Science.gov

Sample records for horizontal branch morphology

  1. On the red giant branch mass loss in 47 Tucanae: Constraints from the horizontal branch morphology

    NASA Astrophysics Data System (ADS)

    Salaris, Maurizio; Cassisi, Santi; Pietrinferni, Adriano

    2016-05-01

    We obtain stringent constraints on the actual efficiency of mass loss for red giant branch stars in the Galactic globular cluster 47 Tuc, by comparing synthetic modelling based on stellar evolution tracks with the observed distribution of stars along the horizontal branch in the colour-magnitude-diagram. We confirm that the observed, wedge-shaped distribution of the horizontal branch can only be reproduced by accounting for a range of initial He abundances, in agreement with inferences from the analysis of the main sequence, and a red giant branch mass loss with a small dispersion. We carefully investigated several possible sources of uncertainty that could affect the results of the horizontal branch modelling, stemming from uncertainties in both stellar model computations and cluster properties, such as heavy element abundances, reddening, and age. We determine a firm lower limit of ~0.17M⊙ for the mass lost by red giant branch stars, corresponding to horizontal branch stellar masses between ~0.65M⊙ and ~0.73M⊙ (the range driven by the range of initial helium abundances). We also derive that in this cluster the amount of mass lost along the asymptotic giant branch stars is comparable to the mass lost during the previous red giant branch phase. These results confirm, for this cluster, the disagreement between colour-magnitude-diagram analyses and inferences from recent studies of the dynamics of the cluster stars, which predict a much less efficient red giant branch mass loss. A comparison between the results from these two techniques applied to other clusters is required to gain more insights about the origin of this disagreement.

  2. Effects of tidally enhanced stellar wind on the horizontal branch morphology of globular clusters

    NASA Astrophysics Data System (ADS)

    Lei, Z.-X.; Chen, X.-F.; Zhang, F.-H.; Han, Z.

    2013-01-01

    Context. Metallicity is the first parameter to influence the horizontal branch (HB) morphology of globular clusters (GCs). It has been found, however, that some other parameters may also play an important role in affecting the morphology. While the nature of these important parameters remains unclear, they are believed to be likely correlated with wind mass-loss of red giants, since this mass loss determines their subsequent locations on the HB. Unfortunately, the mass loss during the red giant stages of the stellar evolution is poorly understood at present. Aims: The stellar winds of red giants may be tidally enhanced by companion stars if they are in binary systems. We investigate the evolutionary consequences of red giants in binaries by including tidally enhanced stellar winds, and examine the effects on the HB morphology of GCs. Methods: We used Eggleton's stellar evolution code to study the binary evolution. The tidally enhanced stellar-wind model of Tout & Eggleton is incorporated into this code, where the tidal enhancement parameter, Bw, has various values (e.g., 10 000 and 500) to examine the dependency of the final results on this parameter. A Monte Carlo simulation was performed to generate a group of binary systems. The position of each primary star on the HB in the Hertzsprung-Russell diagram in this sample is obtained through interpolations among the constructed HB evolutionary tracks. Finally, a synthetic HB in the color-magnitude diagram is obtained by transforming the effective temperature and luminosity of each primary star on the HB into B - V colors and absolute magnitude. Results: We find that red, blue, and extreme horizontal branch stars are all produced under the effects of tidally enhanced stellar wind without any additional assumptions on the mass-loss dispersion. Furthermore, the horizontal branch morphology is found to be insensitive to the tidal enhancement parameter, Bw. We compare our theoretical results with the observed horizontal

  3. Global and nonglobal parameters of horizontal-branch morphology of globular clusters

    SciTech Connect

    Milone, A. P.; Marino, A. F.; Dotter, A.; Norris, J. E.; Jerjen, H.; Asplund, M. E-mail: amarino@mso.anu.edu.au E-mail: jerjen@mso.anu.edu.au; and others

    2014-04-10

    The horizontal-branch (HB) morphology of globular clusters (GCs) is mainly determined by metallicity. However, the fact that GCs with almost the same metallicity exhibit different HB morphologies demonstrates that at least one more parameter is needed to explain the HB morphology. It has been suggested that one of these should be a global parameter that varies from GC to GC and the other a nonglobal parameter that varies within the GC. In this study we provide empirical evidence corroborating this idea. We used the photometric catalogs obtained with the Advanced Camera for Surveys of the Hubble Space Telescope and analyze the color-magnitude diagrams of 74 GCs. The HB morphology of our sample of GCs has been investigated on the basis of the two new parameters L1 and L2 that measure the distance between the red giant branch and the coolest part of the HB and the color extension of the HB, respectively. We find that L1 correlates with both metallicity and age, whereas L2 most strongly correlates with the mass of the hosting GC. The range of helium abundance among the stars in a GC, characterized by ΔY and associated with the presence of multiple stellar populations, has been estimated in a few GCs to date. In these GCs we find a close relationship among ΔY, GC mass, and L2. We conclude that age and metallicity are the main global parameters, while the range of helium abundance within a GC is the main nonglobal parameter defining the HB morphology of Galactic GCs.

  4. Tidally Enhanced Stellar Wind in Binaries as a Second Parameter for the Horizontal Branch Morphology of Globular Clusters

    NASA Astrophysics Data System (ADS)

    Han, Z.; Lei, Z.

    2014-04-01

    Metallicity is the first parameter to influence the horizontal branch morphology of globular clusters. It has been found, however, that some other parameters may also play an important role in affecting the morphology. While the nature of these other important parameters remains unclear, they are believed to be correlated with the mass loss during the red giant stages, from which the horizontal branch stars have descended. Unfortunately, the mass loss during the red giant stages of stellar evolution are poorly understood at present. In this talk, we investigate the physical consequences of tidally-enhanced stellar winds during the evolution of binary stars on enhancing the mass loss of red giant primaries, with accompanying effects for the horizontal branch morphology of globular clusters. In a binary system, the stellar wind of the red giant primary star may be largely enhanced by its companion star. Different separation of the binary system, however, will lead to a different mass loss rate of the primary star. We found that red, blue, and extreme horizontal branch stars are all produced under the effects of tidally-enhanced stellar wind without any additional assumptions on the mass loss dispersion. Furthermore, the horizontal branch morphology is found to be insensitive to the tidal enhancement parameter, B.

  5. The ACS Survey of Galactic Globular Clusters. IX. Horizontal Branch Morphology and the Second Parameter Phenomenon

    NASA Astrophysics Data System (ADS)

    Dotter, Aaron; Sarajedini, Ata; Anderson, Jay; Aparicio, Antonio; Bedin, Luigi R.; Chaboyer, Brian; Majewski, Steven; Marín-Franch, A.; Milone, Antonino; Paust, Nathaniel; Piotto, Giampaolo; Reid, I. Neill; Rosenberg, Alfred; Siegel, Michael

    2010-01-01

    The horizontal branch (HB) morphology of globular clusters (GCs) is most strongly influenced by metallicity. The second parameter phenomenon, first described in the 1960s, acknowledges that metallicity alone is not enough to describe the HB morphology of all GCs. In particular, astronomers noticed that the outer Galactic halo contains GCs with redder HBs at a given metallicity than are found inside the solar circle. Thus, at least a second parameter was required to characterize HB morphology. While the term "second parameter" has since come to be used in a broader context, its identity with respect to the original problem has not been conclusively determined. Here we analyze the median color difference between the HB and the red giant branch, hereafter denoted as Δ(V - I), measured from Hubble Space Telescope (HST) Advanced Camera for Surveys (ACS) photometry of 60 GCs within ~20 kpc of the Galactic center. Analysis of this homogeneous data set reveals that, after the influence of metallicity has been removed from the data, the correlation between Δ(V - I) and age is stronger than that of any other parameter considered. Expanding the sample to include HST ACS and Wide Field Planetary Camera 2 photometry of the six most distant Galactic GCs lends additional support to the correlation between Δ(V - I) and age. This result is robust with respect to the adopted metallicity scale and the method of age determination, but must bear the caveat that high-quality, detailed abundance information is not available for a significant fraction of the sample. Furthermore, when a subset of GCs with similar metallicities and ages is considered, a correlation between Δ(V - I) and central luminosity density is exposed. With respect to the existence of GCs with anomalously red HBs at a given metallicity, we conclude that age is the second parameter and central density is most likely the third. Important problems related to HB morphology in GCs, notably multi-modal distributions and

  6. THE ACS SURVEY OF GALACTIC GLOBULAR CLUSTERS. IX. HORIZONTAL BRANCH MORPHOLOGY AND THE SECOND PARAMETER PHENOMENON

    SciTech Connect

    Dotter, Aaron; Sarajedini, Ata; Anderson, Jay; Bedin, Luigi R.; Paust, Nathaniel; Reid, I. Neill; Aparicio, Antonio; MarIn-Franch, A.; Rosenberg, Alfred; Majewski, Steven; Milone, Antonino; Piotto, Giampaolo; Siegel, Michael E-mail: ata@astro.ufl.ed

    2010-01-01

    The horizontal branch (HB) morphology of globular clusters (GCs) is most strongly influenced by metallicity. The second parameter phenomenon, first described in the 1960s, acknowledges that metallicity alone is not enough to describe the HB morphology of all GCs. In particular, astronomers noticed that the outer Galactic halo contains GCs with redder HBs at a given metallicity than are found inside the solar circle. Thus, at least a second parameter was required to characterize HB morphology. While the term 'second parameter' has since come to be used in a broader context, its identity with respect to the original problem has not been conclusively determined. Here we analyze the median color difference between the HB and the red giant branch, hereafter denoted as DELTA(V - I), measured from Hubble Space Telescope (HST) Advanced Camera for Surveys (ACS) photometry of 60 GCs within approx20 kpc of the Galactic center. Analysis of this homogeneous data set reveals that, after the influence of metallicity has been removed from the data, the correlation between DELTA(V - I) and age is stronger than that of any other parameter considered. Expanding the sample to include HST ACS and Wide Field Planetary Camera 2 photometry of the six most distant Galactic GCs lends additional support to the correlation between DELTA(V - I) and age. This result is robust with respect to the adopted metallicity scale and the method of age determination, but must bear the caveat that high-quality, detailed abundance information is not available for a significant fraction of the sample. Furthermore, when a subset of GCs with similar metallicities and ages is considered, a correlation between DELTA(V - I) and central luminosity density is exposed. With respect to the existence of GCs with anomalously red HBs at a given metallicity, we conclude that age is the second parameter and central density is most likely the third. Important problems related to HB morphology in GCs, notably multi

  7. HORIZONTAL BRANCH MORPHOLOGY AND MULTIPLE STELLAR POPULATIONS IN THE ANOMALOUS GLOBULAR CLUSTER M 22

    SciTech Connect

    Marino, A. F.; Milone, A. P.; Lind, K. E-mail: milone@iac.es

    2013-05-01

    M 22 is an anomalous globular cluster that hosts two groups of stars with different metallicity and s-element abundance. The star-to-star light-element variations in both groups, with the presence of individual Na-O and C-N anticorrelations, demonstrates that this Milky Way satellite has experienced a complex star formation history. We have analyzed FLAMES/UVES spectra for seven stars covering a small color interval on the reddest horizontal branch (HB) portion of this cluster and investigated possible relations between the chemical composition of a star and its location along the HB. Our chemical abundance analysis takes into account effects introduced by deviations from the local thermodynamic equilibrium (NLTE effects), which are significant for the measured spectral lines in the atmospheric parameters range spanned by our stars. We find that all the analyzed stars are barium-poor and sodium-poor, thus supporting the idea that the position of a star along the HB is strictly related to the chemical composition, and that the HB morphology is influenced by the presence of different stellar populations.

  8. Theoretical horizontal-branch evolution

    NASA Technical Reports Server (NTRS)

    Sweigart, Allen V.

    1987-01-01

    The general features of the theoretical evolution of canonical horizontal-branch (HB) stars are briefly reviewed with specific emphasis on the track morphology in the HR diagram and the determination of the globular cluster helium abundance. The observational evidence for the occurrence of semiconvection is discussed together with some remaining theoretical uncertainty.

  9. A New Spin for Understanding the Peculiar Horizontal Branch Morphology of the Galactic Globular Clusters NGC 6388 and NGC 6441

    NASA Technical Reports Server (NTRS)

    Busso, G.; Piotto, G.; Cassisi, S.; Romaniello, M.; Castelli, F.; Catelan, M.; Djorgovski, S. G.; King, I. R.; Landsman, W. B.; Blanco, A. Reico; Renzini, A.; Rich, M. R.; Sweigart, A.; Zoccali, M.

    2006-01-01

    In this paper we present multiband optical and UV Hubble Space Telescope photometry of the two Galactic globular clusters NGC 6388 and NGC 6441 Aims. We investigate the properties of their anomalous horizontal branches (HB) in different photometric planes in order to shed light on the nature of the physical mechanism(s) responsible for the existence of an extended HB blue tail, and of a slope in the HB, visible in all the color-magnitude diagrams. Methods. New photometric data have been collected and carefully reduced. Empirical data have been compared with updated stellar models of low-mass, metal-rich, He-burning structures, transformed to the observational plane with appropriate atmosphere models. Results. We have obtained the first UV color-magnitude diagrams for NGC 6388 and NGC 6441. These diagrams confirm previous results, obtained in optical bands, about the presence of a sizeable stellar population of extremely hot Horizontal Branch stars. At least in NGC 6388, we find a clear indication that at the hot end of the horizontal branch the distribution of stars forms a hook-like feature, closely resembling those observed in NGC 2808 and w Centauri. We briefly review the theoretical scenarios which have been suggested for interpreting this observational feature. We investigate also on the tilt in the horizontal branch morphology, and provide further evidence that supports early suggestions according to which this feature cannot be interpreted as an effect of differential reddening or radiative levitation, though these effects contribute to create the anomaly. We demonstrate that a possible solution of the puzzle is to assume that a small fraction (approx. 13% in NGC 6388 and approx. 8% NGC 6441) of the stellar population in the two clusters is strongly helium enriched (Y approx. 0.40 in NGC6388 and Y approx. 0.35 in NGC 6441). This solution necessarily implies the presence of a double generation of stars in the two clusters.

  10. Extreme horizontal branch stars

    NASA Astrophysics Data System (ADS)

    Heber, U.

    A review is presented on the properties, origin and evolutionary links of hot subluminous stars which are generally believed to be extreme Horizontal Branch stars or closely related objects. They exist both in the disk and halo populations (globular clusters) of the Galaxy. Amongst the field stars a large fraction of sdBs are found to reside in close binaries. The companions are predominantly white dwarfs, but also low mass main sequence stars are quite common. Systems with sufficiently massive white dwarf companions may qualify as Supernova Ia progenitors. Recently evidence has been found that the masses of some unseen companions might exceed the Chandrasekhar mass, hence they must be neutron stars or black holes. Even a planet has recently been detected orbiting the pulsating sdB star V391 Peg. Quite to the opposite,in globular clusters, only very few sdB binaries amongst are found indicating that the dominant sdB formation processes is different in a dense environment. Binary population synthesis models identify three formation channels, (i) stable Roche lobe overflow, (ii) one or two common envelope ejection phases and (iii) the merger of two helium white dwarfs. The latter channel may explain the properties of the He-enriched subluminous O stars, the hotter sisters of the sdB stars, because their binary fraction is lower than that of the sdBs by a factor of ten or more. The rivaling ''late hot flasher'' scenario is also discussed. Pulsating subluminous B (sdB) stars play an important role for asteroseismology as this technique has already led to mass determinations for a handful of stars. A unique hyper-velocity sdO star moving so fast that it is unbound to the Galaxy has probably been ejected by the super-massive black hole in the Galactic centre.

  11. HST/WFPC2 imaging of the dwarf satellites And XI and And XIII: horizontal branch morphology and RR Lyraes

    NASA Astrophysics Data System (ADS)

    Yang, S.-C.; Sarajedini, A.

    2012-01-01

    We present a study of the stellar populations in two faint M31 dwarf satellites, Andromeda XI and Andromeda XIII. Using archival images from the Wide Field Planetary Camera 2 onboard the Hubble Space Telescope, we characterize the horizontal branch (HB) morphologies and the RR Lyrae (RRL) populations of these two faint dwarf satellites. Our new template light-curve fitting routine [Robust RR Lyrae light curve FITing (RRFIT)] has been used to detect and characterize RRL populations in both galaxies. The mean periods of RRab (RR0) stars in And XI and And XIII are = 0.621 ± 0.026 (error1) ± 0.022 (error2) and 0.648 ± 0.026 (error1) ± 0.022 (error2), respectively, where 'error1' represents the standard error of the mean, while 'error2' is based on our synthetic light-curve simulations. The RRL populations in these galaxies show a lack of RRab stars with high amplitudes [Amp (V) > 1.0 mag] and relatively short periods (? d), yet their period-V-band amplitude [P- Amp (V)] relations track the relation defined by the M31 field halo RRL populations at ˜11 kpc from the centre of M31. The metallicities of the RRab stars are calculated via a relationship between [Fe/H], log Pab and Amp(V). The resultant abundances ([ Fe/H ]And XI=-1.75; [ Fe/H ]And XIII=-1.74) are consistent with the values calculated from the red giant branch slope, indicating that our measurements are not significantly affected by RRL evolutionary away from the zero-age HB. The distance to each galaxy, based on the absolute V magnitudes of the RRab stars, is (m-M)0, V= 24.33 ± 0.05 for And XI and (m-M)0, V= 24.62 ± 0.05 for And XIII. We discuss the origins of And XI and And XIII based on a comparative analysis of the luminosity-metallicity relation of Local Group dwarf galaxies. Based on observations taken with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute.

  12. Horizontal-branch stellar evolution

    NASA Technical Reports Server (NTRS)

    Sweigart, Allen V.

    1990-01-01

    The results of canonical theory for the evolution of horizontal-branch (HB) stars are examined. Particular attention is given to how an HB star maintains the appropriate composition distribution within the semiconvective zone and how this composition is affected by the finite time-dependence with which convective boundaries actually move. Newly developed models based on time-dependent overshooting are presented for both the core-helium-exhaustion and main HB phases.

  13. Evolutionary sequences for horizontal branch stars

    NASA Technical Reports Server (NTRS)

    Sweigart, Allen V.

    1987-01-01

    A new grid of canonical evolutionary horizontal branch (HB) sequences is presented. Sequences are computed for each combination of the following helium and heavy-element abundances, respectively: Y(main sequence) = 0.20, 0.25, 0.30, and Z = 0.0001, 0.001, and 0.01. The results show that the bifurcation point at which the HB morphology changes from redward-evolving tracks to tracks with blueward loops shifts to higher effective temperatures with increasing helium abundance or metallicity. The sequences can be used to study in more detail how a number of HB properties such as the HB lifetime, the effective temperature at the bifurcation point in the track morphology, the luminosity dropoff of the blue HB, and the luminosity width of the red HB depend on the composition.

  14. TERZAN 5: AN ALTERNATIVE INTERPRETATION FOR THE SPLIT HORIZONTAL BRANCH

    SciTech Connect

    D'Antona, F.; Ventura, P.; Carini, R.; Di Criscienzo, M.; Caloi, V.; D'Ercole, A.; Vesperini, E.

    2010-06-01

    We consider the horizontal branch (HB) of the globular cluster Terzan 5, recently shown to be split into two parts, the fainter one ({delta}M{sub K} {approx} 0.3 mag) having a lower metallicity than the more luminous. Both features show that it contains at least two stellar populations. The separation in magnitude has been ascribed to an age difference of {approx}6 Gyr and interpreted as the result of an atypical evolutionary history for this cluster. We show that the observed HB morphology is also consistent with a model in which the bright HB is composed of second generation stars that are metal enriched and with a helium mass fraction larger (by {delta}Y {approx} 0.07) than that of first generation stars populating the fainter part of the HB. Terzan 5 would therefore be anomalous, compared to most 'normal' clusters hosting multiple populations, only because its second generation is strongly contaminated by supernova ejecta; the previously proposed prolonged period of star formation, however, is not required. The iron enrichment of the bright HB can be ascribed either to contamination from Type Ia supernova ejecta of the low-iron, helium-rich, ejecta of the massive asymptotic giant branch stars of the cluster, or to its mixing with gas, accreting on the cluster from the environment, that has been subject to fast metal enrichment due to its proximity with the galactic bulge. The model proposed here requires only a small age difference of {approx}100 Myr.

  15. The structure of horizontal-branch models. I - The zero-age horizontal branch

    NASA Technical Reports Server (NTRS)

    Dorman, Ben

    1992-01-01

    A detailed study of the structure of zero-age horizontal-branch (ZAHB) models is studied in order to show how the hydrostatic structure of these models changes with the input parameters and determines the H-R diagram location of a given model. The properties of composite polytropes on the homology-invariant (U,V)-plane are demonstrated. A variety of test models and sequences were constructed to elucidate the underlying factors that give rise to the wide variation in HB model properties with composition. The roles of the CNO elements as nuclear catalysts and of the envelope sources, as well as the envelope helium abundance are reexamined. It is found that, for stars of a fixed range of mass arriving on the HB, the stellar distribution is determined mainly by CNO for low metallicities (Fe/H of less than about -1), but mainly by opacity sources for high metallicities. The value of Fe/H where CNO ceases to dominate depends significantly on the adopted opacity and will decrease if and when opacity estimates are revised upward.

  16. Oxygen-enhanced models for globular cluster stars. III - Horizontal-branch sequences

    NASA Technical Reports Server (NTRS)

    Dorman, Ben

    1992-01-01

    A large grid of horizontal-branch (HB) evolutionary sequences which have been calculated with core expansion and semiconvection and with enhanced oxygen composition are presented and described. Tracks for 10 different metallicities are computed; they range from (Fe/H) = -0.47 to -2.26 and comprise a total of 115 sequences. The evolution is traced from the zero-age horizontal-branch (ZAHB) to the lower AGB at a point where log L/solar luminosity = 2.25. All of the sequences are illustrated on both the theoretical H-R diagram and on the B, V color-magnitude diagram. A complete set of tables for the ZAHB models and a representative sample of tabulations of the track parameters are provided. The phenomena which control HB evolution morphology, and existing certainties in theoretical HB models are discussed.

  17. Abundances in A-type Horizontal Branch Stars

    NASA Astrophysics Data System (ADS)

    Wilhelm, R.; Smith, V. V.

    1998-12-01

    As part of a program to explore correlations between abundance anomilies and physical parameters (e.g. Teff, vsini) in horizontal branch stars, we present preliminary results from high-resolution (R ~ 18,000) spectral observations of a small sample of A-type, horizontal branch stars. The sample was obtained using the 2.1m telescope and Sandiford Echelle at McDonald Observatory. A total of six standard FHB stars were observed including two, HD 130095 and HD 167105, which have been previously shown by Adleman and Philip to posses anomalously low [Ca/Fe] values. We have also obtained observations of eight of the brighter (B = 11.5-12.5) FHB stars from the HK objective-prism survey and two BHB stars from the globular cluster, M4. We will present abundance results that include [Ca/Fe], [Mg/Fe], and vsini values for the sample along with O and Na results for the two M4 stars. Our findings will be compared to previously published results for cluster BHB and field HB stars.

  18. The horizontal-branch stars in globular clusters. 2: The second parameter phenomenon

    NASA Technical Reports Server (NTRS)

    Lee, Young-Wook; Demarque, Pierre; Zinn, Robert

    1994-01-01

    Using synthetic horizontal-branch models, we have investigated the origin of the systematic variation in horizontal-branch (HB) morphology with galactocentric distance (R(sub G)) among globular clusters. The variations in He abundance, CNO abundance, and core mass required separately to explain this effect are inconsistent with either the observed properties of the RR Lyrae variables or the observed main-sequence turnoffs in the clusters. There is also no clear evidence that the trend with R(sub G) is related to the central concentrations, central densities, or absolute magnitudes of the clusters. The variations in cluster age required to explain this effect are not in conflict with any observations. A detailed comparison of our synthetic HB calculations with pairs of clusters of very different HB morphology but similar (Fe/H) reveals reasonably good agreement between the age differences inferred from HB morphology and the main-sequence turnoff. The major source of uncertainty is the need for ad hoc hypotheses in the modeling of the HB morphologies of a few peculiar clusters (e.g., NGC 6752). Nonetheless, there is firm evidence for age variations of several gigayears (as much as approximately 5 Gyr) among the halo globular clusters. Our results support the hypothesis of Searle & Zinn that the inner halo is more uniform in age and is older in the mean than the outer halo, and we estimate this difference to be approximately 2 Gyr.

  19. IDENTIFYING BLUE HORIZONTAL BRANCH STARS USING THE z FILTER

    SciTech Connect

    Vickers, John J.; Grebel, Eva K.; Huxor, Avon P.

    2012-04-15

    In this paper we present a new method for selecting blue horizontal branch (BHB) candidates based on color-color photometry. We make use of the Sloan Digital Sky Survey z band as a surface gravity indicator and show its value for selecting BHB stars from quasars, white dwarfs, and main-sequence A-type stars. Using the g, r, i, and z bands, we demonstrate that extraction accuracies on a par with more traditional u, g, and r photometric selection methods may be achieved. We also show that the completeness necessary to probe major Galactic structure may be maintained. Our new method allows us to efficiently select BHB stars from photometric sky surveys that do not include a u-band filter such as the Panoramic Survey Telescope and Rapid Response System.

  20. Testing the Beat Frequency Model of Horizontal Branch Qpos

    NASA Astrophysics Data System (ADS)

    Hertz, Paul

    The beat frequency modulated accretion (BFMA) model requires strong correlations in the horizontal branch quasiperiodic oscillations (HBO) and low frequency noise (LFN) amplitudes on time scales <1 s as they are both carried by the same accreting clumps. But such correlations have not been observed on time scales <8 s. With RXTE individual HBOs will be detectable in GX5-1 at the 1-2 sigma level. Using an optimal filter we will measure the phase coherence, strength, and clustering length of individual HBOs and the overall shot rate. We will test for the correlations between HBO and LFN amplitude predicted by the BFMA model and constrain some of the free observable parameters in the model. Any HBO model must account for these properties.

  1. Chemical Compositions of Field Red Horizontal Branch Stars

    NASA Astrophysics Data System (ADS)

    Afsar, Melike; Sneden, C.; For, B.

