Landau Diamagnetism: A Simple Calculation.
ERIC Educational Resources Information Center
Dupre, A.
1981-01-01
Starting from the energy and degeneracy of the Landau levels of a free-electron gas in a magnetic field, the nonoscillatory term of the Landau diamagnetism is derived for T=O, using elementary algebra only. (Author/JN)
Decoherence and Landau-Damping
Ng, K.Y.; /Fermilab
2005-12-01
The terminologies, decoherence and Landau damping, are often used concerning the damping of a collective instability. This article revisits the difference and relation between decoherence and Landau damping. A model is given to demonstrate how Landau damping affects the rate of damping coming from decoherence.
NASA Astrophysics Data System (ADS)
Habl, Matthias
2007-03-01
In the presence of a perpendicular magnetic field, the quasi-free charge carriers of a two-dimensional electron system condense in equidistant and numerously degenerated Landau levels. Variations of the electrostatic potential locally lift the degeneracy and, therefore, cause the formation of Landau bands. A complex Landau band structure exists in the scope of a tunneling barrier which separates two laterally adjacent electron systems. In the case of weak coupling, the band structure may be described approximately as a superposition of the mirror-inverted dispersions of both subsystems with Landau band gaps lifting the degeneracy at the crossing points. The tunneling current through the barrier becomes maximum when the Fermi level coincides with one of the anticrossings. The first part of this thesis presents a method for calculating the Landau band structure of a quantum Hall system with an unidirectional and piecewise constant potential modulation. In the second part, the knowledge of the energy eigenstates is the prerequisite for the analysis of the magnetic field dependent conductance traces of two laterally coupled electron systems. In the scope of the effective mass approximation, the Schrödinger equation is solved for a 2D-electron which resides both in the parabolic magnetic confinement potential and the piecewise constant conduction band offset of an intrinsic semiconductor heterostructure. The exact solution is possible by using an ansatz with parabolic cylinder functions. After discussing the generic properties of the energy spectrum and the corresponding wave functions, a dedicated algorithm for solving the continuity conditions at the heterojunctions is presented for a system consisting of three domains of constant potential. The numerical method yields the Landau band structure in the scope of a tunneling barrier (biased or not) or a rectangular potential well (quantum wire). Generally, the algorithm is applicable for any harmonic oscillator which is
NASA Technical Reports Server (NTRS)
Aragone, C.
1993-01-01
We introduce a new set of squeezed states through the coupled two-mode squeezed operator. It is shown that their behavior is simpler than the correlated coherent states introduced by Dodonov, Kurmyshev, and Man'ko in order to quantum mechanically describe the Landau system, i.e., a planar charged particle in a uniform magnetic field. We compare results for both sets of squeezed states.
Wittig, Curt
2005-05-05
The Landau-Zener formula for the probability that a nonadiabatic transition has taken place is derived without solving directly the usual second-order differential equation. This is achieved in just a few steps by using contour integration.
Landau's Nobel Prize in Physics
NASA Astrophysics Data System (ADS)
Larsson, M.; Balatsky, A. V.
2016-06-01
Work of Lev Landau had a profound impact on the physics in 20th century. Landau had created the paradigms that had framed the conversations on the outstanding problems in physics for decades. He had laid foundations for our understanding of quantum matter like superfluidity, superconductivity and the theory of Fermi liquid. Here we present some Nobel Archive data on the winning nomination that led to the Nobel Prize in Physics in 1962.
Landau damping of auroral hiss
NASA Technical Reports Server (NTRS)
Morgan, D. D.; Gurnett, D. A.; Menietti, J. D.; Winningham, J. D.; Burch, J. L.
1994-01-01
Auroral hiss is observed to propagate over distances comparable to an Earth radius from its source in the auroral oval. The role of Landau damping is investigated for upward propagating auroral hiss. By using a ray tracing code and a simplified model of the distribution function, the effect of Landau damping is calculated for auroral hiss propagation through the environment around the auroral oval. Landau damping is found to be the likely mechanism for explaining some of the one-sided auroral hiss funnels observed by Dynamics Explorer 1. It is also found that Landau damping puts a lower limit on the wavelength of auroral hiss. Poleward of the auroral oval, Landau damping is found in a typical case to limit omega/k(sub parallel) to values of 3.4 x 10(exp 4) km/s or greater, corresponding to resonance energies of 3.2 keV or greater and wavelengths of 2 km or greater. For equatorward propagation, omega/k(sub parallel) is limited to values greater than 6.8 x 10(exp 4) km/s, corresponding to resonance energies greater than 13 keV and wavelengths greater than 3 km. Independent estimates based on measured ratios of the magnetic to electric field intensity also show that omega/k(sub parallel) corresponds to resonance energies greater than 1 keV and wavelengths greater than 1 km. These results lead to the difficulty that upgoing electron beams sufficiently energetic to directly generate auroral hiss of the inferred wavelength are not usually observed. A partial transmission mechanism utilizing density discontinuities oblique to the magnetic field is proposed for converting auroral hiss to wavelengths long enough to avoid damping of the wave over long distances. Numerous reflections of the wave in an upwardly flared density cavity could convert waves to significantly increased wavelengths and resonance velocities.
Landau Theory of Helical Fermi Liquids.
Lundgren, Rex; Maciejko, Joseph
2015-08-07
We construct a phenomenological Landau theory for the two-dimensional helical Fermi liquid found on the surface of a three-dimensional time-reversal invariant topological insulator. In the presence of rotation symmetry, interactions between quasiparticles are described by ten independent Landau parameters per angular momentum channel, by contrast with the two (symmetric and antisymmetric) Landau parameters for a conventional spin-degenerate Fermi liquid. We project quasiparticle states onto the Fermi surface and obtain an effectively spinless, projected Landau theory with a single projected Landau parameter per angular momentum channel that captures the spin-momentum locking or nontrivial Berry phase of the Fermi surface. As a result of this nontrivial Berry phase, projection to the Fermi surface can increase or lower the angular momentum of the quasiparticle interactions. We derive equilibrium properties, criteria for Fermi surface instabilities, and collective mode dispersions in terms of the projected Landau parameters. We briefly discuss experimental means of measuring projected Landau parameters.
Hydrodynamics from Landau initial conditions
Sen, Abhisek; Gerhard, Jochen; Torrieri, Giorgio; Read jr, Kenneth F.; Wong, Cheuk-Yin
2015-01-01
We investigate ideal hydrodynamic evolution, with Landau initial conditions, both in a semi-analytical 1+1D approach and in a numerical code incorporating event-by-event variation with many events and transverse density inhomogeneities. The object of the calculation is to test how fast would a Landau initial condition transition to a commonly used boost-invariant expansion. We show that the transition to boost-invariant flow occurs too late for realistic setups, with corrections of O (20 - 30%) expected at freezeout for most scenarios. Moreover, the deviation from boost-invariance is correlated with both transverse flow and elliptic flow, with the more highly transversely flowing regions also showing the most violation of boost invariance. Therefore, if longitudinal flow is not fully developed at the early stages of heavy ion collisions, 2+1 dimensional hydrodynamics is inadequate to extract transport coefficients of the quark-gluon plasma. Based on [1, 2
Landau damping in space plasmas
NASA Technical Reports Server (NTRS)
Thorne, Richard M.; Summers, Danny
1991-01-01
The Landau damping of electrostatic Langmuir waves and ion-acoustic waves in a hot, isotropic, nonmagnetized, generalized Lorentzian plasma is analyzed using the modified plasma dispersion function. Numerical solutions for the real and imaginary parts of the wave frequency omega sub 0 - (i)(gamma) have been obtained as a function of the normalized wave number (k)(lambda sub D), where lambda sub D is the electron Debye length. For both particle distributions the electrostatic modes are found to be strongly damped at short wavelengths. At long wavelengths, this damping becomes less severe, but the attenuation of Langmuir waves is much stronger for a generalized Lorentzian plasma than for a Maxwellian plasma. It is concluded that Landau damping of ion-acoustic waves is only slightly affected by the presence of a high energy tail, but is strongly dependent on the ion temperature.
Geometric Landau-Zener interferometry.
Gasparinetti, S; Solinas, P; Pekola, J P
2011-11-11
We propose a new type of interferometry, based on geometric phases accumulated by a periodically driven two-level system undergoing multiple Landau-Zener transitions. As a specific example, we study its implementation in a superconducting charge pump. We find that interference patterns appear as a function of the pumping frequency and the phase bias, and clearly manifest themselves in the pumped charge. We also show that the effects described should persist in the presence of realistic decoherence.
NASA Astrophysics Data System (ADS)
Laohakunakorn, Nadanai; Gollnick, Benjamin; Moreno-Herrero, Fernando; Aarts, Dirk G. A. L.; Dullens, Roel P. A.; Ghosal, Sandip; Keyser, Ulrich F.
2013-11-01
Fluid jets are found in nature at all length scales, from microscopic to cosmological. Here we report on an electroosmotically driven jet from a single glass nanopore about 75 nm in radius with a maximum flow rate ~15 pL/s. A novel anemometry technique allows us to map out the vorticity and velocity fields that show excellent agreement with the classical Landau-Squire solution of the Navier Stokes equations for a point jet. We observe a phenomenon that we call flow rectification: an asymmetry in the flow rate with respect to voltage reversal. Such a nanojet could potentially find applications in micromanipulation, nanopatterning, and as a diode in microfluidic circuits.
KGB's control of Landau and Sakharov
NASA Astrophysics Data System (ADS)
Krivonosov, Yurii I.
1992-08-01
The paper concerns the control by KGB of the personal life and job relations of two of the greatest Soviet physicists Lev Davydovich Landau and Andrei Dmitrievich Sakharov. A part of the paper is regarding the will of Landau to emmigrate from the U.S.S.R.
Photonic Landau levels on cones
NASA Astrophysics Data System (ADS)
Schine, Nathan; Ryou, Albert; Gromov, Andrey; Sommer, Ariel; Simon, Jonathan
2016-05-01
Creating photonic materials with nontrivial topological characteristics has seen burgeoning interest in recent years; however, a major route to topology, a magnetic field for continuum photons, has remained elusive. We present the first experimental realization of a bulk magnetic field for optical photons. By using a non-planar ring resonator, we induce an image rotation on each round trip through the resonator. This results in a Coriolis/Lorentz force and a centrifugal anticonfining force, the latter of which is cancelled by mirror curvature. Spatial- and energy- resolved spectroscopy tracks photonic eigenstates as residual trapping is reduced, and we observe photonic Landau levels as the eigenstates become degenerate. We will discuss the conical geometry of the resulting manifold for photon dynamics and present a measurement of the local density of states that is consistent with Landau levels on a cone. While our work already demonstrates an integer quantum Hall material composed of photons, we have ensured compatibility with strong photon-photon interactions, which will allow quantum optical studies of entanglement and correlation in manybody systems including fractional quantum Hall fluids.
Photonic Landau levels on cones
NASA Astrophysics Data System (ADS)
Schine, Nathan; Ryou, Albert; Gromov, Andrey; Sommer, Ariel; Simon, Jonathan
2016-05-01
We present the first experimental realization of a bulk magnetic field for optical photons. By using a non-planar ring resonator, we induce an image rotation on each round trip through the resonator. This results in a Coriolis/Lorentz force and a centrifugal anticonfining force, the latter of which is cancelled by mirror curvature. Using a digital micromirror device to control both amplitude and phase, we inject arbitrary optical modes into our resonator. Spatial- and energy- resolved spectroscopy tracks photonic eigenstates as residual trapping is reduced, and we observe photonic Landau levels as the eigenstates become degenerate. We show that there is a conical geometry of the resulting manifold for photon dynamics and present a measurement of the local density of states that is consistent with Landau levels on a cone. While our work already demonstrates an integer quantum Hall material composed of photons, we have ensured compatibility with strong photon-photon interactions, which will allow quantum optical studies of entanglement and correlation in manybody systems including fractional quantum Hall fluids.
Laohakunakorn, Nadanai; Gollnick, Benjamin; Moreno-Herrero, Fernando; Aarts, Dirk G. A. L.; Dullens, Roel P. A.; Ghosal, Sandip
2013-01-01
Fluid jets are found in nature at all length scales – microscopic to cosmological. Here we report on an electroosmotically driven jet from a single glass nanopore about 75 nm in radius with a maximum flow rate ~ 30 pL/s. A novel anemometry technique allows us to map out the vorticity and velocity fields which show excellent agreement with the classical Landau-Squire solution of the Navier Stokes equations for a point jet. We observe a phenomenon that we call flow rectification: an asymmetry in the flow rate with respect to voltage reversal. Such a nanojet could potentially find applications in micro manipulation, nano patterning, and as a diode in microfluidic circuits. PMID:24124664
NASA Astrophysics Data System (ADS)
Ghosal, Sandip; Laohakunakorn, Nadanai; Gollnick, Benjamin; Moreno-Herrero, Fernando; Aarts, Dirk G. A. L.; Dullens, Roel P. A.; Keyser, Ulrich F.
2013-11-01
Fluid jets are found in nature at all length scales - microscopic to cosmological. Here we report on what may be the smallest liquid jet ever observed: an electroosmotically driven flow from a single glass nanopore about 75 nm in radius with a maximum flow rate of about 30 pL/s. A novel anemometry technique allows us to map out the vorticity and velocity fields which show excellent agreement with the classical Landau-Squire solution of the Navier Stokes equations for a point jet. We observe a phenomenon that we call flow rectification: an asymmetry in the flow rate with respect to voltage reversal. Such a nanojet could potentially find applications in gene delivery, nano patterning, and as a diode in microfluidic circuits. NIH (R01HG004842) & Leverhulme Trust (SG), George & Lillian Schiff Foundation & Trinity College (NL), Ministry of Education, Spain (BG), Deutsche Froschungsgemeinschaft & European Research Council (UFK).
Bergman kernel from the lowest Landau level
NASA Astrophysics Data System (ADS)
Klevtsov, S.
2009-07-01
We use path integral representation for the density matrix, projected on the lowest Landau level, to generalize the expansion of the Bergman kernel on Kähler manifold to the case of arbitrary magnetic field.
Simplified Model of Nonlinear Landau Damping
N. A. Yampolsky and N. J. Fisch
2009-07-16
The nonlinear interaction of a plasma wave with resonant electrons results in a plateau in the electron distribution function close to the phase velocity of the plasma wave. As a result, Landau damping of the plasma wave vanishes and the resonant frequency of the plasma wave downshifts. However, this simple picture is invalid when the external driving force changes the plasma wave fast enough so that the plateau cannot be fully developed. A new model to describe amplification of the plasma wave including the saturation of Landau damping and the nonlinear frequency shift is proposed. The proposed model takes into account the change of the plasma wave amplitude and describes saturation of the Landau damping rate in terms of a single fluid equation, which simplifies the description of the inherently kinetic nature of Landau damping. A proposed fluid model, incorporating these simplifications, is verified numerically using a kinetic Vlasov code.
Gribov horizon beyond the Landau gauge
NASA Astrophysics Data System (ADS)
Lavrov, Peter M.; Lechtenfeld, Olaf
2013-10-01
Gribov and Zwanziger proposed a modification of Yang-Mills theory in order to cure the Gribov copy problem. We employ field-dependent BRST transformations to generalize the Gribov-Zwanziger model from the Landau gauge to general Rξ gauges. The Gribov horizon functional is presented in explicit form, in both the non-local and local variants. Finally, we show how to reach any given gauge from the Landau one.
Second Landau level fractional quantum Hall effects in the Corbino geometry
NASA Astrophysics Data System (ADS)
Schmidt, B. A.; Bennaceur, K.; Bilodeau, S.; Gervais, G.; Pfeiffer, L. N.; West, K. W.
2015-09-01
For certain measurements, the Corbino geometry has a distinct advantage over the Hall and van der Pauw geometries, in that it provides a direct probe of the bulk 2DEG without complications due to edge effects. This may be important in enabling detection of the non-Abelian entropy of the 5/2 fractional quantum Hall state via bulk thermodynamic measurements. We report the successful fabrication and measurement of a Corbino-geometry sample in an ultra-high mobility GaAs heterostructure, with a focus on transport in the second and higher Landau levels. In particular, we report activation energy gaps of fractional quantum Hall states, with all edge effects ruled out, and extrapolate σ0 from the Arrhenius fits. Our results show that activated transport in the second Landau level remains poorly understood. The development of this Corbino device opens the possibility to study the bulk of the 5/2 state using techniques not possible in other geometries.
NASA Astrophysics Data System (ADS)
Faedo, Antón F.; Mateos, David; Pantelidou, Christiana; Tarrío, Javier
2017-02-01
Holography for UV-incomplete gauge theories is important but poorly understood. A paradigmatic example is d = 4, N=4 super Yang-Mills coupled to N f quark flavors, which possesses a Landau pole at a UV scale ΛLP. The dual gravity solution exhibits a UV singularity at a finite proper distance along the holographic direction. Despite this, holographic renormalization can be fully implemented via analytic continuation to an AdS solution. The presence of a UV cut-off manifests itself in several interesting ways. At energies E ≪ ΛLP no pathologies appear, as expected from effective field theory. In contrast, at scales E ≲ ΛLP the gravitational potential becomes repulsive, and at temperatures T ≲ ΛLP the specific heat becomes negative. Although we focus on N=4 super Yang-Mills with flavor, our qualitative results apply to a much more general class of theories, since they only depend on the fact that the metric near the UV singularity is a hyper-scaling violating metric with exponent θ > d - 1.
Synthetic Landau levels for photons
NASA Astrophysics Data System (ADS)
Schine, Nathan; Ryou, Albert; Gromov, Andrey; Sommer, Ariel; Simon, Jonathan
2016-06-01
Synthetic photonic materials are an emerging platform for exploring the interface between microscopic quantum dynamics and macroscopic material properties. Photons experiencing a Lorentz force develop handedness, providing opportunities to study quantum Hall physics and topological quantum science. Here we present an experimental realization of a magnetic field for continuum photons. We trap optical photons in a multimode ring resonator to make a two-dimensional gas of massive bosons, and then employ a non-planar geometry to induce an image rotation on each round-trip. This results in photonic Coriolis/Lorentz and centrifugal forces and so realizes the Fock-Darwin Hamiltonian for photons in a magnetic field and harmonic trap. Using spatial- and energy-resolved spectroscopy, we track the resulting photonic eigenstates as radial trapping is reduced, finally observing a photonic Landau level at degeneracy. To circumvent the challenge of trap instability at the centrifugal limit, we constrain the photons to move on a cone. Spectroscopic probes demonstrate flat space (zero curvature) away from the cone tip. At the cone tip, we observe that spatial curvature increases the local density of states, and we measure fractional state number excess consistent with the Wen-Zee theory, providing an experimental test of this theory of electrons in both a magnetic field and curved space. This work opens the door to exploration of the interplay of geometry and topology, and in conjunction with Rydberg electromagnetically induced transparency, enables studies of photonic fractional quantum Hall fluids and direct detection of anyons.
Umsetzung der Unternehmensstrategie mit der Balanced Scorecard
NASA Astrophysics Data System (ADS)
Crespo, Isabel; Bergmann, Lars; Portmann, Stefan; Lacker, Thomas; Lacker, Michael; Fleischmann, Jürgen; Kozó, Hans
Die Balanced Scorecard (BSC) ist ein Ansatz zum strategischen Management, der neben der Ausrichtung des Unternehmens auf finanzielle Zielwerte ebenso großes Gewicht auf so genannte weiche Faktoren legt, die den wirtschaftlichen Erfolg eines Unternehmens erst ermöglichen. Das entscheidende Merkmal der Balanced Scorecard ist dabei, dass sie ein ausgewogenes System strategischer Ziele herstellt, welches das Unternehmen hinsichtlich der vier Perspektiven Finanzen, Kunden, interne Prozesse und Mitarbeiter und Potenziale strategisch ausrichtet (Kaplan u. Norton 1997).
The lowest Landau level in QCD
NASA Astrophysics Data System (ADS)
Bruckmann, Falk; Endrőodi, Gergely; Giordano, Matteo; Katz, Sándor D.; Kovács, Tamás G.; Pittler, Ferenc; Wellnhofer, Jacob
2017-03-01
The thermodynamics of Quantum Chromodynamics (QCD) in external (electro-)magnetic fields shows some unexpected features like inverse magnetic catalysis, which have been revealed mainly through lattice studies. Many effective descriptions, on the other hand, use Landau levels or approximate the system by just the lowest Landau level (LLL). Analyzing lattice configurations we ask whether such a picture is justified. We find the LLL to be separated from the rest by a spectral gap in the two-dimensional Dirac operator and analyze the corresponding LLL signature in four dimensions. We determine to what extent the quark condensate is LLL dominated at strong magnetic fields.
Particle systems and nonlinear Landau damping
Villani, Cédric
2014-03-15
Some works dealing with the long-time behavior of interacting particle systems are reviewed and put into perspective, with focus on the classical Kolmogorov–Arnold–Moser theory and recent results of Landau damping in the nonlinear perturbative regime, obtained in collaboration with Clément Mouhot. Analogies are discussed, as well as new qualitative insights in the theory. Finally, the connection with a more recent work on the inviscid Landau damping near the Couette shear flow, by Bedrossian and Masmoudi, is briefly discussed.
Differential formulation of the gyrokinetic Landau operator
NASA Astrophysics Data System (ADS)
Hirvijoki, Eero; Brizard, Alain J.; Pfefferlé, David
2017-02-01
Subsequent to the recent rigorous derivation of an energetically consistent gyrokinetic collision operator in the so-called Landau representation, this paper investigates the possibility of finding a differential formulation of the gyrokinetic Landau collision operator. It is observed that, while a differential formulation is possible in the gyrokinetic phase space, reduction of the resulting system of partial differential equations to five dimensions via gyroaveraging poses a challenge. Based on the present work, it is likely that the gyrocentre analogues of the Rosenbluth-MacDonald-Judd potential functions must be kept gyroangle dependent.
Abraham-Lorentz versus Landau-Lifshitz
NASA Astrophysics Data System (ADS)
Griffiths, David J.; Proctor, Thomas C.; Schroeter, Darrell F.
2010-04-01
The classical Abraham-Lorentz formula for the radiation reaction on a point charge suffers from two notorious defects: runaways and preacceleration. Recently, several authors have advocated as an alternative the Landau-Lifshitz formula, which has neither fault. The latter formula is often presented as an approximation to Abraham-Lorentz, raising the delicate question of how an approximation can be considered more accurate than the original. For a spherical shell of finite size, the equation for the radiation reaction is noncontroversial. We begin there, obtain the Abraham-Lorentz and Landau-Lifshitz expressions as limiting cases, and undertake some numerical studies to determine which is superior.
Wang-Landau integration --- The application of Wang-Landau sampling in numerical integration
NASA Astrophysics Data System (ADS)
Li, Ying Wai; Wuest, Thomas; Landau, David P.; Qing Lin, Hai
2007-03-01
Wang-Landau sampling was first introduced to simulate the density of states in energy space for various physical systems. This technique can be extended to numerical integrations due to certain similarities in nature of these two problems. It can be further applied to study quantum many-body systems. We report the feasibility of this application by discussing the correspondence between Wang-Landau integration and Wang-Landau sampling for Ising model. Numerical results for 1D and 2D integrations are shown. In particular, the utilization of this algorithm in the periodic lattice Anderson model is discussed as an illustrative example.
Erika Landau: A Lifetime of Creativity
ERIC Educational Resources Information Center
Vidergor, Hava
2014-01-01
This article unfolds the personal creative characteristics of an educator in the field of gifted education, and examines creativity as expressed in childhood and its transformation into adulthood. Dr. Erika Landau is a pioneer of gifted education in Israel, an internationally renowned scholar and educator, and the founder of the Young Persons'…
CGL and Landau fluid simulations of turbulence
NASA Astrophysics Data System (ADS)
Hunana, P.; Zank, G. P.; Goldstein, M. L.
2015-12-01
We will present 3 dimensional freely decaying and forced simulations of turbulence with different fluid models such as CGL (double adiabatic) model and Landau fluid models. Simulations will be aimed at the modeling of the spectral break around the proton gyroscale. We will also discuss thresholds and damping rates of firehose and mirror instabilieties.
Landau-Zener problem for trilinear systems
Ishkhanyan, Artur; Mackie, Matt; Carmichael, Andrew; Gould, Phillip L.; Javanainen, Juha
2004-04-01
We consider a nonlinear version of the Landau-Zener problem, focusing on photoassociation of a Bose-Einstein condensate as a specific example. Contrary to the exponential rate dependence obtained for the linear problem, when the resonance is crossed slowly the no-transition probability is directly proportional to the rate at which the resonance is crossed.
Kosmische Katastrophen und der Ursprung der Religion.
NASA Astrophysics Data System (ADS)
Hoyle, F.
This book is a German translation, by V. Delavre, from the English original "The origin of the Universe and the origin of religion", published in 1993. Contents: E. Sens: Die unterbrochene Musikstunde. Einleitung zur deutschen Ausgabe. C. Ryskamp: Einführung. R. N. Anshen: Vorwort. F. Hoyle: Kosmische Katastrophen und der Ursprung der Religion - Die Folgen der Respektabilität; Eiszeiten und Kometen; Die allgemeine Situation in den Nacheiszeiten; Kometen und der Ursprung der Religionen; Der Übergang zu Mittelalter und Neuzeit. Diskussionsbeiträge: Ruth Nanda Anshen, Freeman Dyson, Paul Oscar Kristeller, John Archibald Wheeler, James Schwartz, Roger Shinn, Milton Gatch, Philip Solomon, Norman Newell. F. Hoyle: Schlußwort. A. Tollmann: Nachwort zur deutschen Ausgabe.
Landau-like states in neutral particles
NASA Astrophysics Data System (ADS)
Banerjee, Saikat; Ågren, Hans; Balatsky, A. V.
2016-06-01
We show the emergence of a new type of dispersion relation for neutral atoms with an interesting similarity to the spectrum of two-dimensional electrons in an applied perpendicular constant magnetic field. These neutral atoms can be confined in toroidal optical traps and give quasi-Landau spectra. In strong contrast to the equidistant infinitely degenerate Landau levels for charged particles, the spectral gap for such two-dimensional neutral particles increases in particular electric-field configurations. The idea in the paper is motivated by the development in cold atom experiments and builds on the seminal paper of Aharonov and Casher [Phys. Rev. Lett. 53, 319 (1984), 10.1103/PhysRevLett.53.319].
Nonlinear Landau damping in the ionosphere
NASA Technical Reports Server (NTRS)
Kiwamoto, Y.; Benson, R. F.
1978-01-01
A model is presented to explain the non-resonant waves which give rise to the diffuse resonance observed near 3/2 f sub H by the Alouette and ISIS topside sounders, where f sub H is the ambient electron cyclotron frequency. In a strictly linear analysis, these instability driven waves will decay due to Landau damping on a time scale much shorter than the observed time duration of the diffuse resonance. Calculations of the nonlinear wave particle coupling coefficients, however, indicate that the diffuse resonance wave can be maintained by the nonlinear Landau damping of the sounder stimulated 2f sub H wave. The time duration of the diffuse resonance is determined by the transit time of the instability generated and nonlinearly maintained diffuse resonance wave from the remote short lived hot region back to the antenna. The model is consistent with the Alouette/ISIS observations, and clearly demonstrates the existence of nonlinear wave-particle interactions in the ionosphere.
Landau damping in a turbulent setting
Plunk, G. G.
2013-03-15
To address the problem of Landau damping in kinetic turbulence, we consider the forcing of the linearized Vlasov equation by a stationary random source. It is found that the time-asymptotic density response is dominated by resonant particle interactions that are synchronized with the source. The energy consumption of this response is calculated, implying an effective damping rate, which is the main result of this paper. Evaluating several cases, it is found that the effective damping rate can differ from the Landau damping rate in magnitude and also, remarkably, in sign. A limit is demonstrated in which the density and current become phase-locked, which causes the effective damping to be negligible; this result offers a fresh perspective from which to reconsider recent observations of kinetic turbulence satisfying critical balance.
Mesoscopic Superposition States in Relativistic Landau Levels
Bermudez, A.; Martin-Delgado, M. A.; Solano, E.
2007-09-21
We show that a linear superposition of mesoscopic states in relativistic Landau levels can be built when an external magnetic field couples to a relativistic spin 1/2 charged particle. Under suitable initial conditions, the associated Dirac equation produces unitarily superpositions of coherent states involving the particle orbital quanta in a well-defined mesoscopic regime. We demonstrate that these mesoscopic superpositions have a purely relativistic origin and disappear in the nonrelativistic limit.
Critical endpoint behavior: A Wang Landau study
NASA Astrophysics Data System (ADS)
Landau, D. P.; Wang, Fugao; Tsai, Shan-Ho
2008-07-01
We study the critical endpoint behavior using an asymmetric Ising model with two- and three-body interactions on a triangular lattice, in the presence of an external field. The simulation method we use is Wang-Landau sampling in a two-dimensional parameter space. We observe a clear divergence of the curvature of the spectator phase boundary and of the magnetization coexistence diameter derivative at the critical endpoint, and the exponents for both divergences agree well with previous theoretical predictions.
Spacetime rotation-induced Landau quantization
NASA Astrophysics Data System (ADS)
Konno, Kohkichi; Takahashi, Rohta
2012-03-01
We investigate noninertial and gravitational effects on quantum states in electromagnetic fields and present the analytic solution for energy eigenstates for the Schrödinger equation including noninertial, gravitational, and electromagnetic effects. We find that in addition to the Landau quantization the rotation of spacetime itself leads to the additional quantization, and that the energy levels for an electron are different from those for a proton at the level of gravitational corrections.
Lowest Landau level diamagnetic fluctuations in niobium
NASA Astrophysics Data System (ADS)
Salem-Sugui, Said; Friesen, M.; Alvarenga, A. D.; Schilling, Osvaldo F.; Gandra, F. G.; Doria, M. M.
2004-08-01
We have performed a magnetic study of a bulk metallic sample of Nb with critical temperature Tc = 8.5 K. Magnetization measurements taken for magnetic fields greater than 1 kOe show a superconducting transition that becomes broader as the field is increased. The data are well described by lowest Landau level (LLL) fluctuation theory. A scaling analysis yields values for the superconducting transition temperature under field Tc( H) which are consistent with Hc2( T).
Magnitude of the Wang-Landau error
NASA Astrophysics Data System (ADS)
Brown, Gregory; Rikvold, PA; Odbadrakh, Kh; Nicholson, DM
2016-09-01
The Wang-Landau algorithm is an entropic sampling method that incoroporates an update factor ln fi , which introduces a self-avoidance tendency into the random walk. Continued sampling at constant ln fi leads to a steady state estimate of the density of states ln gi (E). We find numerically that the difference between ln gi (E) and the true density of states ln g (E) is proportional to the update factor.
Filled Landau levels in neutral quantum gases
Oehberg, P.; Juzeliunas, G.; Ruseckas, J.; Fleischhauer, M.
2005-11-15
We consider the signatures of the integer quantum Hall effect in a degenerate gas of electrically neutral atomic fermions. An effective magnetic field is achieved by applying two incident light beams with a high orbital angular momentum. We show how states corresponding to completely filled Landau levels are obtained and discuss various possibilities to measure the incompressible nature of the trapped two-dimensional gas.
Fibonacci oscillators in the Landau diamagnetism problem
NASA Astrophysics Data System (ADS)
Marinho, André A.; Brito, Francisco A.; Chesman, Carlos
2014-10-01
We address the issue of the Landau diamagnetism problem via q-deformed algebra of Fibonacci oscillators through its generalized sequence of two real and independent deformation parameters q1 and q2. We obtain q-deformed thermodynamic quantities such as internal energy, number of particles, magnetization and magnetic susceptibility which recover their usual form in the degenerate limit q12+q22=1.
Akustikgestaltung in der Fahrzeugentwicklung
NASA Astrophysics Data System (ADS)
Pletschen, Bernd
Die zielgerichtete Entwicklung der Fahrzeugakustik stellt eine hochkomplexe, integrative Aufgabenstellung im Rahmen der Fahrkomfortgestaltung des Automobils dar. Die Wahrnehmung der Komforteigenschaften eines Fahrzeugs erfolgt grundsätzlich als Wahrnehmung der Wirkung dieser Eigenschaften über einen oder mehrere Wahrnehmungskanäle des Menschen: visuell, auditiv, haptisch, olfaktorisch. Die individuelle Wahrnehmung ist hierbei subjektiv und daher mit rein physikalisch objektiven Messgrößen allein nur unvollständig zu beschreiben. Sie hängt einerseits von den Eigenschaften des betrachteten Fahrzeugs oder einer erlebten Situation ab und andererseits außerdem von der Sozialisation des Bewertenden und der Umgebung, in der die Bewertung stattfindet (Wikipedia). Der Fahrkomfort, den ein Fahrzeug Fahrer und Beifahrern bietet, wird also wegen unterschiedlicher Erwartungen des Kunden in den verschiedenen Weltmärkten sehr unterschiedlich erlebt.
Nonlinear Landau damping and Alfven wave dissipation
NASA Technical Reports Server (NTRS)
Vinas, Adolfo F.; Miller, James A.
1995-01-01
Nonlinear Landau damping has been often suggested to be the cause of the dissipation of Alfven waves in the solar wind as well as the mechanism for ion heating and selective preacceleration in solar flares. We discuss the viability of these processes in light of our theoretical and numerical results. We present one-dimensional hybrid plasma simulations of the nonlinear Landau damping of parallel Alfven waves. In this scenario, two Alfven waves nonresonantly combine to create second-order magnetic field pressure gradients, which then drive density fluctuations, which in turn drive a second-order longitudinal electric field. Under certain conditions, this electric field strongly interacts with the ambient ions via the Landau resonance which leads to a rapid dissipation of the Alfven wave energy. While there is a net flux of energy from the waves to the ions, one of the Alfven waves will grow if both have the same polarization. We compare damping and growth rates from plasma simulations with those predicted by Lee and Volk (1973), and also discuss the evolution of the ambient ion distribution. We then consider this nonlinear interaction in the presence of a spectrum of Alfven waves, and discuss the spectrum's influence on the growth or damping of a single wave. We also discuss the implications for wave dissipation and ion heating in the solar wind.
Der II. Hauptsatz der Wärmelehre
NASA Astrophysics Data System (ADS)
Heintze, Joachim
Wir haben in (4.44) den II. Hauptsatz als empirische Tatsache folgendermaßen formuliert: (i) Wärmeenergie geht von selbst nur von einem wärmeren Körper auf einen kälteren über, niemals in der umgekehrten Richtung. Nun werden wir beweisen, dass sich aus diesem Prinzip folgende äquivalente Formulierungen für den II. Hauptsatz ableiten lassen: (ii) Es ist unmöglich, ein Perpetuum mobile zweiter Art zu bauen, d. h. eine Maschine, die fortlaufend Wärmeenergie vollständig in mechanische Arbeit umsetzen kann. Eine Wärmekraftmaschine, die einen Kreisprozess mit der höchsten Temperatur Tw und der niedrigsten Temperatur Tk durchläuft, hat höchstens den Carnotschen Wirkungsgrad c = (Tw - Tk)/Tw. Wenn in der Maschine nur reversible Prozesse ablaufen, die gesamte Wärmezufuhr bei der Temperatur Tw erfolgt und ausschließlich bei der Temperatur Tw gekühlt wird, ist ihr Wirkungsgrad = C. Es gibt keine Wärmekraftmaschine, die eine bessere Ausnutzung der Wärmeenergie ermöglicht. (iv) In jedem thermodynamischen System existiert die Zustandsgröße Entropie, definiert durch ihr Differential dS = (dQrev)/T . Entropie kann erzeugt, aber nicht vernichtet werden. Bei Zustandsänderungen, die in einem abgeschlossenen System ablaufen, nimmt die Entropie entweder zu (irreversible Prozesse), oder sie bleibt konstant (reversible Prozesse). Im Anschluss an (iii) werden wir zur Definition der thermodynamischen Temperatur und bei der Diskussion von (iv) zu einem tieferen Verständnis der Entropie gelangen. Es zeigt sich, dass die Entropie das eigentliche Bindeglied zwischen Mechanik und Wärmelehre darstellt. Am Ende des Kapitels werden wir einige Anwendungen des II. Hauptsatzes betrachten.
Imaging the dynamics of free-electron Landau states.
Schattschneider, P; Schachinger, Th; Stöger-Pollach, M; Löffler, S; Steiger-Thirsfeld, A; Bliokh, K Y; Nori, Franco
2014-08-08
Landau levels and states of electrons in a magnetic field are fundamental quantum entities underlying the quantum Hall and related effects in condensed matter physics. However, the real-space properties and observation of Landau wave functions remain elusive. Here we report the real-space observation of Landau states and the internal rotational dynamics of free electrons. States with different quantum numbers are produced using nanometre-sized electron vortex beams, with a radius chosen to match the waist of the Landau states, in a quasi-uniform magnetic field. Scanning the beams along the propagation direction, we reconstruct the rotational dynamics of the Landau wave functions with angular frequency ~100 GHz. We observe that Landau modes with different azimuthal quantum numbers belong to three classes, which are characterized by rotations with zero, Larmor and cyclotron frequencies, respectively. This is in sharp contrast to the uniform cyclotron rotation of classical electrons, and in perfect agreement with recent theoretical predictions.
Test particle study of Landau damping of steepening magnetosonic waves
NASA Technical Reports Server (NTRS)
Matsumoto, H.; Barnes, A.
1982-01-01
A test particle study of Landau damping of steepening large-amplitude magnetosonic waves is made. Motions of test particles in a model of a steepening large-amplitude magnetosonic wave are traced. The kinetic energy change of the ensemble of test particles is computed to estimate the effective Landau damping rate of the magnetosonic wave. The numerical results are compared with the linear kinetic theory of Landau damping and interpreted in terms of a simple physical picture for particle trapping.
Berry's phase for coherent states of Landau levels
Yang, Wen-Long; Chen, Jing-Ling
2007-02-15
The Berry phases for coherent states and squeezed coherent states of Landau levels are calculated. Coherent states of Landau levels are interpreted as a result of a magnetic flux moved adiabatically from infinity to a finite place on the plane. The Abelian Berry phase for coherent states of Landau levels is an analog of the Aharonov-Bohm effect. Moreover, the non-Abelian Berry phase is calculated for the adiabatic evolution of the magnetic field B.
Die Arbeitsunfähigkeit in der Statistik der GKV
NASA Astrophysics Data System (ADS)
Busch, Klaus
Der vorliegende Beitrag gibt anhand der Statistiken des Bundesministeriums für Gesundheit (BMG) einen Überblick über die Arbeitsunfähigkeitsdaten der Gesetzlichen Krankenkassen (GKV). Zunächst werden die Arbeitsunfähigkeitsstatistiken der Krankenkassen und die Erfassung der Arbeitsunfähigkeit erläutert. Hiernach wird auf die Entwicklung der Fehlzeiten auf GKV-Ebene eingegangen. Ebenfalls wird Bezug auf die Unterschiede der Fehlzeiten zwischen den verschiedenen Kassen genommen.
Nonlinear Landau damping of Alfven waves.
NASA Technical Reports Server (NTRS)
Hollweg, J. V.
1971-01-01
Demonstration that large-amplitude linearly or elliptically polarized Alfven waves propagating parallel to the average magnetic field can be dissipated by nonlinear Landau damping. The damping is due to the longitudinal electric field associated with the ion sound wave which is driven (in second order) by the Alfven wave. The damping rate can be large even in a cold plasma (beta much less than 1, but not zero), and the mechanism proposed may be the dominant one in many plasmas of astrophysical interest.
Numerical integration using Wang Landau sampling
NASA Astrophysics Data System (ADS)
Li, Y. W.; Wüst, T.; Landau, D. P.; Lin, H. Q.
2007-09-01
We report a new application of Wang-Landau sampling to numerical integration that is straightforward to implement. It is applicable to a wide variety of integrals without restrictions and is readily generalized to higher-dimensional problems. The feasibility of the method results from a reinterpretation of the density of states in statistical physics to an appropriate measure for numerical integration. The properties of this algorithm as a new kind of Monte Carlo integration scheme are investigated with some simple integrals, and a potential application of the method is illustrated by the evaluation of integrals arising in perturbation theory of quantum many-body systems.
Landau Weak Crystallization Theory and its Applications
NASA Astrophysics Data System (ADS)
Kats, E. I.
Aim of this lecture is to explain main features and ingredients of weak first order phase transitions between liquid-like (uniform in space) and solid-like (non-uniform with characteristic wave vector q0) states. We illustrate how this theory (traditionally termed as Landau weak crystallization theory) works. We consider two examples describing universal temperature dependence of shear viscosity in liquids, and so-called main phase transition in membranes. Our results are in a good qualitative agreement with experimental data, offering a deeper understanding of this kind of phase transitions. We discuss also why and where predicted universal effects can be masked.
Landau gauge Yang-Mills correlation functions
NASA Astrophysics Data System (ADS)
Cyrol, Anton K.; Fister, Leonard; Mitter, Mario; Pawlowski, Jan M.; Strodthoff, Nils
2016-09-01
We investigate Landau gauge S U (3 ) Yang-Mills theory in a systematic vertex expansion scheme for the effective action with the functional renormalization group. Particular focus is put on the dynamical creation of the gluon mass gap at nonperturbative momenta and the consistent treatment of quadratic divergences. The nonperturbative ghost and transverse gluon propagators as well as the momentum-dependent ghost-gluon, three-gluon and four-gluon vertices are calculated self-consistently with the classical action as the only input. The apparent convergence of the expansion scheme is discussed and within the errors, our numerical results are in quantitative agreement with available lattice results.
New physics in the second Landau Level
NASA Astrophysics Data System (ADS)
Csathy, Gabor
2006-03-01
Clean two-dimensional electron systems subjected to perpendicular magnetic fields have a long history of revealing exotic ground states. A large number of these states are only possible in the presence of electron-electron interactions. Two notable examples of such collective ground states are the fractional quantum Hall liquids of the first two Landau levels and the electronic solids called the stripe and bubble phases forming beyond the first Landau level. These two classes of phases are simultaneously present and hence compete in the second Landau level. This talk will highlight our latest results on the evolution of the states of the second Landau level as the magnetic field is tilted away from the direction perpendicular to the sample. The challenging task of cooling to millidegree temperatures and in-situ tilting in this low temperature environment is achieved with a hydraulically driven rotator equipped with sintered Silver heat exchangers mounted onto the nuclear demagnetization stage of a dilution refrigerator. We found that the bubble states are rapidly destroyed with tilt and argue that such a behavior is consistent with the formation of an electronic solid. Furthermore, the well developed ν = 2+1/5 and 2+4/5 liquids are found to be driven insulating while the 2+1/3 and 2+2/3 states survive to the largest tilt angles accessible. The simplest interpretation of the rapid evolution of these states is that bubble phases melt into a classical Hall gas and the ν = 2+1/5 and 2+4/5 liquids solidify with tilt. Our data suggest that spin interaction plays an important role in the formation of these phases. In particular, we surmise that the bubble phases are not fully spin-polarized but most likely have a substantial antiferromagnetic order. These bubble phases could be first examples of antiferromagnetically ordered solids in a single layer two-dimensional electron system. This work was done in collaboration with J.S. Xia, C.L. Vicente, E.D. Adams, N
Landau theory for helical nematic phases
NASA Astrophysics Data System (ADS)
Kats, E. I.; Lebedev, V. V.
2014-09-01
We propose Landau phenomenology for the phase transition from the conventional nematic into the conical helical orientationally non-uniform structure recently identified in liquid crystals formed by "banana"-shaped molecules. The mean field predictions are mostly in agreement with experimental data. Based on the analogy with de Gennes model, we argue that fluctuations of the order parameter turn the transition to the first order phase transition rather than continuous one predicted by the mean-field theory. This conclusion is in agreement with experimental observations. We discuss the new Goldstone mode to be observed in the low-temperature phase.
Kants Theorie der Sonne: Physikgeschichte
NASA Astrophysics Data System (ADS)
Jacobi, Manfred
2005-01-01
Im Rahmen seiner Kosmogonie entwickelte der junge Immanuel Kant eine Theorie der Sonne. Sie ist ein einzigartiges Zeugnis seiner intuitiven Vorstellungskraft und beweist auch die Leistungsfähigkeit der damaligen, vorwiegend von Newton geprägten Weltsicht. Entstehung, Aufbau und Dynamik der Sonne werden in Kants Theorie ebenso erklärt wie etwa das Phänomen der Sonnenflecken.
Landau-Khalatnikov phonon damping in strongly interacting Fermi gases
NASA Astrophysics Data System (ADS)
Kurkjian, Hadrien; Castin, Yvan; Sinatra, Alice
2016-11-01
We derive the phonon damping rate due to the four-phonon Landau-Khalatnikov process in low-temperature strongly interacting Fermi gases using quantum hydrodynamics, correcting and extending the original calculation of Landau and Khalatnikov (Zh. Eksp. Teor. Fiz., 19 (1949) 637). Our predictions can be tested in state-of-the-art experiments with cold atomic gases in the collisionless regime.
Nonlinear Landau damping in quark-gluon plasma
NASA Astrophysics Data System (ADS)
Xiaofei, Zhang; Jiarong, Li
1995-08-01
The semiclassical kinetic equations for the quark-gluon plasma (QGP) are discussed by the multiple time-scale method. The mechanism of nonlinear Landau damping owing to non-Abelian and nonlinear wave-particle interactions in QGP is investigated, and the nonlinear Landau damping rate for the longitudinal color eigenwaves in the long-wavelength limit is calculated.
Relativistic Landau models and generation of fuzzy spheres
NASA Astrophysics Data System (ADS)
Hasebe, Kazuki
2016-07-01
Noncommutative geometry naturally emerges in low energy physics of Landau models as a consequence of level projection. In this work, we proactively utilize the level projection as an effective tool to generate fuzzy geometry. The level projection is specifically applied to the relativistic Landau models. In the first half of the paper, a detail analysis of the relativistic Landau problems on a sphere is presented, where a concise expression of the Dirac-Landau operator eigenstates is obtained based on algebraic methods. We establish SU(2) “gauge” transformation between the relativistic Landau model and the Pauli-Schrödinger nonrelativistic quantum mechanics. After the SU(2) transformation, the Dirac operator and the angular momentum operators are found to satisfy the SO(3, 1) algebra. In the second half, the fuzzy geometries generated from the relativistic Landau levels are elucidated, where unique properties of the relativistic fuzzy geometries are clarified. We consider mass deformation of the relativistic Landau models and demonstrate its geometrical effects to fuzzy geometry. Super fuzzy geometry is also constructed from a supersymmetric quantum mechanics as the square of the Dirac-Landau operator. Finally, we apply the level projection method to real graphene system to generate valley fuzzy spheres.
Landau-Zener approximations for resonant neutrino oscillations
Whisnant, K.
1988-07-15
A simple method for calculating the effects of resonant neutrino oscillations using Landau-Zener approximations is presented. For any given set of oscillation parameters, the method is to use the Landau-Zener approximation which works best in that region.
Wang-Landau sampling for homopolymer collapse
NASA Astrophysics Data System (ADS)
Seaton, Daniel T.; Mitchell, Steven J.; Landau, David P.
2008-03-01
We explore the behavior of a continuum-homopolymer model using the Wang-Landau algorithm, concentrating on phase transitions such as the coil-globule and solid-liquid transitions. Using the density of states generated by the Wang-Landau algorithm, we calculate various thermodynamic quantities, e.g., the internal energy and specific heat. We also study how algorithmic parameters, such as sampling boundaries (maximum and minimum energies for random walks) and the final value of the modification factor, affect these quantities. In particular, we observe how the sampling boundaries can significantly alter the transition behavior. Our results are compared with two recent studies that yielded contradictory results, one using the bond-fluctuation model and the other using a continuum model similar to our own. We find that the transitions seen in our model are much more similar to those in the bond-fluctuation study. The careful analysis of the effects of algorithmic parameters on thermodynamic quantities should be relevant to the study of other polymeric/protein models.
The Wang-Landau Sampling Algorithm
NASA Astrophysics Data System (ADS)
Landau, David P.
2003-03-01
Over the past several decades Monte Carlo simulations[1] have evolved into a powerful tool for the study of wide-ranging problems in statistical/condensed matter physics. Standard methods sample the probability distribution for the states of the system, usually in the canonical ensemble, and enormous improvements have been made in performance through the implementation of novel algorithms. Nonetheless, difficulties arise near phase transitions, either due to critical slowing down near 2nd order transitions or to metastability near 1st order transitions, thus limiting the applicability of the method. We shall describe a new and different Monte Carlo approach [2] that uses a random walk in energy space to determine the density of states directly. Once the density of states is estimated, all thermodynamic properties can be calculated at all temperatures. This approach can be extended to multi-dimensional parameter spaces and has already found use in classical models of interacting particles including systems with complex energy landscapes, e.g., spin glasses, protein folding models, etc., as well as for quantum models. 1. A Guide to Monte Carlo Simulations in Statistical Physics, D. P. Landau and K. Binder (Cambridge U. Press, Cambridge, 2000). 2. Fugao Wang and D. P. Landau, Phys. Rev. Lett. 86, 2050 (2001); Phys. Rev. E64, 056101-1 (2001).
Effects of ion motion on linear Landau damping
NASA Astrophysics Data System (ADS)
Xu, Hui; Sheng, Zheng-Ming; Kong, Xiang-Mu; Su, Fu-Fang
2017-02-01
The effects of ion motion on Landau damping has been studied by the use of one-dimensional Vlasov-Poisson simulation. It is shown that the ion motion may significantly change the development of the linear Landau damping. When the ion mass is multiple of proton mass, its motion will halt the linear Landau damping at some time due to the excitation of ion acoustic waves. The latter will dominate the system evolution at the later stage and hold a considerable fraction of the total energy in the system. With very small ion mass, such as in electron-positron plasma, the ion motion can suppress the linear Landau damping very quickly. When the initial field amplitude is relatively high such as with the density perturbation amplitude δn/n0 > 0.1, the effect of ion motion on Landau damping is found to be weak or even ignorable.
NASA Astrophysics Data System (ADS)
Mittelstraß, J.
Contents: 1. Mythische Eier. 2. Thales-Welten. 3. "Alles ist voller Götter". 4. Griechische Astronomie. 5. "Rettung der Phänomene". 6. Aristotelische Kosmololgie. 7. Aristoteles-Welt und Platon-Welt. 8. Noch einmal: die Göttlichkeit der Welt. 9. Griechischer Idealismus.
Universal Landau Pole at the Planck scale
Andrianov, Alexander A.; Espriu, Domenec; Kurkov, Maxim A.; Lizzi, Fedele
2014-07-23
The concept of quantum gravity entails that the usual geometry loses its meaning at very small distances and therefore the grand unification of all gauge interactions with the property of asymptotic freedom happens to be questionable. We propose an unification of all gauge interactions in the form of an “Universal Landau Pole” (ULP), at which all gauge couplings diverge (or, better to say, become very strong). We show that the Higgs quartic coupling also substantially increases whereas the Yukawa couplings tend to zero. Such a singular (or strong coupling) unification is obtained after adding to the Standard Model matter more fermions with vector gauge couplings and hypercharges identical to the SM fermions. The influence of new particles also may prevent the Higgs quartic coupling from crossing zero, thus avoiding the instability (or metastability) of the SM vacuum. As well this fermion pattern opens a way to partially solve the hierarchy problem between masses of quarks and leptons.
Magnetoacoustic heating by ion Landau damping
NASA Technical Reports Server (NTRS)
Turner, L.
1980-01-01
The Vlasov-fluid model of Freidberg (1972) is used to study the resonance heating of a sharp-boundary screw pinch. The analysis provides the first treatment of the magnetoacoustic heating of a cylindrical plasma by means of ion Landau damping, which was identified as a viable dissipative mechanism for the conversion of magnetoacoustic wave energy into ion thermal energy. In addition, local and global energy conservation are considered, and formulae and numerical results for the thermal energy doubling time and the associated induced rf electric fields are presented. It is shown that collisionless absorption can provide a heating mechanism when an equilibrium plasma column is pumped by oscillations of the confining magnetic field at a frequency near the oblique magnetoacoustic frequency.
Magnetoacoustic heating by ion Landau damping
NASA Astrophysics Data System (ADS)
Turner, L.
1980-07-01
The Vlasov-fluid model of Freidberg (1972) is used to study the resonance heating of a sharp-boundary screw pinch. The analysis provides the first treatment of the magnetoacoustic heating of a cylindrical plasma by means of ion Landau damping, which was identified as a viable dissipative mechanism for the conversion of magnetoacoustic wave energy into ion thermal energy. In addition, local and global energy conservation are considered, and formulae and numerical results for the thermal energy doubling time and the associated induced rf electric fields are presented. It is shown that collisionless absorption can provide a heating mechanism when an equilibrium plasma column is pumped by oscillations of the confining magnetic field at a frequency near the oblique magnetoacoustic frequency.
Discrete coherent states for higher Landau levels
NASA Astrophysics Data System (ADS)
Abreu, L. D.; Balazs, P.; de Gosson, M.; Mouayn, Z.
2015-12-01
We consider the quantum dynamics of a charged particle evolving under the action of a constant homogeneous magnetic field, with emphasis on the discrete subgroups of the Heisenberg group (in the Euclidean case) and of the SL(2 , R) group (in the Hyperbolic case). We investigate completeness properties of discrete coherent states associated with higher order Euclidean and hyperbolic Landau levels, partially extending classic results of Perelomov and of Bargmann, Butera, Girardello and Klauder. In the Euclidean case, our results follow from identifying the completeness problem with known results from the theory of Gabor frames. The results for the hyperbolic setting follow by using a combination of methods from coherent states, time-scale analysis and the theory of Fuchsian groups and their associated automorphic forms.
