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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.

We present a theoretical study of plasmonic lattice solitons (PLSs) formed in two-dimensional (2D) arrays of metallic nanowires embedded into a nonlinear medium with Kerr nonlinearity. We analyze two classes of 2D PLSs families, namely, fundamental and vortical PLSs in both focusing and defocusing media. Their existence, stability, and subwavelength spatial confinement are studied in detai

An experimental and numerical investigation into the properties of quadratic spatialsolitons (QSS) formed in a potassium titanyl phosphate (KTP) crystal was performed. This type II phase-matched crystal allowed for spatialsoliton formation in (2+1) dimensions due to the cascaded second-order nonlinearity. This nonlinearity allowed for a strong localized coupling of the three interacting fields through both second-harmonic generation (SHG) and optical parametric amplification (OPA). From these fundamental properties, potential applications were demonstrated. The properties of type II QSS formed during SHG with unequal fundamental polarization components were investigated. The threshold for soliton formation and the soliton composition was studied for various launching conditions of fundamental intensity imbalance and phase- mismatch configurations. The changing fundamental polarization components in the QSS with input polarization variations provided a mechanism to produce a binary all-optical switch due to spatial walk-off in the critically phase-matched geometry. The robust nature of QSS formation was compared to conventional methods for SHG. Soliton formation occurs due to strong coupling of high intensity fields focused at the entrance face of the crystal while conventional SHG methods produce higher efficiencies through weak focusing at the center of the crystal. The enhanced phase-matching bandwidth provided by QSS formation lends itself to applications where strong temperature and mechanical control are not possible. Additional applications for beam reshaping of elliptical fundamental beams were investigated. The spatial break-up of a quasi-one-dimensional plane- wave due to modulational instabilities was examined numerically and experimentally. The break-up of a highly elliptical spatial profile into a series of circular beams matched with theoretical predictions of modulational instability. Applications for pattern formation in one- and two-transverse dimensions were demonstrated. Soliton formation due to parametric instabilities was investigated at the degeneracy point for parametric amplification in KTP. A strong pump at the harmonic frequency was seeded with a weak fundamental field and QSS formation was shown to occur. The soliton formation threshold and soliton composition was studied for various detunings from phase-matching. Clamped all-optical amplification was demonstrated over a large range of input energies.

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

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

enhancement along with a subwavelength localization of surface plasmons, they enable scaling down the sizeSubwavelength solitons and Faraday waves in two-dimensional lattices of metal nanoparticles Roman E.5403) Plasmonics; (190.6135) Spatialsolitons; (190.3100) Instabilities and chaos; (190.1450) Bistability. http

We have studied Laguerre-Gaussian spatial solitary waves in strongly nonlocal nonlinear media analytically and numerically. An exact analytical solution of two-dimensional self-similar waves is obtained. Furthermore, a family of different spatial solitary waves has been found. It is interesting that the spatialsoliton profile and its width remain unchanged with increasing propagation distance. The theoretical predictions may give new insights into low-energetic spatialsoliton transmission with high fidelity.

Zhong Weiping [State Key Laboratory of Laser Technology, Department of Physics, Huazhong University of Science and Technology, Wuhan 430074 (China); Department of Electronic Engineering, Shunde College, Shunde 528300 (China); Yi Lin [State Key Laboratory of Laser Technology, Department of Physics, Huazhong University of Science and Technology, Wuhan 430074 (China)

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

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

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. PMID:21867335

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.

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

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

We have studied Laguerre-Gaussian spatial solitary waves in strongly nonlocal nonlinear media analytically and numerically. An exact analytical solution of two-dimensional self-similar waves is obtained. Furthermore, a family of different spatial solitary waves has been found. It is interesting that the spatialsoliton profile and its width remain unchanged with increasing propagation distance. The theoretical predictions may give new insights

We study interaction of counterpropagating beams in truncated two-dimensional photonic lattices induced optically in photorefractive crystals, and demonstrate the existence of counterpropagating surface solitons localized in the lattice corners and at the edges. We display intriguing dynamical properties of such composite optical beams and reveal that the lattice surface provides a strong stabilization effect on the beam propagation. We also observe dynamical instabilities for stronger coupling and longer propagation distances in the form of beam splitting. No such instabilities exist in the single beam surface propagation. PMID:19997392

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.

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)

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-dimensionalsolitons against decay or collapse for both attractive and repulsive interactions. The solutions for the soliton stability are investigated analytically, by using a multi-Gaussian variational approach, with the Vakhitov-Kolokolov necessary criterion for stability; and numerically, by using the relaxation method and direct numerical time integrations of the Gross-Pitaevskii equation. Very good agreement of the results corresponding to both treatments is observed.

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

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

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

Quadratic spatialsoliton 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.

We describe the stable existence of quasi-one-dimensional solutions of the two-dimensional cubic-quintic complex Ginzburg-Landau equation for a large range of the bifurcation parameter. By quasi-one-dimensional (quasi-1D) in the present context, we mean solutions of fixed shape in one spatial dimension that are simultaneously fully extended and space filling in a second direction. This class of stable solutions arises for parameter values for which simultaneously other classes of solutions are at least locally stable: the zero solution, 2D fixed shape dissipative solitons, or 2D azimuthally symmetric or asymmetric exploding dissipative solitons. We show that quasi-1D solutions can form stable compound states with 2D stationary dissipative solitons or with azimuthally symmetric exploding dissipative solitons. In addition, we find stable breathing quasi-1D solutions near the transition to collapse. The analogy of several features of the work presented here to recent experimental results on convection by Miranda and Burguete [Phys. Rev. E 78, 046305 (2008); Phys. Rev. E 79, 046201 (2009)] is elucidated. PMID:23496599

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

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

Quadratic spatialsolitons, beams that propagate unchanged in shape and magnitude, are supported by second order optical nonlinearities and can occur in all wave mixing processes under appropriate conditions. They are multi-component, consisting of all the frequency components that are coupled by a second order nonlinear interaction near a phase-matching condition. They have been observed in a number of bulk crystalline media, in LiNbO 3 slab waveguides and in arrays of parallel, weakly coupled, LiNbO 3 channel waveguides. The properties of the solitons and their excitation will be reviewed. To cite this article: G.I. Stegeman, C. R. Physique 8 (2007).

A theoretical description for nonlinear beam propagation in a two-dimensional optical lattice in the presence of a refractive-index gradient has been developed. This problem is associated with nonlinear Bloch oscillations; it has been reduced to a nonlinear Schrödinger equation with a varying dispersion coefficient. It is shown that, if the periodicity of longitudinal modulation coincides with the transverse gradient of the refractive index, a stationary oscillatory picture emerges in the nonlinear regime.

We study the soliton type solutions arising in two-dimensional quantum chromodynamics (QCD$_{2}$). The so-called generalized sine-Gordon model (GSG) arises as the low-energy effective action of bosonized QCD$_{2}$ for unequal quark mass parameters, and it has been shown that the relevant solitons describe the normal and exotic baryonic spectrum of QCD$_{2}$ [JHEP(03)(2007)(055)]. In the first part of this chapter we classify

The structure and motion of complexes of in-phase weakly coupled fundamental solitons in a wide-aperture class A laser with saturable absorption are analysed. The symmetry of the field distribution and its relation to the motion of the complex are studied. Due to the absence of wavefront dislocations in such complexes, the transverse radiation intensity and phase distributions are the symmetry objects, which simplifies analysis compared to the case when wavefront dislocations are present. Four types of the motion of soliton complexes are demonstrated: a motionless complex in the presence of two mirror symmetry axes; linear motion of the complex when only one mirror symmetry axis exists; rotation around a motionless centre of inertia in the absence of the mirror symmetry axis and in the presence of symmetry with respect to rotation through the angle 2{pi}/M (M is an integer); and curvilinear (circular) motion of the centre of inertia and simultaneous rotation of the complex around the instantaneous position of the centre of inertia in the absence of symmetry elements. (nonlinear optical phenomena)

Rosanov, N N; Fedorov, S V; Shatsev, A N [Institute for Laser Physics, Federal State Unitary Enterprise ' Scientific and Industrial Corporation 'Vavilov State Optical Institute', St. Petersburg (Russian Federation)

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

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

We report on the experimental observation of two-dimensional surface solitons residing at the interface between a homogeneous square lattice and a superlattice that consists of alternating 'deep' and 'shallow' waveguides. By exciting single waveguides in the first row of the superlattice, we show that solitons centered on deep sites require much lower powers for their excitation than their respective counterparts centered on shallow sites. Despite the fact that the average refractive index of the superlattice waveguides is equal to the refractive index of the homogeneous lattice, the interface results in clearly asymmetric output patterns.

Heinrich, M.; Ramirez, L. P. R.; Dreisow, F.; Keil, R.; Nolte, S.; Tuennermann, A. [Institute of Applied Physics, Friedrich-Schiller-University Jena, Max-Wien-Platz 1, 07743 Jena (Germany); Kartashov, Y. V.; Vysloukh, V. A.; Torner, L. [ICFO-Institut de Ciencies Fotoniques, and Universitat Politecnica de Catalunya, Mediterranean Technology Park, 08860 Castelldefels (Barcelona) (Spain); Szameit, A. [Physics Department and Solid State Institute, Technion, 32000 Haifa (Israel)

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 spatialsolitons 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 spatialsoliton dragging and the efficient guiding of orthogonally polarized femtosecond pulses by a bright spatialsoliton, 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.

Solitons in the model of nonlinear photonic crystals with the transverse structure based on two-dimensional (2D) quadratic- or rhombic-shaped Kronig-Penney (KP) lattices are studied by means of numerical methods. The model can also applies to a Bose-Einstein condensate (BEC) trapped in a superposition of linear and nonlinear 2D periodic potentials. The analysis is chiefly presented for the self-repulsive nonlinearity, which gives rise to several species of stable fundamental gap solitons, dipoles, four-peak complexes, and vortices in two finite bandgaps of the underlying spectrum. Stable solitons with complex shapes are found, in particular, in the second bandgap of the KP lattice with the rhombic structure. The stability of the localized modes is analyzed in terms of eigenvalues of small perturbations, and tested in direct simulations. Depending on the value of the KP's duty cycle (DC, i.e., the ratio of the void's width to the lattice period), an internal stability boundary for the solitons and vortices may exist inside of the first bandgap. Otherwise, the families of the localized modes are entirely stable or unstable in the bandgaps. With the self-attractive nonlinearity, only unstable solitons and vortices are found in the semi-infinite gap.

Mayteevarunyoo, Thawatchai; Malomed, Boris A.; Roeksabutr, Athikom

We study the soliton type solutions arising in two-dimensional quantum chromodynamics (QCD$_{2}$). The so-called generalized sine-Gordon model (GSG) arises as the low-energy effective action of bosonized QCD$_{2}$ for unequal quark mass parameters, and it has been shown that the relevant solitons describe the normal and exotic baryonic spectrum of QCD$_{2}$ [JHEP(03)(2007)(055)]. In the first part of this chapter we classify the soliton and kink type solutions of the sl(3) GSG model. Related to the GSG model we consider the sl(3) affine Toda model coupled to matter fields (Dirac spinors) (ATM). It has been shown the confinement of the spinors inside the solitons and kinks of the GSG model providing an extended hadron model for "quark" confinement [JHEP(01)(2007)(027)]. In the second part of this chapter we discuss the appearance of the constituent quarks in the context of bosonized QCD$_{2}$ and the relevance of the $sl(2)$ ATM model in order to describe the confinement of the color degrees of freedom. We have shown that QCD$_{2}$ has quark soliton solutions if the quark mass is sufficiently large.

We present a systematic analysis of the outcome of soliton collisions upon variation of the relative phase ? of the solitons, in the two-dimensional cubic-quintic complex Ginzburg-Landau equation in the absence of viscosity. Three generic outcomes are identified: merger of the solitons into a single one, creation of an extra soliton, and quasielastic interaction. The velocities of the merger soliton and the extra soliton can be effectively controlled by ?. In addition, the range of the outcome of creating an extra soliton decreases to zero with the reduction of gain or the increasing of loss. The above features have potential applications in optical switching and logic gates based on interaction of optical solitons. PMID:22181536

We theoretically investigate the propagation of a paraxial beam in two-dimensional media with spatial dispersion. Based on the spatial dispersion theory and the (1+1)-dimensional paraxial wave equation, we get an expression which determines the diffraction of the beam. By fitting the dispersion surface of a typical spatial dispersion medium (a photonic crystal) calculated by the plane-wave-expansion method, the value of the diffraction term is determined, with which one can predict the diffraction of the paraxial beam that propagates in such media. Numerical simulations based on the finite-difference time-domain method confirm the theoretical results.

We use the cubic complex Ginzburg-Landau equation linearly coupled to a dissipative linear equation as a model for lasers with an external frequency-selective feedback. This system may also serve as a general pattern-formation model in media driven by an intrinsic gain and selective feedback. While, strictly speaking, the approximation of the laser nonlinearity by a cubic term is only valid for small field intensities, it qualitatively reproduces results for dissipative solitons obtained in models with a more complex nonlinearity in the whole parameter region where the solitons exist. The analysis is focused on two-dimensional stripe-shaped and vortex solitons. An analytical expression for the stripe solitons is obtained from the known one-dimensional soliton solution, and its relation with vortex solitons is highlighted. The radius of the vortices increases linearly with their topological charge m, therefore the stripe-shaped soliton may be interpreted as the vortex with m=?, and, conversely, vortex solitons can be realized as unstable stripes bent into stable rings. The results for the vortices are applicable for a broad class of physical systems. PMID:22060481

Paulau, P V; Gomila, D; Colet, P; Malomed, B A; Firth, W J

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-dimensionalspatial 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.

A spatialsoliton is a shape invariant self guided beam of light or a self induced waveguide. Spatialsolitons 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 in optical data processing, communications etc. Up to now due to the power required to generate the solitons, and the response times of the soliton supporting media, these special waves of nature could not penetrate the applications arena. Semiconductors, with their resonant nonlinearities, are thought to be ideal candidates for fast switching, low power spatialsolitons. In this dissertation it is shown theoretically and experimentally that it is possible to observe stable spatialsolitons in a periodically patterned semiconductor optical amplifier (PPSOA). The solitons have unique beam profiles that change only with system parameters, like pumping current, etc. Their coherent and incoherent interactions which could lead to all optical devices have been investigated experimentally and theoretically. The formation of filaments or modulational instability has been studied theoretically and yielded analytical formulae for evaluating the filament gain and the maximum spatial frequencies in PPSOA devices. Furthermore, discrete array amplifiers have been analyzed numerically for discrete solitons, and the prospect of using multi peak discrete solitons as laser amplifiers is discussed.

We overview theoretical and experimental results on spatial optical solitons excited in arrays of nonlinear waveguides. First, we briefly summarize the basic properties of the discrete nonlinear Schrödinger (NLS) equation frequently employed to study spatially localized modes in arrays, the so-called discrete solitons. Then, we introduce an improved analytical model that describes a periodic structure of thin-film nonlinear waveguides embedded

Andrey A. Sukhorukov; Yuri S. Kivshar; Hagai S. Eisenberg; Yaron Silberberg

The propagation of a nonlinear low-frequency mode in two-dimensional (2D) monolayer hexagonal dusty plasma crystal in presence of external magnetic field and dust-neutral collision is investigated. The standard perturbative approach leads to a 2D Korteweg-de Vries (KdV) soliton for the well-known dust-lattice mode. However, the Coriolis force due to crystal rotation and Lorentz force due to magnetic field on dust particles introduce a linear forcing term, whereas dust-neutral drag introduce the usual damping term in the 2D KdV equation. This new nonlinear equation is solved both analytically and numerically to show the competition between the linear forcing and damping in the formation of quasilongitudinal soliton in a 2D strongly coupled complex (dusty) plasma. Numerical simulation on the basis of the typical experimental plasma parameters and the analytical solution reveal that the neutral drag force is responsible for the usual exponential decay of the soliton, whereas Coriolis and/or Lorentz force is responsible for the algebraic decay as well as the oscillating tail formation of the soliton. The results are discussed in the context of the plasma crystal experiment.

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

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

We consider the three-dimensional (3D) Gross-Pitaevskii or nonlinear Schrödinger equation with a quasi-2D square-lattice potential (which corresponds to the optical lattice trapping a self-attractive Bose-Einstein condensate, or, in some approximation, to a photonic-crystal fiber, in terms of nonlinear optics). Stable 3D solitons, with embedded vorticity S=1 and 2, are found by means of the variational approximation and in a numerical form. They are built, basically, as sets of four fundamental solitons forming a rhombus, with phase shifts piS2 between adjacent sites, and an empty site in the middle. The results demonstrate two species of stable 3D solitons, which were not studied before, viz., localized vortices ("spinning light bullets," in terms of optics) with S>1 , and vortex solitons (with any S not equal 0 ) supported by a lattice in the 3D space. Typical scenarios of instability development (collapse or decay) of unstable localized vortices are identified too. PMID:17930164

Leblond, Hervé; Malomed, Boris A; Mihalache, Dumitru

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

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

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. PMID:22060510

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.

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

We demonstrate some basic all-optical (electrically unbiased) logic gates in azobenzene liquid crystalline cells, exploiting their large nonlinearity for light localization and the trans-cis photoisomerization for all-optical external control. Spatialsolitons were excited at microwatt power levels at 632.8 nm, whereas gating and switching were achieved with milliwatt beams at 409 nm

Svetlana V. Serak; Nelson V. Tabiryan; Marco Peccianti; Gaetano Assanto

We address the problem of directional mobility of discrete solitons in two-dimensional rectangular lattices, in the framework of a discrete nonlinear Schrödinger model with saturable on-site nonlinearity. A numerical constrained Newton-Raphson method is used to calculate two-dimensional Peierls-Nabarro energy surfaces, which describe a pseudopotential landscape for the slow mobility of coherent localized excitations, corresponding to continuous phase-space trajectories passing close to stationary modes. Investigating the two-parameter space of the model through independent variations of the nonlinearity constant and the power, we show how parameter regimes and directions of good mobility are connected to the existence of smooth surfaces connecting the stationary states. In particular, directions where solutions can move with minimum radiation can be predicted from flatter parts of the surfaces. For such mobile solutions, slight perturbations in the transverse direction yield additional transverse oscillations with frequencies determined by the curvature of the energy surfaces, and with amplitudes that for certain velocities may grow rapidly. We also describe how the mobility properties and surface topologies are affected by inclusion of weak lattice anisotropy. PMID:21517610

Naether, Uta; Vicencio, Rodrigo A; Johansson, Magnus

Solitons, nonlinear self-trapped wavepackets, have been extensively studied in many and diverse branches of physics such as optics, plasmas, condensed matter physics, fluid mechanics, particle physics and even astrophysics. Interestingly, over the past two decades, the field of solitons and related nonlinear phenomena has been substantially advanced and enriched by research and discoveries in nonlinear optics. While optical solitons have been vigorously investigated in both spatial and temporal domains, it is now fair to say that much soliton research has been mainly driven by the work on optical spatialsolitons. This is partly due to the fact that although temporal solitons as realized in fiber optic systems are fundamentally one-dimensional entities, the high dimensionality associated with their spatial counterparts has opened up altogether new scientific possibilities in soliton research. Another reason is related to the response time of the nonlinearity. Unlike temporal optical solitons, spatialsolitons have been realized by employing a variety of noninstantaneous nonlinearities, ranging from the nonlinearities in photorefractive materials and liquid crystals to the nonlinearities mediated by the thermal effect, thermophoresis and the gradient force in colloidal suspensions. Such a diversity of nonlinear effects has given rise to numerous soliton phenomena that could otherwise not be envisioned, because for decades scientists were of the mindset that solitons must strictly be the exact solutions of the cubic nonlinear Schrödinger equation as established for ideal Kerr nonlinear media. As such, the discoveries of optical spatialsolitons in different systems and associated new phenomena have stimulated broad interest in soliton research. In particular, the study of incoherent solitons and discrete spatialsolitons in optical periodic media not only led to advances in our understanding of fundamental processes in nonlinear optics and photonics, but also had a very important impact on a variety of other disciplines in nonlinear science. In this paper, we provide a brief overview of optical spatialsolitons. This review will cover a variety of issues pertaining to self-trapped waves supported by different types of nonlinearities, as well as various families of spatialsolitons such as optical lattice solitons and surface solitons. Recent developments in the area of optical spatialsolitons, such as 3D light bullets, subwavelength solitons, self-trapping in soft condensed matter and spatialsolitons in systems with parity-time symmetry will also be discussed briefly. PMID:22836010

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

environmental research, especially for accurately assessing the water and solute transport processes in watershed scales. This study de- dicator geostatistics and transition probability matrices scribes an efficient Markov chain model for two-dimensional modeling (TPMs) provided by Markov chains. Currently, indica- and simulation of spatial distribution of soil types (or classes). The tor geostatistics (Journel, 1983), especially the sequen- model is

Weidong Li; Chuanrong Zhang; James E. Burt; A.-Xing Zhu; Jan Feyen

We report on what is, to our knowledge, the first experimental observation of spatialsoliton interaction with charged conductive microelectrodes in nematic liquid crystals. We show that solitons can undergo voltage-controlled deflection and reflection with a nematicon steering larger than 100° over distances of a few micrometers. Using bias-defined perturbations, we observe reconfigurable soliton geometries with several reflections. PMID:24690868

We consider the existence, stability and dynamics of the nodeless state and fundamental nonlinear excitations, such as vortices, for a quasi-two-dimensional polariton condensate in the presence of pumping and nonlinear damping. We find a series of interesting features that can be directly contrasted to the case of the typically energy-conserving ultracold alkali-atom Bose-Einstein condensates (BECs). For sizeable parameter ranges, in line with earlier findings, the nodeless state becomes unstable towards the formation of stable nonlinear single or multi-vortex excitations. The potential instability of the single vortex is also examined and is found to possess similar characteristics to those of the nodeless cloud. We also report that, contrary to what is known, e.g., for the atomic BEC case, stable stationary gray ring solitons (that can be thought of as radial forms of Nozaki-Bekki holes) can be found for polariton condensates in suitable parametric regimes. In other regimes, however, these may also suffer symmetry-breaking instabilities. The dynamical, pattern-forming implications of the above instabilities are explored through direct numerical simulations and, in turn, give rise to waveforms with triangular or quadrupolar symmetry. PMID:24674920

Rodrigues, A S; Kevrekidis, P G; Carretero-González, R; Cuevas-Maraver, J; Frantzeskakis, D J; Palmero, F

Two-dimensional Fourier spatial power spectra of equivalent magnetization values are presented for a region that includes a large portion of the western United States. The magnetization values were determined by inversion of POGO satellite data, assuming a magnetic crust 40 km thick, and were located on an 11 x 10 array with 300 km grid spacing. The spectra appear to be in good agreement with values of the crustal geomagnetic field spatial power spectra given by McLeod and Coleman (1980) and with the crustal field model given by Serson and Hannaford (1957). The spectra show evidence of noise at low frequencies in the direction along the satellite orbital track (N-S). indicating that for this particular data set additional filtering would probably be desirable. These findings illustrate the value of two-dimensionalspatial power spectra both for describing the geomagnetic field statistically and as a guide for diagnosing possible noise sources.

