23,856 research outputs found
Top physics in ATLAS
These proceedings summarize the latest measurements on top production, top
properties and searches using the ATLAS detector at the LHC. The measurements
are performed on collision data with a center of mass energy and TeV.Comment: 17th Lomonosov Conference. 4 pages,3 figure
Comment on "Nuclear Emissions During Self-Nucleated Acoustic Cavitation"
In a recent Letter to PRL, Taleyarkhan and coauthors claim to observe DD
fusion produced by acoustic cavitation. Among other evidence, they provide a
proton recoil spectrum that they interpret as arising from 2.45 MeV DD fusion
neutrons. My analysis concludes the spectrum is inconsistent with 2.45 MeV
neutrons, cosmic background, or a PuBe source, but it is consistent with a
Cf-252 source.Comment: 1 page, 1 figure, comment regarding Taleyarkhan et al., PRL 96 034301
(2006), revised and added supplemental methods (physics/0609083), accepted
for publication in PR
Hamiltonisation, measure preservation and first integrals of the multi-dimensional rubber Routh sphere
We consider the multi-dimensional generalisation of the problem of a sphere,
with axi-symmetric mass distribution, that rolls without slipping or spinning
over a plane. Using recent results from Garc\'ia-Naranjo (arXiv: 1805:06393)
and Garc\'ia-Naranjo and Marrero (arXiv: 1812.01422), we show that the reduced
equations of motion possess an invariant measure and may be represented in
Hamiltonian form by Chaplygin's reducing multiplier method. We also prove a
general result on the existence of first integrals for certain Hamiltonisable
Chaplygin systems with internal symmetries that is used to determine conserved
quantities of the problem.Comment: 23 pages, 1 figure. Submitted to the special issue of Theor. Appl.
Mech. in honour of Chaplygin's 150th anniversar
Reduction of Almost Poisson brackets and Hamiltonization of the Chaplygin Sphere
We construct different almost Poisson brackets for nonholonomic systems than
those existing in the literature and study their reduction. Such brackets are
built by considering non-canonical two-forms on the cotangent bundle of
configuration space and then carrying out a projection onto the constraint
space that encodes the Lagrange-D'Alembert principle. We justify the need for
this type of brackets by working out the reduction of the celebrated Chaplygin
sphere rolling problem. Our construction provides a geometric explanation of
the Hamiltonization of the problem given by A. V. Borisov and I. S. Mamaev
Gauge Transformations, Twisted Poisson Brackets and Hamiltonization of Nonholonomic Systems
In this paper we study the problem of Hamiltonization of nonholonomic systems
from a geometric point of view. We use gauge transformations by 2-forms (in the
sense of Severa and Weinstein [29]) to construct different almost Poisson
structures describing the same nonholonomic system. In the presence of
symmetries, we observe that these almost Poisson structures, although gauge
related, may have fundamentally different properties after reduction, and that
brackets that Hamiltonize the problem may be found within this family. We
illustrate this framework with the example of rigid bodies with generalized
rolling constraints, including the Chaplygin sphere rolling problem. We also
see how twisted Poisson brackets appear naturally in nonholonomic mechanics
through these examples
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