent indicators, namely FRET metabolite sensors. We discuss the opportunities and potential pitfalls and the controls that help preclude misinterpretation.
Hydrodynamic simulation and thermodynamic characterization of functionally graded material induced isentropic compression: Towards optimum density profile
Authors: Ray Aditi , Menon S. V. G.
Published: July 2011

Hydrodynamic simulations of dynamic compression experiments reveal that heating as well as entropy production in the target are much lower along quasi-isentropes, generated using impactors employing functionally graded material (FGM), than in shock compression. The possibility of achieving quasi-isentropic compression using FGM, in both gas gun and explosive driven systems, was explored in a recent paper. Qualitative analyses of temporal profiles of pressure pulse generated in the target, obtained with various density distributions within FGM impactors, showed that quadratic density variation is most suitable. This paper attempts to re-establish this finding by identifying the signatures of quasi-isentropic compression from basic thermodynamic aspects. It is shown that quadratic density variation is most suitable candidate as it leads to least entropy increase for a specific peak pressure. Further, the optimum density profile, found by genetic algorithm based optimization tool, with density of individual layers as variables, is shown to have good agreement with quadratic density function. Finally, we explore the possibility of using layers of commonly available materials with increasing shock impedances for a generation of isentropic compression. It is shown that ramp pressure wave can be produced by optimizing the layer thicknesses of the materials used.
Transport and x-ray photoelectron spectroscopy properties of (Ni1−xCux)Mn2O4 and Ni(Mn2−yCuy)O4
Authors: Watanabe N. , Nakayama H. , Fukao K. , Munakata F.
Published: July 2011

The temperature dependence of the electrical resistivity and the thermoelectric power in (Ni1−xCux)Mn2O4 (x = 0 to 0.5) and Ni(Mn2−yCuy)O4 (y = 0 to 0.2) are investigated. The electrical resistivity of samples with x < 0.1 appears to be hardly changed with increasing Cu content. In all of the samples, the electron transfer is thermally activated and shows semiconducting behavior. The electric conductivity is described by a small polaron hopping mechanism except for x ≥ 0.3. The thermoelectric power at 100 °C is found to change sign from negative to positive with Cu substitution both in (Ni1−xCux)Mn2O4 and Ni(Mn2−yCuy)O4. Furthermore, the thermoelectric powers of these samples with x, y < 0.1 are found to change sign from negative to positive with increasing temperature. The valence distribution of the Mn ions is estimated using x-ray photoelectron spectroscopy. The peak intensity ratio of Mn3+/Mn4+ is maximized whereas that of Ni3+/Ni2+ is minimized at about x, y = 0.05 to 0.07. These results suggest that the Mn4+ and Ni2+ ions change disproportionately into Mn3+ and Ni3+ ions with increasing Cu content up to x, y = 0.1. The valence states of Ni in the system are in accordance with those of Mn, which is necessary in order to maintain charge neutrality and oxygen stoichiometry. The normalized peak intensity of the charge transfer satellite peak of Mn 2p3/2 is rapidly increased by Cu substitution up to x, y = 0.1. With further Cu substitution when x, y > 0.1, the ratio of increase in the peak intensity of the charge transfer satellite is decreased. These facts suggest that the decrease of electrical resistivity when x, y ≥ 0.1 is caused by an increase of holes having O 2p character, and the changes of sign in the thermoelectric power might take care of the competition between the electron conduction term and the hole conduction term caused by the charge transfer from O 2p to transition metal 3d orbitals.
Sub-THz dielectric resonance in single crystal yttrium iron garnet and magnetic field tuning of the modes
Authors: Popov M. A. , Zavislyak I. V. , Srinivasan G.
Published: July 2011

The observation of dielectric resonance over the frequency range 40-110 GHz in single crystal yttrium iron garnet (YIG) and its magnetic field tuning characteristics are reported. The dimensions of YIG are appropriately chosen in order to have the dielectric resonance occur at a much higher frequency than the ferromagnetic resonance and avoid any hybrid spin-electromagnetic modes. The dielectric modes are magnetically tunable by 1 GHz with a magnetic field of ∼1.75 kOe. The tuning range and required bias magnetic fields, however, can be controlled with the sample dimensions (or the demagnetization factor Nzz). Theoretical calculations on magnetic field tuning characteristics for the dielectric modes are in reasonable agreement with the data. The theory also predicts a similar magnetic tuning of the dielectric modes in the sub-THz frequency range as well. The dielectric modes that can be tuned with a magnetic field are of importance for the realization of low-loss tunable devices, including resonators, isolators, and phase shifters operating in the sub-THz region.
Resistivity of thin gold films on mica induced by electron-surface scattering from a self-affine fractal surface
Authors: Munoz Raul C. , Gonzalez-Fuentes Claudio A. , Henriquez Ricardo , Espinosa Andres , Kremer German , Moraga Luis , Ibañez-Landeta Antonio , Bahamondes Sebastian , Donoso Sebastian , Flores Marcos
Published: July 2011

