bluuebunny/crossref_metadata_2025 huggingface dataset:
Understanding the large solubility of lidocaine in 1-n-butyl-3-methylimidazolium based ionic liquids using molecular simulation
Authors: Ley Ryan T. , Paluch Andrew S.
Published: February 2016

Room temperature ionic liquids have been proposed as replacement solvents in a wide range of industrial separation processes. Here, we focus on the use of ionic liquids as solvents for the pharmaceutical compound lidocaine. We show that the solubility of lidocaine in seven common 1-n-butyl-3-methylimidazolium based ionic liquids is greatly enhanced relative to water. The predicted solubility is greatest in [BMIM]+[CH3CO2]−, which we find results from favorable hydrogen bonding between the lidocaine amine hydrogen and the [CH3CO2]− oxygen, favorable electrostatic interactions between the lidocaine amide oxygen with the [BMIM]+ aromatic ring hydrogens, while lidocaine does not interfere with the association of [BMIM]+ with [CH3CO2]−. Additionally, by removing functional groups from the lidocaine scaffold while maintaining the important amide group, we found that as the van der Waals volume increases, solubility in [BMIM]+[CH3CO2]− relative to water increases.
A weak-Lp Prodi-Serrin type regularity criterion for the micropolar fluid equations
Authors: Loayza Miguel , Rojas-Medar Marko A.
Published: February 2016

We investigate regularity criteria for weak solutions of the micropolar fluid equations in a bounded three-dimensional domain. We show that the solution (u, w) is strong on [0, T] if either u ∈ Ls(0, T; Lr,∞(Ω)) or ‖u‖Ls,∞(0,T;Lr,∞(Ω)) is bounded from above by a specific constant, where (3/r) + (2/s) = 1 and r > 3.
Digital synthetic impedance for application in vibration damping
Authors: Nečásek J. , Václavík J. , Marton P.
Published: February 2016

In this work we present construction details of a precision, standalone, and compact digital synthetic impedance for application in the field of vibration damping. The presented device is based on an embedded ARM microcontroller with external AD and DA converters and a special analog front-end. The performance of the device is tested by comparing the actually synthesized impedance with several prescribed impedances and shows very good match. Fine-tuning ability of the device, which is crucial for the considered application, is also demonstrated and reaches as small step as 0.1% for the most complicated impedance structure and drops below the level of direct measurability with less complex structures. The real application in vibration damping is demonstrated on a simple and well understood case of a one-dimensional vibrating spring-mass system with piezoelectric actuator embedded as the interface between source of vibrations and vibrating mass.
Breadth versus depth: Interactions that stabilize particle assemblies to changes in density or temperature
Authors: Piñeros William D. , Baldea Michael , Truskett Thomas M.
Published: February 2016

We use inverse methods of statistical mechanics to explore trade-offs associated with designing interactions to stabilize self-assembled structures against changes in density or temperature. Specifically, we find isotropic, convex-repulsive pair potentials that maximize the density range for which a two-dimensional square lattice is the stable ground state subject to a constraint on the chemical potential advantage it exhibits over competing structures (i.e., “depth” of the associated minimum on the chemical potential hypersurface). We formulate the design problem as a nonlinear program, which we solve numerically. This allows us to efficiently find optimized interactions for a wide range of possible chemical potential constraints. We find that assemblies designed to exhibit a large chemical potential advantage at a specified density have a smaller overall range of densities for which they are stable. This trend can be understood by considering the separation-dependent features of the pair potential and its gradient required to enhance the stability of the target structure relative to competitors. Using molecular dynamics simulations, we further show that potentials designed with larger chemical potential advantages exhibit higher melting temperatures.
The motion induced between a rotating plate and a radially stretching or shrinking plate
Authors: Weidman Patrick D. , Perocco Enrico L. M.
Published: February 2016

The flow induced between parallel plates separated by a distance h executing different types of in-plane motion is investigated. The upper plate radially stretches at strain rate a and the lower plate rotates at angular velocity Ω about a common axis. A similarity solution form reduces the Navier-Stokes equations to a coupled pair of ordinary differential equations in two parameters: R = |a| h2/ν and σ = Ω/|a|, where ν is the kinematic viscosity of the fluid. Solutions are obtained for both stretching and shrinking upper plates and numerical results for pressure gradient and wall shear stress parameters are found and compared with low-R series solutions and large-R asymptotic behaviors. Sample radial and azimuthal velocity profiles reveal regions of zero radial and azimuthal wall shear stress which are studied in detail. This work represents the first study of the flow induced between parallel plates for which each plate executes a different type of in-plane motion.
Hilbert space renormalization for the many-electron problem
Authors: Li Zhendong , Chan Garnet Kin-Lic
Published: February 2016

