8,354 research outputs found
Q-ESP: a QoS-compliant Security Protocol to enrich IPSec Framework
IPSec is a protocol that allows to make secure connections between branch
offices and allows secure VPN accesses. However, the efforts to improve IPSec
are still under way; one aspect of this improvement is to take Quality of
Service (QoS) requirements into account. QoS is the ability of the network to
provide a service at an assured service level while optimizing the global usage
of network resources. The QoS level that a flow receives depends on a six-bit
identifier in the IP header; the so-called Differentiated Services code point
(DSCP). Basically, Multi-Field classifiers classify a packet by inspecting
IP/TCP headers, to decide how the packet should be processed. The current IPSec
standard does hardly offer any guidance to do this, because the existing IPSec
ESP security protocol hides much of this information in its encrypted payloads,
preventing network control devices such as routers and switches from utilizing
this information in performing classification appropriately. To solve this
problem, we propose a QoS-friendly Encapsulated Security Payload (Q-ESP) as a
new IPSec security protocol that provides both security and QoS supports. We
also present our NetBSD kernel-based implementation as well as our evaluation
results of Q-ESP
Protein Sequencing with an Adaptive Genetic Algorithm from Tandem Mass Spectrometry
In Proteomics, only the de novo peptide sequencing approach allows a partial
amino acid sequence of a peptide to be found from a MS/MS spectrum. In this
article a preliminary work is presented to discover a complete protein sequence
from spectral data (MS and MS/MS spectra). For the moment, our approach only
uses MS spectra. A Genetic Algorithm (GA) has been designed with a new
evaluation function which works directly with a complete MS spectrum as input
and not with a mass list like the other methods using this kind of data. Thus
the mono isotopic peak extraction step which needs a human intervention is
deleted. The goal of this approach is to discover the sequence of unknown
proteins and to allow a better understanding of the differences between
experimental proteins and proteins from databases
Dissipative hydrodynamics for multi-component systems
Second-order dissipative hydrodynamic equations for each component of a
multi-component system are derived using the entropy principle. Comparison of
the solutions with kinetic transport results demonstrates validity of the
obtained equations. We demonstrate how the shear viscosity of the total system
can be calculated in terms of the involved cross sections and partial
densities. Presence of the inter-species interactions leads to a characteristic
time-dependence of the shear viscosity of the mixture, which also means that
the shear viscosity of a mixture cannot be calculated using the Green-Kubo
formalism the way it has been done recently. This finding is of interest for
understanding of the shear viscosity of a quark-gluon-plasme extracted from
comparisons of hydrodynamic simulations with experimental results from RHIC and
LHC.Comment: 5 pages, 3 figures. Submitted to EPJA topical issue on "Relativistic
Hydro- and Thermodynamics". arXiv admin note: text overlap with
arXiv:1103.403
Chaotic quantization and the mass spectrum of fermions
In order to understand the parameters of the standard model of electroweak
and strong interactions, one needs to embed the standard model into some larger
theory that accounts for the observed values. This means some additional sector
is needed that fixes and stabilizes the values of the fundamental constants of
nature. We describe how such a sector can be constructed using the so-called
chaotic quantization method applied to a system of coupled map lattices. We
restrict ourselves in this short note on verifying how our model correctly
yields the numerical values of Yukawa and gravitational coupling constants of a
collection of heavy and light fermions using a simple principle, the local
minimization of vacuum energy.Comment: 8 pages, 6 figures. To appear in Chaos, Solitons and Fractals (2008
Regularization in regression: comparing Bayesian and frequentist methods in a poorly informative situation
Using a collection of simulated an real benchmarks, we compare Bayesian and
frequentist regularization approaches under a low informative constraint when
the number of variables is almost equal to the number of observations on
simulated and real datasets. This comparison includes new global noninformative
approaches for Bayesian variable selection built on Zellner's g-priors that are
similar to Liang et al. (2008). The interest of those calibration-free
proposals is discussed. The numerical experiments we present highlight the
appeal of Bayesian regularization methods, when compared with non-Bayesian
alternatives. They dominate frequentist methods in the sense that they provide
smaller prediction errors while selecting the most relevant variables in a
parsimonious way
Immersions of surfaces into SL(2,C) and into the space of geodesics of Hyperbolic space
This thesis mainly treats two developments of the classical theory of
hypersurfaces inside pseudo-Riemannian space forms.
The former - a joint work with Francesco Bonsante - consists in the study of
immersions of smooth manifolds into holomorphic Riemannian space forms of
constant curvature -1 (including SL(2,C) with a multiple of its Killing form):
this leads to a Gauss-Codazzi theorem, it suggests an approach to holomorphic
transitioning of immersions into pseudo-Riemannian space forms, a trick to
construct holomorphic maps into the PSL(2,C)-character variety, and leads to a
restatement of Bers theorem.
The latter - a joint work with Andrea Seppi - consists in the study of
immersions of n-manifolds inside the space of geodesics of the hyperbolic
(n+1)-space. We give a characterization, in terms of the para-Sasaki structure
of this space of geodesics, of the Riemannian immersions which turn out to be
Gauss maps of equivariant immersions into the hyperbolic space.Comment: PhD thesis. Partially joint with Francesco Bonsante and Andrea Seppi.
210 pages, 12 figure
A metric uniformizing model for the Quasi-Fuchsian space
We introduce and study a novel uniformization metric model for the
quasi-Fuchsian space QF(S) of a closed oriented surface S, defined through a
class of C-valued bilinear forms on S, called Bers metrics, which coincide with
hyperbolic Riemannian metrics along the Fuchsian locus. By employing this
approach, we present a new model of the holomorphic tangent bundle of QF(S)
that extends the metric model for Teichm\"uller space defined by Berger and
Ebin, and give an integral representation of the Goldman symplectic form and of
the holomorphic extension of the Weil-Petersson metric to QF(S), with a new
proof of its existence and non-degeneracy. We also determine new bounds for the
Schwarzian of Bers projective structures extending Kraus estimate. Lastly, we
use this formalism to give alternative proofs to several classic results in
quasi-Fuchsian theory
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