56 research outputs found
Self-efficacy, metastasis, treatment, and demographics as predictors of functional performance status of adult colorectal cancer patients
The purpose of this study was to assess self-efficacy as a predictor of functional performance status in order to discover correlations that could be used to improve care of the colorectal cancer patient. Thirty participants were accessed through three outpatient cancer clinics during a two-week period. Data was collected through a demographics questionnaire, the Cancer Behavior Inventory Long Form, and the Karnofsky Performance Scale Index. Stepwise multiple regression was used to identify and relationships between the dependent variable, functional performance status, and the independent variables, self-efficacy, age, gender, residence, treatment, and metastasis ( p = .05). Pearson\u27s correlation showed a relatively low correlation among the variables. Results showed self-efficacy ( p = .003) as the number one predictor of performance status, with metastasis following ( p = .000). Future studies are recommended to reinforce these findings. Development of a program to promote self-efficacy for colorectal cancer patients is recommended
Base Isolation of a Chilean Masonry House: A Comparative Study
The objective of this study is to reduce the interstory drifts, floor accelerations,
and shear forces experienced by masonry houses subject to seismic excitation. Ambient
vibration testing was performed on a case study structure in Maip�, Chile, to identify
characteristics of the system. Upon creating a multiple degree-of-freedom (MDOF)
model of the structure, the effect of implementing several base isolation techniques is
assessed. The isolation techniques analyzed include the use of friction pendulum
systems (FPS), high-damping rubber bearings (HDRB), two hybrid systems involving
HDRB and shape memory alloys (SMA), and precast-prestressed pile (PPP) isolators.
The dynamic behavior of each device is numerically modeled using analytical
formulations and experimental data through the means of fuzzy inference systems (FIS)
and S-functions. A multiobjective genetic algorithm is utilized to optimize the
parameters of the FPS and the PPP isolation systems, while a trial-and-error method is
employed to optimize characteristic parameters of the other devices.
Two cases are studied: one case involves using eight devices in each isolation
system and optimizing the parameters of each device, resulting in different isolated
periods for each system, while the other case involves using the number of devices and
device parameters that result in a 1.0 sec fundamental period of vibration for each baseisolated
structure. For both cases, the optimized devices are simulated in the numerical
model of the case study structure, which is subjected to a suite of earthquake records.
Numerical results for the devices studied indicate significant reductions in
responses of the base-isolated structures in comparison with their counterparts in the
fixed-base structure. Metrics monitored include base shear, structural shear, interstory drift, and floor acceleration. In particular, the PPP isolation system in the first case
reduces the peak base shear, RMS floor acceleration, peak structural shear, peak
interstory drift, and peak floor acceleration by at least 88, 87, 95, 95, and 94%,
respectively, for all of the Chilean earthquakes considered. The PPP isolation system in
the second case (yielding a 1.0 sec period) and the FPS isolation systems in both cases
also significantly reduce the response of the base-isolated structure from that of the
fixed-base structure
Discovery of a compact companion to the hot subdwarf star BD+37 442
We report the results of the first X-ray observation of the luminous and
helium-rich O-type subdwarf BD+37 442, carried out with the XMM-Newton
satellite in August 2011. X-ray emission is detected with a flux of about
3x10^(-14) erg/cm2/s (0.2-1 keV) and a very soft spectrum, well fit by the sum
of a blackbody with temperature kT_BB = 45^(+11)_(-9) eV and a power law with a
poorly constrained photon index. Significant pulsations with a period of 19.2 s
are detected, indicating that the X-ray emission originates in a white dwarf or
neutron star companion, most likely powered by accretion from the wind of BD+37
442.Comment: 5 pages, 4 figures, 1 table. Accepted for publication by The
Astrophysical Journal Letter
Discovery of magnetic fields in hot subdwarfs
We present initial results of a project to measure mean longitudinal magnetic
fields in a group of sdB/OB/O stars. The project was inspired by the discovery
of three super-metal-rich sdOB stars, each having metals (e.g. Ti, V) enhanced
by factors of 10^3 to 10^5. Similar behaviour is observed in chemically
peculiar A stars, where strong magnetic fields are responsible for the
enrichment. With this in mind, we obtained circularly polarised spectra of two
of the super-metal-rich sdOBs, two "normal" sdBs and two sdOs using FORS1 on
the ESO/VLT. By examining circular polarisation in the hydrogen Balmer lines
and in helium lines, we have detected magnetic fields with strengths of 1-2 kG
in most of our targets. This suggests that such fields are relatively common in
hot subdwarfs.Comment: 4 pages, to appear in White Dwarfs, eds. D. Koester, S. Moehler, ASP
Conf. serie
Non-LTE Line Formation in the Near-IR: Hot Stars
Line-formation calculations in the Rayleigh-Jeans tail of the spectral energy
distribution are complicated by an amplification of non-LTE effects. For hot
stars this can make quantitative modelling of spectral lines in the near-IR
challenging. An introduction to the modelling problems is given and several
examples in the context of near-IR line formation for hydrogen and helium are
discussed.Comment: 16 pages, 13 figure
Accretion Disks and the Lyman Continuum Polarization of QSOs
HST observations of some QSOs show a strong, abrupt increase in polarization
at rest wavelength about 750 A, suggestive of a connection with the Lyman edge
of hydrogen. Blaes and Agol (1996) have proposed an explanation in terms of
stellar atmosphere effects in an accretion disk around a supermassive black
hole. We have computed the polarized spectrum of a such a disk, including the
effects of the relativistic transfer function. Relativistic effects add an
additional blueshift of the polarization rise sufficient that the model cannot
explain the observations.
