bluuebunny/crossref_metadata_2025 huggingface dataset:
Solvation structure and transport properties of alkali cations in dimethyl sulfoxide under exogenous static electric fields
Authors: Kerisit Sebastien , Vijayakumar M. , Han Kee Sung , Mueller Karl T.
Published: June 2015

A combination of molecular dynamics simulations and pulsed field gradient nuclear magnetic resonance spectroscopy is used to investigate the role of exogenous electric fields on the solvation structure and dynamics of alkali ions in dimethyl sulfoxide (DMSO) and as a function of temperature. Good agreement was obtained, for select alkali ions in the absence of an electric field, between calculated and experimentally determined diffusion coefficients normalized to that of pure DMSO. Our results indicate that temperatures of up to 400 K and external electric fields of up to 1 V nm−1 have minimal effects on the solvation structure of the smaller alkali cations (Li+ and Na+) due to their relatively strong ion-solvent interactions, whereas the solvation structures of the larger alkali cations (K+, Rb+, and Cs+) are significantly affected. In addition, although the DMSO exchange dynamics in the first solvation shell differ markedly for the two groups, the drift velocities and mobilities are not significantly affected by the nature of the alkali ion. Overall, although exogenous electric fields induce a drift displacement, their presence does not significantly affect the random diffusive displacement of the alkali ions in DMSO. System temperature is found to have generally a stronger influence on dynamical properties, such as the DMSO exchange dynamics and the ion mobilities, than the presence of electric fields.
Multiplexed displacement fiber sensor using thin core fiber exciter
Authors: Chen Zhen , Hefferman Gerald , Wei Tao
Published: June 2015

This letter reports a multiplexed optical displacement sensor using a thin core fiber (TCF) exciter. The TCF exciter is followed by a stripped single mode optical fiber. A small section of buffer is used as the movable component along the single mode fiber. Ultra-weak cladding mode reflection (< − 75 dB) was employed to probe the refractive index discontinuity between the air and buffer coating boundary. The position change of the movable buffer segment results in a delay change of the cladding mode reflection. Thus, it is a measure of the displacement of the buffer segment with respect to the glass fiber. The insertion loss of one sensor was measured to be less than 3 dB. A linear relationship was evaluated between the measurement position and absolute position of the moving actuator. Multiplexed capability was demonstrated and no cross talk was found between the sensors.
Fluid-structure interactions in compressible cavity flows
Authors: Wagner Justin L. , Casper Katya M. , Beresh Steven J. , Hunter Patrick S. , Spillers Russell W. , Henfling John F. , Mayes Randall L.
Published: June 2015

Experiments were performed to understand the complex fluid-structure interactions that occur during aircraft internal store carriage. A cylindrical store was installed in a rectangular cavity having a length-to-depth ratio of 3.33 and a length-to-width ratio of 1. The Mach number ranged from 0.6 to 2.5 and the incoming boundary layer was turbulent. Fast-response pressure measurements provided aeroacoustic loading in the cavity, while triaxial accelerometers provided simultaneous store response. Despite occupying only 6% of the cavity volume, the store significantly altered the cavity acoustics. The store responded to the cavity flow at its natural structural frequencies, and it exhibited a directionally dependent response to cavity resonance. Specifically, cavity tones excited the store in the streamwise and wall-normal directions consistently, whereas a spanwise response was observed only occasionally. The streamwise and wall-normal responses were attributed to the longitudinal pressure waves and shear layer vortices known to occur during cavity resonance. Although the spanwise response to cavity tones was limited, broadband pressure fluctuations resulted in significant spanwise accelerations at store natural frequencies. The largest vibrations occurred when a cavity tone matched a structural natural frequency, although energy was transferred more efficiently to natural frequencies having predominantly streamwise and wall-normal motions.
The effective colloid interaction in the Asakura–Oosawa model. Assessment of non-pairwise terms from the virial expansion
Authors: Santos Andrés , López de Haro Mariano , Fiumara Giacomo , Saija Franz
Published: June 2015

The relevance of neglecting three- and four-body interactions in the coarse-grained version of the Asakura–Oosawa model is examined. A mapping between the first few virial coefficients of the binary nonadditive hard-sphere mixture representative of this model and those arising from the coarse-grained (pairwise) depletion potential approximation allows for a quantitative evaluation of the effect of such interactions. This turns out to be especially important for large size ratios and large reservoir polymer packing fractions.
Vibrational modes and changing molecular conformation of perfluororubrene in thin films and solution
Authors: Anger F. , Scholz R. , Gerlach A. , Schreiber F.
Published: June 2015

We investigate the vibrational properties of perfluororubrene (PF-RUB) in thin films on silicon wafers with a native oxide layer as well as on silicon wafers covered with a self-assembled monolayer and in dichloromethane solution. In comparison with computed Raman and IR spectra, we can assign the molecular modes and identify two molecular conformations with twisted and planar tetracene backbones of the molecule. Moreover, we employ Raman imaging techniques to study the morphology and distribution of the molecular conformation in PF-RUB thin films.
Automation of a single-DNA molecule stretching device
Authors: Sørensen Kristian Tølbøl , Lopacinska Joanna M. , Tommerup Niels , Silahtaroglu Asli , Kristensen Anders , Marie Rodolphe
Published: June 2015

