2,116 research outputs found
Minimal model of self-replicating nanocells: a physically embodied information-free scenario
The building of minimal self-reproducing systems with a physical embodiment
(generically called protocells) is a great challenge, with implications for
both theory and applied sciences. Although the classical view of a living
protocell assumes that it includes information-carrying molecules as an
essential ingredient, a dividing cell-like structure can be built from a
metabolism-container coupled system, only. An example of such a system, modeled
with dissipative particle dynamics, is presented here. This article
demonstrates how a simple coupling between a precursor molecule and surfactant
molecules forming micelles can experience a growth-division cycle in a
predictable manner, and analyzes the influence of crucial parameters on this
replication cycle. Implications of these results for origins of cellular life
and living technology are outlined.Comment: 9 pages, 10 figure
Sylvia Plath : Une écriture embryonnaire
Le premier versant de cette étude propose une plongée dans l\u27univers bleu des poèmes de jeunesse de Sylvia Plath, l\u27un des plus grands poètes américain des années 60, pour s\u27achever sur la fulgurance ultime, imprégnée de rouge, d\u27Ariel. Le sujet en gestation se révèle indissociable de l\u27émergence du texte dans l\u27œuvre de ce poète qui est l\u27un des seuls à avoir obtenu le Prix Pulitzer à titre posthume. Maints mythes, rythmes et figures archaïques sont revues et déconstruits pour dire ce monde sous cloche, univers de recherche autant que de détresse.
No collective neutrino flavor conversions during the supernova accretion phase
The large neutrino fluxes emitted with a distinct flavor hierarchy from
core-collapse supernovae (SNe) during the post-bounce accretion phase, offer
the best opportunity to detect effects from neutrino flavor oscillations. We
perform a dedicated study of the SN neutrino flavor evolution during the
accretion phase, using results from recent neutrino radiation hydrodynamics
simulations. In contrast to what expected in the presence of only
neutrino-neutrino interactions, we find that the multi-angle effects associated
with the dense ordinary matter suppress collective oscillations. This is
related to the high matter densities during the accretion phase in
core-collapse SNe of massive iron-core progenitors. The matter suppression
implies that neutrino oscillations will start outside the neutrino transport
region and therefore will have a negligible impact on the neutrino heating and
the explosion dynamics. Furthermore, the possible detection of the next
galactic SN neutrino signal from the accretion phase, based on the usual
Mikheyev- Smirnov-Wolfenstein effect in the SN mantle and Earth matter effects,
can reveal the neutrino mass hierarchy in the case that the mixing angle
is not very small.Comment: (4 pages, 4 eps figures, v2 revised version. Discussion clarified.
Matches the version published on PRL
Stochastic theory of two-species cooperation
Cooperative interactions pervade the dynamics of a broad rage of many-body
systems, such as ecological communities, the organization of social structures,
and economic webs. In this work, we investigate the dynamics of a simple
population model that is driven by cooperative and symmetric interactions
between two species. We develop a mean-field and a stochastic description for
this cooperative two-species reaction scheme. For an isolated population, we
determine the probability to reach a state of fixation, where only one species
survives, as a function of the initial concentrations of the two species. We
also determine the time to reach the fixation state. When each species can
migrate into the population and replace a randomly selected individual, the
population reaches a steady state. We show that this steady-state distribution
undergoes a unimodal to trimodal transition as the migration rate is decreased
beyond a critical value. In this low-migration regime, the steady state is not
truly steady, but instead fluctuates strongly between near-fixation states of
the two species. The characteristic time scale of these fluctuations diverges
as .Comment: 12 pages, 6 figure
Analysis of matter suppression in collective neutrino oscillations during the supernova accretion phase
The usual description of self-induced neutrino flavor conversions in core
collapse supernovae (SNe) is based on the dominance of the neutrino density
n_nu over the net electron density n_e. However, this condition is not met
during the post-bounce accretion phase, when the dense matter in a SN is piled
up above the neutrinosphere. As recently pointed-out, a dominant matter term in
the anisotropic SN environment would dephase the flavor evolution for neutrinos
traveling on different trajectories, challenging the occurrence of the
collective behavior in the dense neutrino gas. Using the results from recent
long term simulations of core-collapse SN explosions, based on three flavor
Boltzmann neutrino transport in spherical symmetry, we find that both the
situations of complete matter suppression (when n_e >> n_nu) and matter-induced
decoherence (when n_e \gtrsim n_nu) of flavor conversions are realized during
the accretion phase. The matter suppression at high densities prevents any
possible impact of the neutrino oscillations on the neutrino heating and hence
on the dynamics of the explosion. Furthermore, it changes the interpretation of
the Earth matter effect on the SN neutrino signal during the accretion phase,
allowing the possibility of the neutrino mass hierarchy discrimination at not
too small values of the leptonic mixing angle \theta_{13} (i.e.
