bluuebunny/crossref_metadata_2025 huggingface dataset:
Uncertainty evaluation of mass discharge estimates from a contaminated site using a fully Bayesian framework
Authors: Troldborg Mads , Nowak Wolfgang , Tuxen Nina , Bjerg Poul L. , Helmig Rainer , Binning Philip J.
Published: December 2010

The estimation of mass discharges from contaminated sites is valuable when evaluating the potential risk to down‐gradient receptors, when assessing the efficiency of a site remediation, or when determining the degree of natural attenuation. Given the many applications of mass discharge estimation, it is important to quantify the associated uncertainties. Here a rigorous approach for quantifying the uncertainty in the mass discharge across a multilevel control plane is presented. The method accounts for (1) conceptual model uncertainty using multiple conceptual models and Bayesian model averaging (BMA), (2) heterogeneity through Bayesian geostatistics with an uncertain geostatistical model, and (3) measurement uncertainty. Through unconditional and conditional Monte Carlo simulation, ensembles of steady state plume realizations are generated. The conditional ensembles honor all measured data at the control plane for each of the conceptual models considered. The probability distribution of mass discharge is obtained by combining all ensembles via BMA. The method was applied to a trichloroethylene‐contaminated site located in northern Copenhagen. Four essentially different conceptual models based on two source zone models and two geological models were set up for this site, each providing substantially different prior mass discharge distributions. After conditioning to data, the predicted mass discharge distributions from each of the four conceptual models all approach each other. This indicates that the data set available at the site is strong and that the estimated mass discharge is robust to the assumed conceptual models and their boundary conditions. On the basis of the results, we discuss which of the conceptual models is most likely to reflect the true site conditions and analyze the relative proportions and importance of uncertainties as well as the impact of different data types on mass discharge uncertainty.
Correlations between experimental and theoretical adiabatic ionization energies for organic compounds and rate constants for atmospheric reactions with hydroxyl radicals
Authors: Rayne Sierra , Forest Kaya
Published: December 2010

Adiabatic ionization energy (AIE) calculations were performed at the AM1, PM3, PM6, PDDG, HF/QZVP, and B3LYP/QZVP levels of theory on 722 atmospherically relevant organic compounds with available experimental rate constants for atmospheric reactions with hydroxyl radicals (k~OH~). From the starting set of molecules, a final suite of 114 mono- and polyfunctionalized compounds provided converged neutral and cationic geometries without imaginary frequencies for all six levels of theory. NIST evaluated AIEs were available for 54 compounds, providing mean absolute AIE prediction errors of 0.31 (AM1), 0.28 (PM3), 0.50 (PM6), 0.36 (PDDG), 1.22 (HF/QZVP), and 0.20 eV (B3LYP/QZVP). Modest correlations were found between the experimental (r=-0.68, SE=0.81) and computationally estimated (r=-0.77 [AM1], -0.75 [PM3], -0.83 [PM6], -0.79 [PDDG], -0.83 [HF/QZVP], and -0.82 [B3LYP/QZVP]; SE=0.75 [AM1], 0.78 [PM3], 0.66 [PM6], 0.73 [PDDG], 0.67 [HF/QZVP], and 0.68 [B3LYP/QZVP]) AIEs and the corresponding experimental log k~OH~. Univariate AIE versus k~OH~ correlations are of lower predictive ability than state-of-the-art multivariate techniques, and are limited by the inability to calculate reliable AIEs for large numbers of atmospherically relevant compounds due either to convergence failures at various levels of theory or the presence of imaginary frequencies for converged cationic geometries.
Stem Cell Antigen CD34 In Native And Engineered Form Alter Its Binding Ability To Stromal Cells And Ligands: A Classical Example Of Clinical Benefits Of Therapeutic Genetic Engineering Of Stem Cells In Transplantation
Authors: Gangenahalli Gurudutta , Singh Vimal Kumar , Tripathi Rajendra Prasad , Verma Yogesh Kumar , Gupta Pallavi , Satija Neeraj Kumar
Published: December 2010

CD34 is a highly glycosylated surface-expressed sialomucin and, because it is present on hematopoietic stem cells (HSCs), has demonstrated immense clinical utility in their enumeration in aphaeresis products, immunoaffinity purification for transplantation, and disease monitoring. The success of CD34 based reagents in identifying hematopoietic progenitors led to the assumption that CD34 is expressed on cells with regenerative potential and is sufficient for hematopoietic reconstitution in marrow-ablated recipients. However, its role has not been identified in substantial detail.With the advent of the fact that CD34 binds adapter protein like CRK-L in cytosol and CD34 knock out studies identified a a signaling role, CD34 antigen has been proposed to play a signaling function. Since it is a sialomucin, a member of the group adhesion molecules, we attempted to identify a role by over-expreesing its gene in cell lines. We report here that CD34 and engineered forms (Ser306 & Tyr318) significantly regulates adhesion to stromal cells, like mesenchymal stem cells and bone marrow ligands. These enhance binding of cells overexpressing CD34 by upregulating integrins and we therefore propose that such cells may effectively potentiate the success of transplantation through greater homing if they are used for transfusion.
Temperature-dependent carrier mobility and threshold voltage of field-effect transistors with tetracene single crystals
Authors: Terao Satoru , Hirai Tadahiko , Morita Naomi , Maeda Hiroaki , Kojima Kenichi , Tachibana Masaru
Published: December 2010

