1,421 research outputs found
Interaction between vortices in models with two order parameters
The interaction energy and force between widely separated strings is analyzed
in a field theory having applications to superconducting cosmic strings, the
SO(5) model of high-temperature superconductivity, and solitons in nonlinear
optics. The field theory has two order parameters, one of which is broken in
the vacuum (giving rise to strings), the other of which is unbroken in the
vacuum but which could nonetheless be broken in the core of the string. If this
does occur, there is an effect on the energetics of widely separated strings.
This effect is important if the length scale of this second order parameter is
longer than that of the other fields in the problem.Comment: 11 pages, 3 figures. Minor changes in the text. Accepted for
publication in Phys. Rev.
Fluid Dynamics of Relativistic Quantum Dust
The microscopic transport equations for free fields are solved using the
Schwinger function. Thus, for general initial conditions, the evolution of the
energy-momentum tensor is obtained, incorporating the quantum effects exactly.
The result for relativistic fermions differs from classical hydrodynamics,
which is illustrated for Landau and Bjorken type initial conditions in this
model of exploding primordial matter. Free fermions behave like classical dust
concerning hydrodynamic observables. However, quantum effects which are present
in the initial state are preserved.Comment: 5 pages; LaTe
Hydrodynamic scaling from the dynamics of relativistic quantum field theory
Hydrodynamic behavior is a general feature of interacting systems with many
degrees of freedom constrained by conservation laws. To date hydrodynamic
scaling in relativistic quantum systems has been observed in many high energy
settings, from cosmic ray detections to accelerators, with large particle
multiplicity final states. Here we show first evidence for the emergence of
hydrodynamic scaling in the dynamics of a relativistic quantum field theory. We
consider a simple scalar model in 1+1 dimensions in the
Hartree approximation and study the dynamics of two colliding kinks at
relativistic speeds as well as the decay of a localized high energy density
region. The evolution of the energy-momentum tensor determines the dynamical
local equation of state and allows the measurement of the speed of sound.
Hydrodynamic scaling emerges at high local energy densities.Comment: 4 pages, 4 color eps figures, uses RevTex, v2 some typos corrected
and references adde
Density-dependence of functional development in spiking cortical networks grown in vitro
During development, the mammalian brain differentiates into specialized
regions with distinct functional abilities. While many factors contribute to
functional specialization, we explore the effect of neuronal density on the
development of neuronal interactions in vitro. Two types of cortical networks,
dense and sparse, with 50,000 and 12,000 total cells respectively, are studied.
Activation graphs that represent pairwise neuronal interactions are constructed
using a competitive first response model. These graphs reveal that, during
development in vitro, dense networks form activation connections earlier than
sparse networks. Link entropy analysis of dense net- work activation graphs
suggests that the majority of connections between electrodes are reciprocal in
nature. Information theoretic measures reveal that early functional information
interactions (among 3 cells) are synergetic in both dense and sparse networks.
However, during later stages of development, previously synergetic
relationships become primarily redundant in dense, but not in sparse networks.
Large link entropy values in the activation graph are related to the domination
of redundant ensembles in late stages of development in dense networks. Results
demonstrate differences between dense and sparse networks in terms of
informational groups, pairwise relationships, and activation graphs. These
differences suggest that variations in cell density may result in different
functional specialization of nervous system tissue in vivo.Comment: 10 pages, 7 figure
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