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Search Results: 1 - 10 of 462209 matches for " A.;Franca "
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Estimating Attractor Dimension on the Nonlinear Pendulum Time Series
Franca, Luiz Fernando P.;Savi, Marcelo A.;
Journal of the Brazilian Society of Mechanical Sciences , 2001, DOI: 10.1590/S0100-73862001000400004
Abstract: chaotic dynamical systems exhibit trajectories in their phase space that converges to a strange attractor. the strangeness of the chaotic attractor is associated with its dimension in which instance it is described by a noninteger dimension. this contribution presents an overview of the main definitions of dimension discussing their evaluation from time series employing the correlation and the generalized dimension. the investigation is applied to the nonlinear pendulum where signals are generated by numerical integration of the mathematical model, selecting a single variable of the system as a time series. in order to simulate experimental data sets, a random noise is introduced in the time series. state space reconstruction and the determination of attractor dimensions are carried out regarding periodic and chaotic signals. results obtained from time series analyses are compared with a reference value obtained from the analysis of mathematical model, estimating noise sensitivity. this procedure allows one to identify the best techniques to be applied in the analysis of experimental data.
Estimating Attractor Dimension on the Nonlinear Pendulum Time Series
Franca Luiz Fernando P.,Savi Marcelo A.
Journal of the Brazilian Society of Mechanical Sciences , 2001,
Abstract: Chaotic dynamical systems exhibit trajectories in their phase space that converges to a strange attractor. The strangeness of the chaotic attractor is associated with its dimension in which instance it is described by a noninteger dimension. This contribution presents an overview of the main definitions of dimension discussing their evaluation from time series employing the correlation and the generalized dimension. The investigation is applied to the nonlinear pendulum where signals are generated by numerical integration of the mathematical model, selecting a single variable of the system as a time series. In order to simulate experimental data sets, a random noise is introduced in the time series. State space reconstruction and the determination of attractor dimensions are carried out regarding periodic and chaotic signals. Results obtained from time series analyses are compared with a reference value obtained from the analysis of mathematical model, estimating noise sensitivity. This procedure allows one to identify the best techniques to be applied in the analysis of experimental data.
Berry's phase in Cavity QED: proposal for observing an effect of field quantization
A. Carollo,M. Franca Santos,V. Vedral
Physics , 2002, DOI: 10.1103/PhysRevA.67.063804
Abstract: Geometric phases are well known in classical electromagnetism and quantum mechanics since the early works of Pantcharatnam and Berry. Their origin relies on the geometric nature of state spaces and has been studied in many different systems such as spins, polarized light and atomic physics. Recent works have explored their application in interferometry and quantum computation. Earlier works suggest how to observe these phases in single quantum systems adiabatically driven by external classical devices or sources, where, by classical, we mean any system whose state does not change considerably during the interaction time: an intense magnetic field interacting with a spin 1/2, or a birefringent medium interacting with polarized light. Here we propose a feasible experiment to investigate quantum effects in these phases, arising when this classical source drives not a single quantum system, but two interacting ones. In particular, we show how to observe a signature of field quantization through a vacuum effect in Berry's phase. To do so, we describe the interaction of an atom and a quantized cavity mode altogether driven by an external quasi-classical field.
Cubic Spline Approximation for Weakly Singular Integral Models  [PDF]
Franca Caliò, Elena Marchetti
Applied Mathematics (AM) , 2013, DOI: 10.4236/am.2013.411211
Abstract: In this paper we propose a numerical collocation method to approximate the solution of linear integral mixed Volterra Fredholm equations of the second kind, with particular weakly singular kernels. The collocation method is based on the class of quasi-interpolatory splines on locally uniform mesh. These approximating functions are particularly suitable to tackle on problems with weakly regular solutions. We analyse the convergence problems and we present some numerical results and comparisons to confirm the efficiency of the numerical model.
The phase distribution of upward co-current bubbly flows in a vertical square channel
Matos, A. de;Rosa, E. S.;Franca, F. A.;
Journal of the Brazilian Society of Mechanical Sciences and Engineering , 2004, DOI: 10.1590/S1678-58782004000300007
Abstract: in this work one shows experimental data and numerical results of the void fraction distribution in vertical upward air-water bubbly flows in a square cross-section channel. to measure the void fraction distribution one used a single wire conductive probe. the averaged void fraction ranged from 3.3% to 15%; the liquid and the gas superficial velocities varied from 0.9 m/s to 3.0 m/s and 0.04 m/s to 0.5 m/s, respectively. the experimental results for the void fraction distribution were compared with numerical calculation performed by an eulerian-eulerian implementation of the two-fluid model. in this work one performs the turbulence modeling with three approaches: using an algebraic model, the k-e two-phase model and the k-e two-phase two-layer model. comparisons between the experimental and numerical data revealed, in general, good agreement.
