Science.gov

Sample records for two-dimensional halbach cylinders

  1. Design of nested Halbach cylinder arrays for magnetic refrigeration applications

    NASA Astrophysics Data System (ADS)

    Trevizoli, Paulo V.; Lozano, Jaime A.; Peixer, Guilherme F.; Barbosa, Jader R., Jr.

    2015-12-01

    We present an experimentally validated analytical procedure to design nested Halbach cylinder arrays for magnetic cooling applications. The procedure aims at maximizing the magnetic flux density variation in the core of the array for a given set of design parameters, namely the inner diameter of the internal magnet, the air gap between the magnet cylinders, the number of segments of each magnet and the remanent flux density of the Nd2Fe14B magnet grade. The design procedure was assisted and verified by 3-D numerical modeling using a commercial software package. An important aspect of the optimal design is to maintain an uniform axial distribution of the magnetic flux density in the region of the inner gap occupied by the active magnetocaloric regenerator. An optimal nested Halbach cylinder array was manufactured and experimentally evaluated for the magnetic flux density in the inner gap. The analytically calculated magnetic flux density variation agreed to within 5.6% with the experimental value for the center point of the magnet gap.

  2. Laser one-dimensional range profile and the laser two-dimensional range profile of cylinders

    NASA Astrophysics Data System (ADS)

    Gong, Yanjun; Wang, Mingjun; Gong, Lei

    2015-10-01

    Laser one-dimensional range profile, that is scattering power from pulse laser scattering of target, is a radar imaging technology. The laser two-dimensional range profile is two-dimensional scattering imaging of pulse laser of target. Laser one-dimensional range profile and laser two-dimensional range profile are called laser range profile(LRP). The laser range profile can reflect the characteristics of the target shape and surface material. These techniques were motivated by applications of laser radar to target discrimination in ballistic missile defense. The radar equation of pulse laser is given in this paper. This paper demonstrates the analytical model of laser range profile of cylinder based on the radar equation of the pulse laser. Simulations results of laser one-dimensional range profiles of some cylinders are given. Laser range profiles of cylinder, whose surface material with diffuse lambertian reflectance, is given in this paper. Laser range profiles of different pulse width of cylinder are given in this paper. The influences of geometric parameters, pulse width, attitude on the range profiles are analyzed.

  3. 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.

  4. A numerical study of the motion of a neutrally buoyant cylinder in two dimensional shear flow

    NASA Astrophysics Data System (ADS)

    Pan, Tsorng-Whay; Huang, Shih-Lin; Chen, Shih-Di; Chu, Chin-Chou; Chang, Chien-Cheng

    2012-11-01

    We have investigated the motion of a neutrally buoyant cylinder of circular or elliptic shape in two dimensional shear flow of a Newtonian fluid by direct numerical simulation. The numerical results are validated by comparisons with existing theoretical, experimental and numerical results, including a power law of the normalized angular speed versus the particle Reynolds number. The centerline between two walls is an expected equilibrium position of the cylinder mass center in shear flow. When placing the particle away from the centerline initially, it migrates toward another equilibrium position for higher Reynolds numbers due to the interplay between the slip velocity, the Magnus force, and the wall repulsion force. T-W Pan acknowledges the support by the US NSF and S-L Huang, S-D Chen, C-C Chu, C-C Chang acknowledge the support by the National Science Council of Taiwan, ROC.

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

    NASA Technical Reports Server (NTRS)

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

    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 an anisotropic k-epsilon model averaged over an integral number of cycles to get the fluctuating energy (organized and turbulent) are compared with experimental data. It is shown that the anisotropic k-epsilon model resolves the anisotropy of the Reynolds stresses and gives mean energy distribution closer to the experiment than the standard k-epsilon model.

  6. Effect of Reynolds Number on the Force and Pressure Distribution Characteristics of a Two-Dimensional Lifting Circular Cylinder

    NASA Technical Reports Server (NTRS)

    Lockwood, Vernard E.; McKinney, Linwood W.

    1960-01-01

    A two-dimensional lifting circular cylinder has been tested over a Mach number range from 0.011 to 0.32 and a Reynolds number range from 135,000 to 1,580,000 to determine the force and pressure distribution characteristics. Two flaps having chords of 0.37 and 6 percent of the cylinder diameter, respectively, and attached normal to the surface were used to generate lift. A third configuration which had 6-percent flaps 1800 apart was also investigated. All flaps were tested through a range of angular positions. The investigation also included tests of a plain cylinder without flaps. The lift coefficient showed a wide variation with Reynolds number for the 6-percent flap mounted on the bottom surface at the 50-percent-diameter station, varying from a low of about 0.2 at a Reynolds number of 165,000 to a high of 1.54 at a Reynolds number of 350,000 and then decreasing almost linearly to a value of 1.0 at a Reynolds number of 1,580,000. The pressure distribution showed that the loss of lift with Reynolds number above the critical was the result of the separation point moving forward on the upper surface. Pressure distributions on a plain cylinder also showed similar trends with respect to the separation point. The variation of drag coefficient with Reynolds number was in direct contrast to the lift coefficient with the minimum drag coefficient of 0.6 occurring at a Reynolds number of 360,000. At this point the lift-drag ratios were a maximum at a value of 2.54. Tests of a flap with a chord of 0.0037 diameter gave a lift coefficient of 0.85 at a Reynolds number of 520,000 with the same lift-drag ratio as the larger flap but the position of the flap for maximum lift was considerably farther forward than on the larger flap. Tests of two 6-percent flaps spaced 180 deg apart showed a change in the sign of the lift developed for angular positions of the flap greater than 132 deg at subcriti- cal Reynolds numbers. These results may find use in application to air- craft using forebody strakes. The drag coefficient developed by the flaps when normal to the relative airstream was approximately equal to that developed by a flat plate in a similar attitude.

  7. 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.

  8. 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.

  9. On the effects of mass and momentum transfer from droplets impacting on steady two-dimensional rimming flow in a horizontal cylinder

    NASA Astrophysics Data System (ADS)

    Williams, J.; Hibberd, S.; Power, H.; Riley, D. S.

    2012-05-01

    Motivated by applications in aero-engines, steady two-dimensional thin-film flow on the inside of a circular cylinder is studied when the film surface is subject to mass and momentum transfer from impacting droplets. Asymptotic analysis is used systematically to identify distinguished limits that incorporate these transfer effects at leading order and to provide a new mathematical model. Applying both analytical and numerical approaches to the model, a set of stable steady, two-dimensional solutions that fit within the rational framework is determined. A number of these solutions feature steep fronts and associated recirculating pools, which are undesirable in an aeroengine since oil may be stripped away from the steep fronts when there is a core flow external to the film, and recirculation may lead to oil degradation. The model, however, provides a means of investigating whether the formation of the steep fronts on the film surface and of internal recirculation pools can be delayed, or inhibited altogether, by designing jets to deliver prescribed distributions of oil droplets or by the judicious siting of oil sinks. Moreover, by studying pathlines, oil-residence times can be predicted and systems optimized.

  10. Halbach Magnetic Rotor Development

    NASA Technical Reports Server (NTRS)

    Gallo, Christopher A.

    2008-01-01

    The NASA John H. Glenn Research Center has a wealth of experience in Halbach array technology through the Fundamental Aeronautics Program. The goals of the program include improving aircraft efficiency, reliability, and safety. The concept of a Halbach magnetically levitated electric aircraft motor will help reduce harmful emissions, reduce the Nation s dependence on fossil fuels, increase efficiency and reliability, reduce maintenance and decrease operating noise levels. Experimental hardware systems were developed in the GRC Engineering Development Division to validate the basic principles described herein and the theoretical work that was performed. A number of Halbach Magnetic rotors have been developed and tested under this program. A separate test hardware setup was developed to characterize each of the rotors. A second hardware setup was developed to test the levitation characteristics of the rotors. Each system focused around a unique Halbach array rotor. Each rotor required original design and fabrication techniques. A 4 in. diameter rotor was developed to test the radial levitation effects for use as a magnetic bearing. To show scalability from the 4 in. rotor, a 1 in. rotor was developed to also test radial levitation effects. The next rotor to be developed was 20 in. in diameter again to show scalability from the 4 in. rotor. An axial rotor was developed to determine the force that could be generated to position the rotor axially while it is rotating. With both radial and axial magnetic bearings, the rotor would be completely suspended magnetically. The purpose of this report is to document the development of a series of Halbach magnetic rotors to be used in testing. The design, fabrication and assembly of the rotors will be discussed as well as the hardware developed to test the rotors.

  11. Interception efficiency in two-dimensional flow past confined porous cylinders Setareh Shahsavari*, Brian L. Wardle, Gareth H. McKinley*1

    E-print Network

    dimensionless numbers: the Reynolds number, the Darcy number (ratio of permeability to the square of cylinder ] permeability [-] porosity [kgm-1 s-1 ] fluid dynamic viscosity [-] interception efficiency), as well as in biomedical research where microfluidic systems are being developed for cell separation (Chen

  12. Pressure Distributions and Wave Drag Due to Two-Dimensional Fabrication-Type Surface Roughness on an Ogive Cylinder at Mach Numbers of 1.61 and 2.01

    NASA Technical Reports Server (NTRS)

    Czarnecki, K. R.; Monta, William J.

    1961-01-01

    An investigation has been made at Mach numbers of 1.61 and 2.01 and over a range of free-stream Reynolds number per foot from about 1.2 x 10(exp 6) to 8.3 x 10(exp 6) to determine the pressure distributions and wave drags due to two-dimensional fabrication-type surface roughness. Ten types of surface roughness, including step, wave, crease, and swept configurations were investigated. The tests were made on an ogive cylinder of fineness ratio 12.2, the roughness elements covering the cylindrical portion of the model. The results indicate that wave drag is the major component of the drag due to roughness at supersonic speeds. The pressure distributions over the roughness elements were generally found to be in good agreement with linearized two-dimensional theory except for regions of the elements affected by boundary-layer separation and shock detachment. There was little or no effect of Reynolds number except on the pressures within the regions influenced by separation or shock detachment. Inasmuch as most of the roughness configurations were affected by flow separation and shock detachment, there was generally an effect of Reynolds number on the roughness wave drag. This wave drag decreased as the free-stream Reynolds number was decreased.

  13. Torque Production in a Halbach Machine

    NASA Technical Reports Server (NTRS)

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

    2006-01-01

    The NASA John H. Glenn Research Center initiated the investigation of torque production in a Halbach machine for the Levitated Ducted Fan (LDF) Project to obtain empirical data in determining the feasibility of using a Halbach motor for the project. LDF is a breakthrough technology for "Electric Flight" with the development of a clean, quiet, electric propulsor system. Benefits include zero emissions, decreased dependence on fossil fuels, increased efficiency, increased reliability, reduced maintenance, and decreased operating noise levels. A commercial permanent magnet brushless motor rotor was tested with a custom stator. An innovative rotor utilizing a Halbach array was designed and developed to fit directly into the same stator. The magnets are oriented at 90deg to the adjacent magnet, which cancels the magnetic field on the inside of the rotor and strengthens the field on the outside of the rotor. A direct comparison of the commercial rotor and the Halbach rotor was made. In addition, various test models were designed and developed to validate the basic principles described, and the theoretical work that was performed. The report concludes that a Halbach array based motor can provide significant improvements in electric motor performance and reliability.

  14. Two dimensional vernier

    NASA Technical Reports Server (NTRS)

    Juday, Richard D. (inventor)

    1992-01-01

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

  15. 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.

  16. Analysis of eddy current losses in cylindrical linear oscillatory actuator with Halbach permanent magnet array mover

    NASA Astrophysics Data System (ADS)

    Ko, Kyoung-Jin; Choi, Ji-Hwan; Jang, Seok-Myeong; Choi, Jang-Young

    2012-04-01

    This paper describes calculations and comparisons of eddy current losses in a cylindrical linear oscillatory actuator with a Halbach array permanent magnet mover for different voltage source waveforms. Using the magnetic vector potential and a two-dimensional cylindrical coordinate system, the paper presents an analytical procedure and obtains solutions for the eddy current losses using the Poynting theorem. To verify the proposed method, the eddy current losses obtained from the analytical solutions are compared with the results of a non-linear finite element method. Moreover, this paper shows that the eddy current losses are more significant when the actuator is driven by a square voltage waveform than when it is driven by a sinusoidal voltage waveform.

  17. Two-Dimensional IHCP Code

    Energy Science and Technology Software Center (ESTSC)

    1997-11-18

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

  18. 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.

  19. 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.

  20. Halbach array DC motor/generator

    DOEpatents

    Merritt, Bernard T. (Livermore, CA); Dreifuerst, Gary R. (Livermore, CA); Post, Richard F. (Walnut Creek, CA)

    1998-01-01

    A new configuration of DC motor/generator is based on a Halbach array of permanent magnets. This motor does not use ferrous materials so that the only losses are winding losses and losses due to bearings and windage. An "inside-out" design is used as compared to a conventional motor/generator design. The rotating portion, i.e., the rotor, is on the outside of the machine. The stationary portion, i.e., the stator, is formed by the inside of the machine. The rotor contains an array of permanent magnets that provide a uniform field. The windings of the motor are placed in or on the stator. The stator windings are then "switched" or "commutated" to provide a DC motor/generator much the same as in a conventional DC motor. The commutation can be performed by mechanical means using brushes or by electronic means using switching circuits. The invention is useful in electric vehicles and adjustable speed DC drives.

  1. Halbach array DC motor/generator

    DOEpatents

    Merritt, B.T.; Dreifuerst, G.R.; Post, R.F.

    1998-01-06

    A new configuration of DC motor/generator is based on a Halbach array of permanent magnets. This motor does not use ferrous materials so that the only losses are winding losses and losses due to bearings and windage. An ``inside-out`` design is used as compared to a conventional motor/generator design. The rotating portion, i.e., the rotor, is on the outside of the machine. The stationary portion, i.e., the stator, is formed by the inside of the machine. The rotor contains an array of permanent magnets that provide a uniform field. The windings of the motor are placed in or on the stator. The stator windings are then ``switched`` or ``commutated`` to provide a DC motor/generator much the same as in a conventional DC motor. The commutation can be performed by mechanical means using brushes or by electronic means using switching circuits. The invention is useful in electric vehicles and adjustable speed DC drives. 17 figs.

  2. Fast two-dimensional model

    NASA Technical Reports Server (NTRS)

    Jackman, Charles H.; Douglass, Anne R.; Stolarski, Richard S.; Guthrie, Paul D.; Thompson, A. M.

    1990-01-01

    A two dimensional (altitude and latitude) model of the atmosphere is used to investigate problems relating to the variability of the dynamics and temperature of the atmosphere on the ozone distribution, solar cycle variations of atmospheric constituents, the sensitivity of model results to tropospheric trace gas sources, and assessment computations of changes in ozone related to manmade influences. In a comparison between two dimensional model results in which the odd nitrogen family was transported together and model results in which the odd nitrogen species was transported separately, it was found that the family approximations are adequate for perturbation scenario calculations.

  3. 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.

  4. Two-dimensional thermofield bosonization

    SciTech Connect

    Amaral, R.L.P.G.

    2005-12-15

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

  5. Observability for two dimensional systems

    NASA Technical Reports Server (NTRS)

    Hunt, L. R.; Su, R.

    1981-01-01

    Sufficient conditions that a two-dimensional system with output is locally observable are presented. Known results depend on time derivatives of the output and the inverse function theorem. In some cases, no informaton is provided by these theories, and one must study observability by other methods. The observability problem is dualized to the controllability problem, and the deep results of Hermes on local controllability are applied to prove a theorem concerning local observability.

  6. Two-Dimensional Vernier Scale

    NASA Technical Reports Server (NTRS)

    Juday, Richard D.

    1992-01-01

    Modified vernier scale gives accurate two-dimensional coordinates from maps, drawings, or cathode-ray-tube displays. Movable circular overlay rests on fixed rectangular-grid overlay. Pitch of circles nine-tenths that of grid and, for greatest accuracy, radii of circles large compared with pitch of grid. Scale enables user to interpolate between finest divisions of regularly spaced rule simply by observing which mark on auxiliary vernier rule aligns with mark on primary rule.

  7. Two dimensional unstable scar statistics.

    SciTech Connect

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

    2006-12-01

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

  8. Two-Dimensional Colloidal Alloys

    NASA Astrophysics Data System (ADS)

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

    2011-03-01

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

  9. Two-dimensional colloidal alloys.

    PubMed

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

    2011-03-25

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

  10. 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

  11. Two-dimensional NMR spectroscopy

    SciTech Connect

    Croasmun, W.R.; Carlson, R.M.K.

    1987-01-01

    Written for chemists and biochemists who are not NMR spectroscopists, but who wish to use the new techniques of two-dimensional NMR spectroscopy, this book brings together for the first time much of the practical and experimental data needed. It also serves as information source for industrial, academic, and graduate student researchers who already use NMR spectroscopy, but not yet in two dimensions. The authors describe the use of 2-D NMR in a wide variety of chemical and biochemical fields, among them peptides, steroids, oligo- and poly-saccharides, nucleic acids, natural products (including terpenoids, alkaloids, and coal-derived heterocyclics), and organic synthetic intermediates. They consider throughout the book both the advantages and limitations of using 2-D NMR.

  12. Two-dimensional capillary origami

    NASA Astrophysics Data System (ADS)

    Brubaker, N. D.; Lega, J.

    2016-01-01

    We describe a global approach to the problem of capillary origami that captures all unfolded equilibrium configurations in the two-dimensional setting where the drop is not required to fully wet the flexible plate. We provide bifurcation diagrams showing the level of encapsulation of each equilibrium configuration as a function of the volume of liquid that it contains, as well as plots representing the energy of each equilibrium branch. These diagrams indicate at what volume level the liquid drop ceases to be attached to the endpoints of the plate, which depends on the value of the contact angle. As in the case of pinned contact points, three different parameter regimes are identified, one of which predicts instantaneous encapsulation for small initial volumes of liquid.

  13. Two-dimensional QCD and strings

    E-print Network

    D. J. Gross; W. Taylor

    1993-11-12

    A review is given of recent research on two-dimensional gauge theories, with particular emphasis on the equivalence between these theories and certain string theories with a two-dimensional target space. Some related open problems are discussed.

  14. Two Dimensional QCD is a String Theory

    E-print Network

    David J. Gross; Washington Taylor

    1993-01-18

    The partition function of two dimensional QCD on a Riemann surface of area $A$ is expanded as a power series in $1/N$ and $A$. It is shown that the coefficients of this expansion are precisely determined by a sum over maps from a two dimensional surface onto the two dimensional target space. Thus two dimensional QCD has a simple interpretation as a closed string theory.

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

    E-print Network

    Rubloff, Gary W.

    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

  16. Experimental two-dimensional field mapping of total internal reflection lateral beam shift in a self-collimated photonic crystal

    NASA Astrophysics Data System (ADS)

    Garcia-Pomar, J. L.; Gollub, J. N.; Mock, J. J.; Smith, D. R.; Nieto-Vesperinas, M.

    2009-02-01

    A lateral beam shift is demonstrated both theoretically and in microwave experiments when total internal reflection takes place at the boundary of a self-collimating two-dimensional photonic crystal consisting of an array of high index dielectric cylinders. We further show the dependence of this shift on the cut of the last row of cylinders that defines the crystal interface.

  17. Two Dimensional QCD as a String Theory

    E-print Network

    David J. Gross

    1992-12-24

    I explore the possibility of finding an equivalent string representation of two dimensional QCD. I develop the large N expansion of the ${\\rm QCD_2}$ partition function on an arbitrary two dimensional Euclidean manifold. If this is related to a two-dimensional string theory then many of the coefficients of the ${1\\over N}$ expansion must vanish. This is shown to be true to all orders, giving strong evidence for the existence of a string representation.

  18. Inductional Effects in a Halbach Magnet Motion Above Distributed Inductance

    NASA Astrophysics Data System (ADS)

    Tchatchoua, Yves; Conrow, Ary; Kim, Dong; Morgan, Daniel; Majewski, Walerian; Zafar, Zaeema

    2013-03-01

    We experimented with attempts to levitate a linear (bar) Halbach array of five 1'' Nd magnets above a linear inductive track. Next, in order to achieve a control over the relative velocity, we designed a different experiment. In it a large wheel with circumferentially positioned along its rim inducting coils rotates, while the magnet is suspended directly above the rim of the wheel on a force sensor. Faraday's Law with the Lenz's Rule is responsible for the lifting and drag forces on the magnet; the horizontal drag force is measured by another force sensor. Approximating the magnet's linear relative motion over inductors with a motion along a large circle, we may use formulas derived earlier in the literature for linear inductive levitation. We measured lift and drag forces as functions of relative velocity of the Halbach magnet and the inductive ``track,'' in an approximate agreement with the existing theory. We then vary the inductance and shape of the inductive elements to find the most beneficial choice for the lift/drag ratio at the lowest relative speed.

  19. Measuring Monotony in Two-Dimensional Samples

    ERIC Educational Resources Information Center

    Kachapova, Farida; Kachapov, Ilias

    2010-01-01

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

  20. Simulation of two-dimensional vortex dynamics

    NASA Astrophysics Data System (ADS)

    Minnhagen, Petter; Westman, Olof

    1994-02-01

    The two-dimensional XY model is simulated with a time-dependent Ginzburg-Landau type dynamics. The data are, in the limit of small driving force, well described by the Minnhagen phenomenology for vortex dynamics of a two-dimensional superfluid. This phenomenology is different and distinguishable from the conventional AHNS phenomenology. The Minnhagen phenomenology has been observed in recent experiments on Josephson-junction arrays and high- Tc BSCCO films. The present simulations suggest that this reflects an intrinsic property of the vortex dynamics for a two-dimensional superfluid.

  1. Two-Dimensional Planetary Surface Lander

    NASA Astrophysics Data System (ADS)

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

    2014-06-01

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

  2. Two-dimensional materials for electronic applications

    E-print Network

    Wang, Han, Ph. D. Massachusetts Institute of Technology

    2013-01-01

    The successful isolation of graphene in 2004 has attracted great interest to search for potential applications of this unique material and other members of the two-dimensional materials family in electronics, optoelectronics ...

  3. Single-sided mobile NMR with a Halbach magnet.

    PubMed

    Chang, Wei-Hao; Chen, Jyh-Horng; Hwang, Lian-Pin

    2006-10-01

    A single-sided mobile NMR apparatus with a small Halbach magnet was constructed for the first time. It is lightweight, compact and exhibits good sensitivity. The weight of the device is only 2 kg, and the NMR signal of the pencil eraser block can be detected in one shot using the device. This study describes the characteristics of this instrument, including the profile of static magnetic flux density, B0, the sensitivity in the depth direction and its effectiveness in one-dimensional profiling. Its usefulness in differentiating soft materials and evaluating the extent of damage of a material is demonstrated based on T2 relaxation data. The moisture absorbance also can be observed from the increase of the echo amplitude of the NMR spin echo signal. PMID:16997080

  4. Two-dimensional order and disorder thermofields

    SciTech Connect

    Belvedere, L. V.

    2006-11-15

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

  5. 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.

  6. 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.

  7. Electrically Charged Two-Dimensional Skyrmions

    NASA Astrophysics Data System (ADS)

    Loginov, A. Yu.

    2015-04-01

    The (2 + 1)-dimensional Skyrme gauge model with a Chern-Simons term is considered. The presence of the Chern-Simons term leads to the result that the Abelian gauge field of the model becomes massive. This, in turn, leads to the existence in the given model of two-dimensional skyrmions carrying magnetic flux and possessing an electric charge and, consequently, nonzero angular momentum. It is shown that the model also admits the existence of two-dimensional skyrmions, whose electrically charged fields rotate with a constant phase frequency. Due to the nontrivial topology of the configurations of the (2 + 1)-dimensional Skyrme gauge model with a Chern-Simons term, the magnetic flux, the electric charge, and the angular momentum of a rotating two-dimensional skyrmion turn out to be interrelated.

  8. Electrical contacts to two-dimensional semiconductors.

    PubMed

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

    2015-12-01

    The performance of electronic and optoelectronic devices based on two-dimensional layered crystals, including graphene, semiconductors of the transition metal dichalcogenide family such as molybdenum disulphide (MoS2) and tungsten diselenide (WSe2), as well as other emerging two-dimensional semiconductors such as atomically thin black phosphorus, is significantly affected by the electrical contacts that connect these materials with external circuitry. Here, we present a comprehensive treatment of the physics of such interfaces at the contact region and discuss recent progress towards realizing optimal contacts for two-dimensional materials. We also discuss the requirements that must be fulfilled to realize efficient spin injection in transition metal dichalcogenides. PMID:26585088

  9. Numerical simulation of a simple low-speed model for an electrodynamic levitation system based on a Halbach magnet array

    NASA Astrophysics Data System (ADS)

    Íñiguez, J.; Raposo, V.

    2010-05-01

    The design and analysis of a small prototype of a magnetic levitation system at low-speed using a Halbach-type magnet array is presented here. For that purpose, we have arranged a copper rim over a carbon fiber wheel, which is driven by an electric motor in presence of the magnet array, in such a manner that allows performing the experiment readily. The analysis of the system is undertaken under a two-dimensional (2D)-approach which permits computing and extending the study of our model to higher speeds. Our work is completed with a series of experimental measurements of lift and drag forces for different circumstances. Initially, the drag force is significant but after the compensation speed (when both forces balance) it slowly decreases. Conversely, the lift force becomes progressively bigger in such a manner that it attains quickly noteworthy values. We observe that the theoretical compensation speed is always minor than the experimental one and that the measured values for both forces are slightly smaller than the expected, although the main features of the experiment are well matched by our numerical simulation.

  10. Drag Law of Two Dimensional Granular Fluids

    E-print Network

    Satoshi Takada; Hisao Hayakawa

    2015-11-04

    The drag force law acting on a moving circular disk in a two-dimensional granular medium is analyzed based on the discrete element method (DEM). It is remarkable that the drag force on the moving disk in moderate dense and pure two-dimensional granular medium can be well reproduced by a perfect fluid with separation from the surface of the tracer. A yield force, being independent of the moving speed of the disk, appears if a dry friction between the granular disks and the bottom plate exists. The perfect fluidity is violated in this case. The yield force and the drag force diverge at the jamming point.

  11. Crossflow in two-dimensional asymmetric nozzles

    NASA Technical Reports Server (NTRS)

    Sebacher, D. I.; Lee, L. P.

    1975-01-01

    An experimental investigation of the crossflow effects in three contoured, two-dimensional asymmetric nozzles is described. The data were compared with theoretical predictions of nozzle flow by using an inviscid method of characteristics solution and two-dimensional turbulent boundary-layer calculations. The effect of crossflow as a function of the nozzle maximum expansion angle was studied by use of oil-flow techniques, static wall-pressure measurements, and impact-pressure surveys at the nozzle exit. Reynolds number effects on crossflow were investigated.

  12. Two-dimensional quantum-reflection traps

    SciTech Connect

    Madronero, Javier; Friedrich, Harald

    2007-06-15

    We study the confining properties of two-dimensional quantum-reflection traps, which are important for the transverse motion in atomic waveguides. For square geometry, the effect of nonseparability of the Schroedinger equation due to the corners is shown to be small. The survival probability due to quantum reflection is very similar for square and circular geometries.

  13. Cosmologies with Two-Dimensional Inhomogeneity

    E-print Network

    A. Feinstein; J. Ibáñez; Ruth Lazkoz

    1995-11-27

    We present a new generating algorithm to construct exact non static solutions of the Einstein field equations with two-dimensional inhomogeneity. Infinite dimensional families of $G_1$ inhomogeneous solutions with a self interacting scalar field, or alternatively with perfect fluid, can be constructed using this algorithm. Some families of solutions and the applications of the algorithm are discussed.

  14. New two dimensional compounds: beyond graphene

    NASA Astrophysics Data System (ADS)

    Lebegue, Sebastien

    2015-03-01

    In the field of nanosciences, the quest for materials with reduced dimensionality is only at its beginning. While a lot of effort has been put initially on graphene, the focus has been extended in the last past years to functionalized graphene, boron nitride, silicene, and transition metal dichalcogenides in the form of single layers. Although these two-dimensional compounds offer a larger range of properties than graphene, there is a constant need for new materials presenting equivalent or superior performances to the ones already known. Here I will present an approach that we have used to discover potential new two-dimensional materials. This approach corresponds to perform datamining in the Inorganic Crystal Structure Database using simple geometrical criterias, and allowed us to identify nearly 40 new materials that could be exfoliated into two-dimensional sheets. Then, their electronic structure (density of states and bandstructure) was obtained with density functional theory to predict whether the two-dimensional material is metallic or insulating, as well as if it undergoes magnetic ordering at low temperatures. If time allows, I will also present some of our recent results concerning the electronic structure of transition metal dichalcogenides bilayers.

  15. Two Dimensional Dictionary Matching Amihood Amir

    E-print Network

    Farach-Colton, Martin

    Two Dimensional Dictionary Matching Amihood Amir Martin Farach Georgia Tech DIMACS September 10 of a given pattern string P in a given text T . Another important paradigm is the dictionary matching problem. Let D = {P1, ..., Pk} be the dictionary. We seek all locations of dictionary patterns that appear

  16. Two-Dimensional Motions of Rockets

    ERIC Educational Resources Information Center

    Kang, Yoonhwan; Bae, Saebyok

    2007-01-01

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

  17. Nitrogenated holey two-dimensional structures

    PubMed Central

    Mahmood, Javeed; Lee, Eun Kwang; Jung, Minbok; Shin, Dongbin; Jeon, In-Yup; Jung, Sun-Min; Choi, Hyun-Jung; Seo, Jeong-Min; Bae, Seo-Yoon; Sohn, So-Dam; Park, Noejung; Oh, Joon Hak; Shin, Hyung-Joon; Baek, Jong-Beom

    2015-01-01

    Recent graphene research has triggered enormous interest in new two-dimensional ordered crystals constructed by the inclusion of elements other than carbon for bandgap opening. The design of new multifunctional two-dimensional materials with proper bandgap has become an important challenge. Here we report a layered two-dimensional network structure that possesses evenly distributed holes and nitrogen atoms and a C2N stoichiometry in its basal plane. The two-dimensional structure can be efficiently synthesized via a simple wet-chemical reaction and confirmed with various characterization techniques, including scanning tunnelling microscopy. Furthermore, a field-effect transistor device fabricated using the material exhibits an on/off ratio of 107, with calculated and experimental bandgaps of approximately 1.70 and 1.96?eV, respectively. In view of the simplicity of the production method and the advantages of the solution processability, the C2N-h2D crystal has potential for use in practical applications. PMID:25744355

  18. Nitrogenated holey two-dimensional structures.

    PubMed

    Mahmood, Javeed; Lee, Eun Kwang; Jung, Minbok; Shin, Dongbin; Jeon, In-Yup; Jung, Sun-Min; Choi, Hyun-Jung; Seo, Jeong-Min; Bae, Seo-Yoon; Sohn, So-Dam; Park, Noejung; Oh, Joon Hak; Shin, Hyung-Joon; Baek, Jong-Beom

    2015-01-01

    Recent graphene research has triggered enormous interest in new two-dimensional ordered crystals constructed by the inclusion of elements other than carbon for bandgap opening. The design of new multifunctional two-dimensional materials with proper bandgap has become an important challenge. Here we report a layered two-dimensional network structure that possesses evenly distributed holes and nitrogen atoms and a C2N stoichiometry in its basal plane. The two-dimensional structure can be efficiently synthesized via a simple wet-chemical reaction and confirmed with various characterization techniques, including scanning tunnelling microscopy. Furthermore, a field-effect transistor device fabricated using the material exhibits an on/off ratio of 10(7), with calculated and experimental bandgaps of approximately 1.70 and 1.96?eV, respectively. In view of the simplicity of the production method and the advantages of the solution processability, the C2N-h2D crystal has potential for use in practical applications. PMID:25744355

  19. Nitrogenated holey two-dimensional structures

    NASA Astrophysics Data System (ADS)

    Mahmood, Javeed; Lee, Eun Kwang; Jung, Minbok; Shin, Dongbin; Jeon, In-Yup; Jung, Sun-Min; Choi, Hyun-Jung; Seo, Jeong-Min; Bae, Seo-Yoon; Sohn, So-Dam; Park, Noejung; Oh, Joon Hak; Shin, Hyung-Joon; Baek, Jong-Beom

    2015-03-01

    Recent graphene research has triggered enormous interest in new two-dimensional ordered crystals constructed by the inclusion of elements other than carbon for bandgap opening. The design of new multifunctional two-dimensional materials with proper bandgap has become an important challenge. Here we report a layered two-dimensional network structure that possesses evenly distributed holes and nitrogen atoms and a C2N stoichiometry in its basal plane. The two-dimensional structure can be efficiently synthesized via a simple wet-chemical reaction and confirmed with various characterization techniques, including scanning tunnelling microscopy. Furthermore, a field-effect transistor device fabricated using the material exhibits an on/off ratio of 107, with calculated and experimental bandgaps of approximately 1.70 and 1.96?eV, respectively. In view of the simplicity of the production method and the advantages of the solution processability, the C2N-h2D crystal has potential for use in practical applications.

  20. TWO DIMENSIONAL COMPUTER SIMULATION OF PLASMA IMMERSION

    E-print Network

    TWO DIMENSIONAL COMPUTER SIMULATION OF PLASMA IMMERSION ION IMPLANTATION K. G. Kostov, J. J Immersion Ion Implantation A novel implantation technique especially developed for fast and efficient;Objectives · Development of realistic, particle-in-cell (PIC), computer simulation of plasma immersion ion

  1. 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…

  2. Halbach array generator/motor having an automatically regulated output voltage and mechanical power output

    DOEpatents

    Post, Richard F.

    2005-02-22

    A motor/generator having its stationary portion, i.e., the stator, positioned concentrically within its rotatable element, i.e., the rotor, along its axis of rotation. The rotor includes a Halbach array. The stator windings are switched or commutated to provide a DC motor/generator much the same as in a conventional DC motor/generator. The voltage and power are automatically regulated by using centrifugal force to change the diameter of the rotor, and thereby vary the radial gap in between the stator and the rotating Halbach array, as a function of the angular velocity of the rotor.

