bluuebunny/crossref_metadata_2025 huggingface dataset:
The Permanent People’s Tribunals and indigenous people’s struggles in Mexico: between coloniality and epistemic justice?
Authors: Icaza Rosalba
Published: August 2015

On 21 October 2011, hundreds of Mexican civil society organizations formally submitted a petition to the Lelio e Lisli Basso Foundation in Rome to justify the opening of a Mexican Chapter of the Permanent People’s Tribunals (PPT). The PPT was established in 1979 as the successor to the Russell Tribunals on Vietnam (1966–1967) and on the Latin American Dictatorships (1974–1976). The PPT is considered an ethical non-governmental tribunal and their sessions are described as a mechanism for raising awareness of national and international public opinion on rights violations. This article investigates the potential of the PPT for contributing to epistemic justice in Mexico, by focusing on indigenous people communities’ long-term struggle for legal pluralism and autonomy. In so doing, it offers an analysis about the coloniality of international human rights law operating in non-governmental mechanisms of popular litigation such as the PPT; a perspective that has remained absent in critical international and global studies. In particular, the article argues that the PPT in Mexico is imbricated with Eurocentric modes of legal production but that it nonetheless has the potential to contribute, in a relevant but fragile way, to epistemic justice. On the one hand, it is observed that PPT key documents and statements explaining different forms of violence in Mexico emphasize causal relationships based on the all-encompassing power or logic of capitalism. This perspective, it is argued, has the effect of epistemic erasure: notions and practices of justice that exceed this logic are silenced in the process of legal translation for the construction of “model cases”. On the other hand, the article highlights the coexistence of different notions of justice in one of the PPT thematic hearings on Violence against Corn, food sovereignty and autonomy hold in Oaxaca, Mexico, to argue for a re-thinking of the monocultural state-centric legal frames that ground PPT legal qualification. As the PPT classify social grievances in legal terms through the lens/gaze of international law, this legal qualification works as an activity of “translation”, in some cases of incommensurable notions of justice or absence of justice, violence or well-being. The article concludes with an emphasis on the potential contributions of the PPT to epistemic justice as the political visibility of the many ways in which justice is understood and experienced despite the many forms of violence and oppression in contemporary Mexico.
Electron temperature and density probe for small aeronomy satellites
Authors: Oyama K.-I. , Hsu Y. W. , Jiang G. S. , Chen W. H. , Cheng C. Z. , Fang H. K. , Liu W. T.
Published: August 2015

A compact and low power consumption instrument for measuring the electron density and temperature in the ionosphere has been developed by modifying the previously developed Electron Temperature Probe (ETP). A circuit block which controls frequency of the sinusoidal signal is added to the ETP so that the instrument can measure both Te in low frequency mode and Ne in high frequency mode from the floating potential shift of the electrode. The floating potential shift shows a minimum at the upper hybrid resonance frequency (fUHR). The instrument which is named “TeNeP” can be used for tiny satellites which do not have enough conductive surface area for conventional DC Langmuir probe measurements. The instrument also eliminates the serious problems associated with the contamination of satellite surface as well as the sensor electrode.
Surrogate immiscible liquid pairs with refractive indexes matchable over a wide range of density and viscosity ratios
Authors: Saksena Rajat , Christensen Kenneth T. , Pearlstein Arne J.
Published: August 2015

In liquid-liquid flows, use of optical diagnostics is limited by interphase refractive index mismatch, which leads to optical distortion and complicates data interpretation, and sometimes also by opacity. Both problems can be eliminated using a surrogate pair of immiscible index-matched transparent liquids, whose density and viscosity ratios match corresponding ratios for the original liquid pair. We show that a wide range of density and viscosity ratios is accessible using aqueous solutions of 1,2-propanediol and CsBr (for which index, density, and viscosity are available), and solutions of light and heavy silicone oils and 1-bromooctane (for which we measured the same properties at 119 compositions). For each liquid phase, polynomials in the composition variables, least-squares fitted to index and density and to the logarithm of kinematic viscosity, were used to determine accessible density and viscosity ratios for each matchable index. Index-matched solution pairs can be prepared with density and viscosity ratios equal to those for water-liquid CO2 at 0 °C over a range of pressure (allowing water-liquid CO2 behavior at inconveniently high pressure to be simulated by 1-bar experiments), and for water-crude oil and water-trichloroethylene (avoiding opacity and toxicity problems, respectively), each over a range of temperature. For representative index-matched solutions, equilibration changes index, density, and viscosity only slightly, and mass spectrometry and elemental analysis show that no component of either phase has significant interphase solubility. Finally, procedures are described for iteratively reducing the residual index mismatch in surrogate solution pairs prepared on the basis of approximate polynomial fits to experimental data, and for systematically dealing with nonzero interphase solubility.
Effect of O2 + O ab initio and Morse additive pairwise potentials on dissociation and relaxation rates for nonequilibrium flow calculations
Authors: Kulakhmetov Marat , Gallis Michael , Alexeenko Alina
Published: August 2015

