Model inspired by population genetics to study fragmentation of brittle plates

We use a model whose rules were inspired by population genetics, the random capability growth model, to describe the statistical details observed in experiments of fragmentation of brittle platelike objects, and in particular the existence of (i) composite scaling laws, (ii) small critical exponents \tau associated with the power-law fragment-size distribution, and (iii) the typical pattern of cracks. The proposed computer simulations do not require numerical solutions of the Newton's equations of motion, nor several additional assumptions normally used in discrete element models. The model is also able to predict some physical aspects which could be tested in new experiments of fragmentation of brittle systems.Comment: We have modified the text in order to make the description of the model more clear. One Figure (Figure 1) was introduced showing the steps of the dynamics of colonization. Twelve references were adde

Evolving division of labor in a response threshold model

The response threshold model explains the emergence of division of labor (i.e., task specialization) in an unstructured population by assuming that the individuals have different propensities to work on different tasks. The incentive to attend to a particular task increases when the task is left unattended and decreases when individuals work on it. Here we derive mean-field equations for the stimulus dynamics and show that they exhibit complex attractors through period-doubling bifurcation cascades when the noise disrupting the thresholds is small. In addition, we show how the fixed threshold can be set to ensure specialization in both the transient and equilibrium regimes of the stimulus dynamics. However, a complete explanation of the emergence of division of labor requires that we address the question of where the threshold variation comes from, starting from a homogeneous population. We then study a structured population scenario, where the population is divided into a large number of independent groups of equal size, and the fitness of a group is proportional to the weighted mean work performed on the tasks during a fixed period of time. Using a winner-take-all strategy to model group competition and assuming an initial homogeneous metapopulation, we find that a substantial fraction of workers specialize in each task, without the need to penalize task switching

Gene phylogenies and protein–protein interactions: possible artifacts resulting from shared protein interaction partners

The study of gene families critically depends on the correct reconstruction of gene genealogies, as for instance in the case of transcription factor genes like Hox genes and Dlx gene families. Proteins belonging to the same family are likely to share some of the same protein interaction partners and may thus face a similar selective environment. This common selective environment can induce co-evolutionary pressures and thus can give rise to correlated rates and patterns of evolution among members of a gene family. In this study, we simulate the evolution of a family of sequences which share a set of interaction partners. Depending on the amount of sequence dedicated to protein–protein interaction and the relative rate parameters of sequence evolution three outcomes are possible: if the fraction of the sequence dedicated to interaction with common co-factors is low and the time since divergence is small, the trees based on sequence information tend to be correct. If the time since gene duplication is long two possible outcomes are observed in our simulations. If the rate of evolution of the interaction partner is small compared to the rate of evolution of the focal protein family, the reconstructed trees tend towards star phylogenies. As the rate of evolution of the interaction partner approaches that of the focal protein family the reconstructed phylogenies tend to be incorrectly resolved. We conclude that the genealogies of gene families can be hard to estimate, in particular if the proteins interact with a conserved set of binding partners, as is likely the case for transcription factors

Complementarity and diversity in a soluble model ecosystem

Complementarity among species with different traits is one of the basic processes affecting biodiversity, defined as the number of species in the ecosystem. We present here a soluble model ecosystem in which the species are characterized by binary traits and their pairwise interactions follow a complementarity principle. Manipulation of the species composition, and so the study of its effects on the species diversity is achieved through the introduction of a bias parameter favoring one of the traits. Using statistical mechanics tools we find explicit expressions for the allowed values of the equilibrium species concentrations in terms of the control parameters of the model

Historical streamflow series analysis applied to furnas HPP reservoir watershed using the SWAT model

Over the last few years, the operation of the Furnas Hydropower Plant (HPP) reservoir, located in the Grande River Basin, has been threatened due to a significant reduction in inflow. In the region, hydrological modelling tools are being used and tested to support decision making and water sustainability. In this study, the streamflow was modelled in the area of direct influence of the Furnas HPP reservoir, and the Soil and Water Assessment Tool (SWAT) model performance was verified for studies in the region. Analyses of sensitivity and uncertainty were undertaken using the Sequential Uncertainty Fitting algorithm (SUFI-2) with a Calibration Uncertainty Program (SWAT-CUP). The hydrological modelling, at a monthly scale, presented good results in the calibration (NS 0.86), with a slight reduction of the coefficient in the validation period (NS 0.64). The results suggested that this tool could be applied in future hydrological studies in the region of study. With the consideration that special attention should be given to the historical series used in the calibration and validation of the models. It is important to note that this region has high demands for water resources, primarily for agricultural use. Water demands must also be taken into account in future hydrological simulations. The validation of this methodology led to important contributions to the management of water resources in regions with tropical climates, whose climatological and geological reality resembles the one studied here

Bounded fitness landscapes and the evolution of the linguistic diversity

A simple spatial computer simulation model was recently introduced to study the evolution of the linguistic diversity. The model considers processes of selective geographic colonization, linguistic anomalous diffusion and mutation. In the approach, we ascribe to each language a fitness function which depends on the number of people that speak that language. Here we extend the aforementioned model to examine the role of saturation of the fitness on the language dynamics. We found that the dependence of the linguistic diversity on the area after colonization displays a power law regime with a nontrivial exponent in very good agreement with the measured exponent associated with the actual distribution of languages on the Earth.Comment: 10 pages, 3 figure

