4,254 research outputs found
Nonequilibrium Thermodynamics of Wealth Condensation
We analyze wealth condensation for a wide class of stochastic economy models
on the basis of the economic analog of thermodynamic potentials, termed
transfer potentials. The economy model is based on three common transfers modes
of wealth: random transfer, profit proportional to wealth and motivation of
poor agents to work harder. The economies never reach steady state. Wealth
condensation is the result of stochastic tunneling through a metastable
transfer potential. In accordance with reality, both wealth and income
distribution transiently show Pareto tails for high income subjects. For
metastable transfer potentials, exponential wealth condensation is a robust
feature. For example with 10 % annual profit 1% of the population owns 50 % of
the wealth after 50 years. The time to reach such a strong wealth condensation
is a hyperbolic function of the annual profit rate.Comment: 8 pages, 8 figure
Wheat Yield Functions for Analysis of Land-Use Change in China
CERES-Wheat, a dynamic process crop growth model is specified and validated for eight sites in the major wheat-growing regions of China. Crop model results are then used to test functional forms for yield response to nitrogen fertilizer, irrigation water, temperature, and precipitation. The resulting functions are designed to be used in a linked biophysical-economic model of land-use and land-cover change. Variables explaining a significant proportion of simulated yield variance are nitrogen, irrigation water, and precipitation; temperature was not a significant component of yield variation within the range of observed year-to-year variability except at the warmest site. The Mitscherlich-Baule function is found to be more appropriate than the quadratic function at most sites. Crop model simulations with a generic soil with median characteristics of the eight sites were compared to simulations with site-specific soils, providing an initial test of the sensitivity of the functional forms to soil specification. The use of the generic soil does not affect the results significantly; thus, the functions may be considered representative of agriculturally productive regions with similar climate in China under intensifying management conditions
The CoRoT primary target HD 52265: models and seismic tests
HD 52265 is the only known exoplanet-host star selected as a main target for
the seismology programme of the CoRoT satellite. As such, it will be observed
continuously during five months, which is of particular interest in the
framework of planetary systems studies. This star was misclassified as a giant
in the Bright Star Catalog, while it is more probably on the main-sequence or
at the beginning of the subgiant branch. We performed an extensive analysis of
this star, showing how asteroseismology may lead to a precise determination of
its external parameters and internal structure. We first reviewed the
observational constraints on the metallicity, the gravity and the effective
temperature derived from the spectroscopic observations of HD 52265. We also
derived its luminosity using the Hipparcos parallax. We computed the
evolutionary tracks for models of various metallicities which cross the
relevant observational error boxes in the gravity-effective temperature plane.
We selected eight different stellar models which satisfy the observational
constraints, computed their p-modes frequencies and analysed specific seismic
tests. The possible models for HD 52265, which satisfy the constraints derived
from the spectroscopic observations, are different in both their external and
internal parameters. They lie either on the main sequence or at the beginning
of the subgiant branch. The differences in the models lead to quite different
properties of their oscillation frequencies. We give evidences of an
interesting specific behaviour of these frequencies in case of helium-rich
cores: the ``small separations'' may become negative and give constraints on
the size of the core. We expect that the observations of this star by the CoRoT
satellite wi ll allow choosing between these possible models.Comment: 11 pages, 7 figures, to be published in Astronomy and Astrophysic
Climate Change and World Food Security: A New Assessment
Building on previous work, quantitative estimates of climate change impacts on global food production have been made for the UK Hadley Centre's HadCM2 greenhouse gas only ensemble experiment and the more recent HadCM3 experiment (Hume et al., 1999). The consequences for world food prices and the number of people at risk of hunger as defined by the Food and Agriculture Organization (FAO, 1998) have also been assessed. Climate change is expected to increase yields at high and mid-latitudes, and lead to decreases at lower latitudes. This pattern becomes more pronounced as time progresses. The food system may be expected to accommodate such regional variations at the global level, with production, prices and the risk of hunger being relatively unaffected by