This work quantifies the sensitivity of O2 + O dissociation rates and relaxation to interatomic potential energy surfaces at high-enthalpy, nonequilibrium flow conditions. State-to-state cross sections are obtained by quasi-classical trajectory (QCT) calculations with two potential surfaces. The first is a Morse additive pairwise potential for O3 that is constructed based on O2(3Σg−) spectroscopic measurements and the second is a double many-body expansion potential by Varandas and Pais [Mol. Phys. 65, 843–860 (1988)]. The QCT calculations of cross sections and rates with the two surfaces are compared to each other and shock tube measurements. It is found that, at temperatures between 2500 K and 20 000 K, the equilibrium dissociation rates predicted by the two potentials agree within 12%, and they are bound by experimental dissociation measurements. In contrast, above 10 000 K, ab initio based equilibrium dissociation rates are about a factor of two higher than the widely used Park’s model. The nonequilibrium dissociation rates calculated by the two potentials are within 70% while phenomenological models differ by two orders of magnitude for vibrationally cold conditions of shocks. The analyses provide an approach for improving accuracy of nonequilibrium high-enthalpy flow modeling when ab initio potentials are not available.
Reduced graphene oxide wrapped Cu2O supported on C3N4: An efficient visible light responsive semiconductor photocatalyst
Authors: Ganesh Babu S. , Vinoth R. , Surya Narayana P. , Bahnemann Detlef , Neppolian B.
Published: August 2015

Herein, Cu2O spheres were prepared and encapsulated with reduced graphene oxide (rGO). The Cu2O–rGO–C3N4 composite covered the whole solar spectrum with significant absorption intensity. rGO wrapped Cu2O loading caused a red shift in the absorption with respect to considering the absorption of bare C3N4. The photoluminescence study confirms that rGO exploited as an electron transport layer at the interface of Cu2O and C3N4 heterojunction. Utmost, ∼2 fold synergistic effect was achieved with Cu2O–rGO–C3N4 for the photocatalytic reduction of 4-nitrophenol to 4-aminophenol in comparison with Cu2O–rGO and C3N4. The Cu2O–rGO–C3N4 photocatalyst was reused for four times without loss in its activity.
Using multiple secondary fusion products to evaluate fuel ρR, electron temperature, and mix in deuterium-filled implosions at the NIF
Authors: Rinderknecht H. G. , Rosenberg M. J. , Zylstra A. B. , Lahmann B. , Séguin F. H. , Frenje J. A. , Li C. K. , Gatu Johnson M. , Petrasso R. D. , Berzak Hopkins L. F. , Caggiano J. A. , Divol L. , Hartouni E. P. , Hatarik R. , Hatchett S. P. , Le Pape S. , Mackinnon A. J. , McNaney J. M. , Meezan N. B. , Moran M. J. , Bradley P. A. , Kline J. L. , Krasheninnikova N. S. , Kyrala G. A. , Murphy T. J. , Schmitt M. J. , Tregillis I. L. , Batha S. H. , Knauer J. P. , Kilkenny J. D.
Published: August 2015

In deuterium-filled inertial confinement fusion implosions, the secondary fusion processes D(3He,p)4He and D(T,n)4He occur, as the primary fusion products 3He and T react in flight with thermal deuterons. In implosions with moderate fuel areal density (∼5–100 mg/cm2), the secondary D-3He reaction saturates, while the D-T reaction does not, and the combined information from these secondary products is used to constrain both the areal density and either the plasma electron temperature or changes in the composition due to mix of shell material into the fuel. The underlying theory of this technique is developed and applied to three classes of implosions on the National Ignition Facility: direct-drive exploding pushers, indirect-drive 1-shock and 2-shock implosions, and polar direct-drive implosions. In the 1- and 2-shock implosions, the electron temperature is inferred to be 0.65 times and 0.33 times the burn-averaged ion temperature, respectively. The inferred mixed mass in the polar direct-drive implosions is in agreement with measurements using alternative techniques.
The influence of the “cage effect” on the mechanism of reversible bimolecular multistage chemical reactions in solutions
Authors: Doktorov Alexander B.
Published: August 2015

Manifestations of the “cage effect” at the encounters of reactants are theoretically treated by the example of multistage reactions in liquid solutions including bimolecular exchange reactions as elementary stages. It is shown that consistent consideration of quasi-stationary kinetics of multistage reactions (possible only in the framework of the encounter theory) for reactions proceeding near reactants contact can be made on the basis of the concepts of a “cage complex.” Though mathematically such a consideration is more complicated, it is more clear from the standpoint of chemical notions. It is established that the presence of the “cage effect” leads to some important effects not inherent in reactions in gases or those in solutions proceeding in the kinetic regime, such as the appearance of new transition channels of reactant transformation that cannot be caused by elementary event of chemical conversion for the given mechanism of reaction. This results in that, for example, rate constant values of multistage reaction defined by standard kinetic equations of formal chemical kinetics from experimentally measured kinetics can differ essentially from real values of these constants.
Theoretical description of spin-selective reactions of radical pairs diffusing in spherical 2D and 3D microreactors
Authors: Ivanov Konstantin L. , Sadovsky Vladimir M. , Lukzen Nikita N.
Published: August 2015

