Browsing by Issue Date, starting with "2013-03"
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- Predicting progression of mild cognitive impairment to dementia using neuropsychological data: a supervised learning approach using time windowsPublication . Pereira, Telma; Lemos, Luis; Cardoso, Sandra; Silva, Dina; Rodrigues, Ana; Santana, Isabel; de Mendonca, Alexandre; Guerreiro, Manuela; Madeira, Sara C.Background: Predicting progression from a stage of Mild Cognitive Impairment to dementia is a major pursuit in current research. It is broadly accepted that cognition declines with a continuum between MCI and dementia. As such, cohorts of MCI patients are usually heterogeneous, containing patients at different stages of the neurodegenerative process. This hampers the prognostic task. Nevertheless, when learning prognostic models, most studies use the entire cohort of MCI patients regardless of their disease stages. In this paper, we propose a Time Windows approach to predict conversion to dementia, learning with patients stratified using time windows, thus fine-tuning the prognosis regarding the time to conversion. Methods: In the proposed Time Windows approach, we grouped patients based on the clinical information of whether they converted (converter MCI) or remained MCI (stable MCI) within a specific time window. We tested time windows of 2, 3, 4 and 5 years. We developed a prognostic model for each time window using clinical and neuropsychological data and compared this approach with the commonly used in the literature, where all patients are used to learn the models, named as First Last approach. This enables to move from the traditional question "Will a MCI patient convert to dementia somewhere in the future" to the question "Will a MCI patient convert to dementia in a specific time window". Results: The proposed Time Windows approach outperformed the First Last approach. The results showed that we can predict conversion to dementia as early as 5 years before the event with an AUC of 0.88 in the cross-validation set and 0.76 in an independent validation set. Conclusions: Prognostic models using time windows have higher performance when predicting progression from MCI to dementia, when compared to the prognostic approach commonly used in the literature. Furthermore, the proposed Time Windows approach is more relevant from a clinical point of view, predicting conversion within a temporal interval rather than sometime in the future and allowing clinicians to timely adjust treatments and clinical appointments.
- The influence of coastal processes on inner shelf sediment distribution: The Eastern Algarve Shelf (Southern Portugal)Publication . Rosa, F.; Rufino, M. M.; Ferreira, O.; Matias, Ana; Brito, Ana C.; Gaspar, MiguelThis study examines sediment distribution patterns in the Southeastern Algarve inner shelf (southern Portugal), an area characterized by marked variations in its coastal environment and low continental supply of sediments. The specific goals of this study were to identify the principal sediment sources and the factors influencing sediment transport paths and deposition. A total of 199 samples, collected along the shelf from the Guadiana River mouth to Olhos de Agua, were analyzed. Grain-size distribution and parameters were measured for all the samples. Terrigenous and biogenic components of sand were identified in 38 samples, and results analyzed using multivariate non-linear multidimension scaling (MDS) and cluster analysis. Patterns of sediment distribution in this area of the inner shelf vary according to water depth and exhibit significant longshore variation, related mainly to coastal processes (littoral drift and storm currents) and to a lower degree to sediment sources. Sand is dominant at all depths, reflecting the influence of littoral drift in the supply and redistribution of shelf sediments. Fine and gravel-sized deposits are significant in specific areas and are usually associated with changes in sediment composition. Five sectors have been identified according to sedimentary dynamics. The results, based on geostatistical and multivariate analysis, have allowed detailed sediment distribution maps to be generated, which represent an update of the existing cartography and serve as a tool for the management of coastal and marine resources. They have been furthermore compared with inner shelf sediment dynamics in other regions worldwide, to distinguish between specific regional responses to forcing mechanisms and processes that are more generalized within this type of shelf environments. In this context, the results obtained results in the Algarve study area are of great interest for the understanding of sediment dynamics of sand dominated inner shelves with reduced continental supply.
- Advantages, limitations, and solutions in the use of ERP systems: a case study in the hospitality industryPublication . Azevedo, Paula Serdeira; Romão, Mário; Rebelo, EfigénioEnterprise Resource Planning (ERP) systems have emerged as solutions oriented to manage organizations’ resources in an integrated way. They allow the automation of department activities, make information available to users at the right time, and support more accurately their decision-making needs. However, although the implementation of these systems has brought considerable benefits to users, they do not cover all processes from all industries. Many organizations have recognized this limitation and consequently felt the need to implement specific solutions to their industry, sector, or line of business. From the collected case study business drivers and objectives, the authors analyze the advantages and limitations of ERP Systems in the hospitality industry in order to understand how this industry uses ERP Systems and solves the challenge of integrating information spread through several heterogeneous information systems.
