3,447 research outputs found
Apparent Horizons with Nontrivial Topology and the Hyperhoop Conjecture in Six-Dimensional Space-Times
We investigate the validity of the hyperhoop conjecture, which claims to
determine a necessary and sufficient condition for the formation of black hole
horizons in higher-dimensional space-times. Here we consider momentarily
static, conformally flat initial data sets each describing a gravitational
field of uniform massive k-sphere sources, for k=1,2, on the five-dimensional
Cauchy surface. The numerical result shows the validity of the hyperhoop
conjecture for a wide range of model parameters. We also confirm for the first
time the existence of an apparent horizon homeomorphism to S**2 x S**2 or S**1
x S**3, which is a higher-dimensional generalization of the black ring.Comment: 17 pages, 12 figures. to appear in Phys. Rev.
Symmetry breaking and other phenomena in the optimization of eigenvalues for composite membranes
We consider the following eigenvalue optimization problem: Given a bounded
domain and numbers , ,
find a subset of area for which the first Dirichlet
eigenvalue of the operator is as small as possible.
We prove existence of solutions and investigate their qualitative properties.
For example, we show that for some symmetric domains (thin annuli and dumbbells
with narrow handle) optimal solutions must possess fewer symmetries than
; on the other hand, for convex reflection symmetries are
preserved.
Also, we present numerical results and formulate some conjectures suggested
by them.Comment: 24 pages; 3 figures (as separate files); (shortened previous
version); to appear in Comm. Math. Phy
Disorder-induced topological change of the superconducting gap structure in iron pnictides
In superconductors with unconventional pairing mechanisms, the energy gap in
the excitation spectrum often has nodes, which allow quasiparticle excitations
at low energies. In many cases, e.g. -wave cuprate superconductors, the
position and topology of nodes are imposed by the symmetry, and thus the
presence of gapless excitations is protected against disorder. Here we report
on the observation of distinct changes in the gap structure of iron-pnictide
superconductors with increasing impurity scattering. By the successive
introduction of nonmagnetic point defects into BaFe(AsP)
crystals via electron irradiation, we find from the low-temperature penetration
depth measurements that the nodal state changes to a nodeless state with fully
gapped excitations. Moreover, under further irradiation the gapped state
evolves into another gapless state, providing bulk evidence of unconventional
sign-changing -wave superconductivity. This demonstrates that the topology
of the superconducting gap can be controlled by disorder, which is a strikingly
unique feature of iron pnictides.Comment: 5 pages, 4 figure
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Contribution of biomass and biofuel emissions to trace gas distributions in Asia during the TRACE-P experiment
Metal-insulator transition in the In/Si(111) surface
The metal-insulator transition observed in the In/Si(111)-4x1 reconstruction
is studied by means of ab initio calculations of a simplified model of the
surface. Different surface bands are identified and classified according to
their origin and their response to several structural distortions. We support
the, recently proposed [New J. of Phys. 7 (2005) 100], combination of a shear
and a Peierls distortions as the origin of the metal-insulator transition. Our
results also seem to favor an electronic driving force for the transition.Comment: Presented in the 23 European Conference in Surface Science, Berlin,
September 2005. Submitted to Surface Science (proceedings of the conference)
in August 200
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