4,206 research outputs found
Panel collapse and its applications
We describe a procedure called panel collapse for replacing a CAT(0) cube
complex by a "lower complexity" CAT(0) cube complex
whenever contains a codimension- hyperplane that is extremal in one
of the codimension- hyperplanes containing it. Although is
not in general a subcomplex of , it is a subspace consisting of a
subcomplex together with some cubes that sit inside "diagonally". The
hyperplanes of extend to hyperplanes of . Applying this
procedure, we prove: if a group acts cocompactly on a CAT(0) cube complex
, then there is a CAT(0) cube complex so that acts
cocompactly on and for each hyperplane of , the stabiliser
in of acts on essentially.
Using panel collapse, we obtain a new proof of Stallings's theorem on groups
with more than one end. As another illustrative example, we show that panel
collapse applies to the exotic cubulations of free groups constructed by Wise.
Next, we show that the CAT(0) cube complexes constructed by Cashen-Macura can
be collapsed to trees while preserving all of the necessary group actions. (It
also illustrates that our result applies to actions of some non-discrete
groups.) We also discuss possible applications to quasi-isometric rigidity for
certain classes of graphs of free groups with cyclic edge groups. Panel
collapse is also used in forthcoming work of the first-named author and Wilton
to study fixed-point sets of finite subgroups of on the
free splitting complex. Finally, we apply panel collapse to a conjecture of
Kropholler, obtaining a short proof under a natural extra hypothesis.Comment: Revised according to referee comments. This version accepted in
"Groups, Geometry, and Dynamics
Materials review for improved automotive gas turbine engine
The potential role of superalloys, refractory alloys, and ceramics in the hottest sections of engines operating with turbine inlet temperatures as high as 1370 C is examined. The convential superalloys, directionally solidified eutectics, oxide dispersion strenghened alloys, and tungsten fiber reinforced superalloys are reviewed and compared on the basis of maximum turbine blade temperature capability. Improved high temperature protective coatings and special fabrication techniques for these advanced alloys are discussed. Chromium, columbium, molybdenum, tantalum, and tungsten alloys are also reviewed. Molbdenum alloys are found to be the most suitable for mass produced turbine wheels. Various forms and fabrication processes for silicon nitride, silicon carbide, and SIALON's are investigated for use in highstress and medium stress high temperature environments
Static quark-antiquark potential and Dirac eigenvector correlators
We represent the Polyakov loop correlator as a spectral sum of correlators of
eigenvectors of the lattice Dirac operator. This spectral representation is
studied numerically using quenched SU(3) configurations below and above the
deconfinement temperature. We analyze whether the individual Dirac eigenvector
correlators differ in the confined and deconfined phases. The decay properties
of the normalized Dirac eigenvector correlators turn out to be essentially
identical in the two phases, but the amplitudes change. This change of the
amplitudes shifts the relative contributions of the individual Dirac
eigenvector correlators and is the driving mechanism for the transition from
the confining static potential into the deconfining one
New Gauge Invariant Formulation of the Chern-Simons Gauge Theory
A new gauge invariant formulation of the relativistic scalar field
interacting with Chern-Simons gauge fields is considered. This formulation is
consistent with the gauge fixed formulation. Furthermore we find that canonical
(Noether) Poincar\'e generators are not gauge invariant even on the constraints
surface and do not satisfy the (classical) Poincar\'e algebra. It is the
improved generators, constructed from the symmetric energy-momentum tensor,
which are (manifestly) gauge invariant and obey the classical Poincar\'e
algebra.Comment: Shortened, to appear as Papid Communication-PRD/Nov/9
Supersymmetry and the Chiral Schwinger Model
We have constructed the N=1/2 supersymmetric general Abelian model with
asymmetric chiral couplings. This leads to a N=1/2 supersymmetrization of the
Schwinger model. We show that the supersymmetric general model is plagued with
problems of infrared divergence. Only the supersymmetric chiral Schwinger model
is free from such problems and is dynamically equivalent to the chiral
Schwinger model because of the peculiar structure of the N=1/2 multiplets.Comment: one 9 pages Latex file, one ps file with one figur
Quantification of finite-temperature effects on adsorption geometries of -conjugated molecules
The adsorption structure of the molecular switch azobenzene on Ag(111) is
investigated by a combination of normal incidence x-ray standing waves and
dispersion-corrected density functional theory. The inclusion of non-local
collective substrate response (screening) in the dispersion correction improves
the description of dense monolayers of azobenzene, which exhibit a substantial
torsion of the molecule. Nevertheless, for a quantitative agreement with
experiment explicit consideration of the effect of vibrational mode
anharmonicity on the adsorption geometry is crucial.Comment: 12 pages, 3 figure
Operator Ordering Problem of the Nonrelativistic Chern-Simons Theory
The operator ordering problem due to the quantization or regularization
ambiguity in the Chern-Simons theory exists. However, we show that this can be
avoided if we require Galilei covariance of the nonrelativistic Abelian
Chern-Simons theory even at the quantum level for the extended sources. The
covariance can be recovered only by choosing some particular operator orderings
for the generators of the Galilei group depending on the quantization
ambiguities of the commutation relation. We show that the
desired ordering for the unusual prescription is not the same as the well-known
normal ordering but still satisfies all the necessary conditions. Furthermore,
we show that the equations of motion can be expressed in a similar form
regardless of the regularization ambiguity. This suggests that the different
regularization prescriptions do not change the physics. On the other hand, for
the case of point sources the regularization prescription is uniquely
determined, and only the orderings, which are equivalent to the usual one, are
allowed.Comment: 18 page
On the existence of Killing vector fields
In covariant metric theories of coupled gravity-matter systems the necessary
and sufficient conditions ensuring the existence of a Killing vector field are
investigated. It is shown that the symmetries of initial data sets are
preserved by the evolution of hyperbolic systems.Comment: 9 pages, no figure, to appear in Class. Quant. Gra
Anyonic physical observables and spin phase transition
The quantization of charged matter system coupled to Chern-Simons gauge
fields is analyzed in a covariant gauge fixing, and gauge invariant physical
anyon operators satisfying fractional statistics are constructed in a symmetric
phase, based on Dirac's recipe performed on QED. This method provides us a
definite way of identifying physical spectrums free from gauge ambiguity and
constructing physical anyon operators under a covariant gauge fixing. We then
analyze the statistical spin phase transition in a symmetry-broken phase and
show that the Higgs mechanism transmutes an anyon satisfying fractional
statistics into a canonical boson, a spin 0 Higgs boson or a topologically
massive photon.Comment: 14 pages, added references, a few improvement
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