bluuebunny/crossref_metadata_2025 huggingface dataset:
Development of a neural network technique for KSTAR Thomson scattering diagnostics
Authors: Lee Seung Hun , Lee J. H. , Yamada I. , Park Jae Sun
Published: August 2016

Neural networks provide powerful approaches of dealing with nonlinear data and have been successfully applied to fusion plasma diagnostics and control systems. Controlling tokamak plasmas in real time is essential to measure the plasma parameters in situ. However, the χ2 method traditionally used in Thomson scattering diagnostics hampers real-time measurement due to the complexity of the calculations involved. In this study, we applied a neural network approach to Thomson scattering diagnostics in order to calculate the electron temperature, comparing the results to those obtained with the χ2 method. The best results were obtained for 103 training cycles and eight nodes in the hidden layer. Our neural network approach shows good agreement with the χ2 method and performs the calculation twenty times faster.
Electrostatic interactions between charged dielectric particles in an electrolyte solution
Authors: Derbenev Ivan N. , Filippov Anatoly V. , Stace Anthony J. , Besley Elena
Published: August 2016

Theory is developed to address a significant problem of how two charged dielectric particles interact in the presence of a polarizable medium that is a dilute solution of a strong electrolyte. The electrostatic force is defined by characteristic parameters for the interacting particles (charge, radius, and dielectric constant) and for the medium (permittivity and Debye length), and is expressed in the form of a converging infinite series. The limiting case of weak screening and large inter-particle separation is considered, which corresponds to small (macro)ions that carry constant charge. The theory yields a solution in the limit of monopole and dipole terms that agrees exactly with existing analytical expressions, which are generally used to describe ion-ion and ion-molecular interactions in a medium. Results from the theory are compared with DLVO theory and with experimental measurements for the electrostatic force between two PMMA particles contained in a nonpolar solvent (hexadecane) with an added charge control agent.
A compact neutron scatter camera for field deployment
Authors: Goldsmith John E. M. , Gerling Mark D. , Brennan James S.
Published: August 2016

We describe a very compact (0.9 m high, 0.4 m diameter, 40 kg) battery operable neutron scatter camera designed for field deployment. Unlike most other systems, the configuration of the sixteen liquid-scintillator detection cells are arranged to provide omnidirectional (4π) imaging with sensitivity comparable to a conventional two-plane system. Although designed primarily to operate as a neutron scatter camera for localizing energetic neutron sources, it also functions as a Compton camera for localizing gamma sources. In addition to describing the radionuclide source localization capabilities of this system, we demonstrate how it provides neutron spectra that can distinguish plutonium metal from plutonium oxide sources, in addition to the easier task of distinguishing AmBe from fission sources.
Hydration effects on the electronic properties of eumelanin building blocks
Authors: Assis Oliveira Leonardo Bruno , L. Fonseca Tertius , Costa Cabral Benedito J. , Coutinho Kaline , Canuto Sylvio
Published: August 2016

Theoretical results for the electronic properties of eumelanin building blocks in the gas phase and water are presented. The building blocks presently investigated include the monomeric species DHI (5,6-dihydroxyindole) or hydroquinone (HQ), DHICA (5,6-dihydroxyindole-2-carboxylic acid), indolequinone (IQ), quinone methide (MQ), two covalently bonded dimers [HM ≡ HQ + MQ and IM ≡ IQ + MQ], and two tetramers [HMIM ≡ HQ + IM, IMIM ≡ IM + IM]. The electronic properties in water were determined by carrying out sequential Monte Carlo/time dependent density functional theory calculations. The results illustrate the role played by hydrogen bonding and electrostatic interactions in the electronic properties of eumelanin building blocks in a polar environment. In water, the dipole moments of monomeric species are significantly increased ([54–79]%) relative to their gas phase values. Recently, it has been proposed that the observed enhancement of the higher-energy absorption intensity in eumelanin can be explained by excitonic coupling among eumelanin protomolecules [C.-T. Chen et al., Nat. Commun. 5, 3859 (2014)]. Here, we are providing evidence that for DHICA, IQ, and HMIM, the electronic absorption toward the higher-energy end of the spectrum ([180–220] nm) is enhanced by long-range Coulombic interactions with the water environment. It was verified that by superposing the absorption spectra of different eumelanin building blocks corresponding to the monomers, dimers, and tetramers in liquid water, the behaviour of the experimental spectrum, which is characterised by a nearly monotonic decay from the ultraviolet to the infrared, is qualitatively reproduced. This result is in keeping with a “chemical disorder model,” where the broadband absorption of eumelanin pigments is determined by the superposition of the spectra associated with the monomeric and oligomeric building blocks.
Ground states of nonlinear Choquard equations with multi-well potentials
Authors: Li Shuai , Xiang Jianlin , Zeng Xiaoyu
Published: August 2016

In this paper, we study minimizers of the Hartree-type energy functional Ea(u)≔∫RN∇u(x)2+V(x)u(x)2dx−ap∫RNIα∗u(x)pu(x)pdx,a≥0 under the mass constraint ∫RNu2dx=1, where p=N+α+2N with α ∈ (0, N) for N ≥ 2 is the mass critical exponent. Here Iα denotes the Riesz potential and the trapping potential 0≤V(x)∈Lloc∞(RN) satisfies limx→∞V(x)=∞. We prove that minimizers exist if and only if a satisfies a 0 is small enough. The blow-up behavior of positive minimizers as a↗a∗ is also derived under some general potentials. Especially, we prove that minimizers must blow up at the central point of the biggest inscribed sphere of the set Ω ≔ {x ∈ ℝN, V(x) = 0} if Ω>0.
Dispersion of the electron g factor anisotropy in InAs/InP self-assembled quantum dots
Authors: Belykh V. V. , Yakovlev D. R. , Schindler J. J. , van Bree J. , Koenraad P. M. , Averkiev N. S. , Bayer M. , Silov A. Yu.
Published: August 2016

