bluuebunny/crossref_metadata_2025 huggingface dataset:
Ultrasound Measurements of Brain Tissue Pulsatility Correlate with the Volume of MRI White-Matter Hyperintensity
Authors: Ternifi Redouane , Cazals Xavier , Desmidt Thomas , Andersson Frédéric , Camus Vincent , Cottier Jean-Philippe , Patat Frédéric , Remenieras Jean-Pierre
Published: April 2014

White-matter hyperintensity (WMH) is frequently seen in magnetic resonance imaging (MRI), but the complete physiopathology of WMH remains to be elucidated. In this study, we sought to determine whether there is an association between the maximum brain tissue displacement (maxBTD), as assessed by ultrasound, and the WMH, as observed by MRI. Nine healthy women aged 60 to 85 years underwent ultrasound and MRI assessments. We found a significant negative correlation between maxBTD and WMH (ρ = -0.86, P<0.001), suggesting a link between cerebral hypoperfusion and WMH.
Medullary Norepinephrine Neurons Modulate Local Oxygen Concentrations in the Bed Nucleus of the Stria Terminalis
Authors: Bucher Elizabeth S , Fox Megan E , Kim Laura , Kirkpatrick Douglas C , Rodeberg Nathan T , Belle Anna M , Wightman R Mark
Published: April 2014

Neurovascular coupling is understood to be the underlying mechanism of functional hyperemia, but the actions of the neurotransmitters involved are not well characterized. Here we investigate the local role of the neurotransmitter norepinephrine in the ventral bed nucleus of the stria terminalis (vBNST) of the anesthetized rat by measuring O2, which is delivered during functional hyperemia. Extracellular changes in norepinephrine and O2 were simultaneously monitored using fast-scan cyclic voltammetry. Introduction of norepinephrine by electrical stimulation of the ventral noradrenergic bundle or by iontophoretic ejection induced an initial increase in O2 levels followed by a brief dip below baseline. Supporting the role of a hyperemic response, the O2 increases were absent in a brain slice containing the vBNST. Administration of selective pharmacological agents demonstrated that both phases of this response involve β-adrenoceptor activation, where the delayed decrease in O2 is sensitive to both α- and β-receptor subtypes. Selective lesioning of the locus coeruleus with the neurotoxin DSP-4 confirmed that these responses are caused by the noradrenergic cells originating in the nucleus of the solitary tract and A1 cell groups. Overall, these results support that non-coerulean norepinephrine release can mediate activity-induced O2 influx in a deep brain region.
Theoretical investigation of the borazine–melamine polymer as a novel candidate for hydrogen storage applications
Authors: Dabbagh Hossein A. , Shahraki Maryam , Farrokhpour Hossein
Published: April 2014

Molecular dynamic simulation andab initiocalculations were employed to study the interaction of molecular hydrogen with the borazine–melamine polymer (BMP) in order to explore its potential for hydrogen storage applications.
Relationship between the lipidome, inflammatory markers and insulin resistance
Authors: Wallace Martina , Morris Ciara , O'Grada Colm M. , Ryan Miriam , Dillon Eugene T. , Coleman Eilish , Gibney Eileen R. , Gibney Michael J. , Roche Helen M. , Brennan Lorraine
Published: April 2014

The objectives of the present study were to (1) examine the effects of the phenotypic factors age, gender and BMI on the lipidomic profile and (2) investigate the relationship between the lipidome, inflammatory markers and insulin resistance.
Self-explaining effect in general chemistry instruction: eliciting overt categorical behaviours by design
Authors: Villalta-Cerdas Adrian , Sandi-Urena Santiago
Published: April 2014

Self-explaining refers to the generation of inferences about causal connections between objects and events. In science, this may be summarised as making sense of how and why actual or hypothetical phenomena take place. Research findings in educational psychology show that implementing activities that elicit self-explaining improves learning in general and specifically enhances authentic learning in the sciences. Research also suggests that self-explaining influences many aspects of cognition, including acquisition of problem-solving skills and conceptual understanding. Although the evidence that links self-explaining and learning is substantial, most of the research has been conducted in experimental settings. There remains a need for research conducted in the context of real college science learning environments. Working to address that need, the larger project in which this work is embedded studied the following: (a) the effect of different self-explaining tasks on self-explaining behaviour and (b) the effect of engaging in different levels of self-explaining on learning chemistry concepts. The present study used a multi-condition, mixed-method approach to categorise student self-explaining behaviours in response to learning tasks. Students were randomly assigned to conditions that included the following: explaining correct and incorrect answers, explaining agreement with another's answer, and explaining one's own answer for others to use. Textual, individual data was gathered in the classroom ecology of a university, large-enrolment general chemistry course. Findings support an association between the self-explaining tasks and students' self-explaining behaviours. Thoughtful design of learning tasks can effectively elicit engagement in sophisticated self-explaining in natural, large-enrolment college chemistry classroom environments.
Surfactant-free polymeric nanoparticles composed of PEG, cholic acid and a sucrose moiety
Authors: Crucho Carina I. C. , Barros M. Teresa
Published: April 2014

New amphiphilic polymers synthesized from a sucrose-containing conjugate exhibited interesting self-assembly properties in water. Owing to their amphiphilic characteristics polymeric nanoparticles were prepared by a nanoprecipitation method without any surfactants. These nanoparticles formulated with biocompatible building blocks can be considered a potential candidate for drug delivery applications.
Impact of molecular charge on GLUT-specific cellular uptake of glucose bioprobes and in vivo application of the glucose bioprobe, GB2-Cy3
Authors: Park Jongmin , Um Jung In , Jo Ala , Lee Jinho , Jung Da-Woon , Williams Darren R. , Park Seung Bum
Published: April 2014