    2011-01-01

    Field Red Horizontal Branch stars (RHBs) are alleged to be members of the thick disk of our Galaxy and are an important evolutionary link between horizontal and asymptotic giant branch evolution. They are easy to identify in globular clusters through their color-magnitude diagram positions. However, they are harder to identify as single stars in the general field; thus they have received lesser attention to date. In this study, we composed a large catalog of RHB candidates and performed the first large-sample high-resolution spectroscopic survey of these stars. We have obtained high resolution spectra of a number of candidate field RHBs. The high resolution spectra of these stars were taken with the 2.7m Harlan J. Smith Telescope and Tull 2Dcoude (R=60000) spectrometer at McDonald Observatory. We have derived the metallicities and relative abundance ratios for some of the alpha (Ca and Si) and neutron capture (La and Eu) elements along with the fundamental stellar parameters. We have also determined CNO abundances in order to gain insight into the evolutionary states of the candidates. In particular, we have investigated the 12C/13C ratio using the CN features present in the 8000-8040 A region, which we have also used to obtain the N abundances of the candidates. Plausible RHB stars, members of the thick disk, found in our study, can shed light into Galactic evolutionary models. This project has benefitted from the financial support of NSF (AST-0908978), the Rex G. Baker endowment to the University of Texas Astronomy Dept., and The Scientific and Technological Research Council of Turkey (TUBITAK).

  2. Abundances anomalies and meridional circulation in horizontal branch stars

    NASA Astrophysics Data System (ADS)

    Quievy, D.; Charbonneau, P.; Michaud, G.; Richer, J.

    2009-06-01

    Context: Photospheric chemical abundances on the horizontal branch (HB) show some striking variations with effective temperature (T_eff). The most straightforward explanation is that these anomalies develop through diffusion processes, in particular gravitational settling and radiative levitation. However, the abrupt disappearance of strong abundance anomalies as one moves below about 11 000 K on the HB suggests that another factor plays an important role. Aims: We test an extension to the HB of the diffusion model for main-sequence HgMn stars, where strong anomalies can only develop in the slower rotators. In these rotators the gravitational settling of helium leads to the disappearance of its superficial convection zone, so that chemical separation by radiative levitation can occur all the way to the photosphere. Methods: More specifically, we calculate the critical rotational velocity at which He settling is prevented by rotationally-induced meridional circulation, in a suite of stellar models spanning the zero-age HB. Helium settling serves as the measure of the atomic diffusion of all species. Results: Our abundance evolution calculations show that, for models with T_eff less than about 11 500 K, corresponding to stars typically observed with the same metal composition as giants, meridional circulation is efficient enough to suppress He settling for rotational velocities, in good agreement with observed values. Once the meridional circulation profile of a star rotating as a near rigid body has been adopted, no adjustable parameter is involved. Conclusions: The T_eff dependence of abundance anomalies observed on the HB can be explained by atomic diffusion transport if one introduces the competition of meridional circulation with the observed T_eff dependence of rotation velocity of HB stars.

  3. Discovery of Extended Blue Horizontal Branches in Two Metal-rich Globular Clusters

    NASA Astrophysics Data System (ADS)

    Rich, R. Michael; Sosin, Craig; Djorgovski, S. George; Piotto, Giampaolo; King, Ivan R.; Renzini, Alvio; Phinney, E. Sterl; Dorman, Ben; Liebert, James; Meylan, Georges

    1997-07-01

    We have used WFPC2 to construct B, V color-magnitude diagrams of four metal-rich globular clusters, NGC 104 (47 Tuc), NGC 5927, NGC 6388, and NGC 6441. All four clusters have well populated red horizontal branches (RHB), as expected for their metallicity. However, NGC 6388 and 6441 also exhibit a prominent blue horizontal-branch (BHB) extension, including stars reaching as faint in V as the turnoff luminosity. This discovery demonstrates directly for the first time that a major population of hot horizontal-branch (HB) stars can exist in old, metal-rich systems. This may have important implications for the interpretation of the integrated spectra of elliptical galaxies. The cause of the phenomenon remains uncertain. We examine the possibility that NGC 6388 and 6441 are older than the other clusters, but a simple difference in age may not be sufficient to produce the observed distributions along the HB. The high central densities in NGC 6388 and 6441 suggest that the existence of the BHB tails might be caused by stellar interactions in the dense cores of these clusters, which we calculate to have two of the highest collision rates among globular clusters in the Galaxy. Tidal collisions might act in various ways to enhance loss of envelope mass and therefore populate the blue side of the HB. However, the relative frequency of tidal collisions does not seem large enough (compared to that of the clusters with pure RHBs) to account for such a drastic difference in HB morphology. While a combination of an age difference and dynamical interactions may help, prima facie the lack of a radial gradient in the BHB/RHB star ratio seems to argue against dynamical effects playing a role. Based on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by AURA, Inc., under NASA contract NAS 5-26555.

  4. The Hot Horizontal-Branch Stars in omega Centauri

    NASA Technical Reports Server (NTRS)

    Moehler, S.; Dreizler, S.; Lanz, T.; Bono, G.; Sweigart, A. V.; Calamida, A.; Nonino, M.

    2010-01-01

    Context. UV observations of some massive globular clusters have revealed a significant population of stars hotter and fainter than the hot end of the horizontal branch (HB), the so-called blue hook stars. This feature might be explained either by the late hot flasher scenario where stars experience the helium flash while on the white dwarf cooling curve or by the progeny of the helium-enriched sub-population recently postulated to exist in some clusters. Previous spectroscopic analyses of blue hook stars in co Cen and NGC 2808 support the late hot flasher scenario, but the stars contain much less helium than expected and the predicted C, N enrichment could not be verified. Aims. We compare observed effective temperatures, surface gravities, helium abundances, and carbon line strengths (where detectable) of our targets stars to the predictions of the two scenarios. Methods. Moderately high resolution spectra of hot HB stars in the globular cluster omega-Cen were analysed for radial velocity variations, atmospheric parameters and abundances using LTE and non-LTE model atmospheres. Results. We find no evidence for close binaries among our target stars. All stars below 30 000 K are helium-poor and very similar to HB stars observed in that temperature range in other globular clusters. In the temperature range 30000 K to 50000 K we find that 28% of our stars are helium-poor (log ((sup n)He/(sup n )H)< - 1.6), while 72% have roughly solar or super-solar helium abundance (log ((sup n)He/(sup n )H) >/= -1.5). We also find carbon enrichment strongly correlated with helium enrichment, with a maximum carbon enrichment of 3% by mass. Conclusions. The strong carbon enrichment in tandem with helium enrichment is predicted by the late hot flasher scenario, but not by the helium-enrichment scenario. We conclude that the helium-rich HB stars in omega-Cen cannot be explained solely by the helium-enrichment scenario invoked to explain the blue main sequence.

  5. The horizontal-branch stars in globular clusters. I - The period-shift effect, the luminosity of the horizontal branch, and the age-metallicity relation

    NASA Technical Reports Server (NTRS)

    Lee, Young-Wook; Demarque, Pierre; Zinn, Robert

    1990-01-01

    Synthetic models of the horizontal branches in globular clusters are constructed from a grid of the standard horizontal branch evolutionary tracks. The models are used to study the period shifts at constant T(eff) between RR Lyrae variables in globular clusters of different metallicities and the variation in horizontal-branch luminosity with the Fe/H ratio. The results suggest that the observed differences in the mean periods of the ab variables and the fraction of c-type variables between the two Oosterhoff groups are caused by a difference in the mean luminosity of the ab variables of about 0.18 bolometric mass and by the uneven distribution of variables across the instability strip in the group II clusters.

  6. Inclusion of horizontal branch stars in the derivation of star formation histories of dwarf galaxies: The Carina dSph

    NASA Astrophysics Data System (ADS)

    Savino, Alessandro; Salaris, Maurizio; Tolstoy, Eline

    2015-11-01

    We present a detailed analysis of the horizontal branch of the Carina dwarf spheroidal galaxy by means of synthetic modelling techniques, taking consistently into account the star formation history and metallicity evolution as determined from main sequence and red giant branch spectroscopic observations. We found that a range of integrated red giant branch mass loss values of 0.1-0.14 M⊙ increasing with metallicity is able to reproduce the colour extension of the old horizontal branch. Nonetheless, leaving the mass loss as the only free parameter is not enough to match the detailed morphology of Carina horizontal branch. We then investigated the role played by the star formation history on the discrepancies between synthetic and observed horizontal branches. We derived a "toy" bursty star formation history that reproduces well the observed horizontal branch star counts, and also matches qualitatively the red giant and the turn-off regions. This bursty star formation history is made of a subset of age and [M/H] components of the star formation history based on turn off and red giants only, and entails four separate bursts of star formation of different strengths, centred at 2, 5, 8.6, and 11.5 Gyr, respectively, with mean [M/H] decreasing from ~-1.7 to ~-2.2 when the age of the burst increases, and with a Gaussian spread of σ 0.1 dex around these mean values. The comparison between the metallicity distribution function of our bursty star formation history and the one measured from the infrared CaT feature using a CaT-[Fe/H] calibration shows a qualitative agreement, once the range of [Ca/Fe] abundances measured in a sample of Carina stars have been taken into account, that causes a bias of the derived [Fe/H] distribution toward values that are too low. In conclusion, we show how the information contained within the horizontal branch of Carina (and dwarf galaxies in general) can be extracted and interpreted to refine the star formation history derived exclusively

  7. The luminosities of horizontal branches and RR Lyrae stars in globular clusters

    NASA Astrophysics Data System (ADS)

    McNamara, D. H.; Rose, M. B.; Brown, P. J.; Ketcheson, D. I.; Maxwell, J. E.; Smith, K. M.; Wooley, R. C.

    2004-05-01

    We have utilized the latest stellar models of the Y2 (Yonsei-Yale) collaborators and color-magnitude diagrams of globular clusters to infer ages and absolute magnitudes of their horizontal branches (HB). The intrinsic (B - V), color indices of the turn-offs, (B - V)TO0,of the globular clusters were used to find ages. For 47 clusters that appear to be coeval (within ± 0.7 Gyr), we find an average age of 12.5 Gyr. We adopt this age and infer the absolute magnitudes of the turn-offs, MTOV, from the clusters [Fe/H] values. The absolute magnitudes of the horizontal branches or RR Lyrae stars are the n determined from the difference between the apparent magnitudes of the horizontal branches (or RR Lyrae stars) and the apparent magnitude of the turn-offd, VTO. We conclude: 1) the slope of the MV(HB), [Fe/H] relation is ~0.3 for clusters with [Fe/H] values between -0.5 to -1.5. The relation has zero slope for [Fe/H] values smaller than -1.5. 2) For [Fe/H] < -1.3, the MV(HB) or MV values of RR Lyrae stars are not only a function of [Fe/H], but the horizontal-branch type in the sense that the clusters with the blue horizontal branches have more luminous horizontal branches than clusters with red horizontal branches. The same results are found by inferring the luminosities of the HBs from pulsating blue stragglers.

  8. The Origin of Hot Subluminous Horizontal-Branch Stars in (omega) Centauri and NGC 2808

    NASA Technical Reports Server (NTRS)

    Sweigart, Allen V.; Brown, Thomas M.; Lanz, Thierry; Landsman, Wayne B.; Hubeny, Ivan

    2001-01-01

    Hot subluminous stars lying up to 0.7 mag below the extreme horizontal branch (EHB) are found in the ultraviolet (UV) color magnitude diagrams of both (omega) Cen and NGC 2808. In order to explore the evolutionary status of these subluminous stars, we have evolved a set of low-mass stars continuously from the main sequence through the helium-core flash to the HB (horizontal branch) for a wide range in the mass loss along the red-giant branch (RGB). Stars with the largest mass loss evolve off the RGB to high effective temperatures before igniting helium in their cores. Our results indicate that the subluminous EHB stars, as well as the gap within the EHB of NGC 2808, can be explained if these stars undergo a late helium-core flash while descending the white-dwarf cooling curve. Under these conditions the convection zone produced by the helium flash will penetrate into the stellar envelope, thereby mixing most, if not all, of the envelope hydrogen into the hot helium-burning interior, where it is rapidly consumed. This phenomenon is analogous to the 'born-again' scenario for producing hydrogen-deficient stars following a very late helium-shell flash. This 'flash mixing' of the stellar envelope greatly enhances the envelope helium and carbon abundances and, as a result, leads to a discontinuous jump in the HB effective temperature. We argue that the EHB gap in NGC 2808 is associated with this theoretically predicted dichotomy in the HB morphology. Using new helium- and carbon-rich stellar atmospheres, we show that these changes in the envelope abundances of the flash-mixed stars will suppress the UV flux by the amount needed to explain the hot subluminous EHB stars in (omega) Cen and NGC 2808. Moreover, we demonstrate that models without flash mixing lie, at most, only approximately 0.1 mag below the EHB, and hence fail to explain the observations. Flash mixing may also provide a new evolutionary channel for producing the high gravity, helium-rich sdO and sdB stars.

  9. SODIUM-OXYGEN ANTICORRELATION AMONG HORIZONTAL BRANCH STARS IN THE GLOBULAR CLUSTER M4

    SciTech Connect

    Marino, A. F.; Lind, K.; Villanova, S.; Geisler, D.; Milone, A. P.; Piotto, G.; Stetson, P. B.

    2011-04-01

    The horizontal branch (HB) morphology of globular clusters (GCs) is mainly governed by metallicity. The second parameter problem, well known since the 1960s, states that metallicity alone is not enough to describe the observed HB morphology of many GCs. Despite many efforts to resolve this issue, the second parameter phenomenon still remains without a satisfactory explanation. We have analyzed blue-HB, red-HB, and RR-Lyrae stars in the GC M4 and studied their Fe, Na, and O abundances. Our goal is to investigate possible connections between the bimodal HB of M4 and the chemical signatures of the two stellar populations recently discovered among red giants of this cluster. We obtained FLAMES-UVES/GIRAFFE spectra of a sample of 22 stars covering the HB from the red to the blue region. While iron has the same abundance in both the red-HB and blue-HB segments, the red-HB is composed of stars with scaled-solar sodium abundances, while the blue-HB stars are all sodium enhanced and oxygen depleted. The RR-Lyrae are Na-poor, as the red-HB stars, and O-rich. This is what we expect if the blue-HB consists of a second generation of stars formed from the ejecta produced by an earlier stellar population through high-temperature hydrogen-burning processes that include the CNO, NeNa, and MgAl cycles and are therefore expected to be He-rich. According to this scenario, the sodium and oxygen pattern detected in the blue-HB and red-HB segments suggests helium as the second parameter that rules the HB morphology in M4.

  10. DOUBLE HORIZONTAL BRANCHES IN NGC 6440 AND NGC 6569 UNVEILED BY THE VVV SURVEY

    SciTech Connect

    Mauro, Francesco; Bidin, Christian Moni; Cohen, Roger; Geisler, Doug; Chene, Andre-Nicolas; Villanova, Sandro; Minniti, Dante; Catelan, Marcio

    2012-12-20

    We report the discovery of a peculiar horizontal branch (HB) in NGC 6440 and NGC 6569, two massive and metal-rich Galactic globular clusters (GGCs) located in the Galactic bulge, within 4 kpc from the Galactic center. In both clusters, two distinct clumps are detected at the level of the cluster HB, separated by only {approx}0.1 mag in the K{sub s} band. They were detected with IR photometric data collected with the 'VISTA Variables in the Via Lactea' Survey, and confirmed in independent IR catalogs available in the literature and Hubble Space Telescope optical photometry. Our analysis demonstrates that these clumps are real cluster features, not a product of field contamination or interstellar reddening. The observed split HBs could be a signature of two stellar sub-populations with different chemical composition and/or age, as recently found in Terzan 5, but it cannot be excluded that they are caused by evolutionary effects, in particular for NGC 6440. This interpretation, however, requires an anomalously high helium content (Y > 0.30). Our discovery suggests that such a peculiar HB morphology could be a common feature of massive, metal-rich bulge GGCs.

  11. THE HORIZONTAL BRANCH OF NGC 1851: CONSTRAINTS FROM ITS RR LYRAE VARIABLES

    SciTech Connect

    Kunder, Andrea; De Propris, Roberto; Walker, Alistair; Salaris, Maurizio; Cassisi, Santi; Stetson, Peter B.; Catelan, Marcio; Amigo, Pia E-mail: mcatelan@astro.puc.cl

    2013-01-01

    We use the pulsational properties of the RR Lyrae variables in the globular cluster NGC 1851 to obtain detailed constraints of the various sub-stellar populations present along its horizontal branch. On the basis of detailed synthetic horizontal branch modeling, we find that minor helium variations (Y {approx} 0.248-0.280) are able to reproduce the observed periods and amplitudes of the RR Lyrae variables, as well as the frequency of fundamental and first-overtone RR Lyrae stars. Comparison of number ratios among the blue and red horizontal branch components and the two observed subgiant branches also suggest that the RR Lyrae variables originated from the progeny of the bright subgiant branch. The RR Lyrae variables with slightly enhanced helium (Y {approx} 0.270-0.280) have longer periods at a given amplitude, as is seen with Oosterhoff II (OoII) RR Lyrae variables, whereas the RR Lyrae variables with Y {approx} 0.248-0.270 have shorter periods, exhibiting properties of Oosterhoff I (OoI) variables. This correlation does suggest that the pulsational properties of RR Lyrae stars can be very useful for tracing the various subpopulations and can provide suitable constraints on the multiple population phenomenon. It appears to be of great interest to explore whether this conclusion can be generalized to other globular clusters hosting multiple populations.

  12. Helium enhanced stars and multiple populations along the horizontal branch of NGC 2808: direct spectroscopic measurements

    NASA Astrophysics Data System (ADS)

    Marino, A. F.; Milone, A. P.; Przybilla, N.; Bergemann, M.; Lind, K.; Asplund, M.; Cassisi, S.; Catelan, M.; Casagrande, L.; Valcarce, A. A. R.; Bedin, L. R.; Cortés, C.; D'Antona, F.; Jerjen, H.; Piotto, G.; Schlesinger, K.; Zoccali, M.; Angeloni, R.

    2014-01-01

    We present an abundance analysis of 96 horizontal branch (HB) stars in NGC 2808, a globular cluster exhibiting a complex multiple stellar population pattern. These stars are distributed in different portions of the HB and cover a wide range of temperature. By studying the chemical abundances of this sample, we explore the connection between HB morphology and the chemical enrichment history of multiple stellar populations. For stars lying on the red HB, we use GIRAFFE and UVES spectra to determine Na, Mg, Si, Ca, Sc, Ti, Cr, Mn, Fe, Ni, Zn, Y, Ba and Nd abundances. For colder, blue HB stars, we derive abundances for Na, primarily from GIRAFFE spectra. We were also able to measure direct non-local thermodynamic equilibrium He abundances for a subset of these blue HB stars with temperature higher than ˜9000 K. Our results show that: (i) HB stars in NGC 2808 show different content in Na depending on their position in the colour-magnitude diagram, with blue HB stars having higher Na than red HB stars; (ii) the red HB is not consistent with a uniform chemical abundance, with slightly warmer stars exhibiting a statistically significant higher Na content; and (iii) our subsample of blue HB stars with He abundances shows evidence of enhancement with respect to the predicted primordial He content by ΔY = +0.09 ± 0.01 ± 0.05 (internal plus systematic uncertainty). Our results strongly support theoretical models that predict He enhancement among second-generation(s) stars in globular clusters and provide observational constraints on the second-parameter governing HB morphology.

  13. THE SUPERFICIAL BRANCH OF THE RADIAL NERVE: A MORPHOLOGIC STUDY

    PubMed Central

    Folberg, Celso Ricardo; Ulson, Heitor; Scheidt, Rodrigo Benedet

    2015-01-01

    Study the morphology of the superficial branch of the radial nerve (SBRN) of the forearms and wrists of fresh adult human cadavers. Methods: Twenty three dissections were performed under 3.5x loupe magnification, histological sections of the nerve were obtained in 20 dissections for fascicle identification. Results: The SBRN emerged, in average, at 8.65cm proximal to the radial styloid apophysis (RSA) between the Brachioradialis (BR) and Extensor Carpi Radialis Longus (ECRL) tendons. In 6/23 cases the SBRN emerged between an accessory BR tendon and the main BR tendon. The first branch of the SBRN arose at an average of 4.58 cm proximal to the RSA. A branch running across the RSA was found in 7/23 cases. At that level, the average number of branches crossing the wrist was 3.4. A fascicle count of the nerve and its first branch showed an average of 6.6 and 4.0 fascicles, respectively. Conclusion: Our anatomical findings are similar to those in the revised literature and contribute towards a better knowledge of the SBRN. Great caution is required in surgical procedures such as percutaneous bone fixation of the distal 1/3 of the forearm and wrist and particularly, in those susceptible to SBRN injury, as in seven of the 23 cases the SRBN ran directly accross the RSA. The authors recommend performing small longitudinal incisions down to the subcutaneous tissue, separating the nerve branches by blunt soft tissue dissection, with a delicate haemostat, before introducing the Kirschner wires (minimally invasive procedures). PMID:26998456

  14. THE TEMPERATURE DISTRIBUTION OF HORIZONTAL BRANCH STARS: METHODS AND FIRST RESULTS

    SciTech Connect

    Lagioia, E. P.; Dalessandro, E.; Ferraro, F. R.; Lanzoni, B.; Salaris, M.; Pietrinferni, A.; Cassisi, S.

    2015-02-10

    As part of a large project aimed at characterizing the ultraviolet (UV) properties of globular clusters, we present here a theoretical and observational analysis aimed at setting the framework for the determination of horizontal branch (HB) temperature distributions. Indeed this is crucial information needed to understand the physical parameters shaping the HB morphology in globular clusters and to interpret the UV emission from unresolved stellar systems. We found that the use of zero age HB color-T {sub eff} relations is a robust way to derive effective temperatures of individual HB stars. We investigated the most suitable colors for temperature estimates and the effect on the color-T {sub eff} relations of variations of the initial chemical composition and the evolution off the zero age HB. As a test case, we applied our color-T {sub eff} calibrations to the Galactic globular cluster M15. The photometry of M15 has been obtained with the Wide Field and Planetary Camera 2 on board the Hubble Space Telescope. The HB of M15 turned out to have a multimodal distribution, with a main component peaking at T{sub eff} ∼ 8000 K and confined below T{sub eff} ∼ 10,000 K. The second component peaks at T{sub eff} ∼ 14,000 K and extends up to T{sub eff} ∼ 20,000 K. The vast majority ( ∼ 95%) of the HB stars in M15 is below 20,000 K, in agreement with the lack of a well populated extreme HB observed in other metal-poor globular clusters. We also verified that the temperatures derived with our analysis are consistent with spectroscopic estimates available in the literature.

  15. VizieR Online Data Catalog: HK-Survey field horizontal-branch candidates (Beers+, 2007)

    NASA Astrophysics Data System (ADS)

    Beers, T. C.; Almeida, T.; Rossi, S.; Wilhelm, R.; Marsteller, B.

    2008-11-01

    We present coordinates and available photometric information (either from previous or recent broadband UBV observations, and near-infrared photometry from the 2MASS Point Source Catalog) for 12,056 stars (11,516 of which are unique) identified in the HK Survey of Beers and colleagues as candidate field horizontal-branch or A-type stars. These stars, in the apparent magnitude range 10<=B<=16.0, were selected using an objective-prism/interference-filter survey technique. The availability of 2MASS information permits assembly of a cleaned version of this catalog, comprising likely blue horizontal-branch (BHB) stars or blue stragglers in the color interval [-0.2<=(B-V)0<=+0.2]. (2 data files).

  16. VizieR Online Data Catalog: Candidate field horizontal-branch stars catalog (Beers+, 1988)

    NASA Astrophysics Data System (ADS)

    Beers, T. C.; Preston, G. W.; Shectman, S. A.

    2008-11-01

    Coordinates and brightness estimates are presented for 4408 candidate field horizontal-branch stars selected using an objective-prism, interference-filter survey technique. The candidates lie primarily in the southern Galactic hemisphere, and are distributed in color over the range B-V from -0.2 to 0.40. Previous spectroscopic observation of a subset of these candidates indicates that roughly 85 percent of the catalog objects are bona fide members of the field blue horizontal branch. The remaining candidates include, in order of frequency, stars with main-sequence gravity which are likely to be a mix of metal-deficient turnoff stars and field blue stragglers, metallic line (Am) stars, A stars of near-solar metallicity, and high-luminosity or binary stars. (1 data file).

  17. Extreme horizontal branch stars - Puzzling objects dominating the UV-light in early-type galaxies

    NASA Astrophysics Data System (ADS)

    Geier, Stephan

    2015-08-01

    Extreme horizontal branch stars (also known as hot subdwarf stars, sdO/Bs) are located at the bluest extension of the horizontal branch in the HR-diagram. They burn helium in their cores and are the sources of the UV-excess in elliptical galaxies and other old stellar populations. However, the formation of those stars is still unclear. SdO/B stars in the field show a high binary fraction and are likely formed via binary interactions with low-mass stars, substellar objects or compact stellar remnants. Similar objects in globular clusters on the other hand have a significantly lower binary fraction and might therefore be formed in a different way. I will review the state-of-the-art and confront theories of sdO/B formation with most recent observational evidence.

  18. Physical Parameters of Hot Horizontal-Branch Stars in NGC 6752: Deep Mixing and Radiative Levitation

    NASA Technical Reports Server (NTRS)

    Moehler, S.; Sweigart, A. V.; Landsman, W. B.; Heber, U.; Catelan, M.

    1999-01-01

    Atmospheric parameters (T(sub eff), log g and log n(sub He)/n(sub H-dot)) are derived for 42 hot horizontal branch (HB) stars in the globular cluster NGC 6752. For 19 stars Mg II and Fe II lines are detected indicating an iron enrichment by a factor 50 on average with respect to the cluster abundance whereas the magnesium abundances are consistent with the cluster metallicity. This finding adds to the growing evidence that radiative levitation plays a significant role in determining the physical parameters of blue HB stars. Indeed, we find that iron enrichment can explain part, but not all, of the problem of anomalously low gravities along the blue HB. Thus the physical parameters of horizontal branch stars hotter than about 11,500 K in NGC 6752, as derived in this paper, are best explained by a combination of helium mixing and radiative levitation effects.

  19. Abundance anomalies in hot horizontal-branch stars of the globular cluster NGC 6752

    SciTech Connect

    Glaspey, J.W.; Michaud, G.; Moffat, A.F.J.; Demers, S.

    1989-04-01

    High-resolution spectra of two blue stars on the horizontal branch of the metal-poor globular cluster NGC 6752 have been obtained with an echelle spectrograph and a CCD detector on the CTIO 4 m telescope. A helium underabundance is confirmed in the blue star CL 1083 (Teff = 16,000 K). An overabundance of iron by a factor of 50 compared to the cluster metallicity is also obtained. No abundance anomaly is measured in the cooler star CL 1007 (Teff = 10,000 K). Presumably all stars of this cluster had the same original abundances; hence, the anomalies must be explained by the different properties of individual stars. These results are discussed in the context of the diffusion model originally developed to explain the He underabundance in horizontal-branch stars. 47 refs.

