36 research outputs found
Estimation in a growth study with irregular measurement times
Between 1982 and 1988 a growth study was carried out at the Division of Pediatric Oncology of the University Hospital of Groningen. A special feature of the project was that sample sizes are small and that ages at entry may be very different. In addition the intended design was not fully complied with. This paper highlights some aspects of the statistical analysis which is based on (1) reference scores, (2) statistical procedures allowing for an irregular pattern of measurement times caused by missing data and shifted measurement times
A Brownian particle in a microscopic periodic potential
We study a model for a massive test particle in a microscopic periodic
potential and interacting with a reservoir of light particles. In the regime
considered, the fluctuations in the test particle's momentum resulting from
collisions typically outweigh the shifts in momentum generated by the periodic
force, and so the force is effectively a perturbative contribution. The
mathematical starting point is an idealized reduced dynamics for the test
particle given by a linear Boltzmann equation. In the limit that the mass ratio
of a single reservoir particle to the test particle tends to zero, we show that
there is convergence to the Ornstein-Uhlenbeck process under the standard
normalizations for the test particle variables. Our analysis is primarily
directed towards bounding the perturbative effect of the periodic potential on
the particle's momentum.Comment: 60 pages. We reorganized the article and made a few simplifications
of the conten
Metal-Kondo insulating transitions and transport in one dimension
We study two different metal-insulating transitions possibly occurring in
one-dimensional Kondo lattices. First, we show how doping the pure Kondo
lattice model in the strong-coupling limit, results in a Pokrovsky-Talapov
transition. This produces a conducting state with a charge susceptibility
diverging as the inverse of the doping, that seems in agreement with numerical
datas. Second, in the weak-coupling region, Kondo insulating transitions arise
due to the consequent renormalization of the backward Kondo scattering. Here,
the interplay between Kondo effect and electron-electron interactions gives
rise to significant phenomena in transport, in the high-temperature delocalized
(ballistic) regime. For repulsive interactions, as a perfect signature of Kondo
localization, the conductivity is found to decrease monotonically with
temperature. When interactions become attractive, spin fluctuations in the
electron (Luttinger-type) liquid are suddenly lowered. The latter is less
localized by magnetic impurities than for the repulsive counterpart, and as a
result a large jump in the Drude weight and a maximum in the conductivity arise
in the entrance of the Kondo insulating phase. These can be viewed as remnants
of s-wave superconductivity arising for attractive enough interactions.
Comparisons with transport in the single impurity model are also performed. We
finally discuss the case of randomly distributed magnetic defects, and the
applications on persistent currents of mesoscopic rings.Comment: 21 pages, two columns, 5 figures and 1 table; Final version: To
appear in Physical Review
Note on Randomized Filtered Experiments in Presence of Nuisance Parameters
Note on randomized filtered experiments in presence of nuisance parameter