Temperature-dependent carrier mobility and threshold voltage of organic field effect transistors (OFET) with tetracene single crystals pressed onto a SiO2/Si substrate were measured in the temperature range between 80 and 300 K. The mobility increases with decreasing temperature, reaching a maximum at 240 K. Further reduction of temperature leads to the decrease of the mobility, before leveling out below 140 K. We find that the critical temperature is strongly correlated with that of the threshold voltage which depends on the number of carriers captured in deep traps. From these temperature-dependent OFET characteristics, a carrier transport model including shallow and deep traps is suggested.
Crystal nucleation of hard spheres using molecular dynamics, umbrella sampling, and forward flux sampling: A comparison of simulation techniques
Authors: Filion L. , Hermes M. , Ni R. , Dijkstra M.
Published: December 2010

Over the last number of years several simulation methods have been introduced to study rare events such as nucleation. In this paper we examine the crystal nucleation rate of hard spheres using three such numerical techniques: molecular dynamics, forward flux sampling, and a Bennett–Chandler-type theory where the nucleation barrier is determined using umbrella sampling simulations. The resulting nucleation rates are compared with the experimental rates of Harland and van Megen [Phys. Rev. E 55, 3054 (1997)], Sinn et al. [Prog. Colloid Polym. Sci. 118, 266 (2001)], Schätzel and Ackerson [Phys. Rev. E 48, 3766 (1993)], and the predicted rates for monodisperse and 5% polydisperse hard spheres of Auer and Frenkel [Nature 409, 1020 (2001)]. When the rates are examined in units of the long-time diffusion coefficient, we find agreement between all the theoretically predicted nucleation rates, however, the experimental results display a markedly different behavior for low supersaturation. Additionally, we examined the precritical nuclei arising in the molecular dynamics, forward flux sampling, and umbrella sampling simulations. The structure of the nuclei appears independent of the simulation method, and in all cases, the nuclei contains on average significantly more face-centered-cubic ordered particles than hexagonal-close-packed ordered particles.
Simulations of polyelectrolyte dynamics in an externally applied electric field in confined geometry
Authors: Nedelcu S. , Sommer J.-U.
Published: December 2010

We consider the dynamics of charged polymers in free solution in a slit geometry under the influence of an electrical field, applied at an angle to the plane parallel walls of the confinement. The simulations are carried out using the Brownian dynamics method with explicit counterions and implicit hydrodynamics. The hydrodynamic interactions between all the particles and the plane parallel walls are taken into account using a diffusion matrix which depends on slit geometry and the actual polyelectrolyte-solute conformations. We observe a selective transport of the charged polymers, as a function of the degree of polymerization and slit height.
Chain of Hardy-type local reality constraints for n qubits
Authors: Ghosh Sibasish , Roy Shasanka Mohan
Published: December 2010

Nonlocality without inequality is an elegant argument introduced by Hardy for two qubit systems, and later generalised to n qubits, to establish contradiction of quantum theory with local realism. Interestingly, for n = 2 this argument is actually a corollary of Bell-type inequalities, viz., the CH–Hardy inequality involving Bell correlations, but for n greater than two it involves n-particle probabilities more general than Bell-correlations. In this paper, we first derive a chain of completely new local realistic inequalities involving joint probabilities for n qubits and then associated with each such inequality, we provide a new Hardy-type local reality constraint without inequalities. Quantum mechanical maximal violations of the chain of inequalities and of the associated constraints are also studied by deriving appropriate Cirel'son-type theorems. These results involving joint probabilities more general than Bell correlations are expected to provide a new systematic tool to investigate entanglement.
The effect of exit beam phase aberrations on parallel beam coherent x-ray reconstructions
Authors: Hruszkewycz S. O. , Harder R. , Xiao X. , Fuoss P. H.
Published: December 2010

Diffraction artifacts from imperfect x-ray windows near the sample are an important consideration in the design of coherent x-ray diffraction measurements. In this study, we used simulated and experimental diffraction patterns in two and three dimensions to explore the effect of phase imperfections in a beryllium window (such as a void or inclusion) on the convergence behavior of phasing algorithms and on the ultimate reconstruction. A predictive relationship between beam wavelength, sample size, and window position was derived to explain the dependence of reconstruction quality on beryllium defect size. Defects corresponding to this prediction cause the most damage to the sample exit wave and induce signature error oscillations during phasing that can be used as a fingerprint of experimental x-ray window artifacts. The relationship between x-ray window imperfection size and coherent x-ray diffractive imaging reconstruction quality explored in this work can play an important role in designing high-resolution in situ coherent imaging instrumentation and will help interpret the phasing behavior of coherent diffraction measured in these in situ environments.
Dielectric and ferroelectric response of compositionally graded bilayer and trilayer composites of BaTiO3 and 0.975BaTiO3–0.025Ba(Cu1/3Nb2/3)O3
Authors: Maurya Deepam , Wongdamnern Natthapong , Yimnirun Rattikorn , Priya Shashank
Published: December 2010

