bluuebunny/crossref_metadata_2025 huggingface dataset:
Photoelectron angular distributions from autoionizing 4s14p66p1 states in atomic krypton probed with femtosecond time resolution
Authors: Doughty Benjamin , Haber Louis H. , Hackett Christina , Leone Stephen R.
Published: March 2011

Photoelectron angular distributions (PADs) are obtained for a pair of 4s14p66p1 (a singlet and a triplet) autoionizing states in atomic krypton. A high-order harmonic pulse is used to excite the pair of states and a time-delayed 801 nm ionization pulse probes the PADs to the final 4s14p6 continuum with femtosecond time resolution. The ejected electrons are detected with velocity map imaging to retrieve the time-resolved photoelectron spectrum and PADs. The PAD for the triplet state is inherently separable by virtue of its longer autoionization lifetime. Measuring the total signal over time allows for the PADs to be extracted for both the singlet state and the triplet state. Anisotropy parameters for the triplet state are measured to be β2 = 0.55 ± 0.17 and β4 = −0.01 ± 0.10, while the singlet state yields β2 = 2.19 ± 0.18 and β4 = 1.84 ± 0.14. For the singlet state, the ratio of radial transition dipole matrix elements, X, of outgoing S to D partial waves and total phase shift difference between these waves, Δ, are determined to be X = 0.56 ± 0.08 and Δ = 2.19 ± 0.11 rad. The continuum quantum defect difference between the S and D electron partial waves is determined to be −0.15 ± 0.03 for the singlet state. Based on previous analyses, the triplet state is expected to have anisotropy parameters independent of electron kinetic energy and equal to β2 = 5/7 and β4 = −12/7. Deviations from the predicted values are thought to be a result of state mixing by spin–orbit and configuration interactions in the intermediate and final states; theoretical calculations are required to quantify these effects.
Magnetic field effects in artificial dielectrics with arrays of magnetic wires at microwaves
Authors: Panina L. V. , Ipatov M. , Zhukova V. , Zhukov A. , Gonzalez J.
Published: March 2011

A magnetic field tunable electromagnetic response in periodic lattices of conducting magnetic wires is demonstrated. The wire medium having a negative permittivity in the lower frequency band is customarily investigated as an important component of so-called double negative metamaterials. Here we are interested in a strong dispersion of the permittivity in these structures and a possibility to alter it by changing the losses in magnetic wires with an external magnetic field. The theoretical approach is based on calculating the relaxation parameter depending on the wire surface impedance, and hence, on the wire magnetic properties. Thus, in arrays of Co-based amorphous wires the application of a moderate magnetic field (of about 1–2 kA/m) which causes the magnetization reorientation is capable of few fold permittivity change in the frequency range of 1–2 GHz. Such efficient tuning for certain structural and magnetic parameters was confirmed experimentally by measuring the transmission and reflection spectra from lattices of Co66Fe3.5B16Si11Cr3.5 glass-coated amorphous wires with a different wire cross-section and a different lattice period. The chosen wires are also confirmed to show a large magnetoimpedance effect at GHz frequencies, which constitutes the underlying mechanism of magnetic field dependent permittivity in wire media.
Thermal stability and magnetic properties of partially Co-substituted (Fe71.2B24Y4.8)96Nb4 bulk metallic glasses
Authors: Stoica M. , Kolesar V. , Bednarčic J. , Roth S. , Franz H. , Eckert J.
Published: March 2011

The influence of partial replacement of Fe with Co in the quaternary (Fe71.2B24Y4.8)96Nb4 bulk metallic glasses on their structure, thermal stability and magnetic properties was studied. It was found that Co increases the thermal stability, as well as the Curie temperature, which monotonously increases as the Co content increases. The saturation magnetization shows a maximum of 1.01 μB per magnetic atom for x = 0.1, followed by a perfectly linear decrease for higher Co contents. The extension of the supercooled liquid region may reach even 98 K and the glass transition temperatures approach the theoretical value of 2/3 of the melting temperature. The mean field theory allows to calculate the magnetic exchange stiffness constant and to correlate its variation with the variation of the magnetic saturation.
A high-power spatial filter for Thomson scattering stray light reduction
Authors: Levesque J. P. , Litzner K. D. , Mauel M. E. , Maurer D. A. , Navratil G. A. , Pedersen T. S.
Published: March 2011

The Thomson scattering diagnostic on the High Beta Tokamak-Extended Pulse (HBT-EP) is routinely used to measure electron temperature and density during plasma discharges. Avalanche photodiodes in a five-channel interference filter polychromator measure scattered light from a 6 ns, 800 mJ, 1064 nm Nd:YAG laser pulse. A low cost, high-power spatial filter was designed, tested, and added to the laser beamline in order to reduce stray laser light to levels which are acceptable for accurate Rayleigh calibration. A detailed analysis of the spatial filter design and performance is given. The spatial filter can be easily implemented in an existing Thomson scattering system without the need to disturb the vacuum chamber or significantly change the beamline. Although apertures in the spatial filter suffer substantial damage from the focused beam, with proper design they can last long enough to permit absolute calibration.
A two-dimensional analytical model for the gate–source and gate–drain capacitances of ion-implanted short-channel GaAs metal-semiconductor-field effect transistor under dark and illuminated conditions
Authors: Tripathi Shweta , Jit S.
Published: March 2011

