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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

1998-07-01

2

Complete band gaps of a two-dimensional periodic cylinder sandwich panel  

NASA Astrophysics Data System (ADS)

Complete band gaps (BGs) of a novel two-dimensional periodic cylinder sandwich panel are investigated. Finite element method and Bloch theory are used to study the acoustic wave dispersion relations and eigenmodes. The effects of geometrical parameters of a cylinder on BGs are also given. Results show that three broadband BGs occur in dispersion relations; the starting frequency of the first BG is sensitive to the height of the cylinder, and other frequencies except the starting frequency of the first BG are sensitive to the radius of cylinder; BGs and the parameter sensitivity are also explained with eigenmodes.

Ma, Ting; Chen, Tianning; Wang, Xiaopeng

2013-10-01

3

Characteristics of two-dimensional flow around a rotating circular cylinder near a plane wall  

Microsoft Academic Search

We simulate a two-dimensional incompressible flow around a rotating circular cylinder near a plane wall at the Reynolds number Re=200 by using the lattice Boltzmann equation with multiple relaxation times. We investigate the flow pattern in the parameter space of the rotational rate gamma:=omegaa\\/U and the normalized gap h:=H\\/D, where omega is the angular velocity of the cylinder, a and

Ming Cheng; Li-Shi Luo

2007-01-01

4

Numerical Solution of the Flow Field about Two-Dimensional Shaved Circular Cylinders in Supersonic Flow.  

National Technical Information Service (NTIS)

A theoretical investigation of the flow of a perfect gas over two-dimensional shaved circular cylinders has been conducted at supersonic Mach numbers for the purpose of obtaining shock wave shapes. An integral relation method is used for the numerical sol...

J. S. Huang

1974-01-01

5

ACOUSTIC TWO-DIMENSIONAL RADIATION AND SCATTERING FROM CYLINDERS USING SOURCE DENSITY, SVD AND FOURIER METHODS  

Microsoft Academic Search

Acoustic two-dimensional harmonic radiation and rigid body scattering from cylinders of arbitrary shape with a plane of symmetry are addressed using an internal line monopole and dipole source distribution along the plane of symmetry. A previously developed least mean square error method is used to solve the Neumann boundary value problem. In contrast to the earlier method, Singular Value Decomposition

P. R. Stepanishen

1997-01-01

6

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

Microsoft Academic Search

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

Hajime Fujita

2010-01-01

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

Sound generated in laminar flow past a two-dimensional rectangular cylinder  

Microsoft Academic Search

The far-field sound generated from low Mach number flow past a two-dimensional rectangular cylinder is studied by using a two-step aeroacoustic prediction method. In the first step, the incompressible Navier–Stokes equations are solved numerically. This allows the time-dependent acoustic source to be determined from Powell's vortex sound theory. Using this information, in the second step, the inhomogeneous wave equation is

Y. S. K. Liow; B. T. Tan; M. C. Thompson; K. Hourigan

2006-01-01

9

Wind tunnel tests on in-line oscillation of a two-dimensional circular cylinder  

Microsoft Academic Search

Flow-induced in-line oscillation of a two-dimensional circular cylinder model was experimentally investigated in a wind tunnel by the free-oscillation method in order to understand some of the fundamental characteristics of the system. The response amplitude was measured over a wide range of the mass-damping parameter. The discussion is focused primarily on the effects of model aspect ratio and on the

K Matsuda; H Uejima; T Sugimoto

2003-01-01

10

Characteristics of two-dimensional flow around a rotating circular cylinder near a plane wall  

NASA Astrophysics Data System (ADS)

We simulate a two-dimensional incompressible flow around a rotating circular cylinder near a plane wall at the Reynolds number Re=200 by using the lattice Boltzmann equation with multiple relaxation times. We investigate the flow pattern in the parameter space of the rotational rate ???a/U and the normalized gap h?H/D, where ? is the angular velocity of the cylinder, a and D are the cylinder radius and diameter, respectively, U is the inflow velocity, and H is the gap between the cylinder and the wall. We quantify the effects of ? and h on the hydrodynamic forces and the frequency of vortex shedding from the cylinder. Our results indicate that two critical values of h, hdown and hup, exist, which depend on ?. The flow is steady when hhup. When hdown0, CD is no longer a monotonic function of h. The mean drag coefficient CD varies significantly in the range hdownhup, the wall effect diminishes.

Cheng, Ming; Luo, Li-Shi

2007-06-01

11

Schlieren Investigation of the Flow Phenomena About a Two-Dimensional Circular Cylinder in a Hypersonic Flow.  

National Technical Information Service (NTIS)

An experimental investigation is described of the fluid flow phenomena about a two-dimensional circular cylinder in a hypersonic stream. The data presented was accumulated solely through the use of the Schlieren technique of flow visualization. The primar...

K. H. Token H. Oguro

1964-01-01

12

Two-dimensional backscattering Mueller matrix of sphere-cylinder birefringence media.  

PubMed

We have developed a sphere-cylinder birefringence model (SCBM) for anisotropic media. The new model is based on a previously published sphere-cylinder scattering model (SCSM), but the spherical and cylindrical scatterers are embedded in a linearly birefringent medium. A Monte Carlo simulation program for SCBM was also developed by adding a new module to the SCSM program to take into account the effects of birefringence. Simulations of the backscattering Mueller matrix demonstrate that SCBM results in better agreement with experimental results than SCSM and is more suitable to characterize fibrous tissues such as skeletal muscle. Using Monte Carlo simulations, we also examined the characteristics of two-dimensional backscattering Mueller matrix of SCBM and analyzed the influence of linear birefringence. PMID:23235835

Du, E; He, Honghui; Zeng, Nan; Guo, Yihong; Liao, Ran; He, Yonghong; Ma, Hui

2012-12-01

13

Two-dimensional backscattering Mueller matrix of sphere-cylinder birefringence media  

NASA Astrophysics Data System (ADS)

We have developed a sphere-cylinder birefringence model (SCBM) for anisotropic media. The new model is based on a previously published sphere-cylinder scattering model (SCSM), but the spherical and cylindrical scatterers are embedded in a linearly birefringent medium. A Monte Carlo simulation program for SCBM was also developed by adding a new module to the SCSM program to take into account the effects of birefringence. Simulations of the backscattering Mueller matrix demonstrate that SCBM results in better agreement with experimental results than SCSM and is more suitable to characterize fibrous tissues such as skeletal muscle. Using Monte Carlo simulations, we also examined the characteristics of two-dimensional backscattering Mueller matrix of SCBM and analyzed the influence of linear birefringence.

Du, E.; He, Honghui; Zeng, Nan; Guo, Yihong; Liao, Ran; He, Yonghong; Ma, Hui

2012-12-01

14

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

Microsoft Academic Search

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

Masoud Asgari; Mehdi Akhlaghi; Seyed Mahmoud Hosseini

2009-01-01

15

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

16

Theory and Application of Spectral Methods for the Unsteady Compressible Wake Flow Past a Two-Dimensional Circular Cylinder  

Microsoft Academic Search

An unsteady compressible viscous wake flow past a two-dimensional circular cylinder has been successfully simulated using the Fourier and Chebyshev collocation methods (spectral scheme) and the mixed Fourier collocation\\/finite -difference method (mixed scheme). Various numerical techniques, such as the analytical grid transformation, filtering of the solution and differentiation operators etc., are employed for both numerical schemes. The number of grid

Wai Sun Don

1989-01-01

17

Scaling relations for granular flow in quasi-two-dimensional rotating cylinders  

NASA Astrophysics Data System (ADS)

An experimental study of the flow of different materials (steel balls, glass beads, and sand) in quasi-two-dimensional rotating cylinders is carried out using flow visualization. The flow in the rotating cylinder comprises of a thin-flowing surface layer with the remaining particles rotating as a fixed bed. Experimental results indicate that the scaled layer thickness increases with increasing Froude number (Fr=?2R/g, where ? is the angular speed, R is the cylinder radius, and g the acceleration due to gravity) and with increase in size ratio (s=d/R, where d is the particle diameter). The free surface profile, is nearly flat at low Fr and becomes increasingly S shaped with increasing Fr. The layer thickness profiles, which are symmetric at low Fr become skewed at high values of Fr and small s. The dynamic angles of repose for all the materials studied show a near-linear increase with rotational speed (?). Scaling analysis of the experimental data shows that the shape of the scaled surface profiles and the scaled layer thickness profiles are nearly identical when Froude number and size ratio are held constant, for each material. The surface profiles and layer thickness profiles are also found to be nearly independent of the material used. The dynamic angle of repose (?), however, does not scale with Fr and s and depends on the particle properties. The experimental results are compared to continuum models for flow in the layer. The models of Elperin and Vikhansky [Europhys. Lett. 42, 619 (1998)] and Makse [Phys. Rev. Lett. 83, 3186 (1999)] show good agreement at low Fr while that of Khakhar et al. [Phys. Fluids, 9, 31 (1997)] gives good predictions over the entire range of parameters considered. An analysis of the data indicate that the velocity gradient (??) is nearly constant along the layer at low Fr, and the value calculated at the layer midpoint varies as ??0~[g sin(?0-?s)/d cos ?s]1/2 for all the experimental data, where ?s is the static angle of repose and ?0 is the interface angle at the layer midpoint. An extension of ``heap'' models (BCRE, BRdG) is used to predict the interface angle profiles, which are in reasonable agreement with experimental measurements.

Orpe, Ashish V.; Khakhar, D. V.

2001-09-01

18

Analysis of two-dimensional electromagnetic scattering from a periodic grating of cylinders using a hybrid current model  

NASA Astrophysics Data System (ADS)

A method of moments solution is presented for the problem of two-dimensional electromagnetic scattering from a periodic grating composed of an infinite set of penetrable cylinders illuminated by a TM (transverse magnetic relative to the cylinder axis) plane wave. The reduction of the general problem to a consideration of the fields over a suitably selected period, referred to as the unit cell, is facilitated by the Floquet theorem. The solution then uses fictitious spatially periodic and properly modulated electric current strips to simulate the scattered field in the exterior region within the unit cell and fictitious filamentary currents to simulate the field penetrated into the cylinder enclosed within this cell. The fields radiated by the current strips are represented in terms of Floquet modes. Finally, the simulated fields are forced to obey the continuity conditions for the tangential components of the electric and magnetic fields at a selected set of points on the cylinder boundary within the unit cell. The procedure is simple to implement, rapidly converging, and is applicable to cylinders of arbitrary smooth cross section. Perfectly conducting cylinders are treated as reduced cases of the general procedure for penetrable cylinders. Results are given and compared with available data. The efficiency of the suggested method is demonstrated.

Boag, Amir; Leviatan, Yehuda; Boag, Alona

1988-07-01

19

An approach to microwave imaging using a multiview moment method solution for a two-dimensional infinite cylinder  

Microsoft Academic Search

An approach based on a multiview solution to the inverse-scattering problem of a two-dimensional infinite cylinder is developed in a space-frequency domain. Microwave imaging is simulated by a computer algorithm using the moment method. To overcome ill-conditioning and solve nonsquare systems, a pseudoinverse transformation is employed. The equivalent current density and the complex conductivity are considered as object functions for

S. Caorsi; G. L. Gragnani; M. Pastorino

1991-01-01

20

Accurate analysis of two-dimensional electromagnetic scattering from multilayered periodic arrays of circular cylinders using lattice sums technique  

Microsoft Academic Search

A very efficient and accurate method to characterize two-dimensional (2-D) electromagnetic scattering from multilayered periodic arrays of parallel circular cylinders is presented, using the lattice sums technique, the aggregate T-matrix algorithm, and the generalized reflection and transmission matrices for a layered system. The method is quite general and applies to various configurations of 2-D periodic arrays. The unit cell of

Kiyotoshi Yasumoto; Hiroshi Toyama; Taras Kushta

2004-01-01

21

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

22

Complete Band-Gap in Two-Dimensional Quasiperiod Photonic Crystals with Hollow Cylinders  

NASA Astrophysics Data System (ADS)

The transmission properties of quasiperiodic photonic crystals (QPCs) based on the random square-triangle tiling system are investigated by the multiple scattering method. The hollow cylinders are introduced in our calculation. It is found that QPCs with hollow cylinders also possess a complete band gap common to s- and p-polarized waves when the inner radius of hollow cylinders is larger than a certain value. The QPCs possessing the complete band gap can be applied to the fields of light emitting, wave-guides, optical filters, high-Q resonators and antennas.

Feng, Zhi-Fang; Feng, Shuai; Ren, Kun; Li, Zhi-Yuan; Cheng, Bing-Ying; Zhang, Dao-Zhong

2005-08-01

23

Scattering from cylinders using the two-dimensional vector plane wave spectrum: addendum.  

PubMed

The solution for the vector plane wave spectrum scattering from multiple cylinders by Pawliuk and Yedlin [J. Opt. Soc. A28, 1177 (2011)] only provided the single scattering coefficients for the TM polarization case. The TE solution is similar except for the form of the single scattering coefficients. Here we describe the single scattering coefficients for both polarizations and three types of cylinders: dielectrics, perfect electric conductors, and perfect magnetic conductors. PMID:22472766

Pawliuk, Peter; Yedlin, Matthew

2012-03-01

24

Two-dimensional radiation in a cylinder with spatially varying albedo  

Microsoft Academic Search

The 'discrete ordinates', or S(N) method is presently used to develop a general, accurate scheme for determining two-dimensional radiative transfer in an axisymmetric cylindrical enclosure that contains an absorbing, emitting, and anisotropically scattering medium with spatially varying albedo. The spatial variation of albedo is noted to have significant effects on the heat flux for the optically thick case; for the

M. N. Ozisik; J. R. Tsai; H. Y. Li

1992-01-01

25

Influence of Flow and Rotational Oscillations on the Mechanics of Two-Dimensional Laminar Boundary-Layer Flow past Cylinders, Including Uniform Suction or Blowing.  

National Technical Information Service (NTIS)

A theoretical investigation of the influence of flow oscillation, fluctuating circulation and rotational oscillation upon the transfer of momentum, heat and mass in two-dimensional laminar boundary-layer flow past cylinders with or without uniform suction...

W. J. Yang J. A. Clark

1965-01-01

26

Effective medium theory for two-dimensional random media composed of core–shell cylinders  

NASA Astrophysics Data System (ADS)

In this paper, based on the generalized coated coherent potential approximation method, we derive the mathematical formulae, for the extended effective medium theory, to investigate the optical properties of disordered media composed of core–shell cylinders. The effective indices of such media are obtained in the long-wavelength limit and in the Mie-scattering region. Moreover, we use this method to study optical properties of random media composed of core–shell cylinders with the core layer consisting of epsilon-less-than-one material.

Zhang, Hao; Shen, Yongqiang; Xu, Yuchen; Zhu, Heyuan; Lei, Ming; Zhang, Xiangchao; Xu, Min

2013-10-01

27

Vortex shedding suppression for laminar flow past a square cylinder near a plane wall: a two-dimensional analysis  

Microsoft Academic Search

Summary  A numerical study on the uniform shear flow past a long cylinder of square cross-section placed parallel to a plane wall has\\u000a been made. The cylinder is considered to be within the boundary layer of the wall. The maximum gap between the plane wall\\u000a to the cylinder is taken to be 0.25 times the cylinder height. We investigated the flow

S. Bhattacharyya; D. K. Maiti

2006-01-01

28

Steady and unsteady solutions for coating flow on a rotating horizontal cylinder: Two-dimensional theoretical and numerical modeling  

Microsoft Academic Search

A model for the evolution of a thin liquid coating on a horizontal cylinder is presented. The cylinder rotates about its axis, carrying liquid around its circumference. For a viscous coating, this leads to formation of a relatively thick coating where the cylinder surface moves upward. The model is based on lubrication theory, as the coating is thin compared to

P. L. Evans; L. W. Schwartz; R. V. Roy

2004-01-01

29

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

30

Comparative study of electromagnetic performance of alternative Halbach and conventional radially magnetized permanent magnet brushless motors  

Microsoft Academic Search

In this paper, the static and dynamic electromagnetic performance, including the airgap field distribution, the back-emf waveform, the cogging torque, and the torque-speed characteristic and the efficiency, of three alternative Halbach permanent magnet brushless motors, employing anisotropic bonded NdFeB Halbach cylinder with and without rotor back-iron, as well as segmented Halbach cylinder with sintered NdFeB magnets, are compared by finite

Z. Q. Zhu; Z. P. Xia; D. Howe

2008-01-01

31

PHYSALIS: a new method for particle simulationPart II: two-dimensional Navier-Stokes flow around cylinders  

NASA Astrophysics Data System (ADS)

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

Takagi, S.; Og~Uz, H. N.; Zhang, Z.; Prosperetti, A.

2003-05-01

32

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

33

Two-dimensional and surface backscattering Mueller matrices of anisotropic sphere-cylinder scattering media: a quantitative study of influence from fibrous scatterers.  

PubMed

We present both the two-dimensional backscattering point-illumination and surface-illumination Mueller matrices for the anisotropic sphere-cylinder scattering media. The experimental results of the microsphere-silk sample show that the Mueller matrix elements of an anisotropic scattering medium are different from those of an isotropic medium. Moreover, both the experiments and Monte Carlo simulations show that the directions of the fibrous scatterers have prominent effects on the Mueller matrix elements. As the fibrous samples rotate, the surface-illumination Mueller matrix measurement results for the m12, m21, m13, m31, m22, m23, m32, and m33 elements represent periodical variations. Experiments on skeletal muscle and porcine liver tissue samples confirm that the periodical changes for the surface-illumination Mueller matrix elements are closely related to the well aligned fibrous scatterers. The m22, m23, m32, and m33 elements are powerful tools for quantitative characterization of anisotropic scattering media, including biological tissues. PMID:23552634

He, Honghui; Zeng, Nan; Du, E; Guo, Yihong; Li, Dongzhi; Liao, Ran; He, Yonghong; Ma, Hui

2013-04-01

34

Two Dimensional Schrodinger Equation  

NSDL National Science Digital Library

The Two Dimensional Schrodinger Equation model simulates the time evolution of a two-dimensional wave packet as it moves towards a slit with an obstacle in it, both with variable widths. By changing three parameters via sliders provided, slit width, obstacle width, and initial position of the wave packet, different behaviors can be explored. These phenomena include interference, diffraction produced by a slit, a corner, and an obstacle, and bouncing of the wave packet. In addition, the angle of propagation for the diffracted part of the wave packet can be measured. This simulation is described by a paper in the European Journal of Physics, "A versatile applet to explore the wave behaviour of particles, " J I Fernández Palop, 2009 Eur. J. Phys. 30 771, which outlines the simulation and how the usefulness of the simulation has been tested in the subject of quantum physics. The Two Dimensional Schrodinger Equation model was created using the Easy Java Simulations (EJS) modeling tool. It is distributed as a ready-to-run (compiled) Java archive. Double clicking the ejs_qm_schrodinger2d.jar file will run the program if Java is installed.

Palop, Jose I.

2010-07-16

35

Two dimensional vernier  

NASA Astrophysics Data System (ADS)

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.

1992-01-01

36

Soap film flows: Statistics of two-dimensional turbulence  

Microsoft Academic Search

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

P. Vorobieff; M. Rivera; R. E. Ecke

1999-01-01

37

Two-dimensional cylindrical plasma for intermediate gas pressures  

NASA Astrophysics Data System (ADS)

A two-dimensional hydrodynamic model for a bounded plasma cylinder is developed. This model establishes a bridge between the two limiting cases presented by Godyak and Sternberg (2008 Plasma Sources Sci. Technol. 17 0250042): the diffusion-controlled regime and the free-fall regime. An analysis of the bounded plasma cylinder with arbitrary aspect ratios and arbitrary collisionality is presented. Plasma parameters relevant in applications are found for a wide range of aspect ratios and collisionality.

Sternberg, Natalia; Godyak, Valery

2011-02-01

38

Development and Testing of an Axial Halbach Magnetic Bearing.  

National Technical Information Service (NTIS)

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 ...

D. J. Eichenberg C. A. Gallo W. K. Thompson

2006-01-01

39

Development and Testing of a Radial Halbach Magnetic Bearing.  

National Technical Information Service (NTIS)

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 othe...

C. A. Gallo D. J. Eichenberg W. K. Thompson

2006-01-01

40

Two Dimensional Unstable Scar Statistics.  

National Technical Information Service (NTIS)

This report examines the localization of time harmonic high frequency modal fields in two dimensional cavities along periodic paths between opposing sides of the cavity. The cases where these orbits lead to unstable localized modes are known as scars. Thi...

J. D. Kotulski K. S. H. Lee L. K. Warne R. E. Jorgensen

2006-01-01

41

Two-Dimensional Critical Phenomena.  

National Technical Information Service (NTIS)

Two dimensional critical systems are studied using transformation to free fields and conformal invariance methods. The relations between the two approaches are also studied. The analytical results obtained generally depend on universality hypotheses or on...

H. Saleur

1987-01-01

42

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

43

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

National Technical Information Service (NTIS)

In August 1979, Halbach submitted a paper entitled ''Design of Permanent Multipole Magnets with Oriented Rare Earth Cobalt Material.'' In this paper, he presented a novel method of generating multipole magnetic fields using non-intuitive geometrical arran...

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

1994-01-01

44

Two-dimensional solvable chaos  

NASA Astrophysics Data System (ADS)

Two methods are proposed to construct two-dimensional chaotic maps. Several examples of exactly solvable chaotic maps and their invariant measures are obtained. They are isomorphic maps of square to square, plane to plane and circle to circle having various symmetry such as uniform, rotational and the quartic rotational symmetry.

Sogo, Kiyoshi; Masumizu, Atsushi

2011-09-01

45

Halbach array motor/generators: A novel generalized electric machine  

SciTech Connect

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

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

1994-10-28

46

Two-dimensional thermofield bosonization  

SciTech Connect

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

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

2005-12-15

47

Two-dimensional plasmonic metamaterials  

Microsoft Academic Search

The fabrication of three-dimensional photonic metamaterials faces numerous technological challenges. Many new concepts and\\u000a ideas in the optics of metamaterials may be more easily tested in two spatial dimensions using the planar optics of surface\\u000a plasmon polaritons. In this paper we review recent progress in this direction. Two-dimensional photonic crystals exhibiting\\u000a either positive or negative refraction, and strongly anisotropic metamaterials,

I. I. Smolyaninov

2007-01-01

48

Finding two-dimensional peaks  

Microsoft Academic Search

Two-dimensional generalization of the original peak finding algorithm suggested earlier is given. The ideology of the algorithm\\u000a emerged from the well-known quantum mechanical tunneling property which enables small bodies to penetrate through narrow potential\\u000a barriers. We merge this “quantum” ideology with the philosophy of Particle Swarm Optimization to get the global optimization\\u000a algorithm which can be called Quantum Swarm Optimization.

Z. K. Silagadze

2007-01-01

49

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

50

Two-Dimensional Simulation of Richtmyer-Meshkov Instability  

Microsoft Academic Search

Two-dimensional simulation of a single-mode Richtmyer--Meshkov instability (RMI) is undertaken to validate GASP, which is a structured, multi-block flow solver based on Reynolds-averaged Navier-Stokes equations (RANS). The fluid configuration is comprised of a diffuse SF6 cylinder immersed in air and accelerated by a Mach 1.2 planar shock. Good overall agreement is achieved between our results and the experiment (Tomkins phet

Amol Palekar; Charles R. Truman; Peter Vorobieff

2004-01-01

51

Two-dimensional combustion chamber analysis of Direct Injection Diesel  

Microsoft Academic Search

Re-entrant bowls for high compression ratio heavy-duty turbocharged DI Diesel have been studied by the utilization of a two-dimensional axisymmetric model of the air motion and spray formation inside the cylinder. The trend of the air motion and spray pattern obtained by changing combustion chamber parameters are compared with the trend of the engine performance like smoke, fuel consumption, gaseous

C. Bassoli; G. Biaggini; G. Bodritti; G. M. Cornetti

1984-01-01

52

Two-dimensional colloidal alloys.  

PubMed

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

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

2011-03-24

53

Band gaps of two-dimensional antiferromagnetic photonic crystal  

NASA Astrophysics Data System (ADS)

In an external magnetic field, the band structure of a two-dimensional photonic crystal (PC) composed of parallel antiferromagnetic cylinders in a background dielectric is investigated with a Green's function method. The cylinders with two resonant frequencies form a square lattice and are characterized by a magnetic permeability tensor. In our numerical calculation, we find that this method allows fast convergence and is available in both the resonant and non-resonant frequency ranges. In the non-resonant range, the PC is similar in band structure to an ordinary dielectric PC. Two electromagnetic band gaps, however, appear in the resonant frequency region, and their frequency positions and widths are governed by the external field. The dependence of the electromagnetic gaps on the cylinder radius also is discussed.

Song, Yu-Ling; Ta, Jin-Xing; Wang, Xuan-Zhang

2011-07-01

54

Halbach array DC motor/generator  

SciTech Connect

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

55

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

56

Coherent two-dimensional nanoscopy.  

PubMed

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. PMID:21835982

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

2011-08-11

57

Optimum Allocation of Two-Dimensional Shapes.  

National Technical Information Service (NTIS)

The optimum two-dimensional allocation problem consists in taking a two-dimensional resource and cutting it into a number of two-dimensional shapes in such a way that some objective function is optimized. The paper describes an investigation into methods ...

M. Adamowicz

1971-01-01

58

Two-dimensional visualization of liquid layers on transparent walls.  

PubMed

A new two-dimensional visualization technique based on laser-induced fluorescence for investigation of liquid-fuel films on transparent walls was applied in an SI engine. For optical access the upper part of the engine cylinder is replaced with a quartz ring. An UV laser beam is coupled into the ring, forcing total reflection at quartz-air interfaces. Because of the similar indices of refraction of quartz and fuel, laser light penetrates into the liquid. The corresponding fluorescence signal visualizes areas where wall film is present. It is shown that the technique is an excellent tool for investigation of wall-film development in combustion engines. PMID:18185618

Kull, E; Wiltafsky, G; Stolz, W; Min, K D; Holder, E

1997-05-01

59

Two-dimensional electromagnetic crystals formed by reactively loaded wires.  

PubMed

Two-dimensional electromagnetic crystals formed by rectangular lattices of thin ideally conducting cylinders periodically loaded by bulk reactive impedances are considered. An analytical theory of dispersion and reflection from this medium is presented. The consideration is based on the local field approach. The transcendental dispersion equation is obtained in the closed form and solved numerically. Different types of the loads such as inductive, capacitive, serial, and parallel LC circuits are considered. Typical dispersion curves and reflection coefficients are calculated and analyzed. PMID:12366283

Belov, P A; Simovski, C R; Tretyakov, S A

2002-09-20

60

TWO-DIMENSIONAL BELIEF CHANGE An Advertisement  

Microsoft Academic Search

In this paper I compare two dierent the models of two-dimensional belief change, namely 'revision by comparison' (Ferme and Rott, Artifi- cial Intelligence 157, 2004) and 'bounded revision' (Rott, in Hommagea Wlodek, Uppsala 2007). These revision operations are two-dimensional in the sense that they take as arguments pairs consisting of an input sentence and a reference sentence. Two-dimensional revision operations

Hans Rott

61

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

62

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

Microsoft Academic Search

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

Vakhtang Jandieri; Kiyotoshi Yasumoto; Hiroshi Toyama

2007-01-01

63

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

Microsoft Academic Search

The onset of Karman-vortex shedding is studied experimentally in the wake of different two-dimensional bluff bodies, namely an oblong cylinder, circular cylinders, and plates of rectangular cross section. Different control measures, such as wake heating, transverse body oscillations, and base bleed are investigated. As the steady-periodic Karman shedding has previously been identified as a limit-cycle, i.e. as self-excited oscillations, the

Michael Schumm; Eberhard Berger; Peter A. Monkewitz

1994-01-01

64

Information Extraction by Two Dimensional Parser  

Microsoft Academic Search

This paper proposes a learning algorithm for a two dimensional parser. The parser is designed to analyze page layout of documents and extract information using both textual and layout information. The parsing rules are expressed by an extended stochastic context free grammar that decomposes tokens located in two dimensional space both horizontally and vertically. In this paper we focus on

Atsuhiro Takasu

2008-01-01

65

Recent Development of Halbach Permanent Magnet Machines and Applications  

Microsoft Academic Search

Halbach magnetised PM brushless machines are novel in that their magnetisation is self-shielding. They offer many attractive features, such as sinusoidal airgap field distribution and back-emf waveform, negligible cogging torque, potentially high airgap flux density and no need of rotor back-iron. Hence, they have recently attracted many research and development interests and extensive exploitation for their applications. This paper starts

Z. Q. Zhu

2007-01-01

66

Sweeping and Maintaining Two-Dimensional Arrangements on Surfaces: A First Step  

Microsoft Academic Search

We introduce a general framework for sweeping a set of curves embedded on a two-dimensional parametric surface. We can han- dle planes, cylinders, spheres, tori, and surfaces homeomorphic to them. A major goal of our work is to maximize code reuse by generalizing the prevalent sweep-line paradigm and its implementation so that it can be employed on a large class

Eric Berberich; Efi Fogel; Dan Halperin; Kurt Mehlhorn; Ron Wein

2007-01-01

67

Radiation from a Line Source Embedded in Two-Dimensional Electromagnetic Crystals  

Microsoft Academic Search

The two-dimensional radiation from a localized line source embedded in electromagnetic crystals is formulated in the spectral domain, using the lattice sums, the T-matrix of a circular cylinder, and the generalized reflection and transmission matrices for the layered system. Electromagnetic crystals are periodic dielectric or metallic structures, in which any electromagnetic wave propagation is forbidden within a certain frequency range.

Vakhtang Jandieri; Kiyotoshi Yasumoto

68

Wavelet-based method for calculating elastic band gaps of two-dimensional phononic crystals  

Microsoft Academic Search

A wavelet-based method is developed to calculate elastic band gaps of two-dimensional phononic crystals. The wave field is expanded in the wavelet basis and an equivalent eigenvalue problem is derived in a matrix form involving the adaptive computation of integrals of the wavelets. The method is applied to a binary system. We first compute the band gaps of Au cylinders

Zhi-Zhong Yan; Yue-Sheng Wang

2006-01-01

69

Efficient formulation for band-structure calculations of two-dimensional phononic-crystal plates  

Microsoft Academic Search

Based on Mindlin's plate theory and the plane wave expansion method, a formulation is proposed to study the propagation of Lamb waves in two-dimensional phononic-crystal plates. The method is applied to calculate the frequency band structure of a square array of crystalline gold cylinders in an epoxy matrix with a finite thickness. It is found that complete frequency band gaps

Jin-Chen Hsu; Tsung-Tsong Wu

2006-01-01

70

Art and science of magnet design: A Festschrift in honor of Klaus Halbach. Volume 1.  

National Technical Information Service (NTIS)

This is a collection of technical papers and personal remembrances written expressly for the Halbach Symposium and dedicated to Klaus Halbach. The topics presented offer a hint of the diversity of Klaus's scientific career. Most of the papers deal with ma...

