167 research outputs found
Remote profiling of lake ice using an S-band short pulse radar aboard an all-terrain vehicle
An airborne short-pulse radar system to measure ice thickness was designed. The system supported an effort to develop an all-weather Great Lakes Ice Information System to aid in extending the winter navigation season. Experimental studies into the accuracy and limitations of the system are described. A low power version was operated from an all-terrain vehicle on the Straits of Mackinac during March 1975. The vehicle allowed rapid surveying of large areas and eliminated the ambiguity in location between the radar system and the ground truth ice auger team. It was also possible to the effects of snow cover, surface melt water, pressure ridging, and ice type upon the accuracy of the system. Over 25 sites were explored which had ice thicknesses from 29 to 60 cm. The maximum radar overestimate was 9.8 percent, while the maximum underestimate was 6.6 percent. The average error of the 25 measurements was 0.1 percent
Measurement of lake ice thickness with a short-pulse radar system
Measurements of lake ice thickness were made during March 1975 at the Straits of Mackinac by using a short-pulse radar system aboard an all-terrain vehicle. These measurements were compared with ice thicknesses determined with an auger. Over 25 sites were explored which had ice thicknesses in the range 29 to 60 cm. The maximum difference between radar and auger measurements was less than 9.8 percent. The magnitude of the error was less than + or - 3.5 cm. The NASA operating short-pulse radar system used in monitoring lake ice thickness from an aircraft is also described
Quantum Field Theoretic Description of Matter in the Universe
Quantum field theory at finite temperature and density can be used for
describing the physics of relativistic plasmas. Such systems are frequently
encountered in astrophysical situations, such as the early Universe, Supernova
explosions, and the interior of neutron stars. After a brief introduction to
thermal field theory the usefulness of this approach in astrophysics will be
exemplified in three different cases. First the interaction of neutrinos within
a Supernova plasma will be discussed. Then the possible presence of quark
matter in a neutron star core and finally the interaction of light with the
Cosmic Microwave Background will be considered.Comment: 7 pages, 9 figures, to be published in the Proceedings of the ISSI
Workshop "Matter in the Universe" (Bern, March 19-23, 2001), misprints
correcte
Great Lakes all-weather ice information system
A system is described which utilizes an X-band Side-Looking-Airborne-Radar (SLAR) for determining type, location, and aerial distribution of the ice cover in the Great Lakes and an airborne, S-band, short pulse radar for obtaining ice thickness. The SLAR system is currently mounted aboard a U.S. Coast Guard C-130B aircraft. Digitized SLAR data are relayed in real-time via the NOAA-GOES-1 satellite in geosynchronous orbit to the U.S. Coast Guard Ice Center in Cleveland, Ohio. SLAR images along with hand-drawn interpretative ice charts for various winter shipping areas in the Great Lakes are broadcast to facsimile recorders aboard Great Lakes vessels. The operational aspects of this ice information system are being demonstrated by NASA, U.S. Coast Guard, and NOAA/National Weather Service. Results from the 1974-75 winter season demonstrated the ability of this system to provide all-weather ice information to shippers in a timely manner
Catastrophic rearrangement of a compact star due to the quark core formation
We study properties of compact stars with the deconfinement phase transition
in their interiors. The equation of state of cold baryon-rich matter is
constructed by combining a relativistic mean-field model for the hadronic phase
and the MIT Bag model for the deconfined phase. In a narrow parameter range two
sequences of compact stars (twin stars), which differ by the size of the quark
core, have been found. We demonstrate the possibility of a rapid transition
between the twin stars with the energy release of about ergs. This
transition should be accompanied by the prompt neutrino burst and the delayed
gamma-ray burst.Comment: Latex, 14 pages including five postscript figure
The hadron-quark phase transition in dense matter and neutron stars
We study the hadron-quark phase transition in the interior of neutron stars
(NS's). We calculate the equation of state (EOS) of hadronic matter using the
Brueckner-Bethe-Goldstone formalism with realistic two-body and three-body
forces, as well as a relativistic mean field model. For quark matter we employ
the MIT bag model constraining the bag constant by using the indications coming
from the recent experimental results obtained at the CERN SPS on the formation
of a quark-gluon plasma. We find necessary to introduce a density dependent bag
parameter, and the corresponding consistent thermodynamical formalism. We
calculate the structure of NS interiors with the EOS comprising both phases,
and we find that the NS maximum masses fall in a relatively narrow interval,
. The precise value of the
maximum mass turns out to be only weakly correlated with the value of the
energy density at the assumed transition point in nearly symmetric nuclear
matter.Comment: 25 pages, Revtex4, 16 figures included as postscrip
Hybrid stars with the color dielectric and the MIT bag models
We study the hadron-quark phase transition in the interior of neutron stars
(NS). For the hadronic sector, we use a microscopic equation of state (EOS)
involving nucleons and hyperons derived within the Brueckner-Bethe-Goldstone
many-body theory, with realistic two-body and three-body forces. For the
description of quark matter, we employ both the MIT bag model with a density
dependent bag constant, and the color dielectric model. We calculate the
structure of NS interiors with the EOS comprising both phases, and we find that
the NS maximum masses are never larger than 1.7 solar masses, no matter the
model chosen for describing the pure quark phase.Comment: 11 pages, 5 figures, submitted to Phys. Rev.
