Using High Performance Computing and Open Source Technologies for Solving Behaviour Analytics Problems in E-Learning

In this paper the authors describe solution for solving various analytical problems in E-learning, Course Management Systems like Moodle by using HPC (High Performance Computing) and Apache Hadoop open source technologies in Liepaja University. The problem is that nowadays there are collecting huge amounts of analytics data from several gigabytes to petabytes, which is hard to store, process, analyse and visualize. This article reflects one of the solutions concerning distributed parallel processing of huge amounts of data across inexpensive, industry-standard servers that can store and process the data, can scale without limits and provides technological opportunities of reliable, scalable and distributed computing.

Studies of Variability in Proto-Planetary Nebulae: II. Light and Velocity Curve Analyses of Iras 22272+5435 and 22223+4327

We have carried out a detailed observational study of the light, color, and velocity variations of two bright, carbon-rich proto-planetary nebulae, IRAS 22223+4327 and 22272+5435. The light curves are based upon our observations from 1994 to 2011, together with published data by Arkhipova and collaborators. They each display four significant periods, with primary periods for IRAS 22223+4327 and 22272+5435 being 90 and 132 days, respectively. For each of them, the ratio of secondary to primary period is 0.95, a value much different from that found in Cepheids, but which may be characteristic of post-AGB stars. Fewer significant periods are found in the smaller radial velocity data sets, but they agree with those of the light curves. The color curves generally mimic the light curves, with the objects reddest when faintest. A comparison in seasons when there exist contemporaneous light, color, and velocity curves reveals that the light and color curves are in phase, while the radial velocity curves are 0.25 out of phase with the light curves. Thus they differ from what is seen in Cepheids, in which the radial velocity curve is 0.50 P out of phase with the light curve. Comparison of the observed periods and amplitudes with those of post-AGB pulsation models shows poor agreement, especially for the periods, which are much longer than predicted. These observational data, particularly the contemporaneous light, color, and velocity curves, provide an excellent benchmark for new pulsation models of cool stars in the post-AGB, proto-planetary nebula phase.Comment: 15 Figures plus Erratu

Cerium: the lithium substitute in post-AGB stars

In this letter we present an alternative identification for the line detected in the spectra of s-process enriched low-mass post-AGB stars around 6708A and which was interpreted in the literature as due to Li. Newly released line lists of lanthanide species reveal, however, the likely identification of the line to be due to a CeII transition. We argue that this identification is consistent with the Ce abundance of all the objects discussed in the literature and conclude that in none of the low-mass s-process enriched post-AGB stars there is indication for Li-production.Comment: 5 pages, 2 figures, accepted for publication as A&A Lette

USE OF HIGH PERFORMANCE COMPUTING TECHNOLOGIES AND SCRIPT RUN MEDIATOR MIDDLEWARE FOR EDUCATIONAL PROCESS IN LIEPAJA UNIVERSITY

Abstract. In this paper the authors describe a solution for implementation of the SRM (ScriptRunMediatorCSP) middleware to resolve trusting and secure connection problems to HPC (High Performance Computing) cluster resources in the Liepaja University. The main idea is to develop a specific middleware tool called SRM, which would allow connection to the parallel computing cluster system, namely to the main server masternode, to provide the easiest solution for using HPC technologies in educational processes. Cluster computing resources could be used for solution and analysis of various scientific problems applying mathematical methods and high performance technological solutions for learning and performing parallel computations in the educational process thus increasing the students' theoretical knowledge in practical applications. Keywords: cluster, HPC technologies, Lazarus, SRM middleware, parallel calculations, parallel compilers. Introduction Rapid development of High Performance Computing (HPC) systems in the field of IT is determined by the necessity to solve society and science problems more effectively, for instance, to optimize gas and oil research and acquisition, to forecast climate changes, and also to introduce innovation products and services in industrial and financial fields. Therefore, it is important to provide the HPC technological environment, which is implemented with the help of parallel data processing and computation technologies, applications of cluster networks and information technologies, in order to promote involvement of students as young experts to real problem solution in the field of scientific research. In the academic and research field, HPC utilizes multiple processors to perform concurrent tasks in parallel for solving large cutting-edge research computation problems. At this moment authors provide centralized high-performance computing resources and support to Liepaja University students and researchers in large-scale computing disciplines with the use of advanced computing cluster hardware infrastructure, software, tools and programming techniques.The goal of centralized supercomputing centres and conventional distributed computing systems, such as grids and clusters, and their support service is to enhance research capabilities and effectiveness. The current efforts in the grid computing research focus on a design of the new grid schedulers, that can efficiently optimize the standard scheduling objectives, such as makespan, flowtime and resource utilization, but also can fulfil the security requirements of the grid users and can minimize the energy consumed by all of the system components. These schedulers should also capture the complexity of the whole system and provide meaningful measures for a wide range of grid applications and services. Therefore, energy-efficient and security-aware scheduling in CGs (Computational Grids) becomes a complex research and engineering endeavour mainly due to different priorities and preferences of the grid users and resource owners Several parallel computation clusters with various configurations have been created and tested, where the special middleware SRM (ScriptRunMediatorCSP (ClusterSecurityPackage)) was used in order to implement solutions of direct, indirect and optimisation problems using data parallel processing technologies -computation automation software. Within the research a Beowulf cluster is used, and the operating system adopted is Linux, which is widely available; software tools for message passing such as MP