In this paper, we report the dielectric and ferroelectric response of compositionally graded bilayer and trilayer composites consisting of BaTiO3 (BT) and 0.975BaTiO3–0.025Ba(Cu1/3Nb2/3)O3 (BTBCN). Two types of graded bilayer samples were synthesized, one with same thickness of BT and BTBCN while other with different layer thicknesses. The graded trilayer sample consisted of BT layer sandwiched between two BTBCN layers of equal thickness. Scanning electron microscopy and transmission electron microscopy images showed a sharp interface with needle-shape domains across the interface. The domain size on BT side was found to be larger than that on BTBCN side. The temperature dependence of dielectric response for all composite systems was found to exhibit shifting in characteristic Curie peak compared to constituent material which was associated to coupling between layers. Moreover, the differences in grain size, tetragonality, domain mobility of each layer was found to perturb the electrical response of composite. The polarization mismatch between uncoupled BT and BTBCN established internal electric field in composite specimen and defined new polarization states in each layer by perturbing free energy functional of the composite specimen. Dynamic hysteresis behaviors and power-law scaling relations of all specimens were determined from polarization-electric field hysteresis loop measurements as a function of frequency. All systems were found to exhibit similar dynamic scaling relationships. Hysteresis area ⟨A⟩, Pr, and EC decreased with increasing frequency due to delayed response but increased with increasing applied electric field due to enhancement of driving force. Trilayer system was found to exhibit strong internal-bias field and double hysteresis behavior. The coupling effect resulting due to polarization mismatch between layers had substantial influence on the dynamic hysteresis behavior and power-law scaling relations.
Nanoscale potential measurements in liquid by frequency modulation atomic force microscopy
Authors: Kobayashi Naritaka , Asakawa Hitoshi , Fukuma Takeshi
Published: December 2010

We have developed a method for local potential measurements in liquid using frequency modulation atomic force microscopy. In this method, local potential is calculated from the first and second harmonic vibrations of a cantilever induced by applying an ac bias voltage between a tip and a sample. The use of an ac bias voltage with a relatively high frequency prevents uncontrolled electrochemical reactions and redistribution of ions and water. The nanoscale resolution of the method is demonstrated by imaging potential distribution of a dodecylamine thin film deposited on a graphite surface in 1 mM NaCl solution.
Planar radial weakly dissipative diffeomorphisms
Authors: Simó C. , Vieiro A.
Published: December 2010

We study the effect of a small dissipative radial perturbation acting on a one parameter family of area preserving diffeomorphisms. This is a specific type of dissipative perturbation. The interest is on the global effect of the dissipation on a fixed domain around an elliptic fixed/periodic point of the family, rather than on the effects around a single resonance. We describe the local/global bifurcations observed in the transition from the conservative to a weakly dissipative case: the location of the resonant islands, the changes in the domains of attraction of the foci inside these islands, how the resonances disappear, etc. The possible ω-limits are determined in each case. This topological description gives rise to three different dynamical regimes according to the size of dissipative perturbation. Moreover, we determine the conservative limit of the probability of capture in a generic resonance from the interpolating flow approximation, hence assuming no homoclinics in the resonance. As a paradigm of weakly dissipative radial maps, we use a dissipative version of the Hénon map.
Exact solutions to the sine-Gordon equation
Authors: Aktosun Tuncay , Demontis Francesco , van der Mee Cornelis
Published: December 2010

A systematic method is presented to provide various equivalent solution formulas for exact solutions to the sine-Gordon equation. Such solutions are analytic in the spatial variable x and the temporal variable t, and they are exponentially asymptotic to integer multiples of 2π as x → ±∞. The solution formulas are expressed explicitly in terms of a real triplet of constant matrices. The method presented is generalizable to other integrable evolution equations where the inverse scattering transform is applied via the use of a Marchenko integral equation. By expressing the kernel of that Marchenko equation using a matrix exponential in terms of the matrix triplet and by exploiting the separability of that kernel, an exact solution formula to the Marchenko equation is derived, yielding various equivalent exact solution formulas for the sine-Gordon equation.
Communication: Ionization potentials in the limit of large atomic number
Authors: Constantin Lucian A. , Snyder John C. , Perdew John P. , Burke Kieron
Published: December 2010

By extrapolating the energies of nonrelativistic atoms and their ions with up to 3000 electrons within Kohn–Sham density functional theory, we find that the ionization potential remains finite and increases across a row of the periodic table, even as Z → ∞. The local density approximation for the exchange contribution becomes more accurate (or even exact) in this limit. Extended Thomas–Fermi theory matches the shell average of both the ionization potential and density change.
A study on precipitation characteristics induced strength variation by nonlinear ultrasonic parameter
Authors: Mondal Chandan , Mukhopadhyay Amretendu , Sarkar Rajdeep
Published: December 2010

Nonlinear ultrasonic study has been carried out to characterize the variation in strength induced by precipitation characteristics. An age hardenable aluminum alloy has been taken as a model alloy for the present investigation. It is shown that the second order nonlinear ultrasonic (NLU) parameter scales with strength property that in turn depends on coherent to incoherent precipitation phase transition. The observed variations in NLU parameter has been explained by modifying an existing dislocation-coherent precipitate interaction model for harmonics generation in order to account for a weaker dislocation-semicoherent precipitate interaction. The model proposed can in general be applicable to all precipitation hardenable alloy systems undergoing coherent to incoherent precipitate phase transition.
Enhancement of ultrathin film emission using a waveguiding active layer
Authors: Aad R. , Blaize S. , Bruyant A. , Couteau C. , Lérondel G.
Published: December 2010

