892 research outputs found
Delineation of major soil associations using ERTS-1 imagery
The delineation of a major soil association in the loess region of Obion County has been accomplished using ERTS-1 imagery. Channel 7 provides the clearest differentiation. The separation of other smaller soil associations in an intensive row crop agricultural area is somewhat more difficult. Soil differentiation has been accomplished visually as well as electronically using a scanning microdensitometer. Lower altitude aircraft imagery permits a more refined soil association identification and where imagery is of sufficient scale, even individual soils may be identified
Protostellar collapse: rotation and disk formation
We present some important conclusions from recent calculations pertaining to
the collapse of rotating molecular cloud cores with axial symmetry,
corresponding to evolution of young stellar objects through classes 0 and begin
of class I. Three main issues have been addressed: (1) The typical timescale
for building up a preplanetary disk - once more it turned out that it is of the
order of one free-fall time which is decisively shorter than the widely assumed
timescale related to the so-called 'inside-out collapse'; (2) Redistribution of
angular momentum and the accompanying dissipation of kinetic (rotational)
energy - together these processes govern the mechanical and thermal evolution
of the protostellar core to a large extent; (3) The origin of
calcium-aluminium-rich inclusions (CAIs) - due to the specific pattern of the
accretion flow, material that has undergone substantial chemical and
mineralogical modifications in the hot (exceeding 900 K) interior of the
protostellar core may have a good chance to be advectively transported outward
into the cooler remote parts (beyond 4 AU, say) of the growing disk and to
survive there until it is incorporated into a meteoritic body.Comment: 4 pages, 4 figure
Satellite on-board processing for earth resources data
Results of a survey of earth resources user applications and their data requirements, earth resources multispectral scanner sensor technology, and preprocessing algorithms for correcting the sensor outputs and for data bulk reduction are presented along with a candidate data format. Computational requirements required to implement the data analysis algorithms are included along with a review of computer architectures and organizations. Computer architectures capable of handling the algorithm computational requirements are suggested and the environmental effects of an on-board processor discussed. By relating performance parameters to the system requirements of each of the user requirements the feasibility of on-board processing is determined for each user. A tradeoff analysis is performed to determine the sensitivity of results to each of the system parameters. Significant results and conclusions are discussed, and recommendations are presented
Satellite on-board processing for earth resources data
The feasibility was investigated of an on-board earth resources data processor launched during the 1980-1990 time frame. Projected user applications were studied to define the data formats and the information extraction algorithms that the processor must execute. Based on these constraints, and the constraints imposed by the available technology, on-board processor systems were designed and their feasibility evaluated. Conclusions and recommendations are given
Giant planet formation: episodic impacts vs. gradual core growth
We describe the growth of gas giant planets in the core accretion scenario.
The core growth is not modeled as a gradual accretion of planetesimals but as
episodic impacts of large mass ratios, i.e. we study impacts of 0.02 - 1 Earth
masses onto cores of 1-15 Earth masses. Such impacts could deliver the majority
of solid matter in the giant impact regime. We focus on the thermal response of
the envelope to the energy delivery. Previous studies have shown that sudden
shut off of core accretion can dramatically speed up gas accretion. We
therefore expect that giant impacts followed by periods of very low core
accretion will result in a net increase in gas accretion rate. This study aims
at modelling such a sequence of events and to understand the reaction of the
envelope to giant impacts in more detail.
To model this scenario, we spread the impact energy deposition over a time
that is long compared to the sound crossing time, but very short compared to
the Kelvin-Helmholtz time. The simulations are done in spherical symmetry and
assume quasi-hydrostatic equilibrium.
Results confirm what could be inferred from previous studies: gas can be
accreted faster onto the core for the same net core growth speed while at the
same time rapid gas accretion can occur for smaller cores -- significantly
smaller than the usual critical core mass. Furthermore our simulations show,
that significant mass fractions of the envelope can be ejected by such an
impact
Evolution of Massive Protostars via Disk Accretion
Mass accretion onto (proto-)stars at high accretion rates > 10^-4 M_sun/yr is
expected in massive star formation. We study the evolution of massive
protostars at such high rates by numerically solving the stellar structure
equations. In this paper we examine the evolution via disk accretion. We
consider a limiting case of "cold" disk accretion, whereby most of the stellar
photosphere can radiate freely with negligible backwarming from the accretion
flow, and the accreting material settles onto the star with the same specific
entropy as the photosphere. We compare our results to the calculated evolution
via spherically symmetric accretion, the opposite limit, whereby the material
accreting onto the star contains the entropy produced in the accretion shock
front. We examine how different accretion geometries affect the evolution of
massive protostars. For cold disk accretion at 10^-3 M_sun/yr the radius of a
protostar is initially small, about a few R_sun. After several solar masses
have accreted, the protostar begins to bloat up and for M \simeq 10 M_sun the
stellar radius attains its maximum of 30 - 400 R_sun. The large radius about
100 R_sun is also a feature of spherically symmetric accretion at the same
accreted mass and accretion rate. Hence, expansion to a large radius is a
robust feature of accreting massive protostars. At later times the protostar
eventually begins to contract and reaches the Zero-Age Main-Sequence (ZAMS) for
M \simeq 30 M_sun, independent of the accretion geometry. For accretion rates
exceeding several 10^-3 M_sun/yr the protostar never contracts to the ZAMS. The
