bluuebunny/crossref_metadata_2025 huggingface dataset:
Enhanced thermal shock resistance of ultra-high temperature ceramic by biomimetic surface modification
Authors: Zhang Baoxi , Zhang Xinghong , Qiu Yunfeng , Han Jiecai , Hu PingAn , Hong Changqing , Peng Zujun , Han Wenbo , Chen Guiqing , Hu Ping
Published: December 2014

The manipulation of the heat flow in a ceramic matrix composite is of great importance in industrial and academic fields.
Direct growth of mesoporous carbon-coated Ni nanoparticles on carbon fibers for flexible supercapacitors
Authors: Li Jun , Wang Yuhang , Tang Jing , Wang Yang , Wang Tianyu , Zhang Lijuan , Zheng Gengfeng
Published: December 2014

A solution method for direct growth of mesoporous carbon-coated nickel nanoparticles on carbon fibers is demonstrated for flexible supercapacitors.
Synthesis of ZrO2:Fe nanostructures with visible-light driven H2 evolution activity
Authors: Xiao Mu , Li Yaguang , Lu Yangfan , Ye Zhizhen
Published: December 2014

The cubic form ZrO2:Fe nanostructures with high energy level of CBM and visible light driven hydrogen production performance were synthesized.
The effects of heavy atoms on the exciton diffusion properties in photoactive thin films of tetrakis(4-carbomethoxyphenyl)porphyrins
Authors: Ortiz Angy L. , Collier Graham S. , Marin Dawn M. , Kassel Jennifer A. , Ivins Reynolds J. , Grubich Nicholas G. , Walter Michael G.
Published: December 2014

The exciton diffusion coefficient (D) and exciton diffusion length (LD) for three tetrakis(4-carbomethoxyphenyl)porphyrins were obtained by fitting the quenching efficiency and PL lifetime to a 3D exciton Monte Carlo ediffusion model.
Signal‐to‐interference‐plus‐noise ratio‐based multi‐relay beamforming for multi‐user multiple‐input multiple‐output cognitive relay networks with interference from primary network
Authors: Zhang Guangchi , Li Quanzhong , Zhang Qi , Qin Jiayin , Yang Liang
Published: December 2014

Cognitive radio is a potential technique to solve the spectrum shortage problem in wireless communications. Integrating wireless relaying into the cognitive radio networks can further improve the spectrum efficiency. In this study, a multiple‐input multiple‐output cognitive relay network is considered, where the primary network (PN) consists of one transmitter‐receiver pair and the secondary network consists of multiple active source‐destination pairs and non‐regenerative relays. All nodes in the networks are deployed with multiple antennas. How to avoid interference to the PN is an important task in the secondary network design. The precoders of the secondary sources and the receivers of the secondary destinations are designed in a well‐known zero‐forcing way. The secondary relays forward signals for the secondary source‐destination pairs by beamforming. With interference cancellation constraints and individual transmit power constraints, a relay beamforming scheme is proposed to maximise the total signal‐to‐interference‐plus‐noise ratio (SINR) at the secondary destinations. Then a maximising minimum SINR relay beamforming scheme is further proposed to provide max–min fairness among the secondary source‐destination pairs. The beamforming problems are formulated into the quadratically constrained quadratic fractional programming problems, and are solved by the semi‐definite relaxation technique. The performances of these beamforming schemes have been verified by computer simulations.
Investigation of the sympathetic tripping problem in power systems with large penetrations of distributed generation
Authors: Jennett Kyle I. , Booth Campbell D. , Coffele Federico , Roscoe Andrew J.
Published: December 2014

This study contains an investigation into sympathetic tripping – the undesirable disconnection of distributed generators (DGs) (in accordance with the recently‐introduced G83/2 under voltage protection) when a network fault occurs in the vicinity of the DG and is not cleared quickly enough by the network protection (i.e. before the DG's under voltage protection operates). An evaluation of the severity of and proposal of solutions to the problem of sympathetic tripping on a typical UK distribution power network is presented. An inverter model (as the majority of DGs will be inverter‐interfaced) that characterises the fault response of the inverter and its associated protection functions has been developed for use in simulation through exhaustive laboratory testing of a commercially‐available 3 kW inverter for DG application; the observed responses have been modelled and incorporated in a power system simulation package. It is shown, when using presently‐adopted DG interface and network protection settings, that the risk of sympathetic tripping is high in several future scenarios. To mitigate this risk, the impact of modifying network protection settings is evaluated. This study has two key findings – determination of the conditions at which the risk of sympathetic tripping is high and evaluation of a technique to mitigate this risk.
Numerical simulations for the rheological characteristics of emulsions under several conditions including temperature, shear rate, surfactant concentration and droplet size
Authors: Choi Se Bin , Lee Jung Shin , Baik Seung Joo , Lee Joon Sang
Published: December 2014

An emulsion system was simulated under simple shear rates to analyse its rheological characteristics using the lattice Boltzmann method. The relative viscosity of an emulsion under a simple shear flow along with changes in temperature, shear rate, surfactant concentration and droplet size was calculated. The relative viscosity of emulsions decreased with increase in temperature. The shear thinning phenomena explaining the inverse proportion between shear rate and viscosity were observed. An increase in the surfactant concentration caused an increase in the relative viscosity for a decane‐in‐water emulsion, because the increased deformation caused by the decreased interfacial tension significantly influenced the wall shear stress. An increase in droplet size caused a decrease in the relative viscosity and smaller shear thinning behaviour because of decreased aggregational and repulsive forces within the emulsion system.
Electron transfer activation of a second water channel for proton transport in [FeFe]-hydrogenase
Authors: Sode Olaseni , Voth Gregory A.
Published: December 2014

