bluuebunny/crossref_metadata_2025 huggingface dataset:
Response of the plasma to the size of an anode electrode biased near the plasma potential
Authors: Barnat E. V. , Laity G. R. , Baalrud S. D.
Published: October 2014

As the size of a positively biased electrode increases, the nature of the interface formed between the electrode and the host plasma undergoes a transition from an electron-rich structure (electron sheath) to an intermediate structure containing both ion and electron rich regions (double layer) and ultimately forms an electron-depleted structure (ion sheath). In this study, measurements are performed to further test how the size of an electron-collecting electrode impacts the plasma discharge the electrode is immersed in. This is accomplished using a segmented disk electrode in which individual segments are individually biased to change the effective surface area of the anode. Measurements of bulk plasma parameters such as the collected current density, plasma potential, electron density, electron temperature and optical emission are made as both the size and the bias placed on the electrode are varied. Abrupt transitions in the plasma parameters resulting from changing the electrode surface area are identified in both argon and helium discharges and are compared to the interface transitions predicted by global current balance [S. D. Baalrud, N. Hershkowitz, and B. Longmier, Phys. Plasmas 14, 042109 (2007)]. While the size-dependent transitions in argon agree, the size-dependent transitions observed in helium systematically occur at lower electrode sizes than those nominally derived from prediction. The discrepancy in helium is anticipated to be caused by the finite size of the interface that increases the effective area offered to the plasma for electron loss to the electrode.
Effect of viscogens on the kinetic response of a photoperturbed allosteric protein
Authors: Waldauer Steven A. , Stucki-Buchli Brigitte , Frey Lukas , Hamm Peter
Published: October 2014

By covalently binding a photoswitchable linker across the binding groove of the PDZ2 domain, a small conformational change can be photo-initiated that mimics the allosteric transition of the protein. The response of its binding groove is investigated with the help of ultrafast pump-probe IR spectroscopy from picoseconds to tens of microseconds. The temperature dependence of that response is compatible with diffusive dynamics on a rugged energy landscape without any prominent energy barrier. Furthermore, the dependence of the kinetics on the concentration of certain viscogens, sucrose, and glycerol, has been investigated. A pronounced viscosity dependence is observed that can be best fit by a power law, i.e., a fractional viscosity dependence. The change of kinetics when comparing sucrose with glycerol as viscogen, however, provides strong evidence that direct interactions of the viscogen molecule with the protein do play a role as well. This conclusion is supported by accompanying molecular dynamics simulations.
Measurement of the target current by inductive probe during laser interaction on terawatt laser system PALS
Authors: Cikhardt J. , Krása J. , De Marco M. , Pfeifer M. , Velyhan A. , Krouský E. , Cikhardtová B. , Klír D. , Řezáč K. , Ullschmied J. , Skála J. , Kubeš P. , Kravárik J.
Published: October 2014

Measurements of the return-current flowing through a solid target irradiated with the sub-nanosecond kJ-class Prague Asterix Laser System is reported. A new inductive target probe was developed which allows us measuring the target current derivative in a kA/ns range. The dependences of the target current on the laser pulse energy for cooper, graphite, and polyethylene targets are reported. The experiment shows that the target current is proportional to the deposited laser energy and is strongly affected by the shot-to-shot fluctuations. The corresponding maximum target charge exceeded a value of 10 μC. A return-current dependence of the electromagnetic pulse produced by the laser-target interaction is presented.
Calculation of the fast ion tail distribution for a spherically symmetric hot spot
Authors: McDevitt C. J. , Tang X.-Z. , Guo Z. , Berk H. L.
Published: October 2014

The fast ion tail for a spherically symmetric hot spot is computed via the solution of a simplified Fokker-Planck collision operator. Emphasis is placed on describing the energy scaling of the fast ion distribution function in the hot spot as well as the surrounding cold plasma throughout a broad range of collisionalities and temperatures. It is found that while the fast ion tail inside the hot spot is significantly depleted, leading to a reduction of the fusion yield in this region, a surplus of fast ions is observed in the neighboring cold plasma region. The presence of this surplus of fast ions in the neighboring cold region is shown to result in a partial recovery of the fusion yield lost in the hot spot.
Ultracold plasma expansion as a function of charge neutrality
Authors: Witte Craig , Roberts Jacob L.
Published: October 2014

Ultracold plasmas (UCPs) are created under conditions of near but not perfect neutrality. In the limit of zero electron temperature, electron screening results in non-neutrality manifesting itself as an interior region of the UCP with both electrons and ions and an exterior region composed primarily of ions. The interior region is the region of the most scientific interest for 2-component ultracold plasma physics. This work presents a theoretical model through which the time evolution of non-neutral UCPs is calculated. Despite Debye screening lengths much smaller than the characteristic plasma spatial size, model calculations predict that the expansion rate and the electron temperature of the UCP interior is sensitive to the neutrality of the UCP. The predicted UCP dependence on neutrality has implications for the correct measurement of several UCP properties, such as electron temperature, and a proper understanding of evaporative cooling of the electrons in the UCP.
Investigation on the negative bias illumination stress-induced instability of amorphous indium-tin-zinc-oxide thin film transistors
Authors: Jang Jaeman , Kim Dae Geun , Kim Dong Myong , Choi Sung-Jin , Lim Jun-Hyung , Lee Je-Hun , Kim Yong-Sung , Ahn Byung Du , Kim Dae Hwan
Published: October 2014

