7,548 research outputs found
OH-selected AGB and post-AGB stellar objects II.Blue versus red evolution off the AGB
Using objects found in a systematic survey of the galactic Plane in the
1612-MHz OH line, we discuss in detail two ``sequences'' of post-AGB evolution,
a red and a blue. We argue that the red and the blue groups separate by initial
mass at 4Msun, based on evolutionary-sequence turn-off colours, spectral energy
distributions, outflow velocities and scaleheight. The higher-mass (blue)
objects may have earlier AGB termination. The lower-mass (red) objects undergo
very sudden reddening for IRAS colour R21\sim1.2; these sources must all
undergo a very similar process at AGB termination. The transition colour
corresponds to average initial masses of 1.7Msun. A combined IRAS-MSX colour
proves a very sensitive tool to distinguish lower-mass, early post-AGB objects
from sources still on the AGB and also to distinguish more evolved post-AGB
objects from star-forming regions. The high-mass blue objects are the likely
precursors of bipolar planetary nebulae, whereas the low-mass red objects will
evolve into elliptical planetary nebulae.Comment: 12 pages, LaTex, 7 figures (1 colour), AJ (accepted
OH-selected AGB and post-AGB objects I.Infrared and maser properties
Using 766 compact objects from a survey of the galactic Plane in the 1612-MHz
OH line, new light is cast on the infrared properties of evolved stars on the
TP-AGB and beyond. The usual mid-infrared selection criteria, based on IRAS
colours, largely fail to distinguish early post-AGB stages. A two-colour
diagram from narrower-band MSX flux densities, with bimodal distributions,
provides a better tool to do the latter. Four mutually consistent selection
criteria for OH-masing red PPNe are given, as well as two for early post-AGB
masers and one for all post--AGB masers, including the earliest ones. All these
criteria miss a group of blue, high-outflow post-AGB sources with 60-mum
excess; these will be discussed in detail in Paper II. The majority of post-AGB
sources show regular double-peaked spectra in the OH 1612-MHz line, with fairly
low outflow velocities, although the fractions of single peaks and irregular
spectra may vary with age and mass. The OH flux density shows a fairly regular
relation with the stellar flux and the envelope optical depth, with the maser
efficiency increasing with IRAS colour R21. The OH flux density is linearly
correlated with the 60-mum flux density.Comment: 16 pages, LaTex, 22 figures, AJ (accepted
Mass-luminosity relation and pulsational properties of Wolf-Rayet stars
Evolution of Population I stars with initial masses from 70M_\odot to
130M_\odot is considered under various assumptions on the mass loss rate \dot
M. The mass-luminosity relation of W-R stars is shown to be most sensitive to
the mass loss rate during the helium burning phase \dot M_{3\alpha}. Together
with the mass-luminosity relation obtained for all evolutionary sequences
several more exact relations are determined for the constant ratio
f_{3\alpha}=\dot M/\dot M_{3\alpha} with 0.5 \le f_{3\alpha} \le 3.
