bluuebunny/crossref_metadata_2025 huggingface dataset:
First measurements of Dα spectrum produced by anisotropic fast ions in the gas dynamic trap
Authors: Lizunov A. , Anikeev A.
Published: November 2014

Angled injection of eight deuterium beams in gas dynamic trap (GDT) plasmas builds up the population of fast ions with the distribution function, which conserves a high degree of initial anisotropy in space, energy, and pitch angle. Unlike the Maxwellian distribution case, the fast ion plasma component in GDT cannot be exhaustively characterized by the temperature and density. The instrumentation complex to study of fast ions is comprised of motional Stark effect diagnostic, analyzers of charge exchange atoms, and others. The set of numerical codes using for equilibrium modeling is also an important tool of analysis. In the recent campaign of summer 2014, we recorded first signals from the new fast ion D-alpha diagnostic on GDT. This paper presents the diagnostic description and results of pilot measurements. The diagnostic has four lines of sight, distributed across the radius of an axially symmetric plasma column in GDT. In the present setup, a line-integrated optical signal is measured in each channel. In the transverse direction, the spatial resolution is 18 mm. Collected light comes to the grating spectrometer with the low-noise detector based on a charge-coupled device matrix. In the regime of four spectra stacked vertically on the sensor, the effective spectral resolution of measurements is approximately 0.015 nm. Exposure timing is provided by the fast optical ferroelectric crystal shutter, allowing frames of duration down to 70 μs. This number represents the time resolution of measurements. A large dynamic range of the camera permits for a measurement of relatively small light signals produced by fast ions on top of the bright background emission from the bulk plasma. The fast ion emission has a non-Gaussian spectrum featuring the characteristic width of approximately 4 nm, which can be separated from relatively narrow Gaussian lines of D-alpha and H-alpha coming from the plasma periphery, and diagnostic beam emission. The signal to noise ratio varies from approximately ten for the central channel to approximately five for the outermost channel. We used the special set of Monte Carlo codes to fit the measured spectra. The shape of model fit shows a good agreement with the experimental fast ion D-alpha spectrum.
Multidimensional reaction rate theory with anisotropic diffusion
Authors: Berezhkovskii Alexander M. , Szabo Attila , Greives Nicholas , Zhou Huan-Xiang
Published: November 2014

An analytical expression is derived for the rate constant that describes diffusive transitions between two deep wells of a multidimensional potential. The expression, in contrast to the Kramers-Langer formula for the rate constant, is valid even when the diffusion is highly anisotropic. Our approach is based on a variational principle for the reactive flux and uses a trial function for the splitting probability or commitor. The theoretical result is validated by Brownian dynamics simulations.
Certifying the quantumness of a generalized coherent control scenario
Authors: Scholak Torsten , Brumer Paul
Published: November 2014

We consider the role of quantum mechanics in a specific coherent control scenario, designing a “coherent control interferometer” as the essential tool that links coherent control to quantum fundamentals. Building upon this allows us to rigorously display the genuinely quantum nature of a generalized weak-field coherent control scenario (utilizing 1 vs. 2 photon excitation) via a Bell-CHSH test. Specifically, we propose an implementation of “quantum delayed-choice” in a bichromatic alkali atom photoionization experiment. The experimenter can choose between two complementary situations, which are characterized by a random photoelectron spin polarization with particle-like behavior on the one hand, and by spin controllability and wave-like nature on the other. Because these two choices are conditioned coherently on states of the driving fields, it becomes physically unknowable, prior to measurement, whether there is control over the spin or not.
Development of a microwave capacitive method for the spectroscopy of the complex permittivity
Authors: Jégou C. , Agnus G. , Maroutian T. , Pillard V. , Devolder T. , Crozat P. , Lecoeur P. , Aubert P.
Published: November 2014

We describe a vector network analyzer-based method to study the electromagnetic properties of nanoscale dielectrics at microwave frequencies (1 MHz–40 GHz). The complex permittivity spectrum of a given dielectric can be determined by placing it in a capacitor accessed on its both electrodes by coplanar waveguides. However, inherent propagation delays along the signal paths together with frequency-dependent effective surface of the capacitor at microwave frequencies can lead to significant distortion in the measured permittivity, which in turn can give rise to artificial frequency variations of the complex permittivity. We detail a fully analytical rigorous correction sequence with neither recourse to extrinsic loss mechanisms nor to arbitrary parasitic signal paths. We illustrate our method on 3 emblematic dielectrics: ferroelectric morphotropic lead zirconate titanate, its paraelectric pyrochlore counterpart, and strontium titanate. Permittivity spectra taken at various points along the hysteresis loop help shedding light onto the nature of the different dielectric energy loss mechanisms. Thanks to the analytical character of our method, we can discuss routes to extend it to higher frequencies and we can identify unambiguously the sources of potential artifacts.
Note: Theoretical study on the gas pressure dependence of x-ray yield in TE111 cavity based electron cyclotron resonance x-ray source
Authors: Selvakumaran T. S. , Sen Soubhadra , Baskaran R.
Published: November 2014

