Algorithms and Implementation

In the past few years Tabling has emerged as a powerful logic programming model. The integration of concurrent features into the implementation of Tabling systems is demanded by need to use recently developed tabling applications within distributed systems, where a process has to respond concurrently to several requests. The support for sharing of tables among the concurrent threads of a Tabling process is a desirable feature, to allow one of Tabling’s virtues, the re-use of computations by other threads and to allow efficient usage of available memory. However, the incremental completion of tables which are evaluated concurrently is not a trivial problem. In this dissertation we describe the integration of concurrency mechanisms, by the way of multi-threading, in a state of the art Tabling and Prolog system, XSB. We begin by reviewing the main concepts for a formal description of tabled computations, called SLG resolution and for the implementation of Tabling under the SLG-WAM, the abstract machine supported by XSB. We describe the different scheduling strategies provided by XSB and introduce some new properties of local scheduling, a scheduling strategy for SLG resolution. We proceed to describe our implementation work by describing the process of integrating multi-threading in a Prolog system supporting Tabling, without addressing the problem of shared tables. We describe the trade-offs and implementation decisions involved. We then describe an optimistic algorithm for the concurrent sharing of completed tables, Shared Completed Tables, which allows the sharing of tables without incurring in deadlocks, under local scheduling. This method relies on the execution properties of local scheduling and includes full support for negation. We provide a theoretical framework and discuss the implementation’s correctness and complexity. After that, we describe amethod for the sharing of tables among threads that allows parallelism in the computation of inter-dependent subgoals, which we name Concurrent Completion. We informally argue for the correctness of Concurrent Completion. We give detailed performance measurements of the multi-threaded XSB systems over a variety of machines and operating systems, for both the Shared Completed Tables and the Concurrent Completion implementations. We focus our measurements inthe overhead over the sequential engine and the scalability of the system. We finish with a comparison of XSB with other multi-threaded Prolog systems and we compare our approach to concurrent tabling with parallel and distributed methods for the evaluation of tabling. Finally, we identify future research directions

Sobre as Forças

[Extrato] Em dinâmica de sistemas mecânicos é por demais importante saber identificar os diversos tipos de forças que atuam nos corpos. De uma forma geral, pode definir-se força como sendo uma grandeza física que representa a medida quantitativa da interação dos corpos que constituem as máquinas e mecanismos. Como é sabido, em dinâmica de sistemas mecânicos, as forças tendem a modificar o estado de movimento (ou repouso) dos corpos materiais (...)

Sobre o carro analisado

Este documento contém uma análise descritiva do carro analisado no âmbito da unidade curricular Integradora II

Sobre o desempenho do carro

Este documento contém os procedimentos fundamentais para efetuar o desempenho do carro analisado no âmbito da unidade curricular Integradora II

The old municipal chambers building: damaged but nor destroyed : will it be there in another 125 years?

The Old Municipal Chambers is a Category I heritage building situated in Worcester Street, Christchurch. It was designed by architect Samuel Hurst Seager in the Queen Anne Arts and Crafts Style and was opened in 1887. The two storey building is constructed in solid brick and incorporates several decorative features, and it is an important part of the cultural heritage fabric of Christchurch. Some securing works were undertaken in 1989 to improve its performance under seismic loads. This paper will outline damage during the earthquake on 4 September 2010, subsequent aftershocks and the 22 February 2011 earthquake which resulted in some localised zones of collapse. The structure of the building has been stabilised externally, to secure or allow retrieval of very significant heritage features. The high cost to repair the building makes the future of the building uncertain despite its very significant heritage value.In response to the building’s seismic vulnerability and possible retrofitting, finite element and simplified equivalent frame models were used for pushover analysis, enabling a complementary seismic evaluation from both approaches. The predictions identify the weak parts of the building and its expected failure modes, which are in agreement with the observed damage. The computations appear conservative, because the computed capacity curves provide insufficient capacity of the building to survive the recorded earthquakes. Given that there was uncertainty on the constitution of the floors, they were assumed as unidirectional by default, bidirectional diaphragm floors were also simulated in the simplified model, reflecting the securing works undertaken in 1990. In this case, a significantly better behaviour is observed. This paper will examine the seismic performance of the building, comparing results of analysis including both in-plane and out-of-plane behaviour, with actual damage. It will then consider conceptual scenarios for the future of the building, including comparison of performance and cost of both conventional and base isolation retrofit

Study of the seismic behavior of the “Old Municipal Chambers” building in Christchurch, New Zealand