We automate the manipulation of genomic-length DNA in a nanofluidic device based on real-time analysis of fluorescence images. In our protocol, individual molecules are picked from a microchannel and stretched with pN forces using pressure driven flows. The millimeter-long DNA fragments free flowing in micro- and nanofluidics emit low fluorescence and change shape, thus challenging the image analysis for machine vision. We demonstrate a set of image processing steps that increase the intrinsically low signal-to-noise ratio associated with single-molecule fluorescence microscopy. Furthermore, we demonstrate how to estimate the length of molecules by continuous real-time image stitching and how to increase the effective resolution of a pressure controller by pulse width modulation. The sequence of image-processing steps addresses the challenges of genomic-length DNA visualization; however, they should also be general to other applications of fluorescence-based microfluidics.
Characterization of half-Heusler unicouple for thermoelectric conversion
Authors: Hu Xiaokai , Yamamoto Atsushi , Nagase Kazuo
Published: June 2015

A thermoelectric unicouple is constructed with half-Heusler materials for characterizing power generation. The electric power and heat flow are measured simultaneously under various temperature differences, and the efficiencies are calculated. Phase structures and thermoelectric properties are characterized for the p- and n-type legs; the latter are used for finite-element simulations to calculate numerically the ideal electric power, heat flow and efficiency under the same temperature conditions. Seebeck voltage, internal resistance, electric power, heat flow, and efficiency are compared between the measurement and simulation. Thereby, the contact electrical resistance is estimated, and the extra thermal resistance is analyzed in terms of the compared open-circuit voltage and heat flow. The maximum efficiency of 4.0% is attained from the measurement with the hot side at 470 °C, in contrast to 5.7% from the simulation. The simulation permits an investigation on the one-dimensional heat flow through the p- and n-type legs that is coupled with Peltier, Thomson, and Joule heat.
Measurement of the tradeoff between intrinsic emittance and quantum efficiency from a NaKSb photocathode near threshold
Authors: Maxson Jared , Cultrera Luca , Gulliford Colwyn , Bazarov Ivan
Published: June 2015

We measure the tradeoff between the quantum efficiency and intrinsic emittance from a NaKSb photocathode at three increasing wavelengths (635, 650, and 690 nm) at or below the energy of the bandgap plus the electron affinity, hν≤Eg+Ea. These measurements were performed using a high voltage dc gun for varied photocathode surface fields of 1.4−4.4 MV/m. Measurements of intrinsic emittance are performed using two different methods and were found to agree. At the longest wavelength available, 690 nm, the intrinsic emittance was 0.26 μm/mm-rms with a quantum efficiency of ∼10−4. The suitability of NaKSb emitting at threshold for various low emittance applications is discussed.
Localization and dynamical arrest of colloidal fluids in a disordered matrix of polydisperse obstacles
Authors: Elizondo-Aguilera Luis Fernando , Medina-Noyola Magdaleno
Published: June 2015

The mobility of a colloidal particle in a crowded and confined environment may be severely reduced by its interactions with other mobile colloidal particles and the fixed obstacles through which it diffuses. The latter may be modelled as an array of obstacles with random fixed positions. In this contribution, we report on the effects of the size-polydispersity of such fixed obstacles on the immobilization and dynamical arrest of the diffusing colloidal particles. This complex system is modelled as a monodisperse Brownian hard-sphere fluid diffusing through a polydisperse matrix of fixed hard spheres with a given size distribution. In the Lorentz gas limit (absence of interactions between the mobile particles), we first develop a simple excluded-volume theory to describe the localization transition of the tracer mobile particles. To take into account the interactions among the mobile particles, we adapt the multi-component self-consistent generalized Langevin equation (SCGLE) theory of colloid dynamics, which also allows us to calculate the dynamical arrest transition line, and in general, all the dynamical properties of the mobile particles (mean-squared displacement, self-diffusion coefficient, etc.). The scenarios described by both approaches in the Lorentz gas limit are qualitatively consistent, but the SCGLE formalism describes the dependence of the dynamics of the adsorbed fluid on the polydispersity of the porous matrix at arbitrary concentrations of the mobile spheres and arbitrary volume fractions of the obstacles. Two mechanisms for dynamical arrest (glass transition and localization) are analyzed and we also discuss the crossover between them using the SCGLEs.
Searching for low percolation thresholds within amphiphilic polymer membranes: The effect of side chain branching
Authors: Dorenbos G.
Published: June 2015

Percolation thresholds for solvent diffusion within hydrated model polymeric membranes are derived from dissipative particle dynamics in combination with Monte Carlo (MC) tracer diffusion calculations. The polymer backbones are composed of hydrophobic A beads to which at regular intervals Y-shaped side chains are attached. Each side chain is composed of eight A beads and contains two identical branches that are each terminated with a pendant hydrophilic C bead. Four types of side chains are considered for which the two branches (each represented as [C], [AC], [AAC], or [AAAC]) are splitting off from the 8th, 6th, 4th, or 2nd A bead, respectively. Water diffusion through the phase separated water containing pore networks is deduced from MC tracer diffusion calculations. The percolation threshold for the architectures containing the [C] and [AC] branches is at a water volume fraction of ∼0.07 and 0.08, respectively. These are much lower than those derived earlier for linear architectures of various side chain length and side chain distributions. Control of side chain architecture is thus a very interesting design parameter to decrease the percolation threshold for solvent and proton transports within flexible amphiphilic polymer membranes.
Reference interaction site model and optimized perturbation theories of colloidal dumbbells with increasing anisotropy
Authors: Munaò Gianmarco , Gámez Francisco , Costa Dino , Caccamo Carlo , Sciortino Francesco , Giacometti Achille
Published: June 2015

