bluuebunny/crossref_metadata_2025 huggingface dataset:
Identification of adsorbed molecules via STM tip manipulation: CO, H2O, and O2 on TiO2 anatase (101)
Authors: Setvin Martin , Daniel Benjamin , Aschauer Ulrich , Hou Weiyi , Li Ye-Fei , Schmid Michael , Selloni Annabella , Diebold Ulrike
Published: September 2014

Many small molecules on anatase (101) appear similar when imaged by STM; they can be easily identified by tip-induced manipulations.
The structure of deuterated benzene films adsorbed on the graphite (0001) basal plane: what happens below and above the monolayer coverage?
Authors: Bahn Emanuel , Hedgeland Holly , Jardine Andrew P. , Henry Paul F. , Hansen Thomas C. , Fouquet Peter
Published: September 2014

Neutron scattering gives a detailed picture of structure formation in thin benzene films overturning existing models.
Highly effective design strategy for the heterogenisation of chemo- and enantioselective organocatalysts
Authors: Newland Stephanie H. , Xuereb David J. , Gianotti Enrica , Marchese Leonardo , Rios Ramon , Raja Robert
Published: September 2014

The covalent heterogenisation of cinchonine and 1,4-diazabicyclo[2.2.2]octane within a range of mesoporous silicas affords highly selective and active organocatalysts.
Prussian blue/TiO2 nanocomposites as a heterogeneous photo-Fenton catalyst for degradation of organic pollutants in water
Authors: Li Xuning , Wang Junhu , Rykov Alexandre I. , Sharma Virender K. , Wei Huangzhao , Jin Changzi , Liu Xin , Li Mingrun , Yu Songhua , Sun Chenglin , Dionysiou Dionysios D.
Published: September 2014

The photo-Fenton process of PB/TiO2 to degrade pollutants was investigated with Mössbauer and EPR for the first time.
Efficient and selective copper-grafted nanoporous silica in aqueous conversion of aldehydes to amides
Authors: Rostamnia Sadegh , Nouruzi Nasrin , Xin Hongchuan , Luque Rafael
Published: September 2014

The one-pot conversion of aldehydes to their corresponding primary amides has been studied using SBA-15-grafted ethylenediamine copper complexes (En–Cu).
Ultrafast photophysical processes for Fe(iii)-carboxylates
Authors: Pozdnyakov Ivan P. , Melnikov Alexey A. , Tkachenko Nikolai , Chekalin Sergey V. , Lemmetyinen Helge , Plyusnin Victor F.
Published: September 2014

Recent works devoted to the investigation of ultrafast processes for several environmentally important Fe(iii) carboxylates were observed and discussed.
Facile synthesis of phosphine free ultra-small PbSe nanocrystals and their light harvesting studies in ETA solar cells
Authors: Akhtar Javeed , Banski Mateusz , Malik Mohammad Azad , Revaprasadu Neerish , Podhorodecki Artur , Misiewicz Jan
Published: September 2014

Ultra-small PbSe nanocrystals (NCs) were synthesized via a ‘one-pot’ approach in olive oil as the reaction medium and capping agent.
Surface and subsurface attenuation of trenbolone acetate metabolites and manure-derived constituents in irrigation runoff on agro-ecosystems
Authors: Jones Gerrad D. , Benchetler Peter V. , Tate Kenneth W. , Kolodziej Edward P.
Published: September 2014

Although studies have evaluated the ecotoxicity and fate of trenbolone acetate (TBA) metabolites, namely 17α-trenbolone (17α-TBOH), 17β-trenbolone (17β-TBOH), and trendione (TBO), their environmental transport processes remain poorly characterized with little information available to guide agricultural runoff management.
Metal oxides and polysaccharides: an efficient hybrid association for materials chemistry
Authors: Boury B. , Plumejeau S.
Published: September 2014

Polysaccharides are ideal templates for greening the synthesis of metal oxides by biotemplating and bio-replication.
Tetrahydrofuran (THF)-assisted alkaline extraction to determine hexavalent chromium (Cr(vi)) in retardant polymers containing Sb(iii)
Authors: Kim Y. S. , Choi Y. R. , Kim J. S. , Ko J. H. , Park T. J. , Heo S. B. , Lim H. B.
Published: September 2014

THF-assisted alkaline extraction method was developed to overcome low recovery of hexavalent chromium (Cr(VI)) in polymers due to the reduction to Cr(iii) by Sb(iii).
Vacuolar-type H+-ATPase subunits and the neurogenic protein big brain are required for optimal copper and zinc uptake
Authors: Wang Jianbin , Binks Tim , Warr Coral G. , Burke Richard
Published: September 2014

Disruption of possible endocytic recycling pathways disturbs cellular copper and zinc accumulation inDrosophila.
Oxidation and reduction processes of platinum nanoparticles observed at the atomic scale by environmental transmission electron microscopy
Authors: Yoshida Hideto , Omote Hiroki , Takeda Seiji
Published: September 2014

Atomic layers of Pt oxides were gradually formed on the surface of Pt nanoparticles in O2 and the oxides were reduced to Pt promptly in both vacuum and gas including CO. H2O vapor suppressed the surface oxidation.
Zwitterionic polymerization of glycidyl monomers to cyclic polyethers with B(C6F5)3
Authors: Asenjo-Sanz Isabel , Veloso Antonio , Miranda José I. , Pomposo José A. , Barroso-Bujans Fabienne
Published: September 2014

