Nucleosynthesis Predictions for Intermediate-Mass AGB Stars: Comparison to Observations of Type I Planetary Nebulae

Type I planetary nebulae (PNe) have high He/H and N/O ratios and are thought to be descendants of stars with initial masses of ~3-8Msun. These characteristics indicate that the progenitor stars experienced proton-capture nucleosynthesis at the base of the convective envelope, in addition to the slow neutron capture process operating in the He-shell (the s-process). We compare the predicted abundances of elements up to Sr from models of intermediate-mass asymptotic giant branch (AGB) stars to measured abundances in Type I PNe. In particular, we compare predictions and observations for the light trans-iron elements Se and Kr, in order to constrain convective mixing and the s-process in these stars. A partial mixing zone is included in selected models to explore the effect of a 13C pocket on the s-process yields. The solar-metallicity models produce enrichments of [(Se, Kr)/Fe] < 0.6, consistent with Galactic Type I PNe where the observed enhancements are typically < 0.3 dex, while lower metallicity models predict larger enrichments of C, N, Se, and Kr. O destruction occurs in the most massive models but it is not efficient enough to account for the > 0.3 dex O depletions observed in some Type I PNe. It is not possible to reach firm conclusions regarding the neutron source operating in massive AGB stars from Se and Kr abundances in Type I PNe; abundances for more s-process elements may help to distinguish between the two neutron sources. We predict that only the most massive models would evolve into Type I PNe, indicating that extra-mixing processes are active in lower-mass stars (3-4Msun), if these stars are to evolve into Type I PNe.Comment: 39 pages, accepted for publication in Ap

An investigation of artificial neural network structure and its effects on the estimation of the low-cycle fatigue parameters of various steels

Artificial neural networks (ANNs) are a widely used machine learning approach for estimating low-cycle fatigue parameters. ANN structure has its parameters such as hidden layers, hidden neurons, activation functions, training functions, and so forth, and these parameters have a significant influence over the results. Three hidden layer combinations, the hidden neurons ranging from 1 to 25, and different activation functions like hyperbolic tangent sigmoid (tansig), logistic sigmoid (logsig), and linear (purelin) were used, and their effects on the low-cycle fatigue parameter estimation were investigated to determine optimal ANN structure. Based on the results, suggestions regarding ANN structure for the estimation of the low-cycle fatigue parameters and transition fatigue life were presented. For the output layer and hidden layers, the most suitable activation function was tansig. The optimal hidden neuron range has been found between 4 and 9. The neural network structure with one hidden layer was determined to be most suitable in terms of less knowledge, structural complexity, and computational time and power

The Dynamical Implications of Multiple Stellar Formation Events in Galactic Globular Clusters

Various galactic globular clusters display abundance anomalies that affect the morphology of their colour-magnitude diagrams. In this paper we consider the possibility of helium enhancement in the anomalous horizontal branch of NGC 2808. We examine the dynamics of a self-enrichment scenario in which an initial generation of stars with a top-heavy initial mass function enriches the interstellar medium with helium via the low-velocity ejecta of its asymptotic giant branch stars. This enriched medium then produces a second generation of stars which are themselves helium-enriched. We use a direct N-body approach to perform five simulations and conclude that such two-generation clusters are both possible and would not differ significantly from their single-generation counterparts on the basis of dynamics. We find, however, that the stellar populations of such clusters would differ from single-generation clusters with a standard initial mass function and in particular would be enhanced in white dwarf stars. We conclude, at least from the standpoint of dynamics, that two-generation globular clusters are feasible.Comment: 24 pages, 7 figures, 3 tables. Accepted for publication in Ap

Evaluation of left renal vein and inferior vena cava variations through routine abdominal multi-slice computed tomography

Background: The aim of this study was to evaluate the frequency of left renal vein (LRV) and inferior vena cava (IVC) variations and the effect of gender on this frequency, as well as the presence of associated abdominal pathologies.Materials and methods: Multi-slice computed tomography (MSCT) images from 746 patients were evaluated retrospectively.Results: Left renal vein variations were identified in 9.8% of cases, while retroaortic LRV (RLRV) and circumaortic LRV (CLRV) were found in 7.4% and 2.4% of cases, respectively. No significant correlation was found between gender and LRV variations (p = 0.797). Of the cases with LRV and IVC variations, 73% had abdominal pathologies, the most common of which were nephrolithiasis, which appeared in 18 (32%) cases, and renal cysts, which appeared in 14 (25.4%) cases.Conclusions: MSCT is a rapid and reliable method of identifying LRV and IVC variations and associated abdominal pathologies

FREQUENCY RATIO ASSESSMENT FOR LANDSLIDES TRIGGERED BY 6 FEBRUARY 2023 KAHRAMANMARAS TURKIYE EARTHQUAKES BETWEEN GOLBASI AND ERKENEK