Vortex distribution in the lowest Landau level
Aftalion, Amandine; Blanc, Xavier; Nier, Francis
2006-01-15
We study the vortex distribution of the wave functions minimizing the Gross-Pitaevskii energy for a fast rotating condensate in the lowest Landau level (LLL): we prove that the minimizer cannot have a finite number of zeroes, thus the lattice is infinite, but not uniform. This uses the explicit expression of the projector onto the LLL. We also show that any slow varying envelope function can be approximated in the LLL by distorting the lattice. This is used in particular to approximate the inverted parabola and understand the role of 'invisible' vortices: the distortion of the lattice is very small in the Thomas-Fermi region but quite large outside, where the 'invisible' vortices lie.
Landau-Lifshitz theory of thermomagnonic torque
NASA Astrophysics Data System (ADS)
Kim, Se Kwon; Tserkovnyak, Yaroslav
2015-07-01
We derive the thermomagnonic torque associated with smooth magnetic textures subjected to a temperature gradient in the framework of the stochastic Landau-Lifshitz-Gilbert equation. Our approach captures on equal footing two distinct contributions: (i) a local entropic torque that is caused by a temperature dependence of the effective exchange field, the existence of which had been previously suggested based on numerics, and (ii) the well-known spin-transfer torque induced by thermally induced magnon flow. The dissipative components of two torques have the same structure, following a common phenomenology, but opposite signs, with the twice as large entropic torque leading to a domain-wall motion toward the hotter region. We compare the efficiency of the torque-driven domain-wall motion with the recently proposed Brownian thermophoresis.
Landau-Zener effect in fission
Mirea, M.; Tassan-Got, L.; Stephan, C.; Bacri, C. O.; Bobulescu, R. C.
2007-12-15
A model that takes into account the Landau-Zener promotion mechanism during fission was developed recently. The structures observed in the subthreshold neutron-induced fission of {sup 232}Th are investigated employing this model. Theoretical single-particle excitations of a phenomenological two-humped barrier are determined by solving a system of coupled differential equations for the motion along the optimal fission path. A rather good agreement with experimental data is obtained using a small number of independent parameters. It is predicted that the structure at 1.4 and 1.6 MeV is mainly dominated by a spin 3/2 partial cross section with a small admixture of spin 1/2, while the structure at 1.7 MeV is given by a large partial cross section of spin 5/2.
Universality in dissipative Landau-Zener transitions
Orth, Peter P.; Le Hur, Karyn; Imambekov, Adilet
2010-09-15
We introduce a random-variable approach to investigate the dynamics of a dissipative two-state system. Based on an exact functional integral description, our method reformulates the problem as that of the time evolution of a quantum state vector subject to a Hamiltonian containing random noise fields. This numerically exact, nonperturbative formalism is particularly well suited in the context of time-dependent Hamiltonians, at both zero and finite temperature. As an important example, we consider the renowned Landau-Zener problem in the presence of an Ohmic environment with a large cutoff frequency at finite temperature. We investigate the ''scaling'' limit of the problem at intermediate times, where the decay of the upper-spin-state population is universal. Such a dissipative situation may be implemented using a cold-atom bosonic setup.
Landau-Zener type surface hopping algorithms.
Belyaev, Andrey K; Lasser, Caroline; Trigila, Giulio
2014-06-14
A class of surface hopping algorithms is studied comparing two recent Landau-Zener (LZ) formulas for the probability of nonadiabatic transitions. One of the formulas requires a diabatic representation of the potential matrix while the other one depends only on the adiabatic potential energy surfaces. For each classical trajectory, the nonadiabatic transitions take place only when the surface gap attains a local minimum. Numerical experiments are performed with deterministically branching trajectories and with probabilistic surface hopping. The deterministic and the probabilistic approach confirm the affinity of both the LZ probabilities, as well as the good approximation of the reference solution computed by solving the Schrödinger equation via a grid based pseudo-spectral method. Visualizations of position expectations and superimposed surface hopping trajectories with reference position densities illustrate the effective dynamics of the investigated algorithms.
Landau Zener Effect in Superfluid Nuclear Systems
NASA Astrophysics Data System (ADS)
Mirea, M.
The Landau Zener effect is generalized for many-body systems with pairing residual interactions. The microscopic equations of motion are obtained and the 14C decay of 223Ra spectroscopic factors are deduced. An asymmetric nuclear shape parametrization given by two intersected spheres is used. The single particle level scheme is determined in the frame of the superasymmetric two-center shell model. The deformation energy is computed in the microscopic macroscopic approximation. The penetrabilities are obtained within the WKB approximation. The fine structure of the cluster decay analyzed in the frame of this formalism gives a very good agreement with the experimental ratio of partial half-lives for transition to the first excited state and to the ground state.
Fundamentals and applications of the Landau-Lifshitz-Bloch equation
NASA Astrophysics Data System (ADS)
Atxitia, U.; Hinzke, D.; Nowak, U.
2017-01-01
The influence of thermal excitations on magnetic materials is a topic of increasing relevance in the theory of magnetism. The Landau-Lifshitz-Bloch equation describes magnetisation dynamics at finite temperatures. It can be considered as an extension of already established micromagnetic methods with a comparable numerical effort. This review is a brief summary of this new field of research, with a focus on the fundamentals of the Landau-Lifshitz-Bloch equation, its connection with the stochastic Landau-Lifshitz equation, and its applications in modern magnetism.
Cavity-mediated entanglement generation via Landau-Zener interferometry.
Quintana, C M; Petersson, K D; McFaul, L W; Srinivasan, S J; Houck, A A; Petta, J R
2013-04-26
We demonstrate quantum control and entanglement generation using a Landau-Zener beam splitter formed by coupling two transmon qubits to a superconducting cavity. Single passage through the cavity-mediated qubit-qubit avoided crossing provides a direct test of the Landau-Zener transition formula. Consecutive sweeps result in Landau-Zener-Stückelberg interference patterns, with a visibility that can be sensitively tuned by adjusting the level velocity through both the nonadiabatic and adiabatic regimes. Two-qubit state tomography indicates that a Bell state can be generated via a single passage, with a fidelity of 78% limited by qubit relaxation.
A novel method of including Landau level mixing in numerical studies of the quantum Hall effect
Wooten, Rachel; Quinn, John; Macek, Joseph
2013-12-04
Landau level mixing should influence the quantum Hall effect for all except the strongest applied magnetic fields. We propose a simple method for examining the effects of Landau level mixing by incorporating multiple Landau levels into the Haldane pseudopotentials through exact numerical diagonalization. Some of the resulting pseudopotentials for the lowest and first excited Landau levels will be presented.
Including Landau level mixing in numerical studies of the quantum Hall effect
NASA Astrophysics Data System (ADS)
Wooten, R. E.; Macek, J. H.; Quinn, J. J.
2013-10-01
Landau level mixing should influence the quantum Hall effect for all but the strongest applied magnetic fields. However, the effects of Landau level mixing have proven difficult to model theoretically. We propose a simple method for examining the effects of Landau level mixing on electron pairs for intermediate magnetic fields by incorporating multiple Landau levels into the pseudopotentials on the Haldane sphere.
A novel method of including Landau level mixing in numerical studies of the quantum Hall effect
NASA Astrophysics Data System (ADS)
Wooten, Rachel; Quinn, John; Macek, Joseph
2013-12-01
Landau level mixing should influence the quantum Hall effect for all except the strongest applied magnetic fields. We propose a simple method for examining the effects of Landau level mixing by incorporating multiple Landau levels into the Haldane pseudopotentials through exact numerical diagonalization. Some of the resulting pseudopotentials for the lowest and first excited Landau levels will be presented.
Theoretische Konzepte der Physik
NASA Astrophysics Data System (ADS)
Longair, Malcolm S.; Simon, B.; Simon, H.
"Dies ist kein Lehrbuch der theoretischen Physik, auch kein Kompendium der Physikgeschichte ... , vielmehr eine recht anspruchsvolle Sammlung historischer Miniaturen zur Vergangenheit der theoretischen Physik - ihrer "Sternstunden", wenn man so will. Frei vom Zwang, etwas Erschöpfendes vorlegen zu müssen, gelingt dem Autor etwas Seltenes: einen "lebendigen" Zugang zum Ideengebäude der modernen Physik freizulegen, ... zu zeigen, wie Physik in praxi entsteht... Als Vehikel seiner Absichten dienen dem Autor geschichtliche Fallstudien, insgesamt sieben an der Zahl. Aus ihnen extrahiert er das seiner Meinung nach Lehrhafte, dabei bestrebt, mathematische Anachronismen womöglich zu vermeiden... Als Student hätte ich mir diese gescheiten Essays zum Werden unserer heutigen physikalischen Weltsicht gewünscht. Sie sind originell, didaktisch klug und genieren sich auch nicht, von der Faszination zu sprechen, die ... von der Physik ausgeht. Unnötig darauf hinzuweisen, das sie ein gründliches "konventionelles" Studium weder ersetzen wollen noch können, sie vermögen aber, dazu zu ermuntern." #Astronomische Nachrichten (zur englischen Ausgabe)#1
Nomogramme der Sickerwasserprognose
NASA Astrophysics Data System (ADS)
Schneider, Wilfried; Stöfen, Heinke
Kurzfassung Modelle zur Sickerwasserprognose stehen in unterschiedlicher Komplexität zur Verfügung. Komplexe Modelle werden aufgrund der schwierigen Handhabung und des enormen Eingabedatenumfangs in der Praxis kaum angewandt. Grobe Abschätzmethoden sind dagegen nicht ausreichend wissenschaftlich fundiert, um damit justiziable Ergebnisse erzielen zu können. Um die Kluft zwischen komplexer und einfacher, jedoch justiziabler sowie wissenschaftlich fundierter Methode zu schmälern, wurden Nomogramme für Sickerwasserprognosen zur Berücksichtigung der Endlichkeit der Quelle entwickelt. Mithilfe der Nomogramme können ohne Modellierungserfahrung schnell und einfach die zu erwartenden Schadstoffkonzentrationen am Ort der Beurteilung abgeschätzt werden, falls die Endlichkeit der Quelle der hauptsächlich zur Abminderung führende Prozess ist. Die Nomogramme basieren auf analytischen Lösungen der eindimensionalen Advektions-Dispersions-Gleichung. Sie berücksichtigen die Prozesse Advektion, Diffusion in Bodenwasser und -luft, Dispersion, lineare Sorption, Abbau 1. Ordnung innerhalb einer aus mehreren Bodenschichten bestehenden Sickerwasserzone, wobei die Endlichkeit der Schadstoffmasse in der Bodenkontamination einbezogen wird. Die Genauigkeit der Nomogramme wird dargestellt. Models of different complexity are available for groundwater risk assessment. In practice complex models are hardly used, due to their difficult handling and large data requirement. Rough estimation methods are not sufficiently scientifically founded to produce justiciable results. To reduce the gap between complex and easy to use but justiciable and scientifically founded methods we developed nomograms for groundwater risk assessment which take into account the finite mass of contaminant in the source. With the help of the nomograms the expected concentrations at the point of compliance (transition between the unsaturated and saturated zone) can be estimated easily, fast and without any
High-Dimensional Topological Insulators with Quaternionic Analytic Landau Levels
NASA Astrophysics Data System (ADS)
Li, Yi; Wu, Congjun
2013-05-01
We study the three-dimensional topological insulators in the continuum by coupling spin-1/2 fermions to the Aharonov-Casher SU(2) gauge field. They exhibit flat Landau levels in which orbital angular momentum and spin are coupled with a fixed helicity. The three-dimensional lowest Landau level wave functions exhibit the quaternionic analyticity as a generalization of the complex analyticity of the two-dimensional case. Each Landau level contributes one branch of gapless helical Dirac modes to the surface spectra, whose topological properties belong to the Z2 class. The flat Landau levels can be generalized to an arbitrary dimension. Interaction effects and experimental realizations are also studied.
The role of Wang-Landau sampling in materials development
NASA Astrophysics Data System (ADS)
Landau, David
2012-02-01
An understanding of the thermodynamic behavior of materials as well as the prediction of the properties of ``materials by design'' often depends upon knowledge of the free energy of the system under study. Computer simulations offer a powerful tool for such investigations, but traditional methods often suffer from long time scales and metastable states due to the roughness of the free energy landscape. Wang-Landau samplingootnotetextF. Wang and D. P. Landau, Phys. Rev. Lett. 86, 2050 (2001); F. Wang and D. P. Landau, Phys. Rev. E 64, 05610 (2001). is a powerful alternative to traditional Monte Carlo algorithms which can alleviate many such problems. We will review the Wang-Landau algorithm and discuss various implementations as well as possible application to materials development.
Avoiding boundary effects in Wang-Landau sampling
NASA Astrophysics Data System (ADS)
Schulz, B. J.; Binder, K.; Müller, M.; Landau, D. P.
2003-06-01
A simple modification of the “Wang-Landau sampling” algorithm removes the systematic error that occurs at the boundary of the range of energy over which the random walk takes place in the original algorithm.
Landau damping of a driven plasma wave from laser pulses
Bu Zhigang; Ji Peiyong
2012-01-15
The interaction between a laser pulse and a driven plasma wave with a phase velocity approaching the speed of light is studied, and our investigation is focused on the Gaussian laser pulse. It is demonstrated that when the resonance condition between the plasma wave and the laser pulse is satisfied, the Landau damping phenomenon of the plasma wave originated from the laser pulse will emerge. The dispersion relations for the plasma waves in resonance and non-resonance regions are obtained. It is proved that the Landau damping rate for a driven plasma wave is {gamma}>0 in the resonance region, so the laser pulse can produce an inverse damping effect, namely Landau growth effect, which leads an instability for the plasma wave. The Landau growth means that the energy is transmitted from the laser pulse to the plasma wave, which could be an effective process for enhancing the plasma wave.
The minimum-uncertainty coherent states for Landau levels
NASA Astrophysics Data System (ADS)
Dehghani, A.; Fakhri, H.; Mojaveri, B.
2012-12-01
The Glauber minimum-uncertainty coherent states with two variables for Landau levels, based on the representation of Weyl-Heisenberg algebra by two different modes, have been studied about four decades ago. Here, we introduce new two-variable coherent states with minimum uncertainty relationship for Landau levels in three different methods: the infinite unitary representation of su(1, 1) is realized in two different methods, first, by consecutive levels with the same energy gaps and also with the same value for z-angular momentum quantum number, then, by shifting z-angular momentum mode number by two units while the energy level remaining the same. Besides, for su(2), whether by lowest Landau levels or Landau levels with lowest z-angular momentum, just one finite unitary representation is introduced. Having constructed the generalized Klauder-Perelomov coherent states, for any of the three representations, we obtain their Glauber coherency by displacement operator of Weyl-Heisenberg algebra.
The minimum-uncertainty coherent states for Landau levels
Dehghani, A.; Fakhri, H.; Mojaveri, B.
2012-12-15
The Glauber minimum-uncertainty coherent states with two variables for Landau levels, based on the representation of Weyl-Heisenberg algebra by two different modes, have been studied about four decades ago. Here, we introduce new two-variable coherent states with minimum uncertainty relationship for Landau levels in three different methods: the infinite unitary representation of su(1, 1) is realized in two different methods, first, by consecutive levels with the same energy gaps and also with the same value for z-angular momentum quantum number, then, by shifting z-angular momentum mode number by two units while the energy level remaining the same. Besides, for su(2), whether by lowest Landau levels or Landau levels with lowest z-angular momentum, just one finite unitary representation is introduced. Having constructed the generalized Klauder-Perelomov coherent states, for any of the three representations, we obtain their Glauber coherency by displacement operator of Weyl-Heisenberg algebra.
Neutrino oscillations and the Landau-Zener formula
Kim, C.W.; Sze, W.K.; Nussinov, S.
1987-06-15
We discuss solar-neutrino oscillations and the Landau-Zener probability using a heuristic picture in analogy with an electron spin in a time-dependent magnetic field. The extreme nonadiabatic resonant oscillation is also briefly investigated.
Perturbation Theory For The Landau-Lifshits-Gilbert Equation
2012-09-01
presented in the IEEE Transactions in Magnetics publication entitled “Two-Frequency Excitation of a Magnetic Microwire ” and contains ancillary...expansion in powers of the external field. 15. SUBJECT TERMS Ferromagnetic resonance, nonlinear response, magnetic microwires 16. SECURITY...sort used in laboratories or medical equipment are unavailable. 2. The Landau-Lifshits and Landau-Lifshits-Gilbert Equations In order to estimate
Massively parallel Wang-Landau sampling on multiple GPUs
NASA Astrophysics Data System (ADS)
Yin, Junqi; Landau, D. P.
2012-08-01
Wang-Landau sampling is implemented on the Graphics Processing Unit (GPU) with the Compute Unified Device Architecture (CUDA). Performances on three different GPU cards, including the new generation Fermi architecture card, are compared with that on a Central Processing Unit (CPU). The parameters for massively parallel Wang-Landau sampling are tuned in order to achieve fast convergence. For simulations of the water cluster systems, we obtain an average of over 50 times speedup for a given workload.
Massively parallel Wang Landau sampling on multiple GPUs
Yin, Junqi; Landau, D. P.
2012-01-01
Wang Landau sampling is implemented on the Graphics Processing Unit (GPU) with the Compute Unified Device Architecture (CUDA). Performances on three different GPU cards, including the new generation Fermi architecture card, are compared with that on a Central Processing Unit (CPU). The parameters for massively parallel Wang Landau sampling are tuned in order to achieve fast convergence. For simulations of the water cluster systems, we obtain an average of over 50 times speedup for a given workload.
Landau-Zener treatments of solar neutrino oscillations
Bruggen, M. |; Haxton, W.C.; Qian, Y.Z.
1995-01-01
The authors present a simple derivation of Landau-Zener formulae for nonadiabatic level crossings for linear and exponential density profiles. The derivation depends on a single assumption that applies somewhat differently to the exponential and linear cases, providing some insight into the relationship between the respective formulae. They note that one exponential Landau-Zener formula in common use is only approximately correct. Comparisons with exact calculations are made.
Fault-tolerant Landau-Zener quantum gates
Hicke, C.; Santos, L. F.; Dykman, M. I.
2006-01-15
We present a method to perform fault-tolerant single-qubit gate operations using Landau-Zener tunneling. In a single Landau-Zener pulse, the qubit transition frequency is varied in time so that it passes through the frequency of the radiation field. We show that a simple three-pulse sequence allows eliminating errors in the gate up to the third order in errors in the qubit energies or the radiation frequency.
Landau-Zener treatments of solar neutrino oscillations
Bruggen, M. Institute for Nuclear Theory, NK-12, University of Washington, Seattle, Washington 98195 ); Haxton, W.C.; Qian, Y. )
1995-04-15
We present a simple derivation of the Landau-Zener formulas for nonadiabatic level crossings for linear and exponential density profiles. The derivation depends on a single assumption that applies somewhat differently to the exponential and linear cases, providing some insight into the relationship between the respective formulas. We note that one exponential Landau-Zener formula in common use is only approximately correct. Comparisons with exact calculations are made.
Infrared Behavior and Fixed Points in Landau-Gauge QCD
NASA Astrophysics Data System (ADS)
Pawlowski, Jan M.; Litim, Daniel F.; Nedelko, Sergei; von Smekal, Lorenz
2004-10-01
We investigate the infrared behavior of gluon and ghost propagators in Landau-gauge QCD by means of an exact renormalization group equation. We explain how, in general, the infrared momentum structure of Green functions can be extracted within this approach. An optimization procedure is devised to remove residual regulator dependences. In Landau-gauge QCD this framework is used to determine the infrared leading terms of the propagators. The results support the Kugo-Ojima confinement scenario. Possible extensions are discussed.
Nonlinear Landau damping in the ionosphere
NASA Technical Reports Server (NTRS)
Kiwamoto, Y.; Benson, R. F.
1979-01-01
A model which explains the nonresonant waves which produce the diffuse resonance observed near 3/2 f(H) by the Alouette and Isis topside sounders, where f(H) is the ambient electron cyclotron frequency, is presented. These waves are the result of plasma wave instabilities driven by anisotropic electron velocity distributions initiated by the high-power short-duration sounder pulse. Calculations of the nonlinear wave-particle coupling coefficients show that the diffuse resonance wave can be maintained by nonlinear Landau damping of the sounder-stimulated 2f(H) wave which is observed with a time duration longer than that of the diffuse resonance wave. The time duration of the diffuse resonance is determined by the transit time of the instability-generated and nonlinearly maintained diffuse resonance wave from the remote short-lived hot region back to the antenna. The model is consistent with the Alouette/Isis observations and it demonstrates the existence of nonlinear wave-particle interactions in the ionosphere.
Pairing in half-filled Landau level
NASA Astrophysics Data System (ADS)
Wang, Zhiqiang; Mandal, Ipsita; Chung, Suk Bum; Chakravarty, Sudip
2015-03-01
Pairing of composite fermions in half-filled Landau level state is reexamined by solving the BCS gap equation with full frequency dependent current-current interactions. Our results show that there can be a continuous transition from the Halperin-Lee-Read state to a chiral odd angular momentum Cooper pair state for short-range contact interaction. This is at odds with the previously established conclusion of first order pairing transition, in which the low frequency effective interaction was assumed for the entire frequency range. We find that even if the low frequency effective interaction is repulsive, it is compensated by the high frequency regime, which is attractive. We construct the phase diagrams and show that l = 1 angular momentum channel is quite different from higher angular momentum channel l >= 3 . Remarkably, the full frequency dependent analysis applied to the bilayer Hall system with a total filling fraction ν =1/2 +1/2 is quantitatively changed from the previously established results but not qualitatively. This work was supported by US NSF under the Grant DMR-1004520, the funds from the David S. Saxon Presidential Chair at UCLA(37952), and by the Institute for Basic Science in Korea through the Young Scientist grant (5199-2014003).
Pairing in half-filled Landau level
Wang, Zhiqiang; Mandal, Ipsita; Chung, Suk Bum; Chakravarty, Sudip
2014-12-15
Pairing of composite fermions in half-filled Landau level state is reexamined by solving the BCS gap equation with full frequency dependent current–current interactions. Our results show that there can be a continuous transition from the Halperin–Lee–Read state to a chiral odd angular momentum Cooper pair state for short-range contact interaction. This is at odds with the previously established conclusion of first order pairing transition, in which the low frequency effective interaction was assumed for the entire frequency range. We find that even if the low frequency effective interaction is repulsive, it is compensated by the high frequency regime, which is attractive. We construct the phase diagrams and show that ℓ=1 angular momentum channel is quite different from higher angular momenta ℓ≥3. Remarkably, the full frequency dependent analysis applied to the bilayer Hall system with a total filling fraction ν=1/2 +1/2 is quantitatively changed from the previously established results but not qualitatively.
Loss of Landau Damping for Bunch Oscillations
Burov, A.; /Fermilab
2011-04-11
Conditions for the existence, uniqueness and stability of self-consistent bunch steady states are considered. For the existence and uniqueness problems, simple algebraic criteria are derived for both the action and Hamiltonian domain distributions. For the stability problem, van Kampen theory is used. The onset of a discrete van Kampen mode means the emergence of a coherent mode without any Landau damping; thus, even a tiny couple-bunch or multi-turn wake is sufficient to drive the instability. The method presented here assumes an arbitrary impedance, RF shape, and beam distribution function. Available areas on the intensity-emittance plane are shown for resistive wall wake and single harmonic, bunch shortening and bunch lengthening RF configurations. Thresholds calculated for the Tevatron parameters and impedance model are in agreement with the observations. These thresholds are found to be extremely sensitive to the small-argument behaviour of the bunch distribution function. Accordingly, a method to increase the LLD threshold is suggested. This article summarizes and extends recent author's publications.
On Some Properties of the Landau Kinetic Equation
NASA Astrophysics Data System (ADS)
Bobylev, Alexander; Gamba, Irene; Potapenko, Irina
2015-12-01
We discuss some general properties of the Landau kinetic equation. In particular, the difference between the "true" Landau equation, which formally follows from classical mechanics, and the "generalized" Landau equation, which is just an interesting mathematical object, is stressed. We show how to approximate solutions to the Landau equation by the Wild sums. It is the so-called quasi-Maxwellian approximation related to Monte Carlo methods. This approximation can be also useful for mathematical problems. A model equation which can be reduced to a local nonlinear parabolic equation is also constructed in connection with existence of the strong solution to the initial value problem. A self-similar asymptotic solution to the Landau equation for large v and t is discussed in detail. The solution, earlier confirmed by numerical experiments, describes a formation of Maxwellian tails for a wide class of initial data concentrated in the thermal domain. It is shown that the corresponding rate of relaxation (fractional exponential function) is in exact agreement with recent mathematically rigorous estimates.
Grundbegriffe der Thermodynamik
NASA Astrophysics Data System (ADS)
Heintze, Joachim
In diesem Kapitel geht es darum, Vorgänge zu analysieren, bei denen der thermische Zustand eines Systems verändert wird: Daher der Name "Thermodynamik". Wir werden zunächst untersuchen, unter welchen Umständen man eine Zustandsänderung im Detail beschreiben kann. Hierbei werden wir zwei grundsätzlich verschiedene Arten, Zustandsänderungen herbeizuführen, kennenlernen: reversible und irreversible Prozesse. Sodann werden wir die Eigenschaften von Zustandsgrößen allgemein definieren und dabei auf eine überaus wichtige neue Zustandsgröße, die Entropie, stoßen.
Landau Levels of Majorana Fermions in a Spin Liquid.
Rachel, Stephan; Fritz, Lars; Vojta, Matthias
2016-04-22
Majorana fermions, originally proposed as elementary particles acting as their own antiparticles, can be realized in condensed-matter systems as emergent quasiparticles, a situation often accompanied by topological order. Here we propose a physical system which realizes Landau levels-highly degenerate single-particle states usually resulting from an orbital magnetic field acting on charged particles-for Majorana fermions. This is achieved in a variant of a quantum spin system due to Kitaev which is distorted by triaxial strain. This strained Kitaev model displays a spin-liquid phase with charge-neutral Majorana-fermion excitations whose spectrum corresponds to that of Landau levels, here arising from a tailored pseudomagnetic field. We show that measuring the dynamic spin susceptibility reveals the Landau-level structure by a remarkable mechanism of probe-induced bound-state formation.
Four-Wave Mixing in Landau-Quantized Graphene.
König-Otto, Jacob C; Wang, Yongrui; Belyanin, Alexey; Berger, Claire; de Heer, Walter A; Orlita, Milan; Pashkin, Alexej; Schneider, Harald; Helm, Manfred; Winnerl, Stephan
2017-04-12
For Landau-quantized graphene, featuring an energy spectrum consisting of nonequidistant Landau levels, theory predicts a giant resonantly enhanced optical nonlinearity. We verify the nonlinearity in a time-integrated degenerate four-wave mixing (FWM) experiment in the mid-infrared spectral range, involving the Landau levels LL-1, LL0 and LL1. A rapid dephasing of the optically induced microscopic polarization on a time scale shorter than the pulse duration (∼4 ps) is observed, while a complementary pump-probe experiment under the same experimental conditions reveals a much longer lifetime of the induced population. The FWM signal shows the expected field dependence with respect to lowest order perturbation theory for low fields. Saturation sets in for fields above ∼6 kV/cm. Furthermore, the resonant behavior and the order of magnitude of the third-order susceptibility are in agreement with our theoretical calculations.
Convergence and refinement of the Wang Landau algorithm
NASA Astrophysics Data System (ADS)
Lee, Hwee Kuan; Okabe, Yutaka; Landau, D. P.
2006-07-01
Recently, Wang and Landau proposed a new random walk algorithm that can be very efficiently applied to many problems. Subsequently, there has been numerous studies on the algorithm itself and many proposals for improvements were put forward. However, fundamental questions such as what determines the rate of convergence has not been answered. To understand the mechanism behind the Wang-Landau method, we did an error analysis and found that a steady state is reached where the fluctuations in the accumulated energy histogram saturate at values proportional to [. This value is closely related to the error corrections to the Wang-Landau method. We also study the rate of convergence using different "tuning" parameters in the algorithm.
Nonlinear Landau damping of wave envelopes in a quantum plasma
NASA Astrophysics Data System (ADS)
Chatterjee, Debjani; Misra, A. P.
2016-10-01
The nonlinear theory of Landau damping of electrostatic wave envelopes (WEs) is revisited in a quantum electron-positron pair plasma. Starting from a Wigner-Moyal equation coupled to the Poisson equation and applying the multiple scale technique, we derive a nonlinear Schrödinger (NLS) equation which governs the evolution of electrostatic WEs. It is shown that the coefficients of the NLS equation, including the nonlocal nonlinear term, which appears due to the resonant particles having a group velocity of the WEs, are significantly modified by the particle dispersion. The effects of the quantum parameter H (the ratio of the plasmon energy to the thermal energy densities), associated with the particle dispersion, are examined on the Landau damping rate of carrier waves, as well as on the modulational instability of WEs. It is found that the Landau damping rate and the decay rate of the solitary wave amplitude are greatly reduced compared to their classical values (H = 0).
Landau-Level Splitting in Graphene in High Magnetic Fields
NASA Astrophysics Data System (ADS)
Zhang, Y.; Jiang, Z.; Small, J. P.; Purewal, M. S.; Tan, Y.-W.; Fazlollahi, M.; Chudow, J. D.; Jaszczak, J. A.; Stormer, H. L.; Kim, P.
2006-04-01
The quantum Hall (QH) effect in two-dimensional electrons and holes in high quality graphene samples is studied in strong magnetic fields up to 45 T. QH plateaus at filling factors ν=0,±1,±4 are discovered at magnetic fields B>20T, indicating the lifting of the fourfold degeneracy of the previously observed QH states at ν=±4(|n|+1/2), where n is the Landau-level index. In particular, the presence of the ν=0,±1 QH plateaus indicates that the Landau level at the charge neutral Dirac point splits into four sublevels, lifting sublattice and spin degeneracy. The QH effect at ν=±4 is investigated in a tilted magnetic field and can be attributed to lifting of the spin degeneracy of the n=1 Landau level.
Landau damping of magnetospherically reflected whistlers
NASA Technical Reports Server (NTRS)
Thorne, Richard M.; Horne, Richard B.
1994-01-01
Unducted VLF signals produced by lightning activity can form a population of magnetospherically reflected (MR) whistlers in the inner magnetosphere. It has been suggested recently that in the absence of significant attenuation such waves could merge into a broadband continuum with sufficient intensity to account for plasmaspheric hiss. To test this conjecture we have evaluated the path-integrated attenuation of MR whistlers along representative ray paths using the HOTRAY code. Using a realistic plasma distribution modeled on in-situ data, we find that the majority of MR waves experience significant damping after a few transits across the equator. This is primarily due to Landau resonance with suprathermal (0.1-1 keV) electrons. The attenuation is most pronounced for waves that propagate through the outer plasmasphere; this can readily account for the infrequent occurrence of multiple-hop MR waves for L greater than or equal to 3.5. Selected waves that originate at intermediate latitudes (15 deg is less than or equal to lambda is less than or equal to 35 deg) and whose ray paths are confined to the inner plasma- sphere may experience up to 10 magnetospheric reflections before substantial attentuation occurs. These waves should form the population of observed MR waves. Wave attenuation becomes more pronounced at higher frequencies; this can account for the absence of multiple-hop waves above 5 kHz. Weakly attenuated MR waves tend to migrate outward to the L shell, where their frequency is comparable to the equatorial lower hybrid frequency. The enhanced concentration of waves due to a merging of ray paths would produce a spectral feature that rises in frequency at lower L. This is quite distinct from the reported properties of plasmaspheric hiss, which maintains a constant frequency band throughout the entire plasmasphere. Furthermore, in the absence of mode conversion, waves below 500 Hz, which often form an important if not dominant part of the spectral properties
Update: Therapie der Necrobiosis lipoidica.
Peckruhn, Melanie; Tittelbach, Jörg; Elsner, Peter
2017-02-01
Die Necrobiosis lipoidica ist eine seltene granulomatöse Erkrankung von bisher unzureichend geklärter Ätiologie. Häufig stellt die bei Diabetikern gehäuft zu beobachtende und zur Ulzeration neigende Dermatose eine starke Belastung für die Patienten dar. Bezüglich der Therapie existieren aktuell keine deutschen oder europäischen Leitlinien. Gleichzeitig lässt sich unter der aktuellen Standardtherapie, der lokalen oder intraläsionalen Anwendung von Glukokortikoiden, nicht immer ein zufriedenstellendes Ansprechen beobachten. Daher wurde untersucht, ob seit dem Jahr 2000 publizierte Therapiemodalitäten das Therapiespektrum relevant und erfolgversprechend erweitern. Es erfolgte eine Betrachtung aller Arbeiten im oben genannten Zeitraum, bei denen mehr als ein Einzelfallbericht je Therapiemodalität publiziert wurde. Insgesamt wurden in einem systematischen Review die Daten von 16 verschiedenen, seit 2000 publizierten Therapieverfahren in 49 Publikationen analysiert. Im Ergebnis zeigte sich, dass die meisten Erfahrungen bezüglich der topischen PUVA-Therapie, der photodynamischen Therapie (PDT) und der systemischen Therapie mit Fumarsäureestern vorliegen. Allerdings ist auffällig, dass mit steigender Zahl der pro Behandlungsmodalität behandelten Patienten der Anteil der Patienten, bei denen eine Abheilung bzw. eine teilweise Abheilung berichtet wurde, sinkt. Wir interpretieren diese Beobachtung als Publikationsbias. Daher kann für keines der besprochenen Verfahren eine klare Empfehlung als Therapie der zweiten Wahl nach Versagen der lokalen bzw. intraläsionalen Steroidtherapie gegeben werden.
NASA Astrophysics Data System (ADS)
Uzunov, Ivan M.; Georgiev, Zhivko D.
2014-10-01
We study the dynamics of the localized pulsating solutions of generalized complex cubic- quintic Ginzburg-Landau equation (CCQGLE) in the presence of intrapulse Raman scattering (IRS). We present an approach for identification of periodic attractors of the generalized CCQGLE. At first using ansatz of the travelling wave, and fixing some relations between the material parameters, we derive the strongly nonlinear Lienard - Van der Pol equation for the amplitude of the nonlinear wave. Next, we apply the Melnikov method to this equation to analyze the possibility of existence of limit cycles. For a set of fixed material parameters we show the existence of limit cycle that arises around a closed phase trajectory of the unperturbed system and prove its stability.
Upper bounds for parabolic equations and the Landau equation
NASA Astrophysics Data System (ADS)
Silvestre, Luis
2017-02-01
We consider a parabolic equation in nondivergence form, defined in the full space [ 0 , ∞) ×Rd, with a power nonlinearity as the right-hand side. We obtain an upper bound for the solution in terms of a weighted control in Lp. This upper bound is applied to the homogeneous Landau equation with moderately soft potentials. We obtain an estimate in L∞ (Rd) for the solution of the Landau equation, for positive time, which depends only on the mass, energy and entropy of the initial data.
Electron acceleration by Landau resonance with whistler mode wave packets
NASA Technical Reports Server (NTRS)
Gurnett, D. A.; Reinleitner, L. A.
1983-01-01
Recent observations of electrostatic waves associated with whistler mode chorus emissions provide evidence that electrons are being trapped by Landau resonance interactions with the chorus. In this paper, the trapping, acceleration and escape of electrons in Landau resonance with a whistler mode wave packet are discussed. It is shown that acceleration can occur by both inhomogeneous and dispersive effects. The maximum energy gained is controlled by the points where trapping and escape occur. Large energy changes are possible if the frequency of the wave packet or the magnetic field strength increase between the trapping and escape points. Various trapping and escape mechanisms are discussed.
Landau damping in a multi-component dusty plasma
Zhang, Heng; Yang, Yang; Zhang, Jie; Hong, Xue-Ren; Lin, Mai-Mai; Qi, Xin E-mail: duanws@nwnu.edu.cn; Duan, Wen-Shan E-mail: duanws@nwnu.edu.cn; Yang, Lei
2014-11-15
Effect of the dust size distribution on the landau damping and the wave frequency is studied in the present paper. It is found that wave frequency increases as either the difference between the largest and the smallest dust size increases or the wave number increases. It seems that wave frequency is smaller for dusty plasma whose density of the smaller grains is larger than that of the larger ones, while it is larger in the opposite case. The effect of the dust size distribution can increase the Landau damping in the cases where the temperature of the dust grains is small enough or high enough.
W∞-ALGEBRA for Fermions in the Lowest Landau Level
NASA Astrophysics Data System (ADS)
Myung, Yun Soo
We derive the W∞-algebra directly from the cocycle (translational) transformation of fermions in the lowest Landau level. This happens whenever the translational symmetry is unbroken in the ground state. Under the cocycle transformations, the lowest Landau level condition and fermion number are preserved. In the droplet approximation, the algebra of this system is reduced to the classical w∞-algebra (area-preserving deformations) and is related to condensed matter physics. This describes the edge modes of the fractional quantum Hall effect.
Discretisation errors in Landau gauge on the lattice
Frederic D.R. Bonnet; Patrick O. Bowman; Derek B. Leinweber; Anthony G. Williams; David G. Richards
1999-05-01
Lattice discretization errors in the Landau gauge condition are examined. An improved gauge fixing algorithm in which O(a{sup 2}) errors are removed is presented. O(a{sup 2}) improvement of the gauge fixing condition improves comparison with continuum Landau gauge in two ways: (1) through the elimination of O(a{sup 2}) errors and (2) through a secondary effect of reducing the size of higher-order errors. These results emphasize the importance of implementing an improved gauge fixing condition.
Many body generalization of the Landau-Zener problem.
Altland, Alexander; Gurarie, V
2008-02-15
We formulate and approximately solve a specific many body generalization of the Landau-Zener problem. Unlike with the single particle Landau-Zener problem, our system does not abide in the adiabatic ground state, even at very slow driving rates. The structure of the theory suggests that this finding reflects a more general phenomenon in the physics of adiabatically driven many particle systems. Our solution can be used to understand, for example, the behavior of two-level systems coupled to an electromagnetic field, as realized in cavity QED experiments.
Zum Stellenwert der Unterdruck-Instillationstherapie in der Dermatologie.
Müller, Cornelia Sigrid Lissi; Burgard, Barbara; Zimmerman, Monika; Vogt, Thomas; Pföhler, Claudia
2016-08-01
Die Methoden zur Behandlung akuter und chronischer Wunden unterliegen einer steten Weiterentwicklung, Reevaluierung und Anwendung innovativer Therapieformen. Die Vakuumtherapie zur Wundbehandlung gehört zu den etablierten Behandlungsmodalitäten. Ein innovatives Verfahren kombiniert die Vakuumtherapie mit der automatisierten, kontrollierten Zufuhr und Drainage wirkstoffhaltiger Lösungen zur topischen Wundbehandlung im Wundbett und auch wirkstofffrei durch Instillation physiologischer Kochsalzlösung (Unterdruck-Instillationstherapie). Hierdurch können die Effekte der konventionellen Vakuumtherapie mit denen der lokalen Antisepsis kombiniert werden. Hierdurch kommt es zu einer Reduktion der Wundfläche, einer Induktion von Granulationsgewebe sowie einer Reduktion der Keimbesiedelung der Wunden. Bisher publizierte Studien konzentrieren sich auf die Anwendung dieses Therapieverfahrens zur Behandlung orthopädisch-chirurgischer Krankheiten. Die Datenlage bezüglich der Vakuum-Instillationstherapie in der Dermatochirurgie beschränkt sich derzeit auf Fallberichte und Einzelfallerfahrungen. Randomisierte, prospektive Studien zum Vergleich der Vakuum-Instillationstherapie zur Behandlung dermatologischer Krankheitsbilder existieren bislang nicht. Ziele des vorliegenden Artikels sind die Vorstellung der Vakuumtherapie mit Instillation einschließlich ihres Wirkprinzips, deren mögliche Komplikationen, die Diskussion erdenklicher Kontraindikationen sowie eine Übersicht über die aktuell verfügbare Datenlage. Zusammenfassend scheint sich die Evidenz zu verdichten, dass mittels Unterdruck-Instillationstherapie sowohl einfache als auch komplizierte Wunden effizient behandelt werden können, was sich in einer deutlichen Beschleunigung der Wundgranulation mit konsekutiv früher möglichem Defektverschluss äußert.
Landau damping effects on solar wind fast streams
NASA Technical Reports Server (NTRS)
Dangelo, N.; Joyce, G.; Pesses, M. E.
1979-01-01
Recent measurements by the Pioneer 10 and Helios 1 spacecraft show that the leading edge of a corotating structure spreads as it moves from 0.3 AU to the orbit of the earth and steepens again farther out. By including Landau damping effects in the dynamical behavior of the streams, the above qualitative features can be accounted for.
Language Profile of a Child with Landau-Kleffner Syndrome
ERIC Educational Resources Information Center
Shivashankar, N.; Priya, G. Vishnu; Raksha, H. R.; Ratnavalli, E. R.
2010-01-01
We report here a longitudinal study of a 3.8 year old female child diagnosed as having Landau Kleffner Syndrome (LKS). Speech-language analysis was carried out over a two-year period while the child was on medical treatment regime. The result of the language evaluation suggests that this child demonstrated exacerbation and remission in accordance…
What Every Educator Should Know about Landau-Kleffner Syndrome.
ERIC Educational Resources Information Center
Chapman, Tammy; Stormont, Melissa; McCathren, Rebecca
1998-01-01
Landau-Kleffner syndrome is characterized by difficulty in receptive or expressive language, abnormal electroencephalograms, and seizures. This article describes the primary and secondary characteristics of children with this syndrome and offers educators a framework for intervention techniques. These include using predictable language, creating…
A Simple Approach to the Landau-Zener Formula
ERIC Educational Resources Information Center
Vutha, Amar C.
2010-01-01
The Landau-Zener formula provides the probability of non-adiabatic transitions occurring when two energy levels are swept through an avoided crossing. The formula is derived here in a simple calculation that emphasizes the physics responsible for non-adiabatic population transfer. (Contains 2 figures.)
Polarons in π-Conjugated Polymers: Anderson or Landau?
Barford, William; Marcus, Max; Tozer, Oliver Robert
2016-02-04
Using both analytical expressions and the density matrix renormalization group method, we study the fully quantized disordered Holstein model to investigate the localization of charges and excitons by vibrational or torsional modes-i.e., the formation of polarons-in conformationally disordered π-conjugated polymers. We identify two distinct mechanisms for polaron formation, namely Anderson localization via disorder (causing the formation of Anderson polarons) and self-localization by self-trapping via normal modes (causing the formation of Landau polarons). We identify the regimes where either description is more valid. The key distinction between Anderson and Landau polarons is that for the latter the particle wave function is a strong function of the normal coordinates, and hence the "vertical" and "relaxed" wave functions are different. This has theoretical and experimental consequences for Landau polarons. Theoretically, it means that the Condon approximation is not valid, and so care needs to be taken when evaluating transition rates. Experimentally, it means that the self-localization of the particle as a consequence of its coupling to the normal coordinates may lead to experimental observables, e.g., ultrafast fluorescence depolarization. We apply these ideas to poly(p-phenylenevinylene). We show that the high frequency C-C bond oscillation only causes Landau polarons for a very narrow parameter regime; generally we expect disorder to dominate and Anderson polarons to be a more applicable description. Similarly, for the low frequency torsional fluctuations we show that Anderson polarons are expected for realistic parameters.
Ginzburg-Landau-type theory of nonpolarized spin superconductivity
NASA Astrophysics Data System (ADS)
Lv, Peng; Bao, Zhi-qiang; Guo, Ai-Min; Xie, X. C.; Sun, Qing-Feng
2017-01-01
Since the concept of spin superconductor was proposed, all the related studies concentrate on the spin-polarized case. Here, we generalize the study to the spin-non-polarized case. The free energy of nonpolarized spin superconductor is obtained, and Ginzburg-Landau-type equations are derived by using the variational method. These Ginzburg-Landau-type equations can be reduced to the spin-polarized case when the spin direction is fixed. Moreover, the expressions of super linear and angular spin currents inside the superconductor are derived. We demonstrate that the electric field induced by the super spin current is equal to the one induced by an equivalent charge obtained from the second Ginzburg-Landau-type equation, which shows self-consistency of our theory. By applying these Ginzburg-Landau-type equations, the effect of electric field on the superconductor is also studied. These results will help us get a better understanding of the spin superconductor and related topics such as the Bose-Einstein condensate of magnons and spin superfluidity.
Landau-Zener transitions in an open multilevel quantum system
NASA Astrophysics Data System (ADS)
Ashhab, S.
2016-10-01
We consider the Landau-Zener problem for a multilevel quantum system that is coupled to an external environment. In particular, we consider a number of cases of three-level systems coupled to a harmonic oscillator that represents the external environment. We find that, similar to the case of the Landau-Zener problem with a two-level system, when the quantum system and the environment are both initially in their ground states the probability that the system remains in the same quantum state is not affected by the coupling to the environment. The final occupation probabilities of the other states are well described by a common general principle: the coupling to the environment turns each Landau-Zener transition process in the closed system into a sequence of smaller transitions in the combined Hilbert space of the system and environment, and this sequence of transitions lasts a total duration that increases with increasing system-environment coupling strength. These results provide an intuitive understanding of Landau-Zener transitions in open multilevel quantum systems.
All-optical Landau-Zener tunneling in waveguide arrays.
Fratalocchi, Andrea; Assanto, Gaetano
2006-03-06
We investigate Landau-Zener all-optical tunneling in a voltage-controlled waveguide array realized in undoped nematic liquid crystals. From the material governing equations we derive the original Zener model and demonstrate a novel approach to Floquet-band tunneling.
Fast quantum noise in the Landau-Zener transition
Pokrovsky, V. L.; Sun, D.
2007-07-01
We show by direct calculation starting from a microscopic model that the two-state system with time-dependent energy levels in the presence of fast quantum noise obeys the master equation. The solution of master equation is found analytically and analyzed in a broad range of parameters. The fast transverse noise affects the transition probability during much longer time (the accumulation time) than the longitudinal one. The action of the fast longitudinal noise is restricted by the shorter Landau-Zener time, the same as in the regular Landau-Zener process. The large ratio of time scales allows solving the Landau-Zener problem with longitudinal noise only, and then solving the same problem with the transverse noise only and matching the two solutions. The correlation of the longitudinal and transverse noise renormalizes the Landau-Zener transition matrix element and can strongly enhance the survival probability, whereas the transverse noise always reduces it. If the noise is fast, its intensity at which the multiquantum processes become essential corresponds to a deeply adiabatic regime. We briefly discuss possible applications of the general theory to the molecular magnets.
Nonlinear Landau-Zener tunneling in coupled waveguide arrays
Khomeriki, Ramaz
2010-07-15
The possibility of direct observation of the nonlinear Landau-Zener tunneling effect with a device consisting of two waveguide arrays connected to a tilted reduced refractive index barrier is discussed. Numerical simulations on this realistic setup are interpreted via a simplified double-well system and different asymmetric tunneling scenarios are predicted varying just the injected beam intensity.
Grundlagen der Organisationsgestaltung
NASA Astrophysics Data System (ADS)
Spath, Dieter; Koch, Steffen
In diesem Kapitel werden Grundlagen der Organisationsgestaltung dargestellt. Es scheint nahe liegend, diese Inhalte wie in einem Lehrbuch aufzubereiten. Schließlich handelt es sich um grundlegende Inhalte. Die Neufassung dieses Abschnitts ist aber stärker für Verantwortliche in Unternehmen geschrieben und weniger wissenschaftlich geprägt. Das "Lehrbuchwissen“ wird daher bewusst knapp gehalten. Das betrifft z.B. die Klärung des Organisationsbegriffes und die Fragen nach den Zielsetzungen und den Gestaltungsbereichen von Organisation. Stattdessen widmet sich das Kapitel ausführlicher den Fragen, ob es Trends in der Organisationsgestaltung gibt, welche wichtigen Einflussgrößen existieren und welche übergeordneten und beständigen Leitlinien es gibt.
Nanoscopy of Surface-Induced van der Waals-Zeeman Transitions
Hamamda, M.; Grucker, J.; Dutier, G.; Perales, F.; Baudon, J.; Ducloy, M.; Bocvarski, V.
2008-10-22
van der Waals transitions among magnetic sub-levels of a metastable rare gas atom passing near a surface immersed in a magnetic field, are described. Related transition amplitudes are calculated using both the sudden and the Landau-Zener approximations. Experimental data for Ne*({sup 3}P{sub 2}) atoms traversing a copper grating are presented. For a pair of surfaces (e.g. the opposite edges of a slit) and a sufficiently large coherence width, Fresnel's biprism interference fringes are obtained. From this interference pattern, detailed information about the transition amplitude at a sub-nanometric scale can be derived. The effect of gravity on this pattern is examined.
NASA Astrophysics Data System (ADS)
Müller, Ute; Lücker, Volker
Die Unversehrtheit von Leib und Leben ist das größte Rechtsgut unserer Gesellschaft. Dies macht schon das Grundgesetz in Art. 2 Abs. Satz 1 GG deutlich. Die Öffentlichkeit zeigt daher größtes Interesse an Produkten, welche der Gesundheit dienen und Leben retten oder erhalten. Dieses Interesse gilt einerseits der Entwicklung und Bereitstellung leistungsfähiger Medizinprodukte, andererseits zielt es auf deren Sicherheit. Um vor allem letztere zu gewährleisten, nimmt der Gesetzgeber alle Beteiligten in die Pflicht, die auftretenden Risiken auf das geringstmögliche Maß zu begrenzen. Dies spiegelt sich in den rechtlichen Vorgaben ebenso wie in den Haftungsfolgen, die bei Verletzung dieser Vorgaben greifen, wieder. Diese Folgen können dementsprechend gravierend ausfallen, von Geldstrafen bis zu Freiheitsstrafen, von Bußgeldzahlungen bis zum Schadenersatzansprüchen, die schnell ein wirtschaftliches Aus bedeuten können. Den Beteiligten, allen voran den Herstellern, muss deshalb daran gelegen sein, nicht nur die Produkte, sondern auch deren Sicherheit stetig weiter zu entwickeln.
Evaluation der zentralen TUM-Lernplattform
NASA Astrophysics Data System (ADS)
Schulze, Elvira; Baume, Matthias; Graf, Stephan; Gergintchev, Ivan
Die Notwendigkeit der Qualitätssicherung und -kontrolle für innovative universitäre Lehr-/Lernszenarien ist in der Praxis unbestritten. Die Wirksamkeit der Einführung der zentralen Lernplattform CLIX Campus der imc AG an der TUM wurde mittels quantitativer und qualitativer Evaluation überprüft. Als statistische Bewertungsgrundlage wurde der Erreichungsgrad bestimmter Projektziele herangezogen. Aufbauend auf den theoretischen Grundlagen der Evaluation von Bildungsangeboten gibt diese Studie Aufschluss über die Ergebnisse der Datenerhebungen sowie die Einschätzung der Plattform aus Nutzersicht und belegt die wesentliche Bedeutung der durchgängigen IT-Infrastruktur und speziell der einheitlichen Verfügbarkeit der eLearning Angebote.
On the nature of the Landau-Levich transition
NASA Astrophysics Data System (ADS)
Delon, Giles
2005-11-01
A solid plate can be wetted dynamically by a non-wetting liquid when withdrawn from a bath above a threshold velocity. Landau and Levich described long ago the scaling relation giving the thickness of the entrained film. However the nature of the transition from a static meniscus to the Landau-Levich remained unclear. We demonstrate experimentally and theoretically that liquid entrainment occurs due to the nucleation of a solitary wave, well below the critical point corresponding to the disappearance of stationary meniscus solutions. It has been suggested by Golestanian and Raphael that the dynamically forced wetting transition is critical with diverging time scales. This critical behavior is actually avoided by the development of the remarkable ridge-like front that does not trivially match to the liquid reservoir. The macroscopic properties of this ridge are governed by stress balance at molecular scale, and provide a novel, sensitive probe to unravel the singularity at the contact line.
Fractional quantum Hall effect in the absence of Landau levels.
Sheng, D N; Gu, Zheng-Cheng; Sun, Kai; Sheng, L
2011-07-12
It is well known that the topological phenomena with fractional excitations, the fractional quantum Hall effect, will emerge when electrons move in Landau levels. Here we show the theoretical discovery of the fractional quantum Hall effect in the absence of Landau levels in an interacting fermion model. The non-interacting part of our Hamiltonian is the recently proposed topologically non-trivial flat-band model on a checkerboard lattice. In the presence of nearest-neighbouring repulsion, we find that at 1/3 filling, the Fermi-liquid state is unstable towards the fractional quantum Hall effect. At 1/5 filling, however, a next-nearest-neighbouring repulsion is needed for the occurrence of the 1/5 fractional quantum Hall effect when nearest-neighbouring repulsion is not too strong. We demonstrate the characteristic features of these novel states and determine the corresponding phase diagram.
Landau criterion for an anisotropic Bose-Einstein condensate
NASA Astrophysics Data System (ADS)
Yu, Zeng-Qiang
2017-03-01
In this work we discuss the Landau criterion for anisotropic superfluidity. To this end we consider a pointlike impurity moving in a uniform Bose-Einstein condensate with either interparticle dipole-dipole interaction or Raman-induced spin-orbit coupling. In both cases we find that the Landau critical velocity vc is generally smaller than the sound velocity in the moving direction. Beyond vc, the energy dissipation rate is explicitly calculated via a perturbation approach. In the plane-wave phase of a spin-orbit-coupled Bose gas, the dissipationless motion is suppressed by the Raman coupling even in the direction orthogonal to the recoil momentum. Our predictions can be tested in the experiments with ultracold atoms.
