Noções básicas de variabilidade da frequência cardíaca e sua aplicabilidade clínica

O sistema nervoso autônomo (SNA) desempenha um papel importante na regulação dos processos fisiológicos do organismo humano tanto em condições normais quanto patológicas. Dentre as técnicas utilizadas para sua avaliação, a variabilidade da frequência cardíaca (VFC) tem emergido como uma medida simples e não-invasiva dos impulsos autonômicos, representando um dos mais promissores marcadores quantitativos do balanço autonômico. A VFC descreve as oscilações no intervalo entre batimentos cardíacos consecutivos (intervalos R-R), assim como oscilações entre frequências cardíacas instantâneas consecutivas. Trata-se de uma medida que pode ser utilizada para avaliar a modulação do SNA sob condições fisiológicas, tais como em situações de vigília e sono, diferentes posições do corpo, treinamento físico, e também em condições patológicas. Mudanças nos padrões da VFC fornecem um indicador sensível e antecipado de comprometimentos na saúde. Uma alta variabilidade na frequência cardíaca é sinal de boa adaptação, caracterizando um indivíduo saudável, com mecanismos autonômicos eficientes, enquanto que, baixa variabilidade é frequentemente um indicador de adaptação anormal e insuficiente do SNA, implicando a presença de mau funcionamento fisiológico no indivíduo. Diante da sua importância como um marcador que reflete a atividade do SNA sobre o nódulo sinusal e como uma ferramenta clínica para avaliar e identificar comprometimentos na saúde, este artigo revisa aspectos conceituais da VFC, dispositivos de mensuração, métodos de filtragem, índices utilizados para análise da VFC, limitações de utilização e aplicações clínicas da VFC.

Sobre a natureza dos processos físicos de aquecimento da atmosfera de estrelas do tipo solar

In the present work, we have studied the nature of the physical processes of the coronal heating, considering as basis significant samples of single and binary evolved stars, that have been achieved with the ROSAT satellite. In a total of 191 simple stars were studied, classified in the literature as giants with spectral type F, G and K. The results were compared with those obtained from 106 evolved stars of spectral type F, G and K, which belong to the spectroscopic binary systems. Accurate measurements on rotation and information about binarity were obtained from De Medeiros s catalog. We have analysed the behavior of the coronal activity in function of diverse stellar parameters. With the purpose to better clarify the profile of the stars evolution, the HR diagram was built for the two samples of stars, the single and the binary ones. The evolved traces added in the diagram were obtained from the Toulouse-Geneve code, Nascimento et al. (2000). The stars were segregated in this diagram not only in range of rotational speed but also in range of X-ray flux. Our analysis shows clearly that the single stars and the binary ones have coronal activity controlled by physical process independent on the rotation. Non magnetic processes seem to be strongly influencing the coronal heating. For the binary stars, we have also studied the behavior of the coronal emission as a function of orbital parameters, such as period and eccentricity, in which it was revealed the existence of a discontinuity in the emission of X-rays around an orbital period of 100 days. The study helped to conclude that circular orbits of the binary stars are presented as a necessary property for the existence of a higher level ofX-rays emission, suggesting that the effect of the gravitational tide has an important role in the coronal activity level. When applied the Kolmogorov-Smirnov test (KS test ) for the Vsini and FX parameters to the samples of single and binary stars, we could evidence very relevant aspects for the understanding of the mechanisms inherent to the coronal activity. For the Vsini parameter, the differences between the single stars and the binary ones for rotation over 6.3 km/s were really remarkable. We believe, therefore, that the existence of gravitational tide is, at least, one of the factors that most contribute for this behavior. About the X-rays flux, the KS test showed that the behavior of the single and the binary stars, regarding the coronal activity, comes from the same origin

Análise das curvas de luz do CoroT usando diferentes processos comparativos: estimando períodos de rotação estelar

