1,452 research outputs found
Deccan volcanism at the Cretaceous-Tertiary boundary
The accuracy with which one can claim that Deccan trap volcanism occurred at the Cretaceous-Tertiary boundary (KTB) over a very short time interval is of key importance in deciding whether a volcanic origin of the KTB events should be taken seriously. In the two years since paleomagnetic, paleontological and geodynamic evidence was published, further data have become available and the case now appears to be well constrained. The Ar-40/Ar-39 results from six labs have yielded some 24 reliable plateau ages that narrow the age range to 65 to 69 Ma. Moreover, it appears that a significant part of this range results from inter-lab spread and possible minor alteration. Paleontology demonstrates that volcanism started in the Maestrichtian, more precisely in the A. mayaroensis zone. Paleomagnetism shows that volcanism spanned only 3 chrons and only one correlation remains possible, that of the main central reversed chron with 29R. Therefore, whereas Ar-40/Ar-39 is able only to restrict the duration of volcanism to some 4 Ma, paleomagnetism restricts it to 0.5 Ma. Using some geochemical indicators such as C-13 as proxy, it is suggested that volcanism actually consists of a few shorter events of unequal magnitude. Extrusion rates may be as high as 100 cu km/yr and fissure lengths as long as several 100 km. Such a scenario appears to be at least as successful as others in accounting for most anomalies observed at the KTB. Particularly important are Iridium and other platinum group elements (PGE) profiles, Sr-87/Sr-86, C-13, 0-18, other exotic geochemical signatures, spherules, soot, shocked minerals, selective and stepwise extinctions. The environmental impact of CO2 possibly released during explosive phases of volcanism, and SO2 released during effusive phases, and the ability of volcanism to ensure worldwide distribution of KTB products are now all addressed. In conclusion, the case for a causal link between internal hotspot activity, birth of the Reunion hotspot itself as the Deccan and KTB events appears to rest on an increasingly stronger basis
Pseudo-Riemannian geodesic foliations by circles
We investigate under which assumptions an orientable pseudo-Riemannian
geodesic foliations by circles is generated by an -action. We construct
examples showing that, contrary to the Riemannian case, it is not always true.
However, we prove that such an action always exists when the foliation does not
contain lightlike leaves, i.e. a pseudo-Riemannian Wadsley's Theorem. As an
application, we show that every Lorentzian surface all of whose
spacelike/timelike geodesics are closed, is finitely covered by .
It follows that every Lorentzian surface contains a non-closed geodesic.Comment: 14 page
Charging of DMSP/F6 spacecraft in aurora on 10 January 1983
Spacecraft charging has been widely observed in geosynchronous orbit on the ATS-5 and ATS-6 pair and on the SCATHA spacecraft. An adequate theory for explaining the observations exist. Neither the data or theory can be exported to low polar orbit and its drastically different environment. Evidence of charging on the DMSP F6 spacecraft is presented. A simple model is set up explaining the observations. Two independent instruments on the spacecraft showed charging to a moderate (44 volts) negative potential. The selection spectrometer showed a flux of 2 billion electrons per sq. cm. sec. ster. peaked at 9.5 keV. This was marginally sufficient to overcome the flux of cold ambient ions. Charging calculations are presented showing where simplications are justified and where serious uncertainties exist. More serious charging is predicted for the Shuttle in polar orbit
High Energy exclusive Leptoproduction of the rho-meson: Theory and Phenomenology
We describe the hard leptoproduction of transversally polarized rho-meson, up
to twist 3 accuracy, including 2- and 3- particles Fock-states, in the HERA
kinematics of high center-of-mass energy. We first build a model based on a
simple approach to the unintegrated gluon density (the parton impact factor)
that we compare with H1 and ZEUS data for the ratios of helicity amplitudes
T(gamma*T -> rhoT)/T(gamma*L -> rhoL) and T(gamma*T -> rhoL)/T(gamma*L -> rhoL)
and get a good description of the data. We also show how saturation effects can
be included in this model by extending the dipole representation of the
scattering amplitude in coordinate space up to twist 3.Comment: 4 pages, 3 figures, to appear in the proceedings of 20th
International Workshop on Deep-Inelastic Scattering and Related Subjects (DIS
2012), Bonn, Germany, 26-30 March 201
Theory and phenomenology of helicity amplitudes for high energy exclusive leptoproduction of the rho-meson
We review here two approaches to describe hard leptoproduction of
transversally polarized rho-meson, based on recent calculation of the gamma*T
-> rhoT impact factor up to twist 3 accuracy in the collinear factorization
frame, including 2- and 3- particles Fock-states. The first approach uses a
model of the unintegrated gluon density (the proton impact factor) which allows
a comparison of our predictions with H1 and ZEUS data for the ratios of
helicity amplitudes T(gamma*T -> rhoT)/T(gamma*L -> rhoL) and T(gamma*T ->
rhoL)/T(gamma*L -> rhoL). In the second approach, we transform the gamma*T ->
rhoT impact factor into the impact parameter space. We show that the
transformed amplitude factorizes according to conventional dipole picture. We
shortly discuss a way to implement the nucleon saturation effects in our
approach.Comment: 5 pages, 2 figures, to appear in the proceedings of 6th International
Conference on Quarks and Nuclear Physics (QNP 2012), Palaiseau, France, April
16-20, 201
A phenomenological study of helicity amplitudes of high energy exclusive leptoproduction of the rho meson
We apply a previously developed scheme to consistently include the twist-3
distribution amplitudes for transversely polarized rho meson in order to
evaluate, in the framework of kT factorization, the helicity amplitudes for
exclusive leptoproduction of a light vector meson, at leading order in alphaS.