  20. Coupling between the 45 Hz Horizontal-Branch Oscillation and the Normal-Branch Oscillation in Scorpius X-1

    NASA Astrophysics Data System (ADS)

    Yu, Wenfei

    2007-04-01

    The observations of the bright persistent neutron star low-mass X-ray binary (LMXB) Sco X-1 performed with the Rossi X-Ray Timing Explorer (RXTE) show a ~6 Hz normal-branch oscillation (NBO), a ~45 Hz horizontal-branch oscillation (HBO), and twin kilohertz quasi-periodic oscillations (kHz QPOs) on its normal branch simultaneously. We have found that the fractional amplitude of the HBO corresponding to the NBO phase of high flux is 1.1%, while that of the NBO phase of low flux is undetectable, with a 3 σ upper limit of 0.4%, implying that the HBO strength varies with the NBO phase in a manner opposite that of the lower kHz QPO previously found, and suggests that the condition for the generation of the HBO is met when the NBO flux is high. The 6 Hz NBO in Sco X-1 connects the 45 Hz HBO and the twin kHz QPO together, showing a unique picture indicating a coupling between the QPOs, which has never been observed in other neutron star LMXBs. We discuss the implications for current models of the 45 Hz HBO, the 6 Hz NBO, and the twin kHz QPOs.

  1. The time-delay spectrum of GX 5-1 in its horizontal branch

    NASA Astrophysics Data System (ADS)

    Vaughan, B.; van der Klis, M.; Lewin, W. H. G.; Wijers, R. A. M. J.; van Paradijs, J.; Dotani, T.; Mitsuda, K.

    1994-02-01

    Using a cross-spectral technique we investigate time delays between intensity variations of GX 5-1 in 10 X-ray spectral channels. The data were taken during a 1989 Ginga observation during which the source was in its horizontal-branch spectral state. We develope a new method to measure 'time-delay spectra' in fixed Fourier frequency ranges and use it to determine the energy and intensity dependence of time delays in the low-frequency noise (nu less than 2 Hz), the horizontal branch quasi-periodic oscillations (QPO), and the QPO second harmonic. These are the first time-delay spectra of a Z-source in its horizontal branch, and the first detection of time delays in the second harmonic. We consider two mechanisms for the production of the time lags: Comptonization and evolving shots. We perform Monte Carlo simulations of Compton scattering in a homogeneous, isotropic, central corona and show that it qualitatively explain the observed energy and time-delay spectra, but that it cannot explain the differences in the QPO first and second harmonic time-delay spectra, nor the observed dependence of the QPO fractional rms variability upon energy. We consider implications of our results for millisecond pulsar searches in low-mass X-ray binaries.

  2. The time-delay spectrum of GX 5-1 in its horizontal branch

    NASA Technical Reports Server (NTRS)

    Vaughan, B.; Van Der Klis, M.; Lewin, W. H. G.; Wijers, R. A. M. J.; Van Paradijs, J.; Dotani, T.; Mitsuda, K.

    1994-01-01

    Using a cross-spectral technique we investigate time delays between intensity variations of GX 5-1 in 10 X-ray spectral channels. The data were taken during a 1989 Ginga observation during which the source was in its horizontal-branch spectral state. We develope a new method to measure 'time-delay spectra' in fixed Fourier frequency ranges and use it to determine the energy and intensity dependence of time delays in the low-frequency noise (nu less than 2 Hz), the horizontal branch quasi-periodic oscillations (QPO), and the QPO second harmonic. These are the first time-delay spectra of a Z-source in its horizontal branch, and the first detection of time delays in the second harmonic. We consider two mechanisms for the production of the time lags: Comptonization and evolving shots. We perform Monte Carlo simulations of Compton scattering in a homogeneous, isotropic, central corona and show that it qualitatively explain the observed energy and time-delay spectra, but that it cannot explain the differences in the QPO first and second harmomnic time-delay spectra, nor the observed dependence of the QPO fractional rms variability upon energy. We consider implications of our results for millisecond pulsar searches in low-mass X-ray binaries.

  3. THE CURIOUS RADIAL DISTRIBUTIONS OF HORIZONTAL BRANCH STARS IN NGC 6441

    SciTech Connect

    Krogsrud, David A.; Sandquist, Eric L.; Kato, Tadafumi E-mail: erics@sciences.sdsu.edu

    2013-04-20

    NGC 6441 is one of the most massive and most metal-rich globular clusters in the galaxy, and is noted for an unusual extended horizontal branch that reaches past the instability strip. We find evidence that there are two different populations of stars within the heavily populated red clump. Once a differential reddening correction is applied, a large but compact group of stars is found at the faint red end of the clump in the color-magnitude diagram. Brighter, bluer stars in the clump are found to be more centrally concentrated within the cluster at a very high level of significance. Curiously, the blue horizontal branch stars show a more complex distribution and are not more centrally concentrated than the brighter red clump stars. The spatial distributions of clump stars are in agreement with the idea that the brighter bluer part of the clump is a helium-enriched second generation. The blue horizontal branch stars may be showing evidence that they are being dynamically evaporated.

  4. Torricelli's curtain: morphology of horizontal laminar jets under gravity

    NASA Astrophysics Data System (ADS)

    Ribe, Neil; Paternoster, Gabriel; Rabaud, Marc

    2012-11-01

    It has been ``known'' since the seventeenth century that a jet of water issuing horizontally from a hole in the side of a bucket describes a parabolic trajectory. However, this bit of canonical fluid mechanical lore is wrong in many cases. Our recent experiments performed on laminar jets issuing from a horizontal tube show that the initially round jet typically evolves into a thin vertical curtain bounded by bulbous rims at its upper and lower extremities. Moreover, injected dye reveals the presence of a recirculating flow with helical streamlines around the jet's axis. To understand this behavior, we formulate an analytical model for the near-orifice structure of the jet in the limit of large Froude number Fr ≡ɛ-1 >> 1 . We find that a recirculating flow is generated by the sinusoidal variation of the nonhydrostatic pressure around cross-sections of the jet at order ɛ, and that deformation of the cross-section occurs at order ɛ2. We also use the volume-of-fluid code Gerris to study numerically the evolution of the jet's morphology as a function of the Reynolds, Froude and Ohnesorge numbers, and compare the results with our analytical theory and with laboratory experiments.

  5. The Na-O anticorrelation in horizontal branch stars. V. NGC 6723

    NASA Astrophysics Data System (ADS)

    Gratton, R. G.; Lucatello, S.; Sollima, A.; Carretta, E.; Bragaglia, A.; Momany, Y.; D'Orazi, V.; Salaris, M.; Cassisi, S.; Stetson, P. B.

    2015-01-01

    We used FLAMES+GIRAFFE (Medusa mode) at the VLT to obtain moderately high resolution spectra for 30 red horizontal branch (RHB) stars, 4 RR Lyrae variables, and 17 blue horizontal branch (BHB) stars in the low-concentration, moderately metal-rich globular cluster NGC 6723 ([Fe/H] = -1.22 ± 0.08 from our present sample). The spectra were optimized to derive O and Na abundances. In addition, we obtained abundances for other elements, including N, Fe, Mg, Ca, Ni, and Ba. We used these data to discuss the evidence of a connection between the distribution of stars along the horizontal branch (HB) and the multiple populations that are typically present in globular clusters. We found that all RHB and most (13 out of 17) BHB stars are O-rich, Na-poor, and N-poor; these stars probably belong to the first stellar generation in this cluster. Only the four warmest observed stars are (moderately) O-poor, Na-rich, and N-rich, and they probably belong to the second generation. While our sample is not fully representative of the whole HB population in NGC 6723, our data suggest that in this cluster only HB stars warmer than ~9000 K, that is one fourth of the total, belong to the second generation, if at all. Since in many other clusters this fraction is about two thirds, we conclude that the fraction of first/second generation in globular clusters may be strongly variable. In addition, the wide range in colour of chemically homogeneous first-generation HB stars requires a considerable spread in mass loss (>0.10 M⊙). The reason for this spread is yet to be understood. Finally, we found a high Ba abundance, with a statistically significant radial abundance gradient. Based on observations collected at ESO telescopes under programme 087.D-0230.Tables 2, 3, 5, 7, and 8 are available in electronic form at http://www.aanda.org

  6. RR Lyrae stars and the horizontal branch of NGC 5904 (M5)

    NASA Astrophysics Data System (ADS)

    Arellano Ferro, A.; Luna, A.; Bramich, D. M.; Giridhar, Sunetra; Ahumada, J. A.; Muneer, S.

    2016-05-01

    We report the distance and [Fe/H] value for the globular cluster NGC 5904 (M5) derived from the Fourier decomposition of the light curves of selected RRab and RRc stars. The aim in doing this was to bring these parameters into the homogeneous scales established by our previous work on numerous other globular clusters, allowing a direct comparison of the horizontal branch luminosity in clusters with a wide range of metallicities. Our CCD photometry of the large variable star population of this cluster is used to discuss light curve peculiarities, like Blazhko modulations, on an individual basis. New Blazhko variables are reported.

  7. The Accretion Rate Independence of Horizontal Branch Oscillation in XTE J1701-462

    NASA Astrophysics Data System (ADS)

    Li, Zhaosheng; Chen, Li; Qu, Jinlu; Bu, Qingcui; Wang, Dehua; Xu, Renxin

    2014-05-01

    We study the temporal and energy spectral properties of the unique neutron star low-mass X-ray binary XTE J1701-462. Assuming the horizontal branch/normal branch (HB/NB) vertex as a reference position of the accretion rate, the horizontal branch oscillation (HBO) of the HB/NB vertex is roughly 50 Hz. It indicates that the HBO is independent of the accretion rate or the source intensity. The spectral analysis shows R_{in}\\propto \\dot{M}_{Disk}^{2.9+/- 0.09} in the HB/NB vertex and R_{in}\\propto \\dot{M}_{Disk}^{1.7+/- 0.06} in the NB/flaring branch (FB) vertex, which implies that different accretion rates may be produced in the HB/NB and NB/FB vertex. The Comptonization component could be fitted by a constrained broken power law or nthComp. Unlike GX 17+2, the frequencies of HBO positively correlate with the inner disk radius, which contradict with the prediction of the Lense-Thirring precession model. XTE J1701-462, both in the Cyg-like phase and in the Sco-like phase, follows a positive correlation between the break frequency of broadband noise and the characteristic frequency of HBO, which is called the W-K relation. An anticorrelation between the frequency of HBO and photon energy is observed. Moreover, the rms of HBO increases with photon energy until ~10 keV. We discuss the possible origin of HBO from the corona in XTE J1701-462.

  8. THE CHEMICAL COMPOSITIONS OF NON-VARIABLE RED AND BLUE FIELD HORIZONTAL BRANCH STARS

    SciTech Connect

    For Biqing; Sneden, Christopher

    2010-12-15

    We present a new detailed abundance study of field red horizontal branch (RHB) and blue horizontal branch (BHB) non-variable stars. High resolution and high signal-to-noise ratio echelle spectra of 11 RHB and 12 BHB were obtained with the McDonald 2.7 m telescope, and the RHB sample was augmented by reanalysis of spectra of 25 stars from a recent survey. We derived stellar atmospheric parameters based on spectroscopic constraints and computed relative abundance ratios for 24 species of 19 elements. The species include Si II and Ca II, which have not been previously studied in RHB and BHB (T{sub eff} < 9000 K) stars. The abundance ratios are generally consistent with those of similar-metallicity field stars in different evolutionary stages. We estimated the masses of the RHB and BHB stars by comparing their T{sub eff}-log g positions with HB model evolutionary tracks. The mass distribution suggests that our program stars possess masses of {approx}0.5 M{sub sun}. Finally, we compared the temperature distributions of field RHB and BHB stars with field RR Lyraes in the metallicity range -0.8{approx}> [Fe/H] {approx}>-2.5. This yielded effective temperature estimates of 5900 K and 7400 K for the red and blue edges of the RR Lyrae instability strip.

  9. Line Broadening in Field Metal-Poor Red Giant and Red Horizontal Branch Stars

    NASA Astrophysics Data System (ADS)

    Carney, Bruce W.; Latham, David W.; Stefanik, Robert P.; Laird, John B.

    2008-01-01

    We report 349 radial velocities for 45 metal-poor field red giant branch (RGB) and red horizontal branch (RHB) stars, with time coverage ranging from 1 to 21 years. We have identified one new spectroscopic binary, HD 4306, and one possible such system, HD 184711. We also provide 57 radial velocities for 11 of the 91 stars reported in our previous work. All but one of the 11 stars had been found to have variable radial velocities. New velocities for the long-period spectroscopic binaries BD-1 2582 and HD 108317 have extended the time coverage to 21.7 and 12.5 years, respectively, but in neither case have we yet completed a full orbital period. As was found in the previous study, radial velocity "jitter" is present in many of the most luminous stars. Excluding stars showing spectroscopic binary orbital motion, all 7 of the red giants with estimated MV values more luminous than -2.0 display jitter, as well as 3 of the 14 stars with -2.0 < MV <= -1.4. We have also measured the line broadening in all the new spectra, using synthetic spectra as templates. Comparison with results from high-resolution and higher signal-to-noise (S/N) spectra employed by other workers shows good agreement down to line-broadening levels of 3 km s-1, well below our instrumental resolution of 8.5 km s-1. As the previous work demonstrated, the majority of the most luminous red giants show significant line broadening, as do many of the red horizontal branch stars, and we briefly discuss possible causes. The line broadening appears related to velocity jitter, in that both appear primarily among the highest luminosity red giants.

  10. HST Observations of New Horizontal Branch Structures in the Globular Cluster w Centauri

    NASA Technical Reports Server (NTRS)

    Stecher, Theodore

    1999-01-01

    The globular cluster omega Centauri contains the largest known population of very hot horizontal branch (HB) stars. We have used the Hubble Space Telescope to obtain a far-UV/optical color-magnitude diagram of three fields in omega Cen. We find that over 30% of the HB objects are "extreme" HB or hot post-HB stars. A wide gap in the color distribution of the hot HB stars may correspond to gaps found earlier in several other clusters, which argues for a common mass loss mechanism. The diagram contains a significant population of hot sub-HB stars, which we interpret as the "blue-hook" objects predicted by D'Cruz (1996a). These are produced by late He-flashes in stars which have undergone unusually large giant branch mass loss. Omega Cen has a well-known spread of metal abundance, and the diagram is consistent with a giant branch mass loss efficiency which increases with metallicity. There is no evidence for a dynamical origin of the hot HB stars.

  11. The Hottest Horizontal-Branch Stars in Omega Centauri: Late Hot Flasher vs. Helium Enrichment

    NASA Technical Reports Server (NTRS)

    Moehler, S.; Dreizler, S.; Lanz, T.; Bono, G.; Sweigart, A V.; Calamida, A.; Monelli, M.; Nonino, M.

    2007-01-01

    UV observations of some massive globular clusters uncovered a significant population of very hot stars below the hot end of the horizontal branch (HB), the so-called blue hook stars. This feature might be explained either by the late hot flasher scenario here stars experience the helium flash while on the white dwarf cooling curve or by the helium-rich sub-population recently postulated to exist in some clusters. Spectroscopic analyses of blue hook stars in omega Cen and NGC 2808 support the late hot flasher scenario, but the stars contain much less helium than expected and the predicted C, N enrichment could not be verified from existing data. We want to determine effective temperatures, surface gravities and abundances of He, C, N in blue hook and canonical extreme horizontal branch (EHB) star candidates. Moderately high resolution spectra of stars at the hot end of the blue horizontal branch in the globular cluster omega Cen were analysed for atmospheric parameters (T(sub eff), log g) and abundances using LTE and Non-LTE model atmospheres. In the temperature range 30,000 K to 50,000 K we find that 37% of our stars are helium-poor (log nHe/nH less than -2), 49% have solar helium abundance within a factor of 3 (-1.5 less than or equal to log nHe/nH less than or equal to -0.5) and 14% are helium rich (log nHe/nH greater than -0.4). We also find carbon enrichment in step with helium enrichment, with a maximum carbon enrichment of 3% by mass. At least 30% of the hottest HB stars in omega Centauri show helium abundances well above the predictions from the helium enrichment scenario (Y = 0.42 corresponding to log nHe/nH approximately equal to -0.74). In addition the most helium-rich stars show strong carbon enrichment as predicted by the late hot flasher scenario. We conclude that the helium-rich HB stars in omega Cen cannot be explained solely by the helium-enrichment scenario invoked to explain the blue main sequence.

  12. Constraints on Helium Enhancement in the Globular Cluster M3 (NGC 5272): The Horizontal Branch Test

    NASA Technical Reports Server (NTRS)

    Catelan, M.; Grundahl, F.; Sweigart, A. V.; Valcarce, A. A. R.; Cortes, C.

    2007-01-01

    It has recently been suggested that the presence of multiple populations showing various amounts of helium enhancement is a common feature among globular star clusters. In this scenario, such a helium enhancement would be particularly apparent in the enhanced luminosity of thc blue horizontal branch (HB) stars compared to the red HB stars. In this Letter, wc test this scenario in the case of the Galactic globular cluster M3 (NGC 5272), using high-precision Stromgren photometry and spectroscopic gravities for blue HB stars. We find that any helium enhancement among the cluster's blue HB stars must be significantly less than I%, thus ruling out the much higher helium enhancements that have been proposed in the literature.

  13. VizieR Online Data Catalog: NGC 288 hot horizontal branch stars abundances (Moehler+, 2014)

    NASA Astrophysics Data System (ADS)

    Moehler, S.; Dreizler, S.; Leblanc, F.; Khalack, V.; Michaud, G.; Richer, J.; Sweigart, A. V.; Grundahl, F.

    2014-03-01

    Temperatures, surface gravities, and abundances for hot (Teff>9000K) horizontal branch stars in NGC 288 as derived from medium-resolution FLAMES-GIRAFFE spectra (resolution about 0.7Å). Effective temperatures and surface gravities are derived from line profile fits. The abundances were derived via spectrum synthesis, using the presviously defined effective temperature and surface gravity. Errors are about ±5% in Teff, ±0.1 in logg, ±0.2 (He), ±0.28 (Mg), ±0.34 (Si, P, Fe), ±0.58 (Ti, Mn, Ni). 0.00 means that no abundance could be determined. (2 data files).

  14. THE PECULIAR PROPERTIES OF HORIZONTAL-BRANCH STARS IN {omega} CENTAURI

    SciTech Connect

    Moni Bidin, C.; Villanova, S.; Piotto, G.; Moehler, S.; D'Antona, F.

    2011-09-01

    We measured temperatures, gravities, and masses for a large sample of blue horizontal-branch stars in {omega} Centauri, comparing the results with theoretical expectations for canonical and He-enriched stars, and with previous measurements in three other clusters. The measured gravities of {omega} Cen stars are systematically lower than canonical models, in agreement with expectations for He-enriched stars, and contrary to that observed in the comparison clusters. However, the derived masses are unrealistically too low as well. This cannot be explained by low gravities alone, nor by any of the other parameters entering the calculation. We find that the same stars are not brighter than their analogs in the other clusters, contrary to the expectations of the He-enrichment scenario. The interpretation of the results is thus not straightforward, but they reveal an intrinsic, physical difference between HB stars in {omega} Cen and in the three comparison clusters.

  15. CNO abundances of some field horizontal-branch and Population I A stars

    NASA Technical Reports Server (NTRS)

    Adelman, S. J.; Hayes, D. S.; Davis Philip, A. G.

    1986-01-01

    From observations of infrared lines, oxygen and nitrogen abundances of the prototype field horizontal-branch stars HD 109995 and HD 161817, the somewhat similar star HD 64488, and the sharp-lined Population I A stars Theta Leo and HR 6559 have been obtained, as well as carbon abundances of HD 161817 and Theta Leo. The results for HD 161817 may be in accord with the predictions of Sweigart and Mengel (1979) for dredge-up during the previous red-giant stage if the non-LTE effects for the O I lines have been properly accounted for, and those for the C I and N I lines are small. This star and HD 109995 are apparently both oxygen and nitrogen poor to the same degree although their iron abundances differ by 0.3 dex.

  16. Deep HST Photometry of NGC 6388: Age and Horizontal Branch Luminosity

    NASA Technical Reports Server (NTRS)

    Stetson, Peter B.; Catelan, M.; Pritzl, Barton J.; Smith, Horace A.; Kinemuchi, Karen; Layden, Andrew C.; Sweigart, Allen V.; Rich, R. M.

    2006-01-01

    We present the first deep color-magnitude diagram (CMD) of the Galactic globular cluster NGC 6388, obtained with the Hubble Space Telescope, that is able to reach the main-sequence turnoff point of the cluster. From a detailed comparison between the cluster CMD and that of 47 Tucanae (NGC 104), we find that the bulk of the stars in these two clusters have nearly the same age and chemical composition. On the other hand, our results indicate that the blue horizontal branch and RR Lyrae components in NGC 6388 are intrinsically over-luminous, which must be due to one or more, still undetermined, non-canonical second parameter(s) affecting a relatively minor fraction of the stars in NGC 6388.

  17. THE STRUCTURE OF THE SAGITTARIUS STELLAR STREAM AS TRACED BY BLUE HORIZONTAL BRANCH STARS

    SciTech Connect

    Ruhland, Christine; Rix, Hans-Walter; Bell, Eric F.; Xue Xiangxiang

    2011-04-20

    We use a sample of blue horizontal branch (BHB) stars from the Sloan Digital Sky Survey Data Release 7 to explore the structure of the tidal tails from the Sagittarius Dwarf Galaxy. We use a method yielding BHB star candidates with up to {approx}70% purity from photometry alone. The resulting sample has a distance precision of roughly 5% and can probe distances in excess of 100 kpc. Using this sample, we identify a possible extension to the trailing arm at distances of 60-80 kpc from the Sun with an estimated significance of at least 3.8{sigma}. Current models predict that a distant 'returning' segment of the debris stream should exist, but place it substantially closer to the Sun where no debris is observed in our data. Exploiting the distance precision of our tracers, we estimate the mean line-of-sight thickness of the leading arm to be {approx}3 kpc, and show that the two 'bifurcated' branches of the debris stream differ by only 1-2 kpc in distance. With a spectroscopic very pure BHB star subsample, we estimate the velocity dispersion in the leading arm, 37 km s{sup -1}, which is in reasonable agreement with models of Sgr disruption. We finally present a sample of high-probability Sgr BHB stars in the leading arm of Sgr, selected to have distances and velocities consistent with Sgr membership, to allow further study.

  18. The mosaic multiple stellar populations in ω Centauri: the horizontal branch and the main sequence

    NASA Astrophysics Data System (ADS)

    Tailo, M.; Di Criscienzo, M.; D'Antona, F.; Caloi, V.; Ventura, P.

    2016-04-01

    We interpret the stellar population of ω Centauri by means of a population synthesis analysis, following the most recent observational guidelines for input metallicities, helium and [(C+N+O)/Fe] contents. We deal at the same time with the main sequences, sub-giant and horizontal branch (HB) data. The reproduction of the observed colour-magnitude features is very satisfying and bears interesting hints concerning the evolutionary history of this peculiar stellar ensemble. Our main results are: (1) no significant spread in age is required to fit the colour-magnitude diagram. Indeed, we can use coeval isochrones for the synthetic populations, and we estimate that the ages fall within a ˜0.5 Gyr time interval; in particular the most metal-rich population can be coeval (in the above meaning) with the others, if its stars are very helium-rich (Y ˜ 0.37) and with the observed CNO enhancement ([(C+N+O)/Fe] = +0.7); (2) a satisfactory fit of the whole HB is obtained, consistent with the choice of the populations providing a good reproduction of the main sequence and sub-giant data; (3) the split in magnitude observed in the red HB is well reproduced assuming the presence of two stellar populations in the two different sequences observed: a metal-poor population made of stars evolving from the blue side (luminous branch) and a metal richer one whose stars are in a stage closer to the zero age HB (dimmer branch). This modelization also fits satisfactorily the period and the [Fe/H] distribution of the RR Lyrae stars.

  19. VizieR Online Data Catalog: Horizontal branch stars in 47 Tuc and M5 (Gratton+, 2013)

    NASA Astrophysics Data System (ADS)

    Gratton, R. G.; Lucatello, S.; Sollima, A.; Carretta, E.; Bragaglia, A.; Momany, Y.; D'Orazi, V.; Cassisi, S.; Pietrinferni, A.; Salaris, M.

    2012-10-01

    Tables with basic data and abundances for 110 HB stars in 47 Tuc and 92 Horizontal-Branch (HB) stars in M5. The observations were made with the GIRAFFE fibre-fed spectrograph at the VLT in March 2011 (47 Tuc) and June 2011 (M5). (5 data files).

  20. The distance scale to globular clusters through new horizontal branch models.

    NASA Astrophysics Data System (ADS)

    Caloi, V.; D'Antona, F.; Mazzitelli, I.

    1997-04-01

    As a completion of preceding work (Mazzitelli et al. 1995A&A...302..382M), we present new horizontal branch models with mass fractions of heavy element content Z=2x10^-4^ and 6x10^-4^; we discuss the complete set of models with Z from 10^-4^ to 3x10^-3^, and their implications for the ages of galactic globular clusters. Models at low Z are ~0.15mag more luminous than equivalent models of the previous generation, implying a reduction of globular cluster ages of ~2Gyr. Half of this effect depends on the core masses at the helium flash, which are larger by 0.007Msun_ at Z=10^-4^; the remaining half depends on the new microphysical inputs (equation of state and opacities) in present models. The distance scale resulting from these new models for [Fe/H]<~-1 is consistent with Sandage (1993) and Walker (1992) scales, but not with Carney et al. (1992) scale. The relation M_v_(ZAHB) vs. [Fe/H] is not linear, so that the notion of slope turns out to be an elusive one, and in any case depending on the range of [Fe/H] considered. New computations of the core mass at the helium flash are presented and discussed. We finally show that the luminosity at the tip of the giant branch obtained in our computations is compatible with the maximum luminosity of giants observed in globular clusters by Frogel et al. (1983).

  1. A SEARCH FOR FIELD HORIZONTAL-BRANCH STARS NEAR THE SOUTH GALACTIC POLE

    SciTech Connect

    Ortiz, R.; Wilhelm, R.; Costa, R. D. D.; Rossi, S.

    2010-03-15

    Searches for field horizontal-branch (FHB) stars in the halo of the Galaxy in the past have been carried out by several techniques, such as objective-prism surveys and visual or infrared photometric surveys. By choosing adequate color criteria, it is possible to improve the efficiency of identifying bona fide FHB stars among the other objects that exhibit similar characteristics, such as main-sequence A-stars, blue stragglers, subdwarfs, etc. In this work, we report the results of a spectroscopic survey carried out near the south Galactic pole intended to validate FHB stars originally selected from the HK objective-prism survey of Beers and colleagues, based on near-infrared color indices. A comparison between the stellar spectra obtained in this survey with theoretical stellar atmosphere models allows us to determine T {sub eff}, log g, and [Fe/H] for 13 stars in the sample. Stellar temperatures were calculated from measured (B - V) {sub o}, when this measurement was available (16 stars). The color index criteria adopted in this work are shown to correctly classify 30% of the sample as FHB, 25% as non-FHB (main-sequence stars and subdwarfes), whereas 40% could not be distinguished between FHB and main-sequence stars. We compare the efficacy of different color criteria in the literature intended to select FHB stars, and discuss the use of the Mg II 4481 line to estimate the metallicity.