Two-dimensional Fourier spatial power spectra of equivalent magnetization values are presented for a region that includes a large portion of the western United States. The magnetization values were determined by inversion of POGO satellite data, assuming a magnetic crust 40 km thick, and were located on an 11 x 10 array with 300 km grid spacing. The spectra appear to be in good agreement with values of the crustal geomagnetic field spatial power spectra given by McLeod and Coleman (1980) and with the crustal field model given by Serson and Hannaford (1957). The spectra show evidence of noise at low frequencies in the direction along the satellite orbital track (N-S). indicating that for this particular data set additional filtering would probably be desirable. These findings illustrate the value of two-dimensionalspatial power spectra both for describing the geomagnetic field statistically and as a guide for diagnosing possible noise sources.

We show theoretical evidence that coherent systems based on electromagnetically induced transparency (EIT) can function as optically addressed spatial light modulators with megahertz modulation rates. The transverse spatial properties of cw probe fields can be modulated fast using two-dimensional optical patterns. To exemplify our proposal, we study real-time generation and manipulation of Laguerre-Gaussian beams by means of phase or amplitude modulation using flat-top image-bearing pulse trains as coupling fields in low-cost hot vapor EIT systems. PMID:19571955

We provide a theory for spatialsolitons due to the two-photon photorefractive effect based on the Castro-Camus model [Opt. Lett. 28, 1129 (2003)]. We present the evolution equation of one-dimensional spatialsolitons in two-photon photorefractive media. In steady state and under appropriate external bias conditions, we obtain the dark and bright soliton solutions of the optical wave evolution equation, and also discuss the self-deflection of the bright solitons theoretically by taking into account the diffusion effect.

Hou Chunfeng; Pei Yanbo; Zhou Zhongxiang; Sun Xiudong [Department of Physics, Harbin Institute of Technology, Harbin 150001 (China)

It is commonly known that two-dimensional mean-field models of optical and matter waves with cubic self-attraction cannot produce stable solitons in free space because of the occurrence of collapse in the same setting. By means of numerical analysis and variational approximation, we demonstrate that the two-component model of the Bose-Einstein condensate with the spin-orbit Rashba coupling and cubic attractive interactions gives rise to solitary-vortex complexes of two types: semivortices (SVs, with a vortex in one component and a fundamental soliton in the other), and mixed modes (MMs, with topological charges 0 and ±1 mixed in both components). These two-dimensional composite modes can be created using the trapping harmonic-oscillator (HO) potential, but remain stable in free space, if the trap is gradually removed. The SVs and MMs realize the ground state of the system, provided that the self-attraction in the two components is, respectively, stronger or weaker than the cross attraction between them. The SVs and MMs which are not the ground states are subject to a drift instability. In free space (in the absence of the HO trap), modes of both types degenerate into unstable Townes solitons when their norms attain the respective critical values, while there is no lower existence threshold for the stable modes. Moving free-space stable solitons are also found in the present non-Galilean-invariant system, up to a critical velocity. Collisions between two moving solitons lead to their merger into a single one. PMID:24730926

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

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

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.

Spatialsolitons arise as a result of the interplay between diffraction and a Kerr-like nonlinearity. They are the spatial analog of the better known temporal solitons, which exist e.g. in optical fibers and result in pulse propagation without change of pulse shape. Similarly, spatialsolitons are beams that do not change their shape upon propagation. In an introductory part of this work, the basic concept of spatialsolitons will be reviewed and a number of properties that make them attractive for optical switching and routing devices will be described. Special emphasis will be put on the favorable properties of the AlGaAs material system in the spectral region below in the half bandgap, which were crucial for the experiments performed. One such device, a soliton steering element, has been realized and tested in AlGaAs samples. The device design and the experimental results will be presented in detail. The work performed is intended to demonstrate the basic feasibility of reconfigurable switching devices based on spatialsolitons. Sufficient steering for the separation of four channels was achieved. Furthermore, one of the most interesting features of solitons is their robustness against perturbations. In birefringent media, however, the interaction between birefringence and nonlinearity leads ultimately to a polarization instability. This effect was investigated numerically and experimentally, and a radiation related polarization instability was observed for the first time. Additional work that is related to the field of Kerr spatialsolitons and their generation, specifically an investigation of the linear parameters of a novel nonlinear material, the polydiacetylene p-toluene sulfonate (PTS), and the construction of a color center laser system used for the soliton experiments, are described in two appendices.

We show that a quasi-steady-state photorefractive spatialsoliton 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.

One of the proposals for the exploitation of two-dimensional quantum walks has been the efficient generation of entanglement. Unfortunately, the technological effort required for the experimental realization of standard two-dimensional quantum walks is significantly demanding. In this respect, an alternative scheme with less challenging conditions has been recently studied, particularly in terms of spatial-entanglement generation [C. Di Franco, M. Mc Gettrick, and Th. Busch, Phys. Rev. Lett. 106, 080502 (2011)]. Here, we extend the investigation to a scenario where a measurement is performed on the coin degree of freedom after the evolution, allowing a further comparison with the standard two-dimensional Grover walk.

C. Di Franco; M. Mc Gettrick; T. Machida; Th. Busch

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.

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

A nonlinear, coupled, magneto-optic waveguide system supporting bright and dark spatialsolitons is investigated to determine the stability and possible application of the resulting bright-dark soliton dynamics. An extensive variational analysis is verified by full numerical simulations. It is discovered that the stability of the magneto-optic coupled states can be exploited to give guaranteed isolator functionality, which could lead to

Optics has the intrinsic capability of dramatically improving the fundamental performance of computers. Because silicon-based computing is expected to approach its technological limits in one or two decades, a new computation concept, Solitonic Gateless Computing, has been proposed. This approach is based on the unique collision properties of spatialsolitons, i.e. optical beams that propagate without change of shape due to the balance of diffraction and material nonlinearity. Spatialsolitons have commanded a great deal of attention because of their unusual physical properties, such as their remarkable stability and particle-like behavior upon collisions. A detailed investigation of various existing and new classes of solitons is important in order to assess their value for computing and other applications. The investigation of instabilities of solitons is also critical. For example, polarization instability can limit the stability of various solitons against polarization fluctuations. On the other hand, seeding with an interference pattern can generate via modulational instabilities a periodic array of spatialsolitons, a feature that could be used for computing. In this dissertation, the construction, optimization and full characterization of a versatile tunable picosecond light source for soliton studies-an optical parametric generator-amplifier is described first. Subsequently, spatial noise initiated modulational instability (MI) in media with Kerr (third-order) and quadratic (second-order) nonlinearities in a one dimensional geometry, i.e. slab waveguides, is investigated and the results are compared to analytical theories and numerical simulations. Seeded MI is also studied and the MI gain was measured in lithium niobate waveguides with a quadratic nonlinearity. A closely related phenomenon, fission into multiple solitons, was observed in both lithium niobate waveguides at 1.32 microns and periodically poled lithium niobate waveguides at 1.58 microns. The interaction between birefringence and Kerr nonlinearity leads ultimately to a polarization instability that places an upper limit on the intensity of Kerr and Vector solitons. This effect was investigated experimentally and numerically in aluminum gallium arsenide waveguides. Lastly, the generation and properties of Type I quadratic solitons, that contain two frequency components and form an especially rich family, in bulk non-critically phase- matched potassium niobate is reported.

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 spatialsoliton are obtained for the TM modes of a photorefractive planar waveguide.

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

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 spatialsolitons 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 spatialsolitons generated in the nonlinear regime above the nonlinear supratransmission threshold.

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

Some selected important properties of photorefractive spatialsolitons and their applications have been reviewed in the present paper. Using band transport model, the governing principle of photorefractive nonlinearity has been addressed and nonlinear dynamical equations of spatialsolitons owing to this nonlinearity have been discussed. Mechanisms of formation of screening and photovoltaic solitons of three different configurations i.e., bright, dark and grey varieties have been examined. Incoherently coupled vector solitons due to single and two-photon photorefractive phenomena have been highlighted. Modulation instability, which is precursor to soliton formation has been also discused briefly. Finally possible applications of photorefractive spatialsolitons have been highlighted.

Summary form only given. Recently, soliton splitting has been successfully used to write permanent Y-waveguide structures (3-dB splitters) in the bulk of a photorefractive crystal. Such Y-junctions can then be employed to guide other intense beams at less photosensitive wavelengths (~1.5 ?m) or can be permanently impressed (fixed) into the crystalline lattice. An investigation of the properties of these Y-junction

A. G. Grandpierre; T. H. Coskun; D. N. Christodoulides; M. Segev; Y. S. Kivshar

The time behavior of bright spatialsolitons in biased photorefractive media is investigated within the framework of a bidimensional band transport model. Biasing the photorefractive media requires an externally applied electric field or the presence of a photovoltaic effect. These two basically different phenomena are shown to be equivalent and additive. The mechanism of space-charge field buildup is analytically expressed,

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?1. 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. 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. PMID:24483996

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?1. 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. 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.

We consider the problem of finding a desired item out of N items arranged on the sites of a two-dimensional lattice of size N×N . The previous quantum-walk based algorithms take O(NlnN) steps to solve this problem, and it is an open question whether the performance can be improved. We present an algorithm which solves the problem in O(NlnN) steps,

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

We consider the problem of finding a desired item out of N items arranged on the sites of a two-dimensional lattice of size N×N . The previous quantum-walk based algorithms take O(NlnN) steps to solve this problem, and it is an open question whether the performance can be improved. We present an algorithm which solves the problem in O(NlnN) steps, thus giving an O(lnN) improvement over the known algorithms. The improvement is achieved by controlling the quantum walk on the lattice using an ancilla qubit.

The dynamical evolution of bright spatialsolitons in biased photorefractive crystals is investigated under steady-state conditions. Our numerical study indicates that these optical solitons are stable against small perturbations whereas optical beams that significantly differ from soliton solutions tend to experience larger cycles of compression and expansion. The influence of loss in a typical photorefractive material like SBN:60 is studied

Dynamics of (1+1)D spatialsolitons in photorefractive medium with drift and diffusion nonlinearity is investigated. Propagation of solitons is analyzed theoretically by means of effective-particle approach method. The explicit formula of acceleration of soltion is derived. Analytical results show that the solitons evolve with a constant acceleration along a parabolic trajectory. The acceleration is determined by the input soliton and

Formation of dark spatial optical solitons in planar waveguides produced by implantation of light ions into Fe- or Cudoped X cut lithium niobate wafers is experimentally studied. The implantation both of protons and O3+-ions results in the excellent waveguide layers with their thickness about 3 microns and optical losses less than 1 dB/cm. The soliton states at light wavelengths of 532 nm and 633 nm are developed due to the self-defocusing photorefractive-photovoltaic nonlinearity of lithium niobate. Extraordinarily polarized light beams are used in experiments to form dark solitons and to probe the soliton-induced waveguide channels. Steady-state dark photovoltaic spatialsolitons have been realized in both, H+- implanted and O3+ - implanted planar waveguides at optical powers from 10 to 100 microwatts. The storage time of soliton-induced channel waveguides makes up at least some hours without special illumination of a planar waveguide and they may be erased within some seconds in a case of their permanent readout with stronger light beams. The possibility to form more complicated channel waveguide structures in regimes of dark spatialsolitons is also demonstrated.

Kruglov, Vitaly G.; Shandarov, Vladimir M.; Tan, Yang; Chen, Feng; Kip, Detlef

The evolution of a high-speed, compressible, confined, temporally evolving supersonic mixing layer between hydrogen and oxygen gas streams is examined using time-dependent, two-dimensional, numerical simulations that include the effects of viscosity, molecular diffusion, and thermal conduction. The flow shows three distinct mixing regimes: an apparently ordered, laminar stage in which the structures grow due to the initial perturbation; a convective-mixing regimes in which vortices begin to interact and structures grow; and a diffusive-mixing regime in which vortical structures break down and diffusive mixing dominates. Varying the strength of the diffusion terms shows that these effects are important in the laminar and diffusive-mixing stages, but not in the convective mixing stage. Varying the convective Mach shows that compressibility does not change the general structural features of the mixing process, although higher compressibility results in a slower transition between the various flow regimes. Increasing the size of the computational domain increases the absolute time of transition from convective to diffusive mixing, but does not affect the dimensionless time normalized to the system size.

Using recent advances in the constrained-path auxiliary-field quantum Monte Carlo method, we study the ground state of the two-dimensional, single-band Hubbard model at intermediate interactions (2<=U/t <=8). In the first part of this study [1], we have determined the equation of state and also calculated the spin-spin correlation functions in square lattices up to size 16x16. Shell effects are eliminated and finite-size effects are greatly reduced by boundary condition integration. It was shown that, upon doping, the system separates into a region with antiferromagnetic (AF) order and a hole-containing region without AF order. In the second part, we study rectangular supercells up to 8x64 to examine the nature of this inhomogeneous phase, in particular to probe phase separation versus stripes and spin-density waves of long wave lengths. [1] Chia-Chen Chang and Shiwei Zhang, Phys. Rev. B 78, 165101 (2008)

their application to transport equations. Manteuffel et al. conducted such an exploration in one spatial dimension, using two-cell inversions as the relaxation or smoothing operation, and reported excellent results. In this dissertation we extensively test...

It is known that in the absence of four-wave mixing, spatialsolitons 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.

The spatially periodic 2D patterns at output mirror of solid state microchip laser with high Fresnel number (100-1000) are discussed in view of numerical modeling with split-step FFT code comprising nonlinear gain, relaxation of inversion and paraxial diffraction.

An exact (2 + 1)-dimensional spatial optical soliton of the nonlinear Schrödinger equation with a spatially modulated nonlinearity and a special external potential is discovered in an inhomogeneous nonlinear medium, by utilizing the similarity transformation. Exact analytical solutions are constructed by the products of Whittaker functions and the bright and dark soliton solutions of the standard stationary nonlinear Schrödinger equation. Some examples of such composed solutions are given, in which these spatialsolitons display different localized structures. Numerical calculation shows that the soliton is stable in propagating over long distances, thus also confirming the validity of the exact solution.

Dynamics of (1+1)D spatialsolitons in photorefractive medium with drift and diffusion nonlinearity is investigated. Propagation of solitons is analyzed theoretically by means of effective-particle approach method. The explicit formula of acceleration of soltion is derived. Analytical results show that the solitons evolve with a constant acceleration along a parabolic trajectory. The acceleration is determined by the input soliton and the diffusion nonlinearity. We also simulate the propagation of solitons numerically and excellent agreements are obtained between the theoretical and numerical results.

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

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.

A position sensitive detector (PSD) adapted to the technical and mechanical specifications of our angle and energy resolved electron-ion(s) coincidence experiments is described in this article. The device, whose principle is very similar to the one detailed by J. H. D. Eland [Meas. Sci. Technol. 5, 1501 (1994)], is composed by a set of microchannel plates and a delay line anode. The originality comes from the addition in front of the encoding surface of a ceramic disk covered by a resistive surface. The capacitive coupling between the anode and the resistive plane has the double advantage of eliminating the spatial modulations due to the lattice of the anode and also of sensitizing a greater number of electrodes, increasing thus considerably the accuracy of the position measurements. The tests carried out with a time to digital conversion module of 250 ps resolution showed that a spatial resolution better than 50?m and a dead time of 160 ns can be achieved. Typical images obtained with the help of the EPICEA and DELICIOUS coincidence setups are also shown.

Céolin, D.; Chaplier, G.; Lemonnier, M.; Garcia, G. A.; Miron, C.; Nahon, L.; Simon, M.; Leclercq, N.; Morin, P.

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

Particulate composite reinforcements are good candidates for the fracture toughness of ceramics. In order to predict mechanical response of ceramic matrix composites, an efficient method capable of modelling their complex microstructure is needed. The purpose of this research is the development of such a model using fractal spatial particle distribution. A review of different toughness mechanisms for particulate composites and associated models for deriving their constitutive relationships is presented in chapter 2. These different toughening mechanisms as well constitutive properties depend on particle shape, size and spatial distribution, which lend themselves to a self-similar fractal based modelling approach. A self-similar distribution of particles linked to the fractal geometry is proposed. Fractal geometry provides an ideal tool for describing the randomness and disorder of the system. Its foundations are reviewed in chapter three with emphasis on iterated function systems that are subsequently used to obtain the particle configurations in the proposed model. For the sake of completeness, a review of fractal structure in science is given to illustrate possible applications. Derivation of the volume fraction associated with self similar distributions is provided in chapter 4. This is followed by a description of the numerical model and the boundary conditions. A Finite Element simulation is performed for different volume fractions, generators and number of particles for different displacements (two uniaxial and biaxial cases) and 2-D stress state cases. From these simulations the inverse distribution of the maximum principal stress is computed. Then the self similar models are compared with the model obtained by the Yang Teriari Gokhale (Y.T.G.) method and model obtained by only one iteration. Fractal dimension for real microstructure are computed and microstructure based on the fractal dimension and number of particle is simulated. It can be derived that the fractal dimension can be related to the average radius of circular particle in special cases. General conclusion and recommendation for future work brings this investigation to a close.

Numerical investigations of the interactions among bright screening-photovoltaic solitons are performed in detail by using the Crank-Nicholson scheme. The numerical results show that a number of parameters, such as the initial separation and phase difference between solitons, can determine the interaction forces of solitons. The numerical study indicates that two in-phase solitons attract each other, and soliton fusions do occur

MR thermometry can be a very challenging application, as good resolution may be needed along spatial, temporal, and temperature axes. Given that the heated foci produced during thermal therapies are typically much smaller than the anatomy being imaged, much of the imaged field-of-view is not actually being heated and may not require temperature monitoring. In this work, many-fold improvements were obtained in terms of temporal resolution and/or 3D spatial coverage by sacrificing some of the in-plane spatial coverage. To do so, three fast-imaging approaches were jointly implemented with a spoiled gradient echo sequence: (1) two-dimensionalspatially selective RF excitation, (2) unaliasing by Fourier encoding the overlaps using the temporal dimension (UNFOLD), and (3) parallel imaging. The sequence was tested during experiments with focused ultrasound heating in ex vivo tissue and a tissue-mimicking phantom. Temperature maps were estimated from phase-difference images based on the water proton resonance frequency shift. Results were compared to those obtained from a spoiled gradient echo sequence sequence, using a t-test. Temporal resolution was increased by 24-fold, with temperature uncertainty less than 1°C, while maintaining accurate temperature measurements (mean difference between measurements, as observed in gel = 0.1°C ± 0.6; R = 0.98; P > 0.05). PMID:21337421

Mei, Chang-Sheng; Panych, Lawrence P; Yuan, Jing; McDannold, Nathan J; Treat, Lisa H; Jing, Yun; Madore, Bruno

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

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

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. PMID:24651448

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

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

The effects of linear and two-photon absorption on bright spatialsoliton propagation are studied. A spatialsoliton 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 spatialsoliton 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 spatialsoliton-based logic gates. .

Systematic characterization studies are presented, relating to a previously reported spatial deconvolution operation that seeks to compensate for the information-blurring property of first-order perturbation algorithms for diffuse optical tomography (DOT) image reconstruction. In simulation results that are presented, this deconvolution operation has been applied to two-dimensional DOT images reconstructed by solving a first-order perturbation equation. Under study was the effect on algorithm performance of control parameters in the measurement (number and spatial distribution of sources and detectors, presence of noise, and presence of systematic error), target (medium shape; and number, location, size, and contrast of inclusions), and computational (number of finite-element-method mesh nodes, length of filter-generating linear system, among others) parameter spaces associated with computation and the use of the deconvolution operators. Substantial improvements in reconstructed image quality, in terms of recovered inclusion location, size, and contrast, are found in all cases. A finding of practical importance is that the method is robust to appreciable differences between the optical coefficients of the media used for filter generation and those of the target media to which the filters are subsequently applied. PMID:15835359

Xu, Yong; Graber, Harry L; Pei, Yaling; Barbour, Randall L

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

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

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 spatialsoliton can be changed by varying the nonlinear response of the crystal.

