Two-dimensional solitons in the Gross-Pitaevskii equation with spatially modulated nonlinearity
Sakaguchi, Hidetsugu; Malomed, Boris A.
2006-02-15
We introduce a dynamical model of a Bose-Einstein condensate based on the two-dimensional Gross-Pitaevskii equation, in which the nonlinear coefficient is a function of radius. The model describes a situation with spatial modulation of the negative atomic scattering length, via the Feshbach resonance controlled by a properly shaped magnetic of optical field. We focus on the configuration with the nonlinear coefficient different from zero in a circle or annulus, including the case of a narrow ring. Two-dimensional axisymmetric solitons are found in a numerical form, and also by means of a variational approximation; for an infinitely narrow ring, the soliton is found in an exact form (in the latter case, exact solitons are also found in a two-component model). A stability region for the solitons is identified by means of numerical and analytical methods. In particular, if the nonlinearity is supported on the annulus, the upper stability border is determined by azimuthal perturbations; the stability region disappears if the ratio of the inner and outer radii of the annulus exceeds a critical value {approx_equal}0.47. The model gives rise to bistability, as the stationary solitons coexist with stable axisymmetric breathers, whose stability region extends to higher values of the norm than that of the static solitons. The collapse threshold strongly increases with the radius of the inner hole of the annulus. Vortex solitons are found too, but they are unstable.
Fully localized two-dimensional embedded solitons
Yang Jianke
2010-11-15
We report the prediction of fully localized two-dimensional embedded solitons. These solitons are obtained in a quasi-one-dimensional waveguide array which is periodic along one spatial direction and localized along the orthogonal direction. Under appropriate nonlinearity, these solitons are found to exist inside the Bloch bands (continuous spectrum) of the waveguide and thus are embedded solitons. These embedded solitons are fully localized along both spatial directions. In addition, they are fully stable under perturbations.
Kevrekidis, P. G.; Malomed, Boris A.; Saxena, Avadh; Bishop, A. R.; Frantzeskakis, D. J.
2015-04-07
We consider a two-dimensional (2D) generalization of a recently proposed model [Phys. Rev. E 88, 032905 (2013)], which gives rise to bright discrete solitons supported by the defocusing nonlinearity whose local strength grows from the center to the periphery. We explore the 2D model starting from the anticontinuum (AC) limit of vanishing coupling. In this limit, we can construct a wide variety of solutions including not only single-site excitations, but also dipole and quadrupole ones. Additionally, two separate families of solutions are explored: the usual “extended” unstaggered bright solitons, in which all sites are excited in the AC limit, withmore » the same sign across the lattice (they represent the most robust states supported by the lattice, their 1D counterparts being those considered as 1D bright solitons in the above-mentioned work), and the vortex cross, which is specific to the 2D setting. For all the existing states, we explore their stability (also analytically, when possible). As a result, typical scenarios of instability development are exhibited through direct simulations.« less
Kevrekidis, P. G.; Malomed, Boris A.; Saxena, Avadh; Bishop, A. R.; Frantzeskakis, D. J.
2015-04-07
We consider a two-dimensional (2D) generalization of a recently proposed model [Phys. Rev. E 88, 032905 (2013)], which gives rise to bright discrete solitons supported by the defocusing nonlinearity whose local strength grows from the center to the periphery. We explore the 2D model starting from the anticontinuum (AC) limit of vanishing coupling. In this limit, we can construct a wide variety of solutions including not only single-site excitations, but also dipole and quadrupole ones. Additionally, two separate families of solutions are explored: the usual “extended” unstaggered bright solitons, in which all sites are excited in the AC limit, with the same sign across the lattice (they represent the most robust states supported by the lattice, their 1D counterparts being those considered as 1D bright solitons in the above-mentioned work), and the vortex cross, which is specific to the 2D setting. For all the existing states, we explore their stability (also analytically, when possible). As a result, typical scenarios of instability development are exhibited through direct simulations.
NASA Astrophysics Data System (ADS)
Nesterov, L. A.; Veretenov, N. A.; Rosanov, N. N.
2015-05-01
Quantum fluctuations of one-dimensional dark dissipative solitons sustained by an external radiation in an interferometer with a Kerr nonlinearity are analyzed theoretically. The stability region of classical solitons in this interferometer is studied. The boundaries of this region are determined, and types of excited solitons are classified. Quantum fluctuations of solitons are analyzed in an approximation linear in fluctuations. This problem was solved by linearizing the quantum Langevin equation in a neighborhood of a classical solution for the main type of a soliton from the obtained stability region. The main attention has been paid to studying quantum fluctuations of collective variables of dissipative solitons, namely, the coordinate of the center and momentum of the soliton. Based on the expansion of solutions of the linearized equation in eigenfunctions of the discrete spectrum of this equation, a solution describing quantum fluctuations of these variables is constructed. Using this expansion scheme made it possible to give a rigorous definition of the dissipative soliton position fluctuation operator. The study performed based on this scheme has made it also possible to construct a solution for a one-dimensional dark relaxing dissipative soliton. This soliton generalizes the stationary soliton with allowance for the shift of its center and deformation of its profile followed by the recovery of its initial shape. Average squares of quantum fluctuations of collective variables are calculated. A domain of parameters in which there exist quantum states of solitons with an initially high degree of squeezing with respect to the momentum is found. It is shown that such states are in correspondence with significantly higher velocities of soliton center drift. An experiment that could detect the relative squeezing with respect to the momentum due to the soliton center drift is discussed.
Exciton-polariton gap solitons in two-dimensional lattices.
Cerda-Mndez, E A; Sarkar, D; Krizhanovskii, D N; Gavrilov, S S; Biermann, K; Skolnick, M S; Santos, P V
2013-10-01
We report on the two-dimensional gap-soliton nature of exciton-polariton macroscopic coherent phases (PMCP) in a square lattice with a tunable amplitude. The resonantly excited PMCP forms close to the negative mass M point of the lattice band structure with energy within the lattice band gap and its wave function localized within a few lattice periods. The PMCPs are well described as gap solitons resulting from the interplay between repulsive polariton-polariton interactions and effective attractive forces due to the negative mass. The solitonic nature accounts for the reduction of the PMCP coherence length and optical excitation threshold with increasing lattice amplitude. PMID:24138259
Two-dimensional dynamics of relativistic solitons in cold plasmas
NASA Astrophysics Data System (ADS)
Lehmann, G.; Laedke, E. W.; Spatschek, K. H.
2008-07-01
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.
NASA Astrophysics Data System (ADS)
Burlak, Gennadiy; Malomed, Boris A.
2012-05-01
We report results of systematic numerical studies of two-dimensional matter-wave soliton families supported by an external potential, in a vicinity of the junction between stable and unstable branches of the families, where the norm of the solution attains a minimum, facilitating the creation of the soliton. The model is based on the Gross-Pitaevskii equation for the self-attractive condensate loaded into a quasiperiodic (QP) optical lattice (OL). The same model applies to spatial optical solitons in QP photonic crystals. Dynamical properties and stability of the solitons are analyzed with respect to variations of the depth and wave number of the OL. In particular, it is found that the single-peak solitons are stable or not in exact accordance with the Vakhitov-Kolokolov (VK) criterion, while double-peak solitons, which are found if the OL wave number is small enough, are always unstable against splitting.
Dragging two-dimensional discrete solitons by moving linear defects
Brazhnyi, Valeriy A.; Malomed, Boris A.
2011-07-15
We study the mobility of small-amplitude solitons attached to moving defects which drag the solitons across a two-dimensional (2D) discrete nonlinear Schroedinger 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.
Soliton nanoantennas in two-dimensional arrays of quantum dots.
Gligorić, G; Maluckov, A; Hadžievski, Lj; Slepyan, G Ya; Malomed, B A
2015-06-10
We consider two-dimensional (2D) arrays of self-organized semiconductor quantum dots (QDs) strongly interacting with electromagnetic field in the regime of Rabi oscillations. The QD array built of two-level states is modelled by two coupled systems of discrete nonlinear Schrödinger equations. Localized modes in the form of single-peaked fundamental and vortical stationary Rabi solitons and self-trapped breathers have been found. The results for the stability, mobility and radiative properties of the Rabi modes suggest a concept of a self-assembled 2D soliton-based nano-antenna, which is stable against imperfections In particular, we discuss the implementation of such a nano-antenna in the form of surface plasmon solitons in graphene, and illustrate possibilities to control their operation by means of optical tools. PMID:25985396
Soliton nanoantennas in two-dimensional arrays of quantum dots
NASA Astrophysics Data System (ADS)
Gligorić, G.; Maluckov, A.; Hadžievski, Lj; Slepyan, G. Ya; Malomed, B. A.
2015-06-01
We consider two-dimensional (2D) arrays of self-organized semiconductor quantum dots (QDs) strongly interacting with electromagnetic field in the regime of Rabi oscillations. The QD array built of two-level states is modelled by two coupled systems of discrete nonlinear Schrödinger equations. Localized modes in the form of single-peaked fundamental and vortical stationary Rabi solitons and self-trapped breathers have been found. The results for the stability, mobility and radiative properties of the Rabi modes suggest a concept of a self-assembled 2D soliton-based nano-antenna, which is stable against imperfections In particular, we discuss the implementation of such a nano-antenna in the form of surface plasmon solitons in graphene, and illustrate possibilities to control their operation by means of optical tools.
Two-dimensional solitons in dipolar Bose-Einstein condensates with spin-orbit coupling
NASA Astrophysics Data System (ADS)
Jiang, Xunda; Fan, Zhiwei; Chen, Zhaopin; Pang, Wei; Li, Yongyao; Malomed, Boris A.
2016-02-01
We report families of two-dimensional (2D) composite solitons in spinor dipolar Bose-Einstein condensates, with two localized components linearly mixed by the spin-orbit coupling (SOC), and the intrinsic nonlinearity represented by the dipole-dipole interaction (DDI) between atomic magnetic moments polarized in plane by an external magnetic field. Recently, stable solitons were predicted in the form of semivortices (composites built of coupled fundamental and vortical components) in the 2D system combining the SOC and contact attractive interactions. Replacing the latter by the anisotropic long-range DDI, we demonstrate that, for a fixed norm of the soliton, the system supports a continuous family of stable spatially asymmetric vortex solitons (AVSs), parameterized by an offset of the pivot of the vortical component relative to its fundamental counterpart. The offset is limited by a certain maximum value, while the energy of the AVS practically does not depend on the offset. At small values of the norm, the vortex solitons are subject to a weak oscillatory instability. In the present system, with the Galilean invariance broken by the SOC, the composite solitons are set in motion by a kick the strength of which exceeds a certain depinning value. The kicked solitons feature a negative effective mass, drifting along a spiral trajectory opposite to the direction of the kick. A critical angular velocity, up to which the semivortices may follow rotation of the polarizing magnetic field, is found too.
Two-dimensional discrete solitons in rotating lattices
Cuevas, Jesus; Kevrekidis, P. G.
2007-10-15
We introduce a two-dimensional discrete nonlinear Schroedinger (DNLS) equation with self-attractive cubic nonlinearity in a rotating reference frame. The model applies to a Bose-Einstein condensate stirred by a rotating strong optical lattice, or light propagation in a twisted bundle of nonlinear fibers. Two types of localized states are constructed: off-axis fundamental solitons (FSs), placed at distance R from the rotation pivot, and on-axis (R=0) vortex solitons (VSs), with vorticities S=1 and 2. At a fixed value of rotation frequency {omega}, a stability interval for the FSs is found in terms of the lattice coupling constant C, 0
Matter-wave two-dimensional solitons in crossed linear and nonlinear optical lattices
Luz, H. L. F. da; Gammal, A.; Abdullaev, F. Kh.; Salerno, M.; Tomio, Lauro
2010-10-15
The existence of multidimensional matter-wave solitons in a crossed optical lattice (OL) with a linear optical lattice (LOL) in the x direction and a nonlinear optical lattice (NOL) in the y direction, where the NOL can be generated by a periodic spatial modulation of the scattering length using an optically induced Feshbach resonance is demonstrated. In particular, we show that such crossed LOLs and NOLs allow for stabilizing two-dimensional solitons against decay or collapse for both attractive and repulsive interactions. The solutions for the soliton stability are investigated analytically, by using a multi-Gaussian variational approach, with the Vakhitov-Kolokolov necessary criterion for stability; and numerically, by using the relaxation method and direct numerical time integrations of the Gross-Pitaevskii equation. Very good agreement of the results corresponding to both treatments is observed.
Matter-wave two-dimensional solitons in crossed linear and nonlinear optical lattices
NASA Astrophysics Data System (ADS)
da Luz, H. L. F.; Abdullaev, F. Kh.; Gammal, A.; Salerno, M.; Tomio, Lauro
2010-10-01
The existence of multidimensional matter-wave solitons in a crossed optical lattice (OL) with a linear optical lattice (LOL) in the x direction and a nonlinear optical lattice (NOL) in the y direction, where the NOL can be generated by a periodic spatial modulation of the scattering length using an optically induced Feshbach resonance is demonstrated. In particular, we show that such crossed LOLs and NOLs allow for stabilizing two-dimensional solitons against decay or collapse for both attractive and repulsive interactions. The solutions for the soliton stability are investigated analytically, by using a multi-Gaussian variational approach, with the Vakhitov-Kolokolov necessary criterion for stability; and numerically, by using the relaxation method and direct numerical time integrations of the Gross-Pitaevskii equation. Very good agreement of the results corresponding to both treatments is observed.
Quasi two-dimensional astigmatic solitons in soft chiral metastructures
Laudyn, Urszula A.; Jung, Paweł S.; Karpierz, Mirosław A.; Assanto, Gaetano
2016-01-01
We investigate a non-homogeneous layered structure encompassing dual spatial dispersion: continuous diffraction in one transverse dimension and discrete diffraction in the orthogonal one. Such dual diffraction can be balanced out by one and the same nonlinear response, giving rise to light self-confinement into astigmatic spatial solitons: self-focusing can compensate for the spreading of a bell-shaped beam, leading to quasi-2D solitary wavepackets which result from 1D transverse self-localization combined with a discrete soliton. We demonstrate such intensity-dependent beam trapping in chiral soft matter, exhibiting one-dimensional discrete diffraction along the helical axis and one-dimensional continuous diffraction in the orthogonal plane. In nematic liquid crystals with suitable birefringence and chiral arrangement, the reorientational nonlinearity is shown to support bell-shaped solitary waves with simple astigmatism dependent on the medium birefringence as well as on the dual diffraction of the input wavepacket. The observations are in agreement with a nonlinear nonlocal model for the all-optical response. PMID:26975651
Quasi two-dimensional astigmatic solitons in soft chiral metastructures.
Laudyn, Urszula A; Jung, Paweł S; Karpierz, Mirosław A; Assanto, Gaetano
2016-01-01
We investigate a non-homogeneous layered structure encompassing dual spatial dispersion: continuous diffraction in one transverse dimension and discrete diffraction in the orthogonal one. Such dual diffraction can be balanced out by one and the same nonlinear response, giving rise to light self-confinement into astigmatic spatial solitons: self-focusing can compensate for the spreading of a bell-shaped beam, leading to quasi-2D solitary wavepackets which result from 1D transverse self-localization combined with a discrete soliton. We demonstrate such intensity-dependent beam trapping in chiral soft matter, exhibiting one-dimensional discrete diffraction along the helical axis and one-dimensional continuous diffraction in the orthogonal plane. In nematic liquid crystals with suitable birefringence and chiral arrangement, the reorientational nonlinearity is shown to support bell-shaped solitary waves with simple astigmatism dependent on the medium birefringence as well as on the dual diffraction of the input wavepacket. The observations are in agreement with a nonlinear nonlocal model for the all-optical response. PMID:26975651
Solitons supported by two-dimensional mixed linear-nonlinear complex optical lattices
NASA Astrophysics Data System (ADS)
Ren, Xiaoping; Wang, Hong; Li, Zhen; Wang, Hongcheng
2015-12-01
The evolution of solitons in the two-dimensional mixed linear-nonlinear complex optical lattices is investigated. It is found that the nonlinearity-modulation depth plays a significant role on the existence of solitons. Both the nonlinearity-modulation depth and amplitude of the imaginary part of nonlinear lattice have a great effect on the stability of solitons. Moreover, the period of nonlinear lattice can influence the properties of solitons dramatically. In addition, we also study the mobility of solitons and find that the soliton can maintain its original shape while the mass center of solitons will oscillate periodically in a certain tilt angle range. However, if the tilt angle is large enough, the soliton will be distorted and its mass center oscillates irregularly.
Two-dimensional skyrmions and other solitonic structures in confinement-frustrated chiral nematics.
Ackerman, Paul J; Trivedi, Rahul P; Senyuk, Bohdan; van de Lagemaat, Jao; Smalyukh, Ivan I
2014-07-01
We explore spatially localized solitonic configurations of a director field, generated using optical realignment and laser-induced heating, in frustrated chiral nematic liquid crystals confined between substrates with perpendicular surface anchoring. We demonstrate that, in addition to recently studied torons and Hopf-fibration solitonic structures (hopfions), one can generate a host of other axially symmetric stable and metastable director field configurations where local twist is matched to the surface boundary conditions through introduction of point defects and loops of singular and nonsingular disclinations. The experimentally demonstrated structures include the so-called "baby-skyrmions" in the form of double twist cylinders oriented perpendicular to the confining substrates where their double twist field configuration is matched to the perpendicular boundary conditions by loops of twist disclinations. We also generate complex textures with arbitrarily large skyrmion numbers. A simple back-of-the-envelope theoretical analysis based on free energy considerations and the nonpolar nature of chiral nematics provides insights into the long-term stability and diversity of these inter-related solitonic field configurations, including different types of torons, cholestric-finger loops, two-dimensional skyrmions, and more complex structures comprised of torons, hopfions, and various disclination loops that are experimentally observed in a confinement-frustrated chiral nematic system. PMID:25122322
The asymmetric solitons in two-dimensional parity-time-symmetric potentials
NASA Astrophysics Data System (ADS)
Chen, Haibo; Hu, Sumei
2016-01-01
We investigate the properties in two-dimensional (2D) special parity-time (PT) symmetric complex potentials. The linear case of this special 2D PT-symmetric complex potential and self-focusing nonlinear cases are discussed. For linear case, the eigenvalues and eigenfunction for different loss or gain level of the PT-symmetric complex potentials are obtained numerically. For nonlinear cases, the existence of asymmetric solitons and PT-symmetric solitons is studied in this PT symmetric system. The eigenvalue for linear case is equal to the critical propagation constant bc of existing PT-symmetric solitons. When the PT-symmetric soliton's propagation constant reaches a certain threshold bc1, a branch of asymmetric solitons can bifurcate out from the branch of PT-symmetric solitons.
Complexes of in-phase two-dimensional laser solitons
Rosanov, N N; Fedorov, S V; Shatsev, A N
2008-01-31
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)
Asymmetric spatial soliton dragging.
Blair, S; Wagner, K; McLeod, R
1994-12-01
A new low-latency, cascadable optical logic gate with gain, high contrast, and three-terminal input-output isolation is introduced. The interaction between two orthogonally polarized spatial solitons brought into coincidence at the boundary of a saturating nonlinear medium and propagating in different directions results in the phase-insensitive spatial dragging of a strong pump soliton by a weaker signal. As a result, the strong pump is transmitted through an aperture when the weak signal is not present, and it is dragged to the side by more than a beam width and blocked in the presence of the weak signal, thus implementing an inverter with gain. A multi-input, logically complete NOR gate also can be implemented in a cascaded system. PMID:19855703
NASA Astrophysics Data System (ADS)
Zhu, Xing; Li, Huagang
2016-01-01
We study the existence and stability of multihump solitons in two-dimensional (2D) parity-time (PT)-symmetric periodic potentials with focusing saturable nonlinearity. All the humps of these solitons are in consecutive lattice sites and the adjacent two humps are out-of-phase. These multihump solitons exist in finite regions in the semi-infinite gap and cannot bifurcate from the edge of the first Bloch band. They can be stable in the moderate power region. It is found that the saturation parameter will affect the existence and stability of these multihump gap solitons significantly. The transverse power flow vector in these 2D multihump solitons in focusing saturable media is also investigated.
Photorefractive polymeric optical spatial solitons.
Shih, M F; Sheu, F W
1999-12-15
We predict the formation of optical spatial solitons in photorefractive polymers. The orientational enhancement from the doped chromophores and the dependency of the quantum efficiency of generating mobile holes on the electric field make the polymeric solitons behave differently from other photorefractive solitons. PMID:18079953
Spatiotemporal solitons in the Ginzburg-Landau model with a two-dimensional transverse grating
Mihalache, D.; Mazilu, D.; Lederer, F.; Leblond, H.; Malomed, B. A.
2010-02-15
We explore families of spatiotemporal dissipative solitons in a model of three-dimensional (3D) laser cavities including a combination of gain, saturable absorption, and transverse grating. The model is based on the complex Ginzburg-Landau equation with the cubic-quintic nonlinearity and a two-dimensional (2D) periodic potential representing the grating. Fundamental and vortical solitons are found in a numerical form as attractors in this model and their stability against strong random perturbations is tested by direct simulations. The fundamental solitons are completely stable while the vortices, built as rhombus-shaped complexes of four fundamental solitons, may be split by perturbations into their constituents separating in the temporal direction. Nevertheless, a sufficiently strong grating makes the vortices practically stable objects.
NASA Astrophysics Data System (ADS)
Leblond, Herv; Malomed, Boris A.; Mihalache, Dumitru
2005-03-01
We consider basic types of two-dimensional (2D) vortex solitons in a three-wave model combining quadratic ?(2) and self-defocusing cubic ?-(3) nonlinearities. The system involves two fundamental-frequency (FF) waves with orthogonal polarizations and a single second-harmonic (SH) one. The model makes it possible to introduce a 2D soliton, with hidden vorticity (HV). Its vorticities in the two FF components are S1,2=1 , whereas the SH carries no vorticity, S3=0 . We also consider an ordinary compound vortex, with 2S1=2S2=S3=2 . Without the ?-(3) terms, the HV soliton and the ordinary vortex are moderately unstable. Within the propagation distance z?15 diffraction lengths, Zdiffr , the former one turns itself into a usual zero-vorticity (ZV) soliton, while the latter splits into three ZV solitons (the splinters form a necklace pattern, with its own intrinsic dynamics). To gain analytical insight into the azimuthal instability of the HV solitons, we also consider its one-dimensional counterpart, viz., the modulational instability (MI) of a one-dimensional CW (continuous-wave) state with hidden momentum, i.e., opposite wave numbers in its two components, concluding that such wave numbers may partly suppress the MI. As concerns analytical results, we also find exact solutions for spreading localized vortices in the 2D linear model; in terms of quantum mechanics, these are coherent states with angular momentum (we need these solutions to accurately define the diffraction length of the true solitons). The addition of the ?-(3) interaction strongly stabilizes both the HV solitons and the ordinary vortices, helping them to persist over z up to 50Zdiffr . In terms of the possible experiment, they are completely stable objects. After very long propagation, the HV soliton splits into two ZV solitons, while the vortex with S3=2S1,2=2 splits into a set of three or four ZV solitons.
Liu, Bin; He, Xing-Dao; Li, Shu-Jing
2011-11-01
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
Two-dimensional linear modes and solitons in parity-time symmetry bessel complex-valued potential
NASA Astrophysics Data System (ADS)
Chen, Haibo; Hu, Sumei
2015-11-01
We study the optical properties of two-dimensional linear modes and solitons in parity-time (PT) symmetry Bessel complex-valued potential. The PT-breaking points, the eigenvalues and eigenfunction for different modulated depths of two-dimensional PT symmetry Bessel complex potential are obtained numerically. The PT-breaking points increase linearly with increasing the real part of the modulated depths of PT potential. The existence of fundamental and dipole solitons are studied in self-focusing and self-defocusing media. The eigenvalue for linear case is equal to the critical propagation constant bc of the existing soliton. The fundamental solitons are stable in both the self-focusing and self-defocusing media, and the dipole solitons are stable in the self-defocusing media but unstable in the self-focusing media.
Stable and mobile two-dimensional dipolar ring-dark-in-bright Bose–Einstein condensate soliton
NASA Astrophysics Data System (ADS)
Adhikari, S. K.
2016-03-01
We demonstrate robust, stable, mobile two-dimensional (2D) dipolar ring-dark-in-bright (RDB) Bose–Einstein condensate (BEC) solitons for repulsive contact interaction, subject to a harmonic trap along the y direction perpendicular to the polarisation direction z. Such a RDB soliton has a ring-shaped notch (zero in density) imprinted on a 2D bright soliton free to move in the x ‑ z plane. At medium velocity the head-on collision of two such solitons is found to be quasi-elastic with practically no deformation. The possibility of creating the RDB soliton by phase imprinting is demonstrated. The findings are illustrated using numerical simulation employing realistic interaction parameters in a dipolar 164Dy BEC.
Grinevich, P.G.
1987-05-01
Explicit examples are constructed of two-dimensional rational potentials that decrease at infinity and are reflectionless for given energy. It is shown that these potentials correspond to soliton solutions of the (2 + 1)- dimensional nonlinear equations found by Veselov and Novikov.
Spatial solitons in periodic nanostructures
Gorbach, A. V.; Skryabin, D. V.
2009-05-15
We present the first-principles theory of the existence and stability of TE and TM spatial solitons in a subwavelength periodic semiconductor-dielectric structure. We have found that for the wavelength of 1550 nm and the interface separation close to and less than 100 nm the band structure of the linear TE and TM waves becomes similar to the band structure of a homogeneous medium. The properties of TE solitons change accordingly. However, the transverse profiles of the TM solitons continue to reflect the subwavelength geometry of the structure and develop dominant intensity peaks inside the low-index dielectric slots. Our stability analysis based on the linearized Maxwell equations indicates that the nonlinear TM waves can be approximated as the evanescently coupled modes of the slot waveguides with the low-index dielectric core and the high-index semiconductor cladding. Transition to the regime where the slot waveguides start to determine properties of TM waves is associated with the so-called Brewster condition.
Band-gap boundaries and fundamental solitons in complex two-dimensional nonlinear lattices
Ablowitz, Mark J.; Antar, Nalan; Bakirtas, Ilkay; Ilan, Boaz
2010-03-15
Nonlinear Schroedinger (NLS) equation with external potentials (lattices) possessing crystal and quasicrystal structures are studied. The fundamental solitons and band gaps are computed using a spectral fixed-point numerical scheme. Nonlinear and linear stability properties of the fundamental solitons are investigated by direct simulations and the linear stability properties of the fundamental solitons are confirmed by analysis the linearized eigenvalue problem.
Scattering of two-dimensional dark solitons by a single quantum vortex in a Bose-Einstein condensate
NASA Astrophysics Data System (ADS)
Smirnov, Lev A.; Smirnov, Alexander I.
2015-07-01
We study the process of scattering of two-dimensional dark solitons, and their vortex-antivortex pairs as a specific case, by a single quantum vortex in a Bose-Einstein condensate with repulsive interaction between atoms. An asymptotic theory describing the dynamics of such solitonlike structures in a smoothly inhomogeneous flow of ultracold Bose gas is developed. An analytical expression for the angle of scattering of two-dimensional dark solitons (including vortex pairs) by a single-phase singularity is obtained in the limit of large impact parameters. All theoretical concepts are confirmed by numerical calculations performed directly within the Gross-Pitaevskii equation. It is shown that for small impact parameters, the considered solitonlike structures interact inelastically with the core of a single quantum vortex, scattering over large angles and radiating sound waves.
NASA Astrophysics Data System (ADS)
Feijoo, David; Zezyulin, Dmitry A.; Konotop, Vladimir V.
2015-12-01
We analyze a system of three two-dimensional nonlinear Schrdinger equations coupled by linear terms and with the cubic-quintic (focusing-defocusing) nonlinearity. We consider two versions of the model: conservative and parity-time (PT ) symmetric. These models describe triple-core nonlinear optical waveguides, with balanced gain and losses in the PT -symmetric case. We obtain families of soliton solutions and discuss their stability. The latter study is performed using a linear stability analysis and checked with direct numerical simulations of the evolutional system of equations. Stable solitons are found in the conservative and PT -symmetric cases. Interactions and collisions between the conservative and PT -symmetric solitons are briefly investigated, as well.
Ghosh, Samiran
2014-09-01
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. PMID:25314548
Applications of photorefractive soliton collisions and two-dimensional waveguide arrays
NASA Astrophysics Data System (ADS)
Tang, Yongan
There are two parts in this dissertation. The first part is applications of vector soliton collisions. First, we theoretically and experimentally investigated vector soliton collision(s). Energy exchange upon the collisions was found at a large collision angle that was lager than the critical angle, which is the complement of the waveguide guidance angle. Then, we investigated the detailed facts of the energy exchange in the vector soliton collision, and the results showed that the energy exchange efficiency was affected by the collision angle and the soliton's component ratio. While the collision angle was getting larger the efficiency was getting smaller, and while the soliton's component ratio was getting larger the efficiency was getting larger too. However, the amount of energy exchange wasn't changing, while the soliton's component ratio was getting larger. Finally, we experimentally observed three vector soliton collisions and four vector soliton collisions. These results showed that the previous collision(s) would affect the energy exchange of the following collision(s) in the sequence collisions. After understanding the energy exchange of vector soliton collision(s), we presented some application examples. These included two examples of beam controlling (beam cloning and beam reversing); and two examples of algebra computation matrices (identity and permutation matrix). The second part of this dissertation are applications of 2D waveguide arrays. First, we discussed the theory of discrete diffraction and modulation instability in waveguide arrays. Second, we formed 2D waveguide arrays in SBN:75 with three or four plane beams. The structure and periodicity of the waveguide array could be changed by adjusting the array beams propagating direction(s) and location(s). Then, discrete diffraction in 2D waveguide array was experimentally observed in a fixed 2D square structure waveguide array; normal and anomalous diffraction regions in the lst Brillouin zone of the 2D waveguide array were observed; and discrete diffraction management was proposed based on these diffraction properties. Finally, primary experimental results of MI were observed both in the normal diffraction region with self-focusing nonlinearity and anomalous diffraction regions with self-defocusing nonlinearity, and these MIs could be used to predict discrete soliton in the 2D waveguide array.
Three-dimensional vortex solitons in quasi-two-dimensional lattices
Leblond, Herve; Malomed, Boris A.; Mihalache, Dumitru
2007-08-15
We consider the three-dimensional (3D) Gross-Pitaevskii or nonlinear Schroedinger 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 {pi}S/2 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{ne}0) supported by a lattice in the 3D space. Typical scenarios of instability development (collapse or decay) of unstable localized vortices are identified too.
Magnetic resonance force microscopy with two-dimensional spatial encoding
NASA Astrophysics Data System (ADS)
Eberhardt, Kai W.; Meier, Urban; Hunkeler, Andreas; Meier, Beat H.
2008-03-01
We demonstrate a novel method of creating Magnetic Resonance Force Microscopy (MRFM) images that eliminates the need to scan the probe-sample distance. Conventionally, scanning a magnetic tip over the sample in at least two dimensions is required for imaging with MRFM. At each position the signal from a different slice of the sample is acquired, where the slice is defined by the the rf field and the ferromagnetic gradient tip geometry. An image can be reconstructed by deconvolving the shape of the slice from the data. The new method we demonstrate keeps the sample-tip distance constant and resolves the signal origin by spatial encoding with rf pulses. For spatial encoding in one dimension rf pulses are applied with a gradient field coil. These pulses produce a Fourier-encoding in the longitudinal magnetization. In the second dimension Hadamard encoding [1] is employed. 2D images of a patterned (NH4)2SO4 crystal sample are reconstructed from the known field distributions with a resolution of 1 ?m at room temperature.[1] K. W. Eberhardt et al., Phys. Rev. B 76: 180405 (2007)
NASA Astrophysics Data System (ADS)
Snchez-Arriaga, G.; Lefebvre, E.
2011-09-01
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.
2011-09-15
The dynamics of two-dimensional s-polarized solitary waves is investigated with the aid of particle-in-cell (PIC) simulations. Instead of the usual excitation of the waves with a laser pulse, the PIC code was directly initialized with the numerical solutions from the fluid plasma model. This technique allows the analysis of different scenarios including the theoretical problems of the solitary wave stability and their collision as well as features already measured during laser-plasma experiments such as the emission of electromagnetic bursts when the waves reach the plasma-vacuum interface, or their expansion on the ion time scale, usually named post-soliton evolution. Waves with a single density depression are stable whereas multihump solutions decay to several waves. Contrary to solitons, two waves always interact through a force that depends on their relative phases, their amplitudes, and the distance between them. On the other hand, the radiation pattern at the plasma-vacuum interface was characterized, and the evolution of the diameter of different waves was computed and compared with the ''snow plow'' model.
NASA Astrophysics Data System (ADS)
Cartes, C.; Descalzi, O.; Brand, H. R.
2014-10-01
We review the work on exploding dissipative solitons in one and two spatial dimensions. Features covered include: the transition from modulated to exploding dissipative solitons, the analogue of the Ruelle-Takens scenario for dissipative solitons, inducing exploding dissipative solitons by noise, two classes of exploding dissipative solitons in two spatial dimensions, diffusing asymmetric exploding dissipative solitons as a model for a two-dimensional extended chaotic system. As a perspective we outline the interaction of exploding dissipative solitons with quasi one-dimensional dissipative solitons, breathing quasi one-dimensional solutions and their possible connection with experimental results on convection, and the occurence of exploding dissipative solitons in reaction-diffusion systems. It is a great pleasure to dedicate this work to our long-time friend Hans (Prof. Dr. Hans Jrgen Herrmann) on the occasion of his 60th birthday.
Cascadable spatial-soliton logic gates.
Blair, S; Wagner, K
2000-11-10
The three-terminal spatial-soliton angular-deflection geometry provides the characteristics of an inverting logic gate with gain, and phase-insensitive implementations can be realized by a number of specific nonlinear interactions between orthogonally polarized waves. In particular, numerical simulations of spatial-soliton dragging and collision are used to calculate the transfer functions of inverter and multiple configurations of two-input nor gates and to address their cascadability. These transfer functions converge in cascaded operation and suggest that fan-out greater than 2 with a large noise margin is attainable in a system with standardized signal levels. These results are obtained with the material properties of fused silica and are representative of low-loss Kerr media. PMID:18354606
NASA Astrophysics Data System (ADS)
Kim, Young Cheol; Jang, Sung Ho; Kim, Gun Ho; Chung, Chin Wook
2009-10-01
Real time two-dimensional spatial distribution measurement method of electron temperature and plasma density was developed. It is based on a floating probe method [1] because the floating probe has high time resolution. Two-dimensional array of sensors on a 300 mm diameter wafer-shaped printed circuit board (PCB) and a high speed multiplexer circuit were used for real time distribution measurement. The method was tested at various powers and pressures, spatial distributions of the electron temperature and the plasma density could be obtained. And in the measurement results, asymmetric plasma density distributions caused by pumping port effect could be observed. This method can measure spatial distribution of plasma parameters on the wafer in real time without plasma perturbation, therefore it will be expected to improve the uniformity of processing plasmas such as etching and deposition. [4pt] [1] M. H. Lee, S. H. Jang, C. W. Chung, J. Appl. Phys. 101, 033305 (2007).
Design of a microfluidic device for comprehensive spatial two-dimensional liquid chromatography.
Wouters, Bert; De Vos, Jelle; Desmet, Gert; Terryn, Herman; Schoenmakers, Peter J; Eeltink, Sebastiaan
2015-04-01
This study discusses the design aspects for the construction of a microfluidic device for comprehensive spatial two-dimensional liquid chromatography. In spatial two-dimensional liquid chromatography each peak is characterized by its coordinates in the plane. After completing the first-dimension separation all fractions are analyzed in parallel second-dimension separations. Hence, spatial two-dimensional liquid chromatography potentially provides much higher peak-production rates than a coupled column multi-dimensional liquid chromatography approach in which the second-dimension analyses are performed sequentially. A chip for spatial two-dimensional liquid chromatography has been manufactured from cyclic olefin copolymer and features a first-dimension separation channel and 21 parallel second-dimension separation channels oriented perpendicularly to the former. Compartmentalization of first- and second-dimension developments by physical barriers allowed for a preferential flow path with a minimal dispersion into the second-dimension separation channels. To generate a homogenous flow across all the parallel second-dimension channels, a radially interconnected flow distributor containing two zones of diamond-shaped pillars was integrated on-chip. A methacrylate ester based monolithic stationary phase with optimized macroporous structure was created in situ in the confines of the microfluidic chip. In addition, the use of a photomask was explored to localize monolith formation in the parallel second-dimension channels. Finally, to connect the spatial chip to the liquid chromatography instrument, connector ports were integrated allowing the use of Viper fittings. As an alternative, a chip holder with adjustable clasp locks was designed that allows the clamping force to be adjusted. PMID:25598051
Design and evaluation of microfluidic devices for two-dimensional spatial separations.
Davydova, Ekaterina; Wouters, Sam; Deridder, Sander; Desmet, Gert; Eeltink, Sebastiaan; Schoenmakers, Peter J
2016-02-19
Various designs of chips for comprehensive two-dimensional spatial liquid chromatography were investigated. The performance of these chips was initially evaluated using computational fluid dynamics (CFD). A bifurcating distributor with an angle of 140° between branches was implemented in order to achieve a homogeneous velocity field. The cross-sectional area of the channels of the flow distributor was fixed at 0.5×0.5mm, which allows a robust micromilling technique to be used for chip manufacturing. Experiments were performed with chips featuring purposely introduced imperfections in the structure of the bifurcating flow distributor to study its capacity of overcoming potential local clogging. Split peaks were observed when 75% of one of the flow channels was obstructed, in line with the CFD predictions. The main bottlenecks for the performance of the spatial two-dimensional chips were identified, viz. sample injected in the first dimension diverging into the flow distributor and channel discretization (i.e., remixing of first-dimension separation peaks because of finite number of second-dimension channels). Solutions to the former problem were studied by applying a flow resistance in the vertical segments that formed the outlets of the flow distributor and by simulating the presence of constrictions. It was found that a flow resistance of 1.0×10(11)m(-2) reduced the amount of sample diverging into the flow distributor by a factor of 10. The presence of a constriction of 90% of the segment area and 50% of the segment length decreased the diverging flow by a factor of 5. The influence of the linear velocity was significant. Solutions to the channel discretization problem were sought by investigating different designs of spatial two-dimensional chips. PMID:26810803
Quantifying Two-Dimensional Filamentous and Invasive Growth Spatial Patterns in Yeast Colonies
Binder, Benjamin J.; Sundstrom, Joanna F.; Gardner, Jennifer M.; Jiranek, Vladimir; Oliver, Stephen G.
2015-01-01
The top-view, two-dimensional spatial patterning of non-uniform growth in a Saccharomyces cerevisiae yeast colony is considered. Experimental images are processed to obtain data sets that provide spatial information on the cell-area that is occupied by the colony. A method is developed that allows for the analysis of the spatial distribution with three metrics. The growth of the colony is quantified in both the radial direction from the centre of the colony and in the angular direction in a prescribed outer region of the colony. It is shown that during the period of 100200 hours from the start of the growth of the colony there is an increasing amount of non-uniform growth. The statistical framework outlined in this work provides a platform for comparative quantitative assays of strain-specific mechanisms, with potential implementation in inferencing algorithms used for parameter-rate estimation. PMID:25719406
NASA Astrophysics Data System (ADS)
Sakuma, Daisuke; Shinozaki, Tomoya; Nago, Yusuke; Ishiguro, Ryosuke; Kashiwaya, Satoshi; Nomura, Shintaro; Kono, Kimitoshi; Takayanagi, Hideaki
2016-03-01
We developed a two-dimensional array of superconducting quantum interference devices (SQUIDs) for investigation of fine spatial distribution of magnetization in superconducting Sr2 RuO4 . Micrometer-sized SQUIDs based on homogeneously formed Al/AlOx /Al tunnel-type Josephson junctions were fabricated using shadow evaporation technique. Unnecessary electrodes formed by the shadow evaporation were removed by inductively coupled plasma reactive ion etching, in order to realize a dense array of SQUIDs. We measured the magnetic modulation of the maximum Josephson current of each SQUID in the array and evaluated the interaction among the SQUIDs.
Kumar, Manish Joseph, Joby
2014-08-04
We propose a simple and straightforward method to generate spatially variant lattice structures by optical interference lithography method. Using this method, it is possible to independently vary the orientation and period of the two-dimensional lattice. The method consists of two steps which are: numerical synthesis of corresponding phase mask by employing a two-dimensional integrated gradient calculations and experimental implementation of synthesized phase mask by making use of a phase only spatial light modulator in an optical 4f Fourier filtering setup. As a working example, we provide the experimental fabrication of a spatially variant square lattice structure which has the possibility to guide a Gaussian beam through a 90 bend by photonic crystal self-collimation phenomena. The method is digitally reconfigurable, is completely scalable, and could be extended to other kind of lattices as well.
Kim, Young-Cheol; Jang, Sung-Ho; Oh, Se-Jin; Lee, Hyo-Chang; Chung, Chin-Wook
2013-05-15
A real-time measurement method for two-dimensional (2D) spatial distribution of the electron temperature and plasma density was developed. The method is based on the floating harmonic method and the real time measurement is achieved with little plasma perturbation. 2D arrays of the sensors on a 300 mm diameter wafer-shaped printed circuit board with a high speed multiplexer circuit were used. Experiments were performed in an inductive discharge under various external conditions, such as powers, gas pressures, and different gas mixing ratios. The results are consistent with theoretical prediction. Our method can measure the 2D spatial distribution of plasma parameters on a wafer-level in real-time. This method can be applied to plasma diagnostics to improve the plasma uniformity of plasma reactors for plasma processing.
Kim, Young-Cheol; Jang, Sung-Ho; Oh, Se-Jin; Lee, Hyo-Chang; Chung, Chin-Wook
2013-05-01
A real-time measurement method for two-dimensional (2D) spatial distribution of the electron temperature and plasma density was developed. The method is based on the floating harmonic method and the real time measurement is achieved with little plasma perturbation. 2D arrays of the sensors on a 300 mm diameter wafer-shaped printed circuit board with a high speed multiplexer circuit were used. Experiments were performed in an inductive discharge under various external conditions, such as powers, gas pressures, and different gas mixing ratios. The results are consistent with theoretical prediction. Our method can measure the 2D spatial distribution of plasma parameters on a wafer-level in real-time. This method can be applied to plasma diagnostics to improve the plasma uniformity of plasma reactors for plasma processing. PMID:23742549
Yulianti, Yanti; Su'ud, Zaki; Waris, Abdul; Khotimah, S. N.; Shafii, M. Ali
2010-12-23
The research about fast transient and spatially non-homogenous nuclear reactor accident analysis of two-dimensional nuclear reactor has been done. This research is about prediction of reactor behavior is during accident. In the present study, space-time diffusion equation is solved by using direct methods which consider spatial factor in detail during nuclear reactor accident simulation. Set of equations that obtained from full implicit finite-difference discretization method is solved by using iterative methods ADI (Alternating Direct Implicit). The indication of accident is decreasing macroscopic absorption cross-section that results large external reactivity. The power reactor has a peak value before reactor has new balance condition. Changing of temperature reactor produce a negative Doppler feedback reactivity. The reactivity will reduce excess positive reactivity. Temperature reactor during accident is still in below fuel melting point which is in secure condition.
John, S.; Golubentsev, A. )
1995-01-01
For a topological antiferromagnet on a square lattice, with the standard Hartree-Fock, spin-density-wave decoupling of the on-site Hubbard interaction, there is an exact mapping of the low-energy one-electron excitation spectrum to a relativistic Dirac continuum field theory. In this field theory, the Dirac mass gap is precisely the Mott-Hubbard charge gap and the continuum field variable is an eight-component Dirac spinor describing the components of physical electron-spin amplitude on each of the four sites of the elementary plaquette in the original Hubbard model. Within this continuum model we derive explicitly the existence of hedgehog Skyrmion textures as local minima of the classical magnetic energy. These magnetic solitons carry a topological winding number [mu] associated with the vortex rotation of the background magnetic moment field by a phase angle 2[pi][mu] along a path encircling the soliton. Such solitons also carry a spin flux of [mu][pi] through the plaquette on which they are centered. The [mu]=1 hedgehog Skyrmion describes a local transition from the topological (antiperiodic) sector of the one-electron Hilbert space to the nontopological sector. We derive from first principles the existence of deep level localized electronic states within the Mott-Hubbard charge gap for the [mu]=1 and 2 solitons. The spectrum of localized states is symmetric about [ital E]=0 and each subgap electronic level can be occupied by a pair of electrons in which one electron resides primarily on one sublattice and the second electron on the other sublattice. It is suggested that flux-carrying solitons and the subgap electronic structure which they induce are important in understanding the physical behavior of doped Mott insulators.
Interactions of spatial solitons with fused couplers
NASA Astrophysics Data System (ADS)
Harel, Alon; Malomed, Boris A.
2014-04-01
We study dynamical and stationary states of solitons in dual-core waveguides which are locally coupled (fused) at one or several short segments. The model applies to planar optical waveguides, and to Bose-Einstein condensate in dual traps. Collisions of an incident soliton with single and double locally fused couplers are investigated by means of systematic simulations and several analytical methods (quasilinear, fast-soliton, and adiabatic approximations). Excitation dynamics of a soliton trapped by a local coupler is studied by means of the variational approximation, and verified by simulations. Shuttle motion of a soliton trapped in a cavity between two local couplers, and in a finite array of couplers, is studied too.
Impaired spatial selectivity and intact phase precession in two-dimensional virtual reality.
Aghajan, Zahra M; Acharya, Lavanya; Moore, Jason J; Cushman, Jesse D; Vuong, Cliff; Mehta, Mayank R
2015-01-01
During real-world (RW) exploration, rodent hippocampal activity shows robust spatial selectivity, which is hypothesized to be governed largely by distal visual cues, although other sensory-motor cues also contribute. Indeed, hippocampal spatial selectivity is weak in primate and human studies that use only visual cues. To determine the contribution of distal visual cues only, we measured hippocampal activity from body-fixed rodents exploring a two-dimensional virtual reality (VR). Compared to that in RW, spatial selectivity was markedly reduced during random foraging and goal-directed tasks in VR. Instead we found small but significant selectivity to distance traveled. Despite impaired spatial selectivity in VR, most spikes occurred within ?2-s-long hippocampal motifs in both RW and VR that had similar structure, including phase precession within motif fields. Selectivity to space and distance traveled were greatly enhanced in VR tasks with stereotypical trajectories. Thus, distal visual cues alone are insufficient to generate a robust hippocampal rate code for space but are sufficient for a temporal code. PMID:25420065
NASA Astrophysics Data System (ADS)
Foldes, S. T.; Taylor, D. M.
2011-08-01
Paralyzed individuals can control the movement of an assistive device using changes in electroencephalographic (EEG) power resulting from attempted movements. Simultaneous, proportional control of two-dimensional (2D) device movements can be achieved with the concurrent modulation of brain activity that is associated with the attempted movement and rest of two independent body parts. Movement control may be improved by spatial filtering methods that recombine raw EEGs to form new signals with more focused information about the underlying brain activity. This study compared spatial filters offline for improving simultaneous proportional 2D movement commands from EEGs. Filtering options evaluated were common average referencing, Laplacian, independent component analysis, principle component analysis, and two novel ways of applying common spatial pattern (CSP) analysis. CSP analysis is a supervised algorithm that optimally recombines EEGs collected under two known conditions. Both CSP options resulted in more accurate movement prediction than the other filtering options. CSP was particularly advantageous when separating EEGs associated with neighboring or overlapping areas on the motor homunculus. Finally, CSP performed well using smaller subsets of filtered signals, thus making CSP practical and efficient for simultaneous 2D control. A 2D online cursor control example using CSP filtering is included to show CSP's utility.
Multifrequency spatial filtering: A general property of two-dimensional photonic crystals
NASA Astrophysics Data System (ADS)
Serebryannikov, A. E.; Colak, E.; Petrov, A.; Usik, P. V.; Ozbay, E.
2016-01-01
Spatial filtering, an analog of frequency-domain filtering that can be obtained in the incidence angle domain at a fixed frequency is studied in the transmission mode for slabs of two-dimensional rod-type photonic crystals. In the present paper, the emphasis is put on the demonstration of the possibility to obtain various regimes of spatial filtering, i.e., band-stop, band-pass, and low-pass filtering in different frequency ranges in one simple configuration. The operation is based on the use of several Floquet-Bloch modes with appropriate dispersion properties, so that such one or two co-existing mode(s) contribute to the forming of a proper filter characteristic within each specific frequency range. It is shown that high-efficiency transmission and steep switching between pass and stop bands can be obtained in the angle domain for wide ranges of variation of the problem parameters. In particular, by varying the rod-diameter-to-lattice-constant ratio, one attains lots of freedom in the engineering of spatial filters with desired transmission characteristics.
