14,628 research outputs found
A nonlinear hyperbolic Maxwell system using measure-valued functions
We consider a modified antenna's problem with power-type constitutive laws. This consists in a new nonlinear hyperbolic system that extends a Duvaut-Lions model. Using the Galerkin approximation, properties of the natural functional spaces, and exploring the - duality, we prove the existence of solutions, in a generalized sense, passing to the limit in a family of approximated problems and using measure-valued functions.
In this process the difficulties in obtaining the necessary a priori estimates for the solutions of the finite-dimensional problems are overcome through the use of bases with special properties related to the model.The research of the authors was partially supported by the Research Centre of Mathematics of the University of Minho through the FCT Pluriannual Funding Program
Luttinger liquid superlattices: realization of gapless insulating phases
We investigate Luttinger Liquid superlattices, a periodic structure composed
of two kinds of one-dimensional systems of interacting electrons. We calculate
several properties of the low-energy sector: the effective charge and spin
velocities, the compressibility, various correlation functions, the Landauer
conductance and the Drude weight. The low-energy properties are subsumed into
effective parameters, much like homogeneous one-dimensional systems. A generic
result is the weighted average nature of these parameters, in proportion to the
spatial extent of the underlying subunits, pointing to the possibility of
``engineered'' structures. As a specific realization, we consider a
one-dimensional Hubbard superlattice, which consists of a periodic arrangement
of two long Hubbard chains with different coupling constants and different
hopping amplitudes. This system exhibits a rich phase diagram with several
phases, both metallic and insulating. We have found that gapless insulating
phases are present over a wide range of parameters.Comment: 16 pages, 15 figures, RevTeX
Muonium spectrum beyond the nonrelativistic limit
A generalization of the Gell-Mann-Low theorem is applied to the
antimuon-electron system. The bound state spectrum is extracted numerically. As
a result, fine and hyperfine structure are reproduced correctly near the
nonrelativistic limit (and for arbitrary masses). We compare the spectrum for
the relativistic value alpha = 0.3 with corresponding calculations in
light-front quantization.Comment: 6 pages, LaTeX, 2 figures, uses aipxfm.sty. Talk delivered at the XI
Mexican Workshop on Particles and Fields, Tuxtla Gutierrez, Mexico, November
7-12, 2007; to be published in the proceeding
Neutrino Flavor States and the Quantum Theory of Neutrino Oscillations
The standard theory of neutrino oscillations is reviewed, highlighting the
main assumptions: the definition of the flavor states, the equal-momentum
assumption and the time = distance assumption. It is shown that the standard
flavor states are correct approximations of the states that describe neutrinos
in oscillation experiments. The equal-momentum assumption is shown to be
unnecessary for the derivation of the oscillation probability. The time =
distance assumption derives from the wave-packet character of the propagating
neutrinos. We present a simple quantum-mechanical wave-packet model which
allows us to describe the coherence and localization of neutrino oscillations.Comment: 16 pages; talk presented at the XI Mexican Workshop on Particles and
Fields, 7-12 November 2007, Tuxtla Gutierrez, Chiapas, Mexic
Indigenous yeasts in Madeira wines: impact on the physicochemical and sensorial characterization
O Vinho Madeira é produzido pela fermentação espontânea através de leveduras
indígenas presentes em uvas e adegas. A crescente exigência dos consumidores leva à
necessidade de uniformizar o processo de vinificação. O presente trabalho visa avaliar
a composição química de vinhos Madeira produzidos em diferentes adegas e com uvas
colhidas de diferentes localizações (sul e norte). Depois, isolar e identificar as leveduras
indígenas de mostos da casta Tinta Negra de diferentes localizações e adegas, e avaliar
o impacto do uso de 5 leveduras indígenas não-Saccharomyces selecionadas
(Hanseniaspora uvarum, Starmerella bacillaris, Pichia terricola, Pichia fermentans e
Pichia kluyveri) na produção de vinho Madeira, como culturas puras iniciadoras, na
composição química, perfil volátil e características sensoriais. Os resultados mostraram
variabilibidade na composição química nas diferentes adegas, e baixa reprodutibilidade
entre lotes da mesma adega. Uvas da região sul apresentaram níveis mais elevados de
açúcares (196.32 g/L), polifenóis totais (270.18 mg GAE/L) e potencial antioxidante
(128.48 mg Trolox/L). Os estudos da microflora de leveduas indígenas envolvidas na