A good fit results if the emitted radiation is assumed to have a sharp
increase in polarized flux at the Lyman edge in the rest frame of the orbiting
gas. Relativistic effects then cause the observed polarization to rise sharply
at a wavelength substantially less than 912 A. The blueshift depends on the
angular momentum of the black hole and the inclination of the disk. A good fit
to PG 1630+377 results from a simple model with a dimensionless angular
momentum a = 0.5 and an observer viewing angle cos theta = 0.1. An intermediate
value of a might result from coallescing black holes, successive accretion
events, or electromagnetic extraction of angular momentum from the hole.Comment: 24 pages incl. 9 PostScript figures. Uses aaspp4.sty and flshrt.sty.
To be published in The Astrophysical Journal, Vol. 496 (1988 April 1
On the properties of massive Population III stars and metal-free stellar populations
We present realistic models for massive Population III stars and stellar
populations based on non-LTE model atmospheres, recent stellar evolution tracks
and up-to-date evolutionary synthesis models, to study their spectral
properties, including their dependence on age, star formation history, and IMF.
(..) The main results regarding integrated stellar populations are: * For young
bursts and the case of a constant SFR, nebular continuous emission - neglected
in previous studies - dominates the spectrum redward of Lyman-alpha (...).
Therefore predicted emission line equivalent widths are considerably smaller
than found in earlier studies, whereas the detection of the continuum is eased.
Nebular line and continuous emission strongly affect the broad band photometric
properties of Pop III objects. * Due to stellar evolution, the hardness of the
ionising spectrum decreases rapidly, leading to the disappearance of the
characteristic HeII 1640 recombination lines after ~ 3 Myr in instantaneous
bursts. * The relative efficiency of ionising photon energy to heavy element
rest mass production, eta, of metal-poor and metal-free populations is
increased by factors of ~ 4 to 18 with respect to solar metallicity and for
``standard'' IMFs. * The lowest values of eta ~ 1.6 - 2.2 % are obtained for
IMFs exclusively populated with high mass stars (M_low >~ 50 Msun). If correct,
the yields dominated by pair creation SNae then predict large overabundances of
O/C and Si/C compared to solar abundance ratios. Detailed results are given in
tabular form and as fit formulae for implementation in other calculations.
(abridged abstract)Comment: Accepted for publication in A&A. LaTeX, 15 pages including 8 figures.
