bluuebunny/crossref_metadata_2025 huggingface dataset:
Phonon effect on single-electron transport in two-dot semiconductor devices
Authors: Valentin Audrey , Galdin-Retailleau Sylvie , Dollfus Philippe
Published: August 2009

We have studied the single-electron transport in silicon nanocrystal (NC)-based structures using Monte Carlo simulation including the coupling between two dots. This coupling has been modeled by taking the collisional broadening of energy levels in the dots into account through the spectral function associated with the electron-phonon interaction. The first stage of the calculation is the determination of the phonon spectra in the dots using the adiabatic bond charge model adapted to the case of silicon NCs. A self-consistent Schrödinger–Poisson solver is then used to calculate the electronic structure of the NCs according to the applied bias. The tunneling rates between broadened levels are calculated within the perturbation theory from a tunneling Hamiltonian and introduced in a Monte Carlo algorithm to treat the sequential transport of electrons. We have studied structures consisting of two Si NCs embedded in silicon oxide and two metallic contacts for different parameters as the temperature and the barrier widths. The resulting I-V characteristics exhibit a sharp peak with lateral lobes due to phonon-assisted tunneling. These lobes are strongly influenced by the vibrational surface states.
Chaotic behavior in a charged three-body self-gravitating system
Authors: Koop M. J. , Mann R. B. , Rohanizadegan M.
Published: August 2009

We investigate the equal-mass three-body charged system in general relativistic lineal gravity. The electric properties of the charged particles along with the gravitational self-attraction of the bodies introduce features that do not have a nonrelativistic counterpart. We derive a canonical expression for the Hamiltonian of the system and discuss the numerical solution of the resulting equations of motion. We consider various combinations of charges and find that the structure of the phase space yields a rich variety of interesting dynamics that can be divided into three distinct regions: annulus, pretzel, and chaotic; the first two are regions of quasiperiodicity while the latter is a region of chaos. When the charge configuration is repulsive the amount of chaos is enhanced relative to that of the neutral case (leading to Kolmogorov–Arnold–Moser breakdown), whereas the chaos is only enhanced throughout a band between the annulus and pretzel regions with a significant development of pretzel areas for attractive configurations when two charges have opposite signs. We find a new class of chaotic orbits that are of hourglass shape in the hexagonal representation of the three-body motion.
Tailoring UV cure depth profiles for optimal mechanical properties of organosilicate thin films
Authors: Kim Taek-Soo , Chumakov Dmytro , Zschech Ehrenfried , Dauskardt Reinhold H.
Published: August 2009

The adhesive and cohesive properties of organosilicate thin films are remarkably insensitive to UV curing. We demonstrate how to maximize these properties with UV standing waves together with an optical spacer underlying layer. Using a simulation of the UV cure profile through the film thickness, we demonstrate how a UV transparent SiN optical spacer layer can be selected to maximize curing at both sides of the organosilicate film with marked increases in interfacial fracture energy. On the contrary, a UV absorbing SiCN underlying layer resulted in significantly reduced UV intensities and small improvements of the interfacial fracture energies.
Two-photon absorption laser-induced fluorescence of atomic oxygen in the afterglow of pulsed positive corona discharge
Authors: Ono Ryo , Takezawa Kei , Oda Tetsuji
Published: August 2009

Atomic oxygen is measured in the afterglow of pulsed positive corona discharge using time-resolved two-photon absorption laser-induced fluorescence. The discharge occurs in a 14 mm point-to-plane gap in dry air. After the discharge pulse, the atomic oxygen density decreases at a rate of 5×104 s−1. Simultaneously, ozone density increases at almost the same rate, where the ozone density is measured using laser absorption method. This agreement between the increasing rate of atomic oxygen and decreasing rate of ozone proves that ozone is mainly produced by the well-known three-body reaction, O+O2+M→O3+M. No other process for ozone production such as O2(v)+O2→O3+O is observed. The spatial distribution of atomic oxygen density is in agreement with that of the secondary streamer luminous intensity. This agreement indicates that atomic oxygen is mainly produced in the secondary streamer channels, not in the primary streamer channels.
Global existence of solutions of Cauchy problem for generalized system of nonlinear evolution equations arising from DNA
Authors: Chen Guowang , Guo Hongxia , Zhang Hongwei
Published: August 2009

In this paper, we prove that the Cauchy problem for the generalized system of the nonlinear evolution equations arising from DNA utt−σuxx−uxxtt=f(v)xx, vtt−vxxtt=g(v)xx has a unique global generalized solutions in C2([0,∞);Hs×Hs), a unique global classical solution, and the sufficient conditions of blow up of solution in finite time are given. We also prove that the Cauchy problem has a unique global generalized solution in C2([0,∞);Wm,p∩L∞×Wm,p∩L∞) and a unique global classical solution.
Comparison of scrape-off layer turbulence in Alcator C-Mod with three dimensional gyrofluid computations
Authors: Zweben S. J. , Scott B. D. , Terry J. L. , LaBombard B. , Hughes J. W. , Stotler D. P.
Published: August 2009

