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1

Fully localized two-dimensional embedded solitons

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

2

NASA Astrophysics Data System (ADS)

We report the observation of incoherent collisions between two-dimensional bright photorefractive screening solitons. The solitons remain intact and do not exchange energy whenever the collision angle exceeds the critical angle for guidance in the waveguide that each soliton induces, which is, in turn, fully controlled by the soliton parameters. When the collision angle is much smaller than the critical angle the solitons fuse to form a single beam.

Shih, Ming-Feng; Segev, Mordechai

1996-10-01

3

Symmetry breaking of solitons in two-dimensional complex potentials

NASA Astrophysics Data System (ADS)

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

Yang, Jianke

2015-02-01

4

Two-dimensional solitons in a quintic-septimal medium

NASA Astrophysics Data System (ADS)

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

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

2014-12-01

5

Two-dimensional interaction of ion-acoustic solitons

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

6

Two-dimensional stability of ion-acoustic solitons

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

7

Dynamical properties of two-dimensional Kerr cavity solitons

NASA Astrophysics Data System (ADS)

We present the results of our study of the dynamics of two-dimensional Kerr cavity solitons. The solitons are absolutely stable over a substantial parameter domain. We analyze their dynamics beyond the instability boundary, finding regions of stable oscillation and of fivefold or sixfold azimuthal instability. The Hopf oscillation is surprisingly robust, owing to the influence of a lower-amplitude unstable soliton.

Firth, William J.; Harkness, Graeme K.; Lord, Angus; McSloy, John M.; Gomila, Damià; Colet, Pere

2002-04-01

8

Two-dimensional evolution of an ion-acoustic soliton

The two-dimensional evolution of an ion-acoustic soliton from a grid with regular or random perturbations in the direction transverse to the direction of the soliton propagation is experimentally examined. The soliton initially follows the contour of the exciting grid but evolves into a planar structure. These experimental results are compared with a model based on the higher dimensional Kadomtsev--Petviashvili equation. Both the theoretical and numerical predictions agree with the experiment.

Chang, H.; Lien, C.; Hill, J.; Raychaudhuri, S.; Lonngren, K.E.; Gabl, E.F.

1986-11-01

9

Two-dimensional gravitation and Sine-Gordon-Solitons

Some aspects of two-dimensional gravity coupled to matter fields, especially to the Sine-Gordon-model are examined. General properties and boundary conditions of possible soliton-solutions are considered. Analytic soliton-solutions are discovered and the structure of the induced space-time geometry is discussed. These solutions have interesting features and may serve as a starting point for further investigations.

Bernd Stoetzel

1995-07-07

10

One- and two-dimensional solitons supported by singular modulation of quadratic nonlinearity

NASA Astrophysics Data System (ADS)

We introduce a model of one- and two-dimensional (1D and 2D) optical media with the ?(2 ) nonlinearity whose local strength is subject to cusp-shaped spatial modulation, ?(2 )˜r-? , with ? >0 , which can be induced by spatially nonuniform poling. Using analytical and numerical methods, we demonstrate that this setting supports 1D and 2D fundamental solitons, at ? <1 and ? <2 , respectively. The 1D solitons have a small instability region, while the 2D solitons have a stability region at ? <0.5 and are unstable at ? >0.5 . 2D solitary vortices are found too. They are unstable, splitting into a set of fragments, which eventually merge into a single fundamental soliton pinned to the cusp. Spontaneous symmetry breaking of solitons is studied in the 1D system with a symmetric pair of the cusp-modulation peaks.

Lutsky, Vitaly; Malomed, Boris A.

2015-02-01

11

Two-dimensional gap solitons in elliptic-lattice potentials

We study two-dimensional (2D) matter-wave gap solitons trapped in an elliptically deformed concentric lattice potential, within the framework of the Gross-Pitaevskii equation (GPE) with self-attraction or self-repulsion. For a fixed eccentricity of the lattice, soliton families are found in both the repulsive and attractive models. In the former case, the analysis reveals two kinds of gap solitons trapped in the first oval trough (the ring-shaped potential minimum closest to the center): elliptic annular solitons (EASs), and double solitons (DSs), which are formed by two tightly localized density peaks located at diametrically opposite points of the trough, with zero phase difference between them. With the decrease of the norm, the density distribution in the EAS along the azimuthal direction changes from nearly uniform to double-peaked and, eventually, to the DS. In the attractive model, there exist only DSs in the oval trough, while EASs are not found. All such solitons without the angular momentum (l=0) are fully stable. For l{ne}0, vortical solitons--both EASs with a sufficiently large norm (in the repulsive model) and DSs (in models with both signs of the nonlinearity)--are quasistable, exhibiting rocking motion in the elliptic trough (we consider the cases of l=1 and l=2). At smaller values of the norm, the vortical annular solitons (in the repulsive model) are unstable. Stable fundamental solitons trapped in the central potential well are investigated, too, in both the attractive and repulsive models, by means of the variational approximation and numerical methods.

He Yingji [Department of Physics, Centre for Nonlinear Studies, and The Beijing-Hong Kong-Singapore Joint Centre for Nonlinear and Complex Systems, Hong Kong Baptist University, Kowloon Tong (Hong Kong); School of Electronics and Information, Guangdong Polytechnic Normal University, 510665 Guangzhou (China); Malomed, Boris A. [Department of Physical Electronics, School of Electrical Engineering, Faculty of Engineering, Tel Aviv University, Tel Aviv 69978 (Israel); Hu Bambi [Department of Physics, Centre for Nonlinear Studies, and The Beijing-Hong Kong-Singapore Joint Centre for Nonlinear and Complex Systems, Hong Kong Baptist University, Kowloon Tong (Hong Kong); Department of Physics, University of Houston, Houston, Texas 77204-5005 (United States)

2010-03-15

12

Interaction forces among two-dimensional bright solitons and many-soliton molecules.

We consider two-dimensional bright matter-wave solitons in two-dimensional Bose-Einstein condensates. From the asymptotic form of their wave function, we derive an analytic expression for the force of interaction between solitons in the large separation limit, which turns out to decay with solitons separation ? as F(?)?exp(-?)/??. Simulating the dynamics of two solitons using the relevant Gross-Pitaevskii equation, we obtain the force of the interaction for the full range of ?, which turns out to be of molecular type. We show that many-soliton molecules can exist as a result of such a molecular-type of interaction. These include string-shaped, ring-shaped, or regular-lattice-shaped soliton molecules. By calculating their binding energy, we investigate the stability of these structures. Contrary to one-dimensional soliton molecules, which have no binding energy, two-dimensional molecules of a lattice of solitons with alternating phases are robust and have a negative binding energy. Lattices of size larger than 2 × 2 solitons have many discrete equilibrium values of the separation between two neighboring solitons. PMID:23004892

Al Khawaja, U

2012-05-01

13

Soliton nanoantennas in two-dimensional arrays of quantum dots

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

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

2015-01-01

14

A two-dimensional soliton in a positive ion-negative ion plasma

In this paper experiments in which a two-dimensional soliton in a positive ion-negative ion plasma has been excited are described. The two-dimensional soliton is created by reflecting an incident planar soliton from a concave hemispherical surface. The experimental results are interpreted in terms of the linear waves that can exist in a focused Fabry-Perot resonator.

Cooney, J.L.; Lonngren, K.E. (Iowa Univ., Iowa City, IA (United States). Dept. of Physics and Astronomy); Gavin, M.T.; Tao, J. (Dept. of Electrical and Computer Engineering, Univ. of Iowa, Iowa City, IA (US))

1991-12-01

15

Two-dimensional spatially developing mixing layers

Two-dimensional, incompressible, spatially developing mixing layer simulations are performed with two classes of perturbations applied at the inlet boundary: (1) combinations of discrete modes from linear stability theory, and (2) a broad spectrum of modes derived from experimentally measured velocity spectra. The discrete modes from linear theory are obtained by solving the Orr-Sommerfeld equation, and linear stability analysis is used to investigate the effect of Reynolds number on the stability of mixing layers. Two-point spatial velocity and autocorrelations are used to estimate the size and lifetime of the resulting coherent structures and to explore possible feedback effects. It is shown that by forcing with a broad spectrum of modes derived from an experimental energy spectrum, many experimentally observed phenomena can be reproduced by a two-dimensional simulation.

Wilson, R.V.; Demuren, A.O. [Old Dominion Univ., Norfolk, VA (United States). Dept. of Mechanical Engineering

1996-04-01

16

One- and two-dimensional solitons supported by singular modulation of quadratic nonlinearity

We introduce a model of one- and two-dimensional (1D and 2D) optical media with the $\\chi ^{(2)}$ nonlinearity whose local strength is subject to cusp-shaped spatial modulation, $\\chi ^{(2)}\\sim r^{-\\alpha }$, with $\\alpha >0$, which can be induced by spatially nonuniform poling. Using analytical and numerical methods, we demonstrate that this setting supports 1D and 2D fundamental solitons, at $\\alpha 0.5$. 2D solitary vortices are found too. They are unstable, splitting into a set of fragments, which eventually merge into a single fundamental soliton pinned to the cusp. Spontaneous symmetry breaking of solitons is studied in the 1D system with a symmetric pair of the cusp-modulation peaks.

Lutsky, Vitaly

2015-01-01

17

Matter-wave two-dimensional solitons in crossed linear and nonlinear optical lattices

NASA Astrophysics Data System (ADS)

The existence of multidimensional matter-wave solitons in a crossed optical lattice (OL) with a linear optical lattice (LOL) in the x direction and a nonlinear optical lattice (NOL) in the y direction, where the NOL can be generated by a periodic spatial modulation of the scattering length using an optically induced Feshbach resonance is demonstrated. In particular, we show that such crossed LOLs and NOLs allow for stabilizing two-dimensional solitons against decay or collapse for both attractive and repulsive interactions. The solutions for the soliton stability are investigated analytically, by using a multi-Gaussian variational approach, with the Vakhitov-Kolokolov necessary criterion for stability; and numerically, by using the relaxation method and direct numerical time integrations of the Gross-Pitaevskii equation. Very good agreement of the results corresponding to both treatments is observed.

da Luz, H. L. F.; Abdullaev, F. Kh.; Gammal, A.; Salerno, M.; Tomio, Lauro

2010-10-01

18

Matter-wave two-dimensional solitons in crossed linear and nonlinear optical lattices

The existence of multidimensional matter-wave solitons in a crossed optical lattice (OL) with a linear optical lattice (LOL) in the x direction and a nonlinear optical lattice (NOL) in the y direction, where the NOL can be generated by a periodic spatial modulation of the scattering length using an optically induced Feshbach resonance is demonstrated. In particular, we show that such crossed LOLs and NOLs allow for stabilizing two-dimensional solitons against decay or collapse for both attractive and repulsive interactions. The solutions for the soliton stability are investigated analytically, by using a multi-Gaussian variational approach, with the Vakhitov-Kolokolov necessary criterion for stability; and numerically, by using the relaxation method and direct numerical time integrations of the Gross-Pitaevskii equation. Very good agreement of the results corresponding to both treatments is observed.

Luz, H. L. F. da; Gammal, A. [Instituto de Fisica, Universidade de Sao Paulo, 05508-090 Sao Paulo, Sao Paulo (Brazil); Abdullaev, F. Kh. [CFTC, Complexo Interdisciplinar, Universidade Lisboa, Avenida Professor Gama Pinto, 2, P-1649-003 Lisboa (Portugal); Salerno, M. [Dipartimento di Fisica 'E.R. Caianiello', CNISM and INFN-Gruppo Collegato di Salerno, Universita di Salerno, Via Ponte don Melillo, I-84084 Fisciano (Italy); Tomio, Lauro [Instituto de Fisica, Universidade Federal Fluminense, 24210-346 Niteroi, Rio de Janeiro (Brazil); Instituto de Fisica Teorica, Universidade Estadual Paulista (UNESP), 01140-070 Sao Paulo, Sao Paulo (Brazil)

2010-10-15

19

Two-dimensional discrete solitons in rotating lattices

We introduce a two-dimensional discrete nonlinear Schroedinger (DNLS) equation with self-attractive cubic nonlinearity in a rotating reference frame. The model applies to a Bose-Einstein condensate stirred by a rotating strong optical lattice, or light propagation in a twisted bundle of nonlinear fibers. Two types of localized states are constructed: off-axis fundamental solitons (FSs), placed at distance R from the rotation pivot, and on-axis (R=0) vortex solitons (VSs), with vorticities S=1 and 2. At a fixed value of rotation frequency {omega}, a stability interval for the FSs is found in terms of the lattice coupling constant C, 0

Cuevas, Jesus [Grupo de Fisica No Lineal, Departamento de Fisica Aplicada I, Escuela Universitaria Politecnica, C/ Virgen de Africa, 7, 41011 Sevilla (Spain); Malomed, Boris A. [Department of Physical Electronics, School of Electrical Engineering, Faculty of Engineering, Tel Aviv University, Tel Aviv 69978 (Israel); Kevrekidis, P. G. [Department of Mathematics and Statistics, University of Massachusetts, Amherst, Massachusetts 01003-4515 (United States)

2007-10-15

20

Stable and mobile excited two-dimensional dipolar Bose–Einstein condensate solitons

NASA Astrophysics Data System (ADS)

We demonstrate robust, stable, mobile excited states of quasi-two-dimensional (quasi-2D) dipolar Bose–Einstein condensate (BEC) solitons for repulsive contact interaction with a harmonic trap along the x direction perpendicular to the polarization direction z. Such a soliton can freely move in the y–z plane. A rich variety of such excitations is considered: one quanta of excitation for movement along (i) y axis or (ii) z axis or (iii) both. A proposal for creating these excited solitonic states in a laboratory by phase imprinting is also discussed. We also consider excited states of quasi-2D dipolar BEC soliton where the sign of the dipolar interaction is reversed by a rotating orienting field. In this sign-changed case the soliton moves freely in the x–y plane under the action of a harmonic trap in the z direction. At medium velocity the head-on collision of two such solitons is found to be quasi elastic with practically no deformation. The findings are illustrated using numerical simulation in three and two spatial dimensions employing realistic interaction parameters for a dipolar 164Dy BEC.

Adhikari, S. K.

2014-11-01

21

OPTICAL SOLITONS: Excitation of two-dimensional soliton matrices by fundamental Gaussian beams

NASA Astrophysics Data System (ADS)

The excitation of two-dimensional periodic structures of fields of the first and second radiation harmonics due to the modulation instability of fundamental Gaussian beams is studied in a medium with a quadratic nonlinearity. The distances are found at which soliton matrix structures with a specified period are formed and destroyed. Optical gratings formed due to nonlinear aberration of broad Gaussian beams are considered.

Borovkova, O. V.; Chuprakov, D. A.; Sukhorukov, Anatolii P.

2005-01-01

22

Sharp waveguide bends induced by spatial solitons

We experimentally demonstrate the ability of a self-guided laser beam to induce waveguides with sharp bends. The beam is a two-dimensional photorefractive screening-photovoltaic bright spatial soliton generated inside a biased lithium-niobate crystal shaped as a prism. The soliton robustness against total internal reflections is shown to leave place to a low-loss unimodal waveguide undergoing multiple zero-radius 90 deg. turns.

Jaeger, Robert; Gorza, Simon-Pierre; Cambournac, Cyril; Haelterman, Marc; Chauvet, Mathieu [Universite libre de Bruxelles, Service d'optique et acoustique, B-1050 Brussels (Belgium); Institut Femto-ST, Departement d'optique P-M. Duffieux, UMRS CNRS 6174/Universite de Franche-Comte 6174, F-25030 Besancon cedex (France)

2006-02-06

23

NASA Astrophysics Data System (ADS)

The Manakov soliton is a two-component soliton that was first considered by Manakov in the early 1970s.1 Based on the work of Zakharov and Shabat,2 Manakov found that the coupled nonlinear Schrodinger (CNSE) equations with special choice of the coefficients in front of nonlinear terms can be solved exactly. This system is integrable and solitons have therefore a number of special properties which might be useful in practice. In particular, for same total power, the soliton of a single nonlinear Schrodinger equation and the Manakov soliton behave similarly. There are certain conditions for the integrability of the CNSE. Namely, for the coupled set of equations with cubic nonlinearity, the ratio between the self-phase modulation (SPM) to the cross-phase modulation coefficients has to be equal to unity, and the SPM coefficients need to be equal for the two polarizations. Moreover, the energy exchange terms or four-wave mixing (FWM) terms must be zero. Physically, the Manakov soliton is a mutually trapped state of two orthogonally polarized beams where each component of the soliton experiences exactly the same index potential which is proportional to the total intensity of the beam. There are no crystal symmetries that a priori lead to a SPM/XPM ratio of unity. Thus, the Manakov soliton has not been observed experimentally prior to the work we reported.3 Based on our previous work, we found that in AlGaAs, for photon energies just below half the band gap, the conditions for integrability can be satisfied. This led to the first experimental observation of spatial Manakov solitons.

Kang, J. U.; Stegeman, G. I.; Aitchison, J. S.; Akhmediev, N.

1996-12-01

24

Spatial competition in a two dimensional market

dimensional market and to investigate general aspects of spatial competition. 2 In some respects, we will alter Hotelling's assumptions in order to arrive at a more realistic solution. It should be borne in mind that our only considerations in terms of competition will be spatial. Although price policies on the part of the producers may in reality occur at any

Paul Jonas I

1968-01-01

25

We consider the impact of anisotropic nonlocality on the arrest of the collapse and stabilization of dipole-mode (DM) solitons in two-dimensional (2D) models of optical media with the diffusive nonlinearity. The nonlocal nonlinearity is made anisotropic through elliptic diffusivity. The medium becomes semilocal in the limit case of 1D diffusivity. Families of fundamental and DM solitons are found by means of the variational approximation and in a numerical form. We demonstrate that the collapse of 2D beams is arrested even in the semilocal system. The anisotropic nonlocality readily stabilizes the DM solitons, which are completely unstable in the isotropic medium.

Ye Fangwei; He Yingji [Department of Physics, Centre for Nonlinear Studies, and Beijing-Hong Kong Singapore Joint Centre for Nonlinear and Complex Systems, Hong Kong Baptist University, Kowloon Tong (Hong Kong); Malomed, Boris A. [Department of Physical Electronics, School of Electrical Engineering, Faculty of Engineering, Tel Aviv University, Tel Aviv 69978 (Israel); Hu Bambi [Department of Physics, Centre for Nonlinear Studies, and Beijing-Hong Kong Singapore Joint Centre for Nonlinear and Complex Systems, Hong Kong Baptist University, Kowloon Tong (Hong Kong); Department of Physics, University of Houston, Houston, Texas 77204-5005 (United States)

2010-04-15

26

Two-dimensional gap solitons in a nonlinear periodic slab waveguide

We present a three-dimensional analysis of counterpropagating waves in a periodic nonlinear slab waveguide. The analysis reveals the existence of two-dimensional gap solitons, whose stability depends on their total power`s being above (unstable) or below (stable) a critical power. Numerical experiments validate the analytical results.

Aceves, A.B.; Costantini, B.; De Angelis, C. [Department of Mathematic and Statistics, University of New Mexico, Albuquerque, New Mexico 87131 (United States)

1995-08-01

27

Stable vortex solitons in the two-dimensional Ginzburg-Landau equation

NASA Astrophysics Data System (ADS)

In the framework of the complex cubic-quintic Ginzburg-Landau equation, we perform a systematic analysis of two-dimensional axisymmetric doughnut-shaped localized pulses with the inner phase field in the form of a rotating spiral. We put forward a qualitative argument which suggests that, on the contrary to the known fundamental azimuthal instability of spinning doughnut-shaped solitons in the cubic-quintic NLS equation, their GL counterparts may be stable. This is confirmed by massive direct simulations, and, in a more rigorous way, by calculating the growth rate of the dominant perturbation eigenmode. It is shown that very robust spiral solitons with (at least) the values of the vorticity S=0, 1, and 2 can be easily generated from a large variety of initial pulses having the same values of intrinsic vorticity S. In a large domain of the parameter space, it is found that all the stable solitons coexist, each one being a strong attractor inside its own class of localized two-dimensional pulses distinguished by their vorticity. In a smaller region of the parameter space, stable solitons with S=1 and 2 coexist, while the one with S=0 is absent. Stable breathers, i.e., both nonspiraling and spiraling solitons demonstrating persistent quasiperiodic internal vibrations, are found too.

Crasovan, L.-C.; Malomed, B. A.; Mihalache, D.

2001-01-01

28

Soliton solutions of the two-dimensional KdV-Burgers equation by homotopy perturbation method

In this Letter, the He's homotopy perturbation method (HPM) to finding the soliton solutions of the two-dimensional Korteweg–de Vries Burgers' equation (tdKdVB) for the initial conditions was applied. Numerical solutions of the equation were obtained. The obtained solutions, in comparison with the exact solutions admit a remarkable accuracy. The results reveal that the HPM is very effective and simple.

A. Molabahrami; F. Khani; S. Hamedi-Nezhad

2007-01-01

29

Bright spatial solitons in defocusing Kerr media with PT-symmetric potentials

We show that defocusing Kerr media with parity-time-symmetric potentials can support one- and two-dimensional bright spatial solitons. These solitons are found to be stable over the wide range where they exist. More importantly, we discover an exact one-dimensional solution and a closed two-dimensional solution in the structure.

Shi, Zhiwei; Jiang, Xiujuan [School of Information Engineering, Guangdong University of Technology, Guangzhou 510006 (China); Zhu, Xing [State Key Laboratory of Optoelectronic Materials and Technologies, Sun Yat-Sen University, Guangzhou 510275 (China); Li, Huagang [Department of Physics, Guangdong Institute of Education, Guangzhou 510303 (China)

2011-11-15

30

Spatial Solitons in Algaas Waveguides

NASA Astrophysics Data System (ADS)

In this work, by measuring the two-, three-photon absorption, and the nonlinear refractive index coefficients, a useful bandwidth for an all-optical switching applications in the AlGaAs below half the band gap is identified. Operating in this material system, several types of spatial solitons such as fundamental bright solitons, Vector solitons, and Manakov solitons are experimentally demonstrated. The propagation and the interaction behaviors of these solitons are studied experimentally and numerically. The distinct properties of each soliton are discussed along with some possible applications. Some applications, such as all -optical switching based on spatial soliton dragging and the efficient guiding of orthogonally polarized femtosecond pulses by a bright spatial soliton, are experimentally demonstrated. The signal gain due to an ultrafast polarization coupling, better known as Four Wave Mixing (FWM) is demonstrated in a channel waveguide. The effects of FWM are studied experimentally and numerically. This effect is also used to demonstrate polarization switching. The linear and nonlinear properties of AlGaAs/GaAs multiple quantum well waveguides are measured. Anisotropic two photon absorption and nonlinear refractive indices near half the band gap are measured along with the linear birefringence for several different quantum well structures. The usefulness of multiple quantum well structures for an all -optical switching because of anisotropic nature of this material system is discussed.

Kang, Jin Ung

31

Direct measurement of the transverse velocity of dark spatial solitons.

We describe the direct experimental measurement of the transverse propagation velocities of dark spatial solitons. Good agreement is obtained from a comparison of the velocities measured experimentally and the velocities predicted by the two-dimensional theory of Zakharov and Shabat [Sov. Phys. JETP 37, 823 (1973)]. PMID:19768077

Andersen, D R; Hooton, D E; Swartzlander, G A; Kaplan, A E

1990-07-15

32

Two-dimensional discrete solitons in dipolar Bose-Einstein condensates

We analyze the formation and dynamics of bright unstaggered solitons in the disk-shaped dipolar Bose-Einstein condensate, which features the interplay of contact (collisional) and long-range dipole-dipole (DD) interactions between atoms. The condensate is assumed to be trapped in a strong optical-lattice potential in the disk's plane, hence it may be approximated by a two-dimensional (2D) discrete model, which includes the on-site nonlinearity and cubic long-range (DD) interactions between sites of the lattice. We consider two such models, which differ by the form of the on-site nonlinearity, represented by the usual cubic term, or more accurate nonpolynomial one, derived from the underlying three-dimensional Gross-Pitaevskii equation. Similar results are obtained for both models. The analysis is focused on the effects of the DD interaction on fundamental localized modes in the lattice (2D discrete solitons). The repulsive isotropic DD nonlinearity extends the existence and stability regions of the fundamental solitons. New families of on-site, inter-site, and hybrid solitons, built on top of a finite background, are found as a result of the interplay of the isotropic repulsive DD interaction and attractive contact nonlinearity. By themselves, these solutions are unstable, but they evolve into robust breathers which exist on an oscillating background. In the presence of the repulsive contact interactions, fundamental localized modes exist if the DD interaction (attractive isotropic or anisotropic) is strong enough. They are stable in narrow regions close to the anticontinuum limit, while unstable solitons evolve into breathers. In the latter case, the presence of the background is immaterial.

Gligoric, Goran; Stepic, Milutin; Hadzievski, Ljupco [Vinca Institute of Nuclear Sciences, P.O. Box 522, 11001 Belgrade (Serbia); Maluckov, Aleksandra [Faculty of Sciences and Mathematics, University of Nis, P.O. Box 224, 18001 Nis (Serbia); Malomed, Boris A. [Department of Physical Electronics, School of Electrical Engineering, Faculty of Engineering, Tel Aviv University, Tel Aviv 69978 (Israel)

2010-01-15

33

Extracting joint weak values from two-dimensional spatial displacements

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

Hirokazu Kobayashi; Graciana Puentes; Yutaka Shikano

2012-11-06

34

Spatial solitons in left-handed metamaterials

We predict that both bright and dark spatial solitons can exist in nonlinear left-handed composites with a hysteresis-like magnetic nonlinearity and demonstrate a number of unique properties of such solitons

I. V. Shadrivov; Y. S. Kivshar

2004-01-01

35

Terahertz relativistic spatial solitons in doped graphene metamaterials

We propose an electrically tunable graphene-based metamaterial showing a large nonlinear optical response at THz frequencies, which we calculate analytically for the first time to our knowledge and arises from the intraband current. The structure sustains a novel type of stable two-dimensional spatial solitary wave, a relativistic version of the Townes soliton. These results can be also applied to any material exhibiting a conical dispersion with massless Dirac fermions.

Haiming Dong; Claudio Conti; Fabio Biancalana

2011-07-28

36

It is well known that the two-dimensional (2D) nonlinear Schr\\"odinger equation (NLSE) with the cubic-quintic (CQ) nonlinearity supports a family of stable fundamental solitons, as well as solitary vortices (alias vortex rings), which are stable for sufficiently large values of the norm. We study stationary localized modes in a symmetric linearly coupled system of two such equations, focusing on asymmetric states. The model may describe "optical bullets" in dual-core nonlinear optical waveguides (including spatiotemporal vortices that were not discussed before), or a Bose-Einstein condensate (BEC) loaded into a "dual-pancake" trap. Each family of solutions in the single-component model has two different counterparts in the coupled system, one symmetric and one asymmetric. Similarly to the earlier studied coupled 1D system with the CQ nonlinearity, the present model features bifurcation loops, for fundamental and vortex solitons alike: with the increase of the total energy (norm), the symmetric solitons become...

Dror, Nir

2010-01-01

37

Models of two-dimensional (2D) traps, with double-well structure in the third direction, for Bose-Einstein condensates are introduced with attractive or repulsive interactions between atoms. The models are based on systems of linearly coupled 2D Gross-Pitaevskii equations, where the coupling accounts for tunneling between the wells. Each well carries an optical lattice (OL) (stable 2D solitons cannot exist without OLs). The linear coupling splits each finite band gap in the spectrum of the single-component model into two subgaps. The main subject of the work is spontaneous symmetry breaking (SSB) in two-component 2D solitons and localized vortices (SSB was not considered before in 2D settings). Using variational approximation (VA) and numerical methods, we demonstrate that, in a system with attraction or repulsion, SSB occurs in families of symmetric or antisymmetric solitons (or vortices), respectively. The corresponding bifurcation destabilizes the original solution branch and gives rise to a stable branch of asymmetric solitons or vortices. The VA provides for an accurate description of the emerging branch of asymmetric solitons. In the model with attraction, all stable branches eventually terminate due to the onset of collapse. Stable asymmetric solitons in higher finite band gaps and vortices with a multiple topological charge are found too. The models also give rise to first examples of embedded solitons and embedded vortices (the states located inside Bloch bands) in two dimensions. In the linearly coupled system with opposite signs of the nonlinearity in the two cores, two distinct types of stable solitons and vortices are found, dominated by either the self-attractive component or the self-repulsive one. In the system with a mismatch between the two OLs, a pseudobifurcation is found: when the mismatch attains its largest value ({pi}), the bifurcation does not happen, as branches of different solutions asymptotically approach each other, but fail to merge.

Gubeskys, Arthur; Malomed, Boris A. [Department of Physical Electronics, School of Electrical Engineering, Faculty of Engineering, Tel Aviv University, Tel Aviv 69978 (Israel)

2007-10-15

38

NASA Technical Reports Server (NTRS)

We present what are to our knowledge first-time calculations from vector nonlinear Maxwell's equations of femtosecond soliton propagation and scattering, including carrier waves, in two-dimensional dielectric waveguides. The time integration efficiently implements linear and nonlinear convolutions for the electric polarization, and the nonlinear convolution accounts for two quantum effects, the Kerr and Raman interactions. By retaining the optical carrier, the new method solves for fundamental quantities - optical electric and magnetic fields in space and time - rather than a nonphysical envelope function. It has the potential to provide an unprecedented two- and three-dimensional modeling capability for millimeter-scale integrated-optical circuits with submicrometer engineered inhomogeneities.

Joseph, Rose M.; Goorjian, Peter M.; Taflove, Allen

1993-01-01

39

Discrete solitons and vortices on two-dimensional lattices of -symmetric couplers.

We introduce a 2D network built of -symmetric dimers with on-site cubic nonlinearity, the gain and loss elements of the dimers being linked by parallel square-shaped lattices. The system may be realized as a set of -symmetric dual-core waveguides embedded into a photonic crystal. The system supports -symmetric and antisymmetric fundamental solitons (FSs) and on-site-centered solitary vortices (OnVs). Stability of these discrete solitons is the central topic of the consideration. Their stability regions in the underlying parameter space are identified through the computation of stability eigenvalues, and verified by direct simulations. Symmetric FSs represent the system's ground state, being stable at lowest values of the power, while anti-symmetric FSs and OnVs are stable at higher powers. Symmetric OnVs, which are also stable at lower powers, are remarkably robust modes: on the contrary to other -symmetric states, unstable OnVs do not blow up, but spontaneously rebuild themselves into stable FSs. PMID:25606899

Chen, Zhaopin; Liu, Jingfeng; Fu, Shenhe; Li, Yongyao; Malomed, Boris A

2014-12-01

40

The dynamics of two-dimensional s-polarized solitary waves is investigated with the aid of particle-in-cell (PIC) simulations. Instead of the usual excitation of the waves with a laser pulse, the PIC code was directly initialized with the numerical solutions from the fluid plasma model. This technique allows the analysis of different scenarios including the theoretical problems of the solitary wave stability and their collision as well as features already measured during laser-plasma experiments such as the emission of electromagnetic bursts when the waves reach the plasma-vacuum interface, or their expansion on the ion time scale, usually named post-soliton evolution. Waves with a single density depression are stable whereas multihump solutions decay to several waves. Contrary to solitons, two waves always interact through a force that depends on their relative phases, their amplitudes, and the distance between them. On the other hand, the radiation pattern at the plasma-vacuum interface was characterized, and the evolution of the diameter of different waves was computed and compared with the ''snow plow'' model.

Sanchez-Arriaga, G.; Lefebvre, E. [CEA, DAM, DIF, F-91297 Arpajon (France)

2011-09-15

41

Two-dimensional radiative transfer in cloudy atmospheres: The spherical harmonic spatial grid method

A new two-dimensional monochromatic method that computes the transfer of solar or thermal radiation through atmospheres with arbitrary optical properties is described. The model discretizes the radiative transfer equation by expanding the angular part of the radiance field in a spherical harmonic series and representing the spatial part with a discrete grid. The resulting sparse coupled system of equations is

K. Franklin Evans

1993-01-01

42

Optical spatial solitons: historical overview and recent advances

NASA Astrophysics Data System (ADS)

Solitons, nonlinear self-trapped wavepackets, have been extensively studied in many and diverse branches of physics such as optics, plasmas, condensed matter physics, fluid mechanics, particle physics and even astrophysics. Interestingly, over the past two decades, the field of solitons and related nonlinear phenomena has been substantially advanced and enriched by research and discoveries in nonlinear optics. While optical solitons have been vigorously investigated in both spatial and temporal domains, it is now fair to say that much soliton research has been mainly driven by the work on optical spatial solitons. This is partly due to the fact that although temporal solitons as realized in fiber optic systems are fundamentally one-dimensional entities, the high dimensionality associated with their spatial counterparts has opened up altogether new scientific possibilities in soliton research. Another reason is related to the response time of the nonlinearity. Unlike temporal optical solitons, spatial solitons have been realized by employing a variety of noninstantaneous nonlinearities, ranging from the nonlinearities in photorefractive materials and liquid crystals to the nonlinearities mediated by the thermal effect, thermophoresis and the gradient force in colloidal suspensions. Such a diversity of nonlinear effects has given rise to numerous soliton phenomena that could otherwise not be envisioned, because for decades scientists were of the mindset that solitons must strictly be the exact solutions of the cubic nonlinear Schrödinger equation as established for ideal Kerr nonlinear media. As such, the discoveries of optical spatial solitons in different systems and associated new phenomena have stimulated broad interest in soliton research. In particular, the study of incoherent solitons and discrete spatial solitons in optical periodic media not only led to advances in our understanding of fundamental processes in nonlinear optics and photonics, but also had a very important impact on a variety of other disciplines in nonlinear science. In this paper, we provide a brief overview of optical spatial solitons. This review will cover a variety of issues pertaining to self-trapped waves supported by different types of nonlinearities, as well as various families of spatial solitons such as optical lattice solitons and surface solitons. Recent developments in the area of optical spatial solitons, such as 3D light bullets, subwavelength solitons, self-trapping in soft condensed matter and spatial solitons in systems with parity-time symmetry will also be discussed briefly.

Chen, Zhigang; Segev, Mordechai; Christodoulides, Demetrios N.

2012-08-01

43

In a basic physical model where two-dimensional (2D) matter-wave solitons may be stable, namely, the Gross-Pitaevskii equation with the self-attractive nonlinearity and quasi-one-dimensional (1D) optical-lattice (OL) potential, we test robustness of the solitons against periodic time modulation of the OL strength. Stability diagrams for the 2D solitons are presented in the plane of the modulation depth and frequency. Basic features of the diagrams are explained with the help of the variational approximation for the stationary counterpart of the model. In the Bose-Einstein condensate of {sup 7}Li atoms, the stable 2D solitons may contain the number of atoms in the range of 10{sup 4}-10{sup 5}, relevant values of the OL strength and modulation frequency being, respectively < or approx. 5 recoil energies and < or approx. 10 kHZ. Head-on collisions between stable 2D solitons moving in the unconfined direction are studied in detail too, for velocities up to {approx}5 cm/s. A border between quasi-elastic collisions and merger of the solitons into a single localized state is identified. In some cases, the soliton produced by the merger is stable against collapse, which was not observed before in the static OL potential either.

Mayteevarunyoo, Thawatchai [Department of Telecommunication Engineering, Mahanakorn University of Technology, Bangkok 10530 (Thailand); Department of Physical Electronics, School of Electrical Engineering, Faculty of Engineering, Tel Aviv University, Tel Aviv 69978 (Israel); Malomed, Boris A. [Department of Physical Electronics, School of Electrical Engineering, Faculty of Engineering, Tel Aviv University, Tel Aviv 69978 (Israel); Krairiksh, Monai [Faculty of Engineering and Research Center for Communications and Information Technology, King Mongkut's Institute of Technology, Ladkrabang, Bangkok 10520 (Thailand)

2007-11-15

44

Nonlinear optical catastrophe and dark spatial solitons

NASA Astrophysics Data System (ADS)

This thesis covers different spatial nonlinear optical effects that occur in self-defocusing media. The first effect is the power-dependent evolution of an elliptical Gaussian beam, e.g., the development of peripheral vortex quadrupoles at low powers and a nonlinear cusp diffraction catastrophe at high powers. Up to three quadrupoles were observed, each appearing after equal increments of beam power. Our analysis of this discovery shows that the incremental power is related to the net phase change needed to support a quadrupole. At higher incident power we found a complex interference pattern in the center of the beam that was attributed to the nonlinear cusp catastrophe. By varying the thickness of the liquid column we traced the development of the catastrophe back to an annular ellipse in the middle of the nonlinear cell. Results of this study may be applied to the analysis of patterns appearing when a high-power astigmatic beam is transmitted through a gas or liquid. The second effect concerns the propagation of a single optical vortex in Kerr and thermal defocusing nonlinear optical media. We numerically investigated the abrupt contraction of a vortex whose core size was initially larger than the soliton size. The contraction is accompanied by a bright ring around the vortex core which supports the reduced vortex size over distances exceeding the characteristic nonlinear distance. In thermal medium, the contraction depends on time due to the diffusion of heat into the vortex core. The contraction of the vortex core may be an advantageous feature for optical modulators or transistors, where the vortex beam induces a dynamic waveguide for a signal-carrying beam. Lastly, we experimentally investigated the power- dependent arrangement of a periodic array of one- dimensional dark solitons. The initial field of the soliton array was produced with the aid of computer- generated holography. A unit cell of the array contained a pair of solitons propagating in opposite transverse directions. The speed of each soliton depends on power and thus the solitons are made to collide by increasing the value of power. We observed collisions of up to three pairs of counterpropagating solitons. This experiment prototypes an all-optical switch based on dark solitons.

Deykoon, Anton M.

