15,512 research outputs found
A dynamical and kinematical model of the Galactic stellar halo and possible implications for galaxy formation scenarios
We re-analyse the kinematics of the system of blue horizontal branch field
(BHBF) stars in the Galactic halo (in particular the outer halo), fitting the
kinematics with the model of radial and tangential velocity dispersions in the
halo as a function of galactocentric distance r proposed by Sommer-Larsen,
Flynn & Christensen (1994), using a much larger sample (almost 700) of BHBF
stars. The basic result is that the character of the stellar halo velocity
ellipsoid changes markedly from radial anisotropy at the sun to tangential
anisotropy in the outer parts of the Galactic halo (r greater than approx 20
kpc). Specifically, the radial component of the stellar halo's velocity
ellipsoid decreases fairly rapidly beyond the solar circle, from approx 140 +/-
10 km/s at the sun, to an asymptotic value of 89 +/- 19 km/s at large r. The
rapid decrease in the radial velocity dispersion is matched by an increase in
the tangential velocity dispersion, with increasing r.
Our results may indicate that the Galaxy formed hierarchically (partly or
fully) through merging of smaller subsystems - the 'bottom-up' galaxy formation
scenario, which for quite a while has been favoured by most theorists and
recently also has been given some observational credibility by HST observations
of a potential group of small galaxies, at high redshift, possibly in the
process of merging to a larger galaxy (Pascarelle et al 1996).Comment: Latex, 16 pages. 2 postscript figures. Submitted to the Astrophysical
Journal. also available at http://astro.utu.fi/~cflynn/outerhalo.htm
It's a question of balance: Reconsidering learning partnerships through genuine teacher mentoring conversations
In Australia, and internationally, mentoring is proffered as a powerful professional learning experience for both early career teachers (ECTs) and their mentors alike. However, authentically beneficial learning partnerships have proven challenging to achieve. This paper provides a theoretical and practical response to this issue, arguing the criticality of genuine conversations cultivated through balanced, non-hierarchical questioning to position ECTs and mentors as co-learners. Drawing on positioning theory in conjunction with the concept of genuine conversations, the contents of five recorded mentoring conversations involving Australian ECTs and mentors were analysed. These findings have important implications for mentoring practice across educational contexts
The shock process and light element production in supernovae envelopes
Detailed hydrodynamic modeling of the passage of supernova shocks through the hydrogen envelopes of blue and red progenitor stars was carried out to explore the sensitivity to model conditions of light element production (specifically Li-7 and B-11) which was noted by Dearborn, Schramm, Steigman and Truran (1989) (DSST). It is found that, for stellar models with M is less than or approximately 100 M solar mass, current state of the art supernova shocks do not produce significant light element yields by hydrodynamic processes alone. The dependence of this conclusion on stellar models and on shock strengths is explored. Preliminary implications for Galactic evolution of lithium are discussed, and it is suspected that intermediate mass red giant stars may be the most consistent production site for lithium
Improved Deposition and Performance of a Microencapsulated Sex Pheromone Formulation for Codling Moth (Lepidoptera: Tortricidae) with a Low Volume Application
Experiments were conducted to evaluate the deposition pattern and effectiveness in disrupting male orientation to virgin female-baited traps of a microencapsulated sex pheromone formulation for codling moth, Cydia pomonella (L.) in apple, Malus domestica Bordhausen. The efficacy of two application techniques was evaluated in field trials with the microencapsulated formulation Checkmate® CM-F: a high volume (926 liters per ha) application with an air blast sprayer and a low volume (46 liters per ha) application with a custom-built vertical boom sprayer. These treatments were compared to an unsprayed control and a control treatment where the formulation was applied directly on the ground within the plots. Disruption of virgin female-baited traps was significantly greater in the low volume versus the air blast application and versus the two types of control plots. Levels of disruption in the air blast-sprayed plots were not different from untreated plots or in plots where the sprayable sex pheromone was applied directly on the ground. A significant increase in the proportion of traps catching moths occurred in week 4. A significant interaction occurred among the effects of spray method, tree canopy position, and leaf surface on microcapsule deposition. This interaction was likely due to the low rate of deposition of microcapsules on the undersides of leaves in the lower canopy with the low volume sprayer. The low volume sprayer deposited significantly more microcapsules in the upper canopy than the air blast sprayer. Significantly more microcapsules were deposited on the underside versus the top of leaves in the upper canopy with the air blast but not with the low volume sprayer
The Star Clusters in the Irregular Galaxy NGC 4449
We examine the star clusters in the irregular galaxy NGC 4449. We use a
near-infrared spectrum and broad-band images taken with the HST to place a
limit of 8--15 Myrs on the age of the bright central ojbect in NGC 4449. Its
luminosity and size suggest that it is comparable to young super star clusters.
