1,382 research outputs found
Electromagnetic radiation of accelerated charged particle in the framework of a semiclassical approach
We address the problem of the electromagnetic radiation produced by charge
distributions in the framework of a semiclassical approach proposed in the work
by Bagrov, Gitman, Shishmarev and Farias [J. Synchrotron Rad. (2020). 27,
902-911]. In this approach, currents, generating the radiation are considered
classically, while the quantum nature of the radiation is kept exactly. Quantum
states of the electromagnetic field are solutions of Schr\"odinger's equation
and relevant quantities to the problem are evaluated with the aid of transition
probabilities. This construction allows us to introduce the quantum transition
time in physical quantities and assess its role in radiation problems by
classical currents. We study radiated electromagnetic energies in detail and
present a definition for the rate at which radiation is emitted from sources.
In calculating the total energy and rate radiated by a pointlike charged
particle accelerated by a constant and uniform electric field, we discover that
our results are compatible with results obtained by other authors in the
framework of the classical radiation theory under an appropriate limit. We also
perform numerical and asymptotic analysis of the results.Comment: 22 pages, 3 figure
Optimized perturbation theory for charged scalar fields at finite temperature and in an external magnetic field
Symmetry restoration in a theory of a self-interacting charged scalar field
at finite temperature and in the presence of an external magnetic field is
examined. The effective potential is evaluated nonperturbatively in the context
of the optimized perturbation theory method. It is explicitly shown that in all
ranges of the magnetic field, from weak to large fields, the phase transition
is second order and that the critical temperature increases with the magnetic
field. In addition, we present an efficient way to deal with the sum over the
Landau levels, which is of interest especially in the case of working with weak
magnetic fields.Comment: 18 pages, 7 eps figures. References added and some small improvements
to the tex
Expressão sexual da mamoneira influenciada por adubação e cloreto de Mepiquat.
bitstream/CNPA/19716/1/BOLETIM60.pd
Fluxo de biomassa em capim-tanzânia pastejado por ovinos sob três períodos de descanso.
Resumo: Avaliou-se o fluxo de biomassa em Panicum maximum cv. Tanzânia pastejado por ovinos com três períodos de descanso (PD), definidos pela expansão de 1,5; 2,5 e 3,5 novas folhas por perfilho, em um delineamento inteiramente casualizado, com duas repetições (piquetes). Estimaram-se as taxas de alongamento de lâmina foliar total (TAlF), de senescência de lâminas foliares remanescentes do pastejo anterior (TSFA), de senescência das novas folhas formadas no PD (TSFP) e de senescência total (TSFT=TSFA+TSFP), a taxa de alongamento das hastes (TAlH), a razão entre as TAlF das folhas 1 e 2 (razão TAlF1/TAlF2), a densidade populacional de perfilhos (DPP), o filocrono e as taxas de crescimento (TCC) e de acúmulo (TAC) da cultura. A razão TAlF1/2 não foi afetada pelos PD, mas reduziu ao longo dos ciclos na pastagem sob PD 3,5. A TAlF não foi afetada pelos PD. A TAlH, a TSFA e a TSFT na pastagem sob PD 1,5 foram menores que nas demais. Houve TSFP somente na pastagem sob PD 3,5. O filocrono da pastagem sob PD 1,5 foi superior ao observado nas demais. A densidade populacional de perfilhos (DPP) da pastagem sob o PD 2,5 foi similar à verificada na pastagem sob PD 1,5 e superior à verificada sob PD 3,5. Houve redução na DPP ao longo dos ciclos na pastagem sob PD 3,5. As taxas de crescimento (TCC) e de acúmulo (TAC) foram superiores na pastagem sob PD 2,5. O prolongamento do PD elevou as TAlH e TSFT e reduziu a DPP e a TAC. Portanto, o PD do capim-tanzânia pastejado por ovinos não deve exceder o tempo necessário à expansão de 2,5 novas folhas por perfilho. [Biomass flow in tanzaniagrass pasture under three resting periods grazed by sheep]. Abstract: The biomass flow in Panicum maximum cv. Tanzânia pasture grazed by sheep under three resting periods (PD), defined by the expansion of 1.5; 2.5 and 3.5 new leaves per tiller (1.5F; 2.5F and 3.5F, respectively) was evaluated in a randomized completely design with two replicates (paddocks). It was determined the leaf elongation rate (TAlF), the residual leaf senescence rate (TSFA), the post-grazing leaf senescence rate (TSFP) and the total leaf senescence rate (TSFT), the