bluuebunny/crossref_metadata_2025 huggingface dataset:
ESR and 230Th/234U dating of speleothems from Aladağlar Mountain Range (AMR) in Turkey
Authors: Ulusoy Ülkü , Anbar Gül , Bayarı Serdar , Uysal Tonguç
Published: January 2014

Electron spin resonance (ESR) and 230Th/234U ages of speleothem samples collected from karstic caves located around 3000 m elevation in the Aladağlar Mountain Range (AMR), south-central Turkey, were determined in order to provide new insight and information regarding late Pleistocene climate. ESR ages were validated with the 230Th/234U ages of test samples. The ESR ages of 21 different layers of six speleothem samples were found to range mostly between about 59 and 4 ka, which cover the Marine Oxygen Isotope Stages (MIS) MIS 3 to MIS 1. Among all, only six layers appear to have deposited during MIS 8 and 5. Most of the samples dated were deposited during the late glacial stage (MIS 2). It appears that a cooler climate with a perennial and steady recharge was more conducive to speleothem development rather than a warmer climate with seasonal recharge in the AMR during the late Quaternary. This argument supports previous findings that suggest a two -fold increase in last glacial maximum mean precipitation in Turkey with respect to the present value.
The Faraday threshold in small cylinders and the sidewall non-ideality
Authors: Batson W. , Zoueshtiagh F. , Narayanan R.
Published: January 2014

In this work we investigate, by way of experiments and theory, the Faraday instability threshold in cylinders at low frequencies. This implies large wavelengths where effects from mode discretization cannot be ignored. Careful selection of the working fluids has resulted in an immiscible interface whose apparent contact line with the sidewall can glide over a tiny film of the more wetting fluid, without detachment of its actual contact line. This unique behaviour has allowed for a system whose primary dissipation is defined by the bulk viscous effects, and in doing so, for the first time, close connection is seen with the viscous linear stability theory for which a stress-free condition is assumed at the sidewalls. As predicted, mode selection and co-dimension 2 points are observed in the experiment for a frequency range including subharmonic, harmonic, and superharmonic modes. While agreement with the predictions are generally excellent, there are deviations from the theory for certain modes and these are explained in the context of harmonic meniscus waves. A review of previous work on single-mode excitation in cylinders is given, along with comparison to the viscous model and analysis based upon the conclusions of the current experiments.
A prospective, single-blind, randomised, crossover study comparing three nasal hygiene systems and corresponding patient preference for such devices
Authors: Elmiyeh B , Heywood R L , Prasad V M N , Chatrath P , Bassett P , Quiney R
Published: January 2014

Objective:

To assess subjective preference using three nasal hygiene systems: Stérimar Original®, Emcur® and Sinus Rinse™.

Design:

We used a prospective, single-blind, randomised, crossover study to compare three nasal hygiene systems: Stérimar Original, Emcur and Sinus Rinse.

Subjects:

Eighteen adult volunteers were recruited and were asked to rate their experience over three days using three well-established nasal hygiene systems. A standard visual analogue scale was used to assess five criteria: (1) simplicity of instructions; (2) ease of use; (3) comfort; (4) perceived nasal clearance (effectiveness) and (5) single best overall system.

Results:

Stérimar Original was found to have the easiest instructions to understand compared to the other two systems. There was no significant difference between Stérimar Original and Sinus Rinse with regards to ease of use but they were both significantly easier to use than Emcur (p < 0.05). There was no statistically significant difference between the three systems when comparing the last three criteria. There was no alteration in preference when the cost of each treatment was disclosed to the subjects, and no significant side effects were reported.

Conclusion:

The instructions accompanying Stérimar Original appeared to be the easiest to understand, while Stérimar Original and Sinus Rinse were easier to use than Emcur.
Biotic Interactions in Lichen Community Development: A Review
Authors: Lawrey James D.
Published: January 2014

The extent to which biotic factors (competition, predation/disease, longevity) regulate lichen community development can be addressed by considering a number of general trends expected in higher plant successions and searching for supporting evidence from lichen studies. Four of the most frequently observed (or predicted) trends during succession are that: (1) superior competitors replace poor competitors; (2) ecologically specialized species replace generalists; (3) chemically well-defended species replace poorly-defended species; (4) long-lived species replace ephemeral species. Available evidence suggests that, for many lichen communities, competitive exclusion rarely occurs once thalli are established. This is especially true for communities that develop on the most stable habitats. An absence of competitive exclusion suggests that lichen successions are driven more by additions of colonists than by species replacements, and replacement trends observed in higher plant successions are therefore observed less frequently inlichen successions.
Visualization and quantification of monoallelic TCRα gene rearrangement in αβ T cells
Authors: Winter Manuel , Kashani Elham , Chennupati Vijaykumar , Föhse Lisa , Prinz Immo
Published: January 2014