Gravitational Landau damping for an isotropic cluster of stars
NASA Technical Reports Server (NTRS)
Habib, Salman; Kandrup, Henry E.; Yip, Ping F.
1986-01-01
The problem of ascertaining the dynamical stability and the existence of Landau damping in static, isotropic 'collisionless' star clusters is addressed. The second-order formalism of Kandrup and Sygnet (1985) is applied to a homogeneous and isotropic plasma, demonstrating formally that the unperturbed configuration will always be stable and that the modes must be purely oscillatory. The form of these modes is explicitly examined, culminating in an analytic expression for the time evolution of the density induced by an initial perturbation. It is shown how these considerations can be adapted trivially to localized, nonradial disturbances of a self-gravitating system of stars. The possible existence of gravitational Landau damping for more generic perturbations is discussed.
Ensemble inequivalence: Landau theory and the ABC model
NASA Astrophysics Data System (ADS)
Cohen, O.; Mukamel, D.
2012-12-01
It is well known that systems with long-range interactions may exhibit different phase diagrams when studied within two different ensembles. In many of the previously studied examples of ensemble inequivalence, the phase diagrams differ only when the transition in one of the ensembles is first order. By contrast, in a recent study of a generalized ABC model, the canonical and grand-canonical ensembles of the model were shown to differ even when they both exhibit a continuous transition. Here we show that the order of the transition where ensemble inequivalence may occur is related to the symmetry properties of the order parameter associated with the transition. This is done by analyzing the Landau expansion of a generic model with long-range interactions. The conclusions drawn from the generic analysis are demonstrated for the ABC model by explicit calculation of its Landau expansion.
Wang-Landau sampling with logarithmic windows for continuous models.
Xie, Y L; Chu, P; Wang, Y L; Chen, J P; Yan, Z B; Liu, J-M
2014-01-01
We present a modified Wang-Landau sampling (MWLS) for continuous statistical models by partitioning the energy space into a set of windows with logarithmically shrinking width. To demonstrate its necessity and advantages, we apply this sampling to several continuous models, including the two-dimensional square XY spin model, triangular J1-J2 spin model, and Lennard-Jones cluster model. Given a finite number of bins for partitioning the energy space, the conventional Wang-Landau sampling may not generate sufficiently accurate density of states (DOS) around the energy boundaries. However, it is demonstrated that much more accurate DOS can be obtained by this MWLS, and thus a precise evaluation of the thermodynamic behaviors of the continuous models at extreme low temperature (kBT<0.1) becomes accessible. The present algorithm also allows efficient computation besides the highly reliable data sampling.
Comments on Landau damping due to synchrotron frequency spread
Ng, K.Y.; /Fermilab
2005-01-01
An inductive/space-charge impedance shifts the synchrotron frequency downwards above/below transition, but it is often said that the coherent synchrotron frequency of the bunch is not shifted in the rigid-dipole mode. On the other hand, the incoherent synchrotron frequency due to the sinusoidal rf always spreads in the downward direction. This spread will therefore not be able to cover the coherent synchrotron frequency, implying that there will not be any Landau damping no matter how large the frequency spread is. By studying the dispersion relation, it is shown that the above argument is incorrect, and there will be Landau damping if there is sufficient frequency spread. The main reason is that the coherent frequency of the rigid-dipole mode will no longer remain unshifted in the presence of a synchrotron frequency spread.
Effects of Landau level mixing on the fractional quantum Hall effect in monolayer graphene.
Peterson, Michael R; Nayak, Chetan
2014-08-22
We report results of exact diagonalization studies of the spin- and valley-polarized fractional quantum Hall effect in the N = 0 and N = 1 Landau levels in graphene. We use an effective model that incorporates Landau level mixing to lowest order in the parameter κ = ((e(2)/εℓ)/(ħv(F)/ℓ)) = (e(2)/εv(F)ħ), which is magnetic field independent and can only be varied through the choice of substrate. We find Landau level mixing effects are negligible in the N = 0 Landau level for κ ≲ 2. In fact, the lowest Landau level projected Coulomb Hamiltonian is a better approximation to the real Hamiltonian for graphene than it is for semiconductor based quantum wells. Consequently, the principal fractional quantum Hall states are expected in the N = 0 Landau level over this range of κ. In the N = 1 Landau level, fractional quantum Hall states are expected for a smaller range of κ and Landau level mixing strongly breaks particle-hole symmetry, producing qualitatively different results compared to the N = 0 Landau level. At half filling of the N = 1 Landau level, we predict the anti-Pfaffian state will occur for κ ∼ 0.25-0.75.
NASA Astrophysics Data System (ADS)
Esquivel-Sirvent, Raul; Schatz, George
2014-03-01
The theory of generalized van der Waals forces by Lifshtz when applied to optically anisotropic media predicts the existence of a torque. In this work we present a theoretical calculation of the van der Waals torque for two systems. First we consider two isotropic parallel plates where the anisotropy is induced using an external magnetic field. The anisotropy will in turn induce a torque. As a case study we consider III-IV semiconductors such as InSb that can support magneto plasmons. The calculations of the torque are done in the Voigt configuration, that occurs when the magnetic field is parallel to the surface of the slabs. The change in the dielectric function as the magnetic field increases has the effect of decreasing the van der Waals force and increasing the torque. Thus, the external magnetic field is used to tune both the force and torque. The second example we present is the use of the torque in the non retarded regime to align arrays of nano particle slabs. The torque is calculated within Barash and Ginzburg formalism in the nonretarded limit, and is quantified by the introduction of a Hamaker torque constant. Calculations are conducted between anisotropic slabs of materials including BaTiO3 and arrays of Ag nano particles. Depending on the shape and arrangement of the Ag nano particles the effective dielectric function of the array can be tuned as to make it more or less anisotropic. We show how this torque can be used in self assembly of arrays of nano particles. ref. R. Esquivel-Sirvent, G. C. Schatz, Phys. Chem C, 117, 5492 (2013). partial support from DGAPA-UNAM.
Sideband growth in nonlinear Landau wave-particle interaction.
NASA Technical Reports Server (NTRS)
Brinca, A. L.
1972-01-01
The distortion of the electron velocity distribution caused by a large amplitude Landau wave is determined analytically for the initial-value problem. The resulting stability of electrostatic perturbations impressed on the evolving plasma is studied. Narrow sidebands of the applied frequency experience consecutive growths of large magnitude during the early stages of the nonlinear wave-particle interaction. The significance of the derived results to both wave propagation experiments and triggered VLF emissions in the magnetosphere is discussed.
Generic, hierarchical framework for massively parallel Wang-Landau sampling.
Vogel, Thomas; Li, Ying Wai; Wüst, Thomas; Landau, David P
2013-05-24
We introduce a parallel Wang-Landau method based on the replica-exchange framework for Monte Carlo simulations. To demonstrate its advantages and general applicability for simulations of complex systems, we apply it to different spin models including spin glasses, the Ising model, and the Potts model, lattice protein adsorption, and the self-assembly process in amphiphilic solutions. Without loss of accuracy, the method gives significant speed-up and potentially scales up to petaflop machines.
Generic, Hierarchical Framework for Massively Parallel Wang-Landau Sampling
NASA Astrophysics Data System (ADS)
Vogel, Thomas; Li, Ying Wai; Wüst, Thomas; Landau, David P.
2013-05-01
We introduce a parallel Wang-Landau method based on the replica-exchange framework for Monte Carlo simulations. To demonstrate its advantages and general applicability for simulations of complex systems, we apply it to different spin models including spin glasses, the Ising model, and the Potts model, lattice protein adsorption, and the self-assembly process in amphiphilic solutions. Without loss of accuracy, the method gives significant speed-up and potentially scales up to petaflop machines.
Landau damping of geodesic acoustic mode in toroidally rotating tokamaks
Ren, Haijun; Cao, Jintao
2015-06-15
Geodesic acoustic mode (GAM) is analyzed by using modified gyro-kinetic (MGK) equation applicable to low-frequency microinstabilities in a rotating axisymmetric plasma. Dispersion relation of GAM in the presence of arbitrary toroidal Mach number is analytically derived. The effects of toroidal rotation on the GAM frequency and damping rate do not depend on the orientation of equilibrium flow. It is shown that the toroidal Mach number M increases the GAM frequency and dramatically decreases the Landau damping rate.
Lattice Boltzmann model for the complex Ginzburg-Landau equation.
Zhang, Jianying; Yan, Guangwu
2010-06-01
A lattice Boltzmann model with complex distribution function for the complex Ginzburg-Landau equation (CGLE) is proposed. By using multiscale technique and the Chapman-Enskog expansion on complex variables, we obtain a series of complex partial differential equations. Then, complex equilibrium distribution function and its complex moments are obtained. Based on this model, the rotation and oscillation properties of stable spiral waves and the breaking-up behavior of unstable spiral waves in CGLE are investigated in detail.
Analytical solutions of Landau (1+1)-dimensional hydrodynamics
Wong, Cheuk-Yin; Sen, Abhisek; Gerhard, Jochen; ...
2014-12-17
To help guide our intuition, summarize important features, and point out essential elements, we review the analytical solutions of Landau (1+1)-dimensional hydrodynamics and exhibit the full evolution of the dynamics from the very beginning to subsequent times. Special emphasis is placed on the matching and the interplay between the Khalatnikov solution and the Riemann simple wave solution at the earliest times and in the edge regions at later times.
A generic, hierarchical framework for massively parallel Wang Landau sampling
Vogel, Thomas; Li, Ying Wai; Wuest, Thomas; Landau, David P
2013-01-01
We introduce a parallel Wang Landau method based on the replica-exchange framework for Monte Carlo simulations. To demonstrate its advantages and general applicability for simulations of com- plex systems, we apply it to the self-assembly process in amphiphilic solutions and to lattice protein adsorption. Without loss of accuracy, the method gives significant speed-up on small architectures like multi-core processors, and should be beneficial for petaflop machines.
Enhancement of macroscopic quantum tunneling by Landau-Zener transitions.
Ankerhold, Joachim; Grabert, Hermann
2003-07-04
Motivated by recent realizations of qubits with a readout by macroscopic quantum tunneling in a Josephson junction, we study the problem of barrier penetration in the presence of coupling to a spin-1 / 2 system. It is shown that, when the diabatic potentials for fixed spin intersect in the barrier region, Landau-Zener transitions lead to an enhancement of the tunneling rate. The effect of these spin flips in imaginary time is in qualitative agreement with experimental observations.
Constraints on scattering amplitudes in multistate Landau-Zener theory
NASA Astrophysics Data System (ADS)
Sinitsyn, Nikolai A.; Lin, Jeffmin; Chernyak, Vladimir Y.
2017-01-01
We derive a set of constraints, which we will call hierarchy constraints, on scattering amplitudes of an arbitrary multistate Landau-Zener model (MLZM). The presence of additional symmetries can transform such constraints into nontrivial relations between elements of the transition probability matrix. This observation can be used to derive complete solutions of some MLZMs or, for models that cannot be solved completely, to reduce the number of independent elements of the transition probability matrix.
Constraints on scattering amplitudes in multistate Landau-Zener theory
Sinitsyn, Nikolai A.; Lin, Jeffmin; Chernyak, Vladimir Y.
2017-01-30
Here, we derive a set of constraints, which we will call hierarchy constraints, on scattering amplitudes of an arbitrary multistate Landau-Zener model (MLZM). The presence of additional symmetries can transform such constraints into nontrivial relations between elements of the transition probability matrix. This observation can be used to derive complete solutions of some MLZMs or, for models that cannot be solved completely, to reduce the number of independent elements of the transition probability matrix.
Quantenphysikalischer Ursprung der Eichidee
NASA Astrophysics Data System (ADS)
Bopp, Fritz
Betrachtet man die Quantenphysik als Zusammenspiel von elementaren Erzeugungs- und Vernichtungsprozessen, so sind Eichfeldtheorien nicht nur möglich, sondern auch notwendig. Die komplex konjugierten Phasenfaktoren jedes Paares von Erzeugungs- und Vernichtungsoperatoren sind nämlich. willkürlich wählbar. Darum müssen Quantenfeldtheorien vollständig phaseninvariant sein. Das ist ohne Eichfelder nicht möglich.Dem steht im Wege, daß die Diracgleichung nicht einmal global vollständig phaseninvariant ist. Multipliziert man nämlich die Komponenten der Erzeugungs- und Vernichtungsoperatoren mit verschiedenen konstanten Phasenfaktoren, so ändern sich die Diracmatrizen. Nur die Diracschen Vertauschungsrelationen bleiben invariant. Doch sind die Diracgleichungen vor und nach der Transformation physikalisch äquivalent. Man kann also sagen: Systeme freier Fermionen werden erst durch die Klasse aller äquivalenten Diracgleichungen vollständig dargestellt.Da die Diracschen Vertauschungsrelationen gegen beliebige unitäre Transformationen invariant sind, ist die Klasse äquivalenter Diracgleichungen U 4-invariant. Unitäre Diagonalmatrizen liefern willkürliche Phasentransformationen der Spinorkomponenten, so daß die zur Gruppe U 4 gehörigen Eichfelder zu eine allgemein phaseninvarianten Theorie führen. Sie ist so eng mit der QED verwandt, daß wir von einer erweiterten Quantenelektrodynamik, EQE, sprechen können.Hier soll nur gezeigt werden, daß die EQE existiert. Dabei liefert die invariante Untergruppe U 1 von U 4 die QED. Die komplementäre Untergruppe SU 4 umschließt vier Untergruppen SU 3, drei Untergruppen O 4 und sechs Untergruppen SU 2. Letztere könnten den drei Paaren von Quarks und den drei Paaren von Leptonen entsprechen, wobei sich die Quarkpaare zu einer Gruppe SU 3 zusammenschließen. Mehr als zweimal drei Paare von elementaren Fermionen gibt es in der EQE nicht. Sie wird zwar kaum mit der vereinigten QED und QCD identisch sein. Doch sollte sie
The half-filled Landau level and topological insulator surfaces
NASA Astrophysics Data System (ADS)
Senthil, T.
The metallic state of the half-filled Landau level - described originally in pioneering work by Halperin , Lee, and Read as a liquid of composite fermions - was proposed recently by Son to be described by a particle-hole symmetric effective field theory distinct from that in the prior literature. This talk will develop a simple picture of the particle-hole symmetric composite fermion through a modification of older pictures as electrically neutral ``dipolar'' particles. This picture, and the proposed particle-hole symmetric theory, will be further substantiated through a recently developed deep connection between the half-filled Landau level and correlated surface states of certain three dimensional topological insulators. The phenomenology of composite fermi liquids (with or without particle-hole symmetry) will be revisited. It will be shown that their heat/electrical transport dramatically violates the conventional Wiedemann-Franz law but satisfies a modified one. References: 1. Chong Wang and T. Senthil, ``Half-filled Landau Level, Topological Insulator Surfaces, and Three Dimensional Quantum Spin Liquids,'' cond-mat arXiv:1507.08290 (2015).
Ginzburg-Landau-type theory of spin superconductivity.
Bao, Zhi-qiang; Xie, X C; Sun, Qing-feng
2013-01-01
Spin superconductivity is a recently proposed analogue of conventional charge superconductivity, in which spin currents flow without dissipation but charge currents do not. Here we derive a universal framework for describing the properties of a spin superconductor along similar lines to the Ginzburg-Landau equations that describe conventional superconductors, and show that the second of these Ginzburg-Landau-type equations is equivalent to a generalized London equation. Just as the GL equations enabled researchers to explore the behaviour of charge superconductors, our Ginzburg-Landau-type equations enable us to make a number of non-trivial predictions about the potential behaviour of putative spin superconductor. They enable us to calculate the super spin current in a spin superconductor under a uniform electric field or that induced by a thin conducting wire. Moreover, they allow us to predict the emergence of new phenomena, including the spin-current Josephson effect in which a time-independent magnetic field induces a time-dependent spin current.
Avoidance of a Landau pole by flat contributions in QED
Klaczynski, Lutz; Kreimer, Dirk
2014-05-15
We consider massless Quantum Electrodynamics in the momentum scheme and carry forward an approach based on Dyson–Schwinger equations to approximate both the β-function and the renormalized photon self-energy (Yeats, 2011). Starting from the Callan–Symanzik equation, we derive a renormalization group (RG) recursion identity which implies a non-linear ODE for the anomalous dimension and extract a sufficient but not necessary criterion for the existence of a Landau pole. This criterion implies a necessary condition for QED to have no such pole. Solving the differential equation exactly for a toy model case, we integrate the corresponding RG equation for the running coupling and find that even though the β-function entails a Landau pole it exhibits a flat contribution capable of decreasing its growth, in other cases possibly to the extent that such a pole is avoided altogether. Finally, by applying the recursion identity, we compute the photon propagator and investigate the effect of flat contributions on both spacelike and timelike photons. -- Highlights: •We present an approach to approximate both the β-function and the photon self-energy. •We find a sufficient criterion for the self-energy to entail the existence of a Landau pole. •We study non-perturbative ‘flat’ contributions that emerge within the context of our approach. •We discuss a toy model and how it is affected by flat contributions.
A Landau fluid model for dissipative trapped electron modes
Hedrick, C.L.; Leboeuf, J.N.; Sidikman, K.L.
1995-09-01
A Landau fluid model for dissipative trapped electron modes is developed which focuses on an improved description of the ion dynamics. The model is simple enough to allow nonlinear calculations with many harmonics for the times necessary to reach saturation. The model is motivated by a discussion that starts with the gyro-kinetic equation and emphasizes the importance of simultaneously including particular features of magnetic drift resonance, shear, and Landau effects. To ensure that these features are simultaneously incorporated in a Landau fluid model with only two evolution equations, a new approach to determining the closure coefficients is employed. The effect of this technique is to reduce the matching of fluid and kinetic responses to a single variable, rather than two, and to allow focusing on essential features of the fluctuations in question, rather than features that are only important for other types of fluctuations. Radially resolved nonlinear calculations of this model, advanced in time to reach saturation, are presented to partially illustrate its intended use. These calculations have a large number of poloidal and toroidal harmonics to represent the nonlinear dynamics in a converged steady state which includes cascading of energy to both short and long wavelengths.
Classical analog of quasilinear Landau-Zener tunneling.
Kovaleva, Agnessa; Manevitch, Leonid I
2012-01-01
In this paper we develop an analytical framework to study the effect of nonlinearity on irreversible energy transfer in a system of two weakly coupled oscillators with time-dependent parameters, with special attention to an analogy between classical energy transfer and nonadiabatic quantum tunneling. For preciseness, we suppose that a linear oscillator with constant parameters is excited by an initial impulse but a coupled quasilinear oscillator with slowly varying parameters is initially at rest. It is shown that the equations of the slow passage through resonance in this system are identical to quasilinear equations of nonadiabatic Landau-Zener tunneling. Due to revealed equivalence, a recently found analogy between irreversible energy transfer in a classical linear system and conventional linear Landau-Zener tunneling can be extended to quasilinear systems. An explicit analytical solution of the quasilinear problem is found with the help of an iteration procedure, wherein the linear solution is chosen as an initial approximation. Correctness of the constructed approximations is confirmed by numerical simulations. The results presented in this paper, in addition to providing an analytical framework for understanding the transient dynamics of coupled oscillators, suggest an approximate procedure for solving the quasilinear Landau-Zener equations with arbitrary initial conditions over a finite time interval.
NASA Astrophysics Data System (ADS)
Aichelburg, P. C.
Contents: Einleitung(P. C. Aichelburg). 1. Über Zeit, Bewegung und Veränderung (Aristoteles). 2. Ewigkeit und Zeit (Plotin). 3. Was ist die Zeit? (Augustinus). 4. Von der Zeit (Immanuel Kant). 5. Newtons Ansichten über Zeit, Raum und Bewegung (Ernst Mach). 6. Über die mechanische Erklärung irreversibler Vorgänge (Ludwig Boltzmann). 7. Das Maß der Zeit (Henri Poincaré). 8. Dauer und Intuition (Henri Bergson). 9. Die Geschichte des Unendlichkeitsproblems (Bertrand Russell). 10. Raum und Zeit (Hermann Minkowski). 11. Der Unterschied von Zeit und Raum (Hans Reichenbach). 12. Newtonscher und Bergsonscher Zeitbegriff (Norbert Wiener). 13. Die Bildung des Zeitbegriffs beim Kinde (JeanPiaget).14. Eine Bemerkung über die Beziehungen zwischen Relativitätstheorie und der idealistischen Philosophie (Kurt Gödel). 15. Der zweite Hauptsatz und der Unterschied von Vergangenheit und Zukunft (Carl Friedrich v. Weizsäcker). 16. Zeit als physikalischer Begriff (Friedrich Hund). 17. Zeitmessung und Zeitbegriff in der Astronomie (Otto Heckmann). 18. Kann die Zeit rückwärts gehen? (Martin Gardner). 19. Zeit und Zeiten (Ilya Prigogine, Isabelle Stengers). 20. Zeit als dynamische Größe in der Relativitätstheorie (P. C. Aichelburg).
Entwicklung und Formulierung der Unternehmensstrategie
NASA Astrophysics Data System (ADS)
Crespo, Isabel; Bergmann, Lars; Lacker, Thomas
Ursprünglich stammt der Begriff "Strategie“ aus dem Altgriechischen: "strategos“ bedeutete "Heer“, "Heeresmacht“ und damit auch "konzentrierte Kraft“; das Wort "agein“ bedeutete "tun, machen, treiben“. Ein Stratege war also eine Person, die ein Heer führte und damit Kraft, Macht und Stärke konzentrierte und einsetzen konnte. Strategie bezeichnete dementsprechend die Maßnahmen, die in dieser Funktion entwickelt wurden. Daher ist es leicht verständlich, dass der Begriff Strategie bis in die Mitte des letzten Jahrhunderts in erster Linie militärisch verstanden wurde. Anschließend wurde der Begriff in weiteren Bereichen, wie beispielsweise der Unternehmensführung, verwendet. Im betriebswirtschaftlichen Sinne bedeutet der Begriff Strategie die langfristig geplante Verhaltensweise eines Unternehmens zur Erreichung seiner Ziele.
Robust fractional quantum Hall effect in the N=2 Landau level in bilayer graphene.
Diankov, Georgi; Liang, Chi-Te; Amet, François; Gallagher, Patrick; Lee, Menyoung; Bestwick, Andrew J; Tharratt, Kevin; Coniglio, William; Jaroszynski, Jan; Watanabe, Kenji; Taniguchi, Takashi; Goldhaber-Gordon, David
2016-12-21
The fractional quantum Hall effect is a canonical example of electron-electron interactions producing new ground states in many-body systems. Most fractional quantum Hall studies have focussed on the lowest Landau level, whose fractional states are successfully explained by the composite fermion model. In the widely studied GaAs-based system, the composite fermion picture is thought to become unstable for the N≥2 Landau level, where competing many-body phases have been observed. Here we report magneto-resistance measurements of fractional quantum Hall states in the N=2 Landau level (filling factors 4<|ν|<8) in bilayer graphene. In contrast with recent observations of particle-hole asymmetry in the N=0/N=1 Landau levels of bilayer graphene, the fractional quantum Hall states we observe in the N=2 Landau level obey particle-hole symmetry within the fully symmetry-broken Landau level. Possible alternative ground states other than the composite fermions are discussed.
Robust fractional quantum Hall effect in the N=2 Landau level in bilayer graphene
NASA Astrophysics Data System (ADS)
Diankov, Georgi; Liang, Chi-Te; Amet, François; Gallagher, Patrick; Lee, Menyoung; Bestwick, Andrew J.; Tharratt, Kevin; Coniglio, William; Jaroszynski, Jan; Watanabe, Kenji; Taniguchi, Takashi; Goldhaber-Gordon, David
2016-12-01
The fractional quantum Hall effect is a canonical example of electron-electron interactions producing new ground states in many-body systems. Most fractional quantum Hall studies have focussed on the lowest Landau level, whose fractional states are successfully explained by the composite fermion model. In the widely studied GaAs-based system, the composite fermion picture is thought to become unstable for the N≥2 Landau level, where competing many-body phases have been observed. Here we report magneto-resistance measurements of fractional quantum Hall states in the N=2 Landau level (filling factors 4<|ν|<8) in bilayer graphene. In contrast with recent observations of particle-hole asymmetry in the N=0/N=1 Landau levels of bilayer graphene, the fractional quantum Hall states we observe in the N=2 Landau level obey particle-hole symmetry within the fully symmetry-broken Landau level. Possible alternative ground states other than the composite fermions are discussed.
Physik-Nobelpreis 2004 Von der Freiheit in der Welt der Quarks
NASA Astrophysics Data System (ADS)
Bartels, Jochen
2004-11-01
Die Schwedische Akademie der Wissenschaften vergab in diesem Jahr den Physik-Nobelpreis zu gleichen Teilen an die amerikanischen Physiker David Gross, David Politzer und Frank Wilczek. Sie würdigte damit ihre theoretischen Arbeiten zur asymptotischen Freiheit in der starken Wechselwirkung.
Rotating effects on the Landau quantization for an atom with a magnetic quadrupole moment
Fonseca, I. C.; Bakke, K.
2016-01-07
Based on the single particle approximation [Dmitriev et al., Phys. Rev. C 50, 2358 (1994) and C.-C. Chen, Phys. Rev. A 51, 2611 (1995)], the Landau quantization associated with an atom with a magnetic quadrupole moment is introduced, and then, rotating effects on this analogue of the Landau quantization is investigated. It is shown that rotating effects can modify the cyclotron frequency and breaks the degeneracy of the analogue of the Landau levels.
Rotating effects on the Landau quantization for an atom with a magnetic quadrupole moment.
Fonseca, I C; Bakke, K
2016-01-07
Based on the single particle approximation [Dmitriev et al., Phys. Rev. C 50, 2358 (1994) and C.-C. Chen, Phys. Rev. A 51, 2611 (1995)], the Landau quantization associated with an atom with a magnetic quadrupole moment is introduced, and then, rotating effects on this analogue of the Landau quantization is investigated. It is shown that rotating effects can modify the cyclotron frequency and breaks the degeneracy of the analogue of the Landau levels.
Landau singularities and symbology: one- and two-loop MHV amplitudes in SYM theory
Dennen, Tristan; Spradlin, Marcus; Volovich, Anastasia
2016-03-14
We apply the Landau equations, whose solutions parameterize the locus of possible branch points, to the one- and two-loop Feynman integrals relevant to MHV amplitudes in planar N = 4 super-Yang-Mills theory. We then identify which of the Landau singularities appear in the symbols of the amplitudes, and which do not. Finally, we observe that all of the symbol entries in the two-loop MHV amplitudes are already present as Landau singularities of one-loop pentagon integrals.
Grundlagen und Vollzug der amtlichen Lebensmittelkontrolle in der Schweiz
NASA Astrophysics Data System (ADS)
Hübner, Philipp; Spinner, Christoph
In der Schweiz wird die Mehrheit der hoheitlichen Aufgaben von den 26 Kantonen, die zusammen die schweizerische Eidgenossenschaft bilden, autonom vollzogen. So liegt zum Beispiel die Kompetenz in den Bereichen Steuern, Gesundheit, Schulen oder Polizei grundsätzlich bei den Kantonen. Im Gegensatz dazu ist die Lebensmittelgesetzgebung national durch eidgenössische Erlasse harmonisiert. Die Vollzugsaufgaben liegen aber auch in diesem Bereich, abgesehen vom Vollzug an der Grenze und von einer nationalen Vollzugsaufsicht und Weisungsberechtigung, in kantonaler Kompetenz. Die Kantone können anhand kantonaler Erlasse das Bundesrecht präzisieren - insbesondere die organisatorischen Aspekte - und Regelungen im nicht harmonisierten Bereich treffen.
Coulomb impurity effects on the zero-Landau level splitting of graphene on polar substrates
NASA Astrophysics Data System (ADS)
Xiao, Yao; Li, Wei-Ping; Li, Zhi-Qing; Wang, Zi-Wu
2017-04-01
We theoretically investigate the effects of the Coulomb impurity on the zero-Landau level splitting of graphene on different polar substrates basing on the Fröhlich polaron model, in which the polaron is formed due to the carriers-surface optical phonon coupling. We discuss the influence of Coulomb impurity on the zero-Landau level splitting in the case of weak and strong coupling limits. We find that the splitting energy can be varied in a large scale due to the Coulomb impurity, which provides the possible theoretical explanation for the experimental measurements regarding the energy gap opened and zero-Landau level splitting in Landau quantized graphene.
Verbesserung der Symmetrie von Hirnaufnahmen entlang der Sagittalebene
NASA Astrophysics Data System (ADS)
Ens, Konstantin; Wenzel, Fabian; Fischer, Bernd
Die lokale Symmetrie von Hirnscans entlang der Sagittalebene zu ermitteln und zu modizifieren, ist für eine Reihe neurologischer Anwendungen interessant. Beispielsweise kann der voxelweise Vergleich von rechter und linker Hirnhälfte nur dann Aufschluss über die Lokalisierung von Läsionen geben, wenn durch Transformation ein Hirnscan eine möglichst hohe Symmetrie aufweist. Ein weiteres Anwendungsgebiet ist die Visualisierung von medialen Hirnschnitten, für die die Trennfläche beider Hirnhälfte möglichst eben sein sollte. Diese Arbeit stellt die Entwicklung eines Verfahrens vor, mit dessen Hilfe die Symmetrie von Hirnaufnahmen entlang der Sagittalebene verbessert werden kann. Dies geschieht unter Verwendung von aktiven Konturen, die mit Hilfe einer neuartigen Kostenfunktion gesteuert werden. Experimente am Ende der Arbeit mit strukturellen Kernspinaufnahmen demonstrieren die Leistungsfähigkeit des Verfahrens.
Dialektischer Materialismus in der Quantentheorie
NASA Astrophysics Data System (ADS)
Fuchs, Klaus
Der absolute Determinismus der klassischen Mechanik bietet keine Ansatzpunkte für eine befriedigende Naturphilosophie. Mit der Quantenmechanik werden nicht lediglich die Unzulänglichkeiten einzelner klassischer Begriffe, sondern die des gesamten klassischen Begriffssystems beseitigt.Translated AbstractDialectical Materialism in Quantum TheoryThe absolute determinism of classical mechanics does not provide any base for a satisfactory philosophy of nature. In quantum mechanics the shortcomings of not only some single classical concepts but of the classical description as a whole are removed.
Imaging van der Waals Interactions.
Han, Zhumin; Wei, Xinyuan; Xu, Chen; Chiang, Chi-Lun; Zhang, Yanxing; Wu, Ruqian; Ho, W
2016-12-15
The van der Waals interactions are responsible for a large diversity of structures and functions in chemistry, biology, and materials. Discussion of van der Waals interactions has focused on the attractive potential energy that varies as the inverse power of the distance between the two interacting partners. The origin of the attractive force is widely discussed as being due to the correlated fluctuations of electron charges that lead to instantaneous dipole-induced dipole attractions. Here, we use the inelastic tunneling probe to image the potential energy surface associated with the van der Waals interactions of xenon atoms.
Online Condition Monitoring mit der Stresswellenanalyse
NASA Astrophysics Data System (ADS)
Bruderreck, Frank
Die Anforderungen des heutigen Energiemarkts und damit einhergehende veränderte Einsatzbedingungen für ältere Kraftwerksblöcke haben unvorhergesehene Produktionsausfälle in den letzten Jahren erheblich verteuert. Nach der Optimierung der Kraftwerksprozesse und der Steigerung der Wirkungsgrade richten die Energieversorger ihren Blick daher nun verstärkt auch auf die Verfügbarkeit ihrer Anlagen. Zur Verbesserung der Anlagenverfügbarkeit und der Minimierung der Instandhaltungskosten bietet sich der Einsatz von Condition Monitoring Systemen an. Nach der Erprobung eines Systems zur Vibrationsanalyse setzt die Evonik Steag GmbH jetzt in einem Pilotprojekt die Stresswellenanalyse ein, ein Online Condition Monitoring System auf der Basis von Ultraschallsensoren. Dieser Beitrag erläutert an einem Beispiel die Methode und grenzt sie gegen den De-facto-Standard Vibrationsanalyse ab.
Der evolutionäre Naturalismus in der Ethik
NASA Astrophysics Data System (ADS)
Kaiser, Marie I.
Charles Darwin hat eindrucksvoll gezeigt, dass der Mensch ebenso wie alle anderen Lebewesen ein Produkt der biologischen Evolution ist. Die sich an Darwin anschließende Forschung hat außerdem plausibel gemacht, dass sich nicht nur viele der körperlichen Merkmale des Menschen, sondern auch (zumindest einige) seiner Verhaltensdispositionen in adaptiven Selektionsprozessen herausgebildet haben. Die Vorstellung, dass auch die menschliche Moralität evolutionär bedingt ist, scheint daher auf den ersten Blick ganz überzeugend. Schließlich hat die Evolutionstheorie in den vergangenen Jahrzehnten in vielen Bereichen (auch außerhalb der Biologie) ihre weitreichende Bedeutung unter Beweis gestellt. Warum sollte, so könnte man beispielsweise fragen, gerade die Fähigkeit des Menschen, moralische Normen aufzustellen und gemäß ihnen zu handeln, nicht evolutionär erklärt werden können? Und warum sollte eine solche evolutionäre Erklärung der menschlichen Moralität irrelevant für die Rechtfertigung moralischer Normen sein? Warum sollte die Ethik eine Bastion der Philosophen bleiben, für die evolutionsbiologische Forschungsergebnisse über den Menschen und seine nächsten Verwandten keinerlei Relevanz besitzen?
Fluid moments of the nonlinear Landau collision operator
NASA Astrophysics Data System (ADS)
Hirvijoki, E.; Lingam, M.; Pfefferlé, D.; Comisso, L.; Candy, J.; Bhattacharjee, A.
2016-08-01
An important problem in plasma physics is the lack of an accurate and complete description of Coulomb collisions in associated fluid models. To shed light on the problem, this Letter introduces an integral identity involving the multivariate Hermite tensor polynomials and presents a method for computing exact expressions for the fluid moments of the nonlinear Landau collision operator. The proposed methodology provides a systematic and rigorous means of extending the validity of fluid models that have an underlying inverse-square force particle dynamics to arbitrary collisionality and flow.
Vortex solitons of the discrete Ginzburg-Landau equation
Mejia-Cortes, C.; Soto-Crespo, J. M.; Vicencio, Rodrigo A.; Molina, Mario I.
2011-04-15
We have found several families of vortex soliton solutions in two-dimensional discrete dissipative systems governed by the cubic-quintic complex Ginzburg-Landau equation. There are symmetric and asymmetric solutions, and some of them have simultaneously two different topological charges for two different closed loops encircling, i.e., centered at, the singularity. Their regions of existence and stability are determined. Additionally, we have analyzed the relationship between dissipation and stability for a number of solutions, finding that dissipation favors the stability of the vortex soliton solutions.
Long wave asymptote for the Landau Pomeranchuk Migdal effect
NASA Astrophysics Data System (ADS)
Koshelkin, A. V.
2004-01-01
It is shown that non-small angle multiple elastic scattering in matter leads to much stronger suppression of bremsstrahlung (BS) by high-energy particles in the long wave range of emission spectrum compared with the quenching predicted by Landau L D and Pomeranchuk I Ya (1953 Dokl. Akad. Nauk SSSR 92 535, 735) and Migdal A B (1954 Dokl. Akad. Nauk SSSR 96 49, 1956 Phys. Rev. 103 1811). This manifests itself as the rearrangement of the BS spectrum of soft photons in the far long wave region.
Hydrodynamic Stability of Liquid-Propellant Combustion: Landau's Problem Revisited
NASA Technical Reports Server (NTRS)
Margolis, S. B.
2001-01-01
Hydrodynamic, or Landau, instability in combustion is typically associated with the onset of wrinkling of a flame surface, corresponding to the formation of steady cellular structures as the stability threshold is crossed. As its name suggests, it stems from hydrodynamic effects connected with thermal expansion across the reaction region. In the context of liquid-propellant combustion, the classical models that originally predicted this phenomenon have been extended to include the important effects that arise from a dynamic dependence of the burning rate on the local pressure and temperature fields. Thus, the onset of Landau instability has now been shown to occur for sufficiently small negative values of the pressure sensitivity of the burning rate, significantly generalizing previous classical results for this problem that assumed a constant normal burning rate. It has also been shown that the onset of instability occurs for decreasing values of the disturbance wave number as the gravitational-acceleration parameter decreases. Consequently, in an appropriate weak-gravity limit, Landau instability becomes a long-wave phenomena associated with the formation of large cells on the liquid-propellant surface. Additionally, a pulsating form of hydrodynamic instability has been shown to occur as well, corresponding to the onset of temporal oscillations in the location of the liquid/gas interface. This instability occurs for sufficiently large negative values of the pressure sensitivity, and is enhanced by increasing values of the burning-rate temperature sensitivity. It is further shown that for sufficiently small values of this parameter, there exists a stable range of pressure sensitivities for steady, planar burning such that the classical cellular form of hydrodynamic instability and the more recent pulsating form of hydrodynamic instability can each occur as the corresponding stability threshold is crossed. For larger thermal sensitivities, however, the pulsating
Wang-Landau Simulations of Adsorbed and Confined Lattice Proteins
NASA Astrophysics Data System (ADS)
Pattanasiri, Busara; Li, Ying Wai; Landau, David P.; Wüst, Thomas
2012-08-01
The hydrophobic-polar (HP) model has emerged as one of the standard approaches for simulating protein folding. In this work, we used this model together with Wang-Landau (WL) sampling and appropriate Monte Carlo trial moves to determine the density of states and thermodynamics for two cases: Protein adsorption and protein confinement, in the vicinity of attractive surfaces. The influence on the adsorption behavior of surface attractive strength in the adsorption case and volumetric spaces in the confinement case will be discussed.
Fluid moments of the nonlinear Landau collision operator
Hirvijoki, E.; Lingam, M.; Pfefferle, D.; Comisso, L.; Candy, J.; Bhattacharjee, A.
2016-08-09
An important problem in plasma physics is the lack of an accurate and complete description of Coulomb collisions in associated fluid models. To shed light on the problem, this Letter introduces an integral identity involving the multivariate Hermite tensor polynomials and presents a method for computing exact expressions for the fluid moments of the nonlinear Landau collision operator. In conclusion, the proposed methodology provides a systematic and rigorous means of extending the validity of fluid models that have an underlying inverse-square force particle dynamics to arbitrary collisionality and flow.
Inequalities for the constants of Landau and Lebesgue
NASA Astrophysics Data System (ADS)
Alzer, Horst
2002-02-01
The constants of Landau and Lebesgue are defined for all integers n[greater-or-equal, slanted]0 byrespectively. We establish sharp inequalities for Gn and Ln/2 in terms of the logarithmic derivative of the gamma function. Further, we prove that the sequence ([Delta]Gn) is completely monotonic, we provide best possible upper and lower bounds for the ratios (Gn-1+Gn+1)/Gn and (L(n-1)/2+L(n+1)/2)/Ln/2, and we present sharp bounds for Ln/2/Gn and Ln/2-Gn.
Novel electric field effects on Landau levels in graphene.
Lukose, Vinu; Shankar, R; Baskaran, G
2007-03-16
A new effect in graphene in the presence of crossed uniform electric and magnetic fields is predicted. Landau levels are shown to be modified in an unexpected fashion by the electric field, leading to a collapse of the spectrum, when the value of electric to magnetic field ratio exceeds a certain critical value. Our theoretical results, strikingly different from the standard 2D electron gas, are explained using a "Lorentz boost," and as an "instability of a relativistic quantum field vacuum." It is a remarkable case of emergent relativistic type phenomena in nonrelativistic graphene. We also discuss few possible experimental consequence.
Continuous-wave lasing between Landau levels in graphene
NASA Astrophysics Data System (ADS)
Wang, Yongrui; Tokman, Mikhail; Belyanin, Alexey
2015-03-01
We predict the general feasibility and demonstrate the design of the continuous-wave terahertz laser operating between Landau levels in graphene placed on a polar substrate in a magnetic field of order 1 T. Steady-state population inversion under a continuous-wave optical pumping becomes possible due to surface-phonon-mediated relaxation of carriers. The scheme is scalable to other materials with massless Dirac fermions, for example, surface states in three-dimensional topological insulators such as Bi2Se3 or Bi2Te3 .
Temporal evolutional absorption behaviors of graphene under Landau quantization
NASA Astrophysics Data System (ADS)
Hamedi, H. R.; Sahrai, M.
2017-02-01
We investigate the evolutional absorption behaviors of Landau-quantized graphene structure based on the transient solution to the density matrix equations of the motion. The impact of various system parameters on temporal evolution of probe absorption is studied. In addition, the required times for switching the high-absorption case to the zero-absorption (transparency) of a probe field is discussed. Due to unusual optical and electronic characteristics of graphene resulting from linear, massless dispersion of electrons near the Dirac point and the chiral character of electron states, our study may have potential applications in telecommunication, biomedicine, and optical information processing and may cause significant impact on technological applications.
Ginzburg-Landau theory of a holographic superconductor
NASA Astrophysics Data System (ADS)
Yin, Lei; Hou, Defu; Ren, Hai-cang
2015-01-01
The general Ginzburg-Landau (GL) formulation of a holographic superconductor is developed near the transition temperature in the probe limit for two kinds of conformal dimension. elow the transition temperature, T
A Landau-Ginzburg Description of Sb Overlayers
2001-04-01
Heusler alloy NiMnSb is investigated in terms of the Landau-Ginzburg approach. The half -metallic semi- Heusler alloy NiMnSb acts as a ferromagnetic...NiMnSb layers covered by Sb overlayers. NiMnSb is a halfmetallic semi- Heusler alloy crystallizing in the cubic Cib structure. It may be considered as a...derivate of the parent Heusler alloy Ni2 MnSb and has a I band gap of less than about 0.5 eV [1]. Antimony is a semimetal characterized by a very small
Landau damping of surface plasmons in metal nanostructures
NASA Astrophysics Data System (ADS)
Shahbazyan, Tigran V.
2016-12-01
We develop a quantum-mechanical theory for Landau damping of surface plasmons in metal nanostructures of arbitrary shape. We show that the electron surface scattering, which facilitates plasmon decay in small nanostructures, can be incorporated into the metal dielectric function on par with phonon and impurity scattering. The derived surface scattering rate is determined by the local field polarization relative to the metal-dielectric interface and is highly sensitive to the system geometry. We illustrate our model by providing analytical results for surface scattering rate in some common shape nanostructures. Our results can be used for calculations of hot carrier generation rates in photovoltaics and photochemistry applications.
Convergence for the Wang-Landau density of states.
Brown, G; Odbadrakh, Kh; Nicholson, D M; Eisenbach, M
2011-12-01
The Wang-Landau method of estimating the density of states g(E) has become a powerful tool in statistical mechanics. Here it is shown that the distribution of random walkers sampled using an estimated density of states can always be used to improve the estimate. Specifically, this can be done without resorting to an auxiliary modification factor f, which previously has been used to find g(E) self-consistently through a procedure that reduces f incrementally toward unity. This straightforward approach is validated for multiple, independent random walkers.
Effects of Landau-Lifshitz-Gilbert damping on domain growth.
Kudo, Kazue
2016-12-01
Domain patterns are simulated by the Landau-Lifshitz-Gilbert (LLG) equation with an easy-axis anisotropy. If the Gilbert damping is removed from the LLG equation, it merely describes the precession of magnetization with a ferromagnetic interaction. However, even without the damping, domains that look similar to those of scalar fields are formed, and they grow with time. It is demonstrated that the damping has no significant effects on domain growth laws and large-scale domain structure. In contrast, small-scale domain structure is affected by the damping. The difference in small-scale structure arises from energy dissipation due to the damping.
Anisotropic Landau-Lifshitz-Gilbert models of dissipation in qubits
NASA Astrophysics Data System (ADS)
Crowley, Philip J. D.; Green, A. G.
2016-12-01
We derive a microscopic model for dissipative dynamics in a system of mutually interacting qubits coupled to a thermal bath that generalizes the dissipative model of Landau-Lifshitz-Gilbert to the case of anisotropic bath couplings. We show that the dissipation acts to bias the quantum trajectories towards a reduced phase space. This model applies to a system of superconducting flux qubits whose coupling to the environment is necessarily anisotropic. We study the model in the context of the D-Wave computing device and show that the form of environmental coupling in this case produces dynamics that are closely related to several models proposed on phenomenological grounds.
Thresholds of Raman backscatter: effects of collisions and Landau damping
Estabrook, K.; Kruer, W.L.
1983-11-03
We present 1.5 dimensional simulations and theory of the threshold of Raman backscatter for a variety of density profiles, background temperatures and collision frequencies, nu/sub ei/. The simulations show Raman backscatter of approx. 4 x 10/sup -4/ at intensities approx. 30 times below the del n threshold which we suggest is due to light scattering off of noise electron plasma waves. The absorption drops significantly and the threshold rises as the Landau damping ..omega../sub i/ and/or nu/sub ei/ approach the growth rate ..gamma../sub 0/. Many experiments are already in the collisional regime.
The Nonlinear Landau Damping Rate of a Driven Plasma Wave
Benisti, D; Strozzi, D J; Gremillet, L; Morice, O
2009-08-04
In this Letter, we discuss the concept of the nonlinear Landau damping rate, {nu}, of a driven electron plasma wave, and provide a very simple, practical, analytic formula for {nu} which agrees very well with results inferred from Vlasov simulations of stimulated Raman scattering. {nu} actually is more complicated an operator than a plain damping rate, and it may only be seen as such because it assumes almost constant values before abruptly dropping to 0. The decrease of {nu} to 0 is moreover shown to occur later when the wave amplitude varies in the direction transverse to its propagation.
Dissipation in small systems: Landau-Zener approach
NASA Astrophysics Data System (ADS)
Barra, Felipe; Esposito, Massimiliano
2016-06-01
We establish a stochastic thermodynamics for a Fermionic level driven by a time-dependent force and interacting with initially thermalized levels playing the role of a reservoir. The driving induces consecutive avoided crossings between system and reservoir levels described within Landau-Zener theory. We derive the resulting system dynamics and thermodynamics and identify energy, work, heat, entropy, and dissipation. Our theory perfectly reproduces the numerically exact quantum work statistics obtained using a two point measurements approach of the total energy and provides an explicit expression for the dissipation in terms of diabatic transitions.
Landau-Zener transitions in frozen pairs of Rydberg atoms.
Saquet, Nicolas; Cournol, Anne; Beugnon, Jérôme; Robert, Jacques; Pillet, Pierre; Vanhaecke, Nicolas
2010-04-02
We have induced adiabatic transitions in pairs of frozen Rydberg sodium atoms of a supersonic beam. The diatomic ns+ns-->np+(n-1)p transition takes place in a time-dependent electric field and originates from the adiabatic change of the internal state of the pair induced by the dipole-dipole interaction. This is experimentally achieved by sweeping an electric field across the energy degeneracy ns ns-np(n-1)p. Our results fully agree with a two-level Landau-Zener model in the diatom system.
Nonlinear Landau-Zener tunneling in Majorana's stellar representation
NASA Astrophysics Data System (ADS)
Guo, Qiuyi; Liu, Haodi; Zhou, Tianji; Chen, Xu-Zong; Wu, Biao
2016-06-01
By representing the evolution of a quantum state with the trajectories of the stars on a Bloch sphere, the Majorana's stellar representation provides an intuitive way to understand quantum motion in a high dimensional projective Hilbert space. In this work we show that the Majorana's representation offers a very interesting and intuitive way to understand the nonlinear Landau-Zener tunneling. In particular, the breakdown of adiabaticity in this tunneling phenomenon can be understood as some of the stars never reaching the south pole. We also establish a connection between the Majorana stars in the second quantized model and the single star in the mean field model by using the reduced density matrix.
Dissipation in small systems: Landau-Zener approach.
Barra, Felipe; Esposito, Massimiliano
2016-06-01
We establish a stochastic thermodynamics for a Fermionic level driven by a time-dependent force and interacting with initially thermalized levels playing the role of a reservoir. The driving induces consecutive avoided crossings between system and reservoir levels described within Landau-Zener theory. We derive the resulting system dynamics and thermodynamics and identify energy, work, heat, entropy, and dissipation. Our theory perfectly reproduces the numerically exact quantum work statistics obtained using a two point measurements approach of the total energy and provides an explicit expression for the dissipation in terms of diabatic transitions.
Resonances due to the Landau-Zener transition
Tazawa, T. ); Abe, Y. )
1990-01-01
We have derived a new useful analytic formula for the {ital T} matrix in the quantum-mechanical perturbation approach within the two-state problem with finite-range coupling which is appropriate for the discussion of the Landau-Zener transition. The resonancelike behaviors were predicted by classical or semiclassical approach in which constant coupling between two adiabatic states was assumed. In the quantum-mechanical approach, inclusion of the effect of reasonable finite-range coupling would not destroy the pattern of the resonancelike structures so much, while the magnitude of the calculated cross section is merely about 10% of that calculated by the semiclassical approach.
Asymmetric Landau-Zener tunneling in a periodic potential.
Jona-Lasinio, M; Morsch, O; Cristiani, M; Malossi, N; Müller, J H; Courtade, E; Anderlini, M; Arimondo, E
2003-12-05
Using a simple model for nonlinear Landau-Zener tunneling between two energy bands of a Bose-Einstein condensate in a periodic potential, we find that the tunneling rates for the two directions of tunneling are not the same. Tunneling from the ground state to the excited state is enhanced by the nonlinearity, whereas in the opposite direction it is suppressed. These findings are confirmed by numerical simulations of the condensate dynamics. Measuring the tunneling rates for a condensate of rubidium atoms in an optical lattice, we have found experimental evidence for this asymmetry.
Landau-Zener Transitions in Frozen Pairs of Rydberg Atoms
Saquet, Nicolas; Cournol, Anne; Beugnon, Jerome; Robert, Jacques; Pillet, Pierre; Vanhaecke, Nicolas
2010-04-02
We have induced adiabatic transitions in pairs of frozen Rydberg sodium atoms of a supersonic beam. The diatomic ns+ns{yields}np+(n-1)p transition takes place in a time-dependent electric field and originates from the adiabatic change of the internal state of the pair induced by the dipole-dipole interaction. This is experimentally achieved by sweeping an electric field across the energy degeneracy ns ns-np(n-1)p. Our results fully agree with a two-level Landau-Zener model in the diatom system.
Auf der Suche nach dem Unendlichen.
NASA Astrophysics Data System (ADS)
Fraser, G.; Lillestøl, E.; Sellevåg, I.
This book is a German translation by C. Ascheron and J. Urbahn, of "The search for infinity: solving the mysteries of the universe", published in 1994. Diese Buch beschreibt anschaulich die Meilensteine, die der Mensch seit der Antike auf der Suche nach dem Unendlichen erreicht und hinter sich gelassen hat. Es enthält Kurzbiographien der wichtigsten Forscher, verständlich geschriebene Texte sowie Erläuterungen der entscheidenen Fachtermini.
Van der Waals quintessence stars
Lobo, Francisco S. N.
2007-01-15
The van der Waals quintessence equation of state is an interesting scenario for describing the late universe, and seems to provide a solution to the puzzle of dark energy, without the presence of exotic fluids or modifications of the Friedmann equations. In this work, the construction of inhomogeneous compact spheres supported by a van der Waals equation of state is explored. These relativistic stellar configurations shall be denoted as van der Waals quintessence stars. Despite of the fact that, in a cosmological context, the van der Waals fluid is considered homogeneous, inhomogeneities may arise through gravitational instabilities. Thus, these solutions may possibly originate from density fluctuations in the cosmological background. Two specific classes of solutions, namely, gravastars and traversable wormholes are analyzed. Exact solutions are found, and their respective characteristics and physical properties are further explored.
Chan, Ho Yin; Lubchenko, Vassiliy
2015-09-28
We set up the problem of finding the transition state for phase nucleation in multi-component fluid mixtures, within the Landau-Ginzburg density functional. We establish an expression for the coordinate-dependent local pressure that applies to mixtures, arbitrary geometries, and certain non-equilibrium configurations. The expression allows one to explicitly evaluate the pressure in spherical geometry, à la van der Waals. Pascal's law is recovered within the Landau-Ginzburg density functional theory, formally analogously to how conservation of energy is recovered in the Lagrangian formulation of mechanics. We establish proper boundary conditions for certain singular functional forms of the bulk free energy density that allow one to obtain droplet solutions with thick walls in essentially closed form. The hydrodynamic modes responsible for mixing near the interface are explicitly identified in the treatment; the composition at the interface is found to depend only weakly on the droplet size. Next we develop a Landau-Ginzburg treatment of the effects of amphiphiles on the surface tension; the amphiphilic action is seen as a violation of Pascal's law. We explicitly obtain the binding potential for the detergent at the interface and the dependence of the down-renormalization of the surface tension on the activity of the detergent. Finally, we argue that the renormalization of the activation barrier for escape from long-lived structures in glassy liquids can be viewed as an action of uniformly seeded, randomly oriented amphiphilic molecules on the interface separating two dissimilar aperiodic structures. This renormalization is also considered as a "wetting" of the interface. The resulting conclusions are consistent with the random first order transition theory.
