117,544 research outputs found
THE HOT END OF EVOLUTIONARY HORIZONTAL BRANCHES
No full textIn this paper we investigate the hot end of the horizontal branch (HE), presenting evolutionary constraints concerning the C-M diagram location and the gravity of hot HE stars. According to the adopted evolutionary scenario, we predict an upper limit for HE temperatures of about log T-e = 4.45, remarkably cooler than previous estimates. We find that such a theoretical prescription appears in good agreement with available observational data concerning both stellar temperatures and gravities. Finally, the problem of gaps in the HE distribution is discussed, suggesting that, at least in the case of the cluster NGC 6752, evolutionary gaps, a bimodal distribution of CNO, and stellar rotation should all play a negligible role
ADVANCED EVOLUTIONARY PHASES OF LOW-MASS STARS - THE ROLE OF THE ORIGINAL HELIUM
No full textWe present evolutionary He burning models which cover both the HE and AGE evolutionary phases, as computed for the metallicities Z = 10(-4), 10(-3) and for two assumptions on the value of the original He content Y = 0.20, 0.27. We found that both the difference in luminosity between the AGE and the HE, and the number ratio of AGE to HE stars appear quite unaffected by the amount of original He, allowing a relevant test for the efficiency of internal mixing during the central He burning phase. Data concerning HE evolution have been connected with the evolutionary times of the corresponding RGB stars to recalibrate the parameter R as a function of Y for the two investigated metallicities. Comparisons with previous calibrations disclose variations which are not negligible, and which should be taken into account when R is used to derive constraints on the amount of cosmological helium. The critical role of the HE luminosity on the evaluation of R is briefly discussed
Mass segregation of different populations inside the cluster NGC 6101
No full textWe have used ESO telescopes at La Silla and the Hubble Space Telescope (HST) in order to obtain accurate B, V, I CCD photometry for the stars located within 200" (similar or equal to2 half-mass radii, r(h) = 1.71') from the center of the cluster NGC 6101. Color-Magnitude Diagrams (CMDs) extending from the red-giant tip to about 5 magnitudes below the main-sequence turnoff MSTO (V = 20.05 +/- 0.05) have been constructed. The following results have been obtained from the analysis of the CMDs: a) The overall morphology of the main branches confirms previous results from the literature, in particular the existence of a sizeable population of 73 "blue stragglers" (BSS), which had been already partly detected (27). They are considerably more concentrated than either the subgiant branch (SGB) or the main sequence (MS) stars, and have the same spatial distribution as the horizontal branch (HB) stars (84% probability from K-S test). An hypothesis on the possible BSS progeny is also presented. b) The HB is narrow and the bulk of stars is blue, as expected for a typical metal-poor globular cluster. c) The derived magnitudes for the HB and the MSTO, V-ZAHB = 16.59 +/- 0.10, V-TO = 20.05 +/- 0.05, coupled with the values E(B - V) = 0.1, [Fe/H] = -1.80, Y = 0.23 yield a distance modulus (m - M)(v) = 16.23 and an age similar to other "old" metal-poor globular clusters. In particular, from the comparison with theoretical isochrones, we derive for this cluster an age of 13 Gyrs. d) By using the large statistical sample of Red Giant Branch (RGB) stars, we detected with high accuracy the position of the bump in the RGB luminosity function. This observational feature has been compared with theoretical prescriptions, yielding a good agreement within the current theoretical and observational uncertainties
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Chemical profiling of the fruits of Styrax officinalis L. from Monti Lucretili (Latium region, Central Italy). Chemotaxonomy and nutraceutical potential
No full textIn this work, the first phytochemical analysis ever performed on the fruits of Styrax officinalis L. (Styracaceae) collected from a population vegetating in the Mounts Lucretili National Park (Italy) was reported. Fifteen compounds were identified: tri-α-linolenoyl-sn-glycerol (1), 1,2-di-α-linolenoyl-3-linoleoyl-sn-glycerol (2), 1-α-linolenoyl-2-palmitoyl-sn-glycerol (3), 1,2-di-α-linolenoyl-sn-glycerol (4), egonol (5), emethylegonol (6), homoegonol (7), 1,5-anhydro-D-mannitol (8), glucose (9), sucrose (10), 6'-O-benzoyl-sucrose (11), raffinose (12), lactic acid (13), succinic acid (14) and glutamic acid (15). These compounds belong to seven different classes of natural metabolites and most of them have chemotaxonomic relevance. Moreover, S. officinalis might be an useful source of enantiopure 1,5-anhydro-D-mannitol which has several medicinal potentialities and is a versatile building block in organic synthesis, in particular for what concern the “Green” approaches, of valuable and potentially biologically active molecules. The presence of compounds (1-15) provides also a phytochemical rationale for the ancient ethnopharmacological uses of the species and affords evidences on its nutraceutical potentialities even for their consumption as
food in human nutrition as it actually happens for animals
Square Dancing with the Stars to Enhance Dynamic Hirschman Linkages?
No full textIn this Presidential Address, the author takes the reader on a reconnaissance of his life and time as a regional scientist. He points out scenery he found scintillating along the way, hoping that some may pick up the banner and chew on a few of the ideas for a while. He suggests a revisit to Albert O. Hirschman’s notion of key sectors and more empirical analysis related to Marcus Berliant’s and Masahisa Fujita’s notion of knowledge creation and transfer.Presidential Address, San Antonio, Texas, March 29, 2014 (53rd Meetings of the Southern Regional Science Association
Appropriate Similarity Measures for Author Cocitation Analysis
No full textWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Letter from unknown writer to Jesse L. Boyce
No full textLetter to Jesse L. Boyce from unknown author (possibly Jack) about the investigation into the powder magazine located in the Grand Canyon. Some personal news is included in the letter such as the writer's marriage to the daughter of C.A. Taylor, former Supervisor of Cochise County
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