Repositório Institucional da Universidade de Aveiro
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Cooperation metric for IEEE 802.11 wireless networks
No full textA key design issue in relay based cooperative wireless networks is the design of an appropriate metric for relay selection algorithms. In most cooperative protocols designed for IEEE 802.11 networks, the relay selection metric is based on reducing the transmission delay of relay links. The bandwidth efficiency provided by this metric is beneficial for applications communicating at high data rate, however not all applications will benefit from this simple approach. In this paper, a novel cooperative metric is proposed, which in addition to bandwidth, also considers link reliability and link stability, especially useful in mobile scenarios, and for time sensitive service applications. The proposed metric is applied to the well-known CoopMAC protocol. Simulation results indicate a strong correlation between network performance and proposed cooperative metric
A self-organizing and self-configuration algorithm for resource management in service-oriented systems
No full textWith the ever increasing deployment of service-oriented distributed systems in large-scale and heterogeneous computing environments, clustering and communication overlay topology design has become more and more important to address several challenging issues and conflicting requirements, such as efficient scheduling and distribution of services among computing resources, reducing communication cost between services, high performance service and resource discovery while considering both inter-service and inter-node properties and also increasing the load distribution and the load balance. In this paper, a four-stage hierarchical clustering algorithm is proposed which automates the process of the optimally composing communicating groups in a dynamic way while preserving the proximity of the nodes. The simulation results show the performance of the algorithm with respect to load balance, scalability and efficiency
Interference-aware opportunistic relay selection
No full textRecently, cooperative relaying techniques have been investigated to increase the performance of wireless systems by using diversity created by different single antenna devices. With the introduction of cooperative relaying, relay selection requires special attention, since it has a strong impact on transmission performance. Moreover, cooperation procedures may be very unstable when relay selection relies on current channel conditions and is agnostic of interference induced by simultaneous transmissions. As a result, the performance of cooperative relaying in realistic scenarios may be very different from interference-free scenarios that have been the focus of most of the existing proposals so far. © 2011 Authors
Fast VPN mobility across Wi-Fi hotspots
Get PDFWi-Fi hotspots deployed by domestic networks are an attractive approach to foster ubiquitous Internet access for mobile computers. However, it raises several security issues, since the owners of such hotspots cannot be trusted to be honest; therefore, visitors should consider them as potential Man-in-the-Middle attackers. On the other hand, the owners of such hotspots should not be legally accounted for illegal or unethical activities performed by visitors. We defend that both issues can be tackled by using a VPN-based access architecture for visitors. However, current VPN solutions do not handle gracefully the mobility of clients, an interesting possibility to navigate in a sea of user-provided hotspots. In this paper, we propose a modification of OpenVPN, a very effective and secure, open-source VPN solution, to support the seamless mobility of VPN clients. The proposed modification allows OpenVPN tunnels to be reconfigured as soon as possible after a client handover, in order to minimize outage delays and traffic losses. Performance evaluation with an implemented prototype in different test scenarios showed that we can reduce the handover delay imposed at the VPN level down to 1.7% of the current value, at least
Verifiable anonymous vote submission
No full textThis paper describes a new architecture for supporting the anonymous submission of votes in the REVS voting system. Furthermore, it enables voters to verify during the election that the electoral system processed correctly their anonymously submitted vote. This verification is a weak proof that the vote was effectively considered in the final tally. But since malicious electoral servers have no means to choose which votes should not be considered in the tally, the weak proof is strong enough for ensuring voters that the outcome of the election was not manipulated by the servers towards a particular outcome. In spite have been conceived for the REVS system, our anonymizing architecture can be used in other voting systems as well. The only requirement is that it should be possible to submit the same vote several times and to detect and drop vote replicas at the tallying phase, which is valid for other blind signature voting protocols
Portuguese nurses’ knowledge of and attitudes toward hospitalized older adults
