Demographic growth and the distribution of language sizes

It is argued that the present log-normal distribution of language sizes is, to a large extent, a consequence of demographic dynamics within the population of speakers of each language. A two-parameter stochastic multiplicative process is proposed as a model for the population dynamics of individual languages, and applied over a period spanning the last ten centuries. The model disregards language birth and death. A straightforward fitting of the two parameters, which statistically characterize the population growth rate, predicts a distribution of language sizes in excellent agreement with empirical data. Numerical simulations, and the study of the size distribution within language families, validate the assumptions at the basis of the model.Comment: To appear in Int. J. Mod. Phys. C (2008

Strong correlations between text quality and complex networks features

Concepts of complex networks have been used to obtain metrics that were correlated to text quality established by scores assigned by human judges. Texts produced by high-school students in Portuguese were represented as scale-free networks (word adjacency model), from which typical network features such as the in/outdegree, clustering coefficient and shortest path were obtained. Another metric was derived from the dynamics of the network growth, based on the variation of the number of connected components. The scores assigned by the human judges according to three text quality criteria (coherence and cohesion, adherence to standard writing conventions and theme adequacy/development) were correlated with the network measurements. Text quality for all three criteria was found to decrease with increasing average values of outdegrees, clustering coefficient and deviation from the dynamics of network growth. Among the criteria employed, cohesion and coherence showed the strongest correlation, which probably indicates that the network measurements are able to capture how the text is developed in terms of the concepts represented by the nodes in the networks. Though based on a particular set of texts and specific language, the results presented here point to potential applications in other instances of text analysis.Comment: 8 pages, 8 figure

Análise fitoquímica do extrato etanólico das folhas de Solanum crinitum LAM.

Diante da biodiversidade de plantas medicinais, este trabalho teve como objetivo isolar e caracterizar substâncias presentes nas folhas de S. crinitum, utilizando cromatografia de camada fina

Radiopurity of Micromegas readout planes

Micromesh Gas Amplification Structures (Micromegas) are being used in an increasing number of Particle Physics applications since their conception fourteen years ago. More recently, they are being used or considered as readout of Time Projection Chambers (TPCs) in the field of Rare Event searches (dealing with dark matter, axions or double beta decay). In these experiments, the radiopurity of the detector components and surrounding materials is measured and finely controlled in order to keep the experimental background as low as possible. In the present paper, the first measurement of the radiopurity of Micromegas planes obtained by high purity germanium spectrometry in the low background facilities of the Canfranc Underground Laboratory (LSC) is presented. The obtained results prove that Micromegas readouts of the microbulk type are currently manufactured with radiopurity levels below 30 microBq/cm2 for Th and U chains and ~60 microBq/cm2 for 40K, already comparable to the cleanest detector components of the most stringent low background experiments at present. Taking into account that the studied readouts were manufactured without any specific control of the radiopurity, it should be possible to improve these levels after dedicated development.Comment: 15 pages, 2 figure

Good practices for a literature survey are not followed by authors while preparing scientific manuscripts

The number of citations received by authors in scientific journals has become a major parameter to assess individual researchers and the journals themselves through the impact factor. A fair assessment therefore requires that the criteria for selecting references in a given manuscript should be unbiased with respect to the authors or the journals cited. In this paper, we advocate that authors should follow two mandatory principles to select papers (later reflected in the list of references) while studying the literature for a given research: i) consider similarity of content with the topics investigated, lest very related work should be reproduced or ignored; ii) perform a systematic search over the network of citations including seminal or very related papers. We use formalisms of complex networks for two datasets of papers from the arXiv repository to show that neither of these two criteria is fulfilled in practice

“Um imperceptível traço de goma de tragacanto…”

Sem resum

Towards smaller gap microbulks

Small gap Micromegas detectors (< 50µm) are expected to be optimal for high pres- sure applications. Combining the microbulk manufacturing technique with a small gap can result in attractive detectors for rare event detection, in particular double beta decay or dark matter searches. We present novel results obtained with small gap microbulks (25 and 12.5µm) that have been manufactured recently. For the first time for this type of detectors, we show experimentally that for each amplification gap there is an optimal pressure and that smaller gaps are more suitable for higher pressures

Reduction of sulfenic acids by ascorbate in proteins, connecting thiol-dependent to alternative redox pathways

Sulfenic acids are the primary product of thiol oxidation by hydrogen peroxide and other oxidants. Several aspects of sulfenic acid formation through thiol oxidation were established recently. In contrast, the reduction of sulfenic acids is still scarcely investigated. Here, we characterized the kinetics of the reduction of sulfenic acids by ascorbate in several proteins. Initially, we described the crystal structure of our model protein (Tsa2-C170S). There are other Tsa2 structures in distinct redox states in public databases and all of them are decamers, with the peroxidatic cysteine very accessible to reductants, convenient features to investigate kinetics. We determined that the reaction between Tsa2-C170S-Cys-SOH and ascorbate proceeded with a rate constant of 1.40 ± 0.08 × 103 M−1 s−1 through a competition assay developed here, employing 2,6–dichlorophenol-indophenol (DCPIP). A series of peroxiredoxin enzymes (Prx6 sub family) were also analyzed by this competition assay and we observed that the reduction of sulfenic acids by ascorbate was in the 0.4–2.2 × 103 M−1 s−1 range. We also evaluated the same reaction on glyceraldehyde 3-phosphate dehydrogenase and papain, as the reduction of their sulfenic acids by ascorbate were reported previously. Once again, the rate constants are in the 0.4–2.2 × 103 M−1 s−1 range. We also analyzed the reduction of Tsa2-C170S-SOH by ascorbate by a second, independent method, following hydrogen peroxide reduction through a specific electrode (ISO-HPO-2, World Precision Instruments) and employing a bi-substrate, steady state approach. The was 7.4 ± 0.07 × 103 M−1 s−1, which was in the same order of magnitude as the value obtained by the DCPIP competition assay. In conclusion, our data indicates that reduction of sulfenic acid in various proteins proceed at moderate rate and probably this reaction is more relevant in biological systems where ascorbate concentrations are high

Quantum Phase Transition in the Frustrated Heisenberg Antiferromagnet

Using the J_1-J_2 model, we present a description of quantum phase transition from Neel ordered to the spin-liquid state based on the modified spin wave theory. The general expression for the gap in the spectrum in the spin-liquid phase is presented.Comment: 8 pages of REVTeX 3.0, one PostScript file appended (Eq. 15 corrected, two recent references added, + some minor changes