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1

The application of Halbach cylinders to brushless ac servo motors  

SciTech Connect

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

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

1998-07-01

2

The computation of two-dimensional asymmetrical flows past cylinders  

Microsoft Academic Search

Some problems encountered in the computation of the steady two-dimensional flow of a viscous incompressible fluid past a cylinder in an unbounded field are discussed. They are mainly concerned with the correct satisfaction of the boundary conditions at large distances from the cylinder. It is shown that this is a particularly crucial matter in the case of asymmetrical flows and

S. C. R. Dennis

1978-01-01

3

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

4

Transient radiation and conduction in a two-dimensional participating cylinder subjected to a pulse irradiation  

Microsoft Academic Search

The transient thermal responses in a two-dimensional semitransparent cylinder with black boundary surfaces caused by a pulse irradiation at one end of the cylinder are studied. The processes of the transient coupled radiative-conductive heat transfer in the cylinder are analyzed numerically. An implicit central-difference scheme is employed for handling the energy equation, while a discrete-ordinates method is used to solve

Lin-Hua Liu; He-Ping Tan

2001-01-01

5

Stick-Slip dynamics of one and two dimensional arrays of cylinders  

NASA Astrophysics Data System (ADS)

We have studied the stick-slip behavior of one and two dimensional arrays of cylinders as they are pushed by a known driving force on a planar surface. We present results for the global frictional force and effective inertia as a function of confining mass, number of cylinders, and acceleration rate. We also discuss further plans to test theoretical predictions made by Radjai et al. (Farhang Radjai, Lothar Brendel and Stephane Roux, Nonsmoothness, indeterminacy and friction in two dimensional arrays of rigid particles, Phys. Rev. E, Vol. 54, no. 1, July 1996)

Nakroshis, Paul; Boss, Justin; Smith, Chris

2000-04-01

6

Vortex structures and kinetic energy budget in two-dimensional flow past a square cylinder  

Microsoft Academic Search

Direct Numerical Simulation of unsteady, two-dimensional flow past a square cylinder placed centrally in a channel has been carried out using a higher order finite difference scheme. A Reynolds number of 100 has been considered in the computation. The flow in the wake is found to be unsteady with a strong periodic component. The instantaneous vorticity field at this Reynolds

A. K. Saha; K. Muralidhar; G. Biswas

2000-01-01

7

INVITED PAPER: The characteristics of the Aeolian tone radiated from two-dimensional cylinders  

NASA Astrophysics Data System (ADS)

Aerodynamic sound radiated from cylindrical objects, such as in a pantograph of a train, is a prime noise source in high-speed vehicles. The objective of this paper is to understand the generation mechanism of aerodynamic sound radiated from two-dimensional cylinders. Basic theories for aeroacoustics are reviewed. Three contributions to the field of experimental investigations of the Aeolian tone generation mechanism by the present author are reviewed. The structure of the low-noise wind tunnel and the use of proper model end plate construction to control acoustical and flow fields are discussed in section 3. Experimental investigation on the characteristics of aerodynamic sound radiated from two-dimensional models, such as a circular cylinder, square cylinders with or without rounded corners and a cylinder with modified square cross-section, is discussed in section 4. Experimental investigation of Aeolian tone generation and its relation with surface pressure fluctuation on a circular cylinder at moderate to high Reynolds number flow are discussed in section 5.

Fujita, Hajime

2010-02-01

8

A study of two-dimensional flow past an oscillating cylinder  

Microsoft Academic Search

In this paper we describe a detailed study of the wake structures and flow dynamics associated with simulated two-dimensional flows past a circular cylinder that is either stationary or in simple harmonic cross-flow oscillation. Results are examined for Re=500 and a fixed motion amplitude of ymax\\/D=0.25. The study concentrates on a domain of oscillation frequencies near the natural shedding frequency

H. M. Blackburn; R. D. Henderson

1999-01-01

9

A study of two-dimensional flow past an oscillating cylinder  

Microsoft Academic Search

In this paper we describe a detailed study of the wake structures and flow dynamics associated with simulated two-dimensional flows past a circular cylinder that is either stationary or in simple harmonic cross-flow oscillation. Results are examined for Re = 500 and a xed motion amplitude of ymax=D =0 :25. The study concentrates on a domain of oscillation frequencies near

H. M. B LACKBURN; R. D. H ENDERSON

1999-01-01

10

Steady Two-Dimensional Viscous Flow of an Incompressible Fluid past a Circular Cylinder  

Microsoft Academic Search

Numerical solutions of the steady Navier-Stokes equations are presented for two-dimensional flows past a circular cylinder in an infinite domain. The flow is assumed to be uniform at infinity upstream and the range of Reynolds numbers extends from 1 to 60. The Navier-Stokes equations are replaced by a set of finite difference equations and the numerical solution is obtained by

Hideo Takami; Herbert B. Keller

1969-01-01

11

Two-dimensional mixed convection heat transfer from confined tandem square cylinders in cross-flow at low Reynolds numbers  

Microsoft Academic Search

A two-dimensional numerical simulation is carried out to understand the effects of thermal buoyancy and Prandtl number on flow characteristics and mixed convection heat transfer over two equal isothermal square cylinders placed in a tandem arrangement within a channel at low Reynolds numbers. The spacing between the cylinders is fixed with four widths of the cylinder. The numerical results are

Dipankar Chatterjee; Sakir Amiroudine

2010-01-01

12

Recurrent traveling waves in a two-dimensional saw-toothed cylinder and their average speed  

NASA Astrophysics Data System (ADS)

We study a curvature-dependent motion of plane curves in a two-dimensional infinite cylinder with spatially undulating boundary. The law of motion is given by V=?+A, where V is the normal velocity of the curve, ? is the curvature, and A is a positive constant. The boundary undulation is assumed to be almost periodic, or, more generally, recurrent in a certain sense. We first introduce the definition of recurrent traveling waves and establish a necessary and sufficient condition for the existence of such traveling waves. We then show that the traveling wave is asymptotically stable if it exists. Next we show that a regular traveling wave has a well-defined average speed if the boundary shape is strictly ergodic. Finally we study what we call "virtual pinning", which means that the traveling wave propagates over the entire cylinder with zero average speed. Such a peculiar situation can occur only in non-periodic environments and never occurs if the boundary undulation is periodic.

Lou, Bendong; Matano, Hiroshi; Nakamura, Ken-Ichi

13

Power-series solution for the two-dimensional inviscid flow with a vortex and multiple cylinders  

Microsoft Academic Search

The problem of a point vortex and N fixed cylinders in a two-dimensional inviscid fluid is studied and an analytical-numerical solution in the form of an infinite\\u000a power series for the velocity field is obtained using complex analysis. The velocity distribution for the case of two cylinders\\u000a is compared with the existing results of the problem of a vortex in

Oktay K. Pashaev; Oguz Yilmaz

2009-01-01

14

Two-dimensional order-disorder (melting) transition in a diblock copolymer cylinder-forming thin-film system  

Microsoft Academic Search

We have studied the phase diagram of a two dimensional smectic system, a monolayer film of di-block copolymer cylinders. Previous work was done on sphere-forming diblock polymer films. In this work we anneal PS-PEP 5-13 cylinder-forming diblock copolymer using a temperature gradient system, to investigate the orientational order-disorder (melting) transition. We find that on the high temperature side correlation lengths

Weining Man; Dan E. Angelescu; Mingshaw W. Wu; Douglas H. Adamson; Richard A. Register; Paul M. Chaikin

2005-01-01

15

Design of an End Plate to Promote Quasi-Two-Dimensionality in the Near-Wake of a Circular Cylinder  

NASA Astrophysics Data System (ADS)

To design an end plate that attains nearly parallel vortex shedding from a circular cylinder with an aspect ratio of L/D = 12.3 at ReD=10,000, effect of a rectangular end plate on spanwise flow uniformity is investigated experimentally. Experiments are carried out in a free-surface re-circulating water channel. At one end, the cylinder is bounded by the end plate; and at the other end, by the free surface. Leading edge distance of the end plate from the cylinder axis is varied from 0.5D to 7.0D by the repositioning of the cylinder. The spanwise flow structure on the plane of symmetry of the cylinder, coincident with its centerline, is determined via Particle Image Velocimetry (PIV). Spanwise distributions of streamwise and spanwise velocity contours on this plane are used for the quantitative determination of the degree of spanwise two-dimensionality. Our results indicate that the flow uniformity in the near-wake is highly dependent on the leading/trailing edge distances of the end plate from the cylinder centerline, and a leading edge distance of about 2.5D promotes the best distribution in terms of flow uniformity.

Aydin, Tayfun; Blackmore, Adam; Ekmekci, Alis

2010-11-01

16

Theoretical and experimental studies on the aerodynamic instability of a two-dimensional circular cylinder with a moving attachment  

NASA Astrophysics Data System (ADS)

Rain wind induced vibration of cables in cable-stayed bridges is a worldwide problem of great concern. The effect of the motion of water rivulets on the instability of stay cables has been recognized as one of the mechanisms of this complex phenomenon. In order to investigate how the motion of rivulets affects the unstable vibration of cables without considering the effects of axial flow and axial vortex, a real three-dimensional cable was modeled as a two-dimensional circular cylinder, around which an attachment representing the rivulet can move. This could also be regarded as a new kind of two-dimensional 2-dof dynamic system. This paper studies the aerodynamic instability of the system theoretically and experimentally. Equations governing the motions of the cylinder and the attachment are first established. The Lyapunov stability criterion is applied to the equations of motion to derive the criterion for the unstable balance angle of the attachment. Moreover, a new two-dimensional 2-dof cable model system with a movable attachment is designed and tested in a wind tunnel. Parametric studies are carried out to investigate the effects of major factors such as wind speed, frequency and damping of the dynamic system on the unstable balance angle of the rivulet attachment. Theoretical and experimental results match well. These results may be valuable in elucidating the mechanism of rain wind induced vibration of stay cables.

Gu, M.; Huang, L.

2008-02-01

17

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

Microsoft Academic Search

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

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

1992-01-01

18

Optimal control of two-dimensional nonaxisymmetric temperature field in a hollow cylinder with thermoelastic stress restrictions  

SciTech Connect

A method of inverse problem of thermomechanics and thermal conduction has been developed to solve the problem of optimal (response-speed) control of unsteady one-dimensional thermal regimes with constraints on the thermal stresses and control function. In this study we develop a method of the quasistatic inverse thermoelasticity problem for solving the problem of optimal (response-speed) control of a two-dimensional nonaxisymmetric unsteady thermal regime in a long hollow cylinder with constraints on the thermoelastic stresses. A numerical algorithm is given for solving the optimization problem. 8 refs., 3 figs.

Vigak, V.M.; Svirida, M.I. [National Academy of Sciences of Ukraine, Kiev (Russian Federation)

1995-12-01

19

Multimonostatic Shape Reconstruction of Two-Dimensional Dielectric Cylinders by a Kirchhoff-Based Approach  

Microsoft Academic Search

The inverse problem of reconstructing the shape of dielectric cylinders by aspect-limited multimonostatic multifrequency electromagnetic scattering data is dealt with. The problem is formulated as a linear one by means of the physical-optics approximation distributional approach. The difference with respect to the case of perfectly electrical conducting scatterers is pointed out, since the penetrability of the scatterers is taken into

Adriana Brancaccio; Giovanni Leone

2010-01-01

20

LETTER TO THE EDITOR: Collapsed two-dimensional polymers on a cylinder  

Microsoft Academic Search

Single partially confined collapsed polymers are studied in two dimensions. They are described by self-avoiding random walks with nearest-neighbour attractions below the Theta-point, on the surface of an infinitely long cylinder. For the simulations we employ the pruned-enriched-Rosenbluth method (PERM). The same model had previously been studied for free polymers (infinite lattice, no boundaries) and for polymers on finite lattices

Hsiao-Ping Hsu; Peter Grassberger

2002-01-01

21

Numerical Study of Steady Two-Dimensional Flow past a Square Cylinder in a Channel  

Microsoft Academic Search

Finite-difference solutions of the Navier-Stokes equations are given in stream function-vorticity formulation for a series of Reynolds numbers and for varied positions of the cylinder in the channel. For flows in a doubly connected region, the value of the stream function on the body cannot always be given in advance. A new iteration scheme to solve such a problem is

Yukio Matida; Kunio Kuwahara; Hideo Takami

1975-01-01

22

Two-dimensional viscous flow simulation of a shock accelerated heavy gas cylinder  

NASA Astrophysics Data System (ADS)

Numerical simulation of Richtmyer-Meshkov instability (RMI) is conducted using an improved localized artificial diffusivity (LAD) method, which is used to treat discontinuities in the form of material interfaces and shocks in the flow-field. The RMI occurs on a cylindrical interface between air and SF6 accelerated by a Mach 1.2 shock initially in air. Navier-Stokes simulation is conducted to accurately predict the mixing between the two fluids. The initial conditions for the two-dimensional simulations are matched to previous experimental work by C. Tomkins et al. [``An experimental investigation of mixing mechanisms in shock-accelerated flow,'' J. Fluid Mech. 611, 131 (2008)] and good agreement is found between the experimental data and numerical results. The study on initial condition sensitivity indicates that the initial pressure and density gradient are critical parameters that determine the primary vortex generation responsible for the flow development. A grid convergence study is carried out and the relative contribution of the artificial properties introduced by the LAD method is characterized. Novel to this study is the exploration of the effect of the third species (acetone used as a tracer particle in the experiments to obtain contour fields using planar laser induced florescence). The effect of the presence of the third species on the evolution of the RMI and mixing is shown to be non-negligible and an estimate of the amount of the tracer species that was present in the initial experimental set-up is given.

Shankar, Santhosh K.; Kawai, Soshi; Lele, Sanjiva K.

2011-02-01

23

A direct boundary integral equation formulation for the Oseen flow past a two-dimensional cylinder of arbitrary cross-section  

Microsoft Academic Search

Summary A novel boundary integral formulation is presented for the direct solution of the classical problem of slow flow past a two-dimensional cylinder of arbitrary cross section in an unbounded viscous medium, the equations of motion having first been linearised by the Oseen approximation. It is shown how the governing partial differential equations of motion, together with the no-slip boundary

M. A. Kelmanson

1987-01-01

24

A numerical solution of the Navier-Stokes equations for chemically nonequilibrium, merged stagnation shock layers on spheres and two-dimensional cylinders in air  

NASA Technical Reports Server (NTRS)

Results of solving the Navier-Stokes equations for chemically nonequilibrium, merged stagnation shock layers on spheres and two-dimensional cylinders are presented. The effects of wall catalysis and slip are also examined. The thin shock layer assumption is not made, and the thick viscous shock is allowed to develop within the computational domain. The results show good comparison with existing data. Due to the more pronounced merging of shock layer and boundary layer for the sphere, the heating rates for spheres become higher than those for cylinders as the altitude is increased.

Johnston, K. D.; Hendricks, W. L.

1978-01-01

25

Axial Halbach Magnetic Bearings  

NASA Technical Reports Server (NTRS)

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.

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

2008-01-01

26

Dynamics and heat transfer in a quasi-two-dimensional MHD flow past a circular cylinder in a duct at high Hartmann number  

Microsoft Academic Search

The fluid flow and heat transfer of a liquid metal past a circular cylinder in a rectangular duct (width-to-height aspect ratio of 2) under a strong transverse magnetic field is studied numerically using a quasi-two-dimensional model. Transition from steady to unsteady flow regimes is determined as a function of Hartmann number and blockage ratio, as are Strouhal number, and the

Wisam K. Hussam; Mark C. Thompson; Gregory J. Sheard

2011-01-01

27

Radial Halbach Magnetic Bearings  

NASA Technical Reports Server (NTRS)

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.

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

2009-01-01

28

Halbach Magnetic Rotor Development  

NASA Technical Reports Server (NTRS)

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.

Gallo, Christopher A.

2008-01-01

29

The scenario of two-dimensional instabilities of the cylinder wake under electrohydrodynamic forcing: a linear stability analysis  

NASA Astrophysics Data System (ADS)

We propose to study the stability properties of an air flow wake forced by a dielectric barrier discharge (DBD) actuator, which is a type of electrohydrodynamic (EHD) actuator. These actuators add momentum to the flow around a cylinder in regions close to the wall and, in our case, are symmetrically disposed near the boundary layer separation point. Since the forcing frequencies, typical of DBD, are much higher than the natural shedding frequency of the flow, we will be considering the forcing actuation as stationary. In the first part, the flow around a circular cylinder modified by EHD actuators will be experimentally studied by means of particle image velocimetry (PIV). In the second part, the EHD actuators have been numerically implemented as a boundary condition on the cylinder surface. Using this boundary condition, the computationally obtained base flow is then compared with the experimental one in order to relate the control parameters from both methodologies. After validating the obtained agreement, we study the Hopf bifurcation that appears once the flow starts the vortex shedding through experimental and computational approaches. For the base flow derived from experimentally obtained snapshots, we monitor the evolution of the velocity amplitude oscillations. As to the computationally obtained base flow, its stability is analyzed by solving a global eigenvalue problem obtained from the linearized Navier-Stokes equations. Finally, the critical parameters obtained from both approaches are compared.

D'Adamo, Juan; González, Leo M.; Gronskis, Alejandro; Artana, Guillermo

2012-10-01

30

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)

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.

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

2012-05-01

31

Analysis of the tubular motor with Halbach and radial magnet array  

Microsoft Academic Search

In the machine tool industry, direct drive linear motor technology is of increasing interest as a means to achieve high acceleration, and to increase reliability. This paper analyzes and compares the characteristics of tubular motor with Halbach and radial magnet array respectively. The governing equations established analytically in terms of vector potential, two dimensional cylindrical coordinate system and Maxwell's equations.

Seok Myeong Jang; Jang Young Choi; Sung Ho Lee; Sung Kook Cho; Won Bum Jang

2003-01-01

32

A numerical investigation of wall effects up to high blockage ratios on two-dimensional flow past a confined circular cylinder  

Microsoft Academic Search

A finite volume method based on a velocity-only formulation is used to solve the flow field around a confined circular cylinder in a channel in order to investigate lateral wall proximity effects on stability, Strouhal number, hydrodynamic forces and wake structure behind the cylinder for a wide range of blockage ratios (0.1

Mehmet Sahin; Robert G. Owens

2004-01-01

33

Two-dimensional dynamic analysis of thermal stresses in a finite-length FG thick hollow cylinder subjected to thermal shock loading using an analytical method  

Microsoft Academic Search

This work is aiming to present an analytical method to study the dynamic behavior of thermoelastic stresses in a finite-length\\u000a functionally graded (FG) thick hollow cylinder under thermal shock loading. The thermo-mechanical properties are assumed to\\u000a vary continuously through the radial direction as a nonlinear power function. Using Laplace transform and series solution,\\u000a the thermoelastic Navier equations in displacement form

Ali Safari; Masoud Tahani; Seyed Mahmoud Hosseini

34

Edward A. Halbach 1909-2011  

NASA Astrophysics Data System (ADS)

Edward A. Halbach (1909-2011) was a dedicated, lifelong member of the AAVSO and the Milwaukee Astronomical Society. His service to these organizations, and his valuable contributions to variable star astronomy, are described.

Samolyk, G.

2011-06-01

35

Two-dimensional separated flows  

NASA Astrophysics Data System (ADS)

The state of the art of asymptotic theory is discussed with respect to incompressible two-dimensional separated flows. As an example, the flow over an indented flat plate is considered for two cases: a small separation bubble within the lower part of the boundary layer, and the 'catastrophic' separation of the whole boundary layer with a large recirculating eddy. Separation means failure of Prandtl's boundary layer theory, and alternate theories are required. An example of this is shown in the calculation of circulation in the dent according to triple-deck theory. The free-streamline theory approach is used to examine the indented flat plate and the flow past a circular cylinder. Attention is also given to flow control by continuous injection, combined forced and free convection, unsteady laminar flows, and laminar flows.

Gersten, K.

36

Two Dimensional Finite Difference Analysis of Shape Instabilities in Plates.  

National Technical Information Service (NTIS)

A two-dimensional finite difference analysis is applied to surface diffusion-controlled instabilities of plates. Plates can evolve into cylinders, or if the plates have longitudinal internal boundaries, they may split into two segments. The evolution proc...

T. H. Courtney J. K. Lee

1989-01-01

37

A Coaxial Magnetic Gear With Halbach Permanent-Magnet Arrays  

Microsoft Academic Search

This paper proposes a coaxial magnetic gear that offers higher torque density, lower cogging torque, and lower iron losses than its counterparts. The key is to newly employ a Halbach permanent-magnet (PM) array to constitute the PM poles in the inner rotor and a partial Halbach array (two segments per pole) for the outer rotor. The corresponding magnetic field distributions,

Linni Jian; K. T. Chau

2010-01-01

38

Two-dimensional Distributions  

Microsoft Academic Search

In Chap. 5 is given basic information concerning two-dimensional distributions of random variables. Starting from a classical\\u000a problem of the accuracy of artillery fire it is shown that, besides a traditional analytical procedure, components of a covariance\\u000a tensor may be transformed by means of their representation by Mohr circles. It is shown that this representation, used commonly\\u000a in mechanics of solids,

Zbigniew Kotulski; Wojciech Szczepi?ski

39

Two dimensional vernier  

NASA Technical Reports Server (NTRS)

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.

Juday, Richard D. (inventor)

1992-01-01

40

Development and Testing of a Radial Halbach Magnetic Bearing  

NASA Technical Reports Server (NTRS)

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.

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

2006-01-01

41

Development and Testing of an Axial Halbach Magnetic Bearing  

NASA Technical Reports Server (NTRS)

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.

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

2006-01-01

42

Halbach array DC motor/generator  

DOEpatents

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.

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

1998-01-06

43

Halbach array DC motor/generator  

DOEpatents

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.

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

1998-01-01

44

Two-dimensional wind tunnel  

NASA Technical Reports Server (NTRS)

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

1982-01-01

45

Two-dimensional model networks  

Microsoft Academic Search

The tensio-active properties of different types of polymerizable diesters can be used to synthesize two-dimensional model\\u000a networks at the interface between oil and water. — The adsorbed monolayers can be polymerized and crosslinked by UV-irradiation.\\u000a — The kinetics of surface gelation were systematically investigated by measuring the two-dimensional shear modulus and the\\u000a surface viscosity as a function of the reaction

A. Burger; H. Rehage

46

Design of a Halbach Magnet Array Based on Optimization Techniques  

Microsoft Academic Search

We have designed a Halbach magnet array by using a numerical optimization method based on finite-element analysis. The magnetization direction of each element is defined as the design variable. The optimal magnet arrays composed of two and three linear magnet layers can then be investigated to increase the attractive, repulsive, and tangential magnetic forces between magnet layers. We have applied

Jae-Seok Choi; Jeonghoon Yoo

2008-01-01

47

Symmetrical two dimensional scattering program  

NASA Technical Reports Server (NTRS)

Computer program solves integral equation for currents induced by electric or magnetic plane wave incident upon one or more conducting cylinders with a midplane of symmetry. Program utilizes symmetry of the geometry. Restrictions on the program are given.

Hatfield, J.; Rusch, W. V. T.

1971-01-01

48

Cloaking two-dimensional fermions  

SciTech Connect

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

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

2011-09-15

49

Two-dimensional turbulence models  

NASA Technical Reports Server (NTRS)

Two-dimensional turbulence models are compared with experimental measurements made using an array of instrumented towers. The spatial correlation coefficient, the two-point spectrum or cross spectrum, and the coherence function are discussed. The prediction techniques in general agree reasonably well with the experimental results. Measurements of the integral length scale however, do not correlate well with the prediction model.

Frost, W.; Lin, M. C.

1981-01-01

50

A two-pole Halbach permanent magnet guideway for high temperature superconducting Maglev vehicle  

Microsoft Academic Search

In order to improve the levitation performance of the high temperature superconducting (HTS) magnetic levitation (Maglev) vehicle, a two-pole Halbach array’s permanent magnet guideway (PMG) is proposed, which is called as Halbach PMG. The finite element method (FEM) calculations indicate that Halbach PMG has a wider high-field region than the present PMG of equal PM’s transverse section. The levitation force

H. Jing; J. Wang; S. Wang; L. Wang; L. Liu; J. Zheng; Z. Deng; G. Ma; Y. Zhang; J. Li

2007-01-01

51

Two-dimensional ferroelectric films  

Microsoft Academic Search

Ultrathin crystalline films offer the possibility of exploring phase transitions in the crossover region between two and three dimensions. Second-order ferromagnetic phase transitions have been observed in monolayer magnetic films,, where surface anisotropy energy stabilizes the two-dimensional ferromagnetic state at finite temperature. Similarly, a number of magnetic materials have magnetic surface layers that show a second-order ferromagnetic-paramagnetic phase transition with

A. V. Bune; V. M. Fridkin; Stephen Ducharme; L. M. Blinov; S. P. Palto; A. V. Sorokin; S. G. Yudin; A. Zlatkin

1998-01-01

52

Optical and confinement properties of two-dimensional photonic crystals  

Microsoft Academic Search

We describe experiments on a quasi-two dimensional (2-D) optical system consisting of a triangular array of air cylinders etched through a laser-like Ga(Al)As waveguiding heterostructure. Such a configuration is shown to yield results very well approximated by the infinite 2-D photonic crystal (PC). We first present a set of measurements of the optical properties (transmission, reflection, and diffraction) of slabs

H. Benisty; C. Weisbuch; D. Labilloy; M. Rattier; C. J. M. Smith; T. F. Krauss; R. M. de la Rue; R. Houdre; U. Oesterle; C. Jouanin; D. Cassagne

1999-01-01

53

Energy harvesting from electric power lines employing the Halbach arrays.  

PubMed

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

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

2013-10-01

54

Influence of slip on the dynamics of two-dimensional wakes  

Microsoft Academic Search

(Received 25 March 2009 and in revised form 5 May 2009) We study numerically the two-dimensional flow past a circular cylinder as a prototypical transitional flow, and investigate the influence of a generic slip boundary condition on the wake dynamics. We show that slip significantly delays the onset of recirculation and shedding in the wake behind the cylinder. As expected,

DOMINIQUE L EGENDRE; E RIC L AUGA; JACQUES M AGNAUDET

2009-01-01

55

Integral equation theory of hard sphere liquids on two-dimensional cylindrical surfaces  

Microsoft Academic Search

An integral equation theory has been developed to elucidate the structure of hard sphere liquids on the two dimensional (2D) surface of a cylinder. The 2D cylindrical coordinate breaks the spherical symmetry. Hence, the pair correlation function is reformulated as a function of two variables to account for particles packing along and around the cylinder. Both Percus–Yevick (PY) and Hypernetted

Takafumi Iwaki; Chwen-Yang Shew; Godfrey Gumbs

2006-01-01

56

Extinction paradox and actual power scattered in light beam scattering: a two-dimensional study  

Microsoft Academic Search

The extinction paradox is examined by applying partial-wave analysis to a two-dimensional light beam interacting with a long transverse cylinder without absorption, assuming always short wavelengths. We show that the (conventional) power scattered, Psca, except for a very narrow beam hitting a transparent cylinder on axis, is always double the power directly intercepted by the scatterer, Pitc, including a zero

H. M. Lai; W. Y. Wong; W. H. Wong

2004-01-01

57

Extinction paradox and actual power scattered in light beam scattering: a two-dimensional study  

Microsoft Academic Search

The extinction paradox is examined by applying partial-wave analysis to a two-dimensional light beam inter- acting with a long transverse cylinder without absorption, assuming always short wavelengths. We show that the (conventional) power scattered, P sca , except for a very narrow beam hitting a transparent cylinder on axis, is always double the power directly intercepted by the scatterer, P

H. M. Lai; W. Y. Wong; W. H. Wong

2004-01-01

58

Two-dimensional wavelet processor  

NASA Astrophysics Data System (ADS)

An optical implementation of the two-dimensional (2-D) wavelet transform and inverse wavelet transform is performed in real time by the exploitation of a new multichannel system that processes the different daughter wavelets separately. The so-coined wavelet-processor system relies on a multichannel replication array generated that uses a Dammann grating and is able to handle every wavelet function. All channels process in parallel using a conventional 2-D correlator. Experimental results applying the Mexican-hat wavelet-decomposition technique are presented.

Ouzieli, Ido; Mendlovic, David

1996-10-01

59

Coherent Two-Dimensional Nanoscopy  

NASA Astrophysics Data System (ADS)

We introduce a spectroscopic method that determines nonlinear quantum mechanical response functions beyond the optical diffraction limit and allows direct imaging of nanoscale coherence. In established coherent two-dimensional (2D) spectroscopy, four-wave-mixing responses are measured using three ingoing waves and one outgoing wave; thus, the method is diffraction-limited in spatial resolution. In coherent 2D nanoscopy, we use four ingoing waves and detect the final state via photoemission electron microscopy, which has 50-nanometer spatial resolution. We recorded local nanospectra from a corrugated silver surface and observed subwavelength 2D line shape variations. Plasmonic phase coherence of localized excitations persisted for about 100 femtoseconds and exhibited coherent beats. The observations are best explained by a model in which coupled oscillators lead to Fano-like resonances in the hybridized dark- and bright-mode response.

Aeschlimann, Martin; Brixner, Tobias; Fischer, Alexander; Kramer, Christian; Melchior, Pascal; Pfeiffer, Walter; Schneider, Christian; Strüber, Christian; Tuchscherer, Philip; Voronine, Dmitri V.

2011-09-01

60

Two-dimensional Quantum Gravity  

NASA Astrophysics Data System (ADS)

This Ph.D. thesis pursues two goals: The study of the geometrical structure of two-dimensional quantum gravity and in particular its fractal nature. To address these questions we review the continuum formalism of quantum gravity with special focus on the scaling properties of the theory. We discuss several concepts of fractal dimensions which characterize the extrinsic and intrinsic geometry of quantum gravity. This work is partly based on work done in collaboration with Jan Ambjørn, Dimitrij Boulatov, Jakob L. Nielsen and Yoshiyuki Watabiki (1997). The other goal is the discussion of the discretization of quantum gravity and to address the so called quantum failure of Regge calculus. We review dynamical triangulations and show that it agrees with the continuum theory in two dimensions. Then we discuss Regge calculus and prove that a continuum limit cannot be taken in a sensible way and that it does not reproduce continuum results. This work is partly based on work done in collaboration with Jan Ambjørn, Jakob L. Nielsen and George Savvidy (1997).

Rolf, Juri

1998-10-01

61

Inductional Effects in a Halbach Magnet Motion Above Distributed Inductance  

NASA Astrophysics Data System (ADS)

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.

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

2013-03-01

62

Experiments on Inductive Magnetic Levitation with a Circular Halbach Array  

NASA Astrophysics Data System (ADS)

Using a ring Halbach array, we are investigating a repulsive levitating force and a drag force acting on the magnet from a ring of inductors rotating below the magnet. After measuring induced currents, voltages and magnetic fields in the individual inductors (in the form of short solenoids), we investigated the dependence of lift/drag forces on the speed of relative rotation. The ratio of lift to drag increases with the angular velocity, as expected from a related theory of the induction effects in a linear motion. We are experimenting with the shape and density of inductors, and their material, in an attempt to maximize the lift at a minimal velocity of rotation. Eventually this design could have applications as frictionless bearings or as frictionless gear in a wide range of systems, especially in machinery that cannot be easily accessed.

Bean, Ian; Goncz, Doug; Raymer, Austin; Specht, Jason; Zalles, Ricardo; Majewski, Walerian

2013-03-01

63

Two-dimensional packing problems: A survey  

Microsoft Academic Search

We consider problems requiring to allocate a set of rectangular items to larger rectangular standardized units by minimizing the waste. In two-dimensional bin packing problems these units are finite rectangles, and the objective is to pack all the items into the minimum number of units, while in two-dimensional strip packing problems there is a single standardized unit of given width,

Andrea Lodi; Silvano Martello; Michele Monaci

2002-01-01

64

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)

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.

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

2014-05-01

65

A two-dimensional methodology to predict vertical axis wind turbine performance  

Microsoft Academic Search

An accurate two-dimensional methodology, the COIN Lambda Fast Solver, for the computation of the flow field about a vertical axis wind turbine is presented. Such a technique determines the smooth flow field by integrating the compatibility conditions along the bicharacteristic lines. The time-averaged wind turbine effects are introduced by means of an actuator porous cylinder having the same radius of

B. Fortunato; A. Dadone; V. Trifoni

1995-01-01

66

Two-Dimensional Planetary Surface Lander  

NASA Astrophysics Data System (ADS)

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.

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

2014-06-01

67

Two Dimensional Plasmonic Cavities on Moire Surfaces  

NASA Astrophysics Data System (ADS)

We investigate surface plasmon polariton (SPP) cavitiy modes on two dimensional Moire surfaces in the visible spectrum. Two dimensional hexagonal Moire surface can be recorded on a photoresist layer using Interference lithography (IL). Two sequential exposures at slightly different angles in IL generate one dimensional Moire surfaces. Further sequential exposure for the same sample at slightly different angles after turning the sample 60 degrees around its own axis generates two dimensional hexagonal Moire cavity. Spectroscopic reflection measurements have shown plasmonic band gaps and cavity states at all the azimuthal angles (omnidirectional cavity and band gap formation) investigated. The plasmonic band gap edge and the cavity states energies show six fold symmetry on the two dimensional Moire surface as measured in reflection measurements.

Balci, Sinan; Kocabas, Askin; Karabiyik, Mustafa; Kocabas, Coskun; Aydinli, Atilla

2010-03-01

68

Conoscopic holography: two-dimensional numerical reconstructions.  

PubMed

Conoscopic holography is an incoherent light holographic technique based on the properties of crystal optics. We present experimental results of the numerical reconstruction of a two-dimensional object from its conoscopic hologram. PMID:19798352

Mugnier, L M; Sirat, G Y; Charlot, D

1993-01-01

69

Quasi-two-dimensional superfluid fermionic gases.  

PubMed

We study a quasi-two-dimensional superfluid Fermi gas where the confinement in the third direction is due to a strong harmonic trapping. We investigate the behavior of such a system when the chemical potential is varied and find strong modifications of the superfluid properties due to the discrete harmonic oscillator states. We show that such quasi-two-dimensional behavior can be created and observed with current experimental capabilities. PMID:16383804

Martikainen, J-P; Törmä, P

2005-10-21

70

Flow past a rotating cylinder  

Microsoft Academic Search

Flow past a spinning circular cylinder placed in a uniform stream is investigated via two-dimensional computations. A stabilized finite element method is utilized to solve the incompressible Navier Stokes equations in the primitive variables formulation. The Reynolds number based on the cylinder diameter and free-stream speed of the flow is 200. The non-dimensional rotation rate, [alpha] (ratio of the surface

Sanjay Mittal; Bhaskar Kumar

2003-01-01

71

Optimal Halbach Permanent Magnet Designs for Maximally Pulling and Pushing Nanoparticles  

PubMed Central

Optimization methods are presented to design Halbach arrays to maximize the forces applied on magnetic nanoparticles at deep tissue locations. In magnetic drug targeting, where magnets are used to focus therapeutic nanoparticles to disease locations, the sharp fall off of magnetic fields and forces with distances from magnets has limited the depth of targeting. Creating stronger forces at depth by optimally designed Halbach arrays would allow treatment of a wider class of patients, e.g. patients with deeper tumors. The presented optimization methods are based on semi-definite quadratic programming, yield provably globally optimal Halbach designs in 2 and 3-dimensions, for maximal pull or push magnetic forces (stronger pull forces can collect nano-particles against blood forces in deeper vessels; push forces can be used to inject particles into precise locations, e.g. into the inner ear). These Halbach designs, here tested in simulations of Maxwell’s equations, significantly outperform benchmark magnets of the same size and strength. For example, a 3-dimensional 36 element 2000 cm3 volume optimal Halbach design yields a ×5 greater force at a 10 cm depth compared to a uniformly magnetized magnet of the same size and strength. The designed arrays should be feasible to construct, as they have a similar strength (? 1 Tesla), size (? 2000 cm3), and number of elements (? 36) as previously demonstrated arrays, and retain good performance for reasonable manufacturing errors (element magnetization direction errors ? 5°), thus yielding practical designs to improve magnetic drug targeting treatment depths.

