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Sample records for algaas-based air-bridge-type two-dimensional

  1. Two dimensional vernier

    NASA Technical Reports Server (NTRS)

    Juday, Richard D. (Inventor)

    1992-01-01

    A two-dimensional vernier scale is disclosed utilizing a cartesian grid on one plate member with a polar grid on an overlying transparent plate member. The polar grid has multiple concentric circles at a fractional spacing of the spacing of the cartesian grid lines. By locating the center of the polar grid on a location on the cartesian grid, interpolation can be made of both the X and Y fractional relationship to the cartesian grid by noting which circles coincide with a cartesian grid line for the X and Y direction.

  2. Two-Dimensional IHCP Code

    1997-11-18

    QUENCH2D* is developed for the solution of general, non-linear, two-dimensional inverse heat transfer problems. This program provides estimates for the surface heat flux distribution and/or heat transfer coefficient as a function of time and space by using transient temperature measurements at appropriate interior points inside the quenched body. Two-dimensional planar and axisymmetric geometries such as turnbine disks and blades, clutch packs, and many other problems can be analyzed using QUENCH2D*.

  3. Cloaking two-dimensional fermions

    SciTech Connect

    Lin, De-Hone

    2011-09-15

    A cloaking theory for a two-dimensional spin-(1/2) fermion is proposed. It is shown that the spinor of the two-dimensional fermion can be cloaked perfectly through controlling the fermion's energy and mass in a specific manner moving in an effective vector potential inside a cloaking shell. Different from the cloaking of three-dimensional fermions, the scaling function that determines the invisible region is uniquely determined by a nonlinear equation. It is also shown that the efficiency of the cloaking shell is unaltered under the Aharonov-Bohm effect.

  4. Two-dimensional thermofield bosonization

    SciTech Connect

    Amaral, R.L.P.G.

    2005-12-15

    The main objective of this paper was to obtain an operator realization for the bosonization of fermions in 1 + 1 dimensions, at finite, non-zero temperature T. This is achieved in the framework of the real-time formalism of Thermofield Dynamics. Formally, the results parallel those of the T = 0 case. The well-known two-dimensional Fermion-Boson correspondences at zero temperature are shown to hold also at finite temperature. To emphasize the usefulness of the operator realization for handling a large class of two-dimensional quantum field-theoretic problems, we contrast this global approach with the cumbersome calculation of the fermion-current two-point function in the imaginary-time formalism and real-time formalisms. The calculations also illustrate the very different ways in which the transmutation from Fermi-Dirac to Bose-Einstein statistics is realized.

  5. Two dimensional unstable scar statistics.

    SciTech Connect

    Warne, Larry Kevin; Jorgenson, Roy Eberhardt; Kotulski, Joseph Daniel; Lee, Kelvin S. H. (ITT Industries/AES Los Angeles, CA)

    2006-12-01

    This report examines the localization of time harmonic high frequency modal fields in two dimensional cavities along periodic paths between opposing sides of the cavity. The cases where these orbits lead to unstable localized modes are known as scars. This paper examines the enhancements for these unstable orbits when the opposing mirrors are both convex and concave. In the latter case the construction includes the treatment of interior foci.

  6. Two-Dimensional Optical Storage

    NASA Astrophysics Data System (ADS)

    van der Lee, Alexander; Bruls, Dominique; Busch, Christopher; Immink, Andre; Coene, Wim; Hekstra, Andries

    2004-07-01

    Two-dimensional optical storage aims at increasing the data capacity and data rate for a given physical read-out system. It uses parallel read-out in combination with advanced signal-processing. Experimental results results on read only memory (ROM) discs are presented that proof the concept. Laser beam recorded discs proof the concept, and electron beam recorded disc show the feasibility at real physical parameters for a density at 35 GB with ample tilt margins.

  7. Two-dimensional colloidal alloys.

    PubMed

    Law, Adam D; Buzza, D Martin A; Horozov, Tommy S

    2011-03-25

    We study the structure of mixed monolayers of large (3 μm diameter) and small (1 μm diameter) very hydrophobic silica particles at an octane-water interface as a function of the number fraction of small particles ξ. We find that a rich variety of two-dimensional hexagonal super-lattices of large (A) and small (B) particles can be obtained in this system due to strong and long-range electrostatic repulsions through the nonpolar octane phase. The structures obtained for the different compositions are in good agreement with zero temperature calculations and finite temperature computer simulations. PMID:21517357

  8. Two-Dimensional Colloidal Alloys

    NASA Astrophysics Data System (ADS)

    Law, Adam D.; Buzza, D. Martin A.; Horozov, Tommy S.

    2011-03-01

    We study the structure of mixed monolayers of large (3μm diameter) and small (1μm diameter) very hydrophobic silica particles at an octane-water interface as a function of the number fraction of small particles ξ. We find that a rich variety of two-dimensional hexagonal super-lattices of large (A) and small (B) particles can be obtained in this system due to strong and long-range electrostatic repulsions through the nonpolar octane phase. The structures obtained for the different compositions are in good agreement with zero temperature calculations and finite temperature computer simulations.

  9. Measuring Monotony in Two-Dimensional Samples

    ERIC Educational Resources Information Center

    Kachapova, Farida; Kachapov, Ilias

    2010-01-01

    This note introduces a monotony coefficient as a new measure of the monotone dependence in a two-dimensional sample. Some properties of this measure are derived. In particular, it is shown that the absolute value of the monotony coefficient for a two-dimensional sample is between /"r"/ and 1, where "r" is the Pearson's correlation coefficient for…

  10. Electrical contacts to two-dimensional semiconductors

    NASA Astrophysics Data System (ADS)

    Allain, Adrien; Kang, Jiahao; Banerjee, Kaustav; Kis, Andras

    2015-12-01

    The performance of electronic and optoelectronic devices based on two-dimensional layered crystals, including graphene, semiconductors of the transition metal dichalcogenide family such as molybdenum disulphide (MoS2) and tungsten diselenide (WSe2), as well as other emerging two-dimensional semiconductors such as atomically thin black phosphorus, is significantly affected by the electrical contacts that connect these materials with external circuitry. Here, we present a comprehensive treatment of the physics of such interfaces at the contact region and discuss recent progress towards realizing optimal contacts for two-dimensional materials. We also discuss the requirements that must be fulfilled to realize efficient spin injection in transition metal dichalcogenides.

  11. Electrical contacts to two-dimensional semiconductors.

    PubMed

    Allain, Adrien; Kang, Jiahao; Banerjee, Kaustav; Kis, Andras

    2015-12-01

    The performance of electronic and optoelectronic devices based on two-dimensional layered crystals, including graphene, semiconductors of the transition metal dichalcogenide family such as molybdenum disulphide (MoS2) and tungsten diselenide (WSe2), as well as other emerging two-dimensional semiconductors such as atomically thin black phosphorus, is significantly affected by the electrical contacts that connect these materials with external circuitry. Here, we present a comprehensive treatment of the physics of such interfaces at the contact region and discuss recent progress towards realizing optimal contacts for two-dimensional materials. We also discuss the requirements that must be fulfilled to realize efficient spin injection in transition metal dichalcogenides.

  12. Two Dimensional Mechanism for Insect Hovering

    SciTech Connect

    Jane Wang, Z.

    2000-09-04

    Resolved computation of two dimensional insect hovering shows for the first time that a two dimensional hovering motion can generate enough lift to support a typical insect weight. The computation reveals a two dimensional mechanism of creating a downward dipole jet of counterrotating vortices, which are formed from leading and trailing edge vortices. The vortex dynamics further elucidates the role of the phase relation between the wing translation and rotation in lift generation and explains why the instantaneous forces can reach a periodic state after only a few strokes. The model predicts the lower limits in Reynolds number and amplitude above which the averaged forces are sufficient. (c) 2000 The American Physical Society.

  13. Theory of two-dimensional microcavity lasers

    SciTech Connect

    Harayama, Takahisa; Sunada, Satoshi; Ikeda, Kensuke S.

    2005-07-15

    We present theoretical models of two-dimensional (2D) microcavity lasers. The relation between stationary lasing modes and resonances or metastable states is elucidated for arbitrary shapes of 2D resonant microcavities.

  14. Two-Dimensional Planetary Surface Lander

    NASA Astrophysics Data System (ADS)

    Hemmati, H.; Sengupta, A.; Castillo, J.; McElrath, T.; Roberts, T.; Willis, P.

    2014-06-01

    A systems engineering study was conducted to leverage a new two-dimensional (2D) lander concept with a low per unit cost to enable scientific study at multiple locations with a single entry system as the delivery vehicle.

  15. Two-dimensional order and disorder thermofields

    SciTech Connect

    Belvedere, L. V.

    2006-11-15

    The main objective of this paper was to obtain the two-dimensional order and disorder thermal operators using the Thermofield Bosonization formalism. We show that the general property of the two-dimensional world according with the bosonized Fermi field at zero temperature can be constructed as a product of an order and a disorder variables which satisfy a dual field algebra holds at finite temperature. The general correlation functions of the order and disorder thermofields are obtained.

  16. Efficient Two-Dimensional-FFT Program

    NASA Technical Reports Server (NTRS)

    Miko, J.

    1992-01-01

    Program computes 64 X 64-point fast Fourier transform in less than 17 microseconds. Optimized 64 X 64 Point Two-Dimensional Fast Fourier Transform combines performance of real- and complex-valued one-dimensional fast Fourier transforms (FFT's) to execute two-dimensional FFT and coefficients of power spectrum. Coefficients used in many applications, including analyzing spectra, convolution, digital filtering, processing images, and compressing data. Source code written in C, 8086 Assembly, and Texas Instruments TMS320C30 Assembly languages.

  17. Two-dimensional Topology of Cosmological Reionization

    NASA Astrophysics Data System (ADS)

    Wang, Yougang; Park, Changbom; Xu, Yidong; Chen, Xuelei; Kim, Juhan

    2015-11-01

    We study the two-dimensional topology of the 21-cm differential brightness temperature for two hydrodynamic radiative transfer simulations and two semi-numerical models. In each model, we calculate the two-dimensional genus curve for the early, middle, and late epochs of reionization. It is found that the genus curve depends strongly on the ionized fraction of hydrogen in each model. The genus curves are significantly different for different reionization scenarios even when the ionized faction is the same. We find that the two-dimensional topology analysis method is a useful tool to constrain the reionization models. Our method can be applied to the future observations such as those of the Square Kilometre Array.

  18. TWO-DIMENSIONAL TOPOLOGY OF COSMOLOGICAL REIONIZATION

    SciTech Connect

    Wang, Yougang; Xu, Yidong; Chen, Xuelei; Park, Changbom; Kim, Juhan E-mail: cbp@kias.re.kr

    2015-11-20

    We study the two-dimensional topology of the 21-cm differential brightness temperature for two hydrodynamic radiative transfer simulations and two semi-numerical models. In each model, we calculate the two-dimensional genus curve for the early, middle, and late epochs of reionization. It is found that the genus curve depends strongly on the ionized fraction of hydrogen in each model. The genus curves are significantly different for different reionization scenarios even when the ionized faction is the same. We find that the two-dimensional topology analysis method is a useful tool to constrain the reionization models. Our method can be applied to the future observations such as those of the Square Kilometre Array.

  19. Two-Dimensional Turbulence in Magnetized Plasmas

    ERIC Educational Resources Information Center

    Kendl, A.

    2008-01-01

    In an inhomogeneous magnetized plasma the transport of energy and particles perpendicular to the magnetic field is in general mainly caused by quasi two-dimensional turbulent fluid mixing. The physics of turbulence and structure formation is of ubiquitous importance to every magnetically confined laboratory plasma for experimental or industrial…

  20. Two-Dimensional Motions of Rockets

    ERIC Educational Resources Information Center

    Kang, Yoonhwan; Bae, Saebyok

    2007-01-01

    We analyse the two-dimensional motions of the rockets for various types of rocket thrusts, the air friction and the gravitation by using a suitable representation of the rocket equation and the numerical calculation. The slope shapes of the rocket trajectories are discussed for the three types of rocket engines. Unlike the projectile motions, the…

  1. High-resolution two dimensional advective transport

    USGS Publications Warehouse

    Smith, P.E.; Larock, B.E.

    1989-01-01

    The paper describes a two-dimensional high-resolution scheme for advective transport that is based on a Eulerian-Lagrangian method with a flux limiter. The scheme is applied to the problem of pure-advection of a rotated Gaussian hill and shown to preserve the monotonicity property of the governing conservation law.

  2. Valley excitons in two-dimensional semiconductors

    SciTech Connect

    Yu, Hongyi; Cui, Xiaodong; Xu, Xiaodong; Yao, Wang

    2014-12-30

    Monolayer group-VIB transition metal dichalcogenides have recently emerged as a new class of semiconductors in the two-dimensional limit. The attractive properties include: the visible range direct band gap ideal for exploring optoelectronic applications; the intriguing physics associated with spin and valley pseudospin of carriers which implies potentials for novel electronics based on these internal degrees of freedom; the exceptionally strong Coulomb interaction due to the two-dimensional geometry and the large effective masses. The physics of excitons, the bound states of electrons and holes, has been one of the most actively studied topics on these two-dimensional semiconductors, where the excitons exhibit remarkably new features due to the strong Coulomb binding, the valley degeneracy of the band edges, and the valley dependent optical selection rules for interband transitions. Here we give a brief overview of the experimental and theoretical findings on excitons in two-dimensional transition metal dichalcogenides, with focus on the novel properties associated with their valley degrees of freedom.

  3. Valley excitons in two-dimensional semiconductors

    DOE PAGES

    Yu, Hongyi; Cui, Xiaodong; Xu, Xiaodong; Yao, Wang

    2014-12-30

    Monolayer group-VIB transition metal dichalcogenides have recently emerged as a new class of semiconductors in the two-dimensional limit. The attractive properties include: the visible range direct band gap ideal for exploring optoelectronic applications; the intriguing physics associated with spin and valley pseudospin of carriers which implies potentials for novel electronics based on these internal degrees of freedom; the exceptionally strong Coulomb interaction due to the two-dimensional geometry and the large effective masses. The physics of excitons, the bound states of electrons and holes, has been one of the most actively studied topics on these two-dimensional semiconductors, where the excitons exhibitmore » remarkably new features due to the strong Coulomb binding, the valley degeneracy of the band edges, and the valley dependent optical selection rules for interband transitions. Here we give a brief overview of the experimental and theoretical findings on excitons in two-dimensional transition metal dichalcogenides, with focus on the novel properties associated with their valley degrees of freedom.« less

  4. Program Generates Two-Dimensional Computational Grids

    NASA Technical Reports Server (NTRS)

    Vu, Bruce T.

    1994-01-01

    TDIGG is fast and versatile computer program for generating two-dimensional computational grids for use in programs solving equations of flow by finite-difference methods. Both algebraic and elliptic grid-generation systems included. Enables user to view results of each iteration. Written in FORTRAN 77.

  5. Two-Dimensional NMR Lineshape Analysis

    PubMed Central

    Waudby, Christopher A.; Ramos, Andres; Cabrita, Lisa D.; Christodoulou, John

    2016-01-01

    NMR titration experiments are a rich source of structural, mechanistic, thermodynamic and kinetic information on biomolecular interactions, which can be extracted through the quantitative analysis of resonance lineshapes. However, applications of such analyses are frequently limited by peak overlap inherent to complex biomolecular systems. Moreover, systematic errors may arise due to the analysis of two-dimensional data using theoretical frameworks developed for one-dimensional experiments. Here we introduce a more accurate and convenient method for the analysis of such data, based on the direct quantum mechanical simulation and fitting of entire two-dimensional experiments, which we implement in a new software tool, TITAN (TITration ANalysis). We expect the approach, which we demonstrate for a variety of protein-protein and protein-ligand interactions, to be particularly useful in providing information on multi-step or multi-component interactions. PMID:27109776

  6. Two-dimensional ranking of Wikipedia articles

    NASA Astrophysics Data System (ADS)

    Zhirov, A. O.; Zhirov, O. V.; Shepelyansky, D. L.

    2010-10-01

    The Library of Babel, described by Jorge Luis Borges, stores an enormous amount of information. The Library exists ab aeterno. Wikipedia, a free online encyclopaedia, becomes a modern analogue of such a Library. Information retrieval and ranking of Wikipedia articles become the challenge of modern society. While PageRank highlights very well known nodes with many ingoing links, CheiRank highlights very communicative nodes with many outgoing links. In this way the ranking becomes two-dimensional. Using CheiRank and PageRank we analyze the properties of two-dimensional ranking of all Wikipedia English articles and show that it gives their reliable classification with rich and nontrivial features. Detailed studies are done for countries, universities, personalities, physicists, chess players, Dow-Jones companies and other categories.

  7. Plasmonics with two-dimensional conductors

    PubMed Central

    Yoon, Hosang; Yeung, Kitty Y. M.; Kim, Philip; Ham, Donhee

    2014-01-01

    A wealth of effort in photonics has been dedicated to the study and engineering of surface plasmonic waves in the skin of three-dimensional bulk metals, owing largely to their trait of subwavelength confinement. Plasmonic waves in two-dimensional conductors, such as semiconductor heterojunction and graphene, contrast the surface plasmonic waves on bulk metals, as the former emerge at gigahertz to terahertz and infrared frequencies well below the photonics regime and can exhibit far stronger subwavelength confinement. This review elucidates the machinery behind the unique behaviours of the two-dimensional plasmonic waves and discusses how they can be engineered to create ultra-subwavelength plasmonic circuits and metamaterials for infrared and gigahertz to terahertz integrated electronics. PMID:24567472

  8. Plasmonics with two-dimensional conductors.

    PubMed

    Yoon, Hosang; Yeung, Kitty Y M; Kim, Philip; Ham, Donhee

    2014-03-28

    A wealth of effort in photonics has been dedicated to the study and engineering of surface plasmonic waves in the skin of three-dimensional bulk metals, owing largely to their trait of subwavelength confinement. Plasmonic waves in two-dimensional conductors, such as semiconductor heterojunction and graphene, contrast the surface plasmonic waves on bulk metals, as the former emerge at gigahertz to terahertz and infrared frequencies well below the photonics regime and can exhibit far stronger subwavelength confinement. This review elucidates the machinery behind the unique behaviours of the two-dimensional plasmonic waves and discusses how they can be engineered to create ultra-subwavelength plasmonic circuits and metamaterials for infrared and gigahertz to terahertz integrated electronics.

  9. Two-dimensional optimal sensor placement

    SciTech Connect

    Zhang, H.

    1995-05-01

    A method for determining the optimal two-dimensional spatial placement of multiple sensors participating in a robot perception task is introduced in this paper. This work is motivated by the fact that sensor data fusion is an effective means of reducing uncertainties in sensor observations, and that the combined uncertainty varies with the relative placement of the sensors with respect to each other. The problem of optimal sensor placement is formulated and a solution is presented in the two dimensional space. The algebraic structure of the combined sensor uncertainty with respect to the placement of sensor is studied. A necessary condition for optimal placement is derived and this necessary condition is used to obtain an efficient closed-form solution for the global optimal placement. Numerical examples are provided to illustrate the effectiveness and efficiency of the solution. 11 refs.

  10. Two dimensional wedge/translating shroud nozzle

    NASA Technical Reports Server (NTRS)

    Maiden, D. L. (Inventor)

    1978-01-01

    A jet propulsion exhaust nozzle is reported for multi-engine installations which produces high internal/external, thrust-minus-drag, performance for transonic cruise or transonic acceleration as well as improved performance at subsonic and supersonic speeds. A two dimensional wedge/translating shroud provides the variable nozzle exit geometry needed to achieve high engine performance over a wide range of throttle power settings.

  11. Deeply subrecoil two-dimensional Raman cooling

    SciTech Connect

    Boyer, V.; Phillips, W.D.; Lising, L.J.; Rolston, S.L.

    2004-10-01

    We report the implementation of a two-dimensional Raman cooling scheme using sequential excitations along the orthogonal axes. Using square pulses, we have cooled a cloud of ultracold cesium atoms down to an rms velocity spread of 0.39(5) recoil velocities, corresponding to an effective transverse temperature of 30 nK (0.15T{sub rec}). This technique can be useful to improve cold-atom atomic clocks and is particularly relevant for clocks in microgravity.

  12. Two-Dimensional Synthetic-Aperture Radiometer

    NASA Technical Reports Server (NTRS)

    LeVine, David M.

    2010-01-01

    A two-dimensional synthetic-aperture radiometer, now undergoing development, serves as a test bed for demonstrating the potential of aperture synthesis for remote sensing of the Earth, particularly for measuring spatial distributions of soil moisture and ocean-surface salinity. The goal is to use the technology for remote sensing aboard a spacecraft in orbit, but the basic principles of design and operation are applicable to remote sensing from aboard an aircraft, and the prototype of the system under development is designed for operation aboard an aircraft. In aperture synthesis, one utilizes several small antennas in combination with a signal processing in order to obtain resolution that otherwise would require the use of an antenna with a larger aperture (and, hence, potentially more difficult to deploy in space). The principle upon which this system is based is similar to that of Earth-rotation aperture synthesis employed in radio astronomy. In this technology the coherent products (correlations) of signals from pairs of antennas are obtained at different antenna-pair spacings (baselines). The correlation for each baseline yields a sample point in a Fourier transform of the brightness-temperature map of the scene. An image of the scene itself is then reconstructed by inverting the sampled transform. The predecessor of the present two-dimensional synthetic-aperture radiometer is a one-dimensional one, named the Electrically Scanned Thinned Array Radiometer (ESTAR). Operating in the L band, the ESTAR employs aperture synthesis in the cross-track dimension only, while using a conventional antenna for resolution in the along-track dimension. The two-dimensional instrument also operates in the L band to be precise, at a frequency of 1.413 GHz in the frequency band restricted for passive use (no transmission) only. The L band was chosen because (1) the L band represents the long-wavelength end of the remote- sensing spectrum, where the problem of achieving adequate

  13. Gauge equivalence in two-dimensional gravity

    SciTech Connect

    Fujiwara, T. ); Igarashi, Y. ); Kubo, J. ); Tabei, T. )

    1993-08-15

    Two-dimensional quantum gravity is identified as a second-class system which we convert into a first-class system via the Batalin-Fradkin (BF) procedure. Using the extended phase space method, we then formulate the theory in the most general class of gauges. The conformal gauge action suggested by David, Distler, and Kawai is derived from first principles. We find a local, light-cone gauge action whose Becchi-Rouet-Stora-Tyutin invariance implies Polyakov's curvature equation [partial derivative][sub [minus

  14. Quasicondensation in Two-Dimensional Fermi Gases.

    PubMed

    Wu, Chien-Te; Anderson, Brandon M; Boyack, Rufus; Levin, K

    2015-12-11

    In this paper we follow the analysis and protocols of recent experiments, combined with simple theory, to arrive at a physical understanding of quasi-condensation in two dimensional Fermi gases. A key signature of quasi-condensation, which contains aspects of Berezinskiĭ-Kosterlitz-Thouless behavior, is a strong zero momentum peak in the pair momentum distribution. Importantly, this peak emerges at a reasonably well defined onset temperature. The resulting phase diagram, pair momentum distribution, and algebraic power law decay are compatible with recent experiments throughout the continuum from BEC to BCS. PMID:26705613

  15. Two-dimensional photonic crystal surfactant detection.

    PubMed

    Zhang, Jian-Tao; Smith, Natasha; Asher, Sanford A

    2012-08-01

    We developed a novel two-dimensional (2-D) crystalline colloidal array photonic crystal sensing material for the visual detection of amphiphilic molecules in water. A close-packed polystyrene 2-D array monolayer was embedded in a poly(N-isopropylacrylamide) (PNIPAAm)-based hydrogel film. These 2-D photonic crystals placed on a mirror show intense diffraction that enables them to be used for visual determination of analytes. Binding of surfactant molecules attaches ions to the sensor that swells the PNIPAAm-based hydrogel. The resulting increase in particle spacing red shifts the 2-D diffracted light. Incorporation of more hydrophobic monomers increases the sensitivity to surfactants. PMID:22720790

  16. Pressure of two-dimensional Yukawa liquids

    NASA Astrophysics Data System (ADS)

    Feng, Yan; Goree, J.; Liu, Bin; Wang, Lei; Tian, Wen-de

    2016-06-01

    A simple analytic expression for the pressure of a two-dimensional Yukawa liquid is found by fitting results from a molecular dynamics simulation. The results verify that the pressure can be written as the sum of a potential term which is a simple multiple of the Coulomb potential energy at a distance of the Wigner-Seitz radius, and a kinetic term which is a multiple of the one for an ideal gas. Dimensionless coefficients for each of these terms are found empirically, by fitting. The resulting analytic expression, with its empirically determined coefficients, is plotted as isochores, or curves of constant area. These results should be applicable to monolayer dusty plasmas.

  17. Program For Two-Dimensional Thermoplastic Deformation

    NASA Technical Reports Server (NTRS)

    Orient, George E.

    1993-01-01

    SOLAS contains number of utility programs for use with finite-element simulations. Designed to handle two-dimensional problems of quasi-static thermoplastic deformation. Includes optional postprocessing software, independent of solution codes, generating unified element-by-element list of quantitative results of computation, plus file containing signed equivalent stresses, equivalent strains, and multiaxiality factor parameter. Signs of equivalent quantities expressed either with respect to maximum principal quantities or with respect to directions defined by user. Written in UNIX shell script and FORTRAN 77.

  18. Numerical simulations of two-dimensional QED

    SciTech Connect

    Carson, S.R.; Kenway, R.D.

    1986-02-01

    We describe the computer simulation of two-dimensional QED on a 64 x 64 Euclidean space-time lattice using the Susskind lattice fermion action. Theorder parameter for chiral symmetry breaking and the low-lying meson masses are calculated for both the model with two continuum flavours, which arises naturally in this formulation, and the model with one continuum falvour obtained by including a nonsymmetric mass term and setting one fermion mass equal to the cut-off. Results are compared with those obtined using the quenched approximation, and with analytic predictions.

  19. Can Two-Dimensional Boron Superconduct?

    PubMed

    Penev, Evgeni S; Kutana, Alex; Yakobson, Boris I

    2016-04-13

    Two-dimensional boron is expected to exhibit various structural polymorphs, all being metallic. Additionally, its small atomic mass suggests strong electron-phonon coupling, which in turn can enable superconducting behavior. Here we perform first-principles analysis of electronic structure, phonon spectra, and electron-phonon coupling of selected 2D boron polymorphs and show that the most stable structures predicted to feasibly form on a metal substrate should also exhibit intrinsic phonon-mediated superconductivity, with estimated critical temperature in the range of Tc ≈ 10-20 K.

  20. FRACFLO. Two-Dimensional Ground Water Transport

    SciTech Connect

    Gureghian, A.B.

    1990-07-01

    FRACFLO computes the two-dimensional, space, time dependent, convective dispersive transport of a single radionuclide in an unbounded single or multiple parallel fracture system with constant aperture. It calculates the one-dimensional diffusive transport into the rock matrix as well as the mass flux and cumulative mass flux at any point in the fracture. Steady-state isothermal ground water flow and parallel streamlines are assumed in the fracture, and the rock matrix is considered to be fully saturated with immobile water. The model can treat a single or multiple finite patch source or a Gaussian distributed source subject to a step or band release mode.

  1. Two-dimensional shape memory graphene oxide

    PubMed Central

    Chang, Zhenyue; Deng, Junkai; Chandrakumara, Ganaka G.; Yan, Wenyi; Liu, Jefferson Zhe

    2016-01-01

    Driven by the increasing demand for micro-/nano-technologies, stimuli-responsive shape memory materials at nanoscale have recently attracted great research interests. However, by reducing the size of conventional shape memory materials down to approximately nanometre range, the shape memory effect diminishes. Here, using density functional theory calculations, we report the discovery of a shape memory effect in a two-dimensional atomically thin graphene oxide crystal with ordered epoxy groups, namely C8O. A maximum recoverable strain of 14.5% is achieved as a result of reversible phase transition between two intrinsically stable phases. Our calculations conclude co-existence of the two stable phases in a coherent crystal lattice, giving rise to the possibility of constructing multiple temporary shapes in a single material, thus, enabling highly desirable programmability. With an atomic thickness, excellent shape memory mechanical properties and electric field stimulus, the discovery of a two-dimensional shape memory graphene oxide opens a path for the development of exceptional micro-/nano-electromechanical devices. PMID:27325441

  2. Two-dimensional shape memory graphene oxide

    NASA Astrophysics Data System (ADS)

    Chang, Zhenyue; Deng, Junkai; Chandrakumara, Ganaka G.; Yan, Wenyi; Liu, Jefferson Zhe

    2016-06-01

    Driven by the increasing demand for micro-/nano-technologies, stimuli-responsive shape memory materials at nanoscale have recently attracted great research interests. However, by reducing the size of conventional shape memory materials down to approximately nanometre range, the shape memory effect diminishes. Here, using density functional theory calculations, we report the discovery of a shape memory effect in a two-dimensional atomically thin graphene oxide crystal with ordered epoxy groups, namely C8O. A maximum recoverable strain of 14.5% is achieved as a result of reversible phase transition between two intrinsically stable phases. Our calculations conclude co-existence of the two stable phases in a coherent crystal lattice, giving rise to the possibility of constructing multiple temporary shapes in a single material, thus, enabling highly desirable programmability. With an atomic thickness, excellent shape memory mechanical properties and electric field stimulus, the discovery of a two-dimensional shape memory graphene oxide opens a path for the development of exceptional micro-/nano-electromechanical devices.

  3. Two-dimensional shape memory graphene oxide.

    PubMed

    Chang, Zhenyue; Deng, Junkai; Chandrakumara, Ganaka G; Yan, Wenyi; Liu, Jefferson Zhe

    2016-01-01

    Driven by the increasing demand for micro-/nano-technologies, stimuli-responsive shape memory materials at nanoscale have recently attracted great research interests. However, by reducing the size of conventional shape memory materials down to approximately nanometre range, the shape memory effect diminishes. Here, using density functional theory calculations, we report the discovery of a shape memory effect in a two-dimensional atomically thin graphene oxide crystal with ordered epoxy groups, namely C8O. A maximum recoverable strain of 14.5% is achieved as a result of reversible phase transition between two intrinsically stable phases. Our calculations conclude co-existence of the two stable phases in a coherent crystal lattice, giving rise to the possibility of constructing multiple temporary shapes in a single material, thus, enabling highly desirable programmability. With an atomic thickness, excellent shape memory mechanical properties and electric field stimulus, the discovery of a two-dimensional shape memory graphene oxide opens a path for the development of exceptional micro-/nano-electromechanical devices.

  4. Two-Dimensional Low-Turbulence Tunnel

    NASA Technical Reports Server (NTRS)

    1937-01-01

    Construction of the Two-Dimensional Low-Turbulence Tunnel. The Two-Dimensional Low-Turbulence Tunnel was originally called the Refrigeration or 'Ice' tunnel because it was intended to support research on aircraft icing. The tunnel was built of wood, lined with sheet steel, and heavily insulated on the outside. Refrigeration equipment was installed to generate icing conditions inside the test section. The NACA sent out a questionnaire to airline operators, asking them to detail the specific kinds of icing problems they encountered in flight. The replies became the basis for a comprehensive research program begun in 1938 when the tunnel commenced operation. Research quickly focused on the concept of using exhaust heat to prevent ice from forming on the wing's leading edge. This project was led by Lewis Rodert, who later would win the Collier Trophy for his work on deicing. By 1940, aircraft icing research had shifted to the new Ames Research Laboratory, and the Ice tunnel was refitted with screens and honeycomb. Researchers were trying to eliminate all turbulence in the test section. From TN 1283: 'The Langley two-dimensional low-turbulence pressure tunnel is a single-return closed-throat tunnel.... The tunnel is constructed of heavy steel plate so that the pressure of the air may be varied from approximately full vacuum to 10 atmospheres absolute, thereby giving a wide range of air densities. Reciprocating compressors with a capacity of 1200 cubic feet of free air per minute provide compressed air. Since the tunnel shell has a volume of about 83,000 cubic feet, a compression rate of approximately one atmosphere per hour is obtained. ... The test section is rectangular in shape, 3 feet wide, 7 1/2 feet high, and 7 1/2 feet long. ... The over-all size of the wind-tunnel shell is about 146 feet long and 58 feet wide with a maximum diameter of 26 feet. The test section and entrance and exit cones are surrounded by a 22-foot diameter section of the shell to provide a

  5. Two-Dimensional Low-Turbulence Tunnel

    NASA Technical Reports Server (NTRS)

    1938-01-01

    Construction of the wood frame for the Two-Dimensional Low-Turbulence Tunnel. The Two-Dimensional Low-Turbulence Tunnel was originally called the Refrigeration or 'Ice' tunnel because it was intended to support research on aircraft icing. The tunnel was built of wood, lined with sheet steel, and heavily insulated on the outside. Refrigeration equipment was installed to generate icing conditions inside the test section. The NACA sent out a questionnaire to airline operators, asking them to detail the specific kinds of icing problems they encountered in flight. The replies became the basis for a comprehensive research program begun in 1938 when the tunnel commenced operation. Research quickly focused on the concept of using exhaust heat to prevent ice from forming on the wing's leading edge. This project was led by Lewis Rodert, who later would win the Collier Trophy for his work on deicing. By 1940, aircraft icing research had shifted to the new Ames Research Laboratory, and the Ice tunnel was refitted with screens and honeycomb. Researchers were trying to eliminate all turbulence in the test section. From TN 1283: 'The Langley two-dimensional low-turbulence pressure tunnel is a single-return closed-throat tunnel.... The tunnel is constructed of heavy steel plate so that the pressure of the air may be varied from approximately full vacuum to 10 atmospheres absolute, thereby giving a wide range of air densities. Reciprocating compressors with a capacity of 1200 cubic feet of free air per minute provide compressed air. Since the tunnel shell has a volume of about 83,000 cubic feet, a compression rate of approximately one atmosphere per hour is obtained. ... The test section is rectangular in shape, 3 feet wide, 7 1/2 feet high, and 7 1/2 feet long. ... The over-all size of the wind-tunnel shell is about 146 feet long and 58 feet wide with a maximum diameter of 26 feet. The test section and entrance and exit cones are surrounded by a 22-foot diameter section of the

  6. Two-Dimensional Low-Turbulence Tunnel

    NASA Technical Reports Server (NTRS)

    1938-01-01

    Manometer for the Two-Dimensional Low-Turbulence Tunnel. The Two-Dimensional Low-Turbulence Tunnel was originally called the Refrigeration or 'Ice' tunnel because it was intended to support research on aircraft icing. The tunnel was built of wood, lined with sheet steel, and heavily insulated on the outside. Refrigeration equipment was installed to generate icing conditions inside the test section. The NACA sent out a questionnaire to airline operators, asking them to detail the specific kinds of icing problems they encountered in flight. The replies became the basis for a comprehensive research program begun in 1938 when the tunnel commenced operation. Research quickly focused on the concept of using exhaust heat to prevent ice from forming on the wing's leading edge. This project was led by Lewis Rodert, who later would win the Collier Trophy for his work on deicing. By 1940, aircraft icing research had shifted to the new Ames Research Laboratory, and the Ice tunnel was refitted with screens and honeycomb. Researchers were trying to eliminate all turbulence in the test section. From TN 1283: 'The Langley two-dimensional low-turbulence pressure tunnel is a single-return closed-throat tunnel.... The tunnel is constructed of heavy steel plate so that the pressure of the air may be varied from approximately full vacuum to 10 atmospheres absolute, thereby giving a wide range of air densities. Reciprocating compressors with a capacity of 1200 cubic feet of free air per minute provide compressed air. Since the tunnel shell has a volume of about 83,000 cubic feet, a compression rate of approximately one atmosphere per hour is obtained. ... The test section is rectangular in shape, 3 feet wide, 7 1/2 feet high, and 7 1/2 feet long. ... The over-all size of the wind-tunnel shell is about 146 feet long and 58 feet wide with a maximum diameter of 26 feet. The test section and entrance and exit cones are surrounded by a 22-foot diameter section of the shell to provide a space

  7. Multiscale modeling of two-dimensional contacts.

    PubMed

    Luan, B Q; Hyun, S; Molinari, J F; Bernstein, N; Robbins, Mark O

    2006-10-01

    A hybrid simulation method is introduced and used to study two-dimensional single-asperity and multi-asperity contacts both quasistatically and dynamically. The method combines an atomistic treatment of the interfacial region with a finite-element method description of subsurface deformations. The dynamics in the two regions are coupled through displacement boundary conditions applied at the outer edges of an overlap region. The two solutions are followed concurrently but with different time resolution. The method is benchmarked against full atomistic simulations. Accurate results are obtained for contact areas, pressures, and static and dynamic friction forces. The time saving depends on the fraction of the system treated atomistically and is already more than a factor of 20 for the relatively small systems considered here.

  8. Two-dimensional swimming behavior of bacteria

    NASA Astrophysics Data System (ADS)

    Li, Ye; Zhai, He; Sanchez, Sandra; Kearns, Daniel; Wu, Yilin

    Many bacteria swim by flagella motility which is essential for bacterial dispersal, chemotaxis, and pathogenesis. Here we combined single-cell tracking, theoretical analysis, and computational modeling to investigate two-dimensional swimming behavior of a well-characterized flagellated bacterium Bacillus subtilis at the single-cell level. We quantified the 2D motion pattern of B. subtilis in confined space and studied how cells interact with each other. Our findings shed light on bacterial colonization in confined environments, and will serve as the ground for building more accurate models to understand bacterial collective motion. Mailing address: Room 306 Science Centre North Block, The Chinese University of Hong Kong, Shatin, N.T. Hong Kong SAR. Phone: +852-3943-6354. Fax: +852-2603-5204. E-mail: ylwu@phy.cuhk.edu.hk.

  9. Two-Dimensional Speckle Strain Imaging

    PubMed Central

    Pignatelli, Ricardo; Law, Mark A.; Martinez, Hugo; Altman, Carolyn; Ayres, Nancy; Jefferies, John L.; Ganame, Javier

    2012-01-01

    Two-dimensional speckle-tracking strain imaging (speckle strain imaging) is useful for evaluating left ventricular myocardial function in patients with ischemic heart disease and cardiomyopathy, including hypertrophic and dilated phenotypes. The usefulness of speckle strain imaging in patients with pheochromocytoma who are undergoing adrenal surgery has been described, but we found no reports of the use of this method to evaluate ventricular dysfunction longitudinally in children. Herein, we describe the case of a 10-year-old girl with a paraganglioma, acute junctional tachycardia, and myocardial dysfunction. After control of the tachycardia and partial resection of the tumor, speckle strain imaging enabled clinical management that led to substantial improvement in the patient's initially diffuse myocardial dysfunction. Because conventional echocardiographic methods alone may be inadequate to guide the management of pediatric patients with partially resected neuroendocrine tumors, we recommend speckle strain imaging as an additional noninvasive option for treatment guidance and monitoring of cardiac tissue response. PMID:22412245

  10. Epitaxial growth of two-dimensional stanene

    NASA Astrophysics Data System (ADS)

    Zhu, Feng-Feng; Chen, Wei-Jiong; Xu, Yong; Gao, Chun-Lei; Guan, Dan-Dan; Liu, Can-Hua; Qian, Dong; Zhang, Shou-Cheng; Jia, Jin-Feng

    2015-10-01

    Following the first experimental realization of graphene, other ultrathin materials with unprecedented electronic properties have been explored, with particular attention given to the heavy group-IV elements Si, Ge and Sn. Two-dimensional buckled Si-based silicene has been recently realized by molecular beam epitaxy growth, whereas Ge-based germanene was obtained by molecular beam epitaxy and mechanical exfoliation. However, the synthesis of Sn-based stanene has proved challenging so far. Here, we report the successful fabrication of 2D stanene by molecular beam epitaxy, confirmed by atomic and electronic characterization using scanning tunnelling microscopy and angle-resolved photoemission spectroscopy, in combination with first-principles calculations. The synthesis of stanene and its derivatives will stimulate further experimental investigation of their theoretically predicted properties, such as a 2D topological insulating behaviour with a very large bandgap, and the capability to support enhanced thermoelectric performance, topological superconductivity and the near-room-temperature quantum anomalous Hall effect.

  11. Intrinsic two-dimensional features as textons

    NASA Technical Reports Server (NTRS)

    Barth, E.; Zetzsche, C.; Rentschler, I.

    1998-01-01

    We suggest that intrinsic two-dimensional (i2D) features, computationally defined as the outputs of nonlinear operators that model the activity of end-stopped neurons, play a role in preattentive texture discrimination. We first show that for discriminable textures with identical power spectra the predictions of traditional models depend on the type of nonlinearity and fail for energy measures. We then argue that the concept of intrinsic dimensionality, and the existence of end-stopped neurons, can help us to understand the role of the nonlinearities. Furthermore, we show examples in which models without strong i2D selectivity fail to predict the correct ranking order of perceptual segregation. Our arguments regarding the importance of i2D features resemble the arguments of Julesz and co-workers regarding textons such as terminators and crossings. However, we provide a computational framework that identifies textons with the outputs of nonlinear operators that are selective to i2D features.

  12. Janus Spectra in Two-Dimensional Flows.

    PubMed

    Liu, Chien-Chia; Cerbus, Rory T; Chakraborty, Pinaki

    2016-09-01

    In large-scale atmospheric flows, soap-film flows, and other two-dimensional flows, the exponent of the turbulent energy spectra, α, may theoretically take either of two distinct values, 3 or 5/3, but measurements downstream of obstacles have invariably revealed α=3. Here we report experiments on soap-film flows where downstream of obstacles there exists a sizable interval in which α transitions from 3 to 5/3 for the streamwise fluctuations but remains equal to 3 for the transverse fluctuations, as if two mutually independent turbulent fields of disparate dynamics were concurrently active within the flow. This species of turbulent energy spectra, which we term the Janus spectra, has never been observed or predicted theoretically. Our results may open up new vistas in the study of turbulence and geophysical flows. PMID:27661693

  13. Two-dimensional ultrasound and cardiac operations.

    PubMed

    Spotnitz, H M

    1982-01-01

    Two-dimensional ultrasound was employed for qualitative and quantitative studies during cardiac operations in 74 patients. A gas-sterilized phased-array transducer applied directly to the anterior surface of the heart produced high-quality images without a water path or other special manipulations. The techniques employed were successful in demonstrating alterations in cardiac anatomy associated with valve disease and cardiac tumors. Continuous clouds of microbubbles ejected from the left ventricle immediately following cardiopulmonary bypass were detected in 42% of 45 patients studied. Measurement of short-axis area change during systole proved useful for evaluation of intraoperative changes in left ventricular function. In the perioperative period, with the chest closed, the method detected increasing left ventricular mass during transplant rejection and was useful for monitoring changes in left ventricular performance when image quality was sufficient. The capabilities and limitations of this technique for special studies during cardiac operations should be familiar to surgeons with access to the method.

  14. Two-dimensional nuclear magnetic resonance petrophysics.

    PubMed

    Sun, Boqin; Dunn, Keh-Jim

    2005-02-01

    Two-dimensional nuclear magnetic resonance (2D NMR) opens a wide area for exploration in petrophysics and has significant impact to petroleum logging technology. When there are multiple fluids with different diffusion coefficients saturated in a porous medium, this information can be extracted and clearly delineated from CPMG measurements of such a system either using regular pulsing sequences or modified two window sequences. The 2D NMR plot with independent variables of T2 relaxation time and diffusion coefficient allows clear separation of oil and water signals in the rocks. This 2D concept can be extended to general studies of fluid-saturated porous media involving other combinations of two or more independent variables, such as chemical shift and T1/T2 relaxation time (reflecting pore size), proton population and diffusion contrast, etc. PMID:15833623

  15. Two-dimensional dipolar nematic colloidal crystals.

    PubMed

    Skarabot, M; Ravnik, M; Zumer, S; Tkalec, U; Poberaj, I; Babic, D; Osterman, N; Musevic, I

    2007-11-01

    We study the interactions and directed assembly of dipolar nematic colloidal particles in planar nematic cells using laser tweezers. The binding energies for two stable configurations of a colloidal pair with homeotropic surface alignment are determined. It is shown that the orientation of the dipolar colloidal particle can efficiently be controlled and changed by locally quenching the nematic liquid crystal from the laser-induced isotropic phase. The interaction of a single colloidal particle with a single colloidal chain is determined and the interactions between pairs of colloidal chains are studied. We demonstrate that dipolar colloidal chains self-assemble into the two-dimensional (2D) dipolar nematic colloidal crystals. An odd-even effect is observed with increasing number of colloidal chains forming the 2D colloidal crystal. PMID:18233658

  16. Two-dimensional Inductive Position Sensing System

    NASA Technical Reports Server (NTRS)

    Youngquist, Robert C. (Inventor); Starr, Stanley O. (Inventor)

    2015-01-01

    A two-dimensional inductive position sensing system uses four drive inductors arranged at the vertices of a parallelogram and a sensing inductor positioned within the parallelogram. The sensing inductor is movable within the parallelogram and relative to the drive inductors. A first oscillating current at a first frequency is supplied to a first pair of the drive inductors located at ends of a first diagonal of the parallelogram. A second oscillating current at a second frequency is supplied to a second pair of the drive inductors located at ends of a second diagonal of the parallelogram. As a result, the sensing inductor generates a first output voltage at the first frequency and a second output voltage at the second frequency. A processor determines a position of the sensing inductor relative to the drive inductors using the first output voltage and the second output voltage.

  17. Janus Spectra in Two-Dimensional Flows

    NASA Astrophysics Data System (ADS)

    Liu, Chien-Chia; Cerbus, Rory T.; Chakraborty, Pinaki

    2016-09-01

    In large-scale atmospheric flows, soap-film flows, and other two-dimensional flows, the exponent of the turbulent energy spectra, α , may theoretically take either of two distinct values, 3 or 5 /3 , but measurements downstream of obstacles have invariably revealed α =3 . Here we report experiments on soap-film flows where downstream of obstacles there exists a sizable interval in which α transitions from 3 to 5 /3 for the streamwise fluctuations but remains equal to 3 for the transverse fluctuations, as if two mutually independent turbulent fields of disparate dynamics were concurrently active within the flow. This species of turbulent energy spectra, which we term the Janus spectra, has never been observed or predicted theoretically. Our results may open up new vistas in the study of turbulence and geophysical flows.

  18. Local doping of two-dimensional materials

    DOEpatents

    Wong, Dillon; Velasco, Jr, Jairo; Ju, Long; Kahn, Salman; Lee, Juwon; Germany, Chad E.; Zettl, Alexander K.; Wang, Feng; Crommie, Michael F.

    2016-09-20

    This disclosure provides systems, methods, and apparatus related to locally doping two-dimensional (2D) materials. In one aspect, an assembly including a substrate, a first insulator disposed on the substrate, a second insulator disposed on the first insulator, and a 2D material disposed on the second insulator is formed. A first voltage is applied between the 2D material and the substrate. With the first voltage applied between the 2D material and the substrate, a second voltage is applied between the 2D material and a probe positioned proximate the 2D material. The second voltage between the 2D material and the probe is removed. The first voltage between the 2D material and the substrate is removed. A portion of the 2D material proximate the probe when the second voltage was applied has a different electron density compared to a remainder of the 2D material.

  19. Two-dimensional fourier transform spectrometer

    DOEpatents

    DeFlores, Lauren; Tokmakoff, Andrei

    2013-09-03

    The present invention relates to a system and methods for acquiring two-dimensional Fourier transform (2D FT) spectra. Overlap of a collinear pulse pair and probe induce a molecular response which is collected by spectral dispersion of the signal modulated probe beam. Simultaneous collection of the molecular response, pulse timing and characteristics permit real time phasing and rapid acquisition of spectra. Full spectra are acquired as a function of pulse pair timings and numerically transformed to achieve the full frequency-frequency spectrum. This method demonstrates the ability to acquire information on molecular dynamics, couplings and structure in a simple apparatus. Multi-dimensional methods can be used for diagnostic and analytical measurements in the biological, biomedical, and chemical fields.

  20. Two-dimensional fourier transform spectrometer

    DOEpatents

    DeFlores, Lauren; Tokmakoff, Andrei

    2016-10-25

    The present invention relates to a system and methods for acquiring two-dimensional Fourier transform (2D FT) spectra. Overlap of a collinear pulse pair and probe induce a molecular response which is collected by spectral dispersion of the signal modulated probe beam. Simultaneous collection of the molecular response, pulse timing and characteristics permit real time phasing and rapid acquisition of spectra. Full spectra are acquired as a function of pulse pair timings and numerically transformed to achieve the full frequency-frequency spectrum. This method demonstrates the ability to acquire information on molecular dynamics, couplings and structure in a simple apparatus. Multi-dimensional methods can be used for diagnostic and analytical measurements in the biological, biomedical, and chemical fields.

  1. Two-Dimensional Ground Water Transport

    1992-03-05

    FRACFLO computes the two-dimensional, space, time dependent, convective dispersive transport of a single radionuclide in an unbounded single or multiple parallel fracture system with constant aperture. It calculates the one-dimensional diffusive transport into the rock matrix as well as the mass flux and cumulative mass flux at any point in the fracture. Steady-state isothermal ground water flow and parallel streamlines are assumed in the fracture, and the rock matrix is considered to be fully saturatedmore » with immobile water. The model can treat a single or multiple finite patch source or a Gaussian distributed source subject to a step or band release mode.« less

  2. Two-dimensional Gel Electrophoresis (2DE)

    NASA Astrophysics Data System (ADS)

    Kłodzińska, Ewa; Buszewski, Bogusław

    The chemical compounds, which are present in the environment, increasingly cause bad effects on health. The most serious effects are tumors and various mutations at the cellular level. Such compounds, from the analytical point of view, can serve the function of biomarkers, constituting measurable changes in the organism's cells and biochemical processes occurring therein. The challenge of the twenty-first century is therefore searching for effective and reliable methods of identification of biomarkers as well as understanding bodily functions, which occur in living organisms at the molecular level. The irreplaceable tool for these examinations is proteomics, which includes both quality and quantity analysis of proteins composition, and also makes it possible to learn their functions and expressions. The success of proteomics examinations lies in the usage of innovative analytical techniques, such as electromigration technique, two-dimensional electrophoresis in polyacrylamide gel (2D PAGE), liquid chromatography, together with high resolution mass spectrometry and bio-informatical data analysis. Proteomics joins together a number of techniques used for analysis of hundreds or thousands of proteins. Its main task is not the examination of proteins inside the particular tissue but searching for the differences in the proteins' profile between bad and healthy tissues. These differences can tell us a lot regarding the cause of the sickness as well as its consequences. For instance, using the proteomics analysis it is possible to find relatively fast new biomarkers of tumor diseases, which in the future will be used for both screening and foreseeing the course of illness. In this chapter we focus on two-dimensional electrophoresis because as it seems, it may be of enormous importance when searching for biomarkers of cancer diseases.

  3. Two-dimensional virtual impactors. Final report

    SciTech Connect

    Forney, L.J.; Ravenhall, D.G.

    1980-12-01

    Theoretical predictions using both potential flow analyses and solutions to Navier-Stokes equations are made for the operating characteristics of a two-dimensional virtual impactor. Experiments were performed with 2.5 ..mu..m, uranine tagged, di-octylphthalate (DOP) oil droplets for a wide range of prototype geometries to measure the magnitude of internal losses and to fully characterize the instrument response. The influence of geometry including the throat angle (38/sup 0/ less than or equal to ..beta../sub 0/ less than or equal to 58.2/sup 0/) and normalized void width (0.7 less than or equal to h/w less than or equal to 1.5) on the particle cutoff diameter, efficiency curve steepness and properties of the internal particle loss factor are presented for fixed instrument Reynolds numbers Re = 1540 and bleed flow f = 0.1. The theory, supported by trends in the empirical data, predicts that internal particle losses reduce to zero as the normalized void width increases to h/w = 1.4 +- .1 while the data show a minimum at h/w = 1.6 +- .1. Increasing the void width, however, is shown to substantially reduce the steepness of the particle efficiency curves. Visual observations of the onset of fluid separation for two-dimensional jets impinging upon a void were conducted with a scaled-up water model and correlated with theory. It was found that the limiting void width h/sub lim//w marking the onset of fluid instabilities peaked for an intermediate value of the fluid deflecting plate angle ..beta.. approx. = 80/sup 0/ with larger values of h/sub lim//w corresponding to smaller throat angles ..beta../sub 0/. The limiting void width h/sub lim//w also increased with larger bleed flows into the void. These instabilities may make it difficult to correlate experimental virtual impactor data with theory.

  4. Two-Dimensional Phononic Crystals: Disorder Matters.

    PubMed

    Wagner, Markus R; Graczykowski, Bartlomiej; Reparaz, Juan Sebastian; El Sachat, Alexandros; Sledzinska, Marianna; Alzina, Francesc; Sotomayor Torres, Clivia M

    2016-09-14

    The design and fabrication of phononic crystals (PnCs) hold the key to control the propagation of heat and sound at the nanoscale. However, there is a lack of experimental studies addressing the impact of order/disorder on the phononic properties of PnCs. Here, we present a comparative investigation of the influence of disorder on the hypersonic and thermal properties of two-dimensional PnCs. PnCs of ordered and disordered lattices are fabricated of circular holes with equal filling fractions in free-standing Si membranes. Ultrafast pump and probe spectroscopy (asynchronous optical sampling) and Raman thermometry based on a novel two-laser approach are used to study the phononic properties in the gigahertz (GHz) and terahertz (THz) regime, respectively. Finite element method simulations of the phonon dispersion relation and three-dimensional displacement fields furthermore enable the unique identification of the different hypersonic vibrations. The increase of surface roughness and the introduction of short-range disorder are shown to modify the phonon dispersion and phonon coherence in the hypersonic (GHz) range without affecting the room-temperature thermal conductivity. On the basis of these findings, we suggest a criteria for predicting phonon coherence as a function of roughness and disorder. PMID:27580163

  5. Seismic isolation of two dimensional periodic foundations

    SciTech Connect

    Yan, Y.; Mo, Y. L.; Laskar, A.; Cheng, Z.; Shi, Z.; Menq, F.; Tang, Y.

    2014-07-28

    Phononic crystal is now used to control acoustic waves. When the crystal goes to a larger scale, it is called periodic structure. The band gaps of the periodic structure can be reduced to range from 0.5 Hz to 50 Hz. Therefore, the periodic structure has potential applications in seismic wave reflection. In civil engineering, the periodic structure can be served as the foundation of upper structure. This type of foundation consisting of periodic structure is called periodic foundation. When the frequency of seismic waves falls into the band gaps of the periodic foundation, the seismic wave can be blocked. Field experiments of a scaled two dimensional (2D) periodic foundation with an upper structure were conducted to verify the band gap effects. Test results showed the 2D periodic foundation can effectively reduce the response of the upper structure for excitations with frequencies within the frequency band gaps. When the experimental and the finite element analysis results are compared, they agree well with each other, indicating that 2D periodic foundation is a feasible way of reducing seismic vibrations.

  6. Predicting Two-Dimensional Silicon Carbide Monolayers.

    PubMed

    Shi, Zhiming; Zhang, Zhuhua; Kutana, Alex; Yakobson, Boris I

    2015-10-27

    Intrinsic semimetallicity of graphene and silicene largely limits their applications in functional devices. Mixing carbon and silicon atoms to form two-dimensional (2D) silicon carbide (SixC1-x) sheets is promising to overcome this issue. Using first-principles calculations combined with the cluster expansion method, we perform a comprehensive study on the thermodynamic stability and electronic properties of 2D SixC1-x monolayers with 0 ≤ x ≤ 1. Upon varying the silicon concentration, the 2D SixC1-x presents two distinct structural phases, a homogeneous phase with well dispersed Si (or C) atoms and an in-plane hybrid phase rich in SiC domains. While the in-plane hybrid structure shows uniform semiconducting properties with widely tunable band gap from 0 to 2.87 eV due to quantum confinement effect imposed by the SiC domains, the homogeneous structures can be semiconducting or remain semimetallic depending on a superlattice vector which dictates whether the sublattice symmetry is topologically broken. Moreover, we reveal a universal rule for describing the electronic properties of the homogeneous SixC1-x structures. These findings suggest that the 2D SixC1-x monolayers may present a new "family" of 2D materials, with a rich variety of properties for applications in electronics and optoelectronics. PMID:26394207

  7. Two-dimensional Dirac signature of germanene

    SciTech Connect

    Zhang, L.; Bampoulis, P.; Houselt, A. van; Zandvliet, H. J. W.

    2015-09-14

    The structural and electronic properties of germanene coated Ge{sub 2}Pt clusters have been determined by scanning tunneling microscopy and spectroscopy at room temperature. The interior of the germanene sheet exhibits a buckled honeycomb structure with a lattice constant of 4.3 Å and a buckling of 0.2 Å. The zigzag edges of germanene are reconstructed and display a 4× periodicity. The differential conductivity of the interior of the germanene sheet has a V-shape, which is reminiscent of the density of states of a two-dimensional Dirac system. The minimum of the differential conductivity is located close to the Fermi level and has a non-zero value, which we ascribe to the metallic character of the underlying Ge{sub 2}Pt substrate. Near the reconstructed germanene zigzag edges the shape of the differential conductivity changes from a V-shape to a more parabolic-like shape, revealing that the reconstructed germanene zigzag edges do not exhibit a pronounced metallic edge state.

  8. Predicting Two-Dimensional Silicon Carbide Monolayers.

    PubMed

    Shi, Zhiming; Zhang, Zhuhua; Kutana, Alex; Yakobson, Boris I

    2015-10-27

    Intrinsic semimetallicity of graphene and silicene largely limits their applications in functional devices. Mixing carbon and silicon atoms to form two-dimensional (2D) silicon carbide (SixC1-x) sheets is promising to overcome this issue. Using first-principles calculations combined with the cluster expansion method, we perform a comprehensive study on the thermodynamic stability and electronic properties of 2D SixC1-x monolayers with 0 ≤ x ≤ 1. Upon varying the silicon concentration, the 2D SixC1-x presents two distinct structural phases, a homogeneous phase with well dispersed Si (or C) atoms and an in-plane hybrid phase rich in SiC domains. While the in-plane hybrid structure shows uniform semiconducting properties with widely tunable band gap from 0 to 2.87 eV due to quantum confinement effect imposed by the SiC domains, the homogeneous structures can be semiconducting or remain semimetallic depending on a superlattice vector which dictates whether the sublattice symmetry is topologically broken. Moreover, we reveal a universal rule for describing the electronic properties of the homogeneous SixC1-x structures. These findings suggest that the 2D SixC1-x monolayers may present a new "family" of 2D materials, with a rich variety of properties for applications in electronics and optoelectronics.

  9. Epitaxial Growth of Two-Dimensional Stanene

    NASA Astrophysics Data System (ADS)

    Jia, Jinfeng

    Ultrathin semiconductors present various novel electronic properties. The first experimental realized two-dimensional (2D) material is graphene. Searching 2D materials with heavy elements bring the attention to Si, Ge and Sn. 2D buckled Si-based silicene was realized by molecular beam epitaxy (MBE) growth. Ge-based germanene was realized by mechanical exfoliation. Sn-based stanene has its unique properties. Stanene and its derivatives can be 2D topological insulators (TI) with a very large band gap as proposed by first-principles calculations, or can support enhanced thermoelectric performance, topological superconductivity and the near-room-temperature quantum anomalous Hall (QAH) effect. For the first time, in this work, we report a successful fabrication of 2D stanene by MBE. The atomic and electronic structures were determined by scanning tunneling microscopy (STM) and angle-resolved photoemission spectroscopy (ARPES) in combination with first-principles calculations. This work will stimulate the experimental study and exploring the future application of stanene. In cooperation with Fengfeng Zhu, Wei-jiong Chen, Yong Xu, Chun-lei Gao, Dan-dan Guan, Canhua Liu, Dong Qian, Shou-Cheng Zhang.

