2,862 research outputs found
D-optimal designs via a cocktail algorithm
A fast new algorithm is proposed for numerical computation of (approximate)
D-optimal designs. This "cocktail algorithm" extends the well-known vertex
direction method (VDM; Fedorov 1972) and the multiplicative algorithm (Silvey,
Titterington and Torsney, 1978), and shares their simplicity and monotonic
convergence properties. Numerical examples show that the cocktail algorithm can
lead to dramatically improved speed, sometimes by orders of magnitude, relative
to either the multiplicative algorithm or the vertex exchange method (a variant
of VDM). Key to the improved speed is a new nearest neighbor exchange strategy,
which acts locally and complements the global effect of the multiplicative
algorithm. Possible extensions to related problems such as nonparametric
maximum likelihood estimation are mentioned.Comment: A number of changes after accounting for the referees' comments
including new examples in Section 4 and more detailed explanations throughou
The Hubbard model on a complete graph: Exact Analytical results
We derive the analytical expression of the ground state of the Hubbard model
with unconstrained hopping at half filling and for arbitrary lattice sites.Comment: Email:[email protected]
Ferrohydrodynamics: testing a new magnetization equation
A new magnetization equation recently derived from irreversible
thermodynamics is employed to the calculation of an increase of ferrofluid
viscosity in a magnetic field. Results of the calculations are compared with
those obtained on the basis of two well-known magnetization equations. One of
the two was obtained phenomenologically, another one was derived
microscopically from the Fokker-Planck equation. It is shown that the new
magnetization equation yields a quite satisfactory description of
magnetiviscosity in the entire region of magnetic field strength and the flow
vorticity. This equation turns out to be valid -- like the microscopically
derived equation but unlike the former phenomenological equation -- even far
from equilibrium, and so it should be recommended for further applications.Comment: 4 pages, 3 figures, Submitted to Phys. Rev.
Overscreening Diamagnetism in Cylindrical Superconductor-Normal Metal-Heterostructures
We study the linear diamagnetic response of a superconducting cylinder coated
by a normal-metal layer due to the proximity effect using the clean limit
quasiclassical Eilenberger equations. We compare the results for the
susceptibility with those for a planar geometry. Interestingly, for
the cylinder exhibits a stronger overscreening of the magnetic field, i.e., at
the interface to the superconductor it can be less than (-1/2) of the applied
field. Even for , the diamagnetism can be increased as compared to the
planar case, viz. the magnetic susceptibility becomes smaller than
-3/4. This behaviour can be explained by an intriguing spatial oscillation of
the magnetic field in the normal layer
Enhancing Approximations for Regular Reachability Analysis
This paper introduces two mechanisms for computing over-approximations of
sets of reachable states, with the aim of ensuring termination of state-space
exploration. The first mechanism consists in over-approximating the automata
representing reachable sets by merging some of their states with respect to
simple syntactic criteria, or a combination of such criteria. The second
approximation mechanism consists in manipulating an auxiliary automaton when
applying a transducer representing the transition relation to an automaton
encoding the initial states. In addition, for the second mechanism we propose a
new approach to refine the approximations depending on a property of interest.
The proposals are evaluated on examples of mutual exclusion protocols
Constructing Entanglement Witness Via Real Skew-Symmetric Operators
In this work, new types of EWs are introduced. They are constructed by using
real skew-symmetric operators defined on a single party subsystem of a
bipartite dxd system and a maximal entangled state in that system. A canonical
form for these witnesses is proposed which is called canonical EW in
corresponding to canonical real skew-symmetric operator. Also for each possible
partition of the canonical real skew-symmetric operator corresponding EW is
obtained. The method used for dxd case is extended to d1xd2 systems. It is
shown that there exist Cd2xd1 distinct possibilities to construct EWs for a
given d1xd2 Hilbert space. The optimality and nd-optimality problem is studied
for each type of EWs. In each step, a large class of quantum PPT states is
introduced. It is shown that among them there exist entangled PPT states which
are detected by the constructed witnesses. Also the idea of canonical EWs is
extended to obtain other EWs with greater PPT entanglement detection power.Comment: 40 page
Optical metrics and birefringence of anisotropic media
The material tensor of linear response in electrodynamics is constructed out
of products of two symmetric second rank tensor fields which in the
approximation of geometrical optics and for uniaxial symmetry reduce to
"optical" metrics, describing the phenomenon of birefringence. This
representation is interpreted in the context of an underlying internal
geometrical structure according to which the symmetric tensor fields are
vectorial elements of an associated two-dimensional space.Comment: 24 pages, accepted for publication in GR
Two different quasiparticle scattering rates in vortex line liquid phase of layered d-wave superconductors
We carry out a quantum mechanical analysis of the behavior of nodal
quasiparticles in the vortex line liquid phase of planar d-wave
superconductors. Applying a novel path integral technique we calculate a number
of experimentally relevant observables and demonstrate that in the low-field
regime the quasiparticle scattering rates deduced from photoemission and
thermal transport data can be markedly different from that extracted from
tunneling, specific heat, superfluid stiffness or spin-lattice relaxation time.Comment: Latex, 4 pages, no figure
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