401 research outputs found
G-Structures and Wrapped NS5-Branes
We analyse the geometrical structure of supersymmetric solutions of type II
supergravity of the form R^{1,9-n} x M_n with non-trivial NS flux and dilaton.
Solutions of this type arise naturally as the near-horizon limits of wrapped NS
fivebrane geometries. We concentrate on the case d=7, preserving two or four
supersymmetries, corresponding to branes wrapped on associative or SLAG
three-cycles. Given the existence of Killing spinors, we show that M_7 admits a
G_2-structure or an SU(3)-structure, respectively, of specific type. We also
prove the converse result. We use the existence of these geometric structures
as a new technique to derive some known and new explicit solutions, as well as
a simple theorem implying that we have vanishing NS three-form and constant
dilaton whenever M_7 is compact with no boundary. The analysis extends simply
to other type II examples and also to type I supergravity.Comment: 29 pages. v2: typos fixed, references added, and Discussion expande
All supersymmetric solutions of minimal supergravity in five dimensions
All purely bosonic supersymmetric solutions of minimal supergravity in five
dimensions are classified. The solutions preserve either one half or all of the
supersymmetry. Explicit examples of new solutions are given, including a large
family of plane-fronted waves and a maximally supersymmetric analogue of the
G\"odel universe which lifts to a solution of eleven dimensional supergravity
that preserves 20 supersymmetries.Comment: 63 pages; substantial additions to the analysis of maximally
supersymmetric solutions. Typos corrected and references adde
M-Theory solutions with AdS factors
Solutions of D=7 maximal gauged supergravity are constructed with metrics
that are a product of a n-dimensional anti-de Sitter (AdS) space, with
n=2,3,4,5, and certain Einstein manifolds. The gauge fields have the same form
as in the recently constructed solutions describing the near-horizon limits of
M5-branes wrapping supersymmetric cycles. The new solutions do not preserve any
supersymmetry and can be uplifted to obtain new solutions of D=11 supergravity,
which are warped and twisted products of the D=7 metric with a squashed
four-sphere. Some aspects of the stability of the solutions are discussed.Comment: 30 pages. References adde
The Geometry of D=11 Null Killing Spinors
We determine the necessary and sufficient conditions on the metric and the
four-form for the most general bosonic supersymmetric configurations of D=11
supergravity which admit a null Killing spinor i.e. a Killing spinor which can
be used to construct a null Killing vector. This class covers all
supersymmetric time-dependent configurations and completes the classification
of the most general supersymmetric configurations initiated in hep-th/0212008.Comment: 30 pages, typos corrected, reference added, new solution included in
section 5.1; uses JHEP3.cl
Sharp two-sided heat kernel estimates for critical Schr\"odinger operators on bounded domains
On a smooth bounded domain \Omega \subset R^N we consider the Schr\"odinger
operators -\Delta -V, with V being either the critical borderline potential
V(x)=(N-2)^2/4 |x|^{-2} or V(x)=(1/4) dist (x,\partial\Omega)^{-2}, under
Dirichlet boundary conditions. In this work we obtain sharp two-sided estimates
on the corresponding heat kernels. To this end we transform the Scr\"odinger
operators into suitable degenerate operators, for which we prove a new
parabolic Harnack inequality up to the boundary. To derive the Harnack
inequality we have established a serier of new inequalities such as improved
Hardy, logarithmic Hardy Sobolev, Hardy-Moser and weighted Poincar\'e. As a
byproduct of our technique we are able to answer positively to a conjecture of
E.B.Davies.Comment: 40 page
The Geometry of D=11 Killing Spinors
We propose a way to classify all supersymmetric configurations of D=11
supergravity using the G-structures defined by the Killing spinors. We show
that the most general bosonic geometries admitting a Killing spinor have at
least a local SU(5) or an (Spin(7)\ltimes R^8)x R structure, depending on
whether the Killing vector constructed from the Killing spinor is timelike or
null, respectively. In the former case we determine what kind of local SU(5)
structure is present and show that almost all of the form of the geometry is
determined by the structure. We also deduce what further conditions must be
imposed in order that the equations of motion are satisfied. We illustrate the
formalism with some known solutions and also present some new solutions
including a rotating generalisation of the resolved membrane solutions and
generalisations of the recently constructed D=11 Godel solution.Comment: 36 pages. Typos corrected and discussion on G-structures improved.
Final version to appear in JHE
Producing Enactable Protocols in Artificial Agent Societies
This paper draws upon our previous work [7, 16] in which we proposed the organisation of services around the concept of artificial agent societies and presented a framework for representing roles and protocols using LTSs. The agent would apply for a role in the society, which would result in its participation in a number of protocols. We advocated the use of the games-based metaphor for describing the protocols and presented a framework for assessing the admission of the agent to the society on the basis of its competence. In this work we look at the subsequent question: what information should the agent receive upon entry?. We can not provide it with the full protocol because of security and overload issues. Therefore, we choose to only provide the actions pertinent to the protocols that the role the agent applied for participates in the society. We employ branching bisimulation for producing a protocol equivalent to the original one with all actions not involving the role translated into silent (Ď„) actions. However, this approach sometimes results in non-enactable protocols. In this case, we need to repair the protocol by adding the role in question as a recipient to certain protocol messages that were causing the problems. We present three different approaches for repairing protocols, depending on the number of messages from the original protocol they modify. The modified protocol is adopted as the final one and the agent is given the role automaton that is derived from the branching bisimulation process
GameUp: Exergames for mobility – a project to keep elderly active
A big challenge for Europe is the demographic
shift towards an aging population. Resources in the health care
sector are limited, so it is important that the seniors of tomorrow
will be able to stay healthy and manage themselves as long
as possible, preferably also with a good quality of life. Physical
activity is very important both for mobility and for the general
well-being, but it can be hard to find motivation to exercise
alone at home. Also in rehabilitation there is a need for a more
engaging approach than a sheet of paper describing exercises
that should be performed. In the GameUp project we developed
fun and motivational exergames particularly targeting
elderly in a user centred approach. Physiotherapists ensured
that the movements and exercises were good for flexibility, leg
strength and balance. In addition to seven Kinect games, a
walking app and a professional portal were developed. The
Kinect games can be played in several levels, and those who
are at risk of falling are able to play while seated. The professional
portal ensures that the results of the project also can be
used as a tool in rehabilitation. Test results from 20 elderly
aged 65-95 as well as clinical trials of adherence to the exercises
are encouraging, and the international and multidisciplinary
team behind the project is now looking for ways to commercialize
the project outcomes
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