The quantitative analysis of mechanism on negative bias illumination stress (NBIS)-induced instability of amorphous indium-tin-zinc-oxide thin-film transistor (TFT) was suggested along with the effect of equivalent oxide thickness (EOT) of gate insulator. The analysis was implemented through combining the experimentally extracted density of subgap states and the device simulation. During NBIS, it was observed that the thicker EOT causes increase in both the shift of threshold voltage and the variation of subthreshold swing as well as the hump-like feature in a transfer curve. We found that the EOT-dependence of NBIS instability can be clearly explicated with the donor creation model, in which a larger amount of valence band tail states is transformed into either the ionized oxygen vacancy VO2+ or peroxide O22− with the increase of EOT. It was also found that the VO2+-related extrinsic factor accounts for 80%–92% of the total donor creation taking place in the valence band tail states while the rest is taken by the O22– related intrinsic factor. The ratio of extrinsic factor compared to the total donor creation also increased with the increase of EOT, which could be explained by more prominent oxygen deficiency. The key founding of our work certainly represents that the established model should be considered very effective for analyzing the instability of the post-indium-gallium-zinc-oxide (IGZO) ZnO-based compound semiconductor TFTs with the mobility, which is much higher than those of a-IGZO TFTs.
Calculating electronic tunnel currents in networks of disordered irregularly shaped nanoparticles by mapping networks to arrays of parallel nonlinear resistors
Authors: Aghili Yajadda Mir Massoud
Published: October 2014

We have shown both theoretically and experimentally that tunnel currents in networks of disordered irregularly shaped nanoparticles (NPs) can be calculated by considering the networks as arrays of parallel nonlinear resistors. Each resistor is described by a one-dimensional or a two-dimensional array of equal size nanoparticles that the tunnel junction gaps between nanoparticles in each resistor is assumed to be equal. The number of tunnel junctions between two contact electrodes and the tunnel junction gaps between nanoparticles are found to be functions of Coulomb blockade energies. In addition, the tunnel barriers between nanoparticles were considered to be tilted at high voltages. Furthermore, the role of thermal expansion coefficient of the tunnel junction gaps on the tunnel current is taken into account. The model calculations fit very well to the experimental data of a network of disordered gold nanoparticles, a forest of multi-wall carbon nanotubes, and a network of few-layer graphene nanoplates over a wide temperature range (5-300 K) at low and high DC bias voltages (0.001 mV–50 V). Our investigations indicate, although electron cotunneling in networks of disordered irregularly shaped NPs may occur, non-Arrhenius behavior at low temperatures cannot be described by the cotunneling model due to size distribution in the networks and irregular shape of nanoparticles. Non-Arrhenius behavior of the samples at zero bias voltage limit was attributed to the disorder in the samples. Unlike the electron cotunneling model, we found that the crossover from Arrhenius to non-Arrhenius behavior occurs at two temperatures, one at a high temperature and the other at a low temperature.
Grain size modification in the magnetocaloric and non-magnetocaloric transitions in La0.5Ca0.5MnO3 probed by direct and indirect methods
Authors: Quintero M. , Passanante S. , Irurzun I. , Goijman D. , Polla G.
Published: October 2014

The influence of grain size in the magnetic properties of phase separated manganites is an important issue evidenced more than a decade ago. The formation of long range ordered phases is suppressed as the grain size decreases giving place to a metastable state instead of the ground state. In this work, we present a study of the magnetocaloric effect in the prototypical manganite La0.5Ca0.5MnO3 as a function of the grain size. The differences obtained using direct and indirect methods are discussed in the framework of domain walls in the ferromagnetic phase of the system.
Charge separation at nanoscale interfaces: Energy-level alignment including two-quasiparticle interactions
Authors: Li Huashan , Lin Zhibin , Lusk Mark T. , Wu Zhigang
Published: October 2014

The universal and fundamental criteria for charge separation at interfaces involving nanoscale materials are investigated. In addition to the single-quasiparticle excitation, all the two-quasiparticle effects including exciton binding, Coulomb stabilization, and exciton transfer are considered, which play critical roles on nanoscale interfaces for optoelectronic applications. We propose a scheme allowing adding these two-quasiparticle interactions on top of the single-quasiparticle energy level alignment for determining and illuminating charge separation at nanoscale interfaces. Employing the many-body perturbation theory based on Green's functions, we quantitatively demonstrate that neglecting or simplifying these crucial two-quasiparticle interactions using less accurate methods is likely to predict qualitatively incorrect charge separation behaviors at nanoscale interfaces where quantum confinement dominates.
A microwave resonator for limiting depth sensitivity for electron paramagnetic resonance spectroscopy of surfaces
Authors: Sidabras Jason W. , Varanasi Shiv K. , Mett Richard R. , Swarts Steven G. , Swartz Harold M. , Hyde James S.
Published: October 2014

