1,721,097 research outputs found
Regularizing Effect of a Lower Order Term in Dirichlet Problems with a Singular Convection Term
No full textIn this paper we prove existence and uniqueness results for a lower order perturbation of elliptic Dirichlet problems with a singular convection term in divergence form and L-1 data
Local regularity results to nonlinear elliptic Dirichlet problems with lower order terms
Full text linkIn this paper we study local regularity properties of weak solutions to a class of nonlinear noncoercive elliptic Dirichlet problems with L1 datum. The model example is -Δp(w)+b(x)|Dw|p-1=f(x)inΩ,w=0on∂Ω.Here Ω ⊂ RN is a bounded open subset, N> 1 , - Δ p is the well known p-Laplace operator, 1 < p< N, b is a function in the Lorentz space LN,1(Ω) and f is a function in L1(Ω). We also investigate similar issues for a lower order perturbation of these problems
Strange Quark matter in Astrophysics and Cosmology
No full textL'ipotesi di Bodmer-Witten suggerisce che la materia strana sia il vero stato fondamentale della materia. Questa ipotesi ha significative implicazioni per l'astrofisica e la cosmologia. In cosmologia, grumi di materia di quark strani assolutamente stabili potrebbero costituire la materia oscura. In astrofisica ciò implica l'esistenza di stelle strane in coesistenza con stelle adroniche nello scenario denominato a due famiglie.
In primo luogo, proponiamo un modo per testare questo scenario attraverso l'osservazione delle kilonove prodotte nelle fusioni tra stelle compatte e buchi neri. Studiamo l'impatto dell'equazione di stato della materia nucleare sul materiale espulso in tali eventi e, quindi, sui possibili segnali di kilonova osservati. In particolare, prevediamo la soppressione statistica di tali eventi nello scenario a due famiglie rispetto allo scenario standard.
In una seconda indagine, esploriamo le implicazioni cosmologiche dei strangelet come candidati per la materia oscura. Questo comporta la stima della distribuzione di dimensione e massa degli strangelet, assicurando il loro accordo con i vincoli esistenti sulla materia oscura macroscopica.
In seguito, esaminiamo le conseguenze astrofisiche di questo scenario cosmologico, concentrandoci in particolare su come la presenza di strangelet possa influenzare l'evoluzione stellare. Ci concentriamo su due casi: studiamo come gli strangelet, quando catturati da nane bianche, influenzino la stabilità di queste stelle che diventano a loro volta nane strane; suggeriamo che la presenza di strangelet nel nucleo delle stelle che subiscono una electron-capture supernova possa portare alla formazione di stelle strane di massa inferiore a quella solare, che potrebbero essere già state osservate come nel caso di HESS J1731-347 e SAX J1808.4-3658.The Bodmer-Witten hypothesis suggests that strange quark matter is the true ground state of matter. This hypothesis has significant implications for astrophysics and cosmology. In cosmology, lumps of absolutely stable strange quark matter can constitute dark matter. In astrophysics, it implies the existence of strange stars in coexistence with hadronic stars in the so-called two-families scenario.
First, we propose a way to test this scenario through the observation of the kilonovae produced in mergers between compact stars and black holes. We study the impact of the nuclear matter equation of state on the ejected material in those events, and therefore, on the possible observed kilonova signals. In particular, we predict the statistical suppression of those events in the two-families scenario as compared with the standard scenario.
In a second investigation, we explore the cosmological implications of strangelets as dark matter candidates. This involves assessing the size and mass distribution of strangelets, ensuring their agreement with the existing constraints on macroscopic dark matter.
Therefore, we examine the astrophysical consequences of this cosmological scenario, particularly focusing on how the presence of strangelets might affect the stellar evolution. We focus on two cases: we investigate how strangelets, when captured by white dwarfs, impact the stability of these stars which become strange dwarfs; we suggest that the presence of strangelets in the core of stars which undergoes electron-capture supernova can result in the formation of subsolar mass strange stars, which might have been already observed, as in the case of HESS J1731-347 and SAX J1808.4-3658
Vibrotactile stimulation promotes embodiment of an alien hand in amputees with phantom sensations
No full textThe preload force affects the perception threshold of muscle vibration-induced movement illusions
Full text linkIs the Compact Object Associated with HESS J1731-347 a Strange Quark Star? A Possible Astrophysical Scenario for Its Formation
No full textThe analysis of the central compact object within the supernova (SN) remnant HESS J1731-347 suggests that it has a small radius and, even more interestingly, a mass of the order or smaller than 1 M circle dot. This raises the question of which astrophysical process could lead to such a small mass, since the analysis of various types of SN explosions indicate that is it not possible to produce a neutron star with a mass smaller than about 1.17 M circle dot. Here we show that masses of the order or smaller than 1 M circle dot can be obtained in the case of strange quark stars and that it is possible to build a coherent model explaining not only the mass and the radius of that object, but also its slow cooling suggested in various analyses. We also show that an astrophysical path exists, which leads to the formation of such an object, and we discuss the role played in that scenario by strangelets assumed to constitute the dark matter
Merger of a Neutron Star with a Black Hole: one-family vs. two-families scenario
Full text linkA kilonova signal is generally expected after a Black Hole - Neutron Star
merger. The strength of the signal is related to the equation of state of
neutron star matter and it increases with the stiffness of the latter. The
recent results obtained by NICER from the analyses of PSR J0740+6620 suggest a
rather stiff equation of state and the expected kilonova signal is therefore
strong, at least if the mass of the Black Hole does not exceed and if the adimensional spin parameter is not too small and
the orbit is prograde. We compare the predictions obtained by considering
equations of state of neutron star matter satisfying the most recent
observations and assuming that only one family of compact stars exists with the
results predicted in the two-families scenario. In the latter a soft hadronic
equation of state produces very compact stellar objects while a rather stiff
quark matter equation of state produces massive strange quark stars, satisfying
NICER results. The expected kilonova signal in the two-families scenario is
very weak: in particular the Hadronic Star - Black Hole merger produces a much
weaker signal than in the one-family scenario because the hadronic equation of
state is very soft. Moreover, according to the only existing simulation, the
Strange Quark Star - Black Hole merger does not produce a kilonova signal
because the amount of mass ejected is negligible. These predictions will be
easily tested with the new generation of detectors if Black Holes with an
adimensional spin parameter or a mass can be present in the merger.Comment: 8 pages, 5 figures. Significantly extended, published versio
A novel device for multi-modal sensory feedback in hand prosthetics: design and preliminary prototype
No full text
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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