Droit

Résumé

vignette|La Loi par Jean-Jacques Feuchère. Marbre, 1852. Place du Palais-Bourbon, VIIe arrondissement de Paris. Le droit est défini comme , ou de façon plus complète . Ces règles, appelées règles de droit sont impersonnelles, abstraites, obligatoires et indiquent ce qui « doit être fait ». Ces règles juridiques peuvent trouver leur source dans une source normative « supérieure », extérieure, transcendante, comme le droit naturel, ou découler de normes intrinsèques, issues de la morale et de la raison. Dans ce second cas, les règles sont issues d'usages constatés et acceptés (droit coutumier) ou sont édictées et consacrées par l'autorité vue comme légitime (en général, l'État) chargée de régir l'organisation et le déroulement des relations sociales (droit écrit). La « force» obligatoire du droit suppose :

que la source du droit soit reconnue et acceptée comme légitime ;
que l'énoncé de la loi soit connu de tous, ce qui implique qu'il fasse l'objet d'une large publication ou d'une

Source officielle

https://fr.wikipedia.org/wiki/Droit

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The topics covered by the course are concepts of fluid mechanics, waves, and electromagnetism.

The course first develops the basic laws of electricity and magnetism and illustrates the use in understanding various electromagnetic phenomena.

Introduction à la mécanique des fluides, à l'électromagnétisme et aux phénomènes ondulatoires

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Séances de cours associées (424)

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Covariant formulation of relativistic mechanics

Miguel Alexandre Ribeiro Correia

Accretion disks surrounding compact objects, and other environmental factors, deviate satellites from geodetic motion. Unfortunately, setting up the equations of motion for such relativistic trajectories is not as simple as in Newtonian mechanics. The principle of general (or Lorentz) covariance and the mass-shell constraint make it difficult to parametrize physically adequate 4-forces. Here, we propose a solution to this old problem. We apply our framework to several conservative and dissipative forces. In particular, we propose covariant formulations for Hooke???s law and the constant force and compute the drag due to gravitational and hard-sphere collisions in dust, gas, and radiation media. We recover and covariantly extend known forces such as Epstein drag, Chandrasekhar???s dynamical friction, and Poynting-Robertson drag. Variable-mass effects are also considered, namely, Hoyle-Lyttleton accretion and the variable-mass rocket. We conclude with two applications: (1) The free-falling spring, where we find that Hooke???s law corrects the deviation equation by an effective anti???de Sitter tidal force and (2) black hole infall with drag. We numerically compute some trajectories on a Schwarzschild background supporting a dustlike accretion disk.

AMER PHYSICAL SOC2022

Chargement

This thesis is concerned with regular patterns found in ecology and biology, their linkages and the statistical description of their fluctuations around average trends. Among such patterns, often conforming to power laws, well-known examples include the Species-Area relationship (SAR), quantifying the increase of the number of species S inhabiting an ecosystem with ecosystem area, and the scale-invariant body size spectrum, routinely observed, e.g., in aquatic ecosystems. In biology, Kleiber's law is an allometric relationship describing how metabolic rates scale with an organism's body size. While ecological laws have often been studied independently, simple heuristic reasonings show that they are linked. The need for a unifying effort in ecology, coherently synthesizing the vast and diverse set of empirical observations across scales, has been often voiced. However, a theoretical framework answering this need was still lacking. Furthermore, ecological variables are the result of the interplay between several stochastic ecological processes, and are therefore stochastic variables fluctuating around average values. Ecological and biological scaling laws typically make predictions for such averages, but the issue of fluctuations received scarce attention in the literature. Similarly, biological fluctuations have been typically neglected in the study of the size-scaling of metabolic rates, even though body sizes and metabolic rates may have a significant variability within a species. Fluctuations may be relevant to interpret empirical observations, judge the reliability of predictions and understand ecosystem dynamics. An hypothesis for the distribution of abundances and body sizes of species inhabiting an ecosystem of finite area is proposed here. The hypothesis is inspired by finite-size scaling and is used to derive macroecological patterns and their linkages within a coherent theoretical framework. Stochastic models of community dynamics are used to support the hypothesis, and the derived linkages are tested on empirical datasets. Several stochastic models of community dynamics are also used here to study the fluctuations of S and how they scale with the average S. The intra-specific variability of metabolic rates and body sizes is investigated experimentally using freshwater phytoplankton species by nanoscale secondary ion mass spectrometry (NanoSIMS). The linkages among ecological scaling laws predicted by the theoretical framework are verified in several empirical datasets. Theoretical generalizations including deviations from pure power-law behavior and heavy-tailed intra-specific size distributions are also addressed. The theoretical study of the relative scaling of the fluctuations of S with the mean

\langle S \rangle

in various community dynamics models shows that different ecological processes predict radically different fluctuations scalings, highlighting the need of empirical investigations to sort out which scenario applies to real ecosystems. Experiments on phytoplankton metabolic rate scaling with body size suggest that intra-specific metabolic rate distributions are described by a universal scaling form across different taxa and over three orders of magnitude in body size. This thesis, along with previous works, suggests that scaling concepts derived for inanimate systems can provide new insights into the dynamics of ecosystems and help unraveling regularities across scales of biological complexity.

EPFL2018

Chargement

Time resolved luminescence measurements on polydiacetylenes

Christian Blumer

In this work time resolved luminescence measurements on the red phase of 3BCMU are presented. These polydiacetylenes form an ordered and isolated one dimensional model system. This work is divided in two parts. First we present an excitation spectrum in chapter 4. In the second part, radiative lifetimes are examined at temperatures down to 2 K (chapter 5). We present studies on excitation spectra on the red phase of 3BCMU up to an excitation energy of 850 meV above the zero phonon excitonic line. The vibronic modes of the double and triple bond of the carbon of the backbone and their combinations are identified. Compared to luminescence spectra a small anharmonicity is found. Also a relatively small Huang-Rhys factor is obtained, a parameter describing the decrease in intensity of the successive multiple of a vibronic mode. This is a result expected for such a complex system as a polymer. Furthermore, any signature of the band edge is absent in the spectrum. This result is interesting, as the theory predicts a suppression of the van Hove singularity at the band edge. Experimental results on other one-dimensional systems on this subject are rare. The radiative lifetime is a parameter which is dependent on the dimensionality of the structure. In the special case of one-dimensional systems it is predicted to be proportional to the square root of the temperature. Measurements of other one-dimensional systems show that the law is broken at relatively high temperatures (around 30 K) because of fluctuation of the confinement potential, which leads to localisation. For our sample, the radiative lifetime follows the mentioned law to a temperature down to 2 K. However, we show that in samples of less quality, mainly due to ageing, the law is not valid anymore. This ageing of the sample is caused by a higher polymerisation rate and defect in the crystalline structure.

EPFL2006

Chargement

\langle S \rangle

EPFL2018