Sample records for two-dimensional spatial solitons

  1. Break-up of two-dimensional bright spatial solitons due to transverse modulation instability

    Microsoft Academic Search

    A. V. Mamaev; M. Saffman; A. A. Zozulya

    1996-01-01

    We present the theory and the experimental observation of break-up of two-dimensional bright spatial solitons propagating in a three-dimensional bulk photorefractive nonlinear medium due to transverse modulation instability.

  2. Incoherent collisions between two-dimensional bright steady-state photorefractive spatial screening solitons

    NASA Astrophysics Data System (ADS)

    Shih, Ming-Feng; Segev, Mordechai

    1996-10-01

    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.

  3. Solitons and vortices in two-dimensional discrete nonlinear Schrödinger systems with spatially modulated nonlinearity.

    PubMed

    Kevrekidis, P G; Malomed, Boris A; Saxena, Avadh; Bishop, A R; Frantzeskakis, D J

    2015-04-01

    We consider a two-dimensional (2D) generalization of a recently proposed model [Gligori? et al., Phys. Rev. E 88, 032905 (2013)PLEEE81539-375510.1103/PhysRevE.88.032905], which gives rise to bright discrete solitons supported by the defocusing nonlinearity whose local strength grows from the center to the periphery. We explore the 2D model starting from the anticontinuum (AC) limit of vanishing coupling. In this limit, we can construct a wide variety of solutions including not only single-site excitations, but also dipole and quadrupole ones. Additionally, two separate families of solutions are explored: the usual "extended" unstaggered bright solitons, in which all sites are excited in the AC limit, with the same sign across the lattice (they represent the most robust states supported by the lattice, their 1D counterparts being those considered as 1D bright solitons in the above-mentioned work), and the vortex cross, which is specific to the 2D setting. For all the existing states, we explore their stability (also analytically, when possible). Typical scenarios of instability development are exhibited through direct simulations. PMID:25974604

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

    PubMed

    Yang, Jianke

    2015-02-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

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

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

    PubMed

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

    1998-03-15

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

  7. Quantum fluctuations of one- and two-dimensional spatial dissipative solitons in a nonlinear interferometer: I. One-dimensional dark solitons

    NASA Astrophysics Data System (ADS)

    Nesterov, L. A.; Veretenov, N. A.; Rosanov, N. N.

    2015-05-01

    Quantum fluctuations of one-dimensional dark dissipative solitons sustained by an external radiation in an interferometer with a Kerr nonlinearity are analyzed theoretically. The stability region of classical solitons in this interferometer is studied. The boundaries of this region are determined, and types of excited solitons are classified. Quantum fluctuations of solitons are analyzed in an approximation linear in fluctuations. This problem was solved by linearizing the quantum Langevin equation in a neighborhood of a classical solution for the main type of a soliton from the obtained stability region. The main attention has been paid to studying quantum fluctuations of collective variables of dissipative solitons, namely, the coordinate of the center and momentum of the soliton. Based on the expansion of solutions of the linearized equation in eigenfunctions of the discrete spectrum of this equation, a solution describing quantum fluctuations of these variables is constructed. Using this expansion scheme made it possible to give a rigorous definition of the dissipative soliton position fluctuation operator. The study performed based on this scheme has made it also possible to construct a solution for a one-dimensional dark relaxing dissipative soliton. This soliton generalizes the stationary soliton with allowance for the shift of its center and deformation of its profile followed by the recovery of its initial shape. Average squares of quantum fluctuations of collective variables are calculated. A domain of parameters in which there exist quantum states of solitons with an initially high degree of squeezing with respect to the momentum is found. It is shown that such states are in correspondence with significantly higher velocities of soliton center drift. An experiment that could detect the relative squeezing with respect to the momentum due to the soliton center drift is discussed.

  8. Spatiotemporal surface solitons in two-dimensional photonic lattices

    E-print Network

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

  9. Two-dimensional solitons in irregular lattice systems

    Microsoft Academic Search

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

    2007-01-01

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

  10. Interface solitons in two-dimensional photonic lattices.

    PubMed

    Molina, Mario I; Kivshar, Yuri S

    2008-12-01

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

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

    NASA Astrophysics Data System (ADS)

    Lutsky, Vitaly; Malomed, Boris A.

    2015-02-01

    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.

  12. Finite energy solitons in highly anisotropic two dimensional ferromagnets

    NASA Astrophysics Data System (ADS)

    Ivanov, B. A.; Merkulov, A. Yu.; Stephanovich, V. A.; Zaspel, C. E.

    2006-12-01

    We study the solitons, both topological and nontopological, stabilized by spin precession in a classical two-dimensional lattice model of Heisenberg ferromagnets (FM) with easy-axial anisotropy. These solitons can be regarded as bound states of large number N of magnons, their properties are treated both analytically using a continuous model and numerically for a discrete set of the spins on a square lattice. Both exchange anisotropy with constant ? and single-ion anisotropy with constant K are taken into account. In continuum approximation, both terms give additive contributions to the effective anisotropy constant Keff=K+2? . Beyond this approximation, the properties of solitons depend on the microscopic origin of anisotropy. Solitons can be conveniently classified in the (Keff,N) plane. We have shown that the stable solitons exist for N higher than some critical value Ncr . At N>Ncr and for Keff<0.3J , J is exchange constant, the solitons in FM with any type of anisotropy could be described fairly well by continuum model. The continuum description fails at Keff?(0.3˜0.4)J for exchange anisotropy, but still valid for FM’s with a single-ion anisotropy up to Keff˜0.6J . For higher values of anisotropy, the continuous approach is no more valid and the above discrete model should be used. For Keff>0.6J , in the entire range of N values, we found some fundamentally new soliton features absent in continuum models. Namely, the soliton energy E(N) becomes non-monotonic with the minima at some “magic numbers” of N . In this case, the soliton frequency ?(N)=dE(N)/dN have quite irregular behavior, with step-like jumps and negative values of ? for some N regions. In these regions, the static soliton textures, stabilized by the lattice effects, are present.

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

    NASA Astrophysics Data System (ADS)

    Brazhnyi, Valeriy A.; Malomed, Boris A.

    2011-07-01

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

  14. Two-dimensional gap solitons in elliptic-lattice potentials

    SciTech Connect

    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

    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.

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

    NASA Astrophysics Data System (ADS)

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

    2015-06-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2010-10-01

    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.

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

    SciTech Connect

    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

    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.

  18. Two-dimensional discrete solitons in rotating lattices

    SciTech Connect

    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

    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, 0solitons are considered too, their stability regions being weakly affected by {omega}{ne}0.

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

    NASA Astrophysics Data System (ADS)

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

    2005-01-01

    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.

  20. Solitons in two-dimensional lattices possessing defects, dislocations, and quasicrystal structures

    Microsoft Academic Search

    Mark J. Ablowitz; Boaz Ilan; Ethan Schonbrun; Rafael Piestun

    2006-01-01

    Localized nonlinear modes, or solitons, are obtained for the two-dimensional nonlinear Schrödinger equation with various external potentials that possess large variations from periodicity, i.e., vacancy defects, edge dislocations, and quasicrystal structure. The solitons are obtained by employing a spectral fixed-point computational scheme. Investigation of soliton evolution by direct numerical simulations shows that irregular-lattice solitons can be stable, unstable, or undergo

  1. Two-dimensional steady-state photorefractive screening solitons.

    PubMed

    Shih, M F; Leach, P; Segev, M; Garrett, M H; Salamo, G; Valley, G C

    1996-03-01

    We study experimentally steady-state photorefractive screening solitons trapped in both transverse dimensionsand measure their beam profiles as they propagate throughout the crystal. The solitons are observed to be axially symmetric, and they self-bend. We characterize the soliton dependence on the optical intensity, appliedelectric-field strength, and beam diameter. PMID:19865393

  2. Two-dimensional steady-state photorefractive screening solitons

    NASA Astrophysics Data System (ADS)

    Shih, Ming-Feng; Leach, Patrick; Segev, Mordechai; Garrett, Mark H.; Salamo, Greg J.; Valley, George C.

    1996-03-01

    We study experimentally steady-state photorefractive screening solitons trapped in both transverse dimensions and measure their beam profiles as they propagate throughout the crystal. The solitons are observed to be axially symmetric, and they self-bend. We characterize the soliton dependence on the optical intensity, applied electric-field strength, and beam diameter.

  3. Quadratic spatial soliton interactions

    NASA Astrophysics Data System (ADS)

    Jankovic, Ladislav

    Quadratic spatial soliton interactions were investigated in this Dissertation. The first part deals with characterizing the principal features of multi-soliton generation and soliton self-reflection. The second deals with two beam processes leading to soliton interactions and collisions. These subjects were investigated both theoretically and experimentally. The experiments were performed by using potassium niobate (KNBO 3) and periodically poled potassium titanyl phosphate (KTP) crystals. These particular crystals were desirable for these experiments because of their large nonlinear coefficients and, more importantly, because the experiments could be performed under non-critical-phase-matching (NCPM) conditions. The single soliton generation measurements, performed on KNBO3 by launching the fundamental component only, showed a broad angular acceptance bandwidth which was important for the soliton collisions performed later. Furthermore, at high input intensities multi-soliton generation was observed for the first time. The influence on the multi-soliton patterns generated of the input intensity and beam symmetry was investigated. The combined experimental and theoretical efforts indicated that spatial and temporal noise on the input laser beam induced multi-soliton patterns. Another research direction pursued was intensity dependent soliton routing by using of a specially engineered quadratically nonlinear interface within a periodically poled KTP sample. This was the first time demonstration of the self-reflection phenomenon in a system with a quadratic nonlinearity. The feature investigated is believed to have a great potential for soliton routing and manipulation by engineered structures. A detailed investigation was conducted on two soliton interaction and collision processes. Birth of an additional soliton resulting from a two soliton collision was observed and characterized for the special case of a non-planar geometry. A small amount of spiraling, up to 30 degrees rotation, was measured in the experiments performed. The parameters relevant for characterizing soliton collision processes were also studied in detail. Measurements were performed for various collision angles (from 0.2 to 4 degrees), phase mismatch, relative phase between the solitons and the distance to the collision point within the sample (which affects soliton formation). Both the individual and combined effects of these collision variables were investigated. Based on the research conducted, several all-optical switching scenarios were proposed.

  4. Two-Dimensional Optical Lattice Solitons in Photovoltaic-Photorefractive Crystals

    NASA Astrophysics Data System (ADS)

    Guo, Jian-Bang; Lu, Ke-Qing; Niu, Ping-Juan; Yu, Li-Yuan; Xing, Hai-Ying

    2012-08-01

    We study two families of two-dimensional bright lattice solitons in photovoltaic-photorefractive crystals. It is shown that self-focusing and self-defocusing lattice solitons are possible only when their power level exceeds a critical threshold. It is found that self-focusing lattice solitons exist not only in the semi-infinite band gap, but also in the first band gap, whereas self-defocusing lattice solitons exist only in the first band gap. The structures of these lattice solitons are also analyzed. Our results indicate that a self-focusing lattice soliton in the semi-infinite band gap is more confined than in the first band gap so its tails in the first band gap occupy many lattice sites; when a self-defocusing lattice soliton is close to the second band, the self-defocusing lattice soliton is more confined so its tails occupy a few lattice sites.

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

    Microsoft Academic Search

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

    1999-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2014-07-01

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

  7. Spatial competition in a two dimensional market

    Microsoft Academic Search

    Paul Jonas I

    1968-01-01

    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

  8. Manakov spatial solitons

    NASA Astrophysics Data System (ADS)

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

    1996-12-01

    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.

  9. Two-dimensional solitons in triangular photonic lattices with parity-time symmetry

    NASA Astrophysics Data System (ADS)

    Wang, Hong; Shi, Shuang; Ren, Xiaoping; Zhu, Xing; Malomed, Boris A.; Mihalache, Dumitru; He, Yingji

    2015-01-01

    We report the existence and stability of two-dimensional (2D) fundamental, dipole-mode, vortex, and multipole solitons in parity-time (PT) symmetric triangular lattices with the Kerr self-focusing nonlinearity. It is demonstrated that the structure of such complex lattice potentials strongly affects the shape of the solitons, enabling the formation of stable out-of-phase dipole and multipole solitons, as well as vortices. The solitons of all these species have their stability regions in the semi-infinite gap. We also identify the point of the PT-symmetry-breaking phase transition in this lattice.

  10. Two-dimensional nonlocal vortices, multipole solitons, and rotating multisolitons in dipolar Bose-Einstein condensates

    NASA Astrophysics Data System (ADS)

    Lashkin, V. M.

    2007-04-01

    We have performed numerical analysis of the two-dimensional (2D) soliton solutions in Bose-Einstein condensates with nonlocal dipole-dipole interactions. For the modified 2D Gross-Pitaevski equation with nonlocal and attractive local terms, we have found numerically different types of nonlinear localized structures such as fundamental solitons, radially symmetric vortices, nonrotating multisolitons (dipoles and quadrupoles), and rotating multisolitons (azimuthons). By direct numerical simulations we show that these structures can be made stable.

  11. Spatiotemporal solitons in the Ginzburg-Landau model with a two-dimensional transverse grating

    NASA Astrophysics Data System (ADS)

    Mihalache, D.; Mazilu, D.; Lederer, F.; Leblond, H.; Malomed, B. A.

    2010-02-01

    We explore families of spatiotemporal dissipative solitons in a model of three-dimensional (3D) laser cavities including a combination of gain, saturable absorption, and transverse grating. The model is based on the complex Ginzburg-Landau equation with the cubic-quintic nonlinearity and a two-dimensional (2D) periodic potential representing the grating. Fundamental and vortical solitons are found in a numerical form as attractors in this model and their stability against strong random perturbations is tested by direct simulations. The fundamental solitons are completely stable while the vortices, built as rhombus-shaped complexes of four fundamental solitons, may be split by perturbations into their constituents separating in the temporal direction. Nevertheless, a sufficiently strong grating makes the vortices practically stable objects.

  12. Statics and dynamics of single-electron solitons in two-dimensional arrays of ultrasmall tunnel junctions

    Microsoft Academic Search

    N. S. Bakhvalov; G. S. Kazacha; K. K. Likharev; S. I. Serdyukova

    1991-01-01

    We have analyzed the distribution and transfer of electric charge in a uniform two-dimensional array of ultrasmall tunnel junctions. The effects can be most adequately described in terms of topological solitons with charge +\\/-e. Field distribution in the soliton, its intrinsic energy, and the energy of interaction between the solitons and array edges have been calculated and compared with those

  13. Charge-soliton transport in two-dimensional arrays of small tunnel junctions

    Microsoft Academic Search

    Akinobu Kanda; Shun-Ichi Kobayashi

    1996-01-01

    We have measured the temperature dependence of charge-soliton transport properties in two-dimensional arrays of highly resistive\\u000a small tunnel junctions. Both in normal and superconducting states, square-root-cusp temperature dependence of the zero-bias\\u000a resistance, which is characteristic of the precursor of the charge Kosterlitz-Thouless (KT) transition, was observed in a\\u000a limited temperature range, although the transition itself did not take place. The

  14. Spatial Solitons in Algaas Waveguides

    NASA Astrophysics Data System (ADS)

    Kang, Jin Ung

    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.

  15. Two-dimensional discrete solitons in dipolar Bose-Einstein condensates

    SciTech Connect

    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

    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.

  16. Multi-Dark Soliton Solutions of the Two-Dimensional Multi-Component Yajima–Oikawa Systems

    NASA Astrophysics Data System (ADS)

    Chen, Junchao; Chen, Yong; Feng, Bao-Feng; Maruno, Ken-ichi

    2015-03-01

    We present a general form of multi-dark soliton solutions of two-dimensional (2D) multi-component soliton systems. Multi-dark soliton solutions of the 2D and 1D multi-component Yajima-Oikawa (YO) systems, which are often called the 2D and 1D multi-component long wave-short wave resonance interaction systems, are studied in detail. Taking the 2D coupled YO system with two short wave and one long wave components as an example, we derive the general N-dark-dark soliton solution in both the Gram type and Wronski type determinant forms for the 2D coupled YO system via the KP hierarchy reduction method. By imposing certain constraint conditions, the general N-dark-dark soliton solution of the 1D coupled YO system is further obtained. The dynamics of one dark-dark and two dark-dark solitons are analyzed in detail. In contrast with bright-bright soliton collisions, it is shown that dark-dark soliton collisions are elastic and there is no energy exchange among solitons in different components. Moreover, the dark-dark soliton bound states including the stationary and moving ones are discussed. For the stationary case, the bound states exist up to arbitrary order, whereas, for the moving case, only the two-soliton bound state is possible under the condition that the coefficients of nonlinear terms have opposite signs.

  17. Two dimensional spatial distortion correction algorithm for scintillation GAMMA cameras

    SciTech Connect

    Chaney, R.; Gray, E.; Jih, F.; King, S.E.; Lim, C.B.

    1985-05-01

    Spatial distortion in an Anger gamma camera originates fundamentally from the discrete nature of scintillation light sampling with an array of PMT's. Historically digital distortion correction started with the method based on the distortion measurement by using 1-D slit pattern and the subsequent on-line bi-linear approximation with 64 x 64 look-up tables for X and Y. However, the X, Y distortions are inherently two-dimensional in nature, and thus the validity of this 1-D calibration method becomes questionable with the increasing distortion amplitude in association with the effort to get better spatial and energy resolutions. The authors have developed a new accurate 2-D correction algorithm. This method involves the steps of; data collection from 2-D orthogonal hole pattern, 2-D distortion vector measurement, 2-D Lagrangian polynomial interpolation, and transformation to X, Y ADC frame. The impact of numerical precision used in correction and the accuracy of bilinear approximation with varying look-up table size have been carefully examined through computer simulation by using measured single PMT light response function together with Anger positioning logic. Also the accuracy level of different order Lagrangian polynomial interpolations for correction table expansion from hole centroids were investigated. Detailed algorithm and computer simulation are presented along with camera test results.

  18. Stable spatial solitons in semiconductor optical amplifiers

    Microsoft Academic Search

    Erdem Ultanir

    2004-01-01

    A spatial soliton is a shape invariant self guided beam of light or a self induced waveguide. Spatial solitons appear as a result of the balance of diffraction and nonlinear focusing in a system. They have been observed in many different conservative media in the last couple of years. Solitons are ubiquitous, because of the probability of using their interactions

  19. Terahertz relativistic spatial solitons in doped graphene metamaterials

    E-print Network

    Haiming Dong; Claudio Conti; Fabio Biancalana

    2011-07-28

    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.

  20. Observation of self-trapping and rotation of higher-band gap solitons in two-dimensional photonic lattices.

    PubMed

    Xia, Shiqiang; Song, Daohong; Zong, Yuanyuan; Tang, Liqin; Chen, Zhigang

    2015-02-23

    We demonstrate self-trapping and rotation of higher-band dipole and quadruple-like gap solitons by single-site excitation in a two-dimensional square photonic lattice under self-focusing nonlinearity. Experimental results show that the second-band dipole gap solitons reside in the first photonic (Bragg reflection) gap, whereas the quadruple-like gap solitons are formed in an even higher photonic gap, resulting from modes of the third-band. Moreover, both dipole and quadruple-like gap solitons exhibit dynamical rotation around the lattice principle axes and the direction of rotation is changing periodically during propagation, provided that they are excited under appropriate initial conditions. In the latter case, the nonlinear rotation is accompanied by periodic transitions between quadruple and doubly-charged vortex states. Our numerical simulations find good agreement with the experimental observations. PMID:25836476

  1. Two-dimensional intra-band solitons in lattice potentials with local defects and self-focusing nonlinearity

    E-print Network

    Zeng, Jianhua

    2013-01-01

    It is commonly known that stable bright solitons in periodic potentials, which represent gratings in photonics/plasmonics, or optical lattices in quantum gases, exist either in the spectral semi-infinite gap (SIG) or in finite bandgaps. Using numerical methods, we demonstrate that, under the action of the cubic self-focusing nonlinearity, defects in the form of "holes" in two-dimensional (2D) lattices support continuous families of 2D solitons \\textit{embedded} into the first two Bloch bands of the respective linear spectrum, where solitons normally do not exist. The two families of the \\textit{embedded defect solitons} (EDSs) are found to be continuously linked by the branch of \\textit{gap defect solitons} (GDSs) populating the first finite bandgap. Further, the EDS branch traversing the first band links the GDS family with the branch of regular defect-supported solitons populating the SIG. Thus, we construct a continuous chain of regular, embedded, and gap-mode solitons ("superfamily") threading the entire ...

  2. Band-gap boundaries and fundamental solitons in complex two-dimensional nonlinear lattices

    SciTech Connect

    Ablowitz, Mark J.; Antar, Nalan; Bakirtas, Ilkay; Ilan, Boaz [Department of Applied Mathematics, University of Colorado, Colorado 80309-0526 (United States); Istanbul Technical University, Maslak 34469, Istanbul (Turkey); School of Natural Sciences, University of California at Merced, Merced, California 95344 (United States)

    2010-03-15

    Nonlinear Schroedinger (NLS) equation with external potentials (lattices) possessing crystal and quasicrystal structures are studied. The fundamental solitons and band gaps are computed using a spectral fixed-point numerical scheme. Nonlinear and linear stability properties of the fundamental solitons are investigated by direct simulations and the linear stability properties of the fundamental solitons are confirmed by analysis the linearized eigenvalue problem.

  3. Spatial solitons in periodic nanostructures

    SciTech Connect

    Gorbach, A. V.; Skryabin, D. V. [Department of Physics, Centre for Photonics and Photonic Materials, University of Bath, Bath BA2 7AY (United Kingdom)

    2009-05-15

    We present the first-principles theory of the existence and stability of TE and TM spatial solitons in a subwavelength periodic semiconductor-dielectric structure. We have found that for the wavelength of 1550 nm and the interface separation close to and less than 100 nm the band structure of the linear TE and TM waves becomes similar to the band structure of a homogeneous medium. The properties of TE solitons change accordingly. However, the transverse profiles of the TM solitons continue to reflect the subwavelength geometry of the structure and develop dominant intensity peaks inside the low-index dielectric slots. Our stability analysis based on the linearized Maxwell equations indicates that the nonlinear TM waves can be approximated as the evanescently coupled modes of the slot waveguides with the low-index dielectric core and the high-index semiconductor cladding. Transition to the regime where the slot waveguides start to determine properties of TM waves is associated with the so-called Brewster condition.

  4. Luminescence-induced photorefractive spatial solitons

    NASA Astrophysics Data System (ADS)

    Fazio, E.; Alonzo, M.; Devaux, F.; Toncelli, A.; Argiolas, N.; Bazzan, M.; Sada, C.; Chauvet, M.

    2010-03-01

    We report the observation of spatial confinement of a pump beam into a photorefractive solitonic channel induced by luminescence [luminescence induced spatial soliton (LISS)]. Trapped beams have been obtained in erbium doped lithium niobate crystals at concentrations as high as 0.7 mol % of erbium. By pumping at 980 nm, erbium ions emit photons at 550 nm by two-step absorption, wavelength which can be absorbed by lithium niobate and originates the photorefractive effect. The luminescence at 550 nm generates at the same time the solitonic channel and the background illumination reaching a steady-state soliton regime.

  5. Directional spatial frequency distribution of two-dimensional signals

    NASA Astrophysics Data System (ADS)

    Hollinberger, David E.; Madhavan, P. G.

    1996-10-01

    The time-frequency analysis techniques developed for 1D time series are extended to determine the spatial frequencies at a specific point on a 2D surface or image. The 2D surface/image is sampled along a number of evenly angularly- spaced axes passing through the point of interest. The time- frequency analysis techniques are then applied to each of the 1D data sets. When taken together, the results from the Directional Spatial Frequency Distribution (DSFD), a 2D plot of spectral energy as a function of spatial frequency and the direction. When the 2D data consists of planar waves, a spatial correlation masking process can be used on the DSFD to produce a localized estimate of spatial frequency and direction of measurement called the Equivalent Planar Wave Sinusoidal Decomposition (EPWSD). The DSFD and EPWSD are calculated for simulated 2D data consisting of sinusoids and chirp signals from single and multiple directions as well as ocean wave measurements made by an airborne scanning radar altimeter and compared to a standard 2D Fourier transform. It is shown that the EPWSD technique provides a very localized estimate of frequency and direction of arrival even if the frequency is changing rapidly with position.

  6. The interaction of in-band and in-gap lattice soliton trains in optically induced two-dimensional photonic lattices

    NASA Astrophysics Data System (ADS)

    Liu, Sheng; Zhang, Peng; Xiao, Fa-Jun; Gan, Xue-Tao; Zhao, Jian-Lin

    2010-06-01

    We demonstrate the coherent interactions of lattice soliton trains, including in-band solitons (IBSs) and gap soliton trains (GSTs), in optically induced two-dimensional photonic lattices with self-defocusing nonlinearity. It is revealed that the ?-staggered phase structures of the lattice soliton trains will lead to anomalous interactions. Solely by changing their initial separations, the transition between attractive and repulsive interaction forces or reversion of the energy transfer can be obtained. The 'negative refraction' effect of the soliton trains on the interaction is also discussed. Moreover, two interacting IBSs can merge into one GST when attraction or energy transfer happens.