We present a theoretical study on the impact of a waveguiding active layer on the emission properties of an ultrathin luminescent film. While the study can be generalized to any material, we focus here on a simple layered medium composed of a conjugated polymers (CPs) thin film, a zinc oxide layer (ZnO) and a sapphire substrate. The study spreads throughout variable aspects including the effect of the structure parameters on the CP luminescence and radiation pattern and more specifically the influence of the absorption and emission properties of the active layer. Comparing between the passive and active layer cases, the obtained results show that an enhancement of the CP luminescence of more than 20 times can be obtained by using an optically active waveguiding underlying layer. The results can be explained in terms of photon recycling where the optically active layer acts as a photon reservoir and a secondary light source for the ultrathin film. This general concept is of a special interest for ultratrace chemosensor.
Effect of graphene oxide nanomaterial in electroclinic liquid crystals
Authors: Malik A. , Choudhary A. , Silotia P. , Biradar A. M. , Singh V. K. , Kumar N.
Published: December 2010

The collective dielectric relaxation studies have been carried out on the electroclinic liquid crystals (ELCs) doped with 0.1 to 0.2 wt % of graphene oxide (GO) in the frequency range of 20 Hz to 1 MHz. The GO favors for a good quality vertical alignment without any surface treatment of the substrates. The coupling of GO with indium tin oxide (ITO) substrate and ELC materials affects the molecular ordering and supports the ELC molecules to be aligned along the GO attached to the ITO surface in vertical direction. The vertical alignment can be changed to homogeneous by applying a high bias field to the sample and such converted homogeneous cell shows an additional dielectric relaxation peak in the low frequency side of Goldstone mode in SmC∗ phase due to presence of GO whereas in the pure material no such peak was observed. The frequency separation of both peaks (Goldstone mode and an additional peak) increases with temperature and low frequency peak vanishes near transition temperature.
Effect of gigaelectron volt Au-ion irradiation on the characteristics of ultrananocrystalline diamond films
Authors: Chen Huang-Chin , Teng Kuang-Yau , Tang Chen-Yau , Sundaravel Balakrishnan , Amirthapandian Sankarakumar , Lin I-Nan
Published: December 2010

The effect of 2.245 GeV Au-ion irradiation/postannealing processes on the electron field emission (EFE) properties of ultrananocrystalline diamond (UNCD) films was investigated. Au-ion irradiation with a fluence of around 8.4×1013 ions/cm2 is required to induce a large improvement in the EFE properties of the UNCD films. Postannealing the Au-ion irradiated films at 1000 °C for 1 h slightly degraded the EFE properties of the films but the resulting EFE behavior was still markedly superior to that of pristine UNCD films. Transmission electron microscopy examinations revealed that the EFE properties of the UNCD films are primarily improved by Au-ion irradiation/postannealing processes because of the formation of nanographites along the trajectory of the irradiating ions, which results in an interconnected path for electron transport. In contrast, the induction of grain growth process due to Au-ion irradiation in UNCD films is presumed to insignificantly degrade the EFE properties for the films as the aggregates are scarcely distributed and do not block the electron conducting path.
Evaluation of barrier uniformity in magnetic tunnel junctions prepared using natural oxidation of thin Mg layers
Authors: Seki Takayuki , Kubota Hitoshi , Fukushima Akio , Yakushiji Kay , Yuasa Shinji , Ando Koji , Maehara Hiroki , Yamagata Shinji , Okuyama Hiroki , Tsunekawa Koji
Published: December 2010

We fabricated submicron magnetic tunnel junctions (MTJs) using natural oxidation of thin Mg layers deposited by dc sputtering. The MTJs exhibited magnetoresistance (MR) ratios of up to about 150% with a low resistance-area product (RpA) of 8 Ω μm2, which are comparable to those for radio-frequency-sputtered MgO barriers. The submicron MTJs had highly variable MR and RpA values due to a high pinhole density (20 μm−2) in the barriers, whereas current-in-plane-tunneling (CIPT) measurements on the same MTJ films revealed highly reproducible MR and RpA values. This indicates that reproducible CIPT measurements do not necessarily give accurate results of MR and RpA at high pinhole densities.
Theory of hole mobility in strained Ge and III-V p-channel inversion layers with high-κ insulators
Authors: Zhang Yan , Fischetti M. V. , Sorée B. , O’Regan T.
Published: December 2010

We present a comprehensive investigation of the low-field hole mobility in strained Ge and III-V (GaAs, GaSb, InSb, and In1−xGaxAs) p-channel inversion layers with both SiO2 and high-κ insulators. The valence (sub)band structure of Ge and III-V channels, relaxed and under biaxial strain (tensile and compressive) is calculated using an efficient self-consistent method based on the six-band k⋅p perturbation theory. The hole mobility is then computed using the Kubo–Greenwood formalism accounting for nonpolar hole-phonon scattering (acoustic and optical), surface roughness scattering, polar phonon scattering (III-Vs only), alloy scattering (alloys only) and remote phonon scattering, accounting for multisubband dielectric screening. As expected, we find that Ge and III-V semiconductors exhibit a mobility significantly larger than the “universal” Si mobility. This is true for MOS systems with either SiO2 or high-κ insulators, although the latter ones are found to degrade the hole mobility compared to SiO2 due to scattering with interfacial optical phonons. In addition, III-Vs are more sensitive to the interfacial optical phonons than Ge due to the existence of the substrate polar phonons. Strain—especially biaxial tensile stress for Ge and biaxial compressive stress for III-Vs (except for GaAs)—is found to have a significant beneficial effect with both SiO2 and HfO2. Among strained p-channels, InSb exhibits the largest mobility enhancement. In0.7Ga0.3As also exhibits an increased hole mobility compared to Si, although the enhancement is not as large. Finally, our theoretical results are favorably compared with available experimental data for a relaxed Ge p-channel with a HfO2 insulator.
Microwave air plasma source at atmospheric pressure: Experiment and theory
Authors: Tatarova E. , Dias F. M. , Felizardo E. , Henriques J. , Pinheiro M. J. , Ferreira C. M. , Gordiets B.
Published: December 2010