J. Cross

1995-01-01

71

Electronic properties of two-dimensional systems  

Microsoft Academic Search

The electronic properties of inversion and accumulation layers at semiconductor-insulator interfaces and of other systems that exhibit two-dimensional or quasi-two-dimensional behavior, such as electrons in semiconductor heterojunctions and superlattices and on liquid helium, are reviewed. Energy levels, transport properties, and optical properties are considered in some detail, especially for electrons at the (100) silicon-silicon dioxide interface. Other systems are discussed

Tsuneya Ando; Alan B. Fowler; Frank Stern

1982-01-01

72

Conjugate forced convection–conduction heat transfer analysis of a heat generating vertical cylinder  

Microsoft Academic Search

Conjugate heat transfer by forced convection over a vertical cylinder without heat generation has been a subject of many investigations in the recent past. In the present work, the radial heat conduction along with heat generation in a vertical cylinder is considered for analysis. The steady two-dimensional conduction equation for the heat generating cylinder and steady two-dimensional laminar boundary layer

G Jilani; S Jayaraj; M Adeel Ahmad

2002-01-01

73

Guided circumferential waves in layered cylinders  

Microsoft Academic Search

This paper examines the propagation of time harmonic circumferential waves in a two-dimensional (infinitely long) hollow cylinder with an inner shaft. The boundary condition at the interface (between the inner shaft and the outer cylinder) is assumed as free-sliding; that is, the interfacial shear stresses are assumed to be zero, and the normal stress and radial displacements are continuous. The

Christine Valle; Jianmin Qu; Laurence J. Jacobs

1999-01-01

74

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

75

Superconductivity at the Two-dimensional Limit  

NASA Astrophysics Data System (ADS)

Superconductivity in the extreme two-dimensional limit is studied on ultra-thin lead (Pb) films down to two atomic layers, where only a single channel of quantum well states exist. Scanning tunneling spectroscopy reveals that local superconducting order remains robust until two atomic layers, where the transition temperature abruptly plunges to lower values depending sensitively on the exact atomic structure of the film. Our result shows that Cooper pairs can still form in the last two dimensional channel of electron states, although their binding are strongly affected by the substrate [1]. In this presentation, I will also discuss this new result in comparison with several recent experimental results on ultra-thin metallic films performed using local STS probes and macroscopic transport measurements.[4pt] [1] ``Superconductivity at the Two-dimensional Limit,'' Shengyong Qin, Jungdae Kim, Qian Niu and Chih-Kang Shih, Science 324, 1314 (2009).

Shih, Chih-Kang

2010-03-01

76

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

77

Phase Transitions in Two-Dimensional Superconductors  

NASA Astrophysics Data System (ADS)

In this thesis, we describe a number of experiments which are designed to explore the theoretically predicted phase transitions for two-dimensional superconductors. We first examine the behavior of a two-dimensional superconductor in the absence of a magnetic field, where the fluctuations in the phase of the superconducting order parameter results in the reduction of the superconducting transition temperature for a two-dimensional superconductor below the mean field transition temperature. The experimental results presented show the importance of the vortex unbinding mechanism; however they challenge some of the predictions of the current theoretical model for the normal/superconducting transition. We then turn our attention to the behavior of two-dimensional superconductors in the presence of a magnetic field. In this case, our experimental results show that vortices in weakly disordered two-dimensional superconducting films freeze into locally correlated areas at temperatures below the mean field transition temperature. The experimentally measured phase boundary between the liquid phase and the locally ordered solid phase for the vortices in our samples shows good agreement with that predicted by the dislocation unbinding melting mechanism for the two-dimensional vortex lattice. For this transition, we have also done a detailed study of the correlations in the vortex lattices as a function of the strength of pinning in our samples and established a connection between the melting theory and collective pinning theory for vortices in two dimensions. To fully examine the phase diagram of a two-dimensional superconductor we have extended our studies of the properties of this system to the limit of strong disorder, where superconductivity is weak. In this limit, we report experimental evidence for a zero temperature field-tuned superconducting-insulating phase transition driven by quantum fluctuation of the phase of the superconducting order parameter. Overall, the results of this thesis provide an experimental bases for a number of phase transitions in two-dimensional superconductors, thereby establishing a rich phase diagram for this system as a function of the temperature, the magnetic field, and the amount of disorder.

Yazdani, Ali

1995-01-01

78

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)

1999-08-01

79

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

80

Two-Dimensional Motions of Rockets  

ERIC Educational Resources Information Center

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

Kang, Yoonhwan; Bae, Saebyok

2007-01-01

81

Two-dimensional Markovian holonomy fields  

Microsoft Academic Search

We define a notion of Markov process indexed by curves drawn on a compact surface and taking its values in a compact Lie group. We call such a process a two-dimensional Markovian holonomy field. The prototype of this class of processes, and the only one to have been constructed before the present work, is the canonical process under the Yang-Mills

Thierry Lévy

2008-01-01

82

Two-dimensional turbulence: a physicist approach  

Microsoft Academic Search

Much progress has been made on two-dimensional turbulence, these last two decades, but still, a number of fundamental questions remain unanswered. The objective of the present review is to collect and organize the available information on the subject, emphasizing on aspects accessible to experiment, and outlining contributions made on simple flow configurations. Whenever possible, open questions are made explicit. Various

Patrick Tabeling

2002-01-01

83

Imaging Properties of Two-Dimensional Microlenses  

Microsoft Academic Search

Despite strong experimental and theoretical evidence supporting superresolution imaging based on microlenses, imaging mechanisms involved are not well understood. Based on the transformation optics approach, we demonstrate that microlenses may act as two-dimensional fisheye or Eaton lenses. An asymmetric Eaton lens may exhibit considerable image magnification, which has been confirmed experimentally.

Vera N. Smolyaninova; Igor I. Smolyaninov; Alexander V. Kildishev; Vladimir M. Shalaev

2010-01-01

84

Two dimensional quantum gravity coupled to matter  

NASA Astrophysics Data System (ADS)

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

Mann, R. B.

1992-11-01

85

Constitutive Theory for Two Dimensional Liquid Crystals  

Microsoft Academic Search

Two dimensional liquid crystal are considered as mathematical surfaces of discontinuity of the bulk fields. The equations of motion for the relevant surface fields in the presence of electromagnetic fields are summarized. These are the mechanical balance equations, Maxwell's equations, and an equation of motion for the second order alignment tensor. The restrictions to constitutive functions implied by the Second

C. Papenfuss; W. Muschik

1995-01-01

86

Two-dimensional Penrose lattice: dc conductivity  

Microsoft Academic Search

The dc conductivity for a tight-binding Hamiltonian on a two-dimensional Penrose lattice is computed numerically for finite systems from Kubo's formula using the recursion method. Results are suggestive of a weak metallic behavior where states are more localized than in the case of a pure crystal, in agreement with recent conjectures by Sutherland.

T. C. Choy

1987-01-01

87

Cooperative two-dimensional directed transport  

Microsoft Academic Search

A mechanism for the cooperative directed transport in two-dimensional ratchet potentials is proposed. With the aid of mutual couplings among particles, coordinated unidirectional motion along the ratchet direction can be achieved by transforming the energy from the transversal rocking force (periodic or stochastic) to the work in the longitude direction. Analytical predictions on the relation between the current and other

Zhigang Zheng; Hongbin Chen

2010-01-01

88

The Two-Dimensional Random Walk  

NSDL National Science Digital Library

This is the description and instructions for the Two-Dimensional Random Walk applet. This applet, presented by Boston University's Center for Polymer Studies, relates random coin-flipping to random motion but in more than one direction (dimension). It covers mean squared distance in the discussion. Overall, this is a nice interactive resource for a statistics classroom.

Trunfio, Paul; Mcgath, Gary

2008-12-29

89

Two-dimensional FLD for face recognition  

Microsoft Academic Search

This paper presents a new scheme of face image feature extraction, namely, the two-dimensional Fisher linear discriminant. Experiments on the ORL and the UMIST face databases show that the new scheme outperforms the PCA and the conventional PCA+FLD schemes, not only in its computational efficiency, but also in its performance for the task of face recognition.

Huilin Xiong; M. N. S. Swamy; M. Omair Ahmad

2005-01-01

90

Two-dimensional optimal sensor placement  

SciTech Connect

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

Zhang, H. [Univ. of Alberta, Edmonton, Alberta (Canada)

1995-05-01

91

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

92

Cooperative two-dimensional directed transport  

NASA Astrophysics Data System (ADS)

A mechanism for the cooperative directed transport in two-dimensional ratchet potentials is proposed. With the aid of mutual couplings among particles, coordinated unidirectional motion along the ratchet direction can be achieved by transforming the energy from the transversal rocking force (periodic or stochastic) to the work in the longitude direction. Analytical predictions on the relation between the current and other parameters for the ac-driven cases are given, which are in good agreement with numerical simulations. Stochastic driving forces can give rise to the resonant directional transport. The effect of the free length, which has been explored in experiments on the motility of bipedal molecular motors, is investigated for both the single- and double-channel cases. The mechanism and results proposed in this letter may both shed light on the collective locomotion of molecular motors and open ways on studies in two-dimensional collaborative ratchet dynamics.

Zheng, Zhigang; Chen, Hongbin

2010-11-01

93

Two-dimensional microfabricated electrostatic einzel lens  

Microsoft Academic Search

A two-dimensional electrostatic einzel lens fabricated using microfabrication technology is described. The lens consists of cylindrical electrodes mounted in on two oxidised, silicon substrates, which are held apart by two cylindrical spacers. V-shaped grooves formed by anisotropic wet chemical etching are used to locate the electrodes and the spacers. The electrodes are metal-coated glass rods that are soldered to metal

R. R. A. Syms; L. Michelutti; M. M. Ahmad

2003-01-01

94

Two-dimensional synthesis of anisotropic nanoparticles  

Microsoft Academic Search

A novel approach for the synthesis of nanoparticles has been introduced in which nanoparticles are fabricated via decomposition of an insoluble precursor compound in a monolayer at the gas\\/liquid interface, and nanoparticle growth is an example of a two-dimensional (2-D) process where true 2-D diffusion of precursor molecules, active intermediates, metal atoms and its complexes, nucleus and growing nanoparticles, surfactants

Gennady B Khomutov

2002-01-01

95

Fully localized two-dimensional embedded solitons  

SciTech Connect

We report the prediction of fully localized two-dimensional embedded solitons. These solitons are obtained in a quasi-one-dimensional waveguide array which is periodic along one spatial direction and localized along the orthogonal direction. Under appropriate nonlinearity, these solitons are found to exist inside the Bloch bands (continuous spectrum) of the waveguide and thus are embedded solitons. These embedded solitons are fully localized along both spatial directions. In addition, they are fully stable under perturbations.

Yang Jianke [Department of Mathematics and Statistics, University of Vermont, Burlington, Vermont 05401 (United States)

2010-11-15

96

Stochastic models of two-dimensional fracture  

NASA Astrophysics Data System (ADS)

Two statistical models of (strictly two-dimensional) layer destruction are presented. The first is built as a strict percolation model with an added ``conservation law'' (conservation of mass) as physical constraint. The second allows for damped or limited fracture. Two successive fracture crack thresholds are considered. Percolation (i.e., fracture) probability and cluster distributions are studied by use of numerical simulations. Different fractal dimension, critical exponents for cluster distribution, and universality laws characterize both models.

Ausloos, M.; Kowalski, J. M.

1992-06-01

97

Imaging Properties of Two-Dimensional Microlenses  

Microsoft Academic Search

Despite strong experimental and theoretical evidence supporting\\u000asuperresolution imaging based on microlenses, imaging mechanisms involved are\\u000anot well understood. Based on the transformation optics approach, we\\u000ademonstrate that microlenses may act as two-dimensional fisheye or Eaton\\u000alenses. An asymmetric Eaton lens may exhibit considerable image magnification,\\u000awhich has been confirmed experimentally.

Vera N. Smolyaninova; Igor I. Smolyaninov; Alexander V. Kildishev; Vladimir M. Shalaev

2010-01-01

98

Topics in two-dimensional string theory  

Microsoft Academic Search

We explore various topics in two-dimensional string theory. Firstly, we study particle production in time-dependent backgrounds of the c = 1 matrix model, a holographic description of bosonic string theory in 1+1 dimensions. The process is described most efficiently in terms of anomalies, but we also discuss the explicit mode expansions. In matrix cosmology the usual vacuum ambiguity of quantum

Joshua L. Davis

2006-01-01

99

Superinsulator Phase of Two-Dimensional Superconductors  

Microsoft Academic Search

Using path-integral quantum Monte Carlo we study the low-temperature phase diagram of a two-dimensional superconductor within a phenomenological model, where vortices have a finite mass and move in a dissipative environment modeled by a Caldeira-Leggett term. The quantum vortex liquid at high magnetic fields exhibits superfluidity and thus corresponds to a superinsulating phase which is characterized by a nonlinear voltage-current

A. Krämer; S. Doniach

1998-01-01

100

Superdiffusion in two-dimensional Yukawa liquids  

SciTech Connect

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 Levy 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. [Department of Physics and Astronomy, University of Iowa, Iowa City, Iowa 52242 (United States)

2007-01-15

101

Real time multiple two dimensional barcode reader  

Microsoft Academic Search

The proposed work describes a system that can be used to detect and decode multiple Two-Dimensional (2D) barcodes (i.e. Datamatrix). The proposed system is capable of detecting and decoding of barcodes covered by polyethylene foiling in moving images. The foiling causes reflection on the captured images and hence provides challenges to detection\\/decoding. Similarly the proposed system addresses the problem of

I. Zafar; U. Zakir; E. A. Edirisinghe

2010-01-01

102

Linearized two-dimensional fluid transients  

NASA Astrophysics Data System (ADS)

A numerical analysis of low-velocity two-dimensional transient fluid flow problems is presented. The method is similar in concept to the one-dimensional method of characteristics, but does not follow the traditional characteristics theory for two spatial dimensions. Distinct paths are defined in the three-dimensional space-time domain along which compatibility equations are integrated. The explicit procedure is explained, and validated by comparisons with analytical solutions.

Wylie, E. B.

1984-06-01

103

The tunable acoustic band gaps of two-dimensional phononic crystals with a dielectric elastomer cylindrical actuator  

Microsoft Academic Search

By calculating the transmission coefficients by finite-element software, the study of the tunable acoustic band gap for two-dimensional (2D) phononic crystals composed of a square array of hollow cylinders in an air background is considered. The inclusions are a dielectric elastomer cylindrical actuator, which is made of a hollow cylinder sandwiched between two compliant electrodes. By applying a voltage between

Wen-Pei Yang; Lien-Wen Chen

2008-01-01

104

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

105

Two-dimensional radiative heat-transfer calculations for nonequilibrium flows  

SciTech Connect

The present study details the inclusion of radiative heat-transfer phenomena in the numerical simulation of reactive hypersonic and atmospheric re-entry flows. Truly two-dimensional algorithms are developed for the radiative source term in the governing equations, whereby the determination of the specific intensity field is obtained by means of a numerical integration over directions of propagation of radiation. The one-dimensional slab approximation is lifted, and the analysis presented allows the determination of the radiative characteristics of the entire flowfield, rather than being limited to the stagnation streamline, thereby providing an accurate assessment of two-dimensional relieving effects in the stagnation region. A few preliminary results are presented for the Mach 47 flow over a cylinder, including a comparison of the two-dimensional algorithm with the one-dimensional approximation and an emission-dominated case. The effects of improving the modeling of radiative heat transfer are demonstrated. 31 refs.

Elbert, G.J.; Cinnella, P. [North Carolina A& T State Univ., Greensboro, NC (United States)

1995-03-01

106

Two-dimensional radiative heat-transfer calculations for nonequilibrium flows  

NASA Astrophysics Data System (ADS)

The present study details the inclusion of radiative heat-transfer phenomena in the numerical simulation of reactive hypersonic and atmospheric re-entry flows. Truly two-dimensional algorithms are developed for the radiative source term in the governing equations, whereby the determination of the specific intensity field is obtained by means of a numerical integration over directions of propagation of radiation. The one-dimensional slab approximation is lifted, and the analysis presented allows the determination of the radiative characteristics of the entire flowfield, rather than being limited to the stagnation streamline, thereby providing an accurate assessment of two-dimensional relieving effects in the stagnation region. A few preliminary results are presented for the Mach 47 flow over a cylinder, including a comparison of the two-dimensional algorithm with the one-dimensional approximation and an emission-dominated case. The effects of improving the modeling of radiative heat transfer are demonstrated.

Elbert, Gregory J.; Cinnella, Pasquale

1995-03-01

107

Interface roughening in two-dimensional quasicrystals  

NASA Astrophysics Data System (ADS)

The equilibrium fluctuations of interfaces in two-dimensional quasi-periodic lattices, such as Penrose tilings, are considered. By a transfer-matrix formulation, this problem is mapped to the one-dimensional Schroedinger equation with a quasi-periodic potential; from the scaling properties of the eigenstates near the band edge, it is possible to extract the exponent zeta characterizing the interface roughness. For a cosine potential, a true roughening transition in d = 2 dimensions is found. For a Fibonacci tiling, which approximates the Penrose tiling, zeta is nonuniversal, zeta less than 1/2, and zeta goes to 0 continuously as T goes to 0.

Henley, Christopher L.; Lipowsky, Reinhard

1987-10-01

108

Spontaneous trimerization in two-dimensional antiferromagnets.  

PubMed

In this paper, we propose an exotic quantum paramagnetic state in two-dimensional antiferromagnets-the spontaneous trimer state-which is the direct product state of the trimers of spins. Each trimer is a singlet state formed by three neighboring spins with SU(3) symmetry. A frustrated spin-1 Heisenberg model in the kagome lattice is investigated. By analogy to the pseudo-potential approach in the fractional quantum Hall effect (FQHE), we find that the trimer state provides a good description for the exact ground state of this model. Other interesting properties, such as the local excitations as well as magnetization plateaus have also been investigated. PMID:21694029

Cai, Zi; Chen, Shu; Wang, Yupeng

2009-10-23

109

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

110

Two-dimensional unsaturated flow through a circular inclusion  

NASA Astrophysics Data System (ADS)

Two-dimensional unsaturated flow is considered through a circular inclusion. The hydraulic conductivity is of the form Kiexp(?h) where the saturated conductivity Ki is different in the main flow regime and the inclusion, ? is a constant in the entire flow domain, and h is the pressure head. The problem reduces to the Helmholtz equation as previously used by J. R. Philip and colleagues for solving problems with impermeable regions or cavities in an unsaturated regime. The pressure heads are continuous on the interface of the inclusion. The normal flow velocities at the interface are matched approximately using the analytical element method recently exploited for saturated domains in several studies. Flow enhancement and exclusion through the circular inclusions are dependent on the value of ? and the radius of the cylinder but otherwise are similar to that for the saturated case. For example, for ratios of the inclusion to background saturated conductivity of 0.5 the flow is 0.74 of what it would be without the inclusion compared to 0.67 for the saturated case. This was calculated for a dimensionless radius (0.5 ? multiplied by the physical radius) of 1. When the ratio of the inclusion saturated conductivity to the background is 5, the comparable value for the unsaturated case is 1.45 and for the saturated case is 1.67.

Warrick, A. W.; Knight, J. H.

2002-07-01

111

Two-dimensional photonic band gap crystals  

NASA Astrophysics Data System (ADS)

A photonic crystal is a periodic dielectric structure that possesses a band of frequencies in which propagating electromagnetic waves are forbidden. Two-dimensional photonic crystals exhibit a band gap for waves traveling in the crystal plane, a property that offers promise for improved operation of optoelectronic devices including semiconductor lasers, light-emitting diodes, and frequency filters. A theoretical investigation of two-dimensional photonic band gap crystals has been performed. The plane-wave expansion method is used to solve Maxwell's equations for the electromagnetic frequency bands in several square (Laue group 4mm) and triangular (Laue group 6mm) crystal structures. The size of absolute band gaps is often limited by band degeneracies at lattice symmetry points. By reducing the lattice symmetry, these degeneracies can be lifted to increase the size of existing photonic band gaps, or to create new gaps where none existed for the more symmetric structure. Symmetry analysis also offers a rational approach for exploring and designing new photonic crystal structures. Gap maps for several important crystal structures are presented as a useful reference guide for experimentalists. The utility of photonic crystals for many applications is enhanced through the introduction of a defect into the crystal structure, which creates localized frequency states within the photonic band gap. Defect modes in two- dimensional square photonic crystal structures were studied using a supercell approach. By changing the radius of a single rod, several defect modes with complex electromagnetic field patterns appear within the photonic band gap. The mode frequencies can be tuned by varying the size of the defect rod. The double-rod square structure has two rod types per unit cell, yielding different defect characteristics depending on which rod is altered. In addition, anisotropic etching of patterned silicon has been investigated experimentally using a hyperthermal neutral fluorine atom beam generated by laserinduced detonation of SF6. The detrimental effects of surface charging are eliminated by the use of charge-neutral etch species; however, inelastic scattering of energetic reactive species has a significant effect on the development of the etch profiles, especially at high aspect ratios. Etch profile anomalies including microtrenching and undercutting are observed.

Anderson, Cheryl Marie

1999-07-01

112

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

113

Strongly Interacting Two-Dimensional Bose Gases  

NASA Astrophysics Data System (ADS)

We prepare and study strongly interacting two-dimensional Bose gases in the superfluid, the classical Berezinskii-Kosterlitz-Thouless (BKT) transition, and the vacuum-to-superfluid quantum critical regimes. A wide range of the two-body interaction strength 0.05

Ha, Li-Chung; Hung, Chen-Lung; Zhang, Xibo; Eismann, Ulrich; Tung, Shih-Kuang; Chin, Cheng

2013-04-01

114

Quantum Groups in Two-Dimensional Physics  

NASA Astrophysics Data System (ADS)

This book is an introduction to integrability and conformal field theory in two dimensions using quantum groups. The book begins with a brief introduction to S-matrices, spin chains and vertex models as a prelude to the study of Yang-Baxter algebras and the Bethe ansatz. The authors then introduce the basic ideas of integrable systems, giving particular emphasis to vertex and face models. They give special attention to the underlying mathematical tools, including braid groups, knot invariants, and towers of algebras. The authors then go on to give a detailed introduction to quantum groups before addressing integrable models, two-dimensional conformal field theories, and superconformal field theories. The book contains many diagrams and exercises to illustrate key points in the text and will be appropriate for researchers and graduate students in theoretical physics and mathematics.

Gómez, Cisar; Ruiz-Altaba, Martín; Sierra, German

1996-04-01

115

Intrinsic two-dimensional features as textons.  

PubMed

We suggest that intrinsic two-dimensional (i2D) features, computationally defined as the outputs of nonlinear operators that model the activity of end-stopped neurons, play a role in preattentive texture discrimination. We first show that for discriminable textures with identical power spectra the predictions of traditional models depend on the type of nonlinearity and fail for energy measures. We then argue that the concept of intrinsic dimensionality, and the existence of end-stopped neurons, can help us to understand the role of the nonlinearities. Furthermore, we show examples in which models without strong i2D selectivity fail to predict the correct ranking order of perceptual segregation. Our arguments regarding the importance of i2D features resemble the arguments of Julesz and co-workers regarding textons such as terminators and crossings. However, we provide a computational framework that identifies textons with the outputs of nonlinear operators that are selective to i2D features. PMID:9656473

Barth, E; Zetzsche, C; Rentschler, I

1998-07-01

116

Two-Dimensional Speckle Strain Imaging  

PubMed Central

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

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

2012-01-01

117

Thermodynamics of two-dimensional magnetic nanoparticles  

NASA Astrophysics Data System (ADS)

A two-dimensional magnetic particle in the presence of an external magnetic field is studied. Equilibrium thermodynamical properties are derived by evaluating analytically the partition function. When the external field is applied perpendicular to the anisotropy axis the system exhibits a second-order phase transition with order parameter being the magnetization parallel to the field. In this case the system is isomorph to a mechanical system consisting of a particle moving without friction in a circle rotating about its vertical diameter. Contrary to a paramagnetic particle, equilibrium magnetization shows a maximum at finite temperature. It is also shown that uniaxial anisotropy in a system of noninteracting particles can be misinterpreted as a ferromagnetic or antiferromagnetic coupling among magnetic particles, depending on the angle between the anisotropy axes and magnetic field.

Vargas, P.; Altbir, D.; Knobel, M.; Laroze, D.

2002-05-01

118

Two-dimensional MHD generator model  

NASA Astrophysics Data System (ADS)

A steady state, two dimensional MHD generator code, GEN, is presented. The code solves the equations of conservation of mass, momentum, and energy, using a Von Mises transformation and a local linearization of the equations. By splitting the source terms into a part proportional to the axial pressure gradient and a part independent of the gradient, the pressure distribution along the channel is easily obtained to satisfy various criteria. Thus, the code can run effectively in both design modes, where the channel geometry is determined, and analysis modes, where the geometry is previously known. The code also employs a mixing length concept for turbulent flows, Cebeci and Chang's wall roughness model, and an extension of that model to the effective thermal diffusivities. Results on code validation, as well as comparisons of skin friction and Stanton number calculations with experimental results, are presented.

Geyer, H. K.; Ahluwalia, R. K.; Doss, E. D.

1980-09-01

119

Two-Dimensional Melting under Quenched Disorder  

NASA Astrophysics Data System (ADS)

We study the influence of quenched disorder on the two-dimensional melting behavior of superparamagnetic colloidal particles, using both video microscopy and computer simulations of repulsive parallel dipoles. Quenched disorder is introduced by pinning a fraction of the particles to an underlying substrate. We confirm the occurrence of the Kosterlitz-Thouless-Halperin-Nelson-Young scenario and observe an intermediate hexatic phase. While the fluid-hexatic transition remains largely unaffected by disorder, the hexatic-solid transition shifts to lower temperatures with increasing disorder. This results in a significantly broadened stability range of the hexatic phase. In addition, we observe spatiotemporal critical(like) fluctuations, which are consistent with the continuous character of the phase transitions. Characteristics of first-order transitions are not observed.

Deutschländer, Sven; Horn, Tobias; Löwen, Hartmut; Maret, Georg; Keim, Peter

2013-08-01

120

New Two-Dimensional Ice Models  

NASA Astrophysics Data System (ADS)

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

Kirov, Mikhail V.

2012-11-01

121

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

122

Two-dimensional Quantum Random Walk  

NASA Astrophysics Data System (ADS)

We analyze several families of two-dimensional quantum random walks. The feasible region (the region where probabilities do not decay exponentially with time) grows linearly with time, as is the case with one-dimensional QRW. The limiting shape of the feasible region is, however, quite different. The limit region turns out to be an algebraic set, which we characterize as the rational image of a compact algebraic variety. We also compute the probability profile within the limit region, which is essentially a negative power of the Gaussian curvature of the same algebraic variety. Our methods are based on analysis of the space-time generating function, following the methods of Pemantle and Wilson (J. Comb. Theory, Ser. A 97(1):129-161, 2002).

Baryshnikov, Yuliy; Brady, Wil; Bressler, Andrew; Pemantle, Robin

2011-01-01

123

Two-dimensional Quantum Random Walk  

NASA Astrophysics Data System (ADS)

We analyze several families of two-dimensional quantum random walks. The feasible region (the region where probabilities do not decay exponentially with time) grows linearly with time, as is the case with one-dimensional QRW. The limiting shape of the feasible region is, however, quite different. The limit region turns out to be an algebraic set, which we characterize as the rational image of a compact algebraic variety. We also compute the probability profile within the limit region, which is essentially a negative power of the Gaussian curvature of the same algebraic variety. Our methods are based on analysis of the space-time generating function, following the methods of Pemantle and Wilson (J. Comb. Theory, Ser. A 97(1):129-161, 2002).

Baryshnikov, Yuliy; Brady, Wil; Bressler, Andrew; Pemantle, Robin

2010-12-01

124

Graphene: the new two-dimensional nanomaterial.  

PubMed

Every few years, a new material with unique properties emerges and fascinates the scientific community, typical recent examples being high-temperature superconductors and carbon nanotubes. Graphene is the latest sensation with unusual properties, such as half-integer quantum Hall effect and ballistic electron transport. This two-dimensional material which is the parent of all graphitic carbon forms is strictly expected to comprise a single layer, but there is considerable interest in investigating two-layer and few-layer graphenes as well. Synthesis and characterization of graphenes pose challenges, but there has been considerable progress in the last year or so. Herein, we present the status of graphene research which includes aspects related to synthesis, characterization, structure, and properties. PMID:19784976

Rao, C N R; Sood, A K; Subrahmanyam, K S; Govindaraj, A

2009-01-01

125

Two-dimensional motions of rockets  

NASA Astrophysics Data System (ADS)

We analyse the two-dimensional motions of the rockets for various types of rocket thrusts, the air friction and the gravitation by using a suitable representation of the rocket equation and the numerical calculation. The slope shapes of the rocket trajectories are discussed for the three types of rocket engines. Unlike the projectile motions, the descending parts of the trajectories tend to be gentler and straighter slopes than the ascending parts for relatively large launching angles due to the non-vanishing thrusts. We discuss the ranges, the maximum altitudes and the engine performances of the rockets. It seems that the exponential fuel exhaustion can be the most potent engine for the longest and highest flights.

Kang, Yoonhwan; Bae, Saebyok

2007-01-01

126

Analysis, stability and control of wake flows past a circular cylinder: A numerical and theoretical study  

Microsoft Academic Search

Two-dimensional wake flows past a circular cylinder have been investigated from low to moderately high Reynolds numbers, focusing on the stability and the control by means of low dimensional models and numerical simulations. In the first part of this work, the impulsively started flow past a cylinder is computed by a two-dimensional direct numerical simulation over the range of Reynolds

Shaojie Tang

1997-01-01

127

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

128

Elastic properties of two-dimensional quasicrystals.  

PubMed

Quasicrystals (QC) with two-dimensional quasiperiodic and one-dimensional periodic structure are considered. Their symmetry can be described by embedding the three-dimensional physical space V(E) in a five-dimensional superspace V, which is the direct sum of V(E) and a two-dimensional internal space V(I). A displacement v in V can be written as v = u + w, where u in V(E) and w in V(I). If the QC has a point group P in V(E) that is crystallographic, it is assumed that w and a vector u' in V(E) lying in the plane in which the crystal is quasiperiodic transform under equivalent representations of P, inequivalent ones if the point group is 5-, 8-, 10- or 12-gonal. From the Neumann principle follow restrictions on the form of the phonon, phason and phonon-phason coupling contributions to the elastic stiffness matrix that can be determined by combining the restrictions obtained for a set of elements generating the point group of interest. For the phonon part, the restrictions obtained for the generating elements do not depend on the system to which the point group belongs. This remains true for the phason and coupling parts in the case of crystallographic point groups but, in general, breaks down for the non-crystallographic ones. The form of the symmetric 12 x 12 matrix giving the phonon, phason and phonon-phason coupling contributions to the elastic stiffness is presented in graphic notation. PMID:18560162

Grimmer, Hans

2008-05-12

129

Two-dimensional crystallization of bovine rhodopsin.  