  2. RAPIDLY PULSATING HOT SUBDWARFS IN {omega} CENTAURI: A NEW INSTABILITY STRIP ON THE EXTREME HORIZONTAL BRANCH?

    SciTech Connect

    Randall, S. K.; Calamida, A.; Fontaine, G.; Brassard, P.; Bono, G.

    2011-08-20

    Pulsating extreme horizontal branch (EHB) stars offer the unique opportunity to use asteroseismology to probe their fundamental parameters and thus constrain one of the more poorly understood phases of stellar evolution. However, they have been observed only among the field population, which necessarily prevents asteroseismological tools from being applied to globular cluster EHB stars. We launched a search for rapid EHB pulsators in {omega} Cen on the basis of fast time-series photometry obtained with EFOSC2 at the New Technology Telescope. Fourier analysis uncovered four multi-mode oscillators with rather similar periods between 84 and 124 s and amplitudes up to 2.7% of the mean stellar brightness. Initially, it was assumed that these stars constitute the globular cluster counterparts to the EC 14026 stars, rapid subdwarf B pulsators with T{sub eff} {approx} 31,000 K that have been extensively studied among the field population, yet a subsequent atmospheric analysis of FORS MXU spectra reveals effective temperatures closely clustered around 50,000 K, implying that the four {omega} Cen variables are in fact helium-poor subdwarf O (sdO) stars rather than EC 14026 pulsators. It remains to be seen whether they are related to the one significantly hotter sdO oscillator known among the field star population, or belong to a hitherto unknown class of stellar pulsator that can now be subjected to asteroseismological scrutiny.

  3. Constraints on helium enhancement in the globular cluster M4 (NGC 6121): The horizontal branch test

    SciTech Connect

    Valcarce, A. A. R.; De Medeiros, J. R.; Catelan, M.; Alonso-García, J.; Cortés, C.

    2014-02-20

    Recent pieces of evidence have revealed that most, and possibly all, globular star clusters are composed of groups of stars that formed in multiple episodes with different chemical compositions. In this sense, it has also been argued that variations in the initial helium abundance (Y) from one population to the next are also the rule, rather than the exception. In the case of the metal-intermediate globular cluster M4 (NGC 6121), recent high-resolution spectroscopic observations of blue horizontal branch (HB) stars (i.e., HB stars hotter than the RR Lyrae instability strip) suggest that a large fraction of blue HB stars are second-generation stars formed with high helium abundances. In this paper, we test this scenario by using recent photometric and spectroscopic data together with theoretical evolutionary computations for different Y values. Comparing the photometric data with the theoretically derived color-magnitude diagrams, we find that the bulk of the blue HB stars in M4 have ΔY ≲ 0.01 with respect to the cluster's red HB stars (i.e., HB stars cooler than the RR Lyrae strip)—a result which is corroborated by comparison with spectroscopically derived gravities and temperatures, which also favor little He enhancement. However, the possible existence of a minority population on the blue HB of the cluster with a significant He enhancement level is also discussed.

  4. THE CHEMICAL COMPOSITIONS OF VARIABLE FIELD HORIZONTAL-BRANCH STARS: RR LYRAE STARS

    SciTech Connect

    For Biqing; Sneden, Christopher; Preston, George W.

    2011-12-01

    We present a detailed abundance study of 11 RR Lyrae ab-type variables: AS Vir, BS Aps, CD Vel, DT Hya, RV Oct, TY Gru, UV Oct, V1645 Sgr, WY Ant, XZ Aps, and Z Mic. High-resolution and high signal-to-noise ratio echelle spectra of these variables were obtained with the 2.5 m du Pont telescope at the Las Campanas Observatory. We obtained more than 2300 spectra, roughly 200 spectra per star, distributed more or less uniformly throughout the pulsational cycles. A new method has been developed to obtain the initial effective temperatures of our sample stars at a specific pulsational phase. We find that the abundance ratios are generally consistent with those of similar metallicity field stars in different evolutionary states and throughout the pulsational cycles for RR Lyrae stars. TY Gru remains the only n-capture enriched star among the RRab in our sample. A new relation is found between microturbulence and effective temperature among stars of the horizontal-branch population. In addition, the variation of microturbulence as a function of phase is empirically shown to be similar to the theoretical variation. Finally, we conclude that the derived T{sub eff} and log g values of our sample stars follow the general trend of a single mass evolutionary track.

  5. The Chemical Compositions of Variable Field Horizontal-branch Stars: RR Lyrae Stars

    NASA Astrophysics Data System (ADS)

    For, Bi-Qing; Sneden, Christopher; Preston, George W.

    2011-12-01

    We present a detailed abundance study of 11 RR Lyrae ab-type variables: AS Vir, BS Aps, CD Vel, DT Hya, RV Oct, TY Gru, UV Oct, V1645 Sgr, WY Ant, XZ Aps, and Z Mic. High-resolution and high signal-to-noise ratio echelle spectra of these variables were obtained with the 2.5 m du Pont telescope at the Las Campanas Observatory. We obtained more than 2300 spectra, roughly 200 spectra per star, distributed more or less uniformly throughout the pulsational cycles. A new method has been developed to obtain the initial effective temperatures of our sample stars at a specific pulsational phase. We find that the abundance ratios are generally consistent with those of similar metallicity field stars in different evolutionary states and throughout the pulsational cycles for RR Lyrae stars. TY Gru remains the only n-capture enriched star among the RRab in our sample. A new relation is found between microturbulence and effective temperature among stars of the horizontal-branch population. In addition, the variation of microturbulence as a function of phase is empirically shown to be similar to the theoretical variation. Finally, we conclude that the derived T eff and log g values of our sample stars follow the general trend of a single mass evolutionary track.

  6. A helium-carbon correlation on the extreme horizontal branch in ω Centauri

    SciTech Connect

    Latour, M.; Fontaine, G.; Brassard, P.; Randall, S. K.; Bono, G.; Calamida, A.

    2014-11-10

    Taking advantage of a recent FORS2/VLT spectroscopic sample of extreme horizontal branch (EHB) stars in ω Cen, we isolate 38 spectra well suited for detailed atmospheric studies and determine their fundamental parameters (T {sub eff}, log g, and log N(He)/N(H)) using NLTE, metal line-blanketed models. We find that our targets can be divided into three groups: 6 stars are hot (T {sub eff} ≳ 45,000 K) H-rich subdwarf O stars, 7 stars are typical H-rich sdB stars (T {sub eff} ≲ 35,000 K), and the remaining 25 targets at intermediate effective temperatures are He-rich (log N(He)/N(H) ≳ –1.0) subdwarfs. Surprisingly, and quite interestingly, these He-rich hot subdwarfs in ω Cen cluster in a narrow temperature range (∼35,000 K to ∼40,000 K). We additionally measure the atmospheric carbon abundance and find a most interesting positive correlation between the carbon and helium atmospheric abundances. This correlation certainly bears the signature of diffusion processes—most likely gravitational settling impeded by stellar winds or internal turbulence—but also constrains possible formation scenarios proposed for EHB stars in ω Cen. For the He-rich objects in particular, the clear link between helium and carbon enhancement points toward a late hot flasher evolutionary history.

  7. A giant planet orbiting the 'extreme horizontal branch' star V 391 Pegasi.

    PubMed

    Silvotti, R; Schuh, S; Janulis, R; Solheim, J-E; Bernabei, S; Østensen, R; Oswalt, T D; Bruni, I; Gualandi, R; Bonanno, A; Vauclair, G; Reed, M; Chen, C-W; Leibowitz, E; Paparo, M; Baran, A; Charpinet, S; Dolez, N; Kawaler, S; Kurtz, D; Moskalik, P; Riddle, R; Zola, S

    2007-09-13

    After the initial discoveries fifteen years ago, over 200 extrasolar planets have now been detected. Most of them orbit main-sequence stars similar to our Sun, although a few planets orbiting red giant stars have been recently found. When the hydrogen in their cores runs out, main-sequence stars undergo an expansion into red-giant stars. This expansion can modify the orbits of planets and can easily reach and engulf the inner planets. The same will happen to the planets of our Solar System in about five billion years and the fate of the Earth is matter of debate. Here we report the discovery of a planetary-mass body (Msini = 3.2M(Jupiter)) orbiting the star V 391 Pegasi at a distance of about 1.7 astronomical units (au), with a period of 3.2 years. This star is on the extreme horizontal branch of the Hertzsprung-Russell diagram, burning helium in its core and pulsating. The maximum radius of the red-giant precursor of V 391 Pegasi may have reached 0.7 au, while the orbital distance of the planet during the stellar main-sequence phase is estimated to be about 1 au. This detection of a planet orbiting a post-red-giant star demonstrates that planets with orbital distances of less than 2 au can survive the red-giant expansion of their parent stars. PMID:17851517

  8. Rotation and Macroturbulence in Metal-Poor Field Red Giant and Red Horizontal Branch Stars

    NASA Astrophysics Data System (ADS)

    Carney, Bruce W.; Gray, David F.; Yong, David; Latham, David W.; Manset, Nadine; Zelman, Rachel; Laird, John B.

    2008-03-01

    We report the results for rotational velocities, Vrot sin i, and macroturbulence dispersions, ζRT, for 12 metal-poor field red giant branch (RGB) stars and 7 metal-poor field red horizontal branch (RHB) stars. The results are based on Fourier transform analyses of absorption line profiles from high-resolution (R ≈ 120,000), high-S/N (≈215 per pixel; ≈345 per resolution element) spectra obtained with the Gecko spectrograph at the Canada-France-Hawaii Telescope (CFHT). The stars were selected from the authors' previous studies of 20 RHB and 116 RGB stars, based primarily on larger-than-average line-broadening values. We find that ζRT values for the metal-poor RGB stars are very similar to those for metal-rich disk giants studied earlier by Gray and his collaborators. Six of the RGB stars have small rotational values, less than 2.0 km s-1, while five show significant rotation/enhanced line broadening, over 3 km s-1. We confirm the rapid rotation rate for RHB star HD 195636, found earlier by Preston. This star's rotation is comparable to that of the fastest known rotating blue horizontal branch (BHB) stars, when allowance is made for differences in radii and moments of inertia. The other six RHB stars have somewhat lower rotation but show a trend to higher values at higher temperatures (lower radii). Comparing our results with those for BHB stars from Kinman et al., we find that the fraction of rapidly rotating RHB stars is somewhat lower than is found among BHB stars. The number of rapidly rotating RHB stars is also smaller than we would have expected from the observed rotation of the RGB stars. We devise two empirical methods to translate our earlier line-broadening results into Vrot sin i for all the RGB and RHB stars they studied. Binning the RGB stars by luminosity, we find that most metal-poor field RGB stars show no detectable sign, on average, of rotation, which is not surprising given the stars' large radii. However, the most luminous stars, with MV

  9. FAKE STAR FORMATION BURSTS: BLUE HORIZONTAL BRANCH STARS MASQUERADE AS YOUNG MASSIVE STARS IN OPTICAL INTEGRATED LIGHT SPECTROSCOPY

    SciTech Connect

    Ocvirk, P.

    2010-01-20

    Model color-magnitude diagrams of low-metallicity globular clusters (GCs) usually show a deficit of hot evolved stars with respect to observations. We investigate quantitatively the impact of such modeling inaccuracies on the significance of star formation history reconstructions obtained from optical integrated spectra. To do so, we analyze the sample of spectra of galactic globular clusters of Schiavon et al. with STECKMAP (Ocvirk et al.), and the stellar population models of Vazdekis et al. and Bruzual and Charlot, and focus on the reconstructed stellar age distributions. First, we show that background/foreground contamination correlates with E(B - V), which allows us to define a clean subsample of uncontaminated GCs, on the basis of an E(B - V) filtering. We then identify a 'confusion zone' where fake young bursts of star formation pop up in the star formation history although the observed population is genuinely old. These artifacts appear for 70%-100% of cases depending on the population model used, and contribute up to 12% of the light in the optical. Their correlation with the horizontal branch (HB) ratio indicates that the confusion is driven by HB morphology: red HB clusters are well fitted by old stellar population models while those with a blue HB require an additional hot component. The confusion zone extends over [Fe/H] = [ - 2, - 1.2], although we lack the data to probe extreme high and low metallicity regimes. As a consequence, any young starburst superimposed on an old stellar population in this metallicity range could be regarded as a modeling artifact, if it weighs less than 12% of the optical light, and if no emission lines typical of an H II region are present. This work also provides a practical method for constraining HB morphology from high signal to noise integrated light spectroscopy in the optical. This will allow post-asymptotic giant branch evolution studies in a range of environments and at distances where resolving stellar populations

  10. The Origin of Hot Subluminous Horizontal-Branch Stars in Omega Centauri and NGC 2808

    NASA Technical Reports Server (NTRS)

    Sweigart, Allen V.; Brown, T. M.; Lanz, T.; Landsman, W. B.; Hubeny, I.; Fisher, Richard R. (Technical Monitor)

    2001-01-01

    Hot subluminous stars lying up to 0.7 mag below the extreme horizontal branch (EHB) are found in the ultraviolet color-magnitude diagrams of both omega Cen (DCruz et.al. 2000) and NGC 2808 (Brown et al. 2001). In order to investigate the origin of these subluminous stars, we have constructed a detailed set of evolutionary sequences that follow the evolution of low-mass stars continuously from the zero-age main sequence through the helium-core flash to the HB for a wide range in the mass loss along the red-giant branch (RGB). Stars with the largest mass loss evolve off the RGB to high effective temperatures before igniting helium in their cores (Castellani & Castellani 1993). Our results indicate that the location of the subluminous EHB stars, as well as the high temperature gap along the EHB of NGC 2808, can be explained if these stars undergo a late helium-core flash while descending the white-dwarf cooling curve. Under these conditions the convection zone produced by the main helium flash will penetrate into the stellar envelope, thereby mixing most, if not all, of the envelope hydrogen into the hot helium-burning interior, where it is rapidly consumed (Sweigart 1997). This phenomenon is analogous to the "born-again" scenario for producing hydrogen-deficient stars following a very late helium-shell flash. This "flash mixing" of the envelope during a late helium-core flash greatly enhances the envelope helium and carbon abundances and, as a result, leads to a discontinuous increase in the HB effective temperature. We argue that the hot HB gap observed in NGC 2808 is associated with this theoretically predicted dichotomy in the HB properties. Using new helium- and carbon-rich stellar atmospheres, we show that the changes in the envelope abundances due to flash mixing will suppress the ultraviolet flux in the spectra of hot EHB stars. We suggest that such changes in the emergent spectral energy distribution are primarily responsible for explaining the hot

  11. A New Formation Mechanism for the Hottest Horizontal-Branch Stars

    NASA Technical Reports Server (NTRS)

    Sweigart, Allen V.; Oegerle, William R. (Technical Monitor)

    2002-01-01

    Hot subluminous stars lying up to 0.7 mag below the extreme horizontal branch (EHB) are found in the ultraviolet color-magnitude diagrams (CMDs) of both omega Cen and NGC 2808. In order to investigate the origin of these subluminous stars, we have constructed a detailed set of evolutionary sequences that follow the evolution of low-mass stars continuously from the zero-age main sequence through the helium-core flash to the HB for a wide range in the mass loss along the red-giant branch (RGB). Stars with the largest mass loss evolve off the RGB to high effective temperatures before igniting helium in their cores. Our results indicate that the subluminous EHB stars, as well as the high temperature gap along the EHB of NGC 2808, can be explained if these stars undergo a late helium-core flash while descending the white-dwarf cooling curve. Under these conditions the convection zone produced by the main helium flash will penetrate into the stellar envelope, thereby mixing most, if not all, of the envelope hydrogen into the hot helium-burning interior, where it is rapidly consumed. This phenomenon is analogous to the 'born-again' scenario for producing hydrogen-deficient stars following a very late helium-shell flash. This 'flash mixing' of the envelope during a late helium-core flash greatly enhances the envelope helium and carbon abundances and, as a result, leads to a discontinuous increase in the HB effective temperature. We argue that the hot HB gap observed in NGC 2808 is associated with this theoretically predicted dichotomy in the RB properties. Using new helium- and carbon-rich stellar atmospheres, we show that the changes in the envelope abundances due to flash mixing will suppress the ultraviolet flux in the spectra of hot EHB stars. We suggest that such changes in the emergent spectral energy distribution are primarily responsible for explaining the hot subluminous EHB stars in omega Cen and NGC 2808. Moreover, we demonstrate that models without flash mixing

  12. Origins of the Kilohertz and Horizontal Branch QPOs in the Z Sources

    NASA Astrophysics Data System (ADS)

    Lamb, F. K.; Miller, M. C.; Psaltis, D.

    1999-04-01

    The frequency relationships observed between the upper and lower kilohertz QPOs and the ~ 10--60 Hz horizontal branch oscillations (HBOs) in the Z sources are important indicators of the mechanisms that produce them. We show that in the sonic point model of the kilohertz QPOs, the frequency separation between them is approximately equal to the stellar spin frequency nu_spin , but generally differs from nu_spin and varies with the mass accretion rate. For plausible models of the inner accretion disk, the frequency separation decreases with increasing accretion rate, in quantitative agreement with the variation of the frequency separation observed in Sco X-1. If the moments of inertia of neutron stars have the sizes expected theoretically and their spin frequencies in the Z sources are approximately equal to the frequency separation of the kilohertz QPOs, the Lense-Thirring precession model of the HBOs can account for the frequencies of the HBOs only if the HBO frequency is at least four times the precession frequency. Moreover, the correlation observed between the frequencies of the HBO and the upper kilohertz QPO cannot be accounted for in the Lense-Thirring precession model, even when the effects of classical precession are taken into account. In contrast, the magnetospheric beat-frequency model of the HBOs predicts a power-law relation between HBO frequency and upper kilohertz QPO frequency that is consistent with the relation observed, if the frequency of the upper kilohertz QPO is an orbital frequency in the inner disk. The Z-source magnetic fields inferred from the model are ~ 10(9) --10(10) G.

  13. A Search for Field Horizontal-Branch Stars Near the South Galactic Pole

    NASA Astrophysics Data System (ADS)

    Ortiz, R.; Wilhelm, R.; Costa, R. D. D.; Rossi, S.; Beers, T. C.

    2010-03-01

    Searches for field horizontal-branch (FHB) stars in the halo of the Galaxy in the past have been carried out by several techniques, such as objective-prism surveys and visual or infrared photometric surveys. By choosing adequate color criteria, it is possible to improve the efficiency of identifying bona fide FHB stars among the other objects that exhibit similar characteristics, such as main-sequence A-stars, blue stragglers, subdwarfs, etc. In this work, we report the results of a spectroscopic survey carried out near the south Galactic pole intended to validate FHB stars originally selected from the HK objective-prism survey of Beers and colleagues, based on near-infrared color indices. A comparison between the stellar spectra obtained in this survey with theoretical stellar atmosphere models allows us to determine T eff, log g, and [Fe/H] for 13 stars in the sample. Stellar temperatures were calculated from measured (B - V) o , when this measurement was available (16 stars). The color index criteria adopted in this work are shown to correctly classify 30% of the sample as FHB, 25% as non-FHB (main-sequence stars and subdwarfes), whereas 40% could not be distinguished between FHB and main-sequence stars. We compare the efficacy of different color criteria in the literature intended to select FHB stars, and discuss the use of the Mg II 4481 line to estimate the metallicity. Based on observations obtained at the Pico dos Dias Observatory, operated by the National Laboratory for Astrophysics, Brazil.

  14. A Search for Extreme Horizontal Branch Stars in the General Field Population (Abstract)

    NASA Astrophysics Data System (ADS)

    Walker, D.; Albrow, M.

    2014-12-01

    (Abstract only) The study of pulsating Extreme Horizontal Branch (EHB) stars in globular clusters is a new field of stellar research. The initial discovery of three rapidly pulsating EHB stars in w Centauri was announced at the Fourth Meeting on Hot Subdwarfs and Related Objects held in Shanghai in July 2009. A fourth sdB pulsator was discovered in the remaining photometry data soon afterwards; all were discovered in data obtained by the New Techology Telescope. In March 2013, the Space Telescope Imaging Spectrograph (STIS) was utilized on five consecutive orbits to obtain far-UV imagery of NGC 2808’s core, revealing six sdB pulsators with periods 85 to 149 seconds and UV amplitudes from 2.0 to 6.8%. To date (April 2014), these ten EHB pulsators in w Centauri and NGC 2808 form a unique class of EHB variable closely clustered around Teff ~ 50,000 K. This talk describes an initial candidate search for EHB rapidly pulsating sdB stars in the general galactic field population. The search was conducted with the 1-m McLellan telescope at the Mt. John University Observatory (MJUO) at Lake Tekapo, New Zealand. Observations were conducted utilizing a special high speed f/8 frame-transfer camera called the Puoko-nui. The candidate set of stars was taken from the Edinburgh-Cape Blue Object Survey based on the selection criteria of a (B-V) value of -0.32 to -0.36, corresponding to the desired temperature range Teff ranging from 40,000 to 64,000 K. The objective of this search was to determine whether smaller size telescopes could identify promising sets of candidate sdB pulsators which could be followed up with larger professional systems.

  15. Vertical abundance stratification in the blue horizontal branch star HD 135485

    NASA Astrophysics Data System (ADS)

    Khalack, V. R.; Leblanc, F.; Bohlender, D.; Wade, G. A.; Behr, B. B.

    2007-05-01

    Context: It is commonly believed that the observed overabundances of many chemical species relative to the expected cluster metallicity in blue horizontal branch (BHB) stars appear as a result of atomic diffusion in the photosphere. The slow rotation of BHB stars (with T_eff > 11 500 K), typically v sin{i} < 10 km s-1, is consistent with this idea. Aims: In this work we search for observational evidence of vertical chemical stratification in the atmosphere of HD 135485. If this evidence exists, it will demonstrate the importance of atomic diffusion processes in the atmospheres of BHB stars. Methods: We undertake an extensive abundance stratification analysis of the atmosphere of HD 135485, based on recently acquired high resolution and S/N CFHT ESPaDOnS spectra and a McDonald-CE spectrum. Results: Our numerical simulations show that nitrogen and sulfur reveal signatures of vertical abundance stratification in the stellar atmosphere. It appears that the abundances of these elements increase toward the upper atmosphere. This fact cannot be explained by the influence of microturbulent velocity, because oxygen, carbon, neon, argon, titanium and chromium do not show similar behavior and their abundances remain constant throughout the atmosphere. It seems that the iron abundance may increase marginally toward the lower atmosphere. This is the first demonstration of vertical abundance stratification of metals in a BHB star. Based on observations made with ESPaDOnS at the Canada-France-Hawaii Telescope (CFHT) operated by the National Research Council (NRC) of Canada, the Institut des Sciences de l'Univers of the Centre National de la Recherche Scientifique (CNRS) and the University of Hawaii and on observations made with Echelle Spectrograph on the McDonald Observatory 2.1-m Otto Struve Telescope. Full Table 2 is only available in electronic form at http://www.aanda.org

  16. Chronography of the Milky Way's Halo System with Field Blue Horizontal-branch Stars

    NASA Astrophysics Data System (ADS)

    Santucci, Rafael M.; Beers, Timothy C.; Placco, Vinicius M.; Carollo, Daniela; Rossi, Silvia; Lee, Young Sun; Denissenkov, Pavel; Tumlinson, Jason; Tissera, Patricia B.

    2015-11-01

    In a pioneering effort, Preston et al. reported that the colors of blue horizontal-branch (BHB) stars in the halo of the Galaxy shift with distance, from regions near the Galactic center to about 12 kpc away, and interpreted this as a correlated variation in the ages of halo stars, from older to younger, spanning a range of a few Gyrs. We have applied this approach to a sample of some 4700 spectroscopically confirmed BHB stars selected from the Sloan Digital Sky Survey to produce the first “chronographic map” of the halo of the Galaxy. We demonstrate that the mean de-reddened g - r color, < {(g-r)}0> , increases outward in the Galaxy from -0.22 to -0.08 (over a color window spanning [-0.3: 0.0]) from regions close to the Galactic center to ˜40 kpc, independent of the metallicity of the stars. Models of the expected shift in the color of the field BHB stars based on modern stellar evolutionary codes confirm that this color gradient can be associated with an age difference of roughly 2-2.5 Gyr, with the oldest stars concentrated in the central ˜15 kpc of the Galaxy. Within this central region, the age difference spans a mean color range of about 0.05 mag (˜0.8 Gyr). Furthermore, we show that chronographic maps can be used to identify individual substructures, such as the Sagittarius Stream, and overdensities in the direction of Virgo and Monoceros, based on the observed contrast in their mean BHB colors with respect to the foreground/background field population.

  17. Detailed abundance analysis of five field blue horizontal-branch stars

    NASA Astrophysics Data System (ADS)

    Kafando, I.; LeBlanc, F.; Robert, C.

    2016-06-01

    Previous studies have shown that hot blue horizontal-branch (BHB) stars in globular clusters present abundance anomalies of certain chemical elements in their atmosphere; some metals are overabundant while helium is underabundant. Vertical stratification of chemical species, including iron, is also found in the atmosphere of a number of these objects. The aim of our work is to do a detailed abundance analysis of BHB stars found in the field. We studied the stars HD 128801, HD 143459, HD 213781, and HZ 27, using our high-resolution spectra in the visible region obtained with ESPaDOnS at the Canada-France-Hawaii Telescope, and also Feige 86, using existing Ultraviolet and Visual Echelle Spectrograph visible spectra from the ESO archives. We searched for vertical stratification of the elements identified in our five stars, with the ZEEMAN2 code and stellar model atmospheres of PHOENIX. We confirm here the star rotational and radial velocities previously found, along with their average abundances. For the three cooler stars in our sample (HD 128801, HD 143459, and HZ 27), most elements detected are underabundant. For the two hotter stars (Feige 86 and HD 213781), the abundances of most elements are near or above their solar value. Of all the elements studied, only phosphorus is clearly found to be vertically stratified in the atmosphere of HD 213781. Marginal indications of vertical stratification of iron is observed for Feige 86. The chemical properties of the five field BHB stars are consistent with those of their globular-cluster counterparts.

