bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of pulse release date and soil characteristics on solute transport in a combined vadose zone‐groundwater flow system: Insights from numerical simulations
Authors: Russo David
Published: May 2011

The transport of a conservative tracer (bromide) in a three‐dimensional, heterogeneous combined vadose zone‐groundwater flow system was analyzed through a series of detailed numerical simulations. The scope of the present study was to analyze the effect of both the soil type and the pulse application date on solute movement and spreading in the combined flow system subject to time‐dependent, external forcing conditions, F(t) (characterized by a time period, ), imposed on a flat soil surface. Of particular interest were the suitability of the time‐invariance assumption of the solute travel time distribution and the related issue of the capability of an equivalent, steady state vadose zone flow model to describe solute transport in a realistic flow system. Considering flow systems in which the water table is located at sufficiently large distance from the flat soil surface, the main results of this study suggest that the velocity associated with the wetting front position, which may be considered as an “effective” velocity, is soil‐ and calendar date‐dependent. Consequently, characteristics of the transport (i.e., solute displacement and spreading, first‐ and peak‐arrival times) are soil‐ and pulse release date‐dependent. The soil‐dependent solute travel time PDF at a CP located in the vicinity of the water table, however, may be considered as essentially independent of the pulse release date, particularly in the fine‐textured (clay) soil associated with mean travel time, that substantially exceeds . Furthermore, for , the equivalent steady state definition of the flow problem may be quite effective in describing the solute travel time PDF of the actual transport process occurring under nonmonotonous, transient flow conditions.
Correction to “Numerical evaluation of subsurface soil water evaporation derived from sensible heat balance”
Authors: Sakai Masaru , Jones Scott B. , Tuller Markus
Published: May 2011

Key Points

Heat balance method for subsurface evaporation determination was evaluated

Improved accuracy from tighter near‐surface temperature measurement spacing

Heat pulse probe is more accurate using locally determined thermal conductivity
Influence of high power impulse magnetron sputtering plasma ionization on the microstructure of TiN thin films
Authors: Ehiasarian A. P. , Vetushka A. , Gonzalvo Y. Aranda , Sáfrán G. , Székely L. , Barna P. B.
Published: May 2011

HIPIMS (High Power Impulse Magnetron Sputtering) discharge is a new PVD technology for the deposition of high-quality thin films. The deposition flux contains a high degree of metal ionization and nitrogen dissociation. The microstructure of HIPIMS-deposited nitride films is denser compared to conventional sputter technologies. However, the mechanisms acting on the microstructure, texture and properties have not been discussed in detail so far. In this study, the growth of TiN by HIPIMS of Ti in mixed Ar and N2 atmosphere has been investigated. Varying degrees of metal ionization and nitrogen dissociation were produced by increasing the peak discharge current (Id) from 5 to 30 A. The average power was maintained constant by adjusting the frequency. Mass spectrometry measurements of the deposition flux revealed a high content of ionized film-forming species, such as Ti1+, Ti2+ and atomic nitrogen N1+. Ti1+ ions with energies up to 50 eV were detected during the pulse with reducing energy in the pulse-off times. Langmuir probe measurements showed that the peak plasma density during the pulse was 3 × 1016 m−3. Plasma density, and ion flux ratios of N1+: N21+ and Ti1+: Ti0 increased linearly with peak current. The ratios exceeded 1 at 30 A. TiN films deposited by HIPIMS were analyzed by X-ray diffraction, and transmission electron microscopy. At high Id, N1+: N21+ > 1 and Ti1+: Ti0 > 1 were produced; a strong 002 texture was present and column boundaries in the films were atomically tight. As Id reduced and N1+: N21+ and Ti1+: Ti0 dropped below 1, the film texture switched to strong 111 with a dense structure. At very low Id, porosity between columns developed. The effects of the significant activation of the deposition flux observed in the HIPIMS discharge on the film texture, microstructure, morphology and properties are discussed.
Monte Carlo simulation of electron transport in a graphene diode with a linear energy band dispersion
Authors: Harada Naoki , Awano Yuji , Sato Shintaro , Yokoyama Naoki
Published: May 2011

Electron transport and energy relaxation in a 100-nm channel n+-n-n+ monolayer graphene diode were studied by using semiclassical Monte Carlo particle simulations. A diode with a conventional parabolic band and an identical geometry and scattering process was also analyzed in an attempt to confirm that the characteristic transport properties originated from the linear energy band structure. We took into account two scattering mechanisms: isotropic elastic scattering and inelastic phonon emission. The carrier velocity distributions in the two diodes show remarkable differences reflecting their band dispersions. Electron velocity in the monolayer graphene diode is high in the channel region and remains almost constant until the energy relaxation begins. Inelastic scattering does not reduce electron velocity so severely, whereas elastic scattering significantly decreases it through backscattering of hot electrons with high kinetic energy. Elastic scattering also degrades the ballisticity and the drain current; however, increasing the inelastic scattering offsets these effects. We found that elastic scattering should be suppressed to improve the performance of graphene devices.
Density inhomogeneity driven electrostatic shock waves in planetary rings
Authors: Masood W. , Rizvi H. , Hasnain H. , Siddiq M. , Haque Q.
Published: May 2011

