bluuebunny/crossref_metadata_2025 huggingface dataset:
Driving Saturn's magnetospheric periodicities from the upper atmosphere/ionosphere: Magnetotail response to dual sources
Authors: Jia Xianzhe , Kivelson Margaret G.
Published: October 2012

Despite the high degree of axial symmetry of Saturn's internal magnetic field, rotation‐associated periodicities are evident in Saturn's electromagnetic radiation, its magnetic perturbations and its particle populations. Although close to the mean rotation period of the cloud tops, the electromagnetic period drifts slightly over a time scale of years and, at high latitudes, differs for sources in the north and south. The source of the periodicity remains a mystery. The model investigated here places the momentum source in the upper atmosphere/ionosphere, with the wind patterns in the two hemispheres rotating about the spin axis at different rates typical of the 2005–2006 southern summer for which Cassini data have been extensively analyzed. A source at low altitudes would account for the persistence of phase following solar wind disruption of magnetospheric flow patterns but might not produce appropriate magnetospheric responses. However, a magnetohydrodynamic simulation in which vortical winds in the ionosphere drive field‐aligned currents into the magnetosphere shows that the dual sources account nearly quantitatively for many measured magnetospheric responses. This paper focuses on the magnetotail where the model is shown to reproduce many well‐documented results of data analysis including the features that appear distinctly at each of the two periods and those that appear as a carrier signal with amplitude modulation and phase shifts. In particular, the model accounts for current sheet flapping and modulation of the plasma sheet thickness and for the periodic structure of density enhancements at high latitudes at different periods in the north and the south.
Modeled O2 nightglow distributions in the Venusian atmosphere
Authors: Gagné Marie‐Ève , Melo Stella M. L. , Brecht Amanda S. , Bougher Stephen W. , Strong Kimberly
Published: October 2012

In this paper, we study the global distribution of the O2Infrared Atmospheric (0‐0) emission at 1.27μm in the Venusian atmosphere with an airglow model in combination with atmospheric conditions provided by a three‐dimensional model, the Venus Thermospheric Global Circulation Model. We compare our model simulations with airglow observations of this emission from the Visible and InfraRed Thermal Imaging Spectrometer on board the Venus Express orbiter. Our model is successful in reproducing the latitudinal and temporal trends seen in the observations for latitudes between 0° and 30°, while poleward of 30°, the model results start to diverge away from the measurements. We attribute this discrepancy to the atomic oxygen distribution at these latitudes in our model that is inconsistent with the recent measurements. We also conducted a sensitivity study to explore the dependence of the vertical structure and the distribution of the airglow emission on the atmospheric conditions. The sensitivity study confirms that changes in the distribution of atomic oxygen significantly affect the characteristics of the airglow layer. Therefore, meaningful comparisons with observations require a three‐dimensional model, which accounts for dynamical variations in the background atmosphere. With this investigation, we highlight the impact of the atmospheric conditions on the airglow distribution, which is important for the understanding of how the phenomenon plays.
Lunar floor‐fractured craters: Classification, distribution, origin and implications for magmatism and shallow crustal structure
Authors: Jozwiak Lauren M. , Head James W. , Zuber Maria T. , Smith David E. , Neumann Gregory A.
Published: October 2012

Floor‐Fractured Craters (FFCs) are a class of lunar craters characterized by anomalously shallow floors cut by radial, concentric, and/or polygonal fractures; additional interior features are moats, ridges, and patches of mare material. Two formation mechanisms have been hypothesized—floor uplift in response to shallow magmatic intrusion and sill formation, and floor shallowing in response to thermally driven viscous relaxation. This study combines new Lunar Orbiter Laser Altimeter (LOLA) and Lunar Reconnaissance Orbiter Camera (LROC) data to characterize and categorize the population of FFCs and map their distribution on the Moon, and uses variations in floor‐fractured crater morphology and regional distribution to investigate the proposed formation mechanisms. The population of FFCs was categorized according to the classes outlined by Schultz (1976). The distribution of these FFC categories shows an evolution of crater morphology from areas adjacent to lunar impact basins to areas in the lunar highlands. We propose that this trend is supportive of formation by shallow magmatic intrusion and sill formation—crustal thickness determines the magnitude of magmatic driving pressure, and thus either piston‐like floor uplift for high magnitude, or a convex floor profile for low magnitude. Predictions from previous studies modeling viscous relaxation are inconsistent with the observed altimetric profiles of FFCs. Hence our analysis favors FFC formation by shallow magmatic intrusion, with the variety of FFC morphologies being intimately linked with location and crustal thickness, and the driving pressure of the intrusion. Data from the GRAIL (Gravity Recovery and Interior Laboratory) mission will help to test these conclusions.
Antibodies against the extracellular domain of human Notch1 receptor reveal the critical role of epidermal-growth-factor-like repeats 25–26in ligand binding and receptor activation
Authors: Sharma Ankur , Rangarajan Annapoorni , Dighe Rajan R.
Published: October 2012

