Checkpointing of parallel applications in a Grid environment

The Grid environment is generic, heterogeneous, and dynamic with lots of unreliable resources making it very exposed to failures. The environment is unreliable because it is geographically dispersed involving multiple autonomous administrative domains and it is composed of a large number of components. Examples of failures in the Grid environment can be: application crash, Grid node crash, network failures, and Grid system component failures. These types of failures can affect the execution of parallel/distributed application in the Grid environment and so, protections against these faults are crucial. Therefore, it is essential to develop efficient fault tolerant mechanisms to allow users to successfully execute Grid applications. One of the research challenges in Grid computing is to be able to develop a fault tolerant solution that will ensure Grid applications are executed reliably with minimum overhead incurred. While checkpointing is the most common method to achieve fault tolerance, there is still a lot of work to be done to improve the efficiency of the mechanism. This thesis provides an in-depth description of a novel solution for checkpointing parallel applications executed on a Grid. The checkpointing mechanism implemented allows to checkpoint an application at regions where there is no interprocess communication involved and therefore reducing the checkpointing overhead and checkpoint size

JMSGroups:JMS compliant group communication

Nowadays, computers are the indispensable part of our life. They evolve rapidly and are more and more versatile. Computer networks made the remote corners of the world just a click away. But unavoidably, any software and hardware component is subject to failure. Distributed systems spread on tens or hundreds of machines are particularly vulnerable to failures. Consequently, high availability and fault tolerance became a "must have" feature for such systems. Software fault tolerance is achieved through the technique called replication. In replication several software replicas are executed at the same time. If one or several of them fail, other still provide the service. Software replication is often implemented using group communication, which provides communication primitives with various semantics and greatly simplifies the development of highly available and fault tolerant services. However, despite tremendous advances in research and numerous prototypes, group communication stays confined to small niches and academic prototypes. In contrast, other technology, called messageoriented middleware such as the Java Message Service (JMS) is widely used in distributed systems, and has become a de-facto standard. We believe that the lack of a well-defined and easily understandable standard is the reason that hinders the deployment of group communication systems. Since JMS is a well-established technology, we propose to extend JMS adding group communication primitives to it. Foremost, this requires to extend the traditional semantics of group communication in order to take into account various features of JMS, e.g., durable/non-durable subscriptions and persistent/non-persistent messages. The resulting new group communication specification, together with the corresponding API, defines group communication primitives compatible with JMS, that we call JMSGroups. To validate the specification and API we provide a prototype implementation of JMSGroups. As such, we believe it facilitates the acceptance of group communication by a larger community and provides a powerful environment for building fault-tolerant applications

A PoW-less Bitcoin with Certified Byzantine Consensus

Distributed Ledger Technologies (DLTs), when managed by a few trusted validators, require most but not all of the machinery available in public DLTs. In this work, we explore one possible way to profit from this state of affairs. We devise a combination of a modified Practical Byzantine Fault Tolerant (PBFT) protocol and a revised Flexible Round-Optimized Schnorr Threshold Signatures (FROST) scheme, and then we inject the resulting proof-of-authority consensus algorithm into Bitcoin (chosen for the reliability, openness, and liveliness it brings in), replacing its PoW machinery. The combined protocol may operate as a modern, safe foundation for digital payment systems and Central Bank Digital Currencies (CBDC)