This paper describes quantitative comparisons between turbulence measured in the scrape-off layer (SOL) of Alcator C-Mod [S. Scott, A. Bader, M. Bakhtiari et al., Nucl. Fusion 47, S598 (2007)] and three dimensional computations using electromagnetic gyrofluid equations in a two-dimensional tokamak geometry. These comparisons were made for the outer midplane SOL for a set of inner-wall limited, near-circular Ohmic plasmas. The B field and plasma density were varied to assess gyroradius and collisionality scaling. The poloidal and radial correlation lengths in the experiment and computation agreed to within a factor of 2 and did not vary significantly with either B or density. The radial and poloidal propagation speeds and the frequency spectra and poloidal k-spectra also agreed fairly well. However, the autocorrelation times and relative Da fluctuation levels were higher in the experiment by more than a factor of 2. Possible causes for these disagreements are discussed.
Experimental demonstration of high quality MeV ultrafast electron diffraction
Authors: Li Renkai , Tang Chuanxiang , Du Yingchao , Huang Wenhui , Du Qiang , Shi Jiaru , Yan Lixin , Wang Xijie
Published: August 2009

The simulation optimization and an experimental demonstration of improved performances of mega-electron-volt ultrafast electron diffraction (MeV UED) are reported in this paper. Using ultrashort high quality electron pulses from an S-band photocathode rf gun and a polycrystalline aluminum foil as the sample, we experimentally demonstrated an improved spatial resolution of MeV UED, in which the Debye–Scherrer rings of the (111) and (200) planes were clearly resolved. This result showed that MeV UED is capable to achieve an atomic level spatial resolution and a ∼100 fs temporal resolution simultaneously, and will be a unique tool for ultrafast structural dynamics studies.
Magnetohydrodynamic stability at a separatrix. II. Determination by new conformal map technique
Authors: Webster A. J.
Published: August 2009

It was shown in the first part to this paper how a simple magnetohydrodynamic model can be used to determine the stability of a tokamak plasma’s edge to peeling (external kink) modes. It was found that stability is determined by the value of Δ′, a normalized measure of the discontinuity in the radial derivative of the radial perturbation to the magnetic field at the plasma-vacuum interface. To avoid the possibility that numerical divergences near the X-point might lead to misleading conclusions about plasma stability, this paper calculates the value of Δ′ analytically. This is accomplished by showing that the method of conformal transformations can be applied to systems with a continuously varying nonzero boundary condition and using the technique to obtain analytical expressions for both the vacuum energy and Δ′. A conformal transformation is also used to obtain an equilibrium vacuum field surrounding a plasma with a separatrix and X-point. This allows the analytical expressions for the vacuum energy and Δ′ to be evaluated. The results here, combined with those in the first part of this paper, subsequently provide a quantitative description of the peeling mode’s growth rate as the plasma-vacuum boundary more closely approximates a separatrix with an X-point.
Temperature dependence of the Raman spectra of liquid parahydrogen
Authors: Sliter Russell , Vilesov Andrey F.
Published: August 2009

Vibrational and rotational spectra of liquid para-H2 at temperature T=14–26 K and of solid at T=6–13 K have been obtained using coherent anti-Stokes Raman scattering technique. The vibrational frequency in the liquid increases with temperature by about 2 cm−1 and the shift scales with the square of the sample’s density. An extrapolation of the vibrational frequency in the metastable para-H2 liquid below the freezing point is discussed. The results indicate that the vibron hopping between the molecules is active in the liquid, similar to that previously found in the solid.
Visible to near infrared conversion in Ce3+–Yb3+ Co-doped YAG ceramics
Authors: Ueda Jumpei , Tanabe Setsuhisa
Published: August 2009

In Ce3+–Yb3+ co-doped Y3Al5O12 (YAG) ceramics, possibility of quantum cutting mechanism converting one visible photon into two NIR photons with optimum quantum efficiency approaching 200% have been investigated. In this material, Yb3+ emissions due to the F25/2-F27/2 in the range of 1 μm were observed upon the excitation of 5d level of Ce3+. In addition, excitation spectra of Yb3+ emission corresponded to that of Ce3+ emission completely. Lifetime of the 5d level of Ce3+ decreased with increasing Yb3+ content. These results indicate the energy transfer (ET) from the 5d levels of Ce3+ to the F55/2 level of Yb3+. In (Y0.945Ce0.005Yb0.05) A3l5O12 sample, the directly measured quantum yield (QY) of Yb3+ emission upon the excitation of 5d level of Ce3+ was about 12% and lower than QY (96%) that estimated from the ET efficiency which was calculated with the measured lifetime of Ce3+.
Effects of tube diameter and chirality on the stability of single-walled carbon nanotubes under ion irradiation
Authors: Xu Zijian , Zhang Wei , Zhu Zhiyuan , Ren Cuilan , Li Yong , Huai Ping
Published: August 2009

Using molecular dynamics method, we investigated the influence of tube diameter and chirality on the stability of single-walled carbon nanotubes (CNTs) under ion irradiation. We found that in the energy range below 1 keV, the dependence of CNT stability on the tube diameter is no longer monotonic under C ion irradiation, and the thinner (5, 5) CNT may be more stable than the thicker (7, 7) CNT, while under Ar irradiation, the CNT stability increases still monotonically with the CNT diameter. This stability behavior was further verified by the calculations of the threshold ion energies to produce displacement damage in CNTs. The abnormal stability of thin CNTs is related to their resistance to the instantaneous deformation in the wall induced by ion pushing, the high self-healing capacity, as well as the different interaction properties of C and Ar ions with CNT atoms. We also found that under ion irradiation the stability of a zigzag CNT is better than that of an armchair CNT with the same diameter. This is because of the bonding structure difference between the armchair and the zigzag CNTs with respect to the orientations of graphitic networks as well as the self-healing capacity difference.
Fitting transmission and Faraday rotation spectra of [Bi3Fe5O12/Sm3Ga5O12]m magneto-optical photonic crystals
Authors: Dzibrou D. O. , Grishin A. M.
Published: August 2009

