bluuebunny/crossref_metadata_2025 huggingface dataset:
A circular equilibrium model for local gyrokinetic simulations of ion temperature gradient fluctuations in reversed field pinches
Authors: Tangri Varun , Terry P. W. , Waltz R. E.
Published: May 2011

A simple large-aspect-ratio (R0/r) circular equilibrium model is developed for low-beta reversed field pinch (RFP) geometry. The model is suitable for treating small scale instability and turbulent transport driven by ion temperature gradient (ITG) and related electron drift modes in gyrokinetic simulations. The equilibrium model is an RFP generalization of the common tokamak s-α model to small safety factor (q), where the poloidal field dominates the toroidal field. The model accommodates the RFP toroidal field reversal (where q vanishes) by generalizing the cylindrical force-free Bessel function model (BFM) [J. B. Taylor, Phys. Rev. Lett. 33, 1139 (1974)] to toroidal geometry. The global equilibrium can be described in terms of the RFP field reversal and pinch parameters [F,Θ]. This new toroidal Bessel function model (TBFM) has been incorporated into the gyrokinetic code GYRO [J. Candy and R. E. Waltz, J.Comput. Phys. 186, 545 (2003)] and used here to explore local electrostatic ITG adiabatic electron instability rates for typical low-q RFP parameters.
Silicon colloids: A new enabling nanomaterial
Authors: Meseguer F. , Fenollosa R. , Rodriguez I. , Xifré-Pérez E. , Ramiro-Manzano F. , Garín M. , Tymczenko M.
Published: May 2011

We have recently developed a new type of silicon structure that we refer to as a silicon colloid. This new material consists of almost perfectly spherical silicon micro- and nanoparticles with a very smooth surface. They are able to trap light very efficiently in a large-span frequency range covering the visible to the far infrared regions. Silicon colloids can be thought of as a completely new material for scientific and technological purposes, with manifold applications covering electronics, photonics, cosmetics, or paints, among others. Here, we report on the synthesis of polycrystalline, amorphous, and porous silicon colloids, as well as their optical properties, some applications concerning light filters, and photonic bonding.
Next-generation multijunction solar cells: The promise of II-VI materials
Authors: Garland J. W. , Biegala T. , Carmody M. , Gilmore C. , Sivananthan S.
Published: May 2011

High concentration photovoltaic (HCPV) systems offer the highest photovoltaic (PV) conversion efficiencies. Also, as production is beginning to ramp up, HCPV is becoming cost competitive with thin-film poly-CdTe and crystalline Si systems in high solar insolation regions. High solar concentrations, X ∼ 500, are used to increase cell efficiencies and greatly reduce the cell area per unit of incident solar radiation, thereby greatly reducing the cell cost per watt. The monolithic three-junction (3J) solar cells presently used in HCPV systems typically consist of two epitaxial III-V homojunctions, such as GaInP and GaInAs, grown on an active Ge substrate by metal-organic chemical vapor deposition (MOCVD). The III-V bandgaps are chosen to match the currents generated in each junction and minimize the energy lost to thermalization of the electron-hole pairs generated, subject to the constraint of approximate lattice matching. We propose using cells consisting of one or more CdTe-based II-VI homojunctions grown on large-area active Si substrates by high-throughput MBE or a less expensive high-vacuum deposition technique as an alternative to III-V based multijunction cells grown by MOCVD. The bandgap of Si is more optimal than that of Ge for two-junction (2J) or 3J cells, and lattice mismatches affect the efficiencies of such cells only slightly, which allows greater freedom in the choice of bandgaps, and thus the potential for higher efficiencies. Also, such cells could be manufactured at a much lower cost due to the larger area, much lower cost and superior mechanical properties of Si substrates as compared to Ge substrates. The much lower cell cost also would enable medium concentration PV systems that would require more cell area, but with simplified, less expensive tracking and optics, resulting in lower overall system costs. Promising initial results from material-property measurements and single-junction and 2J CdZnTe/Si cell characterization results are given. Both the promise of the proposed technology and the challenges it faces are discussed.
Pb loss in Pb(Zr,Ti)O3 ceramics observed by in situ ionic conductivity measurements
Authors: Donnelly Niall J. , Randall Clive A.
Published: May 2011

Analysis of the impedance spectra of Nb-doped Pb(Zr,Ti)O3 (PZT) embedded capacitors revealed that the ionic conductivity increased monotonically during annealing at 700 °C. Furthermore, the rate of increase was lowered by a reduction in the ambient pO2. The results could be explained by a model in which oxygen vacancies are generated as a consequence of Pb evaporation from the PZT. At 700 °C, this process is most likely limited by surface kinetics rather than Pb bulk diffusion. It was shown that the Pb loss could be completely recovered by annealing in a high activity Pb source with a commensurate reduction in oxygen vacancy concentration. The electronic conductivity was predominantly p-type and was relatively unaffected by the Pb loss throughout the course of the experiment.
A computational investigation of the impact of aberrated Gaussian laser pulses on electron beam properties in laser-wakefield acceleration experiments
Authors: Cummings P. , Thomas A. G. R.
Published: May 2011

