16,897 research outputs found
Can Punctured Rate-1/2 Turbo Codes Achieve a Lower Error Floor than their Rate-1/3 Parent Codes?
In this paper we concentrate on rate-1/3 systematic parallel concatenated
convolutional codes and their rate-1/2 punctured child codes. Assuming
maximum-likelihood decoding over an additive white Gaussian channel, we
demonstrate that a rate-1/2 non-systematic child code can exhibit a lower error
floor than that of its rate-1/3 parent code, if a particular condition is met.
However, assuming iterative decoding, convergence of the non-systematic code
towards low bit-error rates is problematic. To alleviate this problem, we
propose rate-1/2 partially-systematic codes that can still achieve a lower
error floor than that of their rate-1/3 parent codes. Results obtained from
extrinsic information transfer charts and simulations support our conclusion.Comment: 5 pages, 7 figures, Proceedings of the 2006 IEEE Information Theory
Workshop, Chengdu, China, October 22-26, 200
The runaway black hole GRO J1655-40
We have used the Hubble Space Telescope to measure the motion in the sky and
compute the galactocentric orbit of the black hole X-ray binary GRO J1655-40.
The system moves with a runaway space velocity of km s in a
highly eccentric () orbit. The black hole was formed in the
disk at a distance greater than 3 kpc from the Galactic centre and must have
been shot to such an eccentric orbit by the explosion of the progenitor star.
The runaway linear momentum and kinetic energy of this black hole binary are
comparable to those of solitary neutron stars and millisecond pulsars. GRO
J1655-40 is the first black hole for which there is evidence for a runaway
motion imparted by a natal kick in a supernova explosion.Comment: Published in Astronomy and Astrophysics. 5 pages, 2 color figures.
Color figure and animation can be found at
http://www.iafe.uba.ar/astronomia/mirabel/mirabel.html or
ftp://ftp.cea.fr/incoming/y2k01/mirabe
Milage aprender+ uma app para aprender matemática usando smartphones e tablets
O baixo desempenho dos estudantes na aprendizagem da matemática constitui problema que em alguns países se tem vindo a acentuar nos últimos anos. De acordo com um estudo realizado pelo Departamento de Educação dos EUA, em 2010, as aulas em regime de blended-learning, ou b-learning, apresentam melhores resultados do que as tradicionais aulas presenciais. Por outro lado, observa-se um número crescente de estudantes que usa smartphones e tablets nas escolas, cuja popularidade pode ser aproveitada para estimular a sua utilização em atividades educacionais para melhorar a aprendizagem.
Nesta comunicação apresenta-se uma nova aplicação para dispositivos móveis, smartphones e tablets, app MILAGE, através da qual o aluno pode aceder a conteúdos pedagógicos, dentro e fora da sala de aula. De modo a estimular e apoiar a realização das várias atividades propostas, a interface incorpora características de gamificação e recursos multimédia.info:eu-repo/semantics/publishedVersio
Robustness of reserve selection procedures under temporal species turnover
Complementarity-based algorithms for the selection of reserve networks emphasize the need to represent biodiversity features efficiently, but this may not be sufficient to maintain those features in the long term. Here, we use data from the Common Birds Census in Britain as an exemplar data set to determine guidelines for the selection of reserve networks which are more robust to temporal turnover in features. The extinction patterns found over the 1981-1991 interval suggest that two such guidelines are to represent species in the best sites where they occur (higher local abundance) and to give priority to the rarer species. We tested five reserve selection strategies, one which finds the minimum representation set and others which incorporate the first or both guidelines proposed. Strategies were tested in terms of their efficiency (inversely related to the total area selected) and effectiveness (inversely related to the percentage of species lost) using data on eight pairs of ten-year intervals.
The minimum set strategy was always the most efficient, but suffered higher species loss than the others, suggesting that there is a trade-off between efficiency and effectiveness. A desirable compromise can be achieved by embedding the concerns about the long-term maintenance of the biodiversity features of interest in the complementarity-based algorithms
Development of low-cost culture media for effective biosurfactant production
In this work, biosurfactant production by Pseudomonas aeruginosa and Bacillus subtillis strains was optimized using low-cost substrates. The highest biosurfactant production (3.2 g/L) by the P. aeruginosa strain was obtained using a culture medium containing corn steep liquor (CSL) (10% (v/v)) and molasses (10% (w/v)), whereas the best biosurfactant production by the B. subtillis isolate (1.3 g/L) was obtained using a culture medium consisting of 10% (v/v) of CSL. Subsequently, for the B. subtillis strain, the effect of different metals (iron, manganese and magnesium) on biosurfactant production was evaluated. When the culture medium CSL 10% was supplemented with the optimum concentration of those metals simultaneously, the biosurfactant production was increased up to 4.8 g/L. The biosurfactant produced by the P. aeruginosa strain was characterized as a mixture of eight different rhamnolipid congeners, being the most abundant the mono-rhamnolipid Rha-C10-C10, and the biosurfactant produced by the B. subtillis isolate consisted of a mixture of C13-, C14- and C15-surfactin. Both biosurfactants exhibited a good performance in oil recovery assays when compared with chemical surfactants, suggesting their potential use as an alternative to traditional chemical surfactants in enhanced oil recovery or bioremediation
New microbial surface-active compounds: the ultimate alternative to chemical surfactants?
Surface active compounds (SACs) produced by microorganisms are attracting a pronounced interest due to their potential advantages over synthetic counterparts, and to the fact that they could replace some of the synthetics in many environmental and industrial applications. Bioemulsifier production by a Paenibacillus strain isolated from crude oil was studied. The bioemulsifier was produced using sucrose with and without adding hydrocarbons (paraffin or crude oil) under aerobic and anaerobic conditions at 40ºC. It formed stable emulsions with several hydrocarbons, exhibiting similar or better emulsifying activity when compared with chemical SACs, and its emulsifying ability was not affected by exposure to high salinities (up to 300 g/l), high temperatures (100-121ºC) or a wide range of pH values (2-13). In addition, it presented low toxicity and high biodegradability when compared with chemical surfactants, implying a greater environmental compatibility. A preliminary chemical characterization by Fourier Transform Infrared Spectroscopy (FT-IR), proton and carbon nuclear magnetic resonance (1H NMR and 13C CP-MAS NMR) and size exclusion chromatography indicated that the bioemulsifier is a low molecular weight oligosaccharide-lipid complex. To the best of our knowledge, bioemulsifier production by a Paenibacillus strain has not been previously reported. This is also the first description of a low molecular weight bioemulsifier. The features of this novel bioemulsifier make it an interesting biotechnological product for many environmental and industrial applications.Financial support from the projects BIOCLEAN-Desenvolvimento de produtos contendo surfactantes microbianos para limpeza e desinfeção de superfícies industriais e domésticas.
QREN-n.º 2013/030215, and NCMICROBIOS -Desenvolvimento de bioprocessos
usando microrganismos não convencionais para a produção de biosurfactantes
- Convénio FCT-CNPq Nº 17/2013 – Ref.: Projecto nº 6818
- …