  3. Halbach array generator/motor having mechanically regulated output voltage and mechanical power output

    DOEpatents

    Post, Richard F.

    2005-06-14

    A motor/generator has its stationary portion, i.e., the stator, positioned concentrically within its rotatable element, i.e., the rotor, along the axis of rotation of the rotor. The rotor includes a Halbach array of magnets. The voltage and power outputs are regulated by varying the radial gap in between the stator windings and the rotating Halbach array. The gap is varied by extensible and retractable supports attached to the stator windings that can move the windings in a radial direction.

  4. Two-dimensional ranking of Wikipedia articles

    NASA Astrophysics Data System (ADS)

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

    2010-10-01

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

  5. Plasmonics with two-dimensional conductors

    PubMed Central

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

    2014-01-01

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

  6. Temporal reshaping of two-dimensional pulses.

    PubMed

    Sheppard, Colin J R; Kou, Shan Shan; Lin, Jiao; Sharma, Manjula; Barbastathis, George

    2014-12-29

    An analytic study of complete cylindrical focusing of pulses in two dimensions is presented, and compared with the analogous three-dimensional case of focusing over a complete sphere. Such behavior is relevant for understanding the limiting performance of ultrafast, planar photonic and plasmonic devices. A particular spectral distribution is assumed that contains finite energy. Separate ingoing and outgoing pulsed waves are considered, along with the combination that would be generated in free space by an ingoing wave. It is shown that for the two dimensional case, in order to produce a temporally symmetrical pulse at the focus, an asymmetric pulse must be launched. A symmetrical outgoing pulse is generated from a source with asymmetric time behavior, or an anti-symmetric input pulse. These results are very different from the corresponding three-dimensional case, and imply fundamental limitations on the performance of ultrafast, tightly focused, two-dimensional devices. PMID:25607169

  7. Kirigami for Two-Dimensional Electronic Membranes

    NASA Astrophysics Data System (ADS)

    Qi, Zenan; Bahamon, Dario; Campbell, David; Park, Harold

    2015-03-01

    Two-dimensional materials have recently drawn tremendous attention because of their unique properties. In this work, we introduce the notion of two-dimensional kirigami, where concepts that have been used almost exclusively for macroscale structures are applied to dramatically enhance their stretchability. Specifically, we show using classical molecular dynamics simulations that the yield and fracture strains of graphene and MoS2 can be enhanced by about a factor of three using kirigami as compared to standard monolayers. Finally, using graphene as an example, we demonstrate that the kirigami structure may open up interesting opportunities in coupling to the electronic behavior of 2D materials. Authors acknowledge Mechanical Engineering and Physics departments at Boston University, and Mackgrafe at Mackenzie Presbyterian University.

  8. Two-dimensional optimal sensor placement

    SciTech Connect

    Zhang, H.

    1995-05-01

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

  9. 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.

  10. Two dimensional wedge/translating shroud nozzle

    NASA Technical Reports Server (NTRS)

    Maiden, D. L. (inventor)

    1978-01-01

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

  11. Deeply subrecoil two-dimensional Raman cooling

    SciTech Connect

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

    2004-10-01

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

  12. Two-Dimensional Synthetic-Aperture Radiometer

    NASA Technical Reports Server (NTRS)

    LeVine, David M.

    2010-01-01

    A two-dimensional synthetic-aperture radiometer, now undergoing development, serves as a test bed for demonstrating the potential of aperture synthesis for remote sensing of the Earth, particularly for measuring spatial distributions of soil moisture and ocean-surface salinity. The goal is to use the technology for remote sensing aboard a spacecraft in orbit, but the basic principles of design and operation are applicable to remote sensing from aboard an aircraft, and the prototype of the system under development is designed for operation aboard an aircraft. In aperture synthesis, one utilizes several small antennas in combination with a signal processing in order to obtain resolution that otherwise would require the use of an antenna with a larger aperture (and, hence, potentially more difficult to deploy in space). The principle upon which this system is based is similar to that of Earth-rotation aperture synthesis employed in radio astronomy. In this technology the coherent products (correlations) of signals from pairs of antennas are obtained at different antenna-pair spacings (baselines). The correlation for each baseline yields a sample point in a Fourier transform of the brightness-temperature map of the scene. An image of the scene itself is then reconstructed by inverting the sampled transform. The predecessor of the present two-dimensional synthetic-aperture radiometer is a one-dimensional one, named the Electrically Scanned Thinned Array Radiometer (ESTAR). Operating in the L band, the ESTAR employs aperture synthesis in the cross-track dimension only, while using a conventional antenna for resolution in the along-track dimension. The two-dimensional instrument also operates in the L band to be precise, at a frequency of 1.413 GHz in the frequency band restricted for passive use (no transmission) only. The L band was chosen because (1) the L band represents the long-wavelength end of the remote- sensing spectrum, where the problem of achieving adequate spatial resolution is most critical and (2) imaging airborne instruments that operate in this wavelength range and have adequate spatial resolution are difficult to build and will be needed in future experiments to validate approaches for remote sensing of soil moisture and ocean salinity. The two-dimensional instrument includes a rectangular array of patch antennas arranged in the form of a cross. The ESTAR uses analog correlation for one dimension, whereas the two-dimensional instrument uses digital correlation. In two dimensions, many more correlation pairs are needed and low-power digital correlators suitable for application in spaceborne remote sensing will help enable this technology. The two-dimensional instrument is dual-polarized and, with modification, capable of operating in a polarimetric mode. A flight test of the instrument took place in June 2003 and it participated in soil moisture experiments during the summers of 2003 and 2004.

  13. Two dimensional foam rheology with viscous drag

    E-print Network

    E. Janiaud; D. Weaire; S. Hutzler

    2006-07-18

    We formulate and apply a continuum model that incorporates elasticity, yield stress, plasticity and viscous drag. It is motivated by the two-dimensional foam rheology experiments of Debregeas et al. [G. Debregeas, H. Tabuteau, and J.-M. di Meglio, Phys. Rev. Lett. 87, 178305 (2001)] and Wang et al [Y. Wang, K. Krishan, and M. Dennin, Phys. Rev. E 73, 031401 (2006)], and is successful in exhibiting their principal features an exponentially decaying velocity profile and strain localisation. Transient effects are also identified.

  14. The two-dimensional connectivity of

    NASA Astrophysics Data System (ADS)

    German, R. M.

    1987-06-01

    Liquid phase sintered materials are characterized by a connected microstructure composed of contacting grains in a solidified matrix phase. Observations on the sintered microstructure are typically performed using two-dimensional cross sections. A computer calculation has been performed to determine the variation in the observed contacts per grain vs the true underlying microstructure connectivity. The results show that the observed coordination depends on both the volume fraction of solid phase and the dihedral angle. The findings of the calculation are favorably compared with observations on Fe-Cu and W-Ni-Fe alloys. In the limiting case, the current calculations approach those found for polycrystalline solids and cell networks.

  15. Anisotropic Two-Dimensional Friedel Oscillations

    SciTech Connect

    Hofmann, P.; Plummer, E.W.; Briner, B.G.; Doering, M.; Rust, H.; Bradshaw, A.M.

    1997-07-01

    Scanning tunneling microscopy at 4K shows highly anisotropic screening charge density oscillations on Be(10{ovr 1}0) in the vicinity of surface defects and steps. The forms of these oscillations, which derive from the Friedel oscillations, can be directly related to the two-dimensional band structure of the surface (two electron pockets at the boundary of the surface Brillouin zone). Simple calculations show that the Friedel oscillations in such a case will contain major contributions from wavelengths which do not correspond to any Fermi wave vector. {copyright} {ital 1997} {ital The American Physical Society}

  16. Two-Dimensional Ground Water Transport

    Energy Science and Technology Software Center (ESTSC)

    1992-03-05

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

  17. Vortices in Two- Dimensional Anisotropic ? Models

    NASA Astrophysics Data System (ADS)

    Watanabe, T.; Otsu, H.

    1981-01-01

    We define a topological number and clarify its role played in two-dimensional anisotropic ? models. Non-dissipative metastable states are obtained as counter-examples to which Derrick's theorem cannot be applied. Each metastable state classified by the topological number q turns out to carry |q| vortices and |q| stagnation points for the cases of XY-like anisotropy and to involve |q| antiparallel core spins for those of Ising-like one. The range and strength of vortices are studied in detail for the XY-model obtained from present systems.

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

    SciTech Connect

    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.

  19. A new magnetic bearing using Halbach magnet arrays for a magnetic levitation stage

    NASA Astrophysics Data System (ADS)

    Choi, Young-Man; Lee, Moon G.; Gweon, Dae-Gab; Jeong, Jaehwa

    2009-04-01

    Next-generation lithography requires a high precision stage, which is compatible with a high vacuum condition. A magnetic levitation stage with six degrees-of-freedom is considered state-of-the-art technology for a high vacuum condition. The noncontact characteristic of magnetic levitation enables high precision positioning as well as no particle generation. To position the stage against gravity, z-directional electromagnetic levitation mechanisms are widely used. However, if electromagnetic actuators for levitation are used, heat is inevitably generated, which deforms the structures and degrades accuracy of the stage. Thus, a gravity compensator is required. In this paper, we propose a new magnetic bearing using Halbach magnet arrays for a magnetic levitation stage. The novel Halbach magnetic bearing exerts a force four times larger than a conventional magnetic bearing with the same volume. We also discuss the complementary characteristics of the two magnetic bearings. By modifying the height of the center magnet in a Halbach magnetic bearing, a performance compromise between levitating force density and force uniformity is obtained. The Halbach linear active magnetic bearing can be a good solution for magnetic levitation stages because of its large and uniform levitation force.

  20. Two-dimensional vortices in superconductors

    NASA Astrophysics Data System (ADS)

    Chen, Bo; Halperin, W. P.; Guptasarma, Prasenjit; Hinks, D. G.; Mitrovi?, V. F.; Reyes, A. P.; Kuhns, P. L.

    2007-04-01

    Superconductors have two key characteristics: they expel magnetic field and they conduct electrical current with zero resistance. However, both properties are compromised in high magnetic fields, which can penetrate the material and create a mixed state of quantized vortices. The vortices move in response to an electrical current, dissipating energy and destroying the zero-resistance state. One of the central problems for applications of high-temperature superconductivity is the stabilization of vortices to ensure zero electrical resistance. We find that vortices in the anisotropic superconductor Bi2Sr2CaCu2O8+? (Bi-2212) have a phase transition from a liquid state, which is inherently unstable, to a two-dimensional vortex solid. We show that at high field the transition temperature is independent of magnetic field, as was predicted theoretically for the melting of an ideal two-dimensional vortex lattice. Our results indicate that the stable solid phase can be reached at any field, as may be necessary for applications involving superconducting magnets. The vortex solid is disordered, as suggested by previous studies at lower fields. But its evolution with increasing magnetic field exhibits unexpected threshold behaviour that needs further investigation.

  1. Renormalization of two-dimensional XQCD

    E-print Network

    Fukaya, Hidenori

    2015-01-01

    Recently, Kaplan proposed an interesting extension of QCD named Extended QCD or XQCD with bosonic auxiliary fields [1]. While its partition function is kept exactly the same as that of QCD, XQCD naturally contains properties of low-energy hadrons. We apply this extension to the two-dimensional QCD in the large $N_c$ limit ('t Hooft model) [2]. In this solvable model, it is possible to directly examine the hadronic picture of the 2d XQCD and analyze its renormalization group flow to understand how the auxiliary degrees of freedom behave in the low energy region. We confirm that the additional scalar fields can become dynamical acquiring the kinetic term, and its parity-odd part becomes dominant in the low energy region. This renomalization of XQCD provides an "extension" of the renormalization scheme of QCD, inserting different field variables from those in the original theory, without any changes in physical observables.

  2. Renormalization of two-dimensional XQCD

    E-print Network

    Hidenori Fukaya; Ryo Yamamura

    2015-10-15

    Recently, Kaplan proposed an interesting extension of QCD named Extended QCD or XQCD with bosonic auxiliary fields [1]. While its partition function is kept exactly the same as that of QCD, XQCD naturally contains properties of low-energy hadrons. We apply this extension to the two-dimensional QCD in the large $N_c$ limit ('t Hooft model) [2]. In this solvable model, it is possible to directly examine the hadronic picture of the 2d XQCD and analyze its renormalization group flow to understand how the auxiliary degrees of freedom behave in the low energy region. We confirm that the additional scalar fields can become dynamical acquiring the kinetic term, and its parity-odd part becomes dominant in the low energy region. This renomalization of XQCD provides an "extension" of the renormalization scheme of QCD, inserting different field variables from those in the original theory, without any changes in physical observables.

  3. Two-dimensional Experiments With Descent Algorithms

    NASA Astrophysics Data System (ADS)

    Jakubiak, B.

    We examine the question of convergence of four descent variational algorithms: con- jugate gradient (cg), conjugate gradient squared (cgs), generalized minimum resid- ual (gmres) and transpose-free quasi minimal residual method (tfqmr) using two- dimensional, realistic, randomly located observational network. For the case of ac- curate uncorrelated observations and weakly correlated background error we define three diagnostic techniques and tested them for three different background error cor- relation models: SOAR, Gaussian and compact spline. The convergence rate depends largely on the condition number of innovation matrix. We found that practical mea- sure of the convergence can be based on estimating the norm of the gradient of the cost function. The norm is defined as the square root of the sum of the elements of the gradient and can be estimated at each iteration step. Other diagnostic techniques tested are more costly and can be used in simple situations only.

  4. Two-dimensional Inductive Position Sensing System

    NASA Technical Reports Server (NTRS)

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

    2015-01-01

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

  5. Two-dimensional informative array testing.

    PubMed

    McMahan, Christopher S; Tebbs, Joshua M; Bilder, Christopher R

    2012-09-01

    Array-based group-testing algorithms for case identification are widely used in infectious disease testing, drug discovery, and genetics. In this article, we generalize previous statistical work in array testing to account for heterogeneity among individuals being tested. We first derive closed-form expressions for the expected number of tests (efficiency) and misclassification probabilities (sensitivity, specificity, predictive values) for two-dimensional array testing in a heterogeneous population. We then propose two "informative" array construction techniques which exploit population heterogeneity in ways that can substantially improve testing efficiency when compared to classical approaches that regard the population as homogeneous. Furthermore, a useful byproduct of our methodology is that misclassification probabilities can be estimated on a per-individual basis. We illustrate our new procedures using chlamydia and gonorrhea testing data collected in Nebraska as part of the Infertility Prevention Project. PMID:22212007

  6. Atomic Defects in Two Dimensional Materials.

    PubMed

    Rasool, Haider I; Ophus, Colin; Zettl, Alex

    2015-10-01

    Atomic defects in crystalline structures have pronounced affects on their bulk properties. Aberration-corrected transmission electron microscopy has proved to be a powerful characterization tool for understanding the bonding structure of defects in materials. In this article, recent results on the characterization of defect structures in two dimensional materials are discussed. The dynamic behavior of defects in graphene shows the stability of zigzag edges of the material and gives insights into the dislocation motion. Polycrystalline graphene is characterized using advanced electron microscopy techniques, revealing the global crystal structure of the material, as well as atomic-resolution observation of the carbon atom positions between neighboring crystal grains. Studies of hexagonal boron nitride (hBN) are also visited, highlighting the interlayer bonding, which occurs upon defect formation, and characterization of grain boundary structures. Lastly, defect structures in monolayer polycrystalline transition metal dichalcogenides grown by CVD are discussed. PMID:25946075

  7. Two-dimensional readout of GEM detectors

    E-print Network

    Bressan, A; Gandi, A; Labbé, J C; Ropelewski, Leszek; Sauli, Fabio; Mörmann, D; Müller, T; Simonis, H J

    1999-01-01

    The recently introduced Gas Electron Multiplier (GEM) permits the amplification of electrons released by ionizing radiation in a gas by factors approaching ten thousand, larger gains can be obtained combining two GEMs in cascade. We describe methods for implementing two- and three-dimensional projective localization of radiation, with sub-millimeter accuracy, making use of specially manufactured and patterned pick-up electrodes. Easy to implement and flexible in the choice of the readout geometry, the technology has the distinctive advantage of allowing all pick-up electrodes to be kept at ground potential, thus substantially improving the system simplicity and reliability. Preliminary results demonstrating the two-dimensional imaging capability of the devices are provided and discussed, as well as future perspectives of development.

  8. 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.

  9. Acidity of two-dimensional zeolites.

    PubMed

    Rybicki, Marcin; Sauer, Joachim

    2015-10-14

    Hybrid quantum mechanics:molecular mechanics (QM/MM) calculations of absolute deprotonation energies are performed with periodic boundary conditions for Brønsted sites of aluminosilicate bilayers with various Al/Si ratios (two-dimensional zeolite). The supercell method is applied and density functional theory is used. Much lower values are obtained (1042, 1069 and 1091 kJ mol(-1) for Al/Si = 1/63, 1/7 and 1/3, respectively) than those for bulk zeolites (1233 kJ mol(-1) for H-chabazite with Al/Si = 1/11). We ascribe the much lower deprotonation energy to the smaller effective dielectric constant (1.6-1.9) of an ultra-thin dielectric in a vacuum compared to that of the corresponding bulk systems (3.0 for H-chabazite), which leads to a better stabilization of the charge created upon deprotonation. PMID:26437870

  10. 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

  11. Phonon hydrodynamics in two-dimensional materials

    NASA Astrophysics Data System (ADS)

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

    2015-03-01

    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.

  12. Epitaxial growth of two-dimensional stanene

    NASA Astrophysics Data System (ADS)

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

    2015-10-01

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

  13. Sieving hydrogen isotopes through two dimensional crystals

    E-print Network

    Lozada-Hidalgo, M; Marshall, O; Mishchenko, A; Grigorenko, A N; Dryfe, R A W; Radha, B; Grigorieva, I V; Geim, A K

    2015-01-01

    One-atom-thick crystals are impermeable to atoms and molecules, but hydrogen ions (thermal protons) penetrate through them. We show that monolayers of graphene and boron nitride can be used to separate hydrogen ion isotopes. Employing electrical measurements and mass spectrometry, we find that deuterons permeate through these crystals much slower than protons, resulting in a separation factor of 10 at room temperature. The isotope effect is attributed to a difference of about 60 meV between zero-point energies of incident protons and deuterons, which translates into the equivalent difference in the activation barriers posed by two dimensional crystals. In addition to providing insight into the proton transport mechanism, the demonstrated approach offers a competitive and scalable way for hydrogen isotope enrichment.

  14. Intrinsic two-dimensional features as textons

    NASA Technical Reports Server (NTRS)

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

    1998-01-01

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

  15. A Multi-axis Compact Positioner with a 6-coil Platen Moving Over a Superimposed Halbach Magnet Matrix 

    E-print Network

    Nguyen, Vu Huy

    2012-07-16

    -AXIS COMPACT POSITIONER WITH A 6-COIL PLATEN MOVING OVER A SUPERIMPOSED HALBACH MAGNET MATRIX A Thesis by VU HUY NGUYEN 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 May 2011 Major Subject: Mechanical Engineering A Multi-axis Compact Positioner with a 6-coil Platen Moving Over a Superimposed Halbach Magnet Matrix Copyright 2011 Vu Huy Nguyen...

  16. Information technologies for comprehensive two-dimensional gas chromatography

    E-print Network

    Reichenbach, Stephen E.

    Review Information technologies for comprehensive two-dimensional gas chromatography Stephen E December 2003 Available online 8 March 2004 Abstract Comprehensive two-dimensional gas chromatography (GC Â-dimensional gas chromatography; GCÂGC; Information technology; Image processing; Visualization; Computer

  17. 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 ...

  18. FPT Algorithm for Two-Dimensional Cyclic Convolutions

    NASA Technical Reports Server (NTRS)

    Truong, Trieu-Kie; Shao, Howard M.; Pei, D. Y.; Reed, Irving S.

    1987-01-01

    Fast-polynomial-transform (FPT) algorithm computes two-dimensional cyclic convolution of two-dimensional arrays of complex numbers. New algorithm uses cyclic polynomial convolutions of same length. Algorithm regular, modular, and expandable.

  19. Aerodynamic interaction between vortical wakes and lifting two-dimensional bodies

    NASA Astrophysics Data System (ADS)

    Stremel, Paul M.

    1989-03-01

    Unsteady rotor wake interactions with the empennage, tail boom, and other aerodynamic surfaces of a helicopter have a significant influence on its aerodynamic performance, the ride quality, and vibration. A numerical method for computing the aerodynamic interaction between an interacting vortex wake and the viscous flow about arbitrary two-dimensional bodies was developed to address this helicopter problem. The method solves for the flow field velocities on a body-fitted computational mesh using finite-difference techniques. The interacting vortex wake is represented by an array of discrete vortices which, in turn, are represented by a finite-core model. The evolution of the interacting vortex wake is calculated by Lagrangian techniques. The viscous flow field of the two-dimensional body is calculated on an Eulerian grid. The flow around circular and elliptic cylinders in the absence of an interacting vortex wake was calculated. These results compare very well with other numerical results and with results obtained from experiment and thereby demonstrate the accuracy of the viscous solution. The interaction of a rotor wake with the flow about a 4 to 1 elliptic cylinder at 45 degree incidence was calculated for a Reynolds number of 3000. The results demonstrate the significant variations in the lift and drag on the elliptic cylinder in the presence of the interacting rotor wake.

  20. Imaging Magnetic Focusing in a Two-Dimensional Electron Gas

    E-print Network

    Imaging Magnetic Focusing in a Two-Dimensional Electron Gas A dissertation presented by Katherine E Author Robert M. Westervelt Katherine E. Aidala Imaging Magnetic Focusing in a Two-Dimensional Electron heterostructures is to spatially image their motion. The two-dimensional electron gas has proved its interest

  1. Experimental studies of the development of quasi-two-dimensional turbulence in stably stratified fluid

    NASA Astrophysics Data System (ADS)

    Yap, C. T.; van Atta, C. W.

    1993-10-01

    Quasi-two-dimensional turbulence was generated by towing an array of vertical cylinders through a tank which was filled with a two-layer stratified fluid. Sugar and Epsom salts were used, to give matching refractive indices for the two layers. The interface between the two layers was seeded with approximately 1000 neutrally buoyant particles. The evolution of this quasi-two-dimensional turbulence was visualized by photographing the fluorescent particles illuminated by a horizontal laser sheet traversing in the vertical direction. The three-dimensional particle velocity was obtained by digitizing the streaks. The evolution of the velocity correlations, length scales, one-dimensional and two-dimensional velocity and vorticity spectra were obtained for N = 5.72 s -1, N = 4.43 s -1, and N = 2.55 s -1 (where N is the Brunt-Väisälä frequency). The results showed the physical process of inverse energy cascading and the formation of dominant vortical structures under the influence of density stratification. Compared with idealized two-dimensional turbulence, the flow is highly dissipative at high N, as a result of the frictional dissipation between the interface and the unstratified layers.

  2. Laminar free convection over two-dimensional bodies with uniform surface heat flux

    NASA Technical Reports Server (NTRS)

    Lin, F. N.

    1976-01-01

    A general analysis is presented of the steady nondissipative constant-property laminar boundary layer flow over a two-dimensional body of uniform surface heat flux situated in an infinite ambient fluid of undisturbed temperature. The analysis is then applied to a long horizontal circular cylinder. Numerical solutions to the universal functions associated with the first two terms in the derived series are given for Prandtl numbers 0.7, 1, 3, 5, 7, and 10. The results are compared with those obtained by Koh (1964) whose method is patterned after the Blasius-Frossling procedure for forced convection flow. The study reveals that Wilks' (1972) analysis concerning the external natural convection about two-dimensional bodies with constant heat flux is in error.

  3. Two-Dimensional Black Holes and Planar General Relativity

    E-print Network

    Jose' P. S. Lemos

    1994-07-20

    The Einstein-Hilbert action with a cosmological term is used to derive a new action in 1+1 spacetime dimensions. It is shown that the two-dimensional theory is equivalent to planar symmetry in General Relativity. The two-dimensional theory admits black holes and free dilatons, and has a structure similar to two-dimensional string theories. Since by construction these solutions also solve Einstein's equations, such a theory can bring two-dimensional results into the four-dimensional real world. In particular the two-dimensional black hole is also a black hole in General Relativity.

  4. Two-dimensional conformal field theories The major problems solved Unsolved problems Two-Dimensional Conformal Field Theory

    E-print Network

    Huang, Yi-Zhi

    Two-dimensional conformal field theories The major problems solved Unsolved problems Two-Dimensional Conformal Field Theory Yi-Zhi Huang Department of Mathematics Rutgers University Piscataway, NJ 08854, USA Institute of Mathematics, Chinese Academy of Sciences #12;Two-dimensional conformal field theories The major

  5. Approach for two-dimensional velocity mapping

    NASA Astrophysics Data System (ADS)

    Abado, Shaddy; Gordeyev, Stanislav; Jumper, Eric

    2013-07-01

    A method for extracting the convection speed and direction of aberrations present in wavefronts due to aero-optical turbulence over the pupil of a turret on the side of an airborne platform is addressed. The method is applied to data from the Airborne Aero-Optics Laboratory (AAOL). Such convection information is useful in designing feed-forward adaptive-optic approaches. The method makes use of a four-beam Malley probe technique derived by constructing a two-dimensional (2-D) local convective velocity-distribution over the beam's aperture. This technique is based on extending the analysis of the Notre-Dame-developed Malley probe. Two wavefront datasets (Azimuth 157 deg and Elevation 40 deg Azimuth 42 deg and Elevation 43 deg) from the AAOL are analyzed using the derived method, the first where the laser propagates through fully-separated flow and the second where the laser propagates through an attached-flow region. Finally, the 2-D proper orthogonal decomposition is applied to one in-flight measured dataset to determine the spatial requirements of deformable mirrors in an adaptive-optics system. The paper concludes with a discussion that points out the usefulness of the 2-D velocity-distributions in characterizing the various flow structures which convect over the aperture.

  6. Predicting Two-Dimensional Silicon Carbide Monolayers.

    PubMed

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

    2015-10-27

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

  7. 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. Epitaxial growth of two-dimensional stanene.

    PubMed

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

    2015-10-01

    Following the first experimental realization of graphene, other ultrathin materials with unprecedented electronic properties have been explored, with particular attention given to the heavy group-IV elements Si, Ge and Sn. Two-dimensional buckled Si-based silicene has been recently realized by molecular beam epitaxy growth, whereas Ge-based germanene was obtained by molecular beam epitaxy and mechanical exfoliation. However, the synthesis of Sn-based stanene has proved challenging so far. Here, we report the successful fabrication of 2D stanene by molecular beam epitaxy, confirmed by atomic and electronic characterization using scanning tunnelling microscopy and angle-resolved photoemission spectroscopy, in combination with first-principles calculations. The synthesis of stanene and its derivatives will stimulate further experimental investigation of their theoretically predicted properties, such as a 2D topological insulating behaviour with a very large bandgap, and the capability to support enhanced thermoelectric performance, topological superconductivity and the near-room-temperature quantum anomalous Hall effect. PMID:26237127

  9. Seismic isolation of two dimensional periodic foundations

    NASA Astrophysics Data System (ADS)

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

    2014-07-01

    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.

  10. 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.

  11. Seismic isolation of two dimensional periodic foundations

    SciTech Connect

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

    2014-07-28

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

  12. Braid Entropy of Two-Dimensional Turbulence

    PubMed Central

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

    2015-01-01

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

  13. Two-dimensional Dirac signature of germanene

    NASA Astrophysics Data System (ADS)

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

    2015-09-01

    The structural and electronic properties of germanene coated Ge2Pt clusters have been determined by scanning tunneling microscopy and spectroscopy at room temperature. The interior of the germanene sheet exhibits a buckled honeycomb structure with a lattice constant of 4.3 Å and a buckling of 0.2 Å. The zigzag edges of germanene are reconstructed and display a 4× periodicity. The differential conductivity of the interior of the germanene sheet has a V-shape, which is reminiscent of the density of states of a two-dimensional Dirac system. The minimum of the differential conductivity is located close to the Fermi level and has a non-zero value, which we ascribe to the metallic character of the underlying Ge2Pt substrate. Near the reconstructed germanene zigzag edges the shape of the differential conductivity changes from a V-shape to a more parabolic-like shape, revealing that the reconstructed germanene zigzag edges do not exhibit a pronounced metallic edge state.

  14. Braid Entropy of Two-Dimensional Turbulence.

    PubMed

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

    2015-01-01

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

  15. Dynamics of two-dimensional dipole systems

    SciTech Connect

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

    2010-09-15

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

  16. Two-dimensional materials and their prospects in transistor electronics.

    PubMed

    Schwierz, F; Pezoldt, J; Granzner, R

    2015-05-14

    During the past decade, two-dimensional materials have attracted incredible interest from the electronic device community. The first two-dimensional material studied in detail was graphene and, since 2007, it has intensively been explored as a material for electronic devices, in particular, transistors. While graphene transistors are still on the agenda, researchers have extended their work to two-dimensional materials beyond graphene and the number of two-dimensional materials under examination has literally exploded recently. Meanwhile several hundreds of different two-dimensional materials are known, a substantial part of them is considered useful for transistors, and experimental transistors with channels of different two-dimensional materials have been demonstrated. In spite of the rapid progress in the field, the prospects of two-dimensional transistors still remain vague and optimistic opinions face rather reserved assessments. The intention of the present paper is to shed more light on the merits and drawbacks of two-dimensional materials for transistor electronics and to add a few more facets to the ongoing discussion on the prospects of two-dimensional transistors. To this end, we compose a wish list of properties for a good transistor channel material and examine to what extent the two-dimensional materials fulfill the criteria of the list. The state-of-the-art two-dimensional transistors are reviewed and a balanced view of both the pros and cons of these devices is provided. PMID:25898786

  17. 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.

  18. 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.

  19. Quantitative, single shot, two-dimensional spontaneous Raman measurements for fluid mechanics and engine applications

    NASA Astrophysics Data System (ADS)

    Kyritsis, Dimitrios Constantinou

    Spontaneous Raman Scattering was used for quantitative, two-dimensional, single-shot measurements of species concentration in optically accessible confinements and in an experimental single-cylinder internal combustion engine. The study comprised three parts. In the first part, the technique was used for methane concentration measurements in a laminar jet issuing into compressed nitrogen (10 bar, 293 K). The injection Reynolds number was 550. Initial results showed unexpected structures in the acquired concentration profiles. Thus, the steadiness of the laminar flow was confirmed with high speed shadowgraph movies and laser induced fluorescence measurements. Eventually, it was proven that the structures were due to characteristics of the camera system. A technique was then devised for the proper acquisition and processing of data and spatial resolution of 500 mum was achieved. Methane number density equal to 12% of the number density of pure methane (0.247E+26 molecules/msp3) was then measured with a signal-to-noise ratio of approximately 3. The measurements were compared with the results of direct numerical simulation of the flow field. In the second part, measurements in a laminar hydrogen jet were taken. Because of the reduced Raman signal of hydrogen, the incident laser power was increased by installing the pressurized chamber within the laser cavity. This yielded an increase in power by a factor of 2.5. For the measurement of the laser sheet intensity in the laser cavity, insertion of a fluorescent dye cell and Rayleigh scattering were used and evaluated comparatively. The precise location of the waist of the laser sheet was determined by trial and error. The spatial resolution of the measurements was 650 mum and a number density of 0.371E+26 hydrogen molecules/msp3 was measured with a signal-to-noise ratio of 3. The measurements were again compared with results of direct numerical simulation. In the third part, the feasibility of two-dimensional single-shot Spontaneous Raman measurements in an engine cylinder was established. Measurements of methane concentration after direct injection in the cylinder of an experimental single-cylinder engine were taken. The engine was not fired to avoid laser induced incandescence interference. The spatial resolution was limited to 800 mum by the thickness of the laser sheet. Fast mixing of the methane jet was documented but a precise evaluation of the equivalence ratio was beyond the resolution of this first attempt. Finally, existing hardware for data acquisition and algorithms for two dimensional data reduction were reviewed and recommendations were made for the extraction of quantitative information from two-dimensional, single-shot Spontaneous Raman signals which are weak and noisy.

  20. Some Properties of Large $N$ Two Dimensional Yang--Mills Theory

    E-print Network

    David J. Gross; Andrei Matytsin

    1994-10-09

    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 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.

  1. Two-dimensional tomographic terahertz imaging by homodyne self-mixing.

    PubMed

    Mohr, Till; Breuer, Stefan; Giuliani, G; Elsäßer, Wolfgang

    2015-10-19

    We realize a compact two-dimensional tomographic terahertz imaging experiment involving only one photoconductive antenna (PCA) simultaneously serving as a transmitter and receiver of the terahertz radiation. A hollow-core Teflon cylinder filled with ?-Lactose monohydrate powder is studied at two terahertz frequencies, far away and at a specific absorption line of the powder. This sample is placed between the antenna and a chopper wheel, which serves as back reflector of the terahertz radiation into the PCA. Amplitude and phase information of the continuous-wave (CW) terahertz radiation are extracted from the measured homodyne self-mixing (HSM) signal after interaction with the cylinder. The influence of refraction is studied by modeling the set-up utilizing ZEMAX and is discussed by means of the measured 1D projections. The tomographic reconstruction by using the Simultaneous Algebraic Reconstruction Technique (SART) allows to identify both object geometry and ?-Lactose filling. PMID:26480382

  2. Dynamics of magnetic particles in cylindrical Halbach array: implications for magnetic cell separation and drug targeting.

    TOXLINE Toxicology Bibliographic Information

    Babinec P; Krafcík A; Babincová M; Rosenecker J

    2010-08-01

    Magnetic nanoparticles for therapy and diagnosis are at the leading edge of the rapidly developing field of bionanotechnology. In this study, we have theoretically studied motion of magnetic nano- as well as micro-particles in the field of cylindrical Halbach array of permanent magnets. Magnetic flux density was modeled as magnetostatic problem by finite element method and particle motion was described using system of ordinary differential equations--Newton law. Computations were done for nanoparticles Nanomag-D with radius 65 nm, which are often used in magnetic drug targeting, as well as microparticles DynaBeads-M280 with radius 1.4 microm, which can be used for magnetic separation. Analyzing snapshots of trajectories of hundred magnetite particles of each size in the water as well as in the air, we have found that optimally designed magnetic circuits of permanent magnets in quadrupolar Halbach array have substantially shorter capture time than simple blocks of permanent magnets commonly used in experiments, therefore, such a Halbach array may be useful as a potential source of magnetic field for magnetic separation and targeting of magnetic nanoparticles as well as microparticles for delivery of drugs, genes, and cells in various biomedical applications.