T‐cell receptor α (TCRα) chain rearrangement is not constrained by allelic exclusion and thus αβ T cells frequently have rearranged both alleles of this locus. Thereby, stepwise secondary rearrangements of both TCRα loci further increase the odds for generation of an α‐chain that can be positively selected in combination with a pre‐existing TCRβ chain. Previous studies estimated that approximately 2–12% of murine and human αβ T cells still carry one TCRα locus in germline configuration, which must comprise a partially or even fully rearranged TCRδ locus. However, these estimates are based on a relatively small amount of individual αβ T‐cell clones and αβ T‐cell hybridomas analyzed to date. To address this issue more accurately, we made use of a mouse model, in which a fluorescent reporter protein is introduced into the constant region of the TCRδ locus. In this TcrdH2BeGFP system, fluorescence emanating from retained TCRδ loci enabled us to quantify monoallelically rearranged αβ T cells on a single‐cell basis. Via fluorescence‐activated cell sorting analysis, we determined the frequency of monoallelic TCRα rearrangements to be 1.7% in both peripheral CD4+ and CD8+ αβ T cells. Furthermore, we found a skewed 5′ Jα gene utilization of the rearranged TCRα allele in T cells with monoallelic TCRα rearrangements. This is in line with previous descriptions of a tight interallelic positional coincidence of Jα gene segments used on both TCRα alleles. Finally, analysis of T cells from transgenic mice harboring only one functional TCRα locus implied the existence of very rare unusual translocation or episomal reintegration events of formerly excised TCRδ loci.
Double blanket effect caused by two layers of black carbon aerosols escalates warming in the Brahmaputra River Valley
Authors: Rahul P. R. C. , Bhawar R. L. , Ayantika D. C. , Panicker A. S. , Safai P. D. , Tharaprabhakaran V. , Padmakumari B. , Raju M. P.
Published: January 2014

First ever 3-day aircraft observations of vertical profiles of Black Carbon (BC) were obtained during the Cloud Aerosol Interaction and Precipitation Enhancement Experiment (CAIPEEX) conducted on 30th August, 4th and 6th September 2009 over Guwahati (26°11′N, 91°44′E), the largest metropolitan city in the Brahmaputra River Valley (BRV) region. The results revealed that apart from the surface/near surface loading of BC due to anthropogenic processes causing a heating of 2 K/day, the large-scale Walker and Hadley atmospheric circulations associated with the Indian summer monsoon help in the formation of a second layer of black carbon in the upper atmosphere, which generates an upper atmospheric heating of ~2 K/day. Lofting of BC aerosols by these large-scale circulating atmospheric cells to the upper atmosphere (4–6 Km) could also be the reason for extreme climate change scenarios that are being witnessed in the BRV region.
Increasing BMI is associated with a progressive reduction in physical quality of life among overweight middle-aged men
Authors: Derraik José G. B. , de Bock Martin , Hofman Paul L. , Cutfield Wayne S.
Published: January 2014

We assessed whether increasing body mass index (BMI) affects health-related quality of life in a group of 38 overweight (BMI 25–30 kg/m2) middle-aged (45.9 ± 5.4 years) men, recruited in Auckland (New Zealand). Health-related quality of life was assessed with SF-36v2 at 0, 12 and 30 weeks. Increasing BMI was associated with a progressive reduction in physical component summary score (p = 0.008), as well as lower general health (p = 0.036), physical functioning (p = 0.024) and bodily pain (p = 0.030) scores. Stratified analyses confirmed these findings: participants who were more overweight (n = 19; BMI 27.5–30 kg/m2) had poorer physical component summary (p = 0.005), physical functioning (p = 0.040), bodily pain (p = 0.044) and general health (p = 0.073) scores than the less overweight (n = 19; BMI 25–27.5 kg/m2). Increasing BMI is associated with a progressive reduction in physical quality of life, even within a relatively narrow BMI range encompassing only overweight middle-aged men.
Spatially resolved chemical imaging of individual atmospheric particles using nanoscale imaging mass spectrometry: insight into particle origin and chemistry
Authors: Ghosal Sutapa , Weber Peter K. , Laskin Alexander
Published: January 2014

Knowledge of the spatially resolved composition of atmospheric particles is essential for differentiating between their surface versus bulk chemistry and understanding particle reactivity and the potential environmental impact.
A combination algorithm for variable selection to determine soluble solid content and firmness of pears
Authors: Li Jiangbo , Zhao Chunjiang , Huang Wenqian , Zhang Chi , Peng Yankun
Published: January 2014

A new combination of Monte Carlo-uninformative variable elimination and the successive projections algorithm (MC-UVE-SPA) was proposed to select the most effective variables.
A family of three magnetic metal organic frameworks: their synthesis, structural, magnetic and vapour adsorption study
Authors: Sanda Suresh , Goswami Soumyabrata , Jena Himanshu Sekhar , Parshamoni Srinivasulu , Konar Sanjit
Published: January 2014

Three flexible magnetic metal–organic frameworks (MOFs) have been synthesized and their magnetic and adsorption properties were investigated.
Role of oxygen vacancy and Fe–O–Fe bond angle in compositional, magnetic, and dielectric relaxation on Eu-substituted BiFeO3 nanoparticles
Authors: Tamilselvan A. , Balakumar S. , Sakar M. , Nayek Chiranjib , Murugavel P. , Saravana Kumar K.
Published: January 2014

The influence of oxygen vacancies on the dielectric relaxation behavior of pure and Eu-substituted BiFeO3 nanoparticles synthesized by a sol–gel technique has been studied using impedance spectroscopy in the temperature range of 90 °C to 180 °C.
A remarkable effect of N,N-diethylamino functionality on the optoelectronic properties of a salicylimine-based probe for Al3+
Authors: Neeraj Neeraj , Kumar Ajit , Kumar Virendra , Prajapati Rahul , Asthana Sharad Kumar , Upadhyay K. K. , Zhao Jianzhang
Published: January 2014

