28,145 research outputs found
On the Hamiltonian formulation of Yang--Mills gauge theories
The Hamiltonian formulation of the theory of J-bundles is given both in the
Hamilton--De Donder and in the Multimomentum Hamiltonian geometrical
approaches. (3+3) Yang-Mills gauge theories are dealt with explicitly in order
to restate them in terms of Einstein-Cartan like field theories.Comment: 18 Pages, Submitted to International Journal of Geometric Methods in
Modern Physic
General Relativity as a constrained Gauge Theory
The formulation of General Relativity presented in math-ph/0506077 and the
Hamiltonian formulation of Gauge theories described in math-ph/0507001 are made
to interact. The resulting scheme allows to see General Relativity as a
constrained Gauge theory.Comment: 8 Pages, Submitted to International Journal of Geometric Methods in
Modern Physic
The Demographic Transition and the Sexual Division of Labor
This paper presents a theory where increases in female labor force participation and reductions in the gender wage-gap are generated as part of a single process of demographic transition, characterized by reductions in mortality and fertility. The paper suggests a link between changes in mortality and transformations in the role of women in society that has not been identified before in the literature. Mortality reductions affect the incentives of individuals to invest in human capital and to have children. Particularly, gains in adult longevity reduce fertility, increase investments in market human capital, increase female labor force participation, and reduce the wage differential between men and women. Child mortality reductions, though reducing fertility, do not generate this same pattern of changes. The model reconciles the increase in female labor market participation with the timing of age-specific mortality reductions observed during the demographic transition. It generates changes in fertility, labor market attachment, and the gender wage-gap as part of a single process of social transformation, triggered by reductions in mortality.
Observation of inertial energy cascade in interplanetary space plasma
We show in this article direct evidence for the presence of an inertial
energy cascade, the most characteristic signature of hydromagnetic turbulence
(MHD), in the solar wind as observed by the Ulysses spacecraft. After a brief
rederivation of the equivalent of Yaglom's law for MHD turbulence, we show that
a linear relation is indeed observed for the scaling of mixed third order
structure functions involving Els\"asser variables. This experimental result,
confirming the prescription stemming from a theorem for MHD turbulence, firmly
establishes the turbulent character of low-frequency velocity and magnetic
field fluctuations in the solar wind plasma
The essential oil of Thymbra capitata and its application as a biocide on stone and derived surfaces
Many chemicals used nowadays for the preservation of cultural heritage pose a risk to both human health and the environment. Thus, it is desirable to find new and eco-friendly biocides that can replace the synthetic ones. In this regard, plant essential oils represent effective alternatives to synthetic substances for the preservation of historical monuments. Thymbra capitata (syn. Thymus capitatus) is a medicinal and aromatic plant growing in the Mediterranean area and endowed with important pharmacological properties related to its essential oil. Among them, the antimicrobial ones make the T. capitata essential oil an ideal candidate for industrial applications; for instance, as biocide for the inhibition and elimination of biological patinas of cyanobacteria and green algae on historical monuments. In the present work, we studied the chemical composition of the essential oil from T. capitata growing in Malta by gas chromatography-mass spectrometry (GC/MS). The major volatile component is the phenolic monoterpene carvacrol (73.2%), which is capable of damaging the cytoplasmic membrane and to interfere both in the growth curve and in the invasive capacity, though the contribution of minor components γ-terpinene and p-cymene cannot be disregarded. For the oil application on the stone surface, Pickering emulsions systems were prepared with an essential oil/water 1:3 mass ratio stabilized with kaolinite at 4 mass% in the presence of Laponite®; this allowed to limit the fast volatility of the oil and guaranteed a better application and an easier removal from the artefacts attacked by biodeteriogens both indoor and outdoor. This formulation caused the elimination of biodeteriogens from treated surfaces without residuals or films on artworks surface, and the effect was retained up to four months
Optimal placement of excitations and sensors by simulated annealing
The optimal placement of discrete actuators and sensors is posed as a combinatorial optimization problem. Two examples for truss structures were used for illustration; the first dealt with the optimal placement of passive dampers along existing truss members, and the second dealt with the optimal placement of a combination of a set of actuators and a set of sensors. Except for the simplest problems, an exact solution by enumeration involves a very large number of function evaluations, and is therefore computationally intractable. By contrast, the simulated annealing heuristic involves far fewer evaluations and is best suited for the class of problems considered. As an optimization tool, the effectiveness of the algorithm is enhanced by introducing a number of rules that incorporate knowledge about the physical behavior of the problem. Some of the suggested rules are necessarily problem dependent
Persistence of small-scale anisotropy of magnetic turbulence as observed in the solar wind
The anisotropy of magnetophydrodynamic turbulence is investigated by using
solar wind data from the Helios 2 spacecraft. We investigate the behaviour of
the complete high-order moment tensors of magnetic field increments and we
compare the usual longitudinal structure functions which have both isotropic
and anisotropic contributions, to the fully anisotropic contribution. Scaling
exponents have been extracted by an interpolation scaling function. Unlike the
usual turbulence in fluid flows, small-scale magnetic fluctuations remain
anisotropic. We discuss the radial dependence of both anisotropy and
intermittency and their relationship.Comment: 7 pages, 2 figures, in press on Europhys. Let
Aeolian sans ripples: experimental study of saturated states
We report an experimental investigation of aeolian sand ripples, performed
both in a wind tunnel and on stoss slopes of dunes. Starting from a flat bed,
we can identify three regimes: appearance of an initial wavelength, coarsening
of the pattern and finally saturation of the ripples. We show that both initial
and final wavelengths, as well as the propagative speed of the ripples, are
linear functions of the wind velocity. Investigating the evolution of an
initially corrugated bed, we exhibit non-linear stable solutions for a finite
range of wavelengths, which demonstrates the existence of a saturation in
amplitude. These results contradict most of the models.Comment: 4 pages, 5 figures, submitted to Phys. Rev. Lett. Title changed,
figures corrected and simplified, more field data included, text clarifie
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