bluuebunny/crossref_metadata_2025 huggingface dataset:
Wakimoto discusses role as NSF's incoming assistant director of geosciences
Authors: Showstack Randy
Published: December 2012

Roger Wakimoto's adrenaline “is starting to pump,” the incoming assistant director for geosciences (GEO) at the U.S. National Science Foundation (NSF) told Eos during an exclusive interview at this month's AGU Fall Meeting in San Francisco. Wakimoto, whose scientific expertise is in extreme weather, is scheduled to take charge as head of the NSF directorate for geosciences starting in February 2013. During his 4‐year appointment at NSF, Wakimoto, 59 and an avowed workaholic, will head up the GEO directorate, which has about an $880 million annual funding portfolio and provides about 55% of federal funding for geosciences basic research at U.S. academic institutions. The directorate currently includes the divisions of atmospheric and geospace sciences, Earth sciences, and ocean sciences. In addition, NSF's Office of Polar Programs is slated to become a GEO division under a realignment plan announced on 7 September; Wakimoto said that shift had “no bearing” on his decision to accept the position.
Recent and deep pasts in paleoclimate model intercomparison project
Authors: Crucifix Michel , Harrison Sandy , Brierley Chris
Published: December 2012

Second Workshop of the Palaeoclimate Modelling Intercomparison Project Phase 3;Crewe, United Kingdom, 6–11 May 2012 The Palaeoclimate Modelling Intercomparison Project (PMIP) is an international initiative endorsed by the World Climate Research Programme, the International Geosphere‐Biosphere Programme, and the Past Global Changes Project. Its objective is to provide a coherent framework to assess climate models and investigate climate dynamics on the basis of paleoclimate evidence. To this end, PMIP provides protocols for simulations of a set of past epochs with climate models, centralizes model output and facilitates access to it, and organizes syntheses of paleoclimate observations for model evaluation.
Biological aerosol effects on clouds and precipitation
Authors: Hallar A. Gannet , Huffman J. Alex , Fridlind Ann
Published: December 2012

Bioaerosol Effects on Clouds Workshop;Steamboat Springs, Colorado, 5–6August 2012 Bioaerosols such as bacteria have been proposed as significant contributors to cloud ice nucleation, but too little is known about the properties and impacts of bioaerosol and other ice nuclei to make reliable conclusions about their wide‐scale impact on clouds and precipitation. During late summer an international group of 40 participants met at a Steamboat Springs ski resort to share perspectives on bioaerosol sources, activity, and influence on clouds. Participants who were invited collectively spanned a broad range of expertise, including atmospheric chemistry, microbiology, micrometeorology, and cloud physics, as well as a broad range of research approaches, including laboratory measurement, field measurement, and modeling. Tours of Storm Peak Laboratory (http://www.stormpeak.dri.edu) were offered before and after the workshop.
Global precipitation variability decreased from 1940 to 2009
Authors: Schultz Colin
Published: December 2012

One of the strongly held assumptions of climate change is that the variability of precipitation will grow with an increase in temperature. Storms will become heavier but less frequent. Flash floods and droughts will increase. Regions that see extensive rainfall will get even more while arid regions will dry out. These projections stem from the way temperature affects precipitation patterns in global models. However, drawing on seven databases representing global monthly mean precipitation values, Sun et al. found that from 1940 to 2009 global overland precipitation variability actually decreased. In addition, they found that the changes in precipitation patterns that did occur led to a redistribution of rainfall such that on average wet areas and seasons got drier, and dry areas and seasons got wetter.
Measuring diapycnal diffusion in the tropical northeastern Atlantic
Authors: Schultz Colin
Published: December 2012

In the upper ocean, turbulence‐driven mixing uses energy to drive water flows across density bands. The rate of this flow, called diapycnal diffusion, is thought to have a strong effect on circulation patterns by mediating the global meridional overturning circulation as well as on the vertical exchange of oxygen. Direct observations of the cross‐density‐band flows, however, are scarce, making accurate representations of the mechanism in circulation models difficult. Starting in 1992, researchers began employing large‐scale tracer experiments to measure the rate of diapycnal diffusion in various ocean basins worldwide. Adding to this collection of experiments, Banyte et al. used a trifluoromethyl sulfur pentafluoride tracer to track ocean circulations in the tropical northeastern Atlantic over a 30‐month period from 2008 to 2010. The authors distributed tracer streaks at a depth of around 330 meters, following a band of consistent density, in their study region south of the Cape Verde Islands. Samples taken 7, 20, and 30 months later allowed them to follow the tracers' dispersion.
Most high‐energy particle injections do not reach geostationary orbit
Authors: Schultz Colin
Published: December 2012

The injection of high‐energy particles into the inner magnetotail is often considered a reliable sign of a magnetic substorm. These injections are often thought to be caused by flow bursts, short‐lived periods of narrow fast flow streams in the magnetotail. Analyzing records of flow bursts at the entry to the night‐side inner magnetosphere, from 8 to 13 Earth radii, as seen by Geotail from 1995 to 2005, and by the Time History of Events and Macroscale Interactions During Substorms (THEMIS) satellite from 2008 to 2009, Sergeev et al. found that most flow bursts do not cause the injection of high‐energy particles to geostationary altitudes, and thus such injections are a poor measure of substorm activity.
Hydrological resilience and how catchments can switch steady states
Authors: Schultz Colin
Published: December 2012

