470 research outputs found
Large scale probabilistic available bandwidth estimation
The common utilization-based definition of available bandwidth and many of
the existing tools to estimate it suffer from several important weaknesses: i)
most tools report a point estimate of average available bandwidth over a
measurement interval and do not provide a confidence interval; ii) the commonly
adopted models used to relate the available bandwidth metric to the measured
data are invalid in almost all practical scenarios; iii) existing tools do not
scale well and are not suited to the task of multi-path estimation in
large-scale networks; iv) almost all tools use ad-hoc techniques to address
measurement noise; and v) tools do not provide enough flexibility in terms of
accuracy, overhead, latency and reliability to adapt to the requirements of
various applications. In this paper we propose a new definition for available
bandwidth and a novel framework that addresses these issues. We define
probabilistic available bandwidth (PAB) as the largest input rate at which we
can send a traffic flow along a path while achieving, with specified
probability, an output rate that is almost as large as the input rate. PAB is
expressed directly in terms of the measurable output rate and includes
adjustable parameters that allow the user to adapt to different application
requirements. Our probabilistic framework to estimate network-wide
probabilistic available bandwidth is based on packet trains, Bayesian
inference, factor graphs and active sampling. We deploy our tool on the
PlanetLab network and our results show that we can obtain accurate estimates
with a much smaller measurement overhead compared to existing approaches.Comment: Submitted to Computer Network
Multi-path Probabilistic Available Bandwidth Estimation through Bayesian Active Learning
Knowing the largest rate at which data can be sent on an end-to-end path such
that the egress rate is equal to the ingress rate with high probability can be
very practical when choosing transmission rates in video streaming or selecting
peers in peer-to-peer applications. We introduce probabilistic available
bandwidth, which is defined in terms of ingress rates and egress rates of
traffic on a path, rather than in terms of capacity and utilization of the
constituent links of the path like the standard available bandwidth metric. In
this paper, we describe a distributed algorithm, based on a probabilistic
graphical model and Bayesian active learning, for simultaneously estimating the
probabilistic available bandwidth of multiple paths through a network. Our
procedure exploits the fact that each packet train provides information not
only about the path it traverses, but also about any path that shares a link
with the monitored path. Simulations and PlanetLab experiments indicate that
this process can dramatically reduce the number of probes required to generate
accurate estimates
Energy deposition from focused terawatt laser pulses in air undergoing multifilamentation
Laser filamentation is responsible for the deposition of a significant part
of the laser pulse energy in the propagation medium. We found that using
terawatt laser pulses and relatively tight focusing conditions in air,
resulting in a bundle of co-propagating multifilaments, more than 60 % of the
pulses energy is transferred to the medium, eventually degrading into heat.
This results in a strong hydrodynamic reaction of air with the generation of
shock waves and associated underdense channels for each short-scale filament.
In the focal zone, where filaments are close to each other, these discrete
channels eventually merge to form a single cylindrical low-density tube over a
timescale. We measured the maximum lineic deposited
energy to be more than 1 J/m.Comment: 7 pages, 7 figure
Orange, C. (1997). ProblÚmes et modélisation en biologie : quels apprentissages pour le lycée. Paris : Presses universitaires de France.
Astolfi, J.-P., Darot, Ă., Ginsburger-Vogel, Y. et Toussaint, J. (1997). Mots-clĂ©s de la didactique des sciences : repĂšres, dĂ©finitions, bibliographies. Paris/Bruxelles : De Boeck UniversitĂ©. Astolfi, J.-P., Darot, Ă., Ginsburger-Vogel, Y. et Toussaint, J. (1997). Pratiques de formation en didactique des sciences. Paris/Bruxelles : De Boeck UniversitĂ©.
Investigating the effects of N-methyl-D-aspartate receptor autoantibodies on cortical oscillations in vitro
PhD ThesisN-methyl-D-Aspartate receptors (NMDARs) play a key role in memory formation
and learning, and modulate gamma-frequency oscillations (-: 30-80Hz).