We investigate thermodynamic properties of anisotropic colloidal dumbbells in the frameworks provided by the Reference Interaction Site Model (RISM) theory and an Optimized Perturbation Theory (OPT), this latter based on a fourth-order high-temperature perturbative expansion of the free energy, recently generalized to molecular fluids. Our model is constituted by two identical tangent hard spheres surrounded by square-well attractions with same widths and progressively different depths. Gas-liquid coexistence curves are obtained by predicting pressures, free energies, and chemical potentials. In comparison with previous simulation results, RISM and OPT agree in reproducing the progressive reduction of the gas-liquid phase separation as the anisotropy of the interaction potential becomes more pronounced; in particular, the RISM theory provides reasonable predictions for all coexistence curves, bar the strong anisotropy regime, whereas OPT performs generally less well. Both theories predict a linear dependence of the critical temperature on the interaction strength, reproducing in this way the mean-field behavior observed in simulations; the critical density—that drastically drops as the anisotropy increases—turns to be less accurate. Our results appear as a robust benchmark for further theoretical studies, in support to the simulation approach, of self-assembly in model colloidal systems.
From 1D chain to 3D network: A theoretical study on TiO2 low dimensional structures
Authors: Guo Ling-ju , Zeng Zhi , He Tao
Published: June 2015

We have performed a systematic study on a series of low dimensional TiO2 nanostructures under density functional theory methods. The geometries, stabilities, growth mechanism, and electronic structures of 1D chain, 2D ring, 2D ring array, and 3D network of TiO2 nanostructures are analyzed. Based on the Ti2O4 building unit, a series of 1D TiO2 nano chains and rings can be built. Furthermore, 2D ring array and 3D network nanostructures can be constructed from 1D chains and rings. Among non-periodic TiO2 chain and ring structures, one series of ring structures is found to be more stable. The geometry model of the 2D ring arrays and 3D network structures in this work has provided a theoretical understanding on the structure information in experiments. Based on these semiconductive low dimensional structures, moreover, it can help to understand and design new hierarchical TiO2 nanostructure in the future.
Anisotropy and shear-layer edge dynamics of statistically unsteady, stratified turbulence
Authors: Wingstedt E. M. M. , Fossum H. E. , Pettersson Reif B. A. , Werne J.
Published: June 2015

Direct numerical simulation data of an evolving Kelvin-Helmholtz instability have been analyzed in order to characterize the dynamic and kinematic response of shear-generated turbulent flow to imposed stable stratification. Particular emphasis was put on anisotropy and shear-layer edge dynamics in the net kinetic energy decay phase of the Kelvin-Helmholtz evolution. Results indicate a faster increase of small-scale anisotropy compared to large-scale anisotropy. Also, the anisotropy of thermal dissipation differs significantly from that of viscous dissipation. It is found that the Reynolds stress anisotropy increases up to a stratification level roughly corresponding to Rig ≈ 0.4, but subsequently decreases for higher levels of stratification, most likely due to relaminarization. Coherent large-scale turbulence structures are cylindrical in the center of the shear layer, whereas they become ellipsoidal in the strongly stratified edge-layer region. The structures of the Reynolds stresses are highly one-componental in the center and turn two-componental as stratification increases. Stratification affects all scales, but it seems to affect larger scales to a higher degree than smaller scales and thermal scales more strongly than momentum scales. The effect of strong stable stratification at the edge of the shear layer is highly reminiscent of the non-local pressure effects of solid walls. However, the kinematic blocking inherently associated with impermeable walls is not observed in the edge layer. Vertical momentum flux reversal is found in part of the shear layer. The roles of shear and buoyant production of turbulence kinetic energy are exchanged, and shear production is transferring energy into the mean flow field, which contributes to relaminarization. The change in dynamics near the edge of the shear layer has important implications for predictive turbulence model formulations.
Suspended core-shell Pt-PtOx nanostructure for ultrasensitive hydrogen gas sensor
Authors: Basu Palash Kr. , Kallatt Sangeeth , Anumol Erumpukuthickal A. , Bhat Navakanta
Published: June 2015

High sensitivity gas sensors are typically realized using metal catalysts and nanostructured materials, utilizing non-conventional synthesis and processing techniques, incompatible with on-chip integration of sensor arrays. In this work, we report a new device architecture, suspended core-shell Pt-PtOx nanostructure that is fully CMOS-compatible. The device consists of a metal gate core, embedded within a partially suspended semiconductor shell with source and drain contacts in the anchored region. The reduced work function in suspended region, coupled with built-in electric field of metal-semiconductor junction, enables the modulation of drain current, due to room temperature Redox reactions on exposure to gas. The device architecture is validated using Pt-PtO2 suspended nanostructure for sensing H2 down to 200 ppb under room temperature. By exploiting catalytic activity of PtO2, in conjunction with its p-type semiconducting behavior, we demonstrate about two orders of magnitude improvement in sensitivity and limit of detection, compared to the sensors reported in recent literature. Pt thin film, deposited on SiO2, is lithographically patterned and converted into suspended Pt-PtO2 sensor, in a single step isotropic SiO2 etching. An optimum design space for the sensor is elucidated with the initial Pt film thickness ranging between 10 nm and 30 nm, for low power (<5 μW), room temperature operation.
Spectrum of walk matrix for Koch network and its application
Authors: Xie Pinchen , Lin Yuan , Zhang Zhongzhi
Published: June 2015