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

of polarization states, and therefore these distinct equilibÂ ria can, in theory, be used to store and process to multistability in the modes of scalar solitons #see, for example, Ref. #1##. The phenomenon also differs fromÂ cavity surfaceÂemitting laser #VCSEL# #2#, in being depenÂ dent only on simple soliton collisions

Semiconductor microcavities operating in the polaritonic regime are highly non-linear, high speed systems due to the unique half-light, half-matter nature of polaritons. Here, we report for the first time the observation of propagating multi-soliton polariton patterns consisting of multi-peak structures either along (x) or perpendicular to (y) the direction of propagation. Soliton arrays of up to 5 solitons are observed, with the number of solitons controlled by the size or power of the triggering laser pulse. The break-up along the x direction occurs due to interplay of bistability, negative effective mass and polariton-polariton scattering, while in the y direction the break-up results from nonlinear phase-dependent interactions of propagating fronts. We show the experimental results are in good agreement with numerical modelling. Our observations are a step towards ultrafast all-optical signal processing using sequences of solitons as bits of information.

Chana, J K; Fras, F; Gorbach, A V; Skryabin, D V; Cancellieri, E; Cerda-Méndez, E A; Biermann, K; Hey, R; Santos, P V; Skolnick, M S; Krizhanovskii, D N

We investigate the existence and stability of various types of spatialsolitons in a three-level atomic medium with Laguerre-Gaussian control beam. Radial and azimuthal modulations of the medium properties, introduced by the control beam, provide possibilities for existence of diverse soliton patterns and dynamics. Beam diffraction provides additional soliton controllability. All types of solitons can be generated at very low input energy at a few-photon level.

Hang Chao [Centro de Fisica Teorica e Computacional, Faculdade de Ciencias, Universidade de Lisboa, Avenida Professor Gama Pinto 2, Lisboa PT-1649-003 (Portugal); Department of Physics and State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai CN-200062 (China); Konotop, V. V. [Centro de Fisica Teorica e Computacional, Faculdade de Ciencias, Universidade de Lisboa, Avenida Professor Gama Pinto 2, Lisboa PT-1649-003 (Portugal); Departamento de Fisica, Faculdade de Ciencias, Universidade de Lisboa, Campo Grande, Ed. C8, Piso 6, Lisboa PT-1749-016 (Portugal)

In this paper we address soliton-soliton interactions in a nonlinear cubic-quintic optic media, using for that purpose numerical methods and high performance graphics processor unit (GPU) computing. We describe an implementation of GPU-based computational simulations of the generalized Nonlinear Schrodinger Equation, obtaining simulations more than 40 times faster relative to CPU-based simulations, especially in the multidimensional case. We focus our attention in the study of soliton collisions and scattering phenomena that, offering the possibility of steering light with light, open a path towards future optical devices.

The self-bending process of steady-state bright spatialsolitons in biased photorefractive media is investigated by taking into account diffusion effects. By integrating numerically the nonlinear propagation equation, it is found that the soliton beam evolution is approximately adiabatic. The self-deflection process is further studied using perturbation analysis, which predicts that the center of the optical beam moves on a parabolic

We show that the vector beam evolution equations in properly oriented biased photorefractive media can exhibit bright-dark soliton pair solutions under steady-state conditions. These wave pairs are obtained perturbatively provided that the intensities of the two optical beams are approximately equal. Our analysis indicates that these bright-dark vector solitons exist irrespective of the polarity of the external bias field. The

M. I. Carvalho; S. R. Singh; D. N. Christodoulides; R. I. Joseph

We used an analysis based on a geographic information system (GIS) to determine the amount of rearing habitat and stranding area for subyearling fall chinook salmon Oncorhynchus tshawytscha in the Hanford Reach of the Columbia River at steady-state flows ranging from 1,416 to 11,328 m\\/s. High-resolution river channel bathymetry was used in conjunction with a two-dimensional hydrodynamic model to estimate

Kenneth F. Tiffan; Rodney D. Garland; Dennis W. Rondorf

We study analytically and numerically a kind of diffractive resonant radiation emitted by spatialsolitons, which is generated in waveguide arrays with Kerr nonlinearity. The phase matching condition between soliton and radiation is derived and agrees well with direct pulse propagation simulations. The folded dispersion due to the Brillouin zone leads to a peculiar anomalous soliton recoil that we describe in detail. A linear potential applied across the array generates the analogue of the Raman self-frequency shift in optical fibers, only now applied to the wavenumber. We demonstrate that it is possible to mimic closely temporal fiber-optical dynamics, unveiling the new effects of wavenumber-supercontinuum generation and the compensation of the 'soliton self-wavenumber shift' by the emitted diffractive radiation. This work paves the way for designing unique optical devices that generate spectrally broad supercontinua with a controllable directionality.

We study numerically and experimentally the reflection of spatialsolitons at the interface between a nonlinear saturable-type medium and a linear one. We emphasize on determining the physical conditions under which the reflected beam at the interface conserve its nondiffracting properties. Depending on the incidence angle, we find three critical regions for spatialsoliton conservation after reflection. We numerically show

E. Alvarado-Méndez; R. Rojas-Laguna; J. G. Aviña-Cervantes; M. Torres-Cisneros; J. A. Andrade-Lucio; J. C. Pedraza-Ortega; E. A. Kuzin; J. J. Sánchez-Mondragón; V. Vysloukh

Solitary waves have fascinated the world of nonlinear optics since they were first predicted more than 30 years ago. Predicted initially for spatial self-focusing in Kerr-type materials, they were also predicted-and discovered-in a variety of situations: temporal pulses propagating in optical fibers, photorefractive materials and second-order nonlinear materials, commonly used for second harmonic generation. In this dissertation, cascaded second order nonlinearities were investigated in second-harmonic geometries leading to solitary wave formation. The research presented here started with the investigation of interactions of solitary waves in Type I quadratically nonlinear media, for moderate phase mismatches. To simplify the problem, only one-dimensional geometries were considered. When the phase difference between the input fundamental waves was varied, the results of the collisions exhibited a threshold behavior at a negative phase mismatch and a critical phase difference was identified which marked the transition from attractive (and beam fusion) to repulsive behavior. It was shown that this feature persists even if the fields launched at the input are not exactly solitons. The influence of various parameters was investigated extensively, although not completely. The stability of solitary waves was also investigated, with a focus on the stability of highly asymmetric inputs (elliptic input beams and strip waves). It was found that even if the strip waves are analytical solutions which are stable in an one dimensional geometry, small modulations (periodic or just noise) will lead to the break-up of the beam into a periodic sequence of solitary waves. In the absence of noise, a highly elliptic beam was shown to reshape into a circular solitary wave. However, even a small amount of noise will trigger the breakup of the beam due to modulational instability, given that enough power is present at the input. Although this work is primarily theoretical and several simplifying assumptions were made, many new phenomena were predicted, some of which were observed experimentally. The wealth of new phenomena-including threshold phenomena-open the path to new classes of all-optical devices. Overall, cascaded nonlinearities provide a rich variety of applications for second-order nonlinearities, not yet fully explored.

of polarization states, and therefore these distinct equilib- ria can, in theory, be used to store and process to multistability in the modes of scalar solitons see, for example, Ref. 1 . The phenomenon also differs from other examples of polarization multistabil- ity in specially engineered devices, such as the vertical- cavity

equilibria can, in theory, be used to store and process information. The multistability occursÂshaped solutions of the Manakov equations. This is in contrast to multistability in the modes of scalar solitons multistability in specially engineered devices, such as the verticalÂcavity surfaceÂemitting laser (VCSEL) [2

Optical bistability and bright and dark resonator solitons exist in semiconductor resonator at room temperature [CO. Weis and Ye. Larionova, Rep. Prog. Phys. 70 (2007) 255-335], with the usual semiconductor nonlinearity. At low temperature in the strong coupling regime between quantum well excitons and the optical field in a semiconductor microcavity the nonlinearities are strong and based on \\

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

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.

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

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

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

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

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

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

We analyze and compare the effect of spatial and spin anisotropy on spin conductivity in a twodimensional S = 1/2 Heisenberg quantum magnet on a square lattice. We explore the model in both the Néel antiferromagnetic (AF) phase and the collinear antiferromagnetic (CAF) phase. We find that in contrast to the effects of spin anisotropy in the Heisenberg model, spatial anisotropy in the AF phase does not suppress the zero temperature regular part of the spin conductivity in the zero frequency limit-rather it enhances it. In the CAF phase (within the non-interacting approximation), the zero frequency spin conductivity has a finite value, which is suppressed as the spatial anisotropy parameter is increased. Furthermore, the CAF phase displays a spike in the spin conductivity not seen in the AF phase. We also explore the finite temperature effects on the Drude weight in the AF phase (within the collisionless approximation). We find that enhancing spatial anisotropy increases the Drude weight value and increasing spin anisotropy decreases the Drude weight value. Based on these studies, we conclude that antiferromagnets with spatial anisotropy are better spin conductors than those with spin anisotropy at both zero and finite temperatures.

A Kentech x-ray streak camera was run at the LLNL compact multipulse terawatt (COMET) laser to record simultaneous space- and time-resolved measurements of picosecond laser-produced plasmas. Four different x-ray energy channels were monitored using broadband filters to record the time history of Cu targets heated at irradiances of 1016-1019 W/cm2. Through the Cu filter channel, a time-resolution below 3 ps was obtained. Additionally, an array of 10 ?m diameter pinholes was placed in front of the camera to produce multiple time-resolved x-ray images on the photocathode and time-integrated images on the phosphor with 10 and 15 times magnification, respectively, with spatial resolution of < 13 ?m.

Steel, A. B.; Nagel, S. R.; Dunn, J.; Baldis, H. A.

A Kentech x-ray streak camera was run at the LLNL compact multipulse terawatt (COMET) laser to record simultaneous space- and time-resolved measurements of picosecond laser-produced plasmas. Four different x-ray energy channels were monitored using broadband filters to record the time history of Cu targets heated at irradiances of 10(16)-10(19) W?cm(2). Through the Cu filter channel, a time-resolution below 3 ps was obtained. Additionally, an array of 10 ?m diameter pinholes was placed in front of the camera to produce multiple time-resolved x-ray images on the photocathode and time-integrated images on the phosphor with 10 and 15 times magnification, respectively, with spatial resolution of < 13 ?m. PMID:23127011

Gravel-bed braided rivers are characterized by shallow, branching flow across low relief, complex, and mobile bed topography. These conditions present a major challenge for the application of higher dimensional hydraulic models, the predictions of which are nevertheless vital to inform flood risk and ecosystem management. This paper demonstrates how high-resolution topographic survey and hydraulic monitoring at a density commensurate with model discretization can be used to advance hydrodynamic simulations in braided rivers. Specifically, we detail applications of the shallow water model, Delft3d, to the Rees River, New Zealand, at two nested scales: a 300 m braid bar unit and a 2.5 km reach. In each case, terrestrial laser scanning was used to parameterize the topographic boundary condition at hitherto unprecedented resolution and accuracy. Dense observations of depth and velocity acquired from a mobile acoustic Doppler current profiler (aDcp), along with low-altitude aerial photography, were then used to create a data-rich framework for model calibration and testing at a range of discharges. Calibration focused on the estimation of spatially uniform roughness and horizontal eddy viscosity, ?H, through comparison of predictions with distributed hydraulic data. Results revealed strong sensitivity to ?H, which influenced cross-channel velocity and localization of high shear zones. The high-resolution bed topography partially accounts for form resistance, and the recovered roughness was found to scale by 1.2-1.4 D84 grain diameter. Model performance was good for a range of flows, with minimal bias and tight error distributions, suggesting that acceptable predictions can be achieved with spatially uniform roughness and ?H.

Williams, R. D.; Brasington, J.; Hicks, M.; Measures, R.; Rennie, C. D.; Vericat, D.

The localized 1H MR spectrum of human muscle has recently been reported to feature unassigned, orientation-dependent resonance lines. For their characterization in vivo,various NMR techniques were combined with 3D spatial localization: 2D-J spectroscopy, zero-quantum- and Zeeman-order-filtering, double-quantum-filtering, 2D-constant-time COSY, dipolar-order filtering, and 2D-longitudinal-order separated spectroscopy. The successful implementation of these methods on a whole-body MR system and their application to study human subjects is described. 1H MR spectra of human muscle were found to feature residual dipolar couplings and anisotropic susceptibilities which render resonance frequencies, phases, and—with some sequences—signal intensities orientation dependent. Two of the unidentified resonances unequivocally form a dipolar doublet of two equivalent protons, centered at 3.93 ppm. All unknown as well as previously assigned peaks in the range between 2.7 and 3.6 ppm are either subject to dipolar coupling themselves or overlap with spectral contributions of metabolites involved in dipolar coupling. The methyl protons of creatine are likely to be subject to residual dipolar coupling and do therefore form a dipolar triplet and not a singlet as previously assumed. Finally, X3, a further unidentified peak at 3.5 ppm, appears to be part of a multiplet with its center at 3.3 ppm and overlapping the trimethylammonium resonance.

We consider the numerical solution of the time-fractional diffusion-wave equation on a two-dimensional unbounded spatial domain. Introduce an artificial boundary and find the exact and approximate artificial boundary conditions for the given problem, which lead to a bounded computational domain. Using the exact or approximating boundary conditions on the artificial boundary, the original problem is reduced to an initial-boundary-value problem on the bounded computational domain which is respectively equivalent to or approximates the original problem. A finite difference method is used to solve the reduced problems on the bounded computational domain. The numerical results demonstrate that the method given in this paper is effective and feasible.

Spatially periodic modulation of the intersite coupling in two-dimensional (2D) nonlinear lattices modifies the eigenvalue spectrum by opening mini-gaps in it. This work aims to build stable localized modes in the new bandgaps. Numerical analysis shows that single-peak and composite two- and four-peak discrete static solitons and breathers emerge as such modes in certain parameter areas inside the mini-gaps of the 2D superlattice induced by the periodic modulation of the intersite coupling along both directions. The single-peak solitons and four-peak discrete solitons are stable in a part of their existence domain, while unstable stationary states (in particular, two-soliton complexes) may readily transform into robust localized breathers. PMID:24985438

Gligori?, Goran; Maluckov, Aleksandra; Hadžievski, Ljup?o; Malomed, Boris A

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

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

We theoretically demonstrate a variety of multipole plasmonic lattice solitons, including dipoles, quadrupoles, and necklaces, in two-dimensional metallic nanowire arrays with Kerr-type nonlinearities. Such solitons feature complex internal structures with an ultracompact mode size approaching or smaller than one wavelength. Their mode sizes and the stability characteristics are studied in detail within the framework of coupled mode theory. The conditions to form and stabilize these highly confined solitons are within the experimentally achievable range.

Kou Yao; Ye Fangwei; Chen Xianfeng [Department of Physics, State Key Laboratory on Fiber Optic Local Area Communication Networks and Advanced Optical Communication Systems, Shanghai Jiao Tong University, Shanghai 200240 (China)

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)

We construct dissipative spatialsolitons in one- and two-dimensional (1D and 2D) complex Ginzburg-Landau (CGL) equations with spatially uniform linear gain; fully nonlocal complex nonlinearity, which is proportional to the integral power of the field times the harmonic-oscillator (HO) potential, similar to the model of "accessible solitons;" and a diffusion term. This CGL equation is a truly nonlinear one, unlike its actually linear counterpart for the accessible solitons. It supports dissipative spatialsolitons, which are found in a semiexplicit analytical form, and their stability is studied semianalytically, too, by means of the Routh-Hurwitz criterion. The stability requires the presence of both the nonlocal nonlinear loss and diffusion. The results are verified by direct simulations of the nonlocal CGL equation. Unstable solitons spontaneously spread out into fuzzy modes, which remain loosely localized in the effective complex HO potential. In a narrow zone close to the instability boundary, both 1D and 2D solitons may split into robust fragmented structures, which correspond to excited modes of the 1D and 2D HOs in the complex potentials. The 1D solitons, if shifted off the center or kicked, feature persistent swinging motion. PMID:24229254

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

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

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

In this paper we investigate the properties of self-induced transparency (SIT) solitons, propagating in a {Lambda}-type medium. We find that the interaction between SIT solitons can lead to trapping with their phases preserved in the ground-state coherence of the medium. These phases can be altered in a systematic way by the application of appropriate light fields, such as additional SIT solitons. Furthermore, multiple independent SIT solitons can be made to propagate as bisolitons through their mutual interaction with a separate light field. Finally, we demonstrate that control of the SIT soliton phase can be used to implement an optical exclusive-or (xor) gate.

Beeker, Willem P.; Lee, Chris J.; Boller, Klaus J. [Laser Physics and Nonlinear Optics Group, MESA Research Institute for Nanotechnology, University of Twente, P.O. Box 217, 7500AE Enschede (Netherlands); Can, Edip [Physics of Fluids Group, Faculty of Science and Technology, University of Twente, P.O. Box 217, 7500AE Enschede (Netherlands)

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

This a brief report on the acquisition and implementation of instrumentation which will be used to make two-dimensional velocimetry measurements in a study of premixed turbulent flames. Two-dimensional velocimetry. (eg)

The generalized Thirring model with impurity coupling is defined on two-dimensional noncommutative space-time, a modified propagator and free energy are derived by means of functional integrals method. Moreover, quantum fluctuations and excitation energies are calculated on two-dimensional black hole and soliton background.

Static topologically-nontrivial configurations in sigma-models, for spatial dimension D \\geq 2, are unstable. The question addressed here is whether such sigma-model solitons can be stabilized by steady rotation in internal space; that is, rotation in a global SO(2) symmetry. This is the mechanism which stabilizes Q-balls (non-topological solitons). The conclusion is that the Q-mechanism can stabilize topological solitons in D=2 spatial dimensions, but not for D=3.

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.

Nous avons étudié numériquement et expérimentalement un mécanisme ultra-rapide de remise en forme temporelle d'impulsions, basé sur l'émission d'un solitonspatial quadratique dans un guide Ti:PPLN et combiné à un filtrage spatial. Nous mettons en évidence une remise en forme efficace d'impulsions de durée 4 ps à 1548 nm.

L. Grossard; P.-H. Pioger; V. Couderc; A. Barthélémy; F. Baronio; C. de Angelis; Y. Min; V. Quiring; W. Sohler

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

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

This thesis investigates the dynamical and soliton-like behavior of spatially-partially incoherent light beams in non-instantaneous nonlinear materials. Self-trapping of incoherent beams and their coherence properties are studied in great detail. Two complimentary approaches are developed in order to explain the observed incoherent self-focusing behavior in biased photorefractive media; namely the coherent density approach and the self- consistent incoherent multimode method.

We study pattern formation in a passive nonlinear optical cavity on the basis of the classic Lugiato-Lefever model with a periodically modulated injection. When the injection amplitude sign alternates, e.g., following a sinusoidal modulation in time or in space, a phase-bistable response emerges, which is at the root of the spatial pattern formation in the system. An asymptotic description is given in terms of a damped nonlinear Schrödinger equation with parametric amplification, which allows gaining insight into the basic spatiotemporal dynamics of the system. One- and two-dimensional phase-bistable spatial patterns, such as bright and dark-ring cavity solitons and labyrinths, are demonstrated.

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

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

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

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

In a previous paper, F. Calogero and the author studied the non-linear modulation of dispersive trapped water-waves in a channel or along a beach (edge waves). They showed that the signal envelope, (which is studied with convenient time scale and length scale) obeys Nonlinear Schrödinger Equation. The result is extended here to waves trapped by the bottom geometry of a basin which is infinitely extended into all horizontal directions. One can obtain along the guided path, envelope solitons of Nonlinear Schrödinger Equation for a signal whose amplitude exponentially decreases in transverse directions. These bidimensional solitons are thus shown as asymptotic features for a large class of problems. This class is narrower than in the finite case or in the semiinfinite case because strong conditions must be set either on the linear part or on the nonlinear part of the operator in order to guarantee an exponentially decreasing behavior on both sides. In addition, the envelope solitons are in most cases unstable features, because of side-band instabilities. Nevertheless, the result suggests that the exact bidimensional solitons recently derived by Boiti et al. for special Equations are not an exceptional physical feature of two-dimensional evolutions.

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

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

We analyse the feasibility of using iron-doping in lithium niobate in order to stabilize and permanently fix light-induced integrated structures. General 3D optical interconnections were realized in bulk lithium niobate crystals by means of soliton waveguides exploiting the enhanced photorefractive properties obtainable using specific iron doping. We report an enhancement of the photorefractive properties in doped crystals that can be considered for permanently fixing the integrated circuits. This work opens new directions for realizing permanent self-assembled and self-aligned integrated electro-optic devices and photonic circuits.

Fazio, E.; Zaltron, A.; Belardini, A.; Argiolas, N.; Sada, C.

This article is the second in a two-part series. In part one (ANALYTICAL CHEMISTRY, May 15) the authors discussed one-dimensional nuclear magnetic resonance (NMR) spectra and some relatively advanced nuclear spin gymnastics experiments that provide a capability for selective sensitivity enhancements. In this article and overview and some applications of two-dimensional NMR experiments are presented. These powerful experiments are important complements to the one-dimensional experiments. As in the more sophisticated one-dimensional experiments, the two-dimensional experiments involve three distinct time periods: a preparation period, t/sub 0/; an evolution period, t/sub 1/; and a detection period, t/sub 2/.