The electron g factor in an ensemble of InAs/InP quantum dots with emission wavelengths around 1.4 μm is measured using time-resolved pump-probe Faraday rotation spectroscopy in different magnetic field orientations. Thereby, we can extend recent single dot photoluminescence measurements significantly towards lower optical transition energies through 0.86 eV. This allows us to obtain detailed insight into the dispersion of the recently discovered g factor anisotropy in these infrared emitting quantum dots. We find with decreasing transition energy over a range of 50 meV a strong enhancement of the g factor difference between magnetic field normal and along the dot growth axis, namely, from 1 to 1.7. We argue that the g factor cannot be solely determined by the confinement energy, but the dot asymmetry underlying this anisotropy therefore has to increase with increasing dot size.
Quantifying the transport properties of lipid mesophases by theoretical modelling of diffusion experiments
Authors: Antognini Luca M. , Assenza Salvatore , Speziale Chiara , Mezzenga Raffaele
Published: August 2016

Lyotropic Liquid Crystals (LLCs) are a class of lipid-based membranes with a strong potential for drug-delivery employment. The characterization and control of their transport properties is a central issue in this regard, and has recently prompted a notable volume of research on the topic. A promising experimental approach is provided by the so-called diffusion setup, where the drug molecules diffuse from a feeding chamber filled with water to a receiving one passing through a LLC. In the present work we provide a theoretical framework for the proper description of this setup, and validate it by means of targeted experiments. Due to the inhomogeneity of the system, a rich palette of different diffusion dynamics emerges from the interplay of the different time- and lengthscales thereby present. Our work paves the way to the employment of diffusion experiments to quantitatively characterize the transport properties of LLCs, and provides the basic tools for device diffusion setups with controlled kinetic properties.
Structure of amorphous GeSe9 by neutron diffraction and first-principles molecular dynamics: Impact of trajectory sampling and size effects
Authors: Le Roux Sébastien , Bouzid Assil , Kim Kye Yeop , Han Seungwu , Zeidler Anita , Salmon Philip S. , Massobrio Carlo
Published: August 2016

The structure of glassy GeSe9 was investigated by combining neutron diffraction with density-functional-theory-based first-principles molecular dynamics. In the simulations, three different models of N = 260 atoms were prepared by sampling three independent temporal trajectories, and the glass structures were found to be substantially different from those obtained for models in which smaller numbers of atoms or more rapid quench rates were employed. In particular, the overall network structure is based on Sen chains that are cross-linked by Ge(Se4)1/2 tetrahedra, where the latter are predominantly corner as opposed to edge sharing. The occurrence of a substantial proportion of Ge–Se–Se connections does not support a model in which the material is phase separated into Se-rich and GeSe2-rich domains. The appearance of a first-sharp diffraction peak in the Bhatia-Thornton concentration-concentration partial structure factor does, however, indicate a non-uniform distribution of the Ge-centered structural motifs on an intermediate length scale.
A novel carbon coating technique for foil bolometers
Authors: Sheikh U. A. , Duval B. P. , Labit B. , Nespoli F.
Published: August 2016

Naked foil bolometers can reflect a significant fraction of incident energy and therefore cannot be used for absolute measurements. This paper outlines a novel coating approach to address this problem by blackening the surface of gold foil bolometers using physical vapour deposition. An experimental bolometer was built containing four standard gold foil bolometers, of which two were coated with 100+ nm of carbon. All bolometers were collimated and observed the same relatively high temperature, ohmically heated plasma. Preliminary results showed 13%-15% more incident power was measured by the coated bolometers and this is expected to be much higher in future TCV detached divertor experiments.
Compact and lightweight support platform with electromagnetic disturbance elimination for interferometer on reversed field pinch Keda Torus eXperiment
Authors: Mao Wenzhe , Yuan Peng , Zheng Jian , Ding Weixing , Li Hong , Lan Tao , Liu Adi , Liu Wandong , Xie Jinlin
Published: August 2016

A compact and lightweight support platform has been used as a holder for the interferometer system on the Keda Torus eXperiment (KTX), which is a reversed field pinch device. The vibration caused by the interaction between the time-varying magnetic field and the induced current driven in the metal optical components has been measured and, following comparison with the mechanical vibration of the KTX device and the refraction effect of the ambient turbulent air flow, has been identified as the primary vibration source in this case. To eliminate this electromagnetic disturbance, nonmetallic epoxy resin has been selected as the material for the support platform and the commercially available metal optical mounts are replaced. Following these optimization steps and mechanical reinforcements, the stability of the interferometer platform has improved significantly. The phase shift caused by the vibration has been reduced to the level of background noise.
Calibrations of the LHD Thomson scattering system
Authors: Yamada I. , Funaba H. , Yasuhara R. , Hayashi H. , Kenmochi N. , Minami T. , Yoshikawa M. , Ohta K. , Lee J. H. , Lee S. H.
Published: August 2016