  3. Dynamics of two-dimensional bubbles.

    PubMed

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

    2015-06-01

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

  4. Statistical mechanics of two-dimensional turbulence

    E-print Network

    Sunghwan Jung; P. J. Morrison; Harry L. Swinney

    2006-03-09

    The statistical mechanical description of two-dimensional inviscid fluid turbulence is reconsidered. Using this description, we make predictions about turbulent flow in a rapidly rotating laboratory annulus. Measurements on the continuously forced, weakly dissipative flow reveal coherent vortices in a mean zonal flow. Statistical mechanics has two crucial requirements for equilibrium: statistical independence of macro-cells (subsystems) and additivity of invariants of macro-cells. We use additivity to select the appropriate Casimir invariants from the infinite set available in vortex dynamics, and we do this in such a way that the exchange of micro-cells within a macro-cell does not alter an invariant of a macro-cell. A novel feature of the present study is our choice of macro-cells, which are continuous phase space curves based on mean values of the streamfunction. Quantities such as energy and enstrophy can be defined on each curve, and these lead to a local canonical distribution that is also defined on each curve. Our approach leads to the prediction that on a mean streamfunction curve there should be a linear relation between the ensemble-averaged potential vorticity and the time-averaged streamfunction, and our laboratory data are in good accord with this prediction. Further, the approach predicts that although the probability distribution function for potential vorticity in the entire system is non-Gaussian, the distribution function of micro-cells should be Gaussian on the macro-cells, i.e., for curves defined by mean values of the streamfunction. This prediction is also supported by the data. While the statistical mechanics approach used was motivated by and applied to experiments on turbulence in a rotating annulus, the approach is quite general and is applicable to a large class of Hamiltonian systems.

  5. Dynamics of two-dimensional bubbles

    NASA Astrophysics Data System (ADS)

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

    2015-06-01

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

  6. Two-dimensional vibrational-electronic spectroscopy

    NASA Astrophysics Data System (ADS)

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

    2015-10-01

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

  7. Digital watermarking method using a two-dimensional barcode

    NASA Astrophysics Data System (ADS)

    Jeon, Seong-Goo; Choi, Kyoung-Ho; Park, Chan-Won; Kim, Il-Hwan

    2005-12-01

    This paper proposed a digital watermarking method using a two-dimensional bar code. In general, one-dimensional bar code was just a key that can access detailed information to the host computer database. But a two-dimensional bar code is a new technology capable of holding relatively large amounts of data compared to the conventional one-dimensional bar code. The study used Data Matrix that is the most widely used among the many kinds of two-dimensional bar code. The experimental results show a similarity of the embedded and extracted two-dimensional watermark.

  8. Enhancement of polarizabilities of cylinders with cylinder-slab resonances

    PubMed Central

    Xiao, Meng; Huang, Xueqin; Liu, H.; Chan, C. T.

    2015-01-01

    If an object is very small in size compared with the wavelength of light, it does not scatter light efficiently. It is hence difficult to detect a very small object with light. We show using analytic theory as well as full wave numerical calculation that the effective polarizability of a small cylinder can be greatly enhanced by coupling it with a superlens type metamaterial slab. This kind of enhancement is not due to the individual resonance effect of the metamaterial slab, nor due to that of the object, but is caused by a collective resonant mode between the cylinder and the slab. We show that this type of particle-slab resonance which makes a small two-dimensional object much “brighter” is actually closely related to the reverse effect known in the literature as “cloaking by anomalous resonance” which can make a small cylinder undetectable. We also show that the enhancement of polarizability can lead to strongly enhanced electromagnetic forces that can be attractive or repulsive, depending on the material properties of the cylinder. PMID:25641391

  9. Laboratory investigation of lateral dispersion within dense arrays of randomly distributed cylinders at transitional Reynolds number

    E-print Network

    Nepf, Heidi

    Relative (effective) lateral dispersion of a passive solute was examined at transitional Reynolds numbers within a two-dimensional array of randomly distributed circular cylinders of uniform diameter d. The present work ...

  10. Classification of two dimensional fixed sun angle solar sail trajectories

    E-print Network

    Roberts, Mark

    Classification of two dimensional fixed sun angle solar sail trajectories Stephen Wokes, Phil heliocentric trajectories for fixed sun angle solar sails are examined. The objective of this work which results in a two dimensional phase space interpretation of the problem. For a given sail quality

  11. Terahertz rectification by periodic two-dimensional electron plasma

    SciTech Connect

    Popov, V. V.; Saratov State University, Saratov 410012

    2013-06-24

    The physics of terahertz rectification by periodic two-dimensional electron plasma is discussed. Two different effects yielding terahertz rectification are studied: the plasmonic drag and plasmonic ratchet. Ultrahigh responsivity of terahertz rectification by periodic two-dimensional electron plasma in semiconductor heterostructures and graphene is predicted.

  12. New two-dimensional quantum models with shape invariance

    SciTech Connect

    Cannata, F.; Ioffe, M. V.; Nishnianidze, D. N.

    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.

  13. Large-scale two-dimensional turbulence in the atmosphere

    E-print Network

    Wirosoetisno, Djoko

    Large-scale two-dimensional turbulence in the atmosphere Article Published Version Boer, G. J. and Shepherd, T. G. (1983) Large-scale two- dimensional turbulence in the atmosphere. Journal of the Atmospheric Sciences, 40 (1). pp. 164-184. ISSN 1520-0469 doi: 10.1175/1520-0469(1983)0402.0.CO;2

  14. Beginning Introductory Physics with Two-Dimensional Motion

    ERIC Educational Resources Information Center

    Huggins, Elisha

    2009-01-01

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

  15. PRESSURE MEASUREMENT IN A TWO DIMENSIONAL UNSTEADY FLOW

    E-print Network

    Patil, Mayuresh

    PRESSURE MEASUREMENT IN A TWO DIMENSIONAL UNSTEADY FLOW William Walker Virginia Polytechnic to obtain unsteady aerodynamic data from a two dimensional wing, and analyzing the pressure variations with time over the wing surface. The data was gathered by using electronic pressure transducers

  16. DISSERTATION FREQUENCY ANALYSIS AND TWO-DIMENSIONAL SIMULATIONS

    E-print Network

    Julien, Pierre Y.

    ) calibrate and validate the model to the June 1921 and May 1894 extreme floods on the Arkansas River; (3DISSERTATION FREQUENCY ANALYSIS AND TWO-DIMENSIONAL SIMULATIONS OF EXTREME FLOODS ON A LARGE FREDRICK ENGLAND, JR. ENTITLED FREQUENCY ANALYSIS AND TWO-DIMENSIONAL SIMULATIONS OF EXTREME FLOODS

  17. The Chandrasekhar's Equation for Two-Dimensional Hypothetical White Dwarfs

    E-print Network

    De, Sanchari

    2014-01-01

    In this article we have extended the original work of Chandrasekhar on the structure of white dwarfs to the two-dimensional case. Although such two-dimensional stellar objects are hypothetical in nature, we strongly believe that the work presented in this article may be prescribed as Master of Science level class problem for the students in physics.

  18. Plastic flow in two-dimensional solids Akira Onuki

    E-print Network

    Plastic flow in two-dimensional solids Akira Onuki Department of Physics, Kyoto University, Kyoto-Landau model of plastic deformation in two-dimensional solids is presented. The fundamental dynamic variables in uniaxial stretching. High-density dislocations produced in plastic flow do not disappear even if the flow

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

    SciTech Connect

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

    2014-10-07

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

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

    DOE PAGESBeta

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

    2014-10-07

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

  1. 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.

  2. Third sound in one and two dimensional modulated structures

    SciTech Connect

    Komuro, T.; Kawashima, H., Shirahama, K.; Kono, K.

    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.

  3. Two-dimensional Minkowski causal automorphisms and conformal maps

    NASA Astrophysics Data System (ADS)

    Burgos, Juan Manuel

    2013-02-01

    Treating the two-dimensional Minkowski space as a Wick rotated version of the complex plane, we characterize the causal automorphisms in the two-dimensional Minkowski space as the Märzke-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.

  4. Dynamics of two-dimensional and quasi-two-dimensional polymers

    NASA Astrophysics Data System (ADS)

    Sung, Bong June; Yethiraj, Arun

    2013-06-01

    The dynamic properties of dense two-dimensional (2D) polymer melts are studied using discontinuous molecular dynamics simulations. Both strictly 2D and quasi-2D systems are investigated. The strictly 2D model system consists of a fluid of freely jointed tangent hard disc chains. The translational diffusion coefficient, D, is strongly system size dependent with D ˜ ln L where L is the linear dimension of the square simulation cell. The rotational correlation time, ?rot, is, however, independent of system size. The dynamics is consistent with Rouse behavior with D/ln L ˜ N-1 and ?rot ˜ N2 for all area fractions. Analysis of the intermediate scattering function, Fs(k, t), shows that the dynamics becomes slow for N = 256 and the area fraction of 0.454 and that there might be a glass transition for long polymers at sufficiently high area fractions. The polymer mobility is not correlated with the conformation of the molecules. In the quasi-2D system hard sphere chains are confined between corrugated surfaces so that chains cannot go over each other or into the surfaces. The conformational properties are identical to the 2D case, but D and ?rot are independent of system size. The scaling of D and ?rot with N is similar to that of strictly 2D systems. The simulations suggest that 2D polymers are never entangled and follow Rouse dynamics at all densities.

  5. 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.

  6. A two-dimensional Wigner crystal (Review Article)

    NASA Astrophysics Data System (ADS)

    Monarkha, Yu. P.; Syvokon, V. E.

    2012-12-01

    The current state of theoretical and experimental studies of the Wigner crystallization of a two-dimensional electron gas is reviewed. The Wigner crystal (WC) has first been observed experimentally in a two-dimensional electron system on the surface of liquid helium in 1979. This success was favored by the exceptional purity of the free surface of superfluid liquid and the ability to fairly accurately describe the polaronic deformation phenomena accompanying the crystallization of electrons. Very pure samples of heterostructures (GaAs/GaAlAs) and strong magnetic fields, making easier the localization of electrons in a conducting layer, were necessary in order to observe the Wigner crystallization in semiconductor two-dimensional electron systems This review discusses the basic properties of a two-dimensional WC, common to the both above-mentioned electronic systems, and also major advances in the study of transport properties of WC caused by response of the environment on motion of the electron lattice.

  7. Notes on the two-dimensional fractional Brownian motion

    E-print Network

    Baudoin, Fabrice; Nualart, David

    2006-02-17

    We study the two-dimensional fractional Brownian motion with Hurst parameter H>½. In particular, we show, using stochastic calculus, that this process admits a skew-product decomposition and deduce from this representation some asymptotic properties...

  8. 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....

  9. Single particle spectrum of the two dimensional electron gas

    E-print Network

    Dial, Oliver Eugene, III

    2007-01-01

    Accurate spectroscopy has driven advances in chemistry, materials science, and physics. However, despite their importance in the study of highly correlated systems, two-dimensional systems (2DES) have proven difficult to ...

  10. Geometric coupling thresholds in a two-dimensional strip

    E-print Network

    Geometric coupling thresholds in a two-dimensional strip D. Borisov a , P. Exner, b;c and R. Gadyl, Ufa Science Center, Russian Academy of Sciences, Chernyshevskogo St., 112, 450000, Ufa, Russia Borisov

  11. 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 ...

  12. CHARACTERISTICS OF TWO-DIMENSIONAL PARTICLE EDDY DIFFUSION INOFFICE SPACE

    EPA Science Inventory

    The paper discusses the development of a two-dimensional turbulentkinetic energy - dissipation rate (k-epsilon) turbulence model inthe form of vorticity and stream functions. his turbulence modelprovides the distribution of turbulent kinematic viscosity, used tocalculate the effe...

  13. Spin-imbalanced quasi-two-dimensional Fermi gases.

    PubMed

    Ong, W; Cheng, Chingyun; Arakelyan, I; Thomas, J E

    2015-03-20

    We measure the density profiles for a Fermi gas of (6)Li containing N(1) spin-up atoms and N(2) spin-down atoms, confined in a quasi-two-dimensional geometry. The spatial profiles are measured as a function of spin imbalance N(2)/N(1) and interaction strength, which is controlled by means of a collisional (Feshbach) resonance. The measured cloud radii and central densities are in disagreement with mean-field Bardeen-Cooper-Schrieffer theory for a true two-dimensional system. We find that the data for normal-fluid mixtures are reasonably well fit by a simple two-dimensional polaron model of the free energy. Not predicted by the model is a phase transition to a spin-balanced central core, which is observed above a critical value of N(2)/N(1). Our observations provide important benchmarks for predictions of the phase structure of quasi-two-dimensional Fermi gases. PMID:25839246

  14. Local curvature and stability of two-dimensional systems

    E-print Network

    Guan, Jie

    We propose a fast method to determine the local curvature in two-dimensional (2D) systems with arbitrary shape. The curvature information, combined with elastic constants obtained for a planar system, provides an accurate ...

  15. Optical properties of two-dimensional transition metal dichalcogenides

    E-print Network

    Lin, Yuxuan, S.M. Massachusetts Institute of Technology

    2014-01-01

    The re-discovery of the atomically thin transition metal dichalcogenides (TMDs), which are mostly semiconductors with a wide range of band gaps, has diversified the family of two-dimensional materials and boosted the ...

  16. 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)

  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. Model of a Negatively Curved Two-Dimensional Space.

    ERIC Educational Resources Information Center

    Eckroth, Charles A.

    1995-01-01

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

  19. Supercurrent reversal in two-dimensional topological insulators

    NASA Astrophysics Data System (ADS)

    Zyuzin, Alexander; Alidoust, Mohammad; Klinovaja, Jelena; Loss, Daniel

    2015-11-01

    We calculate a supercurrent across a two-dimensional topological insulator subjected to an external magnetic field. When the edge states of a narrow two-dimensional topological insulator are hybridized, an external magnetic field can close the hybridization gap, thus driving a quantum phase transition from insulator to semimetal states of the topological insulator. We find a sign reversal of the supercurrent at the quantum phase transition revealing intrinsic properties of topological insulators via the Josephson effect.

  20. The Two-Dimensional Analogue of General Relativity

    E-print Network

    Lemos, José P S; 10.1088/0264-9381/11/1/003

    2009-01-01

    General Relativity in three or more dimensions can be obtained by taking the limit $\\omega\\rightarrow\\infty$ in the Brans-Dicke theory. In two dimensions General Relativity is an unacceptable theory. We show that the two-dimensional closest analogue of General Relativity is a theory that also arises in the limit $\\omega\\rightarrow\\infty$ of the two-dimensional Brans-Dicke theory.

  1. Two-Dimensional Imaging of Gauge Fields in Optical Lattices

    SciTech Connect

    Cho, Jaeyoon; Kim, M. S.

    2011-12-23

    We propose a scheme to generate an arbitrary Abelian vector potential for atoms trapped in a two-dimensional optical lattice. By making the optical lattice potential dependent on the atomic state, we transform the problem into that of a two-dimensional imaging. It is shown that an arbitrarily fine pattern of the gauge field in the lattice can be realized without need of diffraction-limited imaging.

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

    NASA Technical Reports Server (NTRS)

    Chang, Jaw John; Yeh, Hen-Geul

    1988-01-01

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

  3. Dynamic response characteristics of high temperature superconducting maglev systems: Comparison between Halbach-type and normal permanent magnet guideways

    NASA Astrophysics Data System (ADS)

    Wang, B.; Zheng, J.; Che, T.; Zheng, B. T.; Si, S. S.; Deng, Z. G.

    2015-12-01

    The permanent magnet guideway (PMG) is very important for the performance of the high temperature superconducting (HTS) system in terms of electromagnetic force and operational stability. The dynamic response characteristics of a HTS maglev model levitating on two types of PMG, which are the normal PMG with iron flux concentration and Halbach-type PMG, were investigated by experiments. The dynamic signals for different field-cooling heights (FCHs) and loading/unloading processes were acquired and analyzed by a vibration analyzer and laser displacement sensors. The resonant frequency, stiffness and levitation height of the model were discussed. It was found that the maglev model on the Halbach-type PMG has higher resonant frequency and higher vertical stiffness compared with the normal PMG. However, the low lateral stiffness of the model on the Halbach-type PMG indicates poor lateral stability. Besides, the Halbach-type PMG has better loading capacity than the normal PMG. These results are helpful to design a suitable PMG for the HTS system in practical applications.

  4. Muscle protein analysis by two-dimensional gel electrophoresis

    SciTech Connect

    Giometti, C.S.

    1982-01-01

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

  5. An Investigation of Two-Dimensional CAD Generated Models with Body Decoupled Cartesian Grids for DSMC

    SciTech Connect

    OTAHAL,THOMAS J.; GALLIS,MICHAIL A.; BARTEL,TIMOTHY J.

    2000-06-27

    This paper presents an investigation of a technique for using two-dimensional bodies composed of simple polygons with a body decoupled uniform Cmtesian grid in the Direct Simulation Monte Carlo method (DSMC). The method employs an automated grid pre-processing scheme beginning form a CAD geometry definition file, and is based on polygon triangulation using a trapezoid algorithm. A particle-body intersection time comparison is presented between the Icarus DSMC code using a body-fitted structured grid and using a structured body-decoupled Cartesian grid with both linear and logarithmic search techniques. A comparison of neutral flow over a cylinder is presented using the structured body fitted grid and the Cartesian body de-coupled grid.

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

    NASA Technical Reports Server (NTRS)

    Sawyer, P. L.

    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 circular cylinder. A description and listing of a computer program based on this procedure are included in this report. The program calculates geometric view factors between individual strips and between individual strips and the collection of occluding cylinders.

  7. 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.

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

    SciTech Connect

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

    1996-09-01

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

  9. Hamiltonian formalism of two-dimensional Vlasov kinetic equation

    PubMed Central

    Pavlov, Maxim V.

    2014-01-01

    In this paper, the two-dimensional Benney system describing long wave propagation of a finite depth fluid motion and the multi-dimensional Russo–Smereka kinetic equation describing a bubbly flow are considered. The Hamiltonian approach established by J. Gibbons for the one-dimensional Vlasov kinetic equation is extended to a multi-dimensional case. A local Hamiltonian structure associated with the hydrodynamic lattice of moments derived by D. J. Benney is constructed. A relationship between this hydrodynamic lattice of moments and the two-dimensional Vlasov kinetic equation is found. In the two-dimensional case, a Hamiltonian hydrodynamic lattice for the Russo–Smereka kinetic model is constructed. Simple hydrodynamic reductions are presented. PMID:25484603

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

    NASA Technical Reports Server (NTRS)

    Edwards, Thomas R.

    1988-01-01

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

  11. Two-Dimensional Electronic Spectroscopy Using Incoherent Light: Theoretical Analysis

    E-print Network

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

    2012-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2015-06-01

    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.

  13. Nonlinear inversion of two-dimensional SH-wave equation

    SciTech Connect

    Hongnian, W.; Jing, X. )

    1991-01-01

    In solving nonlinear inversion problem of two-dimensional SH-wave equation with the use of least square method, a general inversion problem of two-dimensional SH-wave equation can be reduced to a physically realizable optimal control problem in model space by introducing the nonlinear functional of SH-wave velocity variation, so that synthetic seismogram of theoretical model is optimally fitted into real seismic record in the sense of least square. The optimal solution is obtained by adopting gradient method. The gradient is calculated from the forward wave field generated by real seismic sources and the backward wave field created by residual seismic data. Consequently, an iterative inversion scheme can be obtained which is similar to that in seismic migration. The inversion results of synthetic seismograms from two different two-dimensional models prove this approach feasible.

  14. 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

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

    NASA Astrophysics Data System (ADS)

    Silva, Érica de Mello

    2015-10-01

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

  16. Two-dimensional alignment of imogolite on a solid surface.

    PubMed

    Park, Sungjin; Lee, Yunha; Kim, Bumjung; Lee, Jisun; Jeong, Youngdo; Noh, Jaegeun; Takahara, Atsushi; Sohn, Daewon

    2007-07-28

    Surface modified imogolite fiber, hydrated aluminium silicate that has the shape of a rigid hollow cylinder, was aligned with consistent nano spacing and was visualized by scanning tunneling microscopy. PMID:17622430

  17. Quantum walks on two kinds of two-dimensional models

    E-print Network

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

    2015-01-08

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

  18. Two dimensional hydrodynamic and evolution sequences of rotating stars

    SciTech Connect

    Deupree, R. G.; Guzik, J. A.; Neuforge, C. 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.)

  19. Exact Solvability of Two-Dimensional Real Singular Morse Potential

    E-print Network

    M. V. Ioffe; D. N. Nishnianidze

    2007-09-19

    The supersymmetric approach in the form of second order intertwining relations is used to prove the exact solvability of two-dimensional Schrodinger equation with generalized two-dimensional Morse potential for $a_0=-1/2$. This two-parametric model is not amenable to conventional separation of variables, but it is completely integrable: the symmetry operator of fourth order in momenta exists. All bound state energies are found explicitly, and all corresponding wave functions are built analytically. By means of shape invariance property, the result is extended to the hierarchy of Morse models with arbitrary integer and half-integer values $a_k=-(k+1)/2.$

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

    NASA Astrophysics Data System (ADS)

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

    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.

  1. 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; Butterly, Jack G

    1947-01-01

    The theory of the 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 was run using the hydraulic analogy as applied to the flow about circular cylinders of various diameters at subsonic velocities extending into the supercritical 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 air flow about corresponding bodies. This agreement indicated the possibility of extending experimental compressibility research by new methods.

  2. Nonreciprocal self-collimation in two-dimensional gyromagnetic photonic crystals and its applications in signal separation

    NASA Astrophysics Data System (ADS)

    Li, Qing-bo; Li, Zhen; Zhou, Ping; Wu, Rui-xin

    2015-11-01

    We investigate self-collimated electromagnetic waves in two-dimensional gyromagnetic photonic crystals (GPCs) fabricated by semi-cylinder rods. The nonreciprocal self-collimation transmission is found by means of band structure and equi-frequency contour (EFC) calculations. Progressively tilting flat EFC by optimizing the structure of GPC, we show that nonreciprocal spatial wavelength division can be achieved without any corrugations inside the structure. Further, the frequency range for the nonreciprocal spatial wavelength division can be flexibly manipulated by the external static magnetic field.

  3. 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.

  4. Ultrafast two-dimensional NMR spectroscopy using constant acquisition gradients

    E-print Network

    Frydman, Lucio

    Ultrafast two-dimensional NMR spectroscopy using constant acquisition gradients Yoav Shrot NMR spectroscopy plays an important role in the characterization of molecular structure and dynamics for clinical diagnosis within the context of in vivo NMR spectroscopy.1­3 The information content of multidimen

  5. 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.

  6. Winding angle distributions for two-dimensional collapsing polymers

    E-print Network

    Prellberg, Thomas

    Winding angle distributions for two-dimensional collapsing polymers Arturo Narros School provide numerical support for a long-standing prediction of universal scaling of winding angle distributions. Simulations of interacting self-avoiding walks show that the winding angle distribution for N

  7. Conformal invariance in two-dimensional turbulence Antonio Celani

    E-print Network

    Fominov, Yakov

    Conformal invariance in two-dimensional turbulence Antonio Celani CNRS - Institut non linéaire de (CNRS - INLN) Conformal invariance in turbulence Trieste, 12/12/2005 1 / 16 #12;Conformal invariance in statistical physics Homogeneity + isotropy + scale invariance conformal invariance.Holds under broad

  8. Conformal invariance in two-dimensional D. BERNARD1

    E-print Network

    Loss, Daniel

    ARTICLES Conformal invariance in two-dimensional turbulence D. BERNARD1 , G. BOFFETTA2 , A. CELANI3 invariance to a wider class of conformal transformations that allow non-uniform rescaling. Conformal. Is there conformal invariance in 2D turbulence, a paradigmatic example of a strongly interacting non

  9. Two-Dimensional Porous Electrode Model for Capacitive Deionization

    E-print Network

    Santiago, Juan G.

    deionization (CDI). In CDI, a pair of porous carbon electrodes is employed to electrostatically retain of engineered porous carbon electrodes. Upon application of 1 V across these electrodes (the charging processTwo-Dimensional Porous Electrode Model for Capacitive Deionization Ali Hemmatifar, Michael

  10. Study of Protein Aggregation Using Two-Dimensional

    E-print Network

    Pezolet, Michel

    Study of Protein Aggregation Using Two-Dimensional Correlation Infrared Spectroscopy and Spectral Simulations Thierry Lefe` vre Karin Arseneault Michel Pe´ zolet Centre de Recherche en Sciences et Inge obtained from a mutant protein that differs by one amino acid. To determine whether the aggregation

  11. Microdiffraction applications utilizing a two-dimensional proportional detector.

    SciTech Connect

    Tissot, Ralph George, Jr.

    2003-02-01

    Two-dimensional proportional detectors with their faster data collection, large dynamic range, and more available information than point or linear proportional detectors make them ideal for microdiffraction analysis. The unique capabilities of these detectors coupled with a rotating anode source, capillary optics, and a variety of accessories allow for a wide range of applications.

  12. Two-Dimensional Vortex Dynamics With Background Vorticity

    E-print Network

    Schecter, David

    vorticity. Experiments have shown that background vorticity can calm chaotic vortex motion, and cool. To appreciate the influence of background vorticity on the vortex motion, let us first consider the vortexTwo-Dimensional Vortex Dynamics With Background Vorticity David A. Schecter Advanced Study Program

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

    NASA Technical Reports Server (NTRS)

    Montgomery, D.

    1972-01-01

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

  14. 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...

  15. Pairing in two-dimensional boson-fermion mixtures

    SciTech Connect

    Mur-Petit, J.; Polls, A.; Baldo, M.; Schulze, H.-J.

    2004-02-01

    The possibilities of pairing in two-dimensional boson-fermion mixtures are carefully analyzed. It is shown that the boson-induced attraction between two identical fermions dominates the p wave pairing at low density. For a given fermion density, the pairing gap becomes maximal at a certain optimal boson concentration. The conditions for observing pairing in current experiments are discussed.

  16. Chaotic dynamics for two-dimensional tent maps

    NASA Astrophysics Data System (ADS)

    Pumariño, Antonio; Ángel Rodríguez, José; Carles Tatjer, Joan; Vigil, Enrique

    2015-02-01

    For a two-dimensional extension of the classical one-dimensional family of tent maps, we prove the existence of an open set of parameters for which the respective transformation presents a strange attractor with two positive Lyapounov exponents. Moreover, periodic orbits are dense on this attractor and the attractor supports a unique ergodic invariant probability measure.

  17. Two-dimensional plasma acceleration in a divergent magnetic nozzle

    E-print Network

    Carlos III de Madrid, Universidad

    Two-dimensional plasma acceleration in a divergent magnetic nozzle E. Ahedo and M. Merino E of a current-free plasma in a divergent magnetic nozzle with fully magnetically guided electrons is discussed. Introduction A divergent magnetic nozzle, created by a longitudinal magnetic field is being used

  18. Two-dimensional Manifold with Point-like Defects

    NASA Astrophysics Data System (ADS)

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

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

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

    NASA Technical Reports Server (NTRS)

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

    1999-01-01

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

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

    NASA Technical Reports Server (NTRS)

    Santa Maria, Odilyn L.

    1999-01-01

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

  1. Interior design of a two-dimensional semiclassical black hole

    SciTech Connect

    Levanony, Dana; Ori, Amos

    2009-10-15

    We look into the inner structure of a two-dimensional dilatonic evaporating black hole. We establish and employ the homogenous approximation for the black-hole interior. Two kinds of spacelike singularities are found inside the black hole, and their structure is investigated. We also study the evolution of spacetime from the horizon to the singularity.

  2. Error Detection and Recovery in Two Dimensional Topological Navigation

    E-print Network

    ­guided robotics 1 #12; 1 Introduction Our navigational environment consists of identically featured objects by the navigator, they are used to filter the perceptions of the map­maker and the navigator. 1.1 The mapError Detection and Recovery in Two Dimensional Topological Navigation Il­Pyung Park and John R

  3. Two-Dimensional Gel Electrophoresis in Platelet Proteomics Research

    E-print Network

    23 Two-Dimensional Gel Electrophoresis in Platelet Proteomics Research Ángel García Summary Proteomics technology allows a comprehensive and efficient analysis of the proteome and has become electrophoresis (2-DE) in proteomics and its application to platelet research. 2-DE separates proteins according

  4. Consequence in Context: Two-Dimensional Semantics meets Logical Consequence

    E-print Network

    Koolen, Marijn

    Maria Aloni and Dr Catarina Dutilh Novaes, and submitted to the Board of Examiners in partial of the public defense: Members of the Thesis Committee: December 23, 2011 Dr Maria Aloni Dr Paul Dekker Dr Emar Maier Dr Catarina Dutilh Novaes Prof Dr Frank Veltman #12;Abstract Two-dimensional semantics is a formal

  5. A STABLE HIGH-ORDER METHOD FOR TWO-DIMENSIONAL ...

    E-print Network

    SIAM (#1) 1035 2001 Apr 10 12:32:38

    2006-08-10

    A stable and high-order method for solving the Helmholtz equation on a two- dimensional domain exterior ... analytic continuation, implemented via Padé approximation. .... dimensions, and leave the more general three-dimensional setting for future work. ... scattering and recall a classical boundary perturbation algorithm.

  6. Two-dimensional superstrings and the supersymmetric matrix model

    NASA Astrophysics Data System (ADS)

    McGreevy, John; Murthy, Sameer; Verlinde, Herman

    2004-04-01

    We present evidence that the supersymmetric matrix model of Marinari and Parisi represents the world-line theory of N unstable D-particles in type II superstring theory in two dimensions. This identification suggests that the matrix model gives a holographic description of superstrings in a two-dimensional black hole geometry.

  7. 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.

  8. NUMERICAL SIMULATION OF TWO-DIMENSIONAL MELTING AND RESOLIDIFICATION OF

    E-print Network

    Zhang, Yuwen

    uses two types of the metal powders possessing significantly different melting points [3, 4]. The high-melting-point necessary to avoid ``balling.'' Solidification of the low-melting-point metal bonds the high-melting- pointNUMERICAL SIMULATION OF TWO-DIMENSIONAL MELTING AND RESOLIDIFICATION OF A TWO-COMPONENT METAL

  9. Acoustic quasimodes in two-dimensional dispersed random media

    NASA Astrophysics Data System (ADS)

    Zhang, Xin; Liu, Zhengyou; Wu, Fugen; Liu, Youyan

    2006-06-01

    Using the generalized coherent-potential-approximation approach, we present the dispersion relation of the two-dimensional dispersed random media. In the intermediate-frequency regime, two acoustic modes are found in colloidal suspensions including cylindrical plastic rod in water background. The scattering cross section offers a good explanation for the two modes and the observed frequency gaps in the excitation spectra.

  10. Nesting of two-dimensional irregular parts: an integrated approach

    E-print Network

    Wang, Gaofeng Gary

    Nesting of two-dimensional irregular parts: an integrated approach S. Q. XIE*{, G. G. WANG{ and Y The present paper reports an intelligent computer-aided nesting (CAN) system for optimal nesting of two the utilization ratio of sheet materials. This paper also systemically reviews the nesting algorithms that were

  11. A note on two-dimensional asymptotic magnetotail equilibria

    NASA Technical Reports Server (NTRS)

    Voigt, Gerd-Hannes; Moore, Brian D.

    1994-01-01

    In order to understand, on the fluid level, the structure, the time evolution, and the stability of current sheets, such as the magnetotail plasma sheet in Earth's magnetosphere, one has to consider magnetic field configurations that are in magnetohydrodynamic (MHD) force equilibrium. Any reasonable MHD current sheet model has to be two-dimensional, at least in an asymptotic sense (B(sub z)/B (sub x)) = epsilon much less than 1. The necessary two-dimensionality is described by a rather arbitrary function f(x). We utilize the free function f(x) to construct two-dimensional magnetotail equilibria are 'equivalent' to current sheets in empirical three-dimensional models. We obtain a class of asymptotic magnetotail equilibria ordered with respect to the magnetic disturbance index Kp. For low Kp values the two-dimensional MHD equilibria reflect some of the realistic, observation-based, aspects of three-dimensional models. For high Kp values the three-dimensional models do not fit the asymptotic MHD equlibria, which is indicative of their inconsistency with the assumed pressure function. This, in turn, implies that high magnetic activity levels of the real magnetosphere might be ruled by thermodynamic conditions different from local thermodynamic equilibrium.

  12. Nonlinear elastic behavior of two-dimensional molybdenum disulfide

    NASA Astrophysics Data System (ADS)

    Cooper, Ryan C.; Lee, Changgu; Marianetti, Chris A.; Wei, Xiaoding; Hone, James; Kysar, Jeffrey W.

    2013-01-01

    This research explores the nonlinear elastic properties of two-dimensional molybdenum disulfide. We derive a thermodynamically rigorous nonlinear elastic constitutive equation and then calculate the nonlinear elastic response of two-dimensional MoS2 with first-principles density functional theory (DFT) calculations. The nonlinear elastic properties are used to predict the behavior of suspended monolayer MoS2 subjected to a spherical indenter load at finite strains in a multiple-length-scale finite element analysis model. The model is validated experimentally by indenting suspended circular MoS2 membranes with an atomic force microscope. We find that the two-dimensional Young's modulus and intrinsic strength of monolayer MoS2 are 130 and 16.5 N/m, respectively. The results approach Griffith's predicted intrinsic strength limit of ?int˜(E)/(9), where E is the Young's modulus. This study reveals the predictive power of first-principles density functional theory in the derivation of nonlinear elastic properties of two-dimensional MoS2. Furthermore, the study bridges three main gaps that hinder understanding of material properties: DFT to finite element analysis, experimental results to DFT, and the nanoscale to the microscale. In bridging these three gaps, the experimental results validate the DFT calculations and the multiscale constitutive model.