very large radius of several 100s R_sun results in a low effective temperature
and low UV luminosity of the protostar. Such bloated protostars could well
explain the existence of bright high-mass protostellar objects, which lack
detectable HII regions.Comment: 20 pages, 16 figure
A qualitative study of unmet needs and interactions with primary care among cancer survivors
INTRODUCTION: Despite increasing numbers, there is little research investigating the long-term needs of cancer survivors. The aim of this study is to explore the experiences of individuals who have survived at least 5 years following a cancer diagnosis, and to describe perceived unmet needs and interactions with primary care. METHODS: Forty long-term survivors of breast, colorectal and prostate cancer were purposively selected for an in-depth qualitative study. We aimed for a maximum variation sample according to cancer site, gender, time since diagnosis, cancer needs, anxiety and depression. Interviews were audio recorded and transcribed verbatim. Transcripts were coded thematically using a grounded theory approach. RESULTS: Analysis of the interview data is presented in four subthemes: the role they perceived for the general practitioner (GP), unmet needs, reasons for not using primary care for needs they perceived as cancer related, and ongoing care for cancer-related issues. The majority of cancer survivors did not see a role for their GP in their long-term care related to their cancer diagnosis as most considered that they did not need active follow-up, but some expressed a need for psychological services and information on possible long-term effects. Cancer survivors cited three main reasons for not using GP services in relation to their cancer diagnosis: GPs were seen as non-experts in cancer; they were perceived as too busy; and a lack of continuity within primary care made it difficult to talk about long-term issues. There was a wide variation in schedules and notification of PSA tests among the prostate cancer survivors. DISCUSSION: The results from this project suggest that some cancer survivors have specific emotional and physical needs that could benefit from input from their primary care team, but not all cancer survivors look to their GP for their long-term cancer-related care. Better information care planning is required from specialists in order to identify those who would benefit mos
The Transit Light Curve Project. X. A Christmas Transit of HD 17156b
Photometry is presented of the Dec. 25, 2007 transit of HD 17156b, which has
the longest orbital period and highest orbital eccentricity of all the known
transiting exoplanets. New measurements of the stellar radial velocity are also
presented. All the data are combined and integrated with stellar-evolutionary
modeling to derive refined system parameters. The planet's mass and radius are
found to be 3.212_{-0.082}^{+0.069} Jupiter masses and 1.023_{-0.055}^{+0.070}
Jupiter radii. The corresponding stellar properties are 1.263_{-0.047}^{+0.035}
solar masses and 1.446_{-0.067}^{+0.099} solar radii. The planet is smaller by
1 sigma than a theoretical solar-composition gas giant with the same mass and
equilibrium temperature, a possible indication of heavy-element enrichment. The
midtransit time is measured to within 1 min, and shows no deviation from a
linear ephemeris (and therefore no evidence for orbital perturbations from
other planets). We provide ephemerides for future transits and superior
conjunctions. There is an 18% chance that the orbital plane is oriented close
enough to edge-on for secondary eclipses to occur at superior conjunction.
Observations of secondary eclipses would reveal the thermal emission spectrum
of a planet that experiences unusually large tidal heating and insolation
variations.Comment: To appear in ApJ [26 pages
Gravitational Waves from the Dynamical Bar Instability in a Rapidly Rotating Star
A rapidly rotating, axisymmetric star can be dynamically unstable to an m=2
"bar" mode that transforms the star from a disk shape to an elongated bar. The
fate of such a bar-shaped star is uncertain. Some previous numerical studies
indicate that the bar is short lived, lasting for only a few bar-rotation
periods, while other studies suggest that the bar is relatively long lived.
This paper contains the results of a numerical simulation of a rapidly rotating
gamma=5/3 fluid star. The simulation shows that the bar shape is long lived:
once the bar is established, the star retains this shape for more than 10
bar-rotation periods, through the end of the simulation. The results are
consistent with the conjecture that a star will retain its bar shape
indefinitely on a dynamical time scale, as long as its rotation rate exceeds
the threshold for secular bar instability. The results are described in terms
of a low density neutron star, but can be scaled to represent, for example, a
burned-out stellar core that is prevented from complete collapse by centrifugal
forces. Estimates for the gravitational-wave signal indicate that a dynamically
unstable neutron star in our galaxy can be detected easily by the first
generation of ground based gravitational-wave detectors. The signal for an
unstable neutron star in the Virgo cluster might be seen by the planned
advanced detectors. The Newtonian/quadrupole approximation is used throughout
this work.Comment: Expanded version to be published in Phys. Rev. D: 13 pages, REVTeX,
13 figures, 9 TeX input file
Improved Orbital Parameters and Transit Monitoring for HD 156846b
HD 156846b is a Jovian planet in a highly eccentric orbit (e = 0.85) with a
period of 359.55 days. The pericenter passage at a distance of 0.16 AU is
nearly aligned to our line of sight, offering an enhanced transit probability
of 5.4% and a potentially rich probe of the dynamics of a cool planetary
atmosphere impulsively heated during close approach to a bright star (V = 6.5).
We present new radial velocity (RV) and photometric measurements of this star
as part of the Transit Ephemeris Refinement and Monitoring Survey (TERMS). The
RV measurements from Keck-HIRES reduce the predicted transit time uncertainty
to 20 minutes, an order of magnitude improvement over the ephemeris from the
discovery paper. We photometrically monitored a predicted transit window under
relatively poor photometric conditions, from which our non-detection does not
rule out a transiting geometry. We also present photometry that demonstrates
stability at the millimag level over its rotational timescale.Comment: 7 pages, 4 figures, accepted for publication in Ap
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