bluuebunny/crossref_metadata_2025 huggingface dataset:
All solution-processed large-area patterned flexible photodetectors based on ZnOEP/PVK hybrid film
Authors: Wang Feng-Xia , Yang Jia-Mei , Nie Shu-Hong , Su Wen-Ming , Pan Ge-Bo
Published: July 2016

All solution large-area flexible photodetectors have been fabricated based on a hybrid film, showing excellent mechanical stability.
Comparative oxidative stress elicited by nanosilver in stable HSPA1A promoter-driven luciferase reporter HepG2 and A549 cells
Authors: Xin Lili , Wang Jianshu , Fan Guoqiang , Che Bizhong , Cheng Kaiming , Dong Guangzhu
Published: July 2016

HSPA1A promoter-driven luciferase reporter gene assay provides a novel tool for predictive screening of the oxidative stress elicited by nanosilver.
pHluorin enables insights into the transport mechanism of antiporter Mdr1: R215 is critical for drug/H+ antiport
Authors: Redhu Archana Kumari , Khandelwal Nitesh Kumar , Banerjee Atanu , Moreno Alexis , Falson Pierre , Prasad Rajendra
Published: July 2016

Multidrug resistance 1 (MDR1) is a member of the major facilitator superfamily that contributes to MDR of Candida albicans. This antiporter belongs to the drug/H+ antiporter 1 family, pairing the downhill gradient of protons to drug extrusion. Hence, drug efflux from cytosol to extracellular space and the parallel import of H+ towards cytosol are inextricably linked processes. For monitoring the drug/H+ antiporter activity of Mdr1p, we developed a new system, exploiting a GFP variant pHluorin, which changes its fluorescence properties with pH. This enabled us to measure the cytosolic pH correlated to drug efflux. Since protonation of charged residues is a key step in proton movement, we explored the role of all charged residues of the 12 transmembrane segments (TMSs) of Mdr1p in drug/H+ transport by mutational analysis. This revealed that the conserved residue R215, positioned close to the C-terminal end of TMS-4, is critical for drug/H+ antiport, allowing protonation over a range of pH, in contrast with its H215 or K215 variants that failed to transport drugs at basic pH. Mutation of other residues of TMS-4 highlights the role of this TMS in drug transport, as confirmed by in silico modelling of Mdr1p and docking of drugs. The model points to the importance of R215 in proton transport, suggesting that it may adopt two main conformations, one oriented towards the extracellular face and the other towards the centre of Mdr1p. Together, our results not only establish a new system for monitoring drug/H+ transport, but also unveil a positively charged residue critical to Mdr1p function.
Proposal of compensation for intra‐ and inter‐channel nonlinear distortions using optical compensation and nonlinear equalisation
Authors: Kawahara H. , Yamamoto S. , Fukutoku M.
Published: July 2016

A novel transmission system that adaptively compensates for intra‐ and inter‐channel nonlinear distortions while alleviating the computation load is described. It does so by using an optical dispersion compensation at optical nodes and a Volterra‐based multi‐channel nonlinear equalisation. Simulation results show that 3.8 dB Q‐factor improvements are obtained against conventional systems that do not compensate for nonlinear distortions.
Sparse SM‐NLMS algorithm based on correntropy criterion
Authors: Li Yingsong , Wang Yanyan
Published: July 2016

A sparse set‐membership normalised least mean square (SM‐NLMS) algorithm with a correntropy penalty is proposed and its performance is investigated for estimating a sparse echo channel. The proposed sparse SM‐NLMS algorithm is derived by minimising an unconstraint cost function that utilises the correntropy on the weight vector as well as the sum of a symmetric and positive definite matrix constrained Euclidean norm of the differences between the instantaneous error and the upper bound of the SM filtering. Simulation results over a sparse echo channel show that the proposed algorithm is superior to the existing algorithms with respect to the steady‐state misalignment.
High performance silicon carbide avalanche‐p‐i‐n ultraviolet photodiode with dual operation models
Authors: Zhang Mingkun , Wang Kang L. , Jiang Hexin , Hong Rongdun , Wu Zhengyun
Published: July 2016

Silicon carbide‐based quasi‐separated‐absorption‐multiplication ultraviolet avalanche photodiode (APD) with a small‐area multiplication region and a large‐area absorption region, which comprises of a p+nn− junction encircled by a p+n− junction, is proposed, and its optoelectronic performance is modelled. The modelling results show a 4H‐SiC APD with high performance can be achieved. Moreover, when operated at a low reverse bias (e.g. 5.0 V), the photodiode has almost the same optoelectronic characteristics as the 4H‐SiC p‐i‐n photodiode. It is noted that the device has benefited advantages of both conventional separate absorption and multiplication APD and p‐i‐n photodiode in the wavelength range of ultraviolet detection, which enable the dual operation models of the device.
Robust consensus for linear multi‐agent systems with noises
Authors: Wang Zhongmei , Wang Wei , Zhang Huanshui
Published: July 2016

