6,129 research outputs found
Optimal alarm systems for count processes
In many phenomena described by stochastic processes, the implementation of an alarm system becomes fundamental to predict the occurrence of future events. In this work we develop an alarm system to predict whether a count process will upcross a certain level and give an alarm whenever the upcrossing level is predicted. We consider count models with parameters being functions of covariates of interest and varying on time. This article presents classical and Bayesian methodology for producing optimal alarm systems. Both methodologies are illustrated and their performance compared through a simulation study. The work finishes with an empirical application to a set of data concerning the number of sunspot on the surface of the sun
Probing tiny convective cores with the acoustic modes of lowest degree
Solar-like oscillations are expected to be excited in stars of up to about
1.6 solar masses. Most of these stars will have convective cores during their
Main-sequence evolution. At the edges of these convective cores there is a
rapid variation in the sound speed which influences the frequencies of acoustic
oscillations. In this paper we build on earlier work by Cunha and Metcalfe, to
investigate further the impact that these rapid structural variations have on
different p-mode frequency combinations, involving modes of low degree. In
particular, we adopt a different expression to describe the sound speed
variation at the edge of the core, which we show to reproduce more closely the
profiles derived from the equilibrium models. We analyse the impact of this
change on the frequency perturbation derived for radial modes. Moreover, we
consider three different small frequency separations involving, respectively,
modes of degree l = 0, 1, 2, 3; l = 0, 1; and l = 0, 2, and show that they are
all significantly affected by the sharp sound speed variation at the edge of
the core. In particular, we confirm that the frequency derivative of the
diagnostic tool that combines modes of degree up to 3 can potentially be used
to infer directly the amplitude of the relative sound speed variation at the
edge of the core. Concerning the other two diagnostic tools, we show that at
high frequencies they can be up to a few microhertzs smaller than what would be
expected in the absence of the rapid structural variation at the edge of the
core. Also, we show that the absolute values of their frequency derivatives are
significantly increased, in a manner that is strongly dependent on stellar age.Comment: 7 pages. submitted to A&
Use of dialkyldithiocarbamato complexes of bismuth(III) for the preparation of nano- and microsized Bi2S3 particles and the X-ray crystal structures of [Bi{S2CN(CH3)(C6H13)}(3)] and [Bi{S2CN(CH3)(C6H13)}(3)(C12H8N2)]
A range of bismuth(III) dithiocarbamato complexes were prepared and characterized. The
X-ray crystal structures of the compounds [Bi{S2CN(CH3)(C6H13)}3] (1) and [Bi{S2CN(CH3)-
(C6H13)}3(C12H8N2)] (2) are reported. The preparation of Bi2S3 particulates using a wet
chemical method and involving the thermalysis of Bi(III) dialkyldithiocarbamato complexes
is described. The influence of several experimental parameters on the optical and
morphological properties of the Bi2S3 powders was investigated. Nanosized Bi2S3 colloids
were obtained having long-term stability and showing a blue shift on the optical band edge;
the presence of particles exhibiting quantum size effects is discussed. Morphological welldefined Bi2S3 particles were obtained in which the fiber-type morphology is prevalent.FCT - POCTI/1999/CTM/ 3545
The Quantum Algebraic Structure of the Twisted XXZ Chain
We consider the Quantum Inverse Scattering Method with a new R-matrix
depending on two parameters and . We find that the underlying algebraic
structure is the two-parameter deformed algebra enlarged by
introducing an element belonging to the centre. The corresponding Hamiltonian
describes the spin-1/2 XXZ model with twisted periodic boundary conditions.Comment: LateX file, 9 pages, Minor changes (including authors` names in the
hep-th heading
Integer-valued autoregressive processes with periodic structure
In this paper the periodic integer-valued autoregressive model of order one with period T, driven by a periodic sequence of independent Poisson-distributed random variables, is studied in some detail. Basic probabilistic and statistical properties of this model are discussed. Moreover, parameter estimation is also addressed. Specifically, the methods of estimation under analysis are the method of moments, least squares-type and likelihood-based ones. Their performance is compared through a simulation study. (C) 2009 Elsevier B.V. All rights reserved
Prognostic Factors of Tympanoplasty Type I in Pediatric Population – 4 Years Series of Dona Estefânia Hospital (HDE) of Centro Hospitalar Lisboa CentraL (CHLC –EPE)
Objetivos: Identificação de fatores de prognóstico em crianças submetidas a timpanoplastia tipo I.
Materiais e métodos: Estudo retrospetivo baseado na análise de todos os processos clÃnicos de crianças atá aos 15 anos de idade, submetidas a timpanoplastia tipo I de Portmann durante um perÃodo de 4 anos.
Resultados: Das 260 timpanoplastias realizadas neste perÃodo no serviço foram incluÃdos no estudo apenas 109 crianças. Das timpanoplastias realizadas, obteve-se sucesso cirúrgico em 68.8%, não se tendo identificado fatores de mau prognóstico cirúrgico com significância estatÃstica.
Conclusões: As timpanoplastias tipo I em crianças são um procedimento válido e com elevada taxa de sucesso, não tendo sido identificado qualquer fator de mau prognóstico cirúrgico com significado estatÃstico.info:eu-repo/semantics/publishedVersio
Spinor-helicity and the algebraic classification of higher-dimensional spacetimes
The spinor-helicity formalism is an essential technique of the amplitudes community. We draw on this method to construct a scheme for classifying higher-dimensional spacetimes in the style of the 4D Petrov classification and the Newman–Penrose formalism. We focus on the 5D case for concreteness. Our spinorial scheme naturally reproduces the full structure previously seen in both the CMPP and de Smet classifications, and resolves longstanding questions concerning the relationship between the two classifications
P Wave Meson Spectrum in a Relativistic Model with Instanton Induced Interaction
On the basis of the phenomenological relativistic harmonic models for quarks
we have obtained the masses of P wave mesons. The full Hamiltonian used in the
investigation has Lorentz scalar + vector confinement potential, along with one
gluon exchange potential (OGEP) and the instanton-induced quark-antiquark
interaction (III). A good agreement is obtained with the experimental masses.
The respective role of III and OGEP for the determination of the meson masses
is discussed.Comment: Corrected typo
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