522 research outputs found
Type III Einstein-Yang-Mills solutions
We construct two distinct classes of exact type III solutions of the D=4
Einstein-Yang-Mills system. The solutions are embeddings of the non-abelian
plane waves in spacetimes in Kundt's class. Reduction of the solutions to type
N leads to generalized and Kundt waves. The geodesic equations are briefly
discussed.Comment: revtex, 4 pages, minor changes, some factors and references
corrected, footnote adde
Examples of D=11 S-supersymmetric actions for point-like dynamical systems
A non standard super extensions of the Poincare algebra (S-algebra [1,2]),
which seems to be relevant for construction of various D=11 models, are
studied. We present two examples of actions for point-like dynamical systems,
which are invariant under off-shell closed realization of the S-algebra as well
as under local fermionic -symmetry. On this ground, an explicit form of
the S-algebra is advocated.Comment: 18 pages, LaTex fil
GLORIA Slope Approach - Monitoring Plant Community Changes in Mountain Ecosystems
The research described in this presentation is part of the Global Observation Research Initiative in Alpine Environments (GLORIA) whose purpose is to establish and maintain a global, long-term observation network in alpine environments.
Despite changes in mountaintop-vegetation due to recent climate change being observed throughout the world, trends are not consistent. Moreover, as plant communities can be impacted by several different factors, it is important to be able to separate what is due to climate change and what is due to e.g. changes in grazing pressure (see additional file below)
SystÚme politique et mobilité sociale
L'analyse des processus de mobilitĂ© sociale mobilise l'intĂ©rĂȘt des sociologues depuis une trentaine d'annĂ©es ; pourtant ni ce terme ni les concepts auxquels il fait appel ne font l'objet d'un consensus en sociologie. Le dĂ©bat qui s'est dĂ©veloppĂ© autour de ce problĂšme semble s'ordonner selon deux axes. D'une part, des discussions de type technique, de l'autre des oppositions plus radicales de nature thĂ©orique ou Ă©pistĂ©mologique. Le premier plan concerne tous les problĂšmes liĂ©s Ă la constitution et Ă l'interprĂ©tation des indicateurs de mobilitĂ© sociale : dĂ©finition de critĂšres permettant de constituer les classes ou groupes sociaux, mesure du flux de mobilitĂ©, problĂšmes liĂ©s Ă l'existence d'une mobilitĂ© structurelle, etc. Le second axe, d'une nature diffĂ©rente, met en question la lĂ©gitimitĂ© du concept de mobilitĂ© sociale et, par consĂ©quent, l'utilitĂ© de ce type de recherche quelles qu'en soient par ailleurs les modalitĂ©s techniques (...)
Tensorial Central Charges and New Superparticle Models with Fundamental Spinor Coordinates
We consider firstly simple D=4 superalgebra with six real tensorial central
charges , and discuss its possible realizations in massive and
massless cases. Massless case is dynamically realized by generalized
Ferber-Shirafuji (FS) model with fundamental bosonic spinor coordinates. The
Lorentz invariance is not broken due to the realization of central charges
generators in terms of bosonic spinors. The model contains four fermionic
coordinates and possesses three kappa-symmetries thus providing the BPS
configuration preserving 3/4 of the target space supersymmetries. We show that
the physical degrees of freedom (8 real bosonic and 1 real Grassmann variable)
of our model can be described by OSp(8|1) supertwistor. The relation with
recent superparticle model by Rudychev and Sezgin is pointed out. Finally we
propose a higher dimensional generalization of our model with one real
fundamental bosonic spinor. D=10 model describes massless superparticle with
composite tensorial central charges and in D=11 we obtain 0-superbrane model
with nonvanishing mass which is generated dynamically.Comment: 14 pages, latex, no figures, misprints correcte
Green-Schwarz type formulation of D=11 S - invariant superstring and superparticle actions
A manifestly Poincare invariant formulations for and SO(2,9)
superstring actions are proposed. The actions are invariant under a local
fermionic -symmetry as well as under a number of global symmetries,
which turn out to be on-shell realization of the known ``new supersymmetry``
S-algebra. Canonical quantization of the theory is performed and relation of
the quantum state spectrum with that of type IIA Green-Schwarz superstring is
discussed. Besides, a mechanical model is constructed, which is a zero tension
limit of the D=11 superstring and which incorporates all essential features of
the latter. A corresponding action invariant under off-shell closed realization
of the S-algebra is obtained.Comment: Revised version, in particular, discussion of SO(2,9) case is
included. To be published in Int. J. Mod. Phys.