This study investigates robust consensus problem for multi‐agent systems (MASs) with both system and communication noises. The agent state is estimated based on the noisy measurement information by applying Kalman‐filtering theory, and then the estimated state is sent to the neighbour agents through a noisy communication environment. A consensus protocol is proposed based on the relative estimated state, under which the consensus error of the MASs can be characterised precisely via the unique solution of a Lyapunov equation. In addition, the consensusability via dynamic output feedback control of the MASs without noises is studied. Finally, simulation examples are given to show the correctness of the proposed results.
Conservatism reduction in simultaneous output feedback stabilisation of linear systems
Authors: Kohan‐Sedgh Peyman , Khayatian Alireza , Asemani Mohammad H.
Published: July 2016

This study concerns with simultaneous output feedback stabiliser for continuous‐time linear systems. Two convex methods based on structured slack variable and dilated matrix inequalities are proposed. Both methods are based on non‐common Lyapunov approach and designs are independent of controller order. Sufficiency of the first method decreases with increasing the number of system inputs. The second method, namely the dilated method, contains free scalar parameters. These parameters can be used to shape the controller for some performance objectives. In particular, it is proved that the dilated method can give less or at least the same conservative results than existing methods with equality constraints. It is also shown that the feasibility region of these two methods does not coincide and thus combining them can increase the chance of finding simultaneous stabiliser. Extensive numerical studies and benchmark examples are used to reveal the conservatism reduction merit.
Denoising model for parallel magnetic resonance imaging images using higher‐order Markov random fields
Authors: Xu Zhihuo , Shi Quan
Published: July 2016

This study presents a novel robust method for Bayesian denoising of parallel magnetic resonance imaging (pMRI) images. For the first time, the authors’ proposal applies fields of experts (FoE), a filter‐based higher‐order Markov random field (MRF), to model the prior of the pMRI image statistics. The noise in pMRI data behaves to be non‐central Chi (nc‐χ) distributed. In practice, correlation between coils exists, resulting in that nc‐χ distribution does not hold anymore and the spatially varying noise problem. Thus, preservation of fine textures requires to adapt locally the estimation. Therefore, more precisely, the noise is reduced by using a sliding window scheme. In each window, the likelihood probability function is accurately modelled from corrupted data by using an innovative Gaussian mixture model (GMM). The parameters of GMM are calculated by applying an iterative expectation maximisation approach. With the priors via the learned FoE model and the likelihood function via GMM, a maximum a posteriori (MAP) estimator is formulated. Then, the noise in the each window is filtered by applying an efficient non‐linear quasi‐Newton method to explore an optimal solution for the MAP estimator. Finally, experiments have been conducted on both the simulated and real data to compare the proposed model with some state‐of‐the‐art denoising methods. The experimental results demonstrate the robustness and effectiveness of the proposed denoising model.
Closed‐form estimators for the Pareto clutter plus noise parameters based on non‐integer positive and negative order moments
Authors: Sahed Mohamed , Mezache Amar , Soltani Faouzi
Published: July 2016

In this study, closed‐form expressions of the parameters estimators for Pareto distributed clutter plus noise are derived. To achieve this, the authors combine two statistical ratios based principally on non‐integer positive and negative order moments. This allows absolute elimination of all related special functions contained in some existing estimators. For realistic applications, the proposed non‐integer positive and negative order moments based estimators are suited to single‐look and multi‐look data. Simulation results show that the new estimators not only substantially reduce the computational requirements, but also yield accurate and lower variances parameters compared with the methods of moments and z log z obtained in previous works especially in the situations of heavy‐tailed clutter.
Experimental investigation of the external lightning protection of ships through impulse voltage tests on a scaled‐down ship model
Authors: Nicolopoulou Eleni P. , Gonos Ioannis F. , Stathopulos Ioannis A.
Published: July 2016

The impacts of a lightning strike are amplified in an environment with special features such as a ship electric grid, especially within the extended integration of electronic systems. In most marine regulations, lightning protection specifications are inadequate in the cases of metallic vessels, regarding the necessity of installing lightning rods and the method for the definition of their protection zone and subsequently of their height. Therefore, impulse voltage experiments on a scaled‐down ship model were conducted in order to acquire interception probability distributions of its superstructures and to assess the accuracy of various protection zone models, established for isolated rods, on the given complex topology of a ship. The experimental results highlighted the overestimation of the protection zone even by the well‐established rolling sphere model for negative polarity impulses depending on the geometrical conditions and the satisfying performance of statistical models that incorporate proximity effects and lightning interception probability.
Die komplizierte Gicht
Authors: Illgner U. , Maier A. , Bause L. , Seintsch H.
Published: July 2016

Ein 57-jähriger Patient wurde aus der internistischen Abteilung einer auswärtigen Klinik übernommen, mit zahlreichen Gichttophi und einer Überwärmung des rechten Knies und des rechten Ellenbogens. Seit 20 Tagen bestand eine probatorische parenterale Antibiotikatherapie. Durch eine sofortige Punktion des rechten Kniegelenks konnte die Diagnose einer bakteriellen Arthritis gestellt werden. Es erfolgte umgehend eine Operation mit Spülung und ausführlichem Debridement unter der Weiterführung der Antibiotikatherapie. Bei Patienten mit Gicht und Verdacht auf eine zusätzliche Infektion muss immer eine vollständige und konsequente Fokussuche und ggf. eine operative Focussanierung durchgeführt werden.
Lineshape theory of pigment-protein complexes: How the finite relaxation time of nuclei influences the exciton relaxation-induced lifetime broadening
Authors: Dinh Thanh-Chung , Renger Thomas
Published: July 2016

