5,612 research outputs found
Shadows of Relic Neutrino Masses and Spectra on Highest Energy GZK Cosmic Rays
The Ultra High Energy (UHE) neutrino scattering onto relic cosmic neutrinos
in galactic and local halos offers an unique way to overcome GZK cut-off. The
UHE nu secondary of UHE photo-pion decays may escape the GZK cut-off and travel
on cosmic distances hitting local light relic neutrinos clustered in dark
halos. The Z resonant production and the competitive W^+W^-, ZZ pair production
define a characteristic imprint on hadronic consequent UHECR spectra. This
imprint keeps memory both of the primary UHE nu spectra as well as of the
possible relic neutrino masses values, energy spectra and relic densities. Such
an hadronic showering imprint should reflect into spectra morphology of cosmic
rays near and above GZK 10^{19}-10^{21}eV cut-off energies. A possible neutrino
degenerate masses at eVs or a more complex and significant neutrino mass split
below or near Super-Kamiokande \triangle m_{\nu_{SK}}= 0.1 eV masses might be
reflected after each corresponding Z peak showering, into new twin unexpected
UHECR flux modulation behind GZK energies: E_{p} sim 3(frac{triangle
m_{\nu_{SK}}}/m_{\nu}10^{21}),eV.
Other shadowsof lightest, nearly massless, neutrinos m_{nu_{2K} simeq 0.001eV
simeq kT_{\nu}, their lowest relic temperatures, energies and densities might
be also reflected at even higher energies edges near Grand Unification: E_{p}
\sim 2.2(m_{\nu_{2K}/E_{\nu}})10^{23}, eV .Comment: 14 pages, 6 Figures,Invited Talk Heidelberg DARK 200
Paper Session I-B - Science and Application Payloads in the 90\u27s
During the 90\u27s with the operation of the Extended Duration Orbiter (EDO), Space Station Freedom (SSF), large platforms in polar and geosynchronus orbits around the Earth, and supporting systems and technology, an infrastructure will exist that will offer a wide range of opportunities for science and applications payloads. The Marshall Space Flight Center (MSFC) is in a unique position of studying for NASA science missions for all of these systems. This paper will discuss a variety of payloads being studied for NASA at the MSFC that are scheduled for flight in the 90\u27s, in support of space science and Mission to Planet Earth. These science payloads such as the Controls, Astrophysics and Structures Experiment in Space (CASES), Advanced Solar Observatory (ASO), Laser Atmospheric Wind Sounder (LAWS), and Lightning Imaging Sensor (LIS), etc. will fully utilize the capabilities of the EDO, SSF, Earth Observation System (EOS), and Earth Science Geostationary Platform (ESGP). Emphasis will be placed on showing how these scientific payloads can fully exploit the great potential of these new capabilities for exciting new science and application missions
Hydrogen Re-Embrittlement of Aerospace grade High Strength Steels
Hydrogen Re-Embrittlement on anodically coated high strength steels is a relevant risk for aerospace structures due to the possibility of hydrogen uptake during the operative life of the components. AISI 4340 and Maraging 250 unnotched tensile specimens were subjected to SSRT in order to evaluate the influence of test environment on time to failure. Fracture surfaces were examined by SEM analysis to evaluate the degree of embrittlement and to correlate it with hydrogen diffusivity of the tested steels
Hydrogen Re-embrittlement of Aerospace Grade High Strength Steels
Hydrogen Re-Embrittlement on anodically coated high strength steels is a relevant risk for aerospace structures due to the possibility of hydrogen uptake during the operative life of the components. AISI 4340 and Maraging 250 unnotched tensile specimens were subjected to SSRT in order to evaluate the influence of test environment on time to failure. Fracture surfaces were examined by SEM analysis to evaluate the degree of embrittlement and to correlate it with hydrogen diffusivity of the tested steels
The activity of Main Belt comets
Main Belt comets represent a recently discovered class of objects. They are
quite intriguing because, while having a Tisserand invariant value higher than
3, are showing cometary activity. We study the activity of the Main Belt comets
making the assumption that they are icy-bodies and that the activity has been
triggered by an impact. We determine the characteristics of this activity and
if the nowadays impact rate in the Main Asteroid Belt is compatible with the
hypothesis of an activity triggered by a recent impact. Due to the fact that
the Main Belt comets can be considered as a kind of comets, we apply a thermal
evolution model developed for icy bodies in order to simulate their activity.
We also apply a model to derive the impact rate, with respect to the size of
the impactor, in the Main Belt. We demonstrate that a stable activity can
result from a recent impact, able to expose ice-rich layers, and that the
impact rate in the Main Belt is compatible with this explanation.Comment: 9 pages, 7 figure
Electroproduction of nucleon resonances
The unitary isobar model MAID has been extended and used for a partial wave
analysis of pion photo- and electroproduction in the resonance region W < 2
GeV. Older data from the world data base and more recent experimental results
from Mainz, Bates, Bonn and JLab for Q^2 up to 4.0 (GeV/c)^2 have been analyzed
and the Q^2 dependence of the helicity amplitudes have been extracted for a
series of four star resonances. We compare single-Q^2 analyses with a
superglobal fit in a new parametrization of Maid2003 together with predictions
of the hypercentral constituent quark model. As a result we find that the
helicity amplitudes and transition form factors of constituent quark models
should be compared with the analysis of bare resonances, where the pion cloud
contributions have been subtracted.Comment: 6 pages Latex including 5 figures, Invited talk at ICTP 4th
International Conference on Perspectives in Hadronic Physics, Trieste, Italy,
12-16 May 200
Small crater populations on Vesta
The NASA Dawn mission has extensively examined the surface of asteroid Vesta,
the second most massive body in the main belt. The high quality of the gathered
data provides us with an unique opportunity to determine the surface and
internal properties of one of the most important and intriguing main belt
asteroids (MBAs). In this paper, we focus on the size frequency distributions
(SFDs) of sub-kilometer impact craters observed at high spatial resolution on
several selected young terrains on Vesta. These small crater populations offer
an excellent opportunity to determine the nature of their asteroidal precursors
(namely MBAs) at sizes that are not directly observable from ground-based
telescopes (i.e., below ~100 m diameter). Moreover, unlike many other MBA
surfaces observed by spacecraft thus far, the young terrains examined had
crater spatial densities that were far from empirical saturation. Overall, we
find that the cumulative power-law index (slope) of small crater SFDs on Vesta
is fairly consistent with predictions derived from current collisional and
dynamical models down to a projectile size of ~10 m diameter (Bottke et al.,
2005a,b). The shape of the impactor SFD for small projectile sizes does not
appear to have changed over the last several billions of years, and an argument
can be made that the absolute number of small MBAs has remained roughly
constant (within a factor of 2) over the same time period. The apparent steady
state nature of the main belt population potentially provides us with a set of
intriguing constraints that can be used to glean insights into the physical
evolution of individual MBAs as well as the main belt as an ensemble.Comment: Accepted by PSS, to appear on Vesta cratering special issu
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