348 research outputs found
Surface potential at a ferroelectric grain due to asymmetric screening of depolarization fields
Nonlinear screening of electric depolarization fields, generated by a stripe
domain structure in a ferroelectric grain of a polycrystalline material, is
studied within a semiconductor model of ferroelectrics. It is shown that the
maximum strength of local depolarization fields is rather determined by the
electronic band gap than by the spontaneous polarization magnitude.
Furthermore, field screening due to electronic band bending and due to presence
of intrinsic defects leads to asymmetric space charge regions near the grain
boundary, which produce an effective dipole layer at the surface of the grain.
This results in the formation of a potential difference between the grain
surface and its interior of the order of 1 V, which can be of either sign
depending on defect transition levels and concentrations. Exemplary acceptor
doping of BaTiO3 is shown to allow tuning of the said surface potential in the
region between 0.1 and 1.3 V.Comment: 14 pages, 11 figures, submitted to J. Appl. Phy
Phase Space Reduction for Star-Products: An Explicit Construction for CP^n
We derive a closed formula for a star-product on complex projective space and
on the domain using a completely elementary
construction: Starting from the standard star-product of Wick type on and performing a quantum analogue of Marsden-Weinstein
reduction, we can give an easy algebraic description of this star-product.
Moreover, going over to a modified star-product on ,
obtained by an equivalence transformation, this description can be even further
simplified, allowing the explicit computation of a closed formula for the
star-product on \CP^n which can easily transferred to the domain
.Comment: LaTeX, 17 page
Time dependent transformations in deformation quantization
We study the action of time dependent canonical and coordinate
transformations in phase space quantum mechanics. We extend the covariant
formulation of the theory by providing a formalism that is fully invariant
under both standard and time dependent coordinate transformations. This result
considerably enlarges the set of possible phase space representations of
quantum mechanics and makes it possible to construct a causal representation
for the distributional sector of Wigner quantum mechanics.Comment: 16 pages, to appear in the J. Math. Phy
Parent form for higher spin fields on anti-de Sitter space
We construct a first order parent field theory for free higher spin gauge
fields on constant curvature spaces. As in the previously considered flat case,
both Fronsdal's and Vasiliev's unfolded formulations can be reached by two
different straightforward reductions. The parent theory itself is formulated
using a higher dimensional embedding space and turns out to be geometrically
extremely transparent and free of the intricacies of both of its reductions.Comment: 39 pages, LaTeX; misprints corrected, references adde
Generalized Weyl-Wigner map and Vey quantum mechanics
The Weyl-Wigner map yields the entire structure of Moyal quantum mechanics
directly from the standard operator formulation. The covariant generalization
of Moyal theory, also known as Vey quantum mechanics, was presented in the
literature many years ago. However, a derivation of the formalism directly from
standard operator quantum mechanics, clarifying the relation between the two
formulations is still missing. In this paper we present a covariant
generalization of the Weyl order prescription and of the Weyl-Wigner map and
use them to derive Vey quantum mechanics directly from the standard operator
formulation. The procedure displays some interesting features: it yields all
the key ingredients and provides a more straightforward interpretation of the
Vey theory including a direct implementation of unitary operator
transformations as phase space coordinate transformations in the Vey idiom.
These features are illustrated through a simple example.Comment: 15 pages, LaTe
The Weyl bundle as a differentiable manifold
Construction of an infinite dimensional differentiable manifold not modelled on any Banach space is proposed. Definition, metric
and differential structures of a Weyl algebra and a Weyl algebra bundle are
presented. Continuity of the -product in the Tichonov topology is
proved. Construction of the -product of the Fedosov type in terms of theory
of connection in a fibre bundle is explained.Comment: 31 pages; revised version - some typoes have been eliminated,
notation has been simplifie
A Path Integral Approach To Noncommutative Superspace
A path integral formula for the associative star-product of two superfields
is proposed. It is a generalization of the Kontsevich-Cattaneo-Felder's formula
for the star-product of functions of bosonic coordinates. The associativity of
the star-product imposes certain conditions on the background of our sigma
model. For generic background the action is not supersymmetric. The
supersymmetry invariance of the action constrains the background and leads to a
simple formula for the star-product.Comment: Latex 13 pages. v2: references and footnotes adde
Comparison of Recombinant Human Haptocorrin Expressed in Human Embryonic Kidney Cells and Native Haptocorrin
Haptocorrin (HC) is a circulating corrinoid binding protein with unclear function. In contrast to transcobalamin, the other transport protein in blood, HC is heavily glycosylated and binds a variety of cobalamin (Cbl) analogues. HC is present not only in blood but also in various secretions like milk, tears and saliva. No recombinant form of HC has been described so far. We report the expression of recombinant human HC (rhHC) in human embryonic kidney cells. We purified the protein with a yield of 6 mg (90 nmol) per litre of cell culture supernatant. The isolated rhHC behaved as native HC concerning its spectral properties and ability to recognize both Cbl and its baseless analogue cobinamide. Similar to native HC isolated from blood, rhHC bound to the asialoglycoprotein receptor only after removal of terminal sialic acid residues by treatment with neuraminidase. Interestingly, rhHC, that compared to native HC contains four excessive amino acids (…LVPR) at the C-terminus, showed subtle changes in the binding kinetics of Cbl, cobinamide and the fluorescent Cbl conjugate CBC. The recombinant protein has properties very similar to native HC and although showing slightly different ligand binding kinetics, rhHC is valuable for further biochemical and structural studies
Stargenfunctions, generally parametrized systems and a causal formulation of phase space quantum mechanics
We address the deformation quantization of generally parametrized systems
displaying a natural time variable. The purpose of this exercise is twofold:
first, to illustrate through a pedagogical example the potential of quantum
phase space methods in the context of constrained systems and particularly of
generally covariant systems. Second, to show that a causal representation for
quantum phase space quasidistributions can be easily achieved through general
parametrization. This result is succinctly discussed.Comment: 19 pages, to appear in J. Math. Phy
On Gammelgaard's formula for a star product with separation of variables
We show that Gammelgaard's formula expressing a star product with separation
of variables on a pseudo-Kaehler manifold in terms of directed graphs without
cycles is equivalent to an inversion formula for an operator on a formal Fock
space. We prove this inversion formula directly and thus offer an alternative
approach to Gammelgaard's formula which gives more insight into the question
why the directed graphs in his formula have no cycles.Comment: 29 pages, changes made in the last two section
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