  7. Soliton propagation and interaction on a two-dimensional nonlinear transmission line

    Microsoft Academic Search

    John N. Dinkel; Claude Setzer; Sunil Rawal; Karl E. Lonngren

    2001-01-01

    Solitons that propagate on a one-dimensional nonlinear dispersive transmission line can be described with the Korteweg–deVries (KdV) equation. In two dimensions, the solitons are described with the Kadomtsev–Petviashvilli (KP) equation. Both equations are derived for the two transmission lines.

  8. Directional spatial frequency distribution of two-dimensional signals

    Microsoft Academic Search

    David E. Hollinberger; P. G. Madhavan

    1996-01-01

    The time-frequency analysis techniques developed for 1D time series are extended to determine the spatial frequencies at a specific point on a 2D surface or image. The 2D surface\\/image is sampled along a number of evenly angularly- spaced axes passing through the point of interest. The time- frequency analysis techniques are then applied to each of the 1D data sets.

  9. Direct time integration of Maxwell's equations in two-dimensional dielectric waveguides for propagation and scattering of femtosecond electromagnetic solitons

    NASA Technical Reports Server (NTRS)

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

    1993-01-01

    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.

  10. Vacuum-induced jitter in spatial solitons.

    PubMed

    Nagasako, E; Boyd, R; Agarwal, G S

    1998-08-31

    We perform a calculation to determine how quantum mechanical fluctuations influence the propagation of a spatial soliton through a nonlinear material. To do so, we derive equations of motion for the linearized operators describing the deviation of the soliton position and transverse momentum from those of a corresponding classical solution to the nonlinear wave equation, and from these equations we determine the quantum uncertainty in the soliton position and transverse momentum. We find that under realistic laboratory conditions the quantum uncertainty in position is several orders of magnitude smaller the classical width of the soliton. This result suggests that the reliability of photonic devices based on spatial solitons is not compromised by quantum fluctuations. PMID:19384358

  11. Spatial solitons rays in periodic optical lattices

    E-print Network

    Ramaz Khomeriki; Jerome Leon

    2009-09-17

    The light ray of a spatial soliton in an optical film whose refractive index is smoothly modulated (wavelength much larger than the typical soliton width) in both spatial directions is shown to possess chaotic regimes for which the propagation is erratic. This is interpreted as a parametric driven pendulum, obtained by a new perturbative approach of the Maxwell equation. These findings are then demonstrated to compare well to the eikonal law of light ray propagation (nonlinearity compensates diffraction).

  12. Watermarking in the space\\/spatial-frequency domain using two-dimensional Radon-Wigner distribution

    Microsoft Academic Search

    Srdjan Stankovic ´; Igor Djurovic; Ioannis Pitas

    2001-01-01

    A two-dimensional (2-D) signal with a variable spatial frequency is proposed as a watermark in the spatial domain. This watermark is characterized by a linear frequency change. It can be efficiently detected by using 2-D space\\/spatial-frequency distributions. The projections of the 2-D Wigner distribution-the 2-D Radon-Wigner distribution, are used in order to emphasize the watermark detection process. The watermark robustness

  13. Stability of two-dimensional gap solitons in periodic potentials: beyond the fundamental modes.

    PubMed

    Dror, Nir; Malomed, Boris A

    2013-06-01

    Gross-Pitaevskii or nonlinear-Schrödinger equations with a sinusoidal potential is commonly used to describe nonlinear periodic media, such as photonic lattices in optics and Bose-Einstein condensates (BECs) loaded into optical lattices (OLs). Previous studies have shown that the 2D version of this equation, with the self-focusing (SF) nonlinearity, supports stable solitons in the semi-infinite gap. It is known, too, that under both the self-defocusing (SDF) and SF nonlinearities, several families of gap solitons (GSs) exist in finite bandgaps. Here, we investigate the stability of 2D dipole-mode GS families, via the computation of their linear-stability eigenvalues and direct simulations of the perturbed evolution. We demonstrate that, under the SF nonlinearity, one species of dipole GSs is stable in a part of the first finite bandgap, provided that the OL depth exceeds a threshold value, while other dipole and multipole modes are unstable in that case. Bidipole bound states (vertical, horizontal, and diagonal), as well as square- and rhombic-shaped vortices and quadrupoles, built of stable fundamental dipoles, are stable too. Under the SDF nonlinearity, the family of dipole solitons is shown to be stable in a part of the second finite bandgap. Transformations of unstable dipole GSs are studied by means of direct simulations. Direct simulations are also performed to investigate the stability of other GS families, in the first and second bandgaps, under both types of the nonlinearity. In particular, "tripole" solitons, sustained in the second bandgap under the action of the SF nonlinearity, demonstrate stable behavior in the course of long propagation, in a certain region within the bandgap. PMID:23848798

  14. Formation of complex two-dimensional dissipative solitons via spontaneous symmetry breaking

    NASA Astrophysics Data System (ADS)

    Skarka, V.; Aleksi?, N. B.; Leki?, M.; Aleksi?, B. N.; Malomed, B. A.; Mihalache, D.; Leblond, H.

    2014-08-01

    We propose a complex Ginzburg-Landau equation (CGLE) with localized linear gain as a two-dimensional model for pattern formation proceeding via spontaneous breaking of the axial symmetry. Starting from steady-state solutions produced by an extended variational approximation, simulations of the CGLE generate a vast class of robust solitary structures. These are varieties of asymmetric rotating vortices carrying the topological charge (TC), and four- to ten-pointed revolving stars, whose angular momentum is decoupled from the TC. The four- and five-pointed stars feature a cyclic change of their structure in the course of the rotation.

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

    PubMed

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

    2014-12-01

    We introduce a 2D network built of PT-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 PT-symmetric dual-core waveguides embedded into a photonic crystal. The system supports PT-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 PT-symmetric states, unstable OnVs do not blow up, but spontaneously rebuild themselves into stable FSs. PMID:25606899

  16. Two-dimensional s-polarized solitary waves in plasmas. II. Stability, collisions, electromagnetic bursts, and post-soliton evolution

    SciTech Connect

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

    2011-09-15

    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.

  17. Two-dimensional single-pixel imaging by cascaded orthogonal line spatial modulation.

    PubMed

    Winters, David G; Bartels, Randy A

    2015-06-15

    Two-dimensional (2D) images are taken using a single-pixel detector by temporally multiplexing spatial frequency projections from orthogonal, time varying spatial line modulation gratings. Unique temporal frequencies are applied to each point in 2D space, applying a continuous spread of frequencies to one dimension, and an offset frequency applied to each line in the orthogonal dimension. The object contrast information can then be recovered from the electronic spectrum of the single pixel, and through simple processing be reformed into a spatial image. PMID:26076259

  18. Design of a microfluidic device for comprehensive spatial two-dimensional liquid chromatography.

    PubMed

    Wouters, Bert; De Vos, Jelle; Desmet, Gert; Terryn, Herman; Schoenmakers, Peter J; Eeltink, Sebastiaan

    2015-04-01

    This study discusses the design aspects for the construction of a microfluidic device for comprehensive spatial two-dimensional liquid chromatography. In spatial two-dimensional liquid chromatography each peak is characterized by its coordinates in the plane. After completing the first-dimension separation all fractions are analyzed in parallel second-dimension separations. Hence, spatial two-dimensional liquid chromatography potentially provides much higher peak-production rates than a coupled column multi-dimensional liquid chromatography approach in which the second-dimension analyses are performed sequentially. A chip for spatial two-dimensional liquid chromatography has been manufactured from cyclic olefin copolymer and features a first-dimension separation channel and 21 parallel second-dimension separation channels oriented perpendicularly to the former. Compartmentalization of first- and second-dimension developments by physical barriers allowed for a preferential flow path with a minimal dispersion into the second-dimension separation channels. To generate a homogenous flow across all the parallel second-dimension channels, a radially interconnected flow distributor containing two zones of diamond-shaped pillars was integrated on-chip. A methacrylate ester based monolithic stationary phase with optimized macroporous structure was created in situ in the confines of the microfluidic chip. In addition, the use of a photomask was explored to localize monolith formation in the parallel second-dimension channels. Finally, to connect the spatial chip to the liquid chromatography instrument, connector ports were integrated allowing the use of Viper fittings. As an alternative, a chip holder with adjustable clasp locks was designed that allows the clamping force to be adjusted. PMID:25598051

  19. Spatial storage of discrete dark solitons

    NASA Astrophysics Data System (ADS)

    Martínez, Alejandro J.; Zárate, Yair

    2015-04-01

    The interaction between a mobile discrete dark soliton (DDS) and impurities in one-dimensional nonlinear (Kerr) photonic lattices is studied. We found that the scattering is an inelastic process where the DDS can be reflected or transmitted depending on its transversal speed and the strength of the impurities. In particular, in the reflection regime, the DDS increases its transversal speed after each scattering. A method for spatial storage of DDS solutions using two impurities is discussed, where the soliton can be trapped within a storage region until it reaches the critical speed needed to be transmitted. We show numerically, that this method allows the storage of multiple DDSs simultaneously.

  20. An algebraic grid generation technique for time-varying two-dimensional spatial domains

    NASA Astrophysics Data System (ADS)

    Yang, S.-L.; Shih, T. I.-P.

    1986-05-01

    Extending the two-boundary technique of Smith (1980) so that the grid points can move in the spatial domains in addition to nonuniform distribution, an efficient and versatile algebraic technique for generating grid points in irregularly shaped and time-varying spatial domains is presented. The present six-step method is demonstrated by generating grid points inside one of the combustion chambers of a motored two-dimensional rotary engine, and obtaining numerical solutions for the flow field inside one the the combustion chambers.

  1. Optical generation of a spatially variant two-dimensional lattice structure by using a phase only spatial light modulator

    SciTech Connect

    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

    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.

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

    PubMed Central

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

    2015-01-01

    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

  3. The Effects of Two-Dimensional Stimuli and Three-Dimensional Stereoptic Stimuli on Spatial Representation in Drawings

    ERIC Educational Resources Information Center

    McGraw, Tammy M.

    2004-01-01

    Despite the developing infusion of three-dimensional, technological imagery, little has been done to explain the effects of two-dimensional versus three-dimensional imagery on the learning process. This study examined the effects of two-dimensional stimuli and three-dimensional stereoptic stimuli on spatial representation in drawings. A scene was…

  4. Stable mode sorting by two-dimensional parity of photonic transverse spatial states.

    PubMed

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

    2009-02-16

    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(l)(p) modes depending upon whether they have an even or odd value of their orbital angular momentum l. 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 Poincar e sphere of first-order transverse modes. PMID:19219146

  5. Two-dimensional-spatial distribution measurement of electron temperature and plasma density in low temperature plasmas

    SciTech Connect

    Kim, Young-Cheol [Department of Nanoscale Semiconductor Engineering, Hanyang University, 17 Haengdang-dong, Seongdong-gu, Seoul 133-791 (Korea, Republic of); Jang, Sung-Ho; Oh, Se-Jin; Lee, Hyo-Chang; Chung, Chin-Wook [Department of Electrical Engineering, Hanyang University, 17 Haengdang-dong, Seongdong-gu, Seoul 133-791 (Korea, Republic of)

    2013-05-15

    A real-time measurement method for two-dimensional (2D) spatial distribution of the electron temperature and plasma density was developed. The method is based on the floating harmonic method and the real time measurement is achieved with little plasma perturbation. 2D arrays of the sensors on a 300 mm diameter wafer-shaped printed circuit board with a high speed multiplexer circuit were used. Experiments were performed in an inductive discharge under various external conditions, such as powers, gas pressures, and different gas mixing ratios. The results are consistent with theoretical prediction. Our method can measure the 2D spatial distribution of plasma parameters on a wafer-level in real-time. This method can be applied to plasma diagnostics to improve the plasma uniformity of plasma reactors for plasma processing.

  6. Fast Transient And Spatially Non-Homogenous Accident Analysis Of Two-Dimensional Cylindrical Nuclear Reactor

    SciTech Connect

    Yulianti, Yanti [Dept. of Physics, Universitas Lampung (UNILA), Jl. Sumantri Brojonegor No.1 Bandar Lampung (Indonesia); Dept. of Physics, Institut Teknologi Bandung (ITB), Jl. Ganesha 10 Bandung (Indonesia); Su'ud, Zaki; Waris, Abdul; Khotimah, S. N. [Dept. of Physics, Institut Teknologi Bandung (ITB), Jl. Ganesha 10 Bandung (Indonesia); Shafii, M. Ali [Dept. of Physics, Institut Teknologi Bandung (ITB), Jl. Ganesha 10 Bandung (Indonesia); Dept. of Physics, Universitas Andalas (UNAND), Kampus Limau Manis, Padang, Sumatera Barat (Indonesia)

    2010-12-23

    The research about fast transient and spatially non-homogenous nuclear reactor accident analysis of two-dimensional nuclear reactor has been done. This research is about prediction of reactor behavior is during accident. In the present study, space-time diffusion equation is solved by using direct methods which consider spatial factor in detail during nuclear reactor accident simulation. Set of equations that obtained from full implicit finite-difference discretization method is solved by using iterative methods ADI (Alternating Direct Implicit). The indication of accident is decreasing macroscopic absorption cross-section that results large external reactivity. The power reactor has a peak value before reactor has new balance condition. Changing of temperature reactor produce a negative Doppler feedback reactivity. The reactivity will reduce excess positive reactivity. Temperature reactor during accident is still in below fuel melting point which is in secure condition.

  7. Fast Transient And Spatially Non-Homogenous Accident Analysis Of Two-Dimensional Cylindrical Nuclear Reactor

    NASA Astrophysics Data System (ADS)

    Yulianti, Yanti; Su'ud, Zaki; Waris, Abdul; Khotimah, S. N.; Shafii, M. Ali

    2010-12-01

    The research about fast transient and spatially non-homogenous nuclear reactor accident analysis of two-dimensional nuclear reactor has been done. This research is about prediction of reactor behavior is during accident. In the present study, space-time diffusion equation is solved by using direct methods which consider spatial factor in detail during nuclear reactor accident simulation. Set of equations that obtained from full implicit finite-difference discretization method is solved by using iterative methods ADI (Alternating Direct Implicit). The indication of accident is decreasing macroscopic absorption cross-section that results large external reactivity. The power reactor has a peak value before reactor has new balance condition. Changing of temperature reactor produce a negative Doppler feedback reactivity. The reactivity will reduce excess positive reactivity. Temperature reactor during accident is still in below fuel melting point which is in secure condition.

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

    PubMed

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

    2015-01-01

    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

  9. Multifrequency observations of a solar microwave burst with two-dimensional spatial resolution

    SciTech Connect

    Gary, D.E.; Hurford, G.J. (California Institute of Technology, Pasadena (USA))

    1990-09-01

    Frequency-agile interferometry observations using three baselines and the technique of frequency synthesis were used to obtain two-dimensional positions of multiple microwave sources at several frequency ranges in a solar flare. Source size and brightness temperature spectra were obtained near the peak of the burst. The size spectrum shows that the source size decreases rapidly with increasing frequency, but the brightness temperature spectrum can be well-fitted by gyrosynchrotron emission from a nonthermal distribution of electrons with power-law index of 4.8. The spatial structure of the burst showed several characteristics in common with primary/secondary bursts discussed by Nakajima et al. (1985). A source of coherent plasma emission at low frequencies is found near the secondary gyrosynchrotron source, associated with the leader spots of the active region. 37 refs.

  10. Multifrequency observations of a solar microwave burst with two-dimensional spatial resolution

    NASA Technical Reports Server (NTRS)

    Gary, Dale E.; Hurford, G. J.

    1990-01-01

    Frequency-agile interferometry observations using three baselines and the technique of frequency synthesis were used to obtain two-dimensional positions of multiple microwave sources at several frequency ranges in a solar flare. Source size and brightness temperature spectra were obtained near the peak of the burst. The size spectrum shows that the source size decreases rapidly with increasing frequency, but the brightness temperature spectrum can be well-fitted by gyrosynchrotron emission from a nonthermal distribution of electrons with power-law index of 4.8. The spatial structure of the burst showed several characteristics in common with primary/secondary bursts discussed by Nakajima et al. (1985). A source of coherent plasma emission at low frequencies is found near the secondary gyrosynchrotron source, associated with the leader spots of the active region.

  11. On two-dimensional temporal modes in spatially evolving open flows: the flat-plate boundary layer

    Microsoft Academic Search

    Uwe Ehrenstein; François Gallaire

    2005-01-01

    Temporal linear stability modes depending on two space directions are computed for a two-dimensional boundary-layer flow along a flat plate. The spatial structure of each individual temporally stable mode is shown to be reminiscent of the spatial exponential growth of perturbations along the flat plate, as predicted by local analyses. It is shown using an optimal temporal growth analysis, that

  12. Numerical simulation of two-dimensional spatially-developing mixing layers

    NASA Technical Reports Server (NTRS)

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

    1994-01-01

    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.

  13. SOLITONS: Dark photovoltaic spatial solitons in a planar waveguide obtained by proton implantation in lithium niobate

    NASA Astrophysics Data System (ADS)

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

    2008-11-01

    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.

  14. Solitons supported by singular spatial modulation of the Kerr nonlinearity

    NASA Astrophysics Data System (ADS)

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

    2012-02-01

    We introduce a setting based on the one-dimensional nonlinear Schrödinger equation (NLSE) with the self-focusing cubic term modulated by a singular function of the coordinate |x|-?. It may be additionally combined with the uniform self-defocusing (SDF) nonlinear background, and with a similar singular repulsive linear potential. The setting, which can be implemented in optics and Bose-Einstein condensates, aims to extend the general analysis of the existence and stability of solitons in NLSEs. Results for fundamental solitons are obtained analytically and verified numerically. The solitons feature a quasicuspon shape, with the second derivative diverging at the center, and are stable in the entire existence range, which is 0??<1. Dipole (odd) solitons are also found. They are unstable in the infinite domain, but stable in the semi-infinite one. In the presence of the SDF background, there are two subfamilies of fundamental solitons, one stable and one unstable, which exist together above a threshold value of the norm (total power of the soliton). The system, which additionally includes the singular repulsive linear potential, emulates solitons in a uniform space of the fractional dimension, 0two-dimensional extension of the system, based on the quadratic (?(2)) nonlinearity, is also formulated.

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

    E-print Network

    Lansrud, Brian David

    2005-08-29

    ............................................................... 58 x CHAPTER Page III ONE-DIMENSIONAL NUMERICAL RESULTS............................... 62 Introduction to Chapter III ......................................................... 62 Theoretical Results of the One-Dimensional Fourier Analysis..................................171 Introduction to Chapter V ..........................................................171 Fourier Analysis of a Two-Dimensional Multigrid Iterative Method.........................................................173 Two-Dimensional Numerical...

  16. Deflection and trapping of spatial solitons in linear photonic potentials.

    PubMed

    Jisha, Chandroth P; Alberucci, Alessandro; Lee, Ray-Kuang; Assanto, Gaetano

    2013-08-12

    We investigate the dynamics of spatial optical solitons launched in a medium with a finite perturbation of the refractive index. For longitudinally short perturbations of super-Gaussian transverse profile, as the input power varies we observe a transition from a wave-like behavior where solitons break up into multiple fringes to a particle-like behavior where solitons acquire a transverse velocity retaining their shape. For longitudinally long perturbations with an attractive potential solitons get trapped inside the well and propagate with transverse periodic oscillations, resulting in an efficient power-dependent angular steering or deflection. Using the Ehrenfest theorem we derive analytical expressions for soliton trajectory, and achieve excellent agreement between theory and numerical simulations for large powers, that is, narrow solitons. PMID:23938781

  17. Automated estimation of individual conifer tree height and crown diameter via two-dimensional spatial wavelet analysis of lidar data

    Microsoft Academic Search

    Michael J. Falkowski; Alistair M. S. Smith; Andrew T. Hudak; Paul E. Gessler; Lee A. Vierling; Nicholas L. Crookston

    2006-01-01

    We describe and evaluate a new analysis technique, spatial wavelet analysis (SWA), to automatically estimate the location, height, and crown diameter of individual trees within mixed conifer open canopy stands from light detection and ranging (lidar) data. Two-dimensional Mexican hat wavelets, over a range of likely tree crown diameters, were convolved with lidar canopy height models. Identification of local maxima

  18. Two-dimensional encoding scheme for digital spatial domain multiplexed large-scale optical fiber sensor arrays

    Microsoft Academic Search

    Yiqun Hu; Shiping Chen

    1997-01-01

    This paper studies a novel two-dimensional (2-D) encoding scheme to increase the multiplexing capacity of the newly developed digital spatial domain multiplexing technique used for integration of large-scale interferometric fiber-sensor arrays. The feasibility of the scheme is assessed via computer simulation and a preliminary experiment which involved strain measurement at multipositions on a cantilever beam

  19. Collision properties of quasi-one-dimensional spin wave solitons and two-dimensional spin wave bullets

    E-print Network

    Demokritov, S.O.

    in a fiber, electro- magnetic pulses in an artificial nonlinear transmission line, etc. see, e.g., Ref. 2-on collisions of nonlinear spin wave packets based on two different approaches provides a good qualitative-dimensional property. As soon as the nonlinear wave packet becomes two-dimensional ,,de- velops structure along

  20. Waveguides formed by quasi-steady-state photorefractive spatial solitons

    NASA Astrophysics Data System (ADS)

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

    1995-10-01

    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.

  1. Waveguides formed by quasi-steady-state photorefractive spatial solitons.

    PubMed

    Morin, M; Duree, G; Salamo, G; Segev, M

    1995-10-15

    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 longerwavelength 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. PMID:19862252

  2. Spatial-domain design of two-dimensional recursive digital filters

    Microsoft Academic Search

    S. Aly; M. Fahmy

    1980-01-01

    A technique is proposed to design stable two-dimensional (2-D) recursive digital filters that best approximate, in thel_p-sense, a prescribed impulse or step response, using a local state-space model. The Davidon-Fletcher and Powell optimization algorithm is used to minimize the performance measure. Several designs for first-quadrant and asymmetric half-plane filters are solved to illustrate the proposed technique.

  3. Numerical simulation of two dimensional sine-Gordon solitons using modified cubic B-spline differential quadrature method

    NASA Astrophysics Data System (ADS)

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

    2015-01-01

    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.

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

    NASA Astrophysics Data System (ADS)

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

    2015-05-01

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

  5. SOLITONS: Dark spatial optical solitons in planar gradient waveguides in the Z-cut of the 3m symmetry crystals

    NASA Astrophysics Data System (ADS)

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

    2003-11-01

    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.

  6. Spatial vector solitons in a four-level tripod-type atomic system

    SciTech Connect

    Qi Yihong; Huang Ting; Gong Shangqing [Department of Physics, East China University of Science and Technology, Shanghai 200237 (China); Zhou Fengxue; Niu Yueping [Department of Physics, East China University of Science and Technology, Shanghai 200237 (China); State Key Laboratory of High Field Laser Physics, Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Shanghai 201800 (China)

    2011-08-15

    We study the generation of weak-light spatial vector solitons in a cold tripod-type atomic system. The condition of generating spatial vector solitons is discussed by analyzing the linear and nonlinear properties of the system. Due to the balance between the enhanced self-phase and cross-phase modulation of the Kerr nonlinearity and the diffraction effect, two orthogonal polarization components of the weak-light probe field can form various spatial vector solitons in the atomic system, such as bright-bright vector solitons and dark-dark vector solitons. We also demonstrate the possibility of generating Manakov spatial vector solitons in this atomic system.

  7. Oscillatory neck instability of spatial bright solitons in hyperbolic systems.

    PubMed

    Gorza, S-P; Kockaert, P; Emplit, Ph; Haelterman, M

    2009-04-01

    The breakup of spatial bright optical solitons due to oscillatory neck instability is experimentally studied by propagating a laser beam in normally dispersive and self-focusing Kerr media. This intriguing and unusual phenomenon, recently predicted for solitons of the (2+1)-dimensional hyperbolic nonlinear Schrödinger (NLS) equation, is observed in the spatially resolved temporal spectrum. The snake instability that is known to occur in hyperbolic systems is also demonstrated to validate our experimental approach. Our results not only apply to photonics but also to other fields of physics, such as hydrodynamics or plasma physics, in which the hyperbolic NLS equation is used as a canonical model. PMID:19392356

  8. Molecular Framework of a Regulatory Circuit Initiating Two-Dimensional Spatial Patterning of Stomatal Lineage

    PubMed Central

    Rychel, Amanda L.; Garrick, Jacqueline M.; Kawaguchi, Masayoshi; Peterson, Kylee M.; Torii, Keiko U.

