336 research outputs found
Numerical Study of Wave Propagation in Uniaxially Anisotropic Lorentzian Backward Wave Slabs
The propagation and refraction of a cylindrical wave created by a line
current through a slab of backward wave medium, also called left-handed medium,
is numerically studied with FDTD. The slab is assumed to be uniaxially
anisotropic. Several sets of constitutive parameters are considered and
comparisons with theoretical results are made. Electric field distributions are
studied inside and behind the slab. It is found that the shape of the
wavefronts and the regions of real and complex wave vectors are in agreement
with theoretical results.Comment: 6 pages, figure
Density Functional Theory of Multicomponent Quantum Dots
Quantum dots with conduction electrons or holes originating from several
bands are considered. We assume the particles are confined in a harmonic
potential and assume the electrons (or holes) belonging to different bands to
be different types of fermions with isotropic effective masses. The density
functional method with the local density approximation is used. The increased
number of internal (Kohn-Sham) states leads to a generalisation of Hund's first
rule at high densities. At low densitites the formation of Wigner molecules is
favored by the increased internal freedom.Comment: 11 pages, 5 figure
3d physics and the electroweak phase transition: a framework for lattice Monte Carlo analysis
We discuss a framework relying on both perturbative and non-perturbative
lattice computations which will be able to reliably determine the parameters of
the EW phase transition. A motivation for the use of 3d effective theory in the
lattice simulations, rather than the complete 4d one, is provided. We introduce
and compute on the 2-loop level a number of gauge-invariant order parameters --
condensates, which can be measured with high accuracy in MC simulations. The
relation between MSbar and lattice condensates is found, together with the
relation between lattice couplings and continuum parameters (the constant
physics curves). These relations are exact in the continuum limit.Comment: 50 pages, uuencoded compressed postscript fil
Magnetism in one-dimensional quantum dot arrays
We employ the density functional Kohn-Sham method in the local spin-density
approximation to study the electronic structure and magnetism of quasi
one-dimensional periodic arrays of few-electron quantum dots. At small values
of the lattice constant, the single dots overlap, forming a non-magnetic
quantum wire with nearly homogenous density. As the confinement perpendicular
to the wire is increased, i.e. as the wire is squeezed to become more
one-dimensional, it undergoes a spin-Peierls transition. Magnetism sets in as
the quantum dots are placed further apart. It is determined by the electronic
shell filling of the individual quantum dots. At larger values of the lattice
constant, the band structure for odd numbers of electrons per dot indicates
that the array could support spin-polarized transport and therefore act as a
spin filter.Comment: 11 pages, 6 figure
Magnetic phases of one-dimensional lattices with 2 to 4 fermions per site
We study the spectral and magnetic properties of one-dimensional lattices
filled with 2 to 4 fermions (with spin 1/2) per lattice site. We use a
generalized Hubbard model that takes account all interactions on a lattice
site, and solve the many-particle problem by exact diagonalization. We find an
intriguing magnetic phase diagram which includes ferromagnetism, spin-one
Heisenberg antiferromagnetism, and orbital antiferromagnetism.Comment: 8 pages, 6 figure
3d SU(N) + adjoint Higgs theory and finite temperature QCD
We study to what extent the three-dimensional SU(N)+adjoint Higgs theory can
be used as an effective theory for finite temperature SU(N) gauge theory, with
N=2,3. The parameters of the 3d theory are computed in 2-loop perturbation
theory in terms of T/Lambda_MSbar,N,N_f. The perturbative effective potential
of the 3d theory is computed to two loops for N=2. While the Z(N) symmetry
probably driving the 4d confinement-deconfinement phase transition (for N_f=0)
is not explicit in the effective Lagrangian, it is partly reinstated by
radiative effects in the 3d theory. Lattice simulations in the 3d theory are
carried out for N=2, and the static screening masses relevant for the
high-temperature phase of the 4d theory are measured. In particular, we measure
non-perturbatively the O(g^2 T) correction to the Debye screening mass. We find
that non-perturbative effects are much larger in the SU(2) + adjoint Higgs
theory than in the SU(2) + fundamental Higgs theory.Comment: 30 pages, 9 figure
Requirements on unique identifiers for managing product lifecycle information: comparison of alternative approaches
One-variable word equations in linear time
In this paper we consider word equations with one variable (and arbitrary
many appearances of it). A recent technique of recompression, which is
applicable to general word equations, is shown to be suitable also in this
case. While in general case it is non-deterministic, it determinises in case of
one variable and the obtained running time is O(n + #_X log n), where #_X is
the number of appearances of the variable in the equation. This matches the
previously-best algorithm due to D\k{a}browski and Plandowski. Then, using a
couple of heuristics as well as more detailed time analysis the running time is
lowered to O(n) in RAM model. Unfortunately no new properties of solutions are
shown.Comment: submitted to a journal, general overhaul over the previous versio
Mixtures of Bose Gases Confined in a Ring Potential
The rotational properties of a mixture of two distinguishable Bose gases that
are confined in a ring potential provide novel physical effects that we
demonstrate in this study. Persistent currents are shown to be stable for a
range of the population imbalance between the two components at low angular
momentum. At higher values of the angular momentum, even small admixtures of a
second species of atoms make the persistent currents highly fragile.Comment: Final form of the published article, 4 pages, 2 figure
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