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

2011-01-01

72

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

NASA Astrophysics Data System (ADS)

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.

Íñiguez, J.; Raposo, V.

2010-05-01

73

Magnetohydrodynamic flow past a circular cylinder. II  

Microsoft Academic Search

Summary The steady, two-dimensional incompressible MHD flow past a circular cylinder with an applied magnetic field parallel to the main flow is calculated using the method of series truncation. The differential equations are solved numerically. The magnetic Reynolds number is assumed to be small. The results show that with an applied magnetic field the flow stays attached to the cylinder

J. S. Bramley

1975-01-01

74

Structural parameter optimization design for Halbach permanent maglev rail  

NASA Astrophysics Data System (ADS)

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

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

2010-11-01

75

Defect Modes in Two-Dimensional Quasiperiodic Photonic Crystal  

NASA Astrophysics Data System (ADS)

The defect modes and transmission property of a two-dimensional quasiperiodic photonic crystal (QPC) with defects are studied experimentally and theoretically. It is found that the defects, introduced by removing the dielectric cylinders in the central octagon, may result in various defect modes and resonant frequencies. If the defects possess the same rotational symmetry, the resonant frequencies of the defects are identical. However, the corresponding transmittances can be quite different. This is attributed to the different field distribution leading to various coupling strength between the incident and transmitted waves. When it is symmetrically distributed against the central line which is perpendicular to the incident direction, the transmittance enhances drastically. Based on the wave coupling theory, a simple model is given to explain this phenomenon.

Wang, Yiquan; Jin, Chongjun; Han, Shouzhen; Cheng, Bingying; Zhang, Daozhong

2004-04-01

76

Magnet Guideways for Superconducting Maglevs: Comparison Between Halbach-Type and Conventional Arrangements of Permanent Magnets  

NASA Astrophysics Data System (ADS)

The characteristics of the permanent magnets composing the guideway in superconducting magnetic levitation devices are very important for their performance in terms of levitation force and stability. From a model based on minimizing the magnetic energy in the superconductor and considering realistic parameters of actual maglev devices, we calculate the levitation and guidance forces and stability arising from both conventional arrangements and recently proposed Halbach-like arrangements. When a comparison is carefully made under similar conditions, we conclude that not always complicated arrangements based on Halbach arrays bring significant improvements with respect to some simpler arrangements that also provide large force. These results may help improving the design of actual maglev devices.

Del-Valle, Nuria; Sanchez, Alvaro; Navau, Carles; Chen, Du-Xing

2011-01-01

77

Two-dimensional nonlinear beam shaping.  

PubMed

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

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

2012-06-01

78

Two-dimensional nanolithography using atom interferometry  

SciTech Connect

We propose a scheme for the lithography of arbitrary, two-dimensional nanostructures via matter-wave interference. The required quantum control is provided by a {pi}/2-{pi}-{pi}/2 atom interferometer with an integrated atom lens system. The lens system is developed such that it allows simultaneous control over the atomic wave-packet spatial extent, trajectory, and phase signature. We demonstrate arbitrary pattern formations with two-dimensional {sup 87}Rb wave packets through numerical simulations of the scheme in a practical parameter space. Prospects for experimental realizations of the lithography scheme are also discussed.

Gangat, A.; Pradhan, P.; Pati, G.; Shahriar, M.S. [Department of Electrical and Computer Engineering, Northwestern University, Evanston, Illinois 60208 (United States)

2005-04-01

79

Steady viscous flow past a tapered cylinder  

Microsoft Academic Search

The three-dimensional nature of the viscous flow past a linearly tapered circular cylinder is examined at low Reynolds numbers.\\u000a The numerical solution of the unsteady Navier–Stokes equations converges to a steady state. The primary flow in planes perpendicular\\u000a to the cylinder axis is practically indistinguishable from the two-dimensional flow past a uniform cylinder. A secondary spanwise\\u000a flow is observed in

Vagesh D. Narasimhamurthy; Helge I. Andersson; Bjørnar Pettersen

2009-01-01

80

A numerical method for calculating steady flow past a cylinder  

Microsoft Academic Search

Solutions of the Navier-Stokes equations for steady two-dimensional flow past a cylinder is the satisfactory treatment of the boundary conditions at large distances from the cylinder. The assumption of the uniform stream boundary condition at finite distances from the cylinder is not very satisfactory because of the slow decay of the flow in the wake. The flow in the far

S. C. R. Dennis

81

Steady incompressible flow past a row of circular cylinders  

Microsoft Academic Search

Numerical solutions are presented for steady two-dimensional incompressible flow past an infinite row of cylinders (of unit radii, with distances W between their centers). The calculations cover R below 700 for cylinder separations from 5 to infinity and also R = 800 for between 5 and 100 (where R denotes the Reynolds number based on the cylinder diameters). The recirculation

Bengt Fornberg

1991-01-01

82

Soap film flows: Statistics of two-dimensional turbulence  

SciTech Connect

Soap film flows provide a very convenient laboratory model for studies of two-dimensional (2-D) hydrodynamics including turbulence. For a gravity-driven soap film channel with a grid of equally spaced cylinders inserted in the flow, we have measured the simultaneous velocity and thickness fields in the irregular flow downstream from the cylinders. The velocity field is determined by a modified digital particle image velocimetry method and the thickness from the light scattered by the particles in the film. From these measurements, we compute the decay of mean energy, enstrophy, and thickness fluctuations with downstream distance, and the structure functions of velocity, vorticity, thickness fluctuation, and vorticity flux. From these quantities we determine the microscale Reynolds number of the flow R{sub {lambda}}{approx}100 and the integral and dissipation scales of 2D turbulence. We also obtain quantitative measures of the degree to which our flow can be considered incompressible and isotropic as a function of downstream distance. We find coarsening of characteristic spatial scales, qualitative correspondence of the decay of energy and enstrophy with the Batchelor model, scaling of energy in {ital k} space consistent with the k{sup {minus}3} spectrum of the Kraichnan{endash}Batchelor enstrophy-scaling picture, and power-law scalings of the structure functions of velocity, vorticity, vorticity flux, and thickness. These results are compared with models of 2-D turbulence and with numerical simulations. {copyright} {ital 1999 American Institute of Physics.}

Vorobieff, P.; Rivera, M.; Ecke, R.E. [Center for Nonlinear Studies and Condensed Matter and Thermal Physics Group, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)] [Center for Nonlinear Studies and Condensed Matter and Thermal Physics Group, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)

1999-08-01

83

Shape Matching of Two-Dimensional Objects  

Microsoft Academic Search

In this paper we present results in the areas of shape matching of nonoccluded and occluded two-dimensional objects. Shape matching is viewed as a ``segment matching'' problem. Unlike the previous work, the technique is based on a stochastic labeling procedure which explicitly maximizes a criterion function based on the ambiguity and inconsistency of classification. To reduce the computation time, the

Bir Bhanu; Olivier D. Faugeras

1984-01-01

84

Modeling two-dimensional magnetic domain patterns  

Microsoft Academic Search

Two-dimensional magnetic garnets exhibit complex and fascinating magnetic domain structures, like stripes, labyrinths, cells, and mixed states of stripes and cells. These patterns do change in a reversible way when the intensity of an externally applied magnetic field is varied. The main objective of this contribution is to present the results of a model that yields a rich pattern structure

J. R. Iglesias; S. Gonçalves; O. A. Nagel; Miguel Kiwi

2002-01-01

85

Two-dimensional magnetic domain patterns  

Microsoft Academic Search

Two-dimensional magnetic garnets exhibit complex and fascinating magnetic domain structures, like stripes, cells, mixed states of stripes and cells and labyrinths, which have challenged theorists for a long time. They change reversibly when the intensity of an externally applied magnetic field is varied. By Monte Carlo simulations we investigate the pattern formation and the thermodynamics of these systems as a

M. Kiwi; J. R. Iglesias; S. Goncalves; O. Nagel

2001-01-01

86

A Two Dimensional Car Crash Victim Simulation  

Microsoft Academic Search

The purpose of this study was to develop a two dimensional mathematical model of an unrestrained, right, front seat, passenger car occupant, subjected to frontal collision. A 10 degrees of freedom linkage system made of 8 rigid segments connected with revolute joints was used as occupant model. Relative rotation between links were constrained by torsional springs, dampers, Coulomb frictions and

M. Batman; R. Seliktar

1990-01-01

87

Two-Dimensional Turbulence in Magnetized Plasmas  

ERIC Educational Resources Information Center

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…

Kendl, A.

2008-01-01

88

Stability of Two-Dimensional Poiseuille Flow.  

National Technical Information Service (NTIS)

The report is the second in a series in the exact numerical calculations of the stability of viscous flows by the method of quasilinearization. It describes results for the growth or decay of Tollmien-Schlichting type disturbances in a two-dimensional Poi...

J. R. Radbill E. R. van Driest

1967-01-01

89

Two dimensional invisibility cloaking via transformation optics  

Microsoft Academic Search

We investigate two-dimensional invisibility cloaking via transformation optics approach. The cloaking media possess much more singular parameters than those having been considered for three-dimensional cloaking in literature. Finite energy solutions for these cloaking devices are studied in appropriate weighted Sobolev spaces. We derive some crucial properties of the singularly weighted Sobolev spaces. The invisibility cloaking is then justified by decoupling

Hongyu Liu; Ting Zhou

2010-01-01

90

Tunable Two-Dimensional Phononic Materials Research  

Microsoft Academic Search

The base research project is on two-dimensional pho nonic band gap materials whose characteristic stop band can be tun ed by using an eccentric coating layer to the core scatterers. The host institution is the Polytechnic University of Valencia, Spain, whose 1995 article in the Nature magazine was considered by many as the article that started this field of endeavor.

LIANG-WU CAI

91

Two-Dimensional Plasma Actuator Analysis Code.  

National Technical Information Service (NTIS)

A two-dimensional plasma actuator analysis code has been developed. A time-accurate Navier-Stokes CFD code was coupled with a time-dependent, phenomenological model of an alternating current, single dielectric barrier discharge plasma actuator. The accura...

S. Ellison

2006-01-01

92

Optimal Allocation of Two-Dimensional Data  

Microsoft Academic Search

Efficient browsing and retrieval of geographically referenced information requires the allocation of data on different storage devices for concurrent retrieval. By dividing a two dimensional space into tiles, a system can allow users to specify regions of interest using a query rectangle and then retrieving all information related to tiles overlapping with the query. In this paper, we derive the

Khaled A. S. Abdel-ghaffar; Amr El Abbadi

1997-01-01

93

Analysis of Halbach magnet array and its application to linear motor  

Microsoft Academic Search

Using Halbach magnet array, magnetic flux can be enhanced on one side (strong side) of the array while the flux cancelled on the other side (weak side). Inherently, rotor of rotary motor has infinite rotational length with respect to its rotation while mover of the linear motor has finite length with respect to mover’s translation. In this paper, we propose

Moon G. Lee; Sung Q. Lee; Dae-Gab Gweon

2004-01-01

94

Modeling maglev passenger compartment static magnetic fields from linear Halbach permanent-magnet arrays  

Microsoft Academic Search

Passenger compartment magnetic field levels in a low-speed magnetic levitation (maglev) vehicle that uses linear Halbach permanent-magnet arrays for both levitation and propulsion are computed through superposition of fields due to patches of magnetization charge at surfaces where the magnetization is discontinuous. End effects due to the finite lengths of the arrays lead to fields that decay much less rapidly

James F. Hoburg

2004-01-01

95

Optimization shows Halbach arrays to be non-ideal for induction devices  

Microsoft Academic Search

Among the advantages of Halbach magnet arrays is the fact that the magnetic field behind the array is very small, and the magnets act as a natural flux guide. This paper discusses an optimization index that proves useful for objectively examining any magnet array used in induction applications. Multivariate spline tensor analysis and variable metric methods with a boundary element

Kent Davey

2000-01-01

96

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

PubMed

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. PMID:19405690

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

2009-04-01

97

Toward two-dimensional search engines  

NASA Astrophysics Data System (ADS)

We study the statistical properties of various directed networks using ranking of their nodes based on the dominant vectors of the Google matrix known as PageRank and CheiRank. On average PageRank orders nodes proportionally to a number of ingoing links, while CheiRank orders nodes proportionally to a number of outgoing links. In this way, the ranking of nodes becomes two dimensional which paves the way for the development of two-dimensional search engines of a new type. Statistical properties of information flow on the PageRank-CheiRank plane are analyzed for networks of British, French and Italian universities, Wikipedia, Linux Kernel, gene regulation and other networks. A special emphasis is done for British universities networks using the large database publicly available in the UK. Methods of spam links control are also analyzed.

Ermann, L.; Chepelianskii, A. D.; Shepelyansky, D. L.

2012-07-01

98

Two-dimensional ranking of Wikipedia articles  

NASA Astrophysics Data System (ADS)

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.

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

2010-10-01

99

Plasmonics with two-dimensional conductors.  

PubMed

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

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

2014-03-28

100

Two-Dimensional Solitons at Finite Temperature  

Microsoft Academic Search

The partition function of two-dimensional solitons in a heat bath of mesons is worked out to one-loop. For temperatures large compared to the meson mass, the free energy is dominated by the meson-soliton bound states and the zero modes, a consequence of Levinson's theorem. Using the Bethe-Uhlenbeck formula we compare the soliton energy-shift to the shift expected in the pole

M. Kacir; I. Zahed

1996-01-01

101

Superdiffusion in two-dimensional Yukawa liquids  

NASA Astrophysics Data System (ADS)

Superdiffusion of two-dimensional (2D) liquids was studied using an equilibrium molecular dynamics simulation. At intermediate temperatures, the mean-squared displacement, probability distribution function (PDF), and velocity autocorrelation function (VACF) all indicate superdiffusion; the VACF has a long-time tail; and the PDF indicates no Lévy flights. These effects are predicted to occur in 2D dusty plasmas and other 2D liquids that can be modeled with a long-range repulsive potential.

Liu, Bin; Goree, J.

2007-01-01

102

Modeling two-dimensional magnetic domain patterns  

Microsoft Academic Search

Two-dimensional magnetic garnets exhibit complex and fascinating magnetic\\u000adomain structures, like stripes, labyrinths, cells and mixed states of stripes\\u000aand cells. These patterns do change in a reversible way when the intensity of\\u000aan externally applied magnetic field is varied. The main objective of this\\u000acontribution is to present the results of a model that yields a rich pattern\\u000astructure

J. R. Iglesias; S. Goncalves; O. A. Nagel; Miguel Kiwi

2002-01-01

103

Quasi-two-dimensional acoustic metamaterials  

NASA Astrophysics Data System (ADS)

We report the design of quasi-two-dimensional artificial structures that acoustically behave as positive, single negative, double negative or density-near-zero metamaterials. The scattering units consist of a cavity drilled in one surface of a 2D waveguide and they have an inner structure whose geometrical parameters can be selected in order to obtain the desired dynamical behavior. Finally, we report the practical realization of two samples as well as their experimental characterization showing metamaterial features.

Torrent, D.; Graciá-Salgado, R.; García-Chocano, V. M.; Cervera, F.; Sánchez-Dehesa, J.

2014-02-01

104

Two-dimensional effects in conduit flows  

Microsoft Academic Search

As part of a code validation effort supporting the proposed Yucca Mountain Nuclear Waste Repository, we simulate two-dimensional flow of basaltic lava using a multi-fluid, multi-phase continuum fluid dynamics code CFDLib. As a starting point, we look at flow in a straight conduit of circular cross-section. This can be compared with the one-dimensional simulations reported in a companion paper [1

E. S. Gaffney; R. M. Rauenzahn

2003-01-01

105

Two dimensional fiber-optical accelerometer  

Microsoft Academic Search

A new type of simple and reliable two-dimensional fiber-optical accelerometer is developed to measure constant (dc) and variable (ac) accelerations simultaneously in two perpendicular directions (vector acceleration) with a linearity error of less than 0.1%. The sensor is based on a deflection of a uniform round elastic cantilever beam sensed by an optical lever and a continuous position optical sensor.

Petko D. Dinev

1996-01-01

106

Non-symmetrical two dimensional scattering program  

NASA Technical Reports Server (NTRS)

Computer program, 2DSCAT, solves integral equation for currents induced by electric or magnetic plane wave incident upon one or more conducting cylinders. Subroutine, FIELD, assumes that an incident wave is perpendicular to the cylindrical surface. Restrictions on this program are given.

Hatfield, J.; Rusch, W. V. T.

1971-01-01

107

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

Microsoft Academic Search

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.

Dimitrios Constantinou Kyritsis

1998-01-01

108

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

Microsoft Academic Search

Based on the rigorous generalized Mie theory solution of Maxwell's equations for dielectric cylinders we theoretically investigate the optical properties of two-dimensional deterministic structures based on the Fibonacci, Thue–Morse and Rudin–Shapiro aperiodic sequences. In particular, we investigate bandgap formation and mode localization properties in aperiodic photonic structures based on the accurate calculation of their local density of states (LDOS). In

Svetlana V. Boriskina; Ashwin Gopinath; Luca Dal Negro

2009-01-01

109

All-angle negative refraction imaging effect with complex two-dimensional hexagonal photonic crystals  

Microsoft Academic Search

A complex two-dimensional hexagonal photonic crystal consisting of silicon (Si) and silica (SiO2) cylinders embedded in the air background is proposed to achieve the effect of all-angle negative refraction imaging. Compared with normal hexagonal-lattice photonic crystals consisting of Si, the reduction of symmetry of the complex photonic crystal results in a large band gap between the second energy band and

Jian Li; Ming-Hui Lu; Tian Fan; Xiao-Kang Liu; Liang Feng; Yue-Feng Tang; Yan-Feng Chen

2007-01-01

110

Simulation of flow past a rotating circular cylinder near a plane wall  

Microsoft Academic Search

A two dimensional incompressible flow past a rotating circular cylinder near a plane wall at is investigated by using the lattice Boltzmann equation (LBE). The effects of the gap between the cylinder and the wall, and tangential speed of the cylinder on the frequency of vortex shedding, and the lift and drag forces on the cylinder are quantified together with

Ming Cheng; Qiang Yao; Li-Shi Luo

2006-01-01

111

Separation of Creeping Flow past Two Circular Cylinders  

Microsoft Academic Search

The steady two-dimensional Stokes flow past two circular cylinders of equal radii is considered, where the direction of the flow is parallel to the line joining the centers. Separation of the flow from the cylinders occurs if the parameter t{=}(distance between two cylinders)\\/(diameter of the cylinders) is less than 1.57. If t is less than 1.07 the twin eddies attached

Takeshi Miyazaki; Hidenori Hasimoto

1980-01-01

112

Two dimensional mixtures at water surface  

NASA Astrophysics Data System (ADS)

Thiol capped gold nanoparticles (Au NPs) form a simple two dimensional (2D) liquid on water surface but this thin film is unstable under compression. Amphiphilic stearic acid (StA) molecules on water surface, on the other hand, form a complex and more stable 2D liquid. We have initiated a study on a mixture of StA and Au NPs in a monolayer through Surface Pressure (?) - Specific Molecular Area (A) isotherms and Brewster Angle Microscopy (BAM). A mixture of Stearic Acid and Au nanoparticles (10% by weight) produces a monolayer on water surface that acts as a 2D liquid with phases that are completely reversible with negligible hysteresis.

Choudhuri, Madhumita; Datta, Alokmay

2013-02-01

113

Two-dimensional magnetic domain patterns  

NASA Astrophysics Data System (ADS)

Two-dimensional magnetic garnets exhibit complex and fascinating magnetic domain structures, like stripes, cells, mixed states of stripes and cells and labyrinths, which have challenged theorists for a long time. They change reversibly when the intensity of an externally applied magnetic field is varied. By Monte Carlo simulations we investigate the pattern formation and the thermodynamics of these systems as a function of the intensity of the external magnetic field. Our simulations yield patterns which are similar to the ones observed experimentally. The ordering transition temperature, relaxation energy and average domain size of each configuration are computed. General trends, as functions of the model parameters, are presented and discussed.

Kiwi, M.; Iglesias, J. R.; Goncalves, S.; Nagel, O.

2001-03-01

114

Two-dimensional heat flow apparatus  

NASA Astrophysics Data System (ADS)

We have created an apparatus to quantitatively measure two-dimensional heat flow in a metal plate using a grid of temperature sensors read by a microcontroller. Real-time temperature data are collected from the microcontroller by a computer for comparison with a computational model of the heat equation. The microcontroller-based sensor array allows previously unavailable levels of precision at very low cost, and the combination of measurement and modeling makes for an excellent apparatus for the advanced undergraduate laboratory course.

McDougall, Patrick; Ayars, Eric

2014-06-01

115

Morphology of two-dimensional fracture surfaces  

SciTech Connect

We consider the morphology of two-dimensional cracks observed in experimental results obtained from paper samples and compare these results with the numerical simulations of the random fuse model (RFM). We demonstrate that the data obey multiscaling at small scales but cross over to self-affine scaling at larger scales. Next, we show that the roughness exponent of the random fuse model is recovered by a simpler model that produces a connected crack, while a directed crack yields a different result, close to a random walk. We discuss the multiscaling behaviour of all these models.

Alava, Mikko [Helsinki University of Technology, Helsinki, Finland; Nukala, Phani K [ORNL; Zapperi, Stefano [University of La Sapienza, Rome

2006-10-01

116

Two-dimensional leaf orientation distributions  

NASA Technical Reports Server (NTRS)

Combined inclination/azimuth leaf angle distributions are important for accurate models of vegetation canopy reflectance. It is shown that appropriate mathematical representations can be constructed from beta distributions under most circumstances. This is illustrated by analyzing observational data on soybean leaves and balsam fir needles. There are some problems when the data is imprecise and when correlations between inclination and azimuth angle are induced by heliotropism. Otherwise, the two-dimensional beta-type distribution appears to be a versatile tool for describing complete inclination/azimuth leaf angle distributions.

Strebel, D. E.; Goel, N. S.; Ranson, K. J.

1985-01-01

117

A two-dimensional photon counting array  

NASA Astrophysics Data System (ADS)

A two-dimensional photon counting array in operation at Mount Stromlo is described and its performance discussed. The detector consists of a highly intensified Fairchild SL 62925 charge coupled device (CCD) where the spectral response of the system can be varied by the use of intensifiers which have different cathode types (S-20, S-25) as the first electron-emitting surface. The format of the external memory is 760 x 488 event-centered pixels. Prior frame subtraction is used to achieve counting rates of 5 Hz pixel with 3% coincidence correction. The advantages of photon-counting array systems over analog CCD detectors are discussed.

Stapinski, T. E.; Rodgers, A. W.; Ellis, M. J.

1981-04-01

118

Modeling two-dimensional magnetic domain patterns  

NASA Astrophysics Data System (ADS)

Two-dimensional magnetic garnets exhibit complex and fascinating magnetic domain structures, like stripes, labyrinths, cells, and mixed states of stripes and cells. These patterns do change in a reversible way when the intensity of an externally applied magnetic field is varied. The main objective of this contribution is to present the results of a model that yields a rich pattern structure that closely resembles what is observed experimentally. Our model is a generalized two-dimensional Ising-like spin-1 Hamiltonian with long-range interactions, which also incorporates anisotropy and Zeeman terms. The model is studied numerically by means of Monte Carlo simulations. Changing the model parameters, stripes, labyrinth, and/or cellular domain structures are generated. For a variety of cases we display the patterns and determine the average size of the domains, the ordering transition temperature, specific heat, magnetic susceptibility, and hysteresis cycle. Finally, we examine the reversibility of the pattern evolution under variations of the applied magnetic field. The results we obtain are in good qualitative agreement with experiment.

Iglesias, J. R.; Gonçalves, S.; Nagel, O. A.; Kiwi, Miguel

2002-02-01

119

Computation of Flow around 2-D (2-Dimensional) Circular Cylinder.  

National Technical Information Service (NTIS)

Incompressible flows around a two-dimensional circular cylinder were calculated by a finite difference method. Computations were performed in a wide range of Reynolds numbers. Using fine mesh, the varation of flow patterns corresponding to Reynolds number...

T. Ohta S. Shirayama K. Takeda K. Kuwahara

1986-01-01

120

Vortex shedding and three-dimensional behaviour of flow past a cylinder confined in a channel  

Microsoft Academic Search

A numerical investigation of the flow past a circular cylinder centred in a two-dimensional channel of varying width is presented. For low Reynolds numbers, the flow is steady. For higher Reynolds numbers, vortices begin to shed periodically from the cylinder. In general, the Strouhal frequency of the shedding vortices increases with blockage ratio. In addition, a two-dimensional instability of the

Martin D. Griffith; Justin Leontini; Mark C. Thompson; Kerry Hourigan

2011-01-01

121

Two-dimensional difference gel electrophoresis.  

PubMed

Two-dimensional difference gel electrophoresis (2D DIGE) is a modified form of 2D electrophoresis (2DE) that allows one to compare two or three protein samples simultaneously on the same gel. The proteins in each sample are covalently tagged with different color fluorescent dyes that are designed to have no effect on the relative migration of proteins during electrophoresis. Proteins that are common to the samples appear as "spots" with a fixed ratio of fluorescent signals, whereas proteins that differ between the samples have different fluorescence ratios. With the appropriate imaging system, difference gel electrophoresis (DIGE) is capable of reliably detecting as little as 0.2 fmol of protein, and protein differences down to ±15%, over a ?20,000-fold protein concentration range. DIGE combined with digital image analysis therefore greatly improves the statistical assessment of proteome variation. Here we describe a protocol for conducting DIGE experiments, which takes 2-3 days to complete. PMID:22585495

Minden, Jonathan S

2012-01-01

122

Two dimensional nanomaterials for flexible supercapacitors.  

PubMed

Flexible supercapacitors, as one of most promising emerging energy storage devices, are of great interest owing to their high power density with great mechanical compliance, making them very suitable as power back-ups for future stretchable electronics. Two-dimensional (2D) nanomaterials, including the quasi-2D graphene and inorganic graphene-like materials (IGMs), have been greatly explored to providing huge potential for the development of flexible supercapacitors with higher electrochemical performance. This review article is devoted to recent progresses in engineering 2D nanomaterials for flexible supercapacitors, which survey the evolution of electrode materials, recent developments in 2D nanomaterials and their hybrid nanostructures with regulated electrical properties, and the new planar configurations of flexible supercapacitors. Furthermore, a brief discussion on future directions, challenges and opportunities in this fascinating area is also provided. PMID:24614864

Peng, Xu; Peng, Lele; Wu, Changzheng; Xie, Yi

2014-05-21

123

Two-dimensional informative array testing.  

PubMed

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

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

2012-09-01

124

Rationally synthesized two-dimensional polymers.  

PubMed

Synthetic polymers exhibit diverse and useful properties and influence most aspects of modern life. Many polymerization methods provide linear or branched macromolecules, frequently with outstanding functional-group tolerance and molecular weight control. In contrast, extending polymerization strategies to two-dimensional periodic structures is in its infancy, and successful examples have emerged only recently through molecular framework, surface science and crystal engineering approaches. In this Review, we describe successful 2D polymerization strategies, as well as seminal research that inspired their development. These methods include the synthesis of 2D covalent organic frameworks as layered crystals and thin films, surface-mediated polymerization of polyfunctional monomers, and solid-state topochemical polymerizations. Early application targets of 2D polymers include gas separation and storage, optoelectronic devices and membranes, each of which might benefit from predictable long-range molecular organization inherent to this macromolecular architecture. PMID:23695626

Colson, John W; Dichtel, William R

2013-06-01

125

A two dimensional piezoeletric micro-positioner  

NASA Astrophysics Data System (ADS)

A scanning probe microscope can provide very high resolution imaging, but only within a small scanning area. There is a high demand for compact long range positioners, so that distant locations on the same sample can be imaged and studied. We will present information on the design and operation of a piezoelectric driven two-dimensional micropositioner that can provide long range motion in the x- and z-directions. The z-direction motion can be used for coarse approach, while the x-direction motion can be used to scan along the sample surface. The device is build as one single unit, so it is extremely compact and rigid, and can provide a high resonance frequency platform for high performance scanning probe microscopy.

Ng, K.-W.; Nichols, John; Brill, J. W.

2009-03-01

126

Two-dimensional fourier transform spectrometer  

DOEpatents

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.

DeFlores, Lauren; Tokmakoff, Andrei

2013-09-03

127

Methods of Two-Dimensional Spectroscopy  

NASA Astrophysics Data System (ADS)

One of the main fields of solar research is the study of dynamic processes of small-scale structures. For this purpose, time sequences of spectroscopic and polarimetric information in two spatial dimensions with best achievable quality are needed. The present contribution deals with the ways to obtain images in small wavelength bands. Among these are image scanners and the MSDP (Multi-Channel Subtractive Double Pass Spectrograph). Further potential instruments are scanning Fabry-Perot interferometers (FPI). The principles of such instruments are discussed. The results obtained hitherto from the FPI in the Vacuum Tower Telescope at the Observatorio del Teide are promising. Small-band, two-dimensional spectroscopy with spatial resolution close to the telescopic diffraction limit seems possible in the near future.

Kneer, F.

128

Two-dimensional structure of slow shocks  

NASA Technical Reports Server (NTRS)

The two-dimensional (2-D) structure of switch-off slow magnetosonic shocks is investigated using an electromagnetic hybrid (fluid electrons, kinetic ions) code. It is shown that the basic physical processes occurring at 1-D slow shocks are also operative in 2-D. Specifically, the interaction between the upstream ions and those streaming away from the shock results in the excitation of Alfven/ions-cyclotron (AIC) waves. Depending on the plasma parameters, these waves may either stay in the upstream or convect back into the shock resulting in a non-steady shock behavior which prevents the formation of a trailing wave train. Despite this similarity, some slow shocks which are steady in 1-D are found to be non-steady in 2-D. Fourier analysis of the waves downstream of non-steady shocks identifies them as AIC, demonstrating that the waves remain on the same branch as they convect from upstream into the downstream region.

Omidi, N.; Johnson, M.; Krauss-Varban, D.; Karimabadi, H.

1995-01-01

129

Rationally synthesized two-dimensional polymers  

NASA Astrophysics Data System (ADS)

Synthetic polymers exhibit diverse and useful properties and influence most aspects of modern life. Many polymerization methods provide linear or branched macromolecules, frequently with outstanding functional-group tolerance and molecular weight control. In contrast, extending polymerization strategies to two-dimensional periodic structures is in its infancy, and successful examples have emerged only recently through molecular framework, surface science and crystal engineering approaches. In this Review, we describe successful 2D polymerization strategies, as well as seminal research that inspired their development. These methods include the synthesis of 2D covalent organic frameworks as layered crystals and thin films, surface-mediated polymerization of polyfunctional monomers, and solid-state topochemical polymerizations. Early application targets of 2D polymers include gas separation and storage, optoelectronic devices and membranes, each of which might benefit from predictable long-range molecular organization inherent to this macromolecular architecture.

Colson, John W.; Dichtel, William R.

2013-06-01

130

Multiscale modeling of two-dimensional contacts.  

PubMed

A hybrid simulation method is introduced and used to study two-dimensional single-asperity and multi-asperity contacts both quasistatically and dynamically. The method combines an atomistic treatment of the interfacial region with a finite-element method description of subsurface deformations. The dynamics in the two regions are coupled through displacement boundary conditions applied at the outer edges of an overlap region. The two solutions are followed concurrently but with different time resolution. The method is benchmarked against full atomistic simulations. Accurate results are obtained for contact areas, pressures, and static and dynamic friction forces. The time saving depends on the fraction of the system treated atomistically and is already more than a factor of 20 for the relatively small systems considered here. PMID:17155215

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

2006-10-01

131

Two-dimensional Gel Electrophoresis (2DE)  

NASA Astrophysics Data System (ADS)

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

K?odzi?ska, Ewa; Buszewski, Bogus?aw

132

A low-field, low-cost Halbach magnet array for open-access NMR  

Microsoft Academic Search

A working prototype of a novel low-cost Halbach-array-based NMR system is described. The new design provides open access to the sample relative to conventional NMR magnet designs and this facilitates the simultaneous use of multi-sensor techniques on the same sample, in which NMR\\/MRI can potentially be combined with other spectroscopies such as impedance spectroscopy, laser scattering and rheological experiments.

B. P. Hills; K. M. Wright; D. G. Gillies

2005-01-01

133

Comparison of Halbach magnetized brushless motors equipped with air-cored and iron-cored rotors  

NASA Astrophysics Data System (ADS)

The performance of Halbach magnetized brushless motors equipped with air-cored and iron-cored rotors is investigated theoretically and experimentally. It is shown that an optimal combination of magnet thickness and pole number exists for maximum air-gap flux density. By employing a rotor back iron, the air-gap field and hence the output torque can be enhanced significantly if the ratio of the radial thickness of the magnet to the pole pitch is small.

Xia, Z. P.; Zhu, Z. Q.; Jewell, G. W.; Howe, D.

2003-05-01

134

Two-dimensional stability of ion-acoustic solitons  

Microsoft Academic Search

Two dimensional generalizations of the Korteweg-de Vries equation appropriate to the propagation of nonlinear ion-acoustic waves are obtained. Soliton solutions are found to exist and they are shown to be stable to two dimensional perturbations.

M. Kako; G. Rowlands

1976-01-01

135

New approach to observer design for two-dimensional systems  

Microsoft Academic Search

A new method of observer design for shift-invariant two-dimensional digital systems is presented. The method is applicable to a large class of two-dimensional systems and the condition of applicability is very simple to test.