No full textPortugal is impacted by the rapid growth of the aging population, which has significant implications for its health care system. However, nurses have received little education focusing on the unique and complex care needs of older adults. This gap in the nurses′ education has an enormous impact in their knowledge and attitudes and affects the quality of nursing care provided to older adults. A cross-sectional study was conducted among 1068 Portuguese nurses in five hospitals (northern and central region) with the following purposes: (i) explore the knowledge and attitudes of nurses about four common geriatric syndromes (pressure ulcer, incontinence, restraint use and sleep disturbance) in Portuguese hospitals; and (ii) evaluate the influence of demographic, professional and nurses' perception about hospital educational support, geriatric knowledge, and burden of caring for older adults upon geriatric nursing knowledge and attitudes. The mean knowledge and attitudes scores were 0.41 ± 0.15 and 0.40 ± 0.21, respectively (the maximum score was 1). Knowledge of nurses in Portuguese hospitals about the four geriatric syndromes (pressure ulcers, sleep disturbance, urinary incontinence and restraint use) was found inadequate. The nurses' attitudes towards caring for hospitalized older adults were generally negative. Nurses who work in academic hospitals demonstrated significantly more knowledge than nurses in hospital centers. The attitudes of nurses were significantly associated with the hospital and unit type, region, hospital educational support, staff knowledge, and perceived burden of caring for older adults. The study findings support the need for improving nurses' knowledge and attitudes towards hospitalized older adults and implementing evidence-based guidelines in their practice
A simplex like approach based on star sets for recognizing convex-QP adverse graphs
No full textA graph G with convex-QP stability number (or simply a convex-QP graph) is a graph for which the stability number is equal to the optimal value of a convex quadratic program, say P(G). There are polynomial-time procedures to recognize convex-QP graphs, except when the graph G is adverse or contains an adverse subgraph (that is, a non complete graph, without isolated vertices, such that the least eigenvalue of its adjacency matrix and the optimal value of P(G) are both integer and none of them changes when the neighborhood of any vertex of G is deleted). In this paper, from a characterization of convex-QP graphs based on star sets associated to the least eigenvalue of its adjacency matrix, a simplex-like algorithm for the recognition of convex-QP adverse graphs is introduced
U–Pb zircon geochronology, petrochemical and Sr–Nd isotopic characteristic of Late Neoproterozoic granitoids of the Bornaward Complex (Bardaskan-NE Iran)
No full textThe Bornaward Granitoid Complex (BGC) in the Taknar Zone is located in the northeast of Central Iranian Block. The BGC consists of granite, alkaligranite, syenogranite, leucogranite, granophyre, monzogranite, granodiorite, tonalite and diorite that have intruded into the center of Taknar Zone. These intrusive rocks affected by low grade metamorphism. Because of there are no reliable isotope dating data, for the Bornaward Granitoid Complex rocks have been proposed discordant ages (Jurassic, Cretaceous or even younger ages) by many studies. In the present study, new isotopic information based on zircon U–Pb dating has revealed the origin and time of the formation of the BGC. These new results do not confirm previously proposed ages. The results obtained from zircon U–Pb dating of the BGC rocks suggest late-Neoproterozoic (Precambrian) age (540–550 Ma). The Bornaward Granitoid Complex is middle-high metaluminous to lower-middle peraluminous and belongs to tholeiite, calc-alkaline to high-K calc-alkaline rock series with enrichment in LIL (Cs, Rb and Ba, U, K, Zr, Y, Th) and depletion in HIL (Sr and Nb, Ta, Ti) elements. Chondrite-normalized Rare Earth Elements (REE) plots indicate minor enrichment of LREE compared to HREE, and strong negative anomaly of Eu compared to other Rare Earth Elements. Furthermore, initial 87Sr/86Sr and 143Nd/144Nd range from 0.70351 to 0.71689 and 0.511585 to 0.512061, respectively, and initial εNd isotope values for granite, granodiorite and diorite range from −6.73 to 2.52. These all indicate that the BGC has derived from partial melting of distinct basement source regions with very high initial 87Sr/86Sr and undergoing extensive crustal contamination (S-type granite)
Computing Hadamard type operators of variable fractional order
No full textWe consider Hadamard fractional derivatives and integrals of variable fractional order. A new type of fractional operator, which we call the Hadamard-Marchaud fractional derivative, is also considered. The objective is to represent these operators as series of terms involving integer-order derivatives only, and then approximate the fractional operators by a finite sum. An upper bound formula for the error is provided. We exemplify our method by applying the proposed numerical procedure to the solution of a fractional differential equation and a fractional variational problem with dependence on the Hadamard-Marchaud fractional derivative
Prediction of Gestational Diabetes through NMR Metabolomics of Maternal Blood
No full textMetabolic biomarkers of pre- and postdiagnosis gestational diabetes mellitus (GDM) were sought, using nuclear magnetic resonance (NMR) metabolomics of maternal plasma and corresponding lipid extracts. Metabolite differences between controls and disease were identified through multivariate analysis of variable selected 1H NMR spectra. For postdiagnosis GDM, partial least squares regression identified metabolites with higher dependence on normal gestational age evolution. Variable selection of NMR spectra produced good classification models for both pre- and postdiagnostic GDM. Prediagnosis GDM was accompanied by cholesterol increase and minor increases in lipoproteins (plasma), fatty acids, and triglycerides (extracts). Small metabolite changes comprised variations in glucose (up regulated), amino acids, betaine, urea, creatine, and metabolites related to gut microflora. Most changes were enhanced upon GDM diagnosis, in addition to newly observed changes in low-Mw compounds. GDM prediction seems possible e..