16,702 research outputs found
Study of the K+K- Interaction at COSY-11
In this article we present studies of the near threshold pp-->ppK+K- reaction
in view of the K+K- final state interaction. The investigations include
analysis of both the low-energy K+K- invariant mass distributions measured by
COSY-11 collaboration at excess energies of Q = 10 MeV and Q = 28 MeV and the
near threshold excitation function for the pp-->ppK+K- reaction. As a result of
these studies we have estimated the K+K- scattering length more precise
compared to the previous analysis based only on the analysis of the
differential cross sections.Comment: Proceedings from the MESON2010 conference ,3 pages, 3 figure
Electron spin resonance shifts in S=1 antiferromagnetic chains
We discuss electron spin resonance (ESR) shifts in spin-1 Heisenberg
antiferromagnetic chains with a weak single-ion anisotropy based on several
effective field theories, the O(3) nonlinear sigma model (NLSM) in the Haldane
phase, free fermion theories around the lower and the upper critical fields. In
the O(3) NLSM, the single-ion anisotropy corresponds to a composite operator
which creates two magnons at the same time and position. Therefore, even inside
a parameter range where free magnon approximation is valid, we have to take
interactions among magnons into account. Though the O(3) NLSM is only valid in
the Haldane phase, an appropriate translation of Faddeev-Zamolodchikov
operators of the O(3) NLSM to fermion operators enables one to treat ESR shifts
near the lower critical field in a similar manner to discussions in Haldane
phase. We present that our theory gives quantitative agreements with recent ESR
experimental results on an spin-1 chain compounds NDMAP
Relativistic stars in f(R) gravity, and absence thereof
Several f(R) modified gravity models have been proposed which realize the
correct cosmological evolution and satisfy solar system and laboratory tests.
Although nonrelativistic stellar configurations can be constructed, we argue
that relativistic stars cannot be present in such f(R) theories. This problem
appears due to the dynamics of the effective scalar degree of freedom in the
strong gravity regime. Our claim thus raises doubts on the viability of f(R)
models.Comment: 9 pages, 7 figures, v2: references added, minor corrections, version
accepted for publication in PR
Measurement of the Kerr Spin Parameter by Observation of a Compact Object's Shadow
A black hole casts a shadow as an optical appearance because of its strong
gravitational field. We study how to determine the spin parameter and the
inclination angle by observing the apparent shape of the shadow, which is
distorted mainly by those two parameters. Defining some observables
characterizing the apparent shape (its radius and distortion parameter), we
find that the spin parameter and inclination angle of a Kerr black hole can be
determined by the observation. This technique is also extended to the case of a
Kerr naked singularity.Comment: 9 pages, 11 figures; v2: references added, typos corrected; v3:
accepted for publication in Physical Review
Humidity effects on adhesion of nickel-zinc ferrite in elastic contact with magnetic tape and itself
The effects of humidity on the adhesion of Ni-Zn ferrite and magnetic tape in elastic contact with a Ni-Zn ferrite hemispherical pin in moist nitrogen were studied. Adhesion was independent of normal load in dry, humid, and saturated nitrogen. Ferrites adhere to ferrites in a saturated atmosphere primarily from the surface tension effects of a thin film of water adsorbed on the ferrite surfaces. The surface tension of the water film calculated from the adhesion results was 48 times 0.00001 to 56 times 0.00001 N/cm; the accepted value for water is 72.7 x 0.00001 N/cm. The adhesion of ferrite-ferrite contacts increased gradually with increases in relative humidity to 80 percent, but rose rapidly above 80 percent. The adhesion at saturation was 30 times or more greater than that below 80 percent relative humidity. Although the adhesion of magnetic tape - ferrite contacts remained low below 40 percent relative humidity and the effect of humidity was small, the adhesion increased considerably with increasing relative humidity above 40 percent. The changes in adhesion of elastic contacts were reversible on humidifying and dehumidifying
The Progenitor of the Type IIb SN 2008ax Revisited
Hubble Space Telescope observations of the site of the supernova (SN) 2008ax
obtained in 2011 and 2013 reveal that the possible progenitor object detected
in pre-explosion images was in fact multiple. Four point sources are resolved
in the new, higher-resolution images. We identify one of the sources with the
fading SN. The other three objects are consistent with single supergiant stars.
