The effects of double folding cluster model potential on some astrophysical reactions

The Double Folding Cluster Model Potential is constructed using the α - cluster structure of nuclei. It can be derived by folding an α − α interaction with density distributions of α - clusters inside the projectile and target nuclei. This potential has been successfully tested on elastic scattering data of some selected nuclei. In this work, we are interested to investigate the implications of this potential on astrophysical aspects

Ekstremisme agama dalam gerakan Islamic State of Iraq dan Syria (ISIS): satu analisis terhadap akhbar The Star

Kajian ini bertujuan mengkaji berita mengenai isu-isu golongan ekstremisme dari sudut gerakan Islamic State of Iraq and Syria (ISIS) dalam akhbar berbahasa Inggeris iaitu The Star sepanjang tempoh dua tahun, bermula dari Januari 2015 hingga Disember 2016. Ekstremisme agama merupakan isu penting dalam menangani perpaduan dan keselamatan sesebuah negara. Globalisasi telah mengangkat ekstremisme agama ke skala yang lebih besar. Dalam konteks kajian ini, organisasi ektremisme seperti ISIS dilihat sebagai satu ancaman buat sesebuah negara kerana terdapat pelbagai kes tragik menggemparkan dunia yang dikaitkan dengan kumpulan ini. Terdapat kajian yang meneroka ekstremisme agama di Malaysia tetapi tidak secara khusus dalam bidang komunikasi. Justeru, kajian ini meneroka isu ektremisme agama dalam media cetak di Malaysia. Secara khususnya, terdapat dua objektif utama kajian iaitu: i) mengenal pasti tema-tema berita berkenaan ekstremisme, dan ii) mengenal pasti arah berita yang disiarkan. Menggunakan kaedah analisa kandungan, sebanyak 40 berita telah dianalisis. Dapatan kajian mendapati terdapat 13 isu yang berteraskan tiga tema. Majoriti berita yang melaporkan mengenai ISIS adalah ke arah negatif. Kajian ini menyumbang kepada implikasi sosial mengenai kepentingan pemahaman tema dan arah berita ekstremisme agama di Malaysia yang mempunyai impak global. Kajian ini merupakan kajian yang meneroka mengenai isu berkaitan golongan ekstremisme dalam akhbar Bahasa Inggeris yang mempunyai sirkulasi tertinggi di Malaysia

Evolution and fate of very massive stars

There is observational evidence that supports the existence of very massive stars (VMS) in the local universe. First, VMS (Mini ≲ 320 M⊙) have been observed in the Large Magellanic Clouds (LMC). Secondly, there are observed supernovae (SNe) that bear the characteristics of pair creation supernovae (PCSNe, also referred to as pair instability SN) which have VMS as progenitors. The most promising candidate to date is SN 2007bi. In order to investigate the evolution and fate of nearby VMS, we calculated a new grid of models for such objects, for solar, LMC and Small Magellanic Clouds (SMC) metallicities, which covers the initial mass range from 120 to 500 M⊙. Both rotating and non-rotating models were calculated using the GENEVA stellar evolution code and evolved until at least the end of helium burning and for most models until oxygen burning. Since VMS have very large convective cores during the main-sequence phase, their evolution is not so much affected by rotational mixing, but more by mass loss through stellar winds. Their evolution is never far from a homogeneous evolution even without rotational mixing. All the VMS, at all the metallicities studied here, end their life as WC(WO)-type Wolf-Rayet stars. Because of very important mass losses through stellar winds, these stars may have luminosities during the advanced phases of their evolution similar to stars with initial masses between 60 and 120 M⊙. A distinctive feature which may be used to disentangle Wolf-Rayet stars originating from VMS from those originating from lower initial masses would be the enhanced abundances of Ne and Mg at the surface of WC stars. This feature is however not always apparent depending on the history of mass loss. At solar metallicity, none of our models is expected to explode as a PCSN. At the metallicity of the LMC, only stars more massive than 300 M⊙ are expected to explode as PCSNe. At the SMC metallicity, the mass range for the PCSN progenitors is much larger and comprises stars with initial masses between about 100 and 290 M⊙. All VMS in the metallicity range studied here produce either a Type Ib SN or a Type Ic SN but not a Type II SN. We estimate that the progenitor of SN 2007bi, assuming a SMC metallicity, had an initial mass between 160 and 175 M⊙. None of models presented in this grid produces gamma-ray bursts or magnetars. They lose too much angular momentum by mass loss or avoid the formation of a black hole by producing a completely disruptive PCSN