One of the main goals of CoRoT Natal Team is the determination of rotation period for thousand of stars, a fundamental parameter for the study of stellar evolutionary histories. In order to estimate the rotation period of stars and to understand the associated uncertainties resulting, for example, from discontinuities in the curves and (or) low signal-to-noise ratio, we have compared three different methods for light curves treatment. These methods were applied to many light curves with different characteristics. First, a Visual Analysis was undertaken for each light curve, giving a general perspective on the different phenomena reflected in the curves. The results obtained by this method regarding the rotation period of the star, the presence of spots, or the star nature (binary system or other) were then compared with those obtained by two accurate methods: the CLEANest method, based on the DCDFT (Date Compensated Discrete Fourier Transform), and the Wavelet method, based on the Wavelet Transform. Our results show that all three methods have similar levels of accuracy and can complement each other. Nevertheless, the Wavelet method gives more information about the star, from the wavelet map, showing the variations of frequencies over time in the signal. Finally, we discuss the limitations of these methods, the efficiency to give us informations about the star and the development of tools to integrate different methods into a single analysis

Processos de aquecimento na alta atmosfera estelar: emissão coronal em raio-x e emissão cromosférica em CaII

In the present work we study the processes of heating in the high stellar atmosphere, with base in an analysis of behavior of the cromospheric and coronal emission for a sample of single stars classified as giant in the literature. The evolutionary status of the stars of the sample was determined from HIPPARCOS satellite trigonometric parallax measurements and from the Toulouse Genéve code. In this study we show the form of behavior of the CaII emission flux in spectral lines H and K F(CaII) and the X-ray emission flux in function of the rotation, number of Rossby Ro and depth in mass of the convective envelope. In this analysis we show that while the cromospheric activity is dominated clearly by a physical process of heating associated with the rotation, like a magnetic field produced by dynamo effect, the coronal activity seems to be influenced for a mechanism independent of the rotation. We show also that the effective role of the depth in massa of the convective envelope on the stellar activity has an important effect in the responsible physical process for the behavior of the activity in the atmosphere of the stars.

Estudos de modelos Estocásticos: processo de contato, séries aleatórias e processos difusivos

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior

Processos difusivos generalizados

We investigate several diffusion equations which extend the usual one by considering the presence of nonlinear terms or a memory effect on the diffusive term. We also considered a spatial time dependent diffusion coefficient. For these equations we have obtained a new classes of solutions and studied the connection of them with the anomalous diffusion process. We start by considering a nonlinear diffusion equation with a spatial time dependent diffusion coefficient. The solutions obtained for this case generalize the usual one and can be expressed in terms of the q-exponential and q-logarithm functions present in the generalized thermostatistics context (Tsallis formalism). After, a nonlinear external force is considered. For this case the solutions can be also expressed in terms of the q-exponential and q-logarithm functions. However, by a suitable choice of the nonlinear external force, we may have an exponential behavior, suggesting a connection with standard thermostatistics. This fact reveals that these solutions may present an anomalous relaxation process and then, reach an equilibrium state of the kind Boltzmann- Gibbs. Next, we investigate a nonmarkovian linear diffusion equation that presents a kernel leading to the anomalous diffusive process. Particularly, our first choice leads to both a the usual behavior and anomalous behavior obtained through a fractionalderivative equation. The results obtained, within this context, correspond to a change in the waiting-time distribution for jumps in the formalism of random walks. These modifications had direct influence in the solutions, that turned out to be expressed in terms of the Mittag-Leffler or H of Fox functions. In this way, the second moment associated to these distributions led to an anomalous spread of the distribution, in contrast to the usual situation where one finds a linear increase with time