Critical to the performance of any future accelerator based on the laser wakefield accelerator is the response of the system to perturbations from ideal. In this paper, we use particle-in-cell simulation using a modified version of the OSIRIS 2.0 framework to demonstrate that comatic optical aberrations in a nominally Gaussian laser pulse are self-corrected by the plasma response, leading to stable propagation and therefore little variation in peak energy, energy spread, or peak current of the accelerated bunch, even for serious aberrations. However, the comatic aberration does lead to enhanced transverse beam emittance in the direction of the coma. Although this may be deleterious to the performance of an accelerator, one useful outcome is that the increased oscillation amplitude of electrons in the wake structure may lead to increased synchrotron radiation emission, which would be partially polarized in the direction of coma.
Potential profile near singularity point in kinetic Tonks-Langmuir discharges as a function of the ion sources temperature
Authors: Kos L. , Tskhakaya D. D. , Jelić N.
Published: May 2011

A plasma–sheath transition analysis requires a reliable mathematical expression for the plasma potential profile Φ(x) near the sheath edge xs in the limit ɛ≡λD/ℓ=0 (where λD is the Debye length and ℓ is a proper characteristic length of the discharge). Such expressions have been explicitly calculated for the fluid model and the singular (cold ion source) kinetic model, where exact analytic solutions for plasma equation (ɛ=0) are known, but not for the regular (warm ion source) kinetic model, where no analytic solution of the plasma equation has ever been obtained. For the latter case, Riemann [J. Phys. D: Appl. Phys. 24, 493 (1991)] only predicted a general formula assuming relatively high ion-source temperatures, i.e., much higher than the plasma-sheath potential drop. Riemann’s formula, however, according to him, never was confirmed in explicit solutions of particular models (e.g., that of Bissell and Johnson [Phys. Fluids 30, 779 (1987)] and Scheuer and Emmert [Phys. Fluids 31, 3645 (1988)]) since “the accuracy of the classical solutions is not sufficient to analyze the sheath vicinity” [Riemann, in Proceedings of the 62nd Annual Gaseous Electronic Conference, APS Meeting Abstracts, Vol. 54 (APS, 2009)]. Therefore, for many years, there has been a need for explicit calculation that might confirm the Riemann’s general formula regarding the potential profile at the sheath edge in the cases of regular very warm ion sources. Fortunately, now we are able to achieve a very high accuracy of results [see, e.g., Kos et al., Phys. Plasmas 16, 093503 (2009)]. We perform this task by using both the analytic and the numerical method with explicit Maxwellian and “water-bag” ion source velocity distributions. We find the potential profile near the plasma–sheath edge in the whole range of ion source temperatures of general interest to plasma physics, from zero to “practical infinity.” While within limits of “very low” and “relatively high” ion source temperatures, the potential is proportional to the space coordinate powered by rational numbers α=1/2 and α=2/3, with medium ion source temperatures. We found α between these values being a non-rational number strongly dependent on the ion source temperature. The range of the non-rational power-law turns out to be a very narrow one, at the expense of the extension of α=2/3 region towards unexpectedly low ion source temperatures.
Inner/outer layer interactions in turbulent boundary layers: A refined measure for the large-scale amplitude modulation mechanism
Authors: Bernardini Matteo , Pirozzoli Sergio
Published: June 2011

The amplitude modulation (AM) imparted by the outer layer large-scale motions on the near-wall turbulence is studied through direct numerical simulation of compressible boundary layer flow at moderate Reynolds number. Mathis et al. [J. Fluid Mech. 628, 311 (2009)] introduced an amplitude modulation coefficient to quantify this effect, whereby carrier and modulated signals are decoupled through a procedure based on the Hilbert transform of the streamwise velocity signals. However, Schlatter and Örlü [Phys. Fluids 22, 051704 (2010)] have recently shown that a non-zero amplitude modulation coefficient is closely associated to a non-zero value of the velocity skewness, and therefore, it does not necessarily reflect genuine physics. In this paper, the analysis is extended through systematic use of the two-point amplitude modulation correlation, which is shown to be a refined measure of the top-down influence of large-scale outer events on the inner part of the boundary layer.
Reactive instabilities of lower hybrid-like waves in regions with parallel currents
Authors: Verdon A. L. , Cairns Iver H. , Melrose D. B. , Robinson P. A.
Published: May 2011

The dispersion and reactive instabilities of obliquely propagating waves near the lower hybrid (LH) frequency are studied in plasma carrying a current parallel to the magnetic field. Possible applications of these instabilities include magnetic reconnection regions, where LH-like waves may accelerate and heat both ions and electrons. In plasmas with a bulk drift of electrons relative to the ions at speed vd along the magnetic field, the forward and backward propagating LH modes are shown to be replaced by four LH-like modes. Reactive instabilities are discovered here for a forward propagating mode with Re(ω)≈k∥vd/2 and a backward propagating mode with Re(ω) <~5Ωi. Numerical warm, fully electromagnetic, kinetic calculations are compared with cold plasma calculations and agree well, confirming that the discovered instabilities are reactive. In the cold plasma limit, the forward and backward propagating instabilities occur for vd below and above some thresholds, respectively.
Large-eddy simulation of a very large wind farm in a stable atmospheric boundary layer
Authors: Lu Hao , Porté-Agel Fernando
Published: June 2011