Ekstremisme Agama dalam Gerakan Islamic State of Iraq dan Syria (ISIS): Satu Analisis terhadap Akhbar The Star (Religious Extremism in the Islamic State of Iraq and Syria (ISIS) Movement: An Analysis of The Star Newspaper)

The study aims to investigate the issues of extremism of the Islamic State of Iraq and Syria (ISIS) movement in the English-language newspaper, The Star, over a two-year period from January 2015 to December 2016.Religious extremism is an important issue in dealing with the unity and security of a nation.Globalization has raised religious extremism to a larger scale. In the context of this study, an extremist organization such as ISIS is seen as a threat to a country as there are various tragic cases in the world that are associated with this group.There are studies exploring religious extremism in Malaysia but not specifically in the field of communication. Thus, this study explores the issue of religious extremism in the print media in Malaysia. Specifically, there are two objectives of the study: i) identifying news themes of extremism and, ii) identifying the direction of the news. Using content analysis method, 40 news stories have been analyzed.The findings revealed 13 issues that were derived from 3 main themes.The majority of news reporting on ISIS was negative.This study contributes to social implications on the importance of understanding the theme and direction of news about religious extremism in Malaysia that has a global impact.This is an exploratory study on the issue of extremism in the English newspaper that has the highest circulation in Malaysia

Grids of stellar models with rotation - III. Models from 0.8 to 120 Msun at a metallicity Z = 0.002

(shortened) We provide a grid of single star models covering a mass range from 0.8 to 120 Msun with an initial metallicity Z = 0.002 with and without rotation. We discuss the impact of a change in the metallicity by comparing the current tracks with models computed with exactly the same physical ingredients but with a metallicity Z = 0.014 (solar). We show that the width of the main-sequence (MS) band in the upper part of the Hertzsprung-Russell diagram (HRD), for luminosity above log(L/Lsun) > 5.5, is very sensitive to rotational mixing. Strong mixing significantly reduces the MS width. We confirm, but here for the first time on the whole mass range, that surface enrichments are stronger at low metallicity provided that comparisons are made for equivalent initial mass, rotation and evolutionary stage. We show that the enhancement factor due to a lowering of the metallicity (all other factors kept constant) increases when the initial mass decreases. Present models predict an upper luminosity for the red supergiants (RSG) of log (L/Lsun) around 5.5 at Z = 0.002 in agreement with the observed upper limit of RSG in the Small Magellanic Cloud. We show that models using shear diffusion coefficient calibrated to reproduce the surface enrichments observed for MS B-type stars at Z = 0.014 can also reproduce the stronger enrichments observed at low metallicity. In the framework of the present models, we discuss the factors governing the timescale of the first crossing of the Hertzsprung gap after the MS phase. We show that any process favouring a deep localisation of the H-burning shell (steep gradient at the border of the H-burning convective core, low CNO content) and/or the low opacity of the H-rich envelope favour a blue position in the HRD for the whole or at least a significant fraction of the core He-burning phase.Comment: 17 pages, 15 figures, 2 tables. Accepted for publication in Astronomy and Astrophysic

The R136 star cluster hosts several stars whose individual masses greatly exceed the accepted 150 Msun stellar mass limit