The Thomson scattering diagnostic systems are widely used for the measurements of absolute local electron temperatures and densities of fusion plasmas. In order to obtain accurate and reliable temperature and density data, careful calibrations of the system are required. We have tried several calibration methods since the second LHD experiment campaign in 1998. We summarize the current status of the calibration methods for the electron temperature and density measurements by the LHD Thomson scattering diagnostic system. Future plans are briefly discussed.
A recoverable gas-cell diagnostic for the National Ignition Facility
Authors: Ratkiewicz A. , Berzak Hopkins L. , Bleuel D. L. , Bernstein L. A. , van Bibber K. , Cassata W. S. , Goldblum B. L. , Siem S. , Velsko C. A. , Wiedeking M. , Yeamans C. B.
Published: August 2016

The high-fluence neutron spectrum produced by the National Ignition Facility (NIF) provides an opportunity to measure the activation of materials by fast-spectrum neutrons. A new large-volume gas-cell diagnostic has been designed and qualified to measure the activation of gaseous substances at the NIF. This in-chamber diagnostic is recoverable, reusable and has been successfully fielded. Data from the qualification of the diagnostic have been used to benchmark an Monte Carlo N-Particle Transport Code simulation describing the downscattered neutron spectrum seen by the gas cell. We present early results from the use of this diagnostic to measure the activation of natXe and discuss future work to study the strength of interactions between plasma and nuclei.
Filterscope diagnostic system on the Experimental Advanced Superconducting Tokamak (EAST)
Authors: Xu Z. , Wu Z. W. , Gao W. , Chen Y. J. , Wu C. R. , Zhang L. , Huang J. , Chang J. F. , Yao X. J. , Gao W. , Zhang P. F. , Jin Z. , Hou Y. M. , Guo H. Y.
Published: August 2016

A filterscope diagnostic system has been mounted to observe the line emission and visible bremsstrahlung emission from plasma on the experimental advanced superconducting tokamak during the 2014 campaign. By this diagnostic system, multiple wavelengths including Dα (656.1 nm), Dγ (433.9 nm), He ii (468.5 nm), Li i (670.8 nm), Li ii (548.3 nm), C iii (465.0 nm), O ii (441.5 nm), Mo i (386.4 nm), W i (400.9 nm), and visible bremsstrahlung radiation (538.0 nm) are monitored with corresponding wavelength filters. All these multi-channel signals are digitized at up to 200 kHz simultaneously. This diagnostic plays a crucial role in studying edge localized modes and H-mode plasmas, due to the high temporal resolution and spatial resolution that have been designed into it.
A collimated neutron detector for RFP plasmas in MST
Authors: Capecchi W. J. , Anderson J. K. , Bonofiglo P. J. , Kim J. , Sears S.
Published: August 2016

The neutron emissivity profile in the Madison Symmetric Torus is being reconstructed through the use of a collimated neutron detector. A scintillator-photomultiplier tube (PMT) system is employed to detect the fusion neutrons with the plasma viewing volume defined by a 55 cm deep, 5 cm diameter aperture. Effective detection of neutrons from the viewing volume is achieved through neutron moderation using 1300 lbs of high density polyethylene shielding, which modeling predicts attenuates the penetrating flux by a factor of 104 or more. A broad spectrum of gamma radiation is also present due to the unconfined fusion proton bombardment of the thick aluminum vacuum vessel. A 15 cm cylindrical liquid scintillator of 3.8 cm diameter is used to further increase directional sensitivity. A fast (5 ns rise time) preamplifier and digitization at 500 MHz prevent pulse pile-up even at high count rates (∼104/s). The entire neutron camera system is situated on an adjustable inclining base which provides the differing plasma viewing volumes necessary for reconstruction of the neutron emissivity profile. This profile, directly related to the fast-ion population, allows for an investigation of the critical fast-ion pressure gradient required to destabilize a neutral beam driven Alfvénic mode which has been shown to transport fast ions.
Decay of the 3D viscous liquid-gas two-phase flow model with damping
Authors: Zhang Yinghui
Published: August 2016

We establish the optimal Lp − L2(1 ≤ p < 6/5) time decay rates of the solution to the Cauchy problem for the 3D viscous liquid-gas two-phase flow model with damping and analyse the influences of the damping on the qualitative behaviors of solution. It is observed that the fraction effect of the damping affects the dispersion of fluids and enhances the time decay rate of solution. Our method of proof consists of Hodge decomposition technique, Lp − L2 estimates for the linearized equations, and delicate energy estimates.
Competitive and cooperative anisotropy in magnetic nanocrystal chains of magnetotactic bacteria
Authors: Koulialias D. , García-Rubio I. , Rahn-Lee L. , Komeili A. , Löffler J. F. , Gehring A. U. , Charilaou M.
Published: August 2016

The formation of cellular magnetic dipoles by chain assemblies of stable single-domain magnetite nanocrystals is a characteristic feature in magnetotactic bacteria (MTB). The dipole strength depends on the competition or cooperation between the various anisotropic energy contributions, mainly between the magnetocrystalline and the interaction-induced shape anisotropy. Ferromagnetic resonance spectroscopy and numerical simulations of intracellular magnetite assemblies in the MTB Desulfovibrio magneticus strain RS-1 show that the alignment of elongated nanocrystallites leads to a predominant uniaxial anisotropy, which is enhanced when the magnetocrystalline symmetry is collinear to the chain, i.e., the anisotropies are cooperative vs. being competitive. This direct insight into the anisotropy variations in chain assemblies provides a physical framework to tailor magnetic nanocomposites, where the collective magnetic properties result from the interactions between the individual nanocrystalline constituents.
Torus as phase space: Weyl quantization, dequantization, and Wigner formalism
Authors: Ligabò Marilena
Published: August 2016

