5,379 research outputs found
An Attempt to Detect the Galactic Bulge at 12 microns with IRAS
Surface brightness maps at 12 microns, derived from observations with the
Infrared Astronomical Satellite (IRAS), are used to estimate the integrated
flux at this wavelength from the Galactic bulge as a function of galactic
latitude along the minor axis. A simple model was used to remove Galactic disk
emission (e.g. unresolved stars and dust) from the IRAS measurements. The
resulting estimates are compared with predictions for the 12 micron bulge
surface brightness based on observations of complete samples of optically
identified M giants in several minor axis bulge fields. No evidence is found
for any significant component of 12m emission in the bulge other than that
expected from the optically identified M star sample plus normal, lower
luminosity stars. Known large amplitude variables and point sources from the
IRAS catalogue contribute only a small fraction to the total 12 micron flux.Comment: Accepted for publication in ApJ; 13 pages of text including tables in
MS WORD97 generated postscript; 3 figures in postscript by Sigma Plo
The footprint of cometary dust analogues: II. Morphology as a tracer of tensile strength and application to dust collection by the Rosetta spacecraft
The structure of cometary dust is a tracer of growth processes in the
formation of planetesimals. Instrumentation on board the Rosetta mission to
comet 67P/Churyumov- Gerasimenko captured dust particles and analysed them in
situ. However, these deposits are a product of a collision within the
instrument. We conducted laboratory experiments with cometary dust analogues,
simulating the collection process by Rosetta instruments (specifically COSIMA,
MIDAS). In Paper I we reported that velocity is a key driver in determining the
appearance of deposits. Here in Paper II we use materials with different
monomer sizes, and study the effect of tensile strength on the appearance of
deposits. We find that mass transfer efficiency increases from 1 up to
10% with increasing monomer diameter from 0.3 m to 1.5 m (i.e.
tensile strength decreasing from 12 to 3 kPa), and velocities
increasing from 0.5 to 6 m/s. Also, the relative abundance of small fragments
after impact is higher for material with higher tensile strength. The
degeneracy between the effects of velocity and material strength may be lifted
by performing a closer study of the deposits. This experimental method makes it
possible to estimate the mass transfer efficiency in the COSIMA instrument.
Extrapolating these results implies that more than half of the dust collected
during the Rosetta mission has not been imaged. We analysed two COSIMA targets
containing deposits from single collisions. The collision that occurred closest
to perihelion passage led to more small fragments on the target.Comment: 13 pages, 11 figures, accepted for publication in MNRA
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
The footprint of cometary dust analogs: I. Laboratory experiments of low-velocity impacts and comparison with Rosetta data
Cometary dust provides a unique window on dust growth mechanisms during the
onset of planet formation. Measurements by the Rosetta spacecraft show that the
dust in the coma of comet 67P/Churyumov-Gerasimenko has a granular structure at
size scales from sub-um up to several hundreds of um, indicating hierarchical
growth took place across these size scales. However, these dust particles may
have been modified during their collection by the spacecraft instruments. Here
we present the results of laboratory experiments that simulate the impact of
dust on the collection surfaces of COSIMA and MIDAS, instruments onboard the
Rosetta spacecraft. We map the size and structure of the footprints left by the
dust particles as a function of their initial size (up to several hundred um)
and velocity (up to 6 m/s). We find that in most collisions, only part of the
dust particle is left on the target; velocity is the main driver of the
appearance of these deposits. A boundary between sticking/bouncing and
fragmentation as an outcome of the particle-target collision is found at v ~ 2
m/s. For velocities below this value, particles either stick and leave a single
deposit on the target plate, or bounce, leaving a shallow footprint of
monomers. At velocities > 2 m/s and sizes > 80 um, particles fragment upon
collision, transferring up to 50 per cent of their mass in a rubble-pile-like
deposit on the target plate. The amount of mass transferred increases with the
impact velocity. The morphologies of the deposits are qualitatively similar to
those found by the COSIMA instrument.Comment: 14 pages, 12 figures, accepted for publication in MNRA
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.
Anterolateral proximal tibial opening wedge osteotomy for biplanar correction in genu valgum recurvatum using patient specific instrumentation (PSI):A technical note
BACKGROUND: Biplanar anterolateral proximal tibial opening wedge osteotomy has been described as successful for patients with combined recurvatum and valgus alignment. As it is a correction in two planes, it is a technically demanding procedure. We report the use of a novel technique with patient specific instrumentation (PSI) guides for different steps, aiming to reduce the complexity of this procedure. METHODS: One patient was treated for genu valgum recurvatum. A virtual surgical plan was made. A two-step PSI approach was used, consisting of an osteotomy guide and a repositioning guide and a custom trial wedges. RESULTS: Follow-up showed full function and improved VAS and KOOS scores. A neutral alignment was achieved. There was 2.76 degrees less varus compared to pre-operative planning, 1.24 degrees of excess slope and a rotational difference of 0.10 degrees. Saw plane accuracy was within 1 mm. CONCLUSIONS: PSI is a recent technical addition to HTOs as a modality to improve accuracy and reduce surgical complexity. Pre-planning and PSI use in an anterolateral opening wedge PTO allowed for an accurate and reproducible biplanar correction in genu valgum recurvatum. Accuracy was comparable to PSI use in lateral open wedge high tibial osteotomies
The Effect of Unenhanced MRI on the Surgeons' Decision-Making Process in Females with Suspected Appendicitis
This prospective study evaluated the impact of the results of unenhanced magnetic resonance imaging (MRI) on the surgeon's diagnosis of acute appendicitis in potentially fertile females. 112 female patients, aged 12-55, with suspected appendicitis underwent MRI of the abdomen. At three defined intervals; admission and clinical re-evaluation before and after revealing the MRI results, the surgeon recorded the attendance of each patient in operative treatment, observation or discharge. Appendicitis was confirmed or declined by pathology or by telephone follow-up in case of non-intervention. Appendicitis was confirmed in 29 of 112 patients. At admission the surgeon's disposition had a sensitivity of 97 % and specificity of 29 %. After knowing the MRI results, sensitivity was 97 % and specificity 64 %. The sensitivity and specificity of MRI alone were 89 and 100 %, with a negative and positive predictive value of 96 and 100 %, respectively. We believe that MRI should perhaps be standard in all female patients during their reproductive years with suspected appendicitis. It avoids an operation in 32 % of cases and allows earlier planning for patients with an equivocal clinical picture. Trial number: OND1292733 (Narcis.nl)
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
Webteaching: sequencing of subject matter in relation to prior knowledge of pupils
Two experiments are discussed in which the sequencing procedure of webteaching is compared with a linear sequence for the presentation of text material.\ud
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In the first experiment variations in the level of prior knowledge of pupils were studied for their influence on the sequencing mode of text presentation. Prior knowledge greatly reduced the effect of the size of sequencing procedures.\ud
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In the second experiment pupils with a low level of prior knowledge studied a text, following either a websequence or a linear sequence. Webteaching was superior to linear teaching on a number of dependent variables. It is concluded that webteaching is an effective sequencing procedure in those cases where substantial new learning is required
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