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Publications

Publications by LIAAD

2015

A Consumption-Investment Problem with a Diminishing Basket of Goods

Authors
Mousa, AS; Pinheiro, D; Pinto, AA;

Publication
OPERATIONAL RESEARCH: IO 2013 - XVI CONGRESS OF APDIO

Abstract
We consider the problem faced by an economic agent trying to find the optimal strategies for the joint management of her consumption from a basket of K goods that may become unavailable for consumption from some random time tau(i) onwards, and her investment portfolio in a financial market model comprised of one risk-free security and an arbitrary number of risky securities driven by a multidimensional Brownian motion. We apply previous abstract results on stochastic optimal control problem with multiple random time horizons to obtain a sequence of dynamic programming principles and the corresponding Hamilton-Jacobi-Bellman equations. We then proceed with a numerical study of the value function and corresponding optimal strategies for the problem under consideration in the case of discounted constant relative risk aversion utility functions (CRRA).

2015

Mathematics of Energy and Climate Change

Authors
Bourguignon, J; Jeltsch, R; Pinto, AA; Viana, M;

Publication
CIM Series in Mathematical Sciences

Abstract

2015

Clustering of Variables Based on Watson Distribution on Hypersphere: A Comparison of Algorithms

Authors
Figueiredo, A; Gomes, P;

Publication
COMMUNICATIONS IN STATISTICS-SIMULATION AND COMPUTATION

Abstract
We consider n individuals described by p variables, represented by points of the surface of unit hypersphere. We suppose that the individuals are fixed and the set of variables comes from a mixture of bipolar Watson distributions. For the mixture identification, we use EM and dynamic clusters algorithms, which enable us to obtain a partition of the set of variables into clusters of variables.Our aim is to evaluate the clusters obtained in these algorithms, using measures of within-groups variability and between-groups variability and compare these clusters with those obtained in other clustering approaches, by analyzing simulated and real data.

2015

Prevalence of Alcohol Abuse Before and After Bariatric Surgery Associated With Nutritional and Lifestyle Factors: A Study Involving a Portuguese Population

Authors
de Araujo Burgos, MGPD; Cabral, PC; Maio, R; Oliveira, BMPM; Oliveira Dias, MSO; de Figueiredo Melim, DBD; Correia, MF;

Publication
OBESITY SURGERY

Abstract
It has been hypothesized that the metabolism of alcohol is altered following bariatric surgery. However, few studies have evaluated preoperative and postoperative alcohol use. The aims of the study were to characterize alcohol use in the preoperative period and 2 years postoperatively as well as to identify factors associated. A study was conducted using data from the electronic charts of patients submitted to laparoscopic adjustable gastric banding (LAGB) and Roux-en-Y gastric bypass (RYGB) surgery in the city of Porto, Portugal. Associations with the following variables were analyzed: age, marital status, schooling, alcohol use, body mass index, binge eating disorder, and lifestyle habits. Among the 659 patients, 42.0 % completed the 2 years of follow-up. A total of 90.2 % were women; 67.4 % underwent LAGB, and 32.6 % underwent RYGB. The frequency of alcohol use was 24.2 % in the preoperative period and 9.4 % in the postoperative period (p = 0.000). Daily alcohol intake was two drinks in the preoperative period and 1.8 drinks in the postoperative period. Significant associations were found between postoperative alcohol use and the male gender (p = 0.001), age a parts per thousand yen45 years (p = 0.018), and preoperative BMI < 40 kg/m(2) (p = 0.028). No significant associations were found with the surgical technique. No previous nondrinkers became drinkers, and no patients increased the quantity or frequency of alcohol intake in the postoperative period. The prevalence of alcohol use in the sample was low. Moreover, a lower prevalence rate was found in the postoperative period, independently of surgical technique, clinical factors, and percentage of weight loss.

2015

Eating behaviour among undergraduate students. Comparing nutrition students with other courses

Authors
Poinhos, R; Alves, D; Vieira, E; Pinhao, S; Oliveira, BMPM; Correia, F;

Publication
APPETITE

Abstract
Our main aim was to compare eating behaviour between Portuguese undergraduate nutrition students and students attending other courses. Several eating behaviour dimensions were compared between 154 nutrition students and 263 students from other areas. Emotional and external eating were assessed by the Dutch Eating Behavior Questionnaire, dietary restraint was measured using the flexible and rigid control of eating behaviour subscales, binge eating was measured using the Binge Eating Scale, and eating self-efficacy using the General Eating Self-Efficacy Scale. Higher levels of flexible and rigid control were found in nutrition students from both sexes when compared to students from other courses. Female nutrition students also presented higher binge eating levels than their colleagues from other courses. To our knowledge no other work has previously assessed all eating behaviour dimensions considered in the current study among nutrition students. Besides the results by themselves, the data obtained from this study provide several clues to further studies to be developed regarding the still rarely approached issue of eating behaviour among nutrition students.

2015

Eating behavior in Portuguese higher education students: The effect of social desirability

Authors
Poinhos, R; Oliveira, BMPM; Correia, F;

Publication
NUTRITION

Abstract
Objectives: The aim of this study was to relate social desirability with eating behavior dimensions among higher education students in Portugal, and to assess the effect of social desirability on the association between pairs of eating behavior dimensions. Methods: Data from 266 higher education students (62.8% women) aged between 18 and 27 y were evaluated. Social desirability and several eating behavior dimensions (emotional and external eating, flexible and rigid restraint, binge eating, and eating self-efficacy) were assessed. Results: In both women and men, social desirability showed negative associations with emotional, external, and binge eating, and positive associations with eating self-efficacy. For the majority of the correlations, the control for social desirability led to a decrease in the strength of the association: Social desirability showed a greater effect on the associations between external and binge eating, external eating and eating self-efficacy, binge eating and eating self-efficacy, and emotional and external eating. Conclusion: This study demonstrated that social desirability should be considered when assessing the dimensions of eating behavior, namely eating self-efficacy and dimensions related to overeating.

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