In pigment-protein complexes, often the excited states are partially delocalized and the exciton-vibrational coupling in the basis of delocalized states contains large diagonal and small off-diagonal elements. This inequality may be used to introduce potential energy surfaces (PESs) of exciton states and to treat the inter-PES coupling in Markov and secular approximations. The resulting lineshape function consists of a Lorentzian peak that is broadened by the finite lifetime of the exciton states caused by the inter-PES coupling and a vibrational sideband that results from the mutual displacement of the excitonic PESs with respect to that of the ground state. So far analytical expressions have been derived that relate the exciton relaxation-induced lifetime broadening to the Redfield [T. Renger and R. A. Marcus, J. Chem. Phys. 116, 9997 (2002)] or modified Redfield [M. Schröder, U. Kleinekathöfer, and M. Schreiber, J. Chem. Phys. 124, 084903 (2006)] rate constants of exciton relaxation, assuming that intra-PES nuclear relaxation is fast compared to inter-PES transfer. Here, we go beyond this approximation and provide an analytical expression, termed Non-equilibrium Modified Redfield (NeMoR) theory, for the lifetime broadening that takes into account the finite nuclear relaxation time. In an application of the theory to molecular dimers, we find that, for a widely used experimental spectral density of the exciton-vibrational coupling of pigment-protein complexes, the NeMoR spectrum at low-temperatures (T < 150 K) is better approximated by Redfield than by modified Redfield theory. At room temperature, the lifetime broadening obtained with Redfield theory underestimates the NeMoR broadening, whereas modified Redfield theory overestimates it by a similar amount. A fortuitous error compensation in Redfield theory is found to explain the good performance of this theory at low temperatures. Since steady state spectra of PPCs are often measured at low temperatures, Redfield theory still provides a numerically efficient alternative to NeMoR theory. At higher temperatures, we suggest to use NeMoR theory, because it has the same numerical costs as modified Redfield theory, but is more accurate.
Assessment of secondary bubble formation on a backward-facing step geometry
Authors: Juste G. L. , Fajardo P. , Guijarro A.
Published: July 2016

Flow visualization experiments and numerical simulations were performed on a narrow three-dimensional backward-facing step (BFS) flow with the main objective of characterizing the secondary bubble appearing at the top wall. The BFS has been widely studied because of its geometrical simplicity as well as its ability to reproduce most of the flow features appearing in many applications in which separation occurs. A BFS test rig with an expansion ratio of 2 and two aspect ratios (AR = 4 and AR = 8) was developed. Tests were performed at range of Reynolds numbers ranging from 50 to 1000; visualization experiments provided a qualitative description of secondary bubble and wall-jet flows. Large eddy simulations were carried out with two different codes for validation. Numerical solutions, once validated with experimental data from the literature, were used to acquire a deeper understanding of the experimental visualizations, to characterize the secondary bubble as a function of the flow variables (Reynolds and AR) and to analyze the effect of the secondary bubble on primary reattachment length. Finally, to decouple the sidewall effects due to the non-slip condition and the intrinsic flow three-dimensionality, numerical experiments with free-slip conditions over the sidewalls were computed. The main differences were as follows: When the non-slip condition is used, the secondary bubble appears at a Reynolds number of approximately 200, increases with the Reynolds number, and is limited to a small part of the span. This recirculation zone interacts with the wall-jets and causes the maximum and minimum lengths in the reattachment line of the primary recirculation. Under free slip conditions, the recirculation bubble appears at a higher Reynolds number and covers the entire channel span.
Electronic torsional sound in linear atomic chains: Chemical energy transport at 1000 km/s
Authors: Kurnosov Arkady A. , Rubtsov Igor V. , Maksymov Andrii O. , Burin Alexander L.
Published: July 2016

We investigate entirely electronic torsional vibrational modes in linear cumulene chains. The carbon nuclei of a cumulene are positioned along the primary axis so that they can participate only in the transverse and longitudinal motions. However, the interatomic electronic clouds behave as a torsion spring with remarkable torsional stiffness. The collective dynamics of these clouds can be described in terms of electronic vibrational quanta, which we name torsitons. It is shown that the group velocity of the wavepacket of torsitons is much higher than the typical speed of sound, because of the small mass of participating electrons compared to the atomic mass. For the same reason, the maximum energy of the torsitons in cumulenes is as high as a few electronvolts, while the minimum possible energy is evaluated as a few hundred wavenumbers and this minimum is associated with asymmetry of zero point atomic vibrations. Theory predictions are consistent with the time-dependent density functional theory calculations. Molecular systems for experimental evaluation of the predictions are proposed.
Stochastic field-line wandering in magnetic turbulence with shear. I. Quasi-linear theory
Authors: Shalchi A. , Negrea M. , Petrisor I.
Published: July 2016

