38 research outputs found
Nubble, Waisenen-Taminen, Harvard Mines
Guidebook to field trips in southern Maine; 57th meeting, October 8-10, 1965, held at Bowdoin College: Trip
The "toothbrush-relic": evidence for a coherent linear 2-Mpc scale shock wave in a massive merging galaxy cluster?
Some merging galaxy clusters host diffuse extended radio emission, so-called
radio halos and relics. Here we present observations between 147 MHz and 4.9
GHz of a new radio-selected galaxy cluster 1RXS J0603.3+4214 (z=0.225). The
cluster is also detected as an extended X-ray source in the RASS. It hosts a
large bright 1.9 Mpc radio relic, an elongated ~2 Mpc radio halo, and two
smaller radio relics. The large radio relic has a peculiar linear morphology.
For this relic we observe a clear spectral index gradient, in the direction
towards the cluster center. We performed Rotation Measure (RM) Synthesis
between 1.2 and 1.7 GHz. The results suggest that for the west part of the
large relic some of the Faraday rotation is caused by ICM and is not only due
to galactic foregrounds. We also carried out a detailed spectral analysis of
this radio relic and created radio color-color diagrams. We find (i) an
injection spectral index of -0.6 to -0.7, (ii) steepening spectral index and
increasing spectral curvature in the post-shock region, and (iii) an overall
power-law spectrum between 74 MHz and 4.9 GHz with \alpha=-1.10 \pm 0.02.
Mixing of emission in the beam from regions with different spectral ages is
probably the dominant factor that determines the shape of the radio spectra.
Changes in the magnetic field, total electron content, or adiabatic
gains/losses do not play a major role. A model in which particles are
(re)accelerated in a first order Fermi process at the front of the relic
provides the best match to the observed spectra. We speculate that in the
post-shock region particles are re-accelerated by merger induced turbulence to
form the radio halo as the relic and halo are connected. The 1RXS J0603.3+4214
merger is probably more complex than the "simple'" binary merger events that
are thought to give rise to symmetric double radio relics.Comment: 22 pages, 22 figures, accepted for publication in A\&A on September
3, 201
The importance of parameter choice in modelling dynamics of the eye lens
The lens provides refractive power to the eye and is capable of altering ocular focus in response to visual demand. This capacity diminishes with age. Current biomedical technologies, which seek to design an implant lens capable of replicating the function of the biological lens, are unable as yet to provide such an implant with the requisite optical quality or ability to change the focussing power of the eye. This is because the mechanism of altering focus, termed accommodation, is not fully understood and seemingly conflicting theories require experimental support which is difficult to obtain from the living eye. This investigation presents finite element models of the eye lens based on data from human lenses aged 16 and 35 years that consider the influence of various modelling parameters, including material properties, a wide range of angles of force application and capsular thickness. Results from axisymmetric models show that the anterior and posterior zonules may have a greater impact on shape change than the equatorial zonule and that choice of capsular thickness values can influence the results from modelled simulations
The topographic evolution of the Tibetan Region as revealed by palaeontology
The Tibetan Plateau was built through a succession of Gondwanan terranes colliding with Asia during the Mesozoic. These accretions produced a complex Paleogene topography of several predominantly eastâwest trending mountain ranges separated by deep valleys. Despite this piecemeal assembly and resultant complex relief, Tibet has traditionally been thought of as a coherent entity rising as one unit. This has led to the widely used phrase âthe uplift of the Tibetan Plateauâ, which is a false concept borne of simplistic modelling and confounds understanding the complex interactions between topography climate and biodiversity. Here, using the rich palaeontological record of the Tibetan region, we review what is known about the past topography of the Tibetan region using a combination of quantitative isotope and fossil palaeoaltimetric proxies, and present a new synthesis of the orography of Tibet throughout the Paleogene. We show why âthe uplift of the Tibetan Plateauâ never occurred, and quantify a new pattern of topographic and landscape evolution that contributed to the development of todayâs extraordinary Asian biodiversity