bluuebunny/crossref_metadata_2025 huggingface dataset:
Fundamental limitation of the instantaneous approximation in fold‐change detection models
Authors: Skataric Maja , Nikolaev Evgeni V. , Sontag Eduardo D.
Published: August 2014

The phenomenon of fold‐change detection, or scale‐invariance, is exhibited by a variety of sensory systems, in both bacterial and eukaryotic signalling pathways. It has been often remarked in the systems biology literature that certain systems whose output variables respond at a faster time scale than internal components give rise to an approximate scale‐invariant behaviour, allowing approximate fold‐change detection in stimuli. This study establishes a fundamental limitation of such a mechanism, showing that there is a minimal fold‐change detection error that cannot be overcome, no matter how large the separation of time scales is. To illustrate this theoretically predicted limitation, the authors discuss two common biomolecular network motifs, an incoherent feedforward loop and a feedback system, as well as a published model of the chemotaxis signalling pathway of Dictyostelium discoideum.
Conceptual design of a neutron camera for MAST Upgrade
Authors: Weiszflog M. , Sangaroon S. , Cecconello M. , Conroy S. , Ericsson G. , Klimek I. , Keeling D. , Martin R. , Turnyanskiy M.
Published: August 2014

This paper presents two different conceptual designs of neutron cameras for Mega Ampere Spherical Tokamak (MAST) Upgrade. The first one consists of two horizontal cameras, one equatorial and one vertically down-shifted by 65 cm. The second design, viewing the plasma in a poloidal section, also consists of two cameras, one radial and the other one with a diagonal view. Design parameters for the different cameras were selected on the basis of neutron transport calculations and on a set of target measurement requirements taking into account the predicted neutron emissivities in the different MAST Upgrade operating scenarios. Based on a comparison of the cameras’ profile resolving power, the horizontal cameras are suggested as the best option.
Influence of confinement on the oscillations of a free cylinder in a viscous flow
Authors: Gianorio Luciano , D’Angelo Maria Veronica , Cachile Mario , Hulin Jean-Pierre , Auradou Harold
Published: August 2014

We demonstrate and study experimentally two instabilities of a horizontal free cylinder in a vertical viscous Hele-Shaw flow; we show that they depend critically on the confinement of the flow with a different influence of transverse and lateral confinement characterized respectively by the ratios of the diameter (resp. the length) of the cylinder to the gap (resp. the width) of the cell. The onset of the instabilities depends largely on the transverse confinement: for a parameter between 0.4 and 0.6, one observes transverse horizontal oscillationsof the cylinder perpendicular to the walls: their frequency is constant with the lateral and transverse confinements at a given cylinder velocity. This instability is shown to be locally two-dimensional and controlled by the local relative velocity between the cylinder and the fluids: it occurs down to Reynolds numbers based on the cell gap ≃ 15, far below the corresponding 2D vortex shedding thresholds (150−250) for fixed cylinders between parallel planes. Above transverse confinements of the order of 0.55, we observe a fluttering motion with periodic oscillations of the tilt angle of the cylinder from the horizontal and of its horizontal position: their frequency decreases strongly as the lateral confinement increases but is independent of the transverse confinement and the cylinder velocity.
The individual and collective effects of exact exchange and dispersion interactions on the ab initio structure of liquid water
Authors: DiStasio Robert A. , Santra Biswajit , Li Zhaofeng , Wu Xifan , Car Roberto
Published: August 2014

In this work, we report the results of a series of density functional theory (DFT) based ab initio molecular dynamics (AIMD) simulations of ambient liquid water using a hierarchy of exchange-correlation (XC) functionals to investigate the individual and collective effects of exact exchange (Exx), via the PBE0 hybrid functional, non-local van der Waals/dispersion (vdW) interactions, via a fully self-consistent density-dependent dispersion correction, and an approximate treatment of nuclear quantum effects, via a 30 K increase in the simulation temperature, on the microscopic structure of liquid water. Based on these AIMD simulations, we found that the collective inclusion of Exx and vdW as resulting from a large-scale AIMD simulation of (H2O)128 significantly softens the structure of ambient liquid water and yields an oxygen-oxygen structure factor, SOO(Q), and corresponding oxygen-oxygen radial distribution function, gOO(r), that are now in quantitative agreement with the best available experimental data. This level of agreement between simulation and experiment demonstrated herein originates from an increase in the relative population of water molecules in the interstitial region between the first and second coordination shells, a collective reorganization in the liquid phase which is facilitated by a weakening of the hydrogen bond strength by the use of a hybrid XC functional, coupled with a relative stabilization of the resultant disordered liquid water configurations by the inclusion of non-local vdW/dispersion interactions. This increasingly more accurate description of the underlying hydrogen bond network in liquid water also yields higher-order correlation functions, such as the oxygen-oxygen-oxygen triplet angular distribution, POOO(θ), and therefore the degree of local tetrahedrality, as well as electrostatic properties, such as the effective molecular dipole moment, that are in much better agreement with experiment.
Femtosecond time-resolved photoemission electron microscopy for spatiotemporal imaging of photogenerated carrier dynamics in semiconductors
Authors: Fukumoto Keiki , Onda Ken , Yamada Yuki , Matsuki Takashi , Mukuta Tatsuhiko , Tanaka Sei-ichi , Koshihara Shin-ya
Published: August 2014