We compare our results with high energy experimental data for the ratios of
helicity amplitudes T11/T00 and T01/T00 and get a good description of the data.Comment: 20 pages, 11 figures, published version in PR
Holonomy groups of pseudo-quaternionic-K\"ahlerian manifolds of non-zero scalar curvature
The holonomy group of a pseudo-quaternionic-K\"ahlerian manifold of
signature with non-zero scalar curvature is contained in
\Sp(1)\cdot\Sp(r,s) and it contains \Sp(1). It is proved that either is
irreducible, or and preserves an isotropic subspace of dimension
, in the last case, there are only two possibilities for the connected
component of the identity of such . This gives the classification of
possible connected holonomy groups of pseudo-quaternionic-K\"ahlerian manifolds
of non-zero scalar curvature.Comment: 7 pages; Dedicated to Dmitri Vladimirovich Alekseevsky at the
occasion of his 70th birthda
Direct path from microscopic mechanics to Debye shielding, Landau damping, and wave-particle interaction
The derivation of Debye shielding and Landau damping from the -body
description of plasmas is performed directly by using Newton's second law for
the -body system. This is done in a few steps with elementary calculations
using standard tools of calculus, and no probabilistic setting. Unexpectedly,
Debye shielding is encountered together with Landau damping. This approach is
shown to be justified in the one-dimensional case when the number of particles
in a Debye sphere becomes large. The theory is extended to accommodate a
correct description of trapping and chaos due to Langmuir waves. Shielding and
collisional transport are found to be two related aspects of the repulsive
deflections of electrons, in such a way that each particle is shielded by all
other ones while keeping in uninterrupted motion.Comment: arXiv admin note: substantial text overlap with arXiv:1310.3096,
arXiv:1210.154
The isolation of gravitational instantons: Flat tori V flat R^4
The role of topology in the perturbative solution of the Euclidean Einstein
equations about flat instantons is examined.Comment: 15 pages, ICN-UNAM 94-1
EKOKRITIK SASTRA PADA NOVEL RAHASIA PELANGI KARYA RIAWANI ELYTA DAN SABRINA
Masalah utama dalam penulisan ini yaitu bagaimana kearifan lingkungan novel Rahasia Pelangi karya Riawani Elyta dan Sabrina Ws. Penelitian ini bertujuan untuk mengetahui kearifan lingkungan novel Rahasia Pelangi karya Riawani Elyta dan Sabrina Ws. Jenis penelitian ini adalah penelitian deskriptif kualitatif. Prosedur penelitian meliputi reduksi data, penyajian data dan pemeriksaan kesimpulan atau verifikasi. Subjek dalam penelitian ini adalah Novel Rahasia Pelangi karya Riawani Elyta dan Sabrina Ws. Hasil penelitian menunjukkan bahwa terdapat dua puluh dua bentuk kearifan lingkungan yang dikelompokkan menjadi lima aspek, diantaranya sikap hormat terhadap alam, sikap tanggung jawab moral terhadap alam, sikap solidaritas terhadap alam, sikap kasih sayang dan kepedulian terhadap alam, dan sikap tidak mengganggu kehidupan alam. Berdasarkan hasil penelitian tersebut di atas, dapat disimpulkan kearifan lokal lingkungan pada Novel Rahasia Pelangi karya Riawani Elyta dan Sabrina Ws melalui model ekokritik sastra terdapat dua puluh dua.
 
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