19,359 research outputs found
Efficient design of experiment for exponential regression models
In this paper robust and efficient designs are derived for several exponential decay models. These models are widely used in chemistry, pharmacokinetics or microbiology. We propose a maximin approach, which determines the optimal design such that a minimum of the D-efficiencies (taken over a certain range for the nonlinear parameters) becomes maximal. Analytic solutions are derived if optimization is performed in the class of minimal supported designs. In general the optimal designs with respect to the maximin criterion have to be determined numerically and some properties of these designs are also studied. --exponential regression model,D-optimal design,robust design,maximin design,pharmacokinetics,microbiology
Testing Relativity at High Energies Using Spaceborne Detectors
(ABRIDGED) The Gamma-ray Large Area Space Telescope (GLAST) will measure the
spectra of distant extragalactic sources of high energy gamma-rays. GLAST can
look for energy dependent propagation effects from such sources as a signal of
Lorentz invariance violation (LIV). Such sources should also exhibit high
energy spectral cutoffs from pair production interactions with low energy
photons. The properties of such cutoffs can also be used to test LIV. Detectors
to measure gamma-ray polarization can look for the depolarizing effect of
space-time birefingence predicted by loop quantum gravity. A spaceborne
detector array looking down on Earth to study extensive air showers produced by
ultrahigh energy cosmic rays can study their spectral properties and look for a
possible deviation from the predicted GZK effect as another signal of LIV.Comment: 14 pages, Text of invitated talk presented at the "From Quantum to
Cosmos: Fundamental Physics Studies from Space" meeting. More references
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The Effect of Disorder in an Orbitally Ordered Jahn-Teller Insulator
We study a two dimensional, two-band double-exchange model for
electrons coupled to Jahn-Teller distortions in the presence of quenched
disorder using a recently developed Monte-Carlo technique. In the absence of
disorder the half-filled system at low temperatures is an orbitally ordered
ferromagnetic insulator with a staggered pattern of Jahn-Teller distortions. We
examine the finite temperature transition to the orbitally disordered phase and
uncover a qualitative difference between the intermediate and strongly coupled
systems, including a thermally driven insulator to metal crossover in the
former case. Long range orbital order is suppressed in the presence of disorder
and the system displays a tendency towards metastable states consisting of
orbitally disordered stripe-like structures enclosing orbitally ordered
domains.Comment: 10 pages, 9 figure
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