If a system has a positive feedback, then it may have multiple stable states, or attractors, and finite resilience. Traditional techniques to calculate system resilience to outside pressures revolve around identifying the system state at a transition point and then figuring out how far that is from a steady state. An increasing number of hydrological systems with positive feedbacks have been modeled, including peatlands, wetlands, lakes, and saline aquifers. For groundwater, changes in rainfall may lead to a switch in the steadystate groundwater level, even if the rainfall returns to its past values. To date it has been unclear how climate causes a switch between steady states. Using a simple aquifer model, Peterson et al. explored how a catchment switches steady states and the associated groundwater level dynamics.
The 11‐year solar cycle continues during prolonged sunspot minima
Authors: Schultz Colin
Published: December 2012

Streaming into the solar system at nearly the speed of light, galactic cosmic rays (GCRs) are a high‐energy mix of protons, electrons, and atomic nuclei. As they pass into reach of the outflowing solar wind, the propagation of GCRs is inhibited. Galactic cosmic rays that make it to Earth interact with the atmosphere, creating a shower of heavy isotopes including beryllium‐10. Beryllium‐10 isotope concentrations recorded in ice cores provide a long‐term, high temporal resolution record of galactic cosmic ray flux.
Apparent overconsolidation of mudstones in the Kumano Basin of southwest Japan: Implications for fluid pressure and fluid flow within a forearc setting
Authors: Guo Junhua , Underwood Michael B. , Likos William J. , Saffer Demian M.
Published: December 2012

The Kumano Basin is located in the Nankai Trough subduction zone of southwest Japan. During the past 1.6 million years, approximately 800 meters of sandy turbidites and hemipelagic mud were deposited near the distal edge of the forearc basin, at Site C0002 of the Integrated Ocean Drilling Program. Constant‐rate‐of‐strain consolidation tests yield estimates of in situ permeability that range from 2.6 × 10−17 m2 to 2.5 × 10−18 m2; overconsolidation ratios range from 1.7 to 2.6, and values of the compression index range from 0.39 to 0.78. Several processes contributed to the apparent overconsolidation. Strata dip toward land, and pore fluids probably migrate up‐dip and vent along a bathymetric notch near the seaward edge of the basin. Efficient lateral drainage through sandy turbidites has kept pore pressures within interbeds of mudstone at (or close to) hydrostatic. In addition, alteration of dispersed volcanic glass, precipitation of authigenic clay minerals, and collapse of random grain fabric has probably strengthened the bonding among grains. Cementation is particularly likely within the lower basin (unit III), where values of porosity remain anomalously high. If fluid overpressures (and underconsolidation) exist anywhere within the basin, the most likely loci are where sandy turbidites terminate against impermeable mudstones along landward‐dipping on‐lap surfaces. Those types of on‐lap geometries, in addition to structural closures, might provide promising targets for oil/gas accumulation in other forearc basins, particularly where petroleum source rocks have been buried to the optimal depths of catagenesis.
Selecting Skills To Teach Communication Partners: Where Do I Start?
Authors: Binger Cathy , Kent-Walsh Jennifer
Published: December 2012

Clinicians and researchers long have recognized that teaching communication partners how to provide AAC supports is essential to AAC success. One way to improve clinical outcomes is to select appropriate skills to teach communication partners. Although this sometimes seems like it should be a straightforward component of any intervention program, deciding which skills to teach partners can present multiple challenges. In this article, we will troubleshoot common issues and discuss how to select skills systematically, resulting in the desired effects for both communication partners and clients.
Peer-Mediated AAC Instruction for Young Children With Autism and other Developmental Disabilities
Authors: Thiemann-Bourque Kathy
Published: December 2012

Many young children with developmental disabilities (DD) have significant delays in social, communication, and play skills. For those children learning to use augmentative and alternative communication (AAC), successful social interactions with peers will require explicit instruction on the same system for both communication partners. Peer-mediated (PM) interventions are recommended best practice based on more than 30 years of research with young children with autism and other DDs. Integrating direct AAC instruction within PM programs to advance social reciprocity in typical preschool routines is a necessary and important next step for young AAC users. In this article, I will summarize the design and outcomes of two PM AAC studies documenting positive social outcomes for preschool children with severe autism. I will also highlight strategies to recruit peers without disabilities, teach peer partners how to use AAC systems (e.g., Picture Exchange Communication System [PECS], Speech Generating Devices [SGDs]), and engineer the preschool classroom for successful AAC communication. I will describe data collection procedures for measuring changes in reciprocal child and peer social communication interactions.
Understanding the Importance of the Partner in Communication Development for Individuals With Sensory and Multiple Disabilities
Authors: Schweigert Philip D.
Published: December 2012

Consider this: Communication is not just about the means of expression! Too often we see the focus of intervention placed on some symbolic form without consideration for the child's understanding of the purpose of communication. This may be particularly true for children with sensory and multiple impairments. Sensory impairments limit many of these learners' access to partners and topics for communication. Additional disabilities may further restrict their means of communication due to cognitive, motor, and or sensory challenges that could hinder our ability to detect and respond to their attempts to engage their world. In this paper, I will focus on such learners and propose a broadened perspective of communication intervention especially as it relates to the development of a pre-symbolic foundation.
Light intensity dependent Debye screening length in undoped photorefractive titanosillenite crystals
Authors: de Oliveira Ivan , Frejlich Jaime
Published: December 2012