Renormalization is a powerful concept in the many-body problem. Inspired by the highly successful density matrix renormalization group (DMRG) algorithm, and the quantum chemical graphical representation of configuration space, we introduce a new theoretical tool: Hilbert space renormalization, to describe many-electron correlations. While in DMRG, the many-body states in nested Fock subspaces are successively renormalized, in Hilbert space renormalization, many-body states in nested Hilbert subspaces undergo renormalization. This provides a new way to classify and combine configurations. The underlying wavefunction Ansatz, namely, the Hilbert space matrix product state (HS-MPS), has a very rich and flexible mathematical structure. It provides low-rank tensor approximations to any configuration interaction (CI) space through restricting either the “physical indices” or the coupling rules in the HS-MPS. Alternatively, simply truncating the “virtual dimension” of the HS-MPS leads to a family of size-extensive wave function Ansätze that can be used efficiently in variational calculations. We make formal and numerical comparisons between the HS-MPS, the traditional Fock-space MPS used in DMRG, and traditional CI approximations. The analysis and results shed light on fundamental aspects of the efficient representation of many-electron wavefunctions through the renormalization of many-body states.
Electrostatic energy barriers from dielectric membranes upon approach of translocating DNA molecules
Authors: Buyukdagli Sahin , Ala-Nissila T.
Published: February 2016

We probe the electrostatic cost associated with the approach phase of DNA translocation events. Within an analytical theory at the Debye-Hückel level, we calculate the electrostatic energy of a rigid DNA molecule interacting with a dielectric membrane. For carbon or silicon based low permittivity neutral membranes, the DNA molecule experiences a repulsive energy barrier between 10 kBT and 100 kBT. In the case of engineered membranes with high dielectric permittivities, the membrane surface attracts the DNA with an energy of the same magnitude. Both the repulsive and attractive interactions result from image-charge effects and their magnitude survive even for the thinnest graphene-based membranes of size d ≈ 6 Å. For weakly charged membranes, the electrostatic energy is always attractive at large separation distances but switches to repulsive close to the membrane surface. We also characterise the polymer length dependence of the interaction energy. For specific values of the membrane charge density, low permittivity membranes repel short polymers but attract long polymers. Our results can be used to control the strong electrostatic energy of DNA-membrane interactions prior to translocation events by chemical engineering of the relevant system parameters.
Direct numerical simulation of transitional flow in a staggered tube bundle
Authors: Linton D. , Thornber B.
Published: February 2016

A series of Direct Numerical Simulations (DNS) of the flow through a staggered tube bundle has been performed over the range 1030 ≤ Rem ≤ 5572 to capture the flow transition that occurs at the matrix transition point of Rem ≈ 3000. The matrix transition is the point at which a second frequency becomes prominent in tube bundles. To date, this is the highest published Reynolds number at which a DNS has been performed on cross-flow over a tube bundle. This study describes the flow behaviour in terms of: the mean flow field, Strouhal numbers, vortex shedding, 3-D flow features, and turbulence properties. These results support the hypothesis that the transition in the vortex shedding behaviour at Rem ≈ 3000 is similar to that which occurs in single cylinder flow at the equivalent Reynolds number. The visualisations presented also demonstrate the nature of the shedding mechanisms before and after the matrix transition point.
High pressure structural, electronic, and optical properties of polymorphic InVO4 phases
Authors: Mondal S. , Appalakondaiah S. , Vaitheeswaran G.
Published: February 2016

In the present work, we report a detailed density functional theory calculation on polymorphic InVO4 phases by means of projector augmented wave method. The computed first-order structural phase transformation from orthorhombic (Cmcm) to monoclinic (P2/c) structure is found to occur around 5.6 GPa along with a large volume collapse of 16.6%, which is consistent with previously reported experimental data. This transformation also leads to an increase in the coordination number of vanadium atom from 4 to 6. The computed equilibrium and high pressure structural properties of both InVO4 phases, including unit cell parameters, equation of state, and bulk moduli, are in good agreement with the available experimental data. In addition, compressibility is found to be highly anisotropic and the b-axis being more compressible than the other for both the structures. Electronic band structures for both the phases were calculated, and the band gaps for orthorhombic and monoclinic InVO4 are found to be 4.02 and 1.67 eV, respectively, within the Tran-Blaha Modified Becke-Johnson potential as implemented in linearized augmented planewave method. We further examined the optical properties such as dielectric function, refractive index, and absorption spectra for both the structures. From the implications of these results, it can be proposed that the high pressure InVO4 phase can be more useful than orthorhombic phase for photo catalytic applications.
Asymptotic behavior and interpretation of virtual states: The effects of confinement and of basis sets
Authors: Boffi Nicholas M. , Jain Manish , Natan Amir
Published: February 2016

A real-space high order finite difference method is used to analyze the effect of spherical domain size on the Hartree-Fock (and density functional theory) virtual eigenstates. We show the domain size dependence of both positive and negative virtual eigenvalues of the Hartree-Fock equations for small molecules. We demonstrate that positive states behave like a particle in spherical well and show how they approach zero. For the negative eigenstates, we show that large domains are needed to get the correct eigenvalues. We compare our results to those of Gaussian basis sets and draw some conclusions for real-space, basis-sets, and plane-waves calculations.
Equation of state and critical point behavior of hard-core double-Yukawa fluids
Authors: Montes J. , Robles M. , López de Haro M.
Published: February 2016