Gamma-oscillations are important in perception, cognition and memory
formation. They are disrupted in patients with schizophrenia, in whom NMDAR
hypofunction has been posited, and in animal models of schizophrenia.
Furthermore, NMDAR antagonists reduce -oscillation power and frequency in
vitro.
NMDA receptor antibody (NMDAR-Ab) encephalitis recapitulates some of the
features seen with blockade or ablation of NMDARs, including anterograde
memory loss and psychiatric symptoms.
We hypothesised that patientsâ autoantibodies against NMDARs could disrupt
neuronal network activity and that this may be responsible for the
neuropsychiatric symptoms experienced by patients. We examined the effect of
acute and subacute NMDAR-Ab exposure on -frequency oscillations in the
medial entorhinal cortex (mEC), using an in vitro rat brain slice preparation. We
also performed the first comparison of four different diagnostic assays used for
the detection of NMDAR-Abs.
We found that:
1. Cell-based assay using live cells was 100% sensitive but poorly specific
in the detection of NMDAR-Abs. Immunohistochemistry was 100%
specific and also sensitive (85%). Two cell-based assays using fixed
cells produced significant non-specific staining and had intermediate
sensitivity and specificity values.
2. Acute exposure to purified IgG from patients with NMDAR-Ab
encephalitis reduced the power of -frequency oscillations in the mEC
but not in the hippocampus.
3. Immunoglobulin deposition was not found in the slices acutely exposed
to patient or control IgG.
ii
4. Subacute exposure to IgG by single intracerebral injection of either
patient or control IgG did not alter mEC -oscillations ex vivo. No change
in NMDAR-mediated responses was detected.
5. IgG uptake into presumed neurons was detected in slices from these
animals, but it was not possible to co-localise the IgG to either excitatory
neurones or inhibitory interneurones with certainty
The biogeochemical influences of nitrate, dissolved oxygen, and dissolved organic carbon on stream nitrate uptake
Streams are important hotspots for the retention and removal of nitrogen (N), an element that contributes to eutrophication and threatens the stability of coastal ecosystems. Nitrate (NO3-) is the most mobile form of N, and understanding the causal mechanisms that foster optimal NO3- retention and removal in stream systems is critical from both predictive and conservation standpoints. Dissolved organic carbon (DOC) is hypothesized to be a major control of instream NO 3- concentrations, but dissolved oxygen (DO) is also an important control of NO3- removal processes. Assessing the individual impacts of NO3-, DO, and DOC concentrations on stream NO3- removal is difficult due to the natural interdependencies of these nutrients in the carbon and nitrogen cycles. This study took an experimental approach to quantifying the influences of NO3-, DOC, and DO on NO3 - transport within two headwater streams of the Ipswich and Parker River watersheds, MA, with contrasting levels of DOC and DO. In a first set of experiments we added increasing levels of NO3- to address how uptake kinetics differed in a low DO/high DOC stream (Cedar Swamp Creek) versus a high DO/low DOC stream (Cart Creek). In a second set of experiments, we manipulated for the first time at the reach scale both DO and DOC in a factorial experiment. DO was added to the low DO stream by injecting oxygen, and removed from the high DO stream by adding sodium sulfite. DOC was added both alone and in combination with the DO manipulations. Results from the NO3- enrichments suggest NO3 - concentration is an important control of NO3- vertical velocity. Results from the DOC and DO manipulations suggest that DO determines whether a stream has net nitrate uptake or production, and that DOC magnifies these processes. Addition of DOC by itself did not lead to increased nitrate uptake, suggesting that inverse relationships between nitrate and DOC may arise from complex interactions among DOC, DO and nitrate concentrations and how they influence dominant stream processes. In addition to these findings, we also observed organic matter priming effects (Kuzyakov et al. 2000) not previously reported in stream systems
Adversarial Collaboration: How Free and Open Debate Leads to Better Transpersonal Ideas (Editor\u27s Introduction)
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