8,123 research outputs found
The unpolarized two-loop massive pure singlet Wilson coefficients for deep-inelastic scattering
We calculate the massive two--loop pure singlet Wilson coefficients for heavy
quark production in the unpolarized case analytically in the whole kinematic
region and derive the threshold and asymptotic expansions. We also recalculate
the corresponding massless two--loop Wilson coefficients. The complete
expressions contain iterated integrals with elliptic letters. The contributing
alphabets enlarge the Kummer-Poincar\'e letters by a series of square-root
valued letters. A new class of iterated integrals, the Kummer-elliptic
integrals, are introduced. For the structure functions and we also
derive improved asymptotic representations adding power corrections. Numerical
results are presented.Comment: 42, pages Latex, 8 Figure
Are Neutron-Rich Elements Produced in the Collapse of Strange Dwarfs ?
The structure of strange dwarfs and that of hybrid stars with same baryonic
number is compared. There is a critical mass (M~0.24M_sun) in the strange dwarf
branch, below which configurations with the same baryonic number in the hybrid
star branch are more stable. If a transition occurs between both branches, the
collapse releases an energy of about of 3x10^{50} erg, mostly under the form of
neutrinos resulting from the conversion of hadronic matter onto strange quark
matter. Only a fraction (~4%) is required to expel the outer neutron-rich
layers. These events may contribute significantly to the chemical yield of
nuclides with A>80 in the Galaxy, if their frequency is of about one per 1500
years.Comment: Accepted for publication in IJMP
The Initial State QED Corrections to Annihilation to a Neutral Vector Boson Revisited
We calculate the non-singlet, the pure singlet contribution, and their
interference term, at due to electron-pair initial state
radiation to annihilation into a neutral vector boson in a direct
analytic computation without any approximation. The correction is represented
in terms of iterated incomplete elliptic integrals. Performing the limit we find discrepancies with the earlier results of
Ref.~\cite{Berends:1987ab} and confirm results obtained in
Ref.~\cite{Blumlein:2011mi} where the effective method of massive operator
matrix elements has been used, which works for all but the power corrections in
. In this way, we also confirm the validity of the factorization of
massive partons in the Drell-Yan process. We also add non-logarithmic terms at
which have not been considered in \cite{Berends:1987ab}. The
corrections are of central importance for precision analyzes in
annihilation into at high luminosity.Comment: 4 pages Latex, 2 Figures, several style file
Gravitational Model of High Energy Particles in a Collimated Jet
Observations suggest that relativistic particles play a fundamental role in
the dynamics of jets emerging from active galactic nuclei as well as in their
interaction with the intracluster medium. However, no general consensus exists
concerning the acceleration mechanism of those high energy particles. A
gravitational acceleration mechanism is here proposed, in which particles
leaving precise regions within the ergosphere of a rotating supermassive black
hole produce a highly collimated flow. These particles follow unbound geodesics
which are asymptotically parallel to the spin axis of the black hole and are
characterized by the energy , the Carter constant and zero
angular momentum of the component . If environmental effects are
neglected, the present model predicts at distances of about 140 kpc from the
ergosphere the presence of electrons with energies around 9.4 GeV. The present
mechanism can also accelerate protons up to the highest energies observed in
cosmic rays by the present experiments.Comment: 27 pages and 5 figures. Accepted for publication in Astrophysical
Journal. arXiv admin note: text overlap with arXiv:1011.654
Editorial: Crossing boundaries: Learning and teaching in virtual worlds
The January 2010 special issue of the British Journal of Educational Technology presents papers on virtual-world environments into teaching and learning practices. A theme that is present in all papers in this special issue is that of sociability and the capabilities of VirtualWorlds to support groups or communities of learners. Dalgarno and Lee review the unique characteristics of virtual worlds, identifying opportunities for researchers and practitioners to use virtual worlds in education in relation to the potential learning benefits they provide. Bellotti and colleagues in this issue focus on describing the development of tools and processes that allow for the development of re-usable learning tasks that can be embedded across virtual worlds. Veletsianos and colleagues focus on intelligent and conversational pedagogical agents/avatars. The issue ranges from the directions of research and practice in the use and application of virtual worlds for learning and training
Determinação do equivalente de salinidade de sais substitutos do cloreto de sódio.
bitstream/item/74486/1/pub-194.pd
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