bluuebunny/crossref_metadata_2025 huggingface dataset:
Low-temperature magnetic and thermal properties of the frustrated two-dimensional S = 1 compound Ni5(TeO3)4Cl2
Authors: Khatsko E. , Nizhankovskii S. V. , Gnatchenko S. , Zaleski A. , Lemmens P. , Berger H.
Published: January 2012

The temperature and magnetic field dependent magnetization of the two-dimensional quantum spin system Ni5(TeO3)4Cl2 has been investigated using single crystals in temperature range 1.8–100 K and in magnetic fields up to 14 T. The magnetization below the magnetic phase transition demonstrates an unusual temperature behavior with considerable anisotropy. Combined magnetization and specific heat data allowed to determine the critical temperature of the magnetic phase transition, Tc = 28.4 K. Magnetic fields shift this temperature toward lower temperatures.
Resistive current state of a wide superconducting film
Authors: Zolochevskii I. V.
Published: January 2012

The current-voltage characteristics (CVCs) of vortex superconducting films are investigated in a wide temperature range. It is shown for the first time that the experimental CVCs and their parameters are described well enough by asymptotic formulas within the theory of the vortex resistive state of Aslamazov-Lempitsky (AL). It is established that for wide films, the critical current of which corresponds to the AL theory, the differential resistance of a linear segment of a CVC does not depend on temperature that agrees with the model of the vortex resistive state of AL. In the range of much higher temperatures, where the critical current is Ic(T)∝(1−T/Tc)3/2, the decrease of the differential resistance with increasing the temperature is observed that corresponds to predictions of the AL theory. However, in the close vicinity of Tc the increase of the differential resistance of a linear vortex segment of CVCs was found at T → Tc. This effect does not have an explanation in modern theories of a vortex state.
Critical properties of an antiferromagnetic Ising model on a square lattice with interactions of the next-to-nearest neighbors
Authors: Murtazaev A. K. , Ramazanov M. K. , Badiev M. K.
Published: January 2012

The critical properties of an antiferromagnetic Ising model on a square lattice with interactions of the next-to-nearest neighbors are investigated by a replica Monte-Carlo method. Using the finite-size scaling theory the static critical exponents of specific heat, ordering parameter, susceptibility, correlation radius as well as the Fisher exponent are calculated. An analysis of data is performed both with and without taking into account a correction to the finite-size scaling. It was found that in the model under consideration the second order phase transition is observed. It is shown that this model belongs to the new class of universality of critical behavior.
Time-resolved one-dimensional detection of x-ray scattering in pulsed magnetic fields
Authors: Islam Zahirul , Ruff Jacob P. C. , Ross Kate A. , Nojiri Hiroyuki , Gaulin Bruce D.
Published: January 2012

We have developed an application of a one-dimensional micro-strip detector for capturing x-ray diffraction data in pulsed magnetic fields. This detector consists of a large array of 50 μm-wide Si strips with a full-frame read out at 20 kHz. Its use substantially improves data-collection efficiency and quality as compared to point detectors, because diffraction signals are recorded along an arc in reciprocal space in a time-resolved manner. By synchronizing with pulsed fields, the entire field dependence of a two-dimensional swath of reciprocal space may be determined using a small number of field pulses.
Unimolecular thermal decomposition of phenol and d5-phenol: Direct observation of cyclopentadiene formation via cyclohexadienone
Authors: Scheer Adam M. , Mukarakate Calvin , Robichaud David J. , Nimlos Mark R. , Carstensen Hans-Heinrich , Barney Ellison G.
Published: January 2012

The pyrolyses of phenol and d5-phenol (C6H5OH and C6D5OH) have been studied using a high temperature, microtubular (μtubular) SiC reactor. Product detection is via both photon ionization (10.487 eV) time-of-flight mass spectrometry and matrix isolation infrared spectroscopy. Gas exiting the heated reactor (375 K–1575 K) is subject to a free expansion after a residence time in the μtubular reactor of approximately 50–100 μs. The expansion from the reactor into vacuum rapidly cools the gas mixture and allows the detection of radicals and other highly reactive intermediates. We find that the initial decomposition steps at the onset of phenol pyrolysis are enol/keto tautomerization to form cyclohexadienone followed by decarbonylation to produce cyclopentadiene; C6H5OH → c-C6H6 = O → c-C5H6 + CO. The cyclopentadiene loses a H atom to generate the cyclopentadienyl radical which further decomposes to acetylene and propargyl radical; c-C5H6 → c-C5H5 + H → HC≡CH + HCCCH2. At higher temperatures, hydrogen loss from the PhO–H group to form phenoxy radical followed by CO ejection to generate the cyclopentadienyl radical likely contributes to the product distribution; C6H5O–H → C6H5O + H → c-C5H5 + CO. The direct decarbonylation reaction remains an important channel in the thermal decomposition mechanisms of the dihydroxybenzenes. Both catechol (o-HO–C6H4–OH) and hydroquinone (p-HO–C6H4–OH) are shown to undergo decarbonylation at the onset of pyrolysis to form hydroxycyclopentadiene. In the case of catechol, we observe that water loss is also an important decomposition channel at the onset of pyrolysis.
Generalized channels: Channels for convex subsets of the state space
Authors: Jenčová Anna
Published: January 2012

