187 research outputs found
Thermal distributions in stellar plasmas, nuclear reactions and solar neutrinos
The physics of nuclear reactions in stellar plasma is reviewed with special
emphasis on the importance of the velocity distribution of ions. Then the
properties (density and temperature) of the weak-coupled solar plasma are
analysed, showing that the ion velocities should deviate from the Maxwellian
distribution and could be better described by a weakly-nonexstensive
(|q-1|<0.02) Tsallis' distribution. We discuss concrete physical frameworks for
calculating this deviation: the introduction of higher-order corrections to the
diffusion and friction coefficients in the Fokker-Plank equation, the influence
of the electric-microfield stochastic distribution on the particle dynamics, a
velocity correlation function with long-time memory arising from the coupling
of the collective and individual degrees of freedom. Finally, we study the
effects of such deviations on stellar nuclear rates, on the solar neutrino
fluxes, and on the pp neutrino energy spectrum, and analyse the consequences
for the solar neutrino problem.Comment: ReVTeX, 23 pages, 3 figures, to appear in the special issue
(Nonextensive statistical mechanics and thermodynamics) of the Brazilian
Journal of Physic
Parametric study of the influence of the wind assisted propulsion on ships
nologies to increase energy efficiency and reduce ship fuel consumption. Several measures have been identified, or even applied, with the potential to achieve substantial fuel consumption and emission reductions, like slow-steaming, bio-fuels, and alternative propulsion technologies. Slow steaming has been already analysed to a great extent, whereas biofuels have raised concerns about environmental impact and availability. Among alternative propulsion technologies, a resurgence in wind-assisted propulsion is observed in recent years, primarily due to its high potential for fuel consumption and emission reduction. Wind power is currently being developed through both conventional sails and modern alternatives. These include Flettner rotors, kites or spinnakers, soft sails, wing sails and wind turbines. In particular, Flettner rotors are rotating cylinders generating lift when immersed in a fluid stream. This paper presents a ship propulsion model study, able to account for the thrust force produced by the rotor accounting for different vessel speed and weather scenario. This paper aims to assess the improvement of the ship’s energy efficiency and optimise the ship operating conditions in terms of daily performance. The result clearly shows the potential reduction achieved in the propeller delivered power given using the rotor as an auxiliary propulsion device
Nonextensive statistics in stellar plasma and solar neutrinos
Nonextensive and quantum uncertainty effects (related to the quasiparticles
composing the stellar core) have strong influence on the nuclear rates and, of
course, affect solar neutrino fluxes. Both effects do coexist and are due to
the frequent collisions among the ions. The weakly nonextensive nature of the
solar core is confirmed. The range of predictions for the neutrino fluxes is
enlarged and the solar neutrino problem becomes less dramatic.Comment: 4 pages. Proc. of TAUP99, Sept. 6-10 1999, Paris. To appear in Nucl.