This paper presents an analytical model for the internal capacitances of short-channel ion-implanted GaAs MESFETs under dark and illuminated conditions. The device structure considered in this study is a normally-on self-aligned GaAs MESFET with indium tin oxide (ITO) as the Schottky metal for the gate electrode of the device. The gate area of the device is illuminated by an optical radiation of 0.87 μm from an external source which is coupled into the device through the semitransparent ITO metal at Schottky-gate to modulate the electrical and microwave characteristics of the device. The nonanalytic Gaussian doping profile commonly considered for the channel doping of an ion-implanted GaAs MESFET has been replaced by an analytic Gaussianlike function for the simplicity of the present model. The two-dimensional (2D) potential distribution obtained by solving the 2D Poisson’s equation by including the effect of photo-generated carriers due to the incident optical radiation has been utilized to model the depletion region width below the gate of the short-channel GaAs MESFETs. The depletion width model has then been used to model the internal gate-source and gate-drain capacitances of the device operating under both the linear and saturation regions. The effect of illumination on the Schottky junction at the gate of the MESFET has been modeled by considering an induced photo-voltage developed across the junction that is superimposed on the applied gate bias voltage. The proposed model has been verified by comparing the theoretically predicted results with simulated data obtained by using the commercially available ATLASTM 2D device simulator.
Field emission behavior of vertically aligned ZnO nanowire planar cathodes
Authors: Semet V. , Binh Vu Thien , Pauporté Th. , Joulaud L. , Vermersch F. J.
Published: March 2011

A field emission (FE) study by scanning anode field emission microscopy was performed to evaluate the FE properties of vertically aligned zinc oxide (ZnO) nanowire arrays electrodeposited on a plane conductive surface. The specific FE behaviors of the cathode observed experimentally are (1) a turn-on macroscopic field of about 6 V/μm for a FE current density JFE = 5 × 10−4 A/cm2, (2) a stable FE characteristics for 5 × 10−4 < JFE < 5 × 10−2 A/cm2, and (3) a brutal shut down of FE when JFE crossed a limiting value of ∼0.05 A/cm2 due to a rapid evolution of the nanowires toward a bulbous tip geometry or a complete melting. A physical process of FE from ZnO nanostructures is proposed from the experimental data analyses. An effective surface barrier of about 1 eV was determined from the experimental Fowler–Nordheim plot and the presence of a Zn enriched surface was assumed in considering the possibility of important modifications of the crystallography and charge transfers at the surface of ZnO nanowires during the application of the strong electric field required for FE.
Probing the mechanical properties of graphene using a corrugated elastic substrate
Authors: Scharfenberg Scott , Rocklin D. Z. , Chialvo Cesar , Weaver Richard L. , Goldbart Paul M. , Mason Nadya
Published: March 2011

We examine the mechanical properties of graphene samples of thicknesses ranging from 1 to 17 atomic layers, placed on a microscale-corrugated elastic substrate. Using atomic force microscopy, we show that the graphene adheres to the substrate surface and can substantially deform the substrate, with larger graphene thicknesses creating greater deformations. We use linear elasticity theory to model the deformations of the composite graphene-substrate system. We compare experiment and theory, and thereby extract information about graphene’s bending rigidity, adhesion, critical stress for interlayer sliding, and sample-dependent tension.
Magnetic miniband and magnetotransport property of a graphene superlattice
Authors: Jiang Liwei , Zheng Yisong
Published: March 2011

The eigenenergy and the conductivity of a graphene sheet subject to a one-dimensional cosinusoidal potential and in the presence of a magnetic field are calculated. Such a graphene superlattice presents three distinct magnetic miniband structures as the magnetic field increases. They are, respectively; the triply degenerate Landau level spectrum, the nondegenerate minibands with finite dispersion and the same Landau level spectrum with the pristine graphene. The ratio of the magnetic length to the period of the potential function is the characteristic quantity to determine the electronic structure of the superlattice. Corresponding to these distinct electronic structures, the diagonal conductivity presents very strong anisotropy in the weak and moderate magnetic field cases, while the predominant magnetotransport orientation changes from the transverse to the longitudinal direction of the superlattice. More interestingly, in the weak magnetic field case, the superlattice exhibits half-integer quantum Hall effect, but with a large jump between the Hall plateaux. Thus, it is different from the one of the pristine graphene.
Electrostatic modification of oxide semiconductors by electric double layers of microporous SiO2-based solid electrolyte
Authors: Jiang Jie , Dai Minzhi , Sun Jia , Zhou Bin , Lu Aixia , Wan Qing
Published: March 2011

We have studied electrostatic modulation of InGaZnO4 and indium-tin oxide (ITO) channel by using microporous SiO2-based solid electrolyte as gate dielectrics in the field-effect transistors (FETs) structure. H3PO4-treated SiO2-based solid electrolyte was found to be have a large capacitance (9.5 μF/cm2) due to the strong capacitive coupling by electric double layer(EDL) between H3PO4-treated solid electrolyte and active channel. High carrier densities (>1014/cm2) and large metallic conductivities (2180 S/cm) in InGaZnO4 channel were electrostatically induced, while a metal-to-insulator transition (more than 6 orders of magnitude of channel resistance modulation) was observed in ITO channel by using such FET structure. Furthermore, device simulation based on an EDL model can also reproduce the transfer characteristics well. Our result provides a new opportunity for electrostatic modulation of the electronic properties in condensed matter.
A computational study of ultrafast acid dissociation and acid–base neutralization reactions. II. The relationship between the coordination state of solvent molecules and concerted versus sequential acid dissociation
Authors: Maurer Patrick , Thomas Vibin , Iftimie Radu
Published: March 2011

