604 research outputs found
Strangelet spectra from type II supernovae
We study in this work the fate of strangelets injected as a contamination in
the tail of a "strange matter-driven" supernova shock. A simple model for the
fragmentation and braking of the strangelets when they pass through the
expanding oxygen shell is presented and solved to understand the reprocessing
of this component. We find that the escaping spectrum is a scaled-down version
of the one injected at the base of the oxygen shell. The supernova source is
likely to produce low-energy particles of quite independently
of the initial conditions. However, it is difficult that ultrarrelativistic
strangelets (such as the hypothetical Centauro primaries) can have an origin in
those explosive events.Comment: RevTex file, 5 pp., no figure
Quantifying pigment cover to assess variation in animal colouration
The study of animal colouration addresses fundamental and applied aspects relevant to a wide range
of fields, including behavioural ecology, environmental adaptation and visual ecology. Although a
variety of methods are available to measure animal colours, only few focus on chromatophores
(specialized cells containing pigments) and pigment migration. Here, we illustrate a freely available
and user friendly method to quantify pigment cover (PiC) with high precision and low effort using
digital images, where the foreground (i.e., pigments in chromatophores) can be detected and
separated from the background. Images of the brown shrimp, Crangon crangon were used to
compare PiC with the traditional Chromatophore Index (CI). Results indicate that PiC outcompetes CI
for pigment detection and transparency measures in terms of speed, accuracy and precision. The
proposed methodology provides researchers with a useful tool to answer essential physiological,
behavioural and evolutionary questions on animal colouration in a wide range of species
Make Bow-tie Dynamic by Rethinking it as a Hierarchical Bayesian Network. Dynamic Risk Assessment of an LNG Bunkering Operation
In the present era, the spread of cyber-physical systems in the framework of the so-called Industry 4.0, is leading towards a complete automation of industrial processes, which are increasingly decentralized, smart, and require fewer and fewer frontline personnel. The risk assessment process is certainly not excluded from the revolution, and in perspective needs to be automatic, dynamic and linked with the conditions that emerge, moment by moment, in the life of a complex system. Analytical techniques can help in converting data in information and hence system knowledge to spot trends in operational performance, thus improving risk assessment quality. Even though the bow-tie approach is widely used within the context of complex systems, it still evidences several limitations, mainly connected to the actual assessment of likelihood and interdependencies in the fault and event trees. This paper shows how a bow tie analysis can be reframed as a Hierarchical Bayesian Network, where the probability distributions of the network nodes are updated with real time predictions during the operations. The proposed model was then applied to the risk assessment of a shore-to-ship LNG bunkering operation
Decay versus survival of a localized state subjected to harmonic forcing: exact results
We investigate the survival probability of a localized 1-d quantum particle
subjected to a time dependent potential of the form with
or . The particle is
initially in a bound state produced by the binding potential . We
prove that this probability goes to zero as for almost all values
of , , and . The decay is initially exponential followed by a
law if is not close to resonances and is small; otherwise
the exponential disappears and Fermi's golden rule fails. For exceptional sets
of parameters and the survival probability never decays to zero,
corresponding to the Floquet operator having a bound state. We show similar
behavior even in the absence of a binding potential: permitting a free particle
to be trapped by harmonically oscillating delta function potential
Rotation And Magnetic Evolution Of Superconducting Strange Stars
Is pulsar make up of strange matter? The magnetic field decay of a pulsar may
be able to give us an answer. Since Cooper pairing of quarks occurs inside a
sufficiently cold strange star, the strange stellar core is superconducting. In
order to compensate the effect of rotation, different superconducting species
inside a rotating strange star try to set up different values of London fields.
Thus, we have a frustrated system. Using Ginzburg-Landau formalism, I solved
the problem of rotating a superconducting strange star: Instead of setting up a
global London field, vortex bundles carrying localized magnetic fields are
formed. Moreover, the number density of vortex bundles is directly proportional
to the angular speed of the star. Since it is energetically favorable for the
vortex bundles to pin to magnetic flux tubes, the rotational dynamics and
magnetic evolution of a strange star are coupled together, leading to the
magnetic flux expulsion as the star slows down. I investigate this effect
numerically and find that the characteristic field decay time is much less than
20~Myr in all reasonable parameter region. On the other hand, the
characteristic magnetic field decay time for pulsars is ~Myr. Thus, my
finding cast doubt on the hypothesis that pulsars are strange stars.Comment: 42 pages (including 13 eps figures) in AASTex 4.0 style with AMSFont
Diffusive Ionization of Relativistic Hydrogen-Like Atom
Stochastic ionization of highly excited relativistic hydrogenlike atom in the
monochromatic field is investigated. A theoretical analisis of chaotic dynamics
of the relativistic electron based on Chirikov criterion is given for the cases
of one- and three-dimensional atoms. Critical value of the external field is
evaluated analitically. The diffusion coefficient and ionization time are
calculated.Comment: 13 pages, latex, no figures, submitted to PR
The Fermi accelerator in atom optics
We study the classical and quantum dynamics of a Fermi accelerator realized
by an atom bouncing off a modulated atomic mirror. We find that in a window of
the modulation amplitude dynamical localization occurs in both position and
momentum. A recent experiment [A. Steane, P. Szriftgiser, P. Desbiolles, and J.
Dalibard, Phys. Rev. Lett. {\bf 74}, 4972 (1995)] shows that this system can be
implemented experimentally.Comment: 5 pages, 5 figure
Curvature energy effects on strange quark matter nucleation at finite density
We consider the effects of the curvature energy term on thermal strange quark
matter nucleation in dense neutron matter. Lower bounds on the temperature at
which this process can take place are given and compared to those without the
curvature term.Comment: PlainTex, 6 pp., IAG-USP Rep.5
Spontaneous Scalarization and Boson Stars
We study spontaneous scalarization in Scalar-Tensor boson stars. We find that
scalarization does not occur in stars whose bosons have no self-interaction. We
introduce a quartic self-interaction term into the boson Lagrangian and show
that when this term is large, scalarization does occur. Strong self-interaction
leads to a large value of the compactness (or sensitivity) of the boson star, a
necessary condition for scalarization to occur, and we derive an analytical
expression for computing the sensitivity of a boson star in Brans-Dicke theory
from its mass and particle number. Next we comment on how one can use the
sensitivity of a star in any Scalar-Tensor theory to determine how its mass
changes when it undergoes gravitational evolution. Finally, in the Appendix, we
derive the most general form of the boson wavefunction that minimises the
energy of the star when the bosons carry a U(1) charge.Comment: 23 pages, 5 postscript figures. Typing errors corrected. Includes
some new text that relates the paper to several previous results. Accepted
for publication in PR
- âŠ