2001-04-01

45

Stable Mode Sorting by Two-Dimensional Parity of Photonic Transverse Spatial States

We describe a mode sorter for two-dimensional parity of transverse spatial states of light based on an out-of-plane Sagnac interferometer. Both Hermite-Gauss (HG) and Laguerre-Gauss (LG) modes can be guided into one of two output ports according to the two-dimensional parity of the mode in question. Our interferometer sorts HG_nm input modes depending upon whether they have even or odd order n+m; it equivalently sorts LG modes depending upon whether they have an even or odd value of their orbital angular momentum. It functions efficiently at the single-photon level, and therefore can be used to sort single-photon states. Due to the inherent phase stability of this type of interferometer as compared to those of the Mach-Zehnder type, it provides a promising tool for the manipulation and filtering of higher order transverse spatial modes for the purposes of quantum information processing. For example, several similar Sagnacs cascaded together may allow, for the first time, a stable measurement of the orbital angular momentum of a true single-photon state. Furthermore, as an alternative to well-known holographic techniques, one can use the Sagnac in conjunction with a multi-mode fiber as a spatial mode filter, which can be used to produce spatial-mode entangled Bell states and heralded single photons in arbitrary first-order (n+m=1) spatial states, covering the entire Poincare sphere of first-order transverse modes.

C. C. Leary; L. A. Baumgardner; M. G. Raymer

2008-10-14

46

We propose a simple and straightforward method to generate spatially variant lattice structures by optical interference lithography method. Using this method, it is possible to independently vary the orientation and period of the two-dimensional lattice. The method consists of two steps which are: numerical synthesis of corresponding phase mask by employing a two-dimensional integrated gradient calculations and experimental implementation of synthesized phase mask by making use of a phase only spatial light modulator in an optical 4f Fourier filtering setup. As a working example, we provide the experimental fabrication of a spatially variant square lattice structure which has the possibility to guide a Gaussian beam through a 90° bend by photonic crystal self-collimation phenomena. The method is digitally reconfigurable, is completely scalable, and could be extended to other kind of lattices as well.

Kumar, Manish, E-mail: manishk@physics.iitd.ac.in; Joseph, Joby, E-mail: joby@physics.iitd.ac.in [Photonics Research Laboratory, Department of Physics, Indian Institute of Technology Delhi, New Delhi 110016 (India)

2014-08-04

47

Quantifying Two-Dimensional Filamentous and Invasive Growth Spatial Patterns in Yeast Colonies

The top-view, two-dimensional spatial patterning of non-uniform growth in a Saccharomyces cerevisiae yeast colony is considered. Experimental images are processed to obtain data sets that provide spatial information on the cell-area that is occupied by the colony. A method is developed that allows for the analysis of the spatial distribution with three metrics. The growth of the colony is quantified in both the radial direction from the centre of the colony and in the angular direction in a prescribed outer region of the colony. It is shown that during the period of 100–200 hours from the start of the growth of the colony there is an increasing amount of non-uniform growth. The statistical framework outlined in this work provides a platform for comparative quantitative assays of strain-specific mechanisms, with potential implementation in inferencing algorithms used for parameter-rate estimation. PMID:25719406

Binder, Benjamin J.; Sundstrom, Joanna F.; Gardner, Jennifer M.; Jiranek, Vladimir; Oliver, Stephen G.

2015-01-01

48

Photorefractive spatial solitons, induced waveguides, and their applications

NASA Astrophysics Data System (ADS)

This thesis presents theoretical and experimental research on optical spatial solitons and their waveguides. Different applications are proposed and demonstrated. It is shown for the first time that, soliton-induced waveguides can be used to build optical directional couplers. By generating two mutually incoherent parallel solitons at close proximity, efficient energy transfer of a probe beam from one induced waveguide to another is observed, and the efficiency is studied as a function of the distance between the two solitons. Two important applications of soliton-induced waveguides in frequency conversion are proposed and demonstrated: second harmonic generation and optical parametric oscillation. It is shown that with soliton-induced waveguides, the conversion efficiency of second harmonic generation can be greatly improved, and the pump threshold of optical parametric oscillators can be noticeably reduced. In addition to enhanced efficiency conversion, soliton-induced waveguides offer more advantages, such as tunability. Angle tuning and electrical tuning methods are investigated. It is also proposed that optical gratings can be built by launching two coherent counter-propagating spatial solitons. The study of the mutual self-trapping of such two solitons leads to a new concept of vector solitons-counter-propagating solitons. The theories and experimental results of this new vector soliton are presented, and the reflection from the grating is observed. Two other topics of vector solitons are also investigated. (1) Theoretical and experimental results show that the collision between two vector solitons can offer a feather that is not existent with scalar solitons: energy exchange. (2) (2+1)D multimode solitons are demonstrated for the first time.

Lan, Song

49

Impaired spatial selectivity and intact phase precession in two-dimensional virtual reality.

During real-world (RW) exploration, rodent hippocampal activity shows robust spatial selectivity, which is hypothesized to be governed largely by distal visual cues, although other sensory-motor cues also contribute. Indeed, hippocampal spatial selectivity is weak in primate and human studies that use only visual cues. To determine the contribution of distal visual cues only, we measured hippocampal activity from body-fixed rodents exploring a two-dimensional virtual reality (VR). Compared to that in RW, spatial selectivity was markedly reduced during random foraging and goal-directed tasks in VR. Instead we found small but significant selectivity to distance traveled. Despite impaired spatial selectivity in VR, most spikes occurred within ?2-s-long hippocampal motifs in both RW and VR that had similar structure, including phase precession within motif fields. Selectivity to space and distance traveled were greatly enhanced in VR tasks with stereotypical trajectories. Thus, distal visual cues alone are insufficient to generate a robust hippocampal rate code for space but are sufficient for a temporal code. PMID:25420065

Aghajan, Zahra M; Acharya, Lavanya; Moore, Jason J; Cushman, Jesse D; Vuong, Cliff; Mehta, Mayank R

2015-01-01

50

Dynamics and spatial correlation of voids in dense two dimensional colloids

NASA Astrophysics Data System (ADS)

Two dimensional (2D) colloids show interesting phase and dynamic behaviors. In 2D, there is another intermediate phase, called hexatic, between isotropic liquid and solid phases. 2D colloids also show strongly correlated dynamic behaviors in hexatic and solid phases. We perform molecular dynamics simulations for 2D colloids and illustrate how the local structure and dynamics of colloids near phase transitions are reflected in the spatial correlations and dynamics of voids. Colloids are modeled as hard discs and a void is defined as a tangent circle (a pore) to three nearest hard discs. The variation in pore diameters represents the degree of disorder in voids and decreases sharply with the area fraction (?) of colloids after a hexagonal structural motif of colloids becomes significant and the freezing transition begins at ? ? 0.7. The growth of ordered domains of colloids near the phase transition is captured in the spatial correlation functions of pores. We also investigate the topological hopping probability and the topological lifetime of colloids in different topological states, and find that the stability of different topological states should be related to the size variation of local pores: colloids in six-fold states are surrounded by the most ordered and smallest pores with the longest topological lifetime. The topological lifetime of six-fold states increases by about 50 times as ? increases from liquid to hexatic to solid phases. We also compare four characteristic times in order to understand the slow and unique dynamics of two dimensional colloids: a caging time (?c), a topological lifetime (?top), a pore lifetime (?p), and a translational relaxation time (??).

Kim, Jeongmin; Sung, Bong June

2014-07-01

51

Combined Akhmediev breather and Kuznetsov–Ma solitons in a two-dimensional graded-index waveguide

NASA Astrophysics Data System (ADS)

We study the (2 + 1)-dimensional coupled nonlinear Schrödinger equation with variable coefficients in a graded-index waveguide, and present a combined Akhmediev breather and Kuznetsov–Ma soliton solution with nonautonomous characteristics for certain functional relations. From this solution, by modulating the relation between the maximum effective propagation distance Zmax and the periodic locations Zm based on the maximum amplitude of soliton solution, different types of controllable excitation behaviors such as limitation excitation, maintenance and postponement are demonstrated.

Zhu, Hai-Ping; Pan, Zhen-Huan

2014-04-01

52

NASA Astrophysics Data System (ADS)

A photovoltaic dark spatial soliton is generated in a planar waveguide produced by the implantation of protons into a copper-doped lithium niobate crystal. Stationary soliton regimes are achieved at powers 90 and 30 ?W at wavelengths 633 and 532 nm, respectively.

Kruglov, V. G.; Shandarov, V. M.; Tan, Ya; Chen, F.; Kip, D.

2008-11-01

53

Dark spatial solitons splitting in logarithmically saturable nonlinear media

NASA Astrophysics Data System (ADS)

We numerically simulate the evolution of the dark-notch-bearing optical beam in the logarithmically saturable nonlinear media based on beam propagation method (BPM). The simulation results indicate that the multiple dark spatial solitons are deep, possible in this type of nonlinear media. The number of multiple dark spatial solitons depends on the width of the dark notch, the initial conditions and the peak intensity of the initial input beam. Under the odd and even initial conditions, the odd and even number sequence of multiple dark spatial solitons can be obtained, respectively. For an input beam with fixed optical intensity, the number of dark solitons increases with the width of the initial input dark notch. The behavior of the multiple dark solitons in this type of media is similar to that in a photorefractive nonlinear crystal.

Zhang, Yuhong; Liu, Baoyuan; Lu, Keqing; Liu, Wangyun; Han, Jun

2014-12-01

54

ERIC Educational Resources Information Center

We investigated whether and how student performance on three types of spatial cognition tasks differs when worked with two-dimensional or stereoscopic representations. We recruited nineteen middle school students visiting a planetarium in a large Midwestern American city and analyzed their performance on a series of spatial cognition tasks in…

Price, Aaron; Lee, Hee-Sun

2010-01-01

55

Two-dimensional spatially periodic electron flow in various emission regimes

NASA Astrophysics Data System (ADS)

We study the effects of cathode surface curvature on the space charge limited current emitted by a two-dimensional periodic array of field emitters. Each of these emitters has a shape described by a simple analytic function. Linear, quadratic, and Fowler-Nordheim current-field dependences of the cathode emissivity as well as the infinite emissivity Child-Langmuir model are considered. We develop a mathematical anzatz to capture the main features of the potential field structure of this system and supplement it with a set of correction functions with free parameters. A special least square procedure is used for an approximate solution of this nonlinear problem. We find that even a smooth curved cathode can yield significant spatial variations in the current density but for the cases considered it does not change substantially the total current (properly adjusted). When the cathode emissivity and/or the applied voltage are high enough the current density from the top of the cathode bump (where the curvature is maximal) exceeds the current density produced by a flat cathode with infinite emissivity placed at the same distance from the anode. An explanation of this effect is given. The spatial pattern of emission is determined almost solely by the cathode curvature no matter how strong the current is.

Rokhlenko, A.; Lebowitz, J. L.

2010-05-01

56

Beamforming of sound from two-dimensional arrays using spatial matched filters

Fully-sampled two-dimensional (2D) arrays can have two-way focusing of the ultrasound beam in both lateral directions leading to high quality, real-time three-dimensional (3D) imaging. However, fully-sampled 2D arrays with very large element counts (>16?000) are difficult to manufacture due to interconnect density and large element electrical impedance. As an alternative, row-column or crossed electrode arrays have been proposed to simplify transducer fabrication and system integration. These types of arrays consist of two one-dimensional arrays oriented perpendicular to each other. Using conventional delay-and-sum beamforming, each array performs one-way focusing in perpendicular lateral directions which yield higher sidelobe and acoustic clutter levels compared to fully-sampled 2D arrays with two-way focusing. In this paper, the use of spatial matched filters to improve focusing of row-column arrays is investigated. On receive, data from each element are first spatial match filtered in the elevation direction. After summation, the data are filtered again in the azimuth direction. Beam widths comparable to one-way focusing are seen in azimuth and beam widths comparable to two-way focusing are achieved in elevation. 3D beam patterns from computer simulation results using a 7.5?MHz 128?×?128 row-column array are shown with comparison to a fully sampled 2D array. PMID:24180780

Yen, Jesse T.

2013-01-01

57

Numerical simulation of two-dimensional spatially-developing mixing layers

NASA Technical Reports Server (NTRS)

Two-dimensional, incompressible, spatially developing mixing layer simulations are performed at Re = 10(exp 2) and 10(exp 4) with two classes of perturbations applied at the inlet boundary; combinations of discrete modes from linear stability theory, and a broad spectrum of modes derived from experimentally measured velocity spectra. The effect of the type and strength of inlet perturbations on vortex dynamics and time-averaged properties are explored. Two-point spatial velocity and autocorrelations are used to estimate the size and lifetime of the resulting coherent structures and to explore possible feedback effects. The computed time-averaged properties such as mean velocity profiles, turbulent statistics, and spread rates show good agreement with experimentally measured values. It is shown that by forcing with a broad spectrum of modes derived from an experimental energy spectrum many experimentally observed phenomena can be reproduced by a 2-D simulation. The strength of the forcing merely affected the length required for the dominant coherent structures to become fully-developed. Thus intensities comparable to those of the background turbulence in many wind tunnel experiments produced the same results, given sufficient simulation length.

Wilson, R. V.; Demuren, A. O.

1994-01-01

58

NASA Astrophysics Data System (ADS)

The electronic properties of macromolecular semiconductor thin films depend profoundly on their solid-state microstructure, which in turn is governed, among other things, by the processing conditions selected and the polymer's chemical nature and molecular weight. Specifically, low-molecular-weight materials form crystalline domains of cofacially ?-stacked molecules, while the usually entangled nature of higher-molecular-weight polymers leads to microstructures comprised of molecularly ordered crystallites interconnected by amorphous regions. Here, we examine the interplay between extended exciton states delocalized along the polymer backbones and across polymer chains within the ? stack, depending on the structural development with molecular weight. Such two-dimensional excitations can be considered as Frenkel excitons in the limit of weak intersite coupling. We combine optical spectroscopies, thermal probes, and theoretical modeling, focusing on neat poly(3-hexylthiophene) (P3HT)—one of the most extensively studied polymeric semiconductors—of weight-average molecular weight (Mw) of 3-450 kg/mol. In thin-film structures of high-molecular-weight materials (Mw > 50 kg/mol), a balance of intramolecular and intermolecular excitonic coupling results in high exciton coherence lengths along chains (˜4.5 thiophene units), with interchain coherence limited to ˜2 chains. In contrast, for structures of low-Mw P3HT (<50 kg/mol), the interchain exciton coherence is dominant (˜30% higher than in architectures formed by high-molecular-weight materials). In addition, the spatial coherence within the chain is significantly reduced (by nearly 25%). These observations give valuable structural information; they suggest that the macromolecules in aggregated regions of high-molecular-weight P3HT adopt a more planar conformation compared to low-molecular-weight materials. This results in the observed increase in intrachain exciton coherence. In contrast, shorter chains seem to lead to torsionally more disordered architectures. A rigorous, fundamental description of primary photoexcitations in ?-conjugated polymers is hence developed: two-dimensional excitons are defined by the chain-length dependent molecular arrangement and interconnectivity of the conjugated macromolecules, leading to interplay between intramolecular and intermolecular spatial coherence.

Paquin, Francis; Yamagata, Hajime; Hestand, Nicholas J.; Sakowicz, Maciej; Bérubé, Nicolas; Côté, Michel; Reynolds, Luke X.; Haque, Saif A.; Stingelin, Natalie; Spano, Frank C.; Silva, Carlos

2013-10-01

59

Spatial solitons in chi(2) planar photonic crystals.

We analyze light self-confinement induced by multiple nonlinear resonances in a two-dimensional chi(2) photonic crystal. With reference to second-harmonic generation in a hexagonal lattice, we show that the system can not only support two-color (1+1)D solitary waves with enhanced confinement and steering capabilities but also enable novel features such as wavelength-dependent soliton routing. PMID:17975626

Gallo, Katia; Assanto, Gaetano

2007-11-01

60

Waveguides formed by quasi-steady-state photorefractive spatial solitons

NASA Astrophysics Data System (ADS)

We show that a quasi-steady-state photorefractive spatial soliton forms a waveguide structure in the bulk of a photorefractive material. Although the optically induced waveguide is formed by a very low-power (microwatts) soliton beam, it can guide a powerful (watt) beam of a longer wavelength at which the medium is nonphotosensitive. Furthermore, the waveguide survives, either in the dark or when guiding the longer-wavelength beam, for a long time after the soliton beam is turned off. We take advantage of the solitons' property of evolution from a relatively broad input beam into a narrow channel and show that the soliton induces a tapered waveguide (an optical funnel) that improves the coupling efficiency of light into the waveguiding structure.

Morin, Matthew; Duree, Galen; Salamo, Gregory; Segev, Mordechai

1995-10-01

61

Bright and dark spatial solitons in metallic nanowire arrays

NASA Astrophysics Data System (ADS)

We investigate the formation and propagation of bright and dark three-dimensional unstaggered spatial solitons with cylindrical symmetry in a nonlinear nanowire metamaterial. The metamaterial is formed by metallic nanowires embedded in a Kerr-type dielectric host and is modeled using an effective medium approach. Unlike conventional Kerr media, the metamaterial supports bright solitons when the host is a self-defocusing material and dark solitons when the host is a self-focusing material. Our numerical calculations show that the confinement of the spatial-solitons results from the interplay of the host nonlinear response strength and the hyperbolic dispersion of the photonic states in the nanowire array. Subwavelength solitary beams may be observed for sufficiently strong nonlinearities.

Fernandes, David E.; Silveirinha, Mário G.

2014-08-01

62

NASA Astrophysics Data System (ADS)

In this paper, a modified cubic B-spline differential quadrature method (MCB-DQM) is employed for the numerical simulation of two-space dimensional nonlinear sine-Gordon equation with appropriate initial and boundary conditions. The modified cubic B-spline works as a basis function in the differential quadrature method to compute the weighting coefficients. Accordingly, two dimensional sine-Gordon equation is transformed into a system of second order ordinary differential equations (ODEs). The resultant system of ODEs is solved by employing an optimal five stage and fourth-order strong stability preserving Runge-Kutta scheme (SSP-RK54). Numerical simulation is discussed for both damped and undamped cases. Computational results are found to be in good agreement with the exact solution and other numerical results available in the literature.

Shukla, H. S.; Tamsir, Mohammad; Srivastava, Vineet K.

2015-01-01

63

NASA Astrophysics Data System (ADS)

The propagation of light beams is studied in a planar photorefractive waveguide fabricated by high-temperature diffusion of metal ions in the Z-cut substrate of the 3m symmetry crystal. The wave equations are obtained for single-mode light beams with TE and TM polarisations in planar diffusion waveguides, which take into account the two-dimensional distribution of the optical field. Expressions are found for a nonlinear change in the refractive index when the photovoltaic mechanism makes a dominant contribution to the photorefractive effect. The propagation of single-mode light beams is analysed numerically for a Ti:Fe:LiNbO3 waveguide fabricated by the successive diffusion of titanium and iron into lithium niobate. It is shown that single-mode light beams with a smooth amplitude envelope can propagate without significant changes in the region of a dip in the intensity modelling a dark soliton. The relations between the amplitude and width of a dark spatial soliton are obtained for the TM modes of a photorefractive planar waveguide.

Frolova, M. N.; Borodin, M. V.; Shandarov, S. M.; Shandarov, V. M.; Larionov, Yu M.

2003-11-01

64

NASA Astrophysics Data System (ADS)

A new two dimensional codes family, namely two dimensional multi-diagonal (2D-MD) codes, is proposed for spectral/spatial non-coherent OCDMA systems based on the one dimensional MD code. Since the MD code has the property of zero cross correlation, the proposed 2D-MD code also has this property. So that, the multi-access interference (MAI) is fully eliminated and the phase induced intensity noise (PIIN) is suppressed with the proposed code. Code performance is analyzed in terms of bit error rate (BER) while considering the effect of shot noise, PIIN, and thermal noise. The performance of the proposed code is compared with the related MD, modified quadratic congruence (MQC), two dimensional perfect difference (2D-PD) and two dimensional diluted perfect difference (2D-DPD) codes. The analytical and the simulation results reveal that the proposed 2D-MD code outperforms the other codes. Moreover, a large number of simultaneous users can be accommodated at low BER and high data rate.

Kadhim, Rasim Azeez; Fadhil, Hilal Adnan; Aljunid, S. A.; Razalli, Mohamad Shahrazel

2014-10-01

65

Generation and dynamics of quadratic birefringent spatial gap solitons

A method is proposed to generate and study the dynamics of spatial light solitons in a birefringent medium with quadratic nonlinearity. Although no analytical expression for propagating solitons has been obtained, our numerical simulations show the existence of stable localized spatial solitons in the frequency forbidden band gap of the medium. The dynamics of these objects is quite rich and manifests for instance elastic reflections, or inelastic collisions where two solitons merge and propagate as a single solitary wave. We derive the dynamics of the slowly varying envelopes of the three fields (second harmonic pump and two-component signal) and study this new system theoretically. We show that it does present a threshold for nonlinear supratransmission that can be calculated from a series expansion approach with a very high accuracy. Specific physical implications of our theoretical predictions are illustrated on LiGaTe{sub 2} (LGT) crystals. Once irradiated by a cw laser beam of 10 {mu}m wavelength, at an incidence beyond the extinction angle, such crystals will transmit light, in the form of spatial solitons generated in the nonlinear regime above the nonlinear supratransmission threshold.

Anghel-Vasilescu, P. [Max Planck Institute for the Physics of Complex Systems, Noethnitzer Str. 38, D-01187 Dresden (Germany); Dorignac, J.; Geniet, F.; Leon, J. [Laboratoire Charles Coulomb, Departement de Physique Theorique, UMR 5221 CNRS-UM2, Universite Montpellier 2, F-34095 Montpellier Cedex 5 (France); Taki, A. [Laboratoire de Physique des Lasers, Atomes et Molecules, CNRS-INP-UMR8523, Universite des Sciences et Technologies de Lille, F-59655 Villeneuve d'Ascq (France)

2011-04-15

66

Splitting after collision of high-order bright spatial solitons in Kerr media.

By numerically studying the collision between (1 + 1)-Dimensional high order bright spatial solitons in a Kerr nonlinear media we show that after the collision, the high order solitons split into a number of first order solitons that corresponds to its order. Two different collision scenarios are considered: collision between two independent high order solitons and a collision with a virtual soliton simulated by the reflection at an angle of a high order soliton at a linear interface. The results demonstrate that in both cases the high order solitons split showing minor differences. PMID:25607025

Castillo, M D Iturbe; Cerda, S Chavez; Martinez, D Ramirez

2014-12-15

67

Soliton gyroscopes in media with spatially growing repulsive nonlinearity

We find that the recently introduced model of self-trapping supported by a spatially growing strength of a repulsive nonlinearity gives rise to robust vortex-soliton tori, i.e., three-dimensional vortex solitons, with topological charges S. The family with S=1 is completely stable, while the one with S=2 has alternating regions of stability and instability. The families are nearly exactly reproduced in an analytical form by the Thomas-Fermi approximation (TFA). Unstable states with S=2 and 3 split into persistently rotating pairs or triangles of unitary vortices. Application of a moderate torque to the vortex torus initiates a persistent precession mode, with the torus' axle moving along a conical surface. A strong torque heavily deforms the vortex solitons, but, nonetheless, they restore themselves with the axle oriented according to the vectorial addition of angular momenta.

Driben, Rodislav; Malomed, Boris A; Meier, Torsten; Torner, Lluis

2013-01-01

68

Two-dimensional spatial tuning for saccades in human parieto-frontal cortex.

Saccades in the frontoparallel plane are targeted at two-dimensional (2D) locations, defined by direction and amplitude. Macaque neurophysiology has shown that these dimensions are jointly represented in single intraparietal sulcus (IPS) and frontal eye fields (FEF) neurons, constituting multiple maps of 2D saccade space. Human fMRI has shown that the direction of the saccade is topographically represented across large neuronal groups. However, it is unknown whether both direction and amplitude are separable dimensions at the voxel level and whether these tuning variables are organized in large-scale topographic maps. We used fMRI to address these issues in subjects performing an instructed-delay saccade task to 18 locations (6 directions, 3 amplitudes). Singular value decomposition was applied to the corresponding response field of each voxel, providing an index of the separability into direction and amplitude tuning. Our findings show that saccade location tuning is composed of separable direction and amplitude components within voxels across the parieto-frontal network. In both IPS and FEF there were amplitude gradients and reversals of direction tuning across voxels, with a medio-lateral gradient of decreasing saccade amplitude along the IPS. These findings reveal the 2D cortical organization of saccade space within and across voxels and hold great potential for the study of other sensorimotor systems. PMID:24099846

Leoné, Frank T M; Toni, Ivan; Medendorp, W Pieter

2014-02-15

69

Spatial coherence analysis applied to aberration correction using a two-dimensional array system

NASA Astrophysics Data System (ADS)

Complex degree of coherence functions are computed using synthetic and measured ultrasound data to demonstrate noteworthy aspects of coherence analysis in the context of aberration correction. Coherence functions calculated from synthetic data illustrate the importance of proper normalization of the constituent cross-correlation integrals when weak elements and receiver directivity are significant factors. The synthetic data also show that a spike can occur at the zero-lag position of the coherence function when the signal-to-noise ratio is reduced by element directivity near the edges of a large aperture. The latter observation is confirmed by experimental data acquired through tissue-mimicking distributed aberration phantoms using a low f-number two-dimensional array system. The coherence of data acquired at neighboring elements is not changed by time-shift compensation of transmit and receive focusing, but time-shift compensation does improve the coherence of echoes measured over larger separations. The resulting increase in coherence widths evaluated at levels between 0.2 and 0.5 is correlated with narrower -10 dB and -20 dB effective widths in focuses visualized using single-transmit images. Iterative focus compensation methods may benefit from aberration estimation algorithms that take advantage of these longer-range correlations in random-scattering waveforms.

Lacefield, James C.; Waag, Robert C.

2002-12-01

70

A spatial multigrid iterative method for two-dimensional discrete-ordinates transport problems

Iterative solutions of the Boltzmann transport equation are computationally intensive. Spatial multigrid methods have led to efficient iterative algorithms for solving a variety of partial differential equations; thus, it is natural to explore...

Lansrud, Brian David

2005-08-29

71

NASA Astrophysics Data System (ADS)

Complex numerical models of the Earth's environment, based around 3-D or 4-D time and space domains are routinely used for applications including climate predictions, weather forecasts, fishery management and environmental impact assessments. Quantitatively assessing the ability of these models to accurately reproduce geographical patterns at a range of spatial and temporal scales has always been a difficult problem to address. However, this is crucial if we are to rely on these models for decision making. Satellite data are potentially the only observational dataset able to cover the large spatial domains analysed by many types of geophysical models. Consequently optical wavelength satellite data is beginning to be used to evaluate model hindcast fields of terrestrial and marine environments. However, these satellite data invariably contain regions of occluded or missing data due to clouds, further complicating or impacting on any comparisons with the model. A methodology has recently been developed to evaluate precipitation forecasts using radar observations. It allows model skill to be evaluated at a range of spatial scales and rain intensities. Here we extend the original method to allow its generic application to a range of continuous and discontinuous geophysical data fields, and therefore allowing its use with optical satellite data. This is achieved through two major improvements to the original method: (i) all thresholds are determined based on the statistical distribution of the input data, so no a priori knowledge about the model fields being analysed is required and (ii) occluded data can be analysed without impacting on the metric results. The method can be used to assess a model's ability to simulate geographical patterns over a range of spatial scales. We illustrate how the method provides a compact and concise way of visualising the degree of agreement between spatial features in two datasets. The application of the new method, its handling of bias and occlusion and the advantages of the novel method are demonstrated through analyzing model fields from a marine ecosystem model.

Saux Picart, S.; Butenschön, M.; Shutler, J. D.

2011-11-01

72

We have investigated the improvement in the signal-to-noise ratio for a coherent Doppler lidar through the use of a multi-element heterodyne detector array. Such an array enables the spatial summation of atmospheric refractive turbulence induced speckles, and time varying target speckles. Our recent experiments have shown that the non-coherent summation of the lidar signals from a heterodyne detector array can

Kin Pui Chan; Dennis K. Killinger

1992-01-01

73

NASA Astrophysics Data System (ADS)

Complex numerical models of the Earth's environment, based around 3-D or 4-D time and space domains are routinely used for applications including climate predictions, weather forecasts, fishery management and environmental impact assessments. Quantitatively assessing the ability of these models to accurately reproduce geographical patterns at a range of spatial and temporal scales has always been a difficult problem to address. However, this is crucial if we are to rely on these models for decision making. Satellite data are potentially the only observational dataset able to cover the large spatial domains analysed by many types of geophysical models. Consequently optical wavelength satellite data is beginning to be used to evaluate model hindcast fields of terrestrial and marine environments. However, these satellite data invariably contain regions of occluded or missing data due to clouds, further complicating or impacting on any comparisons with the model. This work builds on a published methodology, that evaluates precipitation forecast using radar observations based on predefined absolute thresholds. It allows model skill to be evaluated at a range of spatial scales and rain intensities. Here we extend the original method to allow its generic application to a range of continuous and discontinuous geophysical data fields, and therefore allowing its use with optical satellite data. This is achieved through two major improvements to the original method: (i) all thresholds are determined based on the statistical distribution of the input data, so no a priori knowledge about the model fields being analysed is required and (ii) occluded data can be analysed without impacting on the metric results. The method can be used to assess a model's ability to simulate geographical patterns over a range of spatial scales. We illustrate how the method provides a compact and concise way of visualising the degree of agreement between spatial features in two datasets. The application of the new method, its handling of bias and occlusion and the advantages of the novel method are demonstrated through the analysis of model fields from a marine ecosystem model.

Saux Picart, S.; Butenschön, M.; Shutler, J. D.

2012-02-01

74

Metamaterials for remote generation of spatially controllable two dimensional array of microplasma.

Since the initial demonstration of negative refraction and cloaking using metamaterials, there has been enormous interest and progress in making practical devices based on metamaterials such as electrically small antennas, absorbers, modulators, detectors etc that span over a wide range of electromagnetic spectrum covering microwave, terahertz, infrared (IR) and optical wavelengths. We present metamaterial as an active substrate where each unit cell serves as an element for generation of plasma, the fourth state of matter. Sub-wavelength localization of incident electromagnetic wave energy, one of the most interesting properties of metamaterials is employed here for generating high electric field to ignite and sustain microscale plasmas. Frequency selective nature of the metamaterial unit cells make it possible to generate spatially localized microplasma in a large array using multiple resonators. A dual resonator topology is shown for the demonstration. Since microwave energy couples to the metamaterial through free space, the proposed approach is naturally wireless. Such spatially controllable microplasma arrays provide a fundamentally new material system for future investigations in novel applications, e.g. nonlinear metamaterials. PMID:25098976

Singh, Pramod K; Hopwood, Jeffrey; Sonkusale, Sameer

2014-01-01

75

The electronic properties of macromolecular semiconductor thin films depend profoundly on their solid-state microstructure, which in turn is governed, among other things, by the processing conditions selected and the polymer chemical nature and molecular weight. Specifically, low-molecular-weight materials form crystalline domains of cofacially $\\pi$-stacked molecules, while the usually entangled nature of higher molecular-weight polymers leads to microstructures comprised of molecularly ordered crystallites interconnected by amorphous regions. Here, we examine the interplay between extended exciton states delocalized along the polymer backbones and across polymer chains within the $\\pi$-stack, depending on the structural development with molecular weight. We combine optical spectroscopies, thermal probes, and theoretical modeling, focusing on neat poly(3-hexylthiophene) (P3HT), one of the most extensively studied polymer semiconductors, of weight-average molecular weight of 3-450\\,kg/mol. The spatial coheren...

Paquin, Francis; Hestand, Nicholas J; Sakowicz, Maciej; Bérubé, Nicolas; Côté, Michel; Reynolds, Luke X; Haque, Saif A; Stingelin, Natalie; Spano, Frank C; Silva, Carlos

2013-01-01

76

NASA Technical Reports Server (NTRS)

We have investigated the improvement in the signal-to-noise ratio for a coherent Doppler lidar through the use of a multi-element heterodyne detector array. Such an array enables the spatial summation of atmospheric refractive turbulence induced speckles, and time varying target speckles. Our recent experiments have shown that the non-coherent summation of the lidar signals from a heterodyne detector array can enhance the heterodyne mixing efficiency and thus the signal-to-noise ratio. In this paper, we expand this work to include the coherent summation of array signals. The digitized heterodyne signals were stored in a personal computer. Fast Fourier transforms were performed on both the non-coherent and coherent summations of the detector array signals. It was found that the coherent summation greatly enhanced the accuracy in the Doppler frequency estimate. A theoretical analysis was performed and indicated good agreement with experimental results. We have also applied these results to the more general lidar applications including atmospheric wind sensing, and have found that in most lidar applications the Doppler frequency estimate is increased through the use of the heterodyne detector array.

Chan, Kin Pui; Killinger, Dennis K.

1992-01-01

77

NASA Astrophysics Data System (ADS)

Recent research has shown that KCl:Eu2+ has great potential for use in megavoltage radiation therapy dosimetry because this material exhibits excellent storage performance and is reusable due to strong radiation hardness. This work reports the authors’ attempts to fabricate 2D KCl:Eu2+ storage phosphor films (SPFs) using both a physical vapor deposition (PVD) method and a tape casting method. X-ray diffraction analysis showed that a 10 µm thick PVD sample was composed of highly crystalline KCl. No additional phases were observed, suggesting that the europium activator had been completely incorporated into the KCl matrix. Photostimulated luminescence and photoluminescence spectra suggested that F (Cl-) centers were the electron storage centers post x-ray irradiation and that Eu2+ cations acted as luminescence centers in the photostimulation process. The 150 µm thick casted KCl:Eu2+ SPF showed sub-millimeter spatial-resolution. Monte Carlo simulations further demonstrated that the admixture of 20% KCl:Eu2+ and 80% low Z polymer binder exhibited almost no energy-dependence in a 6 MV beam. KCl:Eu2+ pellet samples showed a large dynamic range from 0.01 cGy to 60 Gy dose-to-water, and saturated at approximately 500 Gy as a result of KCl's intrinsic high radiation hardness. Taken together, this work provides strong evidence that KCl:Eu2+-based SPF with associated readout apparatus could result in a novel electronic film system that has all the desirable features associated with classic radiographic film and, importantly, water equivalence and the capability of permanent identification of each detector.

Li, H. Harold; Driewer, Joseph P.; Han, Zhaohui; Low, Daniel A.; Yang, Deshan; Xiao, Zhiyan

2014-04-01

78

Effect of four-wave mixing on copropagating spatial solitons

NASA Astrophysics Data System (ADS)

It is known that in the absence of four-wave mixing, spatial solitons of two frequencies can copropagate stably in a Kerr-law nonlinear medium. We investigate the effect of including four-wave mixing. We show that when phase-matching conditions are satisfied, Stokes and anti-Stokes waves can be generated to produce a new steady-state solution consisting of four copropagating beams. On the other hand, if weak signal beams are injected along with the pump beams, then four-wave mixing can be used to amplify those side beams. When phase-matching conditions are not satisfied, the Stokes and anti-Stokes waves simply propagate as linear modes in the effective waveguides induced by the pump solitons.

Ansari, Nadeem A.; Sammut, Rowland A.; Tran, Hai-Tan

1996-07-01

79

Spatial optical solitons in highly nonlocal media

NASA Astrophysics Data System (ADS)

We theoretically investigate the propagation of bright spatial solitary waves in highly nonlocal media possessing radial symmetry in a three-dimensional cylindrical geometry. Focusing on a thermal nonlinearity, modeled by a Poisson equation, we show how the profile of the light-induced waveguide strongly depends on the extension of the nonlinear medium in the propagation direction as compared to the beamwidth. We demonstrate that self-trapped beams undergo oscillations in size, either periodically or aperiodically, depending on the input waist and power. The—usually neglected—role of the longitudinal nonlocality as well as the detrimental effect of absorptive losses are addressed.

Alberucci, Alessandro; Jisha, Chandroth P.; Smyth, Noel F.; Assanto, Gaetano

2015-01-01

80

Background Implementation of DWI in the abdomen is challenging due to artifacts, particularly those arising from differences in tissue susceptibility. Two-dimensional, spatially-selective radiofrequency (RF) excitation pulses for single-shot echo-planar imaging (EPI) combined with a reduction in the FOV in the phase-encoding direction (i.e. zooming) leads to a decreased number of k-space acquisition lines, significantly shortening the EPI echo train and potentially susceptibility artifacts. Purpose To assess the feasibility and image quality of a zoomed diffusion-weighted EPI (z-EPI) sequence in MR imaging of the pancreas. The approach is compared to conventional single-shot EPI (c-EPI). Material and Methods 23 patients who had undergone an MRI study of the abdomen were included in this retrospective study. Examinations were performed on a 3T whole-body MR system (Magnetom Skyra, Siemens) equipped with a two-channel fully dynamic parallel transmit array (TimTX TrueShape, Siemens). The acquired sequences consisted of a conventional EPI DWI of the abdomen and a zoomed EPI DWI of the pancreas. For z-EPI, the standard sinc excitation was replaced with a two-dimensional spatially-selective RF pulse using an echo-planar transmit trajectory. Images were evaluated with regard to image blur, respiratory motion artifacts, diagnostic confidence, delineation of the pancreas, and overall scan preference. Additionally ADC values of the pancreatic head, body, and tail were calculated and compared between sequences. Results The pancreas was better delineated in every case (23/23) with z-EPI versus c-EPI. In every case (23/23), both readers preferred z-EPI overall to c-EPI. With z-EPI there was statistically significantly less image blur (p<0.0001) and respiratory motion artifact compared to c-EPI (p<0.0001). Diagnostic confidence was statistically significantly better with z-EPI (p<0.0001). No statistically significant differences in calculated ADC values were observed between the two sequences. Conclusion Zoomed diffusion-weighted EPI leads to substantial image quality improvements with reduction of susceptibility artifacts in pancreatic DWI. PMID:24594702

Riffel, Philipp; Michaely, Henrik J.; Morelli, John N.; Pfeuffer, Josef; Attenberger, Ulrike I.; Schoenberg, Stefan O.; Haneder, Stefan

2014-01-01

81

We present a new method for the determination of the two-dimensional (2D) projected spatial distribution of globular clusters (GCs) in external galaxies. This method is based on the K-Nearest Neighbor density estimator of Dressler, complemented by Monte-Carlo simulations to establish the statistical significance of the results. We apply this method to NGC 4261, a ''test galaxy'' where significant 2D anisotropy in the GC distribution has been reported. We confirm that the 2D distribution of GC is not azimuthally isotropic. Moreover, we demonstrate that the 2D distribution departures from the average GC radial distribution results in highly significant spiral-like or broken shell features. Overall, the same perturbations are found in ''red'' and ''blue'' GCs, but with some differences. In particular, we observe a central feature, roughly aligned with the minor axis of NGC 4261, composed of red and most luminous GCs. Blue and fainter GCs are more frequent at large radial distances and follow the spiral-like features of the overall density structure. These results suggest a complex merging history for NGC 4261.