Based on our study on the effect of the molecular charge of glucose bioprobes, we applied GB2-Cy3 to in vivo imaging in the zebrafish model.
Synthon polymorphs of 1 : 1 co-crystal of 5-fluorouracil and 4-hydroxybenzoic acid: their relative stability and solvent polarity dependence of grinding outcomes
Authors: Li Song , Chen Jia-Mei , Lu Tong-Bu
Published: April 2014

Two synthon polymorphs of 1 : 1 co-crystals of 5-fluorouracil and 4-hydroxybenzoic acid were synthesized, and the crystal structures were determined.
Competition and cooperation: hydrogen and halogen bonding in co-crystals involving 4-iodotetrafluorobenzoic acid, 4-iodotetrafluorophenol and 4-bromotetrafluorophenol
Authors: Takemura Akihiro , McAllister Linda J. , Karadakov Peter B. , Pridmore Natalie E. , Whitwood Adrian C. , Bruce Duncan W.
Published: April 2014

Careful choice of components can lead to the favouring of halogen over hydrogen bonding.
In situ back-side illumination fluorescence XAFS (BI-FXAFS) studies on platinum nanoparticles deposited on a HOPG surface as a model fuel cell: a new approach to the Pt-HOPG electrode/electrolyte interface
Authors: Uehara Hiromitsu , Uemura Yohei , Ogawa Takafumi , Kono Kentaro , Ueno Ryoichi , Niwa Yasuhiro , Nitani Hiroaki , Abe Hitoshi , Takakusagi Satoru , Nomura Masaharu , Iwasawa Yasuhiro , Asakura Kiyotaka
Published: April 2014

We measured the in situ polarization-dependent X-ray absorption fine structure of PtNPs deposited on a flat HOPG substrate.
Size-selected gold clusters on porous titania as the most “gold-efficient” heterogeneous catalysts
Authors: Dollinger Andreas , Stolch Lukas , Luo Yuan , Beck Martin , Strobel Christoph H. , Hagner Matthias , Dilger Stefan , Bein Malin , Polarz Sebastian , Gantefoer Gerd F. , Kim Young-Dok , Proch Sebastian
Published: April 2014

Size-selected gold clusters on titania present highly efficient solution phase catalysts for bromination with NBS reaching TONs of enzymes.
13C NMR relaxation and reorientation dynamics in imidazolium-based ionic liquids: revising interpretation
Authors: Matveev Vladimir V. , Markelov Denis A. , Brui Ekaterina A. , Chizhik Vladimir I. , Ingman Petri , Lähderanta Erkki
Published: April 2014

An applicability of 13C NMR relaxation rate measurement to calculation of characteristic times for reorientation of [bmim]+ cations is confirmed.
Triplet–triplet annihilation photon-upconversion: towards solar energy applications
Authors: Gray Victor , Dzebo Damir , Abrahamsson Maria , Albinsson Bo , Moth-Poulsen Kasper
Published: April 2014

This perspective discusses recent progress in photon upconversion systems and devices for solar energy applications.
Surface modification of layered zirconium phosphates: a novel pathway to multifunctional materials
Authors: Mosby Brian M. , Díaz Agustín , Clearfield Abraham
Published: April 2014

The combination of surface modification and intercalation chemistry of inorganic layered materials allows for the design of nanoparticles for specific applications.
Continuous flow asymmetric cyclopropanation reactions using Cu(i) complexes of Pc-L* ligands supported on silica as catalysts with carbon dioxide as a carrier
Authors: Castano Brunilde , Gallo Emma , Cole-Hamilton David J. , Dal Santo Vladimiro , Psaro Rinaldo , Caselli Alessandro
Published: April 2014

Supported hydrogen-bonded chiral (Pc-L*)Cu(i)-complexes catalysed the asymmetric cyclopropanations under flow conditions, using CO2 as a vector.
Development of five membered heterocyclic frameworks via [3+2] cycloaddition reaction in an aqueous micellar system
Authors: Singh Mandavi , Singh Shyam Babu , Fatma Shahin , Ankit Preyas , Singh Jagdamba
Published: April 2014

A series of novel dihydropyrrolo[2,1-a]isoquinolines and dihydropyrrolo[1,2-a]quinolines have been synthesized from isoquinolines/quinolines, various substituted phenacyl bromides and substituted dialkylacetylenedicarboxylates via [3+2] cycloaddition reaction.
Magnetic refrigeration and slow magnetic relaxation in tetranuclear lanthanide cages (Ln = Gd, Dy) with in situ ligand transformation
Authors: Sheikh Javeed Ahmad , Adhikary Amit , Konar Sanjit
Published: April 2014

Three tetranuclear lanthanide cages featuring either hemicubane (1 and 2) or distorted hemicubane (3) like cores are reported. Magnetic studies reveal significant magnetic entropy changes for complex 1 and a slow relaxation of magnetisation for 3.
Structure inherited synthesis of N-doped highly ordered mesoporous Nb2O5as robust catalysts for improved visible light photoactivity
Authors: Huang Hui , Wang Chao , Huang Jie , Wang Xiaomei , Du Yukou , Yang Ping
Published: April 2014

Structure inherited synthesis of N-doped highly ordered mesoporous Nb2O5as an efficient and stable visible-light-driven photocatalyst for hydrogen evolution.
A Friedel–Crafts alkylation mechanism using an aminoindanol-derived thiourea catalyst
Authors: Roca-López David , Marqués-López Eugenia , Alcaine Ana , Merino Pedro , Herrera Raquel P.
Published: April 2014