    2015-01-01

    Stomata, valves on the plant epidermis, are critical for plant growth and survival, and the presence of stomata impacts the global water and carbon cycle. Although transcription factors and cell-cell signaling components regulating stomatal development have been identified, it remains unclear as to how their regulatory interactions are translated into two-dimensional patterns of stomatal initial cells. Using molecular genetics, imaging, and mathematical simulation, we report a regulatory circuit that initiates the stomatal cell-lineage. The circuit includes a positive feedback loop constituting self-activation of SCREAMs that requires SPEECHLESS. This transcription factor module directly binds to the promoters and activates a secreted signal, EPIDERMAL PATTERNING FACTOR2, and the receptor modifier TOO MANY MOUTHS, while the receptor ERECTA lies outside of this module. This in turn inhibits SPCH, and hence SCRMs, thus constituting a negative feedback loop. Our mathematical model accurately predicts all known stomatal phenotypes with the inclusion of two additional components to the circuit: an EPF2-independent negative-feedback loop and a signal that lies outside of the SPCH•SCRM module. Our work reveals the intricate molecular framework governing self-organizing two-dimensional patterning in the plant epidermis. PMID:26203655

  9. Generation and dynamics of quadratic birefringent spatial gap solitons

    SciTech Connect

    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

    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.

  10. Collective excitations in semiconductor superlattices and plasma modes of a two-dimensional electron gas with spatially modulated charge density

    SciTech Connect

    Eliasson, G.L,

    1987-01-01

    The theory of collective excitations in semiconductor superlattices is formulated by using linear response theory. Different kinds of collective excitations in type I (GaAs-GaAlAs) and type II (GaSb-InAs) superlattices are surveyed. Special attention is paid to the presence of surface and finite-size effects. In calculating the dielectric matrix, the effect of different approximations of the system is discussed. The theory for inelastic length scattering (Raman scattering), and for Electron Energy Loss (EEL) due to collective excitations, is formulated. Calculations for several model systems are presented and the main features of the spectra are discussed. In part II the theory of collective excitations of a two-dimensional electron gas with a spatially periodic equilibrium density is formulated. As a first example a periodic array of two-dimensional electron gas strips with constant equilibrium density is studied. The integral equation that describes the charge fluctuations on the strips is derived and solved numerically. The spatial dependence of the density fluctuation across a single strip can be in the form of either propagating or evanescent waves.

  11. The Effect of Two-dimensional and Stereoscopic Presentation on Middle School Students' Performance of Spatial Cognition Tasks

    NASA Astrophysics Data System (ADS)

    Price, Aaron; Lee, Hee-Sun

    2010-02-01

    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 terms of response accuracy and task completion time. Results show that response accuracy did not differ between the two types of representations while task completion time was significantly greater with the stereoscopic representations. The completion time increased as the number of mental manipulations of 3D objects increased in the tasks. Post-interviews provide evidence that some students continued to think of stereoscopic representations as two-dimensional. Based on cognitive load and cue theories, we interpret that, in the absence of pictorial depth cues, students may need more time to be familiar with stereoscopic representations for optimal performance. In light of these results, we discuss potential uses of stereoscopic representations for science learning.

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

    PubMed

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

    2014-12-15

    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

  13. Soliton gyroscopes in media with spatially growing repulsive nonlinearity

    E-print Network

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

    2013-01-01

    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.

  14. Spatially Averaged Frequency Response Envelopes For One And Two-dimensional Structural Components

    Microsoft Academic Search

    R. S. Langley

    1994-01-01

    Expressions are derived for the envelopes which enclose various spatially averaged frequency response functions. The ultimate aim is to provide a scaling factor which may be applied to the results yielded by Statistical Energy Analysis, Asymptotic Modal Analysis, or Skudrzyk's mean-value method, to convert frequency averaged values to either maximum or minimum response estimates. It is shown that certain semi-empirical

  15. Metamaterials for Remote Generation of Spatially Controllable Two Dimensional Array of Microplasma

    PubMed Central

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

    2014-01-01

    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

  16. Two-dimensional spatial manipulation of microparticles in continuous flows in acoustofluidic systems.

    PubMed

    Gao, Lu; Wyatt Shields, C; Johnson, Leah M; Graves, Steven W; Yellen, Benjamin B; López, Gabriel P

    2015-01-01

    We report a modeling and experimental study of techniques to acoustically focus particles flowing through a microfluidic channel. Our theoretical model differs from prior works in that we solve an approximate 2-D wave transmission model that accounts for wave propagation in both the solid and fluid phases. Our simulations indicate that particles can be effectively focused at driving frequencies as high as 10% off of the resonant condition. This conclusion is supported by experiments on the acoustic focusing of particles in nearly square microchannels, which are studied for different flow rates, driving frequencies and placements of the lead zirconate titanate transducer, either underneath the microchannel or underneath a parallel trough. The relative acoustic potential energy and the resultant velocity fields for particles with positive acoustic contrast coefficients are estimated in the 2-D limit. Confocal microscopy was used to observe the spatial distribution of the flowing microparticles in three dimensions. Through these studies, we show that a single driving frequency from a single piezoelectric actuator can induce the 2-D concentration of particles in a microchannel with a nearly square cross section, and we correlate these behaviors with theoretical predictions. We also show that it is possible to control the extent of focusing of the microparticles, and that it is possible to decouple the focusing of microparticles in the vertical direction from the lateral direction in rectangular channels with anisotropic cross sections. This study provides guidelines to design and operate microchip-based acoustofluidic devices for precise control over the spatial arrangement of microparticles for applications such as flow cytometry and cellular sorting. PMID:25713687

  17. Two-dimensional high spatial-resolution dosimeter using europium doped potassium chloride: a feasibility study

    NASA Astrophysics Data System (ADS)

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

    2014-04-01

    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.

  18. High-spatial-resolution soliton DOFS for smart structures

    NASA Astrophysics Data System (ADS)

    Song, Muping; Tang, Weizhong; Zhou, Wen

    1998-07-01

    From the advantage and defect of current distributed optical- fiber sensors (DOFS) schemes, it could be seen that most of schemes except distributed anti-Stokes Ratio Thermometry (DART) are only possible in experiment, but unpractical. But DART is not able to be used on small and fine things especially for smart structures, because of its poor spatial resolution. As we all know that the relaxation time of Raman scattering is in the femtosecond range, and a optical pulse with width > 1 ps will not receive gain reducing, so the potential spatial resolution of DART can be smaller than 0.1 m, even 1 mm (for a pulse with width < 10 ps). Considering these, we firstly propose a novel scheme of DOFS based on spontaneous Raman back-scattering and the effect of high-order soliton, which uses time-correlated single photon counting as detector. The first-order and high-order solitons' effect in the system are theoretically investigated, and it is found that it is able to improve the spatial resolution observably by using high-order soliton in relatively short sensing distance (< 1 km). In the end, the possibility and difficulties of realizing the system based on present-day level of devices are considered.

  19. Simultaneous compensation for spatial and temporal dispersion of acousto-optical deflectors for two-dimensional scanning with a single prism

    Microsoft Academic Search

    Shaoqun Zeng; Xiaohua Lv; Chen Zhan; Wei R. Chen; Wenhui Xiong; Steven L. Jacques; Qingming Luo

    2006-01-01

    The dispersive nature of the acousto-optical deflector (AOD) presents a challenge to applications of two sequential orthogonal AODs (a two-dimensional AOD) as XY scanners in multiphoton microscopy. Introducing a prism before the two-dimensional (2D) AOD allows both temporal and spatial dispersion to be compensated for simultaneously. A 90fs laser pulse was broadened to 572fs without compensation, and 143fs with compensation.

  20. Effect of four-wave mixing on copropagating spatial solitons

    NASA Astrophysics Data System (ADS)

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

    1996-07-01

    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.

  1. Gray spatial solitons in biased two-photon photovoltaic photorefractive crystals

    NASA Astrophysics Data System (ADS)

    Zhang, Guangyong; Cheng, Yongjin; Luo, Zhongjie; Lv, Tao; Du, Qiujiao

    2010-01-01

    This paper predicts that gray spatial solitons can exist in biased two-photon photovoltaic photorefractive crystals. Under appropriate conditions and in the steady state, the gray spatial solitons solution of the optical evolution equation is obtained. The properties associated with these solitons, such as their intensity profile, intensity full width at half-maximum, width, transverse velocity and phase distribution, are discussed as functions of their normalized intensity and degree of "grayness". Relevant examples are provided.

  2. Spatial solitons in centrosymmetric photorefractive crystals due to the two-photon photorefractive effect

    NASA Astrophysics Data System (ADS)

    Zhan, Kaiyun; Hou, Chunfeng; Tian, Hao; Pu, Shaozhi; Du, Yanwei

    2010-01-01

    We present the evolution equation of one-dimensional spatial solitons in centrosymmetric photorefractive media due to the two-photon photorefractive effect. It is shown theoretically that both dark and bright spatial solitons can exist in two-photon centrosymmetric photorefractive media under steady-state conditions. Moreover, we also investigate the self-deflection of steady-state bright solitons arising from the diffusion effects.

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

    NASA Astrophysics Data System (ADS)

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

    1995-10-01

    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 .

  4. Spatial weak-light solitons in an electro-magnetically induced nonlinear waveguide

    E-print Network

    Tao Hong

    2004-05-22

    We show that a weak probe light beam can form spatial solitons in an electro-magnetically induced transparency (EIT) medium composed of four-level atoms and a coupling light field. We find that the coupling light beam can induce a highly controllable nonlinear waveguide and exert very strong effects on the dynamical behavior of the solitons. Hence, in the EIT medium, it is not only possible to produce spatial solitons at very low light intensities but also simultaneously control these solitons by using the coupling-light-induced nonlinear waveguide.

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

    NASA Astrophysics Data System (ADS)

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

    1996-10-01

    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. .

  6. Spatial control of the competition between self-focusing and de-focusing nonlinearities in one- and two-dimensional systems

    E-print Network

    Hung, Nguyen Viet; Infeld, Eryk; Malomed, Boris A

    2014-01-01

    We introduce a system with competing self-focusing (SF)\\ and de-focusing and (SDF) terms, which have the same scaling dimension. In the one-dimensional (1D) system, this setting is provided by a combination of the SF cubic term multiplied by the delta-function, $\\delta (x)$, and a spatially uniform SDF quintic term. This system gives rise to the most general family of 1D-Townes solitons, the entire family being unstable. However, it is completely stabilized by a finite-width regularization of the $\\delta $-function. The results are produced by means of numerical and analytical methods. We also consider the system with a symmetric pair of regularized $\\delta $-functions, which gives rise to a wealth of symmetric, antisymmetric, and asymmetric solitons, linked by a bifurcation loop, that accounts for the breaking and restoration of the symmetry. Soliton families in 2D versions of both the single- and double-delta-functional systems are also studied. The 1D and 2D settings may be realized for spatial solitons in...

  7. Spatiotemporal electromagnetic soliton and spatial ring formation in nonlinear metamaterials

    SciTech Connect

    Zhang Jinggui; Wen Shuangchun; Xiang Yuanjiang; Wang Youwen; Luo Hailu [Key Laboratory for Micro/Nano Optoelectronic Devices of Ministry of Education, School of Computer and Communication, Hunan University, Changsha 410082 (China)

    2010-02-15

    We present a systematic investigation of ultrashort electromagnetic pulse propagation in metamaterials (MMs) with simultaneous cubic electric and magnetic nonlinearity. We predict that spatiotemporal electromagnetic solitons may exist in the positive-index region of a MM with focusing nonlinearity and anomalous group velocity dispersion (GVD), as well as in the negative-index region of the MM with defocusing nonlinearity and normal GVD. The experimental circumstances for generating and manipulating spatiotemporal electromagnetic solitons can be created by elaborating appropriate MMs. In addition, we find that, in the negative-index region of a MM, a spatial ring may be formed as the electromagnetic pulse propagates for focusing nonlinearity and anomalous GVD; while the phenomenon of temporal splitting of the electromagnetic pulse may appear for the same case except for the defocusing nonlinearity. Finally, we demonstrate that the nonlinear magnetization makes the sign of effective electric nonlinear effect switchable due to the combined action of electric and magnetic nonlinearity, exerting a significant influence on the propagation of electromagnetic pulses.

  8. Exact solutions for bright and dark solitons in spatially inhomogeneous nonlinearity

    NASA Astrophysics Data System (ADS)

    Xie, Qiongtao

    2014-12-01

    We present exact analytical results for bright and dark solitons in a type of one-dimensional spatially inhomogeneous nonlinearity. We show that the competition between a homogeneous self-defocusing (SDF) nonlinearity and a localized self-focusing (SF) nonlinearity supports stable fundamental bright solitons. For a specific choice of the nonlinear parameters, exact analytical solutions for fundamental bright solitons have been obtained. By applying both variational approximation and Vakhitov-Kolokolov stability criterion, it is found that exact fundamental bright solitons are stable. Our analytical results are also confirmed numerically. Additionally, we show that a homogeneous SF nonlinearity modulated by a localized SF nonlinearity allows the existence of exact dark solitons, for certain special cases of nonlinear parameters. By making use of linear stability analysis and direct numerical simulation, it is found that these exact dark solitons are linearly unstable.

  9. Spatial shifts of colliding dark solitons in deformed non-linear Schrödinger models

    NASA Astrophysics Data System (ADS)

    Blas, Harold; Zambrano, Marcos

    2015-07-01

    We derive a closed expression for the spatial shift experienced by a black soliton colliding with a shallow dark soliton in the context of deformed nonlinear Schrödinger (NLS) models. A perturbative scheme is developed based on the expansion parameter 1/(? v)\\ll 1, where v is the velocity of the incoming shallow dark soliton, ? \\equiv 1/\\sqrt{1-{v}2{/v}s2} and vs is the Bogoliubov sound speed, therefore it is not restricted to small deformations of the integrable NLS model. As applications of our formalism we consider the integrable NLS model and the non-integrable cubic-quintic NLS model with non-vanishing boundary conditions. Extensive numerical simulations are performed in order to verify our results. A variant of the analysis for gray–gray soliton collision is discussed regarding a fast broad soliton and a slow thin soliton.

  10. SOLITONS. BREATHERS: Role of the local response of a photorefractive medium in the formation of a spatial screened soliton

    NASA Astrophysics Data System (ADS)

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

    2008-09-01

    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.

  11. Photorefractive bright soliton in erbium doped lithium niobate

    NASA Astrophysics Data System (ADS)

    Pettazzi, Federico; Lehau, Grigore; Alonzo, Massimo; Sada, Cinzia; Bazzan, Marco; Argiolas, Nicola; Mazzoldi, Paolo; Chauvet, Mathieu; Vlad, Valentin I.; Petris, Adrian; Fazio, Eugenio

    2006-04-01

    We present the first investigation of bright screening soliton formation in Erbium doped lithium niobate grown by the Czochrlaski technique (0.7% mol.). We analyse the formation of two-dimensional spatial soliton and study its long term stability. Measurements of photovoltaic current show that presence of erbium in the lattice cause an increase of the current density. Both dynamic of soliton formation and photovoltaic measurements indicates a lower N A content in erbium doped samples compared to undoped samples.

  12. Wireless wafer-type probe system for measurement of two-dimensional plasma parameters and spatial uniformity

    NASA Astrophysics Data System (ADS)

    Kim, Jin-Yong; Oh, Se-Jin; Kim, Young-Cheol; Choi, Ik-Jin; Chung, Chin-Wook

    2013-09-01

    A wireless wafer-type probe system was developed to measure two-dimensional plasma parameters and uniformity. The apparatus uses double probe theory with a harmonic detection method. The plasma parameters, such as the electron temperature, ion density and ion flux, are derived by using the amplitudes of the first and third harmonic currents. The experiment was conducted in an inductively coupled plasma. The measurements of the wireless wafer-type probe were compared with a floating-type Langmuir probe and a similar trend was observed. As the inner and outer antenna current ratio changes, the wireless wafer-type probe was able to measure the evolution of the two-dimensional ion density profiles. Since the wireless wafer-type probe system was electrically isolated and designed to operate stand-alone in the chamber, it can be installed in plasma chambers without any external controllers. This plasma diagnostic system shows promise for processing plasmas.

  13. Effect of long-range spatial correlations on the lifetime statistics of an emitter in a two-dimensional disordered lattice

    NASA Astrophysics Data System (ADS)

    de Sousa, N.; Sáenz, J. J.; García-Martín, A.; Froufe-Pérez, L. S.; Marqués, M. I.

    2014-06-01

    The effect of spatial correlations on the Purcell effect in a bidimensional dispersion of resonant nanoparticles is analyzed. We perform extensive calculations on the fluorescence decay rate of a point emitter embedded in a system of nanoparticles statistically distributed according to a simple two-dimensional lattice-gas model near the critical point. For short-range correlations (high temperature thermalization) the Purcell factors present a long-tailed statistic which evolves towards a bimodal distribution when approaching the critical point where the spatial correlation length diverges. Our results suggest long-range correlations as a possible origin of the large fluctuations of experimental decay rates in disordered metal films.

  14. Scattering due to Schottky barrier height spatial fluctuation on two dimensional electron gas in AlGaN/GaN high electron mobility transistors

    SciTech Connect

    Li, Huijie; Liu, Guipeng, E-mail: liugp@semi.ac.cn; Wei, Hongyuan; Jiao, Chunmei; Wang, Jianxia; Zhang, Heng; Dong Jin, Dong; Feng, Yuxia; Yang, Shaoyan, E-mail: sh-yyang@semi.ac.cn; Wang, Lianshan; Zhu, Qinsheng; Wang, Zhan-Guo [Key Laboratory of Semiconductor Materials Science, Institute of Semiconductors, Chinese Academy of Sciences, P.O. Box 912, Beijing 100083, People's Republic of China and Beijing Key Laboratory of Low Dimensional Semiconductor Materials and Devices, Institute of Semiconductors, Chinese Academy of Sciences, P.O. Box 912, Beijing 100083 (China)] [Key Laboratory of Semiconductor Materials Science, Institute of Semiconductors, Chinese Academy of Sciences, P.O. Box 912, Beijing 100083, People's Republic of China and Beijing Key Laboratory of Low Dimensional Semiconductor Materials and Devices, Institute of Semiconductors, Chinese Academy of Sciences, P.O. Box 912, Beijing 100083 (China)

    2013-12-02

    A scattering mechanism related to the Schottky barrier height (SBH) spatial fluctuation of the two dimensional electron gas (2DEG) in AlGaN/GaN heterostructures is presented. We find that the low field mobility is on the order of 10{sup 4}–10{sup 6} cm{sup 2}/Vs. The 2DEG transport properties are found to be influenced by both the mobility and 2DEG density variations caused by the SBH fluctuation. Our results indicate that a uniform Schottky contact is highly desired to minimize the influence of SBH inhomogeneity on the device performance.

  15. Propagation of spatial optical solitons in a dielectric with adjustable nonlinearity

    SciTech Connect

    Alberucci, A.; Piccardi, A.; Peccianti, M.; Assanto, G. [Nonlinear Optics and OptoElectronics Laboratory (NooEL), University ROMA TRE, Via della Vasca Navale 84, I-00146 Rome (Italy); Kaczmarek, M. [School of Physics and Astronomy, University of Southampton, Southampton SO17 1BJ (United Kingdom)

    2010-08-15

    We investigate spatial optical solitons propagating in a medium with a saturable but adjustable nonlinearity and a fixed degree of nonlocality. We employ nematic liquid crystals in a planar cell with optical properties tuned by an external voltage and solitons excited in the near infrared. We also demonstrate soliton self-bending versus excitation due to nonlinear variations in walk-off. A theoretical model accounting for the longitudinal derivatives is employed to compute the refractive index distribution and is found in excellent agreement with the experimental data.

  16. Spatial distribution clamping of discrete spatial solitons due to three photon absorption in AlGaAs waveguide arrays.

    PubMed

    Hudson, Darren D; Kutz, J Nathan; Schibli, Thomas R; Christodoulides, Demetrios N; Morandotti, Roberto; Cundiff, Steven T

    2012-01-30

    We observe clamping of the output spatial light distribution of a waveguide array. Using a chirped pulse amplifier we reach peak intensities in the waveguides of ~24 GW/cm2. At this level, three photon absorption in the AlGaAs material clamps the discrete spatial soliton to a set distribution. Further increase in intensity does not change the distribution. PMID:22330434

  17. Spatial distribution clamping of discrete spatial solitons due to three photon absorption in AlGaAs waveguide arrays

    E-print Network

    Hudson, Darren D; Schibli, Thomas R; Christodoulides, Demetrios N; Morandotti, Roberto; Cundiff, Steven T

    2011-01-01

    We observe clamping of the output spatial light distribution of a waveguide array. Using a chirped pulse amplifier we reach peak intensities in the waveguides of ~24 GW/cm2. At this level, three photon absorption in the AlGaAs material clamps the discrete spatial soliton to a set distribution. Further increase in intensity does not change the distribution.

  18. Effects of disorder and Coulomb interaction on the spatial dispersion of spin susceptibility in two-dimensional structures

    NASA Astrophysics Data System (ADS)

    Edelstein, Victor M.

    2013-04-01

    The wave-vector- and frequency-dependent spin susceptibility of an interacting disordered two-dimensional electron gas at frequencies near the spin resonance has been considered. It is assumed that the external magnetic field is moderately strong ?-1??c??F and the Coulomb interaction is weak (e2/??)/?c?1 (? stands for the magnetic length). The spin susceptibility has been calculated within the ladder diagram approximation. A way of dealing with the degeneracy of Landau levels has been proposed and a transport-type equation free from the degeneracy indexes has been derived. It has been shown that the resonant part of the spin susceptibility has the form ??(?,q)˜[?-?res-(d'+id'')q2]-1, where in the hydrodynamic limit ?s??1 (?s stands for the Larmour frequency g?BH) and to first order in (e2/??)/?c the imaginary part, which stems from the diffusion of the spin magnetization due to the stochastic scattering on impurities, has a conventional form, d''=(?F?/m)/((?c?)2), while the real part, which characterizes the coherent motion of the spin excitations through the crystal, is d'˜M-1(?s?), where M˜(?e2/?)-1 is the effective mass of the spin excitation in the clean system. Thus, at ?s??1, the disorder strongly impedes the coherent motion of the excitations though it does not forbid it completely. The resonant frequency is unaffected by the Coulomb interaction, ?res=?s, just as in the clean case. The results may be applied to experiments on the spin-flip Raman scattering, where the finite wave-vector susceptibility can be directly measured, as well to the electromagnetic absorption studying by means of a grating superimposed on the structure.

  19. Coherent summation of spatially distorted laser Doppler signals by using a two-dimensional heterodyne detector array

    NASA Technical Reports Server (NTRS)

    Chan, Kin P.; Killinger, Dennis K.

    1992-01-01

    Phase-sensitive coherent summation of individual heterodyne detector array signals was demonstrated 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.

  20. Impacts of elevation data spatial resolution on two-dimensional dam break flood simulation and consequence assessment

    SciTech Connect

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

    2009-01-01

    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.

  1. On the Structure of the Two-Dimensional Spatially Periodic Inner Transition Layers in a Gas-Discharge Plasma

    SciTech Connect

    Voronov, A.Ya. [Russian Federal Nuclear Center, All-Russia Scientific-Research Institute of Experimental Physics, Sarov, Nizhni Novgorod oblast, 607190 (Russian Federation)

    2005-07-01

    We investigate the structure of the spatially periodic inner boundary layers in the plasma of a positive glow-discharge column produced in a long cylindrical tube with an electropositive gas inside. Asymptotic methods, namely, the method of boundary functions, are used to analyze the initial mathematical model. We consider the formation of contrast burst-type structures. We have found all principal terms of the boundary-layer asymptotics of the solution. The results obtained are compared with the available probe measurements of basic physical parameters of ionization waves (strata) in neon at low pressures.

  2. Transformation of the plasmon spectrum in a grating-gate transistor structure with spatially modulated two-dimensional electron channel

    SciTech Connect

    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

    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.

  3. ELECTROMAGNETISM, OPTICS, ACOUSTICS, HEAT TRANSFER, CLASSICAL MECHANICS, AND FLUID DYNAMICS Temporal Behavior of Low-Amplitude Grey Spatial Solitons in Biased Two-Photon Photorefractive Crystals

    Microsoft Academic Search

    Qi-Chang Jiang; Yan-Li Su; Xuan-Mang Ji

    2010-01-01

    The temporal property of grey screening spatial solitons due to two-photon photorefractive effect in low-amplitude regime is analyzed. The results indicate that a broad solitons is generated at the beginning, and as time evolves, the intensity width of grey solitons decreases monotonically to a minimum value toward steady state. In the same propagation time, the FWHM of solitons decreases with

  4. Two-dimensional superresolution multiple-input multiple-output and inverse synthetic aperture radar imaging based on spatial frequency ambiguity resolving

    NASA Astrophysics Data System (ADS)

    Yang, Jianchao; Su, Weimin; Gu, Hong

    2015-01-01

    Combining multiple-input multiple-output (MIMO) radar and inverse synthetic aperture radar (ISAR) techniques can reduce the number of antennas used and shorten the radar integrated time compared with the single-channel ISAR for the same cross-range resolution. In existing MIMO-ISAR processing, the echoes of different sensors are rearranged into an equivalent single-channel ISAR signal. A new method without echo rearrangement is proposed for two-dimensional (2-D) MIMO-ISAR imaging. A 2-D frequency estimation algorithm based on Unitary ESPRIT and projection transformation is used to obtain the spatial and Doppler frequencies of scatterers, and a high cross-range resolution can be achieved. The relationship between the two frequencies is exploited to resolve the ambiguity of spatial frequency. The analysis and simulation results show that, compared with the existing method, the proposed method can decrease the relative rotation angle (or integrated time) required for imaging. Thus, this method is more suitable for imaging targets with limited rotation or high maneuvering.