Let K be a convex subset of the state space of a finite-dimensional C*-algebra. We study the properties of channels on K, which are defined as affine maps from K into the state space of another algebra, extending to completely positive maps on the subspace generated by K. We show that each such map is the restriction of a completely positive map on the whole algebra, called a generalized channel. We characterize the set of generalized channels and also the equivalence classes of generalized channels having the same value on K. Moreover, if K contains the tracial state, the set of generalized channels forms again a convex subset of a multipartite state space, this leads to a definition of a generalized supermap, which is a generalized channel with respect to this subset. We prove a decomposition theorem for generalized supermaps and describe the equivalence classes. The set of generalized supermaps having the same value on equivalent generalized channels is also characterized. Special cases include quantum combs and process positive operator valued measures (POVMs).
A dynamic hybrid Reynolds-averaged Navier Stokes–Large eddy simulation modeling framework
Authors: Bhushan S. , Walters D. K.
Published: January 2012

A dynamic framework for hybrid Reynolds-averaged Navier-Stokes (RANS)—large eddy simulation (LES) modeling is proposed, wherein the RANS-to-LES transition parameter is adjusted to maintain continuity in turbulence production. The model is applied for temporally developing plane channel flow at varying Reynolds numbers with different initial turbulence intensity and grid resolution. On sufficiently fine grids, dynamic hybrid RANS-LES model (DHRL) yields similar results to LES simulations. On coarse grids, DHRL activates RANS mode in the log layer, thus improving the mean flow predictions. The model framework addresses grid sensitivity issues observed in other hybrid RANS-LES approaches and may be used with any desired combination of LES and RANS basis models.
Modeling simple amphiphilic solutes in a Jagla solvent
Authors: Su Zhiqiang , Buldyrev Sergey V. , Debenedetti Pablo G. , Rossky Peter J. , Eugene Stanley H.
Published: January 2012

Methanol is an amphiphilic solute whose aqueous solutions exhibit distinctive physical properties. The volume change upon mixing, for example, is negative across the entire composition range, indicating strong association. We explore the corresponding behavior of a Jagla solvent, which has been previously shown to exhibit many of the anomalous properties of water. We consider two models of an amphiphilic solute: (i) a “dimer” model, which consists of one hydrophobic hard sphere linked to a Jagla particle with a permanent bond, and (ii) a “monomer” model, which is a limiting case of the dimer, formed by concentrically overlapping a hard sphere and a Jagla particle. Using discrete molecular dynamics, we calculate the thermodynamic properties of the resulting solutions. We systematically vary the set of parameters of the dimer and monomer models and find that one can readily reproduce the experimental behavior of the excess volume of the methanol-water system as a function of methanol volume fraction. We compare the pressure and temperature dependence of the excess volume and the excess enthalpy of both models with experimental data on methanol-water solutions and find qualitative agreement in most cases. We also investigate the solute effect on the temperature of maximum density and find that the effect of concentration is orders of magnitude stronger than measured experimentally.
Improving metastable impact electron spectroscopy and ultraviolet photoelectron spectroscopy signals by means of a modified time-of-flight separation
Authors: Spirkl Florian M. , Kunz Sebastian , Schweinberger Florian F. , Farnbacher Adrian N. , Schröter Richard , Heiz Ulrich
Published: January 2012

The separation of ultraviolet photoelectron spectroscopy (UPS) and metastable impact electron spectroscopy (MIES) is usually performed by a time-of-flight (ToF) separation using pre-set ToF for both types of signal. In this work, we present a new, improved ex situ signal separation method for the separation of MIES and UPS for every single measurement. Signal separation issues due to changes of system parameters can be overcome by changing the ToF separation and therefore allowing for the application of a wider range of measuring conditions. The method also enables to identify and achieve separation of the two signals without any time consuming calibration and the use of any special material for the calibration. Furthermore, changes made to the discharge source are described that enable to operate an existing MIES/UPS source over a broader range of conditions. This allows for tuning of the yield of UV photons and metastable rare gas atoms leading to an improved signal to noise ratio. First results of this improved setup are well in agreement with spectra reported in literature and show increased resolution and higher signal intensities for both MIE and UP spectra compared to the previous, non-optimized setup.
The effect of Li-substitution on the M-phases of AgNbO3
Authors: Khan H. U. , Sterianou I. , Miao S. , Pokorny J. , Reaney I. M.
Published: January 2012

Ceramics in the solid solution, LixAg1−xNbO3 (LAN) with 0 ≤ x ≤ 0.20, have been synthesized by the mixed oxide method. X-ray diffraction (XRD) revealed that only compositions with x ≤ 0.05 were single phase which were indexed according to Pbcm symmetry with a unit cell, √2ap × √2ap × 4ap (where ap is the fundamental perovskite lattice parameter). For compositions with x ≥ 0.1, second phase peaks attributed to LiNbO3 were observed and the matrix phase transformed to a metrically rhombohedral structure according to XRD. A phase transition at 0.05 < x ≤ 0.1 was confirmed by Raman spectroscopy and electron diffraction but the latter technique revealed superstructure reflections for x ≥ 0.1 at ±1/6{00l} and 1/2{ooo} ± 1/6{00l} (where o = odd). These support the premise that Li doping invokes a new complex modulated tilt system with a √2ap × √2ap × 6ap unit cell rather than √2ap × √2ap × 4ap (Pbcm). Reflections of the type ±1/6{00l} are, however, streaked along the [001] direction indicating that the structure may be incommensurate or only partially ordered. The appearance of the √2ap × √2ap × 6ap structure is associated with strong asymmetry in the peak in permittivity attributed to the M3–M2 and a decrease in intensity of the peak in permittivity associated with the M2–M1 transition. Slim polarization versus field curves characteristic of weak ferroelectricity were observed for compositions with x ≤ 0.05 but for higher values of x the loops were unsaturated albeit with larger remanent polarization.
Monte Carlo predictions of phase equilibria and structure for dimethyl ether + sulfur dioxide and dimethyl ether + carbon dioxide
Authors: Kamath Ganesh , Ketko MaryBeth , Baker Gary A. , Potoff Jeffrey J.
Published: January 2012