PubMed

Bovine rhodopsin has been clustered into two-dimensional crystals in highly purified native rod disk membranes and studied with negative staining and transmission electron microscopy. The lattice is P2(1) with dimensions of 8.3 X 7.9 nm and interaxis angles of 86 +/- 3 degrees. 110 images of ordered areas were digitized and aligned with computer-correlation methods to calculate an average image with diffraction to the fourth order. The images were computer-filtered and reconstructed to approx. 2 nm resolution. When crystals appeared they covered 20-40% of the surface of the preparation and, since rhodopsin is at least 95% of the protein, there is no doubt that the crystals were due to rhodopsin. There appear to be two rhodopsin dimers per unit cell. Each rhodopsin molecules takes up about 7.5 nm2 of membrane area and is estimated to be associated with about 12 lipids on each side of the membrane. The membrane area found for bovine rhodopsin supports the rhodopsin origin of rarely seen but more highly ordered two-dimensional crystals found in detergent-treated frog rod membranes (Corless, J.M., McCaslin, D.R. and Scott, B.L. (1982) Proc. Natl. Acad. Sci. USA 79, 1116-1120). Furthermore, the rhodopsin membrane area is close to that of bacteriorhodopsin and is consistent with a seven transmembrane helix structure proposed for rhodopsin (for references see Dratz, E.A. and Hargrave, D.A. (1983) Trends Biochem. Sci. 8, 128-131). Crystallization was accomplished by lowering the pH to 5.5 near the isoelectric point of rhodopsin, raising the salt concentration of 2 M (NH4)2SO4, adding 5% glucose and 0.02% Hibitane (Ayerst), a cationic amphipathic antiseptic that favored crystal growth. PMID:4074754

Dratz, E A; Van Breemen, J F; Kamps, K M; Keegstra, W; Van Bruggen, E F

1985-12-20

130

Two-dimensional virtual impactors. Final report  

SciTech Connect

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

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

1980-12-01

131

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

132

An inexpensive rhizotron design for two-dimensional, horizontal root ...  

Treesearch

Title: An inexpensive rhizotron design for two-dimensional, horizontal root ... that supports two-dimensional, horizontal root growth measurements over time ... and (3) acquiring novel rooting data that can be input to a plant growth model.

133

An improved two-dimensional code encoding approach for publications  

Microsoft Academic Search

Nowadays, the publishing industry has begun to use the two-dimensional code in cell phones, but the standard is not defined. Compared with single-dimensional bar code, two-dimensional code contains more information and functions. Nowadays, two-dimensional code has been broadly used in some industries, such as mobile communication, logistics and advertising, but not in publishing. This paper introduces an improved two-dimensional code

Wang Liang; Liu Xiaodan

2010-01-01

134

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

135

Large band gaps in two-dimensional phononic crystals with neck structures  

NASA Astrophysics Data System (ADS)

In this paper, we study the band gap properties of a two-dimensional phononic crystal composed of periodic cylinders embedded in a homogenous matrix. The cylinders are not connected with the matrix directly but linked with it through the neck structures constituted by part of a circle. The dispersion relations, transmission spectra, and displacement fields of the eigenmodes of this phononic crystal are studied using the finite-element method. In contrast to the typical phononic crystals where the cylinders and matrix are in contact completely, the proposed structures with necks display larger band gaps at lower frequencies. The reason for the occurrence of the low-frequency band gaps as well as the effects of the geometrical parameters of the neck structures on the gaps are further explored numerically. Results show that the openings of the band gaps are attributed to the resonance of the cylinders and the interaction between the cylinders and the matrix, resulting from the introduction of the necks. The band gaps are significantly dependent upon the geometrical parameters such as the rotation angle of the necks which is defined as the angle between the centerline of the neck and the x-axis, the arc length of the necks, and also the filling ratio of the inclusions. The study in this paper is relevant to the design of tuning band gaps and isolators in the low-frequency range.

Yu, Kunpeng; Chen, Tianning; Wang, Xiaopeng

2013-04-01

136

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

137

Nonlinear tunneling in two-dimensional lattices  

SciTech Connect

We present a thorough analysis of the nonlinear tunneling of Bose-Einstein condensates in static and accelerating two-dimensional lattices within the framework of the mean-field approximation. We deal with nonseparable lattices, considering different initial atomic distributions in highly symmetric states. For an analytical description of the condensate before instabilities develop, we derive several few-mode models, analyzing essentially both nonlinear and quasilinear regimes of tunneling. By direct numerical simulations, we show that two-mode models provide an accurate description of tunneling when either initially two states are populated or tunneling occurs between two stable states. Otherwise, a two-mode model may give only useful qualitative hints for understanding tunneling, but does not reproduce many features of the phenomenon. This reflects the crucial role of instabilities developed due to two-body interactions resulting in a non-negligible population of the higher bands. This effect becomes even more pronounced in the case of accelerating lattices. In the latter case we show that the direction of the acceleration is a relevant physical parameter which affects the tunneling by changing the atomic rates at different symmetric states and by changing the numbers of bands involved in the atomic transfer.

Brazhnyi, V. A. [Centro de Fisica Teorica e Computacional, Universidade de Lisboa, Complexo Interdisciplinar, Avenida Professor Gama Pinto 2, Lisbon 1649-003 (Portugal); Konotop, V. V. [Centro de Fisica Teorica e Computacional, Universidade de Lisboa, Complexo Interdisciplinar, Avenida Professor Gama Pinto 2, Lisbon 1649-003 (Portugal); Departamento de Fisica, Faculdade de Ciencias, Universidade de Lisboa, Campo Grande, Ed. C8, Piso 6, Lisbon 1749-016 (Portugal); Kuzmiak, V. [Institute of Photonics and Electronics, v.v.i., Czech Academy of Sciences, Chaberska 57, 182 51 Prague 8 (Czech Republic); Shchesnovich, V. S. [Instituto de Fisica, Universidade Federal de Alagoas, Maceio AL 57072-970 (Brazil)

2007-08-15

138

Pressure Fluctuations in Two-dimensional Turbulence  

NASA Astrophysics Data System (ADS)

We investigate pressure fluctuations in two-dimensional (2D) turbulence driven electromagnetically in a freely suspended soap film. The reduced probability distribution function (PDF), P(p/?p), is found to be universal for different Reynolds numbers and consists of asymmetrical exponential wings, where ?p?/?p^3˜-0.5 is significantly smaller than predictions by simple 2D models (Holzer and Siggia, Phys. Fluids A5, 2525 (1993)) but surprisingly close to 3D calculations using a random velocity field with a Kolmogorov energy spectrum E(k)k-5/3. The pressure spectrum Epp(k) scales approximately as Epp(k)k-7/3 in the energy inverse-cascade subrange and k-5 in the enstrophy cascade subrange. These observations suggest that pressure fluctuations is essentially a large-scale phenomenon and the presence of an enstrophy cascade has no effect on the tails of P(p/?p).

Jun, Yonggun; Wu, X. L.

2007-03-01

139

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

140

Order Parameters for Two-Dimensional Networks  

NASA Astrophysics Data System (ADS)

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

Kaatz, Forrest; Bultheel, Adhemar; Egami, Takeshi

2007-10-01

141

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

2003-12-11

142

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

2012-04-10

143

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

144

Diffraction of electromagnetic waves by a two-dimensional periodic waveguide-dielectric array  

NASA Astrophysics Data System (ADS)

An analysis is presented of electromagnetic-wave diffraction by a two-dimensional periodic waveguide array covered by several layers of an inhomogeneous dielectric. For the case of quasi-periodic excitation of the array, the solution is obtained by the method of projection field matching in planes of junctions of longitudinally homogeneous regions. An orthonormal system of eigenvector functions of the transversely inhomogeneous Floquet channel is used as the basis in the two-dimensional periodic dielectric structure. The effectiveness of the proposed algorithm is demonstrated by a calculation of the coefficient of reflection of an incident wave from the aperture of an array of circular waveguides, matched with free space via stepwise dielectric rods. It is shown that the use of stepwise dielectric rods for the matching of waveguide antenna arrays is more effective than the use of dielectric cylinders jutting from the waveguides.

Krekhtunov, V. M.; Tiulin, V. A.

1983-02-01

145

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

146

Statistics of layered zigzags: a two-dimensional generalization of TASEP  

NASA Astrophysics Data System (ADS)

A novel discrete growth model in 2+1 dimensions is presented in three equivalent formulations: (i) directed motion of zigzags on a cylinder, (ii) interacting interlaced TASEP layers and (iii) growing heap over 2D substrate with a restricted minimal local height gradient. We demonstrate that the coarse-grained behavior of this model is described by the two-dimensional Kardar-Parisi-Zhang equation. The coefficients of different terms in this hydrodynamic equation can be derived from the steady state flow-density curve, the so-called fundamental diagram. A conjecture concerning the analytical form of this flow-density curve is presented and is verified numerically.

Tamm, Mikhail; Nechaev, Sergei; Majumdar, Satya N.

2011-01-01

147

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

148

Mass transfer with flow through an array of rectangular cylinders  

Microsoft Academic Search

The mass transfer from an array of naphthalene-coated parallel rectangular cylinders, through which air passes in a slitlike flow, has been measured. The local Sherwood numbers indicate that the flow pattern is asymmetric in spite of using an array of two-dimensional, equally spaced identical cylinders. Smoke-wire flow visualization verifies this asymmetry, showing alternate short and long wakes around the cylinders,

H. H. Cho; M. Y. Jabbari; R. J. Goldstein

1994-01-01

149

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

SciTech Connect

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

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

2005-01-01

150

The solution to water wave scattering and radiation problems involving semi-immersed circular cylinders  

Microsoft Academic Search

In this technical report we describe the method of solution to a variety of two- dimensional problems involving semi-immersed cylinders in the free surface. These include: (i) determining the reflection and transmission coefficients for the scattering of incident waves by a single fixed cylinder; (ii) determining the added mass and radiation damping for a cylinder forced to move with unit

R. Porter

2008-01-01

151

Motion of a circular cylinder in a viscous liquid between parallel plates  

Microsoft Academic Search

The two-dimensional motion of a cylinder in a viscous fluid between two parallel walls of a vertical channel is studied. It is found that when the cylinder moves very closely along one of the channel walls, it always rotates in the direction opposite to that of contact rolling along the nearest wall. When the cylinder is away from the walls,

Howard H. Hu

1995-01-01

152

Art and science of magnet design: Selected notes of Klaus Halbach. Volume 2.  

National Technical Information Service (NTIS)

This volume contains a compilation of 57 notes written by Dr. Klaus Halbach selected from his collection of over 1650 such documents. It provides an historic snapshot of the evolution of magnet technology and related fields as the notes range from as earl...

1995-01-01

153

Melting of a two-dimensional crystal of electrons  

Microsoft Academic Search

Experiments show that a sheet of electrons in image-potential-induced states outside a helium surface forms at low temperatures a two-dimensional crystal (the classical, two-dimensional analog of a Wigner crystal). At higher temperatures the electron crystal melts to form a two-dimensional, classical, one-component plasma. The melting transition occurs at Gammam = 131 +\\/- 7 where Gamma is a measure of the

C. C. Grimes

1981-01-01

154

Lie algebra contractions on two-dimensional hyperboloid  

SciTech Connect

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

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

2010-03-15

155

Symmetry analysis of the localized modes associated with substitutional and interstitial defects in a two-dimensional triangular photonic crystal  

Microsoft Academic Search

By using a finite-difference time-domain numerical method based on the numerical simulation of the excitation of an isolated eigenstate at a specific frequency by using an oscillating dipole embedded in a two-dimensional photonic crystal we have calculated both the eigenfrequencies and eigenfunctions of the localized defect modes induced by defect cylinders placed at the center or in interstitial positions within

Vladimir Kuzmiak; Alexei A. Maradudin

2000-01-01

156

Beginning Introductory Physics with Two-Dimensional Motion  

ERIC Educational Resources Information Center

|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…

Huggins, Elisha

2009-01-01

157

Hitting lines with two-dimensional Brownian motion  

NASA Astrophysics Data System (ADS)

This paper consists of the computation of several hitting time and hitting place distributions for two-dimensional Brownian motion. The motivation for this study is two-fold: first, to get a diffusion model for the firing behavior of a simple network of neurons, and second, to get an interesting two-dimensional version of the inverse Gaussian distribution.

Iyengar, Satish

1990-05-01

158

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

159

A Two-Dimensional Haar-Like Transform.  

National Technical Information Service (NTIS)

The report concerns a transform based on a set of two-dimensional Haarlike functions. Series expansions of two-dimensional functions in terms of this set have convergence properties that are analogous to those of Haar series. Following a brief review of H...

J. E. Shore

1973-01-01

160

Soybean Drying by Two-Dimensional Spouted Bed  

Microsoft Academic Search

Urease activity, cracking, and breakage are important factors in considering the quality of raw soybean for feed meal industries. A two-dimensional spouted bed dryer was investigated to determine its capability for thermally inactivating the urease enzyme and maintaining its other qualities. The experimental results have shown that the drying kinetics of soybean in a two-dimensional spouted bed dryer are of

Songchai Wiriyaumpaiwong; Somchart Soponronnarit; Somkiat Prachayawarakorn

2003-01-01

161

Constrained optimization with use of two-dimensional maximum neurons  

Microsoft Academic Search

A special neuron, which we call two-dimensional maximum neuron is proposed. This type of neuron can eliminate the row and column constraints that occur in many problems, such as the stable marriage problem. A parallel processing algorithm to find the stable marriage matching using the proposed two-dimensional maximum neurons is described and the result is now reported

P. P. C. Yip; Y. Takefuji

1994-01-01

162

MIRAS, a two-dimensional aperture synthesis radiometer  

Microsoft Academic Search

Based on the experimented potential use of aperture synthesis (Le Vine, 1990), the European Space Agency has initiated the study of a spaceborne Microwave Interferometric Radiometer with Two-Dimensional Aperture Synthesis (MIRAS) as well as the development of an airborne version of this instrument. The objective of this radiometer is to study and demonstrate the feasibility of two-dimensional interferometry for measuring

M. Martin-Neira; Y. Menard; J. M. Goutoule; U. Kraft

1994-01-01

163

Local Heating Effect of Flow Past a Circular Cylinder  

NASA Astrophysics Data System (ADS)

Heating effects of air flows past a two-dimensional circular cylinder at low Reynolds numbers and low Mach numbers are investigated by numerical simulation. The cylinder wall is heated partially rather than heated on the whole surface as with previous researches. The heating effects are completely different for various heating locations on the cylinder surface. Heating either windward or leeward side stabilizes the flow and reduces or completely suppresses vortex shedding from the cylinder at supercritical Reynolds numbers, which is consistent with previous results of heating on the whole surface of the cylinder. However, as the lateral sides of the cylinder (perpendicular to the stream-wise direction) are heated, an adverse effect is found for the first time in that the flow is destabilized and vortex shedding can be excited at subcritical Reynolds numbers. As the lateral sides of the cylinder are cooled, the flow is stabilized.

Xin, Xiao-Feng; Chen, Cheng; Wang, Bo-Fu; Ma, Dong-Jun; Sun, De-Jun

2010-04-01

164

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

165

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

PubMed

The dynamic properties of dense two-dimensional (2D) polymer melts are studied using discontinuous molecular dynamics simulations. Both strictly 2D and quasi-2D systems are investigated. The strictly 2D model system consists of a fluid of freely jointed tangent hard disc chains. The translational diffusion coefficient, D, is strongly system size dependent with D ? ln?L where L is the linear dimension of the square simulation cell. The rotational correlation time, ?rot, is, however, independent of system size. The dynamics is consistent with Rouse behavior with D?ln?L ? N(-1) and ?rot ? N(2) for all area fractions. Analysis of the intermediate scattering function, Fs(k, t), shows that the dynamics becomes slow for N = 256 and the area fraction of 0.454 and that there might be a glass transition for long polymers at sufficiently high area fractions. The polymer mobility is not correlated with the conformation of the molecules. In the quasi-2D system hard sphere chains are confined between corrugated surfaces so that chains cannot go over each other or into the surfaces. The conformational properties are identical to the 2D case, but D and ?rot are independent of system size. The scaling of D and ?rot with N is similar to that of strictly 2D systems. The simulations suggest that 2D polymers are never entangled and follow Rouse dynamics at all densities. PMID:23802982

Sung, Bong June; Yethiraj, Arun

2013-06-21

166

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

NASA Astrophysics Data System (ADS)

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

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

1994-07-01

167

Intensity distribution of strong magnetic fields created by opposing linear Halbach assemblies of permanent magnets  

NASA Astrophysics Data System (ADS)

The work is devoted to the geometrical configuration of permanent magnets on the basis of opposing geometrically linear assemblies (e.g. Halbach arrays) for the generation of strong magnetic fields, which have been theoretically modeled and experimentally verified. The implementation of these opposing assemblies using NdFeB magnets of a total weight of 3.75 kg provided a value of magnetic induction in the middle of an air gap of a width of 20 mm that was higher by 56% in comparison with the simplest possible design. When the air gap width was 3 mm, the induction reached a value of 2.16 T, which represents an increase of more than 100%. Simultaneously, however, unlike in the simplest possible parallel configuration, opposing Halbach assemblies have shown, in the middle of an air gap, a significant decrease of the magnetic induction values when passing from the middle of the assemblies in the direction parallel to the x-axis.

Žežulka, Václav; Pištora, Jaromír; Les?ák, Michal; Straka, Pavel; Ciprian, Dalibor; Foukal, Jaroslav

2013-11-01

168

Development of Structure and Strategy in Two-Dimensional Pictures.  

ERIC Educational Resources Information Center

|The development of two structural principles, hierarchical complexity and interruption, was examined in a new domain: two-dimensional pictures. Subjects were 60 4-to 5 1/2-year-old children. (Author/MP)|

Beagles-Roos, Jessica; Greenfield, Patricia Marks

1979-01-01

169

Decoherence in a Landau Quantized Two Dimensional Electron Gas  

NASA Astrophysics Data System (ADS)

We have studied the dynamics of a high mobility two-dimensional electron gas as a function of temperature. The presence of satellite reflections in the sample and magnet can be modeled in the time-domain.

Curtis, Jeremy A.; Tokumoto, Takahisa; Cherian, Judy; Sangala, Bagvanth; McGill, Stephen A.; Hilton, David J.

2013-03-01

170

Two-Dimensional Thomson Scattering System for ATF.  

National Technical Information Service (NTIS)

A two-dimensional Thomson scattering system is being designed for the ATF torsatron experiment. This system will provide electron temperature and density measurements at fifteen points along a vertical chord with each shot from a ruby laser. By relocating...

R. R. Kindsfather D. A. Rasmussen M. Murakami C. E. Thomas S. L. Painter

1986-01-01

171

Model of a Negatively Curved Two-Dimensional Space.  

ERIC Educational Resources Information Center

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

Eckroth, Charles A.

1995-01-01

172

Two-dimensional electronic femtosecond stimulated Raman spectroscopy  

NASA Astrophysics Data System (ADS)

We report two-dimensional electronic spectroscopy with a femtosecond stimulated Raman scattering probe. The method reveals correlations between excitation energy and excited state vibrational structure following photoexcitation. We demonstrate the method in rhodamine 6G.

Wilcox, D. E.; Ogilvie, J. P.

2013-03-01

173

Dynamical Properties of Two-Dimensional Josephson Junction Arrays.  

National Technical Information Service (NTIS)

We have investigated the dynamical properties of two dimensional (2D) Josephson junction arrays at temperatures below the Kosterlitz-Thouless phase transition. We have completed a comprehensive study, based on experiments and simulations, of the effects o...

S. P. Benz

1990-01-01

174

Two-dimensional hydrologic modeling to evaluate aquatic habitat ...  

Treesearch

Title: Two-dimensional hydrologic modeling to evaluate aquatic habitat conditions ... physical and biological parameters such as temperature, dissolved oxygen, ... Government employees on official time, and is therefore in the public domain.

175

Two Dimensional Stochastic Model of a Heterogeneous Geologic System.  

National Technical Information Service (NTIS)

Models based on probabilistic laws are increasingly being employed to simulate heterogeneous geologic systems. One such model, the 'Poisson lines' model, is discussed. This is a two dimensional stochastic model with Markovian properties which is generated...

M. J. Lippmann

1973-01-01

176

Model of a Negatively Curved Two-Dimensional Space.  

ERIC Educational Resources Information Center

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

Eckroth, Charles A.

1995-01-01

177

Difficulties that Students Face with Two-Dimensional Motion  

ERIC Educational Resources Information Center

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

Mihas, P.; Gemousakakis, T.

2007-01-01

178

A two-dimensional polymer prepared by organic synthesis  

NASA Astrophysics Data System (ADS)

Synthetic polymers are widely used materials, as attested by a production of more than 200 millions of tons per year, and are typically composed of linear repeat units. They may also be branched or irregularly crosslinked. Here, we introduce a two-dimensional polymer with internal periodicity composed of areal repeat units. This is an extension of Staudinger's polymerization concept (to form macromolecules by covalently linking repeat units together), but in two dimensions. A well-known example of such a two-dimensional polymer is graphene, but its thermolytic synthesis precludes molecular design on demand. Here, we have rationally synthesized an ordered, non-equilibrium two-dimensional polymer far beyond molecular dimensions. The procedure includes the crystallization of a specifically designed photoreactive monomer into a layered structure, a photo-polymerization step within the crystal and a solvent-induced delamination step that isolates individual two-dimensional polymers as free-standing, monolayered molecular sheets.

Kissel, Patrick; Erni, Rolf; Schweizer, W. Bernd; Rossell, Marta D.; King, Benjamin T.; Bauer, Thomas; Götzinger, Stephan; Schlüter, A. Dieter; Sakamoto, Junji

2012-04-01

179

Time harmonic scar statistics in two dimensional cavities.  

SciTech Connect

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

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

2007-01-01

180

Two-Dimensional Thin-Layer Chromatographic Separation of Steroids.  

National Technical Information Service (NTIS)

A two-dimensional thin-layer chromatographic method was described for the separation of steroids in purified organ extracts. Eighteen steroids were investigated using Merck's silica gel G plates and chloroform/acetone mixtures as chromatographic solvents....

W. Schink H. Struck

1973-01-01

181

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...

182

Quadrantal symmetry associated with two-dimensional digital transfer functions  

Microsoft Academic Search

The class of two-dimensional (2-D) digital transfer functions which possess quadrantal symmetry in their frequency responses is derived. Application of this class in the design of 2-D recursive digital filters is indicated.

P. Karivaratharajan; M. Swamy

1978-01-01

183

Doppler Radar Return from Two-Dimensional Random Rough Surfaces  

Microsoft Academic Search

Doppler return from the general case of a two-dimensional random rough surface is investigated. This is an extension of work recently reported for a special case of rough surface. Helmholtz integral approach is used, employing Kirchhoff's approximations in order to evaluate the integral for the plane-wave case. Two-dimensional transmitter\\/receiver gain function and reflection coefficients are used. The shape of the

Malkiat Sohel; Harbhajan Hayre

1972-01-01

184

Kinetic properties of two-dimensional metal systems  

Microsoft Academic Search

The two-dimensional degenerate Fermi gas of electrons interacting with phonons is considered. The basic mechanisms of momentum relaxation in such a system, associated with electron-phonon, phonon-phonon and electron-electron collisions, are shown to be qualitatively different from similar mechanisms in an ordinary three-dimensional metal. The physical explanation for this is that the two-dimensional system of interacting electrons and phonons breaks down

R. N. Gurzhi; A. I. Kopeliovich; S. B. Rutkevich

1987-01-01

185

Two-dimensional wreath product group-based image processing  

Microsoft Academic Search

This paper is intended to complement and extend this earlier work in the directionof a two-dimensional (2-D) finite group-based theory, again with an intent of applyingthis work to image processing. Historically, the notion of a 2-D transform almost alwaysentails a representation of the signal f as a two-dimensional array so that the transformis given by a matrix multiplication of the

Richard Foote; Gagan Mirchandani; Daniel N. Rockmore

2004-01-01

186

Global spherical harmonic computation by two-dimensional Fourier methods  

Microsoft Academic Search

A method is presented for performing global spherical harmonic computation by two-dimensional Fourier transformations. The method goes back to old literature (Schuster 1902) and tackles the problem of non-orthogonality of Legendre-functions, when discretized on an equi-angular grid. Both analysis and synthesis relations are presented, which link the spherical harmonic spectrum to a two-dimensional Fourier spectrum. As an alternative, certain functions

Nico Sneeuw; Richard Bun

1996-01-01

187

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

188

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

189

Quasinormal modes of a two-dimensional black hole  

NASA Astrophysics Data System (ADS)

For a two-dimensional black hole we determine the quasinormal frequencies of the Klein-Gordon and Dirac fields. In contrast to the well known examples whose spectrum of quasinormal frequencies is discrete, for this black hole we find a continuous spectrum of quasinormal frequencies, but there are unstable quasinormal modes. In the framework of the Hod and Maggiore proposals we also discuss the consequences of these results on the form of the entropy spectrum for the two-dimensional black hole.

Estrada-Jiménez, S.; Gómez-Díaz, J. R.; López-Ortega, A.

2013-11-01

190

New critical point for two dimensional XY-type models  

Microsoft Academic Search

A new critical point is established through Monte Carlo simulations for a class of two dimensional XY models with a modified nearest-neighbor spin interaction. The critical exponents found are nu~=1.4, beta~=0.6, and an alpha<0, consistent with hyperscaling. The phase transition is interpreted as a vortex-unbinding transition. Comparisons are made with the phase diagram of the two dimensional Coulomb gas and

Anna Jonsson; Petter Minnhagen; Mats Nylén

1993-01-01

191

Quasinormal modes of a two-dimensional black hole  

NASA Astrophysics Data System (ADS)

For a two-dimensional black hole we determine the quasinormal frequencies of the Klein-Gordon and Dirac fields. In contrast to the well known examples whose spectrum of quasinormal frequencies is discrete, for this black hole we find a continuous spectrum of quasinormal frequencies, but there are unstable quasinormal modes. In the framework of the Hod and Maggiore proposals we also discuss the consequences of these results on the form of the entropy spectrum for the two-dimensional black hole.

Estrada-Jiménez, S.; Gómez-Díaz, J. R.; López-Ortega, A.

2013-08-01

192

Two-dimensional flag-transitive planes revisited  

Microsoft Academic Search

This paper shows that the odd order two-dimensional flag-transitive planes constructed by Kantor-Suetake constitute the same family of planes as those constructed by Baker-Ebert. Moreover, for orders satisfying a modest number theoretical assumption this family consists of all possible such planes of that order. In particular, it is shown that the number of isomorphism classes of (non-Desarguesian) two-dimensional flag-transitive affine

R. D. Baker; G. L. Ebert

1996-01-01

193

Two-Dimensional Effects in Laser Ablation of Carbon  

Microsoft Academic Search

This article studies the importance of two-dimensional effects in laser ablation of carbon. It describes the process by using the kinetic theory model of laser ablation based on the moment solution of the Boltzmann equation for arbitrary strong evaporation, and compares the predictions of the full two-dimensional model and of the two other models that use quasi-one-dimensional approximation in the

Michael Shusser

2009-01-01

194

Two-Dimensional Imaging of Gauge Fields in Optical Lattices  

SciTech Connect

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

Cho, Jaeyoon; Kim, M. S. [QOLS, Blackett Laboratory, Imperial College London, London SW7 2BW (United Kingdom)

2011-12-23

195

The art and science of magnet design: Selected notes of Klaus Halbach, volume 2  

NASA Astrophysics Data System (ADS)

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

1995-02-01

196

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

197

Aeroelastic instability of rectangular cylinders in a heaving mode  

Microsoft Academic Search

This paper deals with wind tunnel experiments on the aeroelastic instability in a heaving mode of two-dimensional rectangular cylinders in a uniform two-dimensional flow. Both the free oscillation method and the forced oscillation method are employed for the experiments. Emphasis is placed on finding the effect of the ratio c\\/d, which is the ratio of the lengths of the sides

K. Washizu; A. Ohya; Y. Otsuki; K. Fujii

1978-01-01

198

A Comprehensive Two-Dimensional Retention Time Alignment Algorithm To Enhance Chemometric Analysis of Comprehensive Two-Dimensional Separation Data  

Microsoft Academic Search

A comprehensive two-dimensional (2D) retention time alignment algorithm was developed using a novel indexing scheme. The algorithm is termed comprehensive because it functions to correct the entire chromatogram in both dimensions and it preserves the separation information in both dimensions. Although the algorithm is demonstrated by correcting comprehensive two-dimensional gas chromatography (GC x GC) data, the algorithm is designed to

Karisa M. Pierce; Lianna F. Wood; Bob W. Wright; Robert E. Synovec

2005-01-01

199

Hydrodynamic loads during water entry of two-dimensional and axisymmetric bodies  

NASA Astrophysics Data System (ADS)

In this paper the free-surface flow generated by the vertical water entry of two-dimensional symmetric and axisymmetric bodies of arbitrary shape is numerically investigated. The study is carried out in the framework of potential flow of an incompressible fluid with gravity and surface tension effects also neglected. The unsteady flow is computed through a boundary-element formulation and nonlinearities in the free-surface boundary conditions are fully retained. Attention is mainly focused on evaluating the pressure distribution and the total hydrodynamic load acting on the impacting body. For validation, the approach is applied to the water impact of a cone with constant entry velocity, and checks of the self-similarity of the solution are made. Next, the water impact of a circular cylinder and of a sphere are analyzed. Comparisons with available theoretical solutions and experimental data are made.

Battistin, D.; Iafrati, A.

2003-04-01

200

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

201

Separation of Creeping Flow past Two Circular Cylinders  

NASA Astrophysics Data System (ADS)

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

Miyazaki, Takeshi; Hasimoto, Hidenori

1980-10-01

202

Interactions in the far wake behind a pair of cylinders  

Microsoft Academic Search

We present an experimental study of far wakes behind a pair of cylinders (diameter D) separated by a cross-flow axis-to-axis distance S in a quasi-two-dimensional gravity-driven soap-film flow. A secondary vortex street forms in the far wake of each cylinder. As we decrease S, we observe coupling between the structures in the far wake. Visualization of the far wake behind

Tanveer Shakeel; Daniel Georgiev; Jesse Vigil; Peter Vorobieff

2002-01-01

203

Complexity and efficient approximability of two dimensional periodically specified problems  

SciTech Connect

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

Marathe, M.V. [Los Alamos National Lab., NM (United States); Hunt, H.B. III; Stearns, R.E. [State Univ. of New York, Albany, NY (United States). Dept. of Computer Science

1996-09-01

204

Generation of two-dimensional plasmonic bottle beams.  

PubMed

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. PMID:23609739

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

2013-04-22

205

A numerical study of unsteady two-dimensional subsonic compressible base flow  

NASA Astrophysics Data System (ADS)

In subsonic flow, the wake behind a two dimensional body with a blunt trailing edge is dominated by a regular array of alternately shed vortices. This separated flow produces a low pressure on the base of the body, resulting in a drag component known as the base drag, which can constitute a major portion of the total drag of the body in many cases. One of the devices that was found to reduce the base drag in wind-tunnel experiments is a trailing-edge cavity. However, the flow mechanisms responsible for this drag reduction were not determined from the limited experimental data available. Therefore, the unsteady flow past a slender two-dimensional body with and without a trailing-edge cavity were studied using numerical solutions of the Navier-Stokes equations. The solution procedure utilized an explicit finite-difference scheme with second or fourth order accuracy in a space and second order accuracy in time. A major element in the solution procedure was the selection of an outflow boundary condition which minimized reflection from the boundary back into the solution domain. This solution was verified in computations of subsonic flow past square and circular cylinders, for which excellent agreement was obtained between computed shedding frequencies and experimental data. Solutions for the slender body were obtained. The computed shedding frequency was found to increase with increasing Reynolds numbers.

Rudy, David Henry

206

Occurrence conditions for two-dimensional Borromean systems  

NASA Astrophysics Data System (ADS)

We search for Borromean three-body systems of identical bosons in two dimensional geometry, i.e. we search for bound three-boson system without bound two-body subsystems. Unlike three spatial dimensions, in two-dimensional geometry the two- and three-body thresholds often coincide ruling out Borromean systems. We show that Borromean states can only appear for potentials with substantial attractive and repulsive parts. Borromean states are most easily found when a barrier is present outside an attractive pocket. Extensive numerical search did not reveal Borromean states for potentials without an outside barrier. We outline possible experimental setups to observe Borromean systems in two spatial dimensions.

