16,417 research outputs found
The interaction between railway vehicle dynamics and track lateral alignment
Track geometry deteriorates with traffic flow, thus it needs to be regularly restored using tamping or other method. As the deterioration is mainly in the vertical direction this aspect has been widely studied and models for its analysis developed, however, the lateral deterioration of track is not as well understood. This research aims to develop a method that can be used to analyse and predict the lateral deterioration of railway track caused by traffic flows, and investigate the influences of different railway vehicles, running speeds, traffic types and wheel/rail contact conditions
Extended staggered-flux phases in two-dimensional lattices
Based on the so called - model in two-dimensional (2D) lattices, we
investigate the stabilities of a class of extended staggered-flux (SF) phases
(which are the extensions of the SF phase to
generalized spatial periods) against the Fermi-liquid phase. Surprisingly, when
away from the nesting electron filling, some extended-SF phases take over the
dominant SF phase (the SF phase for the square
lattice, a SF phase for the triangular one), compete with the
Fermi-liquid phase in nontrivial patterns, and still occupy significant space
in the phase diagram through the advantage in the total electronic kinetic
energies. The results can be termed as the generalized Perierls
orbital-antiferromagnetic instabilities of the Fermi-liquid phase in 2D
lattice-electron models.Comment: 5 pages, 5 figure
Plaquette Ordered Phase and Quantum Phase Diagram in the Spin-1/2 J1-J2 Square Heisenberg Model
We study the spin-1/2 Heisenberg model on the square lattice with first- and
second-neighbor antiferromagnetic interactions J1 and J2, which possesses a
nonmagnetic region that has been debated for many years and might realize the
interesting Z2 spin liquid. We use the density matrix renormalization group
approach with explicit implementation of SU(2) spin rotation symmetry and study
the model accurately on open cylinders with different boundary conditions. With
increasing J2, we find a Neel phase, a plaquette valence-bond (PVB) phase with
a finite spin gap, and a possible spin liquid in a small region of J2 between
these two phases. From the finite-size scaling of the magnetic order parameter,
we estimate that the Neel order vanishes at J2/J1~0.44. For 0.5<J2/J1<0.61, we
find dimer correlations and PVB textures whose decay lengths grow strongly with
increasing system width, consistent with a long-range PVB order in the
two-dimensional limit. The dimer-dimer correlations reveal the s-wave character
of the PVB order. For 0.44<J2/J1<0.5, spin order, dimer order, and spin gap are
small on finite-size systems and appear to scale to zero with increasing system
width, which is consistent with a possible gapless SL or a near-critical
behavior. We compare and contrast our results with earlier numerical studies.Comment: 11 pages, 17 figures, and 1 tabl
SLE_k: correlation functions in the coefficient problem
We apply the method of correlation functions to the coefficient problem in
stochastic geometry. In particular, we give a proof for some universal patterns
conjectured by M. Zinsmeister for the second moments of the Taylor coefficients
for special values of kappa in the whole-plane Schramm-Loewner evolution
(SLE_kappa). We propose to use multi-point correlation functions for the study
of higher moments in coefficient problem. Generalizations related to the
Levy-type processes are also considered. The exact multifractal spectrum of
considered version of the whole-plane SLE_kappa is discussed
Properties of holographic dark energy at the Hubble length
We consider holographic cosmological models of dark energy in which the
infrared cutoff is set by the Hubble's radius. We show that any interacting
dark energy model, regardless of its detailed form, can be recast as a non
interacting model in which the holographic parameter evolves slowly
with time. Two specific cases are analyzed. We constrain the parameters of both
models with observational data, and show that they can be told apart at the
perturbative level.Comment: 4 pages, 6 figures. Contribution to the Proceedings ERE201
Temperature Dependent Empirical Pseudopotential Theory For Self-Assembled Quantum Dots
We develop a temperature dependent empirical pseudopotential theory to study
the electronic and optical properties of self-assembled quantum dots (QDs) at
finite temperature. The theory takes the effects of both lattice expansion and
lattice vibration into account. We apply the theory to the InAs/GaAs QDs. For
the unstrained InAs/GaAs heterostructure, the conduction band offset increases
whereas the valence band offset decreases with increasing of the temperature,
and there is a type-I to type-II transition at approximately 135 K. Yet, for
InAs/GaAs QDs, the holes are still localized in the QDs even at room
temperature, because the large lattice mismatch between InAs and GaAs greatly
enhances the valence band offset. The single particle energy levels in the QDs
show strong temperature dependence due to the change of confinement potentials.