A new force field for dimethyl ether (DME) based on the Lennard-Jones (LJ) 12-6 plus point charge functional form is presented in this work. This force field reproduces experimental saturated liquid and vapor densities, vapor pressures, heats of vaporization, and critical properties to within the statistical uncertainty of the combined experimental and simulation measurements for temperatures between the normal boiling and critical point. Critical parameters and normal boiling point are predicted to within 0.1% of experiment. This force field is used in grand canonical histogram reweighting Monte Carlo simulations to predict the pressure composition diagrams for the binary mixtures DME + SO2 at 363.15 K and DME + CO2 at 335.15 and 308.15 K. For the DME + SO2 mixture, simulation is able to qualitatively reproduce the minimum pressure azeotropy observed experimentally for this mixture, but quantitative errors exist, suggesting that multibody effects may be important in this system. For the DME + CO2 mixture, simulation is able to predict the pressure-composition behavior within 1% of experimental data. Simulations in the isobaric-isothermal ensemble are used to determine the microstructure of DME + SO2 and DME + CO2 mixtures. The DME + SO2 shows weak pairing between DME and SO2 molecules, while no specific pairing or aggregation is observed for mixtures of DME + CO2.
Turbulent transport of toroidal angular momentum in fusion plasmas
Authors: Holod I. , Lin Z. , Xiao Y.
Published: January 2012

Global nonlinear gyrokinetic simulations of ion temperature gradient (ITG) and collisionless trapped electron mode (CTEM) turbulence find significant spinning up of a plasma in the directions opposite for CTEM and ITG turbulence. The outward momentum convection by the particle flux could be strong enough to overcome the inward momentum pinch and reverse the radial direction of the convective momentum flux. Momentum pinch velocity shows no explicit dependence on background temperature, while it is significantly affected by steepening the background density. Convective momentum fluxes are generally smaller in the CTEM turbulence than the ITG turbulence, while the intrinsic Prandtl number is similar or slightly larger in the CTEM turbulence.
Novel electromagnetic radiation in a semi-infinite space filled with a double-negative metamaterial
Authors: Duan Zhaoyun , Guo Chen , Zhou Jun , Lu Jucheng , Chen Min
Published: January 2012

We have theoretically investigated the electromagnetic radiation excited by a charged particle moving along a semi-infinite space filled with a double-negative metamaterial (DNM). Cherenkov radiation in the double-negative region exhibits reversed or backward radiation behavior. The spectral density of reversed Cherenkov radiation has a continuous distribution over the radiation frequency region. The influence of some important parameters on the Cherenkov radiation energy per unit length has been discussed. The surface wave in the vacuum region presented here also is investigated. We conclude that the amplitude of the surface wave is greatly enhanced over some normal dielectric material cases. The enhanced surface wave may be useful for high frequency and high power vacuum electron devices with the DNM.
A watt-class 1-THz backward-wave oscillator based on sine waveguide
Authors: Xu Xiong , Wei Yanyu , Shen Fei , Yin Hairong , Xu Jin , Gong Yubin , Wang Wenxiang
Published: January 2012

A novel backward wave oscillator was proposed by utilizing a concise sine waveguide slow-wave structure combined with sheet electron beam to operate at terahertz frequency band. First, the design method was described, and the dispersion curve and interaction impedance of the sine waveguide were calculated, then the device oscillation frequency and operating voltage were determined. Next, the circuit transmission losses were learned over the tunable frequency range. Finally, the particle-in-cell simulation method was applied to predict its signal generation performance. The investigation results show that, the backward wave oscillator can produce over 1.9 -W peak power output at the central operating frequency of 1-THz under 27-kV operating voltage and 5-mA beam current. And the interaction efficiency at 1-THz is more than 1.4% with a circuit length of 7.2-mm. It, therefore, will be considered as a promising watt-class terahertz radiation source.
0.7BiFeO3-0.3BaTiO3-Y3Fe5O12 composites with simultaneously improved electrical and magnetic properties
Authors: Yang Haibo , Ke Qingqing , Si Huayan , Chen Jingsheng
Published: January 2012

0.7BiFeO3-0.3BaTiO3-Y3Fe5O12 (BFO-BTO-YIG) composites were synthesized via a modified solid-sate route. The phase composition, microstructure, electrical, and magnetic properties of the composites were investigated. The results show that the BFO-BTO and YIG phases can coexist in the composites without any secondary phase. The electrical and magnetic properties BFO-BTO can be simultaneously improved by the introduction of YIG. Compared with BFO-BTO with weak magnetism, the 0.95(BFO-BTO)-0.05YIG composite shows an obviously enhanced ferromagnetic property with a Ms value of 1.4 emu/g, and a typical square polarization hysteresis loop with a Pr value of 19.3 μC/cm2, which is equal to that of BFO-BTO.
Optical anisotropy in self-assembled InAs nanostructures grown on GaAs high index substrate
Authors: Bennour M. , Saidi F. , Bouzaïene L. , Sfaxi L. , Maaref H.
Published: January 2012