Dust inertia and background density driven dust drift shock waves are theoretically studied in a rotating planetary environment and are subsequently applied to the planetary rings where the collisional effects are pronounced. It has been found that the system under consideration admits significant shock formation if the collision frequency is of the order of or less than the rotational frequency of the Saturn’s rings.
Dissociative excitation and fragmentation of S8 by electron impact
Authors: Brotton S. J. , McConkey J. W.
Published: May 2011

The vacuum-ultraviolet emission spectrum from 136 nm to 168 nm following the dissociative excitation of a predominantly S8 target by electron impact at 100 eV incident energy was measured. The relative cross sections for the dominant multiplets at 138.9, 142.9, 147.9, and 166.7 nm are presented. Excitation functions are shown for electron-impact energies from below threshold to 360 eV for the two most prominent emissions at 142.5 nm and 147.4 nm. Five thresholds are clearly apparent in both excitation functions. For the four highest energy channels, the energy separation between the adjacent thresholds is approximately constant and the cross sections reduce regularly as the threshold energies increase. We suggest possible fragmentation pathways of the dissociating S8 molecule that reproduce the energies of our observed thresholds.
A study of complex scaling transformation using the Wigner representation of wavefunctions
Authors: Kaprálová-Žďánská Petra Ruth
Published: May 2011

The complex scaling operator \documentclass[12pt]{minimal}\begin{document}$\exp (-\theta \hat{x}\hat{p}/\hbar )$\end{document}exp(−θx̂p̂/ℏ), being a foundation of the complex scaling method for resonances, is studied in the Wigner phase-space representation. It is shown that the complex scaling operator behaves similarly to the squeezing operator, rotating and amplifying Wigner quasi-probability distributions of the respective wavefunctions. It is disclosed that the distorting effect of the complex scaling transformation is correlated with increased numerical errors of computed resonance energies and widths. The behavior of the numerical error is demonstrated for a computation of CO2 + vibronic resonances.
Remotely induced atmospheric lasing
Authors: Sprangle Phillip , Peñano Joseph , Hafizi Bahman , Gordon Daniel , Scully Marlan
Published: May 2011

We propose and analyze a remote atmospheric lasing configuration which utilizes a combination of an ultrashort pulse laser to form a plasma filament (seed electrons) by tunneling ionization and a heater pulse which thermalizes the seed electrons. Electrons collisionally excite nitrogen molecules and induce lasing in the ultraviolet. The lasing gain is sufficiently high to reach saturation within the length of the plasma filament. A remotely generated ultraviolet source may have applications for standoff detection of biological and chemical agents.
Conditional Eulerian and Lagrangian velocity increment statistics of fully developed turbulent flow
Authors: Homann Holger , Schulz Daniel , Grauer Rainer
Published: May 2011

Conditional statistics of homogeneous isotropic turbulent flow is investigated by means of high Reynolds number direct numerical simulations performed with 20483 collocation points. Eulerian as well as Lagrangian velocity increment statistics under several conditions are analyzed and compared. In agreement with experimental data, longitudinal probability density functions P(δl||u|εl) conditioned on a scale-averaged energy dissipation rate are close to Gaussian distributions over all scales within the inertial range of scales. Also transverse increments conditioned on either the dissipation rate or the square of the vorticity have quasi-Gaussian probability density functions (PDFs). Concerning Lagrangian statistics we found that conditioning on a trajectory averaged energy dissipation rate ετ significantly reduces the scale dependence of the increment PDFs P(δτui|ετ). By means of dimensional arguments we propose a novel condition for Lagrangian increments which is shown to reduce even more the flatness of the corresponding PDFs and thus intermittency in the inertial range of scales. The conditioned Lagrangian PDF corresponding to the smallest increment considered is reasonably well described by a prediction for the PDF of acceleration of a non-intermittent velocity field. Conditioned structure functions show approximately K41 scaling with a larger scaling range than the unconditioned ones.
Pinch-off and formation number of negatively buoyant jets
Authors: Wang Ruo-Qian , Wing-Keung Law Adrian , Adams E. Eric
Published: May 2011

Previous investigations of starting buoyant jets are extended towards negative buoyancy to address key issues in the formation processes. A series of large-eddy simulations (LES) is performed to identify whether an optimal vortex can be formed with negative buoyancy and if so what the corresponding formation number would be. The numerical code was previously validated for non-buoyant and positively buoyant jets and is further validated here for negatively buoyant jets using literature data on submerged fountains. Subsequently, jets with a range of negative buoyancies are simulated using source Reynolds numbers of 2000 < Re < 3000. A revised, directional form of Richardson number (Rid) is proposed to accommodate the entire range of buoyancy, with Rid > 0 for positively buoyant jets, Rid = 0 for non-buoyant jets, and Rid < 0 for negatively buoyant jets. Simulations identify two ranges of negative buoyancy. For weakly negatively buoyant starting jets (– 0.05 <∼ Rid < 0), the pinch-off and formation of an optimal starting vortex occur, and the corresponding formation number can be determined using a revised algorithm, catering to negative buoyancy, based on the observed step jump in the vortex ring’s circulation. This algorithm suggests a continuation of the declining trend in formation number with declining Rid identified previously for positively buoyant jets. For strongly negatively buoyant jets (Rid < −0.05), the starting vortex falls back onto the stem after the initial roll-up for −2.0 <∼ Rid < −0.05, and the pinch-off process does not exist for Rid <∼ −2.0 with the starting vortex and stem connected at all time. A plot of time-varying vortex circulation and penetration for starting plumes with different Rid unifies our understanding of buoyant vortex dynamics.
Thermoelectric properties of Bi-doped PbTe composites
Authors: Popescu A. , Datta A. , Nolas G. S. , Woods L. M.
Published: May 2011