Volosniev, Artem G.; Fedorov, Dmitri V.; Jensen, Aksel S.; Zinner, Nikolaj T.

2013-05-01

207

Two-dimensional lattice Boltzmann model for magnetohydrodynamics.  

PubMed

We present a lattice Boltzmann model for the simulation of two-dimensional magnetohydro dynamic (MHD) flows. The model is an extension of a hydrodynamic lattice Boltzman model with 9 velocities on a square lattice resulting in a model with 17 velocities. Earlier lattice Boltzmann models for two-dimensional MHD used a bidirectional streaming rule. However, the use of such a bidirectional streaming rule is not necessary. In our model, the standard streaming rule is used, allowing smaller viscosities. To control the viscosity and the resistivity independently, a matrix collision operator is used. The model is then applied to the Hartmann flow, giving reasonable results. PMID:12443375

Schaffenberger, Werner; Hanslmeier, Arnold

2002-10-09

208

Quasi-two-dimensional acoustic metamaterial with negative bulk modulus  

NASA Astrophysics Data System (ADS)

We present the experimental realization and characterization of an acoustic metamaterial with negative bulk modulus. The metamaterial consists of a two-dimensional array of cylindrical cavities, and the bulk modulus is controlled by their radius size and length. Experiments are performed in a two-dimensional waveguide where a slab of seven layers is used to extract the parameters of the metamaterial. A complete characterization of the constructed structure is reported, including the dispersion relation of the acoustic bands and the skin depth effect, which both have been measured, and the data are well supported by semianalytical models and by finite-element simulations.

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

2012-05-01

209

Bulk-Edge Correspondence for Two-Dimensional Topological Insulators  

NASA Astrophysics Data System (ADS)

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

Graf, Gian Michele; Porta, Marcello

2013-10-01

210

On Periodicity of Generalized Two-Dimensional Words  

Microsoft Academic Search

A generalized two-dimensional word is a function on ?2 with finite number of values. The main problem we are interested in is periodicity of two-dimensional words satisfying some\\u000a local conditions. Let \\u000a $\\\\sum\\\\limits_{\\\\scriptsize {c} (y_1, y_2): \\\\\\\\ 0\\\\sum\\\\limits_{\\\\scriptsize \\\\begin{array}{c} (y_1, y_2): \\\\\\\\ 0\\u000a \\u000a \\u000a \\u000a \\u000a \\u000a for every integers x\\u000a 1, x\\u000a 2. We prove that every bounded generalized centered function of radius r?>?1

Svetlana Puzynina

2008-01-01

211

Influence of Forcing Structure on Two-Dimensional Weak Turbulence  

NASA Astrophysics Data System (ADS)

The dependence of the dynamics of two-dimensional turbulence on its forcing topology is an interesting and practical question for experiments. We generate quasi-two-dimensional flows in thin layers of salt water with a forcing geometry that is either a lattice of alternating vortices or an array of alternating shear bands. We observe that the vortex flow has more fluctuating energy, but that the shear flow has larger spatial gradients. We attribute these differences to the fact that shear forcing imposes fewer constraints on the flow and allows the production of smaller length scales.

Liao, Yang; Kelley, Douglas; Ouellette, Nicholas

2011-11-01

212

Density fluctuation spectrum of two-dimensional correlated fermion systems  

NASA Astrophysics Data System (ADS)

Density fluctuation spectrum of two-dimensional fermions that interact with short-range repulsive interaction is calculated with the self-consistent perturbation theory. The spectrum extends beyond the particle-hole continuum band in the noninteracting case because of the multiparticle excitations. At a large wave vector, a peak develops in the spectrum near the lower threshold of the particle-hole continuum. These results are compared with the recent inelastic neutron scattering experiment on two-dimensional 3He adsorbed on graphite.

Kotani, Akihiro; Hirashima, Dai

2012-12-01

213

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

214

Two-dimensional spectroscopy for a two-dimensional rotator coupled to a Gaussian-Markovian noise bath  

NASA Astrophysics Data System (ADS)

The dynamics of a system in the condensed phase are more clearly characterized by multitime correlation functions of physical observables than by two-time ones. We investigate a two-dimensional motion of a rigid rotator coupled to a Gaussian-Markovian harmonic oscillator bath to probe this issue. The analytical expression of a four-time correlation function of a dipole that is the observable of two-dimensional microwave or far-infrared spectroscopy is obtained from a generating functional approach. The spectra in the absence of damping are discrete and reveal transitions between eigenstates of the angular momentum quantized due to the cyclic boundary condition. For a weakly damped case, the two-dimensional spectrum predicts three echolike peaks corresponding to transition processes between the rotational energy levels, which cannot be observed in one-dimensional (linear-absorption) spectroscopy related to the two-time correlation function of the dipole [J. Phys. Soc. Jpn. 71, 2414 (2002)]. The two-dimensional spectra are more sensitive to the noise effects than the one-dimensional spectra. It is because the effects of the initial thermal distribution determine the profile of the continuous line shape in one-dimensional spectroscopy, while such thermal effects are canceled through the higher-order optical transition process in two-dimensional spectroscopy. If the rotator system is strongly coupled to the colored noise bath, the system exhibits one overdamped and other oscillatory motions. We observe peaks arising from interaction between these two modes in the two-dimensional spectra, which are difficult to distinguish in one-dimensional spectra.

Suzuki, Yoko; Tanimura, Yoshitaka

2003-07-01

215

Rényi entropy of a line in two-dimensional Ising models  

NASA Astrophysics Data System (ADS)

We consider the two-dimensional Ising model on an infinitely long cylinder and study the probabilities pi to observe a given spin configuration i along a circular section of the cylinder. These probabilities also occur as eigenvalues of reduced density matrices in some Rokhsar-Kivelson wave functions. We analyze the subleading constant to the Rényi entropy Rn=1/(1-n)ln(?ipin) and discuss its scaling properties at the critical point. Studying three different microscopic realizations, we provide numerical evidence that it is universal and behaves in a steplike fashion as a function of n with a discontinuity at the Shannon point n=1 . As a consequence, a field theoretical argument based on the replica trick would fail to give the correct value at this point. We nevertheless compute it numerically with high precision. Two other values of the Rényi parameter are of special interest: n=1/2 and n=? are related in a simple way to the Affleck-Ludwig boundary entropies associated to free and fixed boundary conditions, respectively.

Stéphan, J.-M.; Misguich, G.; Pasquier, V.

2010-09-01

216

Crystalline yolk spheroids in Drosophila melanogaster oocyte: freeze fracture and two-dimensional reconstruction analysis.  

PubMed

The major sites of energy storage during oogenesis in the Drosophila melanogaster oocyte are the alpha- and beta-yolk spheres. By applying biochemical and transmission electron microscopy (TEM) immunogold techniques we found that the beta-yolk spheres contain mainly polysaccharides, while the three main yolk proteins (YPs) are stored in the alpha-yolk spheres of the developing oocyte. Moreover, by using high-resolution TEM of freeze fractured or cryosectioned follicles, we identified the existence of crystalline structures within the alpha-yolk spheres of the mature oocyte. Our subsequent two-dimensional reconstruction analysis revealed that the unit cell of the crystal is about 113 Angstrom x 113 Angstrom. Assuming that the repeating unit is a cylinder of about 110 Angstrom in length and 25 Angstrom in diameter this cylinder would then have a volume of about 50,000 cubic Angstrom, which corresponds to about 40 kDa of protein. This size fits quite well with the known molecular weight of about 40-45 kDa for each of the three D. melanogaster YPs. Overall, our study identifies for the first time the supramolecular arrangement of the alpha-yolk spheres constituent molecules and provides direct evidence for the "natural" crystallization, and therefore the efficient packaging, of the YPs during oogenesis. PMID:17292389

Papassideri, Issidora S; Trougakos, Ioannis P; Leonard, Kevin R; Margaritis, Lukas H

2007-01-13

217

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

218

Two-Dimensional Diverging Shocks in a Nonuniform Medium  

SciTech Connect

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

Roy A. Axford

1998-08-01

219

Extended de Sitter theory of two-dimensional gravitational forces  

SciTech Connect

We present a simple unifying gauge-theoretical formulation of gravitational theories in two-dimensional spacetime. This formulation includes the effects of a novel matter-gravity coupling which leads to an extended de Sitter symmetry algebra on which the gauge theory is based. Contractions of this theory encompass previously studied cases.

Cangemi, D. (Center for Theoretical Physics, Laboratory for Nuclear Science, Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 (United States)); Dunne, G. (Department of Physics, University of Connecticut, Storrs, Connecticut 06269 (United States))

1993-12-15

220

There is no two dimensional analogue of Lamé's equation  

Microsoft Academic Search

this paper is to prove that there is nonon-trivial two-dimensional analogue of this phenomenon. To make the laststatement precise, we begin with a review of the basic properties of the Lameequation.Fix ! 1 ; ! 2 > 0 . Let}(z) =1

Joel Feldman; Horst Knörrer; Eugene Trubowitz

1992-01-01

221

Progress in two-dimensional plasma edge modelling  

Microsoft Academic Search

A review is given of the status of various approaches dealing with tokamak edge related issues by employing two-dimensional numerical fluid codes for the main components of the edge plasma. The predictive capabilities of these models are assessed, in particular with regard to their completeness and the reliability of the transport coefficients. As the plasma edge characteristics in the favourable

D. Reiter

1992-01-01

222

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

223

Optimal entropic uncertainty relation in two-dimensional Hilbert space  

NASA Astrophysics Data System (ADS)

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

Sánches-Ruiz, Jorge

1998-07-01

224

Optimal entropic uncertainty relation in two-dimensional Hilbert space  

Microsoft Academic Search

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

Jorge Sánches-Ruiz

1998-01-01

225

Two-dimensional heat transfer analysis of radiating plates  

Microsoft Academic Search

The strongly implicit procedure is used to solve nonlinear elliptical two-dimensional heat conduction in radiating plates. A uniform heat flux is applied at one end of the plate which dissipates heat by radiation from one end into a vacuum at 0 K and into an ambient at temperature T(i) from the other. The results are presented with reference to four

K. Badari Narayana; S. U. Kumari

1988-01-01

226

Steady two-dimensional groundwater flow through many elliptical inhomogeneities  

Microsoft Academic Search

A new analytic element solution has been derived for steady two-dimensional groundwater flow through an aquifer that contains an arbitrary number of elliptical inhomogeneities. The hydraulic conductivity of each inhomogeneity is homogeneous and differs from the conductivity of the homogeneous background. In addition to elliptical inhomogeneities, other elements (such as wells and line sinks) may be present. The method is

Raghavendra Suribhatla; Mark Bakker; Karl Bandilla; Igor Jankovic

2004-01-01

227

Two-dimensional flow through large numbers of circular inhomogeneities  

Microsoft Academic Search

An implicit analytic solution is presented for two-dimensional groundwater flow through a large number of non-intersecting circular inhomogeneities in the hydraulic conductivity. The locations, sizes and conductivity of the inhomogeneities may be arbitrarily selected. The influence of each inhomogeneity is expanded in a series that satisfies the Laplace equation exactly. The unknown coefficients in this expansion are related to the

R. Barnes; I. Jankovi?

1999-01-01

228

Two-dimensional electron gas near full polarization  

Microsoft Academic Search

We establish the consistency of the Fermi liquid description and find a relation between the Fermi liquid constants for a two-dimensional electron system near the point of full polarization due to a parallel magnetic field H. Our results enable us to predict connections between different thermodynamic properties of the system. In particular, we find that near the point of full

G. Zala; B. N. Narozhny; I. L. Aleiner; Vladimir I. Fal'Ko

2004-01-01

229

Two-Dimensional Chirality in Three-Dimensional Chemistry.  

ERIC Educational Resources Information Center

The concept of two-dimensional chirality is used to enhance students' understanding of three-dimensional stereochemistry. This chirality is used as a key to teaching/understanding such concepts as enaniotropism, diastereotopism, pseudoasymmetry, retention/inversion of configuration, and stereochemical results of addition to double bonds. (JN)

Wintner, Claude E.

1983-01-01

230

A two dimensional field theory for motion computation  

Microsoft Academic Search

The local extraction of motion information from brightness patterns by individual movement detectors of the correlation-type is considered in the first part of the paper. A two-dimensional field theory of movement detection is developed by treating the distance between two adjacent photoreceptors as a differential. In the first approximation of the theory we only consider linear terms of the time

W. E. Reichardt; R. W. Schlögl

1988-01-01

231

Two-dimensional high speed flow of a radiating gas  

Microsoft Academic Search

In high speed gas dynamics the analysis of two-dimensional flows of hot gases, where the effect of radiation as a mode of energy transfer cannot be neglected, is extremely difficult due to the integro-differential nature of the governing equations. To date, most of the existing literature on radiation gas dynamics is confined to the study of the two asymptotic cases

Prem K. Khosla

1968-01-01

232

Two-Dimensional Flat-Earth Trajectory Computer Program.  

National Technical Information Service (NTIS)

This technical report describes a two-dimensional, flat-earth trajectory computer program written in FORTRAN IV. The report is intended to serve as a complete user's manual and includes a description of the program structure and capabilities, a sample inp...

V. L. Olivier J. C. Vaughan

1968-01-01

233

On the Integrability of Two-Dimensional Flows  

Microsoft Academic Search

This paper deals with the notion of integrability of flows or vector fields on two-dimensional manifolds. We consider the following two key points about first integrals: (1) They must be defined on the whole domain of definition of the flow or vector field, or defined on the complement of some special orbits of the system; (2) How are they computed?

Javier Chavarriga; Hector Giacomini; Jaume Giné; Jaume Llibre

1999-01-01

234

A maximum likelihood approach to two-dimensional crystals  

Microsoft Academic Search

Maximum likelihood (ML) processing of transmission electron microscopy images of protein particles can produce reconstructions of superior resolution due to a reduced reference bias. We have investigated a ML processing approach to images centered on the unit cells of two-dimensional (2D) crystal images. The implemented software makes use of the predictive lattice node tracking in the MRC software, which is

Xiangyan Zeng; Henning Stahlberg; Nikolaus Grigorieff

2007-01-01

235

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

236

Strong exchange narrowing in new two-dimensional paramagnetic systems  

Microsoft Academic Search

Single crystals of (CH3NH3)2 MnCl4 and (C2H5NH3)2 MnCl4 have a strong angular and temperature dependent ESR line width narrowed by exchange interaction. They are very probable two-dimensional paramagnets down to about 50°K.

H. R. Boesch; U. Schmocker; F. Waldner; K. Emerson; J. E. Drumheller

1971-01-01

237

Nonlinear elastic behavior of two-dimensional molybdenum disulfide  

NASA Astrophysics Data System (ADS)

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

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

2013-01-01

238

Two-dimensional representation of a delayed dynamical system  

Microsoft Academic Search

A nonlinear system with delayed feedback, whenever the delay time is much longer than the intrinsic correlation time, displays two widely separated time scales. In such a case, a two-dimensional representation becomes appropriate, because it discloses features otherwise hidden in the one-dimensional sequence of data, and allows use of recognition algorithms developed for spatiotemporal chaos. As an illustration, chaotic time

F. T. Arecchi; G. Giacomelli; A. Lapucci; R. Meucci

1992-01-01

239

Hexagonal structures for two-dimensional photonic crystals  

Microsoft Academic Search

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

D. Cassagne; C. Jouanin; D. Bertho

1996-01-01

240

Torsional springs for two-dimensional dynamic unstructured fluid meshes  

Microsoft Academic Search

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

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

1998-01-01

241

Predictions of axisymmetric and two-dimensional impinging turbulent jets  

Microsoft Academic Search

The k ? ? turbulence model and a version of a second-moment closure, modified to include the effect of pressure reflections from a solid surface, have been used as the basis of predictions of the flow that results from the orthogonal impingement of circular and two-dimensional (2-D) jets on a flat surface. Comparison of model predictions has been made with

W. P. Jones

1996-01-01

242

A two-dimensional model for quantum gravity  

Microsoft Academic Search

Two-dimensional quantum gravity coupled to conformally invariant matter is a good model for the physics of higher-dimensional gravity, provided the central charge of the matter theory is greater than 25. In particular, the theory has a euclidean saddle point of large negative action, analogous to that considered by Baum, Hawking and Coleman in d = 4. Further, the theory is

Joseph Polchinski

1989-01-01

243

Inexpensive two-dimensional measuring device for cryogenic temperatures  

Microsoft Academic Search

A simple device for measuring thermal deformations in two-dimensional samples cooled to liquid nitrogen temperatures is described. The measurement consists of adding liquid nitrogen to a transparent quartz tray, and then scanning the sample from the bottom with a flatbed scanner. As a test of the device, the thermal contraction of aluminum from room temperature to 77 K is measured.

A. Grau Carles

2005-01-01

244

A two-dimensional damaged finite element for fracture applications  

Microsoft Academic Search

A novel finite element was developed for fatigue and fracture applications. The new element is two-dimensional with an embedded edge crack. The crack is not physically modeled within the element, but instead, its influence on the local flexibility of the structure is accounted for by the reduction of the element stiffness as a function of the crack length. The components

G. P. Potirniche; J. Hearndon; S. R. Daniewicz; D. Parker; P. Cuevas; P. T. Wang; M. F. Horstemeyer

2008-01-01

245

Two dimensional frustrated magnets in high magnetic field  

Microsoft Academic Search

Frustrated magnets in high magnetic field have a long history of offering beautiful surprises to the patient investigator. Here we present the results of extensive classical Monte Carlo simulations of a variety of models of two dimensional magnets in magnetic field, together with complementary spin wave analysis. Striking results include (i) a massively enhanced magnetocaloric effect in antiferromagnets bordering on

L. Seabra; N. Shannon; P. Sindzingre; T. Momoi; B. Schmidt; P. Thalmeier

2009-01-01

246

Superpower free electron lasers with two-dimensional distributed feedback  

Microsoft Academic Search

Using time domain analysis we have studied the processes of oscillation build-up and spatial synchronization in FELs with two-dimensional distributed feedback driven by large size sheet and tubular relativistic electron beams. It is proved that the proposed feedback mechanism ensures powerful spatially coherent radiation when the ratio between the transverse sized of the electron beam and the wavelength is up

N. S. Ginzburg; N. Yu. Peskov; A. S. Sergeev; A. V. Arzhannikov; S. L. Sinitsky

1995-01-01

247

Online Shopping Using a Two Dimensional Product Map  

Microsoft Academic Search

In this paper, we propose a user interface for online shopping that uses a two dimensional product map to present products. This map is created using multidimensional scaling (MDS). Dissimilarities between products are computed using an adapted version of Gower's coecient of similarity based on the attributes of the product. The user can zoom in and out by drawing rectangles.

Martijn Kagie; Michiel C. Van Wezel; Patrick J. F. Groenen

2007-01-01

248

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

249

An efficient architecture for two-dimensional discrete wavelet transform  

Microsoft Academic Search

This paper proposes an efficient architecture for the two-dimensional discrete wavelet transform (2-D DWT). The proposed architecture includes a transform module, a RAM module, and a multiplexer. In the transform module, we employ the polyphase decomposition technique and the coefficient folding technique to the decimation filters of stages 1 and 2, respectively. In comparison with other 2-D DWT architectures, the

Po-cheng Wu; Liang-gee Chen

2001-01-01

250

A new two-dimensional millimeter wave imaging radiometer  

Microsoft Academic Search

Synthetic aperture radiometer has the potential to meet the spatial resolution requirement of passive microwave remote sensing from space. This paper introduces a prototype of two-dimensional imaging radiometer at millimeter wave (MMW) band. A G Matrix calibration approach and an iterative gradient inversion method are presented to obtain the brightness temperature image. Total least squares (TLS) image processing algorithms for

Yuanyuan Liu; Lu Zhu; Shan Wang

2010-01-01

251

Two-dimensional spatial light modulators: a tutorial  

Microsoft Academic Search

Two-dimensional spatial light modulators (SLMs) modulate one of the properties of an optical wavefront (amplitude, phase, polarization) as a function of two spatial dimensions and time in response to information-bearing control signals that may be either optical or electrical. These devices form a critical part of optical information processing systems, serving as input transducers as well as performing several basic

J. A. Neff; RAVINDRA A. ATHALE; SING H. LEE

1990-01-01

252

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

253

Ozone perturbation experiments in a two-dimensional circulation model  

Microsoft Academic Search

Experiments to investigate perturbation of the ozone layer by CO2 and chlorofluorocarbons (CFC's) using a two dimensional model are described, and independent as well as simultaneous effects of CO2 and CFC's are examined. The control run experiment confirms that the summer stratosphere is very close to radiative equilibrium. In addition, it is found that CO2 causes an increase in column

J. D. Haigh; J. A. Pyle

1982-01-01

254

Two-dimensional temperature estimation using diagnostic ultrasound  

Microsoft Academic Search

A two-dimensional temperature estimation method was developed based on the detection of shifts in echo location of backscattered ultrasound from a region of tissue undergoing thermal therapy. The echo shifts are due to the combination of the local temperature dependence of speed of sound and thermal expansion in the heated region. A linear relationship between these shifts and the underlying

Claudio Simon; Philip VanBaren; Emad S. Ebbini

1998-01-01

255

TWO-DIMENSIONAL BALANCED SAMPLING PLANS EXCLUDING CONTIGUOUS UNITS  

Microsoft Academic Search

A balanced sampling plan excluding contiguous units (or BSEC for short) was first introduced by Hedayat, Rao and Stufken in 1988. These designs can be used for survey sampling when the units are arranged in one-dimensional ordering and the contiguous units in this ordering provide similar information. In this paper, we generalize the concept of a BSEC to the two-dimensional

Darryn Bryant; Yanxun Chang; C. A. Rodger; R. Wei

2002-01-01

256

A two-dimensional Prony's method for spectral estimation  

Microsoft Academic Search

The problem of estimating the parameters of a model for bidimensional data made up by a linear combination of damped two-dimensional sinusoids is considered. Frequencies, amplitudes, phases, and damping factors are estimated by applying a generalization of the monodimensional Prony's method to spatial data. This procedure finds the desired quantities after an autoregressive model fitting to the data, a polynomial

M. M. Barbieri; P. Barone

1992-01-01

257

Two-dimensional Prony modeling and parameter estimation  

Microsoft Academic Search

A new method for estimating the two-dimensional (2D) exponential modes and amplitude coefficients in a Prony model is presented. This method involves two parts, each utilizing a 1D singular value decomposition-based technique, and is capable of locating frequencies anywhere in the 2D frequency plane. Simulations are shown which demonstrate the performance of the algorithm

Joseph J. Sacchini; William M. Steedly; Randolph L. Moses

1993-01-01

258

Quantized spin currents in two-dimensional chiral magnets  

NASA Astrophysics Data System (ADS)

Two-dimensional quantum magnets in which reflection and time-reversal symmetries are broken may be classified by integers which reflect the topology of the ground state. An analogy with the quantum Hall effect exists: these integers are Chern numbers which describe a quantized spin current response to an inhomogeneous external magnetic field. Implications for spontaneous chiral symmetry breaking are discussed.

Haldane, F. D. M.; Arovas, Daniel P.

1995-08-01

259

Two-dimensional model for circulating fluidized-bed reactors  

Microsoft Academic Search

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

H. Schoenfelder; M. Kruse; J. Werther

1996-01-01

260

Acoustic quasimodes in two-dimensional dispersed random media  

NASA Astrophysics Data System (ADS)

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

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

2006-06-01

261

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

262

Geometry, topology, field theory and two-dimensional quantum gravity  

SciTech Connect

This dissertation presents geometrically a simplified theory of two-dimensional quantum gravity called topological gravity. The motivation for such a simplification is to shed light on the complicated problem of real quantum gravity. The author introduces new supermanifolds called semirigid super Riemann surfaces on which two-dimensional quantum field theories of topological (super) gravity are defined. It is shown that semirigid surfaces are integrable reductions from ordinary complex supermanifolds. Unlike other supergeometries, the semirigid moduli space of topological gravity is as well understood as that of ordinary Riemann surface. The author applies in semirigid gravity the operator formalism to construct correlation functions of observables in two-dimensional spacetime of arbitrarily complicated topology. A one-to-one correspondence is established between the equivalent BRST cohomology of the states in the Hilbert space and the deRham cohomology on the ordinary moduli space. Moreover, the couplings between the observables are topological, coming only through contact interactions. Two recursion relations of observables are derived in the semirigid framework. One involves in particular an observable associated to the two-dimensional cosmological constant and the other the string coupling constant. These are the same recursion relations that partially characterized the [open quotes]one matrix model,[close quotes] a discretized approach to quantum gravity, at its topological critical point. This lends strong support to the hypothesis that semirigid gravity and the one matrix model at the topological critical point are equivalent.

Wong, E.C.M.

1992-01-01

263

Linear wave conversion in a two-dimensional nonuniform plasma  

NASA Astrophysics Data System (ADS)

The linear interaction of electrostatic waves in a warm anisotropic plasma is analyzed in a two-dimensional geometry. The wave modes are found. A system of coupled partial differential equations which determine the wave conversion is constructed. The solution of this equation provides an analytic expression for the field of the excited wave and the wave conversion coefficient.

Kirchner, T.; Shklyar, D. R.

1985-09-01

264

Alternating Direction Implicit Techniques for Two-Dimensional Magnetohydrodynamic Calculations  

Microsoft Academic Search

Alternating direction implicit numerical techniques for solving time-; dependent, two-dimensional, two-fluid MHD equations are presented. The ; techniques are illustrated with applications to the dynamics of a theta pinch and ; the expansion of a laserproduced plasma, and important features of both cases are ; demonstrated. The enhanced numerical stability of the method is discussed. ; (auth);

Irvin Lindemuth; John Killeen

1973-01-01

265

Polarizability of a Two-Dimensional Electron Gas  

Microsoft Academic Search

The response of a two-dimensional electron gas to a longitudinal electric field of arbitrary wave vector and frequency is calculated in the self-consistent-field approximation. The results are used to find the asymptotic screened Coulomb potential and the plasmon dispersion for a plane of electrons imbedded in a three-dimensional dielectric.

Frank Stern

1967-01-01

266

TWO-DIMENSIONAL SOLUBILITY PARAMETER MAPPING OF HEAVY OILS  

Microsoft Academic Search

The solubility and insolubility of heavy oils and their fractions in dilute mixtures with various solvents were used to characterize heavy oil interactions. A two-dimensional solubility parameter, developed for the selection of solvents for organic polymers, was found to group all the solvents for each heavy oil fraction in polygon areas when the complexing solubility parameter component was plotted against

Irwin A. Wiehe

1996-01-01

267

Two-dimensional streaming flows induced by resonating, thin beams  

Microsoft Academic Search

Miniaturized resonating slender beams are finding increased applications as fluidic actuators for portable electronics cooling. Piezoelectric and ultrasonic ``fans'' drive a flexural mode of the beam into resonance thus inducing a streaming flow, which can be used to cool microelectronic components. This paper presents analytical, computational, and experimental investigations of the incompressible two-dimensional streaming flows induced by resonating thin beams.

Tolga Açikalin; Arvind Raman; Suresh V. Garimella

2003-01-01

268

Wave beaming effects in two-dimensional cellular structures  

Microsoft Academic Search

Cellular structures like honeycombs or reticulated micro-frames are widely used in sandwich construction because of their superior structural static and dynamic properties. The aim of this study is to evaluate the dynamic behavior of two-dimensional cellular structures, with the focus on the effect of the geometry of unit cells on the dynamics of the propagation of elastic waves within the

Massimo Ruzzene; Fabrizio Scarpa; Francesco Soranna

2003-01-01

269

Granular dynamics simulations of two-dimensional heap formation  

Microsoft Academic Search

Granular dynamics simulations have been carried out of vertical feed two-dimensional heap formation by a freefall method using a more realistic granule interaction law than has been employed in previous studies to permit prolonged contacts between adjacent granules. Stable heaps are found to form only on a geometrically rough base comprised of discrete particles, and heap formation is only weakly

J. Baxter; U. Tüautzüautn; J. Burnell; D. M. Heyes

1997-01-01

270

Topological states of matter in two-dimensional fermionic systems  

Microsoft Academic Search

Topological states of matter in two-dimensional systems are characterised by the different properties of the edges and the bulk of the system: The edges conduct electrical current while the bulk is insulating. The first well-known example is the quantum Hall effect, which is induced by a perpendicular magnetic field that generates chiral edge channels along which the current propagates. Each

W. Beugeling

2012-01-01

271

Analysis of stable two-dimensional patterns in contractile cytogel  

Microsoft Academic Search

Summary Contractile actomyosin systems play a central role in the generation of intracellular patterns. Models for pattern formation have benefited greatly from the application of mechanochemical theory. However, investigations of the patterns have been primarily qualitative in nature; the two-dimensional nature of the evolving patterns has not yet been addressed mathematically, nor has the evolution of stable heterogeneous steady-state solutions.

M. A. Lewis; J. D. Murray

1991-01-01

272

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

273

Particle distributions in a two-dimensional reconnection field geometry  

Microsoft Academic Search

Particle trajectories in a two-dimensional steady state reconnection field geometry are studied in order to understand phase space density variations near the magnetopause and in the geomagnetic tail. Charged particles are traced back in time from a spacecraft position until they are in the source or inflow region for an entire gyroorbit. The inflow regions for the dayside magnetopause are

D. B. Curran; C. K. Goertz

1989-01-01

274

An iterative scheme for two-dimensional supercavitating flow  

Microsoft Academic Search

In the present research, supercavitating potential flow is studied numerically by the boundary element method (BEM). Using the advantages of BEM, an iterative algorithm has been introduced to capture cavity boundary in two-dimensional symmetric flows. In this algorithm, the cavity length is known and used to find the related cavitation number and cavity profile. In order to obtain finite length

N. M. Nouri; A. Eslamdoost

2009-01-01

275

Dirichlet-to-Neumann map method for analyzing interpenetrating cylinder arrays in a triangular lattice  

Microsoft Academic Search

An efficient numerical method is developed for computing the transmission and reflection spectra of finite two-dimensional photonic crystals composed of circular cylinders in a triangular lattice. Our method manipulates a pair of operators defined on a set of curves and it remains effective when the radius of the cylinders is larger than ? 3\\/4 of the lattice constant — a

Yumao Wu; Ya Yan Lu

2008-01-01

276

Numerical simulations of natural convection heat transfer along a vertical cylinder  

Microsoft Academic Search

Purpose – The purpose of this paper is to present a numerical solution for the problem of steady laminar flow and heat transfer characteristics of viscous incompressible fluid. Design\\/methodology\\/approach – For this purpose a two dimensional code has been developed to simulate the natural convection heat transfer along a vertical cylinder, for four different geometries: from vertical cylinder in infinite

Muhammad Rafique; I. Ahmad; M. Abdul Basit; Romana Begum; Wajid Aziz; Muhammad Farooq; Kamran Rasheed Qureshi

2011-01-01

277

Approach towards self-preservation of turbulent cylinder and screen wakes  

Microsoft Academic Search

Two-dimensional wakes generated from a circular cylinder and a 50% solidity screen have significantly different initial conditions. Accordingly, the approach towards self-preservation is quite different for the two wakes. For the cylinder wake, the normalized Reynolds stresses and spanwise vorticity decrease with increasing distance from the wake generator; the inverse occurs in the screen wake. Distributions of mean velocity, Reynolds

R. A. Antonia; J. Mi

1998-01-01

278

Accurate analysis of electromagnetic scattering from periodic circular cylinder array with defects.  