In this work, we treat spin-selective recombination of a geminate radical pair (RP) in a spherical “microreactor,” i.e., of a RP confined in a micelle, vesicle, or liposome. We consider the microreactor model proposed earlier, in which one of the radicals is located at the center of the micelle and the other one undergoes three-dimensional diffusion inside the micelle. In addition, we suggest a two-dimensional model, in which one of the radicals is located at the “pole” of the sphere, while the other one diffuses on the spherical surface. For this model, we have obtained a general analytical expression for the RP recombination yield in terms of the free Green function of two-dimensional diffusion motion. In turn, this Green function is expressed via the Legendre functions and thus takes account of diffusion over a restricted spherical surface and its curvature. The obtained expression allows one to calculate the RP recombination efficiency at an arbitrary magnetic field strength. We performed a comparison of the two models taking the same geometric parameters (i.e., the microreactor radius and the closest approach distance of the radicals), chemical reactivity, magnetic interactions in the RP and diffusion coefficient. Significant difference between the predictions of the two models is found, which is thus originating solely from the dimensionality effect: for different dimensionality of space, the statistics of diffusional contacts of radicals becomes different altering the reaction yield. We have calculated the magnetic field dependence of the RP reaction yield and chemically induced dynamic nuclear polarization of the reaction products at different sizes of the microreactor, exchange interaction, and spin relaxation rates. Interestingly, due to the intricate interplay of diffusional contacts of reactants and spin dynamics, the dependence of the reaction yield on the microreactor radius is non-monotonous. Our results are of importance for (i) interpreting experimental data for magnetic field effects on RP recombination in confined space and (ii) for describing kinetics of chemical reactions, which occur predominantly on the surfaces of biomembranes, i.e., lipid peroxidation reactions.
Yttrium scandate thin film as alternative high-permittivity dielectric for germanium gate stack formation
Authors: Lu Cimang , Lee Choong Hyun , Nishimura Tomonori , Toriumi Akira
Published: August 2015

We investigated yttrium scandate (YScO3) as an alternative high-permittivity (k) dielectric thin film for Ge gate stack formation. Significant enhancement of k-value is reported in YScO3 comparing to both of its binary compounds, Y2O3 and Sc2O3, without any cost of interface properties. It suggests a feasible approach to a design of promising high-k dielectrics for Ge gate stack, namely, the formation of high-k ternary oxide out of two medium-k binary oxides. Aggressive scaling of equivalent oxide thickness (EOT) with promising interface properties is presented by using YScO3 as high-k dielectric and yttrium-doped GeO2 (Y-GeO2) as interfacial layer, for a demonstration of high-k gate stack on Ge. In addition, we demonstrate Ge n-MOSFET performance showing the peak electron mobility over 1000 cm2/V s in sub-nm EOT region by YScO3/Y-GeO2/Ge gate stack.
Electronic structures and optical spectra of BaO from first principles
Authors: Wu Chang-Wei , Pan Bo , Wang Neng-Ping
Published: August 2015

We present the results of first-principles study for the electronic structure and optical absorption spectrum of the alkaline-earth metal oxide BaO. The quasiparticle band structure is evaluated within the Hedin's GW approximation [Phys. Rev. 139, A796 (1965)]. Thereafter, the electron-hole interaction is taken into consideration and the Bethe-Salpeter equation for the electron-hole two-particle Green function is solved. The calculated quasiparticle band gap of BaO is 4.1 eV, which is in good agreement with the experimental result. The calculated optical absorption spectrum of BaO is also in agreement with the experimental data. In particular, the calculated excitation energy for the lowest exciton peak in the optical absorption spectrum of BaO reproduces very well the corresponding experimental result.
Optimal control of circular cylinder wakes using long control horizons
Authors: Flinois Thibault L. B. , Colonius Tim
Published: August 2015

The classical problem of suppressing vortex shedding in the wake of a circular cylinder by using body rotation is revisited in an adjoint-based optimal control framework. The cylinder’s unsteady and fully unconstrained rotation rate is optimized at Reynolds numbers between 75 and 200 and over horizons that are longer than in previous studies, where they are typically of the order of a vortex shedding period or shorter. In the best configuration, the drag is reduced by 19%, the vortex shedding is effectively suppressed, and this low drag state is maintained with minimal cylinder rotation after transients. Unlike open-loop control, the optimal control is shown to maintain a specific phase relationship between the actuation and the shedding in order to stabilize the wake. A comparison is also given between the performance of optimizations for different Reynolds numbers, cost functions, and horizon lengths. It is shown that the long horizons used are necessary in order to stabilize the vortex shedding efficiently.
Experimental and numerical study of electrically driven magnetohydrodynamic flow in a modified cylindrical annulus. II. Instabilities
Authors: Stelzer Zacharias , Miralles Sophie , Cébron David , Noir Jérôme , Vantieghem Stijn , Jackson Andrew
Published: August 2015

