255 research outputs found
Restrictions on dilatonic brane-world models
We consider dilatonic brane-world models with a non-minimal coupling between
a dilaton and usual matter on a brane. We demonstrate that variation of the
fundamental constants on the brane due to such interaction leads to strong
restrictions on parameters of models. In particular, the experimental bounds on
variation of the fine structure constant rule out non-minimal dilatonic models
with a Liouville-type coupling potential f(varphi) = exp (b varphi) where b is
order of 1.Comment: MiKTeX2-LaTeX2e, 10 pages, minor changes, improved references, to
appear in IJMP
Assessment of the Life Cycle Environmental Impact of the Olive Oil Extraction Solid Wastes in the European Union
There is an increasing interest in developing sustainable systems in the European Union (EU) to recover and upgrade the solid wastes of the olive oil extraction process, i.e. wet husk. A Life Cycle Environmental Impact Assessment (LCIA) of wet husk has been carried out aiming at facilitating an appropriate Life Cycle Management of this biomass. Three scenarios have been considered, i.e. combustion for domestic heat, generation of electric power, and composting. The Environmental Product Declaration and the ReCiPe method were used for Life Cycle Impact Assessment. Domestic heating and power generation were the most important impact factors in damaging human health, ecosystems, and natural
resources depletion. Composting was 2-4 orders of magnitude less impacting than domestic heat and power generation. Considering human health, the impact of climate change, human toxicity and particulate matter formation represented the main impact categories. Considering ecosystems, climate change and natural land transformation were the main impact categories. Within natural resources, fossil fuel depletion was impacted three orders more than metal depletion. Within domestic heating and power generation scenarios, storage of wet husk along with the extraction by organic solvent, and the waste treatment were the most impacting phases for global warming potential, ozone layer depletion, acidification and
non renewable fossil resources depletion. The results obtained for the waste disposal have been comparatively assessed with respect to the environmental impact of the olive oil production chain
Constraining the Variation of G by Cosmic Microwave Background Anisotropies
We use the Cosmic Microwave Background Anisotropies (CMBA) power spectra to
constrain the cosmological variation of gravitational constant G. It is found
that the sensitivity of CMBA to the variation of G is enhanced when G is
required to converge to its present value. The variations of G from the CMB
decoupling epoch z ~ 1000 to the present time are modelled by a step function
and a linear function of scale factor respectively, and the corresponding
95% confidence intervals for G/G_0 are [0.95, 1.05] and [0.89, 1.13], G_0 being
the present value. The CMBA constraint is unique in the sense that it entails
the range of redshift from z \approx 1000 to 0.Comment: 7 pages, 8 figures, discussion added, references adde
Constraining a possible time-variation of the gravitational constant through "gravitochemical heating" of neutron stars
A hypothetical time-variation of the gravitational constant would cause
neutron star matter to depart from beta equilibrium, due to the changing
hydrostatic equilibrium. This forces non-equilibrium beta processes to occur,
which release energy that is invested partly in neutrino emission and partly in
heating the stellar interior. Eventually, the star arrives at a stationary
state in which the temperature remains nearly constant, as the forcing through
the change of is balanced by the ongoing reactions. Comparing the surface
temperature of the nearest millisecond pulsar, PSR J0437-4715, inferred from
ultraviolet observations, with our predicted stationary temperature, we
estimate two upper limits for this variation: (1) yr, if we allow direct Urca reactions operating in the neutron
star core, and (2) yr, considering only
modified Urca reactions. Both results are competitive with those obtained by
other methods, with (2) being among the most restrictive.Comment: 4 pages, including 2 figures. Accepted for publication in Phys. Rev.
Lett. Revised version includes minor changes in the wording, and more
substantial changes in the last 2 paragraphs (Discussion and Conclusions).
Equations, figures, and results are unchange
Cosmological Constraints on Newton's Constant
We present cosmological constraints on deviations of Newton's constant at
large scales, analyzing latest cosmic microwave background (CMB) anisotropies
and primordial abundances of light elements synthesized by big bang
nucleosynthesis (BBN). BBN limits the possible deviation at typical scales of
BBN epoch, say at 10^8 \sim 10^12m, to lie between -5% and +1% of the
experimental value, and CMB restricts the deviation at larger scales 10^2 \sim
10^9pc to be between -26% and +66% at the 2\sigma confidence level. The
cosmological constraints are compared with the astronomical one from the
evolution of isochrone of globular clusters.Comment: 4 pages, 5 figure
The Height of Chromospheric Loops in an Emerging Flux Region
Context. The chromospheric layer observable with the He I 10830 {\AA} triplet
is strongly warped. The analysis of the magnetic morphology of this layer
therefore requires a reliable technique to determine the height at which the He
I absorption takes place.