NASA Astrophysics Data System (ADS)
Chan, Ho Yin; Lubchenko, Vassiliy
2015-09-01
We set up the problem of finding the transition state for phase nucleation in multi-component fluid mixtures, within the Landau-Ginzburg density functional. We establish an expression for the coordinate-dependent local pressure that applies to mixtures, arbitrary geometries, and certain non-equilibrium configurations. The expression allows one to explicitly evaluate the pressure in spherical geometry, à la van der Waals. Pascal's law is recovered within the Landau-Ginzburg density functional theory, formally analogously to how conservation of energy is recovered in the Lagrangian formulation of mechanics. We establish proper boundary conditions for certain singular functional forms of the bulk free energy density that allow one to obtain droplet solutions with thick walls in essentially closed form. The hydrodynamic modes responsible for mixing near the interface are explicitly identified in the treatment; the composition at the interface is found to depend only weakly on the droplet size. Next we develop a Landau-Ginzburg treatment of the effects of amphiphiles on the surface tension; the amphiphilic action is seen as a violation of Pascal's law. We explicitly obtain the binding potential for the detergent at the interface and the dependence of the down-renormalization of the surface tension on the activity of the detergent. Finally, we argue that the renormalization of the activation barrier for escape from long-lived structures in glassy liquids can be viewed as an action of uniformly seeded, randomly oriented amphiphilic molecules on the interface separating two dissimilar aperiodic structures. This renormalization is also considered as a "wetting" of the interface. The resulting conclusions are consistent with the random first order transition theory.
Random attractors for the stochastic coupled fractional Ginzburg-Landau equation with additive noise
Shu, Ji E-mail: 530282863@qq.com; Li, Ping E-mail: 530282863@qq.com; Zhang, Jia; Liao, Ou
2015-10-15
This paper is concerned with the stochastic coupled fractional Ginzburg-Landau equation with additive noise. We first transform the stochastic coupled fractional Ginzburg-Landau equation into random equations whose solutions generate a random dynamical system. Then we prove the existence of random attractor for random dynamical system.
Landau-Zener transition in quadratic nonlinear two-state systems
Ishkhanyan, A. M.
2010-05-15
A comprehensive theory of the Landau-Zener transition in quadratic nonlinear two-state systems is developed. A compact analytic formula involving elementary functions only is derived for the final transition probability. The formula provides a highly accurate approximation for the whole rage of the variation of the Landau-Zener parameter.
Integral definition of transition time in the Landau-Zener model
Yan Yue; Wu Biao
2010-02-15
We give a general definition for the transition time in the Landau-Zener model. This definition allows us to compute numerically the Landau-Zener transition time at any sweeping rate without ambiguity in both diabatic and adiabatic bases. With this new definition, analytical results are obtained in both the adiabatic limit and the sudden limit.
Landau damping and steepening of interplanetary nonlinear hydromagnetic waves
NASA Technical Reports Server (NTRS)
Barnes, A.; Chao, J. K.
1977-01-01
According to collisionless shock theories, the thickness of a shock front should be of the order of the characteristic lengths of the plasmas (the Debye length, the proton and Larmor radii, etc.). Chao and Lepping (1974), found, however, that 30% of the observed interplanetary shocks at 1 AU have thicknesses much larger than these characteristic lengths. It is the objective of the present paper to investigate whether the competition between nonlinear steepening and Landau damping can result in a wave of finite width that does not steepen into a shock. A heuristic model of such a wave is developed and tested by the examples of two structures that are qualitatively shocklike, but thicker than expected from theory. It is found that both events are in the process of steepening and their limiting thicknesses due to Landau damping are greater than the corresponding proton Larmor radius for both structures as observed at Mariner 5 (nearer the sun than 1 AU) but are comparable to the proton Larmor radius for Explorer (near 1 AU) observations.
Landau-Zener transition driven by slow noise
NASA Astrophysics Data System (ADS)
Luo, Zhu-Xi; Raikh, M. E.
2017-02-01
The effect of a slow noise in nondiagonal matrix element J (t ) that describes the diabatic level coupling on the probability of the Landau-Zener transition is studied. For slow noise, the correlation time τc of J (t ) is much longer than the characteristic time of the transition. Existing theory for this case suggests that the average transition probability is the result of averaging of the conventional Landau-Zener probability, calculated for a given constant J , over the distribution of J . We calculate a finite-τc correction for this classical result. Our main finding is that this correction is dominated by sparse realizations of noise for which J (t ) passes through zero within a narrow time interval near the level crossing. Two models of noise, random telegraph noise and Gaussian noise, are considered. Naturally, in both models the average probability of transition decreases upon decreasing τc. For Gaussian noise we identify two domains of this falloff with specific dependencies of average transition probability on τc.
Landau-Zener in a continuously measured molecular spin
NASA Astrophysics Data System (ADS)
Troiani, Filippo; Affronte, Marco; Thiele, Stephan; Godfrin, Clement; Balestro, Franck; Wernsdorfer, Wolfgang; Klyatskaya, Svetlana; Ruben, Mario
The dynamics of a quantum system driven through an avoided level crossing represernts a relevant problem in many physical contexts. Here we present a joint theoretical and experimental investigation of a single-molecule magnet (namely, a terbium double-decker complex) in a three-terminal geometry. The Tb spin is driven through an avoided level crossing by a time-dependent magnetic field, and its dynamics is monitored through a continuous measurement of the conductance. The dependence of the spin-reversal probability on the field sweeping rate presents clear deviations from the Landau-Zener formula, which applies to the case of closed systems. The comparison between direct and inverse Landau-Zener transitions points at the dominance of dephasing, with respect to inelastic incoherent processes. The spin dynamics is simulated within a master equation approach. The observed behaviors are reproduced by assuming that dephasing takes place in the basis of the time-dependent Hamiltonian eigenstates. The spin dephasing is traced back to the continuous measurement of the electron spin, and a fundamental role is played by the finite time resolution of the conductance measurement.
Topological photonics: an observation of Landau levels for optical photons
NASA Astrophysics Data System (ADS)
Schine, Nathan; Ryou, Albert; Sommer, Ariel; Simon, Jonathan
Creating photonic materials with nontrivial topological characteristics has seen burgeoning interest in recent years; however, a major route to topology, a magnetic field for continuum photons, has remained elusive. We present the first experimental realization of a bulk magnetic field for optical photons. By using a non-planar ring resonator, we induce an image rotation on each round trip through the resonator. This results in a Coriolis/Lorentz force and a centrifugal anticonfining force, the latter of which is cancelled by mirror curvature. Spatial- and energy- resolved spectroscopy tracks photonic eigenstates as residual trapping is reduced, and we observe photonic Landau levels as the eigenstates become degenerate. We will discuss the conical geometry of the resulting manifold for photon dynamics and present a measurement of the local density of states that is consistent with Landau levels on a cone. While our work already demonstrates an integer quantum Hall material composed of photons, we have ensured compatibility with strong photon-photon interactions, which will allow quantum optical studies of entanglement and correlation in manybody systems including fractional quantum Hall fluids. This work was supported by DOE, DARPA, and AFOSR.
Topological photonics: an observation of Landau levels for optical photons
NASA Astrophysics Data System (ADS)
Schine, Nathan; Ryou, Albert; Sommer, Ariel; Simon, Jonathan
We present the first experimental realization of a bulk magnetic field for optical photons. By using a non-planar ring resonator, we induce an image rotation on each round trip through the resonator. This results in a Coriolis/Lorentz force and a centrifugal anticonfining force, the latter of which is cancelled by mirror curvature. Using a digital micromirror device to control both amplitude and phase, we inject arbitrary optical modes into our resonator. Spatial- and energy- resolved spectroscopy tracks photonic eigenstates as residual trapping is reduced, and we observe photonic Landau levels as the eigenstates become degenerate. We show that there is a conical geometry of the resulting manifold for photon dynamics and present a measurement of the local density of states that is consistent with Landau levels on a cone. While our work already demonstrates an integer quantum Hall material composed of photons, we have ensured compatibility with strong photon-photon interactions, which will allow quantum optical studies of entanglement and correlation in manybody systems including fractional quantum Hall fluids. This work was supported by DOE, DARPA, and AFOSR.
Tunneling spectra for electrons in the lowest Landau level
NASA Astrophysics Data System (ADS)
Burnell, F. J.; Simon, Steven H.
2010-03-01
The recently developed experimental technique of time dependent capacitance spectroscopy [1] allows for measurements of high-resolution tunneling spectra of 2DEGs in the quantum Hall regime, giving a detailed probe of the single particle spectral function (electron addition and subtraction spectra). These experiments show a number of interesting features including Landau level structure, exchange enhanced Zeeman energy, Coulomb gap physics, effects of fractional quantization, as well as several key features that remain to be explained. While there has been some prior theoretical work[2] towards explaining low energy Coulomb gap features of tunneling spectra found in much earlier tunneling experiments [3], the new experiments[1] have uncovered physics outside of the prior theoretical explanations. Building on a number of these prior theoretical works, we investigate theoretically the expected tunneling spectra for electrons in low Landau levels, including the effects of electron spin and coupling to collective modes. [1] O. E. Dial, R.C. Ashoori, L.N. Pfeiffer, and K.W. West, Nature 448, 176-179 (2007) ; O. E. Dial et al, unpublished. [2] I. Aleiner et al, Phys. Rev. Lett 74 3435; (1994) S. R. E. Yang and A. MacDonald PRL 70 4110 (1993); S. He, P.M. Platzman, and B. I. Halperin, PRL 71 777 (1993). [3] J. P. Eisenstein et al, Phy. Rev. Lett. 69, 3804 (1992).
Landau damping of quantum plasmons in metal nanostructures
Li, Xiaoguang; Xiao, Di; Zhang, Zhenyu
2013-02-06
Using the random phase approximation with both real space and discrete electron–hole (e–h) pair basis sets, we study the broadening of surface plasmons in metal structures of reduced dimensionality, where Landau damping is the dominant dissipation channel and presents an intrinsic limitation to plasmonics technology. We show that for every prototypical class of systems considered, including zero-dimensional nanoshells, one-dimensional coaxial nanotubes and two-dimensional ultrathin films, Landau damping can be drastically tuned due to energy quantization of the individual electron levels and e–h pairs. Both the generic trend and oscillatory nature of the tunability are in stark contrast with the expectationsmore » of the semiclassical surface scattering picture. Our approach also allows to vividly depict the evolution of the plasmons from the quantum to the classical regime, and to elucidate the underlying physical origin of hybridization broadening of nearly degenerate plasmon modes. Lastly, these findings may serve as a guide in the future design of plasmonic nanostructures of desirable functionalities.« less
Landau theory and the emergence of chirality in viral capsids
NASA Astrophysics Data System (ADS)
Dharmavaram, Sanjay; Xie, Fangming; Klug, William; Rudnick, Joseph; Bruinsma, Robijn
2016-10-01
We present a generalized Landau-Brazovskii free energy for the solidification of chiral molecules on a spherical surface in the context of the assembly of viral shells. We encounter two types of solidification transitions. The first type is a conventional first-order phase transition from a uniform to an icosahedral state, described by a single icosahedral spherical harmonic of even l. The chiral pseudo-scalar term in the free energy does not affect the transition. The second type is anomalous: icosahedral spherical harmonics with odd l are unstable. Stability is recovered when admixture with the neighboring l + 1 icosahedral spherical harmonic is included. This is in apparent conflict with the principle of Landau theory that symmetry-breaking transitions are characterized by a single irreducible representation of the symmetry group of the uniform phase. The chiral term selects one of two isomeric mixed-l icosahedral states. A direct transition is possible only over a limited range of parameters. Outside this range, a non-icosahedral state with the symmetry of an isotropy subgroup of the icosahedral group interposes between the uniform and icosahedral states. This paper is dedicated to the memory of our friends and colleagues William Klug and Vladimir Lorman.
Landau damping of quantum plasmons in metal nanostructures
Li, Xiaoguang; Xiao, Di; Zhang, Zhenyu
2013-02-06
Using the random phase approximation with both real space and discrete electron–hole (e–h) pair basis sets, we study the broadening of surface plasmons in metal structures of reduced dimensionality, where Landau damping is the dominant dissipation channel and presents an intrinsic limitation to plasmonics technology. We show that for every prototypical class of systems considered, including zero-dimensional nanoshells, one-dimensional coaxial nanotubes and two-dimensional ultrathin films, Landau damping can be drastically tuned due to energy quantization of the individual electron levels and e–h pairs. Both the generic trend and oscillatory nature of the tunability are in stark contrast with the expectations of the semiclassical surface scattering picture. Our approach also allows to vividly depict the evolution of the plasmons from the quantum to the classical regime, and to elucidate the underlying physical origin of hybridization broadening of nearly degenerate plasmon modes. Lastly, these findings may serve as a guide in the future design of plasmonic nanostructures of desirable functionalities.
Infrared singularities in Landau gauge Yang-Mills theory
Alkofer, Reinhard; Huber, Markus Q.; Schwenzer, Kai
2010-05-15
We present a more detailed picture of the infrared regime of Landau-gauge Yang-Mills theory. This is done within a novel framework that allows one to take into account the influence of finite scales within an infrared power counting analysis. We find that there are two qualitatively different infrared fixed points of the full system of Dyson-Schwinger equations. The first extends the known scaling solution, where the ghost dynamics is dominant and gluon propagation is strongly suppressed. It features in addition to the strong divergences of gluonic vertex functions in the previously considered uniform scaling limit, when all external momenta tend to zero, also weaker kinematic divergences, when only some of the external momenta vanish. The second solution represents the recently proposed decoupling scenario where the gluons become massive and the ghosts remain bare. In this case we find that none of the vertex functions is enhanced, so that the infrared dynamics is entirely suppressed. Our analysis also provides a strict argument why the Landau-gauge gluon dressing function cannot be infrared divergent.
Probing the Nodal Structure of Landau Level Wave Functions in Real Space.
Bindel, J R; Ulrich, J; Liebmann, M; Morgenstern, M
2017-01-06
The inversion layer of p-InSb(110) obtained by Cs adsorption of 1.8% of a monolayer is used to probe the Landau level wave functions within smooth potential valleys by scanning tunneling spectroscopy at 14 T. The nodal structure becomes apparent as a double peak structure of each spin polarized first Landau level, while the zeroth Landau level exhibits a single peak per spin level only. The real space data show single rings of the valley-confined drift states for the zeroth Landau level and double rings for the first Landau level. The result is reproduced by a recursive Green function algorithm using the potential landscape obtained experimentally. We show that the result is generic by comparing the local density of states from the Green function algorithm with results from a well-controlled analytic model based on the guiding center approach.
Observation of Landau levels in potassium-intercalated graphite under a zero magnetic field.
Guo, Donghui; Kondo, Takahiro; Machida, Takahiro; Iwatake, Keigo; Okada, Susumu; Nakamura, Junji
2012-01-01
The charge carriers in graphene are massless Dirac fermions and exhibit a relativistic Landau-level quantization in a magnetic field. Recently, it has been reported that, without any external magnetic field, quantized energy levels have been also observed from strained graphene nanobubbles on a platinum surface, which were attributed to the Landau levels of massless Dirac fermions in graphene formed by a strain-induced pseudomagnetic field. Here we show the generation of the Landau levels of massless Dirac fermions on a partially potassium-intercalated graphite surface without applying external magnetic field. Landau levels of massless Dirac fermions indicate the graphene character in partially potassium-intercalated graphite. The generation of the Landau levels is ascribed to a vector potential induced by the perturbation of nearest-neighbour hopping, which may originate from a strain or a gradient of on-site potentials at the perimeters of potassium-free domains.
Probing the Nodal Structure of Landau Level Wave Functions in Real Space
NASA Astrophysics Data System (ADS)
Bindel, J. R.; Ulrich, J.; Liebmann, M.; Morgenstern, M.
2017-01-01
The inversion layer of p -InSb (110 ) obtained by Cs adsorption of 1.8% of a monolayer is used to probe the Landau level wave functions within smooth potential valleys by scanning tunneling spectroscopy at 14 T. The nodal structure becomes apparent as a double peak structure of each spin polarized first Landau level, while the zeroth Landau level exhibits a single peak per spin level only. The real space data show single rings of the valley-confined drift states for the zeroth Landau level and double rings for the first Landau level. The result is reproduced by a recursive Green function algorithm using the potential landscape obtained experimentally. We show that the result is generic by comparing the local density of states from the Green function algorithm with results from a well-controlled analytic model based on the guiding center approach.
Landau level transitions in doped graphene in a time dependent magnetic field
NASA Astrophysics Data System (ADS)
Ardenghi, J. S.; Bechthold, P.; Jasen, P.; Gonzalez, E.; Nagel, O.
2013-10-01
The aim of this work is to describe the Landau level transitions of Bloch electrons in doped graphene with an arbitrary time dependent magnetic field in the long wavelength approximation. In particular, transitions from the m Landau level to the m±1 and m±2 Landau levels are studied using the time dependent perturbation theory. Time intervals are computed in which transition probabilities tend to zero at a low order in the coupling constant. In particular, Landau level transitions are studied in the case of Bloch electrons traveling in the direction of the applied magnetic force and the results are compared with classical and revival periods of electrical current in graphene. Finally, current probabilities are computed for the n=0 and n=1 Landau levels showing expected oscillating behavior with modified cyclotron frequency.
Composite Fermi liquids in the lowest Landau level
NASA Astrophysics Data System (ADS)
Wang, Chong; Senthil, T.
2016-12-01
We study composite Fermi liquid (CFL) states in the lowest Landau level (LLL) limit at a generic filling ν =1/n . We begin with the old observation that, in compressible states, the composite fermion in the lowest Landau level should be viewed as a charge-neutral particle carrying vorticity. This leads to the absence of a Chern-Simons term in the effective theory of the CFL. We argue here that instead a Berry curvature should be enclosed by the Fermi surface of composite fermions, with the total Berry phase fixed by the filling fraction ϕB=-2 π ν . We illustrate this point with the CFL of fermions at filling fractions ν =1 /2 q and (single and two-component) bosons at ν =1 /(2 q +1 ) . The Berry phase leads to sharp consequences in the transport properties including thermal and spin Hall conductances. We emphasize that these results only rely on the LLL limit and do not require particle-hole symmetry, which is present microscopically only for fermions at ν =1 /2 . Nevertheless, we show that the existing LLL theory of the composite Fermi liquid for bosons at ν =1 does have an emergent particle-hole symmetry. We interpret this particle-hole symmetry as a transformation between the empty state at ν =0 and the boson integer quantum hall state at ν =2 . This understanding enables us to define particle-hole conjugates of various bosonic quantum Hall states which we illustrate with the bosonic Jain and Pfaffian states. For bosons at ν =1 we construct paired non-Abelian states distinct from both the standard bosonic Pfaffian and its particle hole conjugate and show how they may arise naturally out of the neutral vortex composite Fermi liquid. The bosonic particle-hole symmetry can be realized exactly on the surface of a three-dimensional boson topological insulator. We also show that with the particle-hole and spin S U (2 ) rotation symmetries, there is no gapped topological phase for bosons at ν =1 . Finally we comment on systems that are not strictly in the
Fluid moments of the nonlinear Landau collision operator
NASA Astrophysics Data System (ADS)
Hirvijoki, Eero; Lingam, Manasvi; Pfefferlé, David; Comisso, Luca; Candy, Jeff; Bhattacharjee, Amitava
2016-10-01
One important problem in plasma physics is the lack of an accurate and complete description of Coulomb collisions in associated fluid models. To shed light on the problem, this work introduces an integral identity involving the multivariate Hermite tensor polynomials and presents a method for computing exact expressions for the fluid moments of the nonlinear Landau collision operator. The proposed methodology provides a systematic and rigorous means of extending the validity of fluid models that have an underlying inverse-square force particle dynamics to arbitrary collisionality and flow. (For details, see arXiv:1605.07589) This research is supported by the Department of Energy Contract No. DE-AC02-09CH11466 and the National Science Foundation Grant Nos. AGS-1338944 and AGS-1552142.
Scalable replica-exchange framework for Wang-Landau sampling.
Vogel, Thomas; Li, Ying Wai; Wüst, Thomas; Landau, David P
2014-08-01
We investigate a generic, parallel replica-exchange framework for Monte Carlo simulations based on the Wang-Landau method. To demonstrate its advantages and general applicability for massively parallel simulations of complex systems, we apply it to lattice spin models, the self-assembly process in amphiphilic solutions, and the adsorption of molecules on surfaces. While of general current interest, the latter phenomena are challenging to study computationally because of multiple structural transitions occurring over a broad temperature range. We show how the parallel framework facilitates simulations of such processes and, without any loss of accuracy or precision, gives a significant speedup and allows for the study of much larger systems and much wider temperature ranges than possible with single-walker methods.
Improving Wang-Landau sampling with adaptive windows.
Cunha-Netto, A G; Caparica, A A; Tsai, Shan-Ho; Dickman, Ronald; Landau, D P
2008-11-01
Wang-Landau sampling (WLS) of large systems requires dividing the energy range into "windows" and joining the results of simulations in each window. The resulting density of states (and associated thermodynamic functions) is shown to suffer from boundary effects in simulations of lattice polymers and the five-state Potts model. Here, we implement WLS using adaptive windows. Instead of defining fixed energy windows (or windows in the energy-magnetization plane for the Potts model), the boundary positions depend on the set of energy values on which the histogram is flat at a given stage of the simulation. Shifting the windows each time the modification factor f is reduced, we eliminate border effects that arise in simulations using fixed windows. Adaptive windows extend significantly the range of system sizes that may be studied reliably using WLS.
Wang-Landau simulations of polymer adsorption on diluted surfaces
NASA Astrophysics Data System (ADS)
Martins, Paulo; Vogel, Thomas; Landau, David
2012-02-01
We consider a single linear lattice homopolymer in three dimensions that interacts with a diluted planar surface. A fraction p of the total number of the sites on the substrate is attractive, while the remaining 1-p remains neutral. Our focus is on the conformational transitions the polymer can experience under different environmental conditions, for instance, the surface dilution and the strength of the substrate attraction, compared to the intensity of the monomer-monomer interactions. To get insights on the phase diagram we have performed extensive Monte Carlo simulations, by using the Wang-Landau sampling, for different values of the surface attraction ɛ and the concentration of attractive sites p, specially near the surface percolation threshold pc.
Scalable replica-exchange framework for Wang-Landau sampling
NASA Astrophysics Data System (ADS)
Vogel, Thomas; Li, Ying Wai; Wüst, Thomas; Landau, David P.
2014-08-01
We investigate a generic, parallel replica-exchange framework for Monte Carlo simulations based on the Wang-Landau method. To demonstrate its advantages and general applicability for massively parallel simulations of complex systems, we apply it to lattice spin models, the self-assembly process in amphiphilic solutions, and the adsorption of molecules on surfaces. While of general current interest, the latter phenomena are challenging to study computationally because of multiple structural transitions occurring over a broad temperature range. We show how the parallel framework facilitates simulations of such processes and, without any loss of accuracy or precision, gives a significant speedup and allows for the study of much larger systems and much wider temperature ranges than possible with single-walker methods.
Improving Wang-Landau sampling with adaptive windows
NASA Astrophysics Data System (ADS)
Cunha-Netto, A. G.; Caparica, A. A.; Tsai, Shan-Ho; Dickman, Ronald; Landau, D. P.
2008-11-01
Wang-Landau sampling (WLS) of large systems requires dividing the energy range into “windows” and joining the results of simulations in each window. The resulting density of states (and associated thermodynamic functions) is shown to suffer from boundary effects in simulations of lattice polymers and the five-state Potts model. Here, we implement WLS using adaptive windows. Instead of defining fixed energy windows (or windows in the energy-magnetization plane for the Potts model), the boundary positions depend on the set of energy values on which the histogram is flat at a given stage of the simulation. Shifting the windows each time the modification factor f is reduced, we eliminate border effects that arise in simulations using fixed windows. Adaptive windows extend significantly the range of system sizes that may be studied reliably using WLS.
Generic parallel Wang-Landau sampling for complex systems
NASA Astrophysics Data System (ADS)
Li, Ying Wai; Vogel, Thomas; Landau, David P.; Wüst, Thomas
2013-03-01
We introduce a parallel realization for Wang-Landau sampling in Monte Carlo simulations based on a replica-exchange framework. The key idea is to split the entire energy range of the system under consideration into several smaller, overlapping sub intervals. The survey of configurational phase space can then be distributed over multiple processors, with exchanges of random walkers taking place in the overlapping energy windows. To demonstrate the robustness and advantages of this parallel scheme for the simulations of complex systems, we have applied it to protein adsorption problems using the HP lattice protein model[1]. The method gives significant speed-up and achieves strong scaling on small computer architectures like multi-core processors, with a possible improvement in accuracy. We believe that it could be potentially beneficial for large-scale petaflop machines.
Remarks on the geometric quantization of Landau levels
NASA Astrophysics Data System (ADS)
Galasso, Andrea; Spera, Mauro
2016-08-01
In this note, we resume the geometric quantization approach to the motion of a charged particle on a plane, subject to a constant magnetic field perpendicular to the latter, by showing directly that it gives rise to a completely integrable system to which we may apply holomorphic geometric quantization. In addition, we present a variant employing a suitable vertical polarization and we also make contact with Bott’s quantization, enforcing the property “quantization commutes with reduction”, which is known to hold under quite general conditions. We also provide an interpretation of translational symmetry breaking in terms of coherent states and index theory. Finally, we give a representation theoretic description of the lowest Landau level via the use of an S1-equivariant Dirac operator.
Multiple Walkers in the Wang-Landau Algorithm
Brown, G
2005-12-28
The mean cost for converging an estimated density of states using the Wang-Landau algorithm is measured for the Ising and Heisenberg models. The cost increases in a power-law fashion with the number of spins, with an exponent near 3 for one-dimensional models, and closer to 2.4 for two-dimensional models. The effect of multiple, simultaneous walkers on the cost is also measured. For the one-dimensional Ising model the cost can increase with the number of walkers for large systems. For both the Ising and Heisenberg models in two-dimensions, no adverse impact on the cost is observed. Thus multiple walkers is a strategy that should scale well in a parallel computing environment for many models of magnetic materials.
Mirror Symmetry: FJRW-rings and Landau-Ginzburg Orbifolds
NASA Astrophysics Data System (ADS)
Acosta, Pedro
2009-10-01
For any non-degenerate, quasihomogeneous superpotential W and an admissible group of diagonal symmetries G, Fan, Jarvis and Ruan have constructed a quantum cohomological field theory (FJRW-theory) that gives, among other things, a Frobenius algebra HW,G ((a,c) ring) and correlators associated with the superpotential. This construction is analogous to a theory of the Gromov-Witten type. The FJRW- theory is a candidate for the mathematical structure behind N= 2 superconformal Landau-Ginzburg orbifolds. In this presentation I will give an overview of this theory and discuss the Berglund-H"ubsch-Krawitz mirror symmetry conjecture: For a given invertible superpotential W there exists an invertible superpotential W^T such that the Frobenius algebra HW,G is isomorphic to the (c,c) ring of W^T, and the Frobenius algebra HW^T,G^T is isomorphic to the (c,c) ring of W.
Landau-Lifshitz theory of the magnon-drag thermopower
NASA Astrophysics Data System (ADS)
Flebus, B.; Duine, R. A.; Tserkovnyak, Y.
2016-09-01
Metallic ferromagnets subjected to a temperature gradient exhibit a magnonic drag of the electric current. We address this problem by solving a stochastic Landau-Lifshitz equation to calculate the magnon-drag thermopower. The long-wavelength magnetic dynamics result in two contributions to the electromotive force acting on electrons: 1) An adiabatic Berry-phase force related to the solid angle subtended by the magnetic precession and 2) a dissipative correction thereof, which is rooted microscopically in the spin-dephasing scattering. The first contribution results in a net force pushing the electrons towards the hot side, while the second contribution drags electrons towards the cold side, i.e., in the direction of the magnonic drift. The ratio between the two forces is proportional to the ratio between the Gilbert damping coefficient α and the coefficient β parametrizing the dissipative contribution to the electromotive force.
Longitudinal hydrodynamics from event-by-event Landau initial conditions
Sen, Abhisek; Gerhard, Jochen; Torrieri, Giorgio; Read, Kenneth; Wong, Cheuk-Yin
2015-02-02
Here we investigate three-dimensional ideal hydrodynamic evolution, with Landau initial conditions, incorporating event-by-event variation with many events and transverse density inhomogeneities. We show that the transition to boost-invariant flow occurs too late for realistic setups, with corrections of θ (20%-30%) expected at freeze-out for most scenarios. Moreover, the deviation from boost invariance is correlated with both transverse flow and elliptic flow, with the more highly transversely flowing regions also showing the most violation of boost invariance. Therefore, if longitudinal flow is not fully developed at the early stages of heavy ion collisions, hydrodynamics where boost invariance holds at midrapidity is inadequate to extract transport coefficients of the quark-gluon plasma. We conclude by arguing that developing experimental probes of boost invariance is necessary, and suggest some promising directions in this regard.
Longitudinal hydrodynamics from event-by-event Landau initial conditions
Sen, Abhisek; Gerhard, Jochen; Torrieri, Giorgio; ...
2015-02-02
Here we investigate three-dimensional ideal hydrodynamic evolution, with Landau initial conditions, incorporating event-by-event variation with many events and transverse density inhomogeneities. We show that the transition to boost-invariant flow occurs too late for realistic setups, with corrections of θ (20%-30%) expected at freeze-out for most scenarios. Moreover, the deviation from boost invariance is correlated with both transverse flow and elliptic flow, with the more highly transversely flowing regions also showing the most violation of boost invariance. Therefore, if longitudinal flow is not fully developed at the early stages of heavy ion collisions, hydrodynamics where boost invariance holds at midrapidity ismore » inadequate to extract transport coefficients of the quark-gluon plasma. We conclude by arguing that developing experimental probes of boost invariance is necessary, and suggest some promising directions in this regard.« less
Wang-Landau Monte Carlo formalism applied to ferroelectrics
NASA Astrophysics Data System (ADS)
Bin-Omran, S.; Kornev, Igor A.; Bellaiche, L.
2016-01-01
The Wang-Landau Monte Carlo algorithm is implemented within an effective Hamiltonian approach and applied to BaTiO3 bulk. The density of states obtained by this approach allows a highly accurate and straightforward calculation of various thermodynamic properties, including phase transition temperatures, as well as polarization, dielectric susceptibility, specific heat, and electrocaloric coefficient at any temperature. This approach yields rather smooth data even near phase transitions and provides direct access to entropy and free energy, which allow us to compute properties that are typically unaccessible by atomistic simulations. Examples of such latter properties are the nature (i.e., first order versus second order) of the phase transitions for different supercell sizes and the thermodynamic limit of the Curie temperature and latent heat.
Six-dimensional Landau-Ginzburg-Wilson theory
NASA Astrophysics Data System (ADS)
Gracey, J. A.; Simms, R. M.
2017-01-01
We renormalize the six-dimensional cubic theory with an O (N )×O (m ) symmetry at three loops in the modified minimal subtraction (MS ¯ ) scheme. The theory lies in the same universality class as the four-dimensional Landau-Ginzburg-Wilson model. As a check we show that the critical exponents derived from the three-loop renormalization group functions at the Wilson-Fisher fixed point are in agreement with the large N d -dimensional critical exponents of the underlying universal theory. Having established this connection we analyze the fixed point structure of the perturbative renormalization group functions to estimate the location of the conformal window of the O (N )×O (2 ) model.
Nonlinear Ginzburg-Landau-type approach to quantum dissipation.
López, José L
2004-02-01
We formally derive two nonlinear Ginzburg-Landau type models starting from the Wigner-Fokker-Planck system, which rules the evolution of a quantum electron gas interacting with a heat bath in thermodynamic equilibrium. These models mainly consist of a quantum, dissipative O(Planck 3) hydrodynamic/O(Planck 4) stochastic correction to the frictional (Caldeira-Leggett-)Schrödinger equation. The main ingredient lies in the use of the hydrodynamic/stochastic fluid model approach associated with the quantum Fokker-Planck equation and the identification of the associated pressure field. Then, Madelung transformations set the problem in the Schrödinger picture of dissipative quantum mechanics. We also describe the stationary dynamics associated with both systems.
Explosive oscillation death in coupled Stuart-Landau oscillators
NASA Astrophysics Data System (ADS)
Bi, Hongjie; Hu, Xin; Zhang, Xiyun; Zou, Yong; Liu, Zonghua; Guan, Shuguang
2014-12-01
Recently, explosive phase transitions, such as explosive percolation and explosive synchronization, have attracted extensive research interest. So far, most existing works have investigated Kuramoto-type models, where only phase variables are involved. Here, we report the occurrence of explosive oscillation quenching in a system of coupled Stuart-Landau oscillators that incorporates both phase and amplitude dynamics. We observe three typical scenarios with distinct microscopic mechanism of occurrence, i.e., ordinary, hierarchical, and cluster explosive oscillation death, corresponding to different frequency distributions of oscillators. We carry out theoretical analyses and obtain the backward transition point, which is shown to be independent of the specific frequency distributions. Numerical results are consistent with the theoretical predictions.
Landau damping of Langmuir twisted waves with kappa distributed electrons
Arshad, Kashif Aman-ur-Rehman; Mahmood, Shahzad
2015-11-15
The kinetic theory of Landau damping of Langmuir twisted modes is investigated in the presence of orbital angular momentum of the helical (twisted) electric field in plasmas with kappa distributed electrons. The perturbed distribution function and helical electric field are considered to be decomposed by Laguerre-Gaussian mode function defined in cylindrical geometry. The Vlasov-Poisson equation is obtained and solved analytically to obtain the weak damping rates of the Langmuir twisted waves in a nonthermal plasma. The strong damping effects of the Langmuir twisted waves at wavelengths approaching Debye length are also obtained by using an exact numerical method and are illustrated graphically. The damping rates of the planar Langmuir waves are found to be larger than the twisted Langmuir waves in plasmas which shows opposite behavior as depicted in Fig. 3 by J. T. Mendoça [Phys. Plasmas 19, 112113 (2012)].
Landau-Zener Bloch Oscillations with Perturbed Flat Bands.
Khomeriki, Ramaz; Flach, Sergej
2016-06-17
Sinusoidal Bloch oscillations appear in band structures exposed to external fields. Landau-Zener (LZ) tunneling between different bands is usually a counteracting effect limiting Bloch oscillations. Here we consider a flat band network with two dispersive and one flat band, e.g., for ultracold atoms and optical waveguide networks. Using external synthetic gauge and gravitational fields we obtain a perturbed yet gapless band structure with almost flat parts. The resulting Bloch oscillations consist of two parts-a fast scan through the nonflat part of the dispersion structure, and an almost complete halt for substantial time when the atomic or photonic wave packet is trapped in the original flat band part of the unperturbed spectrum, made possible due to LZ tunneling.
Second-quantized Landau-Zener theory for dynamical instabilities
Anglin, J.R.
2003-05-01
State engineering in nonlinear quantum dynamics sometimes may demand driving the system through a sequence of dynamically unstable intermediate states. This very general scenario is especially relevant to the dilute Bose-Einstein condensates, for which ambitious control schemes have been based on the powerful Gross-Pitaevskii mean-field theory. Since this theory breaks down on logarithmically short time scales in the presence of dynamical instabilities, an interval of instabilities introduces quantum corrections, which may possibly derail a control scheme. To provide a widely applicable theory for such quantum corrections, this paper solves a general problem of time-dependent quantum-mechanical dynamical instability, by modeling it as a second-quantized analog of a Landau-Zener avoided crossing: a 'twisted crossing'.
Landau-Zener Bloch Oscillations with Perturbed Flat Bands
NASA Astrophysics Data System (ADS)
Khomeriki, Ramaz; Flach, Sergej
2016-06-01
Sinusoidal Bloch oscillations appear in band structures exposed to external fields. Landau-Zener (LZ) tunneling between different bands is usually a counteracting effect limiting Bloch oscillations. Here we consider a flat band network with two dispersive and one flat band, e.g., for ultracold atoms and optical waveguide networks. Using external synthetic gauge and gravitational fields we obtain a perturbed yet gapless band structure with almost flat parts. The resulting Bloch oscillations consist of two parts—a fast scan through the nonflat part of the dispersion structure, and an almost complete halt for substantial time when the atomic or photonic wave packet is trapped in the original flat band part of the unperturbed spectrum, made possible due to LZ tunneling.
Spin-transistor action via tunable Landau-Zener transitions.
Betthausen, C; Dollinger, T; Saarikoski, H; Kolkovsky, V; Karczewski, G; Wojtowicz, T; Richter, K; Weiss, D
2012-07-20
Spin-transistor designs relying on spin-orbit interaction suffer from low signal levels resulting from low spin-injection efficiency and fast spin decay. Here, we present an alternative approach in which spin information is protected by propagating this information adiabatically. We demonstrate the validity of our approach in a cadmium manganese telluride diluted magnetic semiconductor quantum well structure in which efficient spin transport is observed over device distances of 50 micrometers. The device is turned "off" by introducing diabatic Landau-Zener transitions that lead to a backscattering of spins, which are controlled by a combination of a helical and a homogeneous magnetic field. In contrast to other spin-transistor designs, we find that our concept is tolerant against disorder.
Laser induced inverse Landau damping in metallic nanoparticles
NASA Astrophysics Data System (ADS)
Garcia, Martin E.; Castro, Alberto; Alonso, J. A.; Rubio, Angel
2002-03-01
We perform real space time-dependent density functional calculations to study the response of small metallic nanoparticles to femtosecond laser pulses. In particular, we analyze the role of screening effects for different laser pulse intensities and frequencies. Calculations are performed on sodium clusters using both the Jellium model and pseudopitentials Based on our results we predict that, if a pulse of sufficiently high intensity ( > 10^14 W/cm^2) excites a single-particle state of the nanoparticle, the response of the system involves both the single-particle- and the surface-plasmon states. We argue that this creation of plasmons from the decay of single-particle excitations, which can be viewed as the inverse of the well known Landau-damping effect, is related to the time-evolution of the screening of charge fluctuations.
[A special case of 'deafness'; Landau-Kleffner syndrome].
Stroink, H; Van Dongen, H R; Meulstee, J; Scheltens-de Boer, M; Geesink, H H
1997-08-16
A boy aged 5 had displayed from the age of 3 a fluctuating deficit in understanding spoken language. Audiometric testing proved his hearing to be normal. After 18 months, the parents noticed minor attacks of 'absence'. An EEG showed a normal background pattern and frequent spikes and spike waves complexes; CT-scanning of the brain revealed no abnormalities. On the basis of the acquired language disorder, the seizures and the features of the nocturnal EEG, the diagnosis the syndrome of Landau-Kleffner was made. After treatment with ethosuximide a temporary improvement of the aphasia occurred. A permanent improvement however was realized by treatment with prednisone. The boy could attend a primary school. The syndrome runs a fluctuating course; the patient may recover, but he may also undergo general mental deterioration. Antiepileptic agents only may have a brief favorable effect on the aphasia. In case of failure corticosteroids or even subpial cortical transsection are indicated.
Landau theory of a constrained ferroelastic in two dimensions
NASA Astrophysics Data System (ADS)
Jacobs, A. E.
1995-09-01
The Landau expansion of the elastic energy in powers of the strains and their derivatives is applied to the ferroelastic transformation of a grain constrained so that the displacement vanishes on the boundaries of the grain; the model applies strictly only to the square-rectangular transformation, but some results may apply also to the tetragonal-orthorhombic transformation. The displacement and the strains are obtained by numerical minimization of the elastic energy (with respect to the displacement) for a square column with edges parallel to the 100 and 010 planes of the tetragonal phase. The structure obtained is a sequence of twin boundaries (parallel to the 110 planes of the parent phase) with nonzero dilatational and shear strains near the boundaries. The mean-field transformation temperature Tc(L) is depressed from the bulk value due to the finite width L of the grain, behaving roughly as Tc(L)=Tc(∞)-const/L.
Magnetic Oscillations and Landau Quantization in Decoupled Epitaxial Graphene Multilayers*
NASA Astrophysics Data System (ADS)
Stroscio, Joseph A.
2009-03-01
A fundamental challenge to the development of a new electronics based on single atomic sheets of carbon, known as graphene, is to realize a large-area production platform that can produce a carbon system with the same intrinsic properties as a single sheet of graphene. Multi-layer epitaxial graphene (MEG) grown on SiC substrates has been proposed as a possible platform to this end [1]. The central question is, Can MEG behave as single layer graphene with the same intrinsic electrical characteristics? In this talk we show that MEG graphene on SiC exhibits single layer graphene properties through new tunneling magnetic measurements. The circular motion of electrons in a magnetic field has historically been a powerful probe of the Fermi surface properties of materials. Oscillations in many measureable properties, such as magnetization, thermal conductivity, and resistance, all reflect the Landau quantization of the electron energy levels. In this talk we show the ability to observe tunneling magneto-conductance oscillations (TMCOs) in the tunneling differential conductance as a function of both magnetic field and electron energy. The TMCO arise from intense Dirac quantization of the 2-dimensional Dirac electron and hole quasiparticles in MEG grown on SiC substrates. Spatial profiles of the Landau quantization demonstrate the high quality of MEG on SiC with carrier concentrations that vary less than 10% over hundreds of nm. The single layer quantization observed in these multi-layer samples is attributed to observed rotational stacking domains that effectively decouple the carbon layers in MEG on SiC, thereby yielding single layer graphene properties in a large area carbon production method. *In collaboration with Lee Miller, Kevin Kubista, Gregory M. Rutter, Ming Ruan, Mike Sprinkle, Claire Berger, Walt A. de Heer, and Phillip N. First, Georgia Institute of Technology [1] W.A. de Heer et. al., Solid State Comm. 143, 92 (2007).
Thermodynamics of RNA structures by Wang–Landau sampling
Lou, Feng; Clote, Peter
2010-01-01
Motivation: Thermodynamics-based dynamic programming RNA secondary structure algorithms have been of immense importance in molecular biology, where applications range from the detection of novel selenoproteins using expressed sequence tag (EST) data, to the determination of microRNA genes and their targets. Dynamic programming algorithms have been developed to compute the minimum free energy secondary structure and partition function of a given RNA sequence, the minimum free-energy and partition function for the hybridization of two RNA molecules, etc. However, the applicability of dynamic programming methods depends on disallowing certain types of interactions (pseudoknots, zig-zags, etc.), as their inclusion renders structure prediction an nondeterministic polynomial time (NP)-complete problem. Nevertheless, such interactions have been observed in X-ray structures. Results: A non-Boltzmannian Monte Carlo algorithm was designed by Wang and Landau to estimate the density of states for complex systems, such as the Ising model, that exhibit a phase transition. In this article, we apply the Wang-Landau (WL) method to compute the density of states for secondary structures of a given RNA sequence, and for hybridizations of two RNA sequences. Our method is shown to be much faster than existent software, such as RNAsubopt. From density of states, we compute the partition function over all secondary structures and over all pseudoknot-free hybridizations. The advantage of the WL method is that by adding a function to evaluate the free energy of arbitary pseudoknotted structures and of arbitrary hybridizations, we can estimate thermodynamic parameters for situations known to be NP-complete. This extension to pseudoknots will be made in the sequel to this article; in contrast, the current article describes the WL algorithm applied to pseudoknot-free secondary structures and hybridizations. Availability: The WL RNA hybridization web server is under construction at http
Landau-Zener problem with decay and dephasing
NASA Astrophysics Data System (ADS)
Avishai, Y.; Band, Y. B.
2014-09-01
Two aspects of the classic two-level Landau-Zener (LZ) problem are considered. First, we address the LZ problem when one or both levels decay, i.e., ɛj(t)→ɛj(t)-iΓj/2. We find that if the system evolves from an initial time -T to a final time +T such that |ɛ1(±T)-ɛ2(±T)| is not too large, the LZ survival probability of a state |j> can increase with increasing decay rate of the other state |i≠j>. This surprising result occurs because the decay results in crossing of the two eigenvalues of the instantaneous non-Hermitian Hamiltonian. On the other hand, if |ɛ1(±T)-ɛ2(±T)|→∞ as T →∞, the probability is independent of the decay rate. These results are based on analytic solutions of the time-dependent Schrödinger equations for two cases: (a) the energy levels depend linearly on time, and (b) the energy levels are bounded and of the form ɛ1,2(t)=±ɛtanh(t/T). Second, we study LZ transitions affected by dephasing by formulating the Landau-Zener problem with noise in terms of a Schrödinger-Langevin stochastic coupled set of differential equations. The LZ survival probability then becomes a random variable whose probability distribution is shown to behave very differently for long and short dephasing times. We also discuss the combined effects of decay and dephasing on the LZ probability.
Chern-Simons theory for electrons in high Landau levels
NASA Astrophysics Data System (ADS)
Rosenow, Bernd; Scheidl, Stefan
2000-03-01
The state of a two dimensional electron gas in a magnetic field and in the presence of Coulomb interactions is of fundamental interest. Particular attention has been devoted to a partially filled lowest Landau level (LLL), where the correlation-induced fractional quantum Hall effect and composite fermions were studied. The physics of these phenomena is well described by Chern-Simons (CS) theories. In this contribution we focus on intermediate fields, where a higher Landau level is partially filled. We suggest to use the power of the CS approach to tackle also electron correlations in intermediate LLs. For an interacting electron gas the possibility of an inhomogeneous, charge density wave (CDW) like state has been predicted theoretically [1]. Recent experiments [2] have provided evidence for a large anisotropy in the electrical resistivity, which would be consistent with the formation of a CDW sate. It turns out that a CDW ground state arises naturally in the framework of a CS theory and shows many similarities with the intermediate state of superconductors. To carry through our program, we first map particles in a partially filled higher LL onto an effective LLL system and solve this new problem with the help of statistical transmutation. [1] A.A. Koulakov, M.M. Fogler, and B.I. Shklovskii, Phys. Rev. Lett. 76, 499 (1996); R. Moessner and J. T. Chalker, Phys. Rev. B 54, 5006 (1996). [2] M.P. Lilly et al., Phys. Rev. Lett. 82, 394 (1999); R. R. Du et al., cond-mat/9812925; W. Pan et al., cond-mat/9903160; M. P. Lilly et al., cond-mat/9903196.
NASA Astrophysics Data System (ADS)
Gani, Satrio; Rossi, Enrico
Van der Waals systems formed by two-dimensional (2D) crystals and nanostructures possess electronic properties that make them extremely interesting for basic science and for possible technological applications. By tuning the relative angle (the twist angle) between the layers, or nanostructures, forming the Van der Waals systems experimentalists have been able to control the stacking configuration of such systems. We study the dependence on the twist angle of the electronic properties of two classes of Van der Waals systems: double layers formed by two, one-atom thick, layers of a metal dichalcogenide such as molybdenum disulfide (MoS2), and graphene nanoribbons on a hexagonal boron nitride substrate. We present results that show how, for both classes of systems, the electronic properties can be strongly tuned via the twist angle. Work supported by ACS-PRF-53581-DNI5 and NSF-DMR-1455233.
Coronellis Cosmos in der Melker Stiftsbibliothek.
NASA Astrophysics Data System (ADS)
Glaßner, Gottfried; Pärr, Nora
2009-06-01
Die Melker Stiftsbibliothek besitzt ein Globenpaar des berühmten venezianischen Globenbauers Vincenzo Coronelli (1650-1718), einen Erdglobus von 1688 und einen Himmelsglobus von 1693. Wie und wann die beiden Globen nach Melk gekommen sind, ist nicht bekannt. Dass sie zur ursprünglichen Ausstattung der 1735 fertig gestellten Barockbibliothek gehörten, wird aber aus der zentralen Stellung deutlich, die dem Globus (Erdglobus und Armillarphäre) in dem von Paul Troger 1732 gemalten Deckenfresko zukommt. Mehrfach begegnet das Motiv des Globus als Attribut der Weisheit bzw. Philosophie, der Geographie bzw. Geometrie und der Astronomie in den beiden Hauptsälen wie auch in der Deckenmalerei von Johann Bergl in der Oberen Bibliothek (1768) und in der Kuppel des Gartenpavillons (1764).
NASA Astrophysics Data System (ADS)
Komori, Yosuke; Sakuma, Satoru; Okamoto, Tohru
2007-10-01
A spin current perpendicular to the electric current is investigated around a Landau level filling factor ν=3 in a GaAs/AlGaAs two-dimensional electron system. Measurements of dynamic nuclear polarization in the vicinity of the edge of a specially designed Hall bar sample indicate that the direction of the spin current with respect to the Hall electric field reverses its polarity at ν=3, where the dissipative current carried by holes in the spin up Landau level is replaced with that by electrons in the spin down Landau level.
Ginzburg-Landau free energy for molecular fluids: Determination and coarse-graining
NASA Astrophysics Data System (ADS)
Desgranges, Caroline; Delhommelle, Jerome
2017-02-01
Using molecular simulation, we determine Ginzburg-Landau free energy functions for molecular fluids. To this aim, we extend the Expanded Wang-Landau method to calculate the partition functions, number distributions and Landau free energies for Ar,CO2 and H2O . We then parametrize a coarse-grained free energy function of the density order parameter and assess the performance of this free energy function on its ability to model the onset of criticality in these systems. The resulting parameters can be readily used in hybrid atomistic/continuum simulations that connect the microscopic and mesoscopic length scales.
Demonstration of geometric Landau-Zener interferometry in a superconducting qubit.
Tan, Xinsheng; Zhang, Dan-Wei; Zhang, Zhentao; Yu, Yang; Han, Siyuan; Zhu, Shi-Liang
2014-01-17
Geometric quantum manipulation and Landau-Zener interferometry have been separately explored in many quantum systems. In this Letter, we combine these two approaches to study the dynamics of a superconducting phase qubit. We experimentally demonstrate Landau-Zener interferometry based on the pure geometric phases in this solid-state qubit. We observe the interference caused by a pure geometric phase accumulated in the evolution between two consecutive Landau-Zener transitions, while the dynamical phase is canceled out by a spin-echo pulse. The full controllability of the qubit state as a function of the intrinsically robust geometric phase provides a promising approach for quantum state manipulation.
Gauging a quantum heat bath with dissipative Landau-Zener transitions.
Wubs, Martijn; Saito, Keiji; Kohler, Sigmund; Hänggi, Peter; Kayanuma, Yosuke
2006-11-17
We calculate the exact Landau-Zener transition probabilities for a qubit with an arbitrary linear coupling to a bath at zero temperature. The final quantum state exhibits a peculiar entanglement between the qubit and the bath. In the special case of diagonal coupling, the bath does not influence the transition probability, whatever the speed of the Landau-Zener sweep. It is proposed to use Landau-Zener transitions to determine both the reorganization energy and the integrated spectral density of the bath. Possible applications include circuit QED and molecular nanomagnets.
Gauging a Quantum Heat Bath with Dissipative Landau-Zener Transitions
Wubs, Martijn; Kohler, Sigmund; Haenggi, Peter; Saito, Keiji; Kayanuma, Yosuke
2006-11-17
We calculate the exact Landau-Zener transition probabilities for a qubit with an arbitrary linear coupling to a bath at zero temperature. The final quantum state exhibits a peculiar entanglement between the qubit and the bath. In the special case of diagonal coupling, the bath does not influence the transition probability, whatever the speed of the Landau-Zener sweep. It is proposed to use Landau-Zener transitions to determine both the reorganization energy and the integrated spectral density of the bath. Possible applications include circuit QED and molecular nanomagnets.
Ancillary Services Provided from DER
Campbell, J.B.
2005-12-21
Distributed energy resources (DER) are quickly making their way to industry primarily as backup generation. They are effective at starting and then producing full-load power within a few seconds. The distribution system is aging and transmission system development has not kept up with the growth in load and generation. The nation's transmission system is stressed with heavy power flows over long distances, and many areas are experiencing problems in providing the power quality needed to satisfy customers. Thus, a new market for DER is beginning to emerge. DER can alleviate the burden on the distribution system by providing ancillary services while providing a cost adjustment for the DER owner. This report describes 10 types of ancillary services that distributed generation (DG) can provide to the distribution system. Of these 10 services the feasibility, control strategy, effectiveness, and cost benefits are all analyzed as in the context of a future utility-power market. In this market, services will be provided at a local level that will benefit the customer, the distribution utility, and the transmission company.
Segmentierung der Papille in Fundusaufnahmen Aktives Kreisbogen-Modell
NASA Astrophysics Data System (ADS)
Schmidt, Torsten; Doering, Axel
In der vorliegenden Arbeit präsentieren wir einen praxistauglichen Algorithmus zur automatischen Segmentierung der Disc-Grenze der Papille in Fundusaufnahmen. Ausgehend von einem lokalisierten Papillenpunkt werden Grauwertverläufe in horizontaler und vertikaler Richtung mittels einer Energiefunktion ausgewertet. In einem iterativen Prozess wird die Ellipse der tatsächlichen Disc-Grenze angenähert. Der Papillenrand konnte im Testdatensatz in 88% der Aufnahmen erfolgreich segmentiert werden. Der Algorithmus ist robust gegenüber der Lage des Startpunktes innerhalb der Papille und soll als Unterstützung bei der Glaukombefundung eingesetzt werden.
Luican-Mayer, Adina; Kharitonov, Maxim; Li, Guohong; Lu, Chih-Pin; Skachko, Ivan; Gonçalves, Alem-Mar B; Watanabe, K; Taniguchi, T; Andrei, Eva Y
2014-01-24
We report the observation of an isolated charged impurity in graphene and present direct evidence of the close connection between the screening properties of a 2D electron system and the influence of the impurity on its electronic environment. Using scanning tunneling microscopy and Landau level spectroscopy, we demonstrate that in the presence of a magnetic field the strength of the impurity can be tuned by controlling the occupation of Landau-level states with a gate voltage. At low occupation the impurity is screened, becoming essentially invisible. Screening diminishes as states are filled until, for fully occupied Landau levels, the unscreened impurity significantly perturbs the spectrum in its vicinity. In this regime we report the first observation of Landau-level splitting into discrete states due to lifting the orbital degeneracy.
