2,752 research outputs found
Invariant Killing spinors in 11D and type II supergravities
We present all isotropy groups and associated groups, up to discrete
identifications of the component connected to the identity, of spinors of
eleven-dimensional and type II supergravities. The groups are products
of a Spin group and an R-symmetry group of a suitable lower dimensional
supergravity theory. Using the case of SU(4)-invariant spinors as a paradigm,
we demonstrate that the groups, and so the R-symmetry groups of
lower-dimensional supergravity theories arising from compactifications, have
disconnected components. These lead to discrete symmetry groups reminiscent of
R-parity. We examine the role of disconnected components of the groups
in the choice of Killing spinor representatives and in the context of
compactifications.Comment: 22 pages, typos correcte
The effect of wall cooling on a compressible turbulent boundary layer
Experimental results are presented for two turbulent boundary-layer experiments conducted at a free-stream Mach number of 4 with wall cooling. The first experiment examines a constant-temperature cold-wall boundary layer subjected to adverse and favourable pressure gradients. It is shown that the boundary-layer data display good agreement with Coles’ general composite boundary-layer profile using Van Driest's transformation. Further, the pressure-gradient parameter β_K found in previous studies to correlate adiabatic high-speed data with low-speed data also correlates the present cooled-wall high-speed data. The second experiment treats the response of a constant-pressure high-speed boundary layer to a near step change in wall temperature. It is found that the growth rate of the thermal boundary layer within the existing turbulent boundary layer varies considerably depending upon the direction of the wall temperature change. For the case of an initially cooled boundary layer flowing onto a wall near the recovery temperature, it is found that δ_T ~ x whereas the case of an adiabatic boundary layer flowing onto a cooled wall gives δ_T ~ x^½. The apparent origin of the thermal boundary layer also changes considerably, which is accounted for by the variation in sublayer thicknesses and growth rates within the sublayer
Kappa symmetry, generalized calibrations and spinorial geometry
We extend the spinorial geometry techniques developed for the solution of
supergravity Killing spinor equations to the kappa symmetry condition for
supersymmetric brane probe configurations in any supergravity background. In
particular, we construct the linear systems associated with the kappa symmetry
projector of M- and type II branes acting on any Killing spinor. As an example,
we show that static supersymmetric M2-brane configurations which admit a
Killing spinor representing the SU(5) orbit of are generalized
almost hermitian calibrations and the embedding map is pseudo-holomorphic. We
also present a bound for the Euclidean action of M- and type II branes embedded
in a supersymmetric background with non-vanishing fluxes. This leads to an
extension of the definition of generalized calibrations which allows for the
presence of non-trivial Born-Infeld type of fields in the brane actions.Comment: 9 pages, latex, references added and minor change
The supersymmetric solutions and extensions of ungauged matter-coupled N=1,d=4 supergravity
We find the most general supersymmetric solutions of ungauged N=1,d=4
supergravity coupled to an arbitrary number of vector and chiral
supermultiplets, which turn out to be essentially pp-waves and strings. We also
introduce magnetic 1-forms and their supersymmetry transformations and 2-forms
associated to the isometries of the scalar manifold and their supersymmetry
transformations. Only the latter can couple to BPS objects (strings), in
agreement with our results.Comment: Some misprints and citations correcte
All null supersymmetric backgrounds of N=2, D=4 gauged supergravity coupled to abelian vector multiplets
The lightlike supersymmetric solutions of N=2, D=4 gauged supergravity
coupled to an arbitrary number of abelian vector multiplets are classified
using spinorial geometry techniques. The solutions fall into two classes,
depending on whether the Killing spinor is constant or not. In both cases, we
give explicit examples of supersymmetric backgrounds. Among these BPS
solutions, which preserve one quarter of the supersymmetry, there are
gravitational waves propagating on domain walls or on bubbles of nothing that
asymptote to AdS_4. Furthermore, we obtain the additional constraints obeyed by
half-supersymmetric vacua. These are divided into four categories, that include
bubbles of nothing which are asymptotically AdS_4, pp-waves on domain walls,
