974 research outputs found
Improved estimators for dispersion models with dispersion covariates
In this paper we discuss improved estimators for the regression and the
dispersion parameters in an extended class of dispersion models (J{\o}rgensen,
1996). This class extends the regular dispersion models by letting the
dispersion parameter vary throughout the observations, and contains the
dispersion models as particular case. General formulae for the second-order
bias are obtained explicitly in dispersion models with dispersion covariates,
which generalize previous results by Botter and Cordeiro (1998), Cordeiro and
McCullagh (1991), Cordeiro and Vasconcellos (1999), and Paula (1992). The
practical use of the formulae is that we can derive closed-form expressions for
the second-order biases of the maximum likelihood estimators of the regression
and dispersion parameters when the information matrix has a closed-form.
Various expressions for the second-order biases are given for special models.
The formulae have advantages for numerical purposes because they require only a
supplementary weighted linear regression. We also compare these bias-corrected
estimators with two different estimators which are also bias-free to the
second-order that are based on bootstrap methods. These estimators are compared
by simulation
Microsatellite markers for urochloa Humidicola (poaceae) and their transferability to other urochloa species
Urochloa humidicola is a warm-season grass commonly used as forage in the tropics and is recognized for its tolerance to seasonal flooding. This grass is an important forage species for the Cerrado and Amazon regions of Brazil. U. humidicola is a polyploid species with variable ploidy (6X-9X) and facultative apomixis with high phenotypic plasticity. However, this apomixis and ploidy, as well as the limited knowledge of the genetic basis of the germplasm collection, have constrained genetic breeding activities, yet microsatellite markers may enable a better understanding of the species' genetic composition. This study aimed to develop and characterize new polymorphic microsatellite molecular markers in U. humidicola and to evaluate their transferability to other Urochloa species. Findings: A set of microsatellite markers for U. humidicola was identified from two new enriched genomic DNA libraries: the first library was constructed from a single sexual genotype and the second from a pool of eight apomictic genotypes selected on the basis of previous results. Of the 114 loci developed, 72 primer pairs presented a good amplification product, and 64 were polymorphic among the 34 genotypes tested. The number of bands per simple sequence repeat (SSR) locus ranged from 1 to 29, with a mean of 9.6 bands per locus. The mean polymorphism information content (PIC) of all loci was 0.77, and the mean discrimination power (DP) was 0.87. STRUCTURE analysis revealed differences among U. humidicola accessions, hybrids, and other Urochloa accessions. The transferability of these microsatellites was evaluated in four species of the genus, U. brizantha, U. decumbens, U. ruziziensis, and U. dictyoneura, and the percentage of transferability ranged from 58.33% to 69.44% depending on the species. Conclusions: This work reports new polymorphic microsatellite markers for U. humidicola that can be used for breeding programs of this and other Urochloa species, including genetic linkage mapping, quantitative trait loci identification, and marker-assisted selection8
Photonic entanglement with accelerated light
Accelerated light has been demonstrated with laser light and diffraction.
Within the diffracting field it is possible to identify a portion that carries
most of the beam energy, which propagates in a curved trajectory as it would
have been accelerated by a gravitational field for instance. Here, we analyze
the effects of this kind of acceleration over the entanglement between twin
beams produced in spontaneous parametric down-conversion. Our results show that
acceleration does not affect entanglement significantly, under ideal
conditions. The optical scheme introduced can be useful in the understanding of
processes in the boundary between gravitation and quantum physics.Comment: 5 pages, 3 figure
Caracterização de frutos de ucuquizeiro.
O ucuquizeiro (Pouteria ucuqui), da família Sapotaceae, é uma árvore de porte alto, tronco reto e flor hermafrodita. O fruto, ucuqui, apresenta polpa doce, consumida in natura, porém, a população local consome preferencialmente na forma de mingau. A espécie é nativa da parte noroeste do Amazonas e muito comum ao longo dos rios da região do Alto Rio Negro, sendo pouco conhecida nas demais regiões do Estado. Considerando a importância de valorizar as frutas nativas da Amazônia, o ucuqui foi introduzido na coleção de fruteiras da Embrapa Amazônia Ocidental (código de acesso FN60) e consta atualmente com um único acesso, ainda em fase vegetativa. Sendo uma espécie pouco estudada, o objetivo deste trabalho foi caracterizar os frutos que deram origem ao acesso FN60
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