We constructed an instrument for time-resolved photoemission electron microscopy (TR-PEEM) utilizing femtosecond (fs) laser pulses to visualize the dynamics of photogenerated electrons in semiconductors on ultrasmall and ultrafast scales. The spatial distribution of the excited electrons and their relaxation and/or recombination processes were imaged by the proposed TR-PEEM method with a spatial resolution about 100 nm and an ultrafast temporal resolution defined by the cross-correlation of the fs laser pulses (240 fs). A direct observation of the dynamical behavior of electrons on higher resistivity samples, such as semiconductors, by TR-PEEM has still been facing difficulties because of space and/or sample charging effects originating from the high photon flux of the ultrashort pulsed laser utilized for the photoemission process. Here, a regenerative amplified fs laser with a widely tunable repetition rate has been utilized, and with careful optimization of laser parameters, such as fluence and repetition rate, and consideration for carrier lifetimes, the electron dynamics in semiconductors were visualized. For demonstrating our newly developed TR-PEEM method, the photogenerated carrier lifetimes around a nanoscale defect on a GaAs surface were observed. The obtained lifetimes were on a sub-picosecond time scale, which is much shorter than the lifetimes of carriers observed in the non-defective surrounding regions. Our findings are consistent with the fact that structural defects induce mid-gap states in the forbidden band, and that the electrons captured in these states promptly relax into the ground state.
Franck-Condon factors perturbed by damped harmonic oscillators: Solvent enhanced X 1Ag ↔ A1B1u absorption and fluorescence spectra of perylene
Authors: Wang Chen-Wen , Yang Ling , Zhu Chaoyuan , Yu Jian-Guo , Lin Sheng-Hsien
Published: August 2014

Damped harmonic oscillators are utilized to calculate Franck-Condon factors within displaced harmonic oscillator approximation. This is practically done by scaling unperturbed Hessian matrix that represents local modes of force constants for molecule in gaseous phase, and then by diagonalizing perturbed Hessian matrix it results in direct modification of Huang–Rhys factors which represent normal modes of solute molecule perturbed by solvent environment. Scaling parameters are empirically introduced for simulating absorption and fluorescence spectra of an isolated solute molecule in solution. The present method is especially useful for simulating vibronic spectra of polycyclic aromatic hydrocarbon molecules in which hydrogen atom vibrations in solution can be scaled equally, namely the same scaling factor being applied to all hydrogen atoms in polycyclic aromatic hydrocarbons. The present method is demonstrated in simulating solvent enhanced X 1Ag ↔ A1B1u absorption and fluorescence spectra of perylene (medium-sized polycyclic aromatic hydrocarbon) in benzene solution. It is found that one of six active normal modes v10 is actually responsible to the solvent enhancement of spectra observed in experiment. Simulations from all functionals (TD) B3LYP, (TD) B3LYP35, (TD) B3LYP50, and (TD) B3LYP100 draw the same conclusion. Hence, the present method is able to adequately reproduce experimental absorption and fluorescence spectra in both gas and solution phases.
The effect of defects and disorder on the electronic properties of ZnIr2O4
Authors: Ramo David Muñoz , Bristowe Paul D.
Published: August 2014

We analyze by means of ab initio calculations the role of imperfections on the electronic structure of ZnIr2O4, ranging from point defects in the spinel phase to the fully amorphous phase. We find that interstitial defects and anion vacancies in the spinel have large formation energies, in agreement with the trends observed in other spinels. In contrast, cation vacancies and antisites have lower formation energies. Among them, the zinc antisite and the zinc vacancy are the defects with the lowest formation energy. They are found to act as acceptors, and may be responsible for the spontaneous hole doping in the material. They may also induce optical transitions that would reduce the transparency of the material. Amorphization of ZnIr2O4 leads a large decrease of the band gap and appearance of localized states at the edges of the band gap region, which may act as charge traps and prevent amorphous ZnIr2O4 from being a good hole conductor.
Influence of external electric fields on oxygen vacancies at the anatase (101) surface
Authors: Selçuk Sencer , Selloni Annabella
Published: August 2014

Understanding how defects in solids interact with external electric fields is important for technological applications such as memristor devices. Using Density Functional Theory (DFT) calculations, we have studied the influence of an external electric field on the formation energies and diffusion barriers of surface and subsurface oxygen vacancies at the (101) surface of anatase TiO2. DFT in the generalized gradient approximation as well as DFT+U methods with different U values have been utilized, with the electric field treated self-consistently by adding a sawtooth-like potential to the bare ionic potential. Our results show that the direction and strength of the applied field can have a significant influence on the relative stabilities of surface and subsurface defects, whereas the effect on the subsurface-to-surface defect migration is found to be relatively minor.
A new ion sensing deep atomic force microscope
Authors: Drake Barney , Randall Connor , Bridges Daniel , Hansma Paul K.
Published: August 2014

Here we describe a new deep atomic force microscope (AFM) capable of ion sensing. A novel probe assembly incorporates a micropipette that can be used both for sensing ion currents and as the tip for AFM imaging. The key advance of this instrument over previous ion sensing AFMs is that it uses conventional micropipettes in a novel suspension system. This paper focuses on sensing the ion current passively while using force feedback for the operation of the AFM in contact mode. Two images are obtained simultaneously: (1) an AFM topography image and (2) an ion current image. As an example, two images of a MEMS device with a microchannel show peaks in the ion current as the pipette tip goes over the edges of the channel. This ion sensing AFM can also be used in other modes including tapping mode with force feedback as well as in non-contact mode by utilizing the ion current for feedback, as in scanning ion conductance microscopy. The instrument is gentle enough to be used on some biological samples such as plant leaves.
Unipolar resistive switching behavior of amorphous YCrO3 films for nonvolatile memory applications
Authors: Sharma Yogesh , Misra Pankaj , Katiyar Ram S.
Published: August 2014

