32,185 research outputs found
Gravitation interaction with extra dimension and periodic structure of the hadron scattering amplitude
The behavior of the hadron scattering amplitude determined by the gravitation
interaction of hadron at high energies with impact of the KK-modes in d-brane
models of gravity is examined. The possible periodic structure of the
scattering amplitude and its dependence on the number of additional dimensions
are analyzed. The effects of the gravitational hadron form factors obtained
from the hadron eneralized parton distributions (GPDs) on the behavior of the
interaction potential and the scattering amplitude are analyzed. It is shown
that in most part the periodic structure comes from the approximation of our
calculations.Comment: 9 pages, 8 figures, talk on the Intern. Workshop "Bogoliubov
Readings", Dubna (2010); updated reference
Approximate input physics for stellar modelling
We present a simple and efficient, yet reasonably accurate, equation of
state, which at the moderately low temperatures and high densities found in the
interiors of stars less massive than the Sun is substantially more accurate
than its predecessor by Eggleton, Faulkner & Flannery. Along with the most
recently available values in tabular form of opacities, neutrino loss rates,
and nuclear reaction rates for a selection of the most important reactions,
this provides a convenient package of input physics for stellar modelling. We
briefly discuss a few results obtained with the updated stellar evolution code.Comment: uuencoded compressed postscript. The preprint are also available at
http://www.ast.cam.ac.uk/preprint/PrePrint.htm
On computation of the first Baues--Wirsching cohomology of a freely-generated small category
The Baues--Wirsching cohomology is one of the cohomologies of a small
category. Our aim is to describe the first Baues--Wirsching cohomology of the
small category generated by a finite quiver freely. We consider the case where
the coefficient is a natural system obtained by the composition of a functor
and the target functor. We give an algorithm to obtain generators of the vector
space of inner derivations. It is known that there exists a surjection from the
vector space of derivations of the small category to the first Baues--Wirsching
cohomology whose kernel is the vector space of inner derivations.Comment: 11 page
Revised research about chaotic dynamics in Manko et al. spacetime
A recent work by Dubeibe et al. [Phys. Rev. D 75, 023008 (2007)] stated that
chaos phenomenon of test particles in gravitational field of rotating neutron
stars which are described by Manko, Sanabria-Gomez, and Manko (Manko et al.)
metric can only occur when the stars have oblate deformation. But the chaotic
motions they found are limited in a very narrow zone which is very close to the
center of the massive bodies. This paper argues that this is impossible because
the region is actually inside of the stars, so the motions cannot exist at this
place. In this paper, we scan all parameters space and find chaos and unstable
fixed points outside of stars with big mass-quadrupole moments. The
calculations show that chaos can only occur when the stars have prolate
deformation. Because real deformation of stars should be oblate, all orbits of
test particles around the rotating neutron stars described by Manko et al.
solutions are regular. The case of nonzero dipolar magnetic moment has also
been taken into account in this study.Comment: 6 pages, 5 figure
Hunger Incidence in the Philippines: Facts, Determinants and Challenges
The high level of hunger incidence in the country is perhaps one of the most pressing issues that need to be addressed by our policy makers. Official government statistics and data from self-rated hunger surveys show an increasing trend in hunger incidence among Filipino households. Data from National Statistical Coordination Board (NSCB) show that the percentage of subsistence poor in the country increased to 14.6 percent in 2006 from 13.5 percent in 2003. The Social Weather Stations (SWS) quarterly surveys on hunger incidence also show an increasing trend in the percentage of families that experienced hunger, reaching an alarming level of 24 percent in December 2009, representing about 4.4 million households. One probable cause of the increasing trend in hunger is the rising food prices akin to what the country experienced in 2008. This paper aims to determine the impact of food inflation and underemployment on hunger incidence in the Philippines, using the hunger incidence data from the SWS quarterly surveys on hunger. A vector autoregressive (VAR) model is used to determine the effect of a shock or increase to food inflation and underemployment on total involuntary hunger. Results from the model show that an increase in food prices at the current quarter will increase hunger incidence for a period of five quarters, starting with immediate quarter after the shock occurred. Shocks to underemployment will also increase hunger incidence but the effects last for only two quarters, also starting with immediate quarter after the shock. The results of this study provide relevant information that will be useful in crafting policies related to the Hunger Mitigation Program of the government.hunger; food inflation; underemployment; vector autoregressive models
Hunger Incidence in the Philippines: Facts, Determinants and Challenges
The high level of hunger incidence in the country is perhaps one of the most pressing issues that need to be addressed by our policy makers. Official government statistics and data from self-rated hunger surveys show an increasing trend in hunger incidence among Filipino households. Data from National Statistical Coordination Board (NSCB) show that the percentage of subsistence poor in the country increased to 14.6 percent in 2006 from 13.5 percent in 2003. The Social Weather Stations (SWS) quarterly surveys on hunger incidence also show an increasing trend in the percentage of families that experienced hunger, reaching an alarming level of 24 percent in December 2009, representing about 4.4 million households. One probable cause of the increasing trend in hunger is the rising food prices akin to what the country experienced in 2008. This paper aims to determine the impact of food inflation and underemployment on hunger incidence in the Philippines, using the hunger incidence data from the SWS quarterly surveys on hunger. A vector autoregressive (VAR) model is used to determine the effect of a shock or increase to food inflation and underemployment on total involuntary hunger. Results from the model show that an increase in food prices at the current quarter will increase hunger incidence for a period of five quarters, starting with immediate quarter after the shock occurred. Shocks to underemployment will also increase hunger incidence but the effects last for only two quarters, also starting with immediate quarter after the shock. The results of this study provide relevant information that will be useful in crafting policies related to the Hunger Mitigation Program of the government.Hunger, food inflation, underemployment, vector autoregressive models.
Very low mass white dwarfs with a C-O core
The lower limit for the mass of white dwarfs (WDs) with C-O core is commonly
assumed to be roughly 0.5 Msun. As a consequence, WDs of lower masses are
usually identified as He-core remnants. However, when the initial mass of the
progenitor star is in between 1.8 and 3 Msun, which corresponds to the so
called red giant (RGB) phase transition, the mass of the H-exhausted core at
the tip of the RGB is 0.3 < M_H/Msun < 0.5. Prompted by this well known result
of stellar evolution theory, we investigate the possibility to form C-O WDs
with mass M < 0.5 Msun. The pre-WD evolution of stars with initial mass of
about 2.3 Msun, undergoing anomalous mass-loss episodes during the RGB phase
and leading to the formation of WDs with He-rich or CO-rich cores have been
computed. The cooling sequences of the resulting WDs are also described. We
show that the minimum mass for a C-O WD is about 0.33 Msun, so that both He and
C-O core WDs can exist in the mass range 0.33-0.5 Msun. The models computed for
the present paper provide the theoretical tools to indentify the observational
counterpart of very low mass remnants with a C-O core among those commonly
ascribed to the He-core WD population in the progressively growing sample of
observed WDs of low mass. Moreover, we show that the central He-burning phase
of the stripped progeny of the 2.3 Msun star lasts longer and longer as the
total mass decreases. In particular, the M= 0.33 Msun model takes about 800 Myr
to exhausts its central helium, which is more than three time longer than the
value of the standard 2.3 Msun star: it is, by far, the longest core-He burning
lifetime. Finally, we find the occurrence of gravonuclear instabilities during
the He-burning shell phase.Comment: Accepted for publication in Astronomy and Astrophysics, 9 page
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