The Notch signalling pathway is implicated in a wide variety of cellular processes throughout metazoan development. Although the downstream mechanism of Notch signalling has been extensively studied, the details of its ligand-mediated receptor activation are not clearly understood. Although the role of Notch ELRs [EGF (epidermal growth factor)-like-repeats] 11–12 in ligand binding is known, recent studies have suggested interactions within different ELRs of the Notch receptor whose significance remains to be understood. Here, we report critical inter-domain interactions between human Notch1 ELRs 21–30 and the ELRs 11–15 that are modulated by calcium. Surface plasmon resonance analysis revealed that the interaction between ELRs 21–30 and ELRs 11–15 is ~10-fold stronger than that between ELRs 11–15 and the ligands. Although there was no interaction between Notch1 ELRs 21–30 and the ligands in vitro, addition of pre-clustered Jagged1Fc resulted in the dissociation of the preformed complex between ELRs 21–30 and 11–15, suggesting that inter-domain interactions compete for ligand binding. Furthermore, the antibodies against ELRs 21–30 inhibited ligand binding to the full-length Notch1 and subsequent receptor activation, with the antibodies against ELRs 25–26 being the most effective. These results suggest that the ELRs 25–26 represent a cryptic ligand-binding site which becomes exposed only upon the presence of the ligand. Thus, using specific antibodies against various domains of the Notch1 receptor, we demonstrate that, although ELRs 11–12 are the principal ligand-binding site, the ELRs 25–26 serve as a secondary binding site and play an important role in receptor activation.
Loss of LSD1 (lysine-specific demethylase 1) suppresses growth and alters gene expression of human colon cancer cells in a p53- and DNMT1(DNA methyltransferase 1)-independent manner
Authors: Jin Lihua , Hanigan Christin L. , Wu Yu , Wang Wei , Park Ben Ho , Woster Patrick M. , Casero Robert A.
Published: October 2012

Epigenetic silencing of gene expression is important in cancer. Aberrant DNA CpG island hypermethylation and histone modifications are involved in the aberrant silencing of tumour-suppressor genes. LSD1 (lysine-specific demethylase 1) is a H3K4 (histone H3 Lys4) demethylase associated with gene repression and is overexpressed in multiple cancer types. LSD1 has also been implicated in targeting p53 and DNMT1 (DNA methyltransferase 1), with data suggesting that the demethylating activity of LSD1 on these proteins is necessary for their stabilization. To examine the role of LSD1 we generated LSD1 heterozygous (LSD1+/−) and homozygous (LSD1−/−) knockouts in the human colorectal cancer cell line HCT116. The deletion of LSD1 led to a reduced cell proliferation both in vitro and in vivo. Surprisingly, the knockout of LSD1 in HCT116 cells did not result in global increases in its histone substrate H3K4me2 (dimethyl-H3K4) or changes in the stability or function of p53 or DNMT1. However, there was a significant difference in gene expression between cells containing LSD1 and those null for LSD1. The results of the present study suggested that LSD1 is critical in the regulation of cell proliferation, but also indicated that LSD1 is not an absolute requirement for the stabilization of either p53 or DNMT1.
Treatment of (Central) Auditory Processing Disorder: Bridging the Gap Between the Audiologist and the Speech-Language Pathologist
Authors: Buehler Velvet
Published: October 2012

There is a history of debate and controversy about the assessment and intervention of children diagnosed with auditory processing disorder (APD). Professionals in communication sciences and disorders view APD from different perspectives. Speech-language pathologists (SLPs) tend to view APD from the language and literacy perspective, or a top-down model, whereas audiologists tend to view APD from an auditory perception perspective, or a bottom-up model. Professionals who assess and treat children with APD need to bridge the gap and merge their different perspectives to plan effective intervention for children with APD. A panel of audiologists who demonstrated expertise in the area of Central Auditory Processing Disorders (CAPDs) developed The American Speech-Language-Hearing Association's (ASHA's) technical report on APDs (ASHA, 2005). This report was approved by ASHA's Executive board in 2005. In this report, central auditory processing refers to the efficiency and effectiveness by which the central nervous system uses auditory information. Central auditory processing includes the auditory mechanisms underlying the skills of sound localization and lateralization; auditory discrimination; auditory pattern recognition; temporal aspects of audition, including temporal integration, temporal discrimination, temporal ordering, and temporal masking; auditory performance in competing acoustic signals; and auditory performance with degraded acoustic signals (ASHA, 1996; Bellis, 2003; Chermak & Musiek, 1997; Jerger, 2009). A CAPD is a deficit in processing auditory input that is not due to higher-order language, cognitive, or related factors (Musiek, Bellis, & Chermak, 2005; Musiek & Chermak, 2007). However, children diagnosed with CAPD may experience difficulties in academic learning, speech, language, social skills, and literacy (e.g., encoding, decoding, reading comprehension, reading fluency, and written language).
Photocurrent spectroscopy of intersubband transitions in GaInAsN/(Al)GaAs asymmetric quantum well infrared photodetectors
Authors: Albo Asaf , Fekete Dan , Bahir Gad
Published: October 2012

We have studied the conduction band electronic level structure of GaInAsN/(Al)GaAs-based quantum well (QW) infrared photodetectors using intersubband photocurrent (PC) spectroscopy and dark current analysis. Photoluminescence and intersubband absorption were carried out as complementary spectroscopic techniques. Based on the observed transition energy, we associated the photocurrent peaks with electron excitations from bound states in the quantum wells to quasi-bound states in the continuum. A good agreement with the experimental results was obtained using a 10-band k · p model that took into account the inhomogeneous distribution of nitrogen atoms along the quantum well's growth direction.
Drop impact and wettability: From hydrophilic to superhydrophobic surfaces
Authors: Antonini Carlo , Amirfazli Alidad , Marengo Marco
Published: October 2012