Hydrogenase enzymes are important because they can reversibly catalyze the production of molecular hydrogen. Proton transport mechanisms have been previously studied in residue pathways that lead to the active site of the enzyme via residues Cys299 and Ser319. The importance of this pathway and these residues has been previously exhibited through site-specific mutations, which were shown to interrupt the enzyme activity. It has been shown recently that a separate water channel (WC2) is coupled with electron transport to the active site of the [FeFe]-hydrogenase. The water-mediated proton transport mechanisms of the enzyme in different electronic states have been studied using the multistate empirical valence bond reactive molecular dynamics method, in order to understand any role WC2 may have in facilitating the residue pathway in bringing an additional proton to the enzyme active site. In a single electronic state A2−, a water wire was formed through which protons can be transported with a low free energy barrier. The remaining electronic states were shown, however, to be highly unfavorable to proton transport in WC2. A double amino acid substitution is predicted to obstruct proton transport in electronic state A2- by closing a cavity that could otherwise fill with water near the proximal Fe of the active site.
Statistically optimal analysis of state-discretized trajectory data from multiple thermodynamic states
Authors: Wu Hao , Mey Antonia S. J. S. , Rosta Edina , Noé Frank
Published: December 2014

We propose a discrete transition-based reweighting analysis method (dTRAM) for analyzing configuration-space-discretized simulation trajectories produced at different thermodynamic states (temperatures, Hamiltonians, etc.) dTRAM provides maximum-likelihood estimates of stationary quantities (probabilities, free energies, expectation values) at any thermodynamic state. In contrast to the weighted histogram analysis method (WHAM), dTRAM does not require data to be sampled from global equilibrium, and can thus produce superior estimates for enhanced sampling data such as parallel/simulated tempering, replica exchange, umbrella sampling, or metadynamics. In addition, dTRAM provides optimal estimates of Markov state models (MSMs) from the discretized state-space trajectories at all thermodynamic states. Under suitable conditions, these MSMs can be used to calculate kinetic quantities (e.g., rates, timescales). In the limit of a single thermodynamic state, dTRAM estimates a maximum likelihood reversible MSM, while in the limit of uncorrelated sampling data, dTRAM is identical to WHAM. dTRAM is thus a generalization to both estimators.
Effects of polydispersity on confined homopolymer melts: A Monte Carlo study
Authors: Rorrer Nicholas A. , Dorgan John R.
Published: December 2014

New insight into the molecular scale details of polymer melts under confined conditions is obtained from the first dynamic Monte Carlo study incorporating polydispersity. While confinement effects on polymers have been widely explored, little work exists on the effects of polydispersity. This is surprising given the near universal presence of polydispersity in physical systems. To address this shortcoming, a new variation of on-lattice dynamic Monte Carlo simulation is used to provide an understanding of how polydispersity alters confinement effects on polymer melts. Polymer melts of varying polydispersity are simulated between two hard walls (surface interaction parameter, χs = 0) of variable spacing. As plate spacing decreases, polymer chains adopt conformations in which the end-to-end vector is parallel to the hard walls. However, polydisperse melts with the same length average molecular weight, Nw (which is analogous to the weight average molecular weight, Mw) show reduced orientation effects. Polydispersity provides greater degrees of freedom; that is, there are more configurations for the system to adopt to accommodate confinement without ordering. At plate spacings of four radii of gyration and only modest polydispersity index values (polydispersity index, PDI = 1.42), the order parameters are reduced by 15% compared to the monodisperse case. The same PDI value corresponds to a 10% reduction in the perturbations of the end-to-end vector and Rouse time. Interestingly, length-based migration effects are observed. Longer chains reside away from the walls and the shorter chains are found nearer the walls; at equilibrium there is a molecular weight based fractionation across the gap. Confinement also leads to a “speeding up” of the polymer dynamics. Altered dynamic phenomena include a reduction of the Rouse time for the same average molecular weight and an altered scaling behavior with plate spacing. Reptation times are also reduced and polydispersity smoothes out the transitions between different scaling regimes. The overall picture that emerges is not unexpected – polydispersity profoundly affects the behavior of confined homopolymers.
Ultra-low-temperature reactions of C(3P) atoms with benzene molecules in helium droplets
Authors: Krasnokutski Serge A. , Huisken Friedrich
Published: December 2014

The reaction of carbon atoms with benzene has been investigated in liquid helium droplets at T = 0.37 K. We found an addition of the carbon atom to form an initial intermediate complex followed by a ring opening and the formation of a seven-membered ring. In contrast to a previous gas phase study, the reaction is frozen after these steps and the loss of hydrogen does not occur. A calorimetric technique was applied to monitor the energy balance of the reaction. It was found that more than 267 kJ mol−1 were released in this reaction. This estimation is in line with quantum chemical calculations of the formation energy of a seven-membered carbon ring. It is suggested that reactions of this kind could be responsible for the low abundance of small polycyclic aromatic hydrocarbon molecules in the interstellar medium. We also found the formation of weakly bonded water-carbon adducts, in which the carbon atom is linked to the oxygen atom of the water molecule with a binding energy of about 33.4 kJ mol−1.
Heat trace and functional determinant in one dimension
Authors: Avramidi Ivan G.
Published: December 2014