A microwave Surface Resonator Array (SRA) structure is described for use in Electron Paramagnetic Resonance (EPR) spectroscopy. The SRA has a series of anti-parallel transmission line modes that provides a region of sensitivity equal to the cross-sectional area times its depth sensitivity, which is approximately half the distance between the transmission line centers. It is shown that the quarter-wave twin-lead transmission line can be a useful element for design of microwave resonators at frequencies as high as 10 GHz. The SRA geometry is presented as a novel resonator for use in surface spectroscopy where the region of interest is either surrounded by lossy material, or the spectroscopist wishes to minimize signal from surrounding materials. One such application is in vivo spectroscopy of human finger-nails at X-band (9.5 GHz) to measure ionizing radiation dosages. In order to reduce losses associated with tissues beneath the nail that yield no EPR signal, the SRA structure is designed to limit depth sensitivity to the thickness of the fingernail. Another application, due to the resonator geometry and limited depth penetration, is surface spectroscopy in coating or material science. To test this application, a spectrum of 1.44 μM of Mg2+ doped polystyrene 1.1 mm thick on an aluminum surface is obtained. Modeling, design, and simulations were performed using Wolfram Mathematica (Champaign, IL; v. 9.0) and Ansys High Frequency Structure Simulator (HFSS; Canonsburg, PA; v. 15.0). A micro-strip coupling circuit is designed to suppress unwanted modes and provide a balanced impedance transformation to a 50 Ω coaxial input. Agreement between simulated and experimental results is shown.
Note: Split PID control—Two sensors can be better than one
Authors: Znaimer Leith , Bechhoefer John
Published: October 2014

The traditional proportional-integral-derivative (PID) algorithm for regulation suffers from a tradeoff: placing the sensor near the sample being regulated ensures that its steady-state temperature matches the desired setpoint. However, the propagation delay (lag) between heater and sample can limit the control bandwidth. Moving the sensor closer to the heater reduces the lag and increases the bandwidth but introduces offsets and drifts into the temperature of the sample. Here, we explore the consequences of using two probes—one near the heater, one near the sample—and assigning the integral term to the sample probe and the other terms to the heater probe. The split-PID algorithm can outperform PID control loops based on one sensor.
Comparison of test particle acceleration in torsional spine and fan reconnection regimes
Authors: Hosseinpour M. , Mehdizade M. , Mohammadi M. A.
Published: October 2014

Magnetic reconnection is a common phenomenon taking place in astrophysical and space plasmas, especially in solar flares which are rich sources of highly energetic particles. Torsional spine and fan reconnections are important mechanisms proposed for steady-state three-dimensional null-point reconnection. By using the magnetic and electric fields for these regimes, we numerically investigate the features of test particle acceleration in both regimes with input parameters for the solar corona. By comparison, torsional spine reconnection is found to be more efficient than torsional fan reconnection in an acceleration of a proton to a high kinetic energy. A proton can gain as high as 100 MeV of relativistic kinetic energy within only a few milliseconds. Moreover, in torsional spine reconnection, an accelerated particle can escape either along the spine axis or on the fan plane depending on its injection position. However, in torsional fan reconnection, the particle is only allowed to accelerate along the spine axis. In addition, in both regimes, the particle's trajectory and final kinetic energy depend on the injection position but adopting either spatially uniform or non-uniform localized plasma resistivity does not much influence the features of trajectory.
Theoretical study of high-Q Fano resonance and extrinsic chirality in an ultrathin Babinet-inverted metasurface
Authors: Wang Feng , Wang Zhengping , Shi Jinhui
Published: October 2014

A high-Q Fano resonance and giant extrinsic chirality have been demonstrated in an ultrathin Babinet-inverted metasurface composed of asymmetrical split ring apertures (ASRAs) perforated through a metal plate based on the full-wave simulations. The performance of the Fano resonance at normal incidence strongly depends on the asymmetry of the ASRA. The quality factor is larger than 1000 and the local field enhancement is an order of 104. For oblique incidence, giant extrinsic chirality can be achieved in the Babinet-inverted metasurface. It reveals a cross-polarization transmission band with a ripple-free peak and also a spectrum split for large angles of incidence. The electromagnetic response of the metasurface can be easily tuned via angles of incidence and asymmetry. The proposed ASRA metasurface is of importance to develop many metamaterial-based devices, such as filters and circular polarizers.
Investigation of solution-processed bismuth-niobium-oxide films
Authors: Inoue Satoshi , Ariga Tomoki , Matsumoto Shin , Onoue Masatoshi , Miyasako Takaaki , Tokumitsu Eisuke , Chinone Norimichi , Cho Yasuo , Shimoda Tatsuya
Published: October 2014

The characteristics of bismuth-niobium-oxide (BNO) films prepared using a solution process were investigated. The BNO film annealed at 550 °C involving three phases: an amorphous phase, Bi3NbO7 fluorite microcrystals, and Nb-rich cubic pyrochlore microcrystals. The cubic pyrochlore structure, which was the main phase in this film, has not previously been reported in BNO films. The relative dielectric constant of the BNO film was approximately 140, which is much higher than that of a corresponding film prepared using a conventional vacuum sputtering process. Notably, the cubic pyrochlore microcrystals disappeared with increasing annealing temperature and were replaced with triclinic β-BiNbO4 crystals at 590 °C. The relative dielectric constant also decreased with increasing annealing temperature. Therefore, the high relative dielectric constant of the BNO film annealed at 550 °C is thought to result from the BNO cubic pyrochlore structure. In addition, the BNO films annealed at 500 °C contained approximately 6.5 atm. % carbon, which was lost at approximately 550 °C. This result suggests that the carbon in the BNO film played an important role in the formation of the cubic pyrochlore structure.
The different adsorption mechanism of methane molecule onto a boron nitride and a graphene flakes
Authors: Seyed-Talebi Seyedeh Mozhgan , Neek-Amal M.
Published: October 2014

