Non-equilibrium chemistry and dust formation in AGB stars as probed by SiO line emission

We have performed high spatial resolution observations of SiO line emission for a sample of 11 AGB stars using the ATCA, VLA and SMA interferometers. Detailed radiative transfer modelling suggests that there are steep chemical gradients of SiO in their circumstellar envelopes. The emerging picture is one where the radial SiO abundance distribution starts at an initial high abundance, in the case of M-stars consistent with LTE chemistry, that drastically decreases at a radius of ~1E15 cm. This is consistent with a scenario where SiO freezes out onto dust grains. The region of the wind with low abundance is much more extended, typically ~1E16 cm, and limited by photodissociation. The surpisingly high SiO abundances found in carbon stars requires non-equilibrium chemical processes.Comment: 2 pages, 1 figure. To be published in the proceedings of the conference "Why Galaxies Care about AGB Stars", held in Vienna, August 7-11, 2006; F. Kerschbaum, C. Charbonnel, B. Wing eds, ASP Conf.Ser. in pres

Dynamical Friction on Star Clusters near the Galactic Center

Numerical simulations of the dynamical friction suffered by a star cluster near the Galactic center have been performed with a parallelized tree code. Gerhard (2001) has suggested that dynamical friction, which causes a cluster to lose orbital energy and spiral in towards the galactic center, may explain the presence of a cluster of very young stars in the central parsec, where star formation might be prohibitively difficult owing to strong tidal forces. The clusters modeled in our simulations have an initial total mass of 10^5-10^6 Msun and initial galactocentric radii of 2.5-30 pc. We have identified a few simulations in which dynamical friction indeed brings a cluster to the central parsec, although this is only possible if the cluster is either very massive (~10^6 Msun), or is formed near the central parsec (<~ 5 pc). In both cases, the cluster should have an initially very dense core (> 10^6 Msun pc-3). The initial core collapse and segregation of massive stars into the cluster core, which typically happens on a much shorter time scale than that characterizing the dynamical inspiral of the cluster toward the Galactic center, can provide the requisite high density. Furthermore, because it is the cluster core which is most likely to survive the cluster disintegration during its journey inwards, this can help account for the observed distribution of presumably massive HeI stars in the central parsec.Comment: Accepted for publication in Ap

The GOAL study: a prospective examination of the impact of factor V Leiden and ABO(H) blood groups on haemorrhagic and thrombotic pregnancy outcomes

Factor V Leiden (FVL) and ABO(H) blood groups are the common influences on haemostasis and retrospective studies have linked FVL with pregnancy complications. However, only one sizeable prospective examination has taken place. As a result, neither the impact of FVL in unselected subjects, any interaction with ABO(H) in pregnancy, nor the utility of screening for FVL is defined. A prospective study of 4250 unselected pregnancies was carried out. A venous thromboembolism (VTE) rate of 1·23/1000 was observed, but no significant association between FVL and pre-eclampsia, intra-uterine growth restriction or pregnancy loss was seen. No influence of FVL and/or ABO(H) on ante-natal bleeding or intra-partum or postpartum haemorrhage was observed. However, FVL was associated with birth-weights &gt;90th centile [odds ratio (OR) 1·81; 95% confidence interval (CI&lt;sub&gt;95&lt;/sub&gt;) 1·04–3·31] and neonatal death (OR 14·79; CI&lt;sub&gt;95&lt;/sub&gt; 2·71–80·74). No association with ABO(H) alone, or any interaction between ABO(H) and FVL was observed. We neither confirmed the protective effect of FVL on pregnancy-related blood loss reported in previous smaller studies, nor did we find the increased risk of some vascular complications reported in retrospective studies

Dissection Technique for Cochleas Prepared for Scanning Electron Microscopy

Scanning electron microscopy (SEM) permits a three-dimensional study of the surface morphology of the organ of Corti that is very useful in evaluating the condition of the apical end of the hair cells and the stereocilia. However, some laboratories have experienced problems with curling of the basilar membrane during critical point drying of cochlear specimens prepared For SEM evaluation using the Murakami or osmium thiocarbohydrazide-procedures. This curling of the basilar membrane can obstruct the view of the reticular lamina and the ciliary ends of the hair cells. We have used a dissection method, referred to as the anchor technique, to overcome basilar membrane curling. This technique removes all the structures above the reticular lamina but leaves the basilar membrane attached to the spiral ligament and the lateral bone to which the spiral ligament is anchored. Individual cochlear turns are dissected in this manner and mounted on the same examination stub For SEM evaluation. Maintenance of the lateral attachment of the basilar membrane requires additional dissection time but eliminates the problem of curling during critical point drying. An additional benefit is that mounting the individual turns on the same examination stub Facilitates evaluation and photomicroscopy of the surface morphology. The anchor technique has been used successfully on the guinea pig and should be appropriate for most mammalian cochleas