We report on the experimental evidence of the light intensity dependence of the Debye screening length ls in undoped photorefractive titanosillenite crystals (Bi12TiO20) by measuring the holographic gain and diffraction efficiency in a two-wave mixing experiment under 532 nm wavelength laser light. Debye length shows saturation at high values of the light intensity. Results are in agreement with the theoretical development.
Thin film transistors based on zinc nitride as a channel layer for optoelectronic devices
Authors: García Núñez C. , Pau J. L. , Ruíz E. , Piqueras J.
Published: December 2012

Zinc nitride films were used as an active layer in thin film transistors to assess its performance in optoelectronic applications. Those nitride layers were grown by radio-frequency magnetron sputtering in Ar/N2 ambient using a Zn target. Bottom- and top-gate thin film transistors were fabricated by photolithography processes. Transmission measurements for these particular layers showed an absorption edge around 1.3 eV. Normally off transistor characteristics with a threshold voltage of 6 V were obtained in the bottom-gate configuration without post-growth annealing. In the saturation region, those transistors produced enhanced output characteristics under illumination with infrared/visible light.
The VO2 interface, the metal-insulator transition tunnel junction, and the metal-insulator transition switch On-Off resistance
Authors: Martens K. , Radu I. P. , Mertens S. , Shi X. , Nyns L. , Cosemans S. , Favia P. , Bender H. , Conard T. , Schaekers M. , De Gendt S. , Afanas'ev V. , Kittl J. A. , Heyns M. , Jurczak M.
Published: December 2012

Transition metal compounds showing a metal-insulator transition (MIT) show complex behavior due to strongly correlated electron effects and offer attractive properties for nano-electronics applications, which cannot be obtained with regular semiconductors. MIT based nano-electronics, however, remains unproven, and MIT devices are poorly understood. We point out and single out one of the major hurdles preventing MIT-electronics: obtaining a high Off resistance and high On-Off resistance ratio in an MIT switch. We show a path toward an MIT switch fulfilling strict Off and On resistance criteria by: (1) Obtaining understanding of the VO2-interface, a protoypical MIT material interface. (2) Introducing a MIT tunnel junction concept to tune switch resistances. In this junction, the metal or insulating phase of the MIT material controls how much current flows through. Adapting the junction's parameters allows tuning the MIT switch's Off and On resistance. (3) Providing proof of principle of the junction and its switch resistance tuning capability, experimentally in two forms. (4) Showing theoretically how stringent Off and On resistance specifications can be fulfilled. The prototypical VO2 MIT results in an abrupt change in bulk electrical resistivity at ∼68 °C. We show that the VO2 MIT manifests itself in an abrupt interfacial transition of current across a VO2-barrier interface forming a tunnel junction. In a first tunnel junction form, a two orders of magnitude abrupt change in contact resistivity induced by the bulk MIT is shown in VO2-metal contact structures. VO2-metal contact properties are discussed in detail, and the work function of VO2 is found to be 5.2eV(25 °C)−5.3eV(90 °C). In a second junction form, an abrupt change in tunneling current of up to an order of magnitude caused by the bulk MIT is shown to be present in VO2-insulator-metal capacitor structures with atomic layers deposition (ALD) Al2O3 and HfO2 barrier layers. The capacitors show the feasibility of using the MIT to switch a component to a high Off resistance state. Current and capacitance-voltage characteristics of the capacitors are analyzed as well as voltage or field dependent MITs at VO2 interfaces. The abrupt change in current across the VO2 interface is shown to be driven by the change in free carriers in bulk VO2 across the MIT.
Charge localization at the interface between La1−xSrxMnO3 and the “infinite layers” cuprate CaCuO2
Authors: Yang Nan , Di Castro D. , Aruta C. , Mazzoli C. , Minola M. , Brookes N. B. , Moretti Sala M. , Prellier W. , Lebedev O. I. , Tebano A. , Balestrino G.
Published: December 2012

(CaCuO2)m/(La0.7Sr0.3MnO3)n superlattices, consisting of the infinite layers cuprate CaCuO2 and the optimally doped manganite La1−xSrxMnO3, were grown by pulsed laser deposition. The transport properties are dominated by the manganite block. X-Ray absorption spectroscopy measurements show a clear evidence of an orbital reconstruction at the interface, ascribed to the hybridization between the Cu 3d3z2−r2 and the Mn 3d3z2−r2 orbitals via interface apical oxygen ions. Such a mechanism localizes holes at the interfaces, thus preventing charge transfer to the CaCuO2 block. Some charge (holes) transfer occurs toward the La0.7Sr0.3MnO3 block in strongly oxidized superlattices, contributing to the suppression of the magnetotransport properties.
Observation of the hole state symmetry of MgB2 by inelastic scattering of fast electrons accompanied by boron K-shell excitation
Authors: Saitoh Koh , Momonoi Kota , Tanaka Nobuo , Onari Seiichiro
Published: December 2012