When deployed as large arrays, wind turbines significantly interact among themselves and with the atmospheric boundary layer. In this study, we integrate a three-dimensional large-eddy simulation with an actuator line technique to examine the characteristics of wind-turbine wakes in an idealized wind farm inside a stable boundary layer (SBL). The wind turbines, with a rotor diameter of 112m and a tower height of 119m, were “immersed” in a well-known SBL case that bears a boundary layer height of approximately 175m. Two typical spacing setups were adopted in this investigation. The super-geostrophic low-level jet near the top of the boundary layer was eliminated owing to the energy extraction and the enhanced mixing of momentum. Non-axisymmetric wind-turbine wakes were observed in response to the non-uniform incoming turbulence, the Coriolis effect, and the rotational effects induced by blade motion. The Coriolis force caused a skewed spatial structure and drove a part of the turbulence energy away from the center of the wake. The SBL height was increased, while the magnitude of the surface momentum flux was reduced by more than 30%, and the magnitude of the surface buoyancy flux was reduced by more than 15%. The wind farm was also found to have a strong effect on vertical turbulent fluxes of momentum and heat, an outcome that highlights the potential impact of wind farms on local meteorology.
Self-similar solitary wave family in Bessel lattice
Authors: Cai Zebin , Liang Jianchu , Xia Xiongping , Jiang Yue , Jin Haiqin , Yi Lin
Published: May 2011

We focus on the formation and propagation of self-similar solitary wave family in Kerr nonlinear media with external Bessel lattice. A novel analytical solitary wave solution to (3+1)-dimensional Gross-Pitaevskii equation with varying coefficients and an external potential is obtained. The components of solitary wave family are differentiated by three quantum parameters. The properties and the stability of the solitary wave family are discussed in detail.
Superconductivity of a quantum cylinder
Authors: Eminov P. A. , Uldin A. A.
Published: June 2011

The thermodynamic potential of a superconducting quantum cylinder is calculated. The dependence of the critical temperature and heat capacity of the superconducting system on the surface electron density and nanotube radius is studied. It is shown that the critical temperature oscillates with variations in a parameter equal to the ratio of the Fermi energy to the dimensional confinement energy.
Preparation of CdBa2Cu3O7−δ superconducting ceramic and a study of its electrical properties
Authors: Aliev V. M. , Aliev S. A. , Ragimov S. S. , Sultanov G. J. , Tairov B. A.
Published: June 2011

A new superconducting ceramic material CdBa2Cu3O7−δ is obtained. It is found that the superconducting transition (at 86 K) is retained when yttrium is fully replaced by cadmium in the Y-Ba-Cu-O system. X-ray diffraction studies show that the crystalline structure is unchanged and the identified peaks coincide when Y is replaced by Cd in YBa2Cu3O7−δ. Besides a stable superconducting transition, a phase transition near 275 K was seen in the temperature dependence of the specific resistivity which shifted toward lower temperatures (252 K) and then disappeared completely over repeated measurement cycles. The thermal conductivity k of YBa2Cu3O7−δ and CdBa2Cu3O7−δ was found to vary little with temperature up to the superconducting transition. Substituting Cd for Y in the initial HTSC material led to a substantial increase in the lattice thermal conductivity. Measurements of the thermal emf showed that it is positive in YBa2Cu3O7−δ and negative in CdBa2Cu3O7−δ.
Modulational instability of ion acoustic wave with warm ions in electron-positron-ion plasmas
Authors: Mahmood S. , Siddiqui Sadiya , Jehan Nusrat
Published: May 2011

The nonlinear amplitude modulation of ion acoustic wave is studied in the presence of warm ions in unmagnetized electron-positron-ion plasmas. The Krylov-Bogoliubov-Mitropolsky (KBM) method is used to derive the nonlinear Schrödinger equation. The dispersive and nonlinear coefficients are obtained which depends on the ion temperature and positron density in electron-positron-ion plasmas. The modulationally stable and unstable regions are studied numerically for a wide range of wave number. It is found that both ion temperature and positron density play a significant role in the formation of bright and dark envelope solitons in electron-positron-ion plasmas.
Well-posedness and long-time behavior of Lipschitz solutions to generalized extremal surface equations
Authors: Peng Yue-Jun , Yang Yong-Fu
Published: May 2011

We show that in one space dimension, Lipschitz solutions of generalized extremal surface equations are equivalent to entropy solutions in \documentclass[12pt]{minimal}\begin{document}$L^\infty ({\bb R})$\end{document}L∞(R) of a non-strictly hyperbolic system of conservation laws. We obtain an explicit representation formula and the uniqueness of the entropy solutions to the Cauchy problem of the system. By using this formula, we also obtain the convergence and convergence rates as t → +∞ of the entropy solutions to explicit traveling waves in the \documentclass[12pt]{minimal}\begin{document}$L^1({\bb R})$\end{document}L1(R) norm. Moreover, when initial data are constants outside of a finite space interval, the entropy solutions become the explicit traveling waves after a finite time. Finally, we prove L1 stabilities of the entropy solutions.
Self-similar magnetic structures during the vortex-glass to vortex-liquid transition of type II superconductors
Authors: Krasnyuk I. B. , Taranets R. M. , Yurchenko V. M.
Published: June 2011