Two-Dimensional Planar Lightwave Circuit Integrated Spatial Filter Array and Method of Use Thereof
NASA Technical Reports Server (NTRS)
Ai, Jun (Inventor); Dimov, Fedor (Inventor)
2015-01-01
A large coherent two-dimensional (2D) spatial filter array (SFA), 30 by 30 or larger, is produced by coupling a 2D planar lightwave circuit (PLC) array with a pair of lenslet arrays at the input and output side. The 2D PLC array is produced by stacking a plurality of chips, each chip with a plural number of straight PLC waveguides. A pupil array is coated onto the focal plane of the lenslet array. The PLC waveguides are produced by deposition of a plural number of silica layers on the silicon wafer, followed by photolithography and reactive ion etching (RIE) processes. A plural number of mode filters are included in the silica-on-silicon waveguide such that the PLC waveguide is transparent to the fundamental mode but higher order modes are attenuated by 40 dB or more. XXXX SEA), 30 by 30 or larger, is produced by coupling a 2D planar lightwave circuit (PLC) array with a pair of lenslet arrays at the input and output side. The 2D PLC array is produced by stacking a plurality of chips, each chip with a plural number of straight PLC waveguides. A pupil array is coated onto the focal plane of the lenslet array. The PLC waveguides are produced by deposition of a plural number of silica layers on the silicon wafer, followed by photolithography and reactive ion etching (RIE) processes. A plural number of mode filters are included in the silica-on-silicon waveguide such that the PLC waveguide is transparent to the fundamental mode but higher order modes are attenuated by 40 dB or more. The present invention, ideal for controlling optical wavefronts, comprises a two-dimensional (2-D) array of planar optical waveguides (forming a planar lightwave circuit, or PLC) flanked by two microlens arrays. The PLC array portion of the present invention is assembled to have hexagonal grid geometry so as to optimize the fill factor and optical throughput. All waveguides are precisely positioned by photolithography to precision align to the two microlens arrays. One embodiment of the invention comprises an optical spatial filter array as a two dimensional planar lightwave circuit array, and first and second microlens arrays; the planar light waves circuit array is coupled to the first and second microlens arrays at an inlet and outlet respectively. The planar lightwave circuit array has a plurality of vertically stacked silicon wafer chips with each of the chips having a plurality of straight planar lightwave circuit waveguides. The planar lightwave circuit array may have a hexagonal grid geometry and maintains a spatial and temporal coherency of the transported light. The invention further involves a method of assembling an optical spatial filters array that includes the steps of preparing a plurality of chips from a silicon wafer, forming a plurality of straight planar lightwave circuit waveguides on each said chip to form a waveguide array of about a 30 by 30 array stacking a plurality of said chips and coupling a lenslet array at each of the inlet and the outlet of said waveguide array. The present invention, as disclosed in detail herein, is
Beamforming of sound from two-dimensional arrays using spatial matched filters.
Yen, Jesse T
2013-11-01
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
Beamforming of sound from two-dimensional arrays using spatial matched filters
Yen, Jesse T.
2013-01-01
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
ERIC Educational Resources Information Center
Price, Aaron; Lee, Hee-Sun
2010-01-01
We investigated whether and how student performance on three types of spatial cognition tasks differs when worked with two-dimensional or stereoscopic representations. We recruited nineteen middle school students visiting a planetarium in a large Midwestern American city and analyzed their performance on a series of spatial cognition tasks in
ERIC Educational Resources Information Center
Price, Aaron; Lee, Hee-Sun
2010-01-01
We investigated whether and how student performance on three types of spatial cognition tasks differs when worked with two-dimensional or stereoscopic representations. We recruited nineteen middle school students visiting a planetarium in a large Midwestern American city and analyzed their performance on a series of spatial cognition tasks in…
Two-dimensional radiative transfer in cloudy atmospheres: The spherical harmonic spatial grid method
Evans, K.F. )
1993-09-15
A new two-dimensional monochromatic method that computes the transfer of solar or thermal radiation through atmospheres with arbitrary optical properties is described. The model discretizes the radiative transfer equation by expanding the angular part of the radiance field in a spherical harmonic series and representing the spatial part with a discrete grid. The resulting sparse coupled system of equations is solved iteratively with the conjugate gradient method. A Monte Carlo model is used for extensive verification of outgoing flux and radiance values from both smooth and highly variable (multifractal) media. The spherical harmonic expansion naturally allows for different levels of approximation, but tests show that the 2D equivalent of the two-stream approximation is poor at approximating variations in the outgoing flux. The model developed here is shown to be highly efficient so that media with tens of thousands of grid points can be computed in minutes. The large improvement in efficiency will permit quick, accurate radiative transfer calculations of realistic cloud fields and improve our understanding of the effect of inhomogeneity on radiative transfer in cloudy atmospheres. 21 refs., 7 figs., 3 tabs.
NASA Technical Reports Server (NTRS)
Evans, K. F.
1993-01-01
A new two-dimensional monochromatic method that computes the transfer of solar or thermal radiation through atmospheres with arbitrary optical properties is described. The model discretizes the radiative transfer equation by expanding the angular part of the radiance field in a spherical harmonic series and representing the spatial part with a discrete grid. The resulting sparse coupled system of equations is solved iteratively with the conjugate gradient method. A Monte Carlo model is used for extensive verification of outgoing flux and radiance values from both smooth and highly variable (multifractal) media. The spherical harmonic expansion naturally allows for different levels of approximation, but tests show that the 2D equivalent of the two-stream approximation is poor at approximating variations in the outgoing flux. The model developed here is shown to be highly efficient so that media with tens of thousands of grid points can be computed in minutes. The large improvement in efficiency will permit quick, accurate radiative transfer calculations of realistic cloud fields and improve our understanding of the effect of inhomogeneity on radiative transfer in cloudy atmospheres.
Generation and dynamics of quadratic birefringent spatial gap solitons
Anghel-Vasilescu, P.; Dorignac, J.; Geniet, F.; Leon, J.; Taki, A.
2011-04-15
A method is proposed to generate and study the dynamics of spatial light solitons in a birefringent medium with quadratic nonlinearity. Although no analytical expression for propagating solitons has been obtained, our numerical simulations show the existence of stable localized spatial solitons in the frequency forbidden band gap of the medium. The dynamics of these objects is quite rich and manifests for instance elastic reflections, or inelastic collisions where two solitons merge and propagate as a single solitary wave. We derive the dynamics of the slowly varying envelopes of the three fields (second harmonic pump and two-component signal) and study this new system theoretically. We show that it does present a threshold for nonlinear supratransmission that can be calculated from a series expansion approach with a very high accuracy. Specific physical implications of our theoretical predictions are illustrated on LiGaTe{sub 2} (LGT) crystals. Once irradiated by a cw laser beam of 10 {mu}m wavelength, at an incidence beyond the extinction angle, such crystals will transmit light, in the form of spatial solitons generated in the nonlinear regime above the nonlinear supratransmission threshold.
Micrometric spatial control of rare earth ion emission in LiNbO3: A two-dimensional multicolor array
NASA Astrophysics Data System (ADS)
Molina, P.; Ramrez, M. O.; Garca-Santizo, J. V.; lvarez-Garca, S.; Pazik, R.; Strek, W.; Dere?, P. J.; Baus, L. E.
2009-08-01
We report on the preparation and optical characterization of a two-dimensional multicolor emission arrangement obtained by embedding high refractive-index Er3+ doped CaTiO3 nanoparticles into a Nd3+ doped LiNbO3 crystal substrate prepatterned with an array of microvoids. By controlling the spatial location of the rare earth ions at the micrometer scale, we show the possibility of simultaneous spatial and spectral control of the spontaneous emission in a two-dimensional rare earth optically activated array. The results can be useful for the development of microcomposite rare earth based photonic devices, such as multicolor emission displays or pixelated color structures.
Oh, Se-Jin; Kim, Young-Chul; Chung, Chin-Wook
2011-02-15
An interpolation algorithm for the evaluation of the spatial profile of plasma densities in a cylindrical reactor was developed for low gas pressures. The algorithm is based on a collisionless two-dimensional fluid model. Contrary to the collisional case, i.e., diffusion fluid model, the fitting algorithm depends on the aspect ratio of the cylindrical reactor. The spatial density profile of the collisionless fitting algorithm is presented in two-dimensional images and compared with the results of the diffusion fluid model.
Mighty morphing spatial solitons and bullets.
Snyder, A W; Mitchell, J D
1997-01-01
We give what we believe to be the first closed-form exact expression for the dynamic evolution of nonstationary beams of arbitrary intensity and width propagating in a uniform nonlinear medium and in both two and three dimensions. This shows that periodic and quasi-periodic (nonradiating) beams can exist in a non-Kerr nonlinear medium. The Schrdinger equation is solved for Gaussian beams in a saturable medium. For one critical (initial) beam width, the Gaussian is a stable stationary soliton or bullet, independent of its intensity; otherwise, it breathes. New quasi-periodic beams (mighty morphing solitons) and bullets (mighty morphs) of elliptical cross section also exist whose ellipticity changes with propagation. PMID:18183088
Xuemin Ye; Chunxi Li; Weiping Yan
2002-07-01
The linear spatial evolution formulation of the two-dimensional waves of the evaporating or isothermal or condensing liquid films falling down an inclined wall is established for the film thickness with the collocation method based on the boundary layer theory and complete boundary conditions. The evolution equation indicates that there are two different modes of waves in spatial evolution. And the flow stability is highly dependent on the evaporation or condensation, thermo-capillarity, surface tension, inclination angle and Reynolds number. (authors)
Soliton Gyroscopes in Media with Spatially Growing Repulsive Nonlinearity
NASA Astrophysics Data System (ADS)
Driben, Rodislav; Kartashov, Yaroslav V.; Malomed, Boris A.; Meier, Torsten; Torner, Lluis
2014-01-01
We find that the recently introduced model of self-trapping supported by a spatially growing strength of a repulsive nonlinearity gives rise to robust vortex-soliton tori, i.e., three-dimensional vortex solitons, with topological charges S?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.
Soliton gyroscopes in media with spatially growing repulsive nonlinearity.
Driben, Rodislav; Kartashov, Yaroslav V; Malomed, Boris A; Meier, Torsten; Torner, Lluis
2014-01-17
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
Splitting broad beams into arrays of dissipative spatial solitons by material and virtual gratings
NASA Astrophysics Data System (ADS)
He, Y. J.; Malomed, B. A.; Ye, F.; Dong, J.; Qiu, Z.; Wang, H. Z.; Hu, B.
2010-12-01
We elaborate two generic methods for producing two-dimensional (2D) spatial soliton arrays (SSAs) in the framework of the cubic-quintic (CQ) complex Ginzburg-Landau (CGL) model. The first approach deals with a broad beam launched into the dissipative nonlinear medium which is equipped with an imprinted grating of a sufficiently sharp form. The beam splits into a cluster of jets, each subsequently self-trapping into a stable soliton, if the power is sufficient. We consider two kinds of sharp gratings'raised-cosine' (RC) and Kronig-Penney (KP) latticesand two types of input beams: fundamental and vortical. By selecting appropriate parameters, this method makes it possible to create various types of soliton arrays, such as solid, annular (with single and double rings) and cross-shaped ones. The second method uses a 'virtual lattice', in the form of a periodic transverse phase modulation imprinted into the broad beam which is passed through an appropriate phase mask and then shone into a uniform nonlinear medium. Two different types of masks are considered; in the form of a 'checkerboard' or 'tilings'. In these cases, broad fundamental and vortical beams may also evolve into stable SSAs if the beam power and spacing of the virtual phase lattice are large enough. By means of the latter technique, square-shaped, hexagonal and quasi-crystalline SSAs can be created.
Multiwavelength and multicolor temporal and spatial optical solitons
NASA Astrophysics Data System (ADS)
Kivshar, Yuri S.; Sukhorukov, Andrey A.; Ostrovskaya, Elena A.; Bang, Ole; Clausen, Carl B.
2000-04-01
We present an overview of several novel types of multi- component envelope solitary waves that appear in fiber and waveguide nonlinear optics. In particular, we describe multi-channel solitary waves in bit-parallel-wavelength fiber transmission systems for high performance computer networks, multi-color parametric spatial solitary waves due to cascaded nonlinearities of quadratic materials, and quasiperiodic envelope solitons in Fibonacci optical superlattices.
Rychel, Amanda L.; Garrick, Jacqueline M.; Kawaguchi, Masayoshi; Peterson, Kylee M.; Torii, Keiko U.
2015-01-01
Stomata, valves on the plant epidermis, are critical for plant growth and survival, and the presence of stomata impacts the global water and carbon cycle. Although transcription factors and cell-cell signaling components regulating stomatal development have been identified, it remains unclear as to how their regulatory interactions are translated into two-dimensional patterns of stomatal initial cells. Using molecular genetics, imaging, and mathematical simulation, we report a regulatory circuit that initiates the stomatal cell-lineage. The circuit includes a positive feedback loop constituting self-activation of SCREAMs that requires SPEECHLESS. This transcription factor module directly binds to the promoters and activates a secreted signal, EPIDERMAL PATTERNING FACTOR2, and the receptor modifier TOO MANY MOUTHS, while the receptor ERECTA lies outside of this module. This in turn inhibits SPCH, and hence SCRMs, thus constituting a negative feedback loop. Our mathematical model accurately predicts all known stomatal phenotypes with the inclusion of two additional components to the circuit: an EPF2-independent negative-feedback loop and a signal that lies outside of the SPCHSCRM module. Our work reveals the intricate molecular framework governing self-organizing two-dimensional patterning in the plant epidermis. PMID:26203655
Mixing regimes in a spatially confined, two-dimensional, supersonic shear layer
NASA Astrophysics Data System (ADS)
Vuillermoz, P.; Oran, E. S.
1992-07-01
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.
Mancoff, F.B.; Zielinski, L.J.; Marcus, C.M.; Campman, K.; Gossard, A.C.
1996-03-01
We report measurements of transport in a two-dimensional electron gas in a spatially random magnetic field in which the average magnetic field extends from the classical regime {l_angle}{omega}{sub {ital c}}{r_angle}{tau}{lt}1 into the quantum Hall regime. Experiments make use of a rough Nd-Fe-B permanent magnet on the surface of a GaAs heterostructure. Effective mass, transport and total scattering times, and {ital g}-factor-enhancement values (all measured from Shubnikov{endash}de Haas oscillations) are comparable to those found for potential scattering in a uniform magnetic field. {copyright} {ital 1996 The American Physical Society.}
Spatial solitons under competing linear and nonlinear diffractions
NASA Astrophysics Data System (ADS)
Shen, Y.; Kevrekidis, P. G.; Whitaker, N.; Malomed, Boris A.
2012-02-01
We introduce a general model which augments the one-dimensional nonlinear Schrdinger (NLS) equation by nonlinear-diffraction terms competing with the linear diffraction. The new terms contain two irreducible parameters and admit a Hamiltonian representation in a form natural for optical media. The equation serves as a model for spatial solitons near the supercollimation point in nonlinear photonic crystals. In the framework of this model, a detailed analysis of the fundamental solitary waves is reported, including the variational approximation (VA), exact analytical results, and systematic numerical computations. The Vakhitov-Kolokolov (VK) criterion is used to precisely predict the stability border for the solitons, which is found in an exact analytical form, along with the largest total power (norm) that the waves may possess. Past a critical point, collapse effects are observed, caused by suitable perturbations. Interactions between two identical parallel solitary beams are explored by dint of direct numerical simulations. It is found that in-phase solitons merge into robust or collapsing pulsons, depending on the strength of the nonlinear diffraction.
NASA Astrophysics Data System (ADS)
Jameson, A. R.; Larsen, M. L.
2016-02-01
Microphysical understanding of the variability in rain requires a statistical characterization of different drop sizes both in time and in all dimensions of space. Temporally, there have been several statistical characterizations of raindrop counts. However, temporal and spatial structures are neither equivalent nor readily translatable. While there are recent reports of the one-dimensional spatial correlation functions in rain, they can only be assumed to represent the two-dimensional (2D) correlation function under the assumption of spatial isotropy. To date, however, there are no actual observations of the (2D) spatial correlation function in rain over areas. Two reasons for this deficiency are the fiscal and the physical impossibilities of assembling a dense network of instruments over even hundreds of meters much less over kilometers. Consequently, all measurements over areas will necessarily be sparsely sampled. A dense network of data must then be estimated using interpolations from the available observations. In this work, a network of 19 optical disdrometers over a 100 m by 71 m area yield observations of drop spectra every minute. These are then interpolated to a 1 m resolution grid. Fourier techniques then yield estimates of the 2D spatial correlation functions. Preliminary examples using this technique found that steadier, light rain decorrelates spatially faster than does the convective rain, but in both cases the 2D spatial correlation functions are anisotropic, reflecting an asymmetry in the physical processes influencing the rain reaching the ground not accounted for in numerical microphysical models.
Metamaterials for Remote Generation of Spatially Controllable Two Dimensional Array of Microplasma
Singh, Pramod K.; Hopwood, Jeffrey; Sonkusale, Sameer
2014-01-01
Since the initial demonstration of negative refraction and cloaking using metamaterials, there has been enormous interest and progress in making practical devices based on metamaterials such as electrically small antennas, absorbers, modulators, detectors etc that span over a wide range of electromagnetic spectrum covering microwave, terahertz, infrared (IR) and optical wavelengths. We present metamaterial as an active substrate where each unit cell serves as an element for generation of plasma, the fourth state of matter. Sub-wavelength localization of incident electromagnetic wave energy, one of the most interesting properties of metamaterials is employed here for generating high electric field to ignite and sustain microscale plasmas. Frequency selective nature of the metamaterial unit cells make it possible to generate spatially localized microplasma in a large array using multiple resonators. A dual resonator topology is shown for the demonstration. Since microwave energy couples to the metamaterial through free space, the proposed approach is naturally wireless. Such spatially controllable microplasma arrays provide a fundamentally new material system for future investigations in novel applications, e.g. nonlinear metamaterials. PMID:25098976
Metamaterials for remote generation of spatially controllable two dimensional array of microplasma.
Singh, Pramod K; Hopwood, Jeffrey; Sonkusale, Sameer
2014-01-01
Since the initial demonstration of negative refraction and cloaking using metamaterials, there has been enormous interest and progress in making practical devices based on metamaterials such as electrically small antennas, absorbers, modulators, detectors etc that span over a wide range of electromagnetic spectrum covering microwave, terahertz, infrared (IR) and optical wavelengths. We present metamaterial as an active substrate where each unit cell serves as an element for generation of plasma, the fourth state of matter. Sub-wavelength localization of incident electromagnetic wave energy, one of the most interesting properties of metamaterials is employed here for generating high electric field to ignite and sustain microscale plasmas. Frequency selective nature of the metamaterial unit cells make it possible to generate spatially localized microplasma in a large array using multiple resonators. A dual resonator topology is shown for the demonstration. Since microwave energy couples to the metamaterial through free space, the proposed approach is naturally wireless. Such spatially controllable microplasma arrays provide a fundamentally new material system for future investigations in novel applications, e.g. nonlinear metamaterials. PMID:25098976
Ceolin, D.; Chaplier, G.; Lemonnier, M.; Garcia, G.A.; Miron, C.; Nahon, L.; Simon, M.; Leclercq, N.; Morin, P.
2005-04-01
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 {mu}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.
Spatially-Resolved Modeling of Spin and Valley Hall Effects in Two-Dimensional Semiconductors
NASA Astrophysics Data System (ADS)
Lenferink, E. J.; Jia, Y.; Stern, N. P.
2015-03-01
In monolayers of transition metal dichalcogenides (1L-TMDs), a valley degree of freedom emerges for charge carriers due to the absence of spatial inversion symmetry. Strong spin-orbit interaction couples spin and valley, resulting in correlated spin, valley, and charge transport such as transverse Hall effects. Spatially-resolved measurements of these Hall effects have recently been achieved in monolayer MoS2, necessitating a detailed picture for understanding transport and relaxation mechanisms in 1L-TMDs that considers carrier, valley, and spin motion and generation processes. Here, we study spin and valley Hall effects in 1L-TMD devices by simulating the transport of spin- and valley-polarized carriers with a generalized drift diffusion model incorporating circularly polarized optical excitation. Spin and valley accumulation and the transverse voltage are analyzed in different device geometries. We compare the electron and hole contributions to the transverse voltage and discuss the potential for a measurement of the valley relaxation times of free carriers in 1L-TMDs. This work was supported by the Institute for Sustainability and Energy at Northwestern and the U.S. Department of Energy (DE-SC0012130). N.P.S. acknowledges support as an Alfred P. Sloan Research Fellow.
Instabilities in two-dimensional spatially periodic flows. Part I: Kolmogorov flow
Thess, A. )
1992-07-01
The linear stability of the parallel flow {psi}{sub 0}=sin({ital y}) (Kolmogorov flow) is considered, taking into account viscosity, linear friction, and confinement (lateral walls). The computations provide neutral stability curves in the parameter space, wave numbers, and wave speeds, as well as the spatial structure of first unstable modes. Evidence is presented that stability parameters depend nonuniformly on the confinement. It is shown that already weak transverse confinement significantly decreases the longitudinal wavelength of perturbations at instability onset. Strong confinement changes the character of the instability into an oscillatory one instead of a purely exponential growing mode, which is obtained for weakly confined systems. Theoretical predictions of critical parameters are in reasonable agreement with experimental results in electromagnetically driven flows of conducting fluids.
Two-dimensional spatial manipulation of microparticles in continuous flows in acoustofluidic systems
Gao, Lu; Wyatt Shields, C.; Johnson, Leah M.; Graves, Steven W.; Yellen, Benjamin B.; Lpez, Gabriel P.
2015-01-01
We report a modeling and experimental study of techniques to acoustically focus particles flowing through a microfluidic channel. Our theoretical model differs from prior works in that we solve an approximate 2-D wave transmission model that accounts for wave propagation in both the solid and fluid phases. Our simulations indicate that particles can be effectively focused at driving frequencies as high as 10% off of the resonant condition. This conclusion is supported by experiments on the acoustic focusing of particles in nearly square microchannels, which are studied for different flow rates, driving frequencies and placements of the lead zirconate titanate transducer, either underneath the microchannel or underneath a parallel trough. The relative acoustic potential energy and the resultant velocity fields for particles with positive acoustic contrast coefficients are estimated in the 2-D limit. Confocal microscopy was used to observe the spatial distribution of the flowing microparticles in three dimensions. Through these studies, we show that a single driving frequency from a single piezoelectric actuator can induce the 2-D concentration of particles in a microchannel with a nearly square cross section, and we correlate these behaviors with theoretical predictions. We also show that it is possible to control the extent of focusing of the microparticles, and that it is possible to decouple the focusing of microparticles in the vertical direction from the lateral direction in rectangular channels with anisotropic cross sections. This study provides guidelines to design and operate microchip-based acoustofluidic devices for precise control over the spatial arrangement of microparticles for applications such as flow cytometry and cellular sorting. PMID:25713687
Spatial Patterns of Dissipative Polariton Solitons in Semiconductor Microcavities.
Chana, J K; Sich, M; 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
2015-12-18
We report propagating bound microcavity polariton soliton arrays consisting of multipeak structures either along (x) or perpendicular (y) to the direction of propagation. Soliton arrays of up to five solitons are observed, with the number of solitons controlled by the size and power of the triggering laser pulse. The breakup along the x direction occurs when the effective area of the trigger pulse exceeds the characteristic soliton size determined by polariton-polariton interactions. Narrowing of soliton emission in energy-momentum space indicates phase locking between adjacent solitons, consistent with numerical modeling which predicts stable multihump soliton solutions. In the y direction, the breakup originates from inhomogeneity across the wave front in the transverse direction which develops into a stable array only in the solitonic regime via phase-dependent interactions of propagating fronts. PMID:26722931
Spatial Patterns of Dissipative Polariton Solitons in Semiconductor Microcavities
NASA Astrophysics Data System (ADS)
Chana, J. K.; Sich, M.; Fras, F.; Gorbach, A. V.; Skryabin, D. V.; Cancellieri, E.; Cerda-Mndez, E. A.; Biermann, K.; Hey, R.; Santos, P. V.; Skolnick, M. S.; Krizhanovskii, D. N.
2015-12-01
We report propagating bound microcavity polariton soliton arrays consisting of multipeak structures either along (x ) or perpendicular (y ) to the direction of propagation. Soliton arrays of up to five solitons are observed, with the number of solitons controlled by the size and power of the triggering laser pulse. The breakup along the x direction occurs when the effective area of the trigger pulse exceeds the characteristic soliton size determined by polariton-polariton interactions. Narrowing of soliton emission in energy-momentum space indicates phase locking between adjacent solitons, consistent with numerical modeling which predicts stable multihump soliton solutions. In the y direction, the breakup originates from inhomogeneity across the wave front in the transverse direction which develops into a stable array only in the solitonic regime via phase-dependent interactions of propagating fronts.
Percolation in spatial evolutionary prisoner's dilemma game on two-dimensional lattices
NASA Astrophysics Data System (ADS)
Choi, Woosik; Yook, Soon-Hyung; Kim, Yup
2015-11-01
We study the spatial evolutionary prisoner's dilemma game with updates of imitation max on triangular, hexagonal, and square lattices. We use the weak prisoner's dilemma game with a single parameter b . Due to the competition between the temptation value b and the coordination number z of the base lattice, a greater variety of percolation properties is expected to occur on the lattice with the larger z . From the numerical analysis, we find six different regimes on the triangular lattice (z =6 ). Regardless of the initial densities of cooperators and defectors, cooperators always percolate in the steady state in two regimes for small b . In these two regimes, defectors do not percolate. In two regimes for the intermediate value of b , both cooperators and defectors undergo percolation transitions. The defector always percolates in two regimes for large b . On the hexagonal lattice (z =3 ), there exist two distinctive regimes. For small b , both the cooperators and the defectors undergo percolation transitions while only defectors always percolate for large b . On the square lattice (z =4 ), there exist three regimes. Combining with the finite-size scaling analyses, we show that all the observed percolation transitions belong to the universality class of the random percolation. We also show how the detailed growth mechanism of cooperator and defector clusters decides each regime.
NASA Astrophysics Data System (ADS)
Li, H. Harold; Driewer, Joseph P.; Han, Zhaohui; Low, Daniel A.; Yang, Deshan; Xiao, Zhiyan
2014-04-01
Recent research has shown that KCl:Eu2+ has great potential for use in megavoltage radiation therapy dosimetry because this material exhibits excellent storage performance and is reusable due to strong radiation hardness. This work reports the authors attempts to fabricate 2D KCl:Eu2+ storage phosphor films (SPFs) using both a physical vapor deposition (PVD) method and a tape casting method. X-ray diffraction analysis showed that a 10 m 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 m thick casted KCl:Eu2+ SPF showed sub-millimeter spatial-resolution. Monte Carlo simulations further demonstrated that the admixture of 20% KCl:Eu2+ and 80% low Z polymer binder exhibited almost no energy-dependence in a 6 MV beam. KCl:Eu2+ pellet samples showed a large dynamic range from 0.01 cGy to 60 Gy dose-to-water, and saturated at approximately 500 Gy as a result of KCl's intrinsic high radiation hardness. Taken together, this work provides strong evidence that KCl:Eu2+-based SPF with associated readout apparatus could result in a novel electronic film system that has all the desirable features associated with classic radiographic film and, importantly, water equivalence and the capability of permanent identification of each detector.
Li, H Harold; Driewer, Joseph P; Han, Zhaohui; Low, Daniel A; Yang, Deshan; Xiao, Zhiyan
2014-04-21
Recent research has shown that KCl:Eu? 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:Eu? 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 m 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 Eu? cations acted as luminescence centers in the photostimulation process. The 150 m thick casted KCl:Eu? SPF showed sub-millimeter spatial-resolution. Monte Carlo simulations further demonstrated that the admixture of 20% KCl:Eu? and 80% low Z polymer binder exhibited almost no energy-dependence in a 6 MV beam. KCl:Eu? 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:Eu?-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
Tian, Peifang; Devor, Anna; Sakadi?, Sava; Dale, Anders M.; Boas, David A.
2011-01-01
Absorption or fluorescence-based two-dimensional (2-D) optical imaging is widely employed in functional brain imaging. The image is a weighted sum of the real signal from the tissue at different depths. This weighting function is defined as depth sensitivity. Characterizing depth sensitivity and spatial resolution is important to better interpret the functional imaging data. However, due to light scattering and absorption in biological tissues, our knowledge of these is incomplete. We use Monte Carlo simulations to carry out a systematic study of spatial resolution and depth sensitivity for 2-D optical imaging methods with configurations typically encountered in functional brain imaging. We found the following: (i) the spatial resolution is <200 ?m for NA ?0.2 or focal plane depth ?300 ?m. (ii) More than 97% of the signal comes from the top 500 ?m of the tissue. (iii) For activated columns with lateral size larger than spatial resolution, changing numerical aperature (NA) and focal plane depth does not affect depth sensitivity. (iv) For either smaller columns or large columns covered by surface vessels, increasing NA and?or focal plane depth may improve depth sensitivity at deeper layers. Our results provide valuable guidance for the optimization of optical imaging systems and data interpretation. PMID:21280912
Mei, Chang-Sheng; Panych, Lawrence P; Yuan, Jing; McDannold, Nathan J; Treat, Lisa H; Jing, Yun; Madore, Bruno
2011-07-01
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-dimensional spatially 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 1C, while maintaining accurate temperature measurements (mean difference between measurements, as observed in gel = 0.1C 0.6; R = 0.98; P > 0.05). PMID:21337421
Spatiotemporal electromagnetic soliton and spatial ring formation in nonlinear metamaterials
Zhang Jinggui; Wen Shuangchun; Xiang Yuanjiang; Wang Youwen; Luo Hailu
2010-02-15
We present a systematic investigation of ultrashort electromagnetic pulse propagation in metamaterials (MMs) with simultaneous cubic electric and magnetic nonlinearity. We predict that spatiotemporal electromagnetic solitons may exist in the positive-index region of a MM with focusing nonlinearity and anomalous group velocity dispersion (GVD), as well as in the negative-index region of the MM with defocusing nonlinearity and normal GVD. The experimental circumstances for generating and manipulating spatiotemporal electromagnetic solitons can be created by elaborating appropriate MMs. In addition, we find that, in the negative-index region of a MM, a spatial ring may be formed as the electromagnetic pulse propagates for focusing nonlinearity and anomalous GVD; while the phenomenon of temporal splitting of the electromagnetic pulse may appear for the same case except for the defocusing nonlinearity. Finally, we demonstrate that the nonlinear magnetization makes the sign of effective electric nonlinear effect switchable due to the combined action of electric and magnetic nonlinearity, exerting a significant influence on the propagation of electromagnetic pulses.
Nonlocal gray solitons in parity-time-symmetric potentials with spatially modulated nonlinearity
NASA Astrophysics Data System (ADS)
Zhu, Xing; Shi, Zhiwei; Li, Huagang
2015-11-01
We investigate the nonlocal gray solitons in parity-time (PT)-symmetric potentials with spatially modulated nonlinearity. If the nonlinear modulated function (nonlinear potential) is real, the coefficient of the function can control the grayness and the existence domain of these gray solitons. Especially, if the coefficient of the nonlinear modulated function is below a threshold, the gray solitons will be changed into anti-dark solitons. The effects of the degree of the nonlocality and the imaginary part of the PT-symmetric potentials on the grayness and the existence of the gray solitons are also discussed. If the nonlinear modulated function is also PT symmetric, the imaginary part of the function will obviously affect the existence and stability of the nonlocal gray solitons.
Spatial shifts of colliding dark solitons in deformed non-linear Schrdinger models
NASA Astrophysics Data System (ADS)
Blas, Harold; Zambrano, Marcos
2015-07-01
We derive a closed expression for the spatial shift experienced by a black soliton colliding with a shallow dark soliton in the context of deformed nonlinear Schrdinger (NLS) models. A perturbative scheme is developed based on the expansion parameter 1/(? v)\\ll 1, where v is the velocity of the incoming shallow dark soliton, ? \\equiv 1/\\sqrt{1-{v}2{/v}s2} and vs is the Bogoliubov sound speed, therefore it is not restricted to small deformations of the integrable NLS model. As applications of our formalism we consider the integrable NLS model and the non-integrable cubic-quintic NLS model with non-vanishing boundary conditions. Extensive numerical simulations are performed in order to verify our results. A variant of the analysis for gray-gray soliton collision is discussed regarding a fast broad soliton and a slow thin soliton.
Saulitis, Yu.B.; Liepin'sh, E.E.; Sekatsis, I.P.; Shenderovich, M.D.; Mutulis, F.K.; Mutule, I.E.; Chipens, G.I.
1986-06-01
Assignment of the /sup 1/H NMR signals of (cyclo(9 ..-->.. 1/sup epsilon/), Lys/sup 1/, Gly/sup 6/)bradykinin (CBK) in (CD/sub 3/)/sub 2/SO and H/sub 2/O has been made by the combined analysis of two-dimensional COSY and NOESY spectra. It has been shown that in (CD/sub 3/)/sub 2/SO solution there are two slowly interchanging conformers of CBK; the amount of the minor conformer does not exceed 15%. In aqueous solution the minor conformer is absent, and the chemical shifts of the NH and Csup..cap alpha..H protons of CBK and of the natural peptide differ insignificantly. Models are proposed of the spatial structure of the backbone of fragments 6-9 of CBK, which contain two intramolecular hydrogen bonds with the participation of the NH group of the Arg/sup 9/ residue, the N/sup zeta/H group of the Lys/sup 1/ residue, and the carbonyl groups of the Phe/sup 5/ and Gly/sup 6/ residues
Latini, M; Schilling, O; Don, W
2006-03-16
Finite-difference weighted essentially non-oscillatory (WENO) simulations of the reshocked two-dimensional single-mode Richtmyer-Meshkov instability using third-, fifth- and ninth-order spatial flux reconstruction and uniform spatial grid resolutions corresponding to 128, 256 and 512 points per initial perturbation wavelength are presented. The dependence of the density, vorticity, simulated density Schlieren and baroclinic production fields, mixing layer width, circulation deposition, mixing profiles, chemical products and mixing fractions, energy spectra, statistics, probability distribution functions, effective turbulent kinetic energy and enstrophy production/dissipation rates, numerical Reynolds numbers, and effective numerical viscosity on the order and resolution is comprehensively investigated to long evolution times. The results are interpreted using the computed implicit numerical diffusion arising from the truncation errors in the characteristic projection-based WENO method. It is quantitatively shown that simulations with higher order and higher resolution have lower numerical dissipation. The sensitivity of the quantities considered to the order and resolution is further amplified following reshock, when the energy deposition on the evolving interface by the second shock-interface interaction induces the formation of small-scale structures. Simulations using lower orders of reconstruction and on coarser grids preserve large-scale structures and flow symmetry to late times, while simulations using higher orders of reconstruction and on finer grids exhibit fragmentation of the structures, symmetry breaking and increased mixing. The investigation demonstrates that similar flow features are qualitatively and quantitatively captured by either approximately doubling the order or the resolution. Additionally, the computational scaling shows that increasing the order is more advantageous than doubling the resolution for the complex shock-driven hydrodynamic flow and WENO method considered here. The present investigation suggests that the ninth-order WENO method is well-suited for the simulation and analysis of complex multi-scale flows and mixing generated by shock-induced hydrodynamic instabilities.
Latini, M; Schilling, O; Don, W S
2006-06-12
Weighted essentially non-oscillatory (WENO) simulations of the reshocked two-dimensional single-mode Richtmyer-Meshkov instability using third-, fifth- and ninth-order spatial flux reconstruction and uniform grid resolutions corresponding to 128, 256 and 512 points per initial perturbation wavelength are presented. The dependence of the density, vorticity, simulated density Schlieren and baroclinic production fields, mixing layer width, circulation deposition, mixing profiles, production and mixing fractions, energy spectra, statistics, probability distribution functions, numerical turbulent kinetic energy and enstrophy production/dissipation rates, numerical Reynolds numbers, and numerical viscosity on the order and resolution is investigated to long evolution times. The results are interpreted using the implicit numerical dissipation in the characteristic projection-based, finite-difference WENO method. It is shown that higher order higher resolution simulations have lower numerical dissipation. The sensitivity of the quantities considered to the order and resolution is further amplified following reshock, when the energy deposition by the second shock-interface interaction induces the formation of small-scale structures. Lower-order lower-resolution simulations preserve large-scale structures and flow symmetry to late times, while higher-order higher-resolution simulations exhibit fragmentation of the structures, symmetry breaking and increased mixing. Similar flow features are qualitatively and quantitatively captured by either approximately doubling the order or the resolution. Additionally, the computational scaling shows that increasing the order is more advantageous than increasing the resolution for the flow considered here. The present investigation suggests that the ninth-order WENO method is well-suited for the simulation and analysis of complex multi-scale flows and mixing generated by shock-induced hydrodynamic instabilities.
Petrov, V. A. Nikitin, A. V.
2006-08-15
Effects of recurrence and multiplication in the spatial distribution of the probability-flux density j{sub x}(x, z) (or the quantum-mechanical current density ej{sub x}(x, z), where e is the elementary charge), which arise from electron-wave interference in two-dimensional semiconductor nanostructures, are analyzed, and the possibility of controlling these effects by the application of a dc transverse electric field is examined. A type of nanostructure represented by two rectangular quantum wells (a wide one and a narrow one) whose widths are measured in the direction of the z axis (the quantum-confinement axis) with the wells arranged sequentially in the direction of propagation of the electron wave (the x axis) is considered. It is shown that, for an electron wave entering the wide well from the narrow well, the initial transverse distribution peak j{sub x}(0, z) is reproduced with some accuracy at distances X{sub p} = pX{sub 1} (recurrence) and, in nanostructures symmetric along the z axis, splits at distances X{sub 1}/q into q identical peaks of magnitude reduced by a factor of q (multiplication) (here, p and q are integers). It is demonstrated that these effects can be controlled by a dc electric field applied in the transverse direction (along the z axis) in the region of the wide quantum well. A reduction in the effective well width and appearance of asymmetry in the transverse potential profile upon application of the electric field cause a radical change in the j{sub x}(x, z) distribution in this quantum well and make possible inverse population of the quantum-confinement subbands.
Two-component vector solitons in defocusing Kerr-type media with spatially modulated nonlinearity
Zhong, Wei-Ping; Belić, Milivoj
2014-12-15
We present a class of exact solutions to the coupled (2+1)-dimensional nonlinear Schrödinger equation with spatially modulated nonlinearity and a special external potential, which describe the evolution of two-component vector solitons in defocusing Kerr-type media. We find a robust soliton solution, constructed with the help of Whittaker functions. For specific choices of the topological charge, the radial mode number and the modulation depth, the solitons may exist in various forms, such as the half-moon, necklace-ring, and sawtooth vortex-ring patterns. Our results show that the profile of such solitons can be effectively controlled by the topological charge, the radial mode number, and the modulation depth. - Highlights: • Two-component vector soliton clusters in defocusing Kerr-type media are reported. • These soliton clusters are constructed with the help of Whittaker functions. • The half-moon, necklace-ring and vortex-ring patterns are found. • The profile of these solitons can be effectively controlled by three soliton parameters.
Dark spatial solitons in bulk azo-dye-doped polymer using photoinduced molecular reorientation
Bian Shaoping; Kuzyk, Mark G.
2004-08-16
We report the generation of dark spatial solitons in bulk Disperse Red 1 doped poly(methyl methacrylate) using photoinduced reorientation of azo-dye molecules. Planar solitions are formed when illuminated with a continuous-wave laser at intensities of the order of hundreds of miliwatts per square centimeter. The width of the soliton saturates to a minimum value at high intensity; and when the width of the initial dark notch is reduced, the equilibrium minimum width is unchanged.
Huang, Hui-Chang; He, Ying-Ji; Liu, Yuan-Zhi; Wang, He-Zhou
2011-04-25
We find the existence of two kinds of solitons at the interface of optical superlattices with both spatially modulated nonlinearity and linear refraction index. The first kind of solitons can either drift across the lattice, or deflect to the uniform nonlinear medium. The dynamics of such solitons mainly depends on their powers. The other kind of solitons can stably propagate along the surface, and can be controlled by additional Gaussian beams. In addition, we demonstrate the input-angle-dependent reflection, trapping, and refraction with nearly no losses by launching sech-shaped solitons. PMID:21643131
Two-dimensional solitary kinetic Alfven waves and dipole vortex structures
Wu, D.J.; Wang, D.Y.; Huang, G.L.
1997-03-01
A new type of density soliton, which we call {open_quotes}dipole density soliton,{close_quotes} is discovered in data from the Freja satellite. Like the dip or hump density solitons that were recently discovered in the Freja data [D.-J. Wu, G.-L. Huang, and D.-Y. Wang, Phys. Plasmas {bold 3}, 2879 (1996)], the dipole density solitons are also associated with strong electric spikes ({approximately} a few 100 mV/m) and have a spatial scale length of a few 100 m. This indicates that the three types of density solitons (dip, hump, and dipole) probably have the same physical nature. In this paper, a two-dimensional solitary kinetic Alfven wave (SKAW) model with a dipole vortex structure is proposed to account for the three kinds of density solitons (dip, hump, and dipole), in which the differences in their appearances can naturally be attributed to differences in the positions and directions at which the satellite crosses dipole vortex structures. Some features of this two-dimensional SKAW model are discussed, and the results are compared to the one-dimensional cases. {copyright} {ital 1997 American Institute of Physics.}
Hodson, Benjamin A; Unbekandt, Mathieu; Keighren, Margaret A; Springbett, Anthea; West, John D
2011-01-01
The relative extent of cell mixing in tissues of mouse chimaeras or mosaics can be studied by comparing the distributions of the two cell populations in the tissues. However, the mean patch size is misleading because it is affected by both the extent of cell mixing and the relative contributions of the two cell populations. Previous work suggested that effects attributable to differences in tissue composition among chimaeras can be factored out either by correcting the mean patch size or by using the median patch size for the minority cell population and restricting the analysis to grossly unbalanced chimaeras. In the present study, computer simulations of two-dimensional mosaic arrays of black and white squares (representing cells) were used to simulate chimaeric tissues. Random arrays simulated tissues with extensive cell mixing, arrays of cell clumps (representing coherent clones) simulated less mixed tissues, and striped arrays simulated tissues with elongated but fragmented descendent clones. The computer simulations predicted that (i) the median patch length (minority cell population) and the corrected mean patch length would both distinguish between random and clumped patterns and (ii) differences in the variation of the composition of two perpendicular series of one-dimensional transects would distinguished between stripes and randomly orientated patches. Both predictions were confirmed by analysis of histological sections of the retinal pigment epithelium from fetal and adult mouse chimaeras. This study demonstrates that two types of non-random two-dimensional variegated patterns (clumps and stripes) can be identified in chimaeras without two-dimensional reconstruction of serial sections. PMID:21615733
NASA Astrophysics Data System (ADS)
Shi, Xinrong; Guo, Qi; Hu, Wei
2008-08-01
We address the physical features exhibited by spatial optical solitons propagating in nonlocal Kerr-type media with Gaussian-shaped response and exponential-decay response, respectively. An iteration algorithm based on the split-step Fourier method is developed to obtain the numerical solutions of the solitons for the nonlocal nonlinear Schrdinger equation with arbitrary degrees of nonlocality. Our numerical results show that the soliton properties in the normalized system are different with the change of the degree of nonlocality and with the different responses. The profiles undergo a gradual and continuous transition from a Gaussian-shaped function in the strongly nonlocal case to a hyperbolic secant function in the local case for the Gaussian-shaped response, but for the exponential-decay response, the soliton profile is not Gaussian-shaped even in the strongly nonlocal cases. For the same response function, the stronger the nonlocality is, the higher the critical powers for solitons are and the larger of the phase shifts of the solitons. For the same degrees of nonlocality, when the degrees of nonlocality is larger enough, both the critical power and the phase shift for the Gaussian-shaped response are larger than that for the exponential-decay response.
Switching spatial dissipative solitons in a VCSEL with frequency selective feedback
NASA Astrophysics Data System (ADS)
Radwell, N.; McIntyre, C.; Scroggie, A. J.; Oppo, G. L.; Firth, W. J.; Ackemann, T.
2010-07-01
The process of switching on bistable spatial dissipative solitons in a VCSEL with frequency selective feedback is analyzed experimentally and theoretically. Two regimes of successful writing of spatial solitons with an external pulse are identified: for short durations of the writing beam pulse, the input amplitude has to increase, while for longer durations, the input amplitude can remain constant. Switch on spectrograms of the frequency spectrum show a transient dynamics over many modes of the external cavity with a drift of the central frequency from higher to lower frequency. Such a multi-mode regime is almost independent of the frequency of the writing beam. It is interpreted to be due to the existence of multiple unstable solitons with different frequencies which channel the transient dynamics. Good agreement between experimental results and numerical simulations in both the time and frequency domains is found.
Lie symmetries and solitons in nonlinear systems with spatially inhomogeneous nonlinearities.
Belmonte-Beitia, Juan; Prez-Garca, Vctor M; Vekslerchik, Vadym; Torres, Pedro J
2007-02-01
Using Lie group theory and canonical transformations, we construct explicit solutions of nonlinear Schrdinger equations with spatially inhomogeneous nonlinearities. We present the general theory, use it to show that localized nonlinearities can support bound states with an arbitrary number solitons, and discuss other applications of interest to the field of nonlinear matter waves. PMID:17358944
NASA Astrophysics Data System (ADS)
Parra-Rivas, P.; Gomila, D.; Matas, M. A.; Colet, P.; Gelens, L.
2016-01-01
We have reported in Phys. Rev. Lett. 110, 064103 (2013), 10.1103/PhysRevLett.110.064103 that in systems which otherwise do not show oscillatory dynamics, the interplay between pinning to a defect and pulling by drift allows the system to exhibit excitability and oscillations. Here we build on this work and present a detailed bifurcation analysis of the various dynamical instabilities that result from the competition between a pulling force generated by the drift and a pinning of the solitons to spatial defects. We show that oscillatory and excitable dynamics of dissipative solitons find their origin in multiple codimension-2 bifurcation points. Moreover, we demonstrate that the mechanisms leading to these dynamical regimes are generic for any system admitting dissipative solitons.
NASA Astrophysics Data System (ADS)
Madani, Abbas; Beeckmanc, Jeroen; Neytsc, Kristiaan
2013-07-01
In this paper, the torque, reorientation and the change in angular momentum of the light are firstly discussed. And moreover, the propagation of light beam (optical spatial soliton beam) at the distance of a few millimeters in chiral nematic liquid crystal (CNLC) will be experimentally under study. In spite of the complex structure of these crystals, due to a self-focusing effect, by injection of infrared laser beam with a power of the order of a few tenths of milliwatts into CNLC an optical spatial soliton beam is observed. In addition, we experimentally obtain the formation of splitting of a soliton beam into two soliton beams which have equal powers due to a saturation of the reorientational nonlinearity. As a matter of fact, this saturation of the reorientational nonlinearity can occur at one point of CNLC, due to the nonlocal nonlinearity. Hence this saturation of the reorientation nonlinearity can split one soliton beam to two soliton beams. This splitting can have a great potential interest for applications in all-optical signal processing, reconfigurable optical interconnects and switching.
Zharov, Alexander A; Zharov, Alexander A; Zharova, Nina A
2014-08-01
We show that transverse electromagnetic waves propagating along an external static electric field in liquid metacrystal (LMC) can provoke spontaneous rearrangement of elongated meta-atoms that changes the direction of the anisotropy axis of the LMC. This kind of instability may reorient the meta-atoms from the equilibrium state parallel to a static field to the state along a high-frequency field and back at the different threshold intensities of electromagnetic waves in such a way that bistability in the system takes place. Reorientation of meta-atoms causes a change in the effective refraction index of LMC that creates, in turn, the conditions for the formation of bright spatial solitons. Such spatial solitons are the self-consistent domains of redirected meta-atoms with trapped photons. We find that the instability thresholds as well as energy flux captured by the spatial soliton can be easily managed by variation of the static electric field applied to the LMC. We study the effects of soliton excitation and collisions via numerical simulations. PMID:25215843
Bright spatial solitons, nonlinear guided waves, and complex metamaterial structures
NASA Astrophysics Data System (ADS)
Boardman, A. D.; Egan, P.; Mitchell-Thomas, R. C.; Rapoport, Y. G.; Velasco, L.
2010-04-01
The creation of electromagnetic metamaterials is an important activity. The latter should anticipate the kind of applications in which unique metamaterial behaviour can appear. This paper addresses nonlinear wave phenomena in both the strongly and the weakly nonlinear regimes. It inevitably involves novel nonlinear guided waves and solitonic beam activities. In this context, some magnetooptic control is introduced. In addition, the kind of structural complexity that can lead to trapped rainbows will be briefly examined. Finally, some aspects are made of vortex control in a diffraction-managed metamaterial is presented.
Li, Huijie; Liu, Guipeng Wei, Hongyuan; Jiao, Chunmei; Wang, Jianxia; Zhang, Heng; Dong Jin, Dong; Feng, Yuxia; Yang, Shaoyan Wang, Lianshan; Zhu, Qinsheng; Wang, Zhan-Guo
2013-12-02
A scattering mechanism related to the Schottky barrier height (SBH) spatial fluctuation of the two dimensional electron gas (2DEG) in AlGaN/GaN heterostructures is presented. We find that the low field mobility is on the order of 10{sup 4}–10{sup 6} cm{sup 2}/Vs. The 2DEG transport properties are found to be influenced by both the mobility and 2DEG density variations caused by the SBH fluctuation. Our results indicate that a uniform Schottky contact is highly desired to minimize the influence of SBH inhomogeneity on the device performance.
Tiffan, K.F.; Garland, R.D.; Rondorf, D.W.
2002-01-01
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.
NASA Technical Reports Server (NTRS)
Chan, Kin P.; Killinger, Dennis K.
1992-01-01
Phase-sensitive coherent summation of individual heterodyne detector array signals was demonstrated for the enhanced detection of spatially distorted laser Doppler returns. With the use of a 2 x 2 heterodyne detector array, the phase and amplitude of a time-varying speckle pattern was detected, and the signal-to-noise ratio of the Doppler shift estimate was shown to be improved by a factor of 2, depending on the extent of spatial coherence loss. These results are shown to agree with a first-order analysis and indicate the advantage of coherent summation for both short-range laser Doppler velocimetry and long-range atmospheric coherent lidar.