We investigate the role played by the coordination state of pre-existing water wires during the dissociation of moderately strong acids by means of first-principles molecular dynamics calculations. By preparing 2,4,6-tricyanophenol (calc. pKa∼0.5) in two different initial states, we are able to observe sequential as well as concerted trajectories of dissociation: On one hand, equilibrium dissociation takes place on a ∼50 ps timescale; proton conduction occurs through three-coordinated water wires in this case, by means of sequential Grotthus hopping. On the other hand, by preparing 2,4,6-tricyanophenol in a hydration state inherited from that of equilibrated phenol (calc. pKa = 7.6), the moderately strong acid finds itself in a presolvated state from which dissociation can take place on a ∼1 ps timescale. In this case, concerted dissociation trajectories are observed, which consist of proton translocation through two intervening, four-coordinated, water molecules in 0.1–1.0 ps. The present results suggest that, in general, the mechanism of proton translocation depends on how the excess proton is injected into a hydrogen bond network. In particular, if the initial conditions favour proton release to a fourfold H-bonded water molecule, proton translocation by as much as 6–8 Å can take place on a sub-picosecond timescale.
PbO-deficient PbTiO3: Mass transport, structural effects and possibility for intrinsic screening of the ferroelectric polarization
Authors: Selbach Sverre M. , Tybell Thomas , Einarsrud Mari-Ann , Grande Tor
Published: March 2011

Intrinsic solid solubility in the form of cation nonstoichiometry has been studied in PbO-deficient bulk PbTiO3 prepared by solid-state reaction. The unit cell distortion, or tetragonality c/a, decreases with increasing concentration of Pb and O vacancies across the solid solubility range. Mass transport during solid-state reaction and sintering is sensitive to the nominal stoichiometry of the system: Excess PbO promotes grain growth and densification while excess TiO2 yields coarsening and swelling. These findings are discussed with respect to thin film growth and screening of the ferroelectric polarization by point defect concentration gradients at epitaxial interfaces.
Numerical study on rectangular microhollow cathode discharge
Authors: He Shoujie , Ouyang Jiting , He Feng , Li Shang
Published: March 2011

Rectangular microhollow cathode discharge in argon is investigated by using two-dimensional time-dependent self-consistent fluid model. The electric potential, electric field, particle density, and mean electron energy are calculated. The results show that hollow cathode effect can be onset in the present configuration, with strong electric field and high mean electron energy in the cathode fall while high density and quasineutral plasma in the negative glow. The potential well and electric filed reversal are formed in the negative glow region. It is suggested that the presence of large electron diffusion flux necessitates the field reversal and potential well.
Dynamic microscopic structures and dielectric response in the cubic-to-tetragonal phase transition for BaTiO3 studied by first-principles molecular dynamics simulation
Authors: Xie L. , Li Y. L. , Yu R. , Zhu Jing
Published: March 2011

The dynamic structures of the cubic and tetragonal phase in BaTiO3 and its dielectric response above the cubic-to-tetragonal phase transition temperature (Tp) are studied by first-principles molecular dynamics (MD) simulation. It is shown that the phase transition is due to the condensation of one of the transverse correlations of the off-center displacements. Calculation of the phonon properties for both the cubic and the tetragonal phase shows a saturation of the soft mode frequency at ∼60 cm−1 near Tp and advocates its order-disorder type mechanism. Our calculation also leads directly to a two mode feature of the dielectric function above Tp [H. Presting, J. A. Sanjurjo, and H. Vogt, Phys. Rev. B 28, 6097 (1983)] and the two modes are attributed to the coexistence of renormalized and normal soft mode excitation as a result of strong coupling between the soft mode and the off-center displacements.
Ultrastiffness and metallicity of rhenium nitrides
Authors: Liang Yongcheng , Yuan Xun , Zhang Wenqing
Published: March 2011

The equation of states, mechanical properties and electronic structures of the recently synthesized rhenium nitrides (Re3N and Re2N) and the pure metal Re have been investigated by the density functional theory calculations considering the effect of spin-orbit coupling. Our results not only indicate Re3N and Re3N to be ultrastiff and hard materials but also reveal that they exhibit mechanical stability and metallic character. Furthermore, the mechanical behaviors for Re, Re3N, and Re3N can be qualitatively clarified from their crystal and electronic structures. The metallic, ultrastiff, and hard Re3N and Re2N may find their promising applications as cutting tools and hard conductors at the extreme conditions.
Properties of rotating nanoalloys formed by cluster collision: A computer simulation study
Authors: Paz S. A. , Leiva E. P. M. , Jellinek J. , Mariscal M. M.
Published: March 2011

Results of dynamical simulations of collision-induced formation and properties of bimetallic nanoparticles are presented and analyzed. The analysis includes the effects of the collision energy and the impact parameter. For nonzero impact parameters, the formed (in many cases Janus-type) nanoparticles are rotating. The energy of the rotating nanoparticles is decomposed into the rotational and vibrational components, and the structural effects of these components are analyzed. Comparison is made with the case of the corresponding homoatomic systems, formed by collision of nanoparticles with the same elemental composition.
On the relation between orbital-localization and self-interaction errors in the density functional theory treatment of organic semiconductors
Authors: Körzdörfer T.
Published: March 2011