  5. Exact solutions of the Gross-Pitaevskii equation for stable vortex modes in two-dimensional Bose-Einstein condensates

    SciTech Connect

    Wu Lei; Zhang Jiefang [Institute of Nonlinear Physics, Zhejiang Normal University, Jinhua, Zhejiang 321004 (China); Li Lu [Institute of Theoretical Physics, Shanxi University, Taiyuan, Shanxi 030006 (China); Mihalache, Dumitru [Horia Hulubei National Institute for Physics and Nuclear Engineering, R-077125 Magurele-Bucharest (Romania); Malomed, Boris A. [Department of Physical Electronics, Faculty of Engineering, Tel Aviv University, IL-69978 Tel Aviv (Israel); Liu, W. M. [Institute of Physics, Chinese Academy of Sciences, Beijing 100190 (China)

    2010-06-15

    We construct exact solutions of the Gross-Pitaevskii equation for solitary vortices, and approximate ones for fundamental solitons, in two-dimensional models of Bose-Einstein condensates with a spatially modulated nonlinearity of either sign and a harmonic trapping potential. The number of vortex-soliton (VS) modes is determined by the discrete energy spectrum of a related linear Schroedinger equation. The VS families in the system with the attractive and repulsive nonlinearity are mutually complementary. Stable VSs with vorticity S{>=}2 and those corresponding to higher-order radial states are reported, in the case of the attraction and repulsion, respectively.

  6. Two-dimensional boson model

    Microsoft Academic Search

    Steven A. Moszkowski

    1979-01-01

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

  7. Transverse modulation instability of copropagating light beams and the bright and dark spatial solitons in nonlinear metamaterials

    NASA Astrophysics Data System (ADS)

    Dai, Xiaoyu; Xiang, Yuanjiang; Wen, Shuangchun; Fan, Dianyuan

    2010-08-01

    Through using the standard split-step Fourier method, it is found that the transverse modulation instability (MI)can develop when beams copropagate in the positive- and the negative-index region of the metamaterials (MMs) respectively and it is equivalent with the temporal MI in the case of two pulses copropagate in the anomalous and normal dispersion regions of the optical fibers respectively, which is meaning that bright and dark electromagnetic spatial solitons may generate simultaneously. Furthermore, it is confirmed that the bright and dark electromagnetic spatial solitons may even generate simultaneously when beams copropagate in MM, which is a new way to generate spatial soliton pair for there is only leading to the generation of bright or dark spatial solitons in conventional material when two beams copropagate.

  8. Two dimensional NMR spectroscopy

    SciTech Connect

    Schram, J.; Bellama, J.M.

    1988-01-01

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

  9. June 1, 1999 / Vol. 24, No. 11 / OPTICS LETTERS 759 Spatial optical solitons resulting from multistep cascading

    E-print Network

    a noncentrosymmetric nonlinear medium with a x 2 response. As a first step, the second-harmonic wave with frequency 2vJune 1, 1999 / Vol. 24, No. 11 / OPTICS LETTERS 759 Spatial optical solitons resulting from-order nonlinear cascading processes, second-harmonic generation and sum-frequency mixing. We obtain analytical

  10. Ultra-narrow Bright Spatial Solitons Interacting with Left-handed Surfaces

    E-print Network

    Allan D. Boardman; Larry Velasco; Neil King; Yuriy Rapoport

    2006-03-13

    A vectorial FDTD method is used to present a numerical study of very narrow spatial solitons interacting with the surface of what has become known as a left-handed medium. After a comprehensive discussion of the background and the family of surface modes to be expected on a left-handed material, bounded by dispersion-free right-handed material, it is demonstrated that robust outcomes of the FDTD approach yield dramatic confirmation of these waves. The FDTD results show how the linear and nonlinear surface modes are created and can be tracked in time as they develop. It is shown how they can move backwards, or forwards, depending either upon a critical value of the local nonlinear conditions at the interface, or the ambient linear conditions. Several examples are given to demonstrate the power and versatility of the method, and the sensitivity to the launching conditions.

  11. Entanglement entropy in two dimensional string theory

    E-print Network

    Hartnoll, Sean A

    2015-01-01

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

  12. Topological Solitons in Physics.

    ERIC Educational Resources Information Center

    Parsa, Zohreh

    1979-01-01

    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)

  13. Two-dimensional river modeling

    E-print Network

    Thompson, James Cameron

    1988-01-01

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

  14. Multiscale comparison of spatial patterns using two-dimensional cross-spectral analysis: application to a semi-arid (gapped) landscape

    Microsoft Academic Search

    Nicolas Barbier; Pierre Couteron; Olivier Planchon; Abdoulaye Diouf

    2010-01-01

    Spectral analysis allows the characterization of temporal (1D) or spatial (2D) patterns in terms of their scale (frequency)\\u000a distribution. Cross-spectral analysis can also be used to conduct independent correlation analyses at different scales between\\u000a two variables, even in the presence of a complex superposition of structures, such as structures that are shifted, have different\\u000a scales or have different levels of

  15. CALL FOR PAPERS: Optical solitons

    Microsoft Academic Search

    P. D. Drummond; Marc Haelterman; R. Vilaseca

    2003-01-01

    A topical issue of Journal of Optics B: Quantum and Semiclassical Optics will be devoted to recent advances in optical solitons. The topics to be covered will include, but are not limited to: bulletProperties, control and dynamics of temporal solitons bulletProperties, control and dynamics of spatial solitons bulletCavity solitons in passive and active resonators bulletThree-dimensional spatial solitons bulletDark, bright, grey

  16. Effects of LiDAR-derived, spatially distributed vegetation roughness on two-dimensional hydraulics in a gravel-cobble river at flows of 0.2 to 20 times bankfull

    NASA Astrophysics Data System (ADS)

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

    2014-02-01

    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.

  17. Two-dimensional wind tunnel

    NASA Technical Reports Server (NTRS)

    1982-01-01

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

  18. Cloaking two-dimensional fermions

    SciTech Connect

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

    2011-09-15

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

  19. Soliton ``molecules'': Robust clusters of spatiotemporal optical solitons Lucian-Cornel Crasovan,* Yaroslav V. Kartashov,

    E-print Network

    mechanism for generating clusters which are made of stable fully three-dimensional light bul- lets 11,12 , which allow both, to generate stable fully three-dimensional solitons and to reduce , the structures carrying many interacting individual solitons, recently introduced for two-dimensional solitons

  20. Two-dimensional thermofield bosonization

    SciTech Connect

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

    2005-12-15

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

  1. Two-dimensional flexible nanoelectronics

    NASA Astrophysics Data System (ADS)

    Akinwande, Deji; Petrone, Nicholas; Hone, James

    2014-12-01

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

  2. Two-dimensional Yukawa fluids

    NASA Astrophysics Data System (ADS)

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

    2015-03-01

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

  3. Two-dimensional river modeling 

    E-print Network

    Thompson, James Cameron

    1988-01-01

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

  4. Solitons on Tori and Soliton Crystals

    NASA Astrophysics Data System (ADS)

    Speight, J. M.

    2014-11-01

    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.

  5. Two dimensional bulge disk decomposition

    E-print Network

    Yogesh Wadadekar; Braxton Robbason; Ajit Kembhavi

    1997-05-27

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

  6. Two-Dimensional Photon Model

    NASA Astrophysics Data System (ADS)

    Khodin, Aliaksandr

    2002-05-01

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

  7. Continuously self-focusing and continuously self-defocusing two-dimensional beams in dissipative media

    E-print Network

    Akhmediev, Nail

    Continuously self-focusing and continuously self-defocusing two-dimensional beams in dissipative. These correspond to continuously self-focusing and continuously self-defocusing types of 2D solitons can be found in the literature on this subject 6,7 . In self-focusing conservative media, the main

  8. Spiraling bright spatial solitons formed by the breakup of an optical vortex in a saturable self-focusing medium

    NASA Astrophysics Data System (ADS)

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

    1995-11-01

    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

  9. Applications of two-dimensional infrared spectroscopy.

    PubMed

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

    2015-06-15

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

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

    Microsoft Academic Search

    Katherine E. Aidala

    2006-01-01

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

  11. Turbulent mixing in a two-dimensional jet

    Microsoft Academic Search

    M. S. Uberoi; Param Indar Singh

    1975-01-01

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

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

    NASA Technical Reports Server (NTRS)

    Montgomery, D.; Tappert, F.

    1971-01-01

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

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

    E-print Network

    Kelly, Paul H. J.

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

  14. Matter-wave 2D solitons in crossed linear and nonlinear optical lattices

    E-print Network

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

    2010-11-08

    It is demonstrated the existence of multidimensional matter-wave solitons in a crossed optical lattice (OL) with linear OL in the $x-$direction and nonlinear OL (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. In particular, we show that such crossed linear and nonlinear OL allows to stabilize two-dimensional (2D) 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 (VA), with the Vakhitov-Kolokolov (VK) necessary criterion for stability; and numerically, by using the relaxation method and direct numerical time integrations of the Gross-Pitaevskii equation (GPE). Very good agreement of the results corresponding to both treatments is observed.

  15. Turbulent equipartitions in two dimensional drift convection

    SciTech Connect

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

    1995-07-25

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

  16. Predicting two-dimensional turbulence.

    PubMed

    Cerbus, R T; Goldburg, W I

    2015-04-01

    Prediction is a fundamental objective of science. It is more difficult for chaotic and complex systems like turbulence. Here we use information theory to quantify spatial prediction using experimental data from a turbulent soap film. At high Reynolds number, Re, where a cascade exists, turbulence becomes easier to predict as the inertial range broadens. The development of a cascade at low Re is also detected. PMID:25974576

  17. Modulated transverse off-plane dust-lattice wave packets in hexagonal two-dimensional dusty plasma crystals

    SciTech Connect

    Farokhi, B.; Shahmansouri, M. [Department of Physics, Arak University, Arak P.O. Box 38156-879 (Iran, Islamic Republic of); Kourakis, I. [Department of Physics and Astronomy, Centre for Plasma Physics, Queen's University Belfast, Belfast BT7 1NN Northern Ireland (United Kingdom)

    2009-05-15

    The propagation of nonlinear dust-lattice waves in a two-dimensional hexagonal crystal is investigated. Transverse (off-plane) dust grain oscillatory motion is considered in the form of a backward propagating wave packet whose linear and nonlinear characteristics are investigated. An evolution equation is obtained for the slowly varying amplitude of the first (fundamental) harmonic by making use of a two-dimensional lattice multiple scales technique. An analysis based on the continuum approximation (spatially extended excitations compared to the lattice spacing) shows that wave packets will be modulationally stable and that dark-type envelope solitons (density holes) may occur in the long wavelength region. Evidence is provided of modulational instability and of the occurrence of bright-type envelopes (pulses) at shorter wavelengths. The role of second neighbor interactions is also investigated and is shown to be rather weak in determining the modulational stability region. The effect of dissipation, assumed negligible in the algebra throughout the article, is briefly discussed.

  18. Two-dimensional sensitivity analysis of MIPAS observations.

    PubMed

    Carlotti, M; Magnani, L

    2009-03-30

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

  19. Two dimensional echocardiographic diagnosis of situs

    Microsoft Academic Search

    J C Huhta; J F Smallhorn; F J Macartney

    1982-01-01

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

  20. May 1, 1990 / Vol. 15, No. 9 / OPTICS LETTERS 471 Observation of spatial optical solitons in a nonlinear glass

    E-print Network

    Purdue University

    tofilamentation of the beam and sample breakdown. However,in the two-dimensional case, diffraction and self-focusing only. At this power level (Pt), the induced self-focusing exactly compen- sates for diffraction-photon absorption. Stable self-trapping of a laser beam propagating in two-dimensional space has been predicted

  1. Solitons and ionospheric modification

    NASA Technical Reports Server (NTRS)

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

    1982-01-01

    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.

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

    Microsoft Academic Search

    F. Scarano; B. w. Van Oudheusden

    2003-01-01

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

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

    PubMed

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

    2009-11-01

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

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

    Microsoft Academic Search

    David K. Melgaard; Richard F. Sincovec

    1981-01-01

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

  5. Relativity on two-dimensional spacetimes

    E-print Network

    Do-Hyung Kim

    2013-07-26

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

  6. Mars Pathfinder Two-Dimensional Model

    NSDL National Science Digital Library

    2012-08-03

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

  7. On two-dimensional magnetohydrodynamic turbulence

    Microsoft Academic Search

    A. Pouquet

    1978-01-01

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

  8. Two-dimensional order and disorder thermofields

    SciTech Connect

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

    2006-11-15

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

  9. Two-dimensional photonic band gap crystals

    Microsoft Academic Search

    Cheryl Marie Anderson

    1999-01-01

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

  10. Stability of two-dimensional, controlled, Bose-Einstein coherent states

    NASA Astrophysics Data System (ADS)

    Jovanovi?, D.; Fedele, R.

    2007-12-01

    Two-dimensional stability of a controlled Bose-Einstein condensation state, in the form of a nonlinear Schrödinger soliton [JETP Lett. 80 535 (2004)], is studied for the condensations with both repulsive and attractive inter-atom interactions. The Gross-Pitaevski equation is solved numerically, taking initialy a controlled soliton whose “effective mass” is several times bigger than the critical value for a weak collapse in the absence of a potential well, and allowing for reasonably large errors in the experimental realization of the trapping potential required by the theory. For repulsive and sufficiently weak attractive interactions, the controlled state is shown to remain stable inside a breathing potential well, for a time that is an order of magnitude longer than the characteristic periods of the forced and eigenoscillations of the soliton. The collapse is observed only for attractive interactions, when the nonlinear attraction exceeded the appropriate threshold.

  11. Incoherent solitons in instantaneous nonlocal nonlinear media.

    PubMed

    Cohen, Oren; Buljan, Hrvoje; Schwartz, Tal; Fleischer, Jason W; Segev, Mordechai

    2006-01-01

    We predict random-phase spatial solitons in instantaneous nonlocal nonlinear media. The key mechanism responsible for self-trapping of such incoherent wave packets is played by the nonlocal (rather than the traditional noninstantaneous) nature of the nonlinearity. This kind of incoherent soliton has profoundly different features than other incoherent solitons. PMID:16486207

  12. Two-dimensional phononic crystals: Examples and applications

    NASA Astrophysics Data System (ADS)

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

    2010-08-01

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

  13. Gap solitons due to cascading

    NASA Astrophysics Data System (ADS)

    Kivshar, Yuri S.

    1995-02-01

    It is shown analytically that gap solitons can occur in materials with ?(2) susceptibility due to cascaded second-order nonlinearities. Families of bright and dard spatial gap solitons are described in the framework of asymptotic expansions that are valid, in particular, for nonzero phase mismatch between the first and second harmonics; effective coefficients of self- and cross-phase modulation are calculated.

  14. 3-D Integrated Optical Microcircuits in Lithium Niobate Written by Spatial Solitons

    NASA Astrophysics Data System (ADS)

    Fazio, E.; Chauvet, M.; Vlad, V. I.; Petris, A.; Pettazzi, F.; Coda, V.; Alonzo, M.

    Integrated optical microcircuits are structures based on optical waveguides to confine light and consequently to make it realize operations and functionalities. Consequently, the basic element of any integrated circuit is the waveguide. It is constituted of 3 main spatial regions: the propagating core and the surrounding media, the upper and lower ones. In order to confine light, the propagating core must show a higher refractive index than the surrounding media in order to ensure a total reflection regime of the optical rays trapped inside the core area. Consequently, the propagating light proceeds inside the waveguide with a particular configuration called mode, which means the overall interference between all the trapped waves. According to the refractive index contrast between core and surrounding media and according to the transverse dimension of the waveguide, one or many modes can propagate: however, if there is just one mode or many, the characteristic of every mode is to keep its transverse profile constant along the whole propagation. Thus, the mode is a steady-state solution of the light propagation equation inside the confining structure called eigenstate.

  15. Two-Dimensional Attosecond Electron Wave-Packet Interferometry

    NASA Astrophysics Data System (ADS)

    Xie, Xinhua

    2015-05-01

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

  16. Two-dimensional nonlinear beam shaping.

    PubMed

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

    2012-06-01

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

  17. Detecting disparity in two-dimensional patterns

    Microsoft Academic Search

    Bart Farell

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

  18. Numerical Modelling of the Two-Dimensional

    E-print Network

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

  19. A two-dimensional flame table

    NASA Astrophysics Data System (ADS)

    Daw, Harold A.

    1987-08-01

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

  20. Two Dimensional Quantum Gravity Coupled to Matter

    E-print Network

    R. B. Mann

    1992-06-25

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

  1. Two-Dimensional Turbulence in Magnetized Plasmas

    ERIC Educational Resources Information Center

    Kendl, A.

    2008-01-01

    In an inhomogeneous magnetized plasma the transport of energy and particles perpendicular to the magnetic field is in general mainly caused by quasi two-dimensional turbulent fluid mixing. The physics of turbulence and structure formation is of ubiquitous importance to every magnetically confined laboratory plasma for experimental or industrial…

  2. On the two-dimensional sloshing problem

    PubMed Central

    Kozlov, Vladimir; Kuznetsov, Nikolay; Motygin, Oleg

    2011-01-01

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

  3. Canonical quantization of two-dimensional gravity

    E-print Network

    S. N. Vergeles

    2001-02-01

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

  4. Spontaneous formation and nonequilibrium dynamics of a soliton-shaped Bose-Einstein condensate in a trap

    NASA Astrophysics Data System (ADS)

    Berman, Oleg L.; Kezerashvili, Roman Ya.; Kolmakov, German V.; Pomirchi, Leonid M.

    2015-06-01

    The Bose-stimulated self-organization of a quasi-two-dimensional nonequilibrium Bose-Einstein condensate in an in-plane potential is proposed. We obtained the solution of the nonlinear, driven-dissipative Gross-Pitaevskii equation for a Bose-Einstein condensate trapped in an external asymmetric parabolic potential within the method of the spectral expansion. We found that, in sharp contrast to previous observations, the condensate can spontaneously acquire a solitonlike shape for spatially homogeneous pumping. This condensate soliton performs oscillatory motion in a parabolic trap and, also, can spontaneously rotate. Stability of the condensate soliton in the spatially asymmetric trap is analyzed. In addition to the nonlinear dynamics of nonequilibrium Bose-Einstein condensates of ultracold atoms, our findings can be applied to the condensates of quantum well excitons and cavity polaritons in semiconductor heterostructure, and to the condensates of photons.

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

    PubMed

    Li, Yan; Mei, Jun

    2015-05-01

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

  6. Two-Dimensional Acousto-Optical Spectrum Analyzer

    NASA Technical Reports Server (NTRS)

    Ansari, Homayoon; Lesh, James R.; Metscher, Brian

    1991-01-01

    State-of-the-art two-dimensional acousto-optical spectrum analyzer processes input radio-frequency signal in real time into components in any number of spectral channels up to about 10(Sup5). Input radio-frequency signal to be analyzed launched via transducer into acousto-optical device along x axis. Acousto-optical device becomes Bragg cell. Pulsed plane waves of light from laser aimed at Bragg cell, which spatially modulates phases of plane waves and diffracts waves according to pattern of acoustic signal.

  7. Two-dimensional high temperature strain measurement system

    NASA Technical Reports Server (NTRS)

    Lant, Christian T.; Barranger, John P.

    1989-01-01

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

  8. Coherence Controlled Soliton Interactions Ting-Sen Ku,1

    E-print Network

    response [4]. To support incoherent spatial solitons, the nonlinearity must be noninstantaneous spaced spatial optical solitons as a whole is made partially incoherent. We explain how the character with their coherent nature, and the soliton parameters such as the amplitude, phase, and frequency are well defined

  9. Magnetization study of two dimensional helium three

    NASA Astrophysics Data System (ADS)

    Guo, Lei

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

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

    E-print Network

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

    2013-01-01

    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.

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

    E-print Network

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

    2013-07-09

    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.

  12. Plasmonics with two-dimensional conductors.

    PubMed

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

    2014-03-28

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

  13. Symmetry in two-dimensional gravity

    SciTech Connect

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

    1991-05-30

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

  14. Deeply subrecoil two-dimensional Raman cooling

    SciTech Connect

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

    2004-10-01

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

  15. Two Dimensional Electronic Spectroscopy of Molecular Complexes

    Microsoft Academic Search

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

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

  16. Performance prediction of straight two dimensional diffusers

    NASA Technical Reports Server (NTRS)

    Greywall, M. S.

    1980-01-01

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

  17. Two-dimensional microwave tomographic system

    Microsoft Academic Search

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

    1996-01-01

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

  18. Two-dimensional arrays for medical ultrasound

    Microsoft Academic Search

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

    1991-01-01

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

  19. Two Dimensional Knapsack with Unloading Constraints

    Microsoft Academic Search

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

    2011-01-01

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

  20. Statistical Mechanics of Two-dimensional Foams

    E-print Network

    Marc Durand

    2010-09-07

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

  1. Two-dimensional photonic crystal lasers

    Microsoft Academic Search

    Mitsuru Yokoyama; Masahiro Imada; Susumu Noda

    2002-01-01

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

  2. A Two-Dimensional Photonic Crystal Laser

    Microsoft Academic Search

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

    1999-01-01

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

  3. Two-dimensional position-dependent massive particles: The case of Morse potential

    E-print Network

    Dutra, A de Souza; de Oliveira, J A

    2015-01-01

    In this work we analyze a system consisting in two-dimensional position-dependent massive particles in the presence of a Morse-like potential in two spatial dimensions. We obtain the exact wavefunctions and energies for a complete set of eigenstates for a given dependence of the mass with the spatial variables.

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

    NASA Technical Reports Server (NTRS)

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

    1986-01-01

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

  5. High speed two-dimensional optical beam position detector

    SciTech Connect

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

    2011-07-15

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

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

    SciTech Connect

    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

    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.

  7. Targeted transfer of solitons in continua and lattices.

    PubMed

    Nistazakis, H E; Kevrekidis, P G; Malomed, B A; Frantzeskakis, D J; Bishop, A R

    2002-07-01

    We propose a robust mechanism of targeted energy transfer along a line, as well as on a surface, in the form of transport of coherent solitary-wave structures, driven by a moving, spatially localized external ac field ("arm") in a lossy medium. The efficiency and robustness of the mechanism are demonstrated analytically and numerically in terms of the nonlinear Schrödinger (NLS) equation, and broad regions of stable operation are identified in the model's parameter space. Direct simulations show that the driving arm can manipulate solitons equally well in a lattice NLS model. A salient feature, which is revealed by simulations and explained analytically, is a resonant character of the operation of the driving arm in the lattice medium, both integer and fractional resonances being identified. Numerical experiments also demonstrate that the same solitary-wave-transport mechanism works well in two-dimensional lattice media. PMID:12241419

  8. Stability of Two-Dimensional Soft Quasicrystals

    E-print Network

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

    2015-05-26

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

  9. Intermittency in forced two-dimensional turbulence

    E-print Network

    W. Brent Daniel; Maarten A. Rutgers

    2000-05-03

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

  10. Gauge equivalence in two-dimensional gravity

    SciTech Connect

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

    1993-08-15

    Two-dimensional quantum gravity is identified as a second-class system which we convert into a first-class system via the Batalin-Fradkin (BF) procedure. Using the extended phase space method, we then formulate the theory in the most general class of gauges. The conformal gauge action suggested by David, Distler, and Kawai is derived from first principles. We find a local, light-cone gauge action whose Becchi-Rouet-Stora-Tyutin invariance implies Polyakov's curvature equation [partial derivative][sub [minus

  11. Two-dimensional signatures for molecular identification

    NASA Astrophysics Data System (ADS)

    Qazi, Muhammad; Vogt, Thomas; Koley, Goutam

    2008-03-01

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

  12. Reproducibility of two-dimensional exercise echocardiography.

    PubMed

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

    1989-10-01

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

  13. Two-dimensional phonon transport in graphene.

    PubMed

    Nika, Denis L; Balandin, Alexander A

    2012-06-13

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

  14. Spectral tunneling of lattice nonlocal solitons

    SciTech Connect

    Kartashov, Yaroslav V.; Torner, Lluis [ICFO-Institut de Ciencies Fotoniques, and Universitat Politecnica de Catalunya, Mediterranean Technology Park, 08860 Castelldefels (Barcelona) (Spain); Vysloukh, Victor A. [Departamento de Fisica y Matematicas, Universidad de las Americas-Puebla, Santa Catarina Martir, 72820 Puebla (Mexico)

    2010-07-15

    We address spectral tunneling of walking spatial solitons in photorefractive media with nonlocal diffusion component of the nonlinear response and an imprinted shallow optical lattice. In contrast to materials with local nonlinearities, where solitons traveling across the lattice close to the Bragg angle suffer large radiative losses, in photorefractive media with diffusion nonlinearity resulting in self-bending, solitons survive when their propagation angle approaches and even exceeds the Bragg angle. In the spatial frequency domain this effect can be considered as tunneling through the band of spatial frequencies centered around the Bragg frequency where the spatial group velocity dispersion is positive.