We present a rigorous comparison between resistivity data and theoretical predictions involving the theory of Palasantzas [G. Palasantzas and J. Barnas, Phys. Rev. B 56, 7726 (1997)], and the modified Sheng, Xing, and Wang-fractal theory [R. C. Munoz et al., Phys. Rev. B 66, 205401 (2002)], regarding the resistivity arising from electron scattering by a self-affine fractal surface on gold films using no adjustable parameters. We find that both theories lead to an approximate description of the temperature dependence of the resistivity data. However, the description of charge transport based upon fractal scaling seems oversimplified, and the predicted increase in resistivity arising from electron-surface scattering seems at variance with other experimental results. If the samples are made up of grains such that the mean grain diameter D > ℓ0(300), the electronic mean free path in the bulk at 300 K, then the predicted increase in resistivity at 4 K is of the order of a few percent. This contradicts published measurements of magnetomorphic effects arising from size effects where electron-surface scattering is the dominant electron scattering mechanism at 4 K. On the contrary, if the samples are made out of grains such that D < ℓ0(300), then the dominant electron scattering mechanism controlling the resistivity is not electron-surface scattering but rather electron-grain boundary scattering, and the latter electron scattering mechanism is not included in either theory.
Photoluminescence from silicon nitride—no quantum effect
Authors: Kistner J. , Chen X. , Weng Y. , Strunk H. P. , Schubert M. B. , Werner J. H.
Published: July 2011

Silicon nitride compounds emit photoluminescence all over the visible range. Recent studies ascribed this luminescence to quantum-size effects within silicon nanocrystals that were either shown or assumed to form inside the silicon nitride matrix; the luminescence of the matrix itself was ignored. In contrast, observing the same luminescence even without the presence of silicon crystallites, our work identifies the silicon nitride matrix itself as responsible for the photoluminescence. All experimental observations are well explained by band tail luminescence from the silicon matrix. In contrast to the silicon nanocrystal approach, our model explains all aspects of the luminescence. As a consequence, we conclude that silicon nitride films are inappropriate if one aims at investigating photoluminescence from silicon nanocrystals within such a matrix.
Calculated effects of work function changes on the dispersion of secondary electron emission data: Application for Al and Si and related elements
Authors: Cazaux Jacques
Published: July 2011

The published secondary electron yield (SEY) data, δ = f(E°), are characterized by a poor level of agreement, rarely more than 25% and lower for a common element such as Al. Some possible sources of discrepancies are related to sample preparation, leading to differences in surface composition (contamination and oxidation). This is theoretically explored by a quantitative estimate of a change of the work function, φ (or electron affinity, χ), on the escape probability, A, of secondary electrons (SEs) and consequently on the SEY data of clean and oxidized samples. An electron-stimulated reduction effect may also explain the change of the SEY with the incident electron dose (fluence). Deduced from analytical expressions for the SE angular and energy distributions, ∂δ/∂α and ∂δ/∂Ek, respectively, the present investigation also includes instrumental effects due to work function differences when a partial angular collection of SEs is conducted. Although it is illustrated here for Al and Si, the present methodology may be applied to any type of sample of known physical characteristics. Practical strategies for use in SEY measurement and in scanning electron microscopy are indicated.
Positive ion emission from oxidized aluminum during ultraviolet excimer laser irradiation
Authors: Khan Enamul , Langford S. C. , Dickinson J. T.
Published: July 2011

We report quadrupole mass-selected time-of-flight measurements of positive ions from oxidized aluminum metal (and for comparison, single-crystal sapphire) during pulsed excimer laser irradiation at 193 and 248 nm. This work focuses on laser fluences well below onset of rapid etching or optical breakdown. By far the most intense emissions are due to Al+. On previously unexposed material, the ion kinetic energies are initially well above the photon energy, consistent with the ejection of Al+ sorbed at surface electron traps. During prolonged irradiation, the emission intensities and kinetic energies gradually fall. Emission from patches of oxide would account for previous reports of laser-induced Al+ emission from metallic aluminum surfaces cleaned by ion etching if patches of thin oxide were to survive the etching treatment.
Relationship between electromagnetic and acoustic emissions during plastic deformation of gamma-irradiated LiF monocrystals
Authors: Hadjicontis V. , Mavromatou C. , Mastrogiannis D. , Antsygina T. N. , Chishko K. A.
Published: July 2011