It is commonly argued that the self-interaction error (SIE) inherent in semilocal density functionals is related to the degree of the electronic localization. Yet at the same time there exists a latent ambiguity in the definitions of the terms “localization” and “self-interaction,” which ultimately prevents a clear and readily accessible quantification of this relationship. This problem is particularly pressing for organic semiconductor molecules, in which delocalized molecular orbitals typically alternate with localized ones, thus leading to major distortions in the eigenvalue spectra. This paper discusses the relation between localization and SIEs in organic semiconductors in detail. Its findings provide further insights into the SIE in the orbital energies and yield a new perspective on the failure of self-interaction corrections that identify delocalized orbital densities with electrons.
The effect of correlated bath fluctuations on exciton transfer
Authors: Strümpfer Johan , Schulten Klaus
Published: March 2011

Excitation dynamics of various light harvesting systems have been investigated with many theoretical methods including various non-Markovian descriptions of dissipative quantum dynamics. It is typically assumed that each excited state is coupled to an independent thermal environment, i.e., that fluctuations in different environments are uncorrelated. Here the assumption is dropped and the effect of correlated bath fluctuations on excitation transfer is investigated. Using the hierarchy equations of motion for dissipative quantum dynamics it is shown for models of the B850 bacteriochlorophylls of LH2 that correlated bath fluctuations have a significant effect on the LH2 → LH2 excitation transfer rate. It is also demonstrated that inclusion of static disorder is crucial for an accurate description of transfer dynamics.
Reduction of frequency noise and frequency shift by phase shifting elements in frequency modulation atomic force microscopy
Authors: Kobayashi Kei , Yamada Hirofumi , Matsushige Kazumi
Published: March 2011

We recently reported the analysis of the frequency noise in the frequency modulation atomic force microscopy (FM-AFM) both in high-Q and low-Q environments [Rev. Sci. Instrum. 80, 043708 (2009)]. We showed in the paper that the oscillator noise, the frequency fluctuation of the oscillator, becomes prominent in the modulation frequency lower than f0/2Q, where f0 and Q are the resonance frequency and Q-factor. The magnitude of the oscillator noise is determined by the slope of the phase versus frequency curve of the cantilever at f0. However, in actual FM-AFM in liquids, the phase versus frequency curve may not be always ideal because of the existence of various phase shifting elements (PSEs). For example, the spurious resonance peaks caused by the acoustic excitation and a band-pass filter in the self-oscillation loop increase the slope of the phase versus frequency curve. Due to those PSEs, the effective Q-factor is often increased from the intrinsic Q-factor of the cantilever. In this article, the frequency noise in the FM-AFM system with the PSEs in the self-oscillation loop is analyzed to show that the oscillator noise is reduced by the increase of the effective Q-factor. It is also shown that the oscillation frequency deviates from the resonance frequency due to the increase of the effective Q-factor, thereby causing the reduction in the frequency shift signal with the same factor. Therefore the increase of the effective Q-factor does not affect the signal-to-noise ratio in the frequency shift measurement, but it does affect the quantitativeness of the measured force in the FM-AFM. Furthermore, the reduction of the frequency noise and frequency shift by the increase of the effective Q-factor were confirmed by the experiments.
Random telegraph-signal noise in junctionless transistors
Authors: Nazarov A. N. , Ferain I. , Akhavan N. Dehdashti , Razavi P. , Yu R. , Colinge J. P.
Published: March 2011

Random telegraph-signal noise (RTN) is measured in junctionless metal-oxide-silicon field-effect transistors (JL MOSFETs) as a function of gate and drain voltage and temperature. It is shown that the RTN in JL MOSFETs increases significantly when an accumulation layer is formed. The amplitude of RTN is considerably smaller in JL devices than in inversion-mode MOSFET fabricated using similar fabrication parameters. A measurement technique is developed to extract the main parameters of the traps, including the average charge capture and emission time from the traps.
Fragmentation and reactivity in collisions of protonated diglycine with chemically modified perfluorinated alkylthiolate-self-assembled monolayer surfaces
Authors: Barnes George L. , Young Kelsey , Yang Li , Hase William L.
Published: March 2011

Direct dynamics simulations are reported for quantum mechanical (QM)/molecular mechanical (MM) trajectories of N-protonated diglycine (gly2-H+) colliding with chemically modified perfluorinated octanethiolate self-assembled monolayer (SAM) surfaces. The RM1 semiempirical theory is used for the QM component of the trajectories. RM1 activation and reaction energies were compared with those determined from higher-level ab initio theories. Two chemical modifications are considered in which a head group (–COCl or –CHO) is substituted on the terminal carbon of a single chain of the SAM. These surfaces are designated as the COCl-SAM and CHO-SAM, respectively. Fragmentation, peptide reaction with the SAM, and covalent linkage of the peptide or its fragments with the SAM surface are observed. Peptide fragmentation via concerted CH2–CO bond breakage is the dominant pathway for both surfaces. HCl formation is the dominant species produced by reaction with the COCl-SAM, while for the CHO-SAM a concerted H-atom transfer from the CHO-SAM to the peptide combined with either a H-atom or radical transfer from the peptide to the surface to form singlet reaction products is the dominant pathway. A strong collision energy dependence is found for the probability of peptide fragmentation, its reactivity, and linkage with the SAM. Surface deposition, i.e., covalent linkage between the surface and the peptide, is compared to recent experimental observations of such bonding by Laskin and co-workers [Phys. Chem. Chem. Phys. 10, 1512 (2008)]. Qualitative differences in reactivity are seen between the COCl-SAM and CHO-SAM showing that chemical identity is important for surface reactivity. The probability of reactive surface deposition, which is most closely analogous to experimental observables, peaks at a value of around 20% for a collision energy of 50 eV.
Use of modified smooth exterior scaling method as an absorbing potential and its application
Authors: Kalita Dhruba J. , Gupta Ashish K.
Published: March 2011