ENGIN YAZ

1987-01-01

136

Implementations of two-dimensional liquid chromatography  

SciTech Connect

Today scientists must deal with complex samples that either cannot be adequately separated using one-dimensional chromatography or that require an inordinate amount of time for separation. For these cases we need two-dimensional chromatography because it takes far less time to generate a peak capacity n{sub c} twice in a row than to generate a peak capacity n{sub c}{sup 2} once. Liquid chromatography has been carried out successfully on thin layers of adsorbents and along tubes filled with various adsorbents. The first type of separation sorts out the sample components in a physical separation space that is the layer of packing material. The analysis time is the same for all the components of the sample while their migration distance increases with decreasing retention. The resolution between two components having a certain separation factor (a) increases with increasing migration distance, i.e., from the strongly to the weakly retained compounds. In the second type of separation, the sample components are eluted from the column and separated in the time space, their migration distances are all the same while their retention times increase from the unretained to the strongly retained compounds. Separation efficiency varies little with retention, as long as the components are eluted from the column. We call these two types of separation the chromatographic separations in space (LC{sup x}) and the chromatographic separations in time (LC{sup t}), respectively. In principle, there are four ways to combine these two modes and do two-dimensional chromatographic separations, LC{sup t} x LC{sup t}, LC{sup x} x LC{sup t}, LC{sup t} x LC{sup x}, and LC{sup x} x LC{sup x}. We review, discuss and compare the potential performance of these combinations, their advantages, drawbacks, problems, perspectives and results. Currently, column-based combinations (LC{sup t} x LC{sup t}) are the most actively pursued. We suggest that the combination LC{sup x} x LC{sup t} shows exceptional promise because it permits the simultaneous second-dimension separations of all the fractions separated in the first-dimension, thus providing remarkable time saving.

Guiochon, Georges A [ORNL; Marchetti, Nicola [University of Tennessee, Knoxville (UTK); Mriziq, Khaled S [ORNL; Shalliker, R. Andrew [University of Western Sydney, Australia

2008-01-01

137

Reproducibility of quantitative two-dimensional echocardiography.  

PubMed

In order to assess reproducibility of quantitative planimetry, three physicians trained in two-dimensional echocardiography performed five successive studies on one another over 2 weeks (30 total studies). Then each physician traced each study (90 total tracings) for left ventricular and atrial volumes and ejection fraction by means of a modification of Simpson's rule, and left ventricular mass and average wall thickness by means of a truncated ellipsoid formula. Calculation of intertechnician variability, intertracer variability, and 95% confidence limits showed that measurements of volumes were less reproducible than measurements of ejection fraction, average wall thickness, and mass. Mean intertracer variability of 15% exceeded mean intertechnician variability of 11%; this disparity was magnified in the subject who was technically difficult to image. Ninety-five percent confidence limits were: ejection fraction +/- 7%, average wall thickness +/- 9%, left ventricular mass +/- 12%, left ventricular end-diastolic volume +/- 11%, stroke volume +/- 14%, left ventricular end-systolic volume +/- 15%, and left atrial volume +/- 19%. Reproducible planimetry data can be obtained in normal hearts with the use of a protocol for quantitative imaging and planimetry. PMID:3341178

Himelman, R B; Cassidy, M M; Landzberg, J S; Schiller, N B

1988-02-01

138

Two-dimensional rare gas solids.  

PubMed

Monolayers of rare gas atoms adsorbed onto the basal planes of graphite play the same prototype role in two dimensions that rare gas liquids and solids do in three dimensions. In recent experiments such novel phenomena as continuous melting, the lack of true crystallinity in two dimensions, orientationally ordered fluid phases, and melting from a solid to a reentrant fluid with decreasing temperature have been observed. Because the forces in these rare gas monolayers are simple and well understood, by studying them the investigator can examine a direct interface between experiment and first principles. In order to understand the phases and phase transitions that occur in such materials, it is necessary to consider the geometrical matching of the rare gas overlayer to the graphite substrate. It turns out that in two dimensions both the local and the long-distance behavior are important. These two-dimensional rare gas solids may be effectively probed with synchrotron x-ray techniques, and the results of a series of synchrotron x-ray scattering studies of these solids are presented. PMID:17792141

Birgeneau, R J; Horn, P M

1986-04-18

139

Plastic flow in two-dimensional solids.  

PubMed

A time-dependent Ginzburg-Landau model of plastic deformation in two-dimensional solids is presented. The fundamental dynamic variables are the displacement field u and the lattice velocity v=delta(u)/delta(t). Damping is assumed to arise from the shear viscosity in the momentum equation. The elastic energy density is a periodic function of the shear and tetragonal strains, which enables the formation of slips at large strains. In this work we neglect defects such as vacancies, interstitials, or grain boundaries. The simplest slip consists of two edge dislocations with opposite Burgers vectors. The formation energy of a slip is minimized if its orientation is parallel or perpendicular to the flow in simple shear deformation and if it makes angles of +/-pi/4 with respect to the stretched direction in uniaxial stretching. High-density dislocations produced in plastic flow do not disappear even if the flow is stopped. Thus large applied strains give rise to structurally disordered states, which are metastable due to the Peierls potential. We divide the elastic energy into an elastic part due to affine deformation and a defect part. The latter represents degree of disorder and is nearly constant in plastic flow under cyclic straining. PMID:14754207

Onuki, Akira

2003-12-01

140

Fluctuoscopy of Disordered Two-Dimensional Superconductors  

NASA Astrophysics Data System (ADS)

In this talk I will present our results for the fluctuation conductivity (FC) in disordered two-dimensional superconductors placed in a perpendicular magnetic field. In our works [1,2] we finally derived the complete solution in the temperature-magnetic field phase diagram. The obtained expressions allow both to perform straightforward (numerical) calculation of the FC surface ??(T,H) and to get all 27 asymptotic expressions in the seven qualitatively different domains of the phase diagram. This surface becomes in particular non-trivial at low temperatures, where it is trough-shaped and close to the quantum phase transition non-monotonic, in agreement with experimental findings. I will show our main results and demonstrate how these can be used as a high precision tool (fluctuoscope) to determine the critical temperature, critical magnetic field, and dephasing time from experimental data in superconducting films. [4pt] [1] A. Glatz, A. A. Varlamov, and V. M. Vinokur, EuroPhys. Lett. 94, 47005 (2011).[0pt] [2] A. Glatz, A. A. Varlamov, and V. M. Vinokur, Phys. Rev. B 84, 104510 (2011).

Glatz, Andreas; Varlamov, Andrey; Vinokur, Valerii

2012-02-01

141

Extensivity of two-dimensional turbulence  

NASA Astrophysics Data System (ADS)

This study is concerned with how the attractor dimension of the two-dimensional Navier-Stokes equations depends on characteristic length scales, including the system integral length scale, the forcing length scale, and the dissipation length scale. Upper bounds on the attractor dimension derived by Constantin, Foias and Temam are analysed. It is shown that the optimal attractor-dimension estimate grows linearly with the domain area (suggestive of extensive chaos), for a sufficiently large domain, if the kinematic viscosity and the amplitude and length scale of the forcing are held fixed. For sufficiently small domain area, a slightly “super-extensive” estimate becomes optimal. In the extensive regime, the attractor-dimension estimate is given by the ratio of the domain area to the square of the dissipation length scale defined, on physical grounds, in terms of the average rate of shear. This dissipation length scale (which is not necessarily the scale at which the energy or enstrophy dissipation takes place) can be identified with the dimension correlation length scale, the square of which is interpreted, according to the concept of extensive chaos, as the area of a subsystem with one degree of freedom. Furthermore, these length scales can be identified with a “minimum length scale” of the flow, which is rigorously deduced from the concept of determining nodes.

Tran, Chuong V.; Shepherd, Theodore G.; Cho, Han-Ru

2004-06-01

142

Turbulent equipartitions in two dimensional drift convection  

SciTech Connect

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

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

1995-07-25

143

Two-dimensional flow magnetophoresis of microparticles.  

PubMed

A new two-dimensional micro-flow magnetophoresis device was constructed in a superconducting magnet (10 T) using triangular shaped pole pieces, which could apply a magnetic strength, B(dB/dx), in the range of ca. 0-14,000 T(2) m(-1) across a capillary cell. Polystyrene particles with diameters of 1, 3, and 6 ?m were used as test samples in a paramagnetic medium of 1 M MnCl(2) to evaluate the performance of this method. Microparticles migrated across the capillary along the edge of the pole pieces, and then flowed through the gap in the pole piece at a position defined as the migration distance, depending on the magnetic susceptibility and the size of particles as well as the flow rate. The most effective flow rate to exhibit the largest resolution among the particles was theoretically predicted and experimentally confirmed. By this method, the magnetic susceptibilities of individual deoxygenated and non-deoxygenated red blood cells were measured from the relative migration distance. PMID:22618326

Kawano, Makoto; Watarai, Hitoshi

2012-07-01

144

Compact Two-Dimensional Spectrometer Optics  

NASA Technical Reports Server (NTRS)

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

Hong, John

2008-01-01

145

Dynamics of two-dimensional dipole systems  

SciTech Connect

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.

Golden, Kenneth I.; Kalman, Gabor J.; Hartmann, Peter; Donko, Zoltan [Department of Mathematics and Statistics, Department of Physics, University of Vermont, Burlington, Vermont 05401 (United States); Department of Physics, Boston College, Chestnut Hill, Massachusetts 02467 (United States); Research Institute for Solid State Physics and Optics, Hungarian Academy of Sciences, P.O. Box 49, H-1525 Budapest, Hungary and Department of Physics, Boston College, Chestnut Hill, Massachusetts 02467 (United States)

2010-09-15

146

Burgers approximation for two-dimensional flow past an ellipse  

NASA Technical Reports Server (NTRS)

A motivation is given for studying Burgers flow and a solution technique is outlined which works equally well for Oseen or Burgers flow past a circular cylinder. The separation behind the cylinder, the drag experienced by the cylinder, and asymptotic behavior far from the cylinder are described. It is shown that the predictions of Burgers flow near the cylinder provide a substantial improvement over those of Oseen flow. Finally, the equations of motion for Burgers flow past an ellipse are formulated and solved.

Dorrepaal, J. M.

1982-01-01

147

Electromagnetic scattering by a dielectric cylinder partially covered by conductors  

Microsoft Academic Search

Two-dimensional electromagnetic scattering by a dielectric cylinder partially covered by zero-thickness perfect conductors is studied. The impressed field is either transverse magnetic (TM) or transverse electric (TE) to the cylinder axis. The problem is formulated in terms of two coupled boundary integral equations in each case. For the TM case the unknowns are equivalent electric currents, and for the TE

Xingchao Yuan; Roger F. Harrington; Sang-Seol Lee

1988-01-01

148

A numerical method for calculating steady flow past a cylinder  

Microsoft Academic Search

An asymptotic method is described for calculating the far flow field resulting from the steady two-dimensional incompressible viscous flow past a cylinder. The flow field is divided into an inner and outer region by a contour C surrounding the cylinder at large enough distance from it. The full elliptic Navier-Stokes equations are solved in the inner region by standard methods.

S. C. R. Dennis

1976-01-01

149

Adaptive two-dimensional microgas chromatography.  

PubMed

We proposed and investigated a novel adaptive two-dimensional (2-D) microgas chromatography system, which consists of one 1st-dimensional column, multiple parallel 2nd-dimensional columns, and a decision-making module. The decision-making module, installed between the 1st- and 2nd-dimensional columns, normally comprises an on-column nondestructive vapor detector, a flow routing system, and a computer that monitors the detection signal from the detector and sends out the trigger signal to the flow routing system. During the operation, effluents from the 1st-dimensional column are first detected by the detector and, then, depending on the signal generated by the detector, routed to one of the 2nd-dimensional columns sequentially for further separation. As compared to conventional 2-D GC systems, the proposed adaptive GC scheme has a number of unique and advantageous features. First and foremost, the multiple parallel columns are independent of each other. Therefore, their length, stationary phase, flow rate, and temperature can be optimized for best separation and maximal versatility. In addition, the adaptive GC significantly lowers the thermal modulator modulation frequency and hence power consumption. Finally, it greatly simplifies the postdata analysis process required to reconstruct the 2-D chromatogram. In this paper, the underlying working principle and data analysis of the adaptive GC was first discussed. Then, separation of a mixture of 20 analytes with various volatilities and polarities was demonstrated using an adaptive GC system with a single 2nd-dimensional column. Finally, an adaptive GC system with dual 2nd-dimensional columns was employed, in conjunction with temperature ramping, in a practical application to separate a mixture of plant emitted volatile organic compounds with significantly shortened analysis time. PMID:22468727

Liu, Jing; Khaing Oo, Maung Kyaw; Reddy, Karthik; Gianchandani, Yogesh B; Schultz, Jack C; Appel, Heidi M; Fan, Xudong

2012-05-01

150

Ultrafast two dimensional infrared chemical exchange spectroscopy  

NASA Astrophysics Data System (ADS)

The method of ultrafast two dimensional infrared (2D IR) vibrational echo spectroscopy is described. Three ultrashort IR pulses tuned to the frequencies of the vibrational transitions of interest are directed into the sample. The interaction of these pulses with the molecular vibrational oscillators produces a polarization that gives rise to a fourth pulse, the vibrational echo. The vibrational echo pulse is combined with another pulse, the local oscillator, for heterodyne detection of the signal. For fixed time between the second and third pulses, the waiting time, the first pulse is scanned. Two Fourier transforms of the data yield a 2D IR spectrum. The waiting time is increased, and another spectrum is obtained. The change in the 2D IR spectra with increased waiting time provides information on the time evolution of the structure of the molecular system under observation. In a 2D IR chemical exchange experiment, two species A and B, are undergoing chemical exchange. A's are turning into B's, and B's are turning into A's, but the overall concentrations of the species are not changing. The kinetics of the chemical exchange on the ground electronic state under thermal equilibrium conditions can be obtained 2D IR spectroscopy. A vibration that has a different frequency for the two species is monitored. At very short time, there will be two peaks on the diagonal of the 2D IR spectrum, one for A and one for B. As the waiting time is increased, chemical exchange causes off-diagonal peaks to grow in. The time dependence of the growth of these off-diagonal peaks gives the chemical exchange rate. The method is applied to organic solute-solvent complex formation, orientational isomerization about a carbon-carbon single bond, migration of a hydrogen bond from one position on a molecule to another, protein structural substate interconversion, and water hydrogen bond switching between ions and water molecules.

Fayer, Michael

2011-03-01

151

Two-dimensional gel isoelectric focusing.  

PubMed

Two-dimensional gel isoelectric focusing (2-D gel IEF) is presented as the combination of the same separation method used consecutively in two directions of the same gel. In this new method, after completion of IEF process in the first dimension the gel was cut into the separate strips, each containing selected analytes together with the appropriate part of the original broad pH gradient, and the strips were rotated by 90 degrees (with regard to the first IEF) and left to diffuse overnight. After diffusion the strips were subjected to the second IEF. During the second IEF, the corresponding narrow part of pH gradient in each strip was restored again, however, now along the strip. The progress of the separation process can be monitored visually by using colored low-molecular-weight isoelectric point (pI) markers loaded into the gel simultaneously with proteins. The unique properties of IEF, focusing and resolution power were enhanced by using the same technique twice. Two forms of beta-lactoglobulin (pI values 5.14 and 5.31, respectively) non-separated in the first IEF were successfully separated in the second dimension at relatively low voltage (330 V) with the resolution power comparable to the high-resolution gels requiring the high voltage during the run and long separation time. Glucose oxidase loaded as diluted solution into ten positions across the gel was finally focused into a single band during 2-D gel IEF. Since the first and second IEF are carried out on the same gel, no losses and contamination of analyte occur. The suggested method can be used for separation/fractionation of complex biological mixtures, similarly as other multidimensional separation techniques applied in proteomics, and can be followed by further processing, e.g., mass spectrometry analysis. The focusing properties of IEF could be useful especially in separation of mixtures, where components are at low concentration levels. PMID:16100746

Stastná, Miroslava; Slais, Karel

2005-09-01

152

Two-dimensional Full Waveform Inversion  

NASA Astrophysics Data System (ADS)

A two-dimensional full wavefield inversion for direct imaging of compressional wave and out-of-plane standing wave (SH) velocity distribution is developed, tested and implemented. The inversion is base on the finite difference solution of the full two-dimension scalar wave equation in the time-distance domain and operates on wide-aperture, common-shot data. The computational kernel fully utilizes the reverse-time image reconstruction principles. No travel-time picking and phase identification are required for full waveform inversion. For each shot records, gradients of misfit function (Frechét derivative) are dynamically determined by cross-correlation of the recorded forward propagating wavefield and backward propagating residual wavefield at each time step. Convergence to local minima can be avoided by gradually increasing the wavenumber bandwidth in the estimated velocity distribution and to increase the inversion resolution as iterations proceed. Synthetic examples show that the effects of the multiples, scattering, artificial boundary reflection waves, or noise do not contaminate the final results and convergences successfully to the correct solution. Using full two-way waveform approach for seismic imaging simplifies un-necessary skeleton seismic processing procedures. Furthermore, the resolution of inversion result is limited by the bandwidth of field recordings, source wavelet and dominant frequency. Convergence rate and stability of our in-house development of inversion algorithm is highly depends on step length and the complexity of subsurface structure associate with the steepest decent direction. For land data, near-surface effects including topography, lateral velocity variation, source and receiver static corrections are automatically included. For marine seismic data, multiples generated by water layer can be effectively suppressed through wavefield based seismic processing approach.

Li, K.; Chen, H.

2005-12-01

153

Magnetohydrodynamic flow past a circular cylinder  

Microsoft Academic Search

Summary The steady, two-dimensional incompressible MHD flow past a circular cylinder with an applied magnetic field parallel to the main flow is calculated using the method of series truncation. The differential equations are solved analytically and the Oseen approximation is made. The magnetic Reynolds number is assumed to be small. The results show that with an applied magnetic field the

J. S. Bramley

1974-01-01

154

Drag Reduction on a Circular Cylinder using Spatially Distributed Forcing  

Microsoft Academic Search

This work investigates the use of spatially-distributed open-loop forcing for control of vortex shedding from a circular cylinder. Force-shaped plasma actuators were used to control the flow, with the aim of reducing drag on the circular cylinder at a Reynolds number of 6500. Traditional approaches to cylinder drag reduction have typically involved two-dimensional forcing of the flow field using blowing

James W. Gregory; Christopher O. Porter; Daniel M. Sherman; Thomas E. McLaughlin

2007-01-01

155

Electro-optical modulation in two-dimensional photonic crystal linear waveguides  

NASA Astrophysics Data System (ADS)

The electro-optical modulation in a two-dimensional photonic crystal linear waveguide is presented. In order to create a linear waveguide, the radius of a line of rods is reduced. The linear waveguide composed of a dielectric cylinder in air is studied by solving Maxwell's equations using the plane wave expansion method and the finite-difference time-domain method. The switching mechanism is a change in the conductance in the waveguide region and hence modulating the guided modes and eventually switching is achieved. Such a mechanism of modulation should open up a new application for designing tunable components in photonic integrated circuits.

Liu, Cheng-Yang

2012-09-01

156

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

NASA Astrophysics Data System (ADS)

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

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

2009-05-01

157

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

NASA Astrophysics Data System (ADS)

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.

Kyritsis, Dimitrios Constantinou

158

Applying assist features to improve two dimensional feature process robustness  

NASA Astrophysics Data System (ADS)

Sub-resolution assist features are an important tool for improving process robustness for one-dimensional pattern features at advanced manufacturing process nodes. However, sub-resolution assist feature development efforts have not generally considered optimization for process robustness with two-dimensional pattern features. This generally arises both from conservatively placing SRAFs to avoid the possibility of imaging, and from a desire to simplify SRAF placement rules. By studying two-dimensional features using a manufacturing sensitivity model, one can gain insight into the capabilities of SRAFs regarding two-dimensional pattern features. These insights suggest new methodologies for shaping assist features to enhance two-dimensional feature robustness. In addition, a manufacturing sensitivity model form can be employed to optimize the placement of multiple competing SRAFs in localized two-dimensional regions. Initial studies demonstrate significant pullback reduction for two-dimensional features once SRAF placement has been optimized using the manufacturing sensitivity model form.

Melvin, Lawrence S., III; Painter, Benjamin D.; Barnes, Levi D.

2005-11-01

159

Approximation Properties of Two-Dimensional Continued Fractions  

Microsoft Academic Search

By using the difference formula for approximations of two-dimensional continued fractions, the method of fundamental inequalities, the Stieltjes–Vitali theorem, and generalizations of divided and inverse differences, we estimate the accuracy of approximations of two-dimensional continued fractions with complex elements by their convergents and obtain estimates for the real and imaginary parts of remainders of two-dimensional continued fractions. We also prove

Kh. I. Kuchmins'ka; S. M. Vozna

2003-01-01

160

Stability and synthesis of two-dimensional recursive filters  

Microsoft Academic Search

Two-dimensional recursive filters are conveniently described in terms of two-dimensional z transforms. The designer of these filters faces two fundamental problems, their stability and their synthesis. Stability is determined by the location of the zero-valued region of the filter's denominator polynomial. A conjecture based on a one-dimensional stability theorem leads to a useful empirical stabilization procedure. Two-dimensional recursive filters can

JOHN L. SHANKS; SVEN TREITEL; JAMES H. JUSTICE

1972-01-01

161

Two-Dimensional Chirped-Pulse Fourier Transform Microwave Spectroscopy: Introduction to Two-Dimensional Broadband Techniques  

Microsoft Academic Search

There is a gap in the electromagnetic spectrum where the microwave region is located when considering broadband two-dimensional spectroscopy. We introduce two-dimensional chirped-pulse Fourier transform microwave (CP-FTMW) spectroscopy as a way to directly identify coherences between coupled rotational levels. The theory and application of these experiments is a direct extension of traditional two-dimensional NMR techniques. Several different pulse sequences will

Amanda J. Shirar; Kelly M. Hotopp; David S. Wilcox; Brian C. Dian

2010-01-01

162

Steady thermal stress analysis in two-dimensional problems by thermoelastic displacement potential and boundary-element method  

SciTech Connect

A new numerical method to analyze steady thermal stresses in two-dimensional problems is proposed. Thermoelastic displacement potential is introduced for the analysis. The discontinuities of stresses on the boundary are investigated, and a completely analytic formulation is carried out. In order to investigate the accuracy of this method, steady thermal stress distributions in a square column and a circular cylinder with an eccentric circular hole are obtained.

Ochiai, Y.; Ishida, R.; Sekiya, T. (Osaka Prefectural Industrial Technology Research Institute (Japan) Osaka Prefecture Univ., Sakai (Japan) Osaka Electro-Communication University, Neyagawa (Japan))

1990-01-01

163

The use of a linear Halbach array combined with a step-SPLITT channel for continuous sorting of magnetic species  

Microsoft Academic Search

The Quadrupole Magnetic Sorter (QMS), employing an annular flow channel concentric with the aperture of a quadrupole magnet, is well established for cell and particle separations. Here we propose a magnetic particle separator comprising a linear array of cylindrical magnets, analogous to the array proposed by Klaus Halbach, mated to a substantially improved form of a parallel plate SPLITT channel,

Mauricio Hoyos; Lee Moore; P. Stephen Williams; Maciej Zborowski

2011-01-01

164

Partition function zeros for the two-dimensional Ising model  

Microsoft Academic Search

The distribution of complex temperature zeros of the partition function of the two-dimensional Ising model in the absence of a magnetic field is investigated. For anisotropic square and triangular lattices the distribution function is two-dimensional and satisfies a partial differential equation derived from a generalized scaling theory. Corresponding results for the isotropic square, triangular and honeycomb lattices are also presented.

John Stephenson; Rodney Couzens

1984-01-01

165

New two-dimensional quantum models with shape invariance  

SciTech Connect

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.

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

2011-02-15

166

MOHR: Two-Dimensional Stress Calculation and Display.  

National Technical Information Service (NTIS)

MOHR accepts the values of stress on a two-dimensional element and draws Mohr's Circle for the two-dimensional stress problem. After drawing Mohr's Circle, the user can display the principal stress element, the maximum shear stress element, and an element...

R. S. Hickman

1985-01-01

167

Confined modes in dual-state two-dimensional waveguides.  

PubMed

We consider the confined modes in dual-state two-dimensional waveguides in which each slab segment of waveguides can support two vertically confined modes with different effective indices. A matrix formulation is developed to extend the conventional effective-index method to investigate the two-dimensional confinement in multistate waveguides. The results are presented and discussed. PMID:19829532

Gu, C; Yeh, P; Botez, D

1994-01-01

168

Microscale simulation of bimolecular reaction in two dimensional porous media  

NASA Astrophysics Data System (ADS)

Reactive transport in porous media is typically modeled approximating key processes occurring at the pore-scale through a set of continuum- (or Darcy-) scale partial differential equations, the advection dispersion reaction equation (ADRE) being a widely used model. Such formulations hold under a set of assumptions which are not always met in the context of laboratory and/or field scale applications. These hypotheses involve spatial scale separation and restrictions on the magnitude of dimensionless parameters, such as the Damköhler and the Péclet numbers, characterizing the process. In this context, direct measurements and micro-scale numerical simulations are key to (1) assess the validity of upscaled continuum formulations, and (2) quantify the ability of such models to capture the key features of the process dynamics. Here, we focus on the simulation of a homogeneous irreversible bimolecular reaction of the kind A + B ? C. We analyze the evolution of the process in the presence of different pore scale geometrical settings, upon performing numerical pore-scale simulations in ordered and disordered two dimensional arrays of cylinders. The selected pore scale geometries are characterized by different porosities and by the presence of large cavities and regions with different relative importance of diffusive and advective processes. A particle tracking methodology is employed to study the system dynamics and simulations are performed for a wide range of the Péclet and Damköhler numbers. The evolution of the features of the reactive transport process is analyzed on different observation scales. Our results show that the reactive transport process attains an asymptotic regime for which the reaction is limited by (effective) dispersion. The influence of the pore scale geometry on the asymptotic and pre-asymptotic behavior of the reaction rate globally observed in the domain is quantitatively analyzed. Local mixing features and related characteristic scales are also discussed. In particular, the influence of local velocity distributions and medium geometrical setting on the reaction process is documented. These results provide a framework to discuss the appropriateness of continuum scale formulations which can be employed to describe the target geochemical system. The impact of Péclet and Damköhler numbers and of the pore space geometry on the characterization of the parameters introduced in continuum scale formulations of the system is discussed. Recently an alternative continuum formulation of the system has been provided on the basis of a volume averaging analysis of the reactive transport process analyzed. Here the validity of this formulation is discussed, in comparison with the standard ADRE formulation. We assess (i) the influence of the reactive process on the (upscaled) hydrodynamic dispersion coefficient and (ii) the ability of the continuum modeling strategies considered to represent the effect of pore scale incomplete mixing processes.

Porta, G.; Chaynikov, S.; Thovert, J.; Riva, M.; Guadagnini, A.; Adler, P. M.

2012-12-01

169

Two-dimensional Minkowski causal automorphisms and conformal maps  

NASA Astrophysics Data System (ADS)

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.

Burgos, Juan Manuel

2013-02-01

170

Third sound in one and two dimensional modulated structures  

SciTech Connect

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.

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

1996-02-01

171

Front tracking and two dimensional Riemann problems: a conference report  

SciTech Connect

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

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

1984-01-01

172

Rotating cylinder block piston-cylinder engine  

Microsoft Academic Search

A rotating cylinder block piston-cylinder engine is described comprising: a stator means; a hollow rotor housing rotatably mounted on the stator means for rotation around a rotor housing axis of rotation; a plurality of cylinders radially positioned in the peripheral wall of the hollow rotor housing; a piston slidable in each of the cylinders and having a piston rod rigidly

Newbold

1989-01-01

173

Compound Semiconductor Based Two-Dimensional Photonic Crystal Light Sources.  

National Technical Information Service (NTIS)

Two-dimensional photonic crystals (PC) have emerged as promising building blocks for integrated optics systems. Photonic crystal devices exploit defects, in an otherwise periodic lattice designed to exhibit a wide photonic bandgap (PBG), to form resonant ...

P. Bhattacharya

2004-01-01

174

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...

175

Two-Dimensional Grain Growth as Simulated by Surface Evolver.  

National Technical Information Service (NTIS)

The Surface Evolver program, which is an interactive program for the study of surfaces shaped by surface tension and other energies, has been evaluated for simulation of two-dimensional grain growth. Examples have demonstrated that the grain structure evo...

K. Marthinsen

1994-01-01

176

Unwrapping Two-Dimensional Phase Data in Contour Maps.  

National Technical Information Service (NTIS)

A computer algorithm has been discovered for unwrapping two-dimensional Phase data and producing perfect contour maps without holes or dark bands of erroneous contour lines. The method employs local, temporary unwrapping within single grid squares of rect...

W. H. Carter

1992-01-01

177

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

ERIC Educational Resources Information Center

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)

Edge, R. D.

1989-01-01

178

Pseudospectral solution of two-dimensional gas-dynamic problems  

NASA Technical Reports Server (NTRS)

Chebyshev pseudospectral methods are used to compute two dimensional smooth compressible flows. Grid refinement tests show that spectral accuracy can be obtained. Filtering is not needed if resolution is sufficiently high and if boundary conditions are carefully prescribed.

Kopriva, D. A.; Zang, T. A.; Salas, M. D.; Hussaini, M. Y.

1983-01-01

179

Two-Dimensional Photochemical Model of the Troposphere.  

National Technical Information Service (NTIS)

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 ...

M. W. Carlson

1990-01-01

180

Two-dimensional dispersion module for the TOUGH2 simulator.  

National Technical Information Service (NTIS)

A standard model for hydrodynamic dispersion has been added to TOUGH2- The dispersion model, intended for use with the EOS7 fluid properties module, accounts for the effects of hydrodynamic dispersion and molecular diffusion in two-dimensional rectangular...

C. M. Oldenburg K. Pruess

1993-01-01

181

Two-Dimensional Markov Chains with Geometric Jumps.  

National Technical Information Service (NTIS)

Several queuing problems lead to Markov chains with jumps of unbounded length, particularly with geometric behavior in one or more directions. In the present paper the equilibrium behavior is analyzed for two-dimensional nearest neighbor random walks, whi...

I. J. B. F. Adan J. W. C. H. Visschers J. Wessels

1999-01-01

182

Asymmetrical two-dimensional magnetic lattices for ultracold atoms  

Microsoft Academic Search

A simple method for implementing an asymmetrical two-dimensional magnetic lattice is proposed. The asymmetrical two-dimensional magnetic lattice is created by periodically distributing nonzero magnetic minima across the surface of a magnetic thin film, where the magnetic patterns are formed by milling n×n square holes on the surface of the film. The method is proposed for trapping and confining quantum degenerate

Ahmed Abdelrahman; Mikhail Vasiliev; Kamal Alameh; Peter Hannaford

2010-01-01

183

Monte Carlo simulation of a two-dimensional magnetic foam  

Microsoft Academic Search

A two-dimensional Ising-like model with spin 1 and long-range interactions is studied numerically through a Monte Carlo simulation. The goal of the simulation is to describe pattern formations and critical temperature of two-dimensional magnetic structures. Three sets of parameters are considered, that give rise to stripes, labyrinths or cellular domain structures. We determine for each configuration the transition ordering temperatures,

J. R. Iglesias; O. A. Nagel; S. Gonçalves; M. Kiwi

2001-01-01

184

Monte Carlo simulation of a two-dimensional magnetic foam  

NASA Astrophysics Data System (ADS)

A two-dimensional Ising-like model with spin 1 and long-range interactions is studied numerically through a Monte Carlo simulation. The goal of the simulation is to describe pattern formations and critical temperature of two-dimensional magnetic structures. Three sets of parameters are considered, that give rise to stripes, labyrinths or cellular domain structures. We determine for each configuration the transition ordering temperatures, the relaxation of the energy, the hysteresis cycle, and the average size of the domains.

Iglesias, J. R.; Nagel, O. A.; Gonçalves, S.; Kiwi, M.

2001-05-01

185

Ground ring of two-dimensional string theory  

Microsoft Academic Search

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

Edward Witten

1992-01-01

186

Two-dimensional QCD as a string theory  

Microsoft Academic Search

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

David J. Gross

1993-01-01

187

Beginning Introductory Physics with Two-Dimensional Motion  

NASA Astrophysics Data System (ADS)

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

Huggins, Elisha

2009-04-01

188

Two-dimensional quasicrystal with eightfold rotational symmetry  

Microsoft Academic Search

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

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

1987-01-01

189

Dipolar interaction between two-dimensional magnetic particles  

Microsoft Academic Search

We determine the effective dipolar interaction between single domain two-dimensional ferromagnetic particles (islands or dots), taking into account their finite size. The first correction term decays as 1\\/D5, where D is the distance between particles. If the particles are arranged in a regular two-dimensional array and are magnetized in plane, we show that the correction term reinforces the antiferromagnetic character

Paolo Politi; Maria Gloria Pini

2002-01-01

190

Two-dimensional thermomechanical analysis of continuous casting process  

Microsoft Academic Search

In this work the two-dimensional analysis of continuous casting of low carbon steel was presented. The interaction between moved ingot, copper mould and transport rolls was modeling. The influence of liquid steel ferrostatic pressure and coupled between temperature and deformation fields were taken into consideration.For thermal analysis (with phase change), the two-dimensional unsteady-state heat conduction equation with enthalpy convention was

M. Janik; H. Dyja; S. Berski; G. Banaszek

2004-01-01

191

Three superintegrable two-dimensional oscillators: Superintegrability, nonlinearity, and curvature  

SciTech Connect

The superintegrability of three different two-dimensional oscillators is studied: (i) a nonlinear oscillator dependent on a parameter {lambda} (two-dimensional version of the oscillator of Lakshmanan and Mathews), (ii) a nonlinear oscillator related to the Riccati equation, and (iii) the standard harmonic oscillator on constant curvature spaces. They can be considered as nonlinear deformations, or curvature-dependent versions, of the linear harmonic oscillator.

Carinena, J. F., E-mail: jfc@unizar.es; Ranada, M. F. [Universidad de Zaragoza, Departamento de Fisica Teorica, Facultad de Ciencias (Spain)], E-mail: mfran@unizar.es; Santander, M. [Universidad de Valladolid, Departamento de Fisica Teorica, Facultad de Ciencias (Spain)], E-mail: msn@fta.uva.es

2007-03-15

192

Fidelity susceptibility in two-dimensional spin-orbit models  

Microsoft Academic Search

We study the quantum phase transitions in the two-dimensional spin-orbit models in terms of fidelity susceptibility and reduced fidelity susceptibility. An order-to-order phase transition is identified by fidelity susceptibility in the two-dimensional Heisenberg XXZ model with Dzyaloshinsky-Moriya interaction on a square lattice. The finite size scaling of fidelity susceptibility shows a power-law divergence at criticality, which indicates the quantum phase

Wen-Long You; Yu-Li Dong

2011-01-01

193

Two-dimensional retiming with low memory requirements  

Microsoft Academic Search

This paper considers throughput and memory requirements in architectures which operate on two-dimensional (2D) digital signals. We present a novel technique for retiming a 2D data-flow graph to meet a given throughput constraint while keeping the memory required by the architecture low. This technique, which we call orthogonal two-dimensional retiming, is posed as two linear programming problems which can be

T. C. Denk; Mayukh Majumdar; Keshab K. Parhi

1996-01-01

194

Two-Dimensional Signal Processing in Radon Space  

Microsoft Academic Search

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

Roger Lee Easton Jr.