Simultaneous measurements of acoustic emissions (AE) and electromagnetic emissions (EME) during plastic deformation and destruction under uniaxial compression along 〈001〉 direction are made on LiF monocrystals after gamma irradiation by 60Co source. The irradiation doses are 1, 2, and 10 Mrad. The EME measurements in the radio-frequency range are carried out using two types of electromagnetic sensors: (i) a simple electrical stub antenna and (ii) a toroidal inductance coil. Two checking experiments on unirradiated crystals are performed as the starting point to discover the effect of gamma irradiation on acoustic and electromagnetic emissive ability of plastically deformed ionic crystals. Unirradiated LiF monocrystals demonstrate high-intensive EME at easy glide and work hardening stages, as well as at the fracture during destruction of the sample. At radiation doses more than ∼1 Mrad, in the active loading stage the EME of LiF monocrystals vanishes, except few individual electromagnetic pulses (only at 1 and 2 Mrad doses), which are time correlated with well-defined drop-jumps on the loading diagram and therefore can be associated with macroscopic crack openings. Moderate electromagnetic activity in irradiated crystals occurs only in the final stage of deformation at the complete fracture of the sample. Thus, after gamma irradiation the formation of polarization currents due to dynamic interaction between charged vacancies and moving dislocations is suppressed, and only EME connected with the redistribution of the free charge on the crack branches is observed. Acoustic emission diagrams of low-irradiated LiF are typical for the work hardening stage in crystals containing a great amount of strong point stoppers. At larger irradiation doses the AE diagram displays quite different behavior at low- and high-loading regions with a sharp boundary between them. The low-loading region shows poor AE activity, which changes sharply into high-active burst-like emission with an increase in loading. The boundary between two regions shifts to higher loadings with radiation dose. The higher is the radiation dose the lower is the relative intensity of AE in the high-stressed region. The physical mechanisms of EME and AE in gamma-irradiated ionic crystals are discussed.
Note: Solution NMR probe for the study of CO2 sequestration at elevated pressure and temperature
Authors: Diefenbacher J. , Piwowarczyk J. , Marzke R. F.
Published: July 2011

Nuclear magnetic resonance is widely employed in studies of chemical reactions and molecular motions at moderate pressure and temperature, but for CO2 solutions under supercritical conditions encountered in geological or mineral sequestration (pressures to 150 atm and temperatures to 150 °C) a specialized variable-temperature probe is required. The critical component of such a probe is its pressure chamber, and our working design is presented along with examples of its use in 13C NMR measurements of bicarbonate and dissolved CO2 fractions as functions of time, following initial pressurization to 70 atm. Also shown are final, steady-state values of these fractions as functions of temperature from 50 to 125 °C at 70 atm.
Drain voltage dependent analytical model of tunnel field-effect transistors
Authors: Verhulst Anne S. , Leonelli Daniele , Rooyackers Rita , Groeseneken Guido
Published: July 2011

Tunnel field-effect transistors (TFETs) are potential successors of metal-oxide-semiconductor FETs because they promise superior input characteristics. However, the output characteristics of TFETs are poorly understood, and sometimes a superlinear onset, undesirable for circuit design, is observed. We present the first analytical model to include the impact of the drain voltage on the TFET performance. The model is developed for both a pure line-tunneling TFET and a pure point-tunneling TFET. Good agreement is observed with device simulations, especially for line-tunneling TFETs. Our model highlights and explains the superlinear onset of the output characteristics, thereby enabling an improved analysis of experimental data. Increasing the source doping level and switching to a smaller bandgap material can remove the undesired onset. We confirm this finding with our experimental data.
Magnetic field gradient effects on Rayleigh-Taylor instability with continuous magnetic field and density profiles
Authors: Yang B. L. , Wang L. F. , Ye W. H. , Xue C.
Published: July 2011

In this paper, the effects of magnetic field gradient (i.e., the magnetic field transition layer effects) on the Rayleigh-Taylor instability (RTI) with continuous magnetic field and density profiles are investigated analytically. The transition layers of magnetic field and density with two different typical profiles are studied and the analytic expressions of the linear growth rate of the RTI are obtained. It is found that the magnetic field effects strongly reduce the linear growth rate of the RTI, especially when the perturbation wavelength is short. The linear growth rate of the RTI increases with the thickness of the magnetic field transition layer, especially for the case of small thickness of the magnetic field transition layer. When the magnetic field transition layer width is long enough, the linear growth rate of the RTI can be saturated. Thus when one increases the width of the magnetic field transition layer, the linear growth rate of the RTI increases only in a certain range, which depends on the magnetic field strength. The numerical results are compared with the analytic linear growth rates and they agree well with each other.
A theoretical study of induced-charge dipolophoresis of ideally polarizable asymmetrically slipping Janus particles
Authors: Boymelgreen Alicia M. , Miloh Touvia
Published: July 2011

We consider the non linear electrophoretic transport of uncharged, ideally polarizable hydrodynamic Janus spheres, the inhomogeneity of which is produced by a variable Navier slip condition at the particle surface. A general, three dimensional formulation enabling calculation of the electrophoretic mobility of any patchy particle, with an arbitrary tensorial slip boundary condition is provided. The solution avoids the common assumption of an infinitely thin electric double layer (λ) and Navier slip coefficient (b) and is thereby valid for finite values of these parameters, which is of particular importance at the nanoscale. The specific case of a Janus sphere, consisting of two equal hemispheres, each with a different but constant slip boundary condition is solved semi-analytically and numerically. In the instance where the slip coefficients at each hemisphere are equal, induced charge electro-osmotic flow is evident at an increased rate as compared to a homogeneous sphere with no slip. If the slip coefficients differ from each other, the particle is found to self-align with the electric field and travel with the slip surface facing forward. The increased pumping rates and mobility found in the cases of the homogeneous and Janus spheres respectively, occur as a function of the ratio b/bλλ and are most significant for the combination of a thin electric double layer (EDL) and large slip length. However, it is also illustrated that the size of the EDL independently dominates the effects of slip.
Design and application of a small size SAFT imaging system for concrete structure
Authors: Shao Zhixue , Shi Lihua , Shao Zhe , Cai Jian
Published: July 2011

