Byzantine fault-tolerant agreement protocols for wireless Ad hoc networks

Tese de doutoramento, Informática (Ciências da Computação), Universidade de Lisboa, Faculdade de Ciências, 2010.The thesis investigates the problem of fault- and intrusion-tolerant consensus in resource-constrained wireless ad hoc networks. This is a fundamental problem in distributed computing because it abstracts the need to coordinate activities among various nodes. It has been shown to be a building block for several other important distributed computing problems like state-machine replication and atomic broadcast. The thesis begins by making a thorough performance assessment of existing intrusion-tolerant consensus protocols, which shows that the performance bottlenecks of current solutions are in part related to their system modeling assumptions. Based on these results, the communication failure model is identified as a model that simultaneously captures the reality of wireless ad hoc networks and allows the design of efficient protocols. Unfortunately, the model is subject to an impossibility result stating that there is no deterministic algorithm that allows n nodes to reach agreement if more than n2 omission transmission failures can occur in a communication step. This result is valid even under strict timing assumptions (i.e., a synchronous system). The thesis applies randomization techniques in increasingly weaker variants of this model, until an efficient intrusion-tolerant consensus protocol is achieved. The first variant simplifies the problem by restricting the number of nodes that may be at the source of a transmission failure at each communication step. An algorithm is designed that tolerates f dynamic nodes at the source of faulty transmissions in a system with a total of n 3f + 1 nodes. The second variant imposes no restrictions on the pattern of transmission failures. The proposed algorithm effectively circumvents the Santoro- Widmayer impossibility result for the first time. It allows k out of n nodes to decide despite dn 2 e(nk)+k2 omission failures per communication step. This algorithm also has the interesting property of guaranteeing safety during arbitrary periods of unrestricted message loss. The final variant shares the same properties of the previous one, but relaxes the model in the sense that the system is asynchronous and that a static subset of nodes may be malicious. The obtained algorithm, called Turquois, admits f < n 3 malicious nodes, and ensures progress in communication steps where dnf 2 e(n k f) + k 2. The algorithm is subject to a comparative performance evaluation against other intrusiontolerant protocols. The results show that, as the system scales, Turquois outperforms the other protocols by more than an order of magnitude.Esta tese investiga o problema do consenso tolerante a faltas acidentais e maliciosas em redes ad hoc sem fios. Trata-se de um problema fundamental que captura a essência da coordenação em actividades envolvendo vários nós de um sistema, sendo um bloco construtor de outros importantes problemas dos sistemas distribuídos como a replicação de máquina de estados ou a difusão atómica. A tese começa por efectuar uma avaliação de desempenho a protocolos tolerantes a intrusões já existentes na literatura. Os resultados mostram que as limitações de desempenho das soluções existentes estão em parte relacionadas com o seu modelo de sistema. Baseado nestes resultados, é identificado o modelo de falhas de comunicação como um modelo que simultaneamente permite capturar o ambiente das redes ad hoc sem fios e projectar protocolos eficientes. Todavia, o modelo é restrito por um resultado de impossibilidade que afirma não existir algoritmo algum que permita a n nós chegaram a acordo num sistema que admita mais do que n2 transmissões omissas num dado passo de comunicação. Este resultado é válido mesmo sob fortes hipóteses temporais (i.e., em sistemas síncronos) A tese aplica técnicas de aleatoriedade em variantes progressivamente mais fracas do modelo até ser alcançado um protocolo eficiente e tolerante a intrusões. A primeira variante do modelo, de forma a simplificar o problema, restringe o número de nós que estão na origem de transmissões faltosas. É apresentado um algoritmo que tolera f nós dinâmicos na origem de transmissões faltosas em sistemas com um total de n 3f + 1 nós. A segunda variante do modelo não impõe quaisquer restrições no padrão de transmissões faltosas. É apresentado um algoritmo que contorna efectivamente o resultado de impossibilidade Santoro-Widmayer pela primeira vez e que permite a k de n nós efectuarem progresso nos passos de comunicação em que o número de transmissões omissas seja dn 2 e(n k) + k 2. O algoritmo possui ainda a interessante propriedade de tolerar períodos arbitrários em que o número de transmissões omissas seja superior a . A última variante do modelo partilha das mesmas características da variante anterior, mas com pressupostos mais fracos sobre o sistema. Em particular, assume-se que o sistema é assíncrono e que um subconjunto estático dos nós pode ser malicioso. O algoritmo apresentado, denominado Turquois, admite f < n 3 nós maliciosos e assegura progresso nos passos de comunicação em que dnf 2 e(n k f) + k 2. O algoritmo é sujeito a uma análise de desempenho comparativa com outros protocolos na literatura. Os resultados demonstram que, à medida que o número de nós no sistema aumenta, o desempenho do protocolo Turquois ultrapassa os restantes em mais do que uma ordem de magnitude.FC

