112 research outputs found
Estabelecimento e utilização de uma plataforma diffserv gerida por um Bandwidth Broker
Apresentação efectuada na Conferência sobre Redes de Computadores - Protocolos, Tecnologias e Aplicaçoes para Ambientes Moveis, 6, Bragança, Portugal, September 2003.O Bandwidth Broker (BB) é uma entidade central que num domínio de Serviços Diferenciados realiza o controlo de admissão através da gestão e supervisão global dos recursos disponíveis, podendo também controlar e regular o tráfego aí existente. Este artigo descreve o estabelecimento de uma plataforma experimental gerido por um BB e apresenta um conjunto de testes, realizados com tráfego UDP e TCP, que permitirá avaliar a operacionalidade da plataforma e a importância da utilização do BB na manutenção da QoS requerida pelas aplicações
Wetting of Nematic Liquid Crystals on Crenellated Substrates: A Frank–Oseen Approach
We revisit the wetting of nematic liquid crystals in contact with crenellated substrates, studied previously using the Landau–de Gennes formalism. However, due to computational limitations, the characteristic length scales of the substrate relief considered in that study limited to less than 100 nematic correlation lengths. The current work uses an extended Frank–Oseen formalism, which includes not only the free-energy contribution due to the elastic deformations but also the surface tension contributions and, if disclinations or other orientational field singularities are present, their core contributions. Within this framework, which was successfully applied to the anchoring transitions of a nematic liquid crystal in contact with structured substrates, we extended the study to much larger length scales including the macroscopic scale. In particular, we analyzed the interfacial states and the transitions between them at the nematic–isotropic coexistence
A MAC protocol for quality of service provisioning in adaptive biomedical wireless sensor networks
Doctorate program on Electronics and Computer EngineeringNew healthcare solutions are being explored to improve the quality of care and the
quality of life of patients, as well as the sustainability and efficiency of the healthcare
services. In this context, wireless sensor networks (WSNs) constitute a key technology
for closing the loop between patients and healthcare providers, as WSNs provide
sensing ability, as well as mobility and portability, essential characteristics for wide
acceptance of wireless healthcare technology.
Despite the recent advances in the field, the wide adoption of healthcare WSNs is still
conditioned by quality of service (QoS) issues, namely at the medium access control
(MAC) level. MAC protocols currently available for WSNs are not able to provide the
required QoS to healthcare applications in scenarios of medical emergency or intensive
medical care. To cover this shortage, the present work introduces a MAC protocol with
novel concepts to assure the required QoS regarding the data transmission robustness,
packet delivery deadline, bandwidth efficiency, and energy preservation. The proposed
MAC protocol provides a new and efficient dynamic reconfiguration mechanism, so
that relevant operational parameters may be redefined dynamically in accordance with
the patients’ clinical state. The protocol also provides a channel switching mechanism
and the capacity of forwarding frames in two-tier network structures.
To test the performance of the proposed MAC protocol and compare it with other
MAC protocols, a simulation platform was implemented. In order to validate the
simulation results, a physical testbed was implemented to replicate the tests and verify
the results. Sensor nodes were specifically designed and assembled to implement this
physical testbed. New healthcare solutions are being explored to improve the quality of care and the
quality of life of patients, as well as the sustainability and efficiency of the healthcare
services. In this context, wireless sensor networks (WSNs) constitute a key technology
for closing the loop between patients and healthcare providers, as WSNs provide
sensing ability, as well as mobility and portability, essential characteristics for wide
acceptance of wireless healthcare technology.
Despite the recent advances in the field, the wide adoption of healthcare WSNs is still
conditioned by quality of service (QoS) issues, namely at the medium access control
(MAC) level. MAC protocols currently available for WSNs are not able to provide the
required QoS to healthcare applications in scenarios of medical emergency or intensive
medical care. To cover this shortage, the present work introduces a MAC protocol with
novel concepts to assure the required QoS regarding the data transmission robustness,
packet delivery deadline, bandwidth efficiency, and energy preservation. The proposed
MAC protocol provides a new and efficient dynamic reconfiguration mechanism, so
that relevant operational parameters may be redefined dynamically in accordance with
the patients’ clinical state. The protocol also provides a channel switching mechanism
and the capacity of forwarding frames in two-tier network structures.
To test the performance of the proposed MAC protocol and compare it with other
MAC protocols, a simulation platform was implemented. In order to validate the
simulation results, a physical testbed was implemented to replicate the tests and verify
the results. Sensor nodes were specifically designed and assembled to implement this
physical testbed. Preliminary tests using the simulation and physical platforms showed that simulation
results diverge significantly from reality, if the performance of the WSN software
components is not considered. Therefore, a parametric model was developed to reflect
the impact of this aspect on a physical WSN. Simulation tests using the parametric
model revealed that the results match satisfactorily those obtained in reality.
