On The Origin of Lyman-alpha Absorption in Nearby Starbursts and Implications for Other Galaxies

(Abridged) Despite the privileged position that Lyman-alpha (Lya) emission line holds in the exploration of the distant universe and modern observational cosmology, the origin of the observed diversity of lya profiles remains to be thoroughly explained. Observations of nearby star forming galaxies bring their batch of apparent contradictions between Lya emission and their physical parameters, and call for a detailed understanding of the physical processes at work. IZw 18, one of the most metal-poor galaxies known is of particular interest in this context. We use a 3D Lya radiation transfer code to model Hubble Space Telescope (HST) observations of IZw 18 and to fit its Lya spectrum. Different geometrical configurations of the source and the neutral gas are explored. The integrated Lya profile of NW region of IZw 18 is reproduced using the observed small amount of dust (E(B-V) ~ 0.05) and a spherical HI shell with N(HI) = 6.5 x 10^(21) cm^(-2). Such a high column density makes it possible to transform a strong Lya emission (EW(Lya) = 60 A) into a damped absorption even with a small extinction. When a slab geometry is applied and a given line of sight is chosen, the Lya profile can be successfully reproduced with no dust at all and N(HI) = 3 x 10^(21) cm^(-2). The spatial variations of the profile shape are naturally explained by radiation transfer effects. In the case of outflowing Inter Stellar Medium (ISM), as commonly observed in Lyman Break Galaxies (LBGs), a high N(H) and dust content are required to observe Lya in absorption. For nearly static neutral gas as observed in IZw 18 and other low luminosity galaxies only a small amount of dust is required provided a sufficiently high N(H) covers the galaxy.Comment: 11 pages, 10 figures. Accepted for publication in Astronomy and Astrophysic

High-redshift galaxies and black holes in the eyes of JWST: a population synthesis model from infrared to X-rays

The first billion years of the Universe is a pivotal time: stars, black holes (BHs) and galaxies form and assemble, sowing the seeds of galaxies as we know them today. Detecting, identifying and understand- ing the first galaxies and BHs is one of the current observational and theoretical challenges in galaxy formation. In this paper we present a population synthesis model aimed at galaxies, BHs and Active Galactic Nuclei (AGNs) at high redshift. The model builds a population based on empirical relations. Galaxies are characterized by a spectral energy distribution determined by age and metallicity, and AGNs by a spectral energy distribution determined by BH mass and accretion rate. We validate the model against observational constraints, and then predict properties of galaxies and AGN in other wavelength and/or luminosity ranges, estimating the contamination of stellar populations (normal stars and high-mass X-ray binaries) for AGN searches from the infrared to X-rays, and vice-versa for galaxy searches. For high-redshift galaxies, with stellar ages < 1 Gyr, we find that disentangling stellar and AGN emission is challenging at restframe UV/optical wavelengths, while high-mass X-ray binaries become more important sources of confusion in X-rays. We propose a color-color selection in JWST bands to separate AGN vs star-dominated galaxies in photometric observations. We also esti- mate the AGN contribution, with respect to massive, hot, metal-poor stars, at driving high ionization lines, such as C IV and He II. Finally, we test the influence of the minimum BH mass and occupa- tion fraction of BHs in low mass galaxies on the restframe UV/near-IR and X-ray AGN luminosity function.Comment: Accepted for publication in the Astrophysical Journa

On the influence of physical galaxy properties on Lyman-alpha escape in star-forming galaxies

[abridged] Among the different observational techniques used to select high-redshift galaxies, the hydrogen recombination line Lyman-alpha (Lya) is of particular interest as it gives access to the measurement of cosmological quantities such as the star formation rate of distant galaxy populations. However, the interpretation of this line and the calibration of such observables is still subject to serious uncertainties. Therefore, it important to understand under what conditions the Lya line can be used as a reliable star formation diagnostic tool. We use a sample of 24 Lya emitters at z ~ 0.3 with an optical spectroscopic follow-up to calculate the Lya escape fraction and its dependency upon different physical properties. We also examine the reliability of Lya as a star formation rate indicator. We combine these observations with a compilation of Lya emitters selected at z = 0 - 0.3 to assemble a larger sample. The Lya escape fraction depends clearly on the dust extinction following the relation fesc(Lya) = C(Lya) x 10^(-0.4 E(B-V) k(Lya)), but with a shallower slope than previously reported, with k(Lya) ~ 6.67 and C(Lya) = 0.22. However, the correlation does not follow the expected curve for a simple dust attenuation. We explore the various mechanisms than lead to fesc(Lya) values above the continuum extinction curve, i.e. to an enhancement of the Lya output. We also observe that the strength of Lya and the escape fraction appear unrelated to the galaxy metallicity. Regarding the reliability of Lya as a star formation rate (SFR) indicator, we show that the deviation of SFR(Lya) from the true SFR (as traced by the UV continuum) is a function of the observed SFR(UV), which can be seen as the decrease of fesc(Lya) with increasing UV luminosity. Moreover, we observe a redshift-dependence of this relationship revealing the underlying evolution of fesc(Lya) with redshift.Comment: 17 pages. Accepted for publicatio