An experimental and theoretical investigation of the axial structure of a surface wave (2.45 GHz) driven atmospheric plasma source in air with a small admixture (1%) of water vapor has been performed. Measurements of the gas temperature and of the intensities of the O(777.4 nm), O(844.6 nm), and O(630 nm) atomic lines and the NO(γ) molecular band versus input power and axial position were carried out. Amplitude and phase sensitive measurements have also been performed to derive the surface wave dispersion characteristics. The experimental results are analyzed in terms of a one-dimensional theoretical model based on a self-consistent treatment of particle kinetics, gas dynamics, and wave electrodynamics. The predicted gas temperature and emission line intensities variations with power and axial position are shown to compare well with experiment. “Hot” excited O atoms (with kinetic energy ∼2 eV) have been detected.
A systematic investigation into the conversion of β-Ga2O3 to GaN nanowires using NH3 and H2: Effects on the photoluminescence properties
Authors: Othonos Andreas , Zervos Matthew , Christofides Constantinos
Published: December 2010

GaN nanowires (NWs) with a hexagonal wurtzite crystal structure, diameters of 50 nm and lengths of 10 μm have been obtained from postgrowth nitridation of monoclinic β-Ga2O3 NWs using NH3 between 700–1090 °C. The conversion of β-Ga2O3 to GaN NWs has been investigated in a systematic way by varying the temperature, gas flows and nitridation times using Ar or N2:10% H2. We find that nitridation is most effective at temperatures ≥900 °C using NH3 with N2:10% H2 which promotes the efficient conversion of β-Ga2O3 to GaN, resulting into the enhancement of the band edge emission, suppression of the broad-band photoluminescence (PL) related to oxygen defects and the appearance of red emission due to deep-acceptorlike states. The gradual evolution of the PL spectra from that of β-Ga2O3 to GaN exhibited a clear, systematic dependence on the nitridation temperature and gas flows and the band to band emission lifetime which was found to be τ≈0.35 ns in all cases. In contrast the nitridation of β-Ga2O3 NWs using NH3 and Ar is less effective. Therefore, H2 is essential in removing O2 and also effective since it lead to the complete elimination of the β-Ga2O3 NWs at 1000 °C in the absence of NH3.
Improving Er3+ 1.53 μm luminescence by CeF3 nanocrystallization in aluminosilicate glass
Authors: Yu Yunlong , Shan Zhifa , Chen Daqin , Huang Ping , Lin Hang , Wang Yuansheng
Published: December 2010

In order to develop promising materials for the Er3+-doped fiber amplifier, transparent glass ceramics containing hexagonal CeF3 nanocrystals were prepared by melt-quenching and subsequent heating. The obvious Stark splitting in the absorption and emission spectra, the intensification of the 1.53 μm emission, and the prolongation of the Er3+:I413/2 decay lifetime demonstrated the partition of Er3+ ions into the CeF3 nanocrystals. Evidently, the efficient cross-relaxation between Ce3+ and Er3+, i.e., Er3+:I411/2+Ce3+:F25/2→Er3+:I413/2Ce3+:F27/2 led to the quenching of the upconversion and the enhancing of the desired Er3+ 1.53 μm emission. Based on the emission and absorption spectra, it was further calculated that the glass ceramic possesses broad bandwidth as that of the ZBLAN glass, and large emission cross-section close to the silicate glass, for the 1.53 μm emission.
Polarization control in ferroelectric PbTiO3 nanorods
Authors: Sæterli Ragnhild , Rørvik Per Martin , You Chang Chuan , Holmestad Randi , Tybell Thomas , Grande Tor , van Helvoort Antonius T. J. , Einarsrud Mari-Ann
Published: December 2010

In this work we demonstrate by transmission electron microscopy and piezoresponse force spectroscopy that the polarization direction in hydrothermally synthesized lead titanate (PbTiO3) nanorods can be changed from parallel to the nanorod axis to perpendicular to it by a simple heat treatment above the Curie temperature. The heat treatment also introduced 90° domains, caused a rearrangement of the surface and a reduction in the amounts of defects. The polarization of the heat-treated nanorods could be successively switched in the direction perpendicular to the nanorod axis. This control of the polarization in PbTiO3 nanorods opens up possibilities of tailoring the ferroelectric properties and is therefore highly relevant for the use of ferroelectric nanorods in devices.
Mathematical basis of scattering problems from penetrable obstacles and cracks
Authors: Yan Guozheng , Yao Mao
Published: December 2010

We consider a kind of scattering problem which models the scattering of an electromagnetic time-harmonic plane wave by an infinite cylinder having an open arc and a penetrable obstacle in $R^{2}$R2 as cross section. To this end, we solve a scattering problem for the Helmholtz equation in $R^2$R2 where the scattering object is a combination of a crack Γ and a penetrable obstacle D, and we have Dirichlet-Impedance type boundary condition on Γ and transmission boundary condition on ∂D. Applying potential theory, the problem can be reformulated as a boundary integral system. We establish the existence and uniqueness of a weak solution to the system by using the modified Fredholm theory.
Thermal treatment effects on N-alkyl perylene diimide thin-film transistors with different alkyl chain
Authors: Jeon Hyeon-Gu , Hattori Jinya , Kato Shimpei , Oguma Naomi , Hirata Naoki , Taniguchi Yoshio , Ichikawa Musubu
Published: December 2010