A theoretical study on the equation of state and the critical point behavior of hard-core double-Yukawa fluids is presented. Thermodynamic perturbation theory, restricted to first order in the inverse temperature and having the hard-sphere fluid as the reference system, is used to derive a relatively simple analytical equation of state of hard-core multi-Yukawa fluids. Using such an equation of state, the compressibility factor and phase behavior of six representative hard-core double-Yukawa fluids are examined and compared with available simulation results. The effect of varying the parameters of the hard-core double-Yukawa intermolecular potential on the location of the critical point is also analyzed using different perspectives. The relevance of this analysis for fluids whose molecules interact with realistic potentials is also pointed out.
Electron mean free path in elemental metals
Authors: Gall Daniel
Published: February 2016

The electron mean free path λ and carrier relaxation time τ of the twenty most conductive elemental metals are determined by numerical integration over the Fermi surface obtained from first-principles, using constant λ or τ approximations and wave-vector dependent Fermi velocities vf (k). The average vf deviates considerably from the free-electron prediction, even for elements with spherical Fermi surfaces including Cu (29% deviation). The calculated product of the bulk resistivity times λ indicates that, in the limit of narrow wires, Rh, Ir, and Ni are 2.1, 1.8, and 1.6 times more conductive than Cu, while various metals including Mo, Co, and Ru approximately match the Cu resistivity, suggesting that these metals are promising candidates to replace Cu for narrow interconnect lines.
Contact resistances in trigate and FinFET devices in a non-equilibrium Green's functions approach
Authors: Bourdet Léo , Li Jing , Pelloux-Prayer Johan , Triozon François , Cassé Mikaël , Barraud Sylvain , Martinie Sébastien , Rideau Denis , Niquet Yann-Michel
Published: February 2016

We compute the contact resistances Rc in trigate and FinFET devices with widths and heights in the 4–24 nm range using a Non-Equilibrium Green's Functions approach. Electron-phonon, surface roughness, and Coulomb scattering are taken into account. We show that Rc represents a significant part of the total resistance of devices with sub-30 nm gate lengths. The analysis of the quasi-Fermi level profile reveals that the spacers between the heavily doped source/drain and the gate are major contributors to the contact resistance. The conductance is indeed limited by the poor electrostatic control over the carrier density under the spacers. We then disentangle the ballistic and diffusive components of Rc and analyze the impact of different design parameters (cross section and doping profile in the contacts) on the electrical performances of the devices. The contact resistance and variability rapidly increase when the cross sectional area of the channel goes below ≃50 nm2. We also highlight the role of the charges trapped at the interface between silicon and the spacer material.
Intra-cavity photon-assisted tunneling collector-base voltage-mediated electron-hole spontaneous-stimulated recombination transistor laser
Authors: Feng M. , Qiu Junyi , Wang C. Y. , Holonyak N.
Published: February 2016

Optical absorption in a p-n junction diode for a direct-gap semiconductor can be enhanced by photon-assisted tunneling in the presence of a static or dynamic electrical field. In the transistor laser, the coherent photons generated at the base quantum-well interact with the collector field and “assist” optical cavity electron tunneling from the valence band of the base to the conduction band states of the collector. In the present work, we study the cavity coherent photon intensity effect on intra-cavity photon-assisted tunneling (ICPAT) in the transistor laser and realize photon-field enhanced optical absorption. This ICPAT in a transistor laser is the unique property of voltage (field) modulation and the basis for ultrahigh speed direct laser modulation and switching.
Initial result of confinement of weakly magnetized lithium ion plasmas in a harmonic potential well of the beam experiment upgrade linear trap
Authors: Kawai S. , Himura H. , Masamune S. , Aoki J.
Published: February 2016

This paper presents the initial results of the confinement of weakly magnetized pure lithium ion (Li+) plasmas. Time evolutions of two-dimensional images are successfully investigated for the first time, using an end-on fluorescent screen attached to a micro-channel plate. Simultaneously, the total particle numbers of the Li+ plasmas are obtained from the secondary electron current. Despite the formed Li+ plasma being “kinetic” and the ion density being on the order of the Brillouin density limit, the image on the screen is not disrupted. The confinement occurs over a period of ≈9 s, which is likely to be limited by the conventional diffusion process.
High-resolution simulations of non-Boussinesq downslope gravity currents in the acceleration phase
Authors: Dai Albert , Huang Yu-lin
Published: February 2016

Gravity currents generated from an instantaneous buoyancy source of density contrast in the density ratio range of 0.3 ≤ γ ≤ 0.998 propagating downslope in the slope angle range of 0° ≤ θ < 90° have been investigated in the acceleration phase by means of high-resolution two-dimensional simulations of the incompressible variable-density Navier-Stokes equations. For all density contrasts considered in this study, front velocity history shows that, after the heavy fluid is released from rest, the gravity currents go through the acceleration phase, reaching a maximum front velocity Uf,max, followed by the deceleration phase. It is found that Uf,max increases as the density contrast increases and such a relationship is, for the first time, quantitatively described by the improved thermal theory considering the non-Boussinesq effects. Energy budgets show that, as the density contrast increases, the heavy fluid retains more fraction of potential energy loss while the ambient fluid receives less fraction of potential energy loss in the process of energy transfer during the propagation of downslope gravity currents. Previously, it was reported that for the Boussinesq case, the downslope gravity currents have a maximum of Uf,max at θ ≈ 40°. It is found, as is also confirmed by the energy budgets in this study, that the slope angle at which the downslope gravity currents have a maximum of Uf,max may increase beyond 40° as the density contrast increases.
Study of matrix crack-tilted fiber bundle interaction using caustics and finite element method
Authors: Hao Wenfeng , Zhu Jianguo , Zhu Qi , Yuan Yanan
Published: February 2016