  13. Nonlinear Optical Processes in Two-Dimensional Semiconductor Structures 

    E-print Network

    Wang, Yongrui

    2015-07-28

    The optical properties of two types of two-dimensional (2D) semiconductor structures are studied. One of them is for structures based on quantum wells (QWs), and the other is graphene. We study the dynamics of optically excited electron-hole plasma...

  14. Lattice Boltzmann simulation for forced two-dimensional turbulence

    NASA Astrophysics Data System (ADS)

    Xia, YuXian; Qian, YueHong

    2014-08-01

    The direct numerical simulations of forced two-dimensional turbulent flow are presented by using the lattice Boltzmann method. The development of an energy-enstrophy double cascade is investigated in the two cases of external force of two-dimensional turbulence, Gaussian force and Kolmogorov force. It is found that the friction force is a necessary condition of the occurrence of a double cascade. The energy spectrum k-3 in the enstrophy inertial range is in accord with the classical Kraichnan theory for both external forces. The energy spectrum of the Gaussian force case in an inverse cascade is k-2; however, the Kolmogorov force drives the k-5/3 energy in a backscatter cascade. The result agrees with Scott's standpoint, which describes nonrobustness of the two-dimensional turbulent inverse cascade. Also, intermittency is found for the enstrophy cascade in two cases of the external force form. Intermittency refers to the nonuniform distribution of saddle points in the two-dimensional turbulent flow.

  15. 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

  16. 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...

  17. An Optimization Model for Aesthetic TwoDimensional

    E-print Network

    Chang, Ee-Chien

    An Optimization Model for Aesthetic TwoDimensional Barcodes Fang Chengfang, Zhang Chunwang Barcodes · 2D barcodes visually resemble random dots. We want to make them visually interesting barcodes. From 15 Beautiful and Creative QR Codes. ( http://mashable.com/2011/07/23/creativeqrcodes/ ) 9Jan

  18. Operator splitting for two-dimensional incompressible fluid equations

    E-print Network

    Holden, Helge; Karper, Trygve K

    2011-01-01

    We analyze splitting algorithms for a class of two-dimensional fluid equations, which includes the incompressible Navier-Stokes equations and the surface quasi-geostrophic equation. Our main result is that the Godunov and Strang splitting methods converge with the expected rates provided the initial data are sufficiently regular.

  19. 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.

  20. 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.

  1. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2015-06-01

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

  3. The Cylinder and Semicylinder in Subsonic Flow

    NASA Technical Reports Server (NTRS)

    Bingham, Harry J.; Weimer, David K..; Griffith, Wayland

    1952-01-01

    In studying the diffraction of shock waves around various two-dimensional obstacles we have observed that flow separation and the formation of vortices contributes in an important way to transient loading of the obstacle. The cases of a cylinder and semicylinder are especially interesting because the breakaway point is not clearly defined as it is for objects having sharp corners. Accordingly a number of experiments have been made in the shock tube to observe the influence of Reynolds number and Mach number on the transient flow patterns about a cylinder and about a semicylinder mounted on a smooth plane. Some differences might be anticipated since the plane would impose a symmetry on the flow and produce a viscous boundary layer for which there is no counterpart with the cylinder. In the course of these experiments it was noted that a condition of steady subsonic flow about both the cylinder and semicylinder was approached. Thus a comparison with von Karrnan's theoretical calculation of the drag on a cylinder, from certain characteristics of its wake or "vortex street", was undertaken.

  4. Quick release engine cylinder

    DOEpatents

    Sunnarborg, Duane A. (1123 Lucille St., Livermore, Alameda County, CA 94550)

    2000-01-01

    A quick release engine cylinder allows optical access to an essentially unaltered combustion chamber, is suitable for use with actual combustion processes, and is amenable to rapid and repeated disassembly and cleaning. A cylinder member, adapted to constrain a piston to a defined path through the cylinder member, sealingly engages a cylinder head to provide a production-like combustion chamber. A support member mounts with the cylinder member. The support-to-cylinder mounting allows two relationships therebetween. In the first mounting relationship, the support engages the cylinder member and restrains the cylinder against the head. In the second mounting relationship, the cylinder member can pass through the support member, moving away from the head and providing access to the piston-top and head.

  5. COMPARING TECHNIQUES FOR COMPARATIVE PROTEOMICS: TWO-DIMENSIONAL GEL ELECTROPHORESIS AND TWO-DIMENSIONAL LIQUID CHROMATOGRAPHY SEPARATION

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The accepted method for comparing bacterial proteomes has traditionally been two-dimensional (2D) gel electrophoresis. However, in recent years, new procedures for protein separation have been introduced. One of these new procedures utilizes column-based liquid chromatography separation. The tech...

  6. Two-dimensional multiscale windowed Fourier transform based on two-dimensional wavelet transform for fringe pattern demodulation

    NASA Astrophysics Data System (ADS)

    Li, Hai; Yang, Chuping

    2011-02-01

    A two-dimensional multiscale windowed Fourier transform (2D-MWFT), based on two-dimensional Gabor wavelet transform (2D-GWT), for the phase extraction from a spatial fringe pattern in fringe projection profilometry is presented. First, the instantaneous frequencies on x and y direction of the modulated fringe pattern are determined by 2D-GWT, and then the local stationary lengths are obtained. The 2D-MWFT with different two-dimensional Gaussian windows whose width is set according to the local stationary length is preformed for each section of the modulated fringe pattern to achieve multiresolution analysis and phase demodulation. Comparing the result of the phase demodulated by 2D-GWT and two-dimensional windowed Fourier transform (2D-WFT) with that by 2D-MWFT in a numerical simulation, we show that the 2D-MWFT method is superior to these methods, especially for the local non-stationary signal with low frequency. The theory and the results of a simulation and experiment are shown.

  7. On comparing helioseismic two-dimensional inversion methods

    NASA Technical Reports Server (NTRS)

    Schou, J.; Christensen-Dalsgaard, J.; Thompson, M. J.

    1994-01-01

    We consider inversion techniques for investigating the structure and dynamics of the solar interior as functions of radius and latitude. In particular, we look at the problem of inferring the radial and latitudinal dependence of the Sun's internal rotation, using a fully two-dimensional least-squares inversion algorithm. Concepts such as averaging kernels, measures of resolution, and trade-off curves, which have previously been used in the one-dimensional case, are generalized to facilitate a comparison of two-dimensional methods. We investigate the weighting given to different modes and discuss the implications of this for observational strategies. As an illustration we use a mode set whose properties are similar to those expected for data from the GONG network.

  8. Entanglement Entropy in Two-Dimensional String Theory

    NASA Astrophysics Data System (ADS)

    Hartnoll, Sean A.; Mazenc, Edward A.

    2015-09-01

    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.

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

    PubMed

    Xie, Xinhua

    2015-05-01

    We propose a two-dimensional interferometry based on the electron wave-packet interference by using a cycle-shaped orthogonally polarized two-color laser field. With such a method, the subcycle and intercycle interferences can be disentangled into different directions in the measured photoelectron momentum spectra. The Coulomb influence can be minimized and the overlapping of interference fringes with the complicated low-energy structures can be avoided as well. The contributions of the excitation effect and the long-range Coulomb potential can be traced in the Fourier domain of the photoelectron distribution. Because of these advantages, precise information on valence electron dynamics of atoms or molecules with attosecond temporal resolution and additional spatial information with angstrom resolution can be obtained with the two-dimensional electron wave-packet interferometry. PMID:25978229

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

    NASA Astrophysics Data System (ADS)

    Tollestrup, Eric V.; Harvey, Paul M.

    1989-10-01

    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.

  11. 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.

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

    SciTech Connect

    Zhu, Chongqin; Li, Hui; Meng, Sheng

    2014-11-14

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

  13. Entanglement Entropy in Two-Dimensional String Theory.

    PubMed

    Hartnoll, Sean A; Mazenc, Edward A

    2015-09-18

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

  14. Tunable refraction in a two dimensional quantum metamaterial

    E-print Network

    M. J. Everitt; J. H. Samson; S. E. Savelev; T. P. Spiller; R. Wilson; A. M. Zagoskin

    2012-08-22

    In this paper we consider a two-dimensional metamaterial comprising an array of qubits (two level quantum objects). Here we show that a two-dimensional quantum metamaterial may be controlled, e.g. via the application of a magnetic flux, so as to provide controllable refraction of an input signal. Our results are consistent with a material that could be quantum birefringent (beam splitter) or not dependent on the application of this control parameter. We note that quantum metamaterials as proposed here may be fabricated from a variety of current candidate technologies from superconducting qubits to quantum dots. Thus the ideas proposed in this work would be readily testable in existing state of the art laboratories.

  15. Some applications of two-dimensional stress transfer analyses

    SciTech Connect

    Hsueh, C.H.

    1998-03-23

    Two-dimensional stress transfer analyses are performed for the following system: a long central plate bonded on opposite sides along its length to two short plates and subjected to tensile loading at its ends. The load transfers from the long plate to the short plate through the interfacial shear stress. The system represents the unit cell of platelet-reinforced composites, in which parallel matrix cracks are uniformly spaced and are bridged by the platelet, in a two-dimensional sense. Analytical solutions for the crack opening displacement, the additional displacement of the composite due to the presence of cracks, and stress intensity factor at the crack tip are derived. Letting the long plate and the short plates have the same mechanical properties, the analytical solutions are compared to the existing numerical solutions for tensile loading of both a double edge notch strip and a semi-infinite plane with parallel edge cracks.

  16. Unshielded fetal magnetocardiography system using two-dimensional gradiometers

    NASA Astrophysics Data System (ADS)

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

    2008-03-01

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

  17. The stability of a two-dimensional rising bubble

    SciTech Connect

    Nie, Q.; Tanveer, S.

    1995-06-01

    The stability of an inviscid two-dimensional bubble subject to two-dimensional disturbances is considered and the bubbles are found to be linearly stable for all Weber numbers, for which a steady solution is known. Certain aspects of the nonlinear initial value problem are also studied. An initial condition that consists of a superposition of a suitable symmetric eigenmode (of the linear stability operator) on a steady state is found to result in pinching of the bubble neck as it tends to oscillate about the steady state. An estimate of the threshold amplitude of such a disturbance needed to cause breakup of a large aspect ratio bubble is obtained. The presence of gravity appears to inhibit this pinching process.

  18. 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

  19. 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.

  20. 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.

  1. Accelerating universe in two-dimensional noncommutative dilaton cosmology

    E-print Network

    Wontae Kim; Myung Seok Yoon

    2006-12-01

    We show that the phase transition from the decelerating universe to the accelerating universe, which is of relevance to the cosmological coincidence problem, is possible in the semiclassically quantized two-dimensional dilaton gravity by taking into account the noncommutative field variables during the finite time. Initially, the quantum-mechanically induced energy from the noncommutativity among the fields makes the early universe decelerate and subsequently the universe is accelerating because the dilaton driven cosmology becomes dominant later.

  2. Notes on quantum fields on two dimensional spacetimes

    E-print Network

    Leonardo Ortíz

    2014-11-23

    We point out how to construct the Hartle-Hawking-Israel state for the minimaly coupled massless quantum real scalar field in the two dimensional BTZ black hole. We also calculate the renormalized energy-momentum tensor for the same field in the eternal CGHS black hole, AdS, Robertson-Walker and Rindler spacetime in two dimensions. We also discuss the Boulware, the Hartle-Hawking-Israel and the Unruh state for the eternal CGHS black hole.

  3. Two-Dimensional Laser-Speckle Surface-Strain Gauge

    NASA Technical Reports Server (NTRS)

    Barranger, John P.; Lant, Christian

    1992-01-01

    Extension of Yamaguchi's laser-speckle surface-strain-gauge method yields data on two-dimensional surface strains in times as short as fractions of second. Laser beams probe rough spot on surface of specimen before and after processing. Changes in speckle pattern of laser light reflected from spot indicative of changes in surface strains during processing. Used to monitor strains and changes in strains induced by hot-forming and subsequent cooling of steel.

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

    SciTech Connect

    Dreyer, K.A.

    1985-05-01

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

  5. Spirals and Skyrmions in two dimensional oxide heterostructures.

    PubMed

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

    2014-02-14

    We construct the general free energy governing long-wavelength magnetism in two dimensional oxide heterostructures, which applies irrespective of the microscopic mechanism for magnetism. This leads, in the relevant regime of weak but non-negligible spin-orbit coupling, to a rich phase diagram containing in-plane ferromagnetic, spiral, cone, and Skyrmion lattice phases, as well as a nematic state stabilized by thermal fluctuations. PMID:24580706

  6. Spiral vortices in a two-dimensional ferromagnet

    SciTech Connect

    Borisov, A.B.; Bostrem, I.G.; Ovchinnikov, A.S.

    2005-10-01

    We present a study of a class of exact solutions having a form of spiral vortices for an isotropic two-dimensional Heisenberg ferromagnet using a continuum theory and direct numerical simulations of the spin system on a square lattice. We find their features issued from the conservation laws and describe their interaction. Reasons behind the formation of the proper spin configurations on a square lattice are investigated.

  7. Interior design of a two-dimensional semiclassic black hole

    E-print Network

    Levanony, Dana; 10.1103/PhysRevD.80.084008

    2009-01-01

    We look into the inner structure of a two-dimensional dilatonic evaporating black hole. We establish and employ the homogenous approximation for the black-hole interior. The field equations admit two types of singularities, and their local asymptotic structure is investigated. One of these singularities is found to develop, as a spacelike singularity, inside the black hole. We then study the internal structure of the evaporating black hole from the horizon to the singularity.

  8. Interior design of a two-dimensional semiclassic black hole

    E-print Network

    Dana Levanony; Amos Ori

    2009-12-28

    We look into the inner structure of a two-dimensional dilatonic evaporating black hole. We establish and employ the homogenous approximation for the black-hole interior. The field equations admit two types of singularities, and their local asymptotic structure is investigated. One of these singularities is found to develop, as a spacelike singularity, inside the black hole. We then study the internal structure of the evaporating black hole from the horizon to the singularity.

  9. Suspended two-dimensional electron and hole gases

    SciTech Connect

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

    2013-12-04

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

  10. One- and Two-Dimensional Refocused INADEQUATE NMR Experiments

    NASA Astrophysics Data System (ADS)

    Nakai, T.; Mcdowell, C. A.

    We describe details of the refocused INADEQUATE method, which yields in-phase J doublets from 13C- 13C spin pairs in natural-abundance samples. The procedure for obtaining two-dimensional pure-absorptive INADEQUATE spectra is explained. This is used to determine J coupling constants with high accuracy because of higher spectral resolution than that obtained in magnitude-mode spectra. The method has been demonstrated using hexanoic acid and hexadecanoic acid as test samples.

  11. A two dimensional heat pipe model for vapor temperature calculation

    NASA Astrophysics Data System (ADS)

    Walvekar, Anand K.

    1993-01-01

    A two dimensional heat conduction model is developed for predicting vapor temperature and temperature distribution over outside surface of the heat pipe. The vapor temperature variation is studied with various parameters and performance limit graphs are plotted for a given design of the heat pipe. The performance limit graphs help the experimenter to judge the limiting heat transport of the heat pipe for given boundary condition at the condenser, like convective or radiative cooling.

  12. 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

  13. The scaling state in two-dimensional grain growth

    SciTech Connect

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

    1994-11-01

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

  14. Two-dimensional dipolar bosons with weak disorder

    NASA Astrophysics Data System (ADS)

    Boudjemâa, Abdelâali

    2015-10-01

    We consider two-dimensional dipolar bosonic gas with dipoles oriented perpendicularly to the plane in a weak random potential. We investigate analytically and numerically the condensate depletion, the one-body density-matrix, the ground state energy, the sound velocity and the superfluid fraction. Concentrating on the regime where a roton-like excitation spectrum forms, our results show that the superfluidity disappears below a critical value of disorder strength yielding the transition to a non-trivial quantum regime.

  15. The Study of Two-dimensional Polytropic Stars

    E-print Network

    Sanchari De; Somenath Chakrabarty

    2015-10-09

    In this article we have studied the structure of hypothetical two-dimensional polytropic stars. Considering some academic interest, we have developed a formalism to investigate some of the gross properties of such stellar objects. However, we strongly believe that the formalism developed here may be prescribed as class problem for post-graduate level students in physics or a post-graduate dissertation project work in physics.

  16. Thermodynamic Studies of Two-Dimensional Correlated Electron Systems

    NASA Astrophysics Data System (ADS)

    Pudalov, V. M.; Kuntsevich, A. Yu.; Burmistrov, I. S.; Reznikov, M.

    2015-11-01

    This paper describes recent developments in experimental techniques for thermodynamic measurements. Particularly, we focus on the derivatives of the chemical potential with respect to magnetic field and temperature. The former enables to determine the spin magnetization per electron and the latter the entropy per electron. We briefly describe recent results obtained with these techniques and their impact on the current understanding of the still challenging problem of the ground state(s) of strongly correlated two-dimensional electron systems.

  17. Particle transport in a two-dimensional septate channel

    NASA Astrophysics Data System (ADS)

    Borromeo, M.; Marchesoni, F.

    2010-10-01

    We analyze the transport properties of a Brownian particle diffusing along a two-dimensional septate channel, namely, a channel formed by equal rectangular cavities separated by narrow pores, subjected to an external longitudinal drive. We determine analytical formulas for the dependence of the particle mobility and diffusivity on the geometric channel parameters at zero and large applied drives. Finally, we rule out anomalous negative mobility for pointlike particles in a septate channel.

  18. In vivo two-dimensional NMR correlation spectroscopy

    NASA Astrophysics Data System (ADS)

    Kraft, Robert A.

    1999-10-01

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

  19. Dirac Points in Two-Dimensional Inverse Opals

    NASA Astrophysics Data System (ADS)

    Mahan, G. D.

    2013-10-01

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

  20. Two-dimensional potential double layers and discrete auroras

    NASA Technical Reports Server (NTRS)

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

    1979-01-01

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

  1. Two-dimensional DNA fingerprinting of human individuals

    SciTech Connect

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

    1989-04-01

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

  2. 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.

  3. Two dimensional liquid crystal devices and their computer simulations

    NASA Astrophysics Data System (ADS)

    Wang, Bin

    The main focus of the dissertation is design and optimization two dimensional liquid crystal devices, which means the liquid crystal director configurations vary in two dimensions. Several optimized and designed devices are discussed in the dissertation. They include long-term bistable twisted nematic liquid crystal display (BTN LCD), which is very low power consumption LCD and suitable for E-book application; wavelength tunable liquid crystal Fabry-Perot etalon filter, which is one of the key components in fiber optic telecommunications; high speed refractive index variable devices, which can be used in infrared beam steering and telecommunications; high density polymer wall diffractive liquid crystal on silicon (PWD-LCoS) light valve, which is a promising candidate for larger screen projection display and also can be used in other display applications. Two dimensional liquid crystal director simulation program (relaxation method) and two dimensional optical propagation simulation program (finite-difference time-domain, FDTD method) are developed. The algorithms of these programs are provided. It has been proved that they are the very efficient tools that used in design and optimization the devices described above.

  4. 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

  5. Diversity of puroindolines as revealed by two-dimensional electrophoresis.

    PubMed

    Branlard, Gérard; Amiour, Nardjis; Igrejas, Gilberto; Gaborit, Thérèse; Herbette, Stephane; Dardevet, Mireille; Marion, Didier

    2003-02-01

    Puroindolines are endosperm lipid binding proteins, which are separated by reversed phase-high-performance liquid chromatography or cation exchange chromatography into two isoforms, puroindoline-a (PIN-a) and puroindoline-b (PIN-b). Being very basic and close in molecular weight, PIN-a and PIN-b have never been separated using conventional isoelectric focusing and sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). A two-dimensional electrophoresis method, linear immobiline pH gradient (IPGxSDS-PAGE), was developed, using 6-11 linear immobiline Dry Strips in the first dimension, which allowed the puroindolines to be focused between isoelectric point 10.5 and 11. Immunoblotting revealed that both PIN-a and PIN-b were each composed of several spots. Two-dimensional patterns from unrelated wheat varieties revealed that several spots can be highlighted among varieties. Matrix-assisted laser desorption/ionization-time of flight spectrometry allowed the majority of the spots revealed in the puroindoline zone to be identified. The two-dimensional IPGxSDS-PAGE of these very basic wheat endosperm proteins, puroindolines and related grain softness proteins should facilitate the identification of the proteins associated with wheat endosperm texture that have a strong effect on milling, dough properties and end-uses of wheats. PMID:12601809

  6. Enhanced diffraction radiation from two dimensional periodical structure

    NASA Astrophysics Data System (ADS)

    Zhao, Tao; Zhong, Renbin; Gong, Sen; Zhang, Ping; Chen, Xiaoxing; Hu, Min; Liu, Shenggang

    2014-10-01

    Stronger surface plasmon polaritons (SPPs) enhanced diffraction radiation will be obtained on rectangular metallic bigrating comparing to one dimensional grating excited by a uniformly parallel moving electron beam, the stronger enhancement comes from the interaction effect of two SPPs excited simultaneously along the orthogonal period structure of rectangular metallic bigrating. Based on the advantage of rectangular bigrating, we presented and explored a novel metal film attached two-dimensional periodical lattice structure by reducing the thickness of the bigrating substrate to tens of nanometers. In this structure, with the excitation of uniform electron beam moving above the metal film surface, SPPs are firstly excited on the metal film, which will couple with the electromagnetic fields in the two-dimensional periodical lattice, and then transformed into enhanced radiation wave by diffracting of the rectangular lattice. The radiation power can reach 2.7 times that of the bigrating with dramatically decreased exciting beam energy, the fields can radiate to the whole space comparing to only the upper half space for the bigrating. To obtain better radiation behavior, double metal films sandwiched two-dimensional periodical lattice structure is proposed, which provides radiation power over 10 times that of bigrating. The results will be beneficial to electromagnetic radiation source based on SPPs in ultraviolet region.

  7. a Two-Dimensional Radiative-Convective Climate Model.

    NASA Astrophysics Data System (ADS)

    Kiehl, Jeffrey Theodore

    A two-dimensional radiative-convective climate model has been developed, which includes meridional heat transport, surface albedo feedback and lapse rate feedback. The radiative part of the model is based upon the one-dimensional radiative-convective model of Ramanathan (1976). The two -dimensional model is designed to calculate a mean annual zonally averaged temperature profile for a symmetric model earth. The two-dimensional model calculates the vertical temperature profile for six latitudinal belts of 15(DEGREES) width. These six belts serve as a basis set from which the temperature at any latitude can be calculated. The heat transport is parameterized in terms of a diffuse transport mechanism. The surface albedo feedback for latitudes above 45(DEGREES)N is derived from seasonal data for the present atmosphere. The lapse rate feedback is based upon the suggestions for Stone and Carlson (1979). Three climatic studies have been carried out with the model: increased CO(,2), variation of the solar constant, and variation of cloud amount and height. These studies suggest that the lapse rate parameterization of Stone and Carlson (1979) is extremely sensitive to climatic perturbations. The model proves to be very stable to variations in the solar constant when lapse rate feedback is removed. A great advantage to this model is its flexibility. The model is also computationally efficient compared to the three-dimensional models. Because of the flexibility and computational efficiency, this model can serve as a useful tool in studying the importance of various atmospheric processes.

  8. Two-dimensional oxides: multifunctional materials for advanced technologies.

    PubMed

    Pacchioni, Gianfranco

    2012-08-13

    The last decade has seen spectacular progress in the design, preparation, and characterization down to the atomic scale of oxide ultrathin films of few nanometers thickness grown on a different material. This has paved the way towards several sophisticated applications in advanced technologies. By playing around with the low-dimensionality of the oxide layer, which sometimes leads to truly two-dimensional systems, one can exploit new properties and functionalities that are not present in the corresponding bulk materials or thick films. In this review we provide some clues about the most recent advances in the design of these systems based on modern electronic structure theory and on their preparation and characterization with specifically developed growth techniques and analytical methods. We show how two-dimensional oxides can be used in mature technologies by providing added value to existing materials, or in new technologies based on completely new paradigms. The fields in which two-dimensional oxides are used are classified based on the properties that are exploited, chemical or physical. With respect to chemical properties we discuss use of oxide ultrathin films in catalysis, solid oxide fuel cells, gas sensors, corrosion protection, and biocompatible materials; regarding the physical properties we discuss metal-oxide field effect transistors and memristors, spintronic devices, ferroelectrics and thermoelectrics, and solar energy materials. PMID:22847915

  9. Approach for two-dimensional velocity Shaddy Abado

    E-print Network

    Gordeyev, Stanislav

    of a turret on the side of an airborne platform is addressed. The method is applied to data from the Airborne, hemisphere- on-cylinder turret; flat windowed turret. Paper 120758SSP received May 25, 2012; accepted in flows over and around a turret on an airborne laser platform.1 The magnitude of these aberrations can

  10. A Experimental Study of the Development of Quasi Two-Dimensional Turbulence in a Stably Stratified Fluid

    NASA Astrophysics Data System (ADS)

    Yap, Chee Tiong

    Turbulence was generated by towing an array of vertical cylinders through a tank which was filled with a two-layer stratified fluid. Sugar and epsom salt were used for matching the refractive indices of the two layers. Approximately one thousand neutrally buoyant particles were seeded at the interface between the two layers. The evolution of this quasi-two-dimensional turbulence was visualized by photographing the fluoroscent particles illuminated by a horizontal laser sheet traversing in the vertical direction. The three dimensional particle velocity was obtained by digitizing the streaks. The evolution of the velocity correlations, length scales, one-dimensional and two-dimensional velocity and vorticity spectra were obtained for N = 5.72sec ^{-1}, N = 4.43sec^ {-1} and N = 2.55sec^{ -1}. The results showed the physical process of inverse energy cascading and the formation of dominant vortical structures under the influence of density stratification. However, compared with the idealized two-dimensional turbulence, the flow is highly dissipative at high N due to the frictional dissipation in between the interface and the unstratified layers. The power law obtained by plotting the number of vortices against time is compared with the result from recent numerical simulations.

  11. 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.

  12. Halbach arrays consisting of cubic elements optimised for high field gradients in magnetic drug targeting applications

    NASA Astrophysics Data System (ADS)

    Barnsley, Lester C.; Carugo, Dario; Owen, Joshua; Stride, Eleanor

    2015-11-01

    A key challenge in the development of magnetic drug targeting (MDT) as a clinically relevant technique is designing systems that can apply sufficient magnetic force to actuate magnetic drug carriers at useful tissue depths. In this study an optimisation routine was developed to generate designs of Halbach arrays consisting of multiple layers of high grade, cubic, permanent magnet elements, configured to deliver the maximum pull or push force at a position of interest between 5 and 50?mm from the array, resulting in arrays capable of delivering useful magnetic forces to depths past 20?mm. The optimisation routine utilises a numerical model of the magnetic field and force generated by an arbitrary configuration of magnetic elements. Simulated field and force profiles of optimised arrays were evaluated, also taking into account the forces required for assembling the array in practice. The resultant selection for the array, consisting of two layers, was then constructed and characterised to verify the simulations. Finally the array was utilised in a set of in vitro experiments to demonstrate its capacity to separate and retain microbubbles loaded with magnetic nanoparticles against a constant flow. The optimised designs are presented as light-weight, inexpensive options for applying high-gradient, external magnetic fields in MDT applications.

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

    NASA Technical Reports Server (NTRS)

    Cai, Wei

    1993-01-01

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

  14. Dissipative vortex solitons in two-dimensional lattices

    SciTech Connect

    Mejia-Cortes, C.; Soto-Crespo, J. M.; Molina, Mario I.; Vicencio, Rodrigo A.

    2010-12-15

    We report the existence of stable symmetric vortex-type solutions for two-dimensional nonlinear discrete dissipative systems governed by a cubic-quintic complex Ginzburg-Landau equation. We construct a whole family of vortex solitons with a topological charge S=1. Surprisingly, the dynamical evolution of unstable solutions of this family does not significantly alter their profile, but instead their phase distribution completely changes; they transform into two-charge swirl-vortex solitons. We dynamically excite this structure showing its experimental feasibility.

  15. On Two-Dimensional Sonic-Subsonic Flow

    NASA Astrophysics Data System (ADS)

    Chen, Gui-Qiang; Dafermos, Constantine M.; Slemrod, Marshall; Wang, Dehua

    2007-05-01

    A compensated compactness framework is established for sonic-subsonic approximate solutions to the two-dimensional Euler equations for steady irrotational flows that may contain stagnation points. Only crude estimates are required for establishing compactness. It follows that the set of subsonic irrotational solutions to the Euler equations is compact; thus flows with sonic points over an obstacle, such as an airfoil, may be realized as limits of sequences of strictly subsonic flows. Furthermore, sonic-subsonic flows may be constructed from approximate solutions. The compactness framework is then extended to self-similar solutions of the Euler equations for unsteady irrotational flows.

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

    SciTech Connect

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

    1983-09-01

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

  17. Scattering and bound states in two-dimensional anisotropic potentials

    E-print Network

    Matthias Rosenkranz; Weizhu Bao

    2012-01-30

    We propose a framework for calculating scattering and bound state properties in anisotropic two-dimensional potentials. Using our method, we derive systematic approximations of partial wave phase shifts and binding energies. Moreover, the method is suitable for efficient numerical computations. We calculate the s-wave phase shift and binding energy of polar molecules in two layers polarized by an external field along an arbitrary direction. We find that scattering depends strongly on their polarization direction and that absolute interlayer binding energies are larger than thermal energies at typical ultracold temperatures.

  18. Approaching two-dimensional polymers with macroscopic sizes.

    PubMed

    Payamyar, Payam; Sakamoto, Junji; Schlüter, A Dieter

    2013-01-01

    We describe the challenges involved with extending the limited lateral size of two-dimensional polymers (2DPs). An amphiphilic monomer with three-fold symmetry is chosen to form an ideally tessellated monolayer at the air/water interface. Anthracene [4+4] photo-dimerization is chosen as the growth reaction. Formation of covalent net-points upon anthracene dimerization has an influence on the mechanical coherence of the resulting sheets which could be investigated qualitatively and quantitatively by means of AFM nano-indentation. PMID:23967707

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

    SciTech Connect

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

    2011-07-15

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

  20. 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.

  1. Two-dimensional laminar incompressible separated flow past airfoils

    NASA Technical Reports Server (NTRS)

    Plotkin, A.

    1973-01-01

    A method is proposed to treat the problem of steady, two-dimensional, laminar, incompressible high Reynolds number separated flow past thin airfoils. An integral form of the boundary layer equations with interaction is used and the interaction between the inviscid and viscous flow fields is provided for by use of a thin-airfoil integral. Documentation of the attempts at obtaining a solution is presented. A survey of the current state-of-the-art of problems involving viscous-inviscid interactions in flow fields with separation is given.

  2. 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.

  3. Structure determination of two-dimensional adenine crystals on graphite

    NASA Astrophysics Data System (ADS)

    Freund, J. E.; Edelwirth, M.; Kröautbel, P.; Heckl, W. M.

    1997-02-01

    Two-dimensional molecular-packing structure and monolayer preparation of adenine adsorbates on the graphite (0001) surface have been studied using scanning tunneling microscopy, low-energy electron diffraction, and thermal-desorption spectroscopy. By combining real-space images and diffraction data a close-packed hydrogen-bonded network of adenine dimers is proposed, containing two dimers in a unit cell with the symmetry group p2gg. The energy-minimized molecular arrangement could be determined by force field calculations. Adenine adsorbate layers were prepared by sublimation in UHV.

  4. Two-Dimensional Electron Gases at Complex Oxide Interfaces

    NASA Astrophysics Data System (ADS)

    Stemmer, Susanne; James Allen, S.

    2014-07-01

    Two-dimensional electron gases (2DEGs) at oxide interfaces may exhibit unique properties, including effects from strong electron correlations, extremely high electron densities, magnetism, and 2D superconductivity. This article discusses routes to high-mobility 2DEGs in complex oxide heterostructures, with a particular focus on 2DEGs that involve transport in SrTiO3. We discuss what is known about the electronic states in SrTiO3 2DEGs, both experimentally and theoretically. Examples from the current literature are summarized.

  5. Illustrations of Two-Dimensional and Three-Dimensional Pancaking

    NASA Astrophysics Data System (ADS)

    Buchert, T.; Klaffl, R.

    We present first results of some high-resolution studies of the large-scale structure distribution resulting from the pancake-approach. We show two sequences of pictures, one with a resolution of the spatial distribution of caustics computed from a two-dimensional flat spectrum with Gaussian distribution of amplitudes and cut-off (Buchert 1989), the second illustrating three-dimensional structures corresponding to the evolution of a three-dimensional flat Gaussian spectrum with cut-off (Klaffl 1988). Both sequences give new insight into details of the structures due to the use of special numerical programs.

  6. Particle acceleration at a two dimensional dipolarization front

    NASA Astrophysics Data System (ADS)

    Zimbardo, Gaetano; Greco, Antonella; Artemyev, Anton

    2014-05-01

    We consider the particle acceleration at dipolarization fronts that can be formed in the Earth's magnetotail in association with strong reconnection events. We set up an analytical two-dimensional model of the front which is a solution of the full set of Maxwell equation. A test particle simulation is performed to explore the influence of the various physical parameters, which are modelled according to the spacecraft observations. We find that energies up to a few tens of keV can be obtained, in reasonable agreement with observations. Application of this model to the heating of heavy ions in the solar corona are also discussed.

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

    NASA Astrophysics Data System (ADS)

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

    1992-11-01

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

  8. Entropy, topology of two-dimensional extreme black holes

    E-print Network

    Bin Wang; Ru-Keng Su

    1999-01-29

    Through direct thermodynamic calculations we have shown that different classical entropies of two-dimensional extreme black holes appear due to two different treatments, namely Hawking's treatment and Zaslavskii's treatment. Geometrical and topological properties corresponding to these different treatments are investigated. Quantum entropies of the scalar fields on the backgrounds of these black holes concerning different treatments are also exhibited. Different results of entropy and geometry lead us to argue that there are two kinds of extreme black holes in the nature. Explanation of black hole phase transition has also been given from the quantum point of view.