We present a study of the optical properties of InAs self-assembled nanostructures grown by molecular beam epitaxy on GaAs(11N)A substrates (N = 3–5). Photoluminescence (PL) measurements revealed good optical properties of InAs quantum dots (QDs) grown on GaAs(115)A compared to those grown on GaAs(113)A and (114)A orientations substrate. An additional peak localized at 1.39 eV has been shown on PL spectra of both GaAs(114)A and (113)A samples. This peak persists even at lower power density. Supporting on the polarized photoluminescence characterization, we have attributed this additional peak to the quantum strings (QSTs) emission. A theoretical study based on the resolution of the three dimensional Schrödinger equation, using the finite element method, including strain and piezoelectric-field effect was adopted to distinguish the observed photoluminescence emission peaks. The mechanism of QDs and QSTs formation on such a high index GaAs substrates was explained in terms of piezoelectric driven atoms and the equilibrium surfaces at edges.
Perovskite phase transformation in 0.65Pb(Mg1/3Nb2/3)O3-0.35PbTiO3 nanoparticles derived by sol-gel
Authors: Singh Satyendra , Krupanidhi S. B.
Published: January 2012

Fabrication of 0.65Pb(Mg1/3Nb2/3)O3-0.35PbTiO3 (PMN-PT) nanoparticles with an average size of about 40 nm and their phase transformation behavior from pyrochlore to perovskite phase is investigated. A novel sol-gel method was used for the synthesis of air-stable and precipitate-free diol-based sol of PMN-PT which was dried and partially calcined at 450 °C for 1 h to decompose organics and bring down the free energy barrier for perovskite crystallization and then finally annealed in the temperature range 600 to 700 °C. Annealed at around 700 °C for 1 h, PMN-PT gel powder exhibited nanocrystalline morphology with perovskite phase as confirmed by the transmission electron microscopy and X-ray diffraction techniques.
Thermoelectric properties of indium filled and germanium doped Co4Sb12 skutterudites
Authors: Chandra Mallik Ramesh , Mueller Eckhard , Kim Il-Ho
Published: January 2012

In-filled and Ge-doped Co4Sb12 skutterudites materials were synthesized by an induction melting process which was followed by annealing at 650 °C for 7 days. A structural, compositional, and morphological study was carried out by X-ray diffraction (XRD), electron probe micro analysis (EPMA), and scanning electron microscopy (SEM). The formation of a single skutterudite phase (δ-CoSb3) was confirmed by XRD and the composition of all the samples was verified by EPMA. The homogeneity and morphology of the samples was observed by potential Seebeck microprobe (PSM) and SEM, respectively. The PSM result confirmed the inhomogeneity of the samples. The temperature dependence of the Seebeck coefficient, electrical conductivity, and thermal conductivity were measured in the temperature range of 300–650 K. The samples of In0.16Co4Sb12−xGex (x = 0.05, 0.1, and 0.2) show a negative Seebeck coefficient confirming an n-type conductivity and the In0.16Co4Sb11.7Ge0.3 sample shows a positive Seebeck coefficient confirming a p-type conductivity. There was a change in the Seebeck coefficient from an n-type to a p-type at the doping concentration of x = 0.3 due to the excess Ge which increases in hole carrier concentration. Electrical conductivity decreases with an increase in Ge doping concentrations and with increases in temperature due to the bipolar effect. Thermal conductivity increases with an increase in carrier concentration and decreases when the temperature is increased. The highest ZT = 0.58 was achieved by In0.16Co4Sb11.95Ge0.05 at 673 K and In-filled and Ge-doped Co4Sb12 was not effective in improving the figure of merit.
Fast magnetization reversal of nanoclusters in resonator
Authors: Yukalov V. I. , Yukalova E. P.
Published: January 2012

An effective method for ultrafast magnetization reversal of nanoclusters is suggested. The method is based on coupling a nanocluster to a resonant electric circuit. This coupling causes the appearance of a magnetic feedback field acting on the cluster, which drastically shortens the magnetization reversal time. The influence of the resonator properties, nanocluster parameters, and external fields on the magnetization dynamics and reversal time is analyzed. The magnetization reversal time can be made many orders shorter than the natural relaxation time. The reversal is studied for both the cases of a single nanocluster as well as for the system of many nanoclusters interacting through dipole forces.
Evolution of ferromagnetic and spin-wave resonances with crystalline order in thin films of full-Heusler alloy Co2MnSi
Authors: Pandey Himanshu , Joshi P. C. , Pant R. P. , Prasad R. , Auluck S. , Budhani R. C.
Published: January 2012

We report the evolution of magnetic moment as well as magnetic anisotropy with crystalline order in Co2MnSi thin films grown on (100) MgO by pulsed laser deposition. The films become more ordered as the annealing temperature (TA) increases from 400 to 600 °C. The extent of L21 ordering in the films annealed at 600 °C is ≈96%. The static magnetization measurements by vibrating sample magnetometry shows a maximum moment of 4.95 μB per formula unit with low coercivity (HC ≈ 65 Oe) in the films annealed at 600 °C. A rigorous analysis of the azimuthal and polar angle dependent ferromagnetic resonance (FMR) measured at several temperatures allows determination of various anisotropy fields relevant to our system as a function of TA. Finally, we have evaluated the exchange stiffness constant down to 100 K using spin wave modes in FMR spectra. We have also estimated the exchange energies as well as stiffness constant by ab initio calculations using the Korringa-Kohn-Rostoker method.
Interband cascade infrared photodetectors with enhanced electron barriers and p-type superlattice absorbers
Authors: Tian Z. , Hinkey R. T. , Yang Rui Q. , Lubyshev D. , Qiu Y. , Fastenau J. M. , Liu W. K. , Johnson M. B.
Published: January 2012