A method of ultrasonic imaging detection is presented for quick non-destructive testing (NDT) of concrete structures using synthesized aperture focusing technology (SAFT). A low cost ultrasonic sensor array consisting of 12 market available low frequency ultrasonic transducers is designed and manufactured. A channel compensation method is proposed to improve the consistency of different transducers. The controlling devices for array scan as well as the virtual instrument for SAFT imaging are designed. In the coarse scan mode with the scan step of 50 mm, the system can quickly give an image display of a cross section of 600 mm (L) × 300 mm (D) by one measurement. In the refined scan model, the system can reduce the scan step and give an image display of the same cross section by moving the sensor array several times. Experiments on staircase specimen, concrete slab with embedded target, and building floor with underground pipe line all verify the efficiency of the proposed method.
Eigenvalue problems of the model from nonlocal continuum mechanics
Authors: Qi Jiangang , Chen Shaozhu
Published: July 2011

This article studies the eigenvalue problem of a fractional differential equation which is a foundation model of a bar of finite length with long-range interactions arising from non-local continuum mechanics. We show that this problem has countable simple real eigenvalues and the corresponding eigenfunctions form a complete orthogonal system in the Hilbert space L2. Furthermore, the asymptotic behavior of eigenvalues and the numbers of zeros of eigenfunctions are studied by using the analytic perturbation theory.
A new perspective on transition states: χ1 separatrix
Authors: Ledbetter Paul J. , Clementi Cecilia
Published: July 2011

We present a new definition of the transition state for chemical reactions, named the χ1 separatrix. In contrast to previous transition state definitions which depend on the choice of reaction coordinates, the χ1 separatrix is defined by choosing a time scale for observation and is connected to exact rate constants in the high friction limit. We demonstrate that this separatrix appears in the isomerization of alanine dipeptide as a stationary population in quasi-equilibrium, without assuming a particular coordinate system or reactant and product surfaces.
GVVPT2 energy gradient using a Lagrangian formulation
Authors: Theis Daniel , Khait Yuriy G. , Hoffmann Mark R.
Published: July 2011

A Lagrangian based approach was used to obtain analytic formulas for GVVPT2 energy nuclear gradients. The formalism can use either complete or incomplete model (or reference) spaces, and is limited, in this regard, only by the capabilities of the MCSCF program. An efficient means of evaluating the gradient equations is described. Demonstrative calculations were performed and compared with finite difference calculations on several molecules and show that the GVVPT2 gradients are accurate. Of particular interest, the suggested formalism can straightforwardly use state-averaged MCSCF descriptions of the reference space in which the states have arbitrary weights. This capability is demonstrated by some calculations on the ground and first excited singlet states of LiH, including calculations near an avoided crossing. The accuracy and usefulness of the GVVPT2 method and its gradient are highlighted by comparing the geometry of the near-C2v minimum on the conical intersection seam between the 1 1A1 and 2 1A1 surfaces of O3 with values that were calculated at the multireference configuration interaction, including single and double excitations (MRCISD), level of theory.
Role of inter-diffusion on the crystallization dynamics in polyethylene/poly(ethylene-alt-propylene) blend system
Authors: Li Junyu , Li Wei , Li Zhiyong , Cheng He , Li Yang , Han Charles C.
Published: July 2011

Influence of inter-diffusion on the crystallization dynamics in polyethylene/poly(ethylene-alt-propylene) (PE/PEP) blends was studied by a combination of optical microscopy (OM), differential scanning calorimetry (DSC), and Fourier transform infrared spectroscopy (FTIR). OM measurements showed that the crystal nuclei may be first generated at phase separated interface where concentration fluctuation is greatly enhanced in the temperature quench process. After the formation of crystal nuclei, the only crystallizable components, PE chains, are necessary to reach the nucleation site via inter-diffusion to continue the secondary nucleation and growth process. DSC showed that there is only one 96 °C crystallization peak when PE (MW = 52 kg/mol) is blended with low molecular weight PEP (MW = 32 kg/mol); while there are two crystallization peaks, which are 96 °C and 72 °C, respectively, when the same PE is blended with high molecular weight PEP (MW = 110 kg/mol). The origin of the 72 °C crystallization peak was studied by DSC isothermal crystallization and time resolved FTIR. It was proved that the 72 °C crystallization peak is resulted from the smaller inter-diffusion coefficient in the PEP-rich region. Both slow mode theory and fast mode/constraint release models of inter-diffusion can be used to explain the smaller inter-diffusion coefficient in the PEP-rich region, which dynamically results in the disappearance of the 72 °C crystallization peak after isothermal crystallization at 90 °C for 60 min. Therefore, inter-diffusion plays an important role on crystallization dynamics in multi-component and multi-phase polymeric blends.
Phonon mode and phase transition behaviors of (1-x)PbSc1/2Ta1/2O3-xPbHfO3 relaxor ferroelectric ceramics determined by temperature-dependent Raman spectra
Authors: Zhang W. J. , Li W. W. , Chen X. G. , Hu Z. G. , Liu W. , Wang G. S. , Dong X. L. , Chu J. H.
Published: July 2011