Experiments to understand the effect of surface wettability on impact characteristics of water drops onto solid dry surfaces were conducted. Various surfaces were used to cover a wide range of contact angles (advancing contact angle from 48° to 166°, and contact angle hysteresis from 5° to 56°). Several different impact conditions were analyzed (12 impact velocities on 9 different surfaces, among which 2 were superhydrophobic). Results from impact tests with millimetric drops show that two different regimes can be identified: a moderate Weber number regime (30 < We < 200), in which wettability affects both drop maximum spreading and spreading characteristic time; and a high Weber number regime (We > 200), in which wettability effect is secondary, because capillary forces are overcome by inertial effects. In particular, results show the role of advancing contact angle and contact angle hysteresis as fundamental wetting parameters to allow understanding of different phases of drop spreading and beginning of recoiling. It is also shown that drop spreading on hydrophilic and superhydrophobic surfaces occurs with different time scales. Finally, if the surface is superhydrophobic, eventual impalement, i.e., transition from Cassie to Wenzel wetting state, which might occur in the vicinity of the drop impact area, does not influence drop maximum spreading.
Spring constant calibration of atomic force microscope cantilevers of arbitrary shape
Authors: Sader John E. , Sanelli Julian A. , Adamson Brian D. , Monty Jason P. , Wei Xingzhan , Crawford Simon A. , Friend James R. , Marusic Ivan , Mulvaney Paul , Bieske Evan J.
Published: October 2012

The spring constant of an atomic force microscope cantilever is often needed for quantitative measurements. The calibration method of Sader et al. [Rev. Sci. Instrum. 70, 3967 (1999)]10.1063/1.1150021 for a rectangular cantilever requires measurement of the resonant frequency and quality factor in fluid (typically air), and knowledge of its plan view dimensions. This intrinsically uses the hydrodynamic function for a cantilever of rectangular plan view geometry. Here, we present hydrodynamic functions for a series of irregular and non-rectangular atomic force microscope cantilevers that are commonly used in practice. Cantilever geometries of arrow shape, small aspect ratio rectangular, quasi-rectangular, irregular rectangular, non-ideal trapezoidal cross sections, and V-shape are all studied. This enables the spring constants of all these cantilevers to be accurately and routinely determined through measurement of their resonant frequency and quality factor in fluid (such as air). An approximate formulation of the hydrodynamic function for microcantilevers of arbitrary geometry is also proposed. Implementation of the method and its performance in the presence of uncertainties and non-idealities is discussed, together with conversion factors for the static and dynamic spring constants of these cantilevers. These results are expected to be of particular value to the design and application of micro- and nanomechanical systems in general.
A photonic wall pressure sensor for fluid mechanics applications
Authors: Manzo M. , Ioppolo T. , Ayaz U. K. , LaPenna V. , Ötügen M. V.
Published: October 2012

In this paper, we demonstrate a micro-optical wall pressure sensor concept based on the optical modes of dielectric resonators. The sensing element is a spherical micro-resonator with a diameter of a few hundred micrometers. A latex membrane that is flush mounted on the wall transmits the normal pressure to the sensing element. Changes in the wall pressure perturb the sphere's morphology, leading to a shift in the optical modes. The wall pressure is measured by monitoring the shifts in the optical modes. Prototype sensors with polydimethylsiloxane micro-spheres are tested in a steady two-dimensional channel flow and in a plane wave acoustic tube. Results indicate sensor resolutions of ∼20 mPa and bandwidth of up to 2 kHz.
The quantum free particle on spherical and hyperbolic spaces: A curvature dependent approach. II
Authors: Cariñena José F. , Rañada Manuel F. , Santander Mariano
Published: October 2012

This paper is the second part of a study of the quantum free particle on spherical and hyperbolic spaces by making use of a curvature-dependent formalism. Here we study the analogues, on the three-dimensional spherical and hyperbolic spaces, \documentclass[12pt]{minimal}\begin{document}$S_\kappa ^3$\end{document}Sκ3 (κ > 0) and \documentclass[12pt]{minimal}\begin{document}$H_k^3$\end{document}Hk3 (κ < 0), to the standard spherical waves in E3. The curvature κ is considered as a parameter and for any κ we show how the radial Schrödinger equation can be transformed into a κ-dependent Gauss hypergeometric equation that can be considered as a κ-deformation of the (spherical) Bessel equation. The specific properties of the spherical waves in the spherical case are studied with great detail. These have a discrete spectrum and their wave functions, which are related with families of orthogonal polynomials (both κ-dependent and κ-independent), and are explicitly obtained.
Quantum mechanics in fractional and other anomalous spacetimes
Authors: Calcagni Gianluca , Nardelli Giuseppe , Scalisi Marco
Published: October 2012

We formulate quantum mechanics in spacetimes with real-order fractional geometry and more general factorizable measures. In spacetimes where coordinates and momenta span the whole real line, Heisenberg's principle is proven and the wave-functions minimizing the uncertainty are found. In spite of the fact that ordinary time and spatial translations are broken and the dynamics is not unitary, the theory is in one-to-one correspondence with a unitary one, thus allowing us to employ standard tools of analysis. These features are illustrated in the examples of the free particle and the harmonic oscillator. While fractional (and the more general anomalous-spacetime) free models are formally indistinguishable from ordinary ones at the classical level, at the quantum level they differ both in the Hilbert space and for a topological term fixing the classical action in the path integral formulation. Thus, all non-unitarity in fractional quantum dynamics is encoded in a contribution depending only on the initial and final states.
Entropy distance: New quantum phenomena
Authors: Weis Stephan , Knauf Andreas
Published: October 2012