  9. Optical and electronic properties of two dimensional graphitic silicon carbide

    E-print Network

    Lin, Xiao; Lin, Shisheng; Hakro, Ayaz Ali; Cao, Te; Chen, Hongsheng; Zhang, Baile

    2012-01-01

    Optical and electronic properties of two dimensional few layers graphitic silicon carbide (GSiC), in particular monolayer and bilayer, are investigated by density functional theory and found different from that of graphene and silicene. Monolayer GSiC has direct bandgap while few layers exhibit indirect bandgap. The bandgap of monolayer GSiC can be tuned by an in-plane strain. Properties of bilayer GSiC are extremely sensitive to the interlayer distance. These predictions promise that monolayer GSiC could be a remarkable candidate for novel type of light-emitting diodes utilizing its unique optical properties distinct from graphene, silicene and few layers GSiC.

  10. Statistical Mechanics of Unbound Two Dimensional Self-Gravitating Systems

    E-print Network

    Tarcísio N. Teles; Yan Levin; Renato Pakter; Felipe B. Rizzato

    2010-04-19

    We study, using both theory and molecular dynamics simulations, the relaxation dynamics of a microcanonical two dimensional self-gravitating system. After a sufficiently large time, a gravitational cluster of N particles relaxes to the Maxwell-Boltzmann distribution. The time to reach the thermodynamic equilibrium, however, scales with the number of particles. In the thermodynamic limit, $N\\to\\infty$ at fixed total mass, equilibrium state is never reached and the system becomes trapped in a non-ergodic stationary state. An analytical theory is presented which allows us to quantitatively described this final stationary state, without any adjustable parameters.

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

    NASA Technical Reports Server (NTRS)

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

    1977-01-01

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

  12. Two-dimensional simulations of magnetically-driven instabilities

    SciTech Connect

    Peterson, D.; Bowers, R.; Greene, A.E.; Brownell, J.

    1986-01-01

    A two-dimensional Eulerian MHD code is used to study the evolution of magnetically-driven instabilities in cylindrical geometry. The code incorporates an equation of state, resistivity, and radiative cooling model appropriate for an aluminum plasma. The simulations explore the effects of initial perturbations, electrical resistivity, and radiative cooling on the growth and saturation of the instabilities. Comparisons are made between the 2-D simulations, previous 1-D simulations, and results from the Pioneer experiments of the Los Alamos foil implosion program.

  13. Terahertz plasmons in coupled two-dimensional semiconductor resonators

    NASA Astrophysics Data System (ADS)

    Sydoruk, O.; Wu, J. B.; Mayorov, A.; Wood, C. D.; Mistry, D. K.; Cunningham, J. E.

    2015-11-01

    Advances in theory are needed to match recent progress in measurements of coupled semiconductor resonators supporting terahertz plasmons. Here, we present a field-based model of plasmonic resonators that comprise gated and ungated two-dimensional electron systems. The model is compared to experimental measurements of a representative system, in which the interaction between the gated and ungated modes leads to a rich spectrum of hybridized resonances. A theoretical framework is thus established for the analysis and design of gated low-dimensional systems used as plasmonic resonators, underlining their potential application in the manipulation of terahertz frequency range signals.

  14. Efficient Bragg diffraction in thin semiconductor two-dimensional gratings.

    PubMed

    He, Q; Zaquine, I; André, R; Roosen, G; Frey, R

    2008-12-01

    Highly improved diffraction properties are demonstrated in a two-dimensional [2D] grating consisting of a transmission grating optically recorded in a semiconductor one-dimensional photonic crystal (1D-PC). Near unity internal diffraction efficiency, high wavelength selectivity, and Bragg diffraction regime operation are demonstrated when the read beam is set at Bragg incidence on the transmission grating while its wavelength corresponds to the band edge of the 3 microm thick 1D-PC. When the 2D grating is grown on a Bragg mirror, a single diffracted beam is obtained, which makes the device promising for optical signal processing. PMID:19037455

  15. Alignment of Two-Dimensional Rods under Shear

    NASA Astrophysics Data System (ADS)

    Schwartz, Daniel K.; Kurnaz, M. Levent

    1997-03-01

    Langmuir monolayers of NBD-stearic acid were observed in the coexistence region between two dimensional (2D) liquid and crystalline phases using Brewster angle microscopy and fluorescence microscopy. The solid phase domains were rod-shaped (aspect ratio of about 10) due to highly anisotropic molecular interactions. In a 2D shear flow the rods were observed to tumble in the 2D version of a Jeffery orbit - the rotational velocity slowed dramatically as the rods approached alignment with the flow direction. This resulted in a non-zero value of the nematic order parameter under shear, even for very dilute rod concentrations.

  16. Crystalline two-dimensional domains of cyanine dyes at interfaces

    NASA Astrophysics Data System (ADS)

    Kirstein, S.; Möhwald, H.; Shimomura, M.

    1989-01-01

    The formation of two-dimensional crystalline J-aggregates of a negatively charged water-soluble cyanine dye at a monolayer of a dimethylammonium amphiphile is observed by fluorescence microscopy and spectroscopy. It is demonstrated that domain size and morphology and spectroscopic properties can be controlled via the surface layer. The formation of rod-shaped crystalline aggregates tightly bound to the surface layer is established. These domains are of uniform size and shape, and order due to long-rang electrostatic repulsion.

  17. A Two-Dimensional Compressible Gas Flow Code

    Energy Science and Technology Software Center (ESTSC)

    1995-03-17

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

  18. Birth and Growth of Two-dimensional Universe

    E-print Network

    Tetsuyuki Yukawa

    2011-11-30

    A master equation for the evolution of two-dimensional universe is derived based on the simplicial quantum gravity regarding the evolution as the Markov process of a space-time lattice. Three typical phases, expanding, elongating and collapsing phase, which have been found in the numerical simulation, are studied together with their boundaries, analytically. Asymptotic solutions of the evolution equation for statistical quantities, such as averaged area, boundary length, and correlation of fluctuations, are obtained for each phase and boundary.After introducing a physical time the cosmological significance of each phase is discussed.

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

    SciTech Connect

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

    2014-07-15

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

  20. Operational manual for two-dimensional transonic code TSFOIL

    NASA Technical Reports Server (NTRS)

    Stahara, S. S.

    1978-01-01

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

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

    NASA Technical Reports Server (NTRS)

    Wernet, Mark P.

    1991-01-01

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

  2. Simulation of structural phase transition in two dimensional ionic crystal

    NASA Astrophysics Data System (ADS)

    Zhang, Dongsheng; Vernizzi, Graziano; Olvera de La Cruz, Monica

    2010-03-01

    We investigate the structure of a two-dimensional monovalent ionic crystal observed in cationic-anionic molecules adsorbed into surfaces by molecular dynamics simulations. The pair interaction between ions include a short-range Lennard-Jones term and a long-range electrostatic term. When the dielectric constant is small, electrostatic interactions dominate and the crystal form a regular square lattice. At large values of the dielectric constant the Lennard-Jones attraction dominates, and the crystal form a triangular lattice. We study the phase diagram of this model and the properties of the structural transition.

  3. Blind deconvolution of two-dimensional complex data

    SciTech Connect

    Ghiglia, D.C.; Romero, L.A.

    1994-01-01

    Inspired by the work of Lane and Bates on automatic multidimensional deconvolution, the authors have developed a systematic approach and an operational code for performing the deconvolution of multiply-convolved two-dimensional complex data sets in the absence of noise. They explain, in some detail, the major algorithmic steps, where noise or numerical errors can cause problems, their approach in dealing with numerical rounding errors, and where special noise-mitigating techniques can be used toward making blind deconvolution practical. Several examples of deconvolved imagery are presented, and future research directions are noted.

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

    SciTech Connect

    Salasnich, Luca

    2007-07-15

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

  5. 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.

  6. 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.

  7. Two-dimensional dynamics of relativistic solitons in cold plasmas

    NASA Astrophysics Data System (ADS)

    Lehmann, G.; Laedke, E. W.; Spatschek, K. H.

    2008-07-01

    The two-dimensional dynamics of solitons appearing during relativistic laser-plasma interaction is investigated. The analysis starts from known soliton models in one space-dimension (1D). Some of the soliton solutions are already unstable in 1D, and all suffer from transverse instability in two dimensions (2D). The most unstable modes are calculated. They give a hint to the 2D structures which appear because of transversal effects. The linear stability considerations are supplemented by full 2D nonlinear simulations.

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

    SciTech Connect

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

    2014-11-24

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

  9. 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.

  10. 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.

  11. Multiphoton excitation in spin split two-dimensional electron gas

    NASA Astrophysics Data System (ADS)

    Gumber, Sukirti; Kumar, Manoj; Jha, Pradip Kumar; Mohan, Man

    2015-12-01

    The terahertz radiation induced multiphoton excitation processes have been studied in a two dimensional electron gas where the mixing of spin-up and spin-down states of neighbouring Landau levels by Rashba spin orbit interaction results in two new, unequally spaced energy branches. The multiphoton transitions between different quasi-spin branches of electron gas are found to be dominant over transitions involving the states from the same branch. It has been observed that enhancement and power-broadening of absorption spectrum can be effectively tuned by strength and frequency of the laser field as well as the spin-orbit coupling.

  12. Bubble breakup in two-dimensional Stokes flow

    SciTech Connect

    Tanveer, S.; Vasconcelos, G.L. )

    1994-11-21

    A new class of exact solutions is reported for an evolving bubble in a two-dimensional slow viscous flow. It is observed that for an expanding bubble the interface grows smoother with time, whereas the contracting-bubble solutions display a tendency to form sharp corners ( near cusps'') for small values of surface tension. In the latter case, we also obtain analytic solutions that describe bubble breakup: For a large class of initial shapes, the interface will eventually develop a thin neck'' whose width goes to zero before the bubble is completely removed from the liquid.

  13. Optimum high temperature strength of two-dimensional nanocomposites

    SciTech Connect

    Monclús, M. A.; Molina-Aldareguía, J. M.; Polcar, T.; Llorca, J.

    2013-11-01

    High-temperature nanoindentation was used to reveal nano-layer size effects on the hardness of two-dimensional metallic nanocomposites. We report the existence of a critical layer thickness at which strength achieves optimal thermal stability. Transmission electron microscopy and theoretical bicrystal calculations show that this optimum arises due to a transition from thermally activated glide within the layers to dislocation transmission across the layers. We demonstrate experimentally that the atomic-scale properties of the interfaces profoundly affect this critical transition. The strong implications are that interfaces can be tuned to achieve an optimum in high temperature strength in layered nanocomposite structures.

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

    PubMed

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

    2015-12-18

    At the atomic-cluster scale, pure boron is markedly similar to carbon, forming simple planar molecules and cage-like fullerenes. Theoretical studies predict that two-dimensional (2D) boron sheets will adopt an atomic configuration similar to that of boron atomic clusters. We synthesized atomically thin, crystalline 2D boron sheets (i.e., borophene) on silver surfaces under ultrahigh-vacuum conditions. Atomic-scale characterization, supported by theoretical calculations, revealed structures reminiscent of fused boron clusters with multiple scales of anisotropic, out-of-plane buckling. Unlike bulk boron allotropes, borophene shows metallic characteristics that are consistent with predictions of a highly anisotropic, 2D metal. PMID:26680195

  15. Logarithmic divergent thermal conductivity in two-dimensional nonlinear lattices

    NASA Astrophysics Data System (ADS)

    Wang, Lei; Hu, Bambi; Li, Baowen

    2012-10-01

    Heat conduction in three two-dimensional (2D) momentum-conserving nonlinear lattices are numerically calculated via both nonequilibrium heat-bath and equilibrium Green-Kubo algorithms. It is expected by mainstream theories that heat conduction in such 2D lattices is divergent and the thermal conductivity ? increases with lattice length N logarithmically. Our simulations for the purely quartic lattice firmly confirm it. However, very robust finite-size effects are observed in the calculations for the other two lattices, which well explain some existing studies and imply the extreme difficulties in observing their true asymptotic behaviors with affordable computation resources.

  16. 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.

  17. Numerical study of two-dimensional freezing in an annulus

    SciTech Connect

    Sablani, S.S.; Venkateshan, S.P.; Sastri, V.M.K. )

    1990-07-01

    An evaluation is made of the results of a numerical study on two-dimensional freezing in an annulus made up of an initially superheated phase-change medium. Numerical results are used to deduce a relation between the nondimensional discharge time and the other parameters. The velocity of the freeze front decreases with time because of the increase of interface area as the freezing proceeds radially outward, followed by a marginal decrease in the freezing rate due to the presence of the adiabatic surface; sensible cooling then occurs only where the freeze front has already reached the adiabatic surface. 6 refs.

  18. General relativity as a two-dimensional CFT

    NASA Astrophysics Data System (ADS)

    Adamo, Tim

    2015-11-01

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

  19. Dynamical matrix of two-dimensional electron crystals

    NASA Astrophysics Data System (ADS)

    Côté, R.; Lemonde, M.-A.; Doiron, C. B.; Ettouhami, A. M.

    2008-03-01

    In a quantizing magnetic field, the two-dimensional electron gas has a rich phase diagram with broken translational symmetry phases such as Wigner, bubble, and stripe crystals. In this paper, we derive a method to obtain the dynamical matrix of these crystals from a calculation of the density response function performed in the generalized random-phase approximation (GRPA). We discuss the validity of our method by comparing the dynamical matrix calculated from the GRPA with that obtained from standard elasticity theory with the elastic coefficients obtained from a calculation of the deformation energy of the crystal.

  20. Three-Particle Complexes in Two-Dimensional Semiconductors

    NASA Astrophysics Data System (ADS)

    Ganchev, Bogdan; Drummond, Neil; Aleiner, Igor; Fal'ko, Vladimir

    2015-03-01

    We evaluate binding energies of trions X±, excitons bound by a donor or acceptor charge XD (A ) , and overcharged acceptors or donors in two-dimensional atomic crystals by mapping the three-body problem in two dimensions onto one particle in a three-dimensional potential treatable by a purposely developed boundary-matching-matrix method. We find that in monolayers of transition metal dichalcogenides the dissociation energy of X± is typically much larger than that of localized exciton complexes, so that trions are more resilient to heating, despite the fact that their recombination line in optics is less redshifted from the exciton line than the line of XD (A ) .

  1. 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.

  2. Two-dimensional approach to relativistic positioning systems

    SciTech Connect

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

    2006-04-15

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

  3. Effective complex permittivity tensor of a periodic array of cylinders

    NASA Astrophysics Data System (ADS)

    Godin, Yuri A.

    2013-05-01

    We determine the effective complex permittivity of a two-dimensional composite, consisting of an arbitrary doubly periodic array of identical circular cylinders in a homogeneous matrix, and whose dielectric properties are complex-valued. Efficient formulas are provided to determine the effective complex permittivity tensor which are in excellent agreement with numerical calculations. We also show that in contrast to the real-valued case, the real and imaginary parts of the effective complex-valued tensor can exhibit non-monotonic behavior as functions of volume fraction of cylinders, and can be either greater or less than that of the constituents.

  4. 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.

  5. 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

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

    PubMed

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

    2015-01-01

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

  7. Matter waves in two-dimensional arbitrary atomic crystals

    NASA Astrophysics Data System (ADS)

    Bartolo, Nicola; Antezza, Mauro

    2014-09-01

    We present a general scheme to realize a cold-atom quantum simulator of bidimensional atomic crystals. Our model is based on the use of two independently trapped atomic species: the first one, subject to a strong in-plane confinement, constitutes a two-dimensional matter wave which interacts only with atoms of the second species, deeply trapped around the nodes of a two-dimensional optical lattice. By introducing a general analytic approach we show that the system Green function can be exactly determined, allowing for the investigation of the matter-wave transport properties. We propose some illustrative applications to both Bravais (square, triangular) and non-Bravais (graphene, kagomé) lattices, studying both ideal periodic systems and experimental-size and disordered ones. Some remarkable spectral properties of these atomic artificial lattices are pointed out, such as the emergence of single and multiple gaps, flat bands, and Dirac cones. All these features can be manipulated via the interspecies interaction, which proves to be widely tunable due to the interplay between scattering length and confinements.

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

    PubMed

    Ahmadpoor, Fatemeh; Sharma, Pradeep

    2015-10-01

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

  9. Two-dimensional phased array probe shape corrections

    NASA Astrophysics Data System (ADS)

    Lupien, Vincent; Cancre, Fabrice; Lacroix, Benolt; Miller, Ted; Selman, John; Kinney, Andy; Duffy, Tim; Herzog, Pamela G.

    2002-05-01

    The availability of non-destructive testing hardware capable of controlling large numbers of elements has made possible forays into two-dimensional ultrasonic arrays. Here, we explore two such arrays. The first is a conical matrix array for three-dimensional imaging of fastener holes in aircraft wing structures, and the second is an annular-sectorial array with a compound radius of curvature for the inspection of aircraft engine grade billets. In both prototypes, significant departures of the true shape of the probe face from its ideal value are observed. Since the shape aberrations are many wavelengths in magnitude, it is impossible to arrive at the desired beam profile using the beamforming parameters for the ideal probe shape. We detail our approach for correcting the beamforming process. It is based on a combination of parametric representations of probe shape families and experimental measurements with specially designed targets. While exposing current limitations in the probe manufacturing process, our results demonstrate that complicated probe malformations of many wavelengths in magnitude can easily be corrected and that the spatially disjoint nature of two-dimensional arrays becomes an opportunity for such corrections.

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

    DOE PAGESBeta

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

    2015-04-10

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

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

    SciTech Connect

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

    2015-04-10

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

  12. Colloidal nanoplatelets with two-dimensional electronic structure

    NASA Astrophysics Data System (ADS)

    Ithurria, S.; Tessier, M. D.; Mahler, B.; Lobo, R. P. S. M.; Dubertret, B.; Efros, Al. L.

    2011-12-01

    The syntheses of strongly anisotropic nanocrystals with one dimension much smaller than the two others, such as nanoplatelets, are still greatly underdeveloped. Here, we demonstrate the formation of atomically flat quasi-two-dimensional colloidal CdSe, CdS and CdTe nanoplatelets with well-defined thicknesses ranging from 4 to 11 monolayers. These nanoplatelets have the electronic properties of two-dimensional quantum wells formed by molecular beam epitaxy, and their thickness-dependent absorption and emissionspectra are described very well within an eight-band Pidgeon-Brown model. They present an extremely narrow emission spectrum with full-width at half-maximum less than 40?meV at room temperature. The radiative fluorescent lifetime measured in CdSe nanoplatelets decreases with temperature, reaching 1?ns at 6?K, two orders of magnitude less than for spherical CdSe nanoparticles. This makes the nanoplatelets the fastest colloidal fluorescent emitters and strongly suggests that they show a giant oscillator strength transition.

  13. Two-dimensional phase transition models and ??^4 field theory

    E-print Network

    A. I. Sokolov

    2007-06-24

    The overview is given of the results obtained recently in the course of renormalization-group (RG) study of two-dimensional (2D) models. RG functions of the two-dimensional n-vector \\lambda \\phi^4 Euclidean field theory are written down up to the five-loop terms and perturbative series are resummed by the Pade-Borel-Leroy techniques. An account for the five-loop term is shown to shift the Wilson fixed point only briefly, leaving it outside the segment formed by the results of the lattice calculations. This is argued to reflect the influence of the non-analytical contribution to the \\beta-function. The evaluation of the critical exponents for n = 1, n = 0 and n = -1 in the five-loop approximation and comparison of the results with known exact values confirm the conclusion that non-analytical contributions are visible in two dimensions. The estimates obtained on the base of pseudo-\\epsilon expansions originating from the 5-loop 2D RG series are also discussed.

  14. Experimental studies on two dimensional shock boundary layer interactions

    NASA Technical Reports Server (NTRS)

    Skebe, S. A.; Greber, I.; Hingst, W. R.

    1984-01-01

    Experiments have been performed on the interaction of oblique shock waves with flat plate boundary layers in the 30.48 cm x 30.48 cm (1 ft. x 1 ft.) supersonic wind tunnel at NASA Lewis Research Center. High accuracy measurements of the plate surface static pressure and shear stress distributions as well as boundary layer velocity profiles were obtained through the interaction region. Documentation was also performed of the tunnel test section flow field and of the two-dimensionality of the interaction regions. The findings provide detailed description of two-dimensional interaction with initially laminar boundary layers over the Mach number range 2.0 to 4.0. Additional information with regard to interactions involving initially transitional boundary layers is presented over the Mach number range 2.0 to 3.0 and those for initially turbulent boundary layers at Mach 2.0. These experiments were directed toward providing well documented information of high accuracy useful as test cases for analytic and numerical calculations. Flow conditions encompassed a Reynolds number range of 4.72E6 to 2.95E7 per meter. The shock boundary layer interaction results were found to be generally in good agreement with the experimental work of previous authors both in terms of direct numerical comparison and in support of correlations establishing laminar separation characteristics.

  15. Two-dimensional fluorescence lifetime correlation spectroscopy. 1. Principle.

    PubMed

    Ishii, Kunihiko; Tahara, Tahei

    2013-10-01

    Fluorescence correlation spectroscopy (FCS) is a unique tool for investigating microsecond molecular dynamics of complex molecules in equilibrium. However, application of FCS in the study of molecular dynamics has been limited, owing to the complexity in the extraction of physically meaningful information. In this work, we develop a new method that combines FCS and time-correlated single photon counting (TCPSC) to extract unambiguous information about equilibrium dynamics of complex molecular systems. In this method, which we name two-dimensional fluorescence lifetime correlation spectroscopy (2D FLCS), we analyze the correlation of the fluorescence photon pairs, referring to the fluorescence lifetime. We first obtain the correlations of the photon pairs with respect to the excitation-emission delay times in the form of a two-dimensional (2D) map. Then, the 2D map is converted to the correlations between different species that have distinct fluorescence lifetimes using inverse Laplace transformation. This 2D FLCS is capable of visualizing the equilibration dynamics of complex molecules with microsecond time resolution at the single-molecule level. We performed a kinetic Monte Carlo simulation of a TCPSC-FCS experiment as a proof-of-principle example. The result clearly shows the validity of the proposed method and its high potential in analyzing the photon data of dynamic systems. PMID:23977832

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

    PubMed Central

    Goldman, D; Merril, C R

    1983-01-01

    A survey of 186 soluble lymphocyte proteins for genetic polymorphism was carried out utilizing two-dimensional electrophoresis of 14C-labeled phytohemagglutinin (PHA)-stimulated human lymphocyte proteins. Nineteen of these proteins exhibited positional variation consistent with independent genetic polymorphism in a primary sample of 28 individuals. Each of these polymorphisms was characterized by quantitative gene-dosage dependence insofar as the heterozygous phenotype expressed approximately 50% of each allelic gene product as was seen in homozygotes. Patterns observed were also identical in monozygotic twins, replicate samples, and replicate gels. The three expected phenotypes (two homozygotes and a heterozygote) were observed in each of 10 of these polymorphisms while the remaining nine had one of the homozygous classes absent. The presence of the three phenotypes, the demonstration of gene-dosage dependence, and our own and previous pedigree analysis of certain of these polymorphisms supports the genetic basis of these variants. Based on this data, the frequency of polymorphic loci for man is: P = 19/186 = .102, and the average heterozygosity is .024. This estimate is approximately 1/3 to 1/2 the rate of polymorphism previously estimated for man in other studies using one-dimensional electrophoresis of isozyme loci. The newly described polymorphisms and others which should be detectable in larger protein surveys with two-dimensional electrophoresis hold promise as genetic markers of the human genome for use in gene mapping and pedigree analyses. Images Fig. 1 Fig. 3 PMID:6577787

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

    NASA Astrophysics Data System (ADS)

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

    2015-04-01

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

  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 interpreter for field-reversed configurations

    SciTech Connect

    Steinhauer, Loren

    2014-08-15

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

  20. Comprehensive two-dimensional gas chromatography with pattern modulation.

    PubMed

    Seeley, John V; Seeley, Stacy K

    2015-11-20

    Comprehensive two-dimensional gas chromatography (GC×GC) modulators normally transfer primary column effluent to the head of the secondary column as a series of sharp pulses. Such pulses are produced with time-varying temperature gradients in thermal modulation or with time-varying flow patterns in flow modulation. Thermal modulators produce narrow peaks at optimal flow rates, but require large amounts of consumables or a highly engineered heating/cooling system. Flow modulators involve simpler hardware and no additional consumables. However, flow modulators require a large increase in secondary column flow or transfer only a small portion of the primary effluent to the secondary column. This study examines a new method of producing GC×GC separations with a flow modulator. Instead of injecting narrow pulses, the modulator transfers primary effluent to the secondary column in the form of an intricate injection pattern. The detector signal is deconvoluted and converted to a two-dimensional chromatogram. The high duty cycle of the technique (>50%) leads to deconvoluted peaks with twenty times greater intensity than those produced by conventional modulation with a Deans switch modulator. Pattern modulation can be produced without requiring elevated carrier flows. This study evaluates the efficacy of pattern modulation GC×GC by analyzing a standard mixture of 43 oxygenated organic compounds and an E85 fuel sample. PMID:26278359

  1. A Two-Dimensional Linear Bicharacteristic Scheme for Electromagnetics

    NASA Technical Reports Server (NTRS)

    Beggs, John H.

    2002-01-01

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

  2. Two-dimensional nuclear magnetic resonance of quadrupolar systems

    SciTech Connect

    Wang, Shuanhu

    1997-09-17

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

  3. Two Dimensional Intermodulation Distortion Scanning of Superconducting Filter Resonators

    NASA Astrophysics Data System (ADS)

    Bischak, Michael; Remillard, Stephen

    2015-03-01

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

  4. a Two-Dimensional Free Lagrangian Hydrodynamics Model.

    NASA Astrophysics Data System (ADS)

    Trease, Harold Eugene

    This thesis describes development of a two-dimensional Lagrangian hydrodynamics computer model. The model numerically integrates the time-dependent, compressible fluid flow equations in two-dimensional Cartesian geometry by using an explicit finite difference scheme on a free Lagrangian grid of Lagrangian mass points. An artificial viscosity tensor is introduced into the flow equations to resolve shock discontinuities in two dimensions. Use of a free Lagrangian grid eliminates the classical mesh tangling problems associated with standard Lagrangian models. This is done by giving each Lagrangian mass point the freedom to associate with a variable set of nearest neighbors. Identifying the nearest neighbors of each mass point is accomplished through the construction of a Voronoi mesh made up of Voronoi cells (convex polygons). The common edges of each Voronoi cell identify pairs of nearest neighbors. Since the change in volume of a Voronoi cell is continuous, two nearest neighbors become associated and disassociated in a continuous manner as the edge of the Voronoi cell separating two neighbors grows and shrinks. The concept of free Lagrangian hydrodynamics, as formulated in this thesis, is tested by modeling several example problems involving the development and propagation of shock waves in various geometric setups. The results of these test problems are compared with both analytic shock relations and experimental data. Through these comparison cases we find the free Lagrangian hydrodynamic scheme used in formulating the Free Lagrangian Model to be both consistent and stable.

  5. 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

  6. Flexoelectricity in two-dimensional crystalline and biological membranes

    NASA Astrophysics Data System (ADS)

    Ahmadpoor, Fatemeh; Sharma, Pradeep

    2015-10-01

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

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

    PubMed

    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. PMID:25122322

  8. 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.

  9. 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.

  10. Fokker-Planck description of the inverse cascade in two-dimensional turbulence

    NASA Astrophysics Data System (ADS)

    Kamps, Oliver; Vosskuhle, Michel

    2012-11-01

    In many approaches the mathematical description of fully developed turbulence relies on the statistical properties of the longitudinal velocity increments ? (r) = U (x + r) - U (x) . In the increment statistics is described as a Markov process in scale, leading to a Fokker-Planck description of the probability density functions (PDFs) for the velocity increments. The universality of this approach was tested for different kinds of three-dimensional flows like inhomogeneous turbulence, fractal grid generated turbulence and for the transition of a flow from a vortex street to fully developed turbulence in a cylinder wake the flow. In this talk we want to extend the test for the universality of the Markov description by analyzing data from numerical simulations of the inverse energy cascade in two-dimensional turbulence. The central question is whether the velocity field of the inverse cascade can be modeled as Markov process in scale similar to the three-dimensional case. By estimating the coefficients of the Fokker-Planck equation we are able to discuss the role of intermittency and differences to three-dimensional flows.

  11. 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

  12. 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.

  13. Engine Cylinder Temperature Control

    DOEpatents

    Kilkenny, Jonathan Patrick (Peoria, IL); Duffy, Kevin Patrick (Metamora, IL)

    2005-09-27

    A method and apparatus for controlling a temperature in a combustion cylinder in an internal combustion engine. The cylinder is fluidly connected to an intake manifold and an exhaust manifold. The method and apparatus includes increasing a back pressure associated with the exhaust manifold to a level sufficient to maintain a desired quantity of residual exhaust gas in the cylinder, and varying operation of an intake valve located between the intake manifold and the cylinder to an open duration sufficient to maintain a desired quantity of fresh air from the intake manifold to the cylinder, wherein controlling the quantities of residual exhaust gas and fresh air are performed to maintain the temperature in the cylinder at a desired level.

  14. Cylinder monitoring program

    SciTech Connect

    Alderson, J.H.

    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.

  15. 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.

  16. Two-dimensional silicon-carbon hybrids with a honeycomb lattice: New family for two-dimensional photovoltaic materials

    NASA Astrophysics Data System (ADS)

    Zhang, Jin; Ren, Jun; Fu, HuiXia; Ding, ZiJing; Li, Hui; Meng, Sheng

    2015-10-01

    We predict a series of new two-dimensional (2D) inorganic materials made of silicon and carbon elements (2D Si x C1- x ) based on density functional theory. Our calculations on optimized structure, phonon dispersion, and finite temperature molecular dynamics confirm the stability of 2D Si x C1- x sheets in a two-dimensional, graphene-like, honeycomb lattice. The electronic band gaps vary from zero to 2.5 eV as the ratio x changes in 2D Si x C1- x changes, suggesting a versatile electronic structure in these sheets. Interestingly, among these structures Si0.25C0.75 and Si0.75C0.25 with graphene-like superlattices are semimetals with zero band gap as their ? and ?* bands cross linearly at the Fermi level. Atomic structural searches based on particle-swarm optimization show that the ordered 2D Si x C1- x structures are energetically favorable. Optical absorption calculations demonstrate that the 2D silicon-carbon hybrid materials have strong photoabsorption in visible light region, which hold promising potential in photovoltaic applications. Such unique electronic and optical properties in 2D Si x C1- x have profound implications in nanoelectronic and photovoltaic device applications.

  17. An algorithm for simulating image formation in optical coherence tomography for cylinder scattering

    NASA Astrophysics Data System (ADS)

    Brenner, Thomas; Reitzle, Dominik; Kienle, Alwin

    2015-07-01

    An algorithm for the simulation of Fourier domain optical coherence tomography (OCT) images of a cylinder based on an analytical solution of Maxwell's equations is presented. The characteristics of the simulated OCT signal are discussed and the whispering gallery modes as well as the geometrical optics signals from the cylinder are identified. An OCT scanner with an incident Gaussian beam is implemented to simulate two-dimensional B-scans.

  18. Optical properties of two-dimensional metamaterial photonic crystals

    SciTech Connect

    Mejía-Salazar, J. R.

    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.

  19. Ultrasonic transducer with a two-dimensional Gaussian field profile

    NASA Technical Reports Server (NTRS)

    Claus, R. O.; Zerwekh, P. S.

    1983-01-01

    A transducer is described which generates a two-dimensional Gaussian field by controlling both the position of multiple circular electrodes and the voltage applied to each electrode. The transducer is constructed by depositing concentric rings electrodes onto one flat surface of a circular piezoelectric crystal disk and attaching the rings to an impedance matching network which acts as a voltage divider. Geometrical inter-ring separations and electrical inter-ring impedances are designed to minimize the error between the generated acoustic field, modeled as a piecewise linear function, and the desired Gaussian distribution. Total mean squared error between the averaged far-field data and a Gaussian shape is less than two percent.

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

    PubMed

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

    2015-06-10

    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. PMID:25985396

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

    NASA Astrophysics Data System (ADS)

    El Khoury, Youssef; Van Wilderen, Luuk J. G. W.; Vogt, Tim; Winter, Ernst; Bredenbeck, Jens

    2015-08-01

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

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

    SciTech Connect

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

    2013-08-15

    A sample of quasi-two-dimensional graphite (QTDG) whose magnetic properties are described within the Dirac fermion model is investigated by the nuclear magnetic resonance (NMR) and scanning tunneling microscopy (STM) techniques. The broad spectrum of the sample points to a large dispersion of crystallite sizes in this system, which is also confirmed by STM data. It is established that the local diamagnetic susceptibility may substantially exceed the average value over the sample and reaches an abnormally high value of -1.3 Multiplication-Sign 10{sup -4} emu/g at T = 4.2 K, which is greater than the corresponding value of highly oriented graphite by a factor of four.

  3. Studying biomacromolecules with two-dimensional infrared spectroscopy.

    PubMed

    Hill, Rachel E; Hunt, Neil T; Hirst, Jonathan D

    2013-01-01

    Two-dimensional infrared (2DIR) spectroscopy is a rapidly developing nonlinear spectroscopy, which allows access to greater structural detail than traditional vibrational spectroscopies. The ability to gain extra structural insight is particularly relevant to the study of biomacromolecules, whose Fourier transform infrared (FTIR) spectra are often congested, due to the large number of vibrations. The subpicosecond timescale of the spectroscopy gives the opportunity to follow the fluctuations of a molecule in the time domain. Theoretical and experimental techniques are well developed for 2DIR, and they have already given insight into some of the fundamental aspects of the structure and dynamics of proteins and nucleic acids. This chapter reviews some of these recent studies and showcases the potential of the method. PMID:24018321

  4. 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

  5. Exploring the Thermodynamics of a Two-Dimensional Bose Gas

    SciTech Connect

    Yefsah, Tarik; Desbuquois, Remi; Chomaz, Lauriane; Guenter, Kenneth J.; Dalibard, Jean

    2011-09-23

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

  6. Numerical solution of a two-dimensional fluidized bed model

    NASA Astrophysics Data System (ADS)

    Christie, I.; Ganser, G. H.; Wilder, J. W.