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

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

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

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

In this Letter we show how nontrivial forms of spatially localized oscillations or breathers can occur in two-dimensional excitable neural media with short-range excitation and long-range inhibition. The basic dynamical mechanism involves a Hopf bifurcation of a stationary pulse solution in the presence of a spatially localized input. Such an input could arise from external stimuli or reflect changes in the excitability of local populations of neurons as a precursor for epileptiform activity. The resulting dynamical instability breaks the underlying radial symmetry of the stationary pulse, leading to the formation of a nonradially symmetric breather. The number of breathing lobes is consistent with the order of the dominant unstable Fourier mode associated with perturbations of the stationary pulse boundary

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.

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

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

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

We exhibit soliton solutions of QCD in two dimensions that have the quantum numbers of quarks. They exist only for quarks heavier than the dimensional gauge coupling, and have infinite energy, corresponding to the presence of a string carrying the non-singlet color flux off to spatial infinity. The quark solitons also disappear at finite temperature, as the temperature-dependent effective quark mass is reduced in the approach to the quark/hadron phase transition.

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

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

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

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

We introduce a lattice model for a classical doped twodimensional antiferromagnet which has no quenched disorder, yet displays slow dynamics similar to those observed in supercooled liquids. We calculate two-time spatial and spin correlations via Monte Carlo simulations and find that for sufficiently low temperatures, there is anomalous diffusion and stretched-exponential relaxation of spin correlations. The relaxation times associated

Malcolm P. Kennett; Claudio Chamon; Leticia F. Cugliandolo

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.

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

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

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

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

Well known classical spinor relativistic-invariant two-dimensional field theory models, including the Gross-Neveu, Vaks-Larkin-Nambu-Jona-Lasinio and some other models, are shown to be integrable by means of the inverse scattering problem method. These models are shown to be naturally connected with the principal chiral fields on the symplectic, unitary and orthogonal Lie groups. The respective technique for construction of the soliton-like solutions

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

Collisional diffusion in a two-dimensional point vortex gas or a two-dimensional plasma Daniel H. E of a multispecies two-dimensional 2D point vortex gas, or a 2D plasma, in the presence of retrograde shear of point vortices, Onsager relations require that the diffusive flux conserves the total vorticity (r

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

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

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

We introduce a lattice model for a classical doped two-dimensional antiferromagnet that has no quenched disorder, yet displays slow dynamics similar to those observed in supercooled liquids. We calculate two-time spatial and spin correlations via Monte Carlo simulations and find that for sufficiently low temperatures, there is anomalous diffusion and stretched-exponential relaxation of spin correlations. The relaxation times associated with

Malcolm P. Kennett; Claudio Chamon; Leticia F. Cugliandolo

In two-dimensional echocardiography the sonographer must synthesize multiple tomographic slices into a mental three-dimensional (3D) model of the heart. Computer graphics and virtual reality environments are ideal to visualize complex 3D spatial relationships. In augmented reality (AR) applications, real and virtual image data are linked, to increase the information content. In the presented AR simulator a 3D surface model of

M. Weidenbach; C. Wick; S. Pieper; K. J. Quast; T. Fox; G. Grunst; D. A. Redel

A universal theory of steady-state one-dimensional photorefractive spatialsolitons is developed which applies to the steady-state one-dimensional photorefractive solitons under various realizations, including the screening solitons in a biased photorefractive medium, the photovoltaic solitons in open- and closed-circuit photovoltaic-photorefractive media and the screening-photovoltaic solitons in biased photovoltaic-photorefractive media. Previous theories advanced individually elsewhere for these solitons can be obtained by

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 spatialsolitons bulletCavity solitons in passive and active resonators bulletThree-dimensional spatialsolitons bulletDark, bright, grey solitons; interface dynamics bulletCompound or vector solitons; incoherent solitons bulletLight and matter solitons in BEC bulletNonlinear localized structures in microstructured and nanostructured materials (photonic crystals, etc) bulletAngular momentum effects associated with localized light structures; vortex solitons bulletQuantum effects associated with localized light structures bulletInteraction of solitons with atoms and other media bulletApplications of optical solitons The DEADLINE for submission of contributions is 31 July 2003 to allow the topical issue to appear in about February 2004. All papers will be peer-reviewed in accordance with the normal refereeing procedures and standards of Journal of Optics B: Quantum and Semiclassical Optics. Advice on publishing your work in the journal may be found at www.iop.org/journals/authors/jopb. Submissions should ideally be in either standard LaTeX form or Microsoft Word. There are no page charges for publication. In addition to the usual 50 free reprints, the corresponding author of each paper published will receive a complimentary copy of the topical issue. Contributions to the topical issue should if possible be submitted electronically at www.iop.org/journals/jopb. or by e-mail to jopb@iop.org. Authors unable to submit online or by e-mail may send hard copy contributions (enclosing the electronic code) to: Dr Claire Bedrock (Publisher), Journal of Optics B: Quantum and Semiclassical Optics, Institute of Physics Publishing, Dirac House, Temple Back, Bristol BS1 6BE, UK. All contributions should be accompanied by a readme file or covering letter, quoting `JOPB topical issue - Optical Solitons', giving the postal and e-mail addresses for correspondence. Any subsequent change of address should be notified to the publishing office. We look forward to receiving your contribution to this topical issue.

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.

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

We address spectral tunneling of walking spatialsolitons 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.

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)

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

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

Extraordinary phenomena can occur at the interface between two oxide materials. A spectacular example is a formation of a two-dimensional electron gas (2DEG) at the SrTiO3/LaAlO3 interface. In this dissertation the properties of the 2DEG are investigated from first principles. The spatial extent of the 2DEG formed at the SrTiO3/LaAlO 3 n-type interface is studied. It is shown that the confinement of the 2DEG is controlled by metal induced gap states formed in the band gap of SrTiO 3. The confinement width is then determined by the attenuation length of the metal induced gap states into SrTiO3 which is governed by the lowest decay rate evanescent states of bulk SrTiO3 which in turn can be found from the complex band structure of bulk SrTiO3. Magnetic properties of the 2DEG formed at the n-type interface of the SrTiO3/LaAlO3 superlattices are investigated. It is found that for a thin SrTiO3 film the interface is ferromagnetic but for a thicker SrTiO3 film the magnetic moment decreases and eventually disappears. This is a result of delocalization of the 2DEG that spreads over thicker SrTiO3 film which leads to violation of the Stoner criterion. Further, it is shown that inclusion of the Hubbard U interaction enhances the Stoner parameter and stabilizes the magnetism. The effect of the 2DEG and the polar interfaces for the thin film ferroelectricity is investigated using both first principles and model calculations. Using a TiO2-terminated BaTiO3 film with LaO monolayers at the two interfaces it is shown that the intrinsic electric field produced by the polar interface forces ionic displacements in BaTiO3 to produce the electric polarization directed into the interior of the BaTiO 3 layer. This creates a ferroelectric dead layer near the interfaces that is non-switchable and thus detrimental to ferroelectricity. It is found that the effect is stronger for a larger effective ionic charge at the interface and longer screening length due to a stronger intrinsic electric field that penetrates deeper into the ferroelectric.

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

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…

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

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

A two-dimensional variable area gas turbine engine exhaust nozzle is described having thrust reversing capability, the nozzle including spaced apart side wall means and upper and lower flap assemblies connected to the side wall means defining an exhaust gas flow path wihtin the nozzle, the nozzle having a centerline.

We investigate the routing of vortex beams in nonlocal media by means of coaxial, co-propagating spatial optical solitons. By introducing a refractive index perturbation in the form of a localized defect or a dielectric interface, the soliton waveguide can be curved and, therefore, can deviate the collinear vortex, effectively routing it, while preventing its destabilization and breakup. PMID:24487852

Assanto, Gaetano; Minzoni, Antonmaria A; Smyth, Noel F

This dissertation discusses a magnetization study of a twodimensional Fermi system. Our group developed a SQUID NMR system to study the magnetization of twodimensional 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 twodimensional 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 twodimensional 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 twodimensional 3He films on both Grafoil and highly oriented ZYX grade exfoliated graphite. The dipolar field plays an important role in magnetic ordering in twodimensional 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.

The coherent matter waves of a dipolar condensate in deep two-dimensional (2D) tilted and nontilted optical lattices are studied both analytically and numerically. It is shown that, in tilted lattices, by properly designing the sign and the magnitude of the contact interaction and the dipolar interaction, it is possible to control the decoherence of Bloch oscillations. Contrary to the usual short-range interacting Bose system, long-lived Bloch oscillations of the dipolar condensate are achieved when the dipolar interaction, the contact interaction, and the lattice dimension satisfy an analytical condition. Furthermore, we predict that, in untilted lattices, stable coherent 2D moving soliton and breather states of the dipolar condensate exist. This fact is very different from the purely short-range interacting Bose system (where the moving soliton cannot be stabilized in high-dimensional lattices). The dipolar interaction can lead to some novel phenomena that can not appear in short-range interacting BEC system.

Zhang Aixia; Xue Jukui [Physics and Electronics Engineering College, Northwest Normal University, Lanzhou 730070 (China)

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

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.

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

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.

We describe the unramified Langlands correspondence for two-dimensional local fields and construct a categorical analogue of the unramified principal series representation and study its properties. The main tool for this description is the construction of a certain central extension. For this and other central extensions, we prove non-commutative reciprocity laws (that is, splitting of the central extensions over certain subgroups) for arithmetic surfaces and projective surfaces over finite fields. These reciprocity laws connect central extensions constructed locally and globally.

The temperature dependence of the diamagnetic susceptibility of quasi-two-dimensional graphites is studied in the temperature interval 4.2-1000 K. At low temperatures, the large diamagnetic susceptibility, in comparison with the exponentially small value predicted by current theories, is attributable to the effect of scattering of electrons by the structural defects on the smearing of the energy spectrum near a conic singularity. 8 references.

Two-dimensional sinusoid fitting and Fourier transform methods of analyzing fringes to determine the wave-front topography are described. The methods are easy to apply because they do not require finding fringe centers and fringe orders. Also, they are accurate. For an active optics experiment in which these techniques have been used, experimental noise exceeds the error resulting from analysis of noise-free

Two families of two-dimensional orthogonal complete complementary codes (2D-OCCC) are presented They can be constructed, for example, over binary or complex symbols. The new 2D-OCCC retain most of the properties of the 1D-OCCC. The autocorrelation function is equal to zero for all nonzero shifts in both dimensions of any signature selected from the code. The cross-correlation for any pair of

The general objective of this presentation is to demonstrate the great potential of twodimensional (2D) Photonic Crystals (PC) based on InP-membranes bonded onto silica on silicon substrates, with a special emphasis on the development of various classes of 2D PC microlasers. The basic building block consists in an InP (and related material) membrane including a 2D PC formed by

Pierre Viktorovitch; Christelle Monat; J. Mouette; Christian Seassal; Xavier Letartre; Pedro Rojo-Romeo; Marine Le Vassor d'Yerville; David Cassagne; Jean-Paul Albert; E. Jalaguier; S. Pocas; B. Aspar

Superdiffusion of two-dimensional (2D) liquids was studied using an equilibrium molecular dynamics simulation. At intermediate temperatures, the mean-squared displacement, probability distribution function (PDF), and velocity autocorrelation function (VACF) all indicate superdiffusion; the VACF has a long-time tail; and the PDF indicates no Lévy flights. These effects are predicted to occur in 2D dusty plasmas and other 2D liquids that can be modeled with a long-range repulsive potential. PMID:17358266

We investigate the influence of the isospin asymmetry on the phase structure of quark matter near the chiral critical point systematically using a generalized version of Ginzburg-Landau approach. The effect has proven to be so profound that it brings about not only a shift of the critical point but also a rich variety of phases in its neighborhood. In particular, there shows up a phase with spatially varying charged pion condensate which we name the “solitonic pion condensate” in addition to the “chiral defect lattice” where the chiral condensate is partially destructed by periodic placements of two-dimensional wall-like defects. Our results suggest that there may be an island of solitonic pion condensate in the low temperature and high density side of QCD phase diagram.

In widefield fluorescence microscopy, images from all but very flat samples suffer from fluorescence emission from layers above or below the focal plane of the objective lens. Structured illumination microscopy provides an elegant approach to eliminate this unwanted image contribution. To this end a line grid is projected onto the sample and phase images are taken at different positions of the line grid. Using suitable algorithms 'quasi-confocal images' can be derived from a given number of such phase-images. Here, we present an alternative structured illumination microscopy approach, which employs two-dimensional patterns instead of a one-dimensional one. While in one-dimensional structured illumination microscopy the patterns are shifted orthogonally to the pattern orientation, in our two-dimensional approach it is shifted at a single, pattern-dependent angle, yet it already achieves an isotropic power spectral density with this unidirectional shift, which otherwise would require a combination of pattern-shift and -rotation. Moreover, our two-dimensional approach also yields a better signal-to-noise ratio in the evaluated image. PMID:25113075

For such solitons Hopf index #12;Analytical approach. Twodimensional elliptic problem: Numerical approach. Energy method. Each of the calculation process takes about 4 hours of CPUs time on a standard server computer. Energy versus the speed for solitons with same precession frequency. #12;Energy distribution in hopfions

A two-dimensional truncated singular value decomposi-tion (TSVD) technique is first proposed to enhance spa-tial resolution of earth observation (EO) products re- lated to ocean-atmosphere interaction. The technique is based on the assumption that the gain function is a two-dimensional tensor product. To set the value of the truncation parameter the Generalized Cross Validation is adopted. Experiments undertaken on a data set of simulated two- dimensional radiometer measurements show the robust- ness of the technique against the additive noise level and its effectivenes

Lenti, F.; Migliaccio, M.; Nunziata, F.; Rodriguez, G.

Two-dimensional Bragg resonators based on planar dielectric waveguides are analysed. It is shown that the doubly periodic corrugation deposited on the dielectric surface in the form of two gratings with translational vectors directed perpendicular to each other ensures effective selection of modes along two coordinates at large Fresnel parameters. This result is obtained both by the method of coupled waves (geometrical optics approximation) and by the direct numerical simulations. Two-dimensional Bragg resonators make it possible to fabricate two-dimensional distributed feedback lasers and to provide generation of spatially coherent radiation in large-volume active media.

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

The interplay of electron-phonon coupling and strong electronic correlations is studied in the frame of the two-dimensional Hubbard-Holstein model. Static and dynamic properties are determined by quantum Monte Carlo simulations and by Migdal-Eliashberg theory. The comparison allows us to assess the diagrammatic approach. The competition between the phonon-mediated electron-electron attraction and the local Coulomb repulsion leads to a rich phase diagram, which we study in detail for a wide range of parameters. We address the question, to which extent the systems can be described by an effective negative-U Hubbard model.

Oscillatory shear on two-dimensional monodisperse liquid foams was performed. We show that the effect of the oscillatory shear is to cause the migration of bubbles which size is greater than that of a typical bubble of the foam. These so-called flaws move towards the periphery of the foam in a non random motion, thus realizing size segregation in a system which is by construction gravity insensitive. We also show that elongated cavities in the foam could be relaxed towards a more isotropic form with oscillatory shear, and we discuss the pertinent parameters of this relaxation.

C. Quilliet; M. A. P. Idiart; B. Dollet; L. Berthier; A. Yekini

We propose a new method to improve the accuracy of Text Categorization using twodimensional clustering. In a number of previous probabilistic approaches, texts in the same category are implicitly assumed to be generated from an identical distribution. We empirically show that this assumption is not accurate, and propose a new framework based on twodimensional clustering to alleviate this problem. In our method, training texts are clustered so that the assumption is more likely to be true, and at the same time, features are also clustered in order to tackle the data sparseness problem. We conduct some experiments to validate the proposed two-dimensional clustering method.

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

We report the numerical existence of dipole and vortex solitons for the two-dimensional nonlinear Schrödinger (NLS) equation with external potentials that possess strong irregularities, i.e., edge dislocations and a vacancy defects. Multi-humped solitons are computed by employing a spectral fixed-point computational scheme. The nonlinear stability of these solitons is investigated using direct simulations of the NLS equation and it is observed that these multi-humped modes in the defect lattices can be stable or unstable.

A two-dimensional (r,z) fluid model has been developed to study plasma transport in inductively coupled plasmas (ICP). Electron heating is treated by assuming a fixed, spatially varing power deposition profile in the electron energy balance equation. A high aspect ration ICP reactor geometry has been studied, with two assumed power profiles: spatially uniform and localized to within several skin depths

We present a Dirac quantization of generic single-horizon black holes in two-dimensional dilaton gravity. The classical theory is first partially reduced by a spatial gauge choice under which the spatial surfaces extend from a black or white hole singularity to a spacelike infinity. The theory is then quantized in a metric representation, solving the quantum Hamiltonian constraint in terms of

Summary form only given. Photorefractive spatial screening solitons exist in biased photorefractive media where the incident beam modifies the index of refraction in such a way that the beam becomes the first guided mode of its own self-induced waveguide. A beam of a given intensity (in units of the equivalent dark irradiance or of the background illumination) self traps in

C. Anasrassiou; M. Mitchell; Ming-Feng Shih; J. Giormaine; J. Martin; M. Segev

Construction of the wood frame for the Two-Dimensional Low-Turbulence Tunnel. The Two-Dimensional Low-Turbulence Tunnel was originally called the Refrigeration or 'Ice' tunnel because it was intended to support research on aircraft icing. The tunnel was built of wood, lined with sheet steel, and heavily insulated on the outside. Refrigeration equipment was installed to generate icing conditions inside the test section. The NACA sent out a questionnaire to airline operators, asking them to detail the specific kinds of icing problems they encountered in flight. The replies became the basis for a comprehensive research program begun in 1938 when the tunnel commenced operation. Research quickly focused on the concept of using exhaust heat to prevent ice from forming on the wing's leading edge. This project was led by Lewis Rodert, who later would win the Collier Trophy for his work on deicing. By 1940, aircraft icing research had shifted to the new Ames Research Laboratory, and the Ice tunnel was refitted with screens and honeycomb. Researchers were trying to eliminate all turbulence in the test section. From TN 1283: 'The Langley two-dimensional low-turbulence pressure tunnel is a single-return closed-throat tunnel.... The tunnel is constructed of heavy steel plate so that the pressure of the air may be varied from approximately full vacuum to 10 atmospheres absolute, thereby giving a wide range of air densities. Reciprocating compressors with a capacity of 1200 cubic feet of free air per minute provide compressed air. Since the tunnel shell has a volume of about 83,000 cubic feet, a compression rate of approximately one atmosphere per hour is obtained. ... The test section is rectangular in shape, 3 feet wide, 7 1/2 feet high, and 7 1/2 feet long. ... The over-all size of the wind-tunnel shell is about 146 feet long and 58 feet wide with a maximum diameter of 26 feet. The test section and entrance and exit cones are surrounded by a 22-foot diameter section of the shell to provide a space to house much of the essential equipment.

Construction of the Two-Dimensional Low-Turbulence Tunnel. The Two-Dimensional Low-Turbulence Tunnel was originally called the Refrigeration or 'Ice' tunnel because it was intended to support research on aircraft icing. The tunnel was built of wood, lined with sheet steel, and heavily insulated on the outside. Refrigeration equipment was installed to generate icing conditions inside the test section. The NACA sent out a questionnaire to airline operators, asking them to detail the specific kinds of icing problems they encountered in flight. The replies became the basis for a comprehensive research program begun in 1938 when the tunnel commenced operation. Research quickly focused on the concept of using exhaust heat to prevent ice from forming on the wing's leading edge. This project was led by Lewis Rodert, who later would win the Collier Trophy for his work on deicing. By 1940, aircraft icing research had shifted to the new Ames Research Laboratory, and the Ice tunnel was refitted with screens and honeycomb. Researchers were trying to eliminate all turbulence in the test section. From TN 1283: 'The Langley two-dimensional low-turbulence pressure tunnel is a single-return closed-throat tunnel.... The tunnel is constructed of heavy steel plate so that the pressure of the air may be varied from approximately full vacuum to 10 atmospheres absolute, thereby giving a wide range of air densities. Reciprocating compressors with a capacity of 1200 cubic feet of free air per minute provide compressed air. Since the tunnel shell has a volume of about 83,000 cubic feet, a compression rate of approximately one atmosphere per hour is obtained. ... The test section is rectangular in shape, 3 feet wide, 7 1/2 feet high, and 7 1/2 feet long. ... The over-all size of the wind-tunnel shell is about 146 feet long and 58 feet wide with a maximum diameter of 26 feet. The test section and entrance and exit cones are surrounded by a 22-foot diameter section of the shell to provide a space to house much of the essential equipment.

Manometer for the Two-Dimensional Low-Turbulence Tunnel. The Two-Dimensional Low-Turbulence Tunnel was originally called the Refrigeration or 'Ice' tunnel because it was intended to support research on aircraft icing. The tunnel was built of wood, lined with sheet steel, and heavily insulated on the outside. Refrigeration equipment was installed to generate icing conditions inside the test section. The NACA sent out a questionnaire to airline operators, asking them to detail the specific kinds of icing problems they encountered in flight. The replies became the basis for a comprehensive research program begun in 1938 when the tunnel commenced operation. Research quickly focused on the concept of using exhaust heat to prevent ice from forming on the wing's leading edge. This project was led by Lewis Rodert, who later would win the Collier Trophy for his work on deicing. By 1940, aircraft icing research had shifted to the new Ames Research Laboratory, and the Ice tunnel was refitted with screens and honeycomb. Researchers were trying to eliminate all turbulence in the test section. From TN 1283: 'The Langley two-dimensional low-turbulence pressure tunnel is a single-return closed-throat tunnel.... The tunnel is constructed of heavy steel plate so that the pressure of the air may be varied from approximately full vacuum to 10 atmospheres absolute, thereby giving a wide range of air densities. Reciprocating compressors with a capacity of 1200 cubic feet of free air per minute provide compressed air. Since the tunnel shell has a volume of about 83,000 cubic feet, a compression rate of approximately one atmosphere per hour is obtained. ... The test section is rectangular in shape, 3 feet wide, 7 1/2 feet high, and 7 1/2 feet long. ... The over-all size of the wind-tunnel shell is about 146 feet long and 58 feet wide with a maximum diameter of 26 feet. The test section and entrance and exit cones are surrounded by a 22-foot diameter section of the shell to provide a space to house much of the essential equipment.

