5,641 research outputs found
Integration of streaming services and TCP data transmission in the Internet
We study in this paper the integration of elastic and streaming traffic on a
same link in an IP network. We are specifically interested in the computation
of the mean bit rate obtained by a data transfer. For this purpose, we consider
that the bit rate offered by streaming traffic is low, of the order of
magnitude of a small parameter \eps \ll 1 and related to an auxiliary
stationary Markovian process (X(t)). Under the assumption that data transfers
are exponentially distributed, arrive according to a Poisson process, and share
the available bandwidth according to the ideal processor sharing discipline, we
derive the mean bit rate of a data transfer as a power series expansion in
\eps. Since the system can be described by means of an M/M/1 queue with a
time-varying server rate, which depends upon the parameter \eps and process
(X(t)), the key issue is to compute an expansion of the area swept under the
occupation process of this queue in a busy period. We obtain closed formulas
for the power series expansion in \eps of the mean bit rate, which allow us to
verify the validity of the so-called reduced service rate at the first order.
The second order term yields more insight into the negative impact of the
variability of streaming flows
Generating sequences and Poincar\'e series for a finite set of plane divisorial valuations
Let be a finite set of divisorial valuations centered at a 2-dimensional
regular local ring . In this paper we study its structure by means of the
semigroup of values, , and the multi-index graded algebra defined by ,
\gr_V R. We prove that is finitely generated and we compute its minimal
set of generators following the study of reduced curve singularities. Moreover,
we prove a unique decomposition theorem for the elements of the semigroup.
The comparison between valuations in , the approximation of a reduced
plane curve singularity by families of sets of divisorial
valuations, and the relationship between the value semigroup of and the
semigroups of the sets , allow us to obtain the (finite) minimal
generating sequences for as well as for .
We also analyze the structure of the homogeneous components of \gr_V R. The
study of their dimensions allows us to relate the Poincar\'e series for and
for a general curve of . Since the last series coincides with the
Alexander polynomial of the singularity, we can deduce a formula of A'Campo
type for the Poincar\'e series of . Moreover, the Poincar\'e series of
could be seen as the limit of the series of ,
Nondiagonal Coset Models and their Poincar\'E Polynomials
coset models of the type with nondiagonal
modular invariants for both and are considered. Poincar\'e
polynomials of the corresponding chiral rings of these algebras are
constructed. They are used to compute the number of chiral generations of the
associated string compactifications. Moddings by discrete symmetries are also
discussed.Comment: 22 pages, (RevTex), preprint GTCRG-92-1 and CNEA-CAB-039/92. % Minor
changes in the result
A short note on the nested-sweep polarized traces method for the 2D Helmholtz equation
We present a variant of the solver in Zepeda-N\'u\~nez and Demanet (2014),
for the 2D high-frequency Helmholtz equation in heterogeneous acoustic media.
By changing the domain decomposition from a layered to a grid-like partition,
this variant yields improved asymptotic online and offline runtimes and a lower
memory footprint. The solver has online parallel complexity that scales
\emph{sub linearly} as , where is
the number of volume unknowns, and is the number of processors, provided
that . The variant in Zepeda-N\'u\~nez and Demanet
(2014) only afforded . Algorithmic scalability is a
prime requirement for wave simulation in regimes of interest for geophysical
imaging.Comment: 5 pages, 5 figure
Duality between Topologically Massive and Self-Dual models
We show that, with the help of a general BRST symmetry, different theories in
3 dimensions can be connected through a fundamental topological field theory
related to the classical limit of the Chern-Simons model.Comment: 13 pages, LaTe
Temperature and doping dependence of normal state spectral properties in a two-orbital model for ferropnictides
Using a second-order perturbative Green's functions approach we determined
the normal state single-particle spectral function
employing a minimal effective model for iron-based superconductors. The
microscopic model, used before to study magnetic fluctuations and
superconducting properties, includes the two effective tight-binding bands
proposed by S.Raghu et al. [Phys. Rev. B 77, 220503 (R) (2008)], and intra- and
inter-orbital local electronic correlations, related to the Fe-3d orbitals.
Here, we focus on the study of normal state electronic properties, in
particular the temperature and doping dependence of the total density of
states, , and of in different Brillouin zone
regions, and compare them to the existing angle resolved photoemission
spectroscopy (ARPES) and previous theoretical results in ferropnictides. We
obtain an asymmetric effect of electron and hole doping, quantitative agreement
with the experimental chemical potential shifts as a function of doping, as
well as spectral weight redistributions near the Fermi level as a function of
temperature consistent with the available experimental data. In addition, we
predict a non-trivial dependence of the total density of states with the
temperature, exhibiting clear renormalization effects by correlations.
Interestingly, investigating the origin of this predicted behaviour by
analyzing the evolution with temperature of the k-dependent self-energy
obtained in our approach, we could identify a number of specific Brillouin zone
points, none of them probed by ARPES experiments yet, where the largest
non-trivial effects of temperature on the renormalization are present.Comment: Manuscript accepted in Physics Letters A on Feb. 25, 201
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