  10. Photodetectors based on two dimensional materials

    NASA Astrophysics Data System (ADS)

    Zheng, Lou; Zhongzhu, Liang; Guozhen, Shen

    2016-09-01

    Two-dimensional (2D) materials with unique properties have received a great deal of attention in recent years. This family of materials has rapidly established themselves as intriguing building blocks for versatile nanoelectronic devices that offer promising potential for use in next generation optoelectronics, such as photodetectors. Furthermore, their optoelectronic performance can be adjusted by varying the number of layers. They have demonstrated excellent light absorption, enabling ultrafast and ultrasensitive detection of light in photodetectors, especially in their single-layer structure. Moreover, due to their atomic thickness, outstanding mechanical flexibility, and large breaking strength, these materials have been of great interest for use in flexible devices and strain engineering. Toward that end, several kinds of photodetectors based on 2D materials have been reported. Here, we present a review of the state-of-the-art in photodetectors based on graphene and other 2D materials, such as the graphene, transition metal dichalcogenides, and so on. Project supported by the National Natural Science Foundation of China (Nos. 61377033, 61574132, 61504136) and the State Key Laboratory of Applied Optics, Changchun Institute of Optics, Fine Mechanics and Physics, Chinese Academy of Sciences.

  11. Braid Entropy of Two-Dimensional Turbulence.

    PubMed

    Francois, Nicolas; Xia, Hua; Punzmann, Horst; Faber, Benjamin; Shats, Michael

    2015-12-22

    The evolving shape of material fluid lines in a flow underlies the quantitative prediction of the dissipation and material transport in many industrial and natural processes. However, collecting quantitative data on this dynamics remains an experimental challenge in particular in turbulent flows. Indeed the deformation of a fluid line, induced by its successive stretching and folding, can be difficult to determine because such description ultimately relies on often inaccessible multi-particle information. Here we report laboratory measurements in two-dimensional turbulence that offer an alternative topological viewpoint on this issue. This approach characterizes the dynamics of a braid of Lagrangian trajectories through a global measure of their entanglement. The topological length NE of material fluid lines can be derived from these braids. This length is found to grow exponentially with time, giving access to the braid topological entropy SBraid. The entropy increases as the square root of the turbulent kinetic energy and is directly related to the single-particle dispersion coefficient. At long times, the probability distribution of NE is positively skewed and shows strong exponential tails. Our results suggest that SBraid may serve as a measure of the irreversibility of turbulence based on minimal principles and sparse Lagrangian data.

  12. Two-dimensional cyanates: stabilization through hydrogenation.

    PubMed

    Tsetseris, Leonidas

    2016-06-01

    According to first-principles calculations, it should be possible to grow two-dimensional (2D) forms of copper thio-cyanate (CuSCN) and copper seleno-cyanate (CuSeCN) since their energies are only marginally higher than those of their most stable three-dimensional (3D) wurtzite structures. Here we show using the same theoretical approach that chemisorption reactions of hydrogen molecules with the above-mentioned 2D CuSCN and CuSeCN systems enhance their stability as they decrease the energy difference with respect to the corresponding hydrogenated forms of the wurtzite crystals. Hydrogenation causes a sizeable decrease in the energy band gap by 0.56 eV and 0.65 eV for hydrogenated 2D-CuSCN (CuSCNH2) and 2D-CuSeCN (CuSeCNH2), respectively. Finally, we describe the stability of hydrogen vacancies in CuSCNH2 and CuSeCNH2 and show that the presence of isolated single H vacancies or di-vacancies does not affect significantly the electronic properties of the host systems close to the valence and conduction band edges. PMID:27183226

  13. Two-dimensional atomic crystals beyond graphene

    NASA Astrophysics Data System (ADS)

    Kaul, Anupama B.

    2014-06-01

    Carbon-based nanostructures have been the center of intense research and development for more than two decades now. Of these materials, graphene, a two-dimensional (2D) layered material system, has had a significant impact on science and technology over the past decade after monolayers of this material were experimentally isolated in 2004. The recent emergence of other classes of 2D graphene-like layered materials has added yet more exciting dimensions for research in exploring the diverse properties and applications arising from these 2D material systems. For example, hexagonal-BN, a layered material closest in structure to graphene, is an insulator, while NbSe2, a transition metal di-chalcogenide, is metallic and monolayers of other transition metal di-chalcogenides such as MoS2 are direct band-gap semiconductors. The rich spectrum of properties that 2D layered material systems offer can potentially be engineered ondemand, and creates exciting prospects for using such materials in applications ranging from electronics, sensing, photonics, energy harvesting and flexible electronics over the coming years.

  14. Two-Dimensional Phononic Crystals: Disorder Matters.

    PubMed

    Wagner, Markus R; Graczykowski, Bartlomiej; Reparaz, Juan Sebastian; El Sachat, Alexandros; Sledzinska, Marianna; Alzina, Francesc; Sotomayor Torres, Clivia M

    2016-09-14

    The design and fabrication of phononic crystals (PnCs) hold the key to control the propagation of heat and sound at the nanoscale. However, there is a lack of experimental studies addressing the impact of order/disorder on the phononic properties of PnCs. Here, we present a comparative investigation of the influence of disorder on the hypersonic and thermal properties of two-dimensional PnCs. PnCs of ordered and disordered lattices are fabricated of circular holes with equal filling fractions in free-standing Si membranes. Ultrafast pump and probe spectroscopy (asynchronous optical sampling) and Raman thermometry based on a novel two-laser approach are used to study the phononic properties in the gigahertz (GHz) and terahertz (THz) regime, respectively. Finite element method simulations of the phonon dispersion relation and three-dimensional displacement fields furthermore enable the unique identification of the different hypersonic vibrations. The increase of surface roughness and the introduction of short-range disorder are shown to modify the phonon dispersion and phonon coherence in the hypersonic (GHz) range without affecting the room-temperature thermal conductivity. On the basis of these findings, we suggest a criteria for predicting phonon coherence as a function of roughness and disorder.

  15. Dynamics of two-dimensional dipole systems

    SciTech Connect

    Golden, Kenneth I.; Kalman, Gabor J.; Hartmann, Peter; Donko, Zoltan

    2010-09-15

    Using a combined analytical/molecular dynamics approach, we study the current fluctuation spectra and longitudinal and transverse collective mode dispersions of the classical two-dimensional (point) dipole system (2DDS) characterized by the {phi}{sub D}(r)={mu}{sup 2}/r{sup 3} repulsive interaction potential; {mu} is the electric dipole strength. The interest in the 2DDS is twofold. First, the quasi-long-range 1/r{sup 3} interaction makes the system a unique classical many-body system, with a remarkable collective mode behavior. Second, the system may be a good model for a closely spaced semiconductor electron-hole bilayer, a system that is in the forefront of current experimental interest. The longitudinal collective excitations, which are of primary interest for the liquid phase, are acoustic at long wavelengths. At higher wave numbers and for sufficiently high coupling strength, we observe the formation of a deep minimum in the dispersion curve preceded by a sharp maximum; this is identical to what has been observed in the dispersion of the zero-temperature bosonic dipole system, which in turn emulates so-called roton-maxon excitation spectrum of the superfluid {sup 4}He. The analysis we present gives an insight into the emergence of this apparently universal structure, governed by strong correlations. We study both the liquid and the crystalline solid state. We also observe the excitation of combination frequencies, resembling the roton-roton, roton-maxon, etc. structures in {sup 4}He.

  16. An atlas of two-dimensional materials.

    PubMed

    Miró, Pere; Audiffred, Martha; Heine, Thomas

    2014-09-21

    The discovery of graphene and other two-dimensional (2D) materials together with recent advances in exfoliation techniques have set the foundations for the manufacturing of single layered sheets from any layered 3D material. The family of 2D materials encompasses a wide selection of compositions including almost all the elements of the periodic table. This derives into a rich variety of electronic properties including metals, semimetals, insulators and semiconductors with direct and indirect band gaps ranging from ultraviolet to infrared throughout the visible range. Thus, they have the potential to play a fundamental role in the future of nanoelectronics, optoelectronics and the assembly of novel ultrathin and flexible devices. We categorize the 2D materials according to their structure, composition and electronic properties. In this review we distinguish atomically thin materials (graphene, silicene, germanene, and their saturated forms; hexagonal boron nitride; silicon carbide), rare earth, semimetals, transition metal chalcogenides and halides, and finally synthetic organic 2D materials, exemplified by 2D covalent organic frameworks. Our exhaustive data collection presented in this Atlas demonstrates the large diversity of electronic properties, including band gaps and electron mobilities. The key points of modern computational approaches applied to 2D materials are presented with special emphasis to cover their range of application, peculiarities and pitfalls. PMID:24825454

  17. Braid Entropy of Two-Dimensional Turbulence

    PubMed Central

    Francois, Nicolas; Xia, Hua; Punzmann, Horst; Faber, Benjamin; Shats, Michael

    2015-01-01

    The evolving shape of material fluid lines in a flow underlies the quantitative prediction of the dissipation and material transport in many industrial and natural processes. However, collecting quantitative data on this dynamics remains an experimental challenge in particular in turbulent flows. Indeed the deformation of a fluid line, induced by its successive stretching and folding, can be difficult to determine because such description ultimately relies on often inaccessible multi-particle information. Here we report laboratory measurements in two-dimensional turbulence that offer an alternative topological viewpoint on this issue. This approach characterizes the dynamics of a braid of Lagrangian trajectories through a global measure of their entanglement. The topological length of material fluid lines can be derived from these braids. This length is found to grow exponentially with time, giving access to the braid topological entropy . The entropy increases as the square root of the turbulent kinetic energy and is directly related to the single-particle dispersion coefficient. At long times, the probability distribution of is positively skewed and shows strong exponential tails. Our results suggest that may serve as a measure of the irreversibility of turbulence based on minimal principles and sparse Lagrangian data. PMID:26689261

  18. Order Parameters for Two-Dimensional Networks

    NASA Astrophysics Data System (ADS)

    Kaatz, Forrest; Bultheel, Adhemar; Egami, Takeshi

    2007-10-01

    We derive methods that explain how to quantify the amount of order in ``ordered'' and ``highly ordered'' porous arrays. Ordered arrays from bee honeycomb and several from the general field of nanoscience are compared. Accurate measures of the order in porous arrays are made using the discrete pair distribution function (PDF) and the Debye-Waller Factor (DWF) from 2-D discrete Fourier transforms calculated from the real-space data using MATLAB routines. An order parameter, OP3, is defined from the PDF to evaluate the total order in a given array such that an ideal network has the value of 1. When we compare PDFs of man-made arrays with that of our honeycomb we find OP3=0.399 for the honeycomb and OP3=0.572 for man's best hexagonal array. The DWF also scales with this order parameter with the least disorder from a computer-generated hexagonal array and the most disorder from a random array. An ideal hexagonal array normalizes a two-dimensional Fourier transform from which a Debye-Waller parameter is derived which describes the disorder in the arrays. An order parameter S, defined by the DWF, takes values from [0, 1] and for the analyzed man-made array is 0.90, while for the honeycomb it is 0.65. This presentation describes methods to quantify the order found in these arrays.

  19. An atlas of two-dimensional materials.

    PubMed

    Miró, Pere; Audiffred, Martha; Heine, Thomas

    2014-09-21

    The discovery of graphene and other two-dimensional (2D) materials together with recent advances in exfoliation techniques have set the foundations for the manufacturing of single layered sheets from any layered 3D material. The family of 2D materials encompasses a wide selection of compositions including almost all the elements of the periodic table. This derives into a rich variety of electronic properties including metals, semimetals, insulators and semiconductors with direct and indirect band gaps ranging from ultraviolet to infrared throughout the visible range. Thus, they have the potential to play a fundamental role in the future of nanoelectronics, optoelectronics and the assembly of novel ultrathin and flexible devices. We categorize the 2D materials according to their structure, composition and electronic properties. In this review we distinguish atomically thin materials (graphene, silicene, germanene, and their saturated forms; hexagonal boron nitride; silicon carbide), rare earth, semimetals, transition metal chalcogenides and halides, and finally synthetic organic 2D materials, exemplified by 2D covalent organic frameworks. Our exhaustive data collection presented in this Atlas demonstrates the large diversity of electronic properties, including band gaps and electron mobilities. The key points of modern computational approaches applied to 2D materials are presented with special emphasis to cover their range of application, peculiarities and pitfalls.

  20. Compact Two-Dimensional Spectrometer Optics

    NASA Technical Reports Server (NTRS)

    Hong, John

    2008-01-01

    The figure is a simplified depiction of a proposed spectrometer optical unit that would be suitable for incorporation into a remote-sensing instrumentation system. Relative to prior spectrometer optical assemblies, this unit would be compact and simple, largely by virtue of its predominantly two-dimensional character. The proposed unit would be a combination of two optical components. One component would be an arrayed-waveguide grating (AWG) an integrated-optics device, developed for use in wavelength multiplexing in telecommunications. The other component would be a diffraction grating superimposed on part of the AWG. The function of an AWG is conceptually simple. Input light propagates along a single-mode optical waveguide to a point where it is split to propagate along some number (N) of side-by-side waveguides. The lengths of the optical paths along these waveguides differ such that, considering the paths in a sequence proceeding across the array of waveguides, the path length increases linearly. These waveguides launch quasi-free-space waves into a planar waveguide-coupling region. The waves propagate through this region to interfere onto an array of output waveguides. Through proper choice of key design parameters (waveguide lengths, size and shape of the waveguide coupling region, and lateral distances between waveguides), one can cause the input light to be channeled into wavelength bins nominally corresponding to the output waveguides.

  1. Two-dimensional laser interferometry analysis

    NASA Astrophysics Data System (ADS)

    Mehr, Leo; Concepcion, Ricky; Duggan, Robert; Moore, Hannah; Novick, Asher; Ransohoff, Lauren; Gourdain, Pierre-Alexandre; Hammer, David; Kusse, Bruce

    2013-10-01

    The objective of our research was to create a two-dimensional interferometer which we will use to measure plasma densities at the Cornell Research Beam Accelerator (COBRA). We built two shearing interferometers and mounted them on an optics table. They intercept the probe laser beam which travels directly through the plasma and is captured by a 16-bit CCD camera. In comparing the interferometer images before the shot and during the plasma shot, we observed both lateral and vertical shifts in the interference pattern caused by the change of the refractive index due to the plasma electrons. We developed a computer program using Matlab to map a vector field depicting the shift between the two images. This shift is proportional to the line integral of electron density through the plasma chamber. We show this method provides a reliable way to determine the plasma electron density profile. Additionally, we hope this method can improve upon the diagnostic capabilities and efficiency of data collection used with standard one-dimensional interferometry. Undergraduate.

  2. Calculation of two-dimensional lambda modes

    SciTech Connect

    Belchior, A. Jr. ); Moreira, J.M.L. )

    1991-01-01

    A system for on-line monitoring of power distribution in small reactors (known as MAP) is under development at COPESP-IPEN. Signals of self-powered neutron detectors are input to a program that estimates the power distribution as an expansion of lambda modes. The modal coefficients are obtained from a least-mean-squares technique adequate for real-time analysis. Three-dimensional lambda modes are synthesized out of one- and two-dimensional lambda modes. As a part of this project, a modification of a computer code was carried out in order to obtain the lambda modes. The results of this effort are summarized. The lambda modes are the solutions of the time-independent multigroup neutron diffusion equation, an eigenvalue equation. Normally, the computer codes produce the fundamental mode corresponding to the largest eigenvalue; their respective interpretations are neutron flux distribution and effective multiplication factor. For calculating higher order lambda modes it is usually necessary to eliminate the contribution of the lower modes from the fission source.

  3. Dynamics of two-dimensional bubbles.

    PubMed

    Piedra, Saúl; Ramos, Eduardo; Herrera, J Ramón

    2015-06-01

    The dynamics of two-dimensional bubbles ascending under the influence of buoyant forces is numerically studied with a one-fluid model coupled with the front-tracking technique. The bubble dynamics are described by recording the position, shape, and orientation of the bubbles as functions of time. The qualitative properties of the bubbles and their terminal velocities are described in terms of the Eötvos (ratio of buoyancy to surface tension) and Archimedes numbers (ratio of buoyancy to viscous forces). The terminal Reynolds number result from the balance of buoyancy and drag forces and, consequently, is not an externally fixed parameter. In the cases that yield small Reynolds numbers, the bubbles follow straight paths and the wake is steady. A more interesting behavior is found at high Reynolds numbers where the bubbles follow an approximately periodic zigzag trajectory and an unstable wake with properties similar to the Von Karman vortex street is formed. The dynamical features of the motion of single bubbles are compared to experimental observations of air bubbles ascending in a water-filled Hele-Shaw cell. Although the comparison is not strictly valid in the sense that the effect of the lateral walls is not incorporated in the model, most of the dynamical properties observed are in good qualitative agreement with the numerical calculations. Hele-Shaw cells with different gaps have been used to determine the degree of approximation of the numerical calculation. It is found that for the relation between the terminal Reynolds number and the Archimedes number, the numerical calculations are closer to the observations of bubble dynamics in Hele-Shaw cells of larger gaps. PMID:26172798

  4. Two-dimensional dynamic fluid bowtie attenuators.

    PubMed

    Hermus, James R; Szczykutowicz, Timothy P

    2016-01-01

    Fluence field modulated (FFM) CT allows for improvements in image quality and dose reduction. To date, only one-dimensional modulators have been proposed, as the extension to two-dimensional (2-D) modulation is difficult with solid-metal attenuation-based fluence field modulated designs. This work proposes to use liquid and gas to attenuate the x-ray beam, as unlike solids, these materials can be arranged allowing for 2-D fluence modulation. The thickness of liquid and the pressure for a given path length of gas were determined that provided the same attenuation as 30 cm of soft tissue at 80, 100, 120, and 140 kV. Liquid iodine, zinc chloride, cerium chloride, erbium oxide, iron oxide, and gadolinium chloride were studied. Gaseous xenon, uranium hexafluoride, tungsten hexafluoride, and nickel tetracarbonyl were also studied. Additionally, we performed a proof-of-concept experiment using a 96 cell array in which the liquid thickness in each cell was adjusted manually. Liquid thickness varied as a function of kV and chemical composition, with erbium oxide allowing for the smallest thickness. For the gases, tungsten hexaflouride required the smallest pressure to compensate for 30 cm of soft tissue. The 96 cell iodine attenuator allowed for a reduction in both dynamic range to the detector and scatter-to-primary ratio. For both liquids and gases, when k-edges were located within the diagnostic energy range used for imaging, the mean beam energy exhibited the smallest change with compensation amount. The thickness of liquids and the gas pressure seem logistically implementable within the space constraints of C-arm-based cone beam CT (CBCT) and diagnostic CT systems. The gas pressures also seem logistically implementable within the space and tube loading constraints of CBCT and diagnostic CT systems. PMID:26835499

  5. Dynamics of two-dimensional bubbles

    NASA Astrophysics Data System (ADS)

    Piedra, Saúl; Ramos, Eduardo; Herrera, J. Ramón

    2015-06-01

    The dynamics of two-dimensional bubbles ascending under the influence of buoyant forces is numerically studied with a one-fluid model coupled with the front-tracking technique. The bubble dynamics are described by recording the position, shape, and orientation of the bubbles as functions of time. The qualitative properties of the bubbles and their terminal velocities are described in terms of the Eötvos (ratio of buoyancy to surface tension) and Archimedes numbers (ratio of buoyancy to viscous forces). The terminal Reynolds number result from the balance of buoyancy and drag forces and, consequently, is not an externally fixed parameter. In the cases that yield small Reynolds numbers, the bubbles follow straight paths and the wake is steady. A more interesting behavior is found at high Reynolds numbers where the bubbles follow an approximately periodic zigzag trajectory and an unstable wake with properties similar to the Von Karman vortex street is formed. The dynamical features of the motion of single bubbles are compared to experimental observations of air bubbles ascending in a water-filled Hele-Shaw cell. Although the comparison is not strictly valid in the sense that the effect of the lateral walls is not incorporated in the model, most of the dynamical properties observed are in good qualitative agreement with the numerical calculations. Hele-Shaw cells with different gaps have been used to determine the degree of approximation of the numerical calculation. It is found that for the relation between the terminal Reynolds number and the Archimedes number, the numerical calculations are closer to the observations of bubble dynamics in Hele-Shaw cells of larger gaps.

  6. Dynamics of two-dimensional bubbles.

    PubMed

    Piedra, Saúl; Ramos, Eduardo; Herrera, J Ramón

    2015-06-01

    The dynamics of two-dimensional bubbles ascending under the influence of buoyant forces is numerically studied with a one-fluid model coupled with the front-tracking technique. The bubble dynamics are described by recording the position, shape, and orientation of the bubbles as functions of time. The qualitative properties of the bubbles and their terminal velocities are described in terms of the Eötvos (ratio of buoyancy to surface tension) and Archimedes numbers (ratio of buoyancy to viscous forces). The terminal Reynolds number result from the balance of buoyancy and drag forces and, consequently, is not an externally fixed parameter. In the cases that yield small Reynolds numbers, the bubbles follow straight paths and the wake is steady. A more interesting behavior is found at high Reynolds numbers where the bubbles follow an approximately periodic zigzag trajectory and an unstable wake with properties similar to the Von Karman vortex street is formed. The dynamical features of the motion of single bubbles are compared to experimental observations of air bubbles ascending in a water-filled Hele-Shaw cell. Although the comparison is not strictly valid in the sense that the effect of the lateral walls is not incorporated in the model, most of the dynamical properties observed are in good qualitative agreement with the numerical calculations. Hele-Shaw cells with different gaps have been used to determine the degree of approximation of the numerical calculation. It is found that for the relation between the terminal Reynolds number and the Archimedes number, the numerical calculations are closer to the observations of bubble dynamics in Hele-Shaw cells of larger gaps.

  7. Thermopower in Two-Dimensional Electron Systems

    NASA Astrophysics Data System (ADS)

    Chickering, William Elbridge

    The subject of this thesis is the measurement and interpretation of thermopower in high-mobility two-dimensional electron systems (2DESs). These 2DESs are realized within state-of-the-art GaAs/AlGaAs heterostructures that are cooled to temperatures as low as T = 20 mK. Much of this work takes place within strong magnetic fields where the single-particle density of states quantizes into discrete Landau levels (LLs), a regime best known for the quantum Hall effect (QHE). In addition, we review a novel hot-electron technique for measuring thermopower of 2DESs that dramatically reduces the influence of phonon drag. Early chapters concentrate on experimental materials and methods. A brief overview of GaAs/AlGaAs heterostructures and device fabrication is followed by details of our cryogenic setup. Next, we provide a primer on thermopower that focuses on 2DESs at low temperatures. We then review our experimental devices, temperature calibration methods, as well as measurement circuits and protocols. Latter chapters focus on the physics and thermopower results in the QHE regime. After reviewing the basic phenomena associated with the QHE, we discuss thermopower in this regime. Emphasis is given to the relationship between diffusion thermopower and entropy. Experimental results demonstrate this relationship persists well into the fractional quantum Hall (FQH) regime. Several experimental results are reviewed. Unprecedented observations of the diffusion thermopower of a high-mobility 2DES at temperatures as high as T = 2 K are achieved using our hot-electron technique. The composite fermion (CF) effective mass is extracted from measurements of thermopower at LL filling factor nu = 3/2. The thermopower versus magnetic field in the FQH regime is shown to be qualitatively consistent with a simple entropic model of CFs. The thermopower at nu = 5/2 is shown to be quantitatively consistent with the presence of non-Abelian anyons. An abrupt collapse of thermopower is observed at

  8. Vortices of Two Dimensional Guiding Center Plasmas.

    NASA Astrophysics Data System (ADS)

    Ting, Antonio Chofai

    A system of two dimensional guiding center plasma in a square conducting boundary is used as a model to study the anomalous transport is magnetically confined plasma. An external gravitational force is introduced to simulate the curvature and gradient of the magnetic field. For finite boundaries, it is a Hamiltonian system with finite phase space and negative temperature states are allowed. The statistical equilibrium states of this system are described by the solutions of a Poisson's equation with self-consistently determined charge density. In the limit of zero gravity, it can be reduced to the sinh-Poisson equation (DEL)('2)u + (lamda)('2)sinh u = 0. Previous numerical efforts have found solutions with vortex structures. A novel method of generating general exact solutions to this nonlinear boundary value problem is presented. These solutions are given by. (DIAGRAM, TABLE OR GRAPHIC OMITTED...PLEASE SEE DAI). where E(,i)'s are constants and the dependence of (gamma)(,j)'s on x and y are given by a set of coupled first order nonlinear ordinary differential equations. These equations can be linearized to give u(x,y) in terms of Riemann theta functions u(x,y) = 2ln (THETA)(l + 1/2)(THETA)(l) . The phases l evolve linearly in x and y while nonlinear superposition is displayed in the solution u(x,y). The self-consistent Poisson's equation with gravity is studied numerically. Different branches of solutions are obtained and their relations to the zero gravity solutions are discussed. The thermodynamically most favored structure of the system carries the feature of a heavy ion vortex on top of the light electron vortex. Branches of solutions are found to merge into each other as parameters in the equations were smoothly varied. A critical value of gravitational force exists such that below which there is a possibility of hysteresis between different equilibrium states. With the help of the nonzero gravity solutions, we also have a clearer picture of the transition from

  9. Two-dimensional vibrational-electronic spectroscopy

    NASA Astrophysics Data System (ADS)

    Courtney, Trevor L.; Fox, Zachary W.; Slenkamp, Karla M.; Khalil, Munira

    2015-10-01

    Two-dimensional vibrational-electronic (2D VE) spectroscopy is a femtosecond Fourier transform (FT) third-order nonlinear technique that creates a link between existing 2D FT spectroscopies in the vibrational and electronic regions of the spectrum. 2D VE spectroscopy enables a direct measurement of infrared (IR) and electronic dipole moment cross terms by utilizing mid-IR pump and optical probe fields that are resonant with vibrational and electronic transitions, respectively, in a sample of interest. We detail this newly developed 2D VE spectroscopy experiment and outline the information contained in a 2D VE spectrum. We then use this technique and its single-pump counterpart (1D VE) to probe the vibrational-electronic couplings between high frequency cyanide stretching vibrations (νCN) and either a ligand-to-metal charge transfer transition ([FeIII(CN)6]3- dissolved in formamide) or a metal-to-metal charge transfer (MMCT) transition ([(CN)5FeIICNRuIII(NH3)5]- dissolved in formamide). The 2D VE spectra of both molecules reveal peaks resulting from coupled high- and low-frequency vibrational modes to the charge transfer transition. The time-evolving amplitudes and positions of the peaks in the 2D VE spectra report on coherent and incoherent vibrational energy transfer dynamics among the coupled vibrational modes and the charge transfer transition. The selectivity of 2D VE spectroscopy to vibronic processes is evidenced from the selective coupling of specific νCN modes to the MMCT transition in the mixed valence complex. The lineshapes in 2D VE spectra report on the correlation of the frequency fluctuations between the coupled vibrational and electronic frequencies in the mixed valence complex which has a time scale of 1 ps. The details and results of this study confirm the versatility of 2D VE spectroscopy and its applicability to probe how vibrations modulate charge and energy transfer in a wide range of complex molecular, material, and biological systems.

  10. Two-dimensional material confined water.

    PubMed

    Li, Qiang; Song, Jie; Besenbacher, Flemming; Dong, Mingdong

    2015-01-20

    CONSPECTUS: The interface between water and other materials under ambient conditions is of fundamental importance due to its relevance in daily life and a broad range of scientific research. The structural and dynamic properties of water at an interface have been proven to be significantly difference than those of bulk water. However, the exact nature of these interfacial water adlayers at ambient conditions is still under debate. Recent scanning probe microscopy (SPM) experiments, where two-dimensional (2D) materials as ultrathin coatings are utilized to assist the visualization of interfacial water adlayers, have made remarkable progress on interfacial water and started to clarify some of these fundamental scientific questions. In this Account, we review the recently conducted research exploring the properties of confined water between 2D materials and various surfaces under ambient conditions. Initially, we review the earlier studies of water adsorbed on hydrophilic substrates under ambient conditions in the absence of 2D coating materials, which shows the direct microscopic results. Subsequently, we focus on the studies of water adlayer growth at both hydrophilic and hydrophobic substrates in the presence of 2D coating materials. Ice-like water adlayers confined between hydrophobic graphene and hydrophilic substrates can be directly observed in detail by SPM. It was found that the packing structure of the water adlayer was determined by the hydrophilic substrates, while the orientation of intercalation water domains was directed by the graphene coating. In contrast to hydrophilic substrates, liquid-like nanodroplets confined between hydrophobic graphene and hydrophobic substrates appear close to step edges and atomic-scale surface defects, indicating that atomic-scale surface defects play significant roles in determining the adsorption of water on hydrophobic substrates. In addition, we also review the phenomena of confined water between 2D hydrophilic MoS2 and

  11. Two-dimensional vibrational-electronic spectroscopy

    SciTech Connect

    Courtney, Trevor L.; Fox, Zachary W.; Slenkamp, Karla M.; Khalil, Munira

    2015-10-21

    Two-dimensional vibrational-electronic (2D VE) spectroscopy is a femtosecond Fourier transform (FT) third-order nonlinear technique that creates a link between existing 2D FT spectroscopies in the vibrational and electronic regions of the spectrum. 2D VE spectroscopy enables a direct measurement of infrared (IR) and electronic dipole moment cross terms by utilizing mid-IR pump and optical probe fields that are resonant with vibrational and electronic transitions, respectively, in a sample of interest. We detail this newly developed 2D VE spectroscopy experiment and outline the information contained in a 2D VE spectrum. We then use this technique and its single-pump counterpart (1D VE) to probe the vibrational-electronic couplings between high frequency cyanide stretching vibrations (ν{sub CN}) and either a ligand-to-metal charge transfer transition ([Fe{sup III}(CN){sub 6}]{sup 3−} dissolved in formamide) or a metal-to-metal charge transfer (MMCT) transition ([(CN){sub 5}Fe{sup II}CNRu{sup III}(NH{sub 3}){sub 5}]{sup −} dissolved in formamide). The 2D VE spectra of both molecules reveal peaks resulting from coupled high- and low-frequency vibrational modes to the charge transfer transition. The time-evolving amplitudes and positions of the peaks in the 2D VE spectra report on coherent and incoherent vibrational energy transfer dynamics among the coupled vibrational modes and the charge transfer transition. The selectivity of 2D VE spectroscopy to vibronic processes is evidenced from the selective coupling of specific ν{sub CN} modes to the MMCT transition in the mixed valence complex. The lineshapes in 2D VE spectra report on the correlation of the frequency fluctuations between the coupled vibrational and electronic frequencies in the mixed valence complex which has a time scale of 1 ps. The details and results of this study confirm the versatility of 2D VE spectroscopy and its applicability to probe how vibrations modulate charge and energy transfer in a

  12. Two-dimensional material confined water.

    PubMed

    Li, Qiang; Song, Jie; Besenbacher, Flemming; Dong, Mingdong

    2015-01-20

    CONSPECTUS: The interface between water and other materials under ambient conditions is of fundamental importance due to its relevance in daily life and a broad range of scientific research. The structural and dynamic properties of water at an interface have been proven to be significantly difference than those of bulk water. However, the exact nature of these interfacial water adlayers at ambient conditions is still under debate. Recent scanning probe microscopy (SPM) experiments, where two-dimensional (2D) materials as ultrathin coatings are utilized to assist the visualization of interfacial water adlayers, have made remarkable progress on interfacial water and started to clarify some of these fundamental scientific questions. In this Account, we review the recently conducted research exploring the properties of confined water between 2D materials and various surfaces under ambient conditions. Initially, we review the earlier studies of water adsorbed on hydrophilic substrates under ambient conditions in the absence of 2D coating materials, which shows the direct microscopic results. Subsequently, we focus on the studies of water adlayer growth at both hydrophilic and hydrophobic substrates in the presence of 2D coating materials. Ice-like water adlayers confined between hydrophobic graphene and hydrophilic substrates can be directly observed in detail by SPM. It was found that the packing structure of the water adlayer was determined by the hydrophilic substrates, while the orientation of intercalation water domains was directed by the graphene coating. In contrast to hydrophilic substrates, liquid-like nanodroplets confined between hydrophobic graphene and hydrophobic substrates appear close to step edges and atomic-scale surface defects, indicating that atomic-scale surface defects play significant roles in determining the adsorption of water on hydrophobic substrates. In addition, we also review the phenomena of confined water between 2D hydrophilic MoS2 and

  13. Exploring two-dimensional electron gases with two-dimensional Fourier transform spectroscopy

    SciTech Connect

    Paul, J.; Dey, P.; Tokumoto, T.; Reno, J. L.; Hilton, D. J.; Karaiskaj, D.

    2014-10-07

    The dephasing of excitons in a modulation doped single quantum well was carefully measured using time integrated four-wave mixing (FWM) and two-dimensional Fourier transform (2DFT) spectroscopy. These are the first 2DFT measurements performed on a modulation doped single quantum well. The inhomogeneous and homogeneous excitonic line widths were obtained from the diagonal and cross-diagonal profiles of the 2DFT spectra. The laser excitation density and temperature were varied and 2DFT spectra were collected. A very rapid increase of the dephasing decay, and as a result, an increase in the cross-diagonal 2DFT linewidths with temperature was observed. Furthermore, the lineshapes of the 2DFT spectra suggest the presence of excitation induced dephasing and excitation induced shift.

  14. Exploring two-dimensional electron gases with two-dimensional Fourier transform spectroscopy

    DOE PAGES

    Paul, J.; Dey, P.; Tokumoto, T.; Reno, J. L.; Hilton, D. J.; Karaiskaj, D.

    2014-10-07

    The dephasing of excitons in a modulation doped single quantum well was carefully measured using time integrated four-wave mixing (FWM) and two-dimensional Fourier transform (2DFT) spectroscopy. These are the first 2DFT measurements performed on a modulation doped single quantum well. The inhomogeneous and homogeneous excitonic line widths were obtained from the diagonal and cross-diagonal profiles of the 2DFT spectra. The laser excitation density and temperature were varied and 2DFT spectra were collected. A very rapid increase of the dephasing decay, and as a result, an increase in the cross-diagonal 2DFT linewidths with temperature was observed. Furthermore, the lineshapes of themore » 2DFT spectra suggest the presence of excitation induced dephasing and excitation induced shift.« less

  15. Beginning Introductory Physics with Two-Dimensional Motion

    ERIC Educational Resources Information Center

    Huggins, Elisha

    2009-01-01

    During the session on "Introductory College Physics Textbooks" at the 2007 Summer Meeting of the AAPT, there was a brief discussion about whether introductory physics should begin with one-dimensional motion or two-dimensional motion. Here we present the case that by starting with two-dimensional motion, we are able to introduce a considerable…

  16. The Development of Two-Dimensional Structure in Cavitons.

    NASA Astrophysics Data System (ADS)

    Eggleston, Dennis Lee

    Experimental observations of the space and time evolution of resonantly enhanced electric fields and plasma density in cylindrical geometry demonstrate the development of two-dimensional caviton structure when an initial density perturbation is imposed on the plasma in the direction perpendicular to the driver field. This two-dimensional structure is observed after the development of profile modification and grows on the ion time scale. The existence of a large azimuthal electric field component is an observational signature of two-dimensional structure. Enhanced electric field maxima are found to be azimuthally correlated with the density minima. Both the density cavities and electric field peaks exhibit increased azimuthal localization with the growth of two-dimensional structure. The two-dimensional development exhibits a strong dependence on both perturbation wavenumber and driver power. The related theoretical literature is reviewed and numerical and analytical models for a driven, two-dimensional, inhomogeneous plasma are presented. It is shown that the experimental results can be explained in a semi-quanitative manner by a model which combines the results of one-dimensional caviton theory with those of two-dimensional Langmuir collapse.

  17. String & Sticky Tape Experiments: Two-Dimensional Collisions Using Pendulums.

    ERIC Educational Resources Information Center

    Edge, R. D.

    1989-01-01

    Introduces a method for two-dimensional kinematics measurements by hanging marbles with long strings. Describes experimental procedures for conservation of momentum and obtaining the coefficient of restitution. Provides diagrams and mathematical expressions for the activities. (YP)

  18. Two-dimensional signal processing with application to image restoration

    NASA Technical Reports Server (NTRS)

    Assefi, T.

    1974-01-01

    A recursive technique for modeling and estimating a two-dimensional signal contaminated by noise is presented. A two-dimensional signal is assumed to be an undistorted picture, where the noise introduces the distortion. Both the signal and the noise are assumed to be wide-sense stationary processes with known statistics. Thus, to estimate the two-dimensional signal is to enhance the picture. The picture representing the two-dimensional signal is converted to one dimension by scanning the image horizontally one line at a time. The scanner output becomes a nonstationary random process due to the periodic nature of the scanner operation. Procedures to obtain a dynamical model corresponding to the autocorrelation function of the scanner output are derived. Utilizing the model, a discrete Kalman estimator is designed to enhance the image.

  19. Power distribution in two-dimensional optical network channels

    NASA Astrophysics Data System (ADS)

    Wang, Dong-Xue; Karim, Mohammad A.

    1996-04-01

    The power distribution in two-dimensional optical network channels is analyzed. The maximum number of allowable channels as determined by the characteristics of optical detector is identified, in particular, for neural-network and wavelet-transform applications.

  20. Model of a Negatively Curved Two-Dimensional Space.

    ERIC Educational Resources Information Center

    Eckroth, Charles A.

    1995-01-01

    Describes the construction of models of two-dimensional surfaces with negative curvature that are used to illustrate differences in the triangle sum rule for the various Big Bang Theories of the universe. (JRH)

  1. Difficulties that Students Face with Two-Dimensional Motion

    ERIC Educational Resources Information Center

    Mihas, P.; Gemousakakis, T.

    2007-01-01

    Some difficulties that students face with two-dimensional motion are addressed. The difficulties addressed are the vectorial representation of velocity, acceleration and force, the force-energy theorem and the understanding of the radius of curvature.

  2. Two-Dimensional Systolic Array For Kalman-Filter Computing

    NASA Technical Reports Server (NTRS)

    Chang, Jaw John; Yeh, Hen-Geul

    1988-01-01

    Two-dimensional, systolic-array, parallel data processor performs Kalman filtering in real time. Algorithm rearranged to be Faddeev algorithm for generalized signal processing. Algorithm mapped onto very-large-scale integrated-circuit (VLSI) chip in two-dimensional, regular, simple, expandable array of concurrent processing cells. Processor does matrix/vector-based algebraic computations. Applications include adaptive control of robots, remote manipulators and flexible structures and processing radar signals to track targets.

  3. Estimating analytical variability in two-dimensional data.

    PubMed

    Budyak, Ivan L; Griffiths, Kristi L; Weiss, William F

    2016-11-15

    Throughout the course of drug development there are many instances in which a variability assessment within a set of analytical data is required, which may be challenging for techniques that produce two-dimensional data. This note describes an interval-based approach to variability assessment and demonstrates its applicability for analysis of near-UV circular dichroism (CD) spectra. The approach is generalizable and could be applied to two-dimensional data from other analytical techniques as well. PMID:27567991

  4. Canine left ventricular mass estimation by two-dimensional echocardiography.

    PubMed

    Schiller, N B; Skiôldebrand, C G; Schiller, E J; Mavroudis, C C; Silverman, N H; Rahimtoola, S H; Lipton, M J

    1983-07-01

    This study was designed to develop a two-dimensional echocardiographic method of measuring the mass of the left ventricle. The general formula for an ellipse was used to derive an algorithm that described the shell volume of concentric truncated ellipsoids. In 10 canine left ventricular two-dimensional echocardiograms, this algorithm accurately predicted postmortem left ventricular mass (r = .98, SEE +/- 6 g) and was independent of cardiac cycle phase (systole vs diastole, r = .92). PMID:6851047

  5. Beginning Introductory Physics with Two-Dimensional Motion

    NASA Astrophysics Data System (ADS)

    Huggins, Elisha

    2009-04-01

    During the session on "Introductory College Physics Textbooks" at the 2007 Summer Meeting of the AAPT, there was a brief discussion about whether introductory physics should begin with one-dimensional motion or two-dimensional motion. Here we present the case that by starting with two-dimensional motion, we are able to introduce a considerable amount of physics even before discussing the constant acceleration formulas or Newton's laws.

  6. Light evolution in arbitrary two-dimensional waveguide arrays

    SciTech Connect

    Szameit, Alexander; Pertsch, Thomas; Dreisow, Felix; Nolte, Stefan; Tuennermann, Andreas; Peschel, Ulf; Lederer, Falk

    2007-05-15

    We introduce an analytical formula for the dynamics of light propagation in a two-dimensional waveguide lattice including diagonal coupling. A superposition of infinite arrays created by imaginary sources is used to derive an expression for boundary reflections. It is shown analytically that for large propagation distances the propagating field reaches uniformity. Furthermore, periodic field recovery is studied and discrete anomalous refraction and diffraction are investigated in arbitrary two-dimensional lattices.

  7. QUENCH2D. Two-Dimensional IHCP Code

    SciTech Connect

    Osman, A.; Beck, J.V.

    1995-01-01

    QUENCH2D* is developed for the solution of general, non-linear, two-dimensional inverse heat transfer problems. This program provides estimates for the surface heat flux distribution and/or heat transfer coefficient as a function of time and space by using transient temperature measurements at appropriate interior points inside the quenched body. Two-dimensional planar and axisymmetric geometries such as turnbine disks and blades, clutch packs, and many other problems can be analyzed using QUENCH2D*.

  8. Muscle protein analysis by two-dimensional gel electrophoresis

    SciTech Connect

    Giometti, C.S.

    1982-01-01

    Two-dimensional electrophoresis of muscle proteins has provided valuable new information concerning the heterogeneity of some of the major contractile proteins, alterations in the protein population of developing muscle fibers during various stages of myogenesis, and protein aberrations that correlate with muscle diseases. As with all electrophoretic techniques, careful attention must be paid to the preparation of samples and the selection of reagents to be used for the protein separations. Two-dimensional electrophoresis is the obvious method of choice when analysis of protein mixtures is required. The routine clinical application of two-dimensional electrophoresis to analysis of muscle tissue remains to be demonstrated. However, methods of sample preparation for two-dimensional electrophoresis compatible with existing clinical procedures have been described, and the equipment for multiple analyses is available. As protein abnormalities related to human myopathy are detected through the use of two-dimensional electrophoresis as a research tool, useful clinical markers of specific myopathic processes will be found. The preliminary work on muscle protein analysis by two-dimensional electrophoresis described in this review has begun a new approach to the enigma of human muscle disease.

  9. Two-Dimensional Grammars And Their Applications To Artificial Intelligence

    NASA Astrophysics Data System (ADS)

    Lee, Edward T.

    1987-05-01

    During the past several years, the concepts and techniques of two-dimensional grammars1,2 have attracted growing attention as promising avenues of approach to problems in picture generation as well as in picture description3 representation, recognition, transformation and manipulation. Two-dimensional grammar techniques serve the purpose of exploiting the structure or underlying relationships in a picture. This approach attempts to describe a complex picture in terms of their components and their relative positions. This resembles the way a sentence is described in terms of its words and phrases, and the terms structural picture recognition, linguistic picture recognition, or syntactic picture recognition are often used. By using this approach, the problem of picture recognition becomes similar to that of phrase recognition in a language. However, describing pictures using a string grammar (one-dimensional grammar), the only relation between sub-pictures and/or primitives is the concatenation; that is each picture or primitive can be connected only at the left or right. This one-dimensional relation has not been very effective in describing two-dimensional pictures. A natural generaliza-tion is to use two-dimensional grammars. In this paper, two-dimensional grammars and their applications to artificial intelligence are presented. Picture grammars and two-dimensional grammars are introduced and illustrated by examples. In particular, two-dimensional grammars for generating all possible squares and all possible rhombuses are presented. The applications of two-dimensional grammars to solving region filling problems are discussed. An algorithm for region filling using two-dimensional grammars is presented together with illustrative examples. The advantages of using this algorithm in terms of computation time are also stated. A high-level description of a two-level picture generation system is proposed. The first level is the picture primitive generation using two-dimensional

  10. Complexity and efficient approximability of two dimensional periodically specified problems

    SciTech Connect

    Marathe, M.V.; Hunt, H.B. III; Stearns, R.E.

    1996-09-01

    The authors consider the two dimensional periodic specifications: a method to specify succinctly objects with highly regular repetitive structure. These specifications arise naturally when processing engineering designs including VLSI designs. These specifications can specify objects whose sizes are exponentially larger than the sizes of the specification themselves. Consequently solving a periodically specified problem by explicitly expanding the instance is prohibitively expensive in terms of computational resources. This leads one to investigate the complexity and efficient approximability of solving graph theoretic and combinatorial problems when instances are specified using two dimensional periodic specifications. They prove the following results: (1) several classical NP-hard optimization problems become NEXPTIME-hard, when instances are specified using two dimensional periodic specifications; (2) in contrast, several of these NEXPTIME-hard problems have polynomial time approximation algorithms with guaranteed worst case performance.

  11. Dynamical class of a two-dimensional plasmonic Dirac system

    NASA Astrophysics Data System (ADS)

    Silva, Érica de Mello

    2015-10-01

    A current goal in plasmonic science and technology is to figure out how to manage the relaxational dynamics of surface plasmons in graphene since its damping constitutes a hinder for the realization of graphene-based plasmonic devices. In this sense we believe it might be of interest to enlarge the knowledge on the dynamical class of two-dimensional plasmonic Dirac systems. According to the recurrence relations method, different systems are said to be dynamically equivalent if they have identical relaxation functions at all times, and such commonality may lead to deep connections between seemingly unrelated physical systems. We employ the recurrence relations approach to obtain relaxation and memory functions of density fluctuations and show that a two-dimensional plasmonic Dirac system at long wavelength and zero temperature belongs to the same dynamical class of standard two-dimensional electron gas and classical harmonic oscillator chain with an impurity mass.

  12. Electronics and optoelectronics of two-dimensional transition metal dichalcogenides.

    PubMed

    Wang, Qing Hua; Kalantar-Zadeh, Kourosh; Kis, Andras; Coleman, Jonathan N; Strano, Michael S

    2012-11-01

    The remarkable properties of graphene have renewed interest in inorganic, two-dimensional materials with unique electronic and optical attributes. Transition metal dichalcogenides (TMDCs) are layered materials with strong in-plane bonding and weak out-of-plane interactions enabling exfoliation into two-dimensional layers of single unit cell thickness. Although TMDCs have been studied for decades, recent advances in nanoscale materials characterization and device fabrication have opened up new opportunities for two-dimensional layers of thin TMDCs in nanoelectronics and optoelectronics. TMDCs such as MoS(2), MoSe(2), WS(2) and WSe(2) have sizable bandgaps that change from indirect to direct in single layers, allowing applications such as transistors, photodetectors and electroluminescent devices. We review the historical development of TMDCs, methods for preparing atomically thin layers, their electronic and optical properties, and prospects for future advances in electronics and optoelectronics.

  13. Two-Dimensional Superfluidity of Exciton Polaritons Requires Strong Anisotropy

    NASA Astrophysics Data System (ADS)

    Altman, Ehud; Sieberer, Lukas M.; Chen, Leiming; Diehl, Sebastian; Toner, John

    2015-01-01

    Fluids of exciton polaritons, excitations of two-dimensional quantum wells in optical cavities, show collective phenomena akin to Bose condensation. However, a fundamental difference from standard condensates stems from the finite lifetime of these excitations, which necessitates continuous driving to maintain a steady state. A basic question is whether a two-dimensional condensate with long-range algebraic correlations can exist under these nonequilibrium conditions. Here, we show that such driven two-dimensional Bose systems cannot exhibit algebraic superfluid order except in low-symmetry, strongly anisotropic systems. Our result implies, in particular, that recent apparent evidence for Bose condensation of exciton polaritons must be an intermediate-scale crossover phenomenon, while the true long-distance correlations fall off exponentially. We obtain these results through a mapping of the long-wavelength condensate dynamics onto the anisotropic Kardar-Parisi-Zhang equation.

  14. Two-dimensional electronic spectroscopy using incoherent light: theoretical analysis.

    PubMed

    Turner, Daniel B; Howey, Dylan J; Sutor, Erika J; Hendrickson, Rebecca A; Gealy, M W; Ulness, Darin J

    2013-07-25

    Electronic energy transfer in photosynthesis occurs over a range of time scales and under a variety of intermolecular coupling conditions. Recent work has shown that electronic coupling between chromophores can lead to coherent oscillations in two-dimensional electronic spectroscopy measurements of pigment-protein complexes measured with femtosecond laser pulses. A persistent issue in the field is to reconcile the results of measurements performed using femtosecond laser pulses with physiological illumination conditions. Noisy-light spectroscopy can begin to address this question. In this work we present the theoretical analysis of incoherent two-dimensional electronic spectroscopy, I((4)) 2D ES. Simulations reveal diagonal peaks, cross peaks, and coherent oscillations similar to those observed in femtosecond two-dimensional electronic spectroscopy experiments. The results also expose fundamental differences between the femtosecond-pulse and noisy-light techniques; the differences lead to new challenges and new opportunities.

  15. Two dimensional convolute integers for machine vision and image recognition

    NASA Technical Reports Server (NTRS)

    Edwards, Thomas R.

    1988-01-01

    Machine vision and image recognition require sophisticated image processing prior to the application of Artificial Intelligence. Two Dimensional Convolute Integer Technology is an innovative mathematical approach for addressing machine vision and image recognition. This new technology generates a family of digital operators for addressing optical images and related two dimensional data sets. The operators are regression generated, integer valued, zero phase shifting, convoluting, frequency sensitive, two dimensional low pass, high pass and band pass filters that are mathematically equivalent to surface fitted partial derivatives. These operators are applied non-recursively either as classical convolutions (replacement point values), interstitial point generators (bandwidth broadening or resolution enhancement), or as missing value calculators (compensation for dead array element values). These operators show frequency sensitive feature selection scale invariant properties. Such tasks as boundary/edge enhancement and noise or small size pixel disturbance removal can readily be accomplished. For feature selection tight band pass operators are essential. Results from test cases are given.

  16. Two-dimensional SCFTs from D3-branes

    NASA Astrophysics Data System (ADS)

    Benini, Francesco; Bobev, Nikolay; Crichigno, P. Marcos

    2016-07-01

    We find a large class of two-dimensional N = (0, 2) SCFTs obtained by compactifying four-dimensional N = 1 quiver gauge theories on a Riemann surface. We study these theories using anomalies and c-extremization. The gravitational duals to these fixed points are new AdS3 solutions of IIB supergravity which we exhibit explicitly. Along the way we uncover a universal relation between the conformal anomaly coefficients of fourdimensional and two-dimensional SCFTs connected by an RG flow across dimensions. We also observe an interesting novel phenomenon in which the superconformal R-symmetry mixes with baryonic symmetries along the RG flow.

  17. Two-dimensional lattice Boltzmann model for magnetohydrodynamics.

    PubMed

    Schaffenberger, Werner; Hanslmeier, Arnold

    2002-10-01

    We present a lattice Boltzmann model for the simulation of two-dimensional magnetohydro dynamic (MHD) flows. The model is an extension of a hydrodynamic lattice Boltzman model with 9 velocities on a square lattice resulting in a model with 17 velocities. Earlier lattice Boltzmann models for two-dimensional MHD used a bidirectional streaming rule. However, the use of such a bidirectional streaming rule is not necessary. In our model, the standard streaming rule is used, allowing smaller viscosities. To control the viscosity and the resistivity independently, a matrix collision operator is used. The model is then applied to the Hartmann flow, giving reasonable results.

  18. Microstructured light guides overcoming the two-dimensional concentration limit.

    PubMed

    Leutz, Ralf; Ries, Harald

    2005-11-10

    Light guides are employed to homogenize an illumination distribution, to translate cross-sectional beam shapes, and to provide concentration. Microstructures enhance the performance of light guides based on the selective mixing of direction vector components in the two-dimensional phase space (etendue) that is perpendicular to the system's optical axis. For linear concentrators we find that the microstructured light guide beats the two-dimensional concentration limit and roughly allows for a three-dimensional concentration ratio. This result is verified in simulation and experiment.

  19. Conduction-electron spin resonance in two-dimensional structures

    NASA Astrophysics Data System (ADS)

    Edelstein, Victor M.

    2016-09-01

    The influence of the conduction-electron spin magnetization density, induced in a two-dimensional electron layer by a microwave electromagnetic field, on the reflection and transmission of the field is considered. Because of the induced magnetization and electric current, both the electric and magnetic components of the field should have jumps on the layer. A way to match the waves on two sides of the layer, valid when the quasi-two-dimensional electron gas is in the one-mode state, is proposed. By following this way, the amplitudes of transmitted and reflected waves as well as the absorption coefficient are evaluated.

  20. Equilibrium state of a trapped two-dimensional Bose gas

    SciTech Connect

    Rath, Steffen P.; Yefsah, Tarik; Guenter, Kenneth J.; Cheneau, Marc; Desbuquois, Remi; Dalibard, Jean; Holzmann, Markus; Krauth, Werner

    2010-07-15

    We study experimentally and numerically the equilibrium density profiles of a trapped two-dimensional {sup 87}Rb Bose gas and investigate the equation of state of the homogeneous system using the local density approximation. We find a clear discrepancy between in situ measurements and quantum Monte Carlo simulations, which we attribute to a nonlinear variation of the optical density of the atomic cloud with its spatial density. However, good agreement between experiment and theory is recovered for the density profiles measured after time of flight, taking advantage of their self-similarity in a two-dimensional expansion.

  1. Quantum Walks on Two Kinds of Two-Dimensional Models

    NASA Astrophysics Data System (ADS)

    Li, Dan; Mc Gettrick, Michael; Zhang, Wei-Wei; Zhang, Ke-Jia

    2015-08-01

    In this paper, we numerically study quantum walks on two kinds of two-dimensional graphs: cylindrical strip and Mobius strip. The two kinds of graphs are typical two-dimensional topological graph. We study the crossing property of quantum walks on these two models. Also, we study its dependence on the initial state, size of the model. At the same time, we compare the quantum walk and classical walk on these two models to discuss the difference of quantum walk and classical walk.

  2. Mapping two-dimensional polar active fluids to two-dimensional soap and one-dimensional sandblasting

    NASA Astrophysics Data System (ADS)

    Chen, Leiming; Lee, Chiu Fan; Toner, John

    2016-07-01

    Active fluids and growing interfaces are two well-studied but very different non-equilibrium systems. Each exhibits non-equilibrium behaviour distinct from that of their equilibrium counterparts. Here we demonstrate a surprising connection between these two: the ordered phase of incompressible polar active fluids in two spatial dimensions without momentum conservation, and growing one-dimensional interfaces (that is, the 1+1-dimensional Kardar-Parisi-Zhang equation), in fact belong to the same universality class. This universality class also includes two equilibrium systems: two-dimensional smectic liquid crystals, and a peculiar kind of constrained two-dimensional ferromagnet. We use these connections to show that two-dimensional incompressible flocks are robust against fluctuations, and exhibit universal long-ranged, anisotropic spatio-temporal correlations of those fluctuations. We also thereby determine the exact values of the anisotropy exponent ζ and the roughness exponents χx,y that characterize these correlations.

  3. Mapping two-dimensional polar active fluids to two-dimensional soap and one-dimensional sandblasting.

    PubMed

    Chen, Leiming; Lee, Chiu Fan; Toner, John

    2016-01-01

    Active fluids and growing interfaces are two well-studied but very different non-equilibrium systems. Each exhibits non-equilibrium behaviour distinct from that of their equilibrium counterparts. Here we demonstrate a surprising connection between these two: the ordered phase of incompressible polar active fluids in two spatial dimensions without momentum conservation, and growing one-dimensional interfaces (that is, the 1+1-dimensional Kardar-Parisi-Zhang equation), in fact belong to the same universality class. This universality class also includes two equilibrium systems: two-dimensional smectic liquid crystals, and a peculiar kind of constrained two-dimensional ferromagnet. We use these connections to show that two-dimensional incompressible flocks are robust against fluctuations, and exhibit universal long-ranged, anisotropic spatio-temporal correlations of those fluctuations. We also thereby determine the exact values of the anisotropy exponent ζ and the roughness exponents χx,y that characterize these correlations. PMID:27452107

  4. Thickness identification of two-dimensional materials by optical imaging.

    PubMed

    Wang, Ying Ying; Gao, Ren Xi; Ni, Zhen Hua; He, Hui; Guo, Shu Peng; Yang, Huan Ping; Cong, Chun Xiao; Yu, Ting

    2012-12-14

    Two-dimensional materials, e.g. graphene and molybdenum disulfide (MoS(2)), have attracted great interest in recent years. Identification of the thickness of two-dimensional materials will improve our understanding of their thickness-dependent properties, and also help with scientific research and applications. In this paper, we propose to use optical imaging as a simple, quantitative and universal way to identify the thickness of two-dimensional materials, i.e. mechanically exfoliated graphene, nitrogen-doped chemical vapor deposition grown graphene, graphene oxide and mechanically exfoliated MoS(2). The contrast value can easily be obtained by reading the red (R), green (G) and blue (B) values at each pixel of the optical images of the sample and substrate, and this value increases linearly with sample thickness, in agreement with our calculation based on the Fresnel equation. This method is fast, easily performed and no expensive equipment is needed, which will be an important factor for large-scale sample production. The identification of the thickness of two-dimensional materials will greatly help in fundamental research and future applications.

  5. Sound waves in two-dimensional ducts with sinusoidal walls

    NASA Technical Reports Server (NTRS)

    Nayfeh, A. H.

    1974-01-01

    The method of multiple scales is used to analyze the wave propagation in two-dimensional hard-walled ducts with sinusoidal walls. For traveling waves, resonance occurs whenever the wall wavenumber is equal to the difference of the wavenumbers of any two duct acoustic modes. The results show that neither of these resonating modes could occur without strongly generating the other.

  6. Two-dimensional vortex motion and 'negative temperatures.'

    NASA Technical Reports Server (NTRS)

    Montgomery, D.

    1972-01-01

    Explanation of the novel phenomenon, tentatively identified as the 'ergodic boundary' in a space of initial conditions for turbulent flow, suggested by the recent numerical integration of the two-dimensional Navier-Stokes equations at high Reynolds numbers reported by Deem and Zabusky (1971). The proposed explanation is presented in terms of negative temperatures for a point vortex model.

  7. Equilibrium structural properties of two-dimensional nonideal systems

    NASA Astrophysics Data System (ADS)

    Vaulina, O. S.; Vasilieva, E. V.; Petrov, O. F.; Fortov, V. E.

    2011-12-01

    The pair correlation functions and the mean squared displacements of charged dust particles were studied experimentally for quasi-two-dimensional (2D) nonideal systems. The experiments were carried out in a plasma of a capacitive radio-frequency (RF-) discharge in argon for monolayers of monodispersed (melamine formaldehyde) spheres. A comparison with the existing theoretical and numerical data is presented.

  8. Two-dimensional probe absorption in coupled quantum dots

    NASA Astrophysics Data System (ADS)

    Liu, Ningwu; Zhang, Yan; Kang, Chengxian; Wang, Zhiping; Yu, Benli

    2016-07-01

    We investigate the two-dimensional (2D) probe absorption in coupled quantum dots. It is found that, due to the position-dependent quantum interference effect, the 2D optical absorption spectrum can be easily controlled via adjusting the system parameters. Thus, our scheme may provide some technological applications in solid-state quantum communication.

  9. Grid generation for two-dimensional finite element flowfield computation

    NASA Technical Reports Server (NTRS)

    Tatum, K. E.

    1980-01-01

    The finite element method for fluid dynamics was used to develop a two dimensional mesh generation scheme. The method consists of shearing and conformal maps with upper and lower surfaces handled independently to allow sharp leading edges. The method also generates meshes of triangular or quadrilateral elements.

  10. Two-Dimensional Fourier Transform Analysis of Helicopter Flyover Noise

    NASA Technical Reports Server (NTRS)

    SantaMaria, Odilyn L.; Farassat, F.; Morris, Philip J.

    1999-01-01

    A method to separate main rotor and tail rotor noise from a helicopter in flight is explored. Being the sum of two periodic signals of disproportionate, or incommensurate frequencies, helicopter noise is neither periodic nor stationary. The single Fourier transform divides signal energy into frequency bins of equal size. Incommensurate frequencies are therefore not adequately represented by any one chosen data block size. A two-dimensional Fourier analysis method is used to separate main rotor and tail rotor noise. The two-dimensional spectral analysis method is first applied to simulated signals. This initial analysis gives an idea of the characteristics of the two-dimensional autocorrelations and spectra. Data from a helicopter flight test is analyzed in two dimensions. The test aircraft are a Boeing MD902 Explorer (no tail rotor) and a Sikorsky S-76 (4-bladed tail rotor). The results show that the main rotor and tail rotor signals can indeed be separated in the two-dimensional Fourier transform spectrum. The separation occurs along the diagonals associated with the frequencies of interest. These diagonals are individual spectra containing only information related to one particular frequency.