1986-01-01

195

Two-dimensional mirror symmetry from M-theory  

Microsoft Academic Search

We construct two-dimensional gauge theories with N = (4,4) supersymmetry from branes of type IIA string theory. Quantum effects in the two-dimensional gauge theory are analyzed by embedding the IIA brane construction into M-theory. We find that the Coulomb branch of one theory and the Higgs branch of a mirror theory become equivalent at strong coupling. A relationship to the

John H. Brodie

1998-01-01

196

Two-dimensional mirror symmetry from M-theory  

Microsoft Academic Search

We construct two-dimensional gauge theories with N= (4,4) supersymmetry from branes of type IIA string theory. Quantum effects in the two-dimensional gauge theory are analyzed by embedding the IIA brane construction into M-theory. We find that the Coulomb branch of one theory and the Higgs branch of a mirror theory become equivalent at strong coupling. A relationship to the decoupling

John H. Brodie

1998-01-01

197

Symmetrical perturbation analysis of complex two-dimensional photonic crystals  

Microsoft Academic Search

We study complex photonic crystals with unit cells that include different dielectric cylinders. A symmetrical perturbation approach is developed here which predicts how the band spectrum of the complex structures evolves from the most symmetrical prophase. As a specific example, we apply this symmetrical approach to the analysis of square lattices with alternating layers of dielectric cylinders perpendicular to one

N. Malkova; S. Kim; V. Gopalan

2002-01-01

198

Two-dimensional ionization chamber arrays for IMRT plan verification  

SciTech Connect

In this paper we describe a concept for dosimetric treatment plan verification using two-dimensional ionization chamber arrays. Two different versions of the 2D-ARRAY (PTW-Freiburg, Germany) will be presented, a matrix of 16x16 chambers (chamber cross section 8 mmx8 mm; the distance between chamber centers, 16 mm) and a matrix of 27x27 chambers (chamber cross section 5 mmx5 mm; the distance between chamber centers is 10 mm). The two-dimensional response function of a single chamber is experimentally determined by scanning it with a slit beam. For dosimetric plan verification, the expected two-dimensional distribution of the array signals is calculated via convolution of the planned dose distribution, obtained from the treatment planning system, with the two-dimensional response function of a single chamber. By comparing the measured two-dimensional distribution of the array signals with the expected one, a distribution of deviations is obtained that can be subjected to verification criteria, such as the gamma index criterion. As an example, this verification method is discussed for one sequence of an IMRT plan. The error detection capability is demonstrated in a case study. Both versions of two-dimensional ionization chamber arrays, together with the developed treatment plan verification strategy, have been found to provide a suitable and easy-to-handle quality assurance instrument for IMRT.

Poppe, Bjoern; Blechschmidt, Arne; Djouguela, Armand; Kollhoff, Ralf; Rubach, Antje; Willborn, Kay C.; Harder, Dietrich [Klinik fuer Strahlentherapie und Internistische Onkologie, Pius-Hospital, Oldenburg, Germany, and Carl-von-Ossietzky-Universitaet Oldenburg, Oldenburg (Germany); Carl-von-Ossietzky-Universitaet Oldenburg, Oldenburg (Germany); Klinik fuer Strahlentherapie und Internistische Onkologie, Pius-Hospital, Oldenburg (Germany); Georg-August-Universitaet Goettingen, Goettingen (Germany)

2006-04-15

199

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

PubMed

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 5mm 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. PMID:21036637

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

2011-01-01

200

Steady Vortex Flows Past a Circular Cylinder  

Microsoft Academic Search

We study the classic problem of symmetric, steady-state, two dimensional inviscid flow past a cylinder. We consider flows for which there is a single region of constant vorticity in the upper half-plane. Various families of flows are obtained numerically by using an iterative procedure to solve the non-linear partial differential equation for the stream function. At each iterative step a

Kenneth Miller; Alan Elcrat; Bengt Fornberg

1999-01-01

201

Uniform shear flow past a circular cylinder  

Microsoft Academic Search

Summary This paper solves the two-dimensional problem of the unsteady shear flow of a viscous incompressible fluid past a circular cylinder. The flow is calculated using two methods. The first takes the form of a double series solution where an expansion is carried out in powers of the time, t, and in powers of the parameter \\u000a\\u000a\\u0009 where R is the

K. Rohlf; S. J. D. D’Alessio

2005-01-01

202

High resolution, two-dimensional imaging, microchannel plate detector for use on a sounding rocket experiment  

NASA Technical Reports Server (NTRS)

We discuss a high resolution microchannel plate (MCP) imaging detector to be used in measurements of Doppler-shifted hydrogen Lyman-alpha line emission from Jupiter and the interplanetary medium. The detector is housed in a vacuum-tight stainless steel cylinder (to provide shielding from magnetic fields) with a MgF2 window. Operating at nominal voltage, the four plate configuration provides a gain of 1.2 x 10 exp 7 electrons per incident photon. The wedge-and-strip anode has two-dimensional imaging capabilities, with a resolution of 40 microns FWHM over a one centimeter diameter area. The detector has a high quantum efficiency while retaining a low background rate. A KBr photocathode is used to enhance the quantum efficiency of the bare MCPs to a value of 35 percent at Lyman-alpha.

Bush, Brett C.; Cotton, Daniel M.; Siegmund, Oswald H.; Chakrabarti, Supriya; Harris, Walter; Clarke, John

1991-01-01

203

Engineering the bandgap of a two-dimensional anisotropic photonic crystal  

NASA Astrophysics Data System (ADS)

The photonic band structures of two-dimensional square lattice photonic crystals made of anisotropic materials with one of the principal axes oriented along the extension direction of cylinders are studied. The band structure of the photonic crystal can be substantially engineered to achieve large bandgaps by reorienting the other two principal axes of the anisotropy media in the periodic plane of the photonic crystal. In particular, it is shown that large full bandgap for H polarization can be created for a photonic crystal with circular holes in an anisotropic matrix medium. For pillar-type photonic crystals, we show that large partial bandgaps for H polarization can be created in half of the irreducible Brillouin zone. With the use of anisotropic materials and the flexibility of arranging the principal axes, the requirement on the filling ratio, refractive index and anisotropy to achieve the largest bandgap is greatly alleviated.

Alagappan, G.; Sun, X. W.; Shum, P.; Yu, M. B.

2006-07-01

204

Models for wave propagation in two-dimensional random composites: A comparative study.  

PubMed

This paper provides a set of benchmark results on existing theoretical models for wave propagation in two-dimensional composite materials. This comparative study is motivated to investigate the reason why results from an accurate ultrasonic measurement often significantly contradict theoretical predictions. Eight different models are evaluated with their numerically calculated effective wave speeds and coherent attenuations. For computational simplicity, the problem of horizontal shear wave propagation in an elastic matrix containing parallel circular cylinders is considered. Numerical calculations are conducted for different composites in wide ranges of material properties, volume concentration, and frequency. Some of the numerical results are compared with experimental data. Judgments are made based on fundamental theoretical and physical criteria as well as relative agreements in the numerical results, and then possible causes of failures are discussed. The effect of microstructure, potentially as a major source of the observed disagreements between models, is also discussed. PMID:20370001

Kim, Jin-Yeon

2010-04-01

205

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

SciTech Connect

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.

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

2000-06-27

206

Noninteraction of Waves in Two-dimensional Conformal Field Theory  

NASA Astrophysics Data System (ADS)

In higher dimensional quantum field theory, irreducible representations of the Poincaré group are associated with particles. Their counterpart in two-dimensional massless models are "waves" introduced by Buchholz. In this paper we show that waves do not interact in two-dimensional Möbius covariant theories and in- and out-asymptotic fields coincide. We identify the set of the collision states of waves with the subspace generated by the chiral components of the Möbius covariant net from the vacuum. It is also shown that Bisognano-Wichmann property, dilation covariance and asymptotic completeness (with respect to waves) imply Möbius symmetry. Under natural assumptions, we observe that the maps which give asymptotic fields in Poincaré covariant theory are conditional expectations between appropriate algebras. We show that a two-dimensional massless theory is asymptotically complete and noninteracting if and only if it is a chiral Möbius covariant theory.

Tanimoto, Yoh

2012-09-01

207

Tracking dynamics of two-dimensional continuous attractor neural networks  

NASA Astrophysics Data System (ADS)

We introduce an analytically solvable model of two-dimensional continuous attractor neural networks (CANNs). The synaptic input and the neuronal response form Gaussian bumps in the absence of external stimuli, and enable the network to track external stimuli by its translational displacement in the two-dimensional space. Basis functions of the two-dimensional quantum harmonic oscillator in polar coordinates are introduced to describe the distortion modes of the Gaussian bump. The perturbative method is applied to analyze its dynamics. Testing the method by considering the network behavior when the external stimulus abruptly changes its position, we obtain results of the reaction time and the amplitudes of various distortion modes, with excellent agreement with simulation results.

Fung, C. C. Alan; Wong, K. Y. Michael; Wu, Si

2009-12-01

208

Construction of solutions for two-dimensional Riemann problems  

SciTech Connect

Solutions to the scalar quasilinear equation with initial data given by a two dimensional Riemann problem are piecewise smooth if f/sub 1/ identical with f/sub 2/ identical with f, and f has at most one inflection point. We show the pieces of this solution can be classified and are expressible in terms of two dimensional non-linear waves in analogy with the non-linear rarefaction and shock waves of the Riemann problem in one spatial dimension. The two dimensional waves can be expressed in almost closed form. Explicit solutions are constructable from these waves. An application is illustrated by calculation of the interaction of water/oil banks in two phase incompressible flow in reservoirs.

Lindquist, W.B.

1984-09-01

209

Generation of two-dimensional plasmonic bottle beams  

NASA Astrophysics Data System (ADS)

By analogy to the three dimensional optical bottle beam, we introduce the plasmonic bottle beam: a two dimensional surface wave which features a lattice of plasmonic bottles, i.e. alternating regions of bright focii surrounded by low intensities. The two-dimensional bottle beam is created by the interference of a non-diffracting beam, a cosine-Gaussian beam, and a plane wave, thus giving rise to a non-diffracting complex intensity distribution. By controlling the propagation constant of the cosine-Gauss beam, the size and number of plasmonic bottles can be engineered. The two dimensional lattice of hot spots formed by this new plasmonic wave could have applications in plasmonic trapping.

Genevet, Patrice; Dellinger, Jean; Blanchard, Romain; She, Alan; Petit, Marlene; Cluzel, Benoit; Kats, Mikhail A.; de Fornel, Frederique; Capasso, Federico

2013-04-01

210

Two-dimensional mirror symmetry from M-theory  

NASA Astrophysics Data System (ADS)

We construct two-dimensional gauge theories with N = (4,4) supersymmetry from branes of type IIA string theory. Quantum effects in the two-dimensional gauge theory are analyzed by embedding the IIA brane construction into M-theory. We find that the Coulomb branch of one theory and the Higgs branch of a mirror theory become equivalent at strong coupling. A relationship to the decoupling limit of the type IIA and IIB 5-branes in Matrix theory is shown. T-duality between the ALE metric and the wormhole metric of Callan, Harvey, and Strominger is discussed from a brane perspective and some puzzles regarding string duality resolved. We comment on the existence of a quantum Higgs branch in two-dimensional theories. Branes prove to be useful tools in analyzing singular conformal field theories.

Brodie, John H.

1998-04-01

211

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

SciTech Connect

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.

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

1980-12-01

212

Two-dimensional spin diffusion in multiterminal lateral spin valves  

NASA Astrophysics Data System (ADS)

The effects of two-dimensional spin diffusion on spin extraction in lateral semiconductor spin valves have been investigated experimentally and theoretically. A ferromagnetic collector terminal of variable size is placed between the ferromagnetic electron spin injector and detector of a conventional lateral spin valve for spin extraction. It is observed that transverse spin diffusion beneath the collector terminal plays an important role along with the conventional longitudinal spin diffusion in describing the overall transport of spin carriers. Two-dimensional spin diffusion reduces the perturbation of the channel electrochemical potentials and improves spin extraction.

Saha, D.; Basu, D.; Holub, M.; Bhattacharya, P.

2008-01-01

213

Network model for two-dimensional coupled laser arrays.  

PubMed

We have developed a network model for two-dimensional phase-locked arrays of coupled lasers that provides a basis for modeling arrays incorporating mixed coupling schemes. With this network approach we show that the modes of two-dimensional arrays that are evanescently coupled in the lateral direction and injection coupled in the longitudinal direction can be expressed in terms of the eigenvalues of matrices separately representing the lateral and longitudinal coupling. As an example, the modes and grating-coupled near-field patterns of a 3 x 3 array injection coupled through surface-emitting second-order Bragg reflectors are determined explicitly. PMID:19749813

Amantea, R; Palfrey, S L; Carlson, N W

1989-01-01

214

Two-Dimensional Infrared Spectroscopy of Photoswitchable Peptides  

Microsoft Academic Search

We present a detailed discussion of the complimentary fields of the application of two-dimensional infrared (2D-IR) spectroscopy in comparison with two-dimensional nuclear magnetic resonance (2D-NMR) spectroscopy. Transient 2D-IR (T2D-IR) spectroscopy of nonequilibrium ensembles is probably one of the most promising strengths of 2D-IR spectroscopy, as the possibilities of 2D-NMR spectroscopy are limited in this regime. T2D-IR spectroscopy uniquely combines ultrafast

Peter Hamm; Jan Helbing; Jens Bredenbeck

2008-01-01

215

Stabilization of two-dimensional spatial solitons in dissipative media  

NASA Astrophysics Data System (ADS)

This work analyzes the dynamics of two-dimensional spatial solitons in dissipative media. Stable solitons are formed in a two-dimensional medium with constant dissipation due to the balancing between dissipation and the instabilities due to nonlinearity. The dynamics have also been studied for linear, quadratic and exponential loss profiles. When a beam propagates in media with dissipation, where dissipation is a function of distance, it becomes compressed. A linear loss profile results in higher compression, while compression is minimal for an exponential profile.

Aysha Muhsina, K.; Subha, P. A.

2014-07-01

216

[A two-dimensional double dispersed hadamard transform spectrometer].  

PubMed

A kind of two-dimensional hadamard transform spectrometer was developed. A grating was used for chromatic dispersion of orders and a prism was used for spectral dispersion. Quite different from traditional CCD detection method, a digital micromirror device (DMD) was applied for optical modulation, and a simple point detector was used as the sensor. Compared with traditional two-dimensional spectrometer, it has the advantage of high resolution and signal-noise-ratio, which was proved by theoretical calculation and computer simulation. PMID:22870674

Liu, Jia; Shi, Lei; Li, Kai; Zheng, Xin-Wen; Zeng, Li-Bo; Wu, Qiong-Shui

2012-06-01

217

A two-dimensional nematic phase of magnetic nanorods.  

PubMed

We report a hybrid mesophase consisting of magnetic nanorods confined between the non-ionic surfactant bilayers of a lamellar phase. The magnetic field-induced ordering of the nanorods was measured experimentally and modeled by a two-dimensional Onsager theory including the third virial coefficient. The nanorods are strongly confined in layers, with no orientational coupling from one layer to the next. At high volume concentration they exhibit spontaneous in-plane orientational ordering and form a stack of independent two-dimensional nematic systems. This isotropic-nematic transition is first-order. PMID:24628202

Slyusarenko, Kostyantyn; Constantin, Doru; Davidson, Patrick

2014-03-14

218

A two-dimensional nematic phase of magnetic nanorods  

NASA Astrophysics Data System (ADS)

We report a hybrid mesophase consisting of magnetic nanorods confined between the non-ionic surfactant bilayers of a lamellar phase. The magnetic field-induced ordering of the nanorods was measured experimentally and modeled by a two-dimensional Onsager theory including the third virial coefficient. The nanorods are strongly confined in layers, with no orientational coupling from one layer to the next. At high volume concentration they exhibit spontaneous in-plane orientational ordering and form a stack of independent two-dimensional nematic systems. This isotropic-nematic transition is first-order.

Slyusarenko, Kostyantyn; Constantin, Doru; Davidson, Patrick

2014-03-01

219

Two-dimensional signal reconstruction: The correlation sampling method  

NASA Astrophysics Data System (ADS)

An accurate approach for reconstructing a time-dependent two-dimensional signal from non-synchronized time series recorded at points located on a grid is discussed. The method, denoted as correlation sampling, improves the standard conditional sampling approach commonly employed in the study of turbulence in magnetoplasma devices. Its implementation is illustrated in the case of an artificial time-dependent signal constructed using a fractal algorithm that simulates a fluctuating surface. A statistical method is also discussed for distinguishing coherent (i.e., collective) from purely random (noisy) behavior for such two-dimensional fluctuating phenomena.

Roman, H. E.

2007-12-01

220

Equilibrium state of a trapped two-dimensional Bose gas  

SciTech Connect

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

Rath, Steffen P.; Yefsah, Tarik; Guenter, Kenneth J.; Cheneau, Marc; Desbuquois, Remi; Dalibard, Jean [Laboratoire Kastler Brossel, CNRS, Universite Pierre et Marie Curie, Ecole Normale Superieure, 24 rue Lhomond, F-75005 Paris (France); Holzmann, Markus [Laboratoire de Physique Theorique de la Matiere Condensee, CNRS, Universite Pierre et Marie Curie, 4 Place Jussieu, F-75005 Paris, France, and Laboratoire de Physique et Modelisation des Milieux Condenses, CNRS, Universite Joseph Fourier, BP 166, F-38042 Grenoble (France); Krauth, Werner [Laboratoire de Physique Statistique, CNRS, Universite Pierre et Marie Curie, Universite Paris Diderot, Ecole Normale Superieure, 24 rue Lhomond, F-75005 Paris (France)

2010-07-15

221

Numerical analysis of vortex cell efficiency in laminar and turbulent flows past a circular cylinder with embedded rotating bodies  

Microsoft Academic Search

The effect of flow intensification in small-sized vortex cells on the flow pattern in the near wake downstream of a cylinder\\u000a and the cylinder drag in laminar and turbulent flows is analyzed on the basis of a numerical simulation of the two-dimensional\\u000a steady-state flow past a circular cylinder with rotating cylindrical bodies built into the cylinder contour.

S. A. Isaev; Yu. S. Prigorodov; A. G. Sudakov

2000-01-01

222

Flow characteristics around a circular cylinder with a slit. II Effect of boundary layer suction  

Microsoft Academic Search

The effects of boundary layer suction are investigated for a circular cylinder with a two-dimensional slit placed along a diameter. Flow characteristics around the cylinder are examined for cases of intermittent boundary layer suction (Pattern I), alternate boundary layer suction and blowing (Pattern II), and the transition regions. Among other results, it is found that the boundary layer suction is

T. Igarashi

1982-01-01

223

Numerical Simulation of Viscoelastic Fluid Flow Past a Cylinder on a Streamfunction Coordinate System  

Microsoft Academic Search

Steady two-dimensional flow of a viscoelastic fluid past a streamlined cylinder is numerically modeled using the von Mises coordinates. The governing equations for a second-order fluid flow past the cylinder are first transformed into a steamfunction coordinate system (phi, psi), where psi is the streamfuntion of the flow. Taking phi - x, the von Mises coordinates (x, psi) are obtained

I. Husain; O. P. Chandna

1993-01-01

224

Entropy generation due to laminar forced convection flow past a parabolic cylinder  

Microsoft Academic Search

This study is focused on the local entropy generation of steady two-dimensional symmetric flow past a parabolic cylinder in a uniform stream parallel to its axis. The effect of both Reynolds number (Re) and temperature difference between the cylinder wall and the freestream (?T) on thermal, viscous, and total entropy generation is investigated for different values of Prandtl number (Pr)

O. M. Haddad; M. Abu-Qudais; A. M. Maqableh

2000-01-01

225

Extinction paradox and actual power scattered in light beam scattering: a two-dimensional study.  

PubMed

The extinction paradox is examined by applying partial-wave analysis to a two-dimensional light beam interacting with a long transverse cylinder without absorption, assuming always short wavelengths. We show that the (conventional) power scattered, Psca, except for a very narrow beam hitting a transparent cylinder on axis, is always double the power directly intercepted by the scatterer, Pitc, including a zero result for Psca when the incident beam is basically off the material surface. This contradicts the interpretation that attributes one half of Psca to edge diffraction by the scatterer. Furthermore, we identify the shadow-forming wave (SFW) from the partial-wave sum in the forward direction and show that the actual power scattered or, equivalently, the power depleted from the incident beam is equal to one unit of Pitc for a narrow beam, gets larger for a broader beam, and approaches 2Pitc for a very broad beam. The larger value in the latter cases is due to the extent of divergence of the SFW beam out of the incident beam at distances well beyond the Rayleigh range. PMID:15603068

Lai, H M; Wong, W Y; Wong, W H

2004-12-01

226

Extinction paradox and actual power scattered in light beam scattering: a two-dimensional study  

NASA Astrophysics Data System (ADS)

The extinction paradox is examined by applying partial-wave analysis to a two-dimensional light beam interacting with a long transverse cylinder without absorption, assuming always short wavelengths. We show that the (conventional) power scattered, Psca, except for a very narrow beam hitting a transparent cylinder on axis, is always double the power directly intercepted by the scatterer, Pitc, including a zero result for Psca when the incident beam is basically off the material surface. This contradicts the interpretation that attributes one half of Psca to edge diffraction by the scatterer. Furthermore, we identify the shadow-forming wave (SFW) from the partial-wave sum in the forward direction and show that the actual power scattered or, equivalently, the power depleted from the incident beam is equal to one unit of Pitc for a narrow beam, gets larger for a broader beam, and approaches 2Pitc for a very broad beam. The larger value in the latter cases is due to the extent of divergence of the SFW beam out of the incident beam at distances well beyond the Rayleigh range.

Lai, H. M.; Wong, W. Y.; Wong, W. H.

2004-12-01

227

Two dimensional computational fluid dynamic models for waste stabilisation ponds  

Microsoft Academic Search

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

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

1998-01-01

228

Particle simulation of a two-dimensional electrostatic plasma.  

National Technical Information Service (NTIS)

Computer simulation is a growing field of research and plasma physics is one of the important areas where it is being applied today. This report describes the particle method of simulating a two-dimensional electrostatic plasma. The methods used to discre...

K. Patel

1989-01-01

229

Hydrogen Molecule for a Two-Dimensional System.  

National Technical Information Service (NTIS)

The two dimensional (2D) energy of the hydrogen molecule is calculated by the Heitler-London method. The 2D integrals (which are more localized compared to 3D ones) are performed in the light of the 3D Slater integrals. Such a 2D system for doped semicond...

A. F. Dasilva M. Fabbri

1983-01-01

230

Two-dimensional interaction of ion-acoustic solitons  

Microsoft Academic Search

The two-dimensional nonlinear interaction of two planar ion-acoustic solitons has been studied experimentally. When the angle between the wave vectors of the two interacting solitons is small and the soliton amplitudes approach a critical value, a resonant three-soliton interaction occurs.

P. A. Folkes; H. Ikezi; R. Davis

1980-01-01

231

Self Organization of Two-dimensional Insect Neural Networks  

Microsoft Academic Search

How single neurons self-organize to form a complex functional system, the neural network, is a fundamental question in developmental neuroscience, computation science, and pattern formation. Two-dimensional in vitro invertebrate preparations offer an attractive model system to tackle this question due to the large size of the neurons, and their ability to grow in relative isolation as well as to develop

Amir Ayali; Orit Shefi; Eshel Ben-Jacob

2002-01-01

232

Numerical Simulation of One and Two-Dimensional ESEEM Experiments  

Microsoft Academic Search

Numerical simulation has become an indispensable tool for the interpretation of pulse EPR experiments. In this work it is shown how automatic orientation selection, grouping of operator factors, and direct selection and elimination of coherences can be used to improve the efficiency of time-domain simulations of one- and two-dimensional electron spin echo envelope modulation (ESEEM) spectra. The program allows for

Z. L. Madi; S. Van Doorslaer; A. Schweiger

2002-01-01

233

Infinite conformal symmetry in two-dimensional quantum field theory  

Microsoft Academic Search

We present an mvestlgaUon of the massless, two-dimensional, interacting field theories Their basic property is their invanance under an lnfimte-dlmenslonal group of conformal (analytic) transformations It is shown that the local fields forlmng the operator algebra can be classified according to the irreducible representations of Vtrasoro algebra, and that the correlation functions are bmlt up of the \\

A A Belavin; A M Polyakov; A B Zamolodchikov

1984-01-01

234

Equilibrium structural properties of two-dimensional nonideal systems  

NASA Astrophysics Data System (ADS)

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

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

2011-12-01

235

Thickness identification of two-dimensional materials by optical imaging.  

PubMed

Two-dimensional materials, e.g. graphene and molybdenum disulfide (MoS(2)), have attracted great interest in recent years. Identification of the thickness of two-dimensional materials will improve our understanding of their thickness-dependent properties, and also help with scientific research and applications. In this paper, we propose to use optical imaging as a simple, quantitative and universal way to identify the thickness of two-dimensional materials, i.e. mechanically exfoliated graphene, nitrogen-doped chemical vapor deposition grown graphene, graphene oxide and mechanically exfoliated MoS(2). The contrast value can easily be obtained by reading the red (R), green (G) and blue (B) values at each pixel of the optical images of the sample and substrate, and this value increases linearly with sample thickness, in agreement with our calculation based on the Fresnel equation. This method is fast, easily performed and no expensive equipment is needed, which will be an important factor for large-scale sample production. The identification of the thickness of two-dimensional materials will greatly help in fundamental research and future applications. PMID:23154446

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

2012-12-14

236

Two Dimensional Modeling of Nonuniformly Doped MESFET Under Illumination  

Microsoft Academic Search

A two dimensional numerical model of an optically gated GaAs MESFET with non uniform channel doping has been developed. This is done to characterize the device as a photo detector. First photo induced voltage (V op ) at the Schottky gate is calculated for estimating the channel profile. Then Poisson's equation for the device is solved numerically under dark and

Mishra B. K; Lochan Jolly; Kalawati Patil

2010-01-01

237

Two-Dimensional Aspects of Thin-Film Solar Cells.  

National Technical Information Service (NTIS)

In the literature, now one-dimensional models of MIS solar cells, emphasizing the interface properties, are described, while in practice the structures are two-dimensional. Two types are considered: thin-film MIS solar cells with a transparent front-elect...

H. J. Pauwels, P. De Visschere, L. Vandendriessche

1982-01-01

238

Electron Vortex Dynamics and Two-Dimensional Field Analysis.  

National Technical Information Service (NTIS)

In recent paper (K. Ito, el al., Jpn. J. Appl. Phys. 40, 2558 (2001)), we present a fast and sufficiently accurate procedure to construct the potential and the electric field distribution from the observed electron density distribution in two-dimensional ...

A. Sanpei K. Ito Y. Kiwamoto

2002-01-01

239

Two Dimensional Array of Antenna-Coupled Microbolometers  

Microsoft Academic Search

Antenna-coupled microbolometers are known for having short time constants and high responsivity, but their small dimensions make them unsuitable for imaging applications where a typical pixel area is generally greater than 20 × 20 µm2. In this paper a two dimensional array of antenna-coupled microbolometers is demonstrated as an area receiver. Using the response of microbolometers to visible frequencies a

F. J. González; M. A. Gritz; C. Fumeaux; G. D. Boreman

2002-01-01

240

A language for two-dimensional digital picture processing  

Microsoft Academic Search

A new system, that of matrix grammars, for two-dimensional pattern processing, is introduced. A hierarchy, induced on Chomsky's is found. Language operations such as union, catenation (row and column), Kleene's closure (row and column), and homomorphisms are investigated. It is found that the smallest class of these languages may serve as the class of regular arrays, which is defined as

Patrick Shen-Pei Wang; William I. Grosky

1976-01-01

241

Adiabatic single scan two-dimensional NMR spectrocopy.  

PubMed

New excitation schemes, based on the use adiabatic pulses, for single scan two-dimensional NMR experiments (Frydman et al., Proc. Nat. Acad. Sci. 2002, 99, 15 858-15 862) are introduced. The advantages are discussed. Applications in homo- and heteronuclear experiments are presented. PMID:14519020

Pelupessy, Philippe

2003-10-01

242

Two-dimensional heat conduction in metal, fluid composites  

NASA Astrophysics Data System (ADS)

Because the size and weight of main propulsion and auxiliary systems are inversely proportional to the ease in which heat or energy is exchanged, a major thrust of the research and development program of the U.S. Navy is toward the design and development of equipment that perform at higher efficiency with a reduction in size and weight. In particular, one area of great interest is the reduction in size and weight of steam condensers. The heat-transfer effectiveness is governed by the amount of surface and the overall resistance to the flow of heat. Filmwise condensation of steam on externally-finned tubes is a very complex process. Recent experiments have shown that enhancement ratios (ratio of steam-side heat-transfer coefficient to that of a smooth tube having the same diameter) exceeded the area enhancement produced by the fins. Moreover, the enhancement ratios for fully flooded tubes exceed the values predicted by a simple, one-dimensional conduction model by a factor of 2 to 4. A new two-dimensional conduction model was developed, which showed that the one-dimensional model overpredicted the two-dimensional results for high conductivity tube-metals such as copper by as much as 13%. The two-dimensional model also showed that variations in fin thickness or spacing can result in an overprediction by the one-dimensional model of the two-dimensional results by as much as twenty-two percent.

Gomori, M. A.

1985-12-01

243

Interior design of a two-dimensional semiclassical black hole  

SciTech Connect

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.

Levanony, Dana; Ori, Amos [Department of Physics, Technion, Haifa 32000 (Israel)

2009-10-15

244

Two-dimensional materials with Dirac cones: Graphynes containing heteroatoms  

NASA Astrophysics Data System (ADS)

Two graphynes, 6(H2),14,18 graphyne and 6BN,6,12 graphyne, that contain the heteroatoms hydrogen or boron and nitrogen, respectively, are shown to feature Dirac points in their band structure according to first-principles electronic structure calculations. This shows that the existence of Dirac points in the band structure of two-dimensional materials is neither restricted to graphene nor to other two-dimensional all-carbon materials. 6(H2),14,18 graphyne and 6BN,6,12 graphyne belong to the rectangular two-dimensional space groups pmm and pm, respectively, and thus exhibit completely different symmetries than graphene. 6BN,6,12 graphyne features a Dirac cone with a band gap originating from an avoided crossing of its valence and conduction band at the Dirac point due to missing reflection symmetry. The examples of 6(H2),14,18 graphyne and 6BN,6,12 graphyne suggest that a wealth of two-dimensional materials with various chemical compositions and with electronic properties equally amazing as those of graphene is awaiting discovery.

Malko, Daniel; Neiss, Christian; Görling, Andreas

2012-07-01

245

Performance Evaluation of Two-Dimensional Phase Unwrapping Algorithms  

Microsoft Academic Search

We present a performance evaluation of eight two-dimensional phase unwrapping methods with respect to correct phase unwrapping and execution times. The evaluated methods are block least squares (BLS), adaptive integration (AI), quality guided path following (QUAL), mask cut (MCUT), multigrid (MGRID), preconditioned conjugate gradient (PCG), Flynn s (FLYNN), and Liang s (LIANG). This set included integration- (path following), least-squares-, L

Jarle Strand; Torfinn Taxt

1999-01-01

246

SAR Processing Based On Two-Dimensional Transfer Function  

NASA Technical Reports Server (NTRS)

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

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

1994-01-01

247

Stability of two-dimensional monopoles in plasmas  

NASA Astrophysics Data System (ADS)

Monopole vortices, obeying the homogeneous Hasegawa-Mima equation or the convective cell equation in magnetized plasmas are considered. It is shown that two-dimensional perturbations of single vortices in the plane perpendicular to the external magnetic field do not grow in time. It is also argued that three-dimensional perturbations will not lead to an instability of monopoles.

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

1985-12-01

248

Channel Models and Detectors for Two-Dimensional Magnetic Recording  

Microsoft Academic Search

Two-dimensional magnetic recording (TDMR) is a novel recording architecture intended to support densities beyond those of conventional recording systems. The gains from TDMR come primarily from more powerful coding and signal processing algorithms that allow the bits to be packed more tightly on the disk, and yet be retrieved with acceptable error rates. In this paper, we present some preliminary

Kheong Sann Chan; Rathnakumar Radhakrishnan; Kwaku Eason; M. R. Elidrissi; Jim J. Miles; Bane Vasic; Anantha Raman Krishnan

2010-01-01

249

Multibeam two-dimensional binary optics laser scanner  

NASA Astrophysics Data System (ADS)

We have developed a two-dimensional, multibeam, binary optic based scanner for transmission/receiver functions for LADAR and other applications under a Small Business Innovation Research (SBIR) contract from Eglin Air Force Base. Multibeam scan provides many unique advantages including: increased data rate for pulsed lasers; increased scan coverage; and programmable broadcasting for optical interconnect applications.

Jain, Anil K.

1994-06-01

250

Dislocation waves in a two-dimensional Coulomb lattice  

Microsoft Academic Search

We calculate the properties of dislocation waves in a two-dimensional Coulomb lattice. Hybridization of states with core location at different points in the lattice leads to a substantial lowering of the dislocation energy. At rs=37, this lowering is comparable to the elastic core energy. The mass of the dislocation waves for motion in the direction of the Burgers vector is

K. Esfarjani; S. T. Chui; Xiu Qiu

1992-01-01

251

Distributions of the Two-Dimensional DCT Coefficients for Images  

Microsoft Academic Search

For a two-dimensional discrete cosine transform (DCT) image coding system, there have been different assumptions concerning the distributions of the transform coefficients. This paper presents results of distribution tests that indicate that for many images the statistics of the coefficients are best approximated by a Gaussian distribution for the DC coefficient and a Laplacian distribution for the other coefficients. Furthermore,

R. Reininger; J. Gibson

1983-01-01

252

Chemical mapping using two-dimensional Hadamard transform Raman spectrometry  

Microsoft Academic Search

A Raman chemical mapping investigation was conducted in the visible spectral region using an automated Spex 14018 double monochromator in concert with a moving two dimensional (2D) Hadamard encoding mask. The 2D Hadamard encoding mask combined with conventional Raman spectrometry was used to create chemical maps of heterogeneous liquid and solid samples. The 2D Hadamard encoding mask is based on

R. A. DeVerse; T. A. Mangold; R. M. Hammaker; W. G. Fateley

1998-01-01

253

Theory and Algorithms of Two-Dimensional Hydrodynamic Potential Coefficients.  

National Technical Information Service (NTIS)

This report describes the theoretical backgrounds and the algorithns for the calculation of the two-dimensional hydrodynamic potential coefficients of ship-like cross sections in deep water. The close-fit multi-parameter conformal mapping method, used to ...

J. M. J. Journee

1990-01-01

254

Dynamics of two-dimensional solitons in weakly dispersive media  

NASA Astrophysics Data System (ADS)

Formation, evolution and interaction of two-dimensional solitons and wave packets in weakly dispersive and dissipative media is studied numerically. The master equation is a hybrid of the Zabolotskaya-Khokhlov and Kadomtsev-Petviashvili equations with a Kawahara term.

Karpman, V. I.; Belashov, V. Yu.