The Weyl quantization of classical observables on the torus (as phase space) without regularity assumptions is explicitly computed. The equivalence class of symbols yielding the same Weyl operator is characterized. The Heisenberg equation for the dynamics of general quantum observables is written through the Moyal brackets on the torus and the support of the Wigner transform is characterized. Finally, a dequantization procedure is introduced that applies, for instance, to the Pauli matrices. As a result we obtain the corresponding classical symbols.
Epitaxial strain and its relaxation at the LaAlO3/SrTiO3 interface
Authors: Liu Guozhen , Lei Qingyu , Wolak Matthäus A. , Li Qun , Chen Long-Qing , Winkler Christopher , Sloppy Jennifer , Taheri Mitra L. , Xi Xiaoxing
Published: August 2016

A series of LaAlO3 thin films with different thicknesses were deposited by pulsed laser deposition at temperatures from 720 °C to 800 °C. The results from grazing incidence x-ray diffraction and reciprocal space mapping indicate that a thin layer of LaAlO3 adjacent to the SrTiO3 substrate remains almost coherently strained to the substrate, while the top layer starts to relax quickly above a certain critical thickness, followed by a gradual relaxation at larger film thickness when they are grown at lower temperatures. The atomic force microscopy results show that the fast relaxation is accompanied by the formation of cracks on the film surface. This can be ascribed to the larger energy release rate when compared with the resistance of LaAlO3 to cracking, according to calculations from the Griffith fracture theory. For films grown at 720 °C, a drop in sheet resistance by two orders of magnitude is observed when the top layer starts to relax, indicating a relationship between the strain and the conductivity of the two-dimensional electron gas at the LaAlO3/SrTiO3 interface. The strain engineered by growth temperature provides a useful tool for the manipulation of the electronic properties of oxide heterointerfaces.
Effective stiffness and formation of secondary structures in a protein-like model
Authors: Škrbić Tatjana , Hoang Trinh X. , Giacometti Achille
Published: August 2016

We use Wang-Landau and replica exchange techniques to study the effect of an increasing stiffness on the formation of secondary structures in protein-like systems. Two possible models are considered. In both models, a polymer chain is formed by tethered beads where non-consecutive backbone beads attract each other via a square-well potential representing the tendency of the chain to fold. In addition, smaller hard spheres are attached to each non-terminal backbone bead along the direction normal to the chain to mimic the steric hindrance of side chains in real proteins. The two models, however, differ in the way bending rigidity is enforced. In the first model, partial overlap between consecutive beads is allowed. This reduces the possible bending angle between consecutive bonds thus producing an effective entropic stiffness that competes with a short-range attraction, and leads to the formation of secondary structures characteristic of proteins. We discuss the low-temperature phase diagram as a function of increasing interpenetration and find a transition from a planar, beta-like structure, to helical shape. In the second model, an energetic stiffness is explicitly introduced by imposing an infinitely large energy penalty for bending above a critical angle between consecutive bonds, and no penalty below it. The low-temperature phase of this model does not show any sign of protein-like secondary structures. At intermediate temperatures, however, where the chain is still in the coil conformation but stiffness is significant, we find the two models to predict a quite similar dependence of the persistence length as a function of the stiffness. This behaviour is rationalized in terms of a simple geometrical mapping between the two models. Finally, we discuss the effect of shrinking side chains to zero and find the above mapping to still hold true.
Soft X-ray absorption spectroscopy investigations of Bi6FeCoTi3O18 and LaBi5FeCoTi3O18 epitaxial thin films
Authors: Cui Zhangzhang , Xu Hui , Yun Yu , Guo Jinghua , Chuang Yi-De , Huang Haoliang , Meng Dechao , Wang Jianlin , Fu Zhengping , Peng Ranran , Knize Randy J. , Brown Gail J. , Zhai Xiaofang , Lu Yalin
Published: August 2016

High-quality single-crystalline Bi6FeCoTi3O18 and LaBi5FeCoTi3O18 thin films were prepared by pulsed laser deposition. X-ray diffraction characterizations indicate a more disordered lattice structure of the LaBi5FeCoTi3O18 film. The magnetic measurement results demonstrated significantly enhanced ferromagnetism in the LaBi5FeCoTi3O18 film. The modulation of oxidation and hybridization states caused by substituting Bi with La was studied using the soft X-ray absorption spectroscopy. The spectroscopic results revealed the reduced concentration of oxygen vacancies and the more distorted lattice structure in the LaBi5FeCoTi3O18 film, which explained the enhanced ferromagnetism.
Spin-splitting in p-type Ge devices
Authors: Holmes S. N. , Newton P. J. , Llandro J. , Mansell R. , Barnes C. H. W. , Morrison C. , Myronov M.
Published: August 2016

