96,711 research outputs found
Transitions to Measure Synchronization in Coupled Hamiltonian Systems
Transitions to measure synchronization in two coupled lattices
are investigated based on numerical simulations. The relationship between
measure synchronization (MS), phase locking and system's total energy is
studied both for periodic and chaotic states. Two different scalings are
discovered during the process to MS according to phase locking. Random walk
like phase synchronization in chaotic measure synchronization is found, and
phase locking interrupted by phase slips irregularly is also investigated.
Meanwhile, related analysis is qualitative given to explain this phenomenon.Comment: 10 pages, 6 figure
Dynamics of multiply charged ions in intense laser fields
We numerically investigate the dynamics of multiply charged hydrogenic ions
in near-optical linearly polarized laser fields with intensities of order 10^16
to 10^17 W/cm^2. Depending on the charge state Z of the ion the relation of
strength between laser field and ionic core changes. We find around Z=12
typical multiphoton dynamics and for Z=3 tunneling behaviour, however with
clear relativistic signatures. In first order in v/c the magnetic field
component of the laser field induces a Z-dependent drift in the laser
propagation direction and a substantial Z-dependent angular momentum with
repect to the ionic core. While spin oscillations occur already in first order
in v/c as described by the Pauli equation, spin induced forces via spin orbit
coupling only appear in the parameter regime where (v/c)^2 corrections are
significant. In this regime for Z=12 ions we show strong splittings of resonant
spectral lines due to spin-orbit coupling and substantial corrections to the
conventional Stark shift due to the relativistic mass shift while those to the
Darwin term are shown to be small. For smaller charges or higher laser
intensities, parts of the electronic wavepacket may tunnel through the
potential barrier of the ionic core, and when recombining are shown to give
rise to keV harmonics in the radiation spectrum. Some parts of the wavepacket
do not recombine after ionisation and we find very energetic electrons in the
weakly relativistic regime of above threshold ionization.Comment: submitte
Stray field and superconducting surface spin valve effect in LaCaMnO/YBaCuO bilayers
Electronic transport and magnetization measurements were performed on
LaCaMnO/YBaCuO (LCMO/YBCO) bilayers
below the superconducting transition temperature in order to study the
interaction between magnetism and superconductivity. This study shows that a
substantial number of weakly pinned vortices are induced in the YBCO layer by
the large out-of-plane stray field in the domain walls. Their motion gives rise
to large dissipation peaks at the coercive field. The angular dependent
magnetoresistance (MR) data reveal the interaction between the stripe domain
structure present in the LCMO layer and the vortices and anti-vortices induced
in the YBCO layer by the out-of-plane stray field. In addition, this study
shows that a superconducting surface spin valve effect is present in these
bilayers as a result of the relative orientation between the magnetization at
the LCMO/YBCO interface and the magnetization in the interior of the LCMO layer
that can be tuned by the rotation of a small . This latter finding will
facilitate the development of superconductive magnetoresistive memory devices.
These low-magnetic field MR data, furthermore, suggest that triplet
superconductivity is induced in the LCMO layer, which is consistent with recent
reports of triplet superconductivity in LCMO/YBCO/LCMO trilayers and LCMO/YBCO
bilayers.Comment: 14 pages, 3 figure
Semantic modelling of learning objects and instruction
We introduce an ontology-based semantic modelling framework that addresses subject domain modelling, instruction modelling, and interoperability aspects in the development of complex reusable learning objects. Ontologies are knowledge representation frameworks, ideally suited to support knowledge-based modelling of these learning objects. We illustrate the benefits of semantic modelling for learning object assemblies within the context of standards such as SCORM Sequencing and Navigation and Learning Object Metadata
Universal scaling functions for bond percolation on planar random and square lattices with multiple percolating clusters
Percolation models with multiple percolating clusters have attracted much
attention in recent years. Here we use Monte Carlo simulations to study bond
percolation on planar random lattices, duals of random
lattices, and square lattices with free and periodic boundary conditions, in
vertical and horizontal directions, respectively, and with various aspect ratio
. We calculate the probability for the appearance of
percolating clusters, the percolating probabilities, , the average
fraction of lattice bonds (sites) in the percolating clusters,
(), and the probability distribution function for the fraction
of lattice bonds (sites), in percolating clusters of subgraphs with
percolating clusters, (). Using a small number of
nonuniversal metric factors, we find that , ,
(), and () for random lattices, duals
of random lattices, and square lattices have the same universal finite-size
scaling functions. We also find that nonuniversal metric factors are
independent of boundary conditions and aspect ratios.Comment: 15 pages, 11 figure
Quantum Brownian motion of multipartite systems and their entanglement dynamics
We solve the model of N quantum Brownian oscillators linearly coupled to an
environment of quantum oscillators at finite temperature, with no extra
assumptions about the structure of the system-environment coupling. Using a
compact phase-space formalism, we give a rather quick and direct derivation of
the master equation and its solutions for general spectral functions and
arbitrary temperatures. Since our framework is intrinsically nonperturbative,
we are able to analyze the entanglement dynamics of two oscillators coupled to
a common scalar field in previously unexplored regimes, such as off resonance
and strong coupling.Comment: 10 pages, 6 figure
Mapping functions and critical behavior of percolation on rectangular domains
The existence probability and the percolation probability of the
bond percolation on rectangular domains with different aspect ratios are
studied via the mapping functions between systems with different aspect ratios.
The superscaling behavior of and for such systems with exponents
and , respectively, found by Watanabe, Yukawa, Ito, and Hu in [Phys. Rev.
Lett. \textbf{93}, 190601 (2004)] can be understood from the lower order
approximation of the mapping functions and for and ,
respectively; the exponents and can be obtained from numerically
determined mapping functions and , respectively.Comment: 17 pages with 6 figure
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