7 research outputs found
Enhancement of photoacoustic detection of inhomogeneities in polymers
We report a series of experiments on laser pulsed photoacoustic excitationin
turbid polymer samples addressed to evaluate the sound speed in the samples and
the presence of inhomogeneities in the bulk. We describe a system which allows
the direct measurement of the speed of the detected waves by engraving the
surface of the piece under study with a fiduciary pattern of black lines. We
also describe how this pattern helps to enhance the sensitivity for the
detection of an inhomogeneity in the bulk. These two facts are useful for
studies in soft matter systems including, perhaps, biological samples. We have
performed an experimental analysis on Grilon(R) samples in different situations
and we show the limitations of the method.Comment: 8 pages, 7 figure
Hybrid stars with sequential phase transitions: the emergence of the g mode
Neutron stars are the densest objects in the Universe, with and km, and the equation of state associated to their
internal composition is still unknown. The extreme conditions to which matter
is subjected inside neutron stars could lead to a phase transition in their
inner cores, giving rise to a hybrid compact object. The observation of
binary pulsars (PSR~J1614-2230, PSR~J03430432 and
PSR~J07406620) strongly constraints theoretical models of the equation of
state. Moreover, the detection of gravitational waves emitted during the binary
neutron star merger, GW170817, and its electromagnetic counterpart, GRB170817A,
impose additional constraints on the tidal deformability. In this work, we
investigate hybrid stars with sequential phase transitions hadron-quark-quark
in their cores. We assume that both phase transitions are sharp and analyse the
rapid and slow phase conversion scenarios. For the outer core, we use modern
hadronic equations of state. For the inner core we employ the constant speed of
sound parametrization for quark matter. We analyze more than 3000 hybrid
equations of state, taking into account the recent observational constraints
from neutron stars. The effects of hadron-quark-quark phase transitions on the
normal oscillation modes and , are studied under the Cowling
relativistic approximation. Our results show that, in the slow conversion
regime, a second quark-quark phase transition gives rise to a new ~mode.
We discuss the observational implications of our results associated to the
gravitational waves detection and the possibility of detecting hints of
sequential phase transitions and the associated ~mode.Comment: 24 pages, 9 figure
Enhancement of photoacoustic detection of inhomogeneities in polymers
We report a series of experiments on laser pulsed photoacoustic excitation in turbid polymer samples addressed to evaluate the sound speed in the samples and the presence of inhomogeneities in the bulk. We describe a system which allows the direct measurement of the speed of the detected waves by engraving the surface of the piece under study with a fiduciary pattern of black lines. We also describe how this pattern helps to enhance the sensitivity for the detection of an inhomogeneity in the bulk. These two facts are useful for studies in soft matter systems including, perhaps, biological samples. We have performed an experimental analysis on Grilon®samples in different situations and we show the limitations of the method.Facultad de IngenierÃ
Enhancement of photoacoustic detection of inhomogeneities in polymers
We report a series of experiments on laser pulsed photoacoustic excitation in turbid polymer samples addressed to evaluate the sound speed in the samples and the presence of inhomogeneities in the bulk. We describe a system which allows the direct measurement of the speed of the detected waves by engraving the surface of the piece under study with a fiduciary pattern of black lines. We also describe how this pattern helps to enhance the sensitivity for the detection of an inhomogeneity in the bulk. These two facts are useful for studies in soft matter systems including, perhaps, biological samples. We have performed an experimental analysis on Grilon®samples in different situations and we show the limitations of the method.Facultad de IngenierÃ
Instability of hyper-compact Kerr-like objects
Viable alternatives to astrophysical black holes include hyper-compact
objects without horizon, such as gravastars, boson stars, wormholes and
superspinars. The authors have recently shown that typical rapidly-spinning
gravastars and boson stars develop a strong instability. That analysis is
extended in this paper to a wide class of horizonless objects with approximate
Kerr-like geometry. A detailed investigation of wormholes and superspinars is
presented, using plausible models and mirror boundary conditions at the
surface. Like gravastars and boson stars, these objects are unstable with very
short instability timescales. This result strengthens previous conclusions that
observed hyper-compact astrophysical objects with large rotation are likely to
be black holes.Comment: 15 pages, 3 figures. To be published in CQ