We study a curve of Gibbsian families of complex 3 × 3-matrices and point out new features, absent in commutative finite-dimensional algebras: a discontinuous maximum-entropy inference, a discontinuous entropy distance, and non-exposed faces of the mean value set. We analyze these problems from various aspects including convex geometry, topology, and information geometry. This research is motivated by a theory of infomax principles, where we contribute by computing first order optimality conditions of the entropy distance.
The influence of the horizontal component of the temperature gradient on nonlinear convective oscillations in two-layer systems
Authors: Simanovskii Ilya B. , Viviani Antonio , Dubois Frank , Legros Jean-Claude
Published: October 2012

The influence of the horizontal component of the temperature gradient on nonlinear oscillatory convective regimes, developed under the joint action of buoyant and thermocapillary effects in the 47 v2 silicone oil-water system, is investigated. Cavities with different lengths have been considered. Transitions between oscillatory flow regimes with different symmetry properties and steady flows have been studied. It is shown that under the action of the horizontal component of the temperature gradient, specific asymmetric oscillatory flow develops in the system.
Effects of moderate Reynolds numbers on subsonic round jets with highly disturbed nozzle-exit boundary layers
Authors: Bogey Christophe , Marsden Olivier , Bailly Christophe
Published: October 2012

The effects of moderate Reynolds numbers on the flow and acoustic fields of initially highly disturbed isothermal round jets at Mach number M = 0.9 and diameter-based Reynolds numbers ReD between 2.5 × 104 and 2 × 105 are investigated using large-eddy simulation under carefully controlled conditions. To the best of our knowledge, this is the first comprehensive study of its kind. The jets originate at z = 0 from a pipe nozzle of radius r0, in which a tripping procedure is applied to the boundary layers. At the nozzle exit, laminar-like mean velocity profiles of thickness δ ≃ 0.15r0 and momentum thickness δθ ≃ 0.018r0, yielding Reynolds numbers Reθ varying from 256 to 1856 depending on ReD, and peak turbulence intensities around 9% of the jet velocity, are thus obtained. As the Reynolds number increases, the mixing layers develop more slowly, with smaller integral length scales and lower levels of velocity fluctuations. The axial profiles of turbulence intensities become smoother, showing a clear overshoot around z = 2r0 at ReD = 2.5 × 104, but a monotonical growth at ReD = 2 × 105. Velocity spectra downstream of the nozzle exit also broaden with ReD, as expected. Large-scale components usually observed in turbulent boundary layers and shear layers, characterized by Strouhal numbers Stθ ≃ 0.013 around z = r0 and by azimuthal spacings λθ ≃ δ, remain dominant, although the contribution of fine-scale structures with λθ ⩽ δ/2 strengthens. Moreover, with rising ReD, the jet potential core lengthens slightly, but the flow properties do not change significantly farther downstream. Finally, lower sound pressure levels are generated, with a decrease of about 2 dB over the range of ReD considered.
Ab initio study of low-lying excited states of HCl: Accurate calculations of optical valence-shell excitations
Authors: Engin Selma , Sisourat Nicolas , Carniato Stéphane
Published: October 2012

We present accurate ab initio potential energy surfaces and dipole transition moments of numerous low-lying states of HCl in a large range of internuclear distances. Using these results, we computed the visible/ultra-violet absorption spectrum of HCl covering the energy range up to the first ionization potential and the absolute optical oscillator strengths for the first discrete electronic transitions. Comparison of these theoretical results is done with the available experimental and theoretical data. Finally, we present a complete peaks-attribution of the HCl electronic absorption spectrum. Our results are in good agreement with the available experimental results.
A Cartesian classical second-quantized many-electron Hamiltonian, for use with the semiclassical initial value representation
Authors: Li Bin , Miller William H.
Published: October 2012

A new classical model for the general second-quantized many-electron Hamiltonian in Cartesian coordinates and momenta is presented; this makes semiclassical (SC) calculations using an initial value representation (IVR) more useful than the classical Hamiltonian in action-angle variables given earlier by Miller and White [J. Chem. Phys. 84, 5059–5066 (1986)]10.1063/1.450655. If only 1-electron terms are included in this Hamiltonian, the classical equations of motion for the Cartesian variables are linear, and the SC-IVR gives exact results for the propagator (and thus for transition probabilities, the energy spectrum, etc.), as confirmed by analytic proof and numerical calculations. Though this new Hamiltonian is not exact when 2-electron interactions are included, we observe good results for the SC-IVR transition probabilities for times that are not too long. Test calculations, for example, show that the SC-IVR is accurate for times long enough to obtain good result for the eigenvalue spectrum (i.e., the energy levels of the electronic system).
Decoupled cantilever arms for highly versatile and sensitive temperature and heat flux measurements
Authors: Burg Brian R. , Tong Jonathan K. , Hsu Wei-Chun , Chen Gang
Published: October 2012

