39,528 research outputs found
Hadron-quark mixed phase in hyperon stars
We analyze the different possibilities for the hadron-quark phase transition
occurring in beta-stable matter including hyperons in neutron stars. We use a
Brueckner-Hartree-Fock approach including hyperons for the hadronic equation of
state and a generalized MIT bag model for the quark part. We then point out in
detail the differences between Maxwell and Gibbs phase transition constructions
including the effects of surface tension and electromagnetic screening. We find
only a small influence on the maximum neutron star mass, whereas the radius of
the star and in particular its internal structure are more affected.Comment: 11 pages, 9 figure
Strangeness in Neutron Stars
It is generally agreed on that the tremendous densities reached in the
centers of neutron stars provide a high-pressure environment in which several
intriguing particles processes may compete with each other. These range from
the generation of hyperons to quark deconfinement to the formation of kaon
condensates and H-matter. There are theoretical suggestions of even more exotic
processes inside neutron stars, such as the formation of absolutely stable
strange quark matter. In the latter event, neutron stars would be largely
composed of strange quark matter possibly enveloped in a thin nuclear crust.
This paper gives a brief overview of these striking physical possibilities with
an emphasis on the role played by strangeness in neutron star matter, which
constitutes compressed baryonic matter at ultra-high baryon number density but
low temperature which is no accessible to relativistic heavy ion collision
experiments.Comment: 16 pages, 5 figures, 3 tables; Accepted for publication in the
Proceedings of the International Workshop on Astronomy and Relativistic
Astrophysics (IWARA) 2005, Int. J. Mod. Phys.
Post-mortem enamel surface texture alteration during taphonomic processes—do experimental approaches reflect natural phenomena?
Experimental approaches are often used to better understand the mechanisms behindand consequences of post-mortem alteration on proxies for diet reconstruction.Dental microwear texture analysis (DMTA) is such a dietary proxy, using dental wearfeatures in extant and extinct taxa to reconstruct feeding behaviour and mechanicalfood properties. In fossil specimens especially, DMTA can be biased by post-mortemalteration caused by mechanical or chemical alteration of the enamel surface. Herewe performed three different dental surface alteration experiments to assess the effectof common taphonomic processes by simplifying them: (1) tumbling in sedimentsuspension to simulate fluvial transport, (2) sandblasting to simulate mechanicalerosion due to aeolian sediment transport, (3) acid etching to simulate chemicaldissolution by stomach acid. For tumbling (1) we found alteration to be mainlydependent on sediment grain size fraction and that on specimens tumbled with sandfractions mainly post-mortem scratches formed on the dental surface, while specimenstumbled with a fine-gravel fraction showed post-mortem formed dales. Sandblasting(2) with loess caused only negligible alteration, however blasting with fine sand quartzparticles resulted in significant destruction of enamel surfaces and formation of largepost-mortem dales. Acid etching (3) using diluted hydrochloric acid solutions inconcentrations similar to that of predator stomachs led to a complete etching of thewhole dental surface, which did not resemble those of teeth recovered from owl pellets.The experiments resulted in post-mortem alteration comparable, but not identical tonaturally occurring post-mortem alteration features. Nevertheless, this study servesas a first assessment and step towards further, more refined taphonomic experimentsevaluating post-mortem alteration of dental microwear texture (DMT)
Elastic anomaly of heavy fermion systems in a crystalline field
An elastic anomaly, observed in the heavy fermi liquid state of Ce alloys
(for example, CeCu and CeTe), is analyzed by using the infinite-
Anderson lattice model. The four atomic energy levels are assumed for
f-electrons. Two of them are mutually degenerate. A small crystalline splitting
is assumed between two energy levels. The fourfold degenerate
conduction bands are also considered in the model. We solve the model using the
mean field approximation to slave bosons, changing the Fermi energy in order to
keep the total electron number constant. The nonzero value of the mean field of
the slave bosons persists over the temperatures much higher than the Kondo
temperature. This is the effect of the constant electron number. Next, the
linear susceptibility with respect to is calculated in order to obtain
the renomalized elastic constant. The resulting temperature dependence of the
constant shows the downward dip. We point out the relation of our finding with
the experimental data.Comment: submitted to J. Phys.: Condens. Matter, please request figure copies
to [email protected]
Characterization of nano-composite M-2411/Y-123 thin films by electron backscatter diffraction and in-field critical current measurements
Thin films of nano-composite Y-Ba-Cu-O (YBCO) superconductors containing nano-sized, non-superconducting particles of Y2Ba 4CuMOx (M-2411 with M = Ag and Nb) have been prepared by the PLD technique. Electron backscatter diffraction (EBSD) has been used to analyze the crystallographic orientation of nano-particles embedded in the film microstructure. The superconducting YBa2Cu3O7 (Y-123) phase matrix is textured with a dominant (001) orientation for all samples, whereas the M-2411 phase exhibits a random orientation. Angular critical current measurements at various temperature (T) and applied magnetic field (B) have been performed on thin films containing different concentration of the M-2411 second phase. An increase in critical current density J c at T < 77 K and B < 6 T is observed for samples with low concentration of the second phase (2 mol % M-2411). Films containing 5 mol % Ag-2411 exhibit lower Jc than pure Y-123 thin films at all fields and temperatures. Samples with 5 mol % Nb-2411 show higher Jc(B) than phase pure Y-123 thin films for T < 77 K
Savory Grazing System: A Research Update
Livestock performance, forage use and soil compaction were studied in Repeated Seasonal (RSG) and High Performance Short Duration Grazing (HPSDG) systems on mixed prairie in good to excellent condition in western South Dakota. In May 1981 and 1982, yearling ewes were allocated to six RSG and six HPSDG pastures and removed in October of each year. Stocking rates in both systems were periodically adjusted to result in 40 to 50% terminal use of shortgrasses. In both years, the stocking rates in HPSDG were approximately twice those in RSG. Livestock performance was the same in both systems. Forage use was more uniform and higher proportions of midgrasses were grazed in HPSDG than in RSG. Soil compaction increased with grazing intensity in RSG but was constant at a value equivalent to moderate grazing intensity in HPSDG
Correlations and fluctuations studied with ALICE
The measurement of particle correlations and event-by-event fluctuations of
physical observables allows to study a large variety of properties of the
matter produced in ultra relativistic heavy-ion collisions. We will present
results for two-particle correlations, mean transverse momentum fluctuations,
and net charge fluctuations in Pb-Pb collisions at 2.76 TeV.Comment: 7 pages, 5 figures, Proceedings submitted for the 28th Winter
Workshop on Nuclear Dynamics, Puerto Rico, April 7-14, 2012; corrected typo
Isoscalar Giant Quadrupole Resonance State in the Relativistic Approach with the Momentum-Dependent Self-Energies
We study the excited energy of the isoscalar giant quadrupole resonance with
the scaling method in the relativistic many-body framework. In this calculation
we introduce the momentum-dependent parts of the Dirac self-energies arising
from the one-pion exchange on the assumption of the pseudo-vector coupling with
nucleon field. It is shown that this momentum-dependence enhances the Landau
mass significantly and thus suppresses the quadrupole resonance energy even
giving the small Dirac effective mass which causes a problem in the
momentum-independent mean-field theory.Comment: 12pages, 2 Postscript figure
- …