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

    NASA Astrophysics Data System (ADS)

    Georgiev, Georgi; Berns, David; Cebe, Peggy

    2001-03-01

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

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

    PubMed

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

    2014-12-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

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

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

    NASA Astrophysics Data System (ADS)

    Ercan, Ali; Kavvas, M. Levent

    2015-07-01

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

  19. Two-dimensional fourier transform spectrometer

    DOEpatents

    DeFlores, Lauren; Tokmakoff, Andrei

    2013-09-03

    The present invention relates to a system and methods for acquiring two-dimensional Fourier transform (2D FT) spectra. Overlap of a collinear pulse pair and probe induce a molecular response which is collected by spectral dispersion of the signal modulated probe beam. Simultaneous collection of the molecular response, pulse timing and characteristics permit real time phasing and rapid acquisition of spectra. Full spectra are acquired as a function of pulse pair timings and numerically transformed to achieve the full frequency-frequency spectrum. This method demonstrates the ability to acquire information on molecular dynamics, couplings and structure in a simple apparatus. Multi-dimensional methods can be used for diagnostic and analytical measurements in the biological, biomedical, and chemical fields.

  20. Two-dimensional melting under quenched disorder

    E-print Network

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

    2013-05-16

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

  1. Phonon hydrodynamics in two-dimensional materials.

    PubMed

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

    2015-01-01

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

  2. New Two-Dimensional Ice Models

    NASA Astrophysics Data System (ADS)

    Kirov, Mikhail V.

    2012-11-01

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

  3. Lightlike shell solitons of extremal space-time film

    E-print Network

    Chernitskii, Alexander A

    2015-01-01

    New exact solution class of Born -- Infeld type nonlinear scalar field model is obtained. The variational principle of this model has a specific form which is characteristic for extremal four-dimensional hypersurface or hyper film in five-dimensional space-time. Obtained solutions are singular solitons propagating with speed of light and having energy, momentum, and angular momentum which can be calculated for explicit conditions. The soliton singularity here is a moving two-dimensional surface or shell, where the model action density becomes zero. The lightlike soliton can have a set of tubelike shells with the appropriate cavities. A twisted lightlike soliton is considered. It is notable that its energy is proportional to its angular momentum in high-frequency approximation. A case with one tubelike cavity is considered. In this case the soliton shell is diffeomorphic to cylindrical surface with cuts by multifilar helix. The shell transverse size of the appropriate finite energy soliton can be converging to...

  4. Internal tide generation by arbitrary two-dimensional topography

    E-print Network

    Peacock, Thomas

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

  5. Dynamics of semiconductor lasers with two-dimensional distributed feedback

    NASA Astrophysics Data System (ADS)

    Ginzburg, N. S.; Baryshev, V. R.; Sergeev, A. S.; Malkin, A. M.

    2015-05-01

    We develop a nonlinear model of a laser exploiting two-dimensional (2D) distributed feedback (2D DFL). This feedback mechanism can be realized in a 2D Bragg resonator formed by a dielectric structure with the thickness having double-periodical sinusoidal or chessboard modulation. A 2D Bragg resonator is shown to possess high selectivity over both the longitudinal and the transverse coordinates and to have fundamental modes in the center of the forbidden band gap. Within the semiclassical approach, we study the nonlinear dynamics of 2D DFL and demonstrate spatial synchronization of radiation from an extended active medium. Specific features of 2D DFL operation with active medium amplifying modes of TM and TE (quantum-well lasers) polarization are also discussed.

  6. Entropically stabilized growth of a two-dimensional random tiling

    NASA Astrophysics Data System (ADS)

    Stannard, Andrew; Blunt, Matthew O.; Beton, Peter H.; Garrahan, Juan P.

    2010-10-01

    The assembly of molecular networks into structures such as random tilings and glasses has recently been demonstrated for a number of two-dimensional systems. These structures are dynamically arrested on experimental time scales, so the critical regime in their formation is that of initial growth. Here, we identify a transition from energetic to entropic stabilization in the nucleation and growth of a molecular rhombus tiling. Calculations based on a lattice-gas model show that clustering of topological defects and the formation of faceted boundaries followed by a slow relaxation to equilibrium occur under conditions of energetic stabilization. We also identify an entropically stabilized regime in which the system grows directly into an equilibrium configuration without the need for further relaxation. Our results provide a methodology for identifying equilibrium and nonequilibrium randomness in the growth of molecular tilings, and we demonstrate that equilibrium spatial statistics are compatible with exponentially slow dynamical behavior.

  7. Entropically stabilized growth of a two-dimensional random tiling.

    PubMed

    Stannard, Andrew; Blunt, Matthew O; Beton, Peter H; Garrahan, Juan P

    2010-10-01

    The assembly of molecular networks into structures such as random tilings and glasses has recently been demonstrated for a number of two-dimensional systems. These structures are dynamically arrested on experimental time scales, so the critical regime in their formation is that of initial growth. Here, we identify a transition from energetic to entropic stabilization in the nucleation and growth of a molecular rhombus tiling. Calculations based on a lattice-gas model show that clustering of topological defects and the formation of faceted boundaries followed by a slow relaxation to equilibrium occur under conditions of energetic stabilization. We also identify an entropically stabilized regime in which the system grows directly into an equilibrium configuration without the need for further relaxation. Our results provide a methodology for identifying equilibrium and nonequilibrium randomness in the growth of molecular tilings, and we demonstrate that equilibrium spatial statistics are compatible with exponentially slow dynamical behavior. PMID:21230240

  8. SCAPS, a two-dimensional ion detector for mass spectrometer

    NASA Astrophysics Data System (ADS)

    Yurimoto, Hisayoshi

    2014-05-01

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

  9. Optical Measurement of Spectra of Two-Dimensional Functions

    Microsoft Academic Search

    Mahinder S. Uberoi

    1962-01-01

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

  10. Foundation of The Two dimensional Quantum Theory of Gravity

    E-print Network

    F. Ghaboussi

    1998-07-16

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

  11. Helical rays in two-dimensional resonant wave conversion

    SciTech Connect

    Kaufman, Allan N.; Tracy, Eugene R.; Brizard, Alain J.

    2004-12-08

    The process of resonant wave conversion (often called linear mode conversion) has traditionally been analyzed with a spatially one-dimensional slab model, for which the rays propagate in a two-dimensional phase space. However, it has recently been shown [E.R. Tracy and A.N. Kaufman, Phys. Rev. Lett. 91, 130402 (2003)] that multidimensional rays have a helical structure for conversion in two or more spatial dimensions (if their dispersion matrix is generic). In that case, a one-dimensional model is inadequate; a correct analysis requires two spatial dimensions and, thus, four-dimensional phase space. In this paper we show that a cold plasma model will exhibit ray helicity in conversion regions where the density and magnetic field gradients are significantly non-parallel. For illustration, we examine a model of the poloidal plane of a deuterium-tritium tokamak plasma, and identify such a region. In this region, characterized by a six-sector topology, rays in the sector for incident and reflected magnetosonic waves exhibit significant helicity. We introduce a ''symmetric-wedge'' model, to develop a detailed analytic and numerical study of helical rays in this sector.

  12. Helical rays in two-dimensional resonant wave conversion

    SciTech Connect

    Kaufman, Allan N.; Tracy, Eugene R.; Brizard, Alain J.

    2004-09-14

    The process of resonant wave conversion (often called linear mode conversion) has traditionally been analyzed with a spatially one-dimensional slab model, for which the rays propagate in a two-dimensional phase space. However, it has recently been shown [E.R. Tracy and A.N. Kaufman, Phys. Rev. Lett. 91, 130402 (2003)] that multidimensional rays have a helical structure for conversion in two or more spatial dimensions (if their dispersion matrix is generic). In that case, a one-dimensional model is inadequate; a correct analysis requires two spatial dimensions and, thus, four-dimensional phase space. In this paper we show that a cold plasma model will exhibit ray helicity in conversion regions where the density and magnetic field gradients are significantly non-parallel. For illustration, we examine a model of the poloidal plane of a deuterium-tritium tokamak plasma, and identify such a region. In this region, characterized by a six-sector topology, rays in the sector for incident and reflected magnetosonic waves exhibit significant helicity. We introduce a ''symmetric-wedge'' model, to develop a detailed analytic and numerical study of helical rays in this sector.

  13. Two-dimensional vortices and accretion disks

    NASA Astrophysics Data System (ADS)

    Nauta, Michiel Doede

    2000-01-01

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

  14. String solitons

    Microsoft Academic Search

    M. J. Duff; Ramzi R. Khuri; J. X. Lu

    1995-01-01

    We review the status of solitons in superstring theory, with a view to understanding the strong coupling regime. These solitonic solutions are non-singular field configurations which solve the empty-space low-energy field equations (generalized, whenever possible, to all orders in ??), carry a non-vanishing topological “magnetic” charge and are stabilized by a topological conservation law. They are compared and contrasted with

  15. Steplike electric conduction in a classical two-dimensional electron system through a narrow

    E-print Network

    Steplike electric conduction in a classical two-dimensional electron system through Non-centrosymmetric superconductivity in d-electron compounds Visualization of the Spatial ferromagnetic quantum criticality in the heavy-fermion iron oxypnictide Ce(Ru1-xFex)PO Vacancy trapping

  16. A STUDY OF MONITOR FUNCTIONS FOR TWO-DIMENSIONAL ADAPTIVE MESH GENERATION

    E-print Network

    Cao, Weiming

    A STUDY OF MONITOR FUNCTIONS FOR TWO-DIMENSIONAL ADAPTIVE MESH GENERATION WEIMING CAO, WEIZHANG generation, mesh adaptation, monitor function, weight function, Green's function AMS subject classifications differential equations (PDEs) is the adaptive generation of the mesh, or grid. In two (or higher) spatial

  17. Two-dimensional self-consistent radiation transport model for plasma display panels

    Microsoft Academic Search

    Hae June Lee; Hyun Chul Kim; Sung Soo Yang; Jae Koo Lee

    2002-01-01

    A two-dimensional radiation transport model is coupled with a ?uid simulation to incorporate the resonance radiation trapping effect in a plasma display panel cell. Compared with the conventional trapping factor approach, this model has an advantage in describing the spatial evolution of the radiative excited-state density. Compared with a Monte Carlo model, it also takes advantage of its fast computation

  18. Gravity Effects on Steady Two-Dimensional Partially Premixed MethaneAir Flames

    E-print Network

    Aggarwal, Suresh K.

    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

  19. An atlas of two-dimensional materials.

    PubMed

    Miró, Pere; Audiffred, Martha; Heine, Thomas

    2014-09-21

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

  20. Seismic isolation of two dimensional periodic foundations

    SciTech Connect

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

    2014-07-28

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

  1. Single Molecule Approaches for Two Dimensional Nanostructures

    NASA Astrophysics Data System (ADS)

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

    2014-03-01

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

  2. Soliton form factors from lattice simulations

    SciTech Connect

    Rajantie, Arttu; Weir, David J. [Theoretical Physics Group, Blackett Laboratory, Imperial College London, London SW7 2AZ (United Kingdom)

    2010-12-01

    The form factor provides a convenient way to describe properties of topological solitons in the full quantum theory, when semiclassical concepts are not applicable. It is demonstrated that the form factor can be calculated numerically using lattice Monte Carlo simulations. The approach is very general and can be applied to essentially any type of soliton. The technique is illustrated by calculating the kink form factor near the critical point in 1+1-dimensional scalar field theory. As expected from universality arguments, the result agrees with the exactly calculable scaling form factor of the two-dimensional Ising model.

  3. KP solitons in shallow water

    E-print Network

    Yuji Kodama

    2010-04-26

    The main purpose of the paper is to provide a survey of our recent studies on soliton solutions of the Kadomtsev-Petviashvili (KP) equation. The classification is based on the far-field patterns of the solutions which consist of a finite number of line-solitons. Each soliton solution is then defined by a point of the totally non-negative Grassmann variety which can be parametrized by a unique derangement of the symmetric group of permutations. Our study also includes certain numerical stability problems of those soliton solutions. Numerical simulations of the initial value problems indicate that certain class of initial waves asymptotically approach to these exact solutions of the KP equation. We then discuss an application of our theory to the Mach reflection problem in shallow water. This problem describes the resonant interaction of solitary waves appearing in the reflection of an obliquely incident wave onto a vertical wall, and it predicts an extra-ordinary four-fold amplification of the wave at the wall. There are several numerical studies confirming the prediction, but all indicate disagreements with the KP theory. Contrary to those previous numerical studies, we find that the KP theory actually provides an excellent model to describe the Mach reflection phenomena when the higher order corrections are included to the quasi-two dimensional approximation. We also present laboratory experiments of the Mach reflection recently carried out by Yeh and his colleagues, and show how precisely the KP theory predicts this wave behavior.

  4. A new method for two-dimensional array signal processing in unknown noise environments

    Microsoft Academic Search

    Pingan Li; Bianzang Yu; Jinchai Sun

    1995-01-01

    This paper deals with the application of the so-called ‘propagator’ approach to perform two-dimensional (2-D) spatial-spectrum estimation in unknown noise environments. On the assumption that the noise correlation is spatially limited, the effects of unknown noise are eliminated by using two subarrays separated far enough, and no constrained modelling of the noise field is required. In the approach, the noise

  5. Two-dimensional dense gas dynamics

    NASA Astrophysics Data System (ADS)

    Brown, Brady Polk

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

  6. Dynamics of two-dimensional bubbles

    NASA Astrophysics Data System (ADS)

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

    2015-06-01

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

  7. Vacuum polarization in two-dimensional static spacetimes and dimensional reduction

    E-print Network

    Roberto Balbinot; Alessandro Fabbri; Piero Nicolini; Patrick J. Sutton

    2002-05-14

    We obtain an analytic approximation for the effective action of a quantum scalar field in a general static two-dimensional spacetime. We apply this to the dilaton gravity model resulting from the spherical reduction of a massive, non-minimally coupled scalar field in the four-dimensional Schwarzschild geometry. Careful analysis near the event horizon shows the resulting two-dimensional system to be regular in the Hartle-Hawking state for general values of the field mass, coupling, and angular momentum, while at spatial infinity it reduces to a thermal gas at the black-hole temperature.

  8. Direct generation of ion beam images with a two-dimensional charge injection device.

    PubMed

    Cable, P R; Parker, M; Marcus, R K; Pochkowski, J M

    1995-02-01

    The use of a two-dimensional charge injection device (CID) to directly image the spatial profile of impingent positively charged ions is described. By this approach, no prior conversion from an ion beam to a photon image is required. Because of the positive response of the device to plasma photons, ions that emanated from the radiofrequency glow discharge source were diverted around a photon stop and focused onto the CID. The resultant ion images were digitized via an external image processor and corrected for dark current contributions. Two-dimensional ion images and single pixel line profiles are presented. PMID:24222076

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

    NASA Technical Reports Server (NTRS)

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

    2011-01-01

    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.

  10. Two-dimensional nanoarchitectonics based on self-assembly

    Microsoft Academic Search

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

    2010-01-01

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

  11. Lie algebra contractions on two-dimensional hyperboloid

    SciTech Connect

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

    2010-03-15

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

  12. Motion, relaxation dynamics, and diffusion processes in two-dimensional colloidal crystals confined between walls

    NASA Astrophysics Data System (ADS)

    Wilms, Dorothea; Virnau, Peter; Snook, Ian K.; Binder, Kurt

    2012-11-01

    The dynamical behavior of single-component two-dimensional colloidal crystals confined in a slit geometry is studied by Langevin dynamics simulation of a simple model. The colloids are modeled as pointlike particles, interacting with the repulsive part of the Lennard-Jones potential, and the fluid molecules in the colloidal suspension are not explicitly considered. Considering a crystalline strip of triangular lattice structure with n=30 rows, the (one-dimensional) walls confining the strip are chosen as two rigidly fixed crystalline rows at each side, commensurate with the lattice structure and, thus, stabilizing long-range order. The case when the spacing between the walls is incommensurate with the ideal triangular lattice is also studied, where (due to a transition in the number of rows, n?n-1) the confined crystal is incommensurate with the confining boundaries, and a soliton staircase forms along the walls. It is shown that mean-square displacements (MSDs) of particles as a function of time show an overshoot and then saturate at a horizontal plateau in the commensurate case, the value of the plateau being largest in the center of the strip. Conversely, when solitons are present, MSDs are largest in the rows containing the solitons, and all MSDs do not settle down at well-defined plateaus in the direction parallel to the boundaries, due to the lack of positional long-range order in ideal two-dimensional crystals. The MSDs of the solitons (which can be treated like quasiparticles at very low temperature) have also been studied and their dynamics are found to be about an order of magnitude slower than that of the colloidal particles themselves. Finally, transport of individual colloidal particles by diffusion processes is studied: both standard vacancy-interstitial pair formation and cooperative ring rotation processes are identified. These processes require thermal activation, with activation energies of the order of 10Tm (Tm being the melting temperature of the crystal), while the motions due to long-wavelength phonons decrease only linearly in temperature.

  13. Solitonic axion condensates modeling dark matter halos

    SciTech Connect

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

    2013-09-15

    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.

  14. Soliton turbulence

    NASA Technical Reports Server (NTRS)

    Tchen, C. M.

    1986-01-01

    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.

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

    E-print Network

    Wong, Limsoon

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

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

    Microsoft Academic Search

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

    1998-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2015-03-01

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

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

    E-print Network

    Ruina, Andy L.

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

  19. New two-dimensional quantum models with shape invariance

    SciTech Connect

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

    2011-02-15

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

  20. Using Two-Dimensional Colloidal Crystals to Understand Crystallography

    E-print Network

    Loening, Niko

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

  1. Two-dimensional digital filters with no overflow oscillations

    Microsoft Academic Search

    N. El-Agizi; M. Fahmy

    1979-01-01

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

  2. Acoustics 2000 1 The Two Dimensional Numerical Modeling

    E-print Network

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

  3. Spontaneous chiral symmetry breaking in two-dimensional aggregation

    NASA Astrophysics Data System (ADS)

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

    1998-08-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2015-06-01

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

  5. Interaction of two-dimensional orthogonally polarised super-Gaussian light beams in a photorefractive crystal

    SciTech Connect

    Davydovskaya, V V; Shepelevich, V V [I P Shamyakin Mozyr State Pedagogical University, Mozyr (Belarus); Matusevich, V; Kisling, A; Kovarshik, R [Friedrich-Schiller-Universitaet Jena, Jena (Germany)

    2010-12-09

    Propagation and interaction of orthogonally polarised two-dimensional super-Gaussian light beams is studied theoretically in a 4mm-symmetry photorefractive crystal in the drift regime when the external electric field is applied to the crystal in the direction of the optical axis. The output beams displaced with respect to each other in directions parallel and perpendicular to the direction of the external electric field strength vector are considered. It is shown that an auxiliary light beam polarised orthogonally to the fundamental light beam makes it possible to carry out efficiently address localisation of the fundamental beam propagating in a quasi-soliton regime. The crystal thicknesses are found, which are optimal from the viewpoint of maximisation of the fundamental light beam deviation. It is shown that 'square' super-Gaussian beams in the near-field diffraction region are focused at smaller values of the external electric field than those of the Gaussian beams. (nonlinear optical phenomena)

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

    NASA Astrophysics Data System (ADS)

    Nikolopoulos, G. M.

    2015-02-01

    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.

  7. The Thirring interaction in the two-dimensional axial-current-pseudoscalar derivative coupling model

    SciTech Connect

    Belvedere, L.V. [Instituto de Fisica, Universidade Federal Fluminense, Av. Litoranea S/N, Boa Viagem, Niteroi, CEP 24210-340, Rio de Janeiro (Brazil)]. E-mail: belve@if.uff.br; Rodrigues, A.F. [Instituto de Fisica, Universidade Federal Fluminense, Av. Litoranea S/N, Boa Viagem, Niteroi, CEP 24210-340, Rio de Janeiro (Brazil)]. E-mail: armflavio@if.uff.br

    2006-12-15

    We reexamine the two-dimensional model of massive fermions interacting with a massless pseudoscalar field via axial-current derivative coupling. The hidden Thirring interaction in the axial-derivative coupling model is exhibited compactly by performing a canonical field transformation on the Bose field algebra and the model is mapped into the Thirring model with an additional vector-current-scalar derivative interaction (Schroer-Thirring model). The Fermi field operator is rewritten in terms of the Mandelstam soliton operator coupled to a free massless scalar field. The charge sectors of the axial-derivative model are mapped into the charge sectors of the massive Thirring model. The complete bosonized version of the model is presented. The bosonized composite operators of the quantum Hamiltonian are obtained as the leading operators in the Wilson short distance expansions.

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

    SciTech Connect

    Schoenfelder, H.; Kruse, M.; Werther, J. [Technical Univ. Hamburg-Harburg, Hamburg (Germany). Dept. of Chemical Engineering] [Technical Univ. Hamburg-Harburg, Hamburg (Germany). Dept. of Chemical Engineering

    1996-07-01

    Circulating fluidized bed reactors are widely used for the combustion of coal in power stations as well as for the cracking of heavy oil in the petroleum industry. A two-dimensional reactor model for circulating fluidized beds (CFB) was studied based on the assumption that at every location within the riser, a descending dense phase and a rising lean phase coexist. Fluid mechanical variables may be calculated from one measured radial solids flux profile (upward and downward). The internal mass-transfer behavior is described on the basis of tracer gas experiments. The CFB reactor model was tested against data from ozone decomposition experiments in a CFB cold flow model (15.6-m height, 0.4-m ID) operated in the ranges 2.5--4.5 m/s and 9--45 kg/(m{sup 2}{center_dot}s) of superficial gas velocity and solids mass flux, respectively. Based on effective reaction rate constants determined from the ozone exit concentration, the model was used to predict the spatial reactant distribution within the reactor. Model predictions agreed well with measurements.

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

    PubMed

    Semenov, S Y; Svenson, R H; Boulyshev, A E; Souvorov, A E; Borisov, V Y; Sizov, Y; Starostin, A N; Dezern, K R; Tatsis, G P; Baranov, V Y

    1996-09-01

    Microwave tomographic imaging is one of the new technologies which has the potential for important applications in medicine. Microwave tomographically reconstructed images may potentially provide information about the physiological state of tissue as well as the anatomical structure of an organ. A two-dimensional (2-D) prototype of a quasi real-time microwave tomographic system was constructed. It was utilized to reconstruct images of physiologically active biological tissues such as an explanted canine perfused heart. The tomographic system consisted of 64 special antennae, divided into 32 emitters and 32 receivers which were electronically scanned. The cylindrical microwave chamber had an internal diameter of 360 mm and was filled with various solutions, including deionized water. The system operated on a frequency of 2.45 GHz. The polarization of the incident electromagnetic field was linear in the vertical direction. Total acquisition time was less than 500 ms. Both accurate and approximation methods of image reconstruction were used. Images of 2-D phantoms, canine hearts, and beating canine hearts have been achieved. In the worst-case situation when the 2-D diffraction model was used for an attempt to "slice" three-dimensional (3-D) object reconstruction, we still achieved spatial resolution of 1 to 2 cm and contrast resolution of 5%. PMID:9214802

  10. Two-dimensional magnetohydrodynamics and turbulent coronal heating

    SciTech Connect

    Dmitruk, P. [Departamento de Fisica, Universidad de Buenos Aires, Pabellon I, Ciudad Universitaria, Buenos Aires (1428) (Argentina); Gomez, D. [Departamento de Fisica, Universidad de Buenos Aires, Pabellon I, Ciudad Universitaria, Buenos Aires (1428) (Argentina); Instituto de Astronomia y Fisica del Espacio, CC 67 Suc 28, Buenos Aires (1428) (Argentina)

    1997-06-05

    We consider the heating of solar coronal active regions within a turbulent scenario. A direct numerical simulation of the equations governing the dynamics of a coronal magnetic loop is performed, assuming that the essential features can be described by an externally driven two-dimensional magnetohydrodynamic system. A stationary and large-scale magnetic forcing was imposed, to model the photospheric motions at the magnetic loop footpoints. A turbulent stationary regime is reached with an energy dissipation rate consistent with the heating requirements of coronal loops. The energy dissipation rate time series shows an intermittent behavior, in the form of impulsive events, superimposed on the stationary component. We associate the impulsive events of magnetic energy dissipation with the so-called nanoflares. A statistical analysis of these events yields a power law distribution as a function of their energies with a slope consistent with those obtained for flare energy distributions reported from X-ray observations. We also show the development of small scales in the spatial distribution of electric currents.