A consistent microscopic approach is developed to simulate the transmittance and Faraday rotation in all-garnet heteroepitaxial magneto-optical photonic crystals (MOPCs). To compare the experimental and simulation results, [Bi3Fe5O12/Sm3Ga5O12]m (BIG/SGG) MOPC designed to operate at a telecommunication wavelength λres=980 nm was chosen. It was composed of [BIG/SGG]5 and [SGG/BIG]5 distributed Bragg reflectors with a microcavity layer of BIG in between. The dispersion relations of the diagonal and off-diagonal elements of the permittivity tensor ε̂ for BIG in the electric dipole approximation were obtained from the simulation of the transmittance and Faraday rotation for a reference single layer BIG film. Revealed dispersion relations were then combined with the 4×4 matrix formalism for magnetic superlattices to compute transmission and Faraday rotation spectra of the MOPC. The results of numerical simulations were found to be in good agreement with the experimental ones.
A plasmonic “ac Wheatstone bridge” circuit for high-sensitivity phase measurement and single-molecule detection
Authors: Davis T. J. , Vernon K. C. , Gómez D. E.
Published: August 2009

In this paper, a plasmonic “ac Wheatstone bridge” circuit is proposed and theoretically modeled for the first time. The bridge circuit consists of three metallic nanoparticles, shaped as rectangular prisms, with two nanoparticles acting as parallel arms of a resonant circuit and the third bridging nanoparticle acting as an optical antenna providing an output signal. Polarized light excites localized surface plasmon resonances in the two arms of the circuit, which generate an optical signal dependent on the phase-sensitive excitations of surface plasmons in the antenna. The circuit is analyzed using a plasmonic coupling theory and numerical simulations. The analyses show that the plasmonic circuit is sensitive to phase shifts between the arms of the bridge and has the potential to detect the presence of single molecules.
Electromagnetic wave propagation through an overdense magnetized collisional plasma layer
Authors: Thoma C. , Rose D. V. , Miller C. L. , Clark R. E. , Hughes T. P.
Published: August 2009

The results of investigations into the feasibility of using a magnetic window to propagate electromagnetic waves through a finite-sized overdense plasma slab are described. We theoretically calculate the transmission coefficients for right- and left-handed circularly polarized plane waves through a uniform magnetized plasma slab. Using reasonable estimates for the plasma properties expected to be found in the ionized shock layer surrounding a hypersonic aircraft traveling in the earth’s upper atmosphere (radio blackout conditions), and assuming a 1 GHz carrier frequency for the radio communications channel, we find that the required magnetic field for propagation of right-handed circularly polarized, or whistler, waves is on the order of a few hundred gauss. Transmission coefficients are calculated as a function of sheath thickness and are shown to be quite sensitive to the electron collision frequency. One-dimensional particle-in-cell simulations are shown to be in good agreement with the theory. These simulations also demonstrate that Ohmic heating of the electrons can be considerable. Two- and three-dimensional particle-in-cell simulations using a simplified waveguide and antenna model illustrate the same general transmission behavior as the theory and one-dimensional simulations. In addition, a net focusing effect due to the plasma is also observed in two and three dimensions. These simulations can be extended to design and analyze more realistic waveguide and antenna models.
Rate coefficient of CN formation through radiative association: A theoretical study of quantum effects
Authors: Antipov Sergey V. , Sjölander Tobias , Nyman Gunnar , Gustafsson Magnus
Published: August 2009

Radiative association of CN is simulated using a quantum dynamical as well as a semiclassical approach. A comparison of the resulting energy-resolved cross sections reveals striking quantum effects that are due to shape resonances. These, in turn, arise because of states that are quasibound by the centrifugal barrier. The quantal rate coefficient for temperatures from 40 to 1900 K has been computed using the Breit–Wigner theory to account for the resonances. Comparison with the results obtained by Singh and Andreazza [Astrophys. J. 537, 261 (2000)] shows that the semiclassical method, which completely omits the shape resonances, is accurate to within 25% above room temperature. At lower temperatures the contribution from the shape resonances to the radiative association rate is more significant.
Relationship between the cathodoluminescence emission and resistivity in In doped CdZnTe crystals
Authors: Rodríguez-Fernández J. , Carcelén V. , Hidalgo P. , Vijayan N. , Piqueras J. , Sochinskii N. V. , Perez J. M. , Diéguez E.
Published: August 2009

Cadmium zinc telluride, CdZnTe, bulk single crystals doped with 1019 at./cm3 of indium in the initial melt were grown by vertical Bridgman technique. The samples were investigated by energy dispersive spectroscopy, cathodoluminiscence (CL), and current-voltage behavior at room temperature. The results shows that Cd and Te vacancy concentration depend on the indium and zinc concentrations. CL measurements indicate a relationship between radiative centers associated to Cd and Te vacancies and resistivity values.
Ion-induced secondary electron emission from K–Cs–Sb, Na–K–Sb, and Cs–Sb photocathodes and its relevance to the operation of gaseous avalanche photomultipliers
Authors: Lyashenko A. , Breskin A. , Chechik R. , Dias T. H. V. T.
Published: August 2009