  11. Two-Dimensional Fourier Transform Applied to Helicopter Flyover Noise

    NASA Technical Reports Server (NTRS)

    Santa Maria, Odilyn L.

    1999-01-01

    A method to separate main rotor and tail rotor noise from a helicopter in flight is explored. Being the sum of two periodic signals of disproportionate, or incommensurate frequencies, helicopter noise is neither periodic nor stationary, but possibly harmonizable. The single Fourier transform divides signal energy into frequency bins of equal size. Incommensurate frequencies are therefore not adequately represented by any one chosen data block size. A two-dimensional Fourier analysis method is used to show helicopter noise as harmonizable. The two-dimensional spectral analysis method is first applied to simulated signals. This initial analysis gives an idea of the characteristics of the two-dimensional autocorrelations and spectra. Data from a helicopter flight test is analyzed in two dimensions. The test aircraft are a Boeing MD902 Explorer (no tail rotor) and a Sikorsky S-76 (4-bladed tail rotor). The results show that the main rotor and tail rotor signals can indeed be separated in the two-dimensional Fourier transform spectrum. The separation occurs along the diagonals associated with the frequencies of interest. These diagonals are individual spectra containing only information related to one particular frequency.

  12. Least squares approximation of two-dimensional FIR digital filters

    NASA Astrophysics Data System (ADS)

    Alliney, S.; Sgallari, F.

    1980-02-01

    In this paper, a new method for the synthesis of two-dimensional FIR digital filters is presented. The method is based on a least-squares approximation of the ideal frequency response; an orthogonality property of certain functions, related to the frequency sampling design, improves the computational efficiency.

  13. Two-dimensional Manifold with Point-like Defects

    NASA Astrophysics Data System (ADS)

    Gani, V. A.; Dmitriev, A. E.; Rubin, S. G.

    We study a class of two-dimensional compact extra spaces isomorphic to the sphere S 2 in the framework of multidimensional gravitation. We show that there exists a family of stationary metrics that depend on the initial (boundary) conditions. All these geometries have a singular point. We also discuss the possibility for these deformed extra spaces to be considered as dark matter candidates.

  14. Two-dimensional optimization of free electron laser designs

    DOEpatents

    Prosnitz, Donald; Haas, Roger A.

    1985-01-01

    Off-axis, two-dimensional designs for free electron lasers that maintain correspondence of a light beam with a "synchronous electron" at an optimal transverse radius r>0 to achieve increased beam trapping efficiency and enhanced laser beam wavefront control so as to decrease optical beam diffraction and other deleterious effects.

  15. Two-dimensional optimization of free-electron-laser designs

    DOEpatents

    Prosnitz, D.; Haas, R.A.

    1982-05-04

    Off-axis, two-dimensional designs for free electron lasers are described that maintain correspondence of a light beam with a synchronous electron at an optimal transverse radius r > 0 to achieve increased beam trapping efficiency and enhanced laser beam wavefront control so as to decrease optical beam diffraction and other deleterious effects.

  16. Adapting Grids For Computing Two-Dimensional Flows

    NASA Technical Reports Server (NTRS)

    Davies, Carol B.; Venkatapathy, Ethiraj

    1992-01-01

    SAGE2D is two-dimensional implementation of Self Adaptive Grid Evolution computer program that intelligently redistributes initial grid points on basis of initial flow-field solution. Grids modified according to initial computed flows enabling recomputation at greater accuracy. Written in FORTRAN 77.

  17. Two-Dimensional Grids About Airfoils and Other Shapes

    NASA Technical Reports Server (NTRS)

    Sorenson, R.

    1982-01-01

    GRAPE computer program generates two-dimensional finite-difference grids about airfoils and other shapes by use of Poisson differential equation. GRAPE can be used with any boundary shape, even one specified by tabulated points and including limited number of sharp corners. Numerically stable and computationally fast, GRAPE provides aerodynamic analyst with efficient and consistant means of grid generation.

  18. Toward the Accurate Simulation of Two-Dimensional Electronic Spectra

    NASA Astrophysics Data System (ADS)

    Giussani, Angelo; Nenov, Artur; Segarra-Martí, Javier; Jaiswal, Vishal K.; Rivalta, Ivan; Dumont, Elise; Mukamel, Shaul; Garavelli, Marco

    2015-06-01

    Two-dimensional pump-probe electronic spectroscopy is a powerful technique able to provide both high spectral and temporal resolution, allowing the analysis of ultrafast complex reactions occurring via complementary pathways by the identification of decay-specific fingerprints. [1-2] The understanding of the origin of the experimentally recorded signals in a two-dimensional electronic spectrum requires the characterization of the electronic states involved in the electronic transitions photoinduced by the pump/probe pulses in the experiment. Such a goal constitutes a considerable computational challenge, since up to 100 states need to be described, for which state-of-the-art methods as RASSCF and RASPT2 have to be wisely employed. [3] With the present contribution, the main features and potentialities of two-dimensional electronic spectroscopy are presented, together with the machinery in continuous development in our groups in order to compute two-dimensional electronic spectra. The results obtained using different level of theory and simulations are shown, bringing as examples the computed two-dimensional electronic spectra for some specific cases studied. [2-4] [1] Rivalta I, Nenov A, Cerullo G, Mukamel S, Garavelli M, Int. J. Quantum Chem., 2014, 114, 85 [2] Nenov A, Segarra-Martí J, Giussani A, Conti I, Rivalta I, Dumont E, Jaiswal V K, Altavilla S, Mukamel S, Garavelli M, Faraday Discuss. 2015, DOI: 10.1039/C4FD00175C [3] Nenov A, Giussani A, Segarra-Martí J, Jaiswal V K, Rivalta I, Cerullo G, Mukamel S, Garavelli M, J. Chem. Phys. submitted [4] Nenov A, Giussani A, Fingerhut B P, Rivalta I, Dumont E, Mukamel S, Garavelli M, Phys. Chem. Chem. Phys. Submitted [5] Krebs N, Pugliesi I, Hauer J, Riedle E, New J. Phys., 2013,15, 08501

  19. Transport behavior of water molecules through two-dimensional nanopores.

    PubMed

    Zhu, Chongqin; Li, Hui; Meng, Sheng

    2014-11-14

    Water transport through a two-dimensional nanoporous membrane has attracted increasing attention in recent years thanks to great demands in water purification and desalination applications. However, few studies have been reported on the microscopic mechanisms of water transport through structured nanopores, especially at the atomistic scale. Here we investigate the microstructure of water flow through two-dimensional model graphene membrane containing a variety of nanopores of different size by using molecular dynamics simulations. Our results clearly indicate that the continuum flow transits to discrete molecular flow patterns with decreasing pore sizes. While for pores with a diameter ≥15 Å water flux exhibits a linear dependence on the pore area, a nonlinear relationship between water flux and pore area has been identified for smaller pores. We attribute this deviation from linear behavior to the presence of discrete water flow, which is strongly influenced by the water-membrane interaction and hydrogen bonding between water molecules.

  20. Transport behavior of water molecules through two-dimensional nanopores

    SciTech Connect

    Zhu, Chongqin; Li, Hui; Meng, Sheng

    2014-11-14

    Water transport through a two-dimensional nanoporous membrane has attracted increasing attention in recent years thanks to great demands in water purification and desalination applications. However, few studies have been reported on the microscopic mechanisms of water transport through structured nanopores, especially at the atomistic scale. Here we investigate the microstructure of water flow through two-dimensional model graphene membrane containing a variety of nanopores of different size by using molecular dynamics simulations. Our results clearly indicate that the continuum flow transits to discrete molecular flow patterns with decreasing pore sizes. While for pores with a diameter ≥15 Å water flux exhibits a linear dependence on the pore area, a nonlinear relationship between water flux and pore area has been identified for smaller pores. We attribute this deviation from linear behavior to the presence of discrete water flow, which is strongly influenced by the water-membrane interaction and hydrogen bonding between water molecules.

  1. Local properties of the two-dimensional Hubbard model

    NASA Astrophysics Data System (ADS)

    Drewes, Jan; Miller, Luke; Cocchi, Eugenio; Chan, Chun Fai; Pertot, Daniel; Brennecke, Ferdinand; Köhl, Michael

    2016-05-01

    Quantum gases of interacting fermionic atoms in optical lattices promise to shed new light on the low-temperature phases of the Hubbard model such as spin-ordered phases, or in particular, on possible d-wave superconductivity. In this context it remains challenging to further reduce the temperature of the trapped gas. We experimentally realize the two-dimensional Hubbard model by loading a quantum degenerate Fermi gas of 40K atoms into a three-dimensional optical lattice geometry. By tuning the interaction between the two lowest hyperfine states to strong repulsion the two-dimensional Mott-insulator is created. High resolution absorption imaging in combination with radio-frequency spectroscopy is applied to spatially resolve the atomic distribution in a single layer in the vertical direction. This measurement scheme gives direct access to the local properties of the trapped gas and we present most recent data on the distribution of entropy and density-density fluctuations.

  2. Entanglement Entropy in Two-Dimensional String Theory.

    PubMed

    Hartnoll, Sean A; Mazenc, Edward A

    2015-09-18

    To understand an emergent spacetime is to understand the emergence of locality. Entanglement entropy is a powerful diagnostic of locality, because locality leads to a large amount of short distance entanglement. Two-dimensional string theory is among the very simplest instances of an emergent spatial dimension. We compute the entanglement entropy in the large-N matrix quantum mechanics dual to two-dimensional string theory in the semiclassical limit of weak string coupling. We isolate a logarithmically large, but finite, contribution that corresponds to the short distance entanglement of the tachyon field in the emergent spacetime. From the spacetime point of view, the entanglement is regulated by a nonperturbative "graininess" of space. PMID:26430982

  3. Coarsening of Two Dimensional Foams on a Curved Surface

    NASA Astrophysics Data System (ADS)

    Roth, Adam; Jones, Chris; Durian, Doug

    2012-02-01

    We report on foam coarsening and statistics of bubble distributions in a closed, two dimensional, hemispheric cell of constant curvature. Using this cell it is possible to observe individual bubbles and measure their coarsening rates. Our results are consistent with the modification to von Neumann's law predicted by Avron and Levine. We observed the relative frequencies of bubbles with a given number of sides and found a shortage of bubbles with few sides as compared to a flat two dimensional cell. We also measured the value of m(n), the average number of sides of an n sided bubble, and found general agreement with the Aboav-Weaire law, although there was greater deviation than for a flat cell.

  4. On two-dimensional flows of compressible fluids

    NASA Technical Reports Server (NTRS)

    Bergman, Stefan

    1945-01-01

    This report is devoted to the study of two-dimensional steady motion of a compressible fluid. It is shown that the complete flow pattern around a closed obstacle cannot be obtained by the method of Chaplygin. In order to overcome this difficulty, a formula for the stream-function of a two-dimensional subsonic flow is derived. The formula involves an arbitrary function of a complex variable and yields all possible subsonic flow patterns of certain types. Conditions are given so that the flow pattern in the physical plane will represent a flow around a closed curve. The formula obtained can be employed for the approximate determination of a subsonic flow around an obstacle. The method can be extended to partially supersonic flows.

  5. Two-dimensional time dependent Riemann solvers for neutron transport

    SciTech Connect

    Brunner, Thomas A. . E-mail: tabrunn@sandia.gov; Holloway, James Paul

    2005-11-20

    A two-dimensional Riemann solver is developed for the spherical harmonics approximation to the time dependent neutron transport equation. The eigenstructure of the resulting equations is explored, giving insight into both the spherical harmonics approximation and the Riemann solver. The classic Roe-type Riemann solver used here was developed for one-dimensional problems, but can be used in multidimensional problems by treating each face of a two-dimensional computation cell in a locally one-dimensional way. Several test problems are used to explore the capabilities of both the Riemann solver and the spherical harmonics approximation. The numerical solution for a simple line source problem is compared to the analytic solution to both the P{sub 1} equation and the full transport solution. A lattice problem is used to test the method on a more challenging problem.

  6. Enstrophy inertial range dynamics in generalized two-dimensional turbulence

    NASA Astrophysics Data System (ADS)

    Iwayama, Takahiro; Watanabe, Takeshi

    2016-07-01

    We show that the transition to a k-1 spectrum in the enstrophy inertial range of generalized two-dimensional turbulence can be derived analytically using the eddy damped quasinormal Markovianized (EDQNM) closure. The governing equation for the generalized two-dimensional fluid system includes a nonlinear term with a real parameter α . This parameter controls the relationship between the stream function and generalized vorticity and the nonlocality of the dynamics. An asymptotic analysis accounting for the overwhelming dominance of nonlocal triads allows the k-1 spectrum to be derived based upon a scaling analysis. We thereby provide a detailed analytical explanation for the scaling transition that occurs in the enstrophy inertial range at α =2 in terms of the spectral dynamics of the EDQNM closure, which extends and enhances the usual phenomenological explanations.

  7. Unshielded fetal magnetocardiography system using two-dimensional gradiometers

    NASA Astrophysics Data System (ADS)

    Seki, Yusuke; Kandori, Akihiko; Kumagai, Yukio; Ohnuma, Mitsuru; Ishiyama, Akihiko; Ishii, Tetsuko; Nakamura, Yoshiyuki; Horigome, Hitoshi; Chiba, Toshio

    2008-03-01

    We developed a fetal magnetocardiography (fMCG) system that uses a pair of two-dimensional gradiometers to achieve high signal-to-noise ratio. The gradiometer, which is based on a low-Tc superconducting quantum interference device, detects the gradient of a magnetic field in two orthogonal directions. Gradiometer position is easy to adjust by operating the gantry to drive the cryostat in both the swinging and axial directions. As a result, a fMCG waveform for 25weeks' gestation was measured under an unshielded environment in real time. Moreover, the P and T waves for 25 and 34weeks' gestation, respectively, were obtained by averaging. These results indicate that this two-dimensional gradiometer is one of the most promising techniques for measuring fetal heart rate and diagnosing fetal arrhythmia.

  8. On two-dimensional water waves in a canal

    NASA Astrophysics Data System (ADS)

    Kozlov, Vladimir; Kuznetsov, Nikolay

    2003-07-01

    This Note deals with an eigenvalue problem that contains a spectral parameter in a boundary condition. The problem for the two-dimensional Laplace equation describes free, time-harmonic water waves in a canal having uniform cross-section and bounded from above by a horizontal free surface. It is shown that there exists a domain for which at least one of eigenfunctions has a nodal line with both ends on the free surface. Since Kuttler essentially used the non-existence of such nodal lines in his proof of simplicity of the fundamental sloshing eigenvalue in the two-dimensional case, we propose a new variational principle for demonstrating this latter fact. To cite this article: V. Kozlov, N. Kuznetsov, C. R. Mecanique 331 (2003).

  9. Two dimensional disorder in black phosphorus and layered monochalcogenides

    NASA Astrophysics Data System (ADS)

    Barraza-Lopez, Salvador; Mehboudi, Mehrshad; Kumar, Pradeep; Harriss, Edmund O.; Churchill, Hugh O. H.; Dorio, Alex M.; Zhu, Wenjuan; van der Zande, Arend; Pacheco Sanjuan, Alejandro A.

    The degeneracies of the structural ground state of materials with a layered orthorhombic structure such as black phosphorus and layered monochalcogenides GeS, GeSe, SnS, and SnSe, lead to an order/disorder transition in two dimensions at finite temperature. This transition has consequences on applications based on these materials requiring a crystalline two-dimensional structure. Details including a Potts model that explains the two-dimensional transition, among other results, will be given in this talk. References: M. Mehboudi, A.M. Dorio, W. Zhu, A. van der Zande, H.O.H. Churchill, A.A. Pacheco Sanjuan, E.O.H. Harris, P. Kumar, and S. Barraza-Lopez. arXiv:1510.09153.

  10. A two-dimensional dam-break flood plain model

    USGS Publications Warehouse

    Hromadka, T.V., II; Berenbrock, C.E.; Freckleton, J.R.; Guymon, G.L.

    1985-01-01

    A simple two-dimensional dam-break model is developed for flood plain study purposes. Both a finite difference grid and an irregular triangle element integrated finite difference formulation are presented. The governing flow equations are approximately solved as a diffusion model coupled to the equation of continuity. Application of the model to a hypothetical dam-break study indicates that the approach can be used to predict a two-dimensional dam-break flood plain over a broad, flat plain more accurately than a one-dimensional model, especially when the flow can break-out of the main channel and then return to the channel at other downstream reaches. ?? 1985.

  11. Modeling and Experimentation on a Two-dimensional Synthetic jet

    NASA Astrophysics Data System (ADS)

    Wang, Yunfei; Mohseni, Kamran

    2007-11-01

    Hotwire anemometry is employed in order to investigate the spatial development of a two-dimensional synthetic jet. Flow velocity at various locations downstream from a slit is measured. A self similar behavior in the measured velocity is observed. An analytical model for a steady synthetic jet is developed that accurately matches the experimental data. As observed by other groups, the two-dimensional synthetic jet spreads at a rate higher than a continuous jet. This rate is accurately predicted by our model. It is identified that the main difference between a continuous jet and a synthetic jet is the higher value of the virtual viscosity (eddy viscosity) in a synthetic jet. This is attributed to the pulsate nature of a synthetic jet that makes it more susceptible to turbulence.

  12. Two-dimensional attosecond electron wave-packet interferometry.

    PubMed

    Xie, Xinhua

    2015-05-01

    We propose a two-dimensional interferometry based on the electron wave-packet interference by using a cycle-shaped orthogonally polarized two-color laser field. With such a method, the subcycle and intercycle interferences can be disentangled into different directions in the measured photoelectron momentum spectra. The Coulomb influence can be minimized and the overlapping of interference fringes with the complicated low-energy structures can be avoided as well. The contributions of the excitation effect and the long-range Coulomb potential can be traced in the Fourier domain of the photoelectron distribution. Because of these advantages, precise information on valence electron dynamics of atoms or molecules with attosecond temporal resolution and additional spatial information with angstrom resolution can be obtained with the two-dimensional electron wave-packet interferometry.

  13. Entanglement Entropy in Two-Dimensional String Theory.

    PubMed

    Hartnoll, Sean A; Mazenc, Edward A

    2015-09-18

    To understand an emergent spacetime is to understand the emergence of locality. Entanglement entropy is a powerful diagnostic of locality, because locality leads to a large amount of short distance entanglement. Two-dimensional string theory is among the very simplest instances of an emergent spatial dimension. We compute the entanglement entropy in the large-N matrix quantum mechanics dual to two-dimensional string theory in the semiclassical limit of weak string coupling. We isolate a logarithmically large, but finite, contribution that corresponds to the short distance entanglement of the tachyon field in the emergent spacetime. From the spacetime point of view, the entanglement is regulated by a nonperturbative "graininess" of space.

  14. Electron fractionalization in two-dimensional graphenelike structures.

    PubMed

    Hou, Chang-Yu; Chamon, Claudio; Mudry, Christopher

    2007-05-01

    Electron fractionalization is intimately related to topology. In one-dimensional systems, fractionally charged states exist at domain walls between degenerate vacua. In two-dimensional systems, fractionalization exists in quantum Hall fluids, where time-reversal symmetry is broken by a large external magnetic field. Recently, there has been a tremendous effort in the search for examples of fractionalization in two-dimensional systems with time-reversal symmetry. In this Letter, we show that fractionally charged topological excitations exist on graphenelike structures, where quasiparticles are described by two flavors of Dirac fermions and time-reversal symmetry is respected. The topological zero modes are mathematically similar to fractional vortices in p-wave superconductors. They correspond to a twist in the phase in the mass of the Dirac fermions, akin to cosmic strings in particle physics. PMID:17501599

  15. Topological states in two-dimensional hexagon lattice bilayers

    NASA Astrophysics Data System (ADS)

    Zhang, Ming-Ming; Xu, Lei; Zhang, Jun

    2016-10-01

    We investigate the topological states of the two-dimensional hexagon lattice bilayer. The system exhibits a quantum valley Hall (QVH) state when the interlayer interaction t⊥ is smaller than the nearest neighbor hopping energy t, and then translates to a trivial band insulator state when t⊥ / t > 1. Interestingly, the system is found to be a single-edge QVH state with t⊥ / t = 1. The topological phase transition also can be presented via changing bias voltage and sublattice potential in the system. The QVH states have different edge modes carrying valley current but no net charge current. The bias voltage and external electric field can be tuned easily in experiments, so the present results will provide potential application in valleytronics based on the two-dimensional hexagon lattice.

  16. Two-Dimensional Attosecond Electron Wave-Packet Interferometry

    NASA Astrophysics Data System (ADS)

    Xie, Xinhua

    2015-05-01

    We propose a two-dimensional interferometry based on the electron wave-packet interference by using a cycle-shaped orthogonally polarized two-color laser field. With such a method, the subcycle and intercycle interferences can be disentangled into different directions in the measured photoelectron momentum spectra. The Coulomb influence can be minimized and the overlapping of interference fringes with the complicated low-energy structures can be avoided as well. The contributions of the excitation effect and the long-range Coulomb potential can be traced in the Fourier domain of the photoelectron distribution. Because of these advantages, precise information on valence electron dynamics of atoms or molecules with attosecond temporal resolution and additional spatial information with angstrom resolution can be obtained with the two-dimensional electron wave-packet interferometry.

  17. Extension of modified power method to two-dimensional problems

    NASA Astrophysics Data System (ADS)

    Zhang, Peng; Lee, Hyunsuk; Lee, Deokjung

    2016-09-01

    In this study, the generalized modified power method was extended to two-dimensional problems. A direct application of the method to two-dimensional problems was shown to be unstable when the number of requested eigenmodes is larger than a certain problem dependent number. The root cause of this instability has been identified as the degeneracy of the transfer matrix. In order to resolve this instability, the number of sub-regions for the transfer matrix was increased to be larger than the number of requested eigenmodes; and a new transfer matrix was introduced accordingly which can be calculated by the least square method. The stability of the new method has been successfully demonstrated with a neutron diffusion eigenvalue problem and the 2D C5G7 benchmark problem.

  18. Acoustic Bloch oscillations in a two-dimensional phononic crystal.

    PubMed

    He, Zhaojian; Peng, Shasha; Cai, Feiyan; Ke, Manzhu; Liu, Zhengyou

    2007-11-01

    We report the observation of acoustic Bloch oscillations at megahertz frequency in a two-dimensional phononic crystal. By creating periodically arrayed cavities with a decreasing gradient in width along one direction in the phononic crystal, acoustic Wannier-Stark ladders are created in the frequency domain. The oscillatory motion of an incident Gaussian pulse inside the sample is demonstrated by both simulation and experiment.

  19. Exact analytic flux distributions for two-dimensional solar concentrators.

    PubMed

    Fraidenraich, Naum; Henrique de Oliveira Pedrosa Filho, Manoel; Vilela, Olga C; Gordon, Jeffrey M

    2013-07-01

    A new approach for representing and evaluating the flux density distribution on the absorbers of two-dimensional imaging solar concentrators is presented. The formalism accommodates any realistic solar radiance and concentrator optical error distribution. The solutions obviate the need for raytracing, and are physically transparent. Examples illustrating the method's versatility are presented for parabolic trough mirrors with both planar and tubular absorbers, Fresnel reflectors with tubular absorbers, and V-trough mirrors with planar absorbers. PMID:23842256

  20. Itinerant ferromagnetism in a two-dimensional atomic gas

    SciTech Connect

    Conduit, G. J.

    2010-10-15

    Motivated by the first experimental evidence of ferromagnetic behavior in a three-dimensional ultracold atomic gas, we explore the possibility of itinerant ferromagnetism in a trapped two-dimensional atomic gas. Firstly, we develop a formalism that demonstrates how quantum fluctuations drive the ferromagnetic reconstruction first order, and consider the consequences of an imposed population imbalance. Secondly, we adapt this formalism to elucidate the key experimental signatures of ferromagnetism in a realistic trapped geometry.

  1. The scaling state in two-dimensional grain growth

    SciTech Connect

    Mulheran, P.A. . Dept. of Physics)

    1994-11-01

    A new model of normal grain growth in two-dimensional systems is derived from considerations of Potts model simulations. This Randomly Connected Bubble model is based on Hillert's theory and combines the essential topological features of the grain boundary network with the action of capillarity. It successfully predicts what the scaling state of the network should be and explains why the system evolves into this state. The implications for grain growth in real materials are also discussed.

  2. In vivo two-dimensional NMR correlation spectroscopy

    NASA Astrophysics Data System (ADS)

    Kraft, Robert A.

    1999-10-01

    The poor resolution of in-vivo one- dimensional nuclear magnetic resonance spectroscopy (NMR) has limited its clinical potential. Currently, only the large singlet methyl resonances arising from N-acetyl aspartate (NAA), choline, and creatine are quantitated in a clinical setting. Other metabolites such as myo- inositol, glutamine, glutamate, lactate, and γ- amino butyric acid (GABA) are of clinical interest but quantitation is difficult due to the overlapping resonances and limited spectral resolution. To improve the spectral resolution and distinguish between overlapping resonances, a series of two- dimensional chemical shift correlation spectroscopy experiments were developed for a 1.5 Tesla clinical imaging magnet. Two-dimensional methods are attractive for in vivo spectroscopy due to their ability to unravel overlapping resonances with the second dimension, simplifying the interpretation and quantitation of low field NMR spectra. Two-dimensional experiments acquired with mix-mode line shape negate the advantages of the second dimension. For this reason, a new experiment, REVOLT, was developed to achieve absorptive mode line shape in both dimensions. Absorptive mode experiments were compared to mixed mode experiments with respect to sensitivity, resolution, and water suppression. Detailed theoretical and experimental calculations of the optimum spin lock and radio frequency power deposition were performed. Two-dimensional spectra were acquired from human bone marrow and human brain tissue. The human brain tissue spectra clearly reveal correlations among the coupled spins of NAA, glutamine, glutamate, lactate, GABA, aspartate and myo-inositol obtained from a single experiment of 23 minutes from a volume of 59 mL. (Copies available exclusively from MIT Libraries, Rm. 14-0551, Cambridge, MA 02139-4307. Ph. 617-253-5668; Fax 617-253-1690.)

  3. Two-dimensional unsteady flow in Comprex rotor

    NASA Astrophysics Data System (ADS)

    Jiang, H.

    1984-08-01

    A two-dimensional model of the unsteady compressible inviscid adiabatic flow in the meridional plane of a Comprex rotor of the type used as a Diesel supercharger is developed. The Euler equations governing the flow are solved numerically by the difference-scheme approach of MacCormack (1969, 1975), and numerical results are compared with experimental data in graphs and tables: good agreement is found.

  4. Viscoelastic effects in a two-dimensional classical electron liquid

    NASA Astrophysics Data System (ADS)

    Mehrotra, Ravi

    1987-08-01

    The shear viscosity of a classical two-dimensional (2D) electron liquid is estimated by adapting the theory of Kirkwood, Buff, and Green for three dimensions to two dimensions. It is found to be large enough so that shear modes, if not overdamped by other scattering mechanisms, should be able to propagate through the electron liquid above a minimum temperature-dependent frequency, which is a small fraction of the highest frequency in the corresponding 2D electron solid.

  5. Electromagnetic scattering in two-dimensional dissipative systems without localization

    NASA Astrophysics Data System (ADS)

    Spieker, H.; Nimtz, G.

    1996-10-01

    Two-dimensional microwave propagation is experimentally studied in strongly scattering and absorbing random media. The results are compared with adapted theories of Genack, Ferrari, and Kaveh, as well as with classical diffusion theory. The diffusion constants and propagation velocities are determined. Most metallic or semiconductor system's localization effects, if they exist, are so weak that a classical description of the system is appropriate within measuring resolution.

  6. Two-Dimensional Protein Patterns in Heterodera glycines

    PubMed Central

    Ferris, V. R.; Ferris, J. M.; Murdock, L. L.

    1985-01-01

    Two-dimensional polyacrylamide gel electrophoretic protein patterns of H. glycines from southern Indiana (Posey County) and northern Indiana (Pulaski County) were largely similar, but many differences existed. The pattern of the Posey isolate was similar to patterns from isolates collected in other areas of the United States. Unique dense protein spots in the pattern of an isolate from Hokkaido, Japan, distinguished it from patterns of six U.S. isolates. PMID:19294120

  7. Two-dimensional correlation spectroscopy in polymer study

    PubMed Central

    Park, Yeonju; Noda, Isao; Jung, Young Mee

    2015-01-01

    This review outlines the recent works of two-dimensional correlation spectroscopy (2DCOS) in polymer study. 2DCOS is a powerful technique applicable to the in-depth analysis of various spectral data of polymers obtained under some type of perturbation. The powerful utility of 2DCOS combined with various analytical techniques in polymer studies and noteworthy developments of 2DCOS used in this field are also highlighted. PMID:25815286

  8. A two-dimensional angular-resolved proton spectrometer

    NASA Astrophysics Data System (ADS)

    Yang, Su; Yuan, Xiaohui; Fang, Yuan; Ge, Xulei; Deng, Yanqing; Wei, Wenqing; Gao, Jian; Fu, Feichao; Jiang, Tao; Liao, Guoqian; Liu, Feng; Chen, Min; Li, Yutong; Zhao, Li; Ma, Yanyun; Sheng, Zhengming; Zhang, Jie

    2016-10-01

    We present a novel design of two-dimensional (2D) angular-resolved spectrometer for full beam characterization of ultrashort intense laser driven proton sources. A rotated 2D pinhole array was employed, as selective entrance before a pair of parallel permanent magnets, to sample the full proton beam into discrete beamlets. The proton beamlets are subsequently dispersed without overlapping onto a planar detector. Representative experimental result of protons generated from femtosecond intense laser interaction with thin foil target is presented.

  9. Phase Diagram of Symmetric Two-Dimensional Traffic Model

    NASA Astrophysics Data System (ADS)

    Ishibashi, Yoshihiro; Fukui, Minoru

    2016-10-01

    On the basis of the critical car density line in the phase diagram of the Biham-Middleton-Levine model for symmetric two-dimensional traffic systems, the formula of the flow in the intermediate jam flow phase is hypothesized. The formula is utilized to obtain the phase boundary between the free flow and jam flow phases, where the flow becomes maximum. The validity of this phase boundary has been confirmed by simulations.

  10. Two dimensional thermal and charge mapping of power thyristors

    NASA Technical Reports Server (NTRS)

    Hu, S. P.; Rabinovici, B. M.

    1975-01-01

    The two dimensional static and dynamic current density distributions within the junction of semiconductor power switching devices and in particular the thyristors were obtained. A method for mapping the thermal profile of the device junctions with fine resolution using an infrared beam and measuring the attenuation through the device as a function of temperature were developed. The results obtained are useful in the design and quality control of high power semiconductor switching devices.

  11. Spirals and Skyrmions in Two Dimensional Oxide Heterostructures

    NASA Astrophysics Data System (ADS)

    Li, Xiaopeng; Liu, W. Vincent; Balents, Leon

    2014-02-01

    We construct the general free energy governing long-wavelength magnetism in two dimensional oxide heterostructures, which applies irrespective of the microscopic mechanism for magnetism. This leads, in the relevant regime of weak but non-negligible spin-orbit coupling, to a rich phase diagram containing in-plane ferromagnetic, spiral, cone, and Skyrmion lattice phases, as well as a nematic state stabilized by thermal fluctuations.

  12. Circular Couette cell for two-dimensional fluid dynamics experiments

    NASA Astrophysics Data System (ADS)

    Fontana, P. W.; Kearney-Fischer, M.; Rogers, S.; Ulmen, J. V.; Windell, S.

    2007-03-01

    A novel experiment to investigate fluid dynamics in quasi-two-dimensional flows has been built. A soap film is suspended horizontally in an annular channel with a rotating outer boundary, providing mean flow shear, and a vortex array is forced electromagnetically. The experiment will investigate sheared flow stability and the effect of mean flow shear on local vorticity and coherent structures. Particle image velocimetry measurements demonstrate the production of mean flow shear and induced vortices.

  13. Exact analytic flux distributions for two-dimensional solar concentrators.

    PubMed

    Fraidenraich, Naum; Henrique de Oliveira Pedrosa Filho, Manoel; Vilela, Olga C; Gordon, Jeffrey M

    2013-07-01

    A new approach for representing and evaluating the flux density distribution on the absorbers of two-dimensional imaging solar concentrators is presented. The formalism accommodates any realistic solar radiance and concentrator optical error distribution. The solutions obviate the need for raytracing, and are physically transparent. Examples illustrating the method's versatility are presented for parabolic trough mirrors with both planar and tubular absorbers, Fresnel reflectors with tubular absorbers, and V-trough mirrors with planar absorbers.

  14. CBEAM. 2-D: a two-dimensional beam field code

    SciTech Connect

    Dreyer, K.A.

    1985-05-01

    CBEAM.2-D is a two-dimensional solution of Maxwell's equations for the case of an electron beam propagating through an air medium. Solutions are performed in the beam-retarded time frame. Conductivity is calculated self-consistently with field equations, allowing sophisticated dependence of plasma parameters to be handled. A unique feature of the code is that it is implemented on an IBM PC microcomputer in the BASIC language. Consequently, it should be available to a wide audience.

  15. Two-dimensional hexagonal smectic structure formed by topological defects.

    PubMed

    Dolganov, P V; Shuravin, N S; Fukuda, Atsuo

    2016-03-01

    A two-dimensional hexagonal smectic structure formed by point topological defects and intersecting defect walls was discovered. This unique structure was predicted theoretically about 30 years ago but not observed. For a long time the hexagonal structure was a challenge for experimentalists. A different type of self-organization in smectic films was found and used to form the hexagonal structure. Methods applied for building the hexagonal phase can be used for the formation of complicated liquid-crystal structures.

  16. Dirac Points in Two-Dimensional Inverse Opals

    NASA Astrophysics Data System (ADS)

    Mahan, G. D.

    2013-10-01

    The electron energy states and energy bands are calculated for a two-dimensional inverse opal structure. Assume that the opal structure is closed-packed circles, the inverse opal has the honeycomb lattice. The honeycomb lattice in two dimensions has a Dirac point. Its properties can be manipulated by altering the structure of the inverse opal: the radius of the circle, and the small gap between circles.

  17. Suspended two-dimensional electron and hole gases

    SciTech Connect

    Kazazis, D.; Bourhis, E.; Gierak, J.; Gennser, U.; Bourgeois, O.; Antoni, T.

    2013-12-04

    We report on the fabrication of fully suspended two-dimensional electron and hole gases in III-V heterostructures. Low temperature transport measurements verify that the properties of the suspended gases are only slightly degraded with respect to the non-suspended gases. Focused ion beam technology is used to pattern suspended nanostructures with minimum damage from the ion beam, due to the small width of the suspended membrane.

  18. HEAT2. Two-Dimensional Heat Transfer Finite Element Code

    SciTech Connect

    Charman, C.

    1993-08-01

    HEAT2 is a finite element program for the transient and steady-state, thermal analysis of two-dimensional solids. Calculates detailed temperature distributions in MHTGR prismatic fuel elements side reflector and core support blocks. Non-linear effects of time and temperature dependent boundary conditions, and heat source generation and material properties are included with user supplied subroutines NPBC, QAREA, SOURCE, and MPROP.

  19. Two-dimensional DNA fingerprinting of human individuals

    SciTech Connect

    Uitterlinden, A.G.; Slagboom, P.E.; Knook, D.L.; Vijg, J. )

    1989-04-01

    The limiting factor in the presently available techniques for the detection of DNA sequence variation in the human genome is the low resolution of Southern blot analysis. To increase the analytical power of this technique, the authors applied size fractionation of genomic DNA restriction fragments in conjunction with their sequence-dependent separation in denaturing gradient gels; the two-dimensional separation patterns obtained were subsequently transferred to nylon membranes. Hybridization analysis using minisatellite core sequences as probes resulted in two-dimensional genomic DNA fingerprints with a resolution of up to 625 separated spots per probe per human individual; by conventional Southern blot analysis, only 20-30 bands can be resolved. Using the two-dimensional DNA fingerprinting technique, they demonstrate in a small human pedigree the simultaneous transmission of 37 polymorphic fragments (out of 365 spots) for probe 33.15 and 105 polymorphic fragments (out of 625 spots) for probe 33.6. In addition, a mutation was detected in this pedigree by probe 33.6. They anticipate that this method will be of great use in studies aimed at (i) measuring human mutation frequencies, (ii) associating genetic variation with disease, (iii) analyzing genomic instability in relation to cancer and aging, and (iv) linkage analysis and mapping of disease genes.

  20. Two-dimensional potential double layers and discrete auroras

    NASA Technical Reports Server (NTRS)

    Kan, J. R.; Lee, L. C.; Akasofu, S.-I.

    1979-01-01

    This paper is concerned with the formation of the acceleration region for electrons which produce the visible auroral arc and with the formation of the inverted V precipitation region. The former is embedded in the latter, and both are associated with field-aligned current sheets carried by plasma sheet electrons. It is shown that an electron current sheet driven from the plasma sheet into the ionosphere leads to the formation of a two-dimensional potential double layer. For a current sheet of a thickness less than the proton gyrodiameter solutions are obtained in which the field-aligned potential drop is distributed over a length much greater than the Debye length. For a current sheet of a thickness much greater than the proton gyrodiameter solutions are obtained in which the potential drop is confined to a distance on the order of the Debye length. The electric field in the two-dimensional double-layer model is the zeroth-order field inherent to the current sheet configuration, in contrast to those models in which the electric field is attributed to the first-order field due to current instabilities or turbulences. The maximum potential in the two-dimensional double-layer models is on the order of the thermal energy of plasma sheet protons, which ranges from 1 to 10 keV.

  1. Experimental realization of two-dimensional boron sheets.

    PubMed

    Feng, Baojie; Zhang, Jin; Zhong, Qing; Li, Wenbin; Li, Shuai; Li, Hui; Cheng, Peng; Meng, Sheng; Chen, Lan; Wu, Kehui

    2016-06-01

    A variety of two-dimensional materials have been reported in recent years, yet single-element systems such as graphene and black phosphorus have remained rare. Boron analogues have been predicted, as boron atoms possess a short covalent radius and the flexibility to adopt sp(2) hybridization, features that favour the formation of two-dimensional allotropes, and one example of such a borophene material has been reported recently. Here, we present a parallel experimental work showing that two-dimensional boron sheets can be grown epitaxially on a Ag(111) substrate. Two types of boron sheet, a β12 sheet and a χ3 sheet, both exhibiting a triangular lattice but with different arrangements of periodic holes, are observed by scanning tunnelling microscopy. Density functional theory simulations agree well with experiments, and indicate that both sheets are planar without obvious vertical undulations. The boron sheets are quite inert to oxidization and interact only weakly with their substrate. We envisage that such boron sheets may find applications in electronic devices in the future. PMID:27219700

  2. Strongly correlated two-dimensional plasma explored from entropy measurements.

    PubMed

    Kuntsevich, A Y; Tupikov, Y V; Pudalov, V M; Burmistrov, I S

    2015-06-23

    Charged plasma and Fermi liquid are two distinct states of electronic matter intrinsic to dilute two-dimensional electron systems at elevated and low temperatures, respectively. Probing their thermodynamics represents challenge because of lack of an adequate technique. Here, we report a thermodynamic method to measure the entropy per electron in gated structures. Our technique appears to be three orders of magnitude superior in sensitivity to a.c. calorimetry, allowing entropy measurements with only 10(8) electrons. This enables us to investigate the correlated plasma regime, previously inaccessible experimentally in two-dimensional electron systems in semiconductors. In experiments with clean two-dimensional electron system in silicon-based structures, we traced entropy evolution from the plasma to Fermi liquid regime by varying electron density. We reveal that the correlated plasma regime can be mapped onto the ordinary non-degenerate Fermi gas with an interaction-enhanced temperature-dependent effective mass. Our method opens up new horizons in studies of low-dimensional electron systems.

  3. Two dimensional particle simulations of Raman backward amplifier

    NASA Astrophysics Data System (ADS)

    Hur, Min; Lindberg, Ryan; Wurtele, Jonathan

    2005-10-01

    We carried out two-dimensional particle simulations of the Raman backward amplifier. The particle code is based on the one-dimensional averaged-PIC (aPIC) code [1]. From the speculation that the longitudinal ponderomotive driving by the two counter-propagating lasers is quite dominant over the transverse one, the two-dimensional version of the aPIC can be easily built up by putting many one-dimensional aPIC solvers in parallel. The solvers are coupled by the diffraction terms of the lasers, which enables one to simulate the transverse effects in the Raman backward amplifier. One of the most important issues regarding the transverse effects is the focusability of the amplified pulse. Previous simulations [2-3], which are based on the fluid model, show that the focusing phase of the seed laser is preserved well during the amplification process. However, there has scarcely been kinetic studies on the same problem. Various simulations from the fully kinetic two-dimensional aPIC are presented. We discuss the kinetic effects (electron trapping) on the focusablity of the amplified seed. [1] M.S. Hur, G. Penn, J.S. Wurtele, and R. Lindberg, Phys. Plasmas vol. 11, p. 5204 (2004). [2] A.A. Solodov, V.M. Malkin, and N.J. Fisch, Phys. Plasmas vol. 10, p. 2540 (2003). [3] G.M. Fraiman, N.A. Yampolsky, V.M. Malkin, and N.J. Fisch, Phys. Plasmas vol. 9, p.3617 (2002).

  4. Freezing of an unconventional two-dimensional plasma

    NASA Astrophysics Data System (ADS)

    Herland, Egil V.; Babaev, Egor; Bonderson, Parsa; Gurarie, Victor; Nayak, Chetan; Radzihovsky, Leo; Sudbø, Asle

    2013-02-01

    We study an unconventional two-dimensional, two-component classical plasma on a sphere, with emphasis on detecting signatures of melting transitions. This system is relevant to Ising-type quantum Hall states, and is unconventional in the sense that it features particles interacting via two different two-dimensional Coulomb interactions. One species of particle in the plasma carries charge of both types (Q1,Q2), while the other species carries only charge of the second type (0,-Q2). We find signatures of a freezing transition at Q12≃140. This means that the species with charge of both types will form a Wigner crystal, whereas the species with charge of the second type also shows signatures of being a Wigner crystal, due to the attractive intercomponent interaction of the second type. Moreover, there is also a Berezinskii-Kosterlitz-Thouless phase transition at Q22≃4, at which the two species of particles bind to form molecules that are neutral with respect to the second Coulomb interaction. These two transitions appear to be independent of each other, giving a rectangular phase diagram. As a special case, Q2=0 describes the (conventional) two-dimensional one-component plasma. Our study is consistent with previous studies of this plasma, and sheds new light on the freezing transition of this system.

  5. Procedures for two-dimensional electrophoresis of proteins

    SciTech Connect

    Tollaksen, S.L.; Giometti, C.S.

    1996-10-01

    High-resolution two-dimensional gel electrophoresis (2DE) of proteins, using isoelectric focusing in the first dimension and sodium dodecyl sulfate/polyacrylamide gel electrophoresis (SDS-PAGE) in the second, was first described in 1975. In the 20 years since those publications, numerous modifications of the original method have evolved. The ISO-DALT system of 2DE is a high-throughput approach that has stood the test of time. The problem of casting many isoelectric focusing gels and SDS-PAGE slab gels (up to 20) in a reproducible manner has been solved by the use of the techniques and equipment described in this manual. The ISO-DALT system of two-dimensional gel electrophoresis originated in the late 1970s and has been modified many times to improve its high-resolution, high-throughput capabilities. This report provides the detailed procedures used with the current ISO-DALT system to prepare, run, stain, and photograph two-dimensional gels for protein analysis.

  6. Experimental realization of two-dimensional boron sheets

    NASA Astrophysics Data System (ADS)

    Feng, Baojie; Zhang, Jin; Zhong, Qing; Li, Wenbin; Li, Shuai; Li, Hui; Cheng, Peng; Meng, Sheng; Chen, Lan; Wu, Kehui

    2016-06-01

    A variety of two-dimensional materials have been reported in recent years, yet single-element systems such as graphene and black phosphorus have remained rare. Boron analogues have been predicted, as boron atoms possess a short covalent radius and the flexibility to adopt sp2 hybridization, features that favour the formation of two-dimensional allotropes, and one example of such a borophene material has been reported recently. Here, we present a parallel experimental work showing that two-dimensional boron sheets can be grown epitaxially on a Ag(111) substrate. Two types of boron sheet, a β12 sheet and a χ3 sheet, both exhibiting a triangular lattice but with different arrangements of periodic holes, are observed by scanning tunnelling microscopy. Density functional theory simulations agree well with experiments, and indicate that both sheets are planar without obvious vertical undulations. The boron sheets are quite inert to oxidization and interact only weakly with their substrate. We envisage that such boron sheets may find applications in electronic devices in the future.

  7. A two-dimensional analytical model of petroleum vapor intrusion

    NASA Astrophysics Data System (ADS)

    Yao, Yijun; Verginelli, Iason; Suuberg, Eric M.

    2016-02-01

    In this study we present an analytical solution of a two-dimensional petroleum vapor intrusion model, which incorporates a steady-state diffusion-dominated vapor transport in a homogeneous soil and piecewise first-order aerobic biodegradation limited by oxygen availability. This new model can help practitioners to easily generate two-dimensional soil gas concentration profiles for both hydrocarbons and oxygen and estimate hydrocarbon indoor air concentrations as a function of site-specific conditions such as source strength and depth, reaction rate constant, soil characteristics and building features. The soil gas concentration profiles generated by this new model are shown in good agreement with three-dimensional numerical simulations and two-dimensional measured soil gas data from a field study. This implies that for cases involving diffusion dominated soil gas transport, steady state conditions and homogenous source and soil, this analytical model can be used as a fast and easy-to-use risk screening tool by replicating the results of 3-D numerical simulations but with much less computational effort.

  8. The NASA Ames Research Center one- and two-dimensional stratospheric models. Part 2: The two-dimensional model

    NASA Technical Reports Server (NTRS)

    Whitten, R. C.; Borucki, W. J.; Watson, V. R.; Shimazaki, T.; Woodward, H. T.; Riegel, C. A.; Capone, L. A.; Becker, T.

    1977-01-01

    The two-dimensional model of stratospheric constituents is presented in detail. The derivation of pertinent transport parameters and the numerical solution of the species continuity equations, including a technique for treating the stiff differential equations that represent the chemical kinetic terms, and appropriate methods for simulating the diurnal variations of the solar zenith angle and species concentrations are discussed. Predicted distributions of tracer constituents (ozone, carbon 14, nitric acid) are compared with observed distributions.

  9. Biological and environmental interactions of emerging two-dimensional nanomaterials.

    PubMed

    Wang, Zhongying; Zhu, Wenpeng; Qiu, Yang; Yi, Xin; von dem Bussche, Annette; Kane, Agnes; Gao, Huajian; Koski, Kristie; Hurt, Robert

    2016-03-21

    Two-dimensional materials have become a major focus in materials chemistry research worldwide with substantial efforts centered on synthesis, property characterization, and technological application. These high-aspect ratio sheet-like solids come in a wide array of chemical compositions, crystal phases, and physical forms, and are anticipated to enable a host of future technologies in areas that include electronics, sensors, coatings, barriers, energy storage and conversion, and biomedicine. A parallel effort has begun to understand the biological and environmental interactions of synthetic nanosheets, both to enable the biomedical developments and to ensure human health and safety for all application fields. This review covers the most recent literature on the biological responses to 2D materials and also draws from older literature on natural lamellar minerals to provide additional insight into the essential chemical behaviors. The article proposes a framework for more systematic investigation of biological behavior in the future, rooted in fundamental materials chemistry and physics. That framework considers three fundamental interaction modes: (i) chemical interactions and phase transformations, (ii) electronic and surface redox interactions, and (iii) physical and mechanical interactions that are unique to near-atomically-thin, high-aspect-ratio solids. Two-dimensional materials are shown to exhibit a wide range of behaviors, which reflect the diversity in their chemical compositions, and many are expected to undergo reactive dissolution processes that will be key to understanding their behaviors and interpreting biological response data. The review concludes with a series of recommendations for high-priority research subtopics at the "bio-nanosheet" interface that we hope will enable safe and successful development of technologies related to two-dimensional nanomaterials. PMID:26923057

  10. P-wave contacts for two dimensional quatum gas

    NASA Astrophysics Data System (ADS)

    Zhang, Yicai; Yu, Zhenhua; Zhang, Shizhong

    The s-wave contact has played an important role in our understanding of the strongly interacting Fermi gases. Recently, theoretical and experimental work has shown that two similar contacts exist for a p-wave interacting Fermi gas in three-dimensions. In this work, we extend the considerations to two dimensional spineless Fermi gas and derive exact results regarding the energy, momentum distributions and in particular, shifts of monopole frequency in a harmonic trap. Asymptotic formula for the frequency shift is given at high temperature via virial expansion and this can be checked by future experiments.

  11. Memory device for two-dimensional radiant energy array computers

    NASA Technical Reports Server (NTRS)

    Schaefer, D. H.; Strong, J. P., III (Inventor)

    1977-01-01

    A memory device for two dimensional radiant energy array computers was developed, in which the memory device stores digital information in an input array of radiant energy digital signals that are characterized by ordered rows and columns. The memory device contains a radiant energy logic storing device having a pair of input surface locations for receiving a pair of separate radiant energy digital signal arrays and an output surface location adapted to transmit a radiant energy digital signal array. A regenerative feedback device that couples one of the input surface locations to the output surface location in a manner for causing regenerative feedback is also included

  12. Quasi-two-dimensional Turing patterns in an imposed gradient

    NASA Astrophysics Data System (ADS)

    Lengyel, István; Kádár, Sándor; Epstein, Irving R.

    1992-11-01

    In experiments on quasi-two-dimensional Turing structures, patterns form perpendicular to a concentration gradient imposed by the boundary conditions. Using linear stability analysis, with the ClO2-I2-MA (malonic acid) reaction as an example, we obtain conditions on the position along the gradient direction and possible three dimensionality of the structures. Experiments on the effects of MA and starch concentrations on the position of the structures support the theory. Simulations taking into account the starch indicator yield Turing patterns even with equal diffusion coefficients for the activator and inhibitor species.

  13. Elastic behavior of a two-dimensional crystal near melting.

    PubMed

    von Grünberg, H H; Keim, P; Zahn, K; Maret, G

    2004-12-17

    Using positional data from video microscopy, we determine the elastic moduli of two-dimensional colloidal crystals as a function of temperature. The moduli are extracted from the wave-vector-dependent normal-mode spring constants in the limit q-->0 and are compared to the renormalized Young's modulus of the Kosterlitz-Thouless-Halperin-Nelson-Young theory. An essential element of this theory is the universal prediction that Young's modulus must approach 16 pi at the melting temperature. This is indeed observed in our experiment.

  14. Correlation effects in two-dimensional topological insulators.

    PubMed

    Hohenadler, M; Assaad, F F

    2013-04-10

    Topological insulators have become one of the most active research areas in condensed matter physics. This article reviews progress on the topic of electronic correlation effects in the two-dimensional case, with a focus on systems with intrinsic spin-orbit coupling and numerical results. Topics addressed include an introduction to the noninteracting case, an overview of theoretical models, correlated topological band insulators, interaction-driven phase transitions, topological Mott insulators and fractional topological states, correlation effects on helical edge states, and topological invariants of interacting systems.

  15. SOLVING THE TWO-DIMENSIONAL DIFFUSION FLOW MODEL.

    USGS Publications Warehouse

    Hromadka, T.V.; Lai, Chintu

    1985-01-01

    A simplification of the two-dimensional (2-D) continuity and momentum equations is the diffusion equation. To investigate its capability, the numerical model using the diffusion approach is applied to a hypothetical failure problem of a regional water reservoir. The model is based on an explicit, integrated finite-difference scheme, and the floodplain is simulated by a popular home computer which supports 64K FORTRAN. Though simple, the 2-D model can simulate some interesting flooding effects that a 1-D full dynamic model cannot.

  16. Topological phases in two-dimensional materials: a review.

    PubMed

    Ren, Yafei; Qiao, Zhenhua; Niu, Qian

    2016-06-01

    Topological phases with insulating bulk and gapless surface or edge modes have attracted intensive attention because of their fundamental physics implications and potential applications in dissipationless electronics and spintronics. In this review, we mainly focus on recent progress in the engineering of topologically nontrivial phases (such as [Formula: see text] topological insulators, quantum anomalous Hall effects, quantum valley Hall effects etc) in two-dimensional systems, including quantum wells, atomic crystal layers of elements from group III to group VII, and the transition metal compounds. PMID:27176924

  17. Nanocavity absorption enhancement for two-dimensional material monolayer systems.

    PubMed

    Song, Haomin; Jiang, Suhua; Ji, Dengxin; Zeng, Xie; Zhang, Nan; Liu, Kai; Wang, Chu; Xu, Yun; Gan, Qiaoqiang

    2015-03-23

    Here we propose a strategy to enhance the light-matter interaction of two-dimensional (2D) material monolayers based on strong interference effect in planar nanocavities, and overcome the limitation between optical absorption and the atomically-thin thickness of 2D materials. By exploring the role of spacer layers with different thicknesses and refractive indices, we demonstrate that a nanocavity with an air spacer layer placed between a graphene monolayer and an aluminum reflector layer will enhance the exclusive absorption in the graphene monolayer effectively, which is particularly useful for the development of atomically-thin energy harvesting/conversion devices.

  18. Two-dimensional chiral topological superconductivity in Shiba lattices

    NASA Astrophysics Data System (ADS)

    Li, Jian; Neupert, Titus; Wang, Zhijun; MacDonald, A. H.; Yazdani, A.; Bernevig, B. Andrei

    2016-07-01

    The chiral p-wave superconductor is the archetypal example of a state of matter that supports non-Abelian anyons, a highly desired type of exotic quasiparticle. With this, it is foundational for the distant goal of building a topological quantum computer. While some candidate materials for bulk chiral superconductors exist, they are subject of an ongoing debate about their actual paring state. Here we propose an alternative route to chiral superconductivity, consisting of the surface of an ordinary superconductor decorated with a two-dimensional lattice of magnetic impurities. We furthermore identify a promising experimental platform to realize this proposal.

  19. Aerodynamics of two-dimensional slotted bluff bodies

    SciTech Connect

    Takahashi, F.; Higuchi, H.

    1988-04-30

    Aerodynamic characteristics of two-dimensional, slotted bluff bodies were experimentally investigated. Flow visualizations, base pressure measurements, mean velocity vector measurements, and drag force measurements were conducted to analyze effects of spacing ratio (i.e., porosity), curvature, and vent. Low porosity model configurations produced stable near-wake patterns with enhanced vortex sheddings of overall wake formations. Model curvature reduced drag forces and weakened the vortex sheddings. Stabilizing effect of curvature on the near-wake patterns was also found. A vent combined with large model curvature was found to control drag force effectively, as well as suppressing vortex sheddings. 10 refs., 52 figs., 1 tab.

  20. Two-dimensional crystals: managing light for optoelectronics.

    PubMed

    Eda, Goki; Maier, Stefan A

    2013-07-23

    Semiconducting two-dimensional (2D) crystals such as MoS2 and WSe2 exhibit unusual optical properties that can be exploited for novel optoelectronics ranging from flexible photovoltaic cells to harmonic generation and electro-optical modulation devices. Rapid progress of the field, particularly in the growth area, is beginning to enable ways to implement 2D crystals into devices with tailored functionalities. For practical device performance, a key challenge is to maximize light-matter interactions in the material, which is inherently weak due to its atomically thin nature. Light management around the 2D layers with the use of plasmonic nanostructures can provide a compelling solution.

  1. Ultra-subwavelength two-dimensional plasmonic circuits.

    PubMed

    Andress, William F; Yoon, Hosang; Yeung, Kitty Y M; Qin, Ling; West, Ken; Pfeiffer, Loren; Ham, Donhee

    2012-05-01

    We report electronics regime (GHz) two-dimensional (2D) plasmonic circuits, which locally and nonresonantly interface with electronics, and thus offer to electronics the benefits of their ultrasubwavelength confinement, with up to 440,000-fold mode-area reduction. By shaping the geometry of 2D plasmonic media 80 nm beneath an unpatterned metallic gate, plasmons are routed freely into various types of reflections and interferences, leading to a range of plasmonic circuits, e.g., plasmonic crystals and plasmonic-electromagnetic interferometers, offering new avenues for electronics.

  2. Two-dimensional molecular crystals of phosphonic acids on graphene.

    PubMed

    Prado, Mariana C; Nascimento, Regiane; Moura, Luciano G; Matos, Matheus J S; Mazzoni, Mario S C; Cancado, Luiz G; Chacham, Helio; Neves, Bernardo R A

    2011-01-25

    The synthesis and characterization of two-dimensional (2D) molecular crystals composed of long and linear phosphonic acids atop graphene is reported. Using scanning probe microscopy in combination with first-principles calculations, we show that these true 2D crystals are oriented along the graphene armchair direction only, thereby enabling an easy determination of graphene flake orientation. We have also compared the doping level of graphene flakes via Raman spectroscopy. The presence of the molecular crystal atop graphene induces a well-defined shift in the Fermi level, corresponding to hole doping, which is in agreement with our ab initio calculations.

  3. External Dissipation in Driven Two-Dimensional Turbulence

    NASA Astrophysics Data System (ADS)

    Rivera, Michael; Wu, X. L.

    2000-07-01

    Turbulence in a freely suspended soap film is created by electromagnetic forcing and measured by particle tracking. The velocity fluctuations are shown to be adequately described by the forced Navier-Stokes equation for an incompressible two-dimensional fluid with a linear drag term to model the frictional coupling to the surrounding air. Using this equation, the energy dissipation rates due to air friction and the film's internal viscosity are measured, as is the rate of energy injection from the electromagnetic forcing. Comparison of these rates demonstrates that the air friction is a significant energy dissipation mechanism in the system.

  4. Two-dimensional chiral topological superconductivity in Shiba lattices.

    PubMed

    Li, Jian; Neupert, Titus; Wang, Zhijun; MacDonald, A H; Yazdani, A; Bernevig, B Andrei

    2016-01-01

    The chiral p-wave superconductor is the archetypal example of a state of matter that supports non-Abelian anyons, a highly desired type of exotic quasiparticle. With this, it is foundational for the distant goal of building a topological quantum computer. While some candidate materials for bulk chiral superconductors exist, they are subject of an ongoing debate about their actual paring state. Here we propose an alternative route to chiral superconductivity, consisting of the surface of an ordinary superconductor decorated with a two-dimensional lattice of magnetic impurities. We furthermore identify a promising experimental platform to realize this proposal. PMID:27465127

  5. Two-dimensional particle displacement tracking in particle imaging velocimetry

    NASA Technical Reports Server (NTRS)

    Wernet, Mark P.

    1991-01-01

    A new particle imaging velocimetry data acquisition and analysis system, which is an order of magnitude faster than any previously proposed system, has been constructed and tested. The new particle displacement tracking (PDT) system is an all electronic technique employing a video camera and a large memory buffer frame-grabber board. Using a simple encoding scheme, a time sequence of single exposure images is time-coded into a single image and then processed to track particle displacements and determine two-dimensional velocity vectors. Use of the PDT technique in a counterrotating vortex flow produced over 1100 velocity vectors in 110 s when processed on an 80386 PC.

  6. Quantum Phases of a Two-Dimensional Dipolar Fermi Gas

    SciTech Connect

    Bruun, G. M.; Taylor, E.

    2008-12-12

    We examine the superfluid and collapse instabilities of a quasi-two-dimensional gas of dipolar fermions aligned by an orientable external field. It is shown that the interplay between the anisotropy of the dipole-dipole interaction, the geometry of the system, and the p-wave symmetry of the superfluid order parameter means that the effective interaction for pairing can be made very large without the system collapsing. This leads to a broad region in the phase diagram where the system forms a stable superfluid. Analyzing the superfluid transition at finite temperatures, we calculate the Berezinskii-Kosterlitz-Thouless temperature as a function of the dipole angle.

