1,818 research outputs found
Avaliação da severidade da murcha de fusário em tomateiro em diferentes níveis de água no solo por meio do teor de clorollila das folhas.
O objetivo deste experimento foi avaliar a severidade da murcha de fusário em 4 diferentes niveis de água no solo por meio do teor de clorofila das folhas.Resumo 820-1
Avaliação da severidade da murcha de fusário em tomateiro em diferentes níveis de água no solo por meio da temperatura na superficie foliar.
O objetivo do trabalho foi avaliar o efeito do manejo de água de irrigação por meio de diferentes níveis de água no solo sobre o desenvolvimento temporal da murcha de fusário em tomateiro.Resumo 849-1
Eddington-limited X-ray Bursts as Distance Indicators. I. Systematic Trends and Spherical Symmetry in Bursts from 4U 1728-34
We investigate the limitations of thermonuclear X-ray bursts as a distance
indicator for the weakly-magnetized accreting neutron star 4U 1728-34. We
measured the unabsorbed peak flux of 81 bursts in public data from the Rossi
X-Ray Timing Explorer (RXTE). The distribution of peak fluxes was bimodal: 66
bursts exhibited photospheric radius expansion and were distributed about a
mean bolometric flux of 9.2e-8 erg/cm^2/s, while the remaining (non-radius
expansion) bursts reached 4.5e-8 erg/cm^2/s, on average. The peak fluxes of the
radius-expansion bursts were not constant, exhibiting a standard deviation of
9.4% and a total variation of 46%. These bursts showed significant correlations
between their peak flux and the X-ray colors of the persistent emission
immediately prior to the burst. We also found evidence for quasi-periodic
variation of the peak fluxes of radius-expansion bursts, with a time scale of
approximately 40 d. The persistent flux observed with RXTE/ASM over 5.8 yr
exhibited quasi-periodic variability on a similar time scale. We suggest that
these variations may have a common origin in reflection from a warped accretion
disk. Once the systematic variation of the peak burst fluxes is subtracted, the
residual scatter is only approximately 3%, roughly consistent with the
measurement uncertainties. The narrowness of this distribution strongly
suggests that i) the radiation from the neutron star atmosphere during
radius-expansion episodes is nearly spherically symmetric, and ii) the
radius-expansion bursts reach a common peak flux which may be interpreted as a
standard candle intensity.Adopting the minimum peak flux for the
radius-expansion bursts as the Eddington flux limit, we derive a distance for
the source of 4.4-4.8 kpc.Comment: 9 pages, 7 figures, accepted by ApJ. Minor referee's revisions, also
includes 9 newly public X-ray burst
Progresso temporal de Septoria lycopersici em tomateiro orgânico em sistemas de irrigação distintos.
O objetivo deste trabalho foi analisar o progresso temporal da septoriose causada por Septoria lycopersici, em distintos sistema de irrigação
Nucleon Polarizibilities for Virtual Photons
We generalize the sum rules for the nucleon electric plus magnetic
polarizability and for the nucleon spin-polarizability
, to virtual photons with . The dominant low energy cross
sections are represented in our calculation by one-pion-loop graphs of
relativistic baryon chiral perturbation theory and the -resonance
excitation. For the proton we find good agreement of the calculated
with empirical values obtained from integrating up
electroproduction data for . The proton spin-polarizability
switches sign around and it joins smoothly the
"partonic" curve, extracted from polarized deep-inelastic scattering, around
. For the neutron our predictions of and
agree reasonably well at with existing determinations.