A new live-cell permeable, fluorescent probe comprised of a simple salicylimine-based Schiff base (SA1) has been developed for Al3+with nano-molar sensitivity in aqueous media.
Gold(iii) assisted C–H activation of 1,4,7-trithiacyclononane: synthesis and spontaneous resolution of a bicyclic chiral sulfonium salt
Authors: Janzen D. E. , Kooyman A. M.
Published: January 2014

A trithiamacrocyclic ligand complex of Au(iii) undergoes a redox-mediated thermal reaction to form a chiral bicyclic sulfonium salt.
Action of an extract from the seeds of Fraxinus excelsior L. on metabolic disorders in hypertensive and obese animal models
Authors: Montó Fermí , Arce Cristina , Noguera Maria Antonia , Ivorra Maria Dolores , Flanagan John , Roller Marc , Issaly Nicolas , D'Ocon Pilar
Published: January 2014

Chronic treatment with FXE resulted in a significant decrease in glycemia, triglyceridemia and body weight in Zucker rats and a significant decrease in SBP in SHR, with a concomitant improvement in endothelial function in both strains.
Towards waste free organic synthesis using nanostructured hybrid silicas
Authors: Ciriminna Rosaria , Ilharco Laura M. , Pandarus Valerica , Fidalgo Alexandra , Béland François , Pagliaro Mario
Published: January 2014

Immobilization and stabilization of metal nanoparticles within an ORMOSIL amorphous structure for highly efficient and selective heterogeneous solid catalysis.
A concise formation of N-substituted 3,4-diarylpyrroles – synthesis and cytotoxic activity
Authors: Egorov Maxim , Delpech Bernard , Aubert Geneviève , Cresteil Thierry , Garcia-Alvarez Maria Concepcion , Collin Pascal , Marazano Christian
Published: January 2014

Sequential condensation of a phenacyl halide with a primary amine and a phenylacetaldehyde led to N-substituted 3,4-diarylpyrroles. Synthesis of analogs of the marine alkaloid halitulin and cytotoxic studies are reported.
Copper-catalyzed annulation of α-substituted diazoacetates with 2-ethynylanilines: the direct synthesis of C2-functionalized indoles
Authors: Liu Gang , Xu Guangyang , Li Jian , Ding Dong , Sun Jiangtao
Published: January 2014

Copper-catalyzed direct annulation of α-substituted diazoacetates with 2-ethynylanilines leading to C2-functionalized indoles was achieved under mild reaction conditions. The C2-(carboxylate methyl) substituted indoles were obtained in moderate to high yields.
Azulene-based conjugated polymers with tuneable near-IR absorption up to 2.5 μm
Authors: Tang Tao , Lin Tingting , Wang FuKe , He Chaobin
Published: January 2014

A series of novel azulene-containing conjugated polymers with tuneable absorption that covers nearly the full near-IR spectrum, ranging from 1.0 to 2.5 μm, were designed and synthesized.
Three-dimensional Gd-doped TiO2 fibrous photoelectrodes for efficient visible light-driven photocatalytic performance
Authors: Choi Junghyun , Sudhagar P. , Lakshmipathiraj P. , Lee Jung Woo , Devadoss Anitha , Lee Sangkyu , Song Taeseup , Hong Seungki , Eito S. , Terashima C. , Han Tae Hee , Kang Jeung Ku , Fujishima A. , Kang Yong Soo , Paik Ungyu
Published: January 2014

Demonstration of the role of electrode geometry on in situ Gd-doping and their effects in the photocatalytic activity.
Modulation of the action of insulin by angiotensin-(1–7)
Authors: Dominici Fernando P. , Burghi Valeria , Muñoz Marina C. , Giani Jorge F.
Published: January 2014

The prevalence of Type 2 diabetes mellitus is predicted to increase dramatically over the coming years and the clinical implications and healthcare costs from this disease are overwhelming. In many cases, this pathological condition is linked to a cluster of metabolic disorders, such as obesity, systemic hypertension and dyslipidaemia, defined as the metabolic syndrome. Insulin resistance has been proposed as the key mediator of all of these features and contributes to the associated high cardiovascular morbidity and mortality. Although the molecular mechanisms behind insulin resistance are not completely understood, a negative cross-talk between AngII (angiotensin II) and the insulin signalling pathway has been the focus of great interest in the last decade. Indeed, substantial evidence has shown that anti-hypertensive drugs that block the RAS (renin–angiotensin system) may also act to prevent diabetes. Despite its long history, new components within the RAS continue to be discovered. Among them, Ang-(1–7) [angiotensin-(1–7)] has gained special attention as a counter-regulatory hormone opposing many of the AngII-related deleterious effects. Specifically, we and others have demonstrated that Ang-(1–7) improves the action of insulin and opposes the negative effect that AngII exerts at this level. In the present review, we provide evidence showing that insulin and Ang-(1–7) share a common intracellular signalling pathway. We also address the molecular mechanisms behind the beneficial effects of Ang-(1–7) on AngII-mediated insulin resistance. Finally, we discuss potential therapeutic approaches leading to modulation of the ACE2 (angiotensin-converting enzyme 2)/Ang-(1–7)/Mas receptor axis as a very attractive strategy in the therapy of the metabolic syndrome and diabetes-associated diseases.
Evolution of surface stress during oxygen exposure of clean Si(111), Si(100), and amorphous Si surfaces
Authors: Flötotto D. , Wang Z. M. , Jeurgens L. P. H. , Mittemeijer E. J.
Published: January 2014

