A stochastic model for protrusion activity

In this work we approach cell migration under a large-scale assumption, so that the system reduces to a particle in motion. Unlike classical particle models, the cell displacement results from its internal activity: the cell velocity is a function of the (discrete) protrusive forces exerted by filopodia on the substrate. Cell polarisation ability is modeled in the feedback that the cell motion exerts on the protrusion rates: faster cells form preferentially protrusions in the direction of motion. By using the mathematical framework of structured population processes previously developed to study population dynamics [Fournier and M{\'e}l{\'e}ard, 2004], we introduce rigorously the mathematical model and we derive some of its fundamental properties. We perform numerical simulations on this model showing that different types of trajectories may be obtained: Brownian-like, persistent, or intermittent when the cell switches between both previous regimes. We find back the trajectories usually described in the literature for cell migration

Preliminary scientific rationale for a voyage to a thousand astronomical units

A proposed mission to 1000 astronomical units (TAU) is under study by the Jet Propulsion Laboratory. Launch date for a TAU mission is likely to be well into the first decade of the 21st century. Study of TAU has focused on the technologies required to carry out this ambitious mission and the identification of preliminary scientific rationale for such a deep space flight. A 1-MW nuclear-powered electric propulsion (NEP) system forms the baseline method for achieving the high velocities required. A solar system escape velocity of 106 km/s is needed to propel the TAU vehicle to 1000 AU in 50 years. The NEP system must accelerate the vehicle for about ten years before this velocity is attained because of the extremely low thrust nature of the xenon-fueled ion engines. At the end of the thrusting phase the NEP system is jettisoned to allow the TAU spacecraft and science experiments to coast out to 1000 AU. Another important technology for TAU is advanced optical communication systems, which are envisioned for transmitting science data to Earth. A 1-m optical telescope combined with a 10-W laser transponder can transmit 20 kbps to a 10-m Earth-orbit-based telescope from 1000 AU

Portfolio Optimization Using Evolutionary Algorithms

Dissertation presented as the partial requirement for obtaining a Master's degree in Data Science and Advanced AnalyticsPortfolio optimization is a widely studied field in modern finance. It involves finding the optimal balance between two contradictory objectives, the risk and the return. As the number of assets rises, the complexity in portfolios increases considerably, making it a computational challenge. This report explores the application of the Multi-Objective Evolutionary Algorithm based on Decomposition (MOEA/D) and Genetic Algorithm (GA) in the field of portfolio optimization. MOEA/D and GA have proven to be effective at finding portfolios. However, it remains unclear how they perform when compared to traditional approaches used in finance. To achieve this, a framework for portfolio optimization is proposed, using MOEA/D, and GA separately as optimization algorithms and Capital Asset Pricing Model (CAPM) and Mean-Variance Model as methods to evaluate portfolios. The proposed framework is able to produce weighted portfolios successfully. These generated portfolios were evaluated using a simulation with subsequent (unseen) prices of the assets included in the portfolio. The simulation was compared with well known portfolios in the same market and other market benchmarks (Security Market Line and Market Portfolio). The results obtained in this investigation exceeded expectation by creating portfolios that perform better than the market. CAPM and Mean-Variance Model, although they fail to model all the variables that affect the stock market, provide a simple valuation for assets and portfolios. MOEA/D using Differential Evolution operators and the CAPM model produced the best portfolios in this research. Work can still be done to accommodate more variables that can affect markets and portfolios, such as taxes, investment horizon and costs for transactions

Numerical solutions of a 2D fluid problem coupled to a nonlinear non-local reaction-advection-diffusion problem for cell crawling migration in a discoidal domain

In this work, we present a numerical scheme for the approximate solutions of a 2D crawling cell migration problem. The model, defined on a non-deformable discoidal domain, consists in a Darcy fluid problem coupled with a Poisson problem and a reaction-advection-diffusion problem. Moreover, the advection velocity depends on boundary values, making the problem nonlinear and non local. \parFor a discoidal domain, numerical solutions can be obtained using the finite volume method on the polar formulation of the model. Simulations show that different migration behaviours can be captured

The role of draper in phagocytic competency, corpse processing, and homeostasis

The clearance of apoptotic cells is an important process in animal development and homeostasis. Failure to dispose of dead cells leads to developmental defects as well as disease. The removal of dead cells within an organism is accomplished by the process of phagocytosis. Phagocytosis of apoptotic cells is the internalization of a dead cell by another cell. Once internalized, the apoptotic cell is subject to various processing events culminating in the complete degradation of the dead cell. Phagocytosis is carried out by specialized cells, known as professional phagocytes. However, phagocytosis can also be carried out by cells that are specialized for functions other than phagocytosis. These cells are known as nonprofessional phagocytes. Although the process of phagocytosis has been extensively studied, the mechanisms are poorly understood. To better understand phagocytosis, this dissertation has focused on the Drosophila receptor Draper (Drpr). Drpr is a highly conserved transmembrane protein that has been shown to be crucial for proper phagocytosis. In this dissertation, I report novel roles for Drpr function. Specifically I show that in the ovary of Drosophila melanogaster, the germline cells can be induced to die by starvation and their remnants are engulfed by surrounding epithelial follicle cells. During this process, the dying germline activates Drpr in the follicle cells. Drpr then activates c-Jun N-terminal kinase (JNK) leading to upregulation of Drpr as well as other engulfment genes. These results suggest that these nonprofessional phagocytes need to acquire a phagocytic phenotype to become phagocytic. We also report that the absence of Drpr in glia leads to an accumulation of apoptotic neurons in the Drosophila brain. These dead cells persist throughout the lifespan of the organism and are associated with age-dependent neurodegeneration. Our data indicate that corpses persist because of defective phagosome maturation. Target of rapamycin complex 1(TORC1) activation in glia is sufficient to rescue corpse accumulation and neurodegeneration. These results suggest that Drpr is important for phagocytic competency, corpse processing, and homeostasis