Judi, David R; Mcpherson, Timothy N; Burian, Steven J
2009-01-01
A grid resolution sensitivity analysis using a two-dimensional flood inundation model has been presented in this paper. Simulations for 6 dam breaches located randomly in the United States were run at 10,30,60,90, and 120 meter resolutions. The dams represent a range of topographic conditions, ranging from 0% slope to 1.5% downstream of the dam. Using 10 meter digital elevation model (DEM) simulation results as the baseline, the coarser simulation results were compared in terms of flood inundation area, peak depths, flood wave travel time, daytime and nighttime population in flooded area, and economic impacts. The results of the study were consistent with previous grid resolution studies in terms of inundated area, depths, and velocity impacts. The results showed that as grid resolution is decreased, the relative fit of inundated area between the baseline and coarser resolution decreased slightly. This is further characterized by increasing over prediction as well as increasing under prediction with decreasing resolution. Comparison of average peak depths showed that depths generally decreased as resolution decreased, as well as the velocity. It is, however, noted that the trends in depth and velocity showed less consistency than the inundation area metrics. This may indicate that for studies in which velocity and depths must be resolved more accurately (urban environments when flow around buildings is important in the calculation of drag effects), higher resolution DEM data should be used. Perhaps the most significant finding from this study is the perceived insensitivity of socio-economic impacts to grid resolution. The difference in population at risk (PAR) and economic cost generally remained within 10% of the estimated impacts using the high resolution DEM. This insensitivity has been attributed to over estimated flood area and associated socio-economic impacts compensating for under estimated flooded area and associated socio-economic impacts. The United States has many dams that are classified as high-hazard potential that need an emergency action plan (EAP). It has been found that the development of EAPs for all high-hazard dams is handicapped due to funding limitations. The majority of the cost associated with developing an EAP is determining the flooded area. The results of this study have shown that coarse resolution dam breach studies can be used to provide an acceptable estimate of the inundated area and economic impacts, with very little computational cost. Therefore, the solution to limited funding may be to perform coarse resolution dam breach studies on high-hazard potential dams and use the results to help prioritize the order in which detailed EAPs should be developed.
Chan, K P; Killinger, D K
1992-09-01
We report what is to our knowledge the first demonstration of phase-sensitive coherent summation of individual heterodyne detector array signals for the enhanced detection of spatially distorted laser Doppler returns. With the use of a 2 x 2 heterodyne detector array, the phase and amplitude of a time-varying speckle pattern was detected, and the signal-to-noise ratio of the Doppler shift estimate was shown to be improved by a factor of 2, depending on the extent of spatial coherence loss. These results are shown to agree with a first-order analysis and indicate the advantage of coherent summation for both short-range laser Doppler velocimetry and long-range atmospheric coherent lidar. PMID:19798145
Adams, Bernhard W; Mane, Anil U; Elam, Jeffrey W; Obaid, Razib; Wetstein, Matthew; Chollet, Matthieu
2015-09-01
X-ray detectors that combine two-dimensional spatial resolution with a high time resolution are needed in numerous applications of synchrotron radiation. Most detectors with this combination of capabilities are based on semiconductor technology and are therefore limited in size. Furthermore, the time resolution is often realised through rapid time-gating of the acquisition, followed by a slower readout. Here, a detector technology is realised based on relatively inexpensive microchannel plates that uses GHz waveform sampling for a millimeter-scale spatial resolution and better than 100?ps time resolution. The technology is capable of continuous streaming of time- and location-tagged events at rates greater than 10(7) events per cm(2). Time-gating can be used for improved dynamic range. PMID:26289271
Fateev, D. V. Popov, V. V.; Shur, M. S.
2010-11-15
We present the theory of plasmon excitation in a grating-gate transistor structure with spatially modulated 2D electron channel. The plasmon spectrum varies depending on the electron density modulation in the transistor channel. We report on the frequency ranges of plasmon mode excitation in the gated and ungated regions of the channel and on the interaction of these different types of plasmon modes. We show that a constructive influence of the ungated regions of the electron channel considerably increases the intensity of the gated plasmon resonances and reduces the plasmon-resonance linewidth in the grating-gated transistor structure.
NASA Astrophysics Data System (ADS)
Steel, A. B.; Nagel, S. R.; Dunn, J.; Baldis, H. A.
2012-10-01
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 μm 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 μm.
Steel, A B; Nagel, S R; Dunn, J; Baldis, H A
2012-10-01
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
NASA Astrophysics Data System (ADS)
Yan, Zhen-Ya; Yan, Fang-Chi
2015-09-01
We study the existence of dark solitons of the defocusing cubic nonlinear Schrdinger (NLS) eqaution with the spatially-periodic potential and nonlinearity. Firstly, we propose six families of upper and lower solutions of the dynamical systems arising from the stationary defocusing NLS equation. Secondly, by regarding a dark soliton as a heteroclinic orbit of the Poincar map, we present some constraint conditions for the periodic potential and nonlinearity to show the existence of stationary dark solitons of the defocusing NLS equation for six different cases in terms of the theory of strict lower and upper solutions and the dynamics of planar homeomorphisms. Finally, we give the explicit dark solitons of the defocusing NLS equation with the chosen periodic potential and nonlinearity. Supported by the National Natural Science Foundation of China under Grant No. 61178091, the National Key Basic Research Program of China under Grant No. 2011CB302400, and the Open Project Program of State Key Laboratory of Theoretical Physics, Institute of Theoretical Physics, Chinese Academy of Sciences, China under Grant No. Y4KF211CJ1
Li, H; Yang, D; Xiao, Z; Driewer, J; Han, Z; Low, D
2014-06-15
Purpose: 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 our attempts to fabricate 2D KCl:Eu2+ storage phosphor films (SPFs) using both a physical vapor deposition (PVD) method and a tape casting method. Methods: A thin layer of KCl:Eu2+ was deposited on a substrate of borosilicate glass (e.g., laboratory slides) with a PVD system. For tape casting, a homogenous suspension containing storage phosphor particles, liquid vehicle and polymer binder was formed and subsequently cast by doctor-blade onto a polyethylene terephthalate substrate to form a 150 μm thick SPF. Results: 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 completed been 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 its intrinsic high radiation hardness. Conclusions: This discovery research 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. This work was supported in part by NIH Grant No. R01CA148853. The authors would like to thank Paul Leblans (AGFA Healthcare, Belgium) for many helpful discussions on this topic.
Thermal lensing-induced bifocusing of spatial solitons in Kerr-type optical media
NASA Astrophysics Data System (ADS)
Dikand, A. M.
2011-05-01
Thermo-optical effects cause a bifocusing of incoming beams in optical media, due to the birefringence created by a thermal lens that can resolve the incoming beams into two-component signals of different polarizations. We propose a nonperturbative theoretical description of the process of formation of double-pulse solitons in Kerr optical media with a thermally induced birefringence, based on solving simultaneously the heat equation and the propagation equation for a beam in a one-dimensional medium with uniform heat flux load. By means of a nonisospectral Inverse Scattering Transform assuming an initial solution with a pulse shape, a one-soliton solution to the wave equation is obtained that represents a double-pulse beam whose characteristic properties depend strongly on the profile of heat spatial distribution.
NASA Astrophysics Data System (ADS)
D'Abrusco, R.; Fabbiano, G.; Mineo, S.; Strader, J.; Fragos, T.; Kim, D.-W.; Luo, B.; Zezas, A.
2014-03-01
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.; Fragos, T.; Kim, D.-W.; Zezas, A.; Strader, J.; Luo, B.
2014-03-01
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.
Topological Solitons in Physics.
ERIC Educational Resources Information Center
Parsa, Zohreh
1979-01-01
A broad definition of solitons and a discussion of their role in physics is given. Vortices and magnetic monopoles which are examples of topological solitons in two and three spatial dimensions are described in some detail. (BB)
Boyarinov, V. F. Kondrushin, A. E. Fomichenko, P. A.
2014-12-15
Two-dimensional time-dependent finite-difference equations of the surface harmonics method (SHM) for the description of the neutron transport are derived for square-lattice reactors. These equations are implemented in the SUHAM-TD code. Verification of the derived equations and the developed code are performed by the example of known test problems, and the potential and efficiency of the SHM as applied to the solution of the time-dependent neutron transport equation in the diffusion approximation in two-dimensional geometry are demonstrated. These results show the substantial advantage of SHM over direct finite-difference modeling in computational costs.
Tan, Chunhua; Cai, Shuhui; Huang, Yuqing
2015-01-01
Background and Purpose Magnetic resonance spectroscopy (MRS) constitutes a mainstream technique for characterizing biological samples. Benefiting from the separation of chemical shifts and J couplings, spatially localized two-dimensional (2D) J-resolved spectroscopy (JPRESS) shows better identification of complex metabolite resonances than one-dimensional MRS does and facilitates the extraction of J coupling information. However, due to variations of macroscopic magnetic susceptibility in biological samples, conventional JPRESS spectra generally suffer from the influence of field inhomogeneity. In this paper, we investigated the implementation of the localized 2D J-resolved spectroscopy based on intermolecular double-quantum coherences (iDQCs) on a 7 T MRI scanner. Materials and Methods A γ-aminobutyric acid (GABA) aqueous solution, an intact pig brain tissue, and a whole fish (Harpadon nehereus) were explored by using the localized iDQC J-resolved spectroscopy (iDQCJRES) method, and the results were compared to those obtained by using the conventional 2D JPRESS method. Results Inhomogeneous line broadening, caused by the variations of macroscopic magnetic susceptibility in the detected biological samples (the intact pig brain tissue and the whole fish), degrades the quality of 2D JPRESS spectra, particularly when a large voxel is selected and some strongly structured components are included (such as the fish spinal cord). By contrast, high-resolution 2D J-resolved information satisfactory for metabolite analyses can be obtained from localized 2D iDQCJRES spectra without voxel size limitation and field shimming. From the contrastive experiments, it is obvious that the spectral information observed in the localized iDQCJRES spectra acquired from large voxels without field shimming procedure (i.e. in inhomogeneous fields) is similar to that provided by the JPRESS spectra acquired from small voxels after field shimming procedure (i.e. in relatively homogeneous fields). Conclusion The localized iDQCJRES method holds advantage for recovering high-resolution 2D J-resolved information from inhomogeneous fields caused by external non-ideal field condition or internal macroscopic magnetic susceptibility variations in biological samples, and it is free of voxel size limitation and time-consuming field shimming procedure. This method presents a complementary way to the conventional JPRESS method for MRS measurements on MRI systems equipped with broad inner bores, and may provide a promising tool for in vivo MRS applications. PMID:26207739
NASA Technical Reports Server (NTRS)
Juday, Richard D. (inventor)
1992-01-01
A two-dimensional vernier scale is disclosed utilizing a cartesian grid on one plate member with a polar grid on an overlying transparent plate member. The polar grid has multiple concentric circles at a fractional spacing of the spacing of the cartesian grid lines. By locating the center of the polar grid on a location on the cartesian grid, interpolation can be made of both the X and Y fractional relationship to the cartesian grid by noting which circles coincide with a cartesian grid line for the X and Y direction.
Matched infrared soliton pairs in graphene under Landau quantization via four-wave mixing
NASA Astrophysics Data System (ADS)
Ding, Chunling; Yu, Rong; Li, Jiahua; Hao, Xiangying; Wu, Ying
2014-10-01
We investigate a type of matched infrared soliton pairs based on four-wave mixng (FWM) in Landau-quantized graphene by using density-matrix method and perturbation theory. The linear and nonlinear dynamical properties of the graphene system are first discussed, and, in particular, we focus on the signatures of nonlinear optical response. Then we present analytical solutions for the fundamental bright and dark solitons, as well as bright two-soliton, which are in good agreement with the results of numerical simulations. Moreover, due to the unusual dispersion relation and chiral character of electron states, we find that the matched spatial soliton pairs can propagate through a two-dimensional crystal of graphene and their carrier frequencies are adjustable within the infrared frequency regimes. Our proposed scheme may provide a route to explore the applications of matched infrared soliton pairs in telecommunication and optical information processing.
NASA Astrophysics Data System (ADS)
Mukhartova, Yulia; Olchev, Alexander; Shapkina, Natalia
2014-05-01
Within the framework of the study a two dimensional hydrodynamic high-resolution model of the energy, H2O, CO2 turbulent exchange was developed and applied to describe effect of the horizontal and vertical heterogeneity of a forest canopy on CO2exchange between soil surface, forest stand and the atmosphere under different weather conditions. Most attention in the study was paid to analyze the influence of forest clearing, windthrow of different sizes, forest edges, etc. on turbulent exchange rate and CO2 flux partitioning between forest overstorey, understorey and soil surface. The modeling experiments were provided under different wind conditions, thermal stratification of the atmospheric boundary layer, incoming solar radiation, etc. To quantify effect of spatial heterogeneity on total ecosystem fluxes the modeling results were compared with CO2 fluxes modeled for a spatially uniform forest canopy under similar ambient conditions. The averaged system of hydrodynamic equations is used for calculating the components of the mean velocity →V = {V1, V2}: ( ( ) ) δVi+ V δVi= - 1-δδP- - -δ- δ E - K δVi-+ δVj- + F, δVi = 0, δt jδxj ρ0 δxi δxj ij δxj δxi i δxi where E is the turbulent kinetic energy (TKE), K is the turbulent diffusivity, δP is the deviation of pressure from the hydrostatic distribution and ρ0→F is the averaged force of air flow interaction with vegetation. F→ was parameterized as →F = -cd ·LAD ·| | ||V→||·→V, where cd is the drag coefficient and LAD is the leaf area density. The turbulent diffusivity K can be expressed by means of TKE and the velocity of TKE dissipation ɛ as follows: K = CμE2ɛ-1, where Cμ is the proportionality coefficient. One of the ways to obtain E and ɛ is to solve the additional system of two differential equations of diffusion-transport type: ( ) ( ) δE- -δE- -δ- -K-δE- δ-ϕ δϕ- -δ- K-δϕ -ϕ ( 1 2 ) δt +Vjδxj = δxi σE δxi +PE - ɛ, δt +Vj δxj = δxi σϕδxi +E C ϕPE - Cϕɛ - Δ ϕ, where σE and σϕ are the Prandtl numbers, PE is the TKE production by shear, Cϕ1 and Cϕ2 are the model constants. The term Δϕ = ϕ- E(C ϕ1 - Cϕ2) · 12Cμ1/2c dLAD||→ || |V |E describes the increase of TKE dissipation due to the interaction with vegetation elements. The function ϕ can be any of the following variables: ɛ, ɛ/ E, or El, where l is the mixing length. Detailed analysis of these equations performed by Sogachev (Sogachev, Panferov, 2006) showed that for ϕ = ɛ/ E the model is less sensible to the errors of the input data. Transfer equation for CO2 within and above a plant canopy can be written as: ( ) δC- -δC- -δ- -K-δC- δt + Vjδxj = δxi σC δxi + FC, where C is CO2 concentration, σC is the Prandtl number, and the term FC describes the sources/sinks of CO2 in the vegetation and soil. For parameterization of the photosynthesis rate in the forest canopy the Monsi and Saeki approach (Monsi M., Saeki T., 1953) was applied. Stem respiration was ignored in the study. The CO2 emission from the soil surface into the atmosphere was assumed to be constant for entire forest area. This study was supported by grants of the Russian Foundation for Basic Research (RFBR 14-04-01568-a).
Spatial solitons in a medium composed of self-focusing and self-defocusing layers
NASA Astrophysics Data System (ADS)
Atai, Javid; Malomed, Boris A.
2002-06-01
We introduce a model combining Kerr nonlinearity with a periodically changing sign (nonlinearity management) and a Bragg grating (BG). The main result, obtained by means of systematic simulations, is presented in the form of a stability diagram on the parameter plane of the model; the diagram turns out to be a universal one, as it practically does not depend on the soliton's power. Moreover, simulations of the nonlinear Schrdinger (NLS) model subjected to the same nonlinearity management demonstrate that the same diagram determines the stability of the NLS solitons, unless they are very narrow. The stability region of very narrow NLS solitons is much smaller, and soliton splitting is readily observed in that case. The universal diagram shows that a minimum nonzero average value of Kerr coefficient is necessary for the existence of stable solitons. Interactions between identical solitons with an initial phase difference between them are simulated too in the BG model, resulting in generation of stable moving solitons. A strong spontaneous symmetry breaking is observed in the case when in-phase solitons pass through each other due to attraction between them.
NASA Astrophysics Data System (ADS)
Shwetanshumala, S.
2016-02-01
Evolution of bright optical spatial solitons in biased photovoltaic photorefractive (PVPR) medium is investigated in the present work. The space-charge field developed in the medium is comprised of local and nonlocal parts. Lowest order charge drift results in the buildup of the local space-charge field, whereas higher order drift and charge diffusion are responsible for nonlocal field development. The dynamical equation for solitons in the closed circuit PVPR medium is obtained under Akhmanov's paraxial ray approximation. Conditions for stationary propagation are obtained, and the path of soliton in the medium is examined. The asymmetry in the nonlinear refractive index introduced by nonlocal contribution to the space-charge field causes a soliton to deflect from its straight line path in the medium. The roles of charge diffusion and higher order drift on soliton trajectory are examined.
Zellner, Alexander; Suntz, Rainer; Deutschmann, Olaf
2015-02-23
Planar laser-induced fluorescence (PLIF) enables noninvasive in?situ investigations of catalytic flow reactors. The method is based on the selective detection of two-dimensional absolute concentration maps of conversion-relevant species in the surrounding gas phase inside a catalytic channel. Exemplarily, the catalytic reduction of NO with hydrogen (2?NO+5?H2 ?2?H2 O+2?NH3 ) is investigated over a Pt/Al2 O3 coated diesel oxidation catalyst by NO PLIF inside an optically accessible channel reactor. Quenching-corrected 2D concentration maps of the NO fluorescence above the catalytic surface are obtained under both, nonreactive and reactive conditions. The impact of varying feed concentration, temperature, and flow velocities on NO concentration profiles are investigated in steady state. The technique presented has a high potential for a better understanding of interactions of mass transfer and surface kinetics in heterogeneously catalyzed gas-phase reactions. PMID:25641002
Levashov, V A; Stepanov, M G
2016-01-01
Considerations of local atomic-level stresses associated with each atom represent a particular approach to address structures of disordered materials at the atomic level. We studied structural correlations in a two-dimensional model liquid using molecular dynamics simulations in the following way. We diagonalized the atomic-level stress tensor of every atom and investigated correlations between the eigenvalues and orientations of the eigenvectors of different atoms as a function of distance between them. It is demonstrated that the suggested approach can be used to characterize structural correlations in disordered materials. In particular, we found that changes in the stress correlation functions on decrease of temperature are the most pronounced for the pairs of atoms with separation distance that corresponds to the first minimum in the pair density function. We also show that the angular dependencies of the stress correlation functions previously reported by Wu etal. [Phys. Rev. E 91, 032301 (2015)10.1103/PhysRevE.91.032301] do not represent the anisotropic Eshelby's stress fields, as it is suggested, but originate in the rotational properties of the stress tensors. PMID:26871117
NASA Astrophysics Data System (ADS)
Levashov, V. A.; Stepanov, M. G.
2016-01-01
Considerations of local atomic-level stresses associated with each atom represent a particular approach to address structures of disordered materials at the atomic level. We studied structural correlations in a two-dimensional model liquid using molecular dynamics simulations in the following way. We diagonalized the atomic-level stress tensor of every atom and investigated correlations between the eigenvalues and orientations of the eigenvectors of different atoms as a function of distance between them. It is demonstrated that the suggested approach can be used to characterize structural correlations in disordered materials. In particular, we found that changes in the stress correlation functions on decrease of temperature are the most pronounced for the pairs of atoms with separation distance that corresponds to the first minimum in the pair density function. We also show that the angular dependencies of the stress correlation functions previously reported by Wu et al. [Phys. Rev. E 91, 032301 (2015), 10.1103/PhysRevE.91.032301] do not represent the anisotropic Eshelby's stress fields, as it is suggested, but originate in the rotational properties of the stress tensors.
Noncommutative solitons and closed string tachyons
NASA Astrophysics Data System (ADS)
Headrick, Matthew Peter
In the first part of this thesis, we find the moduli space of multi-solitons in noncommutative scalar field theories at large theta, in arbitrary dimension. The existence of a non-trivial moduli space at leading order in 1/theta is a consequence of a Bogomolnyi bound obeyed by the kinetic energy of the theta = infinity solitons. In two spatial dimensions, the parameter space for k solitons is a Kahler de-singularization of the symmetric product (R2)k /Sk. We exploit the existence of this moduli space to construct solitons on quotient spaces of the plane: R2/Zk , cylinder, and T2. However, we show that tori of area less than or equal to 2pitheta do not admit stable solitons. In four dimensions the moduli space provides an explicit Kahler resolution of (R4)k /Sk. In general spatial dimension 2 d, we show it is isomorphic to the Hilbert scheme of k points in Cd , which for d > 2 (and k > 3) is not smooth and can have multiple branches. We also study multi-solitons on the fuzzy sphere and fuzzy hyperbolic plane, finding an effective potential on the moduli space depending on the curvature. In the second part of this thesis, we study renormalization group flows in unitary two dimensional sigma models with asymptotically flat target spaces. Applying an infrared cutoff to the target space, we use the Zamolodchikov c-theorem to demonstrate that the target space ADM energy of the UV fixed point is greater than that of the IR fixed point: spacetime energy decreases under world-sheet RG flow. This result mirrors the well understood decrease of spacetime Bondi energy in the time evolution process of tachyon condensation.
NASA Technical Reports Server (NTRS)
1982-01-01
Information on the Japanese National Aerospace Laboratory two dimensional transonic wind tunnel, completed at the end of 1979 is presented. Its construction is discussed in detail, and the wind tunnel structure, operation, test results, and future plans are presented.
Energy Science and Technology Software Center (ESTSC)
1997-11-18
QUENCH2D* is developed for the solution of general, non-linear, two-dimensional inverse heat transfer problems. This program provides estimates for the surface heat flux distribution and/or heat transfer coefficient as a function of time and space by using transient temperature measurements at appropriate interior points inside the quenched body. Two-dimensional planar and axisymmetric geometries such as turnbine disks and blades, clutch packs, and many other problems can be analyzed using QUENCH2D*.
NASA Astrophysics Data System (ADS)
Abu-Aly, T. R.; Pasternack, G. B.; Wyrick, J. R.; Barker, R.; Massa, D.; Johnson, T.
2014-02-01
The spatially distributed effects of riparian vegetation on fluvial hydrodynamics during low flows to large floods are poorly documented. Drawing on a LiDAR-derived, meter-scale resolution raster of vegetation canopy height as well as an existing algorithm to spatially distribute stage-dependent channel roughness, this study developed a meter-scale two-dimensional hydrodynamic model of ~ 28.3 km of a gravel/cobble-bed river corridor for flows ranging from 0.2 to 20 times bankfull discharge, with and without spatially distributed vegetation roughness. Results were analyzed to gain insight into stage-dependent and scale-dependent effects of vegetation on velocities, depths, and flow patterns. At the floodplain filling flow of 597.49 m3/s, adding spatially distributed vegetation roughness parameters caused 8.0 and 7.4% increases in wetted area and mean depth, respectively, while mean velocity decreased 17.5%. Vegetation has a strong channelization effect on the flow, increasing the difference between mid-channel and bank velocities. It also diverted flow away from densely vegetated areas. On the floodplain, vegetation stands caused high velocity preferential flow paths that were otherwise unaccounted for in the unvegetated model runs. For the river as a whole, as discharge increases, overall roughness increases as well, contrary to popular conception.
Evolution of relativistic solitons in underdense plasmas
NASA Astrophysics Data System (ADS)
Liu, Yue; Klimo, Ondrej; Gu, Yanjun; Kumar, Deepak; Singh, Sushil; Bulanov, Sergei V.; Esirkepov, Timur Zh.; Weber, Stefan; Korn, Georg
2015-05-01
Relativistic solitons arising from the interaction of an intense laser pulse with underdense plasmas are investigated. We show the formation and evolution of the relativistic solitons in a collisionless cold plasma with two dimensional particle-in-cell simulations. Such a kind of solitons will evolve into postsolitons if the time scale is longer than the ion response time. Generally, a substantial part of the pulse energy is transformed into solitons during the soliton formation. This fairly high efficiency of electromagnetic energy transformation can play an important role in the interaction between the laser pulse and the plasma. The energy exchange between the electromagnetic field and the kinetic energy of the soliton is discussed. In homogeneous plasmas, the solitons tend to stay close to the region where they are generated and dissipate due to the interaction with surrounding particles eventually. While the laser pulse propagates through inhomogeneous plasmas, the solitons are accelerated along the plasma density gradient towards lower density.
Interaction of spatial solitons with a gapless stripe embedded into a Bragg-grating area
NASA Astrophysics Data System (ADS)
Mayteevarunyoo, Thawatchai; Malomed, Boris A.
2015-01-01
We introduce a model in which the grating is absent in a finite-width stripe in the waveguide, thus creating a gapless channel in the gapped medium. Two semi-infinite grating separated by the plain stripe may have a relative phase shift. This system modifies the Bragg bandgap, creating intra-gap defect modes (DFs) which are pinned to the gapless channel. A DF solution in the linear system is found analytically. Further, numerical analysis of the full nonlinear system demonstrates that the shape and stability of Bragg solitons are also strongly affected by the presence of the gapless channel, and by the possible phase shift between the two semi-infinite gratings. In particular, asymmetric and flat-top solitons appear.
Two-dimensional material nanophotonics
NASA Astrophysics Data System (ADS)
Xia, Fengnian; Wang, Han; Xiao, Di; Dubey, Madan; Ramasubramaniam, Ashwin
2014-12-01
Two-dimensional materials exhibit diverse electronic properties, ranging from insulating hexagonal boron nitride and semiconducting transition metal dichalcogenides such as molybdenum disulphide, to semimetallic graphene. In this Review, we first discuss the optical properties and applications of various two-dimensional materials, and then cover two different approaches for enhancing their interactions with light: through their integration with external photonic structures, and through intrinsic polaritonic resonances. Finally, we present a narrow-bandgap layered material -- black phosphorus -- that serendipitously bridges the energy gap between the zero-bandgap graphene and the relatively large-bandgap transition metal dichalcogenides. The plethora of two-dimensional materials and their heterostructures, together with the array of available approaches for enhancing the light-matter interaction, offers the promise of scientific discoveries and nanophotonics technologies across a wide range of the electromagnetic spectrum.
NASA Astrophysics Data System (ADS)
Taylor, J. R.
2005-08-01
1. Optical solitons in fibres: theoretical review A. Hasegawa; 2. Solitons in optical fibres: an experimental account L. F. Mollenauer; 3. All-optical long-distance soliton-based transmission systems K. Smith and L. F. Mollenauer; 4. Nonlinear propagation effects in optical fibres: numerical studies K. J. Blow and N. J. Doran; 5. Soliton-soliton interactions C. Desem and P. L. Chu; 6. Soliton amplification in erbium-doped fibre amplifiers and its application to soliton communication M. Nakazawa; 7. Nonlinear transformation of laser radiation and generation of Raman solitons in optical fibres E. M. Dianov, A. B. Grudinin, A. M. Prokhorov and V. N. Serkin; 8. Generation and compression of femtosecond solitons in optical fibers P. V. Mamyshev; 9. Optical fibre solitons in the presence of higher order dispersion and birefringence C. R. Menyuk and Ping-Kong A. Wai; 10. Dark optical solitons A. M. Weiner; 11. Soliton Raman effects J. R. Taylor; Bibliography; Index.
NASA Astrophysics Data System (ADS)
Taylor, J. R.
1992-04-01
1. Optical solitons in fibres: theoretical review A. Hasegawa; 2. Solitons in optical fibres: an experimental account L. F. Mollenauer; 3. All-optical long-distance soliton-based transmission systems K. Smith and L. F. Mollenauer; 4. Nonlinear propagation effects in optical fibres: numerical studies K. J. Blow and N. J. Doran; 5. Soliton-soliton interactions C. Desem and P. L. Chu; 6. Soliton amplification in erbium-doped fibre amplifiers and its application to soliton communication M. Nakazawa; 7. Nonlinear transformation of laser radiation and generation of Raman solitons in optical fibres E. M. Dianov, A. B. Grudinin, A. M. Prokhorov and V. N. Serkin; 8. Generation and compression of femtosecond solitons in optical fibers P. V. Mamyshev; 9. Optical fibre solitons in the presence of higher order dispersion and birefringence C. R. Menyuk and Ping-Kong A. Wai; 10. Dark optical solitons A. M. Weiner; 11. Soliton Raman effects J. R. Taylor; Bibliography; Index.
NASA Astrophysics Data System (ADS)
Gonzalez-Melchor, Minerva; Mendez, Arlette; Alejandre, Jose
2015-03-01
When the movement of particles is performed predominantly in two dimensions, the systems can be considered at a good extent as two-dimensional. For instance the lipids in a bilayer, micrometric particles in a quasi-two-dimensional colloidal suspension, colloids in a monolayer deposited on the air-water interface, and DNA complexes trapped at the water surface can be described at a first approach as bidimensional fluids. These systems are important for many applications in surface and colloidal science. In simulations where the explicit interface between liquid and vapor is present, the line tension can be directly computed. In this work we present molecular dynamics results obtained for the liquid/vapor coexistence curve of 2D Yukawa fluids and for the line tension. A comparison with the three-dimensional case is also presented.
Two-dimensional flexible nanoelectronics
NASA Astrophysics Data System (ADS)
Akinwande, Deji; Petrone, Nicholas; Hone, James
2014-12-01
2014/2015 represents the tenth anniversary of modern graphene research. Over this decade, graphene has proven to be attractive for thin-film transistors owing to its remarkable electronic, optical, mechanical and thermal properties. Even its major drawback--zero bandgap--has resulted in something positive: a resurgence of interest in two-dimensional semiconductors, such as dichalcogenides and buckled nanomaterials with sizeable bandgaps. With the discovery of hexagonal boron nitride as an ideal dielectric, the materials are now in place to advance integrated flexible nanoelectronics, which uniquely take advantage of the unmatched portfolio of properties of two-dimensional crystals, beyond the capability of conventional thin films for ubiquitous flexible systems.
Two-dimensional thermofield bosonization
Amaral, R.L.P.G.
2005-12-15
The main objective of this paper was to obtain an operator realization for the bosonization of fermions in 1 + 1 dimensions, at finite, non-zero temperature T. This is achieved in the framework of the real-time formalism of Thermofield Dynamics. Formally, the results parallel those of the T = 0 case. The well-known two-dimensional Fermion-Boson correspondences at zero temperature are shown to hold also at finite temperature. To emphasize the usefulness of the operator realization for handling a large class of two-dimensional quantum field-theoretic problems, we contrast this global approach with the cumbersome calculation of the fermion-current two-point function in the imaginary-time formalism and real-time formalisms. The calculations also illustrate the very different ways in which the transmutation from Fermi-Dirac to Bose-Einstein statistics is realized.
NASA Technical Reports Server (NTRS)
Juday, Richard D.
1992-01-01
Modified vernier scale gives accurate two-dimensional coordinates from maps, drawings, or cathode-ray-tube displays. Movable circular overlay rests on fixed rectangular-grid overlay. Pitch of circles nine-tenths that of grid and, for greatest accuracy, radii of circles large compared with pitch of grid. Scale enables user to interpolate between finest divisions of regularly spaced rule simply by observing which mark on auxiliary vernier rule aligns with mark on primary rule.
Two dimensional unstable scar statistics.
Warne, Larry Kevin; Jorgenson, Roy Eberhardt; Kotulski, Joseph Daniel; Lee, Kelvin S. H. (ITT Industries/AES Los Angeles, CA)
2006-12-01
This report examines the localization of time harmonic high frequency modal fields in two dimensional cavities along periodic paths between opposing sides of the cavity. The cases where these orbits lead to unstable localized modes are known as scars. This paper examines the enhancements for these unstable orbits when the opposing mirrors are both convex and concave. In the latter case the construction includes the treatment of interior foci.
Two-Dimensional Potential Flows
NASA Technical Reports Server (NTRS)
Schaefer, Manfred; Tollmien, W.
1949-01-01
Contents include the following: Characteristic differential equations - initial and boundary conditions. Integration of the second characteristic differential equations. Direct application of Meyer's characteristic hodograph table for construction of two-dimensional potential flows. Prandtl-Busemann method. Development of the pressure variation for small deflection angles. Numerical table: relation between deflection, pressure, velocity, mach number and mach angle for isentropic changes of state according to Prandtl-Meyer for air (k = 1.405). References.
Aleshkevich, Viktor A; Kartashev, Ya V; Vysloukh, Victor A
1999-07-31
Exact self-bending soliton solutions for the equation of a beam in a photorefractive medium with diffusion and drift components of the nonlinear response are obtained and their stability is analysed. It is shown that the interaction of solitons in a medium with nonlocal nonlinearity is accompanied by energy exchange, which causes, as a rule, the annihilation of one of the solitons. (this issue is dedicated to the memory of s a akhmanov)
Two-Dimensional Colloidal Alloys
NASA Astrophysics Data System (ADS)
Law, Adam D.; Buzza, D. Martin A.; Horozov, Tommy S.
2011-03-01
We study the structure of mixed monolayers of large (3?m diameter) and small (1?m diameter) very hydrophobic silica particles at an octane-water interface as a function of the number fraction of small particles ?. We find that a rich variety of two-dimensional hexagonal super-lattices of large (A) and small (B) particles can be obtained in this system due to strong and long-range electrostatic repulsions through the nonpolar octane phase. The structures obtained for the different compositions are in good agreement with zero temperature calculations and finite temperature computer simulations.
Two-dimensional colloidal alloys.
Law, Adam D; Buzza, D Martin A; Horozov, Tommy S
2011-03-25
We study the structure of mixed monolayers of large (3 ?m diameter) and small (1 ?m diameter) very hydrophobic silica particles at an octane-water interface as a function of the number fraction of small particles ?. We find that a rich variety of two-dimensional hexagonal super-lattices of large (A) and small (B) particles can be obtained in this system due to strong and long-range electrostatic repulsions through the nonpolar octane phase. The structures obtained for the different compositions are in good agreement with zero temperature calculations and finite temperature computer simulations. PMID:21517357
Classically spinning and isospinning solitons
Battye, Richard A.; Haberichter, Mareike
2012-09-26
We investigate classically spinning topological solitons in (2+1)- and (3+1)-dimensional models; more explicitely spinning sigma model solitons in 2+1 dimensions and Skyrme solitons in 2+1 and 3+1 dimensions. For example, such types of solitons can be used to describe quasiparticle excitations in ferromagnetic quantum Hall systems or to model spin and isospin states of nuclei. The standard way to obtain solitons with quantised spin and isospin is the semiclassical quantization procedure: One parametrizes the zero-mode space - the space of energy-degenerate soliton configurations generated from a single soliton by spatial translations and rotations in space and isospace - by collective coordinates which are then taken to be time-dependent. This gives rise to additional dynamical terms in the Hamiltonian which can then be quantized following semiclassical quantization rules. A simplification which is often made in the literature is to apply a simple adiabatic approximation to the (iso)rotational zero modes of the soliton by assuming that the soliton's shape is rotational frequency independent. Our numerical results on classically spinning arbitrarily deforming soliton solutions clearly show that soliton deformation cannot be ignored.
Two-Dimensional Synthetic-Aperture Radiometer
NASA Technical Reports Server (NTRS)
LeVine, David M.
2010-01-01
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.
Soliton-induced Majorana fermions in a one-dimensional atomic topological superfluid
NASA Astrophysics Data System (ADS)
Liu, Xia-Ji
2015-02-01
We theoretically investigate the behavior of dark solitons in a one-dimensional spin-orbit coupled atomic Fermi gas in harmonic traps by solving self-consistently the Bogoliubov-de Gennes equations. The dark soliton—to be created by phase imprinting in future experiments—is characterized by a real order parameter, which changes sign at a point node and hosts localized Andreev bound states near the node. By considering both cases of a single soliton and multiple solitons, we find that the energy of these bound states decreases to zero when the system is tuned to enter the topological superfluid phase by increasing an external Zeeman field. As a result, two Majorana fermions emerge in the vicinity of each soliton, in addition to the well-known Majorana fermions at the trap edges associated with the nontrivial topology of the superfluid. We propose that the soliton-induced Majorana fermions can be directly observed by using spatially resolved radio-frequency spectroscopy or indirectly probed by measuring the density profile at the point node. For the latter, the deep minimum in the density profile will disappear due to the occupation of the soliton-induced zero-energy Majorana fermion modes. Our prediction could be tested in a resonantly interacting spin-orbit coupled 40K Fermi gas confined in a two-dimensional optical lattice.
Bending of solitons in weak and slowly varying inhomogeneous plasma
NASA Astrophysics Data System (ADS)
Mukherjee, Abhik; Janaki, M. S.; Kundu, Anjan
2015-12-01
The bending of solitons in two dimensional plane is presented in the presence of weak and slowly varying inhomogeneous ion density for the propagation of ion acoustic soliton in unmagnetized cold plasma with isothermal electrons. Using reductive perturbation technique, a modified Kadomtsev-Petviashvili equation is obtained with a chosen unperturbed ion density profile. The exact solution of the equation shows that the phase of the solitary wave gets modified by a function related to the unperturbed inhomogeneous ion density causing the soliton to bend in the two dimensional plane, while the amplitude of the soliton remains constant.
Two-dimensional capillary origami
NASA Astrophysics Data System (ADS)
Brubaker, N. D.; Lega, J.
2016-01-01
We describe a global approach to the problem of capillary origami that captures all unfolded equilibrium configurations in the two-dimensional setting where the drop is not required to fully wet the flexible plate. We provide bifurcation diagrams showing the level of encapsulation of each equilibrium configuration as a function of the volume of liquid that it contains, as well as plots representing the energy of each equilibrium branch. These diagrams indicate at what volume level the liquid drop ceases to be attached to the endpoints of the plate, which depends on the value of the contact angle. As in the case of pinned contact points, three different parameter regimes are identified, one of which predicts instantaneous encapsulation for small initial volumes of liquid.
Two-dimensional NMR spectroscopy
Croasmun, W.R.; Carlson, R.M.K.
1987-01-01
Written for chemists and biochemists who are not NMR spectroscopists, but who wish to use the new techniques of two-dimensional NMR spectroscopy, this book brings together for the first time much of the practical and experimental data needed. It also serves as information source for industrial, academic, and graduate student researchers who already use NMR spectroscopy, but not yet in two dimensions. The authors describe the use of 2-D NMR in a wide variety of chemical and biochemical fields, among them peptides, steroids, oligo- and poly-saccharides, nucleic acids, natural products (including terpenoids, alkaloids, and coal-derived heterocyclics), and organic synthetic intermediates. They consider throughout the book both the advantages and limitations of using 2-D NMR.
Dubrovsky, V. G.; Topovsky, A. V.; Basalaev, M. Yu.
2010-09-15
The classes of exactly solvable multiline soliton potentials and corresponding wave functions of two-dimensional stationary Schroedinger equation via {partial_derivative}-dressing method are constructed and their physical interpretation is discussed.
KP solitons, total positivity, and cluster algebras
Kodama, Yuji; Williams, Lauren K.
2011-01-01
Soliton solutions of the KP equation have been studied since 1970, when Kadomtsev and Petviashvili [Kadomtsev BB, Petviashvili VI (1970) Sov Phys Dokl 15:539541] proposed a two-dimensional nonlinear dispersive wave equation now known as the KP equation. It is well-known that the Wronskian approach to the KP equation provides a method to construct soliton solutions. The regular soliton solutions that one obtains in this way come from points of the totally nonnegative part of the Grassmannian. In this paper we explain how the theory of total positivity and cluster algebras provides a framework for understanding these soliton solutions to the KP equation. We then use this framework to give an explicit construction of certain soliton contour graphs and solve the inverse problem for soliton solutions coming from the totally positive part of the Grassmannian. PMID:21562211
Spin-imbalanced quasi-two-dimensional Fermi gases.
Ong, W; Cheng, Chingyun; Arakelyan, I; Thomas, J E
2015-03-20
We measure the density profiles for a Fermi gas of (6)Li containing N(1) spin-up atoms and N(2) spin-down atoms, confined in a quasi-two-dimensional geometry. The spatial profiles are measured as a function of spin imbalance N(2)/N(1) and interaction strength, which is controlled by means of a collisional (Feshbach) resonance. The measured cloud radii and central densities are in disagreement with mean-field Bardeen-Cooper-Schrieffer theory for a true two-dimensional system. We find that the data for normal-fluid mixtures are reasonably well fit by a simple two-dimensional polaron model of the free energy. Not predicted by the model is a phase transition to a spin-balanced central core, which is observed above a critical value of N(2)/N(1). Our observations provide important benchmarks for predictions of the phase structure of quasi-two-dimensional Fermi gases. PMID:25839246
NASA Astrophysics Data System (ADS)
Rajeev, Sarada Gangadharan
In this dissertation we study the soliton models of baryons originally proposed by Skyrme. Baryons are interpreted in the naive quark model as bound states of three quarks. Here, we interpret them as solitonic bound states of mesons. This is natural in Quantum Chromodynamics, the theory of strong interactions. The low energy properties of chromodynamics are well accounted for by the chiral model. The Wess-Zumino anomaly plays a crucial role in this model. A derivation within the canonical formulation of the Wess-Zumino is given. It is shown that the anomaly leads to a modification of the current algebra. An operator that creates solitonic states out of the vacuum is constructed. It is shown that this operator is fermionic if the number of colors is odd. The Wess -Zumino anomaly is shown to be responsible for this fact. The anomaly is studied in detail in the simpler context of a two dimensional theory. The operator creating solitons is constructed and its equations of motion are found. This model has an infinite number of conserved charges satisfying a Kac-Moody algebra. A derivation of the Wess-Zumino anomaly starting from Quantum Chromodynamics is given. Further the Skyrme constant is calculated, within certain approximations. This enables us to calculate the mass of the soliton and it agrees with the baryon mass to 20%. The constants D and F that couple the baryons to mesons are also computed. They also agree to about 20%. Thus the identification of baryons as solitons of the chiral model is established.
Two-dimensional supersonic nonlinear Schroedinger flow past an extended obstacle
El, G. A.; Khodorovskii, V. V.; Kamchatnov, A. M.; Annibale, E. S.; Gammal, A.
2009-10-15
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.
Predicting two-dimensional turbulence
NASA Astrophysics Data System (ADS)
Cerbus, R. T.; Goldburg, W. I.
2015-04-01
Prediction is a fundamental objective of science. It is more difficult for chaotic and complex systems like turbulence. Here we use information theory to quantify spatial prediction using experimental data from a turbulent soap film. At high Reynolds number, Re, where a cascade exists, turbulence becomes easier to predict as the inertial range broadens. The development of a cascade at low Re is also detected.
Nonlinear compressional waves in a two-dimensional Yukawa lattice.
Avinash, K; Zhu, P; Nosenko, V; Goree, J
2003-10-01
A modified Korteweg-de Vries (KdV) equation is obtained for studying the propagation of nonlinear compressional waves and pulses in a chain of particles including the effect of damping. Suitably altering the linear phase velocity makes this equation useful also for the problem of phonon propagation in a two-dimensional (2D) lattice. Assuming a Yukawa potential, we use this method to model compressional wave propagation in a 2D plasma crystal, as in a recent experiment. By integrating the modified KdV equation the pulse is allowed to evolve, and good agreement with the experiment is found. It is shown that the speed of a compressional pulse increases with its amplitude, while the speed of a rarefactive pulse decreases. It is further discussed how the drag due to the background gas has a crucial role in weakening nonlinear effects and preventing the emergence of a soliton. PMID:14683049
Transversely stable soliton trains in photonic lattices
Yang Jianke
2011-09-15
We report the existence of transversely stable soliton trains in optics. These stable soliton trains are found in two-dimensional square photonic lattices when they bifurcate from X-symmetry points with saddle-shaped diffraction inside the first Bloch band and their amplitudes are above a certain threshold. We also show that soliton trains with low amplitudes or bifurcated from edges of the first Bloch band ({Gamma} and M points) still suffer transverse instability. These results are obtained in the continuous lattice model and are further corroborated by the discrete model.
Solitons of axion-dilaton gravity
Bakas, I.
1996-11-01
We use soliton techniques of the two-dimensional reduced {beta}-function equations to obtain nontrivial string backgrounds from flat space. These solutions are characterized by two integers ({ital n},{ital m}) referring to the soliton numbers of the metric and axion-dilaton sectors, respectively. We show that the Nappi-Witten universe associated with the SL(2){times}SU(2)/SO(1,1){times}U(1) CFT coset arises as a (1,1) soliton in this fashion for certain values of the moduli parameters, while for other values of the soliton moduli we arrive at the SL(2)/SO(1,1){times}SO(1,1){sup 2} background. Ordinary four-dimensional black holes arise as two-dimensional (2,0) solitons, while the Euclidean wormhole background is described as a (0,2) soliton on flat space. The soliton transformations correspond to specific elements of the string Geroch group. These could be used as a starting point for exploring the role of {ital U} dualities in string compactifications to two dimensions. {copyright} {ital 1996 The American Physical Society.}
Equilibrium state of a trapped two-dimensional Bose gas
Rath, Steffen P.; Yefsah, Tarik; Guenter, Kenneth J.; Cheneau, Marc; Desbuquois, Remi; Dalibard, Jean; Holzmann, Markus; Krauth, Werner
2010-07-15
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.
A multiprocessor architecture for two-dimensional digital filters
Kim, J.H.; Alexander, W.E.
1987-07-01
In this paper, a generic computational primitive is developed for the implementation of any arbitrary order one-dimensional or two-dimensional FIR or IIR digital filter. This computational primitive can form the basis for a single chip processor for one-dimensional and two-dimensional digital signal processing. A multiprocessor architecture for real-time implementation of spatial domain filters is developed with each processing unit in the network implementing the computational primitive. This multiprocessor system has a simple control scheme, a simple interconnection network, a very high efficiency, and low data transfers and storage requirements. Thus, it avoids the bottlenecks associated with traditional parallel computers and multiprocessor systems.
Measuring Monotony in Two-Dimensional Samples
ERIC Educational Resources Information Center
Kachapova, Farida; Kachapov, Ilias
2010-01-01
This note introduces a monotony coefficient as a new measure of the monotone dependence in a two-dimensional sample. Some properties of this measure are derived. In particular, it is shown that the absolute value of the monotony coefficient for a two-dimensional sample is between /"r"/ and 1, where "r" is the Pearson's correlation coefficient for
Spectral Radiative Properties of Two-Dimensional Rough Surfaces
NASA Astrophysics Data System (ADS)
Xuan, Yimin; Han, Yuge; Zhou, Yue
2012-12-01
Spectral radiative properties of two-dimensional rough surfaces are important for both academic research and practical applications. Besides material properties, surface structures have impact on the spectral radiative properties of rough surfaces. Based on the finite difference time domain algorithm, this paper studies the spectral energy propagation process on a two-dimensional rough surface and analyzes the effect of different factors such as the surface structure, angle, and polarization state of the incident wave on the spectral radiative properties of the two-dimensional rough surface. To quantitatively investigate the spatial distribution of energy reflected from the rough surface, the concept of the bidirectional reflectance distribution function is introduced. Correlation analysis between the reflectance and different impact factors is conducted to evaluate the influence degree. Comparison between the theoretical and experimental data is given to elucidate the accuracy of the computational code. This study is beneficial to optimizing the surface structures of optoelectronic devices such as solar cells.
Approach for two-dimensional velocity mapping
NASA Astrophysics Data System (ADS)
Abado, Shaddy; Gordeyev, Stanislav; Jumper, Eric
2013-07-01
A method for extracting the convection speed and direction of aberrations present in wavefronts due to aero-optical turbulence over the pupil of a turret on the side of an airborne platform is addressed. The method is applied to data from the Airborne Aero-Optics Laboratory (AAOL). Such convection information is useful in designing feed-forward adaptive-optic approaches. The method makes use of a four-beam Malley probe technique derived by constructing a two-dimensional (2-D) local convective velocity-distribution over the beam's aperture. This technique is based on extending the analysis of the Notre-Dame-developed Malley probe. Two wavefront datasets (Azimuth 157 deg and Elevation 40 deg Azimuth 42 deg and Elevation 43 deg) from the AAOL are analyzed using the derived method, the first where the laser propagates through fully-separated flow and the second where the laser propagates through an attached-flow region. Finally, the 2-D proper orthogonal decomposition is applied to one in-flight measured dataset to determine the spatial requirements of deformable mirrors in an adaptive-optics system. The paper concludes with a discussion that points out the usefulness of the 2-D velocity-distributions in characterizing the various flow structures which convect over the aperture.
Strong nonlocal interaction stabilizes cavity solitons with a varying size plateau
NASA Astrophysics Data System (ADS)
Fernandez-Oto, Cristian; Tlidi, Mustapha; Escaff, Daniel; Clerc, Marcel; Kockaert, Pascal
2014-05-01
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 effects. Non-local effects 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 affects 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.
Two Dimensional Mechanism for Insect Hovering
Jane Wang, Z.
2000-09-04
Resolved computation of two dimensional insect hovering shows for the first time that a two dimensional hovering motion can generate enough lift to support a typical insect weight. The computation reveals a two dimensional mechanism of creating a downward dipole jet of counterrotating vortices, which are formed from leading and trailing edge vortices. The vortex dynamics further elucidates the role of the phase relation between the wing translation and rotation in lift generation and explains why the instantaneous forces can reach a periodic state after only a few strokes. The model predicts the lower limits in Reynolds number and amplitude above which the averaged forces are sufficient. (c) 2000 The American Physical Society.
Two dimensional mechanism for insect hovering.
Jane Wang, Z
2000-09-01
Resolved computation of two dimensional insect hovering shows for the first time that a two dimensional hovering motion can generate enough lift to support a typical insect weight. The computation reveals a two dimensional mechanism of creating a downward dipole jet of counterrotating vortices, which are formed from leading and trailing edge vortices. The vortex dynamics further elucidates the role of the phase relation between the wing translation and rotation in lift generation and explains why the instantaneous forces can reach a periodic state after only a few strokes. The model predicts the lower limits in Reynolds number and amplitude above which the averaged forces are sufficient. PMID:10970501
Electrical contacts to two-dimensional semiconductors
NASA Astrophysics Data System (ADS)
Allain, Adrien; Kang, Jiahao; Banerjee, Kaustav; Kis, Andras
2015-12-01
The performance of electronic and optoelectronic devices based on two-dimensional layered crystals, including graphene, semiconductors of the transition metal dichalcogenide family such as molybdenum disulphide (MoS2) and tungsten diselenide (WSe2), as well as other emerging two-dimensional semiconductors such as atomically thin black phosphorus, is significantly affected by the electrical contacts that connect these materials with external circuitry. Here, we present a comprehensive treatment of the physics of such interfaces at the contact region and discuss recent progress towards realizing optimal contacts for two-dimensional materials. We also discuss the requirements that must be fulfilled to realize efficient spin injection in transition metal dichalcogenides.
