181 research outputs found
Clouds, Streams and Bridges: redrawing the blueprint of the Magellanic System with Gaia DR1
No full textWe present the discovery of stellar tidal tails around the Large and the Small Magellanic Clouds in the Gaia DR1 data. In between the Clouds, their tidal arms are stretched towards each other to form an almost continuous stellar bridge. Our analysis relies on the exquisite quality of the Gaia's photometric catalogue to build detailed star-count maps of the Clouds. We demonstrate that the Gaia DR1 data can be used to detect variable stars across the whole sky, and in particular, RR Lyrae stars in and around the LMC and the SMC. Additionally, we use a combination of Gaia and Gale to follow the
distribution of Young Main Sequence stars in the Magellanic System. Viewed by Gaia, the Clouds show unmistakable signs of interaction. Around the LMC, clumps of RR Lyrae are observable as far as ~20 degrees, in agreement with the most recent map of Mira-like stars reported in Deason et al (2016). The SMC's outer stellar density contours show a characteristic S-shape, symptomatic of the on-set of tidal stripping. Beyond several degrees from the center of the dwarf, the Gaia RR Lyrae stars trace the Cloud's trailing arm, extending towards the LMC. This stellar tidal tail mapped with RR Lyrae is not aligned with the gaseous Magellanic Bridge, and is shifted by some ~5 degrees from the Young Main Sequence bridge. We use the offset between the bridges to put constraints on the density of the hot gaseous corona of the Milky Way
The Chemo-Dynamical Groups of Galactic Globular Clusters
No full textWe introduce a multi-component chemo-dynamical method for splitting the
Galactic population of Globular Clusters (GCs) into three distinct
constituents: bulge, disc, and stellar halo. The latter is further decomposed
into the individual large accretion events that built up the Galactic stellar
halo: the Gaia-Enceladus-Sausage, Kraken and Sequoia structures, and the
Sagittarius and Helmi streams. Our modelling is extensively tested using mock
GC samples constructed from the AURIGA suite of hydrodynamical simulations of
Milky Way (MW)-like galaxies. We find that, on average, a proportion of the
accreted GCs cannot be associated with their true infall group and are left
ungrouped, biasing our recovered population numbers to approximately 80 percent
of their true value. Furthermore, the identified groups have a completeness and
a purity of only 65 percent. This reflects the difficulty of the problem, a
result of the large degree of overlap in energy-action space of the debris from
past accretion events. We apply the method to the Galactic data to infer, in a
statistically robust and easily quantifiable way, the GCs associated with each
MW accretion event. The resulting groups' population numbers of GCs, corrected
for biases, are then used to infer the halo and stellar masses of the now
defunct satellites that built up the halo of the MW.Comment: 18 pages, 11 figures, + Appendice
The effects of dynamical substructure on Milky Way mass estimates from the high-velocity tail of the local stellar halo
No full textWe investigate the impact of dynamical streams and substructure on estimates of the local escape speed and total mass of Milky-Way-mass galaxies from modelling the high-velocity tail of local halo stars. We use a suite of high-resolution magnetohydrodynamical cosmological zoom-in simulations that resolve phase space substructure in local volumes around solar-like positions. We show that phase space structure varies significantly between positions in individual galaxies and across the suite. Substructure populates the high-velocity tail unevenly and leads to discrepancies in the mass estimates. We show that a combination of streams, sample noise, and truncation of the high-velocity tail below the escape speed leads to a distribution of mass estimates with a median that falls below the true value by similar to 20 per cent, and a spread of a factor of 2 across the suite. Correcting for these biases, we derive a revised value for the Milky Way mass presented in Deason et al. of 1.29(-0.47)(+0.37) x 10(12) M-circle dot
The local high-velocity tail and the Galactic escape speed
No full textWe model the fastest moving (v_{tot}>300km s^{−1}) local (D ≲ 3 kpc) halo stars using cosmological simulations and six-dimensional Gaia data. Our approach is to use our knowledge of the assembly history and phase-space distribution of halo stars to constrain the form of the high-velocity tail of the stellar halo. Using simple analytical models and cosmological simulations, we find that the shape of the high-velocity tail is strongly dependent on the velocity anisotropy and number density profile of the halo stars – highly eccentric orbits and/or shallow density profiles have more extended high-velocity tails. The halo stars in the solar vicinity are known to have a strongly radial velocity anisotropy, and it has recently been shown the origin of these highly eccentric orbits is the early accretion of a massive (M_{star}∼10^{9}M⊙) dwarf satellite. We use this knowledge to construct a prior on the shape of the high-velocity tail. Moreover, we use the simulations to define an appropriate outer boundary of 2xr_{200}, beyond which stars can escape. After applying our methodology to the Gaia data, we find a local (r_{0} = 8.3 kpc) escape speed of v_{esc}(r_{0})=528 +24 −25 km s^{−1}. We use our measurement of the escape velocity to estimate the total Milky Way mass, and dark halo concentration: M_{200,tot}=1.00 +0.31 −0.24 ×10^{12}M⊙, c_{200}=10.9 +4.4 −3.3. Our estimated mass agrees with recent results in the literature that seem to be converging on a Milky Way mass of M_{200,tot}∼10^{12}M⊙
