11,587 research outputs found
Accurate modeling of parallel scientific computations
Scientific codes are usually parallelized by partitioning a grid among processors. To achieve top performance it is necessary to partition the grid so as to balance workload and minimize communication/synchronization costs. This problem is particularly acute when the grid is irregular, changes over the course of the computation, and is not known until load time. Critical mapping and remapping decisions rest on the ability to accurately predict performance, given a description of a grid and its partition. This paper discusses one approach to this problem, and illustrates its use on a one-dimensional fluids code. The models constructed are shown to be accurate, and are used to find optimal remapping schedules
‘But by blood no wolf am I’: Language and Agency, Instinct and Essence – Transcending Antinomies in Maggie Stiefvater’s Shiver trilogy
Young Adult dark romance is often more questioning than its adult counterpart; different, less constraining commercial imperatives are perhaps at work, or readers’ expectations less fixed. This chapter will show how, woven into a sensitive coming-of-age narrative of first love and familial problems, Maggie Stiefvater’s Shiver trilogy performs a far more sophisticated interrogation of the boundaries of animality and humanity than other such fictions, highlighting the centrality of language and its relationship to agency. The hero, Sam’s, struggle with his lupine nature becomes an existentialist refusal to be defined by nature; other characters are tempted instead to yield to a fatalistic surrender of will. The books are tantalisingly ambivalent about the appeal of the instinctual and the borderline between an embodied humanity and the animal, particularly as manifested in the love affair of the teenage protagonists. For Marcuse, the surplus-repression of the proximity senses (smell, taste) enforces the isolation of individuals in civilisation. Stiefvater continually emphasises the sense of smell both as a trigger to sexual attraction and as an aspect of the pack sociality and sense of belonging of the wolves. Through such devices, she concretely renders the nearness of Grace and Sam (her young lovers) to wolfhood. This is contrasted with her exploration of human subjectivity through language, particularly in the perceptive depiction of silences and miscommunications and her hero’s absorption in books and poetry
Superconformal mechanics, black holes, and non-linear realizations
The OSp(2|2)-invariant planar dynamics of a D=4 superparticle near the
horizon of a large mass extreme black hole is described by an N=2
superconformal mechanics, with the SO(2) charge being the superparticle's
angular momentum. The {\it non-manifest} superconformal invariance of the
superpotential term is shown to lead to a shift in the SO(2) charge by the
value of its coefficient, which we identify as the orbital angular momentum.
The full SU(1,1|2)-invariant dynamics is found from an extension to N=4
superconformal mechanics.Comment: 19 pages, plain latex file. Slightly shortened version, two
references adde
Scaling Cosmologies of N=8 Gauged Supergravity
We construct exact cosmological scaling solutions in N=8 gauged supergravity.
We restrict to solutions for which the scalar fields trace out geodesic curves
on the scalar manifold. Under these restrictions it is shown that the axionic
scalars are necessarily constant. The potential is then a sum of exponentials
and has a very specific form that allows for scaling solutions. The scaling
solutions describe eternal accelerating and decelerating power-law universes,
which are all unstable. An uplift of the solutions to 11-dimensional
supergravity is carried out and the resulting timedependent geometries are
discussed. In the discussion we briefly comment on the fact that N=2 gauged
supergravity allows stable scaling solutions.Comment: 17 pages; referenced added, reportnr changed and some corrections in
section
New Gauged N=8, D=4 Supergravities
New gaugings of four dimensional N=8 supergravity are constructed, including
one which has a Minkowski space vacuum that preserves N=2 supersymmetry and in
which the gauge group is broken to . Previous gaugings used the
form of the ungauged action which is invariant under a rigid symmetry
and promoted a 28-dimensional subgroup ( or the
non-semi-simple contraction ) to a local gauge group. Here, a
dual form of the ungauged action is used which is invariant under
instead of and new theories are obtained by gauging 28-dimensional
subgroups of . The gauge groups are non-semi-simple and are different
real forms of the groups, denoted , and the new
theories have a rigid SU(2) symmetry. The five dimensional gauged N=8
supergravities are dimensionally reduced to D=4. The gauge
theories reduce, after a duality transformation, to the
gauging while the gauge theory reduces to the gauge
theory. The new theories are related to the old ones via an analytic
continuation. The non-semi-simple gaugings can be dualised to forms with
different gauge groups.Comment: 33 pages. Reference adde
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