52 research outputs found
Adaptive Multicast of Multi-Layered Video: Rate-Based and Credit-Based Approaches
Network architectures that can efficiently transport high quality, multicast
video are rapidly becoming a basic requirement of emerging multimedia
applications. The main problem complicating multicast video transport is
variation in network bandwidth constraints. An attractive solution to this
problem is to use an adaptive, multi-layered video encoding mechanism. In this
paper, we consider two such mechanisms for the support of video multicast; one
is a rate-based mechanism that relies on explicit rate congestion feedback from
the network, and the other is a credit-based mechanism that relies on
hop-by-hop congestion feedback. The responsiveness, bandwidth utilization,
scalability and fairness of the two mechanisms are evaluated through
simulations. Results suggest that while the two mechanisms exhibit performance
trade-offs, both are capable of providing a high quality video service in the
presence of varying bandwidth constraints.Comment: 11 page
A Dynamic Analysis of Tuberculosis Dissemination to Improve Control and Surveillance
Background: Detailed analysis of the dynamic interactions among biological, environmental, social, and economic factors that favour the spread of certain diseases is extremely useful for designing effective control strategies. Diseases like tuberculosis that kills somebody every 15 seconds in the world, require methods that take into account the disease dynamics to design truly efficient control and surveillance strategies. The usual and well established statistical approaches provide insights into the cause-effect relationships that favour disease transmission but they only estimate risk areas, spatial or temporal trends. Here we introduce a novel approach that allows figuring out the dynamical behaviour of the disease spreading. This information can subsequently be used to validate mathematical models of the dissemination process from which the underlying mechanisms that are responsible for this spreading could be inferred. Methodology/Principal Findings: The method presented here is based on the analysis of the spread of tuberculosis in a Brazilian endemic city during five consecutive years. The detailed analysis of the spatio-temporal correlation of the yearly geo-referenced data, using different characteristic times of the disease evolution, allowed us to trace the temporal path of the aetiological agent, to locate the sources of infection, and to characterize the dynamics of disease spreading. Consequently, the method also allowed for the identification of socio-economic factors that influence the process. Conclusions/Significance: The information obtained can contribute to more effective budget allocation, drug distribution and recruitment of human skilled resources, as well as guiding the design of vaccination programs. We propose that this novel strategy can also be applied to the evaluation of other diseases as well as other social processes.Instituto do Milenio REDE-TBConselho Nacional de Desenvolvimento Cientifico e Tecnologico (CNPq)Coordenacao de Aperfeicoamento de Pessoal de Nivel Superior (CAPES)Fundacao de Amparo a Pesquisa do Estado de Sao Paulo (FAPESP)Fundacao de Amparo a Ciencia e Tecnologia do Estado de Pernambuco (FACEPE)[0012-05.03/04]Fundacao de Amparo a Ciencia e Tecnologia do Estado de Pernambuco (FACEPE)[0203-1.05/08
Measurement of the cosmic ray spectrum above eV using inclined events detected with the Pierre Auger Observatory
A measurement of the cosmic-ray spectrum for energies exceeding
eV is presented, which is based on the analysis of showers
with zenith angles greater than detected with the Pierre Auger
Observatory between 1 January 2004 and 31 December 2013. The measured spectrum
confirms a flux suppression at the highest energies. Above
eV, the "ankle", the flux can be described by a power law with
index followed by
a smooth suppression region. For the energy () at which the
spectral flux has fallen to one-half of its extrapolated value in the absence
of suppression, we find
eV.Comment: Replaced with published version. Added journal reference and DO
Energy Estimation of Cosmic Rays with the Engineering Radio Array of the Pierre Auger Observatory
The Auger Engineering Radio Array (AERA) is part of the Pierre Auger
Observatory and is used to detect the radio emission of cosmic-ray air showers.
These observations are compared to the data of the surface detector stations of
the Observatory, which provide well-calibrated information on the cosmic-ray
energies and arrival directions. The response of the radio stations in the 30
to 80 MHz regime has been thoroughly calibrated to enable the reconstruction of
the incoming electric field. For the latter, the energy deposit per area is
determined from the radio pulses at each observer position and is interpolated
using a two-dimensional function that takes into account signal asymmetries due
to interference between the geomagnetic and charge-excess emission components.