D'Abrusco, R.; Fabbiano, G.; Zezas, A.; Mineo, S.; Fragos, T.; Kim, D.-W. [Harvard-Smithsonian Astrophysical Observatory, 60 Garden Street, Cambridge, MA 02138 (United States); Strader, J. [Department of Astronomy, Michigan State University, 567 Wilson Road, East Lansing, MI 48824-2320 (United States); Bonfini, P. [Physics Department and Institute of Theoretical and Computational Physics, University of Crete, 71003 Heraklion, Crete (Greece); Luo, B. [Department of Astronomy and Astrophysics, 525 Davey Lab, The Pennsylvania State University, University Park, PA 16802 (United States); King, A. [Department of Physics and Astronomy, University of Leicester, Leicester (United Kingdom)

2013-08-20

82

Weak-beam trapping by bright spatial solitons in AlGaAs planar waveguides

NASA Astrophysics Data System (ADS)

We demonstrate experimentally the trapping and spatial wave breaking of weak signal beams by orthogonally polarized bright spatial solitons. Experiments were performed in an AlGaAs planar waveguide excited at a wavelength of 1.55 mu m .

Kang, J. U.; Stegeman, G. I.; Aitchison, J. S.

1995-10-01

83

Emissive and Langmuir probe techniques have been used to obtain two-dimensional (2D) spatial maps of the plasma potential V{sub p}, electric field E, and ion trajectories in a pulsed bipolar magnetron discharge. The magnetron was pulsed at a frequency of 100 kHz, with a 50% duty cycle and operated at an argon pressure of 0.74 Pa. The pulse wave form was characterized by three distinct phases: the 'overshoot', 'reverse', and 'on' phases. In the 'on' phase of the pulse, when the cathode voltage is driven to -670 V, the 2D spatial distribution of V{sub p} has a similar form to that in dc magnetron, with significant axial and radial electric fields in the bulk plasma, accelerating ions to the sheath edge above the cathode racetrack region. During the 'overshoot' phase (duration 200 ns), V{sub p} is raised to values greater than +330 V, more than 100 V above the cathode potential, with E pointing away from the target. In the 'reverse' phase V{sub p} has a value of +45 V at all measured positions, 2 V more positive than the target potential. In this phase there is no electric field present in the plasma. In the bulk of the plasma, the results from Langmuir probe and the emissive probe are in good agreement, however, in one particular region of the plasma outside the radius of the cathode, the emissive probe measurements are consistently more positive (up to 45 V in the 'on' time). This discrepancy is discussed in terms of the different frequency response of the probes and their perturbation of the plasma. A simple circuit model of the plasma-probe system has been proposed to explain our results. A brief discussion of the effect of the changing plasma potential distribution on the operation of the magnetron is given.

Vetushka, A.; Karkari, S.K.; Bradley, J.W. [Department of Physics, UMIST, Sackville Street, Manchester, M60 1QD (United Kingdom)

2004-11-01

84

Finite-difference weighted essentially non-oscillatory (WENO) simulations of the reshocked two-dimensional single-mode Richtmyer-Meshkov instability using third-, fifth- and ninth-order spatial flux reconstruction and uniform spatial grid resolutions corresponding to 128, 256 and 512 points per initial perturbation wavelength are presented. The dependence of the density, vorticity, simulated density Schlieren and baroclinic production fields, mixing layer width, circulation deposition, mixing profiles, chemical products and mixing fractions, energy spectra, statistics, probability distribution functions, effective turbulent kinetic energy and enstrophy production/dissipation rates, numerical Reynolds numbers, and effective numerical viscosity on the order and resolution is comprehensively investigated to long evolution times. The results are interpreted using the computed implicit numerical diffusion arising from the truncation errors in the characteristic projection-based WENO method. It is quantitatively shown that simulations with higher order and higher resolution have lower numerical dissipation. The sensitivity of the quantities considered to the order and resolution is further amplified following reshock, when the energy deposition on the evolving interface by the second shock-interface interaction induces the formation of small-scale structures. Simulations using lower orders of reconstruction and on coarser grids preserve large-scale structures and flow symmetry to late times, while simulations using higher orders of reconstruction and on finer grids exhibit fragmentation of the structures, symmetry breaking and increased mixing. The investigation demonstrates that similar flow features are qualitatively and quantitatively captured by either approximately doubling the order or the resolution. Additionally, the computational scaling shows that increasing the order is more advantageous than doubling the resolution for the complex shock-driven hydrodynamic flow and WENO method considered here. The present investigation suggests that the ninth-order WENO method is well-suited for the simulation and analysis of complex multi-scale flows and mixing generated by shock-induced hydrodynamic instabilities.

Latini, M; Schilling, O; Don, W

2006-03-16

85

Material figures of merit for spatial soliton interactions in the presence of absorption

NASA Astrophysics Data System (ADS)

The effects of linear and two-photon absorption on bright spatial soliton propagation are studied. A spatial soliton switch that achieves gain through the novel mechanism of colliding, dragging, or trapping of two fundamental solitons of different widths is proposed. Figures of merit for use in evaluating the suitability of absorbing nonlinear media for soliton switching applications are presented. The main effect of linear absorption is to limit the propagation distance, which places an upper bound on the width of the soliton in order to fit sufficient characteristic soliton propagation lengths within the device. The optical limiting nature of two-photon absorption places an upper bound on the gain that an interaction can achieve. The combined effects of linear and two-photon absorption are to reduce the gain upper bound imposed by two-photon absorption alone with the addition of the soliton width constraint. A maximized gain upper bound is determined solely by material parameters and is compared among three promising nonlinear materials. It is shown numerically that the spatial soliton dragging interaction requires shorter propagation distances and achieves greater gain than the collision interaction and that both are tolerant to the presence of absorption and can provide, with high contrast, gains of three or greater using measured material parameters. These results warrant pursuing the implementation of spatial soliton-based logic gates. .

Blair, Steve; Wagner, Kelvin H.; McLeod, Robert

1996-10-01

86

Weighted essentially non-oscillatory (WENO) simulations of the reshocked two-dimensional single-mode Richtmyer-Meshkov instability using third-, fifth- and ninth-order spatial flux reconstruction and uniform grid resolutions corresponding to 128, 256 and 512 points per initial perturbation wavelength are presented. The dependence of the density, vorticity, simulated density Schlieren and baroclinic production fields, mixing layer width, circulation deposition, mixing profiles, production and mixing fractions, energy spectra, statistics, probability distribution functions, numerical turbulent kinetic energy and enstrophy production/dissipation rates, numerical Reynolds numbers, and numerical viscosity on the order and resolution is investigated to long evolution times. The results are interpreted using the implicit numerical dissipation in the characteristic projection-based, finite-difference WENO method. It is shown that higher order higher resolution simulations have lower numerical dissipation. The sensitivity of the quantities considered to the order and resolution is further amplified following reshock, when the energy deposition by the second shock-interface interaction induces the formation of small-scale structures. Lower-order lower-resolution simulations preserve large-scale structures and flow symmetry to late times, while higher-order higher-resolution simulations exhibit fragmentation of the structures, symmetry breaking and increased mixing. Similar flow features are qualitatively and quantitatively captured by either approximately doubling the order or the resolution. Additionally, the computational scaling shows that increasing the order is more advantageous than increasing the resolution for the flow considered here. The present investigation suggests that the ninth-order WENO method is well-suited for the simulation and analysis of complex multi-scale flows and mixing generated by shock-induced hydrodynamic instabilities.

Latini, M; Schilling, O; Don, W S

2006-06-12

87

NASA Astrophysics Data System (ADS)

The propagation of intensity-modulated laser radiation in a barium—sodium niobate crystal is studied in an external electric field. The possibility of controlling a nonlinear local response of the crystal is demonstrated. It is shown experimentally that the conditions of formation of a one-dimensional spatial soliton can be changed by varying the nonlinear response of the crystal.

Assel'born, S. A.; Kundikova, N. D.; Novikov, I. V.

2008-09-01

88

NASA Astrophysics Data System (ADS)

Based on the combined compact difference scheme, an alternating direction implicit method is proposed for solving two-dimensional cubic nonlinear Schrödinger equations. The proposed method is sixth-order accurate in space and second-order accurate in time. The linear Fourier analysis method is exploited to study the stability of the proposed method. The efficiency and accuracy of the proposed method are tested numerically. The common solution pattern of the nonlinear Schrödinger equation is also illustrated using relevant examples known in the literature.

Li, Leonard Z.; Sun, Hai-Wei; Tam, Sik-Chung

2015-02-01

89

An experimental study of spatial resolution of microwave tomography was performed. Our microwave tomographic system with operational frequencies of 0.9 and 2.36 GHz and with signal-to-noise ratio of 30 dB allowed us to achieve a spatial resolution between 7.3-9.5 mm and 6.3-7.8 mm at the former and latter frequencies, respectively. It was shown in experiments, with structurally complicated objects, that

Serguei Y. Semenov; Robert H. Svenson; Alexander E. Bulyshev; Alexander E. Souvorov; Alexei G. Nazarov; Yuri E. Sizov; Vitaly G. Posukh; Andrey V. Pavlovsky; Pavel N. Repin; George P. Tatsis

2000-01-01

90

Two-component vector solitons in defocusing Kerr-type media with spatially modulated nonlinearity

NASA Astrophysics Data System (ADS)

We present a class of exact solutions to the coupled (2 + 1)-dimensional nonlinear Schrödinger equation with spatially modulated nonlinearity and a special external potential, which describe the evolution of two-component vector solitons in defocusing Kerr-type media. We find a robust soliton solution, constructed with the help of Whittaker functions. For specific choices of the topological charge, the radial mode number and the modulation depth, the solitons may exist in various forms, such as the half-moon, necklace-ring, and sawtooth vortex-ring patterns. Our results show that the profile of such solitons can be effectively controlled by the topological charge, the radial mode number, and the modulation depth.

Zhong, Wei-Ping; Beli?, Milivoj

2014-12-01

91

We used an analysis based on a geographic information system (GIS) to determine the amount of rearing habitat and stranding area for subyearling fall chinook salmon Oncorhynchus tshawytscha in the Hanford Reach of the Columbia River at steady-state flows ranging from 1,416 to 11,328 m3/s. High-resolution river channel bathymetry was used in conjunction with a two-dimensional hydrodynamic model to estimate water velocities, depths, and lateral slopes throughout our 33-km study area. To relate the probability of fish presence in nearshore habitats to measures of physical habitat, we developed a logistic regression model from point electrofishing data. We only considered variables that were compatible with a GIS and therefore excluded other variables known to be important to juvenile salmonids. Water velocity and lateral slope were the only two variables included in our final model. The amount of available rearing habitat generally decreased as flow increased, with the greatest decreases occurring between 1,416 and 4,814 m3/s. When river discharges were between 3,682 and 7,080 m3/s, flow fluctuations of 566 m3/s produced the smallest change in available rearing area (from -6.3% to +6.8% of the total). Stranding pool area was greatly reduced at steady-state flows exceeding 4,531 m3/s, but the highest net gain in stranding area was produced by 850 m3/s decreases in flow when river discharges were between 5,381 and 5,664 m3/s. Current measures to protect rearing fall chinook salmon include limiting flow fluctuations at Priest Rapids Dam to 850 m3/s when the dam is spilling water and when the weekly flows average less than 4,814 m3/s. We believe that limiting flow fluctuations at all discharges would further protect subyearling fall chinook salmon.

Tiffan, K.F.; Garland, R.D.; Rondorf, D.W.

2002-01-01

92

A grid resolution sensitivity analysis using a two-dimensional flood inundation model has been presented in this paper. Simulations for 6 dam breaches located randomly in the United States were run at 10,30,60,90, and 120 meter resolutions. The dams represent a range of topographic conditions, ranging from 0% slope to 1.5% downstream of the dam. Using 10 meter digital elevation model (DEM) simulation results as the baseline, the coarser simulation results were compared in terms of flood inundation area, peak depths, flood wave travel time, daytime and nighttime population in flooded area, and economic impacts. The results of the study were consistent with previous grid resolution studies in terms of inundated area, depths, and velocity impacts. The results showed that as grid resolution is decreased, the relative fit of inundated area between the baseline and coarser resolution decreased slightly. This is further characterized by increasing over prediction as well as increasing under prediction with decreasing resolution. Comparison of average peak depths showed that depths generally decreased as resolution decreased, as well as the velocity. It is, however, noted that the trends in depth and velocity showed less consistency than the inundation area metrics. This may indicate that for studies in which velocity and depths must be resolved more accurately (urban environments when flow around buildings is important in the calculation of drag effects), higher resolution DEM data should be used. Perhaps the most significant finding from this study is the perceived insensitivity of socio-economic impacts to grid resolution. The difference in population at risk (PAR) and economic cost generally remained within 10% of the estimated impacts using the high resolution DEM. This insensitivity has been attributed to over estimated flood area and associated socio-economic impacts compensating for under estimated flooded area and associated socio-economic impacts. The United States has many dams that are classified as high-hazard potential that need an emergency action plan (EAP). It has been found that the development of EAPs for all high-hazard dams is handicapped due to funding limitations. The majority of the cost associated with developing an EAP is determining the flooded area. The results of this study have shown that coarse resolution dam breach studies can be used to provide an acceptable estimate of the inundated area and economic impacts, with very little computational cost. Therefore, the solution to limited funding may be to perform coarse resolution dam breach studies on high-hazard potential dams and use the results to help prioritize the order in which detailed EAPs should be developed.

Judi, David R [Los Alamos National Laboratory; Mcpherson, Timothy N [Los Alamos National Laboratory; Burian, Steven J [UNIV OF UTAH

2009-01-01

93

We report what is to our knowledge the first demonstration of phase-sensitive coherent summation of individual heterodyne detector array signals for the enhanced detection of spatially distorted laser Doppler returns. With the use of a 2 x 2 heterodyne detector array, the phase and amplitude of a time-varying speckle pattern was detected, and the signal-to-noise ratio of the Doppler shift estimate was shown to be improved by a factor of 2, depending on the extent of spatial coherence loss. These results are shown to agree with a first-order analysis and indicate the advantage of coherent summation for both short-range laser Doppler velocimetry and long-range atmospheric coherent lidar. PMID:19798145

Chan, K P; Killinger, D K

1992-09-01

94

NASA Astrophysics Data System (ADS)

We demonstrate the existence of one- and two-dimensional (1D and 2D, respectively) bright solitons in the Bose-Einstein condensate with repulsive dipole-dipole interactions induced by a combination of dc and ac polarizing fields, oriented perpendicular to the plane in which the BEC is trapped, assuming that the strength of the fields grows in the radial (r) direction faster than r3. Stable tightly confined 1D and 2D fundamental solitons, twisted solitons in 1D, and solitary vortices in 2D are found in a numerical form. The fundamental solitons remain robust under the action of an expulsive potential, which is induced by the interaction of the dipoles with the polarizing field. The confinement and scaling properties of the soliton families are explained analytically. The Thomas-Fermi approximation is elaborated for fundamental solitons. The mobility of the fundamental solitons is limited to the central area. Stable 1D even and odd solitons are also found in the setting with a double-well modulation function, along with a regime of Josephson oscillations.

Li, Yongyao; Liu, Jingfeng; Pang, Wei; Malomed, Boris A.

2013-11-01

95

We present the theory of plasmon excitation in a grating-gate transistor structure with spatially modulated 2D electron channel. The plasmon spectrum varies depending on the electron density modulation in the transistor channel. We report on the frequency ranges of plasmon mode excitation in the gated and ungated regions of the channel and on the interaction of these different types of plasmon modes. We show that a constructive influence of the ungated regions of the electron channel considerably increases the intensity of the gated plasmon resonances and reduces the plasmon-resonance linewidth in the grating-gated transistor structure.

Fateev, D. V., E-mail: FateevDV@yandex.ru; Popov, V. V. [Kotelnikov Institute of Radio Engineering and Electronics of RAS (Saratov Branch) (Russian Federation); Shur, M. S. [Rensselaer Polytechnic Institute, Department of Electrical, Computer, and System Engineering and Center for Integrated Electronics, CII9015 (United States)

2010-11-15

96

Symmetry-breaking instabilities of spatial parametric solitons Alfredo De Rossi and Stefano Trillo

For three decades optical spatial solitons confined in the transverse plane were commonly believed are strictly speaking solitary waves the model equations are not integrable , a crucial issue developed in Ref. 11 accounts for the dynamics of SHG, whereas the effect of confinement along the ellipse

97

We show that transverse electromagnetic waves propagating along an external static electric field in liquid metacrystal (LMC) can provoke spontaneous rearrangement of elongated meta-atoms that changes the direction of the anisotropy axis of the LMC. This kind of instability may reorient the meta-atoms from the equilibrium state parallel to a static field to the state along a high-frequency field and back at the different threshold intensities of electromagnetic waves in such a way that bistability in the system takes place. Reorientation of meta-atoms causes a change in the effective refraction index of LMC that creates, in turn, the conditions for the formation of bright spatial solitons. Such spatial solitons are the self-consistent domains of redirected meta-atoms with trapped photons. We find that the instability thresholds as well as energy flux captured by the spatial soliton can be easily managed by variation of the static electric field applied to the LMC. We study the effects of soliton excitation and collisions via numerical simulations. PMID:25215843

Zharov, Alexander A; Zharov, Alexander A; Zharova, Nina A

2014-08-01

98

NASA Astrophysics Data System (ADS)

We report significant anisotropies in the projected two-dimensional (2D) spatial distributions of globular clusters (GCs) of the giant Virgo elliptical galaxy NGC 4649 (M60). Similar features are found in the 2D distribution of low-mass X-ray binaries (LMXBs), both associated with GCs and in the stellar field. Deviations from azimuthal symmetry suggest an arc-like excess of GCs extending north at 4-15 kpc galactocentric radii in the eastern side of major axis of NGC 4649. This feature is more prominent for red GCs, but still persists in the 2D distribution of blue GCs. High- and low-luminosity GCs also show some segregation along this arc, with high-luminosity GCs preferentially located in the southern end and low-luminosity GCs in the northern section of the arc. GC-LMXBs follow the anisotropy of red GCs, where most of them reside; however, a significant overdensity of (high-luminosity) field LMXBs is present to the south of the GC arc. These results suggest that NGC 4649 has experienced mergers and/or multiple accretions of less massive satellite galaxies during its evolution, of which the GCs in the arc may be the fossil remnant. We speculate that the observed anisotropy in the field LMXB spatial distribution indicates that these X-ray binaries may be the remnants of a star formation event connected with the merger, or maybe be ejected from the parent red GCs, if the bulk motion of these clusters is significantly affected by dynamical friction. We also detect a luminosity enhancement in the X-ray source population of the companion spiral galaxy NGC 4647. We suggest that these may be younger high mass X-ray binaries formed as a result of the tidal interaction of this galaxy with NGC 4649.

D'Abrusco, R.; Fabbiano, G.; Mineo, S.; Strader, J.; Fragos, T.; Kim, D.-W.; Luo, B.; Zezas, A.

2014-03-01

99

We investigate solitons and nonlinear Bloch waves in Bose-Einstein condensates trapped in optical lattices (OLs). By introducing specially designed localized profiles of the spatial modulation of the attractive nonlinearity, we construct an infinite set of exact soliton solutions in terms of Mathieu and elliptic functions, with the chemical potential belonging to the semi-infinite gap of the OL-induced spectrum. Starting from the particular exact solutions, we employ the relaxation method to construct generic families of soliton solutions in a numerical form. The stability of the solitons is investigated through the computation of the eigenvalues for small perturbations, and also by direct simulations. Finally, we demonstrate a virtually exact (in the numerical sense) composition relation between nonlinear Bloch waves and solitons.

Zhang Jiefang; Meng Jianping; Wu Lei [Institute of Nonlinear Physics, Zhejiang Normal University, Jinhua, Zhejiang 321004 (China); Li Yishen [Department of Mathematics, University of Science and Technology of China, Hefei, Anhui 230026 (China); Malomed, Boris A. [Department of Physical Electronics, Faculty of Engineering, Tel Aviv University, Tel Aviv 69978 (Israel)

2010-09-15

100

Two-dimensional spatially resolved mappings of excitation temperatures, rotational temperatures and electron number densities have been made for capacitively coupled microwave plasmas using argon, nitrogen and air as working gases. The influence of additions of hydrogen to the working gases on the temperature and electron number density profiles in the case of the argon- and nitrogen-CMP is described and found to

N. H. Bings; M. Olschewski; J. A. C. Broekaert

1997-01-01

101

Tablets of amorphous indomethacin were compressed at 10, 25, 50, or 100 MPa using either an unlubricated or a lubricated die and stored individually at 35 °C in sealed Mylar pouches. At selected time points, tablets were analyzed by two-dimensional X-ray diffractometry (2D-XRD), which enabled us to profile the extent of drug crystallization in tablets, in both the radial and axial directions. To evaluate the role of lubricant, magnesium stearate was used as "internal" and/or "external" lubricant. Indomethacin crystallization propensity increased as a function of compression pressure, with 100 MPa pressure causing crystallization immediately after compression (detected using synchrotron radiation). However, the drug crystallization was not uniform throughout the tablets. In unlubricated systems, pronounced crystallization at the radial surface could be attributed to die wall friction. The tablet core remained substantially amorphous, irrespective of the compression pressure. Lubrication of the die wall with magnesium stearate, as external lubricant, dramatically decreased drug crystallization at the radial surface. The spatial heterogeneity in drug crystallization, as a function of formulation composition and compression pressure, was systematically investigated. When formulating amorphous systems as tablets, the potential for compression induced crystallization warrants careful consideration. Very low levels of crystallization on the tablet surface, while profoundly affecting product performance (decrease in dissolution rate), may not be readily detected by conventional analytical techniques. Early detection of crystallization could be pivotal in the successful design of a dosage form where, in order to obtain the desired bioavailability, the drug may be in a high energy state. Specialized X-ray diffractometric techniques (2D; use of high intensity synchrotron radiation) enabled detection of very low levels of drug crystallization and revealed the heterogeneity in crystallization within the tablet. PMID:25438193

Thakral, Naveen K; Mohapatra, Sarat; Stephenson, Gregory A; Suryanarayanan, Raj

2015-01-01

102

Two-dimensional time-dependent finite-difference equations of the surface harmonics method (SHM) for the description of the neutron transport are derived for square-lattice reactors. These equations are implemented in the SUHAM-TD code. Verification of the derived equations and the developed code are performed by the example of known test problems, and the potential and efficiency of the SHM as applied to the solution of the time-dependent neutron transport equation in the diffusion approximation in two-dimensional geometry are demonstrated. These results show the substantial advantage of SHM over direct finite-difference modeling in computational costs.

Boyarinov, V. F., E-mail: boyarinov@dhtp.kiae.ru; Kondrushin, A. E., E-mail: kondrushin@yahoo.com; Fomichenko, P. A. [National Research Center Kurchatov Institute (Russian Federation)

2014-12-15

103

NASA Astrophysics Data System (ADS)

Two-dimensional time-dependent finite-difference equations of the surface harmonics method (SHM) for the description of the neutron transport are derived for square-lattice reactors. These equations are implemented in the SUHAM-TD code. Verification of the derived equations and the developed code are performed by the example of known test problems, and the potential and efficiency of the SHM as applied to the solution of the time-dependent neutron transport equation in the diffusion approximation in two-dimensional geometry are demonstrated. These results show the substantial advantage of SHM over direct finite-difference modeling in computational costs.

Boyarinov, V. F.; Kondrushin, A. E.; Fomichenko, P. A.

2014-12-01

104

Spatially limited ion acoustic drift soliton in electron-positron-ion magnetoplasma

Ion acoustic drift solitary wave with intermediate parametric range in both linear and nonlinear regimes has been studied in electron-positron-ion magnetoplasma. In the spatially limited region dispersion relation in the linear and Zakharov-Kuznetsov-type equation in the nonlinear regime are derived, respectively. Both equations show the coupling of electrostatic drift and ion acoustic waves. The stationary soliton solution for oblique drift solitary waves with the effect of positron concentration and temperature has been discussed analytically and graphically. The results are relevant for astrophysical observations and diagnostics of laboratory electron-positron-ion magnetoplasmas.

Mushtaq, A. [Theoretical Plasma Physics Division, PINSTECH, P. O. Nilore, Islamabad (Pakistan)

2008-08-15

105

NASA Astrophysics Data System (ADS)

Within the framework of the study a two dimensional hydrodynamic high-resolution model of the energy, H2O, CO2 turbulent exchange was developed and applied to describe effect of the horizontal and vertical heterogeneity of a forest canopy on CO2exchange between soil surface, forest stand and the atmosphere under different weather conditions. Most attention in the study was paid to analyze the influence of forest clearing, windthrow of different sizes, forest edges, etc. on turbulent exchange rate and CO2 flux partitioning between forest overstorey, understorey and soil surface. The modeling experiments were provided under different wind conditions, thermal stratification of the atmospheric boundary layer, incoming solar radiation, etc. To quantify effect of spatial heterogeneity on total ecosystem fluxes the modeling results were compared with CO2 fluxes modeled for a spatially uniform forest canopy under similar ambient conditions. The averaged system of hydrodynamic equations is used for calculating the components of the mean velocity ?V = {V1, V2}: ( ( ) ) ?Vi+ V ?Vi= - 1-??P- - -?- ? E - K ?Vi-+ ?Vj- + F, ?Vi = 0, ?t j?xj ?0 ?xi ?xj ij ?xj ?xi i ?xi where E is the turbulent kinetic energy (TKE), K is the turbulent diffusivity, ?P is the deviation of pressure from the hydrostatic distribution and ?0?F is the averaged force of air flow interaction with vegetation. F? was parameterized as ?F = -cd ·LAD ·| | ||V?||·?V, where cd is the drag coefficient and LAD is the leaf area density. The turbulent diffusivity K can be expressed by means of TKE and the velocity of TKE dissipation ? as follows: K = C?E2?-1, where C? is the proportionality coefficient. One of the ways to obtain E and ? is to solve the additional system of two differential equations of diffusion-transport type: ( ) ( ) ?E- -?E- -?- -K-?E- ?-? ??- -?- K-?? -? ( 1 2 ) ?t +Vj?xj = ?xi ?E ?xi +PE - ?, ?t +Vj ?xj = ?xi ???xi +E C ?PE - C?? - ? ?, where ?E and ?? are the Prandtl numbers, PE is the TKE production by shear, C?1 and C?2 are the model constants. The term ?? = ?- E(C ?1 - C?2) · 12C?1/2c dLAD||? || |V |E describes the increase of TKE dissipation due to the interaction with vegetation elements. The function ? can be any of the following variables: ?, ?/ E, or El, where l is the mixing length. Detailed analysis of these equations performed by Sogachev (Sogachev, Panferov, 2006) showed that for ? = ?/ E the model is less sensible to the errors of the input data. Transfer equation for CO2 within and above a plant canopy can be written as: ( ) ?C- -?C- -?- -K-?C- ?t + Vj?xj = ?xi ?C ?xi + FC, where C is CO2 concentration, ?C is the Prandtl number, and the term FC describes the sources/sinks of CO2 in the vegetation and soil. For parameterization of the photosynthesis rate in the forest canopy the Monsi and Saeki approach (Monsi M., Saeki T., 1953) was applied. Stem respiration was ignored in the study. The CO2 emission from the soil surface into the atmosphere was assumed to be constant for entire forest area. This study was supported by grants of the Russian Foundation for Basic Research (RFBR 14-04-01568-a).

Mukhartova, Yulia; Olchev, Alexander; Shapkina, Natalia

2014-05-01

106

NASA Technical Reports Server (NTRS)

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

Juday, Richard D. (inventor)

1992-01-01

107

Topological Solitons in Physics.

ERIC Educational Resources Information Center

A broad definition of solitons and a discussion of their role in physics is given. Vortices and magnetic monopoles which are examples of topological solitons in two and three spatial dimensions are described in some detail. (BB)

Parsa, Zohreh

1979-01-01

108

Bright dipolar Bose-Einstein-condensate soliton mobile in a direction perpendicular to polarization

NASA Astrophysics Data System (ADS)

We demonstrate stable, robust, bright one-dimensional dipolar Bose-Einstein-condensate (BEC) solitons, moving in a direction perpendicular to the polarization direction, formed due to dipolar interaction for repulsive contact interaction. At medium velocity the head on collision of two such solitons is found to be quasielastic with practically no deformation. Upon small perturbation the solitons are found to exhibit sustained breathing oscillation. The findings are illustrated by numerical simulation using the three-dimensional mean-field Gross-Pitaevskii equation and a reduced two-dimensional model in three and two spatial dimensions employing realistic interaction parameters for a dipolar 164Dy BEC.

Adhikari, S. K.

2014-11-01

109

Multidimensional solitons in a low-dimensional periodic potential

Using the variational approximation and direct simulations in real and imaginary time, we find stable two-dimensional (2D) and 3D solitons in the self-attractive Gross-Pitaevskii equation (GPE) with a potential which is uniform in one direction (z) and periodic in the others (however, the quasi-1D potentials cannot stabilize 3D solitons). The family of solitons includes single- and multiple-peaked ones. The results apply to Bose-Einstein condensates (BEC's) in optical lattices (OL's) and to spatial or spatiotemporal solitons in layered optical media. This is the first prediction of mobile 2D and 3D solitons in BEC's, as they keep mobility along z. Head-on collisions of in-phase solitons lead to their fusion into a collapsing pulse. Slow collisions between two multiple-peaked solitons whose main peaks are separated by an intermediate channel end up with their fusion into one single-peaked soliton in the middle channel, {approx_equal}1/3 of the original number of atoms being shed off. Stable localized states in the self-repulsive GPE with the low-dimensional OL combined with a parabolic trap are found too. Two such pulses in one channel perform recurrent elastic collisions, periodically featuring sharp interference patterns in the strong-overlap state.

Baizakov, Bakhtiyor B.; Salerno, Mario [Dipartimento di Fisica 'E.R. Caianiello' and Istituto Nazionale di Fisica della Materia (INFM), Universita di Salerno, I-84081 Baronissi, SA (Italy); Malomed, Boris A. [Department of Interdisciplinary Studies, Faculty of Engineering, Tel Aviv University, Tel Aviv 69978 (Israel)

2004-11-01

110

We theoretically demonstrate the realization of a complete canonical set of all-optical logic gates (AND, OR, NOT), with a persistent (stored) output, by combining propagative spatial solitons in a photorefractive crystal and dissipative cavity solitons in a downstream broad-area vertical cavity surface emitting laser (VCSEL). The system uses same-color, optical-axis aligned input and output channels with fixed readout locations, while switching from one gate to another is achieved by simply varying the potential applied to the photorefractive crystal. The inputs are Gaussian beams launched in the photorefractive crystal and the output is a bistable, persistent soliton in the VCSEL with a 'robust' eye diagram and large signal-to-noise ratio (SNR). Fast switching and intrinsic parallelism suggest that high bit flow rates can be obtained. PMID:24664042

Columbo, L L; Rizza, C; Brambilla, M; Prati, F; Tissoni, G

2014-03-24

111

NASA Astrophysics Data System (ADS)

Spatial rocking is a kind of resonant forcing able to convert a self-oscillatory system into a phase-bistable, pattern forming system, whereby the phase of the spatially averaged oscillation field locks to one of two values differing by ?. We propose the spatial rocking in an experimentally relevant system—the vertical-cavity surface-emitting laser (VCSEL)—and demonstrate its feasibility through analytical and numerical tools applied to a VCSEL model. We show phase bistability, spatial patterns, such as roll patterns, domain walls, and phase (dark-ring) solitons, which could be useful for optical information storage and processing purposes.

Fernandez-Oto, C.; de Valcárcel, G. J.; Tlidi, M.; Panajotov, K.; Staliunas, K.

2014-05-01

112

Composite Multihump Vector Solitons Carrying Topological Charge

We propose composite solitons carrying topological charge: multicomponent two dimensional [ \\\\(2+1\\\\)D] vector (Manakov-like) solitons for which at least one component carries topological charge. These multimode solitons can have a single hump or exhibit a multihump structure. The ``spin'' carried by these multimode composite solitons suggests 3D soliton interactions in which the particlelike behavior includes spin, in addition to effective

Ziad H. Musslimani; Mordechai Segev; Demetrios N. Christodoulides; Marin SoljaciC

2000-01-01

113

Solitons in atomic condensates, with optical lattices and field-induced dipole moments

NASA Astrophysics Data System (ADS)

We report some investigations on the existence of matter-wave solitons when considering cross-combined optical lattices (OL) in three dimensions (3D), where we have a nonlinear OL in one of the directions, which is perpendicular to a two-dimensional (2D) plane with linear OLs in either one or both directions. This study can be useful to manage 3D solitons through spatial modulations of the scattering length in one of the OL directions. Another independent study is reported, by considering bright solitons manifested in a bosonic condensate gas carrying collinear dipole moments, which induces an external polarizing field with strength periodically modulated along one of the coordinates. This leads to an effective nonlocal nonlinear lattice, with solitonic solutions. Their dynamics and mobility can be investigated by an effective one-dimensional (1D) model. Interactions between solitons are also reported within this 1D model. In all the cases, we consider full numerical and variational approaches.

Tomio, Lauro; da Luz, H. F.; Gammal, A.; Abdullaev, F. Kh

2015-03-01

114

Matched infrared soliton pairs in graphene under Landau quantization via four-wave mixing

NASA Astrophysics Data System (ADS)

We investigate a type of matched infrared soliton pairs based on four-wave mixng (FWM) in Landau-quantized graphene by using density-matrix method and perturbation theory. The linear and nonlinear dynamical properties of the graphene system are first discussed, and, in particular, we focus on the signatures of nonlinear optical response. Then we present analytical solutions for the fundamental bright and dark solitons, as well as bright two-soliton, which are in good agreement with the results of numerical simulations. Moreover, due to the unusual dispersion relation and chiral character of electron states, we find that the matched spatial soliton pairs can propagate through a two-dimensional crystal of graphene and their carrier frequencies are adjustable within the infrared frequency regimes. Our proposed scheme may provide a route to explore the applications of matched infrared soliton pairs in telecommunication and optical information processing.

Ding, Chunling; Yu, Rong; Li, Jiahua; Hao, Xiangying; Wu, Ying

2014-10-01

115

Laboratory realization of KP-solitons

NASA Astrophysics Data System (ADS)

Kodama and his colleagues presented a classification theorem for exact soliton solutions of the quasi-two-dimensional Kadomtsev-Petviashvili (KP) equation. The classification theorem is related to non-negative Grassmann manifold, Gr(N, M) that is parameterized by a unique chord diagram based on the derangement of the permutation group. The cord diagram can infer the asymptotic behavior of the solution with arbitrary number of line solitons. Here we present the realization of a variety of the KP soliton formations in the laboratory environment. The experiments are performed in a water tank designed and constructed for precision experiments for long waves. The tank is equipped with a directional-wave maker, capable of generating arbitrary-shaped multi-dimensional waves. Temporal and spatial variations of water-surface profiles are captured using the Laser Induces Fluorescent method - a nonintrusive optical measurement technique with sub-millimeter precision. The experiments yield accurate anatomy of the KP soliton formations and their evolution behaviors. Physical interpretations are discussed for a variety of KP soliton formations predicted by the classification theorem.

Yeh, Harry; Li, Wenwen

2014-03-01

116

NASA Astrophysics Data System (ADS)

The spatially distributed effects of riparian vegetation on fluvial hydrodynamics during low flows to large floods are poorly documented. Drawing on a LiDAR-derived, meter-scale resolution raster of vegetation canopy height as well as an existing algorithm to spatially distribute stage-dependent channel roughness, this study developed a meter-scale two-dimensional hydrodynamic model of ~ 28.3 km of a gravel/cobble-bed river corridor for flows ranging from 0.2 to 20 times bankfull discharge, with and without spatially distributed vegetation roughness. Results were analyzed to gain insight into stage-dependent and scale-dependent effects of vegetation on velocities, depths, and flow patterns. At the floodplain filling flow of 597.49 m3/s, adding spatially distributed vegetation roughness parameters caused 8.0 and 7.4% increases in wetted area and mean depth, respectively, while mean velocity decreased 17.5%. Vegetation has a strong channelization effect on the flow, increasing the difference between mid-channel and bank velocities. It also diverted flow away from densely vegetated areas. On the floodplain, vegetation stands caused high velocity preferential flow paths that were otherwise unaccounted for in the unvegetated model runs. For the river as a whole, as discharge increases, overall roughness increases as well, contrary to popular conception.

Abu-Aly, T. R.; Pasternack, G. B.; Wyrick, J. R.; Barker, R.; Massa, D.; Johnson, T.

2014-02-01

117

NASA Technical Reports Server (NTRS)

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

1982-01-01

118

Tongkumchum, P. Two-dimensional box plot Songklanakarin J. Sci. Technol., 2005, 27(4) : 859-866 In this paper we propose a two-dimensional box plot, a simple bivariate extension of the box plot and the scatter plot. This plot comprises a pair of trapeziums oriented in the direction of a fitted straight line, with symbols denoting extreme values. The choice for the fitted

Phattrawan Tongkumchum

119

Two-dimensional material nanophotonics

NASA Astrophysics Data System (ADS)

Two-dimensional materials exhibit diverse electronic properties, ranging from insulating hexagonal boron nitride and semiconducting transition metal dichalcogenides such as molybdenum disulphide, to semimetallic graphene. In this Review, we first discuss the optical properties and applications of various two-dimensional materials, and then cover two different approaches for enhancing their interactions with light: through their integration with external photonic structures, and through intrinsic polaritonic resonances. Finally, we present a narrow-bandgap layered material -- black phosphorus -- that serendipitously bridges the energy gap between the zero-bandgap graphene and the relatively large-bandgap transition metal dichalcogenides. The plethora of two-dimensional materials and their heterostructures, together with the array of available approaches for enhancing the light-matter interaction, offers the promise of scientific discoveries and nanophotonics technologies across a wide range of the electromagnetic spectrum.