After validating the simulation platform, comparative tests against IEEE 802.15.4, a
prominent standard used in many wireless healthcare systems, showed that the proposed
MAC protocol leads to a performance increase regarding diverse QoS metrics, such as
packet loss and bandwidth efficiency, as well as scalability, adaptability, and power
consumption. In this way, AR-MAC is a valuable contribution to the deployment of
wireless e-health technology and related applications.Novas soluções de cuidados de saúde estão a ser exploradas para melhorar a qualidade
de tratamento e a qualidade de vida dos pacientes, assim como a sustentabilidade e
eficiência dos serviços de cuidado de saúde. Neste contexto, as redes de sensores sem
fios (wireless sensor networks - WSN) são uma tecnologia chave para fecharem o ciclo
entre os pacientes e os prestadores de cuidados de saúde, uma vez que as WSNs
proporcionam não só capacidade sensorial mas também mobilidade e portabilidade,
caracteristicas essenciais para a aceitação à larga escala da tecnologia dos cuidados de
saúde sem fios.
Apesar dos avanços recentes na área, a aceitação genérica das WSNs de cuidados de
saúde ainda está condicionada por aspectos relacionados com a qualidade de serviço
(quality of service - QoS), nomeadamente ao nível do controlo de acesso ao meio
(medium access control - MAC). Os protocolos MAC actualmente disponíveis para
WSNs são incapazes de fornecer a QoS desejada pelas aplicações médicas em cenários
de emergência ou cuidados médicos intensivos. Para suprimir esta carência, o presente
trabalho apresenta um protocolo MAC com novos conceitos a fim de assegurar a QoS
respeitante à robustez de transmissão de dados, ao limite temporal da entrega de
pacotes, à utilização da largura de banda e à preservação da energia eléctrica. O
protocolo MAC proposto dispõe de um novo e eficiente mecanismo de reconfiguração
para que os parâmetros operacionais relevantes possam ser redefinidos dinamicamente
de acordo com o estado de saúde do paciente. O protocolo também oferece um
mecanismo autónomo de comutação de canal, bem como a capacidade de encaminhar
pacotes em redes de duas camadas.
Para testar o desempenho do protocolo MAC proposto e compará-lo com outros
protocolos MAC foi implementada uma plataforma de simulação. A fim de validar os
resultados da simulação foi também implementada uma plataforma física para permitir
replicar os testes e verificar os resultados. Esta plataforma física inclui nós sensoriais
concebidos e construídos de raiz para o efeito. Testes preliminares usando as plataformas de simulação e física mostraram que os
resultados de simulação divergem significativamente da realidade, caso o desempenho
dos componentes do software presentes nos componentes da WSN não seja
considerado. Por conseguinte, desenvolveu-se um modelo paramétrico para reflectir o
impacto deste aspecto numa WSN real. Testes de simulação efectuados com o modelo
paramétrico apresentaram resultados muito satisfatórios quando comparados com os
obtidos na realidade.
Uma vez validada a plataforma de simulação, efectuaram-se testes comparativos com
a norma IEEE 802.15.4, proeminentemente usada em projectos académicos de cuidados
de saúde sem fios. Os resultados mostraram que o protocolo MAC conduz a um
desempenho superior no tocante a diversas métricas QoS, tais como perdas de pacotes e
utilização de largura de banda, bem como no respeitante à escalabilidade,
adaptabilidade e consumo de energia eléctrica. Assim sendo, o protocolo MAC proposto
representa um valioso contributo para a concretização efectiva dos cuidados de saúde
sem fios e suas aplicações
A Model to Improve the Accuracy of WSN Simulations
Simulation studies have been extensively adopted in the networking research community. Nevertheless, the performance of the software components running within the network devices is often not modeled by generic network simulators. This aspect is particularly important in wireless sensor networks (WSN). As motes present very limited computing resources, the overhead of the software components cannot be ignored. Consequently, WSN simulation results may diverge significantly from the reality. After showing experimentally the validity of this assumption, the paper proposes a set of generic equations to model the performance of WSN software components. Validation tests using contention and multiplexing-based MAC protocols show that the inclusion of the proposed model in a WSN simulator improves the confidence degree in the simulation results significantly
Modelling the impact of software components on wireless sensor network performance
Network Simulators are often used to study multiple aspects of data communications in distinct scenarios, including wireless sensor networks (WSN). However, the performance of the software components running in the network nodes is normally neglected by the simulators. This aspect is particularly important in WSNs, as nodes have very limited computing resources. In order to study the impact of software components on WSN performance, a simulated WSN and a physical WSN were setup in the IEEE 802.15.4 domain. Tests revealed that the simulator must take into account the software components of the WSN to produce realistic results. To achieve this, new parameters are proposed to model the impact of the software components on a physical WSN. Tests measuring the packet round-trip delay, delivery error ratio, and duplicated packet ratio showed that the inclusion of this model in a simulator improves significantly the accuracy of the results when compared with those obtained in a physical WSN
A time-slot scheduling algorithm for e-health wireless sensor networks