The spatial integral over the signal distribution gives a direct measurement of
the energy transferred from the primary cosmic ray into radio emission in the
AERA frequency range. We measure 15.8 MeV of radiation energy for a 1 EeV air
shower arriving perpendicularly to the geomagnetic field. This radiation energy
-- corrected for geometrical effects -- is used as a cosmic-ray energy
estimator. Performing an absolute energy calibration against the
surface-detector information, we observe that this radio-energy estimator
scales quadratically with the cosmic-ray energy as expected for coherent
emission. We find an energy resolution of the radio reconstruction of 22% for
the data set and 17% for a high-quality subset containing only events with at
least five radio stations with signal.Comment: Replaced with published version. Added journal reference and DO
Measurement of the Radiation Energy in the Radio Signal of Extensive Air Showers as a Universal Estimator of Cosmic-Ray Energy
We measure the energy emitted by extensive air showers in the form of radio
emission in the frequency range from 30 to 80 MHz. Exploiting the accurate
energy scale of the Pierre Auger Observatory, we obtain a radiation energy of
15.8 \pm 0.7 (stat) \pm 6.7 (sys) MeV for cosmic rays with an energy of 1 EeV
arriving perpendicularly to a geomagnetic field of 0.24 G, scaling
quadratically with the cosmic-ray energy. A comparison with predictions from
state-of-the-art first-principle calculations shows agreement with our
measurement. The radiation energy provides direct access to the calorimetric
energy in the electromagnetic cascade of extensive air showers. Comparison with
our result thus allows the direct calibration of any cosmic-ray radio detector
against the well-established energy scale of the Pierre Auger Observatory.Comment: Replaced with published version. Added journal reference and DOI.
Supplemental material in the ancillary file
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An end-to-end source-adaptive multi-layered multicast (SAMM) algorithm
Layered encoding is often recommended as a solution to the problem of varying bandwidth constraints in video multicast applications. However, multi-layered encoding of video is not sufficient to provide ideal video quality and bandwidth utilization, because network bandwidth constraints change over time. Adaptive techniques are required. In this paper we consider a rate-based Source-Adaptive Multi-layered Multicast (SAMM) algorithm that operates on an end-to-end basis. Video senders adapt the rates of their video layers in response to congestion feedback from receivers. To prevent feedback implosion, the use of computationally simple feedback merging servers is proposed. Network switches and routers are not required to implement complex flow or congestion control algorithms. The performance of the end-to-end SAMM algorithm is evaluated through simulations and compared with that of a non-source-adaptive mechanism
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Fair queueing with feedback-based policing
End-to-end congestion control is an important reason why the Internet is robust, scalable and simple to use. Unfortunately, purely end-to-end congestion control algorithms are incapable of preventing the unfair bandwidth allocations and congestion collapse caused by unresponsive applications, which are becoming increasingly prevalent in the Internet. In this paper, we propose a new mechanism called Fair Queueing with Feedback-based Policing (FQFP) to address unfair bandwidth allocation and congestion collapse in the Internet. We demonstrate the promise of FQFP through simluations and suggest ways in which FQFP may leverage the mechanisms currently being developed in the context of differentiated services. The FQFP mechanism is compliant with the Internet philosophy of keeping router implementations simple and pushing complexity toward the edges of the network
Credit-Based Source-Adaptive Multi-Layered Video Multicast
Spatial and temporal variations in network bandwidth constraints constitute serious challenges to the multicast distribution of real-time video content. This paper presents a video multicast algorithm that combines multi-layered video encoding with feedback-based source adaptation in order to address varying bandwidth constraints in a multicast tree. The proposed algorithm uses a novel credit-based, hop-by-hop multicast #ow control mechanism in conjunction with explicit rate congestion feedback. It achieves nearly optimal network utilization at the expense of packet losses that are isolated to low priority video content. The responsiveness, bandwidth utilization, scalability, video quality and fairness of the proposed mechanism are evaluated through simulations, and results suggest that the proposed mechanism is capable of providing a high quality video service in the presence of varying bandwidth constraints. Keywords: Video Multicast, Multi-Layered Video Encoding, Credit-Based Flow ..
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