Compressively strained Ge quantum well devices have a spin-splitting in applied magnetic field that is entirely consistent with a Zeeman effect in the heavy hole valence band. The spin orientation is determined by the biaxial strain in the quantum well with the relaxed SiGe buffer layers and is quantized in the growth direction perpendicular to the conducting channel. The measured spin-splitting in the resistivity ρxx agrees with the predictions of the Zeeman Hamiltonian where the Shubnikov-deHaas effect exhibits a loss of even filling factor minima in the resistivity ρxx with hole depletion from a gate field, increasing disorder or increasing temperature. There is no measurable Rashba spin-orbit coupling irrespective of the structural inversion asymmetry of the confining potential in low p-doped or undoped Ge quantum wells from a density of 6 × 1010 cm−2 in depletion mode to 1.7 × 1011 cm−2 in enhancement.
Determination of axial and lateral exciton diffusion length in GaN by electron energy dependent cathodoluminescence
Authors: Hocker Matthias , Maier Pascal , Jerg Lisa , Tischer Ingo , Neusser Gregor , Kranz Christine , Pristovsek Markus , Humphreys Colin J. , Leute Robert A. R. , Heinz Dominik , Rettig Oliver , Scholz Ferdinand , Thonke Klaus
Published: August 2016

We demonstrate the application of low-temperature cathodoluminescence (CL) with high lateral, depth, and spectral resolution to determine both the lateral (i.e., perpendicular to the incident primary electron beam) and axial (i.e., parallel to the electron beam) diffusion length of excitons in semiconductor materials. The lateral diffusion length in GaN is investigated by the decrease of the GaN-related luminescence signal when approaching an interface to Ga(In)N based quantum well stripes. The axial diffusion length in GaN is evaluated from a comparison of the results of depth-resolved CL spectroscopy (DRCLS) measurements with predictions from Monte Carlo simulations on the size and shape of the excitation volume. The lateral diffusion length was found to be (95 ± 40) nm for nominally undoped GaN, and the axial exciton diffusion length was determined to be (150 ± 25) nm. The application of the DRCLS method is also presented on a semipolar (112¯2) sample, resulting in a value of (70 ± 10) nm in p-type GaN.
Electrohydrodynamic printing of organic polymeric resistors on flat and uneven surfaces
Authors: Maktabi Sepehr , Chiarot Paul R.
Published: August 2016

In materials printing applications, the ability to generate fine droplets is critical for achieving high-resolution features. Other desirable characteristics are high print speeds, large stand-off distances, and minimal instrumentation requirements. In this work, a tunable electrohydrodynamic (EHD) printing technique capable of generating micron-sized droplets is reported. This method was used to print organic resistors on flat and uneven substrates. These ubiquitous electronic components were built using the commercial polymer-based conductive ink poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS), which has been widely used in the manufacturing of organic electronic devices. Resistors with widths from 50 to 500 μm and resistances from 1 to 70 Ω/μm were created. An array of emission modes for EHD printing was identified. Among these, the most promising is the microdripping mode, where droplets 10 times smaller than the nozzle's inner diameter were created at frequencies in excess of 5 kHz. It was found that the ink flow rate, applied voltage, and stand-off distance all significantly influence the droplet generation frequency. In particular, the experimental results reveal that the frequency increases nonlinearly with the applied voltage. The non-Newtonian shear thinning behavior of PEDOT:PSS strongly influenced the droplet frequency. Finally, the topology of a 3-dimensional target substrate had a significant effect on the structure and function of a printed resistor.
Leakage current phenomena in Mn-doped Bi(Na,K)TiO3-based ferroelectric thin films
Authors: Walenza-Slabe J. , Gibbons B. J.
Published: August 2016

Mn-doped 80(Bi0.5Na0.5)TiO3-20(Bi0.5K0.5)TiO3 thin films were fabricated by chemical solution deposition on Pt/TiO2/SiO2/Si substrates. Steady state and time-dependent leakage current were investigated from room temperature to 180 °C. Undoped and low-doped films showed space-charge-limited current (SCLC) at high temperatures. The electric field marking the transition from Ohmic to trap-filling-limited current increased monotonically with Mn-doping. With 2 mol. % Mn, the current was Ohmic up to 430 kV/cm, even at 180 °C. Modeling of the SCLC showed that all films exhibited shallow trap levels and high trap concentrations. In the regime of steady state leakage, there were also observations of negative differential resistivity and positive temperature coefficient of resistivity near room temperature. Both of these phenomena were confined to relatively low temperatures (below ∼60 °C). Transient currents were observed in the time-dependent leakage data, which was measured out to several hundred seconds. In the undoped films, these were found to be a consequence of oxygen vacancy migration modulating the electronic conductivity. The mobility and thermal activation energy for oxygen vacancies was extracted as μion ≈ 1.7 × 10−12 cm2 V−1 s−1 and EA,ion ≈ 0.92 eV, respectively. The transient current displayed different characteristics in the 1 mol. % Mn-doped films which were not readily explained by oxygen vacancy migration.
Short-pulse amplification by strongly coupled stimulated Brillouin scattering
Authors: Edwards Matthew R. , Jia Qing , Mikhailova Julia M. , Fisch Nathaniel J.
Published: August 2016

We examine the feasibility of strongly coupled stimulated Brillouin scattering as a mechanism for the plasma-based amplification of sub-picosecond pulses. In particular, we use fluid theory and particle-in-cell simulations to compare the relative advantages of Raman and Brillouin amplification over a broad range of achievable parameters.
The effect of surfaces on molecular ordering in thin liquid-crystal systems
Authors: Śliwa I. , Jeżewski W. , Zakharov A. V.
Published: August 2016

