5,658 research outputs found
Non-radial oscillation modes as a probe of density discontinuities in neutron stars
A phase transition occurring in the inner core of a neutron star could be
associated to a density discontinuity that would affect the frequency spectrum
of the non-radial oscillation modes in two ways. Firstly, it would produce a
softening of the equation of state, leading to more compact equilibrium
configurations and changing the frequency of the fundamental and pressure modes
of the neutron star. Secondly, a new non-zero frequency g-- mode would appear,
associated to each discontinuity. These discontinuity g--modes have typical
frequencies larger than those of g--modes previously studied in the literature
(thermal, core g-- modes, or g--modes due to chemical inhomogeneities in the
outer layers), and smaller than that of the fundamental mode; therefore they
should be distinguishable from the other modes of non radial oscillation. In
this paper we investigate how high density discontinuities change the frequency
spectrum of the non-radial oscillations, in the framework of the general
relativistic theory of stellar perturbations. Our purpose is to understand
whether a gravitational signal, emitted at the frequencies of the quasi normal
modes, may give some clear information on the equation of state of the neutron
star and, in particular, on the parameters that characterize the density
discontinuity. We discuss some astrophysical processes that may be associated
to the excitation of these modes, and estimate how much gravitational energy
should the modes convey to produce a signal detectable by high frequency
gravitational detectors.Comment: submitted to MNRA
The dish-Rankine SCSTPE program (Engineering Experiment no. 1)
Activities planned for phase 2 Of the Small Community Solar Thermal Power Experiment (PFDR) program are summarized with emphasis on a dish-Rankine point focusing distributed receiver solar thermal electric system. Major design efforts include: (1) development of an advanced concept indirect-heated receiver;(2) development of hardware and software for a totally unmanned power plant control system; (3) implementation of a hybrid digital simulator which will validate plant operation prior to field testing; and (4) the acquisition of an efficient organic Rankine cycle power conversion unit. Preliminary performance analyses indicate that a mass-produced dish-Rankine PFDR system is potentially capable of producing electricity at a levelized busbar energy cost of 60 to 70 mills per KWh and with a capital cost of about $1300 per KW
Spatial repartition of local plastic processes in different creep regimes in a granular material
Granular packings under constant shear stress display below the Coulomb
limit, a logarithmic creep dynamics. However the addition of small stress
modulations induces a linear creep regime characterized by an effective viscous
response. Using Diffusing Wave Spectroscopy, we investigate the relation
between creep and local plastic events spatial distribution ("hot-spots")
contributing to the plastic yield. The study is done in the two regimes, i.e.
with and without mechanical activation. The hot-spot dynamics is related to the
material effective fluidity. We show that far from the threshold, a local
visco-elastic rheology coupled to an ageing of the fluidity parameter, is able
to render the essential spatio-temporal features of the observed creep
dynamics
Influence of the Feedback Filter on the Response of the Pulsed Digital Oscillator
This paper introduces a new feedback topology for the Pulsed Digital
Oscillator (PDO) and compares it to the classical topology. The `classic' or
single feedback topology, introduced in previous works, shows a strong behavior
dependence on the damping losses in the MEMS resonator. A new double feedback
topology is introduced here in order to help solving this problem. Comparative
discrete-time simulations and preliminary experimental measurements have been
carried out for both topologies, showing how the new double feedback topology
may increase PDO performance for some frequency ranges.Comment: Submitted on behalf of TIMA Editions
(http://irevues.inist.fr/tima-editions
Morfotopografia y patogenia del infarto hemorrágico encefálico en la hipertensión arterial
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