The symmetry of the p-hole state of a superconductor of MgB2 was studied by the observation of inelastic scattering anisotropy of fast electrons accompanied by boron K-shell excitation. A series of the energy-selected diffraction patterns taken at successive energy losses were decomposed into two components; the σ and π components, respectively. The magnitudes of the σ and π components as a function of energy loss, or partial electron energy-loss spectroscopy spectra, show a good correspondence to the partial density of states obtained by a theoretical calculation. A significant occupation of the σ state at just above the Fermi level, which is considered to play an important role for the formation of the superconductive state, was confirmed.
Combined fitting of alternative and direct susceptibility curves of assembled nanostructures
Authors: Hillion A. , Pauly M. , Tamion A. , Tournus F. , Hillenkamp M. , Pichon B. P. , Begin-Colin S. , Dupuis V.
Published: December 2012

Experimental ac-susceptibility curves at different frequencies (0.1 Hz ≤ f ≤ 1 kHz) were performed on samples prepared by physical and chemical pathways. By combining the triple fit method and a careful analysis of ac-experimental curves, we demonstrate an unambiguous and consistent determination method of both the magnetic particle size distribution and anisotropy for diluted granular nanostructures of magnetic clusters. Specifically, we highlight the importance of the size distribution in the determination of the magnetic anisotropy constant as well as the low relevance of the deduced parameters by considering alternative measurements alone.
Ab-initio calculations of the electronic and magnetic structures of Co2Cr1−xMnxAl alloys
Authors: Abu Alhaj Bedor , Hamad Bothina
Published: December 2012

Density functional theory based on full-potential linearized augmented plane-wave method is used to investigate the structural, electronic, and magnetic properties of Co2Cr1−xMnxAl (x = 0, 0.25, 0.5, 0.75, 1) alloys. The parent full Heusler alloy (Co2CrAl) exhibits the least total magnetic moment of 3 μB/f.u. For the alloyed structures, this value is found to increase as a function of Mn concentration. The magnitudes of Co2Cr1−xMnxAl total magnetic moment show a trend consistent with the Slater–Pauling behavior. Co2CrAl full Heusler alloy reveals a half-metallic behavior with an indirect band gap along the Γ-X symmetry line. For the non-stoichiometric structures, the energy levels of the valence band shift to higher energies until they cross the Fermi level for x = 0.75 and 1.
Site-controlled Ag nanocrystals grown by molecular beam epitaxy—Towards plasmonic integration technology
Authors: Urbańczyk Adam , Nötzel Richard
Published: December 2012

We demonstrate site-controlled growth of epitaxial Ag nanocrystals on patterned GaAs substrates by molecular beam epitaxy with high degree of long-range uniformity. The alignment is based on lithographically defined holes in which position controlled InAs quantum dots are grown. The Ag nanocrystals self-align preferentially on top of the InAs quantum dots. No such ordering is observed in the absence of InAs quantum dots, proving that the ordering is strain-driven. The presented technique facilitates the placement of active plasmonic nanostructures at arbitrarily defined positions enabling their integration into complex devices and plasmonic circuits.
Influence of noble gas ion polishing species on extreme ultraviolet mirrors
Authors: van den Boogaard A. J. R. , Zoethout E. , Makhotkin I. A. , Louis E. , Bijkerk F.
Published: December 2012

Low energy ion polishing is attractive in thin films because of the small interaction zone with the treated material. In this context, various noble gases (Ne, Ar, Kr, and Xe) have been applied for low energy ion polishing of interfaces in nanoscale optical Mo/Si multilayers in order to mitigate the evolving roughness during the deposition process. The interface morphology has been studied by grazing incidence small angle x-ray scattering, the multilayer composition by x-ray photoelectron spectroscopy, and the general performance by extreme ultraviolet (EUV) reflectometry. Both the average roughness level and the vertical correlation length of the roughness can be reduced significantly by increasing the atomic mass of the ion species applied for polishing. Maximum EUV reflectance is observed for Kr+-polishing, while Xe+-polishing shows a superior structure. This apparent contradiction is explained by taking into account the optical absorption from noble gas residuals in the amorphous silicon layers.
The influence of material properties on the elastic band structures of one-dimensional functionally graded phononic crystals
Authors: Su Xing-liang , Gao Yuan-wen , Zhou You-he
Published: December 2012

We study the influence of material parameters on elastic band gaps of one-dimensional functionally graded phononic crystals (FGPCs). By using plane-wave expansion, we calculate the first four band structures of FGPCs consisting of functionally graded materials (FGMs). These structures vary exponentially. We systematically study the influence of material parameters for four different FGPC models. Compared with traditional phononic crystals (PCs), the FGPC band gaps are clearly changed by FGMs. We also consider the influence of material composition, material properties and geometrical parameters on band gaps. Results show that different FGM properties can change the band structures remarkably. Our work can facilitate the design of vibration filters and noise insulators and provide more design freedom in engineering.
Ratcheted molecular-dynamics simulations identify efficiently the transition state of protein folding
Authors: Tiana Guido , Camilloni Carlo
Published: December 2012

