40,009 research outputs found
A cluster expansion approach to exponential random graph models
The exponential family of random graphs is among the most widely-studied
network models. We show that any exponential random graph model may
alternatively be viewed as a lattice gas model with a finite Banach space norm.
The system may then be treated by cluster expansion methods from statistical
mechanics. In particular, we derive a convergent power series expansion for the
limiting free energy in the case of small parameters. Since the free energy is
the generating function for the expectations of other random variables, this
characterizes the structure and behavior of the limiting network in this
parameter region.Comment: 15 pages, 1 figur
Meson-Meson Scattering in Relativistic Constraint Dynamics
Dirac's relativistic constraint dynamics have been successfully applied to
obtain a covariant nonperturbative description of QED and QCD bound states. We
use this formalism to describe a microscopic theory of meson-meson scattering
as a relativistic generalization of the nonrelativistic quark-interchange model
developed by Barnes and Swanson.Comment: 5 pages, 1 figure in LaTex, talk present at the First Meeting of the
APS Topical Group on Hadronic Physics (Fermilab, October 24-26, 2004
FRW and domain walls in higher spin gravity
We present exact solutions to Vasiliev's bosonic higher spin gravity
equations in four dimensions with positive and negative cosmological constant
that admit an interpretation in terms of domain walls, quasi-instantons and
Friedman-Robertson-Walker (FRW) backgrounds. Their isometry algebras are
infinite dimensional higher-spin extensions of spacetime isometries generated
by six Killing vectors. The solutions presented are obtained by using a method
of holomorphic factorization in noncommutative twistor space and gauge
functions. In interpreting the solutions in terms of Fronsdal-type fields in
spacetime, a field-dependent higher spin transformation is required, which is
implemented at leading order. To this order, the scalar field solves
Klein-Gordon equation with conformal mass in (anti) de Sitter space. We
interpret the FRW solution with de Sitter asymptotics in the context of
inflationary cosmology and we expect that the domain wall and FRW solutions are
associated with spontaneously broken scaling symmetries in their holographic
description. We observe that the factorization method provides a convenient
framework for setting up a perturbation theory around the exact solutions, and
we propose that the nonlinear completion of particle excitations over FRW and
domain wall solutions requires black hole-like states.Comment: 63 page
Carbon coating of the SPS dipole chambers
The Electron Multipacting (EM) phenomenon is a limiting factor for the
achievement of high luminosity in accelerators for positively charged particles
and for the performance of RF devices. At CERN, the Super Proton Synchrotron
(SPS) must be upgraded in order to feed the Large Hadron Collider (LHC) with 25
ns bunch spaced beams. At such small bunch spacing, EM may limit the
performance of the SPS and consequently that of the LHC. To mitigate this
phenomenon CERN is developing a carbon thin film coating with low Secondary
Electron Yield (SEY) to coat the internal walls of the SPS dipoles beam pipes.
This paper presents the progresses in the coating technology, the performance
of the carbon coatings and the strategy for a large scale production.Comment: 7 pages, contribution to the Joint INFN-CERN-EuCARD-AccNet Workshop
on Electron-Cloud Effects: ECLOUD'12; 5-9 Jun 2012, La Biodola, Isola d'Elba,
Italy; CERN Yellow Report CERN-2013-002, pp.141-14
Determinants of emerging technology commercialization: Empirical evidences from MEMS technology
Currently most of studies on commercialization of the emerging technology considered the context in developed
countries like US, Japan, and EU with few research on developing country like China. To fill this gap, taking 112 Chinese Micro-Electro-Mechanical Systems (MEMS) enterprises as a sample, this thesis empirically investigated the determinants of emerging technology in China. Through multiple regression analysis, the empirical results show that technology property, market conditions, regional innovation network, and enterprise capability are main determinants of MEMS commercialization whereas social environment and policy and regulation do not have significant impact on the performance of MEMS commercialization.info:eu-repo/semantics/publishedVersio
Nanostructuring lithium niobate substrates by focused ion beam milling
We report on two novel ways for patterning Lithium Niobate (LN) at
submicronic scale by means of focused ion beam (FIB) bombardment. The first
method consists of direct FIB milling on LiNbO3 and the second one is a
combination of FIB milling on a deposited metallic layer and subsequent RIE
(Reactive Ion Etching) etching. FIB images show in both cases homogeneous
structures with well reproduced periodicity. These methods open the way to the
fabrication of photonic crystals on LiNbO3 substrates
Spiking Neurons Learning Phase Delays
Time differences between the two ears are an important cue for animals to azimuthally locate a sound source. The first binaural brainstem nucleus, in mammals the medial superior olive, is generally believed to perform the necessary computations. Its cells are sensitive to variations of interaural time differences of about 10 ÎĽs. The classical explanation of such a neuronal time-difference tuning is based on the physical concept of delay lines. Recent data, however, are inconsistent with a temporal delay and rather favor a phase delay. By means of a biophysical model we show how spike-timing-dependent synaptic learning explains precise interplay of excitation and inhibition and, hence, accounts for a physical realization of a phase delay
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