567 research outputs found
Variation of fluxes of RR Tel emission lines measured in 2000 with respect to 1996
The aim of this work is to make available unpublished non-Fe+ emission line
fluxes from optical spectra of the symbiotic nova RR Tel which were taken in
2000, and to compare them with fluxes of the same lines from spectra taken in
1996. After leaving out blends and misidentifications, as well as the
unreliable far-red and violet lines, we present the log (F2000/F1996) flux
ratios for identified non-Fe+ lines. Mean values of log (F2000/F1996) for
different ionization potential ranges of the ions producing the lines are shown
separately for the permitted and forbidden lines. All means show fading, which
is larger in the lowest range of ionization potential. Provisional
interpretations are suggested. We also measured the values of FWHM in 2000; the
previously known decrease with time of FWHM of lines due to the same ion has
continued.Comment: 16 pages, 5 figure
The Role of Spatial Coherence and Orbital Angular Momentum of Light in Astronomy
The orbital angular momentum (OAM) of light is potentially interesting for
astronomical study of rotating objects such as black holes, but the effect of
reduced spatial coherence of astronomical light sources such as stars is
largely unknown. In a lab-scale experiment, we find that the detected OAM
spectrum depends strongly on the position of the light-twisting object along
the line of sight. We develop a simple intuitive model to predict the influence
of reduced spatial coherence in astronomical observations, and discuss
line-of-sight and intensity issues.Comment: updated versio
Microcavity resonance condition, quality factor, and mode volume are determined by different penetration depths
The penetration depth in a Distributed Bragg Reflector (DBR) co-determines
the resonance condition, quality factor, and mode volume of DBR-based
microcavities. Recent studies have used an incomplete description of the
penetration depth and incorrect equations. We present a complete analysis that
involves three different penetration depths. We also present a series of
experiments on microcavities to accurately determine the frequency and modal
penetration depth of our DBRs and compare these results with theoretical
predictions. The obtained results are relevant for anyone who models a DBR as
an effective hard mirror if lengths of the order of the wavelength are
relevant, as is the case for microcavities.Comment: 16 pages, 7 figure
Observation of Goos-H\"{a}nchen shifts in metallic reflection
We report the first observation of the Goos-Hnchen
shift of a light beam incident on a metal surface. This phenomenon is
particularly interesting because the Goos-Hnchen shift
for polarized light in metals is negative and much bigger than the positive
shift for polarized light. The experimental result for the measured shifts
as a function of the angle of incidence is in excellent agreement with
theoretical predictions. In an energy-flux interpretation, our measurement
shows the existence of a backward energy flow at the bare metal surface when
this is excited by a polarized beam of light.Comment: The parer was published on Optics Express. The new version is
modified according to the reviewers suggestion
Optimisation of sample thickness for THz-TDS measurements
How thick should the sample be for a transmission THz-TDS measurement? Should
the sample be as thick as possible? The answer is `no'. Although more thickness
allows T-rays to interact more with bulk material, SNR rolls off with thickness
due to signal attenuation. Then, should the sample be extremely thin? Again,
the answer is `no'. A sample that is too thin renders itself nearly invisible
to T-rays, in such a way that the system can hardly sense the difference
between the sample and a free space path. So, where is the optimal boundary
between `too thick' and `too thin'? The trade-off is analysed and revealed in
this paper, where our approach is to find the optimal thickness that results in
the minimal variance of measured optical constants.Comment: 13 pages, 11 figure
Absolute dimensions of solar-type eclipsing binaries. EF Aquarii: a G0 test for stellar evolution models
Recent studies have shown that stellar chromospheric activity, and its effect
on convective energy transport in the envelope, is most likely the cause of
significant radius and temperature discrepancies between theoretical evolution
models and observations. We aim to determine absolute dimensions and abundances
for the solar-type detached eclipsing binary EF Aqr, and to perform a detailed
comparison with results from recent stellar evolutionary models. uvby-beta
standard photometry was obtained with the Stromgren Automatic Telescope. The
broadening function formalism was applied on spectra observed with HERMES at
