29,670 research outputs found
Maximum entropy generation in open systems: the Fourth Law?
This paper develops an analytical and rigorous formulation of the maximum
entropy generation principle. The result is suggested as the Fourth Law of
Thermodynamics
Entropy generation and jet engine optimization
In 2009, it was shown that, with an original approach to hydrodynamic
cavitation, a phenomenological model was realized in order to compute some of
the physical parameters needed for the design of the most common technological
applications (turbo-machinery, etc.) with an economical saving in planning
because this analysis could allow engineers to reduce the experimental tests
and the consequent costs in the design process. Here the same approach has been
used to obtain range of some physical quantity for jet engine optimization
Hilbert Irreducibility above algberaic groups
The paper offers versions of Hilbert's Irreducibility Theorem for the lifting
of points in a cyclic subgroup of an algebraic group to a ramified cover. A
version of Bertini Theorem in this context is also obtained.Comment: 22 page
Effective Field Theory Methods in Gravitational Physics and Tests of Gravity
In this PhD thesis I make use of the "Effective Field Theory of Gravity for
Extended Objects" by Goldberger and Rothstein in order to investigate theories
of gravity and to take a different point of view on the physical information
that can be extracted from experiments. In the first work I present, I study a
scalar-tensor theory of gravity and I address the renormalization of the
energy-momentum tensor for point-like and string-like sources. The second and
third study I report are set in the context of testing gravity. So far
experiments have probed dynamical regimes only up to order (v/c)^5 in the
post-Newtonian expansion, which corresponds to the very first term of the
radiative sector in General Relativity. In contrast, by means of
gravitational-wave astronomy, one aims at testing General Relativity up to
(v/c)^(12)! It is then relevant to envisage testing frameworks which are
appropriate to this strong-field/radiative regime. In the last two chapters of
this thesis a new such framework is presented. Using the effective field theory
approach, General Relativity non-linearities are described by Feynman diagrams
in which classical gravitons interact with matter sources and among themselves.
Tagging the self-interaction vertices of gravitons with parameters it is
possible, for example, to translate the measure of the period decay of
Hulse-Taylor pulsar in a constraint on the three-graviton vertex at the 0.1%
level; for comparison, LEP constraints on the triple-gauge-boson couplings of
weak interactions are accurate at 3%. With future observations of gravitational
waves, higher order graviton vertices can in principle be constrained through a
Fisher matrix analysis.Comment: This PhD Thesis has been conducted at the University of Geneva
(Switzerland) under the direction of Professor Michele Maggiore and the
codirection of Doctor Riccardo Sturani. Version 2: abstract slightly changed;
one typo corrected; layout issue fixe
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