Evaluation of the regulatory preparedness for health threats and health crisis

Tese de mestrado, Regulação e Avaliação do Medicamento e Produtos de Saúde, 2020, Universidade de Lisboa, Faculdade de Farmácia.Num mundo global e interconectado, as doenças infeciosas de âmbito internacional são inevitáveis e imprevisíveis, atingindo as comunidades de forma devastadora. Quando ameaças de saúde pública (re)emergem, o sistema de saúde pública trabalha para mitigar seu impacto, reduzir o número de mortes e a morbilidade associada. Dentro dos sistemas de saúde pública, o sistema regulamentar tem um papel crítico na resposta a estas ameaças, com pressão para o desenvolvimento e acesso a medicamentos, vacinas e testes de diagnóstico o mais rapidamente possível. Neste contexto, é importante compreender a forma como o sistema regulamentar está preparado, como pode acelerar a avaliação e a disponibilização de soluções terapêuticas, e identificar oportunidades de melhoria. Este trabalho apresenta uma análise minuciosa do desempenho do sistema regulamentar nas recentes crises da saúde do Ébola, seguida pela identificação dos mecanismos atuais implementados pelas principais Autoridades Regulamentares e possíveis oportunidades de melhoria. O surto de 2014-2016 na África Ocidental, o maior e mais mortífero surto de Ébola até ao presente, marcou um ponto de viragem na capacidade de preparação e resposta global e regulamentar. Os esforços conjugados de vários stakeholders levaram ao desenvolvimento acelerado de vacinas e medicamentos para o Ébola, num contexto catastrófico. No entanto, este surto expôs também fraquezas na capacidade de resposta rápida e efetiva dos sistemas regulamentares às ameaças de saúde pública. Durante o surto, apenas um ensaio clínico foi capaz de reunir dados suficientes para avaliar a eficácia de uma vacina, e várias dúvidas sobre segurança, tolerabilidade ou imunogenicidade ficaram sem resposta. Como consequência, muitas lições foram discutidas e tidas em conta posteriormente, com destaque para a inclusão da investigação clínica nos planos para futuras crises de saúde e maior integração nas respostas às epidemias. Com base nessas lições, a resposta ao segundo maior surto de Ébola, dois anos depois, foi rápida, mais organizada e melhor coordenada, culminando na aprovação da primeira vacina contra o Ébola (um marco na capacidade de preparação em saúde pública). A análise da resposta aos surtos de Ébola demonstrou a implementação bem-sucedida de mecanismos regulamentares diversificados, que promoveram o desenvolvimento, o acesso antecipado e a avaliação rápida de medicamentos, vacinas e testes de diagnóstico, incluindo revisão prioritária, autorização condicional de introdução no mercado e revisões contínuas. Esta análise também mostrou a flexibilidade do sistema regulamentar, a sua capacidade de resposta e capacidade de adotar soluções inovadoras, mantendo os padrões de qualidade, segurança e eficácia. Existem algumas oportunidades de melhoria no atual quadro regulamentar, incluindo uma coordenação mais centralizada, melhor capacidade regulamentar e harmonização nos países em desenvolvimento, maior transparência e comunicação mais clara. Apesar disso, o sistema regulamentar parece capaz e adequado para lidar positivamente com atuais e futuras crises de saúde pública. Não obstante não poder impedir a sua ocorrência, pode minimizar os seus impactos e proteger a saúde global.In a globalized and highly interconnected world, infectious diseases of international concern are inevitable and unpredictable, hitting communities in devastating ways. When public health threats (re-)emerge, the public health system works towards mitigating their impact, reduce the death toll and any associated morbidity. Within it, the regulatory system has a critical role in responding to such threats, with pressure being applied to the development and access to medicinal products, vaccines and diagnostic tests as quickly as possible. In this context, it is important to understand how the regulatory system is prepared, how it can accelerate the assessment and availability of therapeutic solutions and identify possible opportunities for improvement. This work presents a thorough analysis of the regulatory system’s performance in recent Ebola health crises, followed by the identification of the current mechanisms put in place by the main Regulatory Authorities and possible opportunities for improvement. The 2014-2016 West African Outbreak, the largest and deadliest Ebola outbreak in history so far, marked a turning point in regulatory and global health preparedness. Efforts across multiple stakeholders led to the accelerated development of Ebola virus vaccines and medicinal products, in a catastrophic environment. However, this outbreak also exposed weaknesses in the worldwide regulatory systems’ capacity to respond rapidly and effectively to health threats. Only one vaccine clinical trial was able to gather enough data to assess efficacy during the outbreak, and several doubts on safety, tolerability or immunogenicity were left unanswered. Consequently, important lessons were discussed and considered thereafter, mainly the inclusion of clinical research in the plans for future health crisis and further integration in epidemic responses. Based on these lessons, the response to the second largest Ebola outbreak, two years later, was swift, more organized and better coordinated, culminating in the approval of the first vaccine against Ebola (a landmark moment in public health preparedness). The analysis of the response to the Ebola outbreaks demonstrated the successful implementation of diversified regulatory mechanisms that fostered the development, early access and expedite assessment of medicinal products, vaccines and diagnostic tests, including priority review, conditional marketing authorization and rolling reviews. It also showcased the regulatory system’s flexibility, response capacity and ability to embrace innovative solutions, while keeping the standards of quality, safety and efficacy. Some opportunities for improvement exist within the current regulatory framework, including a more centralized coordination, better regulatory capacity and harmonization in low and middle-income countries, transparency and clearer communication. Despite these, the regulatory system seems capable and adequate to positively address both current and future public health crisis. It cannot stop them from occurring, but it can minimize their impact and protect our global health

Wireless Sensor Networks

The aim of this book is to present few important issues of WSNs, from the application, design and technology points of view. The book highlights power efficient design issues related to wireless sensor networks, the existing WSN applications, and discusses the research efforts being undertaken in this field which put the reader in good pace to be able to understand more advanced research and make a contribution in this field for themselves. It is believed that this book serves as a comprehensive reference for graduate and undergraduate senior students who seek to learn latest development in wireless sensor networks

Models of higher-order, type-safe, distributed computation over autonomous persistent object stores

A remote procedure call (RPC) mechanism permits the calling of procedures in another address space. RPC is a simple but highly effective mechanism for interprocess communication and enjoys nowadays a great popularity as a tool for building distributed applications. This popularity is partly a result of their overall simplicity but also partly a consequence of more than 20 years of research in transpaxent distribution that have failed to deliver systems that meet the expectations of real-world application programmers. During the same 20 years, persistent systems have proved their suitability for building complex database applications by seamlessly integrating features traditionally found in database management systems into the programming language itself. Some research. effort has been invested on distributed persistent systems, but the outcomes commonly suffer from the same problems found with transparent distribution. In this thesis I claim that a higher-order persistent RPC is useful for building distributed persistent applications. The proposed mechanism is: realistic in the sense that it uses current technology and tolerates partial failures; understandable by application programmers; and general to support the development of many classes of distributed persistent applications. In order to demonstrate the validity of these claims, I propose and have implemented three models for distributed higher-order computation over autonomous persistent stores. Each model has successively exposed new problems which have then been overcome by the next model. Together, the three models provide a general yet simple higher-order persistent RPC that is able to operate in realistic environments with partial failures. The real strength of this thesis is the demonstration of realism and simplicity. A higherorder persistent RPC was not only implemented but also used by programmers without experience of programming distributed applications. Furthermore, a distributed persistent application has been built using these models which would not have been feasible with a traditional (non-persistent) programming language