  11. Three-Dimensional Hermite—Bessel—Gaussian Soliton Clusters in Strongly Nonlocal Media

    NASA Astrophysics Data System (ADS)

    Jin, Hai-Qin; Liang, Jian-Chu; Cai, Ze-Bin; Liu, Fei; Yi, Lin

    2012-12-01

    We analytically and numerically demonstrate the existence of Hermite—Bessel—Gaussian spatial soliton clusters in three-dimensional strongly nonlocal media. It is found that the soliton clusters display the vortex, dipole azimuthon and quadrupole azimuthon in geometry, and the total number of solitons in the necklaces depends on the quantum number n and m of the Hermite functions and generalized Bessel polynomials. The numerical simulation is basically identical to the analytical solution, and white noise does not lead to collapse of the soliton, which confirms the stability of the soliton waves. The theoretical predictions may give new insights into low-energetic spatial soliton transmission with high fidelity.

  12. Quantum holographic encoding in a two-dimensional electron gas

    SciTech Connect

    Moon, Christopher

    2010-05-26

    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.

  13. Two-dimensional electronic spectroscopy of molecular aggregates.

    PubMed

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

    2009-09-15

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

  14. Lightlike shell solitons of extremal space-time film

    E-print Network

    Alexander A. Chernitskii

    2015-06-30

    New exact solution class of Born -- Infeld type nonlinear scalar field model is obtained. The variational principle of this model has a specific form which is characteristic for extremal four-dimensional hypersurface or hyper film in five-dimensional space-time. Obtained solutions are singular solitons propagating with speed of light and having energy, momentum, and angular momentum which can be calculated for explicit conditions. The soliton singularity here is a moving two-dimensional surface or shell, where the model action density becomes zero. The lightlike soliton can have a set of tubelike shells with the appropriate cavities. A twisted lightlike soliton is considered. It is notable that its energy is proportional to its angular momentum in high-frequency approximation. A case with one tubelike cavity is considered. In this case the soliton shell is diffeomorphic to cylindrical surface with cuts by multifilar helix. The shell transverse size of the appropriate finite energy soliton can be converging to zero at infinity. The ideal gas of such lightlike solitons with minimal twist parameter is considered in a finite volume. Explicit conditions provide that the angular momentum of each soliton in the volume equals Planck constant. The equilibrium energy spectral density for the solitons is obtained. It has the form of Planck distribution in some approximation. A beam of twisted lightlike solitons is considered. The representation of arbitrary polarization for beam with twisted lightlike solitons is discussed. It is shown that this beam provides the effect of mechanical angular momentum transfer to absorbent by circularly polarized beam. This effect well known for photon beam. Thus the soliton solution which have determinate likeness with photon is obtained in particular.

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

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

    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.

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

    PubMed

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

    2014-10-28

    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

  17. Two-dimensional simulation of a miniaturized inductively coupled plasma reactor

    Microsoft Academic Search

    Sang Ki Nam; Demetre J. Economou

    2004-01-01

    A two-dimensional self-consistent simulation of a miniaturized inductively coupled plasma (mICP) reactor was developed. The coupled equations for plasma power deposition, electron temperature, and charged and neutral species densities, were solved to obtain the spatial distribution of an argon discharge. The effect of control parameters, such as power and pressure, on the evolution of plasma density and electron temperature was

  18. Scaling and Correlation Functions in a Model of a Two-dimensional Earthquake Fault

    E-print Network

    Thordur Jonsson; Sigurdur Freyr Marinosson

    1997-03-18

    We study numerically a two-dimensional version of the Burrige-Knopoff model. We calculate spatial and temporal correlation functions and compare their behavior with the results found for the one-dimensional model. The Gutenberg-Richter law is only obtained for special choices of parameters in the relaxation function. We find that the distribution of the fractal dimension of the slip zone exhibits two well-defined peaks coeersponding to intermediate size and large events.

  19. Thermal relaxation of a two dimensional plasma in a dc magnetic field. Part 2: Numerical simulation

    NASA Technical Reports Server (NTRS)

    Hsu, J. Y.; Joyce, G.; Montgomery, D.

    1974-01-01

    The thermal relaxation process for a spatially uniform two dimensional plasma in a uniform dc magnetic field is simulated numerically. Thermal relaxation times are defined in terms of the time necessary for the numerically computer Boltzman H-function to decrease through a given part of the distance to its minimum value. Dependence of relaxation time on two parameters is studied: number of particles per Debye square and ratio of gyrofrequency to plasma frequency.

  20. Two-dimensional electronic spectroscopy and photosynthesis: Fundamentals and applications to photosynthetic light-harvesting

    Microsoft Academic Search

    Gabriela S. Schlau-Cohen; Akihito Ishizaki; Graham R. Fleming

    2011-01-01

    In natural light harvesting systems, pigment-protein complexes are able to harvest sunlight with near unity quantum efficiency. These complexes exhibit emergent properties that cannot be simply extrapolated from knowledge of their component parts. In this perspective, we focus on how two-dimensional electronic spectroscopy (2DES) can provide an incisive tool to probe the electronic, energetic, and spatial landscapes that must be

  1. The use of compact boundary value method for the solution of two-dimensional Schrödinger equation

    Microsoft Academic Search

    Akbar Mohebbi; Mehdi Dehghan

    2009-01-01

    In this paper, a high-order and accurate method is proposed for solving the unsteady two-dimensional Schrödinger equation. We apply a compact finite difference approximation of fourth-order for discretizing spatial derivatives and a boundary value method of fourth-order for the time integration of the resulting linear system of ordinary differential equations. The proposed method has fourth-order accuracy in both space and

  2. Two-dimensional gate-controlled photodiode array for optical computing

    SciTech Connect

    Sun, C.C. (Univ., of Toronto, Dept. of Electrical Engineering, Toronto (CA))

    1989-08-01

    A new semiconductor device, the gate-controlled photodiode (GCPD), has been experimentally demonstrated. A two-dimensional (2-D) GCPD array may fulfill the combined function of a 2-D spatial light modulator (SLM) and a photodetector array in some applications. Its high parallelism, simplicity, and compatibility are attractive for optical signal processing and computing, optical interconnection for VLSI circuits, and artificial neural networks. Some typical applications for optical computing are discussed.

  3. Dipole and Quadrupole Solitons in Optically Induced Two-Dimensional Photonic Lattices

    E-print Network

    Yang, Jianke

    of Vermont, 16 Colchester Avenue, Burlington, VT 05401-1455; e-mail: jyang@emba.uvm.edu STUDIES IN APPLIED MATHEMATICS 113:389­412 389 C 2004 by the Massachusetts Institute of Technology Published by Blackwell

  4. Dynamics of vector solitons and vortices in two-dimensional photonic lattices

    E-print Network

    with a split-step Fourier method. We find that for 0.8 A 1.2 the two mutually incoher- ent beams evolve methods; second, it can be considered as a first-order approximation of more complicated mod- els

  5. Magnetoconductivity of two-dimensional electron systems

    NASA Astrophysics Data System (ADS)

    Kuehnel, Frank Oliver

    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.

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

    SciTech Connect

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

    1984-01-01

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

  7. Two-dimensional Minkowski causal automorphisms and conformal maps

    E-print Network

    Juan Manuel Burgos

    2013-05-04

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

  8. Third sound in one and two dimensional modulated structures

    SciTech Connect

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

    1996-02-01

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

  9. Ion acoustic solitons in Earth's upward current region

    SciTech Connect

    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

    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.

  10. Continuous Solitons in a Lattice Nonlinearity

    NASA Astrophysics Data System (ADS)

    Pierangeli, D.; Flammini, M.; Di Mei, F.; Parravicini, J.; de Oliveira, C. E. M.; Agranat, A. J.; DelRe, E.

    2015-05-01

    We study theoretically and experimentally the propagation of optical solitons in a lattice nonlinearity, a periodic pattern that both affects and is strongly affected by the wave. Observations are carried out using spatial photorefractive solitons in a volume microstructured crystal with a built-in oscillating low-frequency dielectric constant. The pattern causes an oscillating electro-optic response that induces a periodic optical nonlinearity. On-axis results in potassium-lithium-tantalate-niobate indicate the appearance of effective continuous saturated-Kerr solitons, where all spatial traces of the lattice vanish, independently of the ratio between beam width and lattice constant. Decoupling the lattice nonlinearity allows the detection of discrete delocalized and localized light distributions, demonstrating that the continuous solitons form out of the combined compensation of diffraction and of the underlying periodic volume pattern.

  11. Continuous Solitons in a Lattice Nonlinearity.

    PubMed

    Pierangeli, D; Flammini, M; Di Mei, F; Parravicini, J; de Oliveira, C E M; Agranat, A J; DelRe, E

    2015-05-22

    We study theoretically and experimentally the propagation of optical solitons in a lattice nonlinearity, a periodic pattern that both affects and is strongly affected by the wave. Observations are carried out using spatial photorefractive solitons in a volume microstructured crystal with a built-in oscillating low-frequency dielectric constant. The pattern causes an oscillating electro-optic response that induces a periodic optical nonlinearity. On-axis results in potassium-lithium-tantalate-niobate indicate the appearance of effective continuous saturated-Kerr solitons, where all spatial traces of the lattice vanish, independently of the ratio between beam width and lattice constant. Decoupling the lattice nonlinearity allows the detection of discrete delocalized and localized light distributions, demonstrating that the continuous solitons form out of the combined compensation of diffraction and of the underlying periodic volume pattern. PMID:26047230

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

    PubMed

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

    2014-10-01

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

  13. Time-Space Noncommutative Abelian Solitons

    E-print Network

    Chong-Sun Chu; Olaf Lechtenfeld

    2005-07-06

    We demonstrate the construction of solitons for a time-space Moyal-deformed integrable U(n) sigma model (the Ward model) in 2+1 dimensions. These solitons cannot travel parallel to the noncommutative spatial direction. For the U(1) case, the rank-one single-soliton configuration is constructed explicitly and is singular in the commutative limit. The projection to 1+1 dimensions reduces it to a noncommutative instanton-like configuration. The latter is governed by a new integrable equation, which describes a Moyal-deformed sigma model with a particular Euclidean metric and a magnetic field.

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

    E-print Network

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

    2005-01-01

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

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

    ERIC Educational Resources Information Center

    Edge, R. D.

    1989-01-01

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

  16. Fast Two-Dimensional Digital-Filter Hardware

    NASA Technical Reports Server (NTRS)

    Edwards, T. R.

    1985-01-01

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

  17. Difficulties that Students Face with Two-Dimensional Motion

    ERIC Educational Resources Information Center

    Mihas, P.; Gemousakakis, T.

    2007-01-01

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

  18. Time harmonic scar statistics in two dimensional cavities.

    SciTech Connect

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

    2007-01-01

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

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

    E-print Network

    Rice, Marie C

    2014-01-01

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

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

    E-print Network

    Gu, Zheng-Cheng

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

  1. Near-Surface Geophysics: Two-Dimensional Resistivity

    USGS Multimedia Gallery

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

  2. Transformation optics scheme for two-dimensional materials

    E-print Network

    Kumar, Anshuman

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

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

    Microsoft Academic Search

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

    2009-01-01

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

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

    PubMed

    Nomura, Kentaro; Koshino, Mikito; Ryu, Shinsei

    2007-10-01

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

  5. Two-dimensional quasicrystal with eightfold rotational symmetry

    Microsoft Academic Search

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

    1987-01-01

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

  6. Two-Dimensional Signal Processing in Radon Space

    Microsoft Academic Search

    Roger Lee Easton Jr.

    1986-01-01

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

  7. Two-Dimensional Cure Simulation of Thick Thermosetting Composites

    Microsoft Academic Search

    Travis A. Bogetti; John W. Gillespie

    1991-01-01

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

  8. Ground ring of two-dimensional string theory

    Microsoft Academic Search

    Edward Witten

    1992-01-01

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

  9. Two-dimensional QCD as a string theory

    Microsoft Academic Search

    David J. Gross

    1993-01-01

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

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

    Microsoft Academic Search

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

    2001-01-01

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

  11. Two dimensional NMR of liquids and oriented molecules

    SciTech Connect

    Gochin, M.

    1987-02-01

    Chapter 1 discusses the quantum mechanical formalism used for describing the interaction between magnetic dipoles that dictates the appearance of a spectrum. The NMR characteristics of liquids and liquid crystals are stressed. Chapter 2 reviews the theory of multiple quantum and two dimensional NMR. Properties of typical spectra and phase cycling procedures are discussed. Chapter 3 describes a specific application of heteronuclear double quantum coherence to the removal of inhomogeneous broadening in liquids. Pulse sequences have been devised which cancel out any contribution from this inhomogeneity to the final spectrum. An interpretation of various pulse sequences for the case of /sup 13/C and /sup 1/H is given, together with methods of spectral editing by removal or retention of the homo- or heteronuclear J coupling. The technique is applied to a demonstration of high resolution in both frequency and spatial dimensions with a surface coil. In Chapter 4, multiple quantum filtered 2-D spectroscopy is demonstrated as an effective means of studying randomly deuterated molecules dissolved in a nematic liquid crystal. Magnitudes of dipole coupling constants have been determined for benzene and hexane, and their signs and assignments found from high order multiple quantum spectra. For the first time, a realistic impression of the conformation of hexane can be estimated from these results. Chapter 5 is a technical description of the MDB DCHIB-DR11W parallel interface which has been set up to transfer data between the Data General Nova 820 minicomputer, interfaced to the 360 MHz spectrometer, and the Vax 11/730. It covers operation of the boards, physical specifications and installation, and programs for testing and running the interface.

  12. Modeling Meandering Channel by Two-Dimensional Shallow Water Equations

    NASA Astrophysics Data System (ADS)

    Yu, C.; Duan, J. G.

    2014-12-01

    This research is to simulate the process of channel meandering using a two-dimensional depth-averaged hydrodynamic model. The multiple interactions between unsteady flow, turbulence, secondary flow, nonequilibrium sediment transport and bank erosion are considered by the model. The governing equations are the 2D depth-averaged Reynolds-averaged Navier-Stokes (2D-RANS) equations and the Exner equation for bed elevation evolution. The Reynolds stresses are calculated by the k-? turbulence model. The secondary flow, is modeled by the dispersion terms in momentum equations. The spatial lag between the instantaneous flow properties and the rate of sediment transport is simulated by the nonequilibrium sediment transport model. During the process of adaptation, the sediment transport rate gradually develops into the transport capacity of a given flow condition. The evolution of channel bed and bank is modeled by the general Exner equation that accounts for both vertical deformation of bed elevation as well as lateral migration of bank. The system of governing equations is solved by a semi-implicit finite volume method over the Cartesian mesh. The advective fluxes across each cell interface are simultaneously calculated by the extended HLL Riemann solver. At each time step, the diffusion terms in the governing equations are solved by the implicit Euler scheme. The source terms are discretized in a well-balanced way to retain the C-property of the proposed model. Application of the model to different test cases indicates that the model can correctly simulate different phases of meandering channel evolution which include streamwise migration, transverse migration and rotation of channel bends.

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

    PubMed

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

    2007-04-01

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

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

    NASA Technical Reports Server (NTRS)

    Kouatchou, Jules

    1999-01-01

    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.

  15. Entanglement of arbitrary superpositions of modes within two-dimensional orbital angular momentum state spaces

    SciTech Connect

    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

    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.

  16. Soliton matter as a model of dense nuclear matter

    SciTech Connect

    Glendenning, N.K.

    1985-01-01

    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.

  17. Numerical simulations of Kadomtsev-Petviashvili soliton interactions

    NASA Astrophysics Data System (ADS)

    Infeld, E.; Senatorski, A.; Skorupski, A. A.

    1995-04-01

    The Kadomtsev-Petviashvili equation generalizes that of Korteweg and de Vries to two space dimensions and arises in various weakly dispersive media. Two very different species of soliton solutions are known for one variant, KPI. The first species to be discovered are line solitons, the second are two dimensional lumps. This paper describes numerical simulations, consistent with all constraints of the equation, in which very distorted line solitons break up into smaller line solitons and arrays of lumps. The arrays can interact with one another. In some cases, aspects of the results of the simulations can be understood in the light of specially constructed exact solutions. Simulations in which initial conditions fail to satisfy the constraints of the equation are also described.

  18. Scanning tunneling spectroscopy study of the proximity effect in a disordered two-dimensional metal.

    PubMed

    Serrier-Garcia, L; Cuevas, J C; Cren, T; Brun, C; Cherkez, V; Debontridder, F; Fokin, D; Bergeret, F S; Roditchev, D

    2013-04-12

    The proximity effect between a superconductor and a highly diffusive two-dimensional metal is revealed in a scanning tunneling spectroscopy experiment. The in situ elaborated samples consist of superconducting single crystalline Pb islands interconnected by a nonsuperconducting atomically thin disordered Pb wetting layer. In the vicinity of each superconducting island the wetting layer acquires specific tunneling characteristics which reflect the interplay between the proximity-induced superconductivity and the inherent electron correlations of this ultimate diffusive two-dimensional metal. The observed spatial evolution of the tunneling spectra is accounted for theoretically by combining the Usadel equations with the theory of dynamical Coulomb blockade; the relevant length and energy scales are extracted and found in agreement with available experimental data. PMID:25167301

  19. A finite element method for the two-dimensional extended Boussinesq equations

    NASA Astrophysics Data System (ADS)

    Walkley, Mark; Berzins, Martin

    2002-08-01

    A new numerical method for Nwogu's (ASCE Journal of Waterway, Port, Coastal and Ocean Engineering 1993; 119:618)two-dimensional extended Boussinesq equations is presented using a linear triangular finite element spatial discretization coupled with a sophisticated adaptive time integration package. The authors have previously presented a finite element method for the one-dimensional form of these equations (M. Walkley and M. Berzins (International Journal for Numerical Methods in Fluids 1999; 29(2):143)) and this paper describes the extension of these ideas to the two-dimensional equations and the application of the method to complex geometries using unstructured triangular grids. Computational results are presented for two standard test problems and a realistic harbour model. Copyright

  20. Fast Multi-voxel Two-dimensional Spectroscopic Imaging at 3T

    PubMed Central

    Kim, Dong-Hyun; Henry, Roland; Spielman, Daniel M.

    2007-01-01

    The utility of multi-voxel two-dimensional chemical shift imaging in the clinical environment will ultimately be determined by the imaging time and the metabolite peaks that can be detected. Different k-space sampling schemes can be characterized by their minimum required imaging time. The use of spiral-based readout gradients effectively reduces this minimum scan time due to simultaneous data acquisition in three k-space dimensions (kx, ky, and kf2). A 3T spiral-based multi-voxel two-dimensional spectroscopic imaging sequence using the PRESS excitation scheme was implemented. Good performance was demonstrated by acquiring preliminary in vivo data for applications including brain glutamate imaging, metabolite T2 quantification, and high spatial resolution prostate spectroscopic imaging. All protocols were designed to acquire the data within a 17 minute scan time at a field strength of 3T. PMID:17418519

  1. Two-dimensional particle-in-cell simulations of plasma cavitation and bursty Brillouin backscattering for nonrelativistic laser intensities

    SciTech Connect

    Riconda, C.; Weber, S.; Tikhonchuk, V. T.; Adam, J.-C.; Heron, A. [Centre Lasers Intenses et Applications (CELIA), UMR 5107 CNRS Universite Bordeaux 1 CEA, Universite Bordeaux 1, 33405 Talence, France and Centre de Physique Theorique (CPHT), UMR 7644 CNRS Ecole Polytechnique, Ecole Polytechnique, 91128 Palaiseau Cedex (France); Centre Lasers Intenses et Applications (CELIA), UMR 5107 CNRS Universite Bordeaux 1 CEA, Universite Bordeaux 1, 33405 Talence (France); Centre de Physique Theorique (CPHT), UMR 7644 CNRS Ecole Polytechnique, Ecole Polytechnique, 91128 Palaiseau Cedex (France)

    2006-08-15

    Two-dimensional particle-in-cell simulations of laser-plasma interaction using a plane-wave geometry show strong bursty stimulated Brillouin backscattering, rapid filamentation, and subsequent plasma cavitation. It is shown that the cavitation is not induced by self-focusing. The electromagnetic fields below the plasma frequency that are excited are related to transient soliton-like structures. At the origin of these solitons is a three-wave decay process exciting new modes in the plasma. The cavitation is responsible for a strong local reduction of the reflectivity and goes along with an efficient but transient heating of the electrons. Once heating ceases, transmission starts to increase. Local as well as global average reflectivities attain a very low value due to strong plasma density variations brought about by the cavitation process. On the one hand, the simulations confirm the existence of a new mechanism of cavity and soliton formation in nonrelativistic laser-plasma interaction in two dimensions, which was shown to exist in one-dimensional simulations [S. Weber, C. Riconda, and V. T. Tikhonchuk, Phys. Rev. Lett. 94, 055005 (2005)]. On the other hand, new aspects are introduced inherently related to the additional degree of freedom.

  2. SOLITONS: Optimal control of optical soliton parameters: Part 2. Concept of nonlinear Bloch waves in the problem of soliton management

    NASA Astrophysics Data System (ADS)

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

    2001-11-01

    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.

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

    NASA Astrophysics Data System (ADS)

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

    2002-04-01

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

  4. Two-Dimensional Superfluidity of Exciton Polaritons Requires Strong Anisotropy

    NASA Astrophysics Data System (ADS)

    Altman, Ehud; Sieberer, Lukas M.; Chen, Leiming; Diehl, Sebastian; Toner, John

    2015-01-01

    Fluids of exciton polaritons, excitations of two-dimensional quantum wells in optical cavities, show collective phenomena akin to Bose condensation. However, a fundamental difference from standard condensates stems from the finite lifetime of these excitations, which necessitates continuous driving to maintain a steady state. A basic question is whether a two-dimensional condensate with long-range algebraic correlations can exist under these nonequilibrium conditions. Here, we show that such driven two-dimensional Bose systems cannot exhibit algebraic superfluid order except in low-symmetry, strongly anisotropic systems. Our result implies, in particular, that recent apparent evidence for Bose condensation of exciton polaritons must be an intermediate-scale crossover phenomenon, while the true long-distance correlations fall off exponentially. We obtain these results through a mapping of the long-wavelength condensate dynamics onto the anisotropic Kardar-Parisi-Zhang equation.

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

    PubMed

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

    2009-06-01

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

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

    PubMed

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

    2015-01-01

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

  7. Reconstruction of two-dimensional magnetization and susceptibility distributions from the magnetic field of soft magnetic materials

    Microsoft Academic Search

    Shaofen Tan; Yu Pei Ma; I. M. Thomas

    1996-01-01

    We apply a spatial filtering technique to solve the two-dimensional magnetization imaging problem. This allows us to reconstruct the magnetization distribution from the measured magnetic field above a planar soft magnetic sample exposed to an applied magnetic field. Knowledge of the magnetizing field distribution can then be used to determine the susceptibility distribution and hence to obtain information about the

  8. Two-dimensional direct simulation Monte Carlo (DSMC) of reactive neutral and ion flow in a high density plasma reactor

    Microsoft Academic Search

    Demetxe J. Economou; Timothy J. Bartel; Richard S. Wise; Dimitris P. Lymberopoulos

    1995-01-01

    We present a two dimensional direct simulation Monte Carlo (DSMC) study of the rarefied reactive flow of neutrals and ions in a low pressure inductively coupled plasma reactor. The spatially-dependent rate coefficients of electron impact reactions and the electrostatic field were obtained from a fluid plasma simulation. Neutral and ion etching of polysilicon with chlorine gas was studied with emphasis

  9. Interpolation of Rainfall Data with Thin Plate Smoothing Splines - Part I: Two Dimensional Smoothing of Data with Short Range Correlation

    Microsoft Academic Search

    Michael F. Hutchinson

    1998-01-01

    Two dimensional thin plate smoothing splines were used to interpolate 100 daily rainfall values, with the degree of data smoothing determined by minimizing the generalised cross validation. Analyses were performed on the square roots of the rainfall values, permitting robust calibration of spatially distributed standard errors which are correlated with rainfall amount. Initial model calibration was made difficult by apparent

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

    NASA Astrophysics Data System (ADS)

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

    2001-03-01

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

  11. Two dimensional hydrodynamic and evolution sequences of rotating stars

    SciTech Connect

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

    2001-01-01

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

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

    E-print Network

    G. M. Graf; M. Porta

    2013-03-19

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

  13. Planar Visibility Graph Network Algorithm For Two Dimensional Timeseries

    E-print Network

    Jie Liu; Qingqing Li

    2014-11-24

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

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

    PubMed Central

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

    2007-01-01

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

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

    PubMed Central

    2015-01-01

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

  16. Two-dimensional photonic crystal color filter development.

    PubMed

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

    2009-05-11

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

  17. Stable nonlinear amplification of solitons without gain saturation

    NASA Astrophysics Data System (ADS)

    Borovkova, O. V.; Lobanov, V. E.; Malomed, B. A.

    2012-02-01

    We demonstrate that the cubic gain applied in a localized region, which is embedded into a bulk waveguide with the cubic-quintic nonlinearity and uniform linear losses, supports stable spatial solitons in the absence of the quintic dissipation. The system, featuring the bistability between the solitons and the zero state (which are separated by a family of unstable solitons), may be used as a nonlinear amplifier for optical and plasmonic solitons, which, on the contrary to previously known settings, does not require gain saturation. The results are obtained in an analytical form and corroborated by the numerical analysis.

  18. String solitons

    NASA Astrophysics Data System (ADS)

    Duff, M. J.; Khuri, Ramzi R.; Lu, J. X.