Various structural and dynamical properties of a network are encoded in the eigenvalues of walk matrix describing random walks on the network. In this paper, we study the spectra of walk matrix of the Koch network, which displays the prominent scale-free and small-world features. Utilizing the particular architecture of the network, we obtain all the eigenvalues and their corresponding multiplicities. Based on the link between the eigenvalues of walk matrix and random target access time defined as the expected time for a walker going from an arbitrary node to another one selected randomly according to the steady-state distribution, we then derive an explicit solution to the random target access time for random walks on the Koch network. Finally, we corroborate our computation for the eigenvalues by enumerating spanning trees in the Koch network, using the connection governing eigenvalues and spanning trees, where a spanning tree of a network is a subgraph of the network, that is, a tree containing all the nodes.
Controlling the polarity of metalorganic vapor phase epitaxy-grown GaP on Si(111) for subsequent III-V nanowire growth
Authors: Paszuk A. , Brückner S. , Steidl M. , Zhao W. , Dobrich A. , Supplie O. , Kleinschmidt P. , Prost W. , Hannappel T.
Published: June 2015

Nanowire growth on heteroepitaxial GaP/Si(111) by metalorganic vapor phase epitaxy requires the [-1-1-1] face, i.e., GaP(111) material with B-type polarity. Low-energy electron diffraction (LEED) allows us to identify the polarity of GaP grown on Si(111), since (2×2) and (1×1) surface reconstructions are associated with GaP(111)A and GaP(111)B, respectively. In dependence on the pre-growth treatment of the Si(111) substrates, we were able to control the polarity of the GaP buffers. GaP films grown on the H-terminated Si(111) surface exhibited A-type polarity, while GaP grown on Si surfaces terminated with arsenic exhibited a (1×1) LEED pattern, indicating B-type polarity. We obtained vertical GaAs nanowire growth on heteroepitaxial GaP with (1×1) surface reconstruction only, in agreement with growth experiments on homoepitaxially grown GaP(111).
Graded band gap GaInNAs solar cells
Authors: Langer F. , Perl S. , Höfling S. , Kamp M.
Published: June 2015

Dilute nitride GaInN(Sb)As with a band gap (Eg) of 1.0 eV is a promising material for the integration in next generation multijunction solar cells. We have investigated the effect of a compositionally graded GaInNAs absorber layer on the spectral response of a GaInNAs sub cell. We produced band gap gradings (ΔEg) of up to 39 meV across a 1 μm thick GaInNAs layer. Thereby, the external quantum efficiency—compared to reference cells—was increased due to the improved extraction of photo-generated carriers from 34.0% to 36.7% for the wavelength range from 900 nm to 1150 nm. However, this device figure improvement is accompanied by a small decrease in the open circuit voltage of about 20 mV and the shift of the absorption edge to shorter wavelengths.
Study on splitting of a toroidal bubble near a rigid boundary
Authors: Zhang A. M. , Li S. , Cui J.
Published: June 2015

The splitting of a toroidal bubble near a rigid boundary is commonly observed in experiments, which is a quite complex phenomenon in bubble dynamics and still not yet well understood. In present study, the bubble splitting phenomenon is studied using the boundary integral method. The vortex ring model is extended to multiple vortex rings to simulate the interaction between two toroidal bubbles after splitting. Buoyancy and non-buoyancy cases are investigated numerically in this study. Numerical results with buoyancy effects show favorable agreement with the experimental observations, which validates the present model. Generally, the first split of the toroidal bubble occurs when an annular “sideways jet” collides with the other side of the bubble. After the toroidal bubble splitting, some new phenomena are found as follows: (i) An annular high pressure region is generated at the splitting location, and the maximum pressure is associated with the velocity differences between the two sides therein just before splitting. (ii) The total volume varies continuously, while the two sub-bubbles vary differently in volume after splitting. (iii) The sideways jet continues propagating on a sub-bubble surface, which would cause more splits or partial breakup of the splash film into droplets. This may be an important reason for the formation of bubble cloud and the rough bubble surface in the rebounding process.
Minima of the fluctuations of the order parameter of global seismicity
Authors: Sarlis N. V. , Christopoulos S.-R. G. , Skordas E. S.
Published: June 2015

It has been recently shown [N. V. Sarlis, Phys. Rev. E 84, 022101 (2011) and N. V. Sarlis and S.-R. G. Christopoulos, Chaos 22, 023123 (2012)] that earthquakes of magnitude M greater or equal to 7 are globally correlated. Such correlations were identified by studying the variance κ1 of natural time which has been proposed as an order parameter for seismicity. Here, we study the fluctuations of this order parameter using the Global Centroid Moment Tensor catalog for a magnitude threshold Mthres = 5.0 and focus on its behavior before major earthquakes. Natural time analysis reveals that distinct minima of the fluctuations of the order parameter of seismicity appear within almost five and a half months on average before all major earthquakes of magnitude larger than 8.4. This phenomenon corroborates the recent finding [N. V. Sarlis et al., Proc. Natl. Acad. Sci. U.S.A. 110, 13734 (2013)] that similar minima of the seismicity order parameter fluctuations had preceded all major shallow earthquakes in Japan. Moreover, on the basis of these minima a statistically significant binary prediction method for earthquakes of magnitude larger than 8.4 with hit rate 100% and false alarm rate 6.67% is suggested.
Correlation between switching to n-type conductivity and structural defects in highly Mg-doped InN
Authors: Khromov S. , Persson P. O. Å. , Wang X. , Yoshikawa A. , Monemar B. , Rosen J. , Janzén E. , Darakchieva V.
Published: June 2015