We examine the response to an external magnetic field by a multi-layer superconductor with an electrical resistance ρff(b)αbσ, where b is the dimensionless magnetic induction and σ is a parameter characterizing the ratio of the pinning activation energy to the energy of thermal fluctuations. When σ > 1 the sample is in the vortex glass phase, when 0 < σ < 1, it is in the vortex liquid phase, and a vortex glass to vortex liquid phase transition takes place at σ = 1. In the vortex glass phase, the magnetic field penetrates into the superconductor in the form of a self-similar wave. At all times it penetrates to a finite depth and its front moves at a finite velocity which depends on the parameters of the problem, such as the rate of pumping by the external magnetic field. In the vortex liquid phase the magnetic field penetrates to an infinite depth. Thus, the magnetic field penetrates to an infinite depth in the superconductor during a transition from the vortex glass phase into the vortex liquid phase.
Nonlinear ion-acoustic structures in dusty plasma with superthermal electrons and positrons
Authors: El-Tantawy S. A. , El-Bedwehy N. A. , Moslem W. M.
Published: May 2011

Nonlinear ion-acoustic structures are investigated in an unmagnetized, four-component plasma consisting of warm ions, superthermal electrons and positrons, as well as stationary charged dust impurities. The basic set of fluid equations is reduced to modified Korteweg-de Vries equation. The latter admits both solitary waves and double layers solutions. Numerical calculations indicate that these nonlinear structures cannot exist for all physical parameters. Therefore, the existence regions for both solitary and double layers excitations have been defined precisely. Furthermore, the effects of temperature ratios of ions-to-electrons and electrons-to-positrons, positrons and dust concentrations, as well as superthermal parameters on the profiles of the nonlinear structures are investigated. Also, the acceleration and deceleration of plasma species have been highlight. It is emphasized that the present investigation may be helpful in better understanding of nonlinear structures which propagate in astrophysical environments, such as in interstellar medium.
A shallow water model for magnetohydrodynamic flows with turbulent Hartmann layers
Authors: Pothérat Alban , Schweitzer Jean-Philippe
Published: May 2011

We establish a shallow water model for flows of electrically conducting fluids in homogeneous static magnetic fields that are confined between two parallel planes where turbulent Hartmann layers are present. This is achieved by modelling the wall shear stress in these layers using Prandtl’s mixing length model, as did by Alboussière and Lingwood [Phys. Fluids 12(6), 1535 (2000)]. The idea for this new model arose from the failure of previous shallow water models that assumed a laminar Hartmann layer to recover the correct amount of dissipation found in some regimes of the MATUR experiment. This experiment, conducted by Messadek and Moreau [J. Fluid Mech. 456, 137 (2002)], consisted of a thin layer of mercury electrically driven in differential rotation in a transverse magnetic field. Numerical simulations of our new model in the configuration of this experiment allowed us to recover experimental values of both the global angular momentum and the local velocity up to a few percent when the Hartmann layer was in a sufficiently well developed turbulent state. We thus provide an evidence that the unexplained level of dissipation observed in MATUR in these specific regimes was caused by turbulence in the Hartmann layers. A parametric analysis of the flow, made possible by the simplicity of our model, also revealed that turbulent friction in the Hartmann layer prevented quasi-2D turbulence from becoming more intense and limited the size of the large scales.
Refocusing of light rays in space-time
Authors: Kinlaw Paul A.
Published: May 2011

We discuss several definitions of refocusing of null-geodesics in a strongly causal space-time and prove their equivalence. A space-time which is strongly refocusing at a point x is refocusing at x. Examples are provided of space-times which are refocusing at a point x but not strongly refocusing at x. However, they are strongly refocusing at other points. It is unknown if refocusing implies strong refocusing. Furthermore, the set of points at which a strongly causal space-time is refocusing is closed. A space-time covering of a refocusing space-time is also refocusing. This generalizes the result of Chernov and Rudyak [Comm. Math. Phys. 279, 309 (2008)] for globally hyperbolic space-times. As a consequence of the recent results on refocusing and of the Elliptization Conjecture proved by Perelman, any globally hyperbolic refocusing space-time of dimension ⩽4 admits a strongly refocusing metric.
Acoustic oscillations of spherical metallic nanoparticles in dielectric media driven by ultrashort laser pulses
Authors: Grigorchuk N. I.
Published: June 2011

A theory is developed for the acoustic oscillations of small-sized spherical metallic particles in a dielectric medium driven by ultrashort laser pulses. Analytic expressions are obtained for the amplitude and power of the longitudinal spherical acoustic oscillations as functions of the density and elastic properties of the medium, the laser pulse duration, electron temperature, particle radii, and electron-phonon coupling constant. The factors affecting the dynamics of the damping of the power of these waves are studied in detail and illustrated for the example of Au, Ag, and Cu particles embedded in a plexiglas matrix.
He
+
O
2
+
H
2
O
plasmas as a source of reactive oxygen species
Authors: Liu D. X. , Iza F. , Wang X. H. , Kong M. G. , Rong M. Z.
Published: June 2011