  18. Characterizing stellar halo populations II: The age gradient in blue horizontal-branch stars

    NASA Astrophysics Data System (ADS)

    Das, Payel; Williams, Angus; Binney, James

    2016-08-01

    The distribution of Milky Way halo blue horizontal-branch (BHB) stars is examined using action-based extended distribution functions (EDFs) that describe the locations of stars in phase space, metallicity, and age. The parameters of the EDFs are fitted using stars observed in the Sloan Extension for Galactic Understanding and Exploration-II (SEGUE-II) survey that trace the phase-space kinematics and chemistry out to ˜70 kpc. A maximum a posteriori probability (MAP) estimate method and a Markov Chain Monte Carlo method are applied, taking into account the selection function in positions, distance, and metallicity for the survey. The best-fit EDF declines with actions less steeply at actions characteristic of the inner halo than at the larger actions characteristic of the outer halo, and older ages are found at smaller actions than at larger actions. In real space, the radial density profile steepens smoothly from -2 at ˜2 kpc to -4 in the outer halo, with an axis ratio ˜0.7 throughout. There is no indication for rotation in the BHBs, although this is highly uncertain. A moderate level of radial anisotropy is detected, with βs varying from isotropic to between ˜0.1 and ˜0.3 in the outer halo depending on latitude. The BHB data are consistent with an age gradient of -0.03 Gyr kpc-1, with some uncertainty in the distribution of the larger ages. These results are consistent with a scenario in which older, larger systems contribute to the inner halo, whilst the outer halo is primarily comprised of younger, smaller systems.

  19. CHEMICAL COMPOSITIONS OF THIN-DISK, HIGH-METALLICITY RED HORIZONTAL-BRANCH FIELD STARS

    SciTech Connect

    Afsar, M.; Sneden, C.; For, B.-Q. E-mail: afsar@astro.as.utexas.edu E-mail: biqing@astro.as.utexas.edu

    2012-07-15

    We present a detailed abundance analysis and atmospheric parameters of 76 stars from a survey to identify field Galactic red horizontal-branch (RHB) stars. High-resolution echelle spectra (R {approx_equal} 60,000, S/N {>=} 100) were obtained with the 2.7 m Harlan J. Smith Telescope at McDonald Observatory. The target stars were selected only by color and parallax information. Overall metallicities and relative abundances of proton-capture elements (C, N, O, Li), {alpha}-elements (Ca and Si), and neutron-capture elements (Eu and La) were determined by either equivalent width or synthetic spectrum analyses. We used CN features at the {lambda}{lambda}7995-8040 region in order to determine the {sup 12}C/{sup 13}C ratios of our targets. Investigation of the evolutionary stages, using spectroscopic T{sub eff} and log g values along with derived {sup 12}C/{sup 13}C ratios, revealed the presence of 18 probable RHB stars in our sample. We also derived kinematics of the stars with available distance information. Taking into account both the kinematics and probable evolutionary stages, we conclude that our sample contains 5 thick-disk and 13 thin-disk RHB stars. Up until now, RHB stars have been considered as members of the thick disk, and were expected to have large space velocities and sub-solar metallicities. However, our sample is dominated by low-velocity solar-metallicity RHB stars; their existence cannot be easily explained with standard stellar evolution.

  20. THE KINEMATICS AND CHEMISTRY OF RED HORIZONTAL BRANCH STARS IN THE SAGITTARIUS STREAMS

    SciTech Connect

    Shi, W. B.; Chen, Y. Q.; Carrell, K.; Zhao, G. E-mail: cyq@bao.ac.cn E-mail: gzhao@nao.cas.cn

    2012-06-01

    We have selected 556 red horizontal branch stars along the streams of the Sagittarius (Sgr) dwarf galaxy from Sloan Digital Sky Survey DR7 spectroscopic data using a theoretical model. The metallicity and {alpha}-element distributions are investigated for stars in the Sgr streams and for Galactic stars at the same locations. We find that the Sgr stars have two peaks in the metallicity distribution while the Galactic stars have a more prominent metal-poor peak. Meanwhile, [{alpha}/Fe] ratios of the Sgr stars are lower than those of the Galactic stars. Among the Sgr stars, we find a difference in the metallicity distribution between the leading and trailing arms of the Sgr tidal tails. The metallicity and [{alpha}/Fe] distribution of the leading arm is similar to that of the Galaxy. The trailing arm is composed mainly of a metal-rich component and [{alpha}/Fe] is obviously lower than that of the Galactic stars. The metallicity gradient is -(1.8 {+-} 0.3) Multiplication-Sign 10{sup -3} dex deg{sup -1} in the first wrap of the trailing arm and -(1.5 {+-} 0.4) Multiplication-Sign 10{sup -3} dex deg{sup -1} in the first wrap of the leading arm. No significant gradient exists along the second wraps of the leading or trailing arms. It seems that the Sgr dwarf galaxy initially lost the metal-poor component in the second wrap (older) arms due to the tidal force of our Galaxy and then the metal-rich component is disrupted in the first wrap (younger) arms. Finally, we found that the velocity dispersion of the trailing arm from 88 Degree-Sign < {Lambda}{sub Sun} < 112 Degree-Sign is {sigma} = 9.808 {+-} 1.0 km s{sup -1}, which is consistent with previous work in the literature.

  1. ANCIENT STARS BEYOND THE LOCAL GROUP: RR LYRAE VARIABLES AND BLUE HORIZONTAL BRANCH STARS IN SCULPTOR GROUP DWARF GALAXIES

    SciTech Connect

    Da Costa, G. S.; Jerjen, H.; Rejkuba, M.; Grebel, E. K.

    2010-01-10

    We have used Hubble Space Telescope Advanced Camera for Surveys images to generate color-magnitude diagrams that reach below the magnitude of the horizontal branch in the Sculptor Group dwarf galaxies ESO294-010 and ESO410-005. In both diagrams, blue horizontal branch stars are unambiguously present, a signature of the existence of an ancient stellar population whose age is comparable to that of the Galactic halo globular clusters. The result is reinforced by the discovery of numerous RR Lyrae variables in both galaxies. The occurrence of these stars is the first direct confirmation of the existence of ancient stellar populations beyond the Local Group and indicates that star formation can occur at the earliest epochs even in low-density environments.

  2. A Search for Extreme Horizontal Branch Stars in the General Field Population

    NASA Astrophysics Data System (ADS)

    Walker, Douglas; Albrow, Michael

    2014-05-01

    The study of pulsating Extreme Horizontal Branch (EHB) stars in globular clusters is a new field of stellar research. The initial discovery of three rapidly pulsating EHB stars in omega Centauri was announced at the Fourth Meeting on Hot Subdwarfs and Related Objects held in Shanghai in July 2009. A fourth sdB pulsator was discovered in the remaining photometry data soon afterwards; all discovered in data obtained by the New Technology Telescope. In March 2013, the Space Telescope Imaging Spectrograph (STIS) was utilized on five consecutive orbits to obtain far-UV imagery of NGC 2808's core revealing six sdB pulsators with periods 85 to 149 seconds and UV amplitudes from 2.0 to 6.8%. To date (April, 2014), these 10 EHB pulsators in omega Centauri and NGC 2808 form a unique class of EHB variable closely clustered around Teff ~50,000 K. Based on a lack of information, a more in-depth observational search is needed for sdB variables both in the general field population and other clusters focusing particularly on He-poor sdB stars around and above Teff ~50,000 K. This talk describes an initial candidate search for EHB rapidly pulsating sdB stars in the general galactic field population. The search was conducted with the 1-m McLellan telescope at the Mt John University Observatory (MJUO), at Lake Tekapo, New Zealand. Observations were conducted utilizing a special high speed f/8 frametransfer camera called the Puoko-nui. The candidate set of stars were taken from the Edinburgh-Cape Blue Object Survey based on the selection criteria of a (B-V) value of -0.32 to -0.36 corresponding to the desired temperature range Teff ranging from 40,000 to 64,000 K. The objective of this search was to determine whether smaller size telescopes could identify promising sets of candidate sdB pulsators which could be followed up with larger professional systems.

  3. Chronography of the Milky Way's Halo System with Field Blue Horizontal-Branch Stars

    NASA Astrophysics Data System (ADS)

    Beers, Timothy C.; Placco, Vinicius M.; Carollo, Daniela; Santucci, Rafael; Rossi, Siliva; Lee, Young Sun; Denissenkov, Pavel; Tumlinson, Jason; Tissera, Patricia; Lentner, Geoffrey

    2016-01-01

    In a pioneering effort, Preston et al. (1991, AJ 375, 121) reported that the colors of blue horizontal-branch (BHB) stars in the halo of the Galaxy shift with distance, from regions near the Galactic center to about 12 kpc away, and interpreted this as a correlated variation in the ages of halo stars, from older to younger, spanning a range of a few Gyrs. We have applied this approach to a sample of some 4700 spectroscopically confirmed BHB stars selected from the Sloan Digital Sky Survey to produce the first "chronographic map" of the halo of the Galaxy.We demonstrate that the mean de-reddened g-r color increases outward in the Galaxy from -0.22 to -0.08 (over a color window spanning [-0.3:0.0]) from regions close to the Galactic center to ~40 kpc, independent of the metallicity of the stars. Models of the expected shift in the color of the field BHB stars based on modern stellar evolutionary codes confirm that this color gradient can be associated with an age difference of roughly 2-2.5 Gyrs, with the oldest stars concentrated in the central ~15 kpc of the Galaxy. Within this centralregion, which we refer to as the Ancient Chronographic Sphere (ACS), the age difference spans a mean color range of about 0.05 mag (~0.8 Gyrs). Interestingly, the ACS extends far enough to include the Solar Neighborhood, suggesting that ancient metal-poor stars should be readily detectable in the vicinity of the Sun. Furthermore, we show that chronographic maps can be used to identify individual substructures, such as the Sagittarius Stream, and overdensities in the direction of Virgo and Monoceros, based on the observed contrast in their mean BHB colors with respect to the foreground/background field population.We acknowledge partial support from the grant PHY 14-30152; Physics Frontier Center/JINA Center for the Evolution of the Elements (JINA-CEE), awarded by the US National Science Foundation.

  4. Level of helium enhancement among M3's horizontal branch stars

    NASA Astrophysics Data System (ADS)

    Valcarce, A. A. R.; Catelan, M.; Alonso-García, J.; Contreras Ramos, R.; Alves, S.

    2016-04-01

    Context. The color and luminosity distribution of horizontal branch (HB) stars in globular clusters (GCs) are sensitive probes of the original helium abundances of those clusters. In this sense, recently the distributions of HB stars in GC color-magnitude diagrams (CMDs) have been extensively used as indicators of possible variations in the helium content Y among the different generations of stars within individual GCs. However, recent analyses based on visual and near-ultraviolet (UV) CMDs have provided conflicting results. Aims: To clarify the situation, we address the optimum ranges of applicability (in terms of the Teff range covered by the HB stars) for visual and near-UV CMDs, as far as application of this "HB Y test" goes. Methods: We considered both Strömgren and Hubble Space Telescope (HST) bandpasses. In particular, we focus on the F336W filter of the HST, but also discuss several bluer UV bandpasses, such as F160BW, F255W, and F300W. Using the Princeton-Goddard-PUC (PGPUC) code, we computed a large set of zero-age HB (ZAHB) loci and HB evolutionary models for masses ranging from MHB = 0.582 to 0.800 M⊙, assuming an initial helium abundance Y = 0.246, 0.256, and 0.266, with a global metallicity Z = 0.001. The results of these calculations were compared against the observations of M3 (NGC 5272), with special attention on the y vs. (b - y) and F336W vs. (F336W-F555W) CMDs. Results: Our results indicate that, from an evolutionary perspective, the distributions of HB stars in the y vs. (b - y) plane can be a reliable indicator of the He content in cool blue HB (BHB) stars, particularly when a differential comparison between blue and red HB stars is carried out in the range Teff ≲ 8300 K. Conversely, we demonstrate that CMDs using the F336W filter have a much less straightforward interpretation at the cool end of the BHB because the distributions of HB stars in the F336W vs. (F336W-F555W) plane, for instance, are affected by a triple degeneracy effect. In

  5. Level of helium enhancement among M3's horizontal branch stars

    NASA Astrophysics Data System (ADS)

    Valcarce, A. A. R.; Catelan, M.; Alonso-García, J.; Contreras Ramos, R.; Alves, S.

    2016-05-01

    Context. The color and luminosity distribution of horizontal branch (HB) stars in globular clusters (GCs) are sensitive probes of the original helium abundances of those clusters. In this sense, recently the distributions of HB stars in GC color-magnitude diagrams (CMDs) have been extensively used as indicators of possible variations in the helium content Y among the different generations of stars within individual GCs. However, recent analyses based on visual and near-ultraviolet (UV) CMDs have provided conflicting results. Aims: To clarify the situation, we address the optimum ranges of applicability (in terms of the Teff range covered by the HB stars) for visual and near-UV CMDs, as far as application of this "HB Y test" goes. Methods: We considered both Strömgren and Hubble Space Telescope (HST) bandpasses. In particular, we focus on the F336W filter of the HST, but also discuss several bluer UV bandpasses, such as F160BW, F255W, and F300W. Using the Princeton-Goddard-PUC (PGPUC) code, we computed a large set of zero-age HB (ZAHB) loci and HB evolutionary models for masses ranging from MHB = 0.582 to 0.800 M⊙, assuming an initial helium abundance Y = 0.246, 0.256, and 0.266, with a global metallicity Z = 0.001. The results of these calculations were compared against the observations of M3 (NGC 5272), with special attention on the y vs. (b - y) and F336W vs. (F336W-F555W) CMDs. Results: Our results indicate that, from an evolutionary perspective, the distributions of HB stars in the y vs. (b - y) plane can be a reliable indicator of the He content in cool blue HB (BHB) stars, particularly when a differential comparison between blue and red HB stars is carried out in the range Teff ≲ 8300 K. Conversely, we demonstrate that CMDs using the F336W filter have a much less straightforward interpretation at the cool end of the BHB because the distributions of HB stars in the F336W vs. (F336W-F555W) plane, for instance, are affected by a triple degeneracy effect. In

  6. Patterns of morphological integration in marine modular organisms: supra-module organization in branching octocoral colonies.

    PubMed Central

    Sánchez, Juan Armando; Lasker, Howard R

    2003-01-01

    Despite the relative simplicity of their modular growth, marine invertebrates such as arborescent gorgonian octocorals (Octocorallia: Cnidaria) generate complex colonial forms. Colony form in these taxa is a consequence of modular (polyp) replication, and if there is a tight integration among modular and supramodular traits (e.g. polyp aperture, inter-polyp spacing, branch thickness, internode and branch length), then changes at the module level may lead to changes in colony architecture. Alternatively, different groups of traits may evolve semi-independently (or conditionally independent). To examine the patterns of integration among morphological traits in Caribbean octocorals, we compared five morphological traits across 21 species, correcting for the effects of phylogenetic relationships among the taxa. Graphical modelling and phylogenetic independence contrasts among the five morphological characters indicate two groups of integrated traits based on whether they were polyp- or colony-level traits. Although all characters exhibited bivariate associations, multivariate analyses (partial correlation coefficients) showed the strongest integration among the colony-level characters (internode distance and branch length). It is a quantitative demonstration that branching characters within the octocorals studied are independent of characters of the polyps. Despite the universally recognized modularity of octocorals at the level of polyps, branching during colony development may represent an emergent level of integration and modularity. PMID:14561292

  7. A Catalog of Candidate Field Horizontal-Branch and A-Type Stars. III. A 2MASS-Cleaned Version

    NASA Astrophysics Data System (ADS)

    Beers, Timothy C.; Almeida, Tiago; Rossi, Silvia; Wilhelm, Ronald; Marsteller, Brian

    2007-02-01

    We present coordinates and available photometric information (either from previous or recent broadband UBV observations, and near-infrared photometry from the 2MASS Point Source Catalog) for 12,056 stars (11,516 of which are unique) identified in the HK Survey of Beers and colleagues as candidate field horizontal-branch or A-type stars. These stars, in the apparent magnitude range 10<=B<=16.0, were selected using an objective-prism/interference-filter survey technique. The availability of 2MASS information permits assembly of a cleaned version of this catalog, comprising likely blue horizontal-branch (BHB) stars or blue stragglers in the color interval [-0.2<=(B-V)0<=+0.2], which are of particular interest for investigation of the structure, kinematics, and dynamics of the thick disk and inner halo of the Milky Way, the total mass and mass profile of the Galaxy, and as potential foreground/background objects in efforts to bracket distances to high-velocity clouds of H I. A comparison of the stars classified as high-likelihood BHB candidates with previous classifications based on UBV photometry and medium-resolution spectroscopy indicates that this class contains 78% correct identifications.

  8. Multiple populations on the horizontal branch. I - Observations in the (log g, log T/eff/)-diagram

    NASA Technical Reports Server (NTRS)

    Crocker, Deborah A.; Rood, Robert T.; O'Connell, Robert W.

    1988-01-01

    Log T(eff) and log g have been determined for blue horizontal branch (HB) stars in the globular clusters M15, M3, M5, M92, and NGC 288 as a first step in determining the physical origin of gaps or bimodal distributions in the blue horizontal branches of a number of globular clusters. The (log g, log T/eff/) diagram for the 'normal' HB cluster M5 matches the standard theory quite well. The stars blueward of the gap in NGC 288 and the blue extension of the M3 HB have significantly lower gravity than predicted by the standard theory. The cooler stars in M3 agree well with the standard theory while those of NGC 2988 lie at slightly lower gravity. In M92, the sequence of stars is broadened toward the low gravity side more than expected either from standard evolution or from observational error. The data for M15 are too scattered to support firm conclusions but seem consistent with NGC 288.

  9. On the Giant Horizontal and Asymptotic Branches of Galactic Globular Clusters - Part Five - CCD Photometry of NGC1261

    NASA Astrophysics Data System (ADS)

    Ferraro, F. R.; Clementini, G.; Fusi-Pecci, F.; Vitiello, E.; Buonanno, R.

    1993-09-01

    BV CCD photometry is presented for 3352 stars (18 variables) in the globular cluster NGC 126 t. The main conclusions drawn from the structure of the colour-magnitude diagram (CMD) are as follows. (i) The location and structure of the main branches agree with those found in previous studies, confirming the existence of a well-defined blue horizontal branch (1113) tail in addition to the large number of red 1113 stars. (ii) The mean metallicity derived from CMD indicators calibrated with the Zinn & West scale is [Fe/H] = -1.4±0.2, and the very small intrinsic width of the various branches yields very low upper limits (Δ[Fe/H]≤0.06, Δ[CNO]≤-0.2) for any chemical abundance spread. (iii) The `RGB bump' is detected at V= 16.70±0.05 as a clump of stars in the luminosity function of the red giant branch. (iv) VHB=16.70±0.04 and VTO=20.t4±0.10 yield ΔVTOHB=3.44±0.12. A detailed comparison with the main CMD loci of NGC 288 (a cluster that has similar metallicity but a totally blue 1113) throws doubt on the hypothesis that a clear difference in age (NGC 288 being older) is the `second parameter' necessary to explain the observed differences. (v) Some evidence is found for differences in the spatial distribution of the red and blue 1113 stars that is worthy of further analysis.

  10. Shear-induced enhancements of crystallization kinetics and morphological transformation for long chain branched polylactides with different branching degrees

    PubMed Central

    Wang, Junyang; Bai, Jing; Zhang, Yaqiong; Fang, Huagao; Wang, Zhigang

    2016-01-01

    The effects of long chain branching (LCB) degree on the shear-induced isothermal crystallization kinetics of a series of LCB polylactides (LCB PLAs) have been investigated by using rotational rheometer, polarized optical microscopy (POM) and scanning electron microscopy (SEM). Dynamic viscoelastic properties obtained by small-amplitude oscillatory shear (SAOS) tests indicate that LCB PLAs show more broadened relaxation time spectra with increasing LCB degree. Upon a pre-shear at the shear rate of 1 s−1 LCB PLAs show much faster crystallization kinetics than linear PLA and the crystallization kinetics is enhanced with increasing LCB degree. By modeling the system as a suspension the quantitative evaluation of nucleation density can be derived from rheological experiments. The nucleation density is greatly enhanced with increasing LCB degree and a saturation in shear time is observed. Crystalline morphologies for LCB PLAs observed by POM and SEM demonstrate the enhancement of nucleation density with increasing LCB degree and a transformation from spherulitic to orientated crystalline morphologies. The observation can be ascribed to longer relaxation time of the longest macromolecular chains and broadened, complex relaxation behaviors due to the introduction of LCB into PLA, which is essential in stabilizing the orientated crystal nuclei after pre-shear. PMID:27246803

  11. Shear-induced enhancements of crystallization kinetics and morphological transformation for long chain branched polylactides with different branching degrees

    NASA Astrophysics Data System (ADS)

    Wang, Junyang; Bai, Jing; Zhang, Yaqiong; Fang, Huagao; Wang, Zhigang

    2016-06-01

    The effects of long chain branching (LCB) degree on the shear-induced isothermal crystallization kinetics of a series of LCB polylactides (LCB PLAs) have been investigated by using rotational rheometer, polarized optical microscopy (POM) and scanning electron microscopy (SEM). Dynamic viscoelastic properties obtained by small-amplitude oscillatory shear (SAOS) tests indicate that LCB PLAs show more broadened relaxation time spectra with increasing LCB degree. Upon a pre-shear at the shear rate of 1 s‑1 LCB PLAs show much faster crystallization kinetics than linear PLA and the crystallization kinetics is enhanced with increasing LCB degree. By modeling the system as a suspension the quantitative evaluation of nucleation density can be derived from rheological experiments. The nucleation density is greatly enhanced with increasing LCB degree and a saturation in shear time is observed. Crystalline morphologies for LCB PLAs observed by POM and SEM demonstrate the enhancement of nucleation density with increasing LCB degree and a transformation from spherulitic to orientated crystalline morphologies. The observation can be ascribed to longer relaxation time of the longest macromolecular chains and broadened, complex relaxation behaviors due to the introduction of LCB into PLA, which is essential in stabilizing the orientated crystal nuclei after pre-shear.

  12. Side branch morphology and coarsening in directionally solidified Pb-8.4 at. pct Au

    NASA Technical Reports Server (NTRS)

    Tewari, S. N.; Lee, David; Nesarikar, V. V.

    1989-01-01

    The scaling relationships among the morphological features associated with the formation of perturbations (side branches) in the intercellular regions of a directionally solidified Pg-8.4 at. pct Au alloy were investigated. It is shown that the ratio between the initial side-branch spacing near dendrite tips, lambda-2, and the dendrite-tip radius, r(t), equals 2 to 2.5. The ratio between the distance from the dendrite tip to the location of the first side branch formation, lambda(p), and the t(r) equals 8 to 10. It was found that the model proposed by Kirkwood (1985) for the secondary dendrite arm coarsening shows a very good quantitative fit to the experimentally observed secondary arm coarsening kinetics during directional solidification.

  13. The evolution of high-metallicity horizontal-branch stars and the origin of the ultraviolet light in elliptical galaxies

    NASA Technical Reports Server (NTRS)

    Horch, E.; Demarque, P.; Pinsonneault, M.

    1992-01-01

    Evolutionary calculations of high-metallicity horizontal-branch stars show that for the relevant masses and helium abundances, post-HB evolution in the HR diagram does not proceed toward and along the AGB, but rather toward a 'slow blue phase' in the vicinity of the helium-burning main sequence, following the extinction of the hydrogen shell energy source. For solar and twice solar metallicity, the blue phase begins during the helium shell-burning phase (in agreement with the work of Brocato and Castellani and Tornambe); for 3 times solar metallicity, it begins earlier, during the helium core-burning phase. This behavior differs from what takes place at lower metallicities. The implications for high-metallicity old stellar populations in the Galactic bulge and for the integrated colors of elliptical galaxies are discussed.

  14. MAPPING THE GALACTIC HALO WITH BLUE HORIZONTAL BRANCH STARS FROM THE TWO-DEGREE FIELD QUASAR REDSHIFT SURVEY

    SciTech Connect

    De Propris, Roberto; Harrison, Craig D.; Mares, Peter J.

    2010-08-20

    We use 666 blue horizontal branch stars from the 2Qz Redshift Survey to map the Galactic halo in four dimensions (position, distance, and velocity). We find that the halo extends to at least 100 kpc in Galactocentric distance, and obeys a single power-law density profile of index {approx}-2.5 in two different directions separated by about 150{sup 0} on the sky. This suggests that the halo is spherical. Our map shows no large kinematically coherent structures (streams, clouds, or plumes) and appears homogeneous. However, we find that at least 20% of the stars in the halo reside in substructures and that these substructures are dynamically young. The velocity dispersion profile of the halo appears to increase toward large radii while the stellar velocity distribution is non-Gaussian beyond 60 kpc. We argue that the outer halo consists of a multitude of low luminosity overlapping tidal streams from recently accreted objects.

  15. HOT HORIZONTAL BRANCH STARS IN {omega} CENTAURI: CLUES ABOUT THEIR ORIGIN FROM THE CLUSTER COLOR MAGNITUDE DIAGRAM

    SciTech Connect

    Cassisi, Santi; Pietrinferni, Adriano; Salaris, Maurizio; Anderson, Jay; Bellini, Andrea; Bedin, Luigi R.; Piotto, Giampaolo; Milone, Antonino E-mail: pietrinferni@oa-teramo.inaf.it E-mail: jayander@stsci.edu E-mail: bedin@stsci.edu E-mail: antonino.milone@unipd.it

    2009-09-10

    We investigate a peculiar feature at the hottest, blue end of the horizontal branch of Galactic globular cluster {omega} Centauri, using the high-precision and nearly complete catalog that has been constructed from a survey taken with the Advanced Camera for Survey on board the Hubble Space Telescope, that covers the inner 10 x 10 arcmin. It is a densely populated clump of stars with an almost vertical structure in the F435W-(F435W-F625W) plane, that we termed 'blue clump'. A comparison with theoretical models leads to the conclusion that this feature must necessarily harbor either hot flasher stars or canonical He-rich stars-progeny of the blue main sequence (MS) subpopulation observed in this cluster-or a mixture of both types, plus possibly a component from the normal-He population hosted by the cluster. A strong constraint coming from theory is that the mass of the objects in the 'blue clump' has to be very finely tuned, with a spread of at most only {approx}0.03 M{sub sun}. By comparing observed and theoretical star counts along both the H- and He-burning stages we find that at least 15% of the expected He-rich horizontal branch stars are missing from the color-magnitude diagram. This missing population could be the progeny of red giants that failed to ignite central He-burning and have produced He-core white dwarfs (WDs). Our conclusion supports the scenario recently suggested by Calamida et al. for explaining the observed ratio of WDs to MS stars in {omega} Centauri.

  16. The Hot Horizontal-Branch Stars in NGC288 - Effects of Diffusion and Stratification on Their Atmospheric Parameters*

    NASA Technical Reports Server (NTRS)

    Moehler, S.; Dreizler, S.; LeBlanc, F.; Khalack, V.; Michaud, G.; Richer, J.; Sweigart, Allen V.; Grundahl, F.