The evolutions of the surface stress of Si(111)-7 × 7, Si(100)-2 × 1, and a-Si surfaces upon oxygen exposure at pO2 = 1 × 10−4 Pa and room temperature have been investigated in a comparative manner using a specimen-curvature based technique. To this end, a generally applicable, dedicated set of experiments has been devised and performed to deduce and correct for the surface stress change owing to oxygen reaction(s) at the (poorly-defined) back face of the specimen only. On this basis, it could be demonstrated that exposure of clean Si(111)-7 × 7, Si(100)-2 × 1 and a-Si surfaces to pure oxygen gas results in compressive surface stress changes for all three surfaces due to the incorporation of oxygen into Si backbonds. The measured surface stress change decreases with decreasing atomic packing density at the clean Si surfaces, which complies well with the less-densily packed Si surface regions containing more free volume for the accommodation of adsorbed O atoms.
A method for analyzing the non-stationary nucleation and overall transition kinetics: A case of water
Authors: Mokshin Anatolii V. , Galimzyanov Bulat N.
Published: January 2014

We present the statistical method as a direct extension of the mean first-passage time concept to the analysis of molecular dynamics simulation data of a phase transformation. According to the method, the mean first-passage time trajectories for the first (i = 1) as well as for the subsequent (i = 2, 3, 4,…) nucleation events should be extracted that allows one to calculate the time-dependent nucleation rate, the critical value of the order parameter (the critical size), the waiting times for the nucleation events, and the growth law of the nuclei – i.e., all the terms, which are usually necessary to characterize the overall transition kinetics. There are no restrictions in the application of the method by the specific thermodynamic regions; and the nucleation rate parameters are extracted according to their basic definitions. The method differs from the Wedekind-Bartell scheme and its modification [A. V. Mokshin and B. N. Galimzyanov, J. Phys. Chem. B 116, 11959 (2012)], where the passage-times for the first (largest) nucleus are evaluated only and where the average waiting time for the first nucleation event is accessible instead of the true steady-state nucleation time scale. We demonstrate an efficiency of the method by its application to the analysis of the vapor-to-liquid transition kinetics in water at the different temperatures. The nucleation rate/time characteristics and the droplet growth parameters are computed on the basis of the coarse-grained molecular dynamics simulation data.
Electrode contamination effects of retarding potential analyzer
Authors: Fang H. K. , Oyama K.-I. , Cheng C. Z.
Published: January 2014

The electrode contamination in electrostatic analyzers such as Langmuir probes and retarding potential analyzers (RPA) is a serious problem for space measurements. The contamination layer acts as extra capacitance and resistance and leads to distortion in the measured I–V curve, which leads to erroneous measurement results. There are two main effects of the contamination layer: one is the impedance effect and the other is the charge attachment and accumulation due to the capacitance. The impedance effect can be reduced or eliminated by choosing the proper sweeping frequency. However, for RPA the charge accumulation effect becomes serious because the capacitance of the contamination layer is much larger than that of the Langmuir probe of similar dimension. The charge accumulation on the retarding potential grid causes the effective potential, that ions experience, to be changed from the applied voltage. Then, the number of ions that can pass through the retarding potential grid to reach the collector and, thus, the measured ion current are changed. This effect causes the measured ion drift velocity and ion temperature to be changed from the actual values. The error caused by the RPA electrode contamination is expected to be significant for sounding rocket measurements with low rocket velocity (1–2 km/s) and low ion temperature of 200–300 K in the height range of 100–300 km. In this paper we discuss the effects associated with the RPA contaminated electrodes based on theoretical analysis and experiments performed in a space plasma operation chamber. Finally, the development of a contamination-free RPA for sounding rocket missions is presented.
Multilevel summation for dispersion: A linear-time algorithm for r −6 potentials
Authors: Tameling Daniel , Springer Paul , Bientinesi Paolo , Ismail Ahmed E.
Published: January 2014

We have extended the multilevel summation (MLS) method, originally developed to evaluate long-range Coulombic interactions in molecular dynamics simulations [R. D. Skeel, I. Tezcan, and D. J. Hardy, J. Comput. Chem. 23, 673 (2002)], to handle dispersion interactions. While dispersion potentials are formally short-ranged, accurate calculation of forces and energies in interfacial and inhomogeneous systems require long-range methods. The MLS method offers some significant advantages compared to the particle-particle particle-mesh and smooth particle mesh Ewald methods. Unlike mesh-based Ewald methods, MLS does not use fast Fourier transforms and is thus not limited by communication and bandwidth concerns. In addition, it scales linearly in the number of particles, as compared with the \documentclass[12pt]{minimal}\begin{document}$\mathcal {O}(N \log N)$\end{document}O(NlogN) complexity of the mesh-based Ewald methods. While the structure of the MLS method is invariant for different potentials, every algorithmic step had to be adapted to accommodate the r−6 form of the dispersion interactions. In addition, we have derived error bounds, similar to those obtained by Hardy [“Multilevel summation for the fast evaluation of forces for the simulation of biomolecules,” Ph.D. thesis, University of Illinois at Urbana-Champaign, 2006] for the electrostatic MLS. Using a prototype implementation, we have demonstrated the linear scaling of the MLS method for dispersion, and present results establishing the accuracy and efficiency of the method.
Far-field Fano resonance in nanoring lattices modeled from extracted, point dipole polarizability
Authors: DeJarnette Drew , Blake Phillip , Forcherio Gregory T. , Keith Roper D.
Published: January 2014