We investigate the random walk of magnetic field lines in magnetic turbulence with shear. In the first part of the series, we develop a quasi-linear theory in order to compute the diffusion coefficient of magnetic field lines. We derive general formulas for the diffusion coefficients in the different directions of space. We like to emphasize that we expect that quasi-linear theory is only valid if the so-called Kubo number is small. We consider two turbulence models as examples, namely, a noisy slab model as well as a Gaussian decorrelation model. For both models we compute the field line diffusion coefficients and we show how they depend on the aforementioned Kubo number as well as a shear parameter. It is demonstrated that the shear effect reduces all field line diffusion coefficients.
Frequency analysis of temperature-dependent interferometric signal for the measurement of the temperature coefficient of refractive index
Authors: Zhou Jianqin , Shen Jun , Neill W. Stuart
Published: July 2016

A method of frequency analysis for the measurement of the temperature coefficient of refractive index (dn/dT) using a Fabry–Perot interferometer was developed and tested against ethanol and water. The temperature-dependent interferometric signal described by Airy’s formula was analyzed in both the temperature and frequency domains. By fast Fourier transform, a low-pass filter was designed and employed to eliminate the noise superimposed on the signal. dn/dT was determined accurately from the noise-removed signal by peak analysis. Furthermore, the signal frequency parameters may be utilized for the material thermophysical property characterization. This method lays the foundation for an online dn/dT instrument for monitoring chemical processes.
Narrow-band tunable terahertz emission from ferrimagnetic Mn3-xGa thin films
Authors: Awari N. , Kovalev S. , Fowley C. , Rode K. , Gallardo R. A. , Lau Y.-C. , Betto D. , Thiyagarajah N. , Green B. , Yildirim O. , Lindner J. , Fassbender J. , Coey J. M. D. , Deac A. M. , Gensch M.
Published: July 2016

Narrow-band terahertz emission from coherently excited spin precession in metallic ferrimagnetic Mn3-xGa Heusler alloy nanofilms has been observed. The efficiency of the emission, per nanometer film thickness, is comparable or higher than that of classical laser-driven terahertz sources based on optical rectification. The center frequency of the emission from the films can be tuned precisely via the film composition in the range of 0.20–0.35 THz, making this type of metallic film a candidate for efficient on-chip terahertz emitters. Terahertz emission spectroscopy is furthermore shown to be a sensitive probe of magnetic properties of ultra-thin films.
Isochronal annealing effects on local structure, crystalline fraction, and undamaged region size of radiation damage in Ga-stabilized δ-Pu
Authors: Olive D. T. , Wang D. L. , Booth C. H. , Bauer E. D. , Pugmire A. L. , Freibert F. J. , McCall S. K. , Wall M. A. , Allen P. G.
Published: July 2016

The effects on the local structure due to self-irradiation damage of Ga stabilized δ-Pu stored at cryogenic temperatures have been examined using extended x-ray absorption fine structure (EXAFS) experiments. Extensive damage, seen as a loss of local order, was evident after 72 days of storage below 15 K. The effect was observed from both the Pu and the Ga sites, although less pronounced around Ga. Isochronal annealing was performed on this sample to study the annealing processes that occur between cryogenic and room temperature storage conditions, where damage is mostly reversed. Damage fractions at various points along the annealing curve have been determined using an amplitude-ratio method, a standard EXAFS fitting, and a spherical crystallite model, and provide information complementary to the previous electrical resistivity- and susceptibility-based isochronal annealing studies. The use of a spherical crystallite model accounts for the changes in EXAFS spectra using just two parameters, namely, the crystalline fraction and the particle radius. Together, these results are discussed in terms of changes to the local structure around Ga and Pu throughout the annealing process and highlight the unusual role of Ga in the behavior of the lowest temperature anneals.
Electron diffraction of CBr4 in superfluid helium droplets: A step towards single molecule diffraction
Authors: He Yunteng , Zhang Jie , Kong Wei
Published: July 2016

We demonstrate the practicality of electron diffraction of single molecules inside superfluid helium droplets using CBr4 as a testing case. By reducing the background from pure undoped droplets via multiple doping, with small corrections for dimers and trimers, clearly resolved diffraction rings of CBr4 similar to those of gas phase molecules can be observed. The experimental data from CBr4 doped droplets are in agreement with both theoretical calculations and with experimental results of gaseous species. The abundance of monomers and clusters in the droplet beam also qualitatively agrees with the Poisson statistics. Possible extensions of this approach to macromolecular ions will also be discussed. This result marks the first step in building a molecular goniometer using superfluid helium droplet cooling and field induced orientation. The superior cooling effect of helium droplets is ideal for field induced orientation, but the diffraction background from helium is a concern. This work addresses this background issue and identifies a possible solution. Accumulation of diffraction images only becomes meaningful when all images are produced from molecules oriented in the same direction, and hence a molecular goniometer is a crucial technology for serial diffraction of single molecules.
Research on effect of emission uniformity on X-band relativistic backward oscillator using conformal PIC code
Authors: Chen Zaigao
Published: July 2016

