Sample records for two-dimensional halbach cylinders

  1. The application of Halbach cylinders to brushless AC servo motors

    Microsoft Academic Search

    K. Atallah; D. Howe

    1998-01-01

    Halbach cylinders are applied to brushless ac servo motors. It is shown that a sinusoidal back-emf waveform and a low cogging torque can be achieved without recourse to conventional design features such as distributed windings and\\/or stator\\/rotor skew. A technique for imparting a multipole Halbach magnetization distribution on an isotropic permanent magnet cylinder is described, and it is shown that

  2. The application of Halbach cylinders to brushless ac servo motors

    SciTech Connect

    Atallah, K.; Howe, D. [Univ. of Sheffield (United Kingdom). Dept. of Electronic and Electrical Engineering] [Univ. of Sheffield (United Kingdom). Dept. of Electronic and Electrical Engineering

    1998-07-01

    Halbach cylinders are applied to brushless ac servo motors. It is shown that a sinusoidal back-emf waveform and a low cogging torque can be achieved without recourse to conventional design features such as distributed windings and/or stator/rotor skew. A technique for imparting a multipole Halbach magnetization distribution on an isotropic permanent magnet cylinder is described, and it is shown that the torque capability of a Halbach ac servo motor can be up to 33% higher than conventional brushless permanent magnet ac motors.

  3. Analysis and comparison of two two-dimensional Halbach permanent magnet arrays for magnetically levitated planar motor

    NASA Astrophysics Data System (ADS)

    Zhang, Lu; Kou, Baoquan; Xing, Feng; Zhang, He

    2014-05-01

    A novel 2-D Halbach permanent magnet array which can be used in magnetically levitated planar motor is proposed in this paper. The air-gap flux density distribution of the novel 2-D Halbach permanent magnet array is solved by the scalar magnetic potential equation. In order to compare with the well-known Halbach magnet array that was used by Jansen et al. [IEEE Trans. Ind. Appl. 44(4), 1108 (2008)], harmonic analysis of the x- and z- component of the air-gap flux density are carried out by Fourier decomposition. Comparison of Bx and Bz between the two 2-D Halbach magnet arrays are made. And it is verified that the performance of the new Halbach magnet array is superior to the existing Halbach magnet arrays, its higher magnetic flux density and lower high-order harmonics will help to improve the performance of the magnetically levitated planar motor.

  4. Measurement of the Rheological Properties of Magnetorheological Fluids Using a Double Concentric Halbach Cylinder Array

    NASA Astrophysics Data System (ADS)

    Barroso, Vitor C.; Raich, Hanspeter; Blümler, Peter; Wilhelm, Manfred

    2008-07-01

    A new experimental setup for measuring rheological properties of magnetic fluids at variable magnetic flux density B with increased homogeneity is described. The proposed setup is mounted on a commercial strain-controlled ARES rotational rheometer. The magnetic flux is generated via two concentric Halbach cylindrical arrays made from permanent NdFeB magnets. The use of permanent magnets overcomes some of the disadvantages of electromagnets (e.g., excessive heating of the coils, formation of large radial stray fields, cost of electricity, cooling, etc). The performance of the new setup is tested for a magnetorheological fluid in both steady and oscillatory shear regimes.

  5. Two-dimensional simulation of unsteady heat transfer from a circular cylinder in crossflow

    Microsoft Academic Search

    Salem Bouhairie; Vincent H. Chu

    2007-01-01

    The heat transfer from the surface of a circular cylinder into a crossflow has been computed using a two-dimensional model, for a range of Reynolds numbers from Re=200 to 15550. The boundary-layer separation, the local and overall heat-transfer rates, the eddy- and flare-detachment frequencies and the width of the flares were determined from the numerical simulations. In this range of

  6. Transient scattering from two-dimensional dielectric cylinders of arbitrary shape

    NASA Technical Reports Server (NTRS)

    Vechinski, Douglas A.; Rao, Sadasiva M.

    1992-01-01

    In this work, the problem of transient scattering by arbitrary shaped two-dimensional dielectric cylinders is solved using the marching-on-in-time (MOT) technique. The dielectric problem is approached via the surface equivalence principle. A pair of coupled integral equations are derived by enforcing the continuity of the electric and magnetic fields which are solved by using the method of moments. Numerical results are presented for two cross sections, viz. a circle and a square, and compared with inverse discrete Fourier transform (IDFT) techniques. In each case, good agreement is obtained with the IDFT solution.

  7. Dynamic analysis of two-dimensional functionally graded thick hollow cylinder with finite length under impact loading

    Microsoft Academic Search

    Masoud Asgari; Mehdi Akhlaghi; Seyed Mahmoud Hosseini

    2009-01-01

    In this paper a thick hollow cylinder with finite length made of two-dimensional functionally graded material (2D-FGM) and\\u000a subjected to impact internal pressure is considered. The axisymmetric conditions are assumed for the 2D-FG cylinder. The finite\\u000a element method with graded material properties within each element is used to model the structure, and the Newmark direct\\u000a integration method is implemented to

  8. The Hamiltonian structure of a two-dimensional rigid circular cylinder interacting dynamically with N point vortices

    E-print Network

    Shashikanth, Banavara N.

    The Hamiltonian structure of a two-dimensional rigid circular cylinder interacting dynamically bracket for the dynamics of N point vortices in an unbounded plane. We then use this Hamiltonian structure, New Mexico State University, Las Cruces, New Mexico 88003 Jerrold E. Marsdenb) Control and Dynamical

  9. Erratum: ``The Hamiltonian structure of a two-dimensional rigid circular cylinder interacting dynamically with N point vortices''

    E-print Network

    Shashikanth, Banavara N.

    ERRATA Erratum: ``The Hamiltonian structure of a two-dimensional rigid circular cylinder interacting dynamically with N point vortices'' Phys. Fluids 14, 1214 ,,2002... Banavara N. Shashikantha Mexico 88003 Jerrold E. Marsdenb) Control and Dynamical Systems, 107-81, California Institute

  10. Convection in the vertical midplane of a horizontal cylinder Comparison of two-dimensional approximations with three-dimensional results

    NASA Technical Reports Server (NTRS)

    Bontoux, P.; Roux, B.; Schiroky, G. H.; Markham, B. L.; Rosenberger, F.

    1986-01-01

    Experimental results and numerical data on the flow characteristics of core-driven and boundary-layer-driven regimes (CDRs) and (BLDRs) are compared to two-dimensional solutions for heated convective flow in the vertical midplane of a horizontal cylinder. The data were obtained from laser Doppler velocimetry (LDA) measurements and from three-dimensional numerical solutions. It is shown that the approximate solutions gave the correct Rayleigh-number-dependences and distributions for the velocities in the CDR and BLDR regimes. However, the transition between the CDR and the BLDR, as well as the magnitude of the distribution of velocity components, were found to be dependent on the type of two-dimensional approximation selected. In the case of CDR, core velocities were overestimated by as much as 30 percent by the two-dimensional approximations; and in the case of BLDR, the core velocities were overestimated by 40-50 percent as compared to the measured velocities. A schematic illustration of the flow patterns in the cylinder is provided.

  11. A numerical study of two-dimensional vortex shedding from rectangular cylinders

    Microsoft Academic Search

    A. H. Hadid; Munir M. Sindir; R. I. Issa

    1992-01-01

    An efficient time-marching, non-iterative calculation method is used to analyze time-dependent flows around rectangular cylinders. The turbulent flow in the wake region of a square section cylinder is analyzed using an anisotropic k-epsilon model. Initiation and subsequent development of the vortex shedding phenomenon is naturally captured once a perturbation is introduced in the flow. Transient calculations using standard eddy-viscosity and

  12. Axial Halbach Magnetic Bearings

    NASA Technical Reports Server (NTRS)

    Eichenberg, Dennis J.; Gallo, Christopher A.; Thompson, William K.

    2008-01-01

    Axial Halbach magnetic bearings have been investigated as part of an effort to develop increasingly reliable noncontact bearings for future high-speed rotary machines that may be used in such applications as aircraft, industrial, and land-vehicle power systems and in some medical and scientific instrumentation systems. Axial Halbach magnetic bearings are passive in the sense that unlike most other magnetic bearings that have been developed in recent years, they effect stable magnetic levitation without need for complex active control.

  13. Radial Halbach Magnetic Bearings

    NASA Technical Reports Server (NTRS)

    Eichenberg, Dennis J.; Gallo, Christopher A.; Thompson, William K.

    2009-01-01

    Radial Halbach magnetic bearings have been investigated as part of an effort to develop increasingly reliable noncontact bearings for future high-speed rotary machines that may be used in such applications as aircraft, industrial, and land-vehicle power systems and in some medical and scientific instrumentation systems. Radial Halbach magnetic bearings are based on the same principle as that of axial Halbach magnetic bearings, differing in geometry as the names of these two types of bearings suggest. Both radial and axial Halbach magnetic bearings are passive in the sense that unlike most other magnetic bearings that have been developed in recent years, they effect stable magnetic levitation without need for complex active control. Axial Halbach magnetic bearings were described in Axial Halbach Magnetic Bearings (LEW-18066-1), NASA Tech Briefs, Vol. 32, No. 7 (July 2008), page 85. In the remainder of this article, the description of the principle of operation from the cited prior article is recapitulated and updated to incorporate the present radial geometry. In simplest terms, the basic principle of levitation in an axial or radial Halbach magnetic bearing is that of the repulsive electromagnetic force between (1) a moving permanent magnet and (2) an electric current induced in a stationary electrical conductor by the motion of the magnetic field. An axial or radial Halbach bearing includes multiple permanent magnets arranged in a Halbach array ("Halbach array" is defined below) in a rotor and multiple conductors in the form of wire coils in a stator, all arranged so the rotary motion produces an axial or radial repulsion that is sufficient to levitate the rotor. A basic Halbach array (see Figure 1) consists of a row of permanent magnets, each oriented so that its magnetic field is at a right angle to that of the adjacent magnet, and the right-angle turns are sequenced so as to maximize the magnitude of the magnetic flux density on one side of the row while minimizing it on the opposite side. The advantage of this configuration is that it makes it possible to approach the theoretical maximum force per unit area that could be exerted by a given amount of permanent-magnet material. The configuration is named after physicist Klaus Halbach, who conceived it for use in particle accelerators. Halbach arrays have also been studied for use in magnetic-levitation ("maglev") railroad trains. In a radial Halbach magnetic bearing, the basic Halbach arrangement is modified into a symmetrical arrangement of sector-shaped permanent magnets mounted on the outer cylindrical surface of a drum rotor (see Figure 2). The magnets are oriented to concentrate the magnetic field on their radially outermost surface. The stator coils are mounted in a stator shell surrounding the rotor.

  14. On Two-dimensional Predictions of Turbulent Cross-flow Induced Vibration: Forces on a Cylinder and Wake Interaction

    Microsoft Academic Search

    Amr Elbanhawy; Ali Turan

    2010-01-01

    In this paper a typical fluid-structure interaction scenario is investigated for a turbulent flow past a circular cylinder\\u000a at a relatively low subcritical Reynolds number. Numerous experimental and numerical studies have been undertaken for a baseline\\u000a Reynolds number of 4,000 involving a stationary cylinder to study in detail the near wake mean flow and turbulence characteristics.\\u000a These studies conclusively show

  15. PHYSALIS: a new method for particle simulation. Part II: two-dimensional Navier-Stokes flow around cylinders

    NASA Astrophysics Data System (ADS)

    Takagi, S.; Og˜uz, H. N.; Zhang, Z.; Prosperetti, A.

    2003-05-01

    This paper presents a new approach to the direct numerical simulation of particle flows. The basic idea is to use a local analytic representation valid near the particle to "transfer" the no-slip condition from the particle surface to the adjacent grid nodes. In this way the geometric complexity arising from the irregular relation between the particle boundary and the underlying mesh is avoided and fast solvers can be used. The results suggest that the computational effort increases very slowly with the number of particles so that the method is efficient for large-scale simulations. The focus here is on the two-dimensional case (cylindrical particles), but the same procedure, to be developed in forthcoming papers, applies to three dimensions (spherical particles). Several extensions are briefly discussed.

  16. Acoustic metamaterials for new two-dimensional sonic devices

    Microsoft Academic Search

    Daniel Torrent; José Sánchez-Dehesa

    2007-01-01

    It has been shown that two-dimensional arrays of rigid or fluidlike cylinders in a fluid or a gas define, in the limit of large wavelengths, a class of acoustic metamaterials whose effective parameters (sound velocity and density) can be tailored up to a certain limit. This work goes a step further by considering arrays of solid cylinders in which the

  17. Two dimensional NMR spectroscopy

    SciTech Connect

    Schram, J.; Bellama, J.M.

    1988-01-01

    Two dimensional NMR represents a significant achievement in the continuing effort to increase solution in NMR spectroscopy. This book explains the fundamentals of this new technique and its analytical applications. It presents the necessary information, in pictorial form, for reading the ''2D NMR,'' and enables the practicing chemist to solve problems and run experiments on a commercial spectrometer by using the software provided by the manufacturer.

  18. Two dimensional exchange NMR experiments of natural porous media with portable Halbach-Magnets

    Microsoft Academic Search

    Agnes Haber; Sabina Haber-Pohlmeier; Federico Casanova; Bernhard Blümich

    2010-01-01

    The characterization of pore space and connectivity in soils of different textures is one topic within Cluster A, Partial Project A1. For this purpose low field mobile NMR became a powerful tool following the development of portable NMR sensors for well logging. By now there are numerous applications of mobile NMR in materials analysis and chemical engineering where, for example,

  19. Halbach array motor/generators: A novel generalized electric machine

    SciTech Connect

    Merritt, B.T.; Post, R.F.; Dreifuerst, G.R.; Bender, D.A.

    1994-10-28

    In August 1979, Halbach submitted a paper entitled ``Design of Permanent Multipole Magnets with Oriented Rare Earth Cobalt Material.`` In this paper, he presented a novel method of generating multipole magnetic fields using non-intuitive geometrical arrangements of permanent magnets. In subsequent publications, he further defined these concepts. Of particular interest to one of the authors (RFP) was the special magnet array that generated a uniform dipole field. In 1990 Post proposed the construction of an electric machine (a motor/generator) using a dipole field based on Klaus Halbach`s array of permanent magnets. He further proposed that such a system should be employed as an integral part of ``an electromechanical battery`` (EMB), i.e., a modular flywheel system to be used as a device for storing electrical energy, as an alternative to the electrochemical storage battery. This paper reviews Halbach`s theory for the generation of a dipole field using an array of permanent magnet bars, presents a simple analysis of a family of novel ``ironless`` electric machines designed using the dipole Halbach array, and describes the results obtained when they were tested in the laboratory.

  20. Two-dimensional contact analysis of elastic graded materials

    Microsoft Academic Search

    A. E. Giannakopoulos; P. Pallot

    2000-01-01

    The present paper examines two-dimensional contact of a rigid cylinder on an elastic graded substrate. The normal, sliding and rolling type of contact are addressed. The effect of adhesion in frictionless contact is also examined. The elastically graded substrate is modeled to be locally isotropic with constant Poisson ratio and elastic modulus that varies with depth, y, according to a

  1. Two-dimensional river modeling

    E-print Network

    Thompson, James Cameron

    1988-01-01

    as to the best use of two-dimensional river models, and recommendations are made for the application and further development of two-dimensional river models. This thesis contains four sample applications using the finite Element hzurface-Water godeling ~S...

  2. Development and Testing of a Radial Halbach Magnetic Bearing

    NASA Technical Reports Server (NTRS)

    Eichenberg, Dennis J.; Gallo, Christopher A.; Thompson, William K.

    2006-01-01

    The NASA John H. Glenn Research Center has developed and tested a revolutionary Radial Halbach Magnetic Bearing. The objective of this work is to develop a viable non-contact magnetic bearing utilizing Halbach arrays for all-electric flight, and many other applications. This concept will help reduce harmful emissions, reduce the Nation s dependence on fossil fuels and mitigate many of the concerns and limitations encountered in conventional axial bearings such as bearing wear, leaks, seals and friction loss. The Radial Halbach Magnetic Bearing is inherently stable and requires no active feedback control system or superconductivity as required in many magnetic bearing designs. The Radial Halbach Magnetic Bearing is useful for very high speed applications including turbines, instrumentation, medical applications, manufacturing equipment, and space power systems such as flywheels. Magnetic fields suspend and support a rotor assembly within a stator. Advanced technologies developed for particle accelerators, and currently under development for maglev trains and rocket launchers, served as the basis for this application. Experimental hardware was successfully designed and developed to validate the basic principles and analyses. The report concludes that the implementation of Radial Halbach Magnetic Bearings can provide significant improvements in rotational system performance and reliability.

  3. Development and Testing of an Axial Halbach Magnetic Bearing

    NASA Technical Reports Server (NTRS)

    Eichenberg, Dennis J.; Gallo, Christopher A.; Thompson, William K.

    2006-01-01

    The NASA Glenn Research Center has developed and tested a revolutionary Axial Halbach Magnetic Bearing. The objective of this work is to develop a viable non-contact magnetic thrust bearing utilizing Halbach arrays for all-electric flight, and many other applications. This concept will help to reduce harmful emissions, reduce the Nation s dependence on fossil fuels and mitigate many of the concerns and limitations encountered in conventional axial bearings such as bearing wear, leaks, seals and friction loss. The Axial Halbach Magnetic Bearing is inherently stable and requires no active feedback control system or superconductivity as required in many magnetic bearing designs. The Axial Halbach Magnetic Bearing is useful for very high speed applications including turbines, instrumentation, medical systems, computer memory systems, and space power systems such as flywheels. Magnetic fields suspend and support a rotor assembly within a stator. Advanced technologies developed for particle accelerators, and currently under development for maglev trains and rocket launchers, served as the basis for this application. Experimental hardware was successfully designed and developed to validate the basic principles and analyses. The report concludes that the implementation of Axial Halbach Magnetic Bearings can provide significant improvements in rotational system performance and reliability.

  4. Two-dimensional wind tunnel

    NASA Technical Reports Server (NTRS)

    1982-01-01

    Information on the Japanese National Aerospace Laboratory two dimensional transonic wind tunnel, completed at the end of 1979 is presented. Its construction is discussed in detail, and the wind tunnel structure, operation, test results, and future plans are presented.

  5. Position sensor for linear synchronous motors employing halbach arrays

    DOEpatents

    Post, Richard Freeman

    2014-12-23

    A position sensor suitable for use in linear synchronous motor (LSM) drive systems employing Halbach arrays to create their magnetic fields is described. The system has several advantages over previously employed ones, especially in its simplicity and its freedom from being affected by weather conditions, accumulated dirt, or electrical interference from the LSM system itself.

  6. The Design of Halbach Arrays for Inductrack Maglev Systems

    Microsoft Academic Search

    Richard F. Post; Long Nguyen

    The development of the Inductrack maglev system 1 for urban transportation is being pursued at General Atomics in San Diego, California. Central to this development is the optimization of the configuration of permanent magnets of that system, a configuration based on concepts pioneered by the late Klaus Halbach of the Lawrence Berkeley Laboratory. The tools used in this optimization are

  7. Cloaking two-dimensional fermions

    SciTech Connect

    Lin, De-Hone [Department of Physics, National Sun Yat-sen University, Kaohsiung, Taiwan (China)

    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.

  8. Two-dimensional photonic crystal coupled-defect laser diode

    Microsoft Academic Search

    Thomas D. Happ; Martin Kamp; Alfred Forchel; Jean-Louis Gentner; L. Goldstein

    2003-01-01

    We demonstrate a two-dimensional photonic crystal defect laser diode based on a coupled cavity waveguide. The laser cavity is formed by 40 coupled hexagonal defect microcavities in a triangular lattice of air cylinders, which are etched into an InGaAsP\\/InP laser structure. The coupling of the individual cavity modes creates minibands within the photonic band gap. Stable single-mode lasing occurs on

  9. Two-dimensional thermofield bosonization

    SciTech Connect

    Amaral, R.L.P.G. [Instituto de Fisica, Universidade Federal Fluminense, Av. Litoranea S/N, Boa Viagem, Niteroi, CEP, 24210-340 Rio de Janeiro (Brazil)]. E-mail: rubens@if.uff.br; Belvedere, L.V. [Instituto de Fisica, Universidade Federal Fluminense, Av. Litoranea S/N, Boa Viagem, Niteroi, CEP, 24210-340 Rio de Janeiro (Brazil); Rothe, K.D. [Institut fuer Theoretische Physik, Universitaet Heidelberg, Philosophenweg 16, D-69120 Heidelberg (Germany)

    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.

  10. Two-dimensional flexible nanoelectronics

    NASA Astrophysics Data System (ADS)

    Akinwande, Deji; Petrone, Nicholas; Hone, James

    2014-12-01

    2014/2015 represents the tenth anniversary of modern graphene research. Over this decade, graphene has proven to be attractive for thin-film transistors owing to its remarkable electronic, optical, mechanical and thermal properties. Even its major drawback--zero bandgap--has resulted in something positive: a resurgence of interest in two-dimensional semiconductors, such as dichalcogenides and buckled nanomaterials with sizeable bandgaps. With the discovery of hexagonal boron nitride as an ideal dielectric, the materials are now in place to advance integrated flexible nanoelectronics, which uniquely take advantage of the unmatched portfolio of properties of two-dimensional crystals, beyond the capability of conventional thin films for ubiquitous flexible systems.

  11. Two-dimensional Yukawa fluids

    NASA Astrophysics Data System (ADS)

    Gonzalez-Melchor, Minerva; Mendez, Arlette; Alejandre, Jose

    2015-03-01

    When the movement of particles is performed predominantly in two dimensions, the systems can be considered at a good extent as two-dimensional. For instance the lipids in a bilayer, micrometric particles in a quasi-two-dimensional colloidal suspension, colloids in a monolayer deposited on the air-water interface, and DNA complexes trapped at the water surface can be described at a first approach as bidimensional fluids. These systems are important for many applications in surface and colloidal science. In simulations where the explicit interface between liquid and vapor is present, the line tension can be directly computed. In this work we present molecular dynamics results obtained for the liquid/vapor coexistence curve of 2D Yukawa fluids and for the line tension. A comparison with the three-dimensional case is also presented.

  12. Two-dimensional river modeling 

    E-print Network

    Thompson, James Cameron

    1988-01-01

    The three dimensional flow structure is not required for most river applications. Neglecting vertical velocities and vertical accelerations, the depth-averaged velocity may obtained by integrating the horizontal velocity components from the bed elevation...TWO-DIMENSIONAL RIVER MODELING A Thesis by JAMES CAMERON THOMPSON Submitted to the Office of Graduate Studies of Texas A&M University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE December 1988 Major Subject...

  13. Two-dimensional boson model

    Microsoft Academic Search

    Steven A. Moszkowski

    1979-01-01

    We discuss the spatially symmetric configurations for four particles in the two-dimensional version of the p shell and (s,d) shell with a surface delta interaction and show how these configurations can be described as a system of two interacting bosons. The boson-boson interaction is shown to be predominantly quadrupole with a somewhat weaker hexadecupole component. With increasing numbers of bosons,

  14. Inverted Linear Halbach Array for Separation of Magnetic Nanoparticles

    PubMed Central

    Ijiri, Y.; Poudel, C.; Williams, P.S.; Moore, L.R.; Orita, T.; Zborowski, M.

    2014-01-01

    A linear array of Nd-Fe-B magnets has been designed and constructed in an inverted Halbach configuration for use in separating magnetic nanoparticles. The array provides a large region of relatively low magnetic field, yet high magnetic field gradient in agreement with finite element modeling calculations. The magnet assembly has been combined with a flow channel for magnetic nanoparticle suspensions, such that for an appropriate distance away from the assembly, nanoparticles of higher moment aggregate and accumulate against the channel wall, with lower moment nanoparticles flowing unaffected. The device is demonstrated for iron oxide nanoparticles with diameters of ~ 5 and 20 nm. In comparison to other approaches, the inverted Halbach array is more amenable to modeling and to scaling up to preparative quantities of particles. PMID:25382864

  15. Energy harvesting from electric power lines employing the Halbach arrays.

    PubMed

    He, Wei; Li, Ping; Wen, Yumei; Zhang, Jitao; Lu, Caijiang; Yang, Aichao

    2013-10-01

    This paper proposes non-invasive energy harvesters to scavenge alternating magnetic field energy from electric power lines. The core body of a non-invasive energy harvester is a linear Halbach array, which is mounted on the free end of a piezoelectric cantilever beam. The Halbach array augments the magnetic flux density on the side of the array where the power line is placed and significantly lowers the magnetic field on the other side. Consequently, the magnetic coupling strength is enhanced and more alternating magnetic field energy from the current-carrying power line is converted into electrical energy. An analytical model is developed and the theoretical results verify the experimental results. A power of 566 ?W across a 196 k? resistor is generated from a single wire, and a power of 897 ?W across a 212 k? resistor is produced from a two-wire power cord carrying opposite currents at 10 A. The harvesters employing Halbach arrays for a single wire and a two-wire power cord, respectively, exhibit 3.9 and 3.2 times higher power densities than those of the harvesters employing conventional layouts of magnets. The proposed devices with strong response to the alternating currents are promising to be applied to electricity end-use environment in electric power systems. PMID:24182155

  16. Two dimensional bulge disk decomposition

    E-print Network

    Yogesh Wadadekar; Braxton Robbason; Ajit Kembhavi

    1997-05-27

    We propose a two dimensional galaxy fitting algorithm to extract parameters of the bulge, disk, and a central point source from broad band images of galaxies. We use a set of realistic galaxy parameters to construct a large number of model galaxy images which we then use as input to our galaxy fitting program to test it. We find that our approach recovers all structural parameters to a fair degree of accuracy. We elucidate our procedures by extracting parameters for 3 real galaxies -- NGC 661, NGC 1381, and NGC 1427.

  17. Two-Dimensional Photon Model

    NASA Astrophysics Data System (ADS)

    Khodin, Aliaksandr

    2002-05-01

    Quasi-two-dimensional space-time configuration is presented as a photon model in the frames of a topological approach. The photon configuration is considered in the model as the simplest stable disturbance of non-linear (in relativistic sence) space-time medium. The configuration is governed by the ultimate relativistic condition [1] in its central point for every external time moment as a prerequisite for the configuration' stability under Lorentz transformations. A photon is represented as a localized quasi-two-dimensional spatio-temporal object possessing the Doppler effect behaviour in the case it propagates with the ultimate light velocity only. Characteristic transversal size of a photon is of its wavelength order. Photon spin is ascribed to the configuration's "rotation" around the propagation direction; the only permissible rotation period corresponding to the photon wavelength. It is shown that the ordered one-dimensional superposition of single-photon configurations along the propagation direction composes a restricted stable coherent harmonic-type packet. Two- and three-dimensional coherent superposition of single-photon configurations leads to some types of transversal photons ordering inside the coherent packet. 1. A.Khodin. Hierarchical model of elementary symmetries in configurational approach. EPS-11: Trends in Physics. 11th Gen. Conf. of Eur. Phys. Soc. London, UK, 6-10 Sept.1999.

  18. Optimal Halbach permanent magnet designs for maximally pulling and pushing nanoparticles

    E-print Network

    Shapiro, Benjamin

    Optimal Halbach permanent magnet designs for maximally pulling and pushing nanoparticles A. Sarwar Available online 19 September 2011 Keywords: Magnetic nanoparticle Targeted drug deliver Magnetic drug targeting Optimal permanent magnet Nano-particle trapping Pushing nanoparticle Halbach array design a b

  19. Analysis and modeling of the EDS Maglev system based on the Halbach permanent magnet array

    Microsoft Academic Search

    Qinghua Han

    2004-01-01

    Electro-dynamic suspension (EDS) Magnetic levitation (Maglev) with its advantage in maintenance, safety, efficiency, speed, and noise is regarded as a leading candidate for the next generation transportation\\/space launch assist system. The Halbach array due to its unique magnetic field feature has been widely used in various applications. The EDS system using Halbach arrays leads to the potential EDS system without

  20. Information theoretic aspects of the two-dimensional Ising model.

    PubMed

    Lau, Hon Wai; Grassberger, Peter

    2013-02-01

    We present numerical results for various information theoretic properties of the square lattice Ising model. First, using a bond propagation algorithm, we find the difference 2H(L)(w)-H(2L)(w) between entropies on cylinders of finite lengths L and 2L with open end cap boundaries, in the limit L??. This essentially quantifies how the finite length correction for the entropy scales with the cylinder circumference w. Secondly, using the transfer matrix, we obtain precise estimates for the information needed to specify the spin state on a ring encircling an infinitely long cylinder. Combining both results, we obtain the mutual information between the two halves of a cylinder (the "excess entropy" for the cylinder), where we confirm with higher precision but for smaller systems the results recently obtained by Wilms et al., and we show that the mutual information between the two halves of the ring diverges at the critical point logarithmically with w. Finally, we use the second result together with Monte Carlo simulations to show that also the excess entropy of a straight line of n spins in an infinite lattice diverges at criticality logarithmically with n. We conjecture that such logarithmic divergence happens generically for any one-dimensional subset of sites at any two-dimensional second-order phase transition. Comparing straight lines on square and triangular lattices with square loops and with lines of thickness 2, we discuss questions of universality. PMID:23496480

  1. Entropic C theorems in free and interacting two-dimensional field theories

    Microsoft Academic Search

    Jose Gaite

    2000-01-01

    The relative entropy in two-dimensional field theory is studied on a cylinder geometry, interpreted as finite-temperature field theory. The width of the cylinder provides an infrared scale that allows us to define a dimensionless relative entropy analogous to Zamolodchikov's c function. The one-dimensional quantum thermodynamic entropy gives rise to another monotonic dimensionless quantity. I illustrate these monotonicity theorems with examples

  2. Radiation from a Line Source Placed in Two-dimensional Photonic Crystals

    Microsoft Academic Search

    Vakhtang Jandieri; Kiyotoshi Yasumoto; Hiroshi Toyama

    2007-01-01

    A novel formulation of radiation from a localized line source placed in two-dimensional photonic crystals consisting of layered\\u000a periodic arrays of parallel circular cylinders is presented. The method employs the spectral domain approach. The spectral\\u000a response of the photonic crystals to the line source excitation is calculated using the lattice sums, the T-matrix of a circular\\u000a cylinder, and the generalized

  3. Effect of interfacial characteristics on effective conductivities of isotropic two-dimensional periodic composites

    Microsoft Academic Search

    Shih-Yuan Lu; Hway-Chi Lin

    1995-01-01

    The effect of interfacial characteristics on the effective thermal conductivity, keff, of isotropic two-dimensional periodic composites of infinitely long circular cylinders is studied with a boundary collocation scheme. Three types of problems are investigated: coated inclusion, debonded inclusion and contact resistance problems. It is shown that a critical relative interfacial layer thickness, (?a)c, exists for the first two problems, at

  4. Defect and transmission properties of two-dimensional quasiperiodic photonic band-gap systems

    Microsoft Academic Search

    Samuel S. M. Cheng; Lie-Ming Li; C. T. Chan; Z. Q. Zhang

    1999-01-01

    It has recently been demonstrated that two-dimensional photonic band gaps can be realized in systems comprising of a quasiperiodic arrangement of dielectric cylinders. We show that waveguides crafted out of such photonic ``quasicrystals'' can be used to guide light around sharp corners, just as in the case of periodic photonic band-gap systems, but the quasiperiodic systems tend to be more

  5. Defect and transmission properties of two-dimensional quasiperiodic photonic band-gap systems

    Microsoft Academic Search

    Samuel S. M. Cheng; Lie-Ming Li; C. T. Chan; Z. Q. Zhang

    1999-01-01

    It has recently been demonstrated that two-dimensional photonic band gaps can be realized in systems comprising of a quasiperiodic arrangement of dielectric cylinders. We show that waveguides crafted out of such photonic ''quasicrystals'' can be used to guide light around sharp corners, just as in the case of periodic photonic band-gap systems, but the quasiperiodic systems tend to be more

  6. Existence of Photonic Band Gaps in Two-Dimensional Metallodielectric Photonic Crystals

    Microsoft Academic Search

    Toshio Suzuki; Paul K. L. Yu

    1999-01-01

    Using the method of projection operators based on plane wave expansion, we theoretically investigate photonic band structures in two-dimensional metallodielectric photonic crystals, especially, square arrays of dielectric and perfectly conducting cylinders. Existence of photonic band gaps in metallodielectric photonic crystals and validity of the proposed numerical method are demonstrated.

  7. Two dimensional echocardiographic diagnosis of situs

    Microsoft Academic Search

    J C Huhta; J F Smallhorn; F J Macartney

    1982-01-01

    At present there is no reliable method of recognising atrial isomerism by two dimensional echocardiography. We therefore used two dimensional echocardiography to examine 158 patients including 25 with atrial isomerism and four with situs inversus. Particular attention was paid to the short and long axis subcostal scans of the abdomen. Using the position of the inferior vena cava and the

  8. Torque analysis and measurements of a permanent magnet type Eddy current brake with a Halbach magnet array based on analytical magnetic field calculations

    NASA Astrophysics Data System (ADS)

    Park, Min-Gyu; Choi, Jang-Young; Shin, Hyeon-Jae; Jang, Seok-Myeong

    2014-05-01

    This paper presents the torque analysis and measurements of a permanent magnet (PM) type eddy current brake (ECB) with a Halbach magnet array based on analytical magnetic field calculations. On the basis of a magnetic vector potential and using a two-dimensional (2D) polar coordinate system, the analytical solution for magnetic flux density, including the eddy current reaction is evaluated. Based on these solutions, the magnetic torque is also determined analytically. A 2D finite element analysis is employed to validate the method used. Practical issues in the analytical study of the PM type ECBs, such as the maximum braking torque, the required rotor speed, and the segment-dependent, are fully discussed. Finally, the braking torque as a function of the rotor speed is measured to verify the results of the analytical study.

  9. Analysis and modeling of the EDS Maglev system based on the Halbach permanent magnet array

    NASA Astrophysics Data System (ADS)

    Han, Qinghua

    Electro-dynamic suspension (EDS) Magnetic levitation (Maglev) with its advantage in maintenance, safety, efficiency, speed, and noise is regarded as a leading candidate for the next generation transportation/space launch assist system. The Halbach array due to its unique magnetic field feature has been widely used in various applications. The EDS system using Halbach arrays leads to the potential EDS system without super-conductor (SC) technology. In this thesis, the Halbach array magnetic field and the dynamics of a novel Halbach array EDS Maglev system were considered. The practical Halbach array magnetic field was analyzed using both a Fourier series approach and the finite element method (FEM). In addition, the optimal Halbach array geometry was derived and analyzed. A novel active magnetic array was introduced and used in the Halbach array EDS Maglev configuration. Furthermore, since the system is self-regulated in lateral, roll, pitch, and yaw directions, the control was simplified and can be implemented electronically. The dynamic stability analysis and simulation results showed that the system is marginally stable and a control mechanism is needed for stability and ride comfort control. The six degree of freedom (DOF) dynamics, and the vehicle's mass center offset effects on those dynamics were investigated with multiple passive and active magnetic forces. The results indicated that the vehicle's mass center offset has a strong effect on the dynamics of the Maglev system due to the uniqueness of the magnetic force and also that the mass center offset can cause Maglev oscillations at the take off stage. In order to guarantee the dynamic stability and ride comfort of the Maglev system, an optimized active damping and a linear quadratic regulator (LQR) control were developed. Finally, the simulation confirmed the effectiveness of the proposed multi-input and multi-output (MIMO) control designs.

  10. Relativity on two-dimensional spacetimes

    E-print Network

    Do-Hyung Kim

    2013-07-26

    Lorentz transformation on two-dimensional spacetime is obtained without assumption of linearity. To obtain this, we use the invariance of wave equations, which is recently proved to be equivalent to the causality preservation.

  11. Mars Pathfinder Two-Dimensional Model

    NSDL National Science Digital Library

    2012-08-03

    This activity is about the Mars Pathfinder spacecraft. Using cardboard and other materials, learners will create a two dimensional model of the spacecraft. A diagram with approximate measures of each component is provided.

  12. On two-dimensional magnetohydrodynamic turbulence

    Microsoft Academic Search

    A. Pouquet

    1978-01-01

    The reported investigation shows that two-dimensional MHD turbulence differs basically from two-dimensional nonmagnetic turbulence. Because of the relaxation of the vorticity constraint, the appearance of singularities at a finite time, as in three-dimensional turbulence, cannot be ruled out (at zero viscosity and zero magnetic diffusivity). Upon injection of kinetic and magnetic energy, a quasi-stationary state is obtained with a direct

  13. Two-dimensional order and disorder thermofields

    SciTech Connect

    Belvedere, L. V. [Instituto de Fisica - Universidade Federal Fluminense, Av. Litora circumflex nea S/N, Boa Viagem Niteroi, CEP 24210-340 Rio de Janeiro (Brazil)

    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.

  14. Two-dimensional photonic band gap crystals

    Microsoft Academic Search

    Cheryl Marie Anderson

    1999-01-01

    A photonic crystal is a periodic dielectric structure that possesses a band of frequencies in which propagating electromagnetic waves are forbidden. Two-dimensional photonic crystals exhibit a band gap for waves traveling in the crystal plane, a property that offers promise for improved operation of optoelectronic devices including semiconductor lasers, light-emitting diodes, and frequency filters. A theoretical investigation of two-dimensional photonic

  15. Optimal Halbach Permanent Magnet Designs for Maximally Pulling and Pushing Nanoparticles.

    PubMed

    Sarwar, A; Nemirovski, A; Shapiro, B

    2012-03-01

    Optimization methods are presented to design Halbach arrays to maximize the forces applied on magnetic nanoparticles at deep tissue locations. In magnetic drug targeting, where magnets are used to focus therapeutic nanoparticles to disease locations, the sharp fall off of magnetic fields and forces with distances from magnets has limited the depth of targeting. Creating stronger forces at depth by optimally designed Halbach arrays would allow treatment of a wider class of patients, e.g. patients with deeper tumors. The presented optimization methods are based on semi-definite quadratic programming, yield provably globally optimal Halbach designs in 2 and 3-dimensions, for maximal pull or push magnetic forces (stronger pull forces can collect nano-particles against blood forces in deeper vessels; push forces can be used to inject particles into precise locations, e.g. into the inner ear). These Halbach designs, here tested in simulations of Maxwell's equations, significantly outperform benchmark magnets of the same size and strength. For example, a 3-dimensional 36 element 2000 cm(3) volume optimal Halbach design yields a ×5 greater force at a 10 cm depth compared to a uniformly magnetized magnet of the same size and strength. The designed arrays should be feasible to construct, as they have a similar strength (? 1 Tesla), size (? 2000 cm(3)), and number of elements (? 36) as previously demonstrated arrays, and retain good performance for reasonable manufacturing errors (element magnetization direction errors ? 5°), thus yielding practical designs to improve magnetic drug targeting treatment depths. PMID:23335834

  16. Optimal Halbach permanent magnet designs for maximally pulling and pushing nanoparticles

    NASA Astrophysics Data System (ADS)

    Sarwar, A.; Nemirovski, A.; Shapiro, B.

    2012-03-01

    Optimization methods are presented to design Halbach arrays to maximize the forces applied on magnetic nanoparticles at deep tissue locations. In magnetic drug targeting, where magnets are used to focus therapeutic nanoparticles to disease locations, the sharp fall off of magnetic fields and forces with distances from magnets has limited the depth of targeting. Creating stronger forces at a depth by optimally designed Halbach arrays would allow treatment of a wider class of patients, e.g. patients with deeper tumors. The presented optimization methods are based on semi-definite quadratic programming, yield provably globally optimal Halbach designs in 2 and 3-dimensions, for maximal pull or push magnetic forces (stronger pull forces can collect nanoparticles against blood forces in deeper vessels; push forces can be used to inject particles into precise locations, e.g. into the inner ear). These Halbach designs, here tested in simulations of Maxwell's equations, significantly outperform benchmark magnets of the same size and strength. For example, a 3-dimensional 36 element 2000 cm3 volume optimal Halbach design yields a 5× greater force at a 10 cm depth compared to a uniformly magnetized magnet of the same size and strength. The designed arrays should be feasible to construct, as they have a similar strength (?1 T), size (?2000 cm3), and number of elements (?36) as previously demonstrated arrays, and retain good performance for reasonable manufacturing errors (element magnetization direction errors ?5°), thus yielding practical designs to improve magnetic drug targeting treatment depths.

  17. Acoustic directional radiation operating at the pass band frequency in two-dimensional phononic crystals

    NASA Astrophysics Data System (ADS)

    Wen, Jihong; Yu, Dianlong; Cai, Li; Wen, Xisen

    2009-06-01

    The phase constant surfaces of two-dimensional phononic crystals consisting of steel cylinders in water are calculated to predict the directivity of acoustic wave propagation. A highly directional acoustic source can be obtained at a pass band frequency far away from the band edge states. This observation is quite different from those in the two former approaches, where one is due to the high density of band-edge states and the other is due to the resonant cavity state in two-dimensional phononic crystals. The prediction is validated by the acoustic field distributions of a finite structure with 24 × 24 unit cells.