Here, we propose a new complex path to achieve better absorption during the propagation of a wavepacket. In the proposed modified smooth exterior scaling (SES) method, scaling function, θ(x), has been chosen as a real function rather than complex (as used in a conventional smooth exterior scaling method). It greatly reduces the artificial reflections from the boundary edges. This modified SES method is applied to study the multiphoton dissociation of \documentclass[12pt]{minimal}\begin{document}$ H_{2}^{+}$\end{document}H2+ in intense laser field. The resonance states are calculated accurately.
Investigation of the ellipsoidal-statistical Bhatnagar–Gross–Krook kinetic model applied to gas-phase transport of heat and tangential momentum between parallel walls
Authors: Gallis M. A. , Torczynski J. R.
Published: March 2011

The ellipsoidal-statistical Bhatnagar–Gross–Krook (ES-BGK) kinetic model is investigated for steady gas-phase transport of heat, tangential momentum, and mass between parallel walls (i.e., Fourier, Couette, and Fickian flows). This investigation extends the original study of Cercignani and Tironi, who first applied the ES-BGK model to heat transport (i.e., Fourier flow) shortly after this model was proposed by Holway. The ES-BGK model is implemented in a molecular-gas-dynamics code so that results from this model can be compared directly to results from the full Boltzmann collision term, as computed by the same code with the direct simulation Monte Carlo (DSMC) algorithm of Bird. A gas of monatomic molecules is considered. These molecules collide in a pairwise fashion according to either the Maxwell or the hard-sphere interaction and reflect from the walls according to the Cercignani–Lampis–Lord model with unity accommodation coefficients. Simulations are performed at pressures from near-free-molecular to near-continuum. Unlike the BGK model, the ES-BGK model produces heat-flux and shear-stress values that both agree closely with the DSMC values at all pressures. However, for both interactions, the ES-BGK model produces molecular-velocity-distribution functions that are qualitatively similar to those determined for the Maxwell interaction from Chapman–Enskog theory for small wall temperature differences and moment-hierarchy theory for large wall temperature differences. Moreover, the ES-BGK model does not produce accurate values of the mass self-diffusion coefficient for either interaction. Nevertheless, given its reasonable accuracy for heat and tangential-momentum transport, its sound theoretical foundation (it obeys the H-theorem), and its available extension to polyatomic molecules, the ES-BGK model may be a useful method for simulating certain classes of single-species noncontinuum gas flows, as Cercignani suggested.
Low temperature processed bilayer dielectrics for low-voltage flexible saturated load inverters
Authors: Zhou Ye , Roy V. A. L. , Xu Zong-Xiang , Kwong H. Y. , Wang Hai-Bo , Lee C. S.
Published: March 2011

Saturated load inverters using low temperature processed bilayer n-octadecylphosphonic acid (ODPA)/Al2O3 dielectrics were fabricated on flexible polyethylene terephthalate substrates. The saturated load inverters, which enable simplified processing, could operate at supply voltage as low as –2 V and achieve a gain up to 23 at –5 V. The inverters on ODPA/Al2O3 exhibited better mechanical stability upon bending due to the existence of self-assembled monolayer ODPA, implying their potential application in low voltage inexpensive flexible electronics.
Sufficient conditions for a nondegenerate Hopf bifurcation in a generalized Lagrange–Poisson problem
Authors: Guirao Juan L. G. , Vera Juan A.
Published: March 2011

In this paper we provide sufficient conditions for the existence of a nondegenerate Hamiltonian Hopf bifurcation at the equilibria corresponding to the rotation around the vertical axis of a symmetric gyrostat with a fixed point under the effect of an axially symmetric potential.
Darbouxian integrals for generalized Raychaudhuri equations
Authors: Valls Claudia
Published: March 2011

We give a complete characterization of the Darbouxian first integrals of a generalized Raychaudhuri equation which appears in modern string cosmology and which has the form \documentclass[12pt]{minimal}\begin{document}$\dot{x} =-\frac{1}{2} x^2 -\alpha x -2(y^2 +z^2 -w^2)-2 \beta , \dot{y} =-(\alpha +x) y -\gamma , \dot{z} =-(\alpha +x) z -\delta , \dot{w} =-(\alpha +x) w$\end{document}ẋ=−12x2−αx−2(y2+z2−w2)−2β,ẏ=−(α+x)y−γ,ż=−(α+x)z−δ,ẇ=−(α+x)w, where α, β, γ, δ are real parameters. Our approach uses the Darboux theory of integrability.
Existence of dark solitons in a class of stationary nonlinear Schrödinger equations with periodically modulated nonlinearity and periodic asymptotics
Authors: Belmonte-Beitia J. , Cuevas J.
Published: March 2011

In this paper, we give a proof of the existence of stationary dark soliton solutions or heteroclinic orbits of nonlinear equations of Schrödinger type with periodic inhomogeneous nonlinearity. The result is illustrated with examples of dark solitons for cubic and photorefractive nonlinearities.
Phase transitions for the Brusselator model
Authors: Ma Tian , Wang Shouhong
Published: March 2011

Dynamic phase transitions of the Brusselator model is carefully analyzed, leading to a rigorous characterization of the types and structure of the phase transitions of the model from basic homogeneous states. The study is based on the dynamic transition theory developed recently by the authors.
Canonical quantization of lattice Higgs–Maxwell–Chern–Simons fields: Osterwalder–Schrader positivity
Authors: Bowman Daniel A. , Challifour John L.
Published: March 2011