Explosive emission cathodes (EECs) are adopted in relativistic backward wave oscillators (RBWOs) to generate intense relativistic electron beam. The emission uniformity of the EEC can render saturation of the power generation unstable and the output mode impure. However, the direct measurement of the plasma parameters on the cathode surface is quite difficult and there are very few related numerical study reports about this issue. In this paper, a self-developed three-dimensional conformal fully electromagnetic particle in cell code is used to study the effect of emission uniformity on the X-band RBWO; the electron explosive emission model and the field emission model are both implemented in the same cathode surface, and the local field enhancement factor is also considered in the field emission model. The RBWO with a random nonuniform EEC is thoroughly studied using this code; the simulation results reveal that when the area ratio of cathode surface for electron explosive emission is 80%, the output power is unstable and the output mode is impure. When the annular EEC does not emit electron in the angle range of 30°, the RBWO can also operate normally.
Solvothermal synthesis of Fe7C3 and Fe3C nanostructures with phase and morphology control
Authors: Williams Brent , Clifford Dustin , El-Gendy Ahmed A. , Carpenter Everett E.
Published: July 2016

A phase transition, from orthorhombic Fe3C to hexagonal Fe7C3, was observed using a wet synthesis mediated by hexadecyltrimethylammonium chloride (CTAC). In this study, CTAC has been shown to control carbide phase, morphology, and size of the iron carbide nanostructures. Fe7C3 hexagonal prisms were formed with an average diameter of 960 nm, the thickness of 150 nm, and Fe3C nanostructures with an approximate size of 50 nm. Magnetic studies show ferromagnetic behavior with Ms of 126 emu/g, and Hc of 170 Oe with respect to Fe7C3 and 95 emu/g and 590 Oe with respect to Fe3C. The thermal studies using high temperature x-ray diffraction show stability of Fe7C3 up to 500 °C. Upon slow cooling, the Fe7C3 phase is recovered with an intermediate oxide phase occurring around 300 °C. This study has demonstrated a simple route in synthesizing iron carbides for an in depth magnetic study and crystal phase transition study of Fe7C3 at elevated temperatures.
Elastic behavior of Bi2Se3 2D nanosheets grown by van der Waals epitaxy
Authors: Yan Haoming , Vajner Cooper , Kuhlman Michael , Guo Lingling , Li Lin , Araujo Paulo T. , Wang Hung-Ta
Published: July 2016

Elastic properties of bismuth selenite (Bi2Se3) two-dimensional (2D) nanosheets were investigated using atomic force microscope (AFM) nanoindentations. Bi2Se3 2D nanosheets were synthesized by van der Waals epitaxy and subsequently transferred on SiO2/Si substrates containing pre-fabricated hole arrays. The suspension of 2D nanosheets was confirmed via the distinct optical contrast characteristics and AFM. In nanoindentations, the correlation between a point force load and the elastic response in the deformation depth was found being thickness-dependent, between 7 and 12 quintuple layers. The Young's modulus, E = 17.86–25.45 GPa (fitted value = 20.67 GPa), and the pretension, T = 0.0218–0.0417 N/m, acquired according to the bending plate regime are consistent with ones from the stretching membrane regime. Furthermore, these Bi2Se3 2D nanosheets could elastically endure a 4.0%–8.3% strain before being ruptured with AFM tips. Compliant and robust elastic properties of Bi2Se3 2D nanosheets, as observed, provide a feasible way for exploring the topological phase transition.
Curvature and bow of bulk GaN substrates
Authors: Foronda Humberto M. , Romanov Alexey E. , Young Erin C. , Robertson Christian A. , Beltz Glenn E. , Speck James S.
Published: July 2016

We investigate the bow of free standing (0001) oriented hydride vapor phase epitaxy grown GaN substrates and demonstrate that their curvature is consistent with a compressive to tensile stress gradient (bottom to top) present in the substrates. The origin of the stress gradient and the curvature is attributed to the correlated inclination of edge threading dislocation (TD) lines away from the [0001] direction. A model is proposed and a relation is derived for bulk GaN substrate curvature dependence on the inclination angle and the density of TDs. The model is used to analyze the curvature for commercially available GaN substrates as determined by high resolution x-ray diffraction. The results show a close correlation between the experimentally determined parameters and those predicted from theoretical model.
Stoichiometry as key to ferroelectricity in compressively strained SrTiO3 films
Authors: Haislmaier R. C. , Engel-Herbert R. , Gopalan V.
Published: July 2016

While strain is a powerful tuning parameter for inducing ferroelectricity in thin film oxides, the role of stoichiometry control is critical, but far less explored. A series of compressively strained SrTiO3 films on (001) (LaAlO3)0.3(Sr2AlTaO6)0.35 substrates were grown by hybrid molecular beam epitaxy where the Ti cation was supplied using a metal-organic titanium tetraisopropoxide molecule that helps systematically and precisely control Sr:Ti stoichiometry in the resulting films. A stoichiometric growth window is located through X-ray diffraction and in-situ reflection high-energy electron diffraction measurements, which show a minimum out-of-plane lattice parameter as well as constant growth rate within the stoichiometric growth window range. Using temperature dependent optical second harmonic generation (SHG) characterization, a ferroelectric-to-paraelectric transition at T ∼ 180 K is observed for a stoichiometric SrTiO3 film, as well as a higher temperature structural transition at T ∼ 385 K. Using SHG polarimetry modeling, the polar point group symmetry is determined to be tetragonal 4mm with the polarization pointing out-of-plane of the film. The SHG coefficients, d31/d15=3 and d33/d15=21, were determined at 298 K. The ferroelectric transition disappears in films grown outside the growth window, thus proving the critical role of stoichiometry control in realizing strain-induced ferroelectricity.
Negative stiffness in ZrW2O8 inclusions as a result of thermal stress
Authors: Romao Carl P. , White Mary Anne
Published: July 2016