In this work, the interaction between the matrix crack and a tilted fiber bundle was investigated via caustics and the finite element method (FEM). First, the caustic patterns at the crack tip with different distances from the tilted fiber were obtained and the stress intensity factors were extracted from the geometry of the caustic patterns. Subsequently, the shielding effect of the fiber bundle in front of the crack tip was analyzed. Furthermore, the interaction between the matrix crack and the broken fiber bundle was discussed. Finally, a finite element simulation was carried out using ABAQUS to verify the experimental results. The results demonstrate that the stress intensity factors extracted from caustic experiments are in excellent agreement with the data calculated by FEM.
BaSnO3 as a channel material in perovskite oxide heterostructures
Authors: Krishnaswamy Karthik , Bjaalie Lars , Himmetoglu Burak , Janotti Anderson , Gordon Luke , Van de Walle Chris G.
Published: February 2016

BaSnO3 (BSO) is a transparent perovskite oxide with high room-temperature mobility, a property that is highly desirable for a channel material in transistors. However, its low density of states (DOS) makes it challenging to confine a high-density two-dimensional electron gas (2DEG). Using hybrid density functional theory, we calculate the band structure of BSO, its DOS, and its band offsets with candidate barrier materials, such as SrTiO3 (STO), LaInO3, and KTaO3. With the calculated material parameters as input, Schrödinger-Poisson simulations are then performed on BSO heterostructures to quantitatively address the issue of 2DEG confinement. The BSO/STO interface with a conduction-band offset of 1.14 eV limits the 2DEG density confined within BSO to 8×1013 cm−2. Strategies to improve the confinement via band-offset engineering are discussed.
Surface- and strain-tuning of the optical dielectric function in epitaxially grown CaMnO3
Authors: Imbrenda Dominic , Yang Dongyue , Wang Hongwei , Akbashev Andrew R. , Kasaei Leila , Davidson Bruce A. , Wu Xifan , Xi Xiaoxing , Spanier Jonathan E.
Published: February 2016

We report a strong thickness dependence of the complex frequency-dependent optical dielectric function ϵ̃(ω) over a spectral range from 1.24 to 5 eV in epitaxial CaMnO3(001) thin films on SrTiO3(001), LaAlO3(001), and SrLaAlO4(001). A doubling of the peak value of the imaginary part of ϵ̃(ω) and spectral shifts of 0.5 eV for a given magnitude of absorption are observed. On the basis of experimental analyses and first-principles density functional theory calculations, contributions from both surface states and epitaxial strain to the optical dielectric function of CaMnO3 are seen. Its evolution with thickness from 4 to 63 nm has several regimes. In the thinnest, strain-coherent films, the response is characterized by a significant contribution from the free surface that dominates strain effects. However, at intermediate and larger thicknesses approaching the bulk-like film, strain coherence and partial strain relaxation coexist and influence ϵ̃(ω).
Optimisation of simulations of stochastic processes by removal of opposing reactions
Authors: Spill Fabian , Maini Philip K. , Byrne Helen M.
Published: February 2016

Models invoking the chemical master equation are used in many areas of science, and, hence, their simulation is of interest to many researchers. The complexity of the problems at hand often requires considerable computational power, so a large number of algorithms have been developed to speed up simulations. However, a drawback of many of these algorithms is that their implementation is more complicated than, for instance, the Gillespie algorithm, which is widely used to simulate the chemical master equation, and can be implemented with a few lines of code. Here, we present an algorithm which does not modify the way in which the master equation is solved, but instead modifies the transition rates. It works for all models in which reversible reactions occur by replacing such reversible reactions with effective net reactions. Examples of such systems include reaction-diffusion systems, in which diffusion is modelled by a random walk. The random movement of particles between neighbouring sites is then replaced with a net random flux. Furthermore, as we modify the transition rates of the model, rather than its implementation on a computer, our method can be combined with existing algorithms that were designed to speed up simulations of the stochastic master equation. By focusing on some specific models, we show how our algorithm can significantly speed up model simulations while maintaining essential features of the original model.
Multifractal scaling and intermittency in hybrid Vlasov-Maxwell simulations of plasma turbulence
Authors: Leonardis E. , Sorriso-Valvo L. , Valentini F. , Servidio S. , Carbone F. , Veltri P.
Published: February 2016

By employing Hybrid Vlasov-Maxwell simulations in 2D-3V phase space configuration (2D in physical space and 3D in velocity space) of plasma turbulence, the statistical properties of the energy cascade at kinetic scales have been investigated. High-order moments of the magnetic field fluctuations have been inspected in order to quantify the intermittency phenomenon. At scales l larger than the ion skin depth di, fluctuations exhibit anomalous scaling, suggesting the presence of a multifractal intermittent turbulent cascade. For l<di, fluctuations show monoscaling, indicating Gaussian statistics. This scenario is consistent with the statistics of the dissipation fields J·E and J2, suggesting that the processes of dissipation, intended as a conversion of energy from electromagnetic fluctuations to electron Ohmic heating and non-thermal proton effects, occur non-homogeneously in space.
Interplay between toroidal rotation and flow shear in turbulence stabilisation
Authors: Camenen Y. , Casson F. J. , Manas P. , Peeters A. G.
Published: February 2016

