784 research outputs found
Removing black-hole singularities with nonlinear electrodynamics
We propose a way to remove black hole singularities by using a particular
nonlinear electrodynamics Lagrangian that has been recently used in various
astrophysics and cosmological frameworks. In particular, we adapt the
cosmological analysis discussed in a previous work to the black hole physics.
Such analysis will be improved by applying the Oppenheimer-Volkoff equation to
the black hole case. At the end, fixed the radius of the star, the final
density depends only on the introduced quintessential density term
and on the mass.Comment: In this last updated version we correct two typos which were present
in Eqs. (21) and (22) in the version of this letter which has been published
in Mod. Phys. Lett. A 25, 2423-2429 (2010). In the present version, both of
Eqs. (21) and (22) are dimensionally and analytically correc
Autistic adults' personal experiences of navigating a social world prior to and during Covid-19 lockdown in Spain
BACKGROUND: The SARS-CoV-2 coronavirus pandemic brought significant movement restrictions and national lockdowns. These drastic changes impacted routines, social life and support networks for the autistic community. AIMS: This study investigated the lived experiences of autistic adults with social expectations before and during the first Covid-19 lockdown in Spain. METHODS: A qualitative Reflexive Thematic Analysis was applied to 10 Photo Elicitation Interviews using images provided by five autistic adults. Interviews were conducted at two time points, before the pandemic and during the first lockdown. FINDINGS: Three themes before the pandemic were identified: (1) everyday interactions, (2) finding sense of belonging, and (3) fractured wellbeing, which revealed the participants' eagerness to fit in socially whilst experiencing rejection, weakening their mental health. During the first Covid-19 lockdown, two master themes were identified: (1) daily, positive experiences, and (2) surfacing failures, which emphasised an increased lived stigma as well as an ineffective autism support network, contributing to a heightened anxiety. CONCLUSIONS: The current study provides further support to the recent findings highlighting lack of appropriate mental health support for the autistic communities during the pandemic, across the world. Future research should aim to provide more data on the experiences and needs of autistic communities when sudden societal changes are imposed
Introducing Hyaluronic Acid into Supramolecular Polymers and Hydrogels
[Abstract] The use of supramolecular polymers to construct functional biomaterials is gaining more attention due to the tunable dynamic behavior and fibrous structures of supramolecular polymers, which resemble those found in natural systems, such as the extracellular matrix. Nevertheless, to obtain a biomaterial capable of mimicking native systems, complex biomolecules should be incorporated, as they allow one to achieve essential biological processes. In this study, supramolecular polymers based on water-soluble benzene-1,3,5-tricarboxamides (BTAs) were assembled in the presence of hyaluronic acid (HA) both in solution and hydrogel states. The coassembly of BTAs bearing tetra(ethylene glycol) at the periphery (BTA-OEG4) and HA at different ratios showed strong interactions between the two components that led to the formation of short fibers and heterogeneous hydrogels. BTAs were further covalently linked to HA (HA-BTA), resulting in a polymer that was unable to assemble into fibers or form hydrogels due to the high hydrophilicity of HA. However, coassembly of HA-BTA with BTA-OEG4 resulted in the formation of long fibers, similar to those formed by BTA-OEG4 alone, and hydrogels were produced with tunable stiffness ranging from 250 to 700 Pa, which is 10-fold higher than that of hydrogels assembled with only BTA-OEG4. Further coassembly of BTA-OEG4 fibers with other polysaccharides showed that except for dextran, all polysaccharides studied interacted with BTA-OEG4 fibers. The possibility of incorporating polysaccharides into BTA-based materials paves the way for the creation of dynamic complex biomaterials.The authors acknowledge the ICMS Animation Studio for providing the artwork. S.V.-A. and G.M. acknowledge the funding received by Gravitation Program âMaterials Driven Regeneration,â funded by the Netherlands Organization for Scientific Research (024.003.013). J.M. acknowledges a Marie SkĆodowska-Curie postdoctoral fellowship (794016) for financial support. G.M. acknowledges the funding received by the Swiss National Science Foundation (SNSF âEarly PostDoc Mobilityâ P2EZP2-178435). R.C. acknowledges TA Instruments for providing the DHR-3 rheometer under the Young Distinguished Rheologist Award instrument grant. S.S. and E.W.M acknowledge the European Research Council (H2020-EU.1.1., SYNMAT project, ID 788618).Netherlands Organisation for Scientific Research; 024.003.013Swiss National Science Foundation; P2EZP2-17843
Bardeen-Petterson effect and the disk structure of the Seyfert galaxy NGC 1068
VLBA high spatial resolution observations of the disk structure of the active
galactic nucleus NGC 1068 has recently revealed that the kinematics and
geometry of this AGN is well characterized by an outer disk of H2O maser
emission having a compact milliarcsecond (parsec) scale structure, which is
encircling a thin rotating inner disk surrounding a ~10^7 M_\sun compact
mass, likely a black hole. A curious feature in this source is the occurrence
of a misalignment between the inner and outer parts of the disk, with the
galaxy's radio jet being orthogonal to the inner disk. We interpret this
peculiar configuration as due to the Bardeen-Petterson effect, a general
relativistic effect that warps an initially inclined (to the black hole
equator) viscous disk, and drives the angular momentum vector of its inner part
into alignment with the rotating black hole spin. We estimate the time-scale
for both angular momenta to get aligned as a function the spin parameter of the
Kerr black hole. We also reproduce the shape of the parsec and kiloparsec scale
jets, assuming a model in which the jet is precessing with a period and