    1995-08-01

    We review the status of solitons in superstring theory, with a view to understanding the strong coupling regime. These solitonic solutions are non-singular field configurations which solve the empty-space low-energy field equations (generalized, whenever possible, to all orders in ??), carry a non-vanishing topological “magnetic” charge and are stabilized by a topological conservation law. They are compared and contrasted with the elementary solutions which are singular solutions of the field equations with a ?-model source term and carry a non-vanishing Noether “electric” charge. In both cases, the solutions of most interest are those which preserve half the space-time supersymmetries and saturate a Bogomol'nyi bound. They typically arise as the extreme mass = charge limit of more general two-parameter solutions with event horizons. We also describe the theory dual to the fundamental string for which the roles of elementary and soliton solutions are interchanged. In 10 space-time dimensions, this dual theory is a superfivebrane and this gives rise to a string/fivebrane duality conjecture according to which the fivebrane may be regarded as fundamental in its own right, with the strongly coupled string corresponding to the weakly coupled fivebrane and vice versa. After compactification to four space-time dimensions, the fivebrane appears as a magnetic monopole or a dual string according as it wraps around five or four of the compactified dimensions. This gives rise to a four-dimensional string/string duality conjecture which subsumes a Montonen-Olive type duality in that the magnetic monopoles of the fundamental string correspond to the electric winding states of the dual string. This leads to a duality of dualities whereby under string/string duality the strong/weak coupling S-duality trades places with the minimum/maximum length T-duality. Since these magnetic monopoles are extreme black holes, a prediction of S-duality is that the corresponding electric massive states of the fundamental string are also extreme black holes. This is indeed the case.

  19. Finite Element Simulation of Two-Dimensional Incompressible Magnetohydrodynamic Flows

    NASA Astrophysics Data System (ADS)

    Ip, Justin Tsz Ching

    A new finite element code has been developed for simulation of the dynamics of two-dimensional incompressible magnetohydrodynamic flows. The solution scheme used in spatial discretization is the Galerkin weighted-residual finite-element method, incorporating the mixed interpolation technique, and a combination of the penalty and pseudocompressibility methods for implementing the incompressibility constraint. An implicit and stable theta-weighting finite difference scheme is used for integration in time, and a non-iterative time-level averaging method is employed for treatment of nonlinear terms. The code has been extensively benchmarked against known analytical solutions in magnetohydrodynamics and has been found to produce highly accurate results. The tearing-mode instability of a magnetic-field-reversing current sheet in the presence of coplanar stagnation-point flow, in which the unperturbed equilibrium state is an exact solution of the steady-state dissipative MHD equations, has been examined by use of the code. Simulation results indicate stability for sufficiently small values of the viscous Lundquist number, S_nu, or the resistive Lundquist number, S_eta : a curve in the S_nu -S_eta plane separating the stable and unstable regions has been found. In the unstable regime, the results show occurrence of multiple x-line reconnection along the center of the current sheet at x = 0. Small-scale structures of vorticity and current density near the x-point reconnection sites are observed and are found to be consistent with results obtained by Matthaeus (1982). Average linear growth rates are estimated for modest values of S_eta. In the range S_eta<=500, the number of magnetic islands is found to be independent of Seta, which implies that there exists a single dominant wavelength of the tearing-mode in this range. The stretching of magnetic islands which is present in this configuration but not in the perpendicular flow and field configuration examined by Phan and Sonnerup (1991), caused a substantial decrease in linear growth rate relative to that obtained by those authors. It is of particular interest that, unlike most simulations of the tearing-mode, no symmetry conditions are imposed on the perturbations; nevertheless they develop in an anti -symmetric manner.

  20. Spatiotemporal dynamics of multimode optical solitons.

    PubMed

    Wright, Logan G; Renninger, William H; Christodoulides, Demetrios N; Wise, Frank W

    2015-02-01

    As optical fiber communications and fiber lasers approach fundamental limits there is considerable interest in multimode fibers. In nonlinear science, they represent an exciting environment for complex nonlinear waves. As in single-mode fiber, solitons may be particularly important. Multimode solitons consist of synchronized, non-dispersive pulses in multiple spatial modes, which interact via the Kerr nonlinearity of the fiber. They are expected to exhibit novel spatiotemporal characteristics, dynamics and, like single-mode solitons, may provide a convenient intuitive tool for understanding more complex nonlinear phenomena in multimode fibers. Here we explore experimentally and numerically basic properties and spatiotemporal behaviors of these solitons: their formation, fission, and Raman dynamics. PMID:25836204

  1. Solitons shedding from Airy beams and bound states of breathing Airy solitons in nonlocal nonlinear media.

    PubMed

    Shen, Ming; Gao, Jinsong; Ge, Lijuan

    2015-01-01

    We investigate the spatially optical solitons shedding from Airy beams and anomalous interactions of Airy beams in nonlocal nonlinear media by means of direct numerical simulations. Numerical results show that nonlocality has profound effects on the propagation dynamics of the solitons shedding from the Airy beam. It is also shown that the strong nonlocality can support periodic intensity distribution of Airy beams with opposite bending directions. Nonlocality also provides a long-range attractive force between Airy beams, leading to the formation of stable bound states of both in-phase and out-of-phase breathing Airy solitons which always repel in local media. PMID:25900878

  2. Solitons shedding from Airy beams and bound states of breathing Airy solitons in nonlocal nonlinear media

    PubMed Central

    Shen, Ming; Gao, Jinsong; Ge, Lijuan

    2015-01-01

    We investigate the spatially optical solitons shedding from Airy beams and anomalous interactions of Airy beams in nonlocal nonlinear media by means of direct numerical simulations. Numerical results show that nonlocality has profound effects on the propagation dynamics of the solitons shedding from the Airy beam. It is also shown that the strong nonlocality can support periodic intensity distribution of Airy beams with opposite bending directions. Nonlocality also provides a long-range attractive force between Airy beams, leading to the formation of stable bound states of both in-phase and out-of-phase breathing Airy solitons which always repel in local media. PMID:25900878

  3. Solitons in ? -helical proteins

    NASA Astrophysics Data System (ADS)

    Brizhik, L.; Eremko, A.; Piette, B.; Zakrzewski, W.

    2004-09-01

    We investigate some aspects of the soliton dynamics in an ? -helical protein macromolecule within the steric Davydov-Scott model. Our main objective is to elucidate the important role of the helical symmetry in the formation, stability, and dynamical properties of Davydov’s solitons in an ? helix. We show, analytically and numerically, that the corresponding system of nonlinear equations admits several types of stationary soliton solutions and that solitons which preserve helical symmetry are dynamically unstable: once formed, they decay rapidly when they propagate. On the other hand, the soliton which spontaneously breaks the local translational and helical symmetries possesses the lowest energy and is a robust localized entity. We also demonstrate that this soliton is the result of a hybridization of the quasiparticle states from the two lowest degenerate bands and has an inner structure which can be described as a modulated multihump amplitude distribution of excitations on individual spines. The complex and composite structure of the soliton manifests itself distinctly when the soliton is moving and some interspine oscillations take place. Such a soliton structure and the interspine oscillations have previously been observed numerically [A. C. Scott, Phys. Rev. A 26, 578 (1982)]. Here we argue that the solitons studied by Scott are hybrid solitons and that the oscillations arise due to the helical symmetry of the system and result from the motion of the soliton along the ? helix. The frequency of the interspine oscillations is shown to be proportional to the soliton velocity.

  4. Two-dimensional direction finding of acoustic sources by a vector sensor array using the propagator method

    Microsoft Academic Search

    Jin He; Zhong Liu

    2008-01-01

    This paper considers a new azimuth-elevation direction finding algorithm for multiple acoustic plane wave signals using acoustic vector array. Firstly, a planar-plus-an-isolated sensor array geometry [P. Li, J. Sun, B. Yu, Two-dimensional spatial spectrum estimation of coherent signals without spatial smoothing and eigendecomposition, IEE Proc.-Radar Sonar Navigat. 143(5) (October 1996) 295–299] is exploited and a cross-covariance matrix is defined. Then

  5. Stochastic acceleration of solitons for the nonlinear Schrödinger equation

    E-print Network

    Walid K. Abou Salem; Catherine Sulem

    2008-06-15

    The effective dynamics of solitons for the generalized nonlinear Schr\\"odinger equation in a random potential is rigorously studied. It is shown that when the external potential varies slowly in space compared to the size of the soliton, the dynamics of the center of the soliton is almost surely described by Hamilton's equations for a classical particle in the random potential, plus error terms due to radiation damping. Furthermore, a limit theorem for the dynamics of the center of mass of the soliton in the weak-coupling and space-adiabatic limit is proven in two and higher dimensions: Under certain mixing hypotheses for the potential, the momentum of the center of mass of the soliton converges in law to a diffusion process on a sphere of constant momentum. Moreover, in three and higher dimensions, the trajectory of the center of mass of the soliton converges to a spatial Brownian motion.

  6. Ponderable soliton stars

    NASA Technical Reports Server (NTRS)

    Chiu, Hong-Yee

    1990-01-01

    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.

  7. Ponderable soliton stars

    NASA Astrophysics Data System (ADS)

    Chiu, Hong-Yee

    1990-12-01

    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.

  8. Smoothed Two-Dimensional Edges for Laminar Flow

    NASA Technical Reports Server (NTRS)

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

    1986-01-01

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

  9. Inversion of the two dimensional Radon transformation by diagonalisation

    E-print Network

    Knill, Oliver

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

  10. Hall effect in the two-dimensional Luttinger liquid

    Microsoft Academic Search

    P. Anderson

    1991-01-01

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

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

    Microsoft Academic Search

    H. Schoenfelder; M. Kruse; J. Werther

    1996-01-01

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

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

    Microsoft Academic Search

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

    1998-01-01

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

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

    Microsoft Academic Search

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

    1997-01-01

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

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

    NASA Astrophysics Data System (ADS)

    Sánches-Ruiz, Jorge

    1998-07-01

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

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

    EPA Science Inventory

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

  16. A Family of Two-Dimensional Nonseparable Malvar Wavelets

    Microsoft Academic Search

    Xiang-Gen Xia; Bruce W. Suter

    1995-01-01

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

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

    Microsoft Academic Search

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

    2007-01-01

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

  18. Acoustic metamaterials for new two-dimensional sonic devices

    Microsoft Academic Search

    Daniel Torrent; José Sánchez-Dehesa

    2007-01-01

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

  19. Two-Dimensional Grids About Airfoils and Other Shapes

    NASA Technical Reports Server (NTRS)

    Sorenson, R.

    1982-01-01

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

  20. Two-dimensional contact analysis of elastic graded materials

    Microsoft Academic Search

    A. E. Giannakopoulos; P. Pallot

    2000-01-01

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

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

    Microsoft Academic Search

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

    1994-01-01

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

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

    E-print Network

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

    2009-11-17

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

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

    Microsoft Academic Search

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

    2008-01-01

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

  4. Quantum of optical absorption in two-dimensional semiconductors

    E-print Network

    California at Irvine, University of

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

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

    E-print Network

    R. Balbinot; A. Fabbri

    1996-07-04

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

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

    E-print Network

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

  7. Numerical simulation of two?dimensional tsunami runup

    Microsoft Academic Search

    Z. Kowalik; T. S. Murty

    1993-01-01

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

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

    E-print Network

    Joachim Stubbe

    2008-07-25

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

  9. Intensity coding in two-dimensional excitable neural networks

    Microsoft Academic Search

    Mauro Copelli; Osame Kinouchi

    2005-01-01

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

  10. Hexagonal structures for two-dimensional photonic crystals

    Microsoft Academic Search

    D. Cassagne; C. Jouanin; D. Bertho

    1996-01-01

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

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

    Microsoft Academic Search

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

    1998-01-01

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

  12. Describing two-dimensional vortical flows the typhoon case

    E-print Network

    Spineanu, F

    2005-01-01

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

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

    NASA Astrophysics Data System (ADS)

    Minotti, F. O.

    2003-11-01

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

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

    Microsoft Academic Search

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

    1997-01-01

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

  15. Two-Dimensional Sensor Integration Using Resonant Proximity Connector

    E-print Network

    Shinoda, Hiroyuki

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

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

    Microsoft Academic Search

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

    2005-01-01

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

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

    Microsoft Academic Search

    Leigh Anderson; Norman G. Anderson

    1977-01-01

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

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

    E-print Network

    Fleming, Graham R.

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

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

    PubMed

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

    2013-01-28

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

  20. Charged black holes in two-dimensional string theory

    Microsoft Academic Search

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

    1991-01-01

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

  1. SAR Processing Based On Two-Dimensional Transfer Function

    NASA Technical Reports Server (NTRS)

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

    1994-01-01

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

  2. Sound waves in two-dimensional ducts with sinusoidal walls

    NASA Technical Reports Server (NTRS)

    Nayfeh, A. H.

    1974-01-01

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

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

    E-print Network

    Olberding, Bruce

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

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

    E-print Network

    Motygin, Oleg V.

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

  5. Morphometric investigations in mitral stenosis using two dimensional echocardiography

    Microsoft Academic Search

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

    1982-01-01

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

  6. Two-Dimensional Diverging Shocks in a Nonuniform Medium

    SciTech Connect

    Roy A. Axford

    1998-08-01

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

  7. Preliminary Two Dimensional Haptic Thresholds and Task Performance Enhancements

    E-print Network

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

  8. Robotic deburring of two dimensional parts with unknown geometry

    Microsoft Academic Search

    H. Kazerooni; M. G. Her

    1988-01-01

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

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

    E-print Network

    Jackman, Charles H.

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

  10. On the stability of two-dimensional digital filters

    Microsoft Academic Search

    G. Maria; M. Fahmy

    1973-01-01

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

  11. Two-dimensional optimization of free electron laser designs

    DOEpatents

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

    1985-01-01

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

  12. Two-dimensional optimization of free-electron-laser designs

    DOEpatents

    Prosnitz, D.; Haas, R.A.

    1982-05-04

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

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

    SciTech Connect

    Brink, D.M.; Klarsfeld, S.

    1985-11-01

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

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

    Microsoft Academic Search

    A. Barra; D. Cassagne; C. Jouanin

    1999-01-01

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

  15. Self Organization of Two-dimensional Insect Neural Networks

    E-print Network

    Jacob, Eshel Ben

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

  16. Two Dimensional Optimal Mechanism Design for a Sequencing Problem

    E-print Network

    Al Hanbali, Ahmad

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

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

    Microsoft Academic Search

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

    1989-01-01

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

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

    E-print Network

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

    2007-01-01

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

  19. Two-Dimensional Range Diameter Queries Pooya Davoodi1

    E-print Network

    Smid, Michiel

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

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

    Microsoft Academic Search

    Asbjørn Strand; Ø. Hov

    1994-01-01

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

  1. Automated design of two-dimensional rational decimation systems

    Microsoft Academic Search

    Brian L. Evans; Jurgen Teich; Christian Schwarz

    1994-01-01

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

  2. TWO DIMENSIONAL IMMERSED BOUNDARY SIMULATIONS OF SWIMMING JELLYFISH

    E-print Network

    Stockie, John

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

  3. Surface solitons in left-handed metamaterials

    E-print Network

    G. T. Adamashvili; A. Knorr

    2007-09-08

    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.

  4. Optical solitons and quasisolitons

    Microsoft Academic Search

    V. E. Zakharov; E. A. Kuznetsov

    1998-01-01

    Optical solitons and quasisolitons are investigated in reference to Cherenkov radiation. It is shown that both solitons and\\u000a quasisolitons can exist, if the linear operator specifying their asymptotic behavior at infinity is sign-definite. In particular,\\u000a the application of this criterion to stationary optical solitons shifts the soliton carrier frequency at which the first derivative\\u000a of the dielectric constant with respect

  5. Autophasing of solitons

    SciTech Connect

    Batalov, S. V. [Russian Academy of Sciences, Ural Branch, Institute of Metal Physics (Russian Federation); Maslov, E. M. [Russian Academy of Sciences, Institute of Terrestrial Magnetism, Ionosphere, and Radiowave Propagation (Russian Federation)], E-mail: zheka@izmiran.ru; Shagalov, A. G. [Russian Academy of Sciences, Ural Branch, Institute of Metal Physics (Russian Federation)

    2009-05-15

    The effect of an external wave perturbation with a slowly varying frequency on a soliton of the nonlinear Schroedinger equation is investigated. The equations that describe the time evolution of the perturbed-soliton parameters are derived. The necessary and sufficient soliton phase locking conditions that relate the rate of change in the frequency of the perturbation, its amplitude, wave number, and phase to the initial values of parameters for the soliton have been found.

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

    E-print Network

    Pouquet, Annick

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

  7. Vector Soliton Fiber Lasers

    Microsoft Academic Search

    Han Zhang

    2011-01-01

    Solitons, as stable localized wave packets that can propagate long distance in dispersive media without changing their shapes, are ubiquitous in nonlinear physical systems. Since the first experimental realization of optical bright solitons in the anomalous dispersion single mode fibers (SMF) by Mollenauer et al. in 1980 and optical dark solitons in the normal dispersion SMFs by P. Emplit et

  8. Universal velocity profile for coherent vortices in two-dimensional turbulence.

    PubMed

    Chertkov, M; Kolokolov, I; Lebedev, V

    2010-01-01

    Two-dimensional turbulence generated in a finite box produces large-scale coherent vortices coexisting with small-scale fluctuations. We present a rigorous theory explaining the eta=1/4 scaling in the V is proportional to r(-eta) law of the velocity spatial profile within a vortex, where r is the distance from the vortex center. This scaling, consistent with earlier numerical and laboratory measurements, is universal in its independence of details of the small-scale injection of turbulent fluctuations and details of the shape of the box. PMID:20365424

  9. Solution of two-dimensional Euler equations: Experience with a finite volume code

    NASA Astrophysics Data System (ADS)

    Kroll, Norbert; Jain, Romesh Kumar

    1987-09-01

    A numerical method for the solution of two-dimensional Euler equations using a finite volume spatial discretization and Runge Kutta time stepping schemes, given by Jameson, Schmidt, and Turkel (1981) is described. Critical features of the algorithm like implementation of boundary conditions, influence of the artificial dissipation, multistage time stepping schemes, and acceleration techniques for the convergence to steady state, are analyzed. Accuracy and reliability of the computer code is tested in computing subsonic and transonic flows around various airfoils. Results are satisfactory.

  10. Synchronization of particle motion induced by mode coupling in a two-dimensional plasma crystal.

    PubMed

    Couëdel, L; Zhdanov, S; Nosenko, V; Ivlev, A V; Thomas, H M; Morfill, G E

    2014-05-01

    The kinematics of dust particles during the early stage of mode-coupling induced melting of a two-dimensional plasma crystal is explored. It is found that the formation of the hybrid mode causes the particle vibrations to partially synchronize at the hybrid frequency. Phase- and frequency-locked hybrid particle motion in both vertical and horizontal directions (hybrid mode) is observed. The system self-organizes in a rhythmic pattern of alternating in-phase and antiphase oscillating chains of particles. The spatial orientation of the synchronization pattern correlates well with the directions of the maximal increment of the shear-free hybrid mode. PMID:25353905

  11. Two-dimensional integrating matrices on rectangular grids. [solving differential equations associated with rotating structures

    NASA Technical Reports Server (NTRS)

    Lakin, W. D.

    1981-01-01

    The use of integrating matrices in solving differential equations associated with rotating beam configurations is examined. In vibration problems, by expressing the equations of motion of the beam in matrix notation, utilizing the integrating matrix as an operator, and applying the boundary conditions, the spatial dependence is removed from the governing partial differential equations and the resulting ordinary differential equations can be cast into standard eigenvalue form. Integrating matrices are derived based on two dimensional rectangular grids with arbitrary grid spacings allowed in one direction. The derivation of higher dimensional integrating matrices is the initial step in the generalization of the integrating matrix methodology to vibration and stability problems involving plates and shells.

  12. Two-dimensional micron-step probe drive for laboratory plasma measurement

    SciTech Connect

    Collette, A.; Gekelman, W. [Department of Physics and Astronomy, University of California, Los Angeles, 1000 Veteran Ave., Suite 15-70, California 90095 (United States)

    2008-08-15

    Laboratory measurement of small-scale ({approx}1 mm) magnetic phenomena over an extended area is a challenge requiring precise diagnostics. We present a novel two dimensional magnetic probe platform capable of directly measuring the magnetic field over a 36 cm{sup 2} region at spatial resolutions better than 1 mm. The platform is discussed in the context of an experiment at the Large Plasma Device facility at UCLA, designed to measure the magnetic interaction between two counterpropagating laser-produced plasmas. The use of a precise, repeatable positioning platform enables the recovery of information about the interaction using cross-correlation techniques.

  13. Using the two-dimensional anisotropic wavelet transform for exploring anisotropy from a digitized core image

    NASA Astrophysics Data System (ADS)

    Gaci, Said; Zaourar, Naima; Hachay, Olga

    2015-04-01

    A natural process is the mixture of various components of different scales. The two-dimensional anisotropic wavelet analysis appears to be perfectly appropriate to investigate such processes and to highlight details at a given analyzing scale. Here, we present a wavelet-based technique, which is specifically the Normalized Optimized Anisotropic Wavelet Coefficient (NOAWC). Then, the potential of the latter is demonstrated through its application on a digitized image of a core extracted from an Algerian exploration borehole. The NOAWC method has allowed to accurately quantify anisotropies of orientation, shape and spatial distributions of the investigated core at different scales, and thus to provide supplementary information enriching the conventional analysis.

  14. Terahertz wideband spectroscopic imaging based on two-dimensional electro-optic sampling technique

    NASA Astrophysics Data System (ADS)

    Usami, Mamoru; Yamashita, Masatsugu; Fukushima, Kazushiro; Otani, Chiko; Kawase, Kodo

    2005-04-01

    We extended the bandwidth of a terahertz (THz) spectroscopic imaging system based on two-dimensional electro-optic sampling. By using an optical-rectification emitter, formed by a ZnTe crystal, a high-frequency component of more than 2.0THz was detected. A calibration-free procedure with polarity inversion of the THz beam ensures us precise spectroscopy: the polarity was inverted by rotating the emitter crystal. The spatial patterns of the chemicals were extracted from the THz multispectral images in the extended spectral region.

  15. Experimental observation of local rearrangements in dense quasi-two-dimensional emulsion flow

    NASA Astrophysics Data System (ADS)

    Chen, Dandan; Desmond, Kenneth W.; Weeks, Eric R.

    2015-06-01

    We experimentally study rearranging regions in slow athermal flow by observing the flow of a concentrated oil-in-water emulsion in a thin chamber with a constricting hopper shape. The gap of the chamber is smaller than the droplet diameters, so that the droplets are compressed into quasi-two-dimensional pancakes. We focus on localized rearrangements known as "T1 events" where four droplets exchange neighbors. Flowing droplets are deformed due to forces from neighboring droplets, and these deformations are decreased by nearby T1 events, with a spatial dependence related to the local structure. We see a tendency of the T1 events to occur in small clusters.

  16. Excitation of coherent polaritons in a two-dimensional atomic lattice

    E-print Network

    Barinov, I O; Arakelian, S M

    2009-01-01

    We describe a new type of spatially periodic structure (lattice models): a polaritonic crystal (PolC) formed by a two-dimensional lattice of trapped two-level atoms interacting with quantised electromagnetic field in a cavity (or in a one-dimensional array of tunnelling-coupled microcavities), which allows polaritons to be fully localised. Using a one-dimensional polaritonic crystal as an example, we analyse conditions for quantum degeneracy of a low-branch polariton gas and those for quantum optical information recording and storage.

  17. Two-dimensional diffractive coherent combining of 15 fiber amplifiers into a 600 W beam.

    PubMed

    Thielen, Peter A; Ho, James G; Burchman, David A; Goodno, Gregory D; Rothenberg, Joshua E; Wickham, Michael G; Flores, Angel; Lu, Chunte A; Pulford, Benjamin; Robin, Craig; Sanchez, Anthony D; Hult, D; Rowland, K B

    2012-09-15

    We demonstrate coherent beam combining using a two-dimensionally patterned diffractive optic combining element. Fifteen Yb-doped fiber amplifier beams arranged in a 3×5 array were combined into a single 600 W, M²=1.1 output beam with 68% combining efficiency. Combining losses under thermally stable conditions at 485 W were found to be dominated by spatial mode-mismatch between the free space input beams, in quantitative agreement with calculations using the measured amplitude and phase profiles of the input beams. PMID:23041844

  18. Soliton deflexion for(1 + 3)D Kadomtsev-Petviashvili Equation

    NASA Astrophysics Data System (ADS)

    Li, Donglong; Lin, Jianqiang; Liu, Xuhong

    2009-09-01

    Two types of soliton deflexion of (1 + 3)D Kadomtsev-Petviashvili (K-P) equation are considered. Using the Hirota bilinear form and the new technique of "homoclinic test", a type of exact periodic soliton solution of the K-P equation with positive transverse dispersion effects is obtained. Another type of periodic soliton solution is found by means of the periodic soliton solution of the K-P equation with negative transverse dispersion effects and a temporal and spatial transformation. It is also investigated that the equilibrium solution u0=-{1}/{6} is an unique deflexion point, periodic soliton of traveling in different spatial directions will be interchanged with the solution varying from one side of -1/6 to the other side.

