μ-MAC : an energy-efficient medium access control for wireless sensor networks

For the long-term deployment of wireless sensor networks, energy efficient MAC protocols are necessary. The transceiver of a sensor node should only consume energy while actively taking part in communication. Energy consumption in idle mode should be avoided as much as possible. In this paper it is shown how application layer knowledge in the form of flow specifications can be used to improve the energy properties of a MAC protocol. A new protocol, named m-MAC, is proposed and evaluated through simulations

Tolerance After Liver Transplantation: Where Are We?

info:eu-repo/semantics/publishedVersio

Scattering Cross Section and Stability of Global Monopoles

We study the scattering of scalar waves propagating on the global monopole background. Since the scalar wave operator in this topological defect is not essentially self-adjoint, its solutions are not uniquely determined until a boundary condition at the origin is specified. As we show, this boundary condition manifests itself in the differential cross section and can be inferred by measuring the amplitude of the backscattered wave. We further demonstrate that whether or not the spacetime is stable under scalar perturbations also relies on the chosen boundary condition. In particular, we identify a class of such boundary conditions which significantly affects the differential cross section without introducing an instability.Comment: 6 pages, 1 figure. To appear in Phys Rev

A gestão da observação nas aulas de campo em ciências

Este trabalho aborda o papel da observação na construção de conhecimento em aulas expositivas no ensino de ciências. A partir da análise da interação discursiva entre professor e alunos em aulas expositivas de campo para estudo de ecossistemas costeiros, apontamos algumas estratégias de controle temático utilizadas na construção da narrativa científica. Os resultados sugerem que a observação é utilizada pelo professor como estratégia retórica, definindo os itens temáticos que participam da construção da narrativa, e como recurso de produção de referenciais compartilhados, por meio da definição do ponto de vista comum de observação. A função de marco referencial da observação controlada do meio material parece não se encaixar nas categorias de marco social e de marco específico propostas por Coll et al. (1992), sendo sugerida a categoria de marco referencial empírico

Stellar population synthesis models between 2.5 and 5 {\mu}m based on the empirical IRTF stellar library

We present the first single-burst stellar population models in the infrared wavelength range between 2.5 and 5 {\mu}m which are exclusively based on empirical stellar spectra. Our models take as input 180 spectra from the stellar IRTF (Infrared Telescope Facility) library. Our final single-burst stellar population models are calculated based on two different sets of isochrones and various types of initial mass functions of different slopes, ages larger than 1 Gyr and metallicities between [Fe/H] = -0.70 and 0.26. They are made available online to the scientific community on the MILES web page. We analyse the behaviour of the Spitzer [3.6]-[4.5] colour calculated from our single stellar population models and find only slight dependences on both metallicity and age. When comparing to the colours of observed early-type galaxies, we find a good agreement for older, more massive galaxies that resemble a single-burst population. Younger, less massive and more metal-poor galaxies show redder colours with respect to our models. This mismatch can be explained by a more extended star formation history of these galaxies which includes a metal-poor or/and young population. Moreover, the colours derived from our models agree very well with most other models available in this wavelength range. We confirm that the mass-to-light ratio determined in the Spitzer [3.6] {\mu}m band changes much less as a function of both age and metallicity than in the optical bands.Comment: 25 pages, 19 figures, published in MNRAS, models can be downloaded from http://miles.iac.e

BDGS: A Scalable Big Data Generator Suite in Big Data Benchmarking

Data generation is a key issue in big data benchmarking that aims to generate application-specific data sets to meet the 4V requirements of big data. Specifically, big data generators need to generate scalable data (Volume) of different types (Variety) under controllable generation rates (Velocity) while keeping the important characteristics of raw data (Veracity). This gives rise to various new challenges about how we design generators efficiently and successfully. To date, most existing techniques can only generate limited types of data and support specific big data systems such as Hadoop. Hence we develop a tool, called Big Data Generator Suite (BDGS), to efficiently generate scalable big data while employing data models derived from real data to preserve data veracity. The effectiveness of BDGS is demonstrated by developing six data generators covering three representative data types (structured, semi-structured and unstructured) and three data sources (text, graph, and table data)