Amorphous YCrO3 (YCO) films were prepared on Pt/TiO2/SiO2/Si substrate by pulsed laser deposition in order to investigate resistive switching (RS) phenomenon. The Pt/YCO/Pt device showed stable unipolar RS with resistance ratio of ∼105 between low and high resistance states, excellent endurance and retention characteristics, as well as, non-overlapping switching voltages with narrow dispersions. Based on the x-ray photoelectron spectroscopy and temperature dependent switching characteristics, observed RS was mainly ascribed to the oxygen vacancies. Moreover, current-voltage characteristics of the device in low and high resistance states were described by Ohmic and trap controlled space–charge limited conduction mechanisms, respectively.
Numerical studies of two-dimensional hydroelastic periodic and generalised solitary waves
Authors: Gao Tao , Vanden-Broeck Jean-Marc
Published: August 2014

Hydroelastic waves propagating at a constant velocity at the surface of a fluid are considered. The flow is assumed to be two-dimensional and potential. Gravity is included in the dynamic boundary condition. The fluid is bounded above by an elastic sheet which is described by the Plotnikov-Toland model. Fully nonlinear solutions are computed by a series truncation method. The findings generalised previous results where the sheet was described by a simplified model known as the Kirchhoff-Love model. Periodic and generalised solitary waves are computed. The results strongly suggest that there are no true solitary waves (i.e., solitary waves characterised by a flat free surface in the far field). Detailed comparisons with results obtained with the Kirchhoff-Love model and for the related problem of gravity capillary waves are also presented.
Electron scattering mechanisms in Cu-Mn films for interconnect applications
Authors: Misják F. , Nagy K. H. , Lobotka P. , Radnóczi G.
Published: August 2014

Electrical properties and corresponding structural features of Cu-Mn alloy films with potential application as barrier and interconnect layers were studied. Cu-Mn films were deposited by DC magnetron sputtering at room temperature on SiO2 substrates. Electrical resistivity measurements were made as a function of film composition and temperature. The specific resistivity varies linearly with the Mn content showing a maximum of 205 μΩcm at 80 at. % Mn. The temperature coefficient of resistance (TCR) of all alloy films is low, showing non-metallic conductivity for most compositions. Also a minimum TCR has been observed in the 40–80 at. % Mn range which was attributed to a magnetic transformation around 200–300 K. Electrical resistivity measurements are correlated with the film structure revealed by transmission electron microscopy to clarify the phase regions throughout the composition range. In the 20–40 at. % and 70–80 at. % Mn ranges, two-phase structures were identified, where Cu- or Mn-rich solid solution grains were surrounded by a thin amorphous covering layer. Based on the revealed phase regions and morphologies electron scattering mechanisms in the system were evaluated by combining the Matthiessen's rule and the Mayadas-Schatzkes theory. Grain boundary reflectivity coefficients (r = 0.6–0.8) were calculated from fitting the model to the measurements. The proposed model indicates that, in a binary system, the special arrangement of the two phases results in new scattering mechanisms. The results are of value in optimizing the various parameters needed to produce a suitable barrier layer.
Broadband negative permeability using hybridized metamaterials: Characterization, multiple hybridization, and terahertz response
Authors: Tung Nguyen Thanh , Tung Bui Son , Janssens Ewald , Lievens Peter , Lam Vu Dinh
Published: August 2014

There is an increased interest to create artificial magnetic metamaterials that show a negative permeability over a wide frequency range. In this paper, we experimentally and numerically demonstrate a broadband negative permeability using symmetric cut-wire-pair metamaterial structures. This finding is based on the second-order hybridization, which is activated by manipulating the correlation between the coupling within a single cut-wire pair and the coupling between neighboring cut-wire pairs. An effective medium analysis is performed to identify the role of the internal and external interactions in the hybridized metamaterials. An extended second-order hybridization scheme is proposed, which describes the electromagnetic response of more complex systems that exhibit an extremely wide band of negative permeability. In addition, the terahertz response of the cut-wire-pair dimer is further explored by scaling down the dimensions of the structures.
Flexible cadmium telluride thin films grown on electron-beam-irradiated graphene/thin glass substrates
Authors: Seo Won-Oh , Koo Yong Hwan , Kim Byungnam , Lee Byung Cheol , Kim Donghwan , Kim Jihyun
Published: August 2014

We demonstrate the close-spaced sublimation growth of polycrystalline cadmium telluride (CdTe) thin films on a flexible graphene electrode/thin glass substrate structure. Prior to the growth of CdTe films, chemical-vapor-deposited graphene was transferred onto a flexible glass substrate and subjected to electron-beam irradiation at an energy of 0.2 MeV in order to intentionally introduce the defects into it in a controlled manner. Micro-Raman spectroscopy and sheet resistance measurements were employed to monitor the damage and disorder in the electron-beam irradiated graphene layers. The morphology and optical properties of the CdTe thin films deposited on a graphene/flexible glass substrate were systematically characterized. The integration of the defective graphene layers with a flexible glass substrate can be a useful platform to grow various thin-film structures for flexible electronic and optoelectronic devices.
Metal-organic molecular device for non-volatile memory storage
Authors: Radha B. , Sagade Abhay A. , Kulkarni G. U.
Published: August 2014