  19. The mixing layer and its coherence examined from the point of view of two-dimensional turbulence

    NASA Astrophysics Data System (ADS)

    Lesieur, Marcel; Staquet, Chantal; Le Roy, Pascal; Comte, Pierre

    1988-07-01

    A two-dimensional numerical large-eddy simulation of a temporal mixing layer subjected to a white-noise perturbation is presented. The first pairing of vortices having the same sign is shown to be responsible for the formation of a continuous spatial longitudinal energy spectrum of slope between k exp -4 and k exp -3. Pairs of flows differing slightly at the first roll-up are studied, and it is found that in an infinite domain the two fields become completely decorrelated. It is demonstrated that the two-dimensional mixing layer is an example of flow that is upredictable and possesses a broadband kinetic energy spectrum. Within the framework of a one-mode spectral truncation in the spanwise direction, it is shown how the present two-dimensional predictability analysis can be associated with the growth of a particular spanwise perturbation developing on a Kelvin-Helmholtz billow.

  20. Solitons in nonlinear optics

    SciTech Connect

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

    2010-11-13

    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)

  1. Meshless local Petrov-Galerkin (MLPG) approximation to the two dimensional sine-Gordon equation

    NASA Astrophysics Data System (ADS)

    Mirzaei, Davoud; Dehghan, Mehdi

    2010-03-01

    During the past few years, the idea of using meshless methods for numerical solution of partial differential equations (PDEs) has received much attention throughout the scientific community, and remarkable progress has been achieved on meshless methods. The meshless local Petrov-Galerkin (MLPG) method is one of the "truly meshless" methods since it does not require any background integration cells. The integrations are carried out locally over small sub-domains of regular shapes, such as circles or squares in two dimensions and spheres or cubes in three dimensions. In this paper the MLPG method for numerically solving the non-linear two-dimensional sine-Gordon (SG) equation is developed. A time-stepping method is employed to deal with the time derivative and a simple predictor-corrector scheme is performed to eliminate the non-linearity. A brief discussion is outlined for numerical integrations in the proposed algorithm. Some examples involving line and ring solitons are demonstrated and the conservation of energy in undamped SG equation is investigated. The final numerical results confirm the ability of proposed method to deal with the unsteady non-linear problems in large domains.

  2. Two-Photon Cavity Solitons in Active Optical Media

    SciTech Connect

    Vilaseca, R.; Torrent, M. C.; Garcia-Ojalvo, J.; Brambilla, M.; San Miguel, M.

    2001-08-20

    We show that broad-area cascade lasers with no absorbing intracavity elements support the spontaneous formation of two-dimensional bright localized structures in a dark background. These cavity solitons consist of islands of two-photon emission embedded in a background of single-photon emission. We discuss the mechanisms through which these structures are formed and interact, along with their properties and stability.

  3. Soliton dynamics in the multiphoton plasma regime

    PubMed Central

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

    2013-01-01

    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.

  4. Soliton dynamics in the multiphoton plasma regime

    NASA Astrophysics Data System (ADS)

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

    2013-01-01

    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.

  5. Two-dimensional Raman-terahertz spectroscopy of water

    PubMed Central

    Savolainen, Janne; Ahmed, Saima; Hamm, Peter

    2013-01-01

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

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

    E-print Network

    Cahangirov, S

    2014-01-01

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

  7. F2D: A two dimensional compressible gas flow code

    SciTech Connect

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

    1993-01-20

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

  8. F2D: A two dimensional compressible gas flow code

    NASA Astrophysics Data System (ADS)

    Ahti, Suo-Anttila

    1993-01-01

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

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

    SciTech Connect

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

    2014-11-14

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

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

    NASA Technical Reports Server (NTRS)

    Tollestrup, Eric V.; Harvey, Paul M.

    1989-01-01

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

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

    NASA Astrophysics Data System (ADS)

    Sarkar, S.; Gupta, G. S.

    2008-10-01

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

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

    SciTech Connect

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

    2010-01-11

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

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

    USGS Publications Warehouse

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

    1985-01-01

    A simple two-dimensional dam-break model is developed for flood plain study purposes. Both a finite difference grid and an irregular triangle element integrated finite difference formulation are presented. The governing flow equations are approximately solved as a diffusion model coupled to the equation of continuity. Application of the model to a hypothetical dam-break study indicates that the approach can be used to predict a two-dimensional dam-break flood plain over a broad, flat plain more accurately than a one-dimensional model, especially when the flow can break-out of the main channel and then return to the channel at other downstream reaches. ?? 1985.

  14. Two-Dimensional Computational Model for Wave Rotor Flow Dynamics

    NASA Technical Reports Server (NTRS)

    Welch, Gerard E.

    1996-01-01

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

  15. Disordered quantum walks in two-dimensional lattices plink

    NASA Astrophysics Data System (ADS)

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

    2015-01-01

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

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

    NASA Astrophysics Data System (ADS)

    Lucas, Andrew; Chesler, Paul M.

    2015-03-01

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

  17. Multigrid Navier-Stokes calculation for two dimensional cascades

    NASA Astrophysics Data System (ADS)

    Yang, Ce; Lao, Dazhong; Jiang, Zikang

    1998-03-01

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

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

    SciTech Connect

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

    2010-06-15

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

  19. Folding two dimensional crystals by swift heavy ion irradiation

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

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

  20. Gas Kinetic Approach to Two-Dimensional Traffic Flow

    NASA Astrophysics Data System (ADS)

    Nagatani, Takashi

    1996-10-01

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

  1. Stable three-dimensional solitons in attractive Bose-Einstein condensates loaded in an optical lattice

    SciTech Connect

    Mihalache, D. [ICFO-Institut de Ciencies Fotoniques, and Department of Signal Theory and Communications, Universitat Politecnica de Catalunya, 08034 Barcelona (Spain); Institute of Solid State Theory and Theoretical Optics, Friedrich-Schiller Universitaet Jena, Max-Wien-Platz 1, D-077743 Jena (Germany); Horia Hulubei National Institute of Physics and Nuclear Engineering, Department of Theoretical Physics, P.O. Box MG-6, Bucharest (Romania); Mazilu, D. [Institute of Solid State Theory and Theoretical Optics, Friedrich-Schiller Universitaet Jena, Max-Wien-Platz 1, D-077743 Jena (Germany); Horia Hulubei National Institute of Physics and Nuclear Engineering, Department of Theoretical Physics, P.O. Box MG-6, Bucharest (Romania); Lederer, F. [Institute of Solid State Theory and Theoretical Optics, Friedrich-Schiller Universitaet Jena, Max-Wien-Platz 1, D-077743 Jena (Germany); Malomed, B.A. [Department of Interdisciplinary Studies, Faculty of Engineering, Tel Aviv University, Tel Aviv 69978 (Israel); Crasovan, L.-C. [ICFO-Institut de Ciencies Fotoniques, and Department of Signal Theory and Communications, Universitat Politecnica de Catalunya, 08034 Barcelona (Spain); Horia Hulubei National Institute of Physics and Nuclear Engineering, Department of Theoretical Physics, P.O. Box MG-6, Bucharest (Romania); Kartashov, Y.V.; Torner, L. [ICFO-Institut de Ciencies Fotoniques, and Department of Signal Theory and Communications, Universitat Politecnica de Catalunya, 08034 Barcelona (Spain)

    2005-08-15

    The existence and stability of solitons in Bose-Einstein condensates with attractive interatomic interactions, described by the Gross-Pitaevskii equation with a three-dimensional (3D) periodic potential, are investigated in a systematic form. We find a one-parameter family of stable 3D solitons in a certain interval of values of their norm, provided that the strength of the potential exceeds a threshold value. The minimum number of {sup 7}Li atoms in the stable solitons is 60, and the energy of the soliton at the stability threshold is {approx_equal}6 recoil energies in the lattice. The respective energy versus norm diagram features two cuspidal points, resulting in a typical swallowtail pattern, which is a generic feature of 3D solitons supported by quasi-two-dimensional or fully dimensional lattice potentials.

  2. Stable three-dimensional solitons in attractive Bose-Einstein condensates loaded in an optical lattice

    NASA Astrophysics Data System (ADS)

    Mihalache, D.; Mazilu, D.; Lederer, F.; Malomed, B. A.; Crasovan, L.-C.; Kartashov, Y. V.; Torner, L.

    2005-08-01

    The existence and stability of solitons in Bose-Einstein condensates with attractive interatomic interactions, described by the Gross-Pitaevskii equation with a three-dimensional (3D) periodic potential, are investigated in a systematic form. We find a one-parameter family of stable 3D solitons in a certain interval of values of their norm, provided that the strength of the potential exceeds a threshold value. The minimum number of Li7 atoms in the stable solitons is 60, and the energy of the soliton at the stability threshold is ?6 recoil energies in the lattice. The respective energy versus norm diagram features two cuspidal points, resulting in a typical swallowtail pattern, which is a generic feature of 3D solitons supported by quasi-two-dimensional or fully dimensional lattice potentials.

  3. Quantum computation with two-dimensional graphene quantum dots

    Microsoft Academic Search

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

    2012-01-01

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

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

    Microsoft Academic Search

    Hirosi Ooguri; Cumrun Vafa

    1996-01-01

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

  5. Hall effect in the two-dimensional Luttinger liquid

    SciTech Connect

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

    1991-10-07

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

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

    Microsoft Academic Search

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

    1999-01-01

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

  7. Electromagnetic Two-Dimensional Scanner Using Radial Magnetic Field

    Microsoft Academic Search

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

    2007-01-01

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

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

    Microsoft Academic Search

    Hoang Manh Chu; Kazuhiro Hane

    2010-01-01

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

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

    Microsoft Academic Search

    Takenobu Nakamura; Michio Otsuki; Shin-Ichi Sasa

    2005-01-01

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

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

    Microsoft Academic Search

    C. B. Whan

    1997-01-01

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

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

    Microsoft Academic Search

    Eric V. Tollestrup; Paul M. Harvey

    1989-01-01

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

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

    Microsoft Academic Search

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

    1997-01-01

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

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

    Microsoft Academic Search

    Marco Tomassini; Mathieu Perrenoud

    2000-01-01

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

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

    Microsoft Academic Search

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

    1996-01-01

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

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

    Microsoft Academic Search

    Ishtiaque Hossain; Mahmoud R. El-Sakka

    2012-01-01

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

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

    PubMed

    Géminard, J-C; Laroche, C

    2004-08-01

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

  17. Two dimensional thermal and charge mapping of power thyristors

    NASA Technical Reports Server (NTRS)

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

    1975-01-01

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

  18. A two-dimensional theory of fracture propagation

    Microsoft Academic Search

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

    1982-01-01

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

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

    Microsoft Academic Search

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

    2006-01-01

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

  20. Two-Dimensional Bernstein-Greene-Kruskal Solution

    NASA Astrophysics Data System (ADS)

    Ishibashi, Nobuo; Kitahara, Kazuo

    1992-08-01

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

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

    Microsoft Academic Search

    F. Scarano; B. W. van Oudheusden

    2003-01-01

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

  2. Two-dimensional correlation spectroscopy in polymer study

    PubMed Central

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

    2015-01-01

    This review outlines the recent works of two-dimensional correlation spectroscopy (2DCOS) in polymer study. 2DCOS is a powerful technique applicable to the in-depth analysis of various spectral data of polymers obtained under some type of perturbation. The powerful utility of 2DCOS combined with various analytical techniques in polymer studies and noteworthy developments of 2DCOS used in this field are also highlighted. PMID:25815286

  3. A Calculation Procedure for Two-Dimensional Elliptic Situations

    Microsoft Academic Search

    Suhas Patankar

    1981-01-01

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

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

    Microsoft Academic Search

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

    2006-01-01

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

  5. Multigrid Navier-Stokes calculation for two dimensional cascades

    Microsoft Academic Search

    Ce Yang; Dazhong Lao; Zikang Jiang

    1998-01-01

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

  6. Instability of two-dimensional heterotic stringy black holes

    NASA Astrophysics Data System (ADS)

    Azreg-Aïnou, Mustapha

    1999-01-01

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

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

    PubMed

    Kozlov, Vladimir; Kuznetsov, Nikolay; Motygin, Oleg

    2011-08-01

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

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

    Microsoft Academic Search

    Stephen W. Smith; Edward D. Light

    1993-01-01

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

  9. Exact analytic flux distributions for two-dimensional solar concentrators.

    PubMed

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

    2013-07-01

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

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

    Microsoft Academic Search

    Giovanni Sordi; A.-M. S. Tremblay

    2010-01-01

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

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

    Microsoft Academic Search

    A. Abo-Taleb; M. Fahmy

    1984-01-01

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

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

    SciTech Connect

    Jardin, S.C.; Park, W.

    1980-09-01

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

  13. Nonlinear two-dimensional potential plasma wake waves

    SciTech Connect

    Amatuni, A.Ts.

    1995-12-01

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

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

    Microsoft Academic Search

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

    1998-01-01

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

  15. The Dirichlet problem on two-dimensional stratified sets

    NASA Astrophysics Data System (ADS)

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

    2015-02-01

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

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

    NASA Astrophysics Data System (ADS)

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

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

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

    Microsoft Academic Search

    Gwo-Lianq Chern; Yuan-Chin Chang

    2006-01-01

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

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

    Microsoft Academic Search

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

    2009-01-01

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

  19. Multigrid ADI method for two-dimensional electromagnetic simulations

    Microsoft Academic Search

    Shumin Wang; J. Chen

    2006-01-01

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

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

    Microsoft Academic Search

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

    2010-01-01

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

  1. Two-dimensional photonic crystal hexagonal waveguide ring laser

    Microsoft Academic Search

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

    2002-01-01

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

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

    Microsoft Academic Search

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

    2003-01-01

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

  3. Harmonic Oscillator in Noncommuting Two-Dimensional Space

    NASA Astrophysics Data System (ADS)

    Streklas, Antony

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

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

    NASA Astrophysics Data System (ADS)

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

    2006-05-01

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

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

    PubMed

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

    2015-01-01

    Charged plasma and Fermi liquid are two distinct states of electronic matter intrinsic to dilute two-dimensional electron systems at elevated and low temperatures, respectively. Probing their thermodynamics represents challenge because of lack of an adequate technique. Here, we report a thermodynamic method to measure the entropy per electron in gated structures. Our technique appears to be three orders of magnitude superior in sensitivity to a.c. calorimetry, allowing entropy measurements with only 10(8) electrons. This enables us to investigate the correlated plasma regime, previously inaccessible experimentally in two-dimensional electron systems in semiconductors. In experiments with clean two-dimensional electron system in silicon-based structures, we traced entropy evolution from the plasma to Fermi liquid regime by varying electron density. We reveal that the correlated plasma regime can be mapped onto the ordinary non-degenerate Fermi gas with an interaction-enhanced temperature-dependent effective mass. Our method opens up new horizons in studies of low-dimensional electron systems. PMID:26099565

  6. Procedures for two-dimensional electrophoresis of proteins

    SciTech Connect

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

    1996-10-01

    High-resolution two-dimensional gel electrophoresis (2DE) of proteins, using isoelectric focusing in the first dimension and sodium dodecyl sulfate/polyacrylamide gel electrophoresis (SDS-PAGE) in the second, was first described in 1975. In the 20 years since those publications, numerous modifications of the original method have evolved. The ISO-DALT system of 2DE is a high-throughput approach that has stood the test of time. The problem of casting many isoelectric focusing gels and SDS-PAGE slab gels (up to 20) in a reproducible manner has been solved by the use of the techniques and equipment described in this manual. The ISO-DALT system of two-dimensional gel electrophoresis originated in the late 1970s and has been modified many times to improve its high-resolution, high-throughput capabilities. This report provides the detailed procedures used with the current ISO-DALT system to prepare, run, stain, and photograph two-dimensional gels for protein analysis.

  7. Photon trapping and transfer with solitons

    E-print Network

    Steiglitz, Ken

    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 ...

  8. Nonlinear waves and solitons in molecular clouds

    NASA Technical Reports Server (NTRS)

    Adams, Fred C.; Fatuzzo, Marco

    1993-01-01

    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.

  9. Variational and accessible soliton approximations to multidimensional solitons in highly nonlocal nonlinear media.

    PubMed

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

    2014-12-29

    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

  10. Transport and diffusion properties of interacting colloidal particles in two-dimensional microchannels with a periodic potential.

    PubMed

    Siems, Ullrich; Nielaba, Peter

    2015-02-01

    We report a Brownian dynamics simulation study of a two-dimensional system of repulsive colloidal particles in a channel geometry with a sinusoidal substrate potential under influence of a constant driving. The effect of this driving on the structure, mobility, and diffusion is discussed as well as the appearance of kink and antikink solitons. The competing order principles of the hexagonal crystal structure, the period of the substrate, and the layering due to the confining walls can be either commensurable or incommensurable. The combination of those three leads to new effects. The simultaneous occurrence of kinks and antikinks can be observed, due to the energy difference between boundary- and midlanes, and similarities to the electron-hole conductivity in a semiconductor can be found. PMID:25768511

  11. Transport and diffusion properties of interacting colloidal particles in two-dimensional microchannels with a periodic potential

    NASA Astrophysics Data System (ADS)

    Siems, Ullrich; Nielaba, Peter

    2015-02-01

    We report a Brownian dynamics simulation study of a two-dimensional system of repulsive colloidal particles in a channel geometry with a sinusoidal substrate potential under influence of a constant driving. The effect of this driving on the structure, mobility, and diffusion is discussed as well as the appearance of kink and antikink solitons. The competing order principles of the hexagonal crystal structure, the period of the substrate, and the layering due to the confining walls can be either commensurable or incommensurable. The combination of those three leads to new effects. The simultaneous occurrence of kinks and antikinks can be observed, due to the energy difference between boundary- and midlanes, and similarities to the electron-hole conductivity in a semiconductor can be found.

  12. Quasi-one-dimensional optical lattices for soliton manipulation.

    PubMed

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

    2014-11-15

    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

  13. Spin solitons and waves in chiral molecular ferrimagnets

    SciTech Connect

    Morgunov, R. B., E-mail: morgunov2005@yandex.ru; Kirman, M. V. [Russian Academy of Sciences, Institute of Problems of Chemical Physics (Russian Federation); Berdinskii, V. L. [Orenburg State University (Russian Federation); Inoue, K. [Hiroshima University, Graduated School of Science (Japan); Kishine, J. [Kushu University of Technology, Faculty of Engineering (Japan)

    2008-07-15

    Resonance modes corresponding to a spin-soliton resonance have been found in the electron spin resonance spectra of [Cr(CN){sub 6}][Mn(S)-pnH-(H{sub 2}O)]H{sub 2}O two-dimensional (2D) chiral single crystals and [Mn{l_brace}(R/S)-pn{r_brace}]{sub 2}[Mn{l_brace}(R/S)-pn{r_brace}{sub 2}(H{sub 2}O)][Cr(CN){sub 6}]{sub 2} chiral single crystals with a 3D magnetic order. It is also established that the chiral crystals of both types exhibit a spin-wave resonance analogous to the excitation of standing spin waves in thin magnetic films. At the same time, racemic crystals of the first type do not exhibit spin-soliton resonance. The entire body of experimental data indicates that the chirality of crystals influences the spin excitations (standing spin waves and solitons) in these media.

  14. Optical two-dimensional fourier transform spectroscopy of semiconductor quantum wells.

    PubMed

    Cundiff, Steven T; Zhang, Tianhao; Bristow, Alan D; Karaiskaj, Denis; Dai, Xingcan

    2009-09-15

    Coherent light-matter interactions of direct-gap semiconductor nanostructures provide a great test system for fundamental research into quantum electronics and many-body physics. The understanding gained from studying these interactions can facilitate the design of optoelectronic devices. Recently, we have used optical two-dimensional Fourier-transform spectroscopy to explore coherent light-matter interactions in semiconductor quantum wells. Using three laser pulses to generate a four-wave-mixing signal, we acquire spectra by tracking the phase of the signal with respect to two time axes and then Fourier transforming them. In this Account, we show several two-dimensional projections and demonstrate techniques to isolate different contributions to the coherent response of semiconductors. The low-temperature spectrum of semiconductor quantum wells is dominated by excitons, which are electron-hole pairs bound through Coulombic interactions. Excitons are sensitive to their electronic and structural environment, which influences their optical resonance energies and line widths. In near perfect quantum wells, a small fluctuation of the quantum well thickness leads to spatial localization of the center-of-mass wave function of the excitons and inhomogeneous broadening of the optical resonance. The inhomogeneous broadening often masks the homogeneous line widths associated with the scattering of the excitons. In addition to forming excitons, Coulombic correlations also form excitonic molecules, called biexcitons. Therefore, the coherent response of the quantum wells encompasses the intra-action and interaction of both excitons and biexcitons in the presence of inhomogeneous broadening. Transient four-wave-mixing studies combined with microscopic theories have determined that many-body interactions dominate the strong coherent response from quantum wells. Although the numerous competing interactions cannot be easily separated in either the spectral or temporal domains, they can be separated using two-dimensional Fourier transform spectroscopy. The most common two-dimensional Fourier spectra are S(I)(omega(tau),T,omega(t)) in which the second time period is held fixed. The result is a spectrum that unfolds congested one-dimensional spectra, separates excitonic pathways, and shows which excitons are coherently coupled. This method also separates the biexciton contributions and isolates the homogeneous and inhomogeneous line widths. For semiconductor excitons, the line shape in the real part of the spectrum is sensitive to the many-body interactions, which we can suppress by exploiting polarization selection rules. In an alternative two-dimensional projection, S(I)(tau,omega(Tau),omega(t)), the nonradiative Raman coherent interactions are isolated. Finally, we show S(III)(tau,omega(Tau),omega(t)) spectra that isolate the two-quantum coherences associated with the biexciton. These spectra reveal previously unobserved many-body correlations. PMID:19555068

  15. Solitons versus parametric instabilities during ionospheric heating

    NASA Technical Reports Server (NTRS)

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

    1984-01-01

    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).

  16. Incoherently coupled dark-bright photorefractive solitons

    NASA Astrophysics Data System (ADS)

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

    1996-11-01

    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.

  17. Gyroelectric cubic-quintic dissipative solitons

    Microsoft Academic Search

    Allan D. Boardman; Larry Velasco

    2006-01-01

    The influence of an externally applied magnetic field upon classic cubic quintic dissipative solitons is investigated using both exact simulations and a Lagrangian technique. The basic approach is to use a spatially inhomogeneous magnetic field and to consider two important geometries, namely the Voigt and the Faraday effects. A layered structure is selected for the Voigt case, with the principal

  18. The NASA Ames Research Center one- and two-dimensional stratospheric models. Part 2: The two-dimensional model

    NASA Technical Reports Server (NTRS)

    Whitten, R. C.; Borucki, W. J.; Watson, V. R.; Shimazaki, T.; Woodward, H. T.; Riegel, C. A.; Capone, L. A.; Becker, T.

    1977-01-01

    The two-dimensional model of stratospheric constituents is presented in detail. The derivation of pertinent transport parameters and the numerical solution of the species continuity equations, including a technique for treating the stiff differential equations that represent the chemical kinetic terms, and appropriate methods for simulating the diurnal variations of the solar zenith angle and species concentrations are discussed. Predicted distributions of tracer constituents (ozone, carbon 14, nitric acid) are compared with observed distributions.

  19. Strong Raman-induced non-instantaneous soliton interactions in gas-filled photonic crystal fibers

    E-print Network

    Saleh, Mohammed F; Marini, Andrea; Biancalana, Fabio

    2015-01-01

    We have developed an analytical model based on the perturbation theory in order to study the optical propagation of two successive intense solitons in hollow-core photonic crystal fibers filled with Raman-active gases. Based on the time delay between the two solitons, we have found that the trailing soliton dynamics can experience unusual nonlinear phenomena such as spectral and temporal soliton oscillations and transport towards the leading soliton. The overall dynamics can lead to a spatiotemporal modulation of the refractive index with a uniform temporal period and a uniform or chirped spatial period.

  20. Estimation of the vortex length scale and intensity from two-dimensional samples

    NASA Technical Reports Server (NTRS)

    Reuss, D. L.; Cheng, W. P.

    1992-01-01

    A method is proposed for estimating flow features that influence flame wrinkling in reciprocating internal combustion engines, where traditional statistical measures of turbulence are suspect. Candidate methods were tested in a computed channel flow where traditional turbulence measures are valid and performance can be rationally evaluated. Two concepts are tested. First, spatial filtering is applied to the two-dimensional velocity distribution and found to reveal structures corresponding to the vorticity field. Decreasing the spatial-frequency cutoff of the filter locally changes the character and size of the flow structures that are revealed by the filter. Second, vortex length scale and intensity is estimated by computing the ensemble-average velocity distribution conditionally sampled on the vorticity peaks. The resulting conditionally sampled 'average vortex' has a peak velocity less than half the rms velocity and a size approximately equal to the two-point-correlation integral-length scale.