Comparing Different Methods for Disfluency Structure Detection

This paper presents a number of experiments focusing on assessing the performance of different machine learning methods on the identification of disfluencies and their distinct structural regions over speech data. Several machine learning methods have been applied, namely Naive Bayes, Logistic Regression, Classification and Regression Trees (CARTs), J48 and Multilayer Perceptron. Our experiments show that CARTs outperform the other methods on the identification of the distinct structural disfluent regions. Reported experiments are based on audio segmentation and prosodic features, calculated from a corpus of university lectures in European Portuguese, containing about 32h of speech and about 7.7% of disfluencies. The set of features automatically extracted from the forced alignment corpus proved to be discriminant of the regions contained in the production of a disfluency. This work shows that using fully automatic prosodic features, disfluency structural regions can be reliably identified using CARTs, where the best results achieved correspond to 81.5% precision, 27.6% recall, and 41.2% F-measure. The best results concern the detection of the interregnum, followed by the detection of the interruption point

Rapid Sap Nutrient Analysis Methods in Malus Domestica Borkh Cv. ‘Gala’

Sap quick tests are well established in vegetable crops. However, there is less equivalent investigation for perennial crops, such as apple trees. Accessing the nutrient content, as opposed to the foliar analysis, would increase the opportunity of adjusting the fertilization, along the growing cycle. This work evaluates the relation between the NO3 −, K+, Ca2+, Mg2+, PO4 3- and NH4 + contents in apple petiole sap, measured with the RQflex® test strips and laboratory methods to assess the possibility of using this tool with accuracy in in-situ sap analysis. Petiole samples were collected from six apple tree orchards, frozen and pressed. Dilution was mandatory for all nutrient determination, except NO3 −. The dilution factor varied with the stage of the annual cycle. The levels of NO3 −, K+, Mg2+, and Ca2+ followed the same pattern during the growing cycle, with both methods. Regression analysis resulted in high determination coefficients for NO3 − (R2 = 0.85), K+ (R2 = 0.86), Mg2+ (R2 = 0.81) and Ca2+ (R2 = 0.95), between RQflex® and laboratory methods. No equivalent relation was found for ammonium and phosphate determination. These tests can be useful tools for rational fertilization management, mainly in high-density apple orchards. The calcium content in 45 DAFB leaves correlated well with the calcium content in sap at the same timinginfo:eu-repo/semantics/publishedVersio

A case-control study of contextual factors for SARS-CoV-2 transmission

Funding Information: This study has been partially funded by the Regional Administration of Health of Lisbon and Tagus Valley, the NOVA National School of Public Health, and National Funds through Foundation for Science and Technology, I.P., within the scope of the Epidemiology Research Unit–Institute of Public Health, University of Porto (EPIUnit) [UIDB/04750/2020]. Funding Information: The authors thank Dire??o-Geral da Sa?de and Servi?os Partilhados Minist?rio da Sa?de for data sharing, Administra??o Regional de Sa?de de Lisboa e Vale do Tejo for funding, Public Health Units in the area for informing potentially eligible cases of the study, and the participants for their valuable time. We also thank all interviewers for their perseverance, which was essential to collect these data. Publisher Copyright: © Copyright © 2021 Leite, Leão, Soares, Severo, Moniz, Lucas, Aguiar, Meireles, Lunet, Nunes and Barros.Background: Knowledge on the settings and activities associated with a higher risk of SARS-CoV-2 transmission is essential to inform decision-making. We thus designed a case-control study to identify relevant settings for community transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in Portugal. Methods: We evaluated 1,088 cases, identified through the national surveillance system, and 787 community controls, recruited using random digit dialing. Sociodemographic characteristics, individual protective measures, and activities or visited settings were obtained through telephone interview. We report sex-, age-, education-, and citizenship-adjusted odds ratios (aOR) with 95% confidence intervals (95% CI). Results: Household overcrowding (aOR = 1.47; 95% CI 1.14–1.91) and work in senior care (4.99; 1.30–33.08) increased while working remotely decreased the risk of infection (0.30; 0.22–0.42). Going to restaurants/other dining spaces (0.73; 0.59–0.91), grocery stores (0.44; 0.34–0.57) or hair salons (0.51; 0.39–0.66), or the use of public transportation did not present a higher risk of infection (0.98; 0.75–1.29), under existing mitigation strategies. Lower education (≤ 4 years vs. tertiary education: 1.79; 1.33–2.42) and no Portuguese citizenship (5.47; 3.43–9.22) were important risk factors. Conclusions: The utilization of public transportation, restaurants, and commercial spaces was not associated with increased risk of infection, under capacity restrictions, physical distancing, use of masks, and hygiene measures. Overcrowding, foreign citizenship, low education and working on-site were positively associated with SARS-CoV-2 infection.publishersversionpublishe