Adopting Langevin methodology, a pressure dependent frictional force term which represents the collisional effect is added to the Lorentz equation. The electrons are assumed to be starting from the uniformly distributed co-ordinates on the central plane. The trajectory of each electron is numerically simulated by solving the modified Lorentz equation for a given pressure. The Bremsstrahlung x-ray energy spectrum for each electron crossing the cavity wall boundary is obtained using the Duane-Hunt law. The total x-ray yield is estimated by adding the spectral contribution of each electron. The calculated yields are compared with the experimental results and a good agreement is found.
Communication: Estimating the initial biasing potential for λ-local-elevation umbrella-sampling (λ-LEUS) simulations via slow growth
Authors: Bieler Noah S. , Hünenberger Philippe H.
Published: November 2014

In a recent article [Bieler et al., J. Chem. Theory Comput. 10, 3006–3022 (2014)], we introduced a combination of the λ-dynamics (λD) approach for calculating alchemical free-energy differences and of the local-elevation umbrella-sampling (LEUS) memory-based biasing method to enhance the sampling along the alchemical coordinate. The combined scheme, referred to as λ-LEUS, was applied to the perturbation of hydroquinone to benzene in water as a test system, and found to represent an improvement over thermodynamic integration (TI) in terms of sampling efficiency at equivalent accuracy. However, the preoptimization of the biasing potential required in the λ-LEUS method requires “filling up” all the basins in the potential of mean force. This introduces a non-productive pre-sampling time that is system-dependent, and generally exceeds the corresponding equilibration time in a TI calculation. In this letter, a remedy is proposed to this problem, termed the slow growth memory guessing (SGMG) approach. Instead of initializing the biasing potential to zero at the start of the preoptimization, an approximate potential of mean force is estimated from a short slow growth calculation, and its negative used to construct the initial memory. Considering the same test system as in the preceding article, it is shown that of the application of SGMG in λ-LEUS permits to reduce the preoptimization time by about a factor of four.
Epitaxial thin film growth of LiH using a liquid-Li atomic template
Authors: Oguchi Hiroyuki , Ikeshoji Tamio , Ohsawa Takeo , Shiraki Susumu , Kuwano Hiroki , Orimo Shin-ichi , Hitosugi Taro
Published: November 2014

We report on the synthesis of lithium hydride (LiH) epitaxial thin films through the hydrogenation of a Li melt, forming abrupt LiH/MgO interface. Experimental and first-principles molecular dynamics studies reveal a comprehensive microscopic picture of the crystallization processes, which sheds light on the fundamental atomistic growth processes that have remained unknown in the vapor-liquid-solid method. We found that the periodic structure that formed, because of the liquid-Li atoms at the film/MgO-substrate interface, serves as an atomic template for the epitaxial growth of LiH crystals. In contrast, films grown on the Al2O3 substrates indicated polycrystalline films with a LiAlO2 secondary phase. These results and the proposed growth process provide insights into the preparation of other alkaline metal hydride thin films on oxides. Further, our investigations open the way to explore fundamental physics and chemistry of metal hydrides including possible phenomena that emerge at the heterointerfaces of metal hydrides.
Temperature-dependent nonlinear phonon behavior in high-density carbon nanotube thin films
Authors: Duzynska A. , Judek J. , Zdrojek M.
Published: November 2014

We report the temperature-dependent Raman spectra for high-density single-walled carbon nanotube thin films. We show that the position of the main Raman mode (G) softens as the temperature increases and is nonlinear in the range of 70–270 K. This effect is explained by optical phonon decay. In the linear regime, the first-order temperature coefficient (χT) equals −0.02 cm−1/K, which is lower than for any other carbon nanotubes. Importantly, we found that local laser-induced temperature change shows a nonlinear trend as a function of global temperature with a minimum at 270 K. Our results contribute to understand the thermal properties of carbon nanotube thin films that could be applied, for example, in photovoltaic or thermoelectric devices.
Enhanced spin-orbit torques in Pt/Co/Ta heterostructures
Authors: Woo Seonghoon , Mann Maxwell , Tan Aik Jun , Caretta Lucas , Beach Geoffrey S. D.
Published: November 2014

Spin-orbit torques (SOTs) are studied in perpendicularly magnetized ultrathin Co films sandwiched between two heavy metals, Pt and Ta. A significant enhancement of the Slonczewski-like torque is achieved by placing dissimilar metals with opposite spin Hall angles on opposite sides of the ferromagnet. SOTs were characterized through harmonic measurements and the contribution by the Ta overlayer was isolated by systematically varying its thickness. An effective spin Hall angle of up to 34% is observed, along with a sizable field-like torque that increases with increasing Ta layer thickness. Current-induced switching measurements reveal a corresponding increase in switching efficiency, suggesting that by engineering both interfaces in trilayer structures, the SOTs can be significantly improved.
Simulation of peeling-ballooning modes with pellet injection
Authors: Chen S. Y. , Huang J. , Sun T. T. , Wang Z. H. , Tang C. J.
Published: November 2014

The influence of pellet ablation on the evolution of peeling-ballooning (P-B) modes is studied with BOUT++ code. The atoms coming from pellet ablation can significantly reshape the plasma pressure profile, so the behaviors of P-B modes and edge localized mode (ELM) are modified dramatically. This paper shows that the energy loss associated with an ELM increases substantially over that without the pellet, if the pellet is deposited at the top of the pedestal. On the contrary, for pellet deposition in the middle of the pedestal region the ELM energy loss can be less.
How the “main condition” of phase stability can explain the effect of the velocity deviation of secondary electrons in DC-biased single-sided multipactors
Authors: Mostajeran M.
Published: November 2014

