8,278 research outputs found
The full set of -invariant factorized -matrices
We use the method of the tensor product graph to construct rational (Yangian
invariant) solutions of the Yang-Baxter equation in fundamental representations
of and thence the full set of -invariant factorized -matrices.
Brief comments are made on their bootstrap structure and on Belavin's scalar
Yangian conserved charges.Comment: 10p
Microstructure-property relationships in directionally solidified single crystal nickel-base superalloys
Some of the microstructural features which influence the creep properties of directionally solidified and single crystal nickel-base superalloys are discussed. Gamma precipitate size and morphology, gamma-gamma lattice mismatch, phase instability, alloy composition, and processing variations are among the factors considered. Recent experimental results are reviewed and related to the operative deformation mechanisms and to the corresponding mechanical properties. Special emphasis is placed on the creep behavior of single crystal superalloys at high temperatures, where directional gamma coarsening is prominent, and at lower temperatures, where gamma coarsening rates are significantly reduced. It can be seen that very subtle changes in microstructural features can have profound effects on the subsequent properties of these materials
Towards gravitationally assisted negative refraction of light by vacuum
Propagation of electromagnetic plane waves in some directions in
gravitationally affected vacuum over limited ranges of spacetime can be such
that the phase velocity vector casts a negative projection on the time-averaged
Poynting vector. This conclusion suggests, inter alia, gravitationally assisted
negative refraction by vacuum.Comment: 6 page
Comprehensive cosmographic analysis by Markov Chain Method
We study the possibility to extract model independent information about the
dynamics of the universe by using Cosmography. We intend to explore it
systematically, to learn about its limitations and its real possibilities. Here
we are sticking to the series expansion approach on which Cosmography is based.
We apply it to different data sets: Supernovae Type Ia (SNeIa), Hubble
parameter extracted from differential galaxy ages, Gamma Ray Bursts (GRBs) and
the Baryon Acoustic Oscillations (BAO) data. We go beyond past results in the
literature extending the series expansion up to the fourth order in the scale
factor, which implies the analysis of the deceleration, q_{0}, the jerk, j_{0}
and the snap, s_{0}. We use the Markov Chain Monte Carlo Method (MCMC) to
analyze the data statistically. We also try to relate direct results from
Cosmography to dark energy (DE) dynamical models parameterized by the
Chevalier-Polarski-Linder (CPL) model, extracting clues about the matter
content and the dark energy parameters. The main results are: a) even if
relying on a mathematical approximate assumption such as the scale factor
series expansion in terms of time, cosmography can be extremely useful in
assessing dynamical properties of the Universe; b) the deceleration parameter
clearly confirms the present acceleration phase; c) the MCMC method can help
giving narrower constraints in parameter estimation, in particular for higher
order cosmographic parameters (the jerk and the snap), with respect to the
literature; d) both the estimation of the jerk and the DE parameters, reflect
the possibility of a deviation from the LCDM cosmological model.Comment: 24 pages, 7 figure
Process of designing robust, dependable, safe and secure software for medical devices: Point of care testing device as a case study
This article has been made available through the Brunel Open Access Publishing Fund.Copyright © 2013 Sivanesan Tulasidas et al. This paper presents a holistic methodology for the design of medical device software, which encompasses of a new way of eliciting requirements, system design process, security design guideline, cloud architecture design, combinatorial testing process and agile project management. The paper uses point of care diagnostics as a case study where the software and hardware must be robust, reliable to provide accurate diagnosis of diseases. As software and software intensive systems are becoming increasingly complex, the impact of failures can lead to significant property damage, or damage to the environment. Within the medical diagnostic device software domain such failures can result in misdiagnosis leading to clinical complications and in some cases death. Software faults can arise due to the interaction among the software, the hardware, third party software and the operating environment. Unanticipated environmental changes and latent coding errors lead to operation faults despite of the fact that usually a significant effort has been expended in the design, verification and validation of the software system. It is becoming increasingly more apparent that one needs to adopt different approaches, which will guarantee that a complex software system meets all safety, security, and reliability requirements, in addition to complying with standards such as IEC 62304. There are many initiatives taken to develop safety and security critical systems, at different development phases and in different contexts, ranging from infrastructure design to device design. Different approaches are implemented to design error free software for safety critical systems. By adopting the strategies and processes presented in this paper one can overcome the challenges in developing error free software for medical devices (or safety critical systems).Brunel Open Access Publishing Fund
Multibreathers in Klein-Gordon chains with interactions beyond nearest neighbors
We study the existence and stability of multibreathers in Klein-Gordon chains
with interactions that are not restricted to nearest neighbors. We provide a
general framework where such long range effects can be taken into consideration
for arbitrarily varying (as a function of the node distance) linear couplings
between arbitrary sets of neighbors in the chain. By examining special case
examples such as three-site breathers with next-nearest-neighbors, we find {\it
crucial} modifications to the nearest-neighbor picture of one-dimensional
oscillators being excited either in- or anti-phase. Configurations with
nontrivial phase profiles, arise, as well as spontaneous symmetry breaking
(pitchfork) bifurcations, when these states emerge from (or collide with) the
ones with standard (0 or ) phase difference profiles. Similar
bifurcations, both of the supercritical and of the subcritical type emerge when
examining four-site breathers with either next-nearest-neighbor or even
interactions with the three-nearest one-dimensional neighbors. The latter
setting can be thought of as a prototype for the two-dimensional building
block, namely a square of lattice nodes, which is also examined. Our analytical
predictions are found to be in very good agreement with numerical results
Universal diffusion near the golden chaos border
We study local diffusion rate in Chirikov standard map near the critical
golden curve. Numerical simulations confirm the predicted exponent
for the power law decay of as approaching the golden curve via principal
resonances with period (). The universal
self-similar structure of diffusion between principal resonances is
demonstrated and it is shown that resonances of other type play also an
important role.Comment: 4 pages Latex, revtex, 3 uuencoded postscript figure
On the algebra A_{\hbar,\eta}(osp(2|2)^{(2)}) and free boson representations
A two-parameter quantum deformation of the affine Lie super algebra
is introduced and studied in some detail. This algebra is the
first example associated with nonsimply-laced and twisted root systems of a
quantum current algebra with the structure of a so-called infinite Hopf family
of (super)algebras. A representation of this algebra at is realized in
the product Fock space of two commuting sets of Heisenberg algebras.Comment: 14 pages, LaTe
The SO(N) principal chiral field on a half-line
We investigate the integrability of the SO(N) principal chiral model on a
half-line, and find that mixed Dirichlet/Neumann boundary conditions (as well
as pure Dirichlet or Neumann) lead to infinitely many conserved charges
classically in involution. We use an anomaly-counting method to show that at
least one non-trivial example survives quantization, compare our results with
the proposed reflection matrices, and, based on these, make some preliminary
remarks about expected boundary bound-states.Comment: 7 pages, Late
Yangians, Integrable Quantum Systems and Dorey's rule
We study tensor products of fundamental representations of Yangians and show
that the fundamental quotients of such tensor products are given by Dorey's
rule.Comment: We have made corrections to the results for the Yangians associated
to the non--simply laced algebra
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