the additional stress of climate change. By the 2080s the additional number of people at risk of hunger due to climate change is about 80 million (+/- 10 million depending on which of the four HadCM2 ensemble members are selected). However, some regions (particularly the arid and sub-humid tropics) will be adversely affected. A particular example is Africa, which is expected to experience marked reduction in yield, decreases in production, and increases in the risk of hunger as a result of climate change. The continent can expect to have between 55 and 65 million extra people at risk of hunger by the 2080s under the HadCM2 climate scenario. Under the HadCM3 climate scenario, the effect is even more severe, producing an estimated additional 70+ million people at risk of hunger in Africa
Pre-conceptual Design Assessment of DEMO Remote Maintenance
EDFA, as part of the Power Plant Physics and Technology programme, has been
working on the pre-conceptual design of a Demonstration Power Plant (DEMO). As
part of this programme, a review of the remote maintenance strategy considered
maintenance solutions compatible with expected environmental conditions, whilst
showing potential for meeting the plant availability targets. A key finding was
that, for practical purposes, the expected radiation levels prohibit the use of
complex remote handling operations to replace the first wall. In 2012/13, these
remote maintenance activities were further extended, providing an insight into
the requirements, constraints and challenges. In particular, the assessment of
blanket and divertor maintenance, in light of the expected radiation conditions
and availability, has elaborated the need for a very different approach from
that of ITER. This activity has produced some very informative virtual reality
simulations of the blanket segments and pipe removal that are exceptionally
valuable in communicating the complexity and scale of the required operations.
Through these simulations, estimates of the maintenance task durations have
been possible demonstrating that a full replacement of the blankets within 6
months could be achieved. The design of the first wall, including the need to
use sacrificial limiters must still be investigated. In support of the
maintenance operations, a first indication of the requirements of an Active
Maintenance Facility (AMF) has been elaborated.Comment: 6 pages, 5 figure
Agroclimatic conditions in Europe under climate change
o date, projections of European crop yields under climate change have been based almost entirely on the outputs of crop-growth models. While this strategy can provide good estimates of the effects of climatic factors, soil conditions and management on crop yield, these models usually do not capture all of the important aspects related to crop management, or the relevant environmental factors. Moreover, crop-simulation studies often have severe limitations with respect to the number of crops covered or the spatial extent. The present study, based on agroclimatic indices, provides a general picture of agroclimatic conditions in western and central Europe (study area lays between 8.5°W–27°E and 37–63.5°N), which allows for a more general assessment of climate-change impacts. The results obtained from the analysis of data from 86 different sites were clustered according to an environmental stratification of Europe. The analysis was carried for the baseline (1971–2000) and future climate conditions (time horizons of 2030, 2050 and with a global temperature increase of 5 °C) based on outputs of three global circulation models. For many environmental zones, there were clear signs of deteriorating agroclimatic condition in terms of increased drought stress and shortening of the active growing season, which in some regions become increasingly squeezed between a cold winter and a hot summer. For most zones the projections show a marked need for adaptive measures to either increase soil water availability or drought resistance of crops. This study concludes that rainfed agriculture is likely to face more climate-related risks, although the analyzed agroclimatic indicators will probably remain at a level that should permit rainfed production. However, results suggests that there is a risk of increasing number of extremely unfavorable years in many climate zones, which might result in higher interannual yield variability and constitute a challenge for proper crop management
Synthetic prions generated in vitro are similar to a newly identified subpopulation of PrPSc from sporadic Creutzfeldt-Jakob disease