This paper presents a study of the seismic behavior of the “Old Municipal Chambers” building in Christchurch, which was damaged by earthquakes in 2010 and 2011. In view of its seismic vulnerability and retrofitting, finite element and equivalent frame models were used for pushover analysis. Predictions allow identifying the weak parts of the building and its expected failure modes, which are in agreement with the observed damage. Computations seem however conservative, because the building capacity curves provide insufficient strength to survive the registered earthquakes. By considering the floors as bidirectional diaphragms in the simplified model, a better behavior is observed.The authors gratefully acknowledge Professor Jason Ingham and his research group at University of Auckland for providing experimental data in Christchurch and their recommendations on materials properties to be expected. The two first authors acknowledge the financial support from the Portuguese Foundation for Science and Technology (FCT) through Ph.D. grants SFRH/BD/41221/2007 and SFRH/BD/45436/2008

A systematic review and bibliometric analysis of wildland fire behavior modeling

Wildland fires have become a major research subject among the national and international research community. Different simulation models have been developed to prevent this phenomenon. Nevertheless, fire propagation models are, until now, challenging due to the complexity of physics and chemistry, high computational requirements to solve physical models, and the difficulty defining the input parameters. Nevertheless, researchers have made immense progress in understanding wildland fire spread. This work reviews the state-of-the-art and lessons learned from the relevant literature to drive further advancement and provide the scientific community with a comprehensive summary of the main developments. The major findings or general research-based trends were related to the advancement of technology and computational resources, as well as advances in the physical interpretation of the acceleration of wildfires. Although wildfires result from the interaction between fundamental processes that govern the combustion at the solid- and gas-phase, the subsequent heat transfer and ignition of adjacent fuels are still not fully resolved at a large scale. However, there are some research gaps and emerging trends within this issue that should be given more attention in future investigations. Hence, in view of further improvements in wildfire modeling, increases in computational resources will allow upscaling of physical models, and technological advancements are being developed to provide near real-time predictive fire behavior modeling. Thus, the development of two-way coupled models with weather prediction and fire propagation models is the main direction of future work.This work was supported by the Portuguese Foundation for Science and Technology (FCT) within the R&D Units Project Scope UIDB/00319/2020 (ALGORITMI) and R&D Units Project Scope UIDP/04077/2020 (METRICS) and through project: PCIF/GRF/0141/2019: “O3F—An Optimization Framework to reduce Forest Fire

Dermatologists' attitude towards psoriasis treatment during the COVID-19 pandemic

Publisher Copyright: Copyright © 2021 Torres T, Pereira M, Paiva Lopes MJ, Rebelo C, Pedro Andrade P, Henrique M, Oliveira H, Ferreira P, Marques Pinto G, Menezes Brandão F, Rozeira J, Filipe P, Tavares Bello R. Copyright: Copyright 2021 Elsevier B.V., All rights reserved.Background: The COVID-19 pandemic introduced new challenges in several dimensions in healthcare services. Herein, we describe the real-life strategies and therapeutic options adopted by dermatologists regarding their patients with psoriasis being treated with or with an indication for systemic therapy during the first COVID-19 lockdown period in Portugal. Methods: The study involves a web-based survey on the clinical management of systemic therapy for psoriasis during the COVID-19 pandemic administered to Portuguese dermatologists. The survey consisted of 55 questions (4 openended questions; 51 closed-ended questions), grouped into 6 sections. Results: A total of 60 dermatologists voluntarily participated in this survey. Nearly 63% of the participants opted for suspending biologics during the COVID-19 lockdown period and 23.3% increased the time between drug administrations. Eighty percent of the participants agreed that biologics did not change the probability of acquiring COVID-19 and 58.4% believed that these drugs decreased or did not change the severity of the disease. Approximately one-third of the participants opted not to prescribe a biological agent in patients despite clinical indication over the duration of the pandemic. Nearly 25% of the participants opted for suspending traditional immunosuppressant administration. Virtual appointments were an option for 93.3% of the participants. Conclusion: The COVID-19 pandemic has significantly affected the management of patients with psoriasis being treated with or with an indication for systemic therapy. Some of the decisions made during the first lockdown period were contrary to what we know today. These decisions might have had a significant impact on patients' quality of life and on future therapeutic success. An adequate interpretation and analysis of the available data will be extremely important to an insightful adaptation of the clinical practice in future confinement or restrictive scenarios.publishersversionpublishe

Portugal e a defesa europeia

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A política comum de segurança e defesa e o Conselho Europeu de Dezembro de 2013

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