Computational calculations based on experimental results shed light on the mechanistic proposal for a Friedel–Crafts alkylation reaction between indole and nitroalkenes, catalysed by a chiral aminoindanol-derived thiourea.
Palladium mediated intramolecular multiple C–X/C–H cross coupling and C–H activation: synthesis of carbazole alkaloids calothrixin B and murrayaquinone A
Authors: Kaliyaperumal Srinivasan A. , Banerjee Shyamapada , U. K. Syam Kumar
Published: April 2014

Straightforward palladium mediated syntheses of calothrixin B and murrayaquinone A are described.
Palladium-catalyzed three-component reaction of N-tosylhydrazone, norbornene and aryl halide
Authors: Hu Fangdong , Xia Ying , Liu Zhenxing , Ma Chen , Zhang Yan , Wang Jianbo
Published: April 2014

A palladium-catalyzed three-component reaction that involves an intermolecular Heck-type reaction and alkyl palladium carbene migratory insertion has been demonstrated.
One-dimensional ZnO/Mn3O4 core/shell nanorod and nanotube arrays with high supercapacitive performance for electrochemical energy storage
Authors: Li Nan , Wang Ji-Yu , Liu Zhao-Qing , Guo Yun-Ping , Wang Dong-Yao , Su Yu-Zhi , Chen Shuang
Published: April 2014

A facile electrochemical method to prepare one-dimensional ZnO/Mn3O4 core/shell nanorod and nanotube arrays is reported and their applications as electrodes in supercapacitors are examined. The as-prepated ZnO/Mn3O4 core/shell nanoarray structures exhibit excellent capacitance and superior rate performance.
Efficient synthesis of 2,4-disubstituted quinolines: calix[n]arene-catalyzed Povarov-hydrogen-transfer reaction cascade
Authors: Simões Juliana Baptista , de Fátima Ângelo , Sabino Adão Aparecido , Almeida Barbosa Luiz Claudio , Fernandes Sergio Antonio
Published: April 2014

A new calixarene-catalyzed cascade process, involving Povarov reaction and hydrogen transfer, for the synthesis of 2,4-disubstituted quinolines is described.
Highly active half-sandwich chromium(iii) catalysts bearing bis(imino)pyrrole ligands for ethylene (co)polymerization
Authors: Liu Jing-Yu , Tao Ping , Wang Yong-Xia , Li Yue-Sheng
Published: April 2014

A series of novel half-sandwich chromium(iii) complexes bearing bis(imino)pyrrole complexes was synthesized, characterized, and investigated as catalyst precursors for ethylene polymerization and ethylene/norbornene copolymerization.
CO2 capture on easily regenerable hybrid adsorbents based on polyamines and mesocellular silica foam. Effect of pore volume of the support and polyamine molecular weight
Authors: Zhang Hang , Goeppert Alain , Czaun Miklos , Prakash G. K. Surya , Olah George A.
Published: April 2014

Mesocellular foams (MCFs) with a wide range of pore volumes and pore sizes were prepared and impregnated with PEI. CO2 adsorption on these adsorbents was studied.
Leidenfrost vapour layer moderation of the drag crisis and trajectories of superhydrophobic and hydrophilic spheres falling in water
Authors: Vakarelski Ivan U. , Chan Derek Y. C. , Thoroddsen Sigurdur T.
Published: April 2014

We demonstrate that a stable Leidenfrost vapour layer sustained on the surface of a steel sphere falling through water can reduce the hydrodynamic drag by up to 75% and stabilize the sphere trajectory.
One-pot synthesis of core/shell Co@C spheres by catalytic carbonization of mixed plastics and their application in the photo-degradation of Congo red
Authors: Gong Jiang , Liu Jie , Chen Xuecheng , Jiang Zhiwei , Wen Xin , Mijowska Ewa , Tang Tao
Published: April 2014

Co3O4 catalyzed carbonization of plastics into Co@C spheres via a one-pot approach, which shows high performance in photo-degradation of Congo red.
The general synthesis of Ag nanoparticles anchored on silver vanadium oxides: towards high performance cathodes for lithium-ion batteries
Authors: Zhou Jiang , Liang Qiang , Pan Anqiang , Zhang Xuelin , Zhu Qinyu , Liang Shuquan , Cao Guozhong
Published: April 2014

A general approach has been developed to synthesize a series of silver vanadium oxides (SVOs) anchored with Ag nanoparticles (including AgVO3, Ag2V4O11, Ag0.33V2O5 and Ag1.2V3O8), which exhibit highly improved electrochemical performances.
Histone chaperone Chz1 facilitates the disfavouring property of Spt16 to H2A.Z-containing genes in Saccharomyces cerevisiae
Authors: Liu Hongde , Luo Kun , Zhou Zikai , Mu Yawen , Wan Yakun
Published: April 2014

Htz1 (histone 2A Z1) deposition at promoters is involved in the transcriptional activation of quiescent genes. Chz1 [chaperone for Htz1 (or H2A)–H2B dimer] is an Htz1–H2B-specific chaperone that delivers histone H2A.Z that substitutes for H2A. Spt16 (suppressor of Ty) functions in transcription elongation and also possesses a histone chaperone activity. However, the links among Chz1, Htz1 and Spt16 remain unknown. In the present study, we determined the genomic binding profiling of Htz1, Pol II (RNA polymerase II) and Spt16 using ChIP microarray experiments and sequenced nucleosomal DNA using a next-generation sequencing technique in wild-type and chz1-deletion strains of Saccharomyces cerevisiae. The results of the present study revealed that Spt16 and Pol II are associated, bind at nucleosome-depleted regions, and are positively correlated with the transcription rate. Importantly, Spt16 disfavours the Htz1-bound genes, and this discrimination is impaired upon the deletion of chz1. The negative correlation between the binding profiles of Spt16 and Htz1 at promoters is not an intrinsic repulsion, but is probably due to a requirement for transcription initiation. We showed that chz1 deletion decreases Htz1 binding at promoters and telomeres. Also, in the chz1-deletion mutant, Spt16 binding at ribosomal genes was lost. The results of the present study suggest that the discrimination of Spt16 to Htz1-bound genes is due to the priority of Chz1 over Spt16 in binding to the Htz1-bound genomic regions. Chz1-escorted Htz1 therefore impairs Spt16 binding at chromatin.
Bandpass filter using open/shorted dual‐behaviour resonators
Authors: Feng Wenjie , Che Wenquan
Published: April 2014