Strain-Induced Landau Levels in Arbitrary Dimensions with an Exact Spectrum.
Rachel, Stephan; Göthel, Ilja; Arovas, Daniel P; Vojta, Matthias
2016-12-23
Certain nonuniform strain applied to graphene flakes has been shown to induce pseudo-Landau levels in the single-particle spectrum, which can be rationalized in terms of a pseudomagnetic field for electrons near the Dirac points. However, this Landau level structure is, in general, approximate and restricted to low energies. Here, we introduce a family of strained bipartite tight-binding models in arbitrary spatial dimension d and analytically prove that their entire spectrum consists of perfectly degenerate pseudo-Landau levels. This construction generalizes the case of triaxial strain on graphene's honeycomb lattice to arbitrary d; in d=3, our model corresponds to tetraxial strain on the diamond lattice. We discuss general aspects of pseudo-Landau levels in arbitrary d.
Toward the Landau-Lifshitz version of the Thomson electrostatics theorem
NASA Astrophysics Data System (ADS)
Grinfeld, Michael; Grinfeld, Pavel
In the classical textbook (Landau and Lifshitz, 1963), Landau and Lifshtz suggested their version of the famous Thomson variational principle (a.k.a Thomson theorem.) So far, their version has not gained the interest it deserves, either among physicists or among applied mathematicians. Partially, the lack of interest can be explained because of the quality of the suggested proof of the principle. It is considerably lower than the standards accepted in classical electrostatics and mathematical physics. Even more importantly, Landau and Lifshitz did not demostrate the minimum property of the electrostatic energy at equilibrium. In this note, we, first, modify and specify the Landau-Lifshitz formulation of the principle presenting it as the isoperimetric variational problem. Then, for this isoperimetric problem we calculate the first and second variations, and we prove that the first variation vanishes, whereas the second variation appears to be positive.
Competing Quantum Hall Phases in the Second Landau Level in Low Density Limit
Pan, Wei; Serafin, A.; Xia, J. S.; Liang, Y.; Sullivan, N. S.; Baldwin, K. W.; West, K. W.; Pfeiffer, L. N.; Tsui, D. C.
2015-01-01
Up to date, studies of the fractional quantum Hall effect (FQHE) states in the second Landau level have mainly been carried out in the high electron density regime, where the electron mobility is the highest. Only recently, with the advance of high quality low density MBE growth, experiments have been pushed to the low density regime [1], where the electron-electron interactions are strong and the Landau level mixing parameter, defined by κ = e^{2}/εI_{B}/ℏω_{e}, is large. Here, l_{B} = (ℏe/B)^{1/2} is the magnetic length and ω_{c} = eB/m the cyclotron frequency. All other parameters have their normal meanings. It has been shown that a large Landau level mixing effect strongly affects the electron physics in the second Landau level [2].
Landau and Lifshitz' formulation of Le Chatelier's principle: an insight into symbiosis?
Halabi, T
2013-12-01
A correspondence allows application of Landau and Lifshitz' formulation of Le Chatelier's principle from statistical physics to a simple 2-D model of biological symbiosis. The insight: symbionts stabilize the occupation of narrow peaks on fitness landscape.
Ginzburg-Landau theory of a trapped Fermi gas with a BEC-BCS crossover
Huang Kun; Yu Zengqiang; Yin Lan
2009-05-15
The Ginzburg-Landau theory of a trapped Fermi gas with a BEC-BCS crossover is derived by the path-integral method. In addition to the standard Ginzburg-Landau equation, a second equation describing the total atom density is obtained. These two coupled equations are necessary to describe both homogeneous and inhomogeneous systems. The Ginzburg-Landau theory is valid near the transition temperature T{sub c} on both sides of the crossover. In the weakly interacting BEC region, it is also accurate at zero temperature where the Ginzburg-Landau equation can be mapped onto the Gross-Pitaevskii (GP) equation. The applicability of GP equation at finite temperature is discussed. On the BEC side, the fluctuation of the order parameter is studied and the renormalization to the molecule coupling constant is obtained.
Landau retardation on the occurrence scattering time in quantum electron-hole plasmas
NASA Astrophysics Data System (ADS)
Hong, Woo-Pyo; Jung, Young-Dae
2016-03-01
The Landau damping effects on the occurrence scattering time in electron collisions are investigated in a quantum plasma composed of electrons and holes. The Shukla-Stenflo-Bingham effective potential model is employed to obtain the occurrence scattering time in a quantum electron-hole plasma. The result shows that the influence of Landau damping produces the imaginary term in the scattering amplitude. It is then found that the Landau damping generates the retardation effect on the occurrence scattering time. It is found that the occurrence scattering time increases in forward scattering domains and decreases in backward scattering domains with an increase of the Landau parameter. It is also found that the occurrence scattering time decreases with increasing collision energy. In addition, it is found that the quantum shielding effect enhances the occurrence scattering time in the forward scattering and, however, suppresses the occurrence scattering time in the backward scattering.
Strain-Induced Landau Levels in Arbitrary Dimensions with an Exact Spectrum
NASA Astrophysics Data System (ADS)
Rachel, Stephan; Göthel, Ilja; Arovas, Daniel P.; Vojta, Matthias
2016-12-01
Certain nonuniform strain applied to graphene flakes has been shown to induce pseudo-Landau levels in the single-particle spectrum, which can be rationalized in terms of a pseudomagnetic field for electrons near the Dirac points. However, this Landau level structure is, in general, approximate and restricted to low energies. Here, we introduce a family of strained bipartite tight-binding models in arbitrary spatial dimension d and analytically prove that their entire spectrum consists of perfectly degenerate pseudo-Landau levels. This construction generalizes the case of triaxial strain on graphene's honeycomb lattice to arbitrary d ; in d =3 , our model corresponds to tetraxial strain on the diamond lattice. We discuss general aspects of pseudo-Landau levels in arbitrary d .
Capri, M.A.L. . E-mail: marcio@dft.if.uerj.br; Sobreiro, R.F. . E-mail: sobreiro@uerj.br; Sorella, S.P. . E-mail: sorella@uerj.br; Thibes, R. . E-mail: thibes@dft.if.uerj.br
2007-08-15
A detailed discussion of the renormalization properties of a class of gauges which interpolates among the Landau, Coulomb and maximal Abelian gauges is provided in the framework of the algebraic renormalization in Euclidean Yang-Mills theories in four dimensions.
Experimental evidence and the Landau-Zener promotion in nucleus-nucleus collisions
Cindro, N.; Freeman, R.M.; Haas, F.
1986-04-01
Recent data from C+O collisions are analyzed in terms of the Landau-Zener promotion in nuclei. Evidence for the presence of this mechanism in nuclear collisions is of considerable interest, since it provides a signature of single-particle orbitals in molecular-type potentials and, at the same time, paves the way to a microscopic understanding of the collision dynamics, in particular of the energy dissipation rate. The analyzed data are of two types: integrated cross sections and angular distributions of inelastically scattered particles. The first set of data shows structure qualitatively consistent with recent calculations of the Landau-Zener effect; for this set of data no other reasonable explanation is presently available. The second set of data, while consistent with the presence of the Landau-Zener promotion, is examined in terms of other possible explanations too. The combined data show evidence favoring the presence of the Landau-Zener promotion in nucleus-nucleus collisions.
A new paradigm for petascale Monte Carlo simulation: Replica exchange Wang-Landau sampling
NASA Astrophysics Data System (ADS)
Li, Ying Wai; Vogel, Thomas; Wüst, Thomas; Landau, David P.
2014-05-01
We introduce a generic, parallel Wang-Landau method that is naturally suited to implementation on massively parallel, petaflop supercomputers. The approach introduces a replica-exchange framework in which densities of states for overlapping sub-windows in energy space are determined iteratively by traditional Wang-Landau sampling. The advantages and general applicability of the method are demonstrated for several distinct systems that possess discrete or continuous degrees of freedom, including those with complex free energy landscapes and topological constraints.
FROM THE HISTORY OF PHYSICS: L D Landau in the Soviet Atomic Project: a documentary study
NASA Astrophysics Data System (ADS)
Kiselev, G. V.
2008-09-01
The article presents information about the participation of Academician L D Landau in the Soviet Atomic Project and is based on a study of archive documents of the First Main Directorate. Their analysis points to L D Landau's important contribution to the development of the theory of heterogeneous nuclear reactors and to the computational justification of the first designs of atomic and hydrogen bombs. Many of the quoted documents have never been published before.
An unphysical result for the Landau-Lifshitz equation of motion for a charged particle
NASA Astrophysics Data System (ADS)
de Parga, G. A.; Mares, R.; Dominguez, S.
2006-04-01
An unphysical result for the Landau-Lifshitz equation of motion for a charged particle is presented. The similarity with the Lorentz-Dirac equation is discussed. Indeed the reaction force obtained for the uniform electric field vanishes when the motion is parallel to it in both cases. A discussion of this unphysical result is given and the need for of an expression for the radiation rate of energy for the Landau-Lifshitz theory is emphasized.
Landau-Zener problem in a three-level neutrino system with nonlinear time dependence
Keraenen, P.; Maalampi, J.; Myyrylaeinen, M.; Riittinen, J.
2007-02-01
We consider the level-crossing problem in a three-level system with nonlinearly time-varying Hamiltonian (time-dependence t{sup -3}). We study the validity of the so-called independent crossing approximation in the Landau-Zener model by making comparison with results obtained numerically in the density matrix approach. We also demonstrate the failure of the so-called 'nearest zero' approximation of the Landau-Zener level-crossing probability integral.
NASA Astrophysics Data System (ADS)
Barkeshli, Maissam; McGreevy, John
2012-08-01
One of the most successful theories of a non-Fermi-liquid metallic state is the composite Fermi-liquid (CFL) theory of the half-filled Landau level. In this paper, we study continuous quantum phase transitions out of the CFL state and into a Landau Fermi liquid, in the limit of no disorder and fixed particle number. This transition can be induced by tuning the bandwidth of the Landau level relative to the interaction energy, for instance through an externally applied periodic potential. We find a transition to the Landau Fermi liquid through a gapless Mott insulator with a Fermi surface of neutral fermionic excitations. In the presence of spatial symmetries, we also find a direct continuous transition between the CFL and the Landau Fermi liquid. The transitions have a number of characteristic observable signatures, including the presence of two crossover temperature scales, resistivity jumps, and vanishing compressibility. When the composite fermions are paired instead, our results imply quantum critical points between various non-Abelian topological states, including the ν=1/2 Moore-Read Pfaffian [Ising × U(1) topological order], a version of the Kitaev B phase (Ising topological order), and paired electronic superconductors. To study such transitions, we use a projective construction of the CFL, which goes beyond the conventional framework of flux attachment to include a broader set of quantum fluctuations. These considerations suggest a possible route to fractionalized Mott insulators by starting with fractional quantum Hall states and tuning the Landau-level bandwidth.
Robust fractional quantum Hall effect in the N=2 Landau level in bilayer graphene
Diankov, Georgi; Liang, Chi-Te; Amet, François; Gallagher, Patrick; Lee, Menyoung; Bestwick, Andrew J.; Tharratt, Kevin; Coniglio, William; Jaroszynski, Jan; Watanabe, Kenji; Taniguchi, Takashi; Goldhaber-Gordon, David
2016-01-01
The fractional quantum Hall effect is a canonical example of electron–electron interactions producing new ground states in many-body systems. Most fractional quantum Hall studies have focussed on the lowest Landau level, whose fractional states are successfully explained by the composite fermion model. In the widely studied GaAs-based system, the composite fermion picture is thought to become unstable for the N≥2 Landau level, where competing many-body phases have been observed. Here we report magneto-resistance measurements of fractional quantum Hall states in the N=2 Landau level (filling factors 4<|ν|<8) in bilayer graphene. In contrast with recent observations of particle–hole asymmetry in the N=0/N=1 Landau levels of bilayer graphene, the fractional quantum Hall states we observe in the N=2 Landau level obey particle–hole symmetry within the fully symmetry-broken Landau level. Possible alternative ground states other than the composite fermions are discussed. PMID:28000663
Exploring HP protein models using Wang-Landau sampling
NASA Astrophysics Data System (ADS)
Wuest, Thomas; Landau, David P.
2008-03-01
The hydrophobic-polar (HP) protein model has become a standard in assessing the efficiency of computational methods for protein structure prediction as well as for exploring the statistical physics of protein folding in general. Numerous methods have been proposed to address the challenges of finding minimal energy conformations within the rough energy landscape of this lattice heteropolymer model. However, only a few studies have been dedicated to the more revealing - but also more demanding - problem of estimating the density of states which allows access to thermodynamic properties of a system at any temperature. Here, we show that Wang-Landau sampling, in connection with a suitable move set (``pull moves''), provides a powerful route for the ground state search and the precise determination of the density of states for HP sequences (with up to 100 monomers) in both, two and three dimensions. Our procedure possesses an intrinsic simplicity and overcomes the inevitable limitations inherent in other more tailored approaches. The main advantage lies in its general applicability to a broad range of lattice protein models that go beyond the scope of the HP model.
Shear Alfven waves with Landau and collisional effects
Hedrick, C.L.; Leboeuf, J.; Spong, D.A.
1995-06-01
Shear Alfven waves can be driven unstable by hot particles such as alpha particles in an ignited fusion device or hot ions in existing devices. Motivated by rather collisional Wendelstein 7 Advanced Stellarator (W7-AS) [Phys. Rev. Lett. {bold 72}, 1220 (1994)] beam-driven global Alfven instability experiments, the effect of electron and ion collisions on these modes has been examined. Collisions broaden and suppress the peak associated with Landau effects. This broadening makes ion damping more important, while the electron damping is suppressed. Additional resistive effects provide increased damping for the main part of the spectrum, which can have a rather high phase velocity. Of more general interest is the fact that collisional and collisionless resistivity has a numerically stabilizing effect that is known to be important for nonlinear resistive magnetohydrodynamics (MHD). This can preclude the need for introducing and testing the sensitivity to similar ad hoc effects. Numerical and analytic results for both a particle-conserving Krook collision operator and a Lorentz (pitch angle) collision operator are compared and contrasted.
Landau-Ginzburg orbifolds and symmetries of K3 CFTs
Cheng, Miranda C. N.; Ferrari, Francesca; Harrison, Sarah M.; ...
2017-01-11
Recent developments in the study of the moonshine phenomenon, including umbral and Conway moonshine, suggest that it may play an important role in encoding the action of finite symmetry groups on the BPS spectrum of K3 string theory. To test and clarify these proposed K3-moonshine connections, we study Landau-Ginzburg orbifolds that flow to conformal field theories in the moduli space of K3 sigma models. We compute K3 elliptic genera twined by discrete symmetries that are manifest in the UV description, though often inaccessible in the IR. We obtain various twining functions coinciding with moonshine predictions that have not been observedmore » in physical theories before. These include twining functions arising from Mathieu moonshine, other cases of umbral moonshine, and Conway moonshine. For instance, all functions arising from M11 c 2.M12 moonshine appear as explicit twining genera in the LG models, which moreover admit a uniform description in terms of its natural 12-dimensional representation. Finally, our results provide strong evidence for the relevance of umbral moonshine for K3 symmetries, as well as new hints for its eventual explanation.« less
Landau quantization in the spinning cosmic string spacetime
NASA Astrophysics Data System (ADS)
Muniz, C. R.; Bezerra, V. B.; Cunha, M. S.
2014-11-01
We analyze the quantum phenomenon arising from the interaction of a spinless charged particle with a rotating cosmic string, under the action of a static and uniform magnetic field parallel to the string. We calculate the energy levels of the particle in the non-relativistic approach, showing how these energies depend on the parameters involved in the problem. In order to do this, we solve the time independent Schrödinger equation in the geometry of the spinning cosmic string, taking into account that the coupling between the rotation of the spacetime and the angular momentum of the particle is very weak, such that makes sense to apply the Schrödinger equation in a curved background whose metric has an off diagonal term which involves time and space. It is also assumed that the particle orbits sufficiently far from the boundary of the region of closed timelike curves which exist around this topological defect. Finally, we find the Landau levels of the particle in the presence of a spinning cosmic string endowed with internal structure, i.e., having a finite width and uniformly filled with both material and vacuum energies.
Extended Ginzburg-Landau formalism for two-band superconductors.
Shanenko, A A; Milošević, M V; Peeters, F M; Vagov, A V
2011-01-28
Recent observation of unusual vortex patterns in MgB(2) single crystals raised speculations about possible "type-1.5" superconductivity in two-band materials, mixing the properties of both type-I and type-II superconductors. However, the strict application of the standard two-band Ginzburg-Landau (GL) theory results in simply proportional order parameters of the two bands-and does not support the "type-1.5" behavior. Here we derive the extended GL formalism (accounting all terms of the next order over the small τ=1-T/T(c) parameter) for a two-band clean s-wave superconductor and show that the two condensates generally have different spatial scales, with the difference disappearing only in the limit T→T(c). The extended version of the two-band GL formalism improves the validity of GL theory below T(c) and suggests revisiting the earlier calculations based on the standard model.
Hot nuclei -- Landau theory, thermal fluctuations and dissipation
Alhassid, Y.
1990-01-01
The basic ideas and theoretical methods used in the description of hot nuclei are reviewed. In particular, a macroscopic approach to shape transitions is discussed in the framework of the Landau theory in which the quadrupole shape degrees of freedom play the role of the order parameters. This theory describes the universal features of the nuclear shape evolution with temperature and spin. A unified description of fluctuations in all five quadrupole degrees of freedom is introduced and plays an important role in the calculation of physical observables. A macroscopic approach to the giant dipole resonance (GDR) in hot nuclei is developed. With all parameters fixed by the zero temperature nuclear properties, the theory predicts both the GDR cross-section and angular anisotropy of the {gamma}-rays in very good agreement with recent experiments. The intrinsic shape fluctuations are the main cause for the resonance broadening at higher temperatures, while the orientation fluctuations are responsible for the observed attenuation in the angular anisotropy. Dissipation at finite temperature is discussed in the framework of a Langevin-like equation describing the time-dependent shape fluctuations. Non-adiabatic effects may cause motional narrowing of the resonance.
Hot nuclei -- Landau theory, thermal fluctuations and dissipation
Alhassid, Y.
1990-12-31
The basic ideas and theoretical methods used in the description of hot nuclei are reviewed. In particular, a macroscopic approach to shape transitions is discussed in the framework of the Landau theory in which the quadrupole shape degrees of freedom play the role of the order parameters. This theory describes the universal features of the nuclear shape evolution with temperature and spin. A unified description of fluctuations in all five quadrupole degrees of freedom is introduced and plays an important role in the calculation of physical observables. A macroscopic approach to the giant dipole resonance (GDR) in hot nuclei is developed. With all parameters fixed by the zero temperature nuclear properties, the theory predicts both the GDR cross-section and angular anisotropy of the {gamma}-rays in very good agreement with recent experiments. The intrinsic shape fluctuations are the main cause for the resonance broadening at higher temperatures, while the orientation fluctuations are responsible for the observed attenuation in the angular anisotropy. Dissipation at finite temperature is discussed in the framework of a Langevin-like equation describing the time-dependent shape fluctuations. Non-adiabatic effects may cause motional narrowing of the resonance.
Landau quantization and Fermi velocity renormalization in twisted graphene bilayers
NASA Astrophysics Data System (ADS)
Yin, Long-Jing; Qiao, Jia-Bin; Wang, Wen-Xiao; Zuo, Wei-Jie; Yan, Wei; Xu, Rui; Dou, Rui-Fen; Nie, Jia-Cai; He, Lin
2015-11-01
Currently there is a lively discussion concerning Fermi velocity renormalization in twisted bilayers and several contradicted experimental results are reported. Here we study electronic structures of the twisted bilayers by scanning tunneling microscopy (STM) and spectroscopy (STS). The interlayer coupling strengths between the adjacent bilayers are measured according to energy separations of two pronounced low-energy van Hove singularities (VHSs) in the STS spectra. We demonstrate that there is a large range of values for the interlayer interaction not only in different twisted bilayers, but also in twisted bilayers with the same rotation angle. Below the VHSs, the observed Landau quantization in the twisted bilayers is identical to that of massless Dirac fermions in graphene monolayer, which allows us to measure the Fermi velocity directly. Our result indicates that the Fermi velocity of the twisted bilayers depends remarkably on both the twisted angles and the interlayer coupling strengths. This removes the discrepancy about the Fermi velocity renormalization in the twisted bilayers and provides a consistent interpretation of all current data.
Quantum criticality: beyond the Landau-Ginzburg-Wilson paradigm
NASA Astrophysics Data System (ADS)
Sachdev, Subir
2004-03-01
I will describe a variety of quantum critical points in metal and insulators which do not fall into the conventional Landau-Ginzburg-Wilson framework of fluctuating order parameters. In some cases, one of the phases adjoining the critical point is characterized by topological order and emergent gauge excitations, such as the fractionalized Fermi liquid (T. Senthil, S. Sachdev, and M. Vojta, Phys. Rev. Lett. 90), 216403 (2003).; the quantum critical point is characterized by non-Fermi liquid behavior in its thermodynamic and transport properties. In other cases(T. Senthil, A. Vishwanath, L. Balents, S. Sachdev, and M.P.A. Fisher, cond-mat/0311326.), both phases adjoining the critical point are characterized only by conventional order parameters and do not possess any fractionalized excitations: nevertheless, the critical theory is expressed in terms of fractionalized degrees of freedom and contains emergent gauge modes. The quantum `disordering' transition of the S=1/2 antiferromagnet with Neel order on the square lattice falls into the latter class (in this case the `disordered' phase has conventional valence bond order). I will comment on the broader implications of our results for the experimental study of quantum criticality in metals, insulators and superconductors.
Accessible solitons in complex Ginzburg-Landau media
NASA Astrophysics Data System (ADS)
He, Yingji; Malomed, Boris A.
2013-10-01
We construct dissipative spatial solitons in one- and two-dimensional (1D and 2D) complex Ginzburg-Landau (CGL) equations with spatially uniform linear gain; fully nonlocal complex nonlinearity, which is proportional to the integral power of the field times the harmonic-oscillator (HO) potential, similar to the model of “accessible solitons;” and a diffusion term. This CGL equation is a truly nonlinear one, unlike its actually linear counterpart for the accessible solitons. It supports dissipative spatial solitons, which are found in a semiexplicit analytical form, and their stability is studied semianalytically, too, by means of the Routh-Hurwitz criterion. The stability requires the presence of both the nonlocal nonlinear loss and diffusion. The results are verified by direct simulations of the nonlocal CGL equation. Unstable solitons spontaneously spread out into fuzzy modes, which remain loosely localized in the effective complex HO potential. In a narrow zone close to the instability boundary, both 1D and 2D solitons may split into robust fragmented structures, which correspond to excited modes of the 1D and 2D HOs in the complex potentials. The 1D solitons, if shifted off the center or kicked, feature persistent swinging motion.
Landau quantization in the spinning cosmic string spacetime
Muniz, C.R.; Bezerra, V.B.; Cunha, M.S.
2014-11-15
We analyze the quantum phenomenon arising from the interaction of a spinless charged particle with a rotating cosmic string, under the action of a static and uniform magnetic field parallel to the string. We calculate the energy levels of the particle in the non-relativistic approach, showing how these energies depend on the parameters involved in the problem. In order to do this, we solve the time independent Schrödinger equation in the geometry of the spinning cosmic string, taking into account that the coupling between the rotation of the spacetime and the angular momentum of the particle is very weak, such that makes sense to apply the Schrödinger equation in a curved background whose metric has an off diagonal term which involves time and space. It is also assumed that the particle orbits sufficiently far from the boundary of the region of closed timelike curves which exist around this topological defect. Finally, we find the Landau levels of the particle in the presence of a spinning cosmic string endowed with internal structure, i.e., having a finite width and uniformly filled with both material and vacuum energies. - Highlights: • Solution of the wave equation characterizing the problem. • Energy levels of the particle in spacetime of the structureless string. • Expression for an analogous of the quadratic Zeeman effect. • Energy levels of the particle in spacetime of the string with internal structure. • Evidence of the string structure by the internal existence of the vacuum energy.
Landau-Ginzburg orbifolds and symmetries of K3 CFTs
NASA Astrophysics Data System (ADS)
Cheng, Miranda C. N.; Ferrari, Francesca; Harrison, Sarah M.; Paquette, Natalie M.
2017-01-01
Recent developments in the study of the moonshine phenomenon, including umbral and Conway moonshine, suggest that it may play an important role in encoding the action of finite symmetry groups on the BPS spectrum of K3 string theory. To test and clarify these proposed K3-moonshine connections, we study Landau-Ginzburg orbifolds that flow to conformal field theories in the moduli space of K3 sigma models. We compute K3ellipticgeneratwinedbydiscretesymmetriesthataremanifestintheUVdescription, though often inaccessible in the IR. We obtain various twining functions coinciding with moonshine predictions that have not been observed in physical theories before. These include twining functions arising from Mathieu moonshine, other cases of umbral moonshine, and Conway moonshine. For instance, all functions arising from M 11 ⊂ 2 .M 12 moonshine appear as explicit twining genera in the LG models, which moreover admit a uniform description in terms of its natural 12-dimensional representation. Our results provide strong evidence for the relevance of umbral moonshine for K3 symmetries, as well as new hints for its eventual explanation.
Surface Waves and Landau Resonant Heating in Unmagnetized Bounded Plasmas
NASA Astrophysics Data System (ADS)
Bowers, Kevin
2001-10-01
Owing to the large areas and high plasma densities found in some recently developed devices [1], electrostatic theories of plasma resonances and surface wave [2-3] propagation in such devices are suspect as the size of the device is much larger than the free space wavelength associated with the peak plasma frequency. Accordingly, an electromagnetic model of surface wave propagation has been developed appropriate for large area plasmas. The predicted wave dispersion of the two models differs for extremely long wavelengths but is degenerate in devices small compared with wavelength. First principles particle-in-cell simulations using new techniques developed for the demanding simulation regime have been conducted which support these results. Given the slow wave character and boundary localized fields of surface waves, a periodic electrode may be used to resonantly excite a strong wave-particle interaction between surface waves and electrons. At saturation, the electron velocity distribution is enhanced above the phase velocity of the applied wave and suppressed below. The use of this technique (``Landau resonant heating'') to selectively heat the electron high energy tail to enhance electron-impact ionization is demonstrated using particle-in-cell simulation. [1] Matsumoto (Sumitomo Metal Industries). Private Communication. July 1999. [2] Nickel, Parker, Gould. Phys. Fluids. 7:1489. 1964. [3] Cooperberg. Phys. Plasmas. Vol. 5, No. 4, April 1998.
Finite dimensionality in the complex Ginzburg-Landau equation
Doering, C.R.; Gibbon, J.D.; Holm, D.D.; Nicolaenko, B.
1987-01-01
Finite dimensionality is shown to exist in the complex Ginzburg-Landau equation periodic on the interval (0,1). A cone condition is derived and explained which gives upper bounds on the number of Fourier modes required to span the universal attractor and hence upper bounds on the attractor dimension itself. In terms of the parameter R these bounds are not large. For instance, when vertical bar ..mu.. vertical bar less than or equal to ..sqrt..3, the Fourier spanning dimension is 0(R/sup 3/2/). Lower bounds are estimated from the number of unstable side-bands using ideas from work on the Eckhaus instability. Upper bounds on the dimension of the attractor itself are obtained by bounding (or, for vertical bar ..mu.. vertical bar less than or equal to ..sqrt..3, computing exactly) the Lyapunov dimension and invoking a recent theorem of Constantin and Foias, which asserts that the Lyapunov dimension, defined by the Kaplan-Yorke formula, is an upper bound on the Hausdorff dimension. 39 refs., 7 figs.
Monte Carlo simulations of Landau-Ginzburg model for membranes
NASA Astrophysics Data System (ADS)
Koibuchi, Hiroshi; Shobukhov, Andrey
2014-02-01
The Landau-Ginzburg (LG) model for membranes is numerically studied on triangulated spheres in R3. The LG model is in sharp contrast to the model of Helfrich-Polyakov (HP). The reason for this difference is that the curvature energy of the LG (HP) Hamiltonian is defined by means of the tangential (normal) vector of the surface. For this reason, the curvature energy of the LG model includes the in-plane bending or shear energy component, which is not included in the curvature energy of the HP model. From the simulation data, we find that the LG model undergoes a first-order collapse transition. The results of the LG model in the higher-dimensional spaces Rd(d > 3) and on the self-avoiding (SA) surfaces in R3 are presented and discussed. We also study the David-Guitter (DG) model, which is a variant of the LG model, and find that the DG model undergoes a first-order transition. It is also found that the transition can be observed only on the homogeneous surfaces, which are composed of almost uniform triangles according to the condition that the induced metric ∂ar ṡ ∂br is close to δab.
The Absence of the FQHE at High Landau Levels
NASA Astrophysics Data System (ADS)
Koulakov, A. A.; Fogler, M. M.
1996-03-01
In our earlier paper (A. A. Koulakov, M. M. Fogler, and B. I. Shklovskii, preprint cond-mat/9508017) we have studied the ground state of a two-dimensional electron liquid in a weak magnetic field using the Hartree-Fock approximation (HFA). We have found that the electron cluster in large ``bubbles'', which form a regular lattice with the period of the order of the cyclotron radius. In this work we numerically compare the energies of the ``bubble'' phase and the Laughlin liquids at Landau level (LL) with indices up to N = 10. In calculations, we take into account the screening of the Coulomb interactions at the upper partially occupied LL by electrons of the lower fully occupied LLs. Using the iterational HFA for the ``bubble'' phase, and ansatz wave-function for FQHE states at N > 0 (A. H. MacDonald and S. M. Girvin, Phys. Rev. B 33), 4009 (1986), we show that 1/3 and 1/5 FQHE states do not withstand the competition with the ``bubble'' phase at N > 1.
Landau levels in uniaxially strained graphene: A geometrical approach
Betancur-Ocampo, Y. Cifuentes-Quintal, M.E.; Cordourier-Maruri, G.; Coss, R. de
2015-08-15
The effect of strain on the Landau levels (LLs) spectra in graphene is studied, using an effective Dirac-like Hamiltonian which includes the distortion in the Dirac cones, anisotropy and spatial-dependence of the Fermi velocity induced by the lattice change through a renormalized linear momentum. We propose a geometrical approach to obtain the electron’s wave-function and the LLs in graphene from the Sturm–Liouville theory, using the minimal substitution method. The coefficients of the renormalized linear momentum are fitted to the energy bands, which are obtained from a Density Functional Theory (DFT) calculation. In particular, we evaluate the case of Dirac cones with an ellipsoidal transversal section resulting from uniaxially strained graphene along the Arm-Chair (AC) and Zig-Zag (ZZ) directions. We found that uniaxial strain in graphene induces a contraction of the LLs spectra for both strain directions. Also, is evaluated the contribution of the tilting of Dirac cone axis resulting from the uniaxial deformations to the contraction of the LLs spectra. - Highlights: • The LLs in uniaxially strained graphene are found using a geometrical approach. • The energy of the LLs in function of the Dirac cone deformation is presented. • We found that uniaxial strain in graphene induces a contraction of the LLs spectra. • Contraction in LLs spectra depends on the geometrical parameters of the Dirac cone.
Organe der Osmoregulation und Exkretion
NASA Astrophysics Data System (ADS)
Møbjerg, Nadja
Die meisten Schädeltiere sind in der Lage, die Wasser- und Ionenkonzentration ihres Innenmilieus zu regulieren, sind also im Hinblick auf ihren Ionenhaushalt weitgehend unabhängig von der Umgebung. Sie halten die Konzentration von Wasser und anorganischen Ionen in ihren Körperflüssigkeiten (interstitielle Flüssigkeit und Blut) innerhalb enger Grenzen konstant (Osmoregulierer). Schleim aale (Myxinoida) können zwar die Konzentration einzelner anorganischer Ionen regulieren, sind aber insgesamt der hohen Osmolarität des Meerwassers angepasst, also isoosmostisch zu diesem. Isoosmotisch oder leic ht hyperosmostisch zur Umgebung sind auch marine Neoselachier und Latimeria chalumnae (Actinistia), die dazu organische Osmolyte (Harnstoff und Trimethylaminoxid) im Blut akkumulieren (Osmokonformer). Bei anderen aquatischen Schädeltieren sind die Körperflüssigkeiten zur Umgebung hypoosmotisch (im Meerwasser) — sie halten Wasser zurück und scheiden anorganiche Ionen aus — oder hyperosmotisch (im Süßwasser), indem sie Wasser abgeben und anorganische Ionen aufnehmen.
Quantitative Analyse und Visualisierung der Herzfunktionen
NASA Astrophysics Data System (ADS)
Sauer, Anne; Schwarz, Tobias; Engel, Nicole; Seitel, Mathias; Kenngott, Hannes; Mohrhardt, Carsten; Loßnitzer, Dirk; Giannitsis, Evangelos; Katus, Hugo A.; Meinzer, Hans-Peter
Die computergestützte bildbasierte Analyse der Herzfunktionen ist mittlerweile Standard in der Kardiologie. Die verfügbaren Produkte erfordern meist ein hohes Maß an Benutzerinteraktion und somit einen erhöhten Zeitaufwand. In dieser Arbeit wird ein Ansatz vorgestellt, der dem Kardiologen eine größtenteils automatische Analyse der Herzfunktionen mittels MRT-Bilddaten ermöglicht und damit Zeitersparnis schafft. Hierbei werden alle relevanten herzphysiologsichen Parameter berechnet und mithilfe von Diagrammen und Graphen visualisiert. Diese Berechnungen werden evaluiert, indem die ermittelten Werte mit manuell vermessenen verglichen werden. Der hierbei berechnete mittlere Fehler liegt mit 2,85 mm für die Wanddicke und 1,61 mm für die Wanddickenzunahme immer noch im Bereich einer Pixelgrösse der verwendeten Bilder.
NASA Astrophysics Data System (ADS)
Wolf, Michael D. C.
2002-04-01
Das Ziel dieser Arbeit ist es, die Strukturen im äueren Erdkern zu untersuchen und Rückschlüsse auf die sich daraus ergebenden Konsequenzen für geodynamische Modellvorstellungen zu ziehen. Die Untersuchung der Kernphasenkaustik B mit Hilfe einer kumulierten Amplituden-Entfernungskurve ist Gegenstand des ersten Teils. Dazu werden die absoluten Amplituden der PKP-Phasen im Entfernungsbereich von 142 ° bis 147 ° bestimmt und mit den Amplituden synthetischer Seismogramme verglichen. Als Datenmaterial dienen die Breitbandregistrierungen des Deutschen Seismologischen Re-gionalnetzes (GRSN 1 ) und des Arrays Gräfenberg (GRF). Die verwendeten Wellen-formen werden im WWSSN-SP-Frequenzbereich gefiltert. Als Datenbasis dienen vier Tiefherdbeben der Subduktionszone der Neuen Hebriden (Vanuatu Island) und vier Nuklearexplosionen, die auf dem Mururoa und Fangataufa Atoll im Südpazifik stattgefunden haben. Beide Regionen befinden sich vom Regionalnetz aus gesehen in einer Epizentraldistanz von ungefähr 145 °. Die Verwendung eines homogen instrumentierten Netzes von Detektoren und die Anwendung von Stations- und Magnitudenkorrekturen verringern den Hauptteil der Streuung bei den Amplitudenwerten. Dies gilt auch im Vergleich zu Untersuchungen von langperiodischen Amplituden im Bereich der Kernphasenkaustik (Häge, 1981). Ein weiterer Grund für die geringe Streuung ist die ausschlieliche Verwendung von Ereignissen mit kurzer impulsiver Herdzeitfunktion. Erst die geringe Streuung der Amplitudenwerte ermöglicht eine Interpretation der Daten. Die theoretischen Amplitudenkurven der untersuchten Erdmodelle zeigen im Bereich der Kaustik B einen gleichartigen Kurvenverlauf. Bei allen Berechnungen wird ein einheitliches Modell für die Güte der P- und S-Wellen verwendet, das sich aus den Q-Werten der Modelle CIT112 und PREM 2 zusammensetzt. Die mit diesem Q-Modell berechneten Amplituden liegen in geringem Mae oberhalb der gemessenen Amplituden. Dies braucht nicht ber
FJRW rings and Landau-Ginzburg mirror symmetry
NASA Astrophysics Data System (ADS)
Krawitz, Marc
In this thesis, we study applications of the Berglund-Hubsch transpose construction to Landau-Ginzburg (LG) mirror symmetry. Given an invertible quasihomogeneous potential W, a dual potential W T is obtained by transposition of the exponent matrix of W. By the work of Fan-Jarvis-Ruan, one can associate a LG A-model to each pair consisting of a potential W and an admissible group G of symmetries of W. On the other hand, Intriligator-Vafa have produced the LG B-model state space associated to such a pair. The first step in this work is to define, given an invertible potential W and group of symmetries G, a dual group GT of symmetries of WT. We then prove that, at the level of (bi-graded) state spaces, the LG A-model of the pair (W,G) is isomorphic to the LG B-model of (WT, CT). In the case where G = Gmax is the maximal diagonal symmetry group of W, the dual group GT is trivial, and the LG B-model is just the local algebra of WT. In particular, both the A-model and the B-model are Frobenius algebras in this case, and we prove that the mirror map preserves this structure. Building on work of Kaufmann, we produce a product structure on the LG B-model orbifolded by a general diagonal symmetry group, and present examples which suggest the mirror map respects this product in non-trivial cases. As an additional application, we interpret Arnol'd strange duality of exceptional singularities in the context of LG mirror symmetry.
Landau level splitting in nitrogen-seeded epitaxial graphene
Rothwell, S. L.; Wang, F.; Liu, G.; ...
2016-07-01
We present a new form of semiconducting graphene grown on C-face silicon carbide, SiC(0001), seeded with a sub-monolayer of nitrogen. This graphene exhibits a gap of 0.3-0.7 eV from the Fermi level to the valence band dependent on lm thickness as measured via angle resolved photo-emission spectroscopy (ARPES). Scanning tunneling microscopy (STM) images imply that the bandgap may be the result of strain-induced confinement. STM indicates that much of the graphene consists of wide at hexagonal plateaus, 8-20 nm2 on average, surrounded by both smooth and disordered folds of length scales from 0.5-2 nm tall, 1-4 nm thick, and 1-20more » nm long. The remainder of the surface is covered in smooth or disordered ripples and folds intermixed. Scanning tunneling spectroscopy (STS) measurements on all features show peaks suggestive of Landau levels, and have been analyzed to give pseudo-magnetic field magnitudes. The magnetic lengths associated with these fields are less than the average plateau diameter but comparable to typical fold widths. We consider a growth process whereby the graphene grows pinned to the substrate by the interface nitrogen. The graphene experiences compressive strain as a result of both this pinning as well as competing thermal expansion forces between the substrate and lm. As a result, graphene on nitrogen-seeded SiC has a more concentrated network of strained ripples and folds than seen on C-face SiC graphene without nitrogen.« less
Landau level splitting in nitrogen-seeded epitaxial graphene
Rothwell, S. L.; Wang, F.; Liu, G.; Xu, C.; Feldman, L. C.; Conrad, E. H.; Guisinger, N. P.; Cohen, P. I.
2016-07-01
We present a new form of semiconducting graphene grown on C-face silicon carbide, SiC(0001), seeded with a sub-monolayer of nitrogen. This graphene exhibits a gap of 0.3-0.7 eV from the Fermi level to the valence band dependent on lm thickness as measured via angle resolved photo-emission spectroscopy (ARPES). Scanning tunneling microscopy (STM) images imply that the bandgap may be the result of strain-induced confinement. STM indicates that much of the graphene consists of wide at hexagonal plateaus, 8-20 nm2 on average, surrounded by both smooth and disordered folds of length scales from 0.5-2 nm tall, 1-4 nm thick, and 1-20 nm long. The remainder of the surface is covered in smooth or disordered ripples and folds intermixed. Scanning tunneling spectroscopy (STS) measurements on all features show peaks suggestive of Landau levels, and have been analyzed to give pseudo-magnetic field magnitudes. The magnetic lengths associated with these fields are less than the average plateau diameter but comparable to typical fold widths. We consider a growth process whereby the graphene grows pinned to the substrate by the interface nitrogen. The graphene experiences compressive strain as a result of both this pinning as well as competing thermal expansion forces between the substrate and lm. As a result, graphene on nitrogen-seeded SiC has a more concentrated network of strained ripples and folds than seen on C-face SiC graphene without nitrogen.
NASA Astrophysics Data System (ADS)
Rompe, Robert
Friedrich Möglich, ein Schüler von Max von Laue und Erwin Schrödinger, übernahm 1947 die Chefredaktion der Annalen der Physik.Translated AbstractFriedrich Möglich - His Contributions to the Formation of Physics in GDRFriedrich Möglich a student of Max von Laue and Erwin Schrödinger took over as editor in chief of Annalen der Physik in 1947.
Tycho Brahe - Instrumentenbauer und Meister der Beobachtungstechnik
NASA Astrophysics Data System (ADS)
Wolfschmidt, Gudrun
Vor der Erfindung des Fernrohrs war der dänische Astronom Tycho Brahe (1546 - 1601) der bedeutendste beobachtende Astronom. Von seinem Observatorium Uraniborg auf der - damals dänischen - Insel Hven ist heute noch der Grundriß erkennbar, von Stjerneborg sind die Fundamente erhalten, die Kuppeln in den 1950er Jahren ergänzt. In der Astronomie-Ausstellung im Deutschen Museum gibt es ein Modell der Sternwarte Uraniborg und der zugehörigen Instrumente (Maßstab 1:10); das größere Modell wurde dem Technischen Museum in Malmö geschenkt. Die Instrumente, die er in den Observatorien Uraniborg und Stjerneborg benutzte, sind nicht erhalten. Aber es gibt gute Beschreibungen der Instrumente (Halbkreis, Quadranten, Sextanten, Armillarsphären, Triquetrum, Himmelsglobus) in seinem Buch Astronomiae instauratae mechanica (Wandsbek 1598). Eine Nachbildung des großen hölzernen Quadranten kann man im Runden Turm in Kopenhagen sehen. Zwei Sextanten, hergestellt für Tycho um 1600 von Jost Bürgi und Erasmus Habermel, gibt es noch im Nationalmuseum für Technik in Prag. Ähnlichkeiten von Tychos Instrumenten mit Groß-Instrumenten aus dem islamischen Kulturkreis sind auffällig. Tycho Brahes Meßgeräte markieren einen großen Fortschritt in der Entwicklung astronomischer Instrumente und Meßtechniken und bilden die Grundlage für den weiteren Fortschritt der Positionsastronomie und der damit verbundenen Tabellenwerke. Die Nachwirkungen sind bis ins 17. und 18. Jahrhundert nachweisbar.
Untersuchung der Richtwirkung der Einkopplung von ebenen Wellen in eine Leitung
NASA Astrophysics Data System (ADS)
Magdowski, M.; Vick, R.
2013-07-01
Elektrische Leitungen und Kabel stellen häufig die Haupteinfallstore für elektromagnetische Felder in die daran angeschlossenen Geräte und Systeme dar. Für die Einkopplung einer ebenen Welle kann der in eine Leitung eingekoppelte Strom unter bestimmten Voraussetzungen mit Hilfe der Leitungstheorie sehr effizient bestimmt werden. Er hängt dabei von den Abmessungen der Leitung, den Leitungsabschlüssen sowie der Amplitude, der Wellenlänge und der Einfallsrichtung der ebenen Welle ab. In dieser Arbeit wird die Abhängigkeit der Einkopplung von der Einfallsrichtung näher untersucht. Dazu werden Richtdiagramme der Einkopplung berechnet, dargestellt und hinsichtlich der mittleren und maximalen Einkopplung über alle Einfallsrichtungen und Polarisationen ausgewertet. Die Ergebnisse werden genutzt, um die maximale Direktivität der Einkopplung in eine Leitung zu bestimmen. Fasst man die Einkopplung externer Felder in eine Leitung als einen Störfestigkeitstest auf, so kann die maximale Direktivität benutzt werden, um einen Vergleich zwischen unterschiedlichen Messumgebungen wie Absorberhallen und Modenverwirbelungskammern herzustellen.
Isotropic Landau levels of relativistic and non-relativistic fermions in 3D flat space
NASA Astrophysics Data System (ADS)
Li, Yi; Wu, Congjun
2012-02-01
The usual Landau level quantization, as demonstrated in the 2D quantum Hall effect, is crucially based on the planar structure. In this talk, we explore its 3D counterpart possessing the full 3D rotational symmetry as well as the time reversal symmetry. We construct the Landau level Hamiltonians in 3 and higher dimensional flat space for both relativistic and non-relativistic fermions. The 3D cases with integer fillings are Z2 topological insulators. The non-relativistic version describes spin-1/2 fermions coupling to the Aharonov-Casher SU(2) gauge field. This system exhibits flat Landau levels in which the orbital angular momentum and the spin are coupled with a fixed helicity. Each filled Landau level contributes one 2D helical Dirac Fermi surface at an open boundary, which demonstrates the Z2 topological nature. A natural generalization to Dirac fermions is found as a square root problem of the above non-relativistic version, which can also be viewed as the Dirac equation defined on the phase space. All these Landau level problems can be generalized to arbitrary high dimensions systematically. [4pt] [1] Yi Li and Congjun Wu, arXiv:1103.5422.[0pt] [2] Yi Li, Ken Intriligator, Yue Yu and Congjun Wu, arXiv:1108.5650.
Electric-field-induced destruction of quasi-Landau levels in bilayer graphene nanoribbons.
Chung, Hsien-Ching; Su, Wu-Pei; Lin, Ming-Fa
2013-01-21
The magneto-electronic properties of bilayer zigzag graphene nanoribbons are investigated by the Peierls tight-binding method. In the presence of magnetic fields, Landau quantization leads to the formation of Landau subbands. For the bilayer nanoribbons, these subbands are partially dispersionless in k-space and are called quasi-Landau levels (QLLs). Perpendicular electric fields, serving as the top gate, push the QLLs to higher state energy and split the flat subbands. From the evidence of band structure and density of states, the QLLs remain dispersionless and the corresponding peaks are still the main structure of density of states, which means that the material properties related to the QLLs are unchanged. However, the wave functions present a totally different evidence that the Landau wave functions are severely mixed, and the corresponding material properties would be strongly affected or destroyed. The wave functions provide an effective way to comprehend the characteristics of the flat subbands and Landau subbands. The energy spectra, density of states, and wave functions are discussed in detail.
Landau-Zener transitions mediated by an environment: population transfer and energy dissipation.
Dodin, Amro; Garmon, Savannah; Simine, Lena; Segal, Dvira
2014-03-28
We study Landau-Zener transitions between two states with the addition of a shared discretized continuum. The continuum allows for population decay from the initial state as well as indirect transitions between the two states. The probability of nonadiabatic transition in this multichannel model preserves the standard Landau-Zener functional form except for a shift in the usual exponential factor, reflecting population transfer into the continuum. We provide an intuitive explanation for this behavior assuming individual, independent transitions between pairs of states. In contrast, the ground state survival probability at long time shows a novel, non-monotonic, functional form with an oscillatory behavior in the sweep rate at low sweep rate values. We contrast the behavior of this open-multistate model to other generalized Landau-Zener models incorporating an environment: the stochastic Landau-Zener model and the dissipative case, where energy dissipation and thermal excitations affect the adiabatic region. Finally, we present evidence that the continuum of states may act to shield the two-state Landau-Zener transition probability from the effect of noise.
Landau damping effects on dust-acoustic solitary waves in a dusty negative-ion plasma
Barman, Arnab; Misra, A. P. E-mail: apmisra@gmail.com
2014-07-15
The nonlinear theory of dust-acoustic waves (DAWs) with Landau damping is studied in an unmagnetized dusty negative-ion plasma in the extreme conditions when the free electrons are absent. The cold massive charged dusts are described by fluid equations, whereas the two-species of ions (positive and negative) are described by the kinetic Vlasov equations. A Korteweg-de Vries (KdV) equation with Landau damping, governing the dynamics of weakly nonlinear and weakly dispersive DAWs, is derived following Ott and Sudan [Phys. Fluids 12, 2388 (1969)]. It is shown that for some typical laboratory and space plasmas, the Landau damping (and the nonlinear) effects are more pronounced than the finite Debye length (dispersive) effects for which the KdV soliton theory is not applicable to DAWs in dusty pair-ion plasmas. The properties of the linear phase velocity, solitary wave amplitudes (in presence and absence of the Landau damping) as well as the Landau damping rate are studied with the effects of the positive ion to dust density ratio (μ{sub pd}) as well as the ratios of positive to negative ion temperatures (σ) and masses (m)
Ising quantum Hall ferromagnetism in Landau levels |N|≥1 of bilayer graphene
NASA Astrophysics Data System (ADS)
Luo, Wenchen; Côté, R.; Bédard-Vallée, Alexandre
2014-08-01
A magnetic field applied perpendicularly to the chiral two-dimensional electron gas (C2DEG) in a Bernal-stacked bilayer graphene quantizes the kinetic energy into a discrete set of Landau levels N =0,±1,±2,.... While Landau level N =0 is eightfold degenerate, higher Landau levels (|N|≥1) are fourfold degenerate when spin and valley degrees of freedom are counted. In this work, the Hartree-Fock approximation is used to study the phase diagram of the C2DEG at integer fillings ν˜=1,2,3 of these higher Landau levels. At these filling factors, the C2DEG is a valley or spin Ising quantum Hall ferromagnet. At odd fillings, the C2DEG is spin polarized and has all its electrons in one valley or the other. There is no intervalley coherence, in contrast with most of the ground states in Landau level N =0. At even filling ν˜=2, the C2DEG is either fully spin polarized with electrons occupying both valleys or spin unpolarized with electrons occupying one of the two valleys. A finite electric field (or bias) applied perpendicularly to the plane of the C2DEG induces a series of first-order phase transitions between these different ground states. The transport gap or its slope is discontinuous at the bias where a transition occurs. Such discontinuity may result in a change in the transport properties of the C2DEG at that bias.
More on Gribov copies and propagators in Landau-gauge Yang-Mills theory
Maas, Axel
2009-01-01
Fixing a gauge in the nonperturbative domain of Yang-Mills theory is a nontrivial problem due to the presence of Gribov copies. In particular, there are different gauges in the nonperturbative regime which all correspond to the same definition of a gauge in the perturbative domain. Gauge-dependent correlation functions may differ in these gauges. Two such gauges are the minimal Landau gauge and the absolute Landau gauge, both corresponding to the perturbative Landau gauge. These, and their numerical implementation, are described and presented in detail. Other choices will also be discussed. This investigation is performed, using numerical lattice gauge theory calculations, by comparing the propagators of gluons and ghosts for the minimal Landau gauge and the absolute Landau gauge in SU(2) Yang-Mills theory. It is found that the propagators are different in the far infrared and even at energy scales of the order of half a GeV. In particular, the finite-volume effects are also modified. This is observed in two and three dimensions. Some remarks on the four-dimensional case are provided as well.
Landau-Zener transitions mediated by an environment: Population transfer and energy dissipation
Dodin, Amro; Simine, Lena; Segal, Dvira; Garmon, Savannah
2014-03-28
We study Landau-Zener transitions between two states with the addition of a shared discretized continuum. The continuum allows for population decay from the initial state as well as indirect transitions between the two states. The probability of nonadiabatic transition in this multichannel model preserves the standard Landau-Zener functional form except for a shift in the usual exponential factor, reflecting population transfer into the continuum. We provide an intuitive explanation for this behavior assuming individual, independent transitions between pairs of states. In contrast, the ground state survival probability at long time shows a novel, non-monotonic, functional form with an oscillatory behavior in the sweep rate at low sweep rate values. We contrast the behavior of this open-multistate model to other generalized Landau-Zener models incorporating an environment: the stochastic Landau-Zener model and the dissipative case, where energy dissipation and thermal excitations affect the adiabatic region. Finally, we present evidence that the continuum of states may act to shield the two-state Landau-Zener transition probability from the effect of noise.
Jeong, Kyoung Yong; Lee, In-Yong; Yong, Tai-Soon; Lee, Jae-Hyun; Kim, Eun-Jin; Lee, Joo-Shil; Hong, Chein-Soo; Park, Jung-Won
2012-09-01
Amino acid sequence variations have possible influences on the allergenicity of allergens and may be important factors in allergen standardization. This study was undertaken to investigate the sequence polymorphisms of group 1 and 2 allergens from Korean isolates of the house dust mites Dermatophagoides farinae and D. pteronyssinus. cDNA sequences encoding group 1 and 2 allergens were amplified by RT-PCR and compared the deduced amino acid sequences. Der f 1.0101, which appeared in 64.0 % of the 50 sequences analyzed, was found to be predominant. Among the Der p 1 sequences, Der p 1.0102 and 1.0105 were predominant (58 %). Among the Der f 2 sequences, Der f 2.0102 (40.7 %) and a new variant with Gly at position 42 (27.8 %) were predominant. The deduced amino acid sequences of 60 Der p 2 clones were examined, and 28 variants with 1-5 amino acid substitutions were found. Interestingly, all of the Der p 2 sequences had Thr instead of Lys at position 49. Two variants (Leu40, Thr49, and Asn114 (26.6 %); Val40, Thr49, and Asn114 (20.0 %)) were found to be the most predominant forms of Der p 2. Der p 1 has a high rate of sporadic substitutions and the group 2 allergens show a more regular pattern with orderly associations of amino acid substitutions. Der f 1 and Der p 2 from Korean mite isolates have unique amino acid sequence polymorphisms. These findings provide important data for house dust mite allergen standardization.