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 twodimensional toy model. •Relations to dark matter collisions in galaxy clusters are proposed.

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

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

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

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

A two-dimensional horn imaging array has been demonstrated at 242 and 93 GHz. In this configuration, a dipole is suspended in a pyramidal horn, fabricated by an anisotropic chemical etch technique, on a 1-?m silicon-oxynitride membrane. This approach leaves room for low-frequency lines and processing electronics. Pattern measurements on a 1.45-? imaging array agree well with theory, show no sidelobes, and a 3-dB beamwidth of 35° and 46° for the E and H planes, respectively. Application areas include a superconducting tunnel-junction receiver for radio astronomy and imaging arrays for real-time electron density mapping in fusion plasmas. Support for this project was provided by DOE contract DE-FG03-86-ER-53225 (subcontracted from U.C.L.A.).

Rebeiz, Gabriel M.; Guo, Yong; Stimson, P. A.; Rutledge, David B.; Kasilingan, Dayalan P.

The Grover walk, which is related to Grover’s search algorithm on a quantum computer, is one of the typical discrete time quantum walks. However, a localization of the two-dimensional Grover walk starting from a fixed point is strikingly different from other types of quantum walks. The present paper explains the reason why the walker who moves according to the degree-four Grover operator can remain at the starting point with a high probability. It is shown that the key factor for the localization is due to the degeneration of eigenvalues of the time evolution operator. In fact, the global time evolution of the quantum walk on a large lattice is mainly determined by the degree of degeneration. The dependence of the localization on the initial state is also considered by calculating the wave function analytically.

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

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

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

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

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

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

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

The paper was aimed to compare performance capabilities of two types of scintillation detectors commonly used for fast neutron imaging: twodimensional and linear ones. Best-case values of quantum efficiency, spatial resolution and capacity were estimated for detectors with plastic converter-screen in case of 14 MeV neutrons. For that there were examined nuclear reactions produced in converter-screen by fast neutrons, spatial distributions of energy release of emerged charged particles and amplitude distributions of scintillations generated by these particles. The paper shows that the efficiency of the linear detector is essentially higher and this detector provides potentially better spatial resolution in comparison with the twodimensional detector. But, the twodimensional detector surpasses the linear one in capacity. The presented results can be used for designing radiographic fast neutron detectors with organic scintillators.

Mikerov, V. I.; Koshelev, A. P.; Ozerov, O. V.; Sviridov, A. S.; Yurkov, D. I.

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

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

A two-dimensionalspatial filter, optimum in the minimum-mean-square error sense, has been used to retrieve atmospheric temperature profiles from TIROS-N and NOAA-6 Microwave Sounding Unit measurements. This approach considers correlations both in the vertical and horizontal (along the orbital track) directions. It is found that lower retrieval errors result from the 2-D technique, compared with the 1-D technique, especially in the troposphere. The additional horizontal information used in the 2-D formulation substantially improves temperature retrievals over a severe cold front where vertical correlations are lessened. The improved results of the 2-D filter in the upper troposphere point to the presence of profile components in the null space of the weighting functions that are horizontally correlated with the observed data.

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

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

We demonstrate that electron transfer induced by fast ion impact can be used as an imaging technique of two-dimensional materials. Applied to a keV proton beam passing through a graphene surface, it is shown that coherent single-electron capture gives a sub-ångström-scale spatial resolution image of the electronic structure of a single sheet. This imaging scheme is shown to be particularly effective, resolving missing atoms (vacancies) in the lattice, in a narrow projectile 5-10-keV energy region, where the capture probability exhibits a minimum at the center of the hexagonal cells. This geometry-dependent phenomenon is caused by the coupling dynamic between the initial state and a multi-electron entangled one-hole state and is therefore highly sample selective.

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

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

modeling and an experimental investigation of two-dimensional photonic crystal microlasers: defect stateTwo-dimensional surface emitting photonic crystal laser with hybrid triangular-graphite structure at room temperature. A two-dimensional photonic crystal lattice conformed in a hybrid triangular- graphite

We show that one- and two-dimensional discrete solitons are in fact possible in biased photorefractive media. This can be accomplished in optically induced photonic crystals\\/waveguides by exploiting the photorefractive screening nonlinearity. In this case, the 2-D lattice is created in the bulk, by appropriately interfering polarized plane-wave pairs.

N. K. Efremidis; D. N. Christodoulides; S. Sears; M. Segev

Boron, a nearest-neighbor of carbon, is possibly the second element that can possess free-standing flat monolayer structures, evidenced by recent successful synthesis of single-walled and multiwalled boron nanotubes (MWBNTs). From an extensive structural search using the first-principles particle-swarm optimization (PSO) global algorithm, two boron monolayers (?(1)- and ?(1)-sheet) are predicted to be the most stable ?- and ?-types of boron sheets, respectively. Both boron sheets possess greater cohesive energies than the state-of-the-art two-dimensional boron structures (by more than 60 meV/atom based on density functional theory calculation using PBE0 hybrid functional), that is, the ?-sheet previously predicted by Tang and Ismail-Beigi and the g(1/8)- and g(2/15)-sheets (both belonging to the ?-type) recently reported by Yakobson and co-workers. Moreover, the PBE0 calculation predicts that the ?-sheet is a semiconductor, while the ?(1)-, ?(1)-, g(1/8)-, and g(2/15)-sheets are all metals. When two ?(1) monolayers are stacked on top each other, the bilayer ?(1)-sheet remains flat with an optimal interlayer distance of ~3.62 Å, which is close to the measured interlayer distance (~3.2 Å) in MWBNTs. PMID:22816319

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

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

A two-dimensional detector of thermal neutrons has been designed and constructed for neutron diffraction experiments at the St. Petersburg Nuclear Physics Institute. It is based on a multiwire proportional chamber (MWPC) with cathode strip delay line readout and has a sensitive area of 170×300 mm 2 and anode wire spacing is 4 mm. It operates with a gas mixture of 1.5 bar 3He+2 bar CF 4. To improve the gas purity by a few orders of magnitude, a new technology for fabrication of the detector's electrodes has been developed. An intrinsic resolution of 0.6 mm (FWHM) and a differential nonlinearity of ±5% are achieved. It was shown that the detector, whose efficiency is about 60% for 9 Å neutrons, has a resolution of 2.5 mm along the fine axis and about 4 mm for the perpendicular discrete axis. The dependence of the measured pulse height spectra from the applied high voltage and the electric field in the drift regions has been investigated. It turns out that for thermal neutrons the measured spectra are very similar to those obtained with proportional neutron counters filled with 10 bar 3He.

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

), then the two-dimensional Fourier series equivalent to f(x, y) is Co CO Co Co f(x, y) = L' L' A sin(nx) sin (my) + Z Z B sin(@x)cos(my) n=l m=1 n=l m=1 1 CG Co co + ? F, B sin(nx) + Z Z C cos (nx) sin(my) + ? Z C sin(my) 2 1 n, o n, m 2 I OIm Co Co OO... 1 + g P D cos(nx)cos(my)+ ? Z D cos(nx) ? g D cos(my) n, m 2 1 n 0 2 o, m + ? D 1 4 o, o where A 1 n, m ? w B 1 n, m 2 w B 1 n, o 2 w C 1 n, m 2 w (w, w) f(x, y) sin (nx) sin(my) d(x, y) (-w, -w) (w, w) f(x, y) sin (nx) cos...

Extensive research suggests that the visual system computes the direction of motion of a two-dimensional pattern from the motion of its oriented spatial frequency components. However, there is some evidence to suggest that the local features in a pattern are also important. In order to demonstrate that the local features contribute to motion perception we have created complex stimuli in which the oriented spatial frequency components have the same direction of motion but the local features move in different directions. The stimuli are multi-component plaid patterns with alternating high and low contrast rows. An analysis based on the oriented spatial frequency components predicts a uniform motion percept for the whole pattern. However, an analysis based on the local features in the pattern predicts that the high-contrast and low-contrast rows would be perceived to move in opposite directions. In a direction discrimination task, observers reported opposite directions of motion for small patches of the pattern that were centred on high and low contrast rows. This supports the hypothesis that the visual system uses local features when computing pattern motion. We show that a simple energy model with localised motion sensors that are broadly tuned for orientation could explain our results. PMID:22484200

Delicato, L S; Serrano-Pedraza, I; Suero, M; Derrington, A M

The observation and theoretical interpretation of various nonpropagating oscillatory solitons is reported. The experiments were performed in a parametrically driven pendulum lattice and in a parametrically driven channel of shallow liquid. In the pendulum lattice, kink and breather solitons were observed. In the channel the first observation of a kink in standing surface waves is reported. Solitons are structures of interest because they represent robust localized motions of a medium. A perturbative analysis of slowly varying modulations of waves in a dispersive nonlinear medium leads to a Nonlinear Schrodinger (NLS) equation which has soliton solutions. The NLS level equations are formulated for both pendulum lattice and surface wave motions. Depending upon the cutoff mode and the sign of the nonlinearity, the solitons can be breathers or kinks. Spatially periodic solutions can be cnoidal, snoidal, or dnoidal waves. Because the NLS equation is a leading order approximation which has the remarkable property of being exactly integrable, one can question whether solitons can exist in real systems. The steady state motions observed in the pendulum lattice and channel persist indefinitely, however. The lattice has a simple novel design that avoids the use of springs. Large amplitude soliton data agree well with an adjustable parameter theory. Small amplitude data deviate significantly from the theory due to nonuniformities. The response of this mesoscopic system as a function of drive parameters is extremely rich and has already been found to exhibit at least five basins of attraction that are characterized by localized modes. Some of these have the nature of NLS solitons and some display quasiperiodic self-focusing. The observed surface wave kink exists in the fundamental cross mode of the channel. A remarkable property of the kink in this system is the extreme sensitivity to non-uniformities, which cause the kink to drift. The large amplitude data significantly deviates from the no-adjustable-parameter theory. The observations suggest that a damped driven soliton is a more general property of nature than the leading -order theory implies. Finally, transverse modulations of damped driven nonlinear standing waves are investigated, with both parametric and direct drives. A linear stability analysis of the resultant NLS equation has shown that some modulations are unstable.

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

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

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.

particles (B=0 T and =0) #12;Ion trajectories #12;Axial distribution of implantation current #12;Energy;Objectives Â· Development of realistic, particle-in-cell (PIC), computer simulation of plasma immersion ion confinement of the secondary electrons #12;2.5D computer simulation with code KARAT Spatial variables

A means of upscaling the effective saturated hydraulic conductivity, $\\\\langle$K$\\\\rangle$, based on spatial variation in the saturated hydraulic conductivity (K) field is essential for the application of flow and transport models to practical problems. Multifractals are inherently scaling and thus may offer solutions to this dilemma. Random two-dimensional geometrical multifractal fields (multifractal Sierpinski carpets with a scale factor b =

S. R. Koirala; E. Perfect; R. W. Gentry; J. W. Kim

propose an optical circulator formed of a magneto-optical cavity in a 2D photonic crystal. With spatiallyOptical circulators in two-dimensional magneto-optical photonic crystals Zheng Wang and Shanhui Fan at different frequencies. By coupling the cavity to three waveguides, and by proper matching of the frequency

In photonic crystal (PC) microlasers with point defect cavities, effective carriers are reduced by the leakage to outside of the defect, surface recombination, spatial carrier hole burning, and Auger recombination. To estimate these effects, we calculated carrier and photon behavior by solving two-dimensional rate equations in space and time domains. The result clearly shows these effects and their dependence on

classes of higher-order spatial optical solitons in analogy with Laguerre-Gaussian and Hermite the intermediate states resembling generalized Hermite-Laguerre-Gaussian modes. DOI: 10.1103/PhysRevLett.98 solitons. Since the ringlike solitons resemble the structure of the Laguerre-Gaussian (LG) linear modes

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.

For a class of self-interacting multicomponent scalar field theories with a global discrete non-Abelian symmetry group, mixed order-disorder correlation functions are defined in terms of Euclidean functional integrals. These correlation functions satisfy Osterwalder-Schrader positivity. From a representation of the correlation functions in terms of the transfer matrix, the dual algebra at fixed time is derived. This algebra implies parafermion operators showing non-Abelian braid group statistics. In a pure phase of spontaneous symmetry breaking for a related class of order-disorder correlation functions a convergent polymer representation is developed, emerging from a combined low- and high-temperature-type expansion. The infinite volume correlation functions of this class show exponential clustering in the disorder fields.

In orthogonal frequency division multiplexing (OFDM) systems, two-dimensional (both time and frequency) minimum mean square error (2D-MMSE) channel estimation is optimum. However, accurate channel statistics are required to realize it, which are often unavailable in practice. In contrast, two-dimensional adaptive channel estimation based on a two-dimensional least mean square (2D-LMS) algorithm does not require any channel statistics, and at the

A positive, diffeomorphism-invariant generalized measure on the space of metrics of a two-dimensional smooth manifold is constructed. We use the term generalized measure analogously with the generalized measures of Ashtekar and Lewandowski and of Baez. A family of actions is presented which, when integrated against this measure gives the two-dimensional axiomatic topological quantum field theories, or TQFTs, in terms of which Durhuus and Jonsson decompose every two-dimensional unitary TQFT as a direct sum.

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.

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

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

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

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.

We investigate the effects of diffusion on the evolution of steady-state dark and gray spatialsolitons in biased photorefractive media. Numerical integration of the nonlinear propagation equation shows that the soliton beams experience a modification of their initial trajectory, as well as a variation of their minimum intensity. This process is further studied using perturbation analysis, which predicts that the

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

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

Bore-Soliton- Splash Onno Bokhove Motivation Splashing Results Mathematical Challenges Relation to Tohoku Tsunami Discussion A Rogue Bore-Soliton-Splash Onno Bokhove with Elena Gagarina, Martin Robinson International Workshop on Rogue Waves November 2011 --Image: DHP #12;Bore-Soliton- Splash Onno Bokhove

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

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

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

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

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

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

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

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.

An approximation theorem is proven which solves a classic problem in two-dimensional (2-D) filter theory. The theorem shows that any continuous two-dimensional spectrum can be uniformly approximated by the squared modulus of a recursively stable finite trigonometric polynomial supported on a nonsymmetric half-plane.

: This paper presents a methodology allowing to estimate the parameters of two-dimensional damped frequency estimator based on the Prony model. At each node resulting from the decomposition, a stopping rule. [2002]). In this paper, we consider the problem of estimat- ing the parameters of two-dimensional NMR

q-Discrete versions of the two-dimensional Toda molecule equation and the two-dimensional Toda lattice equation are proposed through the direct method. The Bäcklund transformation and the Lax pair of the former are obtained. Moreover, the reduction to theq-discrete cylindrical Toda equations is also discussed.

problem in three-dimensional vision is the analysis of object shape and camera motion from images: The structure and motion problem for two-dimensional calibrated vision. Fig. 2.A: Three images or setsMultilinear Constraints in Two-dimensional Vision and Isogonal Conjugacy Kalle AÂ° stroÂ¨m Dept

] for an overview) to develop two-dimensional modal logics taking care of the linguistic phenomenon that the truth (Venema [26]) which is based on the idea that in its semantics, transitions (arrows) do not link the possible worlds, they are the possible worlds. Two-dimensional arrow logic arises if we see transitions

Two-dimensional equations for piezoelectric plates have been very effective in modeling piezoelectric resonators. To predict the behavior of resonators under environmental effects like temperature change or acceleration, the theory of incremental motions in an electroelastic body under biasing fields is necessary. Existing two-dimensional equations for electroelastic plates under biasing fields employ various simplifying assumptions. For example, electroelastic couplings are often

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

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

A simple two-dimensional technique for frequency-wavenumber estimation is presented which is a direct extension of a previously proposed one-dimensional frequency estimation technique. The proposed method is computationally efficient and is shown to be superior to the two-dimensional Fourier transform method in resolving signals closely spaced in frequency and wavenumber.

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

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

A general three-dimensional initial-value perturbation problem is investigated as to effects in a two-dimensional but growing wake. The linearized perturbation analysis considers both the early transient as well as the asymptotic behavior of the disturbance (Blossey, Criminale & Fisher, JFM 2006 submitted). The representation of the mean flow is physically accurate, since it has been obtained by considering the lateral entrainment process and associated streamwise evolution of mass flow (increase) and kinetic energy (decrease) (Tordella & Belan, PoF 2003). This base model is combined with a change of coordinate (moving coordinate trasform) (Criminale & Drazin, Stud. Appl. Math, 1990). The evolution analysis considers inviscid disturbances that are expanded in terms of small values of the wavenumber. The long time behavior is represented by means of a multiple spatial and temporal scale description of the velocity and vorticity perturbations. The limit for small wavenumbers has been studied. It is seen that an increase of the entrainment in the base flow yields instability and grows algebraically in time. This result is also obtained when considering a more general problem where larger wavenumbers, wavelengths of the order of the thickness of the variable shear region, are allowed. Comparison with a recent spatio-temporal multiscale Orr-Sommerfeld analysis of the 2D wake instability (Tordella, Scarsoglio & Belan, PoF 2006). is presented. The perturbation dynamics is examined for different base flow configurations.

Bidomain or monodomain modelling has been used widely to study various issues related to action potential propagation in cardiac tissue. In most of these previous studies, the finite difference method is used to solve the partial differential equations associated with the model. Though the finite difference approach has provided useful insight in many cases, adequate discretisation of cardiac tissue with realistic dimensions often requires a large number of nodes, making the numerical solution process difficult or impossible with available computer resources. Here, a Chebyshev pseudospectral method is presented that allows a significant reduction in the number of nodes required for a given solution accuracy. The new method is used to solve the governing nonlinear partial differential equation for the monodomain model representing a two-dimensional homogeneous sheet of cardiac tissue. The unknown transmembrane potential is expanded in terms of Chebyshev polynomial trial functions and the equation is enforced at the Gauss-Lobatto grid points. Spatial derivatives are obtained using the fast Fourier transform and the solution is advanced in time using an explicit technique. Numerical results indicate that the pseudospectral approach allows the number of nodes to be reduced by a factor of sixteen, while still maintaining the same error performance. This makes it possible to perform simulations with the same accuracy using about twelve times less CPU time and memory. PMID:10912348

The linear bicharacteristic scheme (LBS) was originally developed to improve unsteady solutions in computational acoustics and aeroacoustics. The LBS has previously been extended to treat lossy materials for one-dimensional problems. It is a classical leapfrog algorithm, but is combined with upwind bias in the spatial derivatives. This approach preserves the time-reversibility of the leapfrog algorithm, which results in no dissipation, and it permits more flexibility by the ability to adopt a characteristic based method. The use of characteristic variables allows the LBS to include the Perfectly Matched Layer boundary condition with no added storage or complexity. The LBS offers a central storage approach with lower dispersion than the Yee algorithm, plus it generalizes much easier to nonuniform grids. It has previously been applied to two and three-dimensional free-space electromagnetic propagation and scattering problems. This paper extends the LBS to the two-dimensional case. Results are presented for point source radiation problems, and the FDTD algorithm is chosen as a convenient reference for comparison.

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

Tatsuno, T. [Department of Physics and IREAP, University of Maryland, College Park, Maryland 20742 (United States); Department of Communication Engineering and Informatics, University of Electro-Communications, Chofu, Tokyo 182-8585 (Japan); Plunk, G. G. [Department of Physics and IREAP, University of Maryland, College Park, Maryland 20742 (United States); Max-Planck-Institut fuer Plasmaphysik, 17491 Greifswald (Germany); Barnes, M. [Plasma Science and Fusion Center, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 (United States); Dorland, W. [Department of Physics and IREAP, University of Maryland, College Park, Maryland 20742 (United States); Howes, G. G. [Department of Physics and Astronomy, University of Iowa, Iowa City, Iowa 52242 (United States); Numata, R. [Department of Physics and IREAP, University of Maryland, College Park, Maryland 20742 (United States); Graduate School of Simulation Studies, University of Hyogo, Kobe, Hyogo 650-0047 (Japan)

Time-resolved optical spectroscopy is widely used to study vibrational and electronic dynamics by monitoring transient changes in excited state populations on a femtosecond timescale. Yet the fundamental cause of electronic and vibrational dynamics-the coupling between the different energy levels involved-is usually inferred only indirectly. Two-dimensional femtosecond infrared spectroscopy based on the heterodyne detection of three-pulse photon echoes has recently allowed the direct mapping of vibrational couplings, yielding transient structural information. Here we extend the approach to the visible range and directly measure electronic couplings in a molecular complex, the Fenna-Matthews-Olson photosynthetic light-harvesting protein. As in all photosynthetic systems, the conversion of light into chemical energy is driven by electronic couplings that ensure the efficient transport of energy from light-capturing antenna pigments to the reaction centre. We monitor this process as a function of time and frequency and show that excitation energy does not simply cascade stepwise down the energy ladder. We find instead distinct energy transport pathways that depend sensitively on the detailed spatial properties of the delocalized excited-state wavefunctions of the whole pigment-protein complex.