  18. Development of Halbach magnet for portable NMR device

    NASA Astrophysics Data System (ADS)

    Do?an, N.; Topkaya, R.; Suba?i, H.; Yerli, Y.; Rameev, B.

    2009-03-01

    Nuclear magnetic resonance (NMR) has enormous potential for various applications in industry as the on-line or at-line test/control device of process environments. Advantage of NMR is its non-destructive nature, because it does not require the measurement probe to have a contact with the tested media. Despite of the recent progress in this direction, application of NMR in industry is still very limited. This is related to the technical and analytical complications of NMR as a method, and high cost of NMR analyzers available at the market. However in many applications, NMR is a very useful technique to test various products and to monitor quantitatively industrial processes. Fortunately usually there is no need in a high-field superconducting magnets to obtain the high-resolution spectra with the detailed information on chemical shifts and coupling-constant. NMR analyzers are designed to obtain the relaxation parameters by measuring the NMR spectra in the time domain rather than in frequency domain. Therefore it is possible to use small magnetic field (and low frequency of 2-60 MHz) in NMR systems, based on permanent magnet technology, which are specially designed for specific at-line and on-line process applications. In this work we present the permanent magnet system developed to use in the portative NMR devices. We discuss the experimental parameters of the designed Halbach magnet system and compare them with results of theoretical modelling.

  19. Structural parameter optimization design for Halbach permanent maglev rail

    NASA Astrophysics Data System (ADS)

    Guo, F.; Tang, Y.; Ren, L.; Li, J.

    2010-11-01

    Maglev rail is an important part of the magnetic levitation launch system. Reducing the manufacturing cost of magnetic levitation rail is the key problem for the development of magnetic levitation launch system. The Halbach permanent array has an advantage that the fundamental spatial field is cancelled on one side of the array while the field on the other side is enhanced. So this array used in the design of high temperature superconducting permanent maglev rail could improve the surface magnetic field and the levitation force. In order to make the best use of Nd-Fe-B (NdFeB) material and reduce the cost of maglev rail, the effect of the rail’s structural parameters on levitation force and the utilization rate of NdFeB material are analyzed. The optimal ranges of these structural parameters are obtained. The mutual impact of these parameters is also discussed. The optimization method of these structure parameters is proposed at the end of this paper.

  20. Two-dimensional nonlinear beam shaping.

    PubMed

    Shapira, Asia; Shiloh, Roy; Juwiler, Irit; Arie, Ady

    2012-06-01

    We develop a technique for two-dimensional arbitrary wavefront shaping in quadratic nonlinear crystals by using binary nonlinear computer generated holograms. The method is based on transverse illumination of a binary modulated nonlinear photonic crystal, where the phase matching is partially satisfied through the nonlinear Raman-Nath process. We demonstrate the method experimentally showing a conversion of a fundamental Gaussian beam pump light into three Hermite-Gaussian and three Laguerre-Gaussian beams in the second harmonic. Two-dimensional binary nonlinear computer generated holograms open wide possibilities in the field of nonlinear beam shaping and mode conversion. PMID:22660146

  1. Entanglement entropy in two dimensional string theory

    E-print Network

    Hartnoll, Sean A

    2015-01-01

    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.

  2. Detecting disparity in two-dimensional patterns

    Microsoft Academic Search

    Bart Farell

    One can measure the disparities between two retinal images in several different ways. Experiments were conducted to identify the measure that is invariant at the threshold for detecting the disparity of two-dimensional patterns. The patterns used were stereo plaids, which permit a partial dissociation between the disparity of the pattern and the disparities of its one-dimensional compo- nents. For plaids

  3. Numerical Modelling of the Two-Dimensional

    E-print Network

    potential, and the numerical scheme is formulated so that the continuity equation for the currents that the divergences of the electromagnetic fields are fulfilled up to the local truncation error of the numerical 1Numerical Modelling of the Two-Dimensional Vlasov-Maxwell System Bengt Eliasson Department

  4. A two-dimensional flame table

    NASA Astrophysics Data System (ADS)

    Daw, Harold A.

    1987-08-01

    A two-dimensional flame table was constructed for visually demonstrating acoustical modes in a cavity. This flame table is an extension of the one-dimensional flame tube or Rubens flame tube apparatus. Photographs of some of the lower-order modes on rectangular box and cylindrical box flame table cavities are included.

  5. Two Dimensional Quantum Gravity Coupled to Matter

    E-print Network

    R. B. Mann

    1992-06-25

    A classical two dimensional theory of gravity which has a number of interesting features (including a Newtonian limit, black holes and gravitational collapse) is quantized using conformal field theoretic techniques. The critical dimension depends upon Newton's constant, permitting models with $d=4$. The constraint algebra and scaling properties of the model are computed.

  6. 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…

  7. On the two-dimensional sloshing problem

    PubMed Central

    Kozlov, Vladimir; Kuznetsov, Nikolay; Motygin, Oleg

    2011-01-01

    A correct proof is given for the following assertions about the two-dimensional sloshing problem. The fundamental eigenvalue is simple and the corresponding stream function may be chosen to be non-negative in the closure of the water domain. New proof is based on stricter assumptions about the water domain; namely, it must satisfy John’s condition. PMID:24959097

  8. Canonical quantization of two-dimensional gravity

    E-print Network

    S. N. Vergeles

    2001-02-01

    A canonical quantization of two-dimensional gravity minimally coupled to real scalar and spinor Majorana fields is presented. The physical state space of the theory is completely described and calculations are also made of the average value of the metric tensor relative to states close to the ground state

  9. Transition to two-dimensionality in magnetohydrodynamic turbulent Taylor-Couette flow.

    PubMed

    Zhao, Yurong; Tao, Jianjun; Zikanov, Oleg

    2014-03-01

    Transition from a Taylor-Couette turbulent flow to a completely two-dimensional axisymmetric turbulent state is realized numerically by increasing gradually the strength of the azimuthal magnetic field produced by electric current flowing through the axial rod. With the increase of the Hartmann number, the Taylor-vortex-like structures shrink, move closer to the inner cylinder, and turn into unsteady but perfect tori at sufficiently high Hartmann numbers. PMID:24730932

  10. Magnetization study of two dimensional helium three

    NASA Astrophysics Data System (ADS)

    Guo, Lei

    This dissertation discusses a magnetization study of a two dimensional Fermi system. Our group developed a SQUID NMR system to study the magnetization of two dimensional 3He on both GTA grafoil and ZYX Graphite substrates. Benefiting from SQUID technology, our NMR experiments were performed at very low applied magnetic field thus avoid the masking of ordering by strong external field. Monolayer 3He films adsorbed on crystalline graphite are considered a nearly ideal example of a two dimensional system of highly correlated fermions. By controlling the 3He areal density, adsorbed films exhibit a wide range of structures with different temperature- dependent magnetic properties and heat capacities. Our recent experiments on two dimensional 3He adsorbed on ZYX graphite focused on the anti-ferromagnetic 4/7 phase and the ferromagnetic incommensurate solid state of a second 3He monolayer. Ferromagnetic order was observed in two dimensional 3He films on both Grafoil and highly oriented ZYX grade exfoliated graphite. The dipolar field plays an important role in magnetic ordering in two dimensional spin systems. The dipole-dipole interaction leads to a frequency shift of the NMR absorption line. The resulting 3He NMR lineshape on Grafoil was a broad peak shifted towards lower frequency with a background from the randomly oriented regions extending to positive frequencies. Compared to Grafoil, ZYX graphite has a much greater structural coherence and is more highly oriented. When studying magnetism of 3He films on ZYX substrate we found that the features we observed in our original Grafoil experiment were much more pronounced on ZYX graphite. In addition, we observed some multi-peak structure on the 3He NMR lineshape, which suggest a series of spin wave resonances. We also studied the magnetic properties of the second layer of 3He films on ZYX substrate at density around 4/7 phase. To eliminate the paramagnetic signal of the first layer solid, we pre-plated a 4He layer on the ZYX that serves as a substrate for the 3He layer. In this region of density, the 3He film acts as a quantum antiferromagnet with disordered ground state (Quantum Spin Liquid). Our experimental results are reported and similar work is reviewed.

  11. The art and science of magnet design: Selected notes of Klaus Halbach. Volume 2

    SciTech Connect

    NONE

    1995-02-01

    This volume contains a compilation of 57 notes written by Dr. Klaus Halbach selected from his collection of over 1650 such documents. It provides an historic snapshot of the evolution of magnet technology and related fields as the notes range from as early as 1965 to the present, and is intended to show the breadth of Dr. Halbach`s interest and ability that have long been an inspiration to his many friends and colleagues. As Halbach is an experimental physicist whose scientific interests span many areas, and who does his most innovative work with pencil and paper rather than at the workbench or with a computer, the vast majority of the notes in this volume were handwritten and their content varies greatly--some reflect original work or work for a specific project, while others are mere clarifications of mathematical calculations or design specifications. As the authors converted the notes to electronic form, some were superficially edited and corrected, while others were extensively re-written to reflect current knowledge and notation. The notes are organized under five categories which reflect their primary content: Beam Position Monitors, (bpm), Current Sheet Electron Magnets (csem), Magnet Theory, (thry), Undulators and Wigglers (u-w), and Miscellaneous (misc). Within the category, they are presented chronologically starting from the most recent note and working backwards in time.

  12. 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. PMID:24567472

  13. Symmetry in two-dimensional gravity

    SciTech Connect

    Xu, K.W. (Center for Theoretical Physics, Physics Dept., Texas A and M Univ., TX (US)); Zhu, C.J. (International Center for Theoretical Physics, I-34100 Trieste (IT))

    1991-05-30

    The authors study the symmetry of two-dimensional gravity by choosing a generic gauge. A local action is derived which reduces to either the Liouville action or the Polyakov one by reducing to the conformal or light-cone gauge respectively. The theory is also solved classically. This paper shows that an SL(2,R) covariant gauge can be chosen so that the two-dimensional gravity has a manifest Virasoro and the s1(2,R)-current symmetry discovered by Polyakov. The symmetry algebra of the light-cone gauge is shown to be isomorphic to the Beltrami algebra. By using the contour integration method the authors construct the BRST charge Q{sub B} corresponding to this algebra following the Fradkin-Vilkovisky procedure and prove that the nilpotence of Q{sub B} requires c = 28 and {alpha}{sub 0} = 1.

  14. Deeply subrecoil two-dimensional Raman cooling

    SciTech Connect

    Boyer, V.; Phillips, W.D. [National Institute of Standards and Technology, Gaithersburg, Maryland 20899 (United States); Clarendon Laboratory, University of Oxford, Oxford OX1 3PU (United Kingdom); Lising, L.J.; Rolston, S.L. [National Institute of Standards and Technology, Gaithersburg, Maryland 20899 (United States)

    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.

  15. Two Dimensional Electronic Spectroscopy of Molecular Complexes

    Microsoft Academic Search

    Minhaeng Cho; Tobias Brixner; Igor Stiopkin; Harsha Vaswanib; Graham R. Flemingb

    Two dimensional (2D) heterodyne-detected electronic photon echo spectroscopy is introduced and described. We give an intuitive description of the origin and information content of 2D electronic spectra, focusing on molecular complexes. We identify two important quantities—the transition dipole term, and the transition frequency cross correlation function that controls the appearance of 2D electronic spectra. We also show how the transition

  16. Performance prediction of straight two dimensional diffusers

    NASA Technical Reports Server (NTRS)

    Greywall, M. S.

    1980-01-01

    A method, based on full viscous calculations, is presented to predict performance of straight two dimensional diffusers. The method predicts adequately the experimental pressure recovery data, up to the point of maximum pressure recovery, for small and large inlet boundary layer thicknesses. It is shown that at the point of maximum pressure recovery the streamwise velocity in the very near wall region varies as Z to the 0.22 power, where Z is the distance from the diffuser wall.

  17. Two-dimensional microwave tomographic system

    Microsoft Academic Search

    S. Y. Semenov; A. E. Bulyshev; A. E. Souvorov; R. H. Svenson; Y. E. Sizov; V. Y. Borisov; I. M. Kozlov; V. G. Poskuh; G. P. Tatsis

    1996-01-01

    The results of experiments on the two-dimensional (2D) quasi real-time microwave tomographic system are reported. Reconstruction possibilities of this system are demonstrated on the phantoms and the heart, including canine beating heart. The analysis of the quality of 2D images of the physical and mathematical phantoms is reported. The accurate solution of the inverse problem of the scalar Helmholtz equation

  18. Two-dimensional arrays for medical ultrasound

    Microsoft Academic Search

    S. W. Smith; G. E. Trahey; O. T. von Ramm

    1991-01-01

    The design, fabrication and evaluation of two-dimensional transducer arrays are described for medical ultrasound imaging. A 4×32, 2.8-MHz array was developed to use new signal processing techniques for improved B-scan imaging including elevation focusing, phase correction and synthetic aperture imaging. Laboratory measurements from typical array elements showed 50 ? insertion loss of -56 dB, -6 dB fractional bandwidth of 43%,

  19. Two Dimensional Knapsack with Unloading Constraints

    Microsoft Academic Search

    Jefferson L. M. da Silveira; Eduardo C. Xavier; Flávio K. Miyazawa

    2011-01-01

    n this paper we present approximation algorithms for the two dimensional knapsack problem with unloading constraints. In this problem, we have a bin B of width and height 1, and a list L with n items of C different classes, each item ai with height h(ai), width w(ai), profit p(ai) and class c(ai). We have to pack a subset of

  20. Statistical Mechanics of Two-dimensional Foams

    E-print Network

    Marc Durand

    2010-09-07

    The methods of statistical mechanics are applied to two-dimensional foams under macroscopic agitation. A new variable -- the total cell curvature -- is introduced, which plays the role of energy in conventional statistical thermodynamics. The probability distribution of the number of sides for a cell of given area is derived. This expression allows to correlate the distribution of sides ("topological disorder") to the distribution of sizes ("geometrical disorder") in a foam. The model predictions agree well with available experimental data.

  1. Two-dimensional photonic crystal lasers

    Microsoft Academic Search

    Mitsuru Yokoyama; Masahiro Imada; Susumu Noda

    2002-01-01

    In this article, we report on a two-dimensional (2D) photonic crystal (PhC) laser with a surface-emitting function. First of all, 2D PhC laser with triangular-lattice structure is described. A uniform 2D coherent lasing oscillation based on coupling of lightwaves propagating to six equivalent Gamma-X directions is successfully demonstrated. A large area 2D lasing oscillation over 300 micrometers in diameter and

  2. A Two-Dimensional Photonic Crystal Laser

    Microsoft Academic Search

    Kuon Inoue; Michihide Sasada; Jun Kawamata; Kazuaki Sakoda; Joseph W. Haus

    1999-01-01

    We report on observation of laser action unique to a two-dimensional (2D) photonic lattice.When dye-solution filled in air-holes of a 2D lattice was optically-pumped, laser action withoutexternal mirrors is found to occur at a specific wavelength corresponding to a flat band-dispersionin a high-symmetry direction of the 2D lattice plane; a small group-velocity is responsible for thelasing. On further increasing the

  3. Stability of Two-Dimensional Soft Quasicrystals

    E-print Network

    Kai Jiang; Jiajun Tong; Pingwen Zhang; An-Chang Shi

    2015-05-26

    The relative stability of two-dimensional soft quasicrystals is examined using a recently developed projection method which provides a unified numerical framework to compute the free energy of periodic crystal and quasicrystals. Accurate free energies of numerous ordered phases, including dodecagonal, decagonal and octagonal quasicrystals, are obtained for a simple model, i.e. the Lifshitz-Petrich free energy functional, of soft quasicrystals with two length-scales. The availability of the free energy allows us to construct phase diagrams of the system, demonstrating that, for the Lifshitz-Petrich model, the dodecagonal and decagonal quasicrystals can become stable phases, whereas the octagonal quasicrystal stays as a metastable phase.

  4. Intermittency in forced two-dimensional turbulence

    E-print Network

    W. Brent Daniel; Maarten A. Rutgers

    2000-05-03

    We find strong evidence for intermittency in forced two dimensional (2D) turbulence in a flowing soap film experiment. In the forward enstrophy cascade the structure function scaling exponents are nearly indistinguishable from 3D studies. Intermittency corrections are present in the inverse energy cascade as well, but weaker. Stretched exponential tails of the velocity difference probability distribution functions and shock like events at large velocity differences also resemble 3D studies. For decaying turbulence, where only the forward enstrophy cascade remains, all signs of intermittency disappear.

  5. Gauge equivalence in two-dimensional gravity

    SciTech Connect

    Fujiwara, T. (Department of Physics, Ibaraki University, Mito 310 (Japan)); Igarashi, Y. (Faculty of Education, Niigata University, Niigata 950-21 (Japan)); Kubo, J. (College of Liberal Arts, Kanazawa University, Kanazawa 920 (Japan)); Tabei, T. (Department of Physics, Ibaraki University, Mito 310 (Japan))

    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

  6. Two-dimensional signatures for molecular identification

    NASA Astrophysics Data System (ADS)

    Qazi, Muhammad; Vogt, Thomas; Koley, Goutam

    2008-03-01

    Simultaneous measurements of the conductance and surface work function (SWF) changes on nanostructured graphite layers have been performed to detect several gaseous analyte molecules. It has been observed that the gradient of the SWF versus conductance response plotted for specific analyte molecules is constant irrespective of their concentration or fractional occupancy of surface adsorption sites. The SWF and conductance changes have been found to be uncorrelated for different analyte molecules, resulting in unique gradients that can be used as two-dimensional signatures for molecular identification.

  7. Reproducibility of two-dimensional exercise echocardiography.

    PubMed

    Oberman, A; Fan, P H; Nanda, N C; Lee, J Y; Huster, W J; Sulentic, J A; Storey, O F

    1989-10-01

    To determine the reproducibility of two-dimensional exercise echocardiography, duplicate studies were performed on the same patients a median of 14 days apart. Because measurements are operator-dependent, interobserver variability was calculated for two experienced readers who interpreted the findings independently in a blinded manner. A high degree of interobserver agreement was found in evaluation of both ejection fraction measurements and wall motion abnormalities. Readings for ejection fraction immediately after exercise taken on different days could be estimated within 4% of the values measured in the first test; similarly measured wall motion score index was within 6% of that in the first test. Ejection fractions and wall motion scores were highly correlated between tests 1 and 2. The correlation coefficients between tests 1 and 2 were 0.92 for both the pre- and postexercise ejection fractions and 0.98 for both the pre- and postexercise wall motion scores. Quantitative two-dimensional echocardiography immediately after exercise is highly reproducible, providing a valuable tool for assessing serial changes in left ventricular function. PMID:2794280

  8. Two-dimensional phonon transport in graphene.

    PubMed

    Nika, Denis L; Balandin, Alexander A

    2012-06-13

    Properties of phonons-quanta of the crystal lattice vibrations-in graphene have recently attracted significant attention from the physics and engineering communities. Acoustic phonons are the main heat carriers in graphene near room temperature, while optical phonons are used for counting the number of atomic planes in Raman experiments with few-layer graphene. It was shown both theoretically and experimentally that transport properties of phonons, i.e. energy dispersion and scattering rates, are substantially different in a quasi-two-dimensional system such as graphene compared to the basal planes in graphite or three-dimensional bulk crystals. The unique nature of two-dimensional phonon transport translates into unusual heat conduction in graphene and related materials. In this review, we outline different theoretical approaches developed for phonon transport in graphene, discuss contributions of the in-plane and cross-plane phonon modes, and provide comparison with available experimental thermal conductivity data. Particular attention is given to analysis of recent results for the phonon thermal conductivity of single-layer graphene and few-layer graphene, and the effects of the strain, defects, and isotopes on phonon transport in these systems. PMID:22562955

  9. Flow mediated interactions between two cylinders at finite Re numbers

    NASA Astrophysics Data System (ADS)

    Gazzola, Mattia; Mimeau, Chloe; Tchieu, Andrew A.; Koumoutsakos, Petros

    2012-04-01

    We present simulations of two interacting moving cylinders immersed in a two-dimensional incompressible, viscous flow. Simulations are performed by coupling a wavelet-adapted, remeshed vortex method with the Brinkman penalization and projection approach. This method is validated on benchmark problems and applied to simulations of a master-slave pair of cylinders. The master cylinder's motion is imposed and the slave cylinder is let free to respond to the flow. We study the relative role of viscous and inertia effects in the cylinders interactions and identify related sharp transitions in the response of the slave. The observed differences in the behavior of cylinders with respect to corresponding potential flow simulations are discussed. In addition, it is observed that in certain situations the finite size of the slave cylinders enhances the transport so that the cylinders are advected more effectively than passive tracers placed, respectively, at the same starting position.

  10. Applications of two-dimensional infrared spectroscopy.

    PubMed

    Le Sueur, Amanda L; Horness, Rachel E; Thielges, Megan C

    2015-06-15

    Two-dimensional infrared (2D IR) spectroscopy has recently emerged as a powerful tool with applications in many areas of scientific research. The inherent high time resolution coupled with bond-specific spatial resolution of IR spectroscopy enable direct characterization of rapidly interconverting species and fast processes, even in complex systems found in chemistry and biology. In this minireview, we briefly outline the fundamental principles and experimental procedures of 2D IR spectroscopy. Using illustrative example studies, we explain the important features of 2D IR spectra and their capability to elucidate molecular structure and dynamics. Primarily, this minireview aims to convey the scope and potential of 2D IR spectroscopy by highlighting select examples of recent applications including the use of innate or introduced vibrational probes for the study of nucleic acids, peptides/proteins, and materials. PMID:26007625

  11. 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.

  12. Two-dimensional melting under quenched disorder

    E-print Network

    Sven Deutschländer; Tobias Kruppa; Hartmut Löwen; Georg Maret; Peter Keim

    2013-05-16

    We study the influence of quenched disorder on the two-dimensional melting behavior by using both video-microscopy of superparamagnetic colloidal particles and computer simulations of repulsive parallel dipoles. Quenched disorder is provided by pinning a fraction of the particles. We confirm the occurrence of the Kosterlitz-Thouless-Halperin-Nelson-Young scenario with an intermediate hexatic phase. While the fluid-hexatic transition remains largely unaffected by disorder, the hexatic-solid transition shifts towards lower temperatures for increasing disorder resulting in a significantly broadened stability range of the hexatic phase. In addition, we observe spatio-temporal critical(-like) fluctuations consistent with the continuous character of the phase transitions.

  13. Phonon hydrodynamics in two-dimensional materials.

    PubMed

    Cepellotti, Andrea; Fugallo, Giorgia; Paulatto, Lorenzo; Lazzeri, Michele; Mauri, Francesco; Marzari, Nicola

    2015-01-01

    The conduction of heat in two dimensions displays a wealth of fascinating phenomena of key relevance to the scientific understanding and technological applications of graphene and related materials. Here, we use density-functional perturbation theory and an exact, variational solution of the Boltzmann transport equation to study fully from first-principles phonon transport and heat conductivity in graphene, boron nitride, molybdenum disulphide and the functionalized derivatives graphane and fluorographene. In all these materials, and at variance with typical three-dimensional solids, normal processes keep dominating over Umklapp scattering well-above cryogenic conditions, extending to room temperature and more. As a result, novel regimes emerge, with Poiseuille and Ziman hydrodynamics, hitherto typically confined to ultra-low temperatures, characterizing transport at ordinary conditions. Most remarkably, several of these two-dimensional materials admit wave-like heat diffusion, with second sound present at room temperature and above in graphene, boron nitride and graphane. PMID:25744932

  14. New Two-Dimensional Ice Models

    NASA Astrophysics Data System (ADS)

    Kirov, Mikhail V.

    2012-11-01

    This paper presents a new approach for enumerating all hydrogen bond arrangements of ice-like systems with periodic boundary conditions. It is founded on a topological procedure for the dimensional reduction and a new variant of the transfer matrix method based on small conditional transfer matrices. We consider a couple of new two-dimensional ice models on very unusual lattices. One of them is the twisted square ice model with crossing H-bonds. The other is the digonal-hexagonal model with double H-bonds. In spite of their uncommonness, these models are quite realistic, because from the standpoint of combinatorics and topology they are equivalent to the layers of usual hexagonal ice Ih under periodic boundary conditions in one of the directions. The exact proton configuration statistics for a number of 2D-expanded unit cells of hexagonal ice Ih and the residual entropy of the new ice models in the large system limit are presented.

  15. Internal tide generation by arbitrary two-dimensional topography

    E-print Network

    Peacock, Thomas

    To date, analytical models of internal tide generation by two-dimensional ridges have considered only idealized shapes. Here, we advance the Green function approach to address the generation of internal tides by two-dimensional ...

  16. The development and application of permanent-magnet EDS based on Halbach structure

    Microsoft Academic Search

    He Guang; Long Zhiqiang; Cheng Yuwei

    2010-01-01

    With the permanent-magnet EDS (Electro-dynamic Suspension) system as the background, rectilineal PM Halbach structure is introduced. The theory and stability of permanent-magnet EDS system are analyzed which concludes that permanent-magnet EDS system is of greater advantage under high speed condition. Then two present projects based on the the permanent-magnet EDS which aim at actual application, the GA urban maglev train

  17. Optical Measurement of Spectra of Two-Dimensional Functions

    Microsoft Academic Search

    Mahinder S. Uberoi

    1962-01-01

    The principle of an optical computer for the measurement of two-dimensional spectral and cross-spectral densities is described. The performance of one of the experimental arrangements is checked by measuring the spectral densities of a simple two-dimensional function. The apparatus may be used to compute the Fourier transform of a two-dimensional function.

  18. Foundation of The Two dimensional Quantum Theory of Gravity

    E-print Network

    F. Ghaboussi

    1998-07-16

    The two dimensional substructure of general relativity and gravity, and the two dimensional geometry of quantum effect by black hole are disclosed. Then the canonical quantization of the two dimensional theory of gravity is performed. It is shown that the resulting uncertainty relations can explain black hole quantum effects. A quantum gravitational length is also derived which can clarify the origin of Planck length.

  19. Halbach array type focusing actuator for small and thin optical data storage device

    NASA Astrophysics Data System (ADS)

    Lee, Sung Q.; Park, Kang-Ho; Paek, Mun Chul

    2004-09-01

    The small form factor optical data storage devices are developing rapidly nowadays. Since it is designed for portable and compatibility with flesh memory, its components such as disk, head, focusing actuator, and spindle motor should be assembled within 5 mm. The thickness of focusing actuator is within 2 mm and the total working range is +/-100um, with the resolution of less than 1?m. Since the thickness is limited tightly, it is hard to place the yoke that closes the magnetic circuit and hard to make strong flux density without yoke. Therefore, Halbach array is adopted to increase the magnetic flux of one side without yoke. The proposed Halbach array type focusing actuator has the advantage of thin actuation structure with sacrificing less flex density than conventional magnetic array. The optical head unit is moved on the swing arm type tracking actuator. Focusing coil is attached to swing arm, and Halbach magnet array is positioned at the bottom of deck along the tracking line, and focusing actuator exerts force by the Fleming's left hand rule. The dynamics, working range, control resolution of focusing actuator are analyzed and performed.

  20. Finite element formulation of the two-dimensional nonlinear inverse heat conduction problem

    SciTech Connect

    Bass, B.R.; Ott, L.J.

    1980-01-01

    The calculation of the surface temperature and surface heat flux from measured temperature transients at one or more interior points of a body is identified in the literature as the inverse heat conduction problem. Heretofore, analytical and computational methods of treating this problem have been limited to one-dimensional nonlinear or two-dimensional linear material models. An inverse solution technique applicable to the two-dimensional nonlinear model with temperature-dependent thermophysical properties is presented. This utilizes a finite element heat conduction model and a generalization of Beck's one-dimensional nonlinear estimation procedure. The formulation is applied to the cross section of a composite cylinder with temperature-dependent material properties. Results are presented to demonstrate that the inverse formulation is capable of successfully treating experimental data. An important feature of the method is that small time steps are permitted while avoiding severe oscillations or numerical instabilities due to experimental errors in measured data.

  1. Vorticity shedding over two-dimensional bodies

    NASA Astrophysics Data System (ADS)

    Mathioulakis, D.

    The vorticity shedding characteristics in attached and separated regions were investigated over three configurations, namely a backward facing circular arc, an ellipse at an angle of attack and a pitching airfoil. A fully automated data acquisition system was developed, including a two-component Laser-Velocimetry system in backscatter mode, an accurately controlled traversing mechanism and a MINK-11 minicomputer. Two-component velocity measurements were obtained over the above mentioned bodies, with steady and unsteady free streams. Emphasis was concentrated on the separation region, the free-shear layers and the wake downstream of these bodies. Two inviscid vortex models were developed to predict two different flow phenomena, namely the separated flow over a circular cylinder started impulsively from rest and propagating stall over a linear stationary cascade.

  2. Two-dimensional vortices and accretion disks

    NASA Astrophysics Data System (ADS)

    Nauta, Michiel Doede

    2000-01-01

    Observations show that there are disks around certain stars that slowly rain down on the central (compact) object: accretion disks. The rate of depletion of the disk might be slow but is still larger than was expected on theoretical grounds. That is why it has been suggested that the disks are turbulent. Because the disk is thin and rotating this turbulence might be related to two-dimensional (2D) turbulence which is characterized by energy transfers towards small wave numbers and the formation of 2D-vortices. This hypothesis is investigated in this thesis by numerical simulations. After an introduction, the numerical algorithm that was inplemented is discussed together with its relation to an accretion disk. It performs well under the absence of discontinuities. The code is used to study 2D-turbulence under the influence of background rotation with compressibility and a shearing background flow. The first is found to be of little consequence but the shear flow alters 2D-turbulence siginificantly. Only prograde vortices of enough strength are able to withstand the shear flow. The size of the vortices in the cross stream direction is also found to be smaller than the equivalent of the thickness of an accretion disk. These circulstances imply that the assumption of two-dimensionality is questionable so that 2D-vortices might not abound in accretion disks. However, the existence of such vortices is not ruled out and one such a cortex is studied in detail in chapter 4. The internal structure of the vortex is well described by a balance between Coriolis, centrifugal and pressure forces. The vortex is also accompanied by two spiral compressible waves. These are not responsible for the azimuthal drift of the vortex, which results from secondary vortices, but they might be related to the small radial drift that is observed. Radial drift leads to accretion but it is not very efficient. Multiple vortex interactions are the topic of tha last chapter and though interesting the increase in accretion grows only linearly with the number of vortices.

  3. Optical gaps, mode patterns and dipole radiation in two-dimensional aperiodic photonic structures

    NASA Astrophysics Data System (ADS)

    Boriskina, Svetlana V.; Gopinath, Ashwin; Negro, Luca Dal

    2009-05-01

    Based on the rigorous generalized Mie theory solution of Maxwell's equations for dielectric cylinders we theoretically investigate the optical properties of two-dimensional deterministic structures based on the Fibonacci, Thue-Morse and Rudin-Shapiro aperiodic sequences. In particular, we investigate bandgap formation and mode localization properties in aperiodic photonic structures based on the accurate calculation of their local density of states (LDOS). In addition, we explore the potential of photonic structures based on aperiodic order for the engineering of radiative rates and emission patterns in erbium-doped silicon-rich nitride photonic structures.

  4. A generalized orthogonal coordinate system for describing families of axisymmetric and two-dimensional bodies

    NASA Technical Reports Server (NTRS)

    Gnoffo, P. A.

    1977-01-01

    A generalized curvilinear orthogonal coordinate system is presented which can be used for approximating various axisymmetric and two-dimensional body shapes of interest to aerodynamicists. Such body shapes include spheres, ellipses, spherically capped cones, flat-faced cylinders with rounded corners, circular disks, and planetary probe vehicles. A set of transformation equations is also developed whereby a uniform velocity field approaching a body at any angle of attack can be resolved in the transformed coordinate system. The Navier-Stokes equations are written in terms of a generalized orthogonal coordinate system to show the resultant complexity of the governing equations.

  5. Topological features of massive bosons on two dimensional Einstein space-time

    E-print Network

    Romeo Brunetti; Lorenzo Franceschini; Valter Moretti

    2009-07-10

    In this paper we tackle the problem of constructing explicit examples of topological cocycles of Roberts' net cohomology, as defined abstractly by Brunetti and Ruzzi. We consider the simple case of massive bosonic quantum field theory on the two dimensional Einstein cylinder. After deriving some crucial results of the algebraic framework of quantization, we address the problem of the construction of the topological cocycles. All constructed cocycles lead to unitarily equivalent representations of the fundamental group of the circle (seen as a diffeomorphic image of all possible Cauchy surfaces). The construction is carried out using only Cauchy data and related net of local algebras on the circle.

  6. Turbulent equipartitions in two dimensional drift convection

    SciTech Connect

    Isichenko, M.B.; Yankov, V.V. [Univ. of California, Santa Barbara, CA (United States). Inst. for Theoretical Physics

    1995-07-25

    Unlike the thermodynamic equipartition of energy in conservative systems, turbulent equipartitions (TEP) describe strongly non-equilibrium systems such as turbulent plasmas. In turbulent systems, energy is no longer a good invariant, but one can utilize the conservation of other quantities, such as adiabatic invariants, frozen-in magnetic flux, entropy, or combination thereof, in order to derive new, turbulent quasi-equilibria. These TEP equilibria assume various forms, but in general they sustain spatially inhomogeneous distributions of the usual thermodynamic quantities such as density or temperature. This mechanism explains the effects of particle and energy pinch in tokamaks. The analysis of the relaxed states caused by turbulent mixing is based on the existence of Lagrangian invariants (quantities constant along fluid-particle or other orbits). A turbulent equipartition corresponds to the spatially uniform distribution of relevant Lagrangian invariants. The existence of such turbulent equilibria is demonstrated in the simple model of two dimensional electrostatically turbulent plasma in an inhomogeneous magnetic field. The turbulence is prescribed, and the turbulent transport is assumed to be much stronger than the classical collisional transport. The simplicity of the model makes it possible to derive the equations describing the relaxation to the TEP state in several limits.

  7. 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

  8. Seismic isolation of two dimensional periodic foundations

    SciTech Connect

    Yan, Y.; Mo, Y. L., E-mail: yilungmo@central.uh.edu [University of Houston, Houston, Texas 77004 (United States); Laskar, A. [Indian Institute of Technology Bombay, Powai, Mumbai (India); Cheng, Z.; Shi, Z. [Beijing Jiaotong University, Beijing (China); Menq, F. [University of Texas, Austin, Texas 78712 (United States); Tang, Y. [Argonne National Laboratory, Argonne, Illinois 60439 (United States)

    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.

  9. Single Molecule Approaches for Two Dimensional Nanostructures

    NASA Astrophysics Data System (ADS)

    Baker, Thomas; Guo, Shajun; Koh, Weon-Kyu; Makarov, Nikolay; Fiddler, Andrew; Robel, Istvan; Klimov, Victor

    2014-03-01

    A variety of two dimensional semiconductor nanostructures have been synthesized recently by a number of different groups. Of these, nanoplatelets made of a single to few layers of material have shown interesting promise due to confinement in only a single direction. The photophysics of these types of structures show large exciton binding energies and narrow emission widths in ensemble measurements. Only a few single molecule experiments have been reported in the literature and we hope to expand the insights that single molecule techniques can provide in the understanding of these new materials. Our group has recently extended our synthetic expertise gained from quantum dots into these 2D nanoplatelets including CdSe, MoS2 and graphene. Time correlated single photon counting experiments at the single molecule level provide information on the homogenous linewidths, quantum yield variations, and fluorescence lifetimes. Furthermore, two photon correlations at zero time delay allow us to confirm the single molecule nature of the emission and potentially determine biexciton quantum yields and lifetimes.

  10. Two-dimensional implicit time dependent calculations on adaptive unstructured meshes with time evolving boundaries.

    SciTech Connect

    Lin, Paul Tinphone; Jameson, Antony, 1934- (Stanford University, Stanford, CA -); Baker, Timothy J. (Princeton University, Princeton, NJ); Martinelli, Luigi (Princeton University, Princeton, NJ)

    2005-01-01

    An implicit multigrid-driven algorithm for two-dimensional incompressible laminar viscous flows has been coupled with a solution adaptation method and a mesh movement method for boundary movement. Time-dependent calculations are performed implicitly by regarding each time step as a steady-state problem in pseudo-time. The method of artificial compressibility is used to solve the flow equations. The solution mesh adaptation method performs local mesh refinement using an incremental Delaunay algorithm and mesh coarsening by means of edge collapse. Mesh movement is achieved by modeling the computational domain as an elastic solid and solving the equilibrium equations for the stress field. The solution adaptation method has been validated by comparison with experimental results and other computational results for low Reynolds number flow over a shedding circular cylinder. Preliminary validation of the mesh movement method has been demonstrated by a comparison with experimental results of an oscillating airfoil and with computational results for an oscillating cylinder.

  11. Control of Spin Wave Band Structure and Propagation in Two-Dimensional Magnonic Crystals

    NASA Astrophysics Data System (ADS)

    Sietsema, Glade; Flatté, Michael E.

    2015-03-01

    We have studied the properties of spin waves in two-dimensional magnonic crystals consisting of a magnetic material arranged in a lattice of cylinders and embedded in a second magnetic material. Dispersion curves, linewidths, and spin wave propagation patterns were obtained from the Landau-Lifshitz-Gilbert equation using the plane wave expansion method. We have examined how these results are affected by various parameters including the shape of the cylinders, the lattice structure, the material properties, and the spin-orbit interaction. Adjusting these values can open or close band gaps and drastically shift the frequency range of the band structure. The spin wave propagation patterns were found to exhibit high directionality dependent on the excitation frequency and can also be modified with the aforementioned parameters. This work was supported in part by DARPA/MESO and by C-SPIN, one of six centers of STARnet, a Semiconductor Research Corporation program, sponsored by MARCO and DARPA.

  12. Some properties of large- N two-dimensional Yang-Mills theory

    NASA Astrophysics Data System (ADS)

    Gross, David J.; Matytsin, Andrei

    1995-02-01

    large- N two-dimensional QCD on a cylinder and on a vertex manifold (a sphere with three holes) is investigated. The relation between the saddle-point description and the collective field theory of QCD 2 is established. Using this relation, it is shown that the Douglas-Kazakov phase transition on a cylinder is associated with the presence of a gap in the eigenvalue distributions for Wilson loops. An exact formula for the phase transition on a disc with an arbitrary boundary holonomy is found. The role of instantons in inducing such transitions is discussed. The zero-area limit of the partition function on a vertex manifold is studied. It is found that this partition function vanishes unless the boundary conditions satisfy a certain selection rule which is an analogue of momentum conservation in field theory.

  13. Two-dimensional dense gas dynamics

    NASA Astrophysics Data System (ADS)

    Brown, Brady Polk

    Certain polyatomic fluids with large molecular weights referred to as dense gases exhibit unusual thermodynamic and flow properties in the region of the thermodynamic critical point. A computer program developed to solve two-dimensional flow fields is used to analyze non- classical dense gas phenomena in the single-phase gas region. A two-step, flux-limited, total variation diminishing scheme solves the time-dependent Euler equations for supersonic steady flow fields and mixed subsonic and supersonic transient flow fields. Two non- ideal gas models are incorporated into the numerical scheme in order to simulate dense gas effects. The van der Waals model, which is the simplest gas model that will show dense gas behavior, is employed to economically demonstrate qualitative trends in dense gas flows. The more complex Martin-Hou model is incorporated for cases where quantitative accuracy becomes more important. Simulated flows over simple geometries such as wedges, arcs, ramps, and steps using both the van der Waals gas model and the perfect gas model demonstrate significant differences in wave field configurations between dense gases and ideal gases. Results are also computed using the Martin-Hou equation of state which is more conservative in predicting dense gas effects than the van der Waals model. In addition to exploring the basic nature of dense gas flows for simple geometries, the utilization of dense gas properties to improve the efficiency of organic Rankine- cycle engines is investigated. Simulations of supersonic dense gas flows through impulse turbine cascades demonstrate improvements in flow quality through the cascades by reducing losses due to shock waves.

  14. 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.