We present results on the optical and electrical performance of mid-infrared detectors based on interband-cascade structures. These devices include enhanced electron barriers, designed to suppress intraband-tunneling current between stages, and p-doped type-II InAs/GaSb superlattice absorbers. Within the sample set, we examined devices with different absorber thicknesses and doping levels. Carriers are extracted less efficiently in devices with longer absorbers, which is attributed to more band bending within the absorber due to electric charge accumulation. Also, devices with lower-doped (1 × 1017 cm−3) absorbers are found to have better optical and electrical performances than those with higher levels of doping (3 × 1017 cm−3). The overall performance of these devices was superior to previously reported results, with Johnson-noise limited detectivities, at 4.0 μm, as high as 6.0 × 1012 and 2.5 × 1011 Jones at 80 and 150 K, respectively.
A mathematical model of mixing enhancement in microfluidic channel with a constriction under periodic electro-osmotic flow
Authors: Xu Zhongbin , Yang Yue , Vadillo Damien , Ruan Xiaodong , Fu Xin
Published: January 2012

A microfluidic channel with a constriction produced poor mixing conditions under periodic electro-osmotic flow. However, the mixing performance may be enhanced significantly by altering other parameters. Numerical simulations are used to investigate the effect of the direct current electric field (EDC), phase difference (ϕ), and length of constriction (L). A mathematical model, based on the structural features of the Lagrange function rather than its application, is proposed to establish a relationship between the mixing performance and these three parameters. The feasibility analysis has been carried out, and the results are verified by the data from simulation and experiment.
Free field realization of quantum affine superalgebra $U_q(\widehat{{sl}}(N|1))$Uq(sl̂(N|1))
Authors: Kojima Takeo
Published: January 2012

We construct a free field realization of the quantum affine superalgebra \documentclass[12pt]{minimal}\begin{document}$U_q(\widehat{sl}(N|1))$\end{document}Uq(sl̂(N|1)) for an arbitrary level \documentclass[12pt]{minimal}\begin{document}$k \in {\mathbb C}$\end{document}k∈C.
High-speed force load in force measurement in liquid using scanning probe microscope
Authors: Zhang Yan , Zou Qingze
Published: January 2012

This article presents an inversion-based iterative feedforward-feedback (II-FF/FB) approach to achieve high-speed force load in force measurement of soft materials in liquid using scanning probe microscope (SPM). SPM force measurement under liquid environment is needed to interrogate a wide range of soft materials, particularly live biological samples. Moreover, when dynamic evolution of the sample occurs during the measurement, and/or measuring the rate-dependent viscoelasticity of the sample, the force measurement also needs to be acquired at high-speed. Precision force load in liquid, however, is challenged by adverse effects including the thermal drift effect, the reduction of the signal to noise ratio, the distributive hydrodynamic force effect, and the hysteresis and vibrational dynamics effects of the piezoelectric actuators (for positioning the probe relative to the sample), particularly during high-speed measurement. Thus, the main contribution of the article is the development of the II-FF/FB approach to tackle these challenges. The proposed method is illustrated through an experimental implementation to the force-curve measurement of a poly (dimethylsiloxane) sample in liquid at high-speed.
Increased bandwidth for dielectric spectroscopy of proteins through electrode surface preparation
Authors: Mellor Brett L. , Cortés Efrén Cruz , Khadka Shiul , Mazzeo Brian A.
Published: January 2012

Dielectric spectroscopy measurements of liquids are often limited by electrode polarization. The influence of surface polishing and deposition of the conducting polymer polypyrrole/polystyrenesulfonate (PPy/PSS) on the polarization impedance is investigated. A quantitative description of the electrode polarization contribution to the real-valued permittivity spectrum is derived. This description explains the origin of the \documentclass[12pt]{minimal}\begin{document}$\omega ^{-\rm const}.$\end{document}ω− const . (\documentclass[12pt]{minimal}\begin{document}$\textrm {const}.>1$\end{document} const .>1) dependency commonly observed in permittivity measurements. Electrode surface roughness is correlated with both the magnitude and phase of the constant phase element. Generally, rougher electrodes have better performance, and an order of magnitude bandwidth improvement is achieved using PPy/PSS electrodes.
Electrical characteristics of cadmium doped InAs grown by metalorganic vapor phase epitaxy
Authors: Wagener V. , Wagener M. C. , Botha J. R.
Published: January 2012

The use of dimethylcadmium as a potential p-type dopant source during the growth of InAs by metalorganic vapor phase epitaxy has been investigated. Thermoelectric measurements were used to accurately determine the doping density of the epilayers. A linear doping efficiency was attained for low DMCd mole fractions within the 550 °C to 650 °C growth temperature range with the doping density spanning from low 1016 to a maximum of 6 × 1017 cm−3. The surfactant action of a small mole fraction of Sb increased the maximum p-type doping density by a factor of two.
Template-based synthesis and magnetic properties of Mn-Zn ferrite nanotube and nanowire arrays
Authors: Guo Limin , Wang Xiaohui , Zhong Caifu , Li Longtu
Published: January 2012