Von Humboldt bis Einstein. Berlin als Weltzentrum der exakten Wissenschaften.
NASA Astrophysics Data System (ADS)
Meschkowski, H.
Contents: 1. Die Anfänge. 2. Die Ära Dirichlet-Jacobi. 3. Der Ausbau der experimentellen Naturwissenschaften. 4. Alexander von Humboldt. 5. Berlin wird "Weltzentrum" der Mathematik. 6. Die Ära Helmholtz. 7. Neue Arbeitsweisen der Astronomie. 8. Chemie: Forschung und Industrie. 9. Max Planck. 10. Ins technische Zeitalter. 11. Zur Mathematik der zwanziger Jahre. 12. Albert Einstein. 13. Fortschritte der Grundlagenforschung. 14. Erwin Schrödinger: Physiker, Philosoph und Poet. 15. Zum Schluß.
Der Kalte Krieg in der Peripherie Griechische Physiker und Atomenergie nach dem Zweiten Weltkrieg
NASA Astrophysics Data System (ADS)
Vlahakis, George N.
Die vorliegende Arbeit analysiert Ansichten griechischer Physiker zur Atomenergie und deren mögliche Anwendung nach dem Zweiten Weltkrieg, insbesondere während des Kalten Kriegs. Einerseits werden Ansichten von Physik- Professoren griechischer Universitäten präsentiert - beispielsweise von Dimitrios Hondros, der Student von Arnold Sommerfeld und Mitarbeiter von Peter Debye in München war, und andererseits wird die Politik der griechischen Regierung für die Etablierung eines Forschungsinstitutes diskutiert, das der Entwicklung der Atomenergie dienen sollte; ebenfalls wird eine öffentliche Meinungsumfrage zu diesen Thema, die in den Tageszeitungen der damaligen Zeit präsentiert wurde, diskutiert.
Optically pumped NMR: Revealing spin-dependent Landau level transitions in GaAs
NASA Astrophysics Data System (ADS)
Ramaswamy, K.; Mui, S.; Crooker, S. A.; Pan, X.; Sanders, G. D.; Stanton, C. J.; Hayes, S. E.
2010-08-01
We show that high-resolution optically pumped NMR (OPNMR) studies can reveal spin-dependent optical transitions between valence- and conduction-band Landau levels in bulk semiconductors such as GaAs. The OPNMR signal intensity exhibits oscillations as a function of pump photon energy that evolve with magnetic field. In contrast to standard polarized magnetoabsorption measurements, OPNMR is sensitive to the polarization of the photoexcited electron spins (i.e., the difference between spin-up and spin-down electron populations rather than the sum). This allows one to clearly resolve the spin dependence of optical transitions that might normally be obscured in conventional magnetoabsorption studies. The data are in good agreement with theoretical calculations of the transitions from the spin-split light-hole Landau levels in the valence band to the conduction-band Landau levels of GaAs.
Performance of replica-exchange Wang-Landau sampling for the study of spin systems
NASA Astrophysics Data System (ADS)
Li, Ying Wai; Eisenbach, Markus; Vogel, Thomas; Wüst, Thomas; Landau, David P.
2014-03-01
The recently proposed replica-exchange Wang-Landau sampling (REWL) is a novel, massively parallel Monte Carlo method which allows for the parallelization of Wang-Landau sampling based on a replica-exchange framework. The robustness of the scheme is demonstrated by its broad applicability on a variety of spin systems: from the simplest models with discrete or continuous energy domains, to complex systems captured by large-scale first principles density functional theory calculations. The accuracy of REWL is studied by comparing the thermodynamic properties with exact solutions and results obtained by the original, serial Wang-Landau sampling. The principles for the speed-up, the strong and weak scaling behavior of REWL are also investigated when different parameter settings are employed. We will show, with the aid of selected spin systems, that the method accelerates the simulations significantly with a possible improved accuracy. Phys. Rev. Lett. 110, 210603 (2013)
Magnetic breakdown and Landau level spectra of a tunable double-quantum-well Fermi surface
Simmons, J.A.; Harff, N.E.; Lyo, S.K.; Klem, J.F.; Boebinger, G.S.; Pfeiffer, L.N.; West, K.W.
1997-12-31
By measuring longitudinal resistance, the authors map the Landau level spectra of double quantum wells as a function of both parallel (B{sub {parallel}}) and perpendicular (B{sub {perpendicular}}) magnetic fields. In this continuously tunable highly non-parabolic system, the cyclotron masses of the two Fermi surface orbits change in opposite directions with B{sub {parallel}}. This causes the two corresponding ladders of Landau levels formed at finite B{sub {perpendicular}} to exhibit multiple crossings. They also observe a third set of landau levels, independent of B{sub {parallel}}, which arise from magnetic breakdown of the Fermi surface. Both semiclassical and full quantum mechanical calculations show good agreement with the data.
Temperature dependence of the Landau-Placzek ratio in glass forming liquids.
Popova, V A; Surovtsev, N V
2011-10-07
Here, we studied Rayleigh-Brillouin light scattering in ten different glass-forming liquids (α-picoline, toluene, o-toluidine, ethanol, salol, glycerol, dibutyl phthalate, o-terphenyl, propylene carbonate, and propylene glycol). For each of these liquids it was found that the Landau-Placzek ratio is in a good agreement with the theory at high temperatures and significantly exceeds the theoretical prediction below a certain temperature. Transition between the two temperature regimes occurs near T(A), where T(A) is crossover point from an Arrhenius-like to a non-Arrhenius behavior for the α-relaxation time dependence on temperature. Increase of the Landau-Placzek ratio relative to the theoretical prediction below T(A) seems to be the universal feature of glass-formers. We suggest that formation of locally favored structures in liquids below T(A) causes observed excess of the Landau-Placzek ratio.
Landau damping of the dust-acoustic surface waves in a Lorentzian dusty plasma slab
Lee, Myoung-Jae; Jung, Young-Dae
2016-01-15
Landau damping of a dust-acoustic surface wave propagating at the interfaces of generalized Lorentzian dusty plasma slab bounded by a vacuum is kinetically derived as the surface wave displays the symmetric and the anti-symmetric mode in a plasma slab. In the limiting case of small scaled wave number, we have found that Landau damping is enhanced as the slab thickness is increased. In particular, the damping of anti-symmetric mode is much stronger for a Lorentzian plasma than for a Maxwellian plasma. We have also found that the damping is more affected by superthermal particles in a Lorentzian plasma than by a Maxwellian plasma for both of the symmetric and the anti-symmetric cases. The variations of Landau damping with various parameters are also discussed.
Landau levels of scalar QED in time-dependent magnetic fields
Kim, Sang Pyo
2014-05-15
The Landau levels of scalar QED undergo continuous transitions under a homogeneous, time-dependent magnetic field. We analytically formulate the Klein–Gordon equation for a charged spinless scalar as a Cauchy initial value problem in the two-component first order formalism and then put forth a measure that classifies the quantum motions into the adiabatic change, the nonadiabatic change, and the sudden change. We find the exact quantum motion and calculate the pair-production rate when the magnetic field suddenly changes as a step function. -- Highlights: •We study the Landau levels of scalar QED in time-dependent magnetic fields. •Instantaneous Landau levels make continuous transitions but keep parity. •The Klein–Gordon equation is expressed in the two-component first order formalism. •A measure is advanced that characterizes the quantum motions into three categories. •A suddenly changing magnetic field produces pairs of charged scalars from vacuum.
Spin and valley resolved Landau level crossing in tri-layer ABA stacked graphene
NASA Astrophysics Data System (ADS)
Datta, Biswajit; Gupta, Vishakha; Borah, Abhinandan; Watanabe, Kenji; Taniguchi, Takashi; Deshmukh, Mandar
We present quantum Hall measurements on a high quality encapsulated tri-layer graphene device. Low temperature field effect mobility of this device is around 500,000 cm2/Vs and we see SdH oscillations at a magnetic field as low as 0.3 T. Quantum Hall measurements confirm that the chosen tri layer graphene is Bernal (ABA) stacked. Due to the presence of both mass-less monolayer like Dirac fermions and massive bi-layer like Dirac fermions in Bernal stacked tri-layer graphene, there are Landau level crossings between monolayer and bi-layer bands in quantum Hall regime. Although most of the Landau Level crossings are predominantly present on the electron sides, we also observe signatures of the crossings on the hole side. This behaviour is consistent with the asymmetry of electron and hole in ABA tri-layer graphene. We observe a series of crossings of the spin and valley resolved Landau Levels.
NASA Astrophysics Data System (ADS)
Zhang, Chenglong; Gamba, Irene M.
2016-11-01
We propose a deterministic conservative solver for the inhomogeneous Fokker-Planck-Landau equation coupled with Poisson equation. Through time-splitting scheme, a Vlasov-Poisson (collisionless) problem and a homogeneous Landau (collisional) problem are obtained. These two subproblems can be treated separately. We use operator splitting where the transport dynamics for Runge-Kutta Discontinuous Galerkin (RK-DG) method and the collisional dynamics for homogeneous conservative spectral method are adopted respectively. Since two different numerical schemes are applied separately, we have designed a new conservation correction process such that, after projecting the conservative spectral solution onto the DG mesh, there is no loss of moment consvervation. Parallelization is readily implemented. To verify our solver, numerical experiments on linear and nonlinear Landau damping are provided.
Landau levels of graphene on h-BN probed by magneto-optics
NASA Astrophysics Data System (ADS)
Chen, Zhiguo; Shi, Zhiwen; Yang, Wei; Zhang, Guangyu; Wang, Feng; Li, Zhiqiang
2014-03-01
Hexagonal boron nitride (h-BN) is an ideal substrate for achieving high-mobility graphene devices due to its atomically flat and clean surface. Moreover, the coupling between h-BN and graphene at small twist angles gives rise to a long-range moire supperlattice potential, which can significantly modify the electronic properties of graphene. Here, we will present infrared transmission measurements on graphene on h-BN in high magnetic fields applied perpendicular to the samples. Several inter-Landau-level transitions of graphene on h-BN were observed in fields, which exhibit pronounced deviations from the SQRT(B) field dependence for Landau levels of bare graphene. We will discuss possible mechanisms for the modifications of Landau levels of graphene by h-BN.
Evidence for nuclear Landau-Zener effect: New resonance mechanism in heavy-ion reactions
Abe, Y.; Park, J.Y.
1983-12-01
Characteristic resonancelike peaks recently observed in the angle-integrated inelastic cross sections for the /sup 13/C-/sup 17/O system are understood in terms of the Landau-Zener excitation mechanism at energy level crossings. Angle-integrated inelastic cross sections estimated with the Landau-Zener formula show a series of resonancelike peaks as a function of incident energy, each of which is associated with a grazing angular momentum of the relative motion between nuclei. Simple expressions are given for resonance energies and ''widths'' of new ''resonances.'' This resonance mechanism is a new one, which has not been known in nuclear reactions nor in atomic collisions, although it is based on the well-known Landau-Zener promotion mechanism.
Towards a tunable graphene-based Landau level laser in the terahertz regime
NASA Astrophysics Data System (ADS)
Wendler, Florian; Malic, Ermin
2015-07-01
Terahertz (THz) technology has attracted enormous interest with conceivable applications ranging from basic science to advanced technology. One of the main challenges remains the realization of a well controlled and easily tunable THz source. Here, we predict the occurrence of a long-lived population inversion in Landau-quantized graphene (i.e. graphene in an external magnetic field) suggesting the design of tunable THz Landau level lasers. The unconventional non-equidistant quantization in graphene offers optimal conditions to overcome the counteracting Coulomb- and phonon-assisted scattering channels. In addition to the tunability of the laser frequency, we show that also the polarization of the emitted light can be controlled. Based on our microscopic insights into the underlying many-particle mechanisms, we propose two different experimentally realizable schemes to design tunable graphene-based THz Landau level lasers.
Topika und deren Einsatz in der Dermatologie.
Wohlrab, Johannes
2016-11-01
Grundkenntnisse zur Zusammensetzung und den regulatorischen Hintergründen von Topika gehören zu den alltäglich benötigten Herausforderungen dermatologisch-ärztlichen Handelns. Ein professioneller und indikationsgerechter Umgang bei der Auswahl, Verordnung und Anwendung topischer Präparate ist somit Voraussetzung für eine verantwortungsvolle fachärztliche Tätigkeit. Dabei bereiten die regulatorische Zuordnung (Arzneimittel, Medizinprodukt, Kosmetikum), die Feststellung der Erstattungsfähigkeit durch die GKV und die unzureichende Kennzeichnung des Vehikelsystems einzelner Präparate nicht selten Probleme. Bestreben sollte es sein, neben der Wahl des geeigneten Wirkstoffs und der geeigneten Konzentration ein an die Indikation der Therapie angepasstes galenisches System auszuwählen, um dessen Eigenwirkung für den therapeutischen Effekt nutzen zu können. Bei der Verschreibung von Rezepturarzneimitteln sollte nach Möglichkeit immer auf eine standardisierte Rezeptur (Magistralrezeptur) zurückgegriffen werden. Durch die Vielzahl der möglichen Inhaltsstoffe und der sich daraus ergebenden Komplexität eines galenischen Systems ist eine willkürliche Manipulation durch qualitative oder quantitative Veränderungen einzelner Komponenten mit hohen Risiken für eine Instabilität und damit für Sicherheit und Sinnhaftigkeit verbunden. Eine optimierte Anwendung von Topika setzt zudem Grundlagenkenntnisse zur Pharmakokinetik und zur evidenzbasierten Therapieplanung voraus.
Relativistic Landau-Aharonov Quantization in Topological Defect Space-Time
NASA Astrophysics Data System (ADS)
Bakke, K.; Furtado, C.
In this paper we study the Landau levels arising within the relativistic dynamics of a neutral particle which possesses a permanent magnetic dipole moment interacting with an external electric field in the curved space-time background with the presence of a torsion field. We use the Aharonov-Casher effect to couple this neutral particle with the electric field in this curved background. The eigenfunction and eigenvalues of the Hamiltonian are obtained. We show that the presence of the topological defect breaks the infinite degeneracy of the relativistic Landau levels arising in this system. We study the nonrelativistic limit of the eigenvalues and compare these results with cases studied earlier.
Radial symmetry on three-dimensional shells in the Landau-de Gennes theory
NASA Astrophysics Data System (ADS)
Canevari, Giacomo; Ramaswamy, Mythily; Majumdar, Apala
2016-01-01
We study the radial-hedgehog solution on a three-dimensional (3D) spherical shell with radial boundary conditions, within the Landau-de Gennes theory for nematic liquid crystals. We prove that the radial-hedgehog solution is the unique minimizer of the Landau-de Gennes energy in two separate regimes: (i) for thin shells when the temperature is below the critical nematic supercooling temperature and (ii) for a fixed shell width at sufficiently low temperatures. In case (i), we provide explicit geometry-dependent criteria for the global minimality of the radial-hedgehog solution.
Theory of Landau level mixing in heavily graded graphene p -n junctions
NASA Astrophysics Data System (ADS)
LaGasse, Samuel W.; Lee, Ji Ung
2016-10-01
We demonstrate the use of a quantum transport model to study heavily graded graphene p -n junctions in the quantum Hall regime. A combination of p -n interface roughness and delta function disorder potential allows us to compare experimental results on different devices from the literature. We find that wide p -n junctions suppress mixing of n ≠0 Landau levels. Our simulations spatially resolve carrier transport in the device, revealing separation of higher order Landau levels in strongly graded junctions, which suppresses mixing.
Perera, Meewanage Dilina N; Li, Ying Wai; Eisenbach, Markus; Vogel, Thomas; Landau, David P
2015-01-01
We describe the study of thermodynamics of materials using replica-exchange Wang Landau (REWL) sampling, a generic framework for massively parallel implementations of the Wang Landau Monte Carlo method. To evaluate the performance and scalability of the method, we investigate the magnetic phase transition in body-centered cubic (bcc) iron using the classical Heisenberg model parameterized with first principles calculations. We demonstrate that our framework leads to a significant speedup without compromising the accuracy and precision and facilitates the study of much larger systems than is possible with its serial counterpart.
Integrability and structural stability of solutions to the Ginzburg-Landau equation
NASA Technical Reports Server (NTRS)
Keefe, Laurence R.
1986-01-01
The integrability of the Ginzburg-Landau equation is studied to investigate if the existence of chaotic solutions found numerically could have been predicted a priori. The equation is shown not to possess the Painleveproperty, except for a special case of the coefficients that corresponds to the integrable, nonlinear Schroedinger (NLS) equation. Regarding the Ginzburg-Landau equation as a dissipative perturbation of the NLS, numerical experiments show all but one of a family of two-tori solutions, possessed by the NLS under particular conditions, to disappear under real perturbations to the NLS coefficients of O(10 to the -6th).
Ovchinnikov, Yu. N.
2013-09-15
Solutions to the generalized Ginzburg-Landau equations for superconductors are obtained for a Ginzburg-Landau parameter {kappa} close to unity. The families of solutions with arbitrary number n of flux quanta in a unit cell are analyzed. It is shown that under certain conditions, a cascade of phase transitions between different structures in a magnetic field appears near T{sub c}. Algebraic equations are derived for determining the boundaries of coexistence of different phases on the (T, H{sub 0}) plane.
Buet, C.; Cordier; Degond, P.; Lemou, M.
1997-05-15
We present fast numerical algorithms to solve the nonlinear Fokker-Planck-Landau equation in 3D velocity space. The discretization of the collision operator preserves the properties required by the physical nature of the Fokker-Planck-Landau equation, such as the conservation of mass, momentum, and energy, the decay of the entropy, and the fact that the steady states are Maxwellians. At the end of this paper, we give numerical results illustrating the efficiency of these fast algorithms in terms of accuracy and CPU time. 20 refs., 7 figs.
Terahertz imaging of Landau levels in HgTe-based topological insulators
NASA Astrophysics Data System (ADS)
Kadykov, Aleksandr M.; Torres, Jeremie; Krishtopenko, Sergey S.; Consejo, Christophe; Ruffenach, Sandra; Marcinkiewicz, Michal; But, Dmytro; Knap, Wojciech; Morozov, Sergey V.; Gavrilenko, Vladimir I.; Mikhailov, Nikolai N.; Dvoretsky, Sergey A.; Teppe, Frederic
2016-06-01
We report on sub-terahertz photoconductivity under the magnetic field of a two dimensional topological insulator based on HgTe quantum wells. We perform a detailed visualization of Landau levels by means of photoconductivity measured at different gate voltages. This technique allows one to determine a critical magnetic field, corresponding to topological phase transition from inverted to normal band structure, even in almost gapless samples. The comparison with realistic calculations of Landau levels reveals a smaller role of bulk inversion asymmetry in HgTe quantum wells than it was assumed previously.
Interface electronic complexes and Landau damping of magnons in ultrathin magnets.
Buczek, Paweł; Ernst, Arthur; Sandratskii, Leonid M
2011-04-15
The damping of magnons in ultrathin metallic magnets is studied from first-principles. We contrast Fe/Cu(100) and Fe/W(110) systems for which the influence of the substrate on the magnon life time differs strongly. We introduce the concept of Landau map in momentum space to assess the role of different electronic states in the attenuation. The formation of electronic complexes localized at the film-substrate interface leads to hot spots in the Landau maps and enhances the damping. This finding allows tuning the attenuation of high-frequency magnetization dynamics in nanostructures.
Defect chaos and bursts: hexagonal rotating convection and the complex Ginzburg-Landau equation.
Madruga, Santiago; Riecke, Hermann; Pesch, Werner
2006-02-24
We employ numerical computations of the full Navier-Stokes equations to investigate non-Boussinesq convection in a rotating system using water as the working fluid. We identify two regimes. For weak non-Boussinesq effects the Hopf bifurcation from steady to oscillating (whirling) hexagons is supercritical and typical states exhibit defect chaos that is systematically described by the cubic complex Ginzburg-Landau equation. For stronger non-Boussinesq effects the Hopf bifurcation becomes subcritical and the oscillations exhibit localized chaotic bursting, which is modeled by a quintic complex Ginzburg-Landau equation.
Hall Crystal States at ν = 2 and Moderate Landau Level Mixing
NASA Astrophysics Data System (ADS)
Murthy, Ganpathy
2000-08-01
The ν = 2 quantum Hall state at low Zeeman coupling is well known to be a translationally invariant singlet if Landau level mixing is small. At zero Zeeman interaction, as Landau level mixing increases, the translationally invariant state becomes unstable to an inhomogeneous state. This is the first realistic example of a full Hall crystal, which shows the coexistence of quantum Hall order and density wave order. The full Hall crystal differs from the more familiar Wigner crystal by a topological property, which results in it having only linearly dispersing collective modes at small q, and no q3/2 magnetophonon. I present calculations of the topological number and the collective modes.
Derivation of the Landau-Lifshitz-Bloch equation from continuum thermodynamics
NASA Astrophysics Data System (ADS)
Berti, Alessia; Giorgi, Claudio
2016-11-01
Within the continuum thermodynamic framework, we derive the evolution equation for the magnetization vector in a ferromagnetic body. This procedure leads to an evolution equation that generalizes the well-known Landau-Lifshitz model for magnetically saturated bodies and looks very similar to the Landau-Lifshitz-Bloch equation which was obtained by Garanin in 1997 from statistical mechanics. As a byproduct, we also obtain a generalization of the Gilbert equation when the magnetic field is far from saturation. By virtue of a suitable choice of the Gibbs free energy, this phenomenological model is able to describe the phase transition occurring from the paramagnetic to the ferromagnetic regime in anisotropic ferromagnets.
Time-resolved measurement of Landau-Zener tunneling in periodic potentials.
Zenesini, A; Lignier, H; Tayebirad, G; Radogostowicz, J; Ciampini, D; Mannella, R; Wimberger, S; Morsch, O; Arimondo, E
2009-08-28
We report time-resolved measurements of Landau-Zener tunneling of Bose-Einstein condensates in accelerated optical lattices, clearly resolving the steplike time dependence of the band populations. Using different experimental protocols we were able to measure the tunneling probability both in the adiabatic and in the diabatic bases of the system. We also experimentally determine the contribution of the momentum width of the Bose condensates to the temporal width of the tunneling steps and discuss the implications for measuring the jump time in the Landau-Zener problem.
Time-Resolved Measurement of Landau-Zener Tunneling in Periodic Potentials
Zenesini, A.; Radogostowicz, J.; Ciampini, D.; Mannella, R.; Arimondo, E.; Lignier, H.; Morsch, O.; Tayebirad, G.; Wimberger, S.
2009-08-28
We report time-resolved measurements of Landau-Zener tunneling of Bose-Einstein condensates in accelerated optical lattices, clearly resolving the steplike time dependence of the band populations. Using different experimental protocols we were able to measure the tunneling probability both in the adiabatic and in the diabatic bases of the system. We also experimentally determine the contribution of the momentum width of the Bose condensates to the temporal width of the tunneling steps and discuss the implications for measuring the jump time in the Landau-Zener problem.
Spatial Landau-Zener-Stueckelberg interference in spinor Bose-Einstein condensates
Zhang, J.-N.; Sun, C.-P.; Yi, S.; Nori, Franco
2011-03-15
We investigate the Stueckelberg oscillations of a spin-1 Bose-Einstein condensate subject to a spatially inhomogeneous transverse magnetic field and a periodic longitudinal field. We show that the time-domain Stueckelberg oscillations result in modulations in the density profiles of all spin components due to the spatial inhomogeneity of the transverse field. This phenomenon represents the Landau-Zener-Stueckelberg interference in the space domain. Since the magnetic dipole-dipole interaction between spin-1 atoms induces an inhomogeneous effective magnetic field, interference fringes also appear if a dipolar spinor condensate is driven periodically. We also point out some potential applications of this spatial Landau-Zener-Stuekelberg interference.
Landau-Zener transitions in a multilevel system: An exact result
Shytov, A.V.
2004-11-01
We study the S matrix for the transitions at an avoided crossing of several energy levels, which is a multilevel generalization of the Landau-Zener problem. We demonstrate that, by extending the Schroedinger evolution to complex time, one can obtain an exact answer for some of the transition amplitudes. Similar to the Landau-Zener case, our result covers both the adiabatic (slow evolution) and the diabatic (fast evolution) regimes. The form of the exact transition amplitude coincides with that obtained in a sequential pairwise level crossing approximation, in accord with the conjecture of Brundobler and Elser [J. Phys. A 26, 1211 (1993)].
Four-state nonstationary models in multistate Landau-Zener theory
Ostrovsky, V. N.; Volkov, M. V.; Hansen, J. P.; Selstoe, S.
2007-01-01
A dynamic four-state system is considered within the context of multistate Landau-Zener theory. It is shown that the theory accounts very well for the time-dependent state populations and final transition probabilities even in cases when multiple crossings appear in close vicinity of each other. This is also true for multiple paths systems when the phases are appropriately accounted for. It is found that transitions may take place also between diabatic states that do not couple directly and that the dynamics of such crossings may be accurately described within the multichannel Landau-Zener theory.
NASA Astrophysics Data System (ADS)
Bosyk, G. M.; Zozor, S.; Portesi, M.; Osán, T. M.; Lamberti, P. W.
2014-11-01
We provide a twofold extension of Landau-Pollak uncertainty relations for mixed quantum states and for positive operator-valued measures, by recourse to geometric considerations. The generalization is based on metrics between pure states, having the form of a function of the square of the inner product between the states. The triangle inequality satisfied by such metrics plays a crucial role in our derivation. The usual Landau-Pollak inequality is thus a particular case (derived from Wootters metric) of the family of inequalities obtained, and, moreover, we show that it is the most restrictive relation within the family.
Choi, Eunsil; Kang, Nalae; Jeon, Young; Pai, Hyun-Sook
2016-01-01
ABSTRACT The unique Escherichia coli GTPase Der (double Era-like GTPase), which contains tandemly repeated GTP-binding domains, has been shown to play an essential role in 50S ribosomal subunit biogenesis. The depletion of Der results in the accumulation of precursors of 50S ribosomal subunits that are structurally unstable at low Mg2+ concentrations. Der homologs are ubiquitously found in eubacteria. Conversely, very few are conserved in eukaryotes, and none is conserved in archaea. In the present study, to verify their conserved role in bacterial 50S ribosomal subunit biogenesis, we cloned Der homologs from two gammaproteobacteria, Klebsiella pneumoniae and Salmonella enterica serovar Typhimurium; two pathogenic bacteria, Staphylococcus aureus and Neisseria gonorrhoeae; and the extremophile Deinococcus radiodurans and then evaluated whether they could functionally complement the E. coli der-null phenotype. Only K. pneumoniae and S. Typhimurium Der proteins enabled the E. coli der-null strain to grow under nonpermissive conditions. Sucrose density gradient experiments revealed that the expression of K. pneumoniae and S. Typhimurium Der proteins rescued the structural instability of 50S ribosomal subunits, which was caused by E. coli Der depletion. To determine what allows their complementation, we constructed Der chimeras. We found that only Der chimeras harboring both the linker and long C-terminal regions could reverse the growth defects of the der-null strain. Our findings suggest that ubiquitously conserved essential GTPase Der is involved in 50S ribosomal subunit biosynthesis in various bacteria and that the linker and C-terminal regions may participate in species-specific recognition or interaction with the 50S ribosomal subunit. IMPORTANCE In Escherichia coli, Der (double Era-like GTPase) is an essential GTPase that is important for the production of mature 50S ribosomal subunits. However, to date, its precise role in ribosome biogenesis has not been
Relativistic Landau-Aharonov-Casher quantization based on the Lorentz symmetry violation background
NASA Astrophysics Data System (ADS)
Bakke, K.; Belich, H.; Silva, E. O.
2011-06-01
Based on the discussions about the Aharonov-Casher effect in the Lorentz symmetry violation background, we show that the analogue of the relativistic Landau quantization in the Aharonov-Casher setup can be achieved in the Lorentz-symmetry violation background.
Landau levels of cold dense quark matter in a strong magnetic field
NASA Astrophysics Data System (ADS)
Wen, Xin-Jian; Liang, Jun-Jun
2016-07-01
The occupied Landau levels of strange quark matter are investigated in the framework of the SU(3) NJL model with a conventional coupling and a magnetic-field dependent coupling respectively. At lower density, the Landau levels are mainly dominated by u and d quarks. Threshold values of the chemical potential for the s quark onset are shown in the μ -B plane. The magnetic-field-dependent running coupling can broaden the region of three-flavor matter by decreasing the dynamical masses of s quarks. Before the onset of s quarks, the Landau level number of light quarks is directly dependent on the magnetic field strength B by a simple inverse proportional relation ki ,max≈Bi0/B with Bd0=5 ×1 019 G , which is approximately 2 times Bu0 of u quarks at a common chemical potential. When the magnetic field increases up to Bd0, almost all three flavors are lying in the lowest Landau level.
NASA Technical Reports Server (NTRS)
Streitmatter, R. E.; Stephens, S. A.
1985-01-01
Numerical solutions have been obtained for the one-dimensional atmospheric electromagnetic cascade diffusion equations, including the Landau-Pomeranchuk-Migdal and screening effects. Spectra produced by primary gamma rays of various energies are given at a number of deths in the atmosphere.
ERIC Educational Resources Information Center
McVicar, Kathryn A.; Shinnar, Shlomo
2004-01-01
The Landau-Kleffner syndrome (LKS) and electrical status epilepticus in slow wave sleep (ESES) are rare childhood-onset epileptic encephalopathies in which loss of language skills occurs in the context of an epileptiform EEG activated in sleep. Although in LKS the loss of function is limited to language, in ESES there is a wider spectrum of…
Dynamically optimized Wang-Landau sampling with adaptive trial moves and modification factors.
Koh, Yang Wei; Lee, Hwee Kuan; Okabe, Yutaka
2013-11-01
The density of states of continuous models is known to span many orders of magnitudes at different energies due to the small volume of phase space near the ground state. Consequently, the traditional Wang-Landau sampling which uses the same trial move for all energies faces difficulties sampling the low-entropic states. We developed an adaptive variant of the Wang-Landau algorithm that very effectively samples the density of states of continuous models across the entire energy range. By extending the acceptance ratio method of Bouzida, Kumar, and Swendsen such that the step size of the trial move and acceptance rate are adapted in an energy-dependent fashion, the random walker efficiently adapts its sampling according to the local phase space structure. The Wang-Landau modification factor is also made energy dependent in accordance with the step size, enhancing the accumulation of the density of states. Numerical simulations show that our proposed method performs much better than the traditional Wang-Landau sampling.
Plasma heating and acceleration due to Landau damping of hydromagnetic waves.
NASA Technical Reports Server (NTRS)
Barnes, A.; Hung, R. J.
1972-01-01
We analyze energy and momentum exchange associated with Landau damping of hydromagnetic waves, from a macroscopic viewpoint, and compare the conclusions with those of the resonant quasi-linear theory. It is found that the heating of protons and electrons is correctly given by the resonant theory, but that the momentum exchange is not correctly described by the resonant theory.
Landau-Kleffner Syndrome: An Exploration of Parent Experience of the Diagnostic Process
ERIC Educational Resources Information Center
Lemard-Reid, Daunette
2014-01-01
Landau-Kleffner syndrome (LKS) is a rare childhood disorder that is often misdiagnosed as autism or childhood psychosis because of overlapping symptom presentation. Favorable prognoses in LKS depend on early diagnosis and treatment. While much is known about the clinical basis for LKS diagnosis, little is known about parents' lived experience with…
An introduction to the Ginzburg-Landau theory of phase transitions and nonequilibrium patterns
NASA Astrophysics Data System (ADS)
Hohenberg, P. C.; Krekhov, A. P.
2015-04-01
This paper presents an introduction to phase transitions and critical phenomena on the one hand, and nonequilibrium patterns on the other, using the Ginzburg-Landau theory as a unified language. In the first part, mean-field theory is presented, for both statics and dynamics, and its validity tested self-consistently. As is well known, the mean-field approximation breaks down below four spatial dimensions, where it can be replaced by a scaling phenomenology. The Ginzburg-Landau formalism can then be used to justify the phenomenological theory using the renormalization group, which elucidates the physical and mathematical mechanism for universality. In the second part of the paper it is shown how near pattern forming linear instabilities of dynamical systems, a formally similar Ginzburg-Landau theory can be derived for nonequilibrium macroscopic phenomena. The real and complex Ginzburg-Landau equations thus obtained yield nontrivial solutions of the original dynamical system, valid near the linear instability. Examples of such solutions are plane waves, defects such as dislocations or spirals, and states of temporal or spatiotemporal (extensive) chaos.
Relativistic Landau-Aharonov-Casher quantization based on the Lorentz symmetry violation background
Bakke, K.; Belich, H.; Silva, E. O.
2011-06-15
Based on the discussions about the Aharonov-Casher effect in the Lorentz symmetry violation background, we show that the analogue of the relativistic Landau quantization in the Aharonov-Casher setup can be achieved in the Lorentz-symmetry violation background.
a New Example of N = 2 Supersymmetric Landau-Ginzburg Theories:. the Two-Ring Case
NASA Astrophysics Data System (ADS)
Perelomov, Askold M.; Roan, Shi-Shyr
The new example of N = 2 supersymmetric Landau-Ginzburg theories is considered when the critical values of the superpotential w (x) form the regular two-ring configuration. It is shown that at the deformation, which does not change the form of this configuration, the vacuum state metric satisfies the equation of non-Abelian 2 × 2 Toda system.
Testing the Ginzburg-Landau approximation for three-flavor crystalline color superconductivity
Mannarelli, Massimo; Sharma, Rishi; Rajagopal, Krishna
2006-06-01
It is an open challenge to analyze the crystalline color superconducting phases that may arise in cold dense, but not asymptotically dense, three-flavor quark matter. At present the only approximation within which it seems possible to compare the free energies of the myriad possible crystal structures is the Ginzburg-Landau approximation. Here, we test this approximation on a particularly simple 'crystal' structure in which there are only two condensates
Testing the Ginzburg-Landau approximation for three-flavor crystalline color superconductivity
NASA Astrophysics Data System (ADS)
Mannarelli, Massimo; Rajagopal, Krishna; Sharma, Rishi
2006-06-01
It is an open challenge to analyze the crystalline color superconducting phases that may arise in cold dense, but not asymptotically dense, three-flavor quark matter. At present the only approximation within which it seems possible to compare the free energies of the myriad possible crystal structures is the Ginzburg-Landau approximation. Here, we test this approximation on a particularly simple “crystal” structure in which there are only two condensates ⟨us⟩˜Δexp(iq2·r) and ⟨ud⟩˜Δexp(iq3·r) whose position-space dependence is that of two plane waves with wave vectors q2 and q3 at arbitrary angles. For this case, we are able to solve the mean-field gap equation without making a Ginzburg-Landau approximation. We find that the Ginzburg-Landau approximation works in the Δ→0 limit as expected, find that it correctly predicts that Δ decreases with increasing angle between q2 and q3 meaning that the phase with q2∥q3 has the lowest free energy, and find that the Ginzburg-Landau approximation is conservative in the sense that it underestimates Δ at all values of the angle between q2 and q3.
Landau Damping in Sobolev Spaces for the Vlasov-HMF Model
NASA Astrophysics Data System (ADS)
Faou, Erwan; Rousset, Frédéric
2016-02-01
We consider the Vlasov-HMF (Hamiltonian Mean-Field) model. We consider solutions starting in a small Sobolev neighborhood of a spatially homogeneous state satisfying a linearized stability criterion (Penrose criterion). We prove that these solutions exhibit a scattering behavior to a modified state, which implies a nonlinear Landau damping effect with polynomial rate of damping.
Ginzburg-Landau theory for skyrmions in inversion-symmetric magnets with competing interactions
Lin, Shi-Zeng; Hayami, Satoru
2016-02-01
Magnetic skyrmions have attracted considerable attention recently for their huge potential in spintronic applications. Generally skyrmions are big compared to the atomic lattice constant, which allows for the Ginzburg-Landau type description in the continuum limit. This description successfully captures the main experimental observations on skyrmions in B20 compound without inversion symmetry. Skyrmions can also exist in inversion-symmetric magnets with competing interactions. Here, we derive a general Ginzburg-Landau theory for skyrmions in these magnets valid in the long-wavelength limit. We study the unusual static and dynamical properties of skyrmions based on the derived Ginzburg-Landau theory. We show that an easy axismore » spin anisotropy is sufficient to stabilize a skyrmion lattice. Interestingly, the skyrmion in inversion-symmetric magnets has a new internal degree of freedom associated with the rotation of helicity, i.e., the “spin” of the skyrmion as a particle, in addition to the usual translational motion of skyrmions (orbital motion). The orbital and spin degree of freedoms of an individual skyrmion can couple to each other, and give rise to unusual behavior that is absent for the skyrmions stabilized by the Dzyaloshinskii-Moriya interaction. Finally, the derived Ginzburg-Landau theory provides a convenient and general framework to discuss skyrmion physics and will facilitate the search for skyrmions in inversion-symmetric magnets.« less
Ginzburg-Landau theory of the superheating field anisotropy of layered superconductors
NASA Astrophysics Data System (ADS)
Liarte, Danilo B.; Transtrum, Mark K.; Sethna, James P.
2016-10-01
We investigate the effects of material anisotropy on the superheating field of layered superconductors. We provide an intuitive argument both for the existence of a superheating field, and its dependence on anisotropy, for κ =λ /ξ (the ratio of magnetic to superconducting healing lengths) both large and small. On the one hand, the combination of our estimates with published results using a two-gap model for MgB2 suggests high anisotropy of the superheating field near zero temperature. On the other hand, within Ginzburg-Landau theory for a single gap, we see that the superheating field shows significant anisotropy only when the crystal anisotropy is large and the Ginzburg-Landau parameter κ is small. We then conclude that only small anisotropies in the superheating field are expected for typical unconventional superconductors near the critical temperature. Using a generalized form of Ginzburg Landau theory, we do a quantitative calculation for the anisotropic superheating field by mapping the problem to the isotropic case, and present a phase diagram in terms of anisotropy and κ , showing type I, type II, or mixed behavior (within Ginzburg-Landau theory), and regions where each asymptotic solution is expected. We estimate anisotropies for a number of different materials, and discuss the importance of these results for radio-frequency cavities for particle accelerators.
Competing quantum Hall phases in the second Landau level in low density limit
NASA Astrophysics Data System (ADS)
Pan, Wei; Serafin, A.; Xia, J. S.; Yin, L.; Sullivan, N. S.; Baldwin, K. W.; West, K. W.; Pfeiffer, L. N.; Tsui, D. C.
2015-03-01
We present here the results from two high quality, low density GaAs quantum wells. In sample A of electron density n = 5.0 x 1010 cm-2, anisotropic electronic transport behavior was observed at ν = 7/2 in the second Landau level. We believe that the anisotropy is due to the large Landau level mixing effect in this sample. In sample B of density 4.1 x 1010 cm-2, strong 8/3, 5/2, and 7/3 fractional quantum Hall states were observed. Furthermore, our energy gap data obtained in various samples of different densities suggest that the 5/2 state may be spin unpolarized in the low density limit. The results from both samples show that the strong electron-electron interactions and a large Landau level mixing effect play an import role in the competing ground states in the second landau level. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000. This work was supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, Materials Sciences and Engineering Division.
Landau spectrum and twin boundaries of bismuth in the extreme quantum limit.
Zhu, Zengwei; Fauqué, Benoît; Malone, Liam; Antunes, Arlei Borba; Fuseya, Yuki; Behnia, Kamran
2012-09-11
The Landau spectrum of bismuth is complex and includes many angle-dependent lines in the extreme quantum limit. The adequacy of single-particle theory to describe this spectrum in detail has been an open issue. Here, we present a study of angle-resolved Nernst effect in bismuth, which maps the angle-resolved Landau spectrum for the entire solid angle up to 28 T. The experimental map is in good agreement with the results of a theoretical model with parabolic dispersion for holes and an extended Dirac Hamiltonian for electrons. The angular dependence of additional lines in the Landau spectrum allows us to uncover the mystery of their origin. They correspond to the lines expected for the hole Landau levels in a secondary crystal tilted by 108°, the angle between twinned crystals in bismuth. According to our results, the electron reservoirs of the two identical tilted crystals have different chemical potentials, and carriers across the twin boundary have different concentrations. An exceptional feature of this junction is that it separates two electron-hole compensated reservoirs. The link between this edge singularity and the states wrapping a three-dimensional electron gas in the quantum limit emerges as an outstanding open question.
Landau-Zener tunneling of Bose-Einstein condensates in an optical lattice
Konotop, V.V.; Kevrekidis, P.G.; Salerno, M.
2005-08-15
A theory of the nonsymmetric Landau-Zener tunneling of Bose-Einstein condensates in deep optical lattices is presented. It is shown that periodic exchange of matter between the bands is described by a set of linearly coupled nonlinear Schroedinger equations. The key role of the modulational instability in rendering the interband transitions irreversible is highlighted.
Ginzburg-Landau theory for skyrmions in inversion-symmetric magnets with competing interactions
Lin, Shi-Zeng; Hayami, Satoru
2016-02-01
Magnetic skyrmions have attracted considerable attention recently for their huge potential in spintronic applications. Generally skyrmions are big compared to the atomic lattice constant, which allows for the Ginzburg-Landau type description in the continuum limit. This description successfully captures the main experimental observations on skyrmions in B20 compound without inversion symmetry. Skyrmions can also exist in inversion-symmetric magnets with competing interactions. Here, we derive a general Ginzburg-Landau theory for skyrmions in these magnets valid in the long-wavelength limit. We study the unusual static and dynamical properties of skyrmions based on the derived Ginzburg-Landau theory. We show that an easy axis spin anisotropy is sufficient to stabilize a skyrmion lattice. Interestingly, the skyrmion in inversion-symmetric magnets has a new internal degree of freedom associated with the rotation of helicity, i.e., the “spin” of the skyrmion as a particle, in addition to the usual translational motion of skyrmions (orbital motion). The orbital and spin degree of freedoms of an individual skyrmion can couple to each other, and give rise to unusual behavior that is absent for the skyrmions stabilized by the Dzyaloshinskii-Moriya interaction. Finally, the derived Ginzburg-Landau theory provides a convenient and general framework to discuss skyrmion physics and will facilitate the search for skyrmions in inversion-symmetric magnets.
Binder, Johannes; Withers, Freddie; Molas, Maciej R; Faugeras, Clement; Nogajewski, Karol; Watanabe, Kenji; Taniguchi, Takashi; Kozikov, Aleksey; Geim, Andre K; Novoselov, Kostya S; Potemski, Marek
2017-03-08
We report on experimental investigations of an electrically driven WSe2 based light-emitting van der Waals heterostructure. We observe a threshold voltage for electroluminescence significantly lower than the corresponding single particle band gap of monolayer WSe2. This observation can be interpreted by considering the Coulomb interaction and a tunneling process involving excitons, well beyond the picture of independent charge carriers. An applied magnetic field reveals pronounced magneto-oscillations in the electroluminescence of the free exciton emission intensity with a 1/B periodicity. This effect is ascribed to a modulation of the tunneling probability resulting from the Landau quantization in the graphene electrodes. A sharp feature in the differential conductance indicates that the Fermi level is pinned and allows for an estimation of the acceptor binding energy.
Qualitätsmanagement in der Lebensmittelindustrie
NASA Astrophysics Data System (ADS)
Thorn, Volker
Die wesentlichen Kunden der Lebensmittelindustrie sind der Einzel- und Großhandel und die Verbraucher. Jedes Unternehmen kann mittel- und langfristig nur existieren, wenn seine Kunden zufrieden sind. Kunden sind zufrieden, wenn ihre Erwartungen, die sie an Produkt, Service und Preis stellen, erfüllt werden. Also die bestimmte erwartete Qualität (Leistung) sichergestellt wird. Trotz aller Bemühungen und Anstrengungen der Anbieter, Qualitätsprodukte auf den Markt zu bringen, kames in den letzten Jahren immer wieder zu Lebensmittelskandalen.
NASA Astrophysics Data System (ADS)
Ellis, Richard S.; Machta, Jonathan; Otto, Peter Tak-Hun
2008-10-01
The purpose of this paper is to prove connections among the asymptotic behavior of the magnetization, the structure of the phase transitions, and a class of polynomials that we call the Ginzburg-Landau polynomials. The model under study is a mean-field version of a lattice spin model due to Blume and Capel. It is defined by a probability distribution that depends on the parameters β and K, which represent, respectively, the inverse temperature and the interaction strength. Our main focus is on the asymptotic behavior of the magnetization m( β n , K n ) for appropriate sequences ( β n , K n ) that converge to a second-order point or to the tricritical point of the model and that lie inside various subsets of the phase-coexistence region. The main result states that as ( β n , K n ) converges to one of these points ( β, K), m(βn,Kn)˜ bar{x}|β -βn|^{γ}→ 0 . In this formula γ is a positive constant, and bar{x} is the unique positive, global minimum point of a certain polynomial g. We call g the Ginzburg-Landau polynomial because of its close connection with the Ginzburg-Landau phenomenology of critical phenomena. For each sequence the structure of the set of global minimum points of the associated Ginzburg-Landau polynomial mirrors the structure of the set of global minimum points of the free-energy functional in the region through which ( β n , K n ) passes and thus reflects the phase-transition structure of the model in that region. This paper makes rigorous the predictions of the Ginzburg-Landau phenomenology of critical phenomena and the tricritical scaling theory for the mean-field Blume-Capel model.
Werner Heisenberg zum 100. Geburtstag: Pionier der Quantenmechanik
NASA Astrophysics Data System (ADS)
Jacobi, Manfred
2001-11-01
Werner Heisenberg war eine der prägendsten Gestalten der Physik des 20. Jahrhunderts. Zu seinen wichtigsten Verdiensten gehören die Grundlegung der Quantenmechanik, die Formulierung der Unschärferelationen sowie die Beteiligung an der Ausarbeitung der Kopenhagener Deutung der Quantenmechanik. Darüber hinaus lieferte er Arbeiten von fundamentalem Charakter zur Theorie des Atomkerns, zur kosmischen Strahlung und zur Quantenfeldtheorie. Während des Krieges war er an den Arbeiten des Uranvereins beteiligt, der die Möglichkeit einer Entwicklung von Kernwaffen untersuchte, jedoch über Vorarbeiten zur Reaktorphysik nicht hinauskam. Wegen dieser Tätigkeit wurde er bei Kriegsende für einige Monate in England interniert. Nach seiner Rückkehr widmete er sich vor allem dem Aufbau der Physik in Deutschland, die während der NS-Zeit nahezu ihrer gesamten Substanz beraubt worden war.
de Lima, M M; Kosevich, Yu A; Santos, P V; Cantarero, A
2010-04-23
We present the experimental observation of Bloch oscillations, the Wannier-Stark ladder, and Landau-Zener tunneling of surface acoustic waves in perturbed grating structures on a solid substrate. A model providing a quantitative description of our experimental observations, including multiple Landau-Zener transitions of the anticrossed surface acoustic Wannier-Stark states, is developed. The use of a planar geometry for the realization of the Bloch oscillations and Landau-Zener tunneling allows a direct access to the elastic field distribution. The vertical surface displacement has been measured by interferometry.
Modellbasierte interindividuelle Registrierung an der lateralen Schädelbasis
NASA Astrophysics Data System (ADS)
Riechmann, M.; Lohnstein, P. U.; Raczkowsky, J.; Klenzner, T.; Schipper, J.; Wörn, H.
Bei chirurgischen Eingriffen an der lateralen Schädelbasis wird in der zur Zeit gängigen Praxis das Knochengewebe unter optischer Kontrolle großflächig ablativ entfernt, um den Operationssitus freizulegen und konventionell operieren zu können. Prinzipiell soll dabei die Schonung vital und funktional bedeutender Strukturen berücksichtigt werden. Zur weiteren Minimierung der Traumatisierung und zur Erhaltung der strukturellen anatomischen Integrität soll eine alternative endoskopische Operationstechnik entwickelt werden, bei der der Situs durch dünne im Knochen liegende Bohrkanäle erreicht wird. Im Rahmen der Evaluierung der generellen Eignung der geometrischen Ausprägungen der humanen lateralen Schädelbasis wurden Methoden entwickelt, die anhand virtueller Modelle die Zugänglichkeit der anatomischen Zielstrukturen bestimmen können. Ein dabei auftretendes Problem ist die interindividuelle Vergleichbarkeit der Ergebnisse, da aufgrund der anatomischen Variationen eine zuverlässige interindividuelle Registrierung nicht trivial ist. Diese Arbeit beschreibt ein modellbasiertes Verfahren zur automatischen Registrierung mehrerer Felsenbeine zu einander über die prägnante Geometrie der Cochlea.
Wilden, Sophia M; Lang, Berenice M; Mohr, Peter; Grabbe, Stephan
2016-07-01
Seit Jahrzehnten ist bekannt, dass Tumoren vom Immunsystem erkannt und zerstört werden können. Diese, vor allem in Tierversuchen gewonnene Erkenntnis konnte jedoch in der Vergangenheit nicht zum Nutzen unserer Patienten umgesetzt werden, da immunonkologische Therapieansätze in den letzten Jahrzehnten in der Anwendung beim Menschen stets versagt haben. Daher hat, mit Ausnahme der adjuvanten Interferontherapie, keines dieser Verfahren den Einzug in die klinische Versorgung gefunden. Langzeitüberleben unter guter Lebensqualität war dabei sehr wenigen Patienten vorbehalten. Mit den neuen immunologischen Therapieansätzen wird jedoch sowohl das Langzeitüberleben als auch die Lebensqualität onkologischer Patienten neu definiert. Auf die neuen "Immun-Checkpoint-Inhibitoren" spricht erstmals ein relevanter Teil der behandelten Patienten an und diese zeigen in der Regel langandauernde Remissionen bis hin zur Heilung. Schon jetzt ist klar, dass die Immuntherapie in Zukunft eine der wesentlichen Therapiesäulen bei der Behandlung des metastasierten Melanoms und auch vieler anderer fortgeschrittener Tumoren bilden wird. In dieser Übersicht werden die wichtigsten neuen Therapiemodalitäten besprochen und sowohl deren Wirkprinzip als auch klinische Daten zum Therapieansprechen und zu erwartenden Nebenwirkungen der Therapie referiert.
Landau damping in a dipolar Bose-Fermi mixture in the Bose-Einstein condensation (BEC) limit
NASA Astrophysics Data System (ADS)
Moniri, S. M.; Yavari, H.; Darsheshdar, E.
2016-12-01
By using a mean-field approximation which describes the coupled oscillations of condensate and noncondensate atoms in the collisionless regime, Landau damping in a dilute dipolar Bose-Fermi mixture in the BEC limit where Fermi superfluid is treated as tightly bounded molecules, is investigated. In the case of a uniform quasi-two-dimensional (2D) case, the results for the Landau damping due to the Bose-Fermi interaction are obtained at low and high temperatures. It is shown that at low temperatures, the Landau damping rate is exponentially suppressed. By increasing the strength of dipolar interaction, and the energy of boson quasiparticles, Landau damping is suppressed over a broader temperature range.
2012-01-01
Massless Dirac electrons in graphene fill Landau levels with energies scaled as square roots of their numbers. Coulomb interaction between electrons leads to mixing of different Landau levels. The relative strength of this interaction depends only on dielectric susceptibility of surrounding medium and can be large in suspended graphene. We consider influence of Landau level mixing on the properties of magnetoexcitons and magnetoplasmons—elementary electron-hole excitations in graphene in quantizing magnetic field. We show that, at small enough background dielectric screening, the mixing leads to very essential change of magnetoexciton and magnetoplasmon dispersion laws in comparison with the lowest Landau level approximation. PACS: 73.22.Pr; 71.35.Ji; 73.43.Mp; 71.70.Gm. PMID:22340359
Realization of optical bistability and multistability in Landau-quantized graphene
NASA Astrophysics Data System (ADS)
Hamedi, H. R.; Asadpour, S. H.
2015-05-01
The solution of input-output curves in an optical ring cavity containing Landau-quantized graphene is theoretically investigated taking the advantage of density-matrix method. It is found that under the action of strong magnetic and infrared laser fields, one can efficiently reduce the threshold of the onset of optical bistability (OB) at resonance condition. At non-resonance condition, we observed that graphene metamaterial can support the possibility to obtain optical multistability (OM), which is more practical in all-optical switching or coding elements. We present an analytical approach to elucidate our simulations. Due to very high infrared optical nonlinearity of graphene stemming from very unique and unusual properties of quantized Landau levels near the Dirac point, such controllability on OB and OM may provide new technological possibilities in solid state quantum information science.
Gumbs, Godfrey; Iurov, Andrii; Huang, Danhong; Fekete, Paula; Zhemchuzhna, Liubov
2014-03-31
A two-dimensional periodic array of scatterers has been introduced to a single layer of graphene in the presence of an external magnetic field perpendicular to the graphene layer. The eigenvalue equation for such a system has been solved numerically to display the structure of split Landau subbands as functions of both wave number and magnetic flux. The effects of pseudo-spin coupling and Landau subbands mixing by a strong scattering potential have been demonstrated. Additionally, we investigated the square barrier tunneling problem when magnetic field is present, as well as demonstrate the crucial difference in the modulated band structure between graphene and the two-dimensional electron gas. The low-magnetic field regime is particularly interesting for Dirac fermions and has been discussed. Tunneling of Dirac electrons through a magnetic potential barrier has been investigated to complement the reported results on electrostatic potential scattering in the presence of an ambient magnetic field.