Because of the changes of the band offsets, the electron wave functions
confined in QDs increase by about 1 - 5%, whereas the hole wave functions
decrease by about 30 - 40% when the temperature increases from 0 to 300 K. The
calculated recombination energies of exciton, biexciton and charged excitons
show red shifts with increasing of the temperature, which are in excellent
agreement with available experimental data
Coherent Manipulation of Quantum Delta-kicked Dynamics: Faster-than-classical Anomalous Diffusion
Large transporting regular islands are found in the classical phase space of
a modified kicked rotor system in which the kicking potential is reversed after
every two kicks. The corresponding quantum system, for a variety of system
parameters and over long time scales, is shown to display energy absorption
that is significantly faster than that associated with the underlying classical
anomalous diffusion. The results are of interest to both areas of quantum chaos
and quantum control.Comment: 6 pages, 4 figures, to appear in Physical Review
Control of Dynamical Localization
Control over the quantum dynamics of chaotic kicked rotor systems is
demonstrated. Specifically, control over a number of quantum coherent phenomena
is achieved by a simple modification of the kicking field. These include the
enhancement of the dynamical localization length, the introduction of classical
anomalous diffusion assisted control for systems far from the semiclassical
regime, and the observation of a variety of strongly nonexponential lineshapes
for dynamical localization. The results provide excellent examples of
controlled quantum dynamics in a system that is classically chaotic and offer
new opportunities to explore quantum fluctuations and correlations in quantum
chaos.Comment: 9 pages, 7 figures, to appear in Physical Review
Vertical Assessment of Lidar Bathymetry
Validation of Airborne Light Detection And Ranging (LiDAR) Bathymetry (ALB) is necessary for the production of nautical charts to fill coastal charting gaps and to quickly and accurately measure shallow dynamic seafloors. Previous assessments concentrate on the validation of ALB data within overlapping regions of Multibeam Echo-Sounder (MBES) data. This paper presents new coverage environments to the MBES overlap validation method, and proposes an alternative method for comparison between ALB data and ENC vector information. Analysis of the validation methods favour comparisons using overlapping MBES data; however, the overlap of ALB and ENC information provides an additional assessment method with substantial overlapping regions. The ENC comparison proves to be useful at locations where MBES data is absent and in the assessment of chart adequacy.La validación de la batimetrÃa mediante la detección y el alcance de la luz aerotransportada (LiDAR – Light Detection And Ranging) es necesaria para que la producción de cartas náuticas complete los vacÃos de la cartografÃa costera y mida con rapidez y precisión los fondos marinos dinámicos poco profundos. Las evaluaciones anteriores se concentran en la validación de los datos ALB en el seno de las regiones de solapamiento de los datos de la Ecosonda Multihaz (MBES). Este documento presenta nuevos entornos de cobertura para el método de validación mediante el solapamiento MBES, y propone un método alternativo para la comparación entre los datos del ALB y la información vectorial de las ENCs. El análisis de los métodos de validación favorece las comparaciones utilizando los datos de solapamiento MBES; sin embargo, el solapamiento de la información ALB y ENC proporciona un método de evaluación adicional con importantes regiones de solapamiento. La comparación de las ENCs resulta útil en los lugares en que no hay datos MBES y en la evaluación de la idoneidad de las cartas.La validation des données bathymétriques issues de levés LiDAR (Light Detection And Ranging, en français : détection et estimation de la distance par la lumière) aéroporté (ALB) est nécessaire pour la production de cartes marines afin de combler les trous dans la cartographie côtière et de mesurer rapidement et efficacement l’évolution des planchers océaniques peu profonds. Les évaluations précédentes étaient axées sur la validation de données ALB au sein de régions où des données issues de sondages acoustiques multifaisceaux (SMF) se chevauchaient. Le présent article présente les nouvelles conditions de couverture de la méthode de validation par recoupement des données SMF, et propose une méthode alternative de comparaison entre les données ALB et les informations vectorielles des ENC. L’analyse de ces méthodes de validation favorise les comparaisons utilisant le recoupement des données SMF ; toutefois, le recoupement de données ALB et ENC fournit une méthode additionnelle pour les régions comprenant d’importants chevauchements. La comparaison d’ENC s’avère utile à des endroits où il n’existe pas de données SMF et pour l’évaluation de l’exactitude de la carte
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