In this work, a “main condition” for phase stability has been employed to investigate the effects of the velocity deviation of the electrons in DC-biased single-sided multipactors (MPs). In a previous study [M. Mostajeran, Phys. Plasmas 21, 053108 (2014)], a stability equation was derived, where the secondary electron was assumed to have zero initial velocity and the phase deviation from the resonant phase was considered. In this work, both deviations in phase and velocity from the resonant condition are taken into account, assuming nonzero initial velocity for the secondary electrons. Using the main condition for stability, it is shown that MP discharge can rise in situations, where large velocity deviations from initial velocity and large phase deviations from resonant phase exist. This is contrary to what can be predicted on the basis of the “simple stability condition.” This result is further confirmed by numerical simulations.
Complete set of material constants of single domain (K, Na)(Nb, Ta)O3 single crystal and their orientation dependence
Authors: Zheng Limei , Li Shiyang , Sang Shijing , Wang Junjun , Huo Xiaoqing , Wang Rui , Yuan Zhongyuan , Cao Wenwu
Published: November 2014

A self-consistent complete set of dielectric, piezoelectric, and elastic constants for single domain Ta modified (K, Na)NbO3 (KNN) crystal was determined. This full set constant for single domain KNN-based crystals allowed the prediction of orientation dependence of the longitudinal dielectric, piezoelectric, elastic coefficients, and electromechanical coupling factors. The maximum piezoelectric and electromechanical properties were found to exist near [001]C. In addition, material constants of [001]C poled domain engineered single crystal with 4 mm symmetry were experimentally measured and compared with the calculated values. Based on this, extrinsic contribution to the piezoelectricity was estimated to be ∼20%.
Monitoring Si growth on Ag(111) with scanning tunneling microscopy reveals that silicene structure involves silver atoms
Authors: Prévot G. , Bernard R. , Cruguel H. , Borensztein Y.
Published: November 2014

Using scanning tunneling microscopy (STM), the elaboration of the so-called silicene layer on Ag(111) is monitored in real time during Si evaporation at different temperatures. It is shown that the growth of silicene is accompanied by the release of about 65% of the surface Ag atoms from the Si covered areas. We observe that Si islands develop on the Ag terraces and Si strips at the Ag step edges, progressively forming ordered (4×4), (13×13) R13.9°, and dotted phases. Meanwhile, displaced Ag atoms group to develop additional bare Ag terraces growing round the Si islands from the pristine Ag step edges. This indicates a strong interaction between Si and Ag atoms, with an important modification of the Ag substrate beneath the surface layer. This observation is in contradiction with the picture of a silicene layer weakly interacting with the unreconstructed Ag substrate, and strongly indicates that the structure of silicene on Ag(111) corresponds either to a Si-Ag surface alloy or to a Si plane covered with Ag atoms.
Field dependence of the magnetic structure of TbMn2O5
Authors: Chatterji T. , Brown P. J.
Published: November 2014

The evolution of the magnetic propagation vector of the magnetically ordered phases of TbMn2O5 has been studied as a function of magnetic field applied parallel to both [010] and [100] axes. The results have been used to construct (H, T) phase diagrams showing the regions of stability of the three distinct phases IC1, C, and IC2 known to exist in zero field. Application of magnetic field along [010] increases the stability range of the commensurate C phase at the expense of the two incommensurate phases IC1 and IC2, whereas applying the field along [100] has the opposite effect. The evolution with field of the magnetic structure of the C phase has been determined from the integrated intensities of sets of magnetic reflections measured with different field values. With the field along [010], there are no significant changes in structure in fields up to 6 T. Applying the field parallel to [100] leads to an apparently continuous increase in the z component of the propagation vector from 0.25 in zero field to ≈0.3 in 6 T. This change is accompanied by increasing ferromagnetic polarisation of the Tb sublattices. Polarised neutron measurements made on the fundamental reflections show that there is no significant ferromagnetic polarisation of any the Mn sublattices in fields of up to 6 T.
Zero-conductance resonances and spin polarizations in three-terminal rings in the presence of spin-orbit coupling
Authors: Zhai Li-Xue , Wang Yan , Liu Jian-Jun
Published: November 2014

Spin dependent transport in one-dimensional (1D) three-terminal rings is investigated in the presence of the Rashba spin-orbit coupling (RSOC). We focus on zero-conductance resonances and spin polarizations. For these purposes, the transmission functions are derived analytically. The total conductances are analyzed in the complex energy plane with a focus on the zero-pole structure characteristic of transmission (anti)resonances. The spin polarizations in symmetrically and asymmetrically coupled three-terminal rings are studied as a function of the incident electron energy. It is found that in the absence of the RSOC there are three kinds of conductance zeros. In the presence of the RSOC, the zeros of the first and the third kinds are lifted, while some of the second kind persist. The lifting of the conductance zeros is related to the breaking of the spin-reversal symmetry, and the lifted conductance zeros evolve into spin polarization zeros.
Heat generation in an elastic binder system with embedded discrete energetic particles due to high-frequency, periodic mechanical excitation
Authors: Mares J. O. , Miller J. K. , Gunduz I. E. , Rhoads J. F. , Son S. F.
Published: November 2014