The effect of water in the chemistry of atmospheric-pressure He+O2 plasmas is studied by means of a comprehensive global model. Water enables the generation of reactive oxygen species (ROS) cocktails that are rich not only in O, O2∗, and O3 but also in OH and H2O2. Due to its polar nature, water also leads to cluster formation, possibly affecting the plasma dynamics. Since the lifetime of many of the ROS is short, the plasma chemistry plays two roles: (i) direct interaction with superficial cells and (ii) triggering of a secondary chemistry that propagates the plasma treatment to regions away from the plasma-surface interface.
Multipactor susceptibility on a dielectric with a bias dc electric field and a background gas
Authors: Zhang Peng , Lau Y. Y. , Franzi Matthew , Gilgenbach R. M.
Published: May 2011

We use Monte Carlo simulations and analytical calculations to derive the condition for the onset of multipactor discharge on a dielectric surface at various combinations of the bias dc electric field, rf electric field, and background pressures of noble gases, such as Argon. It is found that the presence of a tangential bias dc electric field on the dielectric surface lowers the magnitude of rf electric field threshold to initiate multipactor, therefore plausibly offering robust protection against high power microwaves. The presence of low pressure gases may lead to a lower multipactor saturation level, however. The combined effects of tangential dc electric field and external gases on multipactor susceptibility are presented.
Effective surface motion on a reactive cylinder of particles that perform intermittent bulk diffusion
Authors: Chechkin Aleksei V. , Zaid Irwin M. , Lomholt Michael A. , Sokolov Igor M. , Metzler Ralf
Published: May 2011

In many biological and small scale technological applications particles may transiently bind to a cylindrical surface. In between two binding events the particles diffuse in the bulk, thus producing an effective translation on the cylindrical surface. We here derive the effective motion on the surface allowing for additional diffusion on the cylindrical surface itself. We find explicit solutions for the number of adsorbed particles at one given instant, the effective surface displacement, as well as the surface propagator. In particular sub- and superdiffusive regimes are found, as well as an effective stalling of diffusion visible as a plateau in the mean squared displacement. We also investigate the corresponding first passage problem.
Conical intersections in solution: Formulation, algorithm, and implementation with combined quantum mechanics/molecular mechanics method
Authors: Cui Ganglong , Yang Weitao
Published: May 2011

The significance of conical intersections in photophysics, photochemistry, and photodissociation of polyatomic molecules in gas phase has been demonstrated by numerous experimental and theoretical studies. Optimization of conical intersections of small- and medium-size molecules in gas phase has currently become a routine optimization process, as it has been implemented in many electronic structure packages. However, optimization of conical intersections of small- and medium-size molecules in solution or macromolecules remains inefficient, even poorly defined, due to large number of degrees of freedom and costly evaluations of gradient difference and nonadiabatic coupling vectors. In this work, based on the sequential quantum mechanics and molecular mechanics (QM/MM) and QM/MM-minimum free energy path methods, we have designed two conical intersection optimization methods for small- and medium-size molecules in solution or macromolecules. The first one is sequential QM conical intersection optimization and MM minimization for potential energy surfaces; the second one is sequential QM conical intersection optimization and MM sampling for potential of mean force surfaces, i.e., free energy surfaces. In such methods, the region where electronic structures change remarkably is placed into the QM subsystem, while the rest of the system is placed into the MM subsystem; thus, dimensionalities of gradient difference and nonadiabatic coupling vectors are decreased due to the relatively small QM subsystem. Furthermore, in comparison with the concurrent optimization scheme, sequential QM conical intersection optimization and MM minimization or sampling reduce the number of evaluations of gradient difference and nonadiabatic coupling vectors because these vectors need to be calculated only when the QM subsystem moves, independent of the MM minimization or sampling. Taken together, costly evaluations of gradient difference and nonadiabatic coupling vectors in solution or macromolecules can be reduced significantly. Test optimizations of conical intersections of cyclopropanone and acetaldehyde in aqueous solution have been carried out successfully.
Bolometric and nonbolometric radio frequency detection in a metallic single-walled carbon nanotube
Authors: Santavicca Daniel F. , Chudow Joel D. , Prober Daniel E. , Purewal Meninder S. , Kim Philip
Published: June 2011

We characterize radio frequency detection in a high-quality metallic single-walled carbon nanotube. At a bath temperature of 77 K, only bolometric (thermal) detection is seen. At a bath temperature of 4.2 K and low bias current, the response is due instead to the electrical nonlinearity of the non-Ohmic contacts. At higher bias currents, the contacts recover Ohmic behavior and the observed response agrees well with the calculated bolometric responsivity. The bolometric response is expected to operate at terahertz frequencies, and we discuss some of the practical issues associated with developing high frequency detectors based on carbon nanotubes.
Coded excitation for infrared non-destructive testing of carbon fiber reinforced plastics
Authors: Mulaveesala Ravibabu , Venkata Ghali Subbarao
Published: May 2011

This paper proposes a Barker coded excitation for defect detection using infrared non-destructive testing. Capability of the proposed excitation scheme is highlighted with recently introduced correlation based post processing approach and compared with the existing phase based analysis by taking the signal to noise ratio into consideration. Applicability of the proposed scheme has been experimentally validated on a carbon fiber reinforced plastic specimen containing flat bottom holes located at different depths.
Nuclear spin selective alignment of ethylene and analogues
Authors: Grohmann Thomas , Leibscher Monika
Published: May 2011

