Browsing by Author "Ferreira, Paulo"
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- Controlo da qualidade dosimétrico no serviço de radioterapia do Hospital CUF Descobertas (HCD): importância do controlo da qualidade do sector da física e resultados da auditoria ESTRO-EQUALPublication . Jacob, Katia; Rosa, Maria João; Ferreira, Paulo; Oliveira, Susana; Sousa, Mónica; Fernandes, Paulo; Parafita, R.; Teixeira, Nuno; Ramalho, Miguel; Rodrigues, RuiA calibração e o controlo da qualidade de um acelerador linear são passos muito importantes num serviço de Radioterapia, para garantir a qualidade dos tratamentos prestados. O sector da Física da Unidade de Radioterapia do Hospital Cuf Descobertas implementou um rigoroso Programa de controlo de qualidade ao equipamento produtor de radiação e aos equipamentos medidores de radiação, de acordo com o Dec-Lei 180/2002 e com os protocolos internacionais. Para tal, foram implementados procedimentos, criadas folhas de cálculo, instruções de trabalho e impressos. Foram ainda implementados testes aos equipamentos com periodicidade definida: controlo de qualidade diário e controlo de qualidade após intervenções (manutenções preventivas e correctivas). No decorrer do ano de 2005, o sector da Física colaborou activamente com toda a equipa da Radioterapia na implementação da Norma ISO 9001:2000 no serviço, contribuindo com o seu know how na implementação desta, numa área tão importante como a da garantia da qualidade dos feixes de radiação e das respectivas calibrações em dose. Numa procura de melhoria contínua da qualidade dos serviços prestados aos pacientes, decorre ainda uma auditoria externa da EQUAL-ESTRO*, intercomparação postal com dosímetros termoluminescentes. A qualidade dos feixes de energias utilizados diariamente é analisada, tanto ao nível das calibrações absolutas de cada um dos feixes de fotões e de electrões, como ao nível dos cálculos de dose obtidos com o sistema de planimetria XiO da CMS. Os resultados das duas primeiras fases da intercomparação, relativa aos dois feixes de fotões de 6 MV e 15 MV e feixes de electrões de 4 MeV, 8 MeV e 12 MeV, foram considerados pela EQUAL-ESTRO num nível óptimo (desvio máximo na dose medida em relação à dose de referência |d| ≤ 3%).
- EVIV: An end-to-end verifiable Internet voting systemPublication . Joaquim, Rui; Ferreira, Paulo; Ribeiro, CarlosTraditionally, a country's electoral system requires the voter to vote at a specific day and place, which conflicts with the mobility usually seen in modern live styles. Thus, the widespread of Internet (mobile) broadband access can be seen as an opportunity to deal with this mobility problem, i.e. the adoption of an Internet voting system can make the live of voter's much more convenient; however, a widespread Internet voting systems adoption relies on the ability to develop trustworthy systems, i.e. systems that are verifiable and preserve the voter's privacy. Building such a system is still an open research problem. Our contribution is a new Internet voting system: EVIV, a highly sound End-to-end Verifiable Internet Voting system, which offers full voter's mobility and preserves the voter's privacy from the vote casting PC even if the voter votes from a public PC, such as a PC at a cybercafe or at a public library. Additionally, EVIV has private vote verification mechanisms, in which the voter just has to perform a simple match of two small strings (4-5 alphanumeric characters), that detect and protect against vote manipulations both at the insecure vote client platform and at the election server side. (c) 2012 Elsevier Ltd. All rights reserved.
- Grid structure impact in sparse point representation of derivativesPublication . Domingues, Margarete O.; Ferreira, Paulo; Gomes, Sónia M.; Gomide, Anamaria; Pereira, José R.; Pinho, PedroIn the Sparse Point Representation (SPR) method the principle is to retain the function data indicated by significant interpolatory wavelet coefficients, which are defined as interpolation errors by means of an interpolating subdivision scheme. Typically, a SPR grid is coarse in smooth regions, and refined close to irregularities. Furthermore, the computation of partial derivatives of a function from the information of its SPR content is performed in two steps. The first one is a refinement procedure to extend the SPR by the inclusion of new interpolated point values in a security zone. Then, for points in the refined grid, such derivatives are approximated by uniform finite differences, using a step size proportional to each point local scale. If required neighboring stencils are not present in the grid, the corresponding missing point values are approximated from coarser scales using the interpolating subdivision scheme. Using the cubic interpolation subdivision scheme, we demonstrate that such adaptive finite differences can be formulated in terms of a collocation scheme based on the wavelet expansion associated to the SPR. For this purpose, we prove some results concerning the local behavior of such wavelet reconstruction operators, which stand for SPR grids having appropriate structures. This statement implies that the adaptive finite difference scheme and the one using the step size of the finest level produce the same result at SPR grid points. Consequently, in addition to the refinement strategy, our analysis indicates that some care must be taken concerning the grid structure, in order to keep the truncation error under a certain accuracy limit. Illustrating results are presented for 2D Maxwell's equation numerical solutions.