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

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

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

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

The paper introduces a two-dimensional space-frequency distribution based method to directly obtain the unwrapped estimate of the phase derivative which corresponds to strain in digital holographic interferometry. In the proposed method, a two-dimensional pseudo Wigner-Ville distribution of the reconstructed interference field is evaluated and the peak of the distribution provides information about the phase derivative. The presence of a two-dimensional window provides high robustness against noise and enables simultaneous measurement of phase derivatives along both spatial directions. Simulation and experimental results are presented to demonstrate the method's applicability for phase derivative estimation. PMID:20721190

We perform full three-dimensional numerical relaxations of isospinning Hopf solitons with Hopf charge up to 8 in the Skyrme-Faddeev model with mass terms included. We explicitly allow the soliton solution to deform and to break the symmetries of the static configuration. It turns out that the model with its rich spectrum of soliton solutions, often of similar energy, allows for transmutations, formation of new solution types, and the rearrangement of the spectrum of minimal-energy solitons in a given topological sector when isospin is added. We observe that the shape of isospinning Hopf solitons can differ qualitatively from that of the static solution. In particular, the solution type of the lowest energy soliton can change. Our numerical results are of relevance for the quantization of the classical soliton solutions.

We have found several families of vortex soliton solutions in two-dimensional discrete dissipative systems governed by the cubic-quintic complex Ginzburg-Landau equation. There are symmetric and asymmetric solutions, and some of them have simultaneously two different topological charges for two different closed loops encircling, i.e., centered at, the singularity. Their regions of existence and stability are determined. Additionally, we have analyzed the relationship between dissipation and stability for a number of solutions, finding that dissipation favors the stability of the vortex soliton solutions.

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

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

A novel two-dimensional x-ray/EUV imaging spectrometer (2DXIS) has been developed to investigate complex, rapidly-evolving plasmas. This novel device uses glass capillaries to multiplex a two-dimensional image of the plasma into an output array of spatially-separated pixels. This array is then spectrally dispersed by a crystal or a multilayer mirror, recorded by a temporally-gated imager, and reconstituted as an image by a computer. The result is a time-gated spectrum for each image point. Polycapillaries are employed, rather than monocapillaries, for a uniform output angular distribution of captured radition. Modular design allows observation of a wide selection of spectral lines. Efficient computer calculations of resonance and satellite lines analyze the high volume of K-shell/L-shell spectroscopic data. Spatial resolution, field of view, wavelength range, and spectroscopic resolution are chosen to yield time-resolved two-dimensional maps of plasma temperature, density, and ionization state. A 100-channel 2DXIS is being installed on SNL-Z to observe Ti K-shell radiation from imploding-Ti-wire-array z-pinches. Two-dimensional x-ray spectroscopy of other wire materials (Al, Ni, Cu, Mo, W, and Au) will also be developed.

Kantsyrev, V. L.; Bauer, B. S.; Presura, R.; Fedin, D. A.; Shlyapsteva, A. S.; Hansen, S.

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

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

We present a technique for spatially controlled chemical vapor deposition of graphene on a dielectric substrate. The technique is based on the surface melting of a thin Cu catalyst film pre-deposited on a dielectric substrate with spatially modified surface. The self-assembling of the liquefied copper in predefined fashion on the substrate enables spatially controlled deposition of graphene on the copper-silica interface. The developed technique that involves neither pre- nor post-deposition patterning of the graphene allowed us to fabricate the twodimensional graphene grating with period of 10 ?m.

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.

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

We develop a theory for optical Faraday rotation noise in two-dimensional Dirac materials. In contrast to spin noise in conventional semiconductors, we find that the Faraday rotation fluctuations are influenced not only by spins but also the valley degrees of freedom attributed to intervalley scattering processes. We illustrate our theory with two-dimensional transition-metal dichalcogenides and discuss signatures of spin and valley noise in the Faraday noise power spectrum. We propose optical Faraday noise spectroscopy as a technique for probing both spin and valley relaxation dynamics in two-dimensional Dirac materials. PMID:25105640

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

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 × 1011 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.

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

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

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

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

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

A CLASS OF OPTIMAL TWO-DIMENSIONAL MULTIMATERIAL CONDUCTING LAMINATES NATHAN ALBIN1, ANDREJ, polyconvexity, rank-one convexity, multiwell variational problem . 1 #12;2 N. ALBIN, A. CHERKAEV, AND V. NESI

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

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

The present invention concerns an extension of data processing concepts and apparatus. For a most important application of these concepts, i.e., performance of two-dimensional correlations and convolutions, it has heretofore been necessary to have two com...

A modification of an implicit approximate-factorization finite-difference algorithm applied to the two-dimensional Euler and Navier-Stokes equations in general curvilinear coordinates is presented for supersonic freestream flow about and through inlets. T...

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.

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

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.

We report an improved interface for two-dimensional capillary electrophoresis. This interface is based on capillary tubing and a Plexiglas chip, both of which were milled using a micro-dicing saw. The interface was evaluated and compared to a traditional interface design for both pseudo one-dimensional and two-dimensional capillary electrophoresis. We observe less than 70% transfer efficiency for the traditional design and greater than 90% transfer efficiency with this new interface. PMID:23702824

Flaherty, Ryan J.; Huge, Bonnie J.; Bruce, Spencer M.; Dada, Oluwatosin O.; Dovichi, Norman J.

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

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

The firing squad synchronization problem on cellular automata has been studied extensively for more than forty years, and a rich variety of synchronization algorithms have been proposed so far. In the present paper, we give a survey on recent developments in firing squad synchronization algorithms for large-scale two-dimensional cellular automata. Several state-efficient implementations of the two-dimensional synchronization algorithms are given.

A technique for the determination of two-dimensional impurity profiles in silicon using methods for emission computed tomography is presented. Several one-dimensional impurity profiles obtained for different directions through the sample are used to reconstruct the two-dimensional profile. A simulation study of the experiment is described, and effects of various experimental and reconstruction parameters are discussed. Reconstructions of an area of

Scott H. Goodwin-johansson; Ravi Subrahmanyan; Carey E. Floyd; Hisham Z. Massoud

We investigate the dynamics of a dilute gas of free spin vortices in a two-dimensional planar magnet. An equation of motion for the spin vortex is presented and compared with the corresponding equation for a vortex in a superfluid film. Exploiting a similar analogy with the dynamics of a two-dimensional plasma in a perpendicular magnetic field we calculate the mean-square

Theories, simulations and experiments on vortex dynamics in quasi-two-dimensional magnetic materials are reviewed. These materials can be modelled by the classical two-dimensional anisotropic Heisenberg model with XY (easy-plane) symmetry. There are two types of vortices, characterized by their polarization (a second topological charge in addition to the vorticity): Planar vortices have Newtonian dynamics (even-order equations of motion) and exhibit strong

Theories, simulations and experiments on vortex dynamics in quasi-two-dimensional magnetic materials are reviewed. These materials\\u000a can be modelled by the classical two-dimensional anisotropic Heisenberg model with XY (easy-plane) symmetry. There are two types of vortices, characterized by their polarization (a second topological charge\\u000a in addition to the vorticity): Planar vortices have Newtonian dynamics (evenorder equations of motion) and exhibit strong

TWODIMENSIONAL PROPERTIES OF METHANE ADSORBED ON POROUS SILICON A Thesis by RICHARD FRANKLIN TENNIS Submitted to the Office of Graduate Studies of Texas ASM University in partial fulfillment of the requirements for the degree of MASTER... OF SCIENCE May 1989 Major Subject: Physics TWODIMENSIONAL PROPERTIES OF METHANE ADSORBED ON POROUS SILICON A Thesis by RICHARD FRANKLIN TENNIS Approved as to style and content by: P. Kirk (C ir of Committee) Glenn olet (M er) Da J. Ernst...

The formation of large-scale vortices is an intriguing phenomenon in two-dimensional turbulence. Such organization is observed\\u000a in large-scale oceanic or atmospheric flows, and can be reproduced in laboratory experiments and numerical simulations. A\\u000a general explanation of this organization was first proposed by Onsager (1949) by considering the statistical mechanics for\\u000a a set of point vortices in two-dimensional hydrodynamics. Similarly, the

We introduce an analytical formula for the dynamics of light propagation in a two-dimensional waveguide lattice including diagonal coupling. A superposition of infinite arrays created by imaginary sources is used to derive an expression for boundary reflections. It is shown analytically that for large propagation distances the propagating field reaches uniformity. Furthermore, periodic field recovery is studied and discrete anomalous refraction and diffraction are investigated in arbitrary two-dimensional lattices.

Szameit, Alexander; Pertsch, Thomas; Dreisow, Felix; Nolte, Stefan; Tuennermann, Andreas; Peschel, Ulf; Lederer, Falk [Institute of Applied Physics, Friedrich-Schiller-University Jena, Max-Wien-Platz 1, 07743 Jena (Germany); Institute of Optics, Information and Photonics, Friedrich-Alexander-University Erlangen-Nuremberg, G.-Scharowsky-Strasse 1, 91058 Erlangen (Germany); Institute for Condensed Matter Theory and Optics, Friedrich-Schiller-University Jena, Max-Wien-Platz 1, 07743 Jena (Germany)

A high-speed photographic recording device has been used to investigate divergence and reflection by a wall of a two-dimensional impulse plasma jet within a closed gas-filled cylindrical container. It is shown that in an electric discharge source, a two-dimensional jet is formed by a number of individual streams. The gas-dynamic structure of the individual plasma streams is examined. Plasma temperature

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

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 twodimensional 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

Sixteen patients had two-dimensional echocardiographic diagnosis of the presence or absence of left ventricular thrombi and anatomical, radiological, or clinical confirmation of the diagnosis. Eleven patients had positive diagnoses, which were confirmed in 10 and possibly incorrect in one. Five other records were reviewed because the patients had undergone aneurysmectomy after two-dimensional echocardiograms: three were true negative and two were false negative studies. Images PMID:508446

Meltzer, R S; Guthaner, D; Rakowski, H; Popp, R L; Martin, R P

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

We consider here the finite-volume approach in developing a two-dimensional, high-order accurate, essentially non-oscillatory shock-capturing scheme. Such a scheme achieves high-order spatial accuracy by a piecewise polynomial approximation of the solution from its cell averages. High-order Runge-Kutta methods are employed for time integration, thus making such schemes best-suited for unsteady problems. The focal point in our development is a high-order

A prototype of a two-dimensional position sensitive X-ray detector was designed and constructed for small angle X-ray scattering experiments at BSFR (Beijing Synchrotron Radiation Facility). The detector is based on MWPC with cathode strip readout, and has a sensitive area of 200 mm×200 mm. The spatial resolution (FWHM) of about 210 ?m along the anode wire direction was obtained from the 55Fe X-ray test of the detector.

The relative impacts of changes in nutrient loading and zebra mussel establishment on plankton in large lakes are strongly influenced by hydrodynamics, yet adequately modelling the temporal-spatial complexity of physical and biological processes has been difficult. We adapted a two-dimensional public domain model, CE-QUAL-W2, to test whether it could provide a hydrodynamically accurate simulation of the seasonal variation in the

L. Boegman; M. R. Loewen; P. F. Hamblin; D. A. Culver

Two-dimensional (2D) multi-wavelength vertical cavity surface emitting laser (VCSEL) arrays is promising for ultrahigh aggregate capacity optical networks. A 2D VCSEL array emitting 140 distinct wavelengths was reported by implementing a spatially graded layer in the VCSEL structure, which in turn creates a wavelength spread. Concentrtion was on epitaxial growth techniques to make reproducible and repeatable multi-wavelength VCSEL arrays. Our

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 twodimensional 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.

In this article a novel system architecture that uses a combination of wavelength and spatial diversity for indoor infrared wireless communications is presented. This configuration promises to fully exploit the available bandwidth of optics and demonstrate all-optical networking. Electronic processing is restricted to mobile terminals, with base stations potentially remaining passive, without any conversion between optics and electronics. For the downlink, multiple transmitter beams with different wavelengths are steered from the fiber infrastructure through the base station to mobile terminals located in different positions. An optimum combination of diffractive optics and reflective optics (a diffraction grating and an array of mirrors) can flexibly steer each transmitter beam and enable full control over the required coverage pattern. For the uplink, in the transmitter, another grating and an array of mirrors can direct multiple beams upward from different mobile users toward the base station. System simulation shows that the downlink has the potential to approach 10 Gbit/s, while maintaining wide-area coverage (such as in a room of 3m×4m×4m) with the help of fine optical tracking. System modeling indicates that the uplink is more susceptible to power losses than the downlink, but the utilization of dynamic beam steering in the uplink can suppress power losses to a tolerable level (e.g. below 30dB). An array of 16 mirrors has been designed to implement point-to-point beam steering in a room of 3m×1m×1m. Two-dimensional coverage patterns measured at a distance of 0.5 m and 1.5 m coincide with simulation results. Operation at 1 Gbit/s has been demonstrated successfully for tracking in two dimensions.

Shi, Haiyan; Liang, Kefei; Sheard, Stephen J.; O'Brien, Dominic C.; Faulkner, Grahame E.

We report the observation of incoherently coupled dark-bright spatialsoliton 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.

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

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

Photosynthesis begins with the harvesting of sunlight by antenna pigments, organized in a network of pigment-protein complexes that rapidly funnel energy to photochemical reaction centers. The intricate design of these systems---the widely varying structural motifs of pigment organization within proteins and protein organization within a larger, cooperative network---underlies the remarkable speed and efficiency of light harvesting. Advances in femtosecond laser spectroscopy have enabled researchers to follow light energy on its course through the energetic levels of photosynthetic systems. Now, newly-developed femtosecond two-dimensional electronic spectroscopy reveals deeper insight into the fundamental molecular interactions and dynamics that emerge in these structures. The following chapters present investigations of a number of natural light-harvesting complexes using two-dimensional electronic spectroscopy. These studies demonstrate the various types of information contained in experimental two-dimensional spectra, and they show that the technique makes it possible to probe pigment-protein complexes on the length- and time-scales relevant to their functioning. New methods are described that further extend the capabilities of two-dimensional electronic spectroscopy, for example, by independently controlling the excitation laser pulse polarizations. The experiments, coupled with theoretical simulation, elucidate spatial pathways of energy flow, unravel molecular and electronic structures, and point to potential new quantum mechanical mechanisms of light harvesting.

Optical breathing solitons are known to display well-resolved cycles where the phase of pulse compression is followed by pulse stretching. Here we show that, in the extreme regimes where the soliton pulse width approaches the field cycle, the field waveform dynamics can drastically differ from this textbook scenario. We demonstrate that such extremely short soliton transients can develop optical shock waves, which seed parametric amplification, facilitating, along with ionization nonlinearity, soliton compression to subcycle pulse widths. This pulse compression scenario is shown to enable the generation of sub-quarter-cycle multigigawatt optical field waveforms in the mid infrared.

The structure of nontopological solutions of Einstein field equations as proposed by Friedberg, Lee, and Pang (1987) is examined. This analysis incorporates finite temperature effects and pair creation. Quarks are assumed to be the only species that exist in interior of soliton stars. The possibility of primordial creation of soliton stars in the incomplete decay of the degenerate vacuum in early universe is explored. Because of dominance of pair creation inside soliton stars, the luminosity of soliton stars is not determined by its radiative transfer characteristics, and the surface temperature of soliton stars can be the same as its interior temperature. It is possible that soliton stars are intense X-ray radiators at large distances. Soliton stars are nearly 100 percent efficient energy converters, converting the rest energy of baryons entering the interior into radiation. It is possible that a sizable number of baryons may also be trapped inside soliton stars during early epochs of the universe. In addition, if soliton stars exist they could assume the role played by massive black holes in galactic centers.

The structure of nontopological solutions of Einstein field equations as proposed by Friedberg, Lee, and Pang (1987) is examined. This analysis incorporates finite temperature effects and pair creation. Quarks are assumed to be the only species that exist in interior of soliton stars. The possibility of primordial creation of soliton stars in the incomplete decay of the degenerate vacuum in early universe is explored. Because of dominance of pair creation inside soliton stars, the luminosity of soliton stars is not determined by its radiative transfer characteristics, and the surface temperature of soliton stars can be the same as its interior temperature. It is possible that soliton stars are intense X-ray radiators at large distances. Soliton stars are nearly 100 percent efficient energy converters, converting the rest energy of baryons entering the interior into radiation. It is possible that a sizable number of baryons may also be trapped inside soliton stars during early epochs of the universe. In addition, if soliton stars exist they could assume the role played by massive black holes in galactic centers.

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

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

We study both numerically and experimentally two-dimensionalsoliton bound states in quadratic media and demonstrate their symmetry-breaking instability. The experiment is performed in a potassium titanyl phosphate crystal in a type-II configuration. The bound state is generated by the copropagation of the antisymmetric fundamental beam locked in phase with the symmetrical second harmonic one. Experimental results are in good agreement with numerical simulations of the nonlinear wave equations.

Delque, Michaeel [Service OPERA-photonique, CP194/5, Universite Libre de Bruxelles U.L.B. Avenue F.D. Roosevelt, B-1050 Bruxelles (Belgium); Departement d'Optique P.M. Duffieux, Institut FEMTO-ST, Universite de Franche-Comte, CNRS UMR 6174, F-25030 Besancon (France); Fanjoux, Gil; Maillotte, Herve; Kockaert, Pascal; Sylvestre, Thibaut; Haelterman, Marc [Departement d'Optique P.M. Duffieux, Institut FEMTO-ST, Universite de Franche-Comte, CNRS UMR 6174, F-25030 Besancon (France)

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.

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)

The fermion soliton stars suggested by Lee and Pang are extended to finite temperature. The degeneracy temperature TD above which the fermion soliton star will become a Boltzmann soliton star is given. We prove that the Boltzmann soliton star cannot exist, because it is unstable.

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

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

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

It is hard to observe relativistic effects in everyday life. However, table experiments using a mechanical transmission line for solitons may be an efficient and simple way to show effects such as Lorentz contraction in a classroom. A kink soliton is a deformation of a lattice of several dozen or more pendulums placed on a wire and connected by a…

Bore-Soliton- Splash Onno Bokhove Introduction BSS with KP BSS with SPH Bores in Boussinesq Models Single-Phase Mixture Theory Geometric Wave Modeling Wave Energy Device Conclusions On Resurging a Bore. Gagarina & W. Zweers (Twente) #12;Bore-Soliton- Splash Onno Bokhove Introduction BSS with KP BSS with SPH

We report on the spin properties of bright polariton solitons supported by an external pump to compensate losses. We observe robust circularly polarized solitons when a circularly polarized pump is applied, a result attributed to phase synchronization between nondegenerate TE and TM polarized polariton modes at high momenta. For the case of a linearly polarized pump, either ?+ or ?- circularly polarized bright solitons can be switched on in a controlled way by a ?+ or ?- writing beam, respectively. This feature arises directly from the widely differing interaction strengths between co- and cross-circularly polarized polaritons. In the case of orthogonally linearly polarized pump and writing beams, the soliton emission on average is found to be unpolarized, suggesting strong spatial evolution of the soliton polarization. The observed results are in agreement with theory, which predicts stable circularly polarized solitons and unstable linearly polarized solitons. PMID:24580473

Sich, M; Fras, F; Chana, J K; Skolnick, M S; Krizhanovskii, D N; Gorbach, A V; Hartley, R; Skryabin, D V; Gavrilov, S S; Cerda-Méndez, E A; Biermann, K; Hey, R; Santos, P V

We have demonstrated the feasibility of extending a point-temperature measurement method to two-dimensional mapping of temperature distributions on surfaces. The point-measurement method used the temperature-dependant characteristics of sharp emission lines from thermographic phosphors to measure temperature. The two-dimensional extrusion uses an ultraviolet light source to illuminate the phosphor-coated surface and a high-grain video camera filtered to select the desired emission line. By changing filters, we acquire video data that are over-laid and analyzed by a video processor, then displayed in contour or pseudocolor maps of the temperature distribution. 13 refs., 14 figs., 1 tabs.

Noel, B.W. (Los Alamos National Lab., NM (USA)); Turley, W.D. (EG and G Energy Measurements, Inc., Goleta, CA (USA)); Cates, M.R.; Tobin, K.W. (Oak Ridge National Lab., TN (USA))

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

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

Slyusarenko, Kostyantyn; Constantin, Doru; Davidson, Patrick

A different technique was developed by which several two-dimensional dielectric optical gratings, consisting 100 or more corrugations, were treated in a numerical reliable approach. The numerical examples that were presented were restricted to gratings made up of sequences of waveguide sections symmetric about the x = 0 plane. The newly developed method was effectively used to investigate the field produced by a two-dimensional focusing grating coupler. Focal-region fields were determined for three symmetrical gratings with 19, 50, and 124 corrugations. For focusing grating coupler with limited length, high-frequency intensity variations were noted in the focal region.

A modification of an implicit approximate-factorization finite-difference algorithm applied to the two-dimensional Euler and Navier-Stokes equations in general curvilinear coordinates is presented for supersonic freestream flow about and through inlets. The modification transforms the coupled system of equations Into an uncoupled diagonal form which requires less computation work. For steady-state applications the resulting diagonal algorithm retains the stability and accuracy characteristics of the original algorithm. Solutions are given for inviscid and laminar flow about a two-dimensional wedge inlet configuration. Comparisons are made between computed results and exact theory.

