2,378 research outputs found
Desenvolvimento de um protótipo aplicador de produtos quÃmicos para um sistema de irrigação pivô central.
Empregando-se um sistema de irrigação pivô central composto por um vão inicial, uma torre móvel e um lance em balanço, foi desenvolvido um protótipo para aplicação de produtos quÃmicos, operando de forma acoplada ao equipamento, utilizando-se da mobilidade da torre como meio de deslocamento para a aplicação de calda através de emissores do tipo microaspersor. Para tanto, foram desenvolvidos diversos conjuntos de componentes, que consistem em: unidade de bombeamento; sistema de filtragem de água e injeção de produtos quÃmicos através de uma bomba dosadora; sistema de adução de calda acoplado a tubulação aérea do pivô central; sistema de controle automatizado da emissão de calda e um conjunto de suporte da linha de microaspersores. Todos os conjuntos de componentes desenvolvidos operaram satisfatoriamente em condições de campo
The Coulomb impurity problem in graphene
We address the problem of an unscreened Coulomb charge in graphene, and
calculate the local density of states and displaced charge as a function of
energy and distance from the impurity. This is done non-perturbatively in two
different ways: (1) solving the problem exactly by studying numerically the
tight-binding model on the lattice; (2) using the continuum description in
terms of the 2D Dirac equation. We show that the Dirac equation, when properly
regularized, provides a qualitative and quantitative low energy description of
the problem. The lattice solution shows extra features that cannot be described
by the Dirac equation, namely bound state formation and strong renormalization
of the van Hove singularities.Comment: 3 Figures; minor typo corrections and minor update in Fig. 3
Uniformidade de distribuição de água e potássio aplicados por um sistema acoplado a um pivô central.
Neste trabalho foi avaliada a distribuição de água e de potássio aplicados por um protótipo aplicador de produtos quÃmicos que opera de forma acoplada a um pivô central, utilizando-se da mobilidade da torre como meio de deslocamento para aplicação de calda através de microaspersores. Concluiu-se que o protótipo apresentou boa uniformidade de distribuição de água, com variações próximas aos microaspersores, devido a respingos causados pelos impactos dos jatos de água no corpo dos mesmos e que a injeção de solução de cloreto de potássio proporcionou concentração uniforme de potássio na solução emitida pelos microaspersores
The timing of formation of the Douro and Tejo rivers and implications for the evolution of the landscapes of central mainland Portugal
10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022.The formation and development of major rivers limits the overall pace of the surrounding landscape
evolution and drives sediment delivery from source to sink. The timings and rates of river incision
may be a response to external influences, such as tectonic or climate driven base-level changes, or
alternatively they may be linked to the breaching of internal thresholds, for example, drainage
capture events. The Tejo and Douro rivers (also known as Tagus and Duero rivers) each drain a
significant portion of the Iberian Peninsula and much of their courses through Portugal are typified
by v-shaped valleys that are deeply incised into the surrounding topography. Earlier work has dated
fluvial terrace deposits, mostly by luminescence techniques, but also by electron spin resonance and
cosmogenic nuclide exposure dating. This has provided constraints on the late Pleistocene histories
of the Tejo and Douro rivers, however, the timing of their transition from endorheic to exorheic is
not precisely known and whether or not their histories are linked to a common mechanism is
unclear.
