1,165 research outputs found
Sigma models with singularities in Euclidean spacetime of dimension 0<=D<4 and in the limit N->infinity
For the case of the single-O()-vector linear sigma models the critical
behaviour following from any singularity in the action is worked out in
the double scaling limit , , . After an exact elimination of Gaussian degrees of freedom, the
critical objects such as coupling constants, indices and susceptibility matrix
are derived for all and spacetime dimensions . There appear
exceptional spacetime dimensions where the degree of the singularity
is more strongly constrained than by the renormalizability requirement.Comment: LaTeX, 25 pages, no figure
Double Scaling Limits, Airy Functions and Multicritical Behaviour in O(N) Vektor Sigma Models
O(N) vector sigma models possessing catastrophes in their action are studied.
Coupling the limit N --> infinity with an appropriate scaling behaviour of the
coupling constants, the partition function develops a singular factor. This is
a generalized Airy function in the case of spacetime dimension zero and the
partition function of a scalar field theory for positive spacetime dimension.Comment: 14 pages, LaTe
On the critical behaviour of hermitean f-matrix models in the double scaling limit with f >= 3
An algorithm for the isolation of any singularity of f-matrix models in the
double scaling limit is presented. In particular it is proved by construction
that only those universality classes exist that are known from 2-matrix models.Comment: 24 pages, LaTex, correction of some notation errors and addition of
four reference
Physics of rotation in stellar models
In these lecture notes, we present the equations presently used in stellar
interior models in order to compute the effects of axial rotation. We discuss
the hypotheses made. We suggest that the effects of rotation might play a key
role at low metallicity.Comment: 32 pages, 7 figures, lectures, CNRS school, will be published by
Springe
Grids of stellar models. VIII. From 0.4 to 1.0 Msun at Z=0.020 and Z=0.001, with the MHD equation of state
We present stellar evolutionary models covering the mass range from 0.4 to 1
Msun calculated for metallicities Z=0.020 and 0.001 with the MHD equation of
state (Hummer & Mihalas, 1988; Mihalas et al. 1988; D\"appen et al. 1988). A
parallel calculation using the OPAL (Rogers et al. 1996) equation of state has
been made to demonstrate the adequacy of the MHD equation of state in the range
of 1.0 to 0.8 Msun (the lower end of the OPAL tables). Below, down to 0.4 Msun,
we have justified the use of the MHD equation of state by theoretical arguments
and the findings of Chabrier & Baraffe (1997).
We use the radiative opacities by Iglesias & Rogers (1996), completed with
the atomic and molecular opacities by Alexander & Fergusson (1994). We follow
the evolution from the Hayashi fully convective configuration up to the red
giant tip for the most massive stars, and up to an age of 20 Gyr for the less
massive ones. We compare our solar-metallicity models with recent models
computed by other groups and with observations.
The present stellar models complete the set of grids computed with the same
up-to-date input physics by the Geneva group [Z=0.020 and 0.001, Schaller et
al. (1992), Bernasconi (1996), and Charbonnel et al. (1996); Z=0.008, Schaerer
et al. (1992); Z=0.004, Charbonnel et al. (1993); Z=0.040, Schaerer et al.
(1993); Z=0.10, Mowlavi et al. (1998); enhanced mass loss rate evolutionary
tracks, Meynet et al. (1994)].Comment: Accepted for publication in A&A Supplement Serie
The Continuous Series of Critical Points of the Two-Matrix Model at N -> infinity in the Double Scaling Limit
The critical points of the continuous series are characterized by two complex
numbers l_1,l_2 (Re(l_1,l_2)=3) which enters
the string susceptibility constant through gamma = -2/(n-1). The critical
potentials are analytic functions with a convergence radius depending on l_1 or
l_2. We use the orthogonal polynomial method and solve the Schwinger-Dyson
equations with a technique borrowed from conformal field theory.Comment: 24 pages, LaTe
Habitability of Super-Earth Planets around Main-Sequence Stars including Red Giant Branch Evolution: Models based on the Integrated System Approach
In a previous study published in Astrobiology, we focused on the evolution of
habitability of a 10 M_E super-Earth planet orbiting a star akin to the Sun.
This study was based on a concept of planetary habitability in accordance to
the integrated system approach that describes the photosynthetic biomass
production taking into account a variety of climatological, biogeochemical, and
geodynamical processes. In the present study, we pursue a significant
augmentation of our previous work by considering stars with zero-age main
sequence masses between 0.5 and 2.0 M_sun with special emphasis on models of
0.8, 0.9, 1.2 and 1.5 M_sun. Our models of habitability consider again
geodynamical processes during the main-sequence stage of these stars as well as
during their red giant branch evolution. Pertaining to the different types of
stars, we identify so-called photosynthesis-sustaining habitable zones (pHZ)
determined by the limits of biological productivity on the planetary surface.
We obtain various sets of solutions consistent with the principal possibility
of life. Considering that stars of relatively high masses depart from the
main-sequence much earlier than low-mass stars, it is found that the biospheric
life-span of super-Earth planets of stars with masses above approximately 1.5
M_sun is always limited by the increase in stellar luminosity. However, for
stars with masses below 0.9 M_sun, the life-span of super-Earths is solely
determined by the geodynamic time-scale. For central star masses between 0.9
and 1.5 M_sun, the possibility of life in the framework of our models depends
on the relative continental area of the super-Earth planet.Comment: 25 pages, 6 figures, 2 tables; submitted to: International Journal of
Astrobiolog
Mitigation and Adaptation Strategies – Organic Agriculture
This psoter presents information on the following
- The concept of organic farming in the context of climate change
- Carbon sequestration on organic farms
- Consequences of an area-wide conversion to organic agricultur
- …