An experimental and theoretical study is presented for n-type Bi-doped PbTe composites with different grain sizes and doping levels. The bulk polycrystalline composites were prepared by spark plasma sintering of the nanocrystals synthesized via micro-emulsion and direct precipitation. This technique is particularly attractive due to its low cost, its reproducibility, and the control of the composition and nanocrystal size that it affords. The thermoelectric properties of the synthesized specimens were experimentally measured and theoretically modeled. Our calculations reveal that the inclusion of electron/grain and phonon/grain interface scattering is crucial for the correct description and interpretation of the measured properties.
Molecular dynamics simulation study of nonconcatenated ring polymers in a melt. II. Dynamics
Authors: Halverson Jonathan D. , Lee Won Bo , Grest Gary S. , Grosberg Alexander Y. , Kremer Kurt
Published: May 2011

Molecular dynamics simulations were conducted to investigate the dynamic properties of melts of nonconcatenated ring polymers and compared to melts of linear polymers. The longest rings were composed of N = 1600 monomers per chain which corresponds to roughly 57 entanglement lengths for comparable linear polymers. The ring melts were found to diffuse faster than their linear counterparts, with both architectures approximately obeying a D ∼ N−2.4 scaling law for large N. The mean-square displacement of the center-of-mass of the rings follows a sub-diffusive behavior for times and distances beyond the ring extension \documentclass[12pt]{minimal}\begin{document}$\langle R_g^2 \rangle$\end{document}⟨Rg2⟩, neither compatible with the Rouse nor the reptation model. The rings relax stress much faster than linear polymers, and the zero-shear viscosity was found to vary as η0 ∼ N1.4 ± 0.2 which is much weaker than the N3.4 behavior of linear chains, not matching any commonly known model for polymer dynamics when compared to the observed mean-square displacements. These findings are discussed in view of the conformational properties of the rings presented in the preceding paper [J. D. Halverson, W. Lee, G. S. Grest, A. Y. Grosberg, and K. Kremer, J. Chem. Phys. 134, 204904 (2011)]10.1063/1.3587137.
The Dugdale model for a semi-infinite crack in a strip of two-dimensional decagonal quasicrystals
Authors: Ling-yun Xie , Tian-you Fan
Published: May 2011

The problem of a semi-infinite crack in a strip is useful in materials science and engineering. The paper proposes a Dugdale model for the configuration of two-dimensional decagonal quasicrystals. Through the complex variable method, we obtain the exact solution of the problem. The plastic zone and the crack tip opening displacement and the most important physical quantity, stress intensity factor, can be expressed in quite a simple form.
A long waves-short waves model: Darboux transformation and soliton solutions
Authors: Ling Liming , Liu Q. P.
Published: May 2011

Darboux transformation is constructed for a third-order spectral problem. By proper reduction, a Darboux transformation for a long-short wave model is obtained. Furthermore, a closed multi-soliton solution formula is found for this equation.
A deeper insight into the dip coating process in the presence of insoluble surfactants: A numerical analysis
Authors: Campana Diego M. , Ubal Sebastián , Giavedoni María D. , Saita Fernando A.
Published: May 2011

A numerical investigation is carried out to study the effects of an insoluble surfactant on the dip coating of a flat substrate. Predictions of both the film thickness and the concentration of surfactant in the film as a function of the capillary number compare well with the solutions of a simpler asymptotic model based on the lubrication approximation. Streamline patterns confirm the existence of a stagnation point located in the bulk phase in the region of the dynamic meniscus—a conjecture postulated forty years ago. The evolution of the flow patterns and the interfacial variables shows how the classical result of Landau and Levich is recovered as the coating speed is augmented. Finally, we show that the effect of inertia forces cannot be neglected when the viscosity of the coating liquid is low.
Exact solution of D
N-type quantum Calogero model through a mapping to free harmonic oscillators
Authors: Banerjee Pratyay , Basu-Mallick B.
Published: May 2011

We solve the eigenvalue problem of the DN-type of Calogero model by mapping it to a set of decoupled quantum harmonic oscillators through a similarity transformation. In particular, we construct the eigenfunctions of this Calogero model from those of bosonic harmonic oscillators having either all even parity or all odd parity. It turns out that the eigenfunctions of this model are orthogonal with respect to a nontrivial inner product, which can be derived from the quasi-Hermiticity property of the corresponding conserved quantities.
Fractional curve flows and solitonic hierarchies in gravity and geometric mechanics
Authors: Baleanu Dumitru , Vacaru Sergiu I.
Published: May 2011