The composition dependence of phase transition temperature in (1-x)PbSc1/2Ta1/2O3-xPbHfO3 (PSTH) ceramics (0≤x≤0.2) has been investigated by Raman spectra. From the typical phonon mode variations, the PSTH ceramics unambiguously undergoes three structural transformations with increasing the temperature from 82 to 673 K. It was found that the F2g phonon mode disappears above the Curie temperature. Moreover, the PSTH ceramics exhibited the paraelectric to ferroelectric phase transitions at 287, 293, 313, 320, and 330 K with the composition. The phenomena can be ascribed to the enhanced length of Pb-O-Ta bonds induced by the incorporation of Hf4+ ions.
Plasmonic optical switches based on Mach-Zender interferometer
Authors: Zhu Jia-Hu , Huang Xu-Guang , Xu Wei , Chen Luan Xiong
Published: July 2011

Electro-optical switches composed of two Mach-Zehnder interferometer waveguides filled with 4-dimethylamino-N-methyl-4-stilbazolium tosylate (DAST) have been proposed and investigated. The characteristics of the switch waveguide are analyzed. The finite-difference time domain simulation results reveal that the structure can operate as an optical switch by controlling the voltage V1 or V2 applied on the region filled with the DAST material with the π phase shift voltage as Vπ = 2.9 V. The structure has a small dimension of hundreds of nanometers.
Particle accumulation on periodic orbits by repeated free surface collisions
Authors: Hofmann Ernst , Kuhlmann Hendrik C.
Published: July 2011

The motion of small particles suspended in cylindrical thermocapillary liquid bridges is investigated numerically in order to explain the experimentally observed particle accumulation structures (PAS) in steady two- and time-dependent three-dimensional flows. Particles moving in this flow are modeled as perfect tracers in the bulk, which can undergo collisions with the free surface. By way of free-surface collisions the particles are transferred among different streamlines which represents the particle trajectories in the bulk. The inter-streamline transfer-process near the free surface together with the passive transport through the bulk is used to construct an iterative map that can describe the accumulation process as an attraction to a stable fixed point which represents PAS. The flow topology of the underlying azimuthally traveling hydrothermal wave turns out to be of key importance for the existence of PAS. In a frame of reference exactly rotating with the hydrothermal wave the three-dimensional flow is steady and exhibits co-existing regular and chaotic streamlines. We find that particles are attracted to accumulation structures if a closed regular streamline exists in the rotating frame of reference which closely approaches the free surface locally. Depending on the closed streamline and the particle radius PAS can arise as a specific trajectory which winds about the closed regular streamline or as the surface of a particular stream tube containing the closed streamline.
Asymptotic behavior of two-dimensional stochastic magneto-hydrodynamics equations with additive noises
Authors: Zhao Wenqiang , Li Yangrong
Published: July 2011

This paper is devoted to the investigation of the asymptotic behavior of solutions of the stochastic magneto-hydrodynamics equations driven by random exterior forced terms both in the velocity and in the magnetic field. The nonlinear term is supposed to be time-dependent and satisfies certain dissipative conditions. The existence of a random attractor for this random dynamical system is obtained.
Approximate variational coupled cluster theory
Authors: Robinson James B. , Knowles Peter J.
Published: July 2011

We show that it is possible to construct an accurate approximation to the variational coupled cluster method, limited to double substitutions, from the minimization of a functional that is rigorously extensive, exact for isolated two-electron subsystems and invariant to transformations of the underlying orbital basis. This approximate variational coupled cluster theory is a modification and enhancement of our earlier linked pair functional theory. It is first motivated by the constraint that the inverse square root of the matrix that transforms the cluster amplitudes must exist. Low-order corrections are then included to enhance the accuracy of the approximation of variational coupled cluster, while ensuring that the computational complexity of the method never exceeds that of the standard traditional coupled cluster method. The effects of single excitations are included by energy minimization with respect to the orbitals defining the reference wavefunction. The resulting quantum chemical method is demonstrated to be a robust approach to the calculation of molecular electronic structure and performs well when static correlation effects are strong.
The study of new vacuum pressure measurement technique using ultrasonic acoustic impedance transducers
Authors: Hong S. S. , Khan Wakil , Shin Y. H. , Cho S. H. , Ahn B. Y. , Chung J. W. , Woo S. Y.
Published: July 2011