The present paper discusses a class of exact two-dimensional kinetic current sheet equilibria. The general solution to the two-dimensional Grad-Shafranov equation was first obtained by Walker in 1915 in terms of the generating function g(?) (? = X + iZ), where X and Z are two dimensionless spatial coordinates. There are infinite choices of g(?), but not every solution yields physically meaningful or mathematically useful form. The known solutions to date with geophysical application include those by [1962], [1965], [1973], [2000], and [2002]. In this paper, these solutions are reviewed systematically, and several new solutions are proposed. These include a generalization of the Harris-Fadeev-Kan-Manankova line of model, a model for an isolated X-line alternative to that of Brittnacher-Whipple, and finally a model which represents an isolated magnetic island.

Solution of the energy dependent diffusion equation in two dimensions is formulated by multigroup approximation of the energy variable and general triangular mesh, finite element discretization of the spatial domain. Finite element formulation is done by Galerkin's method. Based on this formulation, a two-dimensional multigroup finite element diffusion theory code, FENAT, has been developed for the transport of neutral atoms in fusion plasmas. FENAT solves the multigroup diffusion equation in X-Y cartesian and R-Z cylindrical/toroidal geometries. Use of the finite element method allows solution of problems in which the plasma cross-section has an arbitrary shape. The accuracy of FENAT has been verified by comparing results to those obtained using the two-dimensional discrete ordinate transport theory code, DOT-4.3. Results of application of FENAT to the transport of limiter-originated neutral atoms in a tokamak fusion machine are presented.

We describe oblique half-solitons, a new type of topological defects in a two-dimensional spinor Bose-Einstein condensate. A realistic protocol based on the optical spin Hall effect is proposed toward their generation within an exciton-polariton system.

Flayac, H.; Solnyshkov, D. D.; Malpuech, G. [Clermont Universite, Universite Blaise Pascal, LASMEA, BP10448, F-63000 Clermont-Ferrand, France CNRS, UMR6602, LASMEA, F-63177 Aubiere (France)

Linear and nonlinear propagation characteristics of quantum drift ion acoustic waves are investigated in an inhomogeneous two-dimensional plasma employing the quantum hydrodynamic (QHD) model. In this regard, the dispersion relation of the drift ion acoustic waves is derived and limiting cases are discussed. In order to study the drift ion acoustic solitons, nonlinear quantum Kadomstev–Petviashvilli (KP) equation in an inhomogeneous

The effects of solitons on the spectrum of fermion excitations in superfluid (He-3)-A are investigated. It is found that there is a two-dimensional manifold of bound states with energies within the gap of the bulk superfluid. The bound-state spectrum lacks inversion symmetry parallel to the wall.

Ho, T. L.; Fulco, J. R.; Schrieffer, J. R.; Wilczek, F.

Different cases of sequences of the Laplace Transformations for the 2D\\u000aSchrodinger operator in the periodic magnetic field and electric potential are\\u000aconsidered. They lead to the exactly solvable operators with nonstandard\\u000aspectral properties including the double-periodic operators with algebraic\\u000aFermi surface known from the periodic soliton theory. Two appendices are added.\\u000aIn the Appendix I (the author - S.

temperature dependence (d/dT > 0) of the resistivity, , in low-disorder, dilute 2DESs in Si metalÂ oxide temperatures in low-disorder, dilute, two-dimensional (2D) carrier systems is of considerable interest of freedom, namely the valley polarization. Using symmetry-breaking strain together with an in-plane magnetic

Degeneracy of resonant modes in two-dimensional (2-D) photonic crystal cavities are investigated using the symmetry relations. The 2-D photonic crystal cavity tends to have either a pair of doubly degenerate modes or nondegenerate modes. We de- rive simple relations between degenerate modes without using a rigorous group theory. These relations are useful for classifying the resonant modes into degenerate pairs

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

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

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

Joseph J. Sacchini; Williuni M. Steedly; R. L. Moses

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

One of the resource utilization problems is the location of two-dimensional patterns onto stock sheets with finite dimensions. Stock sheets, in this respect, are depletable resources to be used and the remaining material which is known as the scrap (or trim loss) cannot usually be used later for allocating patterns. Thus, a decrease in the amount of scrap yields a

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

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

Comprehensive two-dimensional (2D) chromatographic techniques can be considered innovative methods, only quite recently developed. Since their introduction to the chromatographic community, these techniques have been used in several fields and have gained an excellent reputation as valuable and powerful analytical tools. The revolutionary aspect of comprehensive multidimensional (MD) techniques, in respect to classical MD chromatography, is that the entire sample

Peter Quinto Tranchida; Paola Dugo; Giovanni Dugo; Luigi Mondello

A two-dimensional expression for the flow of a nonisothermic rarefied plasma round a conductive cylinder is numerically solved. A shock wave having an oscillating structure is found to form in front of the cylinder while behind it forms a rarefied wake with focused ions on its axis.

Two-dimensional nanohybridization of gold nanorods and polystyrene colloids Dong Kee Yi,1 Jin hybrid nanomaterials. The process is demonstrated using 0D polystyrene colloids and 1D Au nanorods-dimensional 2D hexagonally ar- rayed submicron sized polystyrene and silica colloids form regularly ordered

In analogy with the structures discovered by Suzuki in alkali halides, in this article we introduce a two-dimensional acoustic system consisting of a periodic distribution of impurities (vacancies) in a host array. A triangular lattice of cylindrical sound scatterers is chosen as the host. The sonic crystal, called the Suzuki phase, shows extraordinary sound transmission properties: it holds the attenuation

D. Caballero; J. Sánchez-Dehesa; R. Martínez-Sala; C. Rubio; J. V. Sánchez-Pérez; L. Sanchis; F. Meseguer

Acoustic transparency is studied in two-dimensional sonic crystals consisting of hexagonal distributions of cylinders with continuously varying properties. The transparency condition is achieved by selectively closing the acoustic bandgaps, which are governed by the structure factor of the cylindrical scatterers. It is shown here that cylindrical scatterers with the proposed continuously varying properties are physically realizable by using metafluids based

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

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

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.

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

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

We derive exact solutions of two-dimensional dilaton gravity coupled to massless spinors for some particular choices of the dilatonic potential. For constant dilatonic potential the model turns out to be completely solvable and the general solution is found. For linear and exponential dilatonic potentials we present the class of exact solutions with a Killing vector.

We derive exact solutions of two-dimensional dilaton gravity coupled to massless spinors for some particular choices of the dilatonic potential. For constant dilatonic potential the model turns out to be completely solvable and the general solution is found. For linear and exponential dilatonic potentials we present the class of exact solutions with a Killing vector.

Marco Cavaglià; Lorenzo Fatibene; Mauro Francaviglia

We consider the evolution of an incompressible two-dimensional perfect fluid as the boundary of its domain is deformed in a prescribed fashion. The flow is taken to be initially steady, and the boundary deformation is assumed to be slow compared to the fluid motion. The Eulerian flow is found to remain approximately steady throughout the evolution. At leading order, the

The present analysis relates to the study of the full two-dimensional Brinkman equation representing the fluid flow through porous medium. The steady, incompressible fluid flow, with a negligible gravitational force, is constrained to flow in an infinitely long channel in which the height assumes a series of piecewise constant values. The control volume method is used to solve the Brinkman

A. K. Al-Hadhrami; L. Elliott; D. B. Ingham; X. Wen

In this article we study the asymptotic behavior of incompressible, ideal, time-dependent twodimensional flow in the exterior of a single smooth obstacle when the size of the obstacle becomes very small. Our main purpose is to identify the equation satisfied by the limit flow. We will see that the asymptotic behavior depends on ?, the circulation around the obstacle.

D. Iftimie; M. C. Lopes Filho; H. J. Nussenzveig Lopes

Studying models of incompressible systems is very important as there are many sytems in dierent areas of physics that may be regarded as incompress- ible. Two particular examples are vortex patches in ideal fluids (1) and two- dimensional electrons systems in the presense of a magnetic eld (2) . Since these systems are incompressible, they are easier to study because

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

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

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.

and applied to the class of 2-D (d, ) constraints. Analytical lower bounds on the rate of these encoders were-dimensional (1-D) track model [1]. This approach gives rise to new types of error patterns, constraints and encoding algorithms. Two- dimensional constraints can be defined over different 2-D lattices, depending

The behavior of a dense two-dimensional soft disc liquid under shear is studied via nonequilibrium molecular dynamics. The structure factor for the liquid at a given shear rate is evaluated directly by plotting the particle positions, taken at random from the NEMD simulation at that shear, onto photographic film and using light scattering to obtain a diffraction pattern. The pair

H. J. M. Hanley; G. P. Morriss; T. R. Welberry; D. J. Evans

HOMOGENIZATION OF TWODIMENSIONAL LINEAR FLOWS WITH INTEGRAL INVARIANCE1 Tamir Tassa Abstract We study the homogenization of 2D linear transport equations, ut + a(x/) Â· xu = 0, where a is a non in the special cases of incompressible flows and shear flows. When the flow on T2 is non-ergodic, the homogenized

We propose two novel algorithms for signal processing of data from a rectangular (twodimensional) antenna array for which the number of complex operations necessary to Implement the algorithms is significantly less than that for the naive extension of the MUSIC algorithm. We present simulation results for both algorithms and discuss these in relation to the information content of the data.

Clarke, Ira J.; de Villiers, Geoffrey D.; Mather, John L.

This paper is concerned with the use of a two-dimensional enclosure with masonry block wall to mitigate compressor noise in a northern California location for consistency with city standards. Sensitive receptors consist of a duplex and single residences across the street from the source. Background sound is provided primarily by a nearby highway that is elevated. Noise reduction is accomplished

This paper studies an invariant solution of rank one of the equations of motion of a polytropic gas that describes two-dimensional\\u000a gas vortices and twisted gas jets. Flow types are classified according to the governing parameter: vortices in the form of\\u000a sources and sinks, unlimited expansion, and collapse.

This paper studies an invariant solution of rank one of the equations of motion of a polytropic gas that describes two-dimensional gas vortices and twisted gas jets. Flow types are classified according to the governing parameter: vortices in the form of sources and sinks, unlimited expansion, and collapse.

The dynamics of the vortex gas associated with the Kosterlitz-Thouless transition in quasi-two-dimensional planar magnets is discussed. It is pointed out that there is a central peak in the Fourier transform of the longitudinal spin autocorrelation function whose width is determined by the vortex velocity autocorrelation function and whose intensity is proportional to the density of mobile vortices.

We report excess longitudinal resistivity of a high-mobility two-dimensional electron gas (2DEG) in a random distribution of submicrometer magnetic-flux tubes (vortices) which are formed at the 2DEG by a superconducting gate layer. The results are explained in terms of small-angle scattering of ballistic electrons by the magnetic-field inhomogeneities.

A. K. Geim; S. J. Bending; I. V. Grigorieva; M. G. Blamire

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

We present the first high resolution spin dynamics simulation of critical dynamics in the classical, two-dimensional XY-model. Using square lattices as large as 204 × 204 with periodic boundaries, we integrate coupled equations of motion and determine the scattering function S( q, ?). At the critical temperature we find a rich structure which is not adequately described by existing theory.

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

We propose an optical cavity implementation of the two-dimensional coined quantum walk on the line. The implementation makes use of only classical resources, and is tunable in the sense that a large number of different unitary transformations can be implemented by tuning some parameters of the device.

The paper reports molecular dynamics (MD) simulations on two-dimensional, strongly-coulped Yukawa liquids. An effective coupling coefficient ?* for the liquid phase is identified; thermodynamic properties such as internal energy, pressure and compressibility, as well as longitudinal and transverse mode dispersions are analysed.

We report on simulations using a lattice gas automaton in which the lattice is replaced by a triangulation of an arbitrary two-dimensional manifold. If the manifold is 2D Euclidean space the particles move on the Kagome lattice. We report results of simulations of channel flow for the flat space model and of simulations in which the particle state can change

Anna Klales; Donato Cianci; Zachary Needell; Peter Love

evaporation and LangmuirÂBlodget deposition, etc. have been used to prepare 2-D colloidal arrays on planarVertical spreading of two-dimensional crystalline colloidal arrays Jian-Tao Zhang,a Luling Wang-dimensional (2-D) ordered monolayer crystalline colloidal arrays (CCAs). This phenom- enon can be used to rapidly

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

three-dimensional (3D) and two-dimensional (2D) interface phonons can contribute to this effect. The TEP (Rxy) does not develop into quantized plateau. The first derivative of Hall resistance with respect a sharp, strongly temperature-dependent minimum cen- tered at = 1/2, whereas concomitant Hall resistance

.Frydman@weizmann.ac.il Published online: 22 April 2007; doi:10.1038/nphys597 Two-dimensional (2D) NMR is an important tool to NMR techniques, resulting in typical acquisition times for 2D NMR spectra ranging from minutes transient, making it a poor starting point for conventional 2D NMR acquisitions. Here, we show

and on continuously flowing samples, as well as the utilization of 2D NMR to follow dynamic biophysical and metabolicUltrafast two-dimensional NMR spectroscopy using constant acquisition gradients Yoav Shrot NMR spectroscopy plays an important role in the characterization of molecular structure and dynamics

The study of absorber structures and shielding screens remains an important topic in EMC. A general two-dimensional boundary integral equation (BIE) technique has been implemented to handle both finite and periodic absorber structures. The generality of the method is twofold: the geometry of the structure may be chosen arbitrary finite or one-dimensional periodic, and the materials being used are uniaxial

In this paper we develop a feedback control law that results in stable walking gaits on flat ground for a three-dimensional bipedal robotic walker given stable walking gaits for a two-dimensional bipedal robotic walker. This is achieved by combining disparate techniques that have been employed in the bipedal robotic community: controlled symmetries, geometric reduction and hybrid zero dynamics. Controlled symmetries

, specifically in the robustness and consistency of an efficient powered walker and the agreement between roboticElectronic Control of a Two- Dimensional, Knee-less, Bipedal Robot Final Report for MAE 490 under Walking Robot successfully demonstrates a stable walking cycle using the same control components

on flat ground for a three- dimensional bipedal robotic walker given stable walking gaits for a two-dimensional bipedal robotic walker. This is achieved by combining disparate techniques that have been employed in the bipedal robotic community: controlled symmetries, geomet- ric reduction and hybrid zero dynamics

As/AlGaAs heterostructure, two-dimensional electron gas, plasmonics, metamaterials, terahertz. Author for correspondence to the study and engineering of surface plasmonic waves in the skin of three-dimensional bulk metals, due, such as semiconductor heterojunction and graphene, contrast the surface plasmonic waves on bulk metals, as the former

We report on a study of advancing quasi-two-dimensional sand fronts on an inclined flat and thin strip confined between two vertical plates. These fronts form when a thin initial stream of sand running down the flat obstacle gets trapped at some distance from the injection point. Right after this trapping, the front starts to advance upstream and grow in time.

J.-F. Boudet; S. Gauthier; Y. Amarouchene; H. Kellay

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

In this paper the behavior of strongly nonlinear waves in two-dimensional resonators filled with thermoviscous fluid is studied. For this purpose a set of differential equations, written in Lagrangian coordinates, is proposed and a time-domain numerical scheme is developed for solving them. Full nonlinear equations are derived from the conservation laws and state equation by assuming an irrotational fluid. Auxiliary conditions are written by considering a rigid-walled cavity, excitation at some points of the boundary, and rest at the outset. Finite differences are applied in the space and time domains, and lead to an implicit scheme. The numerical model solves the problem in terms of displacement vector field. The pressure field is then obtained from the displacement values. The algorithm allows us to analyze the evolution of the behavior of complex standing waves. The nonlinear characteristics of standing waves, well known in one-dimensional chambers, are now apparent in two-dimensional resonators by means of this new computational model. Some numerical experiments are carried out, a validation of the model is achieved, and results are given at a complex mode for which plane wave approximation is not appropriate. Several aspects of the nonlinear pressure field inside two-dimensional resonators are presented, such as harmonic distortion and nonlinear attenuation effects. In particular the quasi-standing character of such waves is detected and described. The effect of redistribution of rms pressure inside a two-dimensional cavity is commented.

://dmawww.epfl.ch/rappaz.mosaic/index.html 1 #12;(3) The heat source is the Joule power density which is related to through a non linearNumerical Modelling of induction heating for twodimensional geometries. P. Dreyfuss J. Rappaz Summary We present both a mathematical model and a numerical method for simulating induction heating

Many extragalactic radio sources contain jets of plasma moving away from a central source at relativistic velocities. A twodimensional, cylindrically symmetric, relativistic hydrodynamics model was created to address the issue of jet stability. A description of the model is presented. The derivation of the relativistic fluid dynamics equations, in both conservative and characteristic forms, with specialization to the two

numerical evidence for a spin glass transition at finite temperature simulating intermediate lattice sizescondÂmat/9801215 v2 26 Jan 1998 Crossovers in the TwoDimensional Ising Spin Glass of extensive computer simulations we analyze in detail the two dimenÂ sional \\SigmaJ Ising spin glass

In the present communication, we describe the properties induced by disorder on an ultracold gas of bosonic atoms loaded into a two-dimensional optical lattice with global confinement ensured by a parabolic potential. Our analysis is centred on the spatial distribution of the various phases, focusing particularly on the superfluid properties of the system as a function of external parameters and

Pierfrancesco Buonsante; Francesco Massel; Vittorio Penna; Alessandro Vezzani

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

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

...of Biomolecules In a Two- Dimensional Array;'' U.S...of Biomolecules In a Two-Dimensional Array;'' U.S...foreign counterparts to 2-D Bio, LLC, having...parallel analysis and twodimensional analyses of...

Experiments on ion-acoustic solitons are reviewed. Theories and numerical simulations which are relevant to experimental results are also presented. The measured velocity and width of planar solitons are compared with the predictions of the Korteweg-deVries (KdV) equation which includes a finite ion temperature. The spatial evolution of compressive or rarefactive pulses is discussed. Cylindrical and spherical solitons are introduced together

We show the possible stable soliton generation for the dark-state polaritons in an electromagnetically induced transparency medium composed of ? -type atoms. Whether the solitons are dark or bright can be controlled by the coupling field intensity and the one-photon detuning of the probe field. The velocity, spatial, and time widths of the solitons can also be adjusted by the coupling light.

The transmissions of matter-wave solitons through linear and nonlinear inhomogeneities induced by the spatial variations of the trap and the scattering length in Bose-Einstein condensates are investigated. The enhanced transmission of a soliton through a linear trap by a modulation of the scattering length, is exhibited. The theory is based on the perturbed inverse scattering transform for solitons, and we show that radiation effects are important. Numerical simulations of the Gross-Pitaevskii equation confirm the theoretical predictions.

Garnier, Josselin [Laboratoire de Probabilites et Modeles Aleatoires and Laboratoire Jacques-Louis Lions, Universite Paris VII, 2 Place Jussieu, 75251 Paris Cedex 5 (France); Abdullaev, Fatkhulla Kh. [Physical-Technical Institute of the Uzbekistan Academy of Sciences, 700084, Tashkent-84, G.Mavlyanov str., 2-b (Uzbekistan)

Finite-volume applications of high-order accurate ENO schemes to two-dimensional boundary-value problems are studied. These schemes achieve high-order spatial accuracy, in smooth regions, by a piecewise polynomial approximation of the solution from cell averages. In addition, this spatial operation involves an adaptive stencil algorithm in order to avoid the oscillatory behavior that is associated with interpolation across steep gradients. High-order TVD

This work proposes a feasible method for fabricating a two-dimensional periodic structure with a sub-micrometer periodicity using a single laser beam, based on polymer-dispersed liquid crystal (PDLC) films. The resulting nano-PDLC morphology is highly symmetrical, and similar to that written using multi-beam interference. The increase in the electric-tunability of the optical behavior, including spatial diffraction and color dispersion, is examined. The color dispersion provides optical evidence of the periodic structure of the PDLC film.

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

The published model [Appl. Phys. Lett. 82, 4379-4381 (2003)] for the two-dimensional transient wave propagation in a cylinder is modified to avoid the inherited integration of the numerical inverse scheme. The Fourier series expansion is introduced for one spatial coordinate to resolve the transient response problem: theoretical radial displacements in either the ablation or the thermoelastic regime are obtained with little numerical noise and short computation time. The normal mode expansion method fails to deliver results with the same accuracy. Acoustic waves are fully identified by the ray trajectory analysis. These identified waves are further verified on the experimental results observed with the laser ultrasonic technique. PMID:16018463

Instead of detecting electrical signals for diagnosing cardiac abnormalities, a promising alternative is to detect the magnetic signals generated from cardiac electrical currents. The system utilizing 64 low-transition-temperature superconducting quantum interference devices was tested to detect the time-dependent magnetocardiac signals that are spatially distributed over the heart. To achieve efficient acquisition and analysis, we propose a method to detect two-dimensionally, the T wave propagation of electromagnetic signals of beating hearts. In addition to characterizing the propagating behaviors, the differences between normal hearts and those with coronary artery disease were investigated.

Wu, C. C.; Huang, H. C.; Liu, Y. B.; Lin, L. C.; Lin, L. Y.; Chen, M. F.; Tsai, M. C.; Gao, Y. L.; Yang, S. Y.; Horng, H. E.; Yang, H. C.; Tseng, W. K.; Lee, T. L.; Hsuan, C. F.; Pan, Y. F.; Lee, Y. H.

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 $V\\propto r^{-\\eta}$ 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.

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

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.

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

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

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

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

An implicit analytic solution is presented for two-dimensional groundwater flow through a large number of non-intersecting circular inhomogeneities in the hydraulic conductivity. The locations, sizes and conductivity of the inhomogeneities may be arbitrarily selected. The influence of each inhomogeneity is expanded in a series that satisfies the Laplace equation exactly. The unknown coefficients in this expansion are related to the coefficients in the expansion of the combined discharge potential from all other elements. Using a least squares formulation for the boundary conditions and an iterative algorithm, solutions can be obtained for a very large number of inhomogeneities (e.g. 10,000) on a personal computer to any desired precision, up to the machine's limit. Such precision and speed allows the development of a numerical laboratory for investigating two-dimensional flow and convective transport.