produção de vinho Madeira permitiram identificar 11 espécies nas adegas
(Hanseniaspora uvarum, Starmerella bacillaris, Pichia kluyveri, Pichia fermentans,
Saccharomyces cerevisiae, Torulaspora delbrueckii, Candida apicola, Cystobasidium
minutum, Pichia terricola, Cystobasidium slooffiae, e Wicheramomyces anolalus) e 6
espécies nas uvas (Hanseniaspora uvarum, Starmerella bacillaris, Pichia kluyveri,
Pichia fermentans, Saccharomyces cerevisiae, and Hanseniaspora opuntiae). Os vinhos
produzidos por Pichia spp. demonstraram níveis mais elevados de polifenóis totais
(367.68 mg GAE/L), enquanto os vinhos produzidos por Starmerella bacillaris
demonstraram maior acidez (9.23 g/L) e menor conteúdo de voláteis (11.26%). O vinho
produzido por Pichia kluyveri destacou-se na concentração total de volatéis (24.50%),
dos quais 77.35% são estéres, obtendo 37% de preferência dos consumidores, com notas
intensas de caramelo e especiarias. Portanto, Pichia kluyveri demonstrou potencial para
ser utilizada como cultura iniciadora de fermentação na produção de vinho Madeira.Madeira wines are produced by spontaneous fermentation with indigenous
yeasts from grapes and wineries. Increasing demands from consumers have led to the
need to standardize the winemaking process. This work aims, first, to evaluate the
chemical composition of Madeira wines produced by different wineries and with grapes
from vineyards located in the south and north regions. Then, to isolate and identify
indigenous yeasts in Tinta Negra grape musts from different vineyard locations and
wineries and evaluate the impact of using five selected indigenous non-Saccharomyces
yeasts (Hanseniaspora uvarum, Starmerella bacillaris, Pichia terricola, Pichia
fermentans, and Pichia kluyveri), as a starter culture, in the chemical composition,
volatile profile, and sensory characteristics of Madeira wines. Results showed
variability in the chemical composition of samples from different wineries and a lack
of reproducibility between batches from the same winery. Grapes from southern
vineyard locations presented higher levels of sugars (196.32 g/L), total phenolic content
(270.18 mg GAE/L), and antioxidant potential (128.48 mg Trolox/L). Studies about the
indigenous yeasts involved in Madeira wine production identified 11 yeast species from
wineries (Hanseniaspora uvarum, Starmerella bacillaris, Pichia kluyveri, Pichia
fermentans, Saccharomyces cerevisiae, Torulaspora delbrueckii, Candida apicola,
Cystobasidium minutum, Pichia terricola, Cystobasidium slooffiae, and
Wicheramomyces anolalus) and 6 yeast species from vineyards (Hanseniaspora
uvarum, Starmerella bacillaris, Pichia kluyveri, Pichia fermentans, Saccharomyces
cerevisiae, and Hanseniaspora opuntiae). Wines produced by Pichia spp. showed
higher total phenolic content (367.68 mg GAE/L), while wines produced by Starmerella
bacillaris showed higher acidity (9.23g/L) and lower volatile content (11.26%). Wines
produced by Pichia kluyveri revealed higher total volatile content (24.50%), of which
77.35% were esters, and a score of 37% in a preference test by regular wine consumers,
described with intense caramel and spicy notes. Therefore, Pichia kluyveri showed
potential to be used as a starter culture in the production of Madeira wines
Coherent nu-N scattering and the search for physics beyond the standard model
We focus in future proposals to measure coherent neutrino-nuclei scattering
and we show that such kind of experiments are very sensitive to nonstandard
neutrino interactions with quarks. First in a model independent parametrization
and then we focused in particular models such as leptoquarks and models with
extra neutral gauge bosons and with R-parity breaking interactions. We show
that in all these three different types of new physics it is possible to obtain
competitive bounds to those of future collider experiments. For the particular
case of leptoquarks we found that the expected sensitivity to the coupling and
mass for most of the future experimental setups is quite better than the
current constraints.Comment: 6 pages, 1 Figure, Talk given at 11th Mexican Workshop on Particles
and Fields 2007, Tuxtla Gutierrez, Mexico, 7-12 Nov 200
Zoneamento, similaridade e diversidade do estrato herbáceo-arbustivo de duas veredas no Distrito Federal
Dissertação (mestrado)—Universidade de Brasília, Instituto de Ciências Biológicas, Programa de Pós-Graduação em Botânica, 2012.A vereda é uma fitofisionomia do bioma Cerrado predominantemente herbáceo-arbustiva, situada em cabeceiras de drenagem e rica em biodiversidade, tendo o buriti como elemento principal. Ocorre em solo saturado durante maior parte do ano, onde a água escoa lentamente. As veredas podem ocorrer em vales com declividade acentuada se o local for geologicamente recente. O grau de deposição de sedimentos é também variável, bem como a vegetação circundante, que é mais lenhosa em veredas de estágio sucessional avançado, com poucos buritis jovens, por causa de mudanças na drenagem. As variações acima, a textura do solo, a profundidade do lençol freático e diferenças edáficas, relacionadas aos nutrientes do solo e matéria orgânica, afetam o zoneamento (definido como a separação florística em zonas da