PubMed

This paper considers the two-dimensional electromagnetic scattering from periodic array of circular cylinders in which some cylinders are removed, and presents a formulation based on the recursive transition-matrix algorithm (RTMA). The RTMA was originally developed as an accurate approach to the scattering problem of a finite number of cylinders, and an approach to the problem of periodic cylinder array was then developed with the help of the lattice sums technique. This paper introduces the concept of the pseudo-periodic Fourier transform to the RTMA with the lattice sums technique, and proposes a spectral-domain approach to the problem of periodic cylinder array with defects. PMID:22565690

Watanabe, Koki; Nakatake, Yoshimasa; Pištora, Jaromír

2012-05-01

279

Radiation from apertures in conducting cylinders of arbitrary cross section  

Microsoft Academic Search

An analysis of two-dimensional radiation from apertures in perfectly conducting cylinders of arbitrary cross section is given. Solutions are expressed in terms of generalized network parameters, obtained by applying moment methods to the superposition integral equation. Formulas are given for current distributions, self- and mutual admittances, and radiation patterns. Representative computations are included to illustrate the theory.

R. Wallenberg; R. Harrington

1969-01-01

280

Active Control of a Circular Cylinder Flow at Transitional Reynolds Numbers  

Microsoft Academic Search

Active and passive control of flow around a circular cylinder, at transitional Reynolds numbers was investigated experimentally\\u000a by measuring cylinder surface pressures and wake velocity profiles. Two- and three-dimensional passive boundary layer tripping\\u000a was considered and periodic active control using piezo-fluidic actuators was introduced from a two-dimensional slot that was\\u000a nearly tangential to the cylinder surface. The slot location was

A. Naim; D. Greenblatt; A. Seifert; I. Wygnanski

2007-01-01

281

Vibrational properties of small two-dimensional classical crystals  

SciTech Connect

Recent computer simulations have stressed the dependence of transport properties on boundary conditions in two dimensions, where fluctuations and boundary conditions are equally important effects of order {ital N}{sup 1/2}. Elastically isotropic harmonic crystals provide a test case in which these two effects can be studied precisely without sacrificing realism. We investigate the boundary dependence of spatial fluctuations in two-dimensional crystals. Our results confirm the expected boundary independence of the extensive vibrational entropy. We find also that clamped crystal boundaries significantly alter the rate of divergence of the root-mean-square (rms) displacement with crystal size, but do not alter the [logarithmic] functional form, which is known to dominate vibrational fluctuations in periodic two-dimensional crystals. {copyright} {ital 1995} {ital American} {ital Institute} {ital of} {ital Physics}.

Hoover, W.G.; Kum, O. [Department of Applied Science, University of California at Davis/Livermore and Lawrence Livermore National Laboratory, Livermore, California 94551-7808 (United States)

1995-07-22

282

Some applications of two-dimensional stress transfer analyses  

SciTech Connect

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

Hsueh, C.H. [Oak Ridge National Lab., TN (United States). Metals and Ceramics Div.

1998-03-23

283

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 (by ˜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

284

Anisotropic superconductivity in the two-dimensional Hubbard model  

SciTech Connect

We address the problem of superconductivity in a system where the only many-body interactions are repulsive. The Eliashberg equations have been generalized to account for possible pairing correlations in the two-dimensional Hubbard model. Details of the two-dimensional band structure have been explicitly taken into account when considering the symmetry of the superconducting state. The pairing kernels have been discussed at low doping and at temperatures close to the superconducting transition temperature. We have proved that local Coulomb repulsion leads to attractive pairing correlations in the d-wave channel. Extended s-wave superconductivity is less likely to occur within this purely electronic model, at least in the physically interesting region of doping. {copyright} {ital 1997} {ital The American Physical Society}

Mierzejewski, M.; Zielinski, J. [Institute of Physics, University of Silesia, 40-007 Katowice (Poland)

1997-11-01

285

Scaling relations in the quasi-two-dimensional Heisenberg antiferromagnet  

NASA Astrophysics Data System (ADS)

The large- N expansion of the quasi-two-dimensional quantum nonlinear ? model is used in order to establish experimentally applicable universal scaling relations for the quasi-two-dimensional Heisenberg antiferromagnet. We show that, at N=? , the renormalized coordination number introduced by Yasuda [Phys. Rev. Lett. 94, 217201 (2005)] is a universal number in the limit of J'/J?0 . Moreover, similar scaling relations proposed by Hastings and Mudry [Phys. Rev. Lett. 96, 027215 (2006)] are derived at N=? for the three-dimensional static spin susceptibility at the wave vector (?,?,0) , as well as for the instantaneous structure factor at the same wave vector. We then use 1/N corrections to study the relation between interplane coupling, correlation length, and critical temperature, and show that the universal scaling relations lead to logarithmic corrections to previous mean-field results.

Praz, Antoine; Mudry, Christopher; Hastings, M. B.

2006-11-01

286

Adaptive rezoner in a two-dimensional Lagrangian hydrodynamic code  

SciTech Connect

In an effort to increase spatial resolution without adding additional meshes, an adaptive mesh was incorporated into a two-dimensional Lagrangian hydrodynamics code along with two-dimensional flux corrected (FCT) remapper. The adaptive mesh automatically generates a mesh based on smoothness and orthogonality, and at the same time also tracks physical conditions of interest by focusing mesh points in regions that exhibit those conditions; this is done by defining a weighting function associated with the physical conditions to be tracked. The FCT remapper calculates the net transportive fluxes based on a weighted average of two fluxes computed by a low-order scheme and a high-order scheme. This averaging procedure produces solutions which are conservative and nondiffusive, and maintains positivity. 10 refs., 12 figs.

Pyun, J.J.; Saltzman, J.S.; Scannapieco, A.J.; Carroll, D.

1985-01-01

287

Two-dimensional theory and simulation of free electron lasers  

NASA Astrophysics Data System (ADS)

Two-dimensional homogeneous theory of free-electron lasers with a wiggler magnetic field of constrant wavelength was formulated. It was found that waves propagating obliquely with respect to the electron beam are always unstable with appreciable growth rates; therefore, mode competition among the on-axis and off-six modes is an important consideration in the design of the free-electron laser. absolutely Due to long nonlinear saturation levels of the low frequency absolute instability, the dynamics of the electron beam, and the generation of the high frequency electromagnetic radiation can be severely affected. Two-dimensional particle simulations show that efficiency of genration of the on-axis high-frequency of the off-axis modes. In addition, complete disruption of the electron beam and laser oscillation due to the onset of the absolute instability were observed in simulations.

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

1981-07-01

288

Strong localization effect in magnetic two-dimensional hole systems  

SciTech Connect

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

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

2010-01-11

289

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

290

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

291

Magnetic order of two-dimensional isotropic dipolar antiferromagnets  

NASA Astrophysics Data System (ADS)

The question of the existence of order in two-dimensional isotropic dipolar Heisenberg antiferromagnets on a square lattice is studied. The spin-wave dispersion is evaluated and it is shown that the dipolar interaction lifts the degeneracy of the two magnon branches. In addition the dipolar interaction leads to a gap in the spin-wave energy and a nonvanishing order parameter. The resulting finite Néel temperature is calculated for a square lattice by means of linear spin-wave theory and a high-temperature expansion via the method of Callen. The transition temperatures are in good agreement with measured values on the quasi two-dimensional antiferromagnets K2MnF4, Rb2MnF4, Rb2MnCl4 and (CH3NH3)2MnCl4. In addition we studied the effect of an external magnetic field on the ground state and observed an intermediate state.

Pich, C.; Schwabl, F.

1995-02-01

292

Calculation of Coulomb interactions in two-dimensionally periodic systems  

NASA Astrophysics Data System (ADS)

A generalized implementation is presented of the Lekner method (Lekner, J., 1991, Physica A, 176 , 485) of calculating Coulomb interactions in two-dimensionally periodic systems. The generalized scheme eliminates the restriction on the shape of the primary cell, so it is now applicable to systems with non-rectangular shape. The generalized scheme retains the simplicity of the original method so it is easy to incorporate it into molecular dynamics and Monte Carlo codes. Comparisons are made with two other methods for calculating long range interactions in two-dimensionally periodic systems which are based on a Ewald type approach (Heyes, D. M., Barber, M., and Clarke, J. H. R., 1977, J. chem. Soc. Faraday Trans ii , 73 , 1485; Hautman, J., and Klein, M. L., 1992, Molec. Phys ., 75 , 379). The results show that the generalized Lekner method is superior in terms of accuracy, and that the speed of the new implementation is comparable with the method devised by Hautman and Klein.

Liem, S. Y.; Clarke, J. H. R.

293

Ground state of a quasi-two-dimensional electron gas  

NASA Astrophysics Data System (ADS)

The ground state of a quasi-two-dimensional electron gas (Q-2DEG) is investigated within a framework of the local spin density approximation (LSDA) with Perdew-Zunger type exchange-correlation energy. The ground state in a Q-2DEG is given as a function of film thickness and electron density. The Wigner rod ground state in a very thin film with low electron areal density is discussed in detail. In addition, the ground state of a two-dimensional electron gas (2DEG) is investigated using the LSDA with Tanatar-Ceperley and Attaccalite-Moroni-Georgi-Bachelet types of exchange-correlation energy. The ground state is found to show a phase transition from a nonmagnetic fluid to a spin-fully-polarized ferromagnetic Wigner ribbon with decreasing areal density. The difference between a 2DEG and a Q-2DEG with infinitesimal film thickness is discussed.

Ito, Yasumitsu; Okazaki, Kazuyuki; Teraoka, Yoshihiro

2004-04-01

294

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

295

Contract carriage: a two dimensional public policy perspective  

SciTech Connect

This paper provides a two dimensional model for the analysis of a contract carriage policy for the interstate natural gas pipeline industry. The two dimensions are: (1) customer flexibility and (2) transmission company operational control of the pipeline. This model suggests that public policymakers should encourage a transporation system that addresses the public's interests, and then adjust the regulatory environment to reflect this public interest perspective. 32 references, 2 figures.

Hurtado, A.P.

1984-05-01

296

Two-dimensional clusters of liquid 4He  

NASA Astrophysics Data System (ADS)

The binding energies of two-dimensional clusters (puddles) of?4He are calculated in the framework of the diffusion Monte Carlo method. The results are well fitted by a mass formula in powers of x=N-1/2, where N is the number of particles. The analysis of the mass formula allows for the extraction of the line tension, which turns out to be 0.121 K/Å. Sizes and density profiles of the puddles are also reported.

Sarsa, A.; Mur-Petit, J.; Polls, A.; Navarro, J.

2003-12-01

297

Density functional study of two-dimensional 4He clusters  

NASA Astrophysics Data System (ADS)

Binding energies and density profiles of two-dimensional systems of liquid He4 with different geometries are studied by means of a zero-range density functional adjusted to reproduce the line tension obtained in a previous diffusion Monte Carlo calculation (?DMC=0.121K/Å) . It is shown that this density functional provides accurate results for the binding energy of large clusters with a reasonable computational effort.

Mur-Petit, J.; Sarsa, A.; Navarro, J.; Polls, A.

2005-09-01

298

Jamming of Granular Flow in a Two-Dimensional Hopper  

Microsoft Academic Search

Granular systems consist of particles which interact among themselves only by interparticle contacts (1-3). In nature, many important phenomena such as avalanche, landslide, soil fluidization, and blood flow can be related to three-dimensional (3D) granular flow. On the other hand, two-dimensional (2D) flow phenomena can be found in the baggage flow on conveyer belts, the transport of cans and bottles

Pik-Yin Lai; H. K. Pak

2001-01-01

299

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

300

Teaching semiconductor device physics with two-dimensional numerical solver  

Microsoft Academic Search

In this paper, the authors propose the teaching of semiconductor device physics with the PC-based two-dimensional numerical partial differential equations solver, PDEase2. This approach avoids many of the restrictive assumptions of one-dimensional analytical solutions and better reflects the actual device operation. The gated diode which demonstrates both p-n junction and surface field effect physics is used to illustrate this new

Y. T. Yeow; C. H. Ling

1999-01-01

301

Nonlinear two-dimensional potential plasma wake waves  

SciTech Connect

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

Amatuni, A.Ts.

1995-12-01

302

Tunable two-dimensional photonic crystals using liquid crystal infiltration  

Microsoft Academic Search

The photonic band gap of a two-dimensional photonic crystal is continuously tuned using the temperature dependent refractive index of a liquid crystal. Liquid crystal E7 was infiltrated into the air pores of a macroporous silicon photonic crystal with a triangular lattice pitch of 1.58 mum and a band gap wavelength range of 3.3-5.7 mum. After infiltration, the band gap for

S. W. Leonard; J. P. Mondia; H. M. van Driel; O. Toader; S. John; K. Busch; A. Birner; U. Gösele; V. Lehmann

2000-01-01

303

Vibrational Beating in Two-Dimensional Electronic Spectra  

NASA Astrophysics Data System (ADS)

We trace vibrational wavepacket motion in two-dimensional electronic spectra of a two-level electronic system. The vibronic evolution induces a periodic beating pattern of the diagonal-to-antidiagonal peak width ratio in the absorptive signal part and a periodic tilt of the nodal line in the dispersive signal part. These modulations can be assigned to periodic modulations of the relative amplitudes of rephasing and non-rephasing contributions to the signal.

Nemeth, Alexandra; Milota, Franz; Man?al, Tomáš; Lukeš, Vladimír; Kauffmann, Harald F.; Sperling, Jaroslaw

304

Comparing Necessary Conditions for Recognizability of Two-Dimensional Languages  

Microsoft Academic Search

\\u000a The main problem in this paper is to find feasible conditions to prove\\/disprove that a given two-dimensional language is tiling\\u000a recognizable. We focus on two known conditions necessarily satisfied by a recognizable language, that are based on the idea\\u000a to reduce the problem from picture to string languages. We emphasize that they are grounded on two lower bound techniques\\u000a for

Marcella Anselmo; Maria Madonia

305

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

306

High-field transport in two-dimensional graphene  

Microsoft Academic Search

Transport of carriers in two-dimensional graphene at high electric fields is investigated by combining semianalytical and Monte Carlo methods. A semianalytical high-field transport model based on the high rate of optical phonon emission provides useful estimates of the saturation currents in graphene. For developing a more accurate picture, the nonequilibrium (hot) phonon effect and the role of electron-electron scattering were

Tian Fang; Aniruddha Konar; Huili Xing; Debdeep Jena

2011-01-01

307

Itinerant ferromagnetism in a two-dimensional atomic gas  

SciTech Connect

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

Conduit, G. J. [Department of Condensed Matter Physics, Weizmann Institute of Science, Rehovot 76100 (Israel) and Physics Department, Ben Gurion University, Beer Sheva 84105 (Israel)

2010-10-15

308

Two-dimensional magnetophotonic crystal: Exactly solvable model  

Microsoft Academic Search

We present an analytical treatment of a two-dimensional (2D) magnetophotonic crystal (MPC) with a square lattice constructed from two infinite arrays of magnetoactive dielectric sheets at right angles, in the limit of very small sheet thickness and very high dielectric constant. Alteration of band structure by an external magnetic field is studied. Two different geometries are examined: the Faraday geometry---magnetic

A. B. Khanikaev; A. V. Baryshev; M. Inoue; A. B. Granovsky; A. P. Vinogradov

2005-01-01

309

Two-dimensional electron liquid in a weak magnetic field  

Microsoft Academic Search

We present an effective theory describing the low-energy properties of an interacting two-dimensional electron gas at large noninteger filling factors nu>>1. Assuming that the interaction is sufficiently weak, rs<1, we integrate out all the fast degrees of freedom, and derive the effective Hamiltonian acting in the Fock space of the partially filled Landau level only. This theory enables us to

I. L. Aleiner; L. I. Glazman

1995-01-01

310

Two-dimensional electron gas near full polarization  

Microsoft Academic Search

We establish the consistency of the Fermi liquid description and find a\\u000arelation between Fermi liquid constants for the two dimensional electron system\\u000anear the point of full polarization due to a parallel magnetic field $H$. Our\\u000aresults enable us to predict connections between different thermodynamic\\u000aproperties of the system. In particular, we find that near the point of full

G. Zala; B. N. Narozhny; I. L. Aleiner; Vladimir I. Fal

2004-01-01

311

Two-dimensional quantum effects in nanoscale MOSFETs  

Microsoft Academic Search

In this paper, a full two-dimensional (2-D) quantum mechanical (QM) device simulator for deep submicron MOSFETs is presented. The model couples a 2-D Schrodinger-Poisson solver with a semiclassical transport model. The validity of the proposed model is first tested against a QM model for transport, developed as a benchmark. Then, QM effects on nanoscale MOSFETs performance are quantitatively addressed and

Agostino Pirovano; Andrea L. Lacaita; Alessandro S. Spinelli

2002-01-01

312

Two-dimensional condensation of nucleic acid components and oligonucleotides  

Microsoft Academic Search

DNA adsorption at the electrode surfaces is of fundamental interest for the development of DNA-based biosensors (1). Purine and pyrimidine derivatives currently occuring in nucleic acids posses an extraordinary high ability of self-association at the electrode surface and can form there by a two-dimensional (2-D) condensation a monomolecular layer (self-assembled monolayer - SAM) (2,3). By this high condensation ability nucleic

Vladimír Vetterl

313

A two-dimensional model of sulfur species and aerosols  

Microsoft Academic Search

A two-dimensional model of sulfate aerosols has been developed. The model includes the sulfate precursor species H2S, CS2, DMS, OCS, and S02. Microphysical processes simulated are homogeneous nucleation, condensation and evaporation, coagulation, and sedimentation. Tropospheric aerosols are removed by washout processes and by surface deposition. We assume that all aerosols are strictly binary water-sulfuric acid solutions without solid cores. The

Debra K. Weisenstein; Glenn K. Yue; Malcolm K. W. Ko; Nien-Dak Sze; Jose M. Rodriguez; Courtney J. Scott

1997-01-01

314

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

SciTech Connect

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

Dreyer, K.A.

1985-05-01

315

Precision fabrication of two-dimensional antiscatter grids  

Microsoft Academic Search

Creatv MicroTech is developing two-dimensional, air-core, anti-scatter grids that have the potential to significantly reduce scatter-to-primary ratio and increase primary transmission in mammography. The fabrication method uses x-ray lithography and electroplating, which allows the fabrication of high aspect ratio metal parts. Two unfocused nickel grids were fabricated, one 1.5 cm X 1.5 cm and the other 1.44 cm X 1.44

Cha-Mei Tang; Kevin Fischer; Bidhan Chadburi; Henry Guckel; Thomas R. Fewell; Robert J. Jennings; Rebecca Fahrig; David A. Jaffray; Martin J. Yaffe

2000-01-01

316

Pairing of Solitons in Two-Dimensional S=1 Magnets  

SciTech Connect

We study a general model of isotropic two-dimensional spin-1 magnet, which is relevant for the physics of ultracold atoms with hyperfine S=1 spins in an optical lattice at odd filling. We demonstrate a novel mechanism of soliton pairing occurring in the vicinity of a special point with an enhanced SU(3) symmetry: upon perturbing the SU(3) symmetry, solitons with odd CP{sup 2} topological charge are confined into pairs that remain stable objects.

Ivanov, B. A. [Institute of Magnetism, National Academy of Sciences and Ministry of Education, 03142 Kiev (Ukraine); T. Shevchenko Kiev National University, 03127 Kiev (Ukraine); Khymyn, R. S. [T. Shevchenko Kiev National University, 03127 Kiev (Ukraine); Kolezhuk, A. K. [Institut fuer Theoretische Physik C, RWTH Aachen, D-52056 Aachen (Germany)

2008-02-01

317

Orthorhombic Two-Dimensional Crystal form of Purple Membrane  

Microsoft Academic Search

A new two-dimensional crystal form of purple membrane has been obtained in vitro. It is produced by the joint use of a cationic detergent, dodecyltrimethylammonium chloride, and the nonionic detergent, Triton X-100. It primarily forms large, rolled-up sheets that look like needles in the light microscope. Liposomes and tubes are also observed. The absorption maximum of the new form of

Hartmut Michel; Dieter Oesterhelt; Richard Henderson

1980-01-01

318

Image Classification by a Two Dimensional Hidden Markov Model  

Microsoft Academic Search

Conventional block-based image classification algorithms, such as CART and VQ based classification,ignore the statistical dependency among image blocks. Consequently, these algorithmsoften suffer from over-localization. In order to benefit from the inter-block dependency, an imageclassification algorithm based on a hidden Markov model (HMM) is developed. An HMM forimage classification, a two dimensional extension of the one dimensional HMM used for speechrecognition,

Jia Li; Amir Najmi; Robert M. Gray

1998-01-01

319

Two-dimensional oscillators with C4v potential functions  

Microsoft Academic Search

A quantum-mechanical investigation of two-dimensional oscillators having C4v potential functions has been performed. The symmetry properties of such systems have been elucidated, and the state symmetries have been correlated with C?v and C2v cases. Numerical calculations are presented to illustrate the behavior of the energy levels as a function of the potential energy coupling term. The results show clearly how

S. N. Mathur; M. D. Harmony

1977-01-01

320

A two-dimensional position-sensitive phoswich detector  

Microsoft Academic Search

A two-dimensional position-sensitive DeltaE-E phoswich detector, 20 cm × 20 cm, was built using the fast plastic scintillator NE 102A for the thin (0.5 mm) DeltaE element, and the new, slow plastic scintillator NE 115 (measured light output 35% of anthracene, decay time 225 ns) for the thick (4.5 mm) E element. Natural light loss arising from multiple reflections at

M. Bantel; R. G. Stokstad; Y. D. Chan; S. Wald; P. J. Countryman

1984-01-01

321

Two-Dimensional Polynomial Phase Signals: Parameter Estimation and Bounds  

Microsoft Academic Search

This paper considers the problem of parametric modeling and estimation of nonhomogeneous two-dimensional (2-D) signals. In particular, we focus our study on the class of constant modulus polynomial-phase 2-D nonhomogeneous signals. We present two different phase models and develop computationally efficient estimation algorithms for the parameters of these models. Both algorithms are based on phase differencing operators. The basic properties

Joseph M. Francos; Benjamin Friedlander

1998-01-01

322

Segregation and convection rolls in two-dimensional packings  

NASA Astrophysics Data System (ADS)

Self-organized pattern formation in two-dimensional packings is reported. Continuous rotation of a densely packed monolayer leads to two possible states: either the packing segregates without any recognizable collective particle motion, or the packing stays mixed and the particles move in regular convection rolls. The reason for the different observations is so far not known. Irrespective of the simplicity of the experiment, the driving mechanism must be completely different from other pattern forming systems in granular media.

Rietz, Frank

2013-06-01

323

Phase-stabilized two-dimensional electronic spectroscopy  

Microsoft Academic Search

Two-dimensional (2D) spectroscopy is a powerful technique to study nuclear and electronic correlations between different transitions or initial and final states. Here we describe in detail our development of inherently phase-stabilized 2D Fourier-transform spectroscopy for electronic transitions. A diffractive-optic setup is used to realize heterodyne-detected femtosecond four-wave mixing in a phase-matched box geometry. Wavelength tunability in the visible range is

Tobias Brixner; Igor V. Stiopkin; Graham R. Fleming

2004-01-01

324

A steady two-dimensional climate model with residual circulation  

Microsoft Academic Search

Based on dynamical energy transport and thermodynamic energy balance in the earth’s atmosphere-ocean system a steady two-dimensional\\u000a climate model with residual circulation is proposed. In the model, we include some important physical processes with feedbacks\\u000a such as ice caps-albedo, water vapor-temperature, etc. The simulated steady tempsrature field is very close to that of the\\u000a real atmosphere. The numerical experiments show

Xun Zhu

1988-01-01

325

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); Hoover, W.G.; Hoover, C.G. [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

326

AN ANALYSIS OF THE TWO-DIMENSIONAL TURBULENT BUOYANT JET  

Microsoft Academic Search

The two-dimensional turbulent buoyant jet is analyzed using a vertical length scale defined by L = M0F0  where Ma is the rate at which momentum is added at the source and F0 is the rate at which buoyancy is added. Introduction of the length scales into the equations of motion shows the ratio x\\/L directly controls the bouyancy term. The

C. B. BAKER; A. J. MAFFE; D. B. TAULBEE

1989-01-01

327

Bifurcations in two-dimensional Rayleigh-Bénard convection  

Microsoft Academic Search

Two-dimensional bouyancy-driven convection in a horizontal fluid layer with stress-free boundary conditions at top and bottom and periodic boundary conditions in the horizontal direction is investigated by means of numerical simulation and bifurcation-analysis techniques. As the bouyancy forces increase, the primary stationary and symmetric convection rolls undergo successive Hopf bifurcations, bifurcations to traveling waves, and phase lockings. We pay attention

E. Zienicke; N. Seehafer; F. Feudel

1998-01-01

328

Unsteady two-dimensional theory of a flapping wing  

NASA Astrophysics Data System (ADS)

An analytical evaluation of the hydrodynamic force on a single flapping wing is presented, based on the two-dimensional inviscid theory, with the addition of an attached leading-edge vortex. The explicit expression of the force is given and compared with some of the measurements by Dickinson et al. [Science 284, 1954 (1999)] and Sane and Dickinson [J. Expl. Biol. 204, 2607 (2001)] for a fruit fly model wing.

Minotti, F. O.

2002-11-01

329

Cooperative Parrondo's games on a two-dimensional lattice  

NASA Astrophysics Data System (ADS)

Cooperative Parrondo's games on a regular two-dimensional lattice are analyzed based on computer simulations and on the discrete-time Markov chain model with exact transition probabilities. The paradox appears in the vicinity of the probabilites characteristic of the “voter model”, suggesting practical applications. As in the one-dimensional case, winning and the occurrence of the paradox depend on the number of players.

Mihailovi?, Zoran; Rajkovi?, Milan

2006-06-01

330

Quasi-two-dimensional Turing patterns in an imposed gradient  

Microsoft Academic Search

In experiments on quasi-two-dimensional Turing structures, patterns form perpendicular to a concentration gradient imposed by the boundary conditions. Using linear stability analysis, with the ClO2-I2-MA (malonic acid) reaction as an example, we obtain conditions on the position along the gradient direction and possible three dimensionality of the structures. Experiments on the effects of MA and starch concentrations on the position

István Lengyel; Sándor Kádár; Irving R. Epstein

1992-01-01

331

Two-dimensional NMR studies of native coenzyme F430  

Microsoft Academic Search

Modern two-dimensional (2D) NMR spectroscopic methods are used to determine signal assignments and structural features of the recently discovered nickel(II)-containing coenzyme F430. This is the first detailed ¹H and ¹³C NMR study of the native form of coenzyme F430. With the use of COSY, HOHAHA, NOESY, and ROESY ¹H-¹H correlated spectroscopies in combination with HMQC and HMBC ¹H-¹³C correlated spectroscopies,

Hoshik Won; Michael F. Summers; Karl D. Olson; Ralph S. Wolfe

1990-01-01

332

Two dimensional COâ-ocean model including the biological processes  

Microsoft Academic Search

A two-dimensional (latitude X depth) multi-box model of the ocean has been developed and used to predict the distribution of carbon dioxide between the ocean and the atmosphere. The model simulates the chemical and biological processes in the ocean that affect this distribution (i.e., ocean-atmosphere exchange of COâ, photosynthesis and decay, calcium carbonate production and dissolution) by means of linear

C. F. Jr. Baes; G. G. Killough

1985-01-01

333

Solvable quantum mechanical model in two-dimensional space  

Microsoft Academic Search

A one-particle non-relativistic quantum mechanical solvable model in two-dimensional space is given. The Hamiltonian is the sum of kinetic and interaction parts. Interactions are separable and can be centred at n arbitrary points of the plane. Conditions for the existence and for the number of bound states in finite linear chains are formulated in terms of the parameters of the

E de Prunelé

2006-01-01

334

Two-dimensional quantum mechanical modeling of nanotransistors  

Microsoft Academic Search

Quantization in the inversion layer and phase coherent transport are anticipated to have significant impact on device performance in ``ballistic'' nanoscale transistors. While the role of some quantum effects have been analyzed qualitatively using simple one-dimensional ballistic models, two-dimensional (2D) quantum mechanical simulation is important for quantitative results. In this paper, we present a framework for 2D quantum mechanical simulation

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

2002-01-01

335

Two-dimensional spectroscopy of electronic couplings in photosynthesis  

Microsoft Academic Search

Time-resolved optical spectroscopy is widely used to study vibrational and electronic dynamics by monitoring transient changes in excited state populations on a femtosecond timescale. Yet the fundamental cause of electronic and vibrational dynamics-the coupling between the different energy levels involved-is usually inferred only indirectly. Two-dimensional femtosecond infrared spectroscopy based on the heterodyne detection of three-pulse photon echoes has recently allowed

Tobias Brixner; Jens Stenger; Harsha M. Vaswani; Minhaeng Cho; Robert E. Blankenship; Graham R. Fleming

2005-01-01

336

Planar diagrams, two-dimensional lattice gravity and surface models  

NASA Astrophysics Data System (ADS)

Some discrete lattice models for quantum two-dimensional euclidean gravity are shown to be equivalent to zero-dimensional planar field theories. Explicit expressions are given for partition functions. A universal continuum limit exists for open surfaces, but not for closed ones, and is argued to describe a space with negative average curvature. Extensions to those models to higher dimensions and to surface models are briefly discussed. Chercheur CNRS.

David, F.

337

Electron-Phonon Coupling in Two-Dimensional Germanene  

NASA Astrophysics Data System (ADS)

The phonon properties of the two-dimensional honeycomb allotrope of germanium, germanene, were studied by first-principles calculations. We found that the highest optical branches on the phonon dispersions at ? and K symmetry points of the first Brillouin zone exhibit similar behavior as in graphene and graphite, indicating possible Kohn anomalies in germanene. Electron-Phonon coupling for the high symmetric modes will be discussed.

Stein, Ryan; Schaefer, David; Yan, Jia-An

2013-03-01

338

Theory of two-dimensional multirate filter banks  

Microsoft Academic Search

Results are presented on 2-D FIR (two-dimensional finite-impulse-response) filter banks for multirate applications. The theory is valid for all sampling lattices; conditions for alias-free and perfect signal reconstruction are derived. Synthesis structures for paraunitary and nonparaunitary polynomial matrices are derived, which yield perfect reconstruction filter banks. The degrees of freedom are given for these systems. Linear phase conditions are posed

G. Karlsson; M. Vetterli

1990-01-01

339

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

340

Two-Dimensional Array Coloring With Many Colors  

Microsoft Academic Search

Given an mtimesn array and k distinct colors with 2lesmlesn and 2lesktwo-dimensional (2-D) interleaving schemes for correcting

Wen-qing Xu; Solomon W. Golomb

2008-01-01

341

On the invariants of two dimensional linear parabolic equations  

NASA Astrophysics Data System (ADS)

We consider the most general two dimensional linear parabolic equations. Motivated by the recent work of Ibragimov et al. [1-3] we construct differential invariants, semi-invariants and invariant equations. These results are achieved with the employment of the equivalence group admitted by this class of parabolic equations. We derive those variable coefficient equations of this class of linear parabolic equations that can be mapped into constant coefficient equations. Further applications are presented.

Tsaousi, C.; Sophocleous, C.; Tracinà, R.