Landslides triggered by earthquakes are significant geological hazards that can have devastating consequences, posing risks to human lives, infrastructure, and the environment. These seismic events may cause the instability of slopes and result in the displacement of soil and rock materials, leading to landslides. It is crucial to understand the characteristics and mechanisms of earthquake-triggered landslides in order to effectively manage and mitigate their associated risks. The number of landslides triggered by the 2023 Kahramanmaraş earthquakes (with magnitudes of 7.7 and 7.6) was over three thousand and their destructive effects were also devastating as secondary hazards. This study aims to examine the characteristics of landslides using the frequency ratio (FR) model. A landslide susceptibility map (LSM) was also produced using the output. For this purpose, in this study, we derived landslides triggered by the earthquakes in a part of the earthquake-affected region, between Golbasi town of Adiyaman and Erkenek village of Malatya covering an area with a size of 625 km2. The study utilized a landslide inventory that was manually delineated by visual interpretation based on pre-event and post-event. These associations can serve as a foundation for the application of various data-driven machine learning techniques. The findings of this study will contribute to the development of accurate LSMs, providing crucial insights into the behavior of earthquake-triggered landslides

Tungsten isotopic compositions in stardust SiC grains from the Murchison meteorite: Constraints on the s-process in the Hf-Ta-W-Re-Os region

We report the first tungsten isotopic measurements in stardust silicon carbide (SiC) grains recovered from the Murchison carbonaceous chondrite. The isotopes 182W, 183W, 184W, 186W and 179Hf, 180Hf were measured on both an aggregate (KJB fraction) and single stardust SiC grains (LS+LU fraction) believed to have condensed in the outflows of low-mass carbon-rich asymptotic giant branch (AGB) stars with close-to-solar metallicity. The SiC aggregate shows small deviations from terrestrial (=solar) composition in the 182W/184W and 183W/184W ratios, with deficits in 182W and 183W with respect to 184W. The 186W/184W ratio, however, shows no apparent deviation from the solar value. Tungsten isotopic measurements in single mainstream stardust SiC grains revealed lower than solar 182W/184W, 183W/184W, and 186W/184W ratios. We have compared the SiC data with theoretical predictions of the evolution of W isotopic ratios in the envelopes of AGB stars. These ratios are affected by the slow neutron-capture process and match the SiC data regarding their 182W/184W, 183W/184W, and 179Hf/180Hf isotopic compositions, although a small adjustment in the s-process production of 183W is needed in order to have a better agreement between the SiC data and model predictions. The models cannot explain the 186W/184W ratios observed in the SiC grains, even when the current 185W neutron-capture cross section is increased by a factor of two. Further study is required to better assess how model uncertainties (e.g., the formation of the 13C neutron source, the mass-loss law, the modelling of the third dredge-up, and the efficiency of the 22Ne neutron source) may affect current s-process predictions.Comment: Accepted for Publication on The Astrophysical Journal 43 pages, 2 tables, 7 figure

Heavy element abundances in giant stars of the globular clusters M4 and M5

We present a comprehensive abundance analysis of 27 heavy elements in bright giant stars of the globular clusters M4 and M5 based on high resolution, high signal-to-noise ratio spectra obtained with the Magellan Clay Telescope. We confirm and expand upon previous results for these clusters by showing that (1) all elements heavier than, and including, Si have constant abundances within each cluster, (2) the elements from Ca to Ni have indistinguishable compositions in M4 and M5, (3) Si, Cu, Zn, and all s-process elements are approximately 0.3 dex overabundant in M4 relative to M5, and (4) the r-process elements Sm, Eu, Gd, and Th are slightly overabundant in M5 relative to M4. The cluster-to-cluster abundance differences for Cu and Zn are intriguing, especially in light of their uncertain nucleosynthetic origins. We confirm that stars other than Type Ia supernovae must produce significant amounts of Cu and Zn at or below the clusters' metallicities. If intermediate-mass AGB stars or massive stars are responsible for the Cu and Zn enhancements in M4, the similar [Rb/Zr] ratios and (preliminary) Mg isotope ratios in both clusters may be problematic for either scenario. For the elements from Ba to Hf, we assume that the s- and r-process contributions are scaled versions of the solar s- and r-process abundances. We quantify the relative fractions of s- and r-process material for each cluster and show that they provide an excellent fit to the observed abundances.Comment: Accepted for publication in Ap

The diffusion-induced nova scenario. CK Vul and PB 8 as possible observational counterparts

We propose a scenario for the formation of DA white dwarfs with very thin helium buffers. For these stars we explore the possible occurrence of diffusion-induced CNO- flashes, during their early cooling stage. In order to obtain very thin helium buffers, we simulate the formation of low mass remnants through an AGB final/late thermal pulse (AFTP/LTP scenario). Then we calculate the consequent white dwarf cooling evolution by means of a consistent treatment of element diffusion and nuclear burning. Based on physically sounding white dwarf models, we find that the range of helium buffer masses for these diffusion-induced novas to occur is significantly smaller than that predicted by the only previous study of this scenario. As a matter of fact, we find that these flashes do occur only in some low-mass (M < 0.6M) and low metallicity (Z_ZAMS <0.001) remnants about 10^6 - 10^7 yr after departing from the AGB. For these objects, we expect the luminosity to increase by about 4 orders of magnitude in less than a decade. We also show that diffusion-induced novas should display a very typical eruption lightcurve, with an increase of about a few magnitudes per year before reaching a maximum of M_V ~ -5 to -6. Our simulations show that surface abundances after the outburst are characterized by logNH/NHe ~ -0.15...0.6 and N>C>O by mass fractions. Contrary to previous speculations we show that these events are not recurrent and do not change substantially the final H-content of the cool (DA) white dwarf. (Abridged)Comment: 16 pages, 8 figures, 3 tables. Replaced to match the final version published by MNRAS. The definitive version is available at http://onlinelibrary.wiley.com/journal/10.1111/%28ISSN%291365-296