4,579 research outputs found
Metrics and spectral triples for Dirichlet and resistance forms
The article deals with intrinsic metrics, Dirac operators and spectral
triples induced by regular Dirichlet and resistance forms. We show, in
particular, that if a local resistance form is given and the space is compact
in resistance metric, then the intrinsic metric yields a geodesic space. Given
a regular Dirichlet form, we consider Dirac operators within the framework of
differential 1-forms proposed by Cipriani and Sauvageot, and comment on its
spectral properties. If the Dirichlet form admits a carr\'e operator and the
generator has discrete spectrum, then we can construct a related spectral
triple, and in the compact and strongly local case the associated Connes
distance coincides with the intrinsic metric. We finally give a description of
the intrinsic metric in terms of vector fields
rcss: R package for optimal convex stochastic switching
© 2018 The R Journal. The R package rcss provides users with a tool to approximate the value functions in the Bellman recursion under certain assumptions that guarantee desirable convergence properties. This R package represents the first software implementation of these methods using matrices and nearest neighbors. This package also employs a pathwise dynamic method to gauge the quality of these value function approximations. Statistical analysis can be performed on the results to obtain other useful practical insights. This paper describes rcss version 1.6
Which Radial Velocity Exoplanets Have Undetected Outer Companions?
(Abridged) The observed radial velocity (RV) eccentricity distribution for
extrasolar planets in single-planet systems shows that a significant fraction
of planets are eccentric (). Here we investigate the effects on an RV
planet's eccentricity produced by undetected outer companions. We have carried
out Monte Carlo simulations of mock RV data to understand this effect and
predict its impact on the observed distribution. We first quantify the
statistical effect of undetected outer companions and show that this alone
cannot explain the observed distribution. We then modify the simulations to
consist of two populations, one of zero-eccentricity planets in double-planet
systems and the other of single planets drawn from an eccentric distribution.
Our simulations show that a good fit to the observed distribution is obtained
with 45% zero-eccentricity double-planets and 55% single eccentric planets.
Matching the observed distribution allows us to determine the probability that
a known RV planet's orbital eccentricity has been biased by an undetected
wide-separation companion. Our simulations show that moderately-eccentric
planets, with and , have a and probability, respectively, of having an undetected outer companion. We
encourage both high-contrast direct imaging and RV follow-up surveys of known
RV planets with moderate eccentricities to test our predictions and look for
previously undetected outer companions.Comment: 23 pages (12 text, 2 tables, 9 figures). Accepted to the
Astrophysical Journal 30 June 200
Algorithms for optimal control of stochastic switching systems
© 2016 Society for Industrial and Applied Mathematics. Optimal control problems of switching type with linear state dynamics are ubiquitous in applications of stochastic optimization. For high-dimensional problems of this type, solutions which utilize some convexity related properties are useful. For such problems, we present novel algorithmic solutions which require minimal assumptions while demonstrating remarkable computational efficiency. Furthermore, we devise procedures of the primal-dual kind to assess the distance to optimality of these approximate solutions
Lessons learned: rearing the crown-boring weevil, Ceutorhynchus scrobicollis (Coleoptera: Curculionidae), in containment for biological control of garlic mustard (Alliaria petiolata)
In this paper, we describe lessons learned and protocols developed after a decade of rearing Ceutorhynchus scrobicollis Nerenscheimer and Wagner in a Biosafety Level 2 containment facility. We have developed these protocols in anticipation of approval to release C. scrobicollis in North America for the biocontrol of garlic mustard. The rearing protocol tried to minimize the potential of attack by the adult parasitoid, Perilitus conseutor, which may be present in field collected C. scrobicollis from Europe to prevent inadvertent introduction of parasitoids into North America.