  15. Threshold gain and gain-enhancement due to distributed-feedback in two-dimensional photonic-crystal lasers

    Microsoft Academic Search

    Nobuhiko Susa; Morinosato Wakamiya

    2001-01-01

    The threshold gain (gth) of a two-dimensional (2D) photonic crystal distributed-feedback (DFB) laser composed of 8×8 dielectric cylinders was one order of magnitude smaller than that of an 8-pair 1D DFB laser with the identical refractive indexes. In the 2D finite-width photonic crystal laser, gth using the 1st photonic band was smaller than that using the higher photonic band, contrary

  16. Two-dimensional nanoarchitectonics based on self-assembly

    Microsoft Academic Search

    Katsuhiko Ariga; Michael V. Lee; Taizo Mori; Xiao-Yan Yu; Jonathan P. Hill

    2010-01-01

    Top–down nanofabrication techniques, especially photolithography, have advanced nanotechnology to a point where system-process integration with bottom–up self-assembly is now required. Because most lithographic techniques are constrained to two-dimensional planes, investigation of integrated self-assembly systems should focus on two-dimensional organization. In this review, research on two-dimensional nanoartchitectonics is classified and summarized according to the type of interface used. Pattern formation following

  17. Lie algebra contractions on two-dimensional hyperboloid

    SciTech Connect

    Pogosyan, G. S., E-mail: pogosyan@ysu.am; Yakhno, A. [Universidad de Guadalajara, Departamento de Matematicas, CUCEI (Mexico)

    2010-03-15

    The Inoenue-Wigner contraction from the SO(2, 1) group to the Euclidean E(2) and E(1, 1) group is used to relate the separation of variables in Laplace-Beltrami (Helmholtz) equations for the four corresponding two-dimensional homogeneous spaces: two-dimensional hyperboloids and two-dimensional Euclidean and pseudo-Euclidean spaces. We show how the nine systems of coordinates on the two-dimensional hyperboloids contracted to the four systems of coordinates on E{sub 2} and eight on E{sub 1,1}. The text was submitted by the authors in English.

  18. Silly Cylinders

    NSDL National Science Digital Library

    Darlene DePalma

    2012-07-09

    This is a short activity where students determine the density of the human body by considering each part of the body to be a cylinder. I use this activity during the 2nd week of school, so students have already had some practice with measurement. In addition to providing students with practice in data collection and problem solving, it is a good activity that allows teachers to measure students’ previous knowledge in these areas.

  19. A Hybrid Approach To Tandem Cylinder Noise

    NASA Technical Reports Server (NTRS)

    Lockard, David P.

    2004-01-01

    Aeolian tone generation from tandem cylinders is predicted using a hybrid approach. A standard computational fluid dynamics (CFD) code is used to compute the unsteady flow around the cylinders, and the acoustics are calculated using the acoustic analogy. The CFD code is nominally second order in space and time and includes several turbulence models, but the SST k - omega model is used for most of the calculations. Significant variation is observed between laminar and turbulent cases, and with changes in the turbulence model. A two-dimensional implementation of the Ffowcs Williams-Hawkings (FW-H) equation is used to predict the far-field noise.

  20. HYBRID REGISTRATION FOR TWO-DIMENSIONAL GEL PROTEIN XIUYING WANG

    E-print Network

    Wong, Limsoon

    HYBRID REGISTRATION FOR TWO-DIMENSIONAL GEL PROTEIN IMAGES XIUYING WANG Biomedical and Multimedia of protein sequence data. But due to the elastic deformations of two-dimensional gel protein eletrophoresis images, their registration still remains a challenge. In this paper, a hybrid 2D gel protein image

  1. Microwave tomography: a two-dimensional Newton iterative scheme

    Microsoft Academic Search

    Alexandre E. Souvorov; Alexander E. Bulyshev; Serguei Y. Semenov; Robert H. Svenson; Alexei G. Nazarov; Yuri E. Sizov; George P. Tatsis

    1998-01-01

    In this paper, a variant of the Newton method, which uses a fast solution of the direct problem and a dual mesh, is proposed. Computational and physical experiments with simple two-dimensional high-contrast phantoms are discussed, and a full-scaled image of a two-dimensional mathematical model of a human torso is obtained

  2. Conical structures of black and blue two-dimensional phosphorus

    NASA Astrophysics Data System (ADS)

    Utt, Kainen; Borunda, Mario; Barraza-Lopez, Salvador

    2015-03-01

    Two-dimensional phosphorus, the most recent addition to the growing list of novel two-dimensional materials, has quickly become the focus of materials science. We create conical configurations of black phosphorus from planar structures with a disclination line, and the properties of these conical structures of phosphorus will be discussed here.

  3. Electronic Control of a Two-Dimensional, Knee-less,

    E-print Network

    Ruina, Andy L.

    Robot Controller The Innovation FIRST Mini Robot Controller was chosen to control the robot becauseElectronic Control of a Two- Dimensional, Knee-less, Bipedal Robot Final Report for T&AM 492 under two dimensional, knee-less, bipedal walking robot. After removing one of several unsuccessful control

  4. New two-dimensional quantum models with shape invariance

    SciTech Connect

    Cannata, F. [INFN, Via Irnerio 46, 40126 Bologna (Italy); Ioffe, M. V. [Saint-Petersburg State University, 198504 St.-Petersburg (Russian Federation); Nishnianidze, D. N. [Saint-Petersburg State University, 198504 St.-Petersburg (Russian Federation); Akaki Tsereteli State University, 4600 Kutaisi (Georgia)

    2011-02-15

    Two-dimensional quantum models which obey the property of shape invariance are built in the framework of polynomial two-dimensional supersymmetric quantum mechanics. They are obtained using the expressions for known one-dimensional shape invariant potentials. The constructed Hamiltonians are integrable with symmetry operators of fourth order in momenta, and they are not amenable to the conventional separation of variables.

  5. Spatiotemporal surface solitons in two-dimensional photonic lattices

    E-print Network

    with respect to the ratio of group velocity dis- persion and coupling constant. The slowly varying normalizedSpatiotemporal surface solitons in two-dimensional photonic lattices Dumitru Mihalache,1 Dumitru lattices and demon- strate the existence of two-dimensional surface light bullets localized in the lattice

  6. Using Two-Dimensional Colloidal Crystals to Understand Crystallography

    E-print Network

    Loening, Niko

    Using Two-Dimensional Colloidal Crystals to Understand Crystallography Instructor Notes Geometric in Figure 1a, 1b, and 1d. #12;2D Crystallography ­ Instructor Notes 2 Figure 1: Geometric constructions). #12;Using Two-Dimensional Colloidal Crystals to Understand Crystallography Instructions for Students

  7. Two-dimensional digital filters with no overflow oscillations

    Microsoft Academic Search

    N. El-Agizi; M. Fahmy

    1979-01-01

    A criterion which sufficiently guarantees the absence of overflow oscillations in two-dimensional digital filters in the state space is given. This criterion is used to identify a certain class of two-dimensional filters for which overflow oscillations are proved to be absent. Such filters, however, are noncanonic.

  8. Acoustics 2000 1 The Two Dimensional Numerical Modeling

    E-print Network

    account for wave propagation in the seabed but an acoustic wave approximation is often used for seabedAcoustics 2000 1 The Two Dimensional Numerical Modeling Of Acoustic Wave Propagation in Shallow on a two dimensional numerical simulation of acoustic wave propagation that has been developed to visualize

  9. Spontaneous chiral symmetry breaking in two-dimensional aggregation

    NASA Astrophysics Data System (ADS)

    Sandler, Ilya M.; Canright, Geoffrey S.; Zhang, Zhenyu; Gao, Hongjun; Xue, Zenquan; Pang, Shijin

    1998-08-01

    We describe a two-dimensional growth model which exhibits a novel form of spontaneous chiral symmetry breaking. The model is inspired by recent aggregation experiments giving quasi-two-dimensional “S”-shaped aggregates, and yields qualitatively similar growth patterns. We also report new growth experiments offering qualitative support for our model.

  10. State space approach to two-dimensional generalized micropolar thermoelasticity

    NASA Astrophysics Data System (ADS)

    Sherief, Hany H.; El-sayed, Amani M.

    2015-06-01

    The state space approach to two-dimensional generalized micropolar thermoelasticity has been formulated. In this formulation, the governing equations are transformed into a matrix equation whose solution enables us to write the solution of any two-dimensional problem in terms of the boundary conditions. The resulting formulation is applied to a half-space problem.

  11. Separation of Creeping Flow past Two Circular Cylinders

    NASA Astrophysics Data System (ADS)

    Miyazaki, Takeshi; Hasimoto, Hidenori

    1980-10-01

    The steady two-dimensional Stokes flow past two circular cylinders of equal radii is considered, where the direction of the flow is parallel to the line joining the centers. Separation of the flow from the cylinders occurs if the parameter t{=}(distance between two cylinders)/(diameter of the cylinders) is less than 1.57. If t is less than 1.07 the twin eddies attached to both cylinders coalesce to form two separation lines joining two cylinders. As t decreases, the number of the separation lines increases, and Moffatt vortices are formed at t{=}0 (i.e. in contact). These results are in accordance with the experiments given by Taneda.

  12. Self-excited oscillations in the wake of two-dimensional bluff bodies and their control

    NASA Astrophysics Data System (ADS)

    Schumm, Michael; Berger, Eberhard; Monkewitz, Peter A.

    1994-07-01

    The onset of Karman-vortex shedding is studied experimentally in the wake of different two-dimensional bluff bodies, namely an oblong cylinder, circular cylinders, and plates of rectangular cross section. Different control measures, such as wake heating, transverse body oscillations, and base bleed are investigated. As the steady-periodic Karman shedding has previously been identified as a limit-cycle, i.e. as self-excited oscillations, the experiments are interpreted in the framework of the Stuart-Landau model. The coefficients of the Stuart-Landau equation for the characteristic vortex shedding amplitude, i.e. the linear temporal growth rate, linear frequency, and the Landau constant, are fully determined for the two cylinders and in part for the plate. For this purpose transients are generated by suddenly switching transverse body oscillations or base bleed on or off. The analysis of these transients by a refined method based on complex demodulation provides reliable estimates of the model coefficients and yields an experimental validation of the concept that a global instability mode grows or decays as a whole. Also, it is demonstrated that the coefficients of the Stuart-Landau equation are independent of the experimental technique used to produce the transients.

  13. Front tracking and two dimensional Riemann problems: a conference report

    SciTech Connect

    Glimm, J.; Klingenberg, C.; McBryan, O.; Plohr, B.; Sharp, D.; Yaniv, S.

    1984-01-01

    A substantial improvement in resolution has been achieved for the computation of jump discontinuities in gas dynamics using the method of front tracking. The essential feature of this method is that a lower dimensional grid is fitted to and follows the discontinuous waves. At the intersection points of these discontinuities, two-dimensional Riemann problems occur. In this paper we study such two-dimensional Riemann problems from both numerical and theoretical points of view. Specifically included is a numerical solution for the Mach reflection, a general classification scheme for two-dimensional elementary waves, and a discussion of problems and conjectures in this area.

  14. Two-dimensional Minkowski causal automorphisms and conformal maps

    E-print Network

    Juan Manuel Burgos

    2013-05-04

    Treating the two-dimensional Minkowski space as a Wick rotated version of the complex plane, we characterize the causal automorphisms in two-dimensional Minkowski space as the M\\"{a}rzke-Wheeler maps of a certain class of observers. We also characterize the differentiable causal automorphisms of this space as the Minkowski conformal maps whose restriction to the time axis belongs to the class of observers mentioned above. We answer a recently raised question about whether causal automorphisms are characterized by their wave equation. As another application of the theory, we give a proper time formula for accelerated observers which solves the twin paradox in two-dimensional Minkowski spacetime.

  15. Third sound in one and two dimensional modulated structures

    SciTech Connect

    Komuro, T.; Kawashima, H., Shirahama, K.; Kono, K. [Univ. of Tokyo, Tokyo (Japan)

    1996-02-01

    An experimental technique is developed to study acoustic transmission in one and two dimensional modulated structures by employing third sound of a superfluid helium film. In particular, the Penrose lattice, which is a two dimensional quasiperiodic structure, is studied. In two dimensions, the scattering of third sound is weaker than in one dimension. Nevertheless, the authors find that the transmission spectrum in the Penrose lattice, which is a two dimensional prototype of the quasicrystal, is observable if the helium film thickness is chosen around 5 atomic layers. The transmission spectra in the Penrose lattice are explained in terms of dynamical theory of diffraction.

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

    PubMed

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

    2014-10-01

    The dephasing of the Fermi edge singularity excitations in two modulation doped single quantum wells of 12 nm and 18 nm thickness and in-well carrier concentration of ?4 × 10(11) cm(-2) was carefully measured using spectrally resolved four-wave mixing (FWM) and two-dimensional Fourier transform (2DFT) spectroscopy. Although the absorption at the Fermi edge is broad at this doping level, the spectrally resolved FWM shows narrow resonances. Two peaks are observed separated by the heavy hole/light hole energy splitting. Temperature dependent "rephasing" (S1) 2DFT spectra show a rapid linear increase of the homogeneous linewidth with temperature. The dephasing rate increases faster with temperature in the narrower 12 nm quantum well, likely due to an increased carrier-phonon scattering rate. The S1 2DFT spectra were measured using co-linear, cross-linear, and co-circular polarizations. Distinct 2DFT lineshapes were observed for co-linear and cross-linear polarizations, suggesting the existence of polarization dependent contributions. The "two-quantum coherence" (S3) 2DFT spectra for the 12 nm quantum well show a single peak for both co-linear and co-circular polarizations. PMID:25296819

  17. Design and analysis of a two-dimensional camera array

    E-print Network

    Yang, Jason C. (Jason Chieh-Sheng), 1977-

    2005-01-01

    I present the design and analysis of a two-dimensional camera array for virtual studio applications. It is possible to substitute conventional cameras and motion control devices with a real-time, light field camera array. ...

  18. 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)

  19. Fast Two-Dimensional Digital-Filter Hardware

    NASA Technical Reports Server (NTRS)

    Edwards, T. R.

    1985-01-01

    Report describes priciples of hardware implementation of two-dimensional 5 by 5 convolute-integer low pass filter. Filter processes image data points fast enough for real-time use in image analysis and enhancement.

  20. 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.

  1. Time harmonic scar statistics in two dimensional cavities.

    SciTech Connect

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

    2007-01-01

    This paper examined the high frequency time harmonic localization of modal fields in two dimensional cavities along unstable periodic orbits. The elliptic formalism, combined with the random phase approach, allowed the treatment of both convex and concave boundary geometries.

  2. Healing of defects in a two-dimensional granular crystal

    E-print Network

    Rice, Marie C

    2014-01-01

    Using a macroscopic analog for a two dimensional hexagonal crystal, we perform an experimental investigation of the self-healing properties of circular grain defects with an emphasis on defect orientation. A circular grain ...

  3. Classification of two-dimensional fermionic and bosonic topological orders

    E-print Network

    Gu, Zheng-Cheng

    The string-net approach by Levin and Wen, and the local unitary transformation approach by Chen, Gu, and Wen, provide ways to classify topological orders with gappable edge in two-dimensional (2D) bosonic systems. The two ...

  4. Near-Surface Geophysics: Two-Dimensional Resistivity

    USGS Multimedia Gallery

    USGS hydrologist conducts a two-dimensional (2D) resistivity survey to investigate and characterize the shallow subsurface. The survey was conducted as part of an applied research effort by the USGS Office of Groundwater Branch of Geophysics in 2006....

  5. Transformation optics scheme for two-dimensional materials

    E-print Network

    Kumar, Anshuman

    Two-dimensional optical materials, such as graphene, can be characterized by surface conductivity. So far, the transformation optics schemes have focused on three-dimensional properties such as permittivity ? and permeability ...

  6. Interface solitons in two-dimensional photonic lattices.

    PubMed

    Molina, Mario I; Kivshar, Yuri S

    2008-12-01

    We analyze localization of light at the interfaces separating square and hexagonal photonic lattices, as recently realized experimentally for two-dimensional laser-written waveguides in silica glass with self-focusing nonlinearity [Opt. Lett.33, 663 (2008)]. We find the conditions for the existence of linear and nonlinear surface states substantially influenced by the lattice topology, and study the effect of different symmetries and couplings on the stability of two-dimensional interface solitons. PMID:19037418

  7. Two-Dimensional Magnetic Recording: Read Channel Modeling and Detection

    Microsoft Academic Search

    Anantha Raman Krishnan; Rathnakumar Radhakrishnan; Bane Vasic; Aleksander Kavcic; William Ryan; Fatih Erden

    2009-01-01

    Abstract—Two-dimensional magnetic recording (TDMR) is a novel storage architecture that, in theory, can achieve a density of upto 10 Tb\\/in,. It uniquely differs from other proposed next-generation architectures because of its reliance on sophis- ticated two-dimensional signal processing algorithms. Recently, a number,of contributions have been made,in the development of read-channel models and detectors for TDMR systems. In this paper, we

  8. Topological delocalization of two-dimensional massless Dirac fermions.

    PubMed

    Nomura, Kentaro; Koshino, Mikito; Ryu, Shinsei

    2007-10-01

    The beta function of a two-dimensional massless Dirac Hamiltonian subject to a random scalar potential, which, e.g., underlies theoretical descriptions of graphene, is computed numerically. Although it belongs to, from a symmetry standpoint, the two-dimensional symplectic class, the beta function monotonically increases with decreasing conductance. We also provide an argument based on the spectral flows under twisting boundary conditions, which shows that none of the states of the massless Dirac Hamiltonian can be localized. PMID:17930701

  9. Two-dimensional quasicrystal with eightfold rotational symmetry

    Microsoft Academic Search

    N. Wang; H. Chen; K. H. Kuo

    1987-01-01

    A two-dimensional quasi-crystal with an eightfold rotational axis has been found in rapidly solidified V-Ni-Si and Cr-Ni-Si alloys by means of transmission electron microscopy. The electron-diffraction pattern taken along this axis shows no periodicity, but a clear eightfold orientation symmetry. The corresponding high-resolution electron-microscopic image agrees well with the two-dimensional eightfold quasi-lattice consisting of squares and 45 deg rhombi.

  10. Two-dimensional spatial frequency response of SQUID planar gradiometers

    Microsoft Academic Search

    E. Andrade Lima; A. C. Bruno; J. Szczupak

    1999-01-01

    Planar gradiometers can be modelled as two-dimensional spatial filters, taking into account area, baseline and shape of the coils. We associate a spatial frequency response with each configuration studied and show that planar gradiometers behave as band-pass spatial filters. Also, in order to determine a spatial frequency range for typical magnetic field sources, we calculate the two-dimensional Fourier transform of

  11. Two-Dimensional Signal Processing in Radon Space

    Microsoft Academic Search

    Roger Lee Easton Jr.

    1986-01-01

    This dissertation considers a method for processing two-dimensional (2-D) signals (e.g. imagery) by transformation to a coordinate space where the 2-D operation separates into orthogonal 1-D operations. After processing, the 2-D output is reconstructed by a second coordinate transformation. This approach is based on the Radon transform, which maps a two-dimensional Cartesian representation of a signal into a series of

  12. Two-Dimensional Cure Simulation of Thick Thermosetting Composites

    Microsoft Academic Search

    Travis A. Bogetti; John W. Gillespie

    1991-01-01

    An investigation into the two-dimensional cure simulation of thick thermosetting composites is presented. Temperature and degree of cure distributions within arbitrary cross-sectional geometries are predicted as a function of the autoclave temperature history. The heat conduction equation for two-dimensional, transient anisotropic heat transfer is coupled to the cure kinetics of the thermosetting composite material. A heat generation term, expressed as

  13. Ground ring of two-dimensional string theory

    Microsoft Academic Search

    Edward Witten

    1992-01-01

    String theories with two-dimensional space-time target spaces are characterized by the existence of a ``ground ring'' of operators of spin (0, 0). By understanding this ring, one can understand the symmetries of the theory and illuminate the relation of the critical string theory to matrix models. The symmetry groups that arise are, roughly, the area-preserving diffeomorphisms of a two-dimensional phase

  14. Two-dimensional QCD as a string theory

    Microsoft Academic Search

    David J. Gross

    1993-01-01

    I explore the possibility of finding an equivalent string representation of\\u000atwo dimensional QCD. I develop the large N expansion of the ${\\\\rm QCD_2}$\\u000apartition function on an arbitrary two dimensional Euclidean manifold. If this\\u000ais related to a two-dimensional string theory then many of the coefficients of\\u000athe ${1\\\\over N}$ expansion must vanish. This is shown to be true

  15. High-Speed, Multicolor Fluorescent Two-Dimensional Gene Scanning

    Microsoft Academic Search

    Sean B McGrath; Mangkey Bounpheng; Loyda Torres; Marco Calavetta; Charles B Scott; Yousin Suh; David Rines; Nathalie van Orsouw; Jan Vijg

    2001-01-01

    Two-dimensional gene scanning (TDGS) is a method for analyzing multiple DNA fragments in parallel for all possible sequence variations, using extensive multiplex PCR and two-dimensional electrophoretic separation on the basis of size and melting temperature. Highthroughput application of TDGS is limited by the prolonged time periods necessary to complete the second-dimension electrophoretic separation step–denaturing gradient gel electrophoresis–and the current need

  16. Molecular packing and symmetry of two-dimensional crystals.

    PubMed

    Plass, Katherine E; Grzesiak, Adam L; Matzger, Adam J

    2007-04-01

    Periodic arrangements on surfaces resulting from monolayer formation are critical in determining the electronic structure of thin films, the adhesion of surface coatings, the properties of lubricants, and the polymorphic form of heteronucleated crystals. Unlike substrate-directed chemisorption, the process of physisorption is highly responsive to molecular structure and stands out as a controllable method of creating variable surface patterns with periodicities on the low end of the nanoscale. Despite decades of study focused upon such ordered structures, the principles guiding the formation of these two-dimensional crystals have been obscured by the lack of a systematic and critical compilation. Thus, prediction of two-dimensional structure based upon the composition of the individual building blocks remains in its infancy. Here we demonstrate through the compilation and analysis of a database of two-dimensional structures that molecular-scale patterns are dictated by the same factors that determine bulk crystal structure, but these factors give rise to different preferred packing symmetries. In marked contrast to three-dimensional systems, achiral molecules in two-dimensional crystals are likely to adopt chiral structures, and racemic mixtures are expected to produce enantiopure domains. The determination of plane group frequencies allowed experimental verification of Kitaigorodskii's 50-year old theory of close packing as applied to two-dimensional tiling. This fundamental comparison between bulk crystals and physisorbed monolayers provides new tools and directions for future exploration in the engineering of surfaces with prescribed two-dimensional patterns. PMID:17437327

  17. Backscatter RCS for TE and TM excitations of dielectric-filled cavity-backed apertures in two-dimensional bodies

    NASA Technical Reports Server (NTRS)

    Goggans, Paul M.; Shumpert, Thomas H.

    1991-01-01

    Transverse electric (TE) and transverse magnetic (TM) scattering from dielectric-filled, cavity-backed apertures in two-dimensional bodies are treated using the method of moments technique to solve a set of combined-field integral equations for the equivalent induced electric and magnetic currents on the exterior of the scattering body and on the associated aperture. Results are presented for the backscatter radar cross section (RCS) versus the electrical size of the scatterer for two different dielectric-filled cavity-backed geometries. The first geometry is a circular cylinder of infinite length which has an infinite length slot aperture along one side. The cavity inside the cylinder is dielectric filled and is also of circular cross section. The two cylinders (external and internal) are of different radii and their respective longitudinal axes are parallel but not collocated. The second is a square cylinder of infinite length which has an infinite length slot aperture along one side. The cavity inside the square cylinder is dielectric-filled and is also of square cross section.

  18. Ring bursting behavior en route to turbulence in quasi two-dimensional Taylor-Couette flows

    E-print Network

    Altmeyer, Sebastian; Lai, Ying-Cheng

    2015-01-01

    We investigate the quasi two-dimensional Taylor-Couette system in the regime where the radius ratio is close to unity - a transitional regime between three and two dimensions. By systematically increasing the Reynolds number we observe a number of standard transitions, such as one from the classical Taylor vortex flow (TVF) to wavy vortex flow (WVF), as well as the transition to fully developed turbulence. Prior to the onset of turbulence we observe intermittent burst patterns of localized turbulent patches, confirming the experimentally observed pattern of very short wavelength bursts (VSWBs). A striking finding is that, for Reynolds number larger than the onset of VSWBs, a new type of intermittently bursting behaviors emerge: burst patterns of azimuthally closed rings of various orders. We call them ring-burst patterns, which surround the cylinder completely but remain localized and separated by non-turbulent mostly wavy structures in the axial direction. We use a number of quantitative measures, including ...

  19. Acoustic resonances in cylinder bundles oscillating in a compressibile fluid

    SciTech Connect

    Lin, W.H.; Raptis, A.C.

    1984-12-01

    This paper deals with an analytical study on acoustic resonances of elastic oscillations of a group of parallel, circular, thin cylinders in an unbounded volume of barotropic, compressible, inviscid fluid. The perturbed motion of the fluid is assumed due entirely to the flexural oscillations of the cylinders. The motion of the fluid disturbances is first formulated in a three-dimensional wave form and then casted into a two-dimensional Helmholtz equation for the harmonic motion in time and in axial space. The acoustic motion in the fluid and the elastic motion in the cylinders are solved simultaneously. Acoustic resonances were approximately determined from the secular (eigenvalue) equation by the method of successive iteration with the use of digital computers for a given set of the fluid properties and the cylinders' geometry and properties. Effects of the flexural wavenumber and the configuration of and the spacing between the cylinders on the acoustic resonances were thoroughly investigated.

  20. A portable Halbach magnet that can be opened and closed without force: The NMR-CUFF

    NASA Astrophysics Data System (ADS)

    Windt, Carel W.; Soltner, Helmut; Dusschoten, Dagmar van; Blümler, Peter

    2011-01-01

    Portable equipment for nuclear magnetic resonance (NMR) is becoming increasingly attractive for use in a variety of applications. One of the main scientific challenges in making NMR portable is the design of light-weight magnets that possess a strong and homogeneous field. Existing NMR magnets can provide such magnetic fields, but only for small samples or in small regions, or are rather heavy. Here we show a simple yet elegant concept for a Halbach-type permanent magnet ring, which can be opened and closed with minimal mechanical force. An analytical solution for an ideal Halbach magnet shows that the magnetic forces cancel if the structure is opened at an angle of 35.3° relative to its poles. A first prototype weighed only 3.1 kg, and provided a flux density of 0.57 T with a homogeneity better than 200 ppm over a spherical volume of 5 mm in diameter without shimming. The force needed to close it was found to be about 20 N. As a demonstration, intact plants were imaged and water (xylem) flow measured. Magnets of this type (NMR-CUFF = Cut-open, Uniform, Force Free) are ideal for portable use and are eminently suited to investigate small or slender objects that are part of a larger or immobile whole, such as branches on a tree, growing fruit on a plant, or non-metallic tubing in industrial installations. This new concept in permanent-magnet design enables the construction of openable, yet strong and homogeneous magnets, which aside from use in NMR or MRI could also be of interest for applications in accelerators, motors, or magnetic bearings.

  1. Two-dimensional crystallization of a bacterial surface protein on lipid vesicles under controlled conditions.

    PubMed Central

    Paul, A; Engelhardt, H; Jakubowski, U; Baumeister, W

    1992-01-01

    The solubilized surface protein of the Gram-negative bacterium Comamonas acidovorans was reconstituted on lipid vesicles by means of controlled dialysis. To this end, a multichamber dialysis apparatus was built which allows one to control the temperature and the dialysis rate, to apply various temperatures or buffer systems and sample conditions in a single experiment, and to monitor the turbidity of the sample by means of light scattering. The reconstitution conditions were optimized such that the surface protein formed two-dimensional crystals suitable for electron crystallography. The recrystallized surface protein arrays gave a resolution of approximately 1.3 nm in projection after correlation averaging of negatively stained preparations. The surface protein assembled into partially self-contained two-dimensional crystals which possess a strong shape-determining effect and formed cylinders and various cone-shaped vesicles. The development of the various vesicle forms is described in a model. Images FIGURE 2 FIGURE 4 FIGURE 5 FIGURE 6 FIGURE 7 FIGURE 9 FIGURE 10 PMID:1540688

  2. ORMDIN: a finite element program for two-dimensional nonlinear inverse heat conduction analysis

    SciTech Connect

    Bass, B.R.; Drake, J.B.; Ott, L.J.

    1980-12-01

    The calculation of the surface temperature and surface heat flux from measured temperature transients at one or more interior points of a body is identified in the literature as the inverse heat conduction problem. Heretofore, analytical and computational methods of treating this problem have been limited to one-dimensional nonlinear or two-dimensional linear material models. This report presents, to the authors' knowledge, the first inverse solution technique applicable to the two-dimensional nonlinear model with temperature-dependent thermophysical properties. This technique, representing an extension of the one-dimensional formulation previously developed by one of the authors, utilizes a finite element heat conduction model and a generalization of Beck's one-dimensional nonlinear estimation procedure. A digital computer program ORMDIN (Oak Ridge Multi-Dimensional INverse) is developed from the formulation and applied to the cross section of a composite cylinder with temperature-dependent material properties. Results are presented to demonstrate that the inverse formulation is capable of successfully treating experimental data. An important feature of the method is that small time steps are permitted while avoiding severe oscillations or numerical instabilities due to experimental errors in measured data.

  3. An ‘ideal’ form of decaying two-dimensional turbulence

    NASA Astrophysics Data System (ADS)

    Iwayama, Takahiro; Shepherd, Theodore G.; Watanabe, Takeshi

    2002-04-01

    In decaying two-dimensional Navier Stokes turbulence, Batchelor's similarity hypothesis fails due to the existence of coherent vortices. However, it is shown that decaying two-dimensional turbulence governed by the Charney Hasegawa Mima (CHM) equation([partial partial differential]/[partial partial differential]t)([nabla del, Hamilton operator]2[curly or open phi][minus sign][lambda]2[curly or open phi]) +J([curly or open phi], [nabla del, Hamilton operator]2[curly or open phi]) = D,where D is a damping, is described well by Batchelor's similarity hypothesis for wave numbers k [double less-than sign] [lambda] (the so-called AM regime). It is argued that CHM turbulence in the AM regime is a more ‘ideal’ form of two-dimensional turbulence than is Navier Stokes turbulence itself.

  4. 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.

  5. Coherently-controlled two-dimensional photon echo electronic spectroscopy.

    PubMed

    Prokhorenko, Valentyn I; Halpin, Alexei; Miller, R J D

    2009-06-01

    Optical two-dimensional photon-echo spectroscopy is realized with shaped excitation pulses, allowing coherent control of twodimensional spectra. This development enables probing of state-selective quantum decoherence and phase/time sensitive couplings between states. The coherently-controlled two-dimensional photon-echo spectrometer with two pulse shapers is based on a passively stabilized four-beam interferometer with diffractive optic, and allows heterodyne detection of signals with a long-term phase stability of approximately Lambda/100. The two-dimensional spectra of Rhodamine 101 in a methanol solution, measured with unshaped and shaped pulses, exhibit significant differences. We observe in particular, the appearance of fine structure in the spectra obtained using shaped excitation pulses. PMID:19506626

  6. A two-dimensional spin liquid in quantum kagome ice.

    PubMed

    Carrasquilla, Juan; Hao, Zhihao; Melko, Roger G

    2015-01-01

    Actively sought since the turn of the century, two-dimensional quantum spin liquids (QSLs) are exotic phases of matter where magnetic moments remain disordered even at zero temperature. Despite ongoing searches, QSLs remain elusive, due to a lack of concrete knowledge of the microscopic mechanisms that inhibit magnetic order in materials. Here we study a model for a broad class of frustrated magnetic rare-earth pyrochlore materials called quantum spin ices. When subject to an external magnetic field along the [111] crystallographic direction, the resulting interactions contain a mix of geometric frustration and quantum fluctuations in decoupled two-dimensional kagome planes. Using quantum Monte Carlo simulations, we identify a set of interactions sufficient to promote a groundstate with no magnetic long-range order, and a gap to excitations, consistent with a Z2 spin liquid phase. This suggests an experimental procedure to search for two-dimensional QSLs within a class of pyrochlore quantum spin ice materials. PMID:26096331

  7. Spatial evolution of a quasi-two-dimensional Kármán vortex street subjected to a strong uniform magnetic field

    NASA Astrophysics Data System (ADS)

    Hamid, Ahmad H. A.; Hussam, Wisam K.; Pothérat, Alban; Sheard, Gregory J.

    2015-05-01

    A vortex decay model for predicting spatial evolution of peak vorticity in a wake behind a cylinder is presented. For wake vortices in the stable region behind the formation region, results have shown that the presented model has a good capability of predicting spatial evolution of peak vorticity within an advecting vortex across 0.1 ? ? ? 0.4, 500 ? H ? 5000, and 1500 ? ReL ? 8250. The model is also generalized to predict the decay behaviour of wake vortices in a class of quasi-two-dimensional magnetohydrodynamic duct flows. Comparison with published data demonstrates remarkable consistency.

  8. Application of the Analogy Between Water Flow with a Free Surface and Two-dimensional Compressible Gas Flow

    NASA Technical Reports Server (NTRS)

    Orlin, W James; Lindner, Norman J; Bitterly, Jack G

    1947-01-01

    The theory of hydraulic analogy, that is, the analogy between water flow with a free surface and two-dimensional compressible gas flow and the limitations and conditions of the analogy are discussed. A test run was made using the hydraulic analogy as applied to the flow about circular cylinders at various diameters at subsonic velocities extending to the super critical range. The apparatus and techniques used in this application are described and criticized. Reasonably satisfactory agreement of pressure distributions and flow fields existed between water and airflow about corresponding bodies. This agreement indicated the possibility of extending experimental compressibility research by new methods.

  9. Two-Dimensional Diffusion of Colloidal Particles in Polymer Solutions

    NASA Astrophysics Data System (ADS)

    Pilaski, Dana; Chao, Ginger; Lee, Tai-Chou; Vo, Trinh; Robert, Marc

    2001-03-01

    We study the two-dimensional diffusion of spherical polystyrene colloidal particles in poly(ethyleneoxide) (PEO)and Lambda DNA solutions. The diameter of the colloidal particles range from 1 to 2.5 micrometers, PEO and Lambda DNA have gyration radii of 0.139 to 0.372 and 0.5 micrometers respectively. Lambda DNA offers the advantage over other polymers to be monodispersed. Two-dimensional cells are prepared for different colloid sizes and polymer concentrations. The trajectories of the colloidal particles are obtained in real time by using video microscopy and image analysis. The diffusivity is determined as a function of polymer concentrations.

  10. Two dimensional hydrodynamic and evolution sequences of rotating stars

    SciTech Connect

    Deupree, R. G. (Robert G.); Guzik, J. A. (Joyce Ann); Neuforge, C. M. (Corinne M.)

    2001-01-01

    Two dimensional hydrodynamic simulations were calculated for ZAMS models with Z=0.02, and masses of 3,5, 8,12, and 20 Ma. For each mass five models were calculated - one nonrotating and four with progressively higher rotation rates. The rotating models were categorized by the ratio of the polar to the equatorial radius, with values of 0.985, 0.92, 0.84, and 0.72. The simulations were performed with the fully two dimensional implicit code ROTORC (actually what is known as 2.5 dimensions, with azimuthal symmetry, but with a conservation law for the rotational velocity in the azimuthal direction.)

  11. Bulk-edge correspondence for two-dimensional topological insulators

    E-print Network

    G. M. Graf; M. Porta

    2013-03-19

    Topological insulators can be characterized alternatively in terms of bulk or edge properties. We prove the equivalence between the two descriptions for two-dimensional solids in the single-particle picture. We give a new formulation of the $\\mathbb{Z}_{2}$-invariant, which allows for a bulk index not relying on a (two-dimensional) Brillouin zone. When available though, that index is shown to agree with known formulations. The method also applies to integer quantum Hall systems. We discuss a further variant of the correspondence, based on scattering theory.

  12. Planar Visibility Graph Network Algorithm For Two Dimensional Timeseries

    E-print Network

    Jie Liu; Qingqing Li

    2014-11-24

    In this brief paper, a simple and fast computational method, the Planar Visibility Graph Networks Algorithm was proposed based on the famous Visibility Graph Algorithm, which can fulfill converting two dimensional timeseries into a planar graph. The constructed planar graph inherits several properties of the series in its structure. Thereby, periodic series, random series, and chaotic series convert into quite different networks with different average degree, characteristic path length, diameter, clustering coefficient, different degree distribution, and modularity, etc. By means of this new approach, with such different networks measures, one can characterize two dimensional timeseries from a new viewpoint of complex networks.

  13. Simulation of two-dimensional infrared spectroscopy of amyloid fibrils

    PubMed Central

    Zhuang, Wei; Abramavicius, Darius; Voronine, Dimitrii V.; Mukamel, Shaul

    2007-01-01

    We propose to use infrared coherent two-dimensional correlation spectroscopy (2DCS) to characterize the fibril structure of Ab42, the dominant composition of Ab deposit, which is crucial for investigating its toxicity and aggregation mechanism. By optimizing the pulse polarization configurations with a genetic algorithm combined with sensitivity analysis, we obtained signals with well resolved cross-peak features attributed to the couplings within and between different structural motifs. These signals may provide new constraints for refining of the currently available NMR structure. Two-dimensional correlation spectroscopy also can differentiate the turn structure of Ab42 and other Ab derivatives. PMID:17675411

  14. Pick's Theorem in Two-Dimensional Subspace of ?3

    PubMed Central

    2015-01-01

    In the Euclidean space ?3, denote the set of all points with integer coordinate by ?3. For any two-dimensional simple lattice polygon P, we establish the following analogy version of Pick's Theorem, k(I(P) + (1/2)B(P) ? 1), where B(P) is the number of lattice points on the boundary of P in ?3, I(P) is the number of lattice points in the interior of P in ?3, and k is a constant only related to the two-dimensional subspace including P. PMID:25802889

  15. Two-dimensional photonic crystal color filter development.

    PubMed

    Cho, Eun-Hyoung; Kim, Hae-Sung; Cheong, Byoung-Ho; Prudnikov, Oleg; Xianyua, Wenxu; Sohn, Jin-Seung; Ma, Dong-Joon; Choi, Hwan-Young; Park, No-Cheol; Park, Young-Pil

    2009-05-11

    Reflective color filters using two-dimensional photonic crystals based on sub-wavelength gratings were proposed and constructed. Using low-cost nanoimprint lithography, an amorphous silicon layer was deposited through the low-temperature PECVD process and patterned into two-dimensional structures. The isolated amorphous silicon patterns were readily crystallized using a multi-shot excimer laser annealing at low energy. A study of the close relationship between color filter reflectance and silicon pattern crystallinity is introduced. Theoretical and experimental results show that the proposed color filters have high reflectance and, moreover, decrease the dependence on incident angle compared to one-dimensional photonic crystal color filters. PMID:19434195

  16. Smoothed Two-Dimensional Edges for Laminar Flow

    NASA Technical Reports Server (NTRS)

    Holmes, B. J.; Liu, C. H.; Martin, G. L.; Domack, C. S.; Obara, C. J.; Hassan, A.; Gunzburger, M. D.; Nicolaides, R. A.

    1986-01-01

    New concept allows passive method for installing flaps, slats, iceprotection equipment, and other leading-edge devices on natural-laminar-flow (NLF) wings without causing loss of laminar flow. Two-dimensional roughness elements in laminar boundary layers strategically shaped to increase critical (allowable) height of roughness. Facilitates installation of leading-edge devices by practical manufacturing methods.

  17. Inversion of the two dimensional Radon transformation by diagonalisation

    E-print Network

    Knill, Oliver

    diagonalisation of Abel's integral operator, we give an inversion of the plane Radon transformation R(f)(p, ) = {x the spectrum and the kernel of ~R. Keywords Computerized Tomography, Abel and Radon transformation, InverseInversion of the two dimensional Radon transformation by diagonalisation Oliver Knill Department

  18. Hall effect in the two-dimensional Luttinger liquid

    Microsoft Academic Search

    P. Anderson

    1991-01-01

    The temperature dependence of the Hall effect in the normal state is a commom theme of all the cuprate superconductors and has been one of the more puzzling observations on these puzzling materials. We describe a general scheme within the Luttinger liquid theory of these two-dimensional quantum fluids which corrrelates the anomalous Hall and resistivity observations on a wide variety

  19. Two-dimensional model for circulating fluidized-bed reactors

    Microsoft Academic Search

    H. Schoenfelder; M. Kruse; J. Werther

    1996-01-01

    Circulating fluidized bed reactors are widely used for the combustion of coal in power stations as well as for the cracking of heavy oil in the petroleum industry. A two-dimensional reactor model for circulating fluidized beds (CFB) was studied based on the assumption that at every location within the riser, a descending dense phase and a rising lean phase coexist.