  7. Hydrometeor classification from two-dimensional video disdrometer data

    NASA Astrophysics Data System (ADS)

    Grazioli, J.; Tuia, D.; Monhart, S.; Schneebeli, M.; Raupach, T.; Berne, A.

    2014-09-01

    The first hydrometeor classification technique based on two-dimensional video disdrometer (2DVD) data is presented. The method provides an estimate of the dominant hydrometeor type falling over time intervals of 60 s during precipitation, using the statistical behavior of a set of particle descriptors as input, calculated for each particle image. The employed supervised algorithm is a support vector machine (SVM), trained over 60 s precipitation time steps labeled by visual inspection. In this way, eight dominant hydrometeor classes can be discriminated. The algorithm achieved high classification performances, with median overall accuracies (Cohen's K) of 90% (0.88), and with accuracies higher than 84% for each hydrometeor class.

  8. Carbon dioxide separation with a two-dimensional polymer membrane.

    PubMed

    Schrier, Joshua

    2012-07-25

    Carbon dioxide gas separation is important for many environmental and energy applications. Molecular dynamics simulations are used to characterize a two-dimensional hydrocarbon polymer, PG-ES1, that uses a combination of surface adsorption and narrow pores to separate carbon dioxide from nitrogen, oxygen, and methane gases. The CO2 permeance is 3 × 10(5) gas permeation units (GPU). The CO2/N2 selectivity is 60, and the CO2/CH4 selectivity exceeds 500. The combination of high CO2 permeance and selectivity surpasses all known materials, enabling low-cost postcombustion CO2 capture, utilization of landfill gas, and horticulture applications.

  9. Two-Dimensional Optoelectronic Graphene Nanoprobes for Neural Nerwork

    NASA Astrophysics Data System (ADS)

    Hong, Tu; Kitko, Kristina; Wang, Rui; Zhang, Qi; Xu, Yaqiong

    2014-03-01

    Brain is the most complex network created by nature, with billions of neurons connected by trillions of synapses through sophisticated wiring patterns and countless modulatory mechanisms. Current methods to study the neuronal process, either by electrophysiology or optical imaging, have significant limitations on throughput and sensitivity. Here, we use graphene, a monolayer of carbon atoms, as a two-dimensional nanoprobe for neural network. Scanning photocurrent measurement is applied to detect the local integration of electrical and chemical signals in mammalian neurons. Such interface between nanoscale electronic device and biological system provides not only ultra-high sensitivity, but also sub-millisecond temporal resolution, owing to the high carrier mobility of graphene.

  10. Superconductivity in the two-dimensional generalized Hubbard model

    NASA Astrophysics Data System (ADS)

    Lima, L. S.

    2016-08-01

    We have used the Green's functions method at finite temperature and the Kubo's formalism, to calculate the electron conductivity σ(ω) in the generalized two-dimensional Hubbard model. We have obtained a behavior superconductor for the system to T > T0. The AC conductivity falls to zero in ω =ω0 , where ω0 depends on Δ, which is the gap of the system. The behavior gotten is according of with the behavior of the superconductors of high Tc where there is a changes abruptly from a Mott's insulator state to superconductor.

  11. Disordered two-dimensional electron systems with chiral symmetry

    NASA Astrophysics Data System (ADS)

    Markoš, P.; Schweitzer, L.

    2012-10-01

    We review the results of our recent numerical investigations on the electronic properties of disordered two dimensional systems with chiral unitary, chiral orthogonal, and chiral symplectic symmetry. Of particular interest is the behavior of the density of states and the logarithmic scaling of the smallest Lyapunov exponents in the vicinity of the chiral quantum critical point in the band center at E=0. The observed peaks or depressions in the density of states, the distribution of the critical conductances, and the possible non-universality of the critical exponents for certain chiral unitary models are discussed.

  12. Optofluidic two-dimensional grating volume refractive index sensor.

    PubMed

    Sarkar, Anirban; Shivakiran Bhaktha, B N; Khastgir, Sugata Pratik

    2016-09-10

    We present an optofluidic reservoir with a two-dimensional grating for a lab-on-a-chip volume refractive index sensor. The observed diffraction pattern from the device resembles the analytically obtained fringe pattern. The change in the diffraction pattern has been monitored in the far-field for fluids with different refractive indices. Reliable measurements of refractive index variations, with an accuracy of 6×10-3 refractive index units, for different fluids establishes the optofluidic device as a potential on-chip tool for monitoring dynamic refractive index changes. PMID:27661360

  13. Two-Dimensional Layered Materials-Based Spintronics

    NASA Astrophysics Data System (ADS)

    Su, Guohui; Wu, Xing; Tong, Wenqi; Duan, Chungang

    2015-12-01

    The recent emergence of two-dimensional (2D) layered materials — graphene and transition metal dichalcogenides — opens a new avenue for exploring the internal quantum degrees of freedom of electrons and their potential for new electronics. Here, we provide a brief review of experimental achievements concerning electrical spin injection, spin transport, graphene nanoribbons spintronics and transition metal dichalcogenides spin and pseudospins. Future research in 2D layered materials spintronics will need to address the development of applications such as spin transistors and spin logic devices, as well as exotic physical properties including pseudospins-valley phenomena in graphene and other 2D materials.

  14. Two-Dimensional Acousto-Optical Spectrum Analyzer

    NASA Technical Reports Server (NTRS)

    Ansari, Homayoon; Lesh, James R.; Metscher, Brian

    1991-01-01

    State-of-the-art two-dimensional acousto-optical spectrum analyzer processes input radio-frequency signal in real time into components in any number of spectral channels up to about 10(Sup5). Input radio-frequency signal to be analyzed launched via transducer into acousto-optical device along x axis. Acousto-optical device becomes Bragg cell. Pulsed plane waves of light from laser aimed at Bragg cell, which spatially modulates phases of plane waves and diffracts waves according to pattern of acoustic signal.

  15. Two-dimensional unsteady lift problems in supersonic flight

    NASA Technical Reports Server (NTRS)

    Heaslet, Max A; Lomax, Harvard

    1949-01-01

    The variation of pressure distribution is calculated for a two-dimensional supersonic airfoil either experiencing a sudden angle-of-attack change or entering a sharp-edge gust. From these pressure distributions the indicial lift functions applicable to unsteady lift problems are determined for two cases. Results are presented which permit the determination of maximum increment in lift coefficient attained by an unrestrained airfoil during its flight through a gust. As an application of these results, the minimum altitude for safe flight through a specific gust is calculated for a particular supersonic wing of given strength and wing loading.

  16. Solving time-dependent two-dimensional eddy current problems

    NASA Technical Reports Server (NTRS)

    Lee, Min Eig; Hariharan, S. I.; Ida, Nathan

    1990-01-01

    Transient eddy current calculations are presented for an EM wave-scattering and field-penetrating case in which a two-dimensional transverse magnetic field is incident on a good (i.e., not perfect) and infinitely long conductor. The problem thus posed is of initial boundary-value interface type, where the boundary of the conductor constitutes the interface. A potential function is used for time-domain modeling of the situation, and finite difference-time domain techniques are used to march the potential function explicitly in time. Attention is given to the case of LF radiation conditions.

  17. Wigner functions from the two-dimensional wavelet group.

    PubMed

    Ali, S T; Krasowska, A E; Murenzi, R

    2000-12-01

    Following a general procedure developed previously [Ann. Henri Poincaré 1, 685 (2000)], here we construct Wigner functions on a phase space related to the similitude group in two dimensions. Since the group space in this case is topologically homeomorphic to the phase space in question, the Wigner functions so constructed may also be considered as being functions on the group space itself. Previously the similitude group was used to construct wavelets for two-dimensional image analysis; we discuss here the connection between the wavelet transform and the Wigner function.

  18. Wake-induced bending of two-dimensional plasma crystals

    SciTech Connect

    Röcker, T. B. Ivlev, A. V. Zhdanov, S. K.; Morfill, G. E.; Couëdel, L.

    2014-07-15

    It is shown that the wake-mediated interactions between microparticles in a two-dimensional plasma crystal affect the shape of the monolayer, making it non-flat. The equilibrium shape is calculated for various distributions of the particle number density in the monolayer. For typical experimental conditions, the levitation height of particles in the center of the crystal can be noticeably smaller than at the periphery. It is suggested that the effect of wake-induced bending can be utilized in experiments, to deduce important characteristics of the interparticle interaction.

  19. Coherent light scattering from a two-dimensional Mott insulator.

    PubMed

    Weitenberg, Christof; Schauss, Peter; Fukuhara, Takeshi; Cheneau, Marc; Endres, Manuel; Bloch, Immanuel; Kuhr, Stefan

    2011-05-27

    We experimentally demonstrate coherent light scattering from an atomic Mott insulator in a two-dimensional lattice. The far-field diffraction pattern of small clouds of a few hundred atoms was imaged while simultaneously laser cooling the atoms with the probe beams. We describe the position of the diffraction peaks and the scaling of the peak parameters by a simple analytic model. In contrast to Bragg scattering, scattering from a single plane yields diffraction peaks for any incidence angle. We demonstrate the feasibility of detecting spin correlations via light scattering by artificially creating a one-dimensional antiferromagnetic order as a density wave and observing the appearance of additional diffraction peaks.

  20. Condensate fraction of a two-dimensional attractive Fermi gas

    SciTech Connect

    Salasnich, Luca

    2007-07-15

    We investigate the Bose-Einstein condensation of fermionic pairs in a two-dimensional uniform two-component Fermi superfluid obtaining an explicit formula for the condensate density as a function of the chemical potential and the energy gap. By using the mean-field extended Bardeen-Cooper-Schrieffer theory, we analyze, as a function of the bound-state energy, the off-diagonal long-range order in the crossover from the Bardeen-Cooper-Schrieffer state of weakly bound Cooper pairs to the Bose-Einstein condensate of strongly-bound molecular dimers.

  1. Magnus force in discrete and continuous two-dimensional superfluids

    SciTech Connect

    Gecse, Z.; Khlebnikov, S.

    2005-08-01

    Motion of vortices in two-dimensional superfluids in the classical limit is studied by solving the Gross-Pitaevskii equation numerically on a uniform lattice. We find that, in the presence of a superflow directed along one of the main lattice periods, vortices move with the superflow on fine lattices but perpendicular to it on coarse ones. We interpret this result as a transition from the full Magnus force in a Galilean-invariant limit to vanishing effective Magnus force in a discrete system, in agreement with the existing experiments on vortex motion in Josephson junction arrays.

  2. General relativity as a two-dimensional CFT

    NASA Astrophysics Data System (ADS)

    Adamo, Tim

    2015-11-01

    The tree-level scattering amplitudes of general relativity (GR) encode the full nonlinearity of the Einstein field equations. Yet remarkably compact expressions for these amplitudes have been found which seem unrelated to a perturbative expansion of the Einstein-Hilbert action. This suggests an entirely different description of GR which makes this on-shell simplicity manifest. Taking our cue from the tree-level amplitudes, we discuss how such a description can be found. The result is a formulation of GR in terms of a solvable two-dimensional conformal field theory (CFT), with the Einstein equations emerging as quantum consistency conditions.

  3. Quantum control in two-dimensional Fourier-transform spectroscopy

    SciTech Connect

    Lim, Jongseok; Lee, Han-gyeol; Lee, Sangkyung; Ahn, Jaewook

    2011-07-15

    We present a method that harnesses coherent control capability to two-dimensional Fourier-transform optical spectroscopy. For this, three ultrashort laser pulses are individually shaped to prepare and control the quantum interference involved in two-photon interexcited-state transitions of a V-type quantum system. In experiments performed with atomic rubidium, quantum control for the enhancement and reduction of the 5P{sub 1/2}{yields} 5P{sub 3/2} transition was successfully tested in which the engineered transitions were distinguishably extracted in the presence of dominant one-photon transitions.

  4. Two-dimensional approach to relativistic positioning systems

    SciTech Connect

    Coll, Bartolome; Ferrando, Joan Josep; Morales, Juan Antonio

    2006-04-15

    A relativistic positioning system is a physical realization of a coordinate system consisting in four clocks in arbitrary motion broadcasting their proper times. The basic elements of the relativistic positioning systems are presented in the two-dimensional case. This simplified approach allows to explain and to analyze the properties and interest of these new systems. The positioning system defined by geodesic emitters in flat metric is developed in detail. The information that the data generated by a relativistic positioning system give on the space-time metric interval is analyzed, and the interest of these results in gravimetry is pointed out.

  5. High order hybrid numerical simulations of two dimensional detonation waves

    NASA Technical Reports Server (NTRS)

    Cai, Wei

    1993-01-01

    In order to study multi-dimensional unstable detonation waves, a high order numerical scheme suitable for calculating the detailed transverse wave structures of multidimensional detonation waves was developed. The numerical algorithm uses a multi-domain approach so different numerical techniques can be applied for different components of detonation waves. The detonation waves are assumed to undergo an irreversible, unimolecular reaction A yields B. Several cases of unstable two dimensional detonation waves are simulated and detailed transverse wave interactions are documented. The numerical results show the importance of resolving the detonation front without excessive numerical viscosity in order to obtain the correct cellular patterns.

  6. Laminar flame and acoustic waves in two-dimensional flow

    SciTech Connect

    Zaytsev, M. L. Akkerman, V. B.

    2011-03-15

    The complete system of fluid dynamics equations describing the development of instability of a reaction front in a two-dimensional flow in reversed time are reduced to a closed system of equations of front dynamics by using Lagrangian variables and integrals of motion. The system can be used to analyze processes behind the front without solving the complete system of fluid dynamics and chemical kinetics equations. It is demonstrated how the gas density disturbances induced by the moving front can be described in the adiabatic approximation.

  7. Path Integral Solubility of Two-Dimensional Models

    SciTech Connect

    Das, Ashok K.; Mathur, Vishnu S.

    1985-07-01

    We apply the technique of Fujikawa to solve for simple two-dimensional models by looking at the nontrivial transformation properties of the fermion measure in the path-integral formalism. We obtain the most general solution for the massless Thirring model and point out how the one-parameter solution reduces to that of Johnson and Sommerfield in a particular limit. We present the most general solution for the massive vector model indicating how it reduces to the solutions of Brown and Sommerfield for different values of the parameter. The solution of a gradient-coupling model is also discussed.

  8. Two-dimensional manifolds with metrics of revolution

    SciTech Connect

    Sabitov, I Kh

    2000-10-31

    This is a study of the topological and metric structure of two-dimensional manifolds with a metric that is locally a metric of revolution. In the case of compact manifolds this problem can be thoroughly investigated, and in particular it is explained why there are no closed analytic surfaces of revolution in R{sup 3} other than a sphere and a torus (moreover, in the smoothness class C{sup {infinity}} such surfaces, understood in a certain generalized sense, exist in any topological class)

  9. Optofluidic two-dimensional grating volume refractive index sensor.

    PubMed

    Sarkar, Anirban; Shivakiran Bhaktha, B N; Khastgir, Sugata Pratik

    2016-09-10

    We present an optofluidic reservoir with a two-dimensional grating for a lab-on-a-chip volume refractive index sensor. The observed diffraction pattern from the device resembles the analytically obtained fringe pattern. The change in the diffraction pattern has been monitored in the far-field for fluids with different refractive indices. Reliable measurements of refractive index variations, with an accuracy of 6×10-3 refractive index units, for different fluids establishes the optofluidic device as a potential on-chip tool for monitoring dynamic refractive index changes.

  10. Ultrafast Charge Transfer Visualized by Two-Dimensional Electronic Spectroscopy

    NASA Astrophysics Data System (ADS)

    Bixner, O.; Christensson, N.; Hauer, J.; Milota, F.; Mančal, T.; Lukeš, V.; Kauffmann, H. F.

    2013-03-01

    Two-dimensional electronic spectroscopy (2D-ES) is used to investigate ultrafast excited-state dynamics in a lutetium bisphthalocyanine dimer. Following optical excitation, a chain of electron and hole transfer steps gives rise to characteristic cross-peak dynamics in the electronic 2D spectra. The combination of density matrix propagation and quantum chemical calculations results in a molecular view of the charge transfer dynamics and highlights the role of the counter-ion in providing an energetic perturbation which promotes charge transfer across the complex.

  11. Topological insulating phases from two-dimensional nodal loop semimetals

    NASA Astrophysics Data System (ADS)

    Li, Linhu; Araújo, Miguel A. N.

    2016-10-01

    Starting from a minimal model for a two-dimensional nodal loop semimetal, we study the effect of chiral mass gap terms. The resulting Dirac loop anomalous Hall insulator's Chern number is the phase-winding number of the mass gap terms on the loop. We provide simple lattice models, analyze the topological phases, and generalize a previous index characterizing topological transitions. The responses of the Dirac loop anomalous Hall and quantum spin Hall insulators to a magnetic field's vector potential are also studied both in weak- and strong-field regimes, as well as the edge states in a ribbon geometry.

  12. Spirals and skyrmions in two dimensional oxide heterostructures

    NASA Astrophysics Data System (ADS)

    Li, Xiaopeng; Liu, W. Vincent; Balents, Leon

    2014-03-01

    A symmetry-based general free energy governing long-wavelength magnetism in two-dimensional oxide heterostructures will be presented. This leads, in the relevant regime of weak but non-negligible spin-orbit coupling, to a rich phase diagram containing in-plane ferromagnetic, spiral, cone, and skyrmion lattice phases, as well as a nematic state stabilized by thermal fluctuations. The general conclusions are vetted by a microscopic derivation for a simple model with Rashba spin-orbit coupling. NSF PHY11-25915, NSF DMR-06809, ARO (W911NF-11-1-0230.

  13. Nonlinear Cascades in Two-Dimensional Turbulent Magnetoconvection

    SciTech Connect

    Skandera, Dan; Mueller, Wolf-Christian

    2009-06-05

    The dynamics of spectral transport in two-dimensional turbulent convection of electrically conducting fluids is studied by means of direct numerical simulations in the frame of the magnetohydrodynamic Boussinesq approximation. The system performs quasioscillations between two different regimes of small-scale turbulence: one dominated by nonlinear magnetohydrodynamic interactions; the other governed by buoyancy forces. The self-excited change of turbulent states is reported here for the first time. The process is controlled by the ideal invariant cross helicity, H{sup C}=SdSv{center_dot}b. The observations are explained by the interplay of convective driving with the nonlinear spectral transfer of total magnetohydrodynamic energy and cross helicity.

  14. Operational manual for two-dimensional transonic code TSFOIL

    NASA Technical Reports Server (NTRS)

    Stahara, S. S.

    1978-01-01

    This code solves the two-dimensional, transonic, small-disturbance equations for flow past lifting airfoils in both free air and various wind-tunnel environments by using a variant of the finite-difference method. A description of the theoretical and numerical basis of the code is provided, together with complete operating instructions and sample cases for the general user. In addition, a programmer's manual is also presented to assist the user interested in modifying the code. Included in the programmer's manual are a dictionary of subroutine variables in common and a detailed description of each subroutine.

  15. Kinetic analysis of two dimensional metallic grating Cerenkov maser

    SciTech Connect

    Zhao Ding

    2011-08-15

    The dispersion relation of two dimensional metallic grating Cerenkov maser has been given by using kinetic analysis, in which the influence of electron movement is directly considered without using an equivalent dielectric medium assumption. The effects of structural parameters and beam state on the interaction gain and synchronous frequency have also been investigated in detail by numerical calculations. To an illustrative case, the quantitative relations produced from varying the gap distance between electron beam and metallic grating, beam current, electron transverse to axial velocity ratio, and electron axial velocity spread have been obtained. The developed method can be used to predict the real interaction system performances.

  16. Two-dimensional chiral topological superconductivity in Shiba lattices

    PubMed Central

    Li, Jian; Neupert, Titus; Wang, Zhijun; MacDonald, A. H.; Yazdani, A.; Bernevig, B. Andrei

    2016-01-01

    The chiral p-wave superconductor is the archetypal example of a state of matter that supports non-Abelian anyons, a highly desired type of exotic quasiparticle. With this, it is foundational for the distant goal of building a topological quantum computer. While some candidate materials for bulk chiral superconductors exist, they are subject of an ongoing debate about their actual paring state. Here we propose an alternative route to chiral superconductivity, consisting of the surface of an ordinary superconductor decorated with a two-dimensional lattice of magnetic impurities. We furthermore identify a promising experimental platform to realize this proposal. PMID:27465127

  17. Particle Diffusion in a Quasi-Two-Dimensional Bacterial Bath

    NASA Astrophysics Data System (ADS)

    Wu, Xiao-Lun; Libchaber, Albert

    2000-03-01

    We study the effect of bacterial motion on micron-scale beads in a freely suspended soap film. Given the sizes of bacteria and beads, the geometry of the experiment is quasi-two-dimensional. Large positional fluctuations are observed for beads as large as 10 μm in diameter, and the measured mean-square displacements indicate superdiffusion in short times and normal diffusion in long times. Though the phenomenon is similar to Brownian motions of small particles, its physical origin is different and can be attributed to the collective dynamics of bacteria.

  18. Synthesis of borophenes: Anisotropic, two-dimensional boron polymorphs.

    PubMed

    Mannix, Andrew J; Zhou, Xiang-Feng; Kiraly, Brian; Wood, Joshua D; Alducin, Diego; Myers, Benjamin D; Liu, Xiaolong; Fisher, Brandon L; Santiago, Ulises; Guest, Jeffrey R; Yacaman, Miguel Jose; Ponce, Arturo; Oganov, Artem R; Hersam, Mark C; Guisinger, Nathan P

    2015-12-18

    At the atomic-cluster scale, pure boron is markedly similar to carbon, forming simple planar molecules and cage-like fullerenes. Theoretical studies predict that two-dimensional (2D) boron sheets will adopt an atomic configuration similar to that of boron atomic clusters. We synthesized atomically thin, crystalline 2D boron sheets (i.e., borophene) on silver surfaces under ultrahigh-vacuum conditions. Atomic-scale characterization, supported by theoretical calculations, revealed structures reminiscent of fused boron clusters with multiple scales of anisotropic, out-of-plane buckling. Unlike bulk boron allotropes, borophene shows metallic characteristics that are consistent with predictions of a highly anisotropic, 2D metal.

  19. Functionalization of Two-Dimensional Transition-Metal Dichalcogenides.

    PubMed

    Chen, Xin; McDonald, Aidan R

    2016-07-01

    Two-dimensional (2D) layered transition-metal dichalcogenides (TMDs) are a fascinating class of nanomaterials that have the potential for application in catalysis, electronics, photonics, energy storage, and sensing. TMDs are rather inert, and thus pose problems for chemical derivatization. However, to further modify the properties of TMDs and fully harness their capabilities, routes towards their chemical functionalization must be identified. Herein, recent efforts toward the chemical (bond-forming) functionalization of 2D TMDs are critically reviewed. Recent successes are highlighted, along with areas where further detailed analyses and experimentation are required. This burgeoning field is very much in its infancy but has already provided several important breakthroughs. PMID:26848815

  20. A fractal transition in the two dimensional shear layer

    NASA Technical Reports Server (NTRS)

    Jimenez, Javier; Martel, Carlos

    1990-01-01

    The dependence of product generation with the Peclet and Reynolds number in a numerically simulated, reacting, two dimensional, temporally growing mixing layer is used to compute the fractal dimension of passive scalar interfaces. A transition from a low dimension of 4/3 to a higher one of 5/3 is identified and shown to be associated to the kinematic distortion on the flow field during the first pairing interaction. It is suggested that the structures responsible for this transition are non-deterministic, non-random, inhomogeneous fractals. Only the large scales are involved. No further transition is found for Reynolds numbers up to 20,000.

  1. Diffusion of light in two-dimensional granular materials

    NASA Astrophysics Data System (ADS)

    Sadjadi, Zeinab; Miri, MirFaez

    2013-06-01

    We study diffusive light transport in a two dimensional packing of monodisperse disks. Ray optics approximation is employed to follow a light beam or photon as it is transmitted or reflected by the grains. We present an analytic expression for the transport-mean-free path based on persistent random walk of photons in a packing of disks and express the diffusion constant of photons in terms of the refractive indices of grains and host medium, grain diameter, and packing fraction. Our analytical results are examined with numerical simulations. The derived results are beneficial for better understanding of the dynamics of granular systems.

  2. Topological phases in two-dimensional materials: a review

    NASA Astrophysics Data System (ADS)

    Ren, Yafei; Qiao, Zhenhua; Niu, Qian

    2016-06-01

    Topological phases with insulating bulk and gapless surface or edge modes have attracted intensive attention because of their fundamental physics implications and potential applications in dissipationless electronics and spintronics. In this review, we mainly focus on recent progress in the engineering of topologically nontrivial phases (such as {{{Z}}2} topological insulators, quantum anomalous Hall effects, quantum valley Hall effects etc) in two-dimensional systems, including quantum wells, atomic crystal layers of elements from group III to group VII, and the transition metal compounds.

  3. Two dimensional crystal tunneling devices for THz operation

    NASA Astrophysics Data System (ADS)

    Kong, B. D.; Zeng, C.; Gaskill, D. K.; Wang, K. L.; Kim, K. W.

    2012-12-01

    Two dimensional crystal heterostructures are shown to possess a unique opportunity for nonlinear THz devices. In contrast to the oxide tunneling barrier, the uniformity of layered crystal insulators provides an ideal condition for tunneling barriers in the atomic scale. Numerical calculations based on a first-principles method clearly indicate the feasibility of diode operation with barriers as thin as two monolayers when placed between graphene-metal asymmetric electrodes. Further analysis predicts cut-off frequencies over 10 THz while maintaining strong nonlinearity for zero-bias rectification. Application to hot electron transistors is also examined, illustrating potentially superior performance in the frequency range inaccessible thus far.

  4. Human muscle proteins: analysis by two-dimensional electrophoresis

    SciTech Connect

    Giometti, C.S.; Danon, M.J.; Anderson, N.G.

    1983-09-01

    Proteins from single frozen sections of human muscle were separated by two-dimensional gel electrophoresis and detected by fluorography or Coomassie Blue staining. The major proteins were identical in different normal muscles obtained from either sex at different ages, and in Duchenne and myotonic dystrophy samples. Congenital myopathy denervation atrophy, polymyositis, and Becker's muscular dystrophy samples, however, showed abnormal myosin light chain compositions, some with a decrease of fast-fiber myosin light chains and others with a decrease of slow-fiber light chains. These protein alterations did not correlate with any specific disease, and may be cause by generalized muscle-fiber damage.

  5. Correction-to-scaling exponent for two-dimensional percolation

    SciTech Connect

    Ziff, Robert M.

    2011-02-15

    We show that the correction-to-scaling exponents in two-dimensional percolation are bounded by {Omega}{<=}72/91, {omega}=D{Omega}{<=}3/2, and {Delta}{sub 1}={nu}{omega}{<=}2, based upon Cardy's result for the crossing probability on an annulus. The upper bounds are consistent with many previous measurements of site percolation on square and triangular lattices and new measurements for bond percolation, suggesting that they are exact. They also agree with exponents for hulls proposed recently by Aharony and Asikainen, based upon results of den Nijs. A corrections scaling form evidently applicable to site percolation is also found.

  6. Soap films as two-dimensional classical fluids

    NASA Astrophysics Data System (ADS)

    Chomaz, J. M.; Cathalau, B.

    1990-02-01

    We present a theoretical derivation of the equations governing the motion of liquid soap film taking into account the physical dynamic as well as the chemical one. Generally, the behavior is specific to soap film, but we define some domains of the parameter space where its dynamic corresponds to classical two-dimensional incompressible flows. In this case we give an equation for the thickness of the membrane. We then simulate on a computer various regimes to explain how the thickness is linked to the internal motion.

  7. A Two-Dimensional Compressible Gas Flow Code

    1995-03-17

    F2D is a general purpose, two dimensional, fully compressible thermal-fluids code that models most of the phenomena found in situations of coupled fluid flow and heat transfer. The code solves momentum, continuity, gas-energy, and structure-energy equations using a predictor-correction solution algorithm. The corrector step includes a Poisson pressure equation. The finite difference form of the equation is presented along with a description of input and output. Several example problems are included that demonstrate the applicabilitymore » of the code in problems ranging from free fluid flow, shock tubes and flow in heated porous media.« less

  8. Application of two dimensional periodic molecular dynamics to interfaces.

    NASA Astrophysics Data System (ADS)

    Gay, David H.; Slater, Ben; Catlow, C. Richard A.

    1997-08-01

    We have applied two-dimensional molecular dynamics to the surface of a crystalline aspartame and the interface between the crystal face and a solvent (water). This has allowed us to look at the dynamic processes at the surface. Understanding the surface structure and properties are important to controlling the crystal morphology. The thermodynamic ensemble was constant Number, surface Area and Temperature (NAT). The calculations have been carried out using a 2D Ewald summation and 2D periodic boundary conditions for the short range potentials. The equations of motion integration has been carried out using the standard velocity Verlet algorithm.

  9. Wall Interference in Two-Dimensional Wind Tunnels

    NASA Technical Reports Server (NTRS)

    Kemp, William B., Jr.

    1986-01-01

    Viscosity and tunnel-wall constraints introduced via boundary conditions. TWINTN4 computer program developed to implement method of posttest assessment of wall interference in two-dimensional wind tunnels. Offers two methods for combining sidewall boundary-layer effects with upper and lower wall interference. In sequential procedure, Sewall method used to define flow free of sidewall effects, then assessed for upper and lower wall effects. In unified procedure, wind-tunnel flow equations altered to incorporate effects from all four walls at once. Program written in FORTRAN IV for batch execution.

  10. Two-dimensional crystallization of avidin on biotinylated lipid monolayers.

    PubMed Central

    Qin, H; Liu, Z; Sui, S F

    1995-01-01

    Two-dimensional crystals of avidin were obtained on mixed lipid monolayers containing biotinylated lipids (N-biotinyl-dipalmitoyl-L-alpha-phosphatidyl ethanolamine and dioleoyl phosphatidyl choline) by specific interaction. Image analysis of electron micrographs of these crystals revealed p2 symmetry with the unit cell parameters a = 66 +/- 2 A, b = 68 +/- 1 A, and gamma = 121 +/- 4 degrees. The projection map showed, at a resolution of about 27 A, that the four subunits within one avidin molecule are separated into two parts. Comparison between avidin and streptavidin reveals that avidin molecule binds to the lipid monolayer in an orientation similar to that of streptavidin. Images FIGURE 2 FIGURE 3 PMID:7647251

  11. Solving time-dependent two-dimensional eddy current problems

    NASA Technical Reports Server (NTRS)

    Lee, Min Eig; Hariharan, S. I.; Ida, Nathan

    1988-01-01

    Results of transient eddy current calculations are reported. For simplicity, a two-dimensional transverse magnetic field which is incident on an infinitely long conductor is considered. The conductor is assumed to be a good but not perfect conductor. The resulting problem is an interface initial boundary value problem with the boundary of the conductor being the interface. A finite difference method is used to march the solution explicitly in time. The method is shown. Treatment of appropriate radiation conditions is given special consideration. Results are validated with approximate analytic solutions. Two stringent test cases of high and low frequency incident waves are considered to validate the results.

  12. Two-Dimensional Spectroscopy with the Cosmic Origins Spectrograph

    NASA Astrophysics Data System (ADS)

    Penton, Steven V.; Sahnow, D.; France, K.

    2011-05-01

    The circular aperture of HSTs' Cosmic Origins Spectrograph (COS) is 2.5" in diameter, but transmission extends out to a 4" diameter. The NUV MAMA and the FUV microchannel plates image the sky over the full extent of the transmission. The cross-dispersion plate scale of the NUV channel is 0.02" and is 0.1" for the FUV channel. In this presentation we will discuss the capabilities and limitations of performing two-dimensional spectroscopy, in the cross-dispersion direction, with COS. In particular, we will discuss FUV detector effects, such as fixed pattern noise, gain sag, and Y walk, and the latest techniques for their correction.

  13. Quantum creep in a highly crystalline two-dimensional superconductor

    NASA Astrophysics Data System (ADS)

    Saito, Yu; Kasahara, Yuichi; Ye, Jianting; Iwasa, Yoshihiro; Nojima, Tsutomu

    Conventional studies on quantum phase transitions, especially on superconductor-insulator or superconductor-metal-insulator transitions have been performed in deposited metallic thin films such as Bismuth or MoGe. Although the techniques of thin films deposition have been considerably improved, unintentional disorder such as impurities and deficiencies, generating the pinning centers, seems to still exist in such systems. The mechanical exfoliated highly crystalline two-dimensional material can be a good candidate to realize a less-disordered 2D superconductor with extremely weak pinning, combined with transfer method or ionic-liquid gating. We report on the quantum metal, namely, magnetic-field-induced metallic state observed in an ion-gated two-dimensional superconductor based on an ultra-highly crystalline layered band insulator, ZrNCl. We found that the superconducting state is extremely fragile against external magnetic fields; that is, zero resistance state immediately disappears, once an external magnetic field switches on. This is because the present system is relatively clean and the pinning potential is extremely weak, which cause quantum tunneling and flux flow of vortices, resulting in metallic ground state.

  14. Two-dimensional fluorescence spectroscopy of laser-produced plasmas.

    PubMed

    Harilal, S S; LaHaye, N L; Phillips, M C

    2016-08-01

    We use a two-dimensional laser-induced fluorescence spectroscopy technique to measure the coupled absorption and emission properties of atomic species in plasmas produced via laser ablation of a solid aluminum target at atmospheric pressure. Emission spectra from the Al I 394.4 nm and Al I 396.15 nm transitions are measured while a frequency-doubled, continuous wave (cw) Ti:sapphire laser is tuned across the Al I 396.15 nm transition. The resulting two-dimensional spectra show the energy coupling between the two transitions via increased emission intensity for both transitions during resonant absorption of the cw laser at one transition. Time-delayed, gated detection of the emission spectrum is used to isolate resonantly excited fluorescence emission from thermally excited emission from the plasma. In addition, the tunable cw laser measures the absorption spectrum of the Al transition with ultrahigh resolution after the plasma has cooled, resulting in narrower spectral linewidths than observed in emission spectra. Our results highlight that fluorescence spectroscopy employing cw laser re-excitation after pulsed laser ablation combines benefits of both traditional emission and absorption spectroscopic methods. PMID:27472615

  15. Two-dimensional echocardiographic assessment of dextrocardia: a segmental approach.

    PubMed

    Huhta, J C; Hagler, D J; Seward, J B; Tajik, A J; Julsrud, P R; Ritter, D G

    1982-12-01

    Two-dimensional echocardiography was used in the prospective evaluation of 40 patients with the clinical diagnosis of dextrocardia. A segmental analysis of the situs, connections, ventricular anatomy, and chamber positions was utilized for a complete diagnostic assessment. An adequate examination was possible in 33 of these patients; the findings were confirmed by cardiac catheterization and angiography in 31 patients and at operation in 26. Use of the location of the liver and the drainage of the hepatic veins and inferior vena cava allowed atrial visceral situs to be defined in 33 patients (solitus 21, inversus 9, and ambiguous 3). Pulmonary venous connections were correctly identified in 27. In 33 patients, atrioventricular (AV) and ventriculoarterial connections and ventricular anatomy were correctly predicted. Twenty patients had 2 separate well-developed ventricles. Ventriculoarterial connections were determined correctly in all 20 patients: concordant in 5, discordant in 6, double-outlet right ventricle in 5, and single-outlet right ventricle (pulmonary atresia) in 4. In 16 patients a ventricular septal defect was correctly identified. In the remainder the ventricular septum was intact. Thirteen patients had univentricular heart: 8 had 2 AV valves (double-inlet ventricle) 3 had common AV inlet, and 2 had atresia of 1 AV connection. Two-dimensional echocardiography allowed the accurate assessment of complex congenital heart defects associated with dextrocardia. Utilizing a segmental approach, one can correctly predict atrial-visceral situs, ventricular morphology and situs, and AV and ventriculoarterial connections.

  16. Human lymphocyte polymorphisms detected by quantitative two-dimensional electrophoresis

    SciTech Connect

    Goldman, D.; Merril, C.R.

    1983-09-01

    A survey of 186 soluble lymphocyte proteins for genetic polymorphism was carried out utilizing two-dimensional electrophoresis of /sup 14/C-labeled phytohemagglutinin (PHA)-stimulated human lymphocyte proteins. Nineteen of these proteins exhibited positional variation consistent with independent genetic polymorphism in a primary sample of 28 individuals. Each of these polymorphisms was characterized by quantitative gene-dosage dependence insofar as the heterozygous phenotype expressed approximately 50% of each allelic gene product as was seen in homozygotes. Patterns observed were also identical in monozygotic twins, replicate samples, and replicate gels. The three expected phenotypes (two homozygotes and a heterozygote) were observed in each of 10 of these polymorphisms while the remaining nine had one of the homozygous classes absent. The presence of the three phenotypes, the demonstration of gene-dosage dependence, and our own and previous pedigree analysis of certain of these polymorphisms supports the genetic basis of these variants. Based on this data, the frequency of polymorphic loci for man is: P . 19/186 . .102, and the average heterozygosity is .024. This estimate is approximately 1/3 to 1/2 the rate of polymorphism previously estimated for man in other studies using one-dimensional electrophoresis of isozyme loci. The newly described polymorphisms and others which should be detectable in larger protein surveys with two-dimensional electrophoresis hold promise as genetic markers of the human genome for use in gene mapping and pedigree analyses.

  17. Two-dimensional nuclear magnetic resonance of quadrupolar systems

    SciTech Connect

    Wang, Shuanhu

    1997-09-17

    This dissertation describes two-dimensional nuclear magnetic resonance theory and experiments which have been developed to study quadruples in the solid state. The technique of multiple-quantum magic-angle spinning (MQMAS) is extensively reviewed and expanded upon in this thesis. Specifically, MQMAS is first compared with another technique, dynamic-angle spinning (DAS). The similarity between the two techniques allows us to extend much of the DAS work to the MQMAS case. Application of MQMAS to a series of aluminum containing materials is then presented. The superior resolution enhancement through MQMAS is exploited to detect the five- and six-coordinated aluminum in many aluminosilicate glasses. Combining the MQMAS method with other experiments, such as HETCOR, greatly expands the possibility of the use of MQMAS to study a large range of problems and is demonstrated in Chapter 5. Finally, the technique switching-angle spinning (SAS) is applied to quadrupolar nuclei to fully characterize a quadrupolar spin system in which all of the 8 NMR parameters are accurately determined. This dissertation is meant to demonstrate that with the combination of two-dimensional NMR concepts and new advanced spinning technologies, a series of multiple-dimensional NMR techniques can be designed to allow a detailed study of quadrupolar nuclei in the solid state.

  18. Emergent friction in two-dimensional Frenkel-Kontorova models.

    PubMed

    Norell, Jesper; Fasolino, Annalisa; de Wijn, Astrid S

    2016-08-01

    Simple models for friction are typically one-dimensional, but real interfaces are two-dimensional. We investigate the effects of the second dimension on static and dynamic friction by using the Frenkel-Kontorova (FK) model. We study the two most straightforward extensions of the FK model to two dimensions and simulate both the static and dynamic properties. We show that the behavior of the static friction is robust and remains similar in two dimensions for physically reasonable parameter values. The dynamic friction, however, is strongly influenced by the second dimension and the accompanying additional dynamics and parameters introduced into the models. We discuss our results in terms of the thermal equilibration and phonon dispersion relations of the lattices, establishing a physically realistic and suitable two-dimensional extension of the FK model. We find that the presence of additional dissipation channels can increase the friction and produces significantly different temperature dependence when compared to the one-dimensional case. We also briefly study the anisotropy of the dynamic friction and show highly nontrivial effects, including that the friction anisotropy can lead to motion in different directions depending on the value of the initial velocity. PMID:27627382

  19. Online comprehensive two-dimensional ion chromatography × capillary electrophoresis.

    PubMed

    Ranjbar, Leila; Gaudry, Adam J; Breadmore, Michael C; Shellie, Robert A

    2015-09-01

    A comprehensively coupled online two-dimensional ion chromatography-capillary electrophoresis (IC × CE) system for quantitative analysis of inorganic anions and organic acids in water is introduced. The system employs an in-house built sequential injection-capillary electrophoresis instrument and a nonfocusing modulation interface comprising a tee-piece and a six-port two-position injection valve that allows comprehensive sampling of the IC effluent. High field strength (+2 kV/cm) enables rapid second-dimension separations in which each peak eluted from the first-dimension separation column is analyzed at least three times in the second dimension. The IC × CE approach has been successfully used to resolve a suite of haloacetic acids, dalapon, and common inorganic anions. Two-dimensional peak capacity for IC × CE was 498 with a peak production rate of 9 peaks/min. Linear calibration curves were obtained for all analytes from 5 to 225 ng/mL (except dibromoacetic acid (10-225 ng/mL) and tribromoacetic acid (25-225 ng/mL)). The developed approach was used to analyze a spiked tap water sample, with good measured recoveries (69-119%).

  20. Prediction of a new two-dimensional metallic carbon allotrope.

    PubMed

    Wang, Xin-Quan; Li, Han-Dong; Wang, Jian-Tao

    2013-02-14

    By means of the first-principles calculations, we predict a new metallic two-dimensional carbon allotrope named net W with Cmmm (D(2h)(19)) symmetry. This new carbon phase consists of squares C(4), hexagons C(6), and octagons C(8), its dynamical stability is validated based on phonon-mode analysis and it is energetically more favored over previously proposed two-dimensional carbon forms such as net C, planar C(4), biphenylene, graphyne, and the recently prepared graphdiyne. On the other hand, we find that net W possesses strong metallicity due to its rather large density of states across the Fermi level contributed by the carbon p(z) orbital. Through first-principles molecular dynamics simulations, we theoretically demonstrate that selective dehydrogenation of the parallel-laid narrowest angular polycyclic aromatic hydrocarbons (4-AGNRs) would lead to a spontaneous interconversion to such a net W carbon phase, the possible synthetic routes are also addressed. Of particular interest, semiconductivity could be introduced when a net W carbon sheet is cut into ribbons of certain widths. Our work shows that the net W carbon sheet and its nanoribbons have great potential for future nanoelectronics. PMID:23264961

  1. Flexoelectricity in two-dimensional crystalline and biological membranes.

    PubMed

    Ahmadpoor, Fatemeh; Sharma, Pradeep

    2015-10-28

    The ability of a material to convert electrical stimuli into mechanical deformation, i.e. piezoelectricity, is a remarkable property of a rather small subset of insulating materials. The phenomenon of flexoelectricity, on the other hand, is universal. All dielectrics exhibit the flexoelectric effect whereby non-uniform strain (or strain gradients) can polarize the material and conversely non-uniform electric fields may cause mechanical deformation. The flexoelectric effect is strongly enhanced at the nanoscale and accordingly, all two-dimensional membranes of atomistic scale thickness exhibit a strong two-way coupling between the curvature and electric field. In this review, we highlight the recent advances made in our understanding of flexoelectricity in two-dimensional (2D) membranes-whether the crystalline ones such as dielectric graphene nanoribbons or the soft lipid bilayer membranes that are ubiquitous in biology. Aside from the fundamental mechanisms, phenomenology, and recent findings, we focus on rapidly emerging directions in this field and discuss applications such as energy harvesting, understanding of the mammalian hearing mechanism and ion transport among others. PMID:26399878

  2. Two-dimensional interpreter for field-reversed configurations

    SciTech Connect

    Steinhauer, Loren

    2014-08-15

    An interpretive method is developed for extracting details of the fully two-dimensional (2D) “internal” structure of field-reversed configurations (FRC) from common diagnostics. The challenge is that only external and “gross” diagnostics are routinely available in FRC experiments. Inferring such critical quantities as the poloidal flux and the particle inventory has commonly relied on a theoretical construct based on a quasi-one-dimensional approximation. Such inferences sometimes differ markedly from the more accurate, fully 2D reconstructions of equilibria. An interpreter based on a fully 2D reconstruction is needed to enable realistic within-the-shot tracking of evolving equilibrium properties. Presented here is a flexible equilibrium reconstruction with which an extensive data base of equilibria was constructed. An automated interpreter then uses this data base as a look-up table to extract evolving properties. This tool is applied to data from the FRC facility at Tri Alpha Energy. It yields surprising results at several points, such as the inferences that the local β (plasma pressure/external magnetic pressure) of the plasma climbs well above unity and the poloidal flux loss time is somewhat longer than previously thought, both of which arise from full two-dimensionality of FRCs.

  3. Two Dimensional Intermodulation Distortion Scanning of Superconducting Filter Resonators

    NASA Astrophysics Data System (ADS)

    Bischak, Michael; Remillard, Stephen

    2015-03-01

    Nonlinear superconducting conductivity produces distortion that has usually been measured globally across the entire sample. In order to fully understand the origin of non linearity, local methods must be used to examine specific points in the sample. The nonlinear Ohm's law, V =IZ(I) includes the current dependence in the impedance. The method in this work raster scans a magnetic loop probe across a sample. In order to address limited resolution, we reduced the size of the magnetic loop probe. Using the electromagnetic field solver, sonnet, two dimensional current simulations of superconducting microwave filters composed of Tl2Ba2CaCu2O8 or of YBa2Cu3O7 reveal microwave current which is bunched up at the corners and sides of the sample. Two dimensional images of third order intermodulation distortion made with the magnetic probe at the same corners and edges reveal elevated distortion in the same places. Using the magnetic probe, third order intermodulation was seen to come from the same corners and edges where the current is bunched. This research was funded by the National Science Foundation under grant number DMR-1206149.

  4. Nonclassical Symmetry Analysis of Heated Two-Dimensional Flow Problems

    NASA Astrophysics Data System (ADS)

    Naeem, Imran; Naz, Rehana; Khan, Muhammad Danish

    2015-12-01

    This article analyses the nonclassical symmetries and group invariant solution of boundary layer equations for two-dimensional heated flows. First, we derive the nonclassical symmetry determining equations with the aid of the computer package SADE. We solve these equations directly to obtain nonclassical symmetries. We follow standard procedure of computing nonclassical symmetries and consider two different scenarios, ξ1≠0 and ξ1=0, ξ2≠0. Several nonclassical symmetries are reported for both scenarios. Furthermore, numerous group invariant solutions for nonclassical symmetries are derived. The similarity variables associated with each nonclassical symmetry are computed. The similarity variables reduce the system of partial differential equations (PDEs) to a system of ordinary differential equations (ODEs) in terms of similarity variables. The reduced system of ODEs are solved to obtain group invariant solution for governing boundary layer equations for two-dimensional heated flow problems. We successfully formulate a physical problem of heat transfer analysis for fluid flow over a linearly stretching porous plat and, with suitable boundary conditions, we solve this problem.

  5. Electronic transport in two-dimensional high dielectric constant nanosystems

    DOE PAGES

    Ortuño, M.; Somoza, A. M.; Vinokur, V. M.; Baturina, T. I.

    2015-04-10

    There has been remarkable recent progress in engineering high-dielectric constant two dimensional (2D) materials, which are being actively pursued for applications in nanoelectronics in capacitor and memory devices, energy storage, and high-frequency modulation in communication devices. Yet many of the unique properties of these systems are poorly understood and remain unexplored. Here we report a numerical study of hopping conductivity of the lateral network of capacitors, which models two-dimensional insulators, and demonstrate that 2D long-range Coulomb interactions lead to peculiar size effects. We find that the characteristic energy governing electronic transport scales logarithmically with either system size or electrostatic screeningmore » length depending on which one is shorter. Our results are relevant well beyond their immediate context, explaining, for example, recent experimental observations of logarithmic size dependence of electric conductivity of thin superconducting films in the critical vicinity of superconductor-insulator transition where a giant dielectric constant develops. Our findings mark a radical departure from the orthodox view of conductivity in 2D systems as a local characteristic of materials and establish its macroscopic global character as a generic property of high-dielectric constant 2D nanomaterials.« less

  6. Unpacking of a Crumpled Wire from Two-Dimensional Cavities.

    PubMed

    Sobral, Thiago A; Gomes, Marcelo A F; Machado, Núbia R; Brito, Valdemiro P

    2015-01-01

    The physics of tightly packed structures of a wire and other threadlike materials confined in cavities has been explored in recent years in connection with crumpled systems and a number of topics ranging from applications to DNA packing in viral capsids and surgical interventions with catheter to analogies with the electron gas at finite temperature and with theories of two-dimensional quantum gravity. When a long piece of wire is injected into two-dimensional cavities, it bends and originates in the jammed limit a series of closed structures that we call loops. In this work we study the extraction of a crumpled tightly packed wire from a circular cavity aiming to remove loops individually. The size of each removed loop, the maximum value of the force needed to unpack each loop, and the total length of the extracted wire were measured and related to an exponential growth and a mean field model consistent with the literature of crumpled wires. Scaling laws for this process are reported and the relationship between the processes of packing and unpacking of wire is commented upon.

  7. Phonons in two-dimensional soft colloidal crystals

    NASA Astrophysics Data System (ADS)

    Chen, Ke; Still, Tim; Schoenholz, Samuel; Aptowicz, Kevin B.; Schindler, Michael; Maggs, A. C.; Liu, Andrea J.; Yodh, A. G.

    2013-08-01

    The vibrational modes of pristine and polycrystalline monolayer colloidal crystals composed of thermosensitive microgel particles are measured using video microscopy and covariance matrix analysis. At low frequencies, the Debye relation for two-dimensional harmonic crystals is observed in both crystal types; at higher frequencies, evidence for van Hove singularities in the phonon density of states is significantly smeared out by experimental noise and measurement statistics. The effects of these errors are analyzed using numerical simulations. We introduce methods to correct for these limitations, which can be applied to disordered systems as well as crystalline ones, and we show that application of the error correction procedure to the experimental data leads to more pronounced van Hove singularities in the pristine crystal. Finally, quasilocalized low-frequency modes in polycrystalline two-dimensional colloidal crystals are identified and demonstrated to correlate with structural defects such as dislocations, suggesting that quasilocalized low-frequency phonon modes may be used to identify local regions vulnerable to rearrangements in crystalline as well as amorphous solids.

  8. Two-dimensional gas of massless Dirac fermions in graphene.

    PubMed

    Novoselov, K S; Geim, A K; Morozov, S V; Jiang, D; Katsnelson, M I; Grigorieva, I V; Dubonos, S V; Firsov, A A

    2005-11-10

    Quantum electrodynamics (resulting from the merger of quantum mechanics and relativity theory) has provided a clear understanding of phenomena ranging from particle physics to cosmology and from astrophysics to quantum chemistry. The ideas underlying quantum electrodynamics also influence the theory of condensed matter, but quantum relativistic effects are usually minute in the known experimental systems that can be described accurately by the non-relativistic Schrödinger equation. Here we report an experimental study of a condensed-matter system (graphene, a single atomic layer of carbon) in which electron transport is essentially governed by Dirac's (relativistic) equation. The charge carriers in graphene mimic relativistic particles with zero rest mass and have an effective 'speed of light' c* approximately 10(6) m s(-1). Our study reveals a variety of unusual phenomena that are characteristic of two-dimensional Dirac fermions. In particular we have observed the following: first, graphene's conductivity never falls below a minimum value corresponding to the quantum unit of conductance, even when concentrations of charge carriers tend to zero; second, the integer quantum Hall effect in graphene is anomalous in that it occurs at half-integer filling factors; and third, the cyclotron mass m(c) of massless carriers in graphene is described by E = m(c)c*2. This two-dimensional system is not only interesting in itself but also allows access to the subtle and rich physics of quantum electrodynamics in a bench-top experiment.

  9. Pressure profiles of nonuniform two-dimensional atomic Fermi gases

    NASA Astrophysics Data System (ADS)

    Martiyanov, Kirill; Barmashova, Tatiana; Makhalov, Vasiliy; Turlapov, Andrey

    2016-06-01

    Spatial profiles of the pressure have been measured in atomic Fermi gases with primarily two-dimensional (2D) kinematics. The in-plane motion of the particles is confined by a Gaussian-shape potential. The two-component deeply degenerate Fermi gases are prepared at different values of the s -wave attraction. The pressure profile is found using the force-balance equation, from the measured density profile and the trapping potential. The pressure is compared to zero-temperature models within the local density approximation. In the weakly interacting regime, the pressure lies above a Landau Fermi-liquid theory and below the ideal-Fermi-gas model, whose prediction coincides with that of the Cooper-pair mean-field theory. The values closest to the data are provided by the approach where the mean field of Cooper pairs is supplemented with fluctuations. In the regime of strong interactions, in response to the increasing attraction, the pressure shifts below this model reaching lower values calculated within Monte Carlo methods. Comparison to models shows that interaction-induced departure from 2D kinematics is either small or absent. In particular, comparison with a lattice Monte Carlo suggests that kinematics is two dimensional in the strongly interacting regime.

  10. A Two-Dimensional Linear Bicharacteristic Scheme for Electromagnetics

    NASA Technical Reports Server (NTRS)

    Beggs, John H.

    2002-01-01

    The upwind leapfrog or Linear Bicharacteristic Scheme (LBS) has previously been implemented and demonstrated on one-dimensional electromagnetic wave propagation problems. This memorandum extends the Linear Bicharacteristic Scheme for computational electromagnetics to model lossy dielectric and magnetic materials and perfect electrical conductors in two dimensions. This is accomplished by proper implementation of the LBS for homogeneous lossy dielectric and magnetic media and for perfect electrical conductors. Both the Transverse Electric and Transverse Magnetic polarizations are considered. Computational requirements and a Fourier analysis are also discussed. Heterogeneous media are modeled through implementation of surface boundary conditions and no special extrapolations or interpolations at dielectric material boundaries are required. Results are presented for two-dimensional model problems on uniform grids, and the Finite Difference Time Domain (FDTD) algorithm is chosen as a convenient reference algorithm for comparison. The results demonstrate that the two-dimensional explicit LBS is a dissipation-free, second-order accurate algorithm which uses a smaller stencil than the FDTD algorithm, yet it has less phase velocity error.

  11. Unpacking of a Crumpled Wire from Two-Dimensional Cavities

    PubMed Central

    Sobral, Thiago A.; Gomes, Marcelo A. F.; Machado, Núbia R.; Brito, Valdemiro P.

    2015-01-01

    The physics of tightly packed structures of a wire and other threadlike materials confined in cavities has been explored in recent years in connection with crumpled systems and a number of topics ranging from applications to DNA packing in viral capsids and surgical interventions with catheter to analogies with the electron gas at finite temperature and with theories of two-dimensional quantum gravity. When a long piece of wire is injected into two-dimensional cavities, it bends and originates in the jammed limit a series of closed structures that we call loops. In this work we study the extraction of a crumpled tightly packed wire from a circular cavity aiming to remove loops individually. The size of each removed loop, the maximum value of the force needed to unpack each loop, and the total length of the extracted wire were measured and related to an exponential growth and a mean field model consistent with the literature of crumpled wires. Scaling laws for this process are reported and the relationship between the processes of packing and unpacking of wire is commented upon. PMID:26047315

  12. Dirac spectra of two-dimensional QCD-like theories

    NASA Astrophysics Data System (ADS)

    Kieburg, Mario; Verbaarschot, Jacobus J. M.; Zafeiropoulos, Savvas

    2014-10-01

    We analyze Dirac spectra of two-dimensional QCD-like theories both in the continuum and on the lattice and classify them according to random matrix theories sharing the same global symmetries. The classification is different from QCD in four dimensions because the antiunitary symmetries do not commute with γ5. Therefore, in a chiral basis, the number of degrees of freedom per matrix element are not given by the Dyson index. Our predictions are confirmed by Dirac spectra from quenched lattice simulations for QCD with two or three colors with quarks in the fundamental representation as well as in the adjoint representation. The universality class of the spectra depends on the parity of the number of lattice points in each direction. Our results show an agreement with random matrix theory that is qualitatively similar to the agreement found for QCD in four dimensions. We discuss the implications for the Mermin-Wagner-Coleman theorem and put our results in the context of two-dimensional disordered systems.

  13. Electronic transport in two-dimensional high dielectric constant nanosystems

    NASA Astrophysics Data System (ADS)

    Ortuño, M.; Somoza, A. M.; Vinokur, V. M.; Baturina, T. I.

    2015-04-01

    There has been remarkable recent progress in engineering high-dielectric constant two dimensional (2D) materials, which are being actively pursued for applications in nanoelectronics in capacitor and memory devices, energy storage, and high-frequency modulation in communication devices. Yet many of the unique properties of these systems are poorly understood and remain unexplored. Here we report a numerical study of hopping conductivity of the lateral network of capacitors, which models two-dimensional insulators, and demonstrate that 2D long-range Coulomb interactions lead to peculiar size effects. We find that the characteristic energy governing electronic transport scales logarithmically with either system size or electrostatic screening length depending on which one is shorter. Our results are relevant well beyond their immediate context, explaining, for example, recent experimental observations of logarithmic size dependence of electric conductivity of thin superconducting films in the critical vicinity of superconductor-insulator transition where a giant dielectric constant develops. Our findings mark a radical departure from the orthodox view of conductivity in 2D systems as a local characteristic of materials and establish its macroscopic global character as a generic property of high-dielectric constant 2D nanomaterials.

  14. Emergent friction in two-dimensional Frenkel-Kontorova models

    NASA Astrophysics Data System (ADS)

    Norell, Jesper; Fasolino, Annalisa; de Wijn, Astrid S.

    2016-08-01

    Simple models for friction are typically one-dimensional, but real interfaces are two-dimensional. We investigate the effects of the second dimension on static and dynamic friction by using the Frenkel-Kontorova (FK) model. We study the two most straightforward extensions of the FK model to two dimensions and simulate both the static and dynamic properties. We show that the behavior of the static friction is robust and remains similar in two dimensions for physically reasonable parameter values. The dynamic friction, however, is strongly influenced by the second dimension and the accompanying additional dynamics and parameters introduced into the models. We discuss our results in terms of the thermal equilibration and phonon dispersion relations of the lattices, establishing a physically realistic and suitable two-dimensional extension of the FK model. We find that the presence of additional dissipation channels can increase the friction and produces significantly different temperature dependence when compared to the one-dimensional case. We also briefly study the anisotropy of the dynamic friction and show highly nontrivial effects, including that the friction anisotropy can lead to motion in different directions depending on the value of the initial velocity.

  15. Two-dimensional effects in imploding plasma liners

    NASA Astrophysics Data System (ADS)

    Roderick, N. F.; Hussey, T. W.

    Analytic modeling and magnetohydrodynamic (MHD) simulations have been conducted to investigate two-dimensional effects in imploding plasma shells. These effects include short wavelength disturbances caused by instabilities at the plasma magnetic field interface, long wavelength instabilities associated with plasma annulus formation, and perturbations resulting from the power flow to the plasma annulus. The numerical calculations were carried out using the two-dimensional single-fluid MHD code MACH2 for different plasma density profiles and electrode geometries. Results for short wavelength perturbations show that these phenomena behave in a manner consistent with analytic linear and heuristic nonlinear models. At stagnation they have a negligible effect on the uniformity during the initial coupling to the target, even for large initial perturbations. The disturbances manifest themselves primarily in a rippling of the back of the plasma shell with significant effects, even in this region, not occurring until late in the stagnation process. Long wavelength perturbations produced by a straight axial gas injection for gas puff implosions can lead to pronounced axial nonuniformity, zippering, at stagnation. Variations of the injection conditions and electrode geometry can produce more uniform stagnation. Changes in the mass profile, gas injection angle, and electrode shape can all be used to achieve significantly greater stagnation uniformity. Consistent calculations for a entire implosion process form gas injection to stagnation including vacuum power flow indicate the degree of coupling of short wavelength, long wavelength and power flow perturbations. Comparison with experimental data show agreement between analytic, numerical and experimental results.

  16. Two-dimensional effects in hollow core z-pinches

    NASA Astrophysics Data System (ADS)

    Roderick, N. F.; Hussey, T. W.

