Maximum Throughput of a Secondary User Cooperating with an Energy-Aware Primary User

This paper proposes a cooperation protocol between a secondary user (SU) and a primary user (PU) which dedicates a free frequency subband for the SU if cooperation results in energy saving. Time is slotted and users are equipped with buffers. Under the proposed protocol, the PU releases portion of its bandwidth for secondary transmission. Moreover, it assigns a portion of the time slot duration for the SU to relay primary packets and achieve a higher successful packet reception probability at the primary receiver. We assume that the PU has three states: idle, forward, and retransmission states. At each of these states, the SU accesses the channel with adaptive transmission parameters. The PU cooperates with the SU if and only if the achievable average number of transmitted primary packets per joule is higher than the number of transmitted packets per joule when it operates alone. The numerical results show the beneficial gains of the proposed cooperative cognitive protocol.Comment: Accepted WiOpt 201

Band Allocation for Cognitive Radios with Buffered Primary and Secondary Users

In this paper, we study band allocation of $\mathcal{M}_s$ buffered secondary users (SUs) to $\mathcal{M}_p$ orthogonal primary licensed bands, where each primary band is assigned to one primary user (PU). Each SU is assigned to one of the available primary bands with a certain probability designed to satisfy some specified quality of service (QoS) requirements for the SUs. In the proposed system, only one SU is assigned to a particular band. The optimization problem used to obtain the stability region's envelope (closure) is shown to be a linear program. We compare the stability region of the proposed system with that of a system where each SU chooses a band randomly with some assignment probability. We also compare with a fixed (deterministic) assignment system, where only one SU is assigned to one of the primary bands all the time. We prove the advantage of the proposed system over the other systems.Comment: Accepted in WCNC 201

Cooperative Cognitive Relaying Under Primary and Secondary Quality of Service Satisfaction

This paper proposes a new cooperative protocol which involves cooperation between primary and secondary users. We consider a cognitive setting with one primary user and multiple secondary users. The time resource is partitioned into discrete time slots. Each time slot, a secondary user is scheduled for transmission according to time division multiple access, and the remainder of the secondary users, which we refer to as secondary relays, attempt to decode the primary packet. Afterwards, the secondary relays employ cooperative beamforming to forward the primary packet and to provide protection to the secondary destination of the secondary source scheduled for transmission from interference. We characterize the diversity-multiplexing tradeoff of the primary source under the proposed protocol. We consider certain quality of service for each user specified by its required throughput. The optimization problem is stated under such condition. It is shown that the optimization problem is linear and can be readily solved. We show that the sum of the secondary required throughputs must be less than or equal to the probability of correct packets reception.Comment: This paper was accepted in PIMRC 201

On Orthogonal Band Allocation for Multi-User Multi-Band Cognitive Radio Networks: Stability Analysis

In this work, we study the problem of band allocation of $M_s$ buffered secondary users (SUs) to $M_p$ primary bands licensed to (owned by) $M_p$ buffered primary users (PUs). The bands are assigned to SUs in an orthogonal (one-to-one) fashion such that neither band sharing nor multi-band allocations are permitted. In order to study the stability region of the secondary network, the optimization problem used to obtain the stability region's envelope (closure) is established and is shown to be a linear program which can be solved efficiently and reliably. We compare our orthogonal allocation system with two typical low-complexity and intuitive band allocation systems. In one system, each cognitive user chooses a band randomly in each time slot with some assignment probability designed such that the system maintained stable, while in the other system fixed (deterministic) band assignment is adopted throughout the lifetime of the network. We derive the stability regions of these two systems. We prove mathematically, as well as through numerical results, the advantages of our proposed orthogonal system over the other two systems.Comment: Conditional Acceptance in IEEE Transactions on Communication