    2014-01-01

    Context. NGC288 is a globular cluster with a well developed blue horizontal branch covering the so-called u-jump which indicates the onset of diffusion. It is therefore well suited to study the effects of diffusion in blue horizontal branch (HB) stars. Aims. We compare observed abundances to predictions from stellar evolution models calculated with diffusion and from stratified atmospheric models. We verify the effect of using stratified model spectra to derive atmospheric parameters. In addition we investigate the nature of the overluminous blue HB stars around the u-jump. Methods. We define a new photometric index sz from uvby measurements that is gravity sensitive between 8 000K and 12 000 K. Using medium-resolution spectra and Stroemgren photometry we determine atmospheric parameters (Teff, logg) and abundances for the blue HB stars. We use both homogeneous and stratified model spectra for our spectroscopic analyses. Results. The atmospheric parameters and masses of the hot HB stars in NGC288 show a behaviour seen also in other clusters for temperatures between 9 000K and 14 000 K. Outside this temperature range, however, they follow rather the results found for such stars in (omega)Cen. The abundances derived from our observations are for most elements (except He and P) within the abundance range expected from evolutionary models that include the effects of atomic diffusion and assume a surface mixed mass of 10(exp -7) M. The abundances predicted by stratified model atmospheres are generally significantly more extreme than observed, except for Mg. The use of stratified model spectra to determine effective temperatures, surface gravities and masses moves the hotter stars to a closer agreement with canonical evolutionary predictions. Conclusions. Our results show definite promise towards solving the long-standing issue of surface gravity and mass discrepancies for hot HB stars, but there is still much work needed to arrive at a self-consistent solution.

  17. The Century Survey Galactic Halo Project. II. Global Properties and the Luminosity Function of Field Blue Horizontal Branch Stars

    NASA Astrophysics Data System (ADS)

    Brown, Warren R.; Geller, Margaret J.; Kenyon, Scott J.; Kurtz, Michael J.; Allende Prieto, Carlos; Beers, Timothy C.; Wilhelm, Ronald

    2005-09-01

    We discuss a 175 deg2 spectroscopic survey for blue horizontal branch (BHB) stars in the Galactic halo. We use the Two Micron All Sky Survey (2MASS) and the Sloan Digital Sky Survey (SDSS) to select BHB candidates, and we find that the 2MASS and SDSS color selection is 38% and 50% efficient, respectively, for BHB stars. Our samples include one likely runaway B7 star 6 kpc below the Galactic plane. The global properties of the BHB samples are consistent with membership in the halo population: the median metallicity is [Fe/H]=-1.7, the velocity dispersion is 108 km s-1, and the mean Galactic rotation of the BHB stars 3 kpc<|z|<15 kpc is -4+/-30 km s-1. We discuss the theoretical basis of the Preston, Shectman, and Beers MV-color relation for BHB stars and conclude that the intrinsic shape of the BHB MV-color relation results from the physics of stars on the horizontal branch. We calculate the luminosity function for the field BHB star samples using the maximum likelihood method of Efstathiou and coworkers, which is unbiased by density variations. The field BHB luminosity function exhibits a steep rise at bright luminosities, a peak between 0.8

  18. Liquid entrainment at an upward oriented vertical branch line from a horizontal pipe

    NASA Astrophysics Data System (ADS)

    Welter, Kent Byron

    Under simulated accident conditions, tees in the primary coolant loop of a Pressurized Water Reactor (PWR) can deviate from their original design purpose and become separators that effectively remove core heat sink capacity. This method of primary coolant removal is a phenomenological subset of phase separation known as liquid entrainment, whereby liquid is forced from its original path by the inertia of the gas. A comprehensive literature review revealed common deficiencies in previous studies. The Westinghouse AP600 advanced reactor design was chosen to assess the validity of entrainment models. Following a systematic scaling analysis of the prototypic design a model separate effects test was proposed and constructed at Oregon State University. Just under 100 tests were run to fill the deficiencies found in the literature review. New data from the Air-water Test Loop for Advanced Thermal-hydraulic Studies (ATLATS) could not be predicted by published correlations. A new theoretical model for predicting liquid entrainment onset and steady state entrainment was developed. Comparison with all available data shows a marked improvement for predicting the mass flow rate out the vertical branch.

  19. THE RR LYRAE VARIABLES AND HORIZONTAL BRANCH OF NGC 6656 (M22) {sup ,}

    SciTech Connect

    Kunder, Andrea; Walker, Alistair R.; Paredes Alvarez, Leonardo; Stetson, Peter B.; Cassisi, Santi; Layden, Andrew; Bono, Giuseppe; Catelan, Márcio; Clem, James L.; Matsunaga, Noriyuki; Salaris, Maurizio; Lee, Jae-Woo; Chaboyer, Brian E-mail: mcatelan@astro.puc.cl

    2013-11-01

    The first calibrated broadband UBVI time-series photometry is presented for the RR Lyrae variable stars in NGC 6656 (M22), with observations spanning a range of 22 years. We have also redetermined the variability types and periods for the RR Lyrae stars identified previously by photographic observations, revising the number of fundamental-mode RR Lyrae variables (RR0) to 10 and the number of first-overtone variables (RR1) to 16. The mean periods of the RR0 and RR1 variables are (P) {sub RR0} = 0.66 ± 0.02 days and (P) {sub RR1} = 0.33 ± 0.01 days, respectively, supporting an Oosterhoff II classification for the cluster. The number ratio of RR1-type to all RR-type variables is N {sub 1}/N{sub RR} = 0.61, also consistent with an Oosterhoff II designation. Both the RR Lyrae stars' minimum light colors and the blue edge of the RR Lyrae instability strip suggest E( B – – V) = 0.36 ± 0.02 mag toward M22. Regarding the HB morphology of M22, we find (B-R)/(B+V+R) = +0.97 ± 0.1 and at least one ''gap'' located in an unusual part of the blue HB, in the middle of the so-called hot HB stars.

  20. Observations of the Hot Horizontal Branch Stars in the Metal-Rich Bulge Globular Cluster NGC 6388

    NASA Technical Reports Server (NTRS)

    Moehler, S.; Sweigart, A. V.

    2006-01-01

    The metal-rich bulge globular cluster NGC 6388 shows a distinct blue horizontal-branch tail in its colour-magnitude diagram (Rich et al. 1997) and is thus a strong case of the well-known 2nd Parameter Problem. In addition, its horizontal branch (HB) shows an upward tilt toward bluer colours, which cannot be explained by canonical evolutionary models. Several non-canonical scenarios have been proposed to explain these puzzling observations. In order to test the predictions of these scenarios, we have obtained medium resolution spectra to determine the atmospheric parameters of a sample of the blue HB stars in NGC 6388.Using the medium resolution spectra, we determine effective temperatures, surface gravities and helium abundances by fitting the observed Balmer and helium lines with appropriate theoretical stellar spectra. As we know the distance to the cluster, we can verify our results by determining masses for the stars. During the data reduction we took special care to correctly subtract the background, which is dominated by the overlapping spectra of cool stars. The cool blue tail stars in our sample with T(sub eff) approximately 10000 K have lower than canonical surface gravities, suggesting that these stars are, on average, approximately equal to 0.4 mag brighter than canonical HB stars in agreement with the observed upward slope of the HB in NGC 6388. Moreover, the mean mass of these stars agrees well with theoretical predictions. In contrast, the hot blue tail stars in our sample with T(sub eff) greater than or equal to 12000 K show significantly lower surface gravities than predicted by any scenario, which can reproduce the photometric observations. Their masses are also too low by about a factor of 2 compared to theoretical predictions. The physical parameters of the blue HB stars at about 10,000 K support the helium pollution scenario. The low gravities and masses of the hot blue tail stars, however, are probably caused by problems with the data reduction

  1. THE PANCHROMATIC HUBBLE ANDROMEDA TREASURY. II. TRACING THE INNER M31 HALO WITH BLUE HORIZONTAL BRANCH STARS

    SciTech Connect

    Williams, Benjamin F.; Dalcanton, Julianne J.; Gilbert, Karoline M.; Rosenfield, Philip; Bell, Eric F.; Guhathakurta, Puragra; Seth, Anil C.; Kalirai, Jason S.; Girardi, Leo E-mail: jd@astro.washington.edu E-mail: philrose@astro.washington.edu E-mail: raja@uco.lick.org E-mail: aseth@astro.utah.edu E-mail: lgirardi@pd.astro.it

    2012-11-01

    We attempt to constrain the shape of M31's inner stellar halo by tracing the surface density of blue horizontal branch (BHB) stars at galactocentric distances ranging from 2 kpc to 35 kpc. Our measurements make use of resolved stellar photometry from a section of the Panchromatic Hubble Andromeda Treasury survey, supplemented by several archival Hubble Space Telescope observations. We find that the ratio of BHB to red giant stars is relatively constant outside of 10 kpc, suggesting that the BHB is as reliable a tracer of the halo population as the red giant branch. In the inner halo, we do not expect BHB stars to be produced by the high-metallicity bulge and disk, making BHB stars a good candidate to be a reliable tracer of the stellar halo to much smaller galactocentric distances. If we assume a power-law profile r {sup -{alpha}} for the two-dimensional (2D) projected surface density BHB distribution, we obtain a high-quality fit with a 2D power-law index of {alpha} = 2.6{sup +0.3} {sub -0.2} outside of 3 kpc, which flattens to {alpha} < 1.2 inside of 3 kpc. This slope is consistent with previous measurements but is anchored to a radial baseline that extends much farther inward. Finally, assuming azimuthal symmetry and a constant mass-to-light ratio, the best-fitting profile yields a total halo stellar mass of 2.1{sup +1.7} {sub -0.4} Multiplication-Sign 10{sup 9} M {sub Sun }. These properties are comparable with both simulations of stellar halo formation by satellite disruption alone and simulations that include some in situ formation of halo stars.

  2. The Mass of the Galaxy from Large Samples of Field Horizontal-Branch Stars in the SDSS Early Data Release

    NASA Astrophysics Data System (ADS)

    Beers, T. C.; Chiba, M.; Sakamoto, T.; Wilhelm, R.; Allende Prieto, C.; Sommer-Larsen, J.; Newberg, H. J.; Yanny, B.; Marsteller, B.; Pier, J. R.

    2004-07-01

    We present a new estimate of the mass of the Milky Way, making use of a large sample of 955 field horizontal-branch (FHB) stars from the Early Data Release of the Sloan Digital Sky Survey. This sample of stars has been classified on the basis of an automated analysis approach, in combination with other methods, in order to obtain estimates of the physical parameters of the stars, i.e., T_eff, log g, [Fe/H], and should be relatively free of contamination from halo blue stragglers. The stars all have measured radial velocities and photometric distance estimates, and the sample includes objects as distant as ˜ 75 kpc from the Galactic center. Application of a Bayesian likelihood method, for a specific model of the Galaxy, indicates that the total mass of the Galaxy lies in the range 1.5-4.0 x 1012 M⊙. Our sample appears to reveal a clear signature of a dual halo population of FHB stars, with the boundary between the inner and outer halo around 20 kpc, and the possibility of rather striking differences in the rotational properties of the Galaxy at low metallicity.

  3. Functional morphology, biomechanics and biomimetic potential of stem-branch connections in Dracaena reflexa and Freycinetia insignis.

    PubMed

    Masselter, Tom; Eckert, Sandra; Speck, Thomas

    2011-01-01

    Branching in plants is one of the most important assets for developing large arborescent growth forms with complex crowns. While the form and development of branching in gymnosperms and dicotyledonous trees is widely understood, very little is known about branching patterns and the structure of branch-stem-junctions in arborescent monocotyledons. For a better and quantitative understanding of the functional morphology of branch-stem-junctions in arborescent monocotyledons, we investigated the two species Dracaena reflexa and Freycinetia insignis. While D. reflexa is able to develop large arborescent forms with conspicuous crowns by anomalous secondary growth, F. insignis remains relatively small and is only capable of primary growth. Biomechanical investigations were performed by applying vertical loads up to rupture to lateral branches of both species. This allows the analysis of the fracture mechanics and the determination of the maximal force, stress and strain at rupture as well as the fracture toughness. Functional morphology was correlated with the mechanical behaviour of these plants and compared to data of other dicotyledonous trees. The high energy absorption found in the rupture process of lateral branches of D. reflexa and F. insignis makes them promising biological concept generators with a high potential for biomimetic implementation, i.e., for the development of branched fibre-reinforced technical composites. A wide range of constructional elements with branched (sub-)structures can be optimised by using solutions inspired by plant ramifications, e.g., in automotive and aerospace engineering, architecture, sports equipment and prosthetic manufacturing. PMID:21977429

  4. Adiabatic Survey of Subdwarf B Star Oscillations. III. Effects of Extreme Horizontal Branch Stellar Evolution on Pulsation Modes

    NASA Astrophysics Data System (ADS)

    Charpinet, S.; Fontaine, G.; Brassard, P.; Dorman, Ben

    2002-06-01

    We present the final results of a large, systematic survey of the adiabatic oscillation properties of models of subdwarf B (sdB) stars. This survey is aimed at providing the minimal theoretical background with which to understand the asteroseismological characteristics of the recently discovered class of pulsating sdB stars (the EC 14026 objects). In this paper, the last of a series of three, we consider the effects of stellar evolution on the pulsation eigenmodes of sdB star models. We specifically analyze the adiabatic properties of 149 equilibrium models culled from seven distinct extreme horizontal branch evolutionary sequences. Those have been chosen in order to span fully the region of parameter space where real sdB stars are found. We primarily focus on the evolution of the pulsation periods (P) and the rates of period change (dP/dt), which are both a priori observable quantities. Both the acoustic and gravity branches of stellar oscillations are considered. In light of the results derived in the first two papers of this series, we discuss how the values of P and dP/dt relate to the various structural adjustments that sdB stars undergo during evolution. We find that the acoustic modes react primarily to the secular variations of the surface gravity. In contrast, we identify three main factors that regulate the period evolution of gravity modes: these are the variations brought about by evolution in both the surface gravity and the effective temperature, as well as the onset and growth of a chemical discontinuity between the C-O-enriched nucleus and the helium-rich mantle. We also find, as expected from our previous results, that the period evolution of the pulsation modes in sdB stars is further complicated by trapping effects (microtrapping in the case of p-modes) and by avoided crossings between modes. The latter occur preferentially in certain regions of parameter space. We provide our final results in the form of extensive tabular data in the appendices

  5. CORRELATIONS IN HORIZONTAL BRANCH OSCILLATIONS AND BREAK COMPONENTS IN XTE J1701-462 AND GX 17+2

    SciTech Connect

    Bu, Qing-cui; Chen, Li; Zhang, Liang; Li, Zhao-sheng; Qu, Jin-lu; Belloni, T. M. E-mail: chenli@bnu.edu.cn E-mail: tomaso.belloni@brera.inaf.it

    2015-01-20

    We studied the horizontal branch oscillations (HBO) and the band-limited components observed in the power spectra of the transient neutron star low-mass X-ray binary XTE J1701-462 and the persistent ''Sco-like'' Z source GX 17+2. These two components were studied based on the state-resolved spectra. We found that the frequencies of XTE J1701-462 lie on the known correlations (WK and PBK), showing consistency with other types of X-ray binaries (black holes, atoll sources, and millisecond X-ray pulsars). However, GX 17+2 is shifted from the WK correlation like other typical Z sources. We suggest that the WK/PBK main track forms a boundary that separates persistent sources from transient sources. The characteristic frequencies of break and HBO are independent of accretion rate in both sources, though it depends on spectral models. We also report the energy dependence of the HBO and break frequencies in XTE J1701-462 and how the temporal properties change with spectral state in XTE J1701-462 and GX 17+2. We studied the correlation between rms at the break and the HBO frequency. We suggest that HBO and break components for both sources probably arise from a similar physical mechanism: Comptonization emission from the corona. These two components could be caused by the same kind of oscillation in a corona with uneven density, and they could be generated from different areas of the corona. We further suggest that different proportions of the Comptonization component in the total flux cause the different distribution between GX 17+2 and XTE J1701-462 in the rms{sub break}-rms{sub HBO} diagram.

  6. BVRI and UBV Photometry of Metal-Poor and Horizontal-Branch Candidates in the Galactic Halo

    NASA Astrophysics Data System (ADS)

    De Lee, N.; Beers, T. C.; Smith, H. A.; Marsteller, B.; Krugler, J.; Lee, Y.; Wilhelm, R.; Terndrup, D.

    2005-12-01

    We report on UBVRI CCD photometry that has been obtained over the course of the past seven years for a sample of over 1600 metal-poor (MP), field horizontal-branch (FHB), and other A-type candidates selected from two large objective-prism surveys, the HK survey of Beers and collaborators and the Hamburg/ESO stellar survey of Christlieb and colleagues. These stars either have, or soon will have, medium-resolution (1-2 Å) spectroscopy obtained with various 2.5m - 4m class telescopes, including the SOAR 4.1m. These observations are being employed for several purposes. In the case of the FHB/A stars, the UBV photometry is useful for separating out low-gravity stars from the high-gravity ones. The subsample of high-gravity A-type stars includes Blue Metal Poor stars, halo and thick-disk blue stragglers, main-sequence A-type dwarfs, and Am and Ap stars. These observations are also being used to derive photometric distance estimates that will aid studies of high-velocity hydrogen clouds in the Galaxy, as well as to refine Galactic mass measurements. The data for the low-metallicity objects will be used to obtain estimates of temperatures that are required for elemental abundance studies based on future high-resolution spectroscopic observations, as well as to estimate distances for use in kinematic studies. T.C.B. and Y.L. acknowledge partial support from grant AST 04-06784, as well as from grant PHY 02-16783, Physics Frontier Center/Joint Institute for Nuclear Astrophysics (JINA), awarded by the US National Science Foundation.

  7. Flash Mixing on the White-Dwarf Cooling Curve: Understanding Hot Horizontal Branch Anomalies in NGC 2808

    NASA Technical Reports Server (NTRS)

    Brown, Thomas M.; Sweigart, Allen V.; Lanz, Thierry; Landsman, Wayne B.; Hubeny, Ivan; Fisher, Richard R. (Technical Monitor)

    2001-01-01

    We present an ultraviolet color-magnitude diagram (CMD) spanning the hot horizontal branch (HB), blue straggler, and white dwarf populations of the globular cluster NGC 2808. These data, obtained with the Space Telescope Imaging Spectrograph (STIS), demonstrate that NGC 2808 harbors a significant population of hot subluminous HB stars, an anomaly only previously reported for the globular cluster omega Cen. Our theoretical modeling indicates that the location of these subluminous stars in the CMD, as well as the high temperature gap along the HB of NGC 2808, can be explained if these stars underwent a late helium-core flash while descending the white dwarf cooling curve. We show that the convective zone produced by such a late helium flash will penetrate into the hydrogen envelope, thereby mixing hydrogen into the hot helium-burning interior, where it is rapidly consumed. This phenomenon is analogous to the "born again" scenario for producing hydrogen-deficient stars following a late helium-shell flash. The flash mixing of the envelope greatly enhances the envelope helium and carbon abundances that, in turn, leads to a discontinuous increase in the HB effective temperatures. We argue that the hot HB gap is associated with this theoretically predicted dichotomy in the HB properties. Moreover, the changes in the emergent spectral energy distribution caused by these abundance changes are primarily responsible for explaining the hot subluminous HB stars. Although further evidence is needed to confirm that a late helium-core flash can account for the subluminous HB stars and the hot HB gap, we demonstrate that an understanding of these stars requires the use of appropriate theoretical models for their evolution, atmospheres, and spectra.

  8. Correlations in Horizontal Branch Oscillations and Break Components in XTE J1701-462 and GX 17+2

    NASA Astrophysics Data System (ADS)

    Bu, Qing-cui; Chen, Li; Li, Zhao-sheng; Qu, Jin-lu; Belloni, T. M.; Zhang, Liang

    2015-01-01

    We studied the horizontal branch oscillations (HBO) and the band-limited components observed in the power spectra of the transient neutron star low-mass X-ray binary XTE J1701-462 and the persistent "Sco-like" Z source GX 17+2. These two components were studied based on the state-resolved spectra. We found that the frequencies of XTE J1701-462 lie on the known correlations (WK and PBK), showing consistency with other types of X-ray binaries (black holes, atoll sources, and millisecond X-ray pulsars). However, GX 17+2 is shifted from the WK correlation like other typical Z sources. We suggest that the WK/PBK main track forms a boundary that separates persistent sources from transient sources. The characteristic frequencies of break and HBO are independent of accretion rate in both sources, though it depends on spectral models. We also report the energy dependence of the HBO and break frequencies in XTE J1701-462 and how the temporal properties change with spectral state in XTE J1701-462 and GX 17+2. We studied the correlation between rms at the break and the HBO frequency. We suggest that HBO and break components for both sources probably arise from a similar physical mechanism: Comptonization emission from the corona. These two components could be caused by the same kind of oscillation in a corona with uneven density, and they could be generated from different areas of the corona. We further suggest that different proportions of the Comptonization component in the total flux cause the different distribution between GX 17+2 and XTE J1701-462 in the rmsbreak-rmsHBO diagram.

  9. The capabilities and limitations of conductance-based compartmental neuron models with reduced branched or unbranched morphologies and active dendrites.

    PubMed

    Hendrickson, Eric B; Edgerton, Jeremy R; Jaeger, Dieter

    2011-04-01

    Conductance-based neuron models are frequently employed to study the dynamics of biological neural networks. For speed and ease of use, these models are often reduced in morphological complexity. Simplified dendritic branching structures may process inputs differently than full branching structures, however, and could thereby fail to reproduce important aspects of biological neural processing. It is not yet well understood which processing capabilities require detailed branching structures. Therefore, we analyzed the processing capabilities of full or partially branched reduced models. These models were created by collapsing the dendritic tree of a full morphological model of a globus pallidus (GP) neuron while preserving its total surface area and electrotonic length, as well as its passive and active parameters. Dendritic trees were either collapsed into single cables (unbranched models) or the full complement of branch points was preserved (branched models). Both reduction strategies allowed us to compare dynamics between all models using the same channel density settings. Full model responses to somatic inputs were generally preserved by both types of reduced model while dendritic input responses could be more closely preserved by branched than unbranched reduced models. However, features strongly influenced by local dendritic input resistance, such as active dendritic sodium spike generation and propagation, could not be accurately reproduced by any reduced model. Based on our analyses, we suggest that there are intrinsic differences in processing capabilities between unbranched and branched models. We also indicate suitable applications for different levels of reduction, including fast searches of full model parameter space. PMID:20623167

  10. The Hubble Space Telescope UV Legacy Survey of Galactic Globular Clusters. VII. Implications from the Nearly Universal Nature of Horizontal Branch Discontinuities

    NASA Astrophysics Data System (ADS)

    Brown, T. M.; Cassisi, S.; D’Antona, F.; Salaris, M.; Milone, A. P.; Dalessandro, E.; Piotto, G.; Renzini, A.; Sweigart, A. V.; Bellini, A.; Ortolani, S.; Sarajedini, A.; Aparicio, A.; Bedin, L. R.; Anderson, J.; Pietrinferni, A.; Nardiello, D.

    2016-05-01

    The UV-initiative Hubble Space Telescope Treasury survey of Galactic globular clusters provides a new window into the phenomena that shape the morphological features of the horizontal branch (HB). Using this large and homogeneous catalog of UV and blue photometry, we demonstrate that the HB exhibits discontinuities that are remarkably consistent in color (effective temperature). This consistency is apparent even among some of the most massive clusters hosting multiple distinct sub-populations (such as NGC 2808, ω Cen, and NGC 6715), demonstrating that these phenomena are primarily driven by atmospheric physics that is independent of the underlying population properties. However, inconsistencies arise in the metal-rich clusters NGC 6388 and NGC 6441, where the discontinuity within the blue HB (BHB) distribution shifts ˜1000–2000 K hotter. We demonstrate that this shift is likely due to a large helium enhancement in the BHB stars of these clusters, which in turn affects the surface convection and evolution of such stars. Our survey also increases the number of Galactic globular clusters known to host blue-hook stars (also known as late hot flashers) from 6 to 23 clusters. These clusters are biased toward the bright end of the globular cluster luminosity function, confirming that blue-hook stars tend to form in the most massive clusters with significant self-enrichment. Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. These observations are associated with program GO-13297.

  11. Functional morphology, biomechanics and biomimetic potential of stem–branch connections in Dracaena reflexa and Freycinetia insignis

    PubMed Central

    Eckert, Sandra; Speck, Thomas

    2011-01-01

    Summary Branching in plants is one of the most important assets for developing large arborescent growth forms with complex crowns. While the form and development of branching in gymnosperms and dicotyledonous trees is widely understood, very little is known about branching patterns and the structure of branch–stem-junctions in arborescent monocotyledons. For a better and quantitative understanding of the functional morphology of branch–stem-junctions in arborescent monocotyledons, we investigated the two species Dracaena reflexa and Freycinetia insignis. While D. reflexa is able to develop large arborescent forms with conspicuous crowns by anomalous secondary growth, F. insignis remains relatively small and is only capable of primary growth. Biomechanical investigations were performed by applying vertical loads up to rupture to lateral branches of both species. This allows the analysis of the fracture mechanics and the determination of the maximal force, stress and strain at rupture as well as the fracture toughness. Functional morphology was correlated with the mechanical behaviour of these plants and compared to data of other dicotyledonous trees. The high energy absorption found in the rupture process of lateral branches of D. reflexa and F. insignis makes them promising biological concept generators with a high potential for biomimetic implementation, i.e., for the development of branched fibre-reinforced technical composites. A wide range of constructional elements with branched (sub-)structures can be optimised by using solutions inspired by plant ramifications, e.g., in automotive and aerospace engineering, architecture, sports equipment and prosthetic manufacturing. PMID:21977429

  12. KINEMATICS OF THE STELLAR HALO AND THE MASS DISTRIBUTION OF THE MILKY WAY USING BLUE HORIZONTAL BRANCH STARS

    SciTech Connect

    Kafle, Prajwal R.; Sharma, Sanjib; Lewis, Geraint F.; Bland-Hawthorn, Joss

    2012-12-20

    Here, we present a kinematic study of the Galactic halo out to a radius of {approx}60 kpc, using 4664 blue horizontal branch stars selected from the SDSS/SEGUE survey to determine key dynamical properties. Using a maximum likelihood analysis, we determine the velocity dispersion profiles in spherical coordinates ({sigma}{sub r}, {sigma}{sub {theta}}, {sigma}{sub {phi}}) and the anisotropy profile ({beta}). The radial velocity dispersion profile ({sigma}{sub r}) is measured out to a galactocentric radius of r {approx} 60 kpc, but due to the lack of proper-motion information, {sigma}{sub {theta}}, {sigma}{sub {phi}}, and {beta} could only be derived directly out to r {approx} 25 kpc. From a starting value of {beta} Almost-Equal-To 0.5 in the inner parts (9 < r/kpc < 12), the profile falls sharply in the range r Almost-Equal-To 13-18 kpc, with a minimum value of {beta} = -1.2 at r = 17 kpc, rising sharply at larger radius. In the outer parts, in the range 25 < r/kpc < 56, we predict the profile to be roughly constant with a value of {beta} Almost-Equal-To 0.5. The newly discovered kinematic anomalies are shown not to arise from halo substructures. We also studied the anisotropy profile of simulated stellar halos formed purely by accretion and found that they cannot reproduce the sharp dip seen in the data. From the Jeans equation, we compute the stellar rotation curve (v{sub circ}) of the Galaxy out to r {approx} 25 kpc. The mass of the Galaxy within r {approx}< 25 kpc is determined to be 2.1 Multiplication-Sign 10{sup 11} M{sub Sun }, and with a three-component fit to v{sub circ}(r), we determine the virial mass of the Milky Way dark matter halo to be M{sub vir} = 0.9{sup +0.4}{sub -0.3} Multiplication-Sign 10{sup 12} M{sub Sun} (R{sub vir} = 249{sup +34}{sub -31} kpc).