Coupling and extinction of light among particles representable as point dipoles can be characterized using the coupled dipole approximation (CDA). The analytic form for dipole polarizability of spheroidal particles supports rapid electrodynamic analysis of nanoparticle lattices using CDA. However, computational expense increases for complex shapes with non-analytical polarizabilities which require discrete dipole (DDA) or higher order approximations. This work shows fast CDA analysis of assembled nanorings is possible using a single dipole nanoring polarizability extrapolated from a DDA calculation by summing contributions from individual polarizable volume elements. Plasmon resonance wavelengths of nanorings obtained using extracted polarizabilities blueshift as wall dimensions-to-inner radius aspect ratio increases, consistent with published theory and experiment. Calculated far-field Fano resonance energy maximum and minimum wavelengths were within 1% of full volume element results. Considering polarizability allows a more complete physical picture of predicting plasmon resonance location than metal dielectric alone. This method reduces time required for calculation of diffractive coupling more than 40 000-fold in ordered nanoring systems for 400–1400 nm incident wavelengths. Extension of this technique beyond nanorings is possible for more complex shapes that exhibit dipolar or quadrupole radiation patterns.
Linear response theory for the density matrix renormalization group: Efficient algorithms for strongly correlated excited states
Authors: Nakatani Naoki , Wouters Sebastian , Van Neck Dimitri , Chan Garnet Kin-Lic
Published: January 2014

Linear response theory for the density matrix renormalization group (DMRG-LRT) was first presented in terms of the DMRG renormalization projectors [J. J. Dorando, J. Hachmann, and G. K.-L. Chan, J. Chem. Phys. 130, 184111 (2009)]. Later, with an understanding of the manifold structure of the matrix product state (MPS) ansatz, which lies at the basis of the DMRG algorithm, a way was found to construct the linear response space for general choices of the MPS gauge in terms of the tangent space vectors [J. Haegeman, J. I. Cirac, T. J. Osborne, I. Pižorn, H. Verschelde, and F. Verstraete, Phys. Rev. Lett. 107, 070601 (2011)]. These two developments led to the formulation of the Tamm-Dancoff and random phase approximations (TDA and RPA) for MPS. This work describes how these LRTs may be efficiently implemented through minor modifications of the DMRG sweep algorithm, at a computational cost which scales the same as the ground-state DMRG algorithm. In fact, the mixed canonical MPS form implicit to the DMRG sweep is essential for efficient implementation of the RPA, due to the structure of the second-order tangent space. We present ab initio DMRG-TDA results for excited states of polyenes, the water molecule, and a [2Fe-2S] iron-sulfur cluster.
Thermodynamic stability of nanosized multicomponent bubbles/droplets: The square gradient theory and the capillary approach
Authors: Wilhelmsen Øivind , Bedeaux Dick , Kjelstrup Signe , Reguera David
Published: January 2014

Formation of nanosized droplets/bubbles from a metastable bulk phase is connected to many unresolved scientific questions. We analyze the properties and stability of multicomponent droplets and bubbles in the canonical ensemble, and compare with single-component systems. The bubbles/droplets are described on the mesoscopic level by square gradient theory. Furthermore, we compare the results to a capillary model which gives a macroscopic description. Remarkably, the solutions of the square gradient model, representing bubbles and droplets, are accurately reproduced by the capillary model except in the vicinity of the spinodals. The solutions of the square gradient model form closed loops, which shows the inherent symmetry and connected nature of bubbles and droplets. A thermodynamic stability analysis is carried out, where the second variation of the square gradient description is compared to the eigenvalues of the Hessian matrix in the capillary description. The analysis shows that it is impossible to stabilize arbitrarily small bubbles or droplets in closed systems and gives insight into metastable regions close to the minimum bubble/droplet radii. Despite the large difference in complexity, the square gradient and the capillary model predict the same finite threshold sizes and very similar stability limits for bubbles and droplets, both for single-component and two-component systems.
Solid phases of spatially nanoconfined oxygen: A neutron scattering study
Authors: Kojda Danny , Wallacher Dirk , Baudoin Simon , Hansen Thomas , Huber Patrick , Hofmann Tommy
Published: January 2014

We present a comprehensive neutron scattering study on solid oxygen spatially confined in 12 nm wide alumina nanochannels. Elastic scattering experiments reveal a structural phase sequence known from bulk oxygen. With decreasing temperature cubic γ-, orthorhombic β- and monoclinic α-phases are unambiguously identified in confinement. Weak antiferromagnetic ordering is observed in the confined monoclinic α-phase. Rocking scans reveal that oxygen nanocrystals inside the tubular channels do not form an isotropic powder. Rather, they exhibit preferred orientations depending on thermal history and the very mechanisms, which guide the structural transitions.
Electron transfer in a two-level system within a Cole-Davidson vitreous bath
Authors: Zarea Mehdi , Ratner Mark A. , Wasielewski Michael R.
Published: January 2014

We study electron transfer (ET) in a two level quantum system coupled to a glassy viscous bath. The bath is modeled by the Cole-Davidson (CD) spectral density. The ET in this model is compared to the ET in a normal Drude-Debye (DD) model. It is shown that at low temperatures and when the coupling to the bath is weak, the viscous bath preserves the quantum coherence for a longer time. However in the strong coupling regime, the tunneling rate is higher in the CD. In the classical high temperature limit the difference between the CD and DD models is negligible.
Investigating the significance of zero-point motion in small molecular clusters of sulphuric acid and water
Authors: Stinson Jake L. , Kathmann Shawn M. , Ford Ian J.
Published: January 2014