Template-based electrophoretic deposition of Mn-Zn ferrite nanotubes (NTs) and nanowires (NWs) were achieved using anodic alumina oxide (AAO) membranes. The effect of electrophoretic current and deposition time on the morphology of the tubes was investigated. The samples show cubic spinel structure with no preferred orientation. Room-temperature magnetic properties of the Mn-Zn ferrite NT/NW arrays were studied. The magnetic easy axis parallels the NT/NW’s channel axis attributing to the large shape anisotropy in this direction, especially for the NTs with a small wall thickness. Magnetocrystalline anisotropy and magnetostatic interactions were found dominant in the samples when applied field was perpendicular to the channel axis.
Modifying thermal transport in electrically conducting polymers: Effects of stretching and combining polymer chains
Authors: Pal Souvik , Balasubramanian Ganesh , Puri Ishwar K.
Published: January 2012

If their thermal conductivity can be lowered, polyacetylene (PA) and polyaniline (PANI) offer examples of electrically conducting polymers that can have potential use as thermoelectrics. Thermal transport in such polymers is primarily influenced by bonded interactions and chain orientations relative to the direction of heat transfer. We employ molecular dynamics simulations to investigate two mechanisms to control the phonon thermal transport in PANI and PA, namely, (1) mechanical strain and (2) polymer combinations. The molecular configurations of PA and PANI have a significant influence on their thermal transport characteristics. The axial thermal conductivity increases when a polymer is axially stretched but decreases under transverse tension. Since the strain dependence of the thermal conductivity is related to the phonon scattering among neighboring polymer chains, this behavior is examined through Herman's orientation factor that quantifies the degree of chain alignment in a given direction. The conductivity is enhanced as adjacent chains become more aligned along the direction of heat conduction but diminishes when they are orthogonally oriented to it. Physically combining these polymers reduces the thermal conductivity, which reaches a minimum value for a 2:3 PANI/PA chain ratio.
Epitaxial oxide bilayer on Pt (001) nanofacets
Authors: Hennessy Daniel , Komanicky Vladimir , Iddir Hakim , Pierce Michael S. , Menzel Andreas , Chang Kee-Chul , Barbour Andi , Zapol Peter , You Hoydoo
Published: January 2012

We observed an epitaxial, air-stable, partially registered (2 × 1) oxide bilayer on Pt (001) nanofacets [V. Komanicky, A. Menzel, K.-C. Chang, and H. You, J. Phys. Chem. 109, 23543 (2005)]. The bilayer is made of two half Pt layers; the top layer has four oxygen bonds and the second layer two. The positions and oxidation states of the Pt atoms are determined by analyzing crystal truncation rods and resonance scattering data. The positions of oxygen atoms are determined by density functional theory (DFT) calculations. Partial registry on the nanofacets and the absence of such registry on the extended Pt (001) surface prepared similarly are explained in DFT calculations by strain relief that can be accommodated only by nanoscale facets.
Piezoelectric response of charged non-180° domain walls in ferroelectric ceramics
Authors: Li Zhanfang , Wu Hao , Cao Wenwu
Published: January 2012

Charged domain walls may have lower energy than charge neutral walls when large amount of aliovalent doping are present or when there are substantial amount of charged defects in the system. Charged domain walls can produce much larger contribution to functional properties than charge neutral domain walls because they are energetically less stable. If there are regions of charged domain walls in ferroelectric ceramic, it can enhance the extrinsic contribution to the piezoelectric and dielectric properties. We have performed a theoretical analysis on charged domain walls based on the time dependent Landau-Ginzburg model, assuming there are charge defects from aliovalent doping to locally stabilize such charged domain walls. Using BaTiO3 and PZT as examples, we have studied the stability of charged walls with defect density and found that piezoelectric properties can be greatly enhanced by charged walls if the charge density ρ is lower than the charges needed to produce local charge balance. If the charge density is equal or more than the amount needed for electrical balance, the walls are pinned, which causes the reduction of piezoelectric effects.
Intravascular ultrasound chirp imaging
Authors: Maresca D. , Jansen K. , Renaud G. , van Soest G. , Li X. , Zhou Q. , de Jong N. , Shung K. K. , van der Steen A. F. W.
Published: January 2012

We demonstrate the feasibility of intravascular ultrasound (IVUS) chirp imaging as well as chirp reversal ultrasound contrast imaging at intravascular ultrasound frequency. Chirp excitations were emitted with a 34 MHz single crystal intravascular transducer and compared to conventional Gaussian-shaped pulses of equal acoustic pressure. The signal to noise ratio of the chirp images was increased by up to 9 dB relative to the conventional images. Imaging of contrast microbubbles was implemented by chirp reversal, achieving a contrast to tissue ratio of 12 dB. The method shows potential for intravascular imaging of structures in and beyond coronary atherosclerotic plaques including vasa vasorum.
Type-II InP-based lasers emitting at 2.55 μm
Authors: Sprengel Stephan , Andrejew Alexander , Vizbaras Kristijonas , Gruendl Tobias , Geiger Kathrin , Boehm Gerhard , Grasse Christian , Amann Markus-Christian
Published: January 2012

Room-temperature lasing at 2.55 μm is reported for InP-based GaInAs/GaAsSb type-II quantum well lasers in pulsed mode up to 42 °C. This record long-wavelength lasing has become feasible by implementing compressive strain in both materials and a carrier confinement design using an AlAsSb/AlGaInAs electron/hole blocking layer. The device concept appears promising for extending the wavelength range further towards 3 μm.
On the influence of a patterned substrate on crystallization in suspensions of hard spheres
Authors: Dorosz Sven , Schilling Tanja
Published: January 2012