We investigate the alignment of ethylene and of some of its analogues via short, non-resonant laser pulses and show that it depends crucially on the nuclear spin of the molecules. We calculate the time-dependent alignment factors of the four nuclear spin isomers of ethylene and analyze them by comparison with the symmetric top molecule allene. Moreover, we explore how the nuclear spin selective alignment depends on the asymmetry of the molecules and on the intensity of the laser pulse. As an application, we discuss how nuclear spin selective alignment could be applied in order to separate different isotopomers of ethylene.
Multidirectional surface-wave splitters
Authors: Zhou Yong Jin , Cui Tie Jun
Published: June 2011

We propose a multidirectional surface-wave splitter excited by a cylindrical wire. Such a splitter could function as a plasmonic wavelength-division multiplexer, since electromagnetic waves at the designed frequencies will be confined and guided along different multiple grating structures that are placed around the cylindrical wire. The experimental verification of the proposed splitter has been implemented in the microwave frequencies. The measurement results have excellent agreements to the full-wave simulations to show the good performance of the splitter. We also propose and simulate a multidirectional surface-wave splitter in the terahertz frequency to validate the concept.
Experimental investigation on line width compression of stimulated Brillouin scattering in water
Authors: Zhang Lei , Zhang Dong , Yang Zhuo , Shi Jinwei , Liu Dahe , Gong Wenping , Fry Edward S.
Published: June 2011

Line width compression of stimulated Brillouin scattering (SBS) in water was investigated experimentally. The results show that, when the water temperature is low, the compressing effect is obvious. However, when the temperature is higher than 25 °C, the line width is almost not compressed in water. Also, the pulse duration compression of SBS was measured simultaneously, and appeared an inherent relation to line width compression. It reveals that the line width can be simply measured by measuring the compressed pulse duration of SBS.
Electric field induced crystallization in phase-change materials for memory applications
Authors: Kohary Krisztian , Wright C. David
Published: June 2011

Emerging electrical memory technologies based on phase-change materials capitalize on a fast amorphous-to-crystalline transition. Recent evidence from measurements of relaxation oscillations and switching statistics in phase-change memory devices indicates the possibility that electric field induced crystal nucleation plays a dominant role in defining the characteristic electrical switching behavior. Here we present a detailed kinetics study of crystallization in the presence of an electric field for the phase-change material Ge2Sb2Te5. We derive quantitative crystallization maps to show the effects of both temperature and electric field on crystallization and we identify field ranges and parameter values where the electric field effects might play a significant role.
Self-heating in piezoresistive cantilevers
Authors: Doll Joseph C. , Corbin Elise A. , King William P. , Pruitt Beth L.
Published: June 2011

We report experiments and models of self-heating in piezoresistive microcantilevers that show how cantilever measurement resolution depends on the thermal properties of the surrounding fluid. The predicted cantilever temperature rise from a finite difference model is compared with detailed temperature measurements on fabricated devices. Increasing the fluid thermal conductivity allows for lower temperature operation for a given power dissipation, leading to lower force and displacement noise. The force noise in air is 76% greater than in water for the same increase in piezoresistor temperature.
High sensitivity magnetometer for measuring the isotropic and anisotropic magnetisation of small samples
Authors: McCollam A. , van Rhee P. G. , Rook J. , Kampert E. , Zeitler U. , Maan J. C.
Published: May 2011

We describe how the full, isotropic and anisotropic, magnetisation of samples as small as tens of micrometers in size can be sensitively measured using a piezoresistive microcantilever and a small, moveable ferromagnet. Depending on the position of the ferromagnet, a strong but highly local field gradient of up to ∼4200 T/m can be applied at the sample or removed completely during a single measurement. In this way, the magnetic force and torque on the sample can be independently determined without moving the sample or cycling the experimental system. The technique can be used from millikelvin temperatures to ∼85 K and in magnetic fields from 2 T to the highest fields available. We demonstrate its application in measurements of the semimagnetic semiconductor Hg1 − xFexSe, where we achieved a moment sensitivity of better than 2.5 × 10−14 J/T for both isotropic and anisotropic components.
Elucidating the interplay between dark current coupling and open circuit voltage in organic photovoltaics
Authors: Erwin Patrick , Thompson Mark E.
Published: June 2011

A short series of alkyl substituted perylenediimides (PDIs) with varying steric bulk are used to demonstrate the relationship between molecular structure, materials properties, and performance characteristics in organic photovoltaics. Devices were made with the structure indium tin oxide/copper phthalocyanine (200 Å)/PDI (200 Å)/bathocuproine (100 Å)/aluminum (1000 Å). We found that PDIs with larger substituents produced higher open circuit voltages (VOC’s) despite the donor acceptor interface gap (ΔEDA) remaining unchanged. Additionally, series resistance was increased simultaneously with VOC the effect of reducing short circuit current, making the addition of steric bulk a tradeoff that needs to be balanced to optimize power conversion efficiency.
Another kinetic mechanism of stabilizing multiple-layer surface steps
Authors: Zhang Ruoxin , Huang Hanchen
Published: June 2011