Complete relativistic equation of state for neutron stars
We construct the equation of state (EOS) in a wide density range for neutron
stars using the relativistic mean field theory. The properties of neutron star
matter with both uniform and non-uniform distributions are studied
consistently. The inclusion of hyperons considerably softens the EOS at high
densities. The Thomas-Fermi approximation is used to describe the non-uniform
matter, which is composed of a lattice of heavy nuclei. The phase transition
from uniform matter to non-uniform matter occurs around ,
and the free neutrons drip out of nuclei at about $2.4 \times 10^{-4}\
\rm{fm^{-3}}$. We apply the resulting EOS to investigate the neutron star
properties such as maximum mass and composition of neutron stars.Comment: 23 pages, REVTeX, 9 ps figures, to appear in Phys. Rev.
Lipidic cubic phase serial millisecond crystallography using synchrotron radiation.
Lipidic cubic phases (LCPs) have emerged as successful matrixes for the crystallization of membrane proteins.Moreover, the viscous LCP also provides a highly effective delivery medium for serial femtosecond crystallography (SFX) at X-ray free-electron lasers (XFELs). Here, the adaptation of this technology to perform serial millisecond crystallography (SMX) at more widely available synchrotron microfocus beamlines is described. Compared with conventional microcrystallography, LCP-SMX eliminates the need for difficult handling of individual crystals and allows for data collection at room temperature. The technology is demonstrated by solving a structure of the light-driven protonpump bacteriorhodopsin (bR) at a resolution of 2.4 A ° . The room-temperature structure of bR is very similar to previous cryogenic structures but shows small yet distinct differences in the retinal ligand and proton-transfer pathway
Phase transitions of hadronic to quark matter at finite T and \mu_B
The phase transition of hadronic to quark matter and the boundaries of the
mixed hadron-quark coexistence phase are studied within the two Equation of
State (EoS) model. The relativistic effective mean field approach with constant
and density dependent meson-nucleon couplings is used to describe hadronic
matter, and the MIT Bag model is adopted to describe quark matter. The
boundaries of the mixed phase for different Bag constants are obtained solving
the Gibbs equations.
We notice that the dependence on the Bag parameter of the critical
temperatures (at zero chemical potential) can be well reproduced by a fermion
ultrarelativistic quark gas model, without contribution from the hadron part.
At variance the critical chemical potentials (at zero temperature) are very
sensitive to the EoS of the hadron sector. Hence the study of the hadronic EoS
is much more relevant for the determination of the transition to the
quark-gluon-plasma at finite baryon density and low-T. Moreover in the low
temperature and finite chemical potential region no solutions of the Gibbs
conditions are existing for small Bag constant values, B < (135 MeV)^4. Isospin
effects in asymmetric matter appear relevant in the high chemical potential
regions at lower temperatures, of interest for the inner core properties of
neutron stars and for heavy ion collisions at intermediate energies.Comment: 24 pages and 16 figures (revtex4
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