The interplay between toroidal rotation u, parallel flow shear u′, and perpendicular flow shear γE in the stabilisation of tokamak turbulence is investigated in non-linear flux-tube gyrokinetic simulations. The simulations are performed for a reference L-mode DIII-D plasma (the so-called shortfall case) at r/a=0.8, varying the flow parameters around their nominal values. Depending on the respective signs of u, u′, and γE, turbulence is found to be enhanced, reduced, or unchanged. When the coupling is favorable, the overall effect on the non-linear heat fluxes can be very large, even at moderate flow values. The ion heat flux is, for instance, decreased by a factor of 3 when the direction of the parallel flow shear is reversed with respect to its nominal value. Even more surprising, keeping u′ and γE at their nominal values, the ion heat flux decreases by more than 50% when the toroidal flow is reversed. The relevance of this mechanism in the experiments which depends on the ability to decouple u, u′, and γE is discussed. The interplay between u and u′ observed in the non-linear simulations qualitatively follows the linear stability results and is interpreted in the frame of a simple fluid model.
Sound transmission properties assisted by the phase resonances of composite acoustic gratings
Authors: Zhang Hui , Fan Li , Qu Jianmin , Zhang Shuyi
Published: February 2016

We investigated composite gratings for their sound transmission properties induced by phase resonances. Each periodic unit of the composite grating consisted of a rectangular slit and a triangular slit. The triangular slit showed special properties in generating enhanced phase resonance and in restraining sound transmission. By adjusting the triangular slit's opening, we could regulate the frequency and sound transmission at phase resonance. These features of the composite grating can be used in designing acoustic filters for sound reduction.
Arbitrary-order Jordan chains associated with quantum-mechanical Hamiltonians: Representations and integral formulas
Authors: Schulze-Halberg Axel
Published: February 2016

We consider Jordan chains of arbitrary order that are associated with quantum-mechanical Hamiltonians. An explicit formula for the connection between integral and differential representations of the Jordan chains is given. As a byproduct, we obtain a method that allows to resolve certain multiple integrals of special functions.
Experimental realization of the Ehrenberg-Siday thought experiment
Authors: Pozzi Giulio , Boothroyd Chris B. , Tavabi Amir H. , Yücelen Emrah , Dunin-Borkowski Rafal E. , Frabboni Stefano , Gazzadi Gian Carlo
Published: February 2016

In 1949, at the end of a paper dedicated to the concept of the refractive index in electron optics, Ehrenberg and Siday noted that wave-optical effects will arise from an isolated magnetic field even when the rays themselves travel in magnetic-field-free space. They proposed a two-slit experiment, in which a magnetic flux is enclosed between interfering electron beams. Now, through access to modern nanotechnology tools, we used a focused ion beam to open two nanosized slits in a gold-coated silicon nitride membrane and focused electron beam induced deposition to fabricate a thin magnetic bar between the two slits. We then performed Fraunhofer experiments in a transmission electron microscope equipped with a field emission gun and a Lorentz lens. By tilting the specimen in the objective lens field of the electron microscope, the magnetization of the bar could be reversed and the corresponding change in the phase of the electron wave observed directly in the form of a shift in the interference fringe pattern.
Disappearance and revival of squeezing in quantum communication with squeezed state over a noisy channel
Authors: Deng Xiaowei , Hao Shuhong , Tian Caixing , Su Xiaolong , Xie Changde , Peng Kunchi
Published: February 2016

Squeezed state can increase the signal-to-noise ratio in quantum communication and quantum measurement. However, losses and noises existing in real communication channels will reduce or even totally destroy the squeezing. The phenomenon of disappearance of the squeezing will result in the failure of quantum communication. In this letter, we present the experimental demonstrations on the disappearance and revival of the squeezing in quantum communication with squeezed state. The experimental results show that the squeezed light is robust (squeezing never disappears) in a pure lossy but noiseless channel. While in a noisy channel, the excess noise will lead to the disappearance of the squeezing, and the squeezing can be revived by the use of a correlated noisy channel (non-Markovian environment). The channel capacity of quantum communication is increased after the squeezing is revived. The presented results provide useful technical references for quantum communication with squeezed light.
Unbiased diffusion in two-dimensional channels with corrugated walls
Authors: Verdel Roberto , Dagdug Leonardo , Berezhkovskii Alexander M. , Bezrukov Sergey M.
Published: February 2016

This paper deals with diffusion of point particles in linearly corrugated two-dimensional channels. Such geometry allows one to obtain an approximate analytical expression that gives the particle effective diffusivity as a function of the geometric parameters of the channel. To establish its accuracy and the range of applicability, the expression is tested against Brownian dynamics simulation results. The test shows that the expression works very well for long channel periods, but fails when the period is not long enough compared to the minimum width of the channel. To fix this deficiency, we propose a simple empirical correction to the analytical expression. The resulting corrected expression for the effective diffusivity is in excellent agreement with the simulation results for all values of the channel period.
Electron impact ionization and multiphoton ionization of doped superfluid helium droplets: A comparison
Authors: He Yunteng , Zhang Jie , Kong Wei
Published: February 2016

