20,294 research outputs found
Changes in the Butterflies (Lepidoptera) of Winneshiek County, Iowa After 90 Years
In 1908, Bert Porter reported the presence of 73 species of butterflies in the Decorah, Iowa area. Since then, no systematic surveys of the butterflies in the Decorah area have been completed despite extensive habitat changes and degradation of native prairie and timber that have occurred over the past 90 years. In 1998, an extensive survey of the butterflies of Winneshiek County confirmed the presence of 55 species of butterflies. Our findings generated a checklist of the butterflies currently found in Winneshiek County, and were compared to Porter\u27s original list. Unfortunately, the regal fritillary, Speyeria idalia, and several other butterfly species found in 1908 apparently no longer occur in the Decorah area
Spectral and temporal signatures of ultrarelativistic protons in compact sources
We present calculations of the spectral and temporal radiative signatures
expected from ultrarelativistic protons in compact sources. The coupling
between the protons and the leptonic component is assumed to occur via
Bethe-Heitler pair production. This process is treated by modeling the results
of Monte-Carlo simulations and incorporating them in a time-dependent kinetic
equation, that we subsequently solve numerically. Thus, the present work is, in
many respects, an extension of the leptonic `one-zone' models to include
hadrons. Several examples of astrophysical importance are presented, such as
the signature resulting from the cooling of relativistic protons on an external
black-body field and that of their cooling in the presence of radiation from
injected electrons. We also investigate and refine the threshold conditions for
the 'Pair Production/Synchrotron' feedback loop which operates when
relativistic protons cool efficiently on the synchrotron radiation of the
internally produced Bethe-Heitler pairs. We demonstrate that an additional
component of injected electrons lowers the threshold for this instability.Comment: 12 pages, 14 figures, accepted for publication in A&
Inertial energy storage hardware definition study (ring rotor)
Rotor analysis, interference stresses, fabrication/assembly, failure analysis, ring tolerances, stren plots, and drawings are discussed
External Compton emission from relativistic jets in Galactic black hole candidates and ultraluminous X-ray sources
Galactic binary systems that contain a black hole candidate emit hard X-rays
in their low luminosity mode. We show that this emission can be understood as
due to the Compton scattering of photons from the companion star and/or the
accretion disk by relativistic electrons in a jet. The same electrons are also
responsible for the radio emission. Two sources -- XTE J1118+480 and Cygnus X-1
-- are modelled as representatives of black holes with low and high luminosity
companion stars respectively. We further show that the ultraluminous compact
X-ray sources observed in nearby galaxies have the properties expected of
stellar mass black holes with high luminosity companions in which the jet is
oriented close to our line of sight.Comment: Submitted to A&A letters, Oct 16, 200
A wind model for high energy pulses
A solution to the sigma problem - that of finding a mechanism capable of
converting Poynting energy flux to particle-borne energy flux in a pulsar wind
- was proposed several years ago by Coroniti and Michel who considered a
particular prescription for magnetic reconnection in a striped wind. This
prescription was later shown to be ineffective. In this paper, we discuss the
basic microphysics of the reconnection process and conclude that a more rapid
prescription is permissible. Assuming dissipation to set in at some distance
outside the light-cylinder, we compute the resulting radiation signature and
find that the synchrotron emission of heated particles appears periodic, in
general showing both a pulse and an interpulse. The predicted spacing of these
agrees well with observation in the case of the Crab and Vela pulsars. Using
parameters appropriate for the Crab pulsar - magnetization parameter at the
light cylinder sigma_L = 6 x 10^4, Lorentz factor Gamma=250 - reasonable
agreement is found with the observed total pulsed luminosity. This suggest that
the high-energy pulses from young pulsars originate not in the co-rotating
magnetosphere within the light cylinder (as in all other models) but from the
radially directed wind well outside it.Comment: 6 pages, 2 figures. To appear in the Proceedings of the 270.
WE-Heraeus Seminar on Neutron Stars, Pulsars and Supernova Remnants, Jan.
21-25, 2002, Physikzentrum Bad Honnef, eds W. Becker, H. Lesch & J. Truemper.
Proceedings are available as MPE-Report 27
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