The operation of visible-sensitive gaseous and to some extent, vacuum-photomultipliers is critically affected by secondary electrons originating from ion impact on the photocathode. A simple method for indirect measurement of the effective ion-induced secondary-electron emission (IISEE) coefficient from the photocathode into a gas medium γ+eff was developed. The experimental results with visible-sensitive K–Cs–Sb, Na–K–Sb, and Cs–Sb photocathodes, yielded γ+eff-values between 0.02 and 0.03 in Ar/CH4(95/5) at 700 mbar; these are in good agreement with theoretical calculations. The corresponding vacuum IISEE coefficients γ+ were estimated, based on a theoretical model, to be 0.47, 0.49, and 0.47 for K–Cs–Sb, Na–K–Sb, and Cs–Sb photocathodes, respectively. The ratio of gas γ+eff and vacuum γ+ IISEE coefficients, calculated to be ∼0.06, is the fraction of secondary electrons surmounted the backscattering in the gas media.
Collinear interferometer with variable delay for carrier-envelope offset frequency measurement
Authors: Pawłowska Monika , Ozimek Filip , Fita Piotr , Radzewicz Czesław
Published: August 2009

We demonstrate a novel scheme for measuring the carrier-envelope offset frequency in a femtosecond optical frequency comb. Our method is based on a common-path interferometer with a calcite Babinet–Soleil compensator employed to control the delay between the two interfering beams of pulses. The large delay range (up to 8 ps) of our device is sufficient for systems that rely on spectral broadening in microstructured fibers. We show an experimental proof that the stability of a common-path arrangement is superior to that of the standard interferometers.
Nonlocal elastic beam models for flexural wave propagation in double-walled carbon nanotubes
Authors: Hu Yan-Gao , Liew K. M. , Wang Q.
Published: August 2009

Flexural wave in a double-walled carbon nanotube is studied. The scale effect of the carbon nanotube on the wave dispersion is investigated through the nonlocal elastic beam theories. The flexural wave dispersion predicted by the nonlocal elastic Timoshenko beam theory has a good agreement with that by molecular dynamics simulations in a wide frequency range up to the terahertz region. The results show that only the nonlocal elastic Timoshenko beam model can predict the small-scale effect on the dispersion of flexural wave in double-walled carbon nanotube when the wave number is large. Moreover, an estimation of the scale coefficient e0 for the nonlocal elastic double Timoshenko beam model is suggested by validations from the molecular dynamics simulations. The noncoaxial flexural vibration of the double-walled carbon nanotube can be observed from molecular dynamics simulations at high frequency range. The van der Waals interaction is found to have little effect on the noncoaxial flexural vibration of the carbon nanotube, and the nonlocal elastic Timoshenko beam theory is found to be inapplicable in modeling the noncoaxial wave propagation in carbon nanotubes.
Nested Markov chain Monte Carlo sampling of a density functional theory potential: Equilibrium thermodynamics of dense fluid nitrogen
Authors: Coe Joshua D. , Sewell Thomas D. , Shaw M. Sam
Published: August 2009

An optimized variant of the nested Markov chain Monte Carlo [n(MC)2] method [J. Chem. Phys. 130, 164104 (2009)] is applied to fluid N2. In this implementation of n(MC)2, isothermal-isobaric (NPT) ensemble sampling on the basis of a pair potential (the “reference” system) is used to enhance the efficiency of sampling based on Perdew–Burke–Ernzerhof density functional theory with a 6-31G* basis set (PBE∕6-31G*, the “full” system). A long sequence of Monte Carlo steps taken in the reference system is converted into a trial step taken in the full system; for a good choice of reference potential, these trial steps have a high probability of acceptance. Using decorrelated samples drawn from the reference distribution, the pressure and temperature of the full system are varied such that its distribution overlaps maximally with that of the reference system. Optimized pressures and temperatures then serve as input parameters for n(MC)2 sampling of dense fluid N2 over a wide range of thermodynamic conditions. The simulation results are combined to construct the Hugoniot of nitrogen fluid, yielding predictions in excellent agreement with experiment.
Detection and imaging in a random medium: A matrix method to overcome multiple scattering and aberration
Authors: Aubry Alexandre , Derode Arnaud
Published: August 2009

We present an imaging technique particularly suited to the detection of a target embedded in a strongly scattering medium. Classical imaging techniques based on the Born approximation fail in this kind of configuration because of multiply scattered echoes and aberration distortions. The experimental setup we consider uses an array of programmable transmitters/receivers. A target is placed behind a scattering medium. The impulse responses between all array elements are measured and form a matrix. The core of the method is to separate the single scattered echo of the target from the multiple scattering background. This is possible because of a deterministic coherence along the antidiagonals of the array response matrix, which is typical of single scattering. Once this operation is performed, target detection is achieved by applying the DORT method (French acronym for decomposition of the time reversal operator). Experimental results are presented in the case of wide-band ultrasonic waves around 3 MHz. A 125-element array is placed in front of a collection of randomly distributed steel rods (diameter of 0.8 mm). The slab thickness is three times the scattering mean free path. The target is a larger steel cylinder (diameter of 15 mm) that we try to detect and localize. The quality of detection is assessed theoretically based on random matrix theory and is shown to be significantly better than what is obtained with classical imaging methods. Aside from multiple scattering, the technique is also shown to reduce the aberrations induced by a heterogeneous layer.
A simple ac bridge for detecting small resistance change
Authors: Song Xiaohui , Jin Yirong , Zhang Xin , Yu Yude , Zhang Dian-lin
Published: August 2009