Methods from the geometry of nonholonomic manifolds and Lagrange–Finsler spaces are applied in fractional calculus with Caputo derivatives and for elaborating models of fractional gravity and fractional Lagrange mechanics. The geometric data for such models are encoded into (fractional) bi–Hamiltonian structures and associated solitonic hierarchies. The constructions yield horizontal/vertical pairs of fractional vector sine–Gordon equations and fractional vector mKdV equations when the hierarchies for corresponding curve fractional flows are described in explicit forms by fractional wave maps and analogs of Schrödinger maps.
Basal plane misfit dislocations and stress relaxation in III-nitride semipolar heteroepitaxy
Authors: Romanov Alexey E. , Young Erin C. , Wu Feng , Tyagi Anurag , Gallinat Chad S. , Nakamura Shuji , DenBaars Steve P. , Speck James S.
Published: May 2011

This article presents a theoretical analysis of dislocation behavior and stress relaxation in semipolar III-nitride heteroepitaxy, e.g., for AlxGa1−xN and InyGa1−yN layers grown on {hh2−h−m}- or {h0h−m}-type semipolar planes of GaN substrates. We demonstrate that the shear stresses on the unique inclined basal (0001) plane do not vanish for such growth geometries. This leads to the onset of relaxation processes in semipolar III-nitride heterostructures via dislocation glide in the basal slip systems 〈1−1−20〉(0001) and to the formation of misfit dislocations (MDs) with Burgers vectors of (a/3)〈1−1−20〉-type at the semipolar heterointerface. Next we calculate the Matthews-Blakeslee critical thickness for MD formation in semipolar III-nitride layers together with the MD equilibrium spacings for complete misfit relaxation. The component of the MD Burgers vector normal to the film/substrate interface will cause a crystal lattice tilt in the epilayer with respect to the GaN substrate. The calculated magnitudes of the tilt angles are 0.62° and 0.67° for AlxGa1−xN and InyGa1−yN alloys with compositions of x = 0.20 and y = 0.07, respectively, grown in the (112−2) semipolar orientation. The modeling results are discussed in light of recent experimental observations [A. Tyagi et al., Appl Phys. Lett. 95, 251905 (2009); E. Young et al., Appl. Phys. Express 3, 011004 (2010); and F. Wu et al., J. Appl. Phys. 109, 033505 (2011)] of MDs and crystal lattice tilt in semipolar III-nitride heteroepitaxial layers.
Tunable photoluminescence and photoconductivity in ZnO one-dimensional nanostructures with a second below-gap beam
Authors: Shih H. Y. , Chen Y. T. , Huang N. H. , Wei C. M. , Chen Y. F.
Published: May 2011

Tunable photoluminescence (PL) and photoconductivity (PC) with a second below-gap beam were demonstrated on ZnO nanorods and nanoribbons. We found that both PL and PC could be quenched as the second beam was applied to the nanostructures, and this behavior was excluded from thermal effect by comparing the phonon replica spectra with that from heating the sample directly. The most quenching effect occurred near the defect transition located at 520 nm. The underlying mechanism of the quenching behavior was attributed to the defect transition between different states of oxygen vacancies. Size-dependence measurement lets us know that the effect occurs near the surface of nanostructures, and the power-dependent measurement further confirms the underlying mechanism we proposed.
First-principles calculations of the structural and dynamic properties, and the equation of state of crystalline iodine oxides I2O4, I2O5, and I2O6
Authors: Wu Zhongqing , Kalia Rajiv K. , Nakano Aiichiro , Vashishta Priya
Published: May 2011

The structural and dynamical correlations, and the equation of state of crystalline I2O4, I2O5, and I2O6 are investigated by first-principles calculations based on the density functional theory (DFT). The lattice dynamics results reveal distinctive features in the phonon density of states among the three crystals. The frequencies of the stretch modes in I2O4 and I2O5 are clearly separated from those of the other (e.g., bending) modes by a gap, with all stretch modes above the gap. In contrast, the gap in I2O6 separates the highest-frequency stretch modes with other stretch modes, and there is no gap between the stretch and the other modes in I2O6. The motion of iodine atoms is involved in all vibrational modes in I2O5, but only in low-frequency lattice modes in I2O6. In I2O4, iodine atoms are involved in modes with frequency below 700 cm−1. Van der Waals correction within our DFT calculations is found to reduce the overestimation of the equilibrium volume, with its effect on structure similar to the pressure effect. Namely, both effects significantly decrease the inter-molecular distances, while slightly increasing the bond lengths within the molecules. This causes the frequencies of some vibrational modes to decrease with pressure, resulting in negative “modes Grüneisen parameters” for those modes. Thermodynamic properties, derived from the equation of state, of crystalline I2O4, I2O5, and I2O6 are discussed within the quasi-harmonic approximation.
Measurement of photostimulated self-diffusion in silicon
Authors: Seebauer Edmund G. , Jung Michael Y. L. , Kwok Charlotte T. M. , Vaidyanathan Ramakrishnan , Kondratenko Yevgeniy V.
Published: May 2011