Gender roles and physical function in old age

Contexte : Les différences de fonctionnement physique entre les hommes et les femmes ne sont pas bien comprises. Les chercheurs ont porté attention aux différences biologiques entre les hommes et les femmes mais ne se sont pas concentrés sur les différences de fonctionnement physique et de mobilité qui pourraient être reliées au sexe et au genre. En particulier, les effets de la masculinité et de la féminité sur le fonctionnement physique des personnes âgées n’ont pas été examinés. Objectifs : L’objectif principal de cette recherche est d’évaluer l’association entre fonctionnement physique et rôles de genre. Pour atteindre cet objectif, nous avons examiné : 1) la validité de la version courte (12 items) de l’Inventaire des rôles sexués de Bem (IRSB) ; 2) les associations transversales et longitudinales entre l’IRSB et des indicateurs de mobilité et de performance physique, et finalement 3) les variables jouant un rôle de médiation entre l’IRSB et la performance physique. Méthodes : Les données de l’étude internationale sur la mobilité au cours du vieillissement (IMIAS) recueillies en 2012 et 2014 ont été utilisées dans cette recherche. Cette étude s’est déroulée dans 5 villes : Saint-Hyacinthe (Québec) and Kingston (Ontario) au Canada, Tirana (Albanie), Manizales (Colombie) et Natal (Brésil), avec un échantillon approximatif à chaque site de 200 hommes et 200 femmes âgés de 65 à 74 ans vivant dans la communauté (N=2004). Deux aspects du fonctionnement physique ont été examinés dans cette thèse : la mobilité et la performance physique. La mobilité a été mesurée par deux questions sur la difficulté à marcher un Km et à monter un étage d’escaliers. La performance physique a été objectivée par le Short Physical Performance Battery (SPPB). Cette batterie inclut des mesures de la marche, de l’équilibre et de la force musculaire et elle mesure le temps requis pour exécuter trois tests : marcher quatre mètres, se tenir début en position de tandem et se lever d’une chaise cinq fois. Pour la validation psychométrique de l’instrument IRSB, des analyses factorielles exploratoires et confirmatoires ont été réalisées. Pour les études d’associations transversales, des analyses de régression de Poisson ont permis l’estimation des ratios de prévalence pour les incapacités de mobilité et la mauvaise performance physique, comparant les rôles masculins, féminins et indifférenciés. Pour l’étude de l’incidence de la mauvaise performance physique, les estimations de risque relatif ont été obtenues à l’aide de la régression de Poisson. L’étude des variables de médiation entre les rôles de genre et la performance physique a inclus le tabagisme, l’inactivité physique, la consommation d’alcool, l’index de masse corporelle élevé, le nombre de maladies chroniques et la dépression. Finalement, une méta-analyse a été effectuée pour examiner l’homogénéité des associations entre les rôles de genre et la performance physique dans les cinq sites de recherche. Résultats : Les résultats des analyses factorielles pour l’instrument de mesure IRSB ont révélé qu’une solution à deux facteurs (instrumentalité-expression) donne une validité conceptuelle satisfaisante, ainsi qu’un ajustement aux données supérieur par rapport à une solution à trois facteurs. La solution à deux facteurs permet d’assigner un score de masculinité et un score de féminité à chaque participant et de classifier les personnes âgées dans quatre catégories selon leur typologie de rôle de genre : masculin, féminin, androgyne et indifférencié. En ce qui concerne les associations avec les indicateurs de mobilité et de fonctionnement physique, les rôles féminins et indifférenciés sont des facteurs indépendants associés à la prévalence des incapacités dans la mobilité et à la mauvaise performance après ajustement avec des variables de confusion potentielle. Les rôles féminins et indifférenciés sont des facteurs de risque associés à une détérioration plus rapide du fonctionnement des extrémités inferieures. Nous avons rapporté une incidence de mauvaise performance physique plus élevée pour ceux qui adoptent un rôle féminin (IRR ajusté=2.36, intervalle de confiance de 95% 1.55-3.60) ou le rôle indifférencié (IRR ajusté=2.19, 95% Intervalle de confiance de 95% 1.45-3.30) comparé au rôle androgyne. Le score de masculinité est associé à la performance physique, alors que le score de féminité ne l’est pas. Une augmentation d’une unité sur le score de masculinité est associée à une incidence de mauvais fonctionnement physique plus faible (IRR ajusté=0.76, 95% intervalle de confiance de 95% 0.67-0.87). Les rôles de genre agissent sur les comportements de santé (tabagisme et inactivité physique), sur l’index de masse corporelle et sur les maladies chroniques et la dépression, tous des facteurs de risque pour la performance physique. Les effets des rôles de genre ne sont que partiellement expliqués par ces facteurs de médiation et un effet direct des rôles de genre sur le fonctionnement physique reste toujours significatif. Conclusion : Les rôles de genre sont présents dans tous les cinq sites de recherche. La mobilité et la performance physique des personnes âgées sont associées au type de rôle de genre avec un possible effet protecteur pour les personnes androgynes, indépendamment du fait qu’ils soient un homme ou une femme. Les rôles de