A simple ac resistance bridge is proposed. The stability of the design is better than 10−6, which is especially suitable for detecting tiny changes of resistance. An example of magnetoresistance measurement for a 220 nm Au film shows the good performance of the bridge.
On supremum of bounded quantum observable
Authors: Weihua Liu , Junde Wu
Published: August 2009

In this paper, we present a new, necessary, and sufficient condition for which the supremum A∨B exists with respect to the logic order ≼. Moreover, we give out a new and much simpler representation of A∨B with respect to ≼. Our results have nice physical meanings.
Highly accurate CCSD(R12) and CCSD(F12) optical response properties using standard triple-ζ basis sets
Authors: Yang Jun , Hättig Christof
Published: August 2009

Coupled-cluster response theory for frequency-dependent optical properties within the coupled-cluster singles-and-doubles model (CCSD) has been derived and implemented for ansatz 2 of the explicitly correlated CCSD(R12) and CCSD(F12) methods as part of the program package DALTON. The basis set convergence of static dipole moments, polarizabilities, and parallel averages of first and second hyperpolarizabilities has been investigated for Ne, BH, N2, CO, and BF. The frequency-dependent results are presented for the electronic second-harmonic generation of N2. With triple-ζ basis sets, the CCSD(F12) correlation contributions using ansatz 2 are close to the basis set limits for dipole moments and second hyperpolarizabilities; the CCSD(R12) results are better than the CCSD results obtained with at least quintuple-ζ basis sets for polarizabilities and first hyperpolarizabilities. The exponent of Slater-type correlation factor for CCSD(F12) ground state energy may not be optimal and has to be re-examined for response properties. We also suggest that the remaining one-electron basis set errors arising within the coupled-cluster singles should be reduced by allowing excitations into the auxiliary orbital space.
The calculation of chemical potential of organic solutes in dense liquid phases by using expanded ensemble Monte Carlo simulations
Authors: Chang Jaeeon
Published: August 2009

In this work, the chemical potentials of organic compounds in dense liquid phases are calculated by using expanded ensemble Monte Carlo simulations. To make insertion of a solute molecule efficiently, Lennard-Jones size parameters and bond lengths are varied with coupling parameter. A robust adaptive scheme is proposed in order to determine biasing weights during the simulation, which enhances the efficiency and applicability of the expanded ensemble method. Using the proposed simulation technique, chemical potentials of organic molecules in dense liquid phases are obtained from a single run of simulation. The excess chemical potentials of several hydrocarbon molecules including n-alkanes, benzene, toluene, and ethanol in aqueous phases at infinite dilution as well as in their pure liquid phases are calculated at 298 K and 1 atm, and simulation results are compared with experimental data.
Electrical conductance of single C60 and benzene molecules bridging between Pt electrode
Authors: Kiguchi Manabu
Published: August 2009

The electrical conductance of single C60 and benzene molecules bridging between Pt electrodes was investigated at room temperature in ultrahigh vacuum. The conductance of the Pt/C60/Pt junction was 0.7 G0(2e2/h), which was close to that of the metal atomic contact. The single C60 molecular junction showed a high and fixed conductance value, by the direct binding of the C60 to the Pt electrodes without using anchoring group. The conductance of the Pt/C60/Pt junction decreased and its stability increased with the amount of deposited C60 molecule, which could be explained by the C60 adsorption on the stem part of the electrode. In contrast with the Pt/C60/Pt junction, the Pt/benzene/Pt junction did not show a fixed conductance value, reflecting the planar molecular shape.
Effects of material gradient on transverse surface waves in piezoelectric coupled solid media
Authors: Qian Zheng-Hua , Jin Feng , Hirose Sohichi , Lu Tian-Jian
Published: August 2009

An analytical study on transverse surface waves propagating in a functionally graded material carrying a piezoelectric layer is carried out by Wentzel–Kramers–Brillouin technique. Dispersion relations for the existence of the waves are obtained for material gradient of arbitrary functions and the effects of material gradient on wave propagation are quantified. Numerical examples show the presence of material gradient significantly affects long waves but has only negligible effects on short waves. Depending on whether the surface wave velocity is smaller or greater than the bulk-shear-wave velocity in the piezoelectric layer, two different types of dispersion behavior are discussed.
Plasmonic light enhancement in the near-field of metallic nanospheroids for application in intermediate band solar cells
Authors: Mendes Manuel J. , Luque Antonío , Tobías Ignacio , Martí Antonio
Published: August 2009

In order to enhance infrared light absorption in sub-bandgap transitions in an intermediate band solar cell, the scattered near-field potential from uncoated and coated metallic nanoparticles with a spheroidal shape is calculated with the electrostatic model. The absorption enhancement produced at the surface plasmon frequency of the nanoparticles can be of several orders of magnitude in some cases.
Monte Carlo study of melting in a finite two-dimensional dusty plasma
Authors: Sheridan T. E.
Published: August 2009