The authors report that thermal treatment effect on various N,N′-dialkyl-3,4,9,10-perylene tetracarbxylic diimides [PTCDI-Cn, alkyl–dodecyl (n=12), butadecyl (n=14), octadecyl (n=18)] thin-film transistors (TFTs) depends on the substituted alkyl chain length. It is clearly demonstrated that there are two kinds of molecular movements during the thermal treatment on PTCDI films; molecular rearrangement in the same layer and molecular migration from the lower layer to the upper layer. The former is directly related to the grain growth and can be controllable by applying an external electric field. The latter is also related not only to the grain growth but also to the formation of cracks between grains. These two movements show opposite dependence on the alkyl chain length during the thermal treatment; the former is more active in longer alkyl chain, but the latter in shorter one. However, they also have opposite effect to TFT performance, and PTCDI films with longer alkyl chains have great advantage on TFT performance for the thermal treatment. Consequently, PTCDI-C18 TFTs show the highest electron mobility as large as 1.2 cm2/V s after the thermal treatment at 140 °C.
Controlled generation of intrinsic localized modes in microelectromechanical cantilever arrays
Authors: Chen Qingfei , Lai Ying-Cheng , Dietz David
Published: December 2010

We propose a scheme to induce intrinsic localized modes (ILMs) at an arbitrary site in microelectromechanical cantilever arrays. The idea is to locate the particular cantilever beam in the array that one wishes to drive to an oscillating state with significantly higher amplitude than the average and then apply small adjustments to the electrical signal that drives the whole array system. Our scheme is thus a global closed-loop control strategy. We argue that the dynamical mechanism on which our global driving scheme relies is spatiotemporal chaos and we develop a detailed analysis based on the standard averaging method in nonlinear dynamics to understand the working of our control scheme. We also develop a Markov model to characterize the transient time required for inducing ILMs.
An invertible linearization map for the quartic oscillator
Authors: Anderson Robert L.
Published: December 2010

The set of world lines for the nonrelativistic quartic oscillator satisfying Newton's equation of motion for all space and time in 1-1 dimensions with no constraints other than the “spring” restoring force is shown to be equivalent (1-1-onto) to the corresponding set for the harmonic oscillator. This is established via an energy preserving invertible linearization map which consists of an explicit nonlinear algebraic deformation of coordinates and a nonlinear deformation of time coordinates involving a quadrature. In the context stated, the map also explicitly solves Newton's equation for the quartic oscillator for arbitrary initial data on the real line. This map is extended to all attractive potentials given by even powers of the space coordinate. It thus provides classes of new solutions to the initial value problem for all these potentials.
Weight modules with a finite dimensional weight space over truncated Virasoro algebras
Authors: Guo Xiangqian , Liu Xuewen
Published: December 2010

Truncated Virasoro algebras can be viewed as quotient algebras of the loop–Virasoro algebra. In this paper, we prove that any weight module M with a finite dimensional weight space over any truncated Virasoro algebra \documentclass[12pt]{minimal}\begin{document}${\cal L}(f)={\rm {Vir}}\otimes (\mathbb {C}[t^{\pm 1}]/f\mathbb {C}[t^{\pm 1}])$\end{document}L(f)= Vir ⊗(C[t±1]/fC[t±1]) has a Harish-Chandra submodule, where Vir is the Virasoro algebra and f is a nonzero and not invertible Laurent polynomial in \documentclass[12pt]{minimal}\begin{document}$\mathbb {C}[t^{\pm 1}]$\end{document}C[t±1]. More precisely, if M has a nontrivial upper bounded Vir-submodule, then it has a highest weight \documentclass[12pt]{minimal}\begin{document}${\cal L}(f)$\end{document}L(f)-submodule; if M has a nontrivial lower bounded Vir-submodule, then it has a lowest weight \documentclass[12pt]{minimal}\begin{document}${\cal L}(f)$\end{document}L(f)-submodule; if M is nontrivial over \documentclass[12pt]{minimal}\begin{document}${\cal L}(f)$\end{document}L(f) and does not contain any nontrivial upper bounded nor any nontrivial lower bounded Vir-submodules, then it has a nontrivial Harish-Chandra \documentclass[12pt]{minimal}\begin{document}${\cal L}(f)$\end{document}L(f)-submodule S such that \documentclass[12pt]{minimal}\begin{document}$\dim S_{\lambda }=1$\end{document}dimSλ=1 for all λ ∈ supp(S)∖{0}. As a corollary, any irreducible weight module with a finite dimensional weight space over \documentclass[12pt]{minimal}\begin{document}${\cal L}(f)$\end{document}L(f) is a Harish-Chandra module.
Waveguiding-assisted random lasing in epitaxial ZnO thin film
Authors: Dupont P.-H. , Couteau C. , Rogers D. J. , Hosseini Téhérani F. , Lérondel G.
Published: December 2010

