22,857 research outputs found
Dynamical complexity of discrete time regulatory networks
Genetic regulatory networks are usually modeled by systems of coupled
differential equations and by finite state models, better known as logical
networks, are also used. In this paper we consider a class of models of
regulatory networks which present both discrete and continuous aspects. Our
models consist of a network of units, whose states are quantified by a
continuous real variable. The state of each unit in the network evolves
according to a contractive transformation chosen from a finite collection of
possible transformations, according to a rule which depends on the state of the
neighboring units. As a first approximation to the complete description of the
dynamics of this networks we focus on a global characteristic, the dynamical
complexity, related to the proliferation of distinguishable temporal behaviors.
In this work we give explicit conditions under which explicit relations between
the topological structure of the regulatory network, and the growth rate of the
dynamical complexity can be established. We illustrate our results by means of
some biologically motivated examples.Comment: 28 pages, 4 figure
Exact Lyapunov Exponent for Infinite Products of Random Matrices
In this work, we give a rigorous explicit formula for the Lyapunov exponent
for some binary infinite products of random real matrices. All
these products are constructed using only two types of matrices, and ,
which are chosen according to a stochastic process. The matrix is singular,
namely its determinant is zero. This formula is derived by using a particular
decomposition for the matrix , which allows us to write the Lyapunov
exponent as a sum of convergent series. Finally, we show with an example that
the Lyapunov exponent is a discontinuous function of the given parameter.Comment: 1 pages, CPT-93/P.2974,late
A cultura da goiaba.
bitstream/item/128279/1/PLANTAR-Goiaba-ed02-2010.pdf2. ed. rev. e ampl.Autores: Adriane Luciana da Silva, Alessandra Monteiro S. Mendes, Anderson Ramos de Oliveira, Beatriz Aguiar Jordão Paranhos, Carlos Antonio Fernades Santos, Davi José Silva, Débora Costa Bastos, Diógenes da Cruz Batista, Flávia Rabelo Barbosa, José Eudes de Morais Oliveira, José Lincoln Pinheiro de Araújo, José Maria Pinto, José Mauro da Cunha e Castro, José Monteiro Soares, LuÃs Henrique Bassoi, Luiz Gonzaga Neto, Magna Soelma Bezerra de Moura, Marcelo Calgaro, Maria Auxiliadora Coêlho de Lima, Mirtes Freitas Lima, Rebert Coelho Correia, Vanderlise Giongo Petrere. Projeto Minibibliotecas
On Matrix Superpotential and Three-Component Normal Modes
We consider the supersymmetric quantum mechanics (SUSY QM) with three-
component normal modes for the Bogomol'nyi-Prasad-Sommerfield (BPS) states. An
explicit form of the SUSY QM matrix superpotential is presented and the
corresponding three-component bosonic zero-mode eigenfunction is investigated.Comment: 17 pages, no figure. Paper accepted for publication in Journal of
Physics A: Mathematical and Theoretica
Survey and significance of filamentous fungi from tap water
Fungi in drinking water are involved in the production of tastes and odours in water. Health problems are possible,
originating from mycotoxins, animal pathogens and allergies. This report concerns the surveillance of mesophilic fungi
in tap water and assessment of their potential for causing problems. The methods for the determination of the
filamentous fungi (ff) were filtering, swabbing and baiting. Tap water, half-strength corn meal, neopeptone–glucose
rose Bengal aureomycin (NGRBA) and oomycete selective agars for the enumeration of colony forming units (cfu)
were used. Samples were taken consecutively over 16 months. Filtration and NGRBA gave the highest ff counts. A
total of 340 taxa were isolated. There appeared to be a negative correlation between bacterial and yeast (b/y) and ff
counts. Highest counts were found in winter months for ff and in the warmer months for b/y. Penicillium (40.6%) and
Acremonium (38.8%) were the most frequently isolated ff. There was a difference in the pattern of isolation of the key
taxa with season: penicillia predominated in early summer and Acremonium in winter. P. expansum was isolated in high
numbers in May 2004. This species is associated with the production of the mycotoxin patulin and the odour secondary
metabolite geosmin. P. brevicompactum was detected throughout the sampling period and is known to produce the
immunosuppressive drug mycophenolic acid. Acremonium is associated with ocentol production which is responsible
for bad tastes and flavours. The remaining taxa were Phialophora sp. (4.1%), Cladosporium sp. (3.5%), Rhizopus
stolonifer (2.9%), Chaetomium sp. (0.6%), Alternaria sp. (0.3%), Aspergillus sp. (0.3%), mycelia sterilia (2.6%) and
unidentified (6.2%). It is emphasised that few Aspergillus and no Fusarium strains were isolated. Rhizopus stolonifer
was obtained. However, none of the fungi isolated at mesophilic temperature used could be described as being involved
with pathogenicity per se.Fundação para a Ciência e a Tecnologia (FCT) - grant FRH/BPD/14923/2004.European Union (EU) - Fifth Framework Programme ‘‘Energy,
environment and sustainable development programme’’
Mycological examination and biofilm formation in drinking water
This study reports the presence of filamentous fungi (ff) in drinking water
including biofilms. Ff are not studied ufficiently in drinking water. Ff were highest in winter and had an indirect relation with other microorganisms.
Pathogenic fungi were not observed at the mesophilic temperatures used.
Penicillium expansum and P. brevicompactum were observed which may affect biofilms by mycotoxin production. FISH and calcofluor methods indicated presumptive ff in biofilms in water distribution systems.European Union within the Fifth Framework Programme
Fundação para a Ciência e a Tecnologia (FCT
Clustering, Angular Size and Dark Energy
The influence of dark matter inhomogeneities on the angular size-redshift
test is investigated for a large class of flat cosmological models driven by
dark energy plus a cold dark matter component (XCDM model). The results are
presented in two steps. First, the mass inhomogeneities are modeled by a
generalized Zeldovich-Kantowski-Dyer-Roeder (ZKDR) distance which is
characterized by a smoothness parameter and a power index ,
and, second, we provide a statistical analysis to angular size data for a large
sample of milliarcsecond compact radio sources. As a general result, we have
found that the parameter is totally unconstrained by this sample of
angular diameter data.Comment: 9 pages, 7 figures, accepted in Physical Review
Physical properties of single-crystalline fibers of the colossal-magnetoresistance manganite La0.7Ca0.3MnO3
We have grown high-quality single crystals of the colossal-magnetoresistance
(CMR) material La0.7Ca0.3MnO3 by using the laser heated pedestal growth (LHPG)
method. Samples were grown as fibers of different diameters, and with lengths
of the order of centimeters. Their composition and structure were verified
through X-ray diffraction, scanning electron microcopy with EDX (Energy
Dispersive X-ray Analysis) and by Rietveld analysis. The quality of the
crystalline fibers was confirmed by Laue and EBSD (Electron Backscatter
Diffraction) patterns. Rocking curves performed along the fiber axis revealed a
half-height width of 0.073 degrees. The CMR behavior was confirmed by
electrical resistivity and magnetization measurements as a function of
temperature.Comment: 11 pages (including 3 figures); to appear in Appl. Phys. Let
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