  13. Pd@Pt Core–Shell Nanoparticles with Branched Dandelion-like Morphology as Highly Efficient Catalysts for Olefin Reduction

    EPA Science Inventory

    A facile synthesis based on the addition of ascorbic acid to a mixture of Na2PdCl4, K2PtCl6, and Pluronic P123 results in highly branched core–shell nanoparticles (NPs) with a micro–mesoporous dandelion-like morphology comprising Pd core and Pt shell. The slow reduction kinetics ...

  14. The discovery of a hard X-ray component in the horizontal branch spectrum of the Z source GX 17+2

    NASA Astrophysics Data System (ADS)

    di Salvo, T.; Stella, L.; Robba, N. R.; Burderi, L.; van der Klis, M.

    2001-09-01

    We report on a long BeppoSAX (0.1 - 200 keV energy range) observation of the Z-source GX 17+2. The source was on Horizontal and Normal branches of the hardness-intensity diagram. Energy spectra were selected based on the source position in this diagram. The spectral continuum is well described by the sum of a ~0.6 keV blackbody and a Comptonized component, resulting from upscattering of ~1 keV seed photons by electrons at a temperature of ~3 keV and optical depth of ~10. Iron K-line and edge were also present at energies ~6.7 and ~8.5 keV, respectively, corresponding to high ionization stages (Fe XXIII-XXV). In the spectra of the Horizontal branch a hard tail was clearly detected at energies above ~30 keV. It can be fit to a power law of photon index ~2.7, contributing ~8% of the source flux. This component gradually disappears as the source moved towards the Normal branch. We discuss the similarities with spectra of accreting black holes and implications on spectral models.

  15. Pulsating hot O subdwarfs in ω Centauri: mapping a unique instability strip on the extreme horizontal branch

    NASA Astrophysics Data System (ADS)

    Randall, S. K.; Calamida, A.; Fontaine, G.; Monelli, M.; Bono, G.; Alonso, M. L.; Van Grootel, V.; Brassard, P.; Chayer, P.; Catelan, M.; Littlefair, S.; Dhillon, V. S.; Marsh, T. R.

    2016-05-01

    We present the results of an extensive survey for rapid pulsators among Extreme Horizontal Branch (EHB) stars in ω Cen. The observations performed consist of nearly 100 h of time-series photometry for several off-centre fields of the cluster, as well as low-resolution spectroscopy for a partially overlapping sample. We obtained photometry for some 300 EHB stars, for around half of which we are able to recover light curves of sufficient quality to either detect or place meaningful non-detection limits for rapid pulsations. Based on the spectroscopy, we derive reliable values of log g, Teff and log N(He) /N(H) for 38 targets, as well as good estimates of the effective temperature for another nine targets, whose spectra are slightly polluted by a close neighbour in the image. The survey uncovered a total of five rapid variables with multi-periodic oscillations between 85 and 125 s. Spectroscopically, they form a homogeneous group of hydrogen-rich subdwarf O stars clustered between 48 000 and 54 000 K. For each of the variables we are able to measure between two and three significant pulsations believed to constitute independent harmonic oscillations. However, the interpretation of the Fourier spectra is not straightforward due to significant fine structure attributed to strong amplitude variations. In addition to the rapid variables, we found an EHB star with an apparently periodic luminosity variation of ~2700 s, which we tentatively suggest may be caused by ellipsoidal variations in a close binary. Using the overlapping photometry and spectroscopy sample we are able to map an empirical ω Cen instability strip in log g - Teff space. This can be directly compared to the pulsation driving predicted from the Montréal "second-generation" models regularly used to interpret the pulsations in hot B subdwarfs. Extending the parameter range of these models to higher temperatures, we find that the region where p-mode excitation occurs is in fact bifurcated, and the well

  16. Morphological, anatomical, and chemical characteristics of needle and branch samples of Siberian fir (Abies Siberica)

    NASA Technical Reports Server (NTRS)

    Rock, B. N.; Williams, D. L.; Kharuk, V. I.; Wessman, C. A.; Moss, D. M.

    1992-01-01

    In August, 1991, needle and branch samples of Siberian fir were collected from undisturbed forest stands along an elevation gradient ranging from 2300 ft to 4450 ft. Four study sites were selected on west-facing slopes, and a standard set of measurements and collections was made. First-, second-, and third-year needles were collected for anatomical assessment. A visual assessment of the forest stand conditions at each site included an evaluation of canopy morphology needle, coloration, increment growth, and the state of health of a specific type of lichen. The heaviest damage to forest stands (extensive foliar loss, needle discoloration, dieback of terminal growth) occurs at an intermediate elevation site (3400 ft/1037 m). The least amount of damage was recorded at the lowest elevation site (2300 ft/701 m). Only slight damage occurs at the highest elevation site (4450 ft/1357 m). Some degree of flagging occurs at all sites. Several lines of evidence suggest that the damage occurring in this area is recent in origin (incipient).

  17. Statistical Properties of Blue Horizontal Branch Stars in the Spheroid: Detection of a Moving Group approximately 50 kpc from the Sun

    SciTech Connect

    Harrigan, Matthew J.; Newberg, Heidi Jo; Newberg, Lee A.; Yanny, Brian; Beers, Timothy C.; Lee, Young Sun; Fiorentin, Paola Re; /Ljubljana U. /Heidelberg, Max Planck Inst. Astron.

    2010-02-01

    A new moving group comprising at least four Blue Horizontal Branch (BHB) stars is identified at (l; b) = (65{sup o}; 48{sup o}). The horizontal branch at g{sub 0} = 18.9 magnitude implies a distance of 50 kpc from the Sun. The heliocentric radial velocity is = -157 {+-} 4 km s{sup -1}, corresponding to V{sub gsr} = -10 km s{sup -1}; the dispersion in line-of-sight velocity is consistent with the instrumental errors for these stars. The mean metallicity of the moving group is [Fe/H] {approx} -2.4, which is significantly more metal poor than the stellar spheroid. We estimate that the BHB stars in the outer halo have a mean metallicity of [Fe/H]=-2.0, with a wide scatter and a distribution that does not change much as a function of distance from the Sun. We explore the systematics of SDSS DR7 surface gravity metallicity determinations for faint BHB stars, and present a technique for estimating the significance of clumps discovered in multidimensional data. This moving group cannot be distinguished in density, and highlights the need to collect many more spectra of Galactic stars to unravel the merger history of the Galaxy.

  18. Relation between the quasi-periodic oscillations and the low-frequency noise of GX 5-1 in the horizontal branch

    NASA Technical Reports Server (NTRS)

    Mitsuda, Kazuhisa; Dotani, Tadayasu; Yoshida, Atsumasa; Vaughan, Brian; Norris, Jay P.

    1991-01-01

    Ginga observations of quasi-periodic oscillations (QPOs) and the low-frequency noise (LFN) from GX 5-1 in its horizontal-branch spectral state are presented. Power spectral fits were attempted using model functions based on simple oscillating shot models. A clear second-harmonic peak of QPO was detected. Variations in the powers of QPO and LFN on timescales of 8-256 s were also studied. These variations were significant for all of the timescales studied, and were uncorrelated with each other on timescales shorter than a few tens of seconds, and correlated on longer timescales. From simulations based on a simple shot model, it was found that the variation amplitude and the lack of correlation on short timescales are not inconsistent with the oscillating shot models. A more complex model is necessary to fully explain the observed properties.

  19. The ultraviolet lines of carbon, nitrogen, and oxygen in the IUE spectrum of the field horizontal-branch A star HD 109995

    NASA Technical Reports Server (NTRS)

    Leckrone, David S.; Adelman, Saul J.

    1986-01-01

    Photospheric abundances of C, N and O of an evolved halo Population 2 star, the field horizontal-branch star HD 109995, based on observations of ultraviolet resonance or low excitation lines are presented. The logarithmic abundance ratio with respect to the Sun O/Fe = +1.5 is substantially higher than previously determined values for Pop. 2 red giants or RR Lyrae stars, but agrees well with a derived value from the OI infrared triplet. This may be direct evidence of Tinsley's (1979) scenario of localized sharply rising interstellar oxygen abundances immediately following bursts of massive star formation. Star HD 109995 may have formed from such highly oxygen-enriched material prior to its dilution by gas with the pre-burst composition. The ratio C/N = -1.3 may reflect the composition of material from which the star formed or CN processing within the star during its evolution.

  20. Dartmouth Stellar Evolution Database and the ACS Survey of Galactic Globular Clusters II. Stellar Evolution Tracks, Isochrones, Luminosity Functions, and Synthetic Horizontal-Branch Models

    DOE Data Explorer

    Dotter, A; Chaboyer, B; Jevremovic, D; Kostov, V; Baron, E; Ferguson, J; Sarajedini, A; Anderson, J

    The Dartmouth Stellar Evolution Database is a collection of stellar evolution tracks and isochrones that spans a range of [Fe/H] from -2.5 to +0.5, [a/Fe] from -0.2 to +0.8 (for [Fe/H]<=0) or +0.2 (for [Fe/H]>0), and initial He mass fractions from Y=0.245 to 0.40. Stellar evolution tracks were computed for masses between 0.1 and 4 Msolar, allowing isochrones to be generated for ages as young as 250 Myr. For the range in masses where the core He flash occurs, separate He-burning tracks were computed starting from the zero age horizontal branch. The tracks and isochrones have been transformed to the observational plane in a variety of photometric systems including standard UBV(RI)C, Stromgren uvby, SDSS ugriz, 2MASS JHKs, and HST ACS/WFC and WFPC2. The Dartmouth Stellar Evolution Database is accessible through a Web site at http://stellar.dartmouth.edu/~models/ where all tracks, isochrones, and additional files can be downloaded. [Copied from online abstract of paper titled "Darmouth Stellar Evolution Database" authored by Dotter, Chaboyer, Jevremovic, Kostov, Baron, Ferguson, and Jason. Abstract is located at http://adsabs.harvard.edu/abs/2008ApJS..178...89D] Web tools are also available at the home page (http://stellar.dartmouth.edu/~models/index.html). These tools allow users to create isochrones and convert them to luminosity functions or create synthetic horizontal branch models.

  1. Elemental abundance analyses with coadded DAO spectrograms. I - The field horizontal-branch stars HD-64488, 109995 and 161817

    NASA Technical Reports Server (NTRS)

    Adelman, Saul J.; Hill, Graham

    1987-01-01

    It is possible to improve the quality of elemental-abundance analyses by using higher-S/N data than has been the practice at high resolution. The procedures developed at the Dominion Astrophysical Observatory to coadd high-dispersion coude spectrograms are used with a minimum of 10 6.5-A/mm IIa-O spectrograms of each of three field hoorizontal-branch (FHB) A stars to increase the S/N of the photographic data over a considerable wavelength region. Fine analyses of the sharp-lined prototype FHB stars HD 109995 and 161817 show an internal consistency which justifies this effort. Their photospheric elemental abundances are similar to those of Population II globular cluster giants. As their photometric and spectrophotometric properties are similar to blue HB stars in such clusters, they are confirmed to be the brighter analogs of such stars. HD 64488, which is photometrically and spectrophotometrically similar to the FHB stars, is found to be metal-poor (Fe/H = -1) with much broader lines (v sin i = 147 km/s). The implications of the abundance anomalies of all three stars are discussed.

  2. Morphology-Controllable Synthesis of Cobalt Telluride Branched Nanostructures on Carbon Fiber Paper as Electrocatalysts for Hydrogen Evolution Reaction.

    PubMed

    Wang, Ke; Ye, Zhiguo; Liu, Chenqi; Xi, Dan; Zhou, Chongjian; Shi, Zhongqi; Xia, Hongyan; Liu, Guiwu; Qiao, Guanjun

    2016-02-10

    Cobalt telluride branched nanostructures on carbon fiber paper (CFP) with two different morphologies were synthesized via solution-based conversion reaction. Both the CoTe2 with nanodendrite and CoTe with nanosheet morphologies on the CoTe2 nanotube (CoTe2 NDs/CoTe2 NTs and CoTe NSs/CoTe2 NTs) supported by CFP exhibit high activities toward hydrogen evolution reaction (HER). Particularly, the CoTe NSs/CoTe2 NTs only require an overpotential of 230.0 mV to deliver the current density of 100 mA cm(-2) in acid solution. After cycling for 5000 cycles or 20 h continual electrolysis, only a small performance loss is observed. PMID:26809181

  3. Self-assembly via branching morphologies in nematic liquid-crystal nanocomposites

    NASA Astrophysics Data System (ADS)

    Gurevich, Sebastian; Soule, Ezequiel; Rey, Alejandro; Reven, Linda; Provatas, Nikolas

    2014-08-01

    We demonstrate that the morphological diversity in liquid-crystal hybrid systems is much richer than previously anticipated. More importantly, we reveal the existence of a dual mechanism for self-assembly of nanoparticles via morphological instabilities at phase boundaries. Using numerical simulations, we study the growth of isolated nematic droplets in an isotropic liquid crystal (LC) doped with nanoparticles (NPs) and provide insight into the nature of microstructure evolution in LC hybrids. Our work expands the numerically accessible time and length scales in these systems, capturing morphologies which develop under the competition of nonequilibrium elastic interactions, diffusive instabilities mediated by NP transport, and the anisotropy of the nematic field. By mapping nematic morphologies, we also propose a methodology for estimating various important LC material parameters that are difficult to obtain experimentally.

  4. Quantifying Morphological Parameters of the Terminal Branching Units in a Mouse Lung by Phase Contrast Synchrotron Radiation Computed Tomography

    PubMed Central

    Hwang, Jeongeun; Kim, Miju; Kim, Seunghwan; Lee, Jinwon

    2013-01-01

    An effective technique of phase contrast synchrotron radiation computed tomography was established for the quantitative analysis of the microstructures in the respiratory zone of a mouse lung. Heitzman’s method was adopted for the whole-lung sample preparation, and Canny’s edge detector was used for locating the air-tissue boundaries. This technique revealed detailed morphology of the respiratory zone components, including terminal bronchioles and alveolar sacs, with sufficiently high resolution of 1.74 µm isotropic voxel size. The technique enabled visual inspection of the respiratory zone components and comprehension of their relative positions in three dimensions. To check the method’s feasibility for quantitative imaging, morphological parameters such as diameter, surface area and volume were measured and analyzed for sixteen randomly selected terminal branching units, each consisting of a terminal bronchiole and a pair of succeeding alveolar sacs. The four types of asymmetry ratios concerning alveolar sac mouth diameter, alveolar sac surface area, and alveolar sac volume are measured. This is the first ever finding of the asymmetry ratio for the terminal bronchioles and alveolar sacs, and it is noteworthy that an appreciable degree of branching asymmetry was observed among the alveolar sacs at the terminal end of the airway tree, despite the number of samples was small yet. The series of efficient techniques developed and confirmed in this study, from sample preparation to quantification, is expected to contribute to a wider and exacter application of phase contrast synchrotron radiation computed tomography to a variety of studies. PMID:23704918

  5. The Abundances of Neutron-capture Species in the Very Metal-poor Globular Cluster M15: A Uniform Analysis of Red Giant Branch and Red Horizontal Branch Stars

    NASA Astrophysics Data System (ADS)

    Sobeck, Jennifer S.; Kraft, Robert P.; Sneden, Christopher; Preston, George W.; Cowan, John J.; Smith, Graeme H.; Thompson, Ian B.; Shectman, Stephen A.; Burley, Gregory S.

    2011-06-01

    The globular cluster M15 is unique in its display of star-to-star variations in the neutron-capture elements. Comprehensive abundance surveys have been previously conducted for handfuls of M15 red giant branch (RGB) and red horizontal branch (RHB) stars. No attempt has been made to perform a single, self-consistent analysis of these stars, which exhibit a wide range in atmospheric parameters. In the current effort, a new comparative abundance derivation is presented for three RGB and six RHB members of the cluster. The analysis employs an updated version of the line transfer code MOOG, which now appropriately treats coherent, isotropic scattering. The apparent discrepancy in the previously reported values for the metallicity of M15 RGB and RHB stars is addressed and a resolute disparity of Δ(RHB - RGB) ≈ 0.1 dex in the iron abundance was found. The anti-correlative behavior of the light neutron-capture elements (Sr, Y, Zr) is clearly demonstrated with both Ba and Eu, standard markers of the s- and r-process, respectively. No conclusive detection of Pb was made in the RGB targets. Consequently for the M15 cluster, this suggests that the main component of the s-process has made a negligible contribution to those elements normally dominated by this process in solar system material. Additionally for the M15 sample, a large Eu abundance spread is confirmed, which is comparable to that of the halo field at the same metallicity. These abundance results are considered in the discussion of the chemical inhomogeneity and nucleosynthetic history of M15.

  6. Poly(L-lactide)/branched β-cyclodextrin blends: Thermal, morphological and mechanical properties.

    PubMed

    Lizundia, E; Gómez-Galván, F; Pérez-Álvarez, L; León, L M; Vilas, J L

    2016-06-25

    In this work we develop poly(L-lactide)/branched β-cyclodextrin (bβCD) blends in an attempt to obtain new biocompatible and biodegradable materials to be used in the emerging fields of pharmaceutical, biomedicine and food industry. Ionic branched β-cyclodextrin (bβCD) was obtained by polycondensation of the β-CD monomer and it was blended with a commercially available PLLA. Fourier transform infrared spectroscopy (FTIR) has been applied to study the occurring interactions between both partners. Thermal properties of blends have been analyzed by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA), while the phase structure of the blends was analyzed by scanning electron microscopy (SEM). Finally, dynamic mechanical analysis (DMA) has been used to provide further insights into the features controlling miscibility between PLLA and bβCD. Results show the presence of a single phase irrespectively of the blend composition. Overall, this work opens new perspectives for the development of naturally available materials with tunable functional properties for applications in which cyclodextrins emerge as a new class of promising candidates. PMID:27083789

  7. The morphology of blends of linear and branched polyethylenes in solid state by small-angle scattering

    SciTech Connect

    Wignall, G.D.; Londono, J.D.; Alamo, R.G.

    1995-12-01

    We have used small-angle neutron and x-ray scattering (SANS And SAXS) to investigate the solid state morphology of blends of high-density and low-density polyethylenes (HDPE and LDPE). The blends are homogenous in the melt as demonstrated by SANS using the contrast obtained by deuterating the linear polymer, though they phase segregate on slow cooling (0.75{degree}C/min). For high concentrations ({theta} {ge} 0.5) of linear polymer, there are separate stacks of HDPE and LDPE lamellae, as indicated by 2-peak SAXS curves. For predominantly branched blends, the phase separation is less complete, and the components are separated within the same lamellar stack, with alternating HDPE and LDPE lamellae. Moreover, the phases no longer consist of the pure components and the HDPE lamellae contain up to 15% LDPE. Rapid quenching into dry-ice/acetone (-78{degree}C) produces only one lamellar stack over the whole concentration range. The blends show extensive cocrystallization with a tendency for the branched material to be preferentially located in the amorphous regions. For high concentrations ({theta} {ge} 0.5) of HDPE-D the overall scattering length density is high and the excess concentration of LDPE between the lamellae enhances the contrast between the crystalline and amorphous phases. Thus, the interlamellar spacing (long period) is clearly visible in the SANS pattern. The blend morphology is a strong function of the quench rate and samples quenched less rapidly (e.g., into water at 23{degree}C) show a similar morphology to slowly cooled samples.

  8. The Century Survey Galactic Halo Project III: A Complete 4300 DEG2 Survey of Blue Horizontal Branch Stars in the Metal-Weak Thick Disk and Inner Halo

    NASA Astrophysics Data System (ADS)

    Brown, Warren R.; Beers, Timothy C.; Wilhelm, Ronald; Allende Prieto, Carlos; Geller, Margaret J.; Kenyon, Scott J.; Kurtz, Michael J.

    2008-02-01

    We present a complete spectroscopic survey of 2414 2MASS-selected blue horizontal branch (BHB) candidates selected over 4300 deg2 of the sky. We identify 655 BHB stars in this non-kinematically selected sample. We calculate the luminosity function of field BHB stars, and find evidence for very few hot BHB stars in the field. The BHB stars located at a distance from the Galactic plane |Z| < 4 kpc trace what is clearly a metal-weak thick disk population, with a mean metallicity of [Fe/H] = -1.7, a rotation velocity gradient of dvrot/d|Z| = -28 ± 3.4 km s-1 in the region |Z| < 6 kpc, and a density scale height of hZ = 1.26 ± 0.1 kpc. The BHB stars located at 5 < |Z| < 9 kpc are a predominantly inner-halo population, with a mean metallicity of [Fe/H] = -2.0 and a mean Galactic rotation of -4 ± 31 km s-1. We infer the density of halo and thick disk BHB stars is 104 ± 37 kpc-3 near the Sun, and the relative normalization of halo to thick-disk BHB stars is 4 ± 1% near the Sun.

  9. Nine new metal-poor stars on the subgiant and red horizontal branches with high levels of r-process enhancement

    NASA Astrophysics Data System (ADS)

    Roederer, Ian U.; Cowan, John J.; Preston, George W.; Shectman, Stephen A.; Sneden, Christopher; Thompson, Ian B.

    2014-12-01

    We report the discovery of nine metal-poor stars with high levels of r-process enhancement (+0.81 ≤ [Eu/Fe] ≤ +1.13), including six subgiants and three stars on the red horizontal branch. We also analyse four previously known r-process-enhanced metal-poor red giants. From this sample of 13 stars, we draw the following conclusions. (1) High levels of r-process enhancement are found in a broad range of stellar evolutionary states, reaffirming that this phenomenon is not associated with a chemical peculiarity of red giant atmospheres. (2) Only 1 of 10 stars observed at multiple epochs shows radial-velocity variations, reaffirming that stars with high levels of r-process enhancement are not preferentially found among binaries. (3) Only 2 of the 13 stars are highly enhanced in C and N, indicating that there is no connection between high levels of r-process enhancement and high levels of C and N. (4) The dispersions in [Sr/Ba] and [Sr/Eu] are larger than the dispersions in [Ba/Eu] and [Yb/Eu], suggesting that the elements below the second r-process peak do not always scale with those in the rare Earth domain, even within the class of highly-r-process-enhanced stars. (5) The light-element (12 ≤ Z ≤ 30) abundances of highly-r-process-enhanced stars are indistinguishable from those with normal levels of r-process material at the limit of our data, 3.5 per cent (0.015 dex) on average. The nucleosynthetic sites responsible for the large r-process enhancements did not produce any detectable light-element abundance signatures distinct from normal core-collapse supernovae.

  10. On the interpretation of sub-giant branch morphologies of intermediate-age star clusters with extended main sequence turnoffs

    NASA Astrophysics Data System (ADS)

    Goudfrooij, Paul; Girardi, Léo; Rosenfield, Philip; Bressan, Alessandro; Marigo, Paola; Correnti, Matteo; Puzia, Thomas H.

    2015-06-01

    High-quality photometry of many star clusters in the Magellanic Clouds with ages of 1-2 Gyr revealed main sequence turnoffs (MSTOs) that are significantly wider than can be accounted for by a simple stellar population (SSP). Such extended MSTOs (eMSTOs) are often interpreted in terms of an age spread of several 108 yr, challenging the traditional view of star clusters as being formed in a single star formation episode. Li et al. and Bastian & Niederhofer recently investigated the sub-giant branches (SGBs) of NGC 1651, NGC 1806, and NGC 1846, three star clusters in the Large Magellanic Cloud (LMC) that exhibit an eMSTO. They argued that the SGB of these star clusters can be explained only by an SSP. We study these and two other similar star clusters in the LMC, using extensive simulations of SSPs including unresolved binaries. We find that the shapes of the cross-SGB profiles of all star clusters in our sample are in fact consistent with their cross-MSTO profiles when the latter are interpreted as age distributions. Conversely, SGB morphologies of star clusters with eMSTOs are found to be inconsistent with those of simulated SSPs. Finally, we create PARSEC isochrones from tracks featuring a grid of convective overshoot levels and a very fine grid of stellar masses. A comparison of the observed photometry with these isochrones shows that the morphology of the red clump (RC) of such star clusters is also consistent with that implied by their MSTO in the age spread scenario. We conclude that the SGB and RC morphologies of star clusters featuring eMSTOs are consistent with the scenario in which the eMSTOs are caused by a distribution of stellar ages.

  11. Anatomy of the lamprey ear: morphological evidence for occurrence of horizontal semicircular ducts in the labyrinth of Petromyzon marinus

    USGS Publications Warehouse

    Maklad, Adel; Reed, Caitlyn; Johnson, Nicholas S.; Fritzsch, Bernd

    2014-01-01

    In jawed (gnathostome) vertebrates, the inner ears have three semicircular canals arranged orthogonally in the three Cartesian planes: one horizontal (lateral) and two vertical canals. They function as detectors for angular acceleration in their respective planes. Living jawless craniates, cyclostomes (hagfish and lamprey) and their fossil records seemingly lack a lateral horizontal canal. The jawless vertebrate hagfish inner ear is described as a torus or doughnut, having one vertical canal, and the jawless vertebrate lamprey having two. These observations on the anatomy of the cyclostome (jawless vertebrate) inner ear have been unchallenged for over a century, and the question of how these jawless vertebrates perceive angular acceleration in the yaw (horizontal) planes has remained open. To provide an answer to this open question we reevaluated the anatomy of the inner ear in the lamprey, using stereoscopic dissection and scanning electron microscopy. The present study reveals a novel observation: the lamprey has two horizontal semicircular ducts in each labyrinth. Furthermore, the horizontal ducts in the lamprey, in contrast to those of jawed vertebrates, are located on the medial surface in the labyrinth rather than on the lateral surface. Our data on the lamprey horizontal duct suggest that the appearance of the horizontal canal characteristic of gnathostomes (lateral) and lampreys (medial) are mutually exclusive and indicate a parallel evolution of both systems, one in cyclostomes and one in gnathostome ancestors.