The nucleation of particles from trace gases in the atmosphere is an important source of cloud condensation nuclei, and these are vital for the formation of clouds in view of the high supersaturations required for homogeneous water droplet nucleation. The methods of quantum chemistry have increasingly been employed to model nucleation due to their high accuracy and efficiency in calculating configurational energies; and nucleation rates can be obtained from the associated free energies of particle formation. However, even in such advanced approaches, it is typically assumed that the nuclei have a classical nature, which is questionable for some systems. The importance of zero-point motion (also known as quantum nuclear dynamics) in modelling small clusters of sulphuric acid and water is tested here using the path integral molecular dynamics method at the density functional level of theory. The general effect of zero-point motion is to distort the mean structure slightly, and to promote the extent of proton transfer with respect to classical behaviour. In a particular configuration of one sulphuric acid molecule with three waters, the range of positions explored by a proton between a sulphuric acid and a water molecule at 300 K (a broad range in contrast to the confinement suggested by geometry optimisation at 0 K) is clearly affected by the inclusion of zero point motion, and similar effects are observed for other configurations.
Temperature effects on adsorption and diffusion dynamics of CH3CH2(ads) and H3C–C≡C(ads) on Ag(111) surface and their self-coupling reactions: Ab initio molecular dynamics approach
Authors: Lu Shao-Yu , Lin Jyh-Shing
Published: January 2014

Density functional theory (DFT)-based molecular dynamics (DFTMD) simulations in combination with a Fourier transform of dipole moment autocorrelation function are performed to investigate the adsorption dynamics and the reaction mechanisms of self-coupling reactions of both acetylide (H3C–C(β)≡C(α) (ads)) and ethyl (H3C(β)–C(α)H2(ads)) with I(ads) coadsorbed on the Ag(111) surface at various temperatures. In addition, the calculated infrared spectra of H3C–C(β)≡C(α)(ads) and I coadsorbed on the Ag(111) surface indicate that the active peaks of –C(β)≡C(α)– stretching are gradually merged into one peak as a result of the dominant motion of the stand-up –C–C(β)≡C(α)– axis as the temperature increases from 200 K to 400 K. However, the calculated infrared spectra of H3C(β)–C(α)H2(ads) and I coadsorbed on the Ag(111) surface indicate that all the active peaks are not altered as the temperature increases from 100 K to 150 K because only one orientation of H3C(β)–C(α)H2(ads) adsorbed on the Ag(111) surface has been observed. These calculated IR spectra are in a good agreement with experimental reflection absorption infrared spectroscopy results. Furthermore, the dynamics behaviors of H3C–C(β)≡C(α)(ads) and I coadsorbed on the Ag(111) surface point out the less diffusive ability of H3C–C(β)≡C(α)(ads) due to the increasing s-character of Cα leading to the stronger Ag–Cα bond in comparison with that of H3C(β)–C(α)H2(ads) and I coadsorbed on the same surface. Finally, these DFTMD simulation results allow us to predict the energetically more favourable reaction pathways for self-coupling of both H3C–C(β)≡C(α)(ads) and H3C(β)–C(α)H2(ads) adsorbed on the Ag(111) surface to form 2,4-hexadiyne (H3C–C≡C–C≡C–CH3(g)) and butane (CH3–CH2–CH2–CH3(g)), respectively. The calculated reaction energy barriers for both H3C–C≡C–C≡C–CH3(g) (1.34 eV) and CH3–CH2–CH2–CH3(g) (0.60 eV) are further employed with the Redhead analysis to estimate the desorption temperatures approximately at 510 K and 230 K, respectively, which are in a good agreement with the experimental low-coverage temperature programmed reaction spectroscopy measurements.
Kinetic partitioning mechanism of HDV ribozyme folding
Authors: Chen Jiawen , Gong Sha , Wang Yujie , Zhang Wenbing
Published: January 2014

RNA folding kinetics is directly tied to RNA biological functions. We introduce here a new approach for predicting the folding kinetics of RNA secondary structure with pseudoknots. This approach is based on our previous established helix-based method for predicting the folding kinetics of RNA secondary structure. In this approach, the transition rates for an elementary step: (1) formation, (2) disruption of a helix stem, and (3) helix formation with concomitant partial melting of an incompatible helix, are calculated with the free energy landscape. The folding kinetics of the Hepatitis delta virus (HDV) ribozyme and the mutated sequences are studied with this method. The folding pathways are identified by recursive searching the states with high net flux-in(out) population starting from the native state. The theory results are in good agreement with that of the experiments. The results indicate that the bi-phasic folding kinetics for the wt HDV sequence is ascribed to the kinetic partitioning mechanism: Part of the population will quickly fold to the native state along the fast pathway, while another part of the population will fold along the slow pathway, in which the population is trapped in a non-native state. Single mutation not only changes the folding rate but also the folding pathway.
Reverse Monte Carlo modeling in confined systems
Authors: Sánchez-Gil V. , Noya E. G. , Lomba E.
Published: January 2014