Materials with negative stiffness, although inherently unstable in isolation, can be stabilized by external constraints, for example, by inclusion within a material with positive stiffness. We have identified ZrW2O8, a material with negative thermal expansion, as a candidate negative-stiffness material arising from its negative bulk modulus during a ferroelastic cubic–orthorhombic pressure-induced phase transition (PIPT). A hyperelastic constituent equation for this transition was developed and implemented in a finite-element model of ZrW2O8 inclusions in positive stiffness, positive thermal expansion matrices. In these matrices, thermal stress during cooling, originating from thermal expansion mismatch, would be sufficient to initiate the PIPT after small temperature drops. The subsequent progress of the PIPT depends strongly on the thermoelastic properties of the matrix, with stiff, low thermal expansion matrices stabilizing the transition state over broad temperature ranges, indicating that ZrW2O8 or materials with similar properties could be used as versatile negative-stiffness inclusion materials. The models were used to understand previous experiments on composites that include ZrW2O8.
Phonon anharmonicity in bulk Td-MoTe2
Authors: Joshi Jaydeep , Stone Iris R. , Beams Ryan , Krylyuk Sergiy , Kalish Irina , Davydov Albert V. , Vora Patrick M.
Published: July 2016

We examine anharmonic contributions to the optical phonon modes in bulk Td-MoTe2 through temperature-dependent Raman spectroscopy. At temperatures ranging from 100 K to 200 K, we find that all modes redshift linearly with temperature in agreement with the Grüneisen model. However, below 100 K, we observe nonlinear temperature-dependent frequency shifts in some modes. We demonstrate that this anharmonic behavior is consistent with the decay of an optical phonon into multiple acoustic phonons. Furthermore, the highest frequency Raman modes show large changes in intensity and linewidth near T ≈ 250 K that correlate well with the Td→1T′ structural phase transition. These results suggest that phonon-phonon interactions can dominate anharmonic contributions at low temperatures in bulk Td-MoTe2, an experimental regime that is currently receiving attention in efforts to understand Weyl semimetals.
Convergence of shock waves between conical and parabolic boundaries
Authors: Yanuka D. , Zinowits H. E. , Antonov O. , Efimov S. , Virozub A. , Krasik Ya. E.
Published: July 2016

Convergence of shock waves, generated by underwater electrical explosions of cylindrical wire arrays, between either parabolic or conical bounding walls is investigated. A high-current pulse with a peak of ∼550 kA and rise time of ∼300 ns was applied for the wire array explosion. Strong self-emission from an optical fiber placed at the origin of the implosion was used for estimating the time of flight of the shock wave. 2D hydrodynamic simulations coupled with the equations of state of water and copper showed that the pressure obtained in the vicinity of the implosion is ∼7 times higher in the case of parabolic walls. However, comparison with a spherical wire array explosion showed that the pressure in the implosion vicinity in that case is higher than the pressure in the current experiment with parabolic bounding walls because of strong shock wave reflections from the walls. It is shown that this drawback of the bounding walls can be significantly minimized by optimization of the wire array geometry.
Bidirectional negative differential thermal resistance phenomenon and its physical mechanism in the Frenkel-Kontorova lattices
Authors: Jianqiang Zhang , Linru Nie , Chongyang Chen , Xinyu Zhang
Published: July 2016

Thermal conduction of the Frenkel-Kontorova (FK) lattices with interfacial coupling is investigated numerically. The results indicate that: (i) For appropriate lattice periods, as the system is symmetric, a bidirectional negative differential thermal resistance (NDTR) phenomenon will appear. If the system is asymmetric, the bidirectional NDTR is gradually converted into an unidirectional NDTR. (ii) The bidirectional NDTR phenomenon effect also depends on the period of the FK lattice as the other parameters remains unchanged. With the increment of the lattice period, the bidirectional NDTR will gradually disappear. (iii) From a stochastic dynamics point of view, thermal transport properties of the system are determined by the competition between the two types of thermal conduction: one comes from the collusion between atoms, the other is due to the elastic coupling between atoms. For the smaller lattice periods, the former type of thermal conduction occupies the dominating position and the NDTR effect will appear.
An X-band parabolic antenna based on gradient metasurface
Authors: Yao Wang , Yang Helin , Huang Xiaojun , Tian Ying , Guo Linyan
Published: July 2016

