bluuebunny/crossref_metadata_2025_split huggingface dataset:
Temporal assessment of heavy metal concentration and surface water quality representing the public health evaluation from the Meghna River estuary, Bangladesh
Authors: Safiur Rahman M. , Shafiuddin Ahmed A. S. , Rahman Md. Moshiur , Omar Faruque Babu S. M. , Sultana Sharmin , Sarker Shafiqul Islam , Awual Rabiul , Rahman Mohammad Majibur , Rahman Mostafizur 
Published: June 2021

AbstractThe Meghna River, the largest and the widest river in Bangladesh, is important for navigation, irrigation, fish spawning and shelter, industrial usages, and drinking water sources for millions of people living in nearby areas. The present study illustrated the seasonal variation of some physicochemical parameters and the four heavy metals (Cr, As, Cd, and Pb) distribution in the surface water of Meghna River estuary. It also evaluated the human health risk for adult and children due to directly contact with the surface water through ingestion and dermal pathways. The ranges of metal concentration in the study area were found in the descending order as: Cr (0.036–0.054; mean 0.045 ± 0.005) > As (0.012–0.036; mean 0.024 ± 0.007) > Cd (0.009–0.050; mean 0.018 ± 0.012) > Pb (0.007–0.014; mean 0.009 ± 0.007). In most cases, the concentrations of As, Cr, Pb, and Cd surpassed the guideline limits of human consumption. However, the one-way ANOVA study revealed that the average concentrations of the selected metals in the ten sampling sites were not significantly different at a 95% confidence level. Therefore, it is assumed that the metal contamination in the study area might have been caused due to the anthropogenic sources along with the natural phenomenon. The distribution of the metal contents and the physicochemical parameters in the surface water greatly were significantly different concerning both winter and summer seasons at a 95% confidence level. The evaluated hazard quotient (HQ) and the hazard index (HI) for the investigated metal compounds were in the acceptable limit (< 1). In addition, the attribution of metal contents did not overweigh the carcinogenic risk (CR) range (10–6 to 10–4), and the adults are more susceptible than the children. Although the risk is within the acceptable level, but adequate monitoring aspects should be implemented to control surface water pollution especially for the metal discharge to the river estuary.
How formal institutional antecedents affect Tunisian venture creation decision scripts
Authors: Haj brahim Abdallah , Morched Salim , Boujelbene Younes 
Published: June 2021

AbstractThe aim of this paper is to reveal the impact of three Tunisian formal institutional systems on their venture creation decision through the study of entrepreneurial scripts of Tunisians nascent entrepreneur post-revolution phase. The method adopted in this study is the cognitive map. This research enriches entrepreneurial process literature by examining a finer-grained linkage between the degree of the development of Tunisian formal institutional systems and the level of expertise in the decision stage as an early process of venture creation. To do this, the cognitive approach is adopted by using the structural analysis method as a tool for structuring ideas and collective reflections. In the field of entrepreneurship, the mentioned approach has been the subject of few empirical studies. This leads to a better understanding of individual’s cognitive universe (actors, coaches, managers, entrepreneurs, etc.). It is important in the context of this study to identify and analyze the influence of formal institutional antecedents on the cognition of Tunisian nascent entrepreneurs and consequently on their decision. Experiments done on 120 born entrepreneurs incubating in the nurseries allowed to present, in the form of a collective map, the formal institutional antecedents that seem to affect their decisions to become entrepreneurs through their NVCD scripts.
Meta-study on the relationship between profitability and liquidity of enterprises in macroeconomic and institutional environment
Authors: Jaworski Jacek , Czerwonka Leszek 
Published: June 2021

AbstractThe main aim of the paper is to determine the relationship between profitability and financial liquidity of a company using meta-analysis. This method is based on a synthesis of many previous studies with the application of econometric tools. The results of the study show that, taking into account 16 economies, it is not possible to identify a common effect describing the relationship between the profitability of enterprises and their financial liquidity measured by the current liquidity ratio. The results of individual empirical studies that underlie the meta-analysis are diverse. This means that there are moderators of the strength and direction of this dependence associated with macroeconomic and institutional conditions. We attempted to separate them by means of meta-regression. This method involves the use of a regression model, where data are derived from both meta-analysis and external sources. We diagnosed two statistically significant moderators of the strength and direction of the relationship between profitability and liquidity. These are two factors: (i) private sector crediting and (ii) capital market development. Our paper contributes to the development of the existing knowledge by summarizing and binding previous individual empirical studies on the relationship between profitability and liquidity of enterprises and identifying factors affecting this relationship. This knowledge can assist financial managers in making more efficient decisions related to liquidity and working capital management.
Stochastic orderings of multivariate elliptical distributions
Authors: Yin Chuancun 
Published: June 2021