Ultrasonic sensors of 500 kHz frequency have been used to study the measuring of gas pressure in the range 1.33 × 103–2.026 × 105 Pa. From the experimental data it was observed that amplitude of the transmitted ultrasound was dependent on gas pressure. The results confirm that by using appropriate instruments including sensors and electronic devices, pressure of the gas can be successfully measured by measuring the magnitude of the received signal. The proposed method is expected to be applied to develop as new vacuum pressure measurement instrument.
Diabatic couplings for charge recombination via Boys localization and spin-flip configuration interaction singles
Authors: Alguire Ethan , Subotnik Joseph E.
Published: July 2011

We describe a straightforward technique for obtaining diabatic couplings applicable to charge transfer from or charge recombination to the electronic ground state. Our method is nearly black box, requiring minimal chemical intuition from the user, and merges two well-established approaches in electronic structure theory: first, smooth and balanced adiabatic states are generated using spin-flip-configuration interaction singles (SF-CIS) based on a triplet HF state; second, Boys localization is applied to rotate all adiabatic states into charge-localized diabatic states. The method is computationally inexpensive, scaling only with the cost of CIS, and does not require a choice of active space, which is usually required for such intrinsically multiconfigurational problems. Molecular LiF in vacuum and LiF solvated by a single water molecule are examined as model systems. We find nearly smooth diabatic potential energy surfaces and couplings and we find that the Condon approximation is obeyed approximately for this model problem.
Atomistic molecular dynamics simulations of shock compressed quartz
Authors: Farrow M. R. , Probert M. I. J.
Published: July 2011

Atomistic non-equilibrium molecular dynamics simulations of shock wave compression of quartz have been performed using the so-called BKS semi-empirical potential of van Beest, Kramer, and van Santen [Phys. Rev. B 43, 5068 (1991)]10.1103/PhysRevB.43.5068 to construct the Hugoniot of quartz. Our scheme mimics the real world experimental set up by using a flyer-plate impactor to initiate the shock wave and is the first shock wave simulation that uses a geometry optimised system of a polar slab in a three-dimensional system employing periodic boundary conditions. Our scheme also includes the relaxation of the surface dipole in the polar quartz slab which is an essential pre-requisite to a stable simulation. The original BKS potential is unsuited to shock wave calculations and so we propose a simple modification. With this modification, we find that our calculated Hugoniot is in good agreement with experimental shock wave data up to 25 GPa, but significantly diverges beyond this point. We conclude that our modified BKS potential is suitable for quartz under representative pressure conditions of the Earth core, but unsuitable for high-pressure shock wave simulations. We also find that the BKS potential incorrectly prefers the β-quartz phase over the α-quartz phase at zero-temperature, and that there is a β → α phase-transition at 6 GPa.
Elastic deformation due to tangential capillary forces
Authors: Das Siddhartha , Marchand Antonin , Andreotti Bruno , Snoeijer Jacco H.
Published: July 2011

A sessile liquid drop can deform the substrate on which it rests if the solid is sufficiently “soft.” In this paper we compute the detailed spatial structure of the capillary forces exerted by the drop on the solid substrate using a model based on Density Functional Theory. We show that, in addition to the normal forces, the drop exerts a previously unaccounted tangential force. The resultant effect on the solid is a pulling force near the contact line directed towards the interior of the drop, i.e., not along the interface. The resulting elastic deformations of the solid are worked out and illustrate the importance of the tangential forces.
Local fluctuations in solution mixtures
Authors: Ploetz Elizabeth A. , Smith Paul E.
Published: July 2011

An extension of the traditional Kirkwood-Buff (KB) theory of solutions is outlined which provides additional fluctuating quantities that can be used to characterize and probe the behavior of solution mixtures. Particle-energy and energy-energy fluctuations for local regions of any multicomponent solution are expressed in terms of experimentally obtainable quantities, thereby supplementing the usual particle-particle fluctuations provided by the established KB inversion approach. The expressions are then used to analyze experimental data for pure water over a range of temperatures and pressures, a variety of pure liquids, and three binary solution mixtures – methanol and water, benzene and methanol, and aqueous sodium chloride. In addition to providing information on local properties of solutions it is argued that the particle-energy and energy-energy fluctuations can also be used to test and refine solute and solvent force fields for use in computer simulation studies.
Surface chemistry and Fermi level movement during the self-cleaning of GaAs by trimethyl-aluminum
Authors: Tallarida M. , Adelmann C. , Delabie A. , Van Elshocht S. , Caymax M. , Schmeisser D.
Published: July 2011

The removal of the native oxides from NH4OH-cleaned p-GaAs (100) by exposure to trimethyl-aluminum (TMA) was studied by in situ photoelectron spectroscopy using synchrotron radiation. The reduction of high-valence As- and Ga-oxides occurred through different routes: while As3+ was reduced to As(1±Δ)+ suboxides (with 0 ≤ Δ ≤ 1), Ga3+ was directly removed. The surface Fermi level was shifted by about 100 meV towards the valence band edge upon TMA exposure. This indicates that removing the native oxide of GaAs by TMA is insufficient to create interfaces between GaAs and Al2O3 with defects densities below the 1012 cm−2 range.
Cross-plane thermal conductivity of a PbSnSe/PbSe superlattice material
Authors: Jeffers James D. , Namjou Khosrow , Cai Zhihua , McCann Patrick J. , Olona Leonard
Published: July 2011