2012-09-01

342

Finite difference methods for two-dimensional fractional dispersion equation  

Microsoft Academic Search

Fractional order partial differential equations, as generalizations of classical integer order partial differential equations, are increasingly used to model problems in fluid flow, finance and other areas of application. In this paper we discuss a practical alternating directions implicit method to solve a class of two-dimensional initial-boundary value fractional partial differential equations with variable coefficients on a finite domain. First-order

Mark M. Meerschaert; Hans-Peter Scheffler; Charles Tadjeran

2006-01-01

343

Critical indexes of conductivity in two-dimensional percolation problems  

Microsoft Academic Search

The results of model experiments for critical behaviour of conductivity in two-dimensional percolation problems are presented. It is found that for the system consisting of conductive and non-conductive elements conductivity vanishes as sigma (x) infinity (xc-x)t; where t is equal to 1.15+or-0.2 for both bond and site percolation problems. For the two-component system consisting of metallic and dielectric elements it

M. E. Levinshtein

1977-01-01

344

Thermal transport in the two-dimensional disordered electron gas  

NASA Astrophysics Data System (ADS)

We develop a theory of thermal transport in the two-dimensional disordered electron gas at low temperatures. Our approach is based on the calculation of the heat density correlation function. To this end we subject the Keldysh nonlinear sigma model in the presence of source fields to a renormalization group analysis. Special care is taken to additionally account for scattering processes with a very small frequency transfer.

Schwiete, Georg; Finkelstein, Alexander

2013-03-01

345

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

346

Dirac Points in Two-Dimensional Inverse Opals  

NASA Astrophysics Data System (ADS)

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

D. Mahan, G.

2013-10-01

347

trntegration of Loss Function in Two Dimensional Deterministic Tolerance Synthesis  

Microsoft Academic Search

The problems of deterministic tolerance synthesis are generally solved using a combinatorial optimization problem, for instance, an integer programming approach, a design of experiments, and the Taguchi method. Researchers generally consider one-dimensional deterministic tolerance synthesis; however, the problems of two or three-dimensional deterministic tolerance synthesis sometimes happen. This paper deals with two-dimensional deterministic tolerance synthesis. Since the objectives of designing

Jirarat Teeravaraprug

348

Two-dimensional remote air-pollution monitoring via tomography  

Microsoft Academic Search

We propose to apply computerized tomography to measure a two-dimensional pollutant-concentration map over an area that may contain several potential sources of pollution. A tunable-laser source at the center of the area generates secondary or virtual light sources around the perimeter of the area that play the role of x rays in conventional computerized tomography of the human body.

Robert L. Byer; Lawrence A. Shepp

1979-01-01

349

Mott transition in the two-dimensional Hubbard model.  

PubMed

Spectral properties of the two-dimensional Hubbard model near the Mott transition are investigated by using cluster perturbation theory. The Mott transition is characterized by freezing of the charge degrees of freedom in a single-particle excitation that leads continuously to the magnetic excitation of the Mott insulator. Various anomalous spectral features observed in cuprate high-temperature superconductors are explained in a unified manner as properties near the Mott transition. PMID:22401230

Kohno, Masanori

2012-02-15

350

Design and fabrication of two-dimensional superconducting bolometer arrays  

Microsoft Academic Search

We have been developing an architecture for producing large format, two-dimensional arrays of close-packed bolometers, which will enable far-infrared to millimeter wavelength (lambda=100µm-2mm) cameras and spectrometers to obtain images and spectra orders of magnitude faster than present instruments. The low backgrounds achieved in these instruments require very sensitive detectors with NEPs ranging from 10-17 to 10-19 W\\/(Hz-1\\/2). Superconducting transition edge

Dominic J. Benford; Johannes G. Staguhn; Gordon J. Stacey; Lyman Page; S. H. Moseley Jr.; Kent D. Irwin; James A. Chervenak; Christine A. Allen

2004-01-01

351

Two-dimensional black hole and singularities of CY manifolds  

Microsoft Academic Search

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

Hirosi Ooguri; Cumrun Vafa

1996-01-01

352

Electron Transport through curved and rolled Two Dimensional Electron Gas  

Microsoft Academic Search

We report on topology dependent electron transport in tubular shaped two-dimensional electron gases. These micron-sized tubes are realized in a strained InGaAs quantum well. This is the first step towards investigating geometric potentials in low dimensional quantum systems. We investigate magneto-resistance of the tubular systems in a perpendicularly applied magnetic field. At low magnetic field, an increased zero field magneto

Nakul Shaji; Hua Qin; Levente Klien; Mark Eriksson; Robert Blick; Christopher Deneke; Oliver Schmidt

2006-01-01

353

Bifurcation phenomena in two-dimensional piecewise smooth discontinuous maps.  

PubMed

In recent years the theory of border collision bifurcations has been developed for piecewise smooth maps that are continuous across the border and has been successfully applied to explain nonsmooth bifurcation phenomena in physical systems. However, there exist a large number of switching dynamical systems that have been found to yield two-dimensional piecewise smooth maps that are discontinuous across the border. In this paper we present a systematic approach to the problem of analyzing the bifurcation phenomena in two-dimensional discontinuous maps, based on a piecewise linear approximation in the neighborhood of the border. We first motivate the analysis by considering the bifurcations occurring in a familiar physical system-the static VAR compensator used in electrical power systems-and then proceed to formulate the theory needed to explain the bifurcation behavior of such systems. We then integrate the observed bifurcation phenomenology of the compensator with the theory developed in this paper. This theory may be applied similarly to other systems that yield two-dimensional discontinuous maps. PMID:20887041

Rakshit, Biswambhar; Apratim, Manjul; Banerjee, Soumitro

2010-09-01

354

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

355

a Two-Dimensional Radiative-Convective Climate Model.  

NASA Astrophysics Data System (ADS)

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

Kiehl, Jeffrey Theodore

356

Bifurcation phenomena in two-dimensional piecewise smooth discontinuous maps  

NASA Astrophysics Data System (ADS)

In recent years the theory of border collision bifurcations has been developed for piecewise smooth maps that are continuous across the border and has been successfully applied to explain nonsmooth bifurcation phenomena in physical systems. However, there exist a large number of switching dynamical systems that have been found to yield two-dimensional piecewise smooth maps that are discontinuous across the border. In this paper we present a systematic approach to the problem of analyzing the bifurcation phenomena in two-dimensional discontinuous maps, based on a piecewise linear approximation in the neighborhood of the border. We first motivate the analysis by considering the bifurcations occurring in a familiar physical system-the static VAR compensator used in electrical power systems-and then proceed to formulate the theory needed to explain the bifurcation behavior of such systems. We then integrate the observed bifurcation phenomenology of the compensator with the theory developed in this paper. This theory may be applied similarly to other systems that yield two-dimensional discontinuous maps.

Rakshit, Biswambhar; Apratim, Manjul; Banerjee, Soumitro

2010-09-01

357

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

358

Chaotic and strange attractors of a two-dimensional map  

Microsoft Academic Search

A family of continuous, invertible standard maps of the torus, cylinder and plane is considered in this paper. Sequences of bifurcations are studied which correspond to the transformation of an invariant curve to chaotic and strange attractors. The characteristic variations of complicated attractors are considered. Hyperbolicity conditions are obtained for the case of piecewise-smooth maps. The maps generating the Henon,

V N Belykh

1995-01-01

359

Endwall boundary layer, cylinder diameter, Reynoldsd number, and surface injection effects on local mass transfer from a cylinder in crossflow  

NASA Astrophysics Data System (ADS)

A naphthalene sublimation technique is used to determine the circumferential and longitudinal variations of mass transfer from a smooth circular cylinder in a crossflow of air. The study is divided into two parts. In the first part, the effects of cylinder diameter and endwall boundary layer on the approaching flow are investigated for a cylinder Reynolds number of 10,000-80,000. High transfer coefficients are detected near the base of the cylinder, and enhancement of the mass transfer over values obtained where the flow is two-dimensional is seen up to a distance of 3.5 cylinder diameters from the tunnel wall. It is shown that the spanwise extent of the strip near the cylinder base where high coefficients are observed is proportional to the cylinder diameter. Mass transfer values near the endwall increase rapidly with Reynolds number; they also depend on the ratio of cylinder length to diameter (the aspect ratio) and the ratio of mainstream boundary layer displacement thickness to cylinder diameter.

Karni, J.

360

Interacting two dimensional systems with a discrete degree of freedom  

NASA Astrophysics Data System (ADS)

This thesis considers several two dimensional and quasi-two dimensional systems in AlAs and GaAs with discrete electronic degrees of freedom, such as spin, valley, and layer indices. Each discrete degree of freedom responds to an externally applied field, allowing us control over the occupation of the levels. Each also enables a new measurement technique, with which we can probe these strongly interacting systems. We confine holes in closely spaced bilayer GaAs quantum well (QW) samples. In this system the holes possess a layer degree of freedom, which we easily manipulate using electric fields from electrostatic gates on the surface and substrate of the sample. Tunneling through the narrow insulating barrier between the QWs couples the two layers, and allows us to use tunneling measurements to probe the energetics of the two dimensional hole system above and below the Fermi energy. By applying a large magnetic field parallel to the system, we probe the in-plane dispersion of strongly interacting holes. We find a striking departure from the expected dispersion for large magnetic fields. Electrons in wide AlAs QWs occupy two degenerate minima in the conduction band, called valleys. We break the degeneracy of these valleys with applied strain in the plane of the QW, applied in-situ using a piezoelectric stack. It is well known that changing valley occupation shows clearly in the changing strength of integer quantum Hall resistance minima. We find analogous behavior in the fractional quantum Hall effect (FQHE) minima around Landau level filling factor nu = 32 . In light of the composite fermion model of the FQHE, we deduce that composite fermions in AlAs have a valley degree of freedom, and determine the valley susceptibility and valley polarization energy.

Bishop, Nathaniel

361

Chaotic and strange attractors of a two-dimensional map  

NASA Astrophysics Data System (ADS)

A family of continuous, invertible standard maps of the torus, cylinder and plane is considered in this paper. Sequences of bifurcations are studied which correspond to the transformation of an invariant curve to chaotic and strange attractors. The characteristic variations of complicated attractors are considered. Hyperbolicity conditions are obtained for the case of piecewise-smooth maps. The maps generating the Henon, Lozi, Belykh attractors belong to our class of standard maps.

Belykh, V. N.

1995-04-01

362

Nonlinear Cascades in Two-Dimensional Turbulent Magnetoconvection  

SciTech Connect

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

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

2009-06-05

363

Condensate fraction of a two-dimensional attractive Fermi gas  

SciTech Connect

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

Salasnich, Luca [CNR-INFM and CNISM, Dipartimento di Fisica 'Galileo Galilei', Universita di Padova, Via Marzolo 8, 35131 Padova (Italy)

2007-07-15

364

Local diamagnetic susceptibility of quasi-two-dimensional graphite  

NASA Astrophysics Data System (ADS)

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

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

2013-08-01

365

Carbon Dioxide Separation with a Two-Dimensional Polymer Membrane.  

PubMed

Carbon dioxide gas separation is important for many environmental and energy applications. Molecular dynamics simulations are used to characterize a two-dimensional hydrocarbon polymer, PG-ES1, that uses a combination of surface adsorption and narrow pores to separate carbon dioxide from nitrogen, oxygen, and methane gases. The CO(2) permeance is 3 × 10(5) gas permeation units (GPU). The CO(2)/N(2) selectivity is 60, and the CO(2)/CH(4) selectivity exceeds 500. The combination of high CO(2) permeance and selectivity surpasses all known materials, enabling low-cost postcombustion CO(2) capture, utilization of landfill gas, and horticulture applications. PMID:22734516

Schrier, Joshua

2012-07-01

366

Two-dimensional metal inclusions in a dielectric crystal  

NASA Astrophysics Data System (ADS)

Highly aggregated color centers in crystals of a wide-band-gap calcium fluoride insulator heated in a reducing atmosphere of vapors of calcium metal cation ("additive coloration" of crystals) have been studied using spectroscopy and atomic-force microscopy methods. These centers are large aggregates of anion vacancies and electrons, which transform into metal structures. The evolution of these structures with increasing number of such components has been traced from individual particles with two-dimensional structure to large film fragments. It has been shown that fragments are concentrated in isolated planes {111}, which are cleavage planes of the crystal with high contents of highly aggregated centers.

Gainutdinov, R. V.; Shcheulin, A. S.; Fedorov, P. P.; Angervaks, A. E.; Ryskin, A. I.

2011-07-01

367

Dynamical generation of mass in a two-dimensional model  

SciTech Connect

The chiral invariant Gross-Neveu model is a field theoretic model in two-dimensional space-time which exhibits dynamical generation of mass in conjunction with asymptotic freedom. By exploiting the Bethe-Ansatz technique, it has been possible to diagonalize exactly the Hamiltonian, classify the physical states and extract the factorizable S-matrix of the model. The present article, primarily a pedagogical introduction to the topic, is an expanded version of an invited talk given at the January, 1981, meeting of the American Physical Society, in New York.

Lowenstein, J.H. (New York Univ., NY (USA). Dept. of Physics)

1981-08-01

368

Transport in two dimensional electronic micro-emulsions  

SciTech Connect

In two dimensional electron systems with Coulomb or dipolar interactions, a direct transition, whether first or second order, from a liquid to a crystalline state is forbidden. As a result, between these phases there must be other (micro-emulsion) phases which can be viewed as a meso-scale mixture of the liquid and crystalline phases. We investigate the transport properties of these new electronic phases and present arguments that they are responsible for the various transport anomalies that have been seen in experiments on the strongly correlated 2DEG in high mobility semiconductor devices with low electron densities.

Spivak, Boris [Department of Physics, University of Washington, Seattle, WA 98195 (United States)]. E-mail: spivak@u.washington.edu; Kivelson, Steven A. [Department of Physics, Stanford University, Stanford, CA 94305-4045 (United States)

2006-09-15

369

Collapse of skyrmions in two-dimensional ferromagnets and antiferromagnets  

NASA Astrophysics Data System (ADS)

Collapse of a skyrmion due to the discreteness of a crystal lattice in isotropic two-dimensional ferromagnets and antiferromagnets has been studied analytically and by numerical solution of equations of motion for up to 2000×2000 classical spins on a square lattice coupled via Heisenberg exchange interaction. Excellent agreement between analytical and numerical results has been achieved. The lifetime of the skyrmion scales with its initial size ?0 as (?0/a)5 in ferromagnets and as (?0/a)2.15 in antiferromagnets with a being the lattice parameter. This makes antiferromagnetic skyrmions significantly shorter lived than ferromagnetic skyrmions.

Cai, Liufei; Chudnovsky, Eugene M.; Garanin, D. A.

2012-07-01

370

Magnetic Reconnection in Two-Dimensional Magnetohydrodynamic Turbulence  

SciTech Connect

Systematic analysis of numerical simulations of two-dimensional magnetohydrodynamic turbulence reveals the presence of a large number of X-type neutral points where magnetic reconnection occurs. We examine the statistical properties of this ensemble of reconnection events that are spontaneously generated by turbulence. The associated reconnection rates are distributed over a wide range of values and scales with the geometry of the diffusion region. Locally, these events can be described through a variant of the Sweet-Parker model, in which the parameters are externally controlled by turbulence. This new perspective on reconnection is relevant in space and astrophysical contexts, where plasma is generally in a fully turbulent regime.

Servidio, S.; Matthaeus, W. H.; Shay, M. A. [Bartol Research Institute and Department of Physics and Astronomy, University of Delaware, Newark, Delaware 19716 (United States); Cassak, P. A. [Department of Physics, West Virginia University, Morgantown, West Virginia 26506 (United States); Dmitruk, P. [Bartol Research Institute and Department of Physics and Astronomy, University of Delaware, Newark, Delaware 19716 (United States); Departmento de Fisica, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Ciudad Universitaria, 1428, Buenos Aires (Argentina)

2009-03-20

371

Controlled assembly of two-dimensional colloidal crystals  

NASA Astrophysics Data System (ADS)

Under the influence of capillary forces, colloidal particles embedded in a soap film self-organize to form polycrystalline monolayers when the film is withdrawn from a concentrated suspension. Here, we show that mechanically generated capillary waves on the free surface of the bulk colloidal suspension can cause migration of grain boundaries, and under certain conditions, completely eliminate them. This dramatic effect, we call ``mechanic annealing,'' provides a robust means of growing two-dimensional single crystals with size that has never been achieved before. The method is expected to be applicable to a variety of self-assembling systems.

Wei, Q.-H.; Cupid, D. M.; Wu, X. L.

2000-09-01

372

Longitudinal viscosity of two-dimensional Yukawa liquids.  

PubMed

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

Feng, Yan; Goree, J; Liu, Bin

2013-01-22

373

Two-Dimensional Droplet Spreading over Random Topographical Substrates  

NASA Astrophysics Data System (ADS)

We examine theoretically the effects of random topographical substrates on the motion of two-dimensional droplets via statistical approaches, by representing substrate families as stationary random functions. The droplet shift variance at both early times and in the long-time limit is deduced and the droplet footprint is found to be a normal random variable at all times. It is shown that substrate roughness inhibits wetting, illustrating also the tendency of the droplet to slide without spreading as equilibrium is approached. Our theoretical predictions are verified by numerical experiments.

Savva, Nikos; Kalliadasis, Serafim; Pavliotis, Grigorios A.

2010-02-01

374

Collective modes of quasi-two-dimensional Yukawa liquids.  

PubMed

Particles in dusty plasmas are often confined to a quasi-two-dimensional arrangement. In such layers--besides the formation of compressional and (in-plane) shear waves--an additional collective excitation may also show up, as small-amplitude oscillations of the particles perpendicular to the plane are also possible. We explore through molecular dynamics simulations the properties (fluctuation spectra, dispersion relation, Einstein frequency) of this out-of-plane transverse mode in the strongly coupled liquid phase of Yukawa systems. PMID:15244656

Donkó, Z; Hartmann, P; Kalman, G J

2004-06-01

375

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

376

Correlation effects in two-dimensional topological insulators  

NASA Astrophysics Data System (ADS)

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

Hohenadler, M.; Assaad, F. F.

2013-04-01

377

Two-dimensional detonation waves in Type IA supernovae  

NASA Astrophysics Data System (ADS)

The propagation of two-dimensional nuclear detonation waves in Type Ia supernovae is calculated from Huygens' principle and the resulting flow is then computed with a hydrodynamic code. This has the advantage that one can study asymmetric explosions using wave speeds determined from one-dimensional calculations which include very detailed nuclear chemistry. The method is applied to two cases, the one-dimensional versions of which have previously been considered by Nomoto. We find that the detonation wave forms a pair of cusps which are likely to have a significant effect on both the abundances and the final asymmetry of the expansion.

Wiggins, D. J. R.; Falle, S. A. E. G.

1997-05-01

378

Supersolids versus phase separation in two-dimensional lattice bosons.  

PubMed

We study the nature of the ground state of the two-dimensional extended boson Hubbard model on a square lattice by quantum Monte Carlo methods. We demonstrate that strong but finite on-site interaction U along with a comparable nearest-neighbor repulsion V result in a thermodynamically stable supersolid ground state for densities larger than 1/2, in contrast to fillings less than 1/2 or for very large U, where the checkerboard supersolid is unstable towards phase separation. We discuss the relevance of our results to realizations of supersolids using cold bosonic atoms in optical lattices. PMID:16090278

Sengupta, Pinaki; Pryadko, Leonid P; Alet, Fabien; Troyer, Matthias; Schmid, Guido

2005-05-23

379

Two-dimensional Fourier transform of scaled Dirac delta curves  

NASA Astrophysics Data System (ADS)

We obtain a Fourier transform scaling relation to find analytically, numerically, or experimentally the spectrum of an arbitrary scaled two-dimensional Dirac delta curve from the spectrum of the nonscaled curve. An amplitude factor is derived and given explicitly in terms of the scaling factors and the angle of the forward tangent at each point of the curve about the positive x axis. With the scaling relation we determine the spectrum of an elliptic curve by a circular geometry instead of an elliptical one. The generalization to N-dimensional Dirac delta curves is also included.

Guizar-Sicairos, Manuel; Gutiérrez-Vega, Julio C.

2004-09-01

380

Two-dimensional dispersive shock waves in dissipative optical media.  

PubMed

We study generation of two-dimensional dispersive shock waves and oblique dark solitons upon interaction of tilted plane waves with negative refractive index defects embedded into defocusing material with linear gain and two-photon absorption. Different evolution regimes are encountered, including the formation of well-localized disturbances for input tilts below critical one, generation of extended shock waves containing multiple intensity oscillations in the "upstream" region, and gradually vanishing oblique dark solitons in the "downstream" region for input tilts exceeding critical one. The generation of stable dispersive shock waves is possible only below certain critical defect strength. PMID:23455300

Kartashov, Yaroslav V; Kamchatnov, Anatoly M

2013-03-01

381

Inverse methods in two-dimensional NMR spectral analysis  

NASA Astrophysics Data System (ADS)

Solid-state NMR is a valuable technique for the study of disordered materials. Analysis of such spectra usually involves solution of so-called ill-posed inverse problems. Here we present a strategy for the analysis of two-parameter two-dimensional NMR problems and test it on 2D DECODER and DOQSY experiments. Using Monte Carlo tests, constraints are determined for the resolution and accuracy of the analysis for both experiments. The methods are finally applied to spectra of spider dragline silk, a heterogeneous solid fibrous protein.

van Beek, Jacco D.; Meier, Beat H.; Schäfer, Hartmut

2003-05-01

382

Collective dynamics of two-dimensional coupled Brownian motors  

NASA Astrophysics Data System (ADS)

The transport properties of coupled Brownian particles in a two-dimensional rocking ratchet are investigated via Langevin simulation. The results show that the average center-of-mass velocity is multi-peaks function of the frequency of the driving force. Furthermore, in the 2D coupled Brownian motor system there are the collective effect and ratchet behavior, which can switch depending on the frequency of driving force. It turns out that the cooperative effect between the interaction of coupled particles and external rocking driving force facilitates collective directional motion and energy conversion.

Wang, Hai-Yan; Bao, Jing-Dong

2013-10-01

383

Two dimensional frustrated magnets in high magnetic field  

NASA Astrophysics Data System (ADS)

Frustrated magnets in high magnetic field have a long history of offering beautiful surprises to the patient investigator. Here we present the results of extensive classical Monte Carlo simulations of a variety of models of two dimensional magnets in magnetic field, together with complementary spin wave analysis. Striking results include (i) a massively enhanced magnetocaloric effect in antiferromagnets bordering on ferromagnetic order, (ii) a route to an m = 1/3 magnetization plateau on a square lattice, and (iii) a cascade of phase transitions in a simple model of AgNiO2.

Seabra, L.; Shannon, N.; Sindzingre, P.; Momoi, T.; Schmidt, B.; Thalmeier, P.

2009-01-01

384

Dissipative vortex solitons in two-dimensional lattices  

SciTech Connect

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

Mejia-Cortes, C.; Soto-Crespo, J. M. [Instituto de Optica, Consejo Superior de Investigaciones Cientificas, Serrano 121, 28006 Madrid (Spain); Molina, Mario I.; Vicencio, Rodrigo A. [Departamento de Fisica, Facultad de Ciencias, Universidad de Chile, Casilla 653, Santiago (Chile); Center for Optics and Photonics, Universidad de Concepcion, Casilla 4016, Concepcion (Chile)

2010-12-15

385

Quasi-two-dimensional Turing patterns in an imposed gradient  

NASA Astrophysics Data System (ADS)

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

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

1992-11-01

386

Annihilation dynamics of two-dimensional magnetic vortex systems  

Microsoft Academic Search

We numerically study the pair-annihilation process of magnetic vortices in two-dimensional type-II superconductors. The dynamics\\u000a for interacting vortices is described in terms of the Langevin-type stochastic equation. Carrying out the Langevin dynamics\\u000a simulation, we find that the power-law behavior of the mean distance among vortices exhibits a crossover phenomenon as a function\\u000a of time t from the t\\u000a 1\\/2-law at

Y. Enomoto; R. Kato

387

Effect of diffusion on nucleation of two-dimensional nanoislands.  

PubMed

Effect of diffusion on the steady-state nucleation of two-dimensional nanoislands is described analytically. New approach takes self-consistently into account coupling between the kinetics of adatoms near the island edge, their diffusion on the surface and annihilation at other islands. It was shown that due to this coupling the nucleation barrier can considerably differ from that predicted by the thermodynamics and can depend on the diffusion parameters of adatoms. This effect can be used for controlling of the kinetics of nanoisland nucleation. PMID:16383613

Sorokin, M V; Volkov, A E

2005-11-30

388

Elastic Behavior of a Two-Dimensional Crystal Near Melting  

NASA Astrophysics Data System (ADS)

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

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

2004-12-01

389

Beam shaping using genetically optimized two-dimensional photonic crystals  

NASA Astrophysics Data System (ADS)

We propose the use of two-dimensional photonic crystals with engineered defects for the generation of an arbitrary-profile beam from a focused input beam. The cylindrical harmonics expansion of complex-source beams is derived and used to compute the scattered wavefunction of a 2D photonic crystal via the multiple scattering method. The beam shaping problem is then solved using a genetic algorithm. We illustrate our procedure by generating different orders of Hermite-Gauss profiles, while maintaining reasonable losses and tolerance to variations in the input beam and the slab refractive index.

Gagnon, Denis; Dumont, Joey; Dubé, Louis J.

2012-12-01

390

Two-dimensional self-assembly in diblock copolymers.  

PubMed

Diblock copolymers confined to a two-dimensional surface may produce uniform features of macromolecular dimensions (approximately 10-100 nm). We present a mathematical model for nanoscale pattern formation in such polymers that captures the dynamic evolution of a solution of poly(styrene)-b-poly(ethylene oxide), PS-b-PEO, in solvent at an air-water interface. The model has no fitting parameters and incorporates the effects of surface tension gradients, entanglement or vitrification, and diffusion. The resultant morphologies are quantitatively compared with experimental data. PMID:16090772

Hosoi, A E; Kogan, Dmitriy; Devereaux, C E; Bernoff, Andrew J; Baker, S M

2005-07-12

391

Disordered two-dimensional electron systems with chiral symmetry  

NASA Astrophysics Data System (ADS)

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

Markoš, P.; Schweitzer, L.

2012-10-01

392

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

393

Glassy behavior of two-dimensional stripe-forming systems.  

PubMed

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. PMID:23848641

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

2013-06-17

394

Two-dimensional simulations of magnetically-driven instabilities  

SciTech Connect

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

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

1986-01-01

395

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

396

Lagrangian statistics in forced two-dimensional turbulence.  

PubMed

We report on simulations of two-dimensional turbulence in the inverse energy cascade regime. Focusing on the statistics of Lagrangian tracer particles, scaling behavior of the probability density functions of velocity fluctuations is investigated. The results are compared to the three-dimensional case. In particular an analysis in terms of compensated cumulants reveals the transition from a strong non-Gaussian behavior with large tails to Gaussianity. The reported computation of correlation functions for the acceleration components sheds light on the underlying dynamics of the tracer particles. PMID:18851157

Kamps, O; Friedrich, R

2008-09-23

397

Two-dimensional metamagnet composed of a cesium copper octacyanotungstate  

Microsoft Academic Search

X-ray crystal structural analysis indicates that a cyano-bridged Cu–W bimetallic assembly, CsICuII[WV(CN)8]·0.5H2O, consists of a two-dimensional (2D) double-layered structure, where CsI penetrates between the anionic double-layers. This compound exhibits spontaneous magnetization below a magnetic critical temperature of 40K and metamagnetic behaviors such as an anomalous magnetization drop below 30K and a spin–flip transition at 90Oe. Calculations based on a magnetic

Souhei Kaneko; Yoshihide Tsunobuchi; Shunsuke Sakurai; Shin-ichi Ohkoshi

2007-01-01

398

Strictly localized states on a two-dimensional Penrose lattice  

NASA Astrophysics Data System (ADS)

Infinitely degenerate states at an energy E=0 on a two-dimensional Penrose lattice are investigated in a tight-binding model where atomic orbitals are located at vertices of rhombuses. The states with E=0 are all strictly localized and have amplitudes only on some specific vertices, which are three-edge vertices and some non-three-edge vertices. A lower bound on the fraction of them is calculated analytically as -50?+81~=9.83×10-2 [?=(?5 +1)/2], which is conjectured to be the exact fraction.

Arai, Masao; Tokihiro, Tetsuji; Fujiwara, Takeo; Kohmoto, Mahito

1988-07-01

399

Exciton-Polariton Gap Solitons in Two-Dimensional Lattices  

NASA Astrophysics Data System (ADS)

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.

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

2013-10-01

400

Two-dimensional manifolds with metrics of revolution  

SciTech Connect

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

Sabitov, I Kh [M.V. Lomonosov Moscow State University, Moscow (Russian Federation)

2000-10-31

401

Electromigration-Induced Breakup of Two-Dimensional Voids  

NASA Astrophysics Data System (ADS)

The motion and shape evolution of a void in a two-dimensional current carrying conductor is studied numerically. A circular void is linearly stable, but becomes unstable beyond a finite threshold deformation amplitude which decreases with increasing void radius. If the void is initially elongated along the current direction it expels small, stable daughter voids, while for elongations perpendicular to the current an invagination occurs which splits the void in two. The behavior near threshold is linked to the non-normality of the eigenmodes of the linearized problem. Perfectly circular voids can also be destabilized by their mutual long-ranged electromagnetic interaction.

Schimschak, M.; Krug, J.

1998-02-01

402

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

403

Focused two-dimensional antiscatter grid for mammography.  

SciTech Connect

We are developing freestanding high-aspect-ratio, focused, two-dimensional antiscatter grids for mammography using deep x-ray lithography and copper electroforming. The exposure is performed using x-rays from bending magnet beamline 2-BM at the Advanced Photon Source (APS) of Argonne National Laboratory. A 2.8-mm-thick prototype freestanding copper antiscatter grid with 25 {micro}m-wide parallel cell walls and 550 {micro}m periodicity has been fabricated. The progress in developing a dynamic double-exposure technique to create the grid with the cell walls aligned to a point x-ray source of the mammography system is discussed.

Makarova, O. V.; Moldovan, N.; Tang, C.-M.; Mancini, D. C.; Divan, R.; Zyryanov, V. N.; Ryding, D. C.; Yaeger, J.; Liu, C.; Creatv MicroTech Inc.

2002-09-01

404

Diffusion in Two-dimensional Magnetized Dusty Plasmas  

NASA Astrophysics Data System (ADS)

A molecular dynamical simulation method is used to investigate the diffusion of the two-dimensional magnetized dusty plasmas. The effects of charge and mass of the particles, as well as the external magnetic field are discussed in detail. It is shown that, relative to the mass of particulate, the charge and magnetic field have a more considerable effect on the diffusion process, particularly on the resulting structure of the system. The dependence of diffusion coefficient on the temperature is shown to be linearly changed over a wide range of temperature.

Kong, Wei; Yang, Fang

2013-09-01

405

Static polarizability of two-dimensional hole gases  

NASA Astrophysics Data System (ADS)

We have calculated the density-density (Lindhard) response function of a homogeneous two-dimensional (2D) hole gas in the static (?=0) limit. The bulk valence-band structure comprising heavy-hole (HH) and light-hole (LH) states is modeled using Luttinger's k p approach within the axial approximation. We elucidate how, in contrast to the case of conduction electrons, the Lindhard function of 2D holes exhibits unique features associated with (i) the confinement-induced HH-LH energy splitting and (ii) the HH-LH mixing arising from the charge carriers' in-plane motion. Implications for the dielectric response and related physical observables are discussed.

