7,109 research outputs found
Trapped and excited w modes of stars with a phase transition and R>=5M
The trapped -modes of stars with a first order phase transition (a density
discontinuity) are computed and the excitation of some of the modes of these
stars by a perturbing shell is investigated. Attention is restricted to odd
parity (``axial'') -modes. With the radius of the star, its mass,
the radius of the inner core and the mass of such core, it is
shown that stars with can have several trapped -modes, as long
as . Excitation of the least damped -mode is confirmed for
a few models. All of these stars can only exist however, for values of the
ratio between the densities of the two phases, greater than . We also
show that stars with a phase transition and a given value of can have far
more trapped modes than a homogeneous single density star with the same value
of , provided both and are smaller than 3. If the
phase transition is very fast, most of the stars with trapped modes are
unstable to radial oscillations. We compute the time of instability, and find
it to be comparable to the damping of the -mode excited in most cases where
-mode excitation is likely. If on the other hand the phase transition is
slow, all the stars are stable to radial oscillations.Comment: To appear in Physical Review
Qualidade fisiológica das sementes do milho híbrido simples HS 200 em relação ao tamanho.
Para uniformizar e facilitar a semeadura, as sementes de milho são cultivadas quanto ao tamanho (espessura, comprimento e largura). A qualidade das sementes, principalmente as arredondadas e as de menor tamanho, tem sido questionada pelos agricultores e produtores de sementes. Com o objetivo de avaliar a qualidade fisiológicas das sementes do milho híbrido simples HS 200, foi realizado um trabalho na Embrapa Milho e Sorgo em Sete Lagoas, MG. Portanto, utilizaram-se sementes de três lotes oriundas de um mesmo campo de produção, as quais ficaram retidas na peneira 15 x 3/4 e também aquelas classificadas pela largura e comprimento (20c, 20L, 22L e 24). O delineamento experimental dos testes conduzidos no laboratório foi inteiramente casualizado e, daqueles conduzidos ao campo, foi em blocos ao acaso, foram realizados os testes de germinação, envelhecimento acelerado, frio modificado e emergência em campo. Pelos resultados, constata-se que as sementes longas de tamanho médio e de forma achatada (20L) apresentaram qualidade fisiológica superior, ao passo que as sementes de maior tamanho (24) e aquelas de forma arredondada retidas na peneira 15 x 3/4) apresentaram menor vigor. Foi verificada, ainda, que o teste de germinação foi o que mais se aproximou do estabelecimento da cultura e se mostrou confiável para produzir a emergência sob condição favorável de campo
Connection between dynamics and thermodynamics of liquids on the melting line
The dynamics of a large number of liquids and polymers exhibit scaling
properties characteristic of a simple repulsive inverse power law (IPL)
potential, most notably the superpositioning of relaxation data as a function
of the variable TV{\gamma}, where T is temperature, V the specific volume, and
{\gamma} a material constant. A related scaling law, TmVm{\Gamma}, with the
same exponent {\Gamma}={\gamma}, links the melting temperature Tm and volume Vm
of the model IPL liquid; liquid dynamics is then invariant at the melting
point. Motivated by a similar invariance of dynamics experimentally observed at
transitions of liquid crystals, we determine dynamic and melting point scaling
exponents {\gamma} and {\Gamma} for a large number of non-associating liquids.
Rigid, spherical molecules containing no polar bonds have {\Gamma}={\gamma};
consequently, the reduced relaxation time, viscosity and diffusion coefficient
are each constant along the melting line. For other liquids {\gamma}>{\Gamma}
always; i.e., the dynamics is more sensitive to volume than is the melting
point, and for these liquids the dynamics at the melting point slows down with
increasing Tm (that is, increasing pressure).Comment: 20 pages, 8 figures, 1 tabl
Side-Effects of Glyphosate to the Parasitoid Telenomus remus Nixon (Hymenoptera: Platygastridae).
Made available in DSpace on 2017-07-13T18:49:51Z (GMT). No. of bitstreams: 1
Steccaetal2016sideeffectsNE.pdf: 310045 bytes, checksum: 6f66c67e32aad75116d10d82e8ec95bc (MD5)
Previous issue date: 2017-02-03201
Railway infrastructure asset management: the whole-system life cost analysis
Delivering the railway infrastructure whose functionality is sustainable and uncompromised in terms of safety and availability under ever decreasing budget constraints is a great challenge. The successful accomplishment of this task relies on the effective management of individual assets within a wider whole system perspective. This is a highly complex decision-making task where mathematical models are required to enable well-informed choices. In this study, a novel modelling framework is proposed for performing the whole system lifecycle cost analysis. The framework is based on two models: railway network performance and costs. Using the former model investigations of the effects of decisions can be carried out for the individual asset and the whole system. A Petri net modelling technique is used to construct the model. A form of Monte Carlo simulation is then used to obtain model results. The infrastructure performance model is then integrated with the cost model to perform the lifecycle cost analysis. A superstructure example is presented to demonstrate the application of the approach. The results show that taking into account interdependencies among the intervention activities greatly influences, not only the performance of the infrastructure, but also its lifecycle costs and thus should be included in the cost analysis
Radiation recoil from highly distorted black holes
We present results from numerical evolutions of single black holes distorted
by axisymmetric, but equatorially asymmetric, gravitational (Brill) waves. Net
radiated energies, apparent horizon embeddings, and recoil velocities are shown
for a range of Brill wave parameters, including both even and odd parity
distortions of Schwarzschild black holes. We find that a wave packet initially
concentrated on the black hole throat, a likely model also for highly
asymmetric stellar collapse and late stage binary mergers, can generate a
maximum recoil velocity of about 150 (23) km/sec for even (odd) parity
perturbations, significantly less than that required to eject black holes from
galactic cores.Comment: 15 pages, 8 figure
Manejo fitotécnico da bananeira, cultivar D'Angola (AAB), visando ao controle da sigatoka-negra.
O trabalho teve como objetivo avaliar alternativas de manejo fitotécnico da bananeira comprida, cultivar D?Angola, visando ao controle da Sigatoka-negra. O experimento foi conduzido no campo experimental da Embrapa Acre no município de Rio Branco-AC com os tratamentos distribuídos em blocos ao acaso, completos, com seis repetições e constituídos por diferentes densidades de plantio, correspondendo: T1 - 3 m x 3 m (1.111 plantas/hectare); T2 - 3 m x 2 m (1.666 plantas/hectare); T3 - 2,5 m x 2 m (2.000 plantas/hectare); T4 - 4 m x 2 m x 1,5 m (1.333 plantas/hectare); T5 - 2 m x 2m (2.500 plantas/hectare) e; T6 - 3 m x 3 m (1.111 plantas/hectare), este último alocado sob o bosque de seringueira. Foram realizadas avaliações durante dois ciclos de produção. As plantas da cv. D'Angola (AAB) cultivadas no espaçamento 3,0 x 3,0m, sombreadas com seringueira, apresentaram maior altura de plantas, maior número de folhas vivas na floração e colheita, maior peso médio do cacho, maior massa das pencas, maior ciclo de produção e menor severidade da Sigatoka-negra. Maiores produtividades foram obtidas quando se adotaram maiores densidades de plantio. O consorciamento de bananeiras com árvores de seringueiras mostrou-se ser uma boa alternativa para viabilizar o cultivo da cv. D'Angola (banana comprida)
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