Non-volatile memory devices have been of immense research interest for their use in active memory storage in powered off-state of electronic chips. In literature, various molecules and metal compounds have been investigated in this regard. Molecular memory devices are particularly attractive as they offer the ease of storing multiple memory states in a unique way and also represent ubiquitous choice for miniaturized devices. However, molecules are fragile and thus the device breakdown at nominal voltages during repeated cycles hinders their practical applicability. Here, in this report, a synergetic combination of an organic molecule and an inorganic metal, i.e., a metal-organic complex, namely, palladium hexadecylthiolate is investigated for memory device characteristics. Palladium hexadecylthiolate following partial thermolysis is converted to a molecular nanocomposite of Pd(II), Pd(0), and long chain hydrocarbons, which is shown to exhibit non-volatile memory characteristics with exceptional stability and retention. The devices are all solution-processed and the memory action stems from filament formation across the pre-formed cracks in the nanocomposite film.
Effects of a modular two-step ozone-water and annealing process on silicon carbide graphene
Authors: Webb Matthew J. , Polley Craig , Dirscherl Kai , Burwell Gregory , Palmgren Pål , Niu Yuran , Lundstedt Anna , Zakharov Alexei A. , Guy Owen J. , Balasubramanian Thiagarajan , Yakimova Rositsa , Grennberg Helena
Published: August 2014

By combining ozone and water, the effect of exposing epitaxial graphene on silicon carbide to an aggressive wet-chemical process has been evaluated after high temperature annealing in ultra high vacuum. The decomposition of ozone in water produces a number of oxidizing species, however, despite long exposure times to the aqueous-ozone environment, no graphene oxide was observed after the two-step process. The systems were comprehensively characterized before and after processing using Raman spectroscopy, core level photoemission spectroscopy, and angle resolved photoemission spectroscopy together with low energy electron diffraction, low energy electron microscopy, and atomic force microscopy. In spite of the chemical potential of the aqueous-ozone reaction environment, the graphene domains were largely unaffected raising the prospect of employing such simple chemical and annealing protocols to clean or prepare epitaxial graphene surfaces.
Intrinsic thermal conductivity and its anisotropy of wurtzite InN
Authors: Ma Jinlong , Li Wu , Luo Xiaobing
Published: August 2014

Despite wurtzite InN being a widely used semiconductor, its intrinsic thermal conductivity (κ) is still little known. In this work, the κ of wurtzite InN is studied from first principles. The calculated room temperature κ is 130 Wm−1K−1 and 145 Wm−1K−1 for the in-plane and out-of-plane direction, respectively, showing an anisotropy of about 11%. The anisotropy increases with decreasing temperature, and it reaches 20% at 100 K. The evident anisotropy is contrast to the conventionally used isotropic assumption, and is explained by performing comprehensive velocity analysis. We also calculate the cumulative κ as a function of mean free path, which can help understand the size dependence of κ in the non-bulk forms. The obtained cumulative κ is in good agreement with the experimental κ of InN films with thicknesses between 0.5 and 2.1 μm, and shows the size effect can persist up to 10 μm thickness at room temperature.
Solution-processed high-performance colloidal quantum dot tandem photodetectors on flexible substrates
Authors: Jiang Zhenyu , You Guanjun , Wang Li , Liu Jie , Hu Wenjia , Zhang Yu , Xu Jian
Published: August 2014

We report a high-performance colloidal quantum dot (CQD)-based near-infrared tandem photodetector fabricated on flexible substrates via solution-processed method. The tandem photodetector on poly(ethylene terephthalate) substrates exhibited low dark current and high detectivities over ∼8.8 × 1011 Jones at near infrared range at −0.5 V bias and over ∼1013 Jones near 0 bias. The critical bend radii of ∼8 mm and ∼3 mm have been demonstrated for tensile and compressive bending, respectively. The performance of photodetectors remains stable under mechanical stress, making PbSe CQD material a promise candidate for flexible infrared sensing applications.
Synchrotron radiation x-ray topography and defect selective etching analysis of threading dislocations in GaN
Authors: Sintonen Sakari , Rudziński Mariusz , Suihkonen Sami , Jussila Henri , Knetzger Michael , Meissner Elke , Danilewsky Andreas , Tuomi Turkka O. , Lipsanen Harri
Published: August 2014

The crystal quality of bulk GaN crystals is continuously improving due to advances in GaN growth techniques. Defect characterization of the GaN substrates by conventional methods is impeded by the very low dislocation density and a large scale defect analysis method is needed. White beam synchrotron radiation x-ray topography (SR-XRT) is a rapid and non-destructive technique for dislocation analysis on a large scale. In this study, the defect structure of an ammonothermal c-plane GaN substrate was recorded using SR-XRT and the image contrast caused by the dislocation induced microstrain was simulated. The simulations and experimental observations agree excellently and the SR-XRT image contrasts of mixed and screw dislocations were determined. Apart from a few exceptions, defect selective etching measurements were shown to correspond one to one with the SR-XRT results.
Thermopower as a tool to investigate many-body effects in quantum systems
Authors: Kristinsdóttir L. H. , Bengtsson J. , Linke H. , Reimann S. M. , Wacker A.
Published: August 2014