    1998-09-01

    The numerical solution of a model describing a two-dimensional fluidized bed is considered. The model takes the form of a hyperbolic system of conservation laws with source term, coupled with an elliptic equation for determining a streamfunction. Operator splitting is used to produce homogeneous one-dimensional hyperbolic systems and ordinary differential equations involving the source term. The one-dimensional hyperbolic problems are solved using Roe's method with the addition of an entropy fix. The numerical procedure is second-order in time and first-order in space. Second-order-accuracy in space is obtained using flux limiting techniques. Numerical experiments which show the development of bubbles in the bed are presented. The familiar kidney-shaped bubble, observed experimentally, is found when using the method which is second-order in space. On the same mesh, the first-order method produces bubbles which are no longer kidney-shaped.

  7. Global geometry of two-dimensional charged black holes

    SciTech Connect

    Frolov, Andrei V.; Kristjansson, Kristjan R.; Thorlacius, Larus

    2006-06-15

    The semiclassical geometry of charged black holes is studied in the context of a two-dimensional dilaton gravity model where effects due to pair-creation of charged particles can be included in a systematic way. The classical mass-inflation instability of the Cauchy horizon is amplified and we find that gravitational collapse of charged matter results in a spacelike singularity that precludes any extension of the spacetime geometry. At the classical level, a static solution describing an eternal black hole has timelike singularities and multiple asymptotic regions. The corresponding semiclassical solution, on the other hand, has a spacelike singularity and a Penrose diagram like that of an electrically neutral black hole. Extremal black holes are destabilized by pair-creation of charged particles. There is a maximally charged solution for a given black hole mass but the corresponding geometry is not extremal. Our numerical data exhibits critical behavior at the threshold for black hole formation.

  8. Two-dimensional electronic spectroscopy with birefringent wedges

    SciTech Connect

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

    2014-12-15

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

  9. 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.

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

    PubMed

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

    2015-01-01

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

  11. 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

  12. Stopping power of two-dimensional spin quantum electron gases

    NASA Astrophysics Data System (ADS)

    Zhang, Ya; Jiang, Wei; Yi, Lin

    2015-04-01

    Quantum effects can contribute significantly to the electronic stopping powers in the interactions between the fast moving beams and the degenerate electron gases. From the Pauli equation, the spin quantum hydrodynamic (SQHD) model is derived and used to calculate the stopping power and the induced electron density for protons moving above a two-dimensional (2D) electron gas with considering spin effect under an external in-plane magnetic field. In our calculation, the stopping power is not only modulated by the spin direction, but also varied with the strength of the spin effect. It is demonstrated that the spin effect can obviously enhance or reduce the stopping power of a 2D electron gas within a laboratory magnetic field condition (several tens of Tesla), thus a negative stopping power appears at some specific proton velocity, which implies the protons drain energy from the Pauli gas, showing another significant example of the low-dimensional physics.

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

    PubMed

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

    2011-05-27

    We experimentally demonstrate coherent light scattering from an atomic Mott insulator in a two-dimensional lattice. The far-field diffraction pattern of small clouds of a few hundred atoms was imaged while simultaneously laser cooling the atoms with the probe beams. We describe the position of the diffraction peaks and the scaling of the peak parameters by a simple analytic model. In contrast to Bragg scattering, scattering from a single plane yields diffraction peaks for any incidence angle. We demonstrate the feasibility of detecting spin correlations via light scattering by artificially creating a one-dimensional antiferromagnetic order as a density wave and observing the appearance of additional diffraction peaks. PMID:21699309

  14. 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

  15. An investigation of a two-dimensional propulsive lifting system

    NASA Technical Reports Server (NTRS)

    Shollenberger, C. A.

    1973-01-01

    Several aspects of the nonhomogeneous flow associated with a system combining lifting and propulsive requirements of an aircraft are considered by analytical and experimental methods. The basic geometry of the problem is that of two lifting surfaces with an actuator disk located between them. The principles governing flow with energy addition are examined. Basic equations and boundary conditions are developed for the complete inviscid and incompressible analysis for the two-dimensional case. The corresponding flow singularities are discussed and the integral equations which completely specify the system are derived. The two special cases of small and large energy addition are considered in detail including solutions. A numerical procedure is developed to solve the full problem including allowance for the wake deflection. Appropriate vorticity forms are used to represent the entire system. An iterative scheme is presented which rapidly converges to a solution for the magnitude and location of the system vorticity distributions. Forces and moments are evaluated on the propulsive lift system.

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

    NASA Technical Reports Server (NTRS)

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

    1976-01-01

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

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

    PubMed

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

    2013-12-01

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

  18. 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.

  19. Probing Mechanics of Rippled Two-Dimensional Materials

    NASA Astrophysics Data System (ADS)

    Nicholl, Ryan; Conely, Hiram; Lavrik, Nickolay; Vlassiouk, Ivan; Bolotin, Kirill

    2015-03-01

    Two-dimensional materials such as graphene tend to ripple in the out of plane direction. These ripples arise both due to thermal fluctuations and uneven stress forces at the boundary. In this work, we study the effect of the rippling on the effective mechanical properties of graphene: Young's modulus and bending rigidity. To accomplish this, we developed a non-contact technique that allows probing mechanical properties of graphene at temperatures between 4K and 400K. We use a high voltage electrostatic force to pull on graphene and high-resolution optical interferometric profilometery to measure its mechanical response. We find that the effective Young's modulus of graphene is significantly softened and the bending rigidity is increased due to rippling.

  20. 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.

  1. Creating an artificial two-dimensional Skyrmion crystal by nanopatterning.

    PubMed

    Sun, L; Cao, R X; Miao, B F; Feng, Z; You, B; Wu, D; Zhang, W; Hu, An; Ding, H F

    2013-04-19

    A Skyrmion crystal typically arises from helical spin structures induced by the Dzyaloshinskii-Moriya interaction. Experimentally its physical exploration has been impeded because it is a rarity and is found only within a narrow temperature and magnetic field range. We present a method for the assembly of a two-dimensional Skyrmion crystal based upon a combination of a perpendicularly magnetized film and nanopatterned arrays of magnetic vortices that are geometrically confined within nanodisks. The practical feasibility of the method is validated by micromagnetic simulations and computed Skyrmion number per unit cell. We also quantify a wide range in temperature and field strength over which the Skyrmion crystal can be stabilized without the need for any intrinsic Dzyaloshinskii-Moriya interactions, which otherwise is needed to underpin the arrangement as is the case in the very few known Skyrmion crystal cases. Thus, our suggested scheme involves a qualitative breakthrough that comes with a substantial quantitative advance. PMID:23679635

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

    PubMed

    West, Brantley A; Moran, Andrew M

    2012-09-20

    Coherent two-dimensional (2D) spectroscopies conducted at visible and infrared wavelengths are having a transformative impact on the understanding of numerous processes in condensed phases. The extension of 2D spectroscopy to the ultraviolet spectral range (2DUV) must contend with several challenges, including the attainment of adequate laser bandwidth, interferometric phase stability, and the suppression of undesired nonlinearities in the sample medium. Solutions to these problems are motivated by the study of a wide range of biological systems whose lowest-frequency electronic resonances are found in the UV. The development of 2DUV spectroscopy also makes possible the attainment of new insights into elementary chemical reaction dynamics (e.g., electrocyclic ring opening in cycloalkenes). Substantial progress has been made in both the implementation and application of 2DUV spectroscopy in the past several years. In this Perspective, we discuss 2DUV methodology, review recent applications, and speculate on what the future will hold. PMID:26295877

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

    NASA Astrophysics Data System (ADS)

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

    2013-11-01

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

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

    E-print Network

    Hartmut Löwen; Tobias Horn; Tim Neuhaus; Borge ten Hagen

    2013-10-30

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

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

    PubMed

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

    2015-02-11

    Optimizing new generations of two-dimensional devices based on van der Waals materials will require techniques capable of measuring variations in electronic properties in situ and with nanometer spatial resolution. We perform scanning microwave microscopy (SMM) imaging of single layers of MoS2 and n- and p-doped WSe2. By controlling the sample charge carrier concentration through the applied tip bias, we are able to reversibly control and optimize the SMM contrast to image variations in electronic structure and the localized effects of surface contaminants. By further performing tip bias-dependent point spectroscopy together with finite element simulations, we distinguish the effects of the quantum capacitance and determine the local dominant charge carrier species and dopant concentration. These results underscore the capability of SMM for the study of 2D materials to image, identify, and study electronic defects. PMID:25625509

  6. Two-dimensional freezing criteria for crystallizing colloidal monolayers

    SciTech Connect

    Wang Ziren; Han Yilong; Alsayed, Ahmed M.

    2010-04-21

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

  7. Spontaneous supersymmetry breaking in two dimensional lattice super QCD

    DOE PAGESBeta

    Catterall, Simon; Veernala, Aarti

    2015-10-02

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

  8. Two-Dimensional Perovskite Activation with an Organic Luminophore.

    PubMed

    Jemli, Khaoula; Audebert, Pierre; Galmiche, Laurent; Trippé-Allard, Gaelle; Garrot, Damien; Lauret, Jean-Sébastien; Deleporte, Emmanuelle

    2015-10-01

    A great advantage of the hybrid organic-inorganic perovskites is the chemical flexibility and the possibility of a molecular engineering of each part of the material (the inorganic part and the organic part respectively) in order to improve or add some functionalities. An adequately chosen organic luminophore has been introduced inside a lead bromide type organic-inorganic perovskite, while respecting the two-dimensional perovskite structure. A substantial increase of the brilliance of the perovskite is obtained. This activation of the perovskite luminescence by the adequate engineering of the organic part is an original approach, and is particularly interesting in the framework of the light-emitting devices such as organic light-emitting diodes (OLEDs) or lasers. PMID:26340054

  9. Atomically thin two-dimensional organic-inorganic hybrid perovskites

    NASA Astrophysics Data System (ADS)

    Dou, Letian; Wong, Andrew B.; Yu, Yi; Lai, Minliang; Kornienko, Nikolay; Eaton, Samuel W.; Fu, Anthony; Bischak, Connor G.; Ma, Jie; Ding, Tina; Ginsberg, Naomi S.; Wang, Lin-Wang; Alivisatos, A. Paul; Yang, Peidong

    2015-09-01

    Organic-inorganic hybrid perovskites, which have proved to be promising semiconductor materials for photovoltaic applications, have been made into atomically thin two-dimensional (2D) sheets. We report the solution-phase growth of single- and few-unit-cell-thick single-crystalline 2D hybrid perovskites of (C4H9NH3)2PbBr4 with well-defined square shape and large size. In contrast to other 2D materials, the hybrid perovskite sheets exhibit an unusual structural relaxation, and this structural change leads to a band gap shift as compared to the bulk crystal. The high-quality 2D crystals exhibit efficient photoluminescence, and color tuning could be achieved by changing sheet thickness as well as composition via the synthesis of related materials.

  10. Atomically thin two-dimensional organic-inorganic hybrid perovskites.

    PubMed

    Dou, Letian; Wong, Andrew B; Yu, Yi; Lai, Minliang; Kornienko, Nikolay; Eaton, Samuel W; Fu, Anthony; Bischak, Connor G; Ma, Jie; Ding, Tina; Ginsberg, Naomi S; Wang, Lin-Wang; Alivisatos, A Paul; Yang, Peidong

    2015-09-25

    Organic-inorganic hybrid perovskites, which have proved to be promising semiconductor materials for photovoltaic applications, have been made into atomically thin two-dimensional (2D) sheets. We report the solution-phase growth of single- and few-unit-cell-thick single-crystalline 2D hybrid perovskites of (C4H9NH3)2PbBr4 with well-defined square shape and large size. In contrast to other 2D materials, the hybrid perovskite sheets exhibit an unusual structural relaxation, and this structural change leads to a band gap shift as compared to the bulk crystal. The high-quality 2D crystals exhibit efficient photoluminescence, and color tuning could be achieved by changing sheet thickness as well as composition via the synthesis of related materials. PMID:26404831

  11. Two-dimensional electrophoresis of proteins secreted from articular cartilage.

    PubMed

    Hermansson, Monika; Saklatvala, Jeremy; Wait, Robin

    2007-01-01

    Two-dimensional electrophoresis (2DE) is a powerful method for separation of complex mixtures of proteins. The standard procedure is not, however, well suited to analysis of articular cartilage, which contains high concentrations of proteoglycans, the polyanionic glycosaminoglycan chains of which interfere with isoelectric focusing. We have developed a method for selective removal of proteoglycans by precipitation with cetylpyridinium chloride, after which the residual cartilage proteins are amenable to conventional 2DE analysis. Using this method, reproducible 2D-patterns can be obtained from proteins secreted by articular cartilage. The separated proteins may then be visualized by metabolic radiolabeling and silver staining, digested in gel with trypsin, and identified by tandem mass spectrometry. PMID:17983159

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

    SciTech Connect

    Fan Weili; Dong Lifang; Zhang Xinchun

    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.

  13. 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.

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

    SciTech Connect

    Kim, D.; Rewoldt, G.

    1984-11-01

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

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

    PubMed Central

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

    2015-01-01

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

  16. Asymmetric two-dimensional jet efflux from a channel

    NASA Technical Reports Server (NTRS)

    Martin, C. S.

    1977-01-01

    Irrotational flow of two-dimensional jets from a channel is treated without direct use of a logarithmic hodograph plane. An analytical approach is introduced for solving the general problem of two jets issuing from a channel with three end plates. Numerical values of the contraction coefficient and the angle of jet deflection are obtained for the special case where the two jets are located symmetrically and all the end plates are in line. Limiting cases of the resulting single-jet problem are the symmetric and asymmetric configurations solved by von Mises (1917). Results for the asymmetric case improve upon the theoretical values reported by von Mises and compare favorably with existing experimental data.

  17. 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.

  18. Extracting joint weak values from two-dimensional spatial displacements

    E-print Network

    Hirokazu Kobayashi; Graciana Puentes; Yutaka Shikano

    2012-11-06

    The joint weak value is a counterfactual quantity related to quantum correlations and quantum dynamics, which can be retrieved via weak measurements, as initiated by Aharonov and colleagues. In this Rapid Communication, we provide a full analytical extension of the method described by Puentes et al. [Phys. Rev. Lett. 109, 040401 (2012)], to extract the joint weak values of single-particle operators from two-dimensional spatial displacements of Laguerre-Gauss probe states, for the case of azimuthal index |l|>1. This method has a statistical advantage over previous ones since information about the conjugate observable, i.e., the momentum displacement of the probe, is not required. Moreover, we demonstrate that under certain conditions, the joint weak value can be extracted directly from spatial displacements without any additional data processing.

  19. Entropic Barriers for Two-Dimensional Quantum Memories

    NASA Astrophysics Data System (ADS)

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

    2014-03-01

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

  20. 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.

  1. Polycrystalline graphene and other two-dimensional materials

    NASA Astrophysics Data System (ADS)

    Yazyev, Oleg V.; Chen, Yong P.

    2014-10-01

    Graphene, a single atomic layer of graphitic carbon, has attracted intense attention because of its extraordinary properties that make it a suitable material for a wide range of technological applications. Large-area graphene films, which are necessary for industrial applications, are typically polycrystalline -- that is, composed of single-crystalline grains of varying orientation joined by grain boundaries. Here, we present a review of the large body of research reported in the past few years on polycrystalline graphene. We discuss its growth and formation, the microscopic structure of grain boundaries and their relations to other types of topological defect such as dislocations. The Review further covers electronic transport, optical and mechanical properties pertaining to the characterizations of grain boundaries, and applications of polycrystalline graphene. We also discuss research, still in its infancy, performed on other two-dimensional materials such as transition metal dichalcogenides, and offer perspectives for future directions of research.

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

    SciTech Connect

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

    1990-11-01

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

  3. A ballistic two-dimensional-electron-gas Andreev interferometer

    SciTech Connect

    Amado, M. Fornieri, A.; Sorba, L.; Giazotto, F.; Biasiol, G.

    2014-06-16

    We report the realization and investigation of a ballistic Andreev interferometer based on an InAs two dimensional electron gas coupled to a superconducting Nb loop. We observe strong magnetic modulations in the voltage drop across the device due to quasiparticle interference within the weak-link. The interferometer exhibits flux noise down to ?80???{sub 0}/?(Hz) and a robust behavior in temperature with voltage oscillations surviving up to ?7?K. Besides this remarkable performance, the device represents a crucial first step for the realization of a fully-tunable ballistic superconducting magnetometer and embodies a potential advanced platform for the investigation of Majorana bound states, non-local entanglement of Cooper pairs, as well as the manipulation and control of spin triplet correlations.

  4. Two-Dimensional Quantum Model of a Nanotransistor

    NASA Technical Reports Server (NTRS)

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

    2009-01-01

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

  5. Anisotropic superconductivity in the two-dimensional Hubbard model

    SciTech Connect

    Zielinski, J.; Mierzejewski, M.; Entel, P.; Grabowski, R. |

    1995-02-01

    The authors address the problem of anisotropic superconductivity in the two-dimensional Hubbard model. The Eliashberg equations have been generalized to the case which accounts for the anisotropy of the order parameter. Strong local correlations are treated within the mean field slave boson approximation. The superconducting transition temperature {Tc} is evaluated as a function of the occupation number. These results indicate that the d-wave state is the most likely channel for superconductivity for small concentration of holes. The authors have also derived an approximate analytical formula for {Tc} valid for any value of the occupation number. In addition, the influence of strong correlations on the electron-phonon coupling function is also discussed.

  6. Spontaneous supersymmetry breaking in two dimensional lattice super QCD

    SciTech Connect

    Catterall, Simon; Veernala, Aarti

    2015-10-02

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

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

    NASA Astrophysics Data System (ADS)

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

    2015-11-01

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

  8. Two-dimensional cellular metals as multifunctional structures: topology optimization

    NASA Astrophysics Data System (ADS)

    Xu, F.; Wen, T.; Lu, T. J.

    2009-02-01

    Highly porous two-dimensional (2D) cellular metals have multifunctional attributes, with tailorable structures to achieve multifunctional performance. The focus of this study is to explore the optimal cellular topology of 2D cellular metals for heat dissipation, and to investigate the eligibility of different heat enhancement techniques for more efficient heat dissipation. An analytical approach for the optimal design of metallic 2D cellular materials, cooled by single-phase laminar forced convection in various flow configurations, is proposed and validated by comparison with full numerical simulations. The optimal design is characterized by two subsidiary dimensionless parameters: one reflecting the trade-off between convection and fluid friction, and the other reflecting the optimal balance between conduction and convection. A heat transfer enhancement technique--boundary layer redevelopment--is subsequently introduced and its feasibility examined experimentally. Future research directions in specific areas are discussed.

  9. Guest Editorial: Two-Dimensional Optical Signal Processing

    NASA Astrophysics Data System (ADS)

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

    1982-10-01

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

  10. Two-dimensional electron cyclotron emission imaging diagnostic for TEXTOR

    SciTech Connect

    Wang, J.; Domier, C.W.; Xia, Z.G.; Liang, Y.; Luhmann, N.C. Jr.; Park, H.; Munsat, T.; Mazzucato, E.; Pol, M.J. van de; Classen, I.G.J.; Donne, A.J.H.

    2004-10-01

    A two-dimensional electron cyclotron emission imaging (ECEI) diagnostic has been developed in which broad bandwidth radiation is collected by a vertically aligned mixer array and separated by frequency band. Using a 16 element array, and an 8 band receiver attached to each array element, time-resolved 16x8 images of electron temperature profiles and fluctuations of the TEXTOR plasma are acquired with vertical and horizontal channel spacings of 11 and 8 mm, and spot sizes of 13 and 9 mm, respectively. The system is wideband tunable from 95 to 130 GHz, and the focus location may be shifted horizontally via translation of one of the optical imaging elements. System design and laboratory testing details of the ECE Imaging optics and multichannel wideband electronics are presented, together with TEXTOR plasma data.

  11. The Two Dimensional Euler Equations on Singular Exterior Domains

    NASA Astrophysics Data System (ADS)

    Gérard-Varet, David; Lacave, Christophe

    2015-12-01

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

  12. Two-dimensional Fourier-transform spectroscopy of potassium vapor

    SciTech Connect

    Dai, X.; Bristow, A. D.; Karaiskaj, D.; Cundiff, S. T.

    2010-11-15

    Optical two-dimensional Fourier-transform (2DFT) spectroscopy is used to study the coherent optical response of potassium vapor in a thin transmission cell. Rephasing and nonrephasing spectra of the D{sub 1} and D{sub 2} transitions are obtained and compared to numerical simulations. Non-perturbative calculations using the optical Bloch equations give very good agreement with the experimental peak strengths and line shapes. Nonradiative Raman-like coherences are isolated using a different 2DFT projection. Comparison between the optical and Raman linewidths shows that dephasing is due to partially correlated energy fluctuations. Density-dependent measurements show distortion of 2DFT spectra due to pulse propagation effects.

  13. Two-dimensional topological insulator edge state backscattering by dephasing

    NASA Astrophysics Data System (ADS)

    Essert, Sven; Krueckl, Viktor; Richter, Klaus

    2015-11-01

    To understand the seemingly absent temperature dependence in the conductance of two-dimensional topological insulator edge states, we perform a numerical study which identifies the quantitative influence of the combined effect of dephasing and elastic scattering in charge puddles close to the edges. We show that this mechanism may be responsible for the experimental signatures in HgTe/CdTe quantum wells if the puddles in the samples are large and weakly coupled to the sample edges. We propose experiments on artificial puddles which allow one to verify this hypothesis and to extract the real dephasing time scale using our predictions. In addition, we present a method to include the effect of dephasing in wave-packet-time-evolution algorithms.

  14. Dynamical percolation transition in the two-dimensional ANNNI model.

    PubMed

    Chandra, Anjan Kumar

    2013-04-01

    The dynamical percolation transition of the two-dimensional axial next nearest-neighbor Ising model due to a pulsed magnetic field has been studied by finite size scaling analysis (by Monte Carlo simulation) for various values of frustration parameters, pulse width and temperature (below the corresponding static transition temperature). It has been found that the size of the largest geometrical cluster shows a transition for a critical field amplitude. Although the transition points shift, the critical exponents remain invariant for a wide range of frustration parameters. They are also the same as those obtained for the 2d Ising model. This suggests that although the static phase diagrams of these two models differ significantly in various aspects, the dynamical percolation transitions of these models belong to the same universality class. PMID:23454866

  15. Regional statistics in confined two-dimensional decaying turbulence.

    PubMed

    Házi, Gábor; Tóth, Gábor

    2011-06-28

    Two-dimensional decaying turbulence in a square container has been simulated using the lattice Boltzmann method. The probability density function (PDF) of the vorticity and the particle distribution functions have been determined at various regions of the domain. It is shown that, after the initial stage of decay, the regional area averaged enstrophy fluctuates strongly around a mean value in time. The ratio of the regional mean and the overall enstrophies increases monotonously with increasing distance from the wall. This function shows a similar shape to the axial mean velocity profile of turbulent channel flows. The PDF of the vorticity peaks at zero and is nearly symmetric considering the statistics in the overall domain. Approaching the wall, the PDFs become skewed owing to the boundary layer. PMID:21576171

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

    NASA Technical Reports Server (NTRS)

    Tanveer, Saleh; Vasconcelos, Giovani L.

    1994-01-01

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

  17. 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.

  18. 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.

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

    SciTech Connect

    Mazzanti, F.; Astrakharchik, G. E.; Boronat, J.; Zillich, R. E.

    2009-03-20

    A detailed microscopic analysis of the dynamic structure function S(k,{omega}) of a two-dimensional Bose system of dipoles polarized along the direction perpendicular to the plane is presented and discussed. Starting from ground-state quantities obtained using a quantum diffusion Monte Carlo algorithm, the density-density response is evaluated in the context of the correlated basis functions (CBF) theory. CBF predicts a sharp peak and a multiexcitation component at higher energies produced by the decay of excitations. We discuss the structure of the phonon-roton peak and show that the Feynman and Bogoliubov predictions depart from the CBF result already at low densities. We finally discuss the emergence of a roton in the spectrum, but find the roton energy not low enough to make the system unstable under density fluctuations up to the highest density considered that is close to the freezing point.

  20. Dynamics across the morphological transition in two-dimensional aggregates

    NASA Astrophysics Data System (ADS)

    Bandi, Mahesh; Das, Tamoghna

    2015-03-01

    Microscopic dynamics of two-dimensional aggregates have been studied by analysing simulated particle trajectories generated by molecular dynamics. Tuning the competition between the short-range attraction and long-range repulsion in a particulate system at fixed temperature and density results in a continuous non-compact to compact morphological transition. The finite-size aggregates, obtained by very slow cooling, show long-time sub-diffusive behaviour irrespective of their morphologies. By analysing the relative displacement fluctuations of particles with respect to their nearest neighbours, non-compact aggregates can be attributed to bonding between particles while caging is found to be responsible for compact clusters. These dynamical mechanisms are further illustrated by the self-displacement fluctuation of particles which show a continuous change from power-law to exponential behaviour across the non-compact to compact transition. This work was supported by the OIST Graduate University with subsidy funding from the Cabinet Office, Government of Japan.

  1. Kinetic theory of a two-dimensional magnetized plasma.

    NASA Technical Reports Server (NTRS)

    Vahala, G.; Montgomery, D.

    1971-01-01

    Several features of the equilibrium and nonequilibrium statistical mechanics of a two-dimensional plasma in a uniform dc magnetic field are investigated. The charges are assumed to interact only through electrostatic potentials. The problem is considered both with and without the guiding-center approximation. With the guiding-center approximation, an appropriate Liouville equation and BBGKY hierarchy predict no approach to thermal equilibrium for the spatially uniform case. For the spatially nonuniform situation, a guiding-center Vlasov equation is discussed and solved in special cases. For the nonequilibrium, nonguiding-center case, a Boltzmann equation, and a Fokker-Planck equation are derived in the appropriate limits. The latter is more tractable than the former, and can be shown to obey conservation laws and an H-theorem, but contains a divergent integral which must be cut off on physical grounds. Several unsolved problems are posed.

  2. Sieving hydrogen isotopes through two-dimensional crystals.

    PubMed

    Lozada-Hidalgo, M; Hu, S; Marshall, O; Mishchenko, A; Grigorenko, A N; Dryfe, R A W; Radha, B; Grigorieva, I V; Geim, A K

    2016-01-01

    One-atom-thick crystals are impermeable to atoms and molecules, but hydrogen ions (thermal protons) penetrate through them. We show that monolayers of graphene and boron nitride can be used to separate hydrogen ion isotopes. Using electrical measurements and mass spectrometry, we found that deuterons permeate through these crystals much slower than protons, resulting in a separation factor of ?10 at room temperature. The isotope effect is attributed to a difference of ?60 milli-electron volts between zero-point energies of incident protons and deuterons, which translates into the equivalent difference in the activation barriers posed by two-dimensional crystals. In addition to providing insight into the proton transport mechanism, the demonstrated approach offers a competitive and scalable way for hydrogen isotope enrichment. PMID:26721995

  3. Diffusion coefficients of two-dimensional viral DNA walks

    NASA Astrophysics Data System (ADS)

    Hsu, Tai-Hsin; Nyeo, Su-Long

    2003-05-01

    DNA sequences are represented as two-dimensional walkers based on groups of mapping rules for the nucleotides in the DNA sequences. Digital sequences from irrational and random numbers in base 4 are generated and their diffusion properties are then compared with those of 21 nucleotide sequences of animal and plant viruses. By defining the diffusion coefficient as a function of the number of steps taken in a walk, we show that the coefficients for the viral DNA sequences generally have maximum values considerably larger than those for the random-number sequences of same lengths. Moreover, using the walker diagrams generated by different mapping groups, we can study the dominance of any of the nucleotide pairs (AG or CT), (AC or GT), or (AT or CG) in a DNA sequence. Other possible studies of this approach are mentioned.

  4. Search for conformal invariance in compressible two-dimensional turbulence

    E-print Network

    S. Stefanus; J. Larkin; W. I. Goldburg

    2011-10-11

    We present a search for conformal invariance in vorticity isolines of two-dimensional compressible turbulence. The vorticity is measured by tracking the motion of particles that float at the surface of a turbulent tank of water. The three-dimensional turbulence in the tank has a Taylor microscale $Re_\\lambda \\simeq 160$. The conformal invariance theory being tested here is related to the behavior of equilibrium systems near a critical point. This theory is associated with the work of L\\"owner, Schramm and others and is usually referred to as Schramm-L\\"owner Evolution (SLE). The system was exposed to several tests of SLE. The results of these tests suggest that zero-vorticity isolines exhibit noticeable departures from this type of conformal invariance.

  5. 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.

  6. Separation of colloidal two dimensional materials by density gradient ultracentrifugation

    NASA Astrophysics Data System (ADS)

    Kuang, Yun; Song, Sha; Huang, Jinyang; Sun, Xiaoming

    2015-04-01

    Two-dimensional (2D) materials have been made through various approaches but obtaining monodispersed simply by synthesis optimization gained little success, which highlighted the need for introducing nanoseparation methods. Density gradient ultracentrifugation method has emerged as a versatile and scalable method for sorting colloidal 2D nanomaterials. Isopycnic separation was applied on thickness-dependent separation of graphene nanosheets. And rate-zonal separation, as a more versatile separation method, demonstrated its capability in sorting nanosheets of chemically modified single layered graphene, layered double hydroxide, and even metallic Ag. Establishing such density gradient ultracentrifugation method not only achieves monodispersed nanosheets and provides new opportunities for investigation on size dependent properties of 2D materials, but also makes the surface modification possible by introducing "reaction zones" during sedimentation of the colloids.

  7. 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)

  8. Dislocations and grain boundaries in two-dimensional boron nitride.

    PubMed

    Liu, Yuanyue; Zou, Xiaolong; Yakobson, Boris I

    2012-08-28

    A new dislocation structure-square-octagon pair (4|8) is discovered in two-dimensional boron nitride (h-BN), via first-principles calculations. It has lower energy than corresponding pentagon-heptagon pairs (5|7), which contain unfavorable homoelemental bonds. On the basis of the structures of dislocations, grain boundaries (GB) in BN are investigated. Depending on the tilt angle of grains, GB can be either polar (B-rich or N-rich), constituted by 5|7s, or unpolar, composed of 4|8s. The polar GBs carry net charges, positive at B-rich and negative at N-rich ones. In contrast to GBs in graphene which generally impede the electronic transport, polar GBs have a smaller bandgap compared to perfect BN, which may suggest interesting electronic and optical applications. PMID:22780217

  9. Spontaneous supersymmetry breaking in two dimensional lattice super QCD

    NASA Astrophysics Data System (ADS)

    Catterall, Simon; Veernala, Aarti

    2015-10-01

    We report on a non-perturbative study of two dimensional N=(2,2) super QCD. Our lattice formulation retains a single exact supersymmetry at non-zero lattice spacing, and contains 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 < N c in agreement with theoretical expectations.

  10. Two-Dimensional Integral Combustion for Multiple Phase Flow

    Energy Science and Technology Software Center (ESTSC)

    1997-05-05

    This ANL multiphase two-dimensional combustion computer code solves conservation equations for gaseous species and solid particles (or droplets) of various sizes. General conservation laws, expressed by ellipitic-type partial differential equations are used in conjunction with rate equations governing the mass, momentum, enthaply, species, turbulent kinetic energy, and turbulent dissipation for a two-phase reacting flow. Associated submodels include an integral combustion, a two-parameter turbulence, a particle evaporation, and interfacial submodels. A newly-developed integral combustion submodel replacingmore »an Arrhenius-type differential reaction submodel is implemented to improve numerical convergence and enhance numerical stability. The two-parameter turbulence submodel is modified for both gas and solid phases. The evaporation submodel treats size dispersion as well as particle evaporation. Interfacial submodels use correlations to model interfacial momentum and energy transfer.« less

  11. 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.

  12. Cooperation in two-dimensional mixed-games

    NASA Astrophysics Data System (ADS)

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

    2015-11-01

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

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

    PubMed

    Merano, Michele

    2016-01-01

    The theory of Bloembergen and Pershan for the light waves at the boundary of nonlinear media is extended to a nonlinear two-dimensional (2D) atomic crystal, i.e., a single planar atomic lattice, placed between linear bulk media. The crystal is treated as a zero-thickness interface, a real 2D system. Harmonic waves emanate from it. Generalization of the laws of reflection and refraction give the direction and the intensity of the harmonic waves. As a particular case that contains all the essential physical features, second-order harmonic generation is considered. The theory, due to its simplicity that stems from the special character of a single planar atomic lattice, is able to elucidate and explain the rich experimental details of harmonic generation from a 2D atomic crystal. PMID:26696190

  14. 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.

  15. Two dimensional hydrodynamic modeling of a high latitude braided river

    NASA Astrophysics Data System (ADS)

    Humphries, E.; Pavelsky, T.; Bates, P. D.

    2014-12-01

    Rivers are a fundamental resource to physical, ecologic and human systems, yet quantification of river flow in high-latitude environments remains limited due to the prevalence of complex morphologies, remote locations and sparse in situ monitoring equipment. Advances in hydrodynamic modeling and remote sensing technology allow us to address questions such as: How well can two-dimensional models simulate a flood wave in a highly 3-dimensional braided river environment, and how does the structure of such a flood wave differ from flow down a similar-sized single-channel river? Here, we use the raster-based hydrodynamic model LISFLOOD-FP to simulate flood waves, discharge, water surface height, and velocity measurements over a ~70 km reach of the Tanana River in Alaska. In order to use LISFLOOD-FP a digital elevation model (DEM) fused with detailed bathymetric data is required. During summer 2013, we surveyed 220,000 bathymetric points along the study reach using an echo sounder system connected to a high-precision GPS unit. The measurements are interpolated to a smooth bathymetric surface, using Topo to Raster interpolation, and combined with an existing five meter DEM (Alaska IfSAR) to create a seamless river terrain model. Flood waves are simulated using varying complexities in model solvers, then compared to gauge records and water logger data to assess major sources of model uncertainty. Velocity and flow direction maps are also assessed and quantified for detailed analysis of braided channel flow. The most accurate model output occurs with using the full two-dimensional model structure, and major inaccuracies appear to be related to DEM quality and roughness values. Future work will intercompare model outputs with extensive ground measurements and new data from AirSWOT, an airborne analog for the Surface Water and Ocean Topography (SWOT) mission, which aims to provide high-resolution measurements of terrestrial and ocean water surface elevations globally.