http://www.ieee-healthcom.org/2010/about.htmlFor e-health wireless sensor networks presenting significant traffic loads, MAC protocols based on deterministic scheduling algorithms are consensually considered more adequate than protocols based on random access algorithms. Indeed, TDMA-based MAC protocols are able to control the delay bound and save power by eliminating collisions. However, these protocols always require some expedite scheme to assign the superframe time-slots to the network devices that need to transmit data. Knowing that patients of an e-health wireless network are normally monitored by the same number and types of motes, originating a regular traffic pattern, a simple collaborative time-slot allocation algorithm can be achieved, as introduced in this paper. In the proposed algorithm, the announcement of time-slot allocation by the network coordinator is avoided, which helps to improve the packet delivery ratio and reduce the energy consumption in the e–health wireless network.(undefined
Pattern-induced anchoring transitions in nematic liquid crystals
In this paper we revisit the problem of a nematic liquid crystal in contact
with patterned substrates. The substrate is modelled as a periodic array of
parallel infinite grooves of well-defined cross section sculpted on a
chemically homogeneous substrate which favors local homeotropic anchoring of
the nematic. We consider three cases: a sawtooth, a crenellated and a
sinusoidal substrate. We analyse this problem within the modified Frank-Oseen
formalism. We argue that, for substrate periodicities much larger than the
extrapolation length, the existence of different nematic textures with distinct
far-field orientations, as well as the anchoring transitions between them, are
associated with the presence of topological defects either on or close to the
substrate. For the sawtooth and sinusoidal case, we observe a homeotropic to
planar anchoring transition as the substrate roughness is increased. On the
other hand, a homeotropic to oblique anchoring transition is observed for
crenellated substrates. In this case, the anchoring phase diagram shows a
complex dependence on the substrate roughness and substrate anchoring strength.Comment: 36 pages, 15 figures, revised version submitted to Journal of
Physics: Condensed Matte
Applications of Microsatellites and Single Nucleotide Polymorphisms for the Genetic Characterization of Cattle and Small Ruminants: An Overview
The status of genetic diversity, adaptation to climate change or the identification of genes associated with traits of interest in livestock populations has been a major concern for scientists in the last decades. Biotechnology has evolved continuously, offering new tools and methodologies to analyse the genomes of livestock species. Biochemical markers or protein polymorphisms were the tools used for population studies many years ago, but over the last three decades the methodologies available to analyse livestock genomes have changed notably. The development of DNA molecular markers, especially microsatellites and Single Nucleotide Polymorphisms, opened new possibilities for a better understanding of livestock genomes, unthinkable until recently. However, Whole-Genome Sequencing technologies or genome editing techniques are changing the way to analyse or interact with the genomes, even before full advantage can be taken of all the possibilities open by the last group of molecular markers. The aim of this review is to summarize the opportunities available through livestock genome analysis in cattle and small ruminant populations, namely through the molecular markers most widely used over the last few years, including microsatellites and Single Nucleotide Polymorphisms.Fac. de VeterinariaTRUEpu
Trade-off analysis of a MAC protocol for wireless e-Emergency systems
Wireless sensor networks are envisioned to be deployed in healthcare.
Since emergency and intensive care applications need to assure reliable
and timely data delivery, they have increased demands for quality of service,
including at the MAC layer. Amongst MAC protocols available for WSNs, the
Low Power Real Time (LPRT) presents suitable characteristics to be deployed
in emergency platforms due to its rational bandwidth allocation, low energy
consumption, and bounded latency. Yet, this protocol may present a significant
packet loss ratio in a wireless channel with bit error ratio. In order to define a
MAC protocol more robust to bit error conditions and able to fulfill the required
quality of service, solutions based on short size beacons and multiple retransmissions
are proposed and tested. The results showed that such strategies led to
meaningful improvements regarding packet loss ratio, without compromising
significantly the energy consumption.Fundação para a Ciência e a Tecnologia (FCT
Wireless sensor networks with QoS for e-health and e-emergency applications
http://www.informatik.uni-trier.de/%7Eley/db/conf/icsoft/ehst2008.htmlMost body sensor networks (BSN) only offer best-effort service delivery, which may compromise the successful operation of emergency healthcare (e-emergency) applications. Due to its real-time nature, e-emergency systems must provide quality of service (QoS) support, in order to provide a pervasive, valuable and fully reliable assistance to patients with risk abnormalities. But what is the real meaning of QoS support within the e-emergency context? What benefits can QoS mechanisms bring to e-emergency systems, and how are they being deployed? In order to answer these questions, this paper firstly discusses the need of QoS in personal wireless healthcare systems, and then presents an overview of such systems with QoS. A case-study requiring QoS support, intended to be deployed in a healthcare unit, is presented, as well as an asynchronous medium access TDMA-based model
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