Xia, Fengnian; Wang, Han; Xiao, Di; Dubey, Madan; Ramasubramaniam, Ashwin

2014-12-01

120

Solitons on Tori and Soliton Crystals

NASA Astrophysics Data System (ADS)

Necessary conditions for a soliton on a torus to be a soliton crystal, that is, a spatially periodic array of topological solitons in stable equilibrium, are derived. The stress tensor of the soliton must be L 2 orthogonal to , the space of parallel symmetric bilinear forms on TM, and, further, a certain symmetric bilinear form on , called the hessian, must be positive. It is shown that, for baby Skyrme models, the first condition actually implies the second. It is also shown that, for any choice of period lattice ?, there is a baby Skyrme model which supports a soliton crystal of periodicity ?. For the three-dimensional Skyrme model, it is shown that any soliton solution on a cubic lattice which satisfies a virial constraint and is equivariant with respect to (a subgroup of) the lattice symmetries automatically satisfies both tests. This verifies, in particular, that the celebrated Skyrme crystal of Castillejo et al., and Kugler and Shtrikman, passes both tests.

Speight, J. M.

2014-11-01

121

Two dimensional radiation detecting apparatus

A two-dimensional X-ray detecting apparatus is comprised of an amorphous silicon layer for trapping electrons in a pattern corresponding to an intensity distribution when it is receiving X-rays, and a scanning device for scanning the surface of the amorphous silicon layer with a laser beam to take out electrons trapped in the silicon layer.

Sugimoto, H.; Naruse, Y.

1985-10-15

122

NASA Astrophysics Data System (ADS)

The first-order spatial correlation function g (1)( r 12) and the polariton density distribution in the condensate of quasi-two-dimensional exciton polaritons formed in a high- Q semiconductor microcavity pillar under nonresonant optical pumping are investigated. It is found that the correlation function in certain regions of the micropillar decreases abruptly with increasing condensate density. It is shown that this behavior of the correlation function is caused by the formation of a localized dark soliton in these regions. A deep minimum of the polariton density and a shift in the phase of the condensate wavefunction by ? occur within the soliton localization area.

Demenev, A. A.; Gavrilov, S. S.; Brichkin, A. S.; Larionov, A. V.; Kulakovskii, V. D.

2014-12-01

123

NASA Astrophysics Data System (ADS)

We study coherent and incoherent interactions between a discrete vortex soliton and a discrete fundamental soliton in two-dimensional photonic lattices, which present a scheme for all-optical routings and topological transformations of vorticities. Due to the multilobe intensity and ?/2-phase delay between each two lobes of the discrete vortex soliton, the coherent soliton interactions allow both solitons to evolve into localized states with a single lobe on multiple different possible destination ports, which depend on the initial phase of the discrete fundamental soliton. We show that charge flippings of phase singularities and orbital angular momentum transfer can occur during the coherent interactions between the two solitons. For incoherent interactions, by controlling the relative powers of the two solitons, we reveal that soliton steering can be realized by either attracting the discrete fundamental soliton to four ports or localizing the four-lobe discrete vortex soliton into a ring soliton.

Gan, Xuetao; Zhang, Peng; Liu, Sheng; Xiao, Fajun; Zhao, Jianlin

2014-01-01

124

Two-dimensional flexible nanoelectronics

NASA Astrophysics Data System (ADS)

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

Akinwande, Deji; Petrone, Nicholas; Hone, James

2014-12-01

125

Two-dimensional thermofield bosonization

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

126

Two-Dimensional Thermofield Bosonization

The main objective of this paper is 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. In order 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.

R. L. P. G. Amaral; L. V. Belvedere; K. D. Rothe

2005-04-01

127

Two dimensional unstable scar statistics.

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

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

2006-12-01

128

Two-Dimensional Quantum Antiferromagnets

NASA Astrophysics Data System (ADS)

This review presents some theoretical advances in the field of quantum magnetism in two-dimensional systems, and quantum spin liquids in particular. The first version published in 2005 has been updated for the present second edition of the book: the section devoted to the kagome antiferromagnet (Sec. 7) has been completely rewritten, as well as the concluding section (Sec. 8). The other sections (Secs. 1-6) are unchanged from the first edition of the book.

Misguich, Grégoire; Lhuillier, Claire

2013-03-01

129

NASA Astrophysics Data System (ADS)

We study analytically the properties of the optical absorption and the spatial weak-light solitons in a quantum dot molecule system with the interdot tunneling coupling (ITC). It is shown that, for the linear case, there exists tunneling induced transparency (TIT) in the context of a weak ITC, while the TIT can be replaced by Autler-Townes splitting in the presence of a strong ITC. For the nonlinear case, it is probable to realize the spatial optical solitons even under weak light intensity. Interestingly, we find that there appears transformation behavior between the bright and dark solitons by properly turning both the ITC strength and the detuning of the probe field. Meanwhile, the transformation condition of the bright and dark solitons is obtained. Additionally it is also found that the amplitude of the solitons first descends and then rises with the increasing of ITC strength. Our results may have potential applications for nonlinear optical experiments and optical telecommunication engineering in solid systems.

Zeng, Kuanhong; Wang, Denglong; She, Yanchao; Luo, Xiaoqin

2013-11-01

130

Two-Dimensional Synthetic-Aperture Radiometer

NASA Technical Reports Server (NTRS)

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

LeVine, David M.

2010-01-01

131

Two-dimensional Pauli operator in a magnetic field

NASA Astrophysics Data System (ADS)

The two-dimensional purely magnetic Schrödinger operator for the nonrelativistic particle with a spin of ½ in a magnetic field has some remarkable properties, that were discovered in the late 70s: its strongly degenerate in the ground state and it admits supersymmetry. In the present work we investigate the special case where the magnetic flux of the periodic field through the elementary cell equals zero. This case has not been covered in the previous publications. An interesting connection with the theory of solitons, in particular with Burgers-like systems and their two-dimensional analogues, is revealed. Their linearizability properties are simpler than some famous systems, such as KdV and KP. Members of the Aharonov-Bohm-type system with quantized magnetic flux play a special role in the investigation of this case.

Grinevich, P. G.; Mironov, A. E.; Novikov, S. P.

2011-10-01

132

Soliton dynamics in modulated Bessel photonic lattices

We address the existence and the controlled stability of two-dimensional solitons in modulated Bessel lattices (MBL) induced by a superposition of nondiffracting Bessel beams. We show that variation of the modulation parameter of the lattice and the initial transverse momentum of the soliton significantly modify the behavior of the solitons. We find that, under suitable and well-identified conditions, solitons propagating in the MBL exhibit six regimes of transverse mobility: stationary, oscillatory, rotating, unbounded or escape, transitional, and unstable. These results report propagating solitons that can develop these dynamics of transverse motion.

Ruelas, Adrian; Lopez-Aguayo, Servando; Gutierrez-Vega, Julio C. [Photonics and Mathematical Optics Group, Tecnologico de Monterrey, Monterrey, Mexico 64849 (Mexico)

2010-12-15

133

Two-Dimensional Colloidal Alloys

NASA Astrophysics Data System (ADS)

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.

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

2011-03-01

134

Two-dimensional colloidal alloys.

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

2011-03-25

135

Fast training and testing procedures are crucial in biometrics recognition research. Conventional algorithms, e.g., principal component analysis (PCA), fail to efficiently work on large-scale and high-resolution image data sets. By incorporating merits from both two-dimensional PCA (2DPCA)-based image decomposition and fast numerical calculations based on Haarlike bases, this technical correspondence first proposes binary 2DPCA (B-2DPCA). Empirical studies demonstrated the advantages of B-2DPCA compared with 2DPCA and binary PCA. PMID:18632407

Pang, Yanwei; Tao, Dacheng; Yuan, Yuan; Li, Xuelong

2008-08-01

136

Soliton-induced Majorana fermions in a one-dimensional atomic topological superfluid

NASA Astrophysics Data System (ADS)

We theoretically investigate the behavior of dark solitons in a one-dimensional spin-orbit coupled atomic Fermi gas in harmonic traps by solving self-consistently the Bogoliubov-de Gennes equations. The dark soliton—to be created by phase imprinting in future experiments—is characterized by a real order parameter, which changes sign at a point node and hosts localized Andreev bound states near the node. By considering both cases of a single soliton and multiple solitons, we find that the energy of these bound states decreases to zero when the system is tuned to enter the topological superfluid phase by increasing an external Zeeman field. As a result, two Majorana fermions emerge in the vicinity of each soliton, in addition to the well-known Majorana fermions at the trap edges associated with the nontrivial topology of the superfluid. We propose that the soliton-induced Majorana fermions can be directly observed by using spatially resolved radio-frequency spectroscopy or indirectly probed by measuring the density profile at the point node. For the latter, the deep minimum in the density profile will disappear due to the occupation of the soliton-induced zero-energy Majorana fermion modes. Our prediction could be tested in a resonantly interacting spin-orbit coupled 40K Fermi gas confined in a two-dimensional optical lattice.

Liu, Xia-Ji

2015-02-01

137

Inelastic collision of spherical ion-acoustic solitons

The collision of spherical ion-acoustic solitons having different centers of symmetry is studied. Unlike one-dimensional collisions, the solitons are significantly changed by the collision. A new two-dimensional nonlinear object is found to be created. Remnants of the solitons that survive are found to be shifted in phase and reduced in amplitude.

Frederic Ze; Noah Hershkowitz; Chung Chan; K. E. Lonngren

1979-01-01

138

NASA Astrophysics Data System (ADS)

We report the generation of three-dimensional bright spatial solitary waves by the breakup of an optical vortex in a saturable self-focusing nonlinear medium. An elliptical Gaussian beam from a Ti:sapphire laser containing a singly charged on-axis vortex was passed through a nonlinear medium consisting of rubidium vapor at low concentrations. The modulational instability resulted in the formation of a pair of out-of-phase solitonlike beams, which spiraled away from each other during propagation as a result of the repulsive nature of their interaction. The rate of rotation and separation of the two soliton beams could be controlled by the parameters of the medium and the laser intensity. Numerical analysis of the propagation based on a model nonlinearity corresponding to a strongly saturated two-level system showed good quantitative agreement with the experimental data. Copyright (c) 1995 Optical Society of America

Tikhonenko, Vladimir; Christou, Jason; Luther-Daves, Barry

1995-11-01

139

Spin-imbalanced quasi-two-dimensional fermi gases.

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

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

2015-03-20

140

This is a sequel to a recent work of Gaudin, who studied the classical equilibrium statistical mechanics of the two-dimensional Coulomb gas on a lattice at a special value of the coupling constant Gamma such that the model is exactly solvable. This model is briefly reviewed, and it is shown that the correlation functions obey the sum rules that characterize a conductive phase. A related model in which the particles are constrained to move on an array of equidistant parallel lines has simpler mathematics, and the asymptotic behavior of its correlation functions is studied in some detail. In the low-density limit, the lattice model is expected to have the same properties as a system of charged, hard disks; the correlation functions, internal energy, and specific heat of the latter are discussed.

Cornu, F.; Jancovici, B.

1987-10-01

141

Two-dimensional NMR spectroscopy

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

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

1987-01-01

142

Class of compound dissipative solitons as a result of collisions in one and two spatial dimensions.

We study the interaction of quasi-one-dimensional (quasi-1D) dissipative solitons (DSs). Starting with quasi-1D solutions of the cubic-quintic complex Ginzburg-Landau (CGL) equation in their temporally asymptotic state as the initial condition, we find, as a function of the approach velocity and the real part of the cubic interaction of the two counterpropagating envelopes: interpenetration, one compound state made of both envelopes or two compound states. For the latter class both envelopes show DSs superposed at two different locations. The stability of this class of compound states is traced back to the quasilinear growth rate associated with the coupled system. We show that this mechanism also works for 1D coupled cubic-quintic CGL equations. For quasi-1D states that are not in their asymptotic state before the collision, a breakup along the crest can be observed, leading to nonunique results after the collision of quasi-1D states. PMID:25215679

Descalzi, Orazio; Brand, Helmut R

2014-08-01

143

Two-dimensional supersonic nonlinear Schroedinger flow past an extended obstacle

Supersonic flow of a superfluid past a slender impenetrable macroscopic obstacle is studied in the framework of the two-dimensional (2D) defocusing nonlinear Schroedinger (NLS) equation. This problem is of fundamental importance as a dispersive analog of the corresponding classical gas-dynamics problem. Assuming the oncoming flow speed is sufficiently high, we asymptotically reduce the original boundary-value problem for a steady flow past a slender body to the one-dimensional dispersive piston problem described by the nonstationary NLS equation, in which the role of time is played by the stretched x coordinate and the piston motion curve is defined by the spatial body profile. Two steady oblique spatial dispersive shock waves (DSWs) spreading from the pointed ends of the body are generated in both half planes. These are described analytically by constructing appropriate exact solutions of the Whitham modulation equations for the front DSW and by using a generalized Bohr-Sommerfeld quantization rule for the oblique dark soliton fan in the rear DSW. We propose an extension of the traditional modulation description of DSWs to include the linear ''ship-wave'' pattern forming outside the nonlinear modulation region of the front DSW. Our analytic results are supported by direct 2D unsteady numerical simulations and are relevant to recent experiments on Bose-Einstein condensates freely expanding past obstacles.

El, G. A.; Khodorovskii, V. V. [Department of Mathematical Sciences, Loughborough University, Loughborough LE11 3TU (United Kingdom); Kamchatnov, A. M. [Institute of Spectroscopy, Russian Academy of Sciences, 142190 Troitsk, Moscow Region (Russian Federation); Annibale, E. S.; Gammal, A. [Instituto de Fisica, Universidade de Sao Paulo, CP 66318, 05315-970 Sao Paulo, SP (Brazil)

2009-10-15

144

Kubo conductivity of a strongly magnetized two-dimensional plasma.

NASA Technical Reports Server (NTRS)

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

Montgomery, D.; Tappert, F.

1971-01-01

145

A two-dimensional computer-controlled visual stimulator

A computer-controlled instrument that creates complex two-dimensional patterns on a CRT monitor is described. These patterns\\u000a are used to elicit visual evoked responses. Patterns are produced on a raster that is rotatable about its center. It is possible\\u000a to assign to arbitrary regions in the raster any of four independent one-dimensional spatial-temporal functions. For each\\u000a spatial-temporal function, the experimenter can

Norman Milkman; Gary Schick; Michelangelo Rossetto; Floyd Ratliff; Robert Shapley; Jonathan Victor

1980-01-01

146

Topological defects in two-dimensional crystals

By using topological current theory, we study the inner topological structure of the topological defects in two-dimensional (2D) crystal. We find that there are two elementary point defects topological current in two-dimensional crystal, one for dislocations and the other for disclinations. The topological quantization and evolution of topological defects in two-dimensional crystals are discussed. Finally, We compare our theory with

Yong Chenand; Wei-Kai Qi

2008-01-01

147

Solitons and ionospheric modification

NASA Technical Reports Server (NTRS)

The possibility of Langmuir soliton formation and collapse during ionospheric modification is investigated. Parameters characterizing former facilities, existing facilities, and planned facilities are considered, using a combination of analytical and numerical techniques. At a spatial location corresponding to the exact classical reflection point of the modifier wave, the Langmuir wave evolution is found to be dominated by modulational instability followed by soliton formation and three-dimensional collapse. The earth's magnetic field is found to affect the shape of the collapsing soliton. These results provide an alternative explanation for some recent observations.

Sheerin, J. P.; Nicholson, D. R.; Payne, G. L.; Hansen, P. J.; Weatherall, J. C.; Goldman, M. V.

1982-01-01

148

Correspondence Quantification in Comprehensive Two-Dimensional

Correspondence Quantification in Comprehensive Two-Dimensional Liquid Chromatography Stephen E 68588-0115 This correspondence corrects the description in a recent paper by Mondello et al., "Quantification in Comprehen- sive Two-Dimensional Liquid Chromatography" [Mon- dello, L.; Herrero, M.; Kumm, T

Reichenbach, Stephen E.

149

Two Dimensional Mechanism for Insect Hovering

Resolved computation of two dimensional insect hovering shows for the first time that a two dimen- sional hovering motion can generate enough lift to support a typical insect weight. The computation reveals a two dimensional mechanism of creating a downward dipole jet of counterrotating vortices, which are formed from leading and trailing edge vortices. The vortex dynamics further elucidates the

Z. Jane Wang

2000-01-01

150

NUMERICAL INVESTIGATION OF A TWO-DIMENSIONAL

We present here a highly efficient and accurate numerical scheme for initial and boundary value problems of a two-dimensional Boussinesq sys- tem which describes three-dimensional water waves over a moving and uneven bottom with surface pressure variation. The scheme is then used to study in details the waves generated from rectangular sources and the two-dimensional wave patterns.

151

Measuring Monotony in Two-Dimensional Samples

ERIC Educational Resources Information Center

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

Kachapova, Farida; Kachapov, Ilias

2010-01-01

152

Accessible solitons in diffusive media.

We investigate spatial solitons in nonlocal media with a nonlinear index well modeled by a diffusive equation. We address the role of nonlocality and its interplay with boundary conditions, shedding light on the behavior of accessible solitons in real samples and discussing the accuracy of the highly nonlocal approximation. We find that symmetric solitons exist only above a power threshold, with an existence region that grows larger and larger with nonlocality in the plane width power. PMID:25078166

Alberucci, Alessandro; Jisha, Chandroth P; Assanto, Gaetano

2014-08-01

153

Two Dimensional Mechanism for Insect Hovering

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

Jane Wang, Z.

2000-09-04

154

Two-Dimensional Proportional Chamber Readout Using Digital Techniques

Two systems of two-dimensional proportional chamber readout are presented, using digital hardware techniques. Centre-of-cluster readout is simple, cheap and very fast: 100 nsec dead-time. Centre-of-gravity readout is slower, with a dead-time of 1 ¿sec, but capable of considerable electronic spatial resolution: 10 ¿m FWHM from 3 mm spaced channels. With this resolution the asymmetry of avalanche formation on anode wires

A. P. Jeavons; N. Ford; B. Lindberg; C. Parkman; Z. Hajduk

1976-01-01

155

Two-dimensional materials for electronic applications

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

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

2013-01-01

156

Relativity on two-dimensional spacetimes

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

Do-Hyung Kim

2013-07-26

157

Electronic properties of two-dimensional systems

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

158

Efficient Two-Dimensional-FFT Program

NASA Technical Reports Server (NTRS)

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

Miko, J.

1992-01-01

159

Spin-Imbalanced Quasi-Two-Dimensional Fermi Gases

NASA Astrophysics Data System (ADS)

We measure the density profiles for a Fermi gas of

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

2015-03-01

160

Oblique collision of plane ion-acoustic solitons

The nonlinear evolution of oblique collisions is investigated experimentally on plane ion-acoustic solitons in two-dimensional space. Many of the observed characteristics of inelastic collisions of solitons are found to be similar to those of resonance interactions described by nonlinear ion-acoustic waves.

Yasushi Nishida; Takeshi Nagasawa

1980-01-01

161

This review volume on topological and nontopological chiral solitons presents a global view on the current developments of this field in particle and nuclear physics. The book addresses problems in quantization, restoration of translational and rotational symmetry, and the field theoretical approach to solitons which are common problems in the field of solitons.

Liu, K.F.

1987-01-01

162

The electrical soliton oscillator

NASA Astrophysics Data System (ADS)

Solitons are a special class of pulse-shaped waves that propagate in nonlinear dispersive media while maintaining their spatial confinement. They are found throughout nature where the proper balance between nonlinearity and dispersion is achieved. Examples of the soliton phenomena include shallow water waves, vibrations in a nonlinear spring-mass lattice, acoustic waves in plasma, and optical pulses in fiber optic cable. In electronics, the nonlinear transmission line (NLTL) serves as a nonlinear dispersive medium that propagates voltage solitons. Electrical solitons on the NLTL have been actively investigated over the last 40 years, particularly in the microwave domain, for sharp pulse generation applications and for high-speed RF and microwave sampling applications. In these past studies the NLTL has been predominantly used as a 2-port system where a high-frequency input is required to generate a sharp soliton output through a transient process. One meaningful extension of the past 2-port NLTL works would be to construct a 1-port self-sustained electrical soliton oscillator by properly combining the NLTL with an amplifier (positive active feedback). Such an oscillator would self-start by growing from ambient noise to produce a train of periodic soliton pulses in steady-state, and hence would make a self-contained soliton generator not requiring an external high-frequency input. While such a circuit may offer a new direction in the field of electrical pulse generation, there has not been a robust electrical soliton oscillator reported to date to the best of our knowledge. In this thesis we introduce the first robust electrical soliton oscillator, which is able to self-generate a stable, periodic train of electrical solitons. This new oscillator is made possible by combining the NLTL with a unique nonlinear amplifier that is able to "tame" the unruly dynamics of the NLTL. The principle contribution of this thesis is the identification of the key instability mechanisms of solitons in a closed-loop oscillator and the development of the necessary stabilizing mechanisms. Demonstration of the concepts developed were in the form of three prototypes: a low MHz discrete prototype, a microwave discrete prototype, and a chip-scale, GHz prototype.

Ricketts, David Shawn

163

Strong nonlocal interaction stabilizes cavity solitons with a varying size plateau

NASA Astrophysics Data System (ADS)

Cavity solitons are localized light peaks in the transverse section of nonlinear resonators. These structures are usually formed under a coexistence condition between a homogeneous background of radiation and a self- organized patterns resulting from a Turing type of instabilities. In this issue, most of studies have been realized ignoring the nonlocal e?ects. Non-local e?ects can play an important role in the formation of cavity solitons in optics, population dynamics and plant ecology. Depending on the choice of the nonlocal interaction function, the nonlocal coupling can be strong or weak. When the nonlocal coupling is strong, the interaction between fronts is controlled by the whole non-local interaction function. Recently it has shown that this type of nonlocal coupling strongly a?ects the dynamics of fronts connecting two homogeneous steady states and leads to the stabilization of cavity solitons with a varying size plateau. Here, we consider a ring passive cavity filled with a Kerr medium like a liquid crystal or left-handed materials and driven by a coherent injected beam. We show that cavity solitons resulting for strong front interaction are stable in one and two-dimensional setting out of any type of Turing instability. Their spatial profile is characterized by a varying size plateau. Our results can apply to large class of spatially extended systems with strong nonlocal coupling.

Fernandez-Oto, Cristian; Tlidi, Mustapha; Escaff, Daniel; Clerc, Marcel; Kockaert, Pascal

2014-05-01

164

Adaptive rezoner in a two-dimensional Lagrangian hydrodynamic code

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

165

Talbot image of two-dimensional fractal grating

NASA Astrophysics Data System (ADS)

Talbot effect of two-dimensional fractal grating built by square aperture arrays is studied theoretically and experimentally in this paper. The amplitude fractal gratings are produced by use of the spatial light modulator, and the diffraction intensity distributions of fractal gratings with different fractal level in Fresnel diffraction field are measured with the help of the two-dimensional CCD. Talbot images of fractal gratings with 1-level and 2-level fractal are obtained in practical experiment. The analytic expression of Fresnel diffraction intensity of the fractal gratings is derived through decomposing fractal gratings into the sum of many periodic gratings. Theoretic results predict the self-image of fractal grating reappears at some certain distance. The numerical calculations also show the Talbot image and the fractional Talbot image of fractal grating. These results may extend the application of fractal grating in the optical processing of information and laser measurement.

Teng, Shuyun; Wang, Junhong; Li, Furui; Zhang, Wei

2014-03-01

166

We report an experimental demonstration of generating gap soliton trains in a four-wave-mixing (FWM) signal. Such spatial FWM surfacelike gap soliton trains are induced in a periodically modulated self-defocusing atomic medium by the cross-phase modulation, which can be reshaped under different experimental conditions, such as different atomic densities, nonlinear dispersions, and dressing fields. Controlling spatial gap solitons can have important applications in image memory, processing, and communication.

Zhang Yanpeng; Wang Zhiguo; Zheng Huaibin; Yuan Chenzhi; Li Changbiao; Lu Keqing [Key Laboratory for Physical Electronics and Devices of the Ministry of Education and Shaanxi Key Lab of Information Photonic Technique, Xi'an Jiaotong University, Xi'an 710049 (China); Xiao Min [Department of Physics, University of Arkansas, Fayetteville, Arkansas 72701 (United States)

2010-11-15

167

Two families of Gaussian-type soliton solutions of the (n+1)-dimensional Schrödinger equation with cubic and power-law nonlinearities in -symmetric potentials are analytically derived. As an example, we discuss some dynamical behaviors of two dimensional soliton solutions. Their phase switches, powers and transverse power-flow densities are discussed. Results imply that the powers flow and exchange from the gain toward the loss regions in the cell. Moreover, the linear stability analysis and the direct numerical simulation are carried out, which indicates that spatial Gaussian-type soliton solutions are stable below some thresholds for the imaginary part of -symmetric potentials in the defocusing cubic and focusing power-law nonlinear medium, while they are always unstable for all parameters in other media. PMID:25542020

Chen, Yi-Xiang; Xu, Fang-Qian

2014-01-01

168

Nitrogenated holey two-dimensional structures

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

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

2015-01-01

169

On the two-dimensional Coulomb gas

This is a sequel to a recent work of Gaudin, who studied the classical equilibrium statistical mechanics of the two-dimensional Coulomb gas on a lattice at a special value of the coupling constant? such that the model is exactly solvable. This model is briefly reviewed, and it is shown that the correlation functions obey the sum rules that characterize a

Françoise Cornu; Bernard Jancovici

1987-01-01

170

Detecting disparity in two-dimensional patterns

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

Bart Farell

171

Nitrogenated holey two-dimensional structures

NASA Astrophysics Data System (ADS)

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

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

2015-03-01

172

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

173

Two-dimensional tunable magnetic photonic crystals

We have calculated the photonic band structure for a cubic block of magnetically saturated ferrite material having a triangular array of circular holes that is under the influence of an external static magnetic field Hex=Hexz applied in the hole direction. In this two-dimensional magnetic photonic crystal, the saturated magnetism can affect the transverse electric (TE) mode whose electric field lies

Chul-Sik Kee; Jae-Eun Kim; Hae Yong Park; H. Lim

2000-01-01

174

A Two Dimensional Car Crash Victim Simulation

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

M. Batman; R. Seliktar

1990-01-01

175

Two-Dimensional Cellular Automata with Memory

Standard Cellular Automata (CA) are ahistoric (memoryless), i.e., the new state of a cell depends on its neighborhood configuration only at the preceding time step. The effect of keeping ahistoric memory of all past iterations in two-dimensional CA, featuring each cell by its most frequent state is analyzed in this work.

Ramón Alonso-Sanz; Margarita Martín

2002-01-01

176

High-resolution two dimensional advective transport

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

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

1989-01-01

177

Evaporation of two-dimensional black holes

An interesting two-dimensional model theory has been proposed that allows one to consider black-hole evaporation in the semiclassical approximation. The semiclassical equations will give a singularity where the dilation field reaches a certain critical value. This singularity will be hidden behind a horizon. As the evaporation proceeds, the dilation field on the horizon will approach the critical value but the

S. W. Hawking

1992-01-01

178

Two Dimensional String Theory And Black Holes

This lecture surveys a few loosely related topics, ranging from the scarcity of quantum field theories -- and the role that this has played, and still plays, in physics -- to paradoxes involving black holes in soluble two dimensional string theory and the question of whether naked singularities might be of even greater interest to string theorists than black holes.

Edward Witten

1992-06-17

179

Nitrogenated holey two-dimensional structures.

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

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

2015-01-01

180

Piezoelectricity in two-dimensional materials.

Powering up 2D materials: Recent experimental studies confirmed the existence of piezoelectricity-the conversion of mechanical stress into electricity-in two-dimensional single-layer MoS2 nanosheets. The results represent a milestone towards embedding low-dimensional materials into future disruptive technologies. PMID:25714055

Wu, Tom; Zhang, Hua

2015-04-01

181

Gap-soliton bullets in waveguide gratings

We derive a perturbed two-dimensional nonlinear Schrödinger equation which describes the propagation of gap-soliton bullets in nonlinear periodic waveguides at frequencies close to the gap for Bragg reflection. Analysis and simulations of this equation show that the bullets amplitude undergoes stable focusing-defocusing cycles. © 2003 Elsevier B.V. All rights reserved.

Alejandro B. Aceves; Gadi Fibich; Boaz Ilan

2004-01-01

182

Measuring system for two-dimensional testing of electrical steel

NASA Astrophysics Data System (ADS)

The measuring system for two-dimensional testing of electrical steel is proposed. In this system the sample in the form of a sheet can be magnetised along arbitrary direction. The magnetizing conditions, the dimensions of the yoke and sheet, the methods of detection of magnetic field strength and flux density are discussed. Both components of magnetic field strength Hx and Hy and flux density Bx and By with respect to the rolling direction or the magnetizing direction can be measured. The examples of tests of grain-oriented steel are presented. The variation of special directions of B and H and the spatial phase shift between these values has been determined.

Tumanski, Slawomir; Bakon, Tomasz

2001-02-01

183

Remarks on Noncommutative Solitons

In the first part of this work we consider an unstable non-BPS Dp-\\bar{Dp}-brane pair in Type II superstring theory. Turning on a background NS-NS B-field (constant and nonzero along two spatial directions), we show that the tachyon responsible for the unstability has a complex GMS solitonic solution, which is interpreted as the low energy remnant of the resulting D(p-2)-brane. In the second part, we apply these results to construct the noncommutative soliton analogous of Witten's superconducting string. This is done by considering the complex GMS soliton arising from the D3-\\bar{D3}-brane annihilation in Type IIB superstring theory. In the presence of left-handed fermions, we apply the Weyl-Wigner-Moyal correspondence and the bosonization technique to show that this object behaves like a superconducting wire.

Hugo Garcia-Compean; Jorge Moreno

2002-02-22

184

Steering the motion of rotary solitons in radial lattices

NASA Astrophysics Data System (ADS)

We demonstrate that rotary motion of a two-dimensional soliton trapped in a Bessel lattice can be precisely controlled by application of a finite-time push to the lattice, due to the transfer of the lattice’s linear momentum to the orbital momentum of the soliton. A simple analytical consideration treating the soliton as a particle provides for an accurate explanation of numerical findings. Some effects beyond the quasi-particle approximation are explored too, such as destruction of the soliton by a hard push.

He, Y. J.; Malomed, Boris A.; Wang, H. Z.

2007-11-01

185

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

186

Two-dimensional ranking of Wikipedia articles

NASA Astrophysics Data System (ADS)

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

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

2010-10-01

187

Plasmonics with two-dimensional conductors

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

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

2014-01-01

188

Electronics based on two-dimensional materials

NASA Astrophysics Data System (ADS)

The compelling demand for higher performance and lower power consumption in electronic systems is the main driving force of the electronics industry's quest for devices and/or architectures based on new materials. Here, we provide a review of electronic devices based on two-dimensional materials, outlining their potential as a technological option beyond scaled complementary metal-oxide-semiconductor switches. We focus on the performance limits and advantages of these materials and associated technologies, when exploited for both digital and analog applications, focusing on the main figures of merit needed to meet industry requirements. We also discuss the use of two-dimensional materials as an enabling factor for flexible electronics and provide our perspectives on future developments.

Fiori, Gianluca; Bonaccorso, Francesco; Iannaccone, Giuseppe; Palacios, Tomás; Neumaier, Daniel; Seabaugh, Alan; Banerjee, Sanjay K.; Colombo, Luigi

2014-10-01

189

Electronics based on two-dimensional materials.

The compelling demand for higher performance and lower power consumption in electronic systems is the main driving force of the electronics industry's quest for devices and/or architectures based on new materials. Here, we provide a review of electronic devices based on two-dimensional materials, outlining their potential as a technological option beyond scaled complementary metal-oxide-semiconductor switches. We focus on the performance limits and advantages of these materials and associated technologies, when exploited for both digital and analog applications, focusing on the main figures of merit needed to meet industry requirements. We also discuss the use of two-dimensional materials as an enabling factor for flexible electronics and provide our perspectives on future developments. PMID:25286272

Fiori, Gianluca; Bonaccorso, Francesco; Iannaccone, Giuseppe; Palacios, Tomás; Neumaier, Daniel; Seabaugh, Alan; Banerjee, Sanjay K; Colombo, Luigi

2014-10-01

190

String breaking in two-dimensional QCD

I present results of a numerical calculation of the effects of light quark-antiquark pairs on the linear heavy-quark potential in light-cone quantized two-dimensional QCD. I extract the potential from the Q-Qbar component of the ground-state wavefunction, and observe string breaking at the heavy-light meson pair threshold. I briefly comment on the states responsible for the breaking.

Hornbostel, K J

1999-01-01

191

Two-dimensional crosstalk avoidance codes

Global buses in deep submicron system-on-chip designs suffer from increasing crosstalk delay as the feature size shrinks. As an technology-independent solution, crosstalk avoidance coding alleviates the problem while requiring less area and power than shielding. Most previously considered crosstalk avoidance codes are one-dimensional, and have limited code rates. In this paper, we propose two-dimensional crosstalk avoidance codes (TDCAC), which achieve

Xuebin Wu; Zhiyuan Yan; Yuan Xie

2008-01-01

192

Statistical Mechanics of Two-dimensional Foams

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

Marc Durand

2010-09-07

193

A two-dimensional lattice of blue detuned atom traps using a projected Gaussian beam array

We describe a new type of blue detuned optical lattice for atom trapping which is intrinsically two dimensional, while providing three-dimensional atom localization. The lattice is insensitive to optical phase fluctuations since it does not depend on field interference between distinct optical beams. The array is created using a novel arrangement of weakly overlapping Gaussian beams that creates a two-dimensional array of dark traps which are suitable for magic trapping of ground and Rydberg states. We analyze the spatial localization that can be achieved and demonstrate trapping and detection of single Cs atoms in 6 and 49 site two-dimensional arrays.

M. J. Piotrowicz; M. Lichtman; K. Maller; G. Li; S. Zhang; L. Isenhower; M. Saffman

2013-07-09

194

Two-dimensional lattice of blue-detuned atom traps using a projected Gaussian beam array

NASA Astrophysics Data System (ADS)

We describe a blue-detuned optical lattice for atom trapping which is intrinsically two-dimensional, while providing three-dimensional atom localization. The lattice is insensitive to optical phase fluctuations since it does not depend on field interference between distinct optical beams. The array is created using an arrangement of weakly overlapping Gaussian beams that creates a two-dimensional array of dark traps which are suitable for magic trapping of ground and Rydberg states. We analyze the spatial localization that can be achieved and demonstrate trapping and detection of single Cs atoms in 6- and 49-site two-dimensional arrays.

Piotrowicz, M. J.; Lichtman, M.; Maller, K.; Li, G.; Zhang, S.; Isenhower, L.; Saffman, M.

2013-07-01

195

A two-dimensional lattice of blue detuned atom traps using a projected Gaussian beam array

We describe a new type of blue detuned optical lattice for atom trapping which is intrinsically two dimensional, while providing three-dimensional atom localization. The lattice is insensitive to optical phase fluctuations since it does not depend on field interference between distinct optical beams. The array is created using a novel arrangement of weakly overlapping Gaussian beams that creates a two-dimensional array of dark traps which are suitable for magic trapping of ground and Rydberg states. We analyze the spatial localization that can be achieved and demonstrate trapping and detection of single Cs atoms in 6 and 49 site two-dimensional arrays.

Piotrowicz, M J; Maller, K; Li, G; Zhang, S; Isenhower, L; Saffman, M

2013-01-01

196

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

197

Ultrashort light bullets described by the two-dimensional sine-Gordon equation

By using a reductive perturbation technique applied to a two-level model, this study puts forward a generic two-dimensional sine-Gordon evolution equation governing the propagation of femtosecond spatiotemporal optical solitons in Kerr media beyond the slowly varying envelope approximation. Direct numerical simulations show that, in contrast to the long-wave approximation, no collapse occurs, and that robust (2+1)-dimensional ultrashort light bullets may form from adequately chosen few-cycle input spatiotemporal wave forms. In contrast to the case of quadratic nonlinearity, the light bullets oscillate in both space and time and are therefore not steady-state lumps.

Leblond, Herve [Laboratoire de Photonique d'Angers, EA 4464 Universite d'Angers, 2 Bd. Lavoisier, FR-49045 Angers Cedex 01 (France); Mihalache, Dumitru [Horia Hulubei National Institute for Physics and Nuclear Engineering (IFIN-HH), 407 Atomistilor, RO-077125 Magurele-Bucharest (Romania); Academy of Romanian Scientists, 54 Splaiul Independentei, RO-050094 Bucharest (Romania)

2010-06-15

198

Wave propagation in two-dimensional periodic lattices.

Plane wave propagation in infinite two-dimensional periodic lattices is investigated using Floquet-Bloch principles. Frequency bandgaps and spatial filtering phenomena are examined in four representative planar lattice topologies: hexagonal honeycomb, Kagomé lattice, triangular honeycomb, and the square honeycomb. These topologies exhibit dramatic differences in their long-wavelength deformation properties. Long-wavelength asymptotes to the dispersion curves based on homogenization theory are in good agreement with the numerical results for each of the four lattices. The slenderness ratio of the constituent beams of the lattice (or relative density) has a significant influence on the band structure. The techniques developed in this work can be used to design lattices with a desired band structure. The observed spatial filtering effects due to anisotropy at high frequencies (short wavelengths) of wave propagation are consistent with the lattice symmetries. PMID:16642813

Phani, A Srikantha; Woodhouse, J; Fleck, N A

2006-04-01

199

Kinetic theory of a two-dimensional magnetized plasma.

NASA Technical Reports Server (NTRS)

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

Vahala, G.; Montgomery, D.

1971-01-01

200

Loop coverings of two dimensional square lattices

NASA Astrophysics Data System (ADS)

In a two dimensional square lattice, where all sites are covered by loops, in the past few years a classical statistical mechanics model of dense loop gas was considered for its relevance for the evaluation of observables of the quantum antiferromagnetic Heisenberg model on the resonating valence bond state. By use of transfer matrices we evaluate several observables for narrow strips with a width of two or three sites. A simple extrapolation, consistent with rigorous bounds, is conjectured for its possible use in a variational ansatz in the Hubbard model.