  20. Two dimensional computational fluid dynamic models for waste stabilisation ponds

    Microsoft Academic Search

    M. G Wood; T Howes; J Keller; M. R Johns

    1998-01-01

    Traditional waste stabilisation pond (WSP) models encounter problems predicting pond performance because they cannot account for the influence of pond features, such as inlet structure or pond geometry, on fluid hydrodynamics. In this study, two dimensional (2-D) computational fluid dynamics (CFD) models were compared to experimental residence time distributions (RTD) from literature. In one of the three geometries simulated, the

  1. Collisions between type II two-dimensional quadratic solitons.

    PubMed

    Costantini, B; De Angelis, C; Barthelemy, A; Bourliaguet, B; Kermene, V

    1998-03-15

    We report experimental and numerical results that describe collisions between two-dimensional type II quadratic solitons excited in a KTP crystal by fundamental waves of orthogonal polarization. Our results provide experimental evidence of the possibility of both inelastic collision (when two quadratic solitons merge at input into a single soliton at output) and quasi-elastic collision. PMID:18084532

  2. Are flows electromagnetically forced in thin stratified layers two dimensional?

    Microsoft Academic Search

    J. Paret; D. Marteau; O. Paireau; P. Tabeling

    1997-01-01

    The relaxation of three-dimensional perturbations in flows generated in thin density stratified layers is discussed. It is found that the relaxation time for such perturbations is small compared to the other characteristic times of the system. These results offer a basis to assess the two dimensionality of freely decaying turbulence prepared in such configurations.

  3. Optimal entropic uncertainty relation in two-dimensional Hilbert space

    NASA Astrophysics Data System (ADS)

    Sánches-Ruiz, Jorge

    1998-07-01

    The exact lower bound on the sum of the information entropies is obtained for arbitrary pairs of observables in two-dimensional Hilbert space. The result coincides with that given by Garrett and Gull for the particular case of real transformation matrices and state vectors. A weaker analytical bound is also obtained.

  4. FLOW AND DISPERSION OF POLLUTANTS WITHIN TWO-DIMENSIONAL VALLEYS

    EPA Science Inventory

    Wind-tunnel experiments and a theoretical model concerning the flow structure and pollutant diffusion over two-dimensional valleys of varying aspect ratio are described and compared. hree model valleys were used, having small, medium, and steep slopes. Measurements of mean and tu...

  5. A Family of Two-Dimensional Nonseparable Malvar Wavelets

    Microsoft Academic Search

    Xiang-Gen Xia; Bruce W. Suter

    1995-01-01

    Malvar wavelets or lapped orthogonal transform (LOT) has been recognized as a useful tool in eliminating blocking effects in transform coding. Recently, it has been also extended to more general forms, which enable one to construct an orthonormal basis from arbitrary local orthonormal bases on different intervals. In this paper, we study two-dimensional cases and construct nonseparable Malvar wavelets, which

  6. Wall slip and hydrodynamics of two-dimensional journal bearing

    Microsoft Academic Search

    G. J. Ma; C. W. Wu; P. Zhou

    2007-01-01

    In the present paper, based on the limiting shear stress model, a multi-linearity finite element algorithm and quadratic programming technique are used to study the influence of wall slip on the hydrodynamic lubrication performance of a two-dimensional journal bearing (finite length journal bearing). It is found that if the lubricated surfaces are designed as homogeneous slip surfaces, the hydrodynamic force

  7. Imaging magnetic focusing in a two-dimensional electron gas

    Microsoft Academic Search

    Katherine E. Aidala

    2006-01-01

    The most direct way to understand how electrons move through semiconductor heterostructures is to spatially image their motion. The two-dimensional electron gas has proved its interest for both device applications and studies of fundamental physics, and offers many more opportunities as we better understand these systems. We wished to examine electron motion in magnetic fields, both to study fundamental physics

  8. 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.

  9. Predicting gas adsorption using two-dimensional equations of state

    Microsoft Academic Search

    Chunhe Zhou; Freddie Hall; Khaled A. M. Gasem; Robert L. Jr. Robinson

    1994-01-01

    Accurate description of gas adsorption on solids is gaining in importance as the number of engineering applications expands. In the present work, a general two-dimensional equation of state (2-D EOS) is presented and the fugacity equations are derived to describe the adsorbed phase for adsorption from gas mixtures. Model constants in the 2-D EOS are determined from pure adsorption equilibria

  10. Higgs algebraic symmetry in the two-dimensional Dirac equation

    E-print Network

    Fu-Lin Zhang; Bo Fu; Jing-Ling Chen

    2009-11-17

    The dynamical symmetry algebra of the two-dimensional Dirac Hamiltonian with equal scalar and vector Smorodinsky-Winternitz potentials is constructed. It is the Higgs algebra, a cubic polynomial generalization of SU(2). With the help of the Casimir operators, the energy levels are derived algebraically.

  11. ISAR imaging based on two-dimensional GTD scattering model

    Microsoft Academic Search

    Anastasios V. Karakasiliotis; Anton D. Lazarov; Panayiotis V. Frangos

    2008-01-01

    In this paper, we briefly outline two scattering models, which can describe the inverse synthetic aperture radar (ISAR) return signal. The first one is a point scatterer model, whereas the second one is based on the geometrical theory of diffraction (GTD). The stepped frequency (SF) modulation case is treated for a two-dimensional ISAR geometry. Well-known ISAR imaging algorithms are applied

  12. Quantum of optical absorption in two-dimensional semiconductors

    E-print Network

    California at Irvine, University of

    Quantum of optical absorption in two-dimensional semiconductors Hui Fanga,b,c , Hans A. Bechteld semiconductor, where is the fine structure con- stant and nc is an optical local field correction factor. The optical properties of heterostructure quantum wells (QWs) have been extensively studied since the 1970s

  13. Two-dimensional black holes in accelerated frames: quantum aspects

    E-print Network

    R. Balbinot; A. Fabbri

    1996-07-04

    By considering charged black hole solutions of a one parameter family of two dimensional dilaton gravity theories, one finds the existence of quantum mechanically stable gravitational kinks with a simple mass to charge relation. Unlike their Einsteinian counterpart (i.e. extreme Reissner-Nordstr\\"om), these have nonvanishing horizon surface gravity.

  14. Shock-Fitted Numerical Solutions for Two-Dimensional Detonations

    E-print Network

    Shock-Fitted Numerical Solutions for Two-Dimensional Detonations with Periodic Boundary Conditions Combustion Granada, Spain Los Alamos National Laboratory University of Notre Dame April 23, 2006 Shock Motivation & Background General Formulation Shock-Fitted Transformation Numerical Method 1-D Limiting Case

  15. Numerical simulation of two?dimensional tsunami runup

    Microsoft Academic Search

    Z. Kowalik; T. S. Murty

    1993-01-01

    The hydrodynamic and mathematical problems connected with discontinuity between wet and dry domains, nonlinearity, friction, and computational instability are the main problems that have to be sorted out in the runup computation. A variety of runup models are analyzed, including the boundary conditions used to move the shoreline. Based on the initial experiments one?dimensional and two?dimensional algorithms are constructed. These

  16. Bound states of two-dimensional Schrödinger-Newton equations

    E-print Network

    Joachim Stubbe

    2008-07-25

    We prove an existence and uniqueness result for ground states and for purely angular excitations of two-dimensional Schr\\"{o}dinger-Newton equations. From the minimization problem for ground states we obtain a sharp version of a logarithmic Hardy-Littlewood-Sobolev type inequality.

  17. Intensity coding in two-dimensional excitable neural networks

    Microsoft Academic Search

    Mauro Copelli; Osame Kinouchi

    2005-01-01

    In the light of recent experimental findings that gap junctions are essential for low level intensity detection in the sensory periphery, the Greenberg–Hastings cellular automaton is employed to model the response of a two-dimensional sensory network to external stimuli. We show that excitable elements (sensory neurons) that have a small dynamical range are shown to give rise to a collective

  18. Hexagonal structures for two-dimensional photonic crystals

    Microsoft Academic Search

    D. Cassagne; C. Jouanin; D. Bertho

    1996-01-01

    Periodic dielectric structures have been recently proposed to inhibit spontaneous emission in semiconductors. From this suggestion, the new concepts of photonic band gap and photonic crystal have been developed. Zero-threshold lasers, waveguides, antenna substrates, filters and polarizers are promising applications. We propose a new class of two-dimensional periodic dielectric structures with hexagonal symmetry. We study the gap opening according to

  19. Torsional springs for two-dimensional dynamic unstructured fluid meshes

    Microsoft Academic Search

    C. Farhat; C. Degand; B. Koobus; M. Lesmoinne

    1998-01-01

    Dynamic fluid grids are commonly used for the solution of flow problems with moving boundaries. They are often represented by a network of fictitious lineal springs that can become unreliable when the fluid mesh undergoes large displacements and\\/or deformations. In this paper, we propose to control the arbitrary motion of two-dimensional dynamic unstructured fluid grids with additional torsional springs. We

  20. Describing two-dimensional vortical flows the typhoon case

    E-print Network

    Spineanu, F

    2005-01-01

    We present results of a numerical study of the differential equation governing the stationary states of the two-dimensional planetary atmosphere and magnetized plasma (within the Charney Hasegawa Mima model). The most strinking result is that the equation appears to be able to reproduce the main features of the flow structure of a typhoon.

  1. Two-dimensional potential theory for translating and rotating solids

    NASA Astrophysics Data System (ADS)

    Minotti, F. O.

    2003-11-01

    Two-dimensional inviscid theory is adapted to evaluate easily the flow, hydrodynamic force and moment of the force on a solid that translates and rotates with rather arbitrary imposed velocities. As an example a moving thin Kutta-Joukowski airfoil is considered.

  2. Phase Diagram of a Two-Dimensional Dilute Binary Alloy

    Microsoft Academic Search

    G. K. Khalil; K. Yaldram; A. Sadiq

    1997-01-01

    Phase diagrams of two-dimensional binary alloy with vacancies (ABV) is studied with pairwise interaction ?AA, ?BB, and ?AB between the nearest neighbors. Attention is focussed on the case where the vacancies are annealed and ?BA = ?, ?AA= ?BB=0. For vacancy concentrations cv<0.2, the critical temperature decreases linearly with cv. The vacancies remain randomly distributed within the A and B

  3. Two-Dimensional Sensor Integration Using Resonant Proximity Connector

    E-print Network

    Shinoda, Hiroyuki

    Two-Dimensional Sensor Integration Using Resonant Proximity Connector -Basic Technology propose "Resonant Proximity Connector (RPC)" that enables non-contact (proximity) connection of the sensor without individual wires. In this paper, we propose "Resonant Proximity Connector (RPC)" that enables non

  4. Giant Optical Activity in Quasi-Two-Dimensional Planar Nanostructures

    Microsoft Academic Search

    Makoto Kuwata-Gonokami; Nobuyoshi Saito; Yusuke Ino; Martti Kauranen; Konstantins Jefimovs; Tuomas Vallius; Jari Turunen; Yuri Svirko

    2005-01-01

    We examine the spectral dependence in the visible frequency range of the polarization rotation of two-dimensional gratings consisting of chiral gold nanostructures with subwavelength features. The gratings, which do not diffract, are shown to exhibit giant specific rotation (˜104°\\/mm) of polarization in direct transmission at normal incidence. The rotation is the same for light incident on the front and back

  5. High Resolution Two-Dimensional Electrophoresis of Human Plasma Proteins

    Microsoft Academic Search

    Leigh Anderson; Norman G. Anderson

    1977-01-01

    The two-dimensional electrophoretic technique of O'Farrell has been adapted to the analysis of human plasma proteins, and 30 polypeptides have been identified in the pattern produced. Genetic variants involving charge (isoelectric point) or size (molecular weight in the presence of sodium dodecyl sulfate) changes should be routinely detectable in at least 20 proteins at once, facilitating studies of human mutation

  6. Accepted Manuscript Two-dimensional Electronic Spectroscopy and Photosynthesis: Fundamentals

    E-print Network

    Fleming, Graham R.

    and Applications to Photosynthetic Light-Harvesting Gabriela S. Schlau-Cohen, Akihito Ishizaki, Graham R. Fleming-Harv esting Gabriela S. Schlau-Cohen, Akihito Ishizaki, and Graham R. Fleming Department of Chemistry Please cite this article as: G.S. Schlau-Cohen, A. Ishizaki, G.R. Fleming, Two-dimensional Electronic

  7. Reflection optical two-dimensional Fourier-transform spectroscopy.

    PubMed

    Li, Hebin; Moody, Galan; Cundiff, Steven T

    2013-01-28

    We have developed a technique to perform optical two-dimensional Fourier-transform (2DFT) spectroscopy in a reflection geometry. Various reflection 2DFT spectra are obtained for an atomic vapor. The technique is useful for the cases where optical 2DFT spectroscopy cannot be performed in the transmission geometry. PMID:23389154

  8. Charged black holes in two-dimensional string theory

    Microsoft Academic Search

    Michael D. McGuigan; Chiara R. Nappi; Scott A. Yost

    1991-01-01

    We discuss two dimensional string theories containing gauge elds, introduced either via coupling to open strings, in which case we get a Born-Infeld type action, or via heterotic compactication. The solutions of the modied background eld equations are charged black holes which exhibit interesting space time geometries. We also compute their masses and charges.

  9. SAR Processing Based On Two-Dimensional Transfer Function

    NASA Technical Reports Server (NTRS)

    Chang, Chi-Yung; Jin, Michael Y.; Curlander, John C.

    1994-01-01

    Exact transfer function, ETF, is two-dimensional transfer function that constitutes basis of improved frequency-domain-convolution algorithm for processing synthetic-aperture-radar, SAR data. ETF incorporates terms that account for Doppler effect of motion of radar relative to scanned ground area and for antenna squint angle. Algorithm based on ETF outperforms others.

  10. 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.

  11. Intersections of valuation overrings of two-dimensional Noetherian domains

    E-print Network

    Olberding, Bruce

    Intersections of valuation overrings of two-dimensional Noetherian domains Bruce Olberding Abstract, where such overrings are viewed as intersections of valuation overrings. Of particular interest are the cases where the domain can be represented uniquely by an irredundant intersection of valuation rings

  12. Turbulent mixing in a two-dimensional jet

    Microsoft Academic Search

    M. S. Uberoi; Param Indar Singh

    1975-01-01

    An ensemble of instantaneous temperature profiles across a two-dimensional heated jet was obtained by shooting a fine platinum resistance thermometer across the jet at speeds much higher than the local velocity of the jet. Each recording of the ensemble was shifted to have a common center, and ensemble averages were obtained counting only the profiles for which the spatial location

  13. On the two-dimensional sloshing problem By Vladimir Kozlova

    E-print Network

    Motygin, Oleg V.

    On the two-dimensional sloshing problem By Vladimir Kozlova , Nikolay Kuznetsovb , Oleg Motyginb to sloshing fre- quencies that describe free oscillations of an inviscid, incompressible, heavy fluid. For this purpose, a new variational principle is proposed for an equivalent statement of the sloshing problem

  14. Morphometric investigations in mitral stenosis using two dimensional echocardiography

    Microsoft Academic Search

    P Schweizer; P Bardos; W Krebs; R Erbel; C Minale; S Imm; B J Messmer; S Effert

    1982-01-01

    A method is proposed for comparing the orifice size and the morphology of stenotic mitral valves, removed intact at the time of replacement, with the preoperative two dimensional echocardiographic cross-sections. The excised mitral valve apparatus is suspended on a specially constructed mounting. To avoid shrinkage the orifice is stabilised with an airfilled balloon. A radiography is taken directing the x-ray

  15. Two-Dimensional Diverging Shocks in a Nonuniform Medium

    SciTech Connect

    Roy A. Axford

    1998-08-01

    An analytic solution is derived from the time evolution of a two- dimensional diverging shock in r - z geometry. The shock propagates through a condensed medium characterized by a Mie-Gruneisen equation of state with a nonzero density gradient in the axial direction.

  16. Preliminary Two Dimensional Haptic Thresholds and Task Performance Enhancements

    E-print Network

    at a 71% accu- racy level using a converging adaptive threshold algorithm. The average haptic threshold an adaptive threshold algorithm to measure the lowest de- tectable forces rendered in the horizontal planePreliminary Two Dimensional Haptic Thresholds and Task Performance Enhancements Gregory S. Lee

  17. Robotic deburring of two dimensional parts with unknown geometry

    Microsoft Academic Search

    H. Kazerooni; M. G. Her

    1988-01-01

    Two of the problems in robotic deburring are addressed: tracking the planar two-dimensional part contour and control of the metal removal process. The tracking mechanism is a roller bearing mounted on a force sensor at the robot endpoint. The tracking controller utilizes the force measured by this force sensor to find the normal vector to the part surface. Using the

  18. Separating chemistry and transport effects in two-dimensional models

    E-print Network

    Jackman, Charles H.

    Separating chemistry and transport effects in two-dimensional models Debra K. Weisenstein, Janusz; accepted 21 June 2004; published 29 September 2004. [1] Representation of transport in numerical models is known to be a major uncertainty in modeling of the atmosphere. Models also differ in their treatment

  19. Kubo conductivity of a strongly magnetized two-dimensional plasma.

    NASA Technical Reports Server (NTRS)

    Montgomery, D.; Tappert, F.

    1971-01-01

    The Kubo formula is used to evaluate the bulk electrical conductivity of a two-dimensional guiding-center plasma in a strong dc magnetic field. The particles interact only electrostatically. An ?anomalous' electrical conductivity is derived for this system, which parallels a recent result of Taylor and McNamara for the coefficient of spatial diffusion.

  20. On the stability of two-dimensional digital filters

    Microsoft Academic Search

    G. Maria; M. Fahmy

    1973-01-01

    This correspondence proposes a method to check the stability of two-dimensional recursive filters. In this method the Jury table is modified and used to check the first condition of Huang's theorem. Some examples are solved to illustrate the method.

  1. Two-dimensional optimization of free electron laser designs

    DOEpatents

    Prosnitz, Donald (Walnut Creek, CA); Haas, Roger A. (Pleasanton, CA)

    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.

  2. 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.

  3. WKB treatment of a simple two-dimensional fission model

    SciTech Connect

    Brink, D.M.; Klarsfeld, S.

    1985-11-01

    We reexamine a simple two-dimensional fission model and show that in the sudden limit the standard Wentzel-Kramers-Brillouin approximation gives results of practically the same accuracy as those obtained earlier by more elaborate semiclassical methods using complex paths.

  4. Two-dimensional absolute photonic band gaps in the visible

    Microsoft Academic Search

    A. Barra; D. Cassagne; C. Jouanin

    1999-01-01

    The most promising two-dimensional photonic crystals are the graphite lattice of dielectric rods in air background and the triangular lattice of air holes in dielectric background. In this paper, we compare their convenience in achieving structures which inhibit the propagation of visible electromagnetic waves. For visible waves, etching is difficult because the structure period must be smaller than the light

  5. Self Organization of Two-dimensional Insect Neural Networks

    E-print Network

    Jacob, Eshel Ben

    Self Organization of Two-dimensional Insect Neural Networks Amir Ayalia , Orit Shefia> and Eshel and neural networks in particular have crossed traditional fields and disciplines of science, from computer science through physics to biology (for recent review, see [17] and references within). The neural network

  6. Two Dimensional Optimal Mechanism Design for a Sequencing Problem

    E-print Network

    Al Hanbali, Ahmad

    an optimal mechanism, that is, a scheduling rule and incentive compatible payments that minimize the totalTwo Dimensional Optimal Mechanism Design for a Sequencing Problem Ruben Hoeksma and Marc Uetz.p.hoeksma, m.uetz}@utwente.nl Abstract. We consider optimal mechanism design for a sequencing prob- lem with n

  7. Two-dimensional sensitivity analysis of MIPAS observations.

    PubMed

    Carlotti, M; Magnani, L

    2009-03-30

    In this paper we propose a new approach to operate two-dimensional sensitivity studies on the observations of MIPAS, an experiment on board the ENVISAT satellite. The proposed analysis system is intended to evaluate the amount and the spatial distribution of the information that is carried by MIPAS observations with respect to the target atmospheric parameters. The new approach enables the definition and assessment of the target-dependent atmospheric sampling of the measurements. The amount of information is evaluated by merging MIPAS measurements, relative to different limb-scans, in a two-dimensional analysis that models the sensitivity of the spectral signals combined with the geometrical redundancy introduced by different observation geometries. The spatial distribution of the information that is obtained with our analysis highlights the advantage of using a two-dimensional retrieval system. Furthermore, within the two-dimensional context, this analysis provides crucial indications for the definition of the optimal retrieval grid and, therefore, for the best exploitation of existing measurements. The proposed analysis is also suited for the design of optimized observation strategies. The sensitivity analysis, applied in this paper to MIPAS observations, can be extended to other orbiting limb sounders that, like MIPAS, continuously measure the atmospheric emission along the orbit track. PMID:19333299

  8. Two-dimensional stress wave analysis in incompressible elastic solids

    Microsoft Academic Search

    Tang Zhi-jing; T. C. T. Ting; Li Yong-chi

    1989-01-01

    Two-dimensional stress waves in a general incompressible elastic solid are investigated. First, basic equations for simple waves and shock waves are presented for a general strain energy function. Then the characteristic wave speeds and the associated characteristic vectors are deduced. It is shown that there usually exist two simple waves and two shock waves. Finally, two examples are given for

  9. Is Morton layout competitive for large two-dimensional arrays?

    E-print Network

    Kelly, Paul H. J.

    Is Morton layout competitive for large two-dimensional arrays? Jeyarajan Thiyagalingam and Paul H J Kelly Department of Computing, Imperial College 180 Queen's Gate, London SW7 2BZ, U.K. fjeyan,phjkg@doc.ic's storage layout in order to maximise spatial locality. Unsophis- ticated programmers do not

  10. Anomalous Hall effect in a two-dimensional electron gas 

    E-print Network

    Nunner, Tamara S.; Sinitsyn, N. A.; Borunda, Mario F.; Dugaev, V. K.; Kovalev, A. A.; Abanov, Artem; Timm, Carsten; Jungwirth, T.; Inoue, Jun-ichiro; MacDonald, A. H.; Sinova, Jairo.

    2007-01-01

    The anomalous Hall effect in a magnetic two-dimensional electron gas with Rashba spin-orbit coupling is studied within the Kubo-Streda formalism in the presence of pointlike potential impurities. We find that all contributions to the anomalous Hall...

  11. Two-Dimensional Range Diameter Queries Pooya Davoodi1

    E-print Network

    Smid, Michiel

    Two-Dimensional Range Diameter Queries Pooya Davoodi1 , Michiel Smid2 , and Freek van Walderveen1 1 MADALGO , Department of Computer Science, Aarhus University, Denmark. 2 School of Computer Science, Carleton University, Ottawa, Canada. Abstract. Given a set of n points in the plane, range diameter queries

  12. A two-dimensional global study of tropospheric ozone production

    Microsoft Academic Search

    Asbjørn Strand; Ø. Hov

    1994-01-01

    The ozone production in the troposphere has been studied by means of a zonally averaged model which consists of a two-dimensional transport model, a description of the emissions, wet and dry deposition, and chemical processes of importance for the ozone production in the troposphere. The transport model describes a closed circulation in the meridional plane below 10 hPa and has

  13. Automated design of two-dimensional rational decimation systems

    Microsoft Academic Search

    Brian L. Evans; Jurgen Teich; Christian Schwarz

    1994-01-01

    The paper gives an automated procedure to design rational decimation compression systems that resample two-dimensional bandpass signals at their Nyquist rates. Our procedure takes a sketch of the desired bandpass shape in the frequency domain, circumscribes it with a parallelogram of minimal area, and linearly maps the minimal enclosing parallelogram onto one period of the frequency domain. From the rational

  14. TWO DIMENSIONAL IMMERSED BOUNDARY SIMULATIONS OF SWIMMING JELLYFISH

    E-print Network

    Stockie, John

    TWO DIMENSIONAL IMMERSED BOUNDARY SIMULATIONS OF SWIMMING JELLYFISH by Haowen Fang B.Eng., Nanjing Simulations Of Swim- ming Jellyfish Examining Committee: Dr. Weiran Sun, Assistant Professor Chair Dr. John iii #12;Abstract The swimming behavior of jellyfish, driven by the periodic contraction of body

  15. Two-dimensional phononic crystals: Examples and applications

    NASA Astrophysics Data System (ADS)

    Pennec, Yan; Vasseur, Jérôme O.; Djafari-Rouhani, Bahram; Dobrzy?ski, Leonard; Deymier, Pierre A.

    2010-08-01

    Phononic crystals are composite materials made of periodic distributions of inclusions embedded in a matrix. Due to their periodic structure, these materials may exhibit under certain conditions, absolute acoustic band gaps i.e. forbidden bands that are independent of the direction of propagation of the incident elastic wave. In the first part of this review paper, we present some examples of two-dimensional bulk phononic crystals i.e. two-dimensional arrays of inclusions assumed of infinite extent along the three spatial directions. We show that the bandwidth of the forbidden band depends strongly on the nature of the constituent materials (solid or fluid), as well as the contrast between the physical characteristics (density and elastic moduli) of the inclusions and of the matrix, the geometry of the array of inclusions, the inclusion shape and the filling factor of inclusions. The second part of this review paper is devoted to some possible applications of these composite materials. In particular, we show that defect modes (cavities, waveguides, stubs, etc.) inserted inside the two-dimensional periodic structure may lead to very selective frequency filters and efficient devices for the wavelength demultiplexing. We present also the possibility of sonic insulators for frequencies of the order of kHz with relatively small thicknesses of phononic crystal samples. Finally we report on the vibration modes of a two-dimensional phononic crystal plate i.e. a phononic crystal of finite thickness along the axis of the inclusions. We discuss guided modes which may occur in the band structure of the plate. Surface acoustic waves propagating in two-dimensional phononic crystals should open new perspectives in high-frequency radio-frequency devices. Throughout the paper, the methods of calculation are presented with some details and some experimental results complete the numerical predictions.

  16. Reflectors, infinite cylinders, intersecting cylinders and criticality

    Microsoft Academic Search

    J. T. Thomas

    1978-01-01

    Calculations of the effective neutron multiplication factor of critical and subcritical infinitely long cylinders of aqueous solutions of fissile materials for various configurations of water and concrete reflectors are presented. The results provide a basis for investigating the criticality of intersecting pipes with similar reflectors. An infinitely long central cylinder with up to four intersections within each 0.46 m increment

  17. Compact Analytic Expression for the Electric Field of a 2DElliptical Charge Distribution Inside a Perfectly Conducting CircularCylinder

    SciTech Connect

    Furman, M.A.

    2007-05-29

    By combining the method of images with calculus of complex variables, we provide a simple expression for the electric field of a two-dimensional (2D) static elliptical charge distribution inside a perfectly conducting cylinder. The charge distribution need not be concentric with the cylinder.

  18. A visual study of phase-change heat transfer in a two-dimensional porous structure with a partial heating boundary

    Microsoft Academic Search

    Q. Liao; T. S. Zhao

    2000-01-01

    A visual study on the phase-change behaviors in a vertical two-dimensional porous structure made of staggered miniature silver–copper circular cylinders has been carried out. Subcooled water was pumped into the porous structure from its bottom due to the capillary action developed in the vicinity of a grooved heating block placed on the top of the porous structure. Using a high-speed

  19. A numerical study of the alpha model for two-dimensional magnetohydrodynamic turbulent flows

    E-print Network

    Pouquet, Annick

    A numerical study of the alpha model for two-dimensional magnetohydrodynamic turbulent flows Pablo the "Lagrangian-averaged" model, for two-dimensional incompressible magnetohydrodynamic (MHD) turbulence

  20. The aerodynamic characteristics at the mid-span of a circular cylinder with tangential blowing

    NASA Astrophysics Data System (ADS)

    Waka, R.; Yoshino, F.; Hayashi, T.; Iwasa, T.

    1983-05-01

    Three different methods were devised to determine the induced angle of attack as a function of lift coefficient at the mid-span of a circular cylinder with tangential blowing immersed in a uniform flow. The characteristic values such as aerodynamic coefficients of the cylinder were corrected to give two-dimensional ones by making use of the induced angle of attack thus obtained. The circumferential static pressure distribution on the surface of the cylinder was also calculated by modified Parkinson-Jandalis method to apply to an asymmetric flow around the cylinder with blowing.

  1. Two-dimensional Raman-terahertz spectroscopy of water

    PubMed Central

    Savolainen, Janne; Ahmed, Saima; Hamm, Peter

    2013-01-01

    Two-dimensional Raman-terahertz (THz) spectroscopy is presented as a multidimensional spectroscopy directly in the far-IR regime. The method is used to explore the dynamics of the collective intermolecular modes of liquid water at ambient temperatures that emerge from the hydrogen-bond networks water forming. Two-dimensional Raman-THz spectroscopy interrogates these modes twice and as such can elucidate couplings and inhomogeneities of the various degrees of freedoms. An echo in the 2D Raman-THz response is indeed identified, indicating that a heterogeneous distribution of hydrogen-bond networks exists, albeit only on a very short 100-fs timescale. This timescale appears to be too short to be compatible with more extended, persistent structures assumed within a two-state model of water. PMID:24297930

  2. Two-dimensional C/BN core/shell structures

    E-print Network

    Cahangirov, S

    2014-01-01

    Single layer core/shell structures consisting of graphene as core and hexagonal boron nitride as shell are studied using first-principles plane wave method within density functional theory. Electronic energy level structure is analysed as a function of the size of both core and shell. It is found that the confinement of electrons in two dimensional graphene quantum dot is reduced by the presence of boron nitride shell. The energy gap is determined by the graphene states. Comparison of round, hexagonal, rectangular and triangular core/shell structures reveals that their electronic and magnetic states are strongly affected by their geometrical shapes. The energy level structure, energy gap and magnetic states can be modified by external charging. The core part acts as a two-dimensional quantum dot for both electrons and holes. The capacity of extra electron intake of these quantum dots is shown to be limited by the Coulomb blockade in two-dimension.

  3. F2D: A two dimensional compressible gas flow code

    SciTech Connect

    Ahti Suo-Anttila (Science Applications International Corporation, 2109 Air Park Road S.E., Albuquerque, New Mexico 87106 (United States))

    1993-01-20

    The F2D computer code is a general-purpose, two-dimensional, fully compressible thermal-fluids code that models most phenomena found in experimental environments with coupled fluid flow and heat transfer. The code solves momentum, continuity, gas energy, and structure energy equations, simultaneously utilizing a predictor-corrector solution algorithm. The F2D code applied to a particle-bed reactor operating at 5 MW/L with a flow-control cold frit, revealed a skew in the temperature contours caused by two-dimensional flow effects. A thermal-fluid stability analysis of particle-bed and NERVA type reactors reveals similar behavior for the stability threshold.

  4. F2D: A two dimensional compressible gas flow code

    NASA Astrophysics Data System (ADS)

    Ahti, Suo-Anttila

    1993-01-01

    The F2D computer code is a general-purpose, two-dimensional, fully compressible thermal-fluids code that models most phenomena found in experimental environments with coupled fluid flow and heat transfer. The code solves momentum, continuity, gas energy, and structure energy equations, simultaneously utilizing a predictor-corrector solution algorithm. The F2D code applied to a particle-bed reactor operating at 5 MW/L with a flow-control cold frit, revealed a skew in the temperature contours caused by two-dimensional flow effects. A thermal-fluid stability analysis of particle-bed and NERVA type reactors reveals similar behavior for the stability threshold.

  5. 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.

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

    SciTech Connect

    Zhu, Chongqin; Li, Hui; Meng, Sheng, E-mail: smeng@iphy.ac.cn [Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing 100190 (China)

    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.

  7. Preliminary results on two-dimensional interferometry of HL Tau

    NASA Technical Reports Server (NTRS)

    Tollestrup, Eric V.; Harvey, Paul M.

    1989-01-01

    Preliminary two-dimensional speckle interferometry results of HL Tau were found to be qualitatively similar to those found with one-dimensional slit scanning techniques; results consist of a resolved component (approximately 0.7 arcsec in size) and an unresolved component. Researchers are currently reducing the rest of the data (taken on three different telescopes and at three different wavelengths) and are also exploring other high resolution methods like the shift and add technique and selecting only the very best images for processing. The availability of even better two-dimensional arrays within the next couple of years promises to make speckle interferometry and other high resolution techniques very powerful and exiting tools for probing a variety of objects in the subarcsec regime.

  8. Two-Dimensional Mathematical Modeling of the Pack Carburizing Process

    NASA Astrophysics Data System (ADS)

    Sarkar, S.; Gupta, G. S.

    2008-10-01

    Pack carburization is the oldest method among the case-hardening treatments, and sufficient attempts have not been made to understand this process in terms of heat and mass transfer, effect of alloying elements, dimensions of the sample, etc. Thus, a two-dimensional mathematical model in cylindrical coordinate is developed for simulating the pack carburization process for chromium-bearing steel in this study. Heat and mass balance equations are solved simultaneously, where the surface temperature of the sample varies with time, but the carbon potential at the surface during the process remains constant. The fully implicit finite volume technique is used to solve the governing equations. Good agreement has been found between the predicted and published data. The effect of temperature, carburizing time, dimensions of the sample, etc. on the pack carburizing process shows some interesting results. It is found that the two-dimensional model gives better insight into understanding the carburizing process.

  9. Strong localization effect in magnetic two-dimensional hole systems

    SciTech Connect

    Wurstbauer, U. [Institute of Experimental and Applied Physics, University of Regensburg, 93040 Regensburg (Germany); Institute of Applied Physics, University of Hamburg, 20355 Hamburg (Germany); Knott, S.; Zolotaryov, A.; Hansen, W. [Institute of Applied Physics, University of Hamburg, 20355 Hamburg (Germany); Schuh, D. [Institute of Experimental and Applied Physics, University of Regensburg, 93040 Regensburg (Germany); Wegscheider, W. [Institute of Experimental and Applied Physics, University of Regensburg, 93040 Regensburg (Germany); Solid State Physics Laboratory, ETH Zurich, 8093 Zurich (Switzerland)

    2010-01-11

    We report an extensive study of the magnetotransport properties of magnetically doped two-dimensional hole systems. Inverted manganese modulation doped InAs quantum wells with localized manganese ions providing a magnetic moment of S=5/2 were grown by molecular beam epitaxy. Strong localization effect found in low-field magnetotransport measurements on these structures can either be modified by the manganese doping density or by tuning the two-dimensional hole density p via field effect. The data reveal that the ratio between p and manganese ions inside or in close vicinity to the channel enlarges the strong localization effect. Moreover, asymmetric broadening of the doping layer due to manganese segregation is significantly influenced by strain in the heterostructure.

  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. Two-Dimensional Computational Model for Wave Rotor Flow Dynamics

    NASA Technical Reports Server (NTRS)

    Welch, Gerard E.

    1996-01-01

    A two-dimensional (theta,z) Navier-Stokes solver for multi-port wave rotor flow simulation is described. The finite-volume form of the unsteady thin-layer Navier-Stokes equations are integrated in time on multi-block grids that represent the stationary inlet and outlet ports and the moving rotor passages of the wave rotor. Computed results are compared with three-port wave rotor experimental data. The model is applied to predict the performance of a planned four-port wave rotor experiment. Two-dimensional flow features that reduce machine performance and influence rotor blade and duct wall thermal loads are identified. The performance impact of rounding the inlet port wall, to inhibit separation during passage gradual opening, is assessed.

  12. Disordered quantum walks in two-dimensional lattices plink

    NASA Astrophysics Data System (ADS)

    Zhang, Rong; Xu, Yun-Qiu; Xue, Peng

    2015-01-01

    The properties of the two-dimensional quantum walk with point, line, and circle disorders in phase are reported. Localization is observed in the two-dimensional quantum walk with certain phase disorder and specific initial coin states. We give an explanation of the localization behavior via the localized stationary states of the unitary operator of the walker + coin system and the overlap between the initial state of the whole system and the localized stationary states. Project supported by the National Natural Science Foundation of China (Grant No. 11174052), the National Basic Research Program of China (Grant No. 2011CB921203), and the Open Fund from the State Key Laboratory of Precision Spectroscopy of East China Normal University.

  13. Vortex annihilation and inverse cascades in two dimensional superfluid turbulence

    NASA Astrophysics Data System (ADS)

    Lucas, Andrew; Chesler, Paul M.

    2015-03-01

    The dynamics of a dilute mixture of vortices and antivortices in a turbulent two-dimensional superfluid at finite temperature is well described by first order Hall-Vinen-Iordanskii equations, or dissipative point vortex dynamics. These equations are governed by a single dimensionless parameter: the ratio of the strength of drag forces to Magnus forces on vortices. When this parameter is small, we demonstrate using numerical simulations that the resulting superfluid enjoys an inverse energy cascade where small scale stirring leads to large scale vortex clustering. We argue analytically and numerically that the vortex annihilation rate in a laminar flow may be parametrically smaller than the rate in a turbulent flow with an inverse cascade. This suggests a new way to detect inverse cascades in experiments on two-dimensional superfluid turbulence using cold atomic gases, where traditional probes of turbulence such as the energy spectrum are not currently accessible.

  14. Multigrid Navier-Stokes calculation for two dimensional cascades

    NASA Astrophysics Data System (ADS)

    Yang, Ce; Lao, Dazhong; Jiang, Zikang

    1998-03-01

    A fast and accurate numerical method for solving the two dimensional Reynolds averaged Navier-Stokes is applied to calculate the internal fluid of turbines and compressors. The code is based on an explicit, time-marching, finite volume technique. In order to accelerate convergence, local time stepping, multigrid method is employed. Four stage Runge-Kutta method is implemented to extend the stability domain. Test cases of Hobson’s impulse cascade, NASA Rotor 37 and Sanz’s supercritical compressor cascade are presented. Results of Mach number distribution on blade surfaces and Mach number contour plots indicate good agreement with experimental data. Compared with full three 3D Navier-Stokes (N-S) codes, the two dimensional code only takes a short time to obtain predicted results. This code can be used widely in practical engineering design.

  15. Direct energy cascade in two-dimensional compressible quantum turbulence

    SciTech Connect

    Numasato, Ryu; Tsubota, Makoto; L'vov, Victor S. [Department of Physics, Osaka City University, Sumiyoshi-ku, Osaka 558-8585 (Japan); Department of Chemical Physics, The Weizmann Institute of Science, Rehovot 76100 (Israel)

    2010-06-15

    We numerically study two-dimensional quantum turbulence with a Gross-Pitaevskii model. With the energy initially accumulated at large scale, quantum turbulence with many quantized vortex points is generated. Due to the lack of enstrophy conservation in this model, direct energy cascade with a Kolmogorov-Obukhov energy spectrum E(k){proportional_to}k{sup -5/3} is observed, which is quite different from two-dimensional incompressible classical turbulence in the decaying case. A positive value for the energy flux guarantees a direct energy cascade in the inertial range (from large to small scales). After almost all the energy at the large scale cascades to the small scale, the compressible kinetic energy realizes the thermodynamic equilibrium state without quantized vortices.

  16. Folding two dimensional crystals by swift heavy ion irradiation

    NASA Astrophysics Data System (ADS)

    Ochedowski, Oliver; Bukowska, Hanna; Freire Soler, Victor M.; Brökers, Lara; Ban-d'Etat, Brigitte; Lebius, Henning; Schleberger, Marika

    2014-12-01

    Ion irradiation of graphene, the showcase model of two dimensional crystals, has been successfully applied to induce various modifications in the graphene crystal. One of these modifications is the formation of origami like foldings in graphene which are created by swift heavy ion irradiation under glancing incidence angle. These foldings can be applied to locally alter the physical properties of graphene like mechanical strength or chemical reactivity. In this work we show that the formation of foldings in two dimensional crystals is not restricted to graphene but can be applied for other materials like MoS2 and hexagonal BN as well. Further we show that chemical vapour deposited graphene forms foldings after swift heavy ion irradiation while chemical vapour deposited MoS2 does not.

  17. Gas Kinetic Approach to Two-Dimensional Traffic Flow

    NASA Astrophysics Data System (ADS)

    Nagatani, Takashi

    1996-10-01

    The kinetics of cars in two-dimensional traffic flow is described in terms of Boltzmann-like gas kinetic equations. Paveri-Fontana's gas kinetic equation for one-dimensional traffic flow is extended to two-dimensional traffic. The desired velocity is taken into account in the gas kinetic equations. A discrete version of the kinetic equations is used to numerically solve the equations. The velocity distributions are calculated by a numerical method. The steady-state velocity distributions are derived numerically for different accelerations and densities. It is shown that the velocity distribution of east-bound cars deviates to the low-velocity side with increasing density of north-bound cars. It is also found that the velocity distribution deviates to the high-velocity side with increasing acceleration under the condition of constant density.

  18. Three-Dimensional Field Solutions for Multi-Pole Cylindrical Halbach Arrays in an Axial Orientation

    NASA Technical Reports Server (NTRS)

    Thompson, William K.