We study the spectral properties of the Laplace type operator on the circle. We discuss various approximations for the heat trace, the zeta function, and the zeta-regularized determinant. We obtain a differential equation for the heat kernel diagonal and a recursive system for the diagonal heat kernel coefficients, which enables us to find closed approximate formulas for the heat trace and the functional determinant which become exact in the limit of infinite radius. The relation to the generalized Korteweg-de Vries hierarchy is discussed as well.
Influence of strain and composition on Tc in FeSe1−xTex films
Authors: Horide Tomoya , Sanyoushi Masahiro , Ichinose Ataru , Matsumoto Kaname
Published: December 2014

FeSe1−xTex films with wide ranging strain and composition were deposited using pulsed laser deposition, and lattice parameters and critical temperature (Tc) were evaluated in the films to understand influence of strain and composition on Tc of FeSe1−xTex films. c was larger than that in bulk and a was smaller than the bulk value due to strain (substrate effect), where c and a are c-axis length (perpendicular to film surface) and a-axis length (parallel to film surface) in the c-axis oriented FeSe1−xTex films. Depending on c value, two kinds of regions were observed regarding relationship between a and Tc. In the case of small c (c < 5.9 Å: small Te content), lattice parameter dependence of Tc in the films was different from that in bulk with different Te content, and Tc strongly increased with decrease in a. On the other hand, in the case of large c (c > 5.9 Å: large Te content), lattice parameter dependence of Tc in the films was similar to that in bulk with different Te content, and in-plane film strain did not vary Tc. In first principle band calculation, ab-plane bi-axial strain varied the Fermi surface in FeSe (c < 5.9 Å), but such strain-induced variation of Fermi surface was smaller in FeSe0.5Te0.5 (c > 5.9 Å), which is consistent with the experimental results. The present results suggest that much higher Tc than the bulk values is obtained by decreasing a (compressive ab-plane strain) with keeping c < 5.9 Å (small Te content) using hydrostatic pressure and/or film strain.
Interface initiation and propagation in liquid demixing with electric fields
Authors: Galanis Jennifer , Tsori Yoav
Published: December 2014

We investigate the dynamics of liquid-liquid phase separation confined in a charged concentric cylindrical geometry. Two main time scales characterize the non-equilibrium interface behavior: (1) the lag time tL for forming an interface, and (2) the relaxation time to equilibrium. We find that tL increases as parameters (temperature, bulk composition, and surface charge) approach the electrostatic spinodal line in the phase diagram. Close to this line, tL is proportional to a renormalized bulk concentration with an exponent of −1.16 ± 0.03. The relaxation of the interface to equilibrium can be divided into three phases: early, intermediate (power-law), and late (exponential). During power-law relaxation, the location of the rescaled interface is proportional to time with an exponent of −0.94 ± 0.04. Exponential relaxation occurs as a consequence of finite-size effects, and the associated time constant decreases with decreasing system size (with a power-law scaling), decreasing concentration, and increasing surface charge. The time constant also decreases with increasing (decreasing) temperature when the concentration is below (above) the critical concentration.
The energetic motions in turbulent pipe flow
Authors: Hellström Leo H. O. , Smits Alexander J.
Published: December 2014

Snapshot and classical proper orthogonal decomposition (POD) are used to examine the large-scale, energetic motions in fully developed turbulent pipe flow at ReD = 47,000 and 93,000. The snapshot POD modes come in pairs, representing the same azimuthal mode number but with a simple phase shift. The first 10 snapshot POD modes, associated with the very large scale motions (VLSMs), contribute 43% of the average Reynolds shear stress, and for first 80 modes u′ and v′ are anti-correlated so that they all contribute to positive shear stress events. The attached motions are contained in the lower order modes, and detached motions do not appear until snapshot POD mode numbers ≥15. We find that snapshot POD can introduce mode mixing, which is avoided in classical POD. Classical POD also gives frequency information, confirming that the low order modes capture well the behavior of the very large scale motions.
On the role of interfacial hydrogen bonds in “on-water” catalysis
Authors: Karhan Kristof , Khaliullin Rustam Z. , Kühne Thomas D.
Published: December 2014

Numerous experiments have demonstrated that many classes of organic reactions exhibit increased reaction rates when performed in heterogeneous water emulsions. Despite enormous practical importance of the observed “on-water” catalytic effect and several mechanistic studies, its microscopic origins remains unclear. In this work, the second generation Car-Parrinello molecular dynamics method is extended to self-consistent charge density-functional based tight-binding in order to study “on-water” catalysis of the Diels-Alder reaction between dimethyl azodicarboxylate and quadricyclane. We find that the stabilization of the transition state by dangling hydrogen bonds exposed at the aqueous interfaces plays a significantly smaller role in “on-water” catalysis than has been suggested previously.
Ni-based nanoalloys: Towards thermally stable highly magnetic materials
Authors: Palagin Dennis , Doye Jonathan P. K.
Published: December 2014