This letter reports that a large three-dimensional Ehrlich–Schwoebel (3D ES) barrier kinetically stabilizes multiple-layer surface steps. The report is based on (1+1)D lattice kinetic Monte Carlo simulations of Cu{111} surfaces. The larger 3D ES barrier leads to slower diffusion over multiple-layer steps, thereby slower dissociation and higher stability. The higher stability of multiple-layer surface steps, in turn, facilitates the operation of the 3D ES barrier; a positive feedback relationship. The mechanism of kinetically stabilizing multiple-layer surface steps allows another way of controlling surface morphology to promote the growth of either nanorods or smooth thin films.
Estimating the viscoelastic moduli of complex fluids from observation of Brownian motion of a particle confined to a harmonic trap
Authors: Felderhof B. U.
Published: May 2011

A procedure is proposed to estimate the viscoelastic properties of a complex fluid from the behavior of the velocity autocorrelation function of a suspended Brownian particle, trapped in a harmonic potential. The procedure is tested for a model complex fluid with a given frequency-dependent shear viscosity. The analysis shows that the procedure can provide a rather accurate prediction of the viscoelastic properties of the fluid on the basis of experimental data on the velocity autocorrelation function of the trapped Brownian particle in a limited range of time.
Transferable model of water with variable molecular size
Authors: Kiss Péter T. , Baranyai András
Published: June 2011

By decreasing the steepness of the repulsive wing in the intermolecular potential, one can extend the applicability of a water model to the high pressure region. Exploiting this trivial possibility, we published a polarizable model of water which provided good estimations not only of gas clusters, ambient liquid, hexagonal ice, but ice VII at very high pressures as well [A. Baranyai and P. Kiss, J. Chem. Phys. 133, 144109 (2010)10.1063/1.3490660]. This straightforward method works well provided the closest O–O distance is reasonably shorter in the high pressure phase than in hexagonal ice. If these O–O distances are close to each other and we fit the interactions to obtain an accurate picture of hexagonal ice, we underestimate the density of the high-pressure phases. This can be overcome if models use contracted molecules under high external pressure.In this paper we present a method, which is capable to describe the contraction of water molecules under high pressure by using two simple repulsion-attraction functions. These functions represent the dispersion interaction under low pressure and high pressure. The switch function varies between 0 and 1 and portions the two repulsions among the individual particles. The argument of the switch function is a virial-type expression, which can be interpreted as a net force compressing the molecule. We calculated the properties of gas clusters, densities, and internal energies of ambient water, hexagonal ice, ice III, ice VI, and ice VII phases and obtained excellent match of experimental data.
Communication: Rovibrationally selected study of the N2+(X; v+ = 1, N+ = 0−8) + Ar charge transfer reaction using the vacuum ultraviolet laser pulsed field ionization-photoion method
Authors: Chang Yih Chung , Xu Hong , Xu Yuntao , Lu Zhou , Chiu Yu-Hui , Levandier Dale J. , Ng C. Y.
Published: May 2011

By employing an electric field pulsing scheme for vacuum ultraviolet laser pulsed field ionization-photoion (PFI-PI) measurements, we have been able to prepare a rovibrationally selected PFI-PI beam of N2+(v+ = 1, N+) with not only high intensity and high quantum state purity, but also high kinetic energy resolution, allowing absolute total cross sections [σ(v+ = 1, N+)] for the N2+(X; v+ = 1, N+) + Ar, N+ = 0–8 charge transfer reaction to be measured at center-of-mass collision energies (Ecm) down to thermal energies. The σ(v+ = 1, N+ = 0–8) values determined at Ecm = 0.04–10.00 eV are in good agreement with the theoretical predictions based on the Landau-Zener-Stückelberg formulism. Taking into account the experimental uncertainties, the σ(v+ = 1, N+), N+ = 0–8, measured at Ecm = 1.56 eV are found to be independent of N+.
Note: Design of transverse electron gun for electron beam based reactive evaporation system
Authors: Maiti Namita , Barve U. D. , Bhatia M. S. , Das A. K.
Published: May 2011

In this paper design of a 10 kV, 10 kW transverse electron gun, suitable for reactive evaporation, supported by simulation and modeling, is presented. Simulation of the electron beam trajectory helps in locating the emergence aperture after 90o bend and also in designing the crucible on which the beam is finally incident after 270o bend. The dimension of emergence aperture plays a vital role in designing the differential pumping system between the gun chamber and the substrate chamber. Experimental validation is done for beam trajectory by piercing a stainless steel plate at 90o position which is kept above the crucible.
Scattering suppression in plasmonic optics using a simple two-layer dielectric structure
Authors: Bezus E. A. , Doskolovich L. L. , Kazanskiy N. L.
Published: June 2011

We demonstrate that a planar structure consisting of two isotropic dielectric layers can be used to minimize parasitic scattering in plasmonic elements. It is shown using rigorous electromagnetic simulations that the utilization of the proposed structure allows reducing the scattering losses by an order-of-magnitude (1%–2%). The proposed approach can be used for the design of various plasmonic elements such as lenses, reflectors, and plasmonic crystals.
MHD free convection flow of a visco-elastic (Kuvshiniski type) dusty gas through a semi infinite plate moving with velocity decreasing exponentially with time and radiative heat transfer
Authors: Prakash Om , Kumar Devendra , Dwivedi Y. K.
Published: May 2011