Glycidyl monomers react with B(C6F5)3 to generate cyclic polyethers decorated with functional groups.
Doubly thermo-responsive nanoparticles constructed with two diblock copolymers prepared through the two macro-RAFT agents co-mediated dispersion RAFT polymerization
Authors: Li Quanlong , He Xin , Cui Yongliang , Shi Pengfei , Li Shentong , Zhang Wangqing
Published: September 2014

Doubly thermo-responsive nanoparticles constructed with two diblock copolymers were prepared, and the nanoparticles exhibit a two-step phase-transition with increasing temperature.
A simple/green process for the preparation of composite carbon nanotube fibers/yarns
Authors: Rahy Abdelaziz , Choudhury Arup , Kim Changheon , Ryu Sungwoo , Hwang Jaewon , Hong Soon Hyung , Yang Duck J.
Published: September 2014

We report a simple and green process to prepare poly(vinyl alcohol)/carbon nanotube (PVA/CNT) composite fibers having high mechanical properties.
Phase stability and elastic properties of (W0.5Al0.5)C phase with a novel NiAs-type structure
Authors: Wang L. L. , Zhao M. , Jiang Q.
Published: September 2014

Using density-functional theory, we show that the NiAs-type is a more favorable structure for the (W0.5Al0.5)C phase than the experimentally proposed WC-type structure when we compare the thermodynamic, dynamic and elastic properties of the two types.
Perovskite solar cells involving poly(tetraphenylbenzidine)s: investigation of hole carrier mobility, doping effects and photovoltaic properties
Authors: Neumann Katharina , Thelakkat Mukundan
Published: September 2014

A detailed study on the important properties of poly(tetraphenylbenzidine) as hole transport material in perovskite solar cells such as the influence of the molecular weight, the doping effects on charge carrier mobility and the polarity of the material is presented.
Influence of draw ratio on the structure and properties of PEDOT-PSS/PAN composite conductive fibers
Authors: Li Xin , Liu Yin , Shi Zhenghao , Li Congju , Chen Guangming
Published: September 2014

Composite conductive fibers based on poly(3,4-ethylenedioxythiophene)-polystyrene sulfonic acid (PEDOT-PSS) solution blended with polyacrylonitrile (PAN) were obtainedviawet spinning.
Plasma-modified SnO2:F substrate for efficient cobalt selenide counter in dye sensitized solar cell
Authors: Luo Yudan , Cheng Rui , Shen Jie , Chen Xiaohong , Lu Zhe , Chen Yiwei , Sun Zhuo , Huang Sumei
Published: September 2014

DC plasma shortened the growth time, improved morphological and electrocatalytic properties of Co0.85Se electrodes, and boosted the efficiency of DSSCs.
Banded spherulite templated three-dimensional interpenetrated nanoporous materials
Authors: Ye Lijun , Qiu Jishan , Wu Tao , Shi Xianchun , Li Yongjin
Published: September 2014

Unique 3-D interconnected nanoporous polymer materials were fabricated by using the banded spherulites as the templates.
Starfish-like Au–CdS hybrids for the highly efficient photocatalytic degradation of organic dyes
Authors: Wang Xinyu , Ying Yulong , Lei Jiahuan , Hu Pan , Peng Xinsheng
Published: September 2014

A novel starfish-like Au–CdS heterostructures are constructed by a simple self-assembling method with centered Au nanoparticles, and exhibit highly efficient visible light photodegradation of organic dyes.
Dendrimer-functionalized electrospun cellulose acetate nanofibers for targeted cancer cell capture applications
Authors: Zhao Yili , Zhu Xiaoyue , Liu Hui , Luo Yu , Wang Shige , Shen Mingwu , Zhu Meifang , Shi Xiangyang
Published: September 2014

Multifunctional folic acid-functionalized dendrimers can be modified on the surface of electrospun cellulose acetate nanofibers for the specific capture of FAR-overexpressing cancer cells.
Nucleotide binding triggers a conformational change of the CBS module of the magnesium transporter CNNM2 from a twisted towards a flat structure
Authors: Corral-Rodríguez María Ángeles , Stuiver Marchel , Abascal-Palacios Guillermo , Diercks Tammo , Oyenarte Iker , Ereño-Orbea June , de Opakua Alain Ibáñez , Blanco Francisco J. , Encinar José Antonio , Spiwok Vojtêch , Terashima Hiroyuki , Accardi Alessio , Müller Dominik , Martínez-Cruz Luis Alfonso
Published: September 2014

Recent studies suggest CNNM2 (cyclin M2) to be part of the long-sought basolateral Mg2+ extruder at the renal distal convoluted tubule, or its regulator. In the present study, we explore structural features and ligand-binding capacities of the Bateman module of CNNM2 (residues 429–584), an intracellular domain structurally equivalent to the region involved in Mg2+ handling by the bacterial Mg2+ transporter MgtE, and AMP binding by the Mg2+ efflux protein CorC. Additionally, we studied the structural impact of the pathogenic mutation T568I located in this region. Our crystal structures reveal that nucleotides such as AMP, ADP or ATP bind at only one of the two cavities present in CNNM2429–584. Mg2+ favours ATP binding by alleviating the otherwise negative charge repulsion existing between acidic residues and the polyphosphate group of ATP. In crystals CNNM2429–584 forms parallel dimers, commonly referred to as CBS (cystathionine β-synthase) modules. Interestingly, nucleotide binding triggers a conformational change in the CBS module from a twisted towards a flat disc-like structure that mostly affects the structural elements connecting the Bateman module with the transmembrane region. We furthermore show that the T568I mutation, which causes dominant hypomagnesaemia, mimics the structural effect induced by nucleotide binding. The results of the present study suggest that the T568I mutation exerts its pathogenic effect in humans by constraining the conformational equilibrium of the CBS module of CNNM2, which becomes ‘locked’ in its flat form.
The structure of the Slrp–Trx1 complex sheds light on the autoinhibition mechanism of the type III secretion system effectors of the NEL family
Authors: Zouhir Samira , Bernal-Bayard Joaquín , Cordero-Alba Mar , Cardenal-Muñoz Elena , Guimaraes Beatriz , Lazar Noureddine , Ramos-Morales Francisco , Nessler Sylvie
Published: September 2014