A novel bandpass filter with multiple transmission zeros using open/shorted dual‐behaviour resonators (DBRs) is proposed. Three transmission zeros on both sides of the bandpass responses can be easily realised. Three additional transmission zeros without bandstop/lowpass networks are used to suppress the second harmonic. A bandpass filter prototype with 15 dB rejection level in the upper stopband from 1.1f0 to 2.72f0 (3 dB fractional bandwidth 7.3%) has been designed and fabricated.
Variable tap‐length linear equaliser with variable tap‐length adaptation step‐size
Authors: Liu Zhiyong
Published: April 2014

A simple method for dynamically adjusting the tap‐length adaptation step‐size of a variable tap‐length linear equaliser based on the fractional tap‐length algorithm is presented. Simulations show that the technique provides a fast convergence of tap‐length and small steady‐state tap‐length fluctuation.
Scanning electron microscopic analysis of the efficacy of acid etching on cat enamel
Authors: Gallottini Claudio , Barraco Giancarlo , Pagano Stefano , De Carolis Carlo , Dolci Alessandro , Chieruzzi Manila , Eramo Stefano
Published: April 2014

The effect of etching on cat enamel made with 40% orthophosphoric acid for different times was evaluated. Twenty‐one cat teeth were selected and randomly divided into three groups of seven teeth each. They were subjected to etching on a circular area of the coronal enamel (diameter = 2 mm) for 30 s (group A), 45 s (group B) and 60 s (group C). The samples obtained were observed by a scanning electron microscope focusing on the border area between etched and unetched enamel, to highlight the differences. The micrographs were subjected to blind assessment of three experienced operators. The groups were statistically assessed with the Wilcoxon test. At 30, 45 and 60 s, the acid attack results only in the formation of an irregular enamel surface and without uncovering and attack of the prismatic organisation. Prismatic areas with preferential interprismatic action could be detected in few samples etched for 60 s. Analysis with ImageJ was also used to quantify the efficacy of acid etching in the conditions used for human enamel, by an evaluation of grey levels. In cat enamel the etching times considered are not as effective as in human enamel for the purpose of adhesion and the presence of a thick prismless layer could explain this result.
Density functional theory study of adsorption of H2O, H, O, and OH on stepped platinum surfaces
Authors: Kolb Manuel J. , Calle-Vallejo Federico , Juurlink Ludo B. F. , Koper Marc T. M.
Published: April 2014

We report on density functional theory (DFT)-GGA (generalized gradient approximation) computed adsorption energetics of water and the water-related fragments OH, O, and H on stepped Pt surfaces in the low coverage limit. The Pt(100) step edge as encountered on Pt(533) shows increased binding for all species studied, while the Pt(110) step edge, as found on Pt(553) shows only significantly enhanced binding for O and OH. Comparing these results to ultra high vacuum experiments reveals that DFT can explain the main experimental trends semiquantitatively.
Second generation fusion neutron time-of-flight spectrometer at optimized rate for fully digital data acquisition
Authors: Zhang X. , Källne J. , Gorini G. , Nocente M. , Fan T. , Yuan X. , Xie X. , Chen Z.
Published: April 2014

The progress on high-rate event recording of data is taken as starting point to revisit the design of fusion neutron spectrometers based on the TOF (time-of-flight) technique. The study performed was aimed at how such instruments for optimized rate (TOFOR) can be further developed to enhance the plasma diagnostic capabilities based on measurement of the 2.5 MeV dd neutron emission from D plasmas, especially the weak spectral components that depend on discrimination of extraneous events. This paper describes a design (TOFOR II) adapted for use with digital wave form recording of all detector pulses providing information on both amplitude (pulse height) and timing. The results of simulations are presented and the performance enhancement is assessed in comparison to the present.
Spin-transfer torque magnetoresistive random-access memory technologies for normally off computing (invited)
Authors: Ando K. , Fujita S. , Ito J. , Yuasa S. , Suzuki Y. , Nakatani Y. , Miyazaki T. , Yoda H.
Published: April 2014

Most parts of present computer systems are made of volatile devices, and the power to supply them to avoid information loss causes huge energy losses. We can eliminate this meaningless energy loss by utilizing the non-volatile function of advanced spin-transfer torque magnetoresistive random-access memory (STT-MRAM) technology and create a new type of computer, i.e., normally off computers. Critical tasks to achieve normally off computers are implementations of STT-MRAM technologies in the main memory and low-level cache memories. STT-MRAM technology for applications to the main memory has been successfully developed by using perpendicular STT-MRAMs, and faster STT-MRAM technologies for applications to the cache memory are now being developed. The present status of STT-MRAMs and challenges that remain for normally off computers are discussed.
Brownian dynamics without Green's functions
Authors: Delong Steven , Usabiaga Florencio Balboa , Delgado-Buscalioni Rafael , Griffith Boyce E. , Donev Aleksandar
Published: April 2014