    Analytic modeling and magnetohydrodynamic simulations have been conducted to investigate two-dimensional effects in imploding plasma shells. These effects include short wavelength disturbances caused by instabilities at the plasma magnetic field interface, long wavelength instabilities associated with plasma annulus formation, and perturbations resulting from the power flow to the plasma annulus. The numerical calculations were carried out using the two-dimensional single-fluid magnetohydrodynamic (MHD) code MACH2 for different plasma density profiles and electrode geometries. Results for short wavelength perturbations show that these phenomena behave in a manner consistent with analytic linear and heuristic nonlinear models. At stagnation they have a negligible effect on the uniformity during the initial coupling to the target, even for large initial perturbations. The disturbances manifest themselves primarily in a rippling of the back of the plasma shell with significant effects, even in this region, not occurring until late in the stagnation process. Long wavelength perturbations produced by a straight axial gas injection for gas puff implosions can lead to pronounced axial nonuniformity, zippering, at stagnation. Variations of the injection conditions and electrode geometry can produce more uniform stagnation. Changes in the mass profile, gas injection angle, and electrode shape can all be used to achieve significantly greater stagnation uniformity. Consistent calculations for an entire implosion process from a gas injection to stagnation including vacuum power flow indicate the degree of coupling of short wavelength, long wavelength and power flow perturbations. Comparison with experimental data show agreement between analytic, numerical and experimental results.

  17. Statistical mechanics of shell models for two-dimensional turbulence

    NASA Astrophysics Data System (ADS)

    Aurell, E.; Boffetta, G.; Crisanti, A.; Frick, P.; Paladin, G.; Vulpiani, A.

    1994-12-01

    We study shell models that conserve the analogs of energy and enstrophy and hence are designed to mimic fluid turbulence in two-dimensions (2D). The main result is that the observed state is well described as a formal statistical equilibrium, closely analogous to the approach to two-dimensional ideal hydrodynamics of Onsager [Nuovo Cimento Suppl. 6, 279 (1949)], Hopf [J. Rat. Mech. Anal. 1, 87 (1952)], and Lee [Q. Appl. Math. 10, 69 (1952)]. In the presence of forcing and dissipation we observe a forward flux of enstrophy and a backward flux of energy. These fluxes can be understood as mean diffusive drifts from a source to two sinks in a system which is close to local equilibrium with Lagrange multipliers (``shell temperatures'') changing slowly with scale. This is clear evidence that the simplest shell models are not adequate to reproduce the main features of two-dimensional turbulence. The dimensional predictions on the power spectra from a supposed forward cascade of enstrophy and from one branch of the formal statistical equilibrium coincide in these shell models in contrast to the corresponding predictions for the Navier-Stokes and Euler equations in 2D. This coincidence has previously led to the mistaken conclusion that shell models exhibit a forward cascade of enstrophy. We also study the dynamical properties of the models and the growth of perturbations.

  18. Two dimensional kinetic analysis of electrostatic harmonic plasma waves

    NASA Astrophysics Data System (ADS)

    Fonseca-Pongutá, E. C.; Ziebell, L. F.; Gaelzer, R.; Yoon, P. H.

    2016-06-01

    Electrostatic harmonic Langmuir waves are virtual modes excited in weakly turbulent plasmas, first observed in early laboratory beam-plasma experiments as well as in rocket-borne active experiments in space. However, their unequivocal presence was confirmed through computer simulated experiments and subsequently theoretically explained. The peculiarity of harmonic Langmuir waves is that while their existence requires nonlinear response, their excitation mechanism and subsequent early time evolution are governed by essentially linear process. One of the unresolved theoretical issues regards the role of nonlinear wave-particle interaction process over longer evolution time period. Another outstanding issue is that existing theories for these modes are limited to one-dimensional space. The present paper carries out two dimensional theoretical analysis of fundamental and (first) harmonic Langmuir waves for the first time. The result shows that harmonic Langmuir wave is essentially governed by (quasi)linear process and that nonlinear wave-particle interaction plays no significant role in the time evolution of the wave spectrum. The numerical solutions of the two-dimensional wave spectra for fundamental and harmonic Langmuir waves are also found to be consistent with those obtained by direct particle-in-cell simulation method reported in the literature.

  19. Unpacking of a Crumpled Wire from Two-Dimensional Cavities.

    PubMed

    Sobral, Thiago A; Gomes, Marcelo A F; Machado, Núbia R; Brito, Valdemiro P

    2015-01-01

    The physics of tightly packed structures of a wire and other threadlike materials confined in cavities has been explored in recent years in connection with crumpled systems and a number of topics ranging from applications to DNA packing in viral capsids and surgical interventions with catheter to analogies with the electron gas at finite temperature and with theories of two-dimensional quantum gravity. When a long piece of wire is injected into two-dimensional cavities, it bends and originates in the jammed limit a series of closed structures that we call loops. In this work we study the extraction of a crumpled tightly packed wire from a circular cavity aiming to remove loops individually. The size of each removed loop, the maximum value of the force needed to unpack each loop, and the total length of the extracted wire were measured and related to an exponential growth and a mean field model consistent with the literature of crumpled wires. Scaling laws for this process are reported and the relationship between the processes of packing and unpacking of wire is commented upon. PMID:26047315

  20. Quantitative prediction for two-dimensional bacterial genomic displays

    NASA Astrophysics Data System (ADS)

    Mercier, Jean-Francois; Kingsburry, Christine; Lafay, Bénédicte; Slater, Gary W.

    2006-03-01

    Two-dimensional bacterial genomic display (2DBGD) is a simple technique that allows one to directly compare complete genomes of closely related bacteria. It consists of two phases. First, polyacrylamide gel electrophoresis (PAGE) is used to separate the DNA fragments resulting from the restriction of the genome by appropriate enzymes according to their size. Then, temperature gradient gel electrophoresis (TGGE) is used in the second dimension to separate the fragments according to their sequence composition. After these two steps, the whole bacterial genome is displayed as clouds of spots on a two-dimensional surface. 2DBGD has been successfully used to distinguish between strains of bacterial species. Unfortunately, this empirical technique remains highly qualitative. We have developed a model to predict the location of DNA spots, as a function of the DNA sequence, the gel electrophoresis and TGGE conditions and the nature of the restriction enzymes used. This model can be used to easily optimize the procedure for the type of bacteria being analyzed.

  1. Lateral epitaxial growth of two-dimensional layered semiconductor heterojunctions.

    PubMed

    Duan, Xidong; Wang, Chen; Shaw, Jonathan C; Cheng, Rui; Chen, Yu; Li, Honglai; Wu, Xueping; Tang, Ying; Zhang, Qinling; Pan, Anlian; Jiang, Jianhui; Yu, Ruqing; Huang, Yu; Duan, Xiangfeng

    2014-12-01

    Two-dimensional layered semiconductors such as MoS₂ and WSe₂ have attracted considerable interest in recent times. Exploring the full potential of these layered materials requires precise spatial modulation of their chemical composition and electronic properties to create well-defined heterostructures. Here, we report the growth of compositionally modulated MoS₂-MoSe₂ and WS₂-WSe₂ lateral heterostructures by in situ modulation of the vapour-phase reactants during growth of these two-dimensional crystals. Raman and photoluminescence mapping studies demonstrate that the resulting heterostructure nanosheets exhibit clear structural and optical modulation. Transmission electron microscopy and elemental mapping studies reveal a single crystalline structure with opposite modulation of sulphur and selenium distributions across the heterostructure interface. Electrical transport studies demonstrate that the WSe₂-WS₂ heterojunctions form lateral p-n diodes and photodiodes, and can be used to create complementary inverters with high voltage gain. Our study is an important advance in the development of layered semiconductor heterostructures, an essential step towards achieving functional electronics and optoelectronics.

  2. Comprehensive two-dimensional liquid chromatographic analysis of poloxamers.

    PubMed

    Malik, Muhammad Imran; Lee, Sanghoon; Chang, Taihyun

    2016-04-15

    Poloxamers are low molar mass triblock copolymers of poly(ethylene oxide) (PEO) and poly(propylene oxide) (PPO), having number of applications as non-ionic surfactants. Comprehensive one and two-dimensional liquid chromatographic (LC) analysis of these materials is proposed in this study. The separation of oligomers of both types (PEO and PPO) is demonstrated for several commercial poloxamers. This is accomplished at the critical conditions for one of the block while interaction for the other block. Reversed phase LC at CAP of PEO allowed for oligomeric separation of triblock copolymers with regard to PPO block whereas normal phase LC at CAP of PPO renders oligomeric separation with respect to PEO block. The oligomeric separation with regard to PEO and PPO are coupled online (comprehensive 2D-LC) to reveal two-dimensional contour plots by unconventional 2D IC×IC (interaction chromatography) coupling. The study provides chemical composition mapping of both PEO and PPO, equivalent to combined molar mass and chemical composition mapping for several commercial poloxamers.

  3. Two-dimensional gene scanning: exploring human genetic variability.

    PubMed

    Vijg, J; van Orsouw, N J

    1999-06-01

    Current methods for mutation detection are not optimized for the generation of highly accurate data on multiple genes of hundreds of individuals in population-based studies. Two-dimensional gene scanning (TDGS) is a high-resolution system for detecting mutational variants in multiple genes in parallel. TDGS is based on a combination of extensive multiplex polymerase chain reaction (PCR) and two-dimensional (2-D) DNA electrophoresis. The latter involves a size separation step followed by denaturing gradient gel electrophoresis (DGGE). TDGS tests for a number of large human disease genes have been designed, using a computer program to optimally position PCR primers around the relevant target sequences (e.g., exons) and evaluated using panels of samples with previously detected mutations. The results indicate a high sensitivity and specificity, equal to nucleotide sequencing, which is generally considered as the gold standard. Here, we describe the different components of the TDGS process and its potential application as a high-throughput system for the systematic identification of human gene variants.

  4. Computerized methods for analyzing two-dimensional agarose gel electropherograms.

    PubMed

    Aldroubi, A; Unser, M; Tietz, D; Trus, B

    1991-01-01

    Previous methods interpret zonal or polydisperse gel patterns of two-dimensional Serwer-type gels in terms of size and free mobility (surface net charge density). These two parameters have been determined for each component without quantitatively measuring the abundance of the components. The present study advances these previous methods by determining the relative concentration of each component by computer evaluation of densitometrically analyzed gel patterns. Suitable procedures and their underlying algorithms are presented. The mathematical routines are implemented in a user-friendly software package, called GelFit and designed for a Macintosh personal computer. The program input consists of digitized images of gel staining patterns exemplified by those obtained from electrophoresis of native subcellular-sized particles. The data are processed through the following steps: (i) Noise reduction and calibration. (ii) Geometrical transformation of the pattern onto a rectangular size/free mobility coordinate system using rationales of the extended Ogston model. (iii) Analysis of the transformed image to determine density maxima, density profiles along iso-free-mobility or iso-size lines, curve fitting of one-dimensional profiles or two-dimensional surfaces using Gaussian functions and curve stripping of surfaces to determine the possible number of particle populations.

  5. Electronic transport in two-dimensional high dielectric constant nanosystems

    SciTech Connect

    Ortuño, M.; Somoza, A. M.; Vinokur, V. M.; Baturina, T. I.

    2015-04-10

    There has been remarkable recent progress in engineering high-dielectric constant two dimensional (2D) materials, which are being actively pursued for applications in nanoelectronics in capacitor and memory devices, energy storage, and high-frequency modulation in communication devices. Yet many of the unique properties of these systems are poorly understood and remain unexplored. Here we report a numerical study of hopping conductivity of the lateral network of capacitors, which models two-dimensional insulators, and demonstrate that 2D long-range Coulomb interactions lead to peculiar size effects. We find that the characteristic energy governing electronic transport scales logarithmically with either system size or electrostatic screening length depending on which one is shorter. Our results are relevant well beyond their immediate context, explaining, for example, recent experimental observations of logarithmic size dependence of electric conductivity of thin superconducting films in the critical vicinity of superconductor-insulator transition where a giant dielectric constant develops. Our findings mark a radical departure from the orthodox view of conductivity in 2D systems as a local characteristic of materials and establish its macroscopic global character as a generic property of high-dielectric constant 2D nanomaterials.

  6. SCAPS, a two-dimensional ion detector for mass spectrometer

    NASA Astrophysics Data System (ADS)

    Yurimoto, Hisayoshi

    2014-05-01

    Faraday Cup (FC) and electron multiplier (EM) are of the most popular ion detector for mass spectrometer. FC is used for high-count-rate ion measurements and EM can detect from single ion. However, FC is difficult to detect lower intensities less than kilo-cps, and EM loses ion counts higher than Mega-cps. Thus, FC and EM are used complementary each other, but they both belong to zero-dimensional detector. On the other hand, micro channel plate (MCP) is a popular ion signal amplifier with two-dimensional capability, but additional detection system must be attached to detect the amplified signals. Two-dimensional readout for the MCP signals, however, have not achieve the level of FC and EM systems. A stacked CMOS active pixel sensor (SCAPS) has been developed to detect two-dimensional ion variations for a spatial area using semiconductor technology [1-8]. The SCAPS is an integrated type multi-detector, which is different from EM and FC, and is composed of more than 500×500 pixels (micro-detectors) for imaging of cm-area with a pixel of less than 20 µm in square. The SCAPS can be detected from single ion to 100 kilo-count ions per one pixel. Thus, SCAPS can be accumulated up to several giga-count ions for total pixels, i.e. for total imaging area. The SCAPS has been applied to stigmatic ion optics of secondary ion mass spectrometer, as a detector of isotope microscope [9]. The isotope microscope has capabilities of quantitative isotope images of hundred-micrometer area on a sample with sub-micrometer resolution and permil precision, and of two-dimensional mass spectrum on cm-scale of mass dispersion plane of a sector magnet with ten-micrometer resolution. The performance has been applied to two-dimensional isotope spatial distribution for mainly hydrogen, carbon, nitrogen and oxygen of natural (extra-terrestrial and terrestrial) samples and samples simulated natural processes [e.g. 10-17]. References: [1] Matsumoto, K., et al. (1993) IEEE Trans. Electron Dev. 40

  7. Airfoil model in Two-Dimensional Low-Turbulence Tunnel

    NASA Technical Reports Server (NTRS)

    1939-01-01

    Airfoil model with pressure taps inside the test section of the Two-Dimensional Low-Turbulence Tunnel. The Two-Dimensional Low-Turbulence Tunnel was originally called the Refrigeration or 'Ice' tunnel because it was intended to support research on aircraft icing. The tunnel was built of wood, lined with sheet steel, and heavily insulated on the outside. Refrigeration equipment was installed to generate icing conditions inside the test section. The NACA sent out a questionnaire to airline operators, asking them to detail the specific kinds of icing problems they encountered in flight. The replies became the basis for a comprehensive research program begun in 1938 when the tunnel commenced operation. Research quickly focused on the concept of using exhaust heat to prevent ice from forming on the wing's leading edge. This project was led by Lewis Rodert, who later would win the Collier Trophy for his work on deicing. By 1940, aircraft icing research had shifted to the new Ames Research Laboratory, and the Ice tunnel was refitted with screens and honeycomb. Researchers were trying to eliminate all turbulence in the test section. From TN 1283: 'The Langley two-dimensional low-turbulence pressure tunnel is a single-return closed-throat tunnel.... The tunnel is constructed of heavy steel plate so that the pressure of the air may be varied from approximately full vacuum to 10 atmospheres absolute, thereby giving a wide range of air densities. Reciprocating compressors with a capacity of 1200 cubic feet of free air per minute provide compressed air. Since the tunnel shell has a volume of about 83,000 cubic feet, a compression rate of approximately one atmosphere per hour is obtained. ... The test section is rectangular in shape, 3 feet wide, 7 1/2 feet high, and 7 1/2 feet long. ... The over-all size of the wind-tunnel shell is about 146 feet long and 58 feet wide with a maximum diameter of 26 feet. The test section and entrance and exit cones are surrounded by a 22-foot

  8. Mobility and Diffusion-Ordered Two-Dimensional NMR Spectroscopy

    NASA Astrophysics Data System (ADS)

    Morris, Kevin Freeman

    Mobility and diffusion-ordered two-dimensional nuclear magnetic resonance spectroscopy experiments have been developed for the analysis of mixtures. In the mobility -ordered experiments, the full range of positive and negative electrophoretic mobilities is displayed in one dimension and chemical shifts are displayed in the other. A concentric cylindrical tube electrophoresis chamber was designed to reduce the effective pathlength for current and to provide unidirectional flow for ions of interest. Techniques based upon the reverse precession method were also implemented to recover the signs of the mobilities and improved resolution in the mobility dimension was obtained by replacing Fourier transformation of truncated data sets with a linear prediction analysis. In the diffusion-ordered two-dimensional NMR experiments, the conventional chemical shift spectrum is resolved in one dimension and spectra of diffusion rates or molecular radii are resolved in the other. Diffusion dependent pulsed field gradient NMR data sets were inverted by means of the computer programs SPLMOD or DISCRETE, when discrete diffusion coefficients were present, and CONTIN when continuous distributions were present. Since the inversion is ill -conditioned, it was necessary to introduce additional information to limit the range of the solutions. In addition to prior knowledge of the decay kernels and non-negativity of amplitudes and damping constants, a set of rejection criteria was constructed for the discrete analysis case that took into account physical limits on diffusion coefficients, experimentally accessible values, and variations in effective decay kernels resulting from instrumental non-linearities. Examples of analyses of simulated data and experimental data for mixtures are presented as well as two-dimensional spectra generated by CONTIN for polydisperse polymer samples. Also, resolution in the diffusion dimension was increased by performing experiments on hydrophobic molecules in

  9. Optimal Padding for the Two-Dimensional Fast Fourier Transform

    NASA Technical Reports Server (NTRS)

    Dean, Bruce H.; Aronstein, David L.; Smith, Jeffrey S.

    2011-01-01

    One-dimensional Fast Fourier Transform (FFT) operations work fastest on grids whose size is divisible by a power of two. Because of this, padding grids (that are not already sized to a power of two) so that their size is the next highest power of two can speed up operations. While this works well for one-dimensional grids, it does not work well for two-dimensional grids. For a two-dimensional grid, there are certain pad sizes that work better than others. Therefore, the need exists to generalize a strategy for determining optimal pad sizes. There are three steps in the FFT algorithm. The first is to perform a one-dimensional transform on each row in the grid. The second step is to transpose the resulting matrix. The third step is to perform a one-dimensional transform on each row in the resulting grid. Steps one and three both benefit from padding the row to the next highest power of two, but the second step needs a novel approach. An algorithm was developed that struck a balance between optimizing the grid pad size with prime factors that are small (which are optimal for one-dimensional operations), and with prime factors that are large (which are optimal for two-dimensional operations). This algorithm optimizes based on average run times, and is not fine-tuned for any specific application. It increases the amount of times that processor-requested data is found in the set-associative processor cache. Cache retrievals are 4-10 times faster than conventional memory retrievals. The tested implementation of the algorithm resulted in faster execution times on all platforms tested, but with varying sized grids. This is because various computer architectures process commands differently. The test grid was 512 512. Using a 540 540 grid on a Pentium V processor, the code ran 30 percent faster. On a PowerPC, a 256x256 grid worked best. A Core2Duo computer preferred either a 1040x1040 (15 percent faster) or a 1008x1008 (30 percent faster) grid. There are many industries that

  10. Enstrophy cascades in two-dimensional dense granular flows.

    PubMed

    Saitoh, Kuniyasu; Mizuno, Hideyuki

    2016-08-01

    Employing two-dimensional molecular dynamics simulations of dense granular materials under simple shear deformations, we investigate vortex structures of particle rearrangements. Introducing vorticity fields as a measure of local spinning motions of the particles, we observe their heterogeneous distributions, where statistics of vorticity fields exhibit the highly non-Gaussian behavior and typical domain sizes of vorticity fields significantly increase if the system is yielding under quasistatic deformations. In such dense granular flows, a power-law decay of vorticity spectra can be observed at mesoscopic scale, implying anomalous local structures of kinetic energy dissipation. We explain the power-law decay, or enstrophy cascades in dense granular materials, by a dimensional analysis, where the dependence of vorticity spectra not only on the wave number, but also on the shear rate, is well explained. From our dimensional analyses, the scaling of granular temperature and rotational kinetic energy is also predicted.

  11. Cooperation in two-dimensional mixed-games

    NASA Astrophysics Data System (ADS)

    Amaral, Marco A.; Wardil, Lucas; da Silva, Jafferson K. L.

    2015-11-01

    Evolutionary game theory is a common framework to study the evolution of cooperation, where it is usually assumed that the same game is played in all interactions. Here, we investigate a model where the game that is played by two individuals is uniformly drawn from a sample of two different games. Using the master equation approach we show that the random mixture of two games is equivalent to play the average game when (i) the strategies are statistically independent of the game distribution and (ii) the transition rates are linear functions of the payoffs. We also use Monte-Carlo simulations in a two-dimensional lattice and mean-field techniques to investigate the scenario when the two above conditions do not hold. We find that even outside of such conditions, several quantities characterizing the mixed-games are still the same as the ones obtained in the average game when the two games are not very different.

  12. Elastic interactions between two-dimensional geometric defects.

    PubMed

    Moshe, Michael; Sharon, Eran; Kupferman, Raz

    2015-12-01

    In this paper, we introduce a methodology applicable to a wide range of localized two-dimensional sources of stress. This methodology is based on a geometric formulation of elasticity. Localized sources of stress are viewed as singular defects-point charges of the curvature associated with a reference metric. The stress field in the presence of defects can be solved using a scalar stress function that generalizes the classical Airy stress function to the case of materials with nontrivial geometry. This approach allows the calculation of interaction energies between various types of defects. We apply our methodology to two physical systems: shear-induced failure of amorphous materials and the mechanical interaction between contracting cells. PMID:26764699

  13. Two-dimensional angular transmission characterization of CPV modules.

    PubMed

    Herrero, R; Domínguez, C; Askins, S; Antón, I; Sala, G

    2010-11-01

    This paper proposes a fast method to characterize the two-dimensional angular transmission function of a concentrator photovoltaic (CPV) system. The so-called inverse method, which has been used in the past for the characterization of small optical components, has been adapted to large-area CPV modules. In the inverse method, the receiver cell is forward biased to produce a Lambertian light emission, which reveals the reverse optical path of the optics. Using a large-area collimator mirror, the light beam exiting the optics is projected on a Lambertian screen to create a spatially resolved image of the angular transmission function. An image is then obtained using a CCD camera. To validate this method, the angular transmission functions of a real CPV module have been measured by both direct illumination (flash CPV simulator and sunlight) and the inverse method, and the comparison shows good agreement. PMID:21165081

  14. Lateral and Vertical Two-Dimensional Layered Topological Insulator Heterostructures.

    PubMed

    Li, Yanbin; Zhang, Jinsong; Zheng, Guangyuan; Sun, Yongming; Hong, Seung Sae; Xiong, Feng; Wang, Shuang; Lee, Hye Ryoung; Cui, Yi

    2015-11-24

    The heterostructured configuration between two-dimensional (2D) semiconductor materials has enabled the engineering of the band gap and the design of novel devices. So far, the synthesis of single-component topological insulator (TI) 2D materials such as Bi2Se3, Bi2Te3, and Sb2Te3 has been achieved through vapor phase growth and molecular beam epitaxy; however, the spatial controlled fabrication of 2D lateral heterostructures in these systems has not been demonstrated yet. Here, we report an in situ two-step synthesis process to form TI lateral heterostructures. Scanning transmission electron microscopy and energy-dispersive X-ray mapping results show the successful spatial control of chemical composition in these as-prepared heterostructures. The edge-induced growth mechanism is revealed by the ex situ atomic force microscope measurements. Electrical transport studies demonstrate the existence of p-n junctions in Bi2Te3/Sb2Te3 heterostructures.

  15. Unsteady Shear Disturbances Within a Two Dimensional Stratified Flow

    NASA Technical Reports Server (NTRS)

    Yokota, Jeffrey W.

    1992-01-01

    The origin and evolution of shear disturbances within a stratified, inviscid, incompressible flow are investigated numerically by a Clebsch/Weber decomposition based scheme. In contrast to homogeneous flows, within which vorticity can be redistributed but not generated, the presence of a density stratification can render an otherwise irrotational flow vortical. In this work, a kinematic decomposition of the unsteady Euler equations separates the unsteady velocity field into rotational and irrotational components. The subsequent evolution of these components is used to study the influence various velocity disturbances have on both stratified and homogeneous flows. In particular, the flow within a two-dimensional channel is used to investigate the evolution of rotational disturbances, generated or convected, downstream from an unsteady inflow condition. Contrasting simulations of both stratified and homogeneous flows are used to distinguish between redistributed inflow vorticity and that which is generated by a density stratification.

  16. Mixing and sorting of bidisperse two-dimensional bubbles

    NASA Astrophysics Data System (ADS)

    Teixeira, P. I. C.; Graner, F.; Fortes, M. A.

    2002-10-01

    We have examined a number of candidates for the minimum-surface-energy arrangement of two-dimensional clusters composed of N bubbles of area 1 and N bubbles of area λ (λ le 1). These include hexagonal bubbles sorted into two monodisperse honeycomb tilings, and various mixed periodic tilings with at most four bubbles per unit cell. We identify, as a function of λ, the minimal configuration for Nrightarrow infty. For finite N, the energy of the external (i.e., cluster-gas) boundary and that of the interface between honeycombs in “phase-separated” clusters have to be taken into account. We estimate these contributions and find the lowest total energy configuration for each pair (N,λ). As λ is varied, this alternates between a circular cluster of one of the mixed tilings, and “partial wetting” of the monodisperse honeycomb of bubble area 1 by the monodisperse honeycomb of bubble area λ.

  17. Efficient solutions of two-dimensional incompressible steady viscous flows

    NASA Technical Reports Server (NTRS)

    Morrison, J. H.; Napolitano, M.

    1986-01-01

    A simple, efficient, and robust numerical technique is provided for solving two dimensional incompressible steady viscous flows at moderate to high Reynolds numbers. The proposed approach employs an incremental multigrid method and an extrapolation procedure based on minimum residual concepts to accelerate the convergence rate of a robust block-line-Gauss-Seidel solver for the vorticity-stream function Navier-Stokes equations. Results are presented for the driven cavity flow problem using uniform and nonuniform grids and for the flow past a backward facing step in a channel. For this second problem, mesh refinement and Richardson extrapolation are used to obtain useful benchmark solutions in the full range of Reynolds numbers at which steady laminar flow is established.

  18. Scalable Transfer of Suspended Two-Dimensional Single Crystals.

    PubMed

    Li, Bo; He, Yongmin; Lei, Sidong; Najmaei, Sina; Gong, Yongji; Wang, Xin; Zhang, Jing; Ma, Lulu; Yang, Yingchao; Hong, Sanghyun; Hao, Ji; Shi, Gang; George, Antony; Keyshar, Kunttal; Zhang, Xiang; Dong, Pei; Ge, Liehui; Vajtai, Robert; Lou, Jun; Jung, Yung Joon; Ajayan, Pulickel M

    2015-08-12

    Large-scale suspended architectures of various two-dimensional (2D) materials (MoS2, MoSe2, WS2, and graphene) are demonstrated on nanoscale patterned substrates with different physical and chemical surface properties, such as flexible polymer substrates (polydimethylsiloxane), rigid Si substrates, and rigid metal substrates (Au/Ag). This transfer method represents a generic, fast, clean, and scalable technique to suspend 2D atomic layers. The underlying principle behind this approach, which employs a capillary-force-free wet-contact printing method, was studied by characterizing the nanoscale solid-liquid-vapor interface of 2D layers with respect to different substrates. As a proof-of-concept, a photodetector of suspended MoS2 has been demonstrated with significantly improved photosensitivity. This strategy could be extended to several other 2D material systems and open the pathway toward better optoelectronic and nanoelectromechnical systems.

  19. Nanoscale integration of two-dimensional materials by lateral heteroepitaxy.

    PubMed

    Sutter, Peter; Huang, Yuan; Sutter, Eli

    2014-08-13

    Materials integration in heterostructures with novel properties different from those of the constituents has become one of the most powerful concepts of modern materials science. Two-dimensional (2D) crystals represent a new class of materials from which such engineered structures can be envisioned. Calculations have predicted emergent properties in 2D heterostructures with nanoscale feature sizes, but methods for their controlled fabrication have been lacking. Here, we use sequential graphene and boron nitride growth on Ru(0001) to show that lateral heteroepitaxy, the joining of 2D materials by preferential incorporation of different atomic species into exposed 1D edges during chemical vapor deposition on a metal substrate, can be used for the bottom-up synthesis of 2D heterostructures with characteristic dimensions on the nanoscale. Our results suggest that on a proper substrate, this method lends itself to building nanoheterostructures from a wide range of 2D materials.

  20. Large-scale intermittency in two-dimensional driven turbulence

    NASA Astrophysics Data System (ADS)

    Jun, Yonggun; Wu, X. L.

    2005-09-01

    It is generally believed that two-dimensional turbulence is immune to intermittency possibly due to the absence of vortex stretching. However, in turbulence created in a freely suspended soap film by electromagnetic forcing, it is found that intermittency is not insignificant. We draw this conclusion based on the measured velocity structure function Sp(l)(≡⟨∣δvl∣p⟩)∝lζp on scales l greater than the energy injection scale linj . The scaling exponent ζp vs p deviates from the expected linear relation and shows intermittent behavior comparable to that observed in fully developed three-dimensional turbulence in wind tunnels. Our measurements demonstrate that intermittency can be accounted for by the nonuniform distribution of saddle points in the flow.

  1. Entropic Barriers for Two-Dimensional Quantum Memories

    NASA Astrophysics Data System (ADS)

    Brown, Benjamin J.; Al-Shimary, Abbas; Pachos, Jiannis K.

    2014-03-01

    Comprehensive no-go theorems show that information encoded over local two-dimensional topologically ordered systems cannot support macroscopic energy barriers, and hence will not maintain stable quantum information at finite temperatures for macroscopic time scales. However, it is still well motivated to study low-dimensional quantum memories due to their experimental amenability. Here we introduce a grid of defect lines to Kitaev's quantum double model where different anyonic excitations carry different masses. This setting produces a complex energy landscape which entropically suppresses the diffusion of excitations that cause logical errors. We show numerically that entropically suppressed errors give rise to superexponential inverse temperature scaling and polynomial system size scaling for small system sizes over a low-temperature regime. Curiously, these entropic effects are not present below a certain low temperature. We show that we can vary the system to modify this bound and potentially extend the described effects to zero temperature.

  2. Universal Conductance Fluctuation in Two-Dimensional Topological Insulators

    PubMed Central

    Choe, Duk-Hyun; Chang, K. J.

    2015-01-01

    Despite considerable interest in two-dimensional (2D) topological insulators (TIs), a fundamental question still remains open how mesoscopic conductance fluctuations in 2D TIs are affected by spin-orbit interaction (SOI). Here, we investigate the effect of SOI on the universal conductance fluctuation (UCF) in disordered 2D TIs. Although 2D TI exhibits UCF like any metallic systems, the amplitude of these fluctuations is distinguished from that of conventional spin-orbit coupled 2D materials. Especially, in 2D systems with mirror symmetry, spin-flip scattering is forbidden even in the presence of strong intrinsic SOI, hence increasing the amplitude of the UCF by a factor of compared with extrinsic SOI that breaks mirror symmetry. We propose an easy way to experimentally observe the existence of such spin-flip scattering in 2D materials. Our findings provide a key to understanding the emergence of a new universal behavior in 2D TIs. PMID:26055574

  3. Two-Dimensional Electronic Spectroscopy in the Ultraviolet Wavelength Range.

    PubMed

    West, Brantley A; Moran, Andrew M

    2012-09-20

    Coherent two-dimensional (2D) spectroscopies conducted at visible and infrared wavelengths are having a transformative impact on the understanding of numerous processes in condensed phases. The extension of 2D spectroscopy to the ultraviolet spectral range (2DUV) must contend with several challenges, including the attainment of adequate laser bandwidth, interferometric phase stability, and the suppression of undesired nonlinearities in the sample medium. Solutions to these problems are motivated by the study of a wide range of biological systems whose lowest-frequency electronic resonances are found in the UV. The development of 2DUV spectroscopy also makes possible the attainment of new insights into elementary chemical reaction dynamics (e.g., electrocyclic ring opening in cycloalkenes). Substantial progress has been made in both the implementation and application of 2DUV spectroscopy in the past several years. In this Perspective, we discuss 2DUV methodology, review recent applications, and speculate on what the future will hold.

  4. Anisotropic electronic conduction in stacked two-dimensional titanium carbide.

    PubMed

    Hu, Tao; Zhang, Hui; Wang, Jiemin; Li, Zhaojin; Hu, Minmin; Tan, Jun; Hou, Pengxiang; Li, Feng; Wang, Xiaohui

    2015-11-09

    Stacked two-dimensional titanium carbide is an emerging conductive material for electrochemical energy storage which requires an understanding of the intrinsic electronic conduction. Here we report the electronic conduction properties of stacked Ti3C2T2 (T = OH, O, F) with two distinct stacking sequences (Bernal and simple hexagonal). On the basis of first-principles calculations and energy band theory analysis, both stacking sequences give rise to metallic conduction with Ti 3d electrons contributing most to the conduction. The conduction is also significantly anisotropic due to the fact that the effective masses of carriers including electrons and holes are remarkably direction-dependent. Such an anisotropic electronic conduction is evidenced by the I-V curves of an individual Ti3C2T2 particulate, which demonstrates that the in-plane electrical conduction is at least one order of magnitude higher than that vertical to the basal plane.

  5. Self-organized defect strings in two-dimensional crystals.

    PubMed

    Lechner, Wolfgang; Polster, David; Maret, Georg; Keim, Peter; Dellago, Christoph

    2013-12-01

    Using experiments with single-particle resolution and computer simulations we study the collective behavior of multiple vacancies injected into two-dimensional crystals. We find that the defects assemble into linear strings, terminated by dislocations with antiparallel Burgers vectors. We show that these defect strings propagate through the crystal in a succession of rapid one-dimensional gliding and rare rotations. While the rotation rate decreases exponentially with the number of defects in the string, the diffusion constant is constant for large strings. By monitoring the separation of the dislocations at the end points, we measure their effective interactions with high precision beyond their spontaneous formation and annihilation, and we explain the double-well form of the dislocation interaction in terms of continuum elasticity theory. PMID:24483371

  6. Analysis of cancellation exponents in two-dimensional Vlasov turbulence

    SciTech Connect

    De Vita, G.; Valentini, F.; Servidio, S.; Primavera, L.; Carbone, V.; Veltri, P.; Sorriso-Valvo, L.

    2014-07-15

    Statistical properties of plasma turbulence are investigated by means of two-dimensional Vlasov simulations. In particular, a classical technique called signed measure is used to characterize the scaling behavior and the topology of sign-oscillating structures in simulations of the hybrid Vlasov-Maxwell model. Exploring different turbulence regimes, varying both the plasma β and the level of fluctuations, it is observed that Vlasov turbulence manifests two ranges with different exponents, the transition being observed near the ion skin depth. These results, which may have applications to both laboratory and astrophysical systems, further confirm the singular nature of small scale fluctuations in a plasma, mainly classified as intermittent, narrow, and intense current sheets.

  7. Time-evolving bubbles in two-dimensional stokes flow

    NASA Technical Reports Server (NTRS)

    Tanveer, Saleh; Vasconcelos, Giovani L.

    1994-01-01

    A general class of exact solutions is presented for a time evolving bubble in a two-dimensional slow viscous flow in the presence of surface tension. These solutions can describe a bubble in a linear shear flow as well as an expanding or contracting bubble in an otherwise quiescent flow. In the case of expanding bubbles, the solutions have a simple behavior in the sense that for essentially arbitrary initial shapes the bubble will asymptote an expanding circle. Contracting bubbles, on the other hand, can develop narrow structures ('near-cusps') on the interface and may undergo 'break up' before all the bubble-fluid is completely removed. The mathematical structure underlying the existence of these exact solutions is also investigated.

  8. Turbulent two-dimensional magnetohydrodynamics and conformal field theory

    SciTech Connect

    Rahimi Tabar, M.R.; Rouhani, S. |

    1996-03-01

    We show that an infinite number of non-unitary minimal models may describe two dimensional turbulent magnetohydrodynamics (MHD), both in the presence and absence of the Alf{close_quote}ven effect. We argue that the existence of a critical dynamical index results in the Alf{close_quote}ven effect or equivalently the equipartition of energy. We show that there are an infinite number of conserved quantities in 2{ital D}{endash}{ital MHD} turbulent systems both in the limit of vanishing the viscocities and in force free case. In the force free case, using the non-unitary minimal model {ital M}{sub 2,7} we derive the correlation functions for the velocity stream function and magnetic flux function. Generalizing this simple model we find the exponents of the energy spectrum in the inertial range for a class of conformal field theories. Copyright {copyright} 1996 Academic Press, Inc.

  9. Two-dimensional Supramolecular Structures by Hydrogen and Halogen Interactions

    NASA Astrophysics Data System (ADS)

    Keon Yoon, Jong; Kim, Howon; Huem Jeon, Jeong; Kahng, Se-Jong

    2010-03-01

    Supramolecualr ordering has been actively studied due to it's possible applications to the fabrication processes of nano-electronic devices. Van der Waals interaction and hydrogen bonding are frequently studied mechanisms for various molecular structures based on non-uniform charge distributions. Halogen atoms in molecules can have electrostatic interactions with similar strength. Big halogen atoms have strong non-uniform charge distributions. To study molecular orderings formed by hydrogen and halogen interactions, we chose a molecular system containing oxygen, hydrogen, and bromine atoms, a bromo-quinone. A two-dimensional molecular network was studied on Au(111) using a low-temperature scanning tunneling microscope. Bromo-quinone molecules form self-assembled square grids having windmill structures. Their molecular orderings, chiral structures, and defects are explained in terms of hydrogen and halogen interactions.

  10. Extension of the approximate two-dimensional electron gas formulation

    NASA Astrophysics Data System (ADS)

    Pierret, R. F.

    1985-07-01

    The functional two-dimensional electron gas (2DEG) formalism employed in the analysis of modulation-doped field-effect transistors is extended to properly account for the bulk charge and to more accurately model sub- and near-threshold behavior. The implemented changes basically transform the functional formulation from an above-threshold formalism for lightly doped structures to one of additional utility which automatically approaches expected limits under widely divergent conditions. Sample computations of the surface carrier concentration, relevant energy level positionings, and the semiconductor depletion width as a function of surface potential and doping are also presented and examined. These computations exhibit the general utility of the extended theory and provide an indirect evaluation of the standard two-level 2DEG theory.

  11. Two-Dimensional Organic-Inorganic Hybrid Perovskite Photonic Films.

    PubMed

    Meng, Ke; Gao, Shanshan; Wu, Longlong; Wang, Geng; Liu, Xin; Chen, Gang; Liu, Zhou; Chen, Gang

    2016-07-13

    Organic-inorganic hybrid perovskites have created enormous expectations for low-cost and high-performance optoelectronic devices. In prospect, future advancements may derive from reaping novel electrical and optical properties beyond pristine perovskites through microscopic structure design and engineering. Herein, we report the successful preparation of two-dimensional inverse-opal perovskite (IOP) photonic films, featuring unique nanostructures and vivid colors. Further compositional and structural managements promise optical property and energy level tunability of the IOP films. They are further functionalized in solar cells, resulting in colorful devices with respectable power conversion efficiency. Such concept has not been previously applied for perovskite-based solar cells, which could open a route for more versatile optoelectronic devices.

  12. Two dimensional velocity distribution in open channels using Renyi entropy

    NASA Astrophysics Data System (ADS)

    Kumbhakar, Manotosh; Ghoshal, Koeli

    2016-05-01

    In this study, the entropy concept is employed for describing the two-dimensional velocity distribution in an open channel. Using the principle of maximum entropy, the velocity distribution is derived by maximizing the Renyi entropy by assuming dimensionless velocity as a random variable. The derived velocity equation is capable of describing the variation of velocity along both the vertical and transverse directions with maximum velocity occurring on or below the water surface. The developed model of velocity distribution is tested with field and laboratory observations and is also compared with existing entropy-based velocity distributions. The present model has shown good agreement with the observed data and its prediction accuracy is comparable with the other existing models.

  13. Quasi-Two-Dimensional Magnetism in Co-Based Shandites

    NASA Astrophysics Data System (ADS)

    Kassem, Mohamed A.; Tabata, Yoshikazu; Waki, Takeshi; Nakamura, Hiroyuki

    2016-06-01

    We report quasi-two-dimensional (Q2D) itinerant electron magnetism in the layered Co-based shandites. Comprehensive magnetization measurements were performed using single crystals of Co3Sn2-xInxS2 (0 ≤ x ≤ 2) and Co3-yFeySn2S2 (0 ≤ y ≤ 0.5). The magnetic parameters of both systems; the Curie temperature TC, effective moment peff and spontaneous moment ps; exhibit almost identical variations against the In- and Fe-concentrations, indicating significance of the electron count on the magnetism in the Co-based shandite. The ferromagnetic-nonmagnetic quantum phase transition is found around xc ˜ 0.8. Analysis based on the extended Q2D spin fluctuation theory clearly reveals the highly Q2D itinerant electron character of the ferromagnetism in the Co-based shandites.

  14. Acoustic resonances in two-dimensional radial sonic crystal shells

    NASA Astrophysics Data System (ADS)

    Torrent, Daniel; Sánchez-Dehesa, José

    2010-07-01

    Radial sonic crystals (RSC) are fluidlike structures infinitely periodic along the radial direction that verify the Bloch theorem and are possible only if certain specially designed acoustic metamaterials with mass density anisotropy can be engineered (see Torrent and Sánchez-Dehesa 2009 Phys. Rev. Lett. 103 064301). A comprehensive analysis of two-dimensional (2D) RSC shells is reported here. A given shell is in fact a circular slab with a central cavity. These finite crystal structures contain Fabry-Perot-like resonances and modes strongly localized at the central cavity. Semi-analytical expressions are developed to obtain the quality factors of the different resonances, their symmetry features and their excitation properties. The results reported here are completely general and can be extended to equivalent 3D spherical shells and to their photonic counterparts.

  15. Two-dimensional lattice-fluid model with waterlike anomalies.

    PubMed

    Buzano, C; De Stefanis, E; Pelizzola, A; Pretti, M

    2004-06-01

    We investigate a lattice-fluid model defined on a two-dimensional triangular lattice, with the aim of reproducing qualitatively some anomalous properties of water. Model molecules are of the "Mercedes Benz" type, i.e., they possess a D3 (equilateral triangle) symmetry, with three bonding arms. Bond formation depends both on orientation and local density. We work out phase diagrams, response functions, and stability limits for the liquid phase, making use of a generalized first order approximation on a triangle cluster, whose accuracy is verified, in some cases, by Monte Carlo simulations. The phase diagram displays one ordered (solid) phase which is less dense than the liquid one. At fixed pressure the liquid phase response functions show the typical anomalous behavior observed in liquid water, while, in the supercooled region, a reentrant spinodal is observed.

  16. Two-dimensional lattice-fluid model with waterlike anomalies

    NASA Astrophysics Data System (ADS)

    Buzano, C.; de Stefanis, E.; Pelizzola, A.; Pretti, M.

    2004-06-01

    We investigate a lattice-fluid model defined on a two-dimensional triangular lattice, with the aim of reproducing qualitatively some anomalous properties of water. Model molecules are of the “Mercedes Benz” type, i.e., they possess a D3 (equilateral triangle) symmetry, with three bonding arms. Bond formation depends both on orientation and local density. We work out phase diagrams, response functions, and stability limits for the liquid phase, making use of a generalized first order approximation on a triangle cluster, whose accuracy is verified, in some cases, by Monte Carlo simulations. The phase diagram displays one ordered (solid) phase which is less dense than the liquid one. At fixed pressure the liquid phase response functions show the typical anomalous behavior observed in liquid water, while, in the supercooled region, a reentrant spinodal is observed.

  17. Nonlinear two-dimensional model for thermoacoustic engines.

    PubMed

    Hamilton, Mark F; Ilinskii, Yurii A; Zabolotskaya, Evgenia A

    2002-05-01

    A two-dimensional model and efficient solution algorithm are developed for studying nonlinear effects in thermoacoustic engines. There is no restriction on the length or location of the stack, and the cross-sectional area of the resonator may vary with position along its axis. Reduced model equations are obtained by ordering spatial derivatives in terms of rapid variations across the pores in the stack, versus slow variations along the resonator axis. High efficiency is achieved with the solution algorithm because the stability condition for numerical integration of the model equations is connected with resonator length rather than pore diameter. Computation time is reduced accordingly, by several orders of magnitude, without sacrificing spatial resolution. The solution algorithm is described in detail, and the results are verified by comparison with established linear theory. Two examples of nonlinear effects are investigated briefly, the onset of instability through to saturation and steady state, and nonlinear waveform distortion as a function of resonator shape.

  18. Two-dimensional freezing criteria for crystallizing colloidal monolayers.

    PubMed

    Wang, Ziren; Alsayed, Ahmed M; Yodh, Arjun G; Han, Yilong

    2010-04-21

    Video microscopy was employed to explore crystallization of colloidal monolayers composed of diameter-tunable microgel spheres. Two-dimensional (2D) colloidal liquids were frozen homogenously into polycrystalline solids, and four 2D criteria for freezing were experimentally tested in thermal systems for the first time: the Hansen-Verlet freezing rule, the Lowen-Palberg-Simon dynamical freezing criterion, and two other rules based, respectively, on the split shoulder of the radial distribution function and on the distribution of the shape factor of Voronoi polygons. Importantly, these freezing criteria, usually applied in the context of single crystals, were demonstrated to apply to the formation of polycrystalline solids. At the freezing point, we also observed a peak in the fluctuations of the orientational order parameter and a percolation transition associated with caged particles. Speculation about these percolated clusters of caged particles casts light on solidification mechanisms and dynamic heterogeneity in freezing. PMID:20423183

  19. Two-dimensional freezing criteria for crystallizing colloidal monolayers

    SciTech Connect

    Wang Ziren; Han Yilong; Alsayed, Ahmed M.

    2010-04-21

    Video microscopy was employed to explore crystallization of colloidal monolayers composed of diameter-tunable microgel spheres. Two-dimensional (2D) colloidal liquids were frozen homogenously into polycrystalline solids, and four 2D criteria for freezing were experimentally tested in thermal systems for the first time: the Hansen-Verlet freezing rule, the Loewen-Palberg-Simon dynamical freezing criterion, and two other rules based, respectively, on the split shoulder of the radial distribution function and on the distribution of the shape factor of Voronoi polygons. Importantly, these freezing criteria, usually applied in the context of single crystals, were demonstrated to apply to the formation of polycrystalline solids. At the freezing point, we also observed a peak in the fluctuations of the orientational order parameter and a percolation transition associated with caged particles. Speculation about these percolated clusters of caged particles casts light on solidification mechanisms and dynamic heterogeneity in freezing.

  20. Synchronization of Coupled Oscillators on a Two-Dimensional Plane.

    PubMed

    Guo, Dameng; Fu, Yong Qing; Zheng, Bo

    2016-08-01

    The effect of the transfer rate of signal molecules on coupled chemical oscillators arranged on a two-dimensional plane was systematically investigated in this paper. A microreactor equipped with a surface acoustic wave (SAW) mixer was applied to adjust the transfer rate of the signal molecules in the microreactor. The SAW mixer with adjustable input powers provided a simple means to generate different mixing rates in the microreactor. A robust synchronization of the oscillators was found at an input radio frequency power of 20 dBm, with which the chemical waves were initiated at a fixed site of the oscillator system. With increasing input power, the frequency of the chemical waves was increased, which agreed well with the prediction given by the time-delayed phase oscillator model. Results from the finite element simulation agreed well with the experimental results. PMID:27124217

  1. Burgers approximation for two-dimensional flow past an ellipse

    NASA Technical Reports Server (NTRS)

    Dorrepaal, J. M.

    1982-01-01

    A linearization of the Navier-Stokes equation due to Burgers in which vorticity is transported by the velocity field corresponding to continuous potential flow is examined. The governing equations are solved exactly for the two dimensional steady flow past an ellipse of arbitrary aspect ratio. The requirement of no slip along the surface of the ellipse results in an infinite algebraic system of linear equations for coefficients appearing in the solution. The system is truncated at a point which gives reliable results for Reynolds numbers R in the range 0 R 5. Predictions of the Burgers approximation regarding separation, drag and boundary layer behavior are investigated. In particular, Burgers linearization gives drag coefficients which are closer to observed experimental values than those obtained from Oseen's approximation. In the special case of flow past a circular cylinder, Burgers approximation predicts a boundary layer whose thickness is roughly proportional to R-1/2.

  2. Real-time two-dimensional temperature imaging using ultrasound.

    PubMed

    Liu, Dalong; Ebbini, Emad S

    2009-01-01

    We present a system for real-time 2D imaging of temperature change in tissue media using pulse-echo ultrasound. The frontend of the system is a SonixRP ultrasound scanner with a research interface giving us the capability of controlling the beam sequence and accessing radio frequency (RF) data in real-time. The beamformed RF data is streamlined to the backend of the system, where the data is processed using a two-dimensional temperature estimation algorithm running in the graphics processing unit (GPU). The estimated temperature is displayed in real-time providing feedback that can be used for real-time control of the heating source. Currently we have verified our system with elastography tissue mimicking phantom and in vitro porcine heart tissue, excellent repeatability and sensitivity were demonstrated.

  3. The development of two-dimensional object identification techniques

    NASA Technical Reports Server (NTRS)

    Lebby, Gary; Sherrod, Earnest E.

    1989-01-01

    This report marks the end of the first year of an anticipated three year effort to study methods for numerically identifying objects according to shape in two dimensions. The method is based upon comparing the unit gradient of an observed object and the unit gradient of a standard object over a specified range of points. The manner in which the gradients are compared forms the basis of a shape recognition scheme, which is then applied to simple closed plane figures. The gradient based method is calibrated by using various distorted objects in comparison with a set of standard reference objects. The use of pattern recognition techniques for computer identification of two-dimensional figures will be investigated during the second and third years of this project.

  4. Two dimensional radiated power diagnostics on Alcator C-Moda)

    NASA Astrophysics Data System (ADS)

    Reinke, M. L.; Hutchinson, I. H.

    2008-10-01

    The radiated power diagnostics for the Alcator C-Mod tokamak have been upgraded to measure two dimensional structure of the photon emissivity profile in order to investigate poloidal asymmetries in the core radiation. Commonly utilized unbiased absolute extreme ultraviolet (AXUV) diode arrays view the plasma along five different horizontal planes. The layout of the diagnostic set is shown and the results from calibrations and recent experiments are discussed. Data showing a significant, 30%-40%, inboard/outboard emissivity asymmetry during ELM-free H-mode are presented. The ability to use AXUV diode arrays to measure absolute radiated power is explored by comparing diode and resistive bolometer-based emissivity profiles for highly radiative L-mode plasmas seeded with argon. Emissivity profiles match in the core but disagree radially outward resulting in an underprediction of Prad of nearly 50% by the diodes compared to Prad determined using resistive bolometers.

  5. Microwave Reflection Spectroscopy of a Two-Dimensional Electron Gas

    NASA Astrophysics Data System (ADS)

    Zhang, Jie; Liu, Ruiyuan; Du, Lingjie; Du, Rui-Rui; Pfeiffer, Loren; West, Ken

    Cyclotron resonance (CR) is a standard method to determine the carrier effective mass in two-dimensional electron systems, typically by measuring/analyzing the absorption or transmission signal. Here we report a microwave spectrometer utilizing the reflection signal. In our experiment setup based on a top-loading helium3 cryostat and a superconducting solenoid, the microwave (up to 40GHz) is sent down via a coax cable to the sample surface, and the reflection signal is then collected by the same cable and fed upward to a directional coupler, and being detected. We demonstrate the applicability of the spectrometer by measuring the CR of high-mobility electrons or holes in GaAs/AlGaAs quantum wells. The construction of spectrometer, preliminary data, and brief discussions will be presented. The work at Rice was supported by Welch Foundation Grant C-1682.

  6. Optical Spectroscopy of Two Dimensional Graphene and Boron Nitride

    NASA Astrophysics Data System (ADS)

    Ju, Long

    This dissertation describes the use of optical spectroscopy in studying the physical properties of two dimensional nano materials like graphene and hexagonal boron nitride. Compared to bulk materials, atomically thin two dimensional materials have a unique character that is the strong dependence of physical properties on external control. Both electronic band structure and chemical potential can be tuned in situ by electric field-which is a powerful knob in experiment. Therefore the optical study at atomic thickness scale can greatly benefit from modern micro-fabrication technique and electric control of the material properties. As will be shown in this dissertation, such control of both gemometric and physical properties enables new possibilities of optical spectroscopic measurement as well as opto-electronic studies. Other experimental techniques like electric transport and scanning tunneling microscopy and spectroscopy are also combined with optical spectroscopy to reveal the physics that is beyond the reach of each individual technique. There are three major themes in the dissertation. The first one is focused on the study of plasmon excitation of Dirac electrons in monolayer graphene. Unlike plasmons in ordinary two dimensional electron gas, plasmons of 2D electrons as in graphene obey unusual scaling laws. We fabricate graphene micro-ribbon arrays with photolithography technique and use optical absorption spectroscopy to study its absorption spectrum. The experimental result demonstrates the extraordinarily strong light-plasmon coupling and its novel dependence on both charge doping and geometric dimensions. This work provides a first glance at the fundamental properties of graphene plasmons and forms the basis of an emerging subfield of graphene research and applications such as graphene terahertz metamaterials. The second part describes the opto-electronic response of heterostructures composed of graphene and hexagonal boron nitride. We found that there is

  7. The domain dependence of chemotaxis in two-dimensional turbulence

    NASA Astrophysics Data System (ADS)

    Tang, Wenbo; Jones, Kimberly; Walker, Phillip

    2015-11-01

    Coherent structures are ubiquitous in environmental and geophysical flows and they affect reaction-diffusion processes in profound ways. In this presentation, we show an example of the domain dependence of chemotaxis process in a two-dimensional turbulent flow. The flow has coherent structures that form barriers that prohibit long-range transport of tracers. Accordingly, the uptake advantage of nutrient by motile and nonmotile species differs significantly if the process start in different locations of the flow. Interestingly, the conventional diagnostic of Finite-time Lyapunov exponents alone is not sufficient to explain the variability -- methods to extract elliptic transport barriers are essential to relate to the explanation. We also offer some explanations of the observed scalar behaviors via analyses of bulk quantities. Support: NSF-DMS-1212144.

  8. Flat Chern Band in a Two-Dimensional Organometallic Framework

    NASA Astrophysics Data System (ADS)

    Liu, Zheng; Wang, Zheng-Fei; Mei, Jia-Wei; Wu, Yong-Shi; Liu, Feng

    2013-03-01

    By combining exotic band dispersion with nontrivial band topology, an interesting type of band structure, namely, the flat Chern band, has recently been proposed to spawn high-temperature fractional quantum Hall states. Despite the proposal of several theoretical lattice models, however, it remains doubtful whether such a “romance of flatland” could exist in a real material. Here, we present a first-principles design of a two-dimensional indium-phenylene organometallic framework that realizes a nearly flat Chern band right around the Fermi level by combining lattice geometry, spin-orbit coupling, and ferromagnetism. An effective four-band model is constructed to reproduce the first-principles results. Our design, in addition, provides a general strategy to synthesize topologically nontrivial materials by virtue of organic chemistry and nanotechnology.

  9. Flat Chern Band in a Two-Dimensional Organometallic Framework

    NASA Astrophysics Data System (ADS)

    Liu, Zheng; Wang, Zheng-Fei; Mei, Jia-Wei; Wu, Yong-Shi; Liu, Feng

    2013-03-01

    By combining exotic band dispersion with nontrivial band topology, an interesting type of band, namely the flat chern band (FCB), has recently been proposed, in which carriers experience strong Coulomb interaction as well as topological frustration that in together spawn unprecedented topological strongly-correlated electronic states, such as high-temperature fractional quantum hall state. Despite the proposal of several theoretical lattice models, however, it remains a doubt whether such a ``romance of flatland'' could exist in a real material. Here, we present a first-principles design to realize a nearly FCB right around the Fermi level in a two-dimensional (2D) Indium-Phenylene Organometallic Framework (IPOF). Our design in addition provides a general strategy to synthesize topologically nontrivial materials in virtue of organic chemistry and nanotechnology. Supported by DOE-BES and ARL

  10. Exploring the thermodynamics of a two-dimensional Bose gas.

    PubMed

    Yefsah, Tarik; Desbuquois, Rémi; Chomaz, Lauriane; Günter, Kenneth J; Dalibard, Jean

    2011-09-23

    Using in situ measurements on a quasi-two-dimensional, harmonically trapped (87)Rb gas, we infer various equations of state for the equivalent homogeneous fluid. From the dependence of the total atom number and the central density of our clouds with chemical potential and temperature, we obtain the equations of state for the pressure and the phase-space density. Then, using the approximate scale invariance of this 2D system, we determine the entropy per particle and find very low values (below 0.1k(B)) in the strongly degenerate regime. This shows that this gas can constitute an efficient coolant for other quantum fluids. We also explain how to disentangle the various contributions (kinetic, potential, interaction) to the energy of the trapped gas using a time-of-flight method, from which we infer the reduction of density fluctuations in a nonfully coherent cloud.

  11. Mixing efficiency in two-dimensional turbulent and chaotic flows

    NASA Astrophysics Data System (ADS)

    Kadoch, Benjamin; Bos, Wouter; Schneider, Kai

    2014-11-01

    We investigate the mixing in a flow generated by a circular rod, describing a figure-eight-shaped motion in a two-dimensional circular vessel. The vessel, the moving rod, and the equations of motion are modeled using a volume penalization method imbedded in a classical Fourier pseudo-spectral code as described in. The influence of the Peclet number on the mixing efficiency is measured for different Stokes and turbulent regimes. Here, the mixing efficiency is measured by evaluating the decay of passive scalar fluctuations for a given energy injection rate. The Stokes regime shows results similar to the ones obtained in for chaotic mixing. For instance, the passive scalar variance decays following a powerlaw, related to the presence of unmixed fluid near the fixed walls, which acts as a reservoir for the mixing away from the wall. For the turbulent regimes, however, the detachment of vorticity in the boundary layer more efficiently injects the unmixed fluid into the domain.

  12. Reentrant melting of a classical two-dimensional binary cluster

    SciTech Connect

    Nelissen, K.; Partoens, B.; Peeters, F.M.; Schweigert, I.

    2005-10-31

    A system of classical charged particles interacting through a dipole repulsive potential, which are confined in a two-dimensional hardwall trap, is studied. The cluster consists of 16 particles, together with 4 defect particles. The technique of Brownian dynamics is used to simulate experimental binary colloidal systems. The melting properties and the reentrant behavior of the system, which was studied before for clusters of identical particles, are studied for the binary mixture. The defect particles, which have a smaller charge than the other particles, stabilize the cluster, melt at a higher value of the coupling parameter {gamma} as compared to the other particles and have a strong influence on the melting properties of the other particles.

  13. Flat Chern band in a two-dimensional organometallic framework.

    PubMed

    Liu, Zheng; Wang, Zheng-Fei; Mei, Jia-Wei; Wu, Yong-Shi; Liu, Feng

    2013-03-01

    By combining exotic band dispersion with nontrivial band topology, an interesting type of band structure, namely, the flat Chern band, has recently been proposed to spawn high-temperature fractional quantum Hall states. Despite the proposal of several theoretical lattice models, however, it remains doubtful whether such a "romance of flatland" could exist in a real material. Here, we present a first-principles design of a two-dimensional indium-phenylene organometallic framework that realizes a nearly flat Chern band right around the Fermi level by combining lattice geometry, spin-orbit coupling, and ferromagnetism. An effective four-band model is constructed to reproduce the first-principles results. Our design, in addition, provides a general strategy to synthesize topologically nontrivial materials by virtue of organic chemistry and nanotechnology.