High-frequency mechanical excitation can induce heating within energetic materials and may lead to advances in explosives detection and defeat. In order to examine the nature of this mechanically induced heating, samples of an elastic binder (Sylgard 184) were embedded with inert and energetic particles placed in a fixed spatial pattern and were subsequently excited with an ultrasonic transducer at discrete frequencies from 100 kHz to 20 MHz. The temperature and velocity responses of the sample surfaces suggest that heating due to frictional effects occurred near the particles at excitation frequencies near the transducer resonance of 215 kHz. An analytical solution involving a heat point source was used to estimate heating rates and temperatures at the particle locations in this frequency region. Heating located near the sample surface at frequencies near and above 1 MHz was attributed to viscoelastic effects related to the surface motion of the samples. At elevated excitation parameters near the transducer resonance frequency, embedded particles of ammonium perchlorate and cyclotetramethylene-tetranitramine were driven to chemical decomposition.
Thermoelectric transport properties of diamond-like Cu1−xFe1+xS2 tetrahedral compounds
Authors: Li Yulong , Zhang Tiansong , Qin Yuting , Day Tristan , Jeffrey Snyder G. , Shi Xun , Chen Lidong
Published: November 2014

Polycrystalline samples with the composition of Cu1−xFe1+xS2 (x = 0, 0.01, 0.03, 0.05, 0.1) were synthesized by a melting-annealing-sintering process. X-ray powder diffraction reveals all the samples are phase pure. The backscattered electron image and X-ray map indicate that all elements are distributed homogeneously in the matrix. The measurements of Hall coefficient, electrical conductivity, and Seebeck coefficient show that Fe is an effective n-type dopant in CuFeS2. The electron carrier concentration of Cu1−xFe1+xS2 is tuned within a wide range leading to optimized power factors. The lattice phonons are also strongly scattered by the substitution of Fe for Cu, leading to reduced thermal conductivity. We use Debye approximation to model the low temperature lattice thermal conductivity. It is found that the large strain field fluctuation introduced by the disordered Fe ions generates extra strong phonon scatterings for lowered lattice thermal conductivity.
Thermal transport behavior of polycrystalline graphene: A molecular dynamics study
Authors: Wu P. H. , Quek S. S. , Sha Z. D. , Dong Z. L. , Liu X. J. , Zhang G. , Pei Q. X. , Zhang Y. W.
Published: November 2014

The thermal transport behavior of polycrystalline graphene is studied using molecular dynamics simulations, with focus on the effects of grain size, tensile strain, and temperature on the thermal conductivity. All the simulation samples have the same overall dimensions of 30 × 30 nm with average grain sizes ranging from 2.5 to 12.5 nm. It is found that polycrystalline graphene exhibits a significant reduction in thermal conductivity compared to single-crystalline graphene, and the smaller the grain size is, the more the thermal conductivity drops. The thermal conductivity of polycrystalline graphene with average grain size of 2.5 nm is only about 20% of single-crystalline graphene. However, the thermal conductivity of polycrystalline graphene is less sensitive to both the applied strain and temperature than that of single-crystalline graphene. The underlying mechanisms for the differences in thermal behavior are examined and discussed. These findings are important for the thermal management of graphene-based devices.
Analysis of shockless dynamic compression data on solids to multi-megabar pressures: Application to tantalum
Authors: Davis Jean-Paul , Brown Justin L. , Knudson Marcus D. , Lemke Raymond W.
Published: November 2014

Magnetically-driven, planar shockless-compression experiments to multi-megabar pressures were performed on tantalum samples using a stripline target geometry. Free-surface velocity waveforms were measured in 15 cases; nine of these in a dual-sample configuration with two samples of different thicknesses on opposing electrodes, and six in a single-sample configuration with a bare electrode opposite the sample. Details are given on the application of inverse Lagrangian analysis (ILA) to these data, including potential sources of error. The most significant source of systematic error, particularly for single-sample experiments, was found to arise from the pulse-shape dependent free-surface reflected wave interactions with the deviatoric-stress response of tantalum. This could cause local, possibly temporary, unloading of material from a ramp compressed state, and thus multi-value response in wave speed that invalidates the free-surface to in-material velocity mapping step of ILA. By averaging all 15 data sets, a final result for the principal quasi-isentrope of tantalum in stress-strain was obtained to a peak longitudinal stress of 330 GPa with conservative uncertainty bounds of ±4.5% in stress. The result agrees well with a tabular equation of state developed at Los Alamos National Laboratory.
Contact-dependent performance variability of monolayer MoS2 field-effect transistors
Authors: Han Gyuchull , Yoon Youngki
Published: November 2014

Using self-consistent quantum transport simulations, we investigate the performance variability of monolayer molybdenum disulfide (MoS2) field-effect transistors (FETs) with various contact properties. Varying the Schottky barrier in MoS2 FETs affects the output characteristics more significantly than the transfer characteristics. If doped contacts are realized, the performance variation due to non-ideal contacts becomes negligible; otherwise, channel doping can effectively suppress the performance variability in metal-contact devices. Our scaling study also reveals that for sub-10-nm channels, doped-contact devices can be more robust in terms of switching, while metal-contact MoS2 FETs can undergo the smaller penalty in output conductance.
Cochlear bionic acoustic metamaterials
Authors: Ma Fuyin , Wu Jiu Hui , Huang Meng , Fu Gang , Bai Changan
Published: November 2014