Measuring the thermopower of a confined quantum system reveals important information about its excitation spectrum. Our simulations show how this kind of transport spectroscopy is able to extract a clear signal for the onset of Wigner localization in a nanowire segment. This demonstrates that thermopower measurements provide a tool for investigating complex many-body quantum effects, which is less intrusive than the usual charge-stability diagram as no high source-drain bias is required. While the effect is most pronounced for weak tunnel coupling and low temperatures, the excited states also significantly affect the thermopower spectrum at moderate temperature, adding distinct features to the characteristic thermopower lineshape.
Investigation of the electrical switching and rectification characteristics of a single standalone n-type ZnO-nanowire/p-Si junction diode
Authors: Das Avishek , Palit Mainak , Paul Somdatta , Chowdhury Basudev Nag , Dutta Himadri Sekhar , Karmakar Anupam , Chattopadhyay Sanatan
Published: August 2014

In this work, n-ZnO-nanowire/p-Si junction diodes have been fabricated and characterized both physically as well as electrically. The measurements are performed on a single standalone nanowire diode for the investigation of electrical transport through the nano-junction. The rectification properties of the single n-ZnO nanowire/p-Si diode have been studied for various input waveforms and frequencies. The diodes exhibit very promising rectification as well as switching behavior with no charge storage effect and consequently, a switching time as small as ∼1 ms has been achieved.
Degradation of the remanent ferromagnetic state under the action of ferroelectric relaxation processes in Co/(1−x)PMN-xPT/Co hybrids: Possible implications on cryogenic and room-temperature applications
Authors: Stamopoulos D. , Zeibekis M. , Vertsioti G. , Zhang S. J.
Published: August 2014

Low-dimensional hybrid structures of heterogeneous constituents usually exhibit abnormal properties, a fact that makes such hybrids attractive for various cryogenic and room-temperature applications. Here, we studied Co/(1 − x)Pb(Mg1/3Nb2/3)O3-xPbTiO3/Co (Co/PMN-xPT/Co) with x = 0.29 and 0.30, specifically focusing on the evolution of the remanent ferromagnetic state, mrem of the Co outer layers in the whole temperature range from 300 K down to 10 K, upon application of an external electric field, Eex. We observed that mrem was vulnerable to degradation through the occurrence of electric field-induced magnetic instabilities (EMIs) that appeared only when Eex ≠ 0 kV/cm and were facilitated as Eex increases. However, EMIs completely ceased below a characteristic temperature Tces = 170 K even for the maximum |Eex| = 5 kV/cm applied in this work. A direct comparison of the magnetization data of the Co/PMN-xPT/Co hybrids reported here with the electromechanical properties of the parent PMN-xPT crystals plausibly indicates that EMIs are motivated by the coupling of the ferromagnetic domains of the Co outer layers with the ferroelectric domains of the PMN-xPT crystal. These results highlight the drawback of EMIs in relevant hybrids and delimit the temperature regime for the reliable operation of the Co/PMN-xPT/Co ones studied here.
Controlling quantum dot energies using submonolayer bandstructure engineering
Authors: Yu L. , Jung D. , Law S. , Shen J. , Cha J. J. , Lee M. L. , Wasserman D.
Published: August 2014

We demonstrate control of energy states in epitaxially-grown quantum dot structures formed by stacked submonolayer InAs depositions via engineering of the internal bandstructure of the dots. Transmission electron microscopy of the stacked sub-monolayer regions shows compositional inhomogeneity, indicative of the presence of quantum dots. The quantum dot ground state is manipulated not only by the number of deposited InAs layers, but also by control of the thickness and material composition of the spacing layers between submonolayer InAs depositions. In this manner, we demonstrate the ability to shift the quantum dot ground state energy at 77 K from 1.38 eV to 1.88 eV. The results presented offer a potential avenue towards enhanced control of dot energies for a variety of optoelectronic applications.
Intrinsic Rashba-like splitting in asymmetric Bi2Te3/Sb2Te3 heterogeneous topological insulator films
Authors: Liu Xiaofei , Guo Wanlin
Published: August 2014

We show by density functional theory calculations that asymmetric hetero-stacking of Bi2Te3/Sb2Te3 films can modulate the topological surface states. Due to the structure inversion asymmetry, an intrinsic Rashba-like splitting of the conical surface bands is aroused. While such splitting in homogeneous Bi2Te3-class topological insulators can be realized in films with more than three quintuple layers under external electric fields, the hetero-stacking breaks the limit of thickness for preserving the topological nature into the thinnest two quintuple layers. These results indicate that the hetero-stacking can serve as an efficient strategy for spin-resolved band engineering of topological insulators.
A modified cryostat for photo-electrical characterization of porous materials in controlled atmosphere at very low gas dosage
Authors: Cultrera Alessandro , Amato Giampiero , Boarino Luca , Lamberti Carlo
Published: August 2014