Cicuta, Giovanni M.; Massari, Francesco

1993-04-01

201

Analytical calculation of two-dimensional spectra.

We demonstrate an analytical calculation of two-dimensional (2D) coherent spectra of electronic or vibrational resonances. Starting with the solution to the optical Bloch equations for a two-level system in the 2D time domain, we show that a fully analytical 2D Fourier transform can be performed if the projection-slice and Fourier-shift theorems of Fourier transforms are applied. Results can be fit to experimental 2D coherent spectra of resonances with arbitrary inhomogeneity. PMID:25831281

Bell, Joshua D; Conrad, Rebecca; Siemens, Mark E

2015-04-01

202

Universal absorption of two-dimensional systems

NASA Astrophysics Data System (ADS)

We discuss the optical conductivity of several noninteracting two-dimensional semiconducting systems focusing on gapped Dirac and Schrödinger fermions as well as on a system mixing these two types. Close to the band gap, we can define a universal optical conductivity quantum of ?0=1/16 e/2? for the pure systems. The effective optical conductivity then depends on the degeneracy factors gs (spin) and gv (valley) and on the curvature around the band gap ? , i.e., it generally reads ? =gsgv? ?0 . For a system composed of both types of carriers, the optical conductivity becomes nonuniversal.

Stauber, T.; Noriega-Pérez, D.; Schliemann, J.

2015-03-01

203

Cosmic Censorship in Two-Dimensional Gravity

A weak version of the cosmic censorship hypothesis is implemented as a set of boundary conditions on exact semi-classical solutions of two-dimensional dilaton gravity. These boundary conditions reflect low-energy matter from the strong coupling region and they also serve to stabilize the vacuum of the theory against decay into negative energy states. Information about low-energy incoming matter can be recovered in the final state but at high energy black holes are formed and inevitably lead to information loss at the semi-classical level.

J. Russo; L. Susskind; L. Thorlacius

1992-09-22

204

Flow transitions in two-dimensional foams.

For sufficiently slow rates of strain, flowing foam can exhibit inhomogeneous flows. The nature of these flows is an area of active study in both two-dimensional model foams and three dimensional foam. Recent work in three-dimensional foam has identified three distinct regimes of flow [S. Rodts, J. C. Baudez, and P. Coussot, Europhys. Lett. 69, 636 (2005)]. Two of these regimes are identified with continuum behavior (full flow and shear banding), and the third regime is identified as a discrete regime exhibiting extreme localization. In this paper, the discrete regime is studied in more detail using a model two-dimensional foam: a bubble raft. We characterize the behavior of the bubble raft subjected to a constant rate of strain as a function of time, system size, and applied rate of strain. We observe localized flow that is consistent with the coexistence of a power-law fluid with rigid-body rotation. As a function of applied rate of strain, there is a transition from a continuum description of the flow to discrete flow when the thickness of the flow region is approximately ten bubbles. This occurs at an applied rotation rate of approximately 0.07 s-1. PMID:17279908

Gilbreth, Christopher; Sullivan, Scott; Dennin, Michael

2006-11-01

205

Two-dimensional phonon transport in graphene.

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

Nika, Denis L; Balandin, Alexander A

2012-06-13

206

Solitonic objects play a central role in gauge and string theory (as, e.g., monopoles, black holes, D-branes, etc.). Certain string backgrounds produce a noncommutative deformation of the low-energy effective field theory, which allows for new types of solitonic solutions. I present the construction, moduli spaces and dynamics of Moyal-deformed solitons, exemplified in the 2+1 dimensional Yang-Mills-Higgs theory and its Bogomolny system, which is gauge-fixed to an integrable chiral sigma model (the Ward model). Noncommutative solitons for various 1+1 dimensional integrable systems (such as sine-Gordon) easily follow by dimensional and algebraic reduction. Supersymmetric extensions exist as well and are related to twistor string theory.

Lechtenfeld, Olaf [Theory Division, Physics Department, CERN, CH-1211 Geneva 23, Switzerland on leave from: Institut fuer Theoretische Physik, Leibniz Universitaet Hannover (Switzerland)

2008-03-06

207

Two-dimensional Effects in High Power Microwave Breakdown

NASA Astrophysics Data System (ADS)

A major limiting factor in transmission of high power microwave radiation is dielectric window breakdown. A one-dimensional particle-in-cell/Monte Carlo collision (PIC/MCC) model was used to study dielectric window breakdown from vacuum multipactor to collisional microwave discharge for noble gases [1]. It showed that multipactor on the dielectric window drives breakdown at low pressure, and volumetric collisional ionization is the main mechanism for breakdown at high pressure. A Monte Carlo (MC) model was also used to investigate dielectric window breakdown in two-dimensionals, including spatial variation of the microwave electric field in transverse direction [2]. The breakdown times were consistent with their experiment data and also showed the interesting feature of electron clusters above the window. MC, however, is not self-consistent and neglects the space charge effect resulting from the charge build-up. In this work, two-dimensional PIC/MCC was employed to investigate the breakdown in oxygen including the space charge effect. [1] H.C. Kim, and J.P. Verboncoeur, Phys. Plasmas, 13, 123506(2006). [2] J.T. Krile, A.A. Neuber, and H. G. Krompholz, Appl. Phys. Lett., 89, 201501(2006).

Nam, Sang Ki; Lim, Chul-Hyun; Verboncoeur, John

2008-10-01

208

Lateral epitaxial growth of two-dimensional layered semiconductor heterojunctions

NASA Astrophysics Data System (ADS)

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

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

2014-12-01

209

Two-Dimensional, Optical Ellipsometric Studies of Polymer Orientation

NASA Astrophysics Data System (ADS)

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

Georgiev, Georgi; Berns, David; Cebe, Peggy

2001-03-01

210

Lateral epitaxial growth of two-dimensional layered semiconductor heterojunctions.

Two-dimensional layered semiconductors such as MoS? and WSe? have attracted considerable interest in recent times. Exploring the full potential of these layered materials requires precise spatial modulation of their chemical composition and electronic properties to create well-defined heterostructures. Here, we report the growth of compositionally modulated MoS?-MoSe? and WS?-WSe? lateral heterostructures by in situ modulation of the vapour-phase reactants during growth of these two-dimensional crystals. Raman and photoluminescence mapping studies demonstrate that the resulting heterostructure nanosheets exhibit clear structural and optical modulation. Transmission electron microscopy and elemental mapping studies reveal a single crystalline structure with opposite modulation of sulphur and selenium distributions across the heterostructure interface. Electrical transport studies demonstrate that the WSe?-WS? heterojunctions form lateral p-n diodes and photodiodes, and can be used to create complementary inverters with high voltage gain. Our study is an important advance in the development of layered semiconductor heterostructures, an essential step towards achieving functional electronics and optoelectronics. PMID:25262331

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

2014-12-01

211

Traveling dark solitons in superfluid Fermi gases

Families of dark solitons exist in superfluid Fermi gases. The energy-velocity dispersion and number of depleted particles completely determine the dynamics of dark solitons on a slowly varying background density. For the unitary Fermi gas, we determine these relations from general scaling arguments and conservation of local particle number. We find solitons to oscillate sinusoidally at the trap frequency reduced by a factor of 1/{radical}(3). Numerical integration of the time-dependent Bogoliubov-de Gennes equation determines spatial profiles and soliton-dispersion relations across the BEC-BCS crossover, and proves consistent with the scaling relations at unitarity.

Liao Renyuan; Brand, Joachim [New Zealand Institute for Advanced Study and Centre for Theoretical Chemistry and Physics, Massey University, Private Bag 102904 NSMC, Auckland 0745 (New Zealand)

2011-04-15

212

Two-dimensional fourier transform spectrometer

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

213

Two-dimensional nuclear magnetic resonance petrophysics.

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

Sun, Boqin; Dunn, Keh-Jim

2005-02-01

214

Transport in two-dimensional disordered semimetals.

We theoretically study transport in two-dimensional semimetals. Typically, electron and hole puddles emerge in the transport layer of these systems due to smooth fluctuations in the potential. We calculate the electric response of the electron-hole liquid subject to zero and finite perpendicular magnetic fields using an effective medium approximation and a complementary mapping on resistor networks. In the presence of smooth disorder and in the limit of a weak electron-hole recombination rate, we find for small but finite overlap of the electron and hole bands an abrupt upturn in resistivity when lowering the temperature but no divergence at zero temperature. We discuss how this behavior is relevant for several experimental realizations and introduce a simple physical explanation for this effect. PMID:25396385

Knap, Michael; Sau, Jay D; Halperin, Bertrand I; Demler, Eugene

2014-10-31

215

Gauge equivalence in two-dimensional gravity

NASA Astrophysics Data System (ADS)

Two-dimensional quantum gravity is identified as a second-class system which we convert into a first-class system via the Batalin-Fradkin (BF) procedure. Using the extended phase space method, we then formulate the theory in the most general class of gauges. The conformal gauge action suggested by David, Distler, and Kawai is derived from first principles. We find a local, light-cone gauge action whose Becchi-Rouet-Stora-Tyutin invariance implies Polyakov's curvature equation ?-R=?3-g++=0, revealing the origin of the SL(2,R) Kac-Moody symmetry. The BF degree of freedom turns out to be dynamically active as the Liouville mode in the conformal gauge, while in the light-cone gauge the conformal degree of freedom plays that role. The inclusion of the cosmological constant term in both gauges is also considered.

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

1993-08-01

216

Phonon hydrodynamics in two-dimensional materials.

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

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

2015-01-01

217

From two-dimensional materials to heterostructures

NASA Astrophysics Data System (ADS)

Graphene, hexagonal boron nitride, molybdenum disulphide, and layered transition metal dichalcogenides (TMDCs) represent a class of two-dimensional (2D) atomic crystals with unique properties due to reduced dimensionality. Stacking these materials on top of each other in a controlled fashion can create heterostructures with tailored properties that offers another promising approach to design and fabricate novel electronic devices. In this report, we attempt to review this rapidly developing field of hybrid materials. We summarize the fabrication methods for different 2D materials, the layer-by-layer growth of various vertical heterostructures and their electronic properties. Particular interests are given to in-situ stack aforementioned 2D materials in controlled sequences, and the TMDCs heterostructures.

Niu, Tianchao; Li, Ang

2015-02-01

218

Tunable two-dimensional femtosecond spectroscopy

NASA Astrophysics Data System (ADS)

We have developed a two-dimensional (2D) Fourier-transform femtosecond spectroscopy technique for the visible spectral region. Three-pulse photon echo signals are generated in a phase-matched noncollinear four-wave mixing box geometry that employs a 3-kHz repetition-rate laser system and optical parametric amplification. Nonlinear signals are fully characterized in amplitude and phase by spectral interferometry. Unlike for previous setups, we achieve long-term phase stability by employing diffractive optics and interferometric accuracy of excitation-pulse time delays by using movable glass wedges. As an example of this technique, 2D correlation and relaxation spectra at 600 nm are shown for a solution of Nile Blue dye in acetonitrile.

Brixner, T.; Stiopkin, I. V.; Fleming, G. R.

2004-04-01

219

Two-dimensional readout of GEM detectors

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

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

1999-01-01

220

Phonon hydrodynamics in two-dimensional materials

NASA Astrophysics Data System (ADS)

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

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

2015-03-01

221

Two-Dimensional Informative Array Testing

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

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

2015-01-01

222

A two dimensional piezoeletric micro-positioner

NASA Astrophysics Data System (ADS)

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

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

2009-03-01

223

Evaporation of Two Dimensional Black Holes

Callan, Giddings, Harvey and Strominger have proposed an interesting two dimensional model theory that allows one to consider black hole evaporation in the semi-classical approximation. They originally hoped the black hole would evaporate completely without a singularity. However, it has been shown that the semi-classical equations will give a singularity where the dilaton field reaches a certain critical value. Initially, it seems this singularity will be hidden inside a black hole. However, as the evaporation proceeds, the dilaton field on the horizon will approach the critical value but the temperature and rate of emission will remain finite. These results indicate either that there is a naked singularity, or (more likely) that the semi-classical approximation breaks down when the dilaton field approaches the critical value.

S. W. Hawking

1992-03-18

224

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

225

Convergence of two-dimensional Fourier series

' 6 (c-a) + 2 M s + ? if n & N. 3 (c, d) Therefore ( f(x, y) sin nxdx & s ' j(a, b) The proof for cos nx is similar. 22o Vl. Ifd Il/2, 12 f, d II I 2 +I ll 2 0 Proof: Consider '0/2 r 2 +I dx = sin x 0 Ti [ 1/2 + cos Q + cos 0 ll ~it +I 't...), then the two-dimensional Fourier series equivalent to f(x, y) is Co CO Co Co f(x, y) = L' L' A sin(nx) sin (my) + Z Z B sin(@x)cos(my) n=l m=1 n=l m=1 1 CG Co co + ? F, B sin(nx) + Z Z C cos (nx) sin(my) + ? Z C sin(my) 2 1 n, o n, m 2 I OIm Co Co OO...

Kidd, Robert Henry, III

1962-01-01

226

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

227

Two-dimensional virtual impactors. Final report

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

228

Stability of vortex solitons under competing local and nonlocal cubic nonlinearities

NASA Astrophysics Data System (ADS)

We investigate systematically the stability of two-dimensional vortex solitons in nonlinear media under competing local and nonlocal cubic nonlinearities. We obtain the analytical results to describe the relations between the parameters of the vortex solitons. When the local cubic nonlinearity is self-focusing, the formation power of the vortex solitons will approach a constant in the limit of strong nonlocality. The long-lived stable vortex solitons can be obtained with moderate degree of nonlocality when the nonlocal cubic nonlinearity is self-focusing. Otherwise, the vortex solitons will suffer from the unstable dynamics, such as splitting, diffraction enhancement, and catastrophic collapse. In the limit of strong degree of nonlocality, the vortex solitons are always unstable which is different from the previous results that the vortex solitons can be stabilized completely. The stability and the dynamics of the vortex solitons are also demonstrated numerically with the split-step Fourier transform method.

Shen, Ming; Li, Bailing; Ge, Lijuan; Chen, Wei; Wu, Di

2015-03-01

229

DARBOUX TRANSFORMATIONS FOR LINEAR OPERATORS ON TWO DIMENSIONAL REGULAR LATTICES

DARBOUX TRANSFORMATIONS FOR LINEAR OPERATORS ON TWO DIMENSIONAL REGULAR LATTICES ADAM DOLIWA AND MACIEJ NIESZPORSKI Abstract. Darboux transformations for (systems of) linear operators on regular two dimensional lattices are reviewed. 1. Introduction The Darboux transformation is a well known tool

230

Internal tide generation by arbitrary two-dimensional topography

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

Peacock, Thomas

231

Families of vortex solitons in periodic media Jiandong Wang and Jianke Yang

in a lot of new physical effects of the wave propagation. For in- stance, in a periodic media, solitons can; published 19 March 2008 Various families of charge-1 vortex solitons in two-dimensional periodic media shapes can belong to the same vortex family, which is quite surprising. DOI: 10.1103/PhysRevA.77

Yang, Jianke

232

2094 OPTICS LETTERS / Vol. 28, No. 21 / November 1, 2003 Fundamental and vortex solitons in a

2094 OPTICS LETTERS / Vol. 28, No. 21 / November 1, 2003 Fundamental and vortex solitons in a two-dimensional optical lattice Jianke Yang Department of Mathematics and Statistics, University of Vermont, Burlington-dimensional optically induced waveguide array are reported. In the strong localization regime the fundamental soliton

Yang, Jianke

233

SCAPS, a two-dimensional ion detector for mass spectrometer

NASA Astrophysics Data System (ADS)

Faraday Cup (FC) and electron multiplier (EM) are of the most popular ion detector for mass spectrometer. FC is used for high-count-rate ion measurements and EM can detect from single ion. However, FC is difficult to detect lower intensities less than kilo-cps, and EM loses ion counts higher than Mega-cps. Thus, FC and EM are used complementary each other, but they both belong to zero-dimensional detector. On the other hand, micro channel plate (MCP) is a popular ion signal amplifier with two-dimensional capability, but additional detection system must be attached to detect the amplified signals. Two-dimensional readout for the MCP signals, however, have not achieve the level of FC and EM systems. A stacked CMOS active pixel sensor (SCAPS) has been developed to detect two-dimensional ion variations for a spatial area using semiconductor technology [1-8]. The SCAPS is an integrated type multi-detector, which is different from EM and FC, and is composed of more than 500×500 pixels (micro-detectors) for imaging of cm-area with a pixel of less than 20 µm in square. The SCAPS can be detected from single ion to 100 kilo-count ions per one pixel. Thus, SCAPS can be accumulated up to several giga-count ions for total pixels, i.e. for total imaging area. The SCAPS has been applied to stigmatic ion optics of secondary ion mass spectrometer, as a detector of isotope microscope [9]. The isotope microscope has capabilities of quantitative isotope images of hundred-micrometer area on a sample with sub-micrometer resolution and permil precision, and of two-dimensional mass spectrum on cm-scale of mass dispersion plane of a sector magnet with ten-micrometer resolution. The performance has been applied to two-dimensional isotope spatial distribution for mainly hydrogen, carbon, nitrogen and oxygen of natural (extra-terrestrial and terrestrial) samples and samples simulated natural processes [e.g. 10-17]. References: [1] Matsumoto, K., et al. (1993) IEEE Trans. Electron Dev. 40, 82-85. [2] Takayanagi et al. (1999) Proc. 1999 IEEE workshop on Charge-Coupled Devices and Advanced Image Sensors, 159-162. [3] Kunihiro et al. (2001) Nucl. Instrum. Methods Phys. Res. Sec. A 470, 512-519. [4] Nagashima et al. (2001) Surface Interface Anal. 31, 131-137. [5] Takayanagi et al. (2003) IEEE Trans. Electron Dev. 50, 70- 76. [6] Sakamoto and Yurimoto (2006) Surface Interface Anal. 38, 1760-1762. [7] Yamamoto et al. (2010) Surface Interface Anal. 42, 1603-1605. [8] Sakamoto et al. (2012) Jpn. J. Appl. Phys. 51, 076701. [9] Yurimoto et al. (2003) Appl. Surf. Sci. 203-204, 793-797. [10] Nagashima et al. (2004) Nature 428, 921-924. [11] Kunihiro et al. (2005) Geochim. Cosmochim. Acta 69, 763-773. [12] Nakamura et al. (2005) Geology 33, 829-832. [13] Sakamoto et al. (2007) Science 317, 231-233. [14] Greenwood et al. (2008) Geophys. Res. Lett., 35, L05203. [15] Greenwood et al. (2011) Nature Geoscience 4, 79-82. [16] Park et al. (2012) Meteorit. Planet. Sci. 47, 2070-2083. [17] Hashiguchi et al. (2013) Geochim. Cosmochim. Acta. 122, 306-323.

Yurimoto, Hisayoshi

2014-05-01

234

Spin precession in inversion-asymmetric two-dimensional systems

NASA Astrophysics Data System (ADS)

We present a theoretical method to calculate the expectation value of spin in an inversion-asymmetric two-dimensional (2D) system with respect to an arbitrarily spin-polarized electron state, injected via an ideal point contact. The 2D system is confined in a [0 0 1]-grown quantum well, where both the Rashba and the Dresselhaus spin-orbit couplings are taken into account. The obtained analytical results allow more concrete description of the spatial behaviors of the spin precession caused individually by the Rashba and the Dresselhaus terms. Applying the calculation on the Datta-Das spin-FET, whose original design considers only the Rashba effect inside the channel, we investigate the possible influence due to the Dresselhaus spin-orbit coupling. Concluded solution is the choice of ±[1±10], in particular [1 1 0], as the channel direction.

Liu, Ming-Hao; Chang, Ching-Ray

2006-09-01

235

Spectral energy transport in two-dimensional quantum vortex dynamics

NASA Astrophysics Data System (ADS)

We explore the possible regimes of decaying two-dimensional quantum turbulence, and elucidate the nature of spectral energy transport by introducing a dissipative point-vortex model with phenomenological vortex-sound interactions. The model is valid for a large system with weak dissipation, and also for systems with strong dissipation, and allows us to extract a meaningful and unambiguous spectral energy flux associated with quantum vortex motion. For weak dissipation and large system size we find a regime of hydrodynamic vortex turbulence in which energy is transported to large spatial scales, resembling the phenomenology of the transient inverse cascade observed in decaying turbulence in classical incompressible fluids. For strong dissipation the vortex dynamics are dominated by dipole recombination and exhibit no appreciable spectral transport of energy.

Billam, T. P.; Reeves, M. T.; Bradley, A. S.

2015-02-01

236

ANALYSIS OF TWO-DIMENSIONAL ELECTROPHORESIS GEL IMAGES

ANALYSIS OF TWO-DIMENSIONAL ELECTROPHORESIS GEL IMAGES Lars Pedersen Informatics and Mathematical of proteomics. The subject is Analysis of Two-dimensional Electrophoresis Gel Images. This work was carried out analysis of two-dimensional gel electrophoresis (2DGE) images. 2DGE is the leading technique to separate

237

Polarization scattering by soliton-soliton collisions

NASA Astrophysics Data System (ADS)

We have discovered experimentally that soliton-soliton collisions in wavelength division multiplexing significantly alter the polarization states of the colliding solitons. Analysis shows that the change in polarization is according to the cross product of the Stokes vectors of the colliding solitons. Birefringence of the fiber spans can turn this polarization scattering into a significant source of timing jitter.

Mollenauer, L. F.; Gordon, J. P.; Heismann, F.

1995-10-01

238

Seismic isolation of two dimensional periodic foundations

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

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

2014-07-28

239

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

240

Two-dimensional flow magnetophoresis of microparticles.

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

Kawano, Makoto; Watarai, Hitoshi

2012-07-01

241

An atlas of two-dimensional materials.

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

Miró, Pere; Audiffred, Martha; Heine, Thomas

2014-09-21

242

Turbulence in two dimensional visco - elastic medium

The properties of decaying turbulence is studied with the help of a Generalized Hydrodynamic (GHD) fluid model in the context of two dimensional visco - elastic medium such as a strongly coupled dusty plasma system. For the incompressible case considered here however, the observations are valid for a wider class of visco - elastic systems not necessarily associated with plasmas only. Our observations show that an initial spectrum that is confined in a limited domain of wave numbers becomes broad, even when the Reynold's number is much less than the critical value required for the onset of turbulence in Newtonian fluids. This is a signature of elastic turbulence where Weissenberg's number also plays a role in the onset of turbulence. This has been reported in several experiments. It is also shown that the existence of memory relaxation time parameter and the transverse shear wave inhibit the normal process (for 2-D systems) of inverse spectral cascade in this case. A detailed simulation study has been carried ...

Tiwari, Sanat Kumar; Das, Amita; Patel, Bhavesh G; Kaw, Predhiman

2014-01-01

243

Seismic isolation of two dimensional periodic foundations

NASA Astrophysics Data System (ADS)

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

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

2014-07-01

244

TWO DIMENSIONAL COMPUTER SIMULATION OF PLASMA IMMERSION

confinement of the secondary electrons #12;2.5D computer simulation with code KARAT Spatial variables of the plasma sheath is followed in the time. #12;Numerical parameters KARAT is run in electrostatic mode vacuum

245

Dynamical properties of a Soliton in a Potential Well

We analyse the scattering of a two-dimensional soliton on a potential well. We show that this soliton can pass through the well, bounce back or become trapped and we study the dependence of the critical velocity on the width and the depth of the well. We also present a model based on a pseudo-geodesic approximation to the full system which shows that the vibrational modes of the soliton play a crucial role in the dynamical properties of its interactions with potential wells.

B. Piette; W. J. Zakrzewski

2006-10-09

246

Gravity Effects on Steady Two-Dimensional Partially Premixed MethaneAir Flames

Gravity Effects on Steady Two-Dimensional Partially Premixed MethaneAir Flames ZHUANG SHU, CHUN W, University of Illinois at Chicago, Chicago, IL 60607-7022 Under normal-gravity conditions the flame heat is only weakly affected by gravity, the outer flame shows significant spatial differences for the two

Aggarwal, Suresh K.

247

NASA Astrophysics Data System (ADS)

In this paper we study the numerical solution of parabolic Volterra integro-differential equations on certain unbounded two-dimensional spatial domains. The method is based on the introduction of a feasible artificial boundary and the derivation of corresponding artificial (fully transparent) boundary conditions. Two examples illustrate the application and numerical performance of the method.

Han, Houde; Zhu, Liang; Brunner, Hermann; Ma, Jingtang

2006-12-01

248

Differences in the Two-Dimensionally Measured Laser Doppler Flow at Different Skin Localisations

The cutaneous microcirculation shows a significant heterogeneity. With high-resolution two-dimensional laser Doppler perfusion imaging (LDPI), spatial and temporal reproducible perfusion measurements can be reached. The objective of this study was the quantification of skin perfusion in 20 defined skin areas with LDPI, in 60 healthy young and old volunteers. The perfusion of the face was significantly higher than that of

M. Stücker; J. Steinberg; U. Memmel; A. Avermaete; K. Hoffmann; P. Altmeyer

2001-01-01

249

NASA Technical Reports Server (NTRS)

Theoretical and numerical works in atmospheric turbulence have used the Navier-Stokes fluid equations exclusively for describing large-scale motions. Controversy over the existence of an average temperature gradient for the very large eddies in the atmosphere suggested that a new theoretical basis for describing large-scale turbulence was necessary. A new soliton formalism as a fluid analogue that generalizes the Schrodinger equation and the Zakharov equations has been developed. This formalism, processing all the nonlinearities including those from modulation provided by the density fluctuations and from convection due to the emission of finite sound waves by velocity fluctuations, treats large-scale turbulence as coalescing and colliding solitons. The new soliton system describes large-scale instabilities more explicitly than the Navier-Stokes system because it has a nonlinearity of the gradient type, while the Navier-Stokes has a nonlinearity of the non-gradient type. The forced Schrodinger equation for strong fluctuations describes the micro-hydrodynamical state of soliton turbulence and is valid for large-scale turbulence in fluids and plasmas where internal waves can interact with velocity fluctuations.

Tchen, C. M.

1986-01-01

250

Two-dimensional mapping of ionospheric structures with a regional GPS network in Japan

GEONET, a regional GPS network, consists of more than one thousand GPS receivers and provides two-dimensional maps of total electron content (TEC) with 20km of spatial resolution and 30 seconds of temporal resolution over Japan. This high-resolution, wide-area and continuous TEC observation makes it possible to distinguish between temporal variations and spatial variations of the ionospheric structures, which is difficult

A. Saito; M. C. Kelley; T. Tsugawa; Y. Otsuka

2001-01-01

251

Responses of V1 Neurons to Two-Dimensional Hermite Functions

Neurons in primary visual cortex are widely considered to be oriented filters or energy detectors that perform one-dimensional feature analysis. The main deviations from this picture are generally thought to include gain controls and modulatory influences. Here we investigate receptive field (RF) properties of single neurons with localized two-dimensional stimuli, the two-dimensional Hermite functions (TDHs). TDHs can be grouped into distinct complete orthonormal bases that are matched in contrast energy, spatial extent, and spatial frequency content but differ in two-dimensional form, and thus can be used to probe spatially specific nonlinearities. Here we use two such bases: Cartesian TDHs, which resemble vignetted gratings and checkerboards, and polar TDHs, which resemble vignetted annuli and dartboards. Of 63 isolated units, 51 responded to TDH stimuli. In 37/51 units, we found significant differences in overall response size (21/51) or apparent RF shape (28/51) that depended on which basis set was used. Because of the properties of the TDH stimuli, these findings are inconsistent with simple feedforward nonlinearities and with many variants of energy models. Rather, they imply the presence of nonlinearities that are not local in either space or spatial frequency. Units showing these differences were present to a similar degree in cat and monkey, in simple and complex cells, and in supragranular, infragranular, and granular layers. We thus find a widely distributed neurophysiological substrate for two-dimensional spatial analysis at the earliest stages of cortical processing. Moreover, the population pattern of tuning to TDH functions suggests that V1 neurons sample not only orientations, but a larger space of two-dimensional form, in an even-handed manner. PMID:16148274

Victor, Jonathan D.; Mechler, Ferenc; Repucci, Michael A.; Purpura, Keith P.; Sharpee, Tatyana

2010-01-01

252

Turbulent equipartitions in two-dimensional drift convection

NASA Astrophysics Data System (ADS)

Unlike the thermodynamic equipartition of energy in conservative systems, turbulent equipartitions (TEP) describe strongly nonequilibrium 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-equlibria. 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.

1997-04-01

253

Dirac solitons in square binary waveguide lattices

NASA Astrophysics Data System (ADS)

We study optical analogs of two-dimensional (2D) Dirac solitons in square binary waveguide lattices with two different topologies in the presence of Kerr nonlinearity. These 2D solitons turn out to be quite robust. We demonstrate that with the found 2D solitons, the coupled mode equations governing light dynamics in square binary waveguide lattices can be converted into the nonlinear relativistic 2D Dirac equation with the four-component bispinor. This paves the way for using binary waveguide lattices as a classical simulator of quantum nonlinear effects arising from the 2D Dirac equation, something that is thought to be impossible to achieve in conventional (i.e., linear) quantum field theory.

Tran, Truong X.; Nguyen, Xuan N.; Biancalana, Fabio

2015-02-01

254

Solitonic axion condensates modeling dark matter halos

Instead of fluid type dark matter (DM), axion-like scalar fields with a periodic self-interaction or some truncations of it are analyzed as a model of galaxy halos. It is probed if such cold Bose–Einstein type condensates could provide a viable soliton type interpretation of the DM ‘bullets’ observed by means of gravitational lensing in merging galaxy clusters. We study solitary waves for two self-interacting potentials in the relativistic Klein–Gordon equation, mainly in lower dimensions, and visualize the approximately shape-invariant collisions of two ‘lump’ type solitons. -- Highlights: •An axion model of dark matter is considered. •Collision of axion type solitons are studied in a two dimensional toy model. •Relations to dark matter collisions in galaxy clusters are proposed.

Castañeda Valle, David, E-mail: casvada@gmail.com; Mielke, Eckehard W., E-mail: ekke@xanum.uam.mx

2013-09-15

255

Theory and application of the RAZOR two-dimensional continuous energy lattice physics code

The theory and application of the RAZOR two-dimensional, continuous energy lattice physics code are discussed. RAZOR solves the continuous energy neutron transport equation in one- and two-dimensional geometries, and calculates equivalent few-group diffusion theory constants that rigorously account for spatial and spectral self-shielding effects. A dual energy resolution slowing down algorithm is used to reduce computer memory and disk storage requirements for the slowing down calculation. Results are presented for a 2D BWR pin cell depletion benchmark problem.

Zerkle, M.L.; Abu-Shumays, I.K.; Ott, M.W.; Winwood, J.P.

1997-04-01

256

NASA Astrophysics Data System (ADS)

We consider single interval Rényi and entanglement entropies for a two dimensional conformal field theory on a circle at nonzero temperature. Assuming that the finite size of the system introduces a unique ground state with a nonzero mass gap, we calculate the leading corrections to the Rényi and entanglement entropy in a low temperature expansion. These corrections have a universal form for any two dimensional conformal field theory that depends only on the size of the mass gap and its degeneracy. We analyze the limits where the size of the interval becomes small and where it becomes close to the size of the spatial circle.

Cardy, John; Herzog, Christopher P.

2014-05-01

257

Two-dimensional angularly selective optical properties of gold nanoshell with holes.

We studied the optical extinction properties of Au nanoshell with two holes by the discrete-dipole approximation method. We found that the extinction spectra of the nanoparticles are sensitive to the angle between the polarization vector of the incident light and either symmetrical axis of the hole on nanoshell and also the sizes of two holes. The nanostructure we proposed provides the additional dimensional angularly selectivity of the optical properties and the plasmon resonances redshift comparing with the nanocup. In addition, the conception of the "two-dimensional" symmetry breaking of the nanoparticle is suggested which can induce the two-dimensional spatial asymmetry of optical properties of nanoparticles. PMID:22714523

Qian, Jun; Chen, Zongqiang; Chen, Jing; Li, Yudong; Xu, Jingjun; Sun, Qian

2012-06-18

258

Nonlinear evolution of interacting oblique waves on two-dimensional shear layers

NASA Technical Reports Server (NTRS)

The effects of critical layer nonlinearity are considered on spatially growing oblique instability waves on nominally two-dimensional shear layers between parallel streams. The analysis shows that three-dimensional effects cause nonlinearity to occur at much smaller amplitudes than it does in two-dimensional flows. The nonlinear instability wave amplitude is determined by an integro-differential equation with cubic type nonlinearity. The numerical solutions to this equation are worked out and discussed in some detail. The numerical solutions always end in a singularity at a finite downstream distance.

Goldstein, M. E.; Choi, S.-W.

1989-01-01

259

Vortices of Two Dimensional Guiding Center Plasmas.

NASA Astrophysics Data System (ADS)

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

Ting, Antonio Chofai

260

Two-dimensional material confined water.

CONSPECTUS: The interface between water and other materials under ambient conditions is of fundamental importance due to its relevance in daily life and a broad range of scientific research. The structural and dynamic properties of water at an interface have been proven to be significantly difference than those of bulk water. However, the exact nature of these interfacial water adlayers at ambient conditions is still under debate. Recent scanning probe microscopy (SPM) experiments, where two-dimensional (2D) materials as ultrathin coatings are utilized to assist the visualization of interfacial water adlayers, have made remarkable progress on interfacial water and started to clarify some of these fundamental scientific questions. In this Account, we review the recently conducted research exploring the properties of confined water between 2D materials and various surfaces under ambient conditions. Initially, we review the earlier studies of water adsorbed on hydrophilic substrates under ambient conditions in the absence of 2D coating materials, which shows the direct microscopic results. Subsequently, we focus on the studies of water adlayer growth at both hydrophilic and hydrophobic substrates in the presence of 2D coating materials. Ice-like water adlayers confined between hydrophobic graphene and hydrophilic substrates can be directly observed in detail by SPM. It was found that the packing structure of the water adlayer was determined by the hydrophilic substrates, while the orientation of intercalation water domains was directed by the graphene coating. In contrast to hydrophilic substrates, liquid-like nanodroplets confined between hydrophobic graphene and hydrophobic substrates appear close to step edges and atomic-scale surface defects, indicating that atomic-scale surface defects play significant roles in determining the adsorption of water on hydrophobic substrates. In addition, we also review the phenomena of confined water between 2D hydrophilic MoS2 and the hydrophilic substrate. Finally, we further discuss researchers taking advantage of 2D graphene coatings to stabilize confined water nanodroplets to manipulate nanofluidics through applying an external force by using novel SPM techniques. Moreover, for future technology application purposes, the doping effect of confined water is also discussed. The use of 2D materials as ultrathin coatings to investigate the properties of confined water under ambient conditions is developing and recognized as a profound approach to gain fundamental knowledge of water. This ideal model system will provide new opportunities in various research fields. PMID:25539031

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

2015-01-20

261

Thermodynamics of Two Dimensional Black Holes

Thermodynamic relations for a class of 2D black holes are obtained corresponding to observations made from finite spatial distances. We also study the thermodynamics of the charged version of the Jackiw-Teitelboim black holes found recently by Lowe and Strominger. Our results corroborate, in appropriate limits, to those obtained previously by other methods. We also analyze the stability of these black holes thermodynamically.

Alok Kumar; Koushik Ray

1994-10-10

262

Front tracking and two-dimensional Riemann problems

NASA Astrophysics Data System (ADS)

Two-dimensional Riemann problems occurring at the intersection points of discontinuous waves in a compressible, inviscid, polytropic gas are studied from both numerical and theoretical points of view using the front tracking method. The results are compared to experimental ones for two specific test problems. An example of how the motion of a two-dimensional coherent wave is determined numerically is given, and it is shown that in two-dimensional compressible gas dynamics there are only a small number of such two-dimensional coherent waves. Outstanding questions related to Riemann problems are also discussed.

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

1985-09-01

263

Two-Dimensional Finite Element Ablative Thermal Response Analysis of an Arcjet Stagnation Test

NASA Technical Reports Server (NTRS)

The finite element ablation and thermal response (FEAtR, hence forth called FEAR) design and analysis program simulates the one, two, or three-dimensional ablation, internal heat conduction, thermal decomposition, and pyrolysis gas flow of thermal protection system materials. As part of a code validation study, two-dimensional axisymmetric results from FEAR are compared to thermal response data obtained from an arc-jet stagnation test in this paper. The results from FEAR are also compared to the two-dimensional axisymmetric computations from the two-dimensional implicit thermal response and ablation program under the same arcjet conditions. The ablating material being used in this arcjet test is phenolic impregnated carbon ablator with an LI-2200 insulator as backup material. The test is performed at the NASA, Ames Research Center Interaction Heating Facility. Spatially distributed computational fluid dynamics solutions for the flow field around the test article are used for the surface boundary conditions.

Dec, John A.; Laub, Bernard; Braun, Robert D.

2011-01-01

264

Transfer of optical signals around bends in two-dimensional linear photonic networks

NASA Astrophysics Data System (ADS)

The ability to navigate light signals in two-dimensional networks of waveguide arrays is a prerequisite for the development of all-optical integrated circuits for information processing and networking. In this article, we present a theoretical analysis of bending losses in linear photonic lattices with engineered couplings, and discuss possible ways for their minimization. In contrast to previous work in the field, the lattices under consideration operate in the linear regime, in the sense that discrete solitons cannot exist. The present results suggest that the functionality of linear waveguide networks can be extended to operations that go beyond the recently demonstrated point-to-point transfer of signals, such as blocking, routing, logic functions, etc.

Nikolopoulos, G. M.

2015-02-01

265

Zero Potts models coupled to two-dimensional quantum gravity

NASA Astrophysics Data System (ADS)

The critical exponents that have been calculated for the Ising and Potts models coupled to two-dimensional quantum gravity correspond to annealed averages in the language of solid state physics. Using the replica trick and the approach of DDK we calculate the critical exponents for the Ising and q = 3, 4 state Potts models coupled to quenched two-dimensional quantum gravity.