Aglomerado estelar M67: processos de diluição e a evolução do Momentum Angular

Galactic stellar clusters have a great variety of physical properties that make valuable probes of stellar and galactic chemical evolution. Current studies show a discrepancy between the standard evolutionary models and observations, mainly considering the level of mixing and convective dilution of light elements, as well as to the evolution of the angular momentum. In order to better settle some of these properties, we present a detailed spectroscopic analysis of 28 evolved stars, from the turn-off to the RGB, belonging to the stellar open cluster M67. The observations were performed using UVES+FLAMES at VLT/UT2. We determined stellar parameters and metallicity from LTE analysis of Fe I and Fe II lines between 420 1100 nm. The Li abundance was obtained using the line at 6707.78 ˚A, for the whole sample of stars. The Li abundances of evolved stars of M67 present a gradual decreasing when decreasing the effective temperature. The Li dilution factor for giant stars of M67 with Teff ∼ 4350K is at least 2300 times greater than that predicted by standard theory for single field giant stars. The Li abundance as a function of rotation exhibits a good correlation for evolved stars of M67, with a much smaller dispersion than the field evolved stars. The mass and the age seem to be some of the parameters that influence this connection. We discovered a Li-rich subgiant star in M67 (S1242). It is member of a spectroscopic binary system with a high eccentricity. Its Li abundance is 2.7, the highest Li content ever measured for an evolved star in M67. Two possibilities could explain this anomalous Li content: (i) preservation of the Li at the post turn off stage due to tidal effects, or (ii) an efficient dredge-up of Li, hidden below the convective zone by atomic diffusion occurring in the post turn off stage. We also study the evolution of the angular momentum for the evolved stars in M67. The results are in agreement with previous studies dedicated to evolved stars of this cluster, where stars in the same region of the CM-diagram have quite similar rotations, but with values that indicate an extra breaking along the main sequence. Finally, we analize the distributions of the average rotational velocity and of the average Li abundance as a function of age. With relation to the average Li abundances, stars in clusters and field stars present the same type of exponencial decay law t−β. Such decay is observed for ages lesser than 2 Gyr. From this age, is observed that the average Li abundance remain constant, differently of the one observed in the rotation age connection, where the average rotational velocity decreases slowly with age

Caracterização estatística de processos sísmicos via Distribuição Generalizada de Pareto. Estudo de caso: João Câmara-RN

The work is to make a brief discussion of methods to estimate the parameters of the Generalized Pareto distribution (GPD). Being addressed the following techniques: Moments (moments), Maximum Likelihood (MLE), Biased Probability Weighted Moments (PWMB), Unbiased Probability Weighted Moments (PWMU), Mean Power Density Divergence (MDPD), Median (MED), Pickands (PICKANDS), Maximum Penalized Likelihood (MPLE), Maximum Goodness-of-fit (MGF) and the Maximum Entropy (POME) technique, the focus of this manuscript. By way of illustration adjustments were made for the Generalized Pareto distribution, for a sequence of earthquakes intraplacas which occurred in the city of João Câmara in the northeastern region of Brazil, which was monitored continuously for two years (1987 and 1988). It was found that the MLE and POME were the most efficient methods, giving them basically mean squared errors. Based on the threshold of 1.5 degrees was estimated the seismic risk for the city, and estimated the level of return to earthquakes of intensity 1.5°, 2.0°, 2.5°, 3.0° and the most intense earthquake never registered in the city, which occurred in November 1986 with magnitude of about 5.2º

Estudo da expressão imuno-histoquímica das MMPs -2, -7, -9 e -26 e TIMPs -1 e -2 em adenomas pleomórficos e carcinomas adenóides císticos de glândulas salivares menores

The balance between the expression of matrix metalloproteinases (MMPs) and their tissue inhibitors (TIMPs) has been related to various physiological and pathological processes, including salivary gland morphogenesis and tumor invasion and metastasis processes. Pleomorphic adenoma (PA) and adenoid cystic carcinoma (ACC) respectively represent benign and malignant neoplasias of salivary glands. Although they share the same cell origin, they present distinct biological behavior. The aim of this study was to compare the immunohistochemical expression of MMPs -2, -7, -9 and -26, and of TIMPs -1 and -2, in cases of PA and ACC of minor salivary glands. Twenty cases of PA and twenty cases of ACC were assessed according to the presence, intensity and location of MMPs and TIMPs in the tumor parenchyma. Most of the PAs and ACCs presented a high expression of MMP -2, -7, -9 and -26 and of TIMP -1 and -2, predominantly located in tumor cells. There was no significant difference in the expression of MMPs -2 (p=0.359), -7 (p=0.081) and -26 (p=0.553), as well as of TIMPs -1 (p=0.657) and -2 (p=0.248), between the parenchyma of PAs and ACCs. However, MMP-9 showed a significant difference of expression between the two tumors, with the ACC showing more intense marking for this gelatinase (p=0.041). The strong expression of MMP-9 observed in the parenchyma suggests that this gelatinase may play an important role in the biological behavior of these tumors. On the other hand, although there was no significant difference between the marking of MMP -2, 7 and 26 in the studied tumors, the data, when analyzed as a whole, suggest that these proteases may take part in the process of tissue remodeling in both tumors, but do not present a direct relation with the pattern of aggressiveness of ACC. Nonetheless, matrilisins may indirectly influence the behavior of this tumor due to their capacity of activating MMP-9, strongly expressed in the parenchyma of ACC