358 research outputs found
Advanced software techniques for space shuttle data management systems Final report
Airborne/spaceborn computer design and techniques for space shuttle data management system
Towards Landslide Predictions: Two Case Studies
In a previous work [Helmstetter, 2003], we have proposed a simple physical
model to explain the accelerating displacements preceding some catastrophic
landslides, based on a slider-block model with a state and velocity dependent
friction law. This model predicts two regimes of sliding, stable and unstable
leading to a critical finite-time singularity. This model was calibrated
quantitatively to the displacement and velocity data preceding two landslides,
Vaiont (Italian Alps) and La Clapi\`ere (French Alps), showing that the former
(resp. later) landslide is in the unstable (resp. stable) sliding regime. Here,
we test the predictive skills of the state-and-velocity-dependent model on
these two landslides, using a variety of techniques. For the Vaiont landslide,
our model provides good predictions of the critical time of failure up to 20
days before the collapse. Tests are also presented on the predictability of the
time of the change of regime for la Clapi\`ere landslide.Comment: 30 pages with 12 eps figure
Survival of branching random walks in random environment
We study survival of nearest-neighbour branching random walks in random
environment (BRWRE) on . A priori there are three different
regimes of survival: global survival, local survival, and strong local
survival. We show that local and strong local survival regimes coincide for
BRWRE and that they can be characterized with the spectral radius of the first
moment matrix of the process. These results are generalizations of the
classification of BRWRE in recurrent and transient regimes. Our main result is
a characterization of global survival that is given in terms of Lyapunov
exponents of an infinite product of i.i.d. random matrices.Comment: 17 pages; to appear in Journal of Theoretical Probabilit
The occupation of a box as a toy model for the seismic cycle of a fault
We illustrate how a simple statistical model can describe the quasiperiodic
occurrence of large earthquakes. The model idealizes the loading of elastic
energy in a seismic fault by the stochastic filling of a box. The emptying of
the box after it is full is analogous to the generation of a large earthquake
in which the fault relaxes after having been loaded to its failure threshold.
The duration of the filling process is analogous to the seismic cycle, the time
interval between two successive large earthquakes in a particular fault. The
simplicity of the model enables us to derive the statistical distribution of
its seismic cycle. We use this distribution to fit the series of earthquakes
with magnitude around 6 that occurred at the Parkfield segment of the San
Andreas fault in California. Using this fit, we estimate the probability of the
next large earthquake at Parkfield and devise a simple forecasting strategy.Comment: Final version of the published paper, with an erratum and an
unpublished appendix with some proof
On the Occurrence of Finite-Time-Singularities in Epidemic Models of Rupture, Earthquakes and Starquakes
We present a new kind of critical stochastic finite-time-singularity, relying
on the interplay between long-memory and extreme fluctuations. We illustrate it
on the well-established epidemic-type aftershock (ETAS) model for aftershocks,
based solely on the most solidly documented stylized facts of seismicity
(clustering in space and in time and power law Gutenberg-Richter distribution
of earthquake energies). This theory accounts for the main observations (power
law acceleration and discrete scale invariant structure) of critical rupture of
heterogeneous materials, of the largest sequence of starquakes ever attributed
to a neutron star as well as of earthquake sequences.Comment: Revtex document of 4 pages including 1 eps figur
A taxonomic, genetic and ecological data resource for the vascular plants of Britain and Ireland
The vascular flora of Britain and Ireland is among the most extensively studied in the world, but the current knowledge base is fragmentary, with taxonomic, ecological and genetic information scattered across different resources. Here we present the first comprehensive data repository of native and alien species optimized for fast and easy online access for ecological, evolutionary and conservation analyses. The inventory is based on the most recent reference flora of Britain and Ireland, with taxon names linked to unique Kew taxon identifiers and DNA barcode data. Our data resource for 3,227 species and 26 traits includes existing and unpublished genome sizes, chromosome numbers and life strategy and life-form assessments, along with existing data on functional traits, species distribution metrics, hybrid propensity, associated biomes, realized niche description, native status and geographic origin of alien species. This resource will facilitate both fundamental and applied research and enhance our understanding of the floraâs composition and temporal changes to inform conservation efforts in the face of ongoing climate change and biodiversity loss