This study aims to provide age constraints on the early history of the Tejo and Douro rivers, and to
examine whether and to what degree the erosion rates of low relief, granite etchplain landscapes
within the river’s catchment areas are responding to the trunk channel incision. We focus on reaches
of the Tejo and Douro rivers located in the eastern sector of mainland Portugal. Samples were
collected for cosmogenic nuclide (10Be and 26Al) surface exposure and burial dating to date upper
fluvial terrace levels. In addition, a combination of cosmogenic nuclide exposure ages and depth
profiles in bedrock outcrops, alongside basin-wide erosion rate determinations will be used constrain
the pace of evolution of nearby granitic landscapes. Preparation of the samples for measurement is
ongoing and we will present our initial findings
Density functional investigations of defect induced mid-gap states in graphane
We have carried out ab initio electronic structure calculations on graphane
(hydrogenated graphene) with single and double vacancy defects. Our analysis of
the density of states reveal that such vacancies induce the mid gap states and
modify the band gap. The induced states are due to the unpaired electrons on
carbon atoms. Interestingly the placement and the number of such states is
found to be sensitive to the distance between the vacancies. Furthermore we
also found that in most of the cases the vacancies induce a local magnetic
moment.Comment: 15 page
A role for endothelin receptor type A in migraine without aura susceptibility? A study in Portuguese patients
Abstract
BACKGROUND AND PURPOSE:
Migraine is a common neurological disabling disorder, and anomalies of vascular function have been implied in its pathophysiology. Several findings point to a possible role of the endothelin receptor type A (EDNRA) in migraine. We aim to assess the involvement of endothelin receptor type A (EDNRA) in migraine susceptibility in a sample of Portuguese migraineurs.
METHODS:
Three tagging SNPs (rs702757, rs5333 and rs5335) were analysed in 188 cases - 111 without aura (MO) and 77 with aura (MA) - and 287 controls. A multivariable logistic regression was performed, including the three SNPs, adjusted for gender. Allelic and haplotypic frequencies were compared between cases and controls. Significant or promising results were confirmed by a multifactor dimensionality reduction analysis (MDR).
RESULTS:
We found a nominal association for the rs702757 T-allele [odds ratio (OR) = 1.44, 95% confidence intervals (CI): 1.05-1.99] and for the TT-genotype (OR = 2.34, 95% CI: 1.12-4.90) for MO, that do not remain significant after multiple test correction. A trend towards an increased risk for MA regarding the C-allele of rs5333 was also found. However, an additional MDR analysis was performed, and highly significant results were found for the two SNPs. The T-C-G haplotype (rs702757-rs5333-rs5335) was found to be significantly overrepresented in the MO subgroup, even after permutation was performed.
CONCLUSIONS:
Our results show additional findings for a role of EDNRA as a susceptibility factor for MO, although we cannot exclude the involvement of this gene in MA susceptibility in our population. Our study also emphasizes the need for replication of association findings in different populations
Overcoming inertia : drivers of the outsourcing process
Almost all managers have directly or indirectly been involved in the practice of outsourcing in recent years. But as they know, outsourcing is not straightforward. Outsourcing inertia, when companies are slow to adapt to changing circumstances that accommodate higher outsourcing levels, may undermine a firm’s performance. This article investigates the presence of outsourcing inertia and the factors that help managers overcome it. Using statistical evidence, we show that positive performance effects related to outsourcing can accumulate when circumstances change. This is then followed by rapid increases in outsourcing levels (i.e. outsourcing processes). We investigate what gives rise to these outsourcing processes through follow-up interviews with sourcing executives, which suggest five drivers behind outsourcing processes: managerial initiative (using outside experience); hierarchy (foreign headquarters); imitation (of competitors and of similar firms); outsider advice (from external institutions); knowledge sources (using external information). These five drivers all offer scope for managerial action. We tie them to academic literatures and suggest ways of investigating their presence and impact on the outsourcing process. Overall, we conclude that while economizing factors play a key role in explaining how much firms outsource, it is socializing factors that tend to drive outsourcing processes
Energy of general 4-dimensional stationary axisymmetric spacetime in the teleparallel geometry
The field equation with the cosmological constant term is derived and the
energy of the general 4-dimensional stationary axisymmetric spacetime is
studied in the context of the hamiltonian formulation of the teleparallel
equivalent of general relativity (TEGR). We find that, by means of the integral
form of the constraints equations of the formalism naturally without any
restriction on the metric parameters, the energy for the asymptotically flat/de
Sitter/Anti-de Sitter stationary spacetimes in the Boyer-Lindquist coordinate
can be expressed as . It is surprised to learn that the
energy expression is relevant to the metric components ,
and only. As examples, by using this formula
we calculate the energies of the Kerr-Newman (KN), Kerr-Newman Anti-de Sitter
(KN-AdS), Kaluza-Klein, and Cveti\v{c}-Youm spacetimes.Comment: 12 page
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