Graphene and single layer hexagonal boron-nitride are two newly discovered 2D materials with wonderful physical properties. Using density functional theory, we study the adsorption mechanism of a methane molecule over a hexagonal flake of single layer hexagonal boron-nitride (h-BN) and compare the results with those of graphene. We found that independent of the used functional in our ab-initio calculations, the adsorption energy in the h-BN flake is larger than that for graphene. Despite of the adsorption energy profile of methane over a graphene flake, we show that there is a long range behavior beyond minimum energy in the adsorption energy of methane over h-BN flake. This result reveals the higher sensitivity of h-BN sheet to the adsorption of a typical closed shell molecule with respect to graphene. The latter gives insight in the recent experiments of graphene over hexagonal boron nitride.
Detection of Dynabeads in small bias magnetic field by a micro fluxgate-based sensing system
Authors: Lei Chong , Sun Xue-Cheng , Liu Cui , Lei Jian , Wang Tao , Yang Zhen , Zhou Yong
Published: October 2014

The micro fluxgate sensors have shown high sensitivity for the magnetic beads detection. For portable magnetic biological detection, Co-based amorphous ribbons with high permeability and low saturation magnetic induction are chosen as core materials to lower the operation requirements of the fluxgate-based magnetic beads detection. The micro fluxgate sensors with single-layer core and bi-layer core are fabricated by Micro-Electro-Mechanical System technologies, which exhibit a power consumption of 10.88 mW and 24.48 mW, a sensitivity of 1644 V/T and 1456 V/T, and a noise of 1.66 nT/Hz1/2@1 Hz and 2.32 nT/Hz1/2@1 Hz, respectively. The Dynabeads with concentrations of 300 μg/ml in 10 μl are detected by the micro fluxgate-based sensing system based on static response, and the results show signal change ratio of 12.2% and 9.2% under the max signal difference at 215 μT and 480 μT of the bias magnetic field for two kinds of the sensors, respectively, which is near the saturation point of the sensors. The fluxgate-based bead detection system with Co-based ribbon core presents low demands for the bias magnetic field and power consumption.
Study of nitrogen flowing afterglow with mercury vapor injection
Authors: Mazánková V. , Trunec D. , Krčma F.
Published: October 2014

The reaction kinetics in nitrogen flowing afterglow with mercury vapor addition was studied by optical emission spectroscopy. The DC flowing post-discharge in pure nitrogen was created in a quartz tube at the total gas pressure of 1000 Pa and discharge power of 130 W. The mercury vapors were added into the afterglow at the distance of 30 cm behind the active discharge. The optical emission spectra were measured along the flow tube. Three nitrogen spectral systems – the first positive, the second positive, and the first negative, and after the mercury vapor addition also the mercury resonance line at 254 nm in the spectrum of the second order were identified. The measurement of the spatial dependence of mercury line intensity showed very slow decay of its intensity and the decay rate did not depend on the mercury concentration. In order to explain this behavior, a kinetic model for the reaction in afterglow was developed. This model showed that the state Hg(6 3P1), which is the upper state of mercury UV resonance line at 254 nm, is produced by the excitation transfer from nitrogen N2(A \documentclass[12pt]{minimal}\begin{document}$^3 \Sigma ^+_u$\end{document}Σu+3) metastables to mercury atoms. However, the N2(A \documentclass[12pt]{minimal}\begin{document}$^3 \Sigma ^+_u$\end{document}Σu+3) metastables are also produced by the reactions following the N atom recombination, and this limits the decay of N2(A \documentclass[12pt]{minimal}\begin{document}$^3 \Sigma ^+_u$\end{document}Σu+3) metastable concentration and results in very slow decay of mercury resonance line intensity. It was found that N atoms are the most important particles in this late nitrogen afterglow, their volume recombination starts a chain of reactions which produce excited states of molecular nitrogen. In order to explain the decrease of N atom concentration, it was also necessary to include the surface recombination of N atoms to the model. The surface recombination was considered as a first order reaction and wall recombination probability γ = (1.35 ± 0.04) × 10−6 was determined from the experimental data. Also sensitivity analysis was applied for the analysis of kinetic model in order to reveal the main control parameters in the model.
Communication: A combined periodic density functional and incremental wave-function-based approach for the dispersion-accounting time-resolved dynamics of 4He nanodroplets on surfaces: 4He/graphene
Authors: de Lara-Castells María Pilar , Stoll Hermann , Civalleri Bartolomeo , Causà Mauro , Voloshina Elena , Mitrushchenkov Alexander O. , Pi Martí
Published: October 2014