Soliton scattering in the Darboux transformation formalism
Matveev, V.B.; Sall', M.A.
1987-05-20
The Darboux transformation technique is applied to derive soliton scattering formulas for the Kadomtsev-Petviashvili equation, the KdV equation, the nonlocal KdV equation, the two-dimensionalized Toda chain and its periodic reductions, in particular the sine-Gordon equation.
Efficient Two-Dimensional-FFT Program
NASA Technical Reports Server (NTRS)
Miko, J.
1992-01-01
Program computes 64 X 64-point fast Fourier transform in less than 17 microseconds. Optimized 64 X 64 Point Two-Dimensional Fast Fourier Transform combines performance of real- and complex-valued one-dimensional fast Fourier transforms (FFT's) to execute two-dimensional FFT and coefficients of power spectrum. Coefficients used in many applications, including analyzing spectra, convolution, digital filtering, processing images, and compressing data. Source code written in C, 8086 Assembly, and Texas Instruments TMS320C30 Assembly languages.
Two-dimensional order and disorder thermofields
Belvedere, L. V.
2006-11-15
The main objective of this paper was to obtain the two-dimensional order and disorder thermal operators using the Thermofield Bosonization formalism. We show that the general property of the two-dimensional world according with the bosonized Fermi field at zero temperature can be constructed as a product of an order and a disorder variables which satisfy a dual field algebra holds at finite temperature. The general correlation functions of the order and disorder thermofields are obtained.
CALL FOR PAPERS: Optical solitons
NASA Astrophysics Data System (ADS)
Drummond, P. D.; Haelterman, Marc; Vilaseca, R.
2003-06-01
A topical issue of Journal of Optics B: Quantum and Semiclassical Optics will be devoted to recent advances in optical solitons. The topics to be covered will include, but are not limited to: bulletProperties, control and dynamics of temporal solitons bulletProperties, control and dynamics of spatial solitons bulletCavity solitons in passive and active resonators bulletThree-dimensional spatial solitons bulletDark, bright, grey 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.
Chen, Yi-Xiang; Xu, Fang-Qian
2014-01-01
Two families of Gaussian-type soliton solutions of the (n+1)-dimensional Schrdinger equation with cubic and power-law nonlinearities in -symmetric potentials are analytically derived. As an example, we discuss some dynamical behaviors of two dimensional soliton solutions. Their phase switches, powers and transverse power-flow densities are discussed. Results imply that the powers flow and exchange from the gain toward the loss regions in the cell. Moreover, the linear stability analysis and the direct numerical simulation are carried out, which indicates that spatial Gaussian-type soliton solutions are stable below some thresholds for the imaginary part of -symmetric potentials in the defocusing cubic and focusing power-law nonlinear medium, while they are always unstable for all parameters in other media. PMID:25542020
Ma Manjun; Carretero-Gonzalez, R.; Frantzeskakis, D. J.; Malomed, B. A.
2010-08-15
We study possibilities to suppress the transverse modulational instability (MI) of dark-soliton stripes in two-dimensional Bose-Einstein condensates (BEC's) and self-defocusing bulk optical waveguides by means of quasi-one-dimensional structures. Adding an external repulsive barrier potential (which can be induced in BEC by a laser sheet, or by an embedded plate in optics), we demonstrate that it is possible to reduce the MI wave number band, and even render the dark-soliton stripe completely stable. Using this method, we demonstrate the control of the number of vortex pairs nucleated by each spatial period of the modulational perturbation. By means of the perturbation theory, we predict the number of the nucleated vortices per unit length. The analytical results are corroborated by the numerical computation of eigenmodes of small perturbations, as well as by direct simulations of the underlying Gross-Pitaevskii/nonlinear Schroedinger equation.
Coherent transfer by adiabatic passage in two-dimensional lattices
NASA Astrophysics Data System (ADS)
Longhi, Stefano
2014-09-01
Coherent tunneling by adiabatic passage (CTAP) is a well-established technique for robust spatial transport of quantum particles in linear chains. Here we introduce two exactly-solvable models where the CTAP protocol can be extended to two-dimensional lattice geometries. Such bi-dimensional lattice models are synthesized from time-dependent second-quantization Hamiltonians, in which the bosonic field operators evolve adiabatically like in an ordinary three-level CTAP scheme thus ensuring adiabatic passage in Fock space.
Spectral tunneling of lattice nonlocal solitons
Kartashov, Yaroslav V.; Torner, Lluis; Vysloukh, Victor A.
2010-07-15
We address spectral tunneling of walking spatial solitons in photorefractive media with nonlocal diffusion component of the nonlinear response and an imprinted shallow optical lattice. In contrast to materials with local nonlinearities, where solitons traveling across the lattice close to the Bragg angle suffer large radiative losses, in photorefractive media with diffusion nonlinearity resulting in self-bending, solitons survive when their propagation angle approaches and even exceeds the Bragg angle. In the spatial frequency domain this effect can be considered as tunneling through the band of spatial frequencies centered around the Bragg frequency where the spatial group velocity dispersion is positive.
Superconductivity at the Two-dimensional Limit
NASA Astrophysics Data System (ADS)
Shih, Chih-Kang
2010-03-01
Superconductivity in the extreme two-dimensional limit is studied on ultra-thin lead (Pb) films down to two atomic layers, where only a single channel of quantum well states exist. Scanning tunneling spectroscopy reveals that local superconducting order remains robust until two atomic layers, where the transition temperature abruptly plunges to lower values depending sensitively on the exact atomic structure of the film. Our result shows that Cooper pairs can still form in the last two dimensional channel of electron states, although their binding are strongly affected by the substrate [1]. In this presentation, I will also discuss this new result in comparison with several recent experimental results on ultra-thin metallic films performed using local STS probes and macroscopic transport measurements.[4pt] [1] ``Superconductivity at the Two-dimensional Limit,'' Shengyong Qin, Jungdae Kim, Qian Niu and Chih-Kang Shih, Science 324, 1314 (2009).
Electrically Charged Two-Dimensional Skyrmions
NASA Astrophysics Data System (ADS)
Loginov, A. Yu.
2015-04-01
The (2 + 1)-dimensional Skyrme gauge model with a Chern-Simons term is considered. The presence of the Chern-Simons term leads to the result that the Abelian gauge field of the model becomes massive. This, in turn, leads to the existence in the given model of two-dimensional skyrmions carrying magnetic flux and possessing an electric charge and, consequently, nonzero angular momentum. It is shown that the model also admits the existence of two-dimensional skyrmions, whose electrically charged fields rotate with a constant phase frequency. Due to the nontrivial topology of the configurations of the (2 + 1)-dimensional Skyrme gauge model with a Chern-Simons term, the magnetic flux, the electric charge, and the angular momentum of a rotating two-dimensional skyrmion turn out to be interrelated.
Electrical contacts to two-dimensional semiconductors.
Allain, Adrien; Kang, Jiahao; Banerjee, Kaustav; Kis, Andras
2015-12-01
The performance of electronic and optoelectronic devices based on two-dimensional layered crystals, including graphene, semiconductors of the transition metal dichalcogenide family such as molybdenum disulphide (MoS2) and tungsten diselenide (WSe2), as well as other emerging two-dimensional semiconductors such as atomically thin black phosphorus, is significantly affected by the electrical contacts that connect these materials with external circuitry. Here, we present a comprehensive treatment of the physics of such interfaces at the contact region and discuss recent progress towards realizing optimal contacts for two-dimensional materials. We also discuss the requirements that must be fulfilled to realize efficient spin injection in transition metal dichalcogenides. PMID:26585088
Crossflow in two-dimensional asymmetric nozzles
NASA Technical Reports Server (NTRS)
Sebacher, D. I.; Lee, L. P.
1975-01-01
An experimental investigation of the crossflow effects in three contoured, two-dimensional asymmetric nozzles is described. The data were compared with theoretical predictions of nozzle flow by using an inviscid method of characteristics solution and two-dimensional turbulent boundary-layer calculations. The effect of crossflow as a function of the nozzle maximum expansion angle was studied by use of oil-flow techniques, static wall-pressure measurements, and impact-pressure surveys at the nozzle exit. Reynolds number effects on crossflow were investigated.
Superconductivity at the two-dimensional limit.
Qin, Shengyong; Kim, Jungdae; Niu, Qian; Shih, Chih-Kang
2009-06-01
Superconductivity in the extreme two-dimensional limit is studied on ultrathin lead films down to two atomic layers, where only a single channel of quantum well states exists. Scanning tunneling spectroscopy reveals that local superconducting order remains robust until two atomic layers, where the transition temperature abruptly plunges to a lower value, depending sensitively on the exact atomic structure of the film. Our result shows that Cooper pairs can still form in the last two-dimensional channel of electron states, although their binding is strongly affected by the substrate. PMID:19407146
Traveling dark solitons in superfluid Fermi gases
Liao Renyuan; Brand, Joachim
2011-04-15
Families of dark solitons exist in superfluid Fermi gases. The energy-velocity dispersion and number of depleted particles completely determine the dynamics of dark solitons on a slowly varying background density. For the unitary Fermi gas, we determine these relations from general scaling arguments and conservation of local particle number. We find solitons to oscillate sinusoidally at the trap frequency reduced by a factor of 1/{radical}(3). Numerical integration of the time-dependent Bogoliubov-de Gennes equation determines spatial profiles and soliton-dispersion relations across the BEC-BCS crossover, and proves consistent with the scaling relations at unitarity.
Ince-Gaussian solitons in strongly nonlocal nonlinear media.
Deng, Dongmei; Guo, Qi
2007-11-01
We have introduced a novel class of higher-order spatial optical Ince-Gaussian solitons (IGSs) that constitute the third complete family of exact and orthogonal soliton solutions of the Snyder-Mitchell model. The transverse structure of the IGSs is characterized by the Ince polynomials and has an inherent elliptical symmetry. The IGSs form the exact and continuous transition modes between Hermite-Gaussian solitons and Laguerre-Gaussian solitons. PMID:17975645
Adaptive rezoner in a two-dimensional Lagrangian hydrodynamic code
Pyun, J.J.; Saltzman, J.S.; Scannapieco, A.J.; Carroll, D.
1985-01-01
In an effort to increase spatial resolution without adding additional meshes, an adaptive mesh was incorporated into a two-dimensional Lagrangian hydrodynamics code along with two-dimensional flux corrected (FCT) remapper. The adaptive mesh automatically generates a mesh based on smoothness and orthogonality, and at the same time also tracks physical conditions of interest by focusing mesh points in regions that exhibit those conditions; this is done by defining a weighting function associated with the physical conditions to be tracked. The FCT remapper calculates the net transportive fluxes based on a weighted average of two fluxes computed by a low-order scheme and a high-order scheme. This averaging procedure produces solutions which are conservative and nondiffusive, and maintains positivity. 10 refs., 12 figs.
Entanglement Entropy in Two-Dimensional String Theory.
Hartnoll, Sean A; Mazenc, Edward A
2015-09-18
To understand an emergent spacetime is to understand the emergence of locality. Entanglement entropy is a powerful diagnostic of locality, because locality leads to a large amount of short distance entanglement. Two-dimensional string theory is among the very simplest instances of an emergent spatial dimension. We compute the entanglement entropy in the large-N matrix quantum mechanics dual to two-dimensional string theory in the semiclassical limit of weak string coupling. We isolate a logarithmically large, but finite, contribution that corresponds to the short distance entanglement of the tachyon field in the emergent spacetime. From the spacetime point of view, the entanglement is regulated by a nonperturbative "graininess" of space. PMID:26430982
Two-Dimensional Attosecond Electron Wave-Packet Interferometry
NASA Astrophysics Data System (ADS)
Xie, Xinhua
2015-05-01
We propose a two-dimensional interferometry based on the electron wave-packet interference by using a cycle-shaped orthogonally polarized two-color laser field. With such a method, the subcycle and intercycle interferences can be disentangled into different directions in the measured photoelectron momentum spectra. The Coulomb influence can be minimized and the overlapping of interference fringes with the complicated low-energy structures can be avoided as well. The contributions of the excitation effect and the long-range Coulomb potential can be traced in the Fourier domain of the photoelectron distribution. Because of these advantages, precise information on valence electron dynamics of atoms or molecules with attosecond temporal resolution and additional spatial information with angstrom resolution can be obtained with the two-dimensional electron wave-packet interferometry.
Two-dimensional attosecond electron wave-packet interferometry.
Xie, Xinhua
2015-05-01
We propose a two-dimensional interferometry based on the electron wave-packet interference by using a cycle-shaped orthogonally polarized two-color laser field. With such a method, the subcycle and intercycle interferences can be disentangled into different directions in the measured photoelectron momentum spectra. The Coulomb influence can be minimized and the overlapping of interference fringes with the complicated low-energy structures can be avoided as well. The contributions of the excitation effect and the long-range Coulomb potential can be traced in the Fourier domain of the photoelectron distribution. Because of these advantages, precise information on valence electron dynamics of atoms or molecules with attosecond temporal resolution and additional spatial information with angstrom resolution can be obtained with the two-dimensional electron wave-packet interferometry. PMID:25978229
Two-dimensional Gram-Charlier reconstruction of velocity correlations
NASA Astrophysics Data System (ADS)
Sullivan, P.; Pollard, A.; Delville, J.; Bonnet, J. P.
1996-10-01
The two-point statistics obtained in a two-dimensional mixing layer and a three-dimensional wall jet are reconstructed from the summation of Hermite Polynomials. The use of Hermite Polynomials allows the rigorous and progressive decomposition of the statistical field into separate components, Gaussian and non-Gaussian. The influence of individual terms can then be investigated. Two different schemes are used: a one-dimensional temporal reconstruction of data from both experiments, which is capable of providing excellent agreement with the measurements, and a two-dimensional scheme with the mixing layer data, which captures spatial and temporal characteristics of the velocity cross-correlation. It is demonstrated that the technique can also recover information that may be lost or missing between two measuring points thereby providing a complementary method to linear stochastic estimation.
Nitrogenated holey two-dimensional structures
Mahmood, Javeed; Lee, Eun Kwang; Jung, Minbok; Shin, Dongbin; Jeon, In-Yup; Jung, Sun-Min; Choi, Hyun-Jung; Seo, Jeong-Min; Bae, Seo-Yoon; Sohn, So-Dam; Park, Noejung; Oh, Joon Hak; Shin, Hyung-Joon; Baek, Jong-Beom
2015-01-01
Recent graphene research has triggered enormous interest in new two-dimensional ordered crystals constructed by the inclusion of elements other than carbon for bandgap opening. The design of new multifunctional two-dimensional materials with proper bandgap has become an important challenge. Here we report a layered two-dimensional network structure that possesses evenly distributed holes and nitrogen atoms and a C2N stoichiometry in its basal plane. The two-dimensional structure can be efficiently synthesized via a simple wet-chemical reaction and confirmed with various characterization techniques, including scanning tunnelling microscopy. Furthermore, a field-effect transistor device fabricated using the material exhibits an on/off ratio of 107, with calculated and experimental bandgaps of approximately 1.70 and 1.96 eV, respectively. In view of the simplicity of the production method and the advantages of the solution processability, the C2N-h2D crystal has potential for use in practical applications. PMID:25744355
Nitrogenated holey two-dimensional structures
NASA Astrophysics Data System (ADS)
Mahmood, Javeed; Lee, Eun Kwang; Jung, Minbok; Shin, Dongbin; Jeon, In-Yup; Jung, Sun-Min; Choi, Hyun-Jung; Seo, Jeong-Min; Bae, Seo-Yoon; Sohn, So-Dam; Park, Noejung; Oh, Joon Hak; Shin, Hyung-Joon; Baek, Jong-Beom
2015-03-01
Recent graphene research has triggered enormous interest in new two-dimensional ordered crystals constructed by the inclusion of elements other than carbon for bandgap opening. The design of new multifunctional two-dimensional materials with proper bandgap has become an important challenge. Here we report a layered two-dimensional network structure that possesses evenly distributed holes and nitrogen atoms and a C2N stoichiometry in its basal plane. The two-dimensional structure can be efficiently synthesized via a simple wet-chemical reaction and confirmed with various characterization techniques, including scanning tunnelling microscopy. Furthermore, a field-effect transistor device fabricated using the material exhibits an on/off ratio of 107, with calculated and experimental bandgaps of approximately 1.70 and 1.96?eV, respectively. In view of the simplicity of the production method and the advantages of the solution processability, the C2N-h2D crystal has potential for use in practical applications.
Two-Dimensional Motions of Rockets
ERIC Educational Resources Information Center
Kang, Yoonhwan; Bae, Saebyok
2007-01-01
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-dimensional quantum-reflection traps
Madronero, Javier; Friedrich, Harald
2007-06-15
We study the confining properties of two-dimensional quantum-reflection traps, which are important for the transverse motion in atomic waveguides. For square geometry, the effect of nonseparability of the Schroedinger equation due to the corners is shown to be small. The survival probability due to quantum reflection is very similar for square and circular geometries.
Two-Dimensional Turbulence in Magnetized Plasmas
ERIC Educational Resources Information Center
Kendl, A.
2008-01-01
In an inhomogeneous magnetized plasma the transport of energy and particles perpendicular to the magnetic field is in general mainly caused by quasi two-dimensional turbulent fluid mixing. The physics of turbulence and structure formation is of ubiquitous importance to every magnetically confined laboratory plasma for experimental or industrial…
Two-Dimensional Turbulence in Magnetized Plasmas
ERIC Educational Resources Information Center
Kendl, A.
2008-01-01
In an inhomogeneous magnetized plasma the transport of energy and particles perpendicular to the magnetic field is in general mainly caused by quasi two-dimensional turbulent fluid mixing. The physics of turbulence and structure formation is of ubiquitous importance to every magnetically confined laboratory plasma for experimental or industrial
Two-Dimensional Motions of Rockets
ERIC Educational Resources Information Center
Kang, Yoonhwan; Bae, Saebyok
2007-01-01
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…
New two dimensional compounds: beyond graphene
NASA Astrophysics Data System (ADS)
Lebegue, Sebastien
2015-03-01
In the field of nanosciences, the quest for materials with reduced dimensionality is only at its beginning. While a lot of effort has been put initially on graphene, the focus has been extended in the last past years to functionalized graphene, boron nitride, silicene, and transition metal dichalcogenides in the form of single layers. Although these two-dimensional compounds offer a larger range of properties than graphene, there is a constant need for new materials presenting equivalent or superior performances to the ones already known. Here I will present an approach that we have used to discover potential new two-dimensional materials. This approach corresponds to perform datamining in the Inorganic Crystal Structure Database using simple geometrical criterias, and allowed us to identify nearly 40 new materials that could be exfoliated into two-dimensional sheets. Then, their electronic structure (density of states and bandstructure) was obtained with density functional theory to predict whether the two-dimensional material is metallic or insulating, as well as if it undergoes magnetic ordering at low temperatures. If time allows, I will also present some of our recent results concerning the electronic structure of transition metal dichalcogenides bilayers.
VLSI Unit for Two-Dimensional Convolutions
NASA Technical Reports Server (NTRS)
Liu, K. Y.
1983-01-01
Universal logic structure allows same VLSI chip to be used for variety of computational functions required for two dimensional convolutions. Fast polynomial transform technique is extended into tree computational structure composed of two units: fast polynomial transform (FPT) unit and Chinese remainder theorem (CRT) computational unit.
Magnetization study of two dimensional helium three
NASA Astrophysics Data System (ADS)
Guo, Lei
This dissertation discusses a magnetization study of a two dimensional Fermi system. Our group developed a SQUID NMR system to study the magnetization of two dimensional 3He on both GTA grafoil and ZYX Graphite substrates. Benefiting from SQUID technology, our NMR experiments were performed at very low applied magnetic field thus avoid the masking of ordering by strong external field. Monolayer 3He films adsorbed on crystalline graphite are considered a nearly ideal example of a two dimensional system of highly correlated fermions. By controlling the 3He areal density, adsorbed films exhibit a wide range of structures with different temperature- dependent magnetic properties and heat capacities. Our recent experiments on two dimensional 3He adsorbed on ZYX graphite focused on the anti-ferromagnetic 4/7 phase and the ferromagnetic incommensurate solid state of a second 3He monolayer. Ferromagnetic order was observed in two dimensional 3He films on both Grafoil and highly oriented ZYX grade exfoliated graphite. The dipolar field plays an important role in magnetic ordering in two dimensional spin systems. The dipole-dipole interaction leads to a frequency shift of the NMR absorption line. The resulting 3He NMR lineshape on Grafoil was a broad peak shifted towards lower frequency with a background from the randomly oriented regions extending to positive frequencies. Compared to Grafoil, ZYX graphite has a much greater structural coherence and is more highly oriented. When studying magnetism of 3He films on ZYX substrate we found that the features we observed in our original Grafoil experiment were much more pronounced on ZYX graphite. In addition, we observed some multi-peak structure on the 3He NMR lineshape, which suggest a series of spin wave resonances. We also studied the magnetic properties of the second layer of 3He films on ZYX substrate at density around 4/7 phase. To eliminate the paramagnetic signal of the first layer solid, we pre-plated a 4He layer on the ZYX that serves as a substrate for the 3He layer. In this region of density, the 3He film acts as a quantum antiferromagnet with disordered ground state (Quantum Spin Liquid). Our experimental results are reported and similar work is reviewed.
NASA Technical Reports Server (NTRS)
Tchen, C. M.
1986-01-01
Theoretical and numerical works in atmospheric turbulence have used the Navier-Stokes fluid equations exclusively for describing large-scale motions. Controversy over the existence of an average temperature gradient for the very large eddies in the atmosphere suggested that a new theoretical basis for describing large-scale turbulence was necessary. A new soliton formalism as a fluid analogue that generalizes the Schrodinger equation and the Zakharov equations has been developed. This formalism, processing all the nonlinearities including those from modulation provided by the density fluctuations and from convection due to the emission of finite sound waves by velocity fluctuations, treats large-scale turbulence as coalescing and colliding solitons. The new soliton system describes large-scale instabilities more explicitly than the Navier-Stokes system because it has a nonlinearity of the gradient type, while the Navier-Stokes has a nonlinearity of the non-gradient type. The forced Schrodinger equation for strong fluctuations describes the micro-hydrodynamical state of soliton turbulence and is valid for large-scale turbulence in fluids and plasmas where internal waves can interact with velocity fluctuations.
Kirigami for Two-Dimensional Electronic Membranes
NASA Astrophysics Data System (ADS)
Qi, Zenan; Bahamon, Dario; Campbell, David; Park, Harold
2015-03-01
Two-dimensional materials have recently drawn tremendous attention because of their unique properties. In this work, we introduce the notion of two-dimensional kirigami, where concepts that have been used almost exclusively for macroscale structures are applied to dramatically enhance their stretchability. Specifically, we show using classical molecular dynamics simulations that the yield and fracture strains of graphene and MoS2 can be enhanced by about a factor of three using kirigami as compared to standard monolayers. Finally, using graphene as an example, we demonstrate that the kirigami structure may open up interesting opportunities in coupling to the electronic behavior of 2D materials. Authors acknowledge Mechanical Engineering and Physics departments at Boston University, and Mackgrafe at Mackenzie Presbyterian University.
Graphane: A two-dimensional hydrocarbon
NASA Astrophysics Data System (ADS)
Sofo, Jorge O.; Chaudhari, Ajay S.; Barber, Greg D.
2007-04-01
We predict the stability of an extended two-dimensional hydrocarbon on the basis of first-principles total-energy calculations. The compound that we call graphane is a fully saturated hydrocarbon derived from a single graphene sheet with formula CH. All of the carbon atoms are in sp3 hybridization forming a hexagonal network and the hydrogen atoms are bonded to carbon on both sides of the plane in an alternating manner. Graphane is predicted to be stable with a binding energy comparable to other hydrocarbons such as benzene, cyclohexane, and polyethylene. We discuss possible routes for synthesizing graphane and potential applications as a hydrogen storage material and in two-dimensional electronics.
Plasmonics with two-dimensional conductors
Yoon, Hosang; Yeung, Kitty Y. M.; Kim, Philip; Ham, Donhee
2014-01-01
A wealth of effort in photonics has been dedicated to the study and engineering of surface plasmonic waves in the skin of three-dimensional bulk metals, owing largely to their trait of subwavelength confinement. Plasmonic waves in two-dimensional conductors, such as semiconductor heterojunction and graphene, contrast the surface plasmonic waves on bulk metals, as the former emerge at gigahertz to terahertz and infrared frequencies well below the photonics regime and can exhibit far stronger subwavelength confinement. This review elucidates the machinery behind the unique behaviours of the two-dimensional plasmonic waves and discusses how they can be engineered to create ultra-subwavelength plasmonic circuits and metamaterials for infrared and gigahertz to terahertz integrated electronics. PMID:24567472
Cooperative two-dimensional directed transport
NASA Astrophysics Data System (ADS)
Zheng, Zhigang; Chen, Hongbin
2010-11-01
A mechanism for the cooperative directed transport in two-dimensional ratchet potentials is proposed. With the aid of mutual couplings among particles, coordinated unidirectional motion along the ratchet direction can be achieved by transforming the energy from the transversal rocking force (periodic or stochastic) to the work in the longitude direction. Analytical predictions on the relation between the current and other parameters for the ac-driven cases are given, which are in good agreement with numerical simulations. Stochastic driving forces can give rise to the resonant directional transport. The effect of the free length, which has been explored in experiments on the motility of bipedal molecular motors, is investigated for both the single- and double-channel cases. The mechanism and results proposed in this letter may both shed light on the collective locomotion of molecular motors and open ways on studies in two-dimensional collaborative ratchet dynamics.
Toward two-dimensional search engines
NASA Astrophysics Data System (ADS)
Ermann, L.; Chepelianskii, A. D.; Shepelyansky, D. L.
2012-07-01
We study the statistical properties of various directed networks using ranking of their nodes based on the dominant vectors of the Google matrix known as PageRank and CheiRank. On average PageRank orders nodes proportionally to a number of ingoing links, while CheiRank orders nodes proportionally to a number of outgoing links. In this way, the ranking of nodes becomes two dimensional which paves the way for the development of two-dimensional search engines of a new type. Statistical properties of information flow on the PageRank-CheiRank plane are analyzed for networks of British, French and Italian universities, Wikipedia, Linux Kernel, gene regulation and other networks. A special emphasis is done for British universities networks using the large database publicly available in the UK. Methods of spam links control are also analyzed.
Two-dimensional ranking of Wikipedia articles
NASA Astrophysics Data System (ADS)
Zhirov, A. O.; Zhirov, O. V.; Shepelyansky, D. L.
2010-10-01
The Library of Babel, described by Jorge Luis Borges, stores an enormous amount of information. The Library exists ab aeterno. Wikipedia, a free online encyclopaedia, becomes a modern analogue of such a Library. Information retrieval and ranking of Wikipedia articles become the challenge of modern society. While PageRank highlights very well known nodes with many ingoing links, CheiRank highlights very communicative nodes with many outgoing links. In this way the ranking becomes two-dimensional. Using CheiRank and PageRank we analyze the properties of two-dimensional ranking of all Wikipedia English articles and show that it gives their reliable classification with rich and nontrivial features. Detailed studies are done for countries, universities, personalities, physicists, chess players, Dow-Jones companies and other categories.
Dimers on Two-Dimensional Lattices
NASA Astrophysics Data System (ADS)
Wu, F. Y.
We consider close-packed dimers, or perfect matchings, on two-dimensional regular lattices. We review known results and derive new expressions for the free energy, entropy, and the molecular freedom of dimers for a number of lattices including the simple-quartic, honeycomb, triangular, kagome, 3-12 and its dual, and 4-8 and its dual Union Jack lattices. The occurrence and nature of phase transitions are also elucidated and discussed in each case.
Performance prediction of straight two dimensional diffusers
NASA Technical Reports Server (NTRS)
Greywall, M. S.
1980-01-01
A method, based on full viscous calculations, is presented to predict performance of straight two dimensional diffusers. The method predicts adequately the experimental pressure recovery data, up to the point of maximum pressure recovery, for small and large inlet boundary layer thicknesses. It is shown that at the point of maximum pressure recovery the streamwise velocity in the very near wall region varies as Z to the 0.22 power, where Z is the distance from the diffuser wall.
Stochastic models of two-dimensional fracture
NASA Astrophysics Data System (ADS)
Ausloos, M.; Kowalski, J. M.
1992-06-01
Two statistical models of (strictly two-dimensional) layer destruction are presented. The first is built as a strict percolation model with an added ``conservation law'' (conservation of mass) as physical constraint. The second allows for damped or limited fracture. Two successive fracture crack thresholds are considered. Percolation (i.e., fracture) probability and cluster distributions are studied by use of numerical simulations. Different fractal dimension, critical exponents for cluster distribution, and universality laws characterize both models.
Experimental Advances in Two-Dimensional Magnetism
NASA Astrophysics Data System (ADS)
Drr, W.; Kerkmann, D.; Pescia, D.
This paper reviews recent experimental advances toward the physical realization of two-dimensional magnetic systems. In particular, it is shown that truly epitaxial ferromagnetic monolayers of 3-d transition metals atop a non-magnetic substrate are within reach of material science. Magnetism in these systems exhibits a rich variety of new phenomena, unknown to our three-dimensional world but in line with our theoretical picture of physcis in two dimensions.
Deeply subrecoil two-dimensional Raman cooling
Boyer, V.; Phillips, W.D.; Lising, L.J.; Rolston, S.L.
2004-10-01
We report the implementation of a two-dimensional Raman cooling scheme using sequential excitations along the orthogonal axes. Using square pulses, we have cooled a cloud of ultracold cesium atoms down to an rms velocity spread of 0.39(5) recoil velocities, corresponding to an effective transverse temperature of 30 nK (0.15T{sub rec}). This technique can be useful to improve cold-atom atomic clocks and is particularly relevant for clocks in microgravity.
Ultrashort light bullets described by the two-dimensional sine-Gordon equation
Leblond, Herve; Mihalache, Dumitru
2010-06-15
By using a reductive perturbation technique applied to a two-level model, this study puts forward a generic two-dimensional sine-Gordon evolution equation governing the propagation of femtosecond spatiotemporal optical solitons in Kerr media beyond the slowly varying envelope approximation. Direct numerical simulations show that, in contrast to the long-wave approximation, no collapse occurs, and that robust (2+1)-dimensional ultrashort light bullets may form from adequately chosen few-cycle input spatiotemporal wave forms. In contrast to the case of quadratic nonlinearity, the light bullets oscillate in both space and time and are therefore not steady-state lumps.
Inviscid dynamics of two-dimensional shear layers
NASA Astrophysics Data System (ADS)
Chien, Kuei-Yuan; Ferguson, Ralph E.; Kuhl, Allen L.; Glaz, Harland M.; Colella, Philip
1991-06-01
The dynamics of unconfined, spatially developing shear layers is studied by numerical solutions of the time-dependent Euler equations using a second-order Godunov scheme. Effects of density and velocity variations between the two streams of the shear layer are studied and color graphics is used to show more clearly the entrainment process of the surrounding streams. The calculations demonstrated that the evolution of the mean flow was dominated by two-dimensional, inviscid effects. The rms fluctuating velocity and density profiles were found to be in good agreement with the measurements of Oster and Wygnanski and of Konrad, except for the peak value of the v-prime profile.
Two dimensional thick center vortex model
NASA Astrophysics Data System (ADS)
Rafibakhsh, Shahnoosh; Ahmadi, Alireza
2016-01-01
The potential between static color source is calculated in the SU (3) gauge group by introducing a two dimensional vortex flux. To generalize the model, the length of the Wilson loop is equal to R oriented along the x axis, and the vortex flux is considered as a function of x and y. The comparison between the generalized model and the original one shows that the intermediate linear regime is increased significantly and better agreement with Casimir scaling is achieved. Furthermore, the model is applied to calculate the potential between baryons.
The two-dimensional connectivity of
NASA Astrophysics Data System (ADS)
German, R. M.
1987-06-01
Liquid phase sintered materials are characterized by a connected microstructure composed of contacting grains in a solidified matrix phase. Observations on the sintered microstructure are typically performed using two-dimensional cross sections. A computer calculation has been performed to determine the variation in the observed contacts per grain vs the true underlying microstructure connectivity. The results show that the observed coordination depends on both the volume fraction of solid phase and the dihedral angle. The findings of the calculation are favorably compared with observations on Fe-Cu and W-Ni-Fe alloys. In the limiting case, the current calculations approach those found for polycrystalline solids and cell networks.
Anisotropic Two-Dimensional Friedel Oscillations
Hofmann, P.; Plummer, E.W.; Briner, B.G.; Doering, M.; Rust, H.; Bradshaw, A.M.
1997-07-01
Scanning tunneling microscopy at 4K shows highly anisotropic screening charge density oscillations on Be(10{ovr 1}0) in the vicinity of surface defects and steps. The forms of these oscillations, which derive from the Friedel oscillations, can be directly related to the two-dimensional band structure of the surface (two electron pockets at the boundary of the surface Brillouin zone). Simple calculations show that the Friedel oscillations in such a case will contain major contributions from wavelengths which do not correspond to any Fermi wave vector. {copyright} {ital 1997} {ital The American Physical Society}
The Dynamics of Two-Dimensional Foams
NASA Astrophysics Data System (ADS)
Chae, Jang Jin
This dissertation describes research on the structure and dynamics of two-dimensional foams. New experimental results are presented and new algorithms developed to study foam dynamics with particular emphasis on foams that evolve with significant rupture. In the introduction, basic principles and statistical properties of two-dimensional coarsening cellular patterns are reviewed. Theoretical and computational models which have been developed are also discussed. In Chapter 2, experimental results are presented for the relaxation of a two dimensional soap foam in which wall breakage is initiated through gentle warming of the foam cell. Significantly different phenomenology from the relaxation of non-breaking foams is observed. At a critical "break time," which depends on the temperature ramping rate and initial conditions, a large scale mechanical cascade of wall rupture sets in leading to a rapid disintegration of the foam. In Chapter 3, an efficient new algorithm for simulating the evolution of two-dimensional dry soap foams is presented. Our physically based model for the evolution is based on a combination of mass transfer, vertex movement, and edge relaxation. The stochastic nature of topological transitions due to numerical error has been carefully examined. In Chapter 4, simulations of breaking foams by this new algorithm are presented. The separation of vertex and edge movements permits a study of foam evolution that includes wall rupture. This evolution exhibits a sensitive dependence on both the type of breaking "rule" chosen as well as the initial conditions. The topological evolution is characterized in terms of certain "evolution exponents," and we show simulation results that agree with theoretical considerations. In Chapter 5, normal grain growth in anisotropic polycrystals is simulated using a new algorithm developed from the one used to simulate normal foams. The simulation results, without breakage, show a decrease in growth exponents which is due to the reduction in the mean surface energy during evolution. However, including breakage of low angle tilt grain boundaries substantially increases the growth exponents. These simulations highlight the fact that competition between anisotropic effects and boundary breakage can lead to a wide range of possible growth exponents.
Two-dimensional signatures for molecular identification
NASA Astrophysics Data System (ADS)
Qazi, Muhammad; Vogt, Thomas; Koley, Goutam
2008-03-01
Simultaneous measurements of the conductance and surface work function (SWF) changes on nanostructured graphite layers have been performed to detect several gaseous analyte molecules. It has been observed that the gradient of the SWF versus conductance response plotted for specific analyte molecules is constant irrespective of their concentration or fractional occupancy of surface adsorption sites. The SWF and conductance changes have been found to be uncorrelated for different analyte molecules, resulting in unique gradients that can be used as two-dimensional signatures for molecular identification.
Quasicondensation in Two-Dimensional Fermi Gases
NASA Astrophysics Data System (ADS)
Wu, Chien-Te; Anderson, Brandon M.; Boyack, Rufus; Levin, K.
2015-12-01
In this paper we follow the analysis and protocols of recent experiments, combined with simple theory, to arrive at a physical understanding of quasi-condensation in two dimensional Fermi gases. A key signature of quasi-condensation, which contains aspects of Berezinskiĭ-Kosterlitz-Thouless behavior, is a strong zero momentum peak in the pair momentum distribution. Importantly, this peak emerges at a reasonably well defined onset temperature. The resulting phase diagram, pair momentum distribution, and algebraic power law decay are compatible with recent experiments throughout the continuum from BEC to BCS.
Superconductivity in two-dimensional boron allotropes
NASA Astrophysics Data System (ADS)
Zhao, Yinchang; Zeng, Shuming; Ni, Jun
2016-01-01
We use ab initio evolutionary algorithm and first-principles calculations to investigate structural, electronic, vibrational, and superconducting properties of two-dimensional (2 D ) boron allotropes. Remarkably, we show that conventional BCS superconductivity in the stable 2 D boron structures is ubiquitous with the critical temperature Tc above the liquid hydrogen temperature for certain configurations. Due to the electronic states of the Fermi surface originating from both ? and ? electrons, the superconductivity of the 2 D structures arises from multiple phonon modes. Our results support that 2 D boron structure may be a pure single-element material with the highest Tc on conditions without high pressure and external strain.
Vortices in Two- Dimensional Anisotropic ? Models
NASA Astrophysics Data System (ADS)
Watanabe, T.; Otsu, H.
1981-01-01
We define a topological number and clarify its role played in two-dimensional anisotropic ? models. Non-dissipative metastable states are obtained as counter-examples to which Derrick's theorem cannot be applied. Each metastable state classified by the topological number q turns out to carry |q| vortices and |q| stagnation points for the cases of XY-like anisotropy and to involve |q| antiparallel core spins for those of Ising-like one. The range and strength of vortices are studied in detail for the XY-model obtained from present systems.
Quasicondensation in Two-Dimensional Fermi Gases.
Wu, Chien-Te; Anderson, Brandon M; Boyack, Rufus; Levin, K
2015-12-11
In this paper we follow the analysis and protocols of recent experiments, combined with simple theory, to arrive at a physical understanding of quasi-condensation in two dimensional Fermi gases. A key signature of quasi-condensation, which contains aspects of Berezinskiĭ-Kosterlitz-Thouless behavior, is a strong zero momentum peak in the pair momentum distribution. Importantly, this peak emerges at a reasonably well defined onset temperature. The resulting phase diagram, pair momentum distribution, and algebraic power law decay are compatible with recent experiments throughout the continuum from BEC to BCS. PMID:26705613
Two dimensional mixtures at water surface
NASA Astrophysics Data System (ADS)
Choudhuri, Madhumita; Datta, Alokmay
2013-02-01
Thiol capped gold nanoparticles (Au NPs) form a simple two dimensional (2D) liquid on water surface but this thin film is unstable under compression. Amphiphilic stearic acid (StA) molecules on water surface, on the other hand, form a complex and more stable 2D liquid. We have initiated a study on a mixture of StA and Au NPs in a monolayer through Surface Pressure (π) - Specific Molecular Area (A) isotherms and Brewster Angle Microscopy (BAM). A mixture of Stearic Acid and Au nanoparticles (10% by weight) produces a monolayer on water surface that acts as a 2D liquid with phases that are completely reversible with negligible hysteresis.
Two-dimensional meniscus in a wedge
Kagan, M.; Pinczewski, W.V.; Oren, P.E.
1995-03-15
This paper presents a closed-form analytical solution of the augmented Young-Laplace equation for the meniscus profile in a two-dimensional wedge-shaped capillary. The solution is valid for monotonic forms of disjoining pressure which are repulsive in nature. In the limit of negligible disjoining pressure, it is shown to reduce to the classical solution of constant curvature. The character of the solution is examined and examples of practical interest which demonstrate the application of the solution to the computation of the meniscus profile in a wedge-shaped capillary are discussed.
Two-Dimensional Ground Water Transport
Steidl, Shirley
1992-03-05
FRACFLO computes the two-dimensional, space, time dependent, convective dispersive transport of a single radionuclide in an unbounded single or multiple parallel fracture system with constant aperture. It calculates the one-dimensional diffusive transport into the rock matrix as well as the mass flux and cumulative mass flux at any point in the fracture. Steady-state isothermal ground water flow and parallel streamlines are assumed in the fracture, and the rock matrix is considered to be fully saturated with immobile water. The model can treat a single or multiple finite patch source or a Gaussian distributed source subject to a step or band release mode.
Two-dimensional crystallogenesis of transmembrane proteins.
Mosser, G
2001-07-01
Two-dimensional crystallogenesis is a crucial step in the long road that leads to the determination of macromolecules structure via electron crystallography. The necessity of having large and highly ordered samples can hold back the resolution of structural works for a long time, and this, despite improvements made in electron microscopes or image processing. Today, finding good conditions for growing two-dimensional crystals still rely on either "biocrystallo-cooks" or on lucky ones. The present review presents the field by first describing the different crystals that one can encounter and the different crystallisation methods used. Then, the effects of different components (such as protein, lipids, detergent, buffer, and temperature) and the different methods (dialysis, hydrophobic adsorption) are discussed. This discussion is punctuated by correspondences made to the world of three-dimensional crystallogenesis. Finally, a guide for setting up 2D crystallogenesis experiments, built on the discussion mentioned before, is proposed to the reader. More than giving recipes, this review is meant to open up the discussions in this field. PMID:11163725
Two-dimensional phonon transport in graphene.
Nika, Denis L; Balandin, Alexander A
2012-06-13
Properties of phonons-quanta of the crystal lattice vibrations-in graphene have recently attracted significant attention from the physics and engineering communities. Acoustic phonons are the main heat carriers in graphene near room temperature, while optical phonons are used for counting the number of atomic planes in Raman experiments with few-layer graphene. It was shown both theoretically and experimentally that transport properties of phonons, i.e. energy dispersion and scattering rates, are substantially different in a quasi-two-dimensional system such as graphene compared to the basal planes in graphite or three-dimensional bulk crystals. The unique nature of two-dimensional phonon transport translates into unusual heat conduction in graphene and related materials. In this review, we outline different theoretical approaches developed for phonon transport in graphene, discuss contributions of the in-plane and cross-plane phonon modes, and provide comparison with available experimental thermal conductivity data. Particular attention is given to analysis of recent results for the phonon thermal conductivity of single-layer graphene and few-layer graphene, and the effects of the strain, defects, and isotopes on phonon transport in these systems. PMID:22562955
Two-dimensional vortices in superconductors
NASA Astrophysics Data System (ADS)
Chen, Bo; Halperin, W. P.; Guptasarma, Prasenjit; Hinks, D. G.; Mitrovi?,
2007-04-01
Superconductors have two key characteristics: they expel magnetic field and they conduct electrical current with zero resistance. However, both properties are compromised in high magnetic fields, which can penetrate the material and create a mixed state of quantized vortices. The vortices move in response to an electrical current, dissipating energy and destroying the zero-resistance state. One of the central problems for applications of high-temperature superconductivity is the stabilization of vortices to ensure zero electrical resistance. We find that vortices in the anisotropic superconductor Bi2Sr2CaCu2O8+? (Bi-2212) have a phase transition from a liquid state, which is inherently unstable, to a two-dimensional vortex solid. We show that at high field the transition temperature is independent of magnetic field, as was predicted theoretically for the melting of an ideal two-dimensional vortex lattice. Our results indicate that the stable solid phase can be reached at any field, as may be necessary for applications involving superconducting magnets. The vortex solid is disordered, as suggested by previous studies at lower fields. But its evolution with increasing magnetic field exhibits unexpected threshold behaviour that needs further investigation.
Resonance vector soliton of the Rayleigh wave
NASA Astrophysics Data System (ADS)
Adamashvili, G. T.
2016-02-01
A theory of acoustic vector solitons of self-induced transparency of the Rayleigh wave is constructed. A thin resonance transition layer on an elastic surface is considered using a model of a two-dimensional gas of impurity paramagnetic atoms or quantum dots. Explicit analytical expressions for the profile and parameters of the Rayleigh vector soliton with two different oscillation frequencies is obtained, as well as simulations of this nonlinear surface acoustic wave with realistic parameters, which can be used in acoustic experiments. It is shown that the properties of a surface vector soliton of the Rayleigh wave depend on the parameters of the resonance layer, the elastic medium, and the transverse structure of the surface acoustic wave.
Solitonic axion condensates modeling dark matter halos
Castaeda Valle, David Mielke, Eckehard W.
2013-09-15
Instead of fluid type dark matter (DM), axion-like scalar fields with a periodic self-interaction or some truncations of it are analyzed as a model of galaxy halos. It is probed if such cold BoseEinstein 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 KleinGordon equation, mainly in lower dimensions, and visualize the approximately shape-invariant collisions of two lump type solitons. -- Highlights: An axion model of dark matter is considered. Collision of axion type solitons are studied in a two dimensional toy model. Relations to dark matter collisions in galaxy clusters are proposed.
NASA Astrophysics Data System (ADS)
Yan, Zhenya; Wen, Zichao; Hang, Chao
2015-08-01
We present a unified theoretical study of the bright solitons governed by self-focusing and defocusing nonlinear Schrdinger (NLS) equations with generalized parity-time- (PT ) symmetric Scarff-II potentials. Particularly, a PT -symmetric k -wave-number Scarff-II potential and a multiwell Scarff-II potential are considered, respectively. For the k -wave-number Scarff-II potential, the parameter space can be divided into different regions, corresponding to unbroken and broken PT symmetry and the bright solitons for self-focusing and defocusing Kerr nonlinearities. For the multiwell Scarff-II potential the bright solitons can be obtained by using a periodically space-modulated Kerr nonlinearity. The linear stability of bright solitons with PT -symmetric k -wave-number and multiwell Scarff-II potentials is analyzed in detail using numerical simulations. Stable and unstable bright solitons are found in both regions of unbroken and broken PT symmetry due to the existence of the nonlinearity. Furthermore, the bright solitons in three-dimensional self-focusing and defocusing NLS equations with a generalized PT -symmetric Scarff-II potential are explored. This may have potential applications in the field of optical information transmission and processing based on optical solitons in nonlinear dissipative but PT -symmetric systems.
A Two-dimensional TSVD Resolution Enhancement for EO Ocean Applications
NASA Astrophysics Data System (ADS)
Lenti, F.; Migliaccio, M.; Nunziata, F.; Rodriguez, G.
2012-03-01
A two-dimensional truncated singular value decomposition (TSVD) technique is first proposed to enhance spatial resolution of earth observation (EO) products related 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 robustness of the technique against the additive noise level and its effectiveness in both reconstruction accurancy and processing time.
A Two-dimensional TSVD Resolution Enhancement for EO Ocean Applications
NASA Astrophysics Data System (ADS)
Lenti, F.; Migliaccio, M.; Nunziata, F.; Rodriguez, G.
2012-03-01
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
Kinetic theory of a two-dimensional magnetized plasma.
NASA Technical Reports Server (NTRS)
Vahala, G.; Montgomery, D.
1971-01-01
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.
NASA Astrophysics Data System (ADS)
Rybakov, Iu. P.
Liapunov's direct method is used to analyze the stability of periodically time-dependent multidimensional soliton solutions. Necessary and sufficient conditions for the stability of charged solitons are formulated. The Hobart-Derrick theorem concerning the energy instability of multidimensional solitons is generalized, and it is shown that Q-theorem conditions are necessary for the stability of nodeless scalar solitons.
Spatial Coherence of a Polariton Condensate
NASA Astrophysics Data System (ADS)
Deng, Hui; Solomon, Glenn S.; Hey, Rudolf; Ploog, Klaus H.; Yamamoto, Yoshihisa
2007-09-01
We perform Youngs double-slit experiment to study the spatial coherence properties of a two-dimensional dynamic condensate of semiconductor microcavity polaritons. The coherence length of the system is measured as a function of the pump rate, which confirms a spontaneous buildup of macroscopic coherence in the condensed phase. An independent measurement reveals that the position and momentum uncertainty product of the condensate is close to the Heisenberg limit. An experimental realization of such a minimum uncertainty wave packet of the polariton condensate opens a door to coherent matter-wave phenomena such as Josephson oscillation, superfluidity, and solitons in solid state condensate systems.
NASA Astrophysics Data System (ADS)
Fuchssteiner, B.
1987-11-01
Several new nonlinear systems are given which are completely integrable. These systems can be considered as flows describing the self-interaction of single solitons in multisoliton fields. The construction of action variables, recursion operators, bi-hamiltonian formulation and the like is performed for these nonlinear systems. Furthermore virtual solitons are introduced and it is shown that 2-solitons in general may be understood as the superposition of two pairs of interacting solitons exchanging one virtual soliton and that the interacting soliton itself can be considered as the result of a collision of a wave with a virtual soliton. In a sense, virtual solitons only pop up during the time that solitons interact with each other. In case of the KdV the details of decomposition into interacting and virtual solitons are plotted, and a qualitative analysis of interaction is given. A brief discussion is appended, how to describe multisolitons by their ``trajectories''.