We conclude that their light contaminated the previously identified progenitor
candidate. After subtraction of these stars, the progenitor appears to be
significantly fainter and bluer than previously measured. Post-explosion
photometry at the SN location indicates that the progenitor object has
disappeared. If single, the progenitor is compatible with a supergiant star of
B to mid-A spectral type, while a Wolf-Rayet (WR) star would be too luminous in
the ultraviolet to account for the observations. Moreover, our hydrodynamical
modelling shows the pre-explosion mass was and the radius was
, which is incompatible with a WR progenitor. We present a
possible interacting binary progenitor computed with our evolutionary models
that reproduces all the observational evidence. A companion star as luminous as
an O9-B0 main-sequence star may have remained after the explosion.Comment: ApJ accepted, 14 pages, 7 figure
MFC: An open-source high-order multi-component, multi-phase, and multi-scale compressible flow solver
MFC is an open-source tool for solving multi-component, multi-phase, and bubbly compressible flows. It is capable of efficiently solving a wide range of flows, including droplet atomization, shock–bubble interaction, and bubble dynamics. We present the 5- and 6-equation thermodynamically-consistent diffuse-interface models we use to handle such flows, which are coupled to high-order interface-capturing methods, HLL-type Riemann solvers, and TVD time-integration schemes that are capable of simulating unsteady flows with strong shocks. The numerical methods are implemented in a flexible, modular framework that is amenable to future development. The methods we employ are validated via comparisons to experimental results for shock–bubble, shock–droplet, and shock–water-cylinder interaction problems and verified to be free of spurious oscillations for material-interface advection and gas–liquid Riemann problems. For smooth solutions, such as the advection of an isentropic vortex, the methods are verified to be high-order accurate. Illustrative examples involving shock–bubble-vessel-wall and acoustic–bubble-net interactions are used to demonstrate the full capabilities of MFC
Nucleosynthesis in Two-Dimensional Delayed Detonation Models of Type Ia Supernova Explosions
The nucleosynthetic characteristics of various explosion mechanisms of Type
Ia supernovae (SNe Ia) is explored based on three two-dimensional explosion
simulations representing extreme cases: a pure turbulent deflagration, a
delayed detonation following an approximately spherical ignition of the initial
deflagration, and a delayed detonation arising from a highly asymmetric
deflagration ignition. Apart from this initial condition, the deflagration
stage is treated in a parameter-free approach. The detonation is initiated when
the turbulent burning enters the distributed burning regime. This occurs at
densities around g cm -- relatively low as compared to existing
nucleosynthesis studies for one-dimensional spherically symmetric models. The
burning in these multidimensional models is different from that in
one-dimensional simulations as the detonation wave propagates both into
unburned material in the high density region near the center of a white dwarf
and into the low density region near the surface. Thus, the resulting yield is
a mixture of different explosive burning products, from carbon-burning products
at low densities to complete silicon-burning products at the highest densities,
as well as electron-capture products synthesized at the deflagration stage. In
contrast to the deflagration model, the delayed detonations produce a
characteristic layered structure and the yields largely satisfy constraints
from Galactic chemical evolution. In the asymmetric delayed detonation model,
the region filled with electron capture species (e.g., Ni, Fe) is
within a shell, showing a large off-set, above the bulk of Ni
distribution, while species produced by the detonation are distributed more
spherically (abridged).Comment: Accepted by the Astrophysical Journal. 15 pages, 14 figures, 4 table
Accelerating Universes in String Theory via Field Redefinition
We study cosmological solutions in the effective heterotic string theory with
-correction terms in string frame. It is pointed out that the
effective theory has an ambiguity via field redefinition and we analyze
generalized effective theories due to this ambiguity. We restrict our analysis
to the effective theories which give equations of motion of second order in the
derivatives, just as "Galileon" field theory. This class of effective actions
contains two free coupling constants. We find de Sitter solutions as well as
the power-law expanding universes in our four-dimensional Einstein frame. The
accelerated expanding universes are always the attractors in the present
dynamical system.Comment: 22 pages, 3 figures, some additional formulae adde
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