We compare characteristics of electron impact ionization (EI) and multiphoton ionization (MPI) of doped superfluid helium droplets using the same droplet source. Selected dopant ion fragments from the two ionization schemes demonstrate different dependence on the doping pressure, which could be attributed to the different ionization mechanisms. While EI directly ionizes helium atoms in a droplet therefore has higher yields for bigger droplets (within a limited size range), MPI is insensitive to the helium in a droplet and is only dependent on the number of dopant molecules. The optimal timing of the ionization pulse also varies with the doping pressure, implying a velocity slip among different sized droplets. Calculations of the doping statistics and ionization probabilities qualitatively agree with the experimental data. Our results offer a word of caution in interpreting the pressure and timing dependence of superfluid helium droplets, and we also devise a scheme in achieving a high degree of doping while limiting the contribution of dopant clusters.
Spallation as a dominant source of pusher-fuel and hot-spot mix in inertial confinement fusion capsules
Authors: Orth Charles D.
Published: February 2016

We suggest that a potentially dominant but previously neglected source of pusher-fuel and hot-spot “mix” may have been the main degradation mechanism for fusion energy yields of modern inertial confinement fusion (ICF) capsules designed and fielded to achieve high yields—not hydrodynamic instabilities. This potentially dominant mix source is the spallation of small chunks or “grains” of pusher material into the fuel regions whenever (1) the solid material adjacent to the fuel changes its phase by nucleation and (2) this solid material spalls under shock loading and sudden decompression. We describe this mix mechanism, support it with simulations and experimental evidence, and explain how to eliminate it and thereby allow higher yields for ICF capsules and possibly ignition at the National Ignition Facility.
Enhanced electron mobility in epitaxial (Ba,La)SnO3 films on BaSnO3(001) substrates
Authors: Lee Woong-Jhae , Kim Hyung Joon , Sohn Egon , Kim Tai Hoon , Park Ju-Young , Park Woanseo , Jeong Hyunhak , Lee Takhee , Kim Jin Hyeok , Choi Ki-Young , Kim Kee Hoon
Published: February 2016

We report the growth of Ba1−xLaxSnO3 (x = 0.00, 0.005, 0.01, 0.02, and 0.04) thin films on the insulating BaSnO3(001) substrate by pulsed laser deposition. The insulating BaSnO3 substrates were grown by the Cu2O-CuO flux, in which the molar fraction of KClO4 was systematically increased to reduce electron carriers and thus induce a doping induced metal-insulator transition, exhibiting a resistivity increase from ∼10−3 to ∼1012 Ω cm at room temperature. We find that all the Ba1−xLaxSnO3 films are epitaxial, showing good in-plane lattice matching with the substrate as confirmed by X-ray reciprocal space mappings and transmission electron microscopy studies. The Ba1−xLaxSnO3 (x = 0.005–0.04) films showed degenerate semiconducting behavior, and the electron mobility at room temperature reached 100 and 85 cm2 V−1 s−1 at doping levels 1.3 × 1020 and 6.8 × 1019 cm−3, respectively. This work demonstrates that thin perovskite stannate films of high quality can be grown on the BaSnO3(001) substrates for potential applications in transparent electronic devices.
Local potential fluctuation of topological surface states in Bi1.5Sb0.5Te1.7Se1.3 observed by Landau level spectroscopy
Authors: Ko Wonhee , Park Joonbum , Jeon Insu , Kim Hyo Won , Kwon Hyeokshin , Oh Youngtek , Kim Jun Sung , Suh Hwansoo , Hwang Sung Woo , Chung Chilhee
Published: February 2016

We report the local observation of the band structure of topological surface states in Bi1.5Sb0.5Te1.7Se1.3 using scanning tunneling microscopy/spectroscopy (STM/STS). The energy-momentum dispersion relation is locally deduced by extracting the Landau level (LL) energies, which are formed in a high magnetic field, from the STS data. Spatial variation of LLs revealed a shift of the Dirac point energy at the nanometer scale. The structure of the potential fluctuation was not correlated with the topography, which indicated that the Te/Se substitution did not induce the potential shift because of their same valence. The results show that disorders from the Te/Se substitution at the surface do not induce any localized charged states and do not affect topological surface states.
Proposal and physics of AlInN-delta-GaN quantum well ultraviolet lasers
Authors: Liu Cheng , Ooi Yu Kee , Zhang Jing
Published: February 2016

The use of AlInN-delta-GaN quantum wells (QWs) active region for ultraviolet (UV) laser with wavelength (λ) ∼ 250–300 nm was proposed and investigated in this work. The design of active region consists of 24 Å staggered Al0.91In0.09N/Al0.82In0.18N layers with a 3 Å lattice-matched GaN delta layer, which enables dominant conduction band (C) to heavy hole (HH) subband transition. In addition, the insertion of the ultra-thin delta GaN layer will strongly localize the electron-hole wave functions toward the center of the QW, which leads to large transverse electric (TE) polarized optical gain. In comparison to the use of a conventional AlGaN QW system, the proposed AlInN-delta-GaN QW structure results in ∼3 times improvement in TE-gain at 255 nm. By tuning the delta-GaN thickness, the TE-polarized optical gain up to 3700 cm−1 can be obtained for λ ∼ 280–300 nm, which is very promising to serve as an alternative active region for high-efficiency UV lasers.
Giant soft-memory in liquid crystal nanocomposites
Authors: Kempaiah Ravindra , Liu Yijing , Nie Zhihong , Basu Rajratan
Published: February 2016