Kernreiter, Thomas; Governale, Michele; Zülicke, Ulrich

2010-09-01

406

Drift modes of a quasi-two-dimensional current sheet  

SciTech Connect

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

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

2012-03-15

407

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

408

Aerodynamics of two-dimensional slotted bluff bodies  

SciTech Connect

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

Takahashi, F.; Higuchi, H.

1988-04-30

409

A simple two-dimensional model for particle segregation  

NASA Astrophysics Data System (ADS)

A simple two-dimensional model for the segregation of particles of different sizes is described. In this model particles are added, one at a time, at the same lateral position to a growing heap of particles. Segregation occurs because large particles can roll more easily over small particles than small particles can roll over large ones. The dependence of the extent of segregation on particle size ratio and the fraction of small particles is explored for binary systems. The degree of segregation is found to increase rapidly as the fraction of large particles is increased and as the particle-size ratio deviates from 1.

Meakin, Paul

1990-03-01

410

Clusterization in Two-Dimensional System of Hard Spheres  

NASA Astrophysics Data System (ADS)

A clusterization process in two-dimensional system of granular hard disks is investigated by two novel numerical methods: the nearest neighbourhood density and the anti-percolation function. The tendency of the band like structures in the clustered state is recognized to be driven by two factors: the stretching forces at the junction of two clusters (or two parts of one cluster) with different kinetic energies and the density fluctuations, which act as a seed for the empty ponds (voids free of particles). Moreover, the examples (and animations) of the collision of two clusters and the breakup of the granular band are presented.

Chrzanowska, A.; Traczuk, G.; Fornal, P.

2008-01-01

411

Comprehensive two-dimensional gas chromatography in metabolomics.  

PubMed

One of the major objectives in metabolomics is the identification of subtle changes in metabolite profiles as affected by genetic or environmental factors. Comprehensive two-dimensional gas chromatography (GC × GC) hyphenated to a fast-acquisition mass spectrometer is a well-established analytical technique to study the composition of complex samples due to its enhanced separation capacity, sensitivity, peak resolution, and reproducibility. This review reports applications of GC × GC to metabolomics studies of sample of different types (biofluid, cells, tissue, bacteria, yeast, plants), and discusses its advantages and limitations. PMID:22249417

Almstetter, Martin F; Oefner, Peter J; Dettmer, Katja

2012-01-17

412

Two-dimensional dose distribution of 125I seeds.  

PubMed

Two-dimensional dose distribution has been measured for the new (model 6711) 125I seeds used in interstitial implants. Two independent methods, using a silicon diode or thermoluminescent dosimeters, yielded identical results. At any given distance r from the seed center, the dose varies with theta, the angle relative to the seed's axis. Similarly, the r dependence of the dose distribution is different at various theta values. These observations can be qualitatively understood in terms of several factors, namely, source encapsulation, geometrical relationship, and attenuation and scatter. Empirical expressions which approximate the measured results have been developed to facilitate clinical dose distribution calculations. PMID:4047002

Ling, C C; Schell, M C; Yorke, E D; Palos, B B; Kubiatowicz, D O

413

Two-dimensional dose distribution of /sup 125/I seeds  

SciTech Connect

Two-dimensional dose distribution has been measured for the new (model 6711) /sup 125/I seeds used in interstitial implants. Two independent methods, using a silicon diode or thermoluminescent dosimeters, yielded identical results. At any given distance r from the seed center, the dose varies with theta, the angle relative to the seed's axis. Similarly, the r dependence of the dose distribution is different at various theta values. These observations can be qualitatively understood in terms of several factors, namely, source encapsulation, geometrical relationship, and attenuation and scatter. Empirical expressions which approximate the measured results have been developed to facilitate clinical dose distribution calculations.

Ling, C.C.; Schell, M.C.; Yorke, E.D.; Palos, B.B.; Kubiatowicz, D.O.

1985-09-01

414

Human muscle proteins: analysis by two-dimensional electrophoresis  

SciTech Connect

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

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

1983-09-01

415

Superfluidity in two-dimensional imbalanced Fermi gases  

NASA Astrophysics Data System (ADS)

We study the zero temperature ground state of a two-dimensional atomic Fermi gas with chemical potential and population imbalance in the mean-field approximation. All calculations are performed in terms of the two-body binding energy ?B, whose variation allows one to investigate the evolution from the BEC to the BCS regimes. By means of analytical and exact expressions we show that, similarly to what is found in three dimensions, at fixed chemical potentials, BCS is the ground state until the critical imbalance hc, after which there is a first-order phase transition to the normal state. We find that hc, the Chandrasekhar-Clogston limit of superfluidity, has the same value as in three-dimensional systems. We show that for a fixed ratio ?B/?F, where ?F is the two-dimensional Fermi energy, as the density imbalance m is increased from zero, the ground state evolves from BCS to phase separation to the normal state. At the critical imbalance mc, phase separation is not supported and the normal phase is energetically preferable. The BCS-BEC crossover is discussed in balanced and imbalanced configurations. Possible pictures of what may be found experimentally in these systems are also shown. We also investigate the necessary conditions for the existence of bound states in the balanced and imbalanced normal phase.

Caldas, Heron; Mota, A. L.; Farias, R. L. S.; Souza, L. A.

2012-10-01

416

Continuous compression waves in the two-dimensional Riemann problem  

NASA Astrophysics Data System (ADS)

The interaction between a plane shock wave in a plate and a wedge is considered within the framework of the nondissipative compressible fluid dynamic equations. The wedge is filled with a material that may differ from that of the plate. Based on the numerical solution of the original equations, self-similar solutions are obtained for several versions of the problem with an iron plate and a wedge filled with aluminum and for the interaction of a shock wave in air with a rigid wedge. The behavior of the solids at high pressures is approximately described by a two-term equation of state. In all the problems, a two-dimensional continuous compression wave develops as a wave reflected from the wedge or as a wave adjacent to the reflected shock. In contrast to a gradient catastrophe typical of one-dimensional continuous compression waves, the spatial gradient of a two-dimensional compression wave decreases over time due to the self-similarity of the solution. It is conjectured that a phenomenon opposite to the gradient catastrophe can occur in an actual flow with dissipative processes like viscosity and heat conduction. Specifically, an initial shock wave is transformed over time into a continuous compression wave of the same amplitude.

Charakhch'yan, A. A.

2009-10-01

417

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

418

Face recognition using two-dimensional nonnegative principal component analysis  

NASA Astrophysics Data System (ADS)

Although two-dimensional principal component analysis (2DPCA) extracts image features directly from 2D image matrices rather than one dimensional vectors, 2DPCA is only based on the whole images to preserve total variances by maximizing the trace of feature covariance matrix. Thus, 2DPCA cannot extract localized components, which are usually important for face recognition. Inspired by nonnegative matrix factorization (NMF), which is based on localized features, we propose a novel algorithm for face recognition called two-dimensional nonnegative principal component analysis (2DNPCA) to extract localized components and maintain the maximal variance property of 2DPCA. 2DNPCA is a matrix-based algorithm to preserve the local structure of facial images and has the nonnegative constraint to learn localized components. Therefore, 2DNPCA has both advantages of 2DPCA and NMF. Furthermore, 2DNPCA solves the time-consuming problem by removing the restriction of minimizing the cost function and extracting only the base matrix. The nearest neighbor (NN) classifier and linear regression (LR) classifier are used for classification and extensive experimental results show that 2DNPCA plus NN and 2DNPCA plus LR are both very efficient approaches for face recognition.

Ma, Peng; Yang, Dan; Ge, Yongxin; Zhang, Xiaohong; Qu, Ying

2012-07-01

419

Phonons in two-dimensional soft colloidal crystals.  

PubMed

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. PMID:24032840

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

2013-08-26

420

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

421

Two-dimensional analytic theory for toroidal Alfven eigenmodes  

SciTech Connect

A two-dimensional analysis of the toroidal Alfven eigenmodes (TAE) is presented, based on an integrodifferential equation describing the shear Alfven perturbation of a toroidal plasma equilibrium in terms of coupling among the toroidal Alfven continua with the usual gap structure. Using a method similar to the Van Kampen--Case analysis for the Vlasov equation, exact analytic expressions are derived for the dispersion function and the two-dimensional eigenmode structure. The dispersion function is expressed in terms of Cauchy-type integrals, which explicitly expresses the global character of TAE modes and facilitates the calculation of their damping. The continuum-damped TAE modes are shown to be, in general, not true eigenmodes of the toroidal plasma equilibrium, but rather resonances corresponding to zeros of the analytic continuation of the dispersion function onto unphysical sheets of its Riemann surface. Approximate but explicit expressions for the dispersion relation and the eigenfunction are also obtained in the limit of vanishing inverse aspect ratio.

Ye, H.; Sedlacek, Z.; Mahajan, S.M. (Institute for Fusion Studies, The University of Texas at Austin, Austin, Texas 78712 (United States))

1993-08-01

422

Emergent Metal in Disordered Two Dimensional Mott Insulator  

NASA Astrophysics Data System (ADS)

We show that disordering a two dimensional Mott insulator leads to an insulator-metal transition, even in the absence of any doping. For disorder strengths comparable to the interaction, the Mott gap closes and extended states develop at the chemical potential. Further increase in disorder drives the emergent metal into a gapless localized insulating phase. We make detailed comparisons of our theoretical predictions on the emergent metal with transport and APRES data on 1T-TaS2 intercalated by Cu. The parent compound 1T-TaS2 is a Mott insulator at low temperature (T<180K). In the commensurate charge density wave (CCDW) phase, the ``star of David'' unit cells with 13 Ta atoms form a commensurate triangular lattice with a single half filled band crossing the Fermi energy. Strong interaction produces a Mott gap in the half filled band. Disorder introduced by intercalating Cu atoms between TaS2 layers closes the Mott gap and drives the material into a metallic phase without destroying the CCDW order in good agreement with theory. Our work presents the first evidence of such an insulator-metal transition in a disordered two-dimensional Mott insulator.

Nganba Meetei, Oinam; Trivedi, Nandini; Lahoud, Elias; Kanigel, Amit

2013-03-01

423

Modeling two-dimensional detonations with detonation shock dynamics  

SciTech Connect

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

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

1988-01-01

424

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

425

Free vibration of two identical circular cylinders in staggered arrangement  

NASA Astrophysics Data System (ADS)

An investigation on flow-induced response characteristics of two identical circular cylinders in staggered arrangement is conducted in the fluid mechanics laboratory of Kitami Institute of Technology, Japan. Each cylinder was two-dimensional, spring mounted, and allowed to vibrate independently in the cross-flow direction. Measurements were conducted at stagger angle ? = 5°, 10°, 15°, 25°, 45° and 60°, L/D ranging from 0.1 to 3.2, with ?L/D = 0.1, where L is the gap width between the cylinders, and D is the diameter of a cylinder. At each position (?, L/D) of the cylinders, dependence of vibration-amplitude-to-diameter ratio a/D on reduced velocity Ur (= U?/(fnD)) is examined, where U? is the free-stream velocity and fn is the natural frequency of the cylinder. There are seven cylinder-response patterns, depending on whether vortex-excited and/or galloping vibrations of the cylinders are generated, in the range ? = 5°-60°, L/D = 0.1-3.2 and Ur = 1.5-26. Pattern I corresponds to no generation of vortex-excited or galloping vibration of either cylinder. In Pattern II the upstream cylinder does not experience vortex-excited or galloping vibration, but the downstream one experiences a galloping vibration. Pattern III involves both vortex-excited and galloping vibrations of the downstream cylinder and only galloping vibration of the upstream cylinder. Pattern IV is associated with generation of vortex-excited vibration of both cylinders at the same Ur range. Pattern V refers to the case where the downstream cylinder experiences vortex-excited vibration, but the upstream cylinder does not. Pattern VI is characterized by vortex-excited vibration of the downstream cylinder in two regimes of Ur, whereas that of the upstream cylinder occurs in one regime only. In Pattern VII the upstream and downstream cylinders experience vortex-excited vibration at two different Ur regimes, respectively. The L/D regime of the vibration patterns generated at each ? is identified.

Mahbub Alam, Md; Kim, Sangil

2009-06-01

426

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

2010-10-30

427

The three-dimensional wake of a cylinder undergoing a combination of translational and rotational oscillation in a quiescent fluid  

Microsoft Academic Search

Previous two-dimensional numerical studies have shown that a circular cylinder undergoing both oscillatory rotational and translational motions can generate thrust so that it will actually self-propel through a stationary fluid. Although a cylinder undergoing a single oscillation has been thoroughly studied, the combination of the two oscillations has not received much attention until now. The current research reported here extends

M. Nazarinia; D. Lo Jacono; M. C. Thompson; J. Sheridan

2009-01-01

428

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

429

A solution-adaptive lattice Boltzmann method for two-dimensional incompressible viscous flows  

NASA Astrophysics Data System (ADS)

A stencil adaptive lattice Boltzmann method (LBM) is developed in this paper. It incorporates the stencil adaptive algorithm developed by Ding and Shu [26] for the solution of Navier-Stokes (N-S) equations into the LBM calculation. Based on the uniform mesh, the stencil adaptive algorithm refines the mesh by two types of 5-points symmetric stencils, which are used in an alternating sequence for increased refinement levels. The two types of symmetric stencils can be easily combined to form a 9-points symmetric structure. Using the one-dimensional second-order interpolation recently developed by Wu and Shu [27] along the straight line and the D2Q9 model, the adaptive LBM calculation can be effectively carried out. Note that the interpolation coefficients are only related to the lattice velocity and stencil size. Hence, the simplicity of LBM is not broken down and the accuracy is maintained. Due to the use of adaptive technique, much less mesh points are required in the simulation as compared to the standard LBM. As a consequence, the computational efficiency is greatly enhanced. The numerical simulation of two dimensional lid-driven cavity flows is carried out. Accurate results and improved efficiency are reached. In addition, the steady and unsteady flows over a circular cylinder are simulated to demonstrate the capability of proposed method for handling problems with curved boundaries. The obtained results compare well with data in the literature.

Wu, J.; Shu, C.

2011-03-01

430

Two-dimensional thermal convection in porous enclosure subjected to the horizontal seepage and gravity modulation  

NASA Astrophysics Data System (ADS)

Coupled effect of horizontal seepage and gravity modulation on the onset and nonlinear regimes of two-dimensional thermal buoyancy convection in horizontal fluid-saturated porous cylinder of rectangular cross section with perfectly conductive boundaries is studied. It is shown that gravity modulation makes destabilizing effect. Null-dimensional dynamical system describing supercritical convective regimes is derived. Conditions for existence of stable periodical regimes are defined. It is found that system demonstrates dynamics on a torus which can be either resonant or non-resonant depending on the parameters. Synchronization domains which correspond to the resonant torus existence in the parameter space are determined by the rotation number technique. It is found that at certain values of the ratio of the cross section height to width, degeneracy takes place. In this case different stable periodical regimes forming one-parametric family coexist. Linear stability and nonlinear dynamics of the system at finite values of the parameters are studied numerically by finite difference method.

Maryshev, Boris; Lyubimova, Tatyana; Lyubimov, Dmitriy

2013-08-01

431

Two-Dimensional Fractal Characteristics of the Martian Surface  

NASA Astrophysics Data System (ADS)

We present global maps of two-dimensional fractal statistics for Mars topography calculated by applying the two-dimensional Fourier spectral approach to MOLA altimetry measurements over spatial scales extending from approximately 450 meters to 15 kilometers. Three global maps were generated: 1) surface (two-dimensional) fractal dimension, 2) roughness amplitude at a scale of one kilometer, and 3) linear model fit error in the log-log relation of mean power spectral density to radial wavenumber. The linear model fit error is a convenient way to judge the appropriateness of the fractal model. Examination of the fractal dimension and model error maps reveals that a majority of the surface is well modeled by fractal geometry. This is evidenced by minimal systematic spatial variation in fractal dimension and low model fit errors, with the northern plains exhibiting slightly higher overall error than the cratered highlands. There are also several spatially coherent regions in the fractal dimension map that have enhanced values. These regions include Amazonis Planitia and southeast Elysium Planitia. On the other hand, Isidis Planitia and portions of the Olympus Mons aureole exhibit high model fit errors which imply a lower applicability of fractal geometry to these terrains. The one kilometer roughness amplitude map exhibits a tremendous amount of spatial detail and clearly delineates differing roughness terrains. The portions of Amazonis Planitia and southeast Elysium Planitia with enhanced fractal dimension have roughness amplitudes significantly below the global mean, while the Valles Marineris system, the circum-Argyre region, and the chaotic and heavily eroded terrains located along the crustal dichotomy boundary exhibit elevated roughness values. The Tharsis region is particularly rich in detail, displaying a wide range of spatially contiguous roughness provinces that are traceable to known surface units. Comparison of the roughness amplitude map to the MOLA pulse width-derived roughness data (75 meter baseline) reveals a strong correlation with a few notable exceptions. The circum-polar debris mantle located 30 to 45 degrees bilaterally from the equator and a small yet distinct terrain located northwest of Olympus Mons are both evident in the 75 m pulse width data but are not expressed in the longer wavelength roughness amplitude map. This implies that the surface processes responsible for producing these terrains are dominant only at shorter length scales.

Seelos, F. P.; Deal, K. S.; Arvidson, R. E.; Neumann, G. A.

2003-12-01

432

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

433

Two-dimensional numerical modeling of the Rheasilvia impact formation  

NASA Astrophysics Data System (ADS)

We numerically modeled the formation of Rheasilvia crater, an enormous impact basin centered on asteroid 4 Vesta's south pole. Using a trial and error method, our models were adjusted to produce the best possible fit to Rheasilvia's size and shape, as observed during the Vesta orbital stage of the Dawn mission. The final model yields estimates of the shock wave decay, escaped material volume, depth of excavation, and other relevant characteristics, to the extent allowed by the two-dimensional (axially symmetric) approximation of the Simplified Arbitrary Lagrangian Eulerian hydrocode. Our model results permit interpretation of the Dawn data on Vesta's shape, topographic crater profiles, and the origin of the Vestoid asteroid family as escaped ejecta from the Rheasilvia crater.

Ivanov, B. A.; Melosh, H. J.

2013-07-01

434

Current fluctuations in a two dimensional model of heat conduction  

NASA Astrophysics Data System (ADS)

In this work we study numerically and analytically current fluctuations in the two-dimensional Kipnis-Marchioro-Presutti (KMP) model of heat conduction. For that purpose, we use a recently introduced algorithm which allows the direct evaluation of large deviations functions. We compare our results with predictions based on the Hydrodynamic Fluctuation Theory (HFT) of Bertini and coworkers, finding very good agreement in a wide interval of current fluctuations. We also verify the existence of a well-defined temperature profile associated to a given current fluctuation which depends exclusively on the magnitude of the current vector, not on its orientation. This confirms the recently introduced Isometric Fluctuation Relation (IFR), which results from the time-reversibility of the dynamics, and includes as a particular instance the Gallavotti-Cohen fluctuation theorem in this context but adds a completely new perspective on the high level of symmetry imposed by timereversibility on the statistics of nonequilibrium fluctuations.

Pérez-Espigares, Carlos; Garrido, Pedro L.; Hurtado, Pablo I.

2011-03-01

435

Two-dimensional angular transmission characterization of CPV modules.  

PubMed

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

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

2010-11-01

436

Exploring the Thermodynamics of a Two-Dimensional Bose Gas  

SciTech Connect

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

Yefsah, Tarik; Desbuquois, Remi; Chomaz, Lauriane; Guenter, Kenneth J.; Dalibard, Jean [Laboratoire Kastler Brossel, CNRS, UPMC, Ecole Normale Superieure, 24 rue Lhomond, F-75005 Paris (France)

2011-09-23

437

Creating an Artificial Two-Dimensional Skyrmion Crystal by Nanopatterning  

NASA Astrophysics Data System (ADS)

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

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

2013-04-01

438

Creating an artificial two-dimensional Skyrmion crystal by nanopatterning.  

PubMed

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

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

2013-04-19

439

Reconnection events in two-dimensional Hall magnetohydrodynamic turbulence  

SciTech Connect

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

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

2012-09-15

440

Statistics of magnetic reconnection in two-dimensional magnetohydrodynamic turbulence  

SciTech Connect

The nonlinear dynamics of magnetic reconnection in turbulence is investigated through direct numerical simulations of decaying, incompressible, two-dimensional magnetohydrodynamics. Recently, it was shown by Servidio et al. [Phys. Rev. Lett. 102, 115003 (2009)] that in fully developed turbulence complex processes of reconnection occur locally. Here, the main statistical features of these multiscale reconnection events are further described, providing details on the methodology. It is found that is possible to describe the reconnection process in turbulence as a generalized local Sweet-Parker process in which the parameters are locally controlled by the turbulence cascade, thus providing a step toward reconciling classical turbulence analysis with reconnection theory. This general description of reconnection may be useful for laboratory and space plasmas, where the presence of turbulence plays a crucial role.

Servidio, S. [Department of Physics and Astronomy and Bartol Research Institute, University of Delaware, Newark, Delaware 19716 (United States); Dipartimento di Fisica, Universita della Calabria, Cosenza I-87036 (Italy); Matthaeus, W. H.; Shay, M. A.; Wan, M. [Department of Physics and Astronomy and Bartol Research Institute, University of Delaware, Newark, Delaware 19716 (United States); Dmitruk, P. [Departamento de Fisica, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Ciudad Universitaria, Buenos Aires 1428 (Argentina); Cassak, P. A. [Department of Physics, West Virginia University, Morgantown, West Virginia 26506 (United States)

2010-03-15

441

Topological states in two-dimensional optical lattices  

SciTech Connect

We present a general analysis of two-dimensional optical lattice models that give rise to topologically nontrivial insulating states. We identify the main ingredients of the lattice models that are responsible for the nontrivial topological character and argue that such states can be realized within a large family of realistic optical lattice Hamiltonians with cold atoms. We focus our quantitative analysis on the properties of topological states with broken time-reversal symmetry specific to cold-atom settings. In particular, we analyze finite-size effects, multiorbital phenomena that give rise to a variety of distinct topological states and transitions between them, the dependence on the trap geometry, and, most importantly, the behavior of the edge states for different types of soft and hard boundaries. Furthermore, we demonstrate the possibility of experimentally detecting the topological states through light Bragg scattering of the edge and bulk states.

Stanescu, Tudor D. [Condensed Matter Theory Center and Joint Quantum Institute, Department of Physics, University of Maryland, College Park, Maryland 20742-4111 (United States); Department of Physics, West Virginia University, Morgantown, West Virginia 26506 (United States); Galitski, Victor; Das Sarma, S. [Condensed Matter Theory Center and Joint Quantum Institute, Department of Physics, University of Maryland, College Park, Maryland 20742-4111 (United States)

2010-07-15

442

High-field transport in two-dimensional graphene  

NASA Astrophysics Data System (ADS)

Transport of carriers in two-dimensional graphene at high electric fields is investigated by combining semianalytical and Monte Carlo methods. A semianalytical high-field transport model based on the high rate of optical phonon emission provides useful estimates of the saturation currents in graphene. For developing a more accurate picture, the nonequilibrium (hot) phonon effect and the role of electron-electron scattering were studied using Monte Carlo simulations. Monte Carlo simulations indicate that the hot phonon effect plays a dominant role in current saturation, and electron-electron scattering strongly thermalizes the hot carrier population in graphene. We also find that electron-electron scattering removes negative differential resistance in graphene. Transient phenomenon such as velocity overshoot can be used to speed up graphene-based high-speed electronic devices by shrinking the channel length below 80 nm if electrostatic control can be exercised in the absence of a band gap.

Fang, Tian; Konar, Aniruddha; Xing, Huili; Jena, Debdeep

2011-09-01

443

Lifshitz Transition in the Two Dimensional Hubbard Model  

NASA Astrophysics Data System (ADS)

Using large-scale dynamical cluster quantum Monte Carlo simulations, we study the Lifshitz transition of the two dimensional Hubbard model with next-nearest-neighbor hopping (t'), chemical potential and temperature as control parameters. At t'<=0, we identify a line of Lifshitz transition points associated with a change of the Fermi surface topology at zero temperature. In the overdoped region, the Fermi surface is complete and electron-like; across the Lifshitz transition, the Fermi surface becomes hole-like and develops a pseudogap. At (or very close to) the Lifshitz transition points, a van Hove singularity in the density of states crosses the Fermi level. The van Hove singularity occurs at finite doping due to correlation effects, and becomes more singular when t' becomes more negative. The resulting temperature dependence on the bare d-wave pairing susceptibility close to the Lifshitz points is significantly different from that found in the traditional van Hove scenarios.

Chen, Kuang-Shing; Meng, Ziyang; Pruschke, Thomas; Moreno, Juana; Jarrell, Mark

2013-03-01

444

Two dimensional radiated power diagnostics on Alcator C-Mod.  

PubMed

The radiated power diagnostics for the Alcator C-Mod tokamak have been upgraded to measure two dimensional structure of the photon emissivity profile in order to investigate poloidal asymmetries in the core radiation. Commonly utilized unbiased absolute extreme ultraviolet (AXUV) diode arrays view the plasma along five different horizontal planes. The layout of the diagnostic set is shown and the results from calibrations and recent experiments are discussed. Data showing a significant, 30%-40%, inboard/outboard emissivity asymmetry during ELM-free H-mode are presented. The ability to use AXUV diode arrays to measure absolute radiated power is explored by comparing diode and resistive bolometer-based emissivity profiles for highly radiative L-mode plasmas seeded with argon. Emissivity profiles match in the core but disagree radially outward resulting in an underprediction of P(rad) of nearly 50% by the diodes compared to P(rad) determined using resistive bolometers. PMID:19044619

Reinke, M L; Hutchinson, I H

2008-10-01

445

Two-dimensional movement control using electrocorticographic signals in humans  

NASA Astrophysics Data System (ADS)

We show here that a brain-computer interface (BCI) using electrocorticographic activity (ECoG) and imagined or overt motor tasks enables humans to control a computer cursor in two dimensions. Over a brief training period of 12-36 min, each of five human subjects acquired substantial control of particular ECoG features recorded from several locations over the same hemisphere, and achieved average success rates of 53-73% in a two-dimensional four-target center-out task in which chance accuracy was 25%. Our results support the expectation that ECoG-based BCIs can combine high performance with technical and clinical practicality, and also indicate promising directions for further research.

Schalk, G.; Miller, K. J.; Anderson, N. R.; Wilson, J. A.; Smyth, M. D.; Ojemann, J. G.; Moran, D. W.; Wolpaw, J. R.; Leuthardt, E. C.

2008-03-01

446

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

447

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

448

Regional statistics in confined two-dimensional decaying turbulence.  

PubMed

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

Házi, Gábor; Tóth, Gábor

2011-06-28

449

Decaying two-dimensional turbulence in a circular container.  

PubMed

We present direct numerical simulations of two-dimensional decaying turbulence at initial Reynolds number 5 x 10(4) in a circular container with no-slip boundary conditions. Starting with random initial conditions the flow rapidly exhibits self-organization into coherent vortices. We study their formation and the role of the viscous boundary layer on the production and decay of integral quantities. The no-slip wall produces vortices which are injected into the bulk flow and tend to compensate the enstrophy dissipation. The self-organization of the flow is reflected by the transition of the initially Gaussian vorticity probability density function (PDF) towards a distribution with exponential tails. Because of the presence of coherent vortices the pressure PDF become strongly skewed with exponential tails for negative values. PMID:16384384

Schneider, Kai; Farge, Marie

2005-12-08

450

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

451

Nonlinear compressional waves in a two-dimensional Yukawa lattice.  

PubMed

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

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

2003-10-08

452

Monte Carlo simulation of the two-dimensional planar model  

SciTech Connect

The authors present results for the two-dimensional planar model on the square lattice. They have developed a Monte Carlo routine which is more efficient than the single-spin-flip algorithms used previously. They report on the variation of the following quantities with temperature: specific heat, energy, magnetization, susceptibility, correlation function, helicity modulus, the density of vortex/antivortex pairs, the average distance between a vortex and its nearest antivortex, and the average distance between a vortex/antivortex pair and the nearest pair. The results are in excellent agreement with the reliable results reported in the literature and are in accord with the general features of the Kosterlitz-Thouless theory.

Bowen, C.; Hunter, D.L.; Jan, N. (St. Francis Xavier Univ., Antigonish, Nova Scotia (Canada))

1992-12-01

453

Holographic entanglement entropy for excited states in two dimensional CFT  

NASA Astrophysics Data System (ADS)

We use holographic methods to study the entanglement entropy for excited states in a two dimensional conformal field theory. The entangling area is a single interval and the excitations are produced by in and out vertex operators with given scaling dimensions. On the gravity side we provide the excitations by turning on a scalar field with an appropriate mass. The calculation amounts to using the gravitational background, with a singular boundary, to find the one point function of the vertex operators. The singular boundary is taken care of by introducing a nontrivial UV regulator surface to calculate gravitational partition functions. By means of holographic methods we reproduce the field theory results for primary excitations.

Astaneh, Amin Faraji; Mosaffa, Amir Esmaeil

2013-03-01

454

Two-dimensional crystal growth from undersaturated solutions.  

PubMed

The solubility of a substance is commonly understood as the minimum concentration necessary for the condensation of a solid phase from solution. Here we report the nucleation and growth of ionic compounds from aqueous concentrations on the order of 0.1 times the solubility. The condensation is catalyzed by a foreign substrate, and the new phase grows as a crystalline monolayer. Undersaturated growth is observed only in cases where the dissolved compound is isomorphic with the substrate and the interaction strength between a dissolved-ion/substrate-ion pair exceeds that between the two dissolved ions. These results are consistent with a simple model in which favorable ion-surface interactions lead to ion enrichment and supersaturation in the two-dimensional interfacial zone. PMID:17455964

Murdaugh, Anne E; Liddelow, Mary; Schmidt, Anneliese M; Manne, Srinivas

2007-04-25

455

Pairing Correlations in the Two-Dimensional Hubbard Model  

SciTech Connect

We present the results of a quantum Monte Carlo study of the extended s and the d{sub x{sup 2}-y{sup 2}} pairing correlation functions for the two-dimensional Hubbard model, computed with the constrained-path Monte Carlo method. For small lattice sizes and weak interactions, we find that the d{sub x{sup 2}-y{sup 2}} pairing correlations are stronger than the extended s pairing correlations and are positive when the pair separation exceeds several lattice constants. As the system size or the interaction strength increases, the magnitude of the long-range part of both correlation functions vanishes. {copyright} {ital 1997} {ital The American Physical Society}

Zhang, S. [Department of Physics, The Ohio State University, Columbus, Ohio 43210 (United States); Carlson, J.; Gubernatis, J.E. [Theoretical Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)

1997-06-01

456

Polariton condensation in an optically induced two-dimensional potential  

NASA Astrophysics Data System (ADS)

We demonstrate experimentally the condensation of exciton polaritons through optical trapping. The nonresonant pump profile is shaped into a ring and projected to a high quality factor microcavity where it forms a two-dimensional repulsive optical potential originating from the interactions of polaritons with the excitonic reservoir. Increasing the population of particles in the trap eventually leads to the emergence of a confined polariton condensate that is spatially decoupled from the decoherence inducing reservoir, before any buildup of coherence on the excitation region. In a reference experiment, where the trapping mechanism is switched off by changing the excitation intensity profile, polariton condensation takes place for excitation densities more than two times higher and the resulting condensate is subject to much stronger dephasing and depletion processes.

