Giorgiutti-Dauphine F.,Fast campus |
Pauchard L.,University Paris - Sud
European Physical Journal E | Year: 2014
The drying of colloidal films usually leads to mechanical instabilities that affect the uniformity of the final deposit. The resulting patterns are the signature of the mechanical stress, and reveal the way the system consolidates. We report experimental results on the crack patterns induced by the drying of sessile drops of concentrated dispersions. Crack patterns exhibit a well-defined spatial order, and a regular temporal periodicity. In addition, the onset of cracking occurs after a well-defined elapsed time that depends on the mechanical properties of the gel, and on the drying kinetics. The estimation of the time elapsed before cracks form is related to the elastic properties of the material. This is supported by quantitative measurements using indentation testing and by a simple scaling law derived from poro-elastic theory. © 2014 EDP Sciences, SIF, Springer-Verlag Berlin Heidelberg.
Di Giuseppe E.,Fast campus |
Moroni M.,University of Rome La Sapienza |
Caputo M.,University of Rome La Sapienza
Transport in Porous Media | Year: 2010
The classic constitutive equation relating fluid flux to a gradient in potential (pressure head plus gravitational energy) through a porous medium was discovered by Darcy in the mid 1800s. This law states that the flux is proportional to the pressure gradient. However, the passage of the fluid through the porous matrix may cause a local variation of the permeability. For example, the flow may perturb the porous formation by causing particle migration resulting in pore clogging or chemically reacting with the medium to enlarge the pores or diminish the size of the pores. In order to adequately represent these phenomena, we modify the constitutive equations by introducing a memory formalism operating on both the pressure gradient-flux and the pressure-density variations. The memory formalism is then represented with fractional order derivatives. We perform a number of laboratory experiments in uniformly packed columns where a constant pressure is applied on the lower boundary. Both homogeneous and heterogeneous media of different characteristic particle size dimension were employed. The low value assumed by the memory parameters, and in particular by the fractional order, demonstrates that memory is largely influencing the experiments. The data and theory show how mechanical compaction can decrease permeability, and consequently flux. © Springer Science+Business Media B.V. 2009.
Valera L.,Fast campus
Medicina nei secoli | Year: 2011
Ecology (from the Greek words οιχοσ, "house" and λογια "study of") is the science of the "house", since it studies the environments where we live. There are three main ways of thinking about Ecology: Ecology as the study of interactions (between humans and the environment, between humans and living beings, between all living beings, etc.), Ecology as the statistical study of interactions, Ecology as a faith, or rather as a science that requires a metaphysical view. The history of Ecology shows us how this view was released by the label of "folk sense" to gain the epistemological status of science, a science that strives to be interdisciplinary. So, the aim of Ecology is to study, through a scientific methodology, the whole natural world, answering to very different questions, that arise from several fields (Economics, Biology, Sociology, Philosophy, etc.). The plurality of issues that Ecology has to face led, during the Twentieth-century, to branch off in several different "ecologies". As a result, each one of these new approaches chose as its own field a more limited and specific portion of reality.
Sauret A.,Universites Aix Marseille |
Cbron D.,Universites Aix Marseille |
Morize C.,Universites Aix Marseille |
Morize C.,Fast campus |
Le Bars M.,Universites Aix Marseille
Journal of Fluid Mechanics | Year: 2010
We study both experimentally and numerically the steady zonal flow generated by longitudinal librations of a spherical rotating container. This study follows the recent weakly nonlinear analysis of Busse (J. Fluid Mech., vol. 650, 2010, pp. 505-512), developed in the limit of small libration frequency-rotation rate ratio and large libration frequency-spin-up time product. Using particle image velocimetry measurements as well as results from axisymmetric numerical simulations, we confirm quantitatively the main features of Busse's analytical solution: the zonal flow takes the form of a retrograde solid-body rotation in the fluid interior, which does not depend on the libration frequency nor on the Ekman number, and which varies as the square of the amplitude of excitation. We also report the presence of an unpredicted prograde flow at the equator near the outer wall. © 2010 Cambridge University Press.
Iram H.,Fast campus |
2015 Power Generation Systems and Renewable Energy Technologies, PGSRET 2015 | Year: 2015
Renewable energy resources are the major demand of the day. As fossil fuels are limited so we just can't rely on them especially in this new age where the demand of energy has increased drastically. Solar energy can be one of the effective renewable energy sources. This is a new way of looking at a solar panel that we can generate alternating current directly from photovoltaic cells. We can use an array of photovoltaic cell pairs that are connected in anti-parallel form to create an AC wave form. Solar panels today produce DC power which has to be firstly converted into AC to be mostly used in business and home appliances. Solar panels become very expensive when we add solar panel's price joint with the price of inverters and phase synchronizers. In addition to that the power losses of different components that are used in the DC to AC converters so it becomes even more unappealing. We show a new technique for the generation of AC power from Solar panel devoid of inverter. By adopting this technique we can remove power losses due to an inverter. There is no need of batteries in our technique so overall cost is also reduced. Another very good aspect of this technique is that we get a very pure sine wave of better efficiency than that of an AC inverter. We can generate the sine wave of any frequency by just controlling the speed of motor used in this technique. So it is a very simple technique with great effects. © 2015 IEEE.