Epitaxial growth of two-dimensional stanene
NASA Astrophysics Data System (ADS)
Zhu, Feng-Feng; Chen, Wei-Jiong; Xu, Yong; Gao, Chun-Lei; Guan, Dan-Dan; Liu, Can-Hua; Qian, Dong; Zhang, Shou-Cheng; Jia, Jin-Feng
2015-10-01
Following the first experimental realization of graphene, other ultrathin materials with unprecedented electronic properties have been explored, with particular attention given to the heavy group-IV elements Si, Ge and Sn. Two-dimensional buckled Si-based silicene has been recently realized by molecular beam epitaxy growth, whereas Ge-based germanene was obtained by molecular beam epitaxy and mechanical exfoliation. However, the synthesis of Sn-based stanene has proved challenging so far. Here, we report the successful fabrication of 2D stanene by molecular beam epitaxy, confirmed by atomic and electronic characterization using scanning tunnelling microscopy and angle-resolved photoemission spectroscopy, in combination with first-principles calculations. The synthesis of stanene and its derivatives will stimulate further experimental investigation of their theoretically predicted properties, such as a 2D topological insulating behaviour with a very large bandgap, and the capability to support enhanced thermoelectric performance, topological superconductivity and the near-room-temperature quantum anomalous Hall effect.
Two-dimensional Inductive Position Sensing System
NASA Technical Reports Server (NTRS)
Youngquist, Robert C. (Inventor); Starr, Stanley O. (Inventor)
2015-01-01
A two-dimensional inductive position sensing system uses four drive inductors arranged at the vertices of a parallelogram and a sensing inductor positioned within the parallelogram. The sensing inductor is movable within the parallelogram and relative to the drive inductors. A first oscillating current at a first frequency is supplied to a first pair of the drive inductors located at ends of a first diagonal of the parallelogram. A second oscillating current at a second frequency is supplied to a second pair of the drive inductors located at ends of a second diagonal of the parallelogram. As a result, the sensing inductor generates a first output voltage at the first frequency and a second output voltage at the second frequency. A processor determines a position of the sensing inductor relative to the drive inductors using the first output voltage and the second output voltage.
Two-dimensional informative array testing.
McMahan, Christopher S; Tebbs, Joshua M; Bilder, Christopher R
2012-09-01
Array-based group-testing algorithms for case identification are widely used in infectious disease testing, drug discovery, and genetics. In this article, we generalize previous statistical work in array testing to account for heterogeneity among individuals being tested. We first derive closed-form expressions for the expected number of tests (efficiency) and misclassification probabilities (sensitivity, specificity, predictive values) for two-dimensional array testing in a heterogeneous population. We then propose two "informative" array construction techniques which exploit population heterogeneity in ways that can substantially improve testing efficiency when compared to classical approaches that regard the population as homogeneous. Furthermore, a useful byproduct of our methodology is that misclassification probabilities can be estimated on a per-individual basis. We illustrate our new procedures using chlamydia and gonorrhea testing data collected in Nebraska as part of the Infertility Prevention Project. PMID:22212007
From two-dimensional materials to heterostructures
NASA Astrophysics Data System (ADS)
Niu, Tianchao; Li, Ang
2015-02-01
Graphene, hexagonal boron nitride, molybdenum disulphide, and layered transition metal dichalcogenides (TMDCs) represent a class of two-dimensional (2D) atomic crystals with unique properties due to reduced dimensionality. Stacking these materials on top of each other in a controlled fashion can create heterostructures with tailored properties that offers another promising approach to design and fabricate novel electronic devices. In this report, we attempt to review this rapidly developing field of hybrid materials. We summarize the fabrication methods for different 2D materials, the layer-by-layer growth of various vertical heterostructures and their electronic properties. Particular interests are given to in-situ stack aforementioned 2D materials in controlled sequences, and the TMDCs heterostructures.
Intrinsic two-dimensional features as textons
NASA Technical Reports Server (NTRS)
Barth, E.; Zetzsche, C.; Rentschler, I.
1998-01-01
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.
Phonon hydrodynamics in two-dimensional materials
NASA Astrophysics Data System (ADS)
Cepellotti, Andrea; Fugallo, Giorgia; Paulatto, Lorenzo; Lazzeri, Michele; Mauri, Francesco; Marzari, Nicola
2015-03-01
The conduction of heat in two dimensions displays a wealth of fascinating phenomena of key relevance to the scientific understanding and technological applications of graphene and related materials. Here, we use density-functional perturbation theory and an exact, variational solution of the Boltzmann transport equation to study fully from first-principles phonon transport and heat conductivity in graphene, boron nitride, molybdenum disulphide and the functionalized derivatives graphane and fluorographene. In all these materials, and at variance with typical three-dimensional solids, normal processes keep dominating over Umklapp scattering well-above cryogenic conditions, extending to room temperature and more. As a result, novel regimes emerge, with Poiseuille and Ziman hydrodynamics, hitherto typically confined to ultra-low temperatures, characterizing transport at ordinary conditions. Most remarkably, several of these two-dimensional materials admit wave-like heat diffusion, with second sound present at room temperature and above in graphene, boron nitride and graphane.
Phonon hydrodynamics in two-dimensional materials.
Cepellotti, Andrea; Fugallo, Giorgia; Paulatto, Lorenzo; Lazzeri, Michele; Mauri, Francesco; Marzari, Nicola
2015-01-01
The conduction of heat in two dimensions displays a wealth of fascinating phenomena of key relevance to the scientific understanding and technological applications of graphene and related materials. Here, we use density-functional perturbation theory and an exact, variational solution of the Boltzmann transport equation to study fully from first-principles phonon transport and heat conductivity in graphene, boron nitride, molybdenum disulphide and the functionalized derivatives graphane and fluorographene. In all these materials, and at variance with typical three-dimensional solids, normal processes keep dominating over Umklapp scattering well-above cryogenic conditions, extending to room temperature and more. As a result, novel regimes emerge, with Poiseuille and Ziman hydrodynamics, hitherto typically confined to ultra-low temperatures, characterizing transport at ordinary conditions. Most remarkably, several of these two-dimensional materials admit wave-like heat diffusion, with second sound present at room temperature and above in graphene, boron nitride and graphane. PMID:25744932
Two-dimensional fourier transform spectrometer
DeFlores, Lauren; Tokmakoff, Andrei
2013-09-03
The present invention relates to a system and methods for acquiring two-dimensional Fourier transform (2D FT) spectra. Overlap of a collinear pulse pair and probe induce a molecular response which is collected by spectral dispersion of the signal modulated probe beam. Simultaneous collection of the molecular response, pulse timing and characteristics permit real time phasing and rapid acquisition of spectra. Full spectra are acquired as a function of pulse pair timings and numerically transformed to achieve the full frequency-frequency spectrum. This method demonstrates the ability to acquire information on molecular dynamics, couplings and structure in a simple apparatus. Multi-dimensional methods can be used for diagnostic and analytical measurements in the biological, biomedical, and chemical fields.
Rationally synthesized two-dimensional polymers
NASA Astrophysics Data System (ADS)
Colson, John W.; Dichtel, William R.
2013-06-01
Synthetic polymers exhibit diverse and useful properties and influence most aspects of modern life. Many polymerization methods provide linear or branched macromolecules, frequently with outstanding functional-group tolerance and molecular weight control. In contrast, extending polymerization strategies to two-dimensional periodic structures is in its infancy, and successful examples have emerged only recently through molecular framework, surface science and crystal engineering approaches. In this Review, we describe successful 2D polymerization strategies, as well as seminal research that inspired their development. These methods include the synthesis of 2D covalent organic frameworks as layered crystals and thin films, surface-mediated polymerization of polyfunctional monomers, and solid-state topochemical polymerizations. Early application targets of 2D polymers include gas separation and storage, optoelectronic devices and membranes, each of which might benefit from predictable long-range molecular organization inherent to this macromolecular architecture.
Acidity of two-dimensional zeolites.
Rybicki, Marcin; Sauer, Joachim
2015-11-01
Hybrid quantum mechanics:molecular mechanics (QM/MM) calculations of absolute deprotonation energies are performed with periodic boundary conditions for Brnsted sites of aluminosilicate bilayers with various Al/Si ratios (two-dimensional zeolite). The supercell method is applied and density functional theory is used. Much lower values are obtained (1042, 1069 and 1091 kJ mol(-1) for Al/Si = 1/63, 1/7 and 1/3, respectively) than those for bulk zeolites (1233 kJ mol(-1) for H-chabazite with Al/Si = 1/11). We ascribe the much lower deprotonation energy to the smaller effective dielectric constant (1.6-1.9) of an ultra-thin dielectric in a vacuum compared to that of the corresponding bulk systems (3.0 for H-chabazite), which leads to a better stabilization of the charge created upon deprotonation. PMID:26437870
Two-Dimensional Ground Water Transport
Energy Science and Technology Software Center (ESTSC)
1992-03-05
FRACFLO computes the two-dimensional, space, time dependent, convective dispersive transport of a single radionuclide in an unbounded single or multiple parallel fracture system with constant aperture. It calculates the one-dimensional diffusive transport into the rock matrix as well as the mass flux and cumulative mass flux at any point in the fracture. Steady-state isothermal ground water flow and parallel streamlines are assumed in the fracture, and the rock matrix is considered to be fully saturatedmore » with immobile water. The model can treat a single or multiple finite patch source or a Gaussian distributed source subject to a step or band release mode.« less
Two-dimensional Gel Electrophoresis (2DE)
NASA Astrophysics Data System (ADS)
K?odzi?ska, Ewa; Buszewski, Bogus?aw
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.
Two-dimensional virtual impactors. Final report
Forney, L.J.; Ravenhall, D.G.
1980-12-01
Theoretical predictions using both potential flow analyses and solutions to Navier-Stokes equations are made for the operating characteristics of a two-dimensional virtual impactor. Experiments were performed with 2.5 ..mu..m, uranine tagged, di-octylphthalate (DOP) oil droplets for a wide range of prototype geometries to measure the magnitude of internal losses and to fully characterize the instrument response. The influence of geometry including the throat angle (38/sup 0/ less than or equal to ..beta../sub 0/ less than or equal to 58.2/sup 0/) and normalized void width (0.7 less than or equal to h/w less than or equal to 1.5) on the particle cutoff diameter, efficiency curve steepness and properties of the internal particle loss factor are presented for fixed instrument Reynolds numbers Re = 1540 and bleed flow f = 0.1. The theory, supported by trends in the empirical data, predicts that internal particle losses reduce to zero as the normalized void width increases to h/w = 1.4 +- .1 while the data show a minimum at h/w = 1.6 +- .1. Increasing the void width, however, is shown to substantially reduce the steepness of the particle efficiency curves. Visual observations of the onset of fluid separation for two-dimensional jets impinging upon a void were conducted with a scaled-up water model and correlated with theory. It was found that the limiting void width h/sub lim//w marking the onset of fluid instabilities peaked for an intermediate value of the fluid deflecting plate angle ..beta.. approx. = 80/sup 0/ with larger values of h/sub lim//w corresponding to smaller throat angles ..beta../sub 0/. The limiting void width h/sub lim//w also increased with larger bleed flows into the void. These instabilities may make it difficult to correlate experimental virtual impactor data with theory.
NASA Astrophysics Data System (ADS)
Mann, R. B.; Pegoraro, L.; Oltean, M.
2011-12-01
We numerically obtain a class of soliton solutions for Einstein gravity in (n+1) dimensions coupled to massive Abelian gauge fields and with a negative cosmological constant with Lifshitz asymptotic behavior. We find that for all n?3, a discrete set of magic values for the charge density at the origin (guaranteeing an asymptotically Lifshitz geometry) exists when the critical exponent associated with the Lifshitz scaling is z=2; moreover, in all cases, a single magic value is obtained for essentially every 1
Two-dimensional phased array probe shape corrections
NASA Astrophysics Data System (ADS)
Lupien, Vincent; Cancre, Fabrice; Lacroix, Benolt; Miller, Ted; Selman, John; Kinney, Andy; Duffy, Tim; Herzog, Pamela G.
2002-05-01
The availability of non-destructive testing hardware capable of controlling large numbers of elements has made possible forays into two-dimensional ultrasonic arrays. Here, we explore two such arrays. The first is a conical matrix array for three-dimensional imaging of fastener holes in aircraft wing structures, and the second is an annular-sectorial array with a compound radius of curvature for the inspection of aircraft engine grade billets. In both prototypes, significant departures of the true shape of the probe face from its ideal value are observed. Since the shape aberrations are many wavelengths in magnitude, it is impossible to arrive at the desired beam profile using the beamforming parameters for the ideal probe shape. We detail our approach for correcting the beamforming process. It is based on a combination of parametric representations of probe shape families and experimental measurements with specially designed targets. While exposing current limitations in the probe manufacturing process, our results demonstrate that complicated probe malformations of many wavelengths in magnitude can easily be corrected and that the spatially disjoint nature of two-dimensional arrays becomes an opportunity for such corrections.
Spectral measurements of two-dimensional color images
NASA Astrophysics Data System (ADS)
Hauta-Kasari, Markku; Miyazawa, Kanae; Toyooka, Satoru; Parkkinen, Jussi P. S.
1999-05-01
In this work we propose a prototype of the spectral vision system, which can be used to measure a color spectrum and two- dimensional spectral images. We first designed a low- dimensional broad band color filter set with a constraint of positive spectral values by the unsupervised neural network. Then we constructed a compact size optical setup for the spectral synthesizer, which can be used to synthesize the light corresponding to the spectral characteristics of the color filter. In the optical setup we implemented the color filters by the use of the liquid crystal spatial light modulator (LCSLM). In our experiments we illuminated a sample of a real world scene by the synthesized lights and detected the intensity images of the filtering process by the CCD- camera. The intensity images correspond to the optically calculated inner products between the color filters and a sample. The data obtained from the filtering process is only a few monochrome images and therefore convenient for storing and transmitting spectral images. From the detected inner products we reconstructed the sample's color spectra by the use of inverse matrix. We present experimental results of measuring a single color spectrum and two-dimensional spectral images.
Scaling and self-similarity in two-dimensional hydrodynamics.
Ercan, Ali; Kavvas, M Levent
2015-07-01
The conditions under which depth-averaged two-dimensional (2D) hydrodynamic equations system as an initial-boundary value problem (IBVP) becomes self-similar are investigated by utilizing one-parameter Lie group of point scaling transformations. Self-similarity conditions due to the 2D k-ε turbulence model are also investigated. The self-similarity conditions for the depth-averaged 2D hydrodynamics are found for the flow variables including the time, the longitudinal length, the transverse length, the water depth, the flow velocities in x- and y-directions, the bed shear stresses in x- and y-directions, the bed shear velocity, the Manning's roughness coefficient, the kinematic viscosity of the fluid, the eddy viscosity, the turbulent kinetic energy, the turbulent dissipation, and the production and the source terms in the k-ε model. By the numerical simulations, it is shown that the IBVP of depth-averaged 2D hydrodynamic flow process in a prototype domain can be self-similar with that of a scaled domain. In fact, by changing the scaling parameter and the scaling exponents of the length dimensions, one can obtain several different scaled domains. The proposed scaling relations obtained by the Lie group scaling approach may provide additional spatial, temporal, and economical flexibility in setting up physical hydraulic models in which two-dimensional flow components are important. PMID:26232977
Two-dimensional structure of auroral poleward boundary intensifications
NASA Astrophysics Data System (ADS)
Zesta, E.; Donovan, E.; Lyons, L.; Enno, G.; Murphree, J. S.; Cogger, L.
2002-11-01
We investigate the two-dimensional structure of auroral poleward boundary intensifications (PBIs). PBIs are a nightside auroral intensification that has been studied primarily with ground-based meridian scanning photometers (MSPs). They have a signature that in the MSP data, appears as an increase in intensity at or near the magnetic separatrix and is often seen to extend equatorward. They are also associated with fast flows in the tail and are thus important to the dynamics of the plasma sheet. MSP data provide information about the temporal evolution of the aurora in one spatial dimension, in this case roughly along a magnetic meridian. This paper is motivated by a desire to determine the physics of PBIs that is revealed by their two-dimensional structure. To do this, we have identified a number of PBI events in the CANOPUS Rankin Inlet and Gillam MSPs that occurred at times when high-resolution, two-dimensional images of the aurora over the same region were also available. The two-dimensional images used in this study were obtained by the Freja UV imager, from October 1992 to January 1993, and by the CANOPUS Gillam all-sky imager during the winter viewing season of 1996-1997. We find that PBIs, as observed by the MSPs, are either equatorward extending or non-equatorward extending. Equatorward extending PBIs are either north-south aligned structures or east-west arcs propagating mostly equatorward, but we were not able to determine without doubt which type is the most prevalent. We suggest that equatorward extending PBIs may be the auroral footprint of two major modes of energy transfer in the plasma sheet: multiple, narrow, earthward fast-flow channels in the plasma sheet and sequences of azimuthally broad and primarily earthward propagating phase fronts initiating near the separatrix. Nonequatorward extending PBIs are found to mostly be a series of multiple bead-like intensifications along the poleward boundary of the aurora zone. Such PBIs may be evidence for shear instabilities at the separatrix boundary on the flanks of the magnetotail.
Scattering of solitons in the formalism of the Darboux transform
Matveev, V.B.; Sall, M.A.
1986-09-01
By means of the technique of Darboux transformations formules are obtained which describe the scattering of solitons in the Kadomtsev-Petviashvili equations; the KdV equation, the nonlocal KdV equation, the two-dimensionalized Toda lattice and its periodic reductions, and, in particular, the Sine-Gordon equation.
Scattering of solitons in the formalism of the Darboux transform
Matveev, V.B.; Sall', M.A.
1986-09-10
By means of the technique of Darboux transformations formulas are obtained which describe the scattering of solitons in the Kadomtsev-Petviashvili equations; the KdV equation, the nonlocal KdV equation, the two-dimensionalized Toda lattice and its periodic reductions, and, in particular, the sine-Gordon equation.
Coherent atomic soliton molecules for matter-wave switching
Yin, Chenyun; Berloff, Natalia G.; Perez-Garcia, Victor M.; Novoa, David; Carpentier, Alicia V.; Michinel, Humberto
2011-05-15
We discuss the dynamics of interacting dark-bright two-dimensional vector solitons in multicomponent immiscible bulk Bose-Einstein condensates. We describe matter-wave molecules without a scalar counterpart that can be seen as bound states of vector objects. We also analyze the possibility of using these structures as building blocks for the design of matter-wave switchers.
Continuous Solitons in a Lattice Nonlinearity.
Pierangeli, D; Flammini, M; Di Mei, F; Parravicini, J; de Oliveira, C E M; Agranat, A J; DelRe, E
2015-05-22
We study theoretically and experimentally the propagation of optical solitons in a lattice nonlinearity, a periodic pattern that both affects and is strongly affected by the wave. Observations are carried out using spatial photorefractive solitons in a volume microstructured crystal with a built-in oscillating low-frequency dielectric constant. The pattern causes an oscillating electro-optic response that induces a periodic optical nonlinearity. On-axis results in potassium-lithium-tantalate-niobate indicate the appearance of effective continuous saturated-Kerr solitons, where all spatial traces of the lattice vanish, independently of the ratio between beam width and lattice constant. Decoupling the lattice nonlinearity allows the detection of discrete delocalized and localized light distributions, demonstrating that the continuous solitons form out of the combined compensation of diffraction and of the underlying periodic volume pattern. PMID:26047230
Implementations of two-dimensional liquid chromatography
Guiochon, Georges A; Marchetti, Nicola; Mriziq, Khaled S; Shalliker, R. Andrew
2008-01-01
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.
Two-dimensional vortices and accretion disks
NASA Astrophysics Data System (ADS)
Nauta, Michiel Doede
2000-01-01
Observations show that there are disks around certain stars that slowly rain down on the central (compact) object: accretion disks. The rate of depletion of the disk might be slow but is still larger than was expected on theoretical grounds. That is why it has been suggested that the disks are turbulent. Because the disk is thin and rotating this turbulence might be related to two-dimensional (2D) turbulence which is characterized by energy transfers towards small wave numbers and the formation of 2D-vortices. This hypothesis is investigated in this thesis by numerical simulations. After an introduction, the numerical algorithm that was inplemented is discussed together with its relation to an accretion disk. It performs well under the absence of discontinuities. The code is used to study 2D-turbulence under the influence of background rotation with compressibility and a shearing background flow. The first is found to be of little consequence but the shear flow alters 2D-turbulence siginificantly. Only prograde vortices of enough strength are able to withstand the shear flow. The size of the vortices in the cross stream direction is also found to be smaller than the equivalent of the thickness of an accretion disk. These circulstances imply that the assumption of two-dimensionality is questionable so that 2D-vortices might not abound in accretion disks. However, the existence of such vortices is not ruled out and one such a cortex is studied in detail in chapter 4. The internal structure of the vortex is well described by a balance between Coriolis, centrifugal and pressure forces. The vortex is also accompanied by two spiral compressible waves. These are not responsible for the azimuthal drift of the vortex, which results from secondary vortices, but they might be related to the small radial drift that is observed. Radial drift leads to accretion but it is not very efficient. Multiple vortex interactions are the topic of tha last chapter and though interesting the increase in accretion grows only linearly with the number of vortices.
FPT Algorithm for Two-Dimensional Cyclic Convolutions
NASA Technical Reports Server (NTRS)
Truong, Trieu-Kie; Shao, Howard M.; Pei, D. Y.; Reed, Irving S.
1987-01-01
Fast-polynomial-transform (FPT) algorithm computes two-dimensional cyclic convolution of two-dimensional arrays of complex numbers. New algorithm uses cyclic polynomial convolutions of same length. Algorithm regular, modular, and expandable.
Solitons with Periodic Behavior in an SBN:75 Photorefractive Crystal
NASA Astrophysics Data System (ADS)
Guo, Qing-Lin; Deng, Gui-Ying; Liang, Bao-Lai; Li, Pan-Lai; Li, Yan; Li, Xu
2010-08-01
We study the formation of spatial solitons in an SBN:75 photorefractive crystal by a 532 nm continuous-wave laser beam. The output beam from the crystal cannot be compressed proportionally to the voltage of the applied electric field. Quasi-steady-state spatial solitons are formed instantaneously at a voltage of 900 V. Interestingly, the quasi-steady-state solitons exhibit a periodic behavior consisting of formation/broken/reformation cycles. If we increase the input intensity of the soliton beam but keep the same signal-to-background intensity ratio, the solitons stay for a longer time in the quasi-steady state and a longer period of soliton formation/broken/reformation cycle is also observed.
Two dimensional and linear scintillation detectors for fast neutron imaging comparative analysis
NASA Astrophysics Data System (ADS)
Mikerov, V. I.; Koshelev, A. P.; Ozerov, O. V.; Sviridov, A. S.; Yurkov, D. I.
2014-05-01
The paper was aimed to compare performance capabilities of two types of scintillation detectors commonly used for fast neutron imaging: two dimensional 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 two dimensional detector. But, the two dimensional detector surpasses the linear one in capacity. The presented results can be used for designing radiographic fast neutron detectors with organic scintillators.
Braid Entropy of Two-Dimensional Turbulence
Francois, Nicolas; Xia, Hua; Punzmann, Horst; Faber, Benjamin; Shats, Michael
2015-01-01
The evolving shape of material fluid lines in a flow underlies the quantitative prediction of the dissipation and material transport in many industrial and natural processes. However, collecting quantitative data on this dynamics remains an experimental challenge in particular in turbulent flows. Indeed the deformation of a fluid line, induced by its successive stretching and folding, can be difficult to determine because such description ultimately relies on often inaccessible multi-particle information. Here we report laboratory measurements in two-dimensional turbulence that offer an alternative topological viewpoint on this issue. This approach characterizes the dynamics of a braid of Lagrangian trajectories through a global measure of their entanglement. The topological length of material fluid lines can be derived from these braids. This length is found to grow exponentially with time, giving access to the braid topological entropy . The entropy increases as the square root of the turbulent kinetic energy and is directly related to the single-particle dispersion coefficient. At long times, the probability distribution of is positively skewed and shows strong exponential tails. Our results suggest that may serve as a measure of the irreversibility of turbulence based on minimal principles and sparse Lagrangian data. PMID:26689261
Braid Entropy of Two-Dimensional Turbulence.
Francois, Nicolas; Xia, Hua; Punzmann, Horst; Faber, Benjamin; Shats, Michael
2015-01-01
The evolving shape of material fluid lines in a flow underlies the quantitative prediction of the dissipation and material transport in many industrial and natural processes. However, collecting quantitative data on this dynamics remains an experimental challenge in particular in turbulent flows. Indeed the deformation of a fluid line, induced by its successive stretching and folding, can be difficult to determine because such description ultimately relies on often inaccessible multi-particle information. Here we report laboratory measurements in two-dimensional turbulence that offer an alternative topological viewpoint on this issue. This approach characterizes the dynamics of a braid of Lagrangian trajectories through a global measure of their entanglement. The topological length of material fluid lines can be derived from these braids. This length is found to grow exponentially with time, giving access to the braid topological entropy . The entropy increases as the square root of the turbulent kinetic energy and is directly related to the single-particle dispersion coefficient. At long times, the probability distribution of is positively skewed and shows strong exponential tails. Our results suggest that may serve as a measure of the irreversibility of turbulence based on minimal principles and sparse Lagrangian data. PMID:26689261
Braid Entropy of Two-Dimensional Turbulence
NASA Astrophysics Data System (ADS)
Francois, Nicolas; Xia, Hua; Punzmann, Horst; Faber, Benjamin; Shats, Michael
2015-12-01
The evolving shape of material fluid lines in a flow underlies the quantitative prediction of the dissipation and material transport in many industrial and natural processes. However, collecting quantitative data on this dynamics remains an experimental challenge in particular in turbulent flows. Indeed the deformation of a fluid line, induced by its successive stretching and folding, can be difficult to determine because such description ultimately relies on often inaccessible multi-particle information. Here we report laboratory measurements in two-dimensional turbulence that offer an alternative topological viewpoint on this issue. This approach characterizes the dynamics of a braid of Lagrangian trajectories through a global measure of their entanglement. The topological length of material fluid lines can be derived from these braids. This length is found to grow exponentially with time, giving access to the braid topological entropy . The entropy increases as the square root of the turbulent kinetic energy and is directly related to the single-particle dispersion coefficient. At long times, the probability distribution of is positively skewed and shows strong exponential tails. Our results suggest that may serve as a measure of the irreversibility of turbulence based on minimal principles and sparse Lagrangian data.
Two-dimensional magnetic colloids under shear.
Mohorič, Tomaž; Dobnikar, Jure; Horbach, Jürgen
2016-04-01
Complex rheological properties of soft disordered solids, such as colloidal gels or glasses, inspire a range of novel applications. However, the microscopic mechanisms of their response to mechanical loading are not well understood. Here, we elucidate some aspects of these mechanisms by studying a versatile model system, i.e. two-dimensional superparamagnetic colloids in a precessing magnetic field, whose structure can be tuned from a hexagonal crystal to a disordered gel network by varying the external field opening angle θ. We perform Langevin dynamics simulations subjecting these structures to a constant shear rate and observe three qualitatively different types of material response. In hexagonal crystals (θ = 0°), at a sufficiently low shear rate, plastic flow occurs via successive stress drops at which the stress releases due to the formation of dislocation defects. The gel network at θ = 48°, on the contrary, via bond rearrangement and transient shear banding evolves into a homogeneously stretched network at large strains. The latter structure remains metastable after switching off of the shear. At θ = 50°, the external shear makes the system unstable against phase separation and causes a failure of the network structure leading to the formation of hexagonal close packed clusters interconnected by particle chains. At a microcopic level, our simulations provide insight into some of the mechanisms by which strain localization as well as material failure occur in a simple gel-like network. Furthermore, we demonstrate that new stretched network structures can be generated by the application of shear. PMID:26877059
Two-dimensional Dirac signature of germanene
NASA Astrophysics Data System (ADS)
Zhang, L.; Bampoulis, P.; van Houselt, A.; Zandvliet, H. J. W.
2015-09-01
The structural and electronic properties of germanene coated Ge2Pt clusters have been determined by scanning tunneling microscopy and spectroscopy at room temperature. The interior of the germanene sheet exhibits a buckled honeycomb structure with a lattice constant of 4.3 and a buckling of 0.2 . The zigzag edges of germanene are reconstructed and display a 4 periodicity. The differential conductivity of the interior of the germanene sheet has a V-shape, which is reminiscent of the density of states of a two-dimensional Dirac system. The minimum of the differential conductivity is located close to the Fermi level and has a non-zero value, which we ascribe to the metallic character of the underlying Ge2Pt substrate. Near the reconstructed germanene zigzag edges the shape of the differential conductivity changes from a V-shape to a more parabolic-like shape, revealing that the reconstructed germanene zigzag edges do not exhibit a pronounced metallic edge state.
An atlas of two-dimensional materials.
Mir, Pere; Audiffred, Martha; Heine, Thomas
2014-09-21
The discovery of graphene and other two-dimensional (2D) materials together with recent advances in exfoliation techniques have set the foundations for the manufacturing of single layered sheets from any layered 3D material. The family of 2D materials encompasses a wide selection of compositions including almost all the elements of the periodic table. This derives into a rich variety of electronic properties including metals, semimetals, insulators and semiconductors with direct and indirect band gaps ranging from ultraviolet to infrared throughout the visible range. Thus, they have the potential to play a fundamental role in the future of nanoelectronics, optoelectronics and the assembly of novel ultrathin and flexible devices. We categorize the 2D materials according to their structure, composition and electronic properties. In this review we distinguish atomically thin materials (graphene, silicene, germanene, and their saturated forms; hexagonal boron nitride; silicon carbide), rare earth, semimetals, transition metal chalcogenides and halides, and finally synthetic organic 2D materials, exemplified by 2D covalent organic frameworks. Our exhaustive data collection presented in this Atlas demonstrates the large diversity of electronic properties, including band gaps and electron mobilities. The key points of modern computational approaches applied to 2D materials are presented with special emphasis to cover their range of application, peculiarities and pitfalls. PMID:24825454
Predicting Two-Dimensional Silicon Carbide Monolayers.
Shi, Zhiming; Zhang, Zhuhua; Kutana, Alex; Yakobson, Boris I
2015-10-27
Intrinsic semimetallicity of graphene and silicene largely limits their applications in functional devices. Mixing carbon and silicon atoms to form two-dimensional (2D) silicon carbide (SixC1-x) sheets is promising to overcome this issue. Using first-principles calculations combined with the cluster expansion method, we perform a comprehensive study on the thermodynamic stability and electronic properties of 2D SixC1-x monolayers with 0 ? x ? 1. Upon varying the silicon concentration, the 2D SixC1-x presents two distinct structural phases, a homogeneous phase with well dispersed Si (or C) atoms and an in-plane hybrid phase rich in SiC domains. While the in-plane hybrid structure shows uniform semiconducting properties with widely tunable band gap from 0 to 2.87 eV due to quantum confinement effect imposed by the SiC domains, the homogeneous structures can be semiconducting or remain semimetallic depending on a superlattice vector which dictates whether the sublattice symmetry is topologically broken. Moreover, we reveal a universal rule for describing the electronic properties of the homogeneous SixC1-x structures. These findings suggest that the 2D SixC1-x monolayers may present a new "family" of 2D materials, with a rich variety of properties for applications in electronics and optoelectronics. PMID:26394207
Two-dimensional Fourier transform electronic spectroscopy
NASA Astrophysics Data System (ADS)
Jonas, David
2012-02-01
Sensitive interference detection of the electric field of femtosecond four-wave mixing signals (stimulated photon echoes) at their point of origin in the sample can be used to record two-dimensional (2D) Fourier transform electronic spectra. In direct analogy to 2D nuclear magnetic resonance, 2D Fourier transform spectra have nearly homogeneous linewidths in each frequency dimension and sort the signal spectrum according to the initial excitation frequency. The initial excitation frequency information is stored in a robust population grating, so 2D spectra can be used to study both coherent and incoherent processes, and have revealed coherent aspects of energy transfer processes. Femtosecond 2D spectra also have the advantage of ``freezing out'' vibrational motions as inhomogeneities, raising interesting questions about what kinds of broadening can be rephased in 2D spectra recorded with stimulated photon echo pulse sequences. This talk will focus on coherent aspects of non-adiabatic electronic curve crossing and their manifestation in 2D electronic spectra.
Two-dimensional optical fibre cantilever accelerometer
NASA Astrophysics Data System (ADS)
Li, Jun; Sun, J. N.; Miliar, M. M.; Dong, F. Z.; Maier, R. R. J.; Hand, D. P.; MacPherson, W. N.
2015-09-01
Focused Ion Beam (FIB) machining has been demonstrated to be capable of fabricating nano and micro scale elements onto optical fibres. In this paper we exploit FIB to fabricate core aligned 45 mirrors at the end of multi-core fibres (MCF). The resulting fibre is used as a component in a two dimensional optical fibre accelerometer. The mirror is produced using a two step process: first a scanning process is used to make a rough cut to define the overall mirror structure. This is followed by a polishing process to create an optical surface finish. The machined 45 mirror can be accurately aligned with optical fibre core, which avoids issues associated with the alignment of external turning mirror components. Proof-of-concept tests demonstrate the use of such a fibre as a two axis acceleration sensor that is interrogated interferometrically. The sensor operated between 0.5g and 4.5g with a cross talk of -24.3dB between axes.
Two-dimensional dirac delta reconsidered
NASA Astrophysics Data System (ADS)
Schmeelk, John
1994-08-01
Distribution theory continues to be of significant importance in many branches of applied mathematics and especially within the research activities of theoretical and applied physicists. It is the belief of the author that the Dirac delta functional offers enormous impact in fostering advances within distribution theory together with its applications. Whenever one requires an example of a singular, ultra or new generalized function, a version of the Dirac delta satisfies that need. In this paper we have collected several very recent and important results for the Dirac delta and formulated them within a two-dimensional domain. We then go on and graph a three-dimensional version of the result implementing the software, Pro-Matlab. Within many branches of signal analysis the geometrical aspects of a particular mathematical concept are of paramount importance to the user. For example, when one implements a transform as a filter, the geometrical considerations give strong evidence of the utility of the filter for the particular application. We have also included a preliminary beginning for considering wavelet transforms applied to distributions.
Epitaxial growth of two-dimensional stanene.
Zhu, Feng-feng; Chen, Wei-jiong; Xu, Yong; Gao, Chun-lei; Guan, Dan-dan; Liu, Can-hua; Qian, Dong; Zhang, Shou-Cheng; Jia, Jin-feng
2015-10-01
Following the first experimental realization of graphene, other ultrathin materials with unprecedented electronic properties have been explored, with particular attention given to the heavy group-IV elements Si, Ge and Sn. Two-dimensional buckled Si-based silicene has been recently realized by molecular beam epitaxy growth, whereas Ge-based germanene was obtained by molecular beam epitaxy and mechanical exfoliation. However, the synthesis of Sn-based stanene has proved challenging so far. Here, we report the successful fabrication of 2D stanene by molecular beam epitaxy, confirmed by atomic and electronic characterization using scanning tunnelling microscopy and angle-resolved photoemission spectroscopy, in combination with first-principles calculations. The synthesis of stanene and its derivatives will stimulate further experimental investigation of their theoretically predicted properties, such as a 2D topological insulating behaviour with a very large bandgap, and the capability to support enhanced thermoelectric performance, topological superconductivity and the near-room-temperature quantum anomalous Hall effect. PMID:26237127
Order Parameters for Two-Dimensional Networks
NASA Astrophysics Data System (ADS)
Kaatz, Forrest; Bultheel, Adhemar; Egami, Takeshi
2007-10-01
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.
Dynamics of two-dimensional dipole systems
Golden, Kenneth I.; Kalman, Gabor J.; Hartmann, Peter; Donko, Zoltan
2010-09-15
Using a combined analytical/molecular dynamics approach, we study the current fluctuation spectra and longitudinal and transverse collective mode dispersions of the classical two-dimensional (point) dipole system (2DDS) characterized by the {phi}{sub D}(r)={mu}{sup 2}/r{sup 3} repulsive interaction potential; {mu} is the electric dipole strength. The interest in the 2DDS is twofold. First, the quasi-long-range 1/r{sup 3} interaction makes the system a unique classical many-body system, with a remarkable collective mode behavior. Second, the system may be a good model for a closely spaced semiconductor electron-hole bilayer, a system that is in the forefront of current experimental interest. The longitudinal collective excitations, which are of primary interest for the liquid phase, are acoustic at long wavelengths. At higher wave numbers and for sufficiently high coupling strength, we observe the formation of a deep minimum in the dispersion curve preceded by a sharp maximum; this is identical to what has been observed in the dispersion of the zero-temperature bosonic dipole system, which in turn emulates so-called roton-maxon excitation spectrum of the superfluid {sup 4}He. The analysis we present gives an insight into the emergence of this apparently universal structure, governed by strong correlations. We study both the liquid and the crystalline solid state. We also observe the excitation of combination frequencies, resembling the roton-roton, roton-maxon, etc. structures in {sup 4}He.
Single Molecule Approaches for Two Dimensional Nanostructures
NASA Astrophysics Data System (ADS)
Baker, Thomas; Guo, Shajun; Koh, Weon-Kyu; Makarov, Nikolay; Fiddler, Andrew; Robel, Istvan; Klimov, Victor
2014-03-01
A variety of two dimensional semiconductor nanostructures have been synthesized recently by a number of different groups. Of these, nanoplatelets made of a single to few layers of material have shown interesting promise due to confinement in only a single direction. The photophysics of these types of structures show large exciton binding energies and narrow emission widths in ensemble measurements. Only a few single molecule experiments have been reported in the literature and we hope to expand the insights that single molecule techniques can provide in the understanding of these new materials. Our group has recently extended our synthetic expertise gained from quantum dots into these 2D nanoplatelets including CdSe, MoS2 and graphene. Time correlated single photon counting experiments at the single molecule level provide information on the homogenous linewidths, quantum yield variations, and fluorescence lifetimes. Furthermore, two photon correlations at zero time delay allow us to confirm the single molecule nature of the emission and potentially determine biexciton quantum yields and lifetimes.
Redox options in two-dimensional electrophoresis.
Wait, R; Begum, S; Brambilla, D; Carabelli, A M; Conserva, F; Rocco Guerini, A; Eberini, I; Ballerio, R; Gemeiner, M; Miller, I; Gianazza, E
2005-05-01
Two-dimensional electrophoresis is usually run on fully reduced samples. Under these conditions even covalently bound oligomers are dissociated and individual polypeptide chains may be fully unfolded by both, urea and SDS, which maximizes the number of resolved components and allows their pI and M(r) to be most accurately evaluated. However, various electrophoretic protocols for protein structure investigation require a combination of steps under varying redox conditions. We review here some of the applications of these procedures. We also present some original data about a few related samples -- serum from four species: Homo sapiens, Mus musculus, Rattus norvegicus, Bos taurus -- which we run under fully unreduced and fully reduced conditions as well as with reduction between first and second dimension. We demonstrate that in many cases the unreduced proteins migrate with a better resolution than reduced proteins, mostly in the crowded 'alpha-globulin' area of pI 4.5-6 and M(r) 50-70 kDa. PMID:15744479
Seismic isolation of two dimensional periodic foundations
Yan, Y.; Mo, Y. L.; Laskar, A.; Cheng, Z.; Shi, Z.; Menq, F.; Tang, Y.
2014-07-28
Phononic crystal is now used to control acoustic waves. When the crystal goes to a larger scale, it is called periodic structure. The band gaps of the periodic structure can be reduced to range from 0.5 Hz to 50 Hz. Therefore, the periodic structure has potential applications in seismic wave reflection. In civil engineering, the periodic structure can be served as the foundation of upper structure. This type of foundation consisting of periodic structure is called periodic foundation. When the frequency of seismic waves falls into the band gaps of the periodic foundation, the seismic wave can be blocked. Field experiments of a scaled two dimensional (2D) periodic foundation with an upper structure were conducted to verify the band gap effects. Test results showed the 2D periodic foundation can effectively reduce the response of the upper structure for excitations with frequencies within the frequency band gaps. When the experimental and the finite element analysis results are compared, they agree well with each other, indicating that 2D periodic foundation is a feasible way of reducing seismic vibrations.
Two-dimensional detector of thermal neutrons
NASA Astrophysics Data System (ADS)
Andreev, V.; Ganzha, G.; Ilyin, D.; Ivanov, E.; Kovalenko, S.; Krivshich, A.; Nadtochy, A.; Runov, V.
2007-10-01
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.
Two-dimensional distributed feedback lasers based on static and dynamic Bragg structures
Baryshev, V R; Ginzburg, N S
2011-09-30
In order to increase the output power of DFB lasers, we consider the possibility of using two-dimensional distributed feedback. Within the framework of this scheme, the feedback circuit includes four partial wave fluxes propagating in mutually orthogonal directions, which makes it possible to provide coherent radiation from a spatially extended planar active medium characterised by large values of the Fresnel parameter. By analogy with the onedimensional distributed feedback, the wave coupling can be ensured by using both the structures with a periodically varying effective refractive index (static two-dimensional Bragg structures) and the gain modulation (photo-induced two-dimensional Bragg structures). Within the semiclassical approximation, the initial conditions and nonlinear dynamics of lasers with the above-described two-dimensional Bragg structures are analysed. Self-similarity conditions are found, allowing one to scale the laser parameters with increasing active region size, which is accompanied by an increase in the integrated output power.
SCAPS, a two-dimensional ion detector for mass spectrometer
NASA Astrophysics Data System (ADS)
Yurimoto, Hisayoshi
2014-05-01
Faraday Cup (FC) and electron multiplier (EM) are of the most popular ion detector for mass spectrometer. FC is used for high-count-rate ion measurements and EM can detect from single ion. However, FC is difficult to detect lower intensities less than kilo-cps, and EM loses ion counts higher than Mega-cps. Thus, FC and EM are used complementary each other, but they both belong to zero-dimensional detector. On the other hand, micro channel plate (MCP) is a popular ion signal amplifier with two-dimensional capability, but additional detection system must be attached to detect the amplified signals. Two-dimensional readout for the MCP signals, however, have not achieve the level of FC and EM systems. A stacked CMOS active pixel sensor (SCAPS) has been developed to detect two-dimensional ion variations for a spatial area using semiconductor technology [1-8]. The SCAPS is an integrated type multi-detector, which is different from EM and FC, and is composed of more than 500×500 pixels (micro-detectors) for imaging of cm-area with a pixel of less than 20 µm in square. The SCAPS can be detected from single ion to 100 kilo-count ions per one pixel. Thus, SCAPS can be accumulated up to several giga-count ions for total pixels, i.e. for total imaging area. The SCAPS has been applied to stigmatic ion optics of secondary ion mass spectrometer, as a detector of isotope microscope [9]. The isotope microscope has capabilities of quantitative isotope images of hundred-micrometer area on a sample with sub-micrometer resolution and permil precision, and of two-dimensional mass spectrum on cm-scale of mass dispersion plane of a sector magnet with ten-micrometer resolution. The performance has been applied to two-dimensional isotope spatial distribution for mainly hydrogen, carbon, nitrogen and oxygen of natural (extra-terrestrial and terrestrial) samples and samples simulated natural processes [e.g. 10-17]. References: [1] Matsumoto, K., et al. (1993) IEEE Trans. Electron Dev. 40, 82-85. [2] Takayanagi et al. (1999) Proc. 1999 IEEE workshop on Charge-Coupled Devices and Advanced Image Sensors, 159-162. [3] Kunihiro et al. (2001) Nucl. Instrum. Methods Phys. Res. Sec. A 470, 512-519. [4] Nagashima et al. (2001) Surface Interface Anal. 31, 131-137. [5] Takayanagi et al. (2003) IEEE Trans. Electron Dev. 50, 70- 76. [6] Sakamoto and Yurimoto (2006) Surface Interface Anal. 38, 1760-1762. [7] Yamamoto et al. (2010) Surface Interface Anal. 42, 1603-1605. [8] Sakamoto et al. (2012) Jpn. J. Appl. Phys. 51, 076701. [9] Yurimoto et al. (2003) Appl. Surf. Sci. 203-204, 793-797. [10] Nagashima et al. (2004) Nature 428, 921-924. [11] Kunihiro et al. (2005) Geochim. Cosmochim. Acta 69, 763-773. [12] Nakamura et al. (2005) Geology 33, 829-832. [13] Sakamoto et al. (2007) Science 317, 231-233. [14] Greenwood et al. (2008) Geophys. Res. Lett., 35, L05203. [15] Greenwood et al. (2011) Nature Geoscience 4, 79-82. [16] Park et al. (2012) Meteorit. Planet. Sci. 47, 2070-2083. [17] Hashiguchi et al. (2013) Geochim. Cosmochim. Acta. 122, 306-323.
Microwave near-field imaging of two-dimensional semiconductors.
Berweger, Samuel; Weber, Joel C; John, Jimmy; Velazquez, Jesus M; Pieterick, Adam; Sanford, Norman A; Davydov, Albert V; Brunschwig, Bruce; Lewis, Nathan S; Wallis, Thomas M; Kabos, Pavel
2015-02-11
Optimizing new generations of two-dimensional devices based on van der Waals materials will require techniques capable of measuring variations in electronic properties in situ and with nanometer spatial resolution. We perform scanning microwave microscopy (SMM) imaging of single layers of MoS2 and n- and p-doped WSe2. By controlling the sample charge carrier concentration through the applied tip bias, we are able to reversibly control and optimize the SMM contrast to image variations in electronic structure and the localized effects of surface contaminants. By further performing tip bias-dependent point spectroscopy together with finite element simulations, we distinguish the effects of the quantum capacitance and determine the local dominant charge carrier species and dopant concentration. These results underscore the capability of SMM for the study of 2D materials to image, identify, and study electronic defects. PMID:25625509
Two-dimensional angular transmission characterization of CPV modules.
Herrero, R; Domínguez, C; Askins, S; Antón, I; Sala, G
2010-11-01
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
Statistical properties of freely decaying two-dimensional hydrodynamic turbulence
NASA Astrophysics Data System (ADS)
Kudryavtsev, A. N.; Kuznetsov, E. A.; Sereshchenko, E. V.
2013-02-01
Statistical characteristics of freely decaying two-dimensional hydrodynamic turbulence at high Reynolds numbers are numerically studied. In particular, numerical experiments (with resolution up to 8192 × 8192) provide a Kraichnan-type turbulence spectrum E k ˜ k -3. By means of spatial filtration, it is found that the main contribution to the spectrum comes from sharp vorticity gradients in the form of quasi-shocks. Such quasi-singularities are responsible for a strong angular dependence of the spectrum owing to well-localized (in terms of the angle) jets with minor and/or large overlapping. In each jet, the spectrum decreases as k -3. The behavior of the third-order structure function accurately agrees with the Kraichnan direct cascade concept corresponding to a constant enstrophy flux. It is shown that the power law exponents ξ n for higher structure functions grow with n more slowly than the linear dependence, thus indicating turbulence intermittency.
NASA Astrophysics Data System (ADS)
Chernitskii, Alexander A.
2016-02-01
New exact solution class of Born - Infeld type nonlinear scalar field model is obtained. These solutions are three-dimensional solitons propagating with speed of light. The appropriate twisted solitons are considered. Energy and absolute value of momentum for such soliton are proportional to absolute value of its angular momentum or spin in some approximation. The model of ideal gas for the twisted lightlike solitons with lowest twist parameter is considered. Explicit conditions provide that the spin of each soliton equals Planck constant. It is shown that these solitons look like photons.
Soliton matter as a model of dense nuclear matter
Glendenning, N.K.
1985-01-01
We employ the hybrid soliton model of the nucleon consisting of a topological meson field and deeply bound quarks to investigate the behavior of the quarks in soliton matter as a function of density. To organize the calculation, we place the solitons on a spatial lattice. The model suggests the transition of matter from a color insulator to a color conductor above a critical density of a few times normal nuclear density. 9 references, 5 figures.
Dynamics of two-dimensional bubbles.
Piedra, Saúl; Ramos, Eduardo; Herrera, J Ramón
2015-06-01
The dynamics of two-dimensional bubbles ascending under the influence of buoyant forces is numerically studied with a one-fluid model coupled with the front-tracking technique. The bubble dynamics are described by recording the position, shape, and orientation of the bubbles as functions of time. The qualitative properties of the bubbles and their terminal velocities are described in terms of the Eötvos (ratio of buoyancy to surface tension) and Archimedes numbers (ratio of buoyancy to viscous forces). The terminal Reynolds number result from the balance of buoyancy and drag forces and, consequently, is not an externally fixed parameter. In the cases that yield small Reynolds numbers, the bubbles follow straight paths and the wake is steady. A more interesting behavior is found at high Reynolds numbers where the bubbles follow an approximately periodic zigzag trajectory and an unstable wake with properties similar to the Von Karman vortex street is formed. The dynamical features of the motion of single bubbles are compared to experimental observations of air bubbles ascending in a water-filled Hele-Shaw cell. Although the comparison is not strictly valid in the sense that the effect of the lateral walls is not incorporated in the model, most of the dynamical properties observed are in good qualitative agreement with the numerical calculations. Hele-Shaw cells with different gaps have been used to determine the degree of approximation of the numerical calculation. It is found that for the relation between the terminal Reynolds number and the Archimedes number, the numerical calculations are closer to the observations of bubble dynamics in Hele-Shaw cells of larger gaps. PMID:26172798
Fast, comprehensive two-dimensional liquid chromatography.
Stoll, Dwight R; Li, Xiaoping; Wang, Xiaoli; Carr, Peter W; Porter, Sarah E G; Rutan, Sarah C
2007-10-19
The absolute need to improve the separating power of liquid chromatography, especially for multi-constituent biological samples, is becoming increasingly evident. In response, over the past few years, there has been a great deal of interest in the development of two-dimensional liquid chromatography (2DLC). Just as 1DLC is preferred to 1DGC based on its compatibility with biological materials we believe that ultimately 2DLC will be preferred to the much more highly developed 2DGC for such samples. The huge advantage of 2D chromatographic techniques over 1D methods is inherent in the tremendous potential increase in peak capacity (resolving power). This is especially true of comprehensive 2D chromatography wherein it is possible, under ideal conditions, to obtain a total peak capacity equal to the product of the peak capacities of the first and second dimension separations. However, the very long timescale (typically several hours to tens of hours) of comprehensive 2DLC is clearly its chief drawback. Recent advances in the use of higher temperatures to speed up isocratic and gradient elution liquid chromatography have been used to decrease the time needed to do the second dimension LC separation of 2DLC to about 20s for a full gradient elution run. Thus, fast, high temperature LC is becoming a very promising technique. Peak capacities of over 2000 and rates of peak capacity production of nearly 1 peak/s have been achieved. In consequence, many real samples showing more than 200 peaks with signal to noise ratios of better than 10:1 have been run in total times of under 30 min. This report is not intended to be a comprehensive review of 2DLC, but is deliberately focused on the issues involved in doing fast 2DLC by means of elevating the column temperature; however, many issues of broader applicability will be discussed. PMID:17888443
Two-dimensional microfabricated sources for nanoelectrospray.