borda, meio e fundo dentro da vereda), além da similaridade e diversidade de espécies vegetais entre veredas diferentes. Foram estudadas duas veredas localizadas no Distrito Federal (Brasil). As duas áreas distam pouco menos de 30 km uma da outra. A primeira, uma
vereda na Floresta Nacional de Brasília (FLONA), ocorre em declive acentuado, sendo alagada no fundo (brejo permanente). A segunda, situada na Estação Ecológica do Jardim Botânico de Brasília (EEJBB), ocorre em declive suave. Uma parte da área na EEJBB é coberta por Trembleya parviflora, onde ocorre estrato herbáceo homogêneo e foi denominada
“trembleial”. Além disto, a EEJBB apresenta campos com murunduns dispersos pela maior
parte da área, resultando em relevo distinto. As duas áreas são, portanto, diferentes em suas características. Os objetivos deste trabalho foram verificar a diferença de diversidade e a
similaridade florística do estrato herbáceo-arbustivo destas duas veredas no Distrito Federal e verificar se, dentro das mesmas, existe zoneamento florístico. Os resultados foram relacionados com as características já citadas, que presumivelmente afetam o zoneamento, a
diferença de diversidade e a similaridade de espécies. As áreas foram amostradas na estação chuvosa. A amostragem da vegetação foi feita pelo método de intersecção na linha. A
diferença de diversidade foi avaliada pelo teste t de Hutchingson e a similaridade pelo índice de Chao-Sørensen. A exploração das variáveis ambientais foi feita pela análise de componentes principais e os dados de solo coletados em campo segundo procedimentos padrões. A detecção do zoneamento florístico foi feita pela análise de cluster, atribuindo-se
linhas amostrais a priori às zonas da borda meio e fundo nas duas veredas (e também zona do “trembleial” na vereda EEJBB). Na vereda EEJBB (onde houve zoneamento) uma análise de
escalonamento multidimensional não métrico complementou a análise, testando a distribuição espacial de espécies mais abundantes a fim de relacioná-las com as variáveis ambientais menos redundantes e o zoneamento. Também na vereda EEJBB, as espécies mais abundantes foram classificadas por intervalos de profundidade do lençol freático onde ocorrem e comparadas com a ocorrência das mesmas na Estação Ecológica de Águas Emendadas. Correlações de Pearson para profundidade do lençol freático, percentagem de argila,
capacidade de troca catiônica e matéria orgânica foram testadas para espécies com valor de importância maior que 8,5 na EEJBB e comparadas com a outra vereda. As diversidades foram diferentes (H’= 3,93 e 3,02; p<0,01, t=13,50) e tiveram alta similaridade (Chao- Ørensen=65,36%± 0,00). A vereda menos diversa foi a EEJBB, devido à homogeneidade florística do trembleial, dominado por Lagenocarpus rigidus, também devido à ausência do
brejo permanente e variações no microrelevo causado pelos campos de murunduns, que favorecem a ocorrência de espécies adaptadas a lençol freático mais profundo. A profundidade do lençol freático, em combinação com as variáveis capacidade de troca catiônica, alumínio e outras foram responsáveis pelo zoneamento e diferenças na abundância de espécies na vereda EEJBB. A variável matéria orgânica, tomada isoladamente, teve as maiores correlações de Pearson com cobertura absoluta das espécies e as correlações foram geralmente maiores na primeira área. As linhas amostrais das duas veredas formaram dois
grupos distintos na análise de cluster, demonstrando que as duas veredas eram florísticamente diferentes, o que confirmou o resultado de similaridade e também provou que não houve correspondência de zoneamento ambiental entre as zonas das duas veredas. As duas únicas zonas formadas na análise de cluster (trembleial e zona do fundo na vereda EEJBB) tiveram seus próprios padrões de composição de espécies. Houve semelhança das classes de
profundidade do lençol freático em que as espécies ocorreram com as mesmas classes em
outra vereda no Distrito Federal (Estação Ecológica de Águas Emendadas). A análise de componentes principais mostrou que as duas veredas foram distintas com relação às variáveis ambientais. As diferenças ambientais entre as veredas explicaram a diferença de diversidade entre as duas e, o nível de similaridade. Entretanto, as diferenças entre as duas veredas