Salmonella infections are a leading cause of bacterial foodborne illness in the U.S.A. and the European Union Antimicrobial therapy is often administered to treat the infection, but increasingly isolates are being detected that demonstrate resistance to multiple antibiotics. Salmonella enterica contains two virulence-related T3SS (type III secretion systems): one promotes invasion of the intestine and the other one mediates systemic disease. Both of them secrete the SlrP protein acting as E3 ubiquitin ligase in human host cells where it targets Trx1 (thioredoxin-1). SlrP belongs to the NEL family of bacterial E3 ubiquitin ligases that have been observed in two distinct autoinhibitory conformations. We solved the 3D structure of the SlrP–Trx1 complex and determined the Trx1 ubiquitination site. The description of the substrate-binding mode sheds light on the first step of the activation mechanism of SlrP. Comparison with the available structural data of other NEL effectors allowed us to gain new insights into their autoinhibitory mechanism. We propose a molecular mechanism for the regulation of SlrP in which structural constraints sequestrating the NEL domain would be sequentially released. This work thus constitutes a new milestone in the understanding of how these T3SS effectors influence pathogen virulence. It also provides the fundamental basis for future development of new antimicrobials.
Size‐controllable fabrication of nano‐to‐microstructures on silicon surface using high‐density ion etching with pulsed bias
Authors: Zhang Li , He Jun , Huang Xian , Zhao Danqi , Zhang Dacheng
Published: September 2014

A ‘black silicon’ (BS) surface with low reflectance was fabricated by a standard pulsed deep reactive etching technology at room temperature. Aiming for a better understanding, a systematic experiment was conducted by varying the etching window size and bias power duty cycle. The samples were measured and analysed by a scanning electron microscope, the Bruker Optical Profiler and a UV‐3400 spectrometer. It was observed that a broad scale range of the surface structures formed on the surface. With the duty cycle at 0.5, only about 100 nanometre scale replicable silicon cones formed on the surface, but as the duty cycle decreased to 0.25, the height of the silicon forest sharply increased to about 10 µm, leading to a low reflectance of 0.9% in the visible range for the surface. To clarify the reason for this trend, the bias effective voltage (BEV) was measured and it was confirmed that the BEV would decrease from 100 to 47 V with the duty cycle adjusted from 1 to 0.25. This suggested that this decrease in BEV leads to a reduction of ion energy and ion flux, and then modifies the fabricated structures. Besides, it was found that the broad etching window area only had a maximum promotion of 20% to the scale of the BS, indicating this method was almost free of loading effect.
Fabrication of piezodriven, free-standing, all-oxide heteroepitaxial cantilevers on silicon
Authors: Banerjee N. , Houwman E. P. , Koster G. , Rijnders G.
Published: September 2014

We report on the fabrication and mechanical properties of all-oxide, free-standing, heteroepitaxial, piezoelectric, microelectromechanical systems (MEMS) on silicon, using PbZr0.52Ti0.48O3 as the key functional material. The fabrication was enabled by the development of an epitaxial lift-off strategy for the patterning of multilayer oxide heterostructures grown on Si(001), employing a high temperature stable, sacrificial oxide template mask to obtain freestanding cantilever MEMS devices after substrate etching. All cantilevers, with lengths in the range 25–325 μm, width 50 μm, and total thickness of 300 nm, can be actuated by an external AC-bias. For lengths 50–125 μm, the second order bending mode formed the dominant resonance, whereas for the other lengths different or multiple modes were present.
Computational evaluation of the flexoelectric effect in dielectric solids
Authors: Abdollahi Amir , Peco Christian , Millán Daniel , Arroyo Marino , Arias Irene
Published: September 2014

Flexoelectricity is a size-dependent electromechanical mechanism coupling polarization and strain gradient. It exists in a wide variety of materials, and is most noticeable for nanoscale objects, where strain gradients are higher. Simulations are important to understand flexoelectricity because experiments at very small scales are difficult, and analytical solutions are scarce. Here, we computationally evaluate the role of flexoelectricity in the electromechanical response of linear dielectric solids in two-dimensions. We deal with the higher-order coupled partial differential equations using smooth meshfree basis functions in a Galerkin method, which allows us to consider general geometries and boundary conditions. We focus on the most common setups to quantify the flexoelectric response, namely, bending of cantilever beams and compression of truncated pyramids, which are generally interpreted through approximate solutions. While these approximations capture the size-dependent flexoelectric electromechanical coupling, we show that they only provide order-of-magnitude estimates as compared with a solution fully accounting for the multidimensional nature of the problem. We discuss the flexoelectric mechanism behind the enhanced size-dependent elasticity in beam configurations. We show that this mechanism is also responsible for the actuation of beams under purely electrical loading, supporting the idea that a mechanical flexoelectric sensor also behaves as an actuator. The predicted actuation-induced curvature is in a good agreement with experimental results. The truncated pyramid configuration highlights the critical role of geometry and boundary conditions on the effective electromechanical response. Our results suggest that computer simulations can help understanding and quantifying the physical properties of flexoelectric devices.
Preparations for the motional Stark effect diagnostic on EAST
Authors: Fu J. , Li Y. Y. , Lyu B. , Sheng P. , Zhang Y. , Yin X. H. , Shi Y. J. , Yu Y. , Ye M. Y. , Wan B. N.
Published: September 2014