A search for diffuse bands in the circumstellar envelopes of post-AGB stars

In this work we present the results of a systematic search for diffuse bands (DBs, hereafter) in the circumstellar envelopes of a carefully selected sample of post-AGB stars. We concentrated on the analysis of 9 of the DBs most commonly found in the interstellar medium. The strength of these features is determined using high resolution optical spectroscopy and the results obtained are compared with literature data on field stars affected only by interstellar reddening. Based on the weak features observed in the subsample of post-AGB stars dominated by circumstellar reddening we conclude that the carrier(s) of these DBs must not be present in the circumstellar environment of these sources, or at least not under the excitation conditions in which DBs are formed. The conclusion is applicable to all the post-AGB stars studied, irrespective of the dominant chemistry or the spectral type of the star considered. A detailed radial velocity analysis of the features observed in individual sources confirms this result, as the Doppler shifts measured are found to be consistent with an interstellar origin.Comment: Accepted for A&

On metal-deficient barium stars and their link with yellow symbiotic stars

This paper addresses the question of why metal-deficient barium stars are not yellow symbiotic stars (YSyS). Samples of (suspected) metal-deficient barium (mdBa) stars and YSyS have been collected from the literature, and their properties reviewed. It appears in particular that the barium nature of the suspected mdBa stars needs to be ascertained by detailed abundance analyses. Abundances are therefore derived for two of them, HD 139409 and HD 148897, which reveal that HD 148897 should not be considered a barium star. HD 139409 is a mild barium star, with overabundances observed only for elements belonging to the first s-process peak (Y and Zr). The evidence for binarity among mdBa stars is then reviewed, using three different methods: (i) radial-velocity variations (from CORAVEL observations), (ii) Hipparcos astrometric data, and (iii) a method based on the comparison between the Hipparcos and Tycho-2 proper motions. A first-time orbit is obtained for HIP 55852, whereas evidence for the (so far unknown) binary nature of HIP 34795, HIP 76605, HIP 97874 and HIP 107478 is presented. Two stars with no evidence for binarity whatsoever (HIP 58596 and BD +3 2688) are candidates low-metallicity thermally-pulsing asymptotic giant branch stars, as inferred from their large luminosities. The reason why mdBa stars are not YSyS is suggested to lie in their different orbital period distributions: mdBa stars have on average longer orbital periods than YSyS, and hence their companion accretes matter at a lower rate, for a given mass loss rate of the giant star. The definite validation of this explanation should nevertheless await the determination of the orbital periods for the many mdBa stars still lacking periods, in order to make the comparison more significant.Comment: Astronomy & Astrophysics, in press; 16 pages, 14 figures; also available at http://www.astro.ulb.ac.be/Html/ps.html#PR

Convective-reactive proton-C12 combustion in Sakurai's object (V4334 Sagittarii) and implications for the evolution and yields from the first generations of stars