A hybrid nanocomposite comprising 5CB liquid crystal (LC) and block copolymer (BCP) functionalized barium titanate ferroelectric nanoparticles was prepared. This hybrid system exhibits a giant soft-memory effect that was detected by dielectric hysteresis. Spontaneous polarization of ferroelectric nanoparticles couples synergistically with the radially aligned BCP chains to create nanoscopic domains where LC mesogens can align directionally. Such domains can be rotated electromechanically and locked in space even after the removal of the applied electric field. The resulting non-volatile memory is several times larger than the non-functionalized sample and provides an insight into the role of non-covalent polymer functionalization on enhancing the size of the nanoscopic domains.
The anisotropic linear and quadratic magneto-optical Kerr effects in epitaxial Fe/GaAs(110) film
Authors: Liang J. H. , Chen Y. L. , Sun L. , Zhou C. , Yang Y. , Wu Y. Z.
Published: February 2016

We investigated the magneto-optical Kerr effects in C2v symmetric Fe/GaAs(110) film and quantitatively separated the linear and quadratic Kerr contributions with the rotating field method. The linear Kerr effect was experimentally found to have twofold anisotropy with crystal orientation, in well agreement with the theoretical prediction. In addition, the quadratic Kerr effects exhibit both twofold and fourfold anisotropy. The calculation based on a 4 × 4 transfer matrix method indicates that the anisotropies of the linear and quadratic Kerr effects both originate from the second order magneto-optical coupling. The C2v symmetric film with anisotropic linear Kerr effect may have a potential application on the future precise magneto-optical sensors.
Imaging defects in a plate with complex geometries
Authors: Hayashi Takahiro
Published: February 2016

This paper discusses a defect imaging technique using signals containing multiple reflected waves, for a plate with complex geometries, in which direct waves from a generating point to a receiving point cannot be measured. This technique utilizes a characteristic of flexural vibrations wherein the amplitude of the received signals is approximately inversely proportional to the thickness of the source of the elastic wave when a laser pulse is applied to the surface of the plate. First, a theoretical modal analysis elucidated that the amplitude distributions obtained by scanning the laser source of the elastic waves consist of thickness distributions and spurious distributions caused by multiple reflections in the plate. The amplitude distributions were then experimentally obtained for a complex-shaped plate with an artificial defect. The distributions were found to consist of a defect image as well as spurious images, and this agreed well with the theoretical discussions. Clearer defect images with small spurious images were obtained even for a plate with complex geometries by taking an average of the images obtained at multiple frequencies.
Near infrared Kerr effect and description of field-induced phase transitions in polymer-stabilized blue phase liquid crystals
Authors: Atorf B. , Rasouli H. , Nordendorf G. , Wilkes D. , Kitzerow H.
Published: February 2016

Studies of the influence of an electric field E on the effective refractive index of a polymer-stabilized blue phase in the near infrared spectral range reveal a considerable field-induced birefringence. At moderate voltages, the birefringence increases linearly with the square of the field strength as expected for the electro-optic Kerr effect, with an effective Kerr constant of K ≈ 6.3 – 6.9 × 10−10 m V−2. However, for E > ≈7.3 V/μm, the slope of the field-induced birefringence versus E2 increases abruptly, before saturation is reached at E > ≈8.5 V/μm. Based on previous observations on blue phases in the visible wavelength range, the discontinuous change can be attributed to a field-induced phase transition. A modification of the extended Kerr model introduced by Wu and coworkers is suggested to take this additional effect into account. In addition to the promising properties of blue phases for improved liquid crystal displays, the observed field-induced birefringence in the infrared region opens interesting perspectives for telecommunication and other non-display applications.
Flow control of an elongated jet in cross-flow: Film cooling effectiveness enhancement using surface dielectric barrier discharge plasma actuator
Authors: Audier P. , Fénot M. , Bénard N. , Moreau E.
Published: February 2016

The case presented here deals with plasma flow control applied to a cross-flow configuration, more specifically to a film cooling system. The ability of a plasma dielectric barrier discharge actuator for film cooling effectiveness enhancement is investigated through an experimental set-up, including a film injection from an elongated slot into a thermally uniform cross-flow. Two-dimensional particle image velocimetry and infrared-thermography measurements are performed for three different blowing ratios of M = 0.4, 0.5, and 1. Results show that the effectiveness can be increased when the discharge is switched on, as predicted by the numerical results available in literature. Whatever the blowing ratio, the actuator induces a deflection of the jet flow towards the wall, increases its momentum, and delays its diffusion in the cross-flow.
Raman spectroscopic characterization of germanium-on-insulator nanolayers
Authors: Poborchii Vladimir , Ishii Hiroyuki , Hattori Hiroyuki , Chang Wen-Hsin , Maeda Tatsuro , Tada Tetsuya , Geshev Pavel I.
Published: February 2016