    2006-01-01

    This article presents three-dimensional B field solutions for the cylindrical Halbach array in an axial orientation. This arrangement has applications in the design of axial motors and passive axial magnetic bearings and couplers. The analytical model described here assumes ideal magnets with fixed and uniform magnetization. The field component functions are expressed as sums of 2-D definite integrals that are easily computed by a number of mathematical analysis software packages. The analysis is verified with sample calculations and the results are compared to equivalent results from traditional finite-element analysis (FEA). The field solutions are then approximated for use in flux linkage and induced EMF calculations in nearby stator windings by expressing the field variance with angular displacement as pure sinusoidal function whose amplitude depends on radial and axial position. The primary advantage of numerical implementation of the analytical approach presented in the article is that it lends itself more readily to parametric analysis and design tradeoffs than traditional FEA models.

  19. Magnetomechanics of internal-dipole, Halbach-array motor/generators.

    SciTech Connect

    Hull, J. R.; Turner, L. R.; Energy Technology

    2000-07-01

    The magnetomechanical behavior of internal-dipole, Halbach-type magnet arrays is analyzed for application as a motor/generator (M/G) with an energy-storage flywheel that is suspended by low-stiffness bearings. Scaling laws for the maximization of torque are derived as a function of geometry. The optimal geometry is relatively insensitive to gap and stator design and occurs approximately at a ratio of inner to outer diameter of the array of 0.8. Values are found for the angular extent of each phase of the stator coil that minimize the stiffness. The negative stiffness of the internal-dipole array is calculated for several manufacturable configurations and is shown to provide an upper limit on the available torque of the M/G according to the positive stiffness of the bearings. Experimental results are reported for an internal-dipole array used as a M/G for a flywheel suspended by a bearing consisting of a permanent-magnet assembly levitated over an array of high-temperature superconductors. Results show that the system is stable and that idling losses are low.

  20. Quantum computation with two-dimensional graphene quantum dots

    Microsoft Academic Search

    Li Jie-Sen; Li Zhi-Bing; Yao Dao-Xin

    2012-01-01

    We study an array of graphene nano sheets that form a two-dimensional S = 1\\/2 Kagome spin lattice used for quantum computation. The edge states of the graphene nano sheets are used to form quantum dots to confine electrons and perform the computation. We propose two schemes of bang-bang control to combat decoherence and realize gate operations on this array

  1. Two-dimensional black hole and singularities of CY manifolds

    Microsoft Academic Search

    Hirosi Ooguri; Cumrun Vafa

    1996-01-01

    We study the degenerating limits of superconformal theories for compactifications on singular K3 and Calabi-Yau threefolds. We find that in both cases the degeneration involves creating an Euclidean two-dimensional black hole coupled weakly to the rest of the system. Moreover we find that the conformal theory of An singularities of K3 are the same as that of the symmetric fivebrane.

  2. Hall effect in the two-dimensional Luttinger liquid

    SciTech Connect

    Anderson, P.W. (Joseph Henry Laboratories of Physics, Jadwin Hall, Princeton University, Princeton, New Jersey (USA))

    1991-10-07

    The temperature dependence of the Hall effect in the normal state is a commom theme of all the cuprate superconductors and has been one of the more puzzling observations on these puzzling materials. We describe a general scheme within the Luttinger liquid theory of these two-dimensional quantum fluids which corrrelates the anomalous Hall and resistivity observations on a wide variety of both pure and doped single crystals, especially the data in the accompanying Letter of Chien, Wang, and Ong.

  3. Two-dimensional simulation of an electron cyclotron resonance discharge

    Microsoft Academic Search

    J. H. Shiau; J. H. Tsai; S. H. Chen; J. Y. Yang; C. J. Chiou

    1999-01-01

    Summary form only given, as follows. A two-dimensional three-moment simulation code was developed and performed for the study of the electron cyclotron resonance (ECR) plasma sources based on the self-consistent fluid model which determines the dynamics of the plasma as well as its interactions with the microwave. In particular, the ECR discharges can be characterized by two major parameters, one

  4. Electromagnetic Two-Dimensional Scanner Using Radial Magnetic Field

    Microsoft Academic Search

    Chang-Hyeon Ji; Moongoo Choi; Sang-Cheon Kim; Ki-Chang Song; Jong-Uk Bu; Hyo-Jin Nam

    2007-01-01

    In this paper, we present the design, fabrication, and measurement results of a two-dimensional electromagnetic scanning micromirror actuated by radial magnetic field. The scanner is realized by combining a gimbaled single-crystal-silicon micromirror with a single turn electroplated metal coil, with a concentric permanent magnet assembly composed of two concentric permanent magnets and an iron yoke. The proposed scanner utilizes the

  5. Vacuum operation characteristics of two-dimensional micro-mirror

    Microsoft Academic Search

    Hoang Manh Chu; Kazuhiro Hane

    2010-01-01

    We present design, fabrication and characteristics of two-dimensional micro-machined scanner. The resonant frequencies of horizontal and vertical axes are 40 kHz and 162 Hz for the inner mirror and gimbal frame, respectively. The optical scanning angles are obtained to be 11.5 and 14 degrees at the low driving voltages of 12 and 10 V in 1 Pa vacuum for the

  6. Anomalous time correlation in two-dimensional driven diffusive systems

    Microsoft Academic Search

    Takenobu Nakamura; Michio Otsuki; Shin-Ichi Sasa

    2005-01-01

    We study the time-correlation function of a density field in two-dimensional driven diffusive systems within the framework of fluctuating hydrodynamics. It is found that the time correlation exhibits power-law behavior in an intermediate time regime in the case that the fluctuation-dissipation relation is violated and that the power-law exponent depends on the extent of this violation. We obtain this result

  7. Hierarchical level-clustering in two-dimensional harmonic oscillators

    Microsoft Academic Search

    C. B. Whan

    1997-01-01

    We present numerical results on the statistical distribution of energy level spacings in two-dimensional (2D) harmonic oscillators with irrational frequency ratio, R ? omega_1\\/omega_2. Unlike the scaled level spacings, the distribution of the true energy level spacings is well behaved and directly reflects the corresponding classical quasiperiodic motion. The histogram of the energy level spacings shows sharp peaks at discontinuous

  8. Preliminary results on two-dimensional interferometry of HL Tau

    Microsoft Academic Search

    Eric V. Tollestrup; Paul M. Harvey

    1989-01-01

    Preliminary two-dimensional speckle interferometry results of HL Tau were found to be qualitatively similar to those found with one-dimensional slit scanning techniques; results consist of a resolved component (approximately 0.7 arcsec in size) and an unresolved component. Researchers are currently reducing the rest of the data (taken on three different telescopes and at three different wavelengths) and are also exploring

  9. Plasma diagnostics using millimetre wave two-dimensional imaging array

    Microsoft Academic Search

    N Oyama; A Mase; T Tokuzawa; K Imamura; A Itakura; Y Ito; T Tamano; Y Harada; K Mizuno

    1997-01-01

    A millimetre wave two-dimensional detector array has been newly developed for application to a phase-imaging interferometer installed in the GAMMA 10 tandem mirror. The interferometer consists of two sources and a quasi-optical transmission system. The transmitted wave is mixed with the local oscillator (LO) wave to provide a 150 MHz intermediate frequency (IF) signal. The detector has 4 × 4

  10. Stream Cyphers with One and Two-Dimensional Cellular Automata

    Microsoft Academic Search

    Marco Tomassini; Mathieu Perrenoud

    2000-01-01

    In the age of universal electronic connectivity and the ensuing possibility of message eavesdropping and electronic fraud,\\u000a cryptography becomes a basic requirement to secure data storage and transmission. In this work we describe a single key cryptographic\\u000a system based on one- and two-dimensional non-uniform cellular automata that produce high-quality pseudo-random bit sequences.\\u000a The robustness of the scheme against cryptanalytic attacks

  11. Microwave tomography: two-dimensional system for biological imaging

    Microsoft Academic Search

    Serguei Y. Semenov; Robert H. Svenson; Alexander E. Boulyshev; Alexander E. Souvorov; Vladimir Y. Borisov; Yuri Sizov; Andrey N. Starostin; Kathy R. Dezern; George P. Tatsis; Vladimir Y. Baranov

    1996-01-01

    Microwave tomographic imaging is one of the new technologies which has the potential for important applications in medicine. Microwave tomographically reconstructed images may potentially provide information about the physiological state of tissue as well as the anatomical structure of an organ. A two-dimensional (2-D) prototype of a quasi real-time microwave tomographic system was constructed. It was utilized to reconstruct images

  12. Prediction with Partial Match using two-dimensional approximate contexts

    Microsoft Academic Search

    Ishtiaque Hossain; Mahmoud R. El-Sakka

    2012-01-01

    The Prediction with Partial Match (PPM) is a context-based lossless compression scheme developed in the mid 80's. Originally it was targeted towards compressing text that can be viewed as a one-dimensional sequence of symbols. When compressing digital images, PPM usually breaks the two-dimensional data into a one-dimensional raster scan form. This paper extends PPM in order to take full advantage

  13. Pressure measurement in two-dimensional horizontal granular gases.

    PubMed

    Géminard, J-C; Laroche, C

    2004-08-01

    A two-dimensional granular gas is produced by vibrating vertically a partial layer of beads on a horizontal plate. Measurements of the force applied by the granular gas to the sidewalls of the container, or granular pressure, are used to study the effect of the shaking strength, density, bead-plate restitution coefficient, and particle size on the steady properties of the gas. PMID:15447484

  14. 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.

  15. A two-dimensional theory of fracture propagation

    Microsoft Academic Search

    M. A. Blot; L. Masse; W. L. Medlin

    1982-01-01

    A basic theory of two-dimensional fracture propagation has been developed using a Lagrangian formulation combined with a virtual work analysis. Fluid leak-off is included by assuming that an incompressible filtrate produces a piston-like displacement of a compressible reservoir fluid with a moving boundary between the two. Poiseuille flow is assumed in the fracture. The authors consider both Newtonian and Non-Newtonian

  16. Ultra-flat bands in two-dimensional photonic crystals

    Microsoft Academic Search

    Mihai Ibanescu; Marin Soljacic; Steven G. Johnson; J. D. Joannopoulos

    2006-01-01

    We show that two-dimensional photonic crystals can be designed to have dispersion relations with an extended ultra-flat cross-section, meaning that for a fixed wave vector component kx the frequency of a band is almost constant when the other wave vector component, ky, takes all possible values. These ultra-flat bands are the result of a non-trivial saddle point in the dispersion

  17. Two-Dimensional Bernstein-Greene-Kruskal Solution

    NASA Astrophysics Data System (ADS)

    Ishibashi, Nobuo; Kitahara, Kazuo

    1992-08-01

    A solution with cylindrical symmetry for the time-independent two-dimensional Vlasov equation is given numerically. It is demonstrated that, by adding appropriate numbers of particles trapped in potential-energy troughs, which are created by beam particles with definite angular momenta, varieties of localized vortical solutions can be constructed. There are an electron density hole and an ion density hole in the central region. Around these holes, electrons and ions are distributed on rings in the configuration space.

  18. Planar velocity measurements of a two-dimensional compressible wake

    Microsoft Academic Search

    F. Scarano; B. w. Van Oudheusden

    2003-01-01

    Abstract The present study describes the application of particle image velocimetry,(PIV) to investigate the com- pressible flow in the wake of a two-dimensional,blunt base at a freestream Mach number,M¥=2. The first part of the study addresses specific issues related to the application of PIV to supersonic wind tunnel flows, such as the seeding particle flow-tracing fidelity and the measurement,spatial resolution.

  19. Planar velocity measurements of a two-dimensional compressible wake

    Microsoft Academic Search

    F. Scarano; B. W. van Oudheusden

    2003-01-01

    The present study describes the application of particle image velocimetry (PIV) to investigate the compressible flow in the wake of a two-dimensional blunt base at a freestream Mach number MX=2. The first part of the study addresses specific issues related to the application of PIV to supersonic wind tunnel flows, such as the seeding particle flow-tracing fidelity and the measurement

  20. 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

  1. A Calculation Procedure for Two-Dimensional Elliptic Situations

    Microsoft Academic Search

    Suhas Patankar

    1981-01-01

    A calculation method based on the control-volume approach has been developed for solving two-dimensional elliptic problems involving fluid flow and heat and mass transfer. The main features of the method include a power-law formulation for the combined convection-diffusion influence, an equation-solving scheme that consists of a block-correction method coupled with a line-by-line procedure, and a new algorithm for handling the

  2. The relative growth of information in two-dimensional partitions

    Microsoft Academic Search

    Karma Dajani; Martijn de Vries; Aimee S. A. Johnson

    2006-01-01

    Let $\\\\overline{x} \\\\in [0,1)^2$. In this paper we find the rate at which knowledge about the partition elements $\\\\overline{x}$ lies in for one sequence of partitions determines the partition elements it lies in for another sequence of partitions. This rate depends on the entropy of these partitions and the geometry of their shapes, and gives a two-dimensional version of Lochs'

  3. Multigrid Navier-Stokes calculation for two dimensional cascades

    Microsoft Academic Search

    Ce Yang; Dazhong Lao; Zikang Jiang

    1998-01-01

    A fast and accurate numerical method for solving the two dimensional Reynolds averaged Navier-Stokes is applied to calculate\\u000a the internal fluid of turbines and compressors. The code is based on an explicit, time-marching, finite volume technique.\\u000a In order to accelerate convergence, local time stepping, multigrid method is employed. Four stage Runge-Kutta method is implemented\\u000a to extend the stability domain. Test

  4. Two-dimensional solitons in irregular lattice systems

    Microsoft Academic Search

    M. J. Ablowitz; B. Ilan; E. Schonbrun; R. Piestun

    2007-01-01

    We compute and study localized nonlinear modes (solitons) in the semi-infinite gap of the focusing two-dimensional nonlinear\\u000a Schrödinger (NLS) equation with various irregular lattice-type potentials. The potentials are characterized by large variations\\u000a from periodicity, such as vacancy defects, edge dislocations, and a quasicrystal structure. We use a spectral fixed-point\\u000a computational scheme to obtain the solitons. The eigenvalue dependence of the

  5. Two-dimensional high temperature strain measurement system

    NASA Technical Reports Server (NTRS)

    Lant, Christian T.; Barranger, John P.

    1989-01-01

    Two-dimensional optical strain measurements on high temperature test specimens are presented. This two-dimensional capability is implemented through a rotatable sensitive strain axis. Three components of surface strain can be measured automatically, from which the first and second principal strains are calculated. One- and two-dimensional strain measurements at temperatures beyond 750 C with a resolution of 15 microstrain are demonstrated. The system is based on a one-dimensional speckle shift technique. The speckle shift technique makes use of the linear relationship between surface strain and the differential shift of laser speckle patterns in the diffraction plane. Laser speckle is a phase effect that occurs when spatially coherent light interacts with an optically rough surface. Since speckle is generated by any diffusely reflecting surface, no specimen preparation is needed to obtain a good signal. Testing was done at room temperature on a flat specimen of Inconel 600 mounted in a fatigue testing machine. A load cell measured the stress on the specimen before and after acquiring the speckle data. Strain components were measured at 0 C (parallel to the load axis) and at plus or minus 45 C, and plots indicate the calculated values of the first and second principal strains. The measured values of Young's modulus and Poisson's ratio are in good agreement with handbook values. Good linearity of the principal strain moduli at high temperatures indicate precision and stability of the system. However, a systematic error in the high-temperature test setup introduced a scale factor in the slopes of the two-dimensional stress-strain curves. No high temperature effects, however, have been observed to degrade speckle correlation.

  6. Instability of two-dimensional heterotic stringy black holes

    NASA Astrophysics Data System (ADS)

    Azreg-Aïnou, Mustapha

    1999-01-01

    We solve the eigenvalue problem of general relativity for the case of charged black holes in two-dimensional heterotic string theory, derived by McGuigan et al. For the case of 0264-9381/16/1/016/img1, we find a physically acceptable time-dependent growing mode; thus the black hole is unstable. The extremal case 0264-9381/16/1/016/img2 is stable.

  7. Erratum: On the two-dimensional sloshing problem.

    PubMed

    Kozlov, Vladimir; Kuznetsov, Nikolay; Motygin, Oleg

    2011-08-01

    A correct proof is given for the following assertions about the two-dimensional sloshing problem. The fundamental eigenvalue is simple and the corresponding stream function may be chosen to be non-negative in the closure of the water domain. New proof is based on stricter assumptions about the water domain; namely, it must satisfy John's condition.[This corrects the article DOI: 10.1098/rspa.2004.1303.]. PMID:24959097

  8. Two-dimensional array transducers using thick film connection technology

    Microsoft Academic Search

    Stephen W. Smith; Edward D. Light

    1993-01-01

    A connection technique for two-dimensional array ultrasound transducers developed by combining a conductive ?\\/4 mismatching layer with a multi-layer ceramic (MLC) connector using thick-film microelectronic technology is described. The connector consists of 20 thick films of alumina and screen printed metallization with customized interconnections between the layers called vias. Ten ground layers are interleaved between ten signal layers to reduce

  9. 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

  10. Doping induced Mott transition in the two dimensional Hubbard model

    Microsoft Academic Search

    Giovanni Sordi; A.-M. S. Tremblay

    2010-01-01

    The description of the Mott transition by single-site dynamical mean-field theory is exact in infinite dimensions but, in two dimensions, substantial deviations from those results have been found for the interaction driven transition [1]. In addition, the experimentally relevant transition for layered systems such as the high-Tc cuprates is doping driven. We thus study this transition in the two dimensional

  11. Design of FIR two- dimensional digital filters by successive projections

    Microsoft Academic Search

    A. Abo-Taleb; M. Fahmy

    1984-01-01

    An iterative optimization technique based on the method of successive projections is proposed for the design of the two-dimensional (2-D) linear phase FIR digital filters. The technique is simple, fast, and compares favorably with the presently available design techniques. To illustrate the method several filters with masks up to25 times 25have been designed. The technique can also be used to

  12. Two-dimensional modeling of the formation of spheromak configurations

    SciTech Connect

    Jardin, S.C.; Park, W.

    1980-09-01

    A reduced set of two-dimensional MHD equations have been derived describing the axisymmetric time evolution of a MHD stable plasma evolving slowly due to resistive diffusion and changing boundary conditions. The equations are restricted to low ..beta.. but allow changing topology. They are integrated in time to demonstrate a possible spheromak formation method. External circuit equations are integrated simultaneously with the plasma equations to determine the electromagnetic boundary conditions self consistently. The effects of a finite conductivity vacuum chamber are included.

  13. Nonlinear two-dimensional potential plasma wake waves

    SciTech Connect

    Amatuni, A.Ts.

    1995-12-01

    The conditions for potential description of the wake waves, generated by flat electron driving bunch in cold plasma, are derived. The nonlinear equation for potential, valid for small values of that, is obtained and exact solutions are found for two-dimensional nonlinear plasma wake-waves. In particular,at some boundary conditions, corresponding to blow-out regime, the solution in form of solitary wave is found.

  14. Mutational Scanning of Mitochondrial DNA by Two-Dimensional Electrophoresis

    Microsoft Academic Search

    Nathalie J. van Orsouw; Xiaomin Zhang; Jeanne Y. Wei; Donald R. Johns; Jan Vijg

    1998-01-01

    An expedient, accurate, and cost-efficient test was developed to scan critical regions of the mitochondrial genome for all possible mutations by two-dimensional DNA electrophoresis. The test involves a two-step multiplex PCR amplification: a long-distance PCR to amplify almost the entire mitochondrial genome, which then serves as template for the amplification of 25 short PCR fragments in two multiplex groups corresponding

  15. The Dirichlet problem on two-dimensional stratified sets

    NASA Astrophysics Data System (ADS)

    Kovaleva, L. A.; Soldatov, A. P.

    2015-02-01

    We consider the Dirichlet problem for harmonic functions on two-dimensional stratified sets, which are assumed for simplicity to be complexes. We show that under certain conditions this problem is Fredholm in the Hölder space and in weighted Hölder spaces of functions satisfying the Hölder condition outside any neighbourhood of the vertex set of the complex and admitting power singularities. We also study the power-logarithmic asymptotics of solutions at these vertices.

  16. Two-dimensional Lennard-Jones liquid-vapour interphase

    NASA Astrophysics Data System (ADS)

    Mederos, L.; Chacón, E.; Navascués, G.; Lombardero, M.

    A functional perturbation theory is used to study the properties of a two-dimensional Lennard-Jones liquid-vapour interphase. The coexistence curve, density profile, line tension, structure factor and isothermal compressibility are obtained and discussed. Comparison with computer simulations is also included. The effects of the dimensionality are also studied. The product of the line tension by the isothermal compressibility is discussed. Several critical exponents are estimated by this theory and compared with the classical and exact values.

  17. Diffusion of circular DNA in two-dimensional cavity arrays.

    PubMed

    Nykypanchuk, Dmytro; Hoagland, David A; Strey, Helmut H

    2009-11-01

    Through a two-dimensional cavity array with connecting pores of submolecular size, diffusion of relaxed circular and linear DNA molecules is visualized by fluorescence microscopy. Across the entropic barriers transport regime, associated with spatially heterogeneous confinement of flexible polymers, circular DNA diffuses slower than linear DNA of the same length, a trend indicating that linear DNA preferably moves through connecting pores by the threading of an end rather than the looping of a midsection. PMID:19821478

  18. Using two-dimensional vibration cutting for micro-milling

    Microsoft Academic Search

    Gwo-Lianq Chern; Yuan-Chin Chang

    2006-01-01

    The purpose of this paper is to investigate the effects of assisted vibration cutting (VC) on the micro-milling quality of aluminum alloy Al 6061-T6. The desired vibration is proposed from the workpiece side by a two-dimensional vibrating worktable we developed. The slot produced by end milling is studied by examining its geometrical shape and machining accuracy. Through extensive experiments with

  19. Two-dimensional almost-Riemannian structures with tangency points

    Microsoft Academic Search

    Andrei A. Agrachev; Ugo V. Boscain; Gregoire Charlot; Roberta Ghezzi; Mario Sigalotti

    2009-01-01

    Two-dimensional almost-Riemannian structures are generalized Riemannian structures on surfaces for which a local orthonormal frame is given by a Lie bracket generating pair of vector fields that can become collinear. We study the relation between the topological invariants of an almost-Riemannian structure on a compact oriented surface and the rank-two vector bundle over the surface which defines the structure. We

  20. Multigrid ADI method for two-dimensional electromagnetic simulations

    Microsoft Academic Search

    Shumin Wang; J. Chen

    2006-01-01

    We propose a multigrid alternating-direction implicit (ADI) method for solving two-dimensional Maxwell's equations. This method is based on interpreting the ADI method as an iterative solver for the Crank-Nicolson (CN) scheme. By introducing a special procedure to solve the residual equation within the ADI framework, multigrid methods are incorporated into the iterative ADI method. The accuracy and efficiency of the

  1. Influence of index contrast in two dimensional photonic crystal lasers

    Microsoft Academic Search

    Mette Marie Jørgensen; Sidsel Rübner Petersen; Mads Brøkner Christiansen; Thomas Buß; Cameron L. C. Smith; Anders Kristensen

    2010-01-01

    The influence of index contrast variations for obtaining single-mode operation and low threshold in dye doped polymer two dimensional photonic crystal (PhC) lasers is investigated. We consider lasers made from Pyrromethene 597 doped Ormocore imprinted with a rectangular lattice PhC having a cavity in the middle of the crystal structure. We demonstrate that the index contrast, neff,high\\/neff,low, is an essential

  2. Two-dimensional photonic crystal hexagonal waveguide ring laser

    Microsoft Academic Search

    Se-Heon Kim; Han-Youl Ryu; Hong-Gyu Park; Guk-Hyun Kim; Yong-Seok Choi; Yong-Hee Lee; Jeong-Soo Kim

    2002-01-01

    Hexagonal ring-type resonators defined by two-dimensional photonic crystal waveguides are proposed and demonstrated. Lasing actions are observed from the photonic crystal ring resonator patterned on a free-standing slab with InGaAsP active layers emitting near 1.55 mum. For a ring resonator with 8-mum diameter, the threshold peak pump power is ~3 mW. The quality factor of the ring resonator mode estimated

  3. General Software for Two-Dimensional Nonlinear Partial Differential Equations

    Microsoft Academic Search

    David K. Melgaard; Richard F. Sincovec

    1981-01-01

    In this paper we describe a software interface to solve time-dependent coupled systems of nonlinear partial differential equations (PDEs), which are defined over a two-dimensional rectangular rebqon. The software interface employs the method of lines technique whereby centered differencing with respect to the two spatial variables results in a system of time-dependent ordinary differential equations (ODEs), which can then be

  4. Cylinder Test Specification

    SciTech Connect

    Richard Catanach; Larry Hill; Herbert Harry; Ernest Aragon; Don Murk

    1999-10-01

    The purpose of the cylinder testis two-fold: (1) to characterize the metal-pushing ability of an explosive relative to that of other explosives as evaluated by the E{sub 19} cylinder energy and the G{sub 19} Gurney energy and (2) to help establish the explosive product equation-of-state (historically, the Jones-Wilkins-Lee (JWL) equation). This specification details the material requirements and procedures necessary to assemble and fire a typical Los Alamos National Laboratory (LANL) cylinder test. Strict adherence to the cylinder. material properties, machining tolerances, material heat-treatment and etching processes, and high explosive machining tolerances is essential for test-to-test consistency and to maximize radial wall expansions. Assembly and setup of the cylinder test require precise attention to detail, especially when placing intricate pin wires on the cylinder wall. The cylinder test is typically fired outdoors and at ambient temperature.

  5. Harmonic Oscillator in Noncommuting Two-Dimensional Space

    NASA Astrophysics Data System (ADS)

    Streklas, Antony

    In the present paper, we study a two-dimensional harmonic oscillator in a constant magnetic field in noncommuting space. We use the following Hamiltonian [ H = 1/2 m (\\hat{p}_1^2+\\hat{p}_2^2) + 1/2 m\\omega_1^2\\hat{q}_1^2+ 1/2 m\\omega_2^2\\hat{q}_2^2, ] with commutation relations [hat {q}1, hat {q}2] = i? , [hat {p}1,hat {p}_2]=i? and [hat {q}j, hat {p}k] = i hbar ? jk. The parameter ? expresses the presence of the magnetic field. We find the exact propagator of the system and the time evolution of the basic operators. We prove that the system is equivalent to a two-dimensional system where the operators of momentum and coordinates of the second dimension satisfy a deformed commutation relation [hat {Q}2, hat {P}2] = i hbar ? . The deformation parameter, ?, depends on ? and ?, and is independent of the Hamiltonian. Finally, we investigate the thermodynamic properties of the system in Boltzmann statistics. We find the statistical density matrix and the partition function, which is equivalent to that of a two-dimensional harmonic oscillator with two deformed frequencies ?1 and ?2.

  6. Two-dimensional optical beam deflector operated by wavelength tuning

    NASA Astrophysics Data System (ADS)

    Toyoshima, Morio; Fidler, Franz; Pfennigbauer, Martin; Leeb, Walter R.

    2006-05-01

    A new method based on an optical delay line structure is proposed for two-dimensional raster optical beam steering. For one-dimensional beam steering, the laser beam to be deflected is split into N co-directional sub-beams of equal intensity with the aid of a plane-parallel plate. These sub-beams experience a relative time delay, which translates into a phase difference, thus forming a phased array. When the laser wavelength is tuned, the relative phase varies and the far-field interference footprint can be steered across a receive plane. By employing two plane-parallel plates in series, the described scheme can be extended to produce a two-dimensional N × N array of sub-beams, allowing two-dimensional beam steering via wavelength tuning. In this case, wavelength tuning over a larger range leads to a linear deflection which repeats itself in a raster-like fashion. One direction of deflection repeats itself multiple times as wavelength is scanned over larger range, that is, a raster effect. In this paper, the principle is theoretically derived and formulated, and the preliminary experimental results with four sub-beams are presented.

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

    PubMed

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

    2015-01-01

    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. PMID:26099565

  8. 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.

  9. Numerical procedure to determine geometric view factors for surfaces occluded by cylinders

    Microsoft Academic Search

    P. L. Sawyer

    1978-01-01

    A numerical procedure was developed to determine geometric view factors between connected infinite strips occluded by any number of infinite circular cylinders. The procedure requires a two-dimensional cross-sectional model of the configuration of interest. The two-dimensional model consists of a convex polygon enclosing any number of circles. Each side of the polygon represents one strip, and each circle represents a

  10. 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.

  11. Standing waves on two-dimensional periodic dielectric waveguides

    NASA Astrophysics Data System (ADS)

    Hu, Zhen; Lu, Ya Yan

    2015-06-01

    Guided modes of a periodic waveguide usually exist below the light line, if the minimum period of the waveguide is used in the definition, but for some periodic waveguides, there are standing waves with the same period as the waveguide. These non-propagating waves localized around the waveguide core are special guided modes above the light line with a zero wavenumber, and they are related to transmission anomalies and other resonant phenomena. In this paper, we analyze the standing waves on two periodic waveguides: a periodic array of circular dielectric cylinders, and a dielectric slab with a periodic array of circular air-holes. Based on an efficient semi-analytic method, the frequencies of standing waves are calculated as functions of the dielectric constant and the radius of cylinders. Our work provides a basis for further studies on these waves and for realizing their potential applications.

  12. Cylinder monitoring program

    SciTech Connect

    Alderson, J.H. [Martin Marietta Energy Systems, Inc., Paducah, KY (United States)

    1991-12-31

    Cylinders containing depleted uranium hexafluoride (UF{sub 6}) in storage at the Department of Energy (DOE) gaseous diffusion plants, managed by Martin Marietta Energy Systems, Inc., are being evaluated to determine their expected storage life. Cylinders evaluated recently have been in storage service for 30 to 40 years. In the present environment, the remaining life for these storage cylinders is estimated to be 30 years or greater. The group of cylinders involved in recent tests will continue to be monitored on a periodic basis, and other storage cylinders will be observed as on a statistical sample population. The program has been extended to all types of large capacity UF{sub 6} cylinders.

  13. Buoyant plane plumes from heated horizontal confined wires and cylinders

    Microsoft Academic Search

    Guy Lauriat; Gilles Desrayaud

    1994-01-01

    Two-dimensional computations are reported for time-dependent laminar buoyancy-induced flows above a horizontal heated source\\u000a immersed in an air-filled vessel. Two kinds of heated source were considered: a line heat source, modelled as a heat source\\u000a term in the energy equation, and a heat-flux cylinder of small diameter. First, comparisons are presented for the results\\u000a obtained for these two heated sources.

  14. The unsteady structure of two-dimensional steady laminar separation

    NASA Astrophysics Data System (ADS)

    Ripley, Matthew D.; Pauley, Laura L.

    1993-12-01

    The two-dimensional unsteady incompressible Navier-Stokes equations, solved by a fractional time-step method, were used to investigate separation due to the application of an adverse pressure gradient to a low-Reynolds number boundary layer flow. The inviscid pressure distribution of Gaster [AGARD CP 4, 813 (1966)] was applied in the present computations to study the development of a laminar separation bubble. In all cases studied, periodic vortex shedding occurred from the primary separation region. The shed vortices initially lifted from the boundary layer and then returned towards the surface downstream. The shedding frequency nondimensionalized by the momentum thickness was found to be independent of Reynolds number. The value of the nondimensional Strouhal number, however, was found to differ from the results of Pauley et al. [J. Fluid Mech. 220, 397 (1990)], indicating that the shedding frequency varies with the nondimensional pressure distribution, Cp. The computational results were time averaged over several shedding cycles and the results were compared with Gaster. The numerical study accurately reproduced the major characteristics of the separation found in Gaster's study such as the separation point, the pressure plateau within the upstream portion of the separation bubble, and the reattachment point. The similarity between the experimental results and the time-averaged two-dimensional computational results indicates that the low-frequency velocity fluctuations detected by Gaster are primarily due to the motion of large vortex structures. This suggests that large-scale two-dimensional structures control bubble reattachment and small-scale turbulence contributes a secondary role.

  15. Monte Carlo Simulations of the two-dimensional dipolar fluid

    E-print Network

    Caillol, Jean-Michel

    2015-01-01

    We study a two-dimensional fluid of dipolar hard disks by Monte Carlo simulations in a square with periodic boundary conditions and on the surface of a sphere. The theory of the dielectric constant and the asymptotic behaviour of the equilibrium pair correlation function in the fluid phase is derived for both geometries. After having established the equivalence of the two methods we study the stability of the liquid phase in the canonical ensemble. We give evidence of a phase made of living polymers at low temperatures and provide a tentative phase diagram.

  16. Two-dimensional approach to relativistic positioning systems

    SciTech Connect

    Coll, Bartolome; Ferrando, Joan Josep; Morales, Juan Antonio [Systemes de reference relativistes, SYRTE-CNRS, Observatoire de Paris, 75014 Paris (France); Departament d'Astronomia i Astrofisica, Universitat de Valencia, 46100 Burjassot, Valencia (Spain)

    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.

  17. Novel Colloidal Crystalline States on Two Dimensional Periodic Substrates

    E-print Network

    C. Reichhardt; C. J. Olson

    2002-01-15

    We show using numerical simulations that a rich variety of novel colloidal crystalline states are realized on square and triangular two dimensional periodic substrates which can be experimentally created using crossed laser arrays. When there are more colloids than potential substrate minima, multiple colloids are trapped at each substrate minima and act as a single particle with a rotational degree of freedom, giving rise to a new type of orientational order. We call these states colloidal molecular crystals. A two-step melting can also occur in which individual colloidal molecules initially rotate, destroying the overall orientational order, followed by the onset of inter-well colloidal hopping.

  18. Two-dimensional symmetrical inlets with external compression

    NASA Technical Reports Server (NTRS)

    Ruden, P

    1950-01-01

    The purpose of inlets like, for instance, those of air-cooled radiators and scoops is to take a certain air quantity out of the free stream and to partly convert the free-stream velocity into pressure. In the extreme case this pressure conversion may occur either entirely in the interior of the inlet (inlet with internal compression) or entirely in the free stream ahead of the inlet (inlet with external compression). In this report a theory for two-dimensional inlets with external compression is developed and illustrated by numerical examples. Intermediary forms between inlets with internal and external compression which can be derived from the latter are briefly discussed.

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

    SciTech Connect

    Röcker, T. B., E-mail: tbr@mpe.mpg.de; Ivlev, A. V., E-mail: ivlev@mpe.mpg.de; Zhdanov, S. K.; Morfill, G. E. [Max Planck Institute for Extraterrestrial Physics, 85741 Garching (Germany); Couëdel, L. [CNRS, Aix-Marseille-Université, Laboratoire de Physique des Interactions Ioniques et Moléculaires, UMR 7345, 13397 Marseille Cedex 20 (France)

    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.

  20. Anomalous time correlation in two-dimensional driven diffusive systems.

    PubMed

    Nakamura, Takenobu; Otsuki, Michio; Sasa, Shin-ichi

    2005-06-01

    We study the time-correlation function of a density field in two-dimensional driven diffusive systems within the framework of fluctuating hydrodynamics. It is found that the time correlation exhibits power-law behavior in an intermediate time regime in the case that the fluctuation-dissipation relation is violated and that the power-law exponent depends on the extent of this violation. We obtain this result by employing a renormalization group method to treat a logarithmic divergence in time. PMID:16089722

  1. Harmonic Oscillator in Noncommuting Two-Dimensional Space

    Microsoft Academic Search

    Antony Streklas

    2007-01-01

    In the present paper, we study a two-dimensional harmonic oscillator in a constant magnetic field in noncommuting space. We use the following Hamiltonian [ H = 1\\/2 m (\\\\hat{p}_1^2+\\\\hat{p}_2^2) + 1\\/2 m\\\\omega_1^2\\\\hat{q}_1^2+ 1\\/2 m\\\\omega_2^2\\\\hat{q}_2^2, ] with commutation relations [hat {q}1, hat {q}2] = itheta , [hat {p}1,hat {p}_2]=ilambda and [hat {q}j, hat {p}k] = i hbar delta jk. The parameter

  2. 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.

  3. Universality of Probability Distributions Among Two-Dimensional Turbulent Flows

    E-print Network

    Norbert Schorghofer

    1999-07-09

    We study statistical properties of two-dimensional turbulent flows. Three systems are considered: the Navier-Stokes equation, surface quasi-geostrophic flow, and a model equation for thermal convection in the Earth's mantle. Direct numerical simulations are used to determine 1-point fluctuation properties. Comparative study shows universality of probability density functions (PDFs) across different types of flow. Especially for the derivatives of the ``advected'' quantity, the shapes of the PDFs are the same for the three flows, once normalized by the average size of fluctuations. Theoretical models for the shape of PDFs are briefly discussed.

  4. Taming chaos by impurities in two-dimensional oscillator arrays

    E-print Network

    M. Weiss; Tsampikos Kottos; T. Geisel

    2001-06-15

    The effect of impurities in a two-dimensional lattice of coupled nonlinear chaotic oscillators and their ability to control the dynamical behavior of the system are studied. We show that a single impurity can produce synchronized spatio-temporal patterns, even though all oscillators and the impurity are chaotic when uncoupled. When a small number of impurities is arranged in a way, that the lattice is divided into two disjoint parts, synchronization is enforced even for small coupling. The synchronization is not affected as the size of the lattice increases, although the impurity concentration tends to zero.

  5. 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

  6. Pattern formation in two-dimensional square-shoulder systems

    NASA Astrophysics Data System (ADS)

    Fornleitner, Julia; Kahl, Gerhard

    2010-03-01

    Using a highly efficient and reliable optimization tool that is based on ideas of genetic algorithms, we have systematically studied the pattern formation of the two-dimensional square-shoulder system. An overwhelming wealth of complex ordered equilibrium structures emerge from this investigation as we vary the shoulder width. With increasing pressure three structural archetypes could be identified: cluster lattices, where clusters of particles occupy the sites of distorted hexagonal lattices, lane formation, and compact particle arrangements with high coordination numbers. The internal complexity of these structures increases with increasing shoulder width.

  7. Pattern formation in two-dimensional square-shoulder systems.

    PubMed

    Fornleitner, Julia; Kahl, Gerhard

    2010-03-17

    Using a highly efficient and reliable optimization tool that is based on ideas of genetic algorithms, we have systematically studied the pattern formation of the two-dimensional square-shoulder system. An overwhelming wealth of complex ordered equilibrium structures emerge from this investigation as we vary the shoulder width. With increasing pressure three structural archetypes could be identified: cluster lattices, where clusters of particles occupy the sites of distorted hexagonal lattices, lane formation, and compact particle arrangements with high coordination numbers. The internal complexity of these structures increases with increasing shoulder width. PMID:21389452

  8. Fringe demodulation using the two-dimensional phase differencing operator.

    PubMed

    Rajshekhar, Gannavarpu; Rastogi, Pramod

    2012-10-15

    The Letter proposes a method for phase estimation from a fringe pattern. The proposed method relies on a parametric approach where the phase is locally approximated as a two-dimensional (2D) polynomial, with the ensuing polynomial coefficients as the respective parameters. These coefficients are then estimated using the phase differencing operator. Because of the 2D formulation, the proposed method simultaneously analyzes signal samples along the horizontal and vertical dimensions, which enables robust estimation in the presence of noise. In addition, the method directly provides the desired phase without the requirement of complex unwrapping algorithms. Simulation and experimental results are presented to validate the method's potential. PMID:23073436

  9. Two-dimensional solitons in a quintic-septimal medium

    NASA Astrophysics Data System (ADS)

    Reyna, Albert S.; Jorge, Kelly C.; de Araújo, Cid B.

    2014-12-01

    We report an observation of spatial solitons in a medium managed to present fifth-seventh (focusing-defocusing) refractive nonlinearities with suppressed third-order nonlinearity. Propagation of two-dimensional bright spatial solitons for ˜10 Rayleigh lengths was observed and characterized in a suspension of silver nanoparticles in acetone using the scattered light imaging method. Numerical calculations based on a nonlinear Schrödinger-type equation, including contributions up to the seventh-order susceptibility, were performed showing good agreement with the experimental results.

  10. Band structure engineering of two-dimensional magnonic vortex crystals

    NASA Astrophysics Data System (ADS)

    Behncke, Carolin; Hänze, Max; Adolff, Christian F.; Weigand, Markus; Meier, Guido

    2015-06-01

    Magnonic vortex crystals are studied via scanning transmission x-ray microscopy and ferromagnetic-resonance spectroscopy. We investigate a two-dimensional vortex crystal by imprinting waves with tunable wave vectors. The dispersion relation ? (k ) is determined via ferromagnetic-resonance spectroscopy with a tunable frequency and wave vector for two vortex core polarization patterns that are adjusted by self-organized state formation prior to the measurement. We demonstrate that the band structure of the crystal is reprogrammed by tuning the vortex polarizations.

