3,169 research outputs found
Core-crust transition pressure for relativistic slowly rotating neutron stars
We study the influence of core-\textit{crust} transition pressure changes on
the general dynamical properties of neutron star configurations. First we study
the matching conditions in core-\textit{crust} transition pressure region,
where phase transitions in the equation of state causes energy density jumps.
Then using a surface \textit{crust} approximation, we can construct
configurations where the matter is described by the equation of state of the
core of the star and the core-\textit{crust} transition pressure. We will
consider neutron stars in the slow rotation limit, considering perturbation
theory up to second order in the angular velocity so that the deformation of
the star is also taken into account. The junction determines the parameters of
the star such as total mass, angular and quadrupolar momentum.Comment: 4 pages, 1 figur
Chiral Lagrangian at finite temperature from the Polyakov-Chiral Quark Model
We analyze the consequences of the inclusion of the gluonic Polyakov loop in
chiral quark models at finite temperature. Specifically, the low-energy
effective chiral Lagrangian from two such quark models is computed. The tree
level vacuum energy density, quark condensate, pion decay constant and
Gasser-Leutwyler coefficients are found to acquire a temperature dependence.
This dependence is, however, exponentially small for temperatures below the
mass gap in the full unquenched calculation. The introduction of the Polyakov
loop and its quantum fluctuations is essential to achieve this result and also
the correct large counting for the thermal corrections. We find that new
coefficients are introduced at to account for the Lorentz
breaking at finite temperature. As a byproduct, we obtain the effective
Lagrangian which describes the coupling of the Polyakov loop to the Goldstone
bosons.Comment: 16 pages, no figure
Soliton structures in a molecular chain model with saturation
In the present work, we study, by means of a one-dimensional lattice model,
the collective excitations corresponding to intra molecular ones of a chain
like proteins. It is shown that such excitations are described by the Nonlinear
Schrodinger equation with saturation. The solutions obtained here are the bell
solitons, bubbles, kinks and crowdons. Since they belong to different sectors
on the parametric space, the bubble condensation could give place to some
important changes of face in this kind of nonlinear system. Additionally, it is
shown that the limiting velocity of the solitons is the velocity of sound waves
corresponding to longitudinal vibrations of molecules.Comment: 12 pages, 4 figure
Determination of combustion gas temperatures by infrared radiometry in sooting and nonsooting flames
Flame temperatures in nonsooting and sooting environments were successfully measured by radiometry for pre-mixed propane-oxygen laminar flames stabilized on a water-cooled, porous sintered-bronze burner. The measured temperatures in the nonsooting flames were compared with fine-wire thermocouple measurements. The results show excellent agreement below 1700 K, and when the thermocouple measurements were corrected for radiation effects, the agreement was good for even higher temperatures. The benefits of radiometry are: (1) the flow is not disturbed by an intruding probe, (2) calibration is easily done using a blackbody source, and (3) measurements can be made even with soot present. The theory involved in the radiometry measurements and the energy balance calculations used to correct the thermocouple temperature measurements are discussed
Born-Infeld Cosmologies
We present a model for an inhomogeneous and anisotropic early universe filled
with a nonlinear electromagnetic field of Born-Infeld (BI) type. The effects of
the BI field are compared with the linear case (Maxwell). Since the curvature
invaria nts are well behaved then we conjecture that our model does not present
an initial big bang singularity. The existence of the BI field modifies the
curvature invariants at t=0 as well as sets bounds on the amplitude of the
conformal metric functionComment: 13 pages, latex, 6 eps figure
Bounds on the mass and abundance of dark compact objects and black holes in dwarf spheroidal galaxy halos
We establish new dynamical constraints on the mass and abundance of compact
objects in the halo of dwarf spheroidal galaxies. In order to preserve
kinematically cold the second peak of the Ursa Minor dwarf spheroidal (UMi
dSph) against gravitational scattering, we place upper limits on the density of
compact objects as a function of their assumed mass. The mass of the dark
matter constituents cannot be larger than 1000 solar masses at a halo density
in UMi's core of 0.35 solar masses/pc^3. This constraint rules out a scenario
in which dark halo cores are formed by two-body relaxation processes. Our
bounds on the fraction of dark matter in compact objects with masses >3000
solar masses improve those based on dynamical arguments in the Galactic halo.
In particular, objects with masses solar masses can comprise no
more than a halo mass fraction . Better determinations of the
velocity dispersion of old overdense regions in dSphs may result in more
stringent constraints on the mass of halo objects. For illustration, if the
preliminary value of 0.5 km/s for the secondary peak of UMi is confirmed,
compact objects with masses above solar masses could be excluded
from comprising all its dark matter halo.Comment: 6 pages, 2 figures, accepted for publication in ApJ Letter
Fuel-rich catalytic combustion of Jet-A fuel-equivalence ratios 5.0 to 8.0
Fuel-rich catalytic combustion (E.R. greater than 5.0) is a unique technique for preheating a hydrocarbon fuel to temperatures much higher than those obtained by conventional heat exchangers. In addition to producing very reactive molecules, the process upgrades the structure of the fuel by the formation of hydrogen and smaller hydrocarbons and produces a cleaner burning fuel by removing some of the fuel carbon from the soot formation chain. With fuel-rich catalytic combustion as the first stage of a two stage combustion system, enhanced fuel properties can be utilized by both high speed engines, where time for ignition and complete combustion is limited, and engines where emission of thermal NO sub x is critical. Two-stage combustion (rich-lean) has been shown to be effective for NO sub x reduction in stationary burners where residence times are long enough to burn-up the soot formed in the first stage. Such residence times are not available in aircraft engines. Thus, the soot-free nature of the present process is critical for high speed engines. The successful application of fuel-rich catalytic combustion to Jet-A, a multicomponent fuel used in gas turbine combustors, is discusssed
El antropomorfismo como herramienta de divulgación científica por televisión: estudio de El Hombre y la Tierra
La tendencia del hombre al antropomorfismo resulta polémica al divulgar la ciencia, pero, ¿qué papel juega en su difusión? Los científicos intentan resolverlo desde mediados del s.XIX. A este interrogante se suma el de los profesionales de la comunicación, en particular, el de los documentalistas de la naturaleza que son quienes afrontan con frecuencia esta disyuntiva. Conocer qué opinan los académicos y realizadores permite ofrecer un posible acuerdo sobre la legitimidad del antropomorfismo para difundir la ciencia por televisión. Un convenio que se ejemplifica con el análisis de El Hombre y la Tierra: la serie documental de divulgación científica más exitosa en Españ
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