We present a computer simulation study on crystal nucleation and growth in supersaturated suspensions of mono-disperse hard spheres induced by a triangular lattice substrate. The main result is that compressed substrates are wet by the crystalline phase (the crystalline phase directly appears without any induction time), while for stretched substrates we observe heterogeneous nucleation. The shapes of the nucleated crystallites fluctuate strongly. In the case of homogeneous nucleation amorphous precursors have been observed [T. Schilling et al., Phys. Rev. Lett. 105(2), 025701 (2010)10.1103/PhysRevLett.105.025701]. For heterogeneous nucleation we do not find such precursors. The fluid is directly transformed into highly ordered crystallites.
Luminescence properties of SiOxNy irradiated by IR laser 808 nm: The role of Si quantum dots and Si chemical environment
Authors: Ruggeri Rosa , Neri Fortunato , Sciuto Antonella , Privitera Vittorio , Spinella Corrado , Mannino Giovanni
Published: January 2012

We investigated optical, structural, and chemical properties of SiOxNy layers irradiated by CW IR laser during a time lapse of few milliseconds. We observed tunable photoluminescence signal at room temperature in the range 750–950 nm, without Si/SiO2 phase separation, depending on the IR laser power irradiation. Furthermore, no photoluminescence signal was recorded when the IR laser power density was high enough to promote phase separation forming Si quantum dots. By chemical analysis the source of the luminescence signal has been identified in a change of silicon chemical environment induced by IR laser annealing inside the amorphous matrix.
Reorientation dynamics of nanoconfined water: Power-law decay, hydrogen-bond jumps, and test of a two-state model
Authors: Laage Damien , Thompson Ward H.
Published: January 2012

The reorientation dynamics of water confined within nanoscale, hydrophilic silica pores are investigated using molecular dynamics simulations. The effect of surface hydrogen-bonding and electrostatic interactions are examined by comparing with both a silica pore with no charges (representing hydrophobic confinement) and bulk water. The OH reorientation in water is found to slow significantly in hydrophilic confinement compared to bulk water, and is well-described by a power-law decay extending beyond one nanosecond. In contrast, the dynamics of water in the hydrophobic pore are more modestly affected. A two-state model, commonly used to interpret confined liquid properties, is tested by analysis of the position-dependence of the water dynamics. While the two-state model provides a good fit of the orientational decay, our molecular-level analysis evidences that it relies on an over-simplified picture of water dynamics. In contrast with the two-state model assumptions, the interface dynamics is markedly heterogeneous, especially in the hydrophilic pore and there is no single interfacial state with a common dynamics.
Time-dynamics of the two-color emission from vertical-external-cavity surface-emitting lasers
Authors: Chernikov A. , Wichmann M. , Shakfa M. K. , Scheller M. , Moloney J. V. , Koch S. W. , Koch M.
Published: January 2012

The temporal stability of a two-color vertical-external-cavity surface-emitting laser is studied using single-shot streak-camera measurements. The collected data is evaluated via quantitative statistical analysis schemes. Dynamically stable and unstable regions for the two-color operation are identified and the dependence on the pump conditions is analyzed.
Surface modification by subsurface pressure induced diffusion
Authors: Zimmermann Claus G.
Published: January 2012

Polycrystalline Ag, covered with a nm thin siloxane layer, was irradiated with ultraviolet light in vacuum at 500 K. Ag particles of different aspect ratios, 50–1000 nm in size, formed on the surface, including a small fraction of nanorods. Pressurized water vapor bubbles are created in the subsurface region by hydrogen radicals photo-chemically released by the siloxane layer. They provide the driving force for a diffusive material flux along grain boundaries to the surface. This mechanism was modeled and found to agree with the experimental timescale: approximately 300 h are required for a 1000 nm particle to form.
High magnetic field annealing effect on visible photoluminescence enhancement of TiO2 nanotube arrays
Authors: Yang Mingjie , Liu Wei , Sun Jia-Lin , Zhu Jia-Lin
Published: January 2012

TiO2 nanotube arrays with remarkable visible photoluminescence were prepared by high magnetic field annealing in air at 450 °C due to the involvement of oxygen vacancies (OVs). A field with the intensities of 0, 2, 4, 6, and 8 T were applied in the annealing processing, along the directions set at 0°, 50°, and 90° from the surface normal of the substrate. The results demonstrated that the density of oxygen vacancies in TiO2 nanotubes can be controlled by varying the intensity and direction of the magnetic field. The mechanism for the effect of the high magnetic field has been investigated. This study opens an effective way to control the oxygen vacancies in nanomaterials to improve their performance.
Transition of beam dynamics in waveguide arrays with commensurate Stark ladders
Authors: Wang G.
Published: January 2012

We theoretically investigate the transition of coherent dynamics of light among different transport regimes in waveguide arrays with commensurate Stark ladders. Applying a transverse confinement to the lattice structure, the eigenvalue spectrum becomes discrete and equidistant, i.e., commensurate Stark ladders. Propagation of light undergoes a crossover from Bloch oscillations to harmonic oscillations, and one class of dynamics named hybrid oscillations appears. The transition is attributed to the localization-delocalization transition of ladders’ properties. Our results offer an extra degree of freedom to manipulate light.
Efficient second harmonic generation in a metamaterial with two resonant modes coupled through two varactor diodes
Authors: Nakanishi Toshihiro , Tamayama Yasuhiro , Kitano Masao
Published: January 2012