We present an investigation of the stability of liquid metal flow under the influence of an imposed magnetic field by means of a laboratory experiment as well as a linear stability analysis of the setup using the finite element method. The experimental device ZUrich Cylindrical CHannel INstability Investigation is a modified cylindrical annulus with electrically driven flow of liquid GaInSn operating at Hartmann and Reynolds numbers up to M = 2022 and Re = 2.6 ⋅ 105, respectively. The magnetic field gives rise to a free shear layer at the prominent inner electrode. We identify several flow regimes characterized by the nature of the instabilities. Above a critical current Ic=O(0.1A), the steady flow is destabilized by a Kelvin-Helmholtz mechanism at the free shear layer. The instability consists of counterrotating vortices traveling with the mean flow. For low forcing, the vortices are restricted to the free shear layer. Their azimuthal wave number m grows with M and decreases with Re. At Re/M ≈ 25, the instability becomes container-filling and energetically significant. It enhances the radial momentum transport which manifests itself in a broadening of the free shear layer width δS. We propose that this transition may be related to an unstable Hartmann layer. At Re/M2=O(1), an abrupt change is observed in the mean azimuthal velocity 〈uϕ¯〉 and the friction factor F, which we interpret as the transition between an inertialess and an inertial regime.
Coupling of alpha channeling to parallel wavenumber upshift in lower hybrid current drive
Authors: Ochs I. E. , Bertelli N. , Fisch N. J.
Published: August 2015

Although lower hybrid (LH) waves have been shown to be effective in driving plasma current in present-day tokamaks, they are predicted to strongly interact with the energetic α particles born from fusion reactions in eventual tokamak reactors. However, in the presence of the expected steep α particle birth gradient, this interaction can produce wave amplification rather than wave damping. Here, we identify the flexibilities and constraints in achieving this amplification effect through a consideration of symmetries in the channeling interaction, in the wave propagation, and in the tokamak field configuration. Interestingly, for standard LH current drive that supports the poloidal magnetic field, we find that wave amplification through α channeling is fundamentally coupled to the poorly understood |k∥| upshift. In so doing, we show that wave launch from the tokamak high-field side is favorable both for α-channeling and for achieving the |k∥| upshift.
Bubble shape and electromagnetic field in the nonlinear regime for laser wakefield acceleration
Authors: Li X. F. , Yu Q. , Gu Y. J. , Huang S. , Kong Q. , Kawata S.
Published: August 2015

The electromagnetic field in the electron “bubble” regime for ultra-intense laser wakefield acceleration was solved using the d'Alembert equations. Ignoring the residual electrons, we assume an ellipsoidal bubble forms under ideal conditions, with bubble velocity equal to the speed of light in vacuum. The general solution for bubble shape and electromagnetic field were obtained. The results were confirmed in 2.5D PIC (particle-in-cell) simulations. Moreover, slopes for the longitudinal electric field of larger than 0.5 were found in these simulations. With spherical bubbles, this slope is always smaller than or equal to 0.5. This behavior validates the ellipsoid assumption.
Moduli spaces of lumps on real projective space
Authors: Krusch Steffen , Muhamed Abera A.
Published: August 2015

Harmonic maps that minimise the Dirichlet energy in their homotopy classes are known as lumps. Lump solutions on real projective space are explicitly given by rational maps subject to a certain symmetry requirement. This has consequences for the behaviour of lumps and their symmetries. An interesting feature is that the moduli space of charge three lumps is a 7-dimensional manifold of cohomogeneity one which can be described as a one-parameter family of symmetry orbits of D2 symmetric maps. In this paper, we discuss the charge three moduli spaces of lumps from two perspectives: discrete symmetries of lumps and the Riemann-Hurwitz formula. We then calculate the metric and find explicit formulas for various geometric quantities. We also discuss the implications for lump decay.
(M-theory-)Killing spinors on symmetric spaces
Authors: Hustler Noel , Lischewski Andree
Published: August 2015

We show how the theory of invariant principal bundle connections for reductive homogeneous spaces can be applied to determine the holonomy of generalised Killing spinor covariant derivatives of the form D = ∇ + Ω in a purely algebraic and algorithmic way, where Ω : TM → Λ∗(TM) is a left-invariant homomorphism. Specialising this to the case of symmetric M-theory backgrounds (i.e., (M, g, F) with (M, g) an eleven-dimensional Lorentzian (locally) symmetric space and F an invariant closed 4-form), we derive several criteria for such a background to preserve some supersymmetry and consequently find all supersymmetric symmetric M-theory backgrounds.
A coarse-grained molecular dynamics study of segmental structure and mobility in capped crosslinked copolymer films
Authors: Davris T. , Lyulin A. V.
Published: August 2015

We present results from molecular-dynamics simulations of a generic bead-spring model of copolymer chains confined between solid walls and report on the glass-transition temperature and segmental dynamics as a function of film thickness and mesh size (the end-to-end distance of the subchains in the crosslinked polymer networks). Apparently, the glass-transition temperature displayed a steep increase for mesh-size values much smaller than the radius of gyration of the bulk chains, otherwise it remained invariant to mesh-size variations. The rise in the glass-transition temperature with decreasing mesh size and film thickness was accompanied by a monotonic slowing-down of segmental dynamics on all studied length scales. This observation is attributed to the correspondingly decreased width of the bulk density layer that was obtained in films whose thickness was larger than the end-to-end distance of the bulk polymer chains. To test this hypothesis, additional simulations were performed in which the crystalline walls were replaced with amorphous or rough walls. In the amorphous case, the high polymer density close to the walls vanished, but the dynamic response of the film was not affected. The rough walls, on the other hand, only slightly decreased the density close to the walls and led to a minor slowing-down in the dynamics at large length-scales.
Enhanced ferroelectric photovoltaic response of BiFeO3/BaTiO3 multilayered structure
Authors: Sharma Savita , Tomar Monika , Kumar Ashok , Puri Nitin K. , Gupta Vinay
Published: August 2015

