16,999 research outputs found
The three-dimensional noncommutative Gross-Neveu model
This work is dedicated to the study of the noncommutative Gross-Neveu model.
As it is known, in the canonical Weyl-Moyal approach the model is inconsistent,
basically due to the separation of the amplitudes into planar and nonplanar
parts. We prove that if instead a coherent basis representation is used, the
model becomes renormalizable and free of the aforementioned difficulty. We also
show that, although the coherent states procedure breaks Lorentz symmetry in
odd dimensions, in the Gross-Neveu model this breaking can be kept under
control by assuming the noncommutativity parameters to be small enough. We also
make some remarks on some ordering prescriptions used in the literature.Comment: 10 pages, IOP article style; v3: revised version, accepted for
publication in J. Phys.
T-Duality in 2-D Integrable Models
The non-conformal analog of abelian T-duality transformations relating pairs
of axial and vector integrable models from the non abelian affine Toda family
is constructed and studied in detail.Comment: 14 pages, Latex, v.2 misprints corrected, reference added, to appear
in J. Phys.
Mercado de leite: uma análise dos preços recebidos pelos produtores nos últimos anos.
A dinâmica do setor leiteiro nos últimos anos, principalmente a partir dos anos 90, tem sido motivo de vários estudos. Entre outras constatações, esses estudos apontam para o crescimento da oferta de leite, decorrente de expressivas taxas de crescimento na produção interna, via um contínuo incremento da produtividade, e também das substanciais importações que foram realizadas. Em relação ao preço do leite, observa-se uma queda persistente ao longo das últimas três décadas, documentada por Barros e Rizzieri (2001), Yamaguchi (2001) e Gomes, S. (2002). O objetivo deste trabalho é descrever e discutir o comportamento do preço recebido pelos produtores de leite após a implantação do Plano Real, cobrindo o período compreendido entre janeiro de 1995 até fevereiro de 2004
On the aether-like Lorentz-breaking actions
We demonstrate the generation of the CPT-even, aether-like Lorentz-breaking
actions for the scalar and electromagnetic fields via their appropriate
Lorentz-breaking coupling to spinor fields in three, four and five space-time
dimensions. Besides, we show that the aether-like terms for the spinor field
also can be generated as a consequence of the same couplings. Also we discuss
the dispersion relations in the theories with aether-like Lorentz-breaking
terms and find the tree-level effective (Breit) potential for fermion
scattering and the one-loop effective potential corresponding to the action of
the scalar field.Comment: 18 pages, version accepted to Physical Review
Algumas características da oferta do leite.
O objetivo do trabalho é estimar a curva de oferta de leite, utilizando dados do período 1970-2001. O modelo estimado possibilita examinar a principal conclusão das comissões de inquérito de algumas assembléias estaduais, pela qual a queda anormal observada no preço do leite, na entressafra de 2001, foi atribuída ao poder de oligopsônio das firmas que processam o leite. Ainda mais, os consumidores não se beneficiaram dos preços baixos em nível de produtor. Assim, a margem de comercialização sofreu, por aquela visão, considerável acréscimo.Na publicação: Eliseu Alves
The Link between General Relativity and Shape Dynamics
We show that one can construct two equivalent gauge theories from a linking
theory and give a general construction principle for linking theories which we
use to construct a linking theory that proves the equivalence of General
Relativity and Shape Dynamics, a theory with fixed foliation but spatial
conformal invariance. This streamlines the rather complicated construction of
this equivalence performed previously. We use this streamlined argument to
extend the result to General Relativity with asymptotically flat boundary
conditions. The improved understanding of linking theories naturally leads to
the Lagrangian formulation of Shape Dynamics, which allows us to partially
relate the degrees of freedom.Comment: 19 pages, LaTeX, no figure
Structural properties of crumpled cream layers
The cream layer is a complex heterogeneous material of biological origin
which forms spontaneously at the air-milk interface. Here, it is studied the
crumpling of a single cream layer packing under its own weight at room
temperature in three-dimensional space. The structure obtained in these
circumstances has low volume fraction and anomalous fractal dimensions. Direct