Microfabricated cantilever beams have been used in microelectromechanical systems for a variety of sensor and actuator applications. Bimorph cantilevers accurately measure temperature change and heat flux with resolutions several orders of magnitude higher than those of conventional sensors such as thermocouples, semiconductor diodes, as well as resistance and infrared thermometers. The use of traditional cantilevers, however, entails a series of important measurement limitations, because their interactions with the sample and surroundings often create parasitic deflection forces and the typical metal layer degrades the thermal sensitivity of the cantilever. The paper introduces a design to address these issues by decoupling the sample and detector section of the cantilever, along with a thermomechanical model, the fabrication, system integration, and characterization. The custom-designed bi-arm cantilever is over one order of magnitude more sensitive than current commercial cantilevers due to the significantly reduced thermal conductance of the cantilever sample arm. The rigid and immobile sample section offers measurement versatility ranging from photothermal absorption, near-field thermal radiation down to contact, conduction, and material thermal characterization measurements in nearly identical configurations.
Curvature singularity in the asymmetric breakup of an underwater air bubble
Authors: Lai Lipeng
Published: October 2012

The presence of slight azimuthal asymmetry in the initial shape of an underwater bubble entirely alters the final breakup dynamics. Here, I examine the influence of initial asymmetry on the final breakup by simulating the bubble surface evolution as a Hamiltonian evolution corresponding to an inviscid, two-dimensional, planar implosion. I find two types of breakups: a previously reported coalescence mode in which distant regions along the air-water surface curve inwards and eventually collide with finite speed, and a hitherto uncharacterized cusp-like mode where the surface develops sharp tips whose radii of curvature are much smaller than the average neck radius. I present three sets of results that characterize the nature of this cusp mode. First, I show that the cusp-like mode corresponds to a phase space trajectory that passes close to a saddle-node structure. In other words, an evolution towards a cross-section shape with sharp tips invariably later evolves away from it. In phase space, this saddle-node separates coalescence modes whose coalescence planes lie along different spatial orientations. Second, I show that the formation of the sharp tips can be interpreted as a weakly first-order transition which becomes second-order, corresponding to the formation of a finite-time curvature singularity, in the limit that the initial perturbation amplitude approaches zero. Third, I show that, as the curvature singularity is approached, the maximum surface curvature diverges approximately as (tc − t)−0.8, where tc is the onset time of the singularity and the maximum velocity diverges approximately as (tc − t)−0.4. In practice, these divergences imply that viscous drag and compressibility of the gas flow, two effects not included in my analysis, become significant as the interface evolves towards the curvature singularity.
Pure rotational spectra of the CO–trans-HOCO complex
Authors: Oyama Takahiro , Sumiyoshi Yoshihiro , Endo Yasuki
Published: October 2012

Pure rotational spectra of the CO–trans-HOCO complex have been observed by Fourier transform microwave (FTMW) and millimeter-wave FTMW double resonance spectroscopy. The complex was produced in a supersonic jet by discharging a mixture gas of CO and H2O diluted in Ar. The molecular constants including the fine and hyperfine coupling constants have been precisely determined. The inter-molecular distance between the CO and trans-HOCO monomers has been determined by fixing the structures of the trans-HOCO and CO monomers, where this complex has the OC⋯HO configuration with the C⋯HO angle almost linear. The C⋯H distance, 2.166 Å, is much shorter than those of the closed shell complexes, CO–CH3OH and CO–H2O. The Fermi contact constant of the proton for the complex was compared with that of the trans-HOCO monomer, leading to a conclusion that there is almost no induced effect for the spin density on the proton of HOCO by the complex formation.
Effective diffusivity through arrays of obstacles under zero-mean periodic driving forces
Authors: Alvarez-Ramirez J. , Dagdug L. , Valdes-Parada F. J.
Published: October 2012

We perform a numerical investigation of the transport of Brownian particles driven by a zero-mean periodic force across two-dimensional arrays of obstacles with finite length. By applying axial and transversal driving forces relative to the diffusion transport direction, the effective diffusivity is determined as function of the array geometry and the driving frequency, finding excess diffusion peaks at certain frequency ranges. The results indicate that a suitable selection of the axial and transversal frequencies yields enhanced diffusion transport along the axial direction. Symmetric and asymmetric arrays are considered, showing that the asymmetry has a detrimental effect in the magnitude of the excess diffusion peaks. This suggests that enhanced diffusion is obtained because the oscillatory driving force exploits preferential transport channels, whose effective obstacle spacing is maximized under symmetric configurations.
Chemical potential evaluation in NVT lattice-gas simulations
Authors: Pazzona Federico G. , Demontis Pierfranco , Suffritti Giuseppe B.
Published: October 2012

The discrete nature of the partition function of a lattice-gas system can be exploited to build an efficient strategy for the evaluation of the chemical potential of a periodic lattice-gas with arbitrarily ranged interactions during a simulation in the canonical ensemble, with the need of no additional sampling as it were required instead by the Widom insertion/deletion approach. The present method is based on the main concepts of the small system grand ensemble [for details, see G. Soto-Campos, D. S. Corti, and H. Reiss, J. Chem. Phys. 108, 2563 (1998)10.1063/1.475640], whose key idea is to study the properties of a sublattice (called small system) and of its complementary (the reservoir sublattice) as they were two separated subsystems. The accuracy of the measured chemical potential can be further improved by artificially “restoring” the missing connections among the reservoir sublattice sites located at the boundaries with the small system. We first illustrate the theory and then we compare μVT with NVT simulation results on several test systems.
Electronic structure and optical band gap of CoFe2O4 thin films
Authors: Ravindra A. V. , Padhan P. , Prellier W.
Published: October 2012

