2,207 research outputs found
Unplugging the Universe: the neglected electromagnetic consequence of decoupling
This letter concentrates on the non-equilibrium evolution of magnetic field
structures at the onset of recombination, when the charged particle current
densities decay as neutrals are formed.
We consider the effect that a decaying magnetic flux has on the acceleration
of particles via the transient induced electric field. Since the residual
charged-particle number density is small as a result of decoupling, we shall
consider the magnetic and electric fields essentially to be imposed, neglecting
the feedback from any minority accelerated population.
We find that the electromagnetic treatment of this phase transition can
produce energetic electrons scattered throughout the Universe. Such particles
could have a significant effect on cosmic evolution in several ways: (i) their
presence could delay the effective end of the recombination era; (ii) they
could give rise to plasma concentrations that could enhance early gravitational
collapse of matter by opposing cosmic expansion to a greater degree than
neutral matter could; (iii) they could continue to be accelerated, and become
the seed for reionisation at the later epoch .Comment: 4 pages, no figure
Analytical and numerical investigation of mixed-type functional differential equations
NOTICE: this is the author’s version of a work that was accepted for publication in Journal of computational and applied mathematics. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Journal of computational and applied mathematics, 234 (2010), doi: 10.1016/j.cam.2010.01.028This journal article is concerned with the approximate solution of a linear non-autonomous functional differential equation, with both advanced and delayed arguments
On the changes in the physical properties of the ionized region around the Weigelt structures in Eta Carinae over the 5.54-yr spectroscopic cycle
We present HST/STIS observations and analysis of two prominent nebular
structures around the central source of Eta Carinae, the knots C and D. The
former is brighter than the latter for emission lines from intermediate or high
ionization potential ions. The brightness of lines from intermediate and high
ionization potential ions significantly decreases at phases around periastron.
We do not see conspicuous changes in the brightness of lines from low
ionization potential (<13.6 eV) that the total extinction towards the Weigelt
structures is that the total extinction towards the Weigelt structures is AsubV
=2/0. that the total extinction towards the Weigelt structures is AV = 2.0.
Weigelt C and D are characterized by an electron density of that the total
extinction towards the Weigelt structures is AV = 2.0. Weigelt C and D are
characterized by an electron density of 10exp6.9 cm-3 that does not
significantly change throughout the orbital cycle. The electron temperature
varies from 5500 K (around periastron) to 7200 K (around apastron). The
relative changes in the brightness of He I lines are well reproduced by the
variations in the electron temperature alone. We found that, at phases around
periastron, the electron temperature seems to be higher for Weigelt C than that
of D. The Weigelt structures are located close to the Homunculus equatorial
plane, at a distance of about 1240 AU from the central source. From the
analysis of proper motion and age, the Weigelt complex can be associated with
the equatorial structure called the Butterfly Nebula surrounding the central
binary system.Comment: 19 pages, 18 figure
Repercusiones de la construcción del embalse de Yesa en la utilización del espacio de la Canal de Berdún (Altoaragón)
8 páginas, 4 tablas, 2 mapas[ES] El trabajo estudia las consecuenclas que, en el uso del espacio: acarrea
la instalación de un gran embalse. Hemos tomado como ejemplo el pantano de Yesa, localizado
en el extremo occidental de la depresión media altoaragonesa. El estudio muestra cómo la nueva organización del espacio supone una ruptura de la antigua gestión integrada del territorio e implica, por una parte,la simplificación del sistema y, por otra, el incremento de la participación
externa (estatal principalmente) en el control de los recursos locales.[IN]This work studies the consequences that, with regard lo the use of space,
the installation of a large dam causes in its environment. We have taken the dam of Yesa as an
example; it is located on the western end of the Upper-Aragon middle depresslon. The paper
shows that the new organization of space means, on the one hand, the rupture of the old integrated
management of territory, causes a simplification of the system and, on the other hand,
increase the external share (mainly state share) in the local resources control.Peer reviewe
Controle do ácaro-da-necrose-do-coqueiro Aceria guerreronis (Acari: Eriophyidae).
O óleo de algodão bruto vem sendo indicado no controle alternativo do ácaro-da-necrose, no entanto há uma carência de estudos que demonstrema eficiência relativa desse produto no controle da praga bem como de sua seletividade a ácaros predadores. O objetivo do trabalho foi avaliar a eficiência do óleo de algodão bruto em comparação com agrotóxicos registrados para o controle do ácaro-da-necrose bem como sua seletividade ao ácaro predador Typhlodromus ornatus (Acari: Phytoseiidae), comumente encontrado em plantios de coqueiro. Avaliações quinzenais das populações do ácaro-da-necrose demonstraram que Fenpiroximato, Abamectina e o óleo de algodão controlaram eficientemente a praga em condições de campo. Adicionalmente, experimentos de laboratório indicaram que além da toxicidade, esses produtos repelem o ácaro-da-necrose e o ácaro predador T. ornatus.
The numerical solution of forward–backward differential equations: Decomposition and related issues
NOTICE: this is the author’s version of a work that was accepted for publication in Journal of computational and applied mathematics. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Journal of computational and applied mathematics, 234,(2010), doi: 10.1016/j.cam.2010.01.039This journal article discusses the decomposition, by numerical methods, of solutions to mixed-type functional differential equations (MFDEs) into sums of “forward” solutions and “backward” solutions
Learning with multiple representations: An example of a revision lesson in mechanics
We describe an example of learning with multiple representations in an
A-level revision lesson on mechanics. The context of the problem involved the
motion of a ball thrown vertically upwards in air and studying how the
associated physical quantities changed during its flight. Different groups of
students were assigned to look at the ball's motion using various
representations: motion diagrams, vector diagrams, free-body diagrams, verbal
description, equations and graphs, drawn against time as well as against
displacement. Overall, feedback from students about the lesson was positive. We
further discuss the benefits of using computer simulation to support and extend
student learning.Comment: 10 pages, 5 figures, 2 tables http://iopscience.iop.org/0031-912
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