Molecular dynamics simulations and density functional theory calculations have been used to demonstrate the possibility of preserving high spin states of the magnetic cores within Ni-based core-shell bimetallic nanoalloys over a wide range of temperatures. We show that, unlike the case of Ni–Al clusters, Ni–Ag clusters preserve high spin states (up to 8 μB in case of Ni13Ag32 cluster) due to small hybridization between the electronic levels of two species. Intriguingly, such clusters are also able to maintain geometrical and electronic integrity of their cores at temperatures up to 1000 K (e.g., for Ni7Ag27 cluster). Furthermore, we also show the possibility of creating ordered arrays of such magnetic clusters on a suitable support by soft-landing pre-formed clusters on the surface, without introducing much disturbance in geometrical and electronic structure of the cluster. We illustrate this approach with the example of Ni13Ag38 clusters adsorbed on the Si(111)–(7×7) surface, which, having two distinctive halves to the unit cell, acts as a selective template for cluster deposition.
Detachment of semiflexible polymer chains from a substrate: A molecular dynamics investigation
Authors: Paturej J. , Erbas A. , Milchev A. , Rostiashvili V. G.
Published: December 2014

Using Molecular Dynamics simulations, we study the force-induced detachment of a coarse-grained model polymer chain from an adhesive substrate. One of the chain ends is thereby pulled at constant speed off the attractive substrate and the resulting saw-tooth profile of the measured mean force ⟨f⟩ vs height D of the end-segment over the plane is analyzed for a broad variety of parameters. It is shown that the observed characteristic oscillations in the ⟨f⟩-D profile depend on the bending and not on the torsional stiffness of the detached chains. Allowing for the presence of hydrodynamic interactions (HI) in a setup with explicit solvent and dissipative particle dynamics-thermostat, rather than the case of Langevin thermostat, one finds that HI have little effect on the ⟨f⟩-D profile. Also the change of substrate affinity with respect to the solvent from solvophilic to solvophobic is found to play negligible role in the desorption process. In contrast, a changing ratio \documentclass[12pt]{minimal}\begin{document}$\epsilon _s^B / \epsilon _s^A$\end{document}εsB/εsA of the binding energies of A- and B-segments in the detachment of an AB-copolymer from adhesive surface strongly changes the ⟨f⟩-D profile whereby the B-spikes vanish when \documentclass[12pt]{minimal}\begin{document}$\epsilon _s^B / \epsilon _s^A < 0.15$\end{document}εsB/εsA<0.15. Eventually, performing an atomistic simulation of (bio)-polymers, we demonstrate that the simulation results, derived from our coarse-grained model, comply favorably with those from the all-atom simulation.
Electronic coupling calculations with transition charges, dipoles, and quadrupoles derived from electrostatic potential fitting
Authors: Fujimoto Kazuhiro J.
Published: December 2014

A transition charge, dipole, and quadrupole from electrostatic potential (TrESP-CDQ) method for electronic coupling calculations is proposed. The TrESP method is based on the classical description of electronic Coulomb interaction between transition densities for individual molecules. In the original TrESP method, only the transition charge interactions were considered as the electronic coupling. In the present study, the TrESP method is extended to include the contributions from the transition dipoles and quadrupoles as well as the transition charges. Hence, the self-consistent transition density is employed in the ESP fitting procedure. To check the accuracy of the present approach, several test calculations are performed to a helium dimer, a methane dimer, and an ethylene dimer. As a result, the TrESP-CDQ method gives a much improved description of the electronic coupling, compared with the original TrESP method. The calculated results also show that the self-consistent treatment to the transition densities contributes significantly to the accuracy of the electronic coupling calculations. Based on the successful description of the electronic coupling, the contributions to the electronic coupling are also analyzed. This analysis clearly shows a negligible contribution of the transition charge interaction to the electronic coupling. Hence, the distribution of the transition density is found to strongly influence the magnitudes of the transition charges, dipoles, and quadrupoles. The present approach is useful for analyzing and understanding the mechanism of excitation-energy transfer.
A bio-inspired memory device based on interfacing Physarum polycephalum with an organic semiconductor
Authors: Romeo Agostino , Dimonte Alice , Tarabella Giuseppe , D’Angelo Pasquale , Erokhin Victor , Iannotta Salvatore
Published: December 2014

The development of devices able to detect and record ion fluxes is a crucial point in order to understand the mechanisms that regulate communication and life of organisms. Here, we take advantage of the combined electronic and ionic conduction properties of a conducting polymer to develop a hybrid organic/living device with a three-terminal configuration, using the Physarum polycephalum Cell (PPC) slime mould as a living bio-electrolyte. An over-oxidation process induces a conductivity switch in the polymer, due to the ionic flux taking place at the PPC/polymer interface. This behaviour endows a current-depending memory effect to the device.
Comparative study of hydration shell dynamics around a hyperactive antifreeze protein and around ubiquitin
Authors: Duboué-Dijon Elise , Laage Damien
Published: December 2014