aperture angle that decrease exponentially with time, as expected from the
Bardeen-Petterson effect.Comment: 12 pages, 3 figures, accepted for publication in The Astrophysical
Journa
Calibration of GRB Luminosity Relations with Cosmography
For the use of Gamma-Ray Bursts (GRBs) to probe cosmology in a
cosmology-independent way, a new method has been proposed to obtain luminosity
distances of GRBs by interpolating directly from the Hubble diagram of SNe Ia,
and then calibrating GRB relations at high redshift. In this paper, following
the basic assumption in the interpolation method that objects at the same
redshift should have the same luminosity distance, we propose another approach
to calibrate GRB luminosity relations with cosmographic fitting directly from
SN Ia data. In cosmography, there is a well-known fitting formula which can
reflect the Hubble relation between luminosity distance and redshift with
cosmographic parameters which can be fitted from observation data. Using the
Cosmographic fitting results from the Union set of SNe Ia, we calibrate five
GRB relations using GRB sample at and deduce distance moduli of GRBs
at by generalizing above calibrated relations at high
redshift. Finally, we constrain the dark energy parameterization models of the
Chevallier-Polarski-Linder (CPL) model, the Jassal-Bagla-Padmanabhan (JBP)
model and the Alam model with GRB data at high redshift, as well as with the
Cosmic Microwave Background radiation (CMB) and the baryonic acoustic
oscillation (BAO) observations, and we find the CDM model is
consistent with the current data in 1- confidence region.Comment: 15 pages, 4 figures, 2 tables; accepted for publication in IJMP
Global Sustainable Tax Governance in the OECD-G20 Transparency and BEPS Initiatives
The main question addressed in this book chapter is:Â Are the OECD transparency and BEPS Framework the right framework for a global and sustainable tax governance that benefits not only OECD and G20countries but also non-OECD and non-G20 countries, including developing countries? In order to answer this question, this chapter will provide an analysis of sustainable tax governance taking into account the sustainable development goals (SDGs) that the global tax initiatives aim to address and the mechanisms to achieve these goals. Seventh Framework Programme (FP7)758671Grenzen van fiscale soevereinitei
A New Microlensing Event in the Doubly-Imaged Quasar Q0957+561
We present evidence for ultraviolet/optical microlensing in the
gravitationally lensed quasar Q0957+561. We combine new measurements from our
optical monitoring campaign at the United States Naval Observatory, Flagstaff
(USNO) with measurements from the literature and find that the
time-delay-corrected r-band flux ratio m_A - m_B has increased by ~0.1
magnitudes over a period of five years beginning in the fall of 2005. We apply
our Monte Carlo microlensing analysis procedure to the composite light curves,
obtaining a measurement of the optical accretion disk size, log
{(r_s/cm)[cos(i)/0.5]^{1/2}} = 16.2^{+0.5}_{-0.6}, that is consistent with the
quasar accretion disk size - black hole mass relation.Comment: Replaced with accepted version. Minor adjustments to text but
conclusions unchanged. Data in Table 2 have been updated and table now
includes additional observation
Nonlinear electrodynamics and CMB polarization
Recently WMAP and BOOMERanG experiments have set stringent constraints on the
polarization angle of photons propagating in an expanding universe: . The polarization of the Cosmic Microwave
Background radiation (CMB) is reviewed in the context of nonlinear
electrodynamics (NLED). We compute the polarization angle of photons
propagating in a cosmological background with planar symmetry. For this
purpose, we use the Pagels-Tomboulis (PT) Lagrangian density describing NLED,
which has the form , where , and the parameter featuring the
non-Maxwellian character of the PT nonlinear description of the electromagnetic
interaction. After looking at the polarization components in the plane
orthogonal to the ()-direction of propagation of the CMB photons, the
polarization angle is defined in terms of the eccentricity of the universe, a
geometrical property whose evolution on cosmic time (from the last scattering
surface to the present) is constrained by the strength of magnetic fields over
extragalactic distances.Comment: 17 pages, 2 figures, minor changes, references adde
Tax and Development: The Link between International Taxation, The Base Erosion Profit Shifting Project and The 2030 Sustainable Development Agenda.
The OECD-G20 project on Base Erosion and Profit Shifting (BEPS) is the largest reform of the international tax architecture in decades. The BEPS project aims to ensure that multinationals pay their taxes in the jurisdictions where they create value and where their economic activity takes place. When it is fully implemented, it will substantially alter the global governance architecture for taxation. This is a commendable goal, yet the BEPS project can be criticized for not sufficiently tailoring to the specific needs of developing countries. While it has made a laudable attempt to be more attentive towards developing countries with the creation of the BEPS inclusive framework, this concerns the implementation phase of BEPS. The agenda-setting and decision-making process only included the G20 and OECD countries. Against this background, it is unclear how and if the BEPS project considered the specific needs of developing countries, especially in light of the Sustainable Development Goals (SDGs). This paper will examine this issue by addressing the following questions: (i) Were the Sustainable Development Goals (SDGs) and the interests of developing countries to attract investment considered throughout the BEPS Process? (ii) What issues of international taxation, beyond BEPS, should be addressed to fulfill developing countries' domestic resource mobilization needs to achieve the 2030 Agenda for Sustainable Development. We conclude with a set of recommendations to the international global tax governance architecture to be more inclusive and responsive to development countriesâ needs.Seventh Framework Programme (FP7)758671Grenzen van fiscale soevereinitei
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