Empirical Estimate of Lyman-alpha Escape Fraction in a Statistical Sample of Lyman-alpha Emitters

The Lyman-alpha (Lya) recombination line is a fundamental tool for galaxy evolution studies and modern observational cosmology. However, subsequent interpretations are still prone to a number of uncertainties. Besides numerical efforts, empirical data are urgently needed for a better understanding of Lya escape process. We empirically estimate the Lyman-alpha escape fraction fesc(Lya) in a statistically significant sample of z ~ 0 - 0.3 galaxies in order to calibrate high-redshift Lyman-alpha observations. An optical spectroscopic follow-up of a sub-sample of 24 Lyman-alpha emitters (LAEs) detected by GALEX at z ~ 0.2-0.3, combined with a UV-optical sample of local starbursts, both with matched apertures, allow us to quantify the dust extinction through Balmer lines, and to estimate the Lyman-alpha escape fraction from the Halpha flux corrected for extinction in the framework of the recombination theory. The global escape fraction of Lyman-alpha radiation spans nearly the entire range of values, from 0.5 to 100 %, and fesc(Lya) clearly decreases with increasing nebular dust extinction E(B-V). Several objects show fesc(Lya) greater than fesc(continuum) which may be an observational evidence for clumpy ISM geometry or for an aspherical ISM. Selection biases and aperture size effects may still prevail between z ~ 0.2-0.3 LAEs and local starbursts, which may explain the difference observed for fesc(Lya).Comment: 4 pages, 2 figures, accepted for publication in Astronomy and Astrophysic

Multicultural youth in Canada: Comparing friendships and perceived social support

There is paucity of research examining the differences between friendships among multicultural youth. Specifically, youth of Arab, East Asian, South Asian, and European descent were examined in this study because these groups are among the largest ethnic groups in Canada and are diverse for the purpose of comparison. Previous researchers have assessed differences between immigrant generations when comparing same- and cross-ethnicity friendships (e.g., Harker, 2001), whereas the effect of cultural group has been neglected. Thus, examination of same- and cross-ethnicity friendships was largely exploratory. Researchers in the past have theorized that individuals of Arab descent may be more likely to have an overlap between family and friends (Abu-Laban & Abu-Laban, 1999). Thus, we hypothesized that Arab youth may be more likely to have related friends (i.e., to identify friends that also happen to be related to them). The results of this study may have implications for improving our understanding of the social support networks of immigrant youth

ANALYSE DES DETERMINANTS DE LA GESTION DES RESULTATS : CAS DES FIRMES CANADIENNES FRANCAISES ET TUNISIENNES

L'objectif de cet article est d'analyser l'impact des déterminants de la gestion des résultats en référence aux modèles comptables Anglo-américain et Euro-continental. La France et le Canada sont, respectivement, issus de deux environnements sociaux-économiques différents. La Tunisie a procédé à la réforme de son système comptable pour passer du modèle comptable Euro-continental au modèle comptable Anglo-américain. Néanmoins les traits de l'environnement socio-économique tunisien demeurent rattachés à l'environnement Euro-continental (préeminence de l'endettement bancaire, gouvernance partenariale, etc.). Nous anticipons que les niveaux de gestion des résultats dans ces pays soient tributaires des spécificités socio-économiques des environnements Anglo-américains et Euro-continental. Nous avons eu recours à des données de panels canadiennes, françaises et tunisiennes composées, respectivement, de 1714, 1741, 283 observations firme-année. En considérant plusieurs niveaux de gestion des résultats (excessive à la hausse ou à la baisse, modérée), nous avons développé un modèle explicatif des pratiques de gestion des résultats fondé sur des régressions logistiques en panels. Globalement, les résultats empiriques sont conformes aux attentes. Les incitations à une gestion excessive pour les firmes tunisiennes sont quasiment similaires à celles dans les firmes françaises. Ces incitations sont notamment liées aux coûts contractuels d'endettement. Cependant, les firmes canadiennes montrent que la gestion excessive est fortement déterminée par des motivations contextuelles rattachées à un marché financier dynamique. Les introductions en bourse et les augmentations de capital par appel public à l'épargne présentent de fortes motivations pour une gestion excessive dans les firmes canadiennes.Gestion des résultats; Accruals Discrétionnaires; Comptabilité financière; Comptabilité internationale