  11. Percolation and epidemics in a two-dimensional small world

    NASA Astrophysics Data System (ADS)

    Newman, M. E.; Jensen, I.; Ziff, R. M.

    2002-02-01

    Percolation on two-dimensional small-world networks has been proposed as a model for the spread of plant diseases. In this paper we give an analytic solution of this model using a combination of generating function methods and high-order series expansion. Our solution gives accurate predictions for quantities such as the position of the percolation threshold and the typical size of disease outbreaks as a function of the density of ``shortcuts'' in the small-world network. Our results agree with scaling hypotheses and numerical simulations for the same model.

  12. SOLVING THE TWO-DIMENSIONAL DIFFUSION FLOW MODEL.

    USGS Publications Warehouse

    Hromadka, T.V., II; 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.

  13. Local diamagnetic susceptibility of quasi-two-dimensional graphite

    NASA Astrophysics Data System (ADS)

    Nikolaev, E. G.; Kotosonov, A. S.; Shalashugina, E. A.; Troyanovskii, A. M.; Tsebro, V. I.

    2013-08-01

    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 × 10-4 emu/g at T = 4.2 K, which is greater than the corresponding value of highly oriented graphite by a factor of four.

  14. 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.

  15. Double Dirac cones in two-dimensional dielectric photonic crystals.

    PubMed

    Li, Yan; Mei, Jun

    2015-05-01

    By exploiting the accidental degeneracy of the doubly-degenerate dipolar and quadrupolar modes, we show that a two-dimensional dielectric photonic crystal (PC) can exhibit the double Dirac cone dispersion relation at the ? point. Using a perturbation method and group theory, we demonstrate that the double cone is composed of two identical and overlapping Dirac cones with predictable linear slopes, and the linearity of the dispersion is guaranteed by the spatial symmetry of the Bloch eigenstates. Numerical simulations including wave-front shaping, unidirectional transmission and perfect tunneling show that the corresponding PC structure can be characterized by a zero effective refractive index. PMID:25969297

  16. Drift modes of a quasi-two-dimensional current sheet

    SciTech Connect

    Artemyev, A. V.; Malova, Kh. V.; Popov, V. Yu.; Zelenyi, L. M. [Russian Academy of Sciences, Space Research Institute (Russian Federation)

    2012-03-15

    Stability of a plasma configuration consisting of a thin one-dimensional current sheet embedded into a two-dimensional background current sheet is studied. Drift modes developing in plasma as unstable waves along the current direction are considered. Dispersion relations for kink and sausage perturbation modes are obtained depending on the ratio of parameters of thin and background current sheets. It is shown that the existence of the background sheet results in a decrease in the instability growth rates and a significant increase in the perturbation wavelengths. The role of drift modes in the excitation of oscillations observed in the current sheet of the Earth's magnetotail is discussed.

  17. Thermodynamics and phase transitions in two-dimensional Yukawa systems

    NASA Astrophysics Data System (ADS)

    Vaulina, O. S.; Koss, X. G.

    2014-10-01

    The results of numerical simulations of strongly-coupled two-dimensional dissipative Yukawa systems are presented. The thermodynamic characteristics of these systems were studied, namely the internal energy, the specific heat and the entropy. For the first time, it is discovered that the considered characteristics have two singular points on the melting line; one of these points corresponds to the first-order phase transition from crystal to the hexatic phase, and another point corresponds to the second-order phase transition from the hexatic phase to the isotropic liquid. The obtained results are compared to the existing numerical and analytical data.

  18. Boundary instability of a two-dimensional electron fluid

    SciTech Connect

    Dyakonov, M. I. [Universite Montpellier 2, CNRS, Laboratoire de Physique Theorique et Astroparticules (France)

    2008-08-15

    It was shown previously that the current-carrying state of a Field Effect Transistor with asymmetric source and drain boundary conditions may become unstable against spontaneous generation of plasma waves. By extending the analysis to the two-dimensional case we find that the dominant instability modes correspond to waves propagating in the direction perpendicular to the current and localized near the boundaries. This new type of instability should result in plasma turbulence with a broad frequency spectrum. More generally, it is shown that a similar instability might exist, when a strong enough current goes through a single boundary between the gated and ungated regions.

  19. Two-Dimensional Manipulation of Magnetic Nanoparticles in Microfluidic Systems

    NASA Astrophysics Data System (ADS)

    Cao, Quanliang; Han, Xiaotao; Li, Liang

    2013-02-01

    A magnetic manipulation technique based on a superimposed gradient magnetic field source for controlling magnetic nanoparticles in microfluidic channels was proposed. The designed magnetic field is composed of one gradient magnetic field generated by micro-electromagnetic coils positioned near a microfluidic channel and one external uniform magnetic field generated by large Helmholtz coil pairs. By controlling the configuration of Helmholtz coils, magnetic nanoparticles can be transported in different movement modes. As a proof of concept, the transport behavior of magnetic nanoparticles under different configurations of Helmholtz coils was successfully performed in two-dimensional (2D) geometries.

  20. The melting of the classical two dimensional Wigner crystal

    E-print Network

    Martial Mazars

    2015-04-08

    We report an extensive Monte-Carlo study of the melting of the classical two dimensional Wigner crystal for a system of point particles interacting via the $1/r$-Coulomb potential. A hexatic phase is found in systems large enough. With the multiple histograms method and the finite size scaling theory, we show that the fluid/hexatic phase transition is weakly first order. No set of critical exponents, consistent with a Kosterlitz-Thouless transition and the finite size scaling analysis for this transition, have been found.

  1. The melting of the classical two-dimensional Wigner crystal

    NASA Astrophysics Data System (ADS)

    Mazars, M.

    2015-04-01

    We report an extensive Monte Carlo study of the melting of the classical two-dimensional Wigner crystal for a system of point particles interacting via the 1/r-Coulomb potential. A hexatic phase is found in large enough systems. With the multiple histograms method and the finite-size scaling theory, we show that the fluid/hexatic phase transition is weakly first order. No set of critical exponents, consistent with a Kosterlitz-Thouless transition and the finite-size scaling analysis for this transition, has been found.

  2. Nonlinear Cascades in Two-Dimensional Turbulent Magnetoconvection

    SciTech Connect

    Skandera, Dan; Mueller, Wolf-Christian [Max-Planck-Institut fuer Plasmaphysik, 85748 Garching (Germany)

    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.

  3. Creating arbitrary arrays of two-dimensional topological defects

    NASA Astrophysics Data System (ADS)

    Murray, Bryce S.; Pelcovits, Robert A.; Rosenblatt, Charles

    2014-11-01

    An atomic force microscope was used to scribe a polyimide-coated substrate with complex patterns that serve as an alignment template for a nematic liquid crystal. By employing a sufficiently large density of scribe lines, two-dimensional topological defect arrays of arbitrary defect strength were patterned on the substrate. When used as the master surface of a liquid crystal cell, in which the opposing slave surface is treated for planar degenerate alignment, the liquid crystal adopts the pattern's alignment with a disclination line emanating at the defect core on one surface and terminating at the other surface.

  4. Creating arbitrary arrays of two-dimensional topological defects.

    PubMed

    Murray, Bryce S; Pelcovits, Robert A; Rosenblatt, Charles

    2014-11-01

    An atomic force microscope was used to scribe a polyimide-coated substrate with complex patterns that serve as an alignment template for a nematic liquid crystal. By employing a sufficiently large density of scribe lines, two-dimensional topological defect arrays of arbitrary defect strength were patterned on the substrate. When used as the master surface of a liquid crystal cell, in which the opposing slave surface is treated for planar degenerate alignment, the liquid crystal adopts the pattern's alignment with a disclination line emanating at the defect core on one surface and terminating at the other surface. PMID:25493804

  5. Longitudinal viscosity of two-dimensional Yukawa liquids

    NASA Astrophysics Data System (ADS)

    Feng, Yan; Goree, J.; Liu, Bin

    2013-01-01

    The longitudinal viscosity ?l is obtained for a two-dimensional (2D) liquid using a Green-Kubo method with a molecular dynamics simulation. The interparticle potential used has the Debye-Hückel or Yukawa form, which models a 2D dusty plasma. The longitudinal ?l and shear ?s viscosities are found to have values that match very closely, with only negligible differences for the entire range of temperatures that is considered. For a 2D Yukawa liquid, the bulk viscosity ?b is determined to be either negligibly small or not a meaningful transport coefficient.

  6. Longitudinal viscosity of two-dimensional Yukawa liquids.

    PubMed

    Feng, Yan; Goree, J; Liu, Bin

    2013-01-01

    The longitudinal viscosity ?(l) is obtained for a two-dimensional (2D) liquid using a Green-Kubo method with a molecular dynamics simulation. The interparticle potential used has the Debye-Hückel or Yukawa form, which models a 2D dusty plasma. The longitudinal ?(l) and shear ?(s) viscosities are found to have values that match very closely, with only negligible differences for the entire range of temperatures that is considered. For a 2D Yukawa liquid, the bulk viscosity ?(b) is determined to be either negligibly small or not a meaningful transport coefficient. PMID:23410445

  7. General relativity as a two-dimensional CFT

    E-print Network

    Tim Adamo

    2015-05-21

    The tree-level scattering amplitudes of general relativity encode the full non-linearity 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 CFT, with the Einstein equations emerging as quantum consistency conditions.

  8. Kinetic analysis of two dimensional metallic grating Cerenkov maser

    SciTech Connect

    Zhao Ding [Key Laboratory of High Power Microwave Sources and Technologies, Institute of Electronics, Chinese Academy of Sciences, Beijing 100190 (China)

    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.

  9. Transfer-matrix analysis of a two-dimensional quasicrystal

    SciTech Connect

    Widom, M.; Deng, D. P.; Henley, C. L.

    1989-07-17

    We investigate the quasicrystalline state of a two-dimensional binary alloy in a discrete tiling approximation. Through transfer-matrix calculations we determine the configurational entropy over a range of concentrations. We find that the entropy density is maximized by a state with tenfold symmetry at the quasicrystal concentration. Derivatives of the entropy density at its maximum yield values for the phason elastic constants. Our results confirm the existence of quasi-long-range translational order in equilibrium quasicrystalline alloys and lend support to the random-tiling model of quasicrystals.

  10. Fractional-step method for two-dimensional estuarine transport

    USGS Publications Warehouse

    Bales, Jerad D.; Holley, Edward R.

    1988-01-01

    The fractional-step method was used in this study to split the longitudinal advective transport term from the other terms in the two-dimensional, laterally-averaged equation for estuarine mass transport. The method of characteristics with spline interpolations was used to approximate the longitudinal advective transport. A general discussion of the fractional-step method, the specific algorithm developed in this investigation, and results of numerical tests are presented. Application of the fractional-step method in conjunction with the characteristic-spline scheme offers the potential for improved simulations of transport for situations in which concentration gradients are steep.

  11. 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.

  12. 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.

  13. 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.

  14. 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.

  15. 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.

  16. Resonance lineshapes in two-dimensional Fourier transform spectroscopy.

    PubMed

    Siemens, Mark E; Moody, Galan; Li, Hebin; Bristow, Alan D; Cundiff, Steven T

    2010-08-16

    We derive an analytical form for resonance lineshapes in two-dimensional (2D) Fourier transform spectroscopy. Our starting point is the solution of the optical Bloch equations for a two-level system in the 2D time domain. Application of the projection-slice theorem of 2D Fourier transforms reveals the form of diagonal and cross-diagonal slices in the 2D frequency data for arbitrary inhomogeneity. The results are applied in quantitative measurements of homogeneous and inhomogeneous broadening of multiple resonances in experimental data. PMID:20721156

  17. Phonon dispersion in hypersonic two-dimensional phononic crystal membranes

    NASA Astrophysics Data System (ADS)

    Graczykowski, B.; Sledzinska, M.; Alzina, F.; Gomis-Bresco, J.; Reparaz, J. S.; Wagner, M. R.; Sotomayor Torres, C. M.

    2015-02-01

    We investigate experimentally and theoretically the acoustic phonon propagation in two-dimensional phononic crystal membranes. Solid-air and solid-solid phononic crystals were made of square lattices of holes and Au pillars in and on 250 nm thick single crystalline Si membrane, respectively. The hypersonic phonon dispersion was investigated using Brillouin light scattering. Volume reduction (holes) or mass loading (pillars) accompanied with second-order periodicity and local resonances are shown to significantly modify the propagation of thermally activated GHz phonons. We use numerical modeling based on the finite element method to analyze the experimental results and determine polarization, symmetry, or three-dimensional localization of observed modes.

  18. Observation of Periodic Orbits on Curved Two - dimensional Geometries

    E-print Network

    M. Avlund; C. Ellegaard; M. Oxborrow; T. Guhr; N. Sondergaard

    2010-04-26

    We measure elastomechanical spectra for a family of thin shells. We show that these spectra can be described by a "semiclassical" trace formula comprising periodic orbits on geodesics, with the periods of these orbits consistent with those extracted from experiment. The influence of periodic orbits on spectra in the case of two-dimensional curved geometries is thereby demonstrated, where the parameter corresponding to Planck's constant in quantum systems involves the wave number and the curvature radius. We use these findings to explain the marked clustering of levels when the shell is hemispherical.

  19. Magnetotransport measurements on freely suspended two-dimensional electron gases

    NASA Astrophysics Data System (ADS)

    Blick, R. H.; Monzon, F. G.; Wegscheider, W.; Bichler, M.; Stern, F.; Roukes, M. L.

    2000-12-01

    We present magnetotransport measurements on freely suspended two-dimensional electron gases from AlxGa1-xAs/GaAs heterostructures. The technique to realize such devices relies on a specially molecular beam epitaxy grown GaAs/AlxGa1-xAs-heterostructure, including a sacrificial layer. We fabricated simple mini-Hall-bars as well as quantum cavities and quantum dot systems. We find well-pronounced Shubnikov-de Haas oscillations and observe commensurability resonances, allowing characterization of the electron gas in these 100-nm thin membranes.

  20. Seabed disposal project two-dimensional axisymmetric penetrometer simulations

    SciTech Connect

    Chavez, P.F.; Dawson, P.R.; Schuler, K.W.

    1980-03-01

    Preliminary two-dimensional, one-constituent hole closure analyses of an experimental apparatus and the flow of in situ ocean sediments following a penetrometer explacement have been performed. Boundary conditions associated with the experimental apparatus were found to greatly affect cavity response. Difficulties were encountered in modelling penetrometer-sediment interfaces and in obtaining smooth stress histories. The use of a different computer code in later analyses led to more realistic penetrometer-sediment interface models and to improved success in obtaining stress histories. These results along with some recommendations for future work are presented.

  1. Autocorrelation-based reconstruction of two-dimensional binary objects

    NASA Astrophysics Data System (ADS)

    Mejia-Barbosa, Yobani; Castaneda-Sepulveda, Roman

    2006-02-01

    A method for reconstructing two-dimensional binary objects from its autocorrelation function is discussed. The objects consist of a finite set of identical elements. The reconstruction algorithm is based on the concept of class of element pairs, defined as the set of element pairs with the same separation vector. This concept allows solving the redundancy introduced by the element pairs of each class. It is also shown that different objects, consisting of equal number of elements and the same classes of pairs, provide Fraunhofer diffraction patterns with identical intensity distributions. However, the method predicts all the possible objects that produce the same Fraunhofer pattern.

  2. 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.

  3. Multi-Instanton Effect in Two-Dimensional QCD

    NASA Astrophysics Data System (ADS)

    Ochiai, Tetsuyuki

    We analyze multi-instanton sector in two-dimensional U(N) Yang-Mills theory on a sphere. We obtain a contour integral representation of the multi-instanton amplitude and find “neutral” configurations of the even number instantons dominate in the large-N limit. Using this representation, we calculate the 1-, 2-, 3-, 4-body interactions and the free energies for N=3, 4, 5 numerically and find that the multi-instanton interaction effect essentially contributes to the large-N phase transition discovered by Douglas and Kazakov.

  4. Two-dimensional conformal field theory and the butterfly effect

    E-print Network

    Daniel A. Roberts; Douglas Stanford

    2015-02-04

    We study chaotic dynamics in two-dimensional conformal field theory through out-of-time order thermal correlators of the form $\\langle W(t)VW(t)V\\rangle$. We reproduce bulk calculations similar to those of [1], by studying the large $c$ Virasoro identity block. The contribution of this block to the above correlation function begins to decrease exponentially after a delay of $\\sim t_* - \\frac{\\beta}{2\\pi}\\log \\beta^2E_w E_v$, where $t_*$ is the scrambling time $\\frac{\\beta}{2\\pi}\\log c$, and $E_w,E_v$ are the energy scales of the $W,V$ operators.

  5. Influence of index contrast in two dimensional photonic crystal lasers

    NASA Astrophysics Data System (ADS)

    Jørgensen, Mette Marie; Petersen, Sidsel Rübner; Christiansen, Mads Brøkner; Buß, Thomas; Smith, Cameron L. C.; Kristensen, Anders

    2010-06-01

    The influence of index contrast variations for obtaining single-mode operation and low threshold in dye doped polymer two dimensional photonic crystal (PhC) lasers is investigated. We consider lasers made from Pyrromethene 597 doped Ormocore imprinted with a rectangular lattice PhC having a cavity in the middle of the crystal structure. We demonstrate that the index contrast, neff,high/neff,low, is an essential parameter for achieving low threshold, and we identify a trade-off between low threshold and single-mode operation.

  6. Competing Orders in two-dimensional Bose-Fermi mixtures

    Microsoft Academic Search

    L. Mathey; S.-W. Tsai; A. H. Castro Neto

    2006-01-01

    Using a functional renormalization group approach we study the zero\\u000atemperature phase diagram of two-dimensional Bose-Fermi mixtures of ultra-cold\\u000aatoms in optical lattices, in the limit when the velocity of bosonic condensate\\u000afluctuations are much larger than the Fermi velocity.\\u000a For spin-1\\/2 fermions we obtain a phase diagram, which shows a competition of\\u000apairing phases of various orbital symmetry ($s$,

  7. Hydrodynamic forces induced by a solitary wave on a submerged circular cylinder

    SciTech Connect

    Clement, A.; Mas, S. [Lab. de Mecanique des Fluides, Nantes (France)

    1995-12-31

    A numerical two dimensional wave basin has been developed in the framework of potential theory on nonlinear free-surface flows. This general purpose computer code was used in this study to investigate systematically the interaction between a solitary wave and a fixed submerged circular cylinder. For a given submergence, different flow evolutions were encountered; their features are shown to depend on soliton amplitude and cylinder diameter. A quantitative study of hydrodynamic forces during the interaction is also presented.

  8. Two-dimensional skyrmions and other solitonic structures in confinement-frustrated chiral nematics

    NASA Astrophysics Data System (ADS)

    Ackerman, Paul J.; Trivedi, Rahul P.; Senyuk, Bohdan; van de Lagemaat, Jao; Smalyukh, Ivan I.

    2014-07-01

    We explore spatially localized solitonic configurations of a director field, generated using optical realignment and laser-induced heating, in frustrated chiral nematic liquid crystals confined between substrates with perpendicular surface anchoring. We demonstrate that, in addition to recently studied torons and Hopf-fibration solitonic structures (hopfions), one can generate a host of other axially symmetric stable and metastable director field configurations where local twist is matched to the surface boundary conditions through introduction of point defects and loops of singular and nonsingular disclinations. The experimentally demonstrated structures include the so-called "baby-skyrmions" in the form of double twist cylinders oriented perpendicular to the confining substrates where their double twist field configuration is matched to the perpendicular boundary conditions by loops of twist disclinations. We also generate complex textures with arbitrarily large skyrmion numbers. A simple back-of-the-envelope theoretical analysis based on free energy considerations and the nonpolar nature of chiral nematics provides insights into the long-term stability and diversity of these inter-related solitonic field configurations, including different types of torons, cholestric-finger loops, two-dimensional skyrmions, and more complex structures comprised of torons, hopfions, and various disclination loops that are experimentally observed in a confinement-frustrated chiral nematic system.

  9. Wavelength dependence of focusing properties of two-dimensional photonic quasicrystal flat lens.

    PubMed

    Liu, Jianjun; Fan, Zhigang; Hu, Haili; Yang, Maohua; Guan, Chunying; Yuan, Libo; Guo, Hao; Zhang, Xiong

    2012-05-15

    We investigated the wavelength dependence of the focusing properties of a germanium-cylinder-based two-dimensional (2D) decagonal Penrose-type photonic quasicrystal (PQC) flat lens for the first time, to the best of our knowledge. We found that near the second bandgap and in the high-frequency side (between the bandgap boundary and the first light intensity peak) of the pass band, the flat lens can exhibit a focusing effect for a point light source and that the focusing wavelengths can directly be drawn from the photonic band structure. For all the focusing wavelengths, the summation of the object distance and the image distance is less than the thickness of the flat lens when the object distance is half the thickness of the flat lens. As the wavelength increases, the image distance, the image quality, and the effective refractive index of the flat lens increase, whereas the image power of the point light source decreases. The effective refractive index of the flat lens is less than -1. PMID:22627552

  10. Guiding airborne sound through surface modes of a two-dimensional phononic crystal

    NASA Astrophysics Data System (ADS)

    Cicek, Ahmet; Gungor, Tayyar; Adem Kaya, Olgun; Ulug, Bulent

    2015-06-01

    Existence and guiding properties of surface modes bound to the interface between a finite two-dimensional phononic crystal and the host medium are experimentally and numerically demonstrated. Surface modes can be observed on both (1?0) and (1?1) surfaces of a square phononic crystal of steel cylinders in air. Numerical investigations of band properties and simulations of mode excitation are carried out through the finite-element method. Excited by the far field of a speaker, existence of surface modes is investigated by recording the sound field in the vicinity of the respective crystal surfaces. Both surface bands of the square phononic crystal depart from bulk bands and extend into the band gap for sufficiently high filling fractions. While such a surface band can be obtained for considerably smaller scatterer radii for the (1?0) surface, significantly higher radii around 0.49 of the lattice constant are required to obtain propagating surface modes on the (1?1) surface. Persistence of the guided surface mode along the (1?0) surface, where it diminishes in a length scale of the lattice constant in the transverse direction is demonstrated. The modes of the (1?1) surface decay faster into the air in the transverse direction. Guided modes on both surfaces propagate in a beating manner where the beat length can be determined by the wave number of the mode.

  11. Two-Dimensional, Optical Ellipsometric Studies of Polymer Orientation

    NASA Astrophysics Data System (ADS)

    Georgiev, Georgi; Berns, David; Cebe, Peggy

    2001-03-01

    Crystalline or liquid crystalline polymers exhibit optical birefringence as a result of formation of superstructures, such as spherulites, axialites, dendrites or liquid crystalline phases. Our method of choice for optical characterization is a variation of ellipsometry based on Stokes analysis. We use ellipsometry to measure the retardation and azimuthal angle of optically anisotropic polymeric materials. In addition, the embodiment of the method provides two-dimensional, i.e., spatially resolved, information about the optical parameters across the field of view. Monochromatic, incoherent light is polarized through states of differing ellipticity using liquid crystal variable retarders as universal compensator, as suggested by the method of Oldenbourg and Mei. After transmission through the polymer sample, the state of ellipticity of the polymer is quantitatively determined at every pixel in the two-dimensional optical image. To date we have investigated zone drawn polyethylene tapes, electrically activated liquid crystal display cells, and several thermotropic liquid crystalline polymers including Vectra. We aim to provide fundamental information about the formation of optically anisotropic structure, including measurement of phase transformation kinetics and development of textures.

  12. 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 MoS? and WSe? 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 MoS?-MoSe? and WS?-WSe? 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 WSe?-WS? 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. PMID:25262331

  13. 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.

  14. 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. PMID:16281030

  15. Analytical study of two-dimensional degenerate metamaterial antennas

    NASA Astrophysics Data System (ADS)

    Sakoda, Kazuaki; Zhou, Haifeng

    2011-07-01

    Dispersion curves of metamaterial steerable antennas composed of two-dimensional arrays of metallic unit structures with the C4v and C6v symmetries are calculated both qualitatively by the tight-binding approximation and quantitatively by the finite-difference time-domain method. Special attention is given to the case of eigenmodes of the E symmetry of the C4v point group and those of the E1 and E2 symmetries of the C6v point group, since they are doubly degenerate on the ? point of the Brillouin zone so that they naturally satisfy the steerability condition. We show that their dispersion curves have quadratic dependence on the wave vector in the vicinity of the ? point. To get a linear dispersion, which is advantageous for steerable antennas, we propose a method of controlled symmetry reduction. The present theory is an extension of our previous one [Opt. Express 18, 27371 (2010)] to two-dimensional systems, for which we can achieve the deterministic degeneracy due to symmetry and the controlled symmetry reduction becomes available. This design of metamaterial steerable antennas is advantageous in the optical frequency.

  16. Nonlocal transport in a hybrid two-dimensional topological insulator

    NASA Astrophysics Data System (ADS)

    Xing, Yanxia; Sun, Qing-feng

    2014-02-01

    We study nonlocal resistance in an H-shaped two-dimensional HgTe/CdTe quantum well consisting of an injector and a detector, both of which can be tuned in the quantum spin Hall or metallic spin Hall regime. Because of strong spin-orbit interaction, there always exists the spin Hall effect and nonlocal resistance in the HgTe/CdTe quantum well. We find that when both the detector and the injector are in the quantum spin Hall regime, the nonlocal resistance is quantized at 0.25he2, which is robust against weak disorder scattering and small magnetic field. When the detector or injector is beyond this regime, the nonlocal resistance decreases rapidly and will be strongly suppressed by disorder and magnetic field. In the presence of a strong magnetic field, the quantum spin Hall regime will be switched into the quantum Hall regime, and the nonlocal resistance will disappear. The nonlocal signal and its various manifestations in different hybrid regimes originate from the special band structure of the HgTe/CdTe quantum well, and they can be considered as the fingerprint of the helical quantum spin Hall edge states in a two-dimensional topological insulator.

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

    NASA Astrophysics Data System (ADS)

    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.

  18. Transient Hydrodynamic Experiments in a Two-Dimensional Axisymmetric Geometry

    NASA Astrophysics Data System (ADS)

    Diab, Aya; Corradini, Michael

    2006-11-01

    Two dimensional experiments have been undertaken to study the phenomenon of liquid entrainment associated with interfacial hydrodynamic instabilities, specifically the Rayleigh Taylor instability. The current work is part of an effort to understand the phenomenon of Rayleigh Taylor instability associated with a rapid superheated steam bubble expansion that may occur in a CANDU reactor. The experiments aim at quantifying the liquid entrainment in a two dimensional axisymmetric geometry for a range of operating pressures. This experimental work is similar to that undertaken three decades ago at MIT, but the geometry has been modified to decrease the blowdown chute volume in order to reduce the experimental uncertainties. The goal of this work is to characterize the entrainment phenomenon by two parameters that can be used to verify a semi-empirical model that is being developed in a parallel modeling effort. Specifically, the first parameter quantifies the width of the mixing zone and the second parameter quantifies the volumetric ratio between the entrained liquid and the mixing zone.

  19. Two-dimensional theory and simulation of free electron lasers

    SciTech Connect

    Kwan, T.J.T.; Cary, J.R.

    1981-01-01

    Two-dimensional homogeneous theory of free-electron lasers with a wiggler magnetic field of constant wavelength is formulated. It has been found from the theory that waves propagating obliquely with respect to the electron beam are always unstable with appreciable growth rates; therefore, mode competition among the on-axis and off-axis modes is an important consideration in the design of the free-electron laser. Furthermore, electromagnetic waves with group velocities opposite to the direction of electron beam propagation are absolutely unstable if k/sub o/v/sub o/ > ..omega../sub pe/(1/..gamma../sup 3/2/ + 1/..gamma../sup 1/2/). Due to strong nonlinear saturation levels of the low-frequency absolute instability, the dynamics of the electron beam and the generation of the high-frequency electromagnetic radiation can be severely affected. Two-dimensional particle simulations show that the efficiency of generation of the on-axis high-frequency electromagnetic wave decreases significantly due to instability of the off-axis modes. In addition, complete disruption of the electron beam and laser oscillation due to the onset of the absolute instability have been observed in simulations.

  20. Modeling two-dimensional detonations with detonation shock dynamics

    SciTech Connect

    Bdzil, J.B.; Stewart, D.S.

    1988-01-01

    In any explosive device, the chemical reaction of the explosive takes place in a thin zone just behind the shock front. The finite size of the reaction zone is responsible for: the pressure generated by the explosive being less near the boundaries, for the detonation velocity being lower near a boundary than away from it, and for the detonation velocity being lower for a divergent wave than for a plane wave. In computer models that are used for engineering design calculations, the simplest treatment of the explosive reaction zone is to ignore it completely. Most explosive modeling is still done this way. The neglected effects are small when the reaction zone is very much smaller than the explosive's physical dimensions. When the ratio of the explosive's detonation reaction-zone length to a representative system dimension is of the order of 1/100, neglecting the reaction zone is not adequate. An obvious solution is to model the reaction zone in full detail. At present, there is not sufficient computer power to do so economically. Recently we have developed an alternative to this standard approach. By transforming the governing equations to the proper intrinsic-coordinate frame, we have simplified the analysis of the two-dimensional reaction-zone problem. When the radius of curvature of the detonation shock is large compared to the reaction-zone length, the calculation of the two-dimensional reaction zone can be reduced to a sequence of one-dimensional problems. 9 refs., 5 figs.

  1. Scaling and self-similarity in two-dimensional hydrodynamics

    NASA Astrophysics Data System (ADS)

    Ercan, Ali; Kavvas, M. Levent

    2015-07-01

    The conditions under which depth-averaged two-dimensional (2D) hydrodynamic equations system as an initial-boundary value problem (IBVP) becomes self-similar are investigated by utilizing one-parameter Lie group of point scaling transformations. Self-similarity conditions due to the 2D k-? turbulence model are also investigated. The self-similarity conditions for the depth-averaged 2D hydrodynamics are found for the flow variables including the time, the longitudinal length, the transverse length, the water depth, the flow velocities in x- and y-directions, the bed shear stresses in x- and y-directions, the bed shear velocity, the Manning's roughness coefficient, the kinematic viscosity of the fluid, the eddy viscosity, the turbulent kinetic energy, the turbulent dissipation, and the production and the source terms in the k-? model. By the numerical simulations, it is shown that the IBVP of depth-averaged 2D hydrodynamic flow process in a prototype domain can be self-similar with that of a scaled domain. In fact, by changing the scaling parameter and the scaling exponents of the length dimensions, one can obtain several different scaled domains. The proposed scaling relations obtained by the Lie group scaling approach may provide additional spatial, temporal, and economical flexibility in setting up physical hydraulic models in which two-dimensional flow components are important.

  2. 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

  3. Integrable quantum hydrodynamics in two-dimensional phase space

    NASA Astrophysics Data System (ADS)

    Bettelheim, E.

    2013-12-01

    Quantum liquids in two dimensions represent interesting dynamical quantum systems for several reasons, among them the possibility of the existence of infinite hidden symmetries, such as conformal symmetry or the symmetry associated with area preserving diffeomorphisms. It is known that when the symmetry algebra is large enough, symmetry may fully prescribe the dynamics. However, the way this is borne out in two-dimensional hydrodynamics, both classical and quantum, is not fully understood. Here we take a step towards clarifying this issue, by focusing on a particular example, namely that of a two-dimensional phase space liquid which emerges when one considers the Calogero model, a many-body one-dimensional system interacting through an inverse square law potential. We demonstrate how the symmetry algebra of conserved quantities of the one-dimensional system is expressed in terms of the incompressible Euler hydrodynamics of point vortices in phase space. Due to a formal relation between quantum hydrodynamics and classical stochastic hydrodynamics, which is inherent in the method of stochastic quantization, the ideas and methods developed here may also have application in the study of stochastic classical hydrodynamics, after suitable modifications.

  4. Two-dimensional retention indices improve component identification in comprehensive two-dimensional gas chromatography of saffron.

    PubMed

    Jiang, Ming; Kulsing, Chadin; Nolvachai, Yada; Marriott, Philip J

    2015-06-01

    Comprehensive two-dimensional gas chromatography hyphenated with accurate mass time-of-flight mass spectrometry (GC × GC-accTOFMS) was applied for improved analytical accuracy of saffron analysis, by using retention indices in the two-dimensional separation. This constitutes 3 dimensions of identification. In addition to accTOFMS specificity, and first dimension retention indices ((1)I), a simple method involving direct multiple injections with stepwise isothermal temperature programming is described for construction of isovolatility curves for reference alkane series in GC × GC. This gives access to calculated second dimension retention indices ((2)I). Reliability of the calculated (2)I was evaluated by using a Grob test mixture, and saturated alkanes, revealing good correlation between previously reported I values from the literature, with R(2) correlation being 0.9997. This essentially recognizes the retention property of peaks in the GC × GC 2D space as being reducible to a retention index in each dimension, which should be a valuable tool supporting identification. The benefit of (2)I data, in supplementing (1)I and MS library matching, was clearly demonstrated by the progressive reduction of the number of possible compound matches for peaks observed in saffron. 114 analytes were assessed according to (1)I and (2)I values within ±20 index unit of reference values, and by MS spectrum matching above a match statistic of 750 (including mass accuracy of the molecular ion <20 ppm) and their possible identities derived. The described method provides a new avenue to utilize the full capability of the two-dimensional separation (GC × GC), in combination with MS library matching in complex sample analysis, to provide improved component identification. PMID:25936794

  5. 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, 82-85. [2] Takayanagi et al. (1999) Proc. 1999 IEEE workshop on Charge-Coupled Devices and Advanced Image Sensors, 159-162. [3] Kunihiro et al. (2001) Nucl. Instrum. Methods Phys. Res. Sec. A 470, 512-519. [4] Nagashima et al. (2001) Surface Interface Anal. 31, 131-137. [5] Takayanagi et al. (2003) IEEE Trans. Electron Dev. 50, 70- 76. [6] Sakamoto and Yurimoto (2006) Surface Interface Anal. 38, 1760-1762. [7] Yamamoto et al. (2010) Surface Interface Anal. 42, 1603-1605. [8] Sakamoto et al. (2012) Jpn. J. Appl. Phys. 51, 076701. [9] Yurimoto et al. (2003) Appl. Surf. Sci. 203-204, 793-797. [10] Nagashima et al. (2004) Nature 428, 921-924. [11] Kunihiro et al. (2005) Geochim. Cosmochim. Acta 69, 763-773. [12] Nakamura et al. (2005) Geology 33, 829-832. [13] Sakamoto et al. (2007) Science 317, 231-233. [14] Greenwood et al. (2008) Geophys. Res. Lett., 35, L05203. [15] Greenwood et al. (2011) Nature Geoscience 4, 79-82. [16] Park et al. (2012) Meteorit. Planet. Sci. 47, 2070-2083. [17] Hashiguchi et al. (2013) Geochim. Cosmochim. Acta. 122, 306-323.

  6. Heated graphite cylinder electrodes

    Microsoft Academic Search

    Jian-Jun Sun; Liang Guo; De-Feng Zhang; Wen-Hui Yin; Guo-Nan Chen

    2007-01-01

    A new heated graphite cylinder electrode (HGCE) has been successfully fabricated, which arrangement is similar to that of the heated metal (Pt or Au) wire electrode invented by Grundler. The cylinders’ diameters range from ca. 95 to 300?m obtained by grinding the commercial available pencil graphite. HGCEs demonstrate rapid responses to the heating up and high thermal stability during being

  7. Optical properties of two-dimensional metamaterial photonic crystals

    SciTech Connect

    Mejía-Salazar, J. R. [Departamento de Física, Universidad del Valle, AA 25360, Cali, Colombia and Instituto de Física, UNICAMP, Campinas-SP 13083-859 (Brazil)

    2013-12-14

    In the present work, we theoretically study a 2D photonic crystal (PC) comprised by double negative (DNG) metamaterial cylinders, showing that such a system presents a superior light-matter interaction when compared with their single negative (SNG) plasmonic PC counterparts, suggesting a route to enhance the performance of sensors and photovoltaic cells. On the other hand, we have observed that depending on the frequency, the mode symmetry resembles either the case of SNG electric (SNG-E) or SNG magnetic (SNG-M) PC, suggesting that either the electric or magnetic character of the DNG metamaterial dominates in each case.

  8. 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 can benefit from this algorithm, including optics, image-processing, signal-processing, and engineering applications.

  9. 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 the presence of surfactant micelles. Finally, the diffusion-ordered experiment was used to study the polymer induced breakdown of micelles consisting of cetyltrimethylammonium bromide and sodium salicylate. Addition of the polymer poly(vinyl methyl ether) resulted in an increase in the micelle diffusion coefficient and at high polymer concentrations and elevated temperatures the polymer and micelle were observed to diffuse at the same rate.

  10. Bond order solid of two-dimensional dipolar fermions.

    PubMed

    Bhongale, S G; Mathey, L; Tsai, Shan-Wen; Clark, Charles W; Zhao, Erhai

    2012-04-01

    The recent experimental realization of dipolar Fermi gases near or below quantum degeneracy provides an opportunity to engineer Hubbard-like models with long-range interactions. Motivated by these experiments, we chart out the theoretical phase diagram of interacting dipolar fermions on the square lattice at zero temperature and half filling. We show that, in addition to p-wave superfluid and charge density wave order, two new and exotic types of bond order emerge generically in dipolar fermion systems. These phases feature homogeneous density but periodic modulations of the kinetic hopping energy between nearest or next-nearest neighbors. Similar, but manifestly different, phases of two-dimensional correlated electrons have previously only been hypothesized and termed "density waves of nonzero angular momentum." Our results suggest that these phases can be constructed flexibly with dipolar fermions, using currently available experimental techniques. PMID:22540802

  11. Two-dimensional optical thermal ratchets based on Fibonacci spirals.

    PubMed

    Xiao, Ke; Roichman, Yael; Grier, David G

    2011-07-01

    An ensemble of symmetric potential energy wells arranged at the vertices of a Fibonacci spiral can serve as the basis for an irreducibly two-dimensional thermal ratchet. Periodic rotation of the potential energy landscape through a three-step cycle drives trapped Brownian particles along spiral trajectories through the pattern. Which spiral is selected depends on the angular displacement at each step, with transitions between selected spirals arising at rational proportions of the golden angle. Fibonacci spiral ratchets therefore display an exceptionally rich range of transport properties, including inhomogeneous states in which different parts of the pattern induce motion in different directions. Both the radial and angular components of these trajectories can undergo flux reversal as a function of the scale of the pattern or the rate of rotation. PMID:21867137

  12. Design and fabrication of a two dimensional valveless micropump

    SciTech Connect

    Kahl, W.K.; Egert, C.M.; Hylton, K.W. [Oak Ridge National Lab., TN (United States)

    1995-12-31

    The scale-down of a liquid mini-pump (order of 10 mm) to a micrometre scale has been attempted using a novel valveless nozzle-diffuser design and new application of an organic physical vapor-deposited membrane. The micropump employs no moving parts other than the membrane and accomplishes the rectification of fluid flow due to pressure recovery differences in the nozzle and diffuser flow directions. More specifically, liquids flow with less resistance (i.e. conduct more fluid) in the diffuser direction than the nozzle direction, for a given pressure differential. At the micrometre scale, the fabrication of the critical nozzle and diffuser elements was performed by focused ion beam (FIB) microlithography of glass slides. Etched slides were sandwiched to make two-dimensional venturis. Sternme and Sternme noted the importance of a lower Reynolds Number linfit on the desired pressure recovery which challenged the fabrication of this pump design at the scale used.

  13. 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

  14. Two-dimensional optical thermal ratchets based on Fibonacci spirals

    NASA Astrophysics Data System (ADS)

    Xiao, Ke; Roichman, Yael; Grier, David G.

    2011-07-01

    An ensemble of symmetric potential energy wells arranged at the vertices of a Fibonacci spiral can serve as the basis for an irreducibly two-dimensional thermal ratchet. Periodic rotation of the potential energy landscape through a three-step cycle drives trapped Brownian particles along spiral trajectories through the pattern. Which spiral is selected depends on the angular displacement at each step, with transitions between selected spirals arising at rational proportions of the golden angle. Fibonacci spiral ratchets therefore display an exceptionally rich range of transport properties, including inhomogeneous states in which different parts of the pattern induce motion in different directions. Both the radial and angular components of these trajectories can undergo flux reversal as a function of the scale of the pattern or the rate of rotation.