We develop a Fluctuating Immersed Boundary (FIB) method for performing Brownian dynamics simulations of confined particle suspensions. Unlike traditional methods which employ analytical Green's functions for Stokes flow in the confined geometry, the FIB method uses a fluctuating finite-volume Stokes solver to generate the action of the response functions “on the fly.” Importantly, we demonstrate that both the deterministic terms necessary to capture the hydrodynamic interactions among the suspended particles, as well as the stochastic terms necessary to generate the hydrodynamically correlated Brownian motion, can be generated by solving the steady Stokes equations numerically only once per time step. This is accomplished by including a stochastic contribution to the stress tensor in the fluid equations consistent with fluctuating hydrodynamics. We develop novel temporal integrators that account for the multiplicative nature of the noise in the equations of Brownian dynamics and the strong dependence of the mobility on the configuration for confined systems. Notably, we propose a random finite difference approach to approximating the stochastic drift proportional to the divergence of the configuration-dependent mobility matrix. Through comparisons with analytical and existing computational results, we numerically demonstrate the ability of the FIB method to accurately capture both the static (equilibrium) and dynamic properties of interacting particles in flow.
Fourth virial coefficient of additive hard-sphere mixtures in the Percus–Yevick and hypernetted-chain approximations
Authors: Beltrán-Heredia Elena , Santos Andrés
Published: April 2014

The fourth virial coefficient of additive hard-sphere mixtures, as predicted by the Percus–Yevick (PY) and hypernetted-chain (HNC) theories, is derived via the compressibility, virial, and chemical-potential routes, the outcomes being compared with exact results. Except in the case of the HNC compressibility route, the other five expressions exhibit a common structure involving the first three moments of the size distribution. In both theories, the chemical-potential route is slightly better than the virial one and the best behavior is generally presented by the compressibility route. Moreover, the PY results with any of the three routes are more accurate than any of the HNC results.
Roaming dynamics in ion-molecule reactions: Phase space reaction pathways and geometrical interpretation
Authors: Mauguière Frédéric A. L. , Collins Peter , Ezra Gregory S. , Farantos Stavros C. , Wiggins Stephen
Published: April 2014

A model Hamiltonian for the reaction \documentclass[12pt]{minimal}\begin{document}${\rm CH}_4^+ \rightarrow$\end{document} CH 4+→ \documentclass[12pt]{minimal}\begin{document}${\rm CH}_3^+$\end{document} CH 3+ + H, parametrized to exhibit either early or late inner transition states, is employed to investigate the dynamical characteristics of the roaming mechanism. Tight/loose transition states and conventional/roaming reaction pathways are identified in terms of time-invariant objects in phase space. These are dividing surfaces associated with normally hyperbolic invariant manifolds (NHIMs). For systems with two degrees of freedom NHIMS are unstable periodic orbits which, in conjunction with their stable and unstable manifolds, unambiguously define the (locally) non-recrossing dividing surfaces assumed in statistical theories of reaction rates. By constructing periodic orbit continuation/bifurcation diagrams for two values of the potential function parameter corresponding to late and early transition states, respectively, and using the total energy as another parameter, we dynamically assign different regions of phase space to reactants and products as well as to conventional and roaming reaction pathways. The classical dynamics of the system are investigated by uniformly sampling trajectory initial conditions on the dividing surfaces. Trajectories are classified into four different categories: direct reactive and non-reactive trajectories, which lead to the formation of molecular and radical products respectively, and roaming reactive and non-reactive orbiting trajectories, which represent alternative pathways to form molecular and radical products. By analysing gap time distributions at several energies, we demonstrate that the phase space structure of the roaming region, which is strongly influenced by nonlinear resonances between the two degrees of freedom, results in nonexponential (nonstatistical) decay.
Electron-ion collisional effect on Weibel instability in a Kappa distributed unmagnetized plasma
Authors: Kumar Kuri Deep , Das Nilakshi
Published: April 2014

Weibel instability has been investigated in the presence of electron-ion collisions by using standard Vlasov-Maxwell equations. The presence of suprathermal electrons has been included here by using Kappa distribution for the particles. The growth rate γ of Weibel instability has been calculated for different values of spectral index κ, collision frequency νei, and temperature anisotropy parameter β. A comparative study between plasma obeying Kappa distribution and that obeying Maxwellian distribution shows that the growth of instability is higher for the Maxwellian particles. However, in the presence of collisions, the suprathermal particles result in lower damping of Weibel mode.
New insights into the decay of ion waves to turbulence, ion heating, and soliton generation
Authors: Chapman T. , Brunner S. , Banks J. W. , Berger R. L. , Cohen B. I. , Williams E. A.
Published: April 2014

The decay of a single-frequency, propagating ion acoustic wave (IAW) via two-ion wave decay to a continuum of IAW modes is found to result in a highly turbulent plasma, ion soliton production, and rapid ion heating. Instability growth rates, thresholds, and sensitivities to plasma conditions are studied via fully kinetic Vlasov simulations. The decay rate of IAWs is found to scale linearly with the fundamental IAW potential amplitude ϕ1 for ZTe/Ti≲20, beyond which the instability is shown to scale with a higher power of ϕ1, where Z is the ion charge number and Te (Ti) is the electron (ion) thermal temperature. The threshold for instability is found to be smaller by an order of magnitude than linear theory estimates. Achieving a better understanding of the saturation of stimulated Brillouin scatter levels observed in laser-plasma interaction experiments is part of the motivation for this study.
Monochromatic short pulse laser produced ion beam using a compact passive magnetic device
Authors: Chen S. N. , Gauthier M. , Higginson D. P. , Dorard S. , Mangia F. , Riquier R. , Atzeni S. , Marquès J.-R. , Fuchs J.
Published: April 2014