Le Gac, Sverine; Arscott, Steve; Cren-Oliv, Ccile; Rolando, Christian
2003-12-01
The idea of a novel two-dimensional (2D) nanoelectrospray ionization emitter tip with the shape of a nib is explored here. This novel planar design is studied as an alternative to the needle-like standard emitter tips that suffer from a lack of reproducibility and robustness and from an inherent incompatibility with high-throughput analysis. The composition of the micro-nib sources is analogous to the working of a simple fountain pen, with a liquid reservoir linked to a micro-nib tip from which the sample is electrosprayed via a capillary slot. The micro-nib prototypes described here were fabricated using microtechnology techniques and using the epoxy-based negative photoresist SU-8. The resulting free-standing micro-nib structure was supported by a silicon wafer. We present here two series of such micro-nib sources, the latter series exhibiting improved characteristics such as a 8 micro m source width of the nib tip. They were tested in mass spectrometry experiments on an ion trap mass spectrometer (LCQ Deca XP+, Thermo Finnigan) using standard peptide samples having concentrations down to 1 micro M and with a high voltage (HV) supply around 1 kV for the second series of micro-nib sources. In addition to the stability of the spray, the obtained mass spectra showed the reliability of these sources for peptide analysis; the signal of the spectra was as intense and the signal-to-noise ratio (S/N) as high as that obtained with the use of standard emitter tips. PMID:14696205
Two-dimensional dynamic fluid bowtie attenuators.
Hermus, James R; Szczykutowicz, Timothy P
2016-01-01
Fluence field modulated (FFM) CT allows for improvements in image quality and dose reduction. To date, only one-dimensional modulators have been proposed, as the extension to two-dimensional (2-D) modulation is difficult with solid-metal attenuation-based fluence field modulated designs. This work proposes to use liquid and gas to attenuate the x-ray beam, as unlike solids, these materials can be arranged allowing for 2-D fluence modulation. The thickness of liquid and the pressure for a given path length of gas were determined that provided the same attenuation as 30cm of soft tissue at 80, 100, 120, and 140kV. Liquid iodine, zinc chloride, cerium chloride, erbium oxide, iron oxide, and gadolinium chloride were studied. Gaseous xenon, uranium hexafluoride, tungsten hexafluoride, and nickel tetracarbonyl were also studied. Additionally, we performed a proof-of-concept experiment using a 96 cell array in which the liquid thickness in each cell was adjusted manually. Liquid thickness varied as a function of kV and chemical composition, with erbium oxide allowing for the smallest thickness. For the gases, tungsten hexaflouride required the smallest pressure to compensate for 30cm of soft tissue. The 96 cell iodine attenuator allowed for a reduction in both dynamic range to the detector and scatter-to-primary ratio. For both liquids and gases, when k-edges were located within the diagnostic energy range used for imaging, the mean beam energy exhibited the smallest change with compensation amount. The thickness of liquids and the gas pressure seem logistically implementable within the space constraints of C-arm-based cone beam CT (CBCT) and diagnostic CT systems. The gas pressures also seem logistically implementable within the space and tube loading constraints of CBCT and diagnostic CT systems. PMID:26835499
Dynamics of two-dimensional bubbles
NASA Astrophysics Data System (ADS)
Piedra, Saúl; Ramos, Eduardo; Herrera, J. Ramón
2015-06-01
The dynamics of two-dimensional bubbles ascending under the influence of buoyant forces is numerically studied with a one-fluid model coupled with the front-tracking technique. The bubble dynamics are described by recording the position, shape, and orientation of the bubbles as functions of time. The qualitative properties of the bubbles and their terminal velocities are described in terms of the Eötvos (ratio of buoyancy to surface tension) and Archimedes numbers (ratio of buoyancy to viscous forces). The terminal Reynolds number result from the balance of buoyancy and drag forces and, consequently, is not an externally fixed parameter. In the cases that yield small Reynolds numbers, the bubbles follow straight paths and the wake is steady. A more interesting behavior is found at high Reynolds numbers where the bubbles follow an approximately periodic zigzag trajectory and an unstable wake with properties similar to the Von Karman vortex street is formed. The dynamical features of the motion of single bubbles are compared to experimental observations of air bubbles ascending in a water-filled Hele-Shaw cell. Although the comparison is not strictly valid in the sense that the effect of the lateral walls is not incorporated in the model, most of the dynamical properties observed are in good qualitative agreement with the numerical calculations. Hele-Shaw cells with different gaps have been used to determine the degree of approximation of the numerical calculation. It is found that for the relation between the terminal Reynolds number and the Archimedes number, the numerical calculations are closer to the observations of bubble dynamics in Hele-Shaw cells of larger gaps.
Two-dimensional materials and their prospects in transistor electronics
NASA Astrophysics Data System (ADS)
Schwierz, F.; Pezoldt, J.; Granzner, R.
2015-04-01
During the past decade, two-dimensional materials have attracted incredible interest from the electronic device community. The first two-dimensional material studied in detail was graphene and, since 2007, it has intensively been explored as a material for electronic devices, in particular, transistors. While graphene transistors are still on the agenda, researchers have extended their work to two-dimensional materials beyond graphene and the number of two-dimensional materials under examination has literally exploded recently. Meanwhile several hundreds of different two-dimensional materials are known, a substantial part of them is considered useful for transistors, and experimental transistors with channels of different two-dimensional materials have been demonstrated. In spite of the rapid progress in the field, the prospects of two-dimensional transistors still remain vague and optimistic opinions face rather reserved assessments. The intention of the present paper is to shed more light on the merits and drawbacks of two-dimensional materials for transistor electronics and to add a few more facets to the ongoing discussion on the prospects of two-dimensional transistors. To this end, we compose a wish list of properties for a good transistor channel material and examine to what extent the two-dimensional materials fulfill the criteria of the list. The state-of-the-art two-dimensional transistors are reviewed and a balanced view of both the pros and cons of these devices is provided.
Two-dimensional materials and their prospects in transistor electronics.
Schwierz, F; Pezoldt, J; Granzner, R
2015-05-14
During the past decade, two-dimensional materials have attracted incredible interest from the electronic device community. The first two-dimensional material studied in detail was graphene and, since 2007, it has intensively been explored as a material for electronic devices, in particular, transistors. While graphene transistors are still on the agenda, researchers have extended their work to two-dimensional materials beyond graphene and the number of two-dimensional materials under examination has literally exploded recently. Meanwhile several hundreds of different two-dimensional materials are known, a substantial part of them is considered useful for transistors, and experimental transistors with channels of different two-dimensional materials have been demonstrated. In spite of the rapid progress in the field, the prospects of two-dimensional transistors still remain vague and optimistic opinions face rather reserved assessments. The intention of the present paper is to shed more light on the merits and drawbacks of two-dimensional materials for transistor electronics and to add a few more facets to the ongoing discussion on the prospects of two-dimensional transistors. To this end, we compose a wish list of properties for a good transistor channel material and examine to what extent the two-dimensional materials fulfill the criteria of the list. The state-of-the-art two-dimensional transistors are reviewed and a balanced view of both the pros and cons of these devices is provided. PMID:25898786
Stabilization of ring dark solitons in Bose-Einstein condensates
NASA Astrophysics Data System (ADS)
Wang, Wenlong; Kevrekidis, P. G.; Carretero-Gonzlez, R.; Frantzeskakis, D. J.; Kaper, Tasso J.; Ma, Manjun
2015-09-01
Earlier work has shown that ring dark solitons in two-dimensional Bose-Einstein condensates are generically unstable. In this work, we propose a way of stabilizing the ring dark soliton via a radial Gaussian external potential. We investigate the existence and stability of the ring dark soliton upon variations of the chemical potential and also of the strength of the radial potential. Numerical results show that the ring dark soliton can be stabilized in a suitable interval of external potential strengths and chemical potentials. We also explore different proposed particle pictures considering the ring as a moving particle and find, where appropriate, results in very good qualitative and also reasonable quantitative agreement with the numerical findings.
Stabilization of ring dark solitons in Bose-Einstein condensates
Wang, Wenlong; Kevrekidis, P. G.; Carretero-González, R.; Frantzeskakis, D. J.; Kaper, Tasso J.; Ma, Manjun
2015-09-14
Earlier work has shown that ring dark solitons in two-dimensional Bose-Einstein condensates are generically unstable. In this work, we propose a way of stabilizing the ring dark soliton via a radial Gaussian external potential. We investigate the existence and stability of the ring dark soliton upon variations of the chemical potential and also of the strength of the radial potential. Numerical results show that the ring dark soliton can be stabilized in a suitable interval of external potential strengths and chemical potentials. Furthermore, we also explore different proposed particle pictures considering the ring as a moving particle and find, wheremore » appropriate, results in very good qualitative and also reasonable quantitative agreement with the numerical findings.« less
Stabilization of ring dark solitons in Bose-Einstein condensates
Wang, Wenlong; Kevrekidis, P. G.; Carretero-González, R.; Frantzeskakis, D. J.; Kaper, Tasso J.; Ma, Manjun
2015-09-14
Earlier work has shown that ring dark solitons in two-dimensional Bose-Einstein condensates are generically unstable. In this work, we propose a way of stabilizing the ring dark soliton via a radial Gaussian external potential. We investigate the existence and stability of the ring dark soliton upon variations of the chemical potential and also of the strength of the radial potential. Numerical results show that the ring dark soliton can be stabilized in a suitable interval of external potential strengths and chemical potentials. Furthermore, we also explore different proposed particle pictures considering the ring as a moving particle and find, where appropriate, results in very good qualitative and also reasonable quantitative agreement with the numerical findings.
NASA Astrophysics Data System (ADS)
Wilms, Dorothea; Virnau, Peter; Snook, Ian K.; Binder, Kurt
2012-11-01
The dynamical behavior of single-component two-dimensional colloidal crystals confined in a slit geometry is studied by Langevin dynamics simulation of a simple model. The colloids are modeled as pointlike particles, interacting with the repulsive part of the Lennard-Jones potential, and the fluid molecules in the colloidal suspension are not explicitly considered. Considering a crystalline strip of triangular lattice structure with n=30 rows, the (one-dimensional) walls confining the strip are chosen as two rigidly fixed crystalline rows at each side, commensurate with the lattice structure and, thus, stabilizing long-range order. The case when the spacing between the walls is incommensurate with the ideal triangular lattice is also studied, where (due to a transition in the number of rows, n?n-1) the confined crystal is incommensurate with the confining boundaries, and a soliton staircase forms along the walls. It is shown that mean-square displacements (MSDs) of particles as a function of time show an overshoot and then saturate at a horizontal plateau in the commensurate case, the value of the plateau being largest in the center of the strip. Conversely, when solitons are present, MSDs are largest in the rows containing the solitons, and all MSDs do not settle down at well-defined plateaus in the direction parallel to the boundaries, due to the lack of positional long-range order in ideal two-dimensional crystals. The MSDs of the solitons (which can be treated like quasiparticles at very low temperature) have also been studied and their dynamics are found to be about an order of magnitude slower than that of the colloidal particles themselves. Finally, transport of individual colloidal particles by diffusion processes is studied: both standard vacancy-interstitial pair formation and cooperative ring rotation processes are identified. These processes require thermal activation, with activation energies of the order of 10Tm (Tm being the melting temperature of the crystal), while the motions due to long-wavelength phonons decrease only linearly in temperature.
NASA Technical Reports Server (NTRS)
Chiu, Hong-Yee
1990-01-01
The theory of Lee and Pang (1987), who obtained solutions for soliton stars composed of zero-temperature fermions and bosons, is applied here to quark soliton stars. Model soliton stars based on a simple physical model of the proton are computed, and the properties of the solitons are discussed, including the important problem of the existence of a limiting mass and thus the possible formation of black holes of primordial origin. It is shown that there is a definite mass limit for ponderable soliton stars, so that during cooling a soliton star might reach a stage beyond which no equilibrium configuration exists and the soliton star probably will collapse to become a black hole. The radiation of ponderable soliton stars may alter the short-wavelength character of the cosmic background radiation, and may be observed as highly redshifted objects at z of about 100,000.
NASA Astrophysics Data System (ADS)
Chiu, Hong-Yee
1990-12-01
The theory of Lee and Pang (1987), who obtained solutions for soliton stars composed of zero-temperature fermions and bosons, is applied here to quark soliton stars. Model soliton stars based on a simple physical model of the proton are computed, and the properties of the solitons are discussed, including the important problem of the existence of a limiting mass and thus the possible formation of black holes of primordial origin. It is shown that there is a definite mass limit for ponderable soliton stars, so that during cooling a soliton star might reach a stage beyond which no equilibrium configuration exists and the soliton star probably will collapse to become a black hole. The radiation of ponderable soliton stars may alter the short-wavelength character of the cosmic background radiation, and may be observed as highly redshifted objects at z of about 100,000.
Two-dimensional vibrational-electronic spectroscopy
NASA Astrophysics Data System (ADS)
Courtney, Trevor L.; Fox, Zachary W.; Slenkamp, Karla M.; Khalil, Munira
2015-10-01
Two-dimensional vibrational-electronic (2D VE) spectroscopy is a femtosecond Fourier transform (FT) third-order nonlinear technique that creates a link between existing 2D FT spectroscopies in the vibrational and electronic regions of the spectrum. 2D VE spectroscopy enables a direct measurement of infrared (IR) and electronic dipole moment cross terms by utilizing mid-IR pump and optical probe fields that are resonant with vibrational and electronic transitions, respectively, in a sample of interest. We detail this newly developed 2D VE spectroscopy experiment and outline the information contained in a 2D VE spectrum. We then use this technique and its single-pump counterpart (1D VE) to probe the vibrational-electronic couplings between high frequency cyanide stretching vibrations (?CN) and either a ligand-to-metal charge transfer transition ([FeIII(CN)6]3- dissolved in formamide) or a metal-to-metal charge transfer (MMCT) transition ([(CN)5FeIICNRuIII(NH3)5]- dissolved in formamide). The 2D VE spectra of both molecules reveal peaks resulting from coupled high- and low-frequency vibrational modes to the charge transfer transition. The time-evolving amplitudes and positions of the peaks in the 2D VE spectra report on coherent and incoherent vibrational energy transfer dynamics among the coupled vibrational modes and the charge transfer transition. The selectivity of 2D VE spectroscopy to vibronic processes is evidenced from the selective coupling of specific ?CN modes to the MMCT transition in the mixed valence complex. The lineshapes in 2D VE spectra report on the correlation of the frequency fluctuations between the coupled vibrational and electronic frequencies in the mixed valence complex which has a time scale of 1 ps. The details and results of this study confirm the versatility of 2D VE spectroscopy and its applicability to probe how vibrations modulate charge and energy transfer in a wide range of complex molecular, material, and biological systems.
Vortices of Two Dimensional Guiding Center Plasmas.
NASA Astrophysics Data System (ADS)
Ting, Antonio Chofai
A system of two dimensional guiding center plasma in a square conducting boundary is used as a model to study the anomalous transport is magnetically confined plasma. An external gravitational force is introduced to simulate the curvature and gradient of the magnetic field. For finite boundaries, it is a Hamiltonian system with finite phase space and negative temperature states are allowed. The statistical equilibrium states of this system are described by the solutions of a Poisson's equation with self-consistently determined charge density. In the limit of zero gravity, it can be reduced to the sinh-Poisson equation (DEL)('2)u + (lamda)('2)sinh u = 0. Previous numerical efforts have found solutions with vortex structures. A novel method of generating general exact solutions to this nonlinear boundary value problem is presented. These solutions are given by. (DIAGRAM, TABLE OR GRAPHIC OMITTED...PLEASE SEE DAI). where E(,i)'s are constants and the dependence of (gamma)(,j)'s on x and y are given by a set of coupled first order nonlinear ordinary differential equations. These equations can be linearized to give u(x,y) in terms of Riemann theta functions u(x,y) = 2ln (THETA)(l + 1/2)(THETA)(l) . The phases l evolve linearly in x and y while nonlinear superposition is displayed in the solution u(x,y). The self-consistent Poisson's equation with gravity is studied numerically. Different branches of solutions are obtained and their relations to the zero gravity solutions are discussed. The thermodynamically most favored structure of the system carries the feature of a heavy ion vortex on top of the light electron vortex. Branches of solutions are found to merge into each other as parameters in the equations were smoothly varied. A critical value of gravitational force exists such that below which there is a possibility of hysteresis between different equilibrium states. With the help of the nonzero gravity solutions, we also have a clearer picture of the transition from negative to positive temperature states. Nonuniform positive temperature states with a heavy ion vortex at the bottom of the square boundary are also found when gravity is present.
Experimental investigation of two-dimensional antiferromagnetic systems
NASA Astrophysics Data System (ADS)
Woodward, Frank Matthew
Quantum fluctuations have a profound effect on the bulk properties of magnetic systems, particularly in low spatial dimension. For example, 1D chains with half integral spins have a gapless excitation spectrum while whole integer spin chains have a (Haldane) gap. The quantum critical behavior of the S = 1/2 2D system is thought to be the origin of high TC superconductivity. Molecular magnets are engineered materials where spin, interaction strength, or dimensionality can be tuned for experimental exploration of magnetism. A conscious effort was made to pick chemical motifs known to generate a quasi two dimensional Heisenberg system and attempt to exploit these motifs by designing classes of compounds based upon them. Creating many similar systems and observing changes in magnetism as a result in changes of chemical structure provides for the development of a phenomenological model of magnetostructural correlations which can then be verified by calculation. This dissertation discusses two distinct classes of antiferromagnetic systems, each based upon entirely different chemical motifs, both exhibiting the desired two dimensional Heisenberg antiferromagnetic behavior. One class is based upon copper tetrabromide: (5gammaAP)2CuBr4 where 5gammaAP = 2-amino-5-gamma-pyridinium with gamma = chloro, bromo, or methyl substituents. These materials are shown, by bulk magnetization and calorimetry studies to possess an exchange strength on the order of J ? -7 to -9 K and ordering temperatures in the range of TN ? 3.5 to 5 K. In the ordered state, these materials are shown to possesses a weak 3D exchange interaction, and exhibit a spin-flop transition to long range order in the magnetism. The other class under investigation is based upon copper pyrazine: Cu(pz) 2(ClO4)2, Cu(pz)2(BF6) 2, and [Cu(pz)2(NO3)](PF6). By bulk magnetic measurements of powder and single crystal samples they are shown to be a very good approximation of the 2D QHAF model. The two dimensional magnetic exchange, J, ranges from -10 K to -20 K while the observed magnetic ordering temperatures, TN range from 4.1 K to 3 K. The nature of the ordering transition in these materials, unlike the copper bromides, has yet to be determined and is fertile ground for further research.
Engineering optical soliton bistability in colloidal media
Matuszewski, Michal
2010-01-15
We consider a mixture consisting of two species of spherical nanoparticles dispersed in a liquid medium. We show that with an appropriate choice of refractive indices and particle diameters, it is possible to observe the phenomenon of optical soliton bistability in two spatial dimensions in a broad beam power range. Previously, this possibility was ruled out in the case of a single-species colloid. As a particular example, we consider the system of hydrophilic silica particles and gas bubbles generated in the process of electrolysis in water. The interaction of two soliton beams can lead to switching of the lower branch solitons to the upper branch, and the interaction of solitons from different branches is phase independent and always repulsive.
Coherent two-dimensional infrared microscopy
NASA Astrophysics Data System (ADS)
Baiz, Carlos; Schach, Denise; Tokmakoff, Andrei
2015-03-01
We developed ultrafast 2D IR spectral microscopy, a new technique to measure spatially-resolved 2D infrared spectra and vibrational dynamics with diffraction-limited spatial resolution and femtosecond time resolution. The key enabling development consists of a new geometry where all three IR pulses propagate fully collinearly through an all-reflective IR microscope. A combination of polarization, chopping, and phase-cycling isolate the 2D IR signal by removing all unwanted signal and interference contributions. The single-beam collinear geometry enables us to implement 2D IR in three configurations: transmission, reflectance, and ATR. In terms of sensitivity, the 6 micron focus size produces an 8-fold enhancement of the signal compared to focusing with standard parabolic mirrors. These methods open up new possibilities for imaging proteins in cells, lipid membranes, or vesicles, as well as performing surface-sensitive studies on biological systems.
Cavity-soliton laser with frequency-selective feedback
Scroggie, A. J.; Firth, W. J.; Oppo, G.-L.
2009-07-15
We present a coupled-cavity model of a laser with frequency-selective feedback, and use it to analyze and explain the existence of stationary and dynamic spatial solitons in the device. Particular features of soliton addressing in this system are discussed. We demonstrate the advantages of our model with respect to the common Lang-Kobayashi approximation.
Shen, Ming; Gao, Jinsong; Ge, Lijuan
2015-01-01
We investigate the spatially optical solitons shedding from Airy beams and anomalous interactions of Airy beams in nonlocal nonlinear media by means of direct numerical simulations. Numerical results show that nonlocality has profound effects on the propagation dynamics of the solitons shedding from the Airy beam. It is also shown that the strong nonlocality can support periodic intensity distribution of Airy beams with opposite bending directions. Nonlocality also provides a long-range attractive force between Airy beams, leading to the formation of stable bound states of both in-phase and out-of-phase breathing Airy solitons which always repel in local media. PMID:25900878
Quantum Criticality in Quasi-Two-Dimensional Itinerant Antiferromagnets.
Varma, C M
2015-10-30
Quasi-two-dimensional itinerant fermions in the antiferromagnetic (AFM) quantum-critical region of their phase diagram, such as in the Fe-based superconductors or in some of the heavy-fermion compounds, exhibit a resistivity varying linearly with temperature and a contribution to specific heat or thermopower proportional to TlnT. It is shown, here, that a generic model of itinerant anti-ferromagnet can be canonically transformed so that its critical fluctuations around the AFM-vector Q can be obtained from the fluctuations in the long wavelength limit of a dissipative quantum XY model. The fluctuations of the dissipative quantum XY model in 2D have been evaluated recently, and in a large regime of parameters, they are determined, not by renormalized spin fluctuations, but by topological excitations. In this regime, the fluctuations are separable in their spatial and temporal dependence and have a spatial correlation length which is proportional to the logarithm of the temporal correlation length, i.e., for some purposes, the effective dynamic exponent z=?. The time dependence gives ?/T scaling at criticality. The observed resistivity and entropy then follow. Several predictions to test the theory are also given. PMID:26565482
Lateral and Vertical Two-Dimensional Layered Topological Insulator Heterostructures.
Li, Yanbin; Zhang, Jinsong; Zheng, Guangyuan; Sun, Yongming; Hong, Seung Sae; Xiong, Feng; Wang, Shuang; Lee, Hye Ryoung; Cui, Yi
2015-11-24
The heterostructured configuration between two-dimensional (2D) semiconductor materials has enabled the engineering of the band gap and the design of novel devices. So far, the synthesis of single-component topological insulator (TI) 2D materials such as Bi2Se3, Bi2Te3, and Sb2Te3 has been achieved through vapor phase growth and molecular beam epitaxy; however, the spatial controlled fabrication of 2D lateral heterostructures in these systems has not been demonstrated yet. Here, we report an in situ two-step synthesis process to form TI lateral heterostructures. Scanning transmission electron microscopy and energy-dispersive X-ray mapping results show the successful spatial control of chemical composition in these as-prepared heterostructures. The edge-induced growth mechanism is revealed by the ex situ atomic force microscope measurements. Electrical transport studies demonstrate the existence of p-n junctions in Bi2Te3/Sb2Te3 heterostructures. PMID:26468661
Quantum Criticality in Quasi-Two-Dimensional Itinerant Antiferromagnets
NASA Astrophysics Data System (ADS)
Varma, C. M.
2015-10-01
Quasi-two-dimensional itinerant fermions in the antiferromagnetic (AFM) quantum-critical region of their phase diagram, such as in the Fe-based superconductors or in some of the heavy-fermion compounds, exhibit a resistivity varying linearly with temperature and a contribution to specific heat or thermopower proportional to T ln T . It is shown, here, that a generic model of itinerant anti-ferromagnet can be canonically transformed so that its critical fluctuations around the AFM-vector Q can be obtained from the fluctuations in the long wavelength limit of a dissipative quantum X Y model. The fluctuations of the dissipative quantum X Y model in 2D have been evaluated recently, and in a large regime of parameters, they are determined, not by renormalized spin fluctuations, but by topological excitations. In this regime, the fluctuations are separable in their spatial and temporal dependence and have a spatial correlation length which is proportional to the logarithm of the temporal correlation length, i.e., for some purposes, the effective dynamic exponent z =? . The time dependence gives ? /T scaling at criticality. The observed resistivity and entropy then follow. Several predictions to test the theory are also given.
Transfer of optical signals around bends in two-dimensional linear photonic networks
NASA Astrophysics Data System (ADS)
Nikolopoulos, G. M.
2015-02-01
The ability to navigate light signals in two-dimensional networks of waveguide arrays is a prerequisite for the development of all-optical integrated circuits for information processing and networking. In this article, we present a theoretical analysis of bending losses in linear photonic lattices with engineered couplings, and discuss possible ways for their minimization. In contrast to previous work in the field, the lattices under consideration operate in the linear regime, in the sense that discrete solitons cannot exist. The present results suggest that the functionality of linear waveguide networks can be extended to operations that go beyond the recently demonstrated point-to-point transfer of signals, such as blocking, routing, logic functions, etc.
The Thirring interaction in the two-dimensional axial-current-pseudoscalar derivative coupling model
Belvedere, L.V. . E-mail: armflavio@if.uff.br
2006-12-15
We reexamine the two-dimensional model of massive fermions interacting with a massless pseudoscalar field via axial-current derivative coupling. The hidden Thirring interaction in the axial-derivative coupling model is exhibited compactly by performing a canonical field transformation on the Bose field algebra and the model is mapped into the Thirring model with an additional vector-current-scalar derivative interaction (Schroer-Thirring model). The Fermi field operator is rewritten in terms of the Mandelstam soliton operator coupled to a free massless scalar field. The charge sectors of the axial-derivative model are mapped into the charge sectors of the massive Thirring model. The complete bosonized version of the model is presented. The bosonized composite operators of the quantum Hamiltonian are obtained as the leading operators in the Wilson short distance expansions.
On the non-relativistic two-dimensional purely magnetic supersymmetric Pauli operator
NASA Astrophysics Data System (ADS)
Grinevich, P. G.; Mironov, A. E.; Novikov, S. P.
2015-04-01
The complete manifold of ground-state eigenfunctions for the purely magnetic two-dimensional Pauli operator is considered as a byproduct of a new reduction (found by the authors several years ago) for the algebro-geometric inverse spectral data (that is, Riemann surfaces and divisors). This reduction is associated with a ({2+1})-soliton hierarchy containing a 2D analogue of the famous `Burgers system'. This paper also surveys previous papers since 1980, including the first topological ideas in the space of quasi-momenta, and presents new results on self-adjoint boundary-value problems for the Pauli operator. The `non-spectral' Bloch-Floquet functions of zero 2D level give discrete points of additional spectrum analogous to the `boundary states' of finite-gap 1D potentials in the gaps. Bibliography: 35 titles.
ERIC Educational Resources Information Center
Sarama, Julie; Clements, Douglas H.; Swaminathan, Sudha; McMillen, Sue; Gonzalez Gomez, Rosa M.
2003-01-01
Investigated the development among fourth-graders of two-dimensional space concepts within a mathematics unit on grids, coordinates, and rectangles. Found that students' knowledge of grid and coordinate systems related to levels of competence in number sense, spatial-geometric relationships, and the ability to discriminate and integrate the two
Demonstration of two-dimensional time-encoded imaging of fast neutrons
Brennan, J.; Brubaker, E.; Gerling, M.; Marleau, P.; McMillan, K.; Nowack, A.; Galloudec, N. Renard-Le; Sweany, M.
2015-09-09
Here, we present a neutron detector system based on time-encoded imaging, and demonstrate its applicability toward the spatial mapping of special nuclear material. We also demonstrate that two-dimensional fast-neutron imaging with 2° resolution at 2 m stand-off is feasible with only two instrumented detectors.
Control of two-dimensional electron population in a semiconductor quantum well
NASA Astrophysics Data System (ADS)
Wang, Guanling; Fang, Zhengchuan; Wu, Feng
2016-01-01
We investigate the two-dimensional (2D) electron population in a semiconductor quantum well. It is found that, due to the position-dependent quantum interference, the 2D spatial distribution of electron population can be easily controlled via adjusting the system parameters. Thus, our scheme shows the underlying probability for the applications in solid-state optoelectronics.
Demonstration of two-dimensional time-encoded imaging of fast neutrons
NASA Astrophysics Data System (ADS)
Brennan, J.; Brubaker, E.; Gerling, M.; Marleau, P.; McMillan, K.; Nowack, A.; Galloudec, N. Renard-Le; Sweany, M.
2015-12-01
We present a neutron detector system based on time-encoded imaging, and demonstrate its applicability toward the spatial mapping of special nuclear material. We demonstrate that two-dimensional fast-neutron imaging with 2 resolution at 2 m stand-off is feasible with only two instrumented detectors.
Demonstration of two-dimensional time-encoded imaging of fast neutrons
Brennan, J.; Brubaker, E.; Gerling, M.; Marleau, P.; McMillan, K.; Nowack, A.; Galloudec, N. Renard-Le; Sweany, M.
2015-09-09
Here, we present a neutron detector system based on time-encoded imaging, and demonstrate its applicability toward the spatial mapping of special nuclear material. We also demonstrate that two-dimensional fast-neutron imaging with 2 resolution at 2 m stand-off is feasible with only two instrumented detectors.
Lie algebra contractions on two-dimensional hyperboloid
Pogosyan, G. S. Yakhno, A.
2010-03-15
The Inoenue-Wigner contraction from the SO(2, 1) group to the Euclidean E(2) and E(1, 1) group is used to relate the separation of variables in Laplace-Beltrami (Helmholtz) equations for the four corresponding two-dimensional homogeneous spaces: two-dimensional hyperboloids and two-dimensional Euclidean and pseudo-Euclidean spaces. We show how the nine systems of coordinates on the two-dimensional hyperboloids contracted to the four systems of coordinates on E{sub 2} and eight on E{sub 1,1}. The text was submitted by the authors in English.
Digital watermarking method using a two-dimensional barcode
NASA Astrophysics Data System (ADS)
Jeon, Seong-Goo; Choi, Kyoung-Ho; Park, Chan-Won; Kim, Il-Hwan
2005-12-01
This paper proposed a digital watermarking method using a two-dimensional bar code. In general, one-dimensional bar code was just a key that can access detailed information to the host computer database. But a two-dimensional bar code is a new technology capable of holding relatively large amounts of data compared to the conventional one-dimensional bar code. The study used Data Matrix that is the most widely used among the many kinds of two-dimensional bar code. The experimental results show a similarity of the embedded and extracted two-dimensional watermark.
Building patterns by traveling dipoles and vortices in two-dimensional periodic dissipative media
NASA Astrophysics Data System (ADS)
Besse, V.; Leblond, H.; Mihalache, D.; Malomed, B. A.
2014-12-01
We analyze pattern-formation scenarios in the two-dimensional (2D) complex Ginzburg-Landau (CGL) equation with the cubic-quintic (CQ) nonlinearity and a cellular potential. The equation models laser cavities with built-in gratings, which stabilize 2D patterns. The pattern-building process is initiated by kicking a compound mode, in the form of a dipole, quadrupole, or vortex which is composed of four local peaks. The hopping motion of the kicked mode through the cellular structure leads to the generation of various extended patterns pinned by the structure. In the ring-shaped system, the persisting freely moving dipole hits the stationary pattern from the opposite side, giving rise to several dynamical regimes, including periodic elastic collisions, i.e., persistent cycles of elastic collisions between the moving and quiescent dissipative solitons, and transient regimes featuring several collisions which end up by absorption of one soliton by the other. Still another noteworthy result is the transformation of a strongly kicked unstable vortex into a stably moving four-peaked cluster.
Nonlinear evolution of interacting oblique waves on two-dimensional shear layers
NASA Technical Reports Server (NTRS)
Goldstein, M. E.; Choi, S.-W.
1989-01-01
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.
Twisted chimera states and multicore spiral chimera states on a two-dimensional torus.
Xie, Jianbo; Knobloch, Edgar; Kao, Hsien-Ching
2015-10-01
Chimera states consisting of domains of coherently and incoherently oscillating oscillators in a two-dimensional periodic array of nonlocally coupled phase oscillators are studied. In addition to the one-dimensional chimera states familiar from one spatial dimension, two-dimensional structures termed twisted chimera states and spiral wave chimera states are identified in simulations. The properties of many of these states, including stability, are determined using an evolution equation for a complex order parameter and are found to be in agreement with the simulations. PMID:26565318
Exploring two-dimensional electron gases with two-dimensional Fourier transform spectroscopy
Paul, J.; Dey, P.; Tokumoto, T.; Reno, J. L.; Hilton, D. J.; Karaiskaj, D.
2014-10-07
The dephasing of excitons in a modulation doped single quantum well was carefully measured using time integrated four-wave mixing (FWM) and two-dimensional Fourier transform (2DFT) spectroscopy. These are the first 2DFT measurements performed on a modulation doped single quantum well. The inhomogeneous and homogeneous excitonic line widths were obtained from the diagonal and cross-diagonal profiles of the 2DFT spectra. The laser excitation density and temperature were varied and 2DFT spectra were collected. A very rapid increase of the dephasing decay, and as a result, an increase in the cross-diagonal 2DFT linewidths with temperature was observed. Furthermore, the lineshapes of themore »2DFT spectra suggest the presence of excitation induced dephasing and excitation induced shift.« less
Exploring two-dimensional electron gases with two-dimensional Fourier transform spectroscopy
Paul, J.; Dey, P.; Tokumoto, T.; Reno, J. L.; Hilton, D. J.; Karaiskaj, D.
2014-10-07
The dephasing of excitons in a modulation doped single quantum well was carefully measured using time integrated four-wave mixing (FWM) and two-dimensional Fourier transform (2DFT) spectroscopy. These are the first 2DFT measurements performed on a modulation doped single quantum well. The inhomogeneous and homogeneous excitonic line widths were obtained from the diagonal and cross-diagonal profiles of the 2DFT spectra. The laser excitation density and temperature were varied and 2DFT spectra were collected. A very rapid increase of the dephasing decay, and as a result, an increase in the cross-diagonal 2DFT linewidths with temperature was observed. Furthermore, the lineshapes of the 2DFT spectra suggest the presence of excitation induced dephasing and excitation induced shift.
Dissipative quadratic solitons supported by a localized gain
NASA Astrophysics Data System (ADS)
Lobanov, Valery E.; Borovkova, Olga V.; Malomed, Boris A.
2014-11-01
We propose two models for the creation of stable dissipative solitons in optical media with the χ(2 ) (quadratic) nonlinearity. To compensate spatially uniform loss in both the fundamental-frequency (FF) and second-harmonic (SH) components of the system, a strongly localized "hot spot" carrying the linear gain is added, acting either on the FF or on the SH component. In both systems, we use numerical methods to find families of dissipative χ(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.
Soliton dynamics in the multiphoton plasma regime
Husko, Chad A.; Combrié, Sylvain; Colman, Pierre; Zheng, Jiangjun; De Rossi, Alfredo; Wong, Chee Wei
2013-01-01
Solitary waves have consistently captured the imagination of scientists, ranging from fundamental breakthroughs in spectroscopy and metrology enabled by supercontinuum light, to gap solitons for dispersionless slow-light, and discrete spatial solitons in lattices, amongst others. Recent progress in strong-field atomic physics include impressive demonstrations of attosecond pulses and high-harmonic generation via photoionization of free-electrons in gases at extreme intensities of 1014 W/cm2. Here we report the first phase-resolved observations of femtosecond optical solitons in a semiconductor microchip, with multiphoton ionization at picojoule energies and 1010 W/cm2 intensities. The dramatic nonlinearity leads to picojoule observations of free-electron-induced blue-shift at 1016 cm−3 carrier densities and self-chirped femtosecond soliton acceleration. Furthermore, we evidence the time-gated dynamics of soliton splitting on-chip, and the suppression of soliton recurrence due to fast free-electron dynamics. These observations in the highly dispersive slow-light media reveal a rich set of physics governing ultralow-power nonlinear photon-plasma dynamics.
Beginning Introductory Physics with Two-Dimensional Motion
ERIC Educational Resources Information Center
Huggins, Elisha
2009-01-01
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
Terahertz rectification by periodic two-dimensional electron plasma
Popov, V. V.; Saratov State University, Saratov 410012
2013-06-24
The physics of terahertz rectification by periodic two-dimensional electron plasma is discussed. Two different effects yielding terahertz rectification are studied: the plasmonic drag and plasmonic ratchet. Ultrahigh responsivity of terahertz rectification by periodic two-dimensional electron plasma in semiconductor heterostructures and graphene is predicted.
Beginning Introductory Physics with Two-Dimensional Motion
ERIC Educational Resources Information Center
Huggins, Elisha
2009-01-01
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…
Two-Dimensional Finite Element Ablative Thermal Response Analysis of an Arcjet Stagnation Test
NASA Technical Reports Server (NTRS)
Dec, John A.; Laub, Bernard; Braun, Robert D.
2011-01-01
The finite element ablation and thermal response (FEAtR, hence forth called FEAR) design and analysis program simulates the one, two, or three-dimensional ablation, internal heat conduction, thermal decomposition, and pyrolysis gas flow of thermal protection system materials. As part of a code validation study, two-dimensional axisymmetric results from FEAR are compared to thermal response data obtained from an arc-jet stagnation test in this paper. The results from FEAR are also compared to the two-dimensional axisymmetric computations from the two-dimensional implicit thermal response and ablation program under the same arcjet conditions. The ablating material being used in this arcjet test is phenolic impregnated carbon ablator with an LI-2200 insulator as backup material. The test is performed at the NASA, Ames Research Center Interaction Heating Facility. Spatially distributed computational fluid dynamics solutions for the flow field around the test article are used for the surface boundary conditions.
On integrability of a noncommutative q-difference two-dimensional Toda lattice equation
NASA Astrophysics Data System (ADS)
Li, C. X.; Nimmo, J. J. C.; Shen, Shoufeng
2015-12-01
In our previous work (C.X. Li and J.J.C. Nimmo, 2009 [18]), we presented a generalized type of Darboux transformations in terms of a twisted derivation in a unified form. The twisted derivation includes ordinary derivatives, forward difference operators, super derivatives and q-difference operators as its special cases. This result not only enables one to recover the known Darboux transformations and quasideterminant solutions to the noncommutative KP equation, the non-Abelian two-dimensional Toda lattice equation, the non-Abelian Hirota-Miwa equation and the super KdV equation, but also inspires us to investigate quasideterminant solutions to q-difference soliton equations. In this paper, we first construct the bilinear Bäcklund transformations for the known bilinear q-difference two-dimensional Toda lattice equation (q-2DTL) and then derive a Lax pair whose compatibility gives a formally different nonlinear q-2DTL equation and finally obtain its quasideterminant solutions by iterating its Darboux transformations.
Two-dimensional, finite Larmor radius magnetohydrodynamics code
Huba, J.D.
1996-12-31
A two-dimensional, finite Larmor radius magnetohydrodynamics (2D FLR MHD) code has been developed. The code solves the 2D FLR equations in the isothermal limit. These equations are presented in Braginskii (1965) and include an anisotropic ion stress tensor in the momentum equation.the FLR MHD equations are solved in conservative form. A non-linear switch between an 8th order spatial scheme and a low-order scheme is used based upon the partial donor cell method (Hain, 1987). The novel feature of the code is the computation of the fluxes across cell interfaces. The code uses a variation of the beam scheme and computes fluxes based upon maxwellian-like distribution functions that contain the magnetic forces. As a test of the code, theoretical and computational results for the Rayleigh-Taylor instability in the FLR MHD regime will be presented. The authors also discuss the transition to the unmagnetized regime where the Hall term becomes important, and applications to plasma boundary layer dynamics.
Two-Dimensional Velocity Measurements Using a Fiber Velocimeter
NASA Astrophysics Data System (ADS)
Rivera, M.; Wu, X. L.; Goldburg, W. I.
1996-11-01
This experiment seeks to quantify and improve an optical fiber velocimeter which can be used to measure velocity fluctuations in a two-dimensional fluid, such as a flowing soap film. When the tip of an optical fiber is thrusted through a flowing soap film, it will experience a small deflection due to the drag force of the surrounding fluid. The resulting deflection can be measured by a position-sensitive detector when a laser light is coupled to the fiber from the other end. The velocimeter is sensitive to velocity fluctuations in both the x and y directions, provided the fluctuating frequency being less than the natural resonance frequency of the fiber, which is typically a few thousand hertz. Measurements of velocity power spectrum in a 2D turbulent soap film give reasonable agreement with that obtained by a laser Doppler velocimeter. We are looking forward to carry out measurements with two or more fibers in the film so that velocity correlations at different spatial locations can be performed. Work supported by The National Science Foundation.
Magnetic coupling of vortices in a two-dimensional lattice
NASA Astrophysics Data System (ADS)
Nissen, D.; Mitin, D.; Klein, O.; Arekapudi, S. S. P. K.; Thomas, S.; Im, M.-Y.; Fischer, P.; Albrecht, M.
2015-11-01
We investigated the magnetization reversal of magnetic vortex structures in a two-dimensional lattice. The structures were formed by permalloy (Py) film deposition onto large arrays of self-assembled spherical SiO2-particles with a diameter of 330 nm. We present the dependence of the nucleation and annihilation field of the vortex structures as a function of the Py layer thickness (aspect ratio) and temperature. By increasing the Py thickness up to 90 nm or alternatively by lowering the temperature the vortex structure becomes more stable as expected. However, the increase of the Py thickness results in the onset of strong exchange coupling between neighboring Py caps due to the emergence of Py bridges connecting them. In particular, we studied the influence of magnetic coupling locally by in-field scanning magneto-resistive microscopy and full-field magnetic soft x-ray microscopy, revealing a domain-like nucleation process of vortex states, which arises via domain wall propagation due to exchange coupling of the closely packed structures. By analyzing the rotation sense of the reversed areas, large connected domains are present with the same circulation sense. Furthermore, the lateral core displacements when an in-plane field is applied were investigated, revealing spatially enlarged vortex cores and a broader distribution with increasing Py layer thickness. In addition, the presence of some mixed states, vortices and c-states, is indicated for the array with the thickest Py layer.
Optoelectronics in two-dimensional semiconductor alloys (Presentation Recording)
NASA Astrophysics Data System (ADS)
Lonard, Franois
2015-08-01
Two -dimensional transition-metal dichalcogenides (2D-TMDs) have attracted attention for applications in electronics and photonics, as well as for the wealth of new scientific phenomena that arise at low dimensionality. Recently, the ability to grow 2D-TMDs by chemical vapor deposition has opened the path to large area devices, but also to the synthesis of semiconductor alloys with tunable bandgaps. In this presentation, I will discuss our recent experimental work in exploring the optoelectronic properties of 2D MoS_2(1-x)Se_2x alloys spanning the compositional range. In particular, we report the observation of a new regime of operation where the photocurrent depends superlinearly on light intensity. We use spatially-resolved photocurrent measurements on devices consisting of CVD-grown monolayers to show the photoconductive nature of the photoresponse, with the photocurrent dominated by recombination and field-induced carrier separation in the channel. Time-dependent photoconductivity measurements show the presence of persistent photoconductivity for the S-rich alloys, while photocurrent measurements at fixed wavelength for devices of different alloy compositions show a systematic decrease of the responsivity with increasing Se content associated with increased linearity of the current-voltage characteristics. A model based on the presence of different types of recombination centers is presented to explain the origin of the superlinear dependence on light intensity, which emerges when the non-equilibrium occupancy of initially empty fast recombination centers becomes comparable to that of slow recombination centers.
A Two-Dimensional Linear Bicharacteristic FDTD Method
NASA Technical Reports Server (NTRS)
Beggs, John H.
2002-01-01
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.
Initial- value problem for the two-dimensional growing wake
NASA Astrophysics Data System (ADS)
Scarsoglio, S.; Tordella, D.; Criminale, W. O.
2006-11-01
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.
Lagrangian statistics in weakly forced two-dimensional turbulence.
Rivera, Michael K; Ecke, Robert E
2016-01-01
Measurements of Lagrangian single-point and multiple-point statistics in a quasi-two-dimensional stratified layer system are reported. The system consists of a layer of salt water over an immiscible layer of Fluorinert and is forced electromagnetically so that mean-squared vorticity is injected at a well-defined spatial scale ri. Simultaneous cascades develop in which enstrophy flows predominately to small scales whereas energy cascades, on average, to larger scales. Lagrangian correlations and one- and two-point displacements are measured for random initial conditions and for initial positions within topological centers and saddles. Some of the behavior of these quantities can be understood in terms of the trapping characteristics of long-lived centers, the slow motion near strong saddles, and the rapid fluctuations outside of either centers or saddles. We also present statistics of Lagrangian velocity fluctuations using energy spectra in frequency space and structure functions in real space. We compare with complementary Eulerian velocity statistics. We find that simultaneous inverse energy and enstrophy ranges present in spectra are not directly echoed in real-space moments of velocity difference. Nevertheless, the spectral ranges line up well with features of moment ratios, indicating that although the moments are not exhibiting unambiguous scaling, the behavior of the probability distribution functions is changing over short ranges of length scales. Implications for understanding weakly forced 2D turbulence with simultaneous inverse and direct cascades are discussed. PMID:26826855
Lagrangian statistics in weakly forced two-dimensional turbulence
NASA Astrophysics Data System (ADS)
Rivera, Michael K.; Ecke, Robert E.
2016-01-01
Measurements of Lagrangian single-point and multiple-point statistics in a quasi-two-dimensional stratified layer system are reported. The system consists of a layer of salt water over an immiscible layer of Fluorinert and is forced electromagnetically so that mean-squared vorticity is injected at a well-defined spatial scale ri. Simultaneous cascades develop in which enstrophy flows predominately to small scales whereas energy cascades, on average, to larger scales. Lagrangian correlations and one- and two-point displacements are measured for random initial conditions and for initial positions within topological centers and saddles. Some of the behavior of these quantities can be understood in terms of the trapping characteristics of long-lived centers, the slow motion near strong saddles, and the rapid fluctuations outside of either centers or saddles. We also present statistics of Lagrangian velocity fluctuations using energy spectra in frequency space and structure functions in real space. We compare with complementary Eulerian velocity statistics. We find that simultaneous inverse energy and enstrophy ranges present in spectra are not directly echoed in real-space moments of velocity difference. Nevertheless, the spectral ranges line up well with features of moment ratios, indicating that although the moments are not exhibiting unambiguous scaling, the behavior of the probability distribution functions is changing over short ranges of length scales. Implications for understanding weakly forced 2D turbulence with simultaneous inverse and direct cascades are discussed.
Soap film flows: Statistics of two-dimensional turbulence
Vorobieff, P.; Rivera, M.; Ecke, R.E.
1999-08-01
Soap film flows provide a very convenient laboratory model for studies of two-dimensional (2-D) hydrodynamics including turbulence. For a gravity-driven soap film channel with a grid of equally spaced cylinders inserted in the flow, we have measured the simultaneous velocity and thickness fields in the irregular flow downstream from the cylinders. The velocity field is determined by a modified digital particle image velocimetry method and the thickness from the light scattered by the particles in the film. From these measurements, we compute the decay of mean energy, enstrophy, and thickness fluctuations with downstream distance, and the structure functions of velocity, vorticity, thickness fluctuation, and vorticity flux. From these quantities we determine the microscale Reynolds number of the flow R{sub {lambda}}{approx}100 and the integral and dissipation scales of 2D turbulence. We also obtain quantitative measures of the degree to which our flow can be considered incompressible and isotropic as a function of downstream distance. We find coarsening of characteristic spatial scales, qualitative correspondence of the decay of energy and enstrophy with the Batchelor model, scaling of energy in {ital k} space consistent with the k{sup {minus}3} spectrum of the Kraichnan{endash}Batchelor enstrophy-scaling picture, and power-law scalings of the structure functions of velocity, vorticity, vorticity flux, and thickness. These results are compared with models of 2-D turbulence and with numerical simulations. {copyright} {ital 1999 American Institute of Physics.}
Anisotropic stress correlations in two-dimensional liquids.
Wu, Bin; Iwashita, Takuya; Egami, Takeshi
2015-03-01
In this paper we demonstrate the presence of anisotropic stress correlations in the simulated two-dimensional liquids. Whereas the temporal correlation of macroscopic shear stress is known to contribute to viscosity via the Green-Kubo formula, the general question regarding angular dependence of the spatial correlation among atomic-level stresses in liquids without external shear has not been explored. We observed the apparent anisotropicity with well-defined symmetry which can be explained in terms of the elastic continuum theory by Eshelby. In addition, we found that the shear stress correlation is screened compared to the prediction by the elastic continuum theory, and the screening length depends on temperature and follows the power law, suggesting divergence around the glass transition temperature. The success of the Eshelby theory to explain the anisotropy of the stress correlations justifies the idea that the mismatch between the atom and its nearest neighbor cage produces the atomic-level stress as well as the long-range stress fields. PMID:25871104
NASA Astrophysics Data System (ADS)
Bednyakova, Anastasia; Turitsyn, Sergei K.
