Connectivity Preservation in Multi-Agent Systems using Model Predictive Control

Flocking of multiagent systems is one of the basic behaviors in the field of control of multiagent systems and it is an essential element of many real-life applications. Such systems under various network structures and environment modes have been extensively studied in the past decades. Navigation of agents in a leader-follower structure while operating in environments with obstacles is particularly challenging. One of the main challenges in flocking of multiagent systems is to preserve connectivity. Gradient descent method is widely utilized to achieve this goal. But the main shortcoming of applying this method for the leader-follower structure is the need for continuous data transmission between agents and/or the preservation of a fixed connection topology. In this research, we propose an innovative model predictive controller based on a potential field that maintains the connectivity of a flock of agents in a leader-follower structure with dynamic topology. The agents navigate through an environment with obstacles that form a path leading to a certain target. Such a control technique avoids collisions of followers with each other without using any communication links while following their leader which navigates in the environment through potential functions for modelling the neighbors and obstacles. The potential field is dynamically updated by introducing weight variables in order to preserve connectivity among the followers as we assume only the leader knows the target position. The values of these weights are changed in real-time according to trajectories of the agents when the critical neighbors of each agent is determined. We compare the performance of our predictive-control based algorithm with other approaches. The results show that our algorithm causes the agents to reach the target in less time. However, our algorithm faces more deadlock cases when the agents go through relatively narrow paths. Due to the consideration of the input costs in our controller, the group of agents reaching the target faster does not necessarily result in the followers consuming more energy than the leader

Social Research For Development: Core Paper

The symposium on Social Research for Development was held on May 5-11, 1981, in Cairo, Egypt; by the Social Research Center (SRC) of The American University in Cairo (AUC). The Symposium was supported by funds from Battelle Human Affairs Research Center, Ford Foundation, International Development Re­search Center {IDRC}, and the Population Council. The theme of the Symposium was selected in respons.e to the increased con­cerns of social scientists, policymakers and funding agencies about the current status and new directions of social science research, its role in the pro­cess of social and economic development, and its contribution to policy-rele­vant issues. The Symposium, therefore, aimed at providing a valuable opportu­nity for the invaed participants to exchange ideas and views on social research findings, methodologies, priorities, strategies, and funding as they relate to policy issues of various aspects of social and economic developmenthttps://fount.aucegypt.edu/faculty_book_chapters/1826/thumbnail.jp

The living aortic valve

Aortic valve disease represents a leading cause of morbidity and mortality for patients with cardiovascular disease. The number of patients requiring aortic valve replacement is in fact expected to triple within the next 40 years. To date, surgical valve replacement represents the only option for patients with aortic valve disease. No treatments exist to slow down or reverse the disease process. This is in large part due to the fact that for a long time, aortic valves were thought to be passive flaps which open and close in responses to changes in transvalvular pressures. However, recent data suggests that aortic valves are dynamic structures with a complex, yet well-preserved macro- and microstructure and unique features which differentiate it from surrounding structures. In light of these findings, we sought to further evaluate the intricate structure and function of the aortic valve. Our hypothesis was that as a living organ, aortic valves will have the capacity to modulate their own properties, to regulate structural changes within them, thus affecting their overall function. The aims of this work were to investigate the structural complexity of the aortic valve at a cellular level, to evaluate the role of aortic valve endothelium in actively regulating valve calcification and modulating valve mechanical properties. We will also seek to evaluate the adaptive properties of heart valves in response to their biomechanical and biochemical environment and the role of a living valve substitute on aortic root flow dynamics. Finally, the clinical implications of a living valve will be highlighted through results of a clinical trial evaluating outcomes following the Ross procedure, the only operation which guarantees long-term viability of the aortic valve. Our findings support the notion that the aortic valve is a dynamic and living structure. Its unique location which exposes it to a variety of side specific hemodynamic and mechanical stresses leads to significant structural and functional adaptive responses on either side of the valve. These responses are operative in physiological conditions but also appear to affect pathological processes within the valve, which could partly explain the pathophysiology of aortic valve disease. In addition, our findings show that aortic valves adapt to their environment by modifying their mechanical properties, in particular their overall stiffness. This could have a major impact on the patterns of flow within the aortic root and stress distribution on the cusps. Using patient-specific computational modelling of aortic root flow dynamics, we show that a living aortic valve following aortic valve replacement such as with the Ross procedure, results in a pattern of flow which closely resembles that of normal subjects. In contrast, non-living valve substitutes such as homografts and xenografts do not provide similar results. Clinically, these differences play an important role as shown in a randomized clinical trial comparing autografts to homografts showing improved survival following autograft root replacement, along with other clinically-relevant endpoints. In conclusion, the aortic valve is a living, dynamic organ with unique features and intricate complexity which allows it to adapt to its complex hemodynamic and biomechanical environment and ensure adequate function. The clinical relevance of a living valve substitute in patients requiring aortic valve replacement is confirmed and highlights the importance of developing tissue-engineered heart valve substitutes. Additional work is required to further understand the molecular complexity of heart valves and understand their immediate impact in the body through new in vivo functional imaging techniques