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

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

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.

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.

We report on foam coarsening and statistics of bubble distributions in a closed, twodimensional, hemispheric cell of constant curvature. Using this cell it is possible to observe individual bubbles and measure their coarsening rates. Our results are consistent with the modification to von Neumann's law predicted by Avron and Levine. We observed the relative frequencies of bubbles with a given number of sides and found a shortage of bubbles with few sides as compared to a flat twodimensional cell. We also measured the value of m(n), the average number of sides of an n sided bubble, and found general agreement with the Aboav-Weaire law, although there was greater deviation than for a flat cell.

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.

Solitons are non-dispersing localized waves that occur in diverse physical settings, including liquids, optical fibres, plasmas and condensed matter. They attract interest owing to their particle-like nature and are useful for applications such as in telecommunications. A variety of optical solitons have been observed, but versions that involve both spatial and temporal degrees of freedom are rare. Optical fibres designed to support multiple transverse modes offer opportunities to study wave propagation in a setting that is intermediate between single-mode fibre and free-space propagation. Here we report the observation of optical solitons and soliton self-frequency shifting in graded-index multimode fibre. These wave packets can be modelled as multicomponent solitons, or as solitons of the Gross-Pitaevskii equation. Solitons in graded-index fibres should enable increased data rates in low-cost telecommunications systems, are pertinent to space-division multiplexing, and can offer a new route to mode-area scaling for high-power lasers and transmission. PMID:23591886

It is shown that a bright stationary light pulse evolving along the slow axis of a birefringent fiber in the anomalous dispersion regime can be locked to move in the same group velocity together with a black-soliton pulse trapped along the fast axis in the normal dispersion regime despite each individual pulse's, in the absence of the other, propagating at different group velocities. Such a stationary copropagation of the bright and the black soliton pulses with the same group velocity in coherent trapping can sustain up to a finite distance owing to polarization modulation instability of the black-pulse background that breaks the stationary evolution into radiation. In incoherent trapping the bright-black paired soliton state also disintegrates with propagation distance, and the disintegration is accompanied by emission of bright and gray solitons that has potential for ultrafast optical switching. On the other hand, it is found that the two black-soliton pulses polarized along the principal axes of the birefringent fiber in the normal dispersion regime can evolve stably, in contrast to the paired spatial black solitons of different frequencies and parametric black solitons that break up with propagation distance owing to modulational instability of the cw backgrounds.

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

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

The excitonic behavior of anisotropic two-dimensional crystals is investigated using numerical methods. We employ a screened potential arising due to the system polarizability to solve the central-potential problem using the Numerov approach. The dependence of the exciton energies on the interaction strength and mass anisotropy is demonstrated. We use our results to obtain the exciton binding energy in phosphorene as a function of the substrate dielectric constant.

We present a type of sonic crystal composed with an array of two-dimensional Helmholtz resonators, which in the long-wave regime have both a high relative acoustic refractive index n and at the same time, a small acoustic impedance Z mismatch with air for airborne sound. We analyze the n and Z of such sonic crystals by finite-difference time-domain simulations, and

A two-dimensional image monitor with high resolution has been implemented on a deep-UV 0.6 NA stepper. The aerial intensity sensor uses a photodiode which is integrated in the wafer chuck and a chromium coated quartz wafer with an array of 0.2 micrometers pinholes. The aerial image is scanned by the sensor which is positioned by the stepper stage. The image

The twodimensional 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.

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

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

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

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

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

We apply a global and geometrically well-defined formalism for spinor-dilaton-gravity to two-dimensional manifolds. We discuss the general formalism and focus attention on some particular choices of the dilatonic potential. For constant dilatonic potential the model turns out to be completely solvable and the general solution is found. For linear and exponential dilatonic potentials we present the class of exact solutions with a Killing vector.

Marco Cavaglia; Lorenzo Fatibene; Mauro Francaviglia

. Within the Lagrangian framework we present an approach yielding some explicit solutions to the incompressible two-dimensional\\u000a Euler equations, generalizing the celebrated Gerstner flow. The solutions so obtained, for which explicit formulas of each\\u000a particle trajectory are provided, represent either flows in domains with a rigid boundary or free-surface flows for a fluid\\u000a of infinite depth. For some of these solutions

Although not able to account for structural properties of the grain-boundaries -at least without the help of statistical mechanics-the formalism of classical equilibrium thermodynamics can be a powerful tool in understanding equilibrium segregation, i.e. chemical properties of the essentially two-dimensional (2D) grain boundaries and their relation to bulk material (3D) properties, in particular precipitation. This is exemplified by the case

The two-dimensional metallic bronzes made of ReO3-type layers of MoO6 or WO6 octahedra present quasi-one-dimensional (1D) electronic structures along three directions of preferential overlap of the t2g transition metal orbitals. They exhibit a Peierls instability towards the formation of charge density waves (CDW) at the 2kF critical wave vector allowing to nest simultaneously the Fermi surfaces associated to two quasi-1D

We performed two-dimensional molecular dynamics simulations of cohesive discs under shear. The cohesion between the discs is added by the action of springs between very next neighbouring discs, modelling capillary forces. The geometry of the cell allows disc-disc shearing and not disc-cell wall shearing as is commonly found in the literature. Does a stick-slip phenomenon happen though the upper cover

Equations are presented for obtaining the wall coordinates of two-dimensional supersonic nozzles. The equations are based on the application of the method of characteristics to irrotational flow of perfect gases in channels. Curves and tables are included for obtaining the parameters required by the equations for the wall coordinates. A brief discussion of characteristics as applied to nozzle design is given to assist in understanding and using the nozzle-design method of this report. A sample design is shown.

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

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

The optical conductivity sigma1(omega) of the two-dimensional Hubbard model on finite clusters of 4×4 and &surd;10 × &surd;10 sites is reported. Experimental features found in the high-Tc cuprate superconductors can be qualitatively reproduced by this model including the presence of mid-infrared spectral weight, a Drude peak whose intensity grows with doping and a total spectral weight that varies slowly as

E. Dagotto; A. Moreo; F. Ortolani; J. Riera; D. J. Scalapino

The effect of confinement from one, two or from all three directions on magnetic ordering has remained an active field of research for almost 100 years. The role of dipolar interactions and anisotropy are important to obtain, the otherwise forbidden, ferromagnetic ordering at finite temperature for ions arranged in two-dimensional (2D) arrays (monolayers). We have demonstrated that conventional low-temperature magnetometry

The effect of confinement from one, two or from all three directions on magnetic ordering has remained an active field of\\u000a research for almost 100 years. The role of dipolar interactions and anistropy are important to obtain, the otherwise forbidden,\\u000a ferromagnetic ordering at finite temperature for ions arranged in two-dimensional (2D) arrays (monlayers). We have demonstrated\\u000a that conventional low-temperature magnetometry

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

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

Construction of a new family of two-dimensional quasi orthogonal complete complementary codes (2D-QOCCC) is presented The new 2D-QOCCC retain most of the properties of the 2D-OCCC except the ideal sum of correlation values within the zero horizontal shift. The benefit is a several times larger number of signatures for a given number of elements, thus the enlargement of a maximum

We report the observation of acoustic Bloch oscillations at megahertz frequency in a two-dimensional phononic crystal. By creating periodically arrayed cavities with a decreasing gradient in width along one direction in the phononic crystal, acoustic Wannier-Stark ladders are created in the frequency domain. The oscillatory motion of an incident Gaussian pulse inside the sample is demonstrated by both simulation and experiment. PMID:18233780

We present high resolution twodimensional velocity fields from integral field spectroscopy along with derived rotation curves for nine low surface brightness galaxies. This is a positive step forward in terms of both data quality and number of objects studied. We fit NFW and pseudo-isothermal halo models to the observations. We find that the pseudo-isothermal halo better represents the data in most cases than the NFW halo, as the resulting concentrations are lower than would be expected for LCDM.

Rachel Kuzio de Naray; Stacy S. McGaugh; W. J. G. de Blok; Albert Bosma

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

The two-dimensional coherence function corresponding to positively charged polarons ("holes") in poly(3- hexylthiophene) ?-stacks is calculated based on a Holstein-style Hamiltonian which treats electronic coupling, vibronic coupling and disorder on equal footing. Assuming a model of isotropic site-energy disorder, the hole is found to be delocalized between 1-2 nm along the polymer chain and between 0.5-1 nm along the stacking axis.

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

Hartmut Michel; Dieter Oesterhelt; Richard Henderson

The development of activities in space and of the corresponding technologies requires research on the behavior of both matter and biological organisms under weightless conditions. Various methods have been invented in order to simulate weightlessness, for example, drop towers, sounding rockets, or parabolic flights. Magnetic field ground-based devices have also been developed. This paper introduces an optimization method of the magnetic field so as to obtain magnetic levitation in a two-dimensional cylindrical geometry.

In this paper, we study the superradiant decay of an ensemble of inverted two-level atoms embedded into a continuous dielectric and a two-dimensional (2-D) photonic crystal with lateral confinement of the radiation. The nonlinear superradiance pulse characteristics are calculated using a Green's-function-based model. Specifically, we predict fast phase synchronization across the ensemble that builds up a distributed feedback structure responsible

Igor V. Mel'nikov; Joseph W. Haus; J. Stewart Aitchison

We model structural transitions of small-size Wigner crystals in laterally compressed two-dimensional traps. Ground and metastable configurations are calculated and their transformations are linked to conspicuous changes in the heat capacity of the system. We show that various types of structural transitions are reflected by characteristic features in the behavior of the heat capacity. For deeper understanding, results produced by the Monte Carlo numerical calculations are compared to predictions of simple one-dimensional models.

Rancova, O.; Anisimovas, E.; Varanavicius, T. [Department of Theoretical Physics, Vilnius University, Sauletekio 9, LT-10222 Vilnius (Lithuania)

Two-dimensional photosynthetic protein crystals provide a high density of aligned reaction centers. We reconstitute the robust light harvesting protein Photosystem I into a 2D crystal with lipids and integrate the crystals into a photo-electrochemical device. A 4-fold photocurrent enhancement is measured by incorporating conjugated oligoelectrolytes to form a supporting conductive bilayer in the device which produces a high photocurrent of ?600 ?A per mg PSI deposited. PMID:25155990

Saboe, Patrick O; Lubner, Carolyn E; McCool, Nicholas S; Vargas-Barbosa, Nella M; Yan, Hengjing; Chan, Stanley; Ferlez, Bryan; Bazan, Guillermo C; Golbeck, John H; Kumar, Manish

The Kubo method is used to calculate the electrical conductivity of a two-dimensional, strongly magnetized plasma. The particles interact through (logarithmic) electrostatic potentials and move with their guiding center drift velocities (Taylor-McNamara model). The thermal equilibrium dc conductivity can be evaluated analytically, but the ac conductivity involves numerical solution of a differential equation. Both conductivities fall off as the inverse first power of the magnetic field strength.

The diffusion of energy that is locally deposited into two-dimensional electron gases by Joule heating generates transverse voltages across devices with broken symmetry. For mesoscopic structures characterized by device dimensions comparable to the energy diffusion length, the resulting thermopower strongly depends on details of the potential profile defined by electric gates. We discuss these mesoscopic features within a diffusion thermopower model and propose schemes to measure the energy diffusion length and its dependence on gate voltage.

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

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

We study the fracture roughness for a two-dimensional central force model by nu- merical simulations to check the conjecture that the fracture roughness is due to the fracture process being a stress-weighted percolation process. The simulations are done on a triangular lattice and the fracture process is quasi-static. The simulations are done in mode I and the elastic equilibrium equations

The dynamics of the ultra-intense circularly polarized solitons under inhomogeneous plasmas are examined. The interaction is modeled by the Maxwell and relativistic hydrodynamic equations and is solved with fully implicit energy-conserving numerical scheme. The soliton is self-consistently generated by the interaction between laser and plasma on the vacuum-plasma interface, and the generation mechanism is well confirmed by twodimensional particle-in-cell simulation. It is shown that a propagating weak soliton can be decreased and reflected by increasing plasma background, which is consistent with the existing studies based on hypothesis of weak density response. However, it is found that ultra-intense soliton is well trapped and kept still when encountering increasing background. Probably, this founding can be applied for trapping and amplifying high-intensity laser-fields.

Wu, Dong [Center for Applied Physics and Technology, Peking University, Beijing 100871 (China) [Center for Applied Physics and Technology, Peking University, Beijing 100871 (China); Key Laboratory of High Energy Density Physics Simulation, Ministry of Education, Peking University, Beijing 100871 (China); Zheng, C. Y.; He, X. T. [Center for Applied Physics and Technology, Peking University, Beijing 100871 (China) [Center for Applied Physics and Technology, Peking University, Beijing 100871 (China); Key Laboratory of High Energy Density Physics Simulation, Ministry of Education, Peking University, Beijing 100871 (China); Institute of Applied Physics and Computational Mathematics, Beijing 100088 (China)

The dynamics of the ultra-intense circularly polarized solitons under inhomogeneous plasmas are examined. The interaction is modeled by the Maxwell and relativistic hydrodynamic equations and is solved with fully implicit energy-conserving numerical scheme. The soliton is self-consistently generated by the interaction between laser and plasma on the vacuum-plasma interface, and the generation mechanism is well confirmed by twodimensional particle-in-cell simulation. It is shown that a propagating weak soliton can be decreased and reflected by increasing plasma background, which is consistent with the existing studies based on hypothesis of weak density response. However, it is found that ultra-intense soliton is well trapped and kept still when encountering increasing background. Probably, this founding can be applied for trapping and amplifying high-intensity laser-fields.

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

We study the transition from one-dimensional to two-dimensional configurations of small clusters of monodisperse dust particles levitated in plasma. Particles are confined by a highly-anisotropic two-dimensional potential well in the Dusty ONU experimenT (DONUT). The well anisotropy, as determined by measuring the center-of-mass oscillation frequencies in the x and y directions using Brownian motion, is found to be ?0y^2/?0x^2=30.7. For n<=9 particles, the cluster is in a linear, one-dimensional configuration. The addition of one more particle (n=10) causes a zig-zag transition to a two-dimensional ``barred-elliptical'' configuration with an ``elliptical'' nucleus and linear tails. As more particles are added the nucleus grows and the tails decline until the cluster becomes an oval. These results are found to be in good agreement with Monte Carlo calculations of particle configurations. The Monte Carlo calculations show that in a linear configuration normal modes are either longitudinal or transverse, so that for low energies the cluster dynamics are one-dimensional.

We present a renormalization group study of two-dimensional oscillator arrays, with dissipative, short-range interactions. We consider the case of non-identical oscillators, with distributed intrinsic frequencies within the array and study the steady-state properties of the system. In two dimensions no macroscopic mutual entrainment is found but, for identical oscillators, critical behaviour of the Berezinskii-Kosterlitz-Thouless (BKT) type is shown to be present. We then discuss the stability of BKT order in the physical case of distributed quenched random frequencies. In order to do that, we show how the steady-state dynamical properties of the two-dimensional array of non-identical oscillators are related to the equilibrium properties of the XY model with quenched randomness, which has already been studied in the past. We propose a novel set of recursion relations to study this system within the Migdal-Kadanoff (MK) renormalization group scheme, by means of a discrete clock state formulation. For identical oscillators, we compute the phase diagram in the presence of random dissipative coupling, at finite values of the clock state parameter. Possible experimental applications in two-dimensional arrays of microelectromechanical oscillators are briefly suggested. This work is devoted to Professor David Sherrington, in occasion of his 65th birthday.

We present a renormalization group study of twodimensional arrays of oscillators, with dissipative, short range interactions. We consider the case of non-identical oscillators, with distributed intrinsic frequencies within the array and study the steady-state properties of the system. In two dimensions no macroscopic mutual entrainment is found but, for identical oscillators, critical behavior of the Berezinskii-Kosterlitz-Thouless type is shown to be present. We then discuss the stability of (BKT) order in the physical case of distributed quenched random frequencies. In order to do that, we show how the steady-state dynamical properties of the twodimensional array of non-identical oscillators are related to the equilibrium properties of the XY model with quenched randomness, that has been already studied in the past. We propose a novel set of recursion relations to study this system within the Migdal Kadanoff renormalization group scheme, by mean of the discrete clock-state formulation. We compute the phase diagram in the presence of random dissipative coupling, at finite values of the clock state parameter. Possible experimental applications in twodimensional arrays of microelectromechanical oscillators are briefly suggested.

The two-dimensional electron gas systems at the interface of polar/non-polar oxides interfaces, e.g. LaAlO3(LAO)/SrTiO3(STO), have received considerable attention due to interesting phenomena stemming from strong electron-electron interactions. A recent experiment [1] showed that the (001) surface of KTaO3 (KTO) can induce two-dimensional electron gas even without external doping. KTO differs from widely studied STO in that KTO has more than 20 times stronger spin-orbit coupling. We carried out density functional theory calculations of vacuum-cleaved KTO surface structure to study the electronic and spin properties of the two-dimensional electrons. The electric field that arises from the surface polarization makes the conduction electrons near the surface, resulting in an orbital ordering similar to LAO/STO interface. Despite the strong spin-orbit coupling, about 400 meV, our result shows the Rashba spin splitting in this perovskite oxide is much smaller than that of conventional semiconductors, which is a good agreement with the angle-resolved photoemission measurement.[1] P. D. C. King, et al. Phys. Rev. Lett. 108, 117602 (2012).

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

Uitterlinden, A.G.; Slagboom, P.E.; Knook, D.L.; Vijg, J. (TNO Institute for Experimental Gerontology, Rijswijk (Netherlands))

In this paper, some recent topics on the modeling of magnetotelluric data are introduced. The focus is on the handling of real field data for two-dimensional resistivity modeling. First, the removal of the effects of near surface heterogeneity is reviewed. It covers telluric distortions (phase mixing and static shift) and magnetic distortions using conventional Groom-Bailey type 3D/2D model (three-dimensional local anomaly underlain by regional two-dimensional structure). The extension of a 3D/2D distortion model for multi-site, multi-frequency is a new development. Magnetic distortion seems to be less significant for land observations, but significant for sea floor data, where the regional magnetic field is weak due to seawater. In special cases involving for example, distortion due to topography and bathymetry, explicit removal is possible. There are some schemes proposed for a 3D/3D model (three-dimensional local anomaly underlain by regional three-dimensional structure). Along with the removal of the distortion, it is important to recognize the dimensionality of the dataset prior to modeling. A property using strike estimates for each site is an indicator for dimensionality which is unaffected by local distortion. Mapping the local strike or a rose diagram is an effective visualization of the dimensionality.Two-dimensional inversion is becoming routine. For the fast calculation of derivatives, approximate calculation, reciprocity or conjugate gradient methods are used. In order to incorporate a priori information and to overcome the intrinsic ill-posed nature of the inversion problem, imposing constraints on the model structure is important. A proper tradeoff between the data fit and constraints should be optimized to obtain minimum structures that are required by the field data. However, the choice of constraints is rather subjective and depends on the geological situations. For field data, two-dimensional inversion has limits on modes, area, and period range. Special care must be taken for the structure outside the profile. Two-dimensional inversion incorporating anisotropy is interesting and becoming popular, but the structure may not be unique. Future development in three-dimensional inversion for real datasets should take the above points into consideration.

We report the observation of highly energetic self-interfering matter-wave (SIMW) patterns generated by a moving obstacle in a two-dimensional Bose-Einstein condensate (BEC) inside a power trap cut off by hard-wall box potential boundaries. The obstacle initially excites circular dispersive waves radiating away from the center of the trap which are reflected from hard-wall box boundaries at the edges of the trap. The resulting interference between outgoing waves from the center of the trap and reflected waves from the box boundaries institutes, to the best of our knowledge, unprecedented SIMW patterns. For this purpose we simulated the time-dependent Gross-Pitaevskii equation using the split-step Crank-Nicolson method and the obstacle was modelled by a moving impenetrable Gaussian potential barrier. Various trapping geometries are considered in which the dynamics of the spatial and momentum density, as well as the energy, are considered. The momentum dynamics reveal an oscillatory behavior for the condensate fraction, indicative of excitations out of and de-excitations back into the condensate state. An oscillatory pattern for the energy dynamics reveals the presence of solitons in the system. Some vortex features are also obtained.

Sakhel, Roger R. [Department of Basic Sciences, Faculty of Information Technology, Isra University, Amman 11622 (Jordan); Sakhel, Asaad R. [Department of Applied Sciences, Faculty of Engineering Technology, Al-Balqa Applied University, Amman 11134 (Jordan); Ghassib, Humam B. [Department of Physics, The University of Jordan, Amman 11942 (Jordan)

Detailed experimental investigations of the recently discovered temporal soliton molecules are reported. The optical fiber length was now extended; thus stable and unstable regimes of the soliton molecule can be distinguished from another more precisely.

The experimental evidence of the correlation between the initial electron density of the plasma and electromagnetic soliton excitation at the wake of an intense (10{sup 19} W/cm{sup 2}) and short (1 ps) laser pulse is presented. The spatial distribution of the solitons, together with their late time evolution into post-solitons, is found to be dependent upon the background plasma parameters, in agreement with published analytical and numerical findings. The measured temporal evolution and electrostatic field distribution of the structures are consistent with their late time evolution and the occurrence of multiple merging of neighboring post-solitons.