181 research outputs found
Charles Williams\u27 P\u27o- L\u27u - the Cthulhu Connection
This presentation delineates the connections between horrific elements in the work of H.P. Lovecraft and the situation of P’o-L’u from Charles Williams
From Dubric to Taliessin: Charles Williams\u27s Early Work on the Arthurian Cycle
Explores the transformation of Dubric into Taliessen, focusing on how Dubric gradually recedes in importance in Williams’s thinking about the Arthur story and is finally transformed into Taliessen
Inverting Phase Functions to Map Exoplanets
We describe how to generate a longitudinal brightness map for a tidally
locked exoplanet from its phase function light curve. We operate under a number
of simplifying assumptions, neglecting limb darkening/brightening, star spots,
detector ramps, as well as time-variability over a single planetary rotation.
We develop the transformation from a planetary brightness map to a phase
function light curve and simplify the expression for the case of an edge-on
system. We introduce two models--composed of longitudinal slices of uniform
brightness, and sinusoidally varying maps, respectively--which greatly simplify
the transformation from map to light curve. We discuss numerical approaches to
extracting a longitudinal map from a phase function light curve, explaining how
to estimate the uncertainty in a computed map and how to choose an appropriate
number of fit parameters. We demonstrate these techniques on a simulated map
and discuss the uses and limitations of longitudinal maps. The sinusoidal model
provides a better fit to the planet's underlying brightness map, although the
slice model is more appropriate for light curves which only span a fraction of
the planet's orbit. Regardless of which model is used, we find that there is a
maximum of ~5 free parameters which can be meaningfully fit based on a full
phase function light curve, due to the insensitivity of the latter to certain
modes of the map.Comment: 5 pages, 3 figures, accepted for publication in ApJ
The climate of HD 189733b from fourteen transits and eclipses measured by Spitzer
We present observations of seven transits and seven eclipses of the
transiting planet system HD 189733 taken with Spitzer IRAC at 8 microns. We use
a new correction for the detector ramp variation with a double-exponential
function. Our main findings are: (1) an upper limit on the variability of the
day-side planet flux of 2.7% (68% confidence); (2) the most precise set of
transit times measured for a transiting planet, with an average accuracy of 3
seconds; (3) a lack of transit-timing variations, excluding the presence of
second planets in this system above 20% of the mass of Mars in low-order
mean-motion resonance at 95% confidence; (4) a confirmation of the planet's
phase variation, finding the night side is 64% as bright as the day side, as
well as an upper limit on the night-side variability of 17% (68% confidence);
(5) a better correction for stellar variability at 8 micron causing the phase
function to peak 3.5 hrs before secondary eclipse, confirming that the
advection and radiation timescales are comparable at the 8 micron photosphere;
(6) variation in the depth of transit, which possibly implies variations in the
surface brightness of the portion of the star occulted by the planet, posing a
fundamental limit on non-simultaneous multi-wavelength transit absorption
measurements of planet atmospheres; (7) a measurement of the infrared
limb-darkening of the star, in agreement with stellar atmosphere models; (8) an
offset in the times of secondary eclipse of 69 sec, which is mostly accounted
for by a 31 sec light travel time delay and 33 sec delay due to the shift of
ingress and egress by the planet hot spot; this confirms that the phase
variation is due to an offset hot spot on the planet; (9) a retraction of the
claimed eccentricity of this system due to the offset of secondary eclipse; and
(10) high precision measurements of the parameters of this system.Comment: 18 pages, 19 figures, accepted for publication in the Astrophysical
Journa
Reviews
Christianity and the Detective Story. Ed. Anya Morlan and Walter Raubicheck. Reviewed by Melody Green.
The Shamanic Odyssey: Homer, Tolkien, and the Visionary Experience Robert Tindall with Susana Bustos. Foreword by John Perkins. Reviewed by Emily E. Auger.
Gaining a Face: The Romanticism of C.S. Lewis. James Prothero and Donald T. Williams. Reviewed by Crystal Hurd.
The A-Z of C.S. Lewis: An Encyclopedia of His Life, Thought and Writings. Colin Duriez. Reviewed by Andrew Stout.
Under The Mercy: Charles Williams & The Holy Grail. Robert Peirano. Reviewed by Eric Rauscher.
Tolkien and the Modernists: Literary Responses to the Dark New Days of the 20th Century. Theresa Freda Nicolay. Reviewed by Robert T. Tally Jr.
Tolkien at Exeter College: How an Oxford undergraduate Created Middle-Earth. John Garth. Reviewed by Mike Foster
Fastitocalon: Studies in Fantasticism Ancient to Modern. Editors in Chief Thomas Honegger and Fanfan Chen. Reviewed by Janet Brennan Croft.
