5,588 research outputs found
Self similar Barkhausen noise in magnetic domain wall motion
A model for domain wall motion in ferromagnets is analyzed. Long-range
magnetic dipolar interactions are shown to give rise to self-similar dynamics
when the external magnetic field is increased adiabatically. The power spectrum
of the resultant Barkhausen noise is of the form , where
can be estimated from the critical exponents for interface
depinning in random media.Comment: 7 pages, RevTex. To appear in Phys. Rev. Let
Phase cascade bridge rectifier array in a 2-D lattice
We report on a novel rectification phenomenon in a 2-D lattice network consisting of N×N sites with diode and AC source elements with controllable phases. A phase cascade configuration is described in which the current ripple in a load resistor goes to zero in the large N limit, enhancing the rectification efficiency without requiring any external capacitor or inductor based filters. The integrated modular configuration is qualitatively different from conventional rectenna arrays in which the source, rectifier and filter systems are physically disjoint. Exact analytical results derived using idealized diodes are compared to a realistic simulation of commercially available diodes. Our results on nonlinear networks of source-rectifier arrays are potentially of interest to a fast evolving field of distributed power networks
Analytic Model for Advection-Dominated Accretion Flows in a Global Magnetic Field
A model for advection-dominated accretion flows (ADAFs) in a global magnetic
field is proposed. In contrast to the well known ADAF models in which the
viscosity of a fluid determines both angular momentum transfer and energy
dissipation in the flow, the magnetic field and the electric resistivity,
respectively, control them in this model. A manageable set of analytic
solutions for the flow and the magnetic field is obtained to vertically
non-integrated basic equations. This set describes mathematically a fully
advective accretion flow and, in physically plausible situations for most AGNs,
it is also confirmed that the radiation cooling estimated on this solution is
really negligible compared with the internal energy of the flow.Comment: 27pages, 1 figure, to appear in ApJ vol 529, Feb.1, 200
Where are all the gravastars? Limits upon the gravastar model from accreting black holes
The gravastar model, which postulates a strongly correlated thin shell of
anisotropic matter surrounding a region of anti-de Sitter space, has been
proposed as an alternative to black holes. We discuss constraints that
present-day observations of well-known black hole candidates place on this
model. We focus upon two black hole candidates known to have extraordinarily
low luminosities: the supermassive black hole in the Galactic Center,
Sagittarius A*, and the stellar-mass black hole, XTE J1118+480. We find that
the length scale for modifications of the type discussed in Chapline et al.
(2003) must be sub-Planckian.Comment: 11 pages, 4 figure
Green-Kubo formula for heat conduction in open systems
We obtain an exact Green-Kubo type linear response result for the heat
current in an open system. The result is derived for classical Hamiltonian
systems coupled to heat baths. Both lattice models and fluid systems are
studied and several commonly used implementations of heat baths, stochastic as
well as deterministic, are considered. The results are valid in arbitrary
dimensions and for any system sizes. Our results are useful for obtaining the
linear response transport properties of mesoscopic systems. Also we point out
that for systems with anomalous heat transport, as is the case in
low-dimensional systems, the use of the standard Green-Kubo formula is
problematic and the open system formula should be used.Comment: 4 page
Phase cascade lattice rectifier array: an exactly solvable nonlinear network circuit
An exact analysis of a 2-D lattice network consisting of N × N sites with rectifier and AC source elements with controllable phases reveals a method for generating ripple-free DC power without the use of any filtering circuit elements. A phase cascade configuration is described in which the current ripple in a load resistor goes to zero in the large N limit, enhancing the rectification efficiency without requiring any additional capacitor or inductor based filters. The integrated modular configuration is qualitatively different from conventional rectenna arrays in which the source, rectifier and filter systems are physically disjoint. Nonlinear networks in the large N limit of source-rectifier arrays are potentially of interest to a fast evolving field of distributed power networks.MNacknowledges support from a Graduate Fellowship in the ECE department at Boston University. We thank CMaedler, R Averitt, and members of the Photonics Center staff for assistance. JC acknowledges support from the Boston University RISE summer program. (Graduate Fellowship in the ECE department at Boston University; Boston University RISE summer program)Published versio
2-loop Functional Renormalization for elastic manifolds pinned by disorder in N dimensions
We study elastic manifolds in a N-dimensional random potential using
functional RG. We extend to N>1 our previous construction of a field theory
renormalizable to two loops. For isotropic disorder with O(N) symmetry we
obtain the fixed point and roughness exponent to next order in epsilon=4-d,
where d is the internal dimension of the manifold. Extrapolation to the
directed polymer limit d=1 allows some handle on the strong coupling phase of
the equivalent N-dimensional KPZ growth equation, and eventually suggests an
upper critical dimension of about 2.5.Comment: 4 pages, 3 figure
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