2015-03-01
The key to generating stable optical pulses is mastery of nonlinear light dynamics in laser resonators. Modern techniques to control the buildup of laser pulses are based on nonlinear science and include classical solitons, dissipative solitons, parabolic pulses (similaritons) and various modifications and blending of these methods. Fiber lasers offer remarkable opportunities to apply one-dimensional nonlinear science models for the design and optimization of very practical laser systems. Here, we propose a new concept of a laser based on the adiabatic amplification of a soliton pulse in the cavitythe adiabatic soliton laser. The adiabatic change of the soliton parameters during evolution in the resonator relaxes the restriction on the pulse energy inherent in traditional soliton lasers. Theoretical analysis is confirmed by extensive numerical modeling.
Blanco-Redondo, Andrea; Martijn, de Sterke C; Sipe, J E; Krauss, Thomas F; Eggleton, Benjamin J; Husko, Chad
2016-01-01
Temporal optical solitons have been the subject of intense research due to their intriguing physics and applications in ultrafast optics and supercontinuum generation. Conventional bright optical solitons result from the interaction of anomalous group-velocity dispersion and self-phase modulation. Here we experimentally demonstrate a class of bright soliton arising purely from the interaction of negative fourth-order dispersion and self-phase modulation, which can occur even for normal group-velocity dispersion. We provide experimental and numerical evidence of shape-preserving propagation and flat temporal phase for the fundamental pure-quartic soliton and periodically modulated propagation for the higher-order pure-quartic solitons. We derive the approximate shape of the fundamental pure-quartic soliton and discover that is surprisingly Gaussian, exhibiting excellent agreement with our experimental observations. Our discovery, enabled by precise dispersion engineering, could find applications in communications, frequency combs and ultrafast lasers. PMID:26822758
Bednyakova, Anastasia; Turitsyn, Sergei K
2015-03-20
The key to generating stable optical pulses is mastery of nonlinear light dynamics in laser resonators. Modern techniques to control the buildup of laser pulses are based on nonlinear science and include classical solitons, dissipative solitons, parabolic pulses (similaritons) and various modifications and blending of these methods. Fiber lasers offer remarkable opportunities to apply one-dimensional nonlinear science models for the design and optimization of very practical laser systems. Here, we propose a new concept of a laser based on the adiabatic amplification of a soliton pulse in the cavity-the adiabatic soliton laser. The adiabatic change of the soliton parameters during evolution in the resonator relaxes the restriction on the pulse energy inherent in traditional soliton lasers. Theoretical analysis is confirmed by extensive numerical modeling. PMID:25839271
NASA Astrophysics Data System (ADS)
Blanco-Redondo, Andrea; Martijn, De Sterke C.; Sipe, J. E.; Krauss, Thomas F.; Eggleton, Benjamin J.; Husko, Chad
2016-01-01
Temporal optical solitons have been the subject of intense research due to their intriguing physics and applications in ultrafast optics and supercontinuum generation. Conventional bright optical solitons result from the interaction of anomalous group-velocity dispersion and self-phase modulation. Here we experimentally demonstrate a class of bright soliton arising purely from the interaction of negative fourth-order dispersion and self-phase modulation, which can occur even for normal group-velocity dispersion. We provide experimental and numerical evidence of shape-preserving propagation and flat temporal phase for the fundamental pure-quartic soliton and periodically modulated propagation for the higher-order pure-quartic solitons. We derive the approximate shape of the fundamental pure-quartic soliton and discover that is surprisingly Gaussian, exhibiting excellent agreement with our experimental observations. Our discovery, enabled by precise dispersion engineering, could find applications in communications, frequency combs and ultrafast lasers.
Blanco-Redondo, Andrea; Martijn, de Sterke C.; Sipe, J.E.; Krauss, Thomas F.; Eggleton, Benjamin J.; Husko, Chad
2016-01-01
Temporal optical solitons have been the subject of intense research due to their intriguing physics and applications in ultrafast optics and supercontinuum generation. Conventional bright optical solitons result from the interaction of anomalous group-velocity dispersion and self-phase modulation. Here we experimentally demonstrate a class of bright soliton arising purely from the interaction of negative fourth-order dispersion and self-phase modulation, which can occur even for normal group-velocity dispersion. We provide experimental and numerical evidence of shape-preserving propagation and flat temporal phase for the fundamental pure-quartic soliton and periodically modulated propagation for the higher-order pure-quartic solitons. We derive the approximate shape of the fundamental pure-quartic soliton and discover that is surprisingly Gaussian, exhibiting excellent agreement with our experimental observations. Our discovery, enabled by precise dispersion engineering, could find applications in communications, frequency combs and ultrafast lasers. PMID:26822758
Quantum holographic encoding in a two-dimensional electron gas
Moon, Christopher
2010-05-26
The advent of bottom-up atomic manipulation heralded a new horizon for attainable information density, as it allowed a bit of information to be represented by a single atom. The discrete spacing between atoms in condensed matter has thus set a rigid limit on the maximum possible information density. While modern technologies are still far from this scale, all theoretical downscaling of devices terminates at this spatial limit. Here, however, we break this barrier with electronic quantum encoding scaled to subatomic densities. We use atomic manipulation to first construct open nanostructures - 'molecular holograms' - which in turn concentrate information into a medium free of lattice constraints: the quantum states of a two-dimensional degenerate Fermi gas of electrons. The information embedded in the holograms is transcoded at even smaller length scales into an atomically uniform area of a copper surface, where it is densely projected into both two spatial degrees of freedom and a third holographic dimension mapped to energy. In analogy to optical volume holography, this requires precise amplitude and phase engineering of electron wavefunctions to assemble pages of information volumetrically. This data is read out by mapping the energy-resolved electron density of states with a scanning tunnelling microscope. As the projection and readout are both extremely near-field, and because we use native quantum states rather than an external beam, we are not limited by lensing or collimation and can create electronically projected objects with features as small as {approx}0.3 nm. These techniques reach unprecedented densities exceeding 20 bits/nm{sup 2} and place tens of bits into a single fermionic state.
Lu, F; Lin, Q; Knox, W H; Agrawal, Govind P
2004-10-29
We investigate the vectorial nature of soliton fission in an isotropic nonlinear medium both theoretically and experimentally. As a specific example, we show that supercontinuum generation in a tapered fiber is extremely sensitive to the input state of polarization. Multiple vector solitons generated through soliton fission exhibit different states of elliptical polarization while emitting nonsolitonic radiation with complicated polarization features. Experiments performed with a tapered fiber agree with our theoretical description. PMID:15525164
Subwavelength binary plasmonic solitons.
Kou, Yao; Förstner, Jens
2015-03-15
We study the formation of subwavelength solitons in binary metal-dielectric lattices. We show that the transverse modulation of the lattice constant breaks the fundamental plasmonic band and suppresses the discrete diffraction of surface plasmon waves. New types of plasmonic solitons are found, and their characteristics are analyzed. We also demonstrate the existence of photonic-plasmonic vector solitons and elucidate their propagation properties. PMID:25768129
Two-dimensional instantons with bosonization and physics of adjoint two-dimensional QCD
NASA Astrophysics Data System (ADS)
Smilga, A. V.
1996-12-01
We evaluate partition functions ZI in topologically nontrivial (instanton) gauge sectors in the bosonized version of the Schwinger model and in a gauged WZNW model corresponding to two-dimensional QCD (QCD2) with adjoint fermions. We show that the bosonized model is equivalent to the fermion model only if a particular form of the WZNW action with a gauge-invariant integrand is chosen. For the exact correspondence, it is necessary to integrate over the ways the gauge group SU(N)/ZN is embedded into the full O(N2-1) group for the bosonized matter field. For even N, one should also take into account the contributions of both disconnected components in O(N2-1). In that case, ZI~mn0 for small fermion masses where 2n0 coincides with the number of fermion zero modes in a particular instanton background. The Taylor expansion of ZI/mn0 in mass involves only even powers of m, as it should. The physics of adjoint QCD2 is discussed. We argue that, for odd N, the discrete chiral symmetry Z2⊗Z2 present in the action is broken spontaneously down to Z2 and the fermion condensate <λ¯λ>0 is formed. The system undergoes a first order phase transition at Tc=0 so that the condensate is zero at an arbitrary small temperature. It is not yet quite clear what happens for even N>=4.
Exploring two-dimensional electron gases with two-dimensional Fourier transform spectroscopy
Paul, J.; Dey, P.; Karaiskaj, D.; Tokumoto, T.; Hilton, D. J.; Reno, J. L.
2014-10-07
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{sup 11} cm{sup −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” (S{sub 1}) 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 S{sub 1} 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” (S{sub 3}) 2DFT spectra for the 12 nm quantum well show a single peak for both co-linear and co-circular polarizations.
Dynamics of two-dimensional and quasi-two-dimensional polymers
NASA Astrophysics Data System (ADS)
Sung, Bong June; Yethiraj, Arun
2013-06-01
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.
Two-Dimensional Nanoparticle Supracrystals: A Model System for Two-Dimensional Melting.
Kim, Jin Young; Kwon, S Joon; Chang, Jae-Byum; Ross, Caroline A; Hatton, T Alan; Stellacci, Francesco
2016-02-10
In a Langmuir trough, successive compression cycles can drive a two-dimensional (2D) nanoparticle supracrystal (NPSC) closer to its equilibrium structure. Here, we show a series of equilibrated 2D NPSCs consisting of gold NPs of uniform size, varying solely in the length of their alkanethiol ligands. The ordering of the NPSC is governed by the ligand length, thus providing a model system to investigate the nature of 2D melting in a system of NPs. As the ligand length increases the supracrystal transitions from a crystalline to a liquid-like phase with evidence of a hexatic phase at an intermediate ligand length. The phase change is interpreted as an entropy-driven phenomenon associated with steric constraints between ligand shells. The density of topological defects scales with ligand length, suggesting an equivalence between ligand length and temperature in terms of melting behavior. On the basis of this equivalence, the experimental evidence indicates a two-stage 2D melting of NPSCs. PMID:26756789
NASA Technical Reports Server (NTRS)
Chiu, Hong-Yee
1990-01-01
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.
Manciu, M.; Sen, S.; Hurd, A.J.
1999-04-12
The authors consider a chain of elastic (Hertzian) grains that repel upon contact according to the potential V = a{delta}{sup u}, u > 2, where {delta} is the overlap between the grains. They present numerical and analytical results to show that an impulse initiated at an end of a chain of Hertzian grains in contact eventually propagates as a soliton for all n > 2 and that no solitons are possible for n {le} 2. Unlike continuous, they find that colliding solitons in discrete media initiative multiple weak solitons at the point of crossing.
NASA Astrophysics Data System (ADS)
Chiu, Hong-Yee
1990-05-01
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.
NASA Astrophysics Data System (ADS)
Dauxois, Thierry; Peyrard, Michel
2010-06-01
List of Portraits; Preface; Part I. Different Classes of Solitons: Introduction; 1. Nontopological solitons: the Korteweg-de Vries equation; 2. Topological soltitons: sine-Gordon equation; 3. Envelope solitons and nonlinear localisation: the nonlinear Schrdinger equation; 4. The modelling process: ion acoustic waves in a plasma; Part II. Mathematical Methods for the Study of Solitons: Introduction; 5. Linearisation around the soliton solution; 6. Collective coordinate method; 7. The inverse-scattering transform; Part III. Examples in Solid State and Atomic Physics: Introduction; 8. The Ferm-Pasta-Ulam problem; 9. A simple model for dislocations in crystals; 10. Ferroelectric domain walls; 11. Incommensurate phases; 12. Solitons in magnetic systems; 13. Solitons in Conducting polymers; 14. Solitons in Bose-Einstein condensates; Part IV. Nonlinear Excitations in Biological Molecules: Introduction; 15. Energy localisation and transfer in proteins; 16. Nonlinear dynamics and statistical physics of DNA; Conclusion: Physical solitons: do they exist?; Part V. Appendices: A. Derivation of the KdV equation for surface hydrodynamic waves; B. Mechanics of a continuous medium; C. Coherent states of an harmonic oscillator; References; Index.
NASA Astrophysics Data System (ADS)
Dauxois, Thierry; Peyrard, Michel
2006-03-01
List of Portraits; Preface; Part I. Different Classes of Solitons: Introduction; 1. Nontopological solitons: the Korteweg-de Vries equation; 2. Topological soltitons: sine-Gordon equation; 3. Envelope solitons and nonlinear localisation: the nonlinear Schrdinger equation; 4. The modelling process: ion acoustic waves in a plasma; Part II. Mathematical Methods for the Study of Solitons: Introduction; 5. Linearisation around the soliton solution; 6. Collective coordinate method; 7. The inverse-scattering transform; Part III. Examples in Solid State and Atomic Physics: Introduction; 8. The Ferm-Pasta-Ulam problem; 9. A simple model for dislocations in crystals; 10. Ferroelectric domain walls; 11. Incommensurate phases; 12. Solitons in magnetic systems; 13. Solitons in Conducting polymers; 14. Solitons in Bose-Einstein condensates; Part IV. Nonlinear Excitations in Biological Molecules: Introduction; 15. Energy localisation and transfer in proteins; 16. Nonlinear dynamics and statistical physics of DNA; Conclusion: Physical solitons: do they exist?; Part V. Appendices: A. Derivation of the KdV equation for surface hydrodynamic waves; B. Mechanics of a continuous medium; C. Coherent states of an harmonic oscillator; References; Index.
NASA Astrophysics Data System (ADS)
Voronin, A. A.; Zheltikov, A. M.
2014-10-01
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.
Fundamental solitons in parity-time symmetric lattice with a vacancy defect
NASA Astrophysics Data System (ADS)
Ba?c?, Mahmut; Bak?rta?, ?lkay; Antar, Nalan
2015-12-01
We put forward a mechanism for delaying the collapse of the fundamental solitons in nonlinear media whose dynamics is governed by two-dimensional nonlinear Schrdinger (NLS) equation with parity-time symmetric (PT-symmetric) periodic potentials with/without a vacancy defect. We observed that strengthened gain-loss component (imaginary part of the potential) in the periodic lattice impoverish the stability properties of the solitons, on the other hand adding a vacancy defect to the periodic PT-symmetric lattice acts as a delaying mechanism for collapsing solitons.
Vector cavity solitons in broad area Vertical-Cavity Surface-Emitting Lasers
Averlant, Etienne; Tlidi, Mustapha; Thienpont, Hugo; Ackemann, Thorsten; Panajotov, Krassimir
2016-01-01
We report the experimental observation of two-dimensional vector cavity solitons in a Vertical-Cavity Surface-Emitting Laser (VCSEL) under linearly polarized optical injection when varying optical injection linear polarization direction. The polarization of the cavity soliton is not the one of the optical injection as it acquires a distinct ellipticity. These experimental results are qualitatively reproduced by the spin-flip VCSEL model. Our findings open the road to polarization multiplexing when using cavity solitons in broad-area lasers as pixels in information technology. PMID:26847004
Vector cavity solitons in broad area Vertical-Cavity Surface-Emitting Lasers
NASA Astrophysics Data System (ADS)
Averlant, Etienne; Tlidi, Mustapha; Thienpont, Hugo; Ackemann, Thorsten; Panajotov, Krassimir
2016-02-01
We report the experimental observation of two-dimensional vector cavity solitons in a Vertical-Cavity Surface-Emitting Laser (VCSEL) under linearly polarized optical injection when varying optical injection linear polarization direction. The polarization of the cavity soliton is not the one of the optical injection as it acquires a distinct ellipticity. These experimental results are qualitatively reproduced by the spin-flip VCSEL model. Our findings open the road to polarization multiplexing when using cavity solitons in broad-area lasers as pixels in information technology.
Vector cavity solitons in broad area Vertical-Cavity Surface-Emitting Lasers.
Averlant, Etienne; Tlidi, Mustapha; Thienpont, Hugo; Ackemann, Thorsten; Panajotov, Krassimir
2016-01-01
We report the experimental observation of two-dimensional vector cavity solitons in a Vertical-Cavity Surface-Emitting Laser (VCSEL) under linearly polarized optical injection when varying optical injection linear polarization direction. The polarization of the cavity soliton is not the one of the optical injection as it acquires a distinct ellipticity. These experimental results are qualitatively reproduced by the spin-flip VCSEL model. Our findings open the road to polarization multiplexing when using cavity solitons in broad-area lasers as pixels in information technology. PMID:26847004
Third sound in one and two dimensional modulated structures
Komuro, T.; Kawashima, H., Shirahama, K.; Kono, K.
1996-02-01
An experimental technique is developed to study acoustic transmission in one and two dimensional modulated structures by employing third sound of a superfluid helium film. In particular, the Penrose lattice, which is a two dimensional quasiperiodic structure, is studied. In two dimensions, the scattering of third sound is weaker than in one dimension. Nevertheless, the authors find that the transmission spectrum in the Penrose lattice, which is a two dimensional prototype of the quasicrystal, is observable if the helium film thickness is chosen around 5 atomic layers. The transmission spectra in the Penrose lattice are explained in terms of dynamical theory of diffraction.
Two-dimensional Minkowski causal automorphisms and conformal maps
NASA Astrophysics Data System (ADS)
Burgos, Juan Manuel
2013-02-01
Treating the two-dimensional Minkowski space as a Wick rotated version of the complex plane, we characterize the causal automorphisms in the two-dimensional Minkowski space as the Märzke-Wheeler maps of a certain class of observers. We also characterize the differentiable causal automorphisms of this space as the Minkowski conformal maps whose restriction to the time axis belongs to the class of observers mentioned above. We answer a recently raised question about whether causal automorphisms are characterized by their wave equation. As another application of the theory, we give a proper time formula for accelerated observers which solves the twin paradox in two-dimensional Minkowski spacetime.
Stable gray soliton pinned by a defect in a microcavity-polariton condensate.
Chen, Ting-Wei; Hsieh, Wen-Feng; Cheng, Szu-Cheng
2015-09-21
We study the spatially localized dark state, called dark soliton, in a one-dimensional system of the non-resonantly pumped microcavity-polariton condensate (MPC). From the recent work by Xue and Matuszewski [Phys. Rev. Lett. 112, 216401 (2014)], we know that the dark soliton in the pure MPC system is unstable. But we find that a dark soliton pinned by a defect in the impure MPC becomes a gray soliton and can be stabilized by the presence of a defect. Moreover, the stable regime of the gray soliton is given in terms of the defect strength and pump parameter. PMID:26406697
Strong Raman-induced noninstantaneous soliton interactions in gas-filled photonic crystal fibers.
Saleh, Mohammed F; Armaroli, Andrea; Marini, Andrea; Biancalana, Fabio
2015-09-01
We have developed an analytical model based on the perturbation theory to study the optical propagation of two successive solitons in hollow-core photonic crystal fibers filled with Raman-active gases. Based on the time delay between the two solitons, we have found that the trailing soliton dynamics can experience unusual nonlinear phenomena, such as spectral and temporal soliton oscillations and transport toward the leading soliton. The overall dynamics can lead to a spatiotemporal modulation of the refractive index with a uniform temporal period and a uniform or chirped spatial period. PMID:26368711
CHARACTERISTICS OF TWO-DIMENSIONAL PARTICLE EDDY DIFFUSION INOFFICE SPACE
The paper discusses the development of a two-dimensional turbulentkinetic energy - dissipation rate (k-epsilon) turbulence model inthe form of vorticity and stream functions. his turbulence modelprovides the distribution of turbulent kinematic viscosity, used tocalculate the effe...
Defect configurations in a two-dimensional classical Wigner crystal
NASA Astrophysics Data System (ADS)
Price, R.; Platzman, P. M.
1991-08-01
We have calculated using a Monte Carlo algorithm, the configuration and energy of vacancies in a classical two-dimensional Wigner crystal. We find, for our 224-electron system, that asymmetric vacancies have the lowest energies.
A two-dimensional Wigner crystal (Review Article)
NASA Astrophysics Data System (ADS)
Monarkha, Yu. P.; Syvokon, V. E.
2012-12-01
The current state of theoretical and experimental studies of the Wigner crystallization of a two-dimensional electron gas is reviewed. The Wigner crystal (WC) has first been observed experimentally in a two-dimensional electron system on the surface of liquid helium in 1979. This success was favored by the exceptional purity of the free surface of superfluid liquid and the ability to fairly accurately describe the polaronic deformation phenomena accompanying the crystallization of electrons. Very pure samples of heterostructures (GaAs/GaAlAs) and strong magnetic fields, making easier the localization of electrons in a conducting layer, were necessary in order to observe the Wigner crystallization in semiconductor two-dimensional electron systems This review discusses the basic properties of a two-dimensional WC, common to the both above-mentioned electronic systems, and also major advances in the study of transport properties of WC caused by response of the environment on motion of the electron lattice.
Difficulties that Students Face with Two-Dimensional Motion
ERIC Educational Resources Information Center
Mihas, P.; Gemousakakis, T.
2007-01-01
Some difficulties that students face with two-dimensional motion are addressed. The difficulties addressed are the vectorial representation of velocity, acceleration and force, the force-energy theorem and the understanding of the radius of curvature.
Two-dimensional materials: Not just a phase
NASA Astrophysics Data System (ADS)
Phillips, Philip W.
2016-03-01
In some two-dimensional materials, there's a puzzling intermediate metallic phase between superconducting and insulating states. Experiments on ultraclean crystalline samples suggest this metallic phase could be bosonic.
Model of a Negatively Curved Two-Dimensional Space.
ERIC Educational Resources Information Center
Eckroth, Charles A.
1995-01-01
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)
Near-Surface Geophysics: Two-Dimensional Resistivity
USGS hydrologist conducts a two-dimensional (2D) resistivity survey to investigate and characterize the shallow subsurface. The survey was conducted as part of an applied research effort by the USGS Office of Groundwater Branch of Geophysics in 2006....
String & Sticky Tape Experiments: Two-Dimensional Collisions Using Pendulums.
ERIC Educational Resources Information Center
Edge, R. D.
1989-01-01
Introduces a method for two-dimensional kinematics measurements by hanging marbles with long strings. Describes experimental procedures for conservation of momentum and obtaining the coefficient of restitution. Provides diagrams and mathematical expressions for the activities. (YP)
Riconda, C.; Weber, S.; Tikhonchuk, V. T.; Adam, J.-C.; Heron, A.
2006-08-15
Two-dimensional particle-in-cell simulations of laser-plasma interaction using a plane-wave geometry show strong bursty stimulated Brillouin backscattering, rapid filamentation, and subsequent plasma cavitation. It is shown that the cavitation is not induced by self-focusing. The electromagnetic fields below the plasma frequency that are excited are related to transient soliton-like structures. At the origin of these solitons is a three-wave decay process exciting new modes in the plasma. The cavitation is responsible for a strong local reduction of the reflectivity and goes along with an efficient but transient heating of the electrons. Once heating ceases, transmission starts to increase. Local as well as global average reflectivities attain a very low value due to strong plasma density variations brought about by the cavitation process. On the one hand, the simulations confirm the existence of a new mechanism of cavity and soliton formation in nonrelativistic laser-plasma interaction in two dimensions, which was shown to exist in one-dimensional simulations [S. Weber, C. Riconda, and V. T. Tikhonchuk, Phys. Rev. Lett. 94, 055005 (2005)]. On the other hand, new aspects are introduced inherently related to the additional degree of freedom.
Vibrational Anharmonicities Revealed by Coherent Two-Dimensional Infrared Spectroscopy
Golonzka, O.; Khalil, M.; Demirdo''ven, N.; Tokmakoff, A.
2001-03-05
Two-dimensional infrared photon echo spectroscopy has been used to describe the anharmonic nuclear potential of two coupled molecular vibrations. The two-dimensional spectrum shows diagonal and off-diagonal features, each composed of two peaks. The splitting between these peaks is directly related to the anharmonicity, while the relative amplitude of the diagonal and off-diagonal features describes the projection angle between interacting dipoles.
Supercurrent reversal in two-dimensional topological insulators
NASA Astrophysics Data System (ADS)
Zyuzin, Alexander; Alidoust, Mohammad; Klinovaja, Jelena; Loss, Daniel
2015-11-01
We calculate a supercurrent across a two-dimensional topological insulator subjected to an external magnetic field. When the edge states of a narrow two-dimensional topological insulator are hybridized, an external magnetic field can close the hybridization gap, thus driving a quantum phase transition from insulator to semimetal states of the topological insulator. We find a sign reversal of the supercurrent at the quantum phase transition revealing intrinsic properties of topological insulators via the Josephson effect.
Two-dimensional hydrodynamic model of St. Lucie Estuary
Hu, G.G.
1999-07-01
A two-dimensional hydrodynamic model of St. Lucie Estuary was developed to assess the impact of drainage canal discharge and storm water runoff. Water surface elevation, two-dimensional velocity field and salinity are collected during 1998--1998 ENSO episode. The data sets cover an eight months period that includes both wet ad dry weather conditions. The model has been applied to St. Lucie Estuary salinity study. It will also provide flow fields to a water quality model.
Observation of two-dimensional exciton-phonon quasibound states
NASA Astrophysics Data System (ADS)
Pelekanos, N. T.; Haas, H.; Magnea, N.; Belitsky, V. I.; Cantarero, A.
1997-10-01
We demonstrate the existence of robust exciton-phonon quasibound states (EPQBS) in a two-dimensional semiconductor system, resulting from the binding of the e1h1 and e1h2 heavy-hole quantum-well excitons with an LO phonon. We show that increasing quantum confinement drastically weakens these two-dimensional EPQBS. A theoretical model including phonon confinement accounts qualitatively for our results.
Light evolution in arbitrary two-dimensional waveguide arrays
Szameit, Alexander; Pertsch, Thomas; Dreisow, Felix; Nolte, Stefan; Tuennermann, Andreas; Peschel, Ulf; Lederer, Falk
2007-05-15
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.
Nicked-sleeve interface for two-dimensional capillary electrophoresis
Flaherty, Ryan J.; Huge, Bonnie J.; Bruce, Spencer M.; Dada, Oluwatosin O.; Dovichi, Norman J.
2013-01-01
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
Soliton scattering as a measurement tool for weak signals
NASA Astrophysics Data System (ADS)
Soloviev, I. I.; Klenov, N. V.; Pankratov, A. L.; Revin, L. S.; Il'ichev, E.; Kuzmin, L. S.
2015-07-01
We have considered relativistic soliton dynamics governed by the sine-Gordon equation and affected by short spatial inhomogeneities of the driving force and thermal noise. Developed analytical and numerical methods for calculation of soliton scattering at the inhomogeneities allowed us to examine the scattering as a measurement tool for sensitive detection of polarity of the inhomogeneities. We have considered the superconducting fluxonic ballistic detector as an example of the device in which the soliton scattering is utilized for quantum measurements of superconducting flux qubits. We optimized the soliton dynamics for the measurement process varying the starting and the stationary soliton velocity as well as configuration of the inhomogeneities. For experimentally relevant parameters we obtained the signal-to-noise ratio above 100 reflecting good practical usability of the measurement concept.
Two-Photon Cavity Solitons in Active Optical Media
Vilaseca, R.; Torrent, M. C.; Garcia-Ojalvo, J.; Brambilla, M.; San Miguel, M.
2001-08-20
We show that broad-area cascade lasers with no absorbing intracavity elements support the spontaneous formation of two-dimensional bright localized structures in a dark background. These cavity solitons consist of islands of two-photon emission embedded in a background of single-photon emission. We discuss the mechanisms through which these structures are formed and interact, along with their properties and stability.
Conservation of the angular momentum for multidimensional optical solitons
Desyatnikov, A S; Maimistov, Andrei I
2000-11-30
Analytic expressions are obtained for spin and orbital moments of multidimensional optical solitons - two-dimensional beams and three-dimensional light bullets. It is shown that for given directions of the incidence of light bullets, the time delay in the pulse sequence determines the direction and value of the orbital moment, and can be used as a parameter to control the structure appearing during the mutual capture. (nonlinear optical phenomena)
Semirelativity and Kink Solitons
ERIC Educational Resources Information Center
Nowak, Mariusz Karol
2014-01-01
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…
Periodic exploding dissipative solitons
NASA Astrophysics Data System (ADS)
Cartes, Carlos; Descalzi, Orazio
2016-03-01
We show the existence of periodic exploding dissipative solitons. These nonchaotic explosions appear when higher-order nonlinear and dispersive effects are added to the complex cubic-quintic Ginzburg-Landau equation modeling fiber soliton lasers. This counterintuitive phenomenon is the result of period-halving bifurcations leading to order (periodic explosions), followed by period-doubling bifurcations leading to chaos (chaotic explosions).
Semirelativity and Kink Solitons
ERIC Educational Resources Information Center
Nowak, Mariusz Karol
2014-01-01
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
Can Boltzmann Soliton Star Exist?
NASA Astrophysics Data System (ADS)
Su, Rukeng; Chen, Xuelei; Pan, Rongshi
1992-12-01
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.
Two dimensional NMR of liquids and oriented molecules
Gochin, M.
1987-02-01
Chapter 1 discusses the quantum mechanical formalism used for describing the interaction between magnetic dipoles that dictates the appearance of a spectrum. The NMR characteristics of liquids and liquid crystals are stressed. Chapter 2 reviews the theory of multiple quantum and two dimensional NMR. Properties of typical spectra and phase cycling procedures are discussed. Chapter 3 describes a specific application of heteronuclear double quantum coherence to the removal of inhomogeneous broadening in liquids. Pulse sequences have been devised which cancel out any contribution from this inhomogeneity to the final spectrum. An interpretation of various pulse sequences for the case of /sup 13/C and /sup 1/H is given, together with methods of spectral editing by removal or retention of the homo- or heteronuclear J coupling. The technique is applied to a demonstration of high resolution in both frequency and spatial dimensions with a surface coil. In Chapter 4, multiple quantum filtered 2-D spectroscopy is demonstrated as an effective means of studying randomly deuterated molecules dissolved in a nematic liquid crystal. Magnitudes of dipole coupling constants have been determined for benzene and hexane, and their signs and assignments found from high order multiple quantum spectra. For the first time, a realistic impression of the conformation of hexane can be estimated from these results. Chapter 5 is a technical description of the MDB DCHIB-DR11W parallel interface which has been set up to transfer data between the Data General Nova 820 minicomputer, interfaced to the 360 MHz spectrometer, and the Vax 11/730. It covers operation of the boards, physical specifications and installation, and programs for testing and running the interface.
Nonstationarity of a two-dimensional perpendicular shock: Competing mechanisms
NASA Astrophysics Data System (ADS)
Lembge, Bertrand; Savoini, Philippe; Hellinger, Petr; Trvn?ek, Pavel M.
2009-03-01
Two-dimensional particle-in-cell (PIC) simulations are used for analyzing in detail different nonstationary behaviors of a perpendicular supercritical shock. A recent study by Hellinger et al. (2007) has shown that the front of a supercritical shock can be dominated by the emission of large-amplitude whistler waves. These waves inhibit the self-reformation driven by the reflected ions; then, the shock front appears almost ``quasi-stationary.'' The present study stresses new complementary results. First, for a fixed ? i value, the whistler waves emission (WWE) persists for high M A above a critical Mach number (i.e., M A >= M A WWE). The quasi-stationarity is only apparent and disappears when considering the full 3-D field profiles. Second, for lower M A , the self-reformation is retrieved and becomes dominant as the amplitude of the whistler waves becomes negligible. Third, there exists a transition regime in M A within which both processes compete each other. Fourth, these results are observed for a strictly perpendicular shock only as B 0 is within the simulation plane. When B 0 is out of the simulation plane, no whistler waves emission is evidenced and only self-reformation is recovered. Fifth, the occurrence and disappearance of the nonlinear whistler waves are well recovered in both 2-D PIC and 2-D hybrid simulations. The impacts on the results of the mass ratio (2-D PIC simulations), of the resistivity and spatial resolution (2-D hybrid simulations), and of the size of the simulation box along the shock front are analyzed in detail.
Modeling Meandering Channel by Two-Dimensional Shallow Water Equations
NASA Astrophysics Data System (ADS)
Yu, C.; Duan, J. G.
2014-12-01
This research is to simulate the process of channel meandering using a two-dimensional depth-averaged hydrodynamic model. The multiple interactions between unsteady flow, turbulence, secondary flow, nonequilibrium sediment transport and bank erosion are considered by the model. The governing equations are the 2D depth-averaged Reynolds-averaged Navier-Stokes (2D-RANS) equations and the Exner equation for bed elevation evolution. The Reynolds stresses are calculated by the k-? turbulence model. The secondary flow, is modeled by the dispersion terms in momentum equations. The spatial lag between the instantaneous flow properties and the rate of sediment transport is simulated by the nonequilibrium sediment transport model. During the process of adaptation, the sediment transport rate gradually develops into the transport capacity of a given flow condition. The evolution of channel bed and bank is modeled by the general Exner equation that accounts for both vertical deformation of bed elevation as well as lateral migration of bank. The system of governing equations is solved by a semi-implicit finite volume method over the Cartesian mesh. The advective fluxes across each cell interface are simultaneously calculated by the extended HLL Riemann solver. At each time step, the diffusion terms in the governing equations are solved by the implicit Euler scheme. The source terms are discretized in a well-balanced way to retain the C-property of the proposed model. Application of the model to different test cases indicates that the model can correctly simulate different phases of meandering channel evolution which include streamwise migration, transverse migration and rotation of channel bends.
Two-dimensional aperture coding for magnetic sector mass spectrometry.
Russell, Zachary E; Chen, Evan X; Amsden, Jason J; Wolter, Scott D; Danell, Ryan M; Parker, Charles B; Stoner, Brian R; Gehm, Michael E; Brady, David J; Glass, Jeffrey T
2015-02-01
In mass spectrometer design, there has been a historic belief that there exists a fundamental trade-off between instrument size, throughput, and resolution. When miniaturizing a traditional system, performance loss in either resolution or throughput would be expected. However, in optical spectroscopy, both one-dimensional (1D) and two-dimensional (2D) aperture coding have been used for many years to break a similar trade-off. To provide a viable path to miniaturization for harsh environment field applications, we are investigating similar concepts in sector mass spectrometry. Recently, we demonstrated the viability of 1D aperture coding and here we provide a first investigation of 2D coding. In coded optical spectroscopy, 2D coding is preferred because of increased measurement diversity for improved conditioning and robustness of the result. To investigate its viability in mass spectrometry, analytes of argon, acetone, and ethanol were detected using a custom 90-degree magnetic sector mass spectrometer incorporating 2D coded apertures. We developed a mathematical forward model and reconstruction algorithm to successfully reconstruct the mass spectra from the 2D spatially coded ion positions. This 2D coding enabled a 3.5 throughput increase with minimal decrease in resolution. Several challenges were overcome in the mass spectrometer design to enable this coding, including the need for large uniform ion flux, a wide gap magnetic sector that maintains field uniformity, and a high resolution 2D detection system for ion imaging. Furthermore, micro-fabricated 2D coded apertures incorporating support structures were developed to provide a viable design that allowed ion transmission through the open elements of the code. PMID:25510933
Two-Dimensional Aperture Coding for Magnetic Sector Mass Spectrometry
NASA Astrophysics Data System (ADS)
Russell, Zachary E.; Chen, Evan X.; Amsden, Jason J.; Wolter, Scott D.; Danell, Ryan M.; Parker, Charles B.; Stoner, Brian R.; Gehm, Michael E.; Brady, David J.; Glass, Jeffrey T.
2015-02-01
In mass spectrometer design, there has been a historic belief that there exists a fundamental trade-off between instrument size, throughput, and resolution. When miniaturizing a traditional system, performance loss in either resolution or throughput would be expected. However, in optical spectroscopy, both one-dimensional (1D) and two-dimensional (2D) aperture coding have been used for many years to break a similar trade-off. To provide a viable path to miniaturization for harsh environment field applications, we are investigating similar concepts in sector mass spectrometry. Recently, we demonstrated the viability of 1D aperture coding and here we provide a first investigation of 2D coding. In coded optical spectroscopy, 2D coding is preferred because of increased measurement diversity for improved conditioning and robustness of the result. To investigate its viability in mass spectrometry, analytes of argon, acetone, and ethanol were detected using a custom 90-degree magnetic sector mass spectrometer incorporating 2D coded apertures. We developed a mathematical forward model and reconstruction algorithm to successfully reconstruct the mass spectra from the 2D spatially coded ion positions. This 2D coding enabled a 3.5 throughput increase with minimal decrease in resolution. Several challenges were overcome in the mass spectrometer design to enable this coding, including the need for large uniform ion flux, a wide gap magnetic sector that maintains field uniformity, and a high resolution 2D detection system for ion imaging. Furthermore, micro-fabricated 2D coded apertures incorporating support structures were developed to provide a viable design that allowed ion transmission through the open elements of the code.
Two-dimensional direct numerical simulation of parametrically excited surface waves in viscous fluid
NASA Astrophysics Data System (ADS)
Murakami, Youichi; Chikano, Masatsugu
2001-01-01
Standing surface waves on a viscous fluid driven parametrically by a vertical harmonic oscillation are investigated, based on direct numerical simulations of the two-dimensional Navier-Stokes equation, together with appropriate boundary conditions. The condition for the onset of the waves in the experiments by Lioubashevski et al. [Phys. Rev. Lett. 76, 3959 (1996)] is reproduced by our numerical simulation. The time evolution and the flow structures are investigated in detail. The form of the surface elevation is analyzed and the dependence of the saturated amplitude on the forcing strength shows a normal bifurcation. Instead of a localized state, spatially uniform standing waves are formed in an extended system. Using initial perturbations of the uniform state, numerical simulations show that the uniform standing waves are stable to two-dimensional disturbances, which suggests that three-dimensionality is essential for the spatially localized state to occur.
Soliton absorption spectroscopy
Kalashnikov, V. L.; Sorokin, E.
2010-01-01
We analyze optical soliton propagation in the presence of weak absorption lines with much narrower linewidths as compared to the soliton spectrum width using the novel perturbation analysis technique based on an integral representation in the spectral domain. The stable soliton acquires spectral modulation that follows the associated index of refraction of the absorber. The model can be applied to ordinary soliton propagation and to an absorber inside a passively modelocked laser. In the latter case, a comparison with water vapor absorption in a femtosecond Cr:ZnSe laser yields a very good agreement with experiment. Compared to the conventional absorption measurement in a cell of the same length, the signal is increased by an order of magnitude. The obtained analytical expressions allow further improving of the sensitivity and spectroscopic accuracy making the soliton absorption spectroscopy a promising novel measurement technique. PMID:21151755
Two-dimensional probe absorption spectrum in a semiconductor quantum well
NASA Astrophysics Data System (ADS)
Wang, Guanling; Wu, Feng
2015-11-01
We investigate the two-dimensional (2D) probe absorption spectrum in a semiconductor quantum well driven by two orthogonal standing-wave lasers. It is found that, due to the position-dependent quantum interference, the 2D spatial distribution of probe absorption spectrum can be easily controlled via adjusting the system parameters. Thus, our scheme shows the underlying probability for the applications in solid-state optic communication and transmission.
Stability analysis of two-dimensional models of three-dimensional convection
Greenside, H.S.; Cross, M.C.
1984-12-01
Analytical and numerical methods are used to study the linear stability of spatially periodic solutions for various two-dimensional equations which model thermal convection in fluids. This analysis suggests new model equations that will be useful for investigating questions such as wave number selection, pattern formation, and the onset of turbulence in large aspect ratio Rayleigh-Benard systems. In particular, we construct a nonrelaxational model that has stability boundaries similar to those calculated for intermediate Prandtl number fluids.
Scaling and correlation functions in a model of a two-dimensional earthquake fault
NASA Astrophysics Data System (ADS)
Jonsson, T.; Marinosson, S. F.
1998-09-01
We study numerically a two-dimensional version of the Burrige-Knopoff model. We calculate spatial and temporal correlation functions and compare their behavior with the results found for the one-dimensional model. The Gutenberg-Richter law is only obtained for special choices of parameters in the relaxation function. We find that the distribution of the fractal dimension of the slip zone exhibits two well-defined peaks coeersponding to intermediate size and large events.
Dynamic patterns in a two-dimensional neural field with refractoriness
NASA Astrophysics Data System (ADS)
Qi, Yang; Gong, Pulin
2015-08-01
The formation of dynamic patterns such as localized propagating waves is a fascinating self-organizing phenomenon that happens in a wide range of spatially extended systems including neural systems, in which they might play important functional roles. Here we derive a type of two-dimensional neural-field model with refractoriness to study the formation mechanism of localized waves. After comparing this model with existing neural-field models, we show that it is able to generate a variety of localized patterns, including stationary bumps, localized waves rotating along a circular path, and localized waves with longer-range propagation. We construct explicit bump solutions for the two-dimensional neural field and conduct a linear stability analysis on how a stationary bump transitions to a propagating wave under different spatial eigenmode perturbations. The neural-field model is then partially solved in a comoving frame to obtain localized wave solutions, whose spatial profiles are in good agreement with those obtained from simulations. We demonstrate that when there are multiple such propagating waves, they exhibit rich propagation dynamics, including propagation along periodically oscillating and irregular trajectories; these propagation dynamics are quantitatively characterized. In addition, we show that these waves can have repulsive or merging collisions, depending on their collision angles and the refractoriness parameter. Due to its analytical tractability, the two-dimensional neural-field model provides a modeling framework for studying localized propagating waves and their interactions.
Effects of spin-dependent interactions on polarization of bright polariton solitons.
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-Mndez, E A; Biermann, K; Hey, R; Santos, P V
2014-01-31
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
Perturbation theory for dark solitons: inverse scattering transform approach and radiative effects.
Lashkin, Volodymyr M
2004-12-01
A perturbation theory for dark solitons of the nonlinear Schrdinger equation is developed. The theory is based on the inverse scattering transform method. Equations describing dynamics discrete (solitonic) and continuous (radiative) scattering data in the presence of perturbations are derived for N-soliton case. Adiabatic equations for soliton parameters and the perturbation-induced radiative field are obtained. The problem of the absence of a threshold for the creation of dark solitons under the action of a perturbation is discussed. A temporal one-soliton pulse with random initial perturbation and a spatial soliton with linear gain and two-photon absorption are considered as examples of application of the developed theory. PMID:15697539
NASA Astrophysics Data System (ADS)
Kopeliovich, A. I.; Pyshkin, P. V.; Kalinenko, A. N.; Yanovsky, A. V.
2016-02-01
It is shown that the normal electron-electron scattering is a source of electrical resistance on non-contact current excitation in two-dimensional spin-split electron systems. In contrast to the contact current injection, non-contact current excitation causes spatially inhomogeneous polarization in a two-dimensional conductor leading to new resistivity mechanisms.
NASA Astrophysics Data System (ADS)
Buchsbaum, Steven Bruce
1990-01-01
Observations of ship wakes have exhibited a compact steep ray within the diverging portion of the traditional Kelvin wake. This ray typically consists of four to eight wave crest contained within an oblique packet profile. This profile does not appear to disperse as rapidly as would be anticipated for linear gravity waves. Quantitative observations of these rays in the wake of the coast guard cutter Point Brower, and model ships during a tank towing experiment, have shown these features to be oblique packet solitons. I use the term soliton to describe a wave packet for which nonlinearities act to balance linear dispersion, rather than the strict mathematical definition. The measured angular position within the wake of these solitons is observed to be a function of speed. It is shown that a ship modeled by a pressure source at the bow, and a pressure sink at the stern can account for the observed speed dependence. Numerical integration of the nonlinear Schrodinger equation has demonstrated that the small deviations of our observations from exact soliton profiles are consistent with soliton like behavior. Indeed these near soliton solutions are shown to be a better match to our observations than exact soliton solutions. Thus I would conclude that a solitary wake feature is a possible explanation for the bright lines observed in sun glitter photos of ship wakes taken from the space shuttle. Solitary wake features may also contribute to the explanation of some of the long bright lines observed in ship wake SAR images observed from SEASAT.
Dynamical class of a two-dimensional plasmonic Dirac system.
Silva, Érica de Mello
2015-10-01
A current goal in plasmonic science and technology is to figure out how to manage the relaxational dynamics of surface plasmons in graphene since its damping constitutes a hinder for the realization of graphene-based plasmonic devices. In this sense we believe it might be of interest to enlarge the knowledge on the dynamical class of two-dimensional plasmonic Dirac systems. According to the recurrence relations method, different systems are said to be dynamically equivalent if they have identical relaxation functions at all times, and such commonality may lead to deep connections between seemingly unrelated physical systems. We employ the recurrence relations approach to obtain relaxation and memory functions of density fluctuations and show that a two-dimensional plasmonic Dirac system at long wavelength and zero temperature belongs to the same dynamical class of standard two-dimensional electron gas and classical harmonic oscillator chain with an impurity mass. PMID:26565207
Dynamical class of a two-dimensional plasmonic Dirac system
NASA Astrophysics Data System (ADS)
Silva, rica de Mello
2015-10-01
A current goal in plasmonic science and technology is to figure out how to manage the relaxational dynamics of surface plasmons in graphene since its damping constitutes a hinder for the realization of graphene-based plasmonic devices. In this sense we believe it might be of interest to enlarge the knowledge on the dynamical class of two-dimensional plasmonic Dirac systems. According to the recurrence relations method, different systems are said to be dynamically equivalent if they have identical relaxation functions at all times, and such commonality may lead to deep connections between seemingly unrelated physical systems. We employ the recurrence relations approach to obtain relaxation and memory functions of density fluctuations and show that a two-dimensional plasmonic Dirac system at long wavelength and zero temperature belongs to the same dynamical class of standard two-dimensional electron gas and classical harmonic oscillator chain with an impurity mass.
Complexity and efficient approximability of two dimensional periodically specified problems
Marathe, M.V.; Hunt, H.B. III; Stearns, R.E.
1996-09-01
The authors consider the two dimensional periodic specifications: a method to specify succinctly objects with highly regular repetitive structure. These specifications arise naturally when processing engineering designs including VLSI designs. These specifications can specify objects whose sizes are exponentially larger than the sizes of the specification themselves. Consequently solving a periodically specified problem by explicitly expanding the instance is prohibitively expensive in terms of computational resources. This leads one to investigate the complexity and efficient approximability of solving graph theoretic and combinatorial problems when instances are specified using two dimensional periodic specifications. They prove the following results: (1) several classical NP-hard optimization problems become NEXPTIME-hard, when instances are specified using two dimensional periodic specifications; (2) in contrast, several of these NEXPTIME-hard problems have polynomial time approximation algorithms with guaranteed worst case performance.
Two-dimensional magic Ag nanopucks on Pb quantum islands
NASA Astrophysics Data System (ADS)
Chiu, Y. P.; Huang, L. W.; Wei, C. M.; Chang, C. S.; Tsong, Tien T.
2006-03-01
Periodic patterns of electronic origin found on Pb quantum islands can be employed as the templates to grow self-organized nanopucks of various materials. Owing to a strong interaction existing between Ag and the template, nearly perfect two-dimensional arrays of Ag nanopucks can be grown from 70 K to 150K. Not only is the notable site-selected feature of Ag nanopucks observed on Pb islands but their size distribution also registers a remarkable abundance variation. Those nanopucks with significantly enhanced intensity are denoted as two dimensional magic Ag nanoclusters. Detailed calculations based on ab initio density functional theory have been made to illuminate how the size and shape effects related to electronic confinement influence the formation of two-dimensional metal nanostructures. Furthermore, when the Ag nanopuck grows to a certain size, the geometrical effect takes hold from the electronic effect as the major attribute, which drive the Ag nanopucks towards well defined hexagonal crystalline structures.
Two dimensional convolute integers for machine vision and image recognition
NASA Technical Reports Server (NTRS)
Edwards, Thomas R.
1988-01-01
Machine vision and image recognition require sophisticated image processing prior to the application of Artificial Intelligence. Two Dimensional Convolute Integer Technology is an innovative mathematical approach for addressing machine vision and image recognition. This new technology generates a family of digital operators for addressing optical images and related two dimensional data sets. The operators are regression generated, integer valued, zero phase shifting, convoluting, frequency sensitive, two dimensional low pass, high pass and band pass filters that are mathematically equivalent to surface fitted partial derivatives. These operators are applied non-recursively either as classical convolutions (replacement point values), interstitial point generators (bandwidth broadening or resolution enhancement), or as missing value calculators (compensation for dead array element values). These operators show frequency sensitive feature selection scale invariant properties. Such tasks as boundary/edge enhancement and noise or small size pixel disturbance removal can readily be accomplished. For feature selection tight band pass operators are essential. Results from test cases are given.
A two-dimensional spin liquid in quantum kagome ice.
Carrasquilla, Juan; Hao, Zhihao; Melko, Roger G
2015-01-01
Actively sought since the turn of the century, two-dimensional quantum spin liquids (QSLs) are exotic phases of matter where magnetic moments remain disordered even at zero temperature. Despite ongoing searches, QSLs remain elusive, due to a lack of concrete knowledge of the microscopic mechanisms that inhibit magnetic order in materials. Here we study a model for a broad class of frustrated magnetic rare-earth pyrochlore materials called quantum spin ices. When subject to an external magnetic field along the [111] crystallographic direction, the resulting interactions contain a mix of geometric frustration and quantum fluctuations in decoupled two-dimensional kagome planes. Using quantum Monte Carlo simulations, we identify a set of interactions sufficient to promote a groundstate with no magnetic long-range order, and a gap to excitations, consistent with a Z2 spin liquid phase. This suggests an experimental procedure to search for two-dimensional QSLs within a class of pyrochlore quantum spin ice materials. PMID:26096331
Hamiltonian formalism of two-dimensional Vlasov kinetic equation
Pavlov, Maxim V.
