1,950 research outputs found
Cone Monotonicity: Structure Theorem, Properties, and Comparisons to Other Notions of Monotonicity
In search of a meaningful 2-dimensional analog to mono- tonicity, we
introduce two new definitions and give examples of and dis- cuss the
relationship between these definitions and others that we found in the
literature. Note: After we published the article in Abstract and Applied
Analysis and after we searched multiple times for previous work, we discovered
that Clarke at al. had introduced the definition of cone monotonicity and given
a characterization. See the addendum at the end of this paper for full
reference information
The Rapidly Rotating, Hydrogen Deficient, Hot Post-Asymptotic Giant Branch Star ZNG 1 in the Globular Cluster M5
We report observations of the hot post-asymptotic giant branch star ZNG 1 in
the globular cluster M5 (NGC 5904) with the Far Ultraviolet Spectroscopic
Explorer (FUSE). From the resulting spectrum, we derive an effective
temperature T_eff = 44300 +/- 300 K, a surface gravity log g = 4.3 +/- 0.1, a
rotational velocity v sin i = 170 +/- 20 km/s, and a luminosity log (L/L_sun) =
3.52 +/- 0.04. The atmosphere is helium-rich (Y = 0.93), with enhanced carbon
(2.6% by mass), nitrogen (0.51%) and oxygen (0.37%) abundances. The spectrum
shows evidence for a wind with terminal velocity near 1000 km/s and an
expanding shell of carbon- and nitrogen-rich material around the star. The
abundance pattern of ZNG 1 is suggestive of the ``born-again'' scenario,
whereby a star on the white-dwarf cooling curve undergoes a very late shell
flash and returns to the AGB, but the star's rapid rotation is more easily
explained by a previous interaction with a binary companion.Comment: 8 pages, 2 PostScript figures, Latex with emulateapj5. Accepted for
publication in ApJ Letter
Final Calibration of the Berkeley Extreme and Far-Ultraviolet Spectrometer on the ORFEUS-SPAS I and II Missions
The Berkeley Extreme and Far-Ultraviolet Spectrometer (BEFS) flew as part of
the ORFEUS telescope on the ORFEUS-SPAS I and II space-shuttle missions in 1993
and 1996, respectively. The data obtained by this instrument have now entered
the public domain. To facilitate their use by the astronomical community, we
have re-extracted and re-calibrated both data sets, converted them into a
standard (FITS) format, and placed them in the Multimission Archive at Space
Telescope (MAST). Our final calibration yields improved wavelength scales and
effective-area curves for both data sets.Comment: To appear in the January 2002 issue of the PASP. 17 pages with 9
embedded postscript figures; uses emulateapj5.st
A self-interacting partially directed walk subject to a force
We consider a directed walk model of a homopolymer (in two dimensions) which
is self-interacting and can undergo a collapse transition, subject to an
applied tensile force. We review and interpret all the results already in the
literature concerning the case where this force is in the preferred direction
of the walk. We consider the force extension curves at different temperatures
as well as the critical-force temperature curve. We demonstrate that this model
can be analysed rigorously for all key quantities of interest even when there
may not be explicit expressions for these quantities available. We show which
of the techniques available can be extended to the full model, where the force
has components in the preferred direction and the direction perpendicular to
this. Whilst the solution of the generating function is available, its analysis
is far more complicated and not all the rigorous techniques are available.
However, many results can be extracted including the location of the critical
point which gives the general critical-force temperature curve. Lastly, we
generalise the model to a three-dimensional analogue and show that several key
properties can be analysed if the force is restricted to the plane of preferred
directions.Comment: 35 pages, 14 figure
Stokes phenomenon and matched asymptotic expansions
This paper describes the use of matched asymptotic expansions to illuminate the description of functions exhibiting Stokes phenomenon. In particular the approach highlights the way in which the local structure and the possibility of finding Stokes multipliers explicitly depend on the behaviour of the coefficients of the relevant asymptotic expansions
Identifying Motivational Factors Impacting Entrepreneurship: Evidence from an Emerging Economy
The development of endo-selective epoxide-opening cascades in water
This tutorial review traces the development of endo-regioselective epoxide-opening reactions in water. Templated, water-promoted epoxide-opening cyclization reactions can offer rapid access to subunits of the ladder polyethers, a fascinating and complex family of natural products. This review may be of interest to those curious about the ladder polyethers and their hypothesized biogenesis, about organic reactions in water, and about the development and application of cascade reactions in organic synthesis
Conservation implications of turtle declines in Australia's Murray River system
Abstract Conservation requires rapid action to be effective, which is often difficult because of funding limitations, political constraints, and limited data. Turtles are among the world’s most endangered vertebrate taxa, with almost half of 356 species threatened with extinction. In Australia’s Murray River, nest predation by invasive foxes (Vulpes vulpes) was predicted to drive turtle declines in the 1980s. We assessed populations of the broad-shelled turtle (Chelodina expansa), eastern long-necked turtle (C. longicollis), and Murray River turtle (Emydura macquarii) in the Murray River and some of its associated waterways. Our results suggest that the predicted decline is occurring. All three species are rare in the lower Murray River region, and were undetected in many locations in South Australia. Moreover, E. macquarii had considerable population aging almost everywhere, possibly due to comprehensive nest destruction by foxes. Chelodina longicollis also had population aging at some sites. Sustained low recruitment has potential to lead to collapses as turtles age, which is particularly worrying because it was predicted over 30 years ago and may have already occurred in South Australia. Our results show that turtle declines were not mitigated since that prediction. If the crash continues, a vertebrate guild responsible for considerable nutrient cycling in the aquatic ecosystem will disappear. Our results highlight a worst-case outcome when species declines are predicted, but insufficiently mitigated
The relationship between the optical Halpha filaments and the X-ray emission in the core of the Perseus cluster
NGC 1275 in the centre of the Perseus cluster of galaxies, Abell 426, is
surrounded by a spectacular filamentary Halpha nebula. Deep Chandra X-ray
imaging has revealed that the brighter outer filaments are also detected in
soft X-rays. This can be due to conduction and mixing of the cold gas in the
filaments with the hot, dense intracluster medium. We show the correspondence
of the filaments in both wavebands and draw attention to the relationship of
two prominent curved NW filaments to an outer, buoyant radio bubble seen as a
hole in the X-ray image. There is a strong resemblance in the shape of the hole
and the disposition of the filaments to the behaviour of a large air bubble
rising in water. If this is a correct analogy, then the flow is laminar and the
intracluster gas around this radio source is not turbulent. We obtain a limit
on the viscosity of this gas.Comment: Accepted for publication in MNRA
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