The present paper is concerned with the study of MHD free convective flow of a visco-elastic (Kuvshinski type) dusty gas through a porous medium induced by the motion of a semi-infinite flat plate under the influence of radiative heat transfer moving with velocity decreasing exponentially with time. The expressions for velocity distribution of a dusty gas and dust particles, concentration profile and temperature field are obtained. The effect of Schmidt number (Sc), Magnetic field parameter (M) and Radiation parameter (N) on velocity distribution of dusty gas and dust particles, concentration and temperature distribution are discussed graphically.
A Study of R&D, Collaboration, and Location Preferences of Health and Agricultural Biotech Firms
Authors: Bagchi-Sen Sharmistha , Kedron Peter , Scully Jennifer
Published: May 2011

The biotechnology industry is now a top priority of state and regional economic development organizations. Existing geographic research focuses on what motivates the development of regional clusters of biotechnology firms in the area of human therapeutics and diagnostics. However, the biotechnology industry is segmented into broad subsectors, such as health and agricultural biotech, and each sector has different types of firms. The purpose of this paper is to characterize firm-specific differences that exist between health and agricultural biotechnology firms. Specifically, we use a survey instrument to understand how firms in each sector perceive and use different forms of collaboration and location factors in their operations. Although firms in each sector may pursue similar goals and support for innovation, they do not necessarily do so in the same fashion. By treating agricultural and health biotechnology sectors separately, we offer new evidence to reevaluate theories explaining regional biotechnology development, and new insights into how development policies impact each sector. The insights provided by this paper are critical given the prevalence of policy initiatives supporting biotechnology.
Conversion as a Mechanism of Hybridization: The Institutional Transfer of Industrial Relations and Vocational Training from Western to Eastern Germany
Authors: Piotti Geny
Published: May 2011

Looking back over the two decades since German unification, the main questions I want to answer are to what extent and through what mechanisms the transfer of the system of industrial relations and vocational training—two cornerstones of the West German model—has occurred in eastern Germany. The literature argues that institutional transfer very often leads to a process of hybridization in institutions. However, the concept of hybridization has also been criticized as being mainly descriptive and vague about the actual mechanisms of hybridization. In this paper I argue that these mechanisms should be specified further and suggest that the hybridization approach can be fruitfully linked to recent theories of institutional change. As far as the transfer of industrial relations and vocational training from western to eastern Germany is concerned, I argue in particular that hybridization has mainly occurred through what institutional literature has recently defined as the mechanism of conversion.
Voluntary Sector Geographies, Intraorganisational Difference, and the Professionalisation of Volunteering: A Study of Land Search and Rescue Organisations in New Zealand
Authors: Yarwood Richard
Published: May 2011

The voluntary sector is playing increasingly important roles in the delivery of services. With greater regulation, some commentators have speculated that a bifurcation of voluntary groups is occurring between large-scale corporatist organisations and poorly funded grassroots organisations. Using the example of voluntary search and rescue teams in New Zealand, I demonstrate that, while an organisation may follow corporatist principles centrally, its branches may resist change and continue along traditional grassroots lines. This study supports the need for a sociocultural approach to understanding the geographies of volunteering and the organisational spaces of voluntary organisations.
Understanding the Scale and Nature of Outcome Change in Area-Regeneration Programmes: Evidence from the New Deal for Communities Programme in England
Authors: Lawless Paul
Published: May 2011

The New Deal for Communities (NDC) programme is one of the most intensive area-based initiatives (ABIs) launched in England. Between 1998 and 2010 thirty-nine NDC partnerships were charged with improving conditions in relation to six outcomes within deprived neighbourhoods, each accommodating around 9800 people. Data point to only modest change, much of which reflects improving attitudes towards the area and the environment. There are problems in identifying positive people-based outcomes because relatively few individuals benefit from relevant initiatives. Few positive benefits leak out of NDC areas. Transformational change was always unlikely bearing in mind the limited nature of additional resources, and because only a minority of individuals directly engage with NDC projects. This evidence supports perspectives of ABIs rooted in ‘local managerialism’.
Cohesion, Sharing, and Integration in Northern Ireland
Authors: Knox Colin
Published: May 2011

The devolved government in Northern Ireland pledged to work for a ‘shared and better future for all’ in its Programme for Government 2008–11. In pursuit of this goal it launched a consultation document entitled Programme for Cohesion, Sharing and Integration which challenged the assumption that division and segregation is a ‘normal’ pattern of living. I locate the policy proposals contained within the new programme in the research on community cohesion in Great Britain. I interrogate, using attitudinal data, people's preferences for the kind of society they want Northern Ireland to become and the policy consequences of their choices. Using two case studies in education and housing, I highlight the benefits of a shared society and question whether Northern Ireland can embrace the core elements of an intercultural society.
The Role of Planning in Housing Design: Design Implications of Land-Use Management
Authors: Smith Harry , Ferrari Soledad Garcia , Jenkins Paul
Published: May 2011

On the basis of findings from a recent project looking at the status of design in the private sector house-building industry in Scotland, commissioned by the Scottish Government, we explore connections between housing design and wider planning department responsibilities including land-use planning and management. We conclude that a broad conception of design is required in order to understand the influences that land-use planning and management have on approaches that house-builders have to housing design, as well as on the outcomes. We consider the current drive to strengthen design skills in planning departments—including in relation to housing design issues—and argue that, in addition to this, a more widely embedded understanding of the design implications of land-use planning and management decisions on the housing development process is needed in order to contribute to optimising conditions for good design.