1991-04-01

255

A counterexample to two-dimensional varimax-rotation  

Microsoft Academic Search

Usually, an iterative procedure based on two-dimensional rotations is employed to find the varimax solution in factor analysis. A matrix is given where this procedure does not yield the maximum value of the varimax criterion. However, random orthogonal transformations of some matrices and subsequent varimax-rotation using the iterative procedure seem to indicate that usually no local maxima exist.

Friedrich Gebhardt

1968-01-01

256

Stable two-dimensional dispersion-managed soliton  

Microsoft Academic Search

The existence of a dispersion-managed soliton in two-dimensional nonlinear Schrödinger equation with periodically varying dispersion has been explored. The averaged equations for the soliton width and chirp are obtained which successfully describe the long time evolution of the soliton. The slow dynamics of the soliton around the fixed points for the width and chirp are investigated and the corresponding frequencies

Fatkhulla Kh. Abdullaev; Bakhtiyor B. Baizakov; Mario Salerno

2003-01-01

257

Gridless Solution Method for Two-Dimensional Unsteady Flow  

Microsoft Academic Search

The main purpose of this paper is to develop a gridless method for unsteady flow simulation. A quadrantal point infilling strategy is developed to generate point and combine clouds of points automatically. A point-moving algorithm is introduced to ensure the clouds of points following the movements of body boundaries. A dual time method for solving the two-dimensional Euler equations in

Gang WANG; Ying-dan SUN; Zheng-yin YE

2005-01-01

258

Fractal Structure in Two-Dimensional Quantum Regge Calculus  

NASA Astrophysics Data System (ADS)

We study the fractal structure of the surface in two-dimensional quantum Regge calculus by performing Monte Carlo simulation with up to 200,000 triangles. The correct scaling behavior has been observed for the type of loop attached to a baby universe, when the scale-invariant measure is taken as the measure of the link-length integration.

Nishimura, J.; Oshikawa, M.

1996-03-01

259

Mobility and Diffusion-Ordered Two-Dimensional NMR Spectroscopy  

Microsoft Academic Search

Mobility and diffusion-ordered two-dimensional nuclear magnetic resonance spectroscopy experiments have been developed for the analysis of mixtures. In the mobility -ordered experiments, the full range of positive and negative electrophoretic mobilities is displayed in one dimension and chemical shifts are displayed in the other. A concentric cylindrical tube electrophoresis chamber was designed to reduce the effective pathlength for current and

Kevin Freeman Morris

1993-01-01

260

Real-Time, Two-Dimensional Terahertz Beam Imaging.  

National Technical Information Service (NTIS)

In ARO STTR Phase 1 program, we have demonstrated the concept and developed a real-time, two-dimensional THz wave imaging system. The THz imaging system uses electro-optic crystals and is capable of time-domain far-infrared spectroscopy across a frequency...

X. Zhang Z. Jiang

1999-01-01

261

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...

262

Two-dimensional optimization of free electron laser designs  

DOEpatents

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.

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

1985-01-01

263

Two-dimensional optimization of free-electron-laser designs  

DOEpatents

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.

Prosnitz, D.; Haas, R.A.

1982-05-04

264

High quality rendering of two-dimensional continuous curves  

Microsoft Academic Search

The paper presents a prefiltering technique for antialiasing two dimensional continuous curves which enables the correct handling of the geometry (self-intersections, small loops, cusps, curves with high and small radius of curvature, etc.) using a generic class of filters. Moreover, the technique allows for rendering curves of arbitrary thickness and can be optimally tuned to the bits used for image

ANTONIO ELIAS FABRIS; A. ROBIN FORREST

1997-01-01

265

Two Dimensional Study of Rotor/Airfoil Interaction in Hover.  

National Technical Information Service (NTIS)

A two dimensional model for the chordwise flow near the wing tip of the tilt rotor in hover is presented. The airfoil is represented by vortex panels and the rotor is modeled by doublet panels. The rotor slipstream and the airfoil wake are simulated by fr...

C. S. Lee

1988-01-01

266

Existence of Cepstra for Two-Dimensional Rational Polynomials.  

National Technical Information Service (NTIS)

In signal-processing problems where two signals are combined by convolution, homomorphic filtering techniques may be useful. The techniques are applied to the problem when a signal and noise are combined by convolution, and the case of the two-dimensional...

D. E. Dudgeon H. S. Hersey R. M. Mersereau

1974-01-01

267

Model of Hypersonic Two-Dimensional Oblique Detonation Wave Ramjet.  

National Technical Information Service (NTIS)

The possibility of using an oblique detonation wave ramjet as a power plant for a hypersonic vehicle is examined. The performance of a model of a two dimensional oblique detonation wave ramjet is analyzed in terms of thrust, lift and fuel consumption.

Y. Sheng J. P. Sislian

1985-01-01

268

Chord intercepts in a two-dimensional cell growth model  

Microsoft Academic Search

The microstructure of a two-dimensional cell growth model at each fraction transformed along Rosiwal's line is characterized. Rosiwal's line cut grains and yields chord intercepts. By the use of probability theory we derive the mean number of chord intercepts per unit length as well as the dependence of the distribution density of the length of these chord intercepts on the

G. E. W. Schulze; L. O. Schwan; R. Willers

1989-01-01

269

Generalized scale length for two-dimensional effects in MOSFETs  

Microsoft Academic Search

We derive a new scale length for two-dimensional (2-D) effects in MOSFETs and discuss its significance. This derivation properly takes into account the difference in permittivity between the Si channel and the gate insulator, and thus permits an accurate understanding of the effects of using insufficiently scaled oxide or thicker higher permittivity gate insulators. The theory shows that the utility

David J. Frank; Yuan Taur; Hon-Sum P. Wong

1998-01-01

270

Two-dimensional dissipation in third sound resonance  

NASA Astrophysics Data System (ADS)

The first determination of non-linear superflow dissipation in a truly two-dimensional helium film is reported. Superfluid velocities were measured using third sound resonance on a closed superfluid film. The predicted power law dissipation function, with exponent of approximately eight, is observed at three temperatures in a film of 0.58 mobile superfluid layers.

Buck, A. L.; Mochel, J. M.

1981-08-01

271

Sound waves in two-dimensional ducts with sinusoidal walls  

NASA Technical Reports Server (NTRS)

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.

Nayfeh, A. H.

1974-01-01

272

High Angle Dark Field Imaging of Two-Dimensional Crystals  

NASA Astrophysics Data System (ADS)

Two-dimensional (2D) materials, graphene, hexagonal boron nitride (h-BN) and transition metal dichalcogenides (TMD) have been investigated by means of Scanning Transmission Electron Microscopy (STEM), in particular via High Angle Annular Dark Field (HAADF) imaging technique. They are compared in terms of their structure and durability under intense electron beams.

Zan, R.; Ramasse, Q. M.; Jalil, R.; Georgiou, T.; Bangert, U.; Novoselov, K. S.

2014-06-01

273

Dilution Effects in Two-Dimensional Quantum Orbital Systems  

Microsoft Academic Search

Interacting orbital degrees of freedom in a Mott insulator are essentially directional and frustrated. In this Letter, the effect of dilution in a quantum-orbital system with this kind of interaction is studied by analyzing a minimal orbital model which we call the two-dimensional quantum compass model. We find that the decrease of the ordering temperature due to dilution is stronger

Takayoshi Tanaka; Sumio Ishihara

2007-01-01

274

A fast two-dimensional median filtering algorithm  

Microsoft Academic Search

We present a fast algorithm for two-dimensional median filtering. It is based on storing and updating the gray level histogram of the picture elements in the window. The algorithm is much faster than conventional sorting methods. For a window size of m × n, the computer time required is 0(n).

Thomas S. Huang; George J. Yang; Gregory Y. Tang

1979-01-01

275

Two-dimensional O2 adsorbed on graphite. [thermodynamic properties  

NASA Technical Reports Server (NTRS)

Properties of two-dimensional O2 adsorbed on graphite are calculated in the extremely low-coverage delta region and for monolayers, with use of pattern-recognition optimization and Monte Carlo techniques. Equilibrium configurations and orientations, orientational order-disorder, melting, and dissociation transitions are predicted at various O2 densities. Phase characteristics, including a plastic crystallite phase, are compared with experiment.

Etters, R. D.; Pan, R.-P.; Chandrasekharan, V.

1980-01-01

276

Flow and Combustion Characteristics of a Two Dimensional Spouted Bed.  

National Technical Information Service (NTIS)

A two dimensional spouted bed laboratory combustor has been designed and constructed with the objective of studying the interaction among the gas flow, particle flow, and combustion. The facility, designed for a maximum thermal power of 20 kW, has a quart...

R. F. Sawyer J. R. Hart K. Ohtake

1982-01-01

277

Thickness identification of two-dimensional materials by optical imaging  

NASA Astrophysics Data System (ADS)

Two-dimensional materials, e.g. graphene and molybdenum disulfide (MoS2), have attracted great interest in recent years. Identification of the thickness of two-dimensional materials will improve our understanding of their thickness-dependent properties, and also help with scientific research and applications. In this paper, we propose to use optical imaging as a simple, quantitative and universal way to identify the thickness of two-dimensional materials, i.e. mechanically exfoliated graphene, nitrogen-doped chemical vapor deposition grown graphene, graphene oxide and mechanically exfoliated MoS2. The contrast value can easily be obtained by reading the red (R), green (G) and blue (B) values at each pixel of the optical images of the sample and substrate, and this value increases linearly with sample thickness, in agreement with our calculation based on the Fresnel equation. This method is fast, easily performed and no expensive equipment is needed, which will be an important factor for large-scale sample production. The identification of the thickness of two-dimensional materials will greatly help in fundamental research and future applications.

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

2012-12-01

278

Automatic Visualization of Two-Dimensional Cellular Complexes  

Microsoft Academic Search

A two-dimensional cellular complex is a partition of a surface into a finite number of elements—faces (open disks), edges (open arcs), and vertices (points). The topology of a cellular complex is the abstract incidence and adjacency relations among its elements. Here we describe a program that, given only the topology of a cellular complex, computes a geometric realization of the

Luis A. P. Lozada; Candido Ferreira Xavier De Mendonça Neto; R. M. Rosi; Jorge Stolfi

1996-01-01

279

Dynamic two-dimensional beam-pattern steering technique  

NASA Technical Reports Server (NTRS)

A dynamic two-dimensional laser-beam-pattern steering technique using photorefractive holograms in conjunction with electrically addressed spatial light modulators is proposed and investigated. The experimental results demonstrate the dynamic steering of random combinations of basis beam patterns. The proposed method has the advantages of random beam-pattern combination, good beam intensity uniformity, and higher diffraction efficiency compared with conventional methods.

Zhou, Shaomin; Yeh, Pochi; Liu, Hua-Kuang

1993-01-01

280

Least-squares two-dimensional phase unwrapping using FFT's  

Microsoft Academic Search

A solution of the least-squares two-dimensional phase-unwrapping problem is presented that is simpler to understand and implement than previously published solutions. It extends the phase function to a periodic function using a mirror reflection, and the resulting equation is solved using the Fourier transform

Mark D. Pritt; Jerome S. Shipman

1994-01-01

281

Application of the analogy between water flow with a free surface and two-dimensional compressible gas flow  

NASA Technical Reports Server (NTRS)

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.

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

1947-01-01

282

Plane wave scattering from 2-D perfectly conducting superquadric cylinders  

Microsoft Academic Search

The plane-wave scattering from perfectly conducting two-dimensional cylinders of arbitrary squareness parameter is investigated. A uniform geometrical optics (UGO) solution valid across the smooth caustics generated by the surface poles or zero curvature (inflection) points is developed based on physical optics (PO). The classical geometrical optics solution is modified using a multiplicative transition function that compensates for the caustic singularities

Evagoras D. Constantinides; R. J. Marhefka

1991-01-01

283

Water impact of horizontal circular cylinders and cylindrical shells  

Microsoft Academic Search

A two-dimensional boundary element method (BEM) is developed to simulate the water flow during the water impact of a horizontal circular cylinder. Exact free surface conditions are satisfied. The non-viscous flow separation on the curved surface of the cylindrical can be simulated by merging a local analytical solution with the numerical method. The BEM is first applied to solve the

Hui Sun; Odd M. Faltinsen

2006-01-01

284

Numerical study on viscous shear flow past a circular cylinder  

Microsoft Academic Search

Numerical solutions of the unsteady Navier-Stokes equations are presented for a two-dimensional flow past a circular cylinder immersed in a uniform shear flow. Although a pair of steady standing vortices is formed in the uniform flow when Re = 40, it is found that a periodic vortex shedding occurs at the same Reynolds number in shear flow with a shear

H. Tamura; M. Kiya; M. Arie

1980-01-01

285

Steady flow past an elliptic cylinder inclined to the stream  

Microsoft Academic Search

The properties of steady two-dimensional flow past an elliptic cylinder inclined to the oncoming stream are investigated for small to moderate values of the Reynolds number for which good accuracy can be assured. The solutions are based on a numerical method of solution of the Navier-Stokes equations for incompressible fluids which ensures that all the correct conditions of the problem

S. C. R. Dennis; P. J. S. Young

2003-01-01

286

The initial oscillatory flow past a circular cylinder  

Microsoft Academic Search

This paper presents results obtained from an initial approximation for the flow around a circular cylinder in two-dimensional oscillating flow. The analysis is developed in terms of the scalar vorticity and stream function. An expansion in powers of time from the start of the motion is obtained using an exact analysis which extends the results of boundary-layer theory by taking

H. M. Badr; S. C. R. Dennis; S. Kocabiyik

1995-01-01

287

Numerical Studies of a Viscous Liquid past a Circular Cylinder  

Microsoft Academic Search

In the study of the steady two-dimensional flows past a circular cylinder in an infinite extent, the two sets of boundary conditions at infinity for the perturbed stream function and the vorticity, which are generally used, are examined numerically on the basis of Navier-Stokes equations. It is confirmed that, for sufficiently small Reynolds number, if points far enough from the

Yorisaburo Takaisi

1969-01-01

288

Stagnation saddle points and flow patterns in Stokes flow between contra-rotating cylinders  

Microsoft Academic Search

The steady flow is considered of a Newtonian fluid, of viscosity [mu], between contra-rotating cylinders with peripheral speeds U1 and U2. The two-dimensional velocity field is determined correct to O(H0\\/2R)1\\/2, where 2H0 is the minimum separation of the cylinders and R an `averaged' cylinder radius. For flooded\\/moderately starved inlets there are two stagnation saddle points, located symmetrically about the nip,

P. H. Gaskell; M. D. Savage; H. M. Thompson

1998-01-01

289

Flow past a cylinder: Effect of surface modification on structure of the near-wake  

Microsoft Academic Search

The near-wake of a cylinder with a surface nonuniformity is addressed. A helical wire pattern about the surface of a cylinder, whereby the wire has a diameter an order of magnitude smaller than the cylinder diameter, induces substantial alterations of both the quasi-two-dimensional (sectional) and the three-dimensional wake structure. A technique of high-image-density particle image velocimetry is employed in order

Nattapong Saelim

2003-01-01

290

E-field and H-field solutions of TE scattering from multiple conducting and dielectric cylinders of arbitrary cross-section  

Microsoft Academic Search

A simple moment solution is given for the problem of electromagnetic scattering from two dimensional structures consisting of multiple perfectly conducting and lossy dielectric cylinders of arbitrary cross-section. The system is excited by a plane wave polarized transverse electric to the axis of the cylinders. The equivalence principle is used to replace the cylinders by equivalent electric and magnetic surface

E. Arvas; Y. Qian; A. Sadigh; T. K. Sarkar; F. Aslan

1989-01-01

291

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

NASA Technical Reports Server (NTRS)

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.

Thompson, William K.

2006-01-01

292

Numerical analysis of a two-dimensional nonsteady detonations  

NASA Technical Reports Server (NTRS)

In the present work a system of two-dimensional nonsteady hydrodynamic and chemical kinetic equations was numerically integrated for an exothermic system. Assumed two-step reaction model simulates practically an oxyhydrogen mixture. The calculation starts from a plane Chapman-Jouguet detonation as an initial condition. Two-dimensional disturbances are generated by artificially placing nonuniformities ahead of the detonation front. Regardless of the difference of the given initial disturbances, a fixed number of triple shock waves were produced for a fixed combination of mixture model and geometry when the transition period was over. This shows that for a given detonation tube geometry any exothermic system has its own characteristic multidimensional structure. The obtained number of triple shock waves contained in the detonation front was in agreement with existing experimental observations under the same condition.

Taki, S.; Fujiwara, T.

1976-01-01

293

Maxillary distraction osteogenesis: a two-dimensional mathematical model.  

PubMed

Patients with cleft lip and palate with severe maxillary retrusion usually have a mandible with anterior-superior autorotation and subsequent overclosure and loss of the vertical facial dimension. Maxillary distraction osteogenesis can correct the sagittal maxillomandibular relationship and should simultaneously reestablish vertical dimension through maxillary vertical height increase and clockwise rotation of the mandible to restore facial balance. We present a two-dimensional mathematical model in the sagittal plane, which reestablishes sagittal and vertical skeletal deficiencies and proper occlusal alignment for planning maxillary advancement with distraction osteogenesis in patients with cleft lip and palate. The model is illustrated in a case of a 13-year-old boy with a complete bilateral cleft lip and palate and severe maxillary retrusion. The two-dimensional mathematical model described in this article allows the surgeon and orthodontist to calculate in a simple and accurate way the ideal distraction vector to advance the maxilla to its desired position. PMID:11314377

Swennen, G; Figueroa, A A; Schierle, H; Polley, J W; Malevez, C

2000-07-01

294

Two-dimensional semi-parametric alignment of chromatograms.  

PubMed

We present a comprehensive alignment algorithm that extends the semi-parametric approach to two dimensions. The algorithm is based on modeling shifts with a two-dimensional "warp function" such that the sample chromatogram - its shifts corrected with the warp function - is adjusted to the reference chromatogram by minimizing the squared intensity difference. A warp function approach has the advantage that overlapping peaks are easily dealt with compared to other proposed two-dimensional algorithms. Another advantage is that missing peaks are allowed if the absence of these peaks has little numerical effect on the warp function computation and if these peaks occur between existing peaks. Performance of the algorithm is demonstrated using GC×GC data from three batches of three diesel oil samples and LC-MS data from a mouse breast cancer data set. PMID:24794941

de Boer, Wim P H; Lankelma, Jan

2014-06-01

295

Two-dimensional solar models: evolution and hydrodynamics  

SciTech Connect

We use the fully-implicit Euler-Lagrange two-dimensional code ROTORC to model evolution of the Sun. The code was developed to model the evolution of rotating stars. The code operates in a quasi-static mode, taking timesteps on an evolutionary scale, or in a hydrodynamics mode, taking short timesteps to track dynamical instabilities at a given point in the evolution. We first calculate a two-dimensional nonrotating solar evolution model using ROTORC, and compare the model structure with that of a one-dimensional model calculated with an updated version of the Iben evolution code. We also calculate the evolution of a solar model with a slow initial rotation rate. We use the code`s hydrodynamic mode to determine whether rotation rate gradients that may develop at the envelope convection zone base cause dynamical instabilities producing large-scale material flows and angular momentum redistribution.

Guzik, J.A.; Deupree, R.G.

1996-12-31

296

Phase separation under two-dimensional Poiseuille flow.  

PubMed

The spinodal decomposition of a two-dimensional binary fluid under Poiseuille flow is studied by numerical simulation. We investigated time dependence of domain sizes in directions parallel and perpendicular to the flow. In an effective region of the flow, the power-law growth of a characteristic length in the direction parallel to the flow changes from the diffusive regime with the growth exponent alpha=1/3 to a new regime. The scaling invariance of the growth in the perpendicular direction is destroyed after the diffusive regime. A recurrent prevalence of thick and thin domains which determines log-time periodic oscillations has not been observed in our model. The growth exponents in the infinite system under two-dimensional Poiseuille flow are obtained by the renormalization group. PMID:11414907

Kiwata, H

2001-05-01

297

On two-dimensional flows of compressible fluids  

NASA Technical Reports Server (NTRS)

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

Bergman, Stefan

1945-01-01

298

Multigrid Navier-Stokes calculation for two dimensional cascades  

NASA Astrophysics Data System (ADS)

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

Yang, Ce; Lao, Dazhong; Jiang, Zikang

1998-03-01

299

Direct energy cascade in two-dimensional compressible quantum turbulence  

SciTech Connect

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

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

2010-06-15

300

Two-Dimensional Planar Chromatography with a Closed Adsorbent Layer  

NASA Astrophysics Data System (ADS)

A new two-dimensional chromatography process on closed plates is proposed. A previously described device with ethanol as a mobile phase is used to experimentally study two-dimensional thin-layer chromatography (2D TLC) on plates with 5 × 5 and 10 × 10 cm sizes. This work includes the experimental study and comparison of the following TLC versions: (1) the proposed 2D TLC version with a closed adsorbent layer with 1D separation on closed plates (an ascending mobile phase flow) and (2) conventional 2D TLC with an open adsorbent layer. The ascending version of 2D TLC with a closed adsorbent layer considerably (byR~55%) shortens the chromatographic time, especially with the use of 5 × 5 cm plates in the 2D separation version compared with the 1D version on 10 × 10 cm plates.

Berezkin, V. G.; Kormishkina, E. V.

2008-03-01

301

Dipolar Fermions in Quasi-Two-Dimensional Square Lattice  

NASA Astrophysics Data System (ADS)

Motivated by recent experimental realization of quantum degenerate dipolar Fermi gas, we study a system of ultralcold single- and two-species polar fermions in a double layer two-dimensional square lattice. The long-range anisotropic nature of dipole-dipole interaction has shown a rich phase diagram on a two dimensional square lattice*. We investigate how the interlayer coupling affects the monolayer system. Our study focuses on the regime where the fermions are closed to half-filling, which is when lattice effects play an important role. We find several correlated phases by using a functional renormalization group technique, which also provides estimates for the critical temperature of each phase. [*] S. G. Bhongale et. al. arXiv:1209.2671 and Phys. Rev. Lett. 108 145301 (2012).

Lai, Chen-Yen; Tsai, Shan-Wen

2013-03-01

302

A two-dimensional dam-break flood plain model  

USGS Publications Warehouse

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.

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

1985-01-01

303

Gas Kinetic Approach to Two-Dimensional Traffic Flow  

NASA Astrophysics Data System (ADS)

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

Nagatani, Takashi

1996-10-01

304

Recombination in one- and two-dimensional fitness landscapes.  

PubMed

We consider many-site mutation-recombination models of molecular evolution, where fitness is a function of a Hamming distance from one (one-dimensional case) or two (two-dimensional case) sequences. For the one-dimensional case, we calculate the population distribution dynamics for a model with zero fitness and an arbitrary symmetric initial distribution and find an error threshold transition point in the single-peak fitness model for a given initial symmetric distribution. We calculate the recombination period in the case of a single-peak fitness function, when the original population is located at one sequence, at some Hamming distance from the peak configuration. Steady-state fitness is calculated with finite genome length corrections. We derive analytical equations for the two-dimensional mutation-recombination model. PMID:20866270

Avetisyan, Zh; Saakian, David B

2010-05-01

305

No-hair conjecture in two-dimensional dilaton supergravity  

NASA Astrophysics Data System (ADS)

We study two-dimensional (2D) dilaton gravity and supergravity following Hamiltonian methods. First, we consider the structure of constraints of 2D dilaton gravity, and then the 2D dilaton supergravity theory is obtained taking the square root of the bosonic constraints. We integrate exactly the equations of motion in both cases, and we show that the solutions of the equation of motion of 2D dilaton supergravity differ from the solutions of 2D dilaton gravity only by boundary conditions on the fermionic variables; i.e., the black holes of 2D dilaton supergravity theory are exactly the same black holes of 2D bosonic dilaton gravity modulo supersymmetry transformations. This result is the two-dimensional analogue of the no-hair theorem for supergravity.

Gamboa, J.; Georgelin, Y.

1993-11-01

306

Unshielded fetal magnetocardiography system using two-dimensional gradiometers  

NASA Astrophysics Data System (ADS)

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 25 weeks' gestation was measured under an unshielded environment in real time. Moreover, the P and T waves for 25 and 34 weeks' 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.

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

2008-03-01

307

Two-dimensional Simulations of Correlation Reflectometry in Fusion Plasmas  

SciTech Connect

A two-dimensional wave propagation code, developed specifically to simulate correlation reflectometry in large-scale fusion plasmas is described. The code makes use of separate computational methods in the vacuum, underdense and reflection regions of the plasma in order to obtain the high computational efficiency necessary for correlation analysis. Simulations of Tokamak Fusion Test Reactor (TFTR) plasma with internal transport barriers are presented and compared with one-dimensional full-wave simulations. It is shown that the two-dimensional simulations are remarkably similar to the results of the one-dimensional full-wave analysis for a wide range of turbulent correlation lengths. Implications for the interpretation of correlation reflectometer measurements in fusion plasma are discussed.

E.J. Valeo; G.J. Kramer; R. Nazikian

2001-07-05

308

Structure of finite two-dimensional Yukawa lattices: dust crystals.  

PubMed

Dust particles in plasmas are often confined near the boundary between the plasma bulk and the sheath where the gravitation is balanced by electrostatic force. To keep dust particles from running away horizontally, an electrostatic potential is usually applied to the electrode surrounding these dusty plasmas and, under appropriate conditions, we have finite two-dimensional lattices of dust particles. Modeling the interaction between dust particles as the isotropic Yukawa interaction, structures of finite two-dimensional Yukawa systems at low temperatures have been analyzed both by numerical simulations and variational methods. The effect of the correlation energy between dust particles is shown to play an important role in the formation of the one-body distribution in these systems. PMID:11736277

Totsuji, H; Totsuji, C; Tsuruta, K

2001-12-01

309

Two-Dimensional Computational Model for Wave Rotor Flow Dynamics  

NASA Technical Reports Server (NTRS)

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.

Welch, Gerard E.

1996-01-01

310

Two-dimensional graphic analysis of DNA sequence homologies.  

PubMed Central

We describe a computer program designed to facilitate the pattern matching analysis of homologies between DNA sequences. It takes advantage of a two-dimensional plot in order to simplify the evaluation of significant structures inherited in the sequences. The program can be divided into three parts, i) algorithm for search of homologies, ii) two-dimensional graphic display of the result, iii) further graphic treatment to enhance significant structures. The power of the graphic display is presented by the following application of the program. We conducted a search for direct repeats in the mouse immunoglobulin kappa-chain genes. Both the five J DNA sequences and other shorter repeats were found. We also found a longer stretch of homology that could indicate the presence of duplicated DNA in the J4, J5 region.

Harr, R; Hagblom, P; Gustafsson, P

1982-01-01

311

On certain one- and two-dimensional hypersingular integral equations  

SciTech Connect

For two-dimensional singular and hypersingular integrals more general definitions than the traditional ones are introduced. For a hypersingular operator on a sphere a new spectral relation is obtained. Quadrature formulae of the kind of discrete vortex pairs for one-dimensional and of the kind of closed vortex frames for two-dimensional hypersingular integrals are considered; questions on their convergence are discussed, as well as the convergence of numerical solutions to the corresponding hypersingular integral equations on a finite line interval and a circle. An experiment on the numerical solution of a hypersingular integral equation on a sphere is carried out, which demonstrates analogies between numerical solutions of hypersingular integral equations on a finite interval and a sphere.

Anfinogenov, A Yu; Lifanov, I K [N.E. Zhukovsky Military Engineering Academy, Moscow (Russian Federation); Lifanov, P I [Institute of Computational Mathematics of the Russian Academy of Sciences, Moscow (Russian Federation)

2001-08-31

312

Two-dimensional Raman-terahertz spectroscopy of water  

PubMed Central

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.

Savolainen, Janne; Ahmed, Saima; Hamm, Peter

2013-01-01

313

Quasi-two-dimensional HEMT model for microwave CAD applications  

NASA Astrophysics Data System (ADS)

A new quasi-two-dimensional HEMT model has been developed that solves the physical device equations in a more rigorous fashion than previously reported. The model incorporates a quantum mechanical description of the free electron concentration, self-consistently solving the Schrodinger and Poisson equations. The influence of traps and incomplete donor ionization are also included. The conventional one-dimensional charge-control approach is shown to be inadequate for HEMT's and is replaced by a two-dimensional version that more accurately describes the channel dynamics under normal bias conditions. This allows the simulation to accurately model pinch-off characteristics, which are essential for digital, power and low-noise device characterization. The scheme also includes a detailed energy transport model, avalanche breakdown and gate conduction terms. The highly efficient model is applied to the dc and microwave characterization of AlGaAs/GaAs and pseudomorphic HEMT's.

Drury, Robert; Snowden, Christopher M.

1995-06-01

314

Rapid photon flux switching in two-dimensional photonic crystals  

Microsoft Academic Search

We have investigated the out-of-plane propagation of light in two-dimensional photonic band-gap crystals consisting of long dielectric nanorods. Defects, which sufficiently break the crystal symmetry, can produce photonic states localized at the defect sites. We show that this localization can result in a sharp transition between the state of the out-of-plane light propagation through the entire photonic crystal, and the

X. Wang; K. Kempa; Z. F. Ren; B. Kimball

2004-01-01

315

Growth morphology of two-dimensional insect neural networks  

Microsoft Academic Search

Abstract How a collection of single neurons self-organize to form a complex functional system, the neural network, is a fundamental question. Two-dimensional in vitro invertebrate preparations o2er an attractive model system to tackle this question due to the large size ofthe neurons, and their ability to grow in relative isolation as well as to develop elaborate networks. We culture locust

Orit Shefi; Eshel Ben-jacob; Amir Ayali

2002-01-01

316

Dragging two-dimensional discrete solitons by moving linear defects  

Microsoft Academic Search

We study the mobility of small-amplitude solitons attached to moving defects which drag the solitons across a two-dimensional (2D) discrete nonlinear Schrödinger 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

Valeriy A. Brazhnyi; Boris A. Malomed

2011-01-01

317

High quality two-dimensional photonic crystal slab cavities  

Microsoft Academic Search

We have fabricated and characterized donor-mode nanocavities formed by a single defect cavity defined within a two-dimensional photonic crystal slab. Quantum dots emitting in the 1.1-1.3 micron range were used as luminescence sources, and a design using fractional edge dislocations was used to demonstrate well-confined dipole modes with high quality factors. By applying the fractional dislocation geometry, the measured quality

Tomoyuki Yoshie; Jelena Vuckovic; Axel Scherer; Hao Chen; Dennis Deppe

2001-01-01

318

Pairing correlations in the two-dimensional Hubbard model  

NASA Astrophysics Data System (ADS)

Using the quantum Monte Carlo method, we study several pairing correlations for the two-dimensional Hubbard model away from half filling. We analyze how the behavior of the correlations as a function of distance affects the existence of long-range order in momentum space. We found that in all channels the correlation length is of the order of one lattice spacing. Thus, we conclude that any enhancement of the correlations observed in momentum space is a short-distance effect.

Moreo, Adriana

1992-03-01

319

Two-Dimensional Regression for Interferometric Phase Extraction  

Microsoft Academic Search

An approach based on two-dimensional iterative nonlinear regression for retrieving phase information from single-frame interferograms was formulated and tested for fluid- and heat-flow measurements. Even though an initial crude phase assignment i.e., fringe-order numbers at limited data points is needed, the approach does not require complete phase unwrapping as in conventional techniques. Testing of computer-simulated and real interferometric data shows

Enxi Yu; Soyoung Stephen Cha

1998-01-01

320

REVIEWS OF TOPICAL PROBLEMS: Quasi-two-dimensional turbulence  

Microsoft Academic Search

We review the results of numerical and experimental studies in quasi-two-dimensional (Q2D) turbulence. We demonstrate that theoretical energy spectra with slopes -5\\/3 and -3 (Kraichnan-Batchelor-Leith) can be observed only for a special set of external parameters. The bottom drag, beta effect, finite Rossby-Obukhov radius or vertical stratification, which distinguish geophysical Q2D turbulence from its purely 2D counterpart, determine the organization

Sergei D. Danilov; D. Gurarie

2000-01-01

321

A two dimensional modeling of capacitively coupled plasma reactor  

Microsoft Academic Search

We have developed a two dimensional modeling based on the relaxation continuum (RCT) model for capacitively coupled plasma(CCP) reactor. Present 2D-model is one of the powerful tool to understand and design dry processes using a nonequilibrium plasma. 2D-t profile of net excitation rate and number densities of charged particles are shown in Ar 0.1-1.0Torr at 13.56MHz, with or without selfbias.

N. Nakano; T. Makabe

1996-01-01

322

Coarsening of Two-Dimensional Nanoclusters on Metal Surfaces  

Microsoft Academic Search

We describe experimental observations and theoretical analysis of the coarsening of distributions of two-dimensional nanoclusters, either adatom islands or vacancy pits, on metal surfaces. A detailed analyses is provided for Ag(111) and Ag(100) surfaces, although we also discuss corresponding behavior for Cu(111) and Cu(100) surfaces. The dominant kinetic pathway for coarsening can be either Ostwald ripening (OR), i.e., growth of

Patricia A. Thiel; Mingmin Shen; Da-Jiang Liu; J. W. Evans

2009-01-01

323

Two dimensional thermal and charge mapping of power thyristors  

NASA Technical Reports Server (NTRS)

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

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

1975-01-01

324

Efficient Method for ECG Compression Using Two Dimensional Multiwavelet Transform  

Microsoft Academic Search

? Abstract—In this paper we introduce an effective ECG compression algorithm based on two dimensional multi- wavelet transform. Multi-wavelets offer simultaneous orthogonality, symmetry and short support, which is not possible with scalar two-channel wavelet systems. These features are known to be important in signal processing. Thus multiwavelet offers the possibility of superior performance for image processing applications. The SPIHT algorithm

Morteza Moazami-Goudarzi; Mohammad H. Moradi; Ali Taheri

2005-01-01

325

A multilevel graph algorithm for two dimensional phase unwrapping  

Microsoft Academic Search

Two-dimensional phase unwrapping is the problem of deducing unambiguous “phase” from values known only modulo 2?. Many authors\\u000a agree that the objective of phase unwrapping should be to find a weighted minimum of the number of places where adjacent (discrete)\\u000a phase values differ by more than ? (called discontinuities). This NP-hard problem is of considerable practical interest, largely\\u000a due to

Iddit Shalem; Irad Yavneh

2008-01-01

326

On the water impact of general two-dimensional sections  

Microsoft Academic Search

We consider the analytic solution of the impact problem of a general two-dimensional body entering initially calm water. Of interest are the water splash-up height, the force history and the pressure distribution on the body. The potential-flow formulation of Wagner (Wagner, H. Math. Mech. 1932;12(4):193–215) is applied and extended to an arbitrary body section with the body boundary condition imposed

Xiaoming Mei; Yuming Liu; Dick K. P. Yue

1999-01-01

327

Two-dimensional condensation of K adatoms on Cu(0011)  

NASA Astrophysics Data System (ADS)

Low-energy electron diffraction observations for a potassium monolayer on Cu(OOl) at 330 K are reported and evidence for two-dimensional condensation of adatoms is presented. The condensation is suggested to be closely connected with the ionic-to-neutral change of adsorbates and the subsequent metallization of a monolayer. Similarity and difference between the present result and previous observations of halo patterns are also discussed.