In this work we propose a general strategy to calculate accurate He–surface interaction potentials. It extends the dispersionless density functional approach recently developed by Pernal et al. [Phys. Rev. Lett. 103, 263201 (2009)] to adsorbate-surface interactions by including periodic boundary conditions. We also introduce a scheme to parametrize the dispersion interaction by calculating two- and three-body dispersion terms at coupled cluster singles and doubles and perturbative triples (CCSD(T)) level via the method of increments [H. Stoll, J. Chem. Phys. 97, 8449 (1992)]. The performance of the composite approach is tested on 4He/graphene by determining the energies of the low-lying selective adsorption states, finding an excellent agreement with the best available theoretical data. Second, the capability of the approach to describe dispersionless correlation effects realistically is used to extract dispersion effects in time-dependent density functional simulations on the collision of 4He droplets with a single graphene sheet. It is found that dispersion effects play a key role in the fast spreading of the 4He nanodroplet, the evaporation-like process of helium atoms, and the formation of solid-like helium structures. These characteristics are expected to be quite general and highly relevant to explain experimental measurements with the newly developed helium droplet mediated deposition technique.
Theoretical studies on the stopping power of deuterium-tritium mixed with uranium plasmas for α particles
Authors: Wang Zhigang , Fu Zhen-Guo , Zhang Ping
Published: October 2014

The stopping power of a compressed and highly ionized deuterium-tritium (DT) and uranium (U) plasma for α particles at very high temperatures (T = 5 keV) is examined theoretically with the dimensional continuation method. We show that with increasing density of U, both the magnitude and width of the resonance peak in the stopping power (as a function of the α particle energy), increases because of the ions, while the penetration distance of the α particles decreases. A simple relation of decreasing penetration distance as a function of plasma density is observed, which may be useful for inertial confinement fusion experiments. Moreover, by comparing the results with the case of a DT plasma mixed with beryllium, we find that the effect of a higher Z plasma is stronger, with regard to energy loss as well as the penetration distance of α particles, than that of a lower Z plasma.
Single atom impurity in a single molecular transistor
Authors: Ray S. J.
Published: October 2014

The influence of an impurity atom on the electrostatic behaviour of a Single Molecular Transistor was investigated through Ab-initio calculations in a double-gated geometry. The charge stability diagram carries unique signature of the position of the impurity atom in such devices which together with the charging energy of the molecule could be utilised as an electronic fingerprint for the detection of such impurity states in a nano-electronic device. The two gated geometry allows additional control over the electrostatics as can be seen from the total energy surfaces (for a specific charge state), which is sensitive to the positions of the impurity. These devices which are operational at room temperature can provide significant advantages over the conventional silicon based single dopant devices functional at low temperature. The present approach could be a very powerful tool for the detection and control of individual impurity atoms in a single molecular device and for applications in future molecular electronics.
Density of states of amorphous In-Ga-Zn-O from electrical and optical characterization
Authors: Yu Eric Kai-Hsiang , Jun Sungwoo , Kim Dae Hwan , Kanicki Jerzy
Published: October 2014

We have developed a subgap density of states (DOS) model of amorphous In-Ga-Zn-O (a-IGZO) based on optical and electrical measurements. We study the optical absorption spectrum of the a-IGZO using UV-Vis spectroscopy. Together with the first-principles calculations and transient photoconductance spectroscopy from the literature, we determine that the valence band tail and deep-gap states are donors and can be described by exponential and Gaussian distributions, respectively. The conduction band tail and deep-gap states are examined using multi-frequency capacitance-voltage spectroscopy on a-IGZO thin-film transistors (TFTs). The extracted conduction band DOS are fitted to exponential (bandtail) and Gaussian (deep-gap) functions and their validity are supported by the activation energy vs. gate-source bias relationship of the a-IGZO TFT. The PL deep-level emission, which is almost identical to the conduction band deep-gap Gaussian, suggests that these states should be assigned as acceptors. The donor/acceptor assignments of subgap states are consistent with the 2D numerical TFT simulations.
Determination of intrinsic spin Hall angle in Pt
Authors: Wang Yi , Deorani Praveen , Qiu Xuepeng , Kwon Jae Hyun , Yang Hyunsoo
Published: October 2014

The spin Hall angle in Pt is evaluated in Pt/NiFe bilayers by spin torque ferromagnetic resonance measurements and is found to increase with increasing the NiFe thickness. To extract the intrinsic spin Hall angle in Pt by estimating the total spin current injected into NiFe from Pt, the NiFe thickness dependent measurements are performed and the spin diffusion in the NiFe layer is taken into account. The intrinsic spin Hall angle of Pt is determined to be 0.068 at room temperature and is found to be almost constant in the temperature range of 13–300 K.
Giant electrocaloric effect in BaZr0.2Ti0.8O3 thick film
Authors: Ye Hui-Jian , Qian Xiao-Shi , Jeong Dae-Yong , Zhang Shujun , Zhou Yue , Shao Wen-Zhu , Zhen Liang , Zhang Q. M.
Published: October 2014