High-intensity laser accelerated protons and ions are emerging sources with complementary characteristics to those of conventional sources, namely high charge, high current, and short bunch duration, and therefore can be useful for dedicated applications. However, these beams exhibit a broadband energy spectrum when, for some experiments, monoenergetic beams are required. We present here an adaptation of conventional chicane devices in a compact form (10 cm × 20 cm) which enables selection of a specific energy interval from the broadband spectrum. This is achieved by employing magnetic fields to bend the trajectory of the laser produced proton beam through two slits in order to select the minimum and maximum beam energy. The device enables a production of a high current, short duration source with a reproducible output spectrum from short pulse laser produced charged particle beams.
Facility for low-temperature spin-polarized-scanning tunneling microscopy studies of magnetic/spintronic materials prepared in situ by nitride molecular beam epitaxy
Authors: Lin Wenzhi , Foley Andrew , Alam Khan , Wang Kangkang , Liu Yinghao , Chen Tianjiao , Pak Jeongihm , Smith Arthur R.
Published: April 2014

Based on the interest in, as well as exciting outlook for, nitride semiconductor based structures with regard to electronic, optoelectronic, and spintronic applications, it is compelling to investigate these systems using the powerful technique of spin-polarized scanning tunneling microscopy (STM), a technique capable of achieving magnetic resolution down to the atomic scale. However, the delicate surfaces of these materials are easily corrupted by in-air transfers, making it unfeasible to study them in stand-alone ultra-high vacuum STM facilities. Therefore, we have carried out the development of a hybrid system including a nitrogen plasma assisted molecular beam epitaxy/pulsed laser epitaxy facility for sample growth combined with a low-temperature, spin-polarized scanning tunneling microscope system. The custom-designed molecular beam epitaxy growth system supports up to eight sources, including up to seven effusion cells plus a radio frequency nitrogen plasma source, for epitaxially growing a variety of materials, such as nitride semiconductors, magnetic materials, and their hetero-structures, and also incorporating in situ reflection high energy electron diffraction. The growth system also enables integration of pulsed laser epitaxy. The STM unit has a modular design, consisting of an upper body and a lower body. The upper body contains the coarse approach mechanism and the scanner unit, while the lower body accepts molecular beam epitaxy grown samples using compression springs and sample skis. The design of the system employs two stages of vibration isolation as well as a layer of acoustic noise isolation in order to reduce noise during STM measurements. This isolation allows the system to effectively acquire STM data in a typical lab space, which during its construction had no special and highly costly elements included, (such as isolated slabs) which would lower the environmental noise. The design further enables tip exchange and tip coating without breaking vacuum, and convenient visual access to the sample and tip inside a superconducting magnet cryostat. A sample/tip handling system is optimized for both the molecular beam epitaxy growth system and the scanning tunneling microscope system. The sample/tip handing system enables in situ STM studies on epitaxially grown samples, and tip exchange in the superconducting magnet cryostat. The hybrid molecular beam epitaxy and low temperature scanning tunneling microscopy system is capable of growing semiconductor-based hetero-structures with controlled accuracy down to a single atomic-layer and imaging them down to atomic resolution.
Theory of ultrafast photoinduced electron transfer from a bulk semiconductor to a quantum dot
Authors: Rasmussen Andrew M. , Ramakrishna S. , Weiss Emily A. , Seideman Tamar
Published: April 2014

This paper describes analytical and numerical results from a model Hamiltonian method applied to electron transfer (ET) from a quasicontinuum (QC) of states to a set of discrete states, with and without a mediating bridge. Analysis of the factors that determine ET dynamics yields guidelines for achieving high-yield electron transfer in these systems, desired for instance for applications in heterogeneous catalysis. These include the choice of parameters of the laser pulse that excites the initial state into a continuum electronic wavepacket and the design of the coupling between the bridge molecule and the donor and acceptor. The vibrational mode on a bridging molecule between donor and acceptor has an influence on the yield of electron transfer via Franck-Condon factors, even in cases where excited vibrational states are only transiently populated. Laser-induced coherence of the initial state as well as energetic overlap is crucial in determining the ET yield from a QC to a discrete state, whereas the ET time is influenced by competing factors from the coupling strength and the coherence properties of the electronic wavepacket.
Conservative and dissipative force field for simulation of coarse-grained alkane molecules: A bottom-up approach
Authors: Trément Sébastien , Schnell Benoît , Petitjean Laurent , Couty Marc , Rousseau Bernard
Published: April 2014

We apply operational procedures available in the literature to the construction of coarse-grained conservative and friction forces for use in dissipative particle dynamics (DPD) simulations. The full procedure rely on a bottom-up approach: large molecular dynamics trajectories of n-pentane and n-decane modeled with an anisotropic united atom model serve as input for the force field generation. As a consequence, the coarse-grained model is expected to reproduce at least semi-quantitatively structural and dynamical properties of the underlying atomistic model. Two different coarse-graining levels are studied, corresponding to five and ten carbon atoms per DPD bead. The influence of the coarse-graining level on the generated force fields contributions, namely, the conservative and the friction part, is discussed. It is shown that the coarse-grained model of n-pentane correctly reproduces self-diffusion and viscosity coefficients of real n-pentane, while the fully coarse-grained model for n-decane at ambient temperature over-predicts diffusion by a factor of 2. However, when the n-pentane coarse-grained model is used as a building block for larger molecule (e.g., n-decane as a two blobs model), a much better agreement with experimental data is obtained, suggesting that the force field constructed is transferable to large macro-molecular systems.
Size dependent transition to solid hydrogen and argon clusters probed via spectroscopy of PTCDA embedded in helium nanodroplets
Authors: Dvorak Matthieu , Müller Markus , Bünermann Oliver , Stienkemeier Frank
Published: April 2014