A design of bionic acoustic metamaterial and acoustic functional devices was proposed by employing the mammalian cochlear as a prototype. First, combined with the experimental data in previous literatures, it is pointed out that the cochlear hair cells and stereocilia cluster are a kind of natural biological acoustic metamaterials with the negative stiffness characteristics. Then, to design the acoustic functional devices conveniently in engineering application, a simplified parametric helical structure was proposed to replace actual irregular cochlea for bionic design, and based on the computational results of such a bionic parametric helical structure, it is suggested that the overall cochlear is a local resonant system with the negative dynamic effective mass characteristics. There are many potential applications in the bandboard energy recovery device, cochlear implant, and acoustic black hole.
Recoverable degradation of blue InGaN-based light emitting diodes submitted to 3 MeV proton irradiation
Authors: De Santi C. , Meneghini M. , Trivellin N. , Gerardin S. , Bagatin M. , Paccagnella A. , Meneghesso G. , Zanoni E.
Published: November 2014

This paper reports on the degradation and recovery of two different series of commercially available InGaN-based blue light emitting diodes submitted to proton irradiation at 3 MeV and various fluences (1011, 1013, and 1014 p+/cm2). After irradiation, we detected (i) an increase in the series resistance, in the sub-turn-on current and in the ideality factor, (ii) a spatially uniform drop of the output optical power, proportional to fluence, and (iii) a reduction of the capacitance of the devices. These results suggest that irradiation induced the generation of non-radiative recombination centers near the active region. This hypothesis is further confirmed by the results of the recovery tests carried out at low temperature (150 °C).
Programming current density reduction for elevated-confined phase change memory with a self-aligned oxidation TiWOx heater
Authors: Yang Hongxin , Lee Hock Koon , Zhao Rong , Shi Luping , Chong Tow Chong
Published: November 2014

The high programming current density of phase change memory (PCM) is an obstacle for its scaling and high density chip development. In this paper, an elevated-confined PCM (e-PCM) with self-aligned oxidation heater was proposed to reduce the programming current density by increasing the Joule heat and reducing heat loss simultaneously. 200 nm diameter size e-PCM with self-aligned TiWOx heater was fabricated and tested. The RESET current is 350 μA with 100 ns pulse and the corresponding programming current density is 1.12 MA/cm2. The low current density indicates this structure as a promising candidate for high density PCM chip applications.
Measurement of the electrostatic edge effect in wurtzite GaN nanowires
Authors: Henning Alex , Klein Benjamin , Bertness Kris A. , Blanchard Paul T. , Sanford Norman A. , Rosenwaks Yossi
Published: November 2014

The electrostatic effect of the hexagonal corner on the electronic structure in wurtzite GaN nanowires (NWs) was directly measured using Kelvin probe force microscopy (KPFM). By correlating electrostatic simulations with the measured potential difference between the nanowire face and the hexagonal vertices, the surface state concentration and band bending of GaN NWs were estimated. The surface band bending is important for an efficient design of high electron mobility transistors and for opto-electronic devices based on GaN NWs. This methodology provides a way to extract NW parameters without making assumptions concerning the electron affinity. We are taking advantage of electrostatic modeling and the high precision that KPFM offers to circumvent a major source of uncertainty in determining the surface band bending.
Anisotropic magnetocaloric effect in TmAl2 single crystal
Authors: Patiño J. Caro , de Oliveira N. A. , von Ranke P. J.
Published: November 2014

In this paper, we theoretically discuss the anisotropic magnetocaloric effect in TmAl2 single crystal. To this end, we use a model Hamiltonian of interacting magnetic moments including an extra term to account for the crystal electric field. Our theoretical calculations are in a reasonable agreement with the available experimental data. Moreover, we predict the existence of an anomalous anisotropic magnetocaloric effect for some values of the applied magnetic field.
Phonon-assisted lasing in ZnO microwires at room temperature
Authors: Michalsky T. , Wille M. , Dietrich C. P. , Röder R. , Ronning C. , Schmidt-Grund R. , Grundmann M.
Published: November 2014

We report on room temperature phonon-assisted whispering gallery mode (WGM) lasing in ZnO microwires. For WGM laser action on the basis of the low gain phonon scattering process high quality resonators with sharp corners and smooth facets are prerequisite. Above the excitation threshold power PTh of typically 100 kW/cm2, the recombination of free excitons under emission of two longitudinal optical phonons provides sufficient gain to overcome all losses in the microresonator and to result in laser oscillation. This threshold behavior is accompanied by a distinct change of the far and near field emission patterns, revealing the WGM related nature of the lasing modes. The spectral evolution as well as the characteristic behavior of the integrated photoluminescence intensity versus the excitation power unambiguously proves laser operation. Polarization-resolved measurements show that the laser emission is linear polarized perpendicular to the microwire axis (TE).
Label-free density difference amplification-based cell sorting
Authors: Song Jihwan , Song Minsun , Kang Taewook , Kim Dongchoul , Lee Luke P.
Published: November 2014