Photostimulated diffusion within solid semiconductors has been examined for many years, but its existence above room temperature has not been unambiguously confirmed. Here, diffusion rates for silicon self-diffusion are shown to change by factors of up to 25 in response to optical fluxes on the order of 1 W/cm2. Results depend on doping type; the rates of both interstitial formation and migration are affected in the case of n-type material. A model based on photostimulated changes in defect charge state explains the primary results, and the basic outlines should apply to a wide variety of semiconductors.
Breakdown of the pseudopotential approximation for magnetizabilities and electric multipole moments: Test calculations for Au, AuF, and Snn cluster (n ⩽ 20)
Authors: Schwerdtfeger Peter , Assadollahzadeh Behnam , Rohrmann Urban , Schäfer Rolf , Cheeseman James R.
Published: May 2011

The response of the electronic wavefunction to an external electric or magnetic field is widely considered to be a typical valence property and should, therefore, be adequately described by accurately adjusted pseudopotentials, especially if a small-core definition is used within this approximation. In this paper we show for atomic Au and Au+, as well as for the molecule AuF and tin clusters, that in contrast to the case of the static electric dipole polarizability or the electric dipole moment, core contributions to the static magnetizability are non-negligible, and can therefore lead to erroneous results within the pseudopotential approximation. This error increases with increasing size of the core chosen. For tin clusters, which are of interest in ongoing molecular beam experiments currently carried out by the Darmstadt group, the diamagnetic and paramagnetic isotropic components of the magnetizability tensor almost cancel out and large-core pseudopotentials do not even predict the correct sign for this property due to erroneous results in both the diamagnetic and (more importantly) the paramagnetic terms. Hence, all-electron calculations or pseudopotentials with very small cores are required to adequately predict magnetizabilities for atoms, molecules and the solid state, making it computationally more difficult to obtain this quantity for future investigations in heavy atom containing molecules or clusters. We also demonstrate for this property that all-electron density functional calculations are quite robust and give results close to wavefunction based methods for the atoms and molecules studied here.
Stability of Ag nanocrystals synthesized by ultra-low energy ion implantation in SiO2 matrices
Authors: Benzo Patrizio , Cattaneo Laura , Farcau Cosmin , Andreozzi Andrea , Perego Michele , Benassayag Gérard , Pécassou Béatrice , Carles Robert , Bonafos Caroline
Published: May 2011

Ultra low energy ion implantation is a promising technique for the wafer-scale fabrication of Silver nanoparticle planar arrays embedded in thermal silica on silicon substrate. The stability versus time of these nanoparticles is studied at ambient conditions on a time scale of months. The plasmonic signature of Ag NPs vanishes several months after implantation for as-implanted samples, while samples annealed at intermediate temperature under N2 remain stable. XPS and HREM analysis evidence the presence of Silver oxide nanoparticles on aged samples and pure Silver nanoparticles on the annealed ones. This thermal treatment does not modify the size-distribution or position of the particles but is very efficient in stabilizing the metallic particles and to prevent any form of oxidation.
Large spectral tunability of narrow geometric resonances of periodic arrays of metallic nanoparticles in a nematic liquid crystal
Authors: Li Jia , Ma Yi , Gu Ying , Khoo Iam-Choon , Gong Qihuang
Published: May 2011

We investigated the geometric resonances of periodic arrays of gold nanoparticles embedded in a nematic liquid crystal using a semi-analytical method. By changing the liquid crystal’s refractive index seen by the scattered light propagating along the array axis, the geometric resonance can be modulated according to an analytical law. The spectral tunability is proportional to the index difference (ne−no) of the liquid crystal and the interparticle distance i.e., Δλ=(ne−no)d, which is as large as 100 nm. The large and easily controlled tunability of this compound structure makes it desirable for design of plasmon-based sensors and switches.
Planar millimeter wave band-stop filters based on the excitation of confined magnetostatic waves in barium hexagonal ferrite thin film strips
Authors: Lu Lei , Song Young-Yeal , Bevivino Joshua , Wu Mingzhong
Published: May 2011

A planar millimeter wave band-stop filter based on confined magnetostatic wave (MSW) excitations in an M-type barium hexagonal ferrite (BaM) film strip was demonstrated. The device consists of a BaM film strip on the top of a coplanar waveguide with the strip length along the signal line. For zero magnetic fields, the device shows a band-stop filtering response at 53 GHz. This response originates from the excitation of confined MSW modes across the BaM strip width. The filter operation frequency is tunable with low fields. This tuning relies on the change in the MSW dispersion with field.
Cavity-enhanced direct band electroluminescence near 1550 nm from germanium microdisk resonator diode on silicon
Authors: Cheng Szu-Lin , Shambat Gary , Lu Jesse , Yu Hyun-Yong , Saraswat Krishna , Kamins Theodore I. , Vuckovic Jelena , Nishi Yoshio
Published: May 2011

We electrically and optically characterize a germanium resonator diode on silicon fabricated by integrating a germanium light emitting diode with a microdisk cavity. Diode current-voltage characteristics show a low ideality factor and a high on/off ratio. The optical transmission of the resonator features whispering gallery modes with quality factors of a few hundred. Direct band gap electroluminescence under continuous current injection shows a clear enhancement of emission by the cavity. At this stage, the pumping level is not high enough to cause linewidth narrowing and invert the material. A higher n-type activated doping of germanium is necessary to achieve lasing.
Subnanosecond electro-optic modulation of triggered single photons from a quantum dot
Authors: Rakher Matthew T. , Srinivasan Kartik
Published: May 2011