We fabricated Ge-on-insulator monocrystalline nanolayers with thickness H = 1–18 nm using SiO2 substrate and studied their Raman spectra. The spectra display longitudinal optical (LO) phonon and confined acoustic phonon bands. For H < 5 nm, additional bands due to amorphous-like inclusions appear in the spectra. With a decrease in H, the LO phonon Raman band displays enhancement and downshift. Also, as H decreases, the band homogeneously broadens proportionally to 1/H. We attribute these findings to a reduction in reflectance plus electron quantum size effect, thickness-dependent stress, and surface-disorder-induced phonon lifetime reduction.
Ligand-surface interactions and surface oxidation of colloidal PbSe quantum dots revealed by thin-film positron annihilation methods
Authors: Shi Wenqin , Eijt Stephan W. H. , Suchand Sandeep C. S. , Siebbeles Laurens D. A. , Houtepen Arjan J. , Kinge Sachin , Brück Ekkes , Barbiellini Bernardo , Bansil Arun
Published: February 2016

Positron Two Dimensional Angular Correlation of Annihilation Radiation (2D-ACAR) measurements reveal modifications of the electronic structure and composition at the surfaces of PbSe quantum dots (QDs), deposited as thin films, produced by various ligands containing either oxygen or nitrogen atoms. In particular, the 2D-ACAR measurements on thin films of colloidal PbSe QDs capped with oleic acid ligands yield an increased intensity in the electron momentum density (EMD) at high momenta compared to PbSe quantum dots capped with oleylamine. Moreover, the EMD of PbSe QDs is strongly affected by the small ethylenediamine ligands, since these molecules lead to small distances between QDs and favor neck formation between near neighbor QDs, inducing electronic coupling between neighboring QDs. The high sensitivity to the presence of oxygen atoms at the surface can be also exploited to monitor the surface oxidation of PbSe QDs upon exposure to air. Our study clearly demonstrates that positron annihilation spectroscopy applied to thin films can probe surface transformations of colloidal semiconductor QDs embedded in functional layers.
Materials design for electrocatalytic carbon capture
Authors: Tan Xin , Tahini Hassan A. , Smith Sean C.
Published: February 2016

We discuss our philosophy for implementation of the Materials Genome Initiative through an integrated materials design strategy, exemplified here in the context of electrocatalytic capture and separation of CO2 gas. We identify for a group of 1:1 X–N graphene analogue materials that electro-responsive switchable CO2 binding behavior correlates with a change in the preferred binding site from N to the adjacent X atom as negative charge is introduced into the system. A reconsideration of conductive N-doped graphene yields the discovery that the N-dopant is able to induce electrocatalytic binding of multiple CO2 molecules at the adjacent carbon sites.
Research Update: Magnetoionic control of magnetization and anisotropy in layered oxide/metal heterostructures
Authors: Duschek K. , Pohl D. , Fähler S. , Nielsch K. , Leistner K.
Published: February 2016

Electric field control of magnetization and anisotropy in layered structures with perpendicular magnetic anisotropy is expected to increase the versatility of spintronic devices. As a model system for reversible voltage induced changes of magnetism by magnetoionic effects, we present several oxide/metal heterostructures polarized in an electrolyte. Room temperature magnetization of Fe-O/Fe layers can be changed by 64% when applying only a few volts in 1M KOH. In a next step, the bottom interface of the in-plane magnetized Fe layer is functionalized by an L10 FePt(001) underlayer exhibiting perpendicular magnetic anisotropy. During subsequent electrocrystallization and electrooxidation, well defined epitaxial Fe3O4/Fe/FePt heterostructures evolve. The application of different voltages leads to a thickness change of the Fe layer sandwiched between Fe-O and FePt. At the point of transition between rigid magnet and exchange spring magnet regime for the Fe/FePt bilayer, this induces a large variation of magnetic anisotropy.
2D-2D tunneling field-effect transistors using WSe2/SnSe2 heterostructures
Authors: Roy Tania , Tosun Mahmut , Hettick Mark , Ahn Geun Ho , Hu Chenming , Javey Ali
Published: February 2016

Two-dimensional materials present a versatile platform for developing steep transistors due to their uniform thickness and sharp band edges. We demonstrate 2D-2D tunneling in a WSe2/SnSe2 van der Waals vertical heterojunction device, where WSe2 is used as the gate controlled p-layer and SnSe2 is the degenerately n-type layer. The van der Waals gap facilitates the regulation of band alignment at the heterojunction, without the necessity of a tunneling barrier. ZrO2 is used as the gate dielectric, allowing the scaling of gate oxide to improve device subthreshold swing. Efficient gate control and clean interfaces yield a subthreshold swing of ∼100 mV/dec for >2 decades of drain current at room temperature, hitherto unobserved in 2D-2D tunneling devices. The subthreshold swing is independent of temperature, which is a clear signature of band-to-band tunneling at the heterojunction. A maximum switching ratio ION/IOFF of 107 is obtained. Negative differential resistance in the forward bias characteristics is observed at 77 K. This work bodes well for the possibilities of two-dimensional materials for the realization of energy-efficient future-generation electronics.