The hydration layer surrounding a protein plays an essential role in its biochemical function and consists of a heterogeneous ensemble of water molecules with different local environments and different dynamics. What determines the degree of dynamical heterogeneity within the hydration shell and how this changes with temperature remains unclear. Here, we combine molecular dynamics simulations and analytic modeling to study the hydration shell structure and dynamics of a typical globular protein, ubiquitin, and of the spruce budworm hyperactive antifreeze protein over the 230–300 K temperature range. Our results show that the average perturbation induced by both proteins on the reorientation dynamics of water remains moderate and changes weakly with temperature. The dynamical heterogeneity arises mostly from the distribution of protein surface topographies and is little affected by temperature. The ice-binding face of the antifreeze protein induces a short-ranged enhancement of water structure and a greater slowdown of water reorientation dynamics than the non-ice-binding faces whose effect is similar to that of ubiquitin. However, the hydration shell of the ice-binding face remains less tetrahedral than the bulk and is not “ice-like”. We finally show that the hydrogen bonds between water and the ice-binding threonine residues are particularly strong due to a steric confinement effect, thereby contributing to the strong binding of the antifreeze protein on ice crystals.
On the Ashtekar-Lewandowski measure as a restriction of the product one
Authors: Tlas Tamer
Published: December 2014

It is known that the k-dimensional Hausdorff measure on a k-dimensional submanifold of ℝn is closely related to the Lebesgue measure on ℝn. We show that the Ashtekar-Lewandowski measure on the space of generalized G-connections for a compact, connected, semi-simple Lie group G is analogously related to the product measure on the set of all G-valued functions on the group of loops. We also show that, under very mild conditions, the Ashtekar-Lewandowski measure is supported on nowhere-continuous generalized connections.
Note: “Lock-in accelerometry” to follow sink dynamics in shaken granular matter
Authors: Sánchez-Colina G. , Alonso-Llanes L. , Martínez E. , Batista-Leyva A. J. , Clement C. , Fliedner C. , Toussaint R. , Altshuler E.
Published: December 2014

Understanding the penetration dynamics of intruders in granular beds is relevant not only for fundamental physics, but also for geophysical processes and construction on sediments or granular soils in areas potentially affected by earthquakes. While the penetration of intruders in two dimensional (2D) laboratory granular beds can be followed using video recording, this is useless in three dimensional (3D) beds of non-transparent materials such as common sand. Here, we propose a method to quantify the sink dynamics of an intruder into laterally shaken granular beds based on the temporal correlations between the signals from a reference accelerometer fixed to the shaken granular bed, and a probe accelerometer deployed inside the intruder. Due to its analogy with the working principle of a lock-in amplifier, we call this technique lock-in accelerometry.
Electric contributions to magnetic force microscopy response from graphene and MoS2 nanosheets
Authors: Li Lu Hua , Chen Ying
Published: December 2014

Magnetic force microscopy (MFM) signals have recently been detected from whole pieces of mechanically exfoliated graphene and molybdenum disulfide (MoS2) nanosheets, and magnetism of the two nanomaterials was claimed based on these observations. However, non-magnetic interactions or artefacts are commonly associated with MFM signals, which make the interpretation of MFM signals not straightforward. A systematic investigation has been done to examine possible sources of the MFM signals from graphene and MoS2 nanosheets and whether the MFM signals can be correlated with magnetism. It is found that the MFM signals have significant non-magnetic contributions due to capacitive and electrostatic interactions between the nanosheets and conductive cantilever tip, as demonstrated by electric force microscopy and scanning Kevin probe microscopy analyses. In addition, the MFM signals of graphene and MoS2 nanosheets are not responsive to reversed magnetic field of the magnetic cantilever tip. Therefore, the observed MFM response is mainly from electric artefacts and not compelling enough to correlate with magnetism of graphene and MoS2 nanosheets.
Electronic and optical properties of NbO2
Authors: O'Hara Andrew , Nunley Timothy N. , Posadas Agham B. , Zollner Stefan , Demkov Alexander A.
Published: December 2014

In the present study, we combine theoretical and experimental approaches in order to gain insight into the electronic properties of both the high-temperature, rutile (metallic) and low-temperature, body-centered tetragonal (insulating) phase of niobium dioxide (NbO2) as well as the optical properties of the low-temperature phase. Theoretical calculations performed at the level of the local density approximation, Hubbard U correction, and hybrid functional are complemented with the spectroscopic ellipsometry (SE) of epitaxial films grown by molecular beam epitaxy. For the rutile phase, the local density approximation (LDA) gives the best description and predicts Fermi surface nesting consistent with wave vectors that lead to niobium-niobium dimerization during the phase transition. For the insulating phase, LDA provides a good quantitative description of the lattice, but only a qualitative description for the band gap. Including a Hubbard U correction opens the band gap at the expense of correctly describing the valence band and lattice of both phases. The hybrid functional slightly overestimates the band gap. Ellipsometric measurement is consistent with insulating behavior with a 1.0 eV band gap. Comparison with the theoretical dielectric functions, obtained utilizing a scissors operator to adjust the LDA band gap to reproduce the ellipsometry data, allows for identification of the SE peak features.
Tunneling transport in a few monolayer-thick WS2/graphene heterojunction
Authors: Yamaguchi Takehiro , Moriya Rai , Inoue Yoshihisa , Morikawa Sei , Masubuchi Satoru , Watanabe Kenji , Taniguchi Takashi , Machida Tomoki
Published: December 2014