We present a novel parabolic antenna by employing reflection gradient metasurface which is composed of a series of circle patches on a grounded dielectric substrate. Similar to the traditional parabolic antenna, the proposed antenna take the metasurface as a “parabolic reflector” and a patch antenna was placed at the focal point of the metasurface as a feed source, then the quasi-spherical wave emitted by the source is reflected and transformed to plane wave with high efficiency. Due to the focus effect of reflection, the beam width of the antenna has been decreased from 85.9° to 13° and the gain has been increased from 6.5 dB to 20.8 dB. Simulation and measurement results of both near and far-field plots demonstrate good focusing properties of the proposed parabolic antenna.
Electron density and plasma dynamics of a colliding plasma experiment
Authors: Wiechula J. , Schönlein A. , Iberler M. , Hock C. , Manegold T. , Bohlender B. , Jacoby J.
Published: July 2016

We present experimental results of two head-on colliding plasma sheaths accelerated by pulsed-power-driven coaxial plasma accelerators. The measurements have been performed in a small vacuum chamber with a neutral-gas prefill of ArH2 at gas pressures between 17 Pa and 400 Pa and load voltages between 4 kV and 9 kV. As the plasma sheaths collide, the electron density is significantly increased. The electron density reaches maximum values of ≈8 ⋅ 1015 cm−3 for a single accelerated plasma and a maximum value of ≈2.6 ⋅ 1016 cm−3 for the plasma collision. Overall a raise of the plasma density by a factor of 1.3 to 3.8 has been achieved. A scaling behavior has been derived from the values of the electron density which shows a disproportionately high increase of the electron density of the collisional case for higher applied voltages in comparison to a single accelerated plasma. Sequences of the plasma collision have been taken, using a fast framing camera to study the plasma dynamics. These sequences indicate a maximum collision velocity of 34 km/s.
Effect of probiotic Bacillus amyloliquefaciens strain H57 on productivity and the incidence of diarrhoea in dairy calves
Authors: Le Oanh T. , Dart Peter J. , Harper Karen , Zhang Dagong , Schofield Benjamin , Callaghan Matthew J. , Lisle Allan T. , Klieve Athol V. , McNeill David M.
Published: July 2016

A spore-forming probiotic, Bacillus amyloliquefaciens strain H57 (H57), was administered to dairy calves in starter pellets to determine effects on liveweight gain, feed conversion efficiency and animal health under summer feeding conditions, without antibiotics. Twenty-four male and female calves were allocated into two groups and from 4 weeks of age individually offered 6 L/day of whole milk and ad libitum starter pellets impregnated with H57 (3.16 × 108 cfu per kg DM) or without (Control) until 12 weeks of age. The calves were housed in a non-air-conditioned animal house, with deep-straw bedding over concrete, under typically challenging subtropical summer conditions. After 12 weeks the calves were released into a grazing paddock as one group and were supplemented ad libitum with control pellets and hay, until 19 weeks of age. From Weeks 4 to 12, liveweight and feed intakes were measured weekly and health status was monitored daily. Rumen fluid and blood were collected at Weeks 4 and 12, and to test for persistence after cessation of feeding H57, each were measured again at Week 19. From Weeks 4 to 12, the H57 calves grew faster (767 vs 551 g/day, P = 0.01), tended to consume more pellets (1013 vs 740 g DM/day, P = 0.07) and were 19% more feed conversion efficiency (2.43 vs 2.90 kg milk + starter DM/kg weight gain, P = 0.01) compared with the Control calves. The mean duration of each diarrhoea event was 2 days less for the H57 calves than the Control (P = 0.01). The H57 calves weaned 9 days earlier (P = 0.02) and were heavier at Week 19 (155 vs 139 kg, P = 0.03) than the Control calves. The only effect of H57 on rumen volatile fatty acid concentrations was an elevation in valerate at Week 12 (4.10 vs 2.47 mmol/L, P = 0.03). Plasma β-hydroxy butyrate was also elevated in the H57 calves at Week 19 (0.24 vs 0.20 mmol/L), indicating the potential of H57 to improve rumen development. H57 can be used to improve the nutritional performance and reduce the risk of diarrhoea in dairy calves as they transition from milk to dry feed.
Spotlight on Varietal Thiols and Precursors in Grapes and Wines
Authors: Jeffery David W.
Published: July 2016

Wine is an amazingly complex natural product that requires dedicated scientists to resolve many of its mysteries. Traditional synthetic organic chemistry and modern analytical techniques are powerful tools at the disposal of wine chemists who tackle the complexities of wine in order to improve scientific understanding and provide practical solutions to industry. Part of this quest for knowledge relates to maintaining or improving wine quality, which underpins consumer acceptance and links to the competitiveness of wineries in a global market. Wine aroma is an important aspect of wine quality and garners much attention from researchers. Grape-derived aroma compounds are one area of particular importance owing to their distinctiveness and ability to impart ‘varietal aromas’ to wines. Varietal thiols imparting tropical and citrus notes that are characteristic of wines such as Sauvignon Blanc have emerged, along with their grape-derived precursors, as an area of interest over the past two decades. These compounds have also caught our attention and we have made some important contributions to this field, including identifying new precursors, developing novel analytical methods, and conducting studies that provide unique insights into the biochemical transformations occurring in grape berries and juice, and during fermentation.
Hierarchical decision processes that operate over distinct timescales underlie choice and changes in strategy
Authors: Purcell Braden A. , Kiani Roozbeh
Published: July 2016