A theoretical method for analyzing the interplay between pair long-range intermolecular forces and nonlocal, relatively short-range, surface interactions in liquid crystals, confined between plates of thin planar cells, is developed. It is shown that this method, as involving the concept of local orientational and translational order parameters, enables detailed investigations of the emergence of smectic A, nematic, and isotopic phases, as well as yields an insight into phase transitions between them, in cases of systems strongly affected by surfaces. The evidence of various surface effects, including the coexistence of different phases and the inward propagation of surface melting under the increase of temperature, is also given. The underlying numerical procedure, based on the algorithm of self-consistent calculations of local order parameters, is found to be very effective, allowing one to consider model systems of rather large thicknesses, corresponding to thicknesses of real sample cells.
Critical Casimir interactions and colloidal self-assembly in near-critical solvents
Authors: Tasios Nikos , Edison John R. , van Roij René , Evans Robert , Dijkstra Marjolein
Published: August 2016

A binary solvent mixture close to critical demixing experiences fluctuations whose correlation length, ξ, diverges as the critical point is approached. The solvent-mediated (SM) interaction that arises between a pair of colloids immersed in such a near-critical solvent can be long-ranged and this so-called critical Casimir interaction is well-studied. How a (dense) suspension of colloids will self-assemble under these conditions is poorly understood. Using a two-dimensional lattice model for the solvent and hard disks to represent the colloids, we perform extensive Monte Carlo simulations to investigate the phase behaviour of this model colloidal suspension as a function of colloid size and wettability under conditions where the solvent reservoir is supercritical. Unlike most other approaches, where the solvent is modelled as an implicit background, our model employs an explicit solvent and treats the suspension as a ternary mixture. This enables us to capture important features, including the pronounced fractionation of the solvent in the coexisting colloidal phases, of this complex system. We also present results for the partial structure factors; these shed light on the critical behaviour in the ternary mixture. The degree to which an effective two-body pair potential description can describe the phase behaviour and structure of the colloidal suspension is discussed briefly.
Anisotropy of Seebeck coefficient in Si/Ge composite quantum dots
Authors: Hsin Cheng-Lun , Tsai Yue-Yun , Lee Sheng-Wei
Published: August 2016

In this report, Si5Ge5 alloy and Si/Ge composite quantum dots (CQDs) layers were grown on Si substrates. Seebeck coefficient (S) of Si and Ge wafers, as well as these two samples, were patterned and measured from 60 to 180 °C in [110] and [010] directions. For Si, Ge, and Si5Ge5, the S of each is a constant in this temperature range. However, the S of the CQDs at 60–80 °C is anomalous and much higher than the others. The behavior of the voltage difference is linear to the temperature difference even as large as 50 °C, except for CQDs at 60–80 °C. This result indicates that a narrow distribution of carriers energy with a sharp change in density of state near Fermi-level and selective carrier scattering in the miniband at Si/Ge interface make the discrepancy of charge transport enhanced. The CQDs can be a good candidate for temperature sensing and thermoelectric applications due to their high S and low thermal conductivity near room temperature.
Templated growth of diamond optical resonators via plasma-enhanced chemical vapor deposition
Authors: Zhang X. , Hu E. L.
Published: August 2016

We utilize plasma-enhanced chemical vapor deposition through a patterned silica mask for templated diamond growth to create optical resonators. The pyramid-shaped structures have quality factors Q up to 600, measured using confocal photoluminescence spectroscopy, and mode volumes V as small as 2.5(λ/n)3 for resonances at wavelengths λ between 550 and 650 nm, and refractive index n, obtained using finite-difference time-domain simulations. Bright luminescence from nitrogen-vacancy and silicon-vacancy centers in the grown diamond is observed. The resonator design and fabrication technique obviates any etching of diamond, which preserves emitter properties in a pristine host lattice.
Communication: Evaporation: Influence of heat transport in the liquid on the interface temperature and the particle flux
Authors: Heinen Matthias , Vrabec Jadran , Fischer Johann
Published: August 2016

Molecular dynamics simulations are reported for the evaporation of a liquid into vacuum, where a Lennard-Jones type fluid with truncated and shifted potential at 2.5σ is considered. Vacuum is enforced locally by particle deletion and the liquid is thermostated in its bulk so that heat flows to the planar interface driving stationary evaporation. The length of the non-thermostated transition region between the bulk liquid and the interface Ln is under study. First, it is found for the reduced bulk liquid temperature Tl/Tc = 0.74 (Tc is the critical temperature) that by increasing Ln from 5.2σ to 208σ the interface temperature Ti drops by 17% and the evaporation flux decreases by a factor of 4.4. From a series of simulations for increasing values of Ln, an asymptotic value Ti∞ of the interface temperature for Ln → ∞ can be estimated which is 21% lower than the bulk liquid temperature Tl. Second, it is found that the evaporation flux is solely determined by the interface temperature Ti, independent on Tl or Ln. Combining these two findings, the evaporation coefficient α of a liquid thermostated on a macroscopic scale is estimated to be α ≈ 0.14 for Tl/Tc = 0.74.
Selective heteroepitaxy on deeply grooved substrate: A route to low cost semipolar GaN platforms of bulk quality
Authors: Tendille Florian , Martin Denis , Vennéguès Philippe , Grandjean Nicolas , De Mierry Philippe
Published: August 2016

Semipolar GaN crystal stripes larger than 100 μm with dislocation densities below 5 × 106 cm−2 are achieved using a low cost fabrication process. An original sapphire patterning procedure is proposed, enabling selective growth of semipolar oriented GaN stripes while confining the defects to specific areas. Radiative and non-radiative crystalline defects are investigated by cathodoluminescence and can be correlated to the development of crystal microstructure during the growth process. A dislocation reduction mechanism, supported by transmission electron microscopy, is proposed. This method represents a step forward toward low-cost quasi-bulk semipolar GaN epitaxial platforms with an excellent structural quality which will allow for even more efficient III-nitride based devices.
Communication: Wigner functions in action-angle variables, Bohr-Sommerfeld quantization, the Heisenberg correspondence principle, and a symmetrical quasi-classical approach to the full electronic density matrix
Authors: Miller William H. , Cotton Stephen J.
Published: August 2016