Predictors of mosquito net use in Ghana
Carol A Baume, Ana Cláudia Franca-Koh
Malaria Journal , 2011, DOI: 10.1186/1475-2875-10-265
Abstract: The data come from an August 2008 survey in Ghana of households with a pregnant woman or a guardian of a child under five, conducted during the rainy season. 1796 households were included in this analysis, which generated a sample of 1,852 mosquito nets. Using each net owned as the unit of analysis, multivariate logistic regression was used to examine the relationship of net used last night with 23 potentially explanatory variables having to do with characteristics of the household, of the respondent, and of the net. Odds Ratios, p-values, and confidence intervals were calculated for each variable to develop an explanatory model.The final multivariate model consisted of 10 variables statistically associated with whether or not the net was used the prior night: rural location, lower SES, not using coils for mosquito control, fewer nets in the household, newer nets and those in better condition, light blue colour, higher level of education of the guardian of the child under five, knowing that mosquitoes transmit malaria, and paying for the net instead of obtaining it free of charge.The results of this study suggest that net use would increase in Ghana if coloured nets were made available in mass distributions as well as in the commercial market; if programmes emphasize that malaria is caused only by night-biting mosquitoes, and that nets protect against mosquitoes better than coils and need to be used even if coils are burning; if donated nets are replaced more frequently so that households have nets that are in good condition; and if there were support for the commercial market so that those who can afford to purchase a net and want to choose their own nets can do so.During the past decade, the malaria control community has been successful in dramatically increasing the number of households that own mosquito nets – particularly ITNs (insecticide-treated nets) and LLINs (long-lasting insecticide-treated nets) – via programmes that made nets available commercially, at
Effect of the extraction conditions of virgin olive oil on the lipoxygenase cascade:Chemical and sensory implications
Morales, María T.,Angerosa, Franca,Aparicio, Ramón
Grasas y Aceites , 1999,
Abstract: The volatile compounds produced through the lipoxygenase cascade are responsible for the most remarkable sensory attributes of virgin olive oil. The paper analyses the evolution of these compounds according to different conditions of temperature and time of the malaxing process. The influence of these parameters on the production of C6 and C5volatile compounds is stated together with the effect that the amount of these compounds has on the most remarkable virgin olive oil sensory descriptors (green, bitter-pungent, sweet and undesirable). Optima values of temperature and time are given for producing high sensory quality virgin olive oils. Three cultivars, Spanish Picual and Italian Frantoio and Coratina, were characterised by sensory attributes and volatile compounds quantified by two different methodologies in order to avoid that results could be circumscribed to a specific cultivar or a quantification method. Los compuestos volátiles producidos a través de la ruta de la Iipoxigenasa son los responsables de los atributos sensoriales más importantes del aceite de oliva virgen. El presente trabajo estudia la evolución de estos compuestos según diferentes condiciones de temperatura y tiempo del proceso de extracción. Se ha determinado la influencia de estos parámetros en la producción de compuestos volátiles C6 y C5 así como el efecto que tienen estos compuestos en los descriptores sensoriales más destacados del aceite de oliva virgen (verde, amargo-picante, dulce e indeseable). Se dan valores óptimos de tiempo y temperatura para la producción de aceites de oliva vírgenes de alta calidad sensorial. Los atributos sensoriales de tres variedades, la espa ola Picual y las italianas Frantoio y Coratina, fueron evaluados y los compuestos volátiles cuantificados mediante dos metodologías diferentes con el fin de evitar que los resultados pudieran circunscribirse a una variedad específica o a un único método de cuantificación.
Microsurgical anatomy of foramen caecum posterius (Vicq d’Azyr foramen): importance for vascular neurology and neurosurgery
Aguiar PH,Tahara A,Franca DB,de Santana Junior PA
Neuroanatomy , 2008,
Abstract: Of 15 fresh cadavers, we studied the pontomedullary junction regarding the arterial source and variations, in the called Vicq d’Azyr foramen. This small triangular depression at the lower boundary of the pons between the pyramids that marks the upper limit of the anterior median fissure of the medulla oblongata is the foramen caecum medullae oblongatae, or Vicq d`Azyr foramen. The results showed a basilar artery of diameter of 6.22mm, 12.37 perforators to the mentioned area, mainly having their origin from basilar artery. The importance of studying this area is to better understand the neurovascular diseases of brain stem and serve as a guide forneurosurgeons operating in this vital area.
Ventila o mecanica na doen a pulmonar obstrutiva cr nica (DPOC) descompensada
Sérgio Jezler,Marcelo A. Holanda,Anderson José,Suelene Franca
Jornal Brasileiro de Pneumologia , 2007, DOI: 10.1590/s1806-37132007000800006
Abstract:
On the Relationship between Optical and X-Ray Luminosity of Quasars
F. la Franca,A. Franceschini,S. Cristiani,R. Vio
Physics , 1994,
Abstract: The issue of the X-ray to optical luminosity relationship ($L_o-L_x$) is addressed for both optically and X-ray selected quasar samples. We have applied a generalized regression algorithm for the case of samples involving censored data, with errors on both the dependent and the independent variable. Contrary to some previous results, we find that such relationship is consistent with being a linear one ($L_x\propto L_o$). We argue that previous reports of non-linear relationships (i.e. $L_x\propto L_o^e$ with $e < 1$) are due to the neglect of the influence of the photometric errors, the precise knowledge of which strongly influences the reliability of the results. Further progresses in the determination of the $L_o-L_x$ relationship can be achieved with ROSAT observations of the new generation of large bright quasar surveys.
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