774 research outputs found
Mean field convergence of a model of multiple TCP connections through a buffer implementing RED
RED (Random Early Detection) has been suggested when multiple TCP sessions
are multiplexed through a bottleneck buffer. The idea is to detect congestion
before the buffer overflows by dropping or marking packets with a probability
that increases with the queue length. The objectives are reduced packet loss,
higher throughput, reduced delay and reduced delay variation achieved through
an equitable distribution of packet loss and reduced synchronization. Baccelli,
McDonald and Reynier [Performance Evaluation 11 (2002) 77--97] have proposed a
fluid model for multiple TCP connections in the congestion avoidance regime
multiplexed through a bottleneck buffer implementing RED. The window sizes of
each TCP session evolve like independent dynamical systems coupled by the queue
length at the buffer. The key idea in [Performance Evaluation 11 (2002) 77--97]
is to consider the histogram of window sizes as a random measure coupled with
the queue. Here we prove the conjecture made in [Performance Evaluation 11
(2002) 77--97] that, as the number of connections tends to infinity, this
system converges to a deterministic mean-field limit comprising the window size
density coupled with a deterministic queue.Comment: Published at http://dx.doi.org/10.1214/105051605000000700 in the
Annals of Applied Probability (http://www.imstat.org/aap/) by the Institute
of Mathematical Statistics (http://www.imstat.org
A confirmed location in the Galactic halo for the high-velocity cloud 'chain A'
The high-velocity clouds of atomic hydrogen, discovered about 35 years ago,
have velocities inconsistent with simple Galactic rotation models that
generally fit the stars and gas in the Milky Way disk. Their origins and role
in Galactic evolution remain poorly understood, largely for lack of information
on their distances. The high-velocity clouds might result from gas blown from
the Milky Way disk into the halo by supernovae, in which case they would enrich
the Galaxy with heavy elements as they fall back onto the disk. Alternatively,
they may consist of metal-poor gas -- remnants of the era of galaxy formation,
accreted by the Galaxy and reducing its metal abundance. Or they might be truly
extragalactic objects in the Local Group of galaxies. Here we report a firm
distance bracket for a large high-velocity cloud, Chain A, which places it in
the Milky Way halo (2.5 to 7 kiloparsecs above the Galactic plane), rather than
at an extragalactic distance, and constrains its gas mass to between 10^5 and 2
times 10^6 solar masses.Comment: 8 pages, including 4 postscript figures. Letter to Nature, 8 July
199
Approaching the Coverability Problem Continuously
The coverability problem for Petri nets plays a central role in the
verification of concurrent shared-memory programs. However, its high
EXPSPACE-complete complexity poses a challenge when encountered in real-world
instances. In this paper, we develop a new approach to this problem which is
primarily based on applying forward coverability in continuous Petri nets as a
pruning criterion inside a backward coverability framework. A cornerstone of
our approach is the efficient encoding of a recently developed polynomial-time
algorithm for reachability in continuous Petri nets into SMT. We demonstrate
the effectiveness of our approach on standard benchmarks from the literature,
which shows that our approach decides significantly more instances than any
existing tool and is in addition often much faster, in particular on large
instances.Comment: 18 pages, 4 figure
The SAMI -- Fornax Dwarfs Survey IV. Star Formation Histories of Dwarf and Early-Type Galaxies: Insights from Full Spectral Fitting
We present a study on the star formation histories (SFHs) of galaxies
covering the range < M/M < , leveraging
full spectral fitting algorithms. Our sample consists of 31 dwarf galaxies from
the SAMI-Fornax Survey with stellar masses between -, early-type galaxies from the ATLAS project with stellar
masses between -, and dwarf galaxies that are
satellites of Andromeda and the Milky Way, with <
M/M < . We find that galaxies from - exhibit the smallest star formation rates (SFRs), while the SFR
increase as we move down or up in mass. In this sense, we find that some
galaxies have cumulative SFHs that are comparable to those
of galaxies. Our study shows that the evolution of giant
galaxies is primarily governed by their internal properties, with timescales
that do not depend on their environmental location. In contrast, dwarf galaxies
below can be significantly affected in dense environments,
such as the inner regions of a cluster, that severely quench the galaxies
before the assembly of their 50% present-day mass. We find that, only dwarfs
with stellar masses between - actively form stars
nowadays, while less massive galaxies seem to remain unaffected by the
environment due to the expulsion of most of their gas at an early stage in
their evolution. Our study highlights and corroborates a critical threshold
around in galaxy evolution from previous studies,
separating more massive galaxies minimally impacted by the environment from
those less massive galaxies quenched by it.Comment: Accepted for publication in MNRA
Pro-oxidant effect of ALA is implicated in mitochondrial dysfunction of HepG2 cells
Heme biosynthesis begins in the mitochondrion with the formation of delta-aminolevulinic acid (ALA). In acute intermittent porphyria, hereditary tyrosinemia type I and lead poisoning patients, ALA is accumulated in plasma and in organs, especially the liver. These diseases are also associated with neuromuscular dysfunction and increased incidence of hepatocellular carcinoma. Many studies suggest that this damage may originate from ALA-induced oxidative stress following its accumulation. Using the MnSOD as an oxidative stress marker, we showed here that ALA treatment of cultured cells induced ROS production, increasing with ALA concentration. The mitochondrial energetic function of ALA-treated HepG2 cells was further explored. Mitochondrial respiration and ATP content were reduced compared to control cells. For the 300 μM treatment, ALA induced a mitochondrial mass decrease and a mitochondrial network imbalance although neither necrosis nor apoptosis were observed. The up regulation of PGC-1, Tfam and ND5 genes was also found; these genes encode mitochondrial proteins involved in mitochondrial biogenesis activation and OXPHOS function. We propose that ALA may constitute an internal bioenergetic signal, which initiates a coordinated upregulation of respiratory genes, which ultimately drives mitochondrial metabolic adaptation within cells. The addition of an antioxidant, Manganese(III) tetrakis(1-methyl-4-pyridyl)porphyrin (MnTMPyP), resulted in improvement of maximal respiratory chain capacity with 300 μM ALA. Our results suggest that mitochondria, an ALA-production site, are more sensitive to pro-oxidant effect of ALA, and may be directly involved in pathophysiology of patients with inherited or acquired porphyria
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