The present work is based on the photovoltaic properties of multilayered structure of Bismuth ferrite (BFO) and Barium titanate (BTO) thin films prepared by pulsed laser deposition technique on platinum coated silicon substrate. The multilayered structure possesses enhanced ferroelectric properties and shows a remarkable increase in photocurrent (from 1.56 × 10−7 A to 6.96 × 10−5 A) upon illumination with laser light of wavelength 405 nm at an intensity of 160 mW/cm2. The values of short circuit photocurrent and open circuit voltage were found to be 0.3184 mA/cm2 and −1.25 V, respectively, with a light-to-electricity conversion efficiency of 0.067%. A relatively high efficiency calculated at 405 nm for the developed multilayered BFO/BTO structure highlights its practical application in ferroelectric photovoltaics.
Direct observation of critical adsorption on colloidal particles
Authors: Bertrand C. E. , Godfrin P. D. , Liu Y.
Published: August 2015

Despite the fundamental role adsorbed solvent layers play in generating critical Casimir forces between colloidal particles, the structure of these layers has yet to be directly determined. Using small-angle neutron scattering, we have measured critical adsorption on the surface of small spherical silica particles suspended in a binary mixture of lutidine and water. The surface concentration profile and excess adsorption Γ were studied as functions of temperature at the critical concentration and three off-critical concentrations. We are able to differentiate three distinct contributions to the excess adsorption including the intrinsic shape of the concentration profile. The adsorption associated with the profile shape is found to increase monotonically with increasing 2,6-lutidine concentration and to decrease with increasing temperature, this later observation is consistent with expectations for curvature induced corrections to planar adsorption and leads to Γ∼(T−Tc)/Tc−0.52, where Tc is the critical temperature. This scaling relation corresponds to a stronger divergence than found in the planar case, but a substantially weaker divergence than found previously.
Varistor piezotronics: Mechanically tuned conductivity in varistors
Authors: Baraki Raschid , Novak Nikola , Hofstätter Michael , Supancic Peter , Rödel Jürgen , Frömling Till
Published: August 2015

The piezoelectric effect of ZnO has been investigated recently with the goal to modify metal/semiconductor Schottky-barriers and p-n-junctions by application of mechanical stress. This research area called “piezotronics” is so far focused on nano structured ZnO wires. At the same time, ZnO varistor materials are already widely utilized and may benefit from a piezotronic approach. In this instance, the grain boundary potential barriers in the ceramic can be tuned by mechanical stress. Polycrystalline varistors exhibit huge changes of resistivity upon applied electrical and mechanical fields and therefore offer descriptive model systems to study the piezotronic effect. If the influence of temperature is contemplated, our current mechanistic understanding can be interrogated and corroborated. In this paper, we present a physical model based on parallel conducting pathways. This affords qualitative and semi-quantitative rationalization of temperature dependent electrical properties. The investigations demonstrate that narrow conductive pathways contribute to the overall current, which becomes increasingly conductive with application of mechanical stress due to lowering of the barrier height. Rising temperature increases the thermionic current through the rest of the material with higher average potential barriers, which are hardly affected by the piezoelectric effect. Hence, relative changes in resistance due to application of stress are higher at low temperature.
Adsorption energies and prefactor determination for CH3OH adsorption on graphite
Authors: Doronin M. , Bertin M. , Michaut X. , Philippe L. , Fillion J.-H.
Published: August 2015

In this paper, we have studied adsorption and thermal desorption of methanol CH3OH on graphite surface, with the specific aim to derive from experimental data quantitative parameters that govern the desorption, namely, adsorption energy Eads and prefactor ν of the Polanyi-Wigner law. In low coverage regime, these two values are interconnected and usually the experiments can be reproduced with any couple (Eads, ν), which makes intercomparison between studies difficult since the results depend on the extraction method. Here, we use a method for determining independently the average adsorption energy and a prefactor value that works over a large range of incident methanol coverage, from a limited set of desorption curves performed at different heating rates. In the low coverage regime the procedure is based on a first order kinetic law, and considers an adsorption energy distribution which is not expected to vary with the applied heating rate. In the case of CH3OH multilayers, Eads is determined as 430 meV with a prefactor of 5 × 1014 s−1. For CH3OH submonolayers on graphite, adsorption energy of 470 ± 30 meV and a prefactor of (8 ± 3) × 1016 s−1 have been found. These last values, which do not change between 0.09 ML and 1 ML initial coverage, suggest that the methanol molecules form island-like structure on the graphite even at low coverage.
Communication: Analytic continuation of the virial series through the critical point using parametric approximants
Authors: Barlow Nathaniel S. , Schultz Andrew J. , Weinstein Steven J. , Kofke David A.
Published: August 2015

The mathematical structure imposed by the thermodynamic critical point motivates an approximant that synthesizes two theoretically sound equations of state: the parametric and the virial. The former is constructed to describe the critical region, incorporating all scaling laws; the latter is an expansion about zero density, developed from molecular considerations. The approximant is shown to yield an equation of state capable of accurately describing properties over a large portion of the thermodynamic parameter space, far greater than that covered by each treatment alone.
Note: A simple image processing based fiducial auto-alignment method for sample registration
Authors: Robertson Wesley D. , Porto Lucas R. , Ip Candice J. X. , Nantel Megan K. T. , Tellkamp Friedjof , Lu Yinfei , Dwayne Miller R. J.
Published: August 2015