Spectroscopic analyses of H-rich WN5-6 stars within the young star clusters NGC 3603 and R136 are presented, using archival HST & VLT spectroscopy, & high spatial resolution near-IR photometry. We derive high T* for the WN stars in NGC 3603 (T*~42+/-2 kK) & R136 (T*~53+/-3 kK) plus clumping-corrected dM/dt ~ 2-5x10^-5 Msun/yr which closely agree with theoretical predictions. These stars make a disproportionate contribution to the global budget of their host clusters. R136a1 alone supplies ~7% of N(LyC) of the entire 30 Dor region. Comparisons with stellar models calculated for the main-sequence evolution of 85-500 Msun suggest ages of ~1.5 Myr & M_init in the range 105 - 170 Msun for 3 systems in NGC 3603, plus 165-320 Msun for 4 stars in R136. Our high stellar masses are supported by dynamical mass determinations for the components of NGC 3603 A1. We consider the predicted L_X of the R136 stars if they were close, colliding wind binaries. R136c is consistent with a colliding wind binary system. However, short period, colliding wind systems are excluded for R136a WN stars if mass ratios are of order unity. Widely separated systems would have been expected to harden owing to early dynamical encounters with other massive stars in such a dense environment. From simulated star clusters, whose constituents are randomly sampled from the Kroupa IMF, both clusters are consistent with a tentative upper mass limit of ~300 Msun. The Arches cluster is either too old, exhibits a deficiency of very massive stars, or more likely stellar masses have been underestimated - M_init for the most luminous stars in the Arches cluster approach 200 Msun according to contemporary stellar & photometric results. The potential for stars greatly exceeding 150 Msun within metal-poor galaxies suggests that such pair-instability SNe could occur within the local universe, as has been claimed for SN 2007bi (abridged).Comment: 20 pages, 14 figures, accepted for MNRAS. Version with higher resolution figures is available from http://pacrowther.staff.shef.ac.uk/R136.pdf See also http://www.eso.org/public/news/eso1030/ from Wed 21 from noon (CEST

Very massive stars : mass determination and fate / Norhasliza binti Yusof

The first generation of stars is thought to have been very massive (150-300 M�) and produces pair creation supernovae (PCSNe) at the end of their life. However, the chemical signature of PCSNe is not observed in extremely metal poor stars (e.g. Umeda & Nomoto, 2002) and it raises the following questions: Were stars born less (or more massive) than the mass range expected to lead to the PCSNe? Or is mass loss too strong during the evolution of these stars and prevented them from retaining enough mass to produce PCSNe? The discovery of very massive stars (VMS, M> 100 M�) in the Milky Way and LMC (Crowther et al., 2010) shows that VMS can form and exist. The observation of PCSN candidates (SN 2006gy & SN 2007bi) also seems to indicate that such supernovae (SNe) may occur. Mass loss plays a crucial role in the life of VMS since the star will only die as a PCSN if the star retains a high mass throughout its life. In this thesis, we shall describe the dependence of VMS evolution on metallicity and present stellar evolution models at various metallicities, including the e�ects of mass loss and rotation. Based on our models, we will give our predictions concerning the fate of these VMS, either a PCSN or supernova Type Ic (SN Ic) as a function of metallicity and mass loss rate prescriptions used. Our models that predict the star will end up as PCSN are models at LMC metallicity with mass around 500 M� and rotating SMC metallicity models with mass 120 < M� < 280. Other than that it will die as a black hole or a core-collapse supernova. We also study the impact of the updated neutrino energy loss from Itoh et al. (1996) that supersedes the neutrino energy loss from Itoh et al. (1989) which has been used in the Geneva stellar evolution code. Neutrino energy loss is an important process in the evolution of advanced stages of massive stars since most of the energy loss is through the neutrino processes. From our study, the VMS do not have any signi�cant e�ects when we update the neutrino energy loss. This is due to the prominent process in neutrino energy loss which is photoneutrino process that remains unchanged in Itoh et al. (1996). Finally we apply an updated nuclear reaction rates using WKB method for 12C(p, )13N, 15N(p, )16O and 16O(p, )17F in the CNO cycle. Evolution of massive and very massive stars are studied and we �nd the new reaction rates in�uence the surface and central abundances of 12C in these stars