It is pointed out that the classical phase space distribution in action-angle (a-a) variables obtained from a Wigner function depends on how the calculation is carried out: if one computes the standard Wigner function in Cartesian variables (p, x), and then replaces p and x by their expressions in terms of a-a variables, one obtains a different result than if the Wigner function is computed directly in terms of the a-a variables. Furthermore, the latter procedure gives a result more consistent with classical and semiclassical theory—e.g., by incorporating the Bohr-Sommerfeld quantization condition (quantum states defined by integer values of the action variable) as well as the Heisenberg correspondence principle for matrix elements of an operator between such states—and has also been shown to be more accurate when applied to electronically non-adiabatic applications as implemented within the recently developed symmetrical quasi-classical (SQC) Meyer-Miller (MM) approach. Moreover, use of the Wigner function (obtained directly) in a-a variables shows how our standard SQC/MM approach can be used to obtain off-diagonal elements of the electronic density matrix by processing in a different way the same set of trajectories already used (in the SQC/MM methodology) to obtain the diagonal elements.
High-performance polyimide nanocomposites with core-shell AgNWs@BN for electronic packagings
Authors: Zhou Yongcun , Liu Feng
Published: August 2016

The increasing density of electronic devices underscores the need for efficient thermal management. Silver nanowires (AgNWs), as one-dimensional nanostructures, possess a high aspect ratio and intrinsic thermal conductivity. However, high electrical conductivity of AgNWs limits their application for electronic packaging. We synthesized boron nitride-coated silver nanowires (AgNWs@BN) using a flexible and fast method followed by incorporation into synthetic polyimide (PI) for enhanced thermal conductivity and dielectric properties of nanocomposites. The thinner boron nitride intermediate nanolayer on AgNWs not only alleviated the mismatch between AgNWs and PI but also enhanced their interfacial interaction. Hence, the maximum thermal conductivity of an AgNWs@BN/PI composite with a filler loading up to 20% volume was increased to 4.33 W/m K, which is an enhancement by nearly 23.3 times compared with that of the PI matrix. The relative permittivity and dielectric loss were about 9.89 and 0.015 at 1 MHz, respectively. Compared with AgNWs@SiO2/PI and Ag@BN/PI composites, boron nitride-coated core-shell structures effectively increased the thermal conductivity and reduced the permittivity of nanocomposites. The relative mechanism was studied and discussed. This study enables the identification of appropriate modifier fillers for polymer matrix nanocomposites.
Carbon nanotube-graphene composite film as transparent conductive electrode for GaN-based light-emitting diodes
Authors: Kang Chun Hong , Shen Chao , M. Saheed M. Shuaib , Mohamed Norani Muti , Ng Tien Khee , Ooi Boon S. , Burhanudin Zainal Arif
Published: August 2016

Transparent conductive electrodes (TCE) made of carbon nanotube (CNT) and graphene composite for GaN-based light emitting diodes (LED) are presented. The TCE with 533-Ω/□ sheet resistance and 88% transmittance were obtained when chemical-vapor-deposition grown graphene was fused across CNT networks. With an additional 2-nm thin NiOx interlayer between the TCE and top p-GaN layer of the LED, the forward voltage was reduced to 5.12 V at 20-mA injection current. Four-fold improvement in terms of light output power was observed. The improvement can be ascribed to the enhanced lateral current spreading across the hybrid CNT-graphene TCE before injection into the p-GaN layer.
Structural defects and recombination behavior of excited carriers in Cu(In,Ga)Se2 solar cells
Authors: Yang J. , Du H. W. , Li Y. , Gao M. , Wan Y. Z. , Xu F. , Ma Z. Q.
Published: August 2016

The carriers’ behavior in neutral region (NTR) and space charged region (SCR) of Cu(In,Ga)Se2 thin film based solar cells has been investigated by temperature dependent photoluminescence (PL-T), electroluminescence (EL-T) and current-voltage (IV-T) from 10 to 300 K. PL-T spectra show that three kinds of defects, namely VSe, InCu and (InCu+VCu), are localized within the band gap of NTR and SCR of CIGS layer, corresponding to the energy levels of EC-0.08, EC-0.20 and EC-0.25 eV, respectively. The InCu and (InCu+VCu) deep level defects are non-radiative recombination centers at room temperature. The IV-T and EL-T analysis reveals that the injection modes of electrons from ZnO conduction band into Cu(In,Ga)Se2 layer are tunneling, thermally-excited tunneling and thermionic emission under 10-40, 60-160, and 180-300 K, respectively. At 10-160 K, the electrons tunnel into (InCu+VCu) and Vse defect levels in band gap of SCR and the drifting is involved in the emission bands at 0.96 and 1.07 eV, which is the direct evidence for a tunneling assisted recombination. At 180-300 K, the electrons are directly injected into the Cu(In,Ga)Se2 conduction band, and the emission of 1.13 eV are ascribed to the transitions from the conduction band to the valence band.
Lattice Boltzmann models for the grain growth in polycrystalline systems
Authors: Zheng Yonggang , Chen Cen , Ye Hongfei , Zhang Hongwu
Published: August 2016