The effect of Mg doping on the microstructure of InN epitaxial films in relation to their free-charge carrier properties has been investigated by transmission electron microscopy (TEM) and aberration corrected scanning TEM. We observe a direct correlation between Mg concentration and the formation of stacking faults. The threading dislocation density is found to be independent of Mg concentration. The critical Mg concentration for the on-set of stacking faults formation is determined and found to correlate with the switch from p- to n-type conductivity in InN. Potential mechanisms involving stacking faults and point defect complexes are invoked in order to explain the observed conductivity reversal. Finally, the stacking faults are structurally determined and their role in the reduction of the free electron mobility in highly doped InN:Mg is discussed.
Non-Markovian character in human mobility: Online and offline
Authors: Zhao Zhi-Dan , Cai Shi-Min , Lu Yang
Published: June 2015

The dynamics of human mobility characterizes the trajectories that humans follow during their daily activities and is the foundation of processes from epidemic spreading to traffic prediction and information recommendation. In this paper, we investigate a massive data set of human activity, including both online behavior of browsing websites and offline one of visiting towers based mobile terminations. The non-Markovian character observed from both online and offline cases is suggested by the scaling law in the distribution of dwelling time at individual and collective levels, respectively. Furthermore, we argue that the lower entropy and higher predictability in human mobility for both online and offline cases may originate from this non-Markovian character. However, the distributions of individual entropy and predictability show the different degrees of non-Markovian character between online and offline cases. To account for non-Markovian character in human mobility, we apply a protype model with three basic ingredients, namely, preferential return, inertial effect, and exploration to reproduce the dynamic process of online and offline human mobilities. The simulations show that the model has an ability to obtain characters much closer to empirical observations.
Electron mean free path from angle-dependent photoelectron spectroscopy of aerosol particles
Authors: Goldmann Maximilian , Miguel-Sánchez Javier , West Adam H. C. , Yoder Bruce L. , Signorell Ruth
Published: June 2015

We propose angle-resolved photoelectron spectroscopy of aerosol particles as an alternative way to determine the electron mean free path of low energy electrons in solid and liquid materials. The mean free path is obtained from fits of simulated photoemission images to experimental ones over a broad range of different aerosol particle sizes. The principal advantage of the aerosol approach is twofold. First, aerosol photoemission studies can be performed for many different materials, including liquids. Second, the size-dependent anisotropy of the photoelectrons can be exploited in addition to size-dependent changes in their kinetic energy. These finite size effects depend in different ways on the mean free path and thus provide more information on the mean free path than corresponding liquid jet, thin film, or bulk data. The present contribution is a proof of principle employing a simple model for the photoemission of electrons and preliminary experimental data for potassium chloride aerosol particles.
Ultraviolet photodissociation dynamics of the n-propyl and i-propyl radicals
Authors: Song Yu , Zheng Xianfeng , Zhou Weidong , Lucas Michael , Zhang Jingsong
Published: June 2015

Ultraviolet (UV) photodissociation dynamics of jet-cooled n-propyl (n-C3H7) radical via the 3s Rydberg state and i-propyl (i-C3H7) radical via the 3p Rydberg states are studied in the photolysis wavelength region of 230–260 nm using high-n Rydberg atom time-of-flight and resonance enhanced multiphoton ionization techniques. The H-atom photofragment yield spectra of the n-propyl and i-propyl radicals are broad and in good agreement with the UV absorption spectra. The H + propene product translational energy distributions, P(ET)’s, of both n-propyl and i-propyl are bimodal, with a slow component peaking around 5-6 kcal/mol and a fast one peaking at ∼50 kcal/mol (n-propyl) and ∼45 kcal/mol (i-propyl). The fraction of the average translational energy in the total excess energy, 〈fT〉, is 0.3 for n-propyl and 0.2 for i-propyl, respectively. The H-atom product angular distributions of the slow components of n-propyl and i-propyl are isotropic, while that of the fast component of n-propyl is anisotropic (with an anisotropy parameter ∼0.8) and that of i-propyl is nearly isotropic. Site-selective loss of the β hydrogen atom is confirmed using the partially deuterated CH3CH2CD2 and CH3CDCH3 radicals. The bimodal translational energy and angular distributions indicate two dissociation pathways to the H + propene products in the n-propyl and i-propyl radicals: (i) a unimolecular dissociation pathway from the hot ground-state propyl after internal conversion from the 3s and 3p Rydberg states and (ii) a direct, prompt dissociation pathway coupling the Rydberg excited states to a repulsive part of the ground-state surface, presumably via a conical intersection.
Nucleation of crystals that are mixed composites of all three polymorphs in the Gaussian core model
Authors: Mithen J. P. , Callison A. J. , Sear R. P.
Published: June 2015