Measurement and control of the current profile is essential for high performance and steady state operation of Experimental Advanced Superconducting Tokamak (EAST). For this purpose, a conventional Motional Stark Effect (MSE) diagnostics utilizing photoelastic modulators is proposed and investigated. The pilot experiment includes one channel to verify the feasibility of MSE, whose sightline intersects with Neutral Beam Injection at major radius of R = 2.12 m. A beam splitter is adopted for simultaneous measurements of Stark multiplets and their polarization directions. A simplified simulation code was also developed to explore the Stark splitting spectra. Finally, the filter is optimized based on the viewing geometry and neutral beam parameters.
Electrostatic correlations near charged planar surfaces
Authors: Deng Mingge , Em Karniadakis George
Published: September 2014

Electrostatic correlation effects near charged planar surfaces immersed in a symmetric electrolytes solution are systematically studied by numerically solving the nonlinear six-dimensional electrostatic self-consistent equations. We compare our numerical results with widely accepted mean-field (MF) theory results, and find that the MF theory remains quantitatively accurate only in weakly charged regimes, whereas in strongly charged regimes, the MF predictions deviate drastically due to the electrostatic correlation effects. We also observe a first-order like phase-transition corresponding to the counterion condensation phenomenon in strongly charged regimes, and compute the phase diagram numerically within a wide parameter range. Finally, we investigate the interactions between two likely-charged planar surfaces, which repulse each other as MF theory predicts in weakly charged regimes. However, our results show that they attract each other above a certain distance in strongly charged regimes due to significant electrostatic correlations.
Quantum evolution in the regime of quantum wells in a semiclassical island with artificial interface conditions
Authors: Mantile Andrea
Published: September 2014

We introduce a modified Schrödinger operator where the semiclassical Laplacian is perturbed by artificial interface conditions occurring at the boundaries of the potential's support. The corresponding dynamics is analyzed in the regime of quantum wells in a semiclassical island. Under a suitable energy constraint for the initial states, we show that the time propagator is stable with respect to the non-self-adjont perturbation, provided that this is parametrized through infinitesimal functions of the semiclassical parameter “h.” It has been recently shown that h-dependent artificial interface conditions allow a new approach to the adiabatic evolution problem for the shape resonances in models of resonant heterostructures. Our aim is to provide with a rigorous justification of this method.
A force balance model for the motion, impact, and bounce of bubbles
Authors: Klaseboer Evert , Manica Rogerio , Hendrix Maurice H. W. , Ohl Claus-Dieter , Chan Derek Y. C.
Published: September 2014

A force balance model has been developed to predict the terminal velocity of a sub-millimetric bubble as its rises in water under buoyancy. The dynamics of repeated collisions and rebounds of the bubble against a horizontal solid surface is modeled quantitatively by including forces due to buoyancy, added mass, drag, and hydrodynamic lubrication—the last arises from the drainage of water trapped in the thin film between the solid surface and the surface of the deformable bubble. The result is a self-contained, parameter-free model that is capable of giving quantitative agreement with measured trajectories and observed collisions and rebounds against a solid surface as well as the spatio-temporal evolution of the thin film during collision as measured by interferometry.
Moving towards the cold region or the hot region? Thermocapillary migration of a droplet attached on a horizontal substrate
Authors: Sui Yi
Published: September 2014

We study computationally thermocapillary migration of a two-dimensional droplet attached on a horizontal substrate with a constant temperature gradient. A level-set approach is employed to track the droplet interface and a Navier slip boundary condition is imposed to alleviate a stress singularity at the moving contact lines. The present numerical model allows us to consider droplets with large contact angles and to take into account effects of the fluid outside the droplet, both have not been well studied so far. In the limits of a zero contact angle hysteresis and a small viscosity ratio of the fluids outside and inside the droplet (μout/μin ⩽ 0.1), we find the droplet finally migrates towards the cold region, and both the steady migration speed and the velocity field inside the droplet obtained from numerical simulation agree very well with the lubrication theory of Ford and Nadim [“Thermocapillary migration of an attached drop on a solid surface,” Phys. Fluids 6, 3183–3185 (1994)] when the contact angles are small (⩽45°). Beyond this regime, increasing the contact angles leads to increased deviations between numerical simulation and the lubrication theory, and the steady migration speed of the droplet towards the cold side decreases with the contact angles. The simulation results show that the droplet could fall in a motionless regime when its contact angles are around 100° even without any contact angle hysteresis. It is very interesting to find that a droplet with even larger contact angles migrates towards the hot region in a steady speed. We also find the transition of the migration direction of a droplet could strongly depend on the viscosity ratio. With increasing the viscosity of the external fluid, the transition could happen at much smaller values of contact angles. We summarize the results in a phase diagram and discuss the effects of other system parameters, including the contact angle hysteresis, the effective Marangoni number, the Prandtl number, and the slip length, on thermocapillary migration of the droplet.
Geometrical effects on the electron residence time in semiconductor nano-particles
Authors: Koochi Hakimeh , Ebrahimi Fatemeh
Published: September 2014