2014-01-01
In this paper, the two-dimensional Benney system describing long wave propagation of a finite depth fluid motion and the multi-dimensional RussoSmereka kinetic equation describing a bubbly flow are considered. The Hamiltonian approach established by J. Gibbons for the one-dimensional Vlasov kinetic equation is extended to a multi-dimensional case. A local Hamiltonian structure associated with the hydrodynamic lattice of moments derived by D.J.Benney is constructed. A relationship between this hydrodynamic lattice of moments and the two-dimensional Vlasov kinetic equation is found. In the two-dimensional case, a Hamiltonian hydrodynamic lattice for the RussoSmereka kinetic model is constructed. Simple hydrodynamic reductions are presented. PMID:25484603
Cubic-quintic solitons in the checkerboard potential
Driben, Rodislav; Zyss, Joseph; Malomed, Boris A.; Gubeskys, Arthur
2007-12-15
We introduce a two-dimensional (2D) model which combines a checkerboard potential, alias the Kronig-Penney (KP) lattice, with the self-focusing cubic and self-defocusing quintic nonlinear terms. The beam-splitting mechanism and soliton multistability are explored in this setting, following the recently considered 1D version of the model. Families of single- and multi-peak solitons (in particular, five- and nine-peak species naturally emerge in the 2D setting) are found in the semi-infinite gap, with both branches of bistable families being robust against perturbations. For single-peak solitons, the variational approximation (VA) is developed, providing for a qualitatively correct description of the transition from monostability to the bistability. 2D solitons found in finite band gaps are unstable. Also constructed are two different species of stable vortex solitons, arranged as four-peak patterns ('oblique' and 'straight' ones). Unlike them, compact 'crater-shaped' vortices are unstable, transforming themselves into randomly walking fundamental beams.
Oblique half-solitons and their generation in exciton-polariton condensates
Flayac, H.; Solnyshkov, D. D.; Malpuech, G.
2011-05-15
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.
Coherent soliton communication lines
NASA Astrophysics Data System (ADS)
Yushko, O. V.; Redyuk, A. A.; Fedoruk, M. P.; Turitsyn, S. K.
2014-11-01
The data transmission in coherent fiber-optical communication lines using solitons with a variable phase is studied. It is shown that nonlinear coherent structures (solitons) can be applied for effective signal transmission over a long distance using amplitude and optical-phase keying of information. The optimum ratio of the pulse width to the bit slot at which the spectral efficiency (transmitted bits per second and hertz) is maximal is determined. It is shown that soliton fiber-optical communication lines can ensure data transmission at a higher spectral efficiency as compared to traditional communication lines and at a high signal-to-noise ratio.
Coherent soliton communication lines
Yushko, O. V. Redyuk, A. A.; Fedoruk, M. P.; Turitsyn, S. K.
2014-11-15
The data transmission in coherent fiber-optical communication lines using solitons with a variable phase is studied. It is shown that nonlinear coherent structures (solitons) can be applied for effective signal transmission over a long distance using amplitude and optical-phase keying of information. The optimum ratio of the pulse width to the bit slot at which the spectral efficiency (transmitted bits per second and hertz) is maximal is determined. It is shown that soliton fiber-optical communication lines can ensure data transmission at a higher spectral efficiency as compared to traditional communication lines and at a high signal-to-noise ratio.
Nontopological chiral soliton bag
Seki, R.; Ohta, S.
1984-02-20
A chiral nontopological soliton bag for baryons is numerically examined for the hedgehog model in the mean field approximation. The chiral invariance in the Lagrangian is preserved by means of the nonlinear sigma model. The radius and energy of the soliton bag slowly decreases in proportion to f/sup -2//sub ..pi../ as f/sup -1//sub ..pi../ decreases from zero to the physical value. The nontopological soliton bag is thus quite similar to the cloudy bag. The perturbative (linear) approximation for the pion field is found to be reasonable.
Finite Differences and Collocation Methods for the Solution of the Two Dimensional Heat Equation
NASA Technical Reports Server (NTRS)
Kouatchou, Jules
1999-01-01
In this paper we combine finite difference approximations (for spatial derivatives) and collocation techniques (for the time component) to numerically solve the two dimensional heat equation. We employ respectively a second-order and a fourth-order schemes for the spatial derivatives and the discretization method gives rise to a linear system of equations. We show that the matrix of the system is non-singular. Numerical experiments carried out on serial computers, show the unconditional stability of the proposed method and the high accuracy achieved by the fourth-order scheme.
Two-dimensional photoelastic stress analysis of traumatized incisor.
Topbasi, B; Gunday, M; Bas, M; Turkmen, C
2001-01-01
In this study, stress of traumatized incisor and the effect of stress on tooth and alveolar bone was studied with two-dimensional photoelasticity. Two homogeneous two-dimensional maxillary central incisor models were prepared. Loads were applied to the labial side of incisal edge and middle third of the crown at angles of 45 degrees and 90 degrees. It was observed that stress was increased on teeth and alveolar bone when load was applied 90 degrees on labial side of incisal edge. PMID:11445918
Two-dimensional lattice Boltzmann model for magnetohydrodynamics.
Schaffenberger, Werner; Hanslmeier, Arnold
2002-10-01
We present a lattice Boltzmann model for the simulation of two-dimensional magnetohydro dynamic (MHD) flows. The model is an extension of a hydrodynamic lattice Boltzman model with 9 velocities on a square lattice resulting in a model with 17 velocities. Earlier lattice Boltzmann models for two-dimensional MHD used a bidirectional streaming rule. However, the use of such a bidirectional streaming rule is not necessary. In our model, the standard streaming rule is used, allowing smaller viscosities. To control the viscosity and the resistivity independently, a matrix collision operator is used. The model is then applied to the Hartmann flow, giving reasonable results. PMID:12443375
Subcritical patterns and dissipative solitons due to intracavity photonic crystals
Gomila, Damia; Oppo, Gian-Luca
2007-10-15
Manipulation of the bifurcation structure of nonlinear optical systems via intracavity photonic crystals is demonstrated. In particular, subcritical regions between spatially periodic states are stabilized by modulations of the material's refractive index. An family of dissipative solitons within this bistability range due to the intracavity photonic crystal is identified and characterized in both one and two transverse dimensions. Nontrivial snaking of the modulated-cavity soliton solutions is also presented.
Variational analysis of soliton scattering by external potentials
NASA Astrophysics Data System (ADS)
Umarov, B. A.; Messikh, A.; Regaa, N.; Baizakov, B. B.
2013-04-01
Dynamics of the width and center-of-mass position of a matter wave soliton subject to interaction with arbitrary external potential is analyzed using the collective coordinates approach. It is shown that approximation of the trial function and external potential only in the interaction region of the spatial domain is sufficient for adequate description of the soliton scattering process. The validity of the developed approach is illustrated for the Gaussian and Pschl-Teller potentials.
Modeling two-dimensional water flow and bromide transport in a heterogeneous lignitic mine soil
Buczko, U.; Gerke, H.H.
2006-02-15
Water and solute fluxes in lignitic mine soils and in many other soils are often highly heterogeneous. Here, heterogeneity reflects dumping-induced inclined structures and embedded heterogeneous distributions of sediment mixtures and of lignitic fragments. Such two-scale heterogeneity effects may be analyzed through the application of two-dimensional models for calculating water and solute fluxes. The objective of this study was to gain more insight to what extent spatial heterogeneity of soil hydraulic parameters contributes to preferential flow at a lignitic mine soil. The simulations pertained to the 'Barenbrucker Hohe' site in Germany where previously water fluxes and applied tracers had been monitored with a cell lysimeter, and from where a soil block had been excavated for detailed two-dimensional characterization of the hydraulic parameters using pedotransfer functions. Based on those previous studies, scenarios with different distributions of hydraulic parameters were simulated. The results show that spatial variability of hydraulic parameters alone can hardly explain the observed flow patterns. The observed preferential flow at the site was probably caused by additional factors such as hydrophobicity, the presence of root channels, anisotropy in the hydraulic conductivity, and heterogeneous root distributions. To study the relative importance of these other factors by applying two-dimensional flow models to such sites, the experimental database must be improved. Single-continuum model approaches may be insufficient for such sites.
Boehm, M.; Mitschke, F.
2007-12-15
We consider the evolution of fiber-optic solitons in the presence of dissipation. Even very low loss ultimately leads to their decay. We derive an explicit expression for the limit of adiabaticity, and discuss the evolution beyond this limit. In determining the soliton content of the optical pulse, we contrast earlier approaches using inverse scattering with a soliton-radiation beat method. It turns out that the evolution beyond adiabaticity is governed by uncertainty, which earlier published studies had missed. Somewhat in analogy to the uncertainty principle of quantum mechanics, we derive a soliton uncertainty relation. We also give simple relations for the evolution of the pulse width which reproduce numerical studies very well.
Coherent imaging with two-dimensional focal-plane arrays: design and applications
Simpson, M.L.; Bennett, C.A.; Emery, M.S.; Hutchinson, D.P.; Miller, G.H.; Richards, R.K.; Sitter, D.N.
1997-09-01
Scanned, single-channel optical heterodyne detection has been used in a variety of lidar applications from ranging and velocity measurements to differential absorption spectroscopy. We describe the design of a coherent camera system that is based on a two-dimensional staring array of heterodyne receivers for coherent imaging applications. Experimental results with a single HgCdTe detector translated in the image plane to form a synthetic two-dimensional array demonstrate the ability to obtain passive heterodyne images of chemical vapor plumes that are invisible to normal video infrared cameras. We describe active heterodyne imaging experiments with use of focal-plane arrays that yield hard-body Doppler lidar images and also demonstrate spatial averaging to reduce speckle effects in static coherent images. {copyright} 1997 Optical Society of America
Coherent imaging with two-dimensional focal-plane arrays: design and applications.
Simpson, M L; Bennett, C A; Emery, M S; Hutchinson, D P; Miller, G H; Richards, R K; Sitter, D N
1997-09-20
Scanned, single-channel optical heterodyne detection has been used in a variety of lidar applications from ranging and velocity measurements to differential absorption spectroscopy. We describe the design of a coherent camera system that is based on a two-dimensional staring array of heterodyne receivers for coherent imaging applications. Experimental results with a single HgCdTe detector translated in the image plane to form a synthetic two-dimensional array demonstrate the ability to obtain passive heterodyne images of chemical vapor plumes that are invisible to normal video infrared cameras. We describe active heterodyne imaging experiments with use of focal-plane arrays that yield hard-body Doppler lidar images and also demonstrate spatial averaging to reduce speckle effects in static coherent images. PMID:18259563
De Haas-van Alphen effect of a two-dimensional ultracold atomic gas
NASA Astrophysics Data System (ADS)
Farias, B.; Furtado, C.
2016-01-01
In this paper, we show how the ultracold atom analogue of the two-dimensional de Haas-van Alphen effect in electronic condensed matter systems can be induced by optical fields in a neutral atomic system. The interaction between the suitable spatially varying laser fields and tripod-type trapped atoms generates a synthetic magnetic field which leads the particles to organize themselves in Landau levels. Initially, with the atomic gas in a regime of lowest Landau level, we display the oscillatory behaviour of the atomic energy and its derivative with respect to the effective magnetic field (B) as a function of 1/B. Furthermore, we estimate the area of the Fermi circle of the two-dimensional atomic gas.
NASA Astrophysics Data System (ADS)
Morikawa, Junko; Hayakawa, Eita; Ikuo, Kazuyuki; Hashimoto, Toshimasa
2010-05-01
We report on the application of two-dimensional micro-scale thermal analysis with a high-speed infrared (IR) camera equipped with an originally designed optics for the optimum wavelength 3 - 5 micron in order to observe the exothermic latent heat and thermal diffusion during the phase transitions of organic molecular crystals (n-alkanes; n- pentacosane, ntetracosane, and n- tricosane) and polymeric spherulites of poly(ethylene oxide) (PEO). The forerunning phenomenon of phase transition was visualized as the spatial temperature fluctuation by a two-dimensional differential calculus. The exothermic heat patterns of the lamellae growth of n- alkanes and that of spherulites in the radial direction of PEO were observed.
New two dimensional position sensitive proportional detectors using charge division
NASA Astrophysics Data System (ADS)
Luther, G. G.; Cowan, P. L.; Henins, A.; Brennan, S.
1986-05-01
Several two dimensional position sensitive proportional counters have been built. The cathodes can encode the position of the event in one or two dimensions using capacitative charge division techniques; a backgammon configuration encodes in one dimension with anode encoding of the second dimension, or a new cathode pattern can be used to encode in two dimensions. Details of the construction and performance are given.
Adiabatic single scan two-dimensional NMR spectrocopy.
Pelupessy, Philippe
2003-10-01
New excitation schemes, based on the use adiabatic pulses, for single scan two-dimensional NMR experiments (Frydman et al., Proc. Nat. Acad. Sci. 2002, 99, 15 858-15 862) are introduced. The advantages are discussed. Applications in homo- and heteronuclear experiments are presented. PMID:14519020
Microdiffraction applications utilizing a two-dimensional proportional detector.
Tissot, Ralph George, Jr.
2003-02-01
Two-dimensional proportional detectors with their faster data collection, large dynamic range, and more available information than point or linear proportional detectors make them ideal for microdiffraction analysis. The unique capabilities of these detectors coupled with a rotating anode source, capillary optics, and a variety of accessories allow for a wide range of applications.
Two-dimensional superstrings and the supersymmetric matrix model
NASA Astrophysics Data System (ADS)
McGreevy, John; Murthy, Sameer; Verlinde, Herman
2004-04-01
We present evidence that the supersymmetric matrix model of Marinari and Parisi represents the world-line theory of N unstable D-particles in type II superstring theory in two dimensions. This identification suggests that the matrix model gives a holographic description of superstrings in a two-dimensional black hole geometry.
Two-dimensional acceptance angles of a proustite upconverter
NASA Astrophysics Data System (ADS)
Koyanagi, K.; Mishima, T.; Sakuraba, I.; Hirayama, H.
1983-01-01
Two-dimensional acceptance angles of a proustite upconverter pumped by a Nd:YAG laser have been measured and compared with theoretical results for several phase-match conditions. A seven degree acceptance angle of infrared upconversion is obtained for a 9.4 mm long proustite crystal under a tangential phase-match condition. The experimental and theoretical results agree reasonably well.
Exact two-dimensional superconformal R symmetry and c extremization.
Benini, Francesco; Bobev, Nikolay
2013-02-01
We uncover a general principle dubbed c extremization, which determines the exact R symmetry of a two-dimensional unitary superconformal field theory with N=(0,2) supersymmetry. To illustrate its utility, we study superconformal theories obtained by twisted compactifications of four-dimensional N=4 super-Yang-Mills theory on Riemann surfaces and construct their gravity duals. PMID:23432232
Two-dimensional optimization of free electron laser designs
Prosnitz, Donald (Walnut Creek, CA); Haas, Roger A. (Pleasanton, CA)
1985-01-01
Off-axis, two-dimensional designs for free electron lasers that maintain correspondence of a light beam with a "synchronous electron" at an optimal transverse radius r>0 to achieve increased beam trapping efficiency and enhanced laser beam wavefront control so as to decrease optical beam diffraction and other deleterious effects.
Two-dimensional optimization of free-electron-laser designs
Prosnitz, D.; Haas, R.A.
1982-05-04
Off-axis, two-dimensional designs for free electron lasers are described that maintain correspondence of a light beam with a synchronous electron at an optimal transverse radius r > 0 to achieve increased beam trapping efficiency and enhanced laser beam wavefront control so as to decrease optical beam diffraction and other deleterious effects.
Two-dimensional Manifold with Point-like Defects
NASA Astrophysics Data System (ADS)
Gani, V. A.; Dmitriev, A. E.; Rubin, S. G.
We study a class of two-dimensional compact extra spaces isomorphic to the sphere S 2 in the framework of multidimensional gravitation. We show that there exists a family of stationary metrics that depend on the initial (boundary) conditions. All these geometries have a singular point. We also discuss the possibility for these deformed extra spaces to be considered as dark matter candidates.
Two-Dimensional Chirality in Three-Dimensional Chemistry.
ERIC Educational Resources Information Center
Wintner, Claude E.
1983-01-01
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)
Interior design of a two-dimensional semiclassical black hole
Levanony, Dana; Ori, Amos
2009-10-15
We look into the inner structure of a two-dimensional dilatonic evaporating black hole. We establish and employ the homogenous approximation for the black-hole interior. Two kinds of spacelike singularities are found inside the black hole, and their structure is investigated. We also study the evolution of spacetime from the horizon to the singularity.
FLOW AND DISPERSION OF POLLUTANTS WITHIN TWO-DIMENSIONAL VALLEYS
Wind-tunnel experiments and a theoretical model concerning the flow structure and pollutant diffusion over two-dimensional valleys of varying aspect ratio are described and compared. hree model valleys were used, having small, medium, and steep slopes. Measurements of mean and tu...
Two-Dimensional Fourier Transform Applied to Helicopter Flyover Noise
NASA Technical Reports Server (NTRS)
Santa Maria, Odilyn L.
1999-01-01
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.
Two-Dimensional Fourier Transform Analysis of Helicopter Flyover Noise
NASA Technical Reports Server (NTRS)
SantaMaria, Odilyn L.; Farassat, F.; Morris, Philip J.
1999-01-01
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.
Two-dimensional generalized harmonic oscillators and their Darboux partners
NASA Astrophysics Data System (ADS)
Schulze-Halberg, Axel
2011-12-01
We construct two-dimensional Darboux partners of the shifted harmonic oscillator potential and of an isotonic oscillator potential belonging to the Smorodinsky-Winternitz class of superintegrable systems. The transformed solutions, their potentials and the corresponding discrete energy spectra are computed in explicit form.
Two-dimensional vortex motion and 'negative temperatures.'
NASA Technical Reports Server (NTRS)
Montgomery, D.
1972-01-01
Explanation of the novel phenomenon, tentatively identified as the 'ergodic boundary' in a space of initial conditions for turbulent flow, suggested by the recent numerical integration of the two-dimensional Navier-Stokes equations at high Reynolds numbers reported by Deem and Zabusky (1971). The proposed explanation is presented in terms of negative temperatures for a point vortex model.
Sound waves in two-dimensional ducts with sinusoidal walls
NASA Technical Reports Server (NTRS)
Nayfeh, A. H.
1974-01-01
The method of multiple scales is used to analyze the wave propagation in two-dimensional hard-walled ducts with sinusoidal walls. For traveling waves, resonance occurs whenever the wall wavenumber is equal to the difference of the wavenumbers of any two duct acoustic modes. The results show that neither of these resonating modes could occur without strongly generating the other.
Two-Dimensional Diverging Shocks in a Nonuniform Medium
Roy A. Axford
1998-08-01
An analytic solution is derived from the time evolution of a two- dimensional diverging shock in r - z geometry. The shock propagates through a condensed medium characterized by a Mie-Gruneisen equation of state with a nonzero density gradient in the axial direction.
Two-Dimensional Grids About Airfoils and Other Shapes
NASA Technical Reports Server (NTRS)
Sorenson, R.
1982-01-01
GRAPE computer program generates two-dimensional finite-difference grids about airfoils and other shapes by use of Poisson differential equation. GRAPE can be used with any boundary shape, even one specified by tabulated points and including limited number of sharp corners. Numerically stable and computationally fast, GRAPE provides aerodynamic analyst with efficient and consistant means of grid generation.
Instabilities of optical solitons and Hamiltonian singular solutions in a medium of finite extension
Assemat, E.; Picozzi, A.; Jauslin, H. R.; Sugny, D.
2011-07-15
We analyze the role of soliton solutions and Hamiltonian singularities in the dynamics of counterpropagating waves in a medium of finite spatial extension. The soliton solution can become unstable due to the finite extension of the system. We show that the spatiotemporal dynamics then relaxes toward a Hamiltonian singular state of a nature different than that of the soliton state. This phenomenon can be explained through a geometrical analysis of the singularities of the stationary Hamiltonian system.
Transmission of matter-wave solitons through nonlinear traps and barriers
Garnier, Josselin; Abdullaev, Fatkhulla Kh.
2006-07-15
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.
Toward the Accurate Simulation of Two-Dimensional Electronic Spectra
NASA Astrophysics Data System (ADS)
Giussani, Angelo; Nenov, Artur; Segarra-Martí, Javier; Jaiswal, Vishal K.; Rivalta, Ivan; Dumont, Elise; Mukamel, Shaul; Garavelli, Marco
2015-06-01
Two-dimensional pump-probe electronic spectroscopy is a powerful technique able to provide both high spectral and temporal resolution, allowing the analysis of ultrafast complex reactions occurring via complementary pathways by the identification of decay-specific fingerprints. [1-2] The understanding of the origin of the experimentally recorded signals in a two-dimensional electronic spectrum requires the characterization of the electronic states involved in the electronic transitions photoinduced by the pump/probe pulses in the experiment. Such a goal constitutes a considerable computational challenge, since up to 100 states need to be described, for which state-of-the-art methods as RASSCF and RASPT2 have to be wisely employed. [3] With the present contribution, the main features and potentialities of two-dimensional electronic spectroscopy are presented, together with the machinery in continuous development in our groups in order to compute two-dimensional electronic spectra. The results obtained using different level of theory and simulations are shown, bringing as examples the computed two-dimensional electronic spectra for some specific cases studied. [2-4] [1] Rivalta I, Nenov A, Cerullo G, Mukamel S, Garavelli M, Int. J. Quantum Chem., 2014, 114, 85 [2] Nenov A, Segarra-Martí J, Giussani A, Conti I, Rivalta I, Dumont E, Jaiswal V K, Altavilla S, Mukamel S, Garavelli M, Faraday Discuss. 2015, DOI: 10.1039/C4FD00175C [3] Nenov A, Giussani A, Segarra-Martí J, Jaiswal V K, Rivalta I, Cerullo G, Mukamel S, Garavelli M, J. Chem. Phys. submitted [4] Nenov A, Giussani A, Fingerhut B P, Rivalta I, Dumont E, Mukamel S, Garavelli M, Phys. Chem. Chem. Phys. Submitted [5] Krebs N, Pugliesi I, Hauer J, Riedle E, New J. Phys., 2013,15, 08501
NASA Astrophysics Data System (ADS)
Lin, Ji; Huang, Guang-Qiao; Chen, Wei-Xiong
2015-07-01
The algebraic mapping relations between the (2+1)-dimensional double sine-Gordon equation and the cubic nonlinear Klein-Gordon equation are constructed. Many new types of two-dimensional resonant kink, bright soliton and solitoff solutions are obtained, such as broken line shape, V shape, snake shape and M shape solitary waves, Zigzag-curve type, ? shape, peroidic-curve type, oscillatory Arch-type and parabolic shape bright soliton waves. We also investigate the propagating properties of some soliton solutions. Supported by the Natural Science Foundation of Zhejiang Province under Grant No. LZ15A050001 and the National Natural Science Foundation of China under Grant No. 11175158
Technology Transfer Automated Retrieval System (TEKTRAN)
The accepted method for comparing bacterial proteomes has traditionally been two-dimensional (2D) gel electrophoresis. However, in recent years, new procedures for protein separation have been introduced. One of these new procedures utilizes column-based liquid chromatography separation. The tech...
Variational calculations for anisotropic solitons in dipolar Bose-Einstein condensates
Eichler, Ruediger; Main, Joerg; Wunner, Guenter
2011-05-15
We present variational calculations using a Gaussian trial function to calculate the ground state of the Gross-Pitaevskii equation (GPE) and to describe the dynamics of the quasi-two-dimensional solitons in dipolar Bose-Einstein condensates (BECs). Furthermore, we extend the ansatz to a linear superposition of Gaussians, improving the results for the ground state to exact agreement with numerical grid calculations using imaginary time and the split-operator method. We are able to give boundaries for the scattering length at which stable solitons may be observed in an experiment. By dynamic calculations with coupled Gaussians, we are able to describe the rather complex behavior of the thermally excited solitons. The discovery of dynamically stabilized solitons indicates the existence of such BECs at experimentally accessible temperatures.
Variational calculations for anisotropic solitons in dipolar Bose-Einstein condensates
NASA Astrophysics Data System (ADS)
Eichler, Rdiger; Main, Jrg; Wunner, Gnter
2011-05-01
We present variational calculations using a Gaussian trial function to calculate the ground state of the Gross-Pitaevskii equation (GPE) and to describe the dynamics of the quasi-two-dimensional solitons in dipolar Bose-Einstein condensates (BECs). Furthermore, we extend the ansatz to a linear superposition of Gaussians, improving the results for the ground state to exact agreement with numerical grid calculations using imaginary time and the split-operator method. We are able to give boundaries for the scattering length at which stable solitons may be observed in an experiment. By dynamic calculations with coupled Gaussians, we are able to describe the rather complex behavior of the thermally excited solitons. The discovery of dynamically stabilized solitons indicates the existence of such BECs at experimentally accessible temperatures.
Two-dimensional particle-in-cell simulation of the expansion of a plasma into a rarefied medium
NASA Astrophysics Data System (ADS)
Sarri, G.; Murphy, G. C.; Dieckmann, M. E.; Bret, A.; Quinn, K.; Kourakis, I.; Borghesi, M.; Drury, L. O. C.; Ynnerman, A.
2011-07-01
The expansion of a dense plasma through a more rarefied ionized medium has been studied by means of two-dimensional particle-in-cell simulations. The initial conditions involve a density jump by a factor of 100, located in the middle of an otherwise equally dense electron-proton plasma with uniform proton and electron temperatures of 10 eV and 1 keV, respectively. Simulations show the creation of a purely electrostatic collisionless shock together with an ion-acoustic soliton tied to its downstream region. The shock front is seen to evolve in filamentary structures consistently with the onset of the ion-ion instability. Meanwhile, an un-magnetized drift instability is triggered in the core part of the dense plasma. Such results explain recent experimental laser-plasma experiments, carried out in similar conditions, and are of intrinsic relevance to non-relativistic shock scenarios in the solar and astrophysical systems.
Noncommuting Momenta of Topological Solitons
NASA Astrophysics Data System (ADS)
Watanabe, Haruki; Murayama, Hitoshi
2014-05-01
We show that momentum operators of a topological soliton may not commute among themselves when the soliton is associated with the second cohomology H2 of the target space. The commutation relation is proportional to the winding number, taking a constant value within each topological sector. The noncommutativity makes it impossible to specify the momentum of a topological soliton, and induces a Magnus force.
NASA Astrophysics Data System (ADS)
Adam, C.; Haberichter, M.; Wereszczynski, A.
2016-03-01
There exists, in general, no unique definition of the size (volume, area, etc., depending on dimension) of a soliton. Here we demonstrate that the geometric volume (area etc.) of a soliton is singled out in the sense that it exactly coincides with the thermodynamical or continuum-mechanical volume. In addition, this volume may be defined uniquely for rather arbitrary solitons in arbitrary dimensions.
Two-dimensional Simulations of Correlation Reflectometry in Fusion Plasmas
E.J. Valeo; G.J. Kramer; R. Nazikian
2001-07-05
A two-dimensional wave propagation code, developed specifically to simulate correlation reflectometry in large-scale fusion plasmas is described. The code makes use of separate computational methods in the vacuum, underdense and reflection regions of the plasma in order to obtain the high computational efficiency necessary for correlation analysis. Simulations of Tokamak Fusion Test Reactor (TFTR) plasma with internal transport barriers are presented and compared with one-dimensional full-wave simulations. It is shown that the two-dimensional simulations are remarkably similar to the results of the one-dimensional full-wave analysis for a wide range of turbulent correlation lengths. Implications for the interpretation of correlation reflectometer measurements in fusion plasma are discussed.
On comparing helioseismic two-dimensional inversion methods
NASA Technical Reports Server (NTRS)
Schou, J.; Christensen-Dalsgaard, J.; Thompson, M. J.
1994-01-01
We consider inversion techniques for investigating the structure and dynamics of the solar interior as functions of radius and latitude. In particular, we look at the problem of inferring the radial and latitudinal dependence of the Sun's internal rotation, using a fully two-dimensional least-squares inversion algorithm. Concepts such as averaging kernels, measures of resolution, and trade-off curves, which have previously been used in the one-dimensional case, are generalized to facilitate a comparison of two-dimensional methods. We investigate the weighting given to different modes and discuss the implications of this for observational strategies. As an illustration we use a mode set whose properties are similar to those expected for data from the GONG network.
Vortex annihilation and inverse cascades in two dimensional superfluid turbulence
NASA Astrophysics Data System (ADS)
Lucas, Andrew; Chesler, Paul M.
2015-03-01
The dynamics of a dilute mixture of vortices and antivortices in a turbulent two-dimensional superfluid at finite temperature is well described by first order Hall-Vinen-Iordanskii equations, or dissipative point vortex dynamics. These equations are governed by a single dimensionless parameter: the ratio of the strength of drag forces to Magnus forces on vortices. When this parameter is small, we demonstrate using numerical simulations that the resulting superfluid enjoys an inverse energy cascade where small scale stirring leads to large scale vortex clustering. We argue analytically and numerically that the vortex annihilation rate in a laminar flow may be parametrically smaller than the rate in a turbulent flow with an inverse cascade. This suggests a new way to detect inverse cascades in experiments on two-dimensional superfluid turbulence using cold atomic gases, where traditional probes of turbulence such as the energy spectrum are not currently accessible.
Object tracking based on two-dimensional PCA
NASA Astrophysics Data System (ADS)
Xu, Fuyuan; Gu, Guohua; Kong, Xiaofang; Wang, Pengcheng; Ren, Kan
2016-01-01
In this paper, we present a novel object tracking method based on two-dimensional PCA. The low quality of images and the changes of the object appearance are very challenging for the object tracking. The representation of the training features is usually used to solve these challenges. Two-dimensional PCA (2DPCA) based on the image covariance matrix is constructed directly using the original image matrices. An appearance model is presented and its likelihood estimation has been established based on 2DPCA representation in this paper. Compared with the state-of-the-art methods, our method has higher reliability and real-time property. The performances of the proposed tracking method are quantitatively and qualitatively shown in experiments.
On two-dimensional flows of compressible fluids
NASA Technical Reports Server (NTRS)
Bergman, Stefan
1945-01-01
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.
Two-dimensional electronic spectroscopy of an excitonically coupled dimer
NASA Astrophysics Data System (ADS)
Kjellberg, Pr; Brggemann, Ben; Pullerits, Tnu
2006-07-01
The two-dimensional three-pulse photon echo signals from a dimer system are investigated in detail. A perturbative approach is used to calculate the response of the system via a numerical propagation of the density matrix in exciton state representation. Exciton vibrational coupling is modeled by Redfield relaxation theory. The main goal of this paper is to dissect the two-dimensional spectrum of the dimer to give better understanding of how the dynamics influence the spectral features. We will show how different Liouville pathways lead to the appearance/disappearance of diagonal and cross peaks. The inclusion of a Gaussian shaped electric field will be contrasted to the use of delta-pulses in the impulsive limit. The impulsive limit is found to be a satisfactory approximation at long population times, while at shorter times, in the pulse-overlap region, more realistic electric fields are called for.
Evaluation of non-separable two-dimensional
NASA Astrophysics Data System (ADS)
Lopez, Vicente; Uzer, T.
In the treatment of reactive collisions by approximate methods such as the Distorted Wave Born Approximation, two-dimensional non-separable integrals are frequently encountered. In this article, we introduce the use of a two-dimensional canonical integral, the hyperbolic umbilic canonical diffraction function, on a model problem which leads to non-separable twodimensional Franck-Condon integrals. The identification of the parameters of the canonical function in terms of the physical parameters of the model is immediate in this case, and we find that the use of this function reproduces numerical quadrature results accurately with substantial savings in computing time. Extensions of the procedure to more general problems, anticipated by Child and Shapiro, are also discussed.
Preliminary results on two-dimensional interferometry of HL Tau
NASA Astrophysics Data System (ADS)
Tollestrup, Eric V.; Harvey, Paul M.
1989-10-01
Preliminary two-dimensional speckle interferometry results of HL Tau were found to be qualitatively similar to those found with one-dimensional slit scanning techniques; results consist of a resolved component (approximately 0.7 arcsec in size) and an unresolved component. Researchers are currently reducing the rest of the data (taken on three different telescopes and at three different wavelengths) and are also exploring other high resolution methods like the shift and add technique and selecting only the very best images for processing. The availability of even better two-dimensional arrays within the next couple of years promises to make speckle interferometry and other high resolution techniques very powerful and exiting tools for probing a variety of objects in the subarcsec regime.
Preliminary results on two-dimensional interferometry of HL Tau
NASA Technical Reports Server (NTRS)
Tollestrup, Eric V.; Harvey, Paul M.
1989-01-01
Preliminary two-dimensional speckle interferometry results of HL Tau were found to be qualitatively similar to those found with one-dimensional slit scanning techniques; results consist of a resolved component (approximately 0.7 arcsec in size) and an unresolved component. Researchers are currently reducing the rest of the data (taken on three different telescopes and at three different wavelengths) and are also exploring other high resolution methods like the shift and add technique and selecting only the very best images for processing. The availability of even better two-dimensional arrays within the next couple of years promises to make speckle interferometry and other high resolution techniques very powerful and exiting tools for probing a variety of objects in the subarcsec regime.
Unshielded fetal magnetocardiography system using two-dimensional gradiometers
NASA Astrophysics Data System (ADS)
Seki, Yusuke; Kandori, Akihiko; Kumagai, Yukio; Ohnuma, Mitsuru; Ishiyama, Akihiko; Ishii, Tetsuko; Nakamura, Yoshiyuki; Horigome, Hitoshi; Chiba, Toshio
2008-03-01
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.
Some applications of two-dimensional stress transfer analyses
Hsueh, C.H.
1998-03-23
Two-dimensional stress transfer analyses are performed for the following system: a long central plate bonded on opposite sides along its length to two short plates and subjected to tensile loading at its ends. The load transfers from the long plate to the short plate through the interfacial shear stress. The system represents the unit cell of platelet-reinforced composites, in which parallel matrix cracks are uniformly spaced and are bridged by the platelet, in a two-dimensional sense. Analytical solutions for the crack opening displacement, the additional displacement of the composite due to the presence of cracks, and stress intensity factor at the crack tip are derived. Letting the long plate and the short plates have the same mechanical properties, the analytical solutions are compared to the existing numerical solutions for tensile loading of both a double edge notch strip and a semi-infinite plane with parallel edge cracks.
Two dimensional time dependent Riemann solvers for neutron transport.
Brunner, Thomas A.; Holloway, James Paul
2004-12-01
A two-dimensional Riemann solver is developed for the spherical harmonics approximation to the time dependent neutron transport equation. The eigenstructure of the resulting equations is explored, giving insight into both the spherical harmonics approximation and the Riemann solver. The classic Roe-type Riemann solver used here was developed for one-dimensional problems, but can be used in multidimensional problems by treating each face of a two-dimensional computation cell in a locally one-dimensional way. Several test problems are used to explore the capabilities of both the Riemann solver and the spherical harmonics approximation. The numerical solution for a simple line source problem is compared to the analytic solution to both the P1 equation and the full transport solution. A lattice problem is used to test the method on a more challenging problem.
Two-dimensional time dependent Riemann solvers for neutron transport
Brunner, Thomas A. . E-mail: tabrunn@sandia.gov; Holloway, James Paul
2005-11-20
A two-dimensional Riemann solver is developed for the spherical harmonics approximation to the time dependent neutron transport equation. The eigenstructure of the resulting equations is explored, giving insight into both the spherical harmonics approximation and the Riemann solver. The classic Roe-type Riemann solver used here was developed for one-dimensional problems, but can be used in multidimensional problems by treating each face of a two-dimensional computation cell in a locally one-dimensional way. Several test problems are used to explore the capabilities of both the Riemann solver and the spherical harmonics approximation. The numerical solution for a simple line source problem is compared to the analytic solution to both the P{sub 1} equation and the full transport solution. A lattice problem is used to test the method on a more challenging problem.
A two-dimensional dam-break flood plain model
Hromadka, T.V., II; Berenbrock, C.E.; Freckleton, J.R.; Guymon, G.L.
1985-01-01
A simple two-dimensional dam-break model is developed for flood plain study purposes. Both a finite difference grid and an irregular triangle element integrated finite difference formulation are presented. The governing flow equations are approximately solved as a diffusion model coupled to the equation of continuity. Application of the model to a hypothetical dam-break study indicates that the approach can be used to predict a two-dimensional dam-break flood plain over a broad, flat plain more accurately than a one-dimensional model, especially when the flow can break-out of the main channel and then return to the channel at other downstream reaches. ?? 1985.
Ultrabroadband femtosecond two-dimensional ultraviolet transient absorption.
Aubck, Gerald; Consani, Cristina; van Mourik, Frank; Chergui, Majed
2012-06-15
We present a broadband two-dimensional transient absorption setup for the UV around 300 nm with a time resolution of 150 fs. A narrowband, frequency tunable pump pulse and a broadband probe pulse are generated from the output of a noncollinear optical parametric amplifier operated at 20 kHz repetition rate and combined in a spectrally resolved transient absorption experiment. The high repetition rate and low noise of the setup allow us to acquire high quality two-dimensional data as a function of time delay with an unsurpassed frequency window of 10,000 and 8000??cm(-1) along the probe and pump axis, respectively. The performance of the setup is demonstrated on 2,5-Diphenyloxazol dissolved in cyclohexane. PMID:22739900
Numerical analysis of a two-dimensional nonsteady detonations
NASA Technical Reports Server (NTRS)
Taki, S.; Fujiwara, T.
1976-01-01
In the present work a system of two-dimensional nonsteady hydrodynamic and chemical kinetic equations was numerically integrated for an exothermic system. Assumed two-step reaction model simulates practically an oxyhydrogen mixture. The calculation starts from a plane Chapman-Jouguet detonation as an initial condition. Two-dimensional disturbances are generated by artificially placing nonuniformities ahead of the detonation front. Regardless of the difference of the given initial disturbances, a fixed number of triple shock waves were produced for a fixed combination of mixture model and geometry when the transition period was over. This shows that for a given detonation tube geometry any exothermic system has its own characteristic multidimensional structure. The obtained number of triple shock waves contained in the detonation front was in agreement with existing experimental observations under the same condition.
Two-Dimensional Computational Model for Wave Rotor Flow Dynamics
NASA Technical Reports Server (NTRS)
Welch, Gerard E.
1996-01-01
A two-dimensional (theta,z) Navier-Stokes solver for multi-port wave rotor flow simulation is described. The finite-volume form of the unsteady thin-layer Navier-Stokes equations are integrated in time on multi-block grids that represent the stationary inlet and outlet ports and the moving rotor passages of the wave rotor. Computed results are compared with three-port wave rotor experimental data. The model is applied to predict the performance of a planned four-port wave rotor experiment. Two-dimensional flow features that reduce machine performance and influence rotor blade and duct wall thermal loads are identified. The performance impact of rounding the inlet port wall, to inhibit separation during passage gradual opening, is assessed.
Asymmetrical two-dimensional magnetic lattices for ultracold atoms
Abdelrahman, A.; Vasiliev, M.; Alameh, K.; Hannaford, P.
2010-07-15
A simple method for implementing an asymmetrical two-dimensional magnetic lattice is proposed. The asymmetrical two-dimensional magnetic lattice is created by periodically distributing nonzero magnetic minima across the surface of a magnetic thin film, where the magnetic patterns are formed by milling nxn square holes on the surface of the film. The method is proposed for trapping and confining quantum degenerate gases, such as Bose-Einstein condensates and ultracold Fermi gases, prepared in low-magnetic-field-seeking states. Analytical expressions and numerical simulation results of the magnetic local minima are shown where we analyze the effect of changing the magnetic lattice parameters, such as the separation of the holes, the hole size, and external bias magnetic fields, to maintain and locate the nonzero local minima at a suitable distance above the film surface to avoid the effect of Majorana spin flips and the Casimir-Polder potential.
Two-dimensional Raman-terahertz spectroscopy of water
Savolainen, Janne; Ahmed, Saima; Hamm, Peter
2013-01-01
Two-dimensional Raman-terahertz (THz) spectroscopy is presented as a multidimensional spectroscopy directly in the far-IR regime. The method is used to explore the dynamics of the collective intermolecular modes of liquid water at ambient temperatures that emerge from the hydrogen-bond networks water forming. Two-dimensional Raman-THz spectroscopy interrogates these modes twice and as such can elucidate couplings and inhomogeneities of the various degrees of freedoms. An echo in the 2D Raman-THz response is indeed identified, indicating that a heterogeneous distribution of hydrogen-bond networks exists, albeit only on a very short 100-fs timescale. This timescale appears to be too short to be compatible with more extended, persistent structures assumed within a two-state model of water. PMID:24297930
Two-dimensional Fibonacci spiral optical thermal ratchets
NASA Astrophysics Data System (ADS)
Xiao, Ke; Grier, David
2011-03-01
A novel two-dimensional optical thermal ratchet has been implemented with holographic optical trapping arrays structured as the ``Fibonacci spiral'' for diffusing colloidal particles. Periodically rotating the optical trapping array by an angle in a three-step cycle yields a two-dimensional time-varying optical landscape that acts either as (1) a deterministic pump when traps are closely dispersed in space, whose induced radial and azimuthal fluxes can be quantitatively mapped out according to the geometry of Fibonacci spiral, or else as (2) an optical thermal ratchet when traps are widely dispersed, whose transport property depends on the competition between the temporal evolution in optical landscapes and Brownian particles' diffusivity. The Fibonacci ratchet displays independent flux reversals in both the radial and azimuthal directions as a function of the cycle frequency and the inter-trap separation.
The stability of a two-dimensional rising bubble
Nie, Q.; Tanveer, S.
1995-06-01
The stability of an inviscid two-dimensional bubble subject to two-dimensional disturbances is considered and the bubbles are found to be linearly stable for all Weber numbers, for which a steady solution is known. Certain aspects of the nonlinear initial value problem are also studied. An initial condition that consists of a superposition of a suitable symmetric eigenmode (of the linear stability operator) on a steady state is found to result in pinching of the bubble neck as it tends to oscillate about the steady state. An estimate of the threshold amplitude of such a disturbance needed to cause breakup of a large aspect ratio bubble is obtained. The presence of gravity appears to inhibit this pinching process.
Boron nitride as two dimensional dielectric: Reliability and dielectric breakdown
NASA Astrophysics Data System (ADS)
Ji, Yanfeng; Pan, Chengbin; Zhang, Meiyun; Long, Shibing; Lian, Xiaojuan; Miao, Feng; Hui, Fei; Shi, Yuanyuan; Larcher, Luca; Wu, Ernest; Lanza, Mario
2016-01-01
Boron Nitride (BN) is a two dimensional insulator with excellent chemical, thermal, mechanical, and optical properties, which make it especially attractive for logic device applications. Nevertheless, its insulating properties and reliability as a dielectric material have never been analyzed in-depth. Here, we present the first thorough characterization of BN as dielectric film using nanoscale and device level experiments complementing with theoretical study. Our results reveal that BN is extremely stable against voltage stress, and it does not show the reliability problems related to conventional dielectrics like HfO2, such as charge trapping and detrapping, stress induced leakage current, and untimely dielectric breakdown. Moreover, we observe a unique layer-by-layer dielectric breakdown, both at the nanoscale and device level. These findings may be of interest for many materials scientists and could open a new pathway towards two dimensional logic device applications.
Transport behavior of water molecules through two-dimensional nanopores
Zhu, Chongqin; Li, Hui; Meng, Sheng
2014-11-14
Water transport through a two-dimensional nanoporous membrane has attracted increasing attention in recent years thanks to great demands in water purification and desalination applications. However, few studies have been reported on the microscopic mechanisms of water transport through structured nanopores, especially at the atomistic scale. Here we investigate the microstructure of water flow through two-dimensional model graphene membrane containing a variety of nanopores of different size by using molecular dynamics simulations. Our results clearly indicate that the continuum flow transits to discrete molecular flow patterns with decreasing pore sizes. While for pores with a diameter ≥15 Å water flux exhibits a linear dependence on the pore area, a nonlinear relationship between water flux and pore area has been identified for smaller pores. We attribute this deviation from linear behavior to the presence of discrete water flow, which is strongly influenced by the water-membrane interaction and hydrogen bonding between water molecules.
Self-propelled two dimensional polymer multilayer plate micromotors.
Gai, Meiyu; Frueh, Johannes; Hu, Narisu; Si, Tieyan; Sukhorukov, Gleb B; He, Qiang
2016-02-01
This communication sheds light on the production method and motion patterns of autonomous moving bubble propelled two dimensional micro-plate motors. The plate motors are produced by the well-known layer-by-layer self-assembly process in combination with micro-contact printing. The motion analysis covers instances of oscillating bubble development on one or more nucleation sites, which influence the motion speed and direction. PMID:26780851
Spirals and Skyrmions in two dimensional oxide heterostructures.
Li, Xiaopeng; Liu, W Vincent; Balents, Leon
2014-02-14
We construct the general free energy governing long-wavelength magnetism in two dimensional oxide heterostructures, which applies irrespective of the microscopic mechanism for magnetism. This leads, in the relevant regime of weak but non-negligible spin-orbit coupling, to a rich phase diagram containing in-plane ferromagnetic, spiral, cone, and Skyrmion lattice phases, as well as a nematic state stabilized by thermal fluctuations. PMID:24580706
Two-dimensional correlation spectroscopy in polymer study
Park, Yeonju; Noda, Isao; Jung, Young Mee
2015-01-01
This review outlines the recent works of two-dimensional correlation spectroscopy (2DCOS) in polymer study. 2DCOS is a powerful technique applicable to the in-depth analysis of various spectral data of polymers obtained under some type of perturbation. The powerful utility of 2DCOS combined with various analytical techniques in polymer studies and noteworthy developments of 2DCOS used in this field are also highlighted. PMID:25815286
Exact analytic flux distributions for two-dimensional solar concentrators.
Fraidenraich, Naum; Henrique de Oliveira Pedrosa Filho, Manoel; Vilela, Olga C; Gordon, Jeffrey M
2013-07-01
A new approach for representing and evaluating the flux density distribution on the absorbers of two-dimensional imaging solar concentrators is presented. The formalism accommodates any realistic solar radiance and concentrator optical error distribution. The solutions obviate the need for raytracing, and are physically transparent. Examples illustrating the method's versatility are presented for parabolic trough mirrors with both planar and tubular absorbers, Fresnel reflectors with tubular absorbers, and V-trough mirrors with planar absorbers. PMID:23842256
In vivo two-dimensional NMR correlation spectroscopy
NASA Astrophysics Data System (ADS)
Kraft, Robert A.
1999-10-01
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.)
Microwave response of a two-dimensional electron stripe
NASA Astrophysics Data System (ADS)
Mikhailov, S. A.; Savostianova, N. A.
2005-01-01
Electromagnetic response of a finite-width two-dimensional electron stripe is theoretically studied. It is shown that retardation and radiative effects substantially modify the absorption spectrum of the system at microwave frequencies, leading to a nontrivial zigzag behavior of the magnetoplasmon-polariton modes in magnetic fields, similar to that recently observed by
Thermodynamic Studies of Two-Dimensional Correlated Electron Systems
NASA Astrophysics Data System (ADS)
Pudalov, V. M.; Kuntsevich, A. Yu.; Burmistrov, I. S.; Reznikov, M.
2015-11-01
This paper describes recent developments in experimental techniques for thermodynamic measurements. Particularly, we focus on the derivatives of the chemical potential with respect to magnetic field and temperature. The former enables to determine the spin magnetization per electron and the latter the entropy per electron. We briefly describe recent results obtained with these techniques and their impact on the current understanding of the still challenging problem of the ground state(s) of strongly correlated two-dimensional electron systems.
Two-dimensional heat conducting simulation of plasma armatures
Huerta, M.A.; Boynton, G. . Dept. of Physics)
1991-01-01
This paper reports on our development of a two-dimensional MHD code to simulate internal motions in a railgun plasma armature. The authors use the equations of resistive MHD, with Ohmic heating, and radiation heat transport. The authors use a Flux Corrected Transport code to advance all quantities in time. Our runs show the development of complex flows, subsequent shedding of secondary arcs, and a drop in the acceleration of the armature.
Scaling relations in two-dimensional relativistic hydrodynamic turbulence
NASA Astrophysics Data System (ADS)
Westernacher-Schneider, John Ryan; Lehner, Luis; Oz, Yaron
2015-12-01
We derive exact scaling relations for two-dimensional relativistic hydrodynamic turbulence in the inertial range of scales. We consider both the energy cascade towards large scales and the enstrophy cascade towards small scales. We illustrate these relations by numerical simulations of turbulent weakly compressible flows. Intriguingly, the fluid-gravity correspondence implies that the gravitational field in black hole/black brane spacetimes with anti-de Sitter asymptotics should exhibit similar scaling relations.
Lekner summation for two-dimensional magnetic dipolar interaction energy
NASA Astrophysics Data System (ADS)
Tang, Ke; Zhang, Huaiwu; Zhong, Zhiyong
2006-02-01
The Lekner method for calculation of dipolar interaction energy in periodically replicated simulation cells is extended to two-dimensional array systems of nanoparticles with point dipoles. The dipolar interaction energy is expressed by rapidly converging series of modified Bessel functions. We emphasize that the self-energy must be included in simulations of the 2D dipolar coupling systems and derive two simple formulas to evaluate the self-energy.
Dirac Points in Two-Dimensional Inverse Opals
NASA Astrophysics Data System (ADS)
Mahan, G. D.
2013-10-01
The electron energy states and energy bands are calculated for a two-dimensional inverse opal structure. Assume that the opal structure is closed-packed circles, the inverse opal has the honeycomb lattice. The honeycomb lattice in two dimensions has a Dirac point. Its properties can be manipulated by altering the structure of the inverse opal: the radius of the circle, and the small gap between circles.
Two-dimensional color-code quantum computation
Fowler, Austin G.
2011-04-15
We describe in detail how to perform universal fault-tolerant quantum computation on a two-dimensional color code, making use of only nearest neighbor interactions. Three defects (holes) in the code are used to represent logical qubits. Triple-defect logical qubits are deformed into isolated triangular sections of color code to enable transversal implementation of all single logical qubit Clifford group gates. Controlled-NOT (CNOT) is implemented between pairs of triple-defect logical qubits via braiding.