1,870 research outputs found
Sensoriamento remoto aplicado a estimativa do sequestro de carbono no Bioma Caatinga.
O presente estudo teve como objetivo analisar o potencial de sequestro de carbono do bioma Caatinga e sua variação espacial e temporal.
Production Capacity and Queues in a Bookstore at Porto Velho, Brazil
The objective of this work was to study the productive capacity and queues in the services of a bookstore in Porto Velho city, Brazil. To do this, the specific objectives were: (1) to study the productive capacity in the operation units of the bookstore; (2) to carry out an analysis of queuing and flow management in the operation units of the bookstore; and (3) to suggest prospects for the development using the SWOT Matrix analysis tool
Second Generation of Composite Fermions in the Hamiltonian Theory
In the framework of a recently developed model of interacting composite
fermions restricted to a single level, we calculate the activation gaps of a
second generation of spin-polarized composite fermions. These composite
particles consist each of a composite fermion of the first generation and a
vortex-like excitation and may be responsible for the recently observed
fractional quantum Hall states at unusual filling factors such as
nu=4/11,5/13,5/17, and 6/17. Because the gaps of composite fermions of the
second generation are found to be more than one order of magnitude smaller than
those of the first generation, these states are less visible than the usual
states observed at filling factors nu=p/(2ps+1). Their stability is discussed
in the context of a pseudopotential expansion of the composite-fermion
interaction potential.Comment: 5 pages, 3 figures; after publication in PRB, we have realized that a
factor was missing in one of the expressions; the erroneous results are now
corrected; an erratum has been sent to PR
suppression in co-doped striped cuprates
We propose a model that explains the reduction of due to the pinning of
stripes by planar impurity co-doping in cuprates. A geometrical argument about
the planar fraction of carriers affected by stripe pinning leads to a a linear
suppression as a function of impurity concentration . The critical
value for the vanishing of superconductivity is shown to scale like
in the under-doped regime and becomes universal in the optimally- and
over-doped regimes. Our theory agrees very well with the experimental data in
single- and bi-layer cuprates co-doped with Zn, Li, Co, etc...Comment: 4 pages, 4 figure
Metastability in Josephson transmission lines
Thermal activation and macroscopic quantum tunneling in current-biased
discrete Josephson transmission lines are studied theoretically. The degrees of
freedom under consideration are the phases across the junctions which are
coupled to each other via the inductances of the system. The resistively
shunted junctions that we investigate constitute a system of N interacting
degrees of freedom with an overdamped dynamics. We calculate the decay rate
within exponential accuracy as a function of temperature and current. Slightly
below the critical current, the decay from the metastable state occurs via a
unique ("rigid") saddlepoint solution of the Euclidean action describing the
simultaneous decay of the phases in all the junctions. When the current is
reduced, a crossover to a regime takes place, where the decay occurs via an
"elastic" saddlepoint solution and the phases across the junctions leave the
metastable state one after another. This leads to an increased decay rate
compared with the rigid case both in the thermal and the quantum regime. The
rigid-to-elastic crossover can be sharp or smooth analogous to first- or
second- order phase transitions, respectively. The various regimes are
summarized in a current-temperature decay diagram.Comment: 11 pages, RevTeX, 3 PS-figures, revised versio
Crossovers in the thermal decay of metastable states in discrete systems
The thermal decay of linear chains from a metastable state is investigated. A
crossover from rigid to elastic decay occurs when the number of particles, the
single particle energy barrier or the coupling strength between the particles
is varied. In the rigid regime, the single particle energy barrier is small
compared to the coupling strength and the decay occurs via a uniform
saddlepoint solution, with all degrees of freedom decaying instantly.
