In this work, we calculate the deflection angle of light in a spacetime that interpolates between regular black holes and traversable wormholes, depending on the free parameter of the metric. ...Afterwards, this angular deflection is substituted into the lens equations which allows us to obtain physically measurable results, such as the position of the relativistic images and the magnifications.
We consider the space-time metric generated by a global monopole in an extension of general relativity (GR) of the form f ( R ) = R − λ R 2 . The theory is formulated in the metric-affine (or ...Palatini) formalism, and exact analytical solutions are obtained. For λ < 0 , one finds that the solution has the same characteristics as the Schwarzschild black hole with a monopole charge in Einstein’s GR. For λ > 0 , instead, the metric is more closely related to the Reissner-Nordström metric with a monopole charge and, in addition, it possesses a wormhole-like structure that allows for the geodesic completeness of the space-time. Our solution recovers the expected limits when λ = 0 and also at the asymptotic far limit. The angular deflection of light in this space-time in the weak field regime is also calculated.
In this paper we consider two different nonlinear σ-models minimally coupled to Eddington-inspired Born-Infeld gravity. We show that the resultant geometries represent minimal modifications with ...respect to those found in GR, though with important physical consequences. In particular, wormhole structures always arise, though this does not guarantee by itself the geodesic completeness of those space-times. In one of the models, quadratic in the canonical kinetic term, we identify a subset of solutions which are regular everywhere and are geodesically complete. We discuss characteristic features of these solutions and their dependence on the relationship between mass and global charge.
In this work we calculate the angular deflection of light in the strong field limit in two spacetimes which were previously studied within the Eddington-inspired Born-Infeld gravity, namely, a black ...hole and a wormhole, both with topological charge. We show that the presence of the parameters characterizing Eddington-inspired Born-Infeld gravity and the topological charge promote significant changes in the angular deflection of light with respect to that one obtained in Schwarzschild spacetime. Using the expression for angular deflection in the strong field limit, we calculate the position and magnification of the respective relativistic images.
A new genus of xyleborine ambrosia beetle, Melanesicus Beaver Petrov gen. n., with type species Xyleborus partitus Browne (1974) is described from the Melanesian region. The following new ...combinations are proposed: M. caledoniae (Beaver Liu, 2016) comb. n., M. deformatus (Browne, 1974) comb. n., M. granulosus (Schedl, 1975) comb. n., all from Xyleborus Eichhoff, 1864. Melanesicus tishechkini Petrov sp. n. is described from Vanuatu, and Melanesicus nukuruanus sp. n. Beaver from Fiji. The taxonomy, distribution and biology of the species included are briefly reviewed.
In this paper, we obtain dispersion relations corresponding to plane wave solutions in Lorentz-breaking extensions of gravity with dimension 3, 4, 5 and 6 operators. We demonstrate that these ...dispersion relations display a usual Lorentz-invariant mode when the corresponding additive term involves higher derivatives.
Cholesterol oxidation products frequently have a high biological activity. In the present study, we have used microelectrode recording of end plate currents and FM-based optical detection of synaptic ...vesicle exo-endocytosis to investigate the effects of two structurally similar oxysterols, olesoxime (cholest-4-en-3-one, oxime) and 5ɑ-cholestan-3-one (5ɑCh3), on neurotransmission at the frog neuromuscular junction. Olesoxime is an exogenous, potentially neuroprotective, substance and 5ɑCh3 is an intermediate product in cholesterol metabolism, which is elevated in the case of cerebrotendinous xanthomatosis. We found that olesoxime slightly increased evoked neurotransmitter release in response to a single stimulus and significantly reduced synaptic depression during high frequency activity. The last effect was due to an increase in both the number of synaptic vesicles involved in exo-endocytosis and the rate of synaptic vesicle recycling. In contrast, 5ɑCh3 reduced evoked neurotransmitter release during the low- and high frequency synaptic activities. The depressant action of 5ɑCh3 was associated with a reduction in the number of synaptic vesicles participating in exo- and endocytosis during high frequency stimulation, without a change in rate of the synaptic vesicle recycling. Of note, olesoxime increased the staining of synaptic membranes with the B-subunit of cholera toxin and the formation of fluorescent ganglioside GM1 clusters, and decreased the fluorescence of 22-NBD-cholesterol, while 5ɑCh3 had the opposite effects, suggesting that the two oxysterols have different effects on lipid raft stability. Taken together, these data show that these two structurally similar oxysterols induce marked different changes in neuromuscular transmission which are related with the alteration in synaptic vesicle cycle.
•We study changes in the neurotransmission at frog neuromuscular junction.•Olesoxime increases evoked, but not spontaneous, neurotransmitter release.•Olesoxime increases exo-endocytosis and the rate of synaptic vesicle recycling.•Olesoxime impacts on synaptic membrane properties/formation of lipid rafts.•The structurally related oxysterol, 5α-cholestan-3one, has opposite actions.
PDF
