No abstract

The molecular basis of anhydrobiosis, the state of suspended animation entered by some species during extreme desiccation, is still poorly understood despite a number of transcriptome and proteome studies. We therefore conducted functional screening by RNA interference (RNAi) for genes involved in anhydrobiosis in the holo-anhydrobiotic nematode Panagrolaimus superbus. A new method of survival analysis, based on staining, and proof-of-principle RNAi experiments confirmed a role for genes involved in oxidative stress tolerance, while a novel medium-scale RNAi workflow identified a further 40 anhydrobiosis-associated genes, including several involved in proteostasis, DNA repair and signal transduction pathways. This suggests that multiple genes contribute to anhydrobiosis in P. superbus.

The Kullback-Leibler distance (or relative entropy) is applied in the analysis of functional magnetic resonance (fMRI) data series. Our study is designed for event-related (ER) experiments, where a brief stimulus is presented and a long period of rest is followed. In particular, this relative entropy is used as a measure of the "distance" between the probability distributions p 1 and p 2 of the signal levels related to stimulus and non-stimulus. In order to avoid undesirable divergences of the Kullback-Leibler distance, a small positive parameter δ is introduced in the definition of the probability functions in such a way that it does not bias the comparison between both distributions. Numerical simulations are performed so as to determine the probability densities of the mean Kullback-Leibler distance D (throughout the N epochs of the whole experiment). For small values of N (N < 30), such probability densities f (D) are found to be fitted very well by Gamma distributions (χ 2 < 0.0009). The sensitivity and specificity of the method are evaluated by construction of the receiver operating characteristic (ROC) curves for some values of signal-to-noise ratio (SNR). The functional maps corresponding to real data series from an asymptomatic volunteer submitted to an ER motor stimulus is obtained by using the proposed technique. The maps present activation in primary and secondary motor brain areas. Both simulated and real data analyses indicate that the relative entropy can be useful for fMRI analysis in the information measure scenario.

h i g h l i g h t s• New measurements based on the concept of activity per agent are proposed.• The variance of the system activity can be used to indicate the critical points of the transition.• The frequency distribution of system activity is able to show the order of the phase transition. • A power law dependence between cluster activity and cluster size is verified. a b s t r a c tAxelrod's model was proposed to study interactions between agents and the formation of cultural domains. It presents a transition from a monocultural to a multicultural steady state which has been studied in the literature by evaluation of the relative size of the largest cluster. In this article, we propose new measurements based on the concept of activity per agent to study the Axelrod's model on the square lattice. We show that the variance of system activity can be used to indicate the critical points of the transition. Furthermore the frequency distribution of the system activity is able to show a coexistence of phases typical of a first order phase transition. Finally, we verify a power law dependence between cluster activity and cluster size for multicultural steady state configurations at the critical point.

Several mathematical models have been proposed to describe the dynamics of irradiated cancer cells and to evaluate the tumour control probability (TCP). In this article, we propose a TCP model-based statistical test for predicting the outcome of a radiation treatment. We determine the foresight capability of prostate tumour erradication (cure) from Monte Carlo simulations of the Dawson-Hillen TCP model. We construct the receiver operating characteristic (ROC) curves of the test from the probability distributions of the fraction of remaining tumour cells for simulated experiments that evolve either to cure or non-cure. Simulations show that a similar procedure may be applicable to clinical data. Results suggest that the evaluation of tumour sizes after the treatment has started may be used for short-term prognosis.

The phase diagram and the tricritical point of a collapsing lattice animal are studied through an extended series expansion of the isothermal compressibility Kr on a square lattice. As a function of the variables x (fugacity) and y = e JIT (T is the reduced temperature), this series Kr is investigated using the partial differential approximants technique. The characteristic flow pattern of partial differential approximant trajectories is determined for a typical stable fIxed point. We obtain satisfactory estimates for the tricritical fugacity Xt = 0.024± 0.005and temperature Tt = 0.54± 0.04.Taking into account only linear scaling fields we are also able to get the scaling exponent r = 1.4 ± 0.2 and the crossover exponent ¢J = 0.66± 0.08. Our results are in good agreement with previous estimates from other methods. We also study ramifIed polYmerizationthrough computational simulations on the square lattice of a kinetic growth model generalized to incorporte branching and impurities. The polYmerconfIguration is identifIed with a bond tree in order to examine its topology. The fractal dimensions of clusters are obtained at criticality. Simulations also allow the study of time evolution of clusters as well as the determination of time autocorrelations and dYnamical critical exponents. In regard to fInite size effects, a fourthorder cumulant technique is employed to estimate the critical branching probability be and the critical exponents v and p. In the absence of impurities, the surface roughness is described in terms of the Hurst exponents. Finally we simulate this kinetic growth model on the square lattice using a Monte Carlo approach in order to study ramifIed polYmerization with short distance attractive interactions between monomers. The phase boundary separating fInite from infInite growth regimes is obtained in the (T,b) space (T is the reduced temperature and b is the branching probability). In the thermodYnamic limit, we extrapolate the temperature T = 0.102± 0.005below which the phase is found to be always infInite. We also observe the occurrence of a roughening transition at the polYmersurface. INTRODU~"OMacromoleculas tais como os acidos nucleicos (DNAe RNA),as proteinas e os polissacarideos san polimeros de importancia fundamental nos processos biologicos. Outros exemplos de polimeros san alguns materiais naturais como a borracha, a madeira e os materiais sinteticos usados na fabricac;ao de plasticos e fibras, todos indispensaveis a civilizac;ao atual, essenciais ao vestuario, abrigo, transportes, comunicac;aoe conveniencias da vida moderna.o grande desenvolvimento da ciencia dos polimeros e a extensa utilizac;aodos materiais polimericos na tecnologia tern contribuido para urn interesse cada vez maior em varios problemas da fisica dos polimeros. Esta e uma combinac;aopeculiar de conceitos basicos, ideias e metodos da fisica molecular, termodinamica, mecanica estatistica e fisica do estado solido.Os polimeros lineares em soluc;ao tern sido objeto de estudo teorico (Flory, 1969; de Gennes, 1975 ...

Se estivéssemos aleatoriamente inseridos no Cosmos, a chance de nos descobrirmos em um planeta ou próximo a um deles seria menos de uma em um bilhão de trilhão de trilhão (1033). " Extraído de COSMOS, de Gari Sagan.