A Euclidean representation is given for a canonically quantized relativistic Maxwell–Chern–Simons field on a lattice, which approximates a complex measure on a space of distributions. Using a path-space formula for the nonself-adjoint Hamiltonian, the relation between Euclidean Osterwalder–Schrader positivity, the Krein metric, and Gauss’ law is examined.
Periodic orbits and nonintegrability of generalized classical Yang–Mills Hamiltonian systems
Authors: Jiménez–Lara Lidia , Llibre Jaume
Published: March 2011

The averaging theory of first order is applied to study a generalized Yang–Mills system with two parameters. Two main results are proved. First, we provide sufficient conditions on the two parameters of the generalized system to guarantee the existence of continuous families of isolated periodic orbits parameterized by the energy, and these families are given up to first order in a small parameter. Second, we prove that for the nonintegrable classical Yang–Mills Hamiltonian systems, in the sense of Liouville–Arnold, which have the isolated periodic orbits found with averaging theory, cannot exist in any second first integral of class \documentclass[12pt]{minimal}\begin{document}$\mathcal {C}^1$\end{document}C1. This is important because most of the results about integrability deals with analytic or meromorphic integrals of motion.
Langmuir rogue waves in electron-positron plasmas
Authors: Moslem W. M.
Published: March 2011

Progress in understanding the nonlinear Langmuir rogue waves which accompany collisionless electron-positron (e-p) plasmas is presented. The nonlinearity of the system results from the nonlinear coupling between small, but finite, amplitude Langmuir waves and quasistationary density perturbations in an e-p plasma. The nonlinear Schrödinger equation is derived for the Langmuir waves’ electric field envelope, accounting for small, but finite, amplitude quasistationary plasma slow motion describing the Langmuir waves’ ponderomotive force. Numerical calculations reveal that the rogue structures strongly depend on the electron/positron density and temperature, as well as the group velocity of the envelope wave. The present study might be helpful to understand the excitation of nonlinear rogue pulses in astrophysical environments, such as in active galactic nuclei, in pulsar magnetospheres, in neutron stars, etc.
Losses in high quality quartz crystal resonators at cryogenic temperatures
Authors: Galliou Serge , Imbaud Joël , Goryachev Maxim , Bourquin Roger , Abbé Philippe
Published: March 2011

Measurement of the mechanical losses of quartz crystal is a topic of interest for communities dealing with the gravitational wave detectors and also the time and frequency domain. About the latter, the authors describe Q-factor measurements of quartz crystal resonators at cryogenic temperatures under 10 K, thanks to a cryocooler-based experimental set-up. A Q-factor of 325 millions at 4 K, on the fifth overtone of the quasilongitudinal mode at 15.9 MHz, has been recorded. As shown, the acoustic wave trapping is suspected to limit the Landau–Rumer regime below 6 K [Landau and Rumer, Phys. Z. Sowjetunion 11, 18 (1937)].
Effect of nanoscale surface roughness on transverse energy spread from GaAs photocathodes
Authors: Karkare Siddharth , Bazarov Ivan
Published: March 2011

High quantum yield, low transverse energy spread, and prompt response time make GaAs activated to negative electron affinity an ideal candidate for a photocathode in high brightness photoinjectors. Even after decades of investigation, the exact mechanism of electron emission from GaAs is not well understood. We show that a nanoscale surface roughness can affect the transverse electron spread from GaAs by nearly an order of magnitude and explain the seemingly controversial experimental results obtained so far. This model can also explain the measured dependence of transverse energy spread on the wavelength of incident light.
Angular momentum at null infinity in five dimensions
Authors: Tanabe Kentaro , Tanahashi Norihiro , Shiromizu Tetsuya
Published: March 2011

In this paper, using the Bondi coordinates, we discuss the angular momentum at null infinity in five dimensions and address the Poincare covariance of the Bondi mass and angular momentum. We also show the angular momentum loss/gain law due to gravitational waves. In four dimensions, the angular momentum at null infinity has the supertranslational ambiguity and then it is known that we cannot construct well-defined angular momentum there. On the other hand, we would stress that we can define angular momentum at null infinity without any ambiguity in higher dimensions. This is because of the nonexistence of supertranslations in higher dimensions.
N site ordering effect on partially ordered Fe16N2
Authors: Ji Nian , Allard Lawrence F. , Lara-Curzio Edgar , Wang Jian-Ping
Published: March 2011

Partially ordered Fe16N2 thin films have been fabricated on Fe (001)-buffered GaAs (001) single-crystal substrates by a facing target sputtering process. The saturation magnetization has been systematically investigated as a function of N site ordering in partially ordered Fe16N2 thin films, which is found to be increased monotonically with the increase in the N site ordering parameter, reaching up to 2.68 T at high ordering case. A model discussion is provided based on the partial localization of 3d electron states in this material system, which successfully rationalizes the formation of the giant saturation magnetization in chemically ordered Fe16N2. We further demonstrate that the average magnetic moment of partially ordered Fe16N2 sensitively depends on the special arrangement of Fe6N clusters, which is the key to realize high magnetic moment in this material system.
Characterization of write-once blu-ray disk containing Cu–Al/Si recording layer using transmission electron microscopy
Authors: Mai Hung-Chuan , Hsieh Tsung-Eong , Jeng Shiang-Yao
Published: March 2011

