51,313 research outputs found
Quantum symmetries and the Weyl-Wigner product of group representations
In the usual formulation of quantum mechanics, groups of automorphisms of
quantum states have ray representations by unitary and antiunitary operators on
complex Hilbert space, in accordance with Wigner's Theorem. In the phase-space
formulation, they have real, true unitary representations in the space of
square-integrable functions on phase-space. Each such phase-space
representation is a Weyl-Wigner product of the corresponding Hilbert space
representation with its contragredient, and these can be recovered by
`factorising' the Weyl-Wigner product. However, not every real, unitary
representation on phase-space corresponds to a group of automorphisms, so not
every such representation is in the form of a Weyl-Wigner product and can be
factorised. The conditions under which this is possible are examined. Examples
are presented.Comment: Latex2e file, 37 page
Plasma accelerator Patent
Crossed-field plasma accelerator for laboratory simulation of atmospheric reentry condition
A dynamical symmetry breaking model in Weyl space
The dynamical process following the breaking of Weyl geometry to Riemannian
geometry is considered by studying the motion of de Sitter bubbles in a Weyl
vacuum. The bubbles are given in terms of an exact, spherically symmetric thin
shell solution to the Einstein equations in a Weyl-Dirac theory with a
time-dependent scalar field of the form beta = f(t)/r. The dynamical solutions
obtained lead to a number of possible applications. An important feature of the
thin shell model is the manner in which beta provides a connection between the
interior and exterior geometries since information about the exterior geometry
is contained in the boundary conditions for beta.Comment: 18 pages, RevTex, to be published in J. Math. Phy
Non-positivity of the Wigner function and bounds on associated integrals
The Wigner function shares several properties with classical distribution
functions on phase space, but is not positive-definite. The integral of the
Wigner function over a given region of phase space can therefore lie outside
the interval [0,1]. The problem of finding best-possible upper and lower bounds
for a given region is the problem of finding the greatest and least eigenvalues
of an associated Hermitian operator. Exactly solvable examples are described,
and possible extensions are indicated.Comment: 5 pages, Latex2e fil
A Coronal Hole's Effects on CME Shock Morphology in the Inner Heliosphere
We use STEREO imagery to study the morphology of a shock driven by a fast
coronal mass ejection (CME) launched from the Sun on 2011 March 7. The source
region of the CME is located just to the east of a coronal hole. The CME ejecta
is deflected away from the hole, in contrast with the shock, which readily
expands into the fast outflow from the coronal hole. The result is a CME with
ejecta not well centered within the shock surrounding it. The shock shape
inferred from the imaging is compared with in situ data at 1 AU, where the
shock is observed near Earth by the Wind spacecraft, and at STEREO-A. Shock
normals computed from the in situ data are consistent with the shock morphology
inferred from imaging.Comment: to appear in The Astrophysical Journa
A Blockchain-based Approach for Data Accountability and Provenance Tracking
The recent approval of the General Data Protection Regulation (GDPR) imposes
new data protection requirements on data controllers and processors with
respect to the processing of European Union (EU) residents' data. These
requirements consist of a single set of rules that have binding legal status
and should be enforced in all EU member states. In light of these requirements,
we propose in this paper the use of a blockchain-based approach to support data
accountability and provenance tracking. Our approach relies on the use of
publicly auditable contracts deployed in a blockchain that increase the
transparency with respect to the access and usage of data. We identify and
discuss three different models for our approach with different granularity and
scalability requirements where contracts can be used to encode data usage
policies and provenance tracking information in a privacy-friendly way. From
these three models we designed, implemented, and evaluated a model where
contracts are deployed by data subjects for each data controller, and a model
where subjects join contracts deployed by data controllers in case they accept
the data handling conditions. Our implementations show in practice the
feasibility and limitations of contracts for the purposes identified in this
paper
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