Melting in a finite two-dimensional dusty plasma has recently been characterized experimentally [T. E. Sheridan, Phys. Plasmas 15, 103702 (2008)] in a system with ≈3900 dust particles. We model this experiment using the Metropolis algorithm to generate thermodynamic configurations for a two-dimensional system of identical particles confined in a parabolic well and interacting through a Debye (Yukawa) potential. Results are computed for a Debye shielding parameter a/λD=0.24, where a is the lattice constant and λD is the Debye length. Configurations are characterized using the pair and bond-orientational correlation functions, defect fractions, and correlation lengths. Distinct crystalline, hexatic, and liquid phases are observed. In the hexatic phase, the decay of the bond-orientational correlation goes as r−η6 where η6≈1, which is greater than the value η6=0.25 predicted by the theory of Kosterlitz, Thouless, Halperin, Nelson, and Young.
Millimeter wave detection of nuclear radiation: An alternative detection mechanism
Authors: Gopalsami N. , Chien H. T. , Heifetz A. , Koehl E. R. , Raptis A. C.
Published: August 2009

We present a nuclear radiation detection mechanism using millimeter waves as an alternative to conventional detection. It is based on the concept that nuclear radiation causes ionization of air and that if we place a dielectric material near the radiation source, it acts as a charge accumulator of the air ions. We have found that millimeter waves can interrogate the charge cloud on the dielectric material remotely. This concept was tested with a standoff millimeter wave system by monitoring the charge levels on a cardboard tube placed in an x-ray beam.
Room temperature ferromagnetism of ZnO nanocrystals in amorphous ZnO–Al2O3 matrix
Authors: Ma Y. W. , Ding J. , Qi D. C. , Yi J. B. , Fan H. M. , Gong H. , Wee A. T. S. , Rusydi A.
Published: August 2009

In this work, we demonstrate room temperature ferromagnetism of ZnO nanocrystals (NCs) embedded in alumina-based amorphous matrix. Our study has shown that solid solution occurred for lower Al concentration [≤x=0.09 for (Zn1−x,Alx)O]. No ferromagnetism appears in Al-doped ZnO with x≤0.09. With higher Al concentration, alumina-based amorphous structure appeared and fully amorphous was found in the composition of (Zn0.30,Al0.70)O. Ferromagnetism was found in (Zn1−x,Alx)O with a threshold of 16 mol % of Al. The room temperature ferromagnetism was found to be attributed to ZnO NCs in an alumina-based amorphous ZnO–Al2O3 matrix. Ferromagnetism reached a maximum with a volume percentage of ZnO NCs to be ∼27 vol %. The detailed investigations (transmission electron microscopy, x-ray photoelectron spectroscopy, and superconducting quantum interference device) show that the optimized size of these NCs is in the range of 4–5 nm. No ferromagnetism appears if the sample contains a fully amorphous structure.
Abnormal frequency dependence of ac susceptibility in melt texture Gd–Ba–Cu–O single domain
Authors: Xu Ke-Xi , Wu Xing-Da , Pan Peng-Jun
Published: August 2009

In this paper, the pinning property of the melt texture Gd–Ba–Cu–O single domain has been examined by ac susceptibility measurements. An unexpected frequency dependence behavior of the irreversibility line Birr(T) has been found, in which the power n for Birr(T)∝(1−t)n is affected by frequencies of the ac fields, no longer kept as a constant as in the Yeshurun and Malozemoff theory. We present the abnormal frequency dependent behavior and interpret it in framework of the flux diffusion model.
Photopatternable ultrathin gate dielectrics for low-voltage-operating organic circuits
Authors: Jang Jaeyoung , Kim Se Hyun , Hwang Jihun , Nam Sooji , Yang Chanwoo , Chung Dae Sung , Park Chan Eon
Published: August 2009

We report here a photopatternable ultrathin gate dielectric for the fabrication of low-voltage-operating organic field-effect transistors (OFETs) and inverters. The gate dielectric material is composed of a photocrosslinkable polymer, poly(vinyl cinnamate), and a thermally crosslinkable silane crosslinking reagent, 1,6-bis(trichlorosilyl)hexane. The spin-coated dielectric is photocured with ultraviolet light, which enables fine film patterning via regular photolithography. After thermal curing (at 110 °C), the dielectric showed excellent insulating properties (a leakage current density of ≈10−7 A/cm2 at 2.0 MV/cm) for an ultrathin film thickness of 70 nm, thus reducing the operating voltage of the OFETs and inverters to −5 V.
Demonstration of nonpolar a-plane InGaN/GaN light emitting diode on r-plane sapphire substrate
Authors: Hwang Sung-Min , Seo Yong Gon , Baik Kwang Hyeon , Cho In-Sung , Baek Jong Hyeob , Jung Sukkoo , Kim Tae Geun , Cho Meoungwhan
Published: August 2009

High crystalline a-plane (112¯0) GaN epitaxial layers with smooth surface morphology were grown on r-plane (11¯02) sapphire substrate by metalorganic chemical vapor deposition. The full width at half maximum of x-ray rocking curve was measured as 407 arc sec along c-axis direction, and the root mean square roughness was 1.23 nm. Nonpolar a-plane InGaN/GaN light emitting diodes were subsequently grown on a-plane GaN template, and the optical output power of 0.72 mW was obtained at drive current of 20 mA (3.36 V) and 2.84 mW at 100 mA (4.62 V) with the peak emission wavelength of 477 nm.
Experimental verification of extraordinary transmission without surface plasmons
Authors: Medina F. , Ruiz-Cruz J. A. , Mesa F. , Rebollar J. M. , Montejo-Garai J. R. , Marqués R.
Published: August 2009