Zinc oxide thin films were grown on c-sapphire substrates using pulsed laser deposition. Pump power dependence of surface emission spectra, acquired using a quadrupled 266 nm laser, revealed room temperature stimulated emission (threshold of 900 kW/cm2). Time dependent spectral analysis plus gain measurements of single-shot, side-emission spectra pumped with a nitrogen laser revealed random lasing indicative of the presence of self-forming laser cavities. It is suggested that random lasing in an epitaxial system rather than a three-dimensional configuration of disordered scattering elements was due to waveguiding in the film. Waveguiding causes light to be amplified within randomly formed closed-loops acting as lasing cavities.
Observation of efficient transfer from Mott–Wannier to Frenkel excitons in a hybrid semiconductor quantum dot/polymer composite at room temperature
Authors: Nizamoglu Sedat , Sun Xiao Wei , Demir Hilmi Volkan
Published: December 2010

Efficient conversion from Mott–Wannier to Frenkel excitons is observed at room temperature. The time-resolved photoluminescence shows that the energy transfer rate and efficiency reach 0.262 ns−1 and 80.9%, respectively. The energy transfer is enabled by strong dipole-dipole coupling in a hybrid inorganic/organic system of CdSe/ZnS core/shell heteronanocrystal and poly[2-methoxy-5-(3,7-dimethyl-octyloxy)-1,4-phenylenevinylene] homopolymer composite, and the measured energy transfer efficiencies are consistent with the analytical model.
Origin of the giant optical nonlinearity of Sb2Te3 phase change materials
Authors: Liu Jing , Liu Shuang , Wei Jingsong
Published: December 2010

We report the giant optical nonlinear absorption and refraction of Sb2Te3 phase change materials at low laser irradiation intensities. The nonlinear absorption and refraction coefficients reach up to −6.63×10−2 m/W and 2.606×10−9 m2/W, respectively. The first principles calculation indicates that the giant nonlinear absorption stems from the band filling effect of the photon induced free carriers under laser irradiation. The band-gap shrinking results in a positive thermo-optic coefficient, thus the giant nonlinear refraction. The numerical results are generally correlated with the experimental findings from z-scan and temperature-variable ellipsometric measurements.
Enhanced photorefractivity in a polymer/nanocrystal composite photorefractive device at telecommunication wavelength
Authors: Zhu Jing , Kim Won Jin , He Guang S. , Seo Jangwon , Yong Ken-Tye , Lee Dongho , Cartwright Alexander N. , Cui Yiping , Prasad Paras N.
Published: December 2010

Enhanced photorefractive (PR) response in nanocrystal-polymer nanocomposite PR devices at the telecommunication wavelength of 1.3 μm is achieved using facile surface treatment of PbS nanocrystals functionalized with thermally cleavable ligands. The cleavage of the ligands, by heat treatment, results in significant improvement in both photocharge generation and PR response, as demonstrated by photoconductivity and two-beam coupling (TBC) experiments, respectively. The TBC experiment shows that the optical gain coefficient is improved drastically (about 63%) at an applied electric field of 84 V/μm.
Electron spin dynamics in heavily Mn-doped (Ga,Mn)As
Authors: Zhu Yonggang , Han Lifen , Chen Lin , Zhang Xinhui , Zhao Jianhua
Published: December 2010

Electron spin relaxation and related mechanisms in heavily Mn-doped (Ga,Mn)As are studied by performing time-resolved magneto-optical Kerr effect measurements. At low temperature, s-d exchange scattering dominates electron spin relaxation, whereas the Bir–Aronov–Pikus mechanism and Mn impurity scattering play important roles at high temperature. The temperature-dependent spin relaxation time exhibits an anomaly around the Curie temperature (Tc) that implies that thermal fluctuation is suppressed by short-range correlated spin fluctuation above Tc.
The role of acceptance angle in measurements with ion energy analyzers: Study by numerical simulations
Authors: Miloch W. J. , Gulbrandsen N. , Mishra L. N. , Fredriksen Å.
Published: December 2010

The importance of an acceptance angle in the plasma diagnostics with ion energy analyzers is investigated by means of numerical simulations. It is shown that wide acceptance angles result in low energy tails in measured ion distribution functions (IDFx). For flowing plasmas or plasmas with beams, the orientation of the analyzer’s orifice gives different results due to bending of ion trajectories in the vicinity of the analyzer. It is demonstrated that the maximum in the IDFx is at energies lower than the plasma potential. Simulations are done with DIP3D, a three-dimensional particle-in-cell code.
Comparative study of field enhancement between isolated and coupled metal nanoparticles: An analytical approach
Authors: Sun G. , Khurgin J. B.
Published: December 2010

We present an analytical model that takes into account the coupling between the surface plasmon modes in complex metal nanostructures. We apply this model to evaluate the field enhancement in the gap of two coupled Au metal spheres embedded in GaN dielectric and compare the result with that obtained by the single sphere. The results show additional improvement can be obtained in the gap depending on the width of the gap. This approach offers a clear physical insight for the enhancement and a straightforward method for optimization.
Terahertz quantum cascade lasers based on type II InGaAs/GaAsSb/InP
Authors: Deutsch Christoph , Benz Alexander , Detz Hermann , Klang Pavel , Nobile Michele , Andrews Aaron Maxwell , Schrenk Werner , Kubis Tillmann , Vogl Peter , Strasser Gottfried , Unterrainer Karl
Published: December 2010

We report the demonstration of a terahertz quantum cascade laser based on the In0.53Ga0.47As/GaAs0.51Sb0.49 type II material system. The combination of low effective electron masses and a moderate conduction band offset makes this material system highly suitable for such devices. The active region is a three-well phonon depopulation design and laser ridges have been processed in a double-metal waveguide configuration. The devices exhibit a threshold current density of 2 kA/cm2, provide peak optical powers of 1.8 mW, and operate up to 102 K. Emission frequencies are in the range between 3.6 and 4.2 THz.
Thermal conductivity of GaAs nanowires studied by micro-Raman spectroscopy combined with laser heating
Authors: Soini Martin , Zardo Ilaria , Uccelli Emanuele , Funk Stefan , Koblmüller Gregor , Fontcuberta i Morral Anna , Abstreiter Gerhard
Published: December 2010