  16. 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).

  17. Two-Dimensional Numerical Modeling of Anthropogenic Beach Berm Erosion

    NASA Astrophysics Data System (ADS)

    Shakeri Majd, M.; Schubert, J.; Gallien, T.; Sanders, B. F.

    2014-12-01

    Anthropogenic beach berms (sometimes called artificial berms or artificial dunes) temporarily enhance the ability of beaches to withstand overtopping and thus guard against coastal flooding. However, the combination of a rising tide, storm surge, and/or waves may erode anthropogenic berms in a matter of hours or less and cause flooding [1]. Accurate forecasts of coastal flooding therefore demand the ability to predict where and when berms fail and the volume of water that overtops into defended coastal lowlands. Here, a two-dimensional numerical model of swash zone waves and erosion is examined as a tool for predicting the erosion of anthropogenic beach berms. The 2D model is known as a Debris Flow Model (DFM) because it tightly couples flow and sediment transport within an approximate Riemann solver and is able to resolve shocks in fluid/sediment interface [2]. The DFM also includes a two dimensional avalanching scheme to account for gravity-driven slumping of steep slopes. The performance of the DFM is examined with field-scale anthropogenic berm erosion data collected at Newport Beach, California. Results show that the DFM can be applied in the swash zone to resolve wave-by-wave flow and sediment transport. Results also show that it is possible to calibrate the model for a particular event, and then predict erosion for another event, but predictions are sensitive to model parameters, such as erosion and avalanching. References: [1] Jochen E. Schubert, Timu W. Gallien, Morteza Shakeri Majd, and Brett F. Sanders. Terrestrial laser scanning of anthropogenic beach berm erosion and overtopping. Journal of Coastal Research In-Press, 2014. [2] Morteza Shakeri Majd and Brett F. Sanders. The LHLLC scheme for Two-Layer and Two-Phase transcritical flows over a mobile bed with avalanching, wetting and drying. Advances in Water Resources, 64, 16-31, 2014.

  18. 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

  19. Remote sensing of two-dimensional magnetopause structures

    SciTech Connect

    Walthour, D.W.; Sonnerup, B.U.O. ); Paschmann, G. ); Luehr, H. ); Klumpar, D. ); Potemra, T. )

    1993-02-01

    A technique is developed for analyzing remote measurements made by a single spacecraft of two dimensional disturbances in the ambient magnetosheath or magnetospheric magnetic field, caused, for example, by flux transfer events or pressure pulses. The methodology is based on a recent linear theory for isentropic field-aligned MHD flow over gently sloping two-dimensional obstacles (Sonnerup et al., 1992). Using only magnetic field measurements, the analysis technique can provide information about the orientation and actual cross-sectional shape of the event, as well as information about the spacecraft trajectory relative to the bulge. If three-dimensional plasma velocity measurements are also available, the technique provides the velocity and size of the event as well, and it allows one to determine whether the current sources causing the disturbance were in fact located on the side of the spacecraft trajectory facing the magnetopause. Analysis of two sample events, one recorded by the spacecraft AMPTE/IRM (Active Magnetospheric Particle Tracer Explorer/Ion Release Module) in the magnetosheath and the other by AMPTE/CCE (Charge Composition Explorer) in the magnetosphere, indicates that the bulges on the magnetopause surface causing the magnetic field and flow perturbations for these events did not have the semicircular cross section suggested in previous work; instead they had a more elongated shape, the dimension tangential to the magnetopause being substantially larger than that normal to it. The calculated invariant axes of the two events were found to differ substantially from the corresponding minimum variance directions of the measured magnetic field. The IRM event was found to move at a speed of 227 km/s away from the subsolar region. For the CCE event, plasma flow data were not available, but it was deduced indirectly that the event moved at a speed of about 90 km/s, presumably away from the subsolar region. 21 refs., 11 figs.

  20. Resonant spin Hall effect in two dimensional electron gas

    NASA Astrophysics Data System (ADS)

    Shen, Shun-Qing

    2005-03-01

    Remarkable phenomena have been observed in 2DEG over last two decades, most notably, the discovery of integer and fractional quantum Hall effect. The study of spin transport provides a good opportunity to explore spin physics in two-dimensional electron gas (2DEG) with spin-orbit coupling and other interaction. It is already known that the spin-orbit coupling leads to a zero-field spin splitting, and competes with the Zeeman spin splitting if the system is subjected to a magnetic field perpendicular to the plane of 2DEG. The result can be detected as beating of the Shubnikov-de Haas oscillation. Very recently the speaker and his collaborators studied transport properties of a two-dimensional electron system with Rashba spin-orbit coupling in a perpendicular magnetic field. The spin-orbit coupling competes with the Zeeman splitting to generate additional degeneracies between different Landau levels at certain magnetic fields. It is predicted theoretically that this degeneracy, if occurring at the Fermi level, gives rise to a resonant spin Hall conductance, whose height is divergent as 1/T and whose weight is divergent as -lnT at low temperatures. The charge Hall conductance changes by 2e^2/h instead of e^2/h as the magnetic field changes through the resonant point. The speaker will address the resonance condition, symmetries in the spin-orbit coupling, the singularity of magnetic susceptibility, nonlinear electric field effect, the edge effect and the disorder effect due to impurities. This work was supported by the Research Grants Council of Hong Kong under Grant No.: HKU 7088/01P. *S. Q. Shen, M. Ma, X. C. Xie, and F. C. Zhang, Phys. Rev. Lett. 92, 256603 (2004) *S. Q. Shen, Y. J. Bao, M. Ma, X. C. Xie, and F. C. Zhang, cond-mat/0410169

  1. Circular Halbach array for fast magnetic separation of hyaluronan-expressing tissue progenitors.

    PubMed

    Joshi, Powrnima; Williams, P Stephen; Moore, Lee R; Caralla, Tonya; Boehm, Cynthia; Muschler, George; Zborowski, Maciej

    2015-10-01

    Connective tissue progenitors (CTPs) are a promising therapeutic agent for bone repair. Hyaluronan, a high molecular mass glycosaminoglycan, has been shown by us to be a suitable biomarker for magnetic separation of CTPs from bone marrow aspirates in a canine model. For the therapy to be applicable in humans, the magnetic separation process requires scale-up without compromising the viability of the cells. The scaled-up device presented here utilizes a circular Halbach array of diametrically magnetized, cylindrical permanent magnets. This allows precise control of the magnetic field gradient driving the separation, with theoretical analysis favoring a hexapole field. The separation vessel has the external diameter of a 50 mL conical centrifuge tube and has an internal rod that excludes cells from around the central axis. The magnet and separation vessel (collectively dubbed the hexapole magnet separator or HMS) was tested on four human and four canine bone marrow aspirates. Each CTP-enriched cell product was tested using cell culture bioassays as surrogates for in vivo engraftment quality. The magnetically enriched cell fractions showed statistically significant, superior performance compared to the unenriched and depleted cell fractions for all parameters tested, including CTP prevalence (CTPs per 10(6) nucleated cells), proliferation by colony forming unit (CFU) counts, and differentiation by staining for the presence of osteogenic and chondrogenic cells. The simplicity and speed of the HMS operation could allow both CTP isolation and engraftment during a single surgical procedure, minimizing trauma to patients and lowering cost to health care providers. PMID:26368657

  2. 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

  3. Comprehensive two-dimensional gas chromatography and food sensory properties: potential and challenges

    E-print Network

    Reichenbach, Stephen E.

    REVIEW Comprehensive two-dimensional gas chromatography and food sensory properties: potential- dimensional gas chromatography and analytical platforms combining two-dimensional gas chromatography chromatography Introduction Targeted omics for food sensory quality objectification Modern omics disciplines

  4. PHYSICAL REVIEW B 87, 235315 (2013) Two-dimensional electron gas at the metastable twisted interfaces

    E-print Network

    Nasipuri, Asis

    2013-01-01

    PHYSICAL REVIEW B 87, 235315 (2013) Two-dimensional electron gas at the metastable twisted optoelectronics and spintronics. High-density two-dimensional electron gas at the metastable twisted interfaces

  5. Reliable Peak Selection for Multisample Analysis with Comprehensive Two-Dimensional Chromatography

    E-print Network

    Reichenbach, Stephen E.

    Reliable Peak Selection for Multisample Analysis with Comprehensive Two-Dimensional Chromatography with samples of complex bio-oils analyzed by comprehensive two-dimensional gas chromatography (GCxGC) coupled-dimensional gas chromatography (GCxGC) and comprehensive two-dimensional liquid chroma- tography (LCxLC), hold

  6. Two-Dimensional ARMA Modeling for Breast Cancer Detection and Classification

    E-print Network

    Bouaynaya, Nidhal

    Two-Dimensional ARMA Modeling for Breast Cancer Detection and Classification Jerzy Zielinski and classification (cancerous v.s. benign) in ultrasound breast images based on a two-dimensional Auto is superior to its one-dimensional homologue. Index Terms--Breast cancer, two-dimensional ARMA models, k

  7. 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

  8. Quantization of systems with internal degrees of freedom in two-dimensional manifolds

    E-print Network

    Ewa Eliza Ro?ko; Ewa Gobcewicz

    2014-02-24

    Presented is a primary step towards quantization of infinitesimal rigid body moving in a two-dimensional manifold. The special stress is laid on spaces of constant curvature like the two-dimensional sphere and pseudosphere (Lobatschevski space). Also two-dimensional torus is briefly discussed as an interesting algebraic manifold.

  9. 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

  10. 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.

  11. Sudden expansion and domain-wall melting of strongly interacting bosons in two-dimensional optical lattices and on multileg ladders

    NASA Astrophysics Data System (ADS)

    Hauschild, Johannes; Pollmann, Frank; Heidrich-Meisner, Fabian

    2015-11-01

    We numerically investigate the expansion of clouds of hard-core bosons in the two-dimensional square lattice using a matrix-product-state-based method. This nonequilibrium setup is induced by quenching the trapping potential to zero and our work is specifically motivated by a recent experiment with interacting bosons in an optical lattice [Ronzheimer et al., Phys. Rev. Lett. 110, 205301 (2013), 10.1103/PhysRevLett.110.205301]. As the anisotropy of the amplitudes Jx and Jy for hopping in different spatial directions is varied from the one- to the two-dimensional case, we observe a crossover from a fast ballistic expansion in the one-dimensional limit Jx?Jy to much slower dynamics in the isotropic two-dimensional limit Jx=Jy . We further study the dynamics on multileg ladders and long cylinders. For these geometries we compare the expansion of a cloud to the melting of a domain wall, which helps us to identify several different regimes of the expansion as a function of time. By studying the dependence of expansion velocities on both the anisotropy Jy/Jx and the number of legs, we observe that the expansion on two-leg ladders, while similar to the two-dimensional case, is slower than on wider ladders. We provide a qualitative explanation for this observation based on an analysis of the rung spectrum.

  12. Interactions in the far wake behind a pair of cylinders

    NASA Astrophysics Data System (ADS)

    Shakeel, Tanveer; Georgiev, Daniel; Vigil, Jesse; Vorobieff, Peter

    2002-11-01

    We present an experimental study of far wakes behind a pair of cylinders (diameter D) separated by a cross-flow axis-to-axis distance S in a quasi-two-dimensional gravity-driven soap-film flow. A secondary vortex street forms in the far wake of each cylinder. As we decrease S, we observe coupling between the structures in the far wake. Visualization of the far wake behind the cylinder pair reveals interactions between the secondary vortex streets, where the streets first synchronize out-of-phase and then change to in-phase synchronization as S/D decreases. This synchronization is achieved at higher S/D values than those observed for similar synchronization between the near-wake vortices.

  13. Causal and conformal structures of two-dimensional globally hyperbolic spacetimes

    NASA Astrophysics Data System (ADS)

    Kim, Do-Hyung

    2015-10-01

    The group of conformal diffeomorphisms and the group of causal automorphisms on two-dimensional globally hyperbolic spacetimes are clarified. It is shown that if two-dimensional spacetimes have non-compact Cauchy surfaces, then the groups are subgroups of that of two-dimensional Minkowski spacetime, and if two-dimensional spacetimes have compact Cauchy surfaces, then the groups are subgroups of that of two-dimensional Einstein's static universe. Also, the groups of such spacetimes are explicitly calculated by use of universal covering spaces.

  14. Acoustic insertion loss due to two dimensional periodic arrays of circular cylinders parallel to a nearby surface

    E-print Network

    Anton Krynkin; Olga Umnova; Juan Vicente Sanchez-Perez; Alvin Y. B. Chong; Shahram Taherzadeh; Keith Attenborough

    2012-07-03

    The acoustical performances of regular arrays of cylindrical elements, with their axes aligned and parallel to a ground plane, have been investigated through predictions and laboratory experiments. Semi-analytical predictions based on multiple scattering theory and numerical simulations based on a boundary element formulation have been made. Measurements have been made in an anechoic chamber using arrays of (a) cylindrical acoustically-rigid scatterers (PVC pipes) and (b) thin elastic shells. Insertion loss (IL) spectra due to the arrays have been measured without and with ground planes for several receiver heights. Data and predictions have been compared. The minima in the excess attenuation spectrum i.e., attenuation maxima due to the ground alone resulting from destructive interference between direct and ground-reflected sound waves, tend to have an adverse influence on the band gaps (BG) related to a periodic array in the free field when these two effects coincide. On the other hand, the presence of rigid ground may result in an IL for an array near the ground similar to or, in the case of the first BG, greater than that resulting from a double array, equivalent to the original array plus its ground plane mirror image, in the free field.

  15. INVESTIGATION OF SHOCK-ACCELERATED, UNSTABLE GAS CYLINDERS USING SIMULTANEOUS DENSITY-FIELD VISUALIZATION AND PIV

    SciTech Connect

    Tomkins, C. D.; Prestridge, K. P.; Zoldi, C. A.; Rightley, P. M.; Vorobieff, P. V.; Benjamin, R. F.

    2001-01-01

    Simultaneous density and particle image velocimetry measurements are performed on a shock-accelerated, unstable cylinder of dense gas. Density-based instability growth estimates show good agreement with two-dimensional simulations by an adaptive-mesh Eulerian solver. However, a more rigorous comparison between the computational velocity field and the PIV data reveals significant differences between the fluctuating velocity magnitudes in the flowfields. Flow visualization results from a double-cylinder gas configuration, in which the unstable cylinders interact spanwise as they evolve, are also compared with a preliminary simulation.

  16. Comprehensive two-dimensional liquid chromatographic analysis of anthocyanins.

    PubMed

    Willemse, Chandré M; Stander, Maria A; Tredoux, Andreas G J; de Villiers, André

    2014-09-12

    Anthocyanins are naturally occurring plant pigments whose accurate analysis is hampered by their complexity and unique chromatographic behaviour associated with on-column conversion reactions. This paper reports the evaluation of off-line comprehensive two-dimensional liquid chromatography (LC×LC) for the analysis of anthocyanins. Hydrophilic interaction chromatography (HILIC) was used in the first dimension in combination with reversed phase liquid chromatography (RP-LC) in the second dimension. For the selective detection of anthocyanins, diode array detection was used, while high resolution quadrupole-time-of-flight mass spectrometry (Q-TOF) was used for compound identification. As application, the HILIC×RP-LC separation of diverse anthocyanins in blueberries, red radish, black beans, red grape skins and red cabbage is demonstrated. Off-line HILIC×RP-LC revealed information which could not be obtained by one-dimensional HPLC methods, while the structured elution order for the anthocyanins simplifies compound identification and facilitates the comparison of anthocyanin content of natural products by means of contour plots. PMID:25113871

  17. Two Dimensional Heat Transfer around Penetrations in Multilayer Insulation

    NASA Technical Reports Server (NTRS)

    Johnson, Wesley L.; Kelly, Andrew O.; Jumper, Kevin M.

    2012-01-01

    The objective of this task was to quantify thermal losses involving integrating MLI into real life situations. Testing specifically focused on the effects of penetrations (including structural attachments, electrical conduit/feedthroughs, and fluid lines) through MLI. While there have been attempts at quantifying these losses both analytically and experimentally, none have included a thorough investigation of the methods and materials that could be used in such applications. To attempt to quantify the excess heat load coming into the system due to the integration losses, a calorimeter was designed to study two dimensional heat transfer through penetrated MLI. The test matrix was designed to take as many variables into account as was possible with the limited test duration and system size. The parameters varied were the attachment mechanism, the buffer material (for buffer attachment mechanisms only), the thickness of the buffer, and the penetration material. The work done under this task is an attempt to measure the parasitic heat loads and affected insulation areas produced by system integration, to model the parasitic loads, and from the model produce engineering equations to allow for the determination of parasitic heat loads in future applications. The methods of integration investigated were no integration, using a buffer to thermally isolate the strut from the MLI, and temperature matching the MLI on the strut. Several materials were investigated as a buffer material including aerogel blankets, aerogel bead packages, cryolite, and even an evacuated vacuum space (in essence a no buffer condition).

  18. Two-dimensional simulations of magma ascent in volcanic conduits

    NASA Astrophysics Data System (ADS)

    Ramos, J. I.

    1999-04-01

    A two-dimensional model for magma ascent in volcanic conduits is presented. The model accounts for the magma rheology, heat flux to the surrounding country rock, planar and axisymmetric geometries, and flow in the mushy region by means of a continuum mixture formulation that does not require keeping track of the liquid-solid interfaces. Numerical experiments for Newtonian and visco-plastic Bingham rheologies of magmas are presented as functions of the volumetric flow rate at the dyke's entrance and wall heat fluxes for both round conduits and fissures. It is shown that, depending on the magma rheology, dyke geometry, volumetric flow rate and wall heat flux, the magma may solidify along the original dyke's walls, thus reducing the available cross-sectional area to the flow, or the original dyke's walls may melt. It is also shown that the dyke's wall temperature may first increase and then decrease, and that the axial velocity profile exhibits a parabolic shape in the core region and a plug zone near the dyke's walls for Bingham rheologies. Copyright

  19. Image encryption using the two-dimensional logistic chaotic map

    NASA Astrophysics Data System (ADS)

    Wu, Yue; Yang, Gelan; Jin, Huixia; Noonan, Joseph P.

    2012-01-01

    Chaos maps and chaotic systems have been proved to be useful and effective for cryptography. In our study, the two-dimensional logistic map with complicated basin structures and attractors are first used for image encryption. The proposed method adopts the classic framework of the permutation-substitution network in cryptography and thus ensures both confusion and diffusion properties for a secure cipher. The proposed method is able to encrypt an intelligible image into a random-like one from the statistical point of view and the human visual system point of view. Extensive simulation results using test images from the USC-SIPI image database demonstrate the effectiveness and robustness of the proposed method. Security analysis results of using both the conventional and the most recent tests show that the encryption quality of the proposed method reaches or excels the current state-of-the-art methods. Similar encryption ideas can be applied to digital data in other formats (e.g., digital audio and video). We also publish the cipher MATLAB open-source-code under the web page https://sites.google.com/site/tuftsyuewu/source-code.

  20. Ab Initio Prediction of Piezoelectricity in Two-Dimensional Materials.

    PubMed

    Blonsky, Michael N; Zhuang, Houlong L; Singh, Arunima K; Hennig, Richard G

    2015-10-27

    Two-dimensional (2D) materials present many unique materials concepts, including material properties that sometimes differ dramatically from those of their bulk counterparts. One of these properties, piezoelectricity, is important for micro- and nanoelectromechanical systems applications. Using symmetry analysis, we determine the independent piezoelectric coefficients for four groups of predicted and synthesized 2D materials. We calculate with density-functional perturbation theory the stiffness and piezoelectric tensors of these materials. We determine the in-plane piezoelectric coefficient d11 for 37 materials within the families of 2D metal dichalcogenides, metal oxides, and III-V semiconductor materials. A majority of the structures, including CrSe2, CrTe2, CaO, CdO, ZnO, and InN, have d11 coefficients greater than 5 pm/V, a typical value for bulk piezoelectric materials. Our symmetry analysis shows that buckled 2D materials exhibit an out-of-plane coefficient d31. We find that d31 for 8 III-V semiconductors ranges from 0.02 to 0.6 pm/V. From statistical analysis, we identify correlations between the piezoelectric coefficients and the electronic and structural properties of the 2D materials that elucidate the origin of the piezoelectricity. Among the 37 2D materials, CdO, ZnO, and CrTe2 stand out for their combination of large piezoelectric coefficient and low formation energy and are recommended for experimental exploration. PMID:26312745

  1. Dragging two-dimensional discrete solitons by moving linear defects

    SciTech Connect

    Brazhnyi, Valeriy A.; Malomed, Boris A.

    2011-07-15

    We study the mobility of small-amplitude solitons attached to moving defects which drag the solitons across a two-dimensional (2D) discrete nonlinear Schroedinger lattice. Findings are compared to the situation when a free small-amplitude 2D discrete soliton is kicked in a uniform lattice. In agreement with previously known results, after a period of transient motion the free soliton transforms into a localized mode pinned by the Peierls-Nabarro potential, irrespective of the initial velocity. However, the soliton attached to the moving defect can be dragged over an indefinitely long distance (including routes with abrupt turns and circular trajectories) virtually without losses, provided that the dragging velocity is smaller than a certain critical value. Collisions between solitons dragged by two defects in opposite directions are studied too. If the velocity is small enough, the collision leads to a spontaneous symmetry breaking, featuring fusion of two solitons into a single one, which remains attached to either of the two defects.

  2. Two-dimensional quantum walk under artificial magnetic field

    NASA Astrophysics Data System (ADS)

    Yalç?nkaya, I.; Gedik, Z.

    2015-10-01

    We introduce the Peierls substitution to a two-dimensional discrete-time quantum walk on a square lattice to examine the spreading dynamics and the coin-position entanglement in the presence of an artificial gauge field. We use the ratio of the magnetic flux through the unit cell to the flux quantum as a control parameter. For a given flux ratio, we obtain faster spreading for a small number of steps and the walker tends to be highly localized around the origin. Moreover, the spreading of the walk can be suppressed and decreased within a limited time interval for specific rational values of flux ratio. When the flux ratio is an irrational number, even for a large number of steps, the spreading exhibits diffusive behavior rather than the well-known ballistic one as in the classical random walk and there is a significant probability of finding the walker at the origin. We also analyze the coin-position entanglement and show that the asymptotic behavior vanishes when the flux ratio is different from zero and the coin-position entanglement become nearly maximal in a periodic manner in a long time range.

  3. Hydration of ions in two-dimensional water

    NASA Astrophysics Data System (ADS)

    Dutta, S.; Lee, Yongjin; Jho, Y. S.

    2015-10-01

    We present a two-dimensional lattice model of water to study the effects of ion hydration on the properties of water. We map the water molecules as lattice particles consisting of a single oxygen atom at the center of a site and two hydrogen atoms on each side. The internal state of the system, such as the dipole moment at a site, is defined with respect to the location of the hydrogen atoms at the site depending on their role in hydrogen bonds (H bonds) being a donor or an acceptor. We study the influence of the charge and the radius of the ion on the insertion energy and on the H bonds in the first and second hydration layers around the ion and in the bulk. In particular we analyze how the competing interactions of the short-ranged H bonds and the long-ranged electrostatics influence the hydration properties. The role of the ion both as a source of the electrostatic interactions as well as a defect is also discussed. Our model also shows the well-known fact that the polarizability of the water molecules destroys the hydrogen bond network and increases the dipole moment of the molecules near the ion.

  4. Persistence in a Two-Dimensional Moving-Habitat Model.

    PubMed

    Phillips, Austin; Kot, Mark

    2015-11-01

    Environmental changes are forcing many species to track suitable conditions or face extinction. In this study, we use a two-dimensional integrodifference equation to analyze whether a population can track a habitat that is moving due to climate change. We model habitat as a simple rectangle. Our model quickly leads to an eigenvalue problem that determines whether the population persists or declines. After surveying techniques to solve the eigenvalue problem, we highlight three findings that impact conservation efforts such as reserve design and species risk assessment. First, while other models focus on habitat length (parallel to the direction of habitat movement), we show that ignoring habitat width (perpendicular to habitat movement) can lead to overestimates of persistence. Dispersal barriers and hostile landscapes that constrain habitat width greatly decrease the population's ability to track its habitat. Second, for some long-distance dispersal kernels, increasing habitat length improves persistence without limit; for other kernels, increasing length is of limited help and has diminishing returns. Third, it is not always best to orient the long side of the habitat in the direction of climate change. Evidence suggests that the kurtosis of the dispersal kernel determines whether it is best to have a long, wide, or square habitat. In particular, populations with platykurtic dispersal benefit more from a wide habitat, while those with leptokurtic dispersal benefit more from a long habitat. We apply our model to the Rocky Mountain Apollo butterfly (Parnassius smintheus). PMID:26582361

  5. ACCRETION DISKS IN TWO-DIMENSIONAL HOYLE-LYTTLETON FLOW

    SciTech Connect

    Blondin, John M.

    2013-04-20

    We investigate the flip-flop instability observed in two-dimensional planar hydrodynamic simulations of Hoyle-Lyttleton accretion in the case of an accreting object with a radius much smaller than the nominal accretion radius, as one would expect in astrophysically relevant situations. Contrary to previous results with larger accretors, accretion from a homogenous medium onto a small accretor is characterized by a robust, quasi-Keplerian accretion disk. For gas with a ratio of specific heats of 5/3, such a disk remains locked in one direction for a uniform ambient medium. The accretion flow is more variable for gas with a ratio of specific heats of 4/3, with more dynamical interaction of the disk flow with the bow shock leading to occasional flips in the direction of rotation of the accretion disk. In both cases the accretion of angular momentum is determined by the flow pattern behind the accretion shock rather than by the parameters of the upstream flow.

  6. Volumetric display containing multiple two-dimensional color motion pictures

    NASA Astrophysics Data System (ADS)

    Hirayama, R.; Shiraki, A.; Nakayama, H.; Kakue, T.; Shimobaba, T.; Ito, T.

    2014-06-01

    We have developed an algorithm which can record multiple two-dimensional (2-D) gradated projection patterns in a single three-dimensional (3-D) object. Each recorded pattern has the individual projected direction and can only be seen from the direction. The proposed algorithm has two important features: the number of recorded patterns is theoretically infinite and no meaningful pattern can be seen outside of the projected directions. In this paper, we expanded the algorithm to record multiple 2-D projection patterns in color. There are two popular ways of color mixing: additive one and subtractive one. Additive color mixing used to mix light is based on RGB colors and subtractive color mixing used to mix inks is based on CMY colors. We made two coloring methods based on the additive mixing and subtractive mixing. We performed numerical simulations of the coloring methods, and confirmed their effectiveness. We also fabricated two types of volumetric display and applied the proposed algorithm to them. One is a cubic displays constructed by light-emitting diodes (LEDs) in 8×8×8 array. Lighting patterns of LEDs are controlled by a microcomputer board. The other one is made of 7×7 array of threads. Each thread is illuminated by a projector connected with PC. As a result of the implementation, we succeeded in recording multiple 2-D color motion pictures in the volumetric displays. Our algorithm can be applied to digital signage, media art and so forth.

  7. Terahertz spectroscopy of two-dimensional subwavelength plasmonic structures

    SciTech Connect

    Azad, Abul K; Chen, Houtong; Taylor, Antoinette; O' Hara, John F; Han, Jiaguang; Lu, Xinchao; Zhang, Weili

    2009-01-01

    The fascinating properties of plasmonic structures have had significant impact on the development of next generation ultracompact photonic and optoelectronic components. We study two-dimensional plasmonic structures functioning at terahertz frequencies. Resonant terahertz response due to surface plasmons and dipole localized surface plasmons were investigated by the state-of-the-art terahertz time domain spectroscopy (THz-TDS) using both transmission and reflection configurations. Extraordinary terahertz transmission was demonstrated through the subwavelength metallic hole arrays made from good conducting metals as well as poor metals. Metallic arrays m!lde from Pb, generally a poor metal, and having optically thin thicknesses less than one-third of a skin depth also contributed in enhanced THz transmission. A direct transition of a surface plasmon resonance from a photonic crystal minimum was observed in a photo-doped semiconductor array. Electrical controls of the surface plasmon resonances by hybridization of the Schottkey diode between the metallic grating and the semiconductor substrate are investigated as a function of the applied reverse bias. In addition, we have demonstrated photo-induced creation and annihilation of surface plasmons with appropriate semiconductors at room temperature. According to the Fano model, the transmission properties are characterized by two essential contributions: resonant excitation of surface plasmons and nonresonant direct transmission. Such plasmonic structures may find fascinating applications in terahertz imaging, biomedical sensing, subwavelength terahertz spectroscopy, tunable filters, and integrated terahertz devices.

  8. Dynamic testing of a two-dimensional box truss beam

    NASA Technical Reports Server (NTRS)

    White, Charles W.

    1987-01-01

    Testing to determine the effects of joint freeplay and pretensioning of diagonal members on the dynamic characteristics of a two-dimensional box truss beam was conducted. The test article was ten bays of planar truss suspended by long wires at each joint. Each bay measured 2 meters per side. Pins of varying size were used to simulate various joint freeplay conditions. Single-point random excitation was the primary method of test. The rational fraction polynomial method was used to extract modal characteristics from test data. A finite element model of the test article was generated from which modal characteristics were predicted. These were compared with those obtained from tests. With the exception of the fundamental mode, correlation of theoretical and experimental results was poor, caused by the resonant coupling of local truss member bending modes with global truss beam modes. This coupling introduced many modes in the frequency range of interest whose frequencies were sensitive to joint boundary conditions. It was concluded that local/global coupling must be avoided in the frequency range where accurate modal characteristics are required.

  9. Thermal Properties of Two-Dimensional Advection Dominated Accretion Flow

    E-print Network

    Myeong-Gu Park; Jeremiah P. Ostriker

    1999-01-20

    We study the thermal structure of the widely adopted two-dimensional advection dominated accretion flow (ADAF) of Narayan & Yi (1995a). The critical radius for a given mass accretion rate, outside of which the optically thin hot solutions do not exist in the equatorial plane, agrees with one-dimensional study. However, we find that, even within the critical radius, there always exists a conical region of the flow, around the pole, which cannot maintain the assumed high electron temperature, regardless of the mass accretion rate, in the absence of radiative heating. This could lead to torus-like advection inflow shape since, in general, the ions too will cool down. We also find that Compton preheating is generally important and, if the radiative efficiency, defined as the luminosity output divided by the mass accretion rate times the velocity of light squared, is above sim 4x10^-3, the polar region of the flow is preheated above the virial temperature by Compton heating and it may result in time-dependent behaviour or outflow while accretion continues in the equatorial plane. Thus, under most relevant circumstances, ADAF solutions may be expected to be accompanied by polar outflow winds. While preheating instabilities exist in ADAF, as for spherical flows, the former are to some extent protected by their characteristically higher densities and higher cooling rates, which reduce their susceptibility to Compton driven overheating.

  10. Exciton radiative lifetimes in two-dimensional transition metal dichalcogenides.

    PubMed

    Palummo, Maurizia; Bernardi, Marco; Grossman, Jeffrey C

    2015-05-13

    Light emission in two-dimensional (2D) transition metal dichalcogenides (TMDs) changes significantly with the number of layers and stacking sequence. While the electronic structure and optical absorption are well understood in 2D-TMDs, much less is known about exciton dynamics and radiative recombination. Here, we show first-principles calculations of intrinsic exciton radiative lifetimes at low temperature (4 K) and room temperature (300 K) in TMD monolayers with the chemical formula MX2 (X = Mo, W, and X = S, Se), as well as in bilayer and bulk MoS2 and in two MX2 heterobilayers. Our results elucidate the time scale and microscopic origin of light emission in TMDs. We find radiative lifetimes of a few picoseconds at low temperature and a few nanoseconds at room temperature in the monolayers and slower radiative recombination in bulk and bilayer than in monolayer MoS2. The MoS2/WS2 and MoSe2/WSe2 heterobilayers exhibit very long-lived (?20-30 ns at room temperature) interlayer excitons constituted by electrons localized on the Mo-based and holes on the W-based monolayer. The wide radiative lifetime tunability, together with the ability shown here to predict radiative lifetimes from computations, hold unique potential to manipulate excitons in TMDs and their heterostructures for application in optoelectronics and solar energy conversion. PMID:25798735

  11. Passive hydrodynamic synchronization of two-dimensional swimming cells

    NASA Astrophysics Data System (ADS)

    Elfring, Gwynn J.; Lauga, Eric

    2011-01-01

    Spermatozoa flagella are known to synchronize when swimming in close proximity. We use a model consisting of two-dimensional sheets propagating transverse waves of displacement to demonstrate that fluid forces lead to such synchronization passively. Using two distinct asymptotic descriptions (small amplitude and long wavelength), we derive the synchronizing dynamics analytically for arbitrarily shaped waveforms in Newtonian fluids, and show that phase-locking will always occur for sufficiently asymmetric shapes. We characterize the effect of the geometry of the waveforms and the separation between the swimmers on the synchronizing dynamics, the final stable conformations, and the energy dissipated by the cells. For two closely swimming cells, synchronization always occurs at the in-phase or opposite-phase conformation, depending solely on the geometry of the cells. In contrast, the work done by the swimmers is always minimized at the in-phase conformation. As the swimmers get further apart, additional fixed points arise at intermediate values of the relative phase. In addition, computations for large amplitude waves using the boundary integral method reveal that the two asymptotic limits capture all the relevant physics of the problem. Our results provide a theoretical framework to address other hydrodynamic interactions phenomena relevant to populations of self-propelled organisms.