Depending on mass and metallicity as well as evolutionary phase, stars occasionally experience convective-reactive nucleosynthesis episodes. We specifically investigate the situation when nucleosynthetically unprocessed, H-rich material is convectively mixed with a He-burning zone, for example in convectively unstable shell on top of electron-degenerate cores in AGB stars, young white dwarfs or X-ray bursting neutron stars. Such episodes are frequently encountered in stellar evolution models of stars of extremely low or zero metal content [...] We focus on the convective-reactive episode in the very-late thermal pulse star Sakurai's object (V4334 Sagittarii). Asplund etal. (1999) determined the abundances of 28 elements, many of which are highly non-solar, ranging from H, He and Li all the way to Ba and La, plus the C isotopic ratio. Our simulations show that the mixing evolution according to standard, one-dimensional stellar evolution models implies neutron densities in the He that are too low to obtain a significant neutron capture nucleosynthesis on the heavy elements. We have carried out 3D hydrodynamic He-shell flash convection [...] we assume that the ingestion process of H into the He-shell convection zone leads only after some delay time to a sufficient entropy barrier that splits the convection zone [...] we obtain significantly higher neutron densities (~few 10^15 1/cm^3) and reproduce the key observed abundance trends found in Sakurai's object. These include an overproduction of Rb, Sr and Y by about 2 orders of magnitude higher than the overproduction of Ba and La. Such a peculiar nucleosynthesis signature is impossible to obtain with the mixing predictions in our one-dimensional stellar evolution models. [...] We determine how our results depend on uncertainties of nuclear reaction rates, for example for the C13(\alpha, n)O16 reaction.Comment: ApJ in press, this revision contains several changes that improve clarity of presentation reflecting the suggestions made by the referee; this version represents no change in substance compared to version 1; some technical material has been moved to an appendix; an additional appendix deals in more detail with the combustion time scales; this version is practically identical to the ApJ versio

An optical absorption study of the Helix Planetary Nebula: NaI and CaII lines, and a search for diffuse bands

We present the results of an optical absorption study of NGC 7293, the Helix planetary nebula (PN), designed to search for diffuse band (DIB) absorptions perhaps arising in the carbon-rich circumstellar matter of the PN. We made high resolution spectra of 8 stars located close to and behind the Helix. Through a detailed analysis of the NaI and CaII lines, we find that two lines of sight situated close to the PN as mapped in CO and HI exhibit very strong NaI absorption. This absorption is due to the PN neutral or molecular material. No corresponding CaII line is observed in agreement with the very high Ca depletion often observed in PNs. No trace of any DIB features was found in these two circumstellar lines of sight (shortened abstract).Comment: 9 pages, 4 figs (1 available by ftp); accepted by Astron. Astrophy

Chemical composition of evolved stars of high galactic latitude

We have carried out abundance analysis for a sample of high galactic latitude supergiants in search of evolved stars. We find that HD 27381 has atmospheric parameters and an abundance pattern very similar to that of the post-AGB star HD 107369. HD 10285 and HD 25291 are moderately metal-poor and show the influence of mixing that has brought the products of NeNa cycle to the surface. The high galactic latitude B supergiant HD 137569 shows selective depletion of refractory elements normally seen in post-AGB stars. We find that the high velocity B type star HD 172324 shows moderate deficiency of Fe group elements but the CNO abundances are very similar to that of disk B supergiants. The observed variations in the radial velocities, transient appearance of emission components in hydrogen line profiles and doubling of O I lines at 7774\AA support the possibility of this star being a pulsating variable or a binary star.Comment: 12 pages, 6 figures. Accepted in A&

Echelle long-slit optical spectroscopy of evolved stars

We present echelle long-slit optical spectra of a sample of objects evolving off the AGB, most of them in the pre-planetary nebula (pPN) phase, obtained with the ESI and MIKE spectrographs at Keck-II and Magellan-I, respectively. The total wavelength range covered with ESI (MIKE) is ~3900 to 10900 A (~3600 to 7200A). In this paper, we focus our analysis mainly on the Halpha profiles. Prominent Halpha emission is detected in half of the objects, most of which show broad Halpha wings (up to ~4000 km/s). In the majority of the Halpha-emission sources, fast, post-AGB winds are revealed by P-Cygni profiles. In ~37% of the objects Halpha is observed in absorption. In almost all cases, the absorption profile is partially filled with emission, leading to complex, structured profiles that are interpreted as an indication of incipient post-AGB mass-loss. All sources in which Halpha is seen mainly in absorption have F-G type central stars, whereas sources with intense Halpha emission span a larger range of spectral types from O to G. Shocks may be an important excitation agent of the close stellar surroundings for objects with late type central stars. Sources with pure emission or P Cygni Halpha profiles have larger J-K color excess than objects with Halpha mainly in absorption, which suggests the presence of warm dust near the star in the former. The two classes of profile sources also segregate in the IRAS color-color diagram in a way that intense Halpha-emitters have dust grains with a larger range of temperatures. (abridged)Comment: 68 pages, 14 figures, accepted for publication in ApJS (abstract abridged