We have used random walk (RW) numerical simulations to investigate the influence of the geometry on the statistics of the electron residence time τr in a trap-limited diffusion process through semiconductor nano-particles. This is an important parameter in coarse-grained modeling of charge carrier transport in nano-structured semiconductor films. The traps have been distributed randomly on the surface (r2 model) or through the whole particle (r3 model) with a specified density. The trap energies have been taken from an exponential distribution and the traps release time is assumed to be a stochastic variable. We have carried out (RW) simulations to study the effect of coordination number, the spatial arrangement of the neighbors and the size of nano-particles on the statistics of τr. It has been observed that by increasing the coordination number n, the average value of electron residence time, \documentclass[12pt]{minimal}\begin{document}$\overline{\tau }_r$\end{document}τ¯r rapidly decreases to an asymptotic value. For a fixed coordination number n, the electron's mean residence time does not depend on the neighbors' spatial arrangement. In other words, \documentclass[12pt]{minimal}\begin{document}$\overline{\tau }_r$\end{document}τ¯r is a porosity-dependence, local parameter which generally varies remarkably from site to site, unless we are dealing with highly ordered structures. We have also examined the effect of nano-particle size d on the statistical behavior of \documentclass[12pt]{minimal}\begin{document}$\overline{\tau }_r$\end{document}τ¯r. Our simulations indicate that for volume distribution of traps, \documentclass[12pt]{minimal}\begin{document}$\overline{\tau }_r$\end{document}τ¯r scales as d2. For a surface distribution of traps \documentclass[12pt]{minimal}\begin{document}$\overline{\tau }_r$\end{document}τ¯r increases almost linearly with d. This leads to the prediction of a linear dependence of the diffusion coefficient D on the particle size d in ordered structures or random structures above the critical concentration which is in accordance with experimental observations.
Packing frustration in dense confined fluids
Authors: Nygård Kim , Sarman Sten , Kjellander Roland
Published: September 2014

Packing frustration for confined fluids, i.e., the incompatibility between the preferred packing of the fluid particles and the packing constraints imposed by the confining surfaces, is studied for a dense hard-sphere fluid confined between planar hard surfaces at short separations. The detailed mechanism for the frustration is investigated via an analysis of the anisotropic pair distributions of the confined fluid, as obtained from integral equation theory for inhomogeneous fluids at pair correlation level within the anisotropic Percus-Yevick approximation. By examining the mean forces that arise from interparticle collisions around the periphery of each particle in the slit, we calculate the principal components of the mean force for the density profile – each component being the sum of collisional forces on a particle's hemisphere facing either surface. The variations of these components with the slit width give rise to rather intricate changes in the layer structure between the surfaces, but, as shown in this paper, the basis of these variations can be easily understood qualitatively and often also semi-quantitatively. It is found that the ordering of the fluid is in essence governed locally by the packing constraints at each single solid-fluid interface. A simple superposition of forces due to the presence of each surface gives surprisingly good estimates of the density profiles, but there remain nontrivial confinement effects that cannot be explained by superposition, most notably the magnitude of the excess adsorption of particles in the slit relative to bulk.
An accurate and efficient Lagrangian sub-grid model
Authors: Mazzitelli Irene M. , Toschi Federico , Lanotte Alessandra S.
Published: September 2014

A computationally efficient model is introduced to account for the sub-grid scale velocities of tracer particles dispersed in statistically homogeneous and isotropic, incompressible turbulent flows. The model embeds the multi-scale nature of turbulent temporal and spatial correlations, that are essential to reproduce multi-particle dispersion. It is capable to describe the Lagrangian diffusion and dispersion of temporally and spatially correlated clouds of particles. Although the model neglects intermittent corrections, we show that pair and tetrad dispersion results nicely compare with Direct Numerical Simulations of statistically isotropic and homogeneous 3D turbulence. This is in agreement with recent observations that deviations from self-similar pair dispersion statistics are rare events.
Investigation of thermal and electrical stabilities of a GdBCO coil using grease as an insulation material for practical superconducting applications
Authors: Kang D. H. , Kim K. L. , Kim Y. G. , Park Y. J. , Kim W. J. , Kim S. H. , Lee H. G.
Published: September 2014

This paper presents the effects of thermal grease on the electrical and thermal characteristics of GdBCO pancake coils, observed through charge-discharge, sudden discharge, over-current, and thermal quench testing. In charge-discharge and sudden discharge tests, a coil using thermal grease as an insulation material demonstrated faster charging/discharging rates compared to a coil without turn-to-turn insulation. In the case of over-current tests, the coil using thermal grease exhibited the highest electrical stability. Furthermore, thermal quench testing showed the coil employing thermal grease to possess superior thermal characteristics, with rapid cooling and low temperature rise. Overall, the use of thermal grease as an insulation material may be a potential solution to the problems observed with the existing insulation materials, possessing fast charging/discharging rates with superior thermal and electrical stabilities.
An estimate of the error caused by the elongation of the wavelength in a focused beam in free-space electromagnetic parameters measurement
Authors: Zhang Yunpeng , Li En , Guo Gaofeng , Xu Jiadi , Wang Chao
Published: September 2014

