IBVPs for Scalar Conservation Laws with Time Discontinuous Fluxes

The initial boundary value problem for a class of scalar non autonomous conservation laws in one space dimension is proved to be well posed and stable with respect to variations in the flux. Targeting applications to traffic, the regularity assumptions on the flow are extended to a merely $\mathbf{L}^{\infty}$ dependence on time. These results ensure, for instance, the well posedness of a class of vehicular traffic models with time dependent speed limits. A traffic management problem is then shown to admit an optimal solution

Non Local Conservation Laws in Bounded Domains

The well posedness for a class of non local systems of conservation laws in a bounded domain is proved and various stability estimates are provided. This construction is motivated by the modelling of crowd dynamics, which also leads to define a non local operator adapted to the presence of a boundary. Numerical integrations show that the resulting model provides qualitatively reasonable solutions

Hyperbolic predators vs parabolic preys

We present a nonlinear predator-prey system consisting of a nonlocal conservation law for predators coupled with a parabolic equation for preys. The drift term in the predators' equation is a nonlocal function of the prey density, so that the movement of predators can be directed towards region with high prey density. Moreover, Lotka-Volterra type right hand sides describe the feeding. A theorem ensuring existence, uniqueness, continuous dependence of weak solutions and various stability estimates is proved, in any space dimension. Numerical integrations show a few qualitative features of the solutions.Comment: 35 pages, 7 figure

New big data platforms are more efficient, but pose a serious threat to privacy

Most new systems offer only basic enforcement, whereas traditional ones have various protection frameworks, write Pietro Colombo and Elena Ferrari. The past few years have seen changes in the organisation of business models and work styles, caused by the rapid evolution of data analysis and data management systems. Business strategies are more and more driven by the integrated analysis of huge ..

Access control technologies for Big Data management systems: literature review and future trends

Abstract Data security and privacy issues are magnified by the volume, the variety, and the velocity of Big Data and by the lack, up to now, of a reference data model and related data manipulation languages. In this paper, we focus on one of the key data security services, that is, access control, by highlighting the differences with traditional data management systems and describing a set of requirements that any access control solution for Big Data platforms may fulfill. We then describe the state of the art and discuss open research issues

Fine-Grained Access Control Within NoSQL Document-Oriented Datastores

The recent years have seen the birth of several NoSQL datastores, which are getting more and more popularity for their ability to handle high volumes of heterogeneous and unstructured data in a very efficient way. In several cases, NoSQL databases proved to outclass in terms of performance, scalability, and ease of use relational database management systems, meeting the requirements of a variety of today ICT applications. However, recent surveys reveal that, despite their undoubted popularity, NoSQL datastores suffer from some weaknesses, among which the lack of effective support for data protection appears among the most serious ones. Proper data protection mechanisms are therefore required to fill this void. In this work, we start to address this issue by focusing on access control and discussing the definition of a fine-grained access control framework for document-oriented NoSQL datastores. More precisely, we first focus on issues and challenges related to the definition of such a framework, considering theoretical, implementation, and integration aspects. Then, we discuss the reasons for which state-of-the-art fine-grained access control solutions proposed for relational database management systems cannot be used within the NoSQL scenario. We then introduce possible strategies to address the identified issues, which are at the basis of the framework development. Finally, we shortly report the outcome of an experience where the proposed framework has been used to enhance the data protection features of a popular NoSQL database

Escribir para aprender en dos disciplinas: construcción conjunta del conocimiento y extensión del tiempo didácticol

In the last decades, the links between writing and learning have been widely studied. In higher education, researchers have focused on students´ productions, on their standpoints towards writing in different disciplines, and on the complex relations between subject contents and writing practices, among others. However, teaching practices that intertwine writing and disciplinary contents have received scarce attention. This work emphasises two key aspects of teaching practices related to writing to learn activities: teaching time and responsibilities in knowledge-construction. A multiple case study was conducted with two first-year courses, one in Linguistics and the other in Biology. These classes were offered in two public universities in Argentina. Data collection techniques included, mainly, classroom documents, class observations and semi-structured interviews with students. Focusing on class observations, this paper shows how the teaching time was extended by intertwining teaching practices with writing as a learning tool. In both courses, writing extended class-time when students had the opportunity to write outside the classrooms and to discuss what they wrote in whole-class discussions. Additionally, these uses of writing helped students and professors to share, in a more symmetrical way, the responsibilities towards knowledge construction.En las últimas décadas, los vínculos entre la escritura y el aprendizaje han sido ampliamente estudiados. En la enseñanza superior, en particular, los investigadores se han centrado en las producciones de los estudiantes, en sus puntos de vista respecto de la escritura en las diferentes disciplinas y en las complejas relaciones entre los contenidos de las disciplinas y las prácticas de escritura, entre otros. Sin embargo, escasas investigaciones se centran en las prácticas docentes que entrelazan la escritura y los contenidos disciplinarios. Este trabajo analiza dos aspectos claves de las prácticas de enseñanza cuando se escribe para aprender: el tiempo didáctico y las responsabilidades en la construcción del conocimiento. Los resultados forman parte de una investigación didáctica diseñada como un estudio de casos múltiples en dos disciplinas universitarias (Lingüística y Biología). Los casos estudiados pertenecen a dos cursos de primer año impartidos en dos de las principales universidades argentinas. Las técnicas de recolección de datos incluyeron, principalmente, análisis de documentos, observaciones de clase y entrevistas semiestructuradas con los estudiantes. En este sentido, centrándose en las observaciones de clase, este trabajo muestra cómo se amplió el tiempo de enseñanza en esos cursos al entrelazar las prácticas de enseñanza con la escritura como herramienta de aprendizaje. En estas clases, la escritura prolongó el tiempo didáctico en la medida en que los estudiantes tuvieron la oportunidad de escribir fuera de las aulas y de discutir lo que escribieron dentro de ellas. Además, esta práctica ayudó a estudiantes y profesores a compartir, de manera más simétrica, las responsabilidades vinculadas con la construcción del conocimiento