84,790 research outputs found
Bicritical and tetracritical phenomena and scaling properties of the SO(5) theory
By large scale Monte Carlo simulations it is shown that the stable fixed
point of the SO(5) theory is either bicritical or tetracritical depending on
the effective interaction between the antiferromagnetism and superconductivity
orders. There are no fluctuation-induced first-order transitions suggested by
epsilon expansions. Bicritical and tetracritical scaling functions are derived
for the first time and critical exponents are evaluated with high accuracy.
Suggestions on experiments are given.Comment: 11 pages, 8 postscript figures, Revtex, revised versio
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
Fluctuations of the vacuum energy density of quantum fields in curved spacetime via generalized zeta functions
For quantum fields on a curved spacetime with an Euclidean section, we derive
a general expression for the stress energy tensor two-point function in terms
of the effective action. The renormalized two-point function is given in terms
of the second variation of the Mellin transform of the trace of the heat kernel
for the quantum fields. For systems for which a spectral decomposition of the
wave opearator is possible, we give an exact expression for this two-point
function. Explicit examples of the variance to the mean ratio of the vacuum energy density of a
massless scalar field are computed for the spatial topologies of and , with results of , and
respectively. The large variance signifies the importance
of quantum fluctuations and has important implications for the validity of
semiclassical gravity theories at sub-Planckian scales. The method presented
here can facilitate the calculation of stress-energy fluctuations for quantum
fields useful for the analysis of fluctuation effects and critical phenomena in
problems ranging from atom optics and mesoscopic physics to early universe and
black hole physics.Comment: Uses revte
Stochastic Theory of Accelerated Detectors in a Quantum Field
We analyze the statistical mechanical properties of n-detectors in arbitrary
states of motion interacting with each other via a quantum field. We use the
open system concept and the influence functional method to calculate the
influence of quantum fields on detectors in motion, and the mutual influence of
detectors via fields. We discuss the difference between self and mutual
impedance and advanced and retarded noise. The mutual effects of detectors on
each other can be studied from the Langevin equations derived from the
influence functional, as it contains the backreaction of the field on the
system self-consistently. We show the existence of general fluctuation-
dissipation relations, and for trajectories without event horizons,
correlation-propagation relations, which succinctly encapsulate these quantum
statistical phenomena. These findings serve to clarify some existing confusions
in the accelerated detector problem. The general methodology presented here
could also serve as a platform to explore the quantum statistical properties of
particles and fields, with practical applications in atomic and optical physics
problems.Comment: 32 pages, Late
A general comparison theorem for 1-dimensional anticipated BSDEs
Anticipated backward stochastic differential equation (ABSDE) studied the
first time in 2007 is a new type of stochastic differential equations. In this
paper, we establish a general comparison theorem for 1-dimensional ABSDEs with
the generators depending on the anticipated term of .Comment: 8 page
A proposed generalized constitutive equation for nonlinear para-isotropic materials
Finite element models of varying complexities were used to solve problems in solid mechanics. Particular emphasis was given to concrete which is nonisotropic at any level of deformation and is also nonlinear in terms of stress-strain relationships
- …