An extension of the well established Reverse Monte Carlo (RMC) method for modeling systems under close confinement has been developed. The method overcomes limitations induced by close confinement in systems such as fluids adsorbed in microporous materials. As a test of the method, we investigate a model system of 36Ar adsorbed into two zeolites with significantly different pore sizes: Silicalite-I (a pure silica form of ZSM-5 zeolite, characterized by relatively narrow channels forming a 3D network) at partial and full loadings and siliceous Faujasite (which exhibits relatively wide channels and large cavities). The model systems are simulated using grand canonical Monte Carlo and, in each case, its structure factor is used as input for the proposed method, which shows a rapid convergence and yields an adsorbate microscopic structure in good agreement with that of the model system, even to the level of three body correlations, when these are induced by the confining media. The application to experimental systems is straightforward incorporating factors such as the experimental resolution and appropriate q-sampling, along the lines of previous experiences of RMC modeling of powder diffraction data including Bragg and diffuse scattering.
Nitrogen-induced reconstruction and faceting of Re($11\bar 21$112¯1)
Authors: Wang Hao , Chen Wenhua , Bartynski Robert A. , Kaghazchi Payam , Jacob Timo
Published: January 2014

The surface morphology of Re($11\bar 21$112¯1), tailored on the nanometer scale by kinetic control of nitrogen, has been investigated using low energy electron diffraction, scanning tunneling microscopy, Auger electron spectroscopy, and density functional theory (DFT) in combination with the ab initio atomistic thermodynamics approach. Experiments show that when exposing to NH3 (>0.5 L) at 300 K followed by annealing in ultra-high vacuum at 700 K or 900 K, the initially planar Re($11\bar 21$112¯1) surface becomes (2 × 1) reconstructed or partially faceted, respectively. Upon annealing in 100 L NH3 at 900 K, Re($11\bar 21$112¯1) becomes fully faceted and covered by N. The fully faceted surface consists of two-sided ridges formed by ($13\bar 42$134¯2) and ($31\bar 42$314¯2) facets. The (2 × 1) reconstruction may serve as a precursor state for faceting of Re($11\bar 21$112¯1). The DFT calculations provide an atomistic understanding of facet formation in terms of binding sites and energies of N on Re surfaces of the substrate and facets as well as the corresponding surface phase diagram. The N-covered faceted Re($11\bar 21$112¯1) surfaces are promising nanoscale model catalysts and nanotemplates. Our findings should be of importance for the design and development of Re-based heterogeneous catalysts operating under nitrogen-rich conditions.
Positive and negative ion formation in deep-core excited molecules: S 1s excitation in dimethyl sulfoxide
Authors: Coutinho L. H. , Gardenghi D. J. , Schlachter A. S. , de Souza G. G. B. , Stolte W. C.
Published: January 2014

The photo-fragmentation of the dimethyl sulfoxide (DMSO) molecule was studied using synchrotron radiation and a magnetic mass spectrometer. The total cationic yield spectrum was recorded in the photon energy region around the sulfur K edge. The sulfur composition of the highest occupied molecular orbital's and lowest unoccupied molecular orbital's in the DMSO molecule has been obtained using both ab initio and density functional theory methods. Partial cation and anion-yield measurements were obtained in the same energy range. An intense resonance is observed at 2475.4 eV. Sulfur atomic ions present a richer structure around this resonant feature, as compared to other fragment ions. The yield curves are similar for most of the other ionic species, which we interpret as due to cascade Auger processes leading to multiply charged species which then undergo Coulomb explosion. The anions S−, C−, and O− are observed for the first time in deep-core-level excitation of DMSO.
Interfacial band alignment and structural properties of nanoscale TiO2 thin films for integration with epitaxial crystallographic oriented germanium
Authors: Jain N. , Zhu Y. , Maurya D. , Varghese R. , Priya S. , Hudait M. K.
Published: January 2014

We have investigated the structural and band alignment properties of nanoscale titanium dioxide (TiO2) thin films deposited on epitaxial crystallographic oriented Ge layers grown on (100), (110), and (111)A GaAs substrates by molecular beam epitaxy. The TiO2 thin films deposited at low temperature by physical vapor deposition were found to be amorphous in nature, and high-resolution transmission electron microscopy confirmed a sharp heterointerface between the TiO2 thin film and the epitaxially grown Ge with no traceable interfacial layer. A comprehensive assessment on the effect of substrate orientation on the band alignment at the TiO2/Ge heterointerface is presented by utilizing x-ray photoelectron spectroscopy and spectroscopic ellipsometry. A band-gap of 3.33 ± 0.02 eV was determined for the amorphous TiO2 thin film from the Tauc plot. Irrespective of the crystallographic orientation of the epitaxial Ge layer, a sufficient valence band-offset of greater than 2 eV was obtained at the TiO2/Ge heterointerface while the corresponding conduction band-offsets for the aforementioned TiO2/Ge system were found to be smaller than 1 eV. A comparative assessment on the effect of Ge substrate orientation revealed a valence band-offset relation of ΔEV(100) > ΔEV(111) > ΔEV(110) and a conduction band-offset relation of ΔEC(110) > ΔEC(111) > ΔEC(100). These band-offset parameters are of critical importance and will provide key insight for the design and performance analysis of TiO2 for potential high-κ dielectric integration and for future metal-insulator-semiconductor contact applications with next generation of Ge based metal-oxide field-effect transistors.
Thermoelectric properties of Tl-filled Co-free p-type skutterudites: Tlx(Fe,Ni)4Sb12
Authors: Choi Seongho , Kurosaki Ken , Ohishi Yuji , Muta Hiroaki , Yamanaka Shinsuke
Published: January 2014