  15. Symmetry breaking of solitons in two-dimensional complex potentials.

    PubMed

    Yang, Jianke

    2015-02-01

    Symmetry breaking is reported for continuous families of solitons in the nonlinear Schrödinger equation with a two-dimensional complex potential. This symmetry breaking is forbidden in generic complex potentials. However, for a special class of partially parity-time-symmetric potentials, it is allowed. At the bifurcation point, two branches of asymmetric solitons bifurcate out from the base branch of symmetry-unbroken solitons. Stability of these solitons near the bifurcation point are also studied, and two novel properties for the bifurcated asymmetric solitons are revealed. One is that at the bifurcation point, zero and simple imaginary linear-stability eigenvalues of asymmetric solitons can move directly into the complex plane and create oscillatory instability. The other is that the two bifurcated asymmetric solitons, even though having identical powers and being related to each other by spatial mirror reflection, can possess different types of unstable eigenvalues and thus exhibit nonreciprocal nonlinear evolutions under random-noise perturbations. PMID:25768620

  16. Application of Two Dimensional Flourescence Spectroscopy to Transition Metal Clusters.

    NASA Astrophysics Data System (ADS)

    Kokkin, Damian L.; Steimle, Timothy

    2014-06-01

    Determining the physical properties (bond lengths, angles, dipole moments, etc) of transition metal oxides and dioxides is relevant to catalysis, high temperature chemistry, materials science and astrophysics. Analysis of optical spectra is a convenient method for extraction of physical properties, but can be difficult because of the density of electronic states and in the case of the dioxides, presence of both the oxide and superoxide forms. Here we demonstrate the application of two dimensional fluorescence spectroscopy for aiding in the assignment and analysis. Particular attention will be paid to the spectroscopy of first row transition metal monoxides and dioxides of Nickel, NiO and NiO_2, and Manganese, MnO. Furthermore, the application of this technique to discovering the spectrum of other transition metal systems such as Metal-dicarbides will be outlined. N.J. Reilly, T.W. Schmidt, S.H. Kable, J. Phys. Chem. A., 110(45), 12355-12359, 2006

  17. 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

  18. Universal Conductance Fluctuation in Two-Dimensional Topological Insulators.

    PubMed

    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

  19. The Two Dimensional Euler Equations on Singular Exterior Domains

    NASA Astrophysics Data System (ADS)

    Gérard-Varet, David; Lacave, Christophe

    2015-05-01

    This paper is a follow-up of uc(Gérard-Varet) and uc(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 uc(Gérard-Varet) and uc(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).

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

    SciTech Connect

    De Vita, G.; Valentini, F.; Servidio, S.; Primavera, L.; Carbone, V.; Veltri, P. [Dipartimento di Fisica, Università della Calabria, 87036 Rende, CS (Italy); Sorriso-Valvo, L. [CNR-IPCF - U.O.S. di Cosenza, 87036 Rende, CS (Italy); Space Sciences Laboratory, University of California, Berkeley, California 94720 (United States)

    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 ? 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.

  1. 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.

  2. Exit Time Distribution in Spherically Symmetric Two-Dimensional Domains

    NASA Astrophysics Data System (ADS)

    Rupprecht, J.-F.; Bénichou, O.; Grebenkov, D. S.; Voituriez, R.

    2015-01-01

    The distribution of exit times is computed for a Brownian particle in spherically symmetric two-dimensional domains (disks, angular sectors, annuli) and in rectangles that contain an exit on their boundary. The governing partial differential equation of Helmholtz type with mixed Dirichlet-Neumann boundary conditions is solved analytically. We propose both an exact solution relying on a matrix inversion, and an approximate explicit solution. The approximate solution is shown to be exact for an exit of vanishing size and to be accurate even for large exits. For angular sectors, we also derive exact explicit formulas for the moments of the exit time. For annuli and rectangles, the approximate expression of the mean exit time is shown to be very accurate even for large exits. The analysis is also extended to biased diffusion. Since the Helmholtz equation with mixed boundary conditions is encountered in microfluidics, heat propagation, quantum billiards, and acoutics, the developed method can find numerous applications beyond exit processes.

  3. 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.

  4. Two-dimensional acoustic metamaterial with negative modulus

    NASA Astrophysics Data System (ADS)

    Ding, Changlin; Hao, Limei; Zhao, Xiaopeng

    2010-10-01

    We designed a two-dimensional acoustic metamaterial with periodical array of split hollow sphere (SHS) and investigated its transmission behaviors in the impedance tube system. The results showed that the acoustic metamaterial exhibited a transmission dip and inverse phase close to 5 kHz, which indicated the local resonance of SHS. Based on the homogeneous-media theory, the effective modulus of the acoustic metamaterial was calculated to be negative. The finite element method and resonant model simulation results also confirmed the local resonance and negative response in acoustic metamaterial, which agreed well with experiment results. This metamaterial is able to achieve the double negative acoustic metamaterial conveniently by arraying acoustic "atoms" with negative mass density in the matrix.

  5. Two dimensional heteronuclear complexes with cyanide and 4-aminomethylpyridine ligands

    NASA Astrophysics Data System (ADS)

    Karaa?aç, Dursun; Kürkçüo?lu, Güne? Süheyla; Ye?ilel, Okan Zafer; MuratTa?

    2014-09-01

    Two new cyano-bridged two-dimensional heteronuclear complexes, [Cd(NH3)2(?-ampy)Ni(?-CN)2(CN)2]n (1) and [Cd(H2O)2(?-ampy)Pt(?-CN)2(CN)2]n (2) (ampy = 4-aminomethylpyridine), were synthesized and characterized by FT-IR and Raman spectroscopic, thermal (TG, DTG and DTA) and elemental analyses and single crystal X-ray diffraction techniques. They crystallize in the triclinic system and P-1 space group. The Ni(II) or Pt(II) ions are four coordinate with four cyanide-carbon atoms in a square planar geometry and the Cd(II) ion exhibits a distorted octahedral coordination by two different N-atoms from two symmetrically equivalent ampy ligands, two ammine or aqua ligands and two bridging cyano groups.The most important features of the complexes are the presence of obvious M⋯? (M = Ni(II) or Pt(II)) interactions.

  6. Supported phospholipid bilayers for two-dimensional protein crystallization.

    PubMed

    Uzgiris, E E

    1986-01-29

    Phospholipid bilayers, supported on UV irradiated carbon shadowed nitrocellulose electron microscope grids, have been used to induce two-dimensional crystal growth of IgE and IgG anti-DNP monoclonal antibodies. The UV irradiation renders the grids hydrophilic in a very uniform fashion and allows for the transfer of phospholipid monolayers from an air/water interface in a sequential dipping procedure. The surface coverage achieved was nearly 100% as measured by antibody binding and by the formation of protein arrays on the bilayer covered grids. The supported bilayers appear to be stably held and are appropriate for slow binding conditions and long incubation times with low concentrations of binding protein. PMID:3947352

  7. Collecting electron crystallographic data of two-dimensional protein crystals.

    PubMed

    Hite, Richard K; Schenk, Andreas D; Li, Zongli; Cheng, Yifan; Walz, Thomas

    2010-01-01

    Similar to X-ray crystallography, which requires three-dimensional (3D) crystals, electron crystallography is used to obtain structural information for proteins that form two-dimensional (2D) crystals. However, unlike data collection in X-ray crystallography, which is typically fast and straightforward, data collection in electron crystallography can take months to years and requires substantial expertise. In this contribution, we first discuss the proper preparation of 2D crystals for electron microscopy, which, besides the quality of the 2D crystals, may be the most defining parameter for successful data collection. In the second part, we describe the procedures used to record high-resolution images and diffraction patterns. PMID:20887861

  8. Two-dimensional quantum gas in a hybrid surface trap

    NASA Astrophysics Data System (ADS)

    Gillen, J. I.; Bakr, W. S.; Peng, A.; Unterwaditzer, P.; Fölling, S.; Greiner, M.

    2009-08-01

    We demonstrate the realization of a two-dimensional (2D) quantum gas in a smooth optical surface trap. Using a combination of evanescent wave, standing wave, and magnetic potentials, we create a long-lived quantum gas deep in the 2D regime at a distance of a few microns from a glass surface. To realize a system suitable for many-body quantum simulation, we introduce methods such as broadband “white” light to create evanescent and standing waves to realize a smooth potential with a trap frequency aspect ratio of 300:1:1. We are able to detect phase fluctuations and vortices, and we demonstrate cooling to degeneracy and low disorder in the 2D configuration.

  9. Dissipative, forced turbulence in two-dimensional magnetohydrodynamics

    NASA Technical Reports Server (NTRS)

    Fyfe, D.; Montgomery, D.; Joyce, G.

    1976-01-01

    The equations of motion for turbulent two-dimensional magnetohydrodynamic flows are solved in the presence of finite viscosity and resistivity, for the case in which external forces (mechanical and/or magnetic) act on the fluid. The goal is to verify the existence of a magnetohydrodynamic dynamo effect which is represented mathematically by a substantial back-transfer of mean square vector potential to the longest allowed Fourier wavelengths. External forces consisting of a random part plus a fraction of the value at the previous time step are employed, after the manner of Lilly for the Navier-Stokes case. The regime explored is that for which the mechanical and magnetic Reynolds numbers are in the region of 100 to 1000. The conclusions are that mechanical forcing terms alone cannot lead to dynamo action, but that dynamo action can result from either magnetic forcing terms or from both mechanical and magnetic forcing terms simultaneously.

  10. Reconnection events in two-dimensional Hall magnetohydrodynamic turbulence

    SciTech Connect

    Donato, S.; Servidio, S.; Carbone, V. [Dipartimento di Fisica, Universita della Calabria, I-87036 Cosenza (Italy); Dmitruk, P. [Departamento de Fisica, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires and Instituto de Fisica de Buenos Aires, CONICET, Buenos Aires (Argentina); Shay, M. A.; Matthaeus, W. H. [Bartol Research Institute and Department of Physics and Astronomy, University of Delaware, Newark, Delaware 19716 (United States); Cassak, P. A. [Department of Physics, West Virginia University, Morgantown, West Virginia 26506 (United States)

    2012-09-15

    The statistical study of magnetic reconnection events in two-dimensional turbulence has been performed by comparing numerical simulations of magnetohydrodynamics (MHD) and Hall magnetohydrodynamics (HMHD). The analysis reveals that the Hall term plays an important role in turbulence, in which magnetic islands simultaneously reconnect in a complex way. In particular, an increase of the Hall parameter, the ratio of ion skin depth to system size, broadens the distribution of reconnection rates relative to the MHD case. Moreover, in HMHD the local geometry of the reconnection region changes, manifesting bifurcated current sheets and quadrupolar magnetic field structures in analogy to laminar studies, leading locally to faster reconnection processes in this case of reconnection embedded in turbulence. This study supports the idea that the global rate of energy dissipation is controlled by the large scale turbulence, but suggests that the distribution of the reconnection rates within the turbulent system is sensitive to the microphysics at the reconnection sites.

  11. Principle of two-dimensional characterization of copolymers.

    PubMed

    Weidner, Steffen; Falkenhagen, Jana; Krueger, Ralph-Peter; Just, Ulrich

    2007-07-01

    Two-dimensional polymer characterization is used for a simultaneous analysis of molar masses and chemical heterogeneities (e.g., end groups, copolymer composition, etc.). This principle is based on coupling of two different chromatographic modes. Liquid adsorption chromatography at critical conditions (LACCC) is applied for a separation according to the chemical heterogeneity, whereas in the second-dimension fractions are analyzed with regard to their molar mass distribution by means of size exclusion chromatography (SEC). Because appropriate standards for a calibration of the SEC are seldom available, matrix-assisted laser desorption/ionization-time-of-flight mass spectrometry (MALDI-TOF MS) was used to substitute the SEC. The LACCC-MALDI MS coupling enables acquiring additional structural information on copolymer composition, which can considerably enhance the performance of this coupled method. PMID:17542553

  12. Holographic two dimensional QCD and Chern-Simons term

    E-print Network

    Ho-Ung Yee; Ismail Zahed

    2011-03-31

    We present a holographic realization of large Nc massless QCD in two dimensions using a D2/D8 brane construction. The flavor axial anomaly is dual to a three dimensional Chern-Simons term which turns out to be of leading order, and it affects the meson spectrum and holographic renormalization in crucial ways. The massless flavor bosons that exist in the spectrum are found to decouple from the heavier mesons, in agreement with the general lore of non-Abelian bosonization. We also show that an external dynamical photon acquires a mass through the three dimensional Chern-Simons term as expected from the Schwinger mechanism. Massless two dimensional QCD at large Nc exhibits anti-vector-meson dominance due to the axial anomaly.

  13. Soliton nanoantennas in two-dimensional arrays of quantum dots

    NASA Astrophysics Data System (ADS)

    Gligori?, G.; Maluckov, A.; Hadžievski, Lj; Slepyan, G. Ya; Malomed, B. A.

    2015-06-01

    We consider two-dimensional (2D) arrays of self-organized semiconductor quantum dots (QDs) strongly interacting with electromagnetic field in the regime of Rabi oscillations. The QD array built of two-level states is modelled by two coupled systems of discrete nonlinear Schrödinger equations. Localized modes in the form of single-peaked fundamental and vortical stationary Rabi solitons and self-trapped breathers have been found. The results for the stability, mobility and radiative properties of the Rabi modes suggest a concept of a self-assembled 2D soliton-based nano-antenna, which is stable against imperfections In particular, we discuss the implementation of such a nano-antenna in the form of surface plasmon solitons in graphene, and illustrate possibilities to control their operation by means of optical tools.

  14. A two-dimensional intensified photodiode array for imaging spectroscopy

    NASA Technical Reports Server (NTRS)

    Tennyson, P. D.; Dymond, K.; Moos, H. W.; Feldman, P. D.; Mackey, E. F.

    1986-01-01

    The Johns Hopkins University is currently developing an instrument to fly aboard NASA's Space Shuttle as a Spartan payload in the late 1980s. This Spartan free flyer will obtain spatially resolved spectra of faint extended emission line objects in the wavelength range 750-1150 A at about 2-A resolution. The use of two-dimensional photon counting detectors will give simultaneous coverage of the 400 A spectral range and the 9 arc-minute spatial resolution along the spectrometer slit. The progress towards the flight detector is reported here with preliminary results from a laboratory breadboard detector, and a comparison with the one-dimensional detector developed for the Hopkins Ultraviolet Telescope. A hardware digital centroiding algorithm has been successfully implemented. The system is ultimately capable of 15-micron resolution in two dimensions at the image plane and can handle continuous counting rates of up to 8000 counts/s.

  15. Dispersion-free continuum two-dimensional electronic spectrometer

    PubMed Central

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

    2015-01-01

    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. PMID:24663470

  16. 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. PMID:25155302

  17. Commensurability resonances in two-dimensional magnetoelectric lateral superlattices

    NASA Astrophysics Data System (ADS)

    Schluck, J.; Fasbender, S.; Heinzel, T.; Pierz, K.; Schumacher, H. W.; Kazazis, D.; Gennser, U.

    2015-05-01

    Hybrid lateral superlattices composed of a square array of antidots and a periodic one-dimensional magnetic modulation are prepared in Ga [Al ]As heterostructures. The two-dimensional electron gases exposed to these superlattices are characterized by magnetotransport experiments in vanishing average perpendicular magnetic fields. Despite the absence of closed orbits, the diagonal magnetoresistivity in the direction perpendicular to the magnetic modulation shows pronounced classical resonances. They are located at magnetic fields where snake trajectories exist which are quasicommensurate with the antidot lattice. The diagonal magnetoresistivity in the direction of the magnetic modulation increases sharply above a threshold magnetic field and shows no fine structure. The experimental results are interpreted with the help of numerical simulations based on the semiclassical Kubo model.

  18. Mixing times in quantum walks on two-dimensional grids

    SciTech Connect

    Marquezino, F. L.; Portugal, R.; Abal, G. [Laboratorio Nacional de Computacao Cientifica-LNCC Avenida Getulio Vargas 333, Petropolis, Rio de Janeiro 25651-075 (Brazil); Instituto de Fisica, Universidad de la Republica Casilla de Correo 30, Codigo Postal 11300, Montevideo (Uruguay)

    2010-10-15

    Mixing properties of discrete-time quantum walks on two-dimensional grids with toruslike boundary conditions are analyzed, focusing on their connection to the complexity of the corresponding abstract search algorithm. In particular, an exact expression for the stationary distribution of the coherent walk over odd-sided lattices is obtained after solving the eigenproblem for the evolution operator for this particular graph. The limiting distribution and mixing time of a quantum walk with a coin operator modified as in the abstract search algorithm are obtained numerically. On the basis of these results, the relation between the mixing time of the modified walk and the running time of the corresponding abstract search algorithm is discussed.

  19. Dirac Cones in two-dimensional conjugated polymer networks

    NASA Astrophysics Data System (ADS)

    Adjizian, Jean-Joseph; Briddon, Patrick; Humbert, Bernard; Duvail, Jean-Luc; Wagner, Philipp; Adda, Coline; Ewels, Christopher

    2014-12-01

    Linear electronic band dispersion and the associated Dirac physics has to date been limited to special-case materials, notably graphene and the surfaces of three-dimensional (3D) topological insulators. Here we report that it is possible to create two-dimensional fully conjugated polymer networks with corresponding conical valence and conduction bands and linear energy dispersion at the Fermi level. This is possible for a wide range of polymer types and connectors, resulting in a versatile new family of experimentally realisable materials with unique tuneable electronic properties. We demonstrate their stability on substrates and possibilities for doping and Dirac cone distortion. Notably, the cones can be maintained in 3D-layered crystals. Resembling covalent organic frameworks, these materials represent a potentially exciting new field combining the unique Dirac physics of graphene with the structural flexibility and design opportunities of organic-conjugated polymer chemistry.

  20. Optical two-dimensional coherent spectroscopy of semiconductor nanostructures

    NASA Astrophysics Data System (ADS)

    Nardin, Gaël.; Autry, Travis M.; Moody, Galan; Singh, Rohan; Li, Hebin; Cundiff, Steven T.

    2014-09-01

    Our recent work on optical two-dimensional coherent spectroscopy (2DCS) of semiconductor materials is reviewed. We present and compare two approaches that are appropriate for the study of semiconductor nanostructures. The first one is based on a non-collinear geometry, where the Four-Wave-Mixing (FWM) signal is detected in the form of a radiated optical field. This approach works for samples with translational symmetry, such as Quantum Wells (QWs), or large and dense ensembles of Quantum Dots (QDs). The second method is based on a collinear geometry, where the FWM is detected in the form of a photocurrent. This second approach enables 2DCS of samples where translational symmetry is broken, such as single QDs, nanowires, or nanotubes, and small ensembles thereof. For each method, we provide an example of experimental results obtained on semiconductor QWs. In particular, it is shown how 2DCS can reveal coherent excitonic coupling between adjacent QWs.

  1. A renormalization group analysis of two-dimensional magnetohydrodynamic turbulence

    NASA Technical Reports Server (NTRS)

    Liang, Wenli Z.; Diamond, P. H.

    1993-01-01

    The renormalization group (RNG) method is used to study the physics of two-dimensional (2D) magnetohydrodynamic (MHD) turbulence. It is shown that, for a turbulent magnetofluid in two dimensions, no RNG transformation fixed point exists on account of the coexistence of energy transfer to small scales and mean-square magnetic flux transfer to large scales. The absence of a fixed point renders the RNG method incapable of describing the 2D MHD system. A similar conclusion is reached for 2D hydrodynamics, where enstrophy flows to small scales and energy to large scales. These analyses suggest that the applicability of the RNG method to turbulent systems is intrinsically limited, especially in the case of systems with dual-direction transfer.

  2. 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.

  3. Two-dimensional plasma photonic crystals in dielectric barrier discharge

    SciTech Connect

    Fan Weili; Dong Lifang [College of Physics Science and Technology, Hebei University, Baoding 071002 (China); Zhang Xinchun [School of Energy and Power Engineering, North China Electric Power University, Baoding 071003 (China)

    2010-11-15

    A series of two-dimensional plasma photonic crystals have been obtained by filaments' self-organization in atmospheric dielectric barrier discharge with two water electrodes, which undergo the transition from square to square superlattice and finally to the hexagon. The spatio-temporal behaviors of the plasma photonic crystals in nanosecond scale have been studied by optical method, which show that the plasma photonic crystal is actually an integration of different transient sublattices. The photonic band diagrams of the transverse electric (TE) mode and transverse magnetic mode for each sublattice of these plasma photonic crystals have been investigated theoretically. A wide complete band gap is formed in the hexagonal plasma photonic crystal with the TE mode. The changes of the band edge frequencies and the band gap widths in the evolvement of different structures are studied. A kind of tunable plasma photonic crystal which can be controlled both in space and time is suggested.

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

    PubMed

    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) (identical to ) proportional to l(zeta(p)) on scales l greater than the energy injection scale l(inj) . The scaling exponent zeta(p) 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. PMID:16241505

  5. Modulational instabilities in two-dimensional magnetized dust-lattice

    SciTech Connect

    Farokhi, B.; Abdikian, A. [Department of Physics, Faculty of Science, Arak-University, 38156-8-8349 Arak (Iran, Islamic Republic of)

    2011-11-15

    The transverse oscillations of paramagnetic dust grains in hexagonal dusty plasma crystal are discussed. The nonlinearity, which is related to the sheath electric/magnetic field(s) and to the weak inter grain interactions (magnetic dipole), is shown to lead to the generation of phase harmonics. In the case of propagating two-dimensional transverse dust-lattice modes in an arbitrary direction, it is shown the modulational instability of the carrier wave is due to self-interaction. The stability depends on the form of the electric field, the magnetic field, and the magnetic permeability of dust particles. The long term evolution of the modulated wave packet is described by a discrete nonlinear Schrodinger equation and it is solved numerically by Adomian decomposition method.

  6. Modulational instabilities in two-dimensional magnetized dust-lattice

    NASA Astrophysics Data System (ADS)

    Farokhi, B.; Abdikian, A.

    2011-11-01

    The transverse oscillations of paramagnetic dust grains in hexagonal dusty plasma crystal are discussed. The nonlinearity, which is related to the sheath electric/magnetic field(s) and to the weak inter grain interactions (magnetic dipole), is shown to lead to the generation of phase harmonics. In the case of propagating two-dimensional transverse dust-lattice modes in an arbitrary direction, it is shown the modulational instability of the carrier wave is due to self-interaction. The stability depends on the form of the electric field, the magnetic field, and the magnetic permeability of dust particles. The long term evolution of the modulated wave packet is described by a discrete nonlinear Schrodinger equation and it is solved numerically by Adomian decomposition method.

  7. Two-dimensional plasma photonic crystals in dielectric barrier discharge

    NASA Astrophysics Data System (ADS)

    Fan, Weili; Zhang, Xinchun; Dong, Lifang

    2010-11-01

    A series of two-dimensional plasma photonic crystals have been obtained by filaments' self-organization in atmospheric dielectric barrier discharge with two water electrodes, which undergo the transition from square to square superlattice and finally to the hexagon. The spatio-temporal behaviors of the plasma photonic crystals in nanosecond scale have been studied by optical method, which show that the plasma photonic crystal is actually an integration of different transient sublattices. The photonic band diagrams of the transverse electric (TE) mode and transverse magnetic mode for each sublattice of these plasma photonic crystals have been investigated theoretically. A wide complete band gap is formed in the hexagonal plasma photonic crystal with the TE mode. The changes of the band edge frequencies and the band gap widths in the evolvement of different structures are studied. A kind of tunable plasma photonic crystal which can be controlled both in space and time is suggested.

  8. 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.

  9. Two-dimensional photonic quasicrystal flat lens with three scatterers

    NASA Astrophysics Data System (ADS)

    Liu, Jianjun; Fan, Zhigang

    2014-07-01

    A two-dimensional (2-D) photonic quasicrystal (PQC) flat lens with three scatterers is proposed, and its focusing characteristics for a point source are analyzed for the case of a continuously changing scatterer radius. The results show that a super-lens can be formed by three scatterers, and there is a threshold for scatterer radius. The focusing characteristics of the flat lens within the focusing radius are changed with regularity. It is reported for the first time that best image quality and the stability of perfect imaging in this 2-D PQC flat lens with three scatterers are superior to those in 2-D PQC or periodic photonic crystal flat lenses with multiple scatterers.

  10. Spontaneous supersymmetry breaking in two dimensional lattice super QCD

    E-print Network

    Catterall, Simon

    2015-01-01

    We report on a non-perturbative study of two dimensional $\\cN=(2,2)$ super QCD. Our lattice formulation retains a single exact supersymmetry at non-zero lattice spacing, and contains $N_f$ fermions in the fundamental representation of a $U(N_c)$ 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. We present evidence that the exact supersymmetry breaks spontaneously when $N_f

  11. Two-dimensional fruit ripeness estimation using thermal imaging

    NASA Astrophysics Data System (ADS)

    Sumriddetchkajorn, Sarun; Intaravanne, Yuttana

    2013-06-01

    Some green fruits do not change their color from green to yellow when being ripe. As a result, ripeness estimation via color and fluorescent analytical approaches cannot be applied. In this article, we propose and show for the first time how a thermal imaging camera can be used to two-dimensionally classify fruits into different ripeness levels. Our key idea relies on the fact that the mature fruits have higher heat capacity than the immature ones and therefore the change in surface temperature overtime is slower. Our experimental proof of concept using a thermal imaging camera shows a promising result in non-destructively identifying three different ripeness levels of mangoes Mangifera indica L.

  12. Electronic properties of two-dimensional covalent organic frameworks.

    PubMed

    Zhu, P; Meunier, V

    2012-12-28

    The electronic properties of a number of two-dimensional covalent organic frameworks are studied using a combination of density functional theory and quasiparticle theory calculations. The effect of composition and system size on the electronic band gap is systematically considered for a series of systems, using van der Waals corrected density functional theory calculations to determine the effect of a graphene substrate on deposited covalent frameworks. We predict that covalent organic frameworks' (COFs') electronic properties, such as their band gap can be fine tuned by appropriate modifications of their structures, specifically by increasing organic chain-links in the framework. The effect of strain on the electronic properties is also studied. The graphene substrate is shown to not significantly alter the properties of COFs, thereby indicating the robustness of COFs' intrinsic properties for practical applications. PMID:23277948

  13. Two-dimensional graphene superlattice made with partial hydrogenation

    NASA Astrophysics Data System (ADS)

    Yang, Ming; Nurbawono, Argo; Zhang, Chun; Feng, Yuan Ping; Ariando

    2010-05-01

    Electronic properties of two-dimensional 2D graphene superlattice made with partial hydrogenation were thoroughly studied via density functional tight binding approach which incorporates the tight-binding method into the density functional formalism. The 2D pattern of hydrogen atoms on graphene was found to have great effects on electronic structures of graphene superlattice. In particular, the edges of the 2D pattern, armchair or zigzag, are essential for the energy band gap opening, and the energy band gap sensitively depends on the shape, size, and the 2D periodicity of the pattern. Based on these findings, we suggested that the 2D graphene superlattice could be used in fabricating graphene quantum dots or heterojunctions without the need for cutting or etching.

  14. 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

  15. An Analysis of Two-dimensional Electrical Impedance Tomography

    NASA Astrophysics Data System (ADS)

    Schultz, William W.; Huang, Cunkui; Ceccio, Steven L.

    1998-11-01

    Electrical impedance tomography (EIT) is an inexpensive alternative to other methods for measuring such things as multiphase flow. Solving this inverse problem to find the location and size of voids requires more extensive analysis although it typically only requires solving the Laplace equation. Here we examine the two-dimensional analysis of these voids by an array of (typically 16) electrodes placed at the perimeter of a pipe. Representing the electrodes as point source/sinks and the voids by a few dipoles, analytical functions and the circle theorem are used to satisfy the insulated pipe wall boundary conditions. Our numerics show how using all possible combinations of electrodes as the anode and cathode obtains a realistic mapping of typical void distributions. Comparisons to experiments and extensions to three-dimensional tomography will be briefly discussed.

  16. High speed two-dimensional optical beam position detector

    SciTech Connect

    Rutten, Paul Edmond [Maypa B.V., Bijsters 2, 5131 NW, Alphen (Netherlands)

    2011-07-15

    Disclosed is the design of a high speed two-dimensional optical beam position detector which outputs the X and Y displacement and total intensity linearly. The experimental detector measures the displacement from DC to 123 MHz and the intensity of an optical spot in a similar way as a conventional quadrant photodiode detector. The design uses four discrete photodiodes and simple dedicated optics for the position decomposition which enables higher spatial accuracy and faster electronic processing than conventional detectors. Measurements of the frequency response and the spatial sensitivity demonstrate high suitability for atomic force microscopy, scanning probe data storage applications, and wideband wavefront sensing. The operation principle allows for position measurements up to 20 GHz and more in bandwidth.

  17. 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.

  18. High Mobility Two-Dimensional Electron Gas in Black Phosphorus

    NASA Astrophysics Data System (ADS)

    Li, Likai; Ye, Guojun; Tran, Vy; Chen, Guorui; Wang, Huichao; Wang, Jian; Watanabe, Kenji; Taniguchi, Takashi; Yang, Li; Chen, Xianhui; Zhang, Yuanbo

    2015-03-01

    Black phosphorus has recently emerged as a new member in the family of two-dimensional (2D) atomic crystals. It is a semiconductor with a tunable bandgap and high carrier mobility - material properties that are important for potential opto-electronic and high-speed device applications. In this work, we achieve a record-high carrier mobility in black phosphorus by placing it on hexagonal boron nitride (h-BN) substrate. The exceptional mobility of the 2D electron gas created at the interface allows us to observe quantum oscillations for the first time in this material. The temperature and magnetic field dependence of the oscillations yields crucial information about the black phosphorus 2DEG, such as cyclotron mass of the charge carriers and their lifetime. Our results pave the way to future research on quantum transport in black phosphorus.

  19. Two dimensional turbulence in inviscid fluids or guiding center plasmas

    NASA Technical Reports Server (NTRS)

    Seyler, C. E., Jr.; Salu, Y.; Montgomery, D.; Knorr, G.

    1975-01-01

    Analytic theory for two-dimensional turbulent equilibria for the inviscid Navier-Stokes equations is examined mathematically. Application of the technique to electrostatic guiding center plasma is discussed. A good fit is demonstrated for the approach to a predicted energy per Fourier mode obtained from a two-temperature canonical ensemble. Negative as well as positive temperature regimes are explored. Fluctuations about the mean energy per mode also compare well with theory. In the regime of alpha less than zero, beta greater than zero, with the minimum value of alpha plus beta times k squared near zero, contour plots of the stream function reveal macroscopic vortex structures similar to those seen previously in discrete vortex simulations. Eulerian direct interaction equations, which can be used to follow the approach to inviscid equilibrium, are derived.

  20. Electrophoresis of DNA on a disordered two-dimensional substrate

    E-print Network

    C. J. Olson Reichhardt; C. Reichhardt

    2006-10-10

    We propose a new method for electrophoretic separation of DNA in which adsorbed polymers are driven over a disordered two-dimensional substrate which contains attractive sites for the polymers. Using simulations of a model for long polymer chains, we show that the mobility increases with polymer length, in contrast to gel electrophoresis techniques, and that separation can be achieved for a range of length scales. We demonstrate that the separation mechanism relies on steric interactions between polymer segments, which prevent substrate disorder sites from trapping more than one DNA segment each. Since thermal activation does not play a significant role in determining the polymer mobility, band broadening due to diffusion can be avoided in our separation method.

  1. Two-dimensional topological order of kinetically constrained quantum particles

    NASA Astrophysics Data System (ADS)

    Kourtis, Stefanos; Castelnovo, Claudio

    2015-04-01

    We investigate how imposing kinetic restrictions on quantum particles that would otherwise hop freely on a two-dimensional lattice can lead to topologically ordered states. The kinetically constrained models introduced here are derived as a generalization of strongly interacting particle systems in which hoppings are given by flux-lattice Hamiltonians and may be relevant to optically driven cold-atom systems. After introducing a broad class of models, we focus on particular realizations and show numerically that they exhibit topological order, as witnessed by topological ground-state degeneracies and the quantization of corresponding invariants. These results demonstrate that the correlations responsible for fractional quantum Hall states in lattices can arise in models involving terms other than density-density interactions.

  2. Dynamics of a Two-Dimensional System of Quantum Dipoles

    SciTech Connect

    Mazzanti, F.; Astrakharchik, G. E.; Boronat, J. [Departament de Fisica i Enginyeria Nuclear, Campus Nord B4-B5, Universitat Politecnica de Catalunya, E-08034 Barcelona (Spain); Zillich, R. E. [Institut fuer Theoretische Physik, Johannes-Kepler Universitaet, Altenbergerstr. 69, 4040 Linz (Austria)

    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.

  3. Analytical two-dimensional solutions for hydrodynamic astrophysical flows.

    NASA Astrophysics Data System (ADS)

    Kakouris, A.; Moussas, X.

    1996-02-01

    A new class of steady state, analytical, two-dimensional, non-separated variables solutions for helicoidal hydrodynamic (HD) outflows from rotating stellar objects is derived selfconsistently from the set of the governing (Eulerian) equations of continuity. The fluid is assumed to be compressible, inviscid and non-polytropic. The families of solutions describe either accelerating or decelerating stellar winds with weak collimation (quasi-spherical) which vanishes with the radial distance. We present four cases of solutions with their velocity maxima either at the poles or at the equator of the central body and some of them can be understood as inflows or as stellar shell formations. One of the solution families, showing an accelerating supersonic outflow, is applied to typical parameters of T Tauri stars keeping the observational outflow velocities and mass loss rates. Under this example, the applicability of these solutions is examined. The new solutions are compared with previous analytical 2-D models.

  4. Higgs mode in a two-dimensional superfluid.

    PubMed

    Pollet, L; Prokof'ev, N

    2012-07-01

    We present solid evidence for the existence of a well-defined Higgs amplitude mode in two-dimensional relativistic field theories based on analytically continued results from quantum Monte Carlo simulations of the Bose-Hubbard model in the vicinity of the superfluid-Mott insulator quantum critical point, featuring emergent particle-hole symmetry and Lorentz invariance. The Higgs boson, seen as a well-defined low-frequency resonance in the spectral density, is quickly pushed to high energies in the superfluid phase and disappears by merging with the broad secondary peak at the characteristic interaction scale. Simulations of a trapped system of ultracold (87)Rb atoms demonstrate that the low-frequency resonance is lost for typical experimental parameters, while the characteristic frequency for the onset of a strong response is preserved. PMID:23031091

  5. Two-dimensional nonlinear map characterized by tunable Lévy flights.

    PubMed

    Méndez-Bermúdez, J A; de Oliveira, Juliano A; Leonel, Edson D

    2014-10-01

    After recognizing that point particles moving inside the extended version of the rippled billiard perform Lévy flights characterized by a Lévy-type distribution P(l)?l(-(1+?)) with ?=1, we derive a generalized two-dimensional nonlinear map M? able to produce Lévy flights described by P(l) with 0

  6. 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.

  7. Two dimensional excitons in thin films of thiophene oligomers

    NASA Astrophysics Data System (ADS)

    Lanzani, G.; Rossi, L.; Stagira, S.; De Silvestri, S.; Garnier, F.

    1998-01-01

    Transient and quasi-steady state photomodulation spectroscopy has been applied to films of substituted sexithiophene, namely ?, ?dihexylsexithiophene (?, ?DHT 6), which is prototype two dimensional organic semiconductor. Two photoexcited states are seen in the ultrafast time domain characterized by photoinduced absorption bands at 1.7 eV and 1.5 eV respectively and different dynamics. We assign them to Frenkel excitons and inter-layer charge transfer excitons. The photoinduced absorption spectrum in the ms time domain shows a very narrow line at 0.7 eV and a broad structure around 1 eV which are assigned to doubly occupied states, ?-dimers and bipolarons respectively.

  8. Two-dimensional flagellar synchronization in viscoelastic fluids

    NASA Astrophysics Data System (ADS)

    Elfring, Gwynn J.; Pak, On Shun; Lauga, Eric

    2010-03-01

    Experimental studies have demonstrated that spermatozoa synchronize their flagella when swimming in close proximity. In a Newtonian fluid, it was shown theoretically that such synchronization arises passively due to hydrodynamic forces between the two swimmers if their waveforms exhibit a front-back geometrical asymmetry. Motivated by the fact that most biological fluids possess a polymeric microstructure, we address here synchronization in a viscoelastic fluid analytically. Using a two-dimensional infinite sheet model we show that the presence of polymeric stresses removes the geometrical asymmetry constraint, and therefore even symmetric swimmers synchronize. Such synchronization occurs on asymptotically faster time scales than in a Newtonian fluid, and the swimmers are seen to be driven into a stable in-phase conformation minimizing the energy dissipated in the surrounding fluid.

  9. 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. ?? 2011 ASCE.

  10. Electronic and vibrational spectra of two-dimensional quasicrystals

    NASA Astrophysics Data System (ADS)

    Odagaki, T.; Nguyen, D.

    1986-02-01

    The tight-binding electronic structure of two-dimensional quasicrystals is studied numerically for three patterns of Penrose tiling with up to 426 vertices. According to the range of interactions, three different models are considered. For the simplest model, two different interactions are assigned to long and short edges of the Penrose tile. Energy spectra show several significant gaps whose width and position depend on the relative strength of the interactions. The cumulative density of states is linear in energy at the band edge, indicating the existence of the Van Hove singularities. The energy spectra for other models show similar band gaps and singularities, though the density of states is asymmetric. Participation ratios are examined. When the relative strength of interactions becomes small, significant numbers of states become localized. Lattice vibration perpendicular to the plane is studied in the harmonic approximation for the simplest model. The vibrational spectra show gaps and singularities similar to the electronic spectra.

  11. Noise correlations of two-dimensional Bose gases

    NASA Astrophysics Data System (ADS)

    Singh, V. P.; Mathey, L.

    2014-05-01

    We analyze density-density correlations of expanding clouds of weakly interacting two-dimensional Bose gases below and above the Berezinskii-Kosterlitz-Thouless transition, with particular focus on short-time expansions. During time-of-flight expansion, phase fluctuations of the trapped system translate into density fluctuations, in addition to the density fluctuations that exist in situ. We calculate the correlations of these fluctuations both in real space and in momentum space and derive analytic expressions in momentum space. Below the transition, the correlation functions show an oscillatory behavior, controlled by the scaling exponent of the quasicondensed phase, due to constructive interference. We argue that this can be used to extract the scaling exponent of the quasicondensate experimentally. Above the transition, the interference is rapidly suppressed when the atoms travel an average distance beyond the correlation length. This can be used to distinguish the two phases qualitatively.

  12. Dynamics of semiconductor lasers with two-dimensional distributed feedback

    NASA Astrophysics Data System (ADS)

    Ginzburg, N. S.; Baryshev, V. R.; Sergeev, A. S.; Malkin, A. M.

    2015-05-01

    We develop a nonlinear model of a laser exploiting two-dimensional (2D) distributed feedback (2D DFL). This feedback mechanism can be realized in a 2D Bragg resonator formed by a dielectric structure with the thickness having double-periodical sinusoidal or chessboard modulation. A 2D Bragg resonator is shown to possess high selectivity over both the longitudinal and the transverse coordinates and to have fundamental modes in the center of the forbidden band gap. Within the semiclassical approach, we study the nonlinear dynamics of 2D DFL and demonstrate spatial synchronization of radiation from an extended active medium. Specific features of 2D DFL operation with active medium amplifying modes of TM and TE (quantum-well lasers) polarization are also discussed.

  13. Entropically stabilized growth of a two-dimensional random tiling

    NASA Astrophysics Data System (ADS)

    Stannard, Andrew; Blunt, Matthew O.; Beton, Peter H.; Garrahan, Juan P.

    2010-10-01

    The assembly of molecular networks into structures such as random tilings and glasses has recently been demonstrated for a number of two-dimensional systems. These structures are dynamically arrested on experimental time scales, so the critical regime in their formation is that of initial growth. Here, we identify a transition from energetic to entropic stabilization in the nucleation and growth of a molecular rhombus tiling. Calculations based on a lattice-gas model show that clustering of topological defects and the formation of faceted boundaries followed by a slow relaxation to equilibrium occur under conditions of energetic stabilization. We also identify an entropically stabilized regime in which the system grows directly into an equilibrium configuration without the need for further relaxation. Our results provide a methodology for identifying equilibrium and nonequilibrium randomness in the growth of molecular tilings, and we demonstrate that equilibrium spatial statistics are compatible with exponentially slow dynamical behavior.