The Importance of Hip Hop Events and their Impact on Event Management in Dubai

Background – Events and concerts give participants a chance to display their talents or showcase a new idea, perspective or invention. Dubai has established itself as one of the major destinations for events, specifically in the genre of Hip Hop. Hip Hop has become a worldwide cultural phenomenon and has impacted Dubai’s large international young community. The world market is becoming increasingly saturated and differentiation has become essential.Purpose – An assessment needs to be conducted on the usage of marketing and event management tools in major hip hop events and their effectiveness in providing economic benefit.Design/methodology/approach – This research study will utilize both primary and secondary data sources, mainly primary, in the form of interviews with industry professionals and experts in Dubai’s event field, to obtain an accurate perspective.Findings – Understanding the importance of hip hop and its economic impact will help to open up a new perspective to current research streams in the field. The research will focus on three key areas through analyzing Dubai’s hip hop events significance:- The city’s ability to differentiate itself through hip hop events.- The ability to attract major artists and audience from the region.- The benefits for the event management sector. Research limitations – At this stage, there is limited secondary data on this topic as Hip Hop events are specifically occurring in select cities with the infrastructural, audience, and economic provisions.Originality/value – Development of surrounding businesses, employment opportunities, culture awareness and crowd attraction are potential outcomes which can be expected from the above presented events in Dubai. The study aims at supporting a successful initiation and execution of hip-hop events which will give Dubai an economic edge against its competitors in this growing sector. Keywords: Culture, Dubai, Events, Event Management, Hip-Ho

Studi Pemasangan Step Voltage Regulator dengan Model Injeksi Daya pada Jaringan Menengah 20 KV Penyulang Katu Gardu Induk Menggala

Intisari---Penyulang Katu GI Menggala PT. PLN (Persero) Distribusi Lampung memiliki panjang saluran sekitar 158 km dengan maksimum beban yang terukur dari GI Menggala sekitar 4,6 MW dan terdiri dari 119 Bus. Kondisi ini mengakibatkan penyulang ini mengalami profil tegangan yang melanggar ketentuan +/- 5% sebagaimana yang dinyatakan dalam Aturan Penyambungan atau Grid Code. Untuk memperbaiki kondisi ini, salah satunya adalah dengan pemasangan step voltage regulator. Dalam penelitian ini, SVR dimodelkan sebagai injeksi daya yang kemudian dikombinasikan dengan persamaan aliran daya. SVR yang dijadikan obyek dalam penelitian ini adalah dari Type B dimana pemasangan SVR Type B dipasang di dekat sumber. Metode analisa aliran daya yang digunakan dalam penelitian ini adalah Metode Newton-Raphson. Hasil penelitian menunjukkan peningkatan tegangan akibat kontrol yang dilakukan oleh SVR. Sebelum pemasangan SVR, tegangan pada Bus 5 Penyulang Katu adalah 16,9828 kV. Setelah pemasangan SVR, terdapat peningkatan sebesar 1,3837 kV sehingga menjadi 18,3665 kV. Namun demikian, pemasangan SVR saja belum dapat memperbaiki profil tegangan secara keseluruhan akibat terlalu jauhnya drop tegangan di Penyulang Katu ini. Sehingga posisi tap maksimum SVR tidak mampu mengkompensasi tegangan yang jauh di bawah 0.95 p.u. yang terjadi di Penyulang Katu. Hasil perhitungan dilakukan dengan menggunakan perangkat lunak yang dikembangkan sendiri dan dibandingkan dengan perangkat lunak komersil yaitu ETAP. Selisih hasil perhitungan berada dalam kisaran 0.0108%.Kata kunci---aliran daya, step voltage regulator, tegangan jatuh , tap SVR . Abstract---Katu feeder of GI Menggala PT. PLN (Persero) Distribusi Lampung is about 158 km length with a maximum measured load from GI Menggala of about 4.6 MW and consists of 119 Buses. These conditions make the feeder suffers voltage profile that violates the limit of +/- 5% as stated in the Connection Code or the Grid Code. In order to correct this condition, installation of a step voltage regulator (SVR) is required. In this thesis, the SVR is modeled as a power injection and combined into the power flow equations. SVR of this research is of Type B where installation this type of SVR is near the source. Power flow analysis method used in this research is the Newton-Raphson method. The results showed an increase in voltage due to the control exercised by the SVR. Before mounting SVR, the voltage on Bus 5 of feeder Katu is 16.9828 kV. After SVR installation, the voltage becomes 18.3665 kV. However, the installation of SVR alone can not fix the overall voltage profile due to the large voltage drop along this feeder although the SVR was set to maximum tap position. The result of the calculation is done by using a self-developed software and compared to a commercial software i.e. ETAP. The difference in calculation results are within the range of 0.0108%.Keywords---power flow, step voltage regulators, voltage drop, tap SVR