A pair of spot-focusing horn lens antenna is the key component in a free-space measurement system. The electromagnetic constitutive parameters of a planar sample are determined using transmitted and reflected electromagnetic beams. These parameters are obtained from the measured scattering parameters by the microwave network analyzer, thickness of the sample, and wavelength of a focused beam on the sample. Free-space techniques introduced by most papers consider the focused wavelength as the free-space wavelength. But in fact, the incident wave projected by a lens into the sample approximates a Gaussian beam, thus, there has an elongation of the wavelength in the focused beam and this elongation should be taken into consideration in dielectric and magnetic measurement. In this paper, elongation of the wavelength has been analyzed and measured. Measurement results show that the focused wavelength in the vicinity of the focus has an elongation of 1%–5% relative to the free-space wavelength. Elongation's influence on the measurement result of the permittivity and permeability has been investigated. Numerical analyses show that the elongation of the focused wavelength can cause the increase of the measured value of the permeability relative to traditionally measured value, but for the permittivity, it is affected by several parameters and may increase or decrease relative to traditionally measured value.
An unload-induced direct-shear model for granular gouge friction in rock discontinuities
Authors: Wu Wei , Zou Yang , Li Xing , Zhao Jian
Published: September 2014

The experimental study introduces an unload-induced direct-shear model to investigate the frictional slip of a layer of simulated granular gouges induced by the combination of a decreasing normal stress and a constant shear stress. A frictional equilibrium state of the gouge layer is initially established under fixed normal and shear stresses. The normal stress is proposed to decrease at a constant unloading rate to induce the frictional slip of the gouge layer, and the shear stress is proposed to keep a constant value during the test. A displacement meter and load cells synchronously measure the slip displacement and the applied normal and shear stresses, respectively. The normal and shear stresses sharply decrease with the frictional slip, owing to damage of gouge contacts. The frictional slip is then gradually arrested with new formation of gouge contacts. A greater initial shear stress induces larger normal and shear stress reductions and a smaller slip displacement. The strain energy stored in the discontinuous system before the frictional slip is found to affect the slip displacement. The advantages and the limitations of this model are discussed at the end.
Tunable all-angle negative refraction and photonic band gaps in two-dimensional plasma photonic crystals with square-like Archimedean lattices
Authors: Zhang Hai-Feng , Liu Shao-Bin , Jiang Yu-Chi
Published: September 2014

In this paper, the tunable all-angle negative refraction and photonic band gaps (PBGs) in two types of two-dimensional (2D) plasma photonic crystals (PPCs) composed of homogeneous plasma and dielectric (GaAs) with square-like Archimedean lattices (ladybug and bathroom lattices) for TM wave are theoretically investigated based on a modified plane wave expansion method. The type-1 structure is dielectric rods immersed in the plasma background, and the complementary structure is named as type-2 PPCs. Theoretical simulations demonstrate that the both types of PPCs with square-like Archimedean lattices have some advantages in obtaining the higher cut-off frequency, the larger PBGs, more number of PBGs, and the relative bandwidths compared to the conventional square lattices as the filling factor or radius of inserted rods is same. The influences of plasma frequency and radius of inserted rod on the properties of PBGs for both types of PPCs also are discussed in detail. The calculated results show that PBGs can be manipulated by the parameters as mentioned above. The possibilities of all-angle negative refraction in such two types of PPCs at low bands also are discussed. Our calculations reveal that the all-angle negative phenomena can be observed in the first two TM bands, and the frequency range of all-angle negative refraction can be tuned by changing plasma frequency. Those properties can be used to design the optical switching and sensor.
Polar state in freestanding strontium titanate nanoparticles
Authors: Tyson Trevor A. , Yu Tian , Croft Mark , Scofield Megan E. , Bobb-Semple Dara , Tao Jing , Jaye Cherno , Fischer Daniel , Wong Stanislaus S.
Published: September 2014

Monodispersed strontium titanate nanoparticles were prepared and studied in detail. It is found that ∼10 nm as-prepared stoichiometric nanoparticles are in a polar structural state (possibly with ferroelectric properties) over a broad temperature range. A tetragonal structure, with possible reduction of the electronic hybridization, is found as the particle size is reduced. In the 10 nm particles, no change in the local Ti-off centering is seen between 20 and 300 K. The results indicate that nanoscale motifs of SrTiO3 may be utilized in data storage as assembled nano-particle arrays in applications where chemical stability, temperature stability, and low toxicity are critical issues.
Intrinsic dissipation in a nano-mechanical resonator
Authors: Kunal K. , Aluru N. R.
Published: September 2014

We investigate the effect of size on intrinsic dissipation in nano-structures. We use molecular dynamics simulation and study dissipation under two different modes of deformation: stretching and bending mode. In the case of stretching deformation (with uniform strain field), dissipation takes place due to Akhiezer mechanism. For bending deformation, in addition to the Akhiezer mechanism, the spatial temperature gradient also plays a role in the process of entropy generation. Interestingly, we find that the bending modes have a higher Q factor in comparison with the stretching deformation (under the same frequency of operation). Furthermore, with the decrease in size, the difference in Q factor between the bending and stretching deformation becomes more pronounced. The lower dissipation for the case of bending deformation is explained to be due to the surface scattering of phonons. A simple model, for phonon dynamics under an oscillating strain field, is considered to explain the observed variation in dissipation rate. We also studied the scaling of Q factor with initial tension, in a beam under flexure. We develop a continuum theory to explain the observed results.
Enhancement of the photovoltaic performance in P3HT: PbS hybrid solar cells using small size PbS quantum dots
Authors: Firdaus Yuliar , Vandenplas Erwin , Justo Yolanda , Gehlhaar Robert , Cheyns David , Hens Zeger , Van der Auweraer Mark
Published: September 2014

