1,498,634 research outputs found
Hermitian structures on six dimensional nilmanifolds
Let (J,g) be a Hermitian structure on a compact nilmanifold M with invariant
complex structure J and compatible metric g, which is not required to be
invariant. We give classifications of 6-dimensional nilmanifolds M admitting
strong K\"ahler with torsion, balanced or locally conformal K\"ahler structures
(J,g).Comment: LaTeX, 24 pages, 1 figur
A canonical structure on the tangent bundle of a pseudo- or para-K\"ahler manifold
It is a classical fact that the cotangent bundle T^* \M of a differentiable
manifold \M enjoys a canonical symplectic form . If
(\M,\j,g,\omega) is a pseudo-K\"ahler or para-K\"ahler -dimensional
manifold, we prove that the tangent bundle T\M also enjoys a natural
pseudo-K\"ahler or para-K\"ahler structure (\J,\G,\Omega), where is
the pull-back by of and \G is a pseudo-Riemannian metric with
neutral signature . We investigate the curvature properties of the
pair (\J,\G) and prove that: \G is scalar-flat, is not Einstein unless
is flat, has nonpositive (resp.\ nonnegative) Ricci curvature if and only if
has nonpositive (resp.\ nonnegative) Ricci curvature as well, and is
locally conformally flat if and only if and has constant curvature,
or and is flat. We also check that (i) the holomorphic sectional
curvature of (\J,\G) is not constant unless is flat, and (ii) in
case, that \G is never anti-self-dual, unless conformally flat.Comment: Clarified the statements on the cotangent bundle. Corrected various
typo
Twisted modules and co-invariants for commutative vertex algebras of jet schemes
Let Z⊂k be an affine scheme over \C and \J Z its jet scheme. It is well-known that \mathbb{C}[\J Z], the coordinate ring of \J Z, has the structure of a commutative vertex algebra. This paper develops the orbifold theory for \mathbb{C}[\J Z]. A finite-order linear automorphism g of Z acts by vertex algebra automorphisms on \mathbb{C}[\J Z]. We show that \mathbb{C}[\J^g Z], where \J^g Z is the scheme of g--twisted jets has the structure of a g-twisted \mathbb{C}[\J Z] module. We consider spaces of orbifold coinvariants valued in the modules \mathbb{C}[\J^g Z] on orbicurves [Y/G], with Y a smooth projective curve and G a finite group, and show that these are isomorphic to ℂ[ZG]
Technological development of cylindrical and flat shaped high energy density capacitors
Cylindrical wound metallized film capacitors rated 2 micron F 500 VDC that had an energy density greater than 0.3 J/g, and flat flexible metallized film capacitors rated at 2 micron F 500 VDC that had an energy density greater than 0.1 J/g were developed. Polysulfone, polycarbonate, and polyvinylidene fluoride (PVF2) were investigated as dielectrics for the cylindrical units. PVF2 in 6.0 micron m thickness was employed in the final components of both types. Capacitance and dissipation factor measurements were made over the range 25 C to 100 C, and 10 Hz to 10 kHz. No pre-life-test burning was performed, and six of ten cylindrical units survived a 2500 hour AC plus DC lift test. Three of the four failures were infant mortality. All but two of the flat components survived 400 hours. Finished energy densities were 0.104 J/g at 500 V and 0.200 J/g at 700 V, the energy density being limited by the availability of thin PVF2 films
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