Johnston, D. A.

1992-03-01

266

Two-Dimensionally Isotropic High Index Metamaterials Yushin Kim1

Two-Dimensionally Isotropic High Index Metamaterials Yushin Kim1 , Muhan Choi1,2 , Seung Hoon Lee1 of Korea bmin@kaist.ac.kr Abstract: We fabricated two-dimensionally isotropic high index metamaterials indices in the terahertz frequency range. OCIS codes: (160.3918) Metamaterials; (300.6495) Spectroscopy

Park, Namkyoo

267

Terahertz demonstrations of effectively two-dimensional photonic bandgap structures

Terahertz demonstrations of effectively two- dimensional photonic bandgap structures Yuguang Zhao March 7, 2006 (Doc. ID 67376) We demonstrate effectively two-dimensional (2D) terahertz (THz) photonic of this effectively 2D embodiment. Our observations of the strongly varying, frequency- dependent transmission through

268

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

269

New two-dimensional quantum models with shape invariance

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

270

Microwave tomography: a two-dimensional Newton iterative scheme

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

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

1998-01-01

271

Plastic flow in two-dimensional solids Akira Onuki

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

272

A SAR processor based on two-dimensional FFT codes

A synthetic aperture radar (SAR) processor approach based on two-dimensional fast Fourier transform (FFT) codes coupled with an asymptotic evaluation of the unit response function is presented. For the latter, no approximation is made to the distance function, so that the full range of geometric aberrations is analytically considered, enabling an effective reference filter to be designed. The two-dimensional FFTs

GIORGIO FRANCESCHETTI; GILDA SCHIRINZI

1990-01-01

273

PRESSURE MEASUREMENT IN A TWO DIMENSIONAL UNSTEADY FLOW

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

Patil, Mayuresh

274

Quantum inequalities in two-dimensional Minkowski spacetime

NASA Astrophysics Data System (ADS)

We generalize some results of Ford and Roman constraining the possible behaviors of the renormalized expected stress-energy tensor of a free massless scalar field in two-dimensional Minkowski spacetime. Ford and Roman showed that the energy density measured by an inertial observer, when averaged with respect to the observers proper time by integrating against some weighting function, is bounded below by a negative lower bound proportional to the reciprocal of the square of the averaging time scale. However, the proof required a particular choice for the weighting function. We extend the Ford-Roman result in two ways. (i) We calculate the optimum (maximum possible) lower bound and characterize the state which achieves this lower bound; the optimum lower bound differs by a factor of six from the bound derived by Ford and Roman for their choice of smearing function. (ii) We calculate the lower bound for arbitrary, smooth positive weighting functions. We also derive similar lower bounds on the spatial average of energy density at a fixed moment of time.

Flanagan, Éanna É.

1997-10-01

275

Anisotropic stress correlations in two-dimensional liquids

NASA Astrophysics Data System (ADS)

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

Wu, Bin; Iwashita, Takuya; Egami, Takeshi

2015-03-01

276

Soap film flows: Statistics of two-dimensional turbulence

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

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

1999-08-01

277

Left atrial ball thrombus diagnosed by two-dimensional echocardiography.

The diagnosis of the ball thrombus in the left atrium has been very difficult by conventional clinical techniques. In the present case, two-dimensional echocardiography successfully demonstrated a spherical tumor moving in unpredictable directions in the left atrium. M-mode echocardiography did not clearly identify the tumor because of the limited visual width and spatial orientation of the technique; however, simultaneous recordings of the M-mode echocardiogram with phonocardiogram, carotid pulse wave, and electrocardiogram provided some diagnostic clues to the occlusive left atrial tumor. In the absence mitral valve occlusion by the tumor, a logarithmic correlation between the ejection time and the preceding R-R interval, and a negative lines correlation between Q to the first sound interval and the preceding R-R interval were found. In the beat following the appearance of the tumor in the mitral orifice, the sudden shortening of the ejection time and the prolongation of Q to the first sound interval were noted. Both of these findings are indirect evidence of decreased left ventricular filling associated with an elevated left atrial pressure resulting from the sudden mitral orifice obstruction by the tumor. Detailed analysis of the data obtained by the conventional noninvasive techniques could provide critical clues for the diagnosis of the occlusive left atrial tumor. PMID:7386368

Sunagawa, K; Orita, Y; Tanaka, S; Kikuchi, Y; Nakamura, M; Hirata, T

1980-07-01

278

Numerical observations of two-dimensional compressible convection

The time dependence and spatial structure of convective flows in a two-dimensional atmosphere spanning several density scale heights in the vertical direction is investigated by means of numerical simulation of the anelastic equations. As an approximation to the full magnetohydrodynamic (MHD) equations filtering out sound waves and fast MHD waves, the anelastic equations are derived by an asymptotic expansion procedure valid in the limit of small superadiabatic temperature gradient and inverse plasma beta. Problems of mass continuity are addressed and it is seen that the presence of a higher order velocity field, which might not vanish at the boundaries, is needed to maintain physical consistency. Numerical solutions on a rectangular Cartesian mesh obtained with the finite-difference, predicter-corrector code SOHO are shown, and algorithm details, tests, and consistency checks are discussed. Focusing on a polytropic atmosphere in the limit of zero magnetic field with an aspect ratio of one, a superadiabatic ratio of 4.0 x 10/sup -3/, and a bottom to top density ratio of 22.4, a set of numerical solutions are presented where the viscosity plays the role of the order parameter. In terms of conventional dimensionless parameters, the set of solutions (which includes results from the onset of convection well into the regime where chaos is present) is represented by Prandtl numbers in the range 10.0-0.05 and normalized Rayleigh numbers in the range 2.9-558.

Ginet, G.P.

1987-01-01

279

New two-dimensional ASICs for solid state pixel detectors

NASA Astrophysics Data System (ADS)

We have developed high energy and high spatial resolution two-dimensional (2D) solid-state imaging pixel detectors and their custom integrated circuits (ICs). Solid-state pixel detectors and their readout ICs are now regarded to be an integral part of position-sensitive semiconductor detectors such as Si, CdTe and CdZnTe for x-ray and gamma-ray imaging. These detectors have a 2D structure. We have also developed one-dimensional (1D) detectors, which are mostly used for scanning type imaging. The new 2D pixel detectors we have developed can be used for both scanning and staring mode imaging applications. Because the requirements of various detector applications tend to be diverse, a custom IC is typically designed for a specific detector array. This often lengthens the time and raises the cost of system development. To help close the readout technology gap and facilitate advances in this field, we have been formulating and implementing strategies for instrumenting different detectors of a given application category with highly versatile ICs that meet a range of requirements. The solid-state pixel detectors that have been developed within this effort are presented below.

Tumer, Tumay O.; Cajipe, Victoria B.; Clajus, Martin; Hayakawa, Satoshi; Volkovskii, Alexander

2008-08-01

280

Ion acoustic solitons in Earth's upward current region

The formation and evolution of ion acoustic solitons in Earth's auroral upward current region are studied using one- and two-dimensional (2D) electrostatic particle-in-cell simulations. The one-dimensional simulations are confined to processes that occur in the auroral cavity and include four plasma populations: hot electrons, H{sup +} and O{sup +} anti-earthward ion beams, and a hot H{sup +} background population. Ion acoustic solitons are found to form for auroral-cavity ion beams consistent with acceleration through double-layer (DL) potentials measured by FAST. A simplified one-dimensional model simulation is then presented in order to isolate the mechanisms that lead to the formation of the ion acoustic soliton. Results of a two-dimensional simulation, which include both the ionosphere and the auroral cavity, separated by a low-altitude DL, are then presented in order to confirm that the soliton forms in a more realistic 2D geometry. The 2D simulation is initialized with a U-shaped potential structure that mimics the inferred shape of the low altitude transition region based on observations. In this simulation, a soliton localized perpendicular to the geomagnetic field is observed to form and reside next to the DL. Finally, the 2D simulation results are compared with FAST data and it is found that certain aspects of the data can be explained by assuming the presence of an ion acoustic soliton.

Main, D. S.; Scholz, C. [Department of Physics, John Brown University, Siloam Springs, Arkansas 72761 (United States); Newman, D. L. [Center for Integrated Plasma Studies, University of Colorado, Boulder, Colorado 80309 (United States); Ergun, R. E. [Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder, Colorado 80303 (United States)

2012-07-15

281

NASA Astrophysics Data System (ADS)

Some applied aspects of solitary electromagnetic waves - solitons - are briefly outlined. A modified definition of a soliton is proposed. The recent results of experimental investigations of solitons in radiofrequency lines are presented including the observation of bound states, stochastic ensembles of solitons, 'soliton lattices', etc. Realizations of 'parametric generators of impulses', systems of multivalue logic and communication systems based on solitons are described as well as the use of nonlinear artificial lines for the analog modelling of nonlinear wave equations. The possible parameters of solitons in the submillimeter and optical ranges are discussed for different cases (semiconductor plasma, excitations in solid lattices, optical fibers, liquids, etc.).

Ostrovskii, L. A.; Gorshkov, K. A.; Papko, V. V.

1979-10-01

282

Two dimensional model for coherent synchrotron radiation

NASA Astrophysics Data System (ADS)

Understanding coherent synchrotron radiation (CSR) effects in a bunch compressor requires an accurate model accounting for the realistic beam shape and parameters. We extend the well-known 1D CSR analytic model into two dimensions and develop a simple numerical model based on the Liénard-Wiechert formula for the CSR field of a coasting beam. This CSR numerical model includes the 2D spatial dependence of the field in the bending plane and is accurate for arbitrary beam energy. It also removes the singularity in the space charge field calculation present in a 1D model. Good agreement is obtained with 1D CSR analytic result for free electron laser (FEL) related beam parameters but it can also give a more accurate result for low-energy/large spot size beams and off-axis/transient fields. This 2D CSR model can be used for understanding the limitation of various 1D models and for benchmarking fully electromagnetic multidimensional particle-in-cell simulations for self-consistent CSR modeling.

Huang, Chengkun; Kwan, Thomas J. T.; Carlsten, Bruce E.

2013-01-01

283

Quantum holographic encoding in a two-dimensional electron gas

The advent of bottom-up atomic manipulation heralded a new horizon for attainable information density, as it allowed a bit of information to be represented by a single atom. The discrete spacing between atoms in condensed matter has thus set a rigid limit on the maximum possible information density. While modern technologies are still far from this scale, all theoretical downscaling of devices terminates at this spatial limit. Here, however, we break this barrier with electronic quantum encoding scaled to subatomic densities. We use atomic manipulation to first construct open nanostructures - 'molecular holograms' - which in turn concentrate information into a medium free of lattice constraints: the quantum states of a two-dimensional degenerate Fermi gas of electrons. The information embedded in the holograms is transcoded at even smaller length scales into an atomically uniform area of a copper surface, where it is densely projected into both two spatial degrees of freedom and a third holographic dimension mapped to energy. In analogy to optical volume holography, this requires precise amplitude and phase engineering of electron wavefunctions to assemble pages of information volumetrically. This data is read out by mapping the energy-resolved electron density of states with a scanning tunnelling microscope. As the projection and readout are both extremely near-field, and because we use native quantum states rather than an external beam, we are not limited by lensing or collimation and can create electronically projected objects with features as small as {approx}0.3 nm. These techniques reach unprecedented densities exceeding 20 bits/nm{sup 2} and place tens of bits into a single fermionic state.

Moon, Christopher

2010-05-26

284

Pinned modes in two-dimensional lossy lattices with local gain and nonlinearity.

We introduce a system with one or two amplified nonlinear sites ('hot spots', HSs) embedded into a two-dimensional linear lossy lattice. The system describes an array of evanescently coupled optical or plasmonic waveguides, with gain applied to selected HS cores. The subject of the analysis is discrete solitons pinned to the HSs. The shape of the localized modes is found in quasi-analytical and numerical forms, using a truncated lattice for the analytical consideration. Stability eigenvalues are computed numerically, and the results are supplemented by direct numerical simulations. In the case of self-focusing nonlinearity, the modes pinned to a single HS are stable and unstable when the nonlinearity includes the cubic loss and gain, respectively. If the nonlinearity is self-defocusing, the unsaturated cubic gain acting at the HS supports stable modes in a small parametric area, whereas weak cubic loss gives rise to a bistability of the discrete solitons. Symmetric and antisymmetric modes pinned to a symmetric set of two HSs are also considered. PMID:25246677

Ding, Edwin; Tang, A Y S; Chow, K W; Malomed, Boris A

2014-10-28

285

Building patterns by traveling dipoles and vortices in two-dimensional periodic dissipative media

NASA Astrophysics Data System (ADS)

We analyze pattern-formation scenarios in the two-dimensional (2D) complex Ginzburg-Landau (CGL) equation with the cubic-quintic (CQ) nonlinearity and a cellular potential. The equation models laser cavities with built-in gratings, which stabilize 2D patterns. The pattern-building process is initiated by kicking a compound mode, in the form of a dipole, quadrupole, or vortex which is composed of four local peaks. The hopping motion of the kicked mode through the cellular structure leads to the generation of various extended patterns pinned by the structure. In the ring-shaped system, the persisting freely moving dipole hits the stationary pattern from the opposite side, giving rise to several dynamical regimes, including periodic elastic collisions, i.e., persistent cycles of elastic collisions between the moving and quiescent dissipative solitons, and transient regimes featuring several collisions which end up by absorption of one soliton by the other. Still another noteworthy result is the transformation of a strongly kicked unstable vortex into a stably moving four-peaked cluster.

Besse, V.; Leblond, H.; Mihalache, D.; Malomed, B. A.

2014-12-01

286

Langevin dynamics simulations of a two-dimensional colloidal crystal under confinement and shear

NASA Astrophysics Data System (ADS)

Langevin dynamics simulations are used to study the effect of shear on a two-dimensional colloidal crystal (with implicit solvent) confined by structured parallel walls. When walls are sheared very slowly, only two or three crystalline layers next to the walls move along with them, while the inner layers of the crystal are only slightly tilted. At higher shear velocities, this inner part of the crystal breaks into several pieces with different orientations. The velocity profile across the slit is reminiscent of shear banding in flowing soft materials, where liquid and solid regions coexist; the difference, however, is that in the latter case the solid regions are glassy while here they are crystalline. At even higher shear velocities, the effect of the shearing becomes smaller again. Also the effective temperature near the walls (deduced from the velocity distributions of the particles) decreases again when the wall velocity gets very large. When the walls are placed closer together, thereby introducing an incommensurability between the periodicity of the confined crystal and the walls, a structure containing a soliton staircase arises in simulations without shear. Introducing shear increases the disorder in these systems until no solitons are visible anymore. Instead, similar structures like in the case without mismatch result. At high shear rates, configurations where the incommensurability of the crystalline structure is compensated by the creation of holes become relevant.

Wilms, D.; Virnau, P.; Sengupta, S.; Binder, K.

2012-06-01

287

Stable topological modes in two-dimensional Ginzburg-Landau models with trapping potentials

Complex Ginzburg-Landau (CGL) models of laser media (with cubic-quintic nonlinearity) do not contain an effective diffusion term, which makes all vortex solitons unstable in these models. Recently, it has been demonstrated that the addition of a two-dimensional periodic potential, which may be induced by a transverse grating in the laser cavity, to the CGL equation stabilizes compound (four-peak) vortices, but the most fundamental 'crater-shaped' vortices (CSVs), alias vortex rings, which are essentially squeezed into a single cell of the potential, have not been found before in a stable form. In this work we report on families of stable compact CSVs with vorticity S=1 in the CGL model with the external potential of two different types: an axisymmetric parabolic trap and the periodic potential. In both cases, we identify a stability region for the CSVs and for the fundamental solitons (S=0). Those CSVs which are unstable in the axisymmetric potential break up into robust dipoles. All the vortices with S=2 are unstable, splitting into tripoles. Stability regions for the dipoles and tripoles are identified, too. The periodic potential cannot stabilize CSVs with S{>=}2 either; instead, families of stable compact square-shaped quadrupoles are found.

Mihalache, D.; Mazilu, D. [Horia Hulubei National Institute for Physics and Nuclear Engineering (IFIN-HH), 407 Atomistilor, Magurele-Bucharest, RO-077125 (Romania); Skarka, V.; Leblond, H. [Laboratoire de Photonique d'Angers, EA 4464 Universite d'Angers, 2 Boulevard Lavoisier, F-49045 Angers Cedex 01 (France); Malomed, B. A. [Department of Physical Electronics, Faculty of Engineering, Tel Aviv University, Tel Aviv 69978 (Israel); Aleksic, N. B. [Institute of Physics, Pregrevica 118, 11000 Belgrade (Serbia); Lederer, F. [Institute of Solid State Theory and Theoretical Optics, Friedrich-Schiller Universitaet Jena, Max-Wien-Platz 1, D-077743 Jena (Germany)

2010-08-15

288

Two-dimensional electronic spectroscopy of molecular aggregates.

The properties of molecular aggregates, coupled clusters of small molecules, are often challenging to unravel because of their inherent complexity and disordered environments. Their structure-function relationships are often far from obvious. However, their ability to efficiently channel excitation energy over remarkable distances, as is the case in photosynthetic light harvesting, is a compelling motivation to investigate them. Understanding and subsequently mimicking the processes in photosynthesis, for example, will set the stage for considerable advances in using light harvesting to fuel renewable energy technologies. Two-dimensional (2D) electronic spectroscopy is emerging as a nonlinear optical technique that provides significant insight into the interactions and dynamics of complex molecular systems. In addition to spectrally resolving excitation and emission energies over significant bandwidths with femtosecond resolution, this technique has already enabled discoveries about the structure and dynamics of photosynthetic light-harvesting complexes and other aggregates. Multiple capabilities unique to 2D electronic spectroscopy enable such findings. For example, the spectral resolution of excitation and emission combined with the ability to eliminate the effects of static disorder can reveal the homogeneous line width of a transition and the different dynamic contributions to it. Two dimensional spectroscopy is also sensitive to electronic coherence and has been employed to identify and characterize coherent excitation energy transfer dynamics in photosynthetic systems and conjugated polymers. The presence of cross-peaks, signals for which excitation and emission occur at different wavelengths, provides multiple forms of information. First, it allows the identification of states in congested spectra and reveals correlations between them. Second, we can track excitation energy flow from origin to terminus through multiple channels simultaneously. Finally, 2D electronic spectroscopy is uniquely sensitive to intermolecular electronic coupling through the sign and amplitude of the cross-peaks. This feature makes it possible to reveal spatial molecular configurations by probing electronic transitions. Another means of "resolving" these angstrom-scale arrangements is to manipulate the probing laser pulse polarizations. In this way, we can isolate and modulate specific processes in order to retrieve structural information. In this Account, we demonstrate these capabilities through a close collaboration between experiments and modeling on isolated photosynthetic pigment-protein complexes and also on J-aggregates. Each of the probed systems we describe offers insights that have both increased the utility of 2D electronic spectroscopy and led to discoveries about the molecular aggregates' dynamics and underlying structure. PMID:19691358

Ginsberg, Naomi S; Cheng, Yuan-Chung; Fleming, Graham R

2009-09-15

289

Magnetoconductivity of two-dimensional electron systems

NASA Astrophysics Data System (ADS)

The conductivity sigmaxx(o) of a low-density nondegenerate 2D electron gas is investigated under conditions where hoc ? kBT ? hgamma (oc is the cyclotron frequency and hgamma is the disorder-induced width of the Landau level). Such conditions have been met for electrons on helium surface, and can also be achieved in ultra high quality heterostructures. Because of the random potential of defects, single-electron states of the lowest Landau level form a band of a width hgamma ? hoc. Almost all of these states are localized. Therefore, for ho c ? kBT ? hgamma, the static single-electron conductivity sigma xx(0) may be expected to be equal to zero. Since for o ? gamma the conductivity should decay, on the whole sigma xx(o) has a peak at a finite frequency. From scaling arguments, we show that in the single-electron approximation sigma xx(o) ? omu for o ? 0, with the exponent mu in the range from 0.21 to 0.22, whereas the frequency dependence of the cyclotron resonance absorption peak is non-critical. The far tails of the conductivity peaks are obtained using the method of optimal fluctuation and are shown to be Gaussian. In order to investigate the shape of the low frequency peak and cyclotron resonance absorption peak, we use the method of moments (MOM). In MOM, the low-frequency conductivity is restored from its 14 spectral moments, whereas the cyclotron resonance absorption is restored from the calculated 10 spectral moments using the continuous fraction expansion. In combination with the analytical asymptotics, both expansions converge rapidly with increasing number of included moments, and give numerically accurate results throughout the region of interest. The effect of electron-electron interaction (EEI) on the low frequency conductivity is also investigated. EEI makes the static conductivity finite. For a low-density system, the effect can be described using the notion of a fluctuational field Efl which drives an electron because of electron density fluctuations. Due to this field, spatial diffusion of electrons in a (comparatively strong) random potential of defects gives rise to energy diffusion of each individual electron, with a diffusion coefficient Depsilon = gammae2< E2fl >h/mo c. In combination with the known power-law asymptotic of the single-electron conductivity for sigmase(o) for o ? 0, this allows us to find the static many-electron conductivity sigma me.

Kuehnel, Frank Oliver

290

Matter-wave solitons in nonlinear optical lattices

NASA Astrophysics Data System (ADS)

We introduce a dynamical model of a Bose-Einstein condensate based on the one-dimensional (1D) Gross-Pitaevskii equation (GPE) with a nonlinear optical lattice (NOL), which is represented by the cubic term whose coefficient is periodically modulated in the coordinate. The model describes a situation when the atomic scattering length is spatially modulated, via the optically controlled Feshbach resonance, in an optical lattice created by interference of two laser beams. Relatively narrow solitons supported by the NOL are predicted by means of the variational approximation (VA), and an averaging method is applied to broad solitons. A different feature is a minimum norm (number of atoms), N=Nmin , necessary for the existence of solitons. The VA predicts Nmin very accurately. Numerical results are chiefly presented for the NOL with the zero spatial average value of the nonlinearity coefficient. Solitons with values of the amplitude A larger than at N=Nmin are stable. Unstable solitons with smaller, but not too small, A rearrange themselves into persistent breathers. For still smaller A , the soliton slowly decays into radiation without forming a breather. Broad solitons with very small A are practically stable, as their decay is extremely slow. These broad solitons may freely move across the lattice, featuring quasielastic collisions. Narrow solitons, which are strongly pinned to the NOL, can easily form stable complexes. Finally, the weakly unstable low-amplitude solitons are stabilized if a cubic term with a constant coefficient, corresponding to weak attraction, is included in the GPE.

Sakaguchi, Hidetsugu; Malomed, Boris A.

2005-10-01

291

Soliton matter as a model of dense nuclear matter

We employ the hybrid soliton model of the nucleon consisting of a topological meson field and deeply bound quarks to investigate the behavior of the quarks in soliton matter as a function of density. To organize the calculation, we place the solitons on a spatial lattice. The model suggests the transition of matter from a color insulator to a color conductor above a critical density of a few times normal nuclear density. 9 references, 5 figures.

Glendenning, N.K.

1985-01-01

292

Front tracking and two dimensional Riemann problems: a conference report

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

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

1984-01-01

293

Front tracking and two dimensional Riemann problems: A conference report

NASA Astrophysics Data System (ADS)

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

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

294

Spin and Valley Noise in Two-Dimensional Dirac Materials

NASA Astrophysics Data System (ADS)

We develop a theory for optical Faraday rotation noise in two-dimensional Dirac materials. In contrast to spin noise in conventional semiconductors, we find that the Faraday rotation fluctuations are influenced not only by spins but also the valley degrees of freedom attributed to intervalley scattering processes. We illustrate our theory with two-dimensional transition-metal dichalcogenides and discuss signatures of spin and valley noise in the Faraday noise power spectrum. We propose optical Faraday noise spectroscopy as a technique for probing both spin and valley relaxation dynamics in two-dimensional Dirac materials.

Tse, Wang-Kong; Saxena, A.; Smith, D. L.; Sinitsyn, N. A.

2014-07-01

295

Initial testing of a new, commercially available, thermoluminescent dosimetry system is reported. The radiation detectors consist of two-dimensional arrays of 104 CaF2:Mn dosimeters, deposited on flexible polyimide sheets. The spatial resolution is 3 mm, and the combined thickness of the dosimeters and the substrate is 185 ?m. Exposed sheets are processed by laser heating. This system is compatible with intense,

D. L. Fehl; D. J. Muron; B. R. Sujka; D. W. Vehar; L. J. Lorence; R. L. Westfall; S. C. Jones; J. A. Sweet; P. Braunlich

1994-01-01

296

Initial testing of a new, commercially available, thermoluminescent dosimetry system is reported. The radiation detectors consist of two-dimensional arrays of 10[sup 4] CaF[sub 2]:Mn dosimeters, deposited on flexible polyimide sheets. The spatial resolution is 3 mm, and the combined thickness of the dosimeters and the substrate is 185 [mu]m. Exposed sheets are processed by laser heating. This system is compatible

D. L. Fehl; D. J. Muron; B. R. Sujka; D. W. Vehar; L. J. Lorence Jr.; R. L. Westfall; S. C. Jones; J. A. Sweet; P. Braunlich

1994-01-01

297

Off-diagonal long-range order in a harmonically confined two-dimensional Bose gas

We investigate the presence of off-diagonal long-range order in a harmonically confined two-dimensional Bose gas. In the noninteracting case, an analytical calculation of the the finite-temperature one-particle density martix provides an exact description of the spatial correlations known to be associated with the existence of a Bose-Einstein condensate below the transition temperature $T^{(0)}_c$. We treat the effects of repulsive interactions

Brandon P. van Zyl

2002-01-01

298

Off-Diagonal Long-Range Order in a Harmonically Confined Two-Dimensional Bose Gas

We investigate the presence of off-diagonal long-range order in a harmonically confined two-dimensional Bose gas. In the noninteracting case, an analytical calculation of the the finite-temperature one-particle density matrix provides an exact description of the spatial correlations known to be associated with the existence of a Bose–Einstein condensate below the transition temperature T(0)c. We treat the effects of repulsive interactions

B. P. van Zyl

2003-01-01

299

Two-dimensional modelling of stream channel dynamics in the Naches River, Washington

The detailed, spatially explicit mapping of fluvial landscapes is fundamental to river science. However, data models capable of incorporating system variability are largely lacking from scientific literature. This research examines a reach of the Naches River, a wandering gravel-bed river located in central Washington State. Stream gauge records are used to calculate flow probabilities, and River2D, a two-dimensional hydrodynamic model,

Luke Swan; Graeme Aggett

2011-01-01

300

NASA Astrophysics Data System (ADS)

We use a three-dimensional self-consistent field model to study copolymer adsorption from polymer melts onto chemically heterogeneous substrates. We show that in situations where the copolymer sequence distribution is commensurate with the spatial distribution of the substrate chemical impurities, the two-dimensional substrate pattern gets transcribed into three dimensions and propagates into the polymer mixture. This transference scheme can assist in designing nanostructures that find use in various areas of science and technology.

Genzer, Jan

2001-02-01

301

Local Electron Correlations in a Two-Dimensional Hubbard Model on the Penrose Lattice

NASA Astrophysics Data System (ADS)

We study electron correlations in the half-filled Hubbard model on a two-dimensional Penrose lattice. Applying real-space dynamical mean-field theory to large clusters, we discuss how low-temperature properties are affected by a quasiperiodic structure. By calculating the double occupancy and renormalization factor at each site, we clarify the existence of the Mott transition. The spatially dependent renormalization characteristic of a geometrical structure is also addressed.

Takemori, Nayuta; Koga, Akihisa

2015-02-01

302

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

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

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

2014-10-01

303

Higher order corrections to dust-acoustic ZK-solitons in a magnetized quantum dusty plasma

NASA Astrophysics Data System (ADS)

Nonlinear propagation of two dimensional dust-acoustic solitary waves in a magnetized quantum dusty plasma whose constituents are electrons, ions, and negatively charged heavy dust particles are investigated using quantum hydrodynamic model. The Zakharov-Kuznetsov (ZK) equation is derived by using reductive perturbation technique (RPT). The higher order inhomogeneous ZK-type differential equation is obtained for the correction to ZK- soliton. The dynamical equation for dressed soliton is solved by using renormalization method. The effects of obliqueness ( l x ) of the wave vector, magnetic field strength ( B 0), quantum parameter for ions ( H i ), soliton velocity ( ?) and Fermi temperature ratio ( ?) on amplitudes and widths of the ZK-soliton and as well as of the dressed soliton are investigated. The conditions for the validity of the higher order correction are described. Suitable parameter ranges for the existence of compressive and rarefactive dressed solitons are also discussed.

Ghorui, Malay Kumar; Mondal, Ganesh; Chatterjee, Prasanta

2013-07-01

304

Optical properties of two-dimensional transition metal dichalcogenides

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

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

2014-01-01

305

A two-dimensional Wigner crystal (Review Article)

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

306

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

307

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

308

Near-Surface Geophysics: Two-Dimensional Resistivity

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

309

Single particle spectrum of the two dimensional electron gas

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

Dial, Oliver Eugene, III

2007-01-01

310

Information technologies for comprehensive two-dimensional gas chromatography

there are generally available information technologies that meet requirements for routine applications. This paperReview Information technologies for comprehensive two-dimensional gas chromatography Stephen E GC) presents information technology challenges in data handling, visualization, processing, analysis

Reichenbach, Stephen E.

311

Healing of defects in a two-dimensional granular crystal

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

Rice, Marie C

2014-01-01

312

Performance Analysis of Metamaterials With Two-dimensional Isotropy

A two-dimensional isotropic metamaterials formed by crossed split-ring resonators (CSRRs) are studied in this paper. The effective characteristic parameters of this media are determined by quasi-static Lorentz theory. The ...

Yao, Hai-Ying

313

CHARACTERISTICS OF TWO-DIMENSIONAL PARTICLE EDDY DIFFUSION INOFFICE SPACE

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...

314

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

ERIC Educational Resources Information Center

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

Edge, R. D.

1989-01-01

315

Two-Dimensional Sensor Integration Using Resonant Proximity Connector

to be useful for inputting users' intention to a machine as well as conventional electromyography. Keywords- Two-Dimensional Communication, Networked Sensing, Man-Machine Interface, Electromyography (EMG). I

Shinoda, Hiroyuki

316

The Discontinuous Galerkin Method for Two-dimensional Hyperbolic Problems

The Discontinuous Galerkin Method for Two-dimensional Hyperbolic Problems Part II: A posteriori mesh refinement for smooth and discontinuous solutions. Keywords: Discontinuous Galerkin method. They also developed the Local Discontinuous Galerkin (LDG) method for convection-diffusion problems [13

Adjerid, Slimane

317

Dynamics of quasi-two-dimensional turbulent jets

and momentum flux of the flow induced by quasi-two-dimensional jets. 174 7.1 Experimental apparatus to study quasi-two-dimensional particle- laden jets (Q2DPL jets). . . . . . . . . . . . . . . . . . . . . . . . 182 7.2 Regime diagram. Three phenomenological... regimes are observed during the Q2DPL jet experiment. . . . . . . . . . . . . . . . . . 183 7.3 Illustration of the fluidization regime. . . . . . . . . . . . . . . . . 185 7.4 Illustration of the oscillatory flow regime. . . . . . . . . . . . . . . 186 7...

Landel, Julien Rémy Dominique Gérard

2012-11-13

318

Two-dimensional topological insulators in quantizing magnetic fields

Two-dimensional topological insulators are characterized by gapped bulk states and gapless helical edge states, i.e. time-reversal symmetric edge states accommodating a pair of counter-propagating electrons. An external magnetic field breaks the time-reversal symmetry. What happens to the edge states in this case? In this paper we analyze the edge-state spectrum and longitudinal conductance in a two-dimensional topological insulator subject to

G. Tkachov; E. M. Hankiewicz

2011-01-01

319

Two-dimensional thermomechanical analysis of continuous casting process

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

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

2004-01-01

320

Ground ring of two-dimensional string theory

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

321

Two-dimensional QCD as a string theory

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

322

Two-dimensional density and density fluctuation diagnostic for the edge plasma in fusion devices

A technique is described for the two-dimensional measurement of electron density profile and fluctuations in edge regions of magnetically confined fusion plasmas. The method is based on existing lithium beam beam emission spectroscopy technique, two-dimensional resolution is achieved by electrostatically scanning the beam. If scanning is performed faster than the lifetime of the turbulent structures in the plasma, the diagnostic is capable of measuring the structure of electron density fluctuations as well. The beam strength of currently available beams makes the detection of single fluctuation events impossible, but the full two-dimensional spatial structure of correlations can still be determined. The article describes the technique and fast beam deflection tests up to 250 kHz. The capabilities of such a diagnostic for fluctuation measurement are explored by simulating measurement signals. Measurement of both the two-dimensional density profile, fluctuation correlation function and poloidal flow velocity are demonstrated at the Wendelstein 7-AS stellarator. The shape of the density profile, the radial and poloidal correlation lengths and the flow velocity are in agreement with expectations and previous Langmuir probe measurement.

Zoletnik, S.; Petravich, G.; Bencze, A.; Berta, M.; Fiedler, S.; McCormick, K.; Schweinzer, J. [KFKI-Research Institute for Particle and Nuclear Physics, P.O.B. 49, H-1525 Budapest (Hungary); Budapest University of Technology and Economics, Institute of Nuclear Techniques 1111 Budapest, Megyetem rkp. 9 and Szechenyi Istvan University, Department of Physics 9026 Gyor, Egyetem ter 1 (Hungary); Max-Planck Institut fuer Plasmaphysik, Association Euratom, Boltzmannstr. 2, D-85748 Garching (Germany)

2005-07-15

323

Real time computerization of two-dimensional echocardiography.

A computerized system was developed for real time acquisition, enhanced processing, analysis, and display of cross-sectional images of the left ventricle derived by two-dimensional echocardiography (2DE). The new methodology couples a standard medical imaging computer system to the video output of any current 2DE unit, uses a 128 x 128 or 64 x 64 matrix window and stores the real time 30 frames/sec digitized images on a magnetic disk. Computerized beat-to-beat and frame-by-frame processing employs space-time smoothing the automatic detection of endocardial interfaces by standard threshold and second derivative techniques. Multiple views are displayed in real time with 256 levels of gray and color. The methodology was used to analyze and graphically display frame-by-frame changes throughout the cardiac cycle. In addition, regional wall motion and thickness were analyzed in 12 sectors of individual cross-sections using a standardized angular subdivision originating at the center of area and indexed by an external reference point. An algorithm was developed to correct cross-sectional interference definition from the commonly used trailing-to-leading edge to the more valid leading-to-leading outline technique. Computerized analysis of spatial and temporal variations of cardiac contraction were demonstrated in several clinical and experimental applications, including bicycle exercise testing, investigation of acute myocardial infarction, and assessment of interventions. Initial evaluation indicates that the new real time computerized digital acquisition and data analysis represents a major advances toward quantitation of left ventricular function using 2DE. PMID:7234656

Garcia, E; Gueret, P; Bennett, M; Corday, E; Zwehl, W; Meerbaum, S; Corday, S; Swan, H J; Berman, D

1981-06-01

324

Two-dimensional aperture coding for magnetic sector mass spectrometry.

In mass spectrometer design, there has been a historic belief that there exists a fundamental trade-off between instrument size, throughput, and resolution. When miniaturizing a traditional system, performance loss in either resolution or throughput would be expected. However, in optical spectroscopy, both one-dimensional (1D) and two-dimensional (2D) aperture coding have been used for many years to break a similar trade-off. To provide a viable path to miniaturization for harsh environment field applications, we are investigating similar concepts in sector mass spectrometry. Recently, we demonstrated the viability of 1D aperture coding and here we provide a first investigation of 2D coding. In coded optical spectroscopy, 2D coding is preferred because of increased measurement diversity for improved conditioning and robustness of the result. To investigate its viability in mass spectrometry, analytes of argon, acetone, and ethanol were detected using a custom 90-degree magnetic sector mass spectrometer incorporating 2D coded apertures. We developed a mathematical forward model and reconstruction algorithm to successfully reconstruct the mass spectra from the 2D spatially coded ion positions. This 2D coding enabled a 3.5× throughput increase with minimal decrease in resolution. Several challenges were overcome in the mass spectrometer design to enable this coding, including the need for large uniform ion flux, a wide gap magnetic sector that maintains field uniformity, and a high resolution 2D detection system for ion imaging. Furthermore, micro-fabricated 2D coded apertures incorporating support structures were developed to provide a viable design that allowed ion transmission through the open elements of the code. PMID:25510933

Russell, Zachary E; Chen, Evan X; Amsden, Jason J; Wolter, Scott D; Danell, Ryan M; Parker, Charles B; Stoner, Brian R; Gehm, Michael E; Brady, David J; Glass, Jeffrey T

2015-02-01

325

Two-Dimensional Aperture Coding for Magnetic Sector Mass Spectrometry

NASA Astrophysics Data System (ADS)

In mass spectrometer design, there has been a historic belief that there exists a fundamental trade-off between instrument size, throughput, and resolution. When miniaturizing a traditional system, performance loss in either resolution or throughput would be expected. However, in optical spectroscopy, both one-dimensional (1D) and two-dimensional (2D) aperture coding have been used for many years to break a similar trade-off. To provide a viable path to miniaturization for harsh environment field applications, we are investigating similar concepts in sector mass spectrometry. Recently, we demonstrated the viability of 1D aperture coding and here we provide a first investigation of 2D coding. In coded optical spectroscopy, 2D coding is preferred because of increased measurement diversity for improved conditioning and robustness of the result. To investigate its viability in mass spectrometry, analytes of argon, acetone, and ethanol were detected using a custom 90-degree magnetic sector mass spectrometer incorporating 2D coded apertures. We developed a mathematical forward model and reconstruction algorithm to successfully reconstruct the mass spectra from the 2D spatially coded ion positions. This 2D coding enabled a 3.5× throughput increase with minimal decrease in resolution. Several challenges were overcome in the mass spectrometer design to enable this coding, including the need for large uniform ion flux, a wide gap magnetic sector that maintains field uniformity, and a high resolution 2D detection system for ion imaging. Furthermore, micro-fabricated 2D coded apertures incorporating support structures were developed to provide a viable design that allowed ion transmission through the open elements of the code.