This letter provides an experimental demonstration of extraordinary transmission in a closed waveguide system loaded with an electrically small diaphragm. This is a situation where the standard surface plasmon polariton (SPP) theory does not apply. The theoretical explanation is then based on the concept of impedance matching. This concept has previously been applied by some of the authors to account for enhanced transmission in situations where surface plasmon theory can be used: periodic arrays of small holes or slits in flat metal screens. The experiment in this letter supports the impedance matching model, valid for when SPPs are present or not.
Single beam acoustic trapping
Authors: Lee Jungwoo , Teh Shia-Yen , Lee Abraham , Kim Hyung Ham , Lee Changyang , Shung K. Kirk
Published: August 2009

A single beam acoustic device, with its relatively simple scheme and low intensity, can trap a single lipid droplet in a manner similar to optical tweezers. Forces in the order of hundreds of nanonewtons direct the droplet toward the beam focus, within the range of hundreds of micrometers. This trapping method, therefore, can be a useful tool for particle manipulation in areas where larger particles or forces are involved.
Temperature dependent optical properties of (002) oriented ZnO thin film using surface plasmon resonance
Authors: Saha Shibu , Mehan Navina , Sreenivas K. , Gupta Vinay
Published: August 2009

Temperature dependent optical properties of c-axis oriented ZnO thin film were investigated using surface plasmon resonance (SPR) technique. SPR data for double layer (prism-Au-ZnO-air) and single layer (prism-Au-air) systems were taken over a temperature range (300–525 K). Dielectric constant at optical frequency and real part of refractive index of the ZnO film shows an increase with temperature. The bandgap of the oriented ZnO film was found to decrease with rise in temperature. The work indicates a promising application of the system as a temperature sensor and highlights an efficient scientific tool to study optical properties of thin film under varying ambient conditions.
Toroidal flow and radial particle flux in tokamak plasmas
Authors: Callen J. D. , Cole A. J. , Hegna C. C.
Published: August 2009

Many effects influence toroidal flow evolution in tokamak plasmas. Momentum sources and radial plasma transport due to collisional processes and microturbulence-induced anomalous transport are usually considered. In addition, toroidal flow can be affected by nonaxisymmetric magnetic fields; resonant components cause localized electromagnetic toroidal torques near rational surfaces in flowing plasmas and nonresonant components induce “global” toroidal flow damping torque throughout the plasma. Also, poloidal magnetic field transients on the magnetic field diffusion time scale can influence plasma transport. Many of these processes can also produce momentum pinch and intrinsic flow effects. This paper presents a comprehensive and self-consistent description of all these effects within a fluid moment context. Plasma processes on successive time scales (and constraints they impose) are considered sequentially: compressional Alfvén waves (Grad–Shafranov equilibrium and ion radial force balance), sound waves (pressure constant along a field line and incompressible flows within a flux surface), and ion collisions (damping of poloidal flow). Finally, plasma transport across magnetic flux surfaces is induced by the many second order (in the small gyroradius expansion) toroidal torque effects indicated above. Nonambipolar components of the induced particle transport fluxes produce radial plasma currents. Setting the flux surface average of the net radial current induced by all these effects to zero yields the transport-time-scale equation for evolution of the plasma toroidal flow. It includes a combination of global toroidal flow damping and resonant torques induced by nonaxisymmetric magnetic field components, poloidal magnetic field transients, and momentum source effects, as well as the usual collision- and microturbulence-induced transport. On the transport time scale, the plasma toroidal rotation determines the radial electric field for net ambipolar particle transport. The ultimate radial particle transport is composed of intrinsically ambipolar fluxes plus nonambipolar fluxes evaluated at this toroidal-rotation-determined radial electric field.
Suppression of the current leakage in charge ordered Lu2Fe2Fe1−xMnxO7 (<x≤0.86)
Authors: Qin Y. B. , Yang H. X. , Zhang Y. , Tian H. F. , Ma C. , Zeng L. J. , Li J. Q.
Published: August 2009

The ferroelectricity, magnetic properties, and charge-ordering modulations in the layered Lu2Fe2Fe1−xMnxO7 have been investigated for x ranging from 0 to 0.86. Experimental measurements reveal that substitution of Mn for Fe could evidently influence the low temperature magnetic transition. Moreover, ferroelectric analysis suggests that introduction of Mn ions in this layered system can efficiently suppress the conducting leakage and result in clear hysteresis loops in the polarization–electric field switching curves. The charge ordering states in Lu2Fe2Fe1−xMnxO7 characterized by two incommensurate modulations has been observed and discussed in association with the local spontaneous polarizations.
Morphology of graphene on SiC(0001¯) surfaces
Authors: Luxmi  , Fisher P. J. , Srivastava N. , Feenstra R. M. , Sun Yugang , Kedzierski J. , Healey P. , Gu Gong
Published: August 2009

