29 research outputs found
Observational Features of Black Holes
Recently considered a very attracting possibility to detect retro-MACHOs,
i.e. retro-images of the Sun by a Schwarzschild black hole. In this paper we
discuss glories (mirages) formed near rapidly rotating Kerr black hole horizons
and propose a procedure to measure masses and rotation parameters analyzing
these forms of mirages. In some sense that is a manifestation of gravitational
lens effect in the strong gravitational field near black hole horizon and a
generalization of the retro-gravitational lens phenomenon. We analyze the case
of a Kerr black hole rotating at arbitrary speed for some selected positions of
a distant observer with respect to the equatorial plane of a Kerr black hole.
We discuss glories (mirages) formed near rapidly rotating Kerr black hole
horizons and propose a procedure to measure masses and rotation parameters
analyzing these forms of mirages. Some time ago suggested to search shadows at
the Galactic Center. In this paper we present the boundaries for shadows
calculated numerically. We also propose to use future radio interferometer
RADIOASTRON facilities to measure shapes of mirages (glories) and to evaluate
the black hole spin as a function of the position angle of a distant observer.Comment: Plenary talk presented at Workshop on High Energy Physics&Field
Theory (Protvino, Russia, 2004
Dark Matter in the Dwarf Galaxy NGC 247
Dwarf galaxies are dominated by dark matter even in the innermost regions
and, therefore, provide excellent probes for the investigation of dark halos.
To that purpose, we analyse ROSAT PSPC-data of the dwarf galaxy NGC 247. We
focus in particular on the diffuse X-ray emission in the keV band.
Assuming an isothermal density profile, we find that the mass of the hot
emitting gas is about , corresponding to
of the total dynamical mass of the galaxy. The total mass of NGC 247, as
derived from the X-ray data agrees quite well with the value obtained from the
measured rotation curve (Burlak). The X-ray profile in the keV and keV band shows an excess at a radial distance of about arcmin from the
center. Such a ``hump'' in the radial X-ray profile can be explained by the
presence of a cluster of young low mass stars or brown dwarfs. Therefore, NGC
247 offers the possibility to observe the formation of a halo of MACHOs.Comment: 6 pages, accepted for publication in A &
On the role of pressure anisotropy for relativistic stars admitting conformal motion
We investigate the spacetime of anisotropic stars admitting conformal motion.
The Einstein field equations are solved using different ansatz of the surface
tension. In this investigation, we study two cases in details with the
anisotropy as: [1] [2] where, n, and are arbitrary constants.
The solutions yield expressions of the physical quantities like pressure
gradients and the mass.Comment: 21 pages, accepted for publication in 'Astrophysics and Space
Science
Supersymmetric dark matter in M31: can one see neutralino annihilation with CELESTE?
It is widely believed that dark matter exists within galaxies and clusters of
galaxies. Under the assumption that this dark matter is composed of the
lightest, stable supersymmetric particle, assumed to be the neutralino, the
feasibility of its indirect detection via observations of a diffuse gamma-ray
signal due to neutralino annihilations within M31 is examined. To this end,
first the dark matter halo of the close spiral galaxy M31 is modeled from
observations, then the resultant gamma-ray flux is estimated within
supersymmetric model configurations. We conclude that under favorable
conditions such as the rapid accretion of neutralinos on the central black hole
in M31 and/or the presence of many clumps inside its halo with inner
profiles, a neutralino annihilation gamma-ray signal is marginally detectable
by the ongoing collaboration CELESTE.Comment: Latex, 32 pages, 12 figures, 5 table
Inhibition of T7 and T3 RNA polymerase directed transcription elongation in vitro.
A class of oligonucleotides which binds to naturally-occurring duplex DNA sites at physiologic pH to form triple helical structures was used as transcription attenuators in an in vitro transcription assay. Oligonucleotides were designed to form triple helices with a purine-rich, double-stranded target by binding in the major groove in an orientation anti-parallel to the most purine-rich strand of the target. A 45 base-pair purine-rich region located within the gag gene of Friend Murine Leukemia Virus (FMLV) was used as the duplex target. The target DNA was inserted by molecular cloning downstream of either the bacterial T7- or T3 promoter. The sequence-specific interaction of the triple helix-forming oligonucleotide (TFO) with the FMLV target was confirmed by DNAse I footprint analysis. The affinity of the TFO, as measured by the equilibrium dissociation constant of the TFO for the duplex, was determined by band shift analysis. When a TFO was allowed to form a triple helix with the target duplex in well-defined buffer conditions before the transcription reaction, truncated transcripts of a predicted size were observed. Attenuation of transcription was observed only when buffer conditions favorable to triple helix formation were used. In addition, oligonucleotides containing a high percentage of guanosine residues were able to inhibit mRNA production of the bacterial T7 polymerase by a mechanism independent of transcription attenuation. The ability of an oligonucleotide-directed triple helical structure to slow down, or even completely stop, RNA chain elongation may expand the utility of triple helix technology in the area of gene regulation
BRAVO: A gaming environment for the treatment of ADHD
Attention-deficit hyperactivity disorder (ADHD) is a neurodevelopmental disorder that is expressed through different symptoms belonging to three different dimensions: inattention, impulsivity and motor hyperactivity, each of which contributes to the learning and adaptation problems within the different contexts of life. ADHD children have to focus on three main elements: learn to self-control, make and keep friends and feel good about themselves. The BRAVO (Beyond the tReatment of the Attention deficit hyperactiVity disOrder) project aims to realize an immersive therapeutic game context, based on an innovative ICT system, with which improving the relationship between young patients and therapies (administered by means of serious games and gamification). By using wearable equipment and Virtual and Augmented Reality devices, new personalized processes of therapy will be implemented. Such processes will be able to dynamically change in order to follow the patients evolution and support the therapists in the rehabilitation program management