A simple method for the location and auto-alignment of sample fiducials for sample registration using widely available MATLAB/LabVIEW software is demonstrated. The method is robust, easily implemented, and applicable to a wide variety of experiment types for improved reproducibility and increased setup speed. The software uses image processing to locate and measure the diameter and center point of circular fiducials for distance self-calibration and iterative alignment and can be used with most imaging systems. The method is demonstrated to be fast and reliable in locating and aligning sample fiducials, provided here by a nanofabricated array, with accuracy within the optical resolution of the imaging system. The software was further demonstrated to register, load, and sample the dynamically wetted array.
Improved performance of Pd/WO3/SiC Schottky-diode hydrogen gas sensor by using fluorine plasma treatment
Authors: Liu Y. , Tang W. M. , Lai P. T.
Published: August 2015

A high-performance Pd/WO3/SiC Schottky-diode hydrogen gas sensor was fabricated by using fluorine plasma treatment on the WO3 film. From the electrical measurements under various hydrogen concentrations and temperatures, the plasma-treated sensor exhibited a maximum barrier-height change of 279 meV and a static gas sensitivity of more than 30 000, which is 30 times higher than that of the untreated sensor. This significant improvement is attributed to the larger adsorption area caused by the plasma-roughened WO3 film and the lower baseline leakage current induced by fluorine passivation of oxide traps. Additionally, the kinetics analysis and hydrogen coverage of the devices were studied to demonstrate the temperature dependence of the gas sensing behaviors. The hydrogen adsorption enthalpy at the Pd-WO3 interface significantly decreased from −31.2 kJ/mol to −57.6 kJ/mol after the plasma treatment. Therefore, the adsorption process on the plasma-treated sample is much easier and the suppression of sensing properties is more obvious at elevated temperatures above 423 K.
Computational study on Kerr constants of neutral and ionized gases
Authors: Sato M. , Kumada A. , Hidaka K.
Published: August 2015

In order to quantitatively examine the measurement capability of Poisson's field using electro-optic Kerr-effect (EOKE), Kerr constants of neutral molecules and ions are examined by means of first principle calculations. We have systematically computed Kerr constants of neutral molecules and ions of several molecular symmetry groups, with consistent theory level and basis sets. Computed Kerr constants of neutral molecules (N2, CO2, SF6, and CF3I) ranging across two orders of magnitudes are within 50% error of the experimental values, which are comparable to the scattering between experimental values itself. The results show that SF6 has smaller Kerr constant due to its high molecular symmetry compared to those of N2 and CO2. In contrast, CF3I has large Kerr constant due to its permanent dipole. Computed Kerr constants for anions are larger by two orders of magnitude than those of neutral molecules, probably due to the shielding effect. For cations, the opposite holds true; however, due to anisotropic polarizability, computed Kerr constants for some cations are comparable to neutral molecules, while others show smaller values. The ratio of Kerr constants of ions to those of neutral molecules are at most 102; EOKE is valid for measuring electric field in weakly ionized gas whose ionization degree is smaller than 10−3.
Electric field induced phase transition and domain structure evolution in (Pb, La)(Zr, Sn, Ti)O3 single crystal
Authors: Gao Jinghan , Li Qiang , Li Yuanyuan , Zhuo Fangping , Yan Qingfeng , Cao Wenwu , Xi Xiaoqing , Zhang Yiling , Chu Xiangcheng
Published: August 2015

Antiferroelectric (Pb, La)(Zr, Sn, Ti)O3 (PLZST) single crystals with composition in the vicinity of morphotropic phase boundary have been grown and studied. From electric measurements, Raman study, and observation of domain structures, we found an electric field induced antiferroelectric to ferroelectric phase transition accompanied with fifteen times of strain difference. After this phase transition, the metastable ferroelectric phase (FEin) is preserved with soften of A1(TO1) mode and increase of long-range force. Coexistence of tetragonal (T) and rhombohedral (R) domains has been observed in virgin sample. Electric field induced T to R phase transition is verified by both extinction angle and domain morphology changes. Clamping “polar” structure formed by the embedded R phase would contribute to increase of long-range force. The remarkable strain difference accompany with induced phase transition makes the PLZST single crystal a promising candidate for electric switch and actuator applications.
A comparative study of magnetic training effect in bulk and nanocrystalline La0.46Ca0.54MnO3 compound
Authors: Das Kalipada , Das I.
Published: August 2015

Transport, magneto-transport, and magnetic properties of La0.46Ca0.54MnO3 compounds having average grain size down to ∼15 nm have been studied. A magnetic training effect due to the external magnetic field cycling was distinctly observed in charge ordered antiferromagnetic bulk compound. Our present study indicates that the training effect was markedly modified along with the modification of the charge ordering due to the reduction of the grain size, and eventually both phenomenons disappeared in case of our lowest particle size sample (∼15 nm). Enhanced ferromagnetic correlation with the reduction of particle size plays the key role for the gradual diminishing of the training effect in the region of nanometer length scale.
Large-scale epitaxial growth kinetics of graphene: A kinetic Monte Carlo study
Authors: Jiang Huijun , Hou Zhonghuai
Published: August 2015

