1,143 research outputs found
The power output of spine and fan magnetic reconnection solutions
The ability of three-dimensional magnetic “spine” and “fan” reconnection solutions to provide flarelike energy release is discussed. It is pointed out, on the basis of exact analytic solutions, that fast dissipation is possible only if the hydromagnetic pressure in the reconnection region becomes unbounded in the limit of small plasma resistivities. The implication is that some “saturation” of the power output is inevitable for realistic coronal plasmas. Estimates of the saturated power, based on limiting the flux pileup in the field, suggest that the geometry of the spine reconnection mechanism precludes significant flare energy release. However, the current sheet structures involved in fan reconnection seem able to release sufficient magnetic energy fast enough to account for modest flares, even under the conservative assumption of classical plasma resistivities
Magnetic reconnection solutions in the presence of multiple nulls
It is known that exact analytic solutions can be constructed for incompressible magnetic reconnection in three space dimensions. In the case of an isolated X-point null, there are two types of reconnection solutions, namely, “spine” and “fan” models, which depend on the form of the X-point disturbance. However, such models cannot describe multiple null “separator” reconnection, for which there is independent observational evidence. Here we show that the spine formalism naturally extends to the case of multiple null fields. Solutions showing the characteristics of fan, spine, and separator are described, and a discussion is given of their energy dissipation properties. We demonstrate a family of multiple null, fast reconnection solutions and point out that the classical Sweet-Parker dissipation rate is the slowest that can be achieved with the present models
Orbiting Resonances and Bound States in Molecular Scattering
A family of orbiting resonances in molecular scattering is globally described
by using a single pole moving in the complex angular momentum plane. The
extrapolation of this pole at negative energies gives the location of the bound
states. Then a single pole trajectory, that connects a rotational band of bound
states and orbiting resonances, is obtained. These complex angular momentum
singularities are derived through a geometrical theory of the orbiting. The
downward crossing of the phase-shifts through pi/2, due to the repulsive region
of the molecular potential, is estimated by using a simple hard-core model.
Some remarks about the difference between diffracted rays and orbiting are also
given.Comment: 18 pages, 3 figures, to appear in Physical Review
Updated tests of scaling and universality for the spin-spin correlations in the 2D and 3D spin-S Ising models using high-temperature expansions
We have extended, from order 12 through order 25, the high-temperature series
expansions (in zero magnetic field) for the spin-spin correlations of the
spin-S Ising models on the square, simple-cubic and body-centered-cubic
lattices. On the basis of this large set of data, we confirm accurately the
validity of the scaling and universality hypotheses by resuming several tests
which involve the correlation function, its moments and the exponential or the
second-moment correlation-lengths.Comment: 21 pages, 8 figure
Elastic Scattering by Deterministic and Random Fractals: Self-Affinity of the Diffraction Spectrum
The diffraction spectrum of coherent waves scattered from fractal supports is
calculated exactly. The fractals considered are of the class generated
iteratively by successive dilations and translations, and include
generalizations of the Cantor set and Sierpinski carpet as special cases. Also
randomized versions of these fractals are treated. The general result is that
the diffraction intensities obey a strict recursion relation, and become
self-affine in the limit of large iteration number, with a self-affinity
exponent related directly to the fractal dimension of the scattering object.
Applications include neutron scattering, x-rays, optical diffraction, magnetic
resonance imaging, electron diffraction, and He scattering, which all display
the same universal scaling.Comment: 20 pages, 11 figures. Phys. Rev. E, in press. More info available at
http://www.fh.huji.ac.il/~dani
Sugars of pearl millet [Pennisetum americanum (L.) Leeke] grains
The sugars in the grains of nine pearl millet cultivars were fractionated through a Biogel column. Five different sugars‘(stachyose, raffinose, sucrose, glucose, and fructose) were identified. Sucrose was predominant in all the cultivars. Raffinose content was high as compared to other cereals, and maltose was absen
Error bounds for the large-argument asymptotic expansions of the Hankel and Bessel functions
In this paper, we reconsider the large-argument asymptotic expansions of the
Hankel, Bessel and modified Bessel functions and their derivatives. New
integral representations for the remainder terms of these asymptotic expansions
are found and used to obtain sharp and realistic error bounds. We also give
re-expansions for these remainder terms and provide their error estimates. A
detailed discussion on the sharpness of our error bounds and their relation to
other results in the literature is given. The techniques used in this paper
should also generalize to asymptotic expansions which arise from an application
of the method of steepest descents.Comment: 32 pages, 2 figures, accepted for publication in Acta Applicandae
Mathematica
The Importance of Time Congruity in the Organisation.
In 1991 Kaufman, Lane, and Lindquist proposed that time congruity in terms of an individual's time preferences and the time use methods of an organisation would lead to satisfactory performance and enhancement of quality of work and general life. The research reported here presents a study which uses commensurate person and job measures of time personality in an organisational setting to assess the effects of time congruity on one aspect of work life, job-related affective well-being. Results show that time personality and time congruity were found to have direct effects on well-being and the influence of time congruity was found to be mediated through time personality, thus contributing to the person–job (P–J) fit literature which suggests that direct effects are often more important than indirect effects. The study also provides some practical examples of ways to address some of the previously cited methodological issues in P–J fit research
Evolution of active and polar photospheric magnetic fields during the rise of Cycle 24 compared to previous cycles
The evolution of the photospheric magnetic field during the declining phase
and minimum of Cycle 23 and the recent rise of Cycle 24 are compared with the
behavior during previous cycles. We used longitudinal full-disk magnetograms
from the NSO's three magnetographs at Kitt Peak, the Synoptic Optical Long-term
Investigations of the Sun (SOLIS) Vector Spectro-Magnetograph (VSM), the
Spectromagnetograph and the 512-Channel Magnetograph instruments, and
longitudinal full-disk magnetograms from the Mt. Wilson 150-foot tower. We
analyzed 37 years of observations from these two observatories that have been
observing daily, weather permitting, since 1974, offering an opportunity to
study the evolving relationship between the active region and polar fields in
some detail over several solar cycles. It is found that the annual averages of
a proxy for the active region poloidal magnetic field strength, the magnetic
field strength of the high-latitude poleward streams, and the time derivative
of the polar field strength are all well correlated in each hemisphere. These
results are based on statistically significant cyclical patterns in the active
region fields and are consistent with the Babcock-Leighton phenomenological
model for the solar activity cycle. There was more hemispheric asymmetry in the
activity level, as measured by total and maximum active region flux, during
late Cycle 23 (after around 2004), when the southern hemisphere was more
active, and Cycle 24 up to the present, when the northern hemisphere has been
more active, than at any other time since 1974. The active region net proxy
poloidal fields effectively disappeared in both hemispheres around 2004, and
the polar fields did not become significantly stronger after this time. We see
evidence that the process of Cycle 24 field reversal has begun at both poles.Comment: Accepted for publication in Solar Physic
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