19,416 research outputs found
Discriminating hadronic and quark stars through gravitational waves of fluid pulsation modes
We investigate non-radial oscillations of hadronic, hybrid and pure
self-bound strange quark stars with maximum masses above the mass of the
recently observed massive pulsars PSR J1614-2230 and PSR J0348-0432 with . For the hadronic equation of state we employ different
parametrizations of a relativistic mean-field model and for quark matter we use
the MIT bag model including the effect of strong interactions and color
superconductivity. We find that the first pressure mode for strange quark stars
has a very different shape than for hadronic and hybrid stars. For strange
quarks stars the frequency of the p1 mode is larger than 6 kHz and diverge at
small stellar masses, but for hadronic and hybrid stars it is in the range 4-6
kHz. This allows an observational identification of strange stars even if extra
information such as the mass, the radius or the gravitational redshift of the
object is unavailable or uncertain. Also, we find as in previous works that the
frequency of the g-mode associated with the quark-hadron discontinuity in a
hybrid star is in the range 0.4-1 kHz for all masses. Thus, compact objects
emitting gravitational waves above 6 kHz should be interpreted as strange quark
stars and those emitting a signal within 0.4-1 kHz should be interpreted as
hybrid stars.Comment: 7 pages, 5 figure
Light Reflectance Characteristics and Remote Sensing of Waterlettuce
Waterlettuce (
Pistia stratiotes
L.) is a free-floating exotic
aquatic weed that often invades and clogs waterways in the
southeastern United States. A study was conducted to evaluate
the potential of using remote sensing technology to distinguish
infestations of waterlettuce in Texas waterways. Field
reflectance measurements showed that waterlettuce had
higher visible green reflectance than associated plant species.
Waterlettuce could be detected in both aerial color- infrared
(CIR) photography and videography where it had
light pink to pinkish-white image tonal responses. Computer
analysis of CIR photographic and videographic images had
overall accuracy assessments of 86% and 84%, respectively. (PDF contains 6 pages.
Renormalized coordinate approach to the thermalization process
We consider a particle in the harmonic approximation coupled linearly to an
environment. modeled by an infinite set of harmonic oscillators. The system
(particle--environment) is considered in a cavity at thermal equilibrium. We
employ the recently introduced notion of renormalized coordinates to
investigate the time evolution of the particle occupation number. For
comparison we first present this study in bare coordinates. For a long ellapsed
time, in both approaches, the occupation number of the particle becomes
independent of its initial value. The value of ocupation number of the particle
is the physically expected one at the given temperature. So we have a Markovian
process, describing the particle thermalization with the environment. With
renormalized coordinates no renormalization procedure is required, leading
directly to a finite result.Comment: 16 pages, LATEX, 2 figure
Fuels characterization studies
Current analytical techniques used in the characterization of broadened properties fuels are briefly described. Included are liquid chromatography, gas chromatography, and nuclear magnetic resonance spectroscopy. High performance liquid chromatographic ground-type methods development is being approached from several directions, including aromatic fraction standards development and the elimination of standards through removal or partial removal of the alkene and aromatic fractions or through the use of whole fuel refractive index values. More sensitive methods for alkene determinations using an ultraviolet-visible detector are also being pursued. Some of the more successful gas chromatographic physical property determinations for petroleum derived fuels are the distillation curve (simulated distillation), heat of combustion, hydrogen content, API gravity, viscosity, flash point, and (to a lesser extent) freezing point
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