Devinsky, Orrin; Goldberg, Rina; Miles, Daniel; Bojko, Aviva; Riviello, James
2014-10-01
We report 2 pediatric patients who presented initially with seizures followed by subacute language regression characterized by a verbal auditory agnosia. These previously normal children had no evidence of expressive aphasia during their symptomatic periods. Further, in both cases, auditory agnosia was associated with sleep-activated electroencephalographic (EEG) epileptiform activity, consistent with Landau-Kleffner syndrome. However, both cases are unique since the episodic auditory agnosia and sleep-activated EEG epileptiform activity rapidly responded to combination therapy with pulse benzodiazepine and corticosteroids. Further, in each case, recurrences were characterized by similar symptoms, EEG findings, and beneficial responses to the pulse benzodiazepine and corticosteroid therapy. These observations suggest that pulse combination high-dose corticosteroid and benzodiazepine therapy may be especially effective in Landau-Kleffner syndrome.
Lee, Y; Tran, D; Myhro, K; Velasco, J; Gillgren, N; Poumirol, J M; Smirnov, D; Barlas, Y; Lau, C N
2016-01-13
Using transport measurements, we investigate multicomponent quantum Hall (QH) ferromagnetism in dual-gated rhombohedral trilayer graphene (r-TLG) in which the real spin, orbital pseudospin, and layer pseudospins of the lowest Landau level form spontaneous ordering. We observe intermediate QH plateaus, indicating a complete lifting of the degeneracy of the zeroth Landau level (LL) in the hole-doped regime. In charge neutral r-TLG, the orbital degeneracy is broken first, and the layer degeneracy is broken last and only in the presence of an interlayer potential U⊥. In the phase space of U⊥ and filling factor ν, we observe an intriguing "hexagon" pattern, which is accounted for by a model based on crossings between symmetry-broken LLs.
Many-body effects of Coulomb interaction on Landau levels in graphene
NASA Astrophysics Data System (ADS)
Sokolik, A. A.; Zabolotskiy, A. D.; Lozovik, Yu. E.
2017-03-01
In strong magnetic fields, massless electrons in graphene populate relativistic Landau levels with the square-root dependence of each level energy on its number and magnetic field. Interaction-induced deviations from this single-particle picture were observed in recent experiments on cyclotron resonance and magneto-Raman scattering. Previous attempts to calculate such deviations theoretically using the unscreened Coulomb interaction resulted in overestimated many-body effects. This work presents many-body calculations of cyclotron and magneto-Raman transitions in single-layer graphene in the presence of Coulomb interaction, which is statically screened in the random-phase approximation. We take into account self-energy and excitonic effects as well as Landau level mixing, and achieve good agreement of our results with the experimental data for graphene on different substrates. The important role of a self-consistent treatment of the screening is found.
NASA Astrophysics Data System (ADS)
Munoz, F.; Collado, H. P. Ojeda; Usaj, Gonzalo; Sofo, Jorge O.; Balseiro, C. A.
2016-06-01
The electronic structure of bilayer graphene under pressure develops very interesting features with an enhancement of the trigonal warping and a splitting of the parabolic touching bands at the K point of the reciprocal space into four Dirac cones, one at K and three along the T symmetry lines. As pressure is increased, these cones separate in reciprocal space and in energy, breaking the electron-hole symmetry. Due to their energy separation, their opposite Berry curvature can be observed in valley Hall effect experiments and in the structure of the Landau levels. Based on the electronic structure obtained by density functional theory, we develop a low energy Hamiltonian that describes the effects of pressure on measurable quantities such as the Hall conductivity and the Landau levels of the system.
Surface Landau levels and spin states in bismuth (111) ultrathin films
Du, Hongjian; Sun, Xia; Liu, Xiaogang; Wu, Xiaojun; Wang, Jufeng; Tian, Mingyang; Zhao, Aidi; Luo, Yi; Yang, Jinlong; Wang, Bing; Hou, J. G.
2016-01-01
The development of next-generation electronics is much dependent on the discovery of materials with exceptional surface-state spin and valley properties. Because of that, bismuth has attracted a renewed interest in recent years. However, despite extensive studies, the intrinsic electronic transport properties of Bi surfaces are largely undetermined due to the strong interference from the bulk. Here we report the unambiguous determination of the surface-state Landau levels in Bi (111) ultrathin films using scanning tunnelling microscopy under magnetic fields perpendicular to the surface. The Landau levels of the electron-like and the hole-like carriers are accurately characterized and well described by the band structure of the Bi (111) surface from density functional theory calculations. Some specific surface spin states with a large g-factor are identified. Our findings shed light on the exploiting surface-state properties of Bi for their applications in spintronics and valleytronics. PMID:26964494
Experimental observation of surface states and Landau levels bending in bilayer graphene
NASA Astrophysics Data System (ADS)
Yin, Long-Jing; Zhang, Yu; Qiao, Jia-Bin; Li, Si-Yu; He, Lin
2016-03-01
We report on microscopic measurements of the low-energy electronic structures both at the zigzag and armchair edges of bilayer graphene using scanning tunneling microscopy and spectroscopy (STM and STS). We have found that, both in the absence and in the presence of a magnetic field, an almost zero-energy peak in the density of states was localized at the zigzag edges, as expected for the surface states at the zigzag edges of bilayer graphene. In the quantum Hall regime, we have clearly observed Landau levels bending away from the charge neutrality point near both the zigzag and armchair edges. Such a result is direct evidence for the evolution of Landau levels into quantum Hall edge states in graphene bilayers. Our experiment indicates that it is possible to explore rich quantum Hall physics in graphene systems using STM and STS.
Solvable four-state Landau-Zener model of two interacting qubits with path interference
Sinitsyn, Nikolai A.
2015-11-30
In this paper, I identify a nontrivial four-state Landau-Zener model for which transition probabilities between any pair of diabatic states can be determined analytically and exactly. The model describes an experimentally accessible system of two interacting qubits, such as a localized state in a Dirac material with both valley and spin degrees of freedom or a singly charged quantum dot (QD) molecule with spin orbit coupling. Application of the linearly time-dependent magnetic field induces a sequence of quantum level crossings with possibility of interference of different trajectories in a semiclassical picture. I argue that this system satisfies the criteria of integrability in the multistate Landau-Zener theory, which allows one to derive explicit exact analytical expressions for the transition probability matrix. Finally, I also argue that this model is likely a special case of a larger class of solvable systems, and present a six-state generalization as an example.
On the Shape of Meissner Solutions to a Limiting Form of Ginzburg-Landau Systems
NASA Astrophysics Data System (ADS)
Xiang, Xingfei
2016-12-01
In this paper we study a semilinear system involving the curl operator, which is a limiting form of the Ginzburg-Landau model for superconductors in R^3 for a large value of the Ginzburg-Landau parameter. We consider the locations of the maximum points of the magnitude of solutions, which are associated with the nucleation of instability of the Meissner state for superconductors when the applied magnetic field is increased in the transition between the Meissner state and the vortex state. For small penetration depth, we prove that the location is not only determined by the tangential component of the applied magnetic field, but also by the normal curvatures of the boundary in some directions. This improves the result obtained by Bates and Pan in Commun. Math. Phys. 276, 571-610 (2007). We also show that the solutions decay exponentially in the normal direction away from the boundary if the penetration depth is small.
Landau levels in 2D materials using Wannier Hamiltonians obtained by first principles
NASA Astrophysics Data System (ADS)
Lado, J. L.; Fernández-Rossier, J.
2016-09-01
We present a method to calculate the Landau levels and the corresponding edge states of two dimensional (2D) crystals using as a starting point their electronic structure as obtained from standard density functional theory (DFT). The DFT Hamiltonian is represented in the basis of maximally localized Wannier functions. This defines a tight-binding Hamiltonian for the bulk that can be used to describe other structures, such as ribbons, provided that atomic scale details of the edges are ignored. The effect of the orbital magnetic field is described using the Peierls substitution in the hopping matrix elements. Implementing this approach in a ribbon geometry, we obtain both the Landau levels and the dispersive edge states for a series of 2D crystals, including graphene, Boron Nitride, MoS2, Black Phosphorous, Indium Selenide and MoO3. Our procedure can readily be used in any other 2D crystal, and provides an alternative to effective mass descriptions.
NASA Astrophysics Data System (ADS)
Escande, D. F.; Elskens, Yves; Doveil, F.
2015-02-01
The derivation of Debye shielding and Landau damping from the N-body description of plasmas is performed directly by using Newton’s second law for the N-body system. This is done in a few steps with elementary calculations using standard tools of calculus and no probabilistic setting. Unexpectedly, Debye shielding is encountered together with Landau damping. This approach is shown to be justified in the one-dimensional case when the number of particles in a Debye sphere becomes large. The theory is extended to accommodate a correct description of trapping and chaos due to Langmuir waves. On top of their well-known production of collisional transport, the repulsive deflections of electrons are shown to produce shielding, in such a way that each particle is shielded by all other ones, while keeping in uninterrupted motion.
Application of the Wang-Landau Monte-Carlo Formalism applied to Ferroelectrics materials
NASA Astrophysics Data System (ADS)
Bin Omran, Saad; Kornev, Igor; Bellaiche, Laurent
The conventional description of phase transitions in ferroelectrics is based on canonical thermodynamic functions and always assumes the thermodynamic limit of an infinite system. However, ferroelectrics at nanoscale recently became of high interest due to their potential applications in minuaturized devices. It is this timely and more appropriate to use the microcanonical ensemble when mimicking ferroelectric systems. Interestingly, a Monte Carlo method based on the density of states (or microcanonical ensemble partition function) proposed by Wang and Landau has the potential to over-come these difficulties. Here, the Wang-Landau Monte Carlo algorithm is implemented within an effective Hamiltonian approach and used to conduct a detailed study of physical properties of BaTiO3 bulk. In this presentation, we will show how this approach allows a highly-accurate and straightforward calculation of various thermodynamic properties, including phase transition temperatures, as well as polarization, dielectric susceptibility, specific heat and electrocaloric coefficient at any temperature.
Dissipative Landau-Zener quantum dynamics with transversal and longitudinal noise
NASA Astrophysics Data System (ADS)
Javanbakht, S.; Nalbach, P.; Thorwart, M.
2015-05-01
We determine the Landau-Zener transition probability in a dissipative environment including both longitudinal as well as transversal quantum-mechanical noise originating from a single noise source. For this, we use the numerically exact quasiadiabatic path integral, as well as the approximative nonequilibrium Bloch equations. We find that transversal quantum noise in general influences the Landau-Zener probability much more strongly than longitudinal quantum noise does at a given temperature and system-bath coupling strength. In other words, transversal noise contributions become important even when the coupling strength of transversal noise is smaller than that of longitudinal noise. We furthermore reveal that transversal noise renormalizes the tunnel coupling independent of temperature. Finally, we show that the effect of mixed longitudinal and transversal noise originating from a single bath cannot be obtained from an incoherent sum of purely longitudinal and purely transversal noise.
Realization of optical bistability and multistability in Landau-quantized graphene
Hamedi, H. R.; Asadpour, S. H.
2015-05-14
The solution of input-output curves in an optical ring cavity containing Landau-quantized graphene is theoretically investigated taking the advantage of density-matrix method. It is found that under the action of strong magnetic and infrared laser fields, one can efficiently reduce the threshold of the onset of optical bistability (OB) at resonance condition. At non-resonance condition, we observed that graphene metamaterial can support the possibility to obtain optical multistability (OM), which is more practical in all-optical switching or coding elements. We present an analytical approach to elucidate our simulations. Due to very high infrared optical nonlinearity of graphene stemming from very unique and unusual properties of quantized Landau levels near the Dirac point, such controllability on OB and OM may provide new technological possibilities in solid state quantum information science.
Spatial Landau damping in plasmas with three-dimensional {kappa} distributions
Podesta, J.J.
2005-05-15
The increase in linear Landau damping in {kappa}-distributed plasmas compared to thermal equilibrium plasmas is studied by solving a boundary value problem for the spatially damped plasma waves generated by a planar grid electrode with an applied time harmonic potential. Solutions are computed for the plasma potential versus the distance from the electrode for different values of the parameter {kappa} (kappa). The velocity parameter v{sub 0} of the distribution function is chosen so that, as the parameter {kappa} varies, the kinetic temperature of the plasma remains constant. The exact solutions of this problem are also compared to approximate solutions derived from the theory of normal modes, that is, from the roots of the dispersion relation. This model problem demonstrates the significant increase in Landau damping by electrons which occurs for small values of the parameter {kappa}.
Cavity Optomechanics with synthetic Landau levels of ultra cold Fermi gas
NASA Astrophysics Data System (ADS)
Ghosh, Sankalpa; Padhi, Bikash
2014-03-01
Ultra cold fermionic atoms placed in a synthetic magnetic field arrange themselves in Landau levels. We theoretically study the optomechanical interaction between the light field and collective excitations of such fermionic atoms in synthetic magnetic field by placing them in side a Fabry Perot cavity. We derive the effective hamiltonian for particle hole excitations from a filled Landau level using a bosonization technique and obtain an expression for the cavity transmission spectrum. Using this we show that the cavity transmission spectrum demonstrates cold atom analogue of Subnikov de Hass oscillation in electronic condensed matter systems. We discuss the experimental consequences for this oscillation for such system and the related optical bistability. Ref. Bikash Padhi and Sankalpa Ghosh, Physical Review Letters, Vol 111, 043603 (2013) PDA Grant, Indian Institute of Technology, Delhi.
Microscopically derived multi-component Ginzburg-Landau theories for s + is superconducting state
NASA Astrophysics Data System (ADS)
Garaud, Julien; Silaev, Mihail; Babaev, Egor
2017-02-01
Starting with the generic Ginzburg-Landau expansion from a microscopic N-band model, we focus on the case of a 3-band model which was suggested to be relevant to describe some iron-based superconductors. This can lead to the so-called s + is superconducting state that breaks time-reversal symmetry due to the competition between different pairing channels. Of particular interest in that context, is the case of an interband dominated pairing with repulsion between different bands. For that case we consider in detail the relevant reduced two-component Ginzburg-Landau theory. We provide detailed analysis of the ground state, length scales and topological properties of that model. Prepared for the proceedings of Vortex IX conference in Rhodes (Sept. 2015).
Analysis of generalized negative binomial distributions attached to hyperbolic Landau levels
NASA Astrophysics Data System (ADS)
Chhaiba, Hassan; Demni, Nizar; Mouayn, Zouhair
2016-07-01
To each hyperbolic Landau level of the Poincaré disc is attached a generalized negative binomial distribution. In this paper, we compute the moment generating function of this distribution and supply its atomic decomposition as a perturbation of the negative binomial distribution by a finitely supported measure. Using the Mandel parameter, we also discuss the nonclassical nature of the associated coherent states. Next, we derive a Lévy-Khintchine-type representation of its characteristic function when the latter does not vanish and deduce that it is quasi-infinitely divisible except for the lowest hyperbolic Landau level corresponding to the negative binomial distribution. By considering the total variation of the obtained quasi-Lévy measure, we introduce a new infinitely divisible distribution for which we derive the characteristic function.
Landsgesell, Jonas; Holm, Christian; Smiatek, Jens
2017-02-14
We present a novel method for the study of weak polyelectrolytes and general acid-base reactions in molecular dynamics and Monte Carlo simulations. The approach combines the advantages of the reaction ensemble and the Wang-Landau sampling method. Deprotonation and protonation reactions are simulated explicitly with the help of the reaction ensemble method, while the accurate sampling of the corresponding phase space is achieved by the Wang-Landau approach. The combination of both techniques provides a sufficient statistical accuracy such that meaningful estimates for the density of states and the partition sum can be obtained. With regard to these estimates, several thermodynamic observables like the heat capacity or reaction free energies can be calculated. We demonstrate that the computation times for the calculation of titration curves with a high statistical accuracy can be significantly decreased when compared to the original reaction ensemble method. The applicability of our approach is validated by the study of weak polyelectrolytes and their thermodynamic properties.
Landau-Placzek ratio for heat density dynamics and its application to heat capacity of liquids.
Bryk, Taras; Ruocco, Giancarlo; Scopigno, Tullio
2013-01-21
Exact relation for contributions to heat capacity of liquids is obtained from hydrodynamic theory. It is shown from analysis of the long-wavelength limit of heat density autocorrelation functions that the heat capacity of simple liquids is represented as a sum of two contributions due to "phonon-like" collective excitations and heat relaxation. The ratio of both contributions being the analogy of Landau-Placzek ratio for heat processes depends on the specific heats ratio. The theory of heat density autocorrelation functions in liquids is verified by computer simulations. Molecular dynamics simulations for six liquids having the ratio of specific heats γ in the range 1.1-2.3, were used for evaluation of the heat density autocorrelation functions and predicted Landau-Placzek ratio for heat processes. The dependence of contributions from collective excitations and heat relaxation process to specific heat on γ is shown to be in excellent agreement with the theory.
LETTER TO THE EDITOR: Instability of a Landau - Fermi liquid as the Mott insulator is approached
NASA Astrophysics Data System (ADS)
Furukawa, N.; Rice, T. M.
1998-06-01
We examine a two-dimensional Fermi liquid with a Fermi surface which touches the Umklapp surface first at the four points 0953-8984/10/23/001/img1 as the electron density is increased. Umklapp processes at the four patches near 0953-8984/10/23/001/img1 lead the renormalization group equations to scale to strong coupling, resembling the behaviour of a two-leg ladder at half-filling. The incompressible character of the fixed point causes a breakdown of Landau theory at these patches. A further increase in density spreads the incompressible regions so that the open Fermi surface shrinks to four disconnected segments. This non-Landau state, in which parts of the Fermi surface are truncated to form an insulating spin liquid, has many features in common with phenomenological models recently proposed for the cuprate superconductors.
Observation of Landau-Zener tunneling through atomic current in the optical lattices
Yan Jieyun; Duan Suqing; Zhang Wei; Zhao Xiangeng
2009-05-15
The atomic current in the Fourier-synthesized optical lattices under a constant external force is investigated theoretically. Based on a two-band model, the atomic current is derived by solving the Boltzmann equations. We find that the stationary atomic current changes with the probability of Landau-Zener tunneling, depending on the adjustable energy structure of the optical lattices. In contrast to the classical results of an electron in superlattices given by the Esaki-Tsu equations, the relation between the stationary atomic current and the strength of the external force in optical lattices is modified significantly. Both these characteristics can be taken as an effective way to observe the Landau-Zener tunneling in the optical lattices.
Time-resolved measurement of Landau-Zener tunneling in different bases
Tayebirad, G.; Loerch, N.; Wimberger, S.; Zenesini, A.; Ciampini, D.; Arimondo, E.; Mannella, R.; Morsch, O.
2010-07-15
A comprehensive study of the tunneling dynamics of a Bose-Einstein condensate in a tilted periodic potential is presented. We report numerical and experimental results on time-resolved measurements of the Landau-Zener tunneling of ultracold atoms introduced by the tilt, which experimentally is realized by accelerating the lattice. The use of different protocols enables us to access the tunneling probability, numerically as well as experimentally, in two different bases, namely, the adiabatic basis and the diabatic basis. The adiabatic basis corresponds to the eigenstates of the lattice, and the diabatic one to the free-particle momentum eigenstates. Our numerical and experimental results are compared with existing two-state Landau-Zener models.
Landau-Zener-Stückelberg-Majorana lasing in circuit quantum electrodynamics
NASA Astrophysics Data System (ADS)
Neilinger, P.; Shevchenko, S. N.; Bogár, J.; Rehák, M.; Oelsner, G.; Karpov, D. S.; Hübner, U.; Astafiev, O.; Grajcar, M.; Il'ichev, E.
2016-09-01
We demonstrate amplification (and attenuation) of a probe signal by a driven two-level quantum system in the Landau-Zener-Stückelberg-Majorana regime by means of an experiment, in which a superconducting qubit was strongly coupled to a microwave cavity, in a conventional arrangement of circuit quantum electrodynamics. Two different types of flux qubit, specifically a conventional Josephson junctions qubit and a phase-slip qubit, show similar results, namely, lasing at the working points where amplification takes place. The experimental data are explained by the interaction of the probe signal with Rabi-like oscillations. The latter are created by constructive interference of Landau-Zener-Stückelberg-Majorana (LZSM) transitions during the driving period of the qubit. A detailed description of the occurrence of these oscillations and a comparison of obtained data with both analytic and numerical calculations are given.
Quantum system driven by incoherent a.c fields: Multi-crossing Landau Zener dynamics
NASA Astrophysics Data System (ADS)
Jipdi, M. N.; Fai, L. C.; Tchoffo, M.
2016-10-01
The paper investigates the multi-crossing dynamics of a Landau-Zener (LZ) system driven by two sinusoidal a.c fields applying the Dynamic Matrix approach (DMA). The system is shown to follow one-crossing and multi-crossing dynamics for low and high frequency regime respectively. It is shown that in low frequency regime, the resonance phenomenon occurs and leads to the decoupling of basis states; the effective gap vanishes and then the complete blockage of the system. For high frequency, the system achieves multi-crossing dynamics with two fictitious crossings; the system models a Landau-Zener-Stückelberg (LZS) interferometer with critical parameters that tailor probabilities. The system is then shown to depend only on the phase that permits the easiest control with possible application in implementing logic gates.
Dissipative Landau-Zener transitions of a qubit: Bath-specific and universal behavior
Saito, Keiji; Wubs, Martijn; Kohler, Sigmund; Haenggi, Peter; Kayanuma, Yosuke
2007-06-01
We study Landau-Zener transitions in a qubit coupled to a bath at zero temperature. A general formula that is applicable to models with a nondegenerate ground state is derived. We calculate exact transition probabilities for a qubit coupled to either a bosonic or a spin bath. The nature of the baths and the qubit-bath coupling is reflected in the transition probabilities. For diagonal coupling, when the bath causes energy fluctuations of the diabatic qubit states but no transitions between them, the transition probability coincides with the standard Landau-Zener probability of an isolated qubit. This result is universal as it does not depend on the specific type of bath. For pure off-diagonal coupling, by contrast, the tunneling probability is sensitive to the coupling strength. We discuss the relevance of our results for experiments on molecular nanomagnets, in circuit QED, and for the fast-pulse readout of superconducting phase qubits.
Nonadiabatic Landau-Zener tunneling in waveguide arrays with a step in the refractive index.
Khomeriki, Ramaz; Ruffo, Stefano
2005-03-25
Landau-Zener tunneling is discussed in connection with optical waveguide arrays. Light injected in a specific band of the Bloch spectrum in the propagation constant can be transmitted to another band, changing its physical properties. This can be achieved using two coupled waveguide arrays with different refractive indices. The step in the refractive index causes wave "acceleration" and thus induces strongly nonadiabatic Landau-Zener tunneling. Theoretically, the analysis is performed by considering a Schrödinger equation in a periodic potential with a step. The region of physical parameters where this phenomenon can occur is analytically determined and a realistic experimental setup is suggested. Its application could allow the realization of light filters.
Landau-Zener-Stueckelberg interferometry with low- and high-frequency driving
NASA Astrophysics Data System (ADS)
Shevchenko, Sergey; Ashhab, Sahel; Nori, Franco
2010-03-01
The problem of a periodically driven two-level system cannot be solved exactly. The rotating-wave approximation (RWA) is the most common approximation used to analyze this problem. I will discuss an alternative approximation that applies in the case of very strong driving, where the RWA is generally invalid. The dynamics is approximated by a sequence of Landau-Zener transitions that can interfere constructively or destructively, depending on the Stueckelberg phase accumulated between transitions. It turns out that the resonance conditions are qualitatively different for the cases of low- and high-frequency driving. I will discuss the two respective limits. I will also show that our theoretical results describe recent experiments on Landau-Zener-Stuckelberg interferometry with superconducting qubits [S.N. Shevchenko, S. Ashhab, and F. Nori, arXiv:0911.1917].
Phase diagram of a graphene bilayer in the zero-energy Landau level
NASA Astrophysics Data System (ADS)
Knothe, Angelika; Jolicoeur, Thierry
2016-12-01
Bilayer graphene under a magnetic field has an octet of quasidegenerate levels due to spin, valley, and orbital degeneracies. This zero-energy Landau level is resolved into several incompressible states whose nature is still elusive. We use a Hartree-Fock treatment of a realistic tight-binding four-band model to understand the quantum ferromagnetism phenomena expected for integer fillings of the octet levels. We include the exchange interaction with filled Landau levels below the octet states. This Lamb-shift-like effect contributes to the orbital splitting of the octet. We give phase diagrams as a function of applied bias and magnetic field. Some of our findings are in agreement with experiments. We discuss the possible appearance of phases with orbital coherence.
Multistable pulselike solutions in a parametrically driven Ginzburg-Landau equation.
Barashenkov, I V; Cross, S; Malomed, Boris A
2003-11-01
It is well known that pulselike solutions of the cubic complex Ginzburg-Landau equation are unstable but can be stabilized by the addition of quintic terms. In this paper we explore an alternative mechanism where the role of the stabilizing agent is played by the parametric driver. Our analysis is based on the numerical continuation of solutions in one of the parameters of the Ginzburg-Landau equation (the diffusion coefficient c), starting from the nonlinear Schrödinger limit (for which c=0). The continuation generates, recursively, a sequence of coexisting stable solutions with increasing number of humps. The sequence "converges" to a long pulse which can be interpreted as a bound state of two fronts with opposite polarities.
Measuring Landau damping in Particle-in-Cell simulations using particles of different charge-weights
NASA Astrophysics Data System (ADS)
Ren, C.; Sarkar, A.; Cao, Y.-X.; Huang, M. C.; Li, J.
2016-10-01
We study whether putting more particles in ``region of interest (ROI)'' in phase space can efficiently increase Particle-in-Cell (PIC) simulation accuracy. We use Landau damping of a plasma wave as a figure of merit and set the ROI near the phase velocity of the wave. Improvement in Landau damping rate measurement is observed in 1D PIC simulations when employing more particles in the ROI but the effect is not monotonic. This is partly due to energy transfer from particles of large charge weights to those of smaller weights through the electric fields. Possible strategies to mitigate the energy transfer will also be discussed. This work is supported by the National Science Foundation under Grant No. PHY-1314734 and by the Department of Energy under Grant No. DE-SC0012316.
Descendants constructed from matter field in Landau-Ginzburg theories coupled to topological gravity
NASA Astrophysics Data System (ADS)
Losev, A.
1993-05-01
It is argued that gravitational descendants in the theory of topological gravity coupled to topological Landau-Ginzburg theory (not necessarily conformal) can be constructed from matter fields alone (without metric fields and ghosts). In this sense topological gravity is “induced.” We discuss the mechanism of this effect (that turns out to be connected with K. Saito's higher residue pairing: Ki(σi(Φ1),Φ2)=K0(Φ1,Φ2)), and demonstrate how it works in a simplest nontrivial example: correlator on a sphere with four marked points. We also discuss some results on k-point correlators on a sphere. From the idea of “induced” topological gravity it follows that the theory of “pure” topological gravity (without topological matter) is equivalent to the “trivial” Landau-Ginzburg theory (with quadratic superpotential).
Symmetry breaking in the zero-energy Landau level in bilayer graphene.
Zhao, Y; Cadden-Zimansky, P; Jiang, Z; Kim, P
2010-02-12
The quantum Hall effect near the charge neutrality point in bilayer graphene is investigated in high magnetic fields of up to 35 T using electronic transport measurements. In the high-field regime, the eightfold degeneracy in the zero-energy Landau level is completely lifted, exhibiting new quantum Hall states corresponding to filling factors nu=0, 1, 2, and 3. Measurements of the activation energy gaps for the nu=2 and 3 filling factors in tilted magnetic fields exhibit no appreciable dependence on the in-plane magnetic field, suggesting that these Landau level splittings are independent of spin. In addition, measurements taken at the nu=0 charge neutral point show that, similar to single layer graphene, the bilayer becomes insulating at high fields.
Stability of the Melting Hedgehog in the Landau-de Gennes Theory of Nematic Liquid Crystals
NASA Astrophysics Data System (ADS)
Ignat, Radu; Nguyen, Luc; Slastikov, Valeriy; Zarnescu, Arghir
2014-09-01
We investigate stability properties of the radially symmetric solution corresponding to the vortex defect (the so called "melting hedgehog") in the framework of the Landau-de Gennes model of nematic liquid crystals. We prove local stability of the melting hedgehog under arbitrary Q-tensor valued perturbations in the temperature regime near the critical supercooling temperature. As a consequence of our method, we also rediscover the loss of stability of the vortex defect in the deep nematic regime.
Stability of the Melting Hedgehog in the Landau-de Gennes Theory of Nematic Liquid Crystals
NASA Astrophysics Data System (ADS)
Ignat, Radu; Nguyen, Luc; Slastikov, Valeriy; Zarnescu, Arghir
2015-02-01
We investigate stability properties of the radially symmetric solution corresponding to the vortex defect (the so called "melting hedgehog") in the framework of the Landau-de Gennes model of nematic liquid crystals. We prove local stability of the melting hedgehog under arbitrary Q-tensor valued perturbations in the temperature regime near the critical supercooling temperature. As a consequence of our method, we also rediscover the loss of stability of the vortex defect in the deep nematic regime.
Wang-Landau sampling in face-centered-cubic hydrophobic-hydrophilic lattice model proteins.
Liu, Jingfa; Song, Beibei; Yao, Yonglei; Xue, Yu; Liu, Wenjie; Liu, Zhaoxia
2014-10-01
Finding the global minimum-energy structure is one of the main problems of protein structure prediction. The face-centered-cubic (fcc) hydrophobic-hydrophilic (HP) lattice model can reach high approximation ratios of real protein structures, so the fcc lattice model is a good choice to predict the protein structures. The lacking of an effective global optimization method is the key obstacle in solving this problem. The Wang-Landau sampling method is especially useful for complex systems with a rough energy landscape and has been successfully applied to solving many optimization problems. We apply the improved Wang-Landau (IWL) sampling method, which incorporates the generation of an initial conformation based on the greedy strategy and the neighborhood strategy based on pull moves into the Wang-Landau sampling method to predict the protein structures on the fcc HP lattice model. Unlike conventional Monte Carlo simulations that generate a probability distribution at a given temperature, the Wang-Landau sampling method can estimate the density of states accurately via a random walk, which produces a flat histogram in energy space. We test 12 general benchmark instances on both two-dimensional and three-dimensional (3D) fcc HP lattice models. The lowest energies by the IWL sampling method are as good as or better than those of other methods in the literature for all instances. We then test five sets of larger-scale instances, denoted by the S, R, F90, F180, and CASP target instances on the 3D fcc HP lattice model. The numerical results show that our algorithm performs better than the other five methods in the literature on both the lowest energies and the average lowest energies in all runs. The IWL sampling method turns out to be a powerful tool to study the structure prediction of the fcc HP lattice model proteins.
Exploring new frontiers in statistical physics with a new, parallel Wang-Landau framework
NASA Astrophysics Data System (ADS)
Vogel, Thomas; Li, Ying Wai; Wüst, Thomas; Landau, David P.
2014-03-01
Combining traditional Wang-Landau sampling for multiple replica systems with an exchange of densities of states between replicas, we describe a general framework for simulations on massively parallel Petaflop supercomputers. The advantages and general applicability of the method for simulations of complex systems are demonstrated for the classical 2D Potts spin model featuring a strong first-order transition and the self-assembly of lipid bilayers in amphiphilic solutions in a continuous model.
Complex Ginzburg-Landau equation on networks and its non-uniform dynamics
NASA Astrophysics Data System (ADS)
Nakao, Hiroya
2014-10-01
Dynamics of the complex Ginzburg-Landau equation describing networks of diffusively coupled limit-cycle oscillators near the Hopf bifurcation is reviewed. It is shown that the Benjamin-Feir instability destabilizes the uniformly synchronized state and leads to non-uniform pattern dynamics on general networks. Nonlinear dynamics on several network topologies, i.e., local, nonlocal, global, and random networks, are briefly illustrated by numerical simulations.
Landau damping of Gardner solitons in a dusty bi-ion plasma
NASA Astrophysics Data System (ADS)
Misra, A. P.; Barman, Arnab
2015-07-01
The effects of linear Landau damping on the nonlinear propagation of dust-acoustic solitary waves (DASWs) are studied in a collisionless unmagnetized dusty plasma with two species of positive ions. The extremely massive, micron-seized, cold, and negatively charged dust particles are described by fluid equations, whereas the two species of positive ions, namely, the cold (heavy) and hot (light) ions are described by the kinetic Vlasov equations. Following Ott and Sudan [Phys. Fluids 12, 2388 (1969)], and by considering lower and higher-order perturbations, the evolution of DASWs with Landau damping is shown to be governed by Korteweg-de Vries (KdV), modified KdV (mKdV), or Gardner (KdV-mKdV)-like equations. The properties of the phase velocity and the Landau damping rate of DASWs are studied for different values of the ratios of the temperatures (σ) and the number densities (μ) of hot and cold ions as well as the cold to hot ion mass ratio m. The distinctive features of the decay rates of the amplitudes of the KdV, mKdV, and Gardner solitons with a small effect of Landau damping are also studied in different parameter regimes. It is found that the Gardner soliton points to lower wave amplitudes than the KdV and mKdV solitons. The results may be useful for understanding the localization of solitary pulses and associated wave damping (collisionless) in laboratory and space plasmas (e.g., the F-ring of Saturn), in which the number density of free electrons is much smaller than that of ions and the heavy, micron seized dust grains are highly charged.
Generalized Klauder-Perelomov and Gazeau-Klauder coherent states for Landau levels
NASA Astrophysics Data System (ADS)
Fakhri, H.
2003-07-01
Based on a pair of representations obtained for Lie algebra h4, the Hilbert space corresponding to all quantum states of Landau levels is split into an infinite direct sum of infinite-dimensional Hilbert subspaces. For any one of the Hilbert subspaces, we get linear combinations of their bases as generalized coherent states-the so-called Klauder-Perelomov and Gazeau-Klauder.
Landau Damping of Transverse Waves in the Exosphere by Fast Particle Fluxes
NASA Technical Reports Server (NTRS)
Tidman, D. A.; Jaggi, R. K.
1962-01-01
We have investigated the Landau damping of transverse waves propagating in the thermal exospheric plasma, by fast particle fluxes which also exist in these regions. The most intense non-thermal fluxes so far detected are those of the auroral producing electrons and protons measured by McIlwain. We find that these fluxes may considerably damp the propagation of whistler modes through some regions. The damping of hydromagnetic waves in the exosphere by this mechanism is negligible.
A fast non-Fourier method for Landau-fluid operators
Dimits, A. M. Joseph, I.; Umansky, M. V.
2014-05-15
An efficient and versatile non-Fourier method for the computation of Landau-fluid (LF) closure operators [Hammett and Perkins, Phys. Rev. Lett. 64, 3019 (1990)] is presented, based on an approximation by a sum of modified-Helmholtz-equation solves (SMHS) in configuration space. This method can yield fast-Fourier-like scaling of the computational time requirements and also provides a very compact data representation of these operators, even for plasmas with large spatial nonuniformity. As a result, the method can give significant savings compared with direct application of “delocalization kernels” [e.g., Schurtz et al., Phys. Plasmas 7, 4238 (2000)], both in terms of computational cost and memory requirements. The method is of interest for the implementation of Landau-fluid models in situations where the spatial nonuniformity, particular geometry, or boundary conditions render a Fourier implementation difficult or impossible. Systematic procedures have been developed to optimize the resulting operators for accuracy and computational cost. The four-moment Landau-fluid model of Hammett and Perkins has been implemented in the BOUT++ code using the SMHS method for LF closure. Excellent agreement has been obtained for the one-dimensional plasma density response function between driven initial-value calculations using this BOUT++ implementation and matrix eigenvalue calculations using both Fourier and SMHS non-Fourier implementations of the LF closures. The SMHS method also forms the basis for the implementation, which has been carried out in the BOUT++ code, of the parallel and toroidal drift-resonance LF closures. The method is a key enabling tool for the extension of gyro-Landau-fluid models [e.g., Beer and Hammett, Phys. Plasmas 3, 4046 (1996)] to codes that treat regions with strong profile variation, such as the tokamak edge and scrapeoff-layer.
Landau damping effects and evolutions of energy spread in small isochronous ring
Li, Yingjie; Wang, Langfa; Lin, Fanglei
2014-11-01
This paper presents the Landau damping effects on the microwave instability of a coasting long bunch in an isochronous ring due to finite energy spread and emittance. Our two-dimensional (2D) dispersion relation gives more accurate predictions of the microwave instability growth rates of short-wavelength perturbations than the conventional 1D formula. The long-term evolution of energy spread is also studied by measurements and simulations.
Exact Lyapunov dimension of the universal attractor for the complex Ginzburg-Landau equation
Doering, C.R.; Gibbon, J.D.; Holm, D.D.; Nicolaenko, B.
1987-12-28
We present an exact analytic computation of the Lyapunov dimension of the universal attractor of the complex Ginzburg-Landau partial differential equation for a finite range of its parameter values. We obtain upper bounds on the attractor's dimension when the parameters do not permit an exact evaluation by our methods. The exact Lyapunov dimension agrees with an estimate of the number of degrees of freedom based on a simple linear stability analysis and mode-counting argument.
Definite evidence of the Landau-Zener transition in nucleus-nucleus collisions
Imanishi, B.; von Oertzen, W.; Voit, H.
1987-01-01
It is shown that the Landau-Zener transition mechanism due to the formation of molecular orbitals of the active neutron exists in the inelastic scattering /sup 13/C(/sup 12/C, /sup 12/C)/sup 13/C/sup */ (3.086 MeV, (1/2)/sup +/). The evidence stems from characteristic changes of the angular distributions observed as a function of the incident energy.
Direct observation of Landau-Zener tunneling in a curved optical waveguide coupler
Dreisow, F.; Szameit, A.; Heinrich, M.; Nolte, S.; Tuennermann, A.; Ornigotti, M.; Longhi, S.
2009-05-15
An electromagnetic realization of Landau-Zener (LZ) tunneling is experimentally demonstrated in femtosecond-laser written waveguide couplers with a cubically bent axis. Quantitative measurements of light evolution inside the coupler, based on fluorescence imaging, enable to trace the detailed dynamics of the LZ process. The experimental results are in good agreement with the theoretical LZ model for linear crossing of energy levels with constant coupling of finite duration.
Atomic Landau-Zener tunneling and Wannier-Stark ladders in optical potentials
Niu, Q.; Zhao, X.; Georgakis, G.; Raizen, M.
1996-06-01
We calculate the quantum motion of ultracold atoms in an accelerating optical potential, and show how they may be used to observe Landau-Zener tunneling and Wannier-Stark ladders, two fundamental quantum effects in solid state physics. The optical potential is spatially periodic, yielding an energy spectrum of Bloch bands for the atoms. The acceleration provides an inertial force in the moving frame, emulating an electric force on Bloch electrons. {copyright} {ital 1996 The American Physical Society.}
Landau-Zener transitions in a dissipative environment: numerically exact results.
Nalbach, P; Thorwart, M
2009-11-27
We study Landau-Zener transitions in a dissipative environment by means of the numerically exact quasiadiabatic propagator path integral. It allows to cover the full range of the involved parameters. We discover a nonmonotonic dependence of the transition probability on the sweep velocity which is explained in terms of a simple phenomenological model. This feature, not captured by perturbative approaches, results from a nontrivial competition between relaxation and the external sweep.
Solvable multistate model of Landau-Zener transitions in cavity QED
NASA Astrophysics Data System (ADS)
Sinitsyn, Nikolai A.; Li, Fuxiang
2016-06-01
We consider the model of a single optical cavity mode interacting with two-level systems (spins) driven by a linearly time-dependent field. When this field passes through values at which spin energy-level splittings become comparable to spin coupling to the optical mode, a cascade of Landau-Zener transitions leads to coflips of spins in exchange for photons of the cavity. We derive exact transition probabilities between different diabatic states induced by such a sweep of the field.
Fractional charge and inter-Landau-level states at points of singular curvature.
Biswas, Rudro R; Son, Dam Thanh
2016-08-02
The quest for universal properties of topological phases is fundamentally important because these signatures are robust to variations in system-specific details. Aspects of the response of quantum Hall states to smooth spatial curvature are well-studied, but challenging to observe experimentally. Here we go beyond this prevailing paradigm and obtain general results for the response of quantum Hall states to points of singular curvature in real space; such points may be readily experimentally actualized. We find, using continuum analytical methods, that the point of curvature binds an excess fractional charge and sequences of quantum states split away, energetically, from the degenerate bulk Landau levels. Importantly, these inter-Landau-level states are bound to the topological singularity and have energies that are universal functions of bulk parameters and the curvature. Our exact diagonalization of lattice tight-binding models on closed manifolds demonstrates that these results continue to hold even when lattice effects are significant. An important technological implication of these results is that these inter-Landau-level states, being both energetically and spatially isolated quantum states, are promising candidates for constructing qubits for quantum computation.
Landau Level Splittings, Phase Transitions, and Nonuniform Charge Distribution in Trilayer Graphene.
Campos, Leonardo C; Taychatanapat, Thiti; Serbyn, Maksym; Surakitbovorn, Kawin; Watanabe, Kenji; Taniguchi, Takashi; Abanin, Dmitry A; Jarillo-Herrero, Pablo
2016-08-05
We report on magnetotransport studies of dual-gated, Bernal-stacked trilayer graphene (TLG) encapsulated in boron nitride crystals. We observe a quantum Hall effect staircase which indicates a complete lifting of the 12-fold degeneracy of the zeroth Landau level. As a function of perpendicular electric field, our data exhibit a sequence of phase transitions between all integer quantum Hall states in the filling factor interval -8<ν<0. We develop a theoretical model and argue that, in contrast to monolayer and bilayer graphene, the observed Landau level splittings and quantum Hall phase transitions can be understood within a single-particle picture, but imply the presence of a charge density imbalance between the inner and outer layers of TLG, even at charge neutrality and zero transverse electric field. Our results indicate the importance of a previously unaccounted band structure parameter which, together with a more accurate estimate of the other tight-binding parameters, results in a significantly improved determination of the electronic and Landau level structure of TLG.
Exploring Replica-Exchange Wang-Landau sampling in higher-dimensional parameter space
NASA Astrophysics Data System (ADS)
Valentim, Alexandra; Rocha, Julio C. S.; Tsai, Shan-Ho; Li, Ying Wai; Eisenbach, Markus; Fiore, Carlos E.; Landau, David P.
2015-09-01
We considered a higher-dimensional extension for the replica-exchange Wang- Landau algorithm to perform a random walk in the energy and magnetization space of the two-dimensional Ising model. This hybrid scheme combines the advantages of Wang-Landau and Replica-Exchange algorithms, and the one-dimensional version of this approach has been shown to be very efficient and to scale well, up to several thousands of computing cores. This approach allows us to split the parameter space of the system to be simulated into several pieces and still perform a random walk over the entire parameter range, ensuring the ergodicity of the simulation. Previous work, in which a similar scheme of parallel simulation was implemented without using replica exchange and with a different way to combine the result from the pieces, led to discontinuities in the final density of states over the entire range of parameters. From our simulations, it appears that the replica-exchange Wang-Landau algorithm is able to overcome this difficulty, allowing exploration of higher parameter phase space by keeping track of the joint density of states.
Highly parallel computational study of amphiphilic molecules using the Wang--Landau method
NASA Astrophysics Data System (ADS)
Vogel, Thomas; Landau, David
2012-02-01
The self-assembly process in amphiphilic solutions is a phenomenon of broad interest. Molecular dynamics simulations generally used to study micelle formation or lipid layer assembly in an explicit solvent are limited in time scale. Vast studies of structure formation processes via standard Markov-chain based Monte Carlo simulations are challenging, but the Wang--Landau method [1] provides a way to efficiently study such systems in a generalized thermodynamic ensemble. This makes it possible, for example, to get results over a broad temperature range from a single simulation. In an attempt to develop highly parallel applications using this method, we study the thermodynamic behavior of a generic coarse-grained model for amphiphilic molecules [2] as well as of a new coarse-grained lipid model specifically designed for dimyristoyl phosphatidylcholine (DMPC) [3]. Here, we focus on the design and the performance of our parallel Wang--Landau simulation on multi-CPU and GPU systems.[4pt] [1] F. Wang and D.P. Landau, Phys. Rev. Lett. 86, 2050 (2001)[0pt] [2] S. Fujiwara et al., J. Chem. Phys. 130, 144901 (2009)[0pt] [3] W. Shinoda et al., J. Phys. Chem. B 114, 6836 (2010)
Longitudinal oscillations and linear Landau damping in quark-gluon plasma.
Murtaza, G; Khattak, N A D; Shah, H A
2003-12-01
On the basis of the semiclassical kinetic Vlasov equation for quark-gluon plasma and the Yang-Mills equation in covariant gauge, linear Landau damping for electrostatic perturbations such as Langmuir waves is investigated for the extreme-relativistic and strongly relativistic cases. It has been observed that for the extreme-relativistic case, wherein the thermal speed of the particles exceeds the phase velocity of the perturbations, the linear Landau damping is absent as has been reported in the literature. However, a departure from extreme-relativistic case generates an imaginary component of the frequency giving rise to linear Landau damping effect. The relevant integral for the conductivity tensor has been evaluated and the dispersion relation for the longitudinal part of the oscillation was obtained. Further, it is also noted that both the real part of the oscillation frequency and the damping rate are sensitive to the choice of the wave number k and the Debye length lambda(D) associated with quark-gluon plasma.
Dynamical traps in Wang-Landau sampling of continuous systems: Mechanism and solution
NASA Astrophysics Data System (ADS)
Koh, Yang Wei; Sim, Adelene Y. L.; Lee, Hwee Kuan
2015-08-01
We study the mechanism behind dynamical trappings experienced during Wang-Landau sampling of continuous systems reported by several authors. Trapping is caused by the random walker coming close to a local energy extremum, although the mechanism is different from that of the critical slowing-down encountered in conventional molecular dynamics or Monte Carlo simulations. When trapped, the random walker misses the entire or even several stages of Wang-Landau modification factor reduction, leading to inadequate sampling of the configuration space and a rough density of states, even though the modification factor has been reduced to very small values. Trapping is dependent on specific systems, the choice of energy bins, and the Monte Carlo step size, making it highly unpredictable. A general, simple, and effective solution is proposed where the configurations of multiple parallel Wang-Landau trajectories are interswapped to prevent trapping. We also explain why swapping frees the random walker from such traps. The efficacy of the proposed algorithm is demonstrated.
NASA Astrophysics Data System (ADS)
Yan, Wei; Li, Si-Yu; Yin, Long-Jing; Qiao, Jia-Bin; Nie, Jia-Cai; He, Lin
2016-05-01
Hybrid quantum Hall (QH) junctions have been extensively studied by transport measurements due to their exciting physics and device applications. Here we report on spatially resolving electronic properties of such a junction on the nanoscale. We present a subnanometer-resolved scanning tunneling microscopy (STM) and scanning tunneling spectroscopy study of a monolayer-bilayer graphene planar junction in the QH regime. The atomically well-defined interface of such a junction allows us to spatially resolve the interface electronic properties. Around the interface, we detect Landau quantization of massless Dirac fermions as expected in the graphene monolayer for filled states of the junction, whereas unexpectedly, only Landau quantization of massive Dirac fermions as expected in the graphene bilayer is observed for empty states. The observed unconventional interface Landau quantization arises from the fact that the quantum conductance across the interface is solely determined by the minimum filling factors (number of edge modes) in the graphene monolayer and bilayer regions of the junction. Our finding opens the way to spatially explore the QH effect of different graphene hybrid structures only using a STM.
Dynamical traps in Wang-Landau sampling of continuous systems: Mechanism and solution.
Koh, Yang Wei; Sim, Adelene Y L; Lee, Hwee Kuan
2015-08-01
We study the mechanism behind dynamical trappings experienced during Wang-Landau sampling of continuous systems reported by several authors. Trapping is caused by the random walker coming close to a local energy extremum, although the mechanism is different from that of the critical slowing-down encountered in conventional molecular dynamics or Monte Carlo simulations. When trapped, the random walker misses the entire or even several stages of Wang-Landau modification factor reduction, leading to inadequate sampling of the configuration space and a rough density of states, even though the modification factor has been reduced to very small values. Trapping is dependent on specific systems, the choice of energy bins, and the Monte Carlo step size, making it highly unpredictable. A general, simple, and effective solution is proposed where the configurations of multiple parallel Wang-Landau trajectories are interswapped to prevent trapping. We also explain why swapping frees the random walker from such traps. The efficacy of the proposed algorithm is demonstrated.
Spontaneous polarization of composite fermions in the n = 1 Landau level of graphene
NASA Astrophysics Data System (ADS)
Coimbatore Balram, Ajit; Tőke, Csaba; Wójs, Arkadiusz; Jain, Jainendra
Motivated by experiments that reveal expansive fractional quantum Hall states in the n = 1 graphene Landau level and suggest a nontrivial role of the spin degree of freedom [Amet et al., Nat. Commun. 6, 5838 (2014)], we perform accurate quantitative study of the the competition between fractional quantum Hall states with different spin polarizations in the n = 1 graphene Landau level. We find that the fractional quantum Hall effect is well described in terms of composite fermions, but the spin physics is qualitatively different from that in the n = 0 Landau level. In particular, for the states at filling factors ν = s / (2 s +/- 1) , s integer, a combination of exact diagonalization and the composite fermion theory shows that the ground state is fully spin polarized and supports a robust spin wave mode even in the limit of vanishing Zeeman coupling. Thus, even though composite fermions are formed, a mean field description that treats them as weakly interacting particles breaks down, and the exchange interaction between them is strong enough to cause a qualitative change in the behavior by inducing full spin polarization. We also find that the fully spin polarized composite fermion Fermi sea has lower energy than the paired Pfaffian state at the relevant half fillings. Award No. DE-SC0005042 (ACB, JKJ), Hungarian Scientific Research Funds No. K105149 (CT), the Polish NCN Grant 2014/14/A/ST3/00654 and the EU Marie Curie Grant PCIG09-GA-2011-294186 (AW).
Landau Level Splittings, Phase Transitions, and Nonuniform Charge Distribution in Trilayer Graphene
NASA Astrophysics Data System (ADS)
Campos, Leonardo C.; Taychatanapat, Thiti; Serbyn, Maksym; Surakitbovorn, Kawin; Watanabe, Kenji; Taniguchi, Takashi; Abanin, Dmitry A.; Jarillo-Herrero, Pablo
2016-08-01
We report on magnetotransport studies of dual-gated, Bernal-stacked trilayer graphene (TLG) encapsulated in boron nitride crystals. We observe a quantum Hall effect staircase which indicates a complete lifting of the 12-fold degeneracy of the zeroth Landau level. As a function of perpendicular electric field, our data exhibit a sequence of phase transitions between all integer quantum Hall states in the filling factor interval -8 <ν <0 . We develop a theoretical model and argue that, in contrast to monolayer and bilayer graphene, the observed Landau level splittings and quantum Hall phase transitions can be understood within a single-particle picture, but imply the presence of a charge density imbalance between the inner and outer layers of TLG, even at charge neutrality and zero transverse electric field. Our results indicate the importance of a previously unaccounted band structure parameter which, together with a more accurate estimate of the other tight-binding parameters, results in a significantly improved determination of the electronic and Landau level structure of TLG.
Exploring Replica-Exchange Wang-Landau sampling in higher-dimensional parameter space
Valentim, Alexandra; Rocha, Julio C. S.; Tsai, Shan-Ho; Li, Ying Wai; Eisenbach, Markus; Fiore, Carlos E; Landau, David P
2015-01-01
We considered a higher-dimensional extension for the replica-exchange Wang-Landau algorithm to perform a random walk in the energy and magnetization space of the two-dimensional Ising model. This hybrid scheme combines the advantages of Wang-Landau and Replica-Exchange algorithms, and the one-dimensional version of this approach has been shown to be very efficient and to scale well, up to several thousands of computing cores. This approach allows us to split the parameter space of the system to be simulated into several pieces and still perform a random walk over the entire parameter range, ensuring the ergodicity of the simulation. Previous work, in which a similar scheme of parallel simulation was implemented without using replica exchange and with a different way to combine the result from the pieces, led to discontinuities in the final density of states over the entire range of parameters. From our simulations, it appears that the replica-exchange Wang-Landau algorithm is able to overcome this diculty, allowing exploration of higher parameter phase space by keeping track of the joint density of states.
Exact solutions to the Mo-Papas and Landau-Lifshitz equations.
Rivera, R; Villarroel, D
2002-10-01
Two exact solutions of the Mo-Papas and Landau-Lifshitz equations for a point charge in classical electrodynamics are presented here. Both equations admit as an exact solution the motion of a charge rotating with constant speed in a circular orbit. These equations also admit as an exact solution the motion of two identical charges rotating with constant speed at the opposite ends of a diameter. These exact solutions allow one to obtain, starting from the equation of motion, a definite formula for the rate of radiation. In both cases the rate of radiation can also be obtained, with independence of the equation of motion, from the well known fields of a point charge, that is, from the Maxwell equations. The rate of radiation obtained from the Mo-Papas equation in the one-charge case coincides with the rate of radiation that comes from the Maxwell equations; but in the two-charge case the results do not coincide. On the other hand, the rate of radiation obtained from the Landau-Lifshitz equation differs from the one that follows from the Maxwell equations in both the one-charge and two-charge cases. This last result does not support a recent statement by Rohrlich in favor of considering the Landau-Lifshitz equation as the correct and exact equation of motion for a point charge in classical electrodynamics.