All C. scrobicollis used for our quarantine rearing were field collected near Berlin, Germany. We have successfully reared C. scrobicollis on caged garlic mustard plants in a growth chamber by alternating temperatures and photoperiods to simulate those in its native range. In Germany, C. scrobicollis produces one generation per year and F1 adults emerge in late May. In containment, a new generation of adults emerged an average of 108 days after adults were placed on plants. We found the optimal time spent to collect F1 adults was four weeks after the appearance of the first F1 adult, with 95% of potential adults collected. Simulating a three-month summer aestivation period, followed by a week of fall, and three weeks of winter conditions resulted in optimum levels of oviposition in F1 females. Larvae first hatched 8- to-10 days after adults were placed on plants at 15/14 C day/night temperatures with a 9.5 hour photoperiod. We therefore recommend that C. scrobicollis adults are removed from garlic mustard rosettes after 8 days. This will maximize the period of female oviposition while minimizing the time when larvae are available for attack from P. conseutor
From non-symmetric particle systems to non-linear PDEs on fractals
We present new results and challenges in obtaining hydrodynamic limits for
non-symmetric (weakly asymmetric) particle systems (exclusion processes on
pre-fractal graphs) converging to a non-linear heat equation. We discuss a
joint density-current law of large numbers and a corresponding large deviations
principle.Comment: v2: 10 pages, 1 figure. To appear in the proceedings for the 2016
conference "Stochastic Partial Differential Equations & Related Fields" in
honor of Michael R\"ockner's 60th birthday, Bielefel
Sensitivity of point scale runoff predictions to rainfall resolution
International audienceThis paper investigates the effects of using non-linear, high resolution rainfall, compared to time averaged rainfall on the triggering of hydrologic thresholds and therefore model predictions of infiltration excess and saturation excess runoff. The bounded random cascade model, parameterized to south western Australian rainfall, was used to scale rainfall intensities at various time resolutions ranging from 1.875 min to 2 h. A one dimensional, conceptual rainfall partitioning model was used that instantaneously partitions water into infiltration excess, infiltration, storage, deep drainage, saturation excess and surface runoff, where the fluxes into and out of the soil store are controlled by thresholds. For example, saturation excess is triggered when the soil water content reaches the storage capacity threshold. The results of the numerical modelling were scaled by relating soil infiltration properties to soil draining properties, and inturn, relating these to average storm intensities. By relating maximum soil infiltration capacities to saturated drainage rates (f*), we were able to split soils into two groups; those where all runoff is a result of infiltration excess alone (f*?0.2) and those susceptible to both infiltration excess and saturation excess runoff (f*>0.2). For all soil types, we related maximum infiltration capacities to average storm intensities (k*) and were able to show where model predictions of infiltration excess were most sensitive to rainfall resolution (ln k=0.4) and where using time averaged rainfall data can lead to an under prediction of infiltration excess and an over prediction of the amount of water entering the soil (ln k*>2). For soils susceptible to both infiltration excess and saturation excess, total runoff sensitivity was scaled by relating saturated drainage rates to average storm intensities (g*) and parameter ranges where predicted runoff was dominated by infiltration excess or saturation excess depending on the resolution of rainfall data was determined (ln g*<2). Infiltration excess predicted from high resolution rainfall is short and intense, whereas saturation excess produced from low resolution rainfall is more constant and less intense. This has important implications for the accuracy of current hydrological models that use time averaged rainfall under these soil and rainfall conditions and predictions of further thresholds such as erosion. It offers insight into areas where the understanding of the dynamics of high resolution rainfall is required and a means by which we can improve our understanding of the way variations in rainfall intensities within a storm relate to hydrological thresholds and model predictions
Dynamical Masses in Luminous Infrared Galaxies
We have studied the dynamics and masses of a sample of ten nearby luminous
and ultraluminous infrared galaxies (LIRGS and ULIRGs), using 2.3 micron CO
absorption line spectroscopy and near-infrared H- and Ks-band imaging. By
combining velocity dispersions derived from the spectroscopy, disk
scale-lengths obtained from the imaging, and a set of likely model density
profiles, we calculate dynamical masses for each LIRG. For the majority of the
sample, it is difficult to reconcile our mass estimates with the large amounts
of gas derived from millimeter observations and from a standard conversion
between CO emission and H_2 mass. Our results imply that LIRGs do not have huge
amounts of molecular gas (10^10-10^11 Msolar) at their centers, and support
previous indications that the standard conversion of CO to H_2 probably
overestimates the gas masses and cannot be used in these environments. This in
turn suggests much more modest levels of extinction in the near-infrared for
LIRGs than previously predicted (A_V~10-20 versus A_V~100-1000). The lower gas
mass estimates indicated by our observations imply that the star formation
efficiency in these systems is very high and is triggered by cloud-cloud
collisions, shocks, and winds rather than by gravitational instabilities in
circumnuclear gas disks.Comment: 14 pages, 2 figures, accepted to Ap
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