We developed an integrated system for photo-electrical characterization of materials for sensing applications in strictly controlled environment conditions. The peculiar aspect of this setup is the capability of a fine-tuned gas dosage and a fast dynamic chamber pressure control, coupled with current and voltage sensing within a modified cryostat. To illustrate the capabilities of our system we have characterised both p+-type mesoporous silicon (meso-PS) membranes and nano-crystalline mesoporous titanium dioxide (nc-TiO2) films. In particular, as a main topic is presented a well-resolved characterization of mesoporous silicon electrical conductivity changes induced by presence of ethanol. At low pore filling level adsorbate-shunted conduction is avoided, while dielectric screening effects on frozen doping centres are observable. Beside we presented observation of mesoporous titanium dioxide photo-conductivity as a function of different gas pressure reporting opposite effects of relatively low- and high-pressure regimes. High reproducibility provided by the system is discussed as a final remark.
Large area graphene ion sensitive field effect transistors with tantalum pentoxide sensing layers for pH measurement at the Nernstian limit
Authors: Fakih Ibrahim , Sabri Shadi , Mahvash Farzaneh , Nannini Matthieu , Siaj Mohamed , Szkopek Thomas
Published: August 2014

We have fabricated and characterized large area graphene ion sensitive field effect transistors (ISFETs) with tantalum pentoxide sensing layers and demonstrated pH sensitivities approaching the Nernstian limit. Low temperature atomic layer deposition was used to deposit tantalum pentoxide atop large area graphene ISFETs. The charge neutrality point of graphene, inferred from quantum capacitance or channel conductance, was used to monitor surface potential in the presence of an electrolyte with varying pH. Bare graphene ISFETs exhibit negligible response, while graphene ISFETs with tantalum pentoxide sensing layers show increased sensitivity reaching up to 55 mV/pH over pH 3 through pH 8. Applying the Bergveld model, which accounts for site binding and a Guoy-Chapman-Stern picture of the surface-electrolyte interface, the increased pH sensitivity can be attributed to an increased buffer capacity reaching up to 1014 sites/cm2. ISFET response was found to be stable to better than 0.05 pH units over the course of two weeks.
2.6 μm MBE grown InGaAs detectors with dark current of SRH and TAT
Authors: Ji Xiaoli , Liu Baiqing , Tang Hengjing , Yang Xuelin , Li Xue , Gong HaiMei , Shen Bo , Han Ping , Yan Feng
Published: August 2014

We fabricate 2.6 μm InGaAs photodetectors by MBE technology and study its dark current mechanisms. Deep-level transient spectroscopy (DLTS) demonstrates a deep-level trap located at Ec - 0.25 eV in the absorption layer. Using the trap parameters, a dark current model is constructed and the device simulation generates the dark current characteristic which agrees well with the experimental data. The model suggests that the dark current at low reverse voltage is dominated by the Shockley-Read-Hall (SRH) and trap-assisted tunneling (TAT). Furthermore, it predicts some basic rules for suppressing the dark current in 2.6 μm InGaAs detectors.
Conductance switching in single light-sensitive molecular device with carbon nanotube electrodes
Authors: Xia Cai-Juan , Gao Kun , Zhang De-Hua , Yang Mao , Feng Fei-Long
Published: August 2014

By applying nonequilibrium Green's function formalism combined first-principles density functional theory, a new mechanism for optical switch of single molecular device with carbon nanotube electrodes is proposed. The molecule comprises the switch can convert between enol and keto isomers upon photoinduced excited state hydrogen transfer in the molecular bridge. Theoretical results show that these two isomers exhibit very different current-voltage characteristics both in armchair and zigzag junction, which can realize the on and off states of the molecular switch. Meantime, the chirality of the single-walled carbon nanotube (SWCNT) electrodes strongly affects the switching characteristics of the molecular junctions. The maximum value of on-off ratio can reach 72 at 1.6 V for the switch with zigzag SWCNT electrodes, suggesting potential applications of this junction in future design of light-driven molecular switches.
High-yielding lines of wheat carrying Gpc-B1 adapted to Mediterranean-type environments of the south and west of Australia
Authors: Eagles H. A. , McLean Robyn , Eastwood R. F. , Appelbee M.-J. , Cane Karen , Martin P. J. , Wallwork H.
Published: August 2014

The Gpc-B1 gene from wild emmer has been proposed as a potential mechanism for improving grain protein in bread wheat without reducing grain yield. Near-isolines with and without the Gpc-B1 gene in three Australian-adapted genetic backgrounds, Gladius, Wyalkatchem and VR1128, were compared in 14 experiments across the south and west of Australia for grain yield, grain protein content and grain weight. The donor parents of Gpc-B1 were the Canadian cultivars Burnside and Somerset. One of the 14 experiments was discarded because of inadequate rust control and confounding effects of Yr36, a gene closely linked to Gpc-B1. Heading date and test weight were measured in five experiments. Across all comparisons, Gpc-B1 increased grain protein content and reduced grain weight, with a negligible effect on grain yield. Selected lines containing Gpc-B1 in a Wyalkatchem background had comparable grain yields to the elite cultivar Mace, but with significantly higher grain protein contents, slightly higher grain weights, similar heading dates and acceptable test weights. The development of agronomically acceptable lines containing Gpc-B1 was partially attributed to the removal of undesirable genes from wild emmer during the breeding of the Canadian donor parents and the use of Australian recurrent parents with high test weights.
Oral health care in residential aged care services: barriers to engaging health-care providers
Authors: Hearn Lydia , Slack-Smith Linda
Published: August 2014

