6,770 research outputs found
Sub-femtosecond electron bunches created by direct laser acceleration in a laser wakefield accelerator with ionization injection
In this work, we will show through three-dimensional particle-in-cell
simulations that direct laser acceleration in laser a wakefield accelerator can
generate sub-femtosecond electron bunches. Two simulations were done with two
laser pulse durations, such that the shortest laser pulse occupies only a
fraction of the first bubble, whereas the longer pulse fills the entire first
bubble. In the latter case, as the trapped electrons moved forward and
interacted with the high intensity region of the laser pulse, micro-bunching
occurred naturally, producing 0.5 fs electron bunches. This is not observed in
the short pulse simulation.Comment: AAC 201
Collapsing shells of radiation in anti-de Sitter spacetimes and the hoop and cosmic censorship conjectures
Gravitational collapse of radiation in an anti-de Sitter background is
studied. For the spherical case, the collapse proceeds in much the same way as
in the Minkowski background, i.e., massless naked singularities may form for a
highly inhomogeneous collapse, violating the cosmic censorship, but not the
hoop conjecture. The toroidal, cylindrical and planar collapses can be treated
together. In these cases no naked singularity ever forms, in accordance with
the cosmic censorship. However, since the collapse proceeds to form toroidal,
cylindrical or planar black holes, the hoop conjecture in an anti-de Sitter
spacetime is violated.Comment: 4 pages, Revtex Journal: to appear in Physical Review
Derivation of an Abelian effective model for instanton chains in 3D Yang-Mills theory
In this work, we derive a recently proposed Abelian model to describe the
interaction of correlated monopoles, center vortices, and dual fields in three
dimensional SU(2) Yang-Mills theory. Following recent polymer techniques,
special care is taken to obtain the end-to-end probability for a single
interacting center vortex, which constitutes a key ingredient to represent the
ensemble integration.Comment: 18 pages, LaTe
Reaction of pyrroles with ethyl 2-nitroso- and 2-azo-propenoates, and with ethyl cyanoformate N-oxide: a comparison of the reaction pathways
The reaction of ethyl 2-nitrosopropenoate 2a with 1 -methylpyrrole, 2.5-dimethylpyrrole and 2.5-
diphenylpyrrole has been investigated. In every case the products result from highly regioselective attack
at C-2 of the pyrrole by the electrophile. The azopropenoate esters 2b and 2c react similarly with pyrroles,
to the extent that even 1 -(triisopropylsilyl)pyrrole is attacked exclusively at the 2-position by the azo
ester 2b. In contrast, the nitrile oxide ethyl cyanoformate N-oxide 12 reacts at the 3-position of 2.5-
dimethyl- and of 2,5-diphenyl-pyrrole. The reactions of the nitroso and azo esters with pyrroles are
interpreted as Diels-Alder cycloadditions with inverse electron demand
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