However, there is a peculiar nucleated-bar structure at the center of this star
cluster, and we suggest that this structure is debris from the interaction that
has produced the counter-rotating gas systems and extended gas streamers in the
galaxy.
From the images we identify 60 other candidate compact star clusters in NGC
4449. Fourteen of these could be background elliptical galaxies or old globular
star clusters. Of the star clusters, three, in addition to the central object,
are potentially super star clusters, and many others are comparable to the
populous clusters found in the LMC. The star clusters span a large range in
ages with no obvious peak in cluster formation that might be attributed to the
interaction that the galaxy has experienced.Comment: To be published in PASP, Feb. 2001; also attainable from
ftp.lowell.edu, cd pub/dah/n4449pape
The initial conditions of observed star clusters - I. Method description and validation
We have coupled a fast, parametrized star cluster evolution code to a Markov
Chain Monte Carlo code to determine the distribution of probable initial
conditions of observed star clusters, which may serve as a starting point for
future -body calculations. In this paper we validate our method by applying
it to a set of star clusters which have been studied in detail numerically with
-body simulations and Monte Carlo methods: the Galactic globular clusters
M4, 47 Tucanae, NGC 6397, M22, Centauri, Palomar 14 and Palomar 4, the
Galactic open cluster M67, and the M31 globular cluster G1. For each cluster we
derive a distribution of initial conditions that, after evolution up to the
cluster's current age, evolves to the currently observed conditions. We find
that there is a connection between the morphology of the distribution of
initial conditions and the dynamical age of a cluster and that a degeneracy in
the initial half-mass radius towards small radii is present for clusters which
have undergone a core collapse during their evolution. We find that the results
of our method are in agreement with -body and Monte Carlo studies for the
majority of clusters. We conclude that our method is able to find reliable
posteriors for the determined initial mass and half-mass radius for observed
star clusters, and thus forms an suitable starting point for modeling an
observed cluster\rq{}s evolution.Comment: 39 pages, 28 figures, accepted for publication in MNRA
Interval training normalizes cCardiomyocyte function, diastolic Ca<sup>2+</sup> control, and SR Ca<sup>2+</sup> release synchronicity in a mouse model of diabetic cardiomyopathy
In the present study we explored the mechanisms behind excitation-contraction (EC)-coupling defects in cardiomyocytes from mice with type-2 diabetes (db/db), and determined whether 13-weeks of aerobic interval training could restore cardiomyocyte Ca2+ cycling and EC-coupling. Reduced contractility in cardiomyocytes isolated from sedentary db/db was associated with increased diastolic sarcoplasmic reticulum (SR)-Ca2+ leak, reduced synchrony of Ca2+ release, reduced transverse (T)-tubule density, and lower peak systolic and diastolic Ca2+ and caffeine-induced Ca2+ release. Additionally, the rate of SR Ca2+ ATPase (SERCA2a)-mediated Ca2+ uptake during diastole was reduced, whereas a faster recovery from caffeine-induced Ca2+ release indicated increased Na+/Ca2+- exchanger (NCX) activity. The increased SR-Ca2+ leak was attributed to increased Ca2+-calmodulindependent protein kinase (CaMKIIδ) phosphorylation, supported by the normalization of SR-Ca2+ leak upon inhibition of CaMKIIδ (AIP). Exercise training restored contractile function associated with restored SR Ca2+ release synchronicity, T-tubule density, twitch Ca2+ amplitude, SERCA2a and NCX activities, and SR-Ca2+ leak. The latter was associated with reduced phosphorylation of cytosolic CaMKIIδ. Despite normal contractile function and Ca2+ handling after the training period, phospholamban was hyperphosphorylated at Serine-16. Protein kinase A (PKA) inhibition (H-89) in cardiomyocytes from the exercised db/db group abolished the differences in SR-Ca2+ load when compared with the sedentary db/db mice. EC-coupling changes were observed without changes in serum insulin or glucose levels, suggesting that the exercise training-induced effects are not via normalization of the diabetic condition. These data demonstrate that aerobic interval training almost completely restored the contractile function of the diabetic cardiomyocyte to levels close to sedentary wild type (WT)
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