5,355 research outputs found
The horizon problem for prevalent surfaces
We investigate the box dimensions of the horizon of a fractal surface defined
by a function . In particular we show that a prevalent surface
satisfies the `horizon property', namely that the box dimension of the horizon
is one less than that of the surface. Since a prevalent surface has box
dimension 3, this does not give us any information about the horizon of
surfaces of dimension strictly less than 3. To examine this situation we
introduce spaces of functions with surfaces of upper box dimension at most
\alpha, for \alpha [2,3). In this setting the behaviour of the horizon is
more subtle. We construct a prevalent subset of these spaces where the lower
box dimension of the horizon lies between the dimension of the surface minus
one and 2. We show that in the sense of prevalence these bounds are as tight as
possible if the spaces are defined purely in terms of dimension. However, if we
work in Lipschitz spaces, the horizon property does indeed hold for prevalent
functions. Along the way, we obtain a range of properties of box dimensions of
sums of functions
Continuum of cardiac care
Ohio Valley Medical Center is 453-bed acute care hospital in Wheeling, West Virginia. The hospital is centrally located in the Upper Ohio Valley and provides tertiary care services to a patient population in excess of 150,000. The hospital provides the full array of cardiac services with the exception of open heart surgery and coronary angioplasty. The hospital must determine the need and financial viability to institute these services. The financial stability of the organization and the health care needs of the patient population depend on the continuum of cardiac care. The researcher established need through a recognized methodology. Need was well documented and financial viability was proven. Alternatives to the establishment of an open heart surgery and coronary angioplasty program at Ohio Valley Medical Center are provided. All documentation was in order with established protocols set forth by the state of West Virginia. The researcher recommended the development of the program after certificate of need approval from the state of West Virginia and provided alternative solutions if the certificate of need was not granted
High velocity clouds in the Galactic All Sky Survey I. Catalogue
We present a catalogue of high-velocity clouds (HVCs) from the Galactic All
Sky Survey (GASS) of southern-sky neutral hydrogen, which has 57 mK sensitivity
and 1 km/s velocity resolution and was obtained with the Parkes Telescope. Our
catalogue has been derived from the stray-radiation corrected second release of
GASS. We describe the data and our method of identifying HVCs and analyse the
overall properties of the GASS population. We catalogue a total of 1693 HVCs at
declinations < 0 deg, including 1111 positive velocity HVCs and 582 negative
velocity HVCs. Our catalogue also includes 295 anomalous velocity clouds
(AVCs). The cloud line-widths of our HVC population have a median FWHM of ~19
km/s, which is lower than found in previous surveys. The completeness of our
catalogue is above 95% based on comparison with the HIPASS catalogue of HVCs,
upon which we improve with an order of magnitude in spectral resolution. We
find 758 new HVCs and AVCs with no HIPASS counterpart. The GASS catalogue will
shed an unprecedented light on the distribution and kinematic structure of
southern-sky HVCs, as well as delve further into the cloud populations that
make up the anomalous velocity gas of the Milky Way.Comment: 21 pages, 14 figures, accepted for publication in ApJ
Measuring the atomic composition of planetary building blocks
Volatile molecules are critical to terrestrial planetary habitability, yet
difficult to observe directly where planets form at the midplanes of
protoplanetary disks. It is unclear whether the inner 1 AU of disks are
volatile-poor or if this region is resupplied with ice-rich dust from colder
disk regions. Dust traps at radial pressure maxima bounding disk gaps can cut
off the inner disk from such volatile reservoirs. However, the trap retention
efficiency and atomic composition of trapped dust have not been measured.
We present a new technique to measure the absolute atomic abundances in gas
accreting onto T Tauri stars and infer the bulk atomic composition and
distribution of midplane solids retained in the disk around the young star TW
Hya. We identify line emission from gas-phase material inside the dust
sublimation rim of TW Hya. Gaussian decomposition of the strongest H Paschen
lines isolates the inner disk hydrogen emission. We measure several key
elemental abundances, relative to hydrogen, using a chemical photoionization
model and infer dust retention in the disk. With a 1D transport model, we
determine approximate radial locations and retention efficiencies of dust traps
for different elements. Volatile and refractory elements are depleted from TW
Hya's hot gas by factors of ~10^2 and up to 10^5, respectively. Dust traps
beyond the CO and N2 snowline cumulatively sequester 96% of the total dust,
while the trap at 2 AU retains 3% of the initial dust mass. The high depletions
of Si, Mg, and Ca are explained by a third trap at 0.3 AU. TW Hya has a
significant volatile reservoir rich in C- and N-ices in its outer ring
structure. However, the lack of C resupply may leave the terrestrial
planet-forming region dry and carbon-poor. Any planets that form within the
silicate dust trap at 0.3 AU may resemble Earth in terms of the degree of their
volatile depletion.Comment: Accepted for publication in A&A Letters. 6 pages, 3 figures, plus
appendice
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