The mass of the Milky Way from satellite dynamics
No full textWe present and apply a method to infer the mass of the Milky Way (MW) by comparing the dynamics of MW satellites to those of model satellites in the eagle cosmological hydrodynamics simulations. A distribution function (DF) for galactic satellites is constructed from eagle using specific angular momentum and specific energy, which are scaled so as to be independent of host halo mass. In this two-dimensional space, the orbital properties of satellite galaxies vary according to the host halo mass. The halo mass can be inferred by calculating the likelihood that the observed satellite population is drawn from this DF. Our method is robustly calibrated on mock eagle systems. We validate it by applying it to the completely independent suite of 30 auriga high-resolution simulations of MW-like galaxies: the method accurately recovers their true mass and associated uncertainties. We then apply it to 10 classical satellites of the MW with six-dimensional phase-space measurements, including updated proper motions from the Gaia satellite. The mass of the MW is estimated to be MMW200=1.17^{+0.21}_{−0.15}×10^12M⊙ (68 per cent confidence limits). We combine our total mass estimate with recent mass estimates in the inner regions of the Galaxy to infer an inner dark matter (DM) mass fraction MDM(<20 kpc)/MDM200=0.12, which is typical of ∼1012M⊙ lambda cold dark matter haloes in hydrodynamical galaxy formation simulations. Assuming a Navarro, Frenk and White (NFW) profile, this is equivalent to a halo concentration of cMW200=10.9^{+2.6}_{−2.0}
A study of ‘calf-path’ in file naming in institutional repositories in India
No full textThis study examined the file naming practices in 39 institutional repositories. There is evidence that calf-path exists infile naming among the curators of institutional repositories in India. The study showed that no standard or logic seems tohave been followed by repositories in the naming of the files, except by the National Digital Library of India (NDLI) and theCSIR-National Institute of Science Communication and Policy Research (CSIR-NIScPR). The study also examined thecomposition of the filenames, which shows that the author names (11.2%), titles (11.9%), journal title with volume and issuenumbers (21.1%) form the basis for the formation of filenames. It is suggested that digital repository managers have to givemore attention to name files in the institutional repository in the interest of uniformity and consistency
Analysis of company's SIA "Alis Co" economic activity ways of improvement thereof
No full textBakalaura darba tēma - Uzņēmuma SIA “Alis Co” saimnieciskās darbības analīze un pilnveidošanas virzieni. Uzņēmuma efektīva saimnieciskā darbība ir viena no centrālajām problēmām, kuru risina uzņēmuma vadība visā pastāvēšanas laikā. Pašlaik valstī šī tēma ir ļoti aktuāla, jo Covid-19 pandēmijas laikā daļa uzņēmumu, nespēj ātri piesaistīt jaunus līdzekļus. Līdz ar to likviditātes trūkums, atkarība no kreditoriem varēja pārvērsties maksātnespējā. Neskatoties uz to, ka valdība atbalstīja privāto sektoru ar īpašiem palīdzības pasākumiem, uzņēmumi saskarās ar tādām problēmām savā saimnieciskajā darbībā ļoti bieži. Bakalaura darba izstrādes mērķis – pamatojoties uz SIA “Alis Co” saimnieciskās darbības analīzes pamatā izstrādāt priekšlikumus uzņēmuma darbības veicināšanai. Izvirzītā mērķa sasniegšanai ir nepieciešams veikt sekojošus uzdevumus: 1.raksturot saimnieciskās darbības analīzes teorētiskus aspektus; 2.veikt SIA “Alis Co” saimnieciskās darbības analīzi, tai skaitā finanšu analīzi un SVID analīzi; 3.izdarīt secinājumus un izstrādāt SIA “Alis Co” darbības pilnveidošanas virzienus. Darbs sastāv no trīs daļām. Pirmajā sadaļā apskatīti saimnieciskās darbības analīzes teorētiskie aspekti, tai skaitā tirdzniecības nozares rādītāji un attīstības prognozes. Otrā sadaļā darba autore veic SIA “Alis Co” saimnieciskās darbības analīzi laika posmā no 2018. gada līdz 2020. gadam. Trešajā sadaļā darba autore izstrādā SIA “Alis Co” darbības pilnveidošanas virzienus. Galvenais autores secinājums pēc analīzes datiem ir tāds, ka uzņēmumam ir visi faktori, kas ļauj uzņēmumam realizēt visas darbības pilnveidošanas virzienus - pazīstamais zīmols tirgū, kā arī uzticama reputācija, kvalitatīvi produkti, lielā pieredze tirgū (strādā no 1994.gadā) un stabils finansiālais stāvoklis. Bakalaura darba apjoms veido 67 lapas (bez pielikumiem). Darbā izmantoti 29 attēli, 23 tabulas un 27 literatūras avoti. Darbam