The cross-plane thermal conductivity of a PbSnSe/PbSe multi-period superlattice (SL) grown by molecular beam epitaxy is obtained from continuous wave photoluminescence (PL) measurements and finite element analysis (FEA). PL measurement and FEA for a structure consisting of a multiple quantum well light emitting layer on top of a PbSnSe/PbSe SL with three different periodicities of 2.4, 3.6, and 4.8 nm revealed a cross-plane lattice thermal conductivity of 0.8 W/mK. The 58% reduction relative to the 1.9 W/mK value for bulk PbSe is attributed to enhanced scattering and/or reflection of acoustic phonons within the short-period SL material.
Determining contact potential barrier effects on electronic transport in single molecular junctions
Authors: Zhou Jianfeng , Xu Bingqian
Published: July 2011

The authors introduced a simplified multiple-barrier model based on the widely accepted traditional tunneling model to describe the electron transport behaviors in single molecule junction systems. The contact potential barrier height Φc and the contact decay constant βc were taken as the key indexes to represent certain contact conformations. By monitoring the dynamic changes of contact potential barriers corresponding to the mechanical extension of contact conformations with our newly developed Scanning Probe Microscope (SPM)-break junction technique and then fitting into the model, we established an in-depth and detailed understanding of the molecule-metal contact effects on electronic transport properties in single molecular junctions.
Giant effect of negative differential conductance in graphene nanoribbon p-n hetero-junctions
Authors: Hung Nguyen V. , Mazzamuto F. , Saint-Martin J. , Bournel A. , Dollfus P.
Published: July 2011

The I-V characteristics of graphene nanoribbon (GNR) p-n junctions have been investigated using atomistic quantum simulation. On the basis of results obtained for simple armchair GNR structures with large bandgap, it is suggested to improve significantly the device operation by inserting a small-bandgap section in the transition region between n and p zones. A giant peak-to-valley ratio (PVR) of negative differential conductance (higher than 103) can be achieved in such hetero-junctions. Additionally, the PVR is proved to be weakly sensitive to the transition length and not strongly degraded by the edge disorder, which is an important feature regarding applications.
Bloch surface waves-controlled emission of organic dyes grafted on a one-dimensional photonic crystal
Authors: Ballarini Mirko , Frascella Francesca , Michelotti Francesco , Digregorio Gabriella , Rivolo Paola , Paeder Vincent , Musi Valeria , Giorgis Fabrizio , Descrovi Emiliano
Published: July 2011

An alternative route to plasmon-controlled fluorescence for improving the detection of fluorescence is proposed. In place of a metallic layer, a suitable silicon-based one-dimensional photonic crystal is used to generate a Bloch surface waves-coupled emission from a thin polymeric layer decorated with a fluorescent dye. Fluorescent radiation coupled to Bloch surface waves is strongly polarized and directional, with an angular divergence of 0.3° corresponding to a spectral bandwidth of 3 nm. Within this range, an overall signal enhancement of a factor larger than 500 is obtained as compared to a conventional glass substrate thanks to an additional enhancement mechanism based on dyes excitation via Bloch surface waves.
Surface spin glass and exchange bias effect in Sm0.5Ca0.5MnO3 manganites nano particles
Authors: Giri S. K. , Poddar A. , Nath T. K.
Published: July 2011

In this letter, we report that the charge/orbital order state of bulk antiferromagnetic Sm0.5Ca0.5MnO3 is suppressed and confirms the appearance of weak ferromagnetism below 65 K followed by a low temperature spin glass like transition at 41 K in its nano metric counterpart. Exchange anisotropy effect has been observed in the nano manganites and can be tuned by the strength of the cooling magnetic field (Hcool). The values of exchange fields (HE), coercivity (HC), remanence asymmetry (ME) and magnetic coercivity (MC) are found to strongly depend on cooling magnetic field and temperature. HE increases with increasing Hcool but for larger Hcool, HE tends to decrease due to the growth of ferromagnetic cluster size. Magnetic training effect has also been observed and it has been analyzed thoroughly using spin relaxation model. A proposed phenomenological core-shell type model is attributed to an exchange coupling between the spin-glass like shell (surrounding) and antiferromagnetic core of Sm0.5Ca0.5MnO3 nano manganites mainly on the basis of uncompensated surface spins. Results suggest that the intrinsic phase inhomogeneity due to the surface effects of the nanostructured manganites may cause exchange anisotropy, which is of special interests for potential application in multifunctional spintronic devices.
Spin transport properties in an organic molecule in the presence of Rashba spin-orbit interaction
Authors: Fallah Farhang , Esmaeilzadeh Mahdi
Published: July 2011