Complexes made of either ArN or (H2)N clusters (N = 1–170) and a single PTCDA molecule (3,4,9,10-perylene-tetracarboxylic-dianhydride) are assembled inside helium droplets and spectroscopically studied via laser-induced fluorescence spectroscopy. The frequency shift and line-broadening are analyzed as a function of N and of the pick-up order of the PTCDA and cluster material in order to track liquid or solid properties of the clusters. For argon, the solid phase is observed for N > 10 above which the pick-up order dramatically influences the localization of the chromophore with respect to the Ar cluster. If the droplets are doped first with Ar, the chromophore remains on the surface of a solid cluster whereas for the reversed pick-up order the molecule is surrounded by an argon shell. At N < 10 wetting and the formation of the first solvation shell are observed. For para-hydrogen, a transition to the solid is observed at N ∼ 20–25, confirming previous theoretical predictions on the existence of a liquid-like phase at such small sizes, even below the bulk hydrogen freezing temperature.
Design and test of a flat-top magnetic field system driven by capacitor banks
Authors: Jiang Fan , Peng Tao , Xiao Houxiu , Zhao Jianlong , Pan Yuan , Herlach Fritz , Li Liang
Published: April 2014

An innovative method for generating a flat-top pulsed magnetic field by means of capacitor banks is developed at the Wuhan National High Magnetic Field Center (WHMFC). The system consists of two capacitor banks as they are normally used to generate a pulsed field. The two discharge circuits (the magnet circuit and the auxiliary circuit) are coupled by a pulse transformer such that the electromotive force (EMF) induced via the transformer in the magnet circuit containing the magnet coil is opposed to the EMF of the capacitor bank. At a certain point before the current pulse in the coil reaches its peak, the auxiliary circuit is triggered. With optimized parameters for charging voltage and trigger delay, the current in the magnet circuit can be approximately kept constant to obtain a flat-top. A prototype was developed at the WHMFC; the magnet circuit was energized by seven 1 MJ (3.2 mF/25 kV) capacitor modules and the auxiliary circuit by four 1 MJ modules. Fields up to 41 T with 6 ms flat-top have been obtained with a conventional user magnet used at the WHMFC.
Note: Application of UF-4 emulsion films to detect low-energy ions from plasmas produced by laser ablation
Authors: Nishio M. , Shrestha I. , Kantsyrev V. L. , Tooth M. , Takasugi K.
Published: April 2014

Detection of low-energy ions via Thomson parabola mass analyzer in the absence of any additional electrical systems is examined. Numerous low-energy ions were recorded on UF-4 solid state emulsion films. Kinetic energies between 1 and 4 keV of ions generated by YAG laser focused on Al and Ti targets were obtained using Thomson parabola measurements. Characteristics of ion tracks on the UF-4 detector are discussed in terms of pressure ranges of vacuum chamber. Moreover, differences in charges of ions between this study and previous spectroscopic measurements are discussed.
Electric field and temperature-induced phase transition in Mn-doped Na1/2Bi1/2TiO3-5.0 at.%BaTiO3 single crystals investigated by micro-Raman scattering
Authors: Chen Chao , Zhang Haiwu , Deng Hao , Huang Ting , Li Xiaobing , Zhao Xiangyong , Hu Zhigao , Wang Dong , Luo Haosu
Published: April 2014

A micro-Raman scattering technique was used to investigate the electric-field and temperature dependent phase stability of Mn-doped Na1/2Bi1/2TiO3-5.0at. %BaTiO3 single crystal. The Ti–O mode was found to exhibit a slight shift at a low electric field (E = 10 kV/cm) and splitting at higher electric field (E ≥ 30 kV/cm), ascribed to field-induced local distortion and phase transition, respectively. The temperature-dependent Raman scattering was also measured over a wide range of 150–800 K to study the phase stability of poled samples. A new Raman mode at about 200 cm−1 and an anomaly in intensity of the Ti-O modes were detected at 390 K, indicating a ferroelectric to antiferroelectric phase transition. The frequency shift of TiO6 octahedral modes implied a transition to a paraelectric state at 550 K. Furthermore, the Ti-O and TiO6 octahedral modes were found to be sustained in the high-temperature paraelectric state.
Boron nitride nanosheets as oxygen-atom corrosion protective coatings
Authors: Yi Min , Shen Zhigang , Zhao Xiaohu , Liang Shuaishuai , Liu Lei
Published: April 2014

The research of two-dimensional nanomaterials for anticorrosion applications is just recently burgeoning. Herein, we demonstrate the boron nitride nanosheets (BNNSs) coatings for protecting polymer from oxygen-atom corrosion. High-quality BNNSs, which are produced by an effective fluid dynamics method with multiple exfoliation mechanisms, can be assembled into coatings with controlled thickness by vacuum filtration. After exposed in atom oxygen, the naked polymer is severely corroded with remarkable mass loss, while the BNNSs-coated polymer remains intact. Barrier and bonding effects of the BNNSs are responsible for the coating's protective performance. These preliminary yet reproducible results pave a way for resisting oxygen-atom corrosion.
Optimal growth and thermal stability of crystalline Be0.25Zn0.75O alloy films on Al2O3(0001)
Authors: Park Dae-Sung , Krupski A. , Sanchez A. M. , Choi Chel-Jong , Yi Min-Su , Lee Hyun-Hwi , McMitchell S. R. C. , McConville C. F.
Published: April 2014