Increasing the barrier one enters the elastic regime, where the decay is due to
bent saddlepoint configurations using the elasticity of the chain to lower
their activation energy. Close to the rigid-to-elastic crossover, nucleation
occurs at the boundaries of the system. However, in large systems, a second
crossover from boundary to bulk nucleation can be found within the elastic
regime, when the single particle energy barrier is further increased. We
compute the decay rate in the rigid and in the elastic regimes within the
Gaussian approximation. Around the rigid-to-elastic crossover, the calculations
are performed beyond the steepest descent approximation. In this region, the
prefactor exhibits a scaling property. The theoretical results are discussed in
the context of discrete Josephson transmission lines and pancake vortex stacks
that are pinned by columnar defects.Comment: 13 pages, RevTeX, 7 PS-figure
Influência topoedafoclimática na produção primária bruta no Semiárido.
O relevo influencia a precipitação, a produção de biomassa e a produção primária bruta (Gross Primary Production-GPP). Em ecossistemas secos qualquer variação GPP tem importância cientifica uma vez que são ecossistemas bastante vulneráveis devido a alta variabilidade espacial e temporaldo clima. Além disso, avaliar a relação entre o relevo e GPP em ecossistemas secos se torna mais fácil por existir um período bem definido com zero de precipitação. O estudo objetivou avaliar a influência do relevo, da altitude, da precipitação e do solo na Gross Primary Production-GPP no Bioma Caatinga. Foram utilizados os produtos MOD17 (GPP), sensor MODIS do satélite Terra e dados de precipitação para os anos de 2015 e 2016, com a aplicação de estatísticas descritivas e multivariadas para identificar correlações e similaridades entre áreas e amostras.Ocorreu grande variação espacial e temporal da GPP em áreas de Caatinga, devido ao relevo, clima e solo. A quantificação da GPP nas áreas de maiores altitudes apresentou médias de 46,87 e 55,84 gC m2 e menores valores de GPP, de 2,49 e 3,75 gC m-2 , em 2015 e 2016, respectivamente. Nas áreas planas, as maiores médias foram 46,03 e 55,84 gC m-2 e as menores 3,75 e 2,49 gC m-², em 2015 e 2016, respectivamente.Ocorreu uma diferença de quase 40% para os menores valores de GPP, quando comparados aosrelativos às áreas mais altas e mais baixas. Foi possível avaliar a influência do relevo na GPP devido existir um período seco bem definido e de precipitação zero. Os anos de maiores precipita ção têm forte influência nos menores valores de GPP das áreas planas. Assim, no período chuvoso é mais difícil identificar a influência de outros fatores, que não sejam a precipitação, na GPP. Esses resultados são de grande importância para mitigar ou avaliar os efeitos das mudanças climáticas sobre os ecossistemas seco
Kaolin and chromic oxide under different forms of administration in a study of consumption and digestibility.
ABSTRACT: Animal nutrition needs simple methodologies to be applied under field conditions, providing valid estimates of consumption and digestibility that can be used by both farmers and animal input industry.Thus, the search for new substances, provided in a practical way, quantified by simple and low-cost analytical methodologies, replacing external indicators (chromic oxide used as reference) would be well accepted by the scientific community. In this context, the aim of this study was to assess the supply of chorionic oxide by esophageal route or mixed in the diet and the use of kaolin as an indicator, under the same forms of administration, to estimate fecal production and digestibility using four castrated male Holstein cattle. The experimental design was a 4 × 4 Latin square design, with four experimental periods of 12 days and six-day intervals between periods. Treatments consisted of supplying chromic oxide by esophageal route (COer), kaolin by esophageal route (Kaoer), chromic oxide mixed to the diet (COdiet), and kaolin mixed to the diet (Kaodiet). The treatment Kaodiet allowed obtaining estimates of fecal production similar to the treatment COer. The treatment COdiet did not differ from the treatment COer (p > 0.05) considering all the assessed parameters, evidencing that the indicator chromic oxide can be supplied mixed directly in the diet without damaging the estimates of fecal production and digestibility. Under the studied conditions, kaolin was not an