Aruga, Tetsuya; Hiroshi, Tochihara; Yoshitada, Murata

1986-09-01

328

Two-dimensional amorphous silicon image sensor arrays  

Microsoft Academic Search

Large two-dimensional amorphous silicon image sensor arrays offer an advantage for high speed document scanning and medical X-ray imaging. We describe our page sized 200 spot per inch imager and the accompanying high speed readout electronics. The spatial resolution performance for white light and X-ray imaging is illustrated. We discuss how the important issues of noise and resolution depend on

X. D. Wu; R. Weisfield; S. Ready; R. Apte; M. Ngyuen; W. B. Jackson; P. Nylen

1996-01-01

329

Néel temperature for quasi-two-dimensional dipolar antiferromagnets  

NASA Astrophysics Data System (ADS)

We calculate the Néel temperature TN for two-dimensional isotropic dipolar Heisenberg antiferromagnets via linear spin-wave theory and a high-temperature expansion, by employing the method of Callen. The theoretical predictions for TN for K2MnF4, Rb2MnF4, Rb2MnCl4, and (CH3NH3)2MnCl4 are in good agreement with the measured values.

Pich, C.; Schwabl, F.

1994-01-01

330

Two-dimensional color-code quantum computation  

SciTech Connect

We describe in detail how to perform universal fault-tolerant quantum computation on a two-dimensional color code, making use of only nearest neighbor interactions. Three defects (holes) in the code are used to represent logical qubits. Triple-defect logical qubits are deformed into isolated triangular sections of color code to enable transversal implementation of all single logical qubit Clifford group gates. Controlled-NOT (CNOT) is implemented between pairs of triple-defect logical qubits via braiding.

Fowler, Austin G. [Centre for Quantum Computation and Communication Technology, School of Physics, University of Melbourne, Victoria 3010 (Australia)

2011-04-15

331

Long-wavelength behavior of two-dimensional photonic crystals  

Microsoft Academic Search

We solve analytically the multiple-scattering equations for two-dimensional photonic crystals in the long-wavelength limit. Different approximations of the electric and magnetic susceptibilities are presented from a unified pseudopotential point of view. The nature of the so-called plasmon-polariton bands is clarified. Its frequency as a function of the wire radius is discussed. The corresponding tunable ``magnetic surface plasmon'' band is pointed

S. T. Chui; Zhifang Lin

2008-01-01

332

Global Gauge Anomalies in Two-Dimensional Bosonic Sigma Models  

Microsoft Academic Search

We revisit the gauging of rigid symmetries in two-dimensional bosonic sigma models with a Wess-Zumino term in the action.\\u000a Such a term is related to a background closed 3-form H on the target space. More exactly, the sigma-model Feynman amplitudes of classical fields are associated to a bundle gerbe with connection of curvature H over the target space. Under conditions

Krzysztof Gawe?dzki; Rafal R. Suszek; Konrad Waldorf

2011-01-01

333

Two-dimensional simulation of plasma-based ion implantation  

Microsoft Academic Search

A particle-in-cell simulation is used to study the time-dependent evolution of the potential and the electrical field surrounding two-dimensional objects during a high voltage pulse in the context of plasma immersion ion implantation. The numerical procedure is based on the solution of Poisson's equation on a grid and the determination of the movement of the particles through the grid. Ion

M. Paulus; L. Stals; U. Rüde; B. Rauschenbach

1999-01-01

334

Nonlinear photonic crystal with two-dimensional dodecagonal superlattice  

Microsoft Academic Search

The LiNbO3 nonlinear photonic crystal with two-dimensional dodecagonal superlattice was proposed for the first time. The distribution of reciprocal vectors in this quasiperiodic structure was analyzed in detail. By quasi-phase matching technique, red, green, blue and yellow harmonic beams were obtained simultaneously in one quasiperiodically poled crystal. And the similar results can be accomplished by rotating around z axis by

Boqin Ma; Yang Lin; Jiao Ouyang

2011-01-01

335

Current injection into a two-dimensional anisotropic bidomain.  

PubMed Central

A two-dimensional sheet of anisotropic cardiac tissue is represented with the bidomain model, and the finite element method is used to solve the bidomain equations. When the anisotropy ratios of the intracellular and extracellular spaces are not equal, the injection of current into the tissue induces a transmembrane potential that has a complicated spatial dependence, including adjacent regions of depolarized and hyperpolarized tissue. This behavior may have important implications for the electrical stimulation of cardiac tissue and for defibrillation.

Sepulveda, N G; Roth, B J; Wikswo, J P

1989-01-01

336

Symmetries of scaler fields. III. Two-dimensional integrable models  

Microsoft Academic Search

The symmetry of the relativistically invariant two-dimensional system \\/phi\\/ââ = f(\\/phi\\/) is investigated. Necessary and sufficient conditions for the system to belong to the Liouville type are obtained. Simple examples of Liouville systems are given. It is shown that to establish all integrable systems it is sufficient to assume that the elements of the Lie-Backlund algebra are polynomials in \\/phi\\/

A. G. Meshkov

1985-01-01

337

Generation and recombination in two-dimensional bipolar transistors  

NASA Astrophysics Data System (ADS)

We study the effects of recombination and generation process on the operation of bipolar junction transistor based on two-dimensional materials, and in particular, graphone. Here, we use Shockley-Read-Hall model to study these process. First, we investigate the current-voltage characteristics of a graphone p- n junction considering generation and recombination process. Then, we calculate the estimated changes in current gain, cutoff frequency, and output characteristics of a graphone bipolar junction transistor designed in a recent study.

Gharekhanlou, Behnaz; Khorasani, Sina

2014-06-01

338

Two-dimensional quantum-corrected eternal black hole  

Microsoft Academic Search

The one-loop quantum corrections to geometry and thermodynamics of black hole\\u000aare studied for the two-dimensional RST model. We chose boundary conditions\\u000acorresponding to the eternal black hole being in the thermal equilibrium with\\u000athe Hawking radiation. The equations of motion are exactly integrated. The one\\u000aof the solutions obtained is the constant curvature space-time with dilaton\\u000abeing a constant

Sergey N. Solodukhin

1996-01-01

339

Topological defect motifs in two-dimensional Coulomb clusters  

Microsoft Academic Search

We study the distribution of topological defects in two-dimensional Coulomb clusters with parabolic lateral confinement. The minima hopping algorithm based on molecular dynamics is used to efficiently locate the ground- and low-energy metastable states, and their structure is analysed by means of the Delaunay triangulation. The size, structure and distribution of geometry-induced lattice imperfections strongly depends on the system size

A. Radzvilavicius; E. Anisimovas

2011-01-01

340

Two-dimensional model for twin-roll continuous casting  

Microsoft Academic Search

A numerical algorithm for the two-dimensional solidification problem in the twin-roll continuous casting system is presented\\u000a in this paper. Attention is focused on the elucidation of heat transfer and flow characteristics in both the liquid and the\\u000a solid phases. The present mathematical model can be applied to general full Navier-Stokes and energy equations, thereby covering\\u000a the wide range of twin-roll

T. Saitoh; H. Hojo; H. Yaguchi; C. G. Kang

1989-01-01

341

Strain rate imaging using two-dimensional speckle tracking  

Microsoft Academic Search

Strain rate images (SRI) of the beating heart have been proposed to identify non-contracting regions of myocardium. Initial attempts used spatial derivatives of tissue velocity (Doppler) signals. Here, an alternate method is proposed based on two-dimensional phase-sensitive speckle tracking applied to very high frame rate, real-time images. This processing can produce high resolution maps of the time derivative of the

K. Kaluzynski; Xunchang Chen; Stanislav Y. Emelianov; Andrei R. Skovoroda; Matthew O'Donnell

2001-01-01

342

Magnetotransport in a nonplanar two-dimensional electron gas  

Microsoft Academic Search

We investigate the magnetoresistance of a nonplanar two-dimensional electron gas (2DEG) fabricated by growth of a GaAs\\/(AlGa)As heterojunction on a wafer prepatterned with facets at 20° to the substrate. Applying a uniform magnetic field (B) produces a spatially nonuniform component of field perpendicular to the 2DEG. With the field in the plane of the substrate, the resistance measured across an

M. L. Leadbeater; C. L. Foden; J. H. Burroughes; M. Pepper; T. M. Burke; L. L. Wang; M. P. Grimshaw; D. A. Ritchie

1995-01-01

343

The two-dimensional lateral injection in-plane laser  

Microsoft Academic Search

In this paper, a two-dimensional (2-D) p-n junction was used for population inversion in a GaAs quantum-well laser. The device, incorporating modulation doping within the core of a separate confinement heterostructure, was designed to exploit the amphoteric behavior of silicon in GaAs [doping p-type on (311)A facets and n-type on (100)]. It is believed to be the first lasing device

Angus North; Jeremy Burroughes; Theresa Burke; Andrew Shields; Carl E. Norman; Michael Pepper

1999-01-01

344

Atomization processes of two-dimensional liquid sheets  

Microsoft Academic Search

Experiments were conducted to characterize the behavior of a two-dimensional liquid sheet exposed to a co-flowing gas. A wide range of flow conditions was explored. The parameters varied were the liquid velocity, gas velocity and liquid sheet thickness. The sheet was studied with co-flow present on one side, co-flow present on both sides and no co-flow. The gas co-flow was

Anne Geraldine Mouis

2003-01-01

345

Kinetic theory of Onsager's vortices in two-dimensional hydrodynamics  

Microsoft Academic Search

Starting from the Liouville equation, and using a BBGKY-like hierarchy, we derive a kinetic equation for the point vortex gas in two-dimensional (2D) hydrodynamics, taking two-body correlations and collective effects into account. This equation is valid at the order 1\\/N where N>>1 is the number of point vortices in the system (we assume that their individual circulation scales like \\\\gamma

Pierre-Henri Chavanis

2011-01-01

346

Microwave absorption of a two-dimensional electron gas  

NASA Astrophysics Data System (ADS)

A frequency tuneable (40 - 60 GHz) EPR spectrometer was used for direct measurements of microwave power absorption of a high mobility two-dimensional electron gas (2DEG) in GaAs/GaAlAs heterojunctions. The spectra reflect a relatively broad absorption band (due to cyclotron resonance absorption), with superimposed sharp features attributed to confined plasmon modes. The influence of the sample size on the sequence of the observed plasmon modes is investigated.

Fedorych, O. M.; Moreau, S.; Byszewski, M.; Sadowski, M. L.; Potemski, M.; Studenikin, S.; Wasilewski, Z. R.

2007-04-01

347

Two-dimensional analysis of Coanda effect in ideal fluid  

Microsoft Academic Search

The Coanda effect, or the phenomenon of a jet running along a curved wall is analyzed with a two-dimensional approach assuming an ideal fluid. A thick jet emerging from a nozzle with an arbitrary kick down angle is mainly concerned, relative to the upper-surface-blowing high lift concept. The result of the free stream line analysis of a jet running along

Kingo Takasawa

1986-01-01

348

Temperature maxima in stable two-dimensional shock waves  

SciTech Connect

We use molecular dynamics to study the structure of moderately strong shock waves in dense two-dimensional fluids, using Lucy{close_quote}s pair potential. The stationary profiles show relatively broad temperature maxima, for both the longitudinal and the average kinetic temperatures, just as does Mott-Smith{close_quote}s model for strong shock waves in dilute three-dimensional gases. {copyright} {ital 1997} {ital The American Physical Society}

Kum, O. [Agency for Defense Development, 138, P.O. Box 35, Yuseong Taejeon, South (Korea)] [Agency for Defense Development, 138, P.O. Box 35, Yuseong Taejeon, South (Korea); Hoover, W.G.; Hoover, C.G. [Department of Applied Science, University of California at Davis/Livermore, Livermore, California 94551-7808 (United States)] [Department of Applied Science, University of California at Davis/Livermore, Livermore, California 94551-7808 (United States); [Lawrence Livermore National Laboratory, Livermore, California 94551-7808 (United States)

1997-07-01

349

Inverse radiative transfer problems in two-dimensional participating media  

Microsoft Academic Search

In the present work inverse radiative transfer problems in two-dimensional heterogeneous participating media are considered. An implicit formulation is used in which the cost functional of the squared residues between calculated and measured exit radiation intensities is minimized. The Levenberg–Marquardt method, a gradient-based minimization algorithm, is used, and therefore at every iteration of the iterative procedure the solution of the

Mariella J. Berrocal Tito; Nilson C. Roberty; Antônio J. Silva Neto; Jorge Bravo Cabrejos

2004-01-01

350

Analytical study of idealized two-dimensional cellular detonations  

Microsoft Academic Search

.   In this study, the idealized two-dimensional detonation cells were decomposed into the primary units referred to as sub-cells.\\u000a Based on the theory of oblique shock waves, an analytical formula was derived to describe the relation between the Mach number\\u000a ratio through triple-shock collision and the geometric properties of the cell. By applying a modified blast wave theory, an\\u000a analytical

X. Y. Hu; D. L. Zhang; Z. L. Jiang

2002-01-01

351

Analytical study of idealized two-dimensional cellular detonations  

Microsoft Academic Search

In this study, the idealized two-dimensional detonation cells were decomposed into the primary units referred to as sub-cells. Based on the theory of oblique shock waves, an analytical formula was derived to describe the relation between the Mach number ratio through triple-shock collision and the geometric properties of the cell. By applying a modified blast wave theory, an analytical model

X. Y. Hu; D. L. Zhang; Z. L. Jiang

2002-01-01

352

Optical properties of a dense two-dimensional electron gas  

Microsoft Academic Search

Electronic surface charge densities on the silicon side of a silicon-silica interface, which are nearly 100 times larger than the densities that can be generated with MOS structures, may be generated with mobile positive ions. Some optical properties of these dense two-dimensional electron gases, e.g., the reflectivity for light incident on the gas and the dispersion of light coupled to

R. C. Alig

1976-01-01

353

Two-dimensional high temperature strain measurement system  

NASA Technical Reports Server (NTRS)

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

Lant, Christian T.; Barranger, John P.

1989-01-01

354

Two-dimensional effects in a triangular convecting fin  

NASA Astrophysics Data System (ADS)

A FEM solution is presented for the two-dimensional triangular fin, together with heat-transfer data for a wide range of Biot number and length-to-base thickness ratio; the information may accordingly be used for purposes of performance prediction as well as design. In the case of design tasks, it must be recalled that the assumption of a constant heat-transfer coefficient constitutes a major limitation of the analysis.

Aziz, A.; Nguyen, H.

1992-03-01

355

Nonlinear optical rectification in a two-dimensional system  

NASA Astrophysics Data System (ADS)

The optical rectification (OR) in the two-dimensional electron-hole system is investigated theoretically. An analytical expression formula of the OR coefficient is obtained via the framework of compact density matrix approach and the iterative method. The results show that the OR coefficient depends strongly on the system?s size and the relaxation time. A more obvious OR coefficient should be found by adjusting an appropriate choice of the system parameters.

Zhu, Xun; Gu, Mingliang; Jia, Jingjing; Zhang, Chaojin

2014-06-01

356

Statistical thermodynamics of a two-dimensional relativistic gas  

Microsoft Academic Search

In this paper we study a fully relativistic model of a two-dimensional hard-disk gas. This model avoids the general problems associated with relativistic particle collisions and is therefore an ideal system to study relativistic effects in statistical thermodynamics. We study this model using molecular-dynamics simulation, concentrating on the velocity distribution functions. We obtain results for x and y components of

Afshin Montakhab; Malihe Ghodrat; Mahmood Barati

2009-01-01

357

Two-dimensional features of strong shock waves in gases  

Microsoft Academic Search

Strong shock wave around 10 km\\/s are generated in low-density (13.3 Pa) air and nitrogen by using a free-piston, double-diaphragm shock tube with the test section of 40mm×40mm. Two-dimensional features of radiation intensity behind the shock waves are observed at the test section by using a combined system of an image converter camera and an image processor. The pseudo-colour representation

H. Iizuka; H. Honma; A. Tsukamoto; T. Ohno

1990-01-01

358

Two-dimensional array transducers using thick film connection technology  

Microsoft Academic Search

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

Stephen W. Smith; Edward D. Light

1993-01-01

359

Accelerating universe in two-dimensional noncommutative dilaton cosmology  

NASA Astrophysics Data System (ADS)

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.

Kim, Wontae; Yoon, Myung Seok

2007-02-01

360

Two Dimensional Electrons in a Lateral Magnetic Superlattice  

NASA Astrophysics Data System (ADS)

We report, for the first time, ballistic magnetoresistance effects in a two-dimensional electron gas (2DEG) subjected to a spatially modulated periodic magnetic field. The periodic magnetic field is formed by the presence of superconducting stripes on the surface of the heterostructure with a 2DEG. We observe oscillatory magnetoresistance due to a commensurability effect between the classical cyclotron diameter and the period of magnetic modulation. The behavior is in agreement with existing theory with no adjustable parameters.

Carmona, H. A.; Geim, A. K.; Nogaret, A.; Main, P. C.; Foster, T. J.; Henini, M.; Beaumont, S. P.; Blamire, M. G.

1995-04-01

361

A Calculation Procedure for Two-Dimensional Elliptic Situations  

Microsoft Academic Search

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

Suhas Patankar

1981-01-01

362

Two-dimensional modeling of the formation of spheromak configurations  

SciTech Connect

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

Jardin, S.C.; Park, W.

1980-09-01

363

Glassy behavior of two-dimensional stripe-forming systems  

NASA Astrophysics Data System (ADS)

We study two-dimensional frustrated but nondisordered systems applying a replica approach to a stripe-forming model with competing interactions. The phenomenology of the model is representative of several well-known systems, like high-Tc superconductors and ultrathin ferromagnetic films, which have been the subject of intense research. We establish the existence of a glass transition to a nonergodic regime accompanied by an exponential number of long-lived metastable states, responsible for slow dynamics and nonequilibrium effects.

Ribeiro Teixeira, Ana C.; Stariolo, Daniel A.; Barci, Daniel G.

2013-06-01

364

Two-dimensional hybrid simulation of a curved bow shock  

Microsoft Academic Search

Results are presented from two-dimensional hybrid simulations of curved collisionless supercritical shocks, retaining both quasi-perpendicular and quasi-parallel sections of the shock in order to study the character and origin of the foreshock ion population. The simulations demonstrate that the foreshock ion population is dominated by ions impinging upon the quasi-parallel side of the shock, while nonlocal transport from the quasi-perpendicular

V. A. Thomas; D. Winske

1990-01-01

365

In vivo two-dimensional NMR correlation spectroscopy  

NASA Astrophysics Data System (ADS)

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.)

Kraft, Robert A.

1999-10-01

366

Computer simulation of two-dimensional impact tests on propellant  

Microsoft Academic Search

Computational simulations were performed of several hazards tests previously carried out by LLNL. The hazards tests consisted of side-on impacts of a propellant cylinder by a massive steel projectile with subsequent blast wave loading from an adjacent explosive charge. The simulations used a dynamic fracture model previously developed by SRI. The computational results showed that whereas the fracture-induced new surface

W. J. Murri; L. Seaman

1983-01-01

367

Symmetrical analysis of complex two-dimensional hexagonal photonic crystals  

Microsoft Academic Search

We study complex hexagonal photonic crystals with unit cells that include different dielectric cylinders. A general symmetrical perturbation approach for a hexagonal lattice with up to three basis rods is presented that systematically develops other structural derivatives including comblike structures. We show how the band spectrum of these complex structures evolves from the most symmetrical prophase. The results are in

N. Malkova; S. Kim; T. Dilazaro; V. Gopalan

2003-01-01

368

Two dimensional liquid crystal devices and their computer simulations  

NASA Astrophysics Data System (ADS)

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.

Wang, Bin

369

Two-dimensional potential double layers and discrete auroras  

NASA Technical Reports Server (NTRS)

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.

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

1979-01-01

370

Fidelity susceptibility in two-dimensional spin-orbit models  

NASA Astrophysics Data System (ADS)

We study the quantum phase transitions in the two-dimensional spin-orbit models in terms of fidelity susceptibility and reduced fidelity susceptibility. An order-to-order phase transition is identified by fidelity susceptibility in the two-dimensional Heisenberg XXZ model with Dzyaloshinsky-Moriya interaction on a square lattice. The finite size scaling of fidelity susceptibility shows a power-law divergence at criticality, which indicates the quantum phase transition is of second order. Two distinct types of quantum phase transitions are witnessed by fidelity susceptibility in Kitaev-Heisenberg model on a hexagonal lattice. We exploit the symmetry of two-dimensional quantum compass model, and obtain a simple analytic expression of reduced fidelity susceptibility. Compared with the derivative of ground-state energy, the fidelity susceptibility is a bit more sensitive to phase transition. The violation of power-law behavior for the scaling of reduced fidelity susceptibility at criticality suggests that the quantum phase transition belongs to a first-order transition. We conclude that fidelity susceptibility and reduced fidelity susceptibility show great advantage to characterize diverse quantum phase transitions in spin-orbit models.

You, Wen-Long; Dong, Yu-Li

2011-11-01

371

Procedures for two-dimensional electrophoresis of proteins  

SciTech Connect

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.

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

1996-10-01

372

Two-dimensional optical beam deflector operated by wavelength tuning.  

PubMed

A new method based on an optical delay line structure is proposed for two-dimensional raster optical beam steering. For one-dimensional beam steering, the laser beam to be deflected is split into N co-directional sub-beams of equal intensity with the aid of a plane-parallel plate. These sub-beams experience a relative time delay, which translates into a phase difference, thus forming a phased array. When the laser wavelength is tuned, the relative phase varies and the far-field interference footprint can be steered across a receive plane. By employing two plane-parallel plates in series, the described scheme can be extended to produce a two-dimensional N x N array of sub-beams, allowing two-dimensional beam steering via wavelength tuning. In this case, wavelength tuning over a larger range leads to a linear deflection which repeats itself in a raster-like fashion. One direction of deflection repeats itself multiple times as wavelength is scanned over larger range, that is, a raster effect. In this paper, the principle is theoretically derived and formulated, and the preliminary experimental results with four sub-beams are presented. PMID:19516557

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

2006-05-01

373

Quick release engine cylinder  

DOEpatents

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.

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

2000-01-01

374

Statistical mechanics of two-dimensional and geophysical flows  

NASA Astrophysics Data System (ADS)

The theoretical study of the self-organization of two-dimensional and geophysical turbulent flows is addressed based on statistical mechanics methods. This review is a self-contained presentation of classical and recent works on this subject; from the statistical mechanics basis of the theory up to applications to Jupiter’s troposphere and ocean vortices and jets. Emphasize has been placed on examples with available analytical treatment in order to favor better understanding of the physics and dynamics. After a brief presentation of the 2D Euler and quasi-geostrophic equations, the specificity of two-dimensional and geophysical turbulence is emphasized. The equilibrium microcanonical measure is built from the Liouville theorem. Important statistical mechanics concepts (large deviations and mean field approach) and thermodynamic concepts (ensemble inequivalence and negative heat capacity) are briefly explained and described. On this theoretical basis, we predict the output of the long time evolution of complex turbulent flows as statistical equilibria. This is applied to make quantitative models of two-dimensional turbulence, the Great Red Spot and other Jovian vortices, ocean jets like the Gulf-Stream, and ocean vortices. A detailed comparison between these statistical equilibria and real flow observations is provided. We also present recent results for non-equilibrium situations, for the studies of either the relaxation towards equilibrium or non-equilibrium steady states. In this last case, forces and dissipation are in a statistical balance; fluxes of conserved quantity characterize the system and microcanonical or other equilibrium measures no longer describe the system.

Bouchet, Freddy; Venaille, Antoine

2012-06-01

375

Two-dimensional 220 MHz Fourier transform EPR imaging  

NASA Astrophysics Data System (ADS)

In the last decade radiofrequency continuous-wave EPR spectrometers have been developed to detect and localize free radicals in vivo. Only recently, pulsed radiofrequency EPR spectrometers have been described for imaging applications with small samples. In the present work, we show the first two-dimensional image obtained at 220 MHz on a large phantom (40 ml) that simulates typical conditions of in vivo EPR imaging. This pulsed EPR apparatus has the potential to make the time required for three-dimensional imaging compatible with the biological half-life of normally used paramagnetic probes.

Placidi, Giuseppe; Brivati, John A.; Alecci, Marcello; Testa, Luca; Sotgiu, Antonello

1998-07-01

376

Investigation of Membrane Peptides by Two-Dimensional Infrared Spectroscopy  

NASA Astrophysics Data System (ADS)

Two-dimensional infrared spectroscopy (2D IR) is a useful tool for studying the structure of membrane peptides. Isotope labeling individual amino acids with 13C=18O decouples the isotope labeled amide I from the other amide I modes in the peptide. Work has been done on both the M2 ion channel and ovispirin antimicrobial peptide, studying the diagonal linewidths of the isotope labeled amide I. The diagonal linewidth of the isotope labeled amide I gives information about the local environment of that residue, which in turn gives structural information about the membrane peptide.

Blanco, Emily Ann; Zanni, Martin T.

2009-06-01

377

Memory device for two-dimensional radiant energy array computers  

NASA Technical Reports Server (NTRS)

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

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

1977-01-01

378

Two-Dimensional Spectroscopy with the Cosmic Origins Spectrograph  

NASA Astrophysics Data System (ADS)

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

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

2011-05-01

379

Two-dimensional neutron scintillation detector with optimal gamma discrimination  

SciTech Connect

The gamma sensitivity of a two-dimensional scintillation neutron detector based on position sensitive photomultipliers (Hamamatsu R2387 PM) has been minimized by a digital differential discrimination unit. Since the photomultiplier gain is position-dependent by [+-]25% a discrimination unit was developed where digital upper and lower discrimination levels are set due to the position-dependent photomultiplier gain obtained from calibration measurements. By this method narrow discriminator windows can be used to reduce the gamma background drastically without effecting the neutron sensitivity of the detector. The new discrimination method and its performance tested by neutron measurements will be described. Experimental results concerning spatial resolution and [gamma]-sensitivity are presented.

Kanyo, M.; Reinartz, R.; Schelten, J.; Mueller, K.D. (Research Center Juelich GmbH (Germany). Central Lab. for Electronics)

1993-08-01

380

Blind deconvolution of two-dimensional complex data  

SciTech Connect

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.

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

1994-01-01

381

Measure of Diracness in two-dimensional semiconductors  

NASA Astrophysics Data System (ADS)

We analyze the low-energy properties of two-dimensional direct-gap semiconductors, such as, for example, the transition-metal dichalcogenides MoS2, WS2, and their diselenide analogues MoSe2, WSe2, etc., which are currently intensively investigated. In general, their electrons have a mixed character —they can be massive Dirac fermions as well as simple Schrödinger particles. We propose a measure (Diracness) for the degree of mixing between the two characters and discuss how this quantity can in principle be extracted experimentally, within magneto-transport measurements, and numerically via ab initio calculations.

Goerbig, M. O.; Montambaux, G.; Piéchon, F.

2014-03-01

382

Highly directional thermal emission from two-dimensional silicon structures.  

PubMed

We simulate, fabricate, and characterize near perfectly absorbing two-dimensional grating structures in the thermal infrared using heavily doped silicon (HdSi) that supports long wave infrared surface plasmon polaritons (LWIR SPP's). The devices were designed and optimized using both finite difference time domain (FDTD) and rigorous coupled wave analysis (RCWA) simulation techniques to satisfy stringent requirements for thermal management applications requiring high thermal radiation absorption over a narrow angular range and low visible radiation absorption over a broad angular range. After optimization and fabrication, characterization was performed using reflection spectroscopy and normal incidence emissivity measurements. Excellent agreement between simulation and experiment was obtained. PMID:23546065

Ribaudo, Troy; Peters, David W; Ellis, A Robert; Davids, Paul S; Shaner, Eric A

2013-03-25

383

Correction-to-scaling exponent for two-dimensional percolation  

SciTech Connect

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

Ziff, Robert M. [Center for the Study of Complex Systems and Department of Chemical Engineering, University of Michigan, Ann Arbor, Michigan 48109 (United States)

2011-02-15

384

Exciton-polariton gap solitons in two-dimensional lattices.  

PubMed

We report on the two-dimensional gap-soliton nature of exciton-polariton macroscopic coherent phases (PMCP) in a square lattice with a tunable amplitude. The resonantly excited PMCP forms close to the negative mass M point of the lattice band structure with energy within the lattice band gap and its wave function localized within a few lattice periods. The PMCPs are well described as gap solitons resulting from the interplay between repulsive polariton-polariton interactions and effective attractive forces due to the negative mass. The solitonic nature accounts for the reduction of the PMCP coherence length and optical excitation threshold with increasing lattice amplitude. PMID:24138259

Cerda-Méndez, E A; Sarkar, D; Krizhanovskii, D N; Gavrilov, S S; Biermann, K; Skolnick, M S; Santos, P V

2013-10-01

385

Basics and recent advances of two dimensional- polyacrylamide gel electrophoresis  

PubMed Central

Gel- based proteomics is one of the most versatile methods for fractionating protein complexes. Among these methods, two dimensional- polyacrylamide gel electrophoresis (2-DE) represents a mainstay orthogonal approach, which is popularly used to simultaneously fractionate, identify, and quantify proteins when coupled with mass spectrometric identification or other immunological tests. Although 2-DE was first introduced more than three decades ago, several challenges and limitations to its utility still exist. This review discusses the principles of 2-DE as well as both recent methodological advances and new applications.

2014-01-01

386

Basics and recent advances of two dimensional- polyacrylamide gel electrophoresis.  

PubMed

Gel- based proteomics is one of the most versatile methods for fractionating protein complexes. Among these methods, two dimensional- polyacrylamide gel electrophoresis (2-DE) represents a mainstay orthogonal approach, which is popularly used to simultaneously fractionate, identify, and quantify proteins when coupled with mass spectrometric identification or other immunological tests. Although 2-DE was first introduced more than three decades ago, several challenges and limitations to its utility still exist. This review discusses the principles of 2-DE as well as both recent methodological advances and new applications. PMID:24735559

Magdeldin, Sameh; Enany, Shymaa; Yoshida, Yutaka; Xu, Bo; Zhang, Ying; Zureena, Zam; Lokamani, Ilambarthi; Yaoita, Eishin; Yamamoto, Tadashi

2014-01-01

387

Holographic two-dimensional photonic crystal of LED decorative illumination  

NASA Astrophysics Data System (ADS)

The film of holographic two-dimensional (2D) photonic crystal is used for the led illumination system. According to the decorative patterns, the structure sizes of 2D photonic crystal and relevant led luminaire have been reasonably designed. Then the master mask of 2D photonic crystal is produced with the method of multiple-beam interference. With the experiment of LED illumination, the results show that it is able to meet the expected decorative patterns of LED illumination. While the master mask is used to copy optical coating of polycarbonate, it will provide a better option for LED decorative illumination under low cost.

Li, Gaoming; Zheng, Yidan; Qiu, Yishen; Huang, Aixian

2012-11-01

388

Two-dimensional model of the plasma thruster  

SciTech Connect

Given the condition that the flow generated by a self-induced magnetic field is two-dimensional and steady, a model for the arc region of the plasma thruster is formulated based on magnetohydrodynamic (MHD) descriptions. Use is made of a generalized Ohm's law that includes the Hall and ion slip terms. Characteristics of the arc region are investigated as functions of system parameters. The study shows that the Hall effect causes the current to concentrate severely at the trailing edge of the anode, and it is suggested that if the plasma thruster is a coaxial type, it is better to have the cathode inside. 7 references.

Park, W.T.; Choi, D.I.

1988-04-01

389

Soap films as two-dimensional classical fluids  

NASA Astrophysics Data System (ADS)

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

Chomaz, J. M.; Cathalau, B.

1990-02-01

390

Two-dimensional crystals: managing light for optoelectronics.  

PubMed

Semiconducting two-dimensional (2D) crystals such as MoS2 and WSe2 exhibit unusual optical properties that can be exploited for novel optoelectronics ranging from flexible photovoltaic cells to harmonic generation and electro-optical modulation devices. Rapid progress of the field, particularly in the growth area, is beginning to enable ways to implement 2D crystals into devices with tailored functionalities. For practical device performance, a key challenge is to maximize light-matter interactions in the material, which is inherently weak due to its atomically thin nature. Light management around the 2D layers with the use of plasmonic nanostructures can provide a compelling solution. PMID:23834654

Eda, Goki; Maier, Stefan A

2013-07-23

391

LETTER: Morphology of two-dimensional fracture surfaces  

NASA Astrophysics Data System (ADS)

We consider the morphology of two-dimensional cracks observed in experimental results obtained from paper samples and compare these results with the numerical simulations of the random fuse model (RFM). We demonstrate that the data obey multiscaling at small scales but cross over to self-affine scaling at larger scales. Next, we show that the roughness exponent of the random fuse model is recovered by a simpler model that produces a connected crack, while a directed crack yields a different result, close to a random walk. We discuss the multiscaling behaviour of all these models.

Alava, Mikko J.; Nukala, Phani K. V. V.; Zapperi, Stefano

2006-10-01

392

Negative Poisson ratio in two-dimensional networks under tension  

NASA Astrophysics Data System (ADS)

The elastic properties of two-dimensional networks under tension are studied by the mean-field approximation and Monte Carlo simulation. The networks are characterized by fixed (polymerized) connectivity and either a square-well or a Hooke's-law interaction among their components. Both self-avoiding and phantom networks are examined. The elastic properties of Hooke's-law networks at large equilibrium length are found to be well represented by a mean-field model. All the networks investigated show a negative Poisson ratio over a range of tension. At finite tension, the phantom networks exhibit a phase transition to a collapsed state.

Boal, David H.; Seifert, Udo; Shillcock, Julian C.

1993-12-01

393

Fringe demodulation using the two-dimensional phase differencing operator.  

PubMed

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

Rajshekhar, Gannavarpu; Rastogi, Pramod

2012-10-15

394

Kinetic analysis of two dimensional metallic grating Cerenkov maser  

SciTech Connect

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

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

2011-08-15

395

Two-dimensional quantum black holes: numerical methods  

NASA Astrophysics Data System (ADS)

We present details of a new numerical code designed to study the formation and evaporation of two-dimensional black holes within the Callan-Giddings-Harvey-Strominger model. We explain several elements of the scheme that are crucial to resolve the late-time behavior of the spacetime, including regularization of the field variables, compactification of the coordinates, the algebraic form of the discretized equations of motion and the use of a modified Richardson extrapolation scheme to achieve high-order convergence. Physical interpretation of our results will be discussed in detail elsewhere.