  14. Anisotropic electronic conduction in stacked two-dimensional titanium carbide

    PubMed Central

    Hu, Tao; Zhang, Hui; Wang, Jiemin; Li, Zhaojin; Hu, Minmin; Tan, Jun; Hou, Pengxiang; Li, Feng; Wang, Xiaohui

    2015-01-01

    Stacked two-dimensional titanium carbide is an emerging conductive material for electrochemical energy storage which requires an understanding of the intrinsic electronic conduction. Here we report the electronic conduction properties of stacked Ti3C2T2 (T = OH, O, F) with two distinct stacking sequences (Bernal and simple hexagonal). On the basis of first-principles calculations and energy band theory analysis, both stacking sequences give rise to metallic conduction with Ti 3d electrons contributing most to the conduction. The conduction is also significantly anisotropic due to the fact that the effective masses of carriers including electrons and holes are remarkably direction-dependent. Such an anisotropic electronic conduction is evidenced by the I−V curves of an individual Ti3C2T2 particulate, which demonstrates that the in-plane electrical conduction is at least one order of magnitude higher than that vertical to the basal plane. PMID:26548439

  15. Exchange interactions of magnetic surfaces below two-dimensional materials

    NASA Astrophysics Data System (ADS)

    Friedrich, Rico; Caciuc, Vasile; Atodiresei, Nicolae; Blügel, Stefan

    2016-06-01

    In this theoretical investigation we demonstrate that the adsorption of spatially extended two-dimensional (2D) π systems such as graphene and hexagonal boron nitride on the ferromagnetic fcc Co(111) surface leads to a specific behavior of the in-plane and interlayer Co-Co magnetic exchange interactions. More specifically, for both systems the magnetic exchange coupling within the first Co layer is enhanced, while the one between the first and the second Co layer is not modified, in contrast to the magnetic interlayer softening induced by organic molecules. Importantly, the in-plane magnetic hardening effect is mainly due to the hybridization between the pz states of the 2D π system and the d states of the Co surface.

  16. Electric and magnetic fields from two-dimensional anisotropic bisyncytia.

    PubMed Central

    Sepulveda, N G; Wikswo, J P

    1987-01-01

    Cardiac tissue can be considered macroscopically as a bidomain, anisotropic conductor in which simple depolarization wavefronts produce complex current distributions. Since such distributions may be difficult to measure using electrical techniques, we have developed a mathematical model to determine the feasibility of magnetic localization of these currents. By applying the finite element method to an idealized two-dimensional bisyncytium with anisotropic conductivities, we have calculated the intracellular and extracellular potentials, the current distributions, and the magnetic fields for a circular depolarization wavefront. The calculated magnetic field 1 mm from the tissue is well within the sensitivity of a SQUID magnetometer. Our results show that complex bisyncytial current patterns can be studied magnetically, and these studies should provide valuable insight regarding the electrical anisotropy of cardiac tissue. PMID:3580484

  17. Two-Dimensional Organic-Inorganic Hybrid Perovskite Photonic Films.

    PubMed

    Meng, Ke; Gao, Shanshan; Wu, Longlong; Wang, Geng; Liu, Xin; Chen, Gang; Liu, Zhou; Chen, Gang

    2016-07-13

    Organic-inorganic hybrid perovskites have created enormous expectations for low-cost and high-performance optoelectronic devices. In prospect, future advancements may derive from reaping novel electrical and optical properties beyond pristine perovskites through microscopic structure design and engineering. Herein, we report the successful preparation of two-dimensional inverse-opal perovskite (IOP) photonic films, featuring unique nanostructures and vivid colors. Further compositional and structural managements promise optical property and energy level tunability of the IOP films. They are further functionalized in solar cells, resulting in colorful devices with respectable power conversion efficiency. Such concept has not been previously applied for perovskite-based solar cells, which could open a route for more versatile optoelectronic devices. PMID:27267266

  18. Guest Editorial: Two-Dimensional Optical Signal Processing

    NASA Astrophysics Data System (ADS)

    Kooij, Theo; Ludman, Jacques E.; Stilwell, P. D., Jr.

    1982-10-01

    When some optical processing systems firms proposed to the Defense Advanced Research Project Agency (DARPA) and the U.S. Navy some years ago that they could beat the ILLIAC-IV-that venerable supercomputer, which until recently was the world's largest by at least a factor of 100, it sounded too good to be true. But they were right, and they did not even have to try hard. The problem was a two-dimensional (2-D) processing task of generating ambiguity surfaces to test whether two received signals came from a common origin, with unknown time and Doppler shifts. The ILLIAC, going all out as an in-line processor for the Acoustic Research Center near San Francisco, California, could just make a handful of such surfaces per second; the optical processors made hundreds, literally sucking their digital inputs dry.

  19. Defect Interactions in Anisotropic Two-Dimensional Fluids

    NASA Astrophysics Data System (ADS)

    Stannarius, R.; Harth, K.

    2016-10-01

    Disclinations in liquid crystals bear striking analogies to defect structures in a wide variety of physical systems, and their straightforward optical observability makes them excellent models to study fundamental properties of defect interactions. We employ freely suspended smectic-C films, which behave as quasi-two-dimensional polar nematics. A procedure to capture high-strength disclinations in localized spots is introduced. These disclinations are released in a controlled way, and the motion of the mutually repelling topological charges with strength +1 is studied quantitatively. We demonstrate that the classical models, which employ elastic one-constant approximation, fail to describe their dynamics correctly. In realistic liquid crystals, even small differences between splay and bend constants lead to the selection of pure splay or pure bend +1 defects. For those, the models work only in very special configurations. In general, additional director walls are involved which reinforce the repulsive interactions substantially.

  20. Equation of State of the Two-Dimensional Hubbard Model.

    PubMed

    Cocchi, Eugenio; Miller, Luke A; Drewes, Jan H; Koschorreck, Marco; Pertot, Daniel; Brennecke, Ferdinand; Köhl, Michael

    2016-04-29

    The subtle interplay between kinetic energy, interactions, and dimensionality challenges our comprehension of strongly correlated physics observed, for example, in the solid state. In this quest, the Hubbard model has emerged as a conceptually simple, yet rich model describing such physics. Here we present an experimental determination of the equation of state of the repulsive two-dimensional Hubbard model over a broad range of interactions 0≲U/t≲20 and temperatures, down to k_{B}T/t=0.63(2) using high-resolution imaging of ultracold fermionic atoms in optical lattices. We show density profiles, compressibilities, and double occupancies over the whole doping range, and, hence, our results constitute benchmarks for state-of-the-art theoretical approaches.

  1. Two-dimensional radiant energy array computers and computing devices

    NASA Technical Reports Server (NTRS)

    Schaefer, D. H.; Strong, J. P., III (Inventor)

    1976-01-01

    Two dimensional digital computers and computer devices operate in parallel on rectangular arrays of digital radiant energy optical signal elements which are arranged in ordered rows and columns. Logic gate devices receive two input arrays and provide an output array having digital states dependent only on the digital states of the signal elements of the two input arrays at corresponding row and column positions. The logic devices include an array of photoconductors responsive to at least one of the input arrays for either selectively accelerating electrons to a phosphor output surface, applying potentials to an electroluminescent output layer, exciting an array of discrete radiant energy sources, or exciting a liquid crystal to influence crystal transparency or reflectivity.

  2. Investigation of Turbulent Flow in a Two-Dimensional Channel

    NASA Technical Reports Server (NTRS)

    Laufer, John

    1951-01-01

    A detailed exploration of the field of mean and fluctuating quantities in a two-dimensional turbulent channel flow is presented. The measurements were repeated at three Reynolds numbers, 12,300, 30,800, and 61,600, based on the half width of the channel and the maximum mean velocity. A channel of 5-inch width and 12:1 aspect ratio was used for the investigation. Mean-speed and axial-fluctuation measurements were made well within the laminar sublayer. The semitheoretical predictions concerning the extent of the laminar sublayer were confirmed. The distribution of the velocity fluctuations in the direction of mean flow u' shows that the influence of the viscosity extends farther from the wall than indicated by the mean velocity profile, the region of influence being approximately four times as wide.

  3. Two-dimensional photonic crystal based sensor for pressure sensing

    NASA Astrophysics Data System (ADS)

    Vijaya Shanthi, Krishnan; Robinson, Savarimuthu

    2014-09-01

    In this paper, a two-dimensional photonic crystal (2DPC) based pressure sensor is proposed and designed, and the sensing characteristics such as the sensitivity and dynamic range are analyzed over the range of pressure from 0 GPa to 7 GPa. The sensor is based on 2DPC with the square array of silicon rods surrounded by air. The sensor consists of two photonic crystal quasi waveguides and L3 defect. The L3 defect is placed in between two waveguides and is formed by modifying the radius of three Si rods. It is noticed that through simulation, the resonant wavelength of the sensor is shifted linearly towards the higher wavelength region while increasing the applied pressure level. The achieved sensitivity and dynamic range of the sensor is 2 nm/GPa and 7 Gpa, respectively.

  4. Thermal properties and two-dimensional photonic band gaps

    NASA Astrophysics Data System (ADS)

    Elsayed, Hussein A.; El-Naggar, Sahar A.; Aly, Arafa H.

    2014-03-01

    The effect of temperature on a two-dimensional square lattice photonic crystal composed of Si rods arranged in an air background was investigated theoretically using the plane-wave expansion method. Both the thermal expansion effect and thermo-optical effect are considered simultaneously. We have discussed the role of temperature in creating the complete photonic band gap as a function of temperature. Two different shapes of rods, i.e. square and circular, are considered in the presence of the two polarization states, i.e. TE and TM waves. The numerical results show that the photonic band gap can be significantly enlarged compared to the photonic band gap at room temperature. The effect of temperature on the complete photonic band width in the cylindrical rods case is more significant. Cylindrical and square Si rods may work as a temperature sensor or filter, among many other potential applications.

  5. Two-dimensional electronic spectroscopy with birefringent wedges

    SciTech Connect

    Réhault, Julien; Maiuri, Margherita; Oriana, Aurelio; Cerullo, Giulio

    2014-12-15

    We present a simple experimental setup for performing two-dimensional (2D) electronic spectroscopy in the partially collinear pump-probe geometry. The setup uses a sequence of birefringent wedges to create and delay a pair of phase-locked, collinear pump pulses, with extremely high phase stability and reproducibility. Continuous delay scanning is possible without any active stabilization or position tracking, and allows to record rapidly and easily 2D spectra. The setup works over a broad spectral range from the ultraviolet to the near-IR, it is compatible with few-optical-cycle pulses and can be easily reconfigured to two-colour operation. A simple method for scattering suppression is also introduced. As a proof of principle, we present degenerate and two-color 2D spectra of the light-harvesting complex 1 of purple bacteria.

  6. Zero modes of two-dimensional chiral p -wave superconductors

    NASA Astrophysics Data System (ADS)

    Gurarie, V.; Radzihovsky, L.

    2007-06-01

    We discuss fermionic zero modes in the two-dimensional chiral p -wave superconductors. We show quite generally that without fine tuning, in a macroscopic sample there is only one or zero of such Majorana-fermion modes depending only on whether the total vorticity of the order parameter is odd or even, respectively. As a special case of this, we find explicitly the one zero mode localized on a single odd-vorticity vortex and show that, in contrast, zero modes are absent for an even-vorticity vortex. One zero mode per odd vortex persists, within an exponential accuracy, for a collection of well-separated vortices, shifting to finite ±E energies as two odd vortices approach. These results should be useful for the demonstration of the non-Abelian statistics that such zero-mode vortices are expected to exhibit and for their possible application in quantum computation.

  7. Equation of State of the Two-Dimensional Hubbard Model.

    PubMed

    Cocchi, Eugenio; Miller, Luke A; Drewes, Jan H; Koschorreck, Marco; Pertot, Daniel; Brennecke, Ferdinand; Köhl, Michael

    2016-04-29

    The subtle interplay between kinetic energy, interactions, and dimensionality challenges our comprehension of strongly correlated physics observed, for example, in the solid state. In this quest, the Hubbard model has emerged as a conceptually simple, yet rich model describing such physics. Here we present an experimental determination of the equation of state of the repulsive two-dimensional Hubbard model over a broad range of interactions 0≲U/t≲20 and temperatures, down to k_{B}T/t=0.63(2) using high-resolution imaging of ultracold fermionic atoms in optical lattices. We show density profiles, compressibilities, and double occupancies over the whole doping range, and, hence, our results constitute benchmarks for state-of-the-art theoretical approaches. PMID:27176527

  8. Self-organized defect strings in two-dimensional crystals.

    PubMed

    Lechner, Wolfgang; Polster, David; Maret, Georg; Keim, Peter; Dellago, Christoph

    2013-12-01

    Using experiments with single-particle resolution and computer simulations we study the collective behavior of multiple vacancies injected into two-dimensional crystals. We find that the defects assemble into linear strings, terminated by dislocations with antiparallel Burgers vectors. We show that these defect strings propagate through the crystal in a succession of rapid one-dimensional gliding and rare rotations. While the rotation rate decreases exponentially with the number of defects in the string, the diffusion constant is constant for large strings. By monitoring the separation of the dislocations at the end points, we measure their effective interactions with high precision beyond their spontaneous formation and annihilation, and we explain the double-well form of the dislocation interaction in terms of continuum elasticity theory.

  9. A spectroelectrochemical cell for ultrafast two-dimensional infrared spectroscopy

    SciTech Connect

    El Khoury, Youssef; Van Wilderen, Luuk J. G. W.; Vogt, Tim; Winter, Ernst; Bredenbeck, Jens E-mail: bredenbeck@biophysik.uni-frankfurt.de

    2015-08-15

    A spectroelectrochemical cell has been designed to combine electrochemistry and ultrafast two-dimensional infrared (2D-IR) spectroscopy, which is a powerful tool to extract structure and dynamics information on the femtosecond to picosecond time scale. Our design is based on a gold mirror with the dual role of performing electrochemistry and reflecting IR light. To provide the high optical surface quality required for laser spectroscopy, the gold surface is made by electron beam evaporation on a glass substrate. Electrochemical cycling facilitates in situ collection of ultrafast dynamics of redox-active molecules by means of 2D-IR. The IR beams are operated in reflection mode so that they travel twice through the sample, i.e., the signal size is doubled. This methodology is optimal for small sample volumes and successfully tested with the ferricyanide/ferrocyanide redox system of which the corresponding electrochemically induced 2D-IR difference spectrum is reported.

  10. Domain engineering of physical vapor deposited two-dimensional materials

    SciTech Connect

    Alam, Tarek; Wang, Baoming; Pulavarthy, Raghu; Haque, M. A.; Muratore, Christopher; Glavin, Nicholas; Roy, Ajit K.; Voevodin, Andrey A.

    2014-11-24

    Physical vapor deposited two-dimensional (2D) materials span larger areas compared to exfoliated flakes, but suffer from very small grain or domain sizes. In this letter, we fabricate freestanding molybdenum disulfide (MoS{sub 2}) and amorphous boron nitride (BN) specimens to expose both surfaces. We performed in situ heating in a transmission electron microscope to observe the domain restructuring in real time. The freestanding MoS{sub 2} specimens showed up to 100× increase in domain size, while the amorphous BN transformed in to polycrystalline hexagonal BN (h-BN) at temperatures around 600 °C much lower than the 850–1000 °C range cited in the literature.

  11. Dispersion-free continuum two-dimensional electronic spectrometer.

    PubMed

    Zheng, Haibin; Caram, Justin R; Dahlberg, Peter D; Rolczynski, Brian S; Viswanathan, Subha; Dolzhnikov, Dmitriy S; Khadivi, Amir; Talapin, Dmitri V; Engel, Gregory S

    2014-03-20

    Electronic dynamics span broad energy scales with ultrafast time constants in the condensed phase. Two-dimensional (2D) electronic spectroscopy permits the study of these dynamics with simultaneous resolution in both frequency and time. In practice, this technique is sensitive to changes in nonlinear dispersion in the laser pulses as time delays are varied during the experiment. We have developed a 2D spectrometer that uses broadband continuum generated in argon as the light source. Using this visible light in phase-sensitive optical experiments presents new challenges in implementation. We demonstrate all-reflective interferometric delays using angled stages. Upon selecting an ~180  nm window of the available bandwidth at ~10  fs compression, we probe the nonlinear response of broadly absorbing CdSe quantum dots and electronic transitions of Chlorophyll a.

  12. Pressure Gradient Effects On Two-Dimensional Plasma Expansion

    SciTech Connect

    Moon, S; Smith, R F; Dunn, J; Keenan, R; Nilsen, J; Hunter, J R; Filevich, J; Rocca, J J; Marconi, M C; Shlyaptsev, V N

    2004-10-05

    Recent advances in interferometry has allowed for the characterization of the electron density expansion within a laser produced plasma to within 10 {micro}m of the target surface and over picosecond timescales. This technique employs the high brightness output of the transient gain Ni-like Pd collisional x-ray laser at 14.7 nm to construct an effective moving picture of the two-dimensional (2-D) expansion of the plasma. We present experimentally measured density profiles of an expanding Al plasma generated through laser irradiation in a 14mm line focus geometry. Significant lateral expansion was observed at all times as well as a pronounced on-axis electron density dip. Detailed modeling with a 2-D plasma physics code gives good agreement to experimental observations. Large pressure gradients associated with the tight focal spot conditions are calculated to dominate in shaping the plasma density profile.

  13. Statistical entropy of charged two-dimensional black holes

    NASA Astrophysics Data System (ADS)

    Teo, Edward

    1998-06-01

    The statistical entropy of a five-dimensional black hole in Type II string theory was recently derived by showing that it is U-dual to the three-dimensional Bañados-Teitelboim-Zanelli black hole, and using Carlip's method to count the microstates of the latter. This is valid even for the non-extremal case, unlike the derivation which relies on D-brane techniques. In this letter, I shall exploit the U-duality that exists between the five-dimensional black hole and the two-dimensional charged black hole of McGuigan, Nappi and Yost, to microscopically compute the entropy of the latter. It is shown that this result agrees with previous calculations using thermodynamic arguments.

  14. The Two Dimensional Euler Equations on Singular Exterior Domains

    NASA Astrophysics Data System (ADS)

    Gérard-Varet, David; Lacave, Christophe

    2015-12-01

    This paper is a follow-up of Gérard-Varet and Lacave (Arch Ration Mech Anal 209(1):131-170, 2013), on the existence of global weak solutions to the two dimensional Euler equations in singular domains. In Gérard-Varet and Lacave (Arch Ration Mech Anal 209(1):131-170, 2013), we have established the existence of weak solutions for a large class of bounded domains, with initial vorticity in L p ( p > 1). For unbounded domains, we have proved a similar result only when the initial vorticity is in {Lpc} ( p > 2) and when the domain is the exterior of a single obstacle. The goal here is to retrieve these two restrictions: we consider general initial vorticity in {L1 {\\cap} Lp} ( p > 1), outside an arbitrary number of obstacles (not reduced to points).

  15. On dynamical behaviour of two-dimensional biological reactors

    NASA Astrophysics Data System (ADS)

    Lara-Cisneros, Gerardo; Femat, Ricardo; Pérez, Elías

    2012-03-01

    The dynamical behaviour for a generic two-dimensional model of a continuous bioreactor is studied in this article. The state variables for the bio-reacting system are restricted to concentrations of substrate and biomass, where the specific growth rate is a smooth function of the substrate concentration, which can be a kinetic function, monotone or non-monotone (as Monod, Haldane, Teissier, etc.). The effect of input (dilution rate) on multiplicity and bifurcation of equilibrium is shown in open-loop configuration. The absence of limit cycles on open-loop configuration and through state-feedback on the dilution rate are demonstrated. The aim of analysing oscillations under state feedback control is related to the possible improvement of reactor yields under this operation regime. An example for a cell-producing bioreactor illustrates the analytical results.

  16. Two Dimensional Antiferromagnetic Chern Insulator: NiRuCl6

    NASA Astrophysics Data System (ADS)

    Zhou, P.; Sun, C. Q.; Sun, L. Z.

    2016-10-01

    Based on DFT and Berry curvature calculations, we predict that quantum anomalous hall effect (QAHE) can be realized in two dimensional anti-ferromagnetic (AFM) NiRuCl6 with zero net magnetic moment. By tuning spin-orbits coupling (SOC), we find that the topological properties of NiRuCl6 come from its energy band reversal. The results indicate that NiRuCl6 behaves as AFM Chern insulator and its spin-polarized electronic structure and strong spin-orbits coupling (SOC) are the origin of QAHE. Considering the compatibility between AFM and insulator, AFM Chern insulator is more suitable to realize high temperature QAHE because generally Neel temperature of AFM systems is more easily improved than Curie temperature of ferromagnetic (FM) systems. Due to the different magnetic coupling mechanism between FM and AFM Chern insulator, AFM Chern insulator provides a new way to archive high temperature QAHE in experiments.

  17. Equation of State of the Two-Dimensional Hubbard Model

    NASA Astrophysics Data System (ADS)

    Cocchi, Eugenio; Miller, Luke A.; Drewes, Jan H.; Koschorreck, Marco; Pertot, Daniel; Brennecke, Ferdinand; Köhl, Michael

    2016-04-01

    The subtle interplay between kinetic energy, interactions, and dimensionality challenges our comprehension of strongly correlated physics observed, for example, in the solid state. In this quest, the Hubbard model has emerged as a conceptually simple, yet rich model describing such physics. Here we present an experimental determination of the equation of state of the repulsive two-dimensional Hubbard model over a broad range of interactions 0 ≲U /t ≲20 and temperatures, down to kBT /t =0.63 (2 ) using high-resolution imaging of ultracold fermionic atoms in optical lattices. We show density profiles, compressibilities, and double occupancies over the whole doping range, and, hence, our results constitute benchmarks for state-of-the-art theoretical approaches.

  18. Extended quantum jump description of vibronic two-dimensional spectroscopy

    SciTech Connect

    Albert, Julian; Falge, Mirjam; Keß, Martin; Wehner, Johannes G.; Engel, Volker; Zhang, Pan-Pan; Eisfeld, Alexander

    2015-06-07

    We calculate two-dimensional (2D) vibronic spectra for a model system involving two electronic molecular states. The influence of a bath is simulated using a quantum-jump approach. We use a method introduced by Makarov and Metiu [J. Chem. Phys. 111, 10126 (1999)] which includes an explicit treatment of dephasing. In this way it is possible to characterize the influence of dissipation and dephasing on the 2D-spectra, using a wave function based method. The latter scales with the number of stochastic runs and the number of system eigenstates included in the expansion of the wave-packets to be propagated with the stochastic method and provides an efficient method for the calculation of the 2D-spectra.

  19. Flat Chern band in a two-dimensional organometallic framework.

    PubMed

    Liu, Zheng; Wang, Zheng-Fei; Mei, Jia-Wei; Wu, Yong-Shi; Liu, Feng

    2013-03-01

    By combining exotic band dispersion with nontrivial band topology, an interesting type of band structure, namely, the flat Chern band, has recently been proposed to spawn high-temperature fractional quantum Hall states. Despite the proposal of several theoretical lattice models, however, it remains doubtful whether such a "romance of flatland" could exist in a real material. Here, we present a first-principles design of a two-dimensional indium-phenylene organometallic framework that realizes a nearly flat Chern band right around the Fermi level by combining lattice geometry, spin-orbit coupling, and ferromagnetism. An effective four-band model is constructed to reproduce the first-principles results. Our design, in addition, provides a general strategy to synthesize topologically nontrivial materials by virtue of organic chemistry and nanotechnology. PMID:23521279

  20. Electromagnetic two-dimensional analysis of trapped-ion eigenmodes

    SciTech Connect

    Kim, D.; Rewoldt, G.

    1984-11-01

    A two-dimensional electromagnetic analysis of the trapped-ion instability for the tokamak case with ..beta.. not equal to 0 has been made, based on previous work in the electrostatic limit. The quasineutrality condition and the component of Ampere's law along the equilibrium magnetic field are solved for the perturbed electrostatic potential and the component of the perturbed vector potential along the equilibrium magnetic field. The general integro-differential equations are converted into a matrix eigenvalue-eigenfunction problem by expanding in cubic B-spline finite elements in the minor radius and in Fourier harmonics in the poloidal angle. A model MHD equilibrium with circular, concentric magnetic surfaces and large aspect ratio is used which is consistent with our assemption that B << 1. The effect on the trapped-ion mode of including these electromagnetic extensions to the calculation is considered, and the temperature (and ..beta..) scaling of the mode frequency is shown and discussed.

  1. Analytic Solution of a Two-Dimensional Hydrogen Atom

    NASA Astrophysics Data System (ADS)

    Yang, Xiao-Li.

    1990-03-01

    The two dimensional hydrogen atom problem is solved analytically in both the relativistic and non-relativistic cases. In the nonrelativistic case, exact formulae for energy eigenvalues and eigenfunctions for both the discrete and continuous parts of the spectrum, dipole matrix elements, DC Stark effect, single- and two-photon transition rate, fine and hyperfine structures are obtained. The binding energy of the ground state is found to be reduced by a factor of four from that of a three dimensional hydrogen atom. In the relativistic case, exact analytic expressions for discrete eigen energy and normalized eigen wave function are derived. It is shown that the solution to the Dirac equation is disjoint in the spin-coordinate space (four -component spinor) in contrast to the three dimensional counterpart. This surprising result is a consequence of the planar motion of the electron.

  2. Enstrophy cascades in two-dimensional dense granular flows

    NASA Astrophysics Data System (ADS)

    Saitoh, Kuniyasu; Mizuno, Hideyuki

    2016-08-01

    Employing two-dimensional molecular dynamics simulations of dense granular materials under simple shear deformations, we investigate vortex structures of particle rearrangements. Introducing vorticity fields as a measure of local spinning motions of the particles, we observe their heterogeneous distributions, where statistics of vorticity fields exhibit the highly non-Gaussian behavior and typical domain sizes of vorticity fields significantly increase if the system is yielding under quasistatic deformations. In such dense granular flows, a power-law decay of vorticity spectra can be observed at mesoscopic scale, implying anomalous local structures of kinetic energy dissipation. We explain the power-law decay, or enstrophy cascades in dense granular materials, by a dimensional analysis, where the dependence of vorticity spectra not only on the wave number, but also on the shear rate, is well explained. From our dimensional analyses, the scaling of granular temperature and rotational kinetic energy is also predicted.

  3. Random diffusion and cooperation in continuous two-dimensional space.

    PubMed

    Antonioni, Alberto; Tomassini, Marco; Buesser, Pierre

    2014-03-01

    This work presents a systematic study of population games of the Prisoner's Dilemma, Hawk-Dove, and Stag Hunt types in two-dimensional Euclidean space under two-person, one-shot game-theoretic interactions, and in the presence of agent random mobility. The goal is to investigate whether cooperation can evolve and be stable when agents can move randomly in continuous space. When the agents all have the same constant velocity cooperation may evolve if the agents update their strategies imitating the most successful neighbor. If a fitness difference proportional is used instead, cooperation does not improve with respect to the static random geometric graph case. When viscosity effects set-in and agent velocity becomes a quickly decreasing function of the number of neighbors they have, one observes the formation of monomorphic stable clusters of cooperators or defectors in the Prisoner's Dilemma. However, cooperation does not spread in the population as in the constant velocity case.

  4. Negative Magnetoresistance in Viscous Flow of Two-Dimensional Electrons

    NASA Astrophysics Data System (ADS)

    Alekseev, P. S.

    2016-10-01

    At low temperatures, in very clean two-dimensional (2D) samples, the electron mean free path for collisions with static defects and phonons becomes greater than the sample width. Under this condition, the electron transport occurs by formation of a viscous flow of an electron fluid. We study the viscous flow of 2D electrons in a magnetic field perpendicular to the 2D layer. We calculate the viscosity coefficients as the functions of magnetic field and temperature. The off-diagonal viscosity coefficient determines the dispersion of the 2D hydrodynamic waves. The decrease of the diagonal viscosity in magnetic field leads to negative magnetoresistance which is temperature and size dependent. Our analysis demonstrates that this viscous mechanism is responsible for the giant negative magnetoresistance recently observed in the ultrahigh-mobility GaAs quantum wells. We conclude that 2D electrons in those structures in moderate magnetic fields should be treated as a viscous fluid.

  5. Two-Dimensional Hexagonal Transition-Metal Oxide for Spintronics.

    PubMed

    Kan, Erjun; Li, Ming; Hu, Shuanglin; Xiao, Chuanyun; Xiang, Hongjun; Deng, Kaiming

    2013-04-01

    Two-dimensional materials have been the hot subject of studies due to their great potential in applications. However, their applications in spintronics have been blocked by the difficulty in producing ordered spin structures in 2D structures. Here we demonstrated that the ultrathin films of recently experimentally realized wurtzite MnO can automatically transform into a stable graphitic structure with ordered spin arrangement via density functional calculation, and the stability of graphitic structure can be enhanced by external strain. Moreover, the antiferromagnetic ordering of graphitic MnO single layer can be switched into half-metallic ferromagnetism by small hole-doping, and the estimated Curie temperature is higher than 300 K. Thus, our results highlight a promising way toward 2D magnetic materials.

  6. Nonlinear screening in large two-dimensional Coulomb clusters.

    PubMed

    Kong, Minghui; Vagov, A; Partoens, B; Peeters, F M; Ferreira, W P; Farias, G A

    2004-11-01

    The distortion due to a fixed point impurity with variable charge placed in the center of a classical harmonically confined two-dimensional (2D) large Coulomb cluster is studied. We find that the net topological charge (N(-)-N+ ) of the system is always equal to six independent of the position and charge of the impurity. In comparison with a 2D cluster without impurity charge, only the breathing mode remains unchanged. The screening length is found to be a highly nonlinear function of the impurity charge. For values of the impurity charge smaller than the charge of the other particles, the system has almost the same screening strength. When the impurity charge is larger, the screening length is strongly enhanced. This result can be explained by the competition between the different forces active in the system.

  7. Nonlinear screening in large two-dimensional Coulomb clusters

    SciTech Connect

    Kong, Minghui; Vagov, A.; Partoens, B.; Peeters, F.M.; Ferreira, W.P.; Farias, G.A.

    2004-11-01

    The distortion due to a fixed point impurity with variable charge placed in the center of a classical harmonically confined two-dimensional (2D) large Coulomb cluster is studied. We find that the net topological charge (N{sub -}-N{sub +}) of the system is always equal to six independent of the position and charge of the impurity. In comparison with a 2D cluster without impurity charge, only the breathing mode remains unchanged. The screening length is found to be a highly nonlinear function of the impurity charge. For values of the impurity charge smaller than the charge of the other particles, the system has almost the same screening strength. When the impurity charge is larger, the screening length is strongly enhanced. This result can be explained by the competition between the different forces active in the system.

  8. Plasmon excitations in two-dimensional atomic cluster systems

    NASA Astrophysics Data System (ADS)

    Yu, Yan-Qin; Yu, Ya-Bin; Xue, Hong-Jie; Wang, Ya-Xin; Chen, Jie

    2016-09-01

    Properties of plasmon excitations in two-dimensional (2D) atomic cluster systems are theoretically studied within an extended Hubbard model. The collective oscillation equations of charge, plasmon eigen-equations and the energy-absorption spectrum formula are presented. The calculated results show that different symmetries of plasmons exist in the cluster systems, and the symmetry of charge distribution in the plasmon resonance originate from the intrinsic symmetry of the corresponding eigen-plasmon modes, but not from the symmetry of applied external fields; however, the plasmon excitation with a certain polarization direction should be excited by the field in this direction, the dipole mode of plasmons can be excited by both uniform and non-uniform fields, but multipole ones cannot be excited by an uniform field. In addition, we show that for a given electron density, plasmon spectra are red-shifted with increasing size of the systems.

  9. Two-Dimensional Massless Light Front Fields and Solvable Models

    NASA Astrophysics Data System (ADS)

    Martinovic̆, L'ubomír; Grangé, Pierre

    2016-07-01

    Quantum field theory formulated in terms of light front (LF) variables has a few attractive as well as some puzzling features. The latter hindered a wider acceptance of LF methods. In two space-time dimensions, it has been a long-standing puzzle how to correctly quantize massless fields, in particular fermions. Here we show that two-dimensional massless LF fields (scalar and fermion) can be recovered in a simple way as limits of the corresponding massive fields and thereby quantized without any loss of physical information. Bosonization of the fermion field then follows in a straightforward manner and the solvable models can be studied directly in the LF theory. We sketch the LF operator solution of the Thirring-Wess model and also point out the closeness of the massless LF fields to those of conformal field theory.

  10. Extended quantum jump description of vibronic two-dimensional spectroscopy.

    PubMed

    Albert, Julian; Falge, Mirjam; Keß, Martin; Wehner, Johannes G; Zhang, Pan-Pan; Eisfeld, Alexander; Engel, Volker

    2015-06-01

    We calculate two-dimensional (2D) vibronic spectra for a model system involving two electronic molecular states. The influence of a bath is simulated using a quantum-jump approach. We use a method introduced by Makarov and Metiu [J. Chem. Phys. 111, 10126 (1999)] which includes an explicit treatment of dephasing. In this way it is possible to characterize the influence of dissipation and dephasing on the 2D-spectra, using a wave function based method. The latter scales with the number of stochastic runs and the number of system eigenstates included in the expansion of the wave-packets to be propagated with the stochastic method and provides an efficient method for the calculation of the 2D-spectra. PMID:26049460

  11. Microwave near-field imaging of two-dimensional semiconductors.

    PubMed

    Berweger, Samuel; Weber, Joel C; John, Jimmy; Velazquez, Jesus M; Pieterick, Adam; Sanford, Norman A; Davydov, Albert V; Brunschwig, Bruce; Lewis, Nathan S; Wallis, Thomas M; Kabos, Pavel

    2015-02-11

    Optimizing new generations of two-dimensional devices based on van der Waals materials will require techniques capable of measuring variations in electronic properties in situ and with nanometer spatial resolution. We perform scanning microwave microscopy (SMM) imaging of single layers of MoS2 and n- and p-doped WSe2. By controlling the sample charge carrier concentration through the applied tip bias, we are able to reversibly control and optimize the SMM contrast to image variations in electronic structure and the localized effects of surface contaminants. By further performing tip bias-dependent point spectroscopy together with finite element simulations, we distinguish the effects of the quantum capacitance and determine the local dominant charge carrier species and dopant concentration. These results underscore the capability of SMM for the study of 2D materials to image, identify, and study electronic defects.

  12. Enstrophy cascades in two-dimensional dense granular flows.

    PubMed

    Saitoh, Kuniyasu; Mizuno, Hideyuki

    2016-08-01

    Employing two-dimensional molecular dynamics simulations of dense granular materials under simple shear deformations, we investigate vortex structures of particle rearrangements. Introducing vorticity fields as a measure of local spinning motions of the particles, we observe their heterogeneous distributions, where statistics of vorticity fields exhibit the highly non-Gaussian behavior and typical domain sizes of vorticity fields significantly increase if the system is yielding under quasistatic deformations. In such dense granular flows, a power-law decay of vorticity spectra can be observed at mesoscopic scale, implying anomalous local structures of kinetic energy dissipation. We explain the power-law decay, or enstrophy cascades in dense granular materials, by a dimensional analysis, where the dependence of vorticity spectra not only on the wave number, but also on the shear rate, is well explained. From our dimensional analyses, the scaling of granular temperature and rotational kinetic energy is also predicted. PMID:27627381

  13. Path planning in a two-dimensional environment

    NASA Astrophysics Data System (ADS)

    Fox, Richard K.; Garcia, Antonio, Jr.; Nelson, Michael L.

    1999-07-01

    This paper presents a path planning algorithm that is part of the STESCA control architecture for autonomous vehicles. The path planning algorithm models an autonomous vehicle's path as a series of line segments in Cartesian space and compares each line segment to a list of known obstacles and hazardous areas to determine if any collisions or hindrances exist. In the event of a detected collision, the algorithm selects a point outside the obstacle or hazardous area, generates two new path segments that avoid the obstruction and recursively checks the new paths for other collisions. Once underway, if the autonomous vehicle encounters previously unknown obstacles or hazardous areas, the path planner operates in a run-time mode that decides how to re-route the path around the obstacle or abort. This paper describes the path planner along with examples of path planning in a two-dimensional environment with a wheeled land-based robotic vehicle.

  14. Inhomogeneous two-dimensional photonic media: A statistical study

    NASA Astrophysics Data System (ADS)

    Bellingeri, M.; Tenca, E.; Scotognella, F.

    2012-10-01

    Photonic media, in which disorder is introduced, are interesting materials for light management. In this paper, we have performed a statistical study of the average light transmission, over the range of wavelengths 450-1400 nm, for two-dimensional photonic structures with different homogeneity (quantified by the Shannon index). The photonic structure is a square lattice of circular pillars and the homogeneity is varied by clustering pillars in the crystal unit cells. We have calculated the light transmission for 50 different crystal realizations (permutating cluster position in the crystal) for each Shannon index value. Such Monte Carlo Markov Chain method produced the "a posteriori" distribution of the light transmission. We have observed a linear trend of the average transmission as a function of the crystal homogeneity. Furthermore, we have found a linear dependence of the average light transmission on the mean distance between pillars in the photonic structures.

  15. Spontaneous supersymmetry breaking in two dimensional lattice super QCD

    SciTech Connect

    Catterall, Simon; Veernala, Aarti

    2015-10-02

    We report on a non-perturbative study of two dimensional N=(2,2) super QCD. Our lattice formulation retains a single exact supersymmetry at non-zero lattice spacing, and contains Nf fermions in the fundamental representation of a U(Nc) gauge group. The lattice action we employ contains an additional Fayet-Iliopoulos term which is also invariant under the exact lattice supersymmetry. This work constitutes the first numerical study of this theory which serves as a toy model for understanding some of the issues that are expected to arise in four dimensional super QCD. As a result, we present evidence that the exact supersymmetry breaks spontaneously when Nf < Nc in agreement with theoretical expectations.

  16. Ultrabroadband two-quantum two-dimensional electronic spectroscopy

    NASA Astrophysics Data System (ADS)

    Gellen, Tobias A.; Bizimana, Laurie A.; Carbery, William P.; Breen, Ilana; Turner, Daniel B.

    2016-08-01

    A recent theoretical study proposed that two-quantum (2Q) two-dimensional (2D) electronic spectroscopy should be a background-free probe of post-Hartree-Fock electronic correlations. Testing this theoretical prediction requires an instrument capable of not only detecting multiple transitions among molecular excited states but also distinguishing molecular 2Q signals from nonresonant response. Herein we describe a 2Q 2D spectrometer with a spectral range of 300 nm that is passively phase stable and uses only beamsplitters and mirrors. We developed and implemented a dual-chopping balanced-detection method to resolve the weak molecular 2Q signals. Experiments performed on cresyl violet perchlorate and rhodamine 6G revealed distinct 2Q signals convolved with nonresonant response. Density functional theory computations helped reveal the molecular origin of these signals. The experimental and computational results demonstrate that 2Q electronic spectra can provide a singular probe of highly excited electronic states.

  17. Approaches to verification of two-dimensional water quality models

    SciTech Connect

    Butkus, S.R. . Water Quality Dept.)

    1990-11-01

    The verification of a water quality model is the one procedure most needed by decision making evaluating a model predictions, but is often not adequate or done at all. The results of a properly conducted verification provide the decision makers with an estimate of the uncertainty associated with model predictions. Several statistical tests are available for quantifying of the performance of a model. Six methods of verification were evaluated using an application of the BETTER two-dimensional water quality model for Chickamauga reservoir. Model predictions for ten state variables were compared to observed conditions from 1989. Spatial distributions of the verification measures showed the model predictions were generally adequate, except at a few specific locations in the reservoir. The most useful statistics were the mean standard error of the residuals. Quantifiable measures of model performance should be calculated during calibration and verification of future applications of the BETTER model. 25 refs., 5 figs., 7 tabs.

  18. Electrical resistance of complex two-dimensional structures of loops

    NASA Astrophysics Data System (ADS)

    Gomes, M. A. F.; Hora, R. R.; Brito, V. P.

    2011-06-01

    This work presents a study of the dc electrical resistance of a recently discovered hierarchical two-dimensional system which has a complex topology consisting of a distribution of disordered macroscopic loops with no characteristic size and a distribution of several types of contacts between loops. In addition to its intrinsic interest in the important context of low-dimensional systems and crumpled systems, the structures under study are of relevance in a number of areas including soft condensed matter and packing of DNA in viral capsids. In the particular case discussed here, the loops are made of layers of graphite with a height of tens of nanometers deposited on a substrate of cellulose. Experiments with these systems indicate an anomalous electrical resistance of sub-diffusive type. The results reported here are explained with scaling arguments and computer simulation. A comparison with the dc electrical properties of percolation clusters is made, and some other experimental issues as future prospects are commented.

  19. Nonlinear compressional waves in a two-dimensional Yukawa lattice.

    PubMed

    Avinash, K; Zhu, P; Nosenko, V; Goree, J

    2003-10-01

    A modified Korteweg-de Vries (KdV) equation is obtained for studying the propagation of nonlinear compressional waves and pulses in a chain of particles including the effect of damping. Suitably altering the linear phase velocity makes this equation useful also for the problem of phonon propagation in a two-dimensional (2D) lattice. Assuming a Yukawa potential, we use this method to model compressional wave propagation in a 2D plasma crystal, as in a recent experiment. By integrating the modified KdV equation the pulse is allowed to evolve, and good agreement with the experiment is found. It is shown that the speed of a compressional pulse increases with its amplitude, while the speed of a rarefactive pulse decreases. It is further discussed how the drag due to the background gas has a crucial role in weakening nonlinear effects and preventing the emergence of a soliton. PMID:14683049

  20. Extrinsic spin Nernst effect in two-dimensional electron systems

    NASA Astrophysics Data System (ADS)

    Akera, Hiroshi; Suzuura, Hidekatsu

    2013-02-01

    The spin accumulation due to the spin current induced by the perpendicular temperature gradient (the spin Nernst effect) is studied in a two-dimensional electron system (2DES) with spin-orbit interaction by employing the Boltzmann equation. The considered 2DES is confined within a symmetric quantum well with δ doping at the center of the well. A symmetry consideration leads to the spin-orbit interaction which is diagonal in the spin component perpendicular to the 2DES. As origins of the spin current, the skew scattering and the side jump are considered at each impurity on the center plane of the well. It is shown that, for repulsive impurity potentials, the spin-Nernst coefficient changes its sign at the impurity density where contributions from the skew scattering and the side jump cancel each other out. This is in contrast to the spin Hall effect in which the sign change of the coefficient occurs for attractive impurity potentials.

  1. Two-dimensional and axisymmetric bifurcated channel flow

    NASA Astrophysics Data System (ADS)

    Goldman, A.

    1981-10-01

    Flow characteristics within the turbofan engine passageway for arbitrary geometries over a range of Reynolds numbers (1350 to 750,000) are determined by constructing a numerical model capable of handling irregularly shaped flow regions with laminar or turbulent flow. This is accomplished by using a vorticity-stream function formulation of the governing equations for two-dimensional and axisymmetrical flows with a two-equation eddy viscosity model for turbulence closure. A body-fitted coordinate system (Chu, 1971; Amsden and Hirt, 1973; Thompson et al., 1974) is used to treat the arbitrary geomtry. All equations are solved using finite-difference techniques (Goldman, 1980). Conclusions are presented, including: first-order terms must be separately upwind differenced to form stable solutions, regardless of whether the term is a true velocity term of a geometrically generated term created by the transformation.

  2. Nonlinear optical response of a two-dimensional atomic crystal.

    PubMed

    Merano, Michele

    2016-01-01

    The theory of Bloembergen and Pershan for the light waves at the boundary of nonlinear media is extended to a nonlinear two-dimensional (2D) atomic crystal, i.e., a single planar atomic lattice, placed between linear bulk media. The crystal is treated as a zero-thickness interface, a real 2D system. Harmonic waves emanate from it. Generalization of the laws of reflection and refraction give the direction and the intensity of the harmonic waves. As a particular case that contains all the essential physical features, second-order harmonic generation is considered. The theory, due to its simplicity that stems from the special character of a single planar atomic lattice, is able to elucidate and explain the rich experimental details of harmonic generation from a 2D atomic crystal.

  3. Finite volume model for two-dimensional shallow environmental flow

    USGS Publications Warehouse

    Simoes, F.J.M.

    2011-01-01

    This paper presents the development of a two-dimensional, depth integrated, unsteady, free-surface model based on the shallow water equations. The development was motivated by the desire of balancing computational efficiency and accuracy by selective and conjunctive use of different numerical techniques. The base framework of the discrete model uses Godunov methods on unstructured triangular grids, but the solution technique emphasizes the use of a high-resolution Riemann solver where needed, switching to a simpler and computationally more efficient upwind finite volume technique in the smooth regions of the flow. Explicit time marching is accomplished with strong stability preserving Runge-Kutta methods, with additional acceleration techniques for steady-state computations. A simplified mass-preserving algorithm is used to deal with wet/dry fronts. Application of the model is made to several benchmark cases that show the interplay of the diverse solution techniques.

  4. Nonlinear plasmonics in a two-dimensional plasma layer

    NASA Astrophysics Data System (ADS)

    Eliasson, Bengt; Liu, Chuan Sheng

    2016-05-01

    The nonlinear electron dynamics in a two-dimensional (2D) plasma layer are investigated theoretically and numerically. In contrast to the Langmuir oscillations in a three-dimensional (3D) plasma, a well-known feature of the 2D system is the square root dependence of the frequency on the wavenumber, which leads to unique dispersive properties of 2D plasmons. It is found that for large amplitude plasmonic waves there is a nonlinear frequency upshift similar to that of periodic gravity waves (Stokes waves). The periodic wave train is subject to a modulational instability, leading to sidebands growing exponentially in time. Numerical simulations show the breakup of a 2D wave train into localized wave packets and later into wave turbulence with immersed large amplitude solitary spikes. The results are applied to systems involving massless Dirac fermions in graphene as well as to sheets of electrons on liquid helium.

  5. Two-dimensional atom localization induced by a squeezed vacuum

    NASA Astrophysics Data System (ADS)

    Wang, Fei; Xu, Jun

    2016-10-01

    A scheme of two-dimensional (2D) atom localization induced by a squeezed vacuum is proposed, in which the three-level V-type atoms interact with two classical standing-wave fields. It is found that when the environment is changed from an ordinary vacuum to a squeezed vacuum, the 2D atom localization is realized by detecting the position-dependent resonance fluorescence spectrum. For comparison, we demonstrate that the atom localization originating from the quantum interference effect is distinct from that induced by a squeezed vacuum. Furthermore, the combined effects of the squeezed vacuum and quantum interference are also discussed under appropriate conditions. The internal physical mechanism is analyzed in terms of dressed-state representation. Project supported by the National Natural Science Foundation of China (Grant Nos. 11574179 and 11204099) and the Natural Science Foundation of Hubei Province, China (Grant No. 2014CFC1148).

  6. Two-dimensional soft nanomaterials: a fascinating world of materials.

    PubMed

    Zhuang, Xiaodong; Mai, Yiyong; Wu, Dongqing; Zhang, Fan; Feng, Xinliang

    2015-01-21

    The discovery of graphene has triggered great interest in two-dimensional (2D) nanomaterials for scientists in chemistry, physics, materials science, and related areas. In the family of newly developed 2D nanostructured materials, 2D soft nanomaterials, including graphene, Bx Cy Nz nanosheets, 2D polymers, covalent organic frameworks (COFs), and 2D supramolecular organic nanostructures, possess great advantages in light-weight, structural control and flexibility, diversity of fabrication approaches, and so on. These merits offer 2D soft nanomaterials a wide range of potential applications, such as in optoelectronics, membranes, energy storage and conversion, catalysis, sensing, biotechnology, etc. This review article provides an overview of the development of 2D soft nanomaterials, with special highlights on the basic concepts, molecular design principles, and primary synthesis approaches in the context.

  7. Two-dimensional colloidal mixtures in magnetic and gravitational fields

    NASA Astrophysics Data System (ADS)

    Löwen, H.; Horn, T.; Neuhaus, T.; ten Hagen, B.

    2013-11-01

    This mini-review is concerned with two-dimensional colloidal mixtures exposed to various kinds of external fields. By a magnetic field perpendicular to the plane, dipole moments are induced in paramagnetic particles which give rise to repulsive interactions leading to complex crystalline alloys in the composition-asymmetry diagram. A quench in the magnetic field induces complex crystal nucleation scenarios. If exposed to a gravitational field, these mixtures exhibit a brazil-nut effect and show a boundary layering which is explained in terms of a depletion bubble picture. The latter persists for time-dependent gravity ("colloidal shaking"). Finally, we summarize crystallization effects when the second species is frozen in a disordered matrix which provides obstacles for the crystallizing component.

  8. Two-Dimensional Quantum Model of a Nanotransistor

    NASA Technical Reports Server (NTRS)

    Govindan, T. R.; Biegel, B.; Svizhenko, A.; Anantram, M. P.

    2009-01-01

    A mathematical model, and software to implement the model, have been devised to enable numerical simulation of the transport of electric charge in, and the resulting electrical performance characteristics of, a nanotransistor [in particular, a metal oxide/semiconductor field-effect transistor (MOSFET) having a channel length of the order of tens of nanometers] in which the overall device geometry, including the doping profiles and the injection of charge from the source, gate, and drain contacts, are approximated as being two-dimensional. The model and software constitute a computational framework for quantitatively exploring such device-physics issues as those of source-drain and gate leakage currents, drain-induced barrier lowering, and threshold voltage shift due to quantization. The model and software can also be used as means of studying the accuracy of quantum corrections to other semiclassical models.

  9. Synchronization of Coupled Oscillators on a Two-Dimensional Plane.

    PubMed

    Guo, Dameng; Fu, Yong Qing; Zheng, Bo

    2016-08-01

    The effect of the transfer rate of signal molecules on coupled chemical oscillators arranged on a two-dimensional plane was systematically investigated in this paper. A microreactor equipped with a surface acoustic wave (SAW) mixer was applied to adjust the transfer rate of the signal molecules in the microreactor. The SAW mixer with adjustable input powers provided a simple means to generate different mixing rates in the microreactor. A robust synchronization of the oscillators was found at an input radio frequency power of 20 dBm, with which the chemical waves were initiated at a fixed site of the oscillator system. With increasing input power, the frequency of the chemical waves was increased, which agreed well with the prediction given by the time-delayed phase oscillator model. Results from the finite element simulation agreed well with the experimental results.

  10. Domain engineering of physical vapor deposited two-dimensional materials

    NASA Astrophysics Data System (ADS)

    Alam, Tarek; Wang, Baoming; Pulavarthy, Raghu; Haque, M. A.; Muratore, Christopher; Glavin, Nicholas; Roy, Ajit K.; Voevodin, Andrey A.

    2014-11-01

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

  11. Local diamagnetic susceptibility of quasi-two-dimensional graphite

    SciTech Connect

    Nikolaev, E. G.; Kotosonov, A. S.; Shalashugina, E. A.; Troyanovskii, A. M.; Tsebro, V. I.

    2013-08-15

    A sample of quasi-two-dimensional graphite (QTDG) whose magnetic properties are described within the Dirac fermion model is investigated by the nuclear magnetic resonance (NMR) and scanning tunneling microscopy (STM) techniques. The broad spectrum of the sample points to a large dispersion of crystallite sizes in this system, which is also confirmed by STM data. It is established that the local diamagnetic susceptibility may substantially exceed the average value over the sample and reaches an abnormally high value of -1.3 Multiplication-Sign 10{sup -4} emu/g at T = 4.2 K, which is greater than the corresponding value of highly oriented graphite by a factor of four.

  12. Dynamics of a Two-Dimensional System of Quantum Dipoles

    SciTech Connect

    Mazzanti, F.; Astrakharchik, G. E.; Boronat, J.; Zillich, R. E.

    2009-03-20

    A detailed microscopic analysis of the dynamic structure function S(k,{omega}) of a two-dimensional Bose system of dipoles polarized along the direction perpendicular to the plane is presented and discussed. Starting from ground-state quantities obtained using a quantum diffusion Monte Carlo algorithm, the density-density response is evaluated in the context of the correlated basis functions (CBF) theory. CBF predicts a sharp peak and a multiexcitation component at higher energies produced by the decay of excitations. We discuss the structure of the phonon-roton peak and show that the Feynman and Bogoliubov predictions depart from the CBF result already at low densities. We finally discuss the emergence of a roton in the spectrum, but find the roton energy not low enough to make the system unstable under density fluctuations up to the highest density considered that is close to the freezing point.

  13. A ballistic two-dimensional-electron-gas Andreev interferometer

    SciTech Connect

    Amado, M. Fornieri, A.; Sorba, L.; Giazotto, F.; Biasiol, G.

    2014-06-16

    We report the realization and investigation of a ballistic Andreev interferometer based on an InAs two dimensional electron gas coupled to a superconducting Nb loop. We observe strong magnetic modulations in the voltage drop across the device due to quasiparticle interference within the weak-link. The interferometer exhibits flux noise down to ∼80 μΦ{sub 0}/√(Hz) and a robust behavior in temperature with voltage oscillations surviving up to ∼7 K. Besides this remarkable performance, the device represents a crucial first step for the realization of a fully-tunable ballistic superconducting magnetometer and embodies a potential advanced platform for the investigation of Majorana bound states, non-local entanglement of Cooper pairs, as well as the manipulation and control of spin triplet correlations.

  14. Two-dimensional heterostructures: fabrication, characterization, and application

    DOE PAGES

    Wang, Hong; Liu, Fucai; Fu, Wei; Fang, Zheyu; Zhou, Wu; Liu, Zheng

    2014-08-13

    Two-dimensional (2D) materials such as graphene, hexagonal boron nitrides (hBN), and transition metal dichalcogenides (TMDs, e.g., MoS2) have attracted considerable attention in the past few years because of their novel properties and versatile potential applications. These 2D layers can be integrated into a monolayer (lateral 2D heterostructure) or a multilayer stack (vertical 2D heterostructure). The resulting artificial 2D structures provide access to new properties and applications beyond their component 2D atomic crystals and hence, they are emerging as a new exciting field of research. Lastly, in this article, we review recent progress on the fabrication, characterization, and applications of variousmore » 2D heterostructures.« less

  15. Two-dimensional heterostructures: fabrication, characterization, and application

    SciTech Connect

    Wang, Hong; Liu, Fucai; Fu, Wei; Fang, Zheyu; Zhou, Wu; Liu, Zheng

    2014-08-13

    Two-dimensional (2D) materials such as graphene, hexagonal boron nitrides (hBN), and transition metal dichalcogenides (TMDs, e.g., MoS2) have attracted considerable attention in the past few years because of their novel properties and versatile potential applications. These 2D layers can be integrated into a monolayer (lateral 2D heterostructure) or a multilayer stack (vertical 2D heterostructure). The resulting artificial 2D structures provide access to new properties and applications beyond their component 2D atomic crystals and hence, they are emerging as a new exciting field of research. Lastly, in this article, we review recent progress on the fabrication, characterization, and applications of various 2D heterostructures.

  16. Superfluid response of two-dimensional parahydrogen clusters in confinement

    SciTech Connect

    Idowu, Saheed; Boninsegni, Massimo

    2015-04-07

    We study by computer simulations the effect of confinement on the superfluid properties of small two-dimensional (2D) parahydrogen clusters. For clusters of fewer than twenty molecules, the superfluid response in the low temperature limit is found to remain comparable in magnitude to that of free clusters, within a rather wide range of depth and size of the confining well. The resilience of the superfluid response is attributable to the “supersolid” character of these clusters. We investigate the possibility of establishing a bulk 2D superfluid “cluster crystal” phase of p-H{sub 2}, in which a global superfluid response would arise from tunnelling of molecules across adjacent unit cells. The computed energetics suggests that for clusters of about ten molecules, such a phase may be thermodynamically stable against the formation of the equilibrium insulating crystal, for values of the cluster crystal lattice constant possibly allowing tunnelling across adjacent unit cells.

  17. Two-Dimensional Integral Combustion for Multiple Phase Flow

    1997-05-05

    This ANL multiphase two-dimensional combustion computer code solves conservation equations for gaseous species and solid particles (or droplets) of various sizes. General conservation laws, expressed by ellipitic-type partial differential equations are used in conjunction with rate equations governing the mass, momentum, enthaply, species, turbulent kinetic energy, and turbulent dissipation for a two-phase reacting flow. Associated submodels include an integral combustion, a two-parameter turbulence, a particle evaporation, and interfacial submodels. A newly-developed integral combustion submodel replacingmore » an Arrhenius-type differential reaction submodel is implemented to improve numerical convergence and enhance numerical stability. The two-parameter turbulence submodel is modified for both gas and solid phases. The evaporation submodel treats size dispersion as well as particle evaporation. Interfacial submodels use correlations to model interfacial momentum and energy transfer.« less

  18. Random diffusion and cooperation in continuous two-dimensional space.

    PubMed

    Antonioni, Alberto; Tomassini, Marco; Buesser, Pierre

    2014-03-01

    This work presents a systematic study of population games of the Prisoner's Dilemma, Hawk-Dove, and Stag Hunt types in two-dimensional Euclidean space under two-person, one-shot game-theoretic interactions, and in the presence of agent random mobility. The goal is to investigate whether cooperation can evolve and be stable when agents can move randomly in continuous space. When the agents all have the same constant velocity cooperation may evolve if the agents update their strategies imitating the most successful neighbor. If a fitness difference proportional is used instead, cooperation does not improve with respect to the static random geometric graph case. When viscosity effects set-in and agent velocity becomes a quickly decreasing function of the number of neighbors they have, one observes the formation of monomorphic stable clusters of cooperators or defectors in the Prisoner's Dilemma. However, cooperation does not spread in the population as in the constant velocity case. PMID:24316109

  19. Crossed Andreev effects in two-dimensional quantum Hall systems

    NASA Astrophysics Data System (ADS)

    Hou, Zhe; Xing, Yanxia; Guo, Ai-Min; Sun, Qing-Feng

    2016-08-01

    We study the crossed Andreev effects in two-dimensional conductor/superconductor hybrid systems under a perpendicular magnetic field. Both a graphene/superconductor hybrid system and an electron gas/superconductor one are considered. It is shown that an exclusive crossed Andreev reflection, with other Andreev reflections being completely suppressed, is obtained in a high magnetic field because of the chiral edge states in the quantum Hall regime. Importantly, the exclusive crossed Andreev reflection not only holds for a wide range of system parameters, e.g., the size of system, the width of central superconductor, and the quality of coupling between the graphene and the superconductor, but also is very robust against disorder. When the applied bias is within the superconductor gap, a robust Cooper-pair splitting process with high-efficiency can be realized in this system.

  20. Two dimensional WS2 lateral heterojunctions by strain modulation

    NASA Astrophysics Data System (ADS)

    Meng, Lan; Zhang, Yuhan; Hu, Song; Wang, Xiangfu; Liu, Chunsheng; Guo, Yandong; Wang, Xinran; Yan, Xiaohong

    2016-06-01

    "Strain engineering" has been widely used to tailor the physical properties of layered materials, like graphene, black phosphorus, and transition-metal dichalcogenides. Here, we exploit thermal strain engineering to construct two dimensional (2D) WS2 in-plane heterojunctions. Kelvin probe force microscopy is used to investigate the surface potentials and work functions of few-layer WS2 flakes, which are grown on SiO2/Si substrates by chemical vapor deposition, followed by a fast cooling process. In the interior regions of strained WS2 flakes, work functions are found to be much larger than that of the unstrained regions. The difference in work functions, together with the variation of band gaps, endows the formation of heterojunctions in the boundaries between inner and outer domains of WS2 flakes. This result reveals that the existence of strain offers a unique opportunity to modulate the electronic properties of 2D materials and construct 2D lateral heterojunctions.

  1. Modeling complexly magnetized two-dimensional bodies of arbitrary shape

    SciTech Connect

    Mariano, J.; Hinze, W.J. . Dept. of Earth and Atmospheric Sciences)

    1993-05-01

    A method has been devised for the forward computation of magnetic anomalies due to two-dimensional (2-D) polygonal bodies with heterogeneously directed magnetization. The calculations are based on the equivalent line source approach wherein the source is subdivided into discrete elements that vary spatially in their magnetic properties. This equivalent dipole line method provides a fast and convenient means of representing and computing magnetic anomalies for bodies possessing complexly varying magnitude and direction of magnetization. The algorithm has been tested and applied to several generalized cases to verify the accuracy of the computation. The technique has also been used to model observed aeromagnetic anomalies associated with the structurally deformed, remanently magnetized Keweenawan volcanic rocks in eastern Lake Superior. This method is also easily adapted to the calculation of anomalies due to two and one-half-dimensional (2.5-D) and three-dimensional (3-D) heterogeneously magnetized sources.

