38,473 research outputs found
Estratificação para a inclusão: enxergar as diferenças para uma efetiva rede de laboratórios.
A análise de conformidade da qualidade dos produtos alimentícios em face da legislação em vigor demanda conhecimento e deve também ser acompanhada de garantias dos resultados das análises laboratoriais. Amparados por normas nacionais e internacionais, os laboratórios de uma determinada rede credenciada podem, entre si, reduzir e controlar a geração de resultados inconsistentes ou contraditórios, ou não conformes, segundo a necessária padronização ? de meios e instrumentos, em um ou mais escopos do seu leque de análises. Este trabalho, fundamentado em alguns dos diversos fatores que permeiam a atual busca pela qualidade dos resultados analíticos nos laboratórios, contextualiza as exigências dos vários órgãos de credenciamento de laboratórios existentes no Brasil e no mundo. A abordagem restringe-se aos laboratórios que controlam determinados produtos de origem vegetal, mas, guardadas as proporções necessárias, pode ser ampliada para outros laboratórios
The Likelihood Ratio Test and Full Bayesian Significance Test under small sample sizes for contingency tables
Hypothesis testing in contingency tables is usually based on asymptotic
results, thereby restricting its proper use to large samples. To study these
tests in small samples, we consider the likelihood ratio test and define an
accurate index, the P-value, for the celebrated hypotheses of homogeneity,
independence, and Hardy-Weinberg equilibrium. The aim is to understand the use
of the asymptotic results of the frequentist Likelihood Ratio Test and the
Bayesian FBST -- Full Bayesian Significance Test -- under small-sample
scenarios. The proposed exact P-value is used as a benchmark to understand the
other indices. We perform analysis in different scenarios, considering
different sample sizes and different table dimensions. The exact Fisher test
for tables that drastically reduces the sample space is also
discussed. The main message of this paper is that all indices have very similar
behavior, so the tests based on asymptotic results are very good to be used in
any circumstance, even with small sample sizes
Quantum Effects in the Spacetime of a Magnetic Flux Cosmic String
In this work we compute the vacuum expectation values of the energy-momentum
tensor and the average value of a massive, charged scalar field in the presence
of a magnetic flux cosmic string for both zero- and finite-temperature cases.Comment: To appear in the Int. Journal of Modern Phys. A (special issue).
Proceedings of the Second International Londrina Winter School on
Mathematical Methods in Physics, Londrina, Brazil, August 200
Temperature effect on (2+1) experimental Kardar-Parisi-Zhang growth
We report on the effect of substrate temperature (T) on both local structure
and long-wavelength fluctuations of polycrystalline CdTe thin films deposited
on Si(001). A strong T-dependent mound evolution is observed and explained in
terms of the energy barrier to inter-grain diffusion at grain boundaries, as
corroborated by Monte Carlo simulations. This leads to transitions from
uncorrelated growth to a crossover from random-to-correlated growth and
transient anomalous scaling as T increases. Due to these finite-time effects,
we were not able to determine the universality class of the system through the
critical exponents. Nevertheless, we demonstrate that this can be circumvented
by analyzing height, roughness and maximal height distributions, which allow us
to prove that CdTe grows asymptotically according to the Kardar-Parisi-Zhang
(KPZ) equation in a broad range of T. More important, one finds positive
(negative) velocity excess in the growth at low (high) T, indicating that it is
possible to control the KPZ non-linearity by adjusting the temperature.Comment: 6 pages, 5 figure
The interplay of university and industry through the FP5 network
To improve the quality of life in a modern society it is essential to reduce
the distance between basic research and applications, whose crucial roles in
shaping today's society prompt us to seek their understanding. Existing studies
on this subject, however, have neglected the network character of the
interaction between university and industry. Here we use state-of-the-art
network theory methods to analyze this interplay in the so-called Framework
Programme--an initiative which sets out the priorities for the European Union's
research and technological development. In particular we study in the 5th
Framework Programme (FP5) the role played by companies and scientific
institutions and how they contribute to enhance the relationship between
research and industry. Our approach provides quantitative evidence that while
firms are size hierarchically organized, universities and research
organizations keep the network from falling into pieces, paving the way for an
effective knowledge transfer.Comment: 21 pages (including Appendix), 8 figures. Published online at
http://stacks.iop.org/1367-2630/9/18
Plasmon polaritons in photonic superlattices containing a left-handed material
We analyze one-dimensional photonic superlattices which alternate layers of
air and a left-handed material. We assume Drude-type dispersive responses for
the dielectric permittivity and magnetic permeability of the left-handed
material. Maxwell's equations and the transfer-matrix technique are used to
derive the dispersion relation for the propagation of obliquely incident
optical fields. The photonic dispersion indicates that the growth-direction
component of the electric (or magnetic) field leads to the propagation of
electric (or magnetic) plasmon polaritons, for either TE or TM configurations.
Furthermore, we show that if the plasma frequency is chosen within the photonic
zeroth-order bandgap, the coupling of light with plasmons
weakens considerably. As light propagation is forbidden in that particular
frequency region, the plasmon-polariton mode reduces to a pure plasmon mode.Comment: 4 pages, 4 figure
Avaliação da mistura formulada de alachlor atrazine no controle de plantas daninhas na cultura do milho (Zea mays L.).
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