Ramazano?lu, Fethi M.; Pretorius, Frans

2010-12-01

396

A two-dimensional permanent magnetic lattice for ultracold atoms  

NASA Astrophysics Data System (ADS)

We propose a permanent magnetic lattice for creating a two-dimensional array of Ioffe-Pritchard permanent magnetic microtraps for holding and controlling ultracold atoms and Bose-Einstein condensates. This atom chip may be fabricated using laser carving on two separate magnetic films such as Tb6Gd10Fe80Co4 with thicknesses of 500 and 50 nm, respectively, and a periodicity of 1 ?m. The trap depth and frequencies are controlled via an external bias field to handle tunneling rates between lattice sites. We present analytical expressions and compare them with numerical calculations.

Mohammadi, Amir; Ghanbari, Saeed; Pariz, Aref

2013-07-01

397

Transfer-matrix analysis of a two-dimensional quasicrystal  

SciTech Connect

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

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

1989-07-17

398

High-Tc superconductors in the two-dimensional limit:  

PubMed

The free modulation of interlayer distance in a layered high-transition temperature (high-Tc) superconductor is of crucial importance not only for the study of the superconducting mechanism but also for the practical application of high-Tc superconducting materials. Two-dimensional (2D) superconductors were achieved by intercalating a long-chain organic compound into bismuth-based high-Tc cuprates. Although the intercalation of the organic chain increased the interlayer distance remarkably, to tens of angstroms, the superconducting transition temperature of the intercalate was nearly the same as that of the pristine material, suggesting the 2D nature of the high-Tc superconductivity. PMID:9616119

Choy; Kwon; Park

1998-06-01

399

Effective theory of chiral two-dimensional superfluids  

NASA Astrophysics Data System (ADS)

We construct, to leading orders in the momentum expansion, an effective theory of a chiral (px+ipy) two-dimensional fermionic superfluid at zero temperature that is consistent with nonrelativistic general coordinate invariance. This theory naturally incorporates the parity and time-reversal violating effects such as the Hall viscosity and the edge current. The particle number current and stress tensor are computed and their linear response to electromagnetic and gravitational sources is calculated. We also consider an isolated vortex in a chiral superfluid and identify the leading chirality effect in the density depletion profile.

Hoyos, Carlos; Moroz, Sergej; Son, Dam Thanh

2014-05-01

400

Two dimensional hydrodynamics with gauge and gravitational anomalies  

NASA Astrophysics Data System (ADS)

We present a new approach to discuss two-dimensional chiral and nonchiral hydrodynamics with gauge and gravitational anomalies. Exact constitutive relations for the stress tensor and charge current are obtained. For the chiral theory, the constitutive relations may be put in the ideal (chiral) fluid form, whereas the constitutive relations corresponding to nonchiral case do not take the ideal fluid form. The constitutive relations in the presence of both gravity and gauge sectors are new. These expressions, in the absence of the gauge sector, reproduce the results obtained in the gradient expansion approach.

Banerjee, Rabin; Dey, Shirsendu; Majhi, Bibhas Ranjan; Mitra, Arpan Krishna

2014-05-01

401

Mott transition in the two-dimensional Hubbard model  

NASA Astrophysics Data System (ADS)

We are interested in the description of the Mott-Hubbard transition from a perturbation theory arising from a two-dimensional Hubbard model. The self-energy within the random phase approximation presents some inconsistencies; one of them is that its imaginary part presents more than one zero, which is a violation of the Luttinger theorem. We use a Bogolyubov transformation and within a spin density wave mean field, we recalculate the self-energy in the new ground state, and it is able to describe the Mott-Hubbard transition, satisfying the Luttinger condition.

Pérez-Navarro, A.; Costa-Quintana, J.; López-Aguilar, F.

1999-01-01

402

Approximation algorithms for maximum two-dimensional pattern matching  

SciTech Connect

We introduce the following optimization version of the classical pattern matching problem (referred to as the maximum pattern matching problem). Given a two-dimensional rectangular text and a 2- dimensional rectangular pattern find the maximum number of non- overlapping occurrences of the pattern in the text. Unlike the classical 2-dimensional pattern matching problem, the maximum pattern matching problem is NP - complete. We devise polynomial time approximation algorithms and approximation schemes for this problem. We also briefly discuss how the approximation algorithms can be extended to include a number of other variants of the problem.

Arikati, S.R. [Memphis Univ., TN (United States); Dessmark, A.; Lingas, A. [Lund Univ. (Sweden); Marathe, M.

1996-07-01

403

Bending Poisson Effect in Two-Dimensional Crystals  

NASA Astrophysics Data System (ADS)

As the Poisson effect formulates, lateral strains in a material can be caused by a uniaxial stress in the perpendicular direction, but no net lateral strain should be induced in a thin homogeneous elastic plate subjected to a pure bending load. Here, we demonstrated by ab initio simulations that significant exotic lateral strains can be induced by pure bending in two-dimensional crystals, in which the lateral components of chemical bonds can respond to bending curvature directly. The bending Poisson ratio, defined as the ratio of lateral strain to the curvature, is a function of curvature depending on chemical constitution, bonding structure, and atomic interaction of the crystal, and is anisotropic.

Liu, Xiaofei; Pan, Douxing; Hong, Yuanzhou; Guo, Wanlin

2014-05-01

404

Spin dynamics in a two-dimensional quantum gas  

NASA Astrophysics Data System (ADS)

We have investigated spin dynamics in a two-dimensional quantum gas. Through spin-changing collisions, two clouds with opposite spin orientations are spontaneously created in a Bose-Einstein condensate. After ballistic expansion, both clouds acquire ring-shaped density distributions with superimposed angular density modulations. The density distributions depend on the applied magnetic field and are well explained by a simple Bogoliubov model. We show that the two clouds are anticorrelated in momentum space. The observed momentum correlations pave the way towards the creation of an atom source with nonlocal Einstein-Podolsky-Rosen entanglement.

Pedersen, Poul L.; Gajdacz, Miroslav; Deuretzbacher, Frank; Santos, Luis; Klempt, Carsten; Sherson, Jacob F.; Hilliard, Andrew J.; Arlt, Jan J.

2014-05-01

405

Modular two-dimensional analysis of SAW filters. I. Theory.  

PubMed

An accurate simulation tool to meet the stringent requirements for broadband surface-acoustic-wave (SAW) filters is described. The primary goal was to develop a modular software tool in which first- and second-order effects can be easily modeled as separate modules providing an overall high-precision model for SAW devices. The model takes into account surface wave diffraction and refraction, quasi-two-dimensional static charge distribution, metal resistance and external load impedances. The angular spectrum of waves formalism is interpreted in such a way as to render possible the simultaneous description of all effects mentioned. A sample of the results is given for the potential distribution. PMID:18263120

Visintini, G; Baghai-Wadji, A R; Manner, O

1992-01-01

406

Nonlinear acoustic propagation in two-dimensional ducts  

NASA Technical Reports Server (NTRS)

The method of multiple scales is used to obtain a second-order uniformly valid expansion for the nonlinear acoustic wave propagation in a two-dimensional duct whose walls are treated with a nonlinear acoustic material. The wave propagation in the duct is characterized by the unsteady nonlinear Euler equations. The results show that nonlinear effects tend to flatten and broaden the absorption versus frequency curve, in qualitative agreement with the experimental observations. Moreover, the effect of the gas nonlinearity increases with increasing sound frequency, whereas the effect of the material nonlinearity decreases with increasing sound frequency.

Nayfeh, A. H.; Tsai, M.-S.

1974-01-01

407

Thermodynamics of the Two-Dimensional Hubbard Model  

NASA Astrophysics Data System (ADS)

The application of a numerically exact continuous time impurity solver with the DCA dynamical mean field theory has allowed us to study the thermodynamics of the two-dimensional Hubbard model for finite, but large cluster sizes. Variation in cluster size, upwards of 50-sites, allows for extrapolation to the thermodynamic limit. We present results relevant to cold gas systems, such as entropy, double occupancy and nearest-neighbour spin correlations as well as discuss the implications of these calculations on pseudogap physics of the High-Tc Cuprate superconductors away from half filling.

Leblanc, James; Gull, Emanuel

2013-03-01

408

Operational manual for two-dimensional transonic code TSFOIL  

NASA Technical Reports Server (NTRS)

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.

Stahara, S. S.

1978-01-01

409

Consistent Theory of Turbulent Transport in Two-Dimensional Magnetohydrodynamics  

SciTech Connect

A theory of turbulent transport is presented in two-dimensional magnetohydrodynamics with background shear and magnetic fields. We provide theoretical predictions for the transport of magnetic flux, momentum, and particles and turbulent intensities, which show stronger reduction compared with the hydrodynamic case, with different dependences on shearing rate, magnetic field, and values of viscosity, Ohmic diffusion, and particle diffusivity. In particular, particle transport is more severely suppressed than momentum transport, effectively leading to a more efficient momentum transport. The role of magnetic fields in quenching transport without altering the amplitude of flow velocity and in inhibiting the generation of shear flows is elucidated. Implications of the results are discussed.

Kim, Eun-jin [Department of Applied Mathematics, University of Sheffield, Sheffield S3 7RH (United Kingdom)

2006-03-03

410

Topological defect motifs in two-dimensional Coulomb clusters.  

PubMed

We study the distribution of topological defects in two-dimensional Coulomb clusters with parabolic lateral confinement. The minima hopping algorithm based on molecular dynamics is used to efficiently locate the ground- and low-energy metastable states, and their structure is analysed by means of the Delaunay triangulation. The size, structure and distribution of geometry-induced lattice imperfections strongly depends on the system size and the energetic state. Besides isolated disclinations and dislocations, classification of defect motifs includes defect compounds-grain boundaries, rosette defects, vacancies and interstitial particles. Proliferation of defects in metastable configurations destroys the orientational order of the Wigner lattice. PMID:21891854

Radzvilavi?ius, A; Anisimovas, E

2011-09-28

411

Topological defect motifs in two-dimensional Coulomb clusters  

NASA Astrophysics Data System (ADS)

We study the distribution of topological defects in two-dimensional Coulomb clusters with parabolic lateral confinement. The minima hopping algorithm based on molecular dynamics is used to efficiently locate the ground- and low-energy metastable states, and their structure is analysed by means of the Delaunay triangulation. The size, structure and distribution of geometry-induced lattice imperfections strongly depends on the system size and the energetic state. Besides isolated disclinations and dislocations, classification of defect motifs includes defect compounds—grain boundaries, rosette defects, vacancies and interstitial particles. Proliferation of defects in metastable configurations destroys the orientational order of the Wigner lattice.

Radzvilavi?ius, A.; Anisimovas, E.

2011-09-01

412

Magnetism and pairing of two-dimensional trapped fermions.  

PubMed

The emergence of local phases in a trapped two-component Fermi gas in an optical lattice is studied using quantum Monte Carlo simulations. We treat temperatures that are comparable to or lower than those presently achievable in experiments and large enough systems that both magnetic and paired phases can be detected by inspection of the behavior of suitable short-range correlations. We use the latter to suggest the interaction strength and temperature range at which experimental observation of incipient magnetism and d-wave pairing are more likely and evaluate the relation between entropy and temperature in two-dimensional confined fermionic systems. PMID:21405279

Chiesa, Simone; Varney, Christopher N; Rigol, Marcos; Scalettar, Richard T

2011-01-21

413

Quasi-two-dimensional optomechanical crystals with a complete phononicbandgap  

NASA Astrophysics Data System (ADS)

A fully planar two-dimensional optomechanical crystal formed in a silicon microchip is used to create a structure devoid of phonons in the GHz frequency range. A nanoscale photonic crystal cavity is placed inside the phononic bandgap crystal in order to probe the properties of the localized acoustic modes. By studying the trends in mechanical damping, mode density, and optomechanical coupling strength of the acoustic resonances over an array of structures with varying geometric properties, clear evidence of a complete phononic bandgap is shown.

Alegre, T.; Safavi-Naeini, A.; Winger, M.; Painter, O.

2011-03-01

414

A numerical study of two-dimensional shock vortex interaction  

NASA Technical Reports Server (NTRS)

The numerical analysis of shock vortex interaction in a two-dimensional channel is discussed in this paper. The Euler equations and the two-step MacCormack scheme are employed in this numerical analysis. The comparison of the numerical results with the theoretical analyses and experimental results in the literature has provided unique insights into the dynamics of the transient interaction process and the needs for further theoretical developments. The results are useful in applications to problems in aeroacoustics and the transient aerodynamics of high performance aircraft.

Pao, S. P.; Salas, M. D.

1981-01-01

415

Application of two dimensional periodic molecular dynamics to interfaces.  

NASA Astrophysics Data System (ADS)

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

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

1997-08-01

416

Two-dimensional multiple scattering for N slit array  

NASA Astrophysics Data System (ADS)

A new method has been proposed to analyze two-dimensional multiple scattering of a plane wave by N parallel cylindrical structures. Diffraction of a plane wave incident on N parallel slits is formulated exactly via Kobayashi-Nomura's method in an asymptotic form in which the (i + 1)-fold scattering field is given in terms of the i-fold scattering field. The solution consists of scattering pattern functions for a single slit and their derivatives. The pattern functions are modified when applied to multiple scattering by cylindrical structures of arbitrary cross sections. Numerical solutions are presented for multiple scattering by strips.

Hongo, K.; Furusawa, N.; Hori, H.

1980-05-01

417

Jamming and geometry of two-dimensional foams  

NASA Astrophysics Data System (ADS)

We experimentally probe the vicinity of the jamming point J, located at a density phi corresponding to random close packing (phircp=0.842), in two dimensional, bidisperse packings of foam bubbles. We vary the density of the foam layer and extract geometrical measures by image analysis. We confirm the predicted scaling of the average contact number Z with phi and compare the distribution of local contact numbers to a simple model. We further establish that the distribution of areas p(A) strongly depends on phi. Finally, we find that the distribution of contact forces p(f) systematically varies with density.

Katgert, G.; van Hecke, M.

2010-11-01

418

A fractal transition in the two dimensional shear layer  

NASA Technical Reports Server (NTRS)

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.

Jimenez, Javier; Martel, Carlos

1990-01-01

419

Two-Dimensional Macroscopic Quantum Dynamics in Ybco Josephson Junctions  

NASA Astrophysics Data System (ADS)

We theoretically study classical thermal activation (TA) and macroscopic quantum tunneling (MQT) for a YBa2Cu3O7-?(YBCO) Josephson junction coupled with an LC circuit. The TA and MQT escape rate are calculated by taking into account the two-dimensional nature of the classical and quantum phase dynamics. We find that the MQT escape rate is largely suppressed by the coupling to the LC circuit. On the other hand, this coupling leads to the slight reduction of the TA escape rate. These results are relevant for the interpretation of a recent experiment on the MQT and TA phenomena in YBCO bi-epitaxial Josephson junctions.

Kawabata, Shiro; Kato, Takeo; Lombardi, Floriana; Bauch, Thilo

2010-12-01

420

Two-Dimensional Macroscopic Quantum Dynamics in Ybco Josephson Junctions  

NASA Astrophysics Data System (ADS)

We theoretically study classical thermal activation (TA) and macroscopic quantum tunneling (MQT) for a YBa2Cu3O7-?(YBCO) Josephson junction coupled with an LC circuit. The TA and MQT escape rate are calculated by taking into account the two-dimensional nature of the classical and quantum phase dynamics. We find that the MQT escape rate is largely suppressed by the coupling to the LC circuit. On the other hand, this coupling leads to the slight reduction of the TA escape rate. These results are relevant for the interpretation of a recent experiment on the MQT and TA phenomena in YBCO bi-epitaxial Josephson junctions.

Kawabata, Shiro; Kato, Takeo; Lombardi, Floriana; Bauch, Thilo

421

Three phonon coupling to a two dimensional helium film  

NASA Astrophysics Data System (ADS)

An experimental measurement of thermal boundary conductance to a two dimensional superfluid has been carried out using third sound resonance. This conductance varies as T 6.5±1 between 0.7K and 0.1K. It is four orders or magnitude smaller, at 0.1K, than even the boundary conductance originally calculated by Khalatnikov for three dimensions. We consider a simple three phonon process which gives a conductance which varies as T 8 and agrees with measurements to within an order of magnitude.

Rutledge, J. E.; McMillan, W. L.; Mochel, J. M.

1981-08-01

422

Growth of correlation in compressible two-dimensional magnetofluid turbulence  

NASA Technical Reports Server (NTRS)

Spectral transfer has been proposed as the primary mechanism for generating outward-propagating Alfven waves in the solar wind. This process has been investigated extensively for imcompressible magnetofluids, but the issue of whether it occurs in compressible magnetofluids such as the solar wind remains unresolved. The results of direct numerical simulations of nonisentropic-compressible two-dimensional MHD turbulence indicate that, for systems with finite initial cross helicity, the correlation between the fluctuating velocity field and the fluctuating magnetic field grows as a function of time. This growth of correlation can be interpreted as a turbulent process, as shown by examination of modal wavenumber spectra.

Dahlburg, R. B.; Picone, J. M.; Karpen, J. T.

1988-01-01

423

Fractional-step method for two-dimensional estuarine transport  

USGS Publications Warehouse

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

Bales, Jerad, D.; Holley, Edward, R.

1988-01-01

424

Dilution effects in two-dimensional quantum orbital systems.  

PubMed

Interacting orbital degrees of freedom in a Mott insulator are essentially directional and frustrated. In this Letter, the effect of dilution in a quantum-orbital system with this kind of interaction is studied by analyzing a minimal orbital model which we call the two-dimensional quantum compass model. We find that the decrease of the ordering temperature due to dilution is stronger than that in spin models, but it is also much weaker than that of the classical model. The difference between the classical and the quantum-orbital systems arises from the enhancement of the effective dimensionality due to quantum fluctuations. PMID:17678040

Tanaka, Takayoshi; Ishihara, Sumio

2007-06-22

425

Dilution Effects in Two-Dimensional Quantum Orbital Systems  

NASA Astrophysics Data System (ADS)

Interacting orbital degrees of freedom in a Mott insulator are essentially directional and frustrated. In this Letter, the effect of dilution in a quantum-orbital system with this kind of interaction is studied by analyzing a minimal orbital model which we call the two-dimensional quantum compass model. We find that the decrease of the ordering temperature due to dilution is stronger than that in spin models, but it is also much weaker than that of the classical model. The difference between the classical and the quantum-orbital systems arises from the enhancement of the effective dimensionality due to quantum fluctuations.

Tanaka, Takayoshi; Ishihara, Sumio

2007-06-01

426

Two-dimensional metamaterial transparent metal electrodes for infrared optoelectronics.  

PubMed

We examine the optical properties of two-dimensionally nanostructured metals in the metamaterial regime for infrared applications. Compared with straight nanowires and nanogrids, serpentine structures exhibit much lower optical losses of less than 7% even at a large metal area fraction of 0.3. The low loss is primarily due to a small effective conductivity of the meandering structures, and self-inductance plays a modest role in reducing losses in these structures. The high transparency at a large metal area coverage would be useful for transparent electrodes in optoelectronic devices. PMID:24978563

Clark, Samuel M; Han, Sang Eon

2014-06-15

427

Two-dimensional dynamics of relativistic solitons in cold plasmas  

SciTech Connect

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.

Lehmann, G.; Laedke, E. W.; Spatschek, K. H. [Institut fuer Theoretische Physik, Heinrich-Heine-Universitaet Duesseldorf, D-40225 Duesseldorf (Germany)

2008-07-15

428

Laminar flame and acoustic waves in two-dimensional flow  

SciTech Connect

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

Zaytsev, M. L., E-mail: mlzaytsev@gmail.com; Akkerman, V. B., E-mail: slava.akkerman@gmail.com [Russian Academy of Sciences, Nuclear Safety Institute (Russian Federation)

2011-03-15

429

Two-dimensional hybrid simulation of a curved bow shock  

NASA Technical Reports Server (NTRS)

Results are presented from two-dimensional hybrid simulations of curved collisionless supercritical shocks, retaining both quasi-perpendicular and quasi-parallel sections of the shock in order to study the character and origin of the foreshock ion population. The simulations demonstrate that the foreshock ion population is dominated by ions impinging upon the quasi-parallel side of the shock, while nonlocal transport from the quasi-perpendicular side of the shock into the foreshock region is minimal. Further, it is shown that the ions gain energy by drifting significantly in the direction of the convection electric field through multiple shock encounters.

Thomas, V. A.; Winske, D.

1990-01-01

430

Flow of an aqueous foam through a two-dimensional porous medium: a pore scale investigation  

NASA Astrophysics Data System (ADS)

Flowing foams are used in many engineering and technical applications. A well-known application is oil recovery. Another one is the remediation of polluted soil: the foam is injected into the ground in order to mobilize chemical species present in the medium. Apart from potential interesting physico-chemical and biochemical properties, foams have peculiar flow properties that might be of benefit to the application. We address here this physical aspect of the topic. As a precursor to the study of foam flow through a complex porous material, we first study the behavior of an aqueous two-dimensional foam flowing through a medium consisting of two parallel channels with different widths, at fixed medium porosity, that is, at fixed total combined width of the two channels. The flow velocity, and hence flux, in each channel is measured by analyzing images of the flowing foam. It is then compared to a theoretical model, the basic assumption of which is that the pressure drop along a channel is identical for both channels. This pressure drop both consists of (i) a dynamic pressure drop, which is controlled by bubble-wall friction and depends on the foam velocity in the channel, and (ii) a capillary pressure drop over the bubble films that emerge at the channel outlet, the latter pressure drop being controlled by the radius of curvature of the bubble film. Based on this assumption, the dependence of the ratio of the foam velocities in the two channels is inferred as a function of the channel width ratio. It compares well to the measurements and shows that the flow behavior is highly dependent on the foam structure within the narrowest of the two channels, especially when a "bamboo" structure is obtained. Consequently, the flux in a channel is found to have a more complicated relation to the channel width than expected for the flow of a standard Newtonian fluid in the same geometry. We provide a comparison to this reference configuration. We then study the flow of the same foam into a two-dimensional porous medium consisting of cylinders that have been positioned randomly between the two plates of the Hele-Shaw cell described above. Intermittent flow and non-stationarity of the velocity field are observed under permanent controlled inlet flow. Flow channeling is also different from what would be expected for a Newtonian fluid, which allows a different part of the pore population to be visited. Foam flow in a two-dimensional porous medium;

Meheust, Y.; Jones, S. A.; Dollet, B.; Cox, S.; Cantat, I.

2012-12-01

431

Quantitative prediction for two-dimensional bacterial genomic displays  

NASA Astrophysics Data System (ADS)

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

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

2006-03-01

432

Construction of a two-dimensional thermal neutron detector  

NASA Astrophysics Data System (ADS)

China Spallation Neutron Source (CSNS) was under construction since 2008. A two-dimensional thermal neutron detector with sensitive area of 200mm×200mm was constructed for the Reflect Spectrometer of CSNS. The detector was based on two-dimensional cathode strip readout MWPC, using 5.5atm3He+2.5atmC3H8 mixture as working gas, and the thickness of the gas volume was 16mm. A readout electronics system was also developed for the detector, which mainly consists of charge-sensitive preamplifiers, amplifiers, charge measurement modules and a 6U VME64x crate. The design maximum neutron count rate of the detector was 105 events per second and the calculated neutron detection efficiency was about 70% for A2 neutrons. A prototype of the detector had been constructed at first, which own an energy resolution (FWHM) of about 23% for 55Fe 5.9keV X-ray, and its spatial resolution (FWHM) along the anode wire direction was about 300?m in X-ray test. The detector was then tested by an Am-Be neutron source. The pulse height spectrum of the neutron signal was studied. The detector can work normally and has a good performance in neutron-gamma ray discrimination.

Wang, Xiao-Hu; Chen, Yuan-Bo; Sheng, Huan-Yi; Zhao, Yu-Bin; Zhang, Hong-Yu; Zhu, Qi-Ming; Liu, Rong-Guang; Zhang, Jian; Xu, Pin

2009-07-01

433

Two-dimensional nuclear magnetic resonance of quadrupolar systems  

SciTech Connect

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.

Wang, Shuanhu

1997-09-17

434

Prediction of a new two-dimensional metallic carbon allotrope.  

PubMed

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

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

2013-02-14

435

Morphometric investigations in mitral stenosis using two dimensional echocardiography.  

PubMed Central

A method is proposed for comparing the orifice size and the morphology of stenotic mitral valves, removed intact at the time of replacement, with the preoperative two dimensional echocardiographic cross-sections. The excised mitral valve apparatus is suspended on a specially constructed mounting. To avoid shrinkage the orifice is stabilised with an airfilled balloon. A radiography is taken directing the x-ray beam perpendicular to the valve orifice. In 40 of 51 patients this method provided the means of relating the echocardiographic cross-sections to the morphology of the valve. Planimetry of the valve area compared favourably with the postoperatively determined orifice size. Agreement was found in 34 of 40 patients in orifice shape between preoperative echocardiograms and x-rays of th excised valve. The relation between intraoperative estimation of size of the valve, using dilators with known diameters, and the postoperative results was less favourable. Areas of calcification were identified on echocardiography as dense conglomerate echoes. In 30 patients (75%) the localisation of calcium deposits and in 67% the degree of calcification was in agreement with the x-rays of the valve taken after operation. In addition to determination of the area, two dimensional echocardiography allows detailed studies of the stenotic valves, and is of particular importance for planning operative treatment. Images

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

1982-01-01

436

A Two-Dimensional Linear Bicharacteristic Scheme for Electromagnetics  

NASA Technical Reports Server (NTRS)

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.

Beggs, John H.

2002-01-01

437

Spectral measurements of two-dimensional color images  

NASA Astrophysics Data System (ADS)

In this work we propose a prototype of the spectral vision system, which can be used to measure a color spectrum and two- dimensional spectral images. We first designed a low- dimensional broad band color filter set with a constraint of positive spectral values by the unsupervised neural network. Then we constructed a compact size optical setup for the spectral synthesizer, which can be used to synthesize the light corresponding to the spectral characteristics of the color filter. In the optical setup we implemented the color filters by the use of the liquid crystal spatial light modulator (LCSLM). In our experiments we illuminated a sample of a real world scene by the synthesized lights and detected the intensity images of the filtering process by the CCD- camera. The intensity images correspond to the optically calculated inner products between the color filters and a sample. The data obtained from the filtering process is only a few monochrome images and therefore convenient for storing and transmitting spectral images. From the detected inner products we reconstructed the sample's color spectra by the use of inverse matrix. We present experimental results of measuring a single color spectrum and two-dimensional spectral images.

Hauta-Kasari, Markku; Miyazawa, Kanae; Toyooka, Satoru; Parkkinen, Jussi P.

1999-05-01

438

Two-dimensional, unstructured mesh generation for tidal models  

NASA Astrophysics Data System (ADS)

The successful implementation of a finite element model for computing shallow-water flow requires the identification and spatial discretization of a surface water region. Since no robust criterion or node spacing routine exists, which incorporates physical characteristics and subsequent responses into the mesh generation process, modelers are left to rely on crude gridding criteria as well as their knowledge of particular domains and their intuition. Two separate methods to generate a finite element mesh are compared for the Gulf of Mexico. A wavelength-based criterion and an alternative approach, which employs a localized truncation error analysis (LTEA), are presented. Both meshes have roughly the same number of nodes, although the distribution of these nodes is very different. Two-dimensional depth-averaged simulations of flow using a linearized form of the generalized wave continuity equation and momentum equations are performed with the LTEA-based mesh and the wavelength-to-gridsize ratio mesh. All simulations are forced with a single tidal constituent, M2. Use of the LTEA-based procedure is shown to produce a superior (i.e., less error) two-dimensional grid because the physics of shallow-water flow, as represented by discrete equations, are incorporated into the mesh generation process. Copyright

Hagen, S. C.; Westerink, J. J.; Kolar, R. L.; Horstmann, O.

2001-03-01

439

Aspects of jamming in two-dimensional athermal frictionless systems  

NASA Astrophysics Data System (ADS)

In this work we provide an overview of jamming transitions in two dimensional systems focusing on the limit of frictionless particle interactions in the absence of thermal fluctuations. We first discuss jamming in systems with short range repulsive interactions, where the onset of jamming occurs at a critical packing density and where certain quantities show a divergence indicative of critical behavior. We describe how aspects of the dynamics change as the jamming density is approached and how these dynamics can be explored using externally driven probes. Different particle shapes can produce jamming densities much lower than those observed for disk-shaped particles, and we show how jamming exhibits fragility for some shapes while for other shapes this is absent. Next we describe the effects of long range interactions and jamming behavior in systems such as charged colloids, vortices in type-II superconductors, and dislocations. We consider the effect of adding obstacles to frictionless jamming systems and discuss connections between this type of jamming and systems that exhibit depinning transitions. Finally, we discuss open questions such as whether the jamming transition in all these different systems can be described by the same or a small subset of universal behaviors, as well as future directions for studies of jamming transitions in two dimensional systems, such as jamming in self-driven or active matter systems.

Reichhardt, C.; Reichhardt, C. J. Olson

440

Phonons in two-dimensional soft colloidal crystals  

NASA Astrophysics Data System (ADS)

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

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

2013-08-01

441

Two-dimensional molecular space with regular molecular structure.  

PubMed

A novel two-dimensional molecular space (layered carboxylpropylamidephenylsilica, CPAPhS) with regular carboxyl groups was successfully synthesized through grafting carboxyl groups in the structure of layered (aminophenyl)silica using butanedioic anhydride. The carboxyl groups regularly arranged in the layered CPAPhS can react with various organic molecules with amino and hydroxyl groups through formation of reactive intermediate with catalyzers, such as SOCl2. In this research, an example was used to prove the reaction properties of regular carboxyl groups in layered CPAPhS. The layered CPAPhS was reacted with SOCl2 to form layered acyl chloridepropylamidephenylsilica (ACPAPhS) and then reacted with n-butylamine and n-butyl alcohol to form layered n-butylamidepropylamidephenylsilica (BAPAPhS) and n-butylesterpropylamidephenylsilica (BEPAPhS) with regular molecular structures. Layered CPAPhS showed the potential as a starting material for formation of a series of novel two-dimensional molecular space with various regular molecular structures, and as a solid acceptor for chemical reagent with amino and hydroxyl groups for chemical processes. PMID:18041857

Yao, Ken; You, Xiaoqing; Shi, Liyi; Wan, Wen; Yu, Futao; Chen, Jianming

2008-01-01

442

Two dimensional modeling of waste combustion in a kiln  

SciTech Connect

A two dimensional model has been developed to model the incineration characteristics in a kiln. The specific configuration considered is a rotary kiln with two off-axis burners, one above the centerline and the other below it. In the two dimensional model the burners and the kiln are considered to be planar. The upper burner feed consists of carbon tetrachloride, methane and oxygen, while the lower burner feed is made up of methane and oxygen. Results are obtained both with and without a solid waste bed. The effect of the solid bed is incorporated through an empirically specified bed volatile release rate. The effect of kiln rotation is neglected. The governing conservation equations are solved by a control volume based finite difference procedure. The results are qualitatively compared with the measurements in a three dimensional kiln operating under similar conditions as the one in this study. In particular strong stratification of temperature and species concentration at the kiln exit is noted. This is validated by similar experimental observations.

Jang, D.S.; Acharya, S. (Mechanical Engineering Dept., Louisiana State Univ., Baton Rouge, LA (US))

1988-01-01

443

Reliability of a two-dimensional footprint measurement approach.  

PubMed

Although footprint evidence can be taken from the scene of a crime, the science underpinning such measurement in forensic science has not been fully explored. A literature search revealed various measuring approaches, all of which demonstrated either little or no measurement rigour in terms of reliability. The aim of this study was to apply a robust measurement approach for testing the reliability of two-dimensional footprint impressions. Three dynamic and three static footprints were taken from the right foot of thirty female and thirty one male volunteers using the 'Inkless Shoeprint Kit'. The images were digitised. Lengths, widths and angles were measured using a selection of currently employed methods. An investigation of the reliability of the chosen measuring method suggested high intra-rater agreement: for example, the length measurement suggested an intraclass correlation coefficient (ICC) 0.99, 95% Confidence Interval (CI) -0.28 to 0.01, standard error of measurement (SEM) 0.07, Limits of Agreement (LOA) -0.91 to 0.65. Inter-rater reliability between three operators was also high: SEM ranged from 0.05 mm to 0.07 mm, ICC 0.99. Our study has established a reliable two-dimensional measuring technique that could be used for footprint comparison in further research. PMID:20709270

Reel, Sarah; Rouse, Simon; Vernon, Wesley; Doherty, Patrick

2010-09-01

444

Analytical study of two-dimensional degenerate metamaterial antennas  

NASA Astrophysics Data System (ADS)

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

Sakoda, Kazuaki; Zhou, Haifeng

2011-07-01

445

Aspects of jamming in two-dimensional athermal frictionless systems.  

PubMed

In this work we provide an overview of jamming transitions in two dimensional systems focusing on the limit of frictionless particle interactions in the absence of thermal fluctuations. We first discuss jamming in systems with short range repulsive interactions, where the onset of jamming occurs at a critical packing density and where certain quantities show a divergence indicative of critical behavior. We describe how aspects of the dynamics change as the jamming density is approached and how these dynamics can be explored using externally driven probes. Different particle shapes can produce jamming densities much lower than those observed for disk-shaped particles, and we show how jamming exhibits fragility for some shapes while for other shapes this is absent. Next we describe the effects of long range interactions and jamming behavior in systems such as charged colloids, vortices in type-II superconductors, and dislocations. We consider the effect of adding obstacles to frictionless jamming systems and discuss connections between this type of jamming and systems that exhibit depinning transitions. Finally, we discuss open questions such as whether the jamming transition in all these different systems can be described by the same or a small subset of universal behaviors, as well as future directions for studies of jamming transitions in two dimensional systems, such as jamming in self-driven or active matter systems. PMID:24695520

Reichhardt, C; Reichhardt, C J Olson

2014-05-01

446

SCAPS, a two-dimensional ion detector for mass spectrometer  

NASA Astrophysics Data System (ADS)

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.

Yurimoto, Hisayoshi

2014-05-01

447

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

SciTech Connect

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.

Furman, M.A.

2007-05-29

448

A numerical study on the fluid flow and heat transfer around a circular cylinder in an aligned magnetic field  

Microsoft Academic Search

The present study numerically investigates two-dimensional laminar fluid flow and heat transfer past a circular cylinder in an aligned magnetic field using the spectral method to insure the accuracy of results. For the purpose of controlling vortex shedding and heat transfer, numerical simulations to calculate the fluid flow and heat transfer past a circular cylinder are performed for different Reynolds

H. S Yoon; H. H Chun; M. Y Ha; H. G Lee

2004-01-01

449

The Cylinder Problem  

NSDL National Science Digital Library

This lesson plan begins with two rectangular pieces of paper -- one forming a cylinder by joining the long sides, the other forming a second cylinder by joining the short sides. Which of these two cylinders will have greater volume? or will they hold the same amount? Students will build a family of cylinders and discover the relation between the dimensions of the generating rectangle and the resulting pair of cylinders. They will also order the cylinders by the amount they hold, and draw a conclusion about the relation between the cylinder's dimensions and the amount it holds. Watch video clips of different classrooms' experiments with this classic conservation problem from Piagetian psychology; see reflections from teachers; read predictions collated from 667 different students.

Forum, The M.