- Improving remote voting security with code votingPublication . Joaquim, Rui; Ribeiro, Carlos; Ferreira, PauloOne of the major problems that prevents the spread of elections with the possibility of remote voting over electronic networks, also called Internet Voting, is the use of unreliable client platforms, such as the voter's computer and the Internet infrastructure connecting it to the election server. A computer connected to the Internet is exposed to viruses, worms, Trojans, spyware, malware and other threats that can compromise the election's integrity. For instance, it is possible to write a virus that changes the voter's vote to a predetermined vote on election's day. Another possible attack is the creation of a fake election web site where the voter uses a malicious vote program on the web site that manipulates the voter's vote (phishing/pharming attack). Such attacks may not disturb the election protocol, therefore can remain undetected in the eyes of the election auditors. We propose the use of Code Voting to overcome insecurity of the client platform. Code Voting consists in creating a secure communication channel to communicate the voter's vote between the voter and a trusted component attached to the voter's computer. Consequently, no one controlling the voter's computer can change the his/her's vote. The trusted component can then process the vote according to a cryptographic voting protocol to enable cryptographic verification at the server's side.
- Locality-aware GC optimisations for big data workloadsPublication . Patrício, Duarte; Bruno, Rodrigo; Simão, José; Ferreira, Paulo; Veiga, LuísMany Big Data analytics and IoT scenarios rely on fast and non-relational storage (NoSQL) to help processing massive amounts of data. In addition, managed runtimes (e.g. JVM) are now widely used to support the execution of these NoSQL storage solutions, particularly when dealing with Big Data key-value store-driven applications. The benefits of such runtimes can however be limited by automatic memory management, i.e., Garbage Collection (GC), which does not consider object locality, resulting in objects that point to each other being dispersed in memory. In the long run this may break the service-level of applications due to extra page faults and degradation of locality on system-level memory caches. We propose, LAG1 (short for Locality-Aware G1), na extension of modern heap layouts to promote locality between groups of related objects. This is done with no previous application profiling and in a way that is transparent to the programmer, without requiring changes to existing code. The heap layout and algorithmic extensions are implemented on top of the Garbage First (G1) garbage collector (the new by-default collector) of the HotSpot JVM. Using the YCSB benchmarking tool to benchmark HBase, a well-known and widely used Big Data application, we show negligible overhead in frequent operations such as the allocation of new objects, and significant improvements when accessing data, supported by higher hits in system-level memory structures.
- Runtime object lifetime profiler for latency sensitive big data applicationsPublication . Rodrigo, Bruno; Patrício, Duarte; Simão, José; Veiga, Luís; Ferreira, PauloLatency sensitive services such as credit-card fraud detection and website targeted advertisement rely on Big Data platforms which run on top of memory managed runtimes, such as the Java Virtual Machine (JVM). These platforms, however, suffer from unpredictable and unacceptably high pause times due to inadequate memory management decisions (e.g., allocating objects with very different lifetimes next to each other, resulting in severe memory fragmentation). This leads to frequent and long application pause times, breaking Service Level Agreements (SLAs). This problem has been previously identified, and results show that current memory management techniques are ill-suited for applications that hold in memory massive amounts of long-lived objects (which is the case for a wide spectrum of Big Data applications). Previous works reduce such application pauses by allocating objects in off-heap, in special allocation regions/generations, or by using ultra-low latency Garbage Collectors (GC). However, all these solutions either require a combination of programmer effort and knowledge, source code access, offline profiling (with clear negative impacts on programmer's productivity), or impose a significant impact on application throughput and/or memory to reduce application pauses. We propose ROLP, a Runtime Object Lifetime Profiler that profiles application code at runtime and helps pretenuring GC algorithms allocating objects with similar lifetimes close to each other so that the overall fragmentation, GC effort, and application pauses are reduced. ROLP is implemented for the OpenJDK 8 and was evaluated with a recently proposed open-source pretenuring collector (NG2C). Results show long tail latencies reductions of up to 51% for Lucene, 85% for GraphChi, and 69% for Cassandra. This is achieved with negligible throughput (< 6%) and memory overhead, with no programmer effort, and no source code access.