Upcoming (polarized) electroproduction experiments will be able to test the
generalized polarizability sum rules investigated here.Comment: 12 pages, 5 figures, submittes to Nuclear Physics
Models of Type I X-Ray Bursts in 4U 1820-30
I present ignition models for Type I X-ray bursts and superbursts from the
ultracompact binary 4U 1820-30. A pure helium secondary is usually assumed for
this system, although some evolutionary models predict a small amount of
hydrogen (around 10% by mass). I show that even this small amount of hydrogen
significantly affects the expected Type I burst properties. Using the 2-4 hour
recurrence times observed during periods of regular bursting, I determine the
accretion rate onto the star for different compositions, a new constraint on
evolutionary models. I show that models with hydrogen predict 10% variations in
burst fluence with recurrence time, which should in future allow the accreted
composition to be determined. For superbursts, I show that the expected
recurrence times are 1-2 years for pure He accretion, and 5-10 years if
hydrogen is present. These results emphasise that a combined analysis of normal
Type I X-ray bursts and superbursts is a promising way to probe the thermal
structure and composition of the neutron star's outer layers.Comment: To appear in the Astrophysical Journal (13 pages; 4 figures
Incidência da murcha bacteriana em tomateiro orgânico sob diferentes sistemas de irrigação, níveis de água e coberturas de solo.
Avaliou-se a incidência da murcha bacteriana (Ralstonia solanacearum) em tomateiro orgânico cultivado em diferentes sistemas de irrigação, níveis de água e coberturas de solo, nas condiçoes de Brasil Central.Resumo 10688. Trabalho apresentado no 7. Congresso Brasileiro de Agroecologia, Fortaleza, 2011
Global properties of Stochastic Loewner evolution driven by Levy processes
Standard Schramm-Loewner evolution (SLE) is driven by a continuous Brownian
motion which then produces a trace, a continuous fractal curve connecting the
singular points of the motion. If jumps are added to the driving function, the
trace branches. In a recent publication [1] we introduced a generalized SLE
driven by a superposition of a Brownian motion and a fractal set of jumps
(technically a stable L\'evy process). We then discussed the small-scale
properties of the resulting L\'evy-SLE growth process. Here we discuss the same
model, but focus on the global scaling behavior which ensues as time goes to
infinity. This limiting behavior is independent of the Brownian forcing and
depends upon only a single parameter, , which defines the shape of the
stable L\'evy distribution. We learn about this behavior by studying a
Fokker-Planck equation which gives the probability distribution for endpoints
of the trace as a function of time. As in the short-time case previously
studied, we observe that the properties of this growth process change
qualitatively and singularly at . We show both analytically and
numerically that the growth continues indefinitely in the vertical direction
for , goes as for , and saturates for . The probability density has two different scales corresponding to
directions along and perpendicular to the boundary. In the former case, the
characteristic scale is . In the latter case the scale
is for , and
for . Scaling functions for the probability density are given for
various limiting cases.Comment: Published versio
Laplace Operators on Fractals and Related Functional Equations
We give an overview over the application of functional equations, namely the
classical Poincar\'e and renewal equations, to the study of the spectrum of
Laplace operators on self-similar fractals. We compare the techniques used to
those used in the euclidean situation. Furthermore, we use the obtained
information on the spectral zeta function to define the Casimir energy of
fractals. We give numerical values for this energy for the Sierpi\'nski gasket
Low-Energy Compton Scattering of Polarized Photons on Polarized Nucleons
The general structure of the cross section of scattering with
polarized photon and/or nucleon in initial and/or final state is systematically
described and exposed through invariant amplitudes. A low-energy expansion of
the cross section up to and including terms of order is given which
involves ten structure parameters of the nucleon (dipole, quadrupole,
dispersion, and spin polarizabilities). Their physical meaning is discussed in
detail. Using fixed-t dispersion relations, predictions for these parameters
are obtained and compared with results of chiral perturbation theory. It is
emphasized that Compton scattering experiments at large angles can fix the most
uncertain of these structure parameters. Predictions for the cross section and
double-polarization asymmetries are given and the convergence of the expansion
is investigated. The feasibility of the experimental determination of some of
the struture parameters is discussed.Comment: 41 pages of text, 9 figures; minor revisions prior to publication in
Phys. Rev.
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