In recent studies, the amyloid form of recombinant prion protein (PrP) encompassing residues 89–230 (rPrP 89-230) produced in vitro induced transmissible prion disease in mice. These studies showed that unlike “classical” PrPSc produced in vivo, the amyloid fibrils generated in vitro were more proteinase-K sensitive. Here we demonstrate that the amyloid form contains a proteinase K-resistant core composed only of residues 152/153–230 and 162–230. The PK-resistant fragments of the amyloid form are similar to those observed upon PK digestion of a minor subpopulation of PrPSc recently identified in patients with sporadic Creutzfeldt-Jakob disease (CJD). Remarkably, this core is sufficient for self-propagating activity in vitro and preserves a β-sheet-rich fibrillar structure. Full-length recombinant PrP 23-230, however, generates two subpopulations of amyloid in vitro: One is similar to the minor subpopulation of PrPSc, and the other to classical PrPSc. Since no cellular factors or templates were used for generation of the amyloid fibrils in vitro, we speculate that formation of the subpopulation of PrPSc with a short PK-resistant C-terminal region reflects an intrinsic property of PrP rather than the influence of cellular environments and/or cofactors. Our work significantly increases our understanding of the biochemical nature of prion infectious agents and provides a fundamental insight into the mechanisms of prions biogenesis
Precise Modeling of the Exoplanet Host Star and CoRoT Main Target HD 52265
This paper presents a detailed and precise study of the characteristics of
the Exoplanet Host Star and CoRoT main target HD 52265, as derived from
asteroseismic studies. The results are compared with previous estimates, with a
comprehensive summary and discussion. The basic method is similar to that
previously used by the Toulouse group for solar-type stars. Models are computed
with various initial chemical compositions and the computed p-mode frequencies
are compared with the observed ones. All models include atomic diffusion and
the importance of radiative accelerations is discussed. Several tests are used,
including the usual frequency combinations and the fits of the \'echelle
diagrams. The possible surface effects are introduced and discussed. Automatic
codes are also used to find the best model for this star (SEEK, AMP) and their
results are compared with that obtained with the detailed method. We find
precise results for the mass, radius and age of this star, as well as its
effective temperature and luminosity. We also give an estimate of the initial
helium abundance. These results are important for the characterization of the
star-planet system.Comment: 9 pages, 6 figures, 7 tables, to be published in Astronomy and
Astrophysic
Covariant Momentum Map Thermodynamics for Parametrized Field Theories
Inspired by Souriau's symplectic generalization of the Maxwell-Boltzmann-Gibbs equilibrium in Lie group thermodynamics, we investigate a spacetime-covariant formalism for statistical mechanics and thermodynamics in the multi-symplectic framework for relativistic field theories. A general-covariant Gibbs state is derived, via a maximal entropy principle approach, in terms of the covariant momentum map associated with the lifted action of the diffeomorphisms group on the extended phase space of the fields. Such an equilibrium distribution induces a canonical spacetime foliation, with a Lie algebra-valued generalized notion of temperature associated to the covariant choice of a reference frame, and it describes a system of fields allowed to have non-vanishing probabilities of occupying states different from the diffeomorphism invariant configuration. We focus on the case of parametrized first-order field theories, as a concrete simplified model for fully constrained field theories sharing fundamental general covariant features with canonical general relativity. In this setting, we investigate how physical equilibrium, hence time evolution, emerge from such a state via a gauge-fixing of the diffeomorphism symmetry
New seismic analysis of the exoplanet-host star Mu Arae
We present detailed modelling of the exoplanet-host star Mu Arae, using a new
method for the asteroseismic analysis, and taking into account the new value
recently derived for the Hipparcos parallax. The aim is to obtain precise
parameters for this star and its internal structure, including constraints on
the core overshooting. We computed new stellar models in a wider range than
Bazot et al. (2005), with various chemical compositions ([Fe/H] and Y), with or
without overshooting at the edge of the core. We computed their adiabatic
oscillation frequencies and compared them to the seismic observations. For each
set of chemical parameters, we kept the model which represented the best fit to
the echelle diagram. Then, by comparing the effective temperatures, gravities
and luminosities of these models with the spectroscopic error boxes, we were
able to derive precise parameters for this star. First we find that all the
models which correctly fit the echelle diagram have the same mass and radius,
with an uncertainty of the order of one percent. Second, the final comparison
with spectroscopic observations leads to the conclusion that besides its high
metallicity, Mu Arae has a high helium abundance of the order of Y=0.3. Knowing
this allows finding precise values for all the other parameters, mass, radius
and age.Comment: Accepted for publication in A&
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