A tale of analogies: gravitomagnetic effects, rotating sources, observers and all that

Gravitoelectromagnetic analogies are somewhat ubiquitous in General Relativity, and they are often used to explain peculiar effects of Einstein's theory of gravity in terms of familiar results from classical electromagnetism. Perhaps, the best known of these analogy pertains to the similarity between the equations of electromagnetism and those of the linearized theory of General Relativity. But the analogy is somewhat deeper and ultimately rooted in the splitting of spacetime, which is preliminary to the definition of the measurement process. In this paper we review the various approaches that lead to the introduction of a magnetic-like part of the gravitational interaction, briefly called gravitomagnetic and, then, we provide a survey of the recent developments both from the theoretical and experimental viewpoints.Comment: Preliminary version of an invited topical review: comments and suggestions of further references are welcom

Black hole attractors and U(1) Fayet-Iliopoulos gaugings: analysis and classification

We classify the critical points of the effective black hole potential which governs the attractor mechanism taking place at the horizon of static dyonic extremal black holes in $\mathcal{N}=2$, $D=4$ Maxwell-Einstein supergravity with $U(1)$ Fayet-Iliopoulos gaugings. We use a manifestly symplectic covariant formalism, and we consider both spherical and hyperbolic horizons, recognizing the relevant sub-classes to which some representative examples belong. We also exploit projective special K\"{a}hler geometry of vector multiplets scalar manifolds, the $U$-duality-invariant quartic structure (and 2-polarizations thereof) in order to retrieve and generalize various expressions of the entropy of asymptotically AdS$_{4}$ BPS black holes, in the cases in which the scalar manifolds are symmetric spaces. Finally, we present a novel static extremal black hole solution to the $STU$ model, in which the dilaton interpolates between an hyperbolic near-horizon geometry and AdS$_{4}$ at infinity.Comment: 58 pages,0 figure

Supersymmetric wormholes in String theory

We construct a large family of Euclidean supersymmetric wormhole solutions of type IIB supergravity which are asymptotically AdS$_5 \times S^5$. The solutions are constructed using consistent truncation to maximally gauged supergravity in five dimensions which is further truncated to a four scalar model. Within this model we perform a full analytic classification of supersymmetric domain wall solutions with flat Euclidean domain wall slices. On each side of the wormhole, the solution asymptotes to AdS$_5$ dual to ${\cal N}= 4$ supersymmetric Yang-Mills deformed by a supersymmetric mass term.Comment: 7 page

Towards a full general relativistic approach to galaxies

We analyze the dynamics of a single spiral galaxy from a general relativistic viewpoint. We employ the known family of stationary axially-symmetric solutions to Einstein gravity coupled with dust in order to model the halo external to the bulge. In particular, we generalize the known results of Balasin and Grumiller, relaxing the condition of co-rotation, thus including non co-rotating dust. This further highlights the discrepancy between Newtonian theory of gravity and general relativity at low velocities and energy densities. We investigate the role of dragging in simulating dark matter effects. In particular, we show that non co-rotance further reduce the amount of energy density required to explain the rotation curves for spiral galaxies.Comment: 13 page

Válvula aórtica cuadricúspide. El trébol de cuatro hojas de la ecocardiografía

The quadricuspid aortic valve (VAoC) is a rare congenital disease. However, with the broad use of the Doppler echocardiogram, its detection begins to be frequent. The incidence of this congenital malformation is very low, and its main complication is aortic regurgitation. We present a short review based on three clinical cases.La válvula aórtica cuadricúspide (VAoC) es una enfermedad congénita rara. Sin embargo, el empleo masivo de la ecocardiografía Doppler hace que su detección sea más frecuente. La incidencia de esta malformación congénita es muy baja y su principal complicación es la insuficiencia aórtica. Se presenta una revisión a propósito de tres casos

Instantons and wormholes in AdS(3) x S-3 x CY2

We study supergravity instantons sourced by axion (and saxion) fields in the Euclidean AdS(3) x S-3 x CY2 vacua of IIB supergravity. Such instantons are described by geodesic curves on the moduli space; the timelike geodesics can describe Euclidean wormholes, the lightlike geodesics describe (generalizations of) D instantons, and spacelike geodesics are subextremal versions thereof. We perform a concrete classification of such geodesics and find that, despite earlier claims, the wormholes fail to be regular. A subclass of the lightlike geodesics is supersymmetric and, up to dualities, lifts to Euclidean strings wrapping 2-cycles in the CY2. The dual of these instantons is expected to be worldsheet instantons of the D1-D5 conformal field theory

Particle motion in a rotating dust spacetime: the Bonnor solution

We investigate the geometrical properties, spectral classification, geodesics, and causal structure of the Bonnor's spacetime [Journal of Physics A Math. Gen., \textbf{10}, 1673 (1977)], i.e., a stationary axisymmetric solution with a rotating dust as a source. This spacetime has a directional singularity at the origin of the coordinates (related to the diverging vorticity field of the fluid there), which is surrounded by a toroidal region where closed timelike curves (CTCs) are allowed, leading to chronology violations. We use the effective potential approach to provide a classification of the different kind of orbits on the symmetry plane as well as to study the motion parallel to the symmetry axis. In the former case we find that as a general feature test particles released from a fixed space point and directed towards the singularity are repelled and scattered back as soon as they approach the CTC boundary, without reaching the central singularity.Comment: 11 pages, 5 figures (10 eps files

Strip Annealing Furnaces for New Galvanizing Lines

Constant improvements to continuous annealing process technology are necessary for the production of bothnew and traditional steel grades to provide good formability and ductility and also gives higher mechanicalproperties when combined with correctly tuned steel chemical compositions.One vertical and one horizontal type furnace are to be started up at Acciaieria Arvedi S.p.A. (Italy) in 2011,these furnaces form part of the Continuous Galvanizing Line (CGL) in the Danieli Cold Mill Complex, thiscomplex also includes a six-high Tandem Coil Mill and Push-Pull Pickling Line.The furnaces will be able to match any market requirements for different annealing cycles, thus combininghigh performance with low investment and transformation costs. Short heat-up, long soaking, both slow andrapid cooling have all been included in equipment design to give any type of annealing curve and include alarge group of steel grades commonly required by the market. Planned expansion will allow for additionalslow cooling and extended over-aging time. High performance direct flame burners and radiant tubes fed bynatural gas are the key to guarantee strip quality and low maintenance costs. Flexible rapid jet coolingperforms different cooling rates to accommodate the metallurgy of several different steel grades