Microstructure change in write-once blu-ray disk containing Cu–Al/Si recording layer was investigated by transmission electron microscopy. Nanoscale crystallites were found to comprise of the Cu–Al/Si recording layer before and after signal writing and the energy dispersive spectroscopy revealed insignificant composition fluctuation in disk sample. Analytical results indicated the signal properties of disk samples are correlated with a moderate improvement of crystallinity and the formation of Cu and Si solid-solution phases due to element mixing in mark area, rather than the formation of Cu3Si silicide and recrystallization of recording layer as reported by previous studies.
Spectral and temporal behavior of an alkali metal plasma extreme ultraviolet source for surface morphology applications
Authors: Higashiguchi Takeshi , Yamaguchi Mami , Otsuka Takamitsu , Terauchi Hiromitsu , Yugami Noboru , Yatagai Toyohiko , D’Arcy Rebekah , Dunne Padraig , O’Sullivan Gerry
Published: March 2011

We have characterized the emission spectrum and temporal history of a pure potassium plasma. Strong broadband emission was observed around 40 nm due to 3s−3p, 3p−3d, and 3d−4f transitions in ions ranging from K2+ to K4+ at a time-averaged electron temperature of about 12 eV. The temporal behavior of this emission strongly follows the recombination phase in the laser-produced plasma and it was reproduced by a hydrodynamic simulation of the potassium plasma which accounted for atomic processes.
Nanometer-scale molecular deposition using the surface Plasmon polariton interference field on a metal film
Authors: Yin Yaling , Li Tao , Xu Ping , Jin Hua , Zhu Shining
Published: March 2011

We explore the possibility of using the surface plasmon polariton interference field to deposit neutral molecules onto a silver film perforated with two double-slits. The Monte Carlo simulated results show that the deposited molecular pattern is the periodic line array with a width resolution of ∼10 nm and a period of 530 nm when the molecular beam is well-collimated. Dependences of the deposition resolution on the system parameters, the potential applications and improvements are also discussed in some detail.
Mesoporous silica nanoparticles encapsulating Gd2O3 as a highly efficient magnetic resonance imaging contrast agent
Authors: Li Shuang , liu Huan , Li Li , Luo Ning-Qi , Cao Ri-Hui , Chen Di-Hu , Shao Yuan-Zhi
Published: March 2011

The water-adsorptive capabilities of Gd2O3@MCM-41 as contrast agents with various gadolinium additions were evaluated by molecular dynamic simulation, which indicates that increasing gadolinum leads to the decrease in water molecules adsorbed on the surfaces of mesoporous silica and Gd2O3 nanocluster. Gd2O3@MCM-41 nanoparticles were synthesized by a one-step method. The measured microstructure and water-adsorptive capability of Gd2O3@MCM-41 consist with their simulated counterparts. The observation disclosed that the nanoparticles injected within mice were distributed in their liver and tumor. The enhancement of in vivo magnetic resonance imaging was detected in the tumor and inferior vena cava of the mice contrasted with Gd2O3@MCM-41.
Order-of-magnitude reduction of carrier lifetimes in [100] n-type GaAs shock-compressed to 4 GPa
Authors: Grivickas P. , McCluskey M. D. , Gupta Y. M.
Published: March 2011

Dynamics of excess carriers, following a short excitation pulse, were recorded in shock-compressed [100] GaAs:Te to 4 GPa using time- and spectral-resolved photoluminescence (PL) measurements. PL signals extending over five orders of magnitude and comprising several recombination mechanisms were detected in single-event experiments. In marked contrast to earlier hydrostatic pressure results, a linear lifetime reduction was observed under uniaxial strain. The present results suggest that the lifetime reaches a minimum at the direct-to-indirect transition.
Competing effects of magnetocrystalline anisotropy and exchange bias in epitaxial Fe/IrMn bilayers
Authors: Zhang Wei , Bowden Mark E. , Krishnan Kannan M.
Published: March 2011

We systematically investigated the possible magnetization reversal behavior in well-characterized, epitaxial, Fe/IrMn exchange-biased bilayers as a function of the antiferromagnetic (AF) layer thickness. Several kinds of multistep loops were observed for the samples measured at various field orientations. The angular dependence of the switching fields, observed using longitudinal and transverse magneto-optic Kerr effect, were shown to depend on the competition between the magnetocrystalline anisotropy and the exchange bias (EB). A modified “effective field” model was applied to quantitatively describe the evolution of the magnetic behavior and correctly predict the occurrence of different magnetic switching processes. The dependence of the effective anisotropy fields on the AF layer thickness directly reflects the competing effects of the pinned and rotatable AF spins at the EB interface.
Experimental demonstration of efficient pulsed terahertz emission from a stacked GaAs/AlGaAs p-i-n-i heterostructure
Authors: Lisauskas A. , Reklaitis A. , Venckevičius R. , Kašalynas I. , Valušis G. , Grigaliūnaitė–Vonsevičienė G. , Maestre H. , Schmidt J. , Blank V. , Thomson M. D. , Roskos H. G. , Köhler K.
Published: March 2011

The pulsed optoelectronic terahertz emitter based on a δ-doped p-i-n-i GaAs/AlxGa1−xAs heterostructure, which was suggested by Reklaitis [Phys. Rev. B 77, 153309 (2008)], is investigated experimentally. It is shown that the heterostructure can serve as efficient antenna- and bias-free surface emitter. Its power exceeds the emission from InGaAs and InAs surfaces for optical excitation fluences below 0.7 μJ/cm2 at 82 MHz pulse repetition rate, respectively, 7 μJ/cm2 at 1 kHz, with potential for further improvement by carrier recombination management.
Low-temperature synthesis of large-area graphene-based transparent conductive films using surface wave plasma chemical vapor deposition
Authors: Kim Jaeho , Ishihara Masatou , Koga Yoshinori , Tsugawa Kazuo , Hasegawa Masataka , Iijima Sumio
Published: March 2011