Epitaxial growth via chemical vapor deposition is considered to be the most promising way towards synthesizing large area graphene with high quality. However, it remains a big theoretical challenge to reveal growth kinetics with atomically energetic and large-scale spatial information included. Here, we propose a minimal kinetic Monte Carlo model to address such an issue on an active catalyst surface with graphene/substrate lattice mismatch, which facilitates us to perform large scale simulations of the growth kinetics over two dimensional surface with growth fronts of complex shapes. A geometry-determined large-scale growth mechanism is revealed, where the rate-dominating event is found to be C1-attachment for concave growth-front segments and C5-attachment for others. This growth mechanism leads to an interesting time-resolved growth behavior which is well consistent with that observed in a recent scanning tunneling microscopy experiment.
Optical properties of amorphous and crystalline Sb-doped SnO2 thin films studied with spectroscopic ellipsometry: Optical gap energy and effective mass
Authors: So Hyeon Seob , Park Jun-Woo , Jung Dae Ho , Ko Kun Hee , Lee Hosun
Published: August 2015

We investigated the optical properties of amorphous and crystalline antimony (Sb)-doped tin dioxide (SnO2) thin films grown using the co-sputtering deposition method at room temperature. We used undoped and Sb-doped (8 wt. %) SnO2 targets. Varying the relative power ratio of the two targets, we controlled the Sb-composition of the SnO2:Sb thin films up to 2.3 at. % of Sb contents. Through annealing, the as-grown amorphous SnO2:Sb thin films were transformed to crystalline thin films. Dielectric functions were obtained from the measured ellipsometry angles, Ψ and Δ, using the Drude and parametric optical constant models. We determined the absorption coefficients and optical gap energies of the SnO2:Sb thin films from the dielectric functions. We found increasing optical gap energy with increasing Sb composition. Increases in the Drude tail amplitudes, a signature of free carrier concentrations, were found in annealed, crystalline thin films with increasing Sb composition. The increase in the optical gap energy with increasing Sb composition was mainly attributed to the Burstein-Moss effect. Using Hall effect measurements, we obtained Hall carrier concentrations (NHall) and electron Hall mobilities (μHall). The carrier concentrations and mobilities increased from 2.6 × 1019 cm−3 and 1.0 cm2/(V s) to 2.0 × 1020 cm−1 and 7.2 cm2/(V s), respectively, with increasing Sb contents. This result suggests that the nominally undoped SnO2 films are unintentionally n-type doped. Assuming that the NHall and optical carrier concentrations (Nopt) were the same, we obtained the effective masses of the SnO2:Sb thin films with increasing Sb compositions. The effective masses of the SnO2:Sb thin films increased from 0.245 m0 to 0.4 m0 with increasing Sb doping contents, and the nonparabolicity of the conduction band was estimated. We discussed the relation between the optical (μopt) and Hall (μHall) mobilities as a function of Sb contents and grain sizes.
Efficiency of a multilayer-Laue-lens with a 102 μm aperture
Authors: Macrander Albert T. , Kubec Adam , Conley Raymond , Bouet Nathalie , Zhou Juan , Wojcik Michael , Maser Jorg
Published: August 2015

A multilayer-Laue-lens (MLL) comprised of WSi2/Al layers stacked to a full thickness of 102 μm was characterized for its diffraction efficiency and dynamical diffraction properties by x-ray measurements made in the far field. The achieved aperture roughly doubles the previous maximum reported aperture for an MLL, thereby doubling the working distance. Negative and positive first orders were found to have 14.2% and 13.0% efficiencies, respectively. A section thickness of 9.6 μm was determined from Laue-case thickness fringes in the diffraction data. A background gas consisting of 90% Ar and 10% N2 was used for sputtering. This material system was chosen to reduce grown-in stress as the multilayer is deposited. Although some regions of the full MLL exhibited defects, the presently reported results were obtained for a region devoid of defects. The data compare well to dynamical diffraction calculations with Coupled Wave Theory (CWT) which provided confirmation of the optical constants and densities assumed for the CWT calculations.
Communication: Conductivity enhancement in plastic-crystalline solid-state electrolytes
Authors: Geirhos K. , Lunkenheimer P. , Michl M. , Reuter D. , Loidl A.
Published: August 2015

Finding new ionic conductors that enable significant advancements in the development of energy-storage devices is a challenging goal of current material science. Aside of material classes as ionic liquids or amorphous ion conductors, the so-called plastic crystals (PCs) have been shown to be good candidates combining high conductivity and favorable mechanical properties. PCs are formed by molecules whose orientational degrees of freedom still fluctuate despite the material exhibits a well-defined crystalline lattice. In the present work, we show that the conductivity of Li+ ions in succinonitrile, the most prominent molecular PC electrolyte, can be enhanced by several decades when replacing part of the molecules in the crystalline lattice by larger ones. Dielectric spectroscopy reveals that this is accompanied by a stronger coupling of ionic and reorientational motions. These findings, which can be understood in terms of an optimized “revolving door” mechanism, open a new path towards the development of better solid-state electrolytes.
First principles design of divacancy defected graphene nanoribbon based rectifying and negative differential resistance device
Authors: Chakrabarty Soubhik , Wasey A. H. M. Abdul , Thapa Ranjit , Das G. P.
Published: August 2015

