1,907 research outputs found
A Comment on "Brans-Dicke Cosmology with a scalar field potential"
We show that a recent letter claiming to present exact cosmological solutions
in Brans-Dicke theory actually uses a flawed set of equations as the starting
point for their analysis. The results presented in the letter are therefore not
valid.Comment: 2 pages, no figures. To appear in Europhysics Letter
A simple and controlled single electron transistor based on doping modulation in silicon nanowires
A simple and highly reproducible single electron transistor (SET) has been
fabricated using gated silicon nanowires. The structure is a
metal-oxide-semiconductor field-effect transistor made on silicon-on-insulator
thin films. The channel of the transistor is the Coulomb island at low
temperature. Two silicon nitride spacers deposited on each side of the gate
create a modulation of doping along the nanowire that creates tunnel barriers.
Such barriers are fixed and controlled, like in metallic SETs. The period of
the Coulomb oscillations is set by the gate capacitance of the transistor and
therefore controlled by lithography. The source and drain capacitances have
also been characterized. This design could be used to build more complex SET
devices.Comment: to be published in Applied Physics Letter
Generalized squeezed-coherent states of the finite one-dimensional oscillator and matrix multi-orthogonality
A set of generalized squeezed-coherent states for the finite u(2) oscillator
is obtained. These states are given as linear combinations of the mode
eigenstates with amplitudes determined by matrix elements of exponentials in
the su(2) generators. These matrix elements are given in the (N+1)-dimensional
basis of the finite oscillator eigenstates and are seen to involve 3x3 matrix
multi-orthogonal polynomials Q_n(k) in a discrete variable k which have the
Krawtchouk and vector-orthogonal polynomials as their building blocks. The
algebraic setting allows for the characterization of these polynomials and the
computation of mean values in the squeezed-coherent states. In the limit where
N goes to infinity and the discrete oscillator approaches the standard harmonic
oscillator, the polynomials tend to 2x2 matrix orthogonal polynomials and the
squeezed-coherent states tend to those of the standard oscillator.Comment: 18 pages, 1 figur
A model for the continuous q-ultraspherical polynomials
We provide an algebraic interpretation for two classes of continuous
-polynomials. Rogers' continuous -Hermite polynomials and continuous
-ultraspherical polynomials are shown to realize, respectively, bases for
representation spaces of the -Heisenberg algebra and a -deformation of
the Euclidean algebra in these dimensions. A generating function for the
continuous -Hermite polynomials and a -analog of the Fourier-Gegenbauer
expansion are naturally obtained from these models
The Dynamics of Sustained Reentry in a Loop Model with Discrete Gap Junction Resistance
Dynamics of reentry are studied in a one dimensional loop of model cardiac
cells with discrete intercellular gap junction resistance (). Each cell is
represented by a continuous cable with ionic current given by a modified
Beeler-Reuter formulation. For below a limiting value, propagation is found
to change from period-1 to quasi-periodic () at a critical loop length
() that decreases with . Quasi-periodic reentry exists from
to a minimum length () that is also shortening with .
The decrease of is not a simple scaling, but the bifurcation can
still be predicted from the slope of the restitution curve giving the duration
of the action potential as a function of the diastolic interval. However, the
shape of the restitution curve changes with .Comment: 6 pages, 7 figure
An Algebraic Model for the Multiple Meixner Polynomials of the First Kind
An interpretation of the multiple Meixner polynomials of the first kind is
provided through an infinite Lie algebra realized in terms of the creation and
annihilation operators of a set of independent oscillators. The model is used
to derive properties of these orthogonal polynomials
The design, construction and evaluation of sprint footwear to investigate increased sprint shoe bending stiffness on sprint performance and dynamics
The design, construction and evaluation of sprint footwear to investigate increased sprint shoe bending stiffness on sprint performance and dynamic
The algebra of dual -1 Hahn polynomials and the Clebsch-Gordan problem of sl_{-1}(2)
The algebra H of the dual -1 Hahn polynomials is derived and shown to arise
in the Clebsch-Gordan problem of sl_{-1}(2). The dual -1 Hahn polynomials are
the bispectral polynomials of a discrete argument obtained from a q-> -1 limit
of the dual q-Hahn polynomials. The Hopf algebra sl_{-1}(2) has four generators
including an involution, it is also a q-> -1 limit of the quantum algebra
sl_{q}(2) and furthermore, the dynamical algebra of the parabose oscillator.
The algebra H, a two-parameter generalization of u(2) with an involution as
additional generator, is first derived from the recurrence relation of the -1
Hahn polynomials. It is then shown that H can be realized in terms of the
generators of two added sl_{-1}(2) algebras, so that the Clebsch-Gordan
coefficients of sl_{-1}(2) are dual -1 Hahn polynomials. An irreducible
representation of H involving five-diagonal matrices and connected to the
difference equation of the dual -1 Hahn polynomials is constructed.Comment: 15 pages, Some minor changes from version #
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