The atomistic characterization of the transition state (TS) is a fundamental step to improve the understanding of the folding mechanism and the function of proteins. From a computational point of view, the identification of the conformations that build out the transition state is particularly cumbersome, mainly because of the large computational cost of generating a statistically sound set of folding trajectories. Here we show that a biasing algorithm, based on the physics of the ratchet-and-pawl, can be used to approximate efficiently the transition state. The basic idea is that the algorithmic ratchet exerts a force on the protein when it is climbing the free-energy barrier, while it is inactive when it is descending. The transition state can be identified as the point of the trajectory where the ratchet changes regime. Besides discussing this strategy in general terms, we test it within a protein model whose transition state can be studied independently by plain molecular dynamics simulations. Finally, we show its power in explicit-solvent simulations, obtaining and characterizing a set of transition-state conformations for Acyl-Coenzyme A-Binding Protein (ACBP) and Chymotrypsin Inhibitor 2 (CI2).
Surface hopping dynamics of direct trans → cis photoswitching of an azobenzene derivative in constrained adsorbate geometries
Authors: Floß Gereon , Granucci Giovanni , Saalfrank Peter
Published: December 2012

With ongoing miniaturization of electronic devices, the need for individually addressable, switchable molecules arises. An example are azobenzenes on surfaces which have been shown to be switchable between trans and cis forms. Here, we examine the “direct” (rather than substrate-mediated) channel of the trans → cis photoisomerization after ππ* excitation of tetra-tert-butyl-azobenzene physisorbed on surfaces mimicking Au(111) and Bi(111), respectively. In spirit of the direct channel, the electronic structure of the surface is neglected, the latter merely acting as a rigid platform which weakly interacts with the molecule via Van-der-Waals forces. Starting from thermal ensembles which represent the trans-form, sudden excitations promote the molecules to ππ*-excited states which are non-adiabatically coupled among themselves and to a nπ*-excited and the ground state, respectively. After excitation, relaxation to the ground state by internal conversion takes place, possibly accompanied by isomerization. The process is described here by “on the fly” semiclassical surface hopping dynamics in conjunction with a semiempirical Hamiltonian (AM1) and configuration-interaction type methods. It is found that steric constraints imposed by the substrate lead to reduced but non-vanishing, trans → cis reaction yields and longer internal conversion times than for the isolated molecule. Implications for recent experiments for azobenzenes on surfaces are discussed.
Large-area GaN n-core/p-shell arrays fabricated using top-down etching and selective epitaxial overgrowth
Authors: Krylyuk Sergiy , Paramanik Dipak , King Matt , Motayed Abhishek , Ha Jong-Yoon , Bonevich John E. , Talin Alec , Davydov Albert V.
Published: December 2012

We present large-area, vertically aligned GaN n-core and p-shell structures on silicon substrates. The GaN pillars were formed by inductively coupled plasma etching of lithographically patterned n-GaN epitaxial layer. Mg-doped p-GaN shells were formed using selective overgrowth by halide vapor phase epitaxy. The diameter of the cores ranged from 250 nm to 10 μm with varying pitch. The p-shells formed truncated hexagonal pyramids with {11¯01} side-facets. Room-temperature photoluminescence and Raman scattering measurements indicate strain-relaxation in the etched pillars and shells. Cross-sectional transmission electron microscopy revealed dislocation bending by 90° at the core-shell interface and reduction in their density in the shells.
Kinetic analysis of the effects of target structure on siRNA efficiency
Authors: Chen Jiawen , Zhang Wenbing
Published: December 2012

RNAi efficiency for target cleavage and protein expression is related to the target structure. Considering the RNA-induced silencing complex (RISC) as a multiple turnover enzyme, we investigated the effect of target mRNA structure on siRNA efficiency with kinetic analysis. The 4-step model was used to study the target cleavage kinetic process: hybridization nucleation at an accessible target site, RISC-mRNA hybrid elongation along with mRNA target structure melting, target cleavage, and enzyme reactivation. At this model, the terms accounting for the target accessibility, stability, and the seed and the nucleation site effects are all included. The results are in good agreement with that of experiments which show different arguments about the structure effects on siRNA efficiency. It shows that the siRNA efficiency is influenced by the integrated factors of target's accessibility, stability, and the seed effects. To study the off-target effects, a simple model of one siRNA binding to two mRNA targets was designed. By using this model, the possibility for diminishing the off-target effects by the concentration of siRNA was discussed.
Orbital localization using fourth central moment minimization
Authors: Høyvik Ida-Marie , Jansik Branislav , Jørgensen Poul
Published: December 2012

We present a new orbital localization function based on the sum of the fourth central moments of the orbitals. To improve the locality, we impose a power on the fourth central moment to act as a penalty on the least local orbitals. With power two, the occupied and virtual Hartree-Fock orbitals exhibit a more rapid tail decay than orbitals from other localization schemes, making them suitable for use in local correlation methods. We propose that the standard orbital spread (the square root of the second central moment) and fourth moment orbital spread (the fourth root of the fourth central moment) are used as complementary measures to characterize the locality of an orbital, irrespective of localization scheme.
On the theory of the proton free induction decay and Hahn echo in polymer systems: The role of intermolecular magnetic dipole-dipole interactions and the modified Anderson–Weiss approximation
Authors: Fatkullin N. , Gubaidullin A. , Mattea C. , Stapf S.
Published: December 2012