The thermal properties of freely suspended GaAs nanowires are investigated by applying a method which relies on laser heating and the determination of the local temperature by Raman spectroscopy. In order to determine the values for the thermal conductivity κ, the fraction of the laser power absorbed inside the GaAs nanowire is estimated by numerical simulations. The thermal conductivity of nanowires with homogeneous diameter is found to lie in the range of 8–36 W m−1 K−1. The change of the temperature profile in the presence of a tapering was investigated. Furthermore, we discuss the influence of laser heating in ambient conditions on the value of κ.
Single electron pumping through a quantum dot-embedded carbon nanotube using surface acoustic wave
Authors: Kim Bum-Kyu , Kim Ju-Jin , Seo Minky , Chung Yunchul , Woo Byung Chil , Kim Jinhee , Song Woon , Kim Nam
Published: December 2010

We have studied acoustoelectric current through a quantum dot-embedded carbon nanotube induced by a surface acoustic wave. The measurements were carried out on a same device but in two very different quantum dot charging energy Ec regimes (∼50 and ∼5 meV). The results showed dramatic differences in induced acoustoelectric current depending on Ec. The induced acoustoelectric current showed a polarity reversal around the Coulomb blockade peak when Ec is small (5 meV). For a large Ec (50 meV), however, a current plateau was observed as a function of surface acoustic wave powers as well as gate voltages.
A two-terminal silicon nanoribbon field-effect pH sensor
Authors: Chen Si , Jokilaakso Nima , Björk Per , Karlström Amelie Eriksson , Zhang Shi-Li
Published: December 2010

This paper reports on a two-terminal silicon nanoribbon (SiNR) field-effect pH sensor operated in electrolyte. Observed experimentally and confirmed by modeling, the sensor is activated by self-gating with a gate bias set by the potential difference of the two terminals. The effect of this gate bias on the SiNR conductance is modulated by the potential drop over the electrical double layer (EDL) established on the SiNR surface, similarly to the threshold voltage modulation by EDL in a three-terminal SiNR field-effect transistor with an independent gate electrode. The potential drop over EDL is determined by the pH value of the electrolyte.
Dislocation movement in GaN films
Authors: Moram M. A. , Sadler T. C. , Häberlen M. , Kappers M. J. , Humphreys C. J.
Published: December 2010

We demonstrate that significant dislocation movement occurs below the surface of heteroepitaxial c-plane GaN films during their growth by metalorganic vapor phase epitaxy. Dislocations move primarily by vacancy-assisted climb, which appears to be driven by the high in-plane biaxial stresses present during growth. Annealing low dislocation density (4.3×108 cm−2) GaN films promotes dislocation climb and thus reduces both dislocation densities and in-plane stresses (at high temperatures), independent of epilayer growth conditions.
Surface roughness scattering in two dimensional electron gas channel
Authors: Liu B. , Lu Y. W. , Jin G. R. , Zhao Y. , Wang X. L. , Zhu Q. S. , Wang Z. G.
Published: December 2010

The mobility of AlxGa1−xN/GaN heterostructure two dimensional electron gas channel limited by surface roughness scattering was calculated considering the strong spontaneous and piezoelectric polarizations in III-group nitride heterostructure. The electronic mobility on the order of 104–105 cm2 V−1 s−1 was estimated. We found that the mobility limited by surface roughness scattering is very sensitive to barrier layer thickness fluctuation.
Structural inhomogeneity and anelastic deformation in metallic glasses revealed by spherical nanoindentation
Authors: Yang Y. , Zeng J. F. , Ye J. C. , Lu J.
Published: December 2010

In this letter, the anelastic deformation of a Zr-based metallic glass (MG) at ambient temperature is revealed through spherical nanoindentation. A general rheological model, which is linked with the atomic structure of MGs, is proposed to explain the observed anelasticity. The experimental and theoretical results clearly indicate the existence of structural inhomogeneity intrinsic to MGs, which causes the anelastic deformation upon mechanical loading under high loading rates before shear banding. The outcome of the current research provides an important insight into the property-structure relation of MGs.
Anticrosstalk characteristics correlated with the set process for α-Fe2O3/Nb–SrTiO3 stack-based resistive switching device
Authors: Chen Y. S. , Chen B. , Gao B. , Zhang F. F. , Qiu Y. J. , Lian G. J. , Liu L. F. , Liu X. Y. , Han R. Q. , Kang J. F.
Published: December 2010

A resistive switching device based on the stacked α-Fe2O3/Nb–SrTiO3 is proposed and fabricated that demonstrates excellent bipolar resistive switching behaviors including the uniformity, endurance, and retention performance. The Schottky-like current-voltage characteristics correlated with set process were observed in both high resistive states (HRSs) and low resistive states (LRSs) of the device. Importantly, the anticrosstalk characteristic, possessing higher reversed-biased LRS resistance than the forwarded-biased HRS resistance, indicates the potential applications of the stacked α-Fe2O3/Nb–SrTiO3 for multilevel storage in the cross-bar memory arrays. The carrier injection and trapping mechanism is suggested to explain the observed phenomena.