10,199 research outputs found
The International Community and the Environment
It is a signal honour to have been asked to deliver this lecture to commemorate the outstanding contributions of Jean Baer and Julian Huxley to the cause of conservation. Both of these great men devoted their genius as scientists to helping us to broaden our perceptions of the human condition and their talents as leaders to establishing the institutions needed to safeguard and to improve the conditions of life on this planet. No two individuals did more to establish the foundations on which environmental conservation can now be seen and dealt with as a critical global issu
N. F. Strong Photo Album
https://digital.kenyon.edu/scrapbooks/1067/thumbnail.jp
Rx for a Nagging Constitutional Headache
Continuing apprehension over seeming Congressional power to curtail constitutional review though control of Supreme Court\u27s Appellate Jurisdiction
Lifetime Constraints for Late Dark Matter Decay
We consider a class of late-decaying dark-matter models, in which a dark
matter particle decays to a heavy stable daughter of approximately the same
mass, together with one or more relativistic particles which carry away only a
small fraction of the parent rest mass. Such decays can affect galactic halo
structure and evolution, and have been invoked as a remedy to some of the small
scale structure-formation problems of cold dark matter. There are existing
stringent limits on the dark matter lifetime if the decays produce photons. By
considering examples in which the relativistic decay products instead consist
of neutrinos or electron-position pairs, we derive stringent limits on these
scenarios for a wide range of dark matter masses. We thus eliminate a sizable
portion of the parameter space for these late decay models if the dominant
decay channel involves Standard Model final states.Comment: 13 pages, 7 figures. Replaced to match published version. Discussion
expanded. References added. Accepted by Phys. Rev
Challenging cosmic ray propagation with antiprotons. Evidence for a "fresh" nuclei component?
Recent measurements of the cosmic ray (CR) antiproton flux have been shown to
challenge existing CR propagation models. It was shown that the reacceleration
models designed to match secondary to primary nuclei ratios (e.g.,
boron/carbon) produce too few antiprotons. Matching both the secondary to
primary nuclei ratio and the antiproton flux requires artificial breaks in the
diffusion coefficient and the primary injection spectrum suggesting the need
for other approaches.
In the present paper we discuss one possibility to overcome these
difficulties. Using the measured antiproton flux AND B/C ratio to fix the
diffusion coefficient, we show that the spectra of primary nuclei as measured
in the heliosphere may contain a fresh local "unprocessed" component at low
energies perhaps associated with the Local Bubble, thus decreasing the measured
secondary to primary nuclei ratio. The independent evidence for SN activity in
the solar vicinity in the last few Myr supports this idea. The model reproduces
antiprotons, B/C ratio, and elemental abundances up to Ni (Z<=28). Calculated
isotopic distributions of Be and B are in perfect agreement with CR data. The
abundances of three "radioactive clock" isotopes in CR, 10Be, 26Al, 36Cl, are
all consistent and indicate a halo size z_h~4 kpc based on the most accurate
data taken by the ACE spacecraft.Comment: To be published in The Astrophysical Journal, v.586, 2003 April 1;
final version: 19 pages, 24 ps-figures, emulateapj5.sty (modified),
natbib.sty, aastex.cls. More details can be found at
http://www.gamma.mpe-garching.mpg.de/~aws/aws.htm
Techniques for carrying out radiative transfer calculations for the Martian atmospheric dust
A description is given of the modification of a theory on the reflectance of particulate media so as to apply it to analysis of the infrared spectra obtained by the IRIS instrument on Mariner 9. With the aid of this theory and the optical constants of muscovite mica, quartz, andesite, anorthosite, diopside pyroxenite, and dunite, modeling calculations were made to refine previous estimates of the mineralogical composition of the Martian dust particles. These calculations suggest that a feldspar rich mixture is a very likely composition for the dust particles. The optical constants used for anorthosite and diopside pyroxenite were derived during this program from reflectance measurements. Those for the mica were derived from literature reflectance data. Finally, a computer program was written to invert the measured radiance data so as to obtain the absorption coefficient spectrum which should then be independent of the temperature profile and gaseous component effects
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