The selective cell separation is a critical step in fundamental life sciences, translational medicine, biotechnology, and energy harvesting. Conventional cell separation methods are fluorescent activated cell sorting and magnetic-activated cell sorting based on fluorescent probes and magnetic particles on cell surfaces. Label-free cell separation methods such as Raman-activated cell sorting, electro-physiologically activated cell sorting, dielectric-activated cell sorting, or inertial microfluidic cell sorting are, however, limited when separating cells of the same kind or cells with similar sizes and dielectric properties, as well as similar electrophysiological phenotypes. Here we report a label-free density difference amplification-based cell sorting (dDACS) without using any external optical, magnetic, electrical forces, or fluidic activations. The conceptual microfluidic design consists of an inlet, hydraulic jump cavity, and multiple outlets. Incoming particles experience gravity, buoyancy, and drag forces in the separation chamber. The height and distance that each particle can reach in the chamber are different and depend on its density, thus allowing for the separation of particles into multiple outlets. The separation behavior of the particles, based on the ratio of the channel heights of the inlet and chamber and Reynolds number has been systematically studied. Numerical simulation reveals that the difference between the heights of only lighter particles with densities close to that of water increases with increasing the ratio of the channel heights, while decreasing Reynolds number can amplify the difference in the heights between the particles considered irrespective of their densities.
To go into hiding on camouflage meta-surfaces
Authors: Yang R. , Gao D. X. , Su H. , Wang Z. X. , Lei Z. Y. , Fan J. , Man M. Y.
Published: November 2014

Inspired by the natural phenomena that rough sea surfaces often mask the ship target when the wind comes big, or another case in point, vehicles can usually hide themselves in the mountains with dense vegetation. Here in this paper, we demonstrate a practical strategy of hiding by using gradient-index meta-surfaces based on the quasi-conformal transformation optics. Different from the prevalent choice of the invisible cloak to virtually extinguish an object that is wrapped inside, our approach aims to suppress the detectability of the target through creating diffuse reflections by proposing the camouflage meta-surface underneath. Our design, possessing a flat and slim profile with solely a few randomly distributed dielectrics on a metallic sheet, can readily offer the perfect cover to mask the hiding object adjacently above in a broad frequency range.
Negative differential transconductance in silicon quantum well metal-oxide-semiconductor field effect/bipolar hybrid transistors
Authors: Naquin Clint , Lee Mark , Edwards Hal , Mathur Guru , Chatterjee Tathagata , Maggio Ken
Published: November 2014

Introducing explicit quantum transport into Si transistors in a manner amenable to industrial fabrication has proven challenging. Hybrid field-effect/bipolar Si transistors fabricated on an industrial 45 nm process line are shown to demonstrate explicit quantum transport signatures. These transistors incorporate a lateral ion implantation-defined quantum well (QW) whose potential depth is controlled by a gate voltage (VG). Quantum transport in the form of negative differential transconductance (NDTC) is observed to temperatures >200 K. The NDTC is tied to a non-monotonic dependence of bipolar current gain on VG that reduces drain-source current through the QW. These devices establish the feasibility of exploiting quantum transport to transform the performance horizons of Si devices fabricated in an industrially scalable manner.
Ultraviolet random lasing from asymmetrically contacted MgZnO metal-semiconductor-metal device
Authors: Morshed Muhammad M. , Suja Mohammad , Zuo Zheng , Liu Jianlin
Published: November 2014

Nitrogen-doped Mg0.12Zn0.88O nanocrystalline thin film was grown on c-plane sapphire substrate. Asymmetric Ni/Au and Ti/Au Schottky contacts and symmetric Ni/Au contacts were deposited on the thin film to form metal-semiconductor-metal (MSM) laser devices. Current-voltage, photocurrent, and electroluminescence characterizations were performed. Evident random lasing with a threshold current of ∼36 mA is demonstrated only from the asymmetric MSM device. Random lasing peaks are mostly distributed between 340 and 360 nm and an output power of 15 nW is measured at 43 mA injection current. The electron affinity difference between the contact metal and Mg0.12Zn0.88O:N layer plays an important role for electron and hole injection and subsequent stimulated random lasing.
Current-modulated optical properties of vanadium dioxide thin films in the phase transition region
Authors: Zhang Shuyan , Kats Mikhail A. , Cui Yanjie , Zhou You , Yao Yu , Ramanathan Shriram , Capasso Federico
Published: November 2014

Vanadium dioxide (VO2) is a correlated electron material which undergoes an insulator-metal transition proximal to room temperature. The large change of optical properties across this phase transition is promising for tunable optical and optoelectronic devices especially at infrared frequencies. We demonstrate the ability to locally tune the optical properties on the micron scale through a simple design consisting of two electrodes patterned on a VO2 thin film. By current injection between the electrodes, a localized conducting path (metallic phase) can be formed within the insulating background. The width of the conducting path can be controlled by varying the applied current. Fourier transform infrared imaging shows that this current-modulated reflectance changes significantly over a distance on the order of the wavelength in the mid-infrared spectral range.
Domain engineering of physical vapor deposited two-dimensional materials
Authors: Alam Tarek , Wang Baoming , Pulavarthy Raghu , Haque M. A. , Muratore Christopher , Glavin Nicholas , Roy Ajit K. , Voevodin Andrey A.
Published: November 2014

Physical vapor deposited two-dimensional (2D) materials span larger areas compared to exfoliated flakes, but suffer from very small grain or domain sizes. In this letter, we fabricate freestanding molybdenum disulfide (MoS2) and amorphous boron nitride (BN) specimens to expose both surfaces. We performed in situ heating in a transmission electron microscope to observe the domain restructuring in real time. The freestanding MoS2 specimens showed up to 100× increase in domain size, while the amorphous BN transformed in to polycrystalline hexagonal BN (h-BN) at temperatures around 600 °C much lower than the 850–1000 °C range cited in the literature.
Size-dependent elastic properties of oxidized silicon nanorods
Authors: Ilinov Andrey , Kuronen Antti
Published: November 2014

