[1] Data gathered with a five-channel radiometer are used to analyze the spectral composition of cloud enhancements and attenuations of UV (305, 320, 340, and 380 nm) and photosynthetically active radiation (PAR) (400-700 nm) at Valdivia, Chile (39.8°S), during summer months and within 3 hours from solar noon. Variations are referred to clear-sky days occurring at not too distant dates or obtained as polynomial fit to cloud-free periods on partially cloudy days. Photographic images of the sky were taken simultaneously with part of the radiometric data. Frequency of occurrence and duration of enhancements were estimated. Most of the enhancements were associated with cumuliform clouds in dissipation stage while the cloud fringes were crossing over the Sun disk. Both attenuations and enhancements present spectral dependence: the first decreasing and the second increasing toward longer wavelengths. Typical magnitude of the enhancement of 1-min averages for PAR is close to 20%, with highest values exceeding 40%, and decreasing to 6% for 305 nm. Cases with well-defined cloud side reflections were not observed. A weak relation between cloud cover and enhancement magnitude was found: Larger cloud cover was associated with higher enhancements.Citation: Lovengreen, C., H. A. Fuenzalida, and L. Videla (2005), On the spectral dependency of UV radiation enhancements due to clouds in Valdivia, Chile (39

Although most biological processes are characterized by a strong temporal asymmetry, several popular mathematical models neglect this issue. Maximum entropy methods provide a principled way of addressing time irreversibility, which leverages powerful results and ideas from the literature of non-equilibrium statistical mechanics. This tutorial provides a comprehensive overview of these issues, with a focus in the case of spike train statistics. We provide a detailed account of the mathematical foundations and work out examples to illustrate the key concepts and results from non-equilibrium statistical mechanics.

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We propose a simple model for interaction between gene candidates in the two strands of bacterial DNA (deoxyribonucleic acid). Our model assumes that 'final' genes appear in one of the two strands, that they do not overlap (in bacteria there is only a small percentage of overlap), and that the final genes maximize the occupancy rate, which is defined to be the proportion of the genome occupied by coding zones. We are more concerned with describing the organization and distribution of genes in bacterial DNA than with the very hard problem of identifying genes. To this end, an algorithm for selecting the final genes according to the previously outlined maximization criterion is proposed. We study the graphical and probabilistic properties of the model resulting from applying the maximization procedure to a Markovian representation of the genic and intergenic zones within the DNA strands, develop theoretical bounds on the occupancy rate (which, in our view, is a rather intractable quantity), and use the model to compute quantities of relevance to the Escherichia coli genome and compare these to annotation data. Although this work focuses on genomic modelling, we point out that the proposed model is not restricted to applications in this setting. It also serves to model other resource allocation problems.

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