729 research outputs found
A comment on some new definitions of fractional derivative
After reviewing the definition of two differential operators which have been
recently introduced by Caputo and Fabrizio and, separately, by Atangana and
Baleanu, we present an argument for which these two integro-differential
operators can be understood as simple realizations of a much broader class of
fractional operators, i.e. the theory of Prabhakar fractional integrals.
Furthermore, we also provide a series expansion of the Prabhakar integral in
terms of Riemann-Liouville integrals of variable order. Then, by using this
last result we finally argue that the operator introduced by Caputo and
Fabrizio cannot be regarded as fractional. Besides, we also observe that the
one suggested by Atangana and Baleanu is indeed fractional, but it is
ultimately related to the ordinary Riemann-Liouville and Caputo fractional
operators. All these statements are then further supported by a precise
analysis of differential equations involving the aforementioned operators. To
further strengthen our narrative, we also show that these new operators do not
add any new insight to the linear theory of viscoelasticity when employed in
the constitutive equation of the Scott-Blair model.Comment: 10 pages, 1 figure, to appear in Nonlinear Dynamics, comment adde
Matter and gravitons in the gravitational collapse
We consider the effects of gravitons in the collapse of baryonic matter that
forms a black hole. We first note that the effective number of (soft off-shell)
gravitons that account for the (negative) Newtonian potential energy generated
by the baryons is conserved and always in agreement with Bekenstein's area law
of black holes. Moreover, their (positive) interaction energy reproduces the
expected post-Newtonian correction and becomes of the order of the total ADM
mass of the system when the size of the collapsing object approaches its
gravitational radius. This result supports a scenario in which the
gravitational collapse of regular baryonic matter produces a corpuscular black
hole without central singularity, in which both gravitons and baryons are
marginally bound and form a Bose-Einstein condensate at the critical point. The
Hawking emission of baryons and gravitons is then described by the quantum
depletion of the condensate and we show the two energy fluxes are comparable,
albeit negligibly small on astrophysical scales.Comment: 4 pages, no figures. Minor changes and typos fixe
Prabhakar-like fractional viscoelasticity
The aim of this paper is to present a linear viscoelastic model based on
Prabhakar fractional operators. In particular, we propose a modification of the
classical fractional Maxwell model, in which we replace the Caputo derivative
with the Prabhakar one. Furthermore, we also discuss how to recover a formal
equivalence between the new model and the known classical models of linear
viscoelasticity by means of a suitable choice of the parameters in the
Prabhakar derivative. Moreover, we also underline an interesting connection
between the theory of Prabhakar fractional integrals and the recently
introduced Caputo-Fabrizio differential operator.Comment: 9 page
The relativistic Green's function model in charged-current quasielastic neutrino and antineutrino scattering at MINERA kinematics
The analysis of charged-current quasielastic neutrino and
antineutrino-nucleus scattering cross sections requires relativistic
theoretical descriptions also accounting for the role of final-state
interactions. We compare the results of the relativistic Green's function model
with the data recently published by the MINERA Collaboration. The model is
able to describe both MINERA and MiniBooNE data.Comment: 6 pages, 3 figure
The role of collapsed matter in the decay of black holes
We try to shed some light on the role of matter in the final stages of black
hole evaporation from the fundamental frameworks of classicalization and the
black-to-white hole bouncing scenario. Despite being based on very different
grounds, these two approaches attempt at going beyond the background field
method and treat black holes as fully quantum systems rather than considering
quantum field theory on the corresponding classical manifolds. They also lead
to the common prediction that the semiclassical description of black hole
evaporation should break down and the system be disrupted by internal quantum
pressure, but they both arrive at this conclusion neglecting the matter that
formed the black hole. We instead estimate this pressure from the bootstrapped
description of black holes, which allows us to express the total
Arnowitt-Deser-Misner mass in terms of the baryonic mass still present inside
the black hole. We conclude that, although these two scenarios provide
qualitatively similar predictions for the final stages, the corpuscular model
does not seem to suggest any sizeable deviation from the semiclassical time
scale at which the disruption should occur, unlike the black-to-white hole
bouncing scenario. This, in turn, makes the phenomenology of corpuscular black
holes more subtle from an astrophysical perspective.Comment: 5 pages, no figur
Final-state interactions effects in neutral-current neutrino and antineutrino cross sections at MiniBooNE kinematics
The analysis of the recent neutral-current elastic neutrino and
antineutrino-nucleus scattering cross sections measured by the MiniBooNE
Collaboration requires relativistic theoretical descriptions also accounting
for the role of final-state interactions. In this work we investigate the
sensitivity to final-state interactions and compare the MiniBooNE data with the
results obtained in the relativistic Green's function model with different
parameterizations for the phenomenological relativistic optical potential.Comment: 4 pages, 3 figures. version published in Physical Review
Early recovery of microvascular perfusion induced by t-PA in combination with abciximab or eptifibatide during postischemic reperfusion
BACKGROUND: GPIIb/IIIa inhibitors abciximab and eptifibatide have been shown to inhibit platelet aggregation in ischemic heart disease. Our aim was to test the efficacy of abiciximab (Reo Pro) or eptifibatide (Integrilin) alone or in combination with plasminogen activator (t-PA) in an experimental model of ischemia reperfusion (I/R) in hamster cheek pouch microcirculation visualized by fluorescence microscopy. Hamsters were treated with saline, or abiciximab or eptifibatide or these drugs combined with t-PA infused intravenously 10 minutes before ischemia and through reperfusion. We measured the microvessel diameter changes, the arteriolar red blood cell (RBC) velocity, the increase in permeability, the perfused capillary length (PCL), and the platelet and leukocyte adhesion on microvessels. RESULTS: I/R elicited large increases in the platelet and leukocyte adhesion and a decrease in microvascular perfusion. These responses were significantly attenuated by abiciximab or eptifibatide (PCL:70 and 65% at 5–10 mins of reperfusion and 85 and 87% at 30 mins of reperfusion, respectively, p < 0.001) while t-PA combined with abiciximab or eptifibatide, was more effective and microvascular perfusion recovered immediately after postischemic reperfusion. CONCLUSIONS: Platelets are crucial in I/R injury, as shown by the treatment with abicixmab or eptifibatide, which decreased platelet aggregation in microvessels, and also decreased leukocyte adhesion in venules. Arterial vasoconstriction, decreased arterial RBC velocity and alterations in the endothelial barrier with increased permeability delayed the complete restoration of blood flow, while t-PA combined with inhibition of platelet aggregation speeded up the capillary perfusion after reperfusion
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