3,627 research outputs found
Exploration of the Federal Communications Commission’s Experimental Radio Service (ERS): Understanding ten years of experimental spectrum licenses
The Experimental Radio Service (ERS) of the Federal Communications Commission (FCC) has awarded experimental licenses for more than thirty years as a means to promote research and innovation in wireless technologies. In this work, we present an exploratory analysis of the details pertaining to the assignment of these licenses during the past ten years (2007-2016). For this purpose, we have built a single repository of technical and non-technical details about license applications by scraping publicly available information in the FCC’s website. This has permitted us systematically categorize among the existing types of experimental licenses and, subsequently, analyze their characteristics. We pay particular attention to the evolution of various parameters such as duration of license, frequency of assignment, processing times, operational parameters, among others. In addition, we explore potential trends hidden in ten years of experimental licenses. This allow us to better understand the time burden of obtaining an authorization or the factors that may influence the license granting process.We conclude this work by delving into the details behind the relationship between ERS authorizations and well known wireless technologies, in particular TV White Spaces and 5G
Fractal Conductance Fluctuations in Gold--Nanowires
A detailed analysis of magneto-conductance fluctuations of quasiballistic
gold-nanowires of various lengths is presented. We find that the variance
when analyzed for much
smaller than the correlation field varies according to with indicating that the graph of
vs. is fractal. We attribute this behavior to the existence of
long-lived states arising from chaotic trajectories trapped close to regular
classical orbits. We find that decreases with increasing length of the
wires.Comment: 5 pages, Revtex with epsf, 4 Postscript figures, final version
accepted as Phys. Rev. Let
Entanglement and Nonunitary Evolution
We consider a collapsing relativistic spherical shell for a free quantum
field. Once the center of the wavefunction of the shell passes a certain radius
R, the degrees of freedom inside R are traced over. We show that an observer
outside this region will determine that the evolution of the system is
nonunitary. We argue that this phenomenon is generic to entangled systems, and
discuss a possible relation to black hole physics.Comment: 14 pages, 1 figure; Added a clarification regarding the relation with
black hole physic
Unstable decay and state selection II
The decay of unstable states when several metastable states are available for
occupation is investigated using path-integral techniques. Specifically, a
method is described which allows the probabilities with which the metastable
states are occupied to be calculated by finding optimal paths, and fluctuations
about them, in the weak noise limit. The method is illustrated on a system
described by two coupled Langevin equations, which are found in the study of
instabilities in fluid dynamics and superconductivity. The problem involves a
subtle interplay between non-linearities and noise, and a naive approximation
scheme which does not take this into account is shown to be unsatisfactory. The
use of optimal paths is briefly reviewed and then applied to finding the
conditional probability of ending up in one of the metastable states, having
begun in the unstable state. There are several aspects of the calculation which
distinguish it from most others involving optimal paths: (i) the paths do not
begin and end on an attractor, and moreover, the final point is to a large
extent arbitrary, (ii) the interplay between the fluctuations and the leading
order contribution are at the heart of the method, and (iii) the final result
involves quantities which are not exponentially small in the noise strength.
This final result, which gives the probability of a particular state being
selected in terms of the parameters of the dynamics, is remarkably simple and
agrees well with the results of numerical simulations. The method should be
applicable to similar problems in a number of other areas such as state
selection in lasers, activationless chemical reactions and population dynamics
in fluctuating environments.Comment: 28 pages, 6 figures. Accepted for publication in Phys. Rev.
Stochastic Gravity: A Primer with Applications
Stochastic semiclassical gravity of the 90's is a theory naturally evolved
from semiclassical gravity of the 70's and 80's. It improves on the
semiclassical Einstein equation with source given by the expectation value of
the stress-energy tensor of quantum matter fields in curved spacetimes by
incorporating an additional source due to their fluctuations. In stochastic
semiclassical gravity the main object of interest is the noise kernel, the
vacuum expectation value of the (operator-valued) stress-energy bi-tensor, and
the centerpiece is the (stochastic) Einstein-Langevin equation. We describe
this new theory via two approaches: the axiomatic and the functional. The
axiomatic approach is useful to see the structure of the theory from the
framework of semiclassical gravity. The functional approach uses the
Feynman-Vernon influence functional and the Schwinger-Keldysh close-time-path
effective action methods which are convenient for computations. It also brings
out the open systems concepts and the statistical and stochastic contents of
the theory such as dissipation, fluctuations, noise and decoherence. We then
describe the application of stochastic gravity to the backreaction problems in
cosmology and black hole physics. Intended as a first introduction to this
subject, this article places more emphasis on pedagogy than completeness.Comment: 46 pages Latex. Intended as a review in {\it Classical and Quantum
Gravity
Deterministic polarization chaos from a laser diode
Fifty years after the invention of the laser diode and fourty years after the
report of the butterfly effect - i.e. the unpredictability of deterministic
chaos, it is said that a laser diode behaves like a damped nonlinear
oscillator. Hence no chaos can be generated unless with additional forcing or
parameter modulation. Here we report the first counter-example of a
free-running laser diode generating chaos. The underlying physics is a
nonlinear coupling between two elliptically polarized modes in a
vertical-cavity surface-emitting laser. We identify chaos in experimental
time-series and show theoretically the bifurcations leading to single- and
double-scroll attractors with characteristics similar to Lorenz chaos. The
reported polarization chaos resembles at first sight a noise-driven mode
hopping but shows opposite statistical properties. Our findings open up new
research areas that combine the high speed performances of microcavity lasers
with controllable and integrated sources of optical chaos.Comment: 13 pages, 5 figure
Enhanced Hsp70 Expression Protects against Acute Lung Injury by Modulating Apoptotic Pathways
The Acute respiratory distress syndrome (ARDS) is a highly lethal inflammatory lung disorder. Apoptosis plays a key role in its pathogenesis. We showed that an adenovirus expressing the 70 kDa heat shock protein Hsp70 (AdHSP) protected against sepsis-induced lung injury. In this study we tested the hypothesis that AdHSP attenuates apoptosis in sepsis-induced lung injury
Transversity distributions in the nucleon in the large-N_c limit
We compute the quark and antiquark transversity distributions in the nucleon
at a low normalization point of 600 MeV in the large- limit, where the
nucleon can be described as a soliton of an effective chiral theory (chiral
quark-soliton model). The flavor-nonsinglet distributions, and , appear in leading order
of the -expansion, while the flavor-singlet distributions, and , are non-zero only in
next-to-leading order. The transversity quark and antiquark distributions are
found to be significantly different from the longitudinally polarized
distributions and , respectively, in contrast to the prediction of the naive
non-relativistic quark model. We show that this affects the predictions for the
spin asymmetries in Drell-Yan pair production in transversely polarized pp and
ppbar collisions.Comment: 45 pages, 16 figure
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