The oral health of older people living in residential aged care facilities has been widely recognised as inadequate. The aim of this paper is to identify barriers to effective engagement of health-care providers in oral care in residential aged care facilities. A literature review was conducted using MEDline, CINAHL, Web of Science, Academic Search Complete and PsychInfo between 2000 and 2013, with a grey literature search of government and non-government organisation policy papers, conference proceedings and theses. Keywords included: dental/oral care, residential aged care, health-care providers, barriers, constraints, and limitations. A thematic framework was used to synthesise the literature according to a series of oral health-care provision barriers, health-care provider barriers, and cross-sector collaborative barriers. A range of system, service and practitioner level barriers were identified that could impede effective communication/collaboration between different health-care providers, residents and carers regarding oral care, and these were further impeded by internal barriers at each level. Findings indicated several areas for investigation and consideration regarding policy and practice improvements. While further research is required, some key areas should be addressed if oral health care in residential aged care services is to be improved.
Aboriginal health promotion through addressing employment discrimination
Authors: Ferdinand Angeline S. , Paradies Yin , Perry Ryan , Kelaher Margaret
Published: August 2014

The Localities Embracing and Accepting Diversity (LEAD) program aimed to improve the mental health of Aboriginal Victorians by addressing racial discrimination and facilitating social and economic participation. As part of LEAD, Whittlesea Council adopted the Aboriginal Employment Pathways Strategy (AEPS) to increase Aboriginal employment and retention within the organisation. The Aboriginal Cultural Awareness Training Program was developed to build internal cultural competency and skills in recruiting and retaining Aboriginal staff. Analysis of surveys conducted before (pre; n = 124) and after (post; n = 107) the training program indicated a significant increase in participant understanding across all program objectives and in support of organisational policies to improve Aboriginal recruitment and retention. Participants ended the training with concrete ideas about intended changes, as well as how these changes could be supported by their supervisors and the wider organisation. Significant resources have since been allocated to implementing the AEPS over 5 years. In line with principles underpinning the National Aboriginal and Torres Strait Islander Health Plan 2013–23, particularly the focus on addressing racism as a determinant of health, this paper explores the AEPS and training program as promising approaches to health promotion through addressing barriers to Aboriginal employment. Possible implications for other large organisations are also considered.
Signalling pathways involved in the synergistic effects of human growth differentiation factor 9 and bone morphogenetic protein 15
Authors: Reader Karen L. , Mottershead David G. , Martin Georgia A. , Gilchrist Robert B. , Heath Derek A. , McNatty Kenneth P. , Juengel Jennifer L.
Published: August 2014

Growth differentiation factor 9 (GDF9) and bone morphogenetic protein 15 (BMP15) act synergistically to regulate granulosa cell proliferation and steroid production in several species. Several non-Sma and mothers against decapentaplegic (SMAD) signalling pathways are involved in the action of murine and ovine GDF9 and BMP15 in combination, with the pathways utilised differing between the two species. The aims of this research were to determine if human GDF9 and BMP15 also act in a synergistic manner to stimulate granulosa cell proliferation and to identify which non-SMAD signalling pathways are activated. Human GDF9 with BMP15 (GDF9 + BMP15) stimulated an increase in 3H-thymidine incorporation (P < 0.001), which was greater than the increase with BMP15 alone, while GDF9 alone had no effect. The stimulation of 3H-thymidine incorporation by GDF9 + BMP15 was reduced by the addition of inhibitors to the SMAD2/3, nuclear factor-KB (NF-KB) and c-Jun N-terminal kinase (JNK) signalling pathways. Inhibitors to the SMAD1/5/8, extracellular signal-regulated kinase mitogen-activated protein kinase (ERK-MAPK) or p38-MAPK pathways had no effect. The addition of the BMP receptor 2 (BMPR2) extracellular domain also inhibited stimulation of 3H-thymidine incorporation by GDF9 + BMP15. In conclusion, human GDF9 and BMP15 act synergistically to stimulate granulosa cell proliferation, a response that also involves species-specific non-SMAD signalling pathways.
Metabolic costs and evolutionary implications of human brain development
Authors: Kuzawa Christopher W. , Chugani Harry T. , Grossman Lawrence I. , Lipovich Leonard , Muzik Otto , Hof Patrick R. , Wildman Derek E. , Sherwood Chet C. , Leonard William R. , Lange Nicholas
Published: August 2014

Significance

The metabolic costs of brain development are thought to explain the evolution of humans’ exceptionally slow and protracted childhood growth; however, the costs of the human brain during development are unknown. We used existing PET and MRI data to calculate brain glucose use from birth to adulthood. We find that the brain’s metabolic requirements peak in childhood, when it uses glucose at a rate equivalent to 66% of the body’s resting metabolism and 43% of the body’s daily energy requirement, and that brain glucose demand relates inversely to body growth from infancy to puberty. Our findings support the hypothesis that the unusually high costs of human brain development require a compensatory slowing of childhood body growth.
Linking knowledge and action through mental models of sustainable agriculture
Authors: Hoffman Matthew , Lubell Mark , Hillis Vicken
Published: August 2014

Significance

Sustainability is notoriously difficult to define and put into practice in the context of agricultural and other social-ecological systems. A crucial task within this debate is to analyze how practitioners understand the idea of sustainability. Using California winegrape growers as an example, this paper uses network science to describe the structure of farmer mental models of sustainable agriculture and link those models to behavioral aspects of sustainable agriculture. California growers have hierarchically organized mental models with more abstract goals in the center and more concrete strategies in the periphery. The concept of sustainability is a viable approach for linking knowledge to action; there are strong positive correlations between the sophistication of an individual’s beliefs about sustainability, participation in local outreach programs, and adoption of sustainable practices.
Nonlytic viral spread enhanced by autophagy components
Authors: Bird Sara Whitney , Maynard Nathaniel D. , Covert Markus W. , Kirkegaard Karla
Published: August 2014