Graphene is formed on SiC(0001¯) surfaces (the so-called C-face of the crystal) by annealing in vacuum, with the resulting films characterized by atomic force microscopy, Auger electron spectroscopy, scanning Auger microscopy, and Raman spectroscopy. Morphology of these films is compared with the graphene films grown on SiC(0001) surfaces (the Si-face). Graphene forms a terraced morphology on the C-face, whereas it forms with a flatter morphology on the Si-face. It is argued that this difference occurs because of differing interface structures in the two cases. For certain SiC wafers, nanocrystalline graphite is found to form on top of the graphene.
Laser-direct photoetching of metal thin film for the electrode of transistor
Authors: Lee Hyeongjae , Shin Hyunkwon , Jeong Youngmin , Moon Jooho , Lee Myeongkyu
Published: August 2009

We report that metal thin films can be directly photoetched by a pulsed neodymium doped yttrium aluminum garnet laser beam irradiating the film surface. This process utilizes a laser-induced thermoelastic force, which plays a role to detach the film from the underlying layer. High-fidelity patterns at the micrometer scales have been fabricated using a spatially modulated laser beam. A zinc-tin-oxide thin film transistor with photoetched Al source and drain electrodes exhibited an on/off ratio higher than 105 and a very low off-current level. This indicates that the metallic layer is completely etched out by this process, making an additional cleaning or etching step unnecessary.
Removal of particles from holes in submerged plates with oscillating bubbles
Authors: Pavard Delphine , Klaseboer Evert , Ohl Siew-Wan , Khoo Boo Cheong
Published: August 2009

This study is motivated by a common problem in submerged tubes and structures, which is the blockage of the tubes by pollutant particles or debris from the surrounding fluid. To clear the obstruction from the tube, an expanding bubble is used to propel the obstruction away from the tube (the tube is represented as a submerged transparent plate with a hole in our experiments). In some cases the obstruction removal effect is reinforced by the impacting jet of such a collapsing bubble. The bubble is generated via a simple low voltage electric spark discharge circuit. The pressure generated by the oscillating bubble effectively pushes the particle away from the tube, thereby successfully clearing the obstruction. High-speed photography is used to record and analyze the phenomenon. The speed of the particle is found to be around 1 m/s shortly after the collapse of the bubble. Interestingly, there is a clear difference between air-backed plates and water-backed plates in terms of bubble and particle dynamics. The bubbles in the current study are typically of millimeter size. Since the physics are similar for smaller bubbles, the process can possibly be downsized for other microapplications such as the removal of blood clots in vessels [S. R. Visuri et al., U.S. Patent No. 6428531 (August 6, 2002)].
Setting cumulative emissions targets to reduce the risk of dangerous climate change
Authors: Zickfeld Kirsten , Eby Michael , Matthews H. Damon , Weaver Andrew J.
Published: August 2009

Avoiding “dangerous anthropogenic interference with the climate system” requires stabilization of atmospheric greenhouse gas concentrations and substantial reductions in anthropogenic emissions. Here, we present an inverse approach to coupled climate-carbon cycle modeling, which allows us to estimate the probability that any given level of carbon dioxide (CO
2
) emissions will exceed specified long-term global mean temperature targets for “dangerous anthropogenic interference,” taking into consideration uncertainties in climate sensitivity and the carbon cycle response to climate change. We show that to stabilize global mean temperature increase at 2 °C above preindustrial levels with a probability of at least 0.66, cumulative CO
2
emissions from 2000 to 2500 must not exceed a median estimate of 590 petagrams of carbon (PgC) (range, 200 to 950 PgC). If the 2 °C temperature stabilization target is to be met with a probability of at least 0.9, median total allowable CO
2
emissions are 170 PgC (range, −220 to 700 PgC). Furthermore, these estimates of cumulative CO
2
emissions, compatible with a specified temperature stabilization target, are independent of the path taken to stabilization. Our analysis therefore supports an international policy framework aimed at avoiding dangerous anthropogenic interference formulated on the basis of total allowable greenhouse gas emissions.
Glutamine-dependent anapleurosis dictates glucose uptake and cell growth by regulating MondoA transcriptional activity
Authors: Kaadige Mohan R. , Looper Ryan E. , Kamalanaadhan Sadhaasivam , Ayer Donald E.
Published: August 2009

Glucose and glutamine are abundant nutrients required for cell growth, yet how cells sense and adapt to changes in their levels is not well understood. The MondoA transcription factor forms a heterocomplex with its obligate partner Mlx to regulate ≈75% of glucose-dependent transcription. By mediating glucose-induced activation of thioredoxin-interacting protein (TXNIP), MondoA:Mlx complexes directly repress glucose uptake. We show here that glutamine inhibits transcriptional activation of TXNIP by triggering the recruitment of a histone deacetylase-dependent corepressor to the amino terminus of MondoA. Therefore, in the presence of both glucose and glutamine, TXNIP expression is low, which favors glucose uptake and aerobic glycolysis; the Warburg effect. Consistent with MondoA functioning upstream of TXNIP, MondoA knockdown reduces TXNIP expression, elevates glucose uptake and stimulates cell proliferation. Although glutamine has many intracellular fates, a cell permeable analog of a tricarboxylic acid cycle (TCA) intermediate, α-ketoglutarate, also blocks the transcriptional activity of MondoA at the TXNIP promoter and stimulates glucose uptake. Together our data suggest that glutamine-dependent mitochondrial anapleurosis dictates glucose uptake and aerobic glycolysis by blocking MondoA:Mlx-dependent transcriptional activation of TXNIP. We propose that this previously unappreciated coordination between glutamine and glucose utilization defines a metabolic checkpoint that restricts cell growth when subthreshold levels of these essential nutrients are available.