We present results of computer simulations of homogeneous crystal nucleation in the Gaussian core model. In our simulations, we study the competition between the body-centered-cubic (bcc), face-centered-cubic (fcc), and hexagonal-close-packed crystal phases. We find that the crystal nuclei that form from the metastable fluid phase are typically “mixed”; they do not consist of a single crystal polymorph. Furthermore, when the fcc phase is stable or fcc and bcc phases are equally stable, this mixed nature is found to persist far beyond the size at the top of the nucleation barrier, that is, far into what would be considered the growth (rather than nucleation) regime. In this region, the polymorph that forms is therefore selected long after nucleation. This has implications. When nucleation is slow, it will be the rate-limiting step for crystallization. Then, the step that determines the time scale for crystallisation is different from the step that controls which polymorph forms. This means that they can be independently controlled. Also between nucleation and polymorph selection, there is a growing phase that is clearly crystalline not fluid, but this phase cannot be assigned to any one polymorph.
Ultra-thin ZrO2/SrO/ZrO2 insulating stacks for future dynamic random access memory capacitor applications
Authors: Knebel Steve , Pešić Milan , Cho Kyuho , Chang Jaewan , Lim Hanjin , Kolomiiets Nadiia , Afanas'ev Valeri V. , Muehle Uwe , Schroeder Uwe , Mikolajick Thomas
Published: June 2015

Aiming for improvement of the ZrO2-based insulator properties as compared to the state-of-the-art ZrO2/Al2O3/ZrO2 stacks beyond 20 nm dynamic random access memory (DRAM) technology applications, ultra-thin (5 nm) ZrO2/SrO/ZrO2 stacks with TiN electrodes deposited by physical vapor deposition are addressed. By replacing the Al2O3 interlayer with SrO, the effective dielectric permittivity of the stack can be increased as indicated by electrical analysis. At the same time, no degradation of the insulating properties of the SrO-containing stacks and minor changes in the reliability, compared to an Al2O3 interlayer, are found. These results are indicating the possibility of further reducing the effective oxide thickness of the ZrO2-based stacks to come close to 0.5 nm for future DRAM capacitors.
Low temperature synthesis of diamond-based nano-carbon composite materials with high electron field emission properties
Authors: Saravanan A. , Huang B. R. , Yeh C. J. , Leou K. C. , Lin I. N.
Published: June 2015

A diamond-based nano-carbon composite (d/NCC) material, which contains needle-like diamond grains encased with the nano-graphite layers, was synthesized at low substrate temperature via a bias enhanced growth process using CH4/N2 plasma. Such a unique granular structure renders the d/NCC material very conductive (σ = 714.8 S/cm), along with superior electron field emission (EFE) properties (E0 = 4.06 V/μm and Je = 3.18 mA/cm2) and long lifetime (τ = 842 min at 2.41 mA/cm2). Moreover, the electrical conductivity and EFE behavior of d/NCC material can be tuned in a wide range that is especially useful for different kind of applications.
Photoacoustic tomography based on the Green's function retrieval with ultrasound interferometry for sample partially behind an acoustically scattering layer
Authors: Yin Jie , Tao Chao , Cai Peng , Liu Xiaojun
Published: June 2015

Acoustically inhomogeneous mediums with multiple scattering are often the nightmare of photoacoustic tomography. In order to break this limitation, a photoacoustic tomography scheme combining ultrasound interferometry and time reversal is proposed to achieve images in acoustically scattering medium. An ultrasound interferometry is developed to determine the unknown Green's function of strong scattering tissue. Using the determined Greens' function, a time-reversal process is carried out to restore images behind an acoustically inhomogeneous layer from the scattering photoacoustic signals. This method effectively decreases the false contrast, noise, and position deviation of images induced by the multiple scattering. Phantom experiment is carried out to validate the method. Therefore, the proposed method could have potential value in extending the biomedical applications of photoacoustic tomography in acoustically inhomogeneous tissue.
Temperature-dependence of structural and mechanical properties of TiB2: A first principle investigation
Authors: Xiang Huimin , Feng Zhihai , Li Zhongping , Zhou Yanchun
Published: June 2015

High temperature mechanical and thermodynamic properties of TiB2 are important to its applications as ultrahigh temperature ceramic, which were not well understood. In this study, the thermodynamic and mechanical properties of TiB2 were investigated by the combination of first principle and phonon dispersion calculations. The thermal expansion of TiB2 was anisotropic, αc/αa is nearly constant (1.46) from 300 K to 1500 K, theoretically. The origination of this anisotropy is the anisotropic compressibility. The heat capacity at constant pressure was estimated from the theoretical entropy and fitted the experimental result quite well when higher-order anharmonic effects were considered. Theoretical isentropic elastic constants and mechanical properties were calculated and their temperature dependence agreed with the existed experiments. From room temperature to 1500 K, the theoretical slope is −0.0211 GPa·K−1, −0.0155 GPa·K−1, and −0.0384 GPa·K−1 for B, G, and E, respectively. Our theoretical results highlight the suitability of this method in predicting temperature dependent properties of ultrahigh temperature ceramics and show ability in selecting and designing of novel ultrahigh temperature ceramics.
A millimeter wave relativistic backward wave oscillator operating in TM03 mode with low guiding magnetic field
Authors: Ye Hu , Teng Yan , Chen Changhua , Ning Hui , Song Zhimin , Cao Yibing , Wu Ping
Published: June 2015

