1,748 research outputs found
Kepler and the Kuiper Belt
The proposed field-of-view of the Kepler mission is at an ecliptic latitude
of ~55 degrees, where the surface density of scattered Kuiper Belt Objects
(KBOs) is a few percent that in the ecliptic plane. The rate of occultations of
Kepler target stars by scattered KBOs with radii r>10km is ~10^-6 to 10^-4 per
star per year, where the uncertainty reflects the current ignorance of the
thickness of the scattered KBO disk and the faint-end slope of their magnitude
distribution. These occultation events will last only ~0.1% of the planned
t_exp=15 minute integration time, and thus will appear as single data points
that deviate by tiny amounts. However, given the target photometric accuracy of
Kepler, these deviations will nevertheless be highly significant, with typical
signal-to-noise ratios of ~10. I estimate that 1-20 of the 10^5 main-sequence
stars in Kepler's field-of-view will exhibit detectable occultations during its
four-year mission. For unresolved events, the signal-to-noise of individual
occultations scales as t_exp^{-1/2}, and the minimum detectable radius could be
decreased by an order of magnitude to ~1 km by searching the individual
3-second readouts for occultations. I propose a number of methods by which
occultation events may be differentiated from systematic effects. Kepler should
measure or significantly constrain the frequency of highly-inclined, ~10
km-sized KBOs.Comment: 5 pages, 1 figure. No changes. Accepted to ApJ, to appear in the
August 1, 2004 issue (v610
A Calibrated Time Domain Envelope Measurement System for the Behavioral Modeling of Power Amplifiers
This paper presents a set-up which enables the generation and the calibrated time domain measurements of complex envelopes of modulated signals at both ports of non linear microwave power amplifiers. The architecture of the characterization tool is given. Examples of error corrected time domain envelopes at the input / output RF ports of a 36 dBm output power – 30dB power gain L-band SSPA are shown. Futhermore, the use of this characterization tool and a suitable processing of measurement data are applied to a novel measurement based behavioral modeling approach of non linear devices accounting for memory effects
A model-based approach to assess the effectiveness of pest biocontrol by natural enemies
Main goal: The aim of this note is to propose a modeling approach for
assessing the effectiveness of pest biocontrol by natural enemies in
diversified agricultural landscapes including several pesticide-based
management strategies. Our approach combines a stochastic landscape model with
a spatially-explicit model of population dynamics. It enables us to analyze the
effect of the landscape composition (proportion of semi-natural habitat,
non-treated crops, slightly treated crops and conventionally treated crops) on
the effectiveness of pest biocontrol. Effectiveness is measured through
environmental and agronomical descriptors, measuring respectively the impact of
the pesticides on the environment and the average agronomic productivity of the
whole landscape taking into account losses caused by pests.
Conclusions: The effectiveness of the pesticide, the intensity of the
treatment and the pest intrinsic growth rate are found to be the main drivers
of landscape productivity. The loss in productivity due to a reduced use of
pesticide can be partly compensated by biocontrol. However, the model suggests
that it is not possible to maintain a constant level of productivity while
reducing the use of pesticides, even with highly efficient natural enemies.
Fragmentation of the semi-natural habitats and increased crop rotation tend to
slightly enhance the effectiveness of biocontrol but have a marginal effect
compared to the predation rate by natural enemies.
This note was written in the framework of the ANR project PEERLESS
"Predictive Ecological Engineering for Landscape Ecosystem Services and
Sustainability"(ANR-12-AGRO-0006)
Min-Max formulae for the speeds of pulsating travelling fronts in periodic excitable media
This paper is concerned with some nonlinear propagation phenomena for
reaction-advection-diffusion equations in a periodic framework. It deals with
travelling wave solutions of the equation propagating with
a speed In the case of a "combustion" nonlinearity, the speed exists
and it is unique, while the front is unique up to a translation in We
give a and a formula for this speed On the other
hand, in the case of a "ZFK" or a "KPP" nonlinearity, there exists a minimal
speed of propagation In this situation, we give a formula
for Finally, we apply this formula to prove a variational
formula involving eigenvalue problems for the minimal speed in the
"KPP" case
Kuiper Belt Object Sizes and Distances from Occultation Observations
There are several observational campaigns under way to detect kilometer size
foreground Kuiper Belt Objects (KBOs) through their occultation of background
stars. The interpretation of an occultation light curve, unfortunately, is
affected by a geometric degeneracy such that one is unable to determine the KBO
size independent of its distance. This degeneracy can be broken through a
precise measurement of the relative velocity obtained from simultaneous
observations of individual events. While an array of telescopes spread over an
area of few square kilometers can be employed, it is unlikely that the relative
velocity can be measured to the required accuracy to help break this geometric
degeneracy. The presence of diffraction fringes in KBO occultation light
curves, when projected sizes of occulted stars are smaller than the Fresnel
scale, improves determination of size and distance significantly. In this
regard, we discuss the potential role of a dedicated satellite mission for KBO
occultation observations. If dwarf stars at the V-band magnitudes of 14th and
fainter can be monitored at time intervals of 0.1 seconds with normalized flux
errors at the level of 1%, the occultation observations will allow individual
KBO sizes and distances to be determined at the level of a few percent or
better.Comment: 4 pages, 2 figures, To appear in ApJ Letter
Glossaires et lexiques médiévaux inédits. Bilan et perspectives, édités par Jacqueline Hamesse et José Meirinhos
Ce volume réunit les communications présentées au Colloque sur les glossaires médiévaux qui s’est déroulé à Paris en 2010; ce domaine, exploré autrefois par M. Roques et J. Monfrin, nécessite encore de recherches approfondies pour faire en sorte que ces instruments de travail importants pour les clercs médiévaux soient connus à fond et exploités convenablement. Pourtant, ces études sont la preuve de la vitalité des nombreuses équipes interdisciplinaires qui s’y consacrent. Trois contributions..
Assessing potential expansion of the pine wood nematode (Bursaphelenchus xylophilus) from the spatial genetic structure of the vector (Monochamus galloprovincialis)
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