We report the giant electrocaloric effect (ECE) of BaZr0.2Ti0.8O3 (BZT) thick film near room temperature. The BZT thick film was fabricated by the tape casting method with the thickness of 12.0 μm. Due to the near invariant critical point composition, relaxor behavior, and the stress generated between the film and the substrate, the thick film exhibits a large adiabatic temperature drop ΔT = −7 °C under 19.5 MV/m electric field, large EC coefficient ΔT/ΔE = 0.50 × 10−6 K · m · V−1, ΔS/ΔE = 0.88 × 10−6 J · m · kg−1 · K−1 · V−1 over a wide temperature range near room temperature, where ΔS is the isothermal entropy change and ΔE is the applied field. These high EC properties and possibility of fabrication of the EC ceramics into multilayer ceramic capacitor configuration provide solution for the application of the EC material for practical cooling device applications.
Magnetorheology of suspensions based on graphene oxide coated or added carbonyl iron microspheres and sunflower oil
Authors: Chen Kaikai , Zhang Wen Ling , Shan Lei , Zhang Xiangjun , Meng Yonggang , Choi Hyoung Jin , Tian Yu
Published: October 2014

Magnetorheological (MR) fluids based on carbonyl iron (CI) particles coated with graphene oxide (GO) and sunflower oils were studied and compared with MR fluids (MRFs) prepared with CI particles added with GO sheets. Adding GO sheets into CI had a negligible effect on the rheological properties of the MRF. Coating the spheres with GO markedly decreased the shear strength at high shear rates due to the remarkable lubricating function of the GO surface. Different behaviors were observed in the shear thickening phenomenon when the GO surface changed the mechanical interaction between particles. The results demonstrated the importance of the role of interparticle friction for MRF in shear mode and discussed the weak shear thickening phenomenon with fine lubricating coating layers and oils.
Effect of doping on the short-circuit current and open-circuit voltage of polymer solar cells
Authors: Zhao Yong , Liang Chunjun , Sun Mengjie , Liu Qian , Zhang Fujun , Li Dan , He Zhiqun
Published: October 2014

The change in doping density in P3HT:PCBM based polymer solar cells (PSCs) with different processing solvents and with/without post-fabrication thermal treatment is investigated with capacitance-voltage measurement and optical microscopic imaging. The results suggest that both slow drying and thermal treatment facilitate the phase-separation and crystallinity of P3HT and PCBM, leading to low defect density and thus low p-type doping. Direct links between the doping density and the performance of the PSCs, specifically the short-circuit current (Jsc) and open-circuit voltage (Voc), are observed. The results show that doping density is one of the decisive factors affecting the photocurrent of the PSCs. Lower doping density leads to a wider depletion region, which is beneficial for carrier collection. The agreement between the calculation and the experiment suggests that the Voc increases monotonically with increasing doping densities in the PSCs. These rules consistently explain our results on the change of Jsc and Voc after thermal annealing in the PSCs with different processing solvents.
Thermal conductivity of vertically aligned carbon nanotube arrays: Growth conditions and tube inhomogeneity
Authors: Bauer Matthew L. , Pham Quang N. , Saltonstall Christopher B. , Norris Pamela M.
Published: October 2014

The thermal conductivity of vertically aligned carbon nanotube arrays (VACNTAs) grown on silicon dioxide substrates via chemical vapor deposition is measured using a 3ω technique. For each sample, the VACNTA layer and substrate are pressed to a heating line at varying pressures to extract the sample's thermophysical properties. The nanotubes' structure is observed via transmission electron microscopy and Raman spectroscopy. The presence of hydrogen and water vapor in the fabrication process is tuned to observe the effect on measured thermal properties. The presence of iron catalyst particles within the individual nanotubes prevents the array from achieving the overall thermal conductivity anticipated based on reported measurements of individual nanotubes and the packing density.
Observation of strongly enhanced inverse spin Hall voltage in Fe3Si/GaAs structures
Authors: Hung H. Y. , Chiang T. H. , Syu B. Z. , Fanchiang Y. T. , Lin J. G. , Lee S. F. , Hong M. , Kwo J.
Published: October 2014

We performed spin pumping experiment on high quality, epitaxial Fe3Si/GaAs structures grown by molecular beam epitaxy. By tailoring the thickness and doping (n, p) level of the conducting GaAs epi-layer, thermal heating common of ferromagnetic metal/semiconductor heterostructure was removed effectively. A large inverse spin Hall Effect (ISHE) voltage up to 49.2 μV was observed for Fe3Si/p-GaAs. Smaller ISHE voltage (VISHE) by a factor of ∼0.4 was obtained for Fe3Si/n-GaAs, as scaled with its resistivity. By taking into account of the “self-induced” ISHE apparently observed in our samples, the minimum value of spin Hall angle θISHE for n-GaAs and p-GaAs was estimated to be 1.9 × 10−4 and 2.8 × 10−5, respectively.
Understanding resonant tunnel transport in non-identical and non-aligned clusters as applied to disordered carbon systems
Authors: Bhattacharyya Somnath , Churochkin Dmitry
Published: October 2014