This paper demonstrates the high-quality tunnel barrier characteristics and layer number controlled tunnel resistance of a transition metal dichalcogenide (TMD) measuring just a few monolayers in thickness. Investigation of vertical transport in WS2 and MoS2 TMDs in graphene/TMD/metal heterostructures revealed that WS2 exhibits tunnel barrier characteristics when its thickness is between 2 and 5 monolayers, whereas MoS2 experiences a transition from tunneling to thermionic emission transport with increasing thickness within the same range. Tunnel resistance in a graphene/WS2/metal heterostructure therefore increases exponentially with the number of WS2 layers, revealing the tunnel barrier height of WS2 to be 0.37 eV.
Use of lateral structures to monitor and evaluate degradation of key photovoltaic parameters in an organic bulk heterojunction material
Authors: Danielson Eric , Ooi Zi-En , Dodabalapur Ananth
Published: December 2014

Charge transport and recombination mechanisms within organic bulk heterojunction (BHJ) systems have been studied using lateral devices to perform in situ potentiometry. We have developed a simplified measurement technique using two types of lateral structures to elicit key charge transport parameters and study the time and process dependence of the carrier mobilities and their ratio. Small geometry lateral devices are used to evaluate the mobility of the slower carrier within the P3HT:PCBM material system. Larger structures with 5 in situ voltage probes are used to construct a simple potential profile of the device channel and accurately determine the carrier mobility ratio. These two measurements enable the calculation of carrier densities and the recombination coefficient. We monitor the change in these parameters as the P3HT:PCBM film degrades in the presence of oxygen and also examine the effect of the solvent additive 1,8-diiodooctane on this degradation mechanism. By exposing ethanol vapor to the BHJ film, we induce traps in the material and monitor the shift in dominant nongeminate recombination mechanism to a more unimolecular type. We are also able to measure the resulting decrease in carrier mobilities due to the presence of dipole-induced traps. Lateral devices are useful material diagnostic structures for studying degradation in BHJ materials.
Compressively strained SiGe band-to-band tunneling model calibration based on p-i-n diodes and prospect of strained SiGe tunneling field-effect transistors
Authors: Kao Kuo-Hsing , Verhulst Anne S. , Rooyackers Rita , Douhard Bastien , Delmotte Joris , Bender Hugo , Richard Olivier , Vandervorst Wilfried , Simoen Eddy , Hikavyy Andriy , Loo Roger , Arstila Kai , Collaert Nadine , Thean Aaron , Heyns Marc M. , Meyer Kristin De
Published: December 2014

Band-to-band tunneling parameters of strained indirect bandgap materials are not well-known, hampering the reliability of performance predictions of tunneling devices based on these materials. The nonlocal band-to-band tunneling model for compressively strained SiGe is calibrated based on a comparison of strained SiGe p-i-n tunneling diode measurements and doping-profile-based diode simulations. Dopant and Ge profiles of the diodes are determined by secondary ion mass spectrometry and capacitance-voltage measurements. Theoretical parameters of the band-to-band tunneling model are calculated based on strain-dependent properties such as bandgap, phonon energy, deformation-potential-based electron-phonon coupling, and hole effective masses of strained SiGe. The latter is determined with a 6-band k·p model. The calibration indicates an underestimation of the theoretical electron-phonon coupling with nearly an order of magnitude. Prospects of compressively strained SiGe tunneling transistors are made by simulations with the calibrated model.
Metal insulator transitions in perovskite SrIrO3 thin films
Authors: Biswas Abhijit , Kim Ki-Seok , Jeong Yoon Hee
Published: December 2014

Understanding of metal insulator transitions in a strongly correlated system, driven by Anderson localization (disorder) and/or Mott localization (correlation), is a long standing problem in condensed matter physics. The prevailing fundamental question would be how these two mechanisms contrive to accomplish emergent anomalous behaviors. Here, we have grown high quality perovskite SrIrO3 thin films, containing a strong spin orbit coupled 5d element Ir, on various substrates such as GdScO3 (110), DyScO3 (110), SrTiO3 (001), and NdGaO3 (110) with increasing lattice mismatch, in order to carry out a systematic study on the transport properties. We found that metal insulator transitions can be induced in this system; by either reducing thickness (on best lattice matched substrate) or changing degree of lattice strain (by lattice mismatch between film and substrates) of films. Surprisingly these two pathways seek two distinct types of metal insulator transitions; the former falls into disorder driven Anderson type whereas the latter turns out to be of unconventional Mott-Anderson type with the interplay of disorder and correlation. More interestingly, in the metallic phases of SrIrO3, unusual non-Fermi liquid characteristics emerge in resistivity as Δρ ∝ Tε with ε evolving from 4/5 to 1 to 3/2 with increasing lattice strain. We discuss theoretical implications of these phenomena to shed light on the metal insulator transitions.
Impact force of a low speed water droplet colliding on a solid surface
Authors: Li Jingyin , Zhang Bin , Guo Penghua , Lv Qian
Published: December 2014