The influence of the intermolecular magnetic dipole-dipole interaction on the free induction decay (FID) as well as on the Hahn-echo of proton spins in polymer melts is investigated. It is shown that for isotropic models of polymer dynamics, when polymer segment displacements do not correlate with an initial chain conformation, the influence of the intermolecular magnetic dipole-dipole interactions to the FID and Hahn echo is increasing more rapidly with evolution time than the corresponding influence of the intramolecular magnetic dipole-dipole interactions. On the other hand, the situation is inverted for the tube-reptation model: here the influence of the intramolecular magnetic dipole-dipole interactions to the FID and Hahn echo is increasing faster with time than the contribution from intermolecular interactions. A simple expression for the relative mean squared displacements of polymer segments from different chains is obtained from the intermolecular contribution to the FID. A modified Anderson–Weiss approximation, taking into account flip-flop transitions between different spins, is proposed and on that basis, the conditions for extracting the relative intermolecular mean squared displacements of polymer segments from the intermolecular contribution to the proton FID is established. Systematic investigations of intermolecular contributions, which were considered as an unimportant factor for FID and Hahn echo in polymer systems by most previous works, actually cannot be considered as negligible and opens a new dimension for obtaining information about polymer dynamics in the millisecond regime.
New dual gas puff imaging system with up-down symmetry on experimental advanced superconducting tokamak
Authors: Liu S. C. , Shao L. M. , Zweben S. J. , Xu G. S. , Guo H. Y. , Cao B. , Wang H. Q. , Wang L. , Yan N. , Xia S. B. , Zhang W. , Chen R. , Chen L. , Ding S. Y. , Xiong H. , Zhao Y. , Wan B. N. , Gong X. Z. , Gao X.
Published: December 2012

Gas puff imaging (GPI) offers a direct and effective diagnostic to measure the edge turbulence structure and velocity in the edge plasma, which closely relates to edge transport and instability in tokamaks. A dual GPI diagnostic system has been installed on the low field side on experimental advanced superconducting tokamak (EAST). The two views are up-down symmetric about the midplane and separated by a toroidal angle of 66.6°. A linear manifold with 16 holes apart by 10 mm is used to form helium gas cloud at the 130×130 mm (radial versus poloidal) objective plane. A fast camera is used to capture the light emission from the image plane with a speed up to 390 804 frames/s with 64×64 pixels and an exposure time of 2.156 μs. The spatial resolution of the system is 2 mm at the objective plane. A total amount of 200 Pa.L helium gas is puffed into the plasma edge for each GPI viewing region for about 250 ms. The new GPI diagnostic has been applied on EAST for the first time during the recent experimental campaign under various plasma conditions, including ohmic, L-mode, and type-I, and type-III ELMy H-modes. Some of these initial experimental results are also presented.
Rigorous results for the minimal speed of Kolmogorov–Petrovskii–Piscounov monotonic fronts with a cutoff
Authors: Benguria Rafael D. , Depassier M. Cristina , Loss Michael
Published: December 2012

We study the effect of a cutoff on the speed of pulled fronts of the one-dimensional reaction diffusion equation. To accomplish this, we first use variational techniques to prove the existence of a heteroclinic orbit in phase space for traveling wave solutions of the corresponding reaction diffusion equation under conditions that include discontinuous reaction profiles. This existence result allows us to prove rigorous upper and lower bounds on the minimal speed of monotonic fronts in terms of the cut-off parameter ɛ. From these bounds we estimate the range of validity of the Brunet–Derrida formula for a general class of reaction terms.
A new ab initio intermolecular potential energy surface and predicted rotational spectra of the Kr−H2O complex
Authors: Lei Jinping , Zhou Yanzi , Xie Daiqian , Zhu Hua
Published: December 2012

We report a new three-dimensional ab initio intermolecular potential energy surface for the Kr−H2O complex with the H2O monomer fixed at its experimental averaged structure. Using the supermolecular approach, the intermolecular potential energies were evaluated at the coupled-cluster singles and doubles level with noniterative inclusion of connected triples with the full counterpoise correction for the basis set superposition error and a large basis set including bond functions. The global minimum corresponding to a planar H-bond configuration was located at the intermolecular distance of 3.82 Å with a well depth of 169.98 cm−1. In addition, two first-order and one second-order saddle points were also identified. The combined radial discrete variable representation/angular finite basis representation method and the Lanczos algorithm were employed to calculate the rovibrational energy levels for 16 isotopic species of the Kr−H2O complexes. The rotational transition frequencies, structure parameters, and nuclear quadrupole coupling constants were also determined for the ground and first intermolecular vibrational excited states and are all in good agreement with the available experimental values.
Structural behavior of the acetylide carbides Li2C2 and CaC2 at high pressure
Authors: Nylén Johanna , Konar Sumit , Lazor Peter , Benson Daryn , Häussermann Ulrich
Published: December 2012

The effects of high pressure (up to 30 GPa) on the structural properties of lithium and calcium carbide, Li2C2 and CaC2, were studied at room temperature by Raman spectroscopy in a diamond anvil cell. Both carbides consist of C2 dumbbells which are coordinated by metal atoms. At standard pressure and temperature two forms of CaC2 co-exist. Monoclinic CaC2-II is not stable at pressures above 2 GPa and tetragonal CaC2-I possibly undergoes a minor structural change between 10 and 12 GPa. Orthorhombic Li2C2 transforms to a new structure type at around 15 GPa. At pressures above 18 GPa (CaC2) and 25 GPa (Li2C2) Raman spectra become featureless, and remain featureless upon decompression which suggests an irreversible amorphization of the acetylide carbides. First principles calculations were used to analyze the pressure dependence of Raman mode frequencies and structural stability of Li2C2 and CaC2. A structure model for the high pressure phase of Li2C2 was searched by applying an evolutionary algorithm.
Structural, elastic, and vibrational properties of layered titanium dichalcogenides: A van der Waals density functional study
Authors: Ding Hong , Xu Bin
Published: December 2012