genre semblent influencer les comportements de santé et les risques de développer une maladie chronique et de souffrir de dépression, ce qui peut avoir des effets sur la fonction physique au cours du vieillissement. Cette étude est la première sur le sujet et nos résultats devraient être confirmés par des études futures avant d’être traduits en interventions concrètes de santé publique.Background: Gender differences in mobility disability among older adults are not well understood. Studies have focused on the biological differences between men and women, but not on the mobility differences due to interrelationships of sex and gender. The associations between masculinity, and femininity on physical function in old age have never been examined. Objective: The main objective of this dissertation is to study the relationships between physical function and gender roles in old age. To accomplish this objective, I have: 1) assessed the psychometric properties and construct validity of the 12-items short form Bem Sex Roles Inventory (BSRI), 2) examined the cross-sectional associations between BSRI and mobility and physical performance, and 3) examined mediating pathways between BSRI and physical performance. Methods: A total of 2004 community-dwelling older adults from the International Mobility in Aging Study (IMIAS) aged 65 to 74 years were recruited in Natal (Brazil), Manizales (Colombia), Tirana (Albania), Kingston (Ontario, Canada), and Saint-Hyacinthe (Quebec, Canada). Two aspects of mobility loss will be assessed in this dissertation: first, Mobility disability is a self-reported measure of the difficulty to walk half a mile or climb one flight of stairs without assistance. Second, poor physical function or performance of the lower extremities which is assessed by an objective tool and defined as inability to perform physical action in the manner considered normal in the short physical performance battery (SPPB). This battery includes three timed tests of lower extremity function: a hierarchical test of standing balance, a four-meter walk, and five repetitive chair stands. To assess the validity of BSRI in old age as a measure of gender roles. The psychometric properties of the 12- items short form BSRI were assessed by means of exploratory (EFA) and confirmatory factor analysis (CFA). To assess the cross-sectional associations between gender roles and both measures of mobility loss, I used Poisson regression analysis to estimate prevalence rate ratios of gender role types using the androgynous type as reference category. To calculate the incidence of poor physical performance after two years of follow up, Poisson regression was conducted for the estimation of relative risks. Body mass index, smoking, alcohol consumption, physical activity, chronic diseases, and depression were tested as potential mediators in the pathway between gender roles and physical performance in old age. Finally, taking account the possible differences in associations between countries, I have conducted a meta-analysis to estimate overall effects of masculinity and femininity scores on physical performance based on five distinct studies representing each research site of IMIAS. Results: The results of Exploratory Factor Analysis revealed a three-factor model. This model was further confirmed by CFA and compared with the original two-factor structure model. CFA results revealed that a two-factor solution (instrumentality-expressiveness) has satisfactory construct validity and superior fit to data compared to the three-factor solution. These factor analysis findings allowed to calculate scores of masculinity and femininity and classify participants into four categories according to gender roles: Masculine, feminine, androgynous and undifferentiated. Feminine and undifferentiated gender roles are independent risk factors associated with the prevalence of mobility disability and low physical performance in older adults. Consistent with cross sectional analysis, higher incidence of poor physical performance was observed among participants endorsing the feminine role or the undifferentiated role compared to the androgynous role. Higher masculinity but not femininity scores predicted good physical performance two years later. Gender roles predicted poor physical performance through statistically significant direct and indirect pathways. Cumulative smoking, BMI, physical activity, multimorbidity, and depression were serial mediators explaining the indirect effect of gender roles on physical performance. These intermediate behavioral and pathological pathways only partially mediated the observed associations. None of the potential serial mediators in the present study could completely account for the association between gender roles and physical performance. Conclusions: Traditional gender roles are existent in the five research sites of IMIAS. Gender roles influence physical function in old age with a possible protective effect of androgyny in old age independent of biological sex. Gender roles influence health behaviors which in turn contribute to chronic conditions and faster decline of lower extremities physical function. This study adds to the scant literature on this topic and the findings obtained from this dissertation need to be confirmed by future longitudinal studies for the appropriate translation into public health actions