We study the conductance spectra and the corresponding current-voltage characteristics of a set of three impurity clusters of different sizes arranged in the form of a scalene triangle and compare with the transport of their horizontal and vertical configurations. The tuning capability of resonant tunnelling features in a quantum dot device made of these non-aligned impurity clusters is demonstrated by re-distributing their diameters and inter-cluster distances in a systematic manner. By manipulating the inter-cluster coupling for a scalene triangular configuration, the transition of current-voltage curves from a step-like feature to a negative differential resistance can be produced. This process also yields conductance features for triangular configurations, which can be compared to the quantum dot structures perfectly aligned to the direction of the propagating wavevector. The strength of inter-cluster coupling or order parameter for these configurations is analysed from the relative variation of the width and the energy difference of the sharp and broad peaks observed in the density of states spectra. Based on the relative change of the inter-cluster coupling with the cluster configurations, a transport model applicable to structurally inhomogeneous systems is proposed in order to explain the experimentally observed variation of the energy band gap with the disorder parameters.
Observation of the fundamental Nyquist noise limit in an ultra-high Q-factor cryogenic bulk acoustic wave cavity
Authors: Goryachev Maxim , Ivanov Eugene N. , van Kann Frank , Galliou Serge , Tobar Michael E.
Published: October 2014

Thermal Nyquist noise fluctuations of high-Q bulk acoustic wave cavities have been observed at cryogenic temperatures with a DC superconducting quantum interference device amplifier. High Q modes with bandwidths of few tens of milliHz produce thermal fluctuations with a signal-to-noise ratio of up to 23 dB. The estimated effective temperature from the Nyquist noise is in good agreement with the physical temperature of the device, confirming the validity of the equivalent circuit model and the non-existence of any excess resonator self-noise. The measurements also confirm that the quality factor remains extremely high (Q > 108 at low order overtones) for very weak (thermal) system motion at low temperatures, when compared to values measured with relatively strong external excitation. This result represents an enabling step towards operating such a high-Q acoustic device at the standard quantum limit.
Spray coated indium-tin-oxide-free organic photodiodes with PEDOT:PSS anodes
Authors: Schmidt Morten , Falco Aniello , Loch Marius , Lugli Paolo , Scarpa Giuseppe
Published: October 2014

In this paper we report on Indium Tin Oxide (ITO)-free spray coated organic photodiodes with an active layer consisting of a poly(3-hexylthiophen) (P3HT) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) blend and patterned poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) electrodes. External quantum efficiency and current voltage characteristics under illuminated and dark conditions as well as cut-off frequencies for devices with varying active and hole conducting layer thicknesses were measured in order to characterize the fabricated devices. 60% quantum efficiency as well as nearly four orders of magnitude on-off ratios have been achieved. Those values are comparable with standard ITO devices.
Helicity conservation by flow across scales in reconnecting vortex links and knots
Authors: Scheeler Martin W. , Kleckner Dustin , Proment Davide , Kindlmann Gordon L. , Irvine William T. M.
Published: October 2014

Significance

Ideal fluids have a conserved quantity—helicity—which measures the degree to which a fluid flow is knotted and tangled. In real fluids (even superfluids), vortex reconnection events disentangle linked and knotted vortices, jeopardizing helicity conservation. By generating vortex trefoil knots and linked rings in water and simulated superfluids, we observe that helicity is remarkably conserved despite reconnections: vortex knots untie and links disconnect, but in the process they create helix-like coils with the same total helicity. This result establishes helicity as a fundamental building block, like energy or momentum, for understanding the behavior of complex knotted structures in physical fields, including plasmas, superfluids, and turbulent flows.
The nature of protein folding pathways
Authors: Englander S. Walter , Mayne Leland
Published: October 2014

How do proteins fold, and why do they fold in that way? This Perspective integrates earlier and more recent advances over the 50-y history of the protein folding problem, emphasizing unambiguously clear structural information. Experimental results show that, contrary to prior belief, proteins are multistate rather than two-state objects. They are composed of separately cooperative foldon building blocks that can be seen to repeatedly unfold and refold as units even under native conditions. Similarly, foldons are lost as units when proteins are destabilized to produce partially unfolded equilibrium molten globules. In kinetic folding, the inherently cooperative nature of foldons predisposes the thermally driven amino acid-level search to form an initial foldon and subsequent foldons in later assisted searches. The small size of foldon units, ∼20 residues, resolves the Levinthal time-scale search problem. These microscopic-level search processes can be identified with the disordered multitrack search envisioned in the “new view” model for protein folding. Emergent macroscopic foldon–foldon interactions then collectively provide the structural guidance and free energy bias for the ordered addition of foldons in a stepwise pathway that sequentially builds the native protein. These conclusions reconcile the seemingly opposed new view and defined pathway models; the two models account for different stages of the protein folding process. Additionally, these observations answer the “how” and the “why” questions. The protein folding pathway depends on the same foldon units and foldon–foldon interactions that construct the native structure.
Protein kinase IKKβ-catalyzed phosphorylation of IRF5 at Ser462 induces its dimerization and nuclear translocation in myeloid cells
Authors: Lopez-Pelaez Marta , Lamont Douglas J. , Peggie Mark , Shpiro Natalia , Gray Nathanael S. , Cohen Philip
Published: October 2014