The escape of Lyman photons from a young starburst: the case of Haro 11

(Abridged) Lyman-alpha (Lya) is a dominant probe of the galaxy population at high-z. However, interpretation of data drawn from Lya alone hinges on the Lya escape fraction which, due to the complex radiative transport, may vary greatly. Here we map the Lya emission from local starburst Haro 11, a Lya emitter and the only known candidate for low-z Lyman continuum emission (LyC). To aid in the interpretation we perform a detailed multi-wavelength analysis and model the stellar population, dust distribution, ionising photon budget, and star-cluster population. We use archival X-ray observations to further constrain properties of the starburst and estimate the HI column density. The Lya morphology is found to be strongly decoupled from stellar and nebular (H-alpha) morphologies. General surface photometry finds only very slight correlation between Lya and H-halpha, E(B-V), and stellar age. Only around the central Lya-bright cluster do we find the Lya/Ha ratio at values predicted by recombination theory. The total Lya escape fraction is found to be just 3%. We compute that ~90% of the Lya photons that escape do so after undergoing multiple resonance scattering events, masking their point of origin. This leads to a largely symmetric distribution and, by increasing the distance that photons must travel to escape, decreases the escape probability significantly. While dust must ultimately be responsible for the destruction of Lya, it plays little role in governing the observed morphology, which is regulated more by ISM kinematics and geometry. We find tentative evidence for local Lya equivalent width in the immediate vicinity of star-clusters being a function of cluster age, consistent with hydrodynamic studies. We estimate the ionising photon production and further constrain the escape fraction at 900 AA to <~9% .Comment: In press for MNRAS. 18 pages, 9 figures. Version with full resolution images to be found at http://www.astro.su.se/~matthew/english/papers/hayes_lya_haro11_hires.pd

Analisis Risiko Kecelakaan Kerja pada Proses Loadout Relokasi Container Crane Menggunakan Skidding System

Pada suatu proyek terdapat berbagai jenis kegiatan yang dilakukan berdasarkan apa yang sudah ditetapkan. Untuk mencapai kesuksesan dan ketercapaian tujuan diperlukan kerjasama antar pihak yang baik. Dikarenakan terdapat banyak pihak yang berpartisipasi dalam suatu proyek maka tidak luput dengan ancaman risiko kecelakaan kerja. Proses loadout adalah menarik deck/platform/module ke atas barge untuk dipindahkan ke tempat yang akan dituju. Container crane (CC-05) merupakan struktur yang akan dimuat ke transportation barge dengan metode skidding. Tentu nya pada proses loadout tersebut diperlukan analisis risiko untuk mencegah atau mengurangi dampak yang ditimbulkan selama proses pelaksanaan proyek. Tujuan dari penelitian tugas akhir ini adalah untuk mengidentifikasi risiko dominan yang dapat menyebabkan kecelakaan kerja pada proses loadout relokasi container crane (CC-05), mencari penyebab dari risiko dominan, serta dapat menganalisa pengendalian risiko dominan yang tepat pada proses loadout. Penelitian ini menggunakan metode Failure Mode and Effect Analysis (FMEA) untuk mmengidentifikasi bahaya dan risiko yang dominan pada proses loadout. Untuk mengetahui risiko dominan yang dihasilkan dilakukan perhitungan RPN. Melalui perhitungan RPN didapatkan 3 risiko dominan tertinggi yaitu tangan pekerja terjepit mesin winch dengan RPN 216, pekerja terkena luka bakar akibat tersengat listrik dengan RPN 200, tangan pekerja terkena luka bakar atau mata terpapar sinar las dan mengalami kerusakan dengan RPN 192. Hasil dari perhitunan RPN kemudian dianalisis menggunakan metode Fault Tree Analysis (FTA) untuk mencari penyebab dari risiko kecelekaan kerja tersebut, dari hasil pengkonstruksian FTA teridentifikasi 18 basic event. Kemudian setelah telah didaptkan risiko dominan dan penyebabnya, dilakukan rekomendasi untuk mencegah terjadinya risiko kecelakaan kerja tersebut