TOLKIEN Studies XI Editors: Michael D.C. Drout, Verlyn Flieger, and David Bratman. Reviewed by Janet Brennan Croft
Synthesis, structure, magnetism, and high temperature thermoelectric properties of Ge doped Yb_(14)MnSb_(11)
The Zintl phase Yb_(14)MnSb_(11) was successfully doped with Ge utilizing a tin flux technique. The stoichiometry was determined by microprobe analysis to be Yb_(13.99(14))Mn_(1.05(5))Sb_(10.89(16))Ge_(0.06(3)). This was the maximum amount of Ge that could be incorporated into the structure via flux synthesis regardless of the amount included in the reaction. Single crystal X-ray diffraction could not unambiguously determine the site occupancy for Ge. Bond lengths varied by about 1% or less, compared with the undoped structure, suggesting that the small amount of Ge dopant does not significantly perturb the structure. Differential scanning calorimetry/thermogravimetry (DSC/TG) show that the doped compound's melting point is greater than 1200 K. The electrical resistivity and magnetism are virtually unchanged from the parent material, suggesting that Yb is present as Yb^(2+) and that the Ge dopant has little effect on the magnetic structure. At 900 K the resistivity and Seebeck coefficient decrease resulting in a zT of 0.45 at 1100 K, significantly lower than the undoped compound
The star formation histories of low surface brightness galaxies
We have performed deep imaging of a diverse sample of 26 low surface brightness galaxies (LSBGs) in the optical and the near-infrared. Using stellar population synthesis models, we find that it is possible to place constraints on the ratio of young to old stars (which we parametrize in terms of the average age of the galaxy), as well as the metallicity of the galaxy, using optical and near-infrared colours. LSBGs have a wide range of morphologies and stellar populations, ranging from older, high-metallicity earlier types to much younger and lower-metallicity late-type galaxies. Despite this wide range of star formation histories, we find that colour gradients are common in LSBGs. These are most naturally interpreted as gradients in mean stellar age, with the outer regions of LSBGs having lower ages than their inner regions. In an attempt to understand what drives the differences in LSBG stellar populations, we compare LSBG average ages and metallicities with their physical parameters. Strong correlations are seen between an LSBG's star formation history and its K-band surface brightness, K-band absolute magnitude and gas fraction. These correlations are consistent with a scenario in which the star formation history of an LSBG primarily correlates with its surface density and its metallicity correlates with both its mass and its surface densit
The Stellar Populations of Low Surface Brightness Galaxies
Near-infrared (NIR) K' images of a sample of five low surface brightness disc
galaxies (LSBGs) were combined with optical data, with the aim of constraining
their star formation histories. Both red and blue LSBGs were imaged to enable
comparison of their stellar populations. For both types of galaxy strong colour
gradients were found, consistent with mean stellar age gradients. Very low
stellar metallicities were ruled out on the basis of metallicity-sensitive
optical-NIR colours. These five galaxies suggest that red and blue LSBGs have
very different star formation histories and represent two independent routes to
low B band surface brightness. Blue LSBGs are well described by models with
low, roughly constant star formation rates, whereas red LSBGs are better
described by a `faded disc' scenario.Comment: 5 pages LaTeX; 2 embedded figures; MNRAS Letters, Accepte
Physico-chemical properties of manufactured nanomaterials - Characterisation and relevant methods. An outlook based on the OECD Testing Programme.
Identifying and characterising nanomaterials require additional information on physico-chemical properties and test methods, compared to chemicals in general. Furthermore, regulatory decisions for chemicals are usually based upon certain toxicological properties, and these effects may not be equivalent to those for nanomaterials. However, regulatory agencies lack an authoritative decision framework for nanomaterials that links the relevance of certain physico-chemical endpoints to toxicological effects. This paper investigates various physico-chemical endpoints and available test methods that could be used to produce such a decision framework for nanomaterials. It presents an overview of regulatory relevance and methods used for testing fifteen proposed physico-chemical properties of eleven nanomaterials in the OECD Working Party on Manufactured Nanomaterials' Testing Programme, complemented with methods from literature, and assesses the methods' adequacy and applications limits. Most endpoints are of regulatory relevance, though the specific parameters depend on the nanomaterial and type of assessment. Size (distribution) is the common characteristic of all nanomaterials and is decisive information for classifying a material as a nanomaterial. Shape is an important particle descriptor. The octanol-water partitioning coefficient is undefined for particulate nanomaterials. Methods, including sample preparation, need to be further standardised, and some new methods are needed. The current work of OECD's Test Guidelines Programme regarding physico-chemical properties is highlighted
- …