Incorporation of plasticity into the Landau-Ginzburg theory of martensitic phase transformations
NASA Astrophysics Data System (ADS)
Gröger, Roman; Lookman, Turab
2008-03-01
The Landau-Ginzburg theory of martensitic phase transformations has been utilized to reproduce the evolution of elastic texture in defect-free materials undergoing structural phase transformations. Generalizations of this theory to phase transformations that are accompanied by significant plastic distortions (as in U6Nb) have been little studied. We propose a simple model that demonstrates how to incorporate plasticity into the Landau-Ginzburg theory. In the presence of topological defects such as dislocations, the usual Saint Venant compatibility constraint becomes an incompatibility constraint and this is represented by a tensor field ηij. In our case, the components of ηij are expressed as gradients of the components of the Nye tensor that represent the dislocation density. The presence of dislocations induces large internal stresses in certain regions of the material, and these act as initiation sites for plastic deformation. When the external loading is applied, dislocations moving from these regions cause strain hardening that is detectable in experimental uniaxial measurements. This model serves as a starting point for further development of the framework of three-dimensional rate-independent theory of plasticity within the Landau-Ginzburg formalism.
Beyond Landau-Pollak and entropic inequalities: Geometric bounds imposed on uncertainties sums
NASA Astrophysics Data System (ADS)
Zozor, S.; Bosyk, G. M.; Portesi, M.; Osán, T. M.; Lamberti, P. W.
2015-01-01
In this paper we propose generalized inequalities to quantify the uncertainty principle. We deal with two observables with finite discrete spectra described by positive operator-valued measures (POVM) and with systems in mixed states. Denoting by p(A;ρ) and p(B;ρ) the probability vectors associated with observables A and B when the system is in the state ρ, we focus on relations of the form Uα(p(A;ρ))+Uβ(p(B;ρ))≥ Bα,β(A,B) where Uλ is a measure of uncertainty and B is a non-trivial state-independent bound for the uncertainty sum. We propose here: (i) an extension of the usual Landau-Pollak inequality for uncertainty measures of the form Uf(p(A;ρ)) = f( maxipi(A;ρ)) issued from well suited metrics; our generalization comes out as a consequence of the triangle inequality. The original Landau-Pollak inequality initially proved for nondegenerate observables and pure states, appears to be the most restrictive one in terms of the maximal probabilities; (ii) an entropic formulation for which the uncertainty measure is based on generalized entropies of Rényi or Havrda-Charvát-Tsallis type: Ug,α(p(A;ρ)) = g(Σ/i[pi(A;ρ)]α) 1-α . Our approach is based on Schur-concavity considerations and on previously derived Landau-Pollak type inequalities.
Integrable extended van der Waals model
NASA Astrophysics Data System (ADS)
Giglio, Francesco; Landolfi, Giulio; Moro, Antonio
2016-10-01
Inspired by the recent developments in the study of the thermodynamics of van der Waals fluids via the theory of nonlinear conservation laws and the description of phase transitions in terms of classical (dissipative) shock waves, we propose a novel approach to the construction of multi-parameter generalisations of the van der Waals model. The theory of integrable nonlinear conservation laws still represents the inspiring framework. Starting from a macroscopic approach, a four parameter family of integrable extended van der Waals models is indeed constructed in such a way that the equation of state is a solution to an integrable nonlinear conservation law linearisable by a Cole-Hopf transformation. This family is further specified by the request that, in regime of high temperature, far from the critical region, the extended model reproduces asymptotically the standard van der Waals equation of state. We provide a detailed comparison of our extended model with two notable empirical models such as Peng-Robinson and Soave's modification of the Redlich-Kwong equations of state. We show that our extended van der Waals equation of state is compatible with both empirical models for a suitable choice of the free parameters and can be viewed as a master interpolating equation. The present approach also suggests that further generalisations can be obtained by including the class of dispersive and viscous-dispersive nonlinear conservation laws and could lead to a new type of thermodynamic phase transitions associated to nonclassical and dispersive shock waves.
Vandiver, Jennifer; Dean, Delphine; Patel, Nelesh; Botelho, Claudia; Best, Serena; Santos, José D; Lopes, Maria A; Bonfield, William; Ortiz, Christine
2006-08-01
The normal intersurface forces between nanosized probe tips functionalized with COO(-)-terminated alkanethiol self-assembling monolayers and dense, polycrystalline silicon-substituted synthetic hydroxyapatite (SiHA) and phase pure hydroxyapatite (HA) were measured via a nanomechanical technique called chemically specific high-resolution force spectroscopy. A significantly larger van der Waals interaction was observed for the SiHA compared to HA; Hamaker constants (A) were found to be A(SiHA) = 35 +/- 27 zJ and A(HA) = 13 +/- 12 zJ. Using the Derjaguin-Landau-Verwey-Overbeek approximation, which assumes linear additivity of the electrostatic double layer and van der Waals components, and the nonlinear Poisson-Boltzmann surface charge model for electrostatic double-layer forces, the surface charge per unit area, sigma (C/m(2)), was calculated as a function of position for specific nanosized areas within individual grains. SiHA was observed to be more negatively charged than HA with sigma(SiHA) = -0.024 +/- 0.013 C/m(2), two times greater than sigma(HA) = -0.011 +/- 0.006 C/m(2). Additionally, SiHA was found to have increased surface adhesion (0.7 +/- 0.3 nN) compared to HA (0.5 +/- 0.3 nN). The characterization of the nanoscale variations in surface forces of SiHA and HA will enable an improved understanding of the initial stages of bone-biomaterial bonding.
Kommunikationsanforderungen an verteilte Echtzeitsysteme in der Fertigungsautomatisierung
NASA Astrophysics Data System (ADS)
Just, Roman; Trsek, Henning
Kommunikationssysteme der Automatisierung müssen hohe zeitliche Anforderungen erfüllen, damit die entsprechenden industriellen Anwendungen realisiert werden können. Im Gegensatz zum IT-Bereich sind diese Anforderungen jedoch häufig nicht genau bekannt, was insbesondere beim Einsatz von drahtlosen Technologien Probleme bereiten kann1. In dieser Arbeit werden Verkehrsmuster einer realen Anlage aus dem Bereich der Fertigungsautomatisierung bestimmt. Die Zwischenankunfts- und Latenzzeiten einzelner Sensorund Aktorsignale ermöglichen Rückschlüsse auf zeitliche Anforderungen und Charakteristiken der untersuchten Anwendung. Im Anschluss werden die erzielten Erkenntnisse hinsichtlich ausgewählter Kommunikationsanforderungen analysiert und aktuell gültige Anforderungen von realen Automatisierungsanlagen abgeleitet. Weiterhin werden sie zukünftig zur Entwicklung realitätsnaher Simulationsmodelle genutzt.
Study of a class of Landau-Lifshitz equations of ferromagnetism without exchange energy
NASA Astrophysics Data System (ADS)
Deng, Wei
Landau-Lifshitz equations of ferromagnetism, which are based on several competing energy contributions, are important mathematical models for the evolution of magnetization field m of a ferromagnetic material. Many problems, such as existence, stability, regularity, asymptotic behavior, thin-film limit and numerical computation, have been well studied for the Landau-Lifshitz equations that include the so-called exchange energy. However, these problems turn out to be quite challenging for equations without the exchange energy. The main reason is that when the exchange energy is included, one automatically has the magnetization vector m ∈ L ∞((0,∞); H1(Ω)) from energy estimates, which gives some compactness and stability that are needed for using the standard methods; however, in the cases without the exchange energy, one only has m ∈ L∞ ((0, ∞); L∞(Ω)), which is too rough to get the needed compactness and stability. In this thesis, we investigate some problems for models of reduced Landau-Lifshitz equations with no-exchange energy. In Chapter 1, we introduce the Landau-Lifshitz theory of ferromagnetism and summarize the main results of the thesis. The readers can check out the main results quickly in this chapter and then go to the corresponding chapters for details of proof, more discussions and further references. In Chapter 2, we study the quasi-stationary limit of a simple Landau-Lifshitz-Maxwell system with the permittivity parameter ɛ approaching zero and, using this quasi-stationary limit, establish the existence of global weak solutions to the reduced Landau-Lifshitz equations with initial value m0∈ L∞(Ω). In Chapter 3, we establish a local L2-stability theorem for the global weak solutions in finite time. The key in the proof of stability theorem is that we split the nonlocal term H m into two parts: one is bounded in L ∞(Ω) and the other bounded in L 2(Ω). Using this stability theorem, we also provide another proof for the
Efficient thermoelectric van der Pauw measurements
NASA Astrophysics Data System (ADS)
de Boor, Johannes; Schmidt, Volker
2011-07-01
The development of powerful thermoelectric materials requires fast and simple characterization techniques. We combine three measurements to obtain a complete thermoelectric characterization. The electrical conductivity is measured by the van der Pauw method, while ZT is determined directly by means of a Harman measurement. Finally, exploiting the analogy between electrical and thermal physics, a thermal van der Pauw measurement is performed and the sample Seebeck coefficient and thermal conductivity can be determined. No temperature differences need to be measured; all quantities can be deduced from voltage measurements concurrently on the same sample which allows for quick and convenient material screening.
Numerische Berechnung von Wirbelstromproblemen mit der Cell-Methode
NASA Astrophysics Data System (ADS)
Frenner, K.; Rucker, W. M.
2006-09-01
In dieser Arbeit wird die Cell-Methode auf die quasistatischen Maxwellgleichungen angewendet. Dabei werden für die notwendige Transformation vom Primärgitter auf das duale Gitter reziproke Basisvektoren verwendet. Anhand der Felddiffusion der magnetischen Induktion in einen zylindrischen Leiter werden Ergebnisse der Cell-Methode mit einer analytischen Vergleichsrechnung präsentiert.
TÜV - Zertifizierungen in der Life Science Branche
NASA Astrophysics Data System (ADS)
Schaff, Peter; Gerbl-Rieger, Susanne; Kloth, Sabine; Schübel, Christian; Daxenberger, Andreas; Engler, Claus
Life Sciences [1] (Lebenswissenschaften) sind ein globales Innovationsfeld mit Anwendungen der Bio- und Medizinwissenschaften, der Pharma-, Chemie-, Kosmetik- und Lebensmittelindustrie. Diese Branche zeichnet sich durch eine stark interdisziplinäre Ausrichtung aus, mit Anwendung wissenschaftlicher Erkenntnisse und Einsatz von Ausgangsstoffen aus der modernen Biologie, Chemie und Humanmedizin sowie gezielter marktwirtschaftlich orientierter Arbeit.
Darwin, Engels und die Rolle der Arbeit in der biologischen und kulturellen Evolution des Menschen
NASA Astrophysics Data System (ADS)
Reichholf, Josef H.
Im Jahre 1876, 5 Jahre nach Erscheinen von Darwins Buch über die Evolution des Menschen und die sexuelle Selektion (Darwin 1871), veröffentlichte Friedrich Engels den berühmt gewordenen Essay "Anteil der Arbeit an der Menschwerdung des Affen“ (Engels 1876). Die Kernfrage darin lautet in Kurzform: Warum hat der Mensch eigentlich ein Bedürfnis nach Arbeit? Engels Antwort wird nachfolgend näher betrachtet und vom gegenwärtigen Kenntnisstand aus beurteilt. Wie sich zeigen wird, beantworten seine Überlegungen die Frage nicht wirklich. Sie ist weiterhin offen. Es können lediglich einige zusätzliche Anhaltspunkte zur Diskussion gestellt werden. Angesichts des drängenden Problems millionenfacher Arbeitslosigkeit und der Forderungen nach einem "Grundrecht auf Arbeit“ kommt den Überlegungen zum möglichen Ursprung des Bedürfnisses nach Arbeit mehr als nur akademisches Interesse zu.
ERIC Educational Resources Information Center
Bauman, Robert P.; Harrison, Joseph G.
1996-01-01
Discusses the difficulties with the standard model for introduction of attractive forces into the van der Waals equation. Presents an analysis in terms of force and time delays and an alternative analysis for more advanced students in terms of energy. (JRH)
Die Evolution der Religiosität
NASA Astrophysics Data System (ADS)
Voland, Eckart
Ein konsequent darwinischer Blick auf den Menschen bedeutet, auch im Denken, Fühlen und Handeln biologische Anpassungsgeschichte zu suchen, denn auch die psychischen und mentalen Eigenheiten des Homo sapiens unterliegen der natürlichen Selektion. Lässt sich die religiöse Lebenspraxis von Menschen daher auch aus einer Fitnessperspektive betrachten?
The Forced van der Pol Equation
ERIC Educational Resources Information Center
Fay, Temple H.
2009-01-01
We report on a study of the forced van der Pol equation x + [epsilon](x[superscript 2] - 1)x + x = F cos[omega]t, by solving numerically the differential equation for a variety of values of the parameters [epsilon], F and [omega]. In doing so, many striking and interesting trajectories can be discovered and phenomena such as frequency entrainment,…
Critical initial-slip scaling for the noisy complex Ginzburg-Landau equation
NASA Astrophysics Data System (ADS)
Liu, Weigang; Täuber, Uwe C.
2016-10-01
We employ the perturbative fieldtheoretic renormalization group method to investigate the universal critical behavior near the continuous non-equilibrium phase transition in the complex Ginzburg-Landau equation with additive white noise. This stochastic partial differential describes a remarkably wide range of physical systems: coupled nonlinear oscillators subject to external noise near a Hopf bifurcation instability; spontaneous structure formation in non-equilibrium systems, e.g., in cyclically competing populations; and driven-dissipative Bose-Einstein condensation, realized in open systems on the interface of quantum optics and many-body physics, such as cold atomic gases and exciton-polaritons in pumped semiconductor quantum wells in optical cavities. Our starting point is a noisy, dissipative Gross-Pitaevski or nonlinear Schrödinger equation, or equivalently purely relaxational kinetics originating from a complex-valued Landau-Ginzburg functional, which generalizes the standard equilibrium model A critical dynamics of a non-conserved complex order parameter field. We study the universal critical behavior of this system in the early stages of its relaxation from a Gaussian-weighted fully randomized initial state. In this critical aging regime, time translation invariance is broken, and the dynamics is characterized by the stationary static and dynamic critical exponents, as well as an independent ‘initial-slip’ exponent. We show that to first order in the dimensional expansion about the upper critical dimension, this initial-slip exponent in the complex Ginzburg-Landau equation is identical to its equilibrium model A counterpart. We furthermore employ the renormalization group flow equations as well as construct a suitable complex spherical model extension to argue that this conclusion likely remains true to all orders in the perturbation expansion.
Energy Dissipation and Landau Damping in Two- and Three-dimensional Plasma Turbulence
NASA Astrophysics Data System (ADS)
Li, Tak Chu; Howes, Gregory G.; Klein, Kristopher G.; TenBarge, Jason M.
2016-12-01
Plasma turbulence is ubiquitous in space and astrophysical plasmas, playing an important role in plasma energization, but the physical mechanisms leading to dissipation of the turbulent energy remain to be definitively identified. Kinetic simulations in two dimensions (2D) have been extensively used to study the dissipation process. How the limitation to 2D affects energy dissipation remains unclear. This work provides a model of comparison between two- and three-dimensional (3D) plasma turbulence using gyrokinetic simulations; it also explores the dynamics of distribution functions during the dissipation process. It is found that both 2D and 3D nonlinear gyrokinetic simulations of a low-beta plasma generate electron velocity-space structures with the same characteristics as that of the linear Landau damping of Alfvén waves in a 3D linear simulation. The continual occurrence of the velocity-space structures throughout the turbulence simulations suggests that the action of Landau damping may be responsible for the turbulent energy transfer to electrons in both 2D and 3D, and makes possible the subsequent irreversible heating of the plasma through collisional smoothing of the velocity-space fluctuations. Although, in the 2D case where variation along the equilibrium magnetic field is absent, it may be expected that Landau damping is not possible, a common trigonometric factor appears in the 2D resonant denominator, leaving the resonance condition unchanged from the 3D case. The evolution of the 2D and 3D cases is qualitatively similar. However, quantitatively, the nonlinear energy cascade and subsequent dissipation is significantly slower in the 2D case.
Merlin, Roberto
2009-02-10
Homogeneous composites, or metamaterials, made of dielectric or metallic particles are known to show magnetic properties that contradict arguments by Landau and Lifshitz [Landau LD, Lifshitz EM (1960) Electrodynamics of Continuous Media (Pergamon, Oxford, UK), p 251], indicating that the magnetization and, thus, the permeability, loses its meaning at relatively low frequencies. Here, we show that these arguments do not apply to composites made of substances with Im square root(epsilon(S)) > lambda/l or Re square root(epsilon(S)) approximately lambda/l (epsilon(S) and l are the complex permittivity and the characteristic length of the particles, and lambda > l is the vacuum wavelength). Our general analysis is supported by studies of split rings, one of the most common constituents of electromagnetic metamaterials, and spherical inclusions. An analytical solution is given to the problem of scattering by a small and thin split ring of arbitrary permittivity. Results reveal a close relationship between epsilon(S) and the dynamic magnetic properties of metamaterials. For |square root(epsilon(S))| < lambda/a (a is the ring cross-sectional radius), the composites exhibit very weak magnetic activity, consistent with the Landau-Lifshitz argument and similar to that of molecular crystals. In contrast, large values of the permittivity lead to strong diamagnetic or paramagnetic behavior characterized by susceptibilities whose magnitude is significantly larger than that of natural substances. We compiled from the literature a list of materials that show high permittivity at wavelengths in the range 0.3-3000 microm. Calculations for a system of spherical inclusions made of these materials, using the magnetic counterpart to Lorentz-Lorenz formula, uncover large magnetic effects the strength of which diminishes with decreasing wavelength.
Wang-Landau Algorithm for Continuous Models and Joint Density of States
Zhou, Chenggang; Schulthess, Thomas C; Torbrugge, S.; Landau, D. P.
2006-01-01
We present a modified Wang-Landau algorithm for models with continuous degrees of freedom. We demonstrate this algorithm with the calculation of the joint density of states of ferromagnet Heisenberg models and a model polymer chain. The joint density of states contains more information than the density of states of a single variable-energy, but is also much more time consuming to calculate. We present strategies to significantly speed up this calculation for large systems over a large range of energy and order parameter.
A Landau-de Gennes theory for hard colloidal rods: Defects and tactoids
NASA Astrophysics Data System (ADS)
Everts, J. C.; Punter, M. T. J. J. M.; Samin, S.; van der Schoot, P.; van Roij, R.
2016-05-01
We construct a phenomenological Landau-de Gennes theory for hard colloidal rods by performing an order parameter expansion of the chemical-potential dependent grand potential. By fitting the coefficients to known results of Onsager theory, we are not only able to describe the isotropic-nematic phase transition as function of density, including the well-known density jump, but also the isotropic-nematic planar interface. The resulting theory is applied in calculations of the isotropic core size in a radial hedgehog defect, the density dependence of linear defects of hard rods in square confinement, and the formation of a nematic droplet in an isotropic background.
Kim, Jong-Won; Ott, Edward
2003-02-01
We study the statistics and characteristics of rare intense events in two types of two-dimensional complex Ginzburg-Landau (CGL) equation based models. Our numerical simulations show finite amplitude collapselike solutions which approach the infinite amplitude solutions of the nonlinear Schrödinger equation in an appropriate parameter regime. We also determine the probability distribution function of the amplitude of the CGL solutions, which is found to have enhanced (as compared to Gaussian) probability for the amplitude to be large. Our results suggest a general picture in which an incoherent background of weakly interacting waves, occasionally, "by chance," initiates intense, coherent, self-reinforcing, highly nonlinear events.
Wang-Landau algorithm for continuous models and joint density of states.
Zhou, Chenggang; Schulthess, T C; Torbrügge, Stefan; Landau, D P
2006-03-31
We present a modified Wang-Landau algorithm for models with continuous degrees of freedom. We demonstrate this algorithm with the calculation of the joint density of states of ferromagnet Heisenberg models and a model polymer chain. The joint density of states contains more information than the density of states of a single variable-energy, but is also much more time consuming to calculate. We present strategies to significantly speed up this calculation for large systems over a large range of energy and order parameter.
Resonance, particle trapping, and Landau damping in finite amplitude obliquely propagating waves
NASA Technical Reports Server (NTRS)
Palmadesso, P. J.
1972-01-01
The equations of motion for a particle in resonance with a small finite amplitude wave are solved approximately, using secularity free perturbation theory. The wave propagates at an arbitrary angle to a uniform background magnetic field in an infinite collisionless plasma. The wave fields include a longitudinal electrostatic component and elliptically polarized transverse electric and magnetic components. The trajectories of trapped and resonant untrapped particles are described, for each of the possible wave-particle resonances. These trajectories are used to construct an estimate of the nonlinear time dependent Landau damping rate of the wave.
Nonlinear equations of motion for Landau resonance interactions with a whistler mode wave
NASA Technical Reports Server (NTRS)
Inan, U. S.; Tkalcevic, S.
1982-01-01
A simple set of equations is presented for the description of the cyclotron averaged motion of Landau resonant particles in a whistler mode wave propagating at an angle to the static magnetic field. A comparison is conducted of the wave magnetic field and electric field effects for the parameters of the magnetosphere, and the parameter ranges for which the wave magnetic field effects would be negligible are determined. It is shown that the effect of the wave magnetic field can be neglected for low pitch angles, high normal wave angles, and/or high normalized wave frequencies.
NASA Astrophysics Data System (ADS)
Wüst, T.; Li, Y. W.; Landau, D. P.
2011-08-01
We describe a class of "bare bones" models of homopolymers which undergo coil-globule collapse and proteins which fold into their native states in free space or into denatured states when captured by an attractive substrate as the temperature is lowered. We then show how, with the use of a properly chosen trial move set, Wang-Landau Monte Carlo sampling can be used to study the rough free energy landscape and ground (native) states of these intriguingly simple systems and thus elucidate their thermodynamic complexity.
A Wang-Landau study of the phase transitions in a flexible homopolymer
NASA Astrophysics Data System (ADS)
Seaton, D. T.; Wüst, T.; Landau, D. P.
2009-04-01
Using Wang-Landau sampling we study the characteristic behavior of a flexible homopolymer (off-lattice) for chain lengths up to N=300. The Hamiltonian consists of a Lennard-Jones potential between all monomers, and an additional FENE potential between bonded monomers. From the resultant density of states, we calculate thermodynamic properties for a wide range of temperatures, including low temperatures that are inaccessible to traditional Monte Carlo algorithms. Peaks in the specific heat and radius of gyration indicate the coil-globule and solid-liquid transitions. With a careful implementation of the algorithm, we find no evidence of a liquid-liquid transition.
Protein folding of the HOP model: A parallel Wang—Landau study
NASA Astrophysics Data System (ADS)
Shi, G.; Wüst, T.; Li, Y. W.; Landau, D. P.
2015-09-01
We propose a simple modification to the hydrophobic-polar (HP) protein model, by introducing a new type of monomer, “0”, with intermediate hydrophobicity of some amino acids between H and P. With the replica-exchange Wang-Landau sampling method, we investigate some widely studied HP sequences as well as their H0P counterparts and observe that the H0P sequences exhibit dramatically reduced ground state degeneracy and more significant transition signals at low temperature for some thermodynamic properties, such as the specific heat.
Two-Dimensional Wang-Landau Sampling of AN Asymmetric Ising Model
NASA Astrophysics Data System (ADS)
Tsai, Shan-Ho; Wang, Fugao; Landau, D. P.
We study the critical endpoint behavior of an asymmetric Ising model with two- and three-body interactions on a triangular lattice, in the presence of an external field. We use a two-dimensional Wang-Landau sampling method to determine the density of states for this model. An accurate density of states allowed us to map out the phase diagram accurately and observe a clear divergence of the curvature of the spectator phase boundary and of the derivative of the magnetization coexistence diameter near the critical endpoint, in agreement with previous theoretical predictions.
Conformational transitions of a confined lattice protein: A Wang-Landau study
NASA Astrophysics Data System (ADS)
Pattanasiri, Busara; Li, Ying Wai; Landau, David P.; Wüst, Thomas; Triampo, Wannapong
2012-12-01
We use Wang-Landau sampling with suitable Monte Carlo trial moves to study a hydrophobic-polar (HP) lattice protein confined between two parallel, attractive walls. The density of states is determined iteratively by a random walk in energy space. Thermodynamic and structural properties, such as specific heat, number of surface contacts and number of H-H monomer pairs, are then calculated. When the surface attraction is comparable to the internal attraction among the hydrophobic monomers in the chain, two conformational “transitions”, adsorption at higher temperature and collapse at lower temperature, have been analyzed based on these properties. This transition behavior depends on the variation of surface separation.
Wang-Landau Algorithm for Continuous Models and Joint Density of States
NASA Astrophysics Data System (ADS)
Zhou, Chenggang; Schulthess, T. C.; Torbrügge, Stefan; Landau, D. P.
2006-03-01
We present a modified Wang-Landau algorithm for models with continuous degrees of freedom. We demonstrate this algorithm with the calculation of the joint density of states of ferromagnet Heisenberg models and a model polymer chain. The joint density of states contains more information than the density of states of a single variable-energy, but is also much more time consuming to calculate. We present strategies to significantly speed up this calculation for large systems over a large range of energy and order parameter.
Resonant generation of an electron–positron pair by two photons to excited Landau levels
Diachenko, M. M. Novak, O. P.; Kholodov, R. I.
2015-11-15
We consider the resonant generation of an electron–positron pair by two polarized photons to arbitrarily low Landau levels. The resonance occurs when the energy of one photon exceeds the one-photon generation threshold, and the energy of the other photon is multiple to the spacing between the levels. The cross section of the process is determined taking into account the spins of particles. The order of magnitude of the cross section is the highest when the magnetic moments of the particles are oriented along the magnetic field.
Very weak solutions of wave equation for Landau Hamiltonian with irregular electromagnetic field
NASA Astrophysics Data System (ADS)
Ruzhansky, Michael; Tokmagambetov, Niyaz
2016-11-01
In this paper, we study the Cauchy problem for the Landau Hamiltonian wave equation, with time-dependent irregular (distributional) electromagnetic field and similarly irregular velocity. For such equations, we describe the notion of a `very weak solution' adapted to the type of solutions that exist for regular coefficients. The construction is based on considering Friedrichs-type mollifier of the coefficients and corresponding classical solutions, and their quantitative behaviour in the regularising parameter. We show that even for distributional coefficients, the Cauchy problem does have a very weak solution, and that this notion leads to classical or distributional-type solutions under conditions when such solutions also exist.
Spatiotemporal chaos control with a target wave in the complex Ginzburg-Landau equation system.
Jiang, Minxi; Wang, Xiaonan; Ouyang, Qi; Zhang, Hong
2004-05-01
An effective method for controlling spiral turbulence in spatially extended systems is realized by introducing a spatially localized inhomogeneity into a two-dimensional system described by the complex Ginzburg-Landau equation. Our numerical simulations show that with the introduction of the inhomogeneity, a target wave can be produced, which will sweep all spiral defects out of the boundary of the system. The effects exist in certain parameter regions where the spiral waves are absolutely unstable. A theoretical explanation is given to reveal the underlying mechanism.
On the Possibility of Using Nonlinear Elements for Landau Damping in High-Intensity Beams
Alexahin, Y.; Gianfelice-Wendt, E.; Lebedev, V.; Valishev, A.
2016-09-30
Direct space-charge force shifts incoherent tunes downwards from the coherent ones breaking the Landau mechanism of coherent oscillations damping at high beam intensity. To restore it nonlinear elements can be employed which move back tunes of large amplitude particles. In the present report we consider the possibility of creating a “nonlinear integrable optics” insertion in the Fermilab Recycler to host either octupoles or hollow electron lens for this purpose. For comparison we also consider the classic scheme with distributed octupole families. It is shown that for the Proton Improvement Plan II (PIP II) parameters the required nonlinear tune shift can be created without destroying the dynamic aperture.
Generalized Ginzburg-Landau approach to inhomogeneous phases in nonlocal chiral quark models
NASA Astrophysics Data System (ADS)
Carlomagno, J. P.; Gómez Dumm, D.; Scoccola, N. N.
2015-05-01
We analyze the presence of inhomogeneous phases in the QCD phase diagram within the framework of nonlocal chiral quark models. We concentrate in particular in the positions of the tricritical (TCP) and Lifshitz (LP) points, which are studied in a general context using a generalized Ginzburg-Landau approach. We find that for all the phenomenologically acceptable model parametrizations considered the TCP is located at a higher temperature and a lower chemical potential in comparison with the LP. Consequently, these models seem to favor a scenario in which the onset of the first order transition between homogeneous phases is not covered by an inhomogeneous, energetically favored phase.
Critical behavior of (2 +1 )-dimensional QED: 1 /Nf corrections in the Landau gauge
NASA Astrophysics Data System (ADS)
Kotikov, A. V.; Shilin, V. I.; Teber, S.
2016-09-01
The dynamical generation of a fermion mass is studied within (2 +1 )-dimensional QED with N four-component fermions in the leading and next-to-leading orders of the 1 /N expansion. The analysis is carried out in the Landau gauge, which is supposed to insure the gauge independence of the critical fermion flavor number, Nc. It is found that the dynamical fermion mass appears for N
Very weak solutions of wave equation for Landau Hamiltonian with irregular electromagnetic field
NASA Astrophysics Data System (ADS)
Ruzhansky, Michael; Tokmagambetov, Niyaz
2017-04-01
In this paper, we study the Cauchy problem for the Landau Hamiltonian wave equation, with time-dependent irregular (distributional) electromagnetic field and similarly irregular velocity. For such equations, we describe the notion of a `very weak solution' adapted to the type of solutions that exist for regular coefficients. The construction is based on considering Friedrichs-type mollifier of the coefficients and corresponding classical solutions, and their quantitative behaviour in the regularising parameter. We show that even for distributional coefficients, the Cauchy problem does have a very weak solution, and that this notion leads to classical or distributional-type solutions under conditions when such solutions also exist.
Symmetry dependence of spin-wave eigenmodes in Landau-domain patterns
NASA Astrophysics Data System (ADS)
Bolte, M.; Meier, G.; Bayer, C.
2007-09-01
Spin-wave eigenmodes in thin permalloy squares with Landau-domain patterns are investigated by micromagnetic simulation. Both the spatial symmetry of an exciting field pulse and the symmetry of the internal field determine the frequency and spatial distribution of the spin waves. With each symmetry, only a subset of all the possible eigenmodes can be observed. Our findings confirm the presence of longitudinally and transversally localized modes. Comparison with dispersion relations from analytical theory allows the unambiguous identification of the modes as backward volume and Damon-Eshbach modes, respectively.
Protein folding of the H0P model: A parallel Wang-Landau study
Shi, Guangjie; Wuest, Thomas; Li, Ying Wai; Landau, David P
2015-01-01
We propose a simple modication to the hydrophobic-polar (HP) protein model, by introducing a new type of monomer, "0", with intermediate hydrophobicity of some amino acids between H and P. With the replica-exchange Wang-Landau sampling method, we investigate some widely studied HP sequences as well as their H0P counterparts and observe that the H0P sequences exhibit dramatically reduced ground state degeneracy and more signicant transition signals at low temperature for some thermodynamic properties, such as the specific heat.
Solvable multistate model of Landau-Zener transitions in cavity QED
Sinitsyn, Nikolai; Li, Fuxiang
2016-06-29
We consider the model of a single optical cavity mode interacting with two-level systems (spins) driven by a linearly time-dependent field. When this field passes through values at which spin energy level splittings become comparable to spin coupling to the optical mode, a cascade of Landau-Zener (LZ) transitions leads to co-flips of spins in exchange for photons of the cavity. We derive exact transition probabilities between different diabatic states induced by such a sweep of the field.
Landau-type order parameter equation for shear banding in granular Couette flow.
Shukla, Priyanka; Alam, Meheboob
2009-08-07
We show that a Landau-type "order-parameter" equation describes the onset of shear-band formation in granular plane Couette flow wherein the flow undergoes an ordering transition into alternate layers of dense and dilute regions of low and high shear rates, respectively, parallel to the flow direction. Even though the linear theory predicts the stability of the homogeneous shear solution in dilute flows, our analytical bifurcation theory suggests that there is a subcritical finite-amplitude instability that is likely to lead to shear-band formation in dilute flows, which is in agreement with previous numerical simulations.
Distribution of Chern number by Landau level broadening in Hofstadter butterfly
NASA Astrophysics Data System (ADS)
Yoshioka, Nobuyuki; Matsuura, Hiroyasu; Ogata, Masao
2015-04-01
We discuss the relationship between the quantum Hall conductance and a fractal energy band structure, Hofstadter butterfly, on a square lattice under a magnetic field. At first, we calculate the Hall conductance of Hofstadter butterfly on the basis of the linear responce theory. By classifying the bands into some groups with a help of continued fraction expansion, we find that the conductance at the band gaps between the groups accord with the denominators of fractions obtained by aborting the expansion halfway. The broadening of Landau levels is given as an account of this correspondance.
D-brane categories for orientifolds—the Landau-Ginzburg case
NASA Astrophysics Data System (ADS)
Hori, Kentaro; Walcher, Johannes
2008-04-01
We construct and classify categories of D-branes in orientifolds based on Landau-Ginzburg models and their orbifolds. Consistency of the worldsheet parity action on the matrix factorizations plays the key role. This provides all the requisite data for an orientifold construction after embedding in string theory. One of our main results is a computation of topological field theory correlators on unoriented worldsheets, generalizing the formulas of Vafa and Kapustin-Li for oriented worldsheets, as well as the extension of these results to orbifolds. We also find a doubling of Knörrer periodicity in the orientifold context.
Bordács, Sándor; Checkelsky, Joseph G; Murakawa, Hiroshi; Hwang, Harold Y; Tokura, Yoshinori
2013-10-18
Optical excitations of BiTeI with large Rashba spin splitting have been studied in an external magnetic field (B) applied parallel to the polar axis. A sequence of transitions between the Landau levels (LLs), whose energies are in proportion to √B were observed, being characteristic of massless Dirac electrons. The large separation energy between the LLs makes it possible to detect the strongest cyclotron resonance even at room temperature in moderate fields. Unlike in 2D Dirac systems, the magnetic field induced rearrangement of the conductivity spectrum is directly observed.
Ginzburg-Landau-type multiphase field model for competing fcc and bcc nucleation.
Tóth, G I; Morris, J R; Gránásy, L
2011-01-28
We address crystal nucleation and fcc-bcc phase selection in alloys using a multiphase field model that relies on Ginzburg-Landau free energies of the liquid-fcc, liquid-bcc, and fcc-bcc subsystems, and determine the properties of the nuclei as a function of composition, temperature, and structure. With a realistic choice for the free energy of the fcc-bcc interface, the model predicts well the fcc-bcc phase-selection boundary in the Fe-Ni system.
Stable and fast semi-implicit integration of the stochastic Landau-Lifshitz equation.
Mentink, J H; Tretyakov, M V; Fasolino, A; Katsnelson, M I; Rasing, Th
2010-05-05
We propose new semi-implicit numerical methods for the integration of the stochastic Landau-Lifshitz equation with built-in angular momentum conservation. The performance of the proposed integrators is tested on the 1D Heisenberg chain. For this system, our schemes show better stability properties and allow us to use considerably larger time steps than standard explicit methods. At the same time, these semi-implicit schemes are also of comparable accuracy to and computationally much cheaper than the standard midpoint implicit method. The results are of key importance for atomistic spin dynamics simulations and the study of spin dynamics beyond the macro spin approximation.
Romá, Federico; Cugliandolo, Leticia F; Lozano, Gustavo S
2014-08-01
We introduce a numerical method to integrate the stochastic Landau-Lifshitz-Gilbert equation in spherical coordinates for generic discretization schemes. This method conserves the magnetization modulus and ensures the approach to equilibrium under the expected conditions. We test the algorithm on a benchmark problem: the dynamics of a uniformly magnetized ellipsoid. We investigate the influence of various parameters, and in particular, we analyze the efficiency of the numerical integration, in terms of the number of steps needed to reach a chosen long time with a given accuracy.
Generalization of the Landau-Lifshitz-Gilbert equation for conducting ferromagnets.
Zhang, Shufeng; Zhang, Steven S-L
2009-02-27
We propose an extension of the Landau-Lifshitz-Gilbert (LLG) equation by explicitly including the role of conduction electrons in magnetization dynamics of conducting ferromagnets. The temporal and spatial dependent magnetization order parameter m(r,t) generates both electrical and spin currents that provide dissipation of the energy and angular momentum of the processing magnet. The resulting LLG equation contains highly spatial dependence of damping term and thus micromagnetic simulations based on the standard LLG equation should be reexamined for magnetization dynamics involving narrow domain walls and spin waves with short wavelengths.
Uniqueness of Landau-Lifshitz energy frame in relativistic dissipative hydrodynamics.
Tsumura, Kyosuke; Kunihiro, Teiji
2013-05-01
We show that the relativistic dissipative hydrodynamic equation derived from the relativistic Boltzmann equation by the renormalization-group method uniquely leads to the one in the energy frame proposed by Landau and Lifshitz, provided that the macroscopic-frame vector, which defines the local rest frame of the flow velocity, is independent of the momenta of constituent particles, as it should. We argue that the relativistic hydrodynamic equations for viscous fluids must be defined on the energy frame if consistent with the underlying relativistic kinetic equation.
Resonant drift of spiral waves in the complex ginzburg-landau equation.
Biktasheva, I V; Elkin, Y E; Biktashev, V N
1999-06-01
Weak periodic external perturbations of an autowave medium can cause large-distance directed motion of the spiral wave. This happens when the period of the perturbation coincides with, or is close to the rotation period of a spiral wave, or its multiple. Such motion is called resonant or parametric drift. It may be used for low-voltage defibrillation of heart tissue. Theory of the resonant drift exists, but so far was used only qualitatively. In this paper, we show good quantitative agreement of the theory with direct numerical simulations. This is done for Complex Ginzburg-Landau Equation, one of the simplest autowave models.
Difference of energy density of states in the Wang-Landau algorithm.
Komura, Yukihiro; Okabe, Yutaka
2012-01-01
Paying attention to the difference of density of states, Δln g(E)≡ln g(E+ΔE)-lng(E), we study the convergence of the Wang-Landau method. We show that this quantity is a good estimator to discuss the errors of convergence and refer to the 1/t algorithm. We also examine the behavior of the first-order transition with this difference of density of states in connection with Maxwell's equal area rule. A general procedure to judge the order of transition is given.
Relativistic Landau damping of electron plasma waves in stimulated Raman scattering
NASA Astrophysics Data System (ADS)
Bers, A.; Shkarofsky, I. P.; Shoucri, M.
2009-02-01
A new formulation of the kinetic (collisionless) electron plasma wave (EPW) damping rate in a relativistic thermal equilibrium plasma is presented, and evaluated for such waves in both forward and backward stimulated Raman scattering (SRS) in laser plasma interactions (LPI) in the temperature regime (5-15keV) of current and near-future deutirium-tritium (DT) fusion plasma experiments. For LPI at typical values of (n0/ncr), the relativistic damping of the EPW in SRS in this temperature range, particularly for forward SRS, is found to be orders of magnitude smaller than one would predict from a nonrelativistic calculation of Landau damping for those EPW.
Landau-Zener Effect In The Time-Dependent Hartree-Fock-Bogoliubov Equations
Mirea, M.
2008-01-24
If the Hartree-Fock-Bogoliubov equations of motion are solved in the case of seniority one nuclear systems, the unpaired nucleon remains on the same orbital. The blocking effect hinders the possibility that the unpaired nucleon skips from one orbital to another. A new set of coupled channel equations based on the time dependent Hartree-Fock-Bogoliubov formalism is deduced. This system includes a mechanism similar to the Landau-Zener effect, allowing that the unpaired nucleon jumps from one level to another.
Atomic Landau-Zener tunneling in Fourier-synthesized optical lattices.
Salger, Tobias; Geckeler, Carsten; Kling, Sebastian; Weitz, Martin
2007-11-09
We report on an experimental study of quantum transport of atoms in variable periodic optical potentials. The band structure of both ratchet-type asymmetric and symmetric lattice potentials is explored. The variable atom potential is realized by superimposing a conventional standing wave potential of lambda/2 spatial periodicity with a fourth-order multiphoton potential of lambda/4 periodicity. We find that the Landau-Zener tunneling rate between the first and the second excited Bloch band depends critically on the relative phase between the two spatial lattice harmonics.
Tailoring population inversion in Landau-Zener-Stückelberg interferometry of flux qubits.
Ferrón, Alejandro; Domínguez, Daniel; Sánchez, María José
2012-12-07
We distinguish different mechanisms for population inversion in flux qubits driven by dc+ac magnetic fields. We show that for driving amplitudes such that there are Landau-Zener-Stückelberg interferences, it is possible to have population inversion solely mediated by the environmental bath. Furthermore, we find that the degree of population inversion can be controlled by tailoring a resonant frequency Ω(p) in the environmental bath. To observe these effects experiments should be performed for long driving times after full relaxation.
Atomic Landau-Zener Tunneling in Fourier-Synthesized Optical Lattices
Salger, Tobias; Geckeler, Carsten; Kling, Sebastian; Weitz, Martin
2007-11-09
We report on an experimental study of quantum transport of atoms in variable periodic optical potentials. The band structure of both ratchet-type asymmetric and symmetric lattice potentials is explored. The variable atom potential is realized by superimposing a conventional standing wave potential of {lambda}/2 spatial periodicity with a fourth-order multiphoton potential of {lambda}/4 periodicity. We find that the Landau-Zener tunneling rate between the first and the second excited Bloch band depends critically on the relative phase between the two spatial lattice harmonics.
Zener tunneling between landau orbits in a high-mobility two-dimensional electron gas.
Yang, C L; Zhang, J; Du, R R; Simmons, J A; Reno, J L
2002-08-12
Magnetotransport in a laterally confined two-dimensional electron gas (2DEG) can exhibit modified scattering channels owing to a tilted Hall potential. Transitions of electrons between Landau levels with shifted guiding centers can be accomplished through a Zener tunneling mechanism, and make a significant contribution to the magnetoresistance. A remarkable oscillation effect in weak field magnetoresistance has been observed in high-mobility 2DEGs in GaAs -Al Ga 0.3As (0.7) heterostructures, and can be well explained by the Zener mechanism.
Characterization of qubit dephasing by Landau-Zener-Stückelberg-Majorana interferometry.
Forster, F; Petersen, G; Manus, S; Hänggi, P; Schuh, D; Wegscheider, W; Kohler, S; Ludwig, S
2014-03-21
Controlling coherent interaction at avoided crossings and the dynamics there is at the heart of quantum information processing. A particularly intriguing dynamics is observed in the Landau-Zener regime, where periodic passages through the avoided crossing result in an interference pattern carrying information about qubit properties. In this Letter, we demonstrate a straightforward method, based on steady-state experiments, to obtain all relevant information about a qubit, including complex environmental influences. We use a two-electron charge qubit defined in a lateral double quantum dot as test system and demonstrate a long coherence time of T2 ≃ 200 ns, which is limited by electron-phonon interaction.
NASA Astrophysics Data System (ADS)
Shevchenko, Sergey; Ashhab, Sahel; Nori, Franco
2013-03-01
We consider theoretically a superconducting qubit - nanomechanical resonator system, which was realized recently by LaHaye et al. [Nature 459, 960 (2009)]. We formulate and solve the inverse Landau-Zener-Stuckelberg problem, where we assume the driven qubit's state to be known (i.e. measured by some other device) and aim to find the parameters of the qubit's Hamiltonian. In particular, for our system the qubit's bias is defined by the nanomechanical resonator's displacement. This may provide a tool for monitoring the nanomechanical resonator 's position. [S. N. Shevchenko, S. Ashhab, and F. Nori, Phys. Rev. B 85, 094502 (2012).
Landau-Kleffner syndrome: a case study with a fourteen-year follow-up.
van Dongen, H R; Meulstee, J; Blauw-van Mourik, M; van Harskamp, F
1989-01-01
In a 14-year follow-up the improvement of language functions and the decrease of EEG abnormalities are described in a girl with the Landau-Kleffner syndrome. In this case, the results of subsequent EEG recordings do not permit conclusions about the course of the aphasia. Disappearance of focal spike and waves, bilateral paroxysms and slow background activity lack synchronicity with improvement of language. Finally, subtle language deficits were still present 14 years after the onset of the aphasia; the lastly recorded EEG showed mild abnormalities.
Higher charges and regularized quantum trace identities in su(1,1) Landau-Lifshitz model
Melikyan, A.; Pinzul, A.; Weber, G.
2010-12-15
We solve the operator ordering problem for the quantum continuous integrable su(1,1) Landau-Lifshitz model, and give a prescription to obtain the quantum trace identities, and the spectrum for the higher-order local charges. We also show that this method, based on operator regularization and renormalization, which guarantees quantum integrability, as well as the construction of self-adjoint extensions, can be used as an alternative to the discretization procedure, and unlike the latter, is based only on integrable representations.
Chen, R Y; Chen, Z G; Song, X-Y; Schneeloch, J A; Gu, G D; Wang, F; Wang, N L
2015-10-23
We present a magnetoinfrared spectroscopy study on a newly identified three-dimensional (3D) Dirac semimetal ZrTe(5). We observe clear transitions between Landau levels and their further splitting under a magnetic field. Both the sequence of transitions and their field dependence follow quantitatively the relation expected for 3D massless Dirac fermions. The measurement also reveals an exceptionally low magnetic field needed to drive the compound into its quantum limit, demonstrating that ZrTe(5) is an extremely clean system and ideal platform for studying 3D Dirac fermions. The splitting of the Landau levels provides direct, bulk spectroscopic evidence that a relatively weak magnetic field can produce a sizable Zeeman effect on the 3D Dirac fermions, which lifts the spin degeneracy of Landau levels. Our analysis indicates that the compound evolves from a Dirac semimetal into a topological line-node semimetal under the current magnetic field configuration.
The Landau-de Gennes free energy expansion of a melt of V-shaped polymer molecules.
Aliev, M A; Ugolkova, E A; Kuzminyh, N Yu
2016-08-28
The phase behavior of a monodisperse melt of polymer molecules consisting of two rod-like segments joined at an angle α has been inspected within the Landau theory of phase transitions. The interactions between monomer units were assumed to be of the Maier-Saupe form. The Landau-de Gennes expansion of the free energy of the melt has been obtained up to the sixth order in powers of the nematic order parameter, the coefficients of this expansion have been calculated from the microscopic model of polymer molecule. The phase diagram contains the regions of stability of isotropic, prolate uniaxial, oblate uniaxial, and biaxial nematic phases. The isotropic-uniaxial nematic and uniaxial-biaxial nematic transitions are of the first and second order, respectively. We found two Landau points in the phase diagram at which continuous transition from biaxial nematic state to isotropic phase occurs.
NASA Astrophysics Data System (ADS)
Chen, R. Y.; Chen, Z. G.; Song, X.-Y.; Schneeloch, J. A.; Gu, G. D.; Wang, F.; Wang, N. L.
2015-10-01
We present a magnetoinfrared spectroscopy study on a newly identified three-dimensional (3D) Dirac semimetal ZrTe5 . We observe clear transitions between Landau levels and their further splitting under a magnetic field. Both the sequence of transitions and their field dependence follow quantitatively the relation expected for 3D massless Dirac fermions. The measurement also reveals an exceptionally low magnetic field needed to drive the compound into its quantum limit, demonstrating that ZrTe5 is an extremely clean system and ideal platform for studying 3D Dirac fermions. The splitting of the Landau levels provides direct, bulk spectroscopic evidence that a relatively weak magnetic field can produce a sizable Zeeman effect on the 3D Dirac fermions, which lifts the spin degeneracy of Landau levels. Our analysis indicates that the compound evolves from a Dirac semimetal into a topological line-node semimetal under the current magnetic field configuration.
The Landau-de Gennes free energy expansion of a melt of V-shaped polymer molecules
NASA Astrophysics Data System (ADS)
Aliev, M. A.; Ugolkova, E. A.; Kuzminyh, N. Yu.
2016-08-01
The phase behavior of a monodisperse melt of polymer molecules consisting of two rod-like segments joined at an angle α has been inspected within the Landau theory of phase transitions. The interactions between monomer units were assumed to be of the Maier-Saupe form. The Landau-de Gennes expansion of the free energy of the melt has been obtained up to the sixth order in powers of the nematic order parameter, the coefficients of this expansion have been calculated from the microscopic model of polymer molecule. The phase diagram contains the regions of stability of isotropic, prolate uniaxial, oblate uniaxial, and biaxial nematic phases. The isotropic-uniaxial nematic and uniaxial-biaxial nematic transitions are of the first and second order, respectively. We found two Landau points in the phase diagram at which continuous transition from biaxial nematic state to isotropic phase occurs.
NASA Astrophysics Data System (ADS)
Arciniaga, Michael; Peterson, Michael R.
2016-07-01
We derive the single-particle eigenenergies and eigenfunctions for massless Dirac fermions confined to the surface of a sphere in the presence of a magnetic monopole, i.e., we solve the Landau level problem for electrons in graphene on the Haldane sphere. With the single-particle eigenfunctions and eigenenergies we calculate the Haldane pseudopotentials for the Coulomb interaction in the second Landau level and calculate the effective pseudopotentials characterizing an effective Landau level mixing Hamiltonian entirely in the spherical geometry to be used in theoretical studies of the fractional quantum Hall effect in graphene. Our treatment is analogous to the formalism in the planar geometry and reduces to the planar results in the thermodynamic limit.
Desgranges, Caroline; Delhommelle, Jerome
2009-06-28
In recent years, powerful and accurate methods, based on a Wang-Landau sampling, have been developed to determine phase equilibria. However, while these methods have been extensively applied to study the phase behavior of model fluids, they have yet to be applied to molecular systems. In this work, we show how, by combining hybrid Monte Carlo simulations in the isothermal-isobaric ensemble with the Wang-Landau sampling method, we determine the vapor-liquid equilibria of various molecular fluids. More specifically, we present results obtained on rigid molecules, such as benzene, as well as on flexible chains of n-alkanes. The reliability of the method introduced in this work is assessed by demonstrating that our results are in excellent agreement with the results obtained in previous work on simple fluids, using either transition matrix or conventional Monte Carlo simulations with a Wang-Landau sampling, and on molecular fluids, using histogram reweighting or Gibbs ensemble Monte Carlo simulations.
NASA Astrophysics Data System (ADS)
Yan, Jie-Yun; Wang, Lan-Yu
2016-09-01
We investigate the atomic current in optical lattices under the presence of both constant and periodic external field with Landau-Zener tunneling considered. By simplifying the system to a two-band model, the atomic current is obtained based on the Boltzmann equations. We focus on three situations to discuss the influence of the Landau-Zener tunneling and periodic field on the atomic current. Numerical calculations show the atomic transient current would finally become the stable oscillation, whose amplitude and average value can be further adjusted by the periodic external field. It is concluded that the periodic external field could provide an effective modulation on the atomic current even when the Landau-Zener tunneling probability has almostly become a constant.
Witthaut, D.; Graefe, E. M.; Korsch, H. J.
2006-06-15
We consider the Landau-Zener problem for a Bose-Einstein condensate in a linearly varying two-level system, for the full many-particle system as well as in the mean-field approximation. Novel nonlinear eigenstates emerge in the mean-field description, which leads to a breakdown of adiabaticity: The Landau-Zener transition probability does not vanish even in the adiabatic limit. It is shown that the emergence of nonlinear eigenstates and thus the breakdown of adiabaticity corresponds to quasi-degenerate avoided crossings of the many-particle levels. The many-particle problem can be solved approximately within an independent crossings approximation, which yields an explicit generalized Landau-Zener formula. A comparison to numerical results for the many-particle system and the mean-field approximation shows an excellent agreement.
Damski, Bogdan
2005-07-15
It can be shown that the dynamics of the Landau-Zener model can be accurately described in terms of the Kibble-Zurek theory of the topological defect production in nonequilibrium phase transitions. The simplest quantum model exhibiting the Kibble-Zurek mechanism is presented. A new intuitive description of Landau-Zener dynamics is found.
Damski, Bogdan
2005-07-15
It can be shown that the dynamics of the Landau-Zener model can be accurately described in terms of the Kibble-Zurek theory of the topological defect production in nonequilibrium phase transitions. The simplest quantum model exhibiting the Kibble-Zurek mechanism is presented. A new intuitive description of Landau-Zener dynamics is found.
Wieser, R
2016-10-05
The derivation of the time dependent Schrödinger equation with transversal and longitudinal relaxation, as the quantum mechanical analog of the classical Landau-Lifshitz-Bloch equation, has been described. Starting from the classical Landau-Lifshitz-Bloch equation the transition to quantum mechanics has been performed and the corresponding von-Neumann equation deduced. In a second step the time Schrödinger equation has been derived. Analytical proofs and computer simulations show the correctness and applicability of the derived Schrödinger equation.
NASA Astrophysics Data System (ADS)
Wieser, R.
2016-10-01
The derivation of the time dependent Schrödinger equation with transversal and longitudinal relaxation, as the quantum mechanical analog of the classical Landau-Lifshitz-Bloch equation, has been described. Starting from the classical Landau-Lifshitz-Bloch equation the transition to quantum mechanics has been performed and the corresponding von-Neumann equation deduced. In a second step the time Schrödinger equation has been derived. Analytical proofs and computer simulations show the correctness and applicability of the derived Schrödinger equation.