Using the van der Waals density functionals (vdW-DFs), we present results of a density functional theory (DFT) study on the structure of layered titanium dichalcogenides TiX2 (X = S, Se, or Te). By accounting for non-local component in long-ranged electron correlation effects, the vdW-DFs lead to more accurate predictions of the structural parameters relative to conventional DFT. In particular, the vdW-optB86b functional [J. Klimeš et al., Phys. Rev. B 83, 195131 (2011)]10.1103/PhysRevB.83.195131 gives the most agreement with experimental measurements for the lattice constant involving the vdW interactions. Based on the relaxed structure, the calculated elastic constants and vibrational frequencies are compared to experimental work and overall good agreement is obtained.
On the r-matrix structure of the hyperbolic BC
n Sutherland model
Authors: Pusztai B. G.
Published: December 2012

Working in a symplectic reduction framework, we construct a dynamical r-matrix for the classical hyperbolic BCn Sutherland model with three independent coupling constants. We also examine the Lax representation of the dynamics and its equivalence with the Hamiltonian equation of motion.
Hydrogen gas sensor based on palladium and yttrium alloy ultrathin film
Authors: Yi Liu , You-ping Chen , Han Song , Gang Zhang
Published: December 2012

Compared with the other hydrogen sensors, optical fiber hydrogen sensors based on thin films exhibits inherent safety, small volume, immunity to electromagnetic interference, and distributed remote sensing capability, but slower response characteristics. To improve response and recovery rate of the sensors, a novel reflection-type optical fiber hydrogen gas sensor with a 10 nm palladium and yttrium alloy thin film is fabricated. The alloy thin film shows a good hydrogen sensing property for hydrogen-containing atmosphere and a complete restorability for dry air at room temperature. The variation in response value of the sensor linearly increases with increased natural logarithm of hydrogen concentration (ln[H2]). The shortest response time and recovery response time to 4% hydrogen are 6 and 8 s, respectively. The hydrogen sensors based on Pd0.91Y0.09 alloy ultrathin film have potential applications in hydrogen detection and measurement.
Hollow core photonic crystal fiber based viscometer with Raman spectroscopy
Authors: Horan L. E. , Ruth A. A. , Garcia Gunning F. C.
Published: December 2012

The velocity of a liquid flowing through the core of a hollow core photonic crystal fiber (driven by capillary forces) is used for the determination of a liquid's viscosity, using volumes of less than 10 nl. The simple optical technique used is based on the change in propagation characteristics of the fiber as it fills with the liquid of interest via capillary action, monitored by a laser source. Furthermore, the liquid filled hollow core photonic crystal fiber is then used as a vessel to collect Raman scattering from the sample to determine the molecular fingerprint of the liquid under study. This approach has a wide variety of indicative uses in cases where nano-liter samples are necessary. We use 10–12 cm lengths of hollow core photonic crystal fibers to determine the viscosity and Raman spectra of small volumes of two types of monosaccharides diluted in a phosphate buffer solution to demonstrate the principle. The observed Raman signal is strongest when only the core of the hollow core photonic crystal fiber is filled, and gradually decays as the rest of the fiber fills with the sample.
Ion Fokker-Planck simulation of D-3He gas target implosions
Authors: Larroche O.
Published: December 2012

Recently performed inertial confinement fusion implosion experiments involving D-3He gas-filled microballoons have shown discrepancies between expected and measured nuclear fusion yields as the relative abundances of D and 3He are varied. The latter have been tentatively attributed to a sedimentation, or stratification phenomenon occurring in the target core. This work investigates the possibility of ion species sedimentation in a detailed way through multi-species ion-kinetic Vlasov-Fokker-Planck simulations of the implosion process. A noticeable amount of sedimentation is found to build up during the main shock propagation to the target center, but then disappears as the implosion proceeds. As a result, only the yield of the first burst of neutrons, associated with shock convergence, is appreciably modified, leaving the main neutron production phase during fuel compression and stagnation unaffected. The sedimentation of fuel ion species found, thus, cannot explain the experimental discrepancies.
Homogeneous superconducting phase in TiN film: A complex impedance study
Authors: Diener P. , Schellevis H. , Baselmans J. J. A.
Published: December 2012

The low frequency complex impedance of a high resistivity 92 μ Ω cm and 100 nm thick TiN superconducting film has been measured via the transmission of several high sensitivity GHz microresonators, down to TC/50. The temperature dependence of the kinetic inductance follows closely BCS local electrodynamics, with one well defined superconducting gap. This evidences the recovery of a homogeneous superconducting phase in TiN far from the disorder and composition driven transitions. Additionally, we observe a linearity between resonator quality factor and frequency temperature changes, which can be described by a two fluid model.
Direct measurements of the ionization profile in krypton helicon plasmas
Authors: Magee R. M. , Galante M. E. , Gulbrandsen N. , McCarren D. W. , Scime E. E.
Published: December 2012

