1,665 research outputs found
First-Passage Time and Large-Deviation Analysis for Erasure Channels with Memory
This article considers the performance of digital communication systems
transmitting messages over finite-state erasure channels with memory.
Information bits are protected from channel erasures using error-correcting
codes; successful receptions of codewords are acknowledged at the source
through instantaneous feedback. The primary focus of this research is on
delay-sensitive applications, codes with finite block lengths and, necessarily,
non-vanishing probabilities of decoding failure. The contribution of this
article is twofold. A methodology to compute the distribution of the time
required to empty a buffer is introduced. Based on this distribution, the mean
hitting time to an empty queue and delay-violation probabilities for specific
thresholds can be computed explicitly. The proposed techniques apply to
situations where the transmit buffer contains a predetermined number of
information bits at the onset of the data transfer. Furthermore, as additional
performance criteria, large deviation principles are obtained for the empirical
mean service time and the average packet-transmission time associated with the
communication process. This rigorous framework yields a pragmatic methodology
to select code rate and block length for the communication unit as functions of
the service requirements. Examples motivated by practical systems are provided
to further illustrate the applicability of these techniques.Comment: To appear in IEEE Transactions on Information Theor
On the Performance of Short Block Codes over Finite-State Channels in the Rare-Transition Regime
As the mobile application landscape expands, wireless networks are tasked
with supporting different connection profiles, including real-time traffic and
delay-sensitive communications. Among many ensuing engineering challenges is
the need to better understand the fundamental limits of forward error
correction in non-asymptotic regimes. This article characterizes the
performance of random block codes over finite-state channels and evaluates
their queueing performance under maximum-likelihood decoding. In particular,
classical results from information theory are revisited in the context of
channels with rare transitions, and bounds on the probabilities of decoding
failure are derived for random codes. This creates an analysis framework where
channel dependencies within and across codewords are preserved. Such results
are subsequently integrated into a queueing problem formulation. For instance,
it is shown that, for random coding on the Gilbert-Elliott channel, the
performance analysis based on upper bounds on error probability provides very
good estimates of system performance and optimum code parameters. Overall, this
study offers new insights about the impact of channel correlation on the
performance of delay-aware, point-to-point communication links. It also
provides novel guidelines on how to select code rates and block lengths for
real-time traffic over wireless communication infrastructures
Role of serosal cavity resident leukocytes in the orchestration of leukocyte recruitment following the induction of experimental inflammation
This study evaluated the role of resident peritoneal and pleural macrophages
(MĪ) in neutrophil (PMN) recruitment in acute peritoneal and pleural inflammation.
I also investigated the role of lymphocytes (LĪ) in peritoneal inflammation by
studying experimental peritonitis in mice deficient in various LĪ populations.The conditional M(t> ablation mice used in these studies are transgenic for the
human diphtheria toxin receptor (DTR) under the CDllb promoter (CDllb-DTR
mice) and exhibit >97% depletion of resident serosal MĪ following intraperitoneal
(IP) administration of diphtheria toxin (DT). I determined leukocyte numbers by
flow cytometry in peritoneal or pleural lavage exudates at various time points after
the initiation of inflammation with various agents following MĪ depletion
(peritoneum: Brewer's thioglycollate [BTG], zymosan; pleural cavity: carrageenan
and fixed staphylococci). I also induced BTG peritonitis in RAG-1 knockout (KO)
mice (mature B and T LĪ deficient), NUDE mice (T LĪ deficient), ÎŧMT mice (B
LĪ deficient) and their respective controls.MĪ ablation markedly inhibited peritoneal and pleural PMN recruitment at
early time points compared to wild type (WT) controls. Administration of MĪ-rich
resident cells, unlike MĪ-depleted resident cells, significantly restored PMN
infiltration. Analysis of PMN C-X-C chemokines in lavage exudate showed that
MĪ-depleted mice had significantly reduced levels of peritoneal and pleural MIP-2
and KC at the lhr time point compared to control mice with more marked MIP-2
reduction compared to KC (>90% reduction vs 25-40%). Reduced levels of
monocyte C-C chemokine and various cytokines were evident in the MĪ-depleted
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mice at early time points. In vitro studies demonstrated that the production of these
chemokines and cytokines from peritoneal and pleural cells was MĪ-dependent.
RAG-1 KO mice exhibited increased early PMN infiltration and blunted MĪ
infiltration. NUDE exhibited increased early PMN infiltration and increased MĪ
infiltration whilst pMT KO mice exhibited decreased PMN influx and a reduced MĪ
influx. Although chemokine analysis of peritoneal exudates in RAG-1 KO mice and
NUDE mice demonstrated some differences in MCP-1 levels, there were no clear
differences evident in ÎŧMT KO mice.These data suggest that resident MĪ play a pivotal role in the orchestration of
PMN infiltration with MĪ-dependent production of MIP-2 being important. The data
suggests that LĪ can modulate leukocyte recruitment in experimental peritonitis with
T cells possibly acting as suppressor cells and B cells facilitating MĪ recruitment.
However, the exact mechanisms of LĪ action remain elusive
On the Queueing Behavior of Random Codes over a Gilbert-Elliot Erasure Channel
This paper considers the queueing performance of a system that transmits
coded data over a time-varying erasure channel. In our model, the queue length
and channel state together form a Markov chain that depends on the system
parameters. This gives a framework that allows a rigorous analysis of the queue
as a function of the code rate. Most prior work in this area either ignores
block-length (e.g., fluid models) or assumes error-free communication using
finite codes. This work enables one to determine when such assumptions provide
good, or bad, approximations of true behavior. Moreover, it offers a new
approach to optimize parameters and evaluate performance. This can be valuable
for delay-sensitive systems that employ short block lengths.Comment: 5 pages, 4 figures, conferenc
The impact of the unilateral EU commitment on the stability of international climate agreements
In this paper we analyze the negotiation strategy of the European Union regarding the formation of an international climate agreement for the post-2012 era. We use game theoretical stability concepts to explore incentives for key players in the climate policy game to join future climate agreements. We compare a minus 20 percent unilateral commitment strategy by the EU with a unilateral minus 30 percent emission reduction strategy for all Annex-B countries. Using a numerical integrated assessment climate-economy simulation model, we find that carbon leakage effects are negligible. Ther EU strategy to reduce emissions by 30% (compared to 1990 levels) by 2020 if other Annex-B countries follow does not induce participation of the USA with a similar 30% reduction commitement. However, the model shows that an appropriate initial allocation of emission allowances may stabilize a larger and more ambitious climate coalition than the Kyoto Protocol in its first commitment period.Climate change, Coalition theory, Integrated assessment model, Kyoto protocol
Thermoelectrical Field Effects in Low Dimensional Structure Solar Cells
Taking into account the temperature gradients in solar cells, it is shown
that their efficiency can be increased beyond the Shockley-Queisser limit (J.
Appl. Phys. 32 (1961) 510). The driving force for this gain is the temperature
gradient between this region and its surroundings.
A quantitative theory is given. Though the effect is found to be weak in
conventional solar cells, it is argued that it can be substantially increased
by proper choice of materials and design of the device. In particular, it is
shown that the insertion of a quantum well can enhance the efficiency beyond
one of the single gap cell, due to the presence of temperature jumps at the
heterojunctions.Comment: Published in Special issue Physica E 14 (1-2) on Nanostructures in
Photovoltaic
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