  14. Entropically stabilized growth of a two-dimensional random tiling.

    PubMed

    Stannard, Andrew; Blunt, Matthew O; Beton, Peter H; Garrahan, Juan P

    2010-10-01

    The assembly of molecular networks into structures such as random tilings and glasses has recently been demonstrated for a number of two-dimensional systems. These structures are dynamically arrested on experimental time scales, so the critical regime in their formation is that of initial growth. Here, we identify a transition from energetic to entropic stabilization in the nucleation and growth of a molecular rhombus tiling. Calculations based on a lattice-gas model show that clustering of topological defects and the formation of faceted boundaries followed by a slow relaxation to equilibrium occur under conditions of energetic stabilization. We also identify an entropically stabilized regime in which the system grows directly into an equilibrium configuration without the need for further relaxation. Our results provide a methodology for identifying equilibrium and nonequilibrium randomness in the growth of molecular tilings, and we demonstrate that equilibrium spatial statistics are compatible with exponentially slow dynamical behavior. PMID:21230240

  15. Normal Modes of Magnetized Finite Two-Dimensional Yukawa Crystals

    NASA Astrophysics Data System (ADS)

    Marleau, Gabriel-Dominique; Kaehlert, Hanno; Bonitz, Michael

    2009-11-01

    The normal modes of a finite two-dimensional dusty plasma in an isotropic parabolic confinement, including the simultaneous effects of friction and an external magnetic field, are studied. The ground states are found from molecular dynamics simulations with simulated annealing, and the influence of screening, friction, and magnetic field on the mode frequencies is investigated in detail. The two-particle problem is solved analytically and the limiting cases of weak and strong magnetic fields are discussed.[4pt] [1] C. Henning, H. K"ahlert, P. Ludwig, A. Melzer, and M.Bonitz. J. Phys. A 42, 214023 (2009)[2] B. Farokhi, M. Shahmansouri, and P. K. Shukla. Phys.Plasmas 16, 063703 (2009)[3] L. Cândido, J.-P. Rino, N. Studart, and F. M. Peeters. J. Phys.: Condens. Matter 10, 11627--11644 (1998)

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

    NASA Astrophysics Data System (ADS)

    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.

  17. Cooperation in two-dimensional mixed-games

    E-print Network

    Amaral, Marco A; Wardil, Lucas

    2015-01-01

    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.

  18. Topological Hofstadter insulators in a two-dimensional quasicrystal

    NASA Astrophysics Data System (ADS)

    Tran, Duc-Thanh; Dauphin, Alexandre; Goldman, Nathan; Gaspard, Pierre

    2015-02-01

    We investigate the properties of a two-dimensional quasicrystal in the presence of a uniform magnetic field. In this configuration, the density of states (DOS) displays a Hofstadter-butterfly-like structure when it is represented as a function of the magnetic flux per tile. We show that the low-DOS regions of the energy spectrum are associated with chiral edge states, in direct analogy with the Chern insulators realized with periodic lattices. We establish the topological nature of the edge states by computing the topological Chern number associated with the bulk of the quasicrystal. This topological characterization of the nonperiodic lattice is achieved through a local (real-space) topological marker. This work opens a route for the exploration of topological-insulating materials in a wide range of nonperiodic lattice systems, including photonic crystals and cold atoms in optical lattices.

  19. Topological states in two-dimensional optical lattices

    NASA Astrophysics Data System (ADS)

    Stanescu, Tudor D.; Galitski, Victor; Das Sarma, S.

    2010-07-01

    We present a general analysis of two-dimensional optical lattice models that give rise to topologically nontrivial insulating states. We identify the main ingredients of the lattice models that are responsible for the nontrivial topological character and argue that such states can be realized within a large family of realistic optical lattice Hamiltonians with cold atoms. We focus our quantitative analysis on the properties of topological states with broken time-reversal symmetry specific to cold-atom settings. In particular, we analyze finite-size effects, multiorbital phenomena that give rise to a variety of distinct topological states and transitions between them, the dependence on the trap geometry, and, most importantly, the behavior of the edge states for different types of soft and hard boundaries. Furthermore, we demonstrate the possibility of experimentally detecting the topological states through light Bragg scattering of the edge and bulk states.

  20. Valley Splitting in a Silicon Two-Dimensional Electron Gas

    NASA Astrophysics Data System (ADS)

    Goswami, Srijit; Friesen, Mark; Truitt, J. L.; Tahan, Charles; Chu, J. O.; van der Weide, D. W.; Coppersmith, S. N.; Joynt, Robert; Eriksson, M. A.

    2006-03-01

    We have performed low-temperature microwave transport spectroscopy of low-lying valley states in a silicon two-dimensional electron gas. The magnitude of this splitting determines whether the ground state is degenerate for purposes of quantum computing with spins. The valley splitting varies linearly with magnetic field from 0.3 to 3 T, reaching 75 ?eV, with no sign of saturation. We unambiguously identify the observed resonance as a valley excitation by comparing with Shubnikov-de Haas oscillations. The origin of the splitting is the coupling of the two z conduction valleys in the silicon band structure, due to quantum well confinement. Previous theory suggests that the valley splitting can be of order 1 meV. However, we present a theory incorporating atomic steps, which are present in experimental systems. The theory leads to small valley splittings at zero magnetic field, and a linearly increasing splitting at nonzero fields, as observed in experiments.

  1. Collisionless reconnection in two-dimensional magnetotail equilibria

    NASA Technical Reports Server (NTRS)

    Pritchett, P. L.; Coroniti, F. V.; Pellat, R.; Karimabadi, H.

    1991-01-01

    A two-dimensional particle simulation model based on the Darwin approximation to Maxwell's equations for studying collisionless reconnection in the magnetotail has been developed. Simulations of the pure ion tearing mode in a thin current sheet with normal B(z) field component demonstrate that in this limit this mode grows more slowly than expected based on previous analytic estimates. The saturation level of the tearing instability greatly surpasses estimates based on a simple trapping argument. The effect of the normal field component on the evolution of the tearing instability is considered. It is found that a normal field of even a few percent on axis strongly inhibits the growth of the instability.

  2. 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.

  3. Two-dimensional skyrmion lattice in a nanopatterned magnetic film

    NASA Astrophysics Data System (ADS)

    Sapozhnikov, M. V.; Ermolaeva, O. L.

    2015-01-01

    We study the possibility of a two-dimensional (2D) skyrmion crystal stabilization in a magnetic film with perpendicular anisotropy in the absence of Dzyaloshinskii-Moriya interaction by creating the regular array of blind holes or stubs. By micromagnetic simulation we demonstrate that skyrmions can be stable in the patterned films with the parameters of ordinary materials such as CoPt, FePt, or FePd. The skyrmion lattices can be initialized in the system by simple magnetization in the uniform external magnetic field. At the zero external field the skyrmion helicity depends on the geometry of the blind hole or stub but also can be tuned by applying the field. The suggested method makes it possible to create dense enough (with the period less than 100 nm) skyrmion lattices which are important to carry out transport measurements.

  4. 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.

  5. Non-monotonic magnetoresistivity in two-dimensional electron systems

    NASA Astrophysics Data System (ADS)

    Wang, Yi-Ting; Woo, Tak-Pong; Lo, Shun-Tsung; Kim, Gil-Ho; Liang, Chi-Te

    2014-11-01

    The connection being studied is the one between the non-monotonic magnetoresistivity (MR) and the electron-electron interaction (EEI) correction in weakly-disordered two-dimensional electron systems (2DESs) in the ballistic region k B T ? / ? > 1, where k B , T, ?, and ? are the Boltzmann constant, the temperature, the scattering time, and the reduced Planck constant, respectively. At zero magnetic field, a transition of the resistivity ?( T) from the insulating region d?/ dT < 0 to the metallic region d?/ dT > 0 is observed. The MR shows a maximum, and with increasing T, the position of the MR maximum in B increases for both GaAs-based (sample A) and GaN-based (sample B) 2DESs. Our data suggest that the EEI plays an important role in such a non-monotonic MR effect and in the temperature dependence of the resistivity.

  6. 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

  7. 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.

  8. Bi-layer excitons in two-dimensional layered materials

    NASA Astrophysics Data System (ADS)

    Neupane, Mahesh; Yin, Gen; Wickramaratne, Darshana; Lake, Roger

    2013-03-01

    Following the prediction of exciton condensation in closely spaced two-dimensional electron-hole bilayer systems, there has been a sustained theoretical and experimental investigation of this condensation phase in coupled quantum well material systems. The electron-hole pairs are bound by the interlayer Coulomb interaction, which is tuned by electrostatic gating of the charge density. The magnitude of this interaction is determined by the binding energy between the electron and the hole. Improvements in the exciton binding energy can be achieved by an appropriate choice of materials. The family of van der Walle materials is considered in this study, and the effect of material choice and insulating layer thickness on the excitonic properties will be discussed and compared to experimental investigations using traditional GaAs-AlGaAs coupled quantum wells. Following the prediction of exciton condensation in closely spaced two-dimensional electron-hole bilayer systems, there has been a sustained theoretical and experimental investigation of this condensation phase in coupled quantum well material systems. The electron-hole pairs are bound by the interlayer Coulomb interaction, which is tuned by electrostatic gating of the charge density. The magnitude of this interaction is determined by the binding energy between the electron and the hole. Improvements in the exciton binding energy can be achieved by an appropriate choice of materials. The family of van der Walle materials is considered in this study, and the effect of material choice and insulating layer thickness on the excitonic properties will be discussed and compared to experimental investigations using traditional GaAs-AlGaAs coupled quantum wells. Microelectronics Advanced Research Corporation Focus Center on Nano Materials (FENA)

  9. On final states of two-dimensional decaying turbulence

    NASA Astrophysics Data System (ADS)

    Yin, Z.

    2004-12-01

    Numerical and analytical studies of final states of two-dimensional (2D) decaying turbulence are carried out. The first part of this work is trying to give a definition for final states of 2D decaying turbulence. The functional relation of ?-?, which is frequently adopted as the characterization of those final states, is merely a sufficient but not necessary condition; moreover, it is not proper to use it as the definition. It is found that the method through the value of the effective area S covered by the scatter ?-? plot, initially suggested by Read, Rhines, and White ["Geostrophic scatter diagrams and potential vorticity dynamics," J. Atmos. Sci. 43, 3226 (1986)] is more general and suitable for the definition. Based on this concept, a definition is presented, which covers all existing results in late states of decaying 2D flows (including some previous unexplainable weird double-valued ?-? scatter plots). The remaining part of the paper is trying to further study 2D decaying turbulence with the assistance of this definition. Some numerical results, leading to "bar" final states and further verifying the predictive ability of statistical mechanics [Yin, Montgomery, and Clercx, "Alternative statistical-mechanical descriptions of decaying two-dimensional turbulence in terms of patches and points," Phys. Fluids 15, 1937 (2003)], are reported. It is realized that some simulations with narrow-band energy spectral initial conditions result in some final states that cannot be very well interpreted by the statistical theory (meanwhile, those final states are still in the scope of the definition).

  10. A two-dimensional global study of tropospheric ozone production

    SciTech Connect

    Strand, A.; Hov, O. [Nansen Environmental and Remote Sensing Center, Bergen (Norway)]|[Univ. of Bergen, Bergen (Norway)

    1994-11-01

    The ozone production in the troposphere has been studied by means of a zonally averaged model which consists of a two-dimensional transport model, a description of the emissions, wet and dry deposition, and chemical processes of importance for the ozone production in the troposphere. The transport model describes a closed circulation in the meridional plane below 10 hPa and has a resolution and a numerical solution which compares favorable with earlier two-dimensional studies. The transport model also takes into account the fast vertical mixing in convective clouds and in frontal circulation. The production of nitrogen oxides by lightning has been coupled to the convection parameterization by assuming that the nitrogen oxides are transported vertically in the thunder clouds and released at the altitudes where boundary layer air entrained in the convective cells is released. Comparisons with observations indicate that the model is able to reproduce the seasonal variation of ozone in the meridional plane quite realistically. The calculated distributions of the chemical species which determine tropospheric ozone also compare well with measurements. The model estimated an annually averaged production of ozone in the troposphere over the northern hemisphere of 16.6 x 10(exp 10) molecules/sq cm/sec and over the southern hemisphere of 5.1 x 10(exp 10) molecules/sq cm/sec. The annually and globally averaged dry deposition is 14.9 x 10(exp 10) molecules/sq cm/sec, and the corresponding injection from the stratosphere is 4.1 x 10(exp 10) molecules/sq cm/sec. A 50% reduction of the man-made emissions from the industrialized society of nitrogen oxides resulted in a reduction in the ozone production of 2.9 x 10(exp 10) molecules/sq cm/sec in the lower troposphere over the northern hemisphere during the period of maximum photochemical production, June-August.

  11. Statistical mechanics of two-dimensional shuffled foams: prediction of the correlation between geometry and topology

    E-print Network

    Cox, Simon

    Statistical mechanics of two-dimensional shuffled foams: prediction of the correlation between for the statistical mechanics of shuffled two-dimensional foams with moderate bubble size polydispersity. It predicts

  12. Two-dimensional fast marching for geometrical optics.

    PubMed

    Capozzoli, Amedeo; Curcio, Claudio; Liseno, Angelo; Savarese, Salvatore

    2014-11-01

    We develop an approach for the fast and accurate determination of geometrical optics solutions to Maxwell's equations in inhomogeneous 2D media and for TM polarized electric fields. The eikonal equation is solved by the fast marching method. Particular attention is paid to consistently discretizing the scatterers' boundaries and matching the discretization to that of the computational domain. The ray tracing is performed, in a direct and inverse way, by using a technique introduced in computer graphics for the fast and accurate generation of textured images from vector fields. The transport equation is solved by resorting only to its integral form, the transport of polarization being trivial for the considered geometry and polarization. Numerical results for the plane wave scattering of two perfectly conducting circular cylinders and for a Luneburg lens prove the accuracy of the algorithm. In particular, it is shown how the approach is capable of properly accounting for the multiple scattering occurring between the two metallic cylinders and how inverse ray tracing should be preferred to direct ray tracing in the case of the Luneburg lens. PMID:25401818

  13. Influence of defect states on band gaps in the two-dimensional phononic crystal of 4340 steel in an epoxy

    NASA Astrophysics Data System (ADS)

    Kong, Xiao-Yan; Yue, Lei-Lei; Chen, Yu; Liu, Ying-Kai

    2012-09-01

    The band structures of a new two-dimensional triangle-shaped array geometry of 4340 steel cylinders of square cross section in an epoxy resin were studied by the plane-wave expansion and supercell calculation method. The band gaps of this type of phononic crystals with different defects were calculated such as defect-free, 60° crystal linear defect states, 120° crystal linear defect states, and 180° crystal linear defect states. It was found that the band gap will emerge in different linear defects of the phononic crystals and the bandwidth of linear defect states is larger than that of the free-defect crystal by about 2.14 times within the filling fraction F = 0.1-0.85. In addition, the influence of the filling fraction on the relative width of the minimum band gap is discussed.

  14. An Automated Two-Dimensional Optical Force Clamp for Single Molecule Studies

    E-print Network

    Asbury, Chip

    force microscopy (to 4 nm), a two-dimensional raster scan to calibrate position detector responseAn Automated Two-Dimensional Optical Force Clamp for Single Molecule Studies Matthew J. Lang a microtubule. The instrument can be operated as a two-dimensional force clamp, applying loads of fixed

  15. ON THE EXISTENCE AND COMPACTNESS OF A TWO-DIMENSIONAL RESONANT SYSTEM OF CONSERVATION LAWS

    E-print Network

    ON THE EXISTENCE AND COMPACTNESS OF A TWO-DIMENSIONAL RESONANT SYSTEM OF CONSERVATION LAWS KENNETH to a two-dimensional resonant 3 Ã? 3 system of conservation laws with BV initial data. Due to possible. Introduction This paper studies certain two-dimensional resonant 3 Ã? 3 systems of conservation laws of the form

  16. An integral-equation solution for TE radiation and scattering from conducting cylinders

    NASA Technical Reports Server (NTRS)

    Richmond, J. H.

    1973-01-01

    The piecewise-sinusoidal reaction technique is applied to low frequency radiation and scattering from noncircular cylinders with perfect or imperfect conductivity. This report presents the theory, computer programs and numerical results for these two-dimensional problems with the TE polarization.

  17. Radiation from an axially slotted cylinder coated with an inhomogeneous dielectric sheath

    Microsoft Academic Search

    C. Yeh; Z. A. Kaprielian

    1963-01-01

    The expressions for the radiated fields of an axially slotted infinite cylinder coated with a radially inhomogeneous dielectric sheath are obtained. The two-dimensional vector wave equation in this inhomogeneous medium is separated using the vector wave function method of Hansen and Stratton. The problem of finding the solution of Maxwell's equation in such an inhomogeneous medium reduces to the solution

  18. Comparative study of in-cylinder tumble flows in an internal combustion engine using different piston shapes---an insight using particle image velocimetry

    Microsoft Academic Search

    B. Murali Krishna; J. M. Mallikarjuna

    2010-01-01

    This paper deals with the experimental investigations of the in-cylinder tumble flows in a single-cylinder engine with five different piston crown shapes at an engine speed of 1,000 rev\\/min., during suction and compression strokes under motoring conditions using particle image velocimetry. Two-dimensional in-cylinder tumble flow measurements and analysis are carried out in combustion space on a vertical plane passing through

  19. Numerical investigation on vortex-induced vibration of an elastically mounted circular cylinder at low Reynolds number using the fictitious domain method

    Microsoft Academic Search

    Chunning Ji; Zhong Xiao; Yuanzhan Wang; Huakun Wang

    2011-01-01

    A direct numerical simulation of two-dimensional (2D) flow past an elastically mounted circular cylinder at low Reynolds number using the fictitious domain method had been undertaken. The cylinder motion was modelled by a two degree-of-freedom mass–spring–damper system. The computing code was verified against a benchmark problem in which flow past a stationary circular cylinder is simulated. Then, analyses of vortex-induced

  20. Tandem Cylinder Noise Predictions

    NASA Technical Reports Server (NTRS)

    Lockhard, David P.; Khorrami, Mehdi R.; CHoudhari, Meelan M.; Hutcheson, Florence V.; Brooks, Thomas F.; Stead, Daniel J.

    2007-01-01

    In an effort to better understand landing-gear noise sources, we have been examining a simplified configuration that still maintains some of the salient features of landing-gear flow fields. In particular, tandem cylinders have been studied because they model a variety of component level interactions. The present effort is directed at the case of two identical cylinders spatially separated in the streamwise direction by 3.7 diameters. Experimental measurements from the Basic Aerodynamic Research Tunnel (BART) and Quiet Flow Facility (QFF) at NASA Langley Research Center (LaRC) have provided steady surface pressures, detailed off-surface measurements of the flow field using Particle Image Velocimetry (PIV), hot-wire measurements in the wake of the rear cylinder, unsteady surface pressure data, and the radiated noise. The experiments were conducted at a Reynolds number of 166 105 based on the cylinder diameter. A trip was used on the upstream cylinder to insure a fully turbulent shedding process and simulate the effects of a high Reynolds number flow. The parallel computational effort uses the three-dimensional Navier-Stokes solver CFL3D with a hybrid, zonal turbulence model that turns off the turbulence production term everywhere except in a narrow ring surrounding solid surfaces. The current calculations further explore the influence of the grid resolution and spanwise extent on the flow and associated radiated noise. Extensive comparisons with the experimental data are used to assess the ability of the computations to simulate the details of the flow. The results show that the pressure fluctuations on the upstream cylinder, caused by vortex shedding, are smaller than those generated on the downstream cylinder by wake interaction. Consequently, the downstream cylinder dominates the noise radiation, producing an overall directivity pattern that is similar to that of an isolated cylinder. Only calculations based on the full length of the model span were able to capture the complete decay in the spanwise correlation, thereby producing reasonable noise radiation levels.

  1. 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 electron systems. In an ultrapure two dimensional electron system (2DES) subjected to high magnetic field and very low temperatures, a large number of many-body ground states can emerge in a purely quantum phenomenon called the Fractional quantum Hall Effect (FQHE). The fractional state at nu=5/2 has drawn significant interest in recent times because of its predicted non-abelian excitations that can be utilized in constructing topologically protected quantum bits. In spite of having made significant advances in this direction, progress is hindered due to the fragility of this exotic state characterized by a small energy gap which puts very stringent requirements on the sample quality and the temperature scale. It is believed that the nu=5/2 activation gap is masked by disorders present in the sample which causes the experimentally observed gap to appear much smaller than the theoretically predicted intrinsic gap originating from purely electron-electron interactions in the clean-limit. Hence categorization of samples based on the strength of the nu=5/2 state hinges on the efficient quantification of disorder which is not a directly measurable quantity. Historically the zero-field transport mobility has been identified as the measure of disorder present in the sample. However careful comparison of data originating in our measurements with existing literature reveals that mobility is rather a weak indicator of the quality of FQHE in the 2nd Landau level and fails to reliably predict the nu=5/2 activation gap in a sample. In the absence of a single reliable indicator of sample quality in the 2nd Landau level, we propose a resistivity measured at nu=5/2 at T=0.3K as an alternative metric to characterize samples. Preliminary measurements involving a limited number of samples indicate that a resistivity measured at nu=5/2 might be better correlated with the nu=5/2 gap than mobility. Results also call for a more holistic approach in sample characterization by taking into consideration the heterostructure design while predicting sample quality. The possibility of quantu

  2. Uniform boundedness and long-time asymptotics for the two-dimensional Navier-Stokes equations in an infinite cylinder

    E-print Network

    Gallay, Thierry

    the total energy of the fluid is a decreasing function of time, the fluid velocity u(x, t) may temporarily, and that the vorticity distribution converges to zero as t . This implies, after a transient period, the emergence with bounded energy density, we would like to estimate the kinetic energy of the solution in a small subdomain

  3. Investigation of In-Cylinder Soot Formation and Oxidation by Means of Two-Dimensional Laser-Induced Incandescence (LII)

    Microsoft Academic Search

    S. Schraml; C. Heimgärtner; C. Fettes; A. Leipertz

    Increasing requirements on the environmental acceptability of internal combustion engines led to strong efforts to meet the continuously getting stricter emission regulations. New concepts of combustion and injection have been developed together with appropriate techniques of exhaust gas aftertreatment. For diesel engines especially modern high pressure injection systems, such as the application of distributor pump and common rail have been

  4. 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 negatively refractive phenomena. They found that in the PC system, negative refraction is neither a prerequisite nor guarantees left-handed behavior. They examined carefully the condition to obtain left-handed behavior in the PC. They proposed a wedge type of experiment, in accordance with the experiment performed on the traditional LHM, to test these conditions. They found that for certain frequencies the PC shows left-handed behavior and acts in some respects like a homogeneous medium with a negative refractive index. they used the realistic PC system for this case to show how negative refraction occurs at the interface between a material with a positive and a material with a negative refractive index. Their findings indicate that the formation of the negatively refracted beam is not instantaneous and involves a transient time. With this time-dependent analysis, they were able to address previous controversial issues about negative refraction concerning causality and the speed of light limit. Finally, they attempt a systematic study of anomalous refractive phenomena that can occur at the air-PC interface. They observe cases where only a single refracted beam (in the positive or negative direction) is present, as well as cases with birefringence. they classify these different effects according to their origin and type of propagation (left-handed or not). For a complete study of the system, they also obtain expressions for the energy and group velocities, and show their equality. For cases with very low index contrast, band folding becomes an artificiality. They discuss the validity of their findings when they move to the limit of photonic crystals with a low index modulation.

  5. Two-dimensional electronic spectroscopy of molecular aggregates.

    PubMed

    Ginsberg, Naomi S; Cheng, Yuan-Chung; Fleming, Graham R

    2009-09-15

    The properties of molecular aggregates, coupled clusters of small molecules, are often challenging to unravel because of their inherent complexity and disordered environments. Their structure-function relationships are often far from obvious. However, their ability to efficiently channel excitation energy over remarkable distances, as is the case in photosynthetic light harvesting, is a compelling motivation to investigate them. Understanding and subsequently mimicking the processes in photosynthesis, for example, will set the stage for considerable advances in using light harvesting to fuel renewable energy technologies. Two-dimensional (2D) electronic spectroscopy is emerging as a nonlinear optical technique that provides significant insight into the interactions and dynamics of complex molecular systems. In addition to spectrally resolving excitation and emission energies over significant bandwidths with femtosecond resolution, this technique has already enabled discoveries about the structure and dynamics of photosynthetic light-harvesting complexes and other aggregates. Multiple capabilities unique to 2D electronic spectroscopy enable such findings. For example, the spectral resolution of excitation and emission combined with the ability to eliminate the effects of static disorder can reveal the homogeneous line width of a transition and the different dynamic contributions to it. Two dimensional spectroscopy is also sensitive to electronic coherence and has been employed to identify and characterize coherent excitation energy transfer dynamics in photosynthetic systems and conjugated polymers. The presence of cross-peaks, signals for which excitation and emission occur at different wavelengths, provides multiple forms of information. First, it allows the identification of states in congested spectra and reveals correlations between them. Second, we can track excitation energy flow from origin to terminus through multiple channels simultaneously. Finally, 2D electronic spectroscopy is uniquely sensitive to intermolecular electronic coupling through the sign and amplitude of the cross-peaks. This feature makes it possible to reveal spatial molecular configurations by probing electronic transitions. Another means of "resolving" these angstrom-scale arrangements is to manipulate the probing laser pulse polarizations. In this way, we can isolate and modulate specific processes in order to retrieve structural information. In this Account, we demonstrate these capabilities through a close collaboration between experiments and modeling on isolated photosynthetic pigment-protein complexes and also on J-aggregates. Each of the probed systems we describe offers insights that have both increased the utility of 2D electronic spectroscopy and led to discoveries about the molecular aggregates' dynamics and underlying structure. PMID:19691358

  6. Quasicrystals and Instabilities of the Two-Dimensional Wigner Crystal.

    NASA Astrophysics Data System (ADS)

    Cockayne, Eric James

    This work concerns two unrelated topics: quasicrystals and the two-dimensional Wigner crystal. Despite a great deal of effort since the discovery of quasicrystals in 1984 determine their atomic structures, it remains an only partially solved problem. One approach to solving the quasicrystal structure problem is to determine the structure of a finite-unit cell crystalline approximant whose structure is related to that of the quasicrystal. The structure of the approximant can be refined with respect to experimental diffraction data. This approach is developed here and then applied to the case of icosahedral AlCuFe, where large single-grain X-ray and neutron diffraction data sets are used in comparing several different models for the structure. A geometry problem that is also of interest in quasicrystallography is the problem: given a sphere radius and a desired quasiperiodic point group, how can one pack these spheres without overlap so as to achieve the highest packing fraction? A technique is, the "pinwheel construction" is given in detail that can increase the packing fraction of certain dodecagonal, octagonal and icosahedral sphere packings over those based on the "cut and project" method that use simpler shapes for the projection window. The ground state of the two-dimensional electron system is a fundamental and difficult problem in physics. Of interest is the transition between the "Wigner crystal" and fluid states and the magnetic state of the crystal. This system is first investigated in the semiclassical limit where the energies of point defects are calculated. These point defects could play a role in the melting transition, although the critical density calculated here is not in agreement with published estimates of the critical density. Then the quantum electron system is considered. Trial wavefunctions for the ground state are used that are linear superpositions of "multigaussians", where a multigaussian is a Slater determinant of gaussian one-electron wavefunctions. Particular wavefunctions are chosen to evaluate various aspects of the 2D electron system. Evidence is found that the Wigner crystal may undergo a transition from an unpolarized state at low density to a ferromagnetic state at higher densities.

  7. Differences in scour around a single surface-piercing cylinder and a submerged cylinder

    NASA Astrophysics Data System (ADS)

    Beninati, M. L.; Volpe, M. A.; Riley, D. R.; Krane, M.

    2011-12-01

    The equilibrium state of scour for a single surface piercing cylinder and a submerged cylinder of specific aspect ratio are presented. The equilibrium state is defined by a scour depth and associated time interval for a given set of flow conditions. Control variables such as sediment coarseness (or grain size) and cylinder size are held constant, while the flow intensity is varied. Sediment bed form topology is characterized with a series of two-dimensional slices across the bed for both the surface-piercing and submerged cylinder cases. Test results will help identify the geometry and pattern of the scour around the cylinders to aid in the optimal design of marine hydrokinetic (MHK) support structures in an effort to help minimize the deleterious impact of these devices on the local substrate. This study is performed in the small-scale testing platform in the hydraulic flume facility (32 ft long, 4 ft wide and 1.25 ft deep) in the Environmental Fluid Mechanics and Hydraulics Laboratory (EFM&H) at Bucknell University. The cylinders, of the same material and diameter, are placed centrally in the sediment filled test section (2.5 ft long, 2 ft wide and 0.75 ft deep) of the platform. Flow field measurements are taken with a 16-MHz Micro Acoustic Doppler Velocimeter while water depth is acquired using an ultrasonic distance sensor. These devices are attached to a gantry system that can be accurately positioned anywhere in the test section. Clear-water conditions (in the absence of live-bed scour) are maintained to study the effect of the horseshoe and wake vortices on the displacement of sediment around the cylinder as well as downstream of the device. Bed form topology is measured using an HR Wallingford 2D Sediment Bed Profiler with a low-powered laser distance sensor to accurately characterize changes in bed form around the cylinders. Additionally, specifications for testing such as operational procedures for start-up and shut-down of the facility are given.

  8. Relativistic Bessel cylinders

    NASA Astrophysics Data System (ADS)

    Krisch, J. P.; Glass, E. N.

    2014-10-01

    A set of cylindrical solutions to Einstein's field equations for power law densities is described. The solutions have a Bessel function contribution to the metric. For matter cylinders regular on axis, the first two solutions are the constant density Gott-Hiscock string and a cylinder with a metric Airy function. All members of this family have the Vilenkin limit to their mass per length. Some examples of Bessel shells and Bessel motion are given.

  9. Two-dimensional water waves in the presence of a freely floating body: conditions for the absence of trapped modes

    E-print Network

    Nikolay Kuznetsov

    2015-03-07

    The coupled motion is investigated for a mechanical system consisting of water and a body freely floating in it. Water occupies either a half-space or a layer of constant depth into which an infinitely long surface-piercing cylinder is immersed, thus allowing us to study two-dimensional modes. Under the assumption that the motion is of small amplitude near equilibrium, a linear setting is applicable and for the time-harmonic oscillations it reduces to a spectral problem with the frequency of oscillations as the spectral parameter. It is essential that one of the problem's relations is linear with respect to the parameter, whereas two others are quadratic with respect to it. Within this framework, it is shown that the total energy of the water motion is finite and the equipartition of energy holds for the whole system. On this basis, it is proved that no wave modes can be trapped provided their frequencies exceed a bound depending on cylinder's properties, whereas its geometry is subject to some restrictions and, in some cases, certain restrictions are imposed on the type of mode.

  10. Global magnetohydrodynamic simulation of the two-dimensional magnetosphere

    NASA Technical Reports Server (NTRS)

    Leboeuf, J. N.; Tajima, T.; Kennel, C. F.; Dawson, J. M.

    1979-01-01

    The time-dependent magnetohydrodynamic interaction of the solar wind with a two-dimensional dipole magnetic field has been simulated using a novel Lagrangian particle type of MHD code that can treat local low density or vacuum regions without numerical instability. This enables one to simulate the time-dependent magnetic tail. When the solar wind field is southward, a magnetic field line topology consistent with Dungey's model emerges in steady state. The tail, however, is short, and the x-points are only slightly shifted from their vacuum locations, because of strong numerical resistivity. Different configurations resulting from different relative orientations of the solar wind magnetic field and dipole axis are also presented. While the magnetic field is relatively steady, the density and flow in the magnetosheath are turbulent, as are the bow shock and magnetopause; the Kelvin-Helmholtz instability may account for these phenomena. We also model a 'substorm' as the passage of a rotational discontinuity in the solar wind over the dipole. Both 90 and 180 deg shifts to a southward solar wind field cause a violent readjustment of the magnetic tail which eventually settles down to the Dungey configuration.

  11. Study of two-dimensional Debye clusters using Brownian motion

    SciTech Connect

    Sheridan, T.E.; Theisen, W.L. [Department of Physics and Astronomy, Ohio Northern University, Ada, Ohio 45810 (United States)

    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.

  12. Two-dimensional fluorescence intensity distribution analysis: theory and applications.

    PubMed Central

    Kask, P; Palo, K; Fay, N; Brand, L; Mets, U; Ullmann, D; Jungmann, J; Pschorr, J; Gall, K

    2000-01-01

    A method of sample analysis is presented which is based on fitting a joint distribution of photon count numbers. In experiments, fluorescence from a microscopic volume containing a fluctuating number of molecules is monitored by two detectors, using a confocal microscope. The two detectors may have different polarizational or spectral responses. Concentrations of fluorescent species together with two specific brightness values per species are determined. The two-dimensional fluorescence intensity distribution analysis (2D-FIDA), if used with a polarization cube, is a tool that is able to distinguish fluorescent species with different specific polarization ratios. As an example of polarization studies by 2D-FIDA, binding of 5'-(6-carboxytetramethylrhodamine) (TAMRA)-labeled theophylline to an anti-theophylline antibody has been studied. Alternatively, if two-color equipment is used, 2D-FIDA can determine concentrations and specific brightness values of fluorescent species corresponding to individual labels alone and their complex. As an example of two-color 2D-FIDA, binding of TAMRA-labeled somatostatin-14 to the human type-2 high-affinity somatostatin receptors present in stained vesicles has been studied. The presented method is unusually accurate among fluorescence fluctuation methods. It is well suited for monitoring a variety of molecular interactions, including receptors and ligands or antibodies and antigens. PMID:10733953

  13. Two-dimensional shape recognition using sparse distributed memory

    NASA Technical Reports Server (NTRS)

    Kanerva, Pentti; Olshausen, Bruno

    1990-01-01

    Researchers propose a method for recognizing two-dimensional shapes (hand-drawn characters, for example) with an associative memory. The method consists of two stages: first, the image is preprocessed to extract tangents to the contour of the shape; second, the set of tangents is converted to a long bit string for recognition with sparse distributed memory (SDM). SDM provides a simple, massively parallel architecture for an associative memory. Long bit vectors (256 to 1000 bits, for example) serve as both data and addresses to the memory, and patterns are grouped or classified according to similarity in Hamming distance. At the moment, tangents are extracted in a simple manner by progressively blurring the image and then using a Canny-type edge detector (Canny, 1986) to find edges at each stage of blurring. This results in a grid of tangents. While the technique used for obtaining the tangents is at present rather ad hoc, researchers plan to adopt an existing framework for extracting edge orientation information over a variety of resolutions, such as suggested by Watson (1987, 1983), Marr and Hildreth (1980), or Canny (1986).

  14. Two-dimensional model for circulating fluidized-bed reactors

    SciTech Connect

    Schoenfelder, H.; Kruse, M.; Werther, J. [Technical Univ. Hamburg-Harburg, Hamburg (Germany). Dept. of Chemical Engineering] [Technical Univ. Hamburg-Harburg, Hamburg (Germany). Dept. of Chemical Engineering

    1996-07-01

    Circulating fluidized bed reactors are widely used for the combustion of coal in power stations as well as for the cracking of heavy oil in the petroleum industry. A two-dimensional reactor model for circulating fluidized beds (CFB) was studied based on the assumption that at every location within the riser, a descending dense phase and a rising lean phase coexist. Fluid mechanical variables may be calculated from one measured radial solids flux profile (upward and downward). The internal mass-transfer behavior is described on the basis of tracer gas experiments. The CFB reactor model was tested against data from ozone decomposition experiments in a CFB cold flow model (15.6-m height, 0.4-m ID) operated in the ranges 2.5--4.5 m/s and 9--45 kg/(m{sup 2}{center_dot}s) of superficial gas velocity and solids mass flux, respectively. Based on effective reaction rate constants determined from the ozone exit concentration, the model was used to predict the spatial reactant distribution within the reactor. Model predictions agreed well with measurements.

  15. Two-dimensional state in driven magnetohydrodynamic turbulence

    SciTech Connect

    Bigot, Barbara [Space Science Center, University of New Hampshire, Durham, New Hampshire 03824 (United States); Center for Integrated Computation and Analysis of Reconnection And Turbulence (United States); Galtier, Sebastien [Universite Paris-Sud, Institut d'Astrophysique Spatiale, bat. 121, F-91405 Orsay (France); Institut universitaire de France (France)

    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.

  16. 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

  17. Two-Dimensional Ffowcs Williams/Hawkings Equation Solver

    NASA Technical Reports Server (NTRS)

    Lockard, David P.

    2005-01-01

    FWH2D is a Fortran 90 computer program that solves a two-dimensional (2D) version of the equation, derived by J. E. Ffowcs Williams and D. L. Hawkings, for sound generated by turbulent flow. FWH2D was developed especially for estimating noise generated by airflows around such approximately 2D airframe components as slats. The user provides input data on fluctuations of pressure, density, and velocity on some surface. These data are combined with information about the geometry of the surface to calculate histories of thickness and loading terms. These histories are fast-Fourier-transformed into the frequency domain. For each frequency of interest and each observer position specified by the user, kernel functions are integrated over the surface by use of the trapezoidal rule to calculate a pressure signal. The resulting frequency-domain signals are inverse-fast-Fourier-transformed back into the time domain. The output of the code consists of the time- and frequency-domain representations of the pressure signals at the observer positions. Because of its approximate nature, FWH2D overpredicts the noise from a finite-length (3D) component. The advantage of FWH2D is that it requires a fraction of the computation time of a 3D Ffowcs Williams/Hawkings solver.

  18. Photon management in two-dimensional disordered media.

    PubMed

    Vynck, Kevin; Burresi, Matteo; Riboli, Francesco; Wiersma, Diederik S

    2012-12-01

    Elaborating reliable and versatile strategies for efficient light coupling between free space and thin films is of crucial importance for new technologies in energy efficiency. Nanostructured materials have opened unprecedented opportunities for light management, notably in thin-film solar cells. Efficient coherent light trapping has been accomplished through the careful design of plasmonic nanoparticles and gratings, resonant dielectric particles and photonic crystals. Alternative approaches have used randomly textured surfaces as strong light diffusers to benefit from their broadband and wide-angle properties. Here, we propose a new strategy for photon management in thin films that combines both advantages of an efficient trapping due to coherent optical effects and broadband/wide-angle properties due to disorder. Our approach consists of the excitation of electromagnetic modes formed by multiple light scattering and wave interference in two-dimensional random media. We show, by numerical calculations, that the spectral and angular responses of thin films containing disordered photonic patterns are intimately related to the in-plane light transport process and can be tuned through structural correlations. Our findings, which are applicable to all waves, are particularly suited for improving the absorption efficiency of thin-film solar cells and can provide a new approach for high-extraction-efficiency light-emitting diodes. PMID:23042416

  19. Two dimensional spatial distortion correction algorithm for scintillation GAMMA cameras

    SciTech Connect

    Chaney, R.; Gray, E.; Jih, F.; King, S.E.; Lim, C.B.

    1985-05-01

    Spatial distortion in an Anger gamma camera originates fundamentally from the discrete nature of scintillation light sampling with an array of PMT's. Historically digital distortion correction started with the method based on the distortion measurement by using 1-D slit pattern and the subsequent on-line bi-linear approximation with 64 x 64 look-up tables for X and Y. However, the X, Y distortions are inherently two-dimensional in nature, and thus the validity of this 1-D calibration method becomes questionable with the increasing distortion amplitude in association with the effort to get better spatial and energy resolutions. The authors have developed a new accurate 2-D correction algorithm. This method involves the steps of; data collection from 2-D orthogonal hole pattern, 2-D distortion vector measurement, 2-D Lagrangian polynomial interpolation, and transformation to X, Y ADC frame. The impact of numerical precision used in correction and the accuracy of bilinear approximation with varying look-up table size have been carefully examined through computer simulation by using measured single PMT light response function together with Anger positioning logic. Also the accuracy level of different order Lagrangian polynomial interpolations for correction table expansion from hole centroids were investigated. Detailed algorithm and computer simulation are presented along with camera test results.

  20. A two-dimensional mixing length theory of convective transport

    NASA Astrophysics Data System (ADS)

    Lesaffre, Pierre; Chitre, Shashikumar M.; Potter, Adrian T.; Tout, Christopher A.

    2013-05-01

    The helioseismic observations of the internal rotation profile of the Sun raise questions about the two-dimensional (2D) nature of the transport of angular momentum in stars. Here we derive a convective prescription for axisymmetric (2D) stellar evolution models. We describe the small-scale motions by a spectrum of unstable linear modes in a Boussinesq fluid. Our saturation prescription makes use of the angular dependence of the linear dispersion relation to estimate the anisotropy of convective velocities. We are then able to provide closed form expressions for the thermal and angular momentum fluxes with only one free parameter, the mixing length. We illustrate our prescription for slow rotation, to first order in the rotation rate. In this limit, the thermodynamical variables are spherically symmetric, while the angular momentum depends on both radius and latitude. We obtain a closed set of equations for stellar evolution, with a self-consistent description for the transport of angular momentum in convective regions. We derive the linear coefficients which link the angular momentum flux to the rotation rate (?-effect) and its gradient (?-effect). We compare our results to former relevant numerical work.