The impact forces of the low-speed water droplet colliding on a light and tiny aluminum plate were measured by using a highly sensitive piezoelectric force transducer. The one-degree freedom vibration model was employed to analyze the oscillation of the measured force signals, and the plate vibration was confirmed as the cause through elaborately designed experiments. The force data were obtained by using the low-pass Finite Impulse Response filter and was verified to be reliable. The effects of impact velocity and diameter of droplets on the impact force evolutions and peak forces were investigated. The results revealed that the impact process of a liquid droplet is quite different from that of a solid ball in the frequency spectrum and in the power function of the peak force. The droplet impact is closer to a plastic impact, while the other behaves more nearly an elastic impact. The influence of droplet size on erosion is dependent on the impact time duration, which increases with droplet diameter. On the other hand, the impact pressure is the main cause of the material erosion when impact velocity is taken as the influence factor.
MHz-level self-sustained pulsation in polymer microspheres on a chip
Authors: Luo Zhou-Chen , Ma Cao-Yuan , Li Bei-Bei , Xiao Yun-Feng
Published: December 2014

We observe MHz-level periodic self-sustained pulsation (SSP) in the transmission spectrum of a polydimethylsiloxane (PDMS) spherical microcavity on a silicon chip, under a fixed-frequency continuous laser excitation. The SSP results from the strong competition between the thermo-optic and thermal expansion effects of PDMS within the cavity mode volume. The experimental results show good agreement with the theoretical prediction by considering the modification of the thermal expansion coefficient and the temperature distribution within the mode volume.
Physical properties of electron beam evaporated CdTe and CdTe:Cu thin films
Authors: Punitha K. , Sivakumar R. , Sanjeeviraja C. , Sathe Vasant , Ganesan V.
Published: December 2014

In this paper, we report on physical properties of pure and Cu doped cadmium telluride (CdTe) films deposited onto corning 7059 microscopic glass substrates by electron beam evaporation technique. X-ray diffraction study showed that all the deposited films belong to amorphous nature. The average transmittance of the films is varied between 77% and 90%. The optical energy band gap of pure CdTe film is 1.57 eV and it decreased to 1.47 eV upon 4 wt. % of Cu addition, which may be due to the extension of localized states in the band structure. The refractive index of the films was calculated using Swanepoel method. It was observed that the dispersion data obeyed the single oscillator of the Wemple-Didomenico model, from which the dispersion energy (Ed) parameters, dielectric constants, plasma frequency, and oscillator energy (Eo) of CdTe and CdTe:Cu films were calculated and discussed in detail with the light of possible mechanisms underlying the phenomena. The variation in intensity of photoluminescence band edge emission peak observed at 820 nm with Cu dopant is due to the change in surface state density. The observed trigonal lattice of Te peaks in the micro-Raman spectra confirms the p-type conductive nature of films, which was further corroborated by the Hall effect measurement. The lowest resistivity of 6.61 × 104 Ω cm was obtained for the CdTe:Cu (3 wt. %) film.
Nonlinear dynamics of large amplitude modes in a magnetized plasma
Authors: Brodin G. , Stenflo L.
Published: December 2014

We derive two equations describing the coupling between electromagnetic and electrostatic oscillations in one-dimensional geometry in a magnetized cold and non-relativistic plasma. The nonlinear interaction between the wave modes is studied numerically. The effects of the external magnetic field strength and the initial electromagnetic polarization are of particular interest here. New results can, thus, be identified.
Electric field-induced nonlinearity enhancement in strained semi-spheroid-shaped quantum dots coupled to wetting layer
Authors: Sabaeian Mohammad , Shahzadeh Mohammadreza , Farbod Mansoor
Published: December 2014

In this work, the effects of vertical electric field on the electronic and optical properties of strained semi-spheroid-shaped InAs/GaAs quantum dot (QD) coupled to its wetting layer (WL) aimed to enhance the nonlinear optical properties were investigated. The dependence of energy eigenvalues of S- and P- states and intersubband P-to-S transition energy on applied electric field was studied. A ∼∓ߙ10 meV Stark shift in the intersubband P-to-S transition energy was calculated for a semi-spheroid-shaped QD with height of 5 nm and base-length of 20 nm when bias voltage was varied from 0 V to ±0.8V. The dependence of transition dipole moment and linear and nonlinear optical properties of the system on bias voltage was also studied. It was concluded that increasing the bias voltage from -0.8V to +0.8V leads to increase in figure of merit of the system from ∼0.153 to ∼0.198.
Oscillation of electron mobility in parabolic double quantum well structure due to applied electric field
Authors: Sahoo Narayan , Sahu Trinath
Published: December 2014

We show that oscillation of low temperature electron mobility μ can be obtained by applying an electric field F along the growth direction of the asymmetrically barrier delta doped AlxGa1-xAs parabolic double quantum well structure. The drastic changes in the subband Fermi energies and distributions of subband wave functions as a function of F yield nonmonotonic intra- and intersubband scattering rate matrix elements mediated by intersubband effects. The oscillatory enhancement of μ, which is attributed to the subband mobilities governed by the ionized impurity scattering, magnifies with increase in well width and decrease in height of the parabolic structure potential. The results can be utilized for nanoscale low temperature device applications.
Testing the regional genetic representativeness of captive koala populations in South-East Queensland
Authors: Seddon Jennifer M. , Lee Kristen E. , Johnston Stephen D. , Nicolson Vere N. , Pyne Michael , Carrick Frank N. , Ellis William A. H.
Published: December 2014