Askitopoulos, A.; Ohadi, H.; Kavokin, A. V.; Hatzopoulos, Z.; Savvidis, P. G.; Lagoudakis, P. G.

2013-07-01

457

Reentrant melting of a classical two-dimensional binary cluster  

SciTech Connect

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

Nelissen, K.; Partoens, B.; Peeters, F.M. [Universiteit antwerpen, Groenborgenlaan 171, 2020 Antwerpen (Belgium); Schweigert, I. [Institute of Semiconductor physics, Lavrentiev Avenue 13, Novosibirsk (Russian Federation)

2005-10-31

458

Two dimensional radiated power diagnostics on Alcator C-Mod  

SciTech Connect

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

Reinke, M. L.; Hutchinson, I. H. [Massachusetts Institute of Technology, 77 Massachusetts Avenue, NW17-225, Cambridge, Massachusetts 02139 (United States)

2008-10-15

459

Interferometric Diagnosis of Two-Dimensional Plasma Expansion  

NASA Astrophysics Data System (ADS)

Recent advances in interferometry has allowed for the characterization of the electron density expansion within a laser produced plasma to within 10 mum of the target surface and over picosecond timescales. This technique employs the high brightness output of the transient gain Ni-like Pd collisional x-ray laser at 14.7 nm to construct an effective moving picture of the two-dimensional (2-D) expansion within the plasma. In this paper we present experimentally measured density profiles from an Al plasma and make comparisons with 1.5-D and 2-D code simulations. The results are discussed along with an analysis of the underlying mechanisms driving the plasma expansion.

Smith, Raymond F.; Moon, Steven; Dunn, James; Nilsen, Joseph; Shlyaptsev, Vyacheslev N.; Hunter, James R.; Rocca, Jorge; Filevich, Jorge; Marconi, Mario C.

2002-11-01

460

Collective modes in two-dimensional binary Yukawa systems.  

PubMed

We analyze via theoretical approaches and molecular dynamics simulations the collective mode structure of strongly coupled two-dimensional binary Yukawa systems, for selected density, mass, and charge ratios, both in the liquid and crystalline solid phases. Theoretically, the liquid phase is described through the quasilocalized charge approximation (QLCA) approach, while in the crystalline phase we study the centered honeycomb and the staggered rectangular crystal structures through the standard harmonic phonon approximation. We identify "longitudinal" and "transverse" acoustic and optic modes and find that the longitudinal acoustic mode evolves from its weakly coupled counterpart in a discontinuous nonperturbative fashion. The low-frequency acoustic excitations are governed by the oscillation frequency of the average atom, while the high-frequency optic excitation frequencies are related to the Einstein frequencies of the systems. PMID:23679526

Kalman, Gabor J; Hartmann, Peter; Donkó, Zoltán; Golden, Kenneth I; Kyrkos, Stamatios

2013-04-12

461

Two-dimensional Fourier-transform spectroscopy of potassium vapor  

SciTech Connect

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

Dai, X.; Bristow, A. D.; Karaiskaj, D.; Cundiff, S. T. [JILA, University of Colorado and National Institute of Standards and Technology, Boulder, Colorado 80309-0440 (United States)

2010-11-15

462

Study of the robustness of two dimensional topological insulators  

NASA Astrophysics Data System (ADS)

Two dimensional topological insulators present gapless spin filtered edge states which are topologically protected against backscattering. As long as disorder does not mix the states of opposite edges or with bulk ones, these states contribute to the two terminal conductance as a single quantum channel regardless of the amount of non-magnetic disorder present in the sample. We address this problem studying the effect of different types of disorder: constrictions and Anderson disorder, for two different materials that have been predicted to present the quantum spin Hall insulator phase, graphene and a bilayer of Bi(111). We also study the effect of the zigzag edge reconstruction of graphene over the robust behavior of the edge states. We describe their electronic structure using an orthogonal tight-binding model in the Slater-Koster approximation including the intra-atomic spin-orbit interaction. The conductance is computed using the Landauer formula making use of the ALACANT transport package.

Gosalbez-Martinez, Daniel; Fernandez-Rossier, Joaquin; Palacios, Juan Jose

2012-02-01

463

Conditional convergence in two-dimensional dislocation dynamics  

NASA Astrophysics Data System (ADS)

For two-dimensional dislocation dynamics simulations under periodic boundary conditions in both directions, the summation of the periodic image stress fields is found to be conditionally convergent. For example, different stress fields are obtained depending on whether the summation in the x-direction is performed before or after the summation in the y-direction. This problem arises because the stress field of a 1D periodic array of dislocations does not necessarily go to zero far away from the dislocation array. The spurious stress fields caused by conditional convergence in the 2D sum are shown to consist of only a linear term and a constant term with no higher order terms. Absolute convergence, and hence self-consistency, is restored by subtracting the spurious stress fields, whose expressions are derived in both isotropic and anisotropic elasticity.

Kuykendall, William P.; Cai, Wei

2013-07-01

464

Two-dimensional freezing criteria for crystallizing colloidal monolayers  

SciTech Connect

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

Wang Ziren; Han Yilong [Department of Physics, Hong Kong University of Science and Technology, Clear Water Bay (Hong Kong); Alsayed, Ahmed M. [Department of Physics and Astronomy, University of Pennsylvania, 209 South 33rd St., Philadelphia, Pennsylvania 19104 (United States); Complex Assemblies of Soft Matter, CNRS/UPENN/Rhodia UMI 3254, Bristol, Pennsylvania 19007 (United States); Yodh, Arjun G. [Department of Physics and Astronomy, University of Pennsylvania, 209 South 33rd St., Philadelphia, Pennsylvania 19104 (United States)

2010-04-21

465

Bound States in a Quasi-Two-Dimensional Fermi Gas  

NASA Astrophysics Data System (ADS)

We consider the problem of N identical fermions of mass m? and one distinguishable particle of mass m? interacting via short-range interactions in a confined quasi-two-dimensional (quasi-2D) geometry. For N=2 and mass ratios m?/m?<13.6, we find non-Efimov trimers that smoothly evolve from 2D to 3D. In the limit of strong 2D confinement, we show that the energy of the N+1 system can be approximated by an effective two-channel model. We use this approximation to solve the 3+1 problem and we find that a bound tetramer can exist for mass ratios m?/m? as low as 5 for strong confinement, thus providing the first example of a universal, non-Efimov tetramer involving three identical fermions.

Levinsen, Jesper; Parish, Meera M.

2013-02-01

466

Bifurcations in two-dimensional Rayleigh-Bénard convection  

NASA Astrophysics Data System (ADS)

Two-dimensional bouyancy-driven convection in a horizontal fluid layer with stress-free boundary conditions at top and bottom and periodic boundary conditions in the horizontal direction is investigated by means of numerical simulation and bifurcation-analysis techniques. As the bouyancy forces increase, the primary stationary and symmetric convection rolls undergo successive Hopf bifurcations, bifurcations to traveling waves, and phase lockings. We pay attention to symmetry breaking and its connection with the generation of large-scale horizontal flows. Calculations of Lyapunov exponents indicate that at a Rayleigh number of 2.3×105 no temporal chaos is reached yet, but the system moves nonchaotically on a 4-torus in phase space.

Zienicke, E.; Seehafer, N.; Feudel, F.

1998-01-01

467

Bond Order Solid of Two-Dimensional Dipolar Fermions  

NASA Astrophysics Data System (ADS)

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

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

2012-04-01

468

Formation of Current Sheets in Two-dimensional Geometry  

NASA Astrophysics Data System (ADS)

We present two examples of current sheets that form in a magnetic configuration when it is subjected to quasi-static motions at the footpoints. The entire system is two-dimensional. There are no preexisting X-points and the footpoint motions are continuous. The calculations are motivated by the hypothesis of Parker that quasi-static deformations of MHD equilibria are generally accompanied by the formation of current sheets. The results demonstrate that three dimensions are not a necessary condition for current sheet formation. In addition, the calculation of Van Ballegooijen is not contradicted, because the initial magnetic field in our case is not dominantly collinear. Possible applications to the solar corona are discussed.

Scheper, R. A.; Hassam, A. B.

1998-11-01

469

Two features at the two-dimensional freezing transitions.  

PubMed

We studied the two-dimensional freezing transitions in monolayers of microgel colloidal spheres with short-ranged repulsions in video-microscopy experiments, and monolayers of hard disks, and Yukawa particles in simulations. These systems share two common features at the freezing points: (1) the bimodal distribution profile of the local orientational order parameter; (2) the two-body excess entropy, s(2), reaches -4.5±0.5?k(B). Both features are robust and sensitive to the freezing points, so that they can potentially serve as empirical freezing criteria in two dimensions. Compared with the conventional freezing criteria, the first feature has no finite-size ambiguities and can be resolved adequately with much less statistics; and the second feature can be directly measured in macroscopic experiments without the need for microscopic information. PMID:21261367

Wang, Ziren; Qi, Weikai; Peng, Yi; Alsayed, Ahmed M; Chen, Yong; Tong, Penger; Han, Yilong

2011-01-21

470

Statistical thermodynamics of a two-dimensional relativistic gas  

NASA Astrophysics Data System (ADS)

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 velocity in the rest frame (?) as well as the moving frame (?') . Our results confirm that Jüttner distribution is the correct generalization of Maxwell-Boltzmann distribution. We obtain the same “temperature” parameter ? for both frames consistent with a recent study of a limited one-dimensional model. We also address the controversial topic of temperature transformation. We show that while local thermal equilibrium holds in the moving frame, relying on statistical methods such as distribution functions or equipartition theorem are ultimately inconclusive in deciding on a correct temperature transformation law (if any).

Montakhab, Afshin; Ghodrat, Malihe; Barati, Mahmood

2009-03-01

471

Comprehensive two-dimensional gas chromatography with fast enantioseparation.  

PubMed

The development of fast chiral analysis for use in comprehensive two-dimensional gas chromatography in which a short second dimension enantioselective capillary column provides a route to precise measurement of chiral ratios of enantiomers is described. Retention times as short as 8 s are reported for (+/-)-limonene, with adequate enantioseparation maintained (Rs approximately 1.0) on a 1-m cyclodextrin derivative-coated capillary column. Sufficiently fast elution on the second column was achieved by using GC/ MS in which the subambient pressure (vacuum outlet) conditions promote increased diffusion coefficients and higher component volatility; a 4-fold reduction of second-dimension retention time was observed, as compared with ambient pressure outlet conditions. The enantiomeric distribution of several monoterpene compounds in bergamot essential oil is reported as a demonstration of the method. Total analysis time of the target components was approximately 8.5 min. PMID:12403603

Shellie, Robert; Marriott, Philip J

2002-10-15

472

Magnetic reconnection in two-dimensional MHD turbulence  

NASA Astrophysics Data System (ADS)

The nonlinear dynamics of magnetic reconnection in broadband turbulence is investigated through direct numerical simulations of decaying, compressible and incompressible, two-dimensional magnetohydrodynamics (MHD). Complex processes of reconnection between magnetic islands (or magnetic vortices), of different size and field strengths, locally occur. Matching classical turbulence analysis with the Sweet-Parker theory, the main statistical features of these multi-scale reconnection events are identified. Locally, magnetic reconnection can be described through a steady state, asymmetric, Sweet-Parker model, in which parameters controlling reconnection rate are determined by the turbulence. Research supported in part by NASA (NNX07AR48G, NNG06GD47G, NNX08AI47G) and NSF (ATM0752135 ATM 0539995).

Servidio, S.; Matthaeus, W. H.; Cassak, P.; Shay, M.; Dmitruk, P.

2008-12-01

473

Turbulent two-dimensional magnetohydrodynamics and conformal field theory  

SciTech Connect

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

Rahimi Tabar, M.R.; Rouhani, S. [Department of Physics, Sharif University of Technology, P.O. Box 11365-9161, Tehran (Iran)]|[Institute for Studies in Theoretical Physics and Mathematics, P.O. Box 19395-5746, Tehran (Iran)

1996-03-01

474

Zero sound in a two-dimensional dipolar Fermi gas  

NASA Astrophysics Data System (ADS)

We study zero sound in a weakly interacting two-dimensional (2D) gas of single-component fermionic dipoles (polar molecules or atoms with a large magnetic moment) tilted with respect to the plane of their translational motion. It is shown that the propagation of zero sound is provided by both mean-field and many-body (beyond mean field) effects, and the anisotropy of the sound velocity is the same as the one of the Fermi velocity. The damping of zero sound modes can be much slower than that of quasiparticle excitations of the same energy. One thus has wide possibilities for the observation of zero sound modes in experiments with 2D fermionic dipoles, although the zero sound peak in the structure function is very close to the particle-hole continuum.

Lu, Zhen-Kai; Matveenko, S. I.; Shlyapnikov, G. V.

2013-09-01

475

Silicon two-dimensional phononic crystal resonators using alternate defects  

NASA Astrophysics Data System (ADS)

We present the numerical and experimental investigations of micromechanical resonators made by creating alternate defects with different central-hole radii (r') in a two-dimensional (2-D) phononic crystal (PnC) slab. The PnC structures were fabricated by etching a square array of cylindrical air holes in a 10 ?m thick free-standing silicon plate using a CMOS-compatible process. Preliminary experimental results show that the performance of the PnC resonators in terms of resonant frequency, Q factor, and insertion loss (IL) is highly dependent on r'. A Q factor of more than 3000 is achieved for the case of r' = 6 ?m while all the designed resonators with alternate defects have higher Q factor and lower IL than the resonators based on the normal Fabry-Perot structure due to the reduction in the mode mismatch.

Wang, Nan; Hsiao, Fu-Li; Palaniapan, Moorthi; Lee, Chengkuo

2011-12-01

476

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

477

High speed two-dimensional optical beam position detector.  

PubMed

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. PMID:21806187

Rutten, Paul Edmond

2011-07-01

478

Inelastic collisions in an ultracold quasi-two-dimensional gas  

SciTech Connect

We present a formalism for rigorous calculations of cross sections for inelastic and reactive collisions of ultracold atoms and molecules confined by laser fields in quasi-two-dimensional geometry. Our results show that the elastic-to-inelastic ratios of collision cross sections are enhanced in the presence of a laser confinement and that the threshold energy dependence of the collision cross sections can be tuned by varying the confinement strength and external magnetic fields. The enhancement of the elastic-to-inelastic ratios is inversely proportional to {radical}({epsilon}/({Dirac_h}/2{pi}){omega}{sub 0}), where {epsilon} is the kinetic energy and {omega}{sub 0} is the oscillation frequency of the trapped particles in the confinement potential.

Li, Z.; Krems, R. V. [Department of Chemistry, University of British Columbia, Vancouver, British Columbia, V6T 1Z1 (Canada)

2009-05-15

479

Discrete Holomorphicity at Two-Dimensional Critical Points  

NASA Astrophysics Data System (ADS)

After a brief review of the historical role of analyticity in the study of critical phenomena, an account is given of recent discoveries of discretely holomorphic observables in critical two-dimensional lattice models. These are objects whose correlation functions satisfy a discrete version of the Cauchy-Riemann relations. Their existence appears to have a deep relation with the integrability of the model, and they are presumably the lattice versions of the truly holomorphic observables appearing in the conformal field theory (CFT) describing the continuum limit. This hypothesis sheds light on the connection between CFT and integrability, and, if verified, can also be used to prove that the scaling limit of certain discrete curves in these models is described by Schramm-Loewner evolution (SLE).

Cardy, John

2009-12-01

480

Coupling between neighboring two-dimensional modes of water waves  

NASA Astrophysics Data System (ADS)

We consider two-dimensional waves in a rectangular container which is periodically excited along its length in the horizontal direction. In general a standing wave of odd mode number whose frequency is close to the forcing frequency is excited. However, we show in this paper that the neighboring even mode, though not directly excited, may be excited through an energy transfer from the odd mode. As a result, the wave response becomes superposition of two standing waves which are not in general in phase with each other. Consequently the mixed-mode wave motion is not standing waves but traveling waves. We employ a perturbation method to derive amplitude equations governing the dynamics of these two modes. Studies of the steady-state solutions and their stability lead to bifurcation diagrams showing the sequences of the events leading to the instability and the parameters for which the standing waves become unstable.

Feng, Z. C.

1998-09-01

481

Triple-spot proteins in two-dimensional gel electrophoresis.  

PubMed Central

A triple-spot pattern of polypeptides occurring in two-dimensional gel electrophoresis of proteins is described. The presence of a mutant protein, Pc 1 Duarte, which results in a splitting of all three polypeptides, is evidence that they are produced by the same gene. This pattern is seen in about 1% of the proteins from a variety of sources. Typically, about 50% of the protein occurs as a single major spot, the remainder occurring as two polypeptides with an additional negative charge and slightly different molecular weight. The reproducibility of this pattern implies a functional significance which is presently unknown. The implication of this configuration for patterns seen by one-dimensional gel electrophoresis is discussed. Images Fig. 1

Comings, D E; Peters, K E

1979-01-01

482

Two-dimensional gel electrophoretic method for mapping DNA replicons  

SciTech Connect

The authors describe in detail a method which allows determination of the directions of replication fork movement through segments of DNA for which cloned probes are available. The method uses two-dimensional neutral-alkaline agarose gel electrophoresis followed by hybridization with short probe sequences. The nascent strands of replicating molecules form an arc separated from parental and nonreplicating strands. The closer a probe is to its replication origin or to the origin-proximal end of its restriction fragment, the shorter the nascent strands that are detected by the probe. The use of multiple probes allows determination of directions of replication fork movement, as well as locations of origins and termini. In this study, the author used simian virus 40 as a model to demonstrate the feasibility of the method, and the authors discuss its applicability to other systems.

Nawotka, K.A.; Huberman, J.A.

1988-04-01

483

Propagating and evanescent modes in two-dimensional wire media.  

PubMed

Electromagnetic waves in an artificial medium formed by two mutually orthogonal lattices of thin ideally conducting straight wires (referred to as a two-dimensional wire medium) are considered. An effective medium approach and a full-wave method based on the dyadic Green's function and the method of moments are developed. Effects of spatial dispersion, such as the appearance of anisotropy in a square lattice and an additional extraordinary wave, as in crystal optics, are demonstrated. Evanescent waves with complex propagation constants are found. The case when both forward and backward extraordinary waves with respect to an interface exist simultaneously is observed and discussed. The effect of birefringence, so that one extraordinary wave has the wave vector making a positive angle to the interface and the other has the wave vector making a negative angle to the interface, is illustrated. PMID:15903811

Nefedov, I S; Viitanen, A J; Tretyakov, S A

2005-04-29

484

Color Image Encryption Based on Two-Dimensional Cellular Automata  

NASA Astrophysics Data System (ADS)

Cellular automaton (CA) has a lot of inherent features, such as simple regular structure, local interaction, random-like behavior and massive parallelism, which make it a good candidate to design cryptosystems. Therefore, a number of CA-based image encryption systems have been proposed, though the drawbacks of small key space and weak security in one-dimensional (1D) CA cryptosystems are obvious. In this paper, a novel image encryption scheme is presented using a two-dimensional (2D) CA with nonlinear balanced rules. During the whole process of encryption, the confusion operation is performed by the nonlinear rule of CA, while the diffusion operation is achieved by the local interactions among cells. So confusion and diffusion are well integrated in our proposed scheme. The corresponding simulations and analyses illustrate that the scheme has quite prominent cryptographic properties as well as high security.

Ping, Ping; Xu, Feng; Wang, Zhi-Jian

2013-10-01

485

Higgs boson in two dimensional superfluid and Mott insulator states  

NASA Astrophysics Data System (ADS)

We find that despite strong decay into Goldstone modes the Higgs boson survives as a well-defined resonance in the two-dimensional relativistic field theory realized in the cold atomic system near the quantum critical point between the superfluid (SF) and Mott insulator(MI) states. Using scaling analysis of analytically continued results from quantum Monte Carlo simulations we construct universal spectral functions for scalar response both for SF and MI phases and reveal that they share similar properties: a resonant peak followed by a broader secondary peak before saturating to a near plateau behavior at higher frequencies, i.e. the Higgs amplitude mode is present in the MI phase under the correlation length scale. Our simulations of a trapped system of ultra-cold ^87Rb atoms explain recent experimental data and how the signal is modified by tight confinement.

Chen, Kun; Huang, Yuan; Liu, Longxiang; Deng, Youjin; Pollet, Lode; Prokofév, Nikolay

2013-03-01

486

Automatic clocking optimization for compensating two-dimensional tolerances.  

PubMed

Clocking of lens elements is frequently used as an effective method of compensating for two-dimensional tolerances such as material inhomogeneity and surface figure errors. Typically, the lens designer has to determine the optimum angles of rotation by manually modeling lens element clocking in the commercial optical design software because the nature of errors resolved by lens clocking does not lead to good convergences for clocking optimization. In this paper, a method of automatic clocking optimization is developed. The method is implemented using a combination of particle swarm optimization algorithm and commercial optical design software. The optimum angles of rotation and predicted imaging performance are automatically calculated using this method. Methods of implementation and optimization examples are also given. PMID:24104106

Xu, Weicai; Huang, Wei; Liu, Chunlai; Shang, Hongbo

2013-09-23

487

Thinnest two-dimensional nanomaterial-graphene for solar energy.  

PubMed

Graphene is a rapidly rising star in materials science. This two-dimensional material exhibits unique properties, such as low resistance, excellent optical transmittance, and high mechanical and chemical stabilities. These exceptional advantages possess great promise for its potential applications in photovoltaic devices. In this Review, we present the status of graphene research for solar energy with emphasis on solar cells. Firstly, the preparation and properties of graphene are described. Secondly, applications of graphene as transparent conductive electrodes and counter electrodes are presented. Thirdly, graphene-based electron- (or hole) accepting materials for solar energy conversion are evaluated. Fourthly, the promoting effect of graphene on photovoltaic devices and the photocatalytic property of graphene-semiconductor composites are discussed. Finally, the challenges to increase the power conversion efficiency of graphene-based solar cells are explored. PMID:20544792

Hu, Yun Hang; Wang, Hui; Hu, Bo

2010-07-19

488

Tuning Magnetic Interactions in a Two Dimensional Matrix  

NASA Astrophysics Data System (ADS)

The layered dichalcogenides can be used as a matrix for incorporating and manipulating dopants in dimensionally constrained manner. The crystal structure of the dichalcogenides is formed of two-dimensional strongly bound layers separated by a van der Waals gap. Dopants can be incorporated between the layers as intercalants through a variety of methods to form semi-ordered phases. These intercalants have a strong impact on the electronic and magnetic properties of the overall system and can be used to tune existing or induce new phase transitions in the pure parent compounds. For magnetic intercalants, RKKY interactions, which have a strong dependence on the ion-ion spacing, appear to determine the overall magnetic character of the system. Herein, we discuss how Coulomb interactions between intercalated magnetic and non-magnetic ions can be used to influence the spacing between magnetic species and drastically alter the overall magnetic properties of the system.

Kidd, Timothy; Roth, Michael; Shand, Paul; Rash, Tyler; Strauss, Laura; Wandling, Brodie

2010-03-01

489

Electromagnetic two-dimensional analysis of trapped-ion eigenmodes  

SciTech Connect

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

Kim, D.; Rewoldt, G.

1984-11-01

490

Velocity statistics in two-dimensional granular turbulence.  

PubMed

We studied the macroscopic statistical properties on the freely evolving quasielastic hard disk (granular) system by performing a large-scale (up to a few million particles) event-driven molecular dynamics systematically and found it to be remarkably analogous to an enstrophy cascade process in the decaying two-dimensional fluid turbulence. There are four typical stages in the freely evolving inelastic hard disk system, which are homogeneous, shearing (vortex), clustering, and final state. In the shearing stage, the self-organized macroscopic coherent vortices become dominant. In the clustering stage, the energy spectra are close to the expectation of Kraichnan-Batchelor theory and the squared two-particle separation strictly obeys Richardson law. PMID:14682915

Isobe, Masaharu

2003-10-22

491

Two-dimensional model for. gamma. -ray bursts  

SciTech Connect

A thermonuclear model of a ..gamma..-ray burst is calculated using a two-dimensional hydrodynamic code. Accretion onto the magnetic pole of a neutron star leads to the formation of a helium lake 90 m deep and 400 m in radius. A thermonuclear runaway initiates at the base of the helium layer and results in a detonation wave. This wave propagates the lake with a velocity of 9000 km s/sup -1/ without dying out, igniting all of the helium and liberating 2.4 x 10/sup 39/ ergs. The rise time of the burst predicted by this model, determined by the time required to propagate the detonation across the helim layer, is about 50 ..mu..s.

Fryxell, B.A.; Woosley, S.E.

1982-07-15

492

Two-dimensional MHD generator model. [GEN code  

SciTech Connect

A steady state, two-dimensional MHD generator code, GEN, is presented. The code solves the equations of conservation of mass, momentum, and energy, using a Von Mises transformation and a local linearization of the equations. By splitting the source terms into a part proportional to the axial pressure gradient and a part independent of the gradient, the pressure distribution along the channel is easily obtained to satisfy various criteria. Thus, the code can run effectively in both design modes, where the channel geometry is determined, and analysis modes, where the geometry is previously known. The code also employs a mixing length concept for turbulent flows, Cebeci and Chang's wall roughness model, and an extension of that model to the effective thermal diffusities. Results on code validation, as well as comparisons of skin friction and Stanton number calculations with experimental results, are presented.

Geyer, H.K.; Ahluwalia, R.K.; Doss, E.D.

1980-09-01

493

Two-dimensional S-matrices from unitarity cuts  

NASA Astrophysics Data System (ADS)

Using unitarity methods, we compute, for several massive two-dimensional models, the cut-constructible part of the one-loop 2 ? 2 scattering S-matrices from the tree-level amplitudes. We apply our method to various integrable theories, finding evidence that for supersymmetric models the one-loop S-matrix is cut-constructible, while for models without supersymmetry (but with integrability) the missing rational terms are proportional to the tree-level S-matrix and therefore can be interpreted as a shift in the coupling. Finally, applying our procedure to the world-sheet theory for the light-cone gauge-fixed AdS5 × S 5 superstring we reproduce, at one-loop in the near-BMN expansion, the S-matrix known from integrability techniques.

Bianchi, Lorenzo; Forini, Valentina; Hoare, Ben

2013-07-01

494

Vortex dynamics for two-dimensional XY models  

NASA Astrophysics Data System (ADS)

Two-dimensional XY models with resistively shunted junction (RSJ) dynamics and time dependent Ginzburg-Landau (TDGL) dynamics are simulated and it is verified that the vortex response is well described by the Minnhagen phenomenology for both types of dynamics. Evidence is presented supporting that the dynamical critical exponent z in the low-temperature phase is given by the scaling prediction (expressed in terms of the Coulomb gas temperature TCG and the vortex renormalization given by the dielectric constant ?~) z=1/?~TCG-2>=2 both for RSJ and TDGL and that the nonlinear IV exponent a is given by a=z+1 in the low-temperature phase. The results are discussed and compared with the results of other recent papers and the importance of the boundary conditions is emphasized.

Kim, Beom Jun; Minnhagen, Petter; Olsson, Peter

1999-05-01

495

Magnetism in the Disordered Two-Dimensional Kondo-Necklace  

NASA Astrophysics Data System (ADS)

We analyze the effects of site-dilution disorder on the thermodynamic properties of the two-dimensional Kondo necklace using finite-temperature stochastic series expansion. Results will be discussed for the dependence on dilution concentration, temperature, and Kondo exchange-coupling strength of the uniform susceptibility, the staggered structure factor, and the Chakravarty-Halperin-Nelson ratio. Dilution is shown to induce effective free-spin clusters in the gapped phase of the clean system with a low-temperature Curie constant renormalized below 1/4. Furthermore, dilution is demonstrated to suppress the quantum critical point of the clean system and to generate antiferromagnetic order in the quantum disordered phase of the clean system, i.e. order-from-disorder.

Brenig, Wolfram

496

Magnetism in the Disordered Two-Dimensional Kondo-Necklace  

NASA Astrophysics Data System (ADS)

We analyze the effects of site-dilution disorder on the thermodynamic properties of the two-dimensional Kondo necklace using finite-temperature stochastic series expansion. Results will be discussed for the dependence on dilution concentration, temperature, and Kondo exchange-coupling strength of the uniform susceptibility, the staggered structure factor, and the Chakravarty-Halperin-Nelson ratio. Dilution is shown to induce effective free-spin clusters in the gapped phase of the clean system with a low-temperature Curie constant renormalized below 1/4. Furthermore, dilution is demonstrated to suppress the quantum critical point of the clean system and to generate antiferromagnetic order in the quantum disordered phase of the clean system, i.e. order-from-disorder.

Brenig, Wolfram

2007-09-01

497

Mixing times in quantum walks on two-dimensional grids  

SciTech Connect

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

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

2010-10-15

498

Manipulation of Dopants in a Two Dimensional Matrix  

NASA Astrophysics Data System (ADS)

The layered dichalcogenides can be used as a matrix for incorporating and manipulating dopants in dimensionally constrained manner. The crystal structure of the dichalcogenides is formed of two-dimensional strongly bound layers separated by a van der Waals gap. Dopants can be incorporated between the layers as intercalants through a variety of methods to form a semi-ordered phase. These intercalants have a strong impact on the electronic and magnetic properties of the overall system and can be used to tune or enhance novel phase transitions found in the pure parent compounds. Herein, we discuss how one can manipulate the arrangement of dopants using self-assembled and top-down methods to yield a high level of control over the local electronic and magnetic structure of these materials.

Kidd, Timothy; Strauss, Laura; Skirtachenko, Polina; Klein, Dustin

2009-11-01

499

Disorder in a two-dimensional quantum spin liquid  

NASA Astrophysics Data System (ADS)

We discuss magnetic field induced phase transition to magnon Bose-Einstein condensate state in a disordered two-dimensional spin gap antiferromagnet. Disorder was introduced into piperazinium hexachlorodicuprate (PHCC) by chemically substituting up to 10% of exchange interaction mediating Cl ions for Br. We present specific heat, magnetization, susceptibility, elastic and inelastic neutron scattering results in fields up to 14T. Data reveals that disorder enlarges significantly the spin gap and induces nonzero susceptibility in the gapped phase. Reduction of magnon bandwidth and lifetime are evident from inelastic neutron scattering measurements. Although the phase transition seems to survive, the condensate wavefunction aquires a history dependence. In contrary to theoretical expectations, the extracted critical exponents show no changes within experimental accuracy.

Huvonen, Dan; Mansson, Martin; Gvasaliya, Severian; Zhao, Shuangyi; Yankova, Tatiana; Glazkov, Vasiliy; Ressouche, Eric; Niedermayer, Christof; Laver, Mark; Ehlers, Georg; Zheludev, Andrey

2012-02-01

500

Two-dimensional electromagnetic field effects in induction plasma modelling  

SciTech Connect

Based on the electromagnetic vector potential representation, a two-dimensional, axisymmetric model is proposed for the calculation of the electromagnetic fields in an inductively coupled, radiofrequency (r.f.) plasma. A comparative analysis made between the flow, temperature, and electromagnetic fields obtained using this model and those given by their earlier one-dimensional electromagnetic fields model show relatively little difference between the temperature fields predicted by the two models. Significant differences are observed, however, between the corresponding flow and electromagnetic fields. The new model offers an effective means of accounting for variations in the coil geometry on the flow and temperature fields in the discharge and for achieving a better representation of the electromagnetic fields under higher frequency conditions (f> 10 MHz).

Mostaghimi, J.; Boulos, M.I. (Univ. of Sherbrooke, Quebec (Canada))

1989-03-01