2001-01-01

450

Cylinder Test Specification  

SciTech Connect

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

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

1999-10-01

451

Two-dimensional restoration of single photon emission computed tomography images using the Kalman filter  

SciTech Connect

The discrete filtered backprojection (DFBP) algorithm used for the reconstruction of single photon emission computed tomography (SPECT) images affects image quality because of the operations of filtering and discretization. The discretization of the filtered backprojection process can cause the modulation transfer function (MTF) of the SPECT imaging system to be anisotropic and nonstationary, especially near the edges of the camera's field of view. The use of shift-invariant restoration techniques fails to restore large images because these techniques do not account for such variations in the MTF. This study presents the application of a two-dimensional (2-D) shift-variant Kalman filter for post-reconstruction restoration of SPECT slices. This filter was applied to SPECT images of a hollow cylinder phantom; a resolution phantom; and a large, truncated cone phantom containing two types of cold spots, a sphere, and a triangular prism. The images were acquired on an ADAC GENESYS camera. A comparison was performed between results obtained by the Kalman filter and those obtained by shift-invariant filters. Quantitative analysis of the restored images performed through measurement of root mean squared errors shows a considerable reduction in error of Kalman-filtered images over images restored using shift-invariant methods.

Boulfelfel, D.; Rangayyan, R.M.; Kuduvalli, G.R. (Univ. of Calgary, Alberta (Canada). Dept. of Electrical and Computer Engineering); Hahn, L.J.; Kloiber, R. (Foothills Hospital, Calgary, Alberta (Canada). Div. of Nuclear Medicine)

1994-03-01

452

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

PubMed

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

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

2012-05-15

453

Two-dimensional finite difference analysis of shape instabilities in plates  

NASA Astrophysics Data System (ADS)

A two-dimensional finite difference analysis is applied to surface diffusion-controlled instabilities of plates. Plates can evolve into “cylinders,” or if the plates have longitudinal internal boundaries, they may split into two segments. The evolution process of plates containing internal boundaries into equilibrium shapes depends on both the initial plate aspect ratio (plate width to thickness) and the ratio of the internal boundary energy to the plate-matrix interface energy. When the internal boundary energy is relatively low or the initial plate aspect ratio is relatively small, the transverse equilibrium cross-sectional area shape is composed of two circular segments, with an appropriate dihedral angle dictated by the ratio of the interface energy terms. As either the internal boundary energy or the initial aspect ratio increases, plate splitting, rather than cylinderization, becomes the dominant instability mode. The results of this work are compared to a recent theory of Courtney and Malzahn Kampe (CMK) on shape instability diagrams.[1] The complicated interactive effects between cylinderization and boundary splitting were not considered in the analytical CMK approach; thus, when they are minimal, the results of this finite difference calculation are in reasonable accord with the CMK results, as far as predicting instability times are concerned. However, when the interaction is significant, cylinderization and/or splitting times are markedly changed. The present accurate calculations allow refinement of the CMK plate instability diagrams.

Lee, J. K.; Courtney, T. H.

1989-08-01

454

Negative mass density and ?-near-zero quasi-two-dimensional metamaterials: Design and applications  

NASA Astrophysics Data System (ADS)

We report the design and the characterization of artificial structures made of periodical distributions of structured cylindrical scatterers embedded in a two-dimensional (2D) waveguide. For certain values of their geometrical parameters they show simultaneously negative effective bulk modulus and negative effective mass density. Here our analysis is focused on the frequencies where they behave like materials with negative density or density near zero (DNZ). The scattering units consist of a rigid cylindrical core surrounded by an anisotropic shell divided in angular sectors. The units are embedded in a 2D waveguide whose height is smaller than the length of the cylinders, which makes the structure quasi-2D. We have obtained the dispersion relation of the surface acoustic waves excited at frequencies with negative effective density. Also, we report phenomena associated with their DNZ behavior, such as tunneling through narrow channels, control of the radiation field, perfect transmission through sharp corners, and power splitting. Preliminary experiments performed on samples with millimeter-scale dimensions demonstrated their single-negative behavior, with the main drawback being the strong losses measured at the frequencies where the negative behavior is observed.

Graciá-Salgado, Rogelio; García-Chocano, Victor M.; Torrent, Daniel; Sánchez-Dehesa, José

2013-12-01

455

Optimal Padding for the Two-Dimensional Fast Fourier Transform  

NASA Technical Reports Server (NTRS)

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.

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

2011-01-01

456

Study of two-dimensional systems of classical particles  

NASA Astrophysics Data System (ADS)

This thesis is dedicated to the study of the structural, dynamical and thermal properties of finite two-dimensional systems of classical particles. In its first part, we study the structures and the vibrational properties of particles of confined systems in the zero temperature case. Specifically, the ordered configurations of a monolayer of interacting magnetic dipoles confined in a circular parabolic potential are investigated as a function of the dipole moment of the particles. Despite the circular confinement, we find very asymmetric ordered structures, like chains and Y-shaped configurations, when a magnetic field is applied parallel to the plane of the particles. Besides, we analyze the dynamic of particles through the study of the normal-mode spectrum. It is studied as a function of the magnetic field and the strength of the dipole moment of the particles. The translational and rotational components of the normal mode spectrum are obtained and investigated in details. In the second part of the thesis, we study the structural dependence of the two-dimensional systems on the temperature. Specifically, we systematically investigate the melting of a finite size binary system consisting of two types of particles having different charges and/or masses, confined in a two-dimensional parabolic trap. It is found that two types of particles melt at different temperatures; e.g., particles with smaller charge melt first. In addition, a remarkable temperature induced spatial separation of the two types of particles is observed. We also study the melting of a competing interacting potential system of classical particles confined in a circular parabolic trap. The particles interact through a short-range attractive, and long-range repulsive, potential. Different behaviors of the melting temperature are found depending on the strength of the attractive part of the interparticle potential. The melting of a system consisting of small bubbles takes place through a two-step melting process. A reentrant behavior and a thermally induced structural phase transition are observed in a small region of a space diagram of the main parameters of the system. A hysteresis effect in the configuration of the particles is observed as a function of temperature.

Munarin, Felipe De Freitas

457

Two-dimensional Electronic Double-Quantum Coherence Spectroscopy  

PubMed Central

CONSPECTUS The theory of electronic structure of many-electron systems like molecules is extraordinarily complicated. A lot can be learned by considering how electron density is distributed, on average, in the average field of the other electrons in the system. That is, mean field theory. However, to describe quantitatively chemical bonds, reactions, and spectroscopy requires consideration of the way that electrons avoid each other by the way they move; this is called electron correlation (or in physics, the many-body problem for fermions). While great progress has been made in theory, there is a need for incisive experimental tests that can be undertaken for large molecular systems in the condensed phase. Here we report a two-dimensional (2D) optical coherent spectroscopy that correlates the double excited electronic states to constituent single excited states. The technique, termed two-dimensional double-coherence spectroscopy (2D-DQCS), makes use of multiple, time-ordered ultrashort coherent optical pulses to create double- and single-quantum coherences over time intervals between the pulses. The resulting two-dimensional electronic spectrum maps the energy correlation between the first excited state and two-photon allowed double-quantum states. The principle of the experiment is that when the energy of the double-quantum state, viewed in simple models as a double HOMO to LUMO excitation, equals twice that of a single excitation, then no signal is radiated. However, electron-electron interactions—a combination of exchange interactions and electron correlation—in real systems generates a signal that reveals precisely how the energy of the double-quantum resonance differs from twice the single-quantum resonance. The energy shift measured in this experiment reveals how the second excitation is perturbed by both the presence of the first excitation and the way that the other electrons in the system have responded to the presence of that first excitation. We compare a series of organic dye molecules and find that the energy offset for adding a second electronic excitation to the system relative to the first excitation is on the order of tens of milli-electronvolts, and it depends quite sensitively on molecular geometry. These results demonstrate the effectiveness of 2D-DQCS for elucidating quantitative information about electron-electron interactions, many-electron wavefunctions, and electron correlation in electronic excited states and excitons.

Kim, Jeongho; Mukamel, Shaul

2009-01-01

458

Two-dimensional NQR using ultra-broadband electronics.  

PubMed

We have recently developed an ultra-broadband instrument that can effectively excite and detect NMR and NQR signals over a wide frequency range. Our current system operates between 100 kHz and 3.2 MHz using an un-tuned sample coil. The major benefits of this instrument compared to conventional NQR/NMR systems include increased robustness, ease of use (in particular for multi-frequency experiments), and elimination of the need for tuning adjustments in the hardware. Here we describe its use for performing two-dimensional (2D) scans, which allow improved interpretation of complex NQR spectra by detecting the connected resonances. Our method relies on population transfers between the three energy levels of spin-1 nuclei (such as (14)N) by using multi-frequency excitation and a single RF coil. Experimental results on pure samples and mixtures are also presented. PMID:24495675

Mandal, S; Song, Y-Q

2014-03-01

459

The world of emotions is not two-dimensional.  

PubMed

For more than half a century, emotion researchers have attempted to establish the dimensional space that most economically accounts for similarities and differences in emotional experience. Today, many researchers focus exclusively on two-dimensional models involving valence and arousal. Adopting a theoretically based approach, we show for three languages that four dimensions are needed to satisfactorily represent similarities and differences in the meaning of emotion words. In order of importance, these dimensions are evaluation-pleasantness, potency-control, activation-arousal, and unpredictability. They were identified on the basis of the applicability of 144 features representing the six components of emotions: (a) appraisals of events, (b) psychophysiological changes, (c) motor expressions, (d) action tendencies, (e) subjective experiences, and (f) emotion regulation. PMID:18031411

Fontaine, Johnny R J; Scherer, Klaus R; Roesch, Etienne B; Ellsworth, Phoebe C

2007-12-01

460

Power spectrum of passive scalars in two dimensional chaotic flows  

SciTech Connect

In this paper the power spectrum of passive scalars transported in two dimensional chaotic fluid flows is studied theoretically. Using a wave-packet method introduced by Antonsen et al., several model flows are investigated, and the fact that the power spectrum has the k{sup -1}-scaling predicted by Batchelor is confirmed. It is also observed that increased intermittency of the stretching tends to make the roll-off of the power spectrum at the high k end of the k{sup -1} scaling range more gradual. These results are discussed in light of recent experiments where a k{sup -1} scaling range was not observed. (c) 2000 American Institute of Physics.

Yuan, Guo-Cheng [Department of Mathematics and Institute for Physical Science and Technology, University of Maryland, College Park, Maryland 20742 (United States)] [Department of Mathematics and Institute for Physical Science and Technology, University of Maryland, College Park, Maryland 20742 (United States); Nam, Keeyeol [Department of Physics and Institute for Plasma Research, University of Maryland, College Park, Maryland 20742 (United States)] [Department of Physics and Institute for Plasma Research, University of Maryland, College Park, Maryland 20742 (United States); Antonsen, Thomas M. Jr. [Department of Physics and Institute for Plasma Research, University of Maryland, College Park, Maryland 20742 (United States)] [Department of Physics and Institute for Plasma Research, University of Maryland, College Park, Maryland 20742 (United States); Ott, Edward [Department of Physics and Institute for Plasma Research, University of Maryland, College Park, Maryland 20742 (United States)] [Department of Physics and Institute for Plasma Research, University of Maryland, College Park, Maryland 20742 (United States); Guzdar, Parvez N. [Institute for Plasma Research, University of Maryland, College Park, Maryland 20742 (United States)] [Institute for Plasma Research, University of Maryland, College Park, Maryland 20742 (United States)

2000-03-01

461

An investigation of a two-dimensional propulsive lifting system  

NASA Technical Reports Server (NTRS)

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.

Shollenberger, C. A.

1973-01-01

462

Two-dimensional classical XY model by HOTRG  

NASA Astrophysics Data System (ADS)

Two-dimensional (2D) classical XY model has a special phase transition, the so-called Kosterlitz-Thouless (KT) transition. Below the transtion temperature, the system has quasi long range order with all spins aligned, and the correlation function decays as power law, while the other unordered phase is exponential. Large size system study by numerical simulation is necessary, but pratically difficult.In this work, we applied a newly well-developed method: high-order tensor renormalization group (HOTRG) to investigate this model. This method is verified by 2D Ising model, and thoretially, it can deal with infinite system size. Some thermodynamic quantities such as entropy, specific heat and magnetic susceptibility etc., are computed, which may be used to find Fisher's zero of the partition function, and then to characterize the transition.

Yu, Ji-Feng; Xie, Zhiyuan; Xiang, Tao

2013-03-01

463

Modeling complexly magnetized two-dimensional bodies of arbitrary shape  

SciTech Connect

A method has been devised for the forward computation of magnetic anomalies due to two-dimensional (2-D) polygonal bodies with heterogeneously directed magnetization. The calculations are based on the equivalent line source approach wherein the source is subdivided into discrete elements that vary spatially in their magnetic properties. This equivalent dipole line method provides a fast and convenient means of representing and computing magnetic anomalies for bodies possessing complexly varying magnitude and direction of magnetization. The algorithm has been tested and applied to several generalized cases to verify the accuracy of the computation. The technique has also been used to model observed aeromagnetic anomalies associated with the structurally deformed, remanently magnetized Keweenawan volcanic rocks in eastern Lake Superior. This method is also easily adapted to the calculation of anomalies due to two and one-half-dimensional (2.5-D) and three-dimensional (3-D) heterogeneously magnetized sources.

Mariano, J.; Hinze, W.J. (Purdue Univ., West Lafayette, IN (United States). Dept. of Earth and Atmospheric Sciences)

1993-05-01

464

Two-dimensional numerical simulation of MPD flows  

SciTech Connect

A two-dimensional numerical model has been developed in order to analyze electromagnetic plasma accelerators also called Self-Field Magneto-Plasma-Dynamic Thrusters. This model uses a Magneto-Hydro-Dynamic description of the gas considered as a fully ionized, isothermal plasma, and takes into account the Hall effect (nonlinear conductivity) and the interaction between the magnetic field and the fluid dynamics of the plasma. The system of equations is discretized into finite volumes, and is solved by a Newton-Raphson scheme. Results from the MHD model were calculated for a mass flow rate of 6 g/s of argon and for currents up to ten kilo-Amperes. 29 references.

Martinez-Sanchez, M.; Chanty, J.M.G.

1987-05-01

465

Entropic barriers for two-dimensional quantum memories.  

PubMed

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. PMID:24724638

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

2014-03-28

466

Global geometry of two-dimensional charged black holes  

SciTech Connect

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.

Frolov, Andrei V.; Kristjansson, Kristjan R.; Thorlacius, Larus [KIPAC/SITP, Stanford University, Stanford, California 94305-4060 (United States); NORDITA, Blegdamsvej 17, 2100 Copenhagen (Denmark); University of Iceland, Science Institute, Dunhaga 3, 107 Reykjavik (Iceland)

2006-06-15

467

Two-dimensional modeling of nickel electrodeposition in LIGA microfabrication.  

SciTech Connect

Two-dimensional processes of nickel electrodeposition in LIGA microfabrication were modeled using the finite-element method and a fully coupled implicit solution scheme via Newtons technique. Species concentrations, electrolyte potential, flow field, and positions of the moving deposition surfaces were computed by solving the species-mass, charge, and momentum conservation equations as well as pseudo-solid mesh-motion equations that employ an arbitrary Lagrangian-Eulerian (ALE) formulation. Coupling this ALE approach with repeated re-meshing and re-mapping makes it possible to track the entire transient deposition processes from start of deposition until the trenches are filled, thus enabling the computation of local current densities that influence the microstructure and functional/mechanical properties of the deposit.

Evans, Gregory Herbert (Sandia National Laboratories, Livermore, CA); Chen, Ken Shuang

2003-07-01

468

Numerical Simulation of One- and Two-Dimensional ESEEM Experiments  

NASA Astrophysics Data System (ADS)

Numerical simulation has become an indispensable tool for the interpretation of pulse EPR experiments. In this work it is shown how automatic orientation selection, grouping of operator factors, and direct selection and elimination of coherences can be used to improve the efficiency of time-domain simulations of one- and two-dimensional electron spin echo envelope modulation (ESEEM) spectra. The program allows for the computation of magnetic interactions of any symmetry and can be used to simulate spin systems with an arbitrary number of nuclei with any spin quantum number. Experimental restrictions due to finite microwave pulse lengths are addressed and the enhancement of forbidden coherences by microwave pulse matching is illustrated. A comparison of simulated and experimental HYSCORE (hyperfine sublevel correlation) spectra of ordered and disordered systems with varying complexity shows good qualitative agreement.

Madi, Z. L.; Van Doorslaer, S.; Schweiger, A.

2002-02-01

469

Dielectric-barrier discharges in two-dimensional lattice potentials.  

PubMed

We use a pin-grid electrode to introduce a corrugated electrical potential into a planar dielectric-barrier discharge (DBD) system, so that the amplitude of the applied electric field has the profile of a two-dimensional square lattice. The lattice potential provides a template for the spatial distribution of plasma filaments in the system and has pronounced effects on the patterns that can form. The positions at which filaments become localized within the lattice unit cell vary with the width of the discharge gap. The patterns that appear when filaments either overfill or underfill the lattice are reminiscent of those observed in other physical systems involving 2D lattices. We suggest that the connection between lattice-driven DBDs and other areas of physics may benefit from the further development of models that treat plasma filaments as interacting particles. PMID:22400753

Sinclair, J; Walhout, M

2012-01-20

470

High speed two-dimensional optical beam position detector  

SciTech Connect

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

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

2011-07-15

471

Density of states in two-dimensional colloidal system  

NASA Astrophysics Data System (ADS)

The vibrational density of states (VDOS) of particles in a two-dimensional binary colloidal system was investigated using video microscopy. Our ultimate goal is to explore how the VDOS varies near the jamming transition [1]. Various distributions of NIPA particles, whose diameters can be tuned by small temperature variations, were loaded into parallel-plate microscope cells, and their motions tracked with video microscopy. This approach permits in-situ observation over a wide range of particle packing fractions, from colloidal fluids to colloidal glasses. A search for excess VDOS at low frequencies in colloidal glass is ongoing. 1. N. Xu, M. Wyart, A. J. Liu, and S. R. Nagel, Phys. Rev. Lett. 98, 175502 (2007) This work is supported by NSF DMR-080488, MRSEC DMR-0520020

Chen, Ke; Zhang, Zexin; Yunker, Peter; Yodh, Arjun

2009-03-01

472

Intersubband relaxation of two-dimensional electrons in heterostructures  

NASA Astrophysics Data System (ADS)

We calculate the lifetime of a nonequilibrium electron in the first excited subband in the low-density heterostructure where this photocreated carrier occurs at the last stage of its cooling. The electron interaction with acoustic phonons gives the dominant intersubband relaxation mechanism, if the intersubband energy splitting and the Fermi energy splitting are relatively small, 1>?F/?10>0.7-0.8. In GaAs-AlxGa1-xAs heterostructures the intersubband relaxation determines the excited-electron lifetime to be of the order of ?phon~nanoseconds, which depends slightly on the value of the two-dimensional electron density. When the ratio ?F/?10 is smaller, the intersubband relaxation is determined by the Auger-like electron-electron scattering whose rate can increase up to the value ?-1Aug~10-10 sec-1.

Fal'ko, Vladimir I.

1993-05-01

473

Two-dimensional freezing criteria for crystallizing colloidal monolayers  

NASA Astrophysics Data System (ADS)

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 Löwen-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.

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

2010-04-01

474

Two-dimensional freezing criteria for crystallizing colloidal monolayers.  

PubMed

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

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

2010-04-21

475

Forced two-dimensional turbulence in spectral and physical space  

SciTech Connect

Two-dimensional (2D) turbulence in the energy range exhibits nonuniversal features, manifested in the departure (at low k) from the k{sup {minus}5/3} energy spectrum law, variable energy flux, and irregular, nonlocal transfers. To unravel the underlying mechanism we conducted a detailed study of the 2D turbulence in spectral and physical space. It revealed complex multiscale organization of vorticity field and dynamic processes, ranging from large-scale meandering jets to strong localized vortices. The latter bear prime responsibility for the nonuniversal behavior of 2D turbulence, and we examined their statistical features and the growth mechanism. Our results are based on the numeric simulation of 2D turbulence on the 512 grid under different forcing-dissipation conditions.

Danilov, Sergey; Gurarie, David

2001-06-01

476

Two-dimensional Supramolecular Structures by Hydrogen and Halogen Interactions  

NASA Astrophysics Data System (ADS)

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.

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

2010-03-01

477

Waves in two-dimensional superparamagnetic dusty plasma liquids.  

PubMed

Wave dispersion relations in the strongly coupled liquid phase of a two-dimensional system of dust grains interacting via both Yukawa and dipole interactions are investigated. The model system comprises a layer of charged superparamagnetic grains in a plasma in an external, uniform magnetic field B whose magnitude and direction can be varied. Because the induced magnetic dipole moments of the grains lie along B, the interaction between the grains becomes anisotropic as B is tilted with respect to the layer. The theoretical approach uses a reformulated quasilocalized charge approximation that can treat dipole interactions, combined with molecular dynamics simulations. The mode dispersion relations are found to depend on the relative strengths of the Yukawa and dipole interactions and the direction of wave propagation in the plane. PMID:24827350

Hartmann, Peter; Donkó, Zoltán; Rosenberg, Marlene; Kalman, Gabor J

2014-04-01

478

Two-dimensional plasma photonic crystals in dielectric barrier discharge  

SciTech Connect

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.

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

2010-11-15

479

Two-dimensional equilibrium of field-reversed ion rings  

NASA Astrophysics Data System (ADS)

The axially symmetric equilibrium of intense ion rings is examined for field-reversed configurations. A rigid rotor model is assumed for the ion distribution, with background or accompanying electrons providing space charge neutralization. This equilibrium configuration is described by three macroscopic quantities, the ring particle density, the ring pressure, and the azimuthal component of the vector potential. Within the Vlasov-Maxwell framework, these quantities must satisfy Ampere's law and the pressure balance equation. The system of equations is completed assuming that the pressure and the density satisfy a general power law (equation of state). The equilibrium solution for intense ion layers (one dimensional problem) is examined in the general case, but for intense ion rings (two dimensional problem) the analysis is restricted to the uniform particle density case. The sharp boundary that separates the constant density and zero density regions is approximated by a stepwise function and determined for several values of the ring parameters.

Ludwig, G. O.

1980-05-01

480

Exploring the thermodynamics of a two-dimensional Bose gas.  

PubMed

Using in situ measurements on a quasi-two-dimensional, harmonically trapped (87)Rb gas, we infer various equations of state for the equivalent homogeneous fluid. From the dependence of the total atom number and the central density of our clouds with chemical potential and temperature, we obtain the equations of state for the pressure and the phase-space density. Then, using the approximate scale invariance of this 2D system, we determine the entropy per particle and find very low values (below 0.1k(B)) in the strongly degenerate regime. This shows that this gas can constitute an efficient coolant for other quantum fluids. We also explain how to disentangle the various contributions (kinetic, potential, interaction) to the energy of the trapped gas using a time-of-flight method, from which we infer the reduction of density fluctuations in a nonfully coherent cloud. PMID:22026829

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

2011-09-23

481

Measuring protein dynamics with ultrafast two-dimensional infrared spectroscopy  

NASA Astrophysics Data System (ADS)

Recent advances in the methodology and application of ultrafast two-dimensional infrared (2D-IR) spectroscopy to biomolecular systems are reviewed. A description of the 2D-IR technique and the molecular contributions to the observed spectra are presented followed by a discussion of recent literature relating to the use of 2D-IR and associated approaches for measuring protein dynamics. In particular, these include the use of diatomic ligand groups for measuring haem protein dynamics, isotopic labelling strategies and the use of vibrational probe groups. The final section reports on the current state of the art regarding the use of 2D-IR methods to provide insights into biological reaction mechanisms.

Adamczyk, Katrin; Candelaresi, Marco; Robb, Kirsty; Gumiero, Andrea; Walsh, Martin A.; Parker, Anthony W.; Hoskisson, Paul A.; Tucker, Nicholas P.; Hunt, Neil T.

2012-06-01

482

Approaches to verification of two-dimensional water quality models  

SciTech Connect

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.

Butkus, S.R. (Tennessee Valley Authority, Chattanooga, TN (USA). Water Quality Dept.)

1990-11-01

483

Two-dimensional nanoarchitectonics: organic and hybrid materials.  

PubMed

Programmed molecular assemblies with molecular-level precision have always intrigued mankind in the quest to master the art of molecular engineering. In this regard, our review seeks to highlight the state of the art in supramolecular engineering. Herein we describe two-dimensional (2D) nanoarchitectonics of organic and organic-inorganic based hybrid materials. Molecular systems ranging from simpler hydrogen bonding driven bis-acylurea and cyclic dipeptide derivatives to complex peptoids, arylenes, cucurbiturils, biphenyls, organosilicons and organometallics, which involve a delicate interplay of multiple noncovalent interactions are discussed. These specifically chosen examples illustrate the molecular design principles and synthetic protocols to realize 2D nanosheets. The description also emphasizes the wide variety of functional properties and technological implications of these 2D nanomaterials besides an outlook for future progress. PMID:22782293

Govindaraju, T; Avinash, M B

2012-10-21

484

Electronic properties of two-dimensional covalent organic frameworks.  

PubMed

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

Zhu, P; Meunier, V

2012-12-28

485

Electronic properties of two-dimensional covalent organic frameworks  

NASA Astrophysics Data System (ADS)

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

Zhu, P.; Meunier, V.

2012-12-01

486

An n-channel two-dimensional covalent organic framework.  

PubMed

Co-condensation of metallophthalocyanine with an electron-deficient benzothiadiazole (BTDA) block leads to the formation of a two-dimensional covalent organic framework (2D-NiPc-BTDA COF) that assumes a belt shape and consists of AA stacking of 2D polymer sheets. Integration of BTDA blocks at the edges of a tetragonal metallophthalocyanine COF causes drastic changes in the carrier-transport mode and a switch from a hole-transporting skeleton to an electron-transporting framework. 2D-NiPc-BTDA COF exhibits broad and enhanced absorbance up to 1000 nm, shows panchromatic photoconductivity, is highly sensitive to near-infrared photons, and has excellent electron mobility as high as 0.6 cm(2) V(-1) s(-1). PMID:21863859

Ding, Xuesong; Chen, Long; Honsho, Yoshihito; Feng, Xiao; Saengsawang, Oraphan; Guo, Jingdong; Saeki, Akinori; Seki, Shu; Irle, Stephan; Nagase, Shigeru; Parasuk, Vudhichai; Jiang, Donglin

2011-09-21

487

Billiards and Two-Dimensional Problems of Optimal Resistance  

NASA Astrophysics Data System (ADS)

A body moves in a medium composed of noninteracting point particles; the interaction of the particles with the body is completely elastic. The problem is: find the body’s shape that minimizes or maximizes resistance of the medium to its motion. This is the general setting of the optimal resistance problem going back to Newton. Here, we restrict ourselves to the two-dimensional problems for rotating (generally non-convex) bodies. The main results of the paper are the following. First, to any compact connected set with piecewise smooth boundary {B subset mathbb{R}^2} we assign a measure ? B on ?(conv B)×[ - ?/2, ?/2] generated by the billiard in {mathbb{R}^2 setminus B} and characterize the set of measures { ? B }. Second, using this characterization, we solve various problems of minimal and maximal resistance of rotating bodies by reducing them to special Monge-Kantorovich problems.

Plakhov, Alexander

2009-11-01

488

The Two-Dimensional Euler Equations on Singular Domains  

NASA Astrophysics Data System (ADS)

We establish the existence of global weak solutions of the two-dimensional incompressible Euler equations for a large class of non-smooth open sets. Loosely, these open sets are the complements (in a simply connected domain) of a finite number of obstacles with positive Sobolev capacity. Existence of weak solutions with L p vorticity is deduced from a property of domain continuity for the Euler equations that relates to the so-called ?-convergence of open sets. Our results complete those obtained for convex domains in Taylor (Progress in Nonlinear Differential Equations and their Applications, Vol. 42, 2000), or for domains with asymptotically small holes (I ftimie et al. in Commun Partial Differ Equ 28(1-2), 349-379, 2003; Lopes Filho in SIAM J Math Anal 39(2), 422-436, 2007).

Gérard-Varet, David; Lacave, Christophe

2013-07-01

489

Signatures of conical intersections in two-dimensional electronic spectra  

NASA Astrophysics Data System (ADS)

Femtosecond two-dimensional (2D) electronic spectroscopy is a versatile technique for the exploration of ultrafast photoinduced dynamics in complex molecular systems. We have performed the first computational simulation of a femtosecond 2D electronic spectrum for a model system with a conical intersection, using the wave-function version of the equation-of-motion phase-matching approach. It is shown that the 2D electronic spectrum of a two-state two-mode conical intersection simultaneously provides information on the complicated energy-level structure of the vibronically coupled states as well as on the time-dependent electronic population decay. The challenges and prospects of future simulations of 2D spectra of multi-mode conical intersections are briefly discussed.

Kr?má?, Jind?ich; Gelin, Maxim F.; Egorova, Dassia; Domcke, Wolfgang

2014-06-01

490

Two-dimensional models for an electrode with adsorption sites  

SciTech Connect

Through a new method, the following model is solved exactly in the framework of classical equilibrium statistical mechanics of two-dimensional Coulomb systems, for the special value /Gamma/ = 2 of the coupling constant: the mobile charges of a one-component plasma are attracted by a line of equidistant sticky adsorption sites embedded in a background, the density of which varies in the direction orthogonal to the line. First the general expression are given for the densities and correlation functions of nonadsorbed and adsorbed particles. Then these results are used to investigate two models of electrodes with localized adsorption: the externally charged hard wall and the impermeable polarized membrane. In each case the influence of the adsorption upon macroscopic features is studied: the potential drop across the interface, the contact theorem, and the Lippmann equation, which involves the surface free energy.

Cornu, F.

1989-02-01

491

Efficient solutions of two-dimensional incompressible steady viscous flows  

NASA Technical Reports Server (NTRS)

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

Morrison, J. H.; Napolitano, M.

1986-01-01

492

Number of arm selection in two-dimensional diffusion processes  

NASA Astrophysics Data System (ADS)

We introduce an algorithm to generate two-dimensional diffusion-limited star-branched aggregates (DLSA) attaching bi-functional monomers successively to a central colloidal particle with any desired number of reactive sites. The proposed algorithm produces star-shaped aggregates that grow forever and show a power law polydispersity in the chemical length of the arms near the central colloid. More interestingly, it gives rise to a number of arm selection consisting in that only a small number of arms (around five) define the final structure at relatively large distances from the central colloid, independently of the initial number of reactive sites and the size of the central colloid. We characterize the structure of the aggregates by means of the particle-particle correlation function, analyze its scaling properties and obtain the fractal dimension.

Mendoza, C. I.; Ramä±Rez-Santiago, G.

2008-09-01

493

Diffusion in the two-dimensional necklace model for reptation  

NASA Astrophysics Data System (ADS)

An extension of a recently introduced one-dimensional model, the necklace model, is used to study the reptation of a chain of N particles in a two-dimensional square lattice. The mobilities of end and middle particles of a chain are governed by three free parameters. This new model mimics the behavior of a long linear and flexible polymer in a gel. Noninteracting and self-avoiding chains are considered. For both cases, analytical approximations for the diffusion coefficient of the center of mass of the chain, for all values of N , are proposed. The validity of these approximations for different values of the free parameters is verified by means of Monte Carlo simulations. Extensions to higher dimensions are also discussed.

Terranova, G.; Aldao, C. M.; Mártin, H. O.

2007-09-01

494

Exciton spectra in two-dimensional graphene derivatives  

NASA Astrophysics Data System (ADS)

The energy spectra and wave functions of bound excitons in important two-dimensional (2D) graphene derivatives, i.e., graphyne and graphane, are found to be strongly modified by quantum confinement, making them qualitatively different from the usual Rydberg series. However, their parity and optical selection rules are preserved. Thus a one-parameter modified hydrogenic model is applied to quantitatively explain the ab initio exciton spectra, and allows one to extrapolate the electron-hole binding energy from optical spectroscopies of 2D semiconductors without costly simulations. Meanwhile, our calculated optical absorption spectrum and enhanced spin singlet-triplet splitting project graphyne, an allotrope of graphene, as a candidate for intriguing energy and biomedical applications.

Huang, Shouting; Liang, Yufeng; Yang, Li

2013-08-01

495

Two-dimensional colloidal crystals formed by thermophoresis and convection  

NASA Astrophysics Data System (ADS)

Temperature gradients can trap micrometer-sized particles into two-dimensional crystals. We form colloidal crystals from otherwise repellent 2 ?m polystyrene beads in diverse thermal convection settings. Our experiments indicate that the accumulation is driven by particle thermophoresis. Particles move along the temperature gradient and are pushed out of the warm liquid to a cold wall. We find reduced accumulation for decreased surface temperature gradients and enhanced salt concentrations. Moreover, thermophoretic fluid dynamics calculations predict flat accumulation profiles with 107-fold enhanced concentrations that are consistent with our experiments. The accumulated crystals could be used as molecular sieves for microfluidic biotechnological applications. A natural environment for similar accumulations are pores of rock near hydrothermal vents.

Duhr, Stefan; Braun, Dieter

2005-03-01

496

Satellite radar interferometry - Two-dimensional phase unwrapping  

NASA Technical Reports Server (NTRS)

Interferometric synthetic aperture radar observations provide a means for obtaining high-resolution digital topographic maps from measurements of amplitude and phase of two complex radar images. The phase of the radar echoes may only be measured modulo 2 pi; however, the whole phase at each point in the image is needed to obtain elevations. An approach to 'unwrapping' the 2 pi ambiguities in the two-dimensional data set is presented. It is found that noise and geometrical radar layover corrupt measurements locally, and these local errors can propagate to form global phase errors that affect the entire image. It is shown that the local errors, or residues, can be readily identified and avoided in the global phase estimation. A rectified digital topographic map derived from the unwrapped phase values is presented.

Goldstein, Richard M.; Zebker, Howard A.; Werner, Charles L.

1988-01-01

497

Shock wave in a two-dimensional dusty plasma crystal  

SciTech Connect

Two-dimensional (2D) shock structures of longitudinal dust lattice wave (LDLW) in a hexagonal Yukawa crystal are studied. The nonlinear evolution equation derived for dusty plasma crystal is found to be a 2D Burgers' equation, where the Burgers' term, i.e., the dissipation is provided by ''hydrodynamic damping'' due to irreversible processes that take place within the system. Analytical and numerical solutions of this equation on the basis of crystal experimental parameters show the development of compressional shock structures of LDLW in 2D dusty plasma crystal. The shock strength decreases (increases) with the increase in lattice parameter {kappa} (angle of propagation of the nonlinear wave). The results are discussed in the context of 2D monolayer hexagonal dusty plasma crystal experiments.

Ghosh, Samiran [Department of Applied Mathematics, University of Calcutta, 92 Acharya Prafulla Chandra Road, Kolkata 700 009 (India)

2009-10-15

498

Noise correlations of two-dimensional Bose gases  

NASA Astrophysics Data System (ADS)

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

Singh, V. P.; Mathey, L.

2014-05-01