Helicons are efficient plasma sources, capable of producing plasma densities of 1019 m−3 with only 100 s W of input rf power. There are often steep density gradients in both the neutral density and plasma density, resulting in a fully ionized core a few cm wide surrounded by a weakly ionized plasma. The ionization profile is usually not well known because the neutral density is typically inferred from indirect spectroscopic measurements or from edge pressure gauge measurements. We have developed a two photon absorption laser induced fluorescence (TALIF) diagnostic capable of directly measuring the neutral density profile. We use TALIF in conjunction with a Langmuir probe to measure the ionization fraction profile as a function of driving frequency, magnetic field, and input power. It is found that when the frequency of the driving wave is greater than a critical frequency, fc≈3flh, where flh is the lower hybrid frequency at the antenna, the ionization fraction is small (0.1%) and the plasma density low (1017 m−3). As the axial magnetic field is increased, or, equivalently, the driving frequency decreased, a transition is observed. The plasma density increases by a factor of 10 or more, the plasma density profile becomes strongly peaked, the neutral density profile becomes strongly hollow, and the ionization fraction in the core approaches 100%. Neutral depletion in the core can be caused by a number of mechanisms. We find that in these experiments the depletion is due primarily to plasma pressure and neutral pumping.
Dynamics of the vortex core in magnetic nanodisks with a ring of magnetic impurities
Authors: Toscano D. , Leonel S. A. , Coura P. Z. , Sato F. , Dias R. A. , Costa B. V.
Published: December 2012

In this work, we used numerical simulations to study the effect of a ring of magnetic impurities on the vortex core dynamics in nanodisks of Permalloy. The presence of the ring not only allowed us to modulate the gyrotropic frequency but also provided us a way to confine the vortex core. We observed that the gyrotropic frequency depends on the ring parameters. Moreover, we have noticed that the switching of the vortex core polarity can be obtained from the vortex core-impurity interaction under peculiar conditions, in particular, when the ring works for pinning the vortex core.
Inducing extended line defects in graphene by linear adsorption of C and N atoms
Authors: Li Yu , Zhang Rui-Qin , Lin Zijing , Van Hove Michel A.
Published: December 2012

We propose a possible approach for controlled formation of various 585 (containing pentagonal and octagonal carbon rings) extended line defects (ELDs) by linear adsorption of various kinds of atoms (C, N, B, O) on a graphene substrate, based upon density functional theory and molecular-dynamics (MD) simulations. We find out that the C and N atoms spontaneously transform to 585 ELDs while other elements find specific stable configurations. To confirm the feasibility of forming the ELD from line adsorption, investigation of the critical transformation conditions of the 585 ELD is involved based upon various adsorption models and adsorption densities.
The role of Euler buckling instability in the fabrication of nanoelectromechanical systems on the basis of GaAs/AlGaAs heterostructures
Authors: Shevyrin A. A. , Pogosov A. G. , Budantsev M. V. , Bakarov A. K. , Toropov A. I. , Ishutkin S. V. , Shesterikov E. V. , Kozhukhov A. S. , Kosolobov S. S. , Gavrilova T. A.
Published: December 2012

Mechanical stresses are investigated in suspended nanowires made on the basis of GaAs/AlGaAs heterostructures. Though there are no intentionally introduced stressor layers in the heterostructure, the nanowires are subject to Euler buckling instability. In the wide nanowires, the out-of-plane buckling is observed at length significantly smaller (3 times) than the theoretically estimated critical value, while in the narrow nanowires, the experimentally measured critical length of the in-plane buckling coincides with the theoretical estimation. The possible reasons for the obtained discrepancy are considered. The observed peculiarities should be taken into account in the fabrication of nanomechanical and nanoelectromechanical systems.
Charge density wave excitations in stripe-type charge ordered Pr0.5Sr0.5MnO3 manganite
Authors: Rana Rakesh , Rana D. S. , Mavani K. R. , Kawayama I. , Murakami H. , Tonouchi M.
Published: December 2012

We show that a charge-density wave mode submerged in large conductivity of the stripe-type charge-ordered (CO) crystal of Pr0.5Sr0.5MnO3 (PSMO) can be extracted by exciting selective crystallographic planes using polarized terahertz field. Low energy (1–7 meV) dynamics have been explored in the (100), (110), and (111) epitaxial films of PSMO manganite. Of (110) and (111) films representing bulk-like CO, the former exhibits a peak in the conductivity-energy spectrum with attributes of charge-density wave mode along a specific in-plane axis. On the contrary, the CO (111) and the phase-separated (100) films lack this low energy mode but exhibit a Drude-like spectral behavior in the metallic regime. These studies reveal a variety in isothermal charge dynamics originating from the anisotropic nature of the stripe charge-order.
Dual electrode cantilevers for ohmic microscopy
Authors: Ignatowitz Markus , Oesterschulze Egbert
Published: December 2012

Spatially resolved electrochemical microscopy with a dual electrode probe necessitates the precise adjustment of the dimensions, geometry, and spacing of the electrodes involved as well as the control of the probe-sample distance. Therefore, we introduce a microfabricated atomic force microscopy cantilever probe consisting of a thin film stack constituting the overlaying dual insulated electrodes. The deposition processes involved impose an inherent precision in one dimension of typically 10 nm. Spatially resolved dual electrode ohmic microscopy measurements demonstrate its sensitivity to electrochemical material contrast and the progress by improving the lateral resolution by two decades.