Electronic structure and optical band gap of CoFe2O4 thin films grown on (001) oriented LaAlO3 have been investigated. Surprisingly, these films show additional Raman modes at room temperature as compared to a bulk spinel structure. The splitting of Raman modes is explained by considering the short-range ordering of Co and Fe cations in octahedral site of spinel structure. In addition, an expansion of band-gap is observed with the reduction of film thickness, which is explained by the quantum size effect and misfit dislocation. Such results provide interesting insights for the growth of spinel phases.
Plasmonic coupling effect between two gold nanospheres for efficient second-harmonic generation
Authors: Wang Ben-Li , Ren Ming-Liang , Li Jia-Fang , Li Zhi-Yuan
Published: October 2012

The coupling effect between two gold nanospheres (GNSs) is investigated for second-harmonic generation (SHG) in this paper. When the two GNSs approach each other, the coupling effect becomes stronger, and it consequently leads to stronger enhancement of SHG. A strong coupling area between two GNSs is also found. We propose a physical quantity, the coupling strength to describe the coupling effect on SHG enhancement and show that it can fully illustrate the relationship between the SHG enhancement and the gap of two GNSs. Moreover, further calculations reveal the existence of hot spots of both fundamental wave (FW) and excited second harmonic wave in the intermediate region of two GNSs. Our study can not only help to understand the coupling effect on SHG precisely but also offer some possibility to design a nonlinear plasmonic nano-ruler.
Piezoelectric and electrostrictive effects in ferroelectret ultrasonic transducers
Authors: Döring Joachim , Bovtun Viktor , Gaal Mate , Bartusch Jürgen , Erhard Anton , Kreutzbruck Marc , Yakymenko Yuriy
Published: October 2012

Electromechanical response of polypropylene ferroelectret transducers under application of high-voltage pulses was measured by laser Doppler vibrometry and compared with results of ultrasonic through-air transmission between two ferroelectret transducers. The electromechanical response was completely explained by piezoelectric and electrostrictive effects. The electrostrictive effect dominates at high voltages and provides significant enlargement of the transducer constant, up to factor of 2.5. The induced strain of 1.7% was achieved at −2000 V. The nonlinear ultrasonic transmission was shown to be well described by the piezoelectric and electrostrictive response of transmitter, except in the range of high negative exciting voltages where some limitation of the transmitted signal was observed. This limitation seems not to be a fundamental one and does not abolish the advantages of high-voltage excitation of polypropylene ferroelectret transducers.
Light trapping with total internal reflection and transparent electrodes in organic photovoltaic devices
Authors: Tvingstedt Kristofer , Tang Zheng , Inganäs Olle
Published: October 2012

Herein, we demonstrate a method to build highly efficient light trapping structures for printed organic solar cells and modules, compatible with roll to roll manufacturing. Echelle grating structures in combination with semitransparent electrodes allow for efficient light trapping via means of total internal reflection. With this method, we demonstrate an increased cell photocurrent response up to 24%, compared to a standard cell configuration with a planar reflector. The demonstrated light trapping approach is expected to be even more useful for photovoltaic modules, where light hitting “dead areas” in between the sub-cells comprising the module will now be utilized.
Particle manipulation using an ultrasonic micro-gripper
Authors: Walker Robert , Gralinski Ian , Keong Lay Kok , Alan Tuncay , Neild Adrian
Published: October 2012

We show that ultrasonic micro-grippers, 100 μm high segmented circular structures actuated with piezoelectric elements, can be used to establish a localised resonant pressure field within a fluid droplet, and hence allow effective manipulation of silica microspheres independently from the global boundaries of the fluid volume. We demonstrate through experiments and simulations that despite variations in the fluid shape and location, the method achieves particle clustering in consistent locations at fixed operating frequencies.
Inclined-incidence quasi-Fresnel lens for prefocusing of synchrotron radiation x-ray beams
Authors: Kagoshima Yasushi , Takano Hidekazu , Takeda Shingo
Published: October 2012

An inclined-incidence quasi-Fresnel lens made of acrylic resin has been developed for prefocusing in synchrotron radiation x-ray beamlines. By inclining the lens, the grating aspect ratio is large enough for x-ray use. As it operates in transmission mode with negligible beam deflection and offset, little additional equipment is needed to introduce it into existing beamlines. It is fabricated by sheet-press forming, enabling inexpensive mass production. The prototype was able to focus a 730-μm-wide beam to a width of 80 μm with a photon flux density gain of 5.6 at an x-ray energy of 10 keV.
Characterizing the energy distribution of laser-generated relativistic electrons in cone-wire targets
Authors: Sawada H. , Higginson D. P. , Link A. , Ma T. , Wilks S. C. , McLean H. S. , Pérez F. , Patel P. K. , Beg F. N.
Published: October 2012

