A model of host response to a multi-stage pathogen

We model the immune surveillance of a pathogen which passes through $n$ immunologically distinct stages. The biological parameters of this system induce a partial order on the stages, and this, in turn, determines which stages will be subject to immune regulation. This corresponds to the system's unique asymptotically stable fixed point.Comment: 22 pages, no figure

Tractable nonlinear memory functions as a tool to capture and explain dynamical behaviours

Mathematical approaches from dynamical systems theory are used in a range of fields. This includes biology where they are used to describe processes such as protein-protein interaction and gene regulatory networks. As such networks increase in size and complexity, detailed dynamical models become cumbersome, making them difficult to explore and decipher. This necessitates the application of simplifying and coarse graining techniques in order to derive explanatory insight. Here we demonstrate that Zwanzig-Mori projection methods can be used to arbitrarily reduce the dimensionality of dynamical networks while retaining their dynamical properties. We show that a systematic expansion around the quasi-steady state approximation allows an explicit solution for memory functions without prior knowledge of the dynamics. The approach not only preserves the same steady states but also replicates the transients of the original system. The method also correctly predicts the dynamics of multistable systems as well as networks producing sustained and damped oscillations. Applying the approach to a gene regulatory network from the vertebrate neural tube, a well characterised developmental transcriptional network, identifies features of the regulatory network responsible dfor its characteristic transient behaviour. Taken together, our analysis shows that this method is broadly applicable to multistable dynamical systems and offers a powerful and efficient approach for understanding their behaviour.Comment: (8 pages, 8 figures

Two-photon imaging through a multimode fiber

In this work we demonstrate 3D imaging using two-photon excitation through a 20 cm long multimode optical fiber (MMF) of 350 micrometers diameter. The imaging principle is similar to single photon fluorescence through a MMF, except that a focused femtosecond pulse is delivered and scanned over the sample. In our approach, focusing and scanning through the fiber is accomplished by digital phase conjugation using mode selection by time gating with an ultra-fast reference pulse. The excited two-photon emission is collected through the same fiber. We demonstrate depth sectioning by scanning the focused pulse in a 3D volume over a sample consisting of fluorescent beads suspended in a polymer. The achieved resolution is 1 micrometer laterally and 15 micrometers axially. Scanning is performed over an 80x80 micrometers field of view. To our knowledge, this is the first demonstration of high-resolution three-dimensional imaging using two-photon fluorescence through a multimode fiber

An algebraic and graph theoretical framework to study monomial dynamical systems over a finite field

An n dimensional monomial dynamical system over a finite field K is a nonlinear deterministic time discrete dynamical system with the property that each of the n component functions is a monic nonzero monomial function in n variables. In this paper we provide an algebraic and graph theoretic framework to study the dynamic properties of monomial dynamical systems over a finite field. Within this framework, characterization theorems for fixed point systems (systems in which all trajectories end in steady states) are proved. In particular, we present an algorithm of polynomial complexity to test whether a given monomial dynamical system over a finite field is a fixed point system. Furthermore, theorems that complement previous work are presented and alternative proofs to previous results are supplied.Comment: 26 pages, typos removed, improved and extended. Currently under revie

Protección de datos personales en redes sociales digitales

El presente trabajo reúne una serie de discusiones y reflexiones sobre la privacidad y la protección datos personales en el ciberespacio, en específico las redes sociales digitales. La forma de uso de estas plataformas tecnológicas puede generar riesgos para la privacidad y los datos personales de los usuarios, se reflexiona sobre posibles mecanismos de protección y autorregulación de la información personal en la red social digital de mayor alcance en el mundo, Facebook. Este trabajo surge como parte de mi realización de prácticas profesionales en El Instituto de Transparencia, Acceso a la Información Pública y Protección de Datos Personales del Estado de México y Municipios (Infoem), en dicho proyecto se buscó entender qué son las redes sociales digitales, qué alcance tienen en el país, qué usos se les pueden dar, qué tipo de información se sube y comparte, así como observar los posibles riesgos a la privacidad, a fin de encontrar mecanismos de protección de datos, pero partiendo del hecho de que en el ciberespacio y las redes sociales no se puede ni debe regular el comportamiento e interacciones de los usuarios, quienes son personas en el mundo real, poseedoras de una personalidad y derechos

Enterprise resource planning adoption and satisfaction determinants

JEL classification: M15 – IT Management, M10 – General Business AdministrationEnterprise Resource Planning (ERP) systems are at the core of every firm. Making people use this costly and time consuming investment is one of the most important issues to deal with. The main objective of the present dissertation is to find the key determinants that open the door to user satisfaction and adoption. A theoretical model was set and an online survey was conducted to understand ERP users’ perspective on such matters. The outcome was the model validation and the understanding that top management support, training, and the system quality are important constructs to assess adoption and user satisfaction. In fact, the latter (system quality) has a significant influence on the behavioural intention to use and also in the overall user satisfaction.Os sistemas de Enterprise Resource Planning (ERP) fazem parte do centro nevrálgico de todas as empresas. Fazer com que as pessoas tirem partido de um investimento desta importância é um aspeto crucial que tem de se levar em conta. É o principal objetivo da presente dissertação identificar os principais determinantes que levam à satisfação e adoção por parte dos utilizadores. Para este efeito foi elaborado um modelo teórico e levado a cabo um questionário online junto dos utilizadores de sistemas ERP. O resultado foi a validação do modelo e a confirmação de que o suporte da gestão de topo, a formação e a qualidade do sistema são construtos decisivos para avaliar a adoção e satisfação por parte dos utilizadores. De fato, a qualidade do sistema tem uma influência muito forte na intenção comportamental de utilizar o sistema e também na satisfação global do utilizador