the Mercator telescope in La Palma, to obtain radial velocity curves. Masses
and radii with a precision of 0.6% and 1.0% respectively have been established
for both components of EF Aqr. The active 0.956 M_sol secondary shows star
spots and strong Ca II H and K emission lines. The 1.224 M_sol primary shows
signs of activity as well, but at a lower level. An [Fe/H] abundance of
0.00+-0.10 is derived with similar abundances for Si, Ca, Sc, Ti, V, Cr, Co,
and Ni. Solar calibrated evolutionary models such as Yonsei-Yale,
Victoria-Regina and BaSTI isochrones and evolutionary tracks are unable to
reproduce EF Aqr, especially for the secondary, which is 9% larger and 400 K
cooler than predicted. Models adopting significantly lower mixing length
parameters l/H_p remove these discrepancies, as seen in other solar type
binaries. For the observed metallicity, Granada models with a mixing length of
l/H_p=1.30 (primary) and 1.05 (secondary) reproduce both components at a common
age of 1.5+-0.6 Gyr. Observations of EF Aqr suggests that magnetic activity,
and its effect on envelope convection, is likely to be the cause of
discrepancies in both radius and temperature, which can be removed by adjusting
the mixing length parameter of the models downwards.Comment: 11 pages, 8 figures, accepted for publication by A&
Herschel PACS and SPIRE observations of blazar PKS 1510-089: a case for two blazar zones
We present the results of observations of blazar PKS 1510-089 with the
Herschel Space Observatory PACS and SPIRE instruments, together with
multiwavelength data from Fermi/LAT, Swift, SMARTS and SMA. The source was
found in a quiet state, and its far-infrared spectrum is consistent with a
power-law with a spectral index of alpha ~ 0.7. Our Herschel observations were
preceded by two 'orphan' gamma-ray flares. The near-infrared data reveal the
high-energy cut-off in the main synchrotron component, which cannot be
associated with the main gamma-ray component in a one-zone leptonic model. This
is because in such a model the luminosity ratio of the External-Compton and
synchrotron components is tightly related to the frequency ratio of these
components, and in this particular case an unrealistically high energy density
of the external radiation would be implied. Therefore, we consider a
well-constrained two-zone blazar model to interpret the entire dataset. In this
framework, the observed infrared emission is associated with the synchrotron
component produced in the hot-dust region at the supra-pc scale, while the
gamma-ray emission is associated with the External-Compton component produced
in the broad-line region at the sub-pc scale. In addition, the optical/UV
emission is associated with the accretion disk thermal emission, with the
accretion disk corona likely contributing to the X-ray emission.Comment: 13 pages, 8 figures, 7 tables; accepted for publication in the
Astrophysical Journa
Integrating Liberal Education Perspectives in a Transdisciplinary Design Studio
Short Abstract:
In this presentation, we describe the evolution of our approach to integrating liberal education perspectives within an innovative transdisciplinary learning program. Our experiences are used to illustrate challenges in systematically incorporating liberal education perspectives, including instructional and student barriers to viewing the world from a variety of disciplinary perspectives.
Full Abstract:
The increasing complexity of design outcomes requires students to develop deep competence in communication and interpersonal skills, including an understanding of how technology is intertwined with societal and human needs. Locating and synthesizing information is crucial to solving interesting and worthwhile problems, but may not be obvious from a solely technical or solely humanities perspective. However, there is relatively little guidance as to how liberal education perspectives might be systematically integrated. In this presentation, we describe the evolution of our approach to integrating liberal education perspectives within an innovative transdisciplinary learning program located at the Purdue Polytechnic Institute. This evolution has included a merger of existing courses, a dual-strand seminar and studio learning experience, and most recently, an integrated studio experience that encapsulates a multiplicity of disciplinary perspectives from liberal education and technology. Our program design experiences are used to illustrate the challenges in systematically incorporating liberal education perspectives in a transdisciplinary learning environment, and the instructional and student barriers to viewing the world through multiple lenses from a variety of disciplinary perspectives
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