8,422 research outputs found
Compact QED3 with theta term and axionic confining strings
We discuss three dimensional compact QED with a theta term due to an axionic
field. The variational gauge invariant functional is considered and it is shown
that the ground state energy is independent of theta in a leading
approximation. The mass gap of the axionic field is found to be dependent upon
theta, the mass gap of the photon field and the scalar potential. The vacuum
expectation of the Wilson loop is shown to be independent of theta in a leading
approximation, to obey the area law and to lead to confinement. We also briefly
discuss the properties of axionic confining strings.Comment: 35 pages, LaTex, typing error correcte
Automatic Electrical Appliances Control Panel Based on Infrared and Wi-Fi: A Framework for Electrical Energy Conservation
-Today, proprietary home automation targets very specific applications which operate mostly on a
cable based infrastructure. In contrast to that, our implementation builds on a wireless platform for the
automatic control of house hold electrical appliances. The nodes gather sensor readings in a home and
transmit them to a central automation server. There, the readings are matched against a list of script
statements. When there is a match, a specific action is performed. An important property of the system is that
the control of all home appliances is done by means of the ubiquitous Infrared and Wi-Fi wireless
technologies. This way, the co-operation between manufacturers is not a necessity in order to connect
devices to the home automation network
Descent Relations and Oscillator Level Truncation Method
We reexamine the oscillator level truncation method in the bosonic String
Field Theory (SFT) by calculation the descent relation =Z_3<V_2|. For
the ghost sector we use the fermionic vertices in the standard oscillator
basis. We propose two new schemes for calculations. In the first one we assume
that the insertion satisfies the overlap equation for the vertices and in the
second one we use the direct calculations. In both schemes we get the correct
structures of the exponent and pre-exponent of the vertex <V_2|, but we find
out different normalization factors Z_3.Comment: 21 pages, 10 figures, Late
Neutrino Phenomenology in a 3+1+1 Framework
Evidence continues to grow in the MiniBooNE (MB) antineutrino mode supporting
a low-energy excess compatible with the MB neutrino mode and possibly also
confirming the results of the LSND experiment. At least one sterile neutrino is
required to explain the anomalies consistent with the observations of other
experiments. At the same time, there is a strong tension between the positive
signals of LSND and MB and the null results of nu_e and nu_mu disappearance
experiments. We explore a scenario, first proposed in \cite{Nelson:2010hz},
where the presence of an additional heavy sterile neutrino (with mass well
above an eV) can alleviate tension between LSND, MB and the null results of
disappearance experiments. We compare and contrast this 3+1+1 scenario with the
more standard 3+1 scenario and carry out global fits to all oscillation data
including new 2011 MB anti-nu data. We find that the tension can be somewhat
alleviated and that a phenomenologically viable window for the heavy neutrino,
consistent with rare decays and BBN constraints, can be found if the fifth
neutrino has a mass of order 0.3 - 10 GeV. We also find, however, that the 2011
MB anti-nu data exacerbates the tension with null experiments in both the 3+1
and 3+1+1 models when the lowest energy bins are included, resulting in little
improvement in the global fit. We also discuss the implications of an
additional neutrino for the reactor and gallium anomalies, and show that an
oscillation explanation of the anomalies is disfavored by cosmological
considerations, direct searches, and precision electroweak tests.Comment: 22 pages, 5 figures; replaced to reflect journal versio
Nomadic Base Station (NBS): a Software Defined Radio (SDR) based Architecture for Capacity Enhancement in Mobile Communications Networks
In this research work, the problem of congestion that leads to dropped calls at GSM cell sites and drastic reduction in network capacity is addressed. We designed a novel GSM base station architecture named Nomadic Base Station (NBS) which is based on Software Defined Radio (SDR) architecture and simulated the LNA for its receiver front-end. The NBS receiver LNA selects and amplifies GSM signal bursts operating at 900MHz and 1800MHz Radio Frequency Band. The later stages translate the Radio Frequency (RF) signal to Intermediate Frequency (IF) signal. This implements the SDR technology by digitizing the IF signal into bit streams that can be processed on generic Central Processing Unit (CPU) using custom written signal processing software
Effect of interchain coupling on conducting polymer luminescence: excimers in derivatives of poly(phenylene vinylene)
Optical excitation of a chain in a polymer film may result in formation of an
excimer, a superposition of on-chain excitons and charge-transfer excitons on
the originally excited chain and a neighboring chain. The excimer emission is
