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 $\sim 1 \mu\mathrm{s}$ timescale. We measured the maximum lineic deposited energy to be more than 1 J/m.Comment: 7 pages, 7 figure

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 patients’ 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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