984 research outputs found
Twisted Quantum Fields on Moyal and Wick-Voros Planes are Inequivalent
The Moyal and Wick-Voros planes A^{M,V}_{\theta} are *-isomorphic. On each of
these planes the Poincar\'e group acts as a Hopf algebra symmetry if its
coproducts are deformed by twist factors. We show that the *-isomorphism T:
A^M_{\theta} to A^V_{\theta} does not also map the corresponding twists of the
Poincar\'e group algebra. The quantum field theories on these planes with
twisted Poincar\'e-Hopf symmetries are thus inequivalent. We explicitly verify
this result by showing that a non-trivial dependence on the non-commutative
parameter is present for the Wick-Voros plane in a self-energy diagram whereas
it is known to be absent on the Moyal plane (in the absence of gauge fields).
Our results differ from these of (arXiv:0810.2095 [hep-th]) because of
differences in the treatments of quantum field theories.Comment: 12 page
Inequivalence of QFT's on Noncommutative Spacetimes: Moyal versus Wick-Voros
In this paper, we further develop the analysis started in an earlier paper on
the inequivalence of certain quantum field theories on noncommutative
spacetimes constructed using twisted fields. The issue is of physical
importance. Thus it is well known that the commutation relations among
spacetime coordinates, which define a noncommutative spacetime, do not
constrain the deformation induced on the algebra of functions uniquely. Such
deformations are all mathematically equivalent in a very precise sense. Here we
show how this freedom at the level of deformations of the algebra of functions
can fail on the quantum field theory side. In particular, quantum field theory
on the Wick-Voros and Moyal planes are shown to be inequivalent in a few
different ways. Thus quantum field theory calculations on these planes will
lead to different physics even though the classical theories are equivalent.
This result is reminiscent of chiral anomaly in gauge theories and has obvious
physical consequences. The construction of quantum field theories on the
Wick-Voros plane has new features not encountered for quantum field theories on
the Moyal plane. In fact it seems impossible to construct a quantum field
theory on the Wick-Voros plane which satisfies all the properties needed of
field theories on noncommutative spaces. The Moyal twist seems to have unique
features which make it a preferred choice for the construction of a quantum
field theory on a noncommutative spacetime.Comment: Revised version accepted for publication in Phys.Rev.D; 18 page
The NIF LinkOut Broker: A Web Resource to Facilitate Federated Data Integration using NCBI Identifiers
This paper describes the NIF LinkOut Broker (NLB) that has been built as part of the Neuroscience Information Framework (NIF) project. The NLB is designed to coordinate the assembly of links to neuroscience information items (e.g., experimental data, knowledge bases, and software tools) that are (1) accessible via the Web, and (2) related to entries in the National Center for Biotechnology Information’s (NCBI’s) Entrez system. The NLB collects these links from each resource and passes them to the NCBI which incorporates them into its Entrez LinkOut service. In this way, an Entrez user looking at a specific Entrez entry can LinkOut directly to related neuroscience information. The information stored in the NLB can also be utilized in other ways. A second approach, which is operational on a pilot basis, is for the NLB Web server to create dynamically its own Web page of LinkOut links for each NCBI identifier in the NLB database. This approach can allow other resources (in addition to the NCBI Entrez) to LinkOut to related neuroscience information. The paper describes the current NLB system and discusses certain design issues that arose during its implementation
The Divertor Tokamak Test facility proposal: Physical requirements and reference design
The main goal of the Divertor Tokamak Test facility (DTT) is to explore alternative power exhaust solutions for DEMO. The principal objective is to mitigate the risk of a difficult extrapolation to fusion reactor of the conventional divertor based on detached conditions under test on ITER. The task includes several issues, as: (i) demonstrating a heat exhaust system capable of withstanding the large load of DEMO in case of inadequate radiated power fraction; (ii) closing the gaps in the exhaust area that cannot be addressed by present devices; (iii) demonstrating how the possible implemented solutions (e.g., advanced divertor configurations or liquid metals) can be integrated in a DEMO device. In view of these goals, the basic physical DTT parameters have been selected according to the following guidelines: (i) edge conditions as close as possible to DEMO in terms of dimensionless parameters; (ii) flexibility to test a wide set of divertor concepts and techniques; (iii) compatibility with bulk plasma performance; (iv) an upper bound of 500 M€ for the investment costs. © 2017 The Author
A variational approach to the optimized phonon technique for electron-phonon problems
An optimized phonon approach for the numerical diagonalization of interacting
electron-phonon systems is proposed. The variational method is based on an
expansion in coherent states that leads to a dramatic truncation in the phonon
space. The reliability of the approach is demonstrated for the extended
Holstein model showing that different types of lattice distortions are present
at intermediate electron-phonon couplings as observed in strongly correlated
systems. The connection with the density matrix renormalization group is
discussed.Comment: 4 figures; submitted to Phys. Rev.
The INCF Digital Atlasing Program: Report on Digital Atlasing Standards in the Rodent Brain
The goal of the INCF Digital Atlasing Program is to provide the vision and direction necessary to make the rapidly growing collection of multidimensional data of the rodent brain (images, gene expression, etc.) widely accessible and usable to the international research community. This Digital Brain Atlasing Standards Task Force was formed in May 2008 to investigate the state of rodent brain digital atlasing, and formulate standards, guidelines, and policy recommendations.

Our first objective has been the preparation of a detailed document that includes the vision and specific description of an infrastructure, systems and methods capable of serving the scientific goals of the community, as well as practical issues for achieving
the goals. This report builds on the 1st INCF Workshop on Mouse and Rat Brain Digital Atlasing Systems (Boline et al., 2007, _Nature Preceedings_, doi:10.1038/npre.2007.1046.1) and includes a more detailed analysis of both the current state and desired state of digital atlasing along with specific recommendations for achieving these goals
Length functions on currents and applications to dynamics and counting
The aim of this (mostly expository) article is twofold. We first explore a
variety of length functions on the space of currents, and we survey recent work
regarding applications of length functions to counting problems. Secondly, we
use length functions to provide a proof of a folklore theorem which states that
pseudo-Anosov homeomorphisms of closed hyperbolic surfaces act on the space of
projective geodesic currents with uniform north-south dynamics.Comment: 35pp, 2 figures, comments welcome! Second version: minor corrections.
To appear as a chapter in the forthcoming book "In the tradition of Thurston"
edited by V. Alberge, K. Ohshika and A. Papadopoulo
Covariant Quantum Fields on Noncommutative Spacetimes
A spinless covariant field on Minkowski spacetime \M^{d+1} obeys the
relation where
is an element of the Poincar\'e group \Pg and is its unitary representation on quantum vector states. It
expresses the fact that Poincar\'e transformations are being unitary
implemented. It has a classical analogy where field covariance shows that
Poincar\'e transformations are canonically implemented. Covariance is
self-reproducing: products of covariant fields are covariant. We recall these
properties and use them to formulate the notion of covariant quantum fields on
noncommutative spacetimes. In this way all our earlier results on dressing,
statistics, etc. for Moyal spacetimes are derived transparently. For the Voros
algebra, covariance and the *-operation are in conflict so that there are no
covariant Voros fields compatible with *, a result we found earlier. The notion
of Drinfel'd twist underlying much of the preceding discussion is extended to
discrete abelian and nonabelian groups such as the mapping class groups of
topological geons. For twists involving nonabelian groups the emergent
spacetimes are nonassociative.Comment: 20 page
Electromechanical dissociation of left atrium in patients with Cardiac Amyloidosis by Magnetic Resonance: Prognostic and clinical correlates
- …