Control of single photon wave-packets is an important resource for developing hybrid quantum systems which are composed of different physical systems interacting via photons. Here, we extend this control to triggered photons emitted by a quantum dot, temporally shaping single photon wave-packets on timescales fast compared to their radiative decay by electro-optic modulation. In particular, telecommunications-band single photons resulting from the recombination of an exciton in a quantum dot with exponentially decaying wave-packets are synchronously modulated to create Gaussian-shaped single photon wave-packets. We explore other pulse shapes and investigate the feasibility of this technique for increasing the indistinguishability of quantum dot generated single photons.
Communication: Atomic and molecular Rydbergs from water
Authors: Rajput Jyoti , Safvan C. P.
Published: May 2011

We report the formation of energetic neutral Rydberg hydrogen atoms and transient Rydberg molecular ions, \documentclass[12pt]{minimal}\begin{document}$[(\text{H}_2\text{O})^{q+}]^{\star }$\end{document}[(H2O)q+]☆ in ion-impact dissociation of isolated water molecules. The kinetic energy spectra of the neutral Rydberg H atoms are determined from the complete study of (H⋆, H+, O+) dissociation channel. This channel of water dissociation is suggested as a possible additional source of the energetic neutrals detected in upper atmospheres of extra solar planets, and of slow electrons which are known to play a major role in radiation induced damage to living cells.
Magnetism and magnetoelectricity of a U-type hexaferrite Sr4Co2Fe36O60
Authors: Okumura K. , Ishikura T. , Soda M. , Asaka T. , Nakamura H. , Wakabayashi Y. , Kimura T.
Published: May 2011

We report on structural, magnetic, and magnetoelectric (ME) properties of a U-type hexaferrite Sr4Co2Fe36O60 prepared by solid state reaction. Samples sintered at 1150–1180 °C in oxygen contain the fewest impurity phases and show highly insulating behavior. Powder neutron diffraction results reveal that a commensurate magnetic order with a (0,0,3/2) propagation vector develops below TN2∼350 K. Corresponding to the appearance of the magnetic order, the sample shows a small ME effect. These results suggest that Sr4Co2Fe36O60 is a room-temperature ME material in which the origin of the ME effect is similar to those of other ME hexaferrites.
Visible electroluminescence from hybrid colloidal silicon quantum dot-organic light-emitting diodes
Authors: Tu Chang-Ching , Tang Liang , Huang Jiangdong , Voutsas Apostolos , Lin Lih Y.
Published: May 2011

We demonstrate hybrid colloidal silicon quantum dot (SiQD)-organic light-emitting diodes with electroluminescence (EL) in the visible wavelengths. The device using blue photoluminescence (PL) SiQDs as emitters shows multiple EL peaks which are attributed to carrier recombination in the core quantum confinement states, the hole-transport-layer and the surface trap states, respectively. However, the red PL SiQD device shows a single EL peak consistent with the PL peak. These findings are in agreement with the previous report that large Stokes shift were observed for oxidized blue emission SiQDs due to oxide states while red emission SiQDs show negligible PL shift after oxidation.
Integrating steepest-descent reaction pathways for large molecules
Authors: Hratchian Hrant P. , Frisch Michael J.
Published: May 2011

Exploring potential energy surfaces of large molecular systems can be quite challenging due to the increased number of nuclear degrees of freedom. Many techniques that are well-suited for small and moderate size systems require diagonalization of the energy second-derivative matrix. Since the cost of this step scales as \documentclass[12pt]{minimal}\begin{document}${\mathcal {O}}(N_{atoms}^{3})$\end{document}O(Natoms3) (where Natoms is the number of atomic centers), such methods quickly become infeasible and are eventually rendered cost prohibitive. In this work, the recently developed Euler-based predictor–corrector reaction path integration method [H. P. Hratchian, M. J. Frisch, and H. B. Schlegel, J. Chem. Phys. 133, 224101 (2010)]10.1063/1.3514202 is enhanced and proposed as a useful alternative to conventional reaction path following schemes in studies on very large systems. Because this integrator does not require Hessian diagonalization, the \documentclass[12pt]{minimal}\begin{document}${\mathcal {O}}(N_{atoms}^{3})$\end{document}O(Natoms3) bottleneck afflicting other approaches is completely avoided. The effectiveness of the integrator in large system studies is demonstrated with an enzyme-catalyzed reaction employing an ONIOM (QM:MM) model chemistry and involving 5368 atomic centers.
Interfacial mixing during annealing of zinc oxide nanoparticle junctions
Authors: Hu Ming , Giapis Konstantinos P. , Poulikakos Dimos
Published: May 2011

The process of forming a junction between crystalline zinc oxide (ZnO) nanoparticles during pulsed thermal annealing in liquid tetradecane is studied using molecular dynamics simulation. Pairs of equal and unequal size particles are considered with emphasis on neck growth and atom mixing. The contact area and interface width of the junction are found to increase with heat pulse power albeit at different rates. The results suggest that it is possible to increase the junction area without significant mixing of atoms across the junction interface by tailoring the heat pulse power.
Generation of high spatial frequency ripples on silicon under ultrashort laser pulses irradiation
Authors: Le Harzic R. , Dörr D. , Sauer D. , Stracke F. , Zimmermann H.
Published: May 2011