- How small and medium enterprises are using social networks? Evidence from the Algarve regionPublication . Belo, Ana; Castela, Guilherme; Fernandes, Silvia BritoThe evolution of internet created new opportunities for small and medium enterprises (SME), among which are social networks. This work aims at analyzing the potential of these networks for the SME in Algarve, creating a questionnaire for the purpose. The empirical study revealed that some firms have already an integrated business strategy with social networks, as well as a group in the firm responsible for it. Most of their managers consider that social networks enhance performance, but few really measure these results. A categorical principal component analysis identified two dimensions of social networks’ use: social networks for product-client interaction and knowledge; and social networks with potential for marketing. A supplementary analysis (hierarchical clustering) identified three patterns of SME’s involvement in social networks: cluster Social Net Level 1, cluster Social Net Level 2 and cluster Social Net Level 3. These groups validated the results described above, indicating a sustainable methodological approach.
- Sensing hydration and behavior of pyrene in POPC and POPC/cholesterol bilayers: A molecular dynamics studyPublication . Loura, Luís M. S.; Martins do Canto, Antonio M. T.; Martins, JorgeMolecular dynamics (MD) simulations of bilayers of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) with varying amounts of cholesterol (0, 5, 20, and 40 mol%) were carried out in the absence and presence of inserted pyrene molecules. Both fluorophore and bilayer parameters were computed, for characterization of probe location and dynamics, as well as its effects on the host bilayer. In agreement with previous studies in fluid disordered bilayers, pyrene prefers to be located in the hydrophobic acyl chain region of POPC bilayers, close to the glycerol group of lipid molecules and causes ordering of the lipid acyl chains. However, incorporation of pyrene in binary POPC/cholesterol bilayers decreases the acyl chain order parameter (especially near the end of the chains), opposing the ordering effect of cholesterol. These effects are modest and mainly felt locally. Significantly, as the bilayer is enriched with cholesterol, the relative position of pyrene and the POPC carbonyl and phosphocholine groups is invariant, and the local water density around the probe decreases. This work clarifies and supports the cautious use of pyrene Ham effect to effectively measure equivalent polarity in lipid bilayers. Within the time scale of the MD simulations, which is of the magnitude of the fluorescence lifetime of pyrene, the thermally averaged polarity of lipid bilayers is nearly out of influence of spurious uncertainty in the transverse location of pyrene in the bilayers. This renders the values of equivalent polarity measurements through the pyrene Ham effect more reliable and reproducible than previously expected. (C) 2012 Elsevier B.V. All rights reserved.
- Plasmodium falciparum drug resistance phenotype as assessed by patient antimalarial drug levels and Its association With pfmdr1 polymorphismsPublication . Malmberg, Maja; Ferreira, Pedro; Tarning, Joel; Ursing, Johan; Ngasala, Billy; Bjorkman, Anders; Martensson, Andreas; Gil, José PedroBackground. Multidrug-resistant Plasmodium falciparum is a major threat to global malaria control. Parasites develop resistance by gradually acquiring genetic polymorphisms that decrease drug susceptibility. The aim of this study was to investigate the extent to which parasites with different genetic characteristics are able to withstand individual drug blood concentrations. Methods. We analyzed 2 clinical trials that assessed the efficacy and effectiveness of artemether-lumefantrine. As a proof of concept, we used measured day 7 lumefantrine concentrations to estimate the concentrations at which reinfections multiplied. P. falciparum multidrug resistance gene 1 (pfmdr1) genotypes of these parasites were then correlated to drug susceptibility. Results. Reinfecting parasites with the pfmdr1 N86/184F/D1246 haplotype were able to withstand lumefantrine blood concentrations 15-fold higher than those with the 86Y/Y184/1246Y haplotype. Conclusions. By estimating drug concentrations, we were able to quantify the contribution of pfmdr1 single-nucleotide polymorphisms to reduced lumefantrine susceptibility. The method can be applied to all long-half-life antimalarial drugs, enables early detection of P. falciparum with reduced drug susceptibility in vivo, and represents a novel way for unveiling molecular markers of antimalarial drug resistance.