Significance

Decisions are guided by available information and strategies that link information to action. Following a bad outcome, two potential sources of error—flawed strategy and poor information—must be distinguished to improve future performance. In a direction discrimination task where subjects decide by accumulating sensory evidence to a bound, we show that humans disambiguate sources of error by integrating expected accuracy and outcome over multiple choices. The strategy switches when the integral reaches a threshold. A hierarchy of decision processes in which lower levels integrate sensory evidence over short timescales, and higher levels interact with lower levels over longer timescales, quantitatively explains the behavior. Expected accuracy links these two levels and enables adaptive changes of decision strategy.
Phylogeographic model selection leads to insight into the evolutionary history of four-eyed frogs
Authors: Thomé Maria Tereza C. , Carstens Bryan C.
Published: July 2016

Phylogeographic research investigates biodiversity at the interface between populations and species, in a temporal and geographic context. Phylogeography has benefited from analytical approaches that allow empiricists to estimate parameters of interest from the genetic data (e.g., θ = 4Neμ, population divergence, gene flow), and the widespread availability of genomic data allow such parameters to be estimated with greater precision. However, the actual inferences made by phylogeographers remain dependent on qualitative interpretations derived from these parameters’ values and as such may be subject to overinterpretation and confirmation bias. Here we argue in favor of using an objective approach to phylogeographic inference that proceeds by calculating the probability of multiple demographic models given the data and the subsequent ranking of these models using information theory. We illustrate this approach by investigating the diversification of two sister species of four-eyed frogs of northeastern Brazil using single nucleotide polymorphisms obtained via restriction-associated digest sequencing. We estimate the composite likelihood of the observed data given nine demographic models and then rank these models using Akaike information criterion. We demonstrate that estimating parameters under a model that is a poor fit to the data is likely to produce values that lead to spurious phylogeographic inferences. Our results strongly imply that identifying which parameters to estimate from a given system is a key step in the process of phylogeographic inference and is at least as important as being able to generate precise estimates of these parameters. They also illustrate that the incorporation of model uncertainty should be a component of phylogeographic hypothesis tests.
Toward a paradigm shift in comparative phylogeography driven by trait-based hypotheses
Authors: Papadopoulou Anna , Knowles L. Lacey
Published: July 2016

For three decades, comparative phylogeography has conceptually and methodologically relied on the concordance criterion for providing insights into the historical/biogeographic processes driving population genetic structure and divergence. Here we discuss how this emphasis, and the corresponding lack of methods for extracting information about biotic/intrinsic contributions to patterns of genetic variation, may bias our general understanding of the factors driving genetic structure. Specifically, this emphasis has promoted a tendency to attribute discordant phylogeographic patterns to the idiosyncracies of history, as well as an adherence to generic null expectations of concordance with reduced predictive power. We advocate that it is time for a paradigm shift in comparative phylogeography, especially given the limited utility of the concordance criterion as genomic data provide ever-increasing levels of resolution. Instead of adhering to the concordance-discordance dichotomy, comparative phylogeography needs to emphasize the contribution of taxon-specific traits that will determine whether concordance is a meaningful criterion for evaluating hypotheses or may predict discordant phylogeographic structure. Through reference to some case studies we illustrate how refined hypotheses based on taxon-specific traits can provide improved predictive frameworks to forecast species responses to climatic change or biogeographic barriers while gaining unique insights about the taxa themselves and their interactions with their environment. We outline a potential avenue toward a synthetic comparative phylogeographic paradigm that includes addressing some important conceptual and methodological challenges related to study design and application of model-based approaches for evaluating support of trait-based hypotheses under the proposed paradigm.
Comparative phylogeography clarifies the complexity and problems of continental distribution that drove A. R. Wallace to favor islands
Authors: Riddle Brett R.
Published: July 2016

Deciphering the geographic context of diversification and distributional dynamics in continental biotas has long been an interest of biogeographers, ecologists, and evolutionary biologists. Thirty years ago, the approach now known as comparative phylogeography was introduced in a landmark study of a continental biota. Here, I use a set of 455 studies to explore the current scope of continental comparative phylogeography, including geographic, conceptual, temporal, ecological, and genomic attributes. Geographically, studies are more frequent in the northern hemisphere, but the south is catching up. Most studies focus on a Quaternary timeframe, but the Neogene is well represented. As such, explanations for geographic structure and history include geological and climatic events in Earth history, and responses include vicariance, dispersal, and range contraction-expansion into and out of refugia. Focal taxa are biased toward terrestrial or semiterrestrial vertebrates, although plants and invertebrates are well represented in some regions. The use of various kinds of nuclear DNA markers is increasing, as are multiple locus studies, but use of organelle DNA is not decreasing. Species distribution models are not yet widely incorporated into studies. In the future, continental comparative phylogeographers will continue to contribute to erosion of the simple vicariance vs. dispersal paradigm, including exposure of the widespread nature of temporal pseudocongruence and its implications for models of diversification; provide new templates for addressing a variety of ecological and evolutionary traits; and develop closer working relationships with earth scientists and biologists in a variety of disciplines.