Different approaches of surface modification of the quantum dots (QDs), namely, solution-phase (octylamine, octanethiol) and post-deposition (acetic acid, 1,4-benzenedithiol) ligand exchange were used in the fabrication of hybrid bulk heterojunction solar cell containing poly (3-hexylthiophene) (P3HT) and small (2.4 nm) PbS QDs. We show that replacing oleic acid by shorter chain ligands improves the figures of merit of the solar cells. This can possibly be attributed to a combination of a reduced thickness of the barrier for electron transfer and an optimized phase separation. The best results were obtained for post-deposition ligand exchange by 1,4-benzenedithiol, which improves the power conversion efficiency of solar cells based on a bulk heterojunction of lead sulfide (PbS) QDs and P3HT up to two orders of magnitude over previously reported hybrid cells based on a bulk heterojunction of P3HT:PbS QDs, where the QDs are capped by acetic acid ligands. The optimal performance was obtained for solar cells with 69 wt. % PbS QDs. Besides the ligand effects, the improvement was attributed to the formation of an energetically favorable bulk heterojunction with P3HT, when small size (2.4 nm) PbS QDs were used. Dark current density-voltage (J-V) measurements carried out on the device provided insight into the working mechanism: the comparison between the dark J-V characteristics of the bench mark system P3HT:PCBM and the P3HT:PbS blends allows us to conclude that a larger leakage current and a more efficient recombination are the major factors responsible for the larger losses in the hybrid system.
Electronic and intraband optical properties of single quantum rings under intense laser field radiation
Authors: Radu A. , Kirakosyan A. A. , Laroze D. , Baghramyan H. M. , Barseghyan M. G.
Published: September 2014

The influence of an intense laser field on one-electron states and intraband optical absorption coefficients is investigated in two-dimensional GaAs/Ga0.7Al0.3As quantum rings. An analytical expression of the effective lateral confining potential induced by the laser field is obtained. The one-electron energy spectrum and wave functions are found using the effective mass approximation and exact diagonalization technique. We have shown that changes in the incident light polarization lead to blue- or redshifts in the intraband optical absorption spectrum. Moreover, we found that only blueshift is obtained with increasing outer radius of the quantum ring.
A comparative study of spin coated and floating film transfer method coated poly (3-hexylthiophene)/poly (3-hexylthiophene)-nanofibers based field effect transistors
Authors: Tiwari Shashi , Takashima Wataru , Nagamatsu S. , Balasubramanian S. K. , Prakash Rajiv
Published: September 2014

A comparative study on electrical performance, optical properties, and surface morphology of poly(3-hexylthiophene) (P3HT) and P3HT-nanofibers based “normally on” type p-channel field effect transistors (FETs), fabricated by two different coating techniques has been reported here. Nanofibers are prepared in the laboratory with the approach of self-assembly of P3HT molecules into nanofibers in an appropriate solvent. P3HT (0.3 wt. %) and P3HT-nanofibers (∼0.25 wt. %) are used as semiconductor transport materials for deposition over FETs channel through spin coating as well as through our recently developed floating film transfer method (FTM). FETs fabricated using FTM show superior performance compared to spin coated devices; however, the mobility of FTM films based FETs is comparable to the mobility of spin coated one. The devices based on P3HT-nanofibers (using both the techniques) show much better performance in comparison to P3HT FETs. The best performance among all the fabricated organic field effect transistors are observed for FTM coated P3HT-nanofibers FETs. This improved performance of nanofiber-FETs is due to ordering of fibers and also due to the fact that fibers offer excellent charge transport facility because of point to point transmission. The optical properties and structural morphologies (P3HT and P3HT-nanofibers) are studied using UV-visible absorption spectrophotometer and atomic force microscopy , respectively. Coating techniques and effect of fiber formation for organic conductors give information for fabrication of organic devices with improved performance.
Experimental investigation of microwave interaction with magnetoplasma in miniature multipolar configuration using impedance measurements
Authors: Dey Indranuj , Toyoda Yuji , Yamamoto Naoji , Nakashima Hideki
Published: September 2014

A miniature microwave plasma source employing both radial and axial magnetic fields for plasma confinement has been developed for micro-propulsion applications. Plasma is initiated by launching microwaves via a short monopole antenna to circumvent geometrical cutoff limitations. The amplitude and phase of the forward and reflected microwave power is measured to obtain the complex reflection coefficient from which the equivalent impedance of the plasma source is determined. Effect of critical plasma density condition is reflected in the measurements and provides insight into the working of the miniature plasma source. A basic impedance calculation model is developed to help in understanding the experimental observations. From experiment and theory, it is seen that the equivalent impedance magnitude is controlled by the coaxial discharge boundary conditions, and the phase is influenced primarily by the plasma immersed antenna impedance.
Graphene-based ion rectifier using macroscale geometric asymmetry
Authors: Martin S. T. , Neild A. , Majumder M.
Published: September 2014

