1,998 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
An infinite family of superintegrable Hamiltonians with reflection in the plane
We introduce a new infinite class of superintegrable quantum systems in the
plane. Their Hamiltonians involve reflection operators. The associated
Schr\"odinger equations admit separation of variables in polar coordinates and
are exactly solvable. The angular part of the wave function is expressed in
terms of little -1 Jacobi polynomials. The spectra exhibit "accidental"
degeneracies. The superintegrability of the model is proved using the
recurrence relation approach. The (higher-order) constants of motion are
constructed and the structure equations of the symmetry algebra obtained.Comment: 19 page
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