We present an effective method to generate second harmonic (SH) waves using nonlinear metamaterial composed of coupled split ring resonators (CSRRs) with varactor (variable capacitance) diodes. The CSRR structure has two resonant modes: a symmetric mode that resonates at the fundamental frequency and an anti-symmetric mode that resonates at the SH frequency. Resonant fundamental waves in the symmetric mode generate resonant SH waves in the anti-symmetric mode. The double resonance contributes to effective SH radiation. In the experiment, we observe 19.6 dB enhancement in the SH radiation in comparison with the nonlinear metamaterial that resonates only for the fundamental waves.
Parabolic tapered photonic crystal cavity in silicon
Authors: Desiatov Boris , Goykhman Ilya , Levy Uriel
Published: January 2012

We demonstrate the design, fabrication, transmission spectrum measurement, and near-field characterization of a parabolic tapered one-dimensional photonic crystal cavity in silicon. The results shows a relatively high quality factor (∼43 000), together with a small modal volume of ∼1.1(λ/n)3. Moreover, the design allows repeatable device fabrication, as evident by the similar characteristics obtained for several tens of devices that were fabricated and tested. These demonstrated 1D PhC cavities may be used as a building block in integrated photonic circuits for optical on-chip interconnects and sensing applications.
Anomalous electron transport in back-gated field-effect transistors with TiTe2 semimetal thin-film channels
Authors: Khan J. , Nolen C. M. , Teweldebrhan D. , Wickramaratne D. , Lake R. K. , Balandin A. A.
Published: January 2012

The authors report on “graphene-like” mechanical exfoliation of thin films of titanium ditelluride and investigation of their electronic properties. The exfoliated crystalline TiTe2 films were used as the channel layers in the back-gated field-effect transistors fabricated with Ti/Al/Au metal contacts on SiO2/Si substrates. The room-temperature current-voltage characteristics revealed strongly non-linear behavior with signatures of the source-drain threshold voltage similar to those observed in the charge-density-wave devices. The drain-current showed an unusual non-monotonic dependence on the gate bias characterized by the presence of multiple peaks. The obtained results can be potentially used for implementation of the non-Boolean logic gates.
Thermal process dependence of Li configuration and electrical properties of Li-doped ZnO
Authors: Zhang Z. , Knutsen K. E. , Merz T. , Kuznetsov A. Yu. , Svensson B. G. , Brillson L. J.
Published: January 2012

We used depth-resolved cathodoluminescence spectroscopy (DRCLS) to describe the strong dependence of Li acceptor formation on thermal treatment in Li-doped ZnO. Within a 500-600 °C annealing temperature range, subsequent quenching ZnO leaves Li as interstitial donors, resulting in low room temperature resistivity, while slow cooling in air allows these interstitials to fill Zn vacancies forming Li acceptors 3.0 eV below the conduction band edge. DRCLS reveals an inverse relationship between the optical emission densities of lithium on zinc sites versus zinc vacancy sites, demonstrating the time dependence of Li interstitials to combine with zinc vacancies in order to form substitutional Li acceptors.
Overcoming the influence of the coupling fluid in photopyroelectric measurements of solid samples
Authors: Salazar Agustín , Oleaga Alberto
Published: January 2012

The thermal diffusivity of solid samples is systematically underestimated in a photopyroelectric technique used in the standard back configuration due to the presence of the coupling fluid between sample and detector. In this work, we propose a new method to overcome the undesired effect of the coupling fluid. It relies on the use of a transparent pyroelectric sensor and a transparent coupling fluid, together with a self-normalization procedure. In this way, we are able to measure accurately (a) the thermal diffusivity of opaque solid samples, and (b) the thermal diffusivity and the optical absorption coefficient of semitransparent solid samples.
The Determinants of Science-Based Cluster Growth: The Case of Nanotechnology
Authors: Mangematin Vincent , Errabi Khalid
Published: January 2012

There are growing academic and policy interests in the factors that underpin the formation and growth of clusters, especially in such ‘hyped-up’ scientific and technological fields as the nano-technologies. With this paper we analyzes the determinants of scientific cluster growth (measured by the number of publications emanating from them), distinguishing between structural effects (ie, initial cluster size, scientific field composition, and geographic location), on the one hand and scientific variety, organizational diversity, and degree of openness (in terms of collaboration with outside actors), on the other. Overall, scientific variety enhances cluster growth, but organizational diversity, slows it down. However, patterns of growth are different in Asia, Europe, and North America, and it seems that cluster evolution is highly contingent on national systems of innovation and on the history of collaboration amongst local actors. Policy makers and cluster strategists must design specific policies according to location and should not simply attempt to replicate best practices from one zone to another. Slow growth may also reflect ‘elitist’ strategies—those based on quality rather than on numbers.
Policy Storylines in Indian Climate Politics: Opening New Political Spaces?
Authors: Fisher Susannah
Published: January 2012

With this paper I consider the role of diffuse nonstate and subnational actors working together in networks in Indian climate politics. The Indian government has maintained several core principles in the United Nations Framework Convention on Climate Change negotiations since the emergence of climate change as a major international issue, and until recently the engagement of nonstate and subnational actors has been limited. However, new networked political actors are emerging that are widely linked into transnational networks, often supported by external funding and bringing new, diverse organisations into the debate. I argue that to understand their role and significance we must be more attentive to the spatiality of the policy process and must reconceptualise the relationship between nonstate actors and the state. The international arena is not the only area of climate politics, or necessarily the most significant, and attention to the role of local politics could develop a more rooted understanding of Indian climate politics.