The living aortic valve: From molecules to function.

The aortic valve lies in a unique hemodynamic environment, one characterized by a range of stresses (shear stress, bending forces, loading forces and strain) that vary in intensity and direction throughout the cardiac cycle. Yet, despite its changing environment, the aortic valve opens and closes over 100,000 times a day and, in the majority of human beings, will function normally over a lifespan of 70-90 years. Until relatively recently heart valves were considered passive structures that play no active role in the functioning of a valve, or in the maintenance of its integrity and durability. However, through clinical experience and basic research the aortic valve can now be characterized as a living, dynamic organ with the capacity to adapt to its complex mechanical and biomechanical environment through active and passive communication between its constituent parts. The clinical relevance of a living valve substitute in patients requiring aortic valve replacement has been confirmed. This highlights the importance of using tissue engineering to develop heart valve substitutes containing living cells which have the ability to assume the complex functioning of the native valve

Effets de la dénudation endothéliale et de la tétrahydrobioptérine sur la fonction endothéliale des artères coronaires épicardiques porcines après transplantation cardiaque

Mémoire numérisé par la Direction des bibliothèques de l'Université de Montréal

Early Marriage and Reproduction in Two Egyptian Villages

As noted in this monograph, marriage forms a central element of social life for Egyptians. Marriage in Egypt is nearly universal, and parents invest heavily to establish their children in married life. Once married, couples are faced with social pressures to begin childbearing immediately, a reflection of the high value placed on parenthood and children. But not all marriages begin with the same prospects for stability and satisfaction. This study draws attention to the problems faced by women who marry at very early ages in parts of rural Egypt. Despite a legal minimum age of 16, significant numbers of young girls marry below that age, and many experience social, emotional, and health-related difficulties. This study tells why these young women married early and how that decision affected their later life. The study points to areas where the aspirations of these girls have been clearly thwarted—to go to school, delay marriage, and postpone childbearing until they feel physically and psychologically ready. A related picture emerges of the social and economic forces that propel rural girls into marriage at very young ages. Each of these problems suggest areas for policy attention

Pattern and degree of left ventricular remodeling following a tailored surgical approach for hypertrophic obstructive cardiomyopathy.

Background The role of a tailored surgical approach for hypertrophic cardiomyopathy (HCM) on regional ventricular remodelling remains unknown. The aims of this study were to evaluate the pattern, extent and functional impact of regional ventricular remodelling after a tailored surgical approach. Methods From 2005 to 2008, 44 patients with obstructive HCM underwent tailored surgical intervention. Of those, 14 were ineligible for cardiac magnetic resonance (CMR) studies. From the remainder, 14 unselected patients (42±12 years) underwent pre- and post-operative CMR studies at a median 12 months post-operatively (range 4-37 months). Regional changes in left ventricular (LV) thickness as well as global LV function following surgery were assessed using CMR Tools (London, UK). Results Pre-operative mean echocardiographic septal thickness was 21±4 mm and mean LV outflow gradient was 69±32 mmHg. Following surgery, there was a significant degree of regional regression of LV thickness in all segments of the LV, ranging from 16% in the antero-lateral midventricular segment to 41% in the anterior basal segment. Wall thickening was significantly increased in basal segments but showed no significant change in the midventricular or apical segments. Globally, mean indexed LV mass decreased significantly after surgery (120±29g/m2 versus 154±36g/m2; p<0.001). There was a trend for increased indexed LV end-diastolic volume (70±13 mL versus 65±11 mL; p=0.16) with a normalization of LV ejection fraction (68±7% versus 75±9%; p<0.01). Conclusion Following a tailored surgical relief of outflow obstruction for HCM, there is a marked regional reverse LV remodelling. These changes could have a significant impact on overall ventricular dynamics and function