Alta freqüência da mutação Q318X em pacientes com hiperplasia adrenal congênita por deficiência da 21-hidroxilase no nordeste do Brasil

OBJETIVES: Deficiency of 21-hydroxylase is the most common form of congenital adrenal hyperplasia (CAH-21OH). The aim of this study was to determine, by allele-specific PCR, the frequency of microconversions of the CYP21A2, in sixteen patients with the classical forms and in 5 patients with the nonclassical (NC) form of CAH-21OH and correlate genotype with phenotype. METHODS: Genotypes were classified into 3 mutation groups (A, B and C), based on the degree of enzymatic activity. Screening for 7 microconversions by allele-specific PCR diagnosed 74.3% (n=26) of the 35 unrelated alleles. RESULTS: The most frequent mutations were Q318X (25.7%), V281L (17.1%), I2 Splice (14.3%), I172N (14.3%), and R356W (14.3%). Genotype was identified in 57.1% of the patients. We observed correlation between genotype and phenotype in 91.7% of the cases. CONCLUSION: The highest frequency for Q318X (25.7%) when compared to other studies may reflect individual sample variations in this Northeastern population.OBJETIVOS: Deficiência de 21-hidroxilase é a forma mais comum de hiperplasia adrenal congênita (CAH-21OH). O objetivo deste estudo foi determinar, por PCR alelo-específica, a freqüência de microconversões no CYP21A2, em 16 pacientes com a forma clássica e em cinco pacientes com a forma não-clássica (NC) de CAH-21OH e correlacionar o genótipo com o fenótipo. MÉTODOS: Genótipo foi classificado em três grupos de mutações (A, B e C), baseado no grau de atividade enzimática. A técnica de PCR alelo-específico diagnosticou 74,3% (n = 26) dos 35 alelos não relacionados. RESULTADOS: As mutações mais freqüentes foram Q318X (25,7%), V281L (17,1%), I2 Splice (14,3%), I172N (14,3%) e R356W (14,3%). O genótipo foi identificado em 57,1% dos pacientes. Houve correlação genótipo-fenótipo em 91,7% dos casos. CONCLUSÃO: A mais alta freqüência da mutação Q318X (25,7%) comparada a outros estudos pode refletir variações individuais desta população do nordeste.Fapitec (FAP - Foundation for Support to Research of Sergipe [Fundep] 02/2002)Federal University of Sergipe - Medicine Post-Graduation Cente

Random replicators with high-order interactions

We use tools of the equilibrium statistical mechanics of disordered systems to study analytically the statistical properties of an ecosystem composed of N species interacting via random, Gaussian interactions of order p >= 2, and deterministic self-interactions u <= 0. We show that for nonzero u the effect of increasing the order of the interactions is to make the system more cooperative, in the sense that the fraction of extinct species is greatly reduced. Furthermore, we find that for p > 2 there is a threshold value which gives a lower bound to the concentration of the surviving species, preventing then the existence of rare species and, consequently, increasing the robustness of the ecosystem to external perturbations.Comment: 7 pages, 4 Postscript figure

Landscape statistics of the p-spin Ising model

The statistical properties of the local optima (metastable states) of the infinite range Ising spin glass with p-spin interactions in the presence of an external magnetic field h are investigated analytically. The average number of optima as well as the typical overlap between pairs of identical optima are calculated for general p. Similarly to the thermodynamic order parameter, for p>2 and small h the typical overlap q_t is a discontinuous function of the energy. The size of the jump in q_t increases with p and decreases with h, vanishing at finite values of the magnetic field.Comment: 12 pages,te

Fatigue Effects in Daily Life Activities of Kidney Transplant Recipients

After undergoing kidney transplantation, some patients still face one symptom that continues after the dialysis sessions: fatigue (physical and mental tiredness that does not get better after resting). Fatigue effects in the everyday lives of kidney transplant patients can be beneficially modified early by changing this scenario. This is a quantitative study about the intensity and impacts of fatigue in kidney transplant patients admitted to the Hypertension and Kidney Hospital from October 2011 to March 2012. the fatigue pictogram was used to evaluate the level of fatigue interference in the daily life activities of kidney transplant patients. the sample consists of 39 patients, and was developed in 2 phases: data collection and attendance after and before the transplantation until hospital discharge. Descriptive statistical analyses were used. in the group at issue, we have noticed the following profile of the sample: 84.3% of transplantations with live donors, most were men, average age 36.5 years old, average hospitalization time 11.1 days, average time of renal failure 66.4 months, systemic arterial hypertension prevalence 66.7%, and the prevalence of at least 1.8 diseases in each individual. the self-referred causes of chronic renal failure were uncontrolled systemic arterial hypertension, glomerulonephritis, and overuse of anti-inflammatory drugs, among others. the study shows that fatigue is directly related to the level of activities of daily living, causing less ability to perform activities in the higher level of fatigue, which is in the immediate postoperative period and only settling fully on the 9th postoperative day.Universidade Federal de São Paulo, Nursing Sch São Paulo, São Paulo, BrazilUniversidade Federal de São Paulo, Kidney & Hypertens Hosp, São Paulo, BrazilUniversidade Federal de São Paulo, Nursing Sch São Paulo, São Paulo, BrazilUniversidade Federal de São Paulo, Kidney & Hypertens Hosp, São Paulo, BrazilWeb of Scienc