The influence of growth temperature on the synthesis of BexZn1−xO alloy films, grown on highly-mismatched Al2O3(0001) substrates, was studied by synchrotron x-ray scattering, high-resolution transmission electron microscopy and photoluminescence measurements. A single-phase BexZn1−xO alloy with a Be concentration of x = 0.25, was obtained at the growth temperature, Tg = 400 °C, and verified by high-resolution transmission electron microscopy. It was found that high-temperature growth, Tg≥600 °C, caused phase separation, resulting in a random distribution of intermixed alloy phases. The inhomogeneity and structural fluctuations observed in the BexZn1−xO films grown at high temperatures are attributed to a variation in Be composition and mosaic distribution via atomic displacement and strain relaxation.
Plasmonic emission enhancement of colloidal quantum dots in the presence of bimetallic nanoparticles
Authors: Sadeghi S. M. , Hatef A. , Nejat A. , Campbell Q. , Meunier M.
Published: April 2014

We studied plasmonic features of bimetallic nanostructures consisting of gold nanoisland cores semi-coated with a chromium layer and explored how they influence emission of CdSe/ZnS quantum dots. We showed that, compared with chromium-covered glass substrates without the gold cores, the bimetallic nanostructures could significantly enhance the emission of the quantum dots. We studied the impact of the excitation intensity and thickness of the chromium layer on this process and utilized numerical means to identify the mechanisms behind it. Our results suggest that when the chromium layer is thin, the enhancement process is the result of the bimetallic plasmonic features of the nanostructures. As the chromium layer becomes thick, the impact of the gold cores is screened and the enhancement mostly happens mostly via the field enhancement of chromium nanoparticles in the absence of significant energy transfer from the quantum dots to these nanoparticles.
Resistive switching properties and physical mechanism of cobalt ferrite thin films
Authors: Hu Wei , Zou Lilan , Chen Ruqi , Xie Wei , Chen Xinman , Qin Ni , Li Shuwei , Yang Guowei , Bao Dinghua
Published: April 2014

We report reproducible resistive switching performance and relevant physical mechanism of sandwiched Pt/CoFe2O4/Pt structures in which the CoFe2O4 thin films were fabricated by a chemical solution deposition method. Uniform switching voltages, good endurance, and long retention have been demonstrated in the Pt/CoFe2O4/Pt memory cells. On the basis of the analysis of current-voltage characteristic and its temperature dependence, we suggest that the carriers transport through the conducting filaments in low resistance state with Ohmic conduction behavior, and the Schottky emission and Poole-Frenkel emission dominate the conduction mechanism in high resistance state. From resistance-temperature dependence of resistance states, we believe that the physical origin of the resistive switching refers to the formation and rupture of the oxygen vacancies related filaments. The nanostructured CoFe2O4 thin films can find applications in resistive random access memory.
Hot electron production in laser solid interactions with a controlled pre-pulse
Authors: Culfa O. , Tallents G. J. , Wagenaars E. , Ridgers C. P. , Dance R. J. , Rossall A. K. , Gray R. J. , McKenna P. , Brown C. D. R. , James S. F. , Hoarty D. J. , Booth N. , Robinson A. P. L. , Lancaster K. L. , Pikuz S. A. , Faenov A. Ya. , Kampfer T. , Schulze K. S. , Uschmann I. , Woolsey N. C.
Published: April 2014

Hot electron generation plays an important role in the fast ignition approach to inertial confinement fusion (ICF) and other applications with ultra-intense lasers. Hot electrons of temperature up to 10–20 MeV have been produced by high contrast picosecond duration laser pulses focussed to intensities of ∼1020 W cm−2 with a deliberate pre-pulse on solid targets using the Vulcan Petawatt Laser facility. We present measurements of the number and temperature of hot electrons obtained using an electron spectrometer. The results are correlated to the density scale length of the plasma produced by a controlled pre-pulse measured using an optical probe diagnostic. 1D simulations predict electron temperature variations with plasma density scale length in agreement with the experiment at shorter plasma scale lengths (<7.5μm), but with the experimental temperatures (13–17 MeV) dropping below the simulation values (20–25 MeV) at longer scale lengths. The experimental results show that longer interaction plasmas produced by pre-pulses enable significantly greater number of hot electrons to be produced.
Time-resolved photoluminescence spectroscopy of localized exciton magnetic polarons in Cd0.70Mn0.30Te spin glass compound
Authors: Gnatenko Yu. P. , Bukivskij P. M. , Piryatinski Yu. P.
Published: April 2014

We have investigated dynamics of different localized exciton magnetic polarons (LEMPs) in Cd0.70Mn0.30Te spin glass (SG) compound below the freezing temperature Tf in the crystal regions, where various microscopic magnetic spin states (MMSSs), namely, “loose” spins, finite, and infinite clusters, are formed. It was shown that there is a broad distribution of the LEMPs lifetimes. The presence of the long-lived LEMPs is caused by the admixture of the optically active bright exciton states to the dark exciton states, i.e., the “brightening” of the dark LEMPs which exist along with the bright LEMPs. The lifetimes of the dark LEMPs correspond to hundreds of nanoseconds. It was found that the time decay of photoluminescence band intensity is approximated by the sum of two functions: a single exponential function and the Kohlrausch–Williams–Watts stretched exponential function. The stretched exponential function describes the recombination processes of the LEMPs formed in the crystal regions of the finite clusters as well as the infinite cluster. This reflects the appearance of spatially heterogeneous dynamics in Cd0.70Mn0.30Te SG compound below Tf which is due to the disorder in the spin distribution caused by the formation of different MMSSs.