In the present work, lattice Boltzmann models are proposed for the computer simulation of normal grain growth in two-dimensional systems with/without immobile dispersed second-phase particles and involving the temperature gradient effect. These models are demonstrated theoretically to be equivalent to the phase field models based on the multiscale expansion. Simulation results of several representative examples show that the proposed models can effectively and accurately simulate the grain growth in various single- and two-phase systems. It is found that the grain growth in single-phase polycrystalline materials follows the power-law kinetics and the immobile second-phase particles can inhibit the grain growth in two-phase systems. It is further demonstrated that the grain growth can be tuned by the second-phase particles and the introduction of temperature gradient is also an effective way for the fabrication of polycrystalline materials with grained gradient microstructures. The proposed models are useful for the numerical design of the microstructure of materials and provide effective tools to guide the experiments. Moreover, these models can be easily extended to simulate two- and three-dimensional grain growth with considering the mobile second-phase particles, transient heat transfer, melt convection, etc.
Analyzing the photonic band gaps in two-dimensional plasma photonic crystals with fractal Sierpinski gasket structure based on the Monte Carlo method
Authors: Zhang Hai-Feng , Liu Shao-Bin
Published: August 2016

In this paper, the properties of photonic band gaps (PBGs) in two types of two-dimensional plasma-dielectric photonic crystals (2D PPCs) under a transverse-magnetic (TM) wave are theoretically investigated by a modified plane wave expansion (PWE) method where Monte Carlo method is introduced. The proposed PWE method can be used to calculate the band structures of 2D PPCs which possess arbitrary-shaped filler and any lattice. The efficiency and convergence of the present method are discussed by a numerical example. The configuration of 2D PPCs is the square lattices with fractal Sierpinski gasket structure whose constituents are homogeneous and isotropic. The type-1 PPCs is filled with the dielectric cylinders in the plasma background, while its complementary structure is called type-2 PPCs, in which plasma cylinders behave as the fillers in the dielectric background. The calculated results reveal that the enough accuracy and good convergence can be obtained, if the number of random sampling points of Monte Carlo method is large enough. The band structures of two types of PPCs with different fractal orders of Sierpinski gasket structure also are theoretically computed for a comparison. It is demonstrate that the PBGs in higher frequency region are more easily produced in the type-1 PPCs rather than in the type-2 PPCs. Sierpinski gasket structure introduced in the 2D PPCs leads to a larger cutoff frequency, enhances and induces more PBGs in high frequency region. The effects of configurational parameters of two types of PPCs on the PBGs are also investigated in detail. The results show that the PBGs of the PPCs can be easily manipulated by tuning those parameters. The present type-1 PPCs are more suitable to design the tunable compacted devices.
pH determines the energetic efficiency of the cyanobacterial CO
2
concentrating mechanism
Authors: Mangan Niall M. , Flamholz Avi , Hood Rachel D. , Milo Ron , Savage David F.
Published: August 2016

Significance

Cyanobacteria are responsible for roughly 10% of global photosynthetic primary production of reduced carbon. Although cyanobacteria are incredibly diverse, all known species contain a complex protein system called the CO
2
concentrating mechanism (CCM), which enables rapid growth even in environments with extremely limited CO
2
. The CCM enables cyanobacteria to accumulate HCO
3
−
and convert this inorganic carbon pool to utilizable CO
2
. We demonstrate here that a quantitative description of the CCM must include the effect of pH on the abundance of HCO
3
−
and H
2
CO
3
. This pH-dependent description is consistent with cyanobacterial physiology. Furthermore, the model predicts that alkaline cytosolic pH reduces the energetic cost of the CCM, consistent with pH measurements of photosynthesizing cyanobacteria.
NK cells activated by Interleukin-4 in cooperation with Interleukin-15 exhibit distinctive characteristics
Authors: Kiniwa Tsuyoshi , Enomoto Yutaka , Terazawa Natsumi , Omi Ai , Miyata Naoko , Ishiwata Kenji , Miyajima Atsushi
Published: August 2016

Significance

Natural killer (NK) cells are well known to serve as effecter cells in Th1-type immune responses, whereas their roles in Th2-type immune responses are largely unknown. In this study, we describe a previously unidentified pathway wherein IL-4, an initiator cytokine of Th2-type immune responses, induces development of highly activated murine NK cells in vivo. We show that IL-4 overexpression remarkably increases tissue-resident macrophages, which contributes to NK-cell proliferation via production of IL-15. The NK cells induced by IL-4 secrete a large amount of IFN-γ in response to IL-12, an initiator cytokine of Th1-type immune responses, and also exhibit high cytotoxicity against tumor cells. These results reveal the novel role of IL-4 in immune responses through the induction of unique NK cells.
Self-regulation via neural simulation
Authors: Gilead Michael , Boccagno Chelsea , Silverman Melanie , Hassin Ran R. , Weber Jochen , Ochsner Kevin N.
Published: August 2016

Significance

As Harper Lee tells us in
To Kill a Mockingbird
, “You never really understand a person until you consider things from his point of view, until you climb in his skin and walk around in it.” Classic theories in social psychology argue that this purported process of social simulation provides the foundations for self-regulation. In light of this, we investigated the neural processes whereby humans may regulate their affective responses to an event by simulating the way others would respond to it. Our results suggest that during perspective-taking, behavioral and neural signatures of negative affect indeed mimic the presumed affective state of others. Furthermore, the anterior medial prefrontal cortex—a region implicated in mental state inference—may orchestrate this affective simulation process.