We have studied using density functional theory and non-equilibrium Green’s function based approach, the electronic structures of 555-777 divacancy (DV) defected armchair edged graphene nanoribbons (AGNR) as well as the transport properties of AGNR based two-terminal devices constructed with one defected electrode and one N doped electrode. Introduction of 555-777 DV defect into AGNR results in shifting of the π and π∗ bands towards the higher energy value indicating a downward shift of the Fermi level. Formation of a potential barrier, analogous to that of conventional p-n junction, has been observed across the junction of defected and N-doped AGNR. The two terminal devices show diode like property with high rectifying efficiency for a wide range of bias voltages. The devices also show robust negative differential resistance with very high peak-to-valley ratio. Shift of the electrode energy states and modification of the transmission function with applied bias have been analyzed, in order to gain an insight into the nonlinear and asymmetric behavior of the current-voltage characteristics. Variation of the transport properties on the width of the ribbons has also been discussed.
Large-area patterning of sub-100 nm epitaxial L1 FePt dots array via nanoimprint lithography
Authors: Li Zheng , Zhang Wei , Krishnan Kannan M.
Published: August 2015

Bit-patterned media, a promising candidate for next generation high density magnetic recording, requires sub-100 nm dots array on a wafer scale, a high degree of patterning control of the size distribution, and a material with high perpendicular anisotropy. In this work, large area (0.75 cm × 0.75 cm) dots array was achieved by nanoimprint lithography and ion milling from L10 FePt thin films that are pre-sputtered at 450 °C with both high crystalline quality and good chemical order. The sub-100 nm dots are decoupled from each other and show both narrow size distributions and high coercivity values on the order of 11 kOe. Our work would cast light for the application of bit-patterned media.
HgCdTe e-avalanche photodiode detector arrays
Authors: Singh Anand , Shukla A. K. , Pal Ravinder
Published: August 2015

Initial results on the MWIR e-APD detector arrays with 30 μm pitch fabricated on LPE grown compositionally graded p-HgCdTe epilayers are presented. High dynamic resistance times active area (R0A) product 2 × 106 Ω-cm2, low dark current density 4 nA/cm2 and high gain 5500 at -8 V were achieved in the n+-υ-p+ HgCdTe e-APD at 80 K. LPE based HgCdTe e-APD development makes this technology amenable for adoption in the foundries established for the conventional HgCdTe photovoltaic detector arrays without any additional investment.
Nitrogen balance in Holstein steers grazing winter oats: effect of nitrogen fertilisation
Authors: Chopa F. Sánchez , Nadin L. B. , Agnelli L. , Trindade J. K. , Gonda H. L.
Published: August 2015

The present study evaluated the effect of nitrogen (N) fertilisation of winter oats on whole-animal N balance (N intake, N excretion in urine and faeces, N retention), partition of urinary N (purine-N derivatives and urea-N) and average daily gain (ADG) in grazing steers. The experimental area was divided in two plots (10 steers/plot), and samples were obtained in two periods (one plot/period).The experimental area was divided in two plots, and each plot in 10 strips. Twenty Holstein steers (161.3 ± 7 kg of initial bodyweight) grazed, for 51 days, individual strips of fertilised (100 kg N/ha; N100) and non-fertilised (N0) winter oats during daylight (10 h/day). The daily individual grazing paddock was adjusted to offer 6 kg DM of green leaf·100 kg/BW.day. Chemical composition of the herbage and N diurnal variation were estimated by collecting three samples per paddock at 0830 hours, 1330 hours and 1830 hours, twice on each sampling period. Forage intake and in vivo digestibility were estimated by the n-alkane technique. Individual N intake was estimated using n-alkane data, the ingestive behaviour data and the diurnal variation of the chemical composition of the forage. N fertilisation increased N content [P < 0.01; N0 = 11.4% crude protein (CP) vs N100 = 13.9% CP] and decreased the water-soluble carbohydrate content (P < 0.01; N0 = 21.1% vs N100 = 16.8%) in the forage, but did not modify herbage mass or the DM content. Dry matter intake (4.72 kg DM/day), water intake (7.57 L/day) and DM digestibility (67%) were not affected by N fertilisation. However, N intake and N digestibility were higher in N100 than in N0 (20 vs 7 g N/day). Although treatments had similar faecal N excretions (average 45.4 g N/day), there was a trend to increase urinary N excretion with N intake (P = 0.08; N100 = 53.3 vs N0 = 47.5 g N/day), a trend to increase N-allantoin excretion (P = 0.11; N100 = 3.18 vs N0 = 2.91 g/day) and an increase in urea-N excretion (P < 0.01; N100 = 30.7 vs N0 = 23.8 g/day). Increasing N intake led to greater N retention (P < 0.02; N100 = 37.9 vs N0 = 20.9 g N/day) and ADG (P < 0.03; N100 = 860 vs N0 = 698 g/day). These results suggest that fertilising winter oats with 100 kg N/ha improves N retention and ADG in young steers under grazing conditions.