18,503 research outputs found
Existence and uniqueness of relative incidence estimates in case-series analysis
Case-series analysis is used to estimate relative incidences of clinical events in defined time intervals after vaccination compared to a control period. It has advantages, in terms of both a reduction in data collection effort, because it uses only data on cases, and a reduction in the resultant variances of estimates, due to individuals being self-controlled. The existence and uniqueness of relative incidence estimates in case-series analysis are investigated. For the relative incidence of a clinical event, a simple condition for existence and uniqueness of the estimate of the parameter vector in a case-series model is established. An algorithm is developed to examine the established condition, which provides a clue for remedy when the condition for existence and uniqueness is not satisfied
Asymptotic behavior of the growth-fragmentation equation with bounded fragmentation rate
We are interested in the large time behavior of the solutions to the
growth-fragmentation equation. We work in the space of integrable functions
weighted with the principal dual eigenfunction of the growth-fragmentation
operator. This space is the largest one in which we can expect convergence to
the steady size distribution. Although this convergence is known to occur under
fairly general conditions on the coefficients of the equation, we prove that it
does not happen uniformly with respect to the initial data when the
fragmentation rate in bounded. First we get the result for fragmentation
kernels which do not form arbitrarily small fragments by taking advantage of
the Dyson-Phillips series. Then we extend it to general kernels by using the
notion of quasi-compactness and the fact that it is a topological invariant
Understanding the bulk electronic structure of Ca1-xSrxVO3
We investigate the electronic structure of Ca1-xSrxVO3 using careful
state-of-the-art experiments and calculations. Photoemission spectra using
synchrotron radiation reveal a hitherto unnoticed polarization dependence of
the photoemission matrix elements for the surface component leading to a
substantial suppression of its intensity. Bulk spectra extracted with the help
of experimentally determined electron escape depth and estimated suppression of
surface contributions resolve outstanding puzzles concerning the electronic
structure in Ca1-xSrxVO3.Comment: 4 pages including 3 figure
Three-dimensional quasi-periodic shifted Green function throughout the spectrum--including Wood anomalies
This work presents an efficient method for evaluation of wave scattering by
doubly periodic diffraction gratings at or near "Wood anomaly frequencies". At
these frequencies, one or more grazing Rayleigh waves exist, and the lattice
sum for the quasi-periodic Green function ceases to exist. We present a
modification of this sum by adding two types of terms to it. The first type
adds linear combinations of "shifted" Green functions, ensuring that the
spatial singularities introduced by these terms are located below the grating
and therefore outside of the physical domain. With suitable coefficient choices
these terms annihilate the growing contributions in the original lattice sum
and yield algebraic convergence. Convergence of arbitrarily high order can be
obtained by including sufficiently many shifts. The second type of added terms
are quasi-periodic plane wave solutions of the Helmholtz equation which
reinstate certain necessary grazing modes without leading to blow-up at Wood
anomalies. Using the new quasi-periodic Green function, we establish, for the
first time, that the Dirichlet problem of scattering by a smooth doubly
periodic scattering surface at a Wood frequency is uniquely solvable. We also
present an efficient high-order numerical method based on the this new Green
function for the problem of scattering by doubly periodic three-dimensional
surfaces at and around Wood frequencies. We believe this is the first solver in
existence that is applicable to Wood-frequency doubly periodic scattering
problems. We demonstrate the proposed approach by means of applications to
problems of acoustic scattering by doubly periodic gratings at various
frequencies, including frequencies away from, at, and near Wood anomalies
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