A V-band overmoded relativistic backward wave oscillator (RBWO) guided by low magnetic field and operating on a TM03 mode is presented to increase both the power handling capacity and the wave-beam interaction conversion efficiency. Trapezoidal slow wave structures (SWSs) with shallow corrugations and long periods are adopted to make the group velocity of TM03 mode at the intersection point close to zero. The coupling impedance and diffraction Q-factor of the RBWO increase, while the starting current decreases owing to the reduction of the group velocity of TM03 mode. In addition, the TM03 mode dominates over the other modes in the startup of the oscillation. Via numerical simulation, the generation of the microwave pulse with an output power of 425 MW and a conversion efficiency of 32% are achieved at 60.5 GHz with an external magnetic field of 1.25 T. This RBWO can provide greater power handling capacity when operating on the TM03 mode than on the TM01 mode.
Suppression of shunting current in a magnetically insulated coaxial vacuum diode
Authors: Yalandin M. I. , Mesyats G. A. , Rostov V. V. , Sharypov K. A. , Shpak V. G. , Shunailov S. A. , Ulmaskulov M. R.
Published: June 2015

Real-time investigations of the dynamics of explosive electron emission from a high-voltage cathode holder made of nonmagnetic stainless steel in a magnetically insulated coaxial vacuum diode have been performed. It has been shown that aging the cathode with several tens of voltage pulses at a field of 1–2 MV/cm provides a stray emission delay ranging from hundreds of picoseconds to a nanosecond or more. In addition, the magnetic field must be configured so that the magnetic lines would not cross the vacuum gap between the diode case and the cathode holder in the region behind the emitting edge of the cathode. These efforts provide conditions for stable emission of the working beam from a graphite cathode with a sharp emitting edge.
Enhanced thermoelectric performance of La-doped BiCuSeO by tuning band structure
Authors: Liu Yaochun , Ding Jingxuan , Xu Ben , Lan Jinle , Zheng Yuanhua , Zhan Bin , Zhang Boping , Lin Yuanhua , Nan Cewen
Published: June 2015

Bi1−xLaxCuSeO ceramic bulks have been prepared by the spark plasma sintering method. Our results indicate that La-doping can lead to an obvious change of the band structure evidenced by the absorption spectra and electric transportation behaviors (e.g., m* and Seebeck coefficient). The variation of band structure results in a great enhancement of carrier mobility caused by a decreased energy offset between the primary and secondary valence bands. A maximum ZT value of 0.74 can be obtained in 8% La-doped BiCuSeO sample at 923 K, which is 37% higher than that of the pure BiCuSeO bulk. Our results reveal that band engineering is an effective way to enhance the thermoelectric properties of BiCuSeO system.
Entire band absorption enhancement in double-side textured ultrathin solar cells by nanoparticle imprinting
Authors: Cai Boyuan , Jia Baohua , Fang Jia , Hou Guofu , Zhang Xiaodan , Zhao Ying , Gu Min
Published: June 2015

Entire band light management is crucial for amorphous silicon (a-Si) solar cells, especially when the absorbing layer becomes ultrathin. Here, we propose and demonstrate a double-side texture strategy to effectively manage light in ultrathin solar cells via a simple and scalable nanoparticle imprinting technique. SiO2 nanoparticles are half embedded into the top surface of the solar cells to introduce the double-side texture. Using a solar cell with a 150 nm thick a-Si layer as an example, we observe significant enhancement over the entire absorption band of a-Si both theoretically and experimentally. A maximum short circuit current density enhancement as high as 43.9% has been achieved experimentally compared with a flat solar cell.
Fabrication and characterization of nanostructured Fe3S4, an isostructural compound of half-metallic Fe3O4
Authors: Li Peng , Xia Chuan , Zhang Qiang , Guo Zaibing , Cui Wenyao , Bai Haili , Alshareef Husam N. , Zhang Xi-xiang
Published: June 2015

High-purity, well-crystallized spinel Fe3S4 nanoplatelets were synthesized by the hydrothermal method, and the saturation magnetic moment of Fe3S4 was measured at 1.83 μB/f.u. The temperature-dependent resistivity of Fe3S4 was metallic-like for T < 180 K: room-temperature resistivity was measured at 7.711 × 103 μΩ cm. The anomalous Hall conductivity of Fe3S4 decreased with increasing longitudinal conductivity, in sharp contrast with the accepted theory of the anomalous Hall effect in a dirty-metal regime. Furthermore, negligible spin-dependent magnetoresistance was observed. Band structure calculations confirmed our experimental observations that Fe3S4 is a metal and not a half metal as expected.
Inflammation negatively regulates FOXP3 and regulatory T-cell function via DBC1
Authors: Gao Yayi , Tang Jiayou , Chen Weiqian , Li Qiang , Nie Jia , Lin Fang , Wu Qingsi , Chen Zuojia , Gao Zhimei , Fan Huimin , Tsun Andy , Shen Jijia , Chen Guihua , Liu Zhongmin , Lou Zhenkun , Olsen Nancy J. , Zheng Song Guo , Li Bin
Published: June 2015