Evolutionary models of W-R stars were used as initial conditions in
hydrodynamic computations of radial nonlinear stellar oscillations. The
oscillation amplitude is larger in W-R stars with smaller initial mass or with
lower mass loss rate due to higher surface abundances of carbon and oxygen. In
the evolving W-R star the oscillation amplitude decreases with decreasing
stellar mass M and for M < 10M_\odot the sufficiently small nonlinear effects
allow us to calculate the integral of the mechanical work W done over the
pulsation cycle in each mass zone of the hydrodynamical model. The only
positive maximum on the radial dependence of W is in the layers with
temperature of T\sim 2e5K where oscillations are excited by the iron Z--bump
kappa-mechanism. Radial oscillations of W-R stars with mass of M > 10M_\odot
are shown to be also excited by the kappa-mechanism but the instability driving
zone is at the bottom of the envelope and pulsation motions exist in the form
of nonlinear running waves propagating outward from the inner layers of the
envelope.Comment: 15 pages, 10 figures, submitted to Astronomy Letter
Dissociation between medial frontal negativity and cardiac responses in the ultimatum game: Effects of offer size and fairness
In the present study, we examined the role of fairness and offer size on brain and cardiac responses in the ultimatum game (UG). Twenty healthy volunteers played the role of responder in a computerized version of the UG in which the fairness and size of the offers were systematically varied. Both fairness and size of the offer influenced the acceptance rates in a predictable way, leading to fewer accepted unfair and low offers. Only unfair high, but not unfair low offers were accompanied by a medial frontal negativity. An unexpected stronger cardiac deceleration to fairer offers was found, which was not affected by the size of the offers. Cardiac and electrocortical measures showed a different relation with performance, and both measures were correlated only modestly. This dissociation between cardiac responses and brain potentials is discussed in terms of a possible differential sensitivity to effects of stimulus probability and violation of the social rules
Proton Motive Force-Dependent Hoechst 33342 Transport by the ABC Transporter LmrA of Lactococcus lactis
The fluorescent compound Hoechst 33342 is a substrate for many multidrug resistance (MDR) transporters and is widely used to characterize their transport activity. We have constructed mutants of the adenosine triphosphate (ATP) binding cassette (ABC)-type MDR transporter LmrA of Lactococcus lactis that are defective in ATP hydrolysis. These mutants and wild-type LmrA exhibited an atypical behavior in the Hoechst 33342 transport assay. In membrane vesicles, Hoechst 33342 transport was shown to be independent of the ATPase activity of LmrA, and it was not inhibited by orthovanadate but sensitive to uncouplers that collapse the proton gradient and to N,N'-dicyclohexylcarbodiimide, an inhibitor of the F0F1-ATPase. In contrast, transport of Hoechst 33342 by the homologous, heterodimeric MDR transporter LmrCD showed a normal ATP dependence and was insensitive to uncouplers of the proton gradient. With intact cells, expression of LmrA resulted in an increased rate of Hoechst 33342 influx while LmrCD caused a decrease in the rate of Hoechst 33342 influx. Cellular toxicity assays using a triple knockout strain, i.e., L. lactis ΔlmrA ΔlmrCD, demonstrate that expression of LmrCD protects cells against the growth inhibitory effects of Hoechst 33342, while in the presence of LmrA, cells are more susceptible to Hoechst 33342. Our data demonstrate that the LmrA-mediated Hoechst 33342 transport in membrane vesicles is influenced by the transmembrane pH gradient due to a pH-dependent partitioning of Hoechst 33342 into the membrane.
The COBE DIRBE Point Source Catalog
We present the COBE DIRBE Point Source Catalog, an all-sky catalog containing
infrared photometry in 10 bands from 1.25 microns to 240 microns for 11,788 of
the brightest near and mid-infrared point sources in the sky. Since DIRBE had
excellent temporal coverage (100 - 1900 independent measurements per object
during the 10 month cryogenic mission), the Catalog also contains information
about variability at each wavelength, including amplitudes of variation
observed during the mission. Since the DIRBE spatial resolution is relatively
poor (0.7 degrees), we have carefully investigated the question of confusion,
and have flagged sources with infrared-bright companions within the DIRBE beam.
In addition, we filtered the DIRBE light curves for data points affected by
companions outside of the main DIRBE beam but within the `sky' portion of the
scan. At high Galactic latitudes (|b| > 5 degrees), the Catalog contains
essentially all of the unconfused sources with flux densities greater than 90,
60, 60, 50, 90, and 165 Jy at 1.25, 2.2, 3.5, 4.9, 12, and 25 microns,
respectively, corresponding to magnitude limits of approximately 3.1, 2.6, 1.7,
1.3, -1.3, and -3.5. At longer wavelengths and in the Galactic Plane, the
completeness is less certain because of the large DIRBE beam and possible
contributions from extended emission. The Catalog also contains the names of
the sources in other catalogs, their spectral types, variability types, and
whether or not the sources are known OH/IR stars. We discuss a few remarkable
objects in the Catalog. [abridged]Comment: Accepted for publication in the Astrophysical Journal Supplement. The
full tables are available at http://www.etsu.edu/physics/bsmith/dirbe
H2O Maser Observations of Candidate Post-AGB Stars and Discovery of Three High-velocity Water Sources
We present the results of 22 GHz H_2O maser observations of a sample of 85
post-Asymptotic Giant Branch (post-AGB) candidate stars, selected on the basis
of their OH 1612 MHz maser and far-infrared properties. All sources were
observed with the Tidbinbilla 70-m radio telescope and 21 detections were made.