Significance

NF-κB and IFN Regulatory Factor 5 (IRF5) are required for the transcription of many proinflammatory cytokines in myeloid cells. The protein kinase IKKβ is the major activator of NF-κB but how IRF5 is activated has been unclear. This paper demonstrates that IKKβ also activates IRF5 by catalyzing the phosphorylation of Ser462. The phosphorylation of this serine induces the dimerization of IRF5 and its translocation to the nucleus. The activation of the master transcription factors of the innate immune system by the same protein kinase provides a mechanism for the coordinated control of IRF5 and NF-κB in response to inflammatory stimuli.
Copula‐Based Models of Systemic Risk in U.S. Agriculture: Implications for Crop Insurance and Reinsurance Contracts
Authors: Goodwin Barry K. , Hungerford Ashley
Published: October 2014

The federal crop insurance program has been a major fixture of U.S. agricultural policy since the 1930s, and continues to grow in size and importance. Indeed, it now represents the most prominent farm policy instrument, accounting for more government spending than any other farm commodity program. The 2014 Farm Bill further expanded the crop insurance program and introduced a number of new county‐level revenue insurance plans. In 2013, over $123 billion in crop value was insured under the program. Crop revenue insurance, first introduced in the 1990s, now accounts for nearly 70% of the total liability in the program. The available plans cover losses that result from a revenue shortfall that can be triggered by multiple, dependent sources of risk—either low prices, low yields, or a combination of both. The actuarial practices currently applied when rating these plans essentially involve the application of a Gaussian copula model to the pricing of dependent risks. We evaluate the suitability of this assumption by considering a number of alternative copula models. In particular, we use combinations of pair‐wise copulas of conditional distributions to model multiple sources of risk. We find that this approach is generally preferred by model‐fitting criteria in the applications considered here. We demonstrate that alternative approaches to modeling dependencies in a portfolio of risks may have significant implications for premium rates in crop insurance.
piPipes: a set of pipelines for piRNA and transposon analysis via small RNA-seq, RNA-seq, degradome- and CAGE-seq, ChIP-seq and genomic DNA sequencing
Authors: Han Bo W. , Wang Wei , Zamore Phillip D. , Weng Zhiping
Published: October 2014

Motivation: PIWI-interacting RNAs (piRNAs), 23–36 nt small silencing RNAs, repress transposon expression in the metazoan germ line, thereby protecting the genome. Although high-throughput sequencing has made it possible to examine the genome and transcriptome at unprecedented resolution, extracting useful information from gigabytes of sequencing data still requires substantial computational skills. Additionally, researchers may analyze and interpret the same data differently, generating results that are difficult to reconcile. To address these issues, we developed a coordinated set of pipelines, ‘piPipes’, to analyze piRNA and transposon-derived RNAs from a variety of high-throughput sequencing libraries, including small RNA, RNA, degradome or 7-methyl guanosine cap analysis of gene expression (CAGE), chromatin immunoprecipitation (ChIP) and genomic DNA-seq. piPipes can also produce figures and tables suitable for publication. By facilitating data analysis, piPipes provides an opportunity to standardize computational methods in the piRNA field.

Supplementary information: Supplementary information, including flowcharts and example figures for each pipeline, are available at Bioinformatics online.

Availability and implementation: piPipes is implemented in Bash, C++, Python, Perl and R. piPipes is free, open-source software distributed under the GPLv3 license and is available at http://bowhan.github.io/piPipes/.

Contact: Phillip.Zamore@umassmed.edu or Zhiping.Weng@umassmed.edu

Supplementary information:  Supplementary Data are available at Bioinformatics online.
SYSBIONS: nested sampling for systems biology
Authors: Johnson Rob , Kirk Paul , Stumpf Michael P. H.
Published: October 2014

Motivation: Model selection is a fundamental part of the scientific process in systems biology. Given a set of competing hypotheses, we routinely wish to choose the one that best explains the observed data. In the Bayesian framework, models are compared via Bayes factors (the ratio of evidences), where a model’s evidence is the support given to the model by the data. A parallel interest is inferring the distribution of the parameters that define a model. Nested sampling is a method for the computation of a model’s evidence and the generation of samples from the posterior parameter distribution.

Results: We present a C-based, GPU-accelerated implementation of nested sampling that is designed for biological applications. The algorithm follows a standard routine with optional extensions and additional features. We provide a number of methods for sampling from the prior subject to a likelihood constraint.

Availability and implementation: The software SYSBIONS is available from http://www.theosysbio.bio.ic.ac.uk/resources/sysbions/

Contact:  m.stumpf@imperial.ac.uk, robert.johnson11@imperial.ac.uk
MOST: a software environment for constraint-based metabolic modeling and strain design
Authors: Kelley James J. , Lane Anatoliy , Li Xiaowei , Mutthoju Brahmaji , Maor Shay , Egen Dennis , Lun Desmond S.
Published: October 2014

Summary: MOST (metabolic optimization and simulation tool) is a software package that implements GDBB (genetic design through branch and bound) in an intuitive user-friendly interface with excel-like editing functionality, as well as implementing FBA (flux balance analysis), and supporting systems biology markup language and comma-separated values files. GDBB is currently the fastest algorithm for finding gene knockouts predicted by FBA to increase production of desired products, but GDBB has only been available on a command line interface, which is difficult to use for those without programming knowledge, until the release of MOST.

Availability and implementation: MOST is distributed for free on the GNU General Public License. The software and full documentation are available at http://most.ccib.rutgers.edu/.

Contact:  dslun@rutgers.edu.