means and noninvasive NMR imaging technique are used to investigate the
internal and external structure of these systems.Comment: 9 pages, 4 figures, accepted in J. Phys. D: Appl. Phy
Fate of conjugated natural and synthetic steroid estrogens in crude sewage and activated sludge batch studies
This document is the unedited author's version of a Submitted Work that was subsequently accepted for publication in Environmental Science & Technology, copyright © American Chemical Society after peer review. To access the final edited and published work see http://pubs.acs.org/doi/abs/10.1021/es801952h.Steroids are excreted from the human body in the conjugated form but are present in sewage influent and effluent as the free steroid, the major source of estrogenic activity observed in water courses. The fate of sulfate and glucuronide conjugated steroid estrogens was investigated in batch studies using activated sludge grown on synthetic sewage in a laboratory-scale Husmann simulation and crude sewage from the field. A clear distinction between the fate of sulfate and glucuronide conjugates was observed in both matrices, with sulfated conjugates proving more recalcitrant and glucuronide deconjugation preferential in crude sewage. For each conjugate, the free steroid was observed in the biotic samples. The degree of free steroid formation was dependent on the conjugate moiety, favoring the glucuronide. Subsequent degradation of the free steroid (and sorption to the activated sludge solid phase) was evaluated. Deconjugation followed the first order reaction rate with rate constants for 17α-ethinylestradiol 3-glucuronide, estriol 16α-glucuronide, and estrone 3-glucuronide determined as 0.32, 0.24, and 0.35 h respectively. The activated sludge solid retention time over the range of 3−9 days had 74 to 94% of sulfate conjugates remaining after 8 h. In contrast, a correlation between increasing temperature and decreasing 17α-ethinylestradiol 3-glucuronide concentrations in the activated sludge observed no conjugate present in the AS following 8 h at 22 °C Based on these batch studies and literature excretion profiles, a hypothesis is presented on which steroids and what form (glucuronide, sulfate, or free) will likely enter the sewage treatment plant.EPSR
Negative Even Grade mKdV Hierarchy and its Soliton Solutions
In this paper we provide an algebraic construction for the negative even mKdV
hierarchy which gives rise to time evolutions associated to even graded Lie
algebraic structure. We propose a modification of the dressing method, in order
to incorporate a non-trivial vacuum configuration and construct a deformed
vertex operator for , that enable us to obtain explicit and
systematic solutions for the whole negative even grade equations
Alimentos e alimentação de ovinos e caprinos no semi-árido brasileiro.
A baixa qualidade e a escassez de forragem, especialmente durante a seca estacional, agravadas pelas doenças que normalmente acometem os rebanhos, são os principais fatores limitantes para a produtividade animal no Nordeste Semi-Árido. De modo geral, nos sistemas de produção extensivos os ganhos obtidos durante o período de relativa abundância pouco mais fazem que repor a condição corporal perdida durante o período de escassez. Ao longo das últimas décadas, estudos desenvolvidos pela Embrapa e seus diversos parceiros têm apontado alternativas para a redução, ou mesmo para a eliminação das perdas verificadas durante o período seco, garantindo incrementos no desempenho animal. Dentre estas, merecem destaque a melhoria das pastagens nativas, a suplementação alimentar (feno, silagem, subprodutos da agricultura e da agroindústria e concentrados protéicos e energéticos), além do cultivo de forrageiras com propósitos específicos (pastagens irrigadas, bancos de proteína etc.). O uso racional dos recursos forrageiros permite elevar a eficiência dos sistemas de produção, indicando o potencial para a competitividade da pecuária nordestina no cenário nacional. Entretanto, necessário se torna uma ampla disseminação dos novos conhecimentos entre os técnicos e produtores envolvidos com o agronegócio da caprinocultura e da ovinocultura. O presente trabalho reúne informações sobre o manejo e sobre o valor nutritivo dos diversos recursos forrageiros disponíveis no semi-árido. Objetiva, no âmbito geral, destacar os novos conhecimentos com vistas a inserir o produtor nordestino no competitivo mercado de produtos derivados dos pequenos ruminantes domésticos.bitstream/CNPC/20675/1/doc67.pd
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