- Transdisciplinary conceptual modeling of a social-ecological system: a case study application in Terceira Island, AzoresPublication . Guimarães, Maria Helena; Ballé-Béganton, Johanna; Bailly, Denis; Newton, Alice; Boski, T.; Dentinho, TomazScience and policy integration towards natural resource management is not novel; however it has not always been successful. Partially, this failure is explained by the lack of consideration of different forms of knowledge. In order to incorporate the diversity of knowledge, transdisciplinary has been proposed and, this paper tests conceptual modeling as a tool to promote it. Qualitative modeling is an intermediate step of Systems Approach Framework (SAF) that is a methodology towards the sustainability of social-ecological systems. SAF has been applied in Praia da Vitoria Bay, in the Azores to analyze the future use of wetlands. We promoted a workshop bringing together 18 stakeholders: scientists, managers, private sectors and Non-Governmental Organizations. This paper presents the procedures and discusses the observed interaction between participants, their views and, how the wetlands services were described. Results show that non-scientists found the exercise particularly challenging but with high value due to: the systemic view and, opportunity of sharing viewpoints. The wetlands were mostly described by the direct benefits. The results show that transdisciplinarity can be operationalized and that conceptual modeling is an adequate exercise to achieve it. However, interdisciplinary work and stakeholders' analysis are also necessary because the knowledge gathered is different.
- Electrostatic repulsion between cucurbit[7]urils can be overcome in [3]pseudorotaxane without adding saltsPublication . Pessêgo, Márcia; Moreira, José; Costa, Ana M. Rosa da; Corrochano, P.; Poblete, F. J.; García-Río, LuísThe host−guest chemistry betweencucurbit[7]uril (CB7) and a series of bolaform (Bn) surfactants with different chain lengths, n = 12−22, was the target of our study. [3]Pseudorotaxanes are formed when the alkyl chain of the bolaform has more than 14 carbon atoms. In these cases, two CB7 molecules can be accommodated between the two head groups of the bolaform without addition of electrolytes to the medium. In the case of a bolaform with 12 carbon atoms, the electrostatic repulsion between the carbonyl groups of the CB7 molecules avoids the threading of a second CB7 molecule yielding a mixed structure formed by a [2]pseudorotaxane and an external host−guest complex. The assembly behavior was investigated using NMR spectroscopy, isothermal titration calorimetry (ITC), and kinetic measurements.
- Artificial reefs: from ecological processes to fishing enhancement toolsPublication . Leitão, Francisco
- Radiographers perceptions of magnetic resonance imaging: a study of the causes that lead to the exams repetitionPublication . Filipe, Tiago; Ribeiro, Luís; Almeida, Rui; Rodrigues, Sónia Isabel do Espírito Santo; Azevedo, Kevin; Silva, Carlos; Abrantes, AntónioPurpose: To know how often occur the repetitions of MRI exams and sequences in radiology departments. Methods and Materials: A self applied-questionnaire was used as instrument and assigned to 57 radiographers who performed MRI exams to determine which were the causes that lead to the repetition. The questionnaires were interpreted and statistically analyzed through descriptive statistics and Spearman’s rho correlations. Results: At a 95% confidence interval, the major results suggest that the patient’s movement during de MRI exams is the main cause to repeat this exams (mean of 3.88 on a 5 points likert scale). However, there are causes related to the radiographer’s and the results showed that the introduction of wrong imaging parameters by the performer are a major cause too (N=26). Spearman rho correlations between radiographer’s time of experience and frequency of MRI exams repetitions were poor and not significant (r=0.141; p=0.297). The correlations between radiographer’s tiredness and frequency of MRI exams repetitions were negative, weak and not significant (r= -0.151; p=0.263). Conclusion: The patients’ movement may disrupt the examination or degrade the images with artifacts. The level of experience doesn’t influence the repetitions of MRI exams, it seems that seniors radiographers don’t have improvements in performance as it should be expected. It’s recommendable to do training courses regularly to improve the performance and systematically evaluate. Several features will need to be identified which would decrease the MRI exams repetitions.