também podem ser devidas ao estágio sucessional. São necessários estudos semelhantes para uma compreensão profunda do tema. _______________________________________________________________________________________ OVERVIEWThe palm swamp is a phytophisiognomy of the Cerrado biome, predominantly herbaceous
and shruby, located in headwater drainages and rich in biodiversity, having the mauritia palm as characteristic species. They occur in soil that is waterlogged during most of the year, where the water flows slowly, and in steep sloped valleys if geologically recent swamps. The degree of siltation is variable, as is the surrounding vegetation and topography, which is woodier when in advanced sucessional stage and has few young specimens of mauritia palms, due to changes in drainage. The above variations plus soil texture, water table depth and edaphic characteristics, related to soil nutrients, affect zonation in the swamp (defined as floristic separation in border, middle and center zones), besides species similarity and diversity between the palm swamps. Two palm swamps were studied in Brazil’s Federal District (DF). The study areas are slightly less than 30 km apart. The first, a palm swamp in Brasilia’s National Forest (FLONA), occurs in a steep slope and has a permanent marsh in the
middle. The second area, located in the Ecological Station of Brasilia’s Botanical Garden (EEJBB), has only a slight slope. Part of EEJBB is covered by Trembleya parviflora, where the herb-subshrub layer is homogeneous and was thus named “trembleial”. Besides all
differences, the EEJBB swamp has murundum mounds through most of the area, resulting in a particular topography. The two areas are, therefore, different in their environmental characteristics. The goals were to verify the differences in floristic diversity and similarity of
the herb-subshrub layer of the two swamps and to test for the occurrence of floristic zonation. The results were confronted with the described characteristics that presumably affect zonation, diversity difference and similarity. Both areas were sampled during the rainy season. Vegetation sampling was carried through the line interception method. Difference in
diversity was tested with Hutchingson’s t test and similarity with the Chao-Sørensen index. Analysis of environmental variables was carried through a principal component analysis and soil data collected based on standard procedures. Detection of floristic zonation was made with a cluster analysis, sorting border, middle and center lines in advance (besides the “trembleial” zone in the EEJBB swamp) in both swamps. In the EEJBB swamp (where zonation was confirmed) a non metric multidimensional scaling analysis supplemented the results, testing the distribution of the most abundant species in relation to the environmental
characteristics. Also in EEJBB, the most abundant species were sorted by water table depth intervals and compared with the abundance of species that occurred in another palm swamp in the region (Águas Emendadas Ecological Station). Pearson correlations for clay percentage, cation exchange capacity, water table depth and soil organic matter were tested for species with IV (relative frequency plus relative cover) higher than 8,5 in the EEJBB and compared with the other swamp. The diversities were different (H’= 3,93 and 3,02; p<0,01, t=13,50) and had a high similarity (Chao-SØrensen=65,36%± 0,00). The least diverse swamp was EEJBB, due to the homogeneous “trembleial”, dominated by Lagenocarpus rigidus, also
e permanent marsh and due to the murundun mounds that favored the adapted to a deeper water table. Water table depth explained most of the two swamps, if combined with cation exchange capacity and other
um. Soil organic matter, taken in isolation, was responsible by the tions values with absolute species cover and the correlations were st area. The sample lines of the two swamps formed distinct groups in howing that they were different. This also confirmed the similarity there was no correspondence of floristic zones between the two palm
s formed in the cluster analysis (trembleial and the center zone in the eir own pattern of species composition, this was also confirmed by the sional scaling. These same species are related, inside each line/zone, edaphic characteristics such as cation exchange capacity, thus the
ic and related to environmental characteristics. There are similarities pth classes the species occurred with the same classes in another palm l District (Águas Emendadas Ecological Station). The principal wed that the two swamps are different according to the environmental ifferences between the areas were small and the overall differences of between the swamps possibly explain the diversity differences and the owever, there is a possibility that different sucessional stages are
erences. More studies are needed to a profound comprehension of the subject
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