Russell, Zachary E.; Chen, Evan X.; Amsden, Jason J.; Wolter, Scott D.; Danell, Ryan M.; Parker, Charles B.; Stoner, Brian R.; Gehm, Michael E.; Brady, David J.; Glass, Jeffrey T.

2015-02-01

326

While a two-dimensional electrophoresis (2-DE) database is a relatively old concept, in recent years it generated renewed interest within the 2-DE community due to two main factors: (i) The high reproducibility of the current 2-DE method allows 2-DE images to be exchanged and compared between laboratories. (ii) The recent development of faster and more powerful techniques for protein identification such as microsequencing, matrix-assisted laser desorption ionization-mass spectrometry (MALDI-MS) and amino acid composition makes the production of reference protein maps and 2-DE databases cost- and time-effective. Additionally, the Internet network's current increase in popularity, combined with the rapid growth of Internet-connected laboratories, provides a straightforward means of publishing and sharing 2-DE data. While a small number of laboratories have already successfully published their data over the net, the increasing number of 2-DE database servers that are currently being set up will sooner or later require some kind of standardization. Unfortunately, standardization can be a long and cumbersome process inevitably leading to undesirable compromises. A federated database offers a simple and efficient way to publish and share 2-DE data without the need for standardization. Taking advantage of Internet protocols such as World Wide Web, they allow each laboratory to maintain their own database and to interconnect it with other similar databases through the use of active cross-references. This paper first presents guidelines for building a federated 2-DE database that may easily be followed by most laboratories. It then briefly reviews the state-of-the-art in networked 2-DE databases, and finally describes the SWISS-2DPAGE database which fully implements the concept of a federated 2-DE database. PMID:8740178

Appel, R D; Bairoch, A; Sanchez, J C; Vargas, J R; Golaz, O; Pasquali, C; Hochstrasser, D F

1996-03-01

327

NASA Astrophysics Data System (ADS)

It is shown that optical solitons in nonlinear fibre-optic communication systems and soliton lasers can be represented as nonlinear Bloch waves in periodic structures. The Bloch theorem is proved for solitons of the nonlinear Schrodinger equation in systems with the dispersion, the nonlinearity, and the gain (absorption coefficient) periodically changing over the length. The dynamics of formation and interaction, as well as stability of the coupled states of nonlinear Bloch waves are investigated. It is shown that soliton Bloch waves exist only under certain self-matching conditions for the basic parameters of the system and reveal a structural instability with respect to the mismatch between the periods of spatial modulation of the dispersion, nonlinearity or gain.

Serkin, Vladimir N.; Belyaeva, T. L.

2001-11-01

328

Cavity-soliton laser with frequency-selective feedback

We present a coupled-cavity model of a laser with frequency-selective feedback, and use it to analyze and explain the existence of stationary and dynamic spatial solitons in the device. Particular features of soliton addressing in this system are discussed. We demonstrate the advantages of our model with respect to the common Lang-Kobayashi approximation.

Scroggie, A. J.; Firth, W. J.; Oppo, G.-L. [Department of Physics, University of Strathclyde, 107 Rottenrow, Glasgow G4 ONG, Scotland (United Kingdom)

2009-07-15

329

Solitons, vortices, and guided waves in plasmonic metamaterials

The history of optical solitons is fascinating and any theory of these has a weakly guiding foundation. Vortex generation and propagation properties have also a beautiful history, and the possibility of generating them together with magnetooptic control in plasmonic metamaterials will be discussed in detail. An emphasis will be placed on the fact that spatial solitons have a lot of

A. D. Boardman; P. Egan; R. C. Mitchell-Thomas; Y. G. Rapoport

2010-01-01

330

Finite Differences and Collocation Methods for the Solution of the Two Dimensional Heat Equation

NASA Technical Reports Server (NTRS)

In this paper we combine finite difference approximations (for spatial derivatives) and collocation techniques (for the time component) to numerically solve the two dimensional heat equation. We employ respectively a second-order and a fourth-order schemes for the spatial derivatives and the discretization method gives rise to a linear system of equations. We show that the matrix of the system is non-singular. Numerical experiments carried out on serial computers, show the unconditional stability of the proposed method and the high accuracy achieved by the fourth-order scheme.

Kouatchou, Jules

1999-01-01

331

We use spatial light modulators (SLMs) to measure correlations between arbitrary superpositions of orbital angular momentum (OAM) states generated by spontaneous parametric down-conversion. Our technique allows us to fully access a two-dimensional OAM subspace described by a Bloch sphere, within the higher-dimensional OAM Hilbert space. We quantify the entanglement through violations of a Bell-type inequality for pairs of modal superpositions that lie on equatorial, polar, and arbitrary great circles of the Bloch sphere. Our work shows that SLMs can be used to measure arbitrary spatial states with a fidelity sufficient for appropriate quantum information processing systems.

Jack, B.; Leach, J.; Franke-Arnold, S.; Ireland, D. G.; Padgett, M. J. [Department of Physics and Astronomy, Scottish Universities Physics Alliance, University of Glasgow, Glasgow G12 8QQ (United Kingdom); Yao, A. M.; Barnett, S. M. [Department of Physics, Scottish Universities Physics Alliance, University of Strathclyde, Glasgow G4 0NG (United Kingdom); Romero, J. [Department of Physics and Astronomy, Scottish Universities Physics Alliance, University of Glasgow, Glasgow G12 8QQ (United Kingdom); Department of Physics, Scottish Universities Physics Alliance, University of Strathclyde, Glasgow G4 0NG (United Kingdom)

2010-04-15

332

Engineering optical soliton bistability in colloidal media

NASA Astrophysics Data System (ADS)

We consider a mixture consisting of two species of spherical nanoparticles dispersed in a liquid medium. We show that with an appropriate choice of refractive indices and particle diameters, it is possible to observe the phenomenon of optical soliton bistability in two spatial dimensions in a broad beam power range. Previously, this possibility was ruled out in the case of a single-species colloid. As a particular example, we consider the system of hydrophilic silica particles and gas bubbles generated in the process of electrolysis in water. The interaction of two soliton beams can lead to switching of the lower branch solitons to the upper branch, and the interaction of solitons from different branches is phase independent and always repulsive.

Matuszewski, Micha?

2010-01-01

333

Magnetic dissipative droplets are localized, strongly nonlinear dynamical modes excited in nanocontact spin valves with perpendicular magnetic anisotropy. These modes find potential application in nanoscale structures for magnetic storage and computation, but dissipative droplet studies have so far been limited to extended thin films. Here, numerical and asymptotic analyses are used to demonstrate the existence and properties of novel solitons in confined structures. As a nanowire's width is decreased with a nanocontact of fixed size at its center, the observed modes undergo transitions from a fully localized two-dimensional droplet into a two-dimensional droplet edge mode and then a pulsating one-dimensional droplet. These solitons are interpreted as dissipative versions of classical, conservative solitons, allowing for an analytical description of the modes and the mechanisms of bifurcation. The presented results open up new possibilities for the study of low-dimensional solitons and droplet applications in nanostructures. PMID:24580485

Iacocca, Ezio; Dumas, Randy K; Bookman, Lake; Mohseni, Majid; Chung, Sunjae; Hoefer, Mark A; Akerman, Johan

2014-01-31

334

NASA Technical Reports Server (NTRS)

The theory of Lee and Pang (1987), who obtained solutions for soliton stars composed of zero-temperature fermions and bosons, is applied here to quark soliton stars. Model soliton stars based on a simple physical model of the proton are computed, and the properties of the solitons are discussed, including the important problem of the existence of a limiting mass and thus the possible formation of black holes of primordial origin. It is shown that there is a definite mass limit for ponderable soliton stars, so that during cooling a soliton star might reach a stage beyond which no equilibrium configuration exists and the soliton star probably will collapse to become a black hole. The radiation of ponderable soliton stars may alter the short-wavelength character of the cosmic background radiation, and may be observed as highly redshifted objects at z of about 100,000.

Chiu, Hong-Yee

1990-01-01

335

We report on the experimental observation of stable dark solitons in an all normal dispersion fiber laser. We found experimentally that dark soliton formation is a generic feature of the fiber laser under strong continuous wave (CW) emission. However, only under appropriate pump strength and negative cavity feedback, stable single or multiple dark soliton could be achieved. Furthermore, we show that the features of the observed dark solitons could be well understood based on the nonlinear Schrodinger equation (NLSE).

H. Zhang; D. Y. Tang; L. M. Zhao; X. Wu; Q. L. Bao; K. P. Loh

2009-05-08

336

Three dimensional Auger elemental distributions have been constructed from the combination of high spatial resolution, two dimensional Auger maps obtained at multiple sputter depths. These three dimensional elemental distributions have been used to compare the interfacial regions for two kinds of silicon on insulator wafers. It is clearly seen that silicon oxide is formed as an island structure for the SIMOX specimen, whereas the UNIBOND specimen has a featureless structure at the Si/SiO{sub 2} interface. Linear least squares fitting from several two dimensional maps obtained at different energies have been used to produce energy dispersive spectra from specific regions of high spatial resolution Auger maps. This technique was used to examine the interface region exposed from sputter craters through a silicon dioxide layer on a silicon substrate and through a Ni silicide film on a silicon substrate. The Si LVV spectra for the elemental silicon, oxide, and silicide components extracted from the multiple energy two dimensional maps can be used to map the chemical components in the interfacial regions.

Urushihara, N.; Iida, S.; Sanada, N.; Suzuki, M.; Paul, D. F.; Bryan, S.; Nakajima, Y.; Hanajiri, T.; Kakushima, K.; Ahmet, P.; Tsutsui, K.; Iwai, H. [ULVAC-PHI, Inc., 370 Enzo, Chigasaki, Kanagawa 253-8522 (Japan); Physical Electronics, Inc., 18725 Lake Drive East, Chanhassen, Minnesota 55317 (United States); Bio-Nano Electronics Research Center, Toyo University, 2100 Kujirai Kawagoe, Saitama 350-8585 (Japan); Department of Electronics and Applied Physics, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama, Kanagawa 225-8502 (Japan)

2008-07-15

337

Soliton Interaction of the Zakharov-Kuznetsov Equations in Plasma Dynamics

NASA Astrophysics Data System (ADS)

In this paper we investigate the constant- and variable-coefficient Zakharov-Kuznetsov (ZK) equations respectively for the electrostatic solitons and two-dimensional ion-acoustic waves obliquely propagating in the inhomogeneous magnetized two-ion-temperature dusty plasmas. By virtue of the symbolic computation and Hirota method, new bilinear forms and N-soliton solutions are both derived. Asymptotic analysis on two-soliton solutions indicates that the soliton interaction is elastic. Propagation characteristics and interaction behavior of the solitons are discussed via graphical analysis. Effects of the dispersive and disturbed coefficients are analyzed. For the constant-coefficient ZK equation, amplitude of the one soliton becomes larger when the absolute value of dispersive coefficient B increases, while interaction between the two solitons varies with the product of B and disturbed coefficient C: when BC>0, two solitons are always parallel, or they interact with each other that way. For the variable-coefficient ZK equation, periodical soliton arises when the disturbed coefficient ?(t) is a periodical function, and periods of the solitons are inversely correlated to the period of ?(t).

Zhen, Hui-Ling; Tian, Bo; Wang, Pan; Liu, Rong-Xiang; Zhong, Hui

2013-04-01

338

These lectures cover aspects of solitons with focus on applications to the quantum dynamics of supersymmetric gauge theories and string theory. The lectures consist of four sections, each dealing with a different soliton. We start with instantons and work down in co-dimension to monopoles, vortices and, eventually, domain walls. Emphasis is placed on the moduli space of solitons and, in

David Tong

2005-01-01

339

Many-body effects of a two-dimensional electron gas on trion-polaritons

NASA Astrophysics Data System (ADS)

We theoretically investigate the trion-polariton and the effects of a two-dimensional electron gas on its single-particle properties. Focusing on the trion and exciton transitions, we set up an effective model and calculate the optical absorption of the quantum well containing the two-dimensional electron gas (2DEG). Including the light-matter coupling, we compute the Rabi splitting and polariton line shapes as a function of 2DEG density. The role of finite temperature is investigated. The spatial extent of the trion-polariton is also calculated. We find a substantial charge buildup at short distances as long as the Rabi frequency does not exceed the trion binding energy. All our calculations take into account the Fermi edge singularity and the Anderson orthogonality catastrophe.

Baeten, Maarten; Wouters, Michiel

2015-03-01

340

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

The two-dimensional vector plane wave spectrum (VPWS) is scattered from parallel circular cylinders using a boundary value solution with the T-matrix formalism. The VPWS allows us to define the incident, two-dimensional electromagnetic field with an arbitrary distribution and polarization, including both radiative and evanescent components. Using the fast Fourier transform, we can quickly compute the multiple scattering of fields that have any particular functional or numerical form. We perform numerical simulations to investigate a grating of cylinders that is capable of converting an evanescent field into a set of propagating beams. The direction of propagation of each beam is directly related to a spatial frequency component of the incident evanescent field. PMID:21643402

Pawliuk, Peter; Yedlin, Matthew

2011-06-01

341

NASA Astrophysics Data System (ADS)

A laboratory instrument that utilizes broadband laser ultrasonics and two-dimensional Fourier transformation for signal processing has been developed to characterize the properties of various foils and plates. Laser ultrasonics generation is achieved by using a pulsed laser which deposits pulsed laser energy on the surface of the specimen. The displacement of the resulting broadband ultrasonic modes is monitored using a two-wave mixing photorefractive interferometer. By means of the two-dimensional Fourier transformation of the detected spatial and temporal displacement wave forms, the image of density of state (DOS) for the excited ultrasound is obtained, and from it the materials properties are extracted. Results are presented for a 150?m thick paper sample, a 50?m stainless steel foil, and a 1.27mm thick aluminum plate. The DOS image demonstrates the ability to measure the properties of each generated ultrasonic modes and provides a direct, nondestructive, measure of elastic moduli of the tested specimens.

Zhang, Xinya; Jackson, Ted; Lafond, Emmanuel

2005-02-01

342

Two-Dimensional Hybrid Model for High-Current Electron Beam Transport in a Dense Plasma

NASA Astrophysics Data System (ADS)

A two-dimensional hybrid code is developed to model the transport of a high-current electron beam in a dense plasma target. The beam electrons are treated as particles and described by particle-in-cell simulation including collisions with the target plasma particles. The background target plasma is assumed to be a stationary fluid with temperature variations. The return current and the self-generated electric and magnetic fields are obtained by combining Ampère's law without the displacement current, the resistive Ohm's law and Faraday's law. The equations are solved in two-dimensional cylindrical geometry with rotational symmetry on a regular grid, with centered spatial differencing and first-order implicit time differencing. The algorithms implemented in the code are described, and a numerical experiment is performed for an electron beam with Maxwellian distribution ejected into a uniform deuterium-tritium plasma target.

Cao, Lihua; Wang, Huan; Zhang, Hua; Liu, Zhanjun; Wu, Junfeng; Li, Baiwen

2014-11-01

343

Phase correlations and quasicondensate in a two-dimensional ultracold Fermi gas

NASA Astrophysics Data System (ADS)

The interplay between dimensionality, coherence and interaction in superfluid Fermi gases is analyzed by the phase correlation function of the field of fermionic pairs. We calculate this phase correlation function for a two-dimensional superfluid Fermi gas with s-wave interactions within the Gaussian pair fluctuation formalism. The spatial behavior of the correlation function is shown to exhibit a rapid (exponential) decay at short distances and a characteristic algebraic decay at large distances, with an exponent matching that expected from the Berezinskii-Kosterlitz-Thouless theory of 2D Bose superfluids. We conclude that the Gaussian pair fluctuation approximation is able to capture the physics of quasi-long-range order in two-dimensional Fermi gases.

Tempere, J.; Klimin, S. N.

2015-02-01

344

The ion acoustic soliton in weakly a relativistic electron-positron-ion plasma with finite ion temperature have been investigated. Such plasmas is frequently occur in astrophysical environment. Using reductive perturbation method we have derived the two dimensional Kadomtsev- Petviashvili(KP) equation to study the characteristics of ion-acoustic soliton in three component plasma at different plasma temperature. The soliton solution of KP equation is

Amandeep Singh Bains; Harvinder Kaur; Tarsem Singh Gill; Nareshpal Singh Saini

2008-01-01

345

Surface solitons in left-handed metamaterials

A theory of self-induced transparency of surface TM-mode propagating along a interface separating conventional and left-handed metamaterials is developed. A transition layer sandwiched between connected media is described using a model of a two-dimensional gas of quantum dots. Explicit analytical expressions for a surface optical soliton in the presence of single and biexciton transitions, depending on the magnetic permeability of the left-handed medium, are obtained with realistic parameters which can be reached in current experiments. It is shown that the sign of the total energy flow the surface mode depends on the material parameters of the quantum dots and the connected media.

G. T. Adamashvili; A. Knorr

2007-09-08

346

Two-dimensional convolute integers for analytical instrumentation

NASA Technical Reports Server (NTRS)

As new analytical instruments and techniques emerge with increased dimensionality, a corresponding need is seen for data processing logic which can appropriately address the data. Two-dimensional measurements reveal enhanced unknown mixture analysis capability as a result of the greater spectral information content over two one-dimensional methods taken separately. It is noted that two-dimensional convolute integers are merely an extension of the work by Savitzky and Golay (1964). It is shown that these low-pass, high-pass and band-pass digital filters are truly two-dimensional and that they can be applied in a manner identical with their one-dimensional counterpart, that is, a weighted nearest-neighbor, moving average with zero phase shifting, convoluted integer (universal number) weighting coefficients.

Edwards, T. R.

1982-01-01

347

Noninteraction of waves in two-dimensional conformal field theory

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

Yoh Tanimoto

2012-08-17

348

Rarefied gas flow through two-dimensional nozzles

NASA Technical Reports Server (NTRS)

A kinetic theory analysis is made of the flow of a rarefied gas from one reservoir to another through two-dimensional nozzles with arbitrary curvature. The Boltzmann equation simplified by a model collision integral is solved by means of finite-difference approximations with the discrete ordinate method. The physical space is transformed by a general grid generation technique and the velocity space is transformed to a polar coordinate system. A numerical code is developed which can be applied to any two-dimensional passage of complicated geometry for the flow regimes from free-molecular to slip. Numerical values of flow quantities can be calculated for the entire physical space including both inside the nozzle and in the outside plume. Predictions are made for the case of parallel slots and compared with existing literature data. Also, results for the cases of convergent or divergent slots and two-dimensional nozzles with arbitrary curvature at arbitrary knudsen number are presented.

De Witt, Kenneth J.; Jeng, Duen-Ren; Keith, Theo G., Jr.; Chung, Chan-Hong

1989-01-01

349

Complexity and efficient approximability of two dimensional periodically specified problems

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

350

Generation of two-dimensional plasmonic bottle beams.

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

351

Bifurcation Phenomena in Two-Dimensional Piecewise Smooth Discontinuous Maps

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, many switching dynamical systems have been found to yield two-dimensional piecewise smooth maps that are discontinuous across the border. The theory for understanding the bifurcation phenomena in such systems is not available yet. In this paper we present the first approach to the problem of analysing and classifying the bifurcation phenomena in two-dimensional discontinuous maps, based on a piecewise linear approximation in the neighborhood of the border. We explain the bifurcations occurring in the static VAR compensator used in electrical power systems, using the theory developed in this paper. This theory may be applied similarly to other systems that yield two-dimensional discontinuous maps.

Biswambhar Rakshit; Manjul Apratim; Parag Jain; Soumitro Banerjee

2008-09-18

352

Hamiltonian formalism of two-dimensional Vlasov kinetic equation.

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

Pavlov, Maxim V

2014-12-01

353

Generation of two-dimensional plasmonic bottle beams

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

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

2013-01-01

354

Full-field two-dimensional least-squares method for phase-shifting interferometry

NASA Astrophysics Data System (ADS)

The most known and used phase shifting interferometry (PSI) demodulation methods are one-dimensional temporal linear systems. These methods use the information of the interferogram sequence at a single pixel to recover the modulating phase. Accordingly, scanning all pixels, we obtain the two-dimensional (2-D) modulated phase sought. As PSI demodulation methods do not take into account spatial information, these methods cannot remove unwanted harmonics or noise from the interferogram image space (spatial domain). To remove these unwanted artifacts from the image space, spatial information must be included in the demodulation model. We are going to show that the well-known least-squares system for PSI can be used as a full-field 2-D linear system that uses the temporal and spatial information in conjunction in order to recover the modulating phase while removing noise, unwanted harmonics, and interpolating small empty sections of the image space all in the same process with a low computational time.

Medina, Orlando; Estrada, Julio C.

2014-11-01

355

Supersolitons: Solitonic Excitations in Atomic Soliton Chains

We show that, by tuning interactions in nonintegrable vector nonlinear Schroedinger equations modeling Bose-Einstein condensates and other relevant physical systems, it is possible to achieve a regime of elastic particlelike collisions between solitons. This would allow one to construct a Newton's cradle with solitons and supersolitons: localized collective excitations in solitary-wave chains.

Novoa, David; Michinel, Humberto [Area de Optica, Facultade de Ciencias, Universidade de Vigo, As Lagoas s/n, Ourense, E-32004 Spain (Spain); Malomed, Boris A. [Department of Physical Electronics, School of Electrical Engineering, Faculty of Engineering, Tel Aviv University, Tel Aviv 69978 (Israel); Perez-Garcia, Victor M. [Departamento de Matematicas, E.T.S.I. Industriales, and Instituto de Matematica Aplicada a la Ciencia y la Ingenieria, Universidad de Castilla-La Mancha, Avenida Camilo Jose Cela, 3, 13071 Ciudad Real (Spain)

2008-10-03

356

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

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

Si, Lin

2015-01-01

357

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

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

2015-01-01

358

Quantum Walks on Two Kinds of Two-Dimensional Models

NASA Astrophysics Data System (ADS)

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

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

2015-01-01

359

TreePM Method for Two-Dimensional Cosmological Simulations

We describe the two-dimensional TreePM method in this paper. The 2d TreePM code is an accurate and efficient technique to carry out large two-dimensional N-body simulations in cosmology. This hybrid code combines the 2d Barnes and Hut Tree method and the 2d Particle-Mesh method. We describe the splitting of force between the PM and the Tree parts. We also estimate error in force for a realistic configuration. Finally, we discuss some tests of the code.

Suryadeep Ray

2004-06-01

360

Quantum walks on two kinds of two-dimensional models

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

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

2015-01-08

361

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

362

Persistence Problem in Two-Dimensional Fluid Turbulence

NASA Astrophysics Data System (ADS)

We present a natural framework for studying the persistence problem in two-dimensional fluid turbulence by using the Okubo-Weiss parameter ? to distinguish between vortical and extensional regions. We then use a direct numerical simulation of the two-dimensional, incompressible Navier-Stokes equation with Ekman friction to study probability distribution functions (PDFs) of the persistence times of vortical and extensional regions by employing both Eulerian and Lagrangian measurements. We find that, in the Eulerian case, the persistence-time PDFs have exponential tails; by contrast, this PDF for Lagrangian particles, in vortical regions, has a power-law tail with an exponent ?=2.9±0.2.

Perlekar, Prasad; Ray, Samriddhi Sankar; Mitra, Dhrubaditya; Pandit, Rahul

2011-02-01

363

Dissipative quadratic solitons supported by a localized gain

NASA Astrophysics Data System (ADS)

We propose two models for the creation of stable dissipative solitons in optical media with the ?(2 ) (quadratic) nonlinearity. To compensate spatially uniform loss in both the fundamental-frequency (FF) and second-harmonic (SH) components of the system, a strongly localized "hot spot" carrying the linear gain is added, acting either on the FF or on the SH component. In both systems, we use numerical methods to find families of dissipative ?(2 ) solitons pinned to the "hot spot". The shape of the existence and stability domains may be rather complex. An existence boundary for the solitons, which corresponds to the guided mode in the linearized version of the systems, is obtained in an analytical form. The solitons demonstrate noteworthy features, such as spontaneous symmetry breaking (of spatially symmetric solitons) and bistability.

Lobanov, Valery E.; Borovkova, Olga V.; Malomed, Boris A.

2014-11-01

364

Dark soliton formation and soliton dynamics in all-normal dispersion cavity fiber ring lasers without an anti-saturable absorber in cavity is studied both theoretically and numerically. It is shown that under suitable conditions the dark solitons formed could be described by the nonlinear Schrödinger equation. The dark soliton formation in an all-normal-dispersion cavity erbium-doped fiber ring laser without an anti-saturable absorber in cavity is first experimentally demonstrated. Individual dark solitons are experimentally identified. Excellent agreement between theory and experiment is observed. PMID:25321066

Tang, Dingyuan; Guo, Jun; Song, Yufeng; Zhang, Han; Zhao, Luming; Shen, Deyuan

2014-08-11

365

The classic examples of optical phenomena resulting in the appearance of solitons are self-focusing, self-induced transparency, and parametric three-wave interaction. To date, the list of the fields of nonlinear optics and models where solitons play an important role has significantly expanded. Now long-lived or stable solitary waves are called solitons, including, for example, dissipative, gap, parametric, and topological solitons. This review considers nonlinear optics models giving rise to the appearance of solitons in a narrow sense: solitary waves corresponding to the solutions of completely integrable systems of equations basic for the models being discussed. (review)

Maimistov, Andrei I [Moscow Institute of Physics and Technology (State University), Dolgoprudnyi, Moscow Region (Russian Federation)

2010-11-13

366

Using numerical simulations of the full nonlinear equations of motion we investigate topological solitons of a modified O(3) sigma model in three space dimensions, in which the solitons are stabilized by the Hopf charge. We find that for solitons up to charge five the solutions have the structure of closed strings, which become increasingly twisted as the charge increases. However, for higher charge the solutions are more exotic and comprise linked loops and knots. We discuss the structure and formation of these solitons and demonstrate that the key property responsible for producing such a rich variety of solitons is that of string reconnection.

Richard Battye; Paul Sutcliffe

1998-11-09

367

Soliton dynamics in the multiphoton plasma regime

Solitary waves have consistently captured the imagination of scientists, ranging from fundamental breakthroughs in spectroscopy and metrology enabled by supercontinuum light, to gap solitons for dispersionless slow-light, and discrete spatial solitons in lattices, amongst others. Recent progress in strong-field atomic physics include impressive demonstrations of attosecond pulses and high-harmonic generation via photoionization of free-electrons in gases at extreme intensities of 1014 W/cm2. Here we report the first phase-resolved observations of femtosecond optical solitons in a semiconductor microchip, with multiphoton ionization at picojoule energies and 1010 W/cm2 intensities. The dramatic nonlinearity leads to picojoule observations of free-electron-induced blue-shift at 1016 cm?3 carrier densities and self-chirped femtosecond soliton acceleration. Furthermore, we evidence the time-gated dynamics of soliton splitting on-chip, and the suppression of soliton recurrence due to fast free-electron dynamics. These observations in the highly dispersive slow-light media reveal a rich set of physics governing ultralow-power nonlinear photon-plasma dynamics.

Husko, Chad A.; Combrié, Sylvain; Colman, Pierre; Zheng, Jiangjun; De Rossi, Alfredo; Wong, Chee Wei

2013-01-01

368

Infinite conformal symmetry in two-dimensional quantum field theory

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

A A Belavin; A M Polyakov; A B Zamolodchikov

1984-01-01

369

Two dimensional measurements of electrical fields in transformer oil

It is demonstrated that the electro-optical Kerr effect with field modulation can be used for angularly resolved field mapping of two-dimensional objects in transformer oils. This technique can determine the amplitude as well as the direction of the electric field in liquid insulation systems relevant for converter transformers. As an example, the technique was applied to two overlapping Macrolon barriers

U. Gafvert

1990-01-01

370

Two-Dimensional Grids About Airfoils and Other Shapes

NASA Technical Reports Server (NTRS)

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

Sorenson, R.

1982-01-01

371

Two dimensional liquid crystal devices and their computer simulations

The main focus of the dissertation is design and optimization two dimensional liquid crystal devices, which means the liquid crystal director configurations vary in two dimensions. Several optimized and designed devices are discussed in the dissertation. They include long-term bistable twisted nematic liquid crystal display (BTN LCD), which is very low power consumption LCD and suitable for E-book application; wavelength

Bin Wang

2002-01-01

372

Stably Extending Two-Dimensional Bipedal Walking to Three Dimensions

dynamically sta- ble bipedal walking were concerned with passive two- dimensional (2D) bipeds walking down the use of hybrid zero dynamics. I. INTRODUCTION The central goal of research in bipedal robotic walking been shown that for certain shallow slopes, these passive bipeds have stable walking gaits

Ames, Aaron

373

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

, they are extremely inefficient, resulting in short runtimes. The passive dynamic approach, on the other hand, models practical use. An approach in between these extremes seeks to apply passive dynamic principles two dimensional, knee-less, bipedal walking robot. After removing one of several unsuccessful control

Ruina, Andy L.

374

Two-dimensional vortex motion and ``negative temperatures''

A recent numerical integration of the two-dimensional Navier-Stokes equations has tentatively identified an ``ergodic boundary'' in the space of initial conditions for the turbulent flow. An explanation is suggested in terms of negative temperatures, for a point vortex model. The author acknowledges valuable discussions with Drs. F. Tapert and R. Hardin.

D. Montgomery

1972-01-01

375

Two-Dimensional Vortex Dynamics With Background Vorticity

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

Schecter, David

376

Two-dimensional vortex motion and 'negative temperatures.'

NASA Technical Reports Server (NTRS)

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

Montgomery, D.

1972-01-01

377

Quantum Magnetoconductance of a Nondegenerate Two-Dimensional Electron Gas

Magnetoconductance measurements are reported for the low-density, two-dimensional classical electron gas formed on the surface of liquid helium. At strong magnetic fields, large deviations from the classical parabolic behaviour are observed. These deviations are described with a quantum-transport theory of scattering within broadened Landau levels.

R. W. van der Heijden; J. H. G. Surewaard; H. M. Gijsman; F. M. Peeters

1988-01-01

378

Magnetoconductivity of disordered two dimensional tight binding electrons in CPA

The magnetotransport properties of a tight binding model of electrons on a two dimensional square lattice with diagonal disorder and in a perpendicular magnetic field is investigated. The disorder is treated in the coherent potential approximation (CPA) and a quasiclassical solution of the Harper equation is used to calculate the one particle Green's function. Analytical expressions for the CPA vertex

P. Kleinert; V. V. Bryksin; H. Schlegel

1993-01-01

379

Conformal Field Theory Properties of Two-Dimensional Percolation

Conformal Field Theory Properties of Two-Dimensional Percolation Michael Flohr and Annekathrin M in two dimensions has interesting features in conformal field theory such as the conformal invari- ance Network HPRN-CT-2002-00325 (EUCLID) anne@th.physik.uni-bonn.de 1 #12;conformal field theory which matches

Flohr, Michael

380

Two-dimensional readout in a liquid xenon ionisation chamber

A two-dimensional readout with metal strips deposited on both sides of a glass plate is investigated aiming to assess the possibility of its use in a liquid xenon ionisation chamber for positron emission tomography. Here, we present results obtained with an ?-source. It is shown that position resolution of ?1mm, fwhm, can be achieved for free charge depositions equivalent to

V. Solovov; V. Chepel; A. Pereira; M. I. Lopes; R. Ferreira Marques; A. J. P. L. Policarpo

2002-01-01

381

Two-dimensional ultrasonic computed tomography of growing bones.

Two-dimensional ultrasonic computed tomography of growing bones. P. Lasaygues, E. Franceschini, R--This study deals with the 2-D ultrasonic qualitative and quantitative imaging of child bone. The inverse: Ultrasonic Computed Tomography, Bone imaging, Born approximation, iterative distorted method I. INTRODUCTION

Paris-Sud XI, UniversitÃ© de

382

FLOW AND DISPERSION OF POLLUTANTS WITHIN TWO-DIMENSIONAL VALLEYS

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

383

Star discrepancy of generalized two-dimensional Hammersley point sets

generalize to arbitrary bases recent results on the star discrepancy of digi- tally shifted two-dimensional Hammersley point sets in base 2 by Kritzer, Larcher and Pillichshammer. The key idea is to link our) states the link between one-dimensional sequences and two-dimentional point sets deduced from them [6, 20

Provence Aix-Marseille I, UniversitÃ© de

384

Numerical simulation of two?dimensional tsunami runup

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

Z. Kowalik; T. S. Murty

1993-01-01

385

condmat/9801215 Crossovers in the Two Dimensional Ising Spin Glass

condmat/9801215 v2 26 Jan 1998 Crossovers in the Two Dimensional Ising Spin Glass of extensive computer simulations we analyze in detail the two dimen sional \\SigmaJ Ising spin glass with ferromagnetic nextnearestneighbor interactions. We found a crossover from ferromagnetic to ``spin glass'' like

Roma "La Sapienza", Università di

386

Two-dimensional optimization of free-electron-laser designs

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

Prosnitz, D.; Haas, R.A.

1982-05-04

387

Two-dimensional optimization of free electron laser designs

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

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

1985-01-01

388

Sound waves in two-dimensional ducts with sinusoidal walls

NASA Technical Reports Server (NTRS)

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

Nayfeh, A. H.

1974-01-01

389

TWO-DIMENSIONAL ARRAY OF RECTANGULAR SLOT ANTENNAS

and analysis for this class of antennas are performed using the Momentum software package of Advanced Design and a smaller size. In addition, a 2D array of this antenna is designed and presented. The numerical simulationTWO-DIMENSIONAL ARRAY OF RECTANGULAR SLOT ANTENNAS TUNED WITH PATCH STUBS FOR WIDE BANDWIDTH

Elsherbeni, Atef Z.

390

Research article Real-time two-dimensional asynchronous

Research article Real-time two-dimensional asynchronous control of a computer cursor with a single the feasibility of controlling a computer cursor asynchronously in two dimensions using one subdural electrode stimulation of the primary motor cortex (MI). Interventions: Power changes in the electrocorticography signals

Popovic, Milos R.

391

Tachyon Hair for Two-Dimensional Black Holes

Using a combination of analytical and numerical methods, we obtain a two-dimensional spacetime describing a black hole with tachyon hair. The physical ADM mass of the black hole is finite. The presence of tachyon hair increases the Hawking temperature.

Alan Kostelecky; Malcolm Perry

1993-11-01

392

Discrete denoising of heterogenous two-dimensional data

We consider discrete denoising of two-dimensional data with characteristics that may be varying abruptly between regions. Using a quadtree decomposition technique and space-filling curves, we extend the recently developed S-DUDE (Shifting Discrete Universal DEnoiser), which was tailored to one-dimensional data, to the two-dimensional case. Our scheme competes with a genie that has access, in addition to the noisy data, also to the underlying noiseless data, and can employ $m$ different two-dimensional sliding window denoisers along $m$ distinct regions obtained by a quadtree decomposition with $m$ leaves, in a way that minimizes the overall loss. We show that, regardless of what the underlying noiseless data may be, the two-dimensional S-DUDE performs essentially as well as this genie, provided that the number of distinct regions satisfies $m=o(n)$, where $n$ is the total size of the data. The resulting algorithm complexity is still linear in both $n$ and $m$, as in the one-dimensional case. Our experimental ...

Moon, Taesup; Kim, Jae-Young

2010-01-01

393

Chaotic dynamics for two-dimensional tent maps

NASA Astrophysics Data System (ADS)

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

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

2015-02-01

394

Two dimensional packing: the power of rotation Leah Epstein y

-dimensional packing problem of packing rectangles into unit squares. However our problem is slightly di#11;er- ent are unit squares. The items are rectangles of sides bounded by 1. The items arrive one by one, each in the study of two-dimensional packing problems. In such problems the input items are rectangles which need

Epstein, Leah

395

Exploring Brain Connectivity with Two-Dimensional Neural Maps

meaningful and familiar coordinates. DWI enables neural pathways in the in vivo brain to be estimatedExploring Brain Connectivity with Two-Dimensional Neural Maps Radu Jianu, Member, IEEE, CÂ¸ agatay for exploring connectivity in the brain. For this, we create standard streamtube models from diffusion

Pratt, Vaughan

396

Two-dimensional black holes in accelerated frames: quantum aspects

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

R. Balbinot; A. Fabbri

1996-07-04

397

Stationary Axisymmetric Fields as Two-Dimensional Geodesics

Einstein's equations for stationary axisymmetric fields are reformulated as the equations for affine geodesics in a two--dimensional space. The affine collineations of this space are investigated and used to relate explicit solutions of Einstein's equations with different physical properties. Particularly, the solutions describing the exterior fields of a dyon and a slowly rotating body are discussed.

D. Nunez; H. Quevedo

1993-10-08

398

Two-Dimensional Fourier Transform Analysis of Helicopter Flyover Noise

NASA Technical Reports Server (NTRS)

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

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

1999-01-01

399

Self Organization of Two-dimensional Insect Neural Networks

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

Jacob, Eshel Ben

400

Two-dimensional mathematical model of evacuated tube solar collector

Analysis of an evacuated tubular solar collector is presented by developing a two-dimensional performance model. The collector uses a thin flat plate spanning its diameter as its absorbing surface. Energy balances are made on collector plate and tube, each considered as a separate unit. It has been found that a zero capacitance model is quite adequate when hourly meteorological data

F. Rahman; S. Al-Zakri; M. A. A. Rahman

1984-01-01

401

Hexagonal structures for two-dimensional photonic crystals

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

402

TWO DIMENSIONAL IMMERSED BOUNDARY SIMULATIONS OF SWIMMING JELLYFISH

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

Stockie, John

403

Physical States in Two-Dimensional Topological Gauge Theories

Physical states of two-dimensional topological gauge theories are studied using the BRST formalism in the light-cone gauge. All physical states are obtained for the abelian theory. There are an infinite number of physical states with different ghost numbers. Simple examples of physical states in a non-abelian theory are also given.