In this work, we have simulated a three point bending test for Si nanorods of different sizes with an oxide coating of different thicknesses using molecular dynamics simulations and the finite element modeling (FEM). We tested nanorods with diameters from 6 to 16 nm, which had lengths from 31 to 62 nm. Our aim was to estimate how well the elastic properties of Si nanorods can be described using the classical continuum mechanics approach. The agreement between the MD simulations and the FEM calculations was consistent for the pristine Si nanorods of all sizes, whereas the oxidized Si nanorods with small length-to-diameter ratio had much smaller effective bending moduli values than predicted by FEM. Our assumption is that it is due to the significant decrease of the shear modulus in the oxide layer of the smallest nanorods. We had also introduced surface stresses into the FEM models and found that their influence on the bending properties is more important for partially oxidized nanorods.
Enhancing the orthorhombicity and antiferromagnetic-insulating state in epitaxial La0.67Ca0.33MnO3/NdGaO3(001) films by inserting a SmFeO3 buffer layer
Authors: Tan Xuelian , Gao Guanyin , Chen Pingfan , Xu Haoran , Zhi Bowen , Jin Feng , Chen Feng , Wu Wenbin
Published: November 2014

Structural and magnetotransport properties of epitaxial La0.67Ca0.33MnO3(30 nm)/NdGaO3(001) [LCMO/NGO(001)] films are tuned by inserting an insulating SmFeO3 (SFO) buffer layer at various thicknesses (t). All the layers and the NGO substrates have the same Pbnm symmetry with the octahedra tilting about the b-axis, but different orthorhombicity (d). We found that as t increases, the fully strained (≤15 nm) or partially relaxed (30–60 nm) SFO layers can produce different d in the upper LCMO films. Correspondingly, the induced antiferromagnetic-insulating (AFI) state in LCMO is greatly enhanced with TAFI shifted from ∼250 K for t ≤ 15 nm to ∼263 K for t = 30–60 nm. We also show that the strain relaxation for t ≥ 30 nm is remarkably anisotropic, with a stable lattice constant a as that of the NGO substrates but increasing b of both SFO and LCMO layers. This indicates the octahedral coupling across the interfaces, leaving the strain along the a-axis accommodated by the octahedral tilts, while along the b-axis most probably by the octahedral deformations. The AFI state in the LCMO layer could be ascribed to the enhanced orthorhombicity with cooperatively increased Jahn-Teller-like distortions and tilting of the MnO6 octahedra. The results strongly suggest that the interfacial octahedral coupling plays a crucial role in epitaxial growth and in tuning functionalities of the perovskite oxide films.
Direct imaging of thermally-activated grain-boundary diffusion in Cu/Co/IrMn/Pt exchange-bias structures using atom-probe tomography
Authors: Letellier F. , Lechevallier L. , Lardé R. , Le Breton J.-M. , Akmaldinov K. , Auffret S. , Dieny B. , Baltz V.
Published: November 2014

Magnetic devices are often subject to thermal processing steps, such as field cooling to set exchange bias and annealing to crystallize amorphous magnetic electrodes. These processing steps may result in interdiffusion and the subsequent deterioration of magnetic properties. In this study, we investigated thermally-activated diffusion in Cu/Co/IrMn/Pt exchange biased polycrystalline thin-film structures using atom probe tomography. Images taken after annealing at 400 °C for 60 min revealed Mn diffusion into Co grains at the Co/IrMn interface and along Pt grain boundaries for the IrMn/Pt stack, i.e., a Harrison type C regime. Annealing at 500 °C showed further Mn diffusion into Co grains. At the IrMn/Pt interface, annealing at 500 °C led to a type B behavior since Mn diffusion was detected both along Pt grain boundaries and also into Pt grains. The deterioration of the films' exchange bias properties upon annealing was correlated to the observed diffusion. In particular, the topmost Pt capping layer thickness turned out to be crucial since a faster deterioration of the exchange bias properties for thicker caps was observed. This is consistent with the idea that Pt acts as a getter for Mn, drawing Mn out of the IrMn layer.
Self-selection bipolar resistive switching phenomena observed in NbON/NbN bilayer for cross-bar array memory applications
Authors: Kim Hee-Dong , Yun Min Ju , Kim Tae Geun
Published: November 2014

In this letter, to integrate bipolar resistive switching cells into cross bar array (CBA) structure, we study one-selector (1S) and one-resistor (1R) behavior of a niobium oxynitride (NbON) and niobium nitride (NbN) bilayer for the applications of resistive random access memory (RRAM). In this structure, a NbN layer exhibits bipolar switching characteristics while a NbON layer acts as the selector. The NbN-based 1S1R devices within a single RRAM memory cell can be directly integrated into a CBA structure without the need of extra diodes; this can significantly reduce the fabrication complexity.
Enhanced field emission properties from aligned graphenes fabricated on micro-hole patterned stainless steel
Authors: Chen Jiangtao , Cui Linfan , Sun Dongfei , Yang Bingjun , Yang Juan , Yan Xingbin
Published: November 2014