  2. Dynamic metastability in the two-dimensional Potts ferromagnet.

    PubMed

    Ibáñez Berganza, Miguel; Petri, Alberto; Coletti, Pietro

    2014-05-01

    We investigate the nonequilibrium dynamics of the two-dimensional (2D) Potts model on the square lattice after a quench below the discontinuous transition point. By means of numerical simulations of systems with q=12, 24, and 48, we observe the onset of a stationary regime below the temperature-driven transition, in a temperature interval decreasing with the system size and increasing with q. These results obtained dynamically agree with those obtained from the analytical continuation of the free energy [J. L. Meunier and A. Morel, Eur. Phys. J. B 13, 341 (2000)], from which metastability in the 2D Potts model results to be a finite-size effect. PMID:25353747

  3. Two-dimensional numerical modeling of the Rheasilvia impact formation

    NASA Astrophysics Data System (ADS)

    Ivanov, B. A.; Melosh, H. J.

    2013-07-01

    We numerically modeled the formation of Rheasilvia crater, an enormous impact basin centered on asteroid 4 Vesta's south pole. Using a trial and error method, our models were adjusted to produce the best possible fit to Rheasilvia's size and shape, as observed during the Vesta orbital stage of the Dawn mission. The final model yields estimates of the shock wave decay, escaped material volume, depth of excavation, and other relevant characteristics, to the extent allowed by the two-dimensional (axially symmetric) approximation of the Simplified Arbitrary Lagrangian Eulerian hydrocode. Our model results permit interpretation of the Dawn data on Vesta's shape, topographic crater profiles, and the origin of the Vestoid asteroid family as escaped ejecta from the Rheasilvia crater.

  4. Analysis of two-dimensional photonic crystal with anisotropic gain.

    PubMed

    Takigawa, Shinichi; Noda, Susumu

    2011-05-01

    Photonic modes in a two-dimensional square-lattice photonic crystal (PC) with anisotropic gain are analyzed for the first time. A plane-wave expansion method is improved to include the gain, which depends on not only the position but also the propagation direction of each plane wave. The anisotropic gain varies the photonic band structure, the near-field distributions, and the gain dispersion curves through variation in PC symmetry. Low-threshold operation of a PC laser with anisotropic-gain material such as nonpolar InGaN requires that the direction of higher gain in the material aligns along the ΓX direction of the PC. PMID:21643205

  5. Kinetic theory of a two-dimensional magnetized plasma.

    NASA Technical Reports Server (NTRS)

    Vahala, G.; Montgomery, D.

    1971-01-01

    Several features of the equilibrium and nonequilibrium statistical mechanics of a two-dimensional plasma in a uniform dc magnetic field are investigated. The charges are assumed to interact only through electrostatic potentials. The problem is considered both with and without the guiding-center approximation. With the guiding-center approximation, an appropriate Liouville equation and BBGKY hierarchy predict no approach to thermal equilibrium for the spatially uniform case. For the spatially nonuniform situation, a guiding-center Vlasov equation is discussed and solved in special cases. For the nonequilibrium, nonguiding-center case, a Boltzmann equation, and a Fokker-Planck equation are derived in the appropriate limits. The latter is more tractable than the former, and can be shown to obey conservation laws and an H-theorem, but contains a divergent integral which must be cut off on physical grounds. Several unsolved problems are posed.

  6. Two-dimensional lattice-fluid model with waterlike anomalies.

    PubMed

    Buzano, C; De Stefanis, E; Pelizzola, A; Pretti, M

    2004-06-01

    We investigate a lattice-fluid model defined on a two-dimensional triangular lattice, with the aim of reproducing qualitatively some anomalous properties of water. Model molecules are of the "Mercedes Benz" type, i.e., they possess a D3 (equilateral triangle) symmetry, with three bonding arms. Bond formation depends both on orientation and local density. We work out phase diagrams, response functions, and stability limits for the liquid phase, making use of a generalized first order approximation on a triangle cluster, whose accuracy is verified, in some cases, by Monte Carlo simulations. The phase diagram displays one ordered (solid) phase which is less dense than the liquid one. At fixed pressure the liquid phase response functions show the typical anomalous behavior observed in liquid water, while, in the supercooled region, a reentrant spinodal is observed. PMID:15244571

  7. Spontaneous supersymmetry breaking in two dimensional lattice super QCD

    DOE PAGES

    Catterall, Simon; Veernala, Aarti

    2015-10-02

    We report on a non-perturbative study of two dimensional N=(2,2) super QCD. Our lattice formulation retains a single exact supersymmetry at non-zero lattice spacing, and contains Nf fermions in the fundamental representation of a U(Nc) gauge group. The lattice action we employ contains an additional Fayet-Iliopoulos term which is also invariant under the exact lattice supersymmetry. This work constitutes the first numerical study of this theory which serves as a toy model for understanding some of the issues that are expected to arise in four dimensional super QCD. As a result, we present evidence that the exact supersymmetry breaks spontaneouslymore » when Nf < Nc in agreement with theoretical expectations.« less

  8. Method and apparatus for two-dimensional absolute optical encoding

    NASA Technical Reports Server (NTRS)

    Leviton, Douglas B. (Inventor)

    2004-01-01

    This invention presents a two-dimensional absolute optical encoder and a method for determining position of an object in accordance with information from the encoder. The encoder of the present invention comprises a scale having a pattern being predetermined to indicate an absolute location on the scale, means for illuminating the scale, means for forming an image of the pattern; and detector means for outputting signals derived from the portion of the image of the pattern which lies within a field of view of the detector means, the field of view defining an image reference coordinate system, and analyzing means, receiving the signals from the detector means, for determining the absolute location of the object. There are two types of scale patterns presented in this invention: grid type and starfield type.

  9. Coherent transfer by adiabatic passage in two-dimensional lattices

    SciTech Connect

    Longhi, Stefano

    2014-09-15

    Coherent tunneling by adiabatic passage (CTAP) is a well-established technique for robust spatial transport of quantum particles in linear chains. Here we introduce two exactly-solvable models where the CTAP protocol can be extended to two-dimensional lattice geometries. Such bi-dimensional lattice models are synthesized from time-dependent second-quantization Hamiltonians, in which the bosonic field operators evolve adiabatically like in an ordinary three-level CTAP scheme thus ensuring adiabatic passage in Fock space. - Highlights: • New ways of coherent transport by adiabatic passage (CTAP) in 2D lattices. • Synthesis of exactly-solvable 2D lattices from a simple three-well model. • CTAP in 2D lattices can be exploited for quantum state transfer.

  10. Two-dimensional inorganic analogues of graphene: transition metal dichalcogenides.

    PubMed

    Jana, Manoj K; Rao, C N R

    2016-09-13

    The discovery of graphene marks a major event in the physics and chemistry of materials. The amazing properties of this two-dimensional (2D) material have prompted research on other 2D layered materials, of which layered transition metal dichalcogenides (TMDCs) are important members. Single-layer and few-layer TMDCs have been synthesized and characterized. They possess a wide range of properties many of which have not been known hitherto. A typical example of such materials is MoS2 In this article, we briefly present various aspects of layered analogues of graphene as exemplified by TMDCs. The discussion includes not only synthesis and characterization, but also various properties and phenomena exhibited by the TMDCs.This article is part of the themed issue 'Fullerenes: past, present and future, celebrating the 30th anniversary of Buckminster Fullerene'.

  11. A computer program for comparing irregular two-dimensional forms.

    PubMed

    Parnell, J N; Lestrel, P E

    1977-09-01

    A shape comparison of two forms requires a procedure that ensures comparability. A computer program has been written to compute a quantitative measure of shape differences between irregular bounded forms. The curve-fitting procedure, utilizing Fourier's series, is particularly well-suited for two-dimensional closed forms. The program provides several alternate methods to eliminate size difference, ensure a common or neutral center for superimposition and provide a rotational orientation which minimizes shape differences. The program contains numerous user-specified options which control input data transformations, algorithmic processing and output. The algorithmic processing provides: (1) generation of Fourier coefficients based on observed data, (2) two methods of producing Fourier coefficients adjusted for positional orientation, (3) two methods of producing Fourier coefficients adjusted for size standardization, (4) two methods of producing Fourier coefficients adjusted for rotational orientation, (5) a cross-correlation technique which rotationally adjusts two superimposed forms to minimize the shape difference, and (6) various standard statistical measures.

  12. Image background removal in comprehensive two-dimensional gas chromatography.

    PubMed

    Reichenbach, Stephen E; Ni, Mingtian; Zhang, Dongmin; Ledford, Edward B

    2003-01-24

    This paper describes a new technique for removing the background level from digital images produced in comprehensive two-dimensional gas chromatography (GCxGC). Background removal is an important first step in the larger problem of quantitative analysis. The approach estimates the background level across the chromatographic image based on structural and statistical properties of GCxGC data. Then, the background level is subtracted from the image, producing a chromatogram in which the peaks rise above a near-zero mean background. After the background level is removed, further analysis is required to determine the quantitative relationship between the peaks and chemicals in the sample. The algorithm is demonstrated experimentally to be effective at determining and removing the background level from GCxGC images. The algorithm has several parametric controls and is incorporated into an interactive program with graphical interface for rapid and accurate detection of GCxGC peaks.

  13. Two dimensional modelling of three core cable transient temperature rise

    SciTech Connect

    Lyall, J. )

    1990-01-01

    This paper describes a study of the transient temperature rise of a three core table. Results from a computer program that models the two dimensional heat flow are compared with those obtained using the normally applied one dimensional model. The modelling technique is an alternative to the finite difference and finite element methods. It develops the concept of a thermal resistance/capacitance analogue as can be done using the finite difference method but does so more directly without the need to use the partial differential equation. In addition, it provides the flexibility of the finite element method when modelling a complex geometry and material combination such as that found in a 3-core cable without the complexity of its mathematics.

  14. Role of intertwined Hamiltonian in two dimensional classical optics

    NASA Astrophysics Data System (ADS)

    Dehdashti, Shahram; Li, Rujiang; Liu, Xu; Raoofi, Mohammadreza; Chen, Hongsheng

    2015-07-01

    Intertwined Hamiltonian formalism originally has its roots in quantum field theory and non-relativistic quantum mechanics. In this work, we develop the non-relativistic two dimensional intertwined Hamiltonian formalism in classical optics. We obtain the properties of the intertwined media in detail and show that the differential part of intertwining operator is a series in Euclidean algebra generators. Also, we investigate quadratic gradient-index medium as an example of this structure, and obtain the intertwining operator and intertwined medium refractive index. Moreover, we study the preservation of quantum properties in the intertwined medium. For this, we consider superposition preservation as the most important property of quantum characters. We show that when a Schrödinger cat state is generated in gradient-index medium, we can construct another Schrödinger cat state in the intertwined one.

  15. Swimming of Vorticella in two-dimensional confinements

    NASA Astrophysics Data System (ADS)

    Sotelo, Luz; Park, Young-Gil; Jung, Sunghwan; Ryu, Sangjin

    2015-03-01

    Vorticellais a ciliate observed in the stalked sessile form (trophont), which consists of an inverted bell-shaped cell body (zooid) and a slender stalk attaching the zooid to a substrate. Having circular cilia bands around the oral part, the stalkless zooid of Vorticella can serve as a model system for microorganism swimming. Here we present how the stalkess trophont zooid of Vorticella swims in two-dimensional confined geometries which are similar to the Hele-Shaw cell. Having harvested stalkless Vorticella zooids, we observed their swimming in water between two glass surfaces using video microscopy. Based on measured swimming trajectories and distributions of zooid orientation and swimming velocity, we analyzed how Vorticella's swimming mobility was influenced by the geometry constraints. Supported by First Award grant from Nebraska EPSCoR.

  16. High-field transport in two-dimensional graphene

    NASA Astrophysics Data System (ADS)

    Fang, Tian; Konar, Aniruddha; Xing, Huili; Jena, Debdeep

    2011-09-01

    Transport of carriers in two-dimensional graphene at high electric fields is investigated by combining semianalytical and Monte Carlo methods. A semianalytical high-field transport model based on the high rate of optical phonon emission provides useful estimates of the saturation currents in graphene. For developing a more accurate picture, the nonequilibrium (hot) phonon effect and the role of electron-electron scattering were studied using Monte Carlo simulations. Monte Carlo simulations indicate that the hot phonon effect plays a dominant role in current saturation, and electron-electron scattering strongly thermalizes the hot carrier population in graphene. We also find that electron-electron scattering removes negative differential resistance in graphene. Transient phenomenon such as velocity overshoot can be used to speed up graphene-based high-speed electronic devices by shrinking the channel length below 80 nm if electrostatic control can be exercised in the absence of a band gap.

  17. Intervalley gap anomaly of two-dimensional electrons in silicon.

    PubMed

    Lai, K; Pan, W; Tsui, D C; Lyon, S; Mühlberger, M; Schäffler, F

    2006-02-24

    We report here a systematic study of the energy gaps at the odd-integer quantum Hall states nu = 3 and 5 under tilted magnetic (B) fields in a high quality Si two-dimensional electron system. Out of the coincidence region, the valley splitting is independent of the in-plane fields. However, the nu = 3 valley gap differs by about a factor of 3 (Deltav approximately 0.4 vs 1.2 K) on different sides of the coincidence. More surprisingly, instead of reducing to zero, the energy gaps at nu = 3 and 5 rise rapidly when approaching the coincidence angles. We believe that such an anomaly is related to strong couplings of the nearly degenerate Landau levels.

  18. Two-dimensional Imaging Velocity Interferometry: Technique and Data Analysis

    SciTech Connect

    Erskine, D J; Smith, R F; Bolme, C; Celliers, P; Collins, G

    2011-03-23

    We describe the data analysis procedures for an emerging interferometric technique for measuring motion across a two-dimensional image at a moment in time, i.e. a snapshot 2d-VISAR. Velocity interferometers (VISAR) measuring target motion to high precision have been an important diagnostic in shockwave physics for many years Until recently, this diagnostic has been limited to measuring motion at points or lines across a target. We introduce an emerging interferometric technique for measuring motion across a two-dimensional image, which could be called a snapshot 2d-VISAR. If a sufficiently fast movie camera technology existed, it could be placed behind a traditional VISAR optical system and record a 2d image vs time. But since that technology is not yet available, we use a CCD detector to record a single 2d image, with the pulsed nature of the illumination providing the time resolution. Consequently, since we are using pulsed illumination having a coherence length shorter than the VISAR interferometer delay ({approx}0.1 ns), we must use the white light velocimetry configuration to produce fringes with significant visibility. In this scheme, two interferometers (illuminating, detecting) having nearly identical delays are used in series, with one before the target and one after. This produces fringes with at most 50% visibility, but otherwise has the same fringe shift per target motion of a traditional VISAR. The 2d-VISAR observes a new world of information about shock behavior not readily accessible by traditional point or 1d-VISARS, simultaneously providing both a velocity map and an 'ordinary' snapshot photograph of the target. The 2d-VISAR has been used to observe nonuniformities in NIF related targets (polycrystalline diamond, Be), and in Si and Al.

  19. Two-Dimensional Numerical Modeling of Anthropogenic Beach Berm Erosion

    NASA Astrophysics Data System (ADS)

    Shakeri Majd, M.; Schubert, J.; Gallien, T.; Sanders, B. F.

    2014-12-01

    Anthropogenic beach berms (sometimes called artificial berms or artificial dunes) temporarily enhance the ability of beaches to withstand overtopping and thus guard against coastal flooding. However, the combination of a rising tide, storm surge, and/or waves may erode anthropogenic berms in a matter of hours or less and cause flooding [1]. Accurate forecasts of coastal flooding therefore demand the ability to predict where and when berms fail and the volume of water that overtops into defended coastal lowlands. Here, a two-dimensional numerical model of swash zone waves and erosion is examined as a tool for predicting the erosion of anthropogenic beach berms. The 2D model is known as a Debris Flow Model (DFM) because it tightly couples flow and sediment transport within an approximate Riemann solver and is able to resolve shocks in fluid/sediment interface [2]. The DFM also includes a two dimensional avalanching scheme to account for gravity-driven slumping of steep slopes. The performance of the DFM is examined with field-scale anthropogenic berm erosion data collected at Newport Beach, California. Results show that the DFM can be applied in the swash zone to resolve wave-by-wave flow and sediment transport. Results also show that it is possible to calibrate the model for a particular event, and then predict erosion for another event, but predictions are sensitive to model parameters, such as erosion and avalanching. References: [1] Jochen E. Schubert, Timu W. Gallien, Morteza Shakeri Majd, and Brett F. Sanders. Terrestrial laser scanning of anthropogenic beach berm erosion and overtopping. Journal of Coastal Research In-Press, 2014. [2] Morteza Shakeri Majd and Brett F. Sanders. The LHLLC scheme for Two-Layer and Two-Phase transcritical flows over a mobile bed with avalanching, wetting and drying. Advances in Water Resources, 64, 16-31, 2014.

  20. Performance Characteristics of Plane-Wall Two-Dimensional Diffusers

    NASA Technical Reports Server (NTRS)

    Reid, Elliott G

    1953-01-01

    Experiments have been made at Stanford University to determine the performance characteristics of plane-wall, two-dimensional diffusers which were so proportioned as to insure reasonable approximation of two-dimensional flow. All of the diffusers had identical entrance cross sections and discharged directly into a large plenum chamber; the test program included wide variations of divergence angle and length. During all tests a dynamic pressure of 60 pounds per square foOt was maintained at the diffuser entrance and the boundary layer there was thin and fully turbulent. The most interesting flow characteristics observed were the occasional appearance of steady, unseparated, asymmetric flow - which was correlated with the boundary-layer coalescence - and the rapid deterioration of flow steadiness - which occurred as soon as the divergence angle for maximum static pressure recovery was exceeded. Pressure efficiency was found to be controlled almost exclusively by divergence angle, whereas static pressure recovery was markedly influenced by area ratio (or length) as well as divergence angle. Volumetric efficiency. diminished as area ratio increased, and at a greater rate with small lengths than with large ones. Large values of the static-pressure-recovery coefficient were attained only with long diffusers of large area ratio; under these conditions pressure efficiency was high and. volumetric efficiency low. Auxiliary tests with asymmetric diffusers demonstrated that longitudinal pressure gradient, rather than wall divergence angle, controlled flow separation. Others showed that the addition of even a short exit duct of uniform section augmented pressure recovery. Finally, it was found that the installation of a thin, central, longitudinal partition suppressed flow separation in short diffusers and thereby improved pressure recovery

  1. Electronic nanobiosensors based on two-dimensional materials

    NASA Astrophysics Data System (ADS)

    Ping, Jinglei

    Atomically-thick two-dimensional (2D) nanomaterials have tremendous potential to be applied as transduction elements in biosensors and bioelectronics. We developed scalable methods for synthesis and large-area transfer of two-dimensional nanomaterials, particularly graphene and metal dichalcogenides (so called ``MX2'' materials). We also developed versatile fabrication methods for large arrays of field-effect transistors (FETs) and micro-electrodes with these nanomaterials based on either conventional photolithography or innovative approaches that minimize contamination of the 2D layer. By functionalizing the FETs with a computationally redesigned water-soluble mu-opioid receptor, we created selective and sensitive biosensors suitable for detection of the drug target naltrexone and the neuropeptide enkephalin at pg/mL concentrations. We also constructed DNA-functionalized biosensors and nano-particle decorated biosensors by applying related bio-nano integration techniques. Our methodology paves the way for multiplexed nanosensor arrays with all-electronic readout suitable for inexpensive point-of-care diagnostics, drug-development and biomedical research. With graphene field-effect transistors, we investigated the graphene/solution interface and developed a quantitative model for the effect of ionic screening on the graphene carrier density based on theories of the electric double layer. Finally, we have developed a technique for measuring low-level Faradaic charge-transfer current (fA) across the graphene/solution interface via real-time charge monitoring of graphene microelectrodes in ionic solution. This technique enables the development of flexible and transparent pH sensors that are promising for in vivo applications. The author acknowledges the support from the Defense Advanced Research Projects Agency (DARPA) and the U. S. Army Research Office under Grant Number W911NF1010093.

  2. Two dimensional hydrodynamic modeling of a high latitude braided river

    NASA Astrophysics Data System (ADS)

    Humphries, E.; Pavelsky, T.; Bates, P. D.

    2014-12-01

    Rivers are a fundamental resource to physical, ecologic and human systems, yet quantification of river flow in high-latitude environments remains limited due to the prevalence of complex morphologies, remote locations and sparse in situ monitoring equipment. Advances in hydrodynamic modeling and remote sensing technology allow us to address questions such as: How well can two-dimensional models simulate a flood wave in a highly 3-dimensional braided river environment, and how does the structure of such a flood wave differ from flow down a similar-sized single-channel river? Here, we use the raster-based hydrodynamic model LISFLOOD-FP to simulate flood waves, discharge, water surface height, and velocity measurements over a ~70 km reach of the Tanana River in Alaska. In order to use LISFLOOD-FP a digital elevation model (DEM) fused with detailed bathymetric data is required. During summer 2013, we surveyed 220,000 bathymetric points along the study reach using an echo sounder system connected to a high-precision GPS unit. The measurements are interpolated to a smooth bathymetric surface, using Topo to Raster interpolation, and combined with an existing five meter DEM (Alaska IfSAR) to create a seamless river terrain model. Flood waves are simulated using varying complexities in model solvers, then compared to gauge records and water logger data to assess major sources of model uncertainty. Velocity and flow direction maps are also assessed and quantified for detailed analysis of braided channel flow. The most accurate model output occurs with using the full two-dimensional model structure, and major inaccuracies appear to be related to DEM quality and roughness values. Future work will intercompare model outputs with extensive ground measurements and new data from AirSWOT, an airborne analog for the Surface Water and Ocean Topography (SWOT) mission, which aims to provide high-resolution measurements of terrestrial and ocean water surface elevations globally.

  3. Two-Dimensional Disorder in Black Phosphorus and Monochalcogenide Monolayers.

    PubMed

    Mehboudi, Mehrshad; Dorio, Alex M; Zhu, Wenjuan; van der Zande, Arend; Churchill, Hugh O H; Pacheco-Sanjuan, Alejandro A; Harriss, Edmund O; Kumar, Pradeep; Barraza-Lopez, Salvador

    2016-03-01

    Ridged, orthorhombic two-dimensional atomic crystals with a bulk Pnma structure such as black phosphorus and monochalcogenide monolayers are an exciting and novel material platform for a host of applications. Key to their crystallinity, monolayers of these materials have a 4-fold degenerate structural ground state, and a single energy scale EC (representing the elastic energy required to switch the longer lattice vector along the x- or y-direction) determines how disordered these monolayers are at finite temperature. Disorder arises when nearest neighboring atoms become gently reassigned as the system is thermally excited beyond a critical temperature Tc that is proportional to EC/kB. EC is tunable by chemical composition and it leads to a classification of these materials into two categories: (i) Those for which EC ≥ kBTm, and (ii) those having kBTm > EC ≥ 0, where Tm is a given material's melting temperature. Black phosphorus and SiS monolayers belong to category (i): these materials do not display an intermediate order-disorder transition and melt directly. All other monochalcogenide monolayers with EC > 0 belonging to class (ii) will undergo a two-dimensional transition prior to melting. EC/kB is slightly larger than room temperature for GeS and GeSe, and smaller than 300 K for SnS and SnSe monolayers, so that these materials transition near room temperature. The onset of this generic atomistic phenomena is captured by a planar Potts model up to the order-disorder transition. The order-disorder phase transition in two dimensions described here is at the origin of the Cmcm phase being discussed within the context of bulk layered SnSe. PMID:26866878

  4. Separation of colloidal two dimensional materials by density gradient ultracentrifugation

    SciTech Connect

    Kuang, Yun; Song, Sha; Huang, Jinyang; Sun, Xiaoming

    2015-04-15

    Two-dimensional (2D) materials have been made through various approaches but obtaining monodispersed simply by synthesis optimization gained little success, which highlighted the need for introducing nanoseparation methods. Density gradient ultracentrifugation method has emerged as a versatile and scalable method for sorting colloidal 2D nanomaterials. Isopycnic separation was applied on thickness-dependent separation of graphene nanosheets. And rate-zonal separation, as a more versatile separation method, demonstrated its capability in sorting nanosheets of chemically modified single layered graphene, layered double hydroxide, and even metallic Ag. Establishing such density gradient ultracentrifugation method not only achieves monodispersed nanosheets and provides new opportunities for investigation on size dependent properties of 2D materials, but also makes the surface modification possible by introducing “reaction zones” during sedimentation of the colloids. - Graphical abstract: Two-dimensional (2D) materials have been made through various approaches but obtaining monodispersed simply by synthesis optimization gained little success, which highlighted the need for introducing nanoseparation methods. Density gradient ultracentrifugation method has emerged as a versatile and scalable method for sorting colloidal 2D nanomaterials according to their size of thickness difference. Establishing such density gradient ultracentrifugation method not only achieves monodispersed nanosheets and provides new opportunities for investigation on size dependent properties of 2D materials, but also makes the surface modification possible by introducing “reaction zones” during sedimentation of the colloids. - Highlights: • Density gradient ultracentrifugation was applied on size separation of 2D material. • Isopycnic separation was applied on separation of low density materials. • Rate-zonal separation was applied on separation of large density materials. • Size

  5. [CSNP discovery by two-dimensional gene scanning (TDGS)].

    PubMed

    Suh, Y

    2001-04-21

    Challenges in the post-genomic era are to use genetic information in correlating individual gene variations (SNPs; single nucleotide polymorphisms, the most common form of genetic variation) with medically important parameters, such as disease susceptibility, individual responses to drugs and prognostic variables. What is missing is a high-throughput technology to identify all possible SNPs in essentially all human genes in population-based studies with high accuracy and speed in a cost-effective manner. Most tests advocated for their high throughput at low cost are actually SNP screening tests. That is, they screen samples for the presence of one or multiple previously identified SNPs. Such screening methods are only useful when all relevant SNPs in the genes of interest are known, which is presently not the case. Moreover, the usefulness of any one SNP varies enormously from population to population. Indeed, for the Korean population, where no information on possible sequence variation is available, a mutational scanning method, capable to detect all possible gene variations will be most useful. Two-Dimensional Gene Scanning (TDGS) is a high-throughput platform that enables to detect all possible SNPs in an entire gene in one gel under one set of conditions, with high sensitivity and specificity. TDGS is based on automated two-dimensional (2-D) DNA electrophoresis according to size and base pair sequence to detect DNA fragments containing all possible variations. Because the 2-D format permits the analysis of as many as 40 fragments of 250 bp on average in parallel, TDGS allows extensive multiplex PCR (megaplex PCR), i.e. up to 26 fragments in one single reaction, resulting in a significant cost reduction. TDGS tests are designed using a computer program to optimally position PCR primers around the relevant target sequences (exons). A simple automated 2-D instrument allows scanning all exons of a large gene in 8 different samples well within 3 hours. Using three

  6. Nanoscale insights on one- and two-dimensional material structures

    NASA Astrophysics Data System (ADS)

    Floresca, Herman Carlo

    The race for smaller, faster and more efficient devices has led researchers to explore the possibilities of utilizing nanostructures for scaling. These one-dimensional and two-dimensional materials have properties that are attractive for this purpose but are still not well controlled. Control comes with a complete understanding of the materials' electrical, thermal, optical and structural characteristics but is difficult to obtain due to their small scale. This work is intended to help researchers overcome the difficulty in studying nanostructures by providing techniques for analysis and insights of nanostructures that have not been previously available. Two nanostructures were studied: silicon nanowires and graphene. The nanowires were prepared for cross-section transmission electron microscopy (TEM) to discover the effects that controlled oxidation has on the dimensions and shape of the nanowires. Since cross-section TEM is not able to provide information about surface structure, a method for manipulating the wires with orientation control was developed. With this ability, all three orthogonal views of the nanowire were compiled for a comprehensive study on its structure in terms of shape and surface roughness. Graphene was used for a two-dimensional analytical technique that took advantage of customized computer programs for data acquisition, measurement and display. With the information provided, distinctions between grain boundary types in polycrystalline graphene were made and supported by statistical information from the software's output. It was also applied to a growth series of graphene samples in conjunction with scanning electron microscopy (SEM) images and electron backscatter diffraction (EBSD) maps. The results help point to origins of graphene's polycrystalline nature. This dissertation concludes with a thought towards the future by highlighting a method that can help analyze nanostructures, which may become incorporated into the structures of large

  7. Two-Dimensional Disorder in Black Phosphorus and Monochalcogenide Monolayers.

    PubMed

    Mehboudi, Mehrshad; Dorio, Alex M; Zhu, Wenjuan; van der Zande, Arend; Churchill, Hugh O H; Pacheco-Sanjuan, Alejandro A; Harriss, Edmund O; Kumar, Pradeep; Barraza-Lopez, Salvador

    2016-03-01

    Ridged, orthorhombic two-dimensional atomic crystals with a bulk Pnma structure such as black phosphorus and monochalcogenide monolayers are an exciting and novel material platform for a host of applications. Key to their crystallinity, monolayers of these materials have a 4-fold degenerate structural ground state, and a single energy scale EC (representing the elastic energy required to switch the longer lattice vector along the x- or y-direction) determines how disordered these monolayers are at finite temperature. Disorder arises when nearest neighboring atoms become gently reassigned as the system is thermally excited beyond a critical temperature Tc that is proportional to EC/kB. EC is tunable by chemical composition and it leads to a classification of these materials into two categories: (i) Those for which EC ≥ kBTm, and (ii) those having kBTm > EC ≥ 0, where Tm is a given material's melting temperature. Black phosphorus and SiS monolayers belong to category (i): these materials do not display an intermediate order-disorder transition and melt directly. All other monochalcogenide monolayers with EC > 0 belonging to class (ii) will undergo a two-dimensional transition prior to melting. EC/kB is slightly larger than room temperature for GeS and GeSe, and smaller than 300 K for SnS and SnSe monolayers, so that these materials transition near room temperature. The onset of this generic atomistic phenomena is captured by a planar Potts model up to the order-disorder transition. The order-disorder phase transition in two dimensions described here is at the origin of the Cmcm phase being discussed within the context of bulk layered SnSe.

  8. Two dimensional electron systems for solid state quantum computation

    NASA Astrophysics Data System (ADS)

    Mondal, Sumit

    Two dimensional electron systems based on GaAs/AlGaAs heterostructures are extremely useful in various scientific investigations of recent times including the search for quantum computational schemes. Although significant strides have been made over the past few years to realize solid state qubits on GaAs/AlGaAs 2DEGs, there are numerous factors limiting the progress. We attempt to identify factors that have material and design-specific origin and develop ways to overcome them. The thesis is divided in two broad segments. In the first segment we describe the realization of a new field-effect induced two dimensional electron system on GaAs/AlGaAs heterostructure where the novel device-design is expected to suppress the level of charge noise present in the device. Modulation-doped GaAs/AlGaAs heterostructures are utilized extensively in the study of quantum transport in nanostructures, but charge fluctuations associated with remote ionized dopants often produce deleterious effects. Electric field-induced carrier systems offer an attractive alternative if certain challenges can be overcome. We demonstrate a field-effect transistor in which the active channel is locally devoid of modulation-doping, but silicon dopant atoms are retained in the ohmic contact region to facilitate low-resistance contacts. A high quality two-dimensional electron gas is induced by a field-effect that is tunable over a density range of 6.5x10 10cm-2 to 2.6x1011cm-2 . Device design, fabrication, and low temperature (T=0.3K) characterization results are discussed. The demonstrated device-design overcomes several existing limitations in the fabrication of field-induced 2DEGs and might find utility in hosting nanostructures required for making spin qubits. The second broad segment describes our effort to correlate transport parameters measured at T=0.3K to the strength of the fractional quantum Hall state observed at nu=5/2 in the second Landau level of high-mobility GaAs/AlGaAs two dimensional

  9. Electromagnetic Wave Propagation in Two-Dimensional Photonic Crystals

    SciTech Connect

    Stavroula Foteinopoulou

    2003-12-12

    In this dissertation, they have undertaken the challenge to understand the unusual propagation properties of the photonic crystal (PC). The photonic crystal is a medium where the dielectric function is periodically modulated. These types of structures are characterized by bands and gaps. In other words, they are characterized by frequency regions where propagation is prohibited (gaps) and regions where propagation is allowed (bands). In this study they focus on two-dimensional photonic crystals, i.e., structures with periodic dielectric patterns on a plane and translational symmetry in the perpendicular direction. They start by studying a two-dimensional photonic crystal system for frequencies inside the band gap. The inclusion of a line defect introduces allowed states in the otherwise prohibited frequency spectrum. The dependence of the defect resonance state on different parameters such as size of the structure, profile of incoming source, etc., is investigated in detail. For this study, they used two popular computational methods in photonic crystal research, the Finite Difference Time Domain method (FDTD) and the Transfer Matrix Method (TMM). The results for the one-dimensional defect system are analyzed, and the two methods, FDTD and TMM, are compared. Then, they shift their attention only to periodic two-dimensional crystals, concentrate on their band properties, and study their unusual refractive behavior. Anomalous refractive phenomena in photonic crystals included cases where the beam refracts on the ''wrong'' side of the surface normal. The latter phenomenon, is known as negative refraction and was previously observed in materials where the wave vector, the electric field, and the magnetic field form a left-handed set of vectors. These materials are generally called left-handed materials (LHM) or negative index materials (NIM). They investigated the possibility that the photonic crystal behaves as a LHM, and how this behavior relates with the observed

  10. Two-dimensional materials for novel liquid separation membranes.

    PubMed

    Ying, Yulong; Yang, Yefeng; Ying, Wen; Peng, Xinsheng

    2016-08-19

    Demand for a perfect molecular-level separation membrane with ultrafast permeation and a robust mechanical property for any kind of species to be blocked in water purification and desalination is urgent. In recent years, due to their intrinsic characteristics, such as a unique mono-atom thick structure, outstanding mechanical strength and excellent flexibility, as well as facile and large-scale production, graphene and its large family of two-dimensional (2D) materials are regarded as ideal membrane materials for ultrafast molecular separation. A perfect separation membrane should be as thin as possible to maximize its flux, mechanically robust and without failure even if under high loading pressure, and have a narrow nanochannel size distribution to guarantee its selectivity. The latest breakthrough in 2D material-based membranes will be reviewed both in theories and experiments, including their current state-of-the-art fabrication, structure design, simulation and applications. Special attention will be focused on the designs and strategies employed to control microstructures to enhance permeation and selectivity for liquid separation. In addition, critical views on the separation mechanism within two-dimensional material-based membranes will be provided based on a discussion of the effects of intrinsic defects during growth, predefined nanopores and nanochannels during subsequent fabrication processes, the interlayer spacing of stacking 2D material flakes and the surface charge or functional groups. Furthermore, we will summarize the significant progress of these 2D material-based membranes for liquid separation in nanofiltration/ultrafiltration and pervaporation. Lastly, we will recall issues requiring attention, and discuss existing questionable conclusions in some articles and emerging challenges. This review will serve as a valuable platform to provide a compact source of relevant and timely information about the development of 2D material-based membranes as

  11. Current two-dimensional electrophoresis technology for proteomics.

    PubMed

    Görg, Angelika; Weiss, Walter; Dunn, Michael J

    2004-12-01

    Two-dimensional gel electrophoresis (2-DE) with immobilized pH gradients (IPGs) combined with protein identification by mass spectrometry (MS) is currently the workhorse for proteomics. In spite of promising alternative or complementary technologies (e.g. multidimensional protein identification technology, stable isotope labelling, protein or antibody arrays) that have emerged recently, 2-DE is currently the only technique that can be routinely applied for parallel quantitative expression profiling of large sets of complex protein mixtures such as whole cell lysates. 2-DE enables the separation of complex mixtures of proteins according to isoelectric point (pI), molecular mass (Mr), solubility, and relative abundance. Furthermore, it delivers a map of intact proteins, which reflects changes in protein expression level, isoforms or post-translational modifications. This is in contrast to liquid chromatography-tandem mass spectrometry based methods, which perform analysis on peptides, where Mr and pI information is lost, and where stable isotope labelling is required for quantitative analysis. Today's 2-DE technology with IPGs (Görg et al., Electrophoresis 2000, 21, 1037-1053), has overcome the former limitations of carrier ampholyte based 2-DE (O'Farrell, J. Biol. Chem. 1975, 250, 4007-4021) with respect to reproducibility, handling, resolution, and separation of very acidic and/or basic proteins. The development of IPGs between pH 2.5-12 has enabled the analysis of very alkaline proteins and the construction of the corresponding databases. Narrow-overlapping IPGs provide increased resolution (delta pI = 0.001) and, in combination with prefractionation methods, the detection of low abundance proteins. Depending on the gel size and pH gradient used, 2-DE can resolve more than 5000 proteins simultaneously (approximately 2000 proteins routinely), and detect and quantify < 1 ng of protein per spot. In this article we describe the current 2-DE/MS workflow including the

  12. Two-dimensional materials for novel liquid separation membranes.

    PubMed

    Ying, Yulong; Yang, Yefeng; Ying, Wen; Peng, Xinsheng

    2016-08-19

    Demand for a perfect molecular-level separation membrane with ultrafast permeation and a robust mechanical property for any kind of species to be blocked in water purification and desalination is urgent. In recent years, due to their intrinsic characteristics, such as a unique mono-atom thick structure, outstanding mechanical strength and excellent flexibility, as well as facile and large-scale production, graphene and its large family of two-dimensional (2D) materials are regarded as ideal membrane materials for ultrafast molecular separation. A perfect separation membrane should be as thin as possible to maximize its flux, mechanically robust and without failure even if under high loading pressure, and have a narrow nanochannel size distribution to guarantee its selectivity. The latest breakthrough in 2D material-based membranes will be reviewed both in theories and experiments, including their current state-of-the-art fabrication, structure design, simulation and applications. Special attention will be focused on the designs and strategies employed to control microstructures to enhance permeation and selectivity for liquid separation. In addition, critical views on the separation mechanism within two-dimensional material-based membranes will be provided based on a discussion of the effects of intrinsic defects during growth, predefined nanopores and nanochannels during subsequent fabrication processes, the interlayer spacing of stacking 2D material flakes and the surface charge or functional groups. Furthermore, we will summarize the significant progress of these 2D material-based membranes for liquid separation in nanofiltration/ultrafiltration and pervaporation. Lastly, we will recall issues requiring attention, and discuss existing questionable conclusions in some articles and emerging challenges. This review will serve as a valuable platform to provide a compact source of relevant and timely information about the development of 2D material-based membranes as

  13. Two-dimensional materials for novel liquid separation membranes

    NASA Astrophysics Data System (ADS)

    Ying, Yulong; Yang, Yefeng; Ying, Wen; Peng, Xinsheng

    2016-08-01

    Demand for a perfect molecular-level separation membrane with ultrafast permeation and a robust mechanical property for any kind of species to be blocked in water purification and desalination is urgent. In recent years, due to their intrinsic characteristics, such as a unique mono-atom thick structure, outstanding mechanical strength and excellent flexibility, as well as facile and large-scale production, graphene and its large family of two-dimensional (2D) materials are regarded as ideal membrane materials for ultrafast molecular separation. A perfect separation membrane should be as thin as possible to maximize its flux, mechanically robust and without failure even if under high loading pressure, and have a narrow nanochannel size distribution to guarantee its selectivity. The latest breakthrough in 2D material-based membranes will be reviewed both in theories and experiments, including their current state-of-the-art fabrication, structure design, simulation and applications. Special attention will be focused on the designs and strategies employed to control microstructures to enhance permeation and selectivity for liquid separation. In addition, critical views on the separation mechanism within two-dimensional material-based membranes will be provided based on a discussion of the effects of intrinsic defects during growth, predefined nanopores and nanochannels during subsequent fabrication processes, the interlayer spacing of stacking 2D material flakes and the surface charge or functional groups. Furthermore, we will summarize the significant progress of these 2D material-based membranes for liquid separation in nanofiltration/ultrafiltration and pervaporation. Lastly, we will recall issues requiring attention, and discuss existing questionable conclusions in some articles and emerging challenges. This review will serve as a valuable platform to provide a compact source of relevant and timely information about the development of 2D material-based membranes as

  14. Ultrafast Band Structure Control of a Two-Dimensional Heterostructure.

    PubMed

    Ulstrup, Søren; Čabo, Antonija Grubišić; Miwa, Jill A; Riley, Jonathon M; Grønborg, Signe S; Johannsen, Jens C; Cacho, Cephise; Alexander, Oliver; Chapman, Richard T; Springate, Emma; Bianchi, Marco; Dendzik, Maciej; Lauritsen, Jeppe V; King, Phil D C; Hofmann, Philip

    2016-06-28

    The electronic structure of two-dimensional (2D) semiconductors can be significantly altered by screening effects, either from free charge carriers in the material or by environmental screening from the surrounding medium. The physical properties of 2D semiconductors placed in a heterostructure with other 2D materials are therefore governed by a complex interplay of both intra- and interlayer interactions. Here, using time- and angle-resolved photoemission, we are able to isolate both the layer-resolved band structure and, more importantly, the transient band structure evolution of a model 2D heterostructure formed of a single layer of MoS2 on graphene. Our results reveal a pronounced renormalization of the quasiparticle gap of the MoS2 layer. Following optical excitation, the band gap is reduced by up to ∼400 meV on femtosecond time scales due to a persistence of strong electronic interactions despite the environmental screening by the n-doped graphene. This points to a large degree of tunability of both the electronic structure and the electron dynamics for 2D semiconductors embedded in a van der Waals-bonded heterostructure. PMID:27267820

  15. Two-dimensional boron nitride structures functionalization: first principles studies.

    PubMed

    Ponce-Pérez, R; Cocoletzi, Gregorio H; Takeuchi, Noboru

    2016-09-01

    Density functional theory calculations have been performed to investigate two-dimensional hexagonal boron nitride (2D hBN) structures functionalization with organic molecules. 2x2, 4x4 and 6x6 periodic 2D hBN layers have been considered to interact with acetylene. To deal with the exchange-correlation energy the generalized gradient approximation (GGA) is invoked. The electron-ion interaction is treated with the pseudopotential method. The GGA with the Perdew-Burke-Ernzerhoff (PBE) functionals together with van der Waals interactions are considered to deal with the composed systems. To investigate the functionalization two main configurations have been explored; in one case the molecule interacts with the boron atom and in the other with the nitrogen atom. Results of the adsorption energies indicate chemisorption in both cases. The total density of states (DOS) displays an energy gap in both cases. The projected DOS indicate that the B-p and N-p orbitals are those that make the most important contribution in the valence band and the H-s and C-p orbitals provide an important contribution in the conduction band to the DOS. Provided that the interactions of the acetylene with the 2D layer modify the structural and electronic properties of the hBN the possibility of structural functionalization using organic molecules may be concluded.

  16. Two-dimensional position sensitive ionization chamber with GEM

    NASA Astrophysics Data System (ADS)

    Kitamura, Noritaka; Noro, Tetsuo; Sakaguchi, Satoshi; Takao, Hideaki; Nishio, Yasutaka

    2014-09-01

    We have been developing a multi-anode ionization chamber for Accelerator Mass Spectrometry (AMS) at Kyushu University. Furthermore, we are planning to construct a neutron detector with high position resolution by combining the chamber with Gas Electron Multiplier (GEM) and a neutron converter. One of purposes is the measurement of p-> , pn knockout reaction from unstable nuclei. The multi-anode ionization chamber is composed of subdivided multiple anodes, a cathode to produce an uniform electric field, and a Frisch grid. The chamber must have position sensitivity because obtaining a beam profile is required for AMS measurements, where counting loss should be avoided. Also in the case of the neutron detector, it is necessary to measure the position to deduce the scattering angles. We have recently established a two-dimensional position readout system by the following methods: the measurement of horizontal position is enabled by trimming some anodes into wedge-like shape, and vertical position can be determined by the ratio of induced charge on the grid to the total charge on anodes. In addition, improvement of S/N ratio is important for isotope separation and position resolution. We installed a rectangular-shaped GEM and tried improving S/N ratio by electron amplification.

  17. Electromagnetic scattering from two-dimensional thick material junctions

    NASA Technical Reports Server (NTRS)

    Ricoy, M. A.; Volakis, John L.

    1990-01-01

    The problem of the plane wave diffraction is examined by an arbitrary symmetric two dimensional junction, where Generalized Impedance Boundary Conditions (GIBCs) and Generalized Sheet Transition Conditions (GSTCs) are employed to simulate the slabs. GIBCs and GSTCs are constructed for multilayer planar slabs of arbitrary thickness and the resulting GIBC/GSTC reflection coefficients are compared with exact counterparts to evaluate the GIBCs/GSTCs. The plane wave diffraction by a multilayer material slab recessed in a perfectly conducting ground plane is formulated and solved via the Generalized Scattering Matrix Formulation (GDMF) in conjunction with the dual integral equation approach. Various scattering patterns are computed and validated with exact results where possible. The diffraction by a material discontinuity in a thick dielectric/ferrite slab is considered by modelling the constituent slabs with GSTCs. A non-unique solution in terms of unknown constants is obtained, and these constants are evaluated for the recessed slab geometry by comparison with the solution obtained therein. Several other simplified cases are also presented and discussed. An eigenfunction expansion method is introduced to determine the unknown solution constants in the general case. This procedure is applied to the non-unique solution in terms of unknown constants; and scattering patterns are presented for various slab junctions and compared with alternative results where possible.

  18. Atmospheric flow over two-dimensional bluff surface obstructions

    NASA Technical Reports Server (NTRS)

    Bitte, J.; Frost, W.

    1976-01-01

    The phenomenon of atmospheric flow over a two-dimensional surface obstruction, such as a building (modeled as a rectangular block, a fence or a forward-facing step), is analyzed by three methods: (1) an inviscid free streamline approach, (2) a turbulent boundary layer approach using an eddy viscosity turbulence model and a horizontal pressure gradient determined by the inviscid model, and (3) an approach using the full Navier-Stokes equations with three turbulence models; i.e., an eddy viscosity model, a turbulence kinetic-energy model and a two-equation model with an additional transport equation for the turbulence length scale. A comparison of the performance of the different turbulence models is given, indicating that only the two-equation model adequately accounts for the convective character of turbulence. Turbulence flow property predictions obtained from the turbulence kinetic-energy model with prescribed length scale are only insignificantly better than those obtained from the eddy viscosity model. A parametric study includes the effects of the variation of the characteristics parameters of the assumed logarithmic approach velocity profile. For the case of the forward-facing step, it is shown that in the downstream flow region an increase of the surface roughness gives rise to higher turbulence levels in the shear layer originating from the step corner.

  19. Spatially clustered zealots in a two-dimensional voter model

    NASA Astrophysics Data System (ADS)

    Stone, Thomas; Ludden, Matthew; McKay, Susan

    The voter model, solvable in all dimensions in its standard form, has been extensively used to study behavior dynamics by using the tools of statistical mechanics. Recently, much work has been focused on determining the effects of zealots in the voter model, where a zealot is an agent that maintains its opinion (akin to an Ising spin variable) no matter the local environment. Here we investigate the effects of spatially clustered zealots in the standard voter model on a two-dimensional square lattice. The clustering of zealots is quantified by the conditional probability that a zealot of the +1 state appears on an adjacent site to a randomly chosen zealot. (All zealots are of the +1 state.) We determine the functional forms of the system consensus time with respect to system size, clustering, and zealot density, and compare these findings to previous results that do not include clustering. We also discuss an interesting random walk problem that arises when one attempts to calculate how clustering affects the consensus time for fixed zealot density and system size.

  20. Two-dimensional quantum walk under artificial magnetic field

    NASA Astrophysics Data System (ADS)

    Yalcinkaya, Iskender; Gedik, Zafer

    We introduce the Peierls substitution to a two-dimensional discrete-time quantum walk on a square lattice to examine the spreading dynamics and the coin-position entanglement in the presence of an artificial gauge field. We use the ratio of the magnetic flux through the unit cell to the flux quantum as a control parameter. For a given flux ratio, we obtain faster spreading for a small number of steps and the walker tends to be highly localized around the origin. Moreover, the spreading of the walk can be suppressed and decreased within a limited time interval for specific rational values of flux ratio. When the flux ratio is an irrational number, even for a large number of steps, the spreading exhibit diffusive behavior rather than the well-known ballistic one as in the classical random walk and there is a significant probability of finding the walker at the origin. We also analyze the coin-position entanglement and show that the asymptotic behavior vanishes when the flux ratio is different from zero and the coin-position entanglement become nearly maximal in a periodic manner in a long time range.

  1. Point-vortex approach in two-dimensional turbulence

    NASA Astrophysics Data System (ADS)

    Kuvshinov, B. N.; Schep, T. J.

    2016-05-01

    The properties of two-dimensional turbulence in a circular domain are investigated within the framework of the punctuated point-vortex model. Vortex dynamics is governed by Hamiltonian equations, and it is interrupted by instantaneous events resulting in vortex merging. Motion of about 100 point vortices is simulated using an accurate, symplectic integration method. Ensembles of like-sign vortices relax to a quasi-lattice state. Vortices with zero total vorticity tend to be randomized. Their motion still does not become fully chaotic. We observe emergence of long lived large dipoles (co-propagating pairs of vortices with opposite signs), which affect the evolution of the whole vortex ensemble. The presence of such dipoles accelerate the vortex decay rate. The decay exponent has been estimated as ξ ≃ 1.7, which is much larger than ξ ≃ 0.7, reported in previous studies of decaying turbulence. Since dipole dynamics depends on specific properties of the point vortex system, our findings suggest that a universal decay exponent in such systems does not exist.

  2. Grain boundaries in hybrid two-dimensional materials

    NASA Astrophysics Data System (ADS)

    Zhang, Zhuhua; Yang, Yang; Yakobson, Boris I.

    2014-10-01

    In two-dimensional (2D) materials, bisector grain boundaries (GBs) are energetically favorable as they allow perfect match of neighbor grains. We demonstrate here a contrasting behavior for GBs in hybrid 2D materials, which tend to be non-bisector and obey a universal law to optimally match the heterogeneous grains: the ratio of cosines of the rotation angles of two neighbor grains equals the ratio of constituent's lattice parameters, reminiscent of Snell's law for light refraction. Details of the optimal GB structures are further formulated in terms of tilt angle, lattice mismatch strain and deviation angle from the bisector line, in good agreement with comprehensive numerical analyses. The ground state structures of the GBs manifest as a series of laterally misaligned bisector segments, which are verified by intensive first-principle calculations. Our findings not only provide a general guidance for exploring GBs in various hybrid 2D materials but also serve as an important stepping stone for understanding mechanical and electronic behaviors in these 2D nanoscale patchworks.

  3. Two-dimensional variational vibroequilibria and Faraday's drops

    NASA Astrophysics Data System (ADS)

    Gavrilyuk, Ivan; Lukovsky, Ivan; Timokha, Alexander

    2004-11-01

    When contacting with acoustically-vibrated structures a fluid volume can take a [time-averaged] geometric shape differing from capillary equilibrium. In accordance with theorems by Beyer et al. (2001) this shape (vibroequilibrium) furnishes a local minimum of a [quasi-potential energy] functional. The variational problem contains five dimensionless parameters evaluating the fluid volume, the wave number of acoustic field in the fluid domain, the contact angle and two newly-introduced numbers (η1, η2) giving relationships between (surface tension, gravitation) and Kapitsa’s vibrational forces/energy. The paper focuses on negligible small wave numbers (incompressible fluid) and two-dimensional flows. Although the variational problem may in some isolated cases have analytical solutions, it requires in general numerical approaches. Numerical examples simulate experiments by Wolf (1969) and Ganiyev et al. (1977) on vibroequilibria in horizontally vibrating tanks. These show that there appear at least two types of stable vibroequilibria associated with symmetric (possible non-connected) and asymmetric surface shapes. The paper represents also numerical results on flattening and vibrostabilisation of a drop hanging beneath a vibrating plate (experiments by Faraday (1831)).

  4. Two-dimensional van der Waals C60 molecular crystal

    PubMed Central

    Reddy, C. D.; Gen Yu, Zhi; Zhang, Yong-Wei

    2015-01-01

    Two-dimensional (2D) atomic crystals, such as graphene and transition metal dichalcogenides et al. have drawn extraordinary attention recently. For these 2D materials, atoms within their monolayer are covalently bonded. An interesting question arises: Can molecules form a 2D monolayer crystal via van der Waals interactions? Here, we first study the structural stability of a free-standing infinite C60 molecular monolayer using molecular dynamic simulations, and find that the monolayer is stable up to 600 K. We further study the mechanical properties of the monolayer, and find that the elastic modulus, ultimate tensile stress and failure strain are 55–100 GPa, 90–155 MPa, and 1.5–2.3%, respectively, depending on the stretching orientation. The monolayer fails due to shearing and cavitation under uniaxial tensile loading. The highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) of the monolayer are found to be delocalized and as a result, the band gap is reduced to only 60% of the isolated C60 molecule. Interestingly, this band gap can be tuned up to ±30% using strain engineering. Owing to its thermal stability, low density, strain-tunable semi-conducting characteristics and large bending flexibility, this van der Waals molecular monolayer crystal presents aplenty opportunities for developing novel applications in nanoelectronics. PMID:26183501

  5. Temporal enhancement of two-dimensional color doppler echocardiography

    NASA Astrophysics Data System (ADS)

    Terentjev, Alexey B.; Settlemier, Scott H.; Perrin, Douglas P.; del Nido, Pedro J.; Shturts, Igor V.; Vasilyev, Nikolay V.

    2016-03-01

    Two-dimensional color Doppler echocardiography is widely used for assessing blood flow inside the heart and blood vessels. Currently, frame acquisition time for this method varies from tens to hundreds of milliseconds, depending on Doppler sector parameters. This leads to low frame rates of resulting video sequences equal to tens of Hz, which is insufficient for some diagnostic purposes, especially in pediatrics. In this paper, we present a new approach for reconstruction of 2D color Doppler cardiac images, which results in the frame rate being increased to hundreds of Hz. This approach relies on a modified method of frame reordering originally applied to real-time 3D echocardiography. There are no previous publications describing application of this method to 2D Color Doppler data. The approach has been tested on several in-vivo cardiac 2D color Doppler datasets with approximate duration of 30 sec and native frame rate of 15 Hz. The resulting image sequences had equivalent frame rates to 500Hz.

  6. Strain engineering in semiconducting two-dimensional crystals.

    PubMed

    Roldán, Rafael; Castellanos-Gomez, Andrés; Cappelluti, Emmanuele; Guinea, Francisco

    2015-08-12

    One of the fascinating properties of the new families of two-dimensional crystals is their high stretchability and the possibility to use external strain to manipulate, in a controlled manner, their optical and electronic properties. Strain engineering, understood as the field that study how the physical properties of materials can be tuned by controlling the elastic strain fields applied to it, has a perfect platform for its implementation in the atomically thin semiconducting materials. The object of this review is to give an overview of the recent progress to control the optical and electronics properties of 2D crystals, by means of strain engineering. We will concentrate on semiconducting layered materials, with especial emphasis in transition metal dichalcogenides (MoS2, WS2, MoSe2 and WSe2). The effect of strain in other atomically thin materials like black phosphorus, silicene, etc, is also considered. The benefits of strain engineering in 2D crystals for applications in nanoelectronics and optoelectronics will be revised, and the open problems in the field will be discussed. PMID:26199038

  7. Two-Dimensional Mesoscale-Ordered Conducting Polymers.

    PubMed

    Liu, Shaohua; Zhang, Jian; Dong, Renhao; Gordiichuk, Pavlo; Zhang, Tao; Zhuang, Xiaodong; Mai, Yiyong; Liu, Feng; Herrmann, Andreas; Feng, Xinliang

    2016-09-26

    Despite the availability of numerous two-dimensional (2D) materials with structural ordering at the atomic or molecular level, direct construction of mesoscale-ordered superstructures within a 2D monolayer remains an enormous challenge. Here, we report the synergic manipulation of two types of assemblies in different dimensions to achieve 2D conducting polymer nanosheets with structural ordering at the mesoscale. The supramolecular assemblies of amphipathic perfluorinated carboxylic acids and block co-polymers serve as 2D interfaces and meso-inducing moieties, respectively, which guide the polymerization of aniline into 2D, free-standing mesoporous conducting polymer nanosheets. Grazing-incidence small-angle X-ray scattering combined with various microscopy demonstrates that the resulting mesoscale-ordered nanosheets have hexagonal lattice with d-spacing of about 30 nm, customizable pore sizes of 7-18 nm and thicknesses of 13-45 nm, and high surface area. Such template-directed assembly produces polyaniline nanosheets with enhanced π-π stacking interactions, thereby resulting in anisotropic and record-high electrical conductivity of approximately 41 S cm(-1) for the pristine polyaniline nanosheet based film and approximately 188 S cm(-1) for the hydrochloric acid-doped counterpart. Our moldable approach creates a new family of mesoscale-ordered structures as well as opens avenues to the programmed assembly of multifunctional materials. PMID:27603275

  8. Two-Dimensional Atomic Crystals: Paving New Ways for Nanoelectronics

    NASA Astrophysics Data System (ADS)

    Fan, Jincheng; Li, Tengfei; Djerdj, Igor

    2015-11-01

    Two-dimensional (2D) atomic crystals are attractive for use in next-generation nanoelectronics, due to their unique performances, which may lead to the resolution of the technological and fundamental challenges in semiconductor industry. Based on the introduction of 2D atomic crystal-based transistors and ambipolar behavior, the review presents a brief summary of 2D atomic crystal integration circuits, including memory, logic gate, amplifier, inverter, oscillator, mixer, switch and modulator. The devices show promising performances for the application in future nanoelectronics. In particular, the 2D atomic crystals, such as graphene, demonstrate good compatibility with the existing semiconductor process. The quaternary digital modulations have been achieved with flexible and transparent all-graphene circuits. Moreover, the heterojunction based on 2D atomic crystals may enable new devices beyond conventional field-effect transistors. The results make us be optimistic that practical 2D atomic crystal technologies with complex functionality will be achieved in the near future. Therefore, 2D atomic crystals are paving new ways for nanoelectronics.

  9. Rotational effect in two-dimensional cooperative directed transport

    NASA Astrophysics Data System (ADS)

    Qiao, Li-Yan; Li, Yun-yun; Zheng, Zhi-Gang

    2015-02-01

    In this review we investigate the rotation effect in the motion of coupled dimer in a two-dimensional asymmetric periodic potential. Free rotation does not generate directed transport in translational direction, while we find it plays an critical role in the motors motility when the dimer moves under the effect of asymmetry ratchet potential. In the presence of external force, we study the relation between the average current and the force numerically and theoretically. The numerical results show that only appropriate driving force could produce nonzero current and there are current transitions when the force is large enough. An analysis of stability analysis of limit cycles is applied to explain the occurrence of these transitions. Moreover, we numerically simulate the transport of this coupled dimer driven by the random fluctuations in the rotational direction. The existence of noise smooths the current transitions induced by the driving force and the resonance-like peaks which depend on the rod length emerge in small noise strength. Thanks to the noise in the rotational direction, autonomous motion emerges without the external force and large noise could make the current reversal happen. Eventually, the new mechanism to generate directed transport by the rotation is studied.

  10. Elastic coupling between layers in two-dimensional materials

    NASA Astrophysics Data System (ADS)

    Gao, Yang; Kim, Suenne; Zhou, Si; Chiu, Hsiang-Chih; Nélias, Daniel; Berger, Claire; de Heer, Walt; Polloni, Laura; Sordan, Roman; Bongiorno, Angelo; Riedo, Elisa

    2015-07-01

    Two-dimensional materials, such as graphene and MoS2, are films of a few atomic layers in thickness with strong in-plane bonds and weak interactions between the layers. The in-plane elasticity has been widely studied in bending experiments where a suspended film is deformed substantially; however, little is known about the films’ elastic modulus perpendicular to the planes, as the measurement of the out-of-plane elasticity of supported 2D films requires indentation depths smaller than the films’ interlayer distance. Here, we report on sub-ångström-resolution indentation measurements of the perpendicular-to-the-plane elasticity of 2D materials. Our indentation data, combined with semi-analytical models and density functional theory, are then used to study the perpendicular elasticity of few-layer-thick graphene and graphene oxide films. We find that the perpendicular Young’s modulus of graphene oxide films reaches a maximum when one complete water layer is intercalated between the graphitic planes. This non-destructive methodology can map interlayer coupling and intercalation in 2D films.

