Uncertainties in AGB Evolution and Nucleosynthesis

We summarise the evolution and nucleosynthesis in AGB and Super-AGB stars. We then examine the major sources of uncertainty, especially mass-loss.Comment: 8 pages, no figures. Invited review presented at The 11th Pacific Rim Conference on Stellar Astrophysics "Physics and Chemistry of the Late Stages of Stellar Evolution

Creative brainstorming and integrative thinking: skills for twenty-first century managers

Purpose – The purpose of this paper is to introduce examples and methods of incorporating creative brainstorming and integrative thinking skills into training programs. Design/methodology/approach – The paper discusses an innovative training program as a case study to demonstrate the application of creative brainstorming and thinking skills into the design of the program. Findings – Interdisciplinary thinking, engagement, flexibility, individual customization, collaboration and inspiration are critical to the development of creative and integrative thinking skills for managers. Practical implications – This paper invites trainers and practitioners to consider new perspectives and customized approaches to develop creative and inter-disciplinary thinking skills for managers. Originality/value – This paper opens up new possibilities for innovation and customization in training programs to develop creative thinking skills

Heavy Element Nucleosynthesis in the Brightest Galactic Asymptotic Giant Branch stars

We present updated calculations of stellar evolutionary sequences and detailed nucleosynthesis predictions for the brightest asymptotic giant branch (AGB) stars in the Galaxy with masses between 5Msun to 9Msun, with an initial metallicity of Z =0.02 ([Fe/H] = 0.14). In our previous studies we used the Vassiliadis & Wood mass-loss rate, which stays low until the pulsation period reaches 500 days after which point a superwind begins. Vassiliadis & Wood noted that for stars over 2.5Msun the superwind should be delayed until P ~ 750 days at 5Msun. We calculate evolutionary sequences where we delay the onset of the superwind to pulsation periods of P ~ 700-800 days in models of M = 5, 6, and 7Msun. Post-processing nucleosynthesis calculations show that the 6 and 7Msun models produce the most Rb, with [Rb/Fe] ~ 1 dex, close to the average of most of the Galactic Rb-rich stars ([Rb/Fe] ~ 1.4 plus or minus 0.8 dex). Changing the rate of the 22Ne + alpha reactions results in variations of [Rb/Fe] as large as 0.5 dex in models with a delayed superwind. The largest enrichment in heavy elements is found for models that adopt the NACRE rate of the 22Ne(a,n)25Mg reaction. Using this rate allows us to best match the composition of most of the Rb-rich stars. A synthetic evolution algorithm is then used to remove the remaining envelope resulting in final [Rb/Fe] of ~ 1.4 dex although with C/O ratios > 1. We conclude that delaying the superwind may account for the large Rb overabundances observed in the brightest metal-rich AGB stars.Comment: 37 pages, accepted for publication in the Astrophysical Journal, minor modifications to text and Tables 2 and 3, reference adde

Updated stellar yields from Asymptotic Giant Branch models

An updated grid of stellar yields for low to intermediate-mass thermally-pulsing Asymptotic Giant Branch (AGB) stars are presented. The models cover a range in metallicity Z = 0.02, 0.008, 0.004, and 0.0001, and masses between 1Msun to 6Msun. New intermediate-mass Z = 0.0001 AGB models are also presented, along with a finer mass grid than used in previous studies. The yields are computed using an updated reaction rate network that includes the latest NeNa and MgAl proton capture rates, with the main result that between ~6 to 30 times less Na is produced by intermediate-mass models with hot bottom burning. In low-mass AGB models we investigate the effect on the production of light elements of including some partial mixing of protons into the intershell region during the deepest extent of each third dredge-up episode. The protons are captured by the abundant 12C to form a 13C pocket. The 13C pocket increases the yields of 19F, 23Na, the neutron-rich Mg and Si isotopes, 60Fe, and 31P. The increase in 31P is by factors of ~4 to 20, depending on the metallicity. Any structural changes caused by the addition of the 13C pocket into the He-intershell are ignored. However, the models considered are of low mass and any such feedback is likely to be small. Further study is required to test the accuracy of the yields from the partial-mixing models. For each mass and metallicity, the yields are presented in a tabular form suitable for use in galactic chemical evolution studies or for comparison to the composition of planetary nebulae.Comment: Accepted for publication in MNRAS; 15 page

Stellar yields from metal-rich asymptotic giant branch models

We present new theoretical stellar yields and surface abundances for three grids of metal-rich asymptotic giant branch (AGB) models. Post-processing nucleosynthesis results are presented for stellar models with initial masses between 1$M_{\odot}$ and 7.5$M_{\odot}$ for $Z=0.007$, and 1$M_{\odot}$ and 8$M_{\odot}$ for $Z=0.014$ (solar) and $Z=0.03$. We include stellar surface abundances as a function of thermal pulse on the AGB for elements from C to Bi and for a selection of isotopic ratios for elements up to Fe and Ni (e.g., $^{12}$C/$^{13}$C), which can be obtained from observations of molecules in stars and from the laboratory analysis of meteoritic stardust grains. Ratios of elemental abundances of He/H, C/O, and N/O are also included, which are useful for direct comparison to observations of AGB stars and their progeny including planetary nebulae. The integrated elemental stellar yields are presented for each model in the grid for hydrogen, helium and all stable elements from C to Bi. Yields of Li are also included for intermediate-mass models with hot bottom burning. We present the first $slow$ neutron-capture ($s$-process) yields for super-solar metallicity AGB stars with $Z=0.03$, and the first complete $s$-process yields for models more massive than 6$M_{\odot}$ at all three metallicities.Comment: 20 pages, 20 figures, includes supplementary surface abundance and yield data tables; accepted for publication in Ap

Physical characteristics of Acidic Mining Lake 111

Measurements of physical properties have been conducted in Mining Lake 111 (ML111), located in Lusatia, Germany over the time period 1996- 2002. In the deepest area of the ML111, a monimolimnion was observed, that persisted for the years 1996-1999. It disappeared in 2000 and again formed in 2001. The definition of the main physical properties, such as the temperature compensation for electrical conductivity, in acidic mining lakes required a lake specific approach. The relation between conductivity, temperature and density was determined for the acidic ML111. The variation in dissolved substances affected these relationships such that conductivity varied with temperature even in different layers of the water column and the limitations for a lake wide correlation was evident. Variation in the conductivity of the epilimnion could be verified, and agreed with the estimates of evaporation from the lake surface during summer stratification. Calculations, following the gradient flux method, indicated vertical transport coefficients between 10-7 and 10-6m2/s throughout the hypolimnion. The heat budget indicated that heat was transferred into the lake bed or the ground during spring

The Effects of Fuel Type Above Magnetic Properties of the Nickel Ferrite Nanoparticles Synthesized with Microwave Method

The synthesis of nickel ferrite nanoparticles was used various fuel substances such as glycine, urea and citric acid. The mixture prepared in stoichiometric rates was put in to the kitchen type microwave oven. In the end of reaction time was obtained a brown-black solid. The obtained solid was characterized with X-Ray Powder Diffraction and Scanning Electron Microscopy. The results of this analysis showed that all of the obtained particles have got nano-size particle size distribution. To determine the magnetic properties of the nanoparticles were analyzed by using a vibrating sample magnetometer. Fuel type used in synthesis is quite effective on the magnetic properties of NiFe2O4 nanoparticles. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3527