Transport of relativistic electrons in a solid Cu wire target has been modeled with the implicit hybrid particle-in-cell code LSP to investigate the electron energy distribution and energy coupling from the high-intensity, short-pulse laser to electrons entering to the wire. Experiments were performed on the TITAN laser using a 1.5 mm long Cu wire attached to a Au cone tip at the laser intensity of 1 × 1020 W/cm2 which was irradiated into the cone. The simulated Cu Kα wire profile and yields matched the measurements using a two-temperature energy distribution. These modeling results show that the cold component of the energy spectrum can be determined with ±100 keV accuracy from the fit to the initial experimental fall-off of the Kα emission while the simulated profiles were relatively insensitive to the hotter component of the electron distribution (>4 MeV). The slope of measured escaped electrons was used to determine the hotter temperature. Using exponential energy distributions, the laser-to-electron-in-wire coupling efficiencies inferred from the fits decreased from 3.4% to 1.5% as the prepulse energy increases up to 1 J. The comparison of the energy couplings using the exponential and Relativistic Maxwellian distribution functions showed that the energy inferred in the cold component is independent of the type of the distribution function.
Millimeterwave Schottky diode on grapene monolayer via asymmetric metal contacts
Authors: Dragoman Mircea , Deligeorgis George , Muller Alexandru , Cismaru Alina , Neculoiu Dan , Konstantinidis George , Dragoman Daniela , Dinescu Adrian , Comanescu Florin
Published: October 2012

The paper presents the experiments regarding a Schottky diode fabricated on a graphene monolayer using asymmetric metallic contacts. The current is in the mA range, which is with orders of magnitude higher than for reported Schottky diodes prepared on graphene bilayers or related graphene materials. Moreover, this device exhibits a DC controllable phase shift of more than 20 degrees in the range 40–65 GHz.
Hard magnetic properties of Mn-Ga melt-spun ribbons
Authors: Saito Tetsuji , Nishimura Ryuji
Published: October 2012

Mn-Ga alloys were produced by melt-spinning followed by various heat treatments. Although the as-rapidly quenched Mn-Ga melt-spun ribbons showed low remanence and coercivity, annealing of the ribbons resulted in an increase in the remanence and coercivity values. The optimally annealed Mn70Ga30melt-spun ribbon with the DO22-Mn3Ga phase exhibited a coercivity of 5.7 kOe. The Curie temperature of the DO22-Mn3Ga phase was found to be around 730 K.
Influence of the surface morphology on the channel mobility of lateral implanted 4H-SiC(0001) metal-oxide-semiconductor field-effect transistors
Authors: Fiorenza Patrick , Giannazzo Filippo , Frazzetto Alessia , Roccaforte Fabrizio
Published: October 2012

The influence of the surface morphology on the channel mobility of 4H-SiC metal-oxide-semiconductor field effect transistors annealed under two different conditions is discussed. The devices were fabricated using post-implantation annealing at 1650 °C. In particular, while the use of a protective capping layer during post-implantation annealing preserved a smooth 4H-SiC surface resulting in a channel mobility of 24 cm2 V−1 s−1, a rougher morphology of the channel region (with the presence of surface macrosteps) was observed in the devices annealed without protection, which in turn exhibited a higher mobility (40 cm2 V−1 s−1). An electrical analysis of SiO2/SiC capacitors demonstrated a reduction of the interface state density from 7.2 × 1011 to 3.6 × 1011 cm−2 eV−1, which is consistent with the observed increase of the mobility. However, high resolution transmission electron microscopy showed an almost atomically perfect SiO2/4H-SiC interface. The electrical results were discussed considering the peculiar surface morphology of the annealed 4H-SiC surfaces, i.e., attributing the overall reduction of the interface state density to the appearance of macrosteps exposing non-basal planes.
Temperature and frequency dependent conductivity of bismuth zinc vanadate semiconducting glassy system
Authors: Punia R. , Kundu R. S. , Dult Meenakshi , Murugavel S. , Kishore N.
Published: October 2012

The ac conductivity of bismuth zinc vanadate glasses with compositions 50V2O5. xBi2O3. (50-x) ZnO has been studied in the frequency range 10−1 Hz to 2 MHz and in temperature range 333.16 K to 533.16 K. The temperature and frequency dependent conductivity is found to obey Jonscher's universal power law for all the compositions of bismuth zinc vanadate glass system. The dc conductivity (σdc), crossover frequency (ωH), and frequency exponent (s) have been estimated from the fitting of experimental data of ac conductivity with Jonscher's universal power law. Enthalpy to dissociate the cation from its original site next to a charge compensating center (Hf) and enthalpy of migration (Hm) have also been estimated. It has been observed that mobility of charge carriers and ac conductivity in case of zinc vanadate glass system increases with increase in Bi2O3 content. In order to determine the conduction mechanism, the ac conductivity and its frequency exponent have been analyzed in the frame work of various theoretical models based on classical hopping over barriers and quantum mechanical tunneling. The ac conduction takes place via tunneling of overlapping large polarons in all the compositions of presently studied vanadate glasses. The fitting of experimental data of ac conductivity with overlapping large polarons tunneling model has also been done. The parameters; density of states at Fermi level (N(EF)), activation energy associated with charge transfer between the overlapping sites (WHO), inverse localization length (α) and polaron radius (rp) obtained from fitting of this model with experimental data are reasonable.
Infrared properties of randomly oriented silver nanowires
Authors: Larciprete M. C. , Albertoni A. , Belardini A. , Leahu G. , Li Voti R. , Mura F. , Sibilia C. , Nefedov I. , Anoshkin I. V. , Kauppinen E. I. , Nasibulin A. G.
Published: October 2012