effective indicator to obtain accurate estimates of fecal production and further studies are needed to adjust the analytical techniques of aluminum extraction as well as to resolve some doubts regarding its digestion process. RESUMO: A nutrição animal necessita de metodologias simples que possam ser aplicadas em condições de campo, que sejam capazes de fornecer estimativas válidas de consumo e digestibilidade e que possam Assim a busca por novas substâncias, fornecidas de forma prática, quantificadas por metodologias analíticas simples e de baixo custo em substituição aos indicadores externos (óxido crômico usado como referência) seriam bem aceitas pela comunidade científica. Neste contexto objetivou-se avaliar o fornecimento do óxido crômico via esofágica ou misturado na ração, e o uso do caulim como indicador, sob as mesmas formas de fornecimento, para estimar a produção fecal e digestibilidade, utilizando quatro bovinos machos castrados da raça Holandesa. Foram testados quatro tratamentos, distribuídos aos animais segundo um delineamento quadrado latino 4x4, sendo o primeiro aquele em que os animais foram submetidos ao fornecimento de óxido crômico fornecido via esofágica (OCesof), no segundo tratamento os animais receberam o caulim via esofágica (Caulesof), no terceiro o fornecimento do óxido crômico aos animais foi misturado à ração (OCrac) e no quarto tratamento o caulim foi administrado misturado à ração (Caulrac), em quatro períodos experimentais de 12 dias, com intervalos de seis dias entre os períodos. O tratamento Caulrac permitiu obter estimativas de produção fecal semelhante ao tratamento OCesof. O tratamento OCrac não diferiu do tratamento OCesof (p > 0,05) em nenhum dos parâmetros avaliados, evidenciando que o indicador óxido crômico pode ser fornecido misturado diretamente na ração sem prejudicar as estimativas de produção fecal e digestibilidade.Título em inglês: Caulim e óxido crômico sob diferentes formas de administração em estudo de consumo e digestibilidade
Decoherence of quantum registers
The dynamical evolution of a quantum register of arbitrary length coupled to
an environment of arbitrary coherence length is predicted within a relevant
model of decoherence. The results are reported for quantum bits (qubits)
coupling individually to different environments (`independent decoherence') and
qubits interacting collectively with the same reservoir (`collective
decoherence'). In both cases, explicit decoherence functions are derived for
any number of qubits. The decay of the coherences of the register is shown to
strongly depend on the input states: we show that this sensitivity is a
characteristic of types of coupling (collective and independent) and not
only of the collective coupling, as has been reported previously. A non-trivial
behaviour ("recoherence") is found in the decay of the off-diagonal elements of
the reduced density matrix in the specific situation of independent
decoherence. Our results lead to the identification of decoherence-free states
in the collective decoherence limit. These states belong to subspaces of the
system's Hilbert space that do not get entangled with the environment, making
them ideal elements for the engineering of ``noiseless'' quantum codes. We also
discuss the relations between decoherence of the quantum register and
computational complexity based on the new dynamical results obtained for the
register density matrix.Comment: Typos corrected. Discussion and references added. 1 figure + 3 tables
added. This updated version contains 13 (double column) pages + 8 figures.
PRA in pres
Crossover from thermal hopping to quantum tunneling in Mn_{12}Ac
The crossover from thermal hopping to quantum tunneling is studied. We show
that the decay rate with dissipation can accurately be determined near
the crossover temperature. Besides considering the Wentzel-Kramers-Brillouin
(WKB) exponent, we also calculate contribution of the fluctuation modes around
the saddle point and give an extended account of a previous study of crossover
region. We deal with two dangerous fluctuation modes whose contribution can't
be calculated by the steepest descent method and show that higher order
couplings between the two dangerous modes need to be taken into considerations.
At last the crossover from thermal hopping to quantum tunneling in the
molecular magnet Mn_{12}Ac is studied.Comment: 10 pages, 3 figure
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