Context Captive breeding for release back to the wild is an important component of ex situ conservation but requires genetic diversity that is representative of the wild population and has the ultimate goal of producing ecologically sustainable and resilient populations. However, defining and testing for representativeness of captive populations is difficult. Koalas (Phascolarctos cinereus) are bred for educational and tourism purposes in zoos and wildlife parks in South-East Queensland, but there are drastic declines evident in some wild koala populations in this region. Aim We compared genetic diversity at microsatellite loci and mitochondrial DNA in two captive koala populations with that of the local, wild koalas of South-East Queensland, determining the degree to which genetic diversity of neutral loci had been preserved and was represented in the captive populations. Key results The expected heterozygosity and the allelic richness was significantly greater in one captive colony than one wild South-East Queensland population. There was low but significant differentiation of the captive from wild populations using FST, with greater differentiation described by Jost’s Dest. In contrast, a newly introduced Kullback–Leibler divergence measure, which assesses similarity of allele frequencies, showed no significant divergence of colony and wild populations. The captive koalas lacked many of the mitochondrial haplotypes identified from South-East Queensland koalas and possessed seven other haplotypes. Conclusions Captive colonies of koalas have maintained levels of overall neutral genetic diversity similar to wild populations at microsatellite loci and low but significant differentiation likely resulted from drift and founder effects in small captive colonies or declining wild populations. Mitochondrial DNA suggests that captive founders were from a wider geographic source or that haplotypes have been lost locally. Implications Overall, tested captive koalas maintain sufficient microsatellite diversity to act as an in situ reservoir for neutral genetic diversity of regional populations.
Bimodal regulation of ICR1 levels generates self-organizing auxin distribution
Authors: Hazak Ora , Obolski Uri , Prat Tomáš , Friml Jiří , Hadany Lilach , Yalovsky Shaul
Published: December 2014

Significance

In nature, patterns form by self-organizing mechanisms that involve distribution of components called morphogens. In many cases, the molecular mechanisms that underlie morphogen distribution in living organisms are not well-known. In plants, a small molecule called auxin serves as a morphogen that regulates diverse developmental processes. The ability of cells to transport or accumulate auxin defines its distribution. Here, we present experimental data and theoretical modeling showing that auxin concentrations regulate the levels of a protein called INTERACTOR of CONSTITUTIVELY active ROP (RHO of Plants) 1 (ICR1), which is required for auxin transport. ICR1 expression is induced by auxin, but when auxin levels exceed a critical concentration, ICR1 is rapidly degraded, leading to auxin accumulation. Thus, auxin self-regulates its distribution by bimodal regulation of ICR1.
Full-length structure of a monomeric histidine kinase reveals basis for sensory regulation
Authors: Rivera-Cancel Giomar , Ko Wen-huang , Tomchick Diana R. , Correa Fernando , Gardner Kevin H.
Published: December 2014

Significance

All organisms regulate biological processes in response to changes in their environment. Bacteria often achieve this control via two-component signal transduction pathways, which use histidine kinases to perceive environmental signals and relay this information to downstream effectors. Despite substantial efforts, key aspects of the mechanisms by which histidine kinases are activated by these signals remain poorly understood. In this paper, we present structural and functional data that shed light on the signaling strategy used by a monomeric histidine kinase. Our results demonstrate the versatility of histidine kinases by expanding the prevailing view that they must form dimers to function, while also highlighting conserved aspects of their signaling strategies.
Constitutively active Notch4 receptor elicits brain arteriovenous malformations through enlargement of capillary-like vessels
Authors: Murphy Patrick A. , Kim Tyson N. , Huang Lawrence , Nielsen Corinne M. , Lawton Michael T. , Adams Ralf H. , Schaffer Chris B. , Wang Rong A.
Published: December 2014

Significance

Brain arteriovenous malformations are focal lesions of enlarged, tangled vessels that shunt blood from arteries directly to veins. They can cause ischemia, hemorrhage, disability, and death, particularly in young people, accounting for 50% of childhood stroke. The molecular etiology of the disease remains poorly understood, hindering the development of therapeutic treatments. Here, we report that, in an animal model, the lesion arises from the enlargement of capillary-like vessels. Notch signaling in the endothelium of microvasculature and veins is critical for the disease initiation by increasing cell areas but not proliferation. Blood flow mediates disease progression by a positive feedback of increasing flow and vessel diameter. Our data shed light on the mechanism underlying the pathogenesis of this devastating disease.
Flagellated bacterial motility in polymer solutions
Authors: Martinez Vincent A. , Schwarz-Linek Jana , Reufer Mathias , Wilson Laurence G. , Morozov Alexander N. , Poon Wilson C. K.
Published: December 2014

Significance

The way microorganisms swim in concentrated polymer solutions has important biomedical implications, i.e., how pathogens invade the mucosal lining of mammal guts. Physicists are also fascinated by self-propulsion in such complex non-Newtonian fluids. The current standard model of how bacteria propelled by rotary helical flagella swim through concentrated polymer solutions postulates bacteria-sized pores, allowing them relative easy passage. Our experiments using high-throughput methods overturn this standard model. Instead, we show that the peculiarities of flagellated bacteria locomotion in concentrated polymer solutions are due to the fast-rotating flagellum, giving rise to a lower local viscosity in its vicinity. The bacterial flagellum is therefore a nano-rheometer for probing flows at the molecular level.