Ion rectification is the asymmetrical conduction of ions through a system under different polarities of applied potentials. In this article we report the finding of a novel form of ion rectification in graphene oxide (GO) and reduced graphene oxide (RGO) films which act as an ensemble array of nanochannels. Rectification is imparted by introducing geometric asymmetry in fluidic inlets to the counter-ion selective nanochannels of GO/RGO which creates asymmetry in the enrichment/depletion effects at the macro-/nano-interface. The devices are made simply by cutting a GO or RGO film into a trapezoid and sealing the film within a Polydimethylsiloxane block so that fluid may only enter through one of two inlets. These devices exhibit rectification ratios larger than 20 (in 1 mM NaCl) while operating at modest voltages [−1 V, +1 V].
Hysteresis and compensation behaviors of spin-3/2 cylindrical Ising nanotube system
Authors: Kocakaplan Yusuf , Keskin Mustafa
Published: September 2014

The hysteresis and compensation behaviors of the spin-3/2 cylindrical Ising nanotube system are studied within the framework of the effective-field theory with correlations. The effects of the Hamiltonian parameters are investigated on the magnetic and thermodynamic quantities, such as the total magnetization, hysteresis curves, and compensation behaviors of the system. Depending on the Hamiltonian parameters, some characteristic hysteresis behaviors are found, such as the existence of double and triple hysteresis loops. According to Néel classification nomenclature, the system displays Q-, R-, P-, N-, M-, and S- types of compensation behaviors for the appropriate values of the system parameters. We also compare our results with some recently published theoretical and experimental works and find a qualitatively good agreement.
Tuning microwave magnetic properties of FeCoN thin films by controlling dc deposition power
Authors: Wu Y. P. , Yang Yong , Yang Z. H. , Ma Fusheng , Zong B. Y. , Ding Jun
Published: September 2014

In this work, we deposited FeCoN thin films by reactive dc magnetron sputtering under various deposition powers. Composition, microstructure, static magnetic properties, and microwave permeability of as-sputtered films were examined. The permeability spectra were theoretically analyzed based on LLG equation. When high deposition power was applied, μ0′ improved significantly due to the increased Ms and decreased Hk. On the other hand, the damping coefficient λ increased with the power, which resulted in the widen permeability spectra. The physical origin of the influences should be related to the change in the film composition and microstructure, which have immediate impact on static magnetic properties and damping effect of the film.
Highly transparent bipolar resistive switching memory with In-Ga-Zn-O semiconducting electrode in In-Ga-Zn-O/Ga2O3/In-Ga-Zn-O structure
Authors: Yan X. B. , Hao H. , Chen Y. F. , Li Y. C. , Banerjee W.
Published: September 2014

In this work, based on wide bandgap Ga2O3 films, we demonstrated a fully transparent bipolar resistive random access memory (RRAM) device with very high average transmittance of 91.7% in the visible region. The semiconducting In-Ga-Zn-O (IGZO) films were used as symmetric electrodes to reduce sneak current. Different I-V performance will introduce a change in the overall oxygen vacancy distribution by an opposite polarity of electroforming voltage. The temperature dependent of I-V characteristics will be fitted to the hopping conduction mechanism for both of the high-resistance states (HRS) and low-resistance states (LRS) with semiconducting nature. The activation energy and trap spacing of LRS were lower and shorter than that of HRS. A model of resistive switching mechanism related to correlated barrier hopping theory has been proposed for the fully transparent IGZO/Ga2O3/IGZO RRAM device.
A particle-in-cell approach to obliquely propagating electrostatic waves
Authors: Koen Etienne J. , Collier Andrew B. , Maharaj Shimul K.
Published: September 2014

The electron-acoustic and beam-driven modes associated with electron beams have previously been identified and studied numerically. These modes are associated with Broadband Electrostatic Noise found in the Earth's auroral and polar cusp regions. Using a 1-D spatial Particle-in-Cell simulation, the electron-acoustic instability is studied for a magnetized plasma, which includes cool ions, cool electrons and a hot, drifting electron beam. Both the weakly and strongly magnetized regimes with varying wave propagation angle, θ, with respect to the magnetic field are studied. The amplitude and frequency of the electron-acoustic mode are found to decrease with increasing θ. The amplitude of the electron-acoustic mode is found to significantly grow at intermediate wavenumber ranges. It reaches a saturation level at the point, where a plateau forms in the hot electron velocity distribution after which the amplitude of the electron-acoustic mode decays.
Enhanced separation efficiency of photoinduced charges for antimony-doped tin oxide (Sb-SnO2)/TiO2 heterojunction semiconductors with varied Sb doping concentration
Authors: Zhang Zhen-Long , Ma Wen-Hai , Mao Yan-Li
Published: September 2014

In this paper, antimony-doped tin oxide (Sb-SnO2) nanoparticles were synthesized with varied Sb doping concentration, and the Sb-SnO2/TiO2 heterojunction semiconductors were prepared with Sb-SnO2 and TiO2. The separation efficiency of photoinduced charges was characterized with surface photovoltage (SPV) technique. Compared with Sb-SnO2 and TiO2, Sb-SnO2/TiO2 presents an enhanced separation efficiency of photoinduced charges, and the SPV enhancements were estimated to be 1.40, 1.43, and 1.99 for Sb-SnO2/TiO2 composed of Sb-SnO2 with the Sb doping concentration of 5%, 10%, and 15%, respectively. To understand the enhancement, the band structure of Sb-SnO2 and TiO2 in the heterojunction semiconductor was determined, and the conduction band offsets (CBO) between Sb-SnO2 and TiO2 were estimated to be 0.56, 0.64, and 0.98 eV for Sb-SnO2/TiO2 composed of Sb-SnO2 with the Sb doping concentration of 5%, 10%, and 15%, respectively. These results indicate that the separation efficiency enhancement is resulting from the energy level matching, and the increase of enhancement is due to the rising of CBO.