  12. The Intrinsic Two-Dimensional Size of Sagittarius A*

    E-print Network

    Bower, Geoffrey C; Brunthaler, Andreas; Law, Casey; Falcke, Heino; Maitra, Dipankar; Clavel, M; Goldwurm, A; Morris, M R; Witzel, Gunther; Meyer, Leo; Ghez, A M

    2014-01-01

    We report the detection of the two-dimensional structure of the radio source associated with the Galactic Center black hole, Sagittarius A*, obtained from Very Long Baseline Array (VLBA) observations at a wavelength of 7mm. The intrinsic source is modeled as an elliptical Gaussian with major axis size 35.4 x 12.6 R_S in position angle 95 deg East of North. This morphology can be interpreted in the context of both jet and accretion disk models for the radio emission. There is supporting evidence in large angular-scale multi-wavelength observations for both source models for a preferred axis near 95 deg. We also place a maximum peak-to-peak change of 15% in the intrinsic major axis size over five different epochs. Three observations were triggered by detection of near infrared (NIR) flares and one was simultaneous with a large X-ray flare detected by NuSTAR. The absence of simultaneous and quasi-simultaneous flares indicates that not all high energy events produce variability at radio wavelengths. This supports...

  13. Broken Ergodicity in Two-Dimensional Homogeneous Magnetohydrodynamic Turbulence

    NASA Technical Reports Server (NTRS)

    Shebalin, John V.

    2010-01-01

    Two-dimensional (2-D) homogeneous magnetohydrodynamic (MHD) turbulence has many of the same qualitative features as three-dimensional (3-D) homogeneous MHD turbulence.The se features include several ideal invariants, along with the phenomenon of broken ergodicity. Broken ergodicity appears when certain modes act like random variables with mean values that are large compared to their standard deviations, indicating a coherent structure or dynamo.Recently, the origin of broken ergodicity in 3-D MHD turbulence that is manifest in the lowest wavenumbers was explained. Here, a detailed description of the origins of broken ergodicity in 2-D MHD turbulence is presented. It will be seen that broken ergodicity in ideal 2-D MHD turbulence can be manifest in the lowest wavenumbers of a finite numerical model for certain initial conditions or in the highest wavenumbers for another set of initial conditions.T he origins of broken ergodicity in ideal 2-D homogeneous MHD turbulence are found through an eigen analysis of the covariance matrices of the modal probability density functions.It will also be shown that when the lowest wavenumber magnetic field becomes quasi-stationary, the higher wavenumber modes can propagate as Alfven waves on these almost static large-scale magnetic structures

  14. Magnetic coupling of vortices in a two-dimensional lattice

    NASA Astrophysics Data System (ADS)

    Nissen, D.; Mitin, D.; Klein, O.; Arekapudi, S. S. P. K.; Thomas, S.; Im, M.-Y.; Fischer, P.; Albrecht, M.

    2015-11-01

    We investigated the magnetization reversal of magnetic vortex structures in a two-dimensional lattice. The structures were formed by permalloy (Py) film deposition onto large arrays of self-assembled spherical SiO2-particles with a diameter of 330 nm. We present the dependence of the nucleation and annihilation field of the vortex structures as a function of the Py layer thickness (aspect ratio) and temperature. By increasing the Py thickness up to 90 nm or alternatively by lowering the temperature the vortex structure becomes more stable as expected. However, the increase of the Py thickness results in the onset of strong exchange coupling between neighboring Py caps due to the emergence of Py bridges connecting them. In particular, we studied the influence of magnetic coupling locally by in-field scanning magneto-resistive microscopy and full-field magnetic soft x-ray microscopy, revealing a domain-like nucleation process of vortex states, which arises via domain wall propagation due to exchange coupling of the closely packed structures. By analyzing the rotation sense of the reversed areas, large connected domains are present with the same circulation sense. Furthermore, the lateral core displacements when an in-plane field is applied were investigated, revealing spatially enlarged vortex cores and a broader distribution with increasing Py layer thickness. In addition, the presence of some mixed states, vortices and c-states, is indicated for the array with the thickest Py layer.

  15. Fluctuoscopy spectroscopy of disordered two-dimensional superconductors.

    SciTech Connect

    Glatz, A.; Varlamov, A. A.; Vinokur, V. M.

    2011-01-01

    We revise the long-studied problem of fluctuation conductivity (FC) in disordered two-dimensional superconductors placed in a perpendicular magnetic field by finally deriving the complete solution in the temperature-magnetic field phase diagram. The obtained expressions allow both to perform straightforward (numerical) calculation of the FC surface {delta}{sigma}{sub xx}{sup (tot)}(T,H) and to get asymptotic expressions in all its qualitatively different domains. This surface becomes in particular nontrivial at low temperatures, where it is trough-shaped with {delta}{sigma}{sub xx}{sup (tot)}(T,H) < 0. In this region, close to the quantum-phase transition, {delta}{sigma}{sub xx}{sup (tot)}(T,H = const) is nonmonotonic, in agreement with experimental findings. We reanalyzed and present comparisons to several experimental measurements. Based on our results we derive a qualitative picture of superconducting fluctuations close to H{sub c2}(0) and T=0 where fluctuation Cooper pairs rotate with cyclotron frequency {omega}{sub c}-{Delta}{sub BCS}{sup -1} and Larmor radius {approx}{zeta}{sub BCS}, forming some kind of quantum liquid with long coherence length {zeta}{sub QF} >> {zeta}{sub BCS} and slow relaxation {tau}{sub QF} >> {h_bar}{Delta}{sub BCS}{sup -1}.

  16. Two-dimensional quantum walk under artificial magnetic field

    E-print Network

    ?. Yalç?nkaya; Z. Gedik

    2015-10-27

    We introduce the Peierls substitution to a two-dimensional discrete-time quantum walk on a square lattice to examine the spreading dynamics and the coin-position entanglement in the presence of an artificial gauge field. We use the ratio of the magnetic flux through the unit cell to the flux quantum as a control parameter. For a given flux ratio, we obtain faster spreading for a small number of steps and the walker tends to be highly localized around the origin. Moreover, the spreading of the walk can be suppressed and decreased within a limited time interval for specific rational values of flux ratio. When the flux ratio is an irrational number, even for a large number of steps, the spreading exhibit diffusive behavior rather than the well-known ballistic one as in the classical random walk and there is a significant probability of finding the walker at the origin. We also analyze the coin-position entanglement and show that the asymptotic behavior vanishes when the flux ratio is different from zero and the coin-position entanglement become nearly maximal in a periodic manner in a long time range.

  17. Structure of self - assembled two-dimensional spherical crystals

    NASA Astrophysics Data System (ADS)

    Bausch, Andreas R.

    2004-03-01

    Dense spherical particles on a flat surface usually pack into a simple triangular lattice, similar to billiard balls at the start of a game. The minimum energy configuration for interacting particles on the curved surface of a sphere, however, presents special difficulties, as recognized already by J.J. Thomson. We describe experimental investigations of the structure of two-dimensional spherical crystals. The crystals, formed by beads self-assembled on water droplets in oil, serve as model systems for exploring very general theories about the minimum energy configurations of particles with arbitrary repulsive interactions on curved surfaces. Above a critical system size we find that crystals develop distinctive high-angle grain boundaries or "scars" not found in planar crystals. The number of excess defects in a scar is shown to grow linearly with the dimensionless system size. First experiments where the melting of the crystal structure was observable will be discussed. Dynamic triangulation methods allow the analysis of the dynamics of the defects. Possible modifications towards mechanically stabilized self assembly structures result in so called Colloidosomes, which are promising for many different encapsulation purposes.

  18. Quantum Criticality in Quasi-Two-Dimensional Itinerant Antiferromagnets.

    PubMed

    Varma, C M

    2015-10-30

    Quasi-two-dimensional itinerant fermions in the antiferromagnetic (AFM) quantum-critical region of their phase diagram, such as in the Fe-based superconductors or in some of the heavy-fermion compounds, exhibit a resistivity varying linearly with temperature and a contribution to specific heat or thermopower proportional to TlnT. It is shown, here, that a generic model of itinerant anti-ferromagnet can be canonically transformed so that its critical fluctuations around the AFM-vector Q can be obtained from the fluctuations in the long wavelength limit of a dissipative quantum XY model. The fluctuations of the dissipative quantum XY model in 2D have been evaluated recently, and in a large regime of parameters, they are determined, not by renormalized spin fluctuations, but by topological excitations. In this regime, the fluctuations are separable in their spatial and temporal dependence and have a spatial correlation length which is proportional to the logarithm of the temporal correlation length, i.e., for some purposes, the effective dynamic exponent z=?. The time dependence gives ?/T scaling at criticality. The observed resistivity and entropy then follow. Several predictions to test the theory are also given. PMID:26565482

  19. Valley Hall Effect in Two-Dimensional Hexagonal Lattices

    NASA Astrophysics Data System (ADS)

    Yamamoto, Michihisa; Shimazaki, Yuya; Borzenets, Ivan V.; Tarucha, Seigo

    2015-12-01

    Valley is a quantum number defined for energetically degenerate but nonequivalent structures in energy bands of a crystalline material. Recent discoveries of two-dimensional (2D) layered materials have shed light on the potential use of this degree of freedom for information carriers because the valley can now be potentially manipulated in integrated 2D architectures. The valleys separated by a long distance in a momentum space are robust against external disturbance and the flow of the valley, the valley current, is nondissipative because it carries no net electronic current. Among the various 2D valley materials, graphene has by far the highest crystal quality, leading to an extremely long valley relaxation length in the bulk. In this review, we first describe the theoretical background of the valley Hall effect, which converts an electric field into a valley current. We then describe the first observation of the valley Hall effect in monolayer MoS2. Finally, we describe experiments on the generation and detection of the pure valley current in monolayer and bilayer graphene, achieved recently using the valley Hall effect and inverse valley Hall effect. While we show unambiguous evidence of a pure valley current flowing in graphene, we emphasize that the field of "valleytronics" is still in its infancy and that further theoretical and experimental investigations are necessary.

  20. Two-dimensional target decoy strategy for shotgun proteomics.

    PubMed

    Bern, Marshall W; Kil, Yong J

    2011-12-01

    The target-decoy approach to estimating and controlling false discovery rate (FDR) has become a de facto standard in shotgun proteomics, and it has been applied at both the peptide-to-spectrum match (PSM) and protein levels. Current bioinformatics methods control either the PSM- or the protein-level FDR, but not both. In order to obtain the most reliable information from their data, users must employ one method when the number of tandem mass spectra exceeds the number of proteins in the database and another method when the reverse is true. Here we propose a simple variation of the standard target-decoy strategy that estimates and controls PSM and protein FDRs simultaneously, regardless of the relative numbers of spectra and proteins. We demonstrate that even if the final goal is a list of PSMs with a fixed low FDR and not a list of protein identifications, the proposed two-dimensional strategy offers advantages over a pure PSM-level strategy. PMID:22010998

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

    NASA Astrophysics Data System (ADS)

    Gu, Zheng-Cheng; Wang, Zhenghan; Wen, Xiao-Gang

    2015-03-01

    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 approaches reveal that the mathematical framework for (2 +1 ) -dimensional (2 +1 )D bosonic topological order with gappable edge is closely related to unitary fusion category theory. In this paper, we generalize these systematic descriptions of topological orders to 2D fermion systems. We find a classification of (2 +1 )D fermionic topological orders with gappable edge in terms of the following set of data (Nki j,Fki j,Fjk n ,? ? i j m ,? ?,di) , which satisfy a set of nonlinear algebraic equations. The exactly soluble Hamiltonians can be constructed from the above data on any lattices to realize the corresponding topological orders. When Fki j=0 , our result recovers the previous classification of 2 +1 D bosonic topological orders with gappable edge.

  2. Two-dimensional, finite Larmor radius magnetohydrodynamics code

    SciTech Connect

    Huba, J.D.

    1996-12-31

    A two-dimensional, finite Larmor radius magnetohydrodynamics (2D FLR MHD) code has been developed. The code solves the 2D FLR equations in the isothermal limit. These equations are presented in Braginskii (1965) and include an anisotropic ion stress tensor in the momentum equation.the FLR MHD equations are solved in conservative form. A non-linear switch between an 8th order spatial scheme and a low-order scheme is used based upon the partial donor cell method (Hain, 1987). The novel feature of the code is the computation of the fluxes across cell interfaces. The code uses a variation of the beam scheme and computes fluxes based upon maxwellian-like distribution functions that contain the magnetic forces. As a test of the code, theoretical and computational results for the Rayleigh-Taylor instability in the FLR MHD regime will be presented. The authors also discuss the transition to the unmagnetized regime where the Hall term becomes important, and applications to plasma boundary layer dynamics.

  3. Two-Dimensional Nonlinear Finite Element Analysis of CMC Microstructures

    NASA Technical Reports Server (NTRS)

    Mital, Subodh K.; Goldberg, Robert K.; Bonacuse, Peter J.

    2012-01-01

    A research program has been developed to quantify the effects of the microstructure of a woven ceramic matrix composite and its variability on the effective properties and response of the material. In order to characterize and quantify the variations in the microstructure of a five harness satin weave, chemical vapor infiltrated (CVI) SiC/SiC composite material, specimens were serially sectioned and polished to capture images that detailed the fiber tows, matrix, and porosity. Open source quantitative image analysis tools were then used to isolate the constituents, from which two dimensional finite element models were generated which approximated the actual specimen section geometry. A simplified elastic-plastic model, wherein all stress above yield is redistributed to lower stress regions, is used to approximate the progressive damage behavior for each of the composite constituents. Finite element analyses under in-plane tensile loading were performed to examine how the variability in the local microstructure affected the macroscopic stress-strain response of the material as well as the local initiation and progression of damage. The macroscopic stress-strain response appeared to be minimally affected by the variation in local microstructure, but the locations where damage initiated and propagated appeared to be linked to specific aspects of the local microstructure.

  4. Two-Dimensional Ordering of DNA Origami Using Stacking Bonds

    NASA Astrophysics Data System (ADS)

    Sugishita, Yosuke; Wizda, Lee; Sharma, Prashant

    2012-02-01

    Utilizing the DNA Origami method we have designed nano-scale self-assembled structures. These structures are made using a 7000 base pair long single stranded DNA as a scaffold that is held in place by shorter single stranded DNA molecules using Watson-Crick DNA base pairings. The staples were chosen to attach at certain specific sites of the scaffold DNA so that a well-defined planar structure of double stranded DNA can be created at room temperature. In designing these origami structures we made use of the computer application caDNAno. Two geometrical structures with differing symmetries were created using the same scaffold. Edges of these structures were modified in such a way that the double stranded DNA of one structure's edge can stack onto the edge of the second structure. Similar modifications were recently shown by Woo and Rothemund (Nat Chem., 1755-4330, 2011) to enable the formation of extended DNA origami structures. We intend to extend this method to create two-dimensional square and triangular lattice structures. We discuss our experimental results and implications of this method for nano-scale self-assembly.

  5. Chaotic dynamics in two-dimensional Rayleigh-Bénard convection

    E-print Network

    Supriyo Paul; Mahendra K. Verma; Pankaj Wahi; Sandeep K. Reddy; Krishna Kumar

    2010-05-30

    We investigate the origin of various convective patterns using bifurcation diagrams that are constructed using direct numerical simulations. We perform two-dimensional pseudospectral simulations for a Prandtl number 6.8 fluid that is confined in a box with aspect ratio $\\Gamma = 2\\sqrt{2}$. Steady convective rolls are born from the conduction state through a pitchfork bifurcation at $r=1$, where $r$ is the reduced Rayleigh number. These fixed points bifurcate successively to time-periodic and quasiperiodic rolls through Hopf and Neimark-Sacker bifurcations at $r \\simeq 80$ and $r \\simeq 500 $ respectively. The system becomes chaotic at $r \\simeq 750$ through a quasiperiodic route to chaos. The size of the chaotic attractor increases at $r \\simeq 840$ through an "attractor-merging crisis" which also results in travelling chaotic rolls. We also observe coexistence of stable fixed points and a chaotic attractor for $ 846 \\le r \\le 849$ as a result of a subcritical Hopf bifurcation. Subsequently the chaotic attractor disappears through a "boundary crisis" and only stable fixed points remain. Later these fixed points become periodic and chaotic through another set of bifurcations which ultimately leads to turbulence.

  6. Recent Advances in Two-Dimensional Materials beyond Graphene.

    PubMed

    Bhimanapati, Ganesh R; Lin, Zhong; Meunier, Vincent; Jung, Yeonwoong; Cha, Judy; Das, Saptarshi; Xiao, Di; Son, Youngwoo; Strano, Michael S; Cooper, Valentino R; Liang, Liangbo; Louie, Steven G; Ringe, Emilie; Zhou, Wu; Kim, Steve S; Naik, Rajesh R; Sumpter, Bobby G; Terrones, Humberto; Xia, Fengnian; Wang, Yeliang; Zhu, Jun; Akinwande, Deji; Alem, Nasim; Schuller, Jon A; Schaak, Raymond E; Terrones, Mauricio; Robinson, Joshua A

    2015-12-22

    The isolation of graphene in 2004 from graphite was a defining moment for the "birth" of a field: two-dimensional (2D) materials. In recent years, there has been a rapidly increasing number of papers focusing on non-graphene layered materials, including transition-metal dichalcogenides (TMDs), because of the new properties and applications that emerge upon 2D confinement. Here, we review significant recent advances and important new developments in 2D materials "beyond graphene". We provide insight into the theoretical modeling and understanding of the van der Waals (vdW) forces that hold together the 2D layers in bulk solids, as well as their excitonic properties and growth morphologies. Additionally, we highlight recent breakthroughs in TMD synthesis and characterization and discuss the newest families of 2D materials, including monoelement 2D materials (i.e., silicene, phosphorene, etc.) and transition metal carbide- and carbon nitride-based MXenes. We then discuss the doping and functionalization of 2D materials beyond graphene that enable device applications, followed by advances in electronic, optoelectronic, and magnetic devices and theory. Finally, we provide perspectives on the future of 2D materials beyond graphene. PMID:26544756

  7. Unexpected Stable Two-dimensional Silicon Phosphides with Different Stoichiometries

    SciTech Connect

    Huang, Bing; Zhuang, Houlong; Yoon, Mina; Wei, Su-Huai; Sumpter, Bobby G

    2015-01-01

    The discovery of stable two-dimensional, earth-abundant, semiconducting materials is of great interest and may impact future electronic technologies. By combining global structural prediction and first-principles calculations, we have theoretically discovered several previously unknown semiconducting silicon phosphides (SixPy) monolayers, which could be formed stably at the stoichiometries of y/x1. Unexpectedly, some of these compounds, i.e., P-6m2 Si1P1 and Pm Si1P2, have comparable or even lower formation enthalpies than their previously known bulk allotropes. The band gaps (Eg) of SixPy compounds can be dramatically tuned in an extremely wide range (0< Eg < 3 eV) by simply changing the number of layers or applying an in-plane strain. Moreover, we find that carrier doping can drive the ground state of C2/m Si1P3 from a nonmagnetic state into a robust half-metallic spin-polarized state, originating from its unique valence band structure, which can extend the use of Si-related compounds for spintronics.

  8. Two-dimensional photochemical model of the troposphere. Master's thesis

    SciTech Connect

    Carlson, M.W.

    1990-01-01

    An experiment using a time-dependent, two-dimensional photochemical model of the troposphere to model the vertical and zonal distribution of ozone and its precursors is presented. The experiment examines two cases. Case I simulates vertical transport due to diffusion and zonal transport due to advection, with surface emissions of ozone precursors in the center of the model domain representing an urban environment with light wind conditions favorable for the formation of ozone in concentrations greater than 80 parts per billion by volume (ppbv). In Case II, an elevated source of ozone and its precursors is introduced at the upstream boundary in order to investigate the role of advection of these chemical species on ozone concentrations. the first simulation produces surface ozone concentrations greater than 120 ppbv in the air above the urban area, and the second simulation produces an increase of 3 - 10 percent in this region. A comparison of Case I and Case II results shows that enhanced photochemical production of ozone due to the addition of ozone's precursors play an important role in this increase.

  9. Orthorhombic two-dimensional crystal form of purple membrane.

    PubMed Central

    Michel, H; Oesterhelt, D; Henderson, R

    1980-01-01

    A new two-dimensional crystal form of purple membrane has been obtained in vitro. It is produced by the joint use of a cationic detergent, dodecyltrimethylammonium chloride, and the nonionic detergent, Triton X-100. It primarily forms large, rolled-up sheets that look like needles in the light microscope. Liposomes and tubes are also observed. The absorption maximum of the new form of purple membrane is blue-shifted by 6 nm and its density is slightly lower than the natural form of purple membrane. The new form of purple membrane is orthorhombic with space group p22121 and cell dimensions 57.6 x 73.5 A. Four molecules of bacteriorhodopsin occupy the unit cell with an area per molecule close to that found in the native p3 structure. The projected structure to 6.5-A resolution was determined by electron microscopy and diffraction. It shows an identical molecular structure to that of the p3 form and determines the position of the polypeptide boundary. Images PMID:6928627

  10. Anisotropic stress correlations in two-dimensional liquids.

    PubMed

    Wu, Bin; Iwashita, Takuya; Egami, Takeshi

    2015-03-01

    In this paper we demonstrate the presence of anisotropic stress correlations in the simulated two-dimensional liquids. Whereas the temporal correlation of macroscopic shear stress is known to contribute to viscosity via the Green-Kubo formula, the general question regarding angular dependence of the spatial correlation among atomic-level stresses in liquids without external shear has not been explored. We observed the apparent anisotropicity with well-defined symmetry which can be explained in terms of the elastic continuum theory by Eshelby. In addition, we found that the shear stress correlation is screened compared to the prediction by the elastic continuum theory, and the screening length depends on temperature and follows the power law, suggesting divergence around the glass transition temperature. The success of the Eshelby theory to explain the anisotropy of the stress correlations justifies the idea that the mismatch between the atom and its nearest neighbor cage produces the atomic-level stress as well as the long-range stress fields. PMID:25871104

  11. Two-Dimensional Atomic Crystals: Paving New Ways for Nanoelectronics

    NASA Astrophysics Data System (ADS)

    Fan, Jincheng; Li, Tengfei; Djerdj, Igor

    2015-11-01

    Two-dimensional (2D) atomic crystals are attractive for use in next-generation nanoelectronics, due to their unique performances, which may lead to the resolution of the technological and fundamental challenges in semiconductor industry. Based on the introduction of 2D atomic crystal-based transistors and ambipolar behavior, the review presents a brief summary of 2D atomic crystal integration circuits, including memory, logic gate, amplifier, inverter, oscillator, mixer, switch and modulator. The devices show promising performances for the application in future nanoelectronics. In particular, the 2D atomic crystals, such as graphene, demonstrate good compatibility with the existing semiconductor process. The quaternary digital modulations have been achieved with flexible and transparent all-graphene circuits. Moreover, the heterojunction based on 2D atomic crystals may enable new devices beyond conventional field-effect transistors. The results make us be optimistic that practical 2D atomic crystal technologies with complex functionality will be achieved in the near future. Therefore, 2D atomic crystals are paving new ways for nanoelectronics.

  12. Freely decaying turbulence in two-dimensional electrostatic gyrokinetics

    SciTech Connect

    Tatsuno, T.; Plunk, G. G.; Barnes, M.; Dorland, W.; Howes, G. G.; Numata, R.

    2012-12-15

    In magnetized plasmas, a turbulent cascade occurs in phase space at scales smaller than the thermal Larmor radius ('sub-Larmor scales') [Tatsuno et al., Phys. Rev. Lett. 103, 015003 (2009)]. When the turbulence is restricted to two spatial dimensions perpendicular to the background magnetic field, two independent cascades may take place simultaneously because of the presence of two collisionless invariants. In the present work, freely decaying turbulence of two-dimensional electrostatic gyrokinetics is investigated by means of phenomenological theory and direct numerical simulations. A dual cascade (forward and inverse cascades) is observed in velocity space as well as in position space, which we diagnose by means of nonlinear transfer functions for the collisionless invariants. We find that the turbulence tends to a time-asymptotic state, dominated by a single scale that grows in time. A theory of this asymptotic state is derived in the form of decay laws. Each case that we study falls into one of three regimes (weakly collisional, marginal, and strongly collisional), determined by a dimensionless number D{sub *}, a quantity analogous to the Reynolds number. The marginal state is marked by a critical number D{sub *}=D{sub 0} that is preserved in time. Turbulence initialized above this value become increasingly inertial in time, evolving toward larger and larger D{sub *}; turbulence initialized below D{sub 0} become more and more collisional, decaying to progressively smaller D{sub *}.

  13. Tunable states of interlayer cations in two-dimensional materials

    SciTech Connect

    Sato, K.; Numata, K.; Dai, W.; Hunger, M.

    2014-03-31

    The local state of cations inside the Ångstrom-scale interlayer spaces is one of the controlling factors for designing sophisticated two-dimensional (2D) materials consisting of 2D nanosheets. In the present work, the molecular mechanism on how the interlayer cation states are induced by the local structures of the 2D nanosheets is highlighted. For this purpose, the local states of Na cations in inorganic 2D materials, in which the compositional fluctuations of a few percent are introduced in the tetrahedral and octahedral units of the 2D nanosheets, were systematically studied by means of {sup 23}Na magic-angle-spinning (MAS) nuclear magnetic resonance (NMR) and {sup 23}Na multiple-quantum MAS (MQMAS) NMR spectroscopy. In contrast with an uniform distribution of Na cations expected so far, various well-defined cation states sensitive to the local structures of the 2D nanosheets were identified. The tunability of the interlayer cation states along with the local structure of the 2D nanosheets, as the smallest structural unit of the 2D material, is discussed.

  14. Two-dimensional CFD modeling of wave rotor flow dynamics

    NASA Technical Reports Server (NTRS)

    Welch, Gerard E.; Chima, Rodrick V.

    1993-01-01

    A two-dimensional Navier-Stokes solver developed for detailed study of wave rotor flow dynamics is described. The CFD model is helping characterize important loss mechanisms within the wave rotor. The wave rotor stationary ports and the moving rotor passages are resolved on multiple computational grid blocks. The finite-volume form of the thin-layer Navier-Stokes equations with laminar viscosity are integrated in time using a four-stage Runge-Kutta scheme. The Roe approximate Riemann solution scheme or the computationally less expensive Advection Upstream Splitting Method (AUSM) flux-splitting scheme are used to effect upwind-differencing of the inviscid flux terms, using cell interface primitive variables set by MUSCL-type interpolation. The diffusion terms are central-differenced. The solver is validated using a steady shock/laminar boundary layer interaction problem and an unsteady, inviscid wave rotor passage gradual opening problem. A model inlet port/passage charging problem is simulated and key features of the unsteady wave rotor flow field are identified. Lastly, the medium pressure inlet port and high pressure outlet port portion of the NASA Lewis Research Center experimental divider cycle is simulated and computed results are compared with experimental measurements. The model accurately predicts the wave timing within the rotor passage and the distribution of flow variables in the stationary inlet port region.

  15. Two-dimensional CFD modeling of wave rotor flow dynamics

    NASA Technical Reports Server (NTRS)

    Welch, Gerard E.; Chima, Rodrick V.

    1994-01-01

    A two-dimensional Navier-Stokes solver developed for detailed study of wave rotor flow dynamics is described. The CFD model is helping characterize important loss mechanisms within the wave rotor. The wave rotor stationary ports and the moving rotor passages are resolved on multiple computational grid blocks. The finite-volume form of the thin-layer Navier-Stokes equations with laminar viscosity are integrated in time using a four-stage Runge-Kutta scheme. Roe's approximate Riemann solution scheme or the computationally less expensive advection upstream splitting method (AUSM) flux-splitting scheme is used to effect upwind-differencing of the inviscid flux terms, using cell interface primitive variables set by MUSCL-type interpolation. The diffusion terms are central-differenced. The solver is validated using a steady shock/laminar boundary layer interaction problem and an unsteady, inviscid wave rotor passage gradual opening problem. A model inlet port/passage charging problem is simulated and key features of the unsteady wave rotor flow field are identified. Lastly, the medium pressure inlet port and high pressure outlet port portion of the NASA Lewis Research Center experimental divider cycle is simulated and computed results are compared with experimental measurements. The model accurately predicts the wave timing within the rotor passages and the distribution of flow variables in the stationary inlet port region.

  16. Predicted two-dimensional electrides: Lithium-carbon monolayer sheet

    NASA Astrophysics Data System (ADS)

    Lu, Mingchun; Zhang, Miao; Liu, Hanyu

    2015-10-01

    Electrides have attracted great attention since they not only show the fascinating chemical properties but also are of fundamental importance for science and technology application. Here we have systematically explored the two-dimensional (2D) structures of Li-C system with different stoichiometric (LixC, x = 1 / 3 , 1 / 2 , 1 , 2 ,and 3) monolayer sheets using unbiased swarm structure search. Interestingly, the predicted 2D structures of LiC2 and LiC3 monolayers are metallic, which can be viewed as lithium doped graphene structures. For the two LiC monolayers (LiC-I and LiC-II), the calculations exhibit they are insulators with very large band gaps of 3.98 eV and 3.46 eV, respectively. Li2C monolayer is found to be a semiconductor with a narrow band gap of 0.21 eV, while Li3C is a metal. In Li-rich Li2C and Li3C monolayers, C atoms exit as the C-pairs in the center of the Li six-membered rings. More interestingly, the electron localization function suggests the Li-C system is likely to become 2D electride compounds. The present results open an avenue to design and understand electride compounds in 2D materials.

  17. The intrinsic two-dimensional size of Sagittarius A*

    SciTech Connect

    Bower, Geoffrey C.; Markoff, Sera; Brunthaler, Andreas; Falcke, Heino; Law, Casey; Maitra, Dipankar; Clavel, M.; Goldwurm, A.; Morris, M. R.; Witzel, Gunther; Meyer, Leo; Ghez, A. M.

    2014-07-20

    We report the detection of the two-dimensional structure of the radio source associated with the Galactic Center black hole, Sagittarius A*, obtained from Very Long Baseline Array observations at a wavelength of 7 mm. The intrinsic source is modeled as an elliptical Gaussian with major-axis size 35.4 × 12.6 R{sub S} in position angle 95° east of north. This morphology can be interpreted in the context of both jet and accretion disk models for the radio emission. There is supporting evidence in large angular-scale multi-wavelength observations for both source models for a preferred axis near 95°. We also place a maximum peak-to-peak change of 15% in the intrinsic major-axis size over five different epochs. Three observations were triggered by detection of near infrared (NIR) flares and one was simultaneous with a large X-ray flare detected by NuSTAR. The absence of simultaneous and quasi-simultaneous flares indicates that not all high energy events produce variability at radio wavelengths. This supports the conclusion that NIR and X-ray flares are primarily due to electron excitation and not to an enhanced accretion rate onto the black hole.

  18. Two-dimensional axisymmetric Child-Langmuir scaling law

    SciTech Connect

    Ragan-Kelley, Benjamin; Verboncoeur, John; Feng Yang

    2009-10-15

    The classical one-dimensional (1D) Child-Langmuir law was previously extended to two dimensions by numerical calculation in planar geometries. By considering an axisymmetric cylindrical system with axial emission from a circular cathode of radius r, outer drift tube radius R>r, and gap length L, we further examine the space charge limit in two dimensions. Simulations were done with no applied magnetic field as well as with a large (100 T) longitudinal magnetic field to restrict motion of particles to 1D. The ratio of the observed current density limit J{sub CL2} to the theoretical 1D value J{sub CL1} is found to be a monotonically decreasing function of the ratio of emission radius to gap separation r/L. This result is in agreement with the planar results, where the emission area is proportional to the cathode width W. The drift tube in axisymmetric systems is shown to have a small but measurable effect on the space charge limit. Strong beam edge effects are observed with J(r)/J(0) approaching 3.5. Two-dimensional axisymmetric electrostatic particle-in-cell simulations were used to produce these results.

  19. Two-Dimensional, Ordered, Double Transition Metals Carbides (MXenes).

    PubMed

    Anasori, Babak; Xie, Yu; Beidaghi, Majid; Lu, Jun; Hosler, Brian C; Hultman, Lars; Kent, Paul R C; Gogotsi, Yury; Barsoum, Michel W

    2015-10-27

    The higher the chemical diversity and structural complexity of two-dimensional (2D) materials, the higher the likelihood they possess unique and useful properties. Herein, density functional theory (DFT) is used to predict the existence of two new families of 2D ordered, carbides (MXenes), M'2M?C2 and M'2M?2C3, where M' and M? are two different early transition metals. In these solids, M' layers sandwich M? carbide layers. By synthesizing Mo2TiC2Tx, Mo2Ti2C3Tx, and Cr2TiC2Tx (where T is a surface termination), we validated the DFT predictions. Since the Mo and Cr atoms are on the outside, they control the 2D flakes' chemical and electrochemical properties. The latter was proven by showing quite different electrochemical behavior of Mo2TiC2Tx and Ti3C2Tx. This work further expands the family of 2D materials, offering additional choices of structures, chemistries, and ultimately useful properties. PMID:26208121

  20. Epoxy nanocomposites with two-dimensional transition metal dichalcogenide additives.

    PubMed

    Eksik, Osman; Gao, Jian; Shojaee, S Ali; Thomas, Abhay; Chow, Philippe; Bartolucci, Stephen F; Lucca, Don A; Koratkar, Nikhil

    2014-05-27

    Emerging two-dimensional (2D) materials such as transition metal dichalcogenides offer unique and hitherto unavailable opportunities to tailor the mechanical, thermal, electronic, and optical properties of polymer nanocomposites. In this study, we exfoliated bulk molybdenum disulfide (MoS2) into nanoplatelets, which were then dispersed in epoxy polymers at loading fractions of up to 1% by weight. We characterized the tensile and fracture properties of the composite and show that MoS2 nanoplatelets are highly effective at enhancing the mechanical properties of the epoxy at very low nanofiller loading fractions (below 0.2% by weight). Our results show the potential of 2D sheets of transition metal dichalcogenides as reinforcing additives in polymeric composites. Unlike graphene, transition metal dichalcogenides such as MoS2 are high band gap semiconductors and do not impart significant electrical conductivity to the epoxy matrix. For many applications, it is essential to enhance mechanical properties while also maintaining the electrical insulation properties and the high dielectric constant of the polymer material. In such applications, conductive carbon based fillers such as graphene cannot be utilized. This study demonstrates that 2D transition metal dichalcogenide additives offer an elegant solution to such class of problems. PMID:24754702