We experimentally investigated the infrared properties of a set of randomly oriented silver nanowires films deposited onto glass substrate. Infrared emission of the obtained films was characterized in the long infrared range, i.e., 8–12 μm, by observing their temperature evolution under heating regime with a focal plane array infrared camera as well as a thermocouple. The obtained experimental results showed that the infrared emission from a mesh composed of silver nanowires might be tailored by opportunely assessing preparation condition, such as the metal filling factor. From the theoretical point of view, the real and imaginary part of the electrical permittivity components were retrieved from the calculations of effective permittivities of in-plane randomly oriented metallic wires, thus giving the refractive index and extinction coefficients for the four different silver nanowires meshes. Due to the correspondence between emissivity and absorbance, the experimental results are interpreted with the reconstructed corresponding absorbance spectra, thus suggesting that these coatings are suitable for infrared signature reduction applications.
Thermal conduction properties of Mo/Si multilayers for extreme ultraviolet optics
Authors: Bozorg-Grayeli Elah , Li Zijian , Asheghi Mehdi , Delgado Gil , Pokrovsky Alexander , Panzer Matthew , Wack Daniel , Goodson Kenneth E.
Published: October 2012

Extreme ultraviolet (EUV) lithography requires nanostructured optical components, whose reliability can be influenced by radiation absorption and thermal conduction. Thermal conduction analysis is complicated by sub-continuum electron and phonon transport and the lack of thermal property data. This paper measures and interprets thermal property data, and their evolution due to heating exposure, for Mo/Si EUV mirrors with 6.9 nm period and Mo/Si thickness ratios of 0.4/0.6 and 0.6/0.4. We use time-domain thermoreflectance and the 3ω method to estimate the thermal resistance between the Ru capping layer and the Mo/Si multilayers (RRu-Mo/Si = 1.5 m2 K GW−1), as well as the out-of-plane thermal conductivity (kMo/Si 1.1 W m−1 K−1) and thermal anisotropy (η = 13). This work also reports the impact of annealing on thermal conduction in a co-deposited MoSi2 layer, increasing the thermal conductivity from 1.7 W m−1 K−1 in the amorphous phase to 2.8 W m−1 K−1 in the crystalline phase.
Anomalous dip observed in intensity autocorrelation function as an inherent nature of single-photon emitters
Authors: Nakajima H. , Kumano H. , Iijima H. , Suemune I.
Published: October 2012

We report the observation of an anomalous antibunching dip in intensity autocorrelation function with photon correlation measurements on a single-photon emitter (SPE). We show that the anomalous dip observed is a manifestation of quantum nature of SPEs. Taking population dynamics in a quantum two-level system into account correctly, we redefine intensity autocorrelation function. This is of primary importance for precisely evaluating the lowest-level probability of multiphoton generation in SPEs toward realizing versatile pure SPEs for quantum information and communication.
Optical phase conjugation in azo-dye doped chiral liquid crystal
Authors: Karpinski Pawel , Miniewicz Andrzej
Published: October 2012

We report on optical phase conjugation phenomenon observed in chiral nematic liquid crystal showing band gap type Bragg reflection. The phase conjugate to the signal beam is observable only in the small temperature interval when the Bragg condition is fulfilled and only for circularly polarized light. The optical phase conjugation signals were observed at low cw laser light intensities (<100 mW/cm2, λ = 532 nm). Estimated value of third order optical susceptibility χ(3) = 2.8 × 10−17 m2/V2 is attributed to enhancement due to photoisomerisation of azo-dye (disperse red 1) inducing molecular reorientation process of liquid crystal molecules.
High-speed plasmonic nanolithography with a solid immersion lens-based plasmonic optical head
Authors: Kim Taeseob , Lee Won-Sup , Joe Hang-Eun , Lim Geon , Choi Guk-Jong , Gang Myeong-Gu , Kang Sung-Mook , Park Kyoung-Su , Min Byung-Kwon , Park Young-Pil , Park No-Cheol
Published: October 2012

This letter describes the use of a plasmonic optical head to achieve high-speed nanopatterning. A plasmonic optical head employs both a sharp-ridged nanoaperture and a nanogap control to maintain the nanogap required for near-field nanolithography. The nanogap control uses a gap error signal produced by evanescent coupling through the air-gap. We demonstrate that a plasmonic optical head achieves a patterning resolution of 70 nm and a patterning speed of 100 mm/s. The proposed combination of a surface plasmon nanoaperture and a nanogap servo system is one of the strategies used to achieve high-speed, high-resolution nanolithography.
Improvement of optical performance of ZnO/GaN p-n junctions with an InGaN interlayer
Authors: Wang T. , Wu H. , Wang Z. , Chen C. , Liu C.
Published: October 2012

The ZnO films were deposited on GaN and with an interlayer of InGaN by atomic layer deposition. The orientation of the ZnO films was 〈0001〉 on InGaN, whereas it was 〈707¯4〉 (perpendicular to (101¯0) plane) on GaN. The lattice mismatch between ZnO and InGaN was about 0.3%, which is lower than that between ZnO and GaN (1.6%). With a lower lattice mismatch, the intensity of the near-band-edge emission increased about 120% and the full width at half maximum decreased 7.3 nm. Furthermore, ZnO/InGaN/GaN heterostructured light emitting diodes were fabricated. The electroluminescence spectra under forward bias showed a blue emission accompanied by a broad peak centered at 600 nm.