27,802 research outputs found
The high-energy gamma-ray light curve of PSR B1259 -63
The high-energy gamma-ray light curve of the binary system PSR B1259 -63, is
computed using the approach that successfully predicted the spectrum at
periastron. The simultaneous INTEGRAL and H.E.S.S. spectra taken 16 days after
periastron currently permit both a model with dominant radiative losses, high
pulsar wind Lorentz factor and modest efficiency as well as one with dominant
adiabatic losses, a slower wind and higher efficiency. In this paper we shown
how the long-term light curve may help to lift this degeneracy.Comment: 4 pages, to appear in proceedings of: Astrophysical Sources of High
Energy Particles and Radiation, Torun (2005
Epidemics on random intersection graphs
In this paper we consider a model for the spread of a stochastic SIR
(Susceptible Infectious Recovered) epidemic on a network of
individuals described by a random intersection graph. Individuals belong to a
random number of cliques, each of random size, and infection can be transmitted
between two individuals if and only if there is a clique they both belong to.
Both the clique sizes and the number of cliques an individual belongs to follow
mixed Poisson distributions. An infinite-type branching process approximation
(with type being given by the length of an individual's infectious period) for
the early stages of an epidemic is developed and made fully rigorous by proving
an associated limit theorem as the population size tends to infinity. This
leads to a threshold parameter , so that in a large population an epidemic
with few initial infectives can give rise to a large outbreak if and only if
. A functional equation for the survival probability of the
approximating infinite-type branching process is determined; if , this
equation has no nonzero solution, while if , it is shown to have
precisely one nonzero solution. A law of large numbers for the size of such a
large outbreak is proved by exploiting a single-type branching process that
approximates the size of the susceptibility set of a typical individual.Comment: Published in at http://dx.doi.org/10.1214/13-AAP942 the Annals of
Applied Probability (http://www.imstat.org/aap/) by the Institute of
Mathematical Statistics (http://www.imstat.org
Preliminary Test of Prescribed Burning for Control of Maple Leaf Cutter (Lepidoptera: Incurvariidae)
Leaf litter burning in the spring resulted in 87.5% mortality of maple leaf cutter pupae, Paraclemensia acerifoliella (Fitch). No apparent damage was observed on sugar maple or beech trees within the burn area
Formulas establish audio range inductance in beryllium coils
Mathematical modeling is used to determine the effects of resistance and capacitance upon the audio-inductance range of beryllium hammer coils and beryllium nylon-potted coils
Equivalence of robust stabilization and robust performance via feedback
One approach to robust control for linear plants with structured uncertainty
as well as for linear parameter-varying (LPV) plants (where the controller has
on-line access to the varying plant parameters) is through
linear-fractional-transformation (LFT) models. Control issues to be addressed
by controller design in this formalism include robust stability and robust
performance. Here robust performance is defined as the achievement of a uniform
specified -gain tolerance for a disturbance-to-error map combined with
robust stability. By setting the disturbance and error channels equal to zero,
it is clear that any criterion for robust performance also produces a criterion
for robust stability. Counter-intuitively, as a consequence of the so-called
Main Loop Theorem, application of a result on robust stability to a feedback
configuration with an artificial full-block uncertainty operator added in
feedback connection between the error and disturbance signals produces a result
on robust performance. The main result here is that this
performance-to-stabilization reduction principle must be handled with care for
the case of dynamic feedback compensation: casual application of this principle
leads to the solution of a physically uninteresting problem, where the
controller is assumed to have access to the states in the artificially-added
feedback loop. Application of the principle using a known more refined
dynamic-control robust stability criterion, where the user is allowed to
specify controller partial-state dimensions, leads to correct
robust-performance results. These latter results involve rank conditions in
addition to Linear Matrix Inequality (LMI) conditions.Comment: 20 page
Household epidemic models with varying infection response
This paper is concerned with SIR (susceptible--infected--removed) household epidemic models in which the infection response may be either mild or severe, with the type of response also affecting the infectiousness of an individual. Two different models are analysed. In the first model, the infection status of an individual is predetermined, perhaps due to partial immunity, and in the second, the infection status of an individual depends on the infection status of its infector and on whether the individual was infected by a within- or between-household contact. The first scenario may be modelled using a multitype household epidemic model, and the second scenario by a model we denote by the infector-dependent-severity household epidemic model. Large population results of the two models are derived, with the focus being on the distribution of the total numbers of mild and severe cases in a typical household, of any given size, in the event that the epidemic becomes established. The aim of the paper is to investigate whether it is possible to determine which of the two underlying explanations is causing the varying response when given final size household outbreak data containing mild and severe cases. We conduct numerical studies which show that, given data on sufficiently many households, it is generally possible to discriminate between the two models by comparing the Kullback-Leibler divergence for the two fitted models to these data
Repeated injection of atrial natriuretic peptide (a-hANP) in normal man: cardiovascular and renal actions
Incompatible sets of gradients and metastability
We give a mathematical analysis of a concept of metastability induced by
incompatibility. The physical setting is a single parent phase, just about to
undergo transformation to a product phase of lower energy density. Under
certain conditions of incompatibility of the energy wells of this energy
density, we show that the parent phase is metastable in a strong sense, namely
it is a local minimizer of the free energy in an neighbourhood of its
deformation. The reason behind this result is that, due to the incompatibility
of the energy wells, a small nucleus of the product phase is necessarily
accompanied by a stressed transition layer whose energetic cost exceeds the
energy lowering capacity of the nucleus. We define and characterize
incompatible sets of matrices, in terms of which the transition layer estimate
at the heart of the proof of metastability is expressed. Finally we discuss
connections with experiment and place this concept of metastability in the
wider context of recent theoretical and experimental research on metastability
and hysteresis.Comment: Archive for Rational Mechanics and Analysis, to appea
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