AbstractFor two n-dimensional elliptical random vectors X and Y, we establish an identity for $\mathbb{E}[f({\bf Y})]- \mathbb{E}[f({\bf X})]$, where $f\,{:}\, \mathbb{R}^n \rightarrow \mathbb{R}$ satisfies some regularity conditions. Using this identity we provide a unified method to derive sufficient and necessary conditions for classifying multivariate elliptical random vectors according to several main integral stochastic orders. As a consequence we obtain new inequalities by applying the method to multivariate elliptical distributions. The results generalize the corresponding ones for multivariate normal random vectors in the literature.
Water cycle algorithm: an approach for improvement of navigational strategy of multiple humanoid robots
Authors: Muni Manoj Kumar , Kumar Saroj , Parhi Dayal R. , Pandey Krishna Kant 
Published: June 2021

AbstractThis paper presents an efficient water cycle algorithm based on the processes of water cycle with movement of streams and rivers in to the sea. This optimization algorithm is applied to obtain the optimal feasible path with minimum travel duration during motion planning of both single and multiple humanoid robots in both static and dynamic cluttered environments. This technique discards the rainfall process considering falling water droplets forming streams during raining and the process of flowing. The flowing process searches the solution space and finds the more accurate solution and represents the local search. Motion planning of humanoids is carried out in V-REP software. The performance of proposed algorithm is tested in experimental scenario under laboratory conditions and shows the developed algorithm performs well in terms of obtaining optimal path length and minimum time span of travel. Here, navigational analysis has been performed on both single as well as multiple humanoid robots. Statistical analysis of results obtained from both simulation and experimental environments is carried out for both single and multiple humanoids, along with the comparison with another existing optimization technique that indicate the strength and effectiveness of the proposed water cycle algorithm.
Automated Search for LSB Galaxies in the Nearby Universe
Authors: Morshidi Z. , Davies J.I. , Smith R.M. 
Published: June 2021

We have carried out a large area survey for nearby LSB galaxies to try and answer the following questions:
1.How are LSB galaxies distributed relative to the normal HSB galaxies? Do they have the same clustering properties suggesting that they trace the same mass distribution?2.What are the implications of the clustering properties on galaxy formation scenarios?3.Can they account for faint blue galaxies at higher redshifts?4.Is there any difference between the field and cluster LSB galaxies?2. The SurveyWe have devised an automated technique to pick out local LSB galaxies using 65 UKSTU photographic plates corresponding to 2187 sq.°. We have imposed stringent selection criteria in order to minimise the background contamination. Our galaxies have μ0 ≥ 22.5 B mag arcsec-2 α ≥ 3.0 arcseconds and BT ≤ 20.0. Our survey areas are confined to the Fornax Cluster, the NGC1400, Sculptor and Dorado Groups and the fields between them. The survey, which was carried out in three stages over a period of 2 years, has produced detections of 2435 LSB galaxies (32 galaxies per field). We have estimated the background contamination in three ways: first, by a limited redshift sample, secondly, by Ferguson’s (1989) classification on the Fornax plate and finally, by a numerical simulation of background galaxies. The first method produced an estimate of 14 galaxies per field, while the second and the third methods produced the same estimate of 19 galaxies.
Star Formation Activity in High MH/LB Galaxies
Authors: Van Zee L. 
Published: June 2021

AbstractThe results of an investigation of the evolutionary status of fifteen gas-rich, low surface brightness dwarf galaxies (LSBDGs) are presented. LSBDGs are defined by unusually high values of MH/LB and the presence of extended HI envelopes. At both the present epoch and the past, the star formation process appears to be inefficient: the LSBDGs are underluminous for their HI mass and very little active star formation is currently observed. Analysis of global optical colors and elemental enrichments indicate that these objects are not “young” systems; rather, star formation has been occurring for several Gyr. One clue to the star formation history of these objects is that the global gas density is significantly lower than the Toomre instability criterion throughout the gas disk. Local peaks in the HI surface density, however, approach the instability criterion and are correlated with sites of active star formation. Thus, while star formation appears to be inhibited globally, the local gas distribution plays a crucial role in regulating the star formation activity in these low mass galaxies.
Dwarf Elliptical Galaxies in the M81 Group: The Structure and Stellar Populations of BK5N and F8D1
Authors: Armandroff Taft E. , Caldwell Nelson , Da Costa G.S. , Seitzer Patrick 
Published: June 2021