Aims. The He I absorption signature connecting two pores of opposite polarity
in an emerging flux region is investigated. This signature is suggestive of a
loop system connecting the two pores. We aim to show that limits can be set on
the height of this chromospheric loop system.
Methods. The increasing anisotropy in the illumination of a thin, magnetic
structure intensifies the linear polarization signal observed in the He I
triplet with height. This signal is altered by the Hanle effect. We apply an
inversion technique incorporating the joint action of the Hanle and Zeeman
effects, with the absorption layer height being one of the free parameters.
Results. The observed linear polarization signal can be explained only if the
loop apex is higher than \approx5 Mm. Best agreement with the observations is
achieved for a height of 6.3 Mm.
Conclusions. The strength of the linear polarization signal in the loop apex
is inconsistent with the assumption of a He I absorption layer at a constant
height level. The determined height supports the earlier conclusion that dark
He 10830 {\AA} filaments in emerging flux regions trace emerging loops.Comment: 7 pages, 4 figure
Screening of Nuclear Reactions in the Sun and Solar Neutrinos
We quantitatively determine the effect and the uncertainty on solar neutrino
production arising from the screening process. We present predictions for the
solar neutrino fluxes and signals obtained with different screening models
available in the literature and by using our stellar evolution code. We explain
these numerical results in terms of simple laws relating the screening factors
with the neutrino fluxes. Futhermore we explore a wider range of models for
screening, obtained from the Mitler model by introducing and varying two
phenomenological parameters, taking into account effects not included in the
Mitler prescription. Screening implies, with respect to a no-screening case, a
central temperat reduction of 0.5%, a 2% (8%) increase of Beryllium
(Boron)-neutrino flux and a 2% (12%) increase of the Gallium (Chlorine) signal.
We also find that uncertainties due to the screening effect ar at the level of
1% for the predicted Beryllium-neutrino flux and Gallium signal, not exceeding
3% for the Boron-neutrino flux and the Chlorine signal.Comment: postscript file 11 pages + 4 figures compressed and uuencoded we have
replaced the previous paper with a uuencoded file (the text is the same) for
any problem please write to [email protected]
Fusion rate enhancement due to energy spread of colliding nuclei
Experimental results for sub-barrier nuclear fusion reactions show cross
section enhancements with respect to bare nuclei which are generally larger
than those expected according to electron screening calculations. We point out
that energy spread of target or projectile nuclei is a mechanism which
generally provides fusion enhancement. We present a general formula for
calculating the enhancement factor and we provide quantitative estimate for
effects due to thermal motion, vibrations inside atomic, molecular or crystal
system, and due to finite beam energy width. All these effects are marginal at
the energies which are presently measurable, however they have to be considered
in future experiments at still lower energies. This study allows to exclude
several effects as possible explanation of the observed anomalous fusion
enhancements, which remain a mistery.Comment: 17 pages with 3 ps figure included. Revtex styl
Possible Tomography of the Sun's Magnetic Field with Solar Neutrinos
The data from solar neutrino experiments together with standard solar model
predictions are used in order to derive the possible profile of the magnetic
field inside the Sun, assuming the existence of a sizeable neutrino magnetic
moment and the resonant spin flavour mechanism. The procedure is based on the
relationship between resonance location and the energy dependent neutrino
suppression, so that a large neutrino suppression at a given energy is taken to
be connected to a large magnetic field in a given region of the Sun. In this
way it is found that the solar field must undergo a very sharp increase by a
factor of at least 6 - 7 over a distance no longer than 7 - 10% of the solar
radius, decreasing gradually towards the surface. The range in which this sharp
increase occurs is likely to be the bottom of the convective zone. There are
also indications in favour of the downward slope being stronger at the start
and more moderate on approaching the solar surface. Typical ranges for the
magnetic moment are from a few times 10^{-13}\mu_B to its laboratory upper
bounds while the mass square difference between neutrino flavours is of order
(0.6-1.9) x 10^{-8}eV^2.Comment: Several minor corrections performed, sunspot anticorrelation
discussed, references added, 29 pages including 8 figures in PostScrip
Recent Advances in Chromospheric and Coronal Polarization Diagnostics
I review some recent advances in methods to diagnose polarized radiation with
which we may hope to explore the magnetism of the solar chromosphere and
corona. These methods are based on the remarkable signatures that the
radiatively induced quantum coherences produce in the emergent spectral line
polarization and on the joint action of the Hanle and Zeeman effects. Some
applications to spicules, prominences, active region filaments, emerging flux
regions and the quiet chromosphere are discussed.Comment: Review paper to appear in "Magnetic Coupling between the Interior and
the Atmosphere of the Sun", eds. S. S. Hasan and R. J. Rutten, Astrophysics
and Space Science Proceedings, Springer-Verlag, 200
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