Antiphospholipid Syndrome Risk Evaluation

The antiphospholipid syndrome is an acquired autoimmune disorder produced by high titers of antiphospholipid antibodies that cause both arterial and veins thrombosis as well as pregnancy-related complications and morbidity, as clinical manifestations. This autoimmune hypercoagulable state, often associated with coronary artery disease and recurrent Acute Myocardium Infraction, has severe consequences for the patients, being one of the main causes of thrombotic disorders and death. Therefore, it is extremely important to be preventive; being aware of how probable is to have that kind of syndrome. Despite the updated of the APS classification published as Sydney criteria, diagnosis of this syndrome remains challenging. Further research on clinically relevant antibodies and standardization of their quantification are required to improve clinical risk assessment in APS. This work will focus on the development of a diagnosis support system to antiphospholipid syndrome, built under a formal framework based on Logic Programming, in terms of its knowledge representation and reasoning procedures, complemented with an approach to computing grounded on Artificial Neural Networks. The proposed model allowed to improve the diagnosis, classifying properly the patients that really presented this pathology (sensitivity about 92%) as well as classifying the absence of APS (specificity ranging from 89% to 94%)

Nutrient Content with Different Fertilizer Management and Influence on Yield and Fruit Quality in Apple cv. Gala

Assessing a plant’s nutritional status and fertilizer rates and types that can optimize fruit quality and yield are critical in intensive apple orchards. The aim of this work was to identify correlations between nutrients in the different organs that allow the early diagnosis of the nutritional status and to assess the impact on the optimal nutrient content in apple leaves, as well as in the yield and quality of chemical and organic fertilization. Five orchards of ‘Gala’ were fertilized with different levels of NPK over a period of four years. Macro and micronutrients of buds, flowers, 45 and 90–110 days after full bloom (DAFB) leaves and 60 DAFB and 15 days before harvest (DBH) fruits were determined. Boron was the only element for which strong correlations, 0.7 < r < 0.9, were observed between all organ pairs. The fertilization treatments did not affect the nutrient concentrations in the leaves of 90–110 DAFB other than P, Ca and Mg and did not affect the macronutrients in the fruit. In one of the five orchards, the yield increased by 26% with double fertilization compared to standard fertilization and, for the other four orchards, the impact depended on the year. Fruit size was more related to crop load than to fertilization and TSS and firmness were not affected by the type or amount of fertilizers. Replacing part of the chemical fertilizer with organic materials did not affect productivity or fruit qualityinfo:eu-repo/semantics/publishedVersio

State-machine replication for planet-scale systems

Online applications now routinely replicate their data at multiple sites around the world. In this paper we present Atlas, the first state-machine replication protocol tailored for such planet-scale systems. Atlas does not rely on a distinguished leader, so clients enjoy the same quality of service independently of their geographical locations. Furthermore, client-perceived latency improves as we add sites closer to clients. To achieve this, Atlas minimizes the size of its quorums using an observation that concurrent data center failures are rare. It also processes a high percentage of accesses in a single round trip, even when these conflict. We experimentally demonstrate that Atlas consistently outperforms state-of-The-Art protocols in planet-scale scenarios. In particular, Atlas is up to two times faster than Flexible Paxos with identical failure assumptions, and more than doubles the performance of Egalitarian Paxos in the YCSB benchmark.H2020 - Horizon 2020 Framework Programme(825184

Resilient architecture (preliminary version)

The main objectives of WP2 are to define a resilient architecture and to develop a range of middleware solutions (i.e. algorithms, protocols, services) for resilience to be applied in the design of highly available, reliable and trustworthy networking solutions. This is the first deliverable within this work package, a preliminary version of the resilient architecture. The deliverable builds on previous results from WP1, the definition of a set of applications and use cases, and provides a perspective of the middleware services that are considered fundamental to address the dependability requirements of those applications. Then it also describes the architectural organisation of these services, according to a number of factors like their purpose, their function within the communication stack or their criticality/specificity for resilience. WP2 proposes an architecture that differentiates between two classes of services, a class including timeliness and trustworthiness oracles, and a class of so called complex services. The resulting architecture is referred to as a "hybrid architecture". The hybrid architecture is motivated and discussed in this document. The services considered within each of the service classes of the hybrid architecture are described. This sets the background for the work to be carried on in the scope of tasks 2.2 and 2.3 of the work package. Finally, the deliverable also considers high-level interfacing aspects, by providing a discussion about the possibility of using existing Service Availability Forum standard interfaces within HIDENETS, in particular discussing possibly necessary extensions to those interfaces in order to accommodate specific HIDENETS services suited for ad-hoc domain