6,735 research outputs found
Anomalous diffusion with log-periodic modulation in a selected time interval
On certain self-similar substrates the time behavior of a random walk is
modulated by logarithmic periodic oscillations on all time scales. We show that
if disorder is introduced in a way that self-similarity holds only in average,
the modulating oscillations are washed out but subdiffusion remains as in the
perfect self-similar case. Also, if disorder distribution is appropriately
chosen the oscillations are localized in a selected time interval. Both the
overall random walk exponent and the period of the oscillations are
analytically obtained and confirmed by Monte Carlo simulations.Comment: 4 pages, 5 figure
Anisotropic anomalous diffusion modulated by log-periodic oscillations
We introduce finite ramified self-affine substrates in two dimensions with a
set of appropriate hopping rates between nearest-neighbor sites, where the
diffusion of a single random walk presents an anomalous {\it anisotropic}
behavior modulated by log-periodic oscillations. The anisotropy is revealed by
two different random walk exponents, and , in the {\it x} and
{\it y} direction, respectively. The values of these exponents, as well as the
period of the oscillation, are analytically obtained and confirmed by Monte
Carlo simulations.Comment: 7 pages, 7 figure
Extremely Sub-wavelength Planar Magnetic Metamaterials
We present highly sub-wavelength magnetic metamaterials designed for
operation at radio frequencies (RFs). A dual layer design consisting of
independent planar spiral elements enables experimental demonstration of a unit
cell size (a) that is ~ 700 times smaller than the resonant wavelength
({\lambda}0). Simulations indicate that utilization of a conductive via to
connect spiral layers permits further optimization and we achieve a unit cell
that is {\lambda}0/a ~ 2000. Magnetic metamaterials are characterized by a
novel time domain method which permits determination of the complex magnetic
response. Numerical simulations are performed to support experimental data and
we find excellent agreement. These new designs make metamaterial low frequency
experimental investigations practical and suggest their use for study of
magneto-inductive waves, levitation, and further enable potential RF
applications.Comment: 5 pages, 4 figure
Muon Detection of TeV Gamma Rays from Gamma Ray Bursts
Because of the limited size of the satellite-borne instruments, it has not
been possible to observe the flux of gamma ray bursts (GRB) beyond GeV energy.
We here show that it is possible to detect the GRB radiation of TeV energy and
above, by detecting the muon secondaries produced when the gamma rays shower in
the Earth's atmosphere. Observation is made possible by the recent
commissioning of underground detectors (AMANDA, the Lake Baikal detector and
MILAGRO) which combine a low muon threshold of a few hundred GeV or less, with
a large effective area of 10^3 m^2 or more. Observations will not only provide
new insights in the origin and characteristics of GRB, they also provide
quantitative information on the diffuse infrared background.Comment: Revtex, 12 pages, 3 postscript figures, uses epsfig.st
Constant effective mass across the phase diagram of high-T cuprates
We investigate the hole dynamics in two prototypical high temperature
superconducting systems: LaSrCuO and YBaCuO using a combination of DC transport and infrared spectroscopy. By
exploring the effective spectral weight obtained with optics in conjunction
with DC Hall results we find that the transition to the Mott insulating state
in these systems is of the "vanishing carrier number" type since we observe no
substantial enhancement of the mass as one proceeds to undoped phases. Further,
the effective mass remains constant across the entire underdoped regime of the
phase diagram. We discuss the implications of these results for the
understanding of both transport phenomena and pairing mechanism in high-T
systems.Comment: 5 pages, 2 figure
First-principles investigation of 180-degree domain walls in BaTiO_3
We present a first-principles study of 180-degree ferroelectric domain walls
in tetragonal barium titanate. The theory is based on an effective Hamiltonian
that has previously been determined from first-principles
ultrasoft-pseudopotential calculations. Statistical properties are investigated
using Monte Carlo simulations. We compute the domain-wall energy, free energy,
and thickness, analyze the behavior of the ferroelectric order parameter in the
interior of the domain wall, and study its spatial fluctuations. An abrupt
reversal of the polarization is found, unlike the gradual rotation typical of
the ferromagnetic case.Comment: Revtex (preprint style, 13 pages) + 3 postscript figures. A version
in two-column article style with embedded figures is available at
http://electron.rutgers.edu/~dhv/preprints/index.html#pad_wal
Design, theory, and measurement of a polarization insensitive absorber for terahertz imaging
We present the theory, design, and realization of a polarization-insensitive
metamaterial absorber for terahertz frequencies. We derive
geometrical-independent conditions for effective medium absorbers in general,
and for resonant metamaterials specically. Our fabricated design reaches and
absorptivity of 78% at 1.145 ThzComment: 6 Pages, 5 figures; figures update
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