The M81 group is one of the nearest groups of galaxies, but its properties are quite different from those of the Local Group. It has therefore provided a different environment for the evolution of its member galaxies. We have carried out a CCD survey of the M81 group to search for analogs to Local Group dwarf elliptical (dE) galaxies. All the M81 dwarfs previously identified in photographic surveys were recovered and we also discovered several new systems whose surface brightnesses fall within the range found for Local Group dE’s.We have obtained HST WFPC2 images through the F555W and F814W filters of two M81 group dE’s: BK5N and a new system, designated F8D1. The resulting color-magnitude diagrams show the upper two magnitudes of the red giant branch. The I magnitudes of the red giant branch tip in both galaxies yield distances that are consistent with membership in the M81 group. Surface brightness and total magnitude measurements indicate that BK5N and F8D1 have similar central surface brightness (24.5 and 25.4 mag arcsec-2 in V, respectively), but F8D1 is larger length scale results in it being 3 magnitudes more luminous than BK5N. BK5N lies on the relation between central surface brightness and absolute magnitude defined by Local Group dwarf ellipticals, but F8D1 does not. F8D1 is more luminous for its central surface brightness than the relation predicts, similar to the large low surface brightness dwarf galaxies found in, for example, Virgo. The mean color of the giant branch is used to establish the mean abundance of each galaxy. F8D1, the more luminous galaxy, is significantly more metal rich ([Fe/H] ≈ -1.0) than BK5N ([Fe/H] ≈ -1.7). Both BK5N and F8D1 lie on the relation between absolute magnitude and metal abundance defined by Local Group dwarf ellipticals. However, as regards the relation between central surface brightness and metal abundance, BK5N again follows the Local Group dwarfs, while F8D1 deviates significantly from this relation. This suggests that the total amount of luminous matter is more fundamental in controlling metal enrichment than the surface density of luminous matter. We have also used the color width of the giant branch compared with the photometric errors to establish abundance ranges in both galaxies, the sizes of which are comparable to those in Local Group dE’s.
New Light on the Origin of Nebular He II Emission in Young Starbursts
Authors: Schaerer Daniel 
Published: June 2021

In the Local Group few Hɪɪ regions exhibit nebular Heɪɪ λ4686 emission, indicative of unusually high excitation. Approximately eight such nebulae are known, all located in low metallicity environments (IC 1613, SMC, LMC) except the Galactic ring nebula G2.4+1.4 (Esteban et al. 1992). The best studied case is the nebula S 3 surrounding the WO3 star DR 1 (Garnett et al. 1991, Kingsburgh &: Barlow 1995). Except for two cases (N 44C, N159 F; Stasińska et al. 1986, Pakull & Angebault 1986) the nebulae are asociated with early WN (cf. Niemela et al. 1991) and WO stars.So far approximately 50 to 60 extragalactic Hɪɪ regions showing nebular Heɪɪ λ4686 are known (Campbell et al. 1986, Izotov et al. 1994, 1997a). Most of them are found in H II galaxies, BCDs and related objects from low metallicity samples used for determinations of the primordial helium abundance. The most prominent case is the low metallicity (Z) record holder I Zw 18. He II emission is typically on the order of 1-5 % of Hβ.Different ionization mechanisms (photoionization by hot stars, shock excitation, photoionization by X-rays) have been put forward to explain the required hard spectrum (Garnett et al. 1991).The first quantitative approach to address this problem are the evolutionary synthesis models of Schaerer (1996) and Schaerer & Vacca (1997), which include well tested evolutionary tracks and recent spherically expanding non-LTE atmosphere models appropriate for WR and O stars.
Overview, Formulation and Current Situation for Precession-Nutation
Authors: Capitaine N. 
Published: June 2021

AbstractThis paper describes the conventional models for precession and nutation, the current procedure for taking them into account in the reduction of highly accurate observations, the recent IAU recommendations on this topic, as well as the current situation for theory and observations. This emphasizes the imperfections in the conventional models and in the current procedure which are not in consistency either with the adoption of the new International Conventional Celestial Reference System (ICRS) or with the high accuracy and resolution of the current observations of Earth rotation. This addresses the question of the adoption of a new formulation and of an improved model combining precession and nutation of the equator with respect to the ICRS as well as the adoption of a revised definition of the Celestial Ephemeris Pole.
Tidal Splitting of Comets in Earth’s Vicinity
Authors: Rickman H. , Greenberg J.M. 
Published: June 2021

AbstractWe present a study of the influence of tidal splitting In order to clarify the role of comets as Earth impactors and bringers of organics to the young planet. Based on low values for the density and material strength, as indicated by Comet Shoemaker-Levy 9, we have modeled the evolution of a comet in an orbit leading to Earth impact. We find that cometary nuclei impacting the Earth with radii ≥ 0.1 - 0.3 km will split just before doing so. Nuclei of several km radius will split when passing within a distance ≤, 5 - 8 Earth radii. Cometary nuclei with radii ≥ 1km stand a much larger chance of being tidally split than of hitting the Earth. Consequently, streams of fragments and debris form in Earth-crossing orbits more often than large nuclei cause impacts. The mass distribution of impacting material is shifted toward sub-km objects, whereby the survivability of organics may be significantly increased. If the cometary impactors move in orbits where ≥ 5 passages within Earth’s Roche zone are expected, we estimate that most of the material reaching Earth’s surface will appear in the form of split fragments.
Long-Term period and Amplitude Variations in β Cephei Stars
Authors: Jerzykiewicz J. 
Published: June 2021