pievienoti 4 pielikumi. Atslēgvārdi: saimnieciskā darbība, pilnveidošanas virzieni, finansiālais stāvoklis, pārdošanas apjomi, tirdzniecības nozare.The topic of the bachelor’s paper is analysis of company’s SIA “Alis Co” economic activity and ways of improvement thereof. Efficient economic activity of a company is one of the central problems solved by company’s management during all period of its existence. Currently, this topic is very topical in the country, because during Covid-19 pandemics most of the companies cannot attract quickly new resources. Consequently, the lack of liquidity, dependence on creditors could turn into insolvency. Despite the fact that the Government supported the private sector with special aid measures, the companies encountered such problems very often in their economic activity. Aim of the bachelor’s paper – develop suggestions to promote the operation of the company on the base of the analysis of economic activity of SIA “Alis Co”. The following must be done to reach the set aim: 1. characterize the theoretical aspects of analysis of economic activity, 2. do the analysis of economic activity of SIA “Alis Co”, including the financial analysis and SWAT analysis, 3. draw conclusions and develop the ways of improvement of operation of SIA “Alis Co”. The paper consists of three chapters. The first chapter discusses the theoretical aspects of analysis of economic activity, including the indicators of sales area and development forecasts. In the second chapter, the author makes the analysis of economic activity of SIA “Alis Co” from 2018 to 2020. In the third chapter, the author develops the ways of improvement of operation of SIA “Alis Co”. The main conclusion of the author according to the data of analysis is that the company has all factors that allow implementing all ways of improvement of its operation – known brand in the market, and trustable reputation, qualitative products, large experience on the market (works from 1994) and stable financial position. The volume of the bachelor’s paper is 67 pages (without annexes). 29 images, 23 tables and 27 bibliography sources are used in the paper. The paper has 4 annexes. Keywords: economic activity, ways of improvement, financial position, sales volumes, sales industry
Simulating cosmological substructure in the solar neighbourhood
No full textWe explore the predictive power of cosmological, hydrodynamical simulations for stellar phase-space substructure and velocity correlations with the AURIGA simulations and AURIGAIA mock Gaia catalogues. We show that at the solar circle the AURIGA simulations commonly host phase-space structures in the stellar component that have constant orbital energies and arise from accreted subhaloes. These structures can persist for a few Gyr, even after coherent streams in position space have been erased. We also explore velocity two-point correlation functions and find this diagnostic is not deterministic for particular clustering patterns in phase space. Finally, we explore these structure diagnostics with the AURIGAIA catalogues and show that current catalogues have the ability to recover some structures in phase space but careful consideration is required to separate physical structures from numerical structures arising from catalogue generation methods
Author self-archiving and licensing policies of open access library and information science journals: a study
No full textExamines self-archiving and licensing clauses of OA journals indexed in DOAJ and SHERPA/RoMEO databases. Findings of the study suggest that RoMEO codings of licensing policies are updated infrequently. The database does not provide all the necessary information in the licensing clauses. Creative Commons licensing ‘by-cd-nd’ is the widely used model. Majority of the journals (23%) permit post-print self-archiving. The most frequently appearing statement in the licensing clauses is "Publisher's version/PDF may be used"
A Scientometric Introspect of Literary Warrants Published in Annals of Library and Information Studies (ALIS) during the Last Decade
No full textScientometric studies are enduring studies that portray an organized visual of messy data. The current study is a scientometric study based on secondary data sets included in Scopus. A corpus of 311 documents published in the journal Annals of Library and Information Studies (ALIS) from 2011 to 2020 was the population of the study. The study focused on several characteristics of the journal, including article distribution, average author per document, average document per year, authorship productivity, collaboration index, country-wise distribution of documents and citation analysis. The study retrieved the most prolific author contributing to this journal with 19 articles. The Council of Scientific and Industrial Research (CSIR) and the University of Delhi were the top literary contributors to the ALIS journal. The University of Kerala got the most citations per document (6.833). The maximum count of author keywords (Scientometrics) used in the journal from 2011 to 2020 was 135
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