stem elongation rate (TAlH), the TAlF of leaves 1 and 2 ratio (TALF1/2), the tiller population density (DPP), the phylochron and the crop growth (TCC) and accumulation (TAC) rates. The TAlF1/2 ratio was not affected by the PD, however, it decreased over the cycles at the 3.5F PD pasture. The TAlF was not affected by the PD. The TAlH was inferior at the 1.5F PD pasture, as well as the TSFA and the TSFT. There was TSFP only at the 3.5F PD pasture. The phylochron of the 1.5F PD pasture was superior to the others. The DPP of the 2.5F PD pasture was similar to that of the 1.5F PD pasture, and it was superior to the 3.5F PD pasture. There was reduction of the DPP following the cycles at the 3.5F PD pasture. The TCC and the TAC of the 2.5F PD pasture were superior than the others. The extension of the PD raised the TAlH and the TSFT and reduced the DPP and the TAC. As a conclusion, the resting period should not exceed the time necessary to the expansion of 2.5 leaves on the tiller for tanzaniagrass pastures grazed by sheep
Hydrogen adsorption on Pd(133) surface
In this study used is an approach based on measurements of the total energy
distribution (TED) of field emitted electrons in order to examine the
properties of Pd (133) from the aspect of both hydrogen adsorption and surface
hydrides formation. The most favourable sites offered to a hydrogen atom to be
adsorbed have been indicated and an attempt to describe the peaks of the
enhancement factor R spectrum to the specific adsorption sites has also been
made.Comment: to be submitted to the Centr. Eur. J. Phy
Time quantization and q-deformations
We extend to quantum mechanics the technique of stochastic subordination, by
means of which one can express any semi-martingale as a time-changed Brownian
motion. As examples, we considered two versions of the q-deformed Harmonic
oscillator in both ordinary and imaginary time and show how these various cases
can be understood as different patterns of time quantization rules.Comment: 4 pages, 2 figure
Polaron effects in electron channels on a helium film
Using the Feynman path-integral formalism we study the polaron effects in
quantum wires above a liquid helium film. The electron interacts with
two-dimensional (2D) surface phonons, i.e. ripplons, and is confined in one
dimension (1D) by an harmonic potential. The obtained results are valid for
arbitrary temperature (), electron-phonon coupling strength (), and
lateral confinement (). Analytical and numerical results are
obtained for limiting cases of , , and . We found the
surprising result that reducing the electron motion from 2D to quasi-1D makes
the self-trapping transition more continuous.Comment: 6 pages, 7 figures, submitted to Phys. Rev.
Avaliação da disponibilidade e da qualidade da forragem de uma área de caatinga utilizando o pacote botanal.
Estudos da composição da vegetação e da disponibilidade de fitomassa tem sido objeto de vários trabalhos,especialmente quando existe a intenção de aproveitar a vegetação natural para a produção animal. Nessesentido, este trabalho objetivou avaliar a disponibilidade e a qualidade da forragem de uma área devegetação da caatinga, no período chuvoso, no sertão de Pernambuc
Isolamento de bactérias associadas a plantas do bioma caatinga no semiárido nordestino.
A Caatinga é um bioma exclusivamente brasileiro e corresponde a 70% do território nordestino. Esse bioma caracteriza-se pela distribuição irregular das chuvas e pelas características sazonais de sua vegetação, que apresenta forte endemismo. Atrelada a essa rica vegetação e adaptada às condições peculiares desta região, está a microbiota, em especial as rizobactérias. Este trabalho teve por objetivo isolar bactérias e avaliar a densidade destes micro-organismos associados à raiz e rizosfera de plantas de cinco famílias botânicas da Caatinga. As amostras foram separadas em solo da rizosfera e raiz, sendo as amostras de tecido radicular submetidas a um processo de desinfecção superficial. As bactérias associadas à raiz e da rizosfera foram isoladas em meio TSA acrescido de 5% de NaCl. A densidade populacional bacteriana associada à raiz variou de 9,3 X 103 (Cobretum sp.) a 1,9 X 108 (Terminalia sp.) UCF/g TVF e da rizosfera a variação foi de 3,3 X 108 (Schinus sp.) e 8,3 X 104 (Cobretum sp.) UCF/g TVF. A variabilidade morfológica encontrada neste trabalho sugere uma ampla diversidade de genótipos bacterianos associados à rizosfera e raízes de plantas destes gêneros encontrados na Caatinga
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