In the present letter, we study the spin-dependent electron transport in a 1,4-2-phenyl-dithiolate molecule using the Hückel method and equilibrium Green's function formalism. The effect of the contacts on spin transport is taken into account. It is shown that spin inversion can occur in the presence of the Rashba spin-orbit interaction. The necessary conditions for complete spin inversion are obtained by using contour maps. This study can provide a new route to design molecular spintronic devices.
Understanding Housing Sprawl: The Case of Flanders, Belgium
Authors: De Decker Pascal
Published: July 2011

Between 1995 and 1999 the Flemish government succeeded in approving pieces of legislation intended to counter the spatial developments that had characterised the preceding periods, namely suburbanisation and urban decay. It passed a law to combat vacancy and slum housing (1995), a law to invest in social urban renewal (1996), a housing law (1997), a new law on spatial planning (1999), and the first comprehensive spatial plan (1997). Unfortunately, recent information and an evaluation of the spatial planning effort reveal that these initiatives have not been successful. The suburbanisation of native Belgians did not stop: on the contrary, it is accelerating again. And the population growth in the cities is due to people coming from abroad (through family reunification or formation or as asylum seekers). In this contribution I investigate suburbanisation and deurbanisation, asking why housing sprawl in Flanders is so persistent. I examine the structures behind sprawl, viewing them as the consequence of a longstanding dialectical process whereby physical artefacts interact with political choices and actions, cultural convictions, and economic possibilities that have reinforced each other in daily practice over and over again in one predominant direction. The basic argument is that Flanders' spatial planning and urban policies are locked into historical choices, making it difficult to implement new options successfully.
Migration as Protest? Negotiating Gender, Class, and Ethnicity in Urban Bolivia
Authors: Bastia Tanja
Published: July 2011

Feminist geographies of migration are often based on the assumption that migration brings about social change, potentially disrupting patriarchal structures and bringing about new spaces where gender relations can be renegotiated and reconfigured. On the basis of multisited research conducted with migrants from the same community of origin in Bolivia, I analyse how gender, class, and ethnicity are renegotiated through internal and cross-border migration. A transnational, multi-scalar, multisited, and intersectional approach is applied to the study of social change through migration, with the aim of investigating whether labour migration provides avenues for greater gender equality. At the individual level there are certainly indications that women achieve greater independence through migration. However, the multiscalar and intersectional analysis suggests that women trade ‘gender gains’ for upward social mobility in the class hierarchy. By doing so, they also contribute to the reproduction of patriarchal social relations.
Coproducing Flood Risk Knowledge: Redistributing Expertise in Critical ‘Participatory Modelling’
Authors: Landström Catharina , Whatmore Sarah J , Lane Stuart N , Odoni Nicholas A , Ward Neil , Bradley Susan
Published: July 2011

This paper suggests that computer simulation modelling can offer opportunities for redistributing expertise between science and affected publics in relation to environmental problems. However, in order for scientific modelling to contribute to the coproduction of new knowledge claims about environmental processes, scientists need to reposition themselves with respect to their modelling practices. In the paper we examine a process in which two hydrological modellers became part of an extended research collective generating new knowledge about flooding in a small rural town in the UK. This process emerged in a project trialling a novel participatory research apparatus—competency groups—aiming to harness the energy generated in public controversy and enable other than scientific expertise to contribute to environmental knowledge. Analysing the process repositioning the scientists in terms of a dynamic of ‘dissociation’ and ‘attachment’, we map the ways in which prevailing alignments of expertise were unravelled and new connections assembled, in relation to the matter of concern. We show how the redistribution of knowledge and skills in the extended research collective resulted in a new computer model, embodying the coproduced flood risk knowledge.
The Politics of Climate Activism in the UK: A Social Movement Analysis
Authors: North Peter
Published: July 2011

This paper uses social movement theory (SMT) as a theoretical ‘gymnasium’ to explore the limits and possibilities of climate activism in the UK. The core SMT concepts are used to explore why climate activism emerged when it did, and how conceptions of there being a problem were translated into arguments about what should be done. If something should be done, is contentious politics or policy change the most appropriate strategy? At what scale should action take place: a local politics of prefiguration, through direct action, or in more visible mass mobilisations? It is argued that climate activism takes place in a diverse range of political spaces and scales and works actively to produce knowledges about the dangers of anthropogenic climate change and responsibilities for it, but it is unclear that it has the motive power to move to more sustainable ways of organising human society.
The Spatial Dynamics of Globalizing Venture Capital in China
Authors: Zhang Jun
Published: July 2011

This paper examines the spatial dynamics and emerging locational hierarchies of the venture capital (VC) industry in China, largely as a result of the global expansion of VC investors from the US and other advanced economies. Based on a comprehensive database compiled by the author from the best available sources, this is the first systemic geographic study on the VC industry in an emerging economy. This study finds that the rising cluster of VC supply and demand in Beijing, Shanghai, and Shenzhen was enabled by the juxtaposition of spatial proximity effects, investment syndication, and interregional office networks within China's unique institutional environment. It further demonstrates that the spatial dynamics of the globalizing venture capitalism has to be understood in light of the geo-institutional mechanisms shaping the whole ‘VC cycle’ of fundraising–investing–divesting.