Peacock Bundles: Bundle Coloring for Graphs with Globality-Locality Trade-off
Bundling of graph edges (node-to-node connections) is a common technique to
enhance visibility of overall trends in the edge structure of a large graph
layout, and a large variety of bundling algorithms have been proposed. However,
with strong bundling, it becomes hard to identify origins and destinations of
individual edges. We propose a solution: we optimize edge coloring to
differentiate bundled edges. We quantify strength of bundling in a flexible
pairwise fashion between edges, and among bundled edges, we quantify how
dissimilar their colors should be by dissimilarity of their origins and
destinations. We solve the resulting nonlinear optimization, which is also
interpretable as a novel dimensionality reduction task. In large graphs the
necessary compromise is whether to differentiate colors sharply between locally
occurring strongly bundled edges ("local bundles"), or also between the weakly
bundled edges occurring globally over the graph ("global bundles"); we allow a
user-set global-local tradeoff. We call the technique "peacock bundles".
Experiments show the coloring clearly enhances comprehensibility of graph
layouts with edge bundling.Comment: Appears in the Proceedings of the 24th International Symposium on
Graph Drawing and Network Visualization (GD 2016
Motions and world-line deviations in Einstein-Maxwell theory
We examine the motion of charged particles in gravitational and
electro-magnetic background fields. We study in particular the deviation of
world lines, describing the relative acceleration between particles on
different space-time trajectories. Two special cases of background fields are
considered in detail: (a) pp-waves, a combination of gravitational and
electro-magnetic polarized plane waves travelling in the same direction; (b)
the Reissner-Nordstr{\o}m solution. We perform a non-trivial check by computing
the precession of the periastron for a charged particle in the
Reissner-Nordstr{\o}m geometry both directly by solving the geodesic equation,
and using the world-line deviation equation. The results agree to the order of
approximation considered.Comment: 23 pages, no figure
Considerations on Super Poincare Algebras and their Extensions to Simple Superalgebras
We consider simple superalgebras which are a supersymmetric extension of
\fspin(s,t) in the cases where the number of odd generators does not exceed
64. All of them contain a super Poincar\'e algebra as a contraction and another
as a subalgebra. Because of the contraction property, some of these algebras
can be interpreted as de Sitter or anti de Sitter superalgebras. However, the
number of odd generators present in the contraction is not always minimal due
to the different splitting properties of the spinor representations under a
subalgebra. We consider the general case, with arbitrary dimension and
signature, and examine in detail particular examples with physical implications
in dimensions and .Comment: 16 pages, AMS-LaTeX. Version to appear in the Reviews in Mathematical
Physic
Hierarchy of Dirac, Pauli and Klein-Gordon conserved operators in Taub-NUT background
The algebra of conserved observables of the SO(4,1) gauge-invariant theory of
the Dirac fermions in the external field of the Kaluza-Klein monopole is
investigated. It is shown that the Dirac conserved operators have physical
parts associated with Pauli operators that are also conserved in the sense of
the Klein-Gordon theory. In this way one gets simpler methods of analyzing the
properties of the conserved Dirac operators and their main algebraic structures
including the representations of dynamical algebras governing the Dirac quantum
modes.Comment: 16 pages, latex, no figure
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