86 GHz SiO Mopra observations of a subset of the sample are also presented. Of
the 21 H_2O detections, 15 are from sources that are likely to be massive AGB
stars and most of these show typical, regular H_2O maser profiles. In contrast,
nearly all the detections of more evolved stars exhibited high-velocity H_2O
maser emission. Of the five sources seen, v223 (W43A, IRAS 18450-0148) is a
well known `water-fountain' source which belongs to a small group of post-AGB
stars with highly collimated, high-velocity H_2O maser emission. A second
source in our sample, v270 (IRAS 18596+0315), is also known to have
high-velocity emission. We report the discovery of similar emission from a
further three sources, d46 (IRAS 15445-5449), d62 (IRAS 15544-5332) and b292
(IRAS 18043-2116). The source d46 is an evolved post-AGB star with highly
unusual maser properties. The H_2O maser emission from d62 is probably
associated with a massive star. The source b292 is a young post-AGB star that
is highly likely to be a water-fountain source, with masers detected over a
velocity range of 210 km s^{-1}.Comment: 47 pages, 9 figures, 4 tables, accepted by Ap
The Influence of BIA-ALCL on the Use of Textured Breast Implant and its Placement:A Survey of Dutch Plastic Surgeons
BACKGROUND: Breast implant-associated anaplastic large-cell lymphoma (BIA-ALCL) and its association with macrotextured breast implants may have induced plastic surgeons to change their breast augmentation and breast reconstruction practice.OBJECTIVES: The aim of this study was to survey Dutch plastic surgeons about the effects of BIA-ALCL on their choice of breast implant texture and placement technique.METHODS: An online questionnaire was distributed to all members of the Dutch Association of Plastic Surgeons. Descriptive data were presented as frequencies and percentages. Technique alterations were analyzed by the marginal homogeneity test for paired nominal data.RESULTS: A total of 63 plastic surgeons completed the questionnaire. The majority of respondents altered their use of textured implants due to BIA-ALCL concerns for both breast augmentation and reconstruction (75.4% and 69.8%, respectively; both being statistically significant, P < .001). Microtextured and smooth/nanotextured breast implants are now most frequently used. BIA-ALCL did not influence the placement technique in breast augmentation and reconstruction (87.7% and 94.3%, respectively). Dual-plane breast implant placement is still the most favored technique for breast augmentation, and submuscular placement is still most favored for breast reconstruction.CONCLUSIONS: BIA-ALCL has had a significant impact on the use of macrotextured breast implants by Dutch plastic surgeons in both aesthetic and reconstructive breast surgery. Breast implant placement technique has not been affected.</p
Investigation of the chemical vicinity of crystal defects in ion-irradiated Mg and AZ31 with coincident Doppler broadening spectroscopy
Crystal defects in magnesium and magnesium based alloys like AZ31 are of
major importance for the understanding of their macroscopic properties. We have
investigated defects and their chemical surrounding in Mg and AZ31 on an atomic
scale with Doppler broadening spectroscopy of the positron annihilation
radiation. In these Doppler spectra the chemical information and the defect
contribution have to be thoroughly separated. For this reason samples of
annealed Mg were irradiated with Mg-ions in order to create exclusively
defects. In addition Al- and Zn-ion irradiation on Mg-samples was performed in
order to create samples with defects and impurity atoms. The ion irradiated
area on the samples was investigated with laterally and depth resolved positron
Doppler broadening spectroscopy (DBS) and compared with preceding
SRIM-simulations of the vacancy distribution, which are in excellent agreement.
The investigation of the chemical vicinity of crystal defects in AZ31 was
performed with coincident Doppler broadening spectroscopy (CDBS) by comparing
Mg-ion irradiated AZ31 with Mg-ion irradiated Mg. No formation of
solute-vacancy complexes was found due to the ion irradiation, despite the high
defect mobility.Comment: Submitted to Physical Review B on March 20 20076. Revised version
submitted on September 28 2007. Accepted on October 19 200
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