Yoshiaki Tanii; Masakazu Yamashita

1993-01-09

404

Transmission characteristics of two-dimensional magnetized magnetic photonic crystals

Transmission characteristics of two-dimensional magnetized magnetic photonic crystals (MPCs) have been studied by electromagnetic simulation and experiments in microwave frequencies. MPCs with square and hexagonal lattices are made of ferrites, and their transmission coefficients are measured in the X waveband with an applied static magnetic field. For the lattices, a stop-band and a band shift with the applied static magnetic

Jie Xu; Rui-xin Wu; Ping Chen; Yue Shi

2007-01-01

405

Sensor Networking Using Two-Dimensional Electromagnetic Wave Yasutoshi Makino*

Communication (TDC)." TDC is communication in which electromagnetic wave propagates within a two dimensional medium and communication is realized be- tween the nodes which are connected to the TDC sheet. In TDC, a large number of communication nodes can connect with each other with no individual wires, while TDC has

Shinoda, Hiroyuki

406

Proximity Connector for Two-Dimensional Electromagnetic Wave Communication

proposed a new physical layer of communication named "Two-Dimensional Communication (TDC)." TDC and power transmission connector that works anywhere on the TDC sheet without presice positioning. Moreover, it works as a proximity connector requiring no electrical contacts to the TDC sheet. If the surfaces

Shinoda, Hiroyuki

407

Duality transformation for two-dimensional static problems

A form of duality transformation, applicable to two-dimensional static problems, is formulated. It transforms electrostatic problems into magnetostatic problems by applying, instead of the common duality between the E and H vectors, one between the vectors E and B. The transformation can be easily applied to straight TEM transmission-line geometries. Its use in teaching basic electromagnetics to electrical engineering students

Ismo Lindell

1995-01-01

408

An efficient architecture for two-dimensional discrete wavelet transform

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

409

Quantum emission from two-dimensional black holes

We investigate Hawking radiation from two-dimensional dilatonic black holes using standard quantization techniques. In the background of a collapsing black-hole solution the Bogoliubov coefficients can be exactly determined. In the regime after the black hole has settled down to an equilibrium'' state but before the back reaction becomes important these give the known result of a thermal distribution of Hawking

Steven B. Giddings; William M. Nelson

1992-01-01

410

Quantum emission from two-dimensional black holes

We investigate Hawking radiation from two-dimensional dilatonic black holes using standard quantization techniques. In the background of a collapsing black-hole solution the Bogoliubov coefficients can be exactly determined. In the regime after the black hole has settled down to an ``equilibrium'' state but before the back reaction becomes important these give the known result of a thermal distribution of Hawking

Steven B. Giddings; William M. Nelson

1992-01-01

411

Investigating Coherent Structures of Quasi Two-Dimensional Flows Subject

edges of the tank. An upward axial magnetic field created by permanent magnets or electromagnets. #12;L electrodes separated by 2 cm Bar magnets Permanent magnets inserted from below: Made of Neodymium. DimensionsInvestigating Coherent Structures of Quasi Two-Dimensional Flows Subject to Electromagnetic Forces

Shihadeh, Alan

412

Ventricular septal defects. Two dimensional echocardiographic and morphological correlations

To evaluate the ability of two dimensional echocardiography to identify and classify ventricular septal defects, 280 infants and children with clinically significant ventricular septal defects were studied. Multiple precordial and subcostal echocardiographic planes were scanned in each patient in an attempt to identify the defects. Defects visualised were classified on the basis of the structures which formed their margins. Subsequent

G R Sutherland; M J Godman; J F Smallhorn; P Guiterras; R H Anderson; S Hunter

1982-01-01

413

Integral invariants of two-dimensional rotational gas flows

for which Euler's equation coincides with Crocco's equation, which describes the two-dimensional rotational flow of a gas. In this paper we shall apply group theoretical methods to the study of this functional and find a group of transformations which leave tt~s functional invariant. Before we proceed to analyze the functional, we note the following property. It is known that the

K. P. Surovikhin

1965-01-01

414

Original article Two-dimensional gel electrophoresis of membrane

Original article Two-dimensional gel electrophoresis of membrane proteins from ectomycorrhizal-dimensional polyacrylamide gels. Gels with limited back- ground staining and streaking and with clearly efficacitÃ© et leur compatibilitÃ© avec l'obtention de gels d'Ã©lectro- phorÃ¨se bidimensionnelle. Une fraction

Paris-Sud XI, UniversitÃ© de

415

Anomalous Hall effect in a two-dimensional electron gas

Anomalous Hall effect in a two-dimensional electron gas Tamara S. Nunner,1 N. A. Sinitsyn,2,3 Mario F. Borunda,2 V. K. Dugaev,4 A. A. Kovalev,2 Ar. Abanov,2 Carsten Timm,5 T. Jungwirth,6,7 Jun-ichiro Inoue,8 A. H. MacDonald,9 and Jairo Sinova2...

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

2007-01-01

416

Two-Dimensional Diverging Shocks in a Nonuniform Medium

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

417

Manipulation of Dopants in a Two Dimensional Matrix

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

Timothy Kidd; Laura Strauss; Polina Skirtachenko; Dustin Klein

2009-01-01

418

Specific heat of two-dimensional diluted magnets

NASA Astrophysics Data System (ADS)

Using Monte Carlo techniques, the two-dimensional site-diluted Ising model is studied. In particular, properties of the specific heat, its critical behaviour and the emergence of a non-singular maximum above the transition temperature at moderate concentration of defects, are discussed.

Selke, W.; Shchur, L. N.; Vasilyev, O. A.

419

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

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

Mark D. Pritt; Jerome S. Shipman

1994-01-01

420

Two-DIMENSIONAL WATER FLOOD AND MUDFLOW SIMULATION

of flow conditions, including flow through subdivisions, street flow, and culvert or flood channelTwo-DIMENSIONAL WATER FLOOD AND MUDFLOW SIMULATION By J. S. O'Brien, 1 P. Y. Julien, 2 and W. T-water floodhazards, mudflows,and debris flowson alluvialfans and urban floodplains. Interactive flood

Julien, Pierre Y.

421

Acoustic metamaterials for new two-dimensional sonic devices

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

Daniel Torrent; José Sánchez-Dehesa

2007-01-01

422

Photon trapping and transfer with solitons

We show, numerically, that a single photon trapped by a soliton in a Kerr nonlinear medium can be transferred from one soliton to another when the captor soliton undergoes collision with a second soliton. Soliton collisions ...

Steiglitz, Ken

423

We apply the variational approach to solitons in highly nonlocal nonlinear media in D = 1, 2, 3 dimensions. We compare results obtained by the variational approach with those obtained by the accessible soliton approximation, by considering the same system of equations in the same spatial region and under the same boundary conditions. To assess the accuracy of these approximations, we also compare them with the numerical solution of the equations. We discover that the accessible soliton approximation suffers from systematic errors, when compared to the variational approach and the numerical solution. The errors increase with the dimension of the system. The variational highly nonlocal approximation provides more accurate results in any dimension and as such is more appropriate solution than the accessible soliton approximation. PMID:25607152

Aleksi?, Branislav N; Aleksi?, Najdan B; Petrovi?, Milan S; Strini?, Aleksandra I; Beli?, Milivoj R

2014-12-29

424

Nonlinear waves and solitons in molecular clouds

NASA Technical Reports Server (NTRS)

We begin a study of nonlinear wave phenomena in molecular clouds. These clouds exhibit highly nonlinear structure that is often described in terms of 'clumps' and 'filaments' which are bouncing around, twisting, and colliding within the cloud. These clouds are important because they ultimately produce the initial conditions for the star formation process. Our motivation is to explore the possibility that solitons (i.e., spatially localized, single-hump wave entities which often exhibit remarkable stability) can live in these molecular clouds and produce their observed structure. In this paper we focus on the case of one spatial dimension, and we show that a rich variety of nonlinear waves can exist in molecular cloud fluid systems (where self-gravity is included). We show that in the absence of magnetic fields no true soliton solutions are allowed, although highly nonlinear waves (whose crests become widely spaced and thus soliton-like) do exist. For clouds with embedded magnetic fields, we derive a model equation which describes the behavior of wave phenomena; this model equation allows solutions which correspond to nonlinear waves, solitons, and topological solitons. We briefly consider the stability of these wave entities and discuss the possible role they play in molecular cloud dynamics.

Adams, Fred C.; Fatuzzo, Marco

1993-01-01

425

Energy transport in a shear flow of particles in a two-dimensional dusty plasma

NASA Astrophysics Data System (ADS)

A shear flow of particles in a laser-driven two-dimensional (2D) dusty plasma is observed in a study of viscous heating and thermal conduction. Video imaging and particle tracking yields particle velocity data, which we convert into continuum data, presented as three spatial profiles: mean particle velocity (i.e., flow velocity), mean-square particle velocity, and mean-square fluctuations of particle velocity. These profiles and their derivatives allow a spatially resolved determination of each term in the energy and momentum continuity equations, which we use for two purposes. First, by balancing these terms so that their sum (i.e., residual) is minimized while varying viscosity ? and thermal conductivity ? as free parameters, we simultaneously obtain values for ? and ? in the same experiment. Second, by comparing the viscous heating and thermal conduction terms, we obtain a spatially resolved characterization of the viscous heating.

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

2012-11-01

426

Two-dimensional Nanoparticle Arrays Show the Organizational Power of Robust DNA Motifs

The bottom-up spatial organization of potential nanoelectronic components is a key intermediate step in the development of molecular electronics. We describe robust 3-space-spanning DNA motifs that are used to organize nanoparticles in 2D. One strand of the motif ends in a gold nanoparticle; only one DNA strand is attached to the particle. By using two of the directions of the motif to produce a two dimensional crystalline array, one direction is free to bind gold nanoparticles. Identical motifs, tailed in different sticky ends enable the 2D periodic ordering of 5 nm and 10 nm diameter gold nanoparticles. PMID:16834438

Zheng, Jiwen; Constantinou, Pamela E.; Micheel, Christine; Alivisatos, A. Paul; Kiehl, Richard A.; Seeman, Nadrian C.

2012-01-01

427

In situ two-dimensional imaging quick-scanning XAFS with pixel array detector

Quick-scanning X-ray absorption fine structure (XAFS) measurements were performed in transmission mode using a PILATUS 100K pixel array detector (PAD). The method can display a two-dimensional image for a large area of the order of a centimetre with a spatial resolution of 0.2?mm at each energy point in the XAFS spectrum. The time resolution of the quick-scanning method ranged from 10?s to 1?min per spectrum depending on the energy range. The PAD has a wide dynamic range and low noise, so the obtained spectra have a good signal-to-noise ratio. PMID:21997918

Tanida, Hajime; Yamashige, Hisao; Orikasa, Yuki; Oishi, Masatsugu; Takanashi, Yu; Fujimoto, Takahiro; Sato, Kenji; Takamatsu, Daiko; Murayama, Haruno; Arai, Hajime; Matsubara, Eiichiro; Uchimoto, Yoshiharu; Ogumi, Zempachi

2011-01-01

428

In situ two-dimensional imaging quick-scanning XAFS with pixel array detector.

Quick-scanning X-ray absorption fine structure (XAFS) measurements were performed in transmission mode using a PILATUS 100K pixel array detector (PAD). The method can display a two-dimensional image for a large area of the order of a centimetre with a spatial resolution of 0.2?mm at each energy point in the XAFS spectrum. The time resolution of the quick-scanning method ranged from 10?s to 1?min per spectrum depending on the energy range. The PAD has a wide dynamic range and low noise, so the obtained spectra have a good signal-to-noise ratio. PMID:21997918

Tanida, Hajime; Yamashige, Hisao; Orikasa, Yuki; Oishi, Masatsugu; Takanashi, Yu; Fujimoto, Takahiro; Sato, Kenji; Takamatsu, Daiko; Murayama, Haruno; Arai, Hajime; Matsubara, Eiichiro; Uchimoto, Yoshiharu; Ogumi, Zempachi

2011-11-01

429

Off-diagonal long-range order in a harmonically confined two-dimensional Bose gas

We investigate the presence of off-diagonal long-range order in a\\u000aharmonically confined two-dimensional Bose gas. In the noninteracting case, an\\u000aanalytical calculation of the the finite-temperature one-particle density\\u000amartix provides an exact description of the spatial correlations known to be\\u000aassociated with the existence of a Bose-Einstein condensate below the\\u000atransition temperature $T^{(0)}_c$. We treat the effects of repulsive\\u000ainteractions

Brandon P. van Zyl

2002-01-01

430

Two-dimensional metamaterial device design in the discrete dipole approximation

NASA Astrophysics Data System (ADS)

We extend the discrete dipole method to enable the analysis and design of two-dimensional magnetoelectric metamaterial devices based on transformation optics. Key to this method is the evaluation of the dipole moments of the metamaterial elements, which can be accomplished within the framework of a rigorous Bloch wave model based on lattice sums. Corrections to the polarizabilities for spatial dispersion and magnetoelectric coupling are included in the formulation of a generalized Clausius-Mossotti relationship. We demonstrate the utility of the extended approach by designing a cloaking structure that shows considerably improved performance over that designed by assuming the standard Clausius-Mossotti relationship between constitutive parameter and polarizability.

Landy, Nathan; Smith, David R.

2014-07-01

431

The spatiotemporal evolution of parametric instabilities such as stimulated Raman scattering is studied analytically in time and two spatial dimensions. Initial and boundary conditions are chosen to represent the entrance, propagation, and exit of a laser pulse of finite extent convecting through a homogeneous collisional plasma with definite boundaries. For most scattering angles the growth is found to be dominated by two-dimensional effects with one-dimensional amplitudes being valid for only a small range of angles corresponding to near forward and near backward scattering. The sideward convection alters the spatiotemporal character of the instability and inhibits but does not suppress its growth. {copyright} {ital 1997 American Institute of Physics.}

McKinstrie, C.J. [Department of Mechanical Engineering, University of Rochester, Rochester, New York 14627 (United States)] [Department of Mechanical Engineering, University of Rochester, Rochester, New York 14627 (United States); [Laboratory for Laser Energetics, 250 East River Road, Rochester, New York 14623 (United States); Turano, E.J. [Department of Physics and Astronomy, University of Rochester, Rochester, New York 14627 (United States)] [Department of Physics and Astronomy, University of Rochester, Rochester, New York 14627 (United States); [Laboratory for Laser Energetics, 250 East River Road, Rochester, New York 14623 (United States)

1997-09-01

432

Two-dimensional atom localization in a four-level tripod system in laser fields

We propose a scheme for two-dimensional (2D) atom localization in a four-level tripod system under an influence of two orthogonal standing-wave fields. Position information of the atom is retained in the atomic internal states by an additional probe field either of a standing or of a running wave. It is shown that the localization factors depend crucially on the atom-field coupling that results in such spatial structures of populations as spikes, craters, and waves. We demonstrate a high-precision localization due to measurement of population in the upper state or in any ground state.

Ivanov, Vladimir [Turku Centre for Quantum Physics, Department of Physics and Astronomy, University of Turku, FIN-20014 Turku (Finland); Saint Petersburg State University of Information Technologies, Mechanics and Optics, 197101 St. Petersburg (Russian Federation); Rozhdestvensky, Yuri [Saint Petersburg State University of Information Technologies, Mechanics and Optics, 197101 St. Petersburg (Russian Federation)

2010-03-15

433

Solitons versus parametric instabilities during ionospheric heating

NASA Technical Reports Server (NTRS)

Various effects associated with ionospheric heating are investigated by numerically solving the modified Zakharov (1972) equations. It is shown that, for typical ionospheric parameters, the modulational instability is more important than the parametric decay instability in the spatial region of strongest heater electric field. It is concluded that the modulational instability leads to the formation of solitons, as originally predicted by Petviashvili (1976).

Nicholson, D. R.; Payne, G. L.; Downie, R. M.; Sheerin, J. P.

1984-01-01

434

Incoherently coupled dark-bright photorefractive solitons

NASA Astrophysics Data System (ADS)

We report the observation of incoherently coupled dark-bright spatial soliton pairs in a biased bulk photorefractive crystal. When such a pair is decoupled, the dark component evolves into a triplet structure, whereas the bright one decays into a self-defocusing beam.

Chen, Zhigang; Segev, Mordechai; Coskun, Tamer H.; Christodoulides, Demetrios N.; Kivshar, Yuri S.; Afanasjev, Vsevolod V.

1996-11-01

435

Quasi-one-dimensional optical lattices for soliton manipulation.

Based on angular spectrum engineering, we report the generation of optical lattices whose two-dimensional transverse nondiffracting pattern can be reduced to a quasi-one-dimensional intensity structure formed by either a single or multiple parallel channels. Remarkably, many features for each channel such as its maximum intensity, modulation, width, or separation among channels, can be controlled and modified in order to meet the requirements of particular applications. In particular, we demonstrate that these lattices can provide useful schemes for soliton routing and steering. We demonstrate the existence domain of ground-state solitons for the single quasi-one-dimensional lattice, and we show that these nondiffracting beams allow "push and pull" dynamics among the neighbor solitons propagated along the nondiffracting channels generated. PMID:25490515

Lopez-Aguayo, Servando; Ruelas-Valdez, Cesar; Perez-Garcia, Benjamin; Ortiz-Ambriz, Antonio; Hernandez-Aranda, Raul I; Gutiérrez-Vega, Julio C

2014-11-15

436

This note is based on the summary of our book entitled "Non-perturbative field theoryfrom two dimensional conformal field theory to QCD in four dimensions", published recently by Cambridge University Press. It includes 436 pages. The book provides a detailed description of the tool box of non-perturbative techniques, presents applications of them to simplified systems, mainly of gauge dynamics in two dimensions, and examines the lessons one can learn from those systems about four dimensional QCD and hadron physics. In particular the book deals with conformal invariance, integrability, bosonization, large N, solitons in two dimensions and monopoles and instantons in four dimensions, confinement versus screening and finally the hadronic spectrum and scattering. We also attach the table of contents and the list of references of the book. We would be grateful for any comments or suggestions related to the material in the book. These may be incorporated in a possible future edition. They may be sent via the e-mails below.

Yitzhak Frishman; Jacob Sonnenschein

2010-05-10

437

Drift ion acoustic shock waves in an inhomogeneous two-dimensional quantum magnetoplasma

Linear and nonlinear propagation characteristics of drift ion acoustic waves are investigated in an inhomogeneous quantum plasma with neutrals in the background employing the quantum hydrodynamics (QHD) model. In this regard, a quantum Kadomtsev-Petviashvili-Burgers (KPB) equation is derived for the first time. It is shown that the ion acoustic wave couples with the drift wave if the parallel motion of ions is taken into account. Discrepancies in the earlier works on drift solitons and shocks in inhomogeneous plasmas are also pointed out and a correct theoretical framework is presented to study the one-dimensional as well as the two-dimensional propagation of shock waves in an inhomogeneous quantum plasma. Furthermore, the solution of KPB equation is presented using the tangent hyperbolic (tanh) method. The variation of the shock profile with the quantum Bohm potential, collision frequency, and ratio of drift to shock velocity in the comoving frame, v{sub *}/u, are also investigated. It is found that increasing the number density and collision frequency enhances the strength of the shock. It is also shown that the fast drift shock (i.e., v{sub *}/u>0) increases, whereas the slow drift shock (i.e., v{sub *}/u<0) decreases the strength of the shock. The relevance of the present investigation with regard to dense astrophysical environments is also pointed out.

Masood, W.; Siddiq, M. [TPPD, PINSTECH, P. O. Nilore, Islamabad 54000 (Pakistan); Karim, S.; Shah, H. A. [Department of Physics, GC University, Lahore 54000 (Pakistan)

2009-04-15

438

Time-dependent hyperspherical studies for a two-dimensional attractive Bose-Einstein condensate

We apply the hyperspherical (HS) method to study a Bose-Einstein condensate in quasi-two-dimensional free space stabilized and confined under the influence of an oscillating magnetic field. The HS method indeed reproduces stabilized breathing mode solutions qualitatively similar to those previously obtained by the Gross-Pitaevskii (GP) equation. Also, the frequencies of our breathing mode solutions are shown to have functional dependence on the physical parameters in a manner similar to the GP results. However, beats in the breathing mode solutions are revealed in the HS approximation, while they are seemingly absent in the GP descriptions. A supplementary analysis of the stationary state solutions shows that the hyperspherical single-particle density exhibits certain characteristic scaling dependence on energy akin to the Townes soliton [Chiao et al., Phys. Rev. Lett. 13, 479 (1964)], but also some difference in detail. The Kapitza averaging leads to an effective time-independent potential and shows how continuously distributed hyperspherical bound states turn into discrete bound states on accounting of the modulating field. The HS method is made subject to the Floquet analysis in order to interpret the beats in the breathing mode as coherent excitation among discrete Floquet states.

Liu, Chien-Nan [Department of Physics, Fu-Jen Catholic University, Taipei 24205, Taiwan (China); Morishita, Toru; Watanabe, Shinichi [Department of Applied Physics and Chemistry, University of Electro-Communications, 1-5-1 Chofu-ga-oka, Chofu-shi, Tokyo 182-8585 (Japan)

2007-02-15

439

A new type of dissipative solitons - dissipative Raman solitons - are revealed on the basis of numerical study of the generalized complex nonlinear Ginzburg-Landau equation. The stimulated Raman scattering significantly affects the energy scalability of the dissipative solitons, causing splitting to multiple pulses. We show, that an appropriate increase of the group-delay dispersion can suppress the multipulsing instability due to formation of the dissipative Raman soliton, which is chirped, has a Stokes-shifted spectrum, and chaotic modulation on its trailing edge. The strong perturbation of a soliton envelope caused by the stimulated Raman scattering confines the energy scalability preventing the so-called dissipative soliton resonance. We show, that in practical implementations, a spectral filter can extend the stability regions of high-energy pulses. PMID:25606940

Kalashnikov, Vladimir L; Sorokin, Evgeni

2014-12-01

440

Silicon-based two dimensional tunable photonic crystal devices

NASA Astrophysics Data System (ADS)

Photonic crystal devices are capable of controlling the flow of light in ultra compact scales. Silicon two dimensional (2D) nanostructures are well developed in the integrated circuit (IC) industry. Silicon is transparent to infrared light and has high refractive index which makes silicon an ideal material for photonic crystals in the infrared spectrum. Silicon 2D photonic crystals have attracted a lot of interest for showing feasibility of photonic integrated circuits. Typical photonic crystal devices are waveguides or cavities, which were developed as mostly passive devices. Various methods can be used to make photonic crystals tunable. In this work, silicon 2D tunable photonic crystal devices are studied using thermo-optic effect of silicon. In addition, this research presents one-step lithography to form micro and nano combined structures for the two-dimensional slab photonic crystals.

Choi, Kyung-Hak

441

Molecular structure by two-dimensional NMR spectroscopy

NASA Astrophysics Data System (ADS)

Two examples are presented of the use of two-dimensional NMR spectroscopy to solve molecular structure problems. The first is called correlation spectroscopy (COSY) and it allows us to disentangle a complex network of spin-spin couplings. By dispersing the NMR information in two frequency dimensions, it facilitates the analysis of very complex spectra of organic and biochemical molecules, normally too crowded to be tractable. The second application exploits the special properties of multiple-quantum coherence to explore the molecular framework one C?C linkage at a time. The natural product panamine is used as a test example; with some supplementary evidence, the structure of this six-ringed heterocyclic molecule is elucidated from the double-quantum filtered two-dimensional spectrum.

Freeman, R.

442

Two-dimensional topological insulators in quantizing magnetic fields

NASA Astrophysics Data System (ADS)

Two-dimensional topological insulators are characterized by gapped bulk states and gapless helical edge states, i.e. time-reversal symmetric edge states accommodating a pair of counter-propagating electrons. An external magnetic field breaks the time-reversal symmetry. What happens to the edge states in this case? In this paper we analyze the edge-state spectrum and longitudinal conductance in a two-dimensional topological insulator subject to a quantizing magnetic field. We show that the helical edge states exist also in this case. The strong magnetic field modifies the group velocities of the counter-propagating channels which are no longer identical. The helical edge states with different group velocities are particularly prone to get coupled via backscattering, which leads to the suppression of the longitudinal edge magnetoconductance.

Tkachov, G.; Hankiewicz, E. M.

2012-02-01

443

Preliminary results on two-dimensional interferometry of HL Tau

NASA Technical Reports Server (NTRS)

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

Tollestrup, Eric V.; Harvey, Paul M.

1989-01-01

444

Disordered quantum walks in two-dimensional lattices plink

NASA Astrophysics Data System (ADS)

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

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

2015-01-01

445

Transport behavior of water molecules through two-dimensional nanopores.

Water transport through a two-dimensional nanoporous membrane has attracted increasing attention in recent years thanks to great demands in water purification and desalination applications. However, few studies have been reported on the microscopic mechanisms of water transport through structured nanopores, especially at the atomistic scale. Here we investigate the microstructure of water flow through two-dimensional model graphene membrane containing a variety of nanopores of different size by using molecular dynamics simulations. Our results clearly indicate that the continuum flow transits to discrete molecular flow patterns with decreasing pore sizes. While for pores with a diameter ?15 Å water flux exhibits a linear dependence on the pore area, a nonlinear relationship between water flux and pore area has been identified for smaller pores. We attribute this deviation from linear behavior to the presence of discrete water flow, which is strongly influenced by the water-membrane interaction and hydrogen bonding between water molecules. PMID:25399193

Zhu, Chongqin; Li, Hui; Meng, Sheng

2014-11-14

446

Two-dimensional Raman-terahertz spectroscopy of water

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

Savolainen, Janne; Ahmed, Saima; Hamm, Peter

2013-01-01

447

Robust L1-norm two-dimensional linear discriminant analysis.

In this paper, we propose an L1-norm two-dimensional linear discriminant analysis (L1-2DLDA) with robust performance. Different from the conventional two-dimensional linear discriminant analysis with L2-norm (L2-2DLDA), where the optimization problem is transferred to a generalized eigenvalue problem, the optimization problem in our L1-2DLDA is solved by a simple justifiable iterative technique, and its convergence is guaranteed. Compared with L2-2DLDA, our L1-2DLDA is more robust to outliers and noises since the L1-norm is used. This is supported by our preliminary experiments on toy example and face datasets, which show the improvement of our L1-2DLDA over L2-2DLDA. PMID:25721558

Li, Chun-Na; Shao, Yuan-Hai; Deng, Nai-Yang

2015-05-01

448

Polaronic aspects of the two-dimensional ferromagnetic Kondo model

NASA Astrophysics Data System (ADS)

The two-dimensional ferromagnetic Kondo model with classical core spins is studied via unbiased Monte Carlo simulations for a hole doping up to x = 12.5%. A canonical algorithm for finite temperatures is developed. We show that, with realistic parameters for the manganites and at low temperatures, the double-exchange mechanism does not lead to phase separation on a two-dimensional lattice but rather stabilizes individual ferromagnetic polarons for this doping range. A detailed analysis of unbiased Monte Carlo results reveals that the polarons can be treated as independent particles for these hole concentrations. It is found that a simple polaron model describes the physics of the ferromagnetic Kondo model amazingly well. The ferromagnetic polaron picture provides an obvious explanation for the pseudogap in the one-particle spectral function Ak(ohgr) observed in the ferromagnetic Kondo model.

Daghofer, M.; Koller, W.; Evertz, H. G.; von der Linden, W.

2004-08-01

449

Revisiting freely decaying two-dimensional turbulence at millennial resolution

NASA Astrophysics Data System (ADS)

We study the evolution of vortex statistics in freely decaying two-dimensional turbulence at very large Reynolds number. The results obtained here confirm that the peak vorticity inside vortex cores is conserved and that the number of vortices as a function of time, N(t), decreases as a power law. In addition, the numerical findings are consistent with the predictions of the scaling theories proposed by Carnevale et al. [Phys. Rev. Lett. 66, 2735 (1991)] and Weiss and McWilliams [Phys. Fluids A 5, 608 (1993)]. We also obtain new evidence for a self-similar distribution of vortex radii and circulations, that suggests the possibility of a generic statistical behavior of the decaying phase of two-dimensional turbulence at high Reynolds number.

Bracco, A.; McWilliams, J. C.; Murante, G.; Provenzale, A.; Weiss, J. B.

2000-11-01

450

Two-dimensional Simulations of Correlation Reflectometry in Fusion Plasmas

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

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

2001-07-05

451

Tunable refraction in a two dimensional quantum metamaterial

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

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

2012-08-22

452

Transport behavior of water molecules through two-dimensional nanopores

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

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

2014-11-14

453

Automatic measurement method of two-dimensional complex geometric features

NASA Astrophysics Data System (ADS)

To realize automatic measurement of two-dimensional complex geometric features on parts with high-precision, the characteristics and advantages of five types of machine vision measurement methods are analyzed. The technological challenges that each method faces in dealing with high-precise automatic measurement of complex geometric features are indicated. To solve the problem, a machine vision measurement method with cooperation of multi field of view, which has a hierarchical structure, is proposed. Its principle and procedures are introduced. The experimental results show that the relative error is less than 0.025% using the method to gauge conventional scale parts. Its outstanding advantage is that the measuring accuracy is NOT influenced by ambient temperature and the precision of machine systems compared with traditional CMM. Therefore, it is an effective method that can be applied in industrial spot to automatically measure normal and large scale two-dimensional complex geometric characteristics with high-precision.

He, Boxia; He, Yong; Ren, Fu-long; Xue, Rong

2013-01-01

454

Two-dimensional time dependent Riemann solvers for neutron transport

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

Brunner, Thomas A. [Sandia National Laboratories, P.O. Box 5800, Albuquerque, NM 87185-1186 (United States)]. E-mail: tabrunn@sandia.gov; Holloway, James Paul [Department of Nuclear Engineering and Radiological Sciences, University of Michigan, Ann Arbor, MI 48109-2014 (United States)

2005-11-20

455

Multiple Potts models coupled to two-dimensional quantum gravity

NASA Astrophysics Data System (ADS)

We perform Monte Carlo simulations using the Wolff cluster algorithm of multiple q=2, 3, 4 state Potts models on dynamical phi-cubed graphs of spherical topology in order to investigate the c>1 region of two-dimensional quantum gravity. Contrary to naive expectation we find no obvious signs of pathological behaviour for c>1. We discuss the results in the light of suggestions that have been made for a modified DDK ansatz for c>1.

Baillie, C. F.; Johnston, D. A.

1992-07-01

456

Acousto-optic efficiency of two-dimensional photonic crystals

NASA Astrophysics Data System (ADS)

The Bragg regime of the acousto-optic (AO) interaction in two-dimensional (2D) photonic crystals (PhCs) is considered. Approximate formulas for the AO figures of merit of PhCs are obtained and their frequency dependences for 2D PhC of the Si-SiO2 system are calculated. It is shown that the figures of merit of a composite PhC can exceed the values of these parameters for the components.

Pyatakova, Z. A.; Belokopytov, G. V.

2011-01-01

457

Two-dimensional black hole and singularities of CY manifolds

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

458

A Calculation Procedure for Two-Dimensional Elliptic Situations

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

Suhas Patankar

1981-01-01

459

Modeling and Simulating for Two Dimensional Infrared Photonic Crystal Devices

In order to design infrared devices efficiently, dispersive properties of two dimensional photonic crystal is studied in this paper. A model of eigenfrequencies is created by combining the variational expression with the conformal finite-difference time-domain (C-FDTD) technique. Useful data obtained by presentation can be applied to the analysis of the dispersion curves and design of the near-infrared waveguides.

Hong-Xing Zheng; Dao-Yin Yu

2004-01-01

460

Two-dimensional process simulation using verified phenomenological models

Two-dimensional (2-D) effects are becoming increasingly important in the diffusion of impurities in submicrometer silicon devices. The authors describe a 2-D process simulator, PREDICT2, that handles implant damage effects, annealing, and lateral diffusion. PREDICT2 simulates the diffusion of impurities in silicon by using phenomenological diffusion coefficients. The phenomenological models are verified by comparing simulated and experimental results. This approach is

Richard B. Fair; Carl L. Gardner; Michael J. Johnson; Stephen W. Kenkel; Donald J. Rose; John E. Rose; Ravi Subrahmanyan

1991-01-01

461

Suspended two-dimensional electron and hole gases

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

Kazazis, D.; Bourhis, E.; Gierak, J.; Gennser, U. [Laboratoire de Photonique et de Nanostructures, CNRS-LPN, Route de Nozay, 91460 Marcoussis (France); Bourgeois, O. [Institut Néel, CNRS-UJF, BP 166, 38042 Grenoble Cedex 9 (France); Antoni, T. [Laboratoire de Photonique et de Nanostructures, CNRS-LPN, Route de Nozay, 91460 Marcoussis, France and Laboratoire Kastler Brossel, Université Pierre et Marie Curie, 4 Place Jussieu, 75005 Paris (France)

2013-12-04

462

Dilute bose gas in a quasi-two dimensional trap

We investigate the behavior of a dilute quasi two-dimensional, harmonically confined, weakly interacting Bose gas within the finite-temperature Thomas-Fermi approximation. We find that the thermodynamic properties of the system are markedly different for repulsive and attractive interactions. Specifically, in contrast to the repulsive case, there appears to be a phase transition when the atoms interact with an attractive pseudo-potential, in

Brandon Peter van Zyl; Rajat Kumar Bhaduri; Justin Sigetich

2002-01-01

463

Dilute Bose gas in a quasi-two-dimensional trap

We investigate the behaviour of a dilute quasi-two-dimensional, harmonically confined, weakly interacting Bose gas within the finite-temperature Thomas-Fermi approximation. We find that the thermodynamic properties of the system are markedly different for repulsive and attractive interactions. Specifically, in contrast to the repulsive case, there appears to be a phase transition when the atoms interact with an attractive pseudo-potential, in the

Brandon P. van Zyl; R. K. Bhaduri; Justin Sigetich

2002-01-01

464

Two-Dimensional Polynomial Phase Signals: Parameter Estimation and Bounds

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

465

Palmprint Recognition Based on Two-dimensional Fisher Linear Discriminant

(Abstract)In the FLD-based recognition, the within-class scatter matrix is always singular. To overcome the above problem, a new way is to directly project the image matrix based on Two-Dimensional FLD(2DFLD). In PolyU palmprint database, this paper applies PCA, PCA+FLD and 2DFLD to extract the palmprint feature subspace. The images to be recognized are projected on small dimension subspace. A classifier

GUO Jin-yu; YUAN Wei-qi

466

Exact analytic flux distributions for two-dimensional solar concentrators.

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

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

2013-07-01

467

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

468

Glassy behavior of two-dimensional stripe-forming systems

NASA Astrophysics Data System (ADS)

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

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

2013-06-01

469

Two-dimensional color-code quantum computation

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

470

The Study of Two-dimensional Polytropic Stars

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

Sanchari De; Somenath Chakrabarty

2014-04-28

471

Two-dimensional Hazard Estimation for Longevity Analysis

We investigate developments in Danish mortality based on data from 1974–1998 working in a two-dimensional model with chronological time and age as the two dimensions. The analyses are done with non-parametric kernel hazard estimation techniques. The only assumption is that the mortality surface is smooth. Cross-validation is applied for optimal bandwidth selection to ensure the proper amount of smoothing to

Peter Fledelius; Montserrat Guillen; Jens Perch Nielsen; Michael Vogelius

2004-01-01

472

Two-dimensional analysis of a dielectric waveguide mirror

We present the two-dimensional (2-D) mode numerical analysis of a dielectric waveguide mirror with arbitrary structure angle. This work is an extension of a previously reported one-dimensional (1-D) mode analysis which accounts for the transverse variation, in addition to the lateral, of the waveguide modes. Inclusion of the transverse confinement is very important and has a significant effect on the

S. T. Lau; J. M. Ballantyne

1997-01-01

473

Two-dimensional void reconstruction by neutron transmission

Contemporary algebraic reconstruction methods are utilized in investigating the two-dimensional void distribution in a water analog from neutron transmission measurements. It is sought to ultimately apply these techniques to the determination of time-averaged void distribution in two-phase flow systems as well as for potential usage in neutron radiography. Initially, projection data were obtained from a digitized model of a hypothetical

G. D. Zakaib; A. A. Harms; J. Vlachopoulos

1978-01-01

474

Coll Positioning systems: a two-dimensional approach

The basic elements of Coll positioning systems (n clocks broadcasting electromagnetic signals in a n-dimensional space-time) are presented in the two-dimensional case. This simplified approach allows us to explain and to analyze the properties and interest of these relativistic positioning systems. The positioning system defined in flat metric by two geodesic clocks is analyzed. The interest of the Coll systems in gravimetry is pointed out.

Joan Josep Ferrando

2006-01-27

475

Two-dimensional correlation spectroscopy in polymer study

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

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

2015-01-01

476

Two dimensional thermal and charge mapping of power thyristors

NASA Technical Reports Server (NTRS)

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

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

1975-01-01

477

Signal processing and coding for two-dimensional optical storage

The paper introduces the concept of two-dimensional optical storage (TwoDOS). In this concept, bits are written in a broad spiral consisting of a number of bit-rows stacked together in a hexagonal packing. Bits with a value '1' are represented physically as circular pit-holes on the disc, while bits with a value '0' are characterized by the absence of such a

A. H. J. Immink; W. M. J. Coene; A. M. van der Lee; C. Busch; A. P. Hekstra; J. W. M. Bergmans; J. Riani; S. J. L. V. Beneden; T. Conway

2003-01-01

478

Chebyshev approximation for two-dimensional nonrecursive digital filters

The Remez exchange algorithm is extended for the design of two-dimensional nonrecursive digital filters approximating circularly symmetrical low-pass specifications according to a weighted Chebyshev error norm. Since the approximating function does not satisfy the Haar condition, the optimal solution is not necessarily unique and a straightforward extension of the one-dimensional exchange method may fail to converge. It is shown how

Y. Kamp; J. Thiran

1975-01-01

479

Easy interpretation of optical two-dimensional correlation spectra.

We demonstrate that the value of the underlying frequency-frequency correlation function can be retrieved from a two-dimensional optical correlation spectrum through a simple relationship. The proposed method yields both intuitive clues and a quantitative measure of the dynamics of the system. The technique is applied to studying the effects of temperature and phase changes on liquid-glass solvent dynamics. PMID:17072421

Lazonder, Kees; Pshenichnikov, Maxim S; Wiersma, Douwe A

2006-11-15

480

Accelerating universe in two-dimensional noncommutative dilaton cosmology

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

Wontae Kim; Myung Seok Yoon

2006-12-01