  11. Broken Ergodicity in Two-Dimensional Homogeneous Magnetohydrodynamic Turbulence

    NASA Technical Reports Server (NTRS)

    Shebalin, John V.

    2010-01-01

    Two-dimensional (2-D) homogeneous magnetohydrodynamic (MHD) turbulence has many of the same qualitative features as three-dimensional (3-D) homogeneous MHD turbulence.The se features include several ideal invariants, along with the phenomenon of broken ergodicity. Broken ergodicity appears when certain modes act like random variables with mean values that are large compared to their standard deviations, indicating a coherent structure or dynamo.Recently, the origin of broken ergodicity in 3-D MHD turbulence that is manifest in the lowest wavenumbers was explained. Here, a detailed description of the origins of broken ergodicity in 2-D MHD turbulence is presented. It will be seen that broken ergodicity in ideal 2-D MHD turbulence can be manifest in the lowest wavenumbers of a finite numerical model for certain initial conditions or in the highest wavenumbers for another set of initial conditions.T he origins of broken ergodicity in ideal 2-D homogeneous MHD turbulence are found through an eigen analysis of the covariance matrices of the modal probability density functions.It will also be shown that when the lowest wavenumber magnetic field becomes quasi-stationary, the higher wavenumber modes can propagate as Alfven waves on these almost static large-scale magnetic structures

  12. Two-dimensional chirped-pulse Fourier transform microwave spectroscopy.

    PubMed

    Wilcox, David S; Hotopp, Kelly M; Dian, Brian C

    2011-08-18

    Two-dimensional (2D) correlation techniques are developed for chirped-pulse Fourier transform microwave (CP-FTMW) spectroscopy. The broadband nature of the spectrometer coupled with fast digital electronics permits the generation of arbitrary pulse sequences and simultaneous detection of the 8-18 GHz region of the microwave spectrum. This significantly increases the number of rotation transitions that can be simultaneously probed, as well as the bandwidth in both frequency dimensions. We theoretically and experimentally evaluate coherence transfer of three- and four-level systems to relate the method with previous studies. We then extend the principles of single-quantum and autocorrelation to incorporate broadband excitation and detection. Global connectivity of the rotational energy level structure is demonstrated through the transfer of multiple coherences in a single 2D experiment. Additionally, open-system effects are observed from irradiating many-level systems. Quadrature detection in the indirectly measured frequency dimension and phase cycling are also adapted for 2D CP-FTMW spectroscopy.

  13. Compact design for two-dimensional electronic spectroscopy

    NASA Astrophysics Data System (ADS)

    Huang, Zheng; Wang, Peng; Shen, Xiong; Yan, Tian-Min; Zhang, Yizhu; Liu, Jun

    2016-03-01

    We present a passively phase-stabilized two-dimensional electronic spectroscopy (2DES) with a compact size, and the ease of implementation and maintenance. Our design relies on a mask beam-splitter with four holes to form non-collinear box geometry, and a homebuilt stacked retroreflector, which introduces the phase-locked pulse sequence, remedying the instability of commonly used translation stages. The minimized size of the setup suppresses the influences of optical path-length fluctuations during measurements, improving the phase stability and precise timing of pulse sequences. In our 2DES, only few conventional optical components are used, which make this sophisticated instrumentation convenient to establish and particularly easy to conduct alignment. In data analysis, the self-referencing spectral interferometry (SRSI) method is first introduced to extract the complex-valued signal from spectral interferometry in 2DES. The alternative algorithm achieves the improvement of the signal-to-noise ratio (SNR) and considerable reduction of data acquisition time. The new setup is suitable over a tunable range of spectroscopic wavelength, from ultraviolet (UV) to the near-infrared (NIR) regime, and for ultra-broadband bandwidth, few-cycle laser pulses.

  14. Interaction and Correlation Effects in Quasi Two-dimensional Materials

    NASA Astrophysics Data System (ADS)

    Louie, Steven G.

    2015-03-01

    Experimental and theoretical studies of atomically thin quasi two-dimensional materials (typically related to some parent van der Waals layered crystals) and their nanostructures have revealed that these systems can exhibit highly unusual behaviors. In this talk, we discuss some theoretical studies of the electronic, transport and optical properties of such systems. We present results on graphene and graphene nanostructures as well as other quasi-2D systems such as monolayer and few-layer transition metal dichalcogenides (e.g., MoS2, MoSe2, WS2, and WSe2) and metal monochalcogenides (such as GaSe and FeSe). Owing to their reduced dimensionality, these systems present opportunities for unusual manifestation of concepts and phenomena that may not be so prominent or have not been seen in bulk materials. Symmetry and many-body interaction effects often play a critical role in shaping qualitatively and quantitatively their properties. Several quantum phenomena are discussed, including novel and dominant exciton effects, tunable magnetism, electron supercollimation by disorder, unusual plasmon behaviors, and possible enhanced superconductivity in some of these systems. We investigate their physical origins and compare theoretical predictions with experimental data. This work was supported by DOE under Contract No. DE-AC02-05CH11231 and by NSF under Grant No. DMR10-1006184. I would like to acknowledge collaborations with members of the Louie group and the experimental groups of Crommie, Heinz, Wang, and Zhang.

  15. Curved Two-Dimensional Electron Systems in Semiconductor Nanoscrolls

    NASA Astrophysics Data System (ADS)

    Peters, Karen; Mendach, Stefan; Hansen, Wolfgang

    The perfect control of strain and layer thickness in epitaxial semiconductor bilayers is employed to fabricate semiconductor nanoscrolls with precisely adjusted scroll diameter ranging between a few nanometers and several tens of microns. Furthermore, semiconductor heteroepitaxy allows us to incorporate quantum objects such as quantum wells, quantum dots, or modulation doped low-dimensional carrier systems into the nanoscrolls. In this review, we summarize techniques that we have developed to fabricate semiconductor nanoscrolls with well-defined location, orientation, geometry, and winding number. We focus on magneto-transport studies of curved two-dimensional electron systems in such nanoscrolls. An externally applied magnetic field results in a strongly modulated normal-to-surface component leading to magnetic barriers, reflection of edge channels, and local spin currents. The observations are compared to finite-element calculations and discussed on the basis of simple models taking into account the influence of a locally modulated state density on the conductivity. In particular, it is shown that the observations in high magnetic fields can be well described considering the transport in edge channels according to the Landauer-Büttiker model if additional magnetic field induced channels aligned along magnetic barriers are accounted for.

  16. Calibration of the ORNL two-dimensional Thomson scattering system

    SciTech Connect

    Thomas, C.E. Jr.; Lazarus, E.A.; Kindsfather, R.R.; Murakami, M.; Stewart, K.A.

    1985-10-01

    A unified presentation of the calibrations needed for accurate calculation of electron temperature and density from Thomson scattering data for the Oak Ridge National Laboratory two-dimensional Thomson scattering system (SCATPAK II) is made. Techniques are described for measuring the range of wavelengths to which each channel is responsive. A statistical method for calibrating the gain of each channel in the system is given, and methods of checking for internal consistency and accuracy are presented. The relationship between the constants describing the relative light collection efficiency of each channel and plasma light-scattering theory is developed, methods for measuring the channel efficiencies and evaluating their accuracy are described, and the effect on these constants of bending fiber optics is discussed. The use of Rayleigh or Raman scattering for absolute efficiency (density) calibration, stray light measurement, and system efficiency evaluation is discussed; the relative merits of Rayleigh vs Raman scattering are presented; and the relationship among the Rayleigh/Raman calibrations, relative channel efficiency constants, and absolute efficiencies is developed.

  17. Measuring Spatial Coherence With a Two-Dimensional Aperture Array

    NASA Astrophysics Data System (ADS)

    González, Aura I.; Mejía, Yobani

    2008-04-01

    The complex degree of spatial coherence of the optical fields, in general, is a shift variant quantity. Therefore to characterize it, in addition to knowing how it changes in function of the separation of the two points under analysis, we require knowing how it changes in function of the location of these points. In order to measure the complex degree of spatial coherence of any quasi-monochromatic optical field, we propose a method that uses a mask with a two-dimensional array of apertures (small circular holes) to sample the optical field. The distribution of the apertures in the mask is made so that we get a non redundant array, it means that the classes of aperture pairs of the mask are composed just by one pair. From the Fourier spectrum of the interference pattern in far field generated by the mask we can determine the magnitude and the phase of the complex degree of spatial coherence. The efficiency of the array is verified with experimental results using a partially coherent beam generated following the rotating glass method. Finally, the results obtained in the experiment are compared with those obtained by means of numerical simulations.

  18. Thermal Convection in a Strongly Stratified Two-dimensional Fluid

    NASA Astrophysics Data System (ADS)

    Zhang, Jie; Wu, X. L.; Xia, K. Q.

    2004-03-01

    Thermal convection occurs when a fluid becomes gravitationally unstable in the presence of a temperature gradient. While most laboratory experiments investigate convections in fluids with a uniform mass distribution, natural convections often take place in fluids whose density is stratified. In the absence of temperature gradient, a freely suspended soap film stratifies under the action of gravity and assumes a nearly exponential thickness profile similar to the distribution of air mass in atmosphere. In the presence of such a gradient, thermal plumes are generated which drives fluid flows and at the time creates two-dimensional (2D) density fluctuations. We studied thickness power spectra in soap film convection by analyzing thermal radiation signal emitting from a single spot at the center of the film. The experiments were performed at different temperature gradients (ΔT), which were imposed vertically across the film. In the buoyancy sub-range, the frequency power spectrum shows a Bolgiano-Obukhov scaling f-1.4 when ΔT ≤ 50K, and a new scaling relation f-1.0 emerges when ΔT > 50K. This latter behavior was observed to coincide with the appearance of a large-scale circulation in the film.

  19. Sensitivity Analysis of Chaotic Flow around Two-Dimensional Airfoil

    NASA Astrophysics Data System (ADS)

    Blonigan, Patrick; Wang, Qiqi; Nielsen, Eric; Diskin, Boris

    2015-11-01

    Computational methods for sensitivity analysis are invaluable tools for fluid dynamics research and engineering design. These methods are used in many applications, including aerodynamic shape optimization and adaptive grid refinement. However, traditional sensitivity analysis methods, including the adjoint method, break down when applied to long-time averaged quantities in chaotic fluid flow fields, such as high-fidelity turbulence simulations. This break down is due to the ``Butterfly Effect'' the high sensitivity of chaotic dynamical systems to the initial condition. A new sensitivity analysis method developed by the authors, Least Squares Shadowing (LSS), can compute useful and accurate gradients for quantities of interest in chaotic dynamical systems. LSS computes gradients using the ``shadow trajectory'', a phase space trajectory (or solution) for which perturbations to the flow field do not grow exponentially in time. To efficiently compute many gradients for one objective function, we use an adjoint version of LSS. This talk will briefly outline Least Squares Shadowing and demonstrate it on chaotic flow around a Two-Dimensional airfoil.

  20. Vortex pairing in two-dimensional Bose gases

    SciTech Connect

    Foster, Christopher J.; Davis, Matthew J.; Blakie, P. Blair

    2010-02-15

    Recent experiments on ultracold Bose gases in two dimensions have provided evidence for the existence of the Berezinskii-Kosterlitz-Thouless (BKT) phase via analysis of the interference between two independent systems. In this work we study the two-dimensional quantum degenerate Bose gas at finite temperature using the projected Gross-Pitaevskii equation classical field method. Although this describes the highly occupied modes of the gas below a momentum cutoff, we have developed a method to incorporate the higher momentum states in our model. We concentrate on finite-sized homogeneous systems in order to simplify the analysis of the vortex pairing. We determine the dependence of the condensate fraction on temperature and compare this to the calculated superfluid fraction. By measuring the first order correlation function we determine the boundary of the Bose-Einstein condensate and BKT phases, and find it is consistent with the superfluid fraction decreasing to zero. We reveal the characteristic unbinding of vortex pairs above the BKT transition via a coarse-graining procedure. Finally, we model the procedure used in experiments to infer system correlations [Hadzibabic et al., Nature 441, 1118 (2006)], and quantify its level of agreement with directly calculated in situ correlation functions.

  1. Beliaev damping in quasi-two-dimensional dipolar condensates

    NASA Astrophysics Data System (ADS)

    Wilson, Ryan M.; Natu, Stefan

    2016-05-01

    We study the effects of quasiparticle interactions in a quasi-two-dimensional (quasi-2D), zero-temperature Bose-Einstein condensate of dipolar atoms, which can exhibit a roton-maxon feature in its quasiparticle spectrum. Our focus is the Beliaev damping process, in which a quasiparticle collides with the condensate and resonantly decays into a pair of quasiparticles. Remarkably, the rate for this process exhibits a highly nontrivial dependence on the quasiparticle momentum and the dipolar interaction strength. For weak interactions, low-energy phonons experience no damping, and higher-energy quasiparticles undergo anomalously weak damping. In contrast, the Beliaev damping rates become anomalously large for stronger dipolar interactions, as rotons become energetically accessible as final states. When the dipoles are tilted off the axis of symmetry, the damping rates acquire an anisotropic character. Surprisingly, this anisotropy does not simply track the anisotropy of the dipolar interactions, rather, the mechanisms for damping are qualitatively modified in the anisotropic case. Our study reveals the unconventional nature of Beliaev damping in dipolar condensates, and has important implications for ongoing studies of equilibrium and nonequilibrium dynamics in these systems. Further, our results are relevant for other 2D superfluids with roton excitations, including spin-orbit-coupled Bose gases, magnon condensates, and 4He films.

  2. Long-distance entanglement generation in two-dimensional networks

    SciTech Connect

    Broadfoot, S.; Dorner, U.; Jaksch, D.

    2010-10-15

    We consider two-dimensional networks composed of nodes initially linked by two-qubit mixed states. In these networks we develop a global error correction scheme that can generate distance-independent entanglement from arbitrary network geometries using rank-2 states. By using this method and combining it with the concept of percolation, we also show that the generation of long-distance entanglement is possible with rank-3 states. Entanglement percolation and global error correction have different advantages depending on the given situation. To reveal the trade-off between them we consider their application to networks containing pure states. In doing so we find a range of pure-state schemes, each of which has applications in particular circumstances: For instance, we can identify a protocol for creating perfect entanglement between two distant nodes. However, this protocol cannot generate a singlet between any two nodes. In contrast, we can also construct schemes for creating entanglement between any nodes, but the corresponding entanglement fidelity is lower.

  3. Monolithic multigrid methods for two-dimensional resistive magnetohydrodynamics

    DOE PAGES

    Adler, James H.; Benson, Thomas R.; Cyr, Eric C.; MacLachlan, Scott P.; Tuminaro, Raymond S.

    2016-01-06

    Magnetohydrodynamic (MHD) representations are used to model a wide range of plasma physics applications and are characterized by a nonlinear system of partial differential equations that strongly couples a charged fluid with the evolution of electromagnetic fields. The resulting linear systems that arise from discretization and linearization of the nonlinear problem are generally difficult to solve. In this paper, we investigate multigrid preconditioners for this system. We consider two well-known multigrid relaxation methods for incompressible fluid dynamics: Braess--Sarazin relaxation and Vanka relaxation. We first extend these to the context of steady-state one-fluid viscoresistive MHD. Then we compare the two relaxationmore » procedures within a multigrid-preconditioned GMRES method employed within Newton's method. To isolate the effects of the different relaxation methods, we use structured grids, inf-sup stable finite elements, and geometric interpolation. Furthermore, we present convergence and timing results for a two-dimensional, steady-state test problem.« less

  4. Self-consistent perturbation theory for two dimensional twisted bilayers

    NASA Astrophysics Data System (ADS)

    Shirodkar, Sharmila N.; Tritsaris, Georgios A.; Kaxiras, Efthimios

    Theoretical modeling and ab-initio simulations of two dimensional heterostructures with arbitrary angles of rotation between layers involve unrealistically large and expensive calculations. To overcome this shortcoming, we develop a methodology for weakly interacting heterostructures that treats the effect of one layer on the other as perturbation, and restricts the calculations to their primitive cells. Thus, avoiding computationally expensive supercells. We start by approximating the interaction potential between the twisted bilayers to that of a hypothetical configuration (viz. ideally stacked untwisted layers), which produces band structures in reasonable agreement with full-scale ab-initio calculations for commensurate and twisted bilayers of graphene (Gr) and Gr/hexagonal boron nitride (h-BN) heterostructures. We then self-consistently calculate the charge density and hence, interaction potential of the heterostructures. In this work, we test our model for bilayers of various combinations of Gr, h-BN and transition metal dichalcogenides, and discuss the advantages and shortcomings of the self-consistently calculated interaction potential. Department of Physics, Harvard University, Cambridge, Massachusetts 02138, USA.

  5. Intermittency measurement in two-dimensional bacterial turbulence

    NASA Astrophysics Data System (ADS)

    Qiu, Xiang; Ding, Long; Huang, Yongxiang; Chen, Ming; Lu, Zhiming; Liu, Yulu; Zhou, Quan

    2016-06-01

    In this paper, an experimental velocity database of a bacterial collective motion, e.g., Bacillus subtilis, in turbulent phase with volume filling fraction 84 % provided by Professor Goldstein at Cambridge University (UK), was analyzed to emphasize the scaling behavior of this active turbulence system. This was accomplished by performing a Hilbert-based methodology analysis to retrieve the scaling property without the β -limitation. A dual-power-law behavior separated by the viscosity scale ℓν was observed for the q th -order Hilbert moment Lq(k ) . This dual-power-law belongs to an inverse-cascade since the scaling range is above the injection scale R , e.g., the bacterial body length. The measured scaling exponents ζ (q ) of both the small-scale (k >kν ) and large-scale (k two-dimensional Ekman-Navier-Stokes equation, a continuum model indicates that the origin of the multifractality could be a result of some additional nonlinear interaction terms, which deservers a more careful investigation.

  6. Correlating hydrodynamic radii with that of two-dimensional nanoparticles

    SciTech Connect

    Yue, Yuan; Kan, Yuwei; Clearfield, Abraham; Choi, Hyunho; Liang, Hong

    2015-12-21

    Dynamic light scattering (DLS) is one of the most adapted methods to measure the size of nanoparticles, as referred to the hydrodynamic radii (R{sub h}). However, the R{sub h} represents only that of three-dimensional spherical nanoparticles. In the present research, the size of two-dimensional (2D) nanoparticles of yttrium oxide (Y{sub 2}O{sub 3}) and zirconium phosphate (ZrP) was evaluated through comparing their hydrodynamic diameters via DLS with lateral sizes obtained using scanning and transmission electron microscopy. We demonstrate that the hydrodynamic radii are correlated with the lateral sizes of both square and circle shaped 2D nanoparticles. Two proportional coefficients, i.e., correcting factors, are proposed for the Brownian motion status of 2D nanoparticles. The correction is possible by simplifying the calculation of integrals in the case of small thickness approximation. The correcting factor has great significance for investigating the translational diffusion behavior of 2D nanoparticles in a liquid and in effective and low-cost measurement in terms of size and morphology of shape-specific nanoparticles.

  7. Lagrangian statistics in weakly forced two-dimensional turbulence.

    PubMed

    Rivera, Michael K; Ecke, Robert E

    2016-01-01

    Measurements of Lagrangian single-point and multiple-point statistics in a quasi-two-dimensional stratified layer system are reported. The system consists of a layer of salt water over an immiscible layer of Fluorinert and is forced electromagnetically so that mean-squared vorticity is injected at a well-defined spatial scale ri. Simultaneous cascades develop in which enstrophy flows predominately to small scales whereas energy cascades, on average, to larger scales. Lagrangian correlations and one- and two-point displacements are measured for random initial conditions and for initial positions within topological centers and saddles. Some of the behavior of these quantities can be understood in terms of the trapping characteristics of long-lived centers, the slow motion near strong saddles, and the rapid fluctuations outside of either centers or saddles. We also present statistics of Lagrangian velocity fluctuations using energy spectra in frequency space and structure functions in real space. We compare with complementary Eulerian velocity statistics. We find that simultaneous inverse energy and enstrophy ranges present in spectra are not directly echoed in real-space moments of velocity difference. Nevertheless, the spectral ranges line up well with features of moment ratios, indicating that although the moments are not exhibiting unambiguous scaling, the behavior of the probability distribution functions is changing over short ranges of length scales. Implications for understanding weakly forced 2D turbulence with simultaneous inverse and direct cascades are discussed.

  8. An organizing principle for two-dimensional strongly correlated superconductivity

    PubMed Central

    Fratino, L.; Sémon, P.; Sordi, G.; Tremblay, A.-M. S.

    2016-01-01

    Superconductivity in the cuprates exhibits many unusual features. We study the two-dimensional Hubbard model with plaquette dynamical mean-field theory to address these unusual features and relate them to other normal-state phenomena, such as the pseudogap. Previous studies with this method found that upon doping the Mott insulator at low temperature a pseudogap phase appears. The low-temperature transition between that phase and the correlated metal at higher doping is first-order. A series of crossovers emerge along the Widom line extension of that first-order transition in the supercritical region. Here we show that the highly asymmetric dome of the dynamical mean-field superconducting transition temperature , the maximum of the condensation energy as a function of doping, the correlation between maximum and normal-state scattering rate, the change from potential-energy driven to kinetic-energy driven pairing mechanisms can all be understood as remnants of the normal state first-order transition and its associated crossovers that also act as an organizing principle for the superconducting state. PMID:26964524

  9. Two dimensional nanoscale reciprocating sliding contacts of textured surfaces

    NASA Astrophysics Data System (ADS)

    Tong, Ruiting; Liu, Geng; Liu, Tianxiang

    2016-05-01

    Detailed behaviors of nanoscale textured surfaces during the reciprocating sliding contacts are still unknown although they are widely used in mechanical components to improve tribological characteristics. The current research of sliding contacts of textured surfaces mainly focuses on the experimental studies, while the cost is too high. Molecular dynamics(MD) simulation is widely used in the studies of nanoscale single-pass sliding contacts, but the CPU cost of MD simulation is also too high to simulate the reciprocating sliding contacts. In this paper, employing multiscale method which couples molecular dynamics simulation and finite element method, two dimensional nanoscale reciprocating sliding contacts of textured surfaces are investigated. Four textured surfaces with different texture shapes are designed, and a rigid cylindrical tip is used to slide on these textured surfaces. For different textured surfaces, average potential energies and average friction forces of the corresponding sliding processes are analyzed. The analyzing results show that "running-in" stages are different for each texture, and steady friction processes are discovered for textured surfaces II, III and IV. Texture shape and sliding direction play important roles in reciprocating sliding contacts, which influence average friction forces greatly. This research can help to design textured surfaces to improve tribological behaviors in nanoscale reciprocating sliding contacts.

  10. Quantum metallicity in a two-dimensional insulator.

    PubMed

    Butko, V Y; Adams, P W

    2001-01-11

    One of the most far-reaching problems in condensed-matter physics is to understand how interactions between electrons, and the resulting correlations, affect the electronic properties of disordered two-dimensional systems. Extensive experimental and theoretical studies have shown that interaction effects are enhanced by disorder, and that this generally results in a depletion of the density of electronic states. In the limit of strong disorder, this depletion takes the form of a complete gap in the density of states. It is known that this 'Coulomb gap' can turn a pure metal film that is highly disordered into a poorly conducting insulator, but the properties of these insulators are not well understood. Here we investigate the electronic properties of disordered beryllium films, with the aim of disentangling the effects of the Coulomb gap and the underlying disorder. We show that the gap is suppressed by a magnetic field and that this drives the strongly insulating beryllium films into a low-temperature 'quantum metal' phase with resistance near the quantum resistance RQ = h/e2, where h is Planck's constant and e is the electron charge.

  11. Two-dimensional electronic spectroscopy signatures of the glass transition

    DOE PAGES

    Lewis, K. L. .. M.; Myers, J. A.; Fuller, F.; Tekavec, P. F.; Ogilvie, J. P.

    2010-01-01

    Two-dimensional electronic spectroscopy is a sensitive probe of solvation dynamics. Using a pump–probe geometry with a pulse shaper [ Optics Express 15 (2007), 16681-16689; Optics Express 16 (2008), 17420-17428], we present temperature dependent 2D spectra of laser dyes dissolved in glass-forming solvents. At low waiting times, the system has not yet relaxed, resulting in a spectrum that is elongated along the diagonal. At longer times, the system loses its memory of the initial excitation frequency, and the 2D spectrum rounds out. As the temperature is lowered, the time scale of this relaxation grows, and the elongation persists for longermore » waiting times. This can be measured in the ratio of the diagonal width to the anti-diagonal width; the behavior of this ratio is representative of the frequency–frequency correlation function [ Optics Letters 31 (2006), 3354–3356]. Near the glass transition temperature, the relaxation behavior changes. Understanding this change is important for interpreting temperature-dependent dynamics of biological systems.« less

  12. Two Dimensional Heat Transfer around Penetrations in Multilayer Insulation

    NASA Technical Reports Server (NTRS)

    Johnson, Wesley L.; Kelly, Andrew O.; Jumper, Kevin M.

    2012-01-01

    The objective of this task was to quantify thermal losses involving integrating MLI into real life situations. Testing specifically focused on the effects of penetrations (including structural attachments, electrical conduit/feedthroughs, and fluid lines) through MLI. While there have been attempts at quantifying these losses both analytically and experimentally, none have included a thorough investigation of the methods and materials that could be used in such applications. To attempt to quantify the excess heat load coming into the system due to the integration losses, a calorimeter was designed to study two dimensional heat transfer through penetrated MLI. The test matrix was designed to take as many variables into account as was possible with the limited test duration and system size. The parameters varied were the attachment mechanism, the buffer material (for buffer attachment mechanisms only), the thickness of the buffer, and the penetration material. The work done under this task is an attempt to measure the parasitic heat loads and affected insulation areas produced by system integration, to model the parasitic loads, and from the model produce engineering equations to allow for the determination of parasitic heat loads in future applications. The methods of integration investigated were no integration, using a buffer to thermally isolate the strut from the MLI, and temperature matching the MLI on the strut. Several materials were investigated as a buffer material including aerogel blankets, aerogel bead packages, cryolite, and even an evacuated vacuum space (in essence a no buffer condition).

  13. Two-dimensional boron nitride structures functionalization: first principles studies.

    PubMed

    Ponce-Pérez, R; Cocoletzi, Gregorio H; Takeuchi, Noboru

    2016-09-01

    Density functional theory calculations have been performed to investigate two-dimensional hexagonal boron nitride (2D hBN) structures functionalization with organic molecules. 2x2, 4x4 and 6x6 periodic 2D hBN layers have been considered to interact with acetylene. To deal with the exchange-correlation energy the generalized gradient approximation (GGA) is invoked. The electron-ion interaction is treated with the pseudopotential method. The GGA with the Perdew-Burke-Ernzerhoff (PBE) functionals together with van der Waals interactions are considered to deal with the composed systems. To investigate the functionalization two main configurations have been explored; in one case the molecule interacts with the boron atom and in the other with the nitrogen atom. Results of the adsorption energies indicate chemisorption in both cases. The total density of states (DOS) displays an energy gap in both cases. The projected DOS indicate that the B-p and N-p orbitals are those that make the most important contribution in the valence band and the H-s and C-p orbitals provide an important contribution in the conduction band to the DOS. Provided that the interactions of the acetylene with the 2D layer modify the structural and electronic properties of the hBN the possibility of structural functionalization using organic molecules may be concluded. PMID:27566317

  14. Transparent Conductive Two-Dimensional Titanium Carbide Epitaxial Thin Films

    PubMed Central

    2014-01-01

    Since the discovery of graphene, the quest for two-dimensional (2D) materials has intensified greatly. Recently, a new family of 2D transition metal carbides and carbonitrides (MXenes) was discovered that is both conducting and hydrophilic, an uncommon combination. To date MXenes have been produced as powders, flakes, and colloidal solutions. Herein, we report on the fabrication of ∼1 × 1 cm2 Ti3C2 films by selective etching of Al, from sputter-deposited epitaxial Ti3AlC2 films, in aqueous HF or NH4HF2. Films that were about 19 nm thick, etched with NH4HF2, transmit ∼90% of the light in the visible-to-infrared range and exhibit metallic conductivity down to ∼100 K. Below 100 K, the films’ resistivity increases with decreasing temperature and they exhibit negative magnetoresistance—both observations consistent with a weak localization phenomenon characteristic of many 2D defective solids. This advance opens the door for the use of MXenes in electronic, photonic, and sensing applications. PMID:24741204

  15. Terahertz spectroscopy of two-dimensional subwavelength plasmonic structures

    SciTech Connect

    Azad, Abul K; Chen, Houtong; Taylor, Antoinette; O' Hara, John F; Han, Jiaguang; Lu, Xinchao; Zhang, Weili

    2009-01-01

    The fascinating properties of plasmonic structures have had significant impact on the development of next generation ultracompact photonic and optoelectronic components. We study two-dimensional plasmonic structures functioning at terahertz frequencies. Resonant terahertz response due to surface plasmons and dipole localized surface plasmons were investigated by the state-of-the-art terahertz time domain spectroscopy (THz-TDS) using both transmission and reflection configurations. Extraordinary terahertz transmission was demonstrated through the subwavelength metallic hole arrays made from good conducting metals as well as poor metals. Metallic arrays m!lde from Pb, generally a poor metal, and having optically thin thicknesses less than one-third of a skin depth also contributed in enhanced THz transmission. A direct transition of a surface plasmon resonance from a photonic crystal minimum was observed in a photo-doped semiconductor array. Electrical controls of the surface plasmon resonances by hybridization of the Schottkey diode between the metallic grating and the semiconductor substrate are investigated as a function of the applied reverse bias. In addition, we have demonstrated photo-induced creation and annihilation of surface plasmons with appropriate semiconductors at room temperature. According to the Fano model, the transmission properties are characterized by two essential contributions: resonant excitation of surface plasmons and nonresonant direct transmission. Such plasmonic structures may find fascinating applications in terahertz imaging, biomedical sensing, subwavelength terahertz spectroscopy, tunable filters, and integrated terahertz devices.

  16. Ab Initio Prediction of Piezoelectricity in Two-Dimensional Materials.

    PubMed

    Blonsky, Michael N; Zhuang, Houlong L; Singh, Arunima K; Hennig, Richard G

    2015-10-27

    Two-dimensional (2D) materials present many unique materials concepts, including material properties that sometimes differ dramatically from those of their bulk counterparts. One of these properties, piezoelectricity, is important for micro- and nanoelectromechanical systems applications. Using symmetry analysis, we determine the independent piezoelectric coefficients for four groups of predicted and synthesized 2D materials. We calculate with density-functional perturbation theory the stiffness and piezoelectric tensors of these materials. We determine the in-plane piezoelectric coefficient d11 for 37 materials within the families of 2D metal dichalcogenides, metal oxides, and III-V semiconductor materials. A majority of the structures, including CrSe2, CrTe2, CaO, CdO, ZnO, and InN, have d11 coefficients greater than 5 pm/V, a typical value for bulk piezoelectric materials. Our symmetry analysis shows that buckled 2D materials exhibit an out-of-plane coefficient d31. We find that d31 for 8 III-V semiconductors ranges from 0.02 to 0.6 pm/V. From statistical analysis, we identify correlations between the piezoelectric coefficients and the electronic and structural properties of the 2D materials that elucidate the origin of the piezoelectricity. Among the 37 2D materials, CdO, ZnO, and CrTe2 stand out for their combination of large piezoelectric coefficient and low formation energy and are recommended for experimental exploration. PMID:26312745

  17. Two Dimensional Organometal Halide Perovskite Nanorods with Tunable Optical Properties.

    PubMed

    Aharon, Sigalit; Etgar, Lioz

    2016-05-11

    Organo-metal halide perovskite is an efficient light harvester in photovoltaic solar cells. Organometal halide perovskite is used mainly in its "bulk" form in the solar cell. Confined perovskite nanostructures could be a promising candidate for efficient optoelectronic devices, taking advantage of the superior bulk properties of organo-metal halide perovskite, as well as the nanoscale properties. In this paper, we present facile low-temperature synthesis of two-dimensional (2D) lead halide perovskite nanorods (NRs). These NRs show a shift to higher energies in the absorbance and in the photoluminescence compared to the bulk material, which supports their 2D structure. X-ray diffraction (XRD) analysis of the NRs demonstrates their 2D nature combined with the tetragonal 3D perovskite structure. In addition, by alternating the halide composition, we were able to tune the optical properties of the NRs. Fast Fourier transform, and electron diffraction show the tetragonal structure of these NRs. By varying the ligands ratio (e.g., octylammonium to oleic acid) in the synthesis, we were able to provide the formation mechanism of these novel 2D perovskite NRs. The 2D perovskite NRs are promising candidates for a variety of optoelectronic applications, such as light-emitting diodes, lasing, solar cells, and sensors. PMID:27089497

  18. Two-dimensional ultrasound image matching system for photodynamic therapy

    NASA Astrophysics Data System (ADS)

    Zaim, Amjad; Keck, Rick W.; Selman, Steven H.; Jankun, Jerzy

    2001-05-01

    Two-dimensional (2D) ultrasound imaging is commonly used for diagnosis in a variety of medical fields. However, there are several drawbacks of conventional 2D-ultrasound imaging. These include prostate or transducer movement that produces sets of different images that are difficult to interpret. Also during patient's reexamination correspondence between sets of images before reexamination and after is difficult to establish. This can be described as a problem of correlation between two sets of images: the first created before distortion or examination, the second one after. We propose a method to register 2D ultrasound volumes based on external markers introduced in the prostate. The metal balls are inserted in the prostate at three distinct locations in the prostate. These appear as bright dots in the ultrasound field, serve as reference points, are then outlined through a user-interactive program from two sets of images. Then, the computer program rotates and translates till they match respectively, and displays the mapped points with their corresponding location. Based on this idea we developed an image-guided system for PDT that require high-precision placement of implants. In the planning stage, the system performs an automatic acquisition of 2D transrectal ultrasound images that will ultimately be used to construct the treatment plan. At the time of the therapy, new sets of ultrasound images are acquired and a match is established between the virtual world and the patient's real world with the aid of manually introduced markers and image matching algorithms.

  19. Gate-induced superconductivity in two-dimensional atomic crystals

    NASA Astrophysics Data System (ADS)

    Saito, Yu; Nojima, Tsutomu; Iwasa, Yoshihiro

    2016-09-01

    Two-dimensional (2D) crystals are attracting growing interest in condensed matter physics, since these systems exhibit not only rich electronic and photonic properties but also exotic electronic phase transitions including superconductivity and charge density wave. Moreover, owing to the recent development of transfer methods after exfoliation and electric-double-layer transistors, superconducting 2D atomic crystals, the thicknesses of which are below 1–2 nm, have been successfully obtained. Here, we present a topical review on the recent discoveries of 2D crystalline superconductors by ionic-liquid gating and a series of their novel properties. In particular, we highlight two topics; quantum metallic states (or possible metallic ground states) and superconductivity robust against in-plane magnetic fields. These phenomena can be discussed with the effects of weakened disorder and/or broken spacial inversion symmetry leading to valley-dependent spin-momentum locking (spin-valley locking). These examples suggest the superconducting 2D crystals are new platforms for investigating the intrinsic quantum phases as well as exotic nature in 2D superconductors.

  20. Two-dimensional collective Hamiltonian for chiral and wobbling modes

    NASA Astrophysics Data System (ADS)

    Chen, Q. B.; Zhang, S. Q.; Zhao, P. W.; Jolos, R. V.; Meng, J.

    2016-10-01

    A two-dimensional collective Hamiltonian (2DCH) on both azimuth and polar motions in triaxial nuclei is proposed to investigate the chiral and wobbling modes. In the 2DCH, the collective potential and the mass parameters are determined from three-dimensional tilted axis cranking (TAC) calculations. The broken chiral and signature symmetries in the TAC solutions are restored by the 2DCH. The validity of the 2DCH is illustrated with a triaxial rotor (γ =-30∘ ) coupling to one h11 /2 proton particle and one h11 /2 neutron hole. By diagonalizing the 2DCH, the angular momenta and energy spectra are obtained. These results agree with the exact solutions of the particle rotor model (PRM) at high rotational frequencies. However, at low frequencies, the energies given by the 2DCH are larger than those by the PRM due to the underestimation of the mass parameters. In addition, with increasing angular momentum, the transitions from the chiral vibration to chiral rotation and further to longitudinal wobbling motion have been presented in the 2DCH.

  1. Defect engineering of two-dimensional transition metal dichalcogenides

    NASA Astrophysics Data System (ADS)

    Lin, Zhong; Carvalho, Bruno R.; Kahn, Ethan; Lv, Ruitao; Rao, Rahul; Terrones, Humberto; Pimenta, Marcos A.; Terrones, Mauricio

    2016-06-01

    Two-dimensional transition metal dichalcogenides (TMDs), an emerging family of layered materials, have provided researchers a fertile ground for harvesting fundamental science and emergent applications. TMDs can contain a number of different structural defects in their crystal lattices which significantly alter their physico-chemical properties. Having structural defects can be either detrimental or beneficial, depending on the targeted application. Therefore, a comprehensive understanding of structural defects is required. Here we review different defects in semiconducting TMDs by summarizing: (i) the dimensionalities and atomic structures of defects; (ii) the pathways to generating structural defects during and after synthesis and, (iii) the effects of having defects on the physico-chemical properties and applications of TMDs. Thus far, significant progress has been made, although we are probably still witnessing the tip of the iceberg. A better understanding and control of defects is important in order to move forward the field of Defect Engineering in TMDs. Finally, we also provide our perspective on the challenges and opportunities in this emerging field.

  2. Two-Dimensional Heat Transfer in a Heterogeneous Fracture Network

    NASA Astrophysics Data System (ADS)

    Gisladottir, V. R.; Roubinet, D.; Tartakovsky, D. M.

    2015-12-01

    Geothermal energy harvesting requires extraction and injection of geothermal fluid. Doing so in an optimal way requires a quantitative understanding of site-specific heat transfer between geothermal fluid and the ambient rock. We develop a heat transfer particle-tracking approach to model that interaction. Fracture-network models of heat transfer in fractured rock explicitly account for the presence of individual fractures, ambient rock matrix, and fracture-matrix interfaces. Computational domains of such models span the meter scale, whereas fracture apertures are on the millimeter scale. The computations needed to model these multi-scale phenomenon can be prohibitively expensive, even for methods using nonuniform meshes. Our approach appreciably decreases the computational costs. Current particle-tracking methods usually assume both infinite matrix and one-dimensional (1D) heat transfer in the matrix blocks. They rely on 1D analytical solutions for heat transfer in a single fracture, which can lead to large predictive errors. Our two-dimensional (2D) heat transfer simulation algorithm is mesh-free and takes into account both longitudinal and transversal heat conduction in the matrix. It uses a probabilistic model to transfer particle to the appropriate neighboring fracture unless it returns to the fracture of origin or remains in the matrix. We use this approach to look at the impact of a fracture-network topology (e.g. the importance of smaller scale fractures), as well as the matrix block distribution on the heat transport in heterogeneous fractured rocks.

  3. Two-dimensional state in driven magnetohydrodynamic turbulence

    SciTech Connect

    Bigot, Barbara; Galtier, Sebastien

    2011-02-15

    The dynamics of the two-dimensional (2D) state in driven three-dimensional (3D) incompressible magnetohydrodynamic turbulence is investigated through high-resolution direct numerical simulations and in the presence of an external magnetic field at various intensities. For such a flow the 2D state (or slow mode) and the 3D modes correspond, respectively, to spectral fluctuations in the plane k{sub ||}=0 and in the area k{sub ||}>0. It is shown that if initially the 2D state is set to zero it becomes nonnegligible in few turnover times, particularly when the external magnetic field is strong. The maintenance of a large-scale driving leads to a break for the energy spectra of 3D modes; when the driving is stopped, the previous break is removed and a decay phase emerges with Alfvenic fluctuations. For a strong external magnetic field the energy at large perpendicular scales lies mainly in the 2D state, and in all situations a pinning effect is observed at small scales.

  4. Synthesis of Two-Dimensional Materials for Capacitive Energy Storage.

    PubMed

    Mendoza-Sánchez, Beatriz; Gogotsi, Yury

    2016-08-01

    The unique properties and great variety of two-dimensional (2D) nanomaterials make them highly attractive for energy storage applications. Here, an insight into the progress made towards the application of 2D nanomaterials for capacitive energy storage is provided. Synthesis methods, and electrochemical performance of various classes of 2D nanomaterials, particularly based on graphene, transition metal oxides, dichalcogenides, and carbides, are presented. The factors that directly influence capacitive performance are discussed throughout the text and include nanosheet composition, morphology and texture, electrode architecture, and device configuration. Recent progress in the fabrication of 2D-nanomaterials-based microsupercapacitors and flexible and free-standing supercapacitors is presented. The main electrode manufacturing techniques with emphasis on scalability and cost-effectiveness are discussed, and include laser scribing, printing, and roll-to-roll manufacture. Various issues that prevent the use of the full energy-storage potential of 2D nanomaterials and how they have been tackled are discussed, and include nanosheet aggregation and the low electrical conductivity of some 2D nanomaterials. Particularly, the design of hybrid and hierarchical 2D and 3D structures based on 2D nanomaterials is presented. Other challenges and opportunities are discussed and include: control of nanosheets size and thickness, chemical and electrochemical instability, and scale-up of electrode films. PMID:27254831

  5. Dissipation in quasi-two-dimensional flowing foams

    NASA Astrophysics Data System (ADS)

    Raufaste, Christophe; Foulon, Amandine; Dollet, Benjamin

    2009-05-01

    The dissipation between two-dimensional (2D) monolayers of bubbles, the so-called quasi-2D foams, and a wall is investigated in two setups: a "liquid pool" system, where the foam is confined between a soap solution and a glass coverslip, and a Hele-Shaw cell, where the foam occupies the narrow gap between two plates. This experimental study reports dissipation measurements for mobile gas/liquid interfaces (free shear boundary condition) over a large range of parameters: in the liquid pool system, velocity and bubble area; in the Hele-Shaw cell, velocity and liquid fraction. The effect of the latter quantity is measured for the first time over more than three orders of magnitude. A full comparison between our results and other experimental studies is proposed and enables to rescale all measurements on a single master curve. It shows that for mobile gas/liquid interfaces, the existing models systematically underestimate the dissipation in flowing foams. This is quantified by a discrepancy factor ξ, ratio of the experimental dissipation measurements to the theoretical predictions, which scales as ξ =1.4(RP/√A )-0.5 with RP the Plateau border radius and A the bubble area, showing that the discrepancy is higher for dry foams.

  6. Dragging two-dimensional discrete solitons by moving linear defects

    SciTech Connect

    Brazhnyi, Valeriy A.; Malomed, Boris A.

    2011-07-15

    We study the mobility of small-amplitude solitons attached to moving defects which drag the solitons across a two-dimensional (2D) discrete nonlinear Schroedinger lattice. Findings are compared to the situation when a free small-amplitude 2D discrete soliton is kicked in a uniform lattice. In agreement with previously known results, after a period of transient motion the free soliton transforms into a localized mode pinned by the Peierls-Nabarro potential, irrespective of the initial velocity. However, the soliton attached to the moving defect can be dragged over an indefinitely long distance (including routes with abrupt turns and circular trajectories) virtually without losses, provided that the dragging velocity is smaller than a certain critical value. Collisions between solitons dragged by two defects in opposite directions are studied too. If the velocity is small enough, the collision leads to a spontaneous symmetry breaking, featuring fusion of two solitons into a single one, which remains attached to either of the two defects.

  7. Electrical Oscillations in Two-Dimensional Microtubular Structures

    NASA Astrophysics Data System (ADS)

    Cantero, María Del Rocío; Perez, Paula L.; Smoler, Mariano; Villa Etchegoyen, Cecilia; Cantiello, Horacio F.

    2016-06-01

    Microtubules (MTs) are unique components of the cytoskeleton formed by hollow cylindrical structures of αβ tubulin dimeric units. The structural wall of the MT is interspersed by nanopores formed by the lateral arrangement of its subunits. MTs are also highly charged polar polyelectrolytes, capable of amplifying electrical signals. The actual nature of these electrodynamic capabilities remains largely unknown. Herein we applied the patch clamp technique to two-dimensional MT sheets, to characterize their electrical properties. Voltage-clamped MT sheets generated cation-selective oscillatory electrical currents whose magnitude depended on both the holding potential, and ionic strength and composition. The oscillations progressed through various modes including single and double periodic regimes and more complex behaviours, being prominent a fundamental frequency at 29 Hz. In physiological K+ (140 mM), oscillations represented in average a 640% change in conductance that was also affected by the prevalent anion. Current injection induced voltage oscillations, thus showing excitability akin with action potentials. The electrical oscillations were entirely blocked by taxol, with pseudo Michaelis-Menten kinetics and a KD of ~1.29 μM. The findings suggest a functional role of the nanopores in the MT wall on the genesis of electrical oscillations that offer new insights into the nonlinear behaviour of the cytoskeleton.

  8. Two-dimensional copper thio- and seleno-cyanates.

    PubMed

    Tsetseris, Leonidas

    2016-03-21

    Based on density-functional theory calculations we identify two-dimensional (2D) forms of copper thio-cyanate (CuSCN) and copper seleno-cyanate (CuSeCN). CuSCN is known to crystallize in two three-dimensional polymorphs, the beta wurtzite and the alpha structure, both with tetrahedral bonding networks. Here we find that CuSCN and CuSeCN may be stabilized also in monolayer geometries with SCN or SeCN groups protruding out of Cu planes. The cohesive energies of stacks made out of these sheets are comparable to those of the alpha and beta structures, so, in principle, 2D CuSCN and CuSeCN may be formed under the appropriate experimental conditions. Other 2D CuSCN and CuSeCN phases with honeycomb-like structures also correspond to local energy minima, but are less stable with respect to the above-mentioned systems. PMID:26911411

  9. Dynamic testing of a two-dimensional box truss beam

    NASA Technical Reports Server (NTRS)

    White, Charles W.

    1987-01-01

    Testing to determine the effects of joint freeplay and pretensioning of diagonal members on the dynamic characteristics of a two-dimensional box truss beam was conducted. The test article was ten bays of planar truss suspended by long wires at each joint. Each bay measured 2 meters per side. Pins of varying size were used to simulate various joint freeplay conditions. Single-point random excitation was the primary method of test. The rational fraction polynomial method was used to extract modal characteristics from test data. A finite element model of the test article was generated from which modal characteristics were predicted. These were compared with those obtained from tests. With the exception of the fundamental mode, correlation of theoretical and experimental results was poor, caused by the resonant coupling of local truss member bending modes with global truss beam modes. This coupling introduced many modes in the frequency range of interest whose frequencies were sensitive to joint boundary conditions. It was concluded that local/global coupling must be avoided in the frequency range where accurate modal characteristics are required.

  10. GW-BSE calculations on two-dimensional MXene phases

    NASA Astrophysics Data System (ADS)

    Li, Zhenglu; Hong, Liang; Jornada, Felipe; Cao, Ting; Ogut, Serdar; Louie, Steven G.

    2015-03-01

    MXene is a promising candidate for new useful two-dimensional (2D) crystals. Experimentally, few-layer samples have been made from the bulk, and they demonstrate many excellent properties for electric and thermal transport, as well as other novel physics. In this work, we have performed GW-BSE calculations based on first-principles calculations to study some of the MXene family. We find that monolayer Ti2CO2 possesses insulating properties. Furthermore, the 2D screening effect is very strong, resulting in a GW band gap correction of almost 1 eV. Based on these initial results, we expect that optical properties of these materials will also have strong excitonic effects. This research was supported by the DOE Theory Program at the Lawrence Berkeley National Lab under Contract No. DE-AC02-05CH11231 and by the National Science Foundation under Grant No. DMR10-1006184. This research used resources NERSC, supported by US DOE.

  11. Transmission noise identification using two-dimensional dynamic signal analysis

    NASA Astrophysics Data System (ADS)

    Pan, Min-Chun; Chen, Jeng-Xin

    2003-04-01

    This study aims at identifying transmission noise of two types of electrical vehicles with different transmission systems using the developed two-dimensional dynamic signal analysis (2DSA). Two electrical scooters, more specifically, with a gear transmission system and a continuous variable transmission (CVT) system, respectively, have been taken as test benches due to the whistle-like noise emitting from their transmission systems. To effectively process dynamic signatures measured from rotary machinery with varying speed, and even varying orders during operation, such as a machine with a CVT system or gear-shifting operation, the 2DSA approaches including the order analysis (OA) and the time-frequency analysis have been developed and implemented as processing tools. The specifications of vehicle transmission systems, especially the ratio of each speed reduction, and the tooth (cog, blade, etc.) number of transmission elements, i.e., geometric analysis, are firstly to be examined. After the 2DSA processes the noise measured from test vehicles during wide-open-throttle operation, dominant annoying transmission noise components can be extracted, and their sources can be identified through comparing feature orders obtained from geometric analysis. The procedure can not only identify noise sources but conclude transmission components to be further modified in respect of annoying noise.

  12. Gate-induced superconductivity in two-dimensional atomic crystals

    NASA Astrophysics Data System (ADS)

    Saito, Yu; Nojima, Tsutomu; Iwasa, Yoshihiro

    2016-09-01

    Two-dimensional (2D) crystals are attracting growing interest in condensed matter physics, since these systems exhibit not only rich electronic and photonic properties but also exotic electronic phase transitions including superconductivity and charge density wave. Moreover, owing to the recent development of transfer methods after exfoliation and electric-double-layer transistors, superconducting 2D atomic crystals, the thicknesses of which are below 1-2 nm, have been successfully obtained. Here, we present a topical review on the recent discoveries of 2D crystalline superconductors by ionic-liquid gating and a series of their novel properties. In particular, we highlight two topics; quantum metallic states (or possible metallic ground states) and superconductivity robust against in-plane magnetic fields. These phenomena can be discussed with the effects of weakened disorder and/or broken spacial inversion symmetry leading to valley-dependent spin-momentum locking (spin-valley locking). These examples suggest the superconducting 2D crystals are new platforms for investigating the intrinsic quantum phases as well as exotic nature in 2D superconductors.

  13. Study of two-dimensional Debye clusters using Brownian motion

    SciTech Connect

    Sheridan, T.E.; Theisen, W.L.

    2006-06-15

    A two-dimensional Debye cluster is a system of n identical particles confined in a parabolic well and interacting through a screened Coulomb (i.e., a Debye-Hueckel or Yukawa) potential with a Debye length {lambda}. Experiments were performed for 27 clusters with n=3-63 particles (9 {mu}m diam) in a capacitively coupled 9 W rf discharge at a neutral argon pressure of 13.6 mTorr. In the strong-coupling regime each particle exhibits small amplitude Brownian motion about its equilibrium position. These motions were projected onto the center-of-mass and breathing modes and Fourier analyzed to give resonance curves from which the mode frequencies, amplitudes, and damping rates were determined. The ratio of the breathing frequency to the center-of-mass frequency was compared with theory to self-consistently determine the Debye shielding parameter {kappa}, Debye length {lambda}, particle charge q, and mode temperatures. It is found that 1 < or approx. {kappa} < or approx. 2, and {kappa} decreases weakly with n. The particle charge averaged over all measurements is -14 200{+-}200 e, and q decreases slightly with n. The two center-of-mass modes and the breathing mode are found to have the same temperature, indicating that the clusters are in thermal equilibrium with the neutral gas. The average cluster temperature is 399{+-}5 K.

  14. Kolmogorov flow in two dimensional strongly coupled dusty plasma

    SciTech Connect

    Gupta, Akanksha; Ganesh, R. Joy, Ashwin

    2014-07-15

    Undriven, incompressible Kolmogorov flow in two dimensional doubly periodic strongly coupled dusty plasma is modelled using generalised hydrodynamics, both in linear and nonlinear regime. A complete stability diagram is obtained for low Reynolds numbers R and for a range of viscoelastic relaxation time τ{sub m} [0 < τ{sub m} < 10]. For the system size considered, using a linear stability analysis, similar to Navier Stokes fluid (τ{sub m} = 0), it is found that for Reynolds number beyond a critical R, say R{sub c}, the Kolmogorov flow becomes unstable. Importantly, it is found that R{sub c} is strongly reduced for increasing values of τ{sub m}. A critical τ{sub m}{sup c} is found above which Kolmogorov flow is unconditionally unstable and becomes independent of Reynolds number. For R < R{sub c}, the neutral stability regime found in Navier Stokes fluid (τ{sub m} = 0) is now found to be a damped regime in viscoelastic fluids, thus changing the fundamental nature of transition of Kolmogorov flow as function of Reynolds number R. A new parallelized nonlinear pseudo spectral code has been developed and is benchmarked against eigen values for Kolmogorov flow obtained from linear analysis. Nonlinear states obtained from the pseudo spectral code exhibit cyclicity and pattern formation in vorticity and viscoelastic oscillations in energy.

  15. Boundary force method for analyzing two-dimensional cracked bodies

    NASA Technical Reports Server (NTRS)

    Tan, P. W.; Raju, I. S.; Newman, J. C., Jr.

    1986-01-01

    The Boundary Force Method (BFM) was formulated for the two-dimensional stress analysis of complex crack configurations. In this method, only the boundaries of the region of interest are modeled. The boundaries are divided into a finite number of straight-line segments, and at the center of each segment, concentrated forces and a moment are applied. This set of unknown forces and moments is calculated to satisfy the prescribed boundary conditions of the problem. The elasticity solution for the stress distribution due to concentrated forces and a moment applied at an arbitrary point in a cracked infinite plate are used as the fundamental solution. Thus, the crack need not be modeled as part of the boundary. The formulation of the BFM is described and the accuracy of the method is established by analyzing several crack configurations for which accepted stress-intensity factor solutions are known. The crack configurations investigated include mode I and mixed mode (mode I and II) problems. The results obtained are, in general, within + or - 0.5 percent of accurate numerical solutions. The versatility of the method is demonstrated through the analysis of complex crack configurations for which limited or no solutions are known.

  16. How two-dimensional bending can extraordinarily stiffen thin sheets

    NASA Astrophysics Data System (ADS)

    Pini, V.; Ruz, J. J.; Kosaka, P. M.; Malvar, O.; Calleja, M.; Tamayo, J.

    2016-07-01

    Curved thin sheets are ubiquitously found in nature and manmade structures from macro- to nanoscale. Within the framework of classical thin plate theory, the stiffness of thin sheets is independent of its bending state for small deflections. This assumption, however, goes against intuition. Simple experiments with a cantilever sheet made of paper show that the cantilever stiffness largely increases with small amounts of transversal curvature. We here demonstrate by using simple geometric arguments that thin sheets subject to two-dimensional bending necessarily develop internal stresses. The coupling between the internal stresses and the bending moments can increase the stiffness of the plate by several times. We develop a theory that describes the stiffness of curved thin sheets with simple equations in terms of the longitudinal and transversal curvatures. The theory predicts experimental results with a macroscopic cantilever sheet as well as numerical simulations by the finite element method. The results shed new light on plant and insect wing biomechanics and provide an easy route to engineer micro- and nanomechanical structures based on thin materials with extraordinary stiffness tunability.

  17. Persistence in a Two-Dimensional Moving-Habitat Model.

    PubMed

    Phillips, Austin; Kot, Mark

    2015-11-01

    Environmental changes are forcing many species to track suitable conditions or face extinction. In this study, we use a two-dimensional integrodifference equation to analyze whether a population can track a habitat that is moving due to climate change. We model habitat as a simple rectangle. Our model quickly leads to an eigenvalue problem that determines whether the population persists or declines. After surveying techniques to solve the eigenvalue problem, we highlight three findings that impact conservation efforts such as reserve design and species risk assessment. First, while other models focus on habitat length (parallel to the direction of habitat movement), we show that ignoring habitat width (perpendicular to habitat movement) can lead to overestimates of persistence. Dispersal barriers and hostile landscapes that constrain habitat width greatly decrease the population's ability to track its habitat. Second, for some long-distance dispersal kernels, increasing habitat length improves persistence without limit; for other kernels, increasing length is of limited help and has diminishing returns. Third, it is not always best to orient the long side of the habitat in the direction of climate change. Evidence suggests that the kurtosis of the dispersal kernel determines whether it is best to have a long, wide, or square habitat. In particular, populations with platykurtic dispersal benefit more from a wide habitat, while those with leptokurtic dispersal benefit more from a long habitat. We apply our model to the Rocky Mountain Apollo butterfly (Parnassius smintheus).

  18. Flow of foams in two-dimensional disordered porous media

    NASA Astrophysics Data System (ADS)

    Dollet, Benjamin; Geraud, Baudouin; Jones, Sian A.; Meheust, Yves; Cantat, Isabelle; Institut de Physique de Rennes Team; Geosciences Rennes Team

    2015-11-01

    Liquid foams are a yield stress fluid with elastic properties. When a foam flow is confined by solid walls, viscous dissipation arises from the contact zones between soap films and walls, giving very peculiar friction laws. In particular, foams potentially invade narrow pores much more efficiently than Newtonian fluids, which is of great importance for enhanced oil recovery. To quantify this effect, we study experimentally flows of foam in a model two-dimensional porous medium, consisting of an assembly of circular obstacles placed randomly in a Hele-Shaw cell, and use image analysis to quantify foam flow at the local scale. We show that bubbles split as they flow through the porous medium, by a mechanism of film pinching during contact with an obstacle, yielding two daughter bubbles per split bubble. We quantify the evolution of the bubble size distribution as a function of the distance along the porous medium, the splitting probability as a function of bubble size, and the probability distribution function of the daughter bubbles. We propose an evolution equation to model this splitting phenomenon and compare it successfully to the experiments, showing how at long distance, the porous medium itself dictates the size distribution of the foam.

  19. Two-dimensional magnetic liquid froth: Coarsening and topological correlations

    NASA Astrophysics Data System (ADS)

    Elias, Florence; Flament, Cyrille; Bacri, Jean-Claude; Cardoso, Olivier; Graner, François

    1997-09-01

    We present an experimental study of a cellular system which may be formed in a two-dimensional (2D) layer made of an immiscible mixture of a magnetic fluid and an oil. We obtain a wet or a dry 2D froth, the characteristics of which are determined by the strength of an externally applied magnetic field. The froth is formed in an equilibrium state; the topological and geometrical features of the froth are fixed by the value of the applied field. The cellular pattern of the froth is stable in time, and a coarseninglike behavior is observed on decreasing the amplitude of the field. This cellular system can be used as a model to study topological processes in the equilibrium state, contrary to soap froths which are nonequilibrium systems because gas diffusion occurs. We show that the topological characteristics are statistically reversible after a magnetic-field cycle, and we present a statistical study of the froth features as a function of the amplitude of the field. The topological correlations between neighboring cells are well described by the Aboav-Weaire law. Finally, we consider the area of an n-sided cell, and show that its growth rate (magnetic field dependent) is, in a surprising manner, proportional to n-6, similarly to the Von Neumann law.

  20. Quantum tunneling of vortices in two-dimensional condensates

    SciTech Connect

    Auerbach, Assa; Arovas, Daniel P.; Ghosh, Sankalpa

    2006-08-01

    The tunneling rate t{sub v}/({Dirac_h}/2{pi}) of a vortex between two pinning sites (of strength V separated by d) is computed using the Bogoliubov expansion of vortex wave-functions overlap. For BCS vortices, tunneling is suppressed beyond a few Fermi wavelengths. For Bose condensates, t{sub v}=V exp(-{pi}n{sub s}d{sup 2}/2), where n{sub s} is the boson density. The analogy between vortex hopping in a superconducting film and two-dimensional electrons in a perpendicular magnetic field is exploited. We derive the variable range hopping temperature, below which vortex tunneling contributes to magnetoresistance. Using the 'quantum Hall insulator' analogy we argue that the Hall conductivity (rather than the inverse Hall resistivity) measures the effective carrier density in domains of mobile vortices. Details of vortex wave functions and overlap calculations, and a general derivation of the Magnus coefficient for any wave function on the sphere, are provided in appendixes.