Periodic high spatial frequency ripples structures have been generated in silicon under femtosecond laser pulses irradiation. The period of the ripples is wavelength dependent. It increases from 110 up to 160 nm when the wavelength varies from 700 to 950 nm, respectively. We propose a refined model of the second harmonic generation ripples spacing theory Λ=λ/2nλ∗ taking into account the modified femtosecond laser excited silicon refractive index n∗ related to the Drude model. Good agreement is found between experimental results and the presented revisited model.
In situ transmission electron microscopy analysis of conductive filament during solid electrolyte resistance switching
Authors: Fujii Takashi , Arita Masashi , Takahashi Yasuo , Fujiwara Ichiro
Published: May 2011

An in situ transmission electron microscopy (TEM) analysis of a solid electrolyte, Cu–GeS, during resistance switching is reported. Real-time observations of the filament formation and disappearance process were performed in the TEM instrument and the conductive-filament-formation model was confirmed experimentally. Narrow conductive filaments were formed corresponding to resistance switching from high- to low-resistance states. When the resistance changed to high-resistance state, the filament disappeared. It was also confirmed by use of selected area diffractometry and energy-dispersive x-ray spectroscopy that the conductive filament was made of nanocrystals composed mainly of Cu.
Competitive Location Modeling with a Rank Proportional Allocation
Authors: Lee Gunhak , O'Kelly Morton E
Published: May 2011

Competitive location modeling deals with a strategic spatial decision which seeks to identify optimal locations for new facilities among existing competing facilities. The capture of customers by a new facility essentially depends on customer-choice behaviors. In this paper, we introduce a competitive location model incorporating a rank proportional choice rule. Also, we explore how the competitive location model with a ranking system differs from other models with two more-typical choice rules—deterministic and probabilistic choices. To do so, we present a numerical example and an illustrative application in the broadband market context, focusing on customer-capture patterns. Our analytical findings reveal that the different choice rules in modeling significantly influence customer-capture and market-share estimates. In particular, a competitive location model with a rank proportional allocation captures fewer customers than other models with different allocation rules, given a fixed number of few facilities.
An Agent-Based Approach to Providing Tourism Planning Support
Authors: Johnson Peter A , Sieber Renee E
Published: May 2011

Agent-based modeling (ABM) is a computer simulation approach that can be used to represent real-world systems and create planning scenarios to examine possible future outcomes of present-day decisions. This approach can be applied in tourism planning, where destinations are exposed to a variety of externalities, and must develop strategies to adapt to changing operational conditions. We describe the development of TourSim, an ABM of tourism dynamics set in the Canadian province of Nova Scotia. We present an overview of the data sources and techniques used to inform agent behavior and the destination landscape, as well as consider aspects of system representation and validation and how these may affect the use of TourSim. TourSim is used to generate three scenarios of tourism dynamics; a base-case scenario, one that simulates the effect of a decrease in visitation from American markets as a result of economic crisis, and the use of advertising as a response to this lower level of visitation. These scenarios are used to evaluate ABM in comparison with other computer-based methods of modeling tourism, namely geographic information systems and system dynamics models.
Planners' Perspectives on Using Technology in Participatory Processes
Authors: Slotterback Carissa Schively
Published: May 2011

This study examined potential opportunities and constraints related to the development and deployment of technology in participation processes, including resources available, benefits and outcomes of technology, and technology implementation. On the basis of a survey of planners relative to eleven technology scenarios, varied access to staff, hardware, and software resources was reported. Potential perceived benefits of technology use included providing information and, to a lesser extent, fostering discussion and attracting additional participants. The findings suggest the greatest potential is for more basic technologies including websites that provide information, as opposed to more advanced technologies that would have greater potential to enhance collaborative and interactive participation approaches. Concerns about equitable access to technology for both planners and participants are also noted by survey respondents. The findings emphasize the importance of using technology as an enhancement to, rather than a replacement for, more traditional participation efforts.
Multiobjective Network Design for Emission and Travel-Time Trade-off for a Sustainable Large Urban Transportation Network
Authors: Sharma Sushant , Mathew Tom V
Published: May 2011

Existing optimal road-network capacity-expansion models are based on minimizing travel time and rarely consider environmental factors such as vehicular emissions. In this study we attempt to solve such a transportation network design problem when the planner is environment conscious and thereby tries to minimize health-damage cost due to vehicular emissions along with total system travel time while performing optimal capacity expansion. This problem can be formulated as a multiobjective optimization model which minimizes emissions in addition to travel time, and under budget constraints. A prerequisite for this model is an accurate estimation of vehicle emissions due to changes in link capacities. Since the current practice of estimation of vehicular emissions by aggregate emission factors does not account for the improved speeds resulting from capacity improvements, speed-dependent emission functions for various transport modes and pollutants are used in this study. These functions help in calculating emission factors for use in the proposed model. The model uses a nondominated sorting genetic algorithm as the optimization tool to solve the network design problem. The model is tested on a small hypothetical network and solved for a real large-sized network in India taking into account three pollutants and five transport modes. The Pareto-optimal solutions generated can act as trade-offs between total emissions and total system travel time to account for the planner's desired objectives. Also, reduction in travel time as well as in emissions supports the present model compared with the single-objective model.
A 17th-Century Demonstration of Language Relationship
Authors: Eros John F.
Published: May 2011