Dragon-kings: mechanisms, statistical methods and empirical evidence
This introductory article presents the special Discussion and Debate volume
"From black swans to dragon-kings, is there life beyond power laws?" published
in Eur. Phys. J. Special Topics in May 2012. We summarize and put in
perspective the contributions into three main themes: (i) mechanisms for
dragon-kings, (ii) detection of dragon-kings and statistical tests and (iii)
empirical evidence in a large variety of natural and social systems. Overall,
we are pleased to witness significant advances both in the introduction and
clarification of underlying mechanisms and in the development of novel
efficient tests that demonstrate clear evidence for the presence of
dragon-kings in many systems. However, this positive view should be balanced by
the fact that this remains a very delicate and difficult field, if only due to
the scarcity of data as well as the extraordinary important implications with
respect to hazard assessment, risk control and predictability.Comment: 20 page
Escape Rates and Physically Relevant Measures for Billiards with Small Holes
We study the billiard map corresponding to a periodic Lorentz gas in
2-dimensions in the presence of small holes in the table. We allow holes in the
form of open sets away from the scatterers as well as segments on the
boundaries of the scatterers. For a large class of smooth initial
distributions, we establish the existence of a common escape rate and
normalized limiting distribution. This limiting distribution is conditionally
invariant and is the natural analogue of the SRB measure of a closed system.
Finally, we prove that as the size of the hole tends to zero, the limiting
distribution converges to the smooth invariant measure of the billiard map.Comment: 39 pages, 4 figure
Molecular Dynamics Studies of Dislocations in CdTe Crystals from a New Bond Order Potential
Cd1-xZnxTe (CZT) crystals are the leading semiconductors for radiation
detection, but their application is limited by the high cost of detector-grade
materials. High crystal costs primarily result from property non-uniformity
that causes low manufacturing yield. While tremendous efforts have been made in
the past to reduce Te inclusions / precipitates in CZT, this has not resulted
in an anticipated improvement in material property uniformity. Moreover, it is
recognized that in addition to Te particles, dislocation cells can also cause
electric field perturbation and the associated property non-uniformity. Further
improvement of the material, therefore, requires that dislocations in CZT
crystals be understood and controlled. Here we use a recently developed CZT
bond order potential to perform representative molecular dynamics simulations
to study configurations, energies, and mobilities of 29 different types of
possible dislocations in CdTe (i.e., x = 1) crystals. An efficient method to
derive activation free energies and activation volumes of thermally activated
dislocation motion will be explored. Our focus gives insight into understanding
important dislocations in the material, and gives guidance toward experimental
efforts for improving dislocation network structures in CZT crystals
Linking Grass Pollen Biodiversity and Human Health: an Environmental Genomic Approach
In Europe and the UK, grass pollen is the single most important outdoor aeroallergen; 27% of the population are sensitised to grass pollen. Grass pollen allergy has been linked to increased risk of allergic asthma exacerbations, which can lead to hospitalisation and fatalities. Sensitivity towards grass pollen varies between species, of which there are over 150 in the UK. However, due to few unique morphological features, grass pollen from different species cannot be discriminated using traditional observational methods. Currently, there is no way of detecting, modelling or forecasting the aerial-dispersion of pollen from the biodiversity of UK grasses. Consequently, grasses are coalesced into a single group in the UK forecast. PollerGEN is an interdisciplinary NERC project with the aim of revolutionising the way that pollen dispersion is measured and forecast, with concomitant synergies for understanding the ecology of aerial dispersed pollen. In collaboration with the UK Met Office, a key goal is to build a more accurate forecast of individual grass pollen species. Using environmental genomics, we will identify which species of grass pollen are present during the summer months across 16 specific collection sites in the UK, and measure the abundance of the different allergenic species of grass. The information will be used to model the spatial and temporal deposition of different species of grass pollen and identify linkages to human health. The project therefore aims to provide a paradigm shift in our understanding of the ecology of windborne pollen in time and space and inform the public about the timing and environmental factors that put them at risk of exposure to pollen they are allergic to; a key strategy in the prevention of allergy and asthma attacks
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