Phys. B, Proc. Supp
The nonrelativistic limit of the Magueijo-Smolin model of deformed special relativity
We study the nonrelativistic limit of the motion of a classical particle in a
model of deformed special relativity and of the corresponding generalized
Klein-Gordon and Dirac equations, and show that they reproduce nonrelativistic
classical and quantum mechanics, respectively, although the rest mass of a
particle no longer coincides with its inertial mass. This fact clarifies the
meaning of the different definitions of velocity of a particle available in DSR
literature. Moreover, the rest mass of particles and antiparticles differ,
breaking the CPT invariance. This effect is close to observational limits and
future experiments may give indications on its effective existence.Comment: 10 pages, plain TeX. Discussion of generalized Dirac equation and CPT
violation adde
Temperature dependence of modified CNO nuclear reaction rates in dense stellar plasmas
We study the dependence of the CNO nuclear reaction rates on temperature, in
the range of K, the typical range of temperature evolution from
a Sun-like star towards a white dwarf. We show that the temperature dependence
of the CNO nuclear reaction rates is strongly affected by the presence of
non-extensive statistical effects in the dense stellar core. A very small
deviation from the Maxwell-Boltzmann particle distribution implies a relevant
enhancement of the CNO reaction rate and could explain the presence of heavier
elements (e.g. Fe, Mg) in the final composition of a white dwarf core. Such a
behavior is consistent with the recent experimental upper limit to the fraction
of energy that the Sun produces via the CNO fusion cycle.Comment: Presented at NEXT2003 (Second International Conference on "News and
Expectations in Thermostatistics"), Villasimius (Cagliari)- Italy in 21-28
September 2003. 7 pages including 3 figure
Incidence of nonextensive thermodynamics in temporal scaling at Feigenbaum points
Recently, in Phys. Rev. Lett. 95, 140601 (2005), P. Grassberger addresses the
interesting issue of the applicability of q-statistics to the renowned
Feigenbaum attractor. He concludes there is no genuine connection between the
dynamics at the critical attractor and the generalized statistics and argues
against its usefulness and correctness. Yet, several points are not in line
with our current knowledge, nor are his interpretations. We refer here only to
the dynamics on the attractor to point out that a correct reading of recent
developments invalidates his basic claim.Comment: To be published in Physica
Collisional cross sections and momentum distributions in astrophysical plasmas: dynamics and statistical mechanics link
We show that, in stellar core plasmas, the one-body momentum distribution
function is strongly dependent, at least in the high velocity regime, on the
microscopic dynamics of ion elastic collisions and therefore on the effective
collisional cross sections, if a random force field is present. We take into
account two cross sections describing ion-dipole and ion-ion screened
interactions. Furthermore we introduce a third unusual cross section, to link
statistical distributions and a quantum effect originated by the
energy-momentum uncertainty owing to many-body collisions, and propose a
possible physical interpretation in terms of a tidal-like force. We show that
each collisional cross section gives rise to a slight peculiar correction on
the Maxwellian momentum distribution function in a well defined velocity
interval. We also find a possible link between microscopical dynamics of ions
and statistical mechanics interpreting our results in the framework of
non-extensive statistical mechanics.Comment: 8 page
Metastable and stable equilibrium states of stellar electron-nuclear plasmas
By minimizing free energy density, we show that the stellar core of a
hydrogen burning star is not in a global thermodynamical equilibrium unless
density, temperature, mass and composition assume given values. The core (as
the solar interior) may be viewed more appropriately as a metastable state with
very long lifetime. Slightly non-extensive distribution function could be the
natural distribution for a weakly non-ideal plasma like a stellar core and
represents a more appropriate approximation to this system than a Maxwellian
distribution, without affecting bulk properties of stars.Comment: 14 pages, to appear in Phys. Lett.
A review and analysis of the uncertainty within cost models for floating offshore wind farms
The development and deployment of offshore wind farms in the last decade have seen a dramatic increase, now totalling 743 GW globally (Global Wind Energy Council, 2022). This rapid increase is expected to further continue now with the potential to explore deeper sites with the adoption of floating offshore platforms. Proof of this growth has recently been seen with an impressive 60% of the 25 GW Scotwind leasing sites planning to install floating platforms in the next ten years (Crown estate, 2022 [1], [2]). One main disadvantage of the advancement offshore is uncertainty and the potential increase in costs due to more complex structures and greater distances to shore. The cost increase for floating platforms is expected to be two to three times more expensive than traditional fixed support structures (Eric Paya, 2020). Thus, this work aims to review existing analytical cost models found within the literature to best determine their level of accuracy and compare the assumptions which have been made. Leading on from this review, a collection of all data found in the reviewed literature is presented, which leads to a data analysis that determines the variation across literature and the potential causes. Assessing this literature shows a wide range of model considerations, often leading to assumptions with little or no data to be validated against. Hence, high levels of variation and a lack of consensus on the cheapest floating platform were noted. All aspects of costs related to floating offshore wind systems vary heavily throughout the literature
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