HIGH DOSE SIMVASTATIN AS A POTENTIAL ANTICANCER THERAPY IN LEUKEMIA PATIENTS

Simvastatin is a 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitor that is used for the treatment of hyperlipidemia. Simvastatin has recently been studied for its potential use in cancer therapy. In-vitro studies have shown that simvastatin displays anticancer activity, but at concentrations unlikely to be achieved in patients being receiving typical antihyperlipidemic treatment doses. Thus, several clinical trials were conducted to study the tolerability of high dose statins in cancer patients. The maximum tolerated dose of simvastatin was determined to be 15 mg/kg/day, 25-fold higher than a typical dose. However, it is not known if simvastatin plasma concentrations can reach those found to be effective in-vitro. In this context, we initiated a clinical study to determine the pharmacokinetics of high dose simvastatin in patients with chronic lymphocytic leukemia. For this purpose, an LC-MS/MS method was developed and validated for the quantitation of simvastatin and its acid form in plasma and peripheral blood mononuclear cells obtained from CLL patients. Results show that simvastatin concentrations were dose proportional relative to the antihyperlipidemic doses, but lower than those required for in-vitro cytotoxicity against cancer cells. These findings demonstrate that the in-vitro effective concentrations of simvastatin are not achievable clinically, which might explain the limited effectiveness of high dose simvastatin in this study and in previous clinical trials. In view of these data, the use of simvastatin as a sole therapy in cancer treatment was not encouraging and led us to examine the use in combination with other anticancer drugs. After screening several chemotherapeutic agents in combination with simvastatin, we showed that tipifarnib (a farnesyltransferase inhibitor) interacts synergistically in several leukemia cell lines. Mechanistically we showed that simvastatin augments the cytotoxicity of tipifarnib by disrupting the localization of RAS in the cell membrane and by subsequent deactivation of the ERK pathway. Consistent with this observation, drug treatment led to the induction of apoptosis through the caspase cascade activation and the cleaved PARP upregulation. Notably, this synergistic effect was observed at clinically achievable concentrations of simvastatin and tipifarnib. Thus, the effectiveness of this combination should be explored further in future clinical studies

Protocol Design and Stability Analysis of Cooperative Cognitive Radio Users

A single cognitive radio transmitter--receiver pair shares the spectrum with two primary users communicating with their respective receivers. Each primary user has a local traffic queue, whereas the cognitive user has three queues; one storing its own traffic while the other two are relaying queues used to store primary relayed packets admitted from the two primary users. A new cooperative cognitive medium access control protocol for the described network is proposed, where the cognitive user exploits the idle periods of the primary spectrum bands. Traffic arrival to each relaying queue is controlled using a tuneable admittance factor, while relaying queues service scheduling is controlled via channel access probabilities assigned to each queue based on the band of operation. The stability region of the proposed protocol is characterized shedding light on its maximum expected throughput. Numerical results demonstrate the performance gains of the proposed cooperative cognitive protocol.Comment: Accepted in WCNC 201