Significance

The cell-to-cell spread of viruses that are not surrounded by membranes was thought to occur only by destruction of the infected cell, as no obvious path for a cytoplasmic particle to penetrate the plasma membrane exists. Nonetheless, it is known that spread within tissues in human infections is not always accompanied by obvious cell death. Here we use quantitative single-cell analysis to show that poliovirus can spread to a neighboring cell prior to bursting and killing the originally infected cell. This type of spread is dependent on components of the autophagy pathway, a recycling pathway that is found in all eukaryotes. This finding identifies targets to block the spread of viruses and other toxic cytoplasmic assemblages.
Ionic liquids as a class of materials for transdermal delivery and pathogen neutralization
Authors: Zakrewsky Michael , Lovejoy Katherine S. , Kern Theresa L. , Miller Tarryn E. , Le Vivian , Nagy Amber , Goumas Andrew M. , Iyer Rashi S. , Del Sesto Rico E. , Koppisch Andrew T. , Fox David T. , Mitragotri Samir
Published: August 2014

Significance

Effective treatment of skin-based bacterial biofilms has been identified as a serious and unmet medical need. Biofilm-protected bacteria account for ∼80% of bacterial infections in humans and are 50–1,000 times more resistant to antibiotics than their planktonic counterparts. Biofilms in skin are further protected by the outermost layer of skin, the stratum corneum, which serves as a natural barrier to most therapeutics. Here, we present compelling evidence for exploiting ionic liquids (ILs) as an arsenal of materials both in a concerted effort to combat antibiotic-resistant bacterial biofilms in skin as well as for topical transdermal drug delivery. Our comprehensive strategy resulted in the identification of ILs that are effective at disrupting biofilms, neutralizing pathogens, and enhancing delivery of antibiotic into skin. Moreover, ILs did not show skin irritation that is typically associated with topical formulations.
Age of Barrier Canyon-style rock art constrained by cross-cutting relations and luminescence dating techniques
Authors: Pederson Joel L. , Chapot Melissa S. , Simms Steven R. , Sohbati Reza , Rittenour Tammy M. , Murray Andrew S. , Cox Gary
Published: August 2014

Significance

Key physical relations between the famous Great Gallery rock art panel in Utah, stream deposits, and a rockfall that removed some art, allow us to disprove all but a late Archaic hypothesis for the age of this type section of the Barrier Canyon style. Use of a new luminescence profile technique on the same rockfall furthermore outlines a window of time A.D. ∼1 to 1100 when the figures could have been painted, generally more recent than expected. Our study illustrates novel and widely applicable approaches for dating rock art that do not require destructive sampling, and results suggest that Barrier Canyon rock art persisted across the transition from the late Archaic into the agrarian Fremont culture in the American Southwest.
Unfolded protein response activation reduces secretion and extracellular aggregation of amyloidogenic immunoglobulin light chain
Authors: Cooley Christina B. , Ryno Lisa M. , Plate Lars , Morgan Gareth J. , Hulleman John D. , Kelly Jeffery W. , Wiseman R. Luke
Published: August 2014

Significance

Light-chain amyloidosis (AL) is a devastating human disease involving the clonal expansion of a plasma cell and the secretion of destabilized, amyloidogenic immunoglobulin light chains (LCs). Secreted amyloidogenic LCs aggregate extracellularly, leading to proteotoxicity on distal tissues. Available therapeutic strategies to treat AL specifically target the cancerous plasma cell population. While this approach is effective in ∼70% of patients, patients who present with substantial LC-related organ proteotoxicity are generally too sick to tolerate standard chemotherapeutics. Here, we show that stress-independent activation of unfolded protein response-associated transcription factors selectively reduces secretion of amyloidogenic LCs and decreases extracellular soluble LC aggregates associated with proteotoxicity in AL. These results identify a promising therapeutic strategy to treat AL patients unserved by current treatments.
MC4R-expressing glutamatergic neurons in the paraventricular hypothalamus regulate feeding and are synaptically connected to the parabrachial nucleus
Authors: Shah Bhavik P. , Vong Linh , Olson David P. , Koda Shuichi , Krashes Michael J. , Ye Chianping , Yang Zongfang , Fuller Patrick M. , Elmquist Joel K. , Lowell Bradford B.
Published: August 2014

Significance

Both in rodents and humans, melanocortin-4 receptors (MC4Rs) suppress appetite and prevent obesity. Unfortunately, the underlying neural mechanisms by which MC4Rs regulate food intake are poorly understood. Unraveling these mechanisms may open up avenues for treating obesity. In the present study we have established that MC4Rs on neurons in the paraventricular nucleus of the hypothalamus are both necessary and sufficient for MC4R control of feeding and that these neurons are glutamatergic and not GABAergic and do not express the neuropeptides oxytocin, corticotropin-releasing hormone, prodynorphin, or vasopressin. In addition, we identify downstream projections from these glutamatergic neurons to the lateral parabrachial nucleus, which could mediate the appetite suppressing effects.