Quantifying the Security of Recognition Passwords: Gestures and Signatures

Gesture and signature passwords are two-dimensional figures created by drawing on the surface of a touchscreen with one or more fingers. Prior results about their security have used resilience to either shoulder surfing, a human observation attack, or dictionary attacks. These evaluations restrict generalizability since the results are: non-comparable to other password systems (e.g. PINs), harder to reproduce, and attacker-dependent. Strong statements about the security of a password system use an analysis of the statistical distribution of the password space, which models a best-case attacker who guesses passwords in order of most likely to least likely. Estimating the distribution of recognition passwords is challenging because many different trials need to map to one password. In this paper, we solve this difficult problem by: (1) representing a recognition password of continuous data as a discrete alphabet set, and (2) estimating the password distribution through modeling the unseen passwords. We use Symbolic Aggregate approXimation (SAX) to represent time series data as symbols and develop Markov chains to model recognition passwords. We use a partial guessing metric, which demonstrates how many guesses an attacker needs to crack a percentage of the entire space, to compare the security of the distributions for gestures, signatures, and Android unlock patterns. We found the lower bounds of the partial guessing metric of gestures and signatures are much higher than the upper bound of the partial guessing metric of Android unlock patterns

Quantitative Evaluation of Scanning Electron Microscopy-Examined Ciliary Morphological Changes in Control and Noise Exposed Guinea Pig Cochleas

Many investigations of noise-induced hearing loss have demonstrated a poor correlation between hearing threshold and hair cell loss. One reason for this is that more subtle changes in the hair cell, such as detailed morphological changes of stereocilia, have not been evaluated. However, examining such changes increases the problem of distinguishing experimental pathological changes from artefacts. Preparation of the specimen for scanning electron microscopy (SEM) may result in too many artefacts for an adequate quantification of defects due to noise exposure. One problem with some earlier studies seems to be lack of controls and/or statistical analysis for the purpose of eliminating the influence of artefacts and spontaneous degeneration. The aim of this study was to compare unexposed and noise-exposed cochleas examined with SEM in order to determine if subtle changes due to noise could be distinguished from preparation artefacts and from spontaneous deterioration. Ten different types of hair cell changes were found in exposed and control animals. By means of using controls for statistical comparison with noise-exposed animals two cell damage categories hair cell loss and missing stereocilia were found to be produced by exposure to noise

Single scattering by realistic, inhomogeneous mineral dust particles with stereogrammetric shapes

Light scattering by single, inhomogeneous mineral dust particles was simulated based on shapes and compositions derived directly from measurements of real dust particles instead of using a mathematical shape model. We demonstrate the use of the stereogrammetric shape retrieval method in the context of single-scattering modelling of mineral dust for four different dust types – all of them inhomogeneous – ranging from compact, equidimensional shapes to very elongated and aggregate shapes. The three-dimensional particle shapes were derived from stereo pairs of scanning-electron microscope images, and inhomogeneous composition was determined by mineralogical interpretation of localized elemental information based on energy-dispersive spectroscopy. Scattering computations were performed for particles of equal-volume diameters, from 0.08 μm up to 2.8 μm at 550 nm wavelength, using the discrete-dipole approximation. Particle-to-particle variation in scattering by mineral dust was found to be quite considerable and was not well reproduced by simplified shapes of homogeneous spheres, spheroids, or Gaussian random spheres. Effective-medium approximation results revealed that particle inhomogeneity should be accounted for even for small amounts of absorbing media (here up to 2% of the volume), especially when considering scattering by inhomogeneous particles at size parameters 3<<i>x</i><8. When integrated over a log-normal size distribution, the linear depolarization ratio and single-scattering albedo were also found to be sensitive to inhomogeneity. The methodology applied is work-intensive and the light-scattering method used quite limited in terms of size parameter coverage. It would therefore be desirable to find a sufficiently accurate but simpler approach with fewer limitations for single-scattering modelling of dust. For validation of such a method, the approach presented here could be used for producing reference data when applied to a suitable set of target particles