red-shifted compared to that of an on-chain exciton by an amount depending on
the interchain coupling . Setting up the excimer wavefunction and
calculating the red shift, we determine average values, referred to a
monomer, of 0.52 eV and 0.16 eV for poly(2,5-hexyloxy -phenylene
cyanovinylene), CN-PPV, and poly[2-methoxy, 5-(2'-ethyl-hexyloxy)-1, 4
p-phenylene vinylene], MEH-PPV, respectively, and use them to determine the
effect of interchain distance on the emission.Comment: 10 pages, RevTeX, 1 PS figure, replaced version of cond-mat/9707095,
accepted for publication in Phys. Rev. B, Rapid Communicatio
A Rigorous Derivation of Electromagnetic Self-force
During the past century, there has been considerable discussion and analysis
of the motion of a point charge, taking into account "self-force" effects due
to the particle's own electromagnetic field. We analyze the issue of "particle
motion" in classical electromagnetism in a rigorous and systematic way by
considering a one-parameter family of solutions to the coupled Maxwell and
matter equations corresponding to having a body whose charge-current density
and stress-energy tensor scale to zero size
in an asymptotically self-similar manner about a worldline as . In this limit, the charge, , and total mass, , of the body go to
zero, and goes to a well defined limit. The Maxwell field
is assumed to be the retarded solution associated with
plus a homogeneous solution (the "external field") that varies
smoothly with . We prove that the worldline must be a
solution to the Lorentz force equations of motion in the external field
. We then obtain self-force, dipole forces, and spin force
as first order perturbative corrections to the center of mass motion of the
body. We believe that this is the first rigorous derivation of the complete
first order correction to Lorentz force motion. We also address the issue of
obtaining a self-consistent perturbative equation of motion associated with our
perturbative result, and argue that the self-force equations of motion that
have previously been written down in conjunction with the "reduction of order"
procedure should provide accurate equations of motion for a sufficiently small
charged body with negligible dipole moments and spin. There is no corresponding
justification for the non-reduced-order equations.Comment: 52 pages, minor correction
An Electronic Protection Unit for Diesel Engine Standby Generators
Today diesel engine-driven standby generators for backup power supply have been adopted for residential,
commercial, and industrial use—especially in some developing countries where power from the utility company
is highly erratic. Although many of these generators function well in operation, certain engine conditions, such as
low oil pressure, high oil and water temperature, abnormally high speed, etc., could lead to malfunction, failure,
or complete breakdown of the engine. Therefore, the focus of this work is to present the implementation of a
simple, but effective electronic protection unit (EPU) capable of mitigating the adverse effect which may arise as
a result of these conditions. It is composed of two major sub-circuits—the main protective sub-circuit and the
timing sub-circuit—realized using a combination of passive and active components. Unlike the common
electrical relay-based protection system, this unit has an additional advantage of being able to keep the faultindicating
system of the generator working even after engine shutdown, thereby facilitating fault tracking. The
unit has been tested on a diesel engine-driven generator and found to function satisfactorily. The test results are
shown
From neurons to epidemics: How trophic coherence affects spreading processes
Trophic coherence, a measure of the extent to which the nodes of a directed
network are organised in levels, has recently been shown to be closely related
to many structural and dynamical aspects of complex systems, including graph
eigenspectra, the prevalence or absence of feed-back cycles, and linear
stability. Furthermore, non-trivial trophic structures have been observed in
networks of neurons, species, genes, metabolites, cellular signalling,
concatenated words, P2P users, and world trade. Here we consider two simple yet
apparently quite different dynamical models -- one a
Susceptible-Infected-Susceptible (SIS) epidemic model adapted to include
complex contagion, the other an Amari-Hopfield neural network -- and show that
in both cases the related spreading processes are modulated in similar ways by
the trophic coherence of the underlying networks. To do this, we propose a
network assembly model which can generate structures with tunable trophic
coherence, limiting in either perfectly stratified networks or random graphs.
We find that trophic coherence can exert a qualitative change in spreading
behaviour, determining whether a pulse of activity will percolate through the
entire network or remain confined to a subset of nodes, and whether such
activity will quickly die out or endure indefinitely. These results could be
important for our understanding of phenomena such as epidemics, rumours, shocks
to ecosystems, neuronal avalanches, and many other spreading processes
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