AdS_3 x R, and spacetimes conformal to AdS_3 times an interval.Comment: 55 pages, uses JHEP3.cls. v2: Minor errors corrected, small changes
in introductio
An experiment on the adiabatic compressible turbulent boundary layer in adverse and favourable pressure gradients
A wind-tunnel model was developed to study the two-dimensional turbulent boundary layer in adverse and favourable pressure gradients with out the effects of streamwise surface curvature. Experiments were performed at Mach 4 with an adiabatic wall, and mean flow measurements within the boundary layer were obtained. The data, when viewed in the velocity transformation suggested by Van Driest, show good general agreement with the composite boundary-layer profile developed for the low-speed turbulent boundary layer. Moreover, the pressure gradient parameter suggested by Alber & Coats was found to correlate the data with low-speed results
All the timelike supersymmetric solutions of all ungauged d=4 supergravities
We determine the form of all timelike supersymmetric solutions of all N
greater or equal than 2, d=4 ungauged supergravities, for N less or equal than
4 coupled to vector supermultiplets, using the $Usp(n+1,n+1)-symmetric
formulation of Andrianopoli, D'Auria and Ferrara and the spinor-bilinears
method, while preserving the global symmetries of the theories all the way. As
previously conjectured in the literature, the supersymmetric solutions are
always associated to a truncation to an N=2 theory that may include
hypermultiplets, although fields which are eliminated in the truncations can
have non-trivial values, as is required by the preservation of the global
symmetry of the theories. The solutions are determined by a number of
independent functions, harmonic in transverse space, which is twice the number
of vector fields of the theory (n+1). The transverse space is flat if an only
if the would-be hyperscalars of the associated N=2 truncation are trivial.Comment: v3: Some changes in the introduction. Version to be published in JHE
Supersymmetric solutions of gauged five-dimensional supergravity with general matter couplings
We perform the characterization program for the supersymmetric configurations
and solutions of the , Supergravity Theory coupled to an
arbitrary number of vectors, tensors and hypermultiplets and with general
non-Abelian gaugins. By using the conditions yielded by the characterization
program, new exact supersymmetric solutions are found in the
model for the hyperscalars and with as the gauge group. The
solutions also content non-trivial vector and massive tensor fields, the latter
being charged under the U(1) sector of the gauge group and with selfdual
spatial components. These solutions are black holes with
near horizon geometry in the gauged version of the theory and for the ungauged
case we found naked singularities. We also analyze supersymmetric solutions
with only the scalars of the vector/tensor multiplets and the metric
as the non-trivial fields. We find that only in the null class the scalars
can be non-constant and for the case of constant we refine
the classification in terms of the contributions to the scalar potential.Comment: Minor changes in wording and some typos corrected. Version to appear
in Class. Quantum Grav. 38 page
Dissecting the oxidative folding of circular cystine knot miniproteins
Cyclotides are plant proteins with exceptional stability owing to the presence of a cyclic backbone and three disulfide bonds arranged in a cystine knot motif. Accordingly, they have been proposed as templates to stabilize bioactive epitopes in drug-design applications. The two main subfamilies, referred to as the Möbius and bracelet cyclotides, require dramatically different in vitro folding conditions to achieve the native fold. To determine the underlying elements that influence cyclotide folding, we examined the in vitro folding of a suite of hybrid cyclotides based on combination of the Möbius cyclotide kalata B1 and the bracelet cyclotide cycloviolacin O1. The folding pathways of the two cyclotide subfamilies were found to be different and influenced by specific residues within intercysteine loops 2 and 6. Two changes in these loops, a substitution in loop 2 and an addition in loop 6, enabled the folding of a cycloviolacin O1 analogue under conditions in which folding does not occur in vitro for the native peptide. A key intermediate contains a native-like hairpin structure that appears to be a nucleation locus early in the folding process. Overall, these mechanistic findings on the folding of cyclotides are potentially valuable for the design of new drug leads. Copyright Mary Ann Liebert, Inc
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