\sin^2{\theta}_{13} \gtrsim 10^{-3}).Comment: Revised version (15 pages, 13 eps figures) published on Physical
Review D. Discussion enlarged, references update
Genetic variability within French race and riding horse breeds from genealogical data and blood marker polymorphisms
An ensemble approach to assess hydrological models’ contribution to uncertainties in the analysis of climate change impact on water resources
Over the recent years, several research efforts investigated the impact of climate
change on water resources for different regions of the world. The projection of future
river flows is affected by different sources of uncertainty in the hydro-climatic modelling chain. One of the aims of the QBic3 5 project (Que´bec-Bavarian International Collaboration on Climate Change) is to assess the contribution to uncertainty of hydrological models by using an ensemble of hydrological models presenting a diversity of structural complexity (i.e. lumped, semi distributed and distributed models). The study investigates two humid, mid-latitude catchments with natural flow conditions; one located in
10 Southern Que´bec (Canada) and one in Southern Bavaria (Germany). Daily flow is simulated with four different hydrological models, forced by outputs from regional climate
models driven by a given number of GCMs’ members over a reference (1971–2000)
and a future (2041–2070) periods. The results show that the choice of the hydrological model does strongly affect the climate change response of selected hydrological indicators, especially those related to low flows. Indicators related to high flows seem less sensitive on the choice of the hydrological model. Therefore, the computationally less demanding models (usually simple, lumped and conceptual) give a significant level of trust for high and overall mean flows
On the need for bias correction in regional climate scenarios to assess climate change impacts on river runoff
In climate change impact research, the assessment of future river runoff as well as the catchment scale water balance is impeded by different sources of modeling uncertainty.
Some research has already been done in order to quantify the uncertainty of climate 5 projections originating from the climate models and the downscaling techniques as well as from the internal variability evaluated from climate model member ensembles.
Yet, the use of hydrological models adds another layer of incertitude. Within the QBic3
project (Qu´ebec-Bavaria International Collaboration on Climate Change) the relative
contributions to the overall uncertainty from the whole model chain (from global climate 10 models to water management models) are investigated using an ensemble of multiple climate and hydrological models.
Although there are many options to downscale global climate projections to the regional
scale, recent impact studies tend to use Regional Climate Models (RCMs). One reason for that is that the physical coherence between atmospheric and land-surface 15 variables is preserved. The coherence between temperature and precipitation is of particular interest in hydrology. However, the regional climate model outputs often are biased compared to the observed climatology of a given region. Therefore, biases in those outputs are often corrected to reproduce historic runoff conditions from hydrological models using them, even if those corrections alter the relationship between temperature and precipitation. So, as bias correction may affect the consistency between RCM output variables, the use of correction techniques and even the use of (biased) climate model data itself is sometimes disputed among scientists. For those reasons, the effect of bias correction on simulated runoff regimes and the relative change in selected runoff indicators is explored. If it affects the conclusion of climate change analysis in 25 hydrology, we should consider it as a source of uncertainty. If not, the application of bias correction methods is either unnecessary in hydro-climatic projections, or safe to use as it does not alter the change signal of river runoff. The results of the present paper highlight the analysis of daily runoff simulated with four different hydrological models in two natural-flow catchments, driven by different regional climate models for a reference and a future period. As expected, bias correction of climate model outputs is important for the reproduction of the runoff regime of the 5 past regardless of the hydrological model used. Then again, its impact on the relative change of flow indicators between reference and future period is weak for most indicators with the exception of the timing of the spring flood peak. Still, our results indicate that the impact of bias correction on runoff indicators increases with bias in the climate simulations
Hydrological responses of a watershed to historical land use evolution and future land use scenarios under climate change conditions
Watershed runoff is closely related to land use but this influence is difficult to quantify. This study focused on the Chaudière River watershed (Québec, Canada) and had two objectives: (i) to quantify the influence of historical agricultural land use evolution on watershed runoff; and (ii) to assess the effect of future land use evolution scenarios under climate change conditions (CC). To achieve this, we used the integrated modeling system GIBSI. Past land use evolution was constructed using satellite images that were integrated into GIBSI. The general trend was an increase of agricultural land in the 80's, a slight decrease in the beginning of the 90's and a steady state over the last ten years. Simulations showed strong correlations between land use evolution and water discharge at the watershed outlet. For the prospective approach, we first assessed the effect of CC and then defined two opposite land use evolution scenarios for the horizon 2025 based on two different trends: agriculture intensification and sustainable development. Simulations led to a wide range of results depending on the climatologic models and gas emission scenarios considered, varying from a decrease to an increase of annual and monthly water discharge. In this context, the two land use scenarios induced opposite effects on water discharge and low flow sequences, especially during the growing season. However, due to the large uncertainty linked to CC simulations, it is difficult to conclude that one land use scenario provides a better adaptation to CC than another. Nevertheless, this study shows that land use is a key factor that has to be taken into account when predicting potential future hydrological responses of a watershed
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