Significance

Treg cells suppress excessive and aberrant immune responses. Impaired function or homeostasis of Treg cells would induce severe autoimmune and inflammatory diseases. Forkhead box P3 (FOXP3), as a master regulator of Treg cells, forms a large complex with other binding factors to modulate Treg-cell function subtly in pathological and physiological conditions. We identified that Deleted in breast cancer 1 (DBC1) is an essential subunit of the FOXP3 complex in human CD4
+
Treg cells. Our results show that the inflammatory cytokines TNF-α or IL-6 trigger FOXP3 degradation, whereas downregulation of DBC1 expression prevents FOXP3 degradation and maintains Treg-cell function under inflammatory stimuli in vitro and in vivo. These findings unveil a previously unidentified pathway for therapeutically modulating FOXP3
+
Treg-cell stability under inflammation.
Conserved SMP domains of the ERMES complex bind phospholipids and mediate tether assembly
Authors: AhYoung Andrew P. , Jiang Jiansen , Zhang Jiang , Khoi Dang Xuan , Loo Joseph A. , Zhou Z. Hong , Egea Pascal F.
Published: June 2015

Significance

Phospholipid exchange between the endoplasmic reticulum (ER) and mitochondria is essential for membrane biogenesis and, ultimately, cell survival. It remains unclear, however, how this exchange is facilitated. Our study investigates a putative involvement of the ER-mitochondrial encounter structure (ERMES), a tethering complex that bridges the ER and mitochondria, in phospholipid transport in yeast. We show that a conserved ERMES domain called the “synaptotagmin-like mitochondrial lipid-binding protein” (SMP) domain preferentially binds phosphatidylcholines and mediates the hierarchical assembly of the tether. The 17-Å-resolution EM structure of the complex formed between the SMP domains present in two ERMES subunits, Mdm12 and Mmm1, reveals an elongated, tubular-shaped heterotetramer traversed by a hydrophobic channel, suggesting a mechanism for lipid transport between the two organelles.
RNASEK is required for internalization of diverse acid-dependent viruses
Authors: Hackett Brent A. , Yasunaga Ari , Panda Debasis , Tartell Michael A. , Hopkins Kaycie C. , Hensley Scott E. , Cherry Sara
Published: June 2015

Significance

Many viruses, including those of global concern, are dependent on internalization for their entry. We found that ribonuclease kappa (RNASEK) is required for infection of every virus we tested that enters cells through an acid-dependent pathway, including dengue, West Nile, Sindbis, Rift Valley Fever, and influenza viruses. Mechanistically, we found that RNASEK has no effect on virus binding to cells but, rather, is required for their uptake. RNASEK was required for diverse viruses that are dependent on clathrin-mediated endocytosis for entry, but we found that RNASEK was dispensable for general endocytic uptake. Therefore, RNASEK appears to play a unique role in viral uptake and may be a therapeutically viable target to inhibit major human viral pathogens.
High-resolution helix orientation in actin-bound myosin determined with a bifunctional spin label
Authors: Binder Benjamin P. , Cornea Sinziana , Thompson Andrew R. , Moen Rebecca J. , Thomas David D.
Published: June 2015

Significance

The interaction between actin and myosin is responsible for driving a vast array of essential biological processes, including the production of force in contracting muscle. However, the structural behavior of the two proteins in complex is not well understood, because high-resolution atomic models are not yet available by traditional methods. We use a bifunctional spin label and site-directed electron paramagnetic resonance spectroscopy to determine orientations of individual α-helices within the complex. We thus quantify for the first time, to our knowledge, structural changes within the motor domain of actin-bound myosin on nucleotide binding and dissociation. Our results provide valuable insight into the mechanism of muscle contraction while showcasing a method with wide applicability to other oriented biological systems.
Identification of a triplet pair intermediate in singlet exciton fission in solution
Authors: Stern Hannah L. , Musser Andrew J. , Gelinas Simon , Parkinson Patrick , Herz Laura M. , Bruzek Matthew J. , Anthony John , Friend Richard H. , Walker Brian J.
Published: June 2015

Significance

We use transient spectroscopy to investigate the mechanism of singlet exciton fission, a quantum mechanical phenomenon in some organic molecules in which a spin-singlet excited state can split into two spin-triplet states. This process may be harnessed to boost solar cell efficiencies, but the underlying mechanism remains poorly understood. Central to most models is a triplet pair state, consisting of two triplets entangled into an overall spin-singlet configuration, but it has never before been optically detected. In a solution-based system, we detect a state with simultaneous singlet and triplet exciton character that dissociates to form triplet excitons in 120% yield. We consider that this intermediate constitutes a triplet pair state, and its observation allows important insight into the nature of triplet exciton coupling.
Essential role of the cytochrome P450 CYP4F22 in the production of acylceramide, the key lipid for skin permeability barrier formation
Authors: Ohno Yusuke , Nakamichi Shota , Ohkuni Aya , Kamiyama Nozomi , Naoe Ayano , Tsujimura Hisashi , Yokose Urara , Sugiura Kazumitsu , Ishikawa Junko , Akiyama Masashi , Kihara Akio
Published: June 2015

Significance

The sphingolipid backbone ceramide is the major lipid species in the stratum corneum and plays a pivotal function in skin permeability barrier formation. Acylceramide is an important epidermis-specific ceramide species. However, the details of acylceramide production, including its synthetic genes, reactions and their orders, and intracellular site for production, have remained unclear. In the present study, we identified the cytochrome P450, family 4, subfamily F, polypeptide 22 (CYP4F22) as the missing fatty acid ω-hydroxylase required for acylceramide synthesis. We also determined that CYP4F22 is a type I endoplasmic reticulum membrane protein and that its substrate is ultra-long-chain fatty acids. Our findings provide important insights into the molecular mechanisms of not only acylceramide production but also skin permeability barrier formation.