11,018 research outputs found
The value of the fine structure constant over cosmological times
The optical spectra of objects classified as QSOs in the SDSS DR6 are
analyzed with the aim of determining the value of the fine structure constant
in the past and then check for possible changes in the constant over
cosmological timescales. The analysis is done by measuring the position of the
fine structure lines of the [OIII] doublet (4959 and 5008) in QSO nebular
emission. From the sample of QSOs at redshifts z < 0.8 a subsample was selected
on the basis of the amplitude and width of the [OIII] lines. Two different
method were used to determine the position of the lines of the [OIII] doublet,
both giving similar results. Using a clean sample containing 1568 of such
spectra, a value of Delta alpha /alpha=(+2.4 +-2.5) x 10^{-5} (in the range of
redshifts 0-0.8) was determined. The use of a larger number of spectra allows a
factor ~5 improvement on previous constraints based on the same method. On the
whole, we find no evidence of changes in alpha on such cosmological timescales.
The mean variation compatible with our results is 1/ Delta
alpha/alpha=(+0.7 +- 0.7) x 10^{-14} yr^{-1}. The analysis was extended to the
[NeIII] and [SII] doublets, although their usefulness is limited due to the
fact that all these doublets in QSOs tend to be fainter than [OIII], and that
some of them are affected by systematics.Comment: 22 pages, 10 figures. Accepted for publication in Astrophysical
Journa
Designing and Building immersive education spaces using Project Wonderland: from pedagogy through to practice
This paper presents work on the JISC funded SIMiLLE project to build a culturally sensitive virtual world to support language learning. This builds on the MiRTLE project (funded by Sun Microsystems), which created a mixed-reality space for teaching and learning. The aim of the SIMiLLE project is to investigate the technical feasibility and pedagogical value of using virtual environments to provide a realistic socio-cultural setting and content for language learning interaction. The paper starts by providing some background information on the Wonderland platform and the MiRTLE project, and then outlines the requirements for SIMiLLE, and how these requirements will be supported through the use of a virtual world based on Project Wonderland. We then present our plans for the evaluation of the system, with a particular focus on the importance of incorporating pedagogy into the design of these systems, and how we can support good practice with the ever-growing use of 3D virtual environments in formalised education
Non-radial Pulsations in the Open Cluster NGC 3766
Non-radial pulsations (NRPs) are a proposed mechanism for the formation of
decretion disks around Be stars and are important tools to study the internal
structure of stars. NGC 3766 has an unusually large fraction of transient Be
stars, so it is an excellent location to study the formation mechanism of Be
star disks. High resolution spectroscopy can reveal line profile variations
from NRPs, allowing measurements of both the degree, l, and azimuthal order, m.
However, spectroscopic studies require large amounts of time with large
telescopes to achieve the necessary high S/N and time domain coverage. On the
other hand, multi-color photometry can be performed more easily with small
telescopes to measure l only. Here, we present representative light curves of
Be stars and non-emitting B stars in NGC 3766 from the CTIO 0.9m telescope in
an effort to study NRPs in this cluster.Comment: 4 pages, to appear in the proceedings of IAU Symposium 266: Star
Cluster
Observation of a parity oscillation in the conductance of atomic wires
Using a scanning tunnel microscope or mechanically controlled break
junctions, atomic contacts of Au, Pt and Ir are pulled to form chains of atoms.
We have recorded traces of conductance during the pulling process and averaged
these for a large amount of contacts. An oscillatory evolution of conductance
is observed during the formation of the monoatomic chain suggesting a
dependence on even or odd numbers of atoms forming the chain. This behaviour is
not only present in the monovalent metal Au, as it has been previously
predicted, but is also found in the other metals which form chains suggesting
it to be a universal feature of atomic wires
Efecto de la probabilidad de errores durante la acción de ataque de esgrima
El propósito de este estudio ha sido comprobar el efecto que tiene la probabilidad de que surja el
error durante la realización de una acción de ataque en esgrima, sobre los parámetros temporales
de las respuestas de reacción (TRR) y la velocidad de desplazamiento del centro de masas (CM).
Han participado 17 esgrimistas (14 hombres y 3 mujeres), con una experiencia en competición
regional de más de cinco años. Para el registro de los datos, se han utilizado dos plataformas de
fuerza, operando a 500 Hz, una cámara de vídeo, a 210 Hz y un cronómetro electrónico adaptado al
sistema de cableado de las armas. Una señal electrónica se utilizó para sincronizar temporalmente
todos los registros. Para la situación experimental donde no existía incertidumbre durante la acción
(CIA), los esgrimistas tenían que realizar un ataque simple con fondo lo más rápidamente posible
al aparecer un círculo en el centro del plastrón (E1), intentando situar la punta de la espada dentro
del círculo. Para la situación experimental donde existía incertidumbre debida a la posibilidad de
error (CIA), los esgrimistas tenían los mismos objetivos que en la situación anterior, aunque debían
de inhibir la acción de ataque a otra de defensiva, en el caso de que el círculo desapareciera del
plastrón durante la acción. Los resultados ponen de manifiesto que, cuando existe la posibilidad de
error durante la realización del ataque en esgrima, se incrementan los parámetros temporales de la
respuesta de reacción (TR y TM) y disminuye la velocidad de ejecución.The main aim of this study has been to verify the effect that has the probability from which the
mistake arises during the accomplishment of an action of assault in fencing, on the temporary
parameters of the answers of reaction (TRR) and the speed of displacement of the center of masses
(CM). 17 fencers (14 men and 3 women), with an experience in regional competition of more than
five years took part in this study. Two force platforms, operating to 500 Hz have been in used, a video
camera, to 210 Hz and an electronic chronometer adapted to the system of wired up of the weapon
for the record of the data. An electronic sign was used for synchronizing temporarily all the records.
For the experimental situation where uncertainty did not exist during the action (CIA), the fencers
had to realize a simple assault with lunge as rapidly as possible when a circle appeared in the center
of the plastron (E1), trying to place the top of the sword inside the circle. For the experimental
situation where there existed uncertainty due to the possibility of mistake (CIA), the fencers had the
same aims that in the previous situation, though they must disable the action of assault to other one
of defensive, in case the circle was disappearing of the plastron during the action. The results reveal
that, when the possibility of mistake exists during the accomplishment of the assault in fencing, there
are increased the temporary parameters of the response of reaction (TR and TM) and it diminishes
the speed of execution.Peer Reviewe
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