5,453 research outputs found
Astrophysical and Cosmological Tests of Quantum Theory
We discuss several proposals for astrophysical and cosmological tests of
quantum theory. The tests are motivated by deterministic hidden-variables
theories, and in particular by the view that quantum physics is merely an
effective theory of an equilibrium state. The proposed tests involve searching
for nonequilibrium violations of quantum theory in: primordial inflaton
fluctuations imprinted on the cosmic microwave background, relic cosmological
particles, Hawking radiation, photons with entangled partners inside black
holes, neutrino oscillations, and particles from very distant sources.Comment: 25 pages. Amendment to section 7. Contribution to: "The Quantum
Universe", special issue of Journal of Physics A, dedicated to Prof. G.-C.
Ghirardi on the occasion of his seventieth birthda
Vlasov simulations of Kinetic Alfv\'en Waves at proton kinetic scales
Kinetic Alfv\'en waves represent an important subject in space plasma
physics, since they are thought to play a crucial role in the development of
the turbulent energy cascade in the solar wind plasma at short wavelengths (of
the order of the proton inertial length and beyond). A full understanding
of the physical mechanisms which govern the kinetic plasma dynamics at these
scales can provide important clues on the problem of the turbulent dissipation
and heating in collisionless systems. In this paper, hybrid Vlasov-Maxwell
simulations are employed to analyze in detail the features of the kinetic
Alfv\'en waves at proton kinetic scales, in typical conditions of the solar
wind environment. In particular, linear and nonlinear regimes of propagation of
these fluctuations have been investigated in a single-wave situation, focusing
on the physical processes of collisionless Landau damping and wave-particle
resonant interaction. Interestingly, since for wavelengths close to and
proton plasma beta of order unity the kinetic Alfv\'en waves have small
phase speed compared to the proton thermal velocity, wave-particle interaction
processes produce significant deformations in the core of the particle velocity
distribution, appearing as phase space vortices and resulting in flat-top
velocity profiles. Moreover, as the Eulerian hybrid Vlasov-Maxwell algorithm
allows for a clean almost noise-free description of the velocity space,
three-dimensional plots of the proton velocity distribution help to emphasize
how the plasma departs from the Maxwellian configuration of thermodynamic
equilibrium due to nonlinear kinetic effects
Assessing the dimensional stability of alkali-activated calcined clays in the fresh state: a time-lapse X-ray imaging approach
Alkali-activated calcined clays are promising candidates for playing a prominent role in the future construction industry. These binders may achieve excellent mechanical performance, but one issue deserving attention is the proneness to plastic shrinkage and surface cracking. Tackling this issue requires the deployment of laboratory techniques that allow shrinkage-inducing mechanisms to be quantitatively assessed. Here, we demonstrate that time-lapse X-ray imaging can be used to quantify shrinkage immediately after mixing, when the binder is still in its fresh state, with excellent time and space resolution. The numeric quantification of strain is complemented by the real time visual inspection of the displacing sample interface and of the bleed aqueous solution layer that may form. Implementation of this method to a set of alkali-activated cement pastes, prepared by combining calcined clays having different mineralogical composition with sodium silicate activating solutions having different SiO 2/Na 2O ratios, suggests that two main mechanisms control the early dimensional stability of alkali-activated calcined clays. These mechanisms are: (a) volumetric contraction occurring in response to capillary stress arising from water evaporation and (b) segregation by particle settling, favoured in the water-saturated regime
Inflationary Cosmology as a Probe of Primordial Quantum Mechanics
We show that inflationary cosmology may be used to test the statistical
predictions of quantum theory at very short distances and at very early times.
Hidden-variables theories, such as the pilot-wave theory of de Broglie and
Bohm, allow the existence of vacuum states with non-standard field fluctuations
('quantum nonequilibrium'). We show that inflationary expansion can transfer
microscopic nonequilibrium to macroscopic scales, resulting in anomalous power
spectra for the cosmic microwave background. The conclusions depend only weakly
on the details of the de Broglie-Bohm dynamics. We discuss, in particular, the
nonequilibrium breaking of scale invariance for the primordial (scalar) power
spectrum. We also show how nonequilibrium can generate primordial perturbations
with non-random phases and inter-mode correlations (primordial
non-Gaussianity). We address the possibility of a low-power anomaly at large
angular scales, and show how it might arise from a nonequilibrium suppression
of quantum noise. Recent observations are used to set an approximate bound on
violations of quantum theory in the early universe.Comment: 44 pages. Minor changes in v
Estimating Technical Efficiency through Reduced Rank Regression
EnIn this paper we develop a statistical approach for verifying the possibility of substituting joint production frontier with single-output specification by means of Reduced Rank Regression (RRR) Our work introduces the multivariate model in the RRR framework which allows us to verify the unitary rank of the regression coefficient matrix. If the rank is one it is possible to express the production frontier in terms of aggregated output through an econometric model. Firm-specific efficiency is also measured
Effect of metal clusters on the swelling of gold-fluorocarbon-polymer composite films
We have investigated the phenomenon of swelling due to acetone diffusion in
fluorocarbon polymer films doped with different gold concentrations below the
percolation threshold. The presence of the gold clusters in the polymer is
shown to improve the mixing between the fluorocarbon polymer and the acetone,
which is not a good solvent for this kind of polymers. In order to explain the
experimental results the stoichiometry and the morphology of the polymer--metal
system have been studied and a modified version of the Flory--Huggins model has
been developed
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