We first consider all β Cephei stars for which long-term behavior of their pulsation periods is known from observations. As it turns out, these objects fall into two categories: one consisting of stars with complex period variations, and the other, with a constant and non-negative rate of period change, Ṗ = const ≥ 0. The problem is that stars with Ṗ close to that predicted for the hydrogen-shell burning phases of evolution are over-represented. We then compare the five β Cephei stars which exhibit long-term variations of the pulsation amplitudes and note that in each case the cause may be individual. In one star, 16 (EN) Lac, two different effects are responsible for the observed variation of the amplitudes.An IAU travel grant is gratefully acknowledged. This work was supported by KBN grant 2P03D01611.
Evidence for Stellar Evolution in Mira Variables
Authors: Whitelock Patricia A 
Published: June 2021

After briefly reviewing our understanding of Miras and their evolutionary status, three aspects of real-time evolution in these and related stars are examined:
1.Chemical changes (O-rich to C-rich) due to third dredge-up,2.Period changes due to the effects of the helium shell-flash,3.The existence of ‘fossil’ dust and gas shells.Studies of resolved gas and dust shells are highlighted as particularly interesting. They will enable us to examine the mass-loss histories of many late-type stars over the last ten thousand years or so. Such observations have only recently become technically feasible and they are expected to provide important new insight into the late stages of stellar evolution.
Observational Constraints on Evolution of Dwarf Novae in and Below ThePeriod Gap
Authors: Nogami D. , Kato T. , Baba H. , Masuda S. 
Published: June 2021

There is a gap in the distribution of the orbital periods of cataclysmic variables (CVs) between 2 and 3 hours. The period gap is explained at present by cessation of the mass transfer making CVs fainter and preventing them from being discovered. After restarting the mass transfer, CVs have been believed to evolve with the orbital periods becoming shorter, as angular momentum is released by gravitational wave radiation. In this view, the mass transfer rate depends almost only on the orbital period.However, reconsideration of these views is urged by a series of recent discoveries of ER UMa stars (a subclass of SU UMa stars having enormous mass-transfer rates), dwarf novae bridging “classical” SU UMa stars and ER UMa stars, and the first in-the-gap dwarf nova, PG 1510+234. These objects suggest two possibilities; 1) (a part of) SU UMa stars undergo large secular changes of the mass-transfer rate, and 2) there exist parameters overlooked but strongly influential in the evolution of CVs.
The Nature of the Chemical Anomalies of the Sirius A
Authors: Leushin V. 
Published: June 2021

On the basis of the analysis of the observed equivalent line widths of FeI, FeII, and TiII in the spectra of Sirius A and Omicron Peg and calculation of abundances of these elements, the oscillator strengths of the lines used are refined. With the improved oscillator strengths, the iron and titanium abundances in the atmosphere of Sirius A are obtained with a higher accuracy than previously:lgN(FeI) = 7.899 ±0.011,lgN(FeII) = 7.908±0.010,lgN(TiII) =5.30±0.02.The improved accuracy allowed one to conclude that the surface magnetic field is absent in the atmosphere of Sirius A: H =3D 0±100 Gs. The equivalent widths of 7 helium lines of the red region of the spectrum are measured. The calculations of these lines (with allowance for their blending with lines of other elements) show normal helium abundance. Following a comparison of features of Sirius A and Omicron Peg, a suggestion is advanced on possible reasons for the existence of Am stars.
Exploration of Stellar Processes Through Interstellar Abund Anci Studies
Authors: Sofia U.J. , Meyer D.M. 
Published: June 2021

Interstellar abundances studies can provide answers to some questions about stellar processes, and they can lead to new questions about others. We will discuss some recent interstellar abundance determinations and their implications for stellar studies.Although Cd and Sn are chemically similar to elements which are moderately to heavily depleted from the gas-phase interstellar medium (ISM), they appear to have solar-like abundances in inter-stellar clouds. This is likelythe result of these elements being depleted from an ISM which has been enriched with Cd and Sn since the formation of the sun. These two elements are mainly produced by s-process neutron capture in intermediate to low mass AGB stars. The present ISM abundances of Cd and Sn can therefore provide information about s-process yields and the cumulative injection of this material into the ISM over the past 4.5 Gy.Recent studies of C and O abundances in the ISM have shown that the C/H and O/H are constant out to approximately 1500pc from the sun. Local B star abundance studies, however, find that C/O is not constant, thereby indicating that the ISM is not well mixed or homogeneous. We currently do not have an explanation for this apparent inconsistency between stars and the ISM.