We present a low-temperature (300–400 °C), large-area (23 cm×20 cm) and efficient synthesis method for graphene-based transparent conductive films using surface wave plasma chemical vapor deposition. The films consist of few-layer graphene sheets. Their transparency and conductivity characteristics make them suitable for practical electrical and optoelectronic applications, which have been demonstrated by the proper operation of a touch panel fabricated using the films. The results confirm that our method could be suitable for the industrial mass production of macroscopic-scale graphene-based films.
Strain engineering of band offsets in Si/Ge core-shell nanowires
Authors: Huang Shouting , Yang Li
Published: March 2011

We present first-principles studies on how to engineer band lineups of nanosized radial heterojunctions, Si/Ge core-shell nanowires. Our calculation reveals that band offsets of these one-dimensional nanostructures can be tailored by applying the axial strain. In particular, the valence band offset can be efficiently tuned in a wide range and even be diminished with applied strain. Two mechanisms contributing to this strain engineering of band offsets are discussed. Our proposed approach to control band offsets in nanosized heterojunctions may be of practical interest for nanoelectronics and photovoltaic applications.
Generalized matching criterion for electrostatic ion solitary propagations in quasineutral magnetized plasmas
Authors: Akbari-Moghanjoughi M.
Published: March 2011

Based on the magnetohydrodynamics model, an exact arbitrary-amplitude general solution is presented for oblique propagation of solitary excitations in two- and three-component quasineutral magnetoplasmas, adopting the standard pseudopotential approach. It is revealed that the necessary matching criterion of existence of such oblique nonlinear propagations in two- and three-fluid magnetoplasmas possesses global features. These features are examined for the cases of electron-ion and electron-positron-ion magnetoplasmas with diverse equations of state. This study also reveals that for electron-ion magnetoplasmas with plasma frequencies larger than the cyclotron frequency (B0<0.137n0) a critical angle of βcr=arccos[B0/(0.137n0)] exists at which propagation of solitary excitation is not possible. The Coriolis effect on allowed soliton matching condition in rotating magnetoplasmas is also considered as an extension to this work. Current investigation can have important implications for nonlinear wave dynamics in astrophysical as well as laboratory magnetoplasmas.
Hydrothermal growth of single crystals of the quantum magnets: Clinoatacamite, paratacamite, and herbertsmithite
Authors: Chu Shaoyan , Müller Peter , Nocera Daniel G. , Lee Young S.
Published: March 2011

We present a hydrothermal method for growing millimeter-sized crystals of the quantum magnets with formula Cu4−xZnx(OH)6Cl2: clinoatacamite (x=0), paratacamite (0.33<x<1) and herbertsmithite (x=1). These highly pure single crystals have been characterized by x-ray diffraction, chemical analysis, Raman spectroscopy, and magnetic susceptibility measurements. This synthesis success opens the door for detailed investigations of the magnetic ground-state properties of these compounds.
Evidence of defect-induced ferromagnetism and its “switch” action in pristine bulk TiO2
Authors: Singhal R. K. , Kumar Sudhish , Kumari P. , Xing Y. T. , Saitovitch E.
Published: March 2011

In this work, we demonstrate that room temperature ferromagnetism can be induced in pristine anatase TiO2 paramagnetic bulk powder through extended hydrogenation. Defect complexes, Ti3+–VO (Ti3+ ions accompanied by oxygen vacancies) are clearly identified in hydrogenated TiO2 by combining x-ray diffraction and photoemission spectroscopy. The observed ferromagnetic ordering is reversible that can be switched between “on” and “off” by inducing or removing, respectively, these defect complex. We convincingly elucidate that the factors (i) Ti 3d–O 2p hybridization (iii) F+ centers (the electrons in singly occupied oxygen vacancies), and (iii) oxygen vacancy assisted fragmentation of grains, compositely contribute to the ferromagnetic ordering.
Magnetic field tuning of a quantum dot strongly coupled to a photonic crystal cavity
Authors: Kim Hyochul , Shen Thomas C. , Sridharan Deepak , Solomon Glenn S. , Waks Edo
Published: March 2011

We apply magnetic fields of up to 7 T to an indium arsenide quantum dot (QD) strongly coupled to a photonic crystal cavity. The field lifts the degeneracy of QD exciton spin states, and tune their emission energy by a combination of diamagnetic and Zeeman energy shifts. We use magnetic field tuning to shift the energies of the two exciton spin states to be selectively on resonance with the cavity. Strong coupling between the cavity and both states is observed. Magnetic field tuning enables energy shifts as large as 0.83 meV without significant degradation of the QD-cavity coupling strength.
Antiphase boundaries in Ba0.75Sr0.25TiO3 epitaxial film grown on (001) LaAlO3 substrate
Authors: Wang Y. Q. , Liang W. S. , Petrov Peter Kr. , Alford Neil McN.
Published: March 2011

Ba 0.75 Sr 0.25 TiO 3 film was epitaxially grown on a (001) LaAlO3 substrate using single-target pulsed laser deposition. The microstructure of the epitaxial film was investigated by conventional and high-resolution transmission electron microscopy. Apart from dislocations and stacking faults, two different kinds of antiphase boundaries, one being straight, and the other being zig-zagged, have been observed. The formation mechanism of these antiphase boundaries is discussed.