Our group has discovered that Tl-filled CoSb3-based skutterudites (TlxCoSb3) show an excellent thermoelectric (TE) figure of merit, ZT, of 0.9 [A. Harnwunggmoung et al., Appl. Phys. Lett. 96, 202107 (2010)]. However, all TlxCoSb3 studied so far show n-type characteristics. Since a powerful TE module requires a similar performance in both n- and p-type TE materials, p-type skutterudites filled by Tl need to be developed. Furthermore, from the viewpoint of cost-effectiveness, Co should be replaced by cheaper elements. Therefore, we attempted to develop Tl-filled Co-free p-type skutterudites with high ZT. We selected the sample compositions to be TlxFe2.5Ni1.5Sb12 and studied the high-temperature TE properties. It was found that the samples with x ≤ 0.6 exhibited p-type characteristics and the sample with x = 0.6 exhibited the best TE performance. The maximum ZT, obtained at 422 K, was 0.16, which is comparable to those of other Tl-filled p-type skutterudites.
Effects of ionic liquids on cation dynamics in amorphous polyethylene oxide electrolytes
Authors: Chattoraj Joyjit , Diddens Diddo , Heuer Andreas
Published: January 2014

We perform extensive molecular dynamics simulations of a poly(ethylene oxide)-based polymer electrolyte material containing lithium bis(trifluoromethanesulfonyl)imide salt for a wide temperature regime above and below the experimental crystallization temperature with and without N-methyl-N-propylpyrrolidinium bis(trifluoromethanesulfonyl)imide ionic liquid (IL). The impact of the IL-concentration on the cation dynamics is studied. The increase of the cation mobility upon addition of IL is significant but temperature-independent. This can be related to distinct variations of the underlying transport properties as expressed within the previously introduced transport model of polymer electrolytes. Even for the largest IL concentration the transport model perfectly predicts the non-trivial time-dependence of the cationic mean square displacement for all temperatures. Finally, we compare our numerical and theoretical findings with the results of recent nuclear magnetic resonance experiments. In this way we can exclusively relate the strong experimentally observed dependence of the low-temperature Li-diffusivity on the IL concentration to the impact of IL on crystallization.
Edge equilibrium code for tokamaks
Authors: Li Xujing , Zakharov Leonid E. , Drozdov Vladimir V.
Published: January 2014

The edge equilibrium code (EEC) described in this paper is developed for simulations of the near edge plasma using the finite element method. It solves the Grad-Shafranov equation in toroidal coordinate and uses adaptive grids aligned with magnetic field lines. Hermite finite elements are chosen for the numerical scheme. A fast Newton scheme which is the same as implemented in the equilibrium and stability code (ESC) is applied here to adjust the grids.
Analysis and experimental study on formation conditions of large-scale barrier-free diffuse atmospheric pressure air plasmas in repetitive pulse mode
Authors: Li Lee , Liu Lun , Liu Yun-Long , Bin Yu , Ge Ya-Feng , Lin Fo-Chang
Published: January 2014

Atmospheric air diffuse plasmas have enormous application potential in various fields of science and technology. Without dielectric barrier, generating large-scale air diffuse plasmas is always a challenging issue. This paper discusses and analyses the formation mechanism of cold homogenous plasma. It is proposed that generating stable diffuse atmospheric plasmas in open air should meet the three conditions: high transient power with low average power, excitation in low average E-field with locally high E-field region, and multiple overlapping electron avalanches. Accordingly, an experimental configuration of generating large-scale barrier-free diffuse air plasmas is designed. Based on runaway electron theory, a low duty-ratio, high voltage repetitive nanosecond pulse generator is chosen as a discharge excitation source. Using the wire-electrodes with small curvature radius, the gaps with highly non-uniform E-field are structured. Experimental results show that the volume-scaleable, barrier-free, homogeneous air non-thermal plasmas have been obtained between the gap spacing with the copper-wire electrodes. The area of air cold plasmas has been up to hundreds of square centimeters. The proposed formation conditions of large-scale barrier-free diffuse air plasmas are proved to be reasonable and feasible.
Ab initio study of irradiation tolerance for different Mn+1AXn phases: Ti3SiC2 and Ti3AlC2
Authors: Zhao Shijun , Xue Jianming , Wang Yugang , Huang Qing
Published: January 2014

Layered ternary Mn+1AXn (MAX) materials are recently proposed to be promising candidates for future fission and fusion programmes because of their unique properties inherited from both ceramics and metals. However, different Mn+1AXn materials demonstrate different behaviors when exposed to energetic neutron or ion irradiations. Based on first-principles calculations, we have investigated the irradiation tolerance of two typical Mn+1AXn materials: Ti3SiC2 and Ti3AlC2 from two aspects. First, we make a detailed analysis on the interatomic bonding characters, which are believed to be responsible for the resistance to radiation-induced amorphization. Second, the formation energies of various intrinsic and antisite defects in these two compounds are calculated in order to elucidate their amorphization mechanism. Our results show that the absence of orbitals overlap of Al-C in Ti3AlC2 renders it more resistant to amorphization compared to Ti3SiC2. In addition, the antisite defects AlTi(1) and AlTi(2) in Ti3AlC2 have much lower formation energies compared to SiTi(1) and SiTi(2) in Ti3SiC2, which implies that the replacement of Ti with Al is easier than Si, thus providing an alternative way to accommodate the defects resulted from irradiation damage cascades. These results indicate that Ti3AlC2 is more irradiation tolerant than Ti3SiC2, in accordance with experimental observations. Our results have profound implications for the choice of appropriate MAX phase with best performance to be used in next reaction reactors.