The graphene emitters on micro-hole patterned stainless steel (SUS304) were prepared using electrophoresis method. The field emission property of three-dimensional graphene emitters was enhanced remarkably compared to that of graphene on flat substrates. The turn-on and threshold fields of the patterned emitter were, respectively, 4.8 and 5.6 V μm−1 lower than those of graphene on flat SUS304 (turn on field is 5.6 V μm−1). The micro-hole patterned cathode provides 10 times higher current density due to vertical aligned sharp edges of graphene in micro holes, and this design may open a potential way to layered-nanomertial-based cold cathodes.
Linking osmotic adjustment and stomatal characteristics with salinity stress tolerance in contrasting barley accessions
Authors: Zhu Min , Zhou Meixue , Shabala Lana , Shabala Sergey
Published: November 2014

Salinity tolerance is a complex trait – both physiologically and genetically – and the issue of which mechanism or trait has bigger contribution towards the overall plant performance is still hotly discussed in the literature. In this work, a broad range of barley (Hordeum vulgare L. and Hordeum spontaneum L.) genotypes contrasting in salinity stress tolerance were used to investigate the causal link between plant stomatal characteristics, tissue ion relations, and salinity tolerance. In total, 46 genotypes (including two wild barleys) were grown under glasshouse conditions and exposed to moderate salinity stress (200mM NaCl) for 5 weeks. The overall salinity tolerance correlated positively with stomata density, leaf K+ concentration and the relative contribution of inorganic ions towards osmotic adjustment in the shoot. At the same time, no correlation between salinity tolerance and stomatal conductance or leaf Na+ content in the shoot was found. Taken together, these results indicate the importance of increasing stomata density as an adaptive tool to optimise efficiency of CO2 assimilation under moderate saline conditions, as well as benefits of the predominant use of inorganic osmolytes for osmotic adjustment in barley. Another finding of note was that wild barleys showed rather different strategies dealing with salinity, as compared with cultivated varieties.
Modifying the Canadian Fine Fuel Moisture Code for masticated surface fuels
Authors: Schiks T. J. , Wotton B. M.
Published: November 2014

Mechanical mastication is a fuel management technique that disrupts the vertical continuity of forest fuels by shredding of trees and understory vegetation into a highly compacted surface fuel bed. Despite the increasing application of mastication to manage wildfire risk, there is little information to date on fuel moisture in masticated fuels and optimal ignition patterns for prescribed burning. We investigated the applicability of the Fine Fuel Moisture Code (FFMC), a component of the Canadian Fire Weather Index (FWI) System, in tracking the diurnal and day-to-day changes in masticated surface fuel moisture, and developed a calibration of the standard conversion between moisture content and FFMC via regression modelling. We also proposed several modifications to the FFMC model (including a solar radiation driven fuel temperature) to better estimate the fuel-specific parameters of small diameter (<1 cm) masticated surface fuels. Model validation was performed using destructive moisture content observations from a mastication treatment in west-central Alberta, Canada. A calibrated form of the moisture content to FFMC conversion produced mean error of –2.3% moisture content, and closely resembled previous FWI System calibrations for fast drying surface fuels. Our modified FFMC-based model fit well with field observations, and was capable of producing mean error of 1.0% moisture content. The fast drying that we observed highlights the need to better understand moisture dynamics of masticated fuel beds.
Enhanced activation of an amino-terminally truncated isoform of the voltage-gated proton channel HVCN1 enriched in malignant B cells
Authors: Hondares Elayne , Brown Mark Adrian , Musset Boris , Morgan Deri , Cherny Vladimir V. , Taubert Christina , Bhamrah Mandeep K. , Coe David , Marelli-Berg Federica , Gribben John G. , Dyer Martin J. S. , DeCoursey Thomas E. , Capasso Melania
Published: November 2014

Significance

B lymphocytes are crucial cells in immune responses. Their activity is regulated by signaling pathways involving reactive oxygen species (ROS). Voltage-gated proton channels modulate B-cell responses by facilitating production of ROS. Here we compare the full-length proton channel HVCN1
L
with a shorter protein isoform, HVCN1
S
, which lacks the first 20 amino acids. Cells with HVCN1
S
display enhanced proton currents upon stimulation. In addition, HVCN1
S
is internalized to a lesser extent by interactions with the B-cell receptor, resulting in greater plasma membrane expression. Finally, HVCN1
S
expression results in greater proliferation and migration. Compared with normal B lymphocytes, HVCN1
S
expression is higher in B-cell lines and in B cells from patients with chronic lymphocytic leukemia, where it may contribute to disease pathogenesis.
SNF2 chromatin remodeler-family proteins FRG1 and -2 are required for RNA-directed DNA methylation
Authors: Groth Martin , Stroud Hume , Feng Suhua , Greenberg Maxim V. C. , Vashisht Ajay A. , Wohlschlegel James A. , Jacobsen Steven E. , Ausin Israel
Published: November 2014

Significance

RNA-directed DNA methylation (RdDM) has traditionally been associated with transposable elements, but more recent studies have shown that RdDM also targets regulatory regions of protein-coding genes. Moreover, DNA methylation in
Arabidopsis
appears to be more dynamic than previously believed and may correlate with transcriptional responses to environmental stresses, such as pathogens. Therefore, the identification and characterization of RdDM mechanisms is fundamental to our understanding of how biological traits are controlled at an epigenetic level. We have performed a screen based on available coexpression data and identified two previously uncharacterized genes,
FRG1
and -
2
, involved in RdDM. This work also shows the validity of coexpression data as an approach to assign new gene functions for RdDM.