Related models are available at http://webast.ast.obs-mip.fr/people/schaerer/
. SEDs will be available by request from the author
(mailto:[email protected]). Y-axis of Figs. 5 correcte
Chemical evolution of high-mass stars in close binaries. I. The eclipsing binary V453 Cygni
The eclipsing and double-lined spectroscopic binary system V453 Cygni
consists of two early B-type stars, one of which is nearing the terminal age
main sequence and one which is roughly halfway through its main sequence
lifetime. Accurate measurements of the masses and radii of the two stars are
available, which makes a detailed abundance analysis both more interesting and
more precise than for isolated stars. We have reconstructed the spectra of the
individual components of V453 Cyg from the observed composite spectra using the
technique of spectral disentangling. From these disentangled spectra we have
obtained improved effective temperature measurements of 27900 +/- 400 K and
26200 +/- 500 K, for the primary and secondary stars respectively, by fitting
non-LTE theoretical line profiles to the hydrogen Balmer lines. Armed with
these high-precision effective temperatures and the accurately known surface
gravities of the stars we have obtained the abundances of helium and metallic
elements. A detailed abundance analysis of the primary star shows a normal
(solar) helium abundance if the microturbulence velocity derived from metallic
lines is used. The elemental abundances show no indication that CNO-processed
material is present in the photosphere of this high-mass terminal age main
sequence star. The elemental abundances of the secondary star were derived by
differential study against a template spectrum of a star with similar
characteristics. Both the primary and secondary components display elemental
abundances which are in the ranges observed in the Galactic OB stars.Comment: 10 pages; accepted for publication in MNRA
Abundance analysis of prime B-type targets for asteroseismology I. Nitrogen excess in slowly-rotating beta Cephei stars
We present the results of a detailed NLTE abundance study of nine beta Cephei
stars, all of them being prime targets for theoretical modelling: gamma Peg,
delta Cet, nu Eri, beta CMa, xi1 CMa, V836 Cen, V2052 Oph, beta Cep and DD (12)
Lac. The following chemical elements are considered: He, C, N, O, Mg, Al, Si, S
and Fe. Our abundance analysis is based on a large number of time-resolved,
high-resolution optical spectra covering in most cases the entire oscillation
cycle of the stars. Nitrogen is found to be enhanced by up to 0.6 dex in four
stars, three of which have severe constraints on their equatorial rotational
velocity, \Omega R, from seismic or line-profile variation studies: beta Cep
(\Omega R~26 km/s), V2052 Oph (\Omega R~56 km/s), delta Cet (\Omega R < 28
km/s) and xi1 CMa (\Omega R sin i < 10 km/s). The existence of core-processed
material at the surface of such largely unevolved, slowly-rotating objects is
not predicted by current evolutionary models including rotation. We draw
attention to the fact that three stars in this subsample have a detected
magnetic field and briefly discuss recent theoretical work pointing to the
occurrence of diffusion effects in beta Cephei stars possibly capable of
altering the nitrogen surface abundance. On the other hand, the abundances of
all the other chemical elements considered are, within the errors,
indistinguishable from the values found for OB dwarfs in the solar
neighbourhood. Despite the mild nitrogen excess observed in some objects, we
thus find no evidence for a significantly higher photospheric metal content in
the studied beta Cephei stars compared to non-pulsating B-type stars of similar
characteristics.Comment: Accepted for publication in A&A, 21 pages, 7 figure
The He II Emitting Nebula N44C in the LMC: Optical/UV Spectroscopy of the Nebula and its Ionizing Star
We present HST spectroscopy and imaging, along with new ground-based
spectroscopy and ROSAT HRI imaging, of the He II emitting nebula N44C and its
ionizing star. A GHRS spectrogram of the ionizing star yields a spectral type
of about O7 for the star. The lack of P Cygni profiles for Si IV and C IV
indicates that the star is not a supergiant. The nebular abundances in the
ionized gas are consistent with average abundances for LMC H II regions, with
the possible exception that nitrogen may be enhanced. Enrichment by a former
evolved companion star is not evident. A long-slit echelle spectrogram in
H-alpha + [N II] shows no evidence for high-velocity gas in N44C. This rules
out high-velocity shocks as the source of the nebular He II emission. A 108 ks
ROSAT HRI image of N44C shows no X-ray point source to a 3-sigma upper limit
L(X) < 10^34 erg s^-1 in the 0.1-2.0 keV band. Based on new measurements of the
electron density in the He II emitting region, we derive recombination
timescales of approximately 20 yrs for He^+2 and approximately 4 yrs for Ne^+4.
If N44C is a fossil X-ray ionized nebula, this places severe constraints on
when the putative X-ray source could have turned off. The presence of strong
[Ne IV] emission in the nebula is puzzling if the ionizing source has turned
off. It is possible the system is related to the Be X-ray binaries, although
the O star in N44C does not show Be characteristics at the present time.
Monitoring of X-rays and He II emission from the nebula, as well as a radial
velocity study of the ionizing star, are needed to fully understand the
emission line spectrum of N44C.Comment: 37 pages, 7 figures (1 color .gif image); accepted for publication in
the 10 Dec 2000 Astrophysical Journal. Complete PostScript and PDF versions
can also be obtained at http://ocotillo.as.arizona.edu/~dgarnet
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