In 1650 Meric Casaubon (1599–1671) published a treatise in which he systematically presented rules for demonstrating language relationship; in his study he applied these rules to English and Greek. The explicitness of his theoretical formulations and the examples contained in his practical application of these rules offer a splendid opportunity for pinpointing the causes of the backwardness of historical linguistics in its so-called prescientific period. Careful observation of Casaubon’s presentation shows that it was his formulation of the rules of generally permissible phonetic changes, more than anything else, that prevented him from writing a really good study.
Ainu applicatives in typological perspective
Authors: Bugaeva Anna
Published: May 2011

This paper explores the polyfunctionality, grammaticalization, and typological relevance of applicatives in Ainu. Applicatives are derived by the valency-increasing prefixes which are generally defined here as instrumental e-, dative ko-, and locative o-. The referential range of the respective constructions stretches over several semantic roles and the exact role is attributed to the interaction between the semantics of the prefix and verb. The typologically unusual properties of Ainu applicatives include the ability of e- applicatives to add the roles of Theme and Content, the ability of the so-called unaccusative intransitives to host applicative prefixes e- and ko-, the possibility of e-ko- and ko-e- double applicatives, the absence of non-applicative paraphrases for some applicatives, and the possibility of applicative object incorporation.
Word order in zero-marking languages
Authors: Sinnemäki Kaius
Published: May 2011

It has often been argued that languages with no morphological marking of core arguments (referred to here as zero-marking languages) should prefer SVO word order. This correlation is tested here by studying the effects of word order, genealogical relatedness, and areal diffusion on the distribution of zero marking with multiple logistic regression. The possible confounding areal and genealogical factors are studied in multiple ways. The results, based on data from 848 languages, suggest that zero marking (morphological simplicity) correlates with SVO (syntactic simplicity), regardless of its areally and genealogically biased distribution. It is argued that this word order preference is affected by functional motivations and language contact.
Local economic strategies: Paradigms for a planned economy?
Authors: Benington John
Published: May 2011

Interventionist local economic strategies are perceived by the present government as a significant threat, as shown by the concerns of the Widdicombe inquiry. But are they of lasting influence, or mere “fashionable playgrounds for the new left”? John Benington identifies a major shift in the way local authorities see their own role as employers and purchasers. But there is also a risk that the new left approach will become depoliticised and bureaucratised, and that certain community and trade union activities which have been strengthened by the local state will become dangerously dependent on it.
The New Local Economics: A Reply to John Benington
Authors: Sharples Adam
Published: May 2011

Attempts are being made to construct a “new local economics” and important claims are being made on its behalf. In present circumstances, its contribution, though with some valuable achievements as John Benington has shown, must nevertheless be marginal. The task is to gain the maximum leverage from minimal resources, and this article suggests that the key priorities should be to use local authorities' influence as purchasers, employers and investors.
Strategic planning and industrial policy
Authors: Best Michael
Published: May 2011

The poor performance of British industry in international markets is partly due to a lack of sector strategic planning. Whereas the Thatcher government looks to an unfettering of the market mechanism as the key to industrial recovery, in fact this is contrary to the experience of several other capitalist countries. The role of banks and government agencies in Japan, of inter-firm co-operation in Italy, and of various corporatist instruments in France and Germany, suggest ways in which local enterprise boards could assist the re-structuring of manufacturing industry in Britain.
Figuring out the MSC
Authors: Lewis Paul
Published: May 2011

Large claims are being made about the merits of the two-year Youth Training Scheme. Paul Lewis, Director of Youthaid, makes a detailed and coherent analysis of these claims.
Community Businesses are their aims confused?
Authors: Jacobs Mike
Published: May 2011

Glen Buchanan has given a chilling outline of the conditions from which community businesses have arisen, and communicated something of the idealism of their genesis. Mike Jacobs shares the ideals, but is worried by the way in which they are expressed. He writes: “Glen claims that community businesses are ‘completely different’ from public and private sector companies. I think they could be, but the way Glen describes them they are probably not.”
Greater London Enterprise Board: Vision and reality
Authors: Newman Ines
Published: May 2011

This article debates the innovative role in the private sector defined for GLEB by the London Industrial Strategy. It suggests that there are substantial problems at both the theoretical level and the level of implementation with the concept of municipal enterprise boards. It concludes that there is a need for further discussion on the objectives of municipal enterprise boards and more assessment of their role in relation to other possible economic initiatives at the local level.
The purpose of local industrial policy
Authors: Gough Jamie
Published: May 2011

It is argued that the local investment strategy proposed by Best in Local Economy 1 is incapable of creating jobs in the way that it claims, and that it tends to perpetuate and create divisions and inequalities within the workforce. Instead local investment strategies need to be centred, not on increasing productivity but on helping to strengthen the collective organisation of workers. Some ways are discussed in which local authorities might begin to do this but to carry this through consistently will require national planning of industries and compulsory powers over investment decisions by private firms.