  12. Morphology-controlled cactus-like branched anatase TiO2 arrays with high light-harvesting efficiency for dye-sensitized solar cells

    NASA Astrophysics Data System (ADS)

    Wu, Wu-Qiang; Rao, Hua-Shang; Feng, Hao-Lin; Guo, Xin-Dong; Su, Cheng-Yong; Kuang, Dai-Bin

    2014-08-01

    The present work establishes a facile process for one-step hydrothermal growth of vertically aligned anatase cactus-like branched TiO2 (CBT) arrays on a transparent conducting oxide (TCO) substrate. Various CBT morphologies are obtained by adjusting the potassium titanium oxide oxalate (PTO) reactant concentration (from 0.05 M to 0.15 M) and this yields a morphologically-controllable branched TiO2 arrays geometry. The CBT arrays consist of a vertically oriented nanowire (NW) or nanosheet (NS) stem and a host of short nanorod (NR) branches. The hierarchical CBT arrays demonstrate their excellent candidatures as photoanodes, which are capable of exhibiting high light-harvesting efficiency in dye-sensitized solar cells (DSSCs). Consequently, DSSCs based on 7 μm long optimized CBT arrays (0.05 M PTO), which are assembled with high density and high aspect-ratio NR branches, exhibit an impressive power conversion efficiency of 6.43% under AM 1.5G one sun illumination. The high performance can be attributed to the prominent light-harvesting efficiency, resulting from larger surface area and superior light-scattering capability.

  13. Allometry of root branching and its relationship to root morphological and functional traits in three range grasses

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Several studies have documented the existence of correlative mechanisms that control lateral root emergence in plants. To better understand root branching responses to nutrients, root growth in three range grasses [Whitmar cultivar of bluebunch wheatgrass (Pseudoroegneria spicata (Pursh) Love), Hyc...

  14. Constraints on the Distance Moduli, Helium and Metal Abundances, and Ages of Globular Clusters from their RR Lyrae and Non-variable Horizontal-branch Stars. I. M3, M15, and M92

    NASA Astrophysics Data System (ADS)

    VandenBerg, Don A.; Denissenkov, P. A.; Catelan, Márcio

    2016-08-01

    Up-to-date isochrones, zero-age horizontal-branch (ZAHB) loci, and evolutionary tracks for core He-burning stars are applied to the color–magnitude diagrams of M3, M15, and M92, focusing in particular on their RR Lyrae populations. Periods for the ab- and c-type variables are calculated using the latest theoretical calibrations of {log} {P}{ab} and {log} {P}c as a function of luminosity, mass, effective temperature ({T}{{eff}}), and metallicity. Our models are generally able to reproduce the measured periods to well within the uncertainties implied by the stellar properties on which pulsation periods depend, as well as the mean periods and cluster-to-cluster differences in < {P}{ab}> and < {P}c> , on the assumption of well-supported values of E(B-V), {(m-M)}V, and [Fe/H]. While many of RR Lyrae in M3 lie close to the same ZAHB that fits the faintest horizontal-branch (HB) stars at bluer or redder colors, the M92 variables are all significantly evolved stars from ZAHB locations on the blue side of the instability strip. M15 appears to contain a similar population of HB stars as M92, along with additional helium-enhanced populations not present in the latter which comprise most of its RR Lyrae stars. The large number of variables in M15 and the similarity of the observed values of < {P}{ab}> and < {P}c> in M15 and M92 can be explained by HB models that allow for variations in Y. Similar ages (˜12.5 Gyr) are found for all three clusters, making them significantly younger than the field halo subgiant HD 140283. Our analysis suggests a preference for stellar models that take diffusive processes into account.

  15. Constraints on the Distance Moduli, Helium and Metal Abundances, and Ages of Globular Clusters from their RR Lyrae and Non-variable Horizontal-branch Stars. I. M3, M15, and M92

    NASA Astrophysics Data System (ADS)

    VandenBerg, Don A.; Denissenkov, P. A.; Catelan, Márcio

    2016-08-01

    Up-to-date isochrones, zero-age horizontal-branch (ZAHB) loci, and evolutionary tracks for core He-burning stars are applied to the color–magnitude diagrams of M3, M15, and M92, focusing in particular on their RR Lyrae populations. Periods for the ab- and c-type variables are calculated using the latest theoretical calibrations of {log} {P}{ab} and {log} {P}c as a function of luminosity, mass, effective temperature ({T}{{eff}}), and metallicity. Our models are generally able to reproduce the measured periods to well within the uncertainties implied by the stellar properties on which pulsation periods depend, as well as the mean periods and cluster-to-cluster differences in < {P}{ab}> and < {P}c> , on the assumption of well-supported values of E(B-V), {(m-M)}V, and [Fe/H]. While many of RR Lyrae in M3 lie close to the same ZAHB that fits the faintest horizontal-branch (HB) stars at bluer or redder colors, the M92 variables are all significantly evolved stars from ZAHB locations on the blue side of the instability strip. M15 appears to contain a similar population of HB stars as M92, along with additional helium-enhanced populations not present in the latter which comprise most of its RR Lyrae stars. The large number of variables in M15 and the similarity of the observed values of < {P}{ab}> and < {P}c> in M15 and M92 can be explained by HB models that allow for variations in Y. Similar ages (∼12.5 Gyr) are found for all three clusters, making them significantly younger than the field halo subgiant HD 140283. Our analysis suggests a preference for stellar models that take diffusive processes into account.

  16. Bundle-Branch Block Morphology and Other Predictors of Outcome After Cardiac Resynchronization Therapy in Medicare Patients

    PubMed Central

    Bilchick, Kenneth C.; Kamath, Sandeep; DiMarco, John P.; Stukenborg, George J.

    2013-01-01

    Background Clinical trials of cardiac resynchronization therapy (CRT) have enrolled a select group of patients, with few patients in subgroups such as right bundle-branch block (RBBB). Analysis of population-based outcomes provides a method to identify real-world predictors of CRT outcomes. Methods and Results Medicare Implantable Cardioverter-Defibrillator Registry (2005 to 2006) data were merged with patient outcomes data. Cox proportional-hazards models assessed death and death/heart failure hospitalization outcomes in patients with CRT and an implantable cardioverter-defibrillator (CRT-D). The 14 946 registry patients with CRT-D (median follow-up, 40 months) had 1-year, 3-year, and overall mortality rates of 12%, 32%, and 37%, respectively. New York Heart Association class IV heart failure status (1-year hazard ratio [HR], 2.23; 3-year HR, 1.98; P<0.001) and age ≥80 years (1-year HR, 1.74; 3-year HR, 1.75; P<0.001) were associated with increased mortality both early and late after CRT-D. RBBB (1-year HR, 1.44; 3-year HR, 1.37; P<0.001) and ischemic cardiomyopathy (1-year HR, 1.39; 3-year HR, 1.44; P<0.001) were the next strongest adjusted predictors of both early and late mortality. RBBB and ischemic cardiomyopathy together had twice the adjusted hazard for death (HR, 1.99; P<0.001) as left BBB and nonischemic cardiomyopathy. QRS duration of at least 150 ms predicted more favorable outcomes in left BBB but had no impact in RBBB. A secondary analysis showed lower hazards for CRT-D compared with standard implantable cardioverter-defibrillators in left BBB compared with RBBB. Conclusions In Medicare patients, RBBB, ischemic cardiomyopathy, New York Heart Association class IV status, and advanced age were powerful adjusted predictors of poor outcome after CRT-D. Real-world mortality rates 3 to 4 years after CRT-D appear higher than previously recognized. PMID:21041691

  17. AMPLITUDE FINE STRUCTURE IN THE CEPHEID P-L RELATION. I. AMPLITUDE DISTRIBUTION ACROSS THE RR LYRAE INSTABILITY STRIP MAPPED USING THE ACCESSIBILITY RESTRICTION IMPOSED BY THE HORIZONTAL BRANCH

    SciTech Connect

    Sandage, Allan

    2010-10-10

    The largest amplitude light curves for both RR Lyrae (RRL) variables and classical Cepheids with periods less than 10 days and greater than 20 days occur at the blue edge of the respective instability strips. It is shown that the equation for the decrease in amplitude with penetration into the strip from the blue edge, and hence the amplitude fine structure within the strip, is the same for RRL and the Cepheids despite their metallicity differences. However, the manifestation of this identity is different between the two classes of variables because the sampling of the RRL strip is restricted by the discrete strip positions of the horizontal branch, a restriction that is absent for the Cepheids in stellar aggregates with a variety of ages. To show the similarity of the strip amplitude fine structure for RRL and Cepheids, we make a grid of lines of constant amplitude in the H-R diagram of the strip using amplitude data for classical Cepheids in the Galaxy, LMC, and SMC. The model implicit in the grid, that also contains lines of constant period, is used to predict the correlations between period, amplitude, and color for the two Oosterhoff RRL groups in globular clusters. The good agreement of the predictions with the observations using the classical Cepheid amplitude fine structure also for the RRL shows one aspect of the unity of the pulsation processes between the two classes of variables.

  18. Biodegradable films of partly branched poly(l-lactide)-co-poly(epsilon-caprolactone) copolymer: modulation of phase morphology, plasticization properties and thermal depolymerization.

    PubMed

    Broström, Jenny; Boss, Annika; Chronakis, Ioannis S

    2004-01-01

    We report on the modulation of phase morphology, plasticization properties, and thermal stability of films of partly branched poly(l-lactide)-co-poly(epsilon-caprolactone) copolymer (PLLA-co-PCL) with additions of low molecular weight compounds, namely, triethyl citrate ester, diethyl phthalate, diepoxy polyether (poly(propylene glycol) diglycidyl ether), and with epoxidized soybean oil (ESO). The PLLA-co-PCL/polyether films showed significant stability against thermal depolymerization, high film flexibility, and good plasticizing properties, probably due to cross-linking and chain branching formation between diepoxy groups with both the end carboxyl and hydroxyl groups of the PLLA copolymer (initially present or generated during the degradation process) to produce primary ester and ether bonds, respectively. Diethyl phthalate and triethyl citrate ester were found to be efficient plasticizers for PLLA copolymer in terms of glass transition and mechanical properties, but the more water-soluble plasticizer triethyl citrate induced a dramatic loss in the molecular weight of the copolymer. Although ESO cannot play the role of a plasticizer, it substantially stabilizes and retards thermal depolymerization of the PLLA copolymer matrix, possibly because of a reaction between epoxy groups with the end carboxyl and hydroxyl groups of the PLLA copolymer. The presence of ESO in PLLA-co-PCL/ESO/triethyl citrate blends enhanced the compatibility and miscibility of the plasticizer with the PLLA copolymer matrix, considerably improved the mechanical properties (elongation at break), and substantially stabilized the copolymer against thermal depolymerization. It seems likely that the epoxy groups interact not only with the end hydroxyl and carboxyl group of the copolymer but as well with the hydroxyl group of triethyl citrate plasticizer to produce a new ether bond (C-O-C) as the cross-linking unit. On the other hand, for PLLA-co-PCL/ESO/polyether blends, (80/10/10) epoxidized oil

  19. Serial Morphological Changes of Side-Branch Ostium after Paclitaxel-Coated Balloon Treatment of De Novo Coronary Lesions of Main Vessels

    PubMed Central

    Her, Ae-Young; Ann, Soe Hee; Singh, Gillian Balbir; Kim, Yong Hoon; Okamura, Takayuki; Garg, Scot; Koo, Bon-Kwon

    2016-01-01

    Purpose The effects on the side-branch (SB) ostium, following paclitaxel-coated balloon (PCB) treatment of de novo coronary lesions of main vessels have not been previously investigated. This study was aimed at evaluating the serial morphological changes of the SB ostium after PCB treatment of de novo coronary lesions of main vessels using optical coherence tomography (OCT). Materials and Methods This prospective, single-center observational study enrolled patients with de novo lesions, which were traversed by at least one SB (≥1.5 mm) and were treated with PCB. The SB ostium was evaluated with serial angiographic and OCT assessments pre- and post-procedure, and at 9-months follow-up. Results Sixteen main vessel lesions were successfully treated with PCB, and 26 SBs were included for analysis. Mean SB ostial lumen area increased at 9-months follow-up (0.92±0.68 mm2 pre-procedure, 1.03±0.77 mm2 post-procedure and 1.42±1.18 mm2 at 9-months). The SB ostial lumen area gain was 0.02±0.24 mm2 between pre- and post-procedure, 0.37±0.64 mm2 between post-procedure and 9-months, and 0.60±0.93 mm2 between pre-procedure and 9-months. The ostial lumen area increased by 3.9% [interquartile range (IQR) of -33.3 to 10.4%] between pre- and post-procedure, 52.1% (IQR of -0.7 to 77.3%) between post-procedure and 9-months and 76.1% (IQR of 18.2 to 86.6%) between pre-procedure and 9-months. Conclusion PCB treatment of de novo coronary lesions of main vessels resulted in an increase in the SB ostial lumen area at 9-months. PMID:26996558

  20. The morphology of the sub-giant branch and red clump reveal no sign of age spreads in intermediate-age clusters

    NASA Astrophysics Data System (ADS)

    Bastian, N.; Niederhofer, F.

    2015-04-01

    A recent surprise in stellar cluster research, made possible through the precision of Hubble Space Telescope photometry, was that some intermediate-age (1-2 Gyr) clusters in the Large and Small Magellanic Clouds have main-sequence turn-off (MSTO) widths that are significantly broader than would be expected for a simple stellar population (SSP). One interpretation of these extended MSTOs (eMSTOs) is that age spreads of the order of ˜500 Myr exist within the clusters, radically redefining our view of stellar clusters, which are traditionally thought of as single-age, single-metallicity stellar populations. Here we test this interpretation by studying other regions of the CMD that should also be affected by such large age spreads, namely the width of the sub-giant branch (SGB) and the red clump (RC). We study two massive clusters in the LMC that display the eMSTO phenomenon (NGC 1806 and NGC 1846) and show that both have SGB and RC morphologies that are in conflict with expectations if large age spreads exist within the clusters. We conclude that the SGB and RC widths are inconsistent with extended star formation histories within these clusters, hence age spreads are not likely to be the cause of the eMSTO phenomenon. Our results are in agreement with recent studies that also have cast doubt on whether large age spreads can exist in massive clusters; namely the failure to find age spreads in young massive clusters, a lack of gas/dust detected within massive clusters, and homogeneous abundances within clusters that exhibit the eMSTO phenomenon.

  1. Shoot branching.

    PubMed

    Ward, Sally P; Leyser, Ottoline

    2004-02-01

    The mature form of a plant shoot system is an expression of several genetically controlled traits, many of which are also environmentally regulated. A major component of this architectural variation is the degree of shoot branching. Recent results indicate conserved mechanisms for shoot branch development across the monocots and eudicots. The existence of a novel long-range branch-inhibiting signal has been inferred from studies of branching mutants in pea and Arabidopsis. PMID:14732444

  2. One-step growth of Si{sub 3}N{sub 4} stem-branch featured nanostructures: Morphology control by VS and VLS mode

    SciTech Connect

    Wang Qiushi; Gao Wei; Shan Lianchen; Zhang Jian; Jin Yunxia; Cong Ridong; Cui Qiliang

    2011-09-15

    We report here one-step synthesis of Si{sub 3}N{sub 4} nanodendrites by selectively applying a vapor-solid (VS) and vapor-liquid-solid (VLS) strategy via direct current arc discharge method. The resultant nanodendrites were characterized by scanning electron microscopy, energy-dispersive X-ray spectroscopy, transmission electron microscopy and X-ray powder diffraction. The spine-shaped nanodendrites were generated by a noncatalytic growth following a VS mode. The uniform secondary nanowire branches were epitaxial grown from two side surfaces of the nanowire stems. The pine-shaped nanodendrites were obtained through a catalytic growth in a VLS process. These branch nanowires were unsystematically grown from the nanocone-like stems. The photoluminescence spectra of the nanodendrites show a strong white light emission around 400-750 nm, suggesting their potential applications in light and electron emission devices. - Graphical abstract: Spine-shaped and pine-shaped Si{sub 3}N{sub 4} hierarchical nanostructures were synthesized by VS and VLS mode with plasma-assisted dc arc discharge method. Highlights: > Si{sub 3}N{sub 4} stem-branch featured nanostructures have been prepared. > Spine-shaped nanodendrites were generated by a noncatalytic growth following a VS mode. > Pine-shaped nanodendrites were obtained through a catalytic growth in a VLS process.

  3. Single chain morphology and nanofiber-like aggregates of branched β-(1 → 3)-D-glucan in water/dimethylsulfoxide solution.

    PubMed

    Chen, Cong; Meng, Yan; Li, Sheng; Wu, Wenhua; Liu, Chuanjun; Xu, Xiaojuan; Zhang, Lina

    2016-02-10

    A polysaccharide coded as PR-CA was extracted from Polyporus rhinoceros and determined to be a β-(1 → 3)-D-glucan with multiple branches. The weight-average molecular weights (Mw) of PR-CA in dimethylsulfoxide (DMSO) and in water were determined with static light scattering (SLS) to be 3.57 × 10(5) and 1.79 × 10(7), indicating existence of the single chains in DMSO and co-existence of single chains and aggregates in water. Moreover, the stiffness of single chains of PR-CA in water was directly visualized by atomic force microscopy (AFM) and transmission electron microscopy (TEM). The hollow structure of PR-CA nanofibers with width of 30-40 nm and length of ∼ 350 nm formed in the water/DMSO (9:1, v:v) was demonstrated by a fluorescent probe tetraphenylethylene (TPE) via aggregation-induced emission (AIE). The formation of PR-CA nanofibers was ascribed to the parallel aggregation of the extended PR-CA chains due to the hydrogen bonding and hydrophobic interaction. This work offered valuable results for promising applications of natural branched β-glucans in the biological fields of drug inclusion, delivery and disease diagnosis. PMID:26686132

  4. Early treatment of anterior open bite: Comparison of the vertical and horizontal morphological changes induced by magnetic bite-blocks and adjusted rapid molar intruders

    PubMed Central

    Takahashi, Ichiro; Sawan, Mhd Naser

    2015-01-01

    Objective This prospective clinical study aims to determine the differences between two treatment modalities for anterior open bite in growing patients. The treatment modalities involved the use of magnetic bite-blocks (MBBs) or rapid molar intruders (RMIs) applied with posterior bite-blocks. Methods Fifteen consecutive patients with a mean age of 11.2 (standard deviation [SD] = 1.6) years and a mean open bite of -3.9 mm were treated with MBBs. Another 15 consecutive patients with a mean age of 10.9 (SD = 1.8) years and a mean open bite of -3.8 mm were treated with RMIs applied on bite-blocks. Cephalometric radiographs were obtained before (T1) and immediately after appliance removal (T2). The treatments lasted four months, during which the appliances were cemented to the teeth. The morphological changes were measured in each group and compared using logistic regression analysis. Results The MBB group exhibited significantly greater decreases in SNA angle, ANB angle, overjet, and maxillary incisor angle (p < 0.05). The MBBs induced greater effects on the maxilla and maxillary dentition. The MBBs restrained maxillary forward growth and retracted the maxillary incisors more effectively than did the RMIs. Consequently, changes in the intermaxillary relationships and overjets were more distinct in the MBB group. Conclusions The anteroposterior differences between the appliances suggest that MBBs should be preferred for the treatment of patients with Class II open bites and maxillary incisor protrusions. PMID:25667916

  5. Metamorphopsia Associated with Branch Retinal Vein Occlusion

    PubMed Central

    Manabe, Koichiro; Tsujikawa, Akitaka; Osaka, Rie; Nakano, Yuki; Fujita, Tomoyoshi; Shiragami, Chieko; Hirooka, Kazuyuki; Uji, Akihito; Muraoka, Yuki

    2016-01-01

    Purpose To apply M-CHARTS for quantitative measurements of metamorphopsia in eyes with acute branch retinal vein occlusion (BRVO) and to elucidate the pathomorphology that causes metamorphopsia. Methods This prospective study consisted of 42 consecutive patients (42 eyes) with acute BRVO. Both at baseline and one month after treatment with ranibizumab, metamorphopsia was measured with M-CHARTS, and the retinal morphological changes were examined with optical coherence tomography. Results At baseline, metamorphopsia was detected in the vertical and/or horizontal directions in 29 (69.0%) eyes; the mean vertical and horizontal scores were 0.59 ± 0.57 and 0.52 ± 0.67, respectively. The maximum inner retinal thickness showed no association with the M-CHARTS score, but the M-CHARTS score was correlated with the total foveal thickness (r = 0.43, p = 0.004), the height of serous retinal detachment (r = 0.31, p = 0.047), and the maximum outer retinal thickness (r = 0.36, p = 0.020). One month after treatment, both the inner and outer retinal thickness substantially decreased. However, metamorphopsia persisted in 26 (89.7%) of 29 eyes. The posttreatment M-CHARTS score was not correlated with any posttreatment morphological parameters. However, the posttreatment M-CHARTS score was weakly correlated with the baseline total foveal thickness (r = 0.35. p = 0.024) and closely correlated with the baseline M-CHARTS score (r = 0.78, p < 0.001). Conclusions Metamorphopsia associated with acute BRVO was quantified using M-CHARTS. Initial microstructural changes in the outer retina from acute BRVO may primarily account for the metamorphopsia. PMID:27123642

  6. 7. Underside of Roadbed (Interior beams cast horizontal, imprints of ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    7. Underside of Roadbed (Interior beams cast horizontal, imprints of timbers used as formwork visible on abutment walls and beams) - North Bridge, Spanning Quarton Lake branch of River Rouge, Birmingham, Oakland County, MI

  7. 7. Underside of Roadbed (Interior beams cast horizontal, imprints of ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    7. Underside of Roadbed (Interior beams cast horizontal, imprints of timbers used as formwork visible on abutment walls and beams) - South Bridge, Spanning Quarton Lake branch of River Rouge, Birmingham, Oakland County, MI

  8. Horizontal drilling technology advances

    SciTech Connect

    Not Available

    1991-03-04

    Horizontal drilling technology is making further advances in the Texas Austin chalk play as such drilling continues to spread in many U.S. land areas. One company has completed a Cretaceous Austin chalk oil well with the longest horizontal well bore in Texas and what at 1 1/6 miles is believed to be the world's longest medium radius horizontal displacement.

  9. Horizontal drilling developments

    SciTech Connect

    Gust, D.

    1997-05-01

    The advantages of horizontal drilling are discussed. Use of horizontal drilling has climbed in the past half decade as technology and familiarity offset higher costs with higher production rates and greater recoveries from new and existing wells. In essence, all types of horizontal wells expose a larger section of the reservoir to the wellbore with a resulting increase in flow rates. (A horizontal well may also be drilled to provide coning control or to intersect vertical fractures.) Thus, drilling horizontally, both onshore and offshore, reduces the number of wells necessary to develop a field.

  10. Tree Branching: Leonardo da Vinci's Rule versus Biomechanical Models

    PubMed Central

    Minamino, Ryoko; Tateno, Masaki

    2014-01-01

    This study examined Leonardo da Vinci's rule (i.e., the sum of the cross-sectional area of all tree branches above a branching point at any height is equal to the cross-sectional area of the trunk or the branch immediately below the branching point) using simulations based on two biomechanical models: the uniform stress and elastic similarity models. Model calculations of the daughter/mother ratio (i.e., the ratio of the total cross-sectional area of the daughter branches to the cross-sectional area of the mother branch at the branching point) showed that both biomechanical models agreed with da Vinci's rule when the branching angles of daughter branches and the weights of lateral daughter branches were small; however, the models deviated from da Vinci's rule as the weights and/or the branching angles of lateral daughter branches increased. The calculated values of the two models were largely similar but differed in some ways. Field measurements of Fagus crenata and Abies homolepis also fit this trend, wherein models deviated from da Vinci's rule with increasing relative weights of lateral daughter branches. However, this deviation was small for a branching pattern in nature, where empirical measurements were taken under realistic measurement conditions; thus, da Vinci's rule did not critically contradict the biomechanical models in the case of real branching patterns, though the model calculations described the contradiction between da Vinci's rule and the biomechanical models. The field data for Fagus crenata fit the uniform stress model best, indicating that stress uniformity is the key constraint of branch morphology in Fagus crenata rather than elastic similarity or da Vinci's rule. On the other hand, mechanical constraints are not necessarily significant in the morphology of Abies homolepis branches, depending on the number of daughter branches. Rather, these branches were often in agreement with da Vinci's rule. PMID:24714065

  11. Biomechanical consequences of branching in flexible wave-swept macroalgae.

    PubMed

    Starko, Samuel; Claman, Barry Z; Martone, Patrick T

    2015-04-01

    Wave-swept macroalgae present an excellent system for studying the effects of chronic physical stress on the morphological evolution of plants. Wave-induced water velocities impose great drag forces, leading to a morphological tradeoff between light interception and drag reduction/tolerance. What are the hydrodynamic consequences of morphological diversification, such as increased branching? Drag was measured on artificial macroalgae of constant 'photosynthetic' area, but differing branching patterns, in a high-speed flume at water velocities up to 3.5 m s(-1). A meta-analysis was used to compare dislodgement forces of branched and unbranched species of comparable sizes in the field to determine if drag-prone morphologies had greater attachment strengths. Branched fronds experienced greater drag than unbranched fronds of the same size. Greater drag in branched forms was not the result of increased projected area but probably resulted from greater pressure or friction drag. In the field, branched species resisted greater dislodgement forces than unbranched species of comparable size, suggesting that branched species compensate for increased drag with stronger attachment to the substratum. Branching has clear biomechanical consequences, increasing drag and the need for increased attachment. This raises questions about physiological and ecological advantages that may have driven the repeated evolution of biomechanically costly, branched morphologies. PMID:25413976

  12. Characterizing Branched Flow

    NASA Astrophysics Data System (ADS)

    Drury, Byron; Klales, Anna; Heller, Eric

    2014-03-01

    Branched flow appears in a variety of physical systems spanning length scales from microns to thousands of kilometers. For instance, it plays an important role in both electron transport in two dimensional electron gases and the propagation of tsunamis in the ocean. Branches have typically been identified with caustics in the theoretical literature, but concentrations of flux recognizable as branches can arise from other mechanisms. We propose a generalized definition of branching based on a local measure of the stability of trajectories. We analytically and numerically study the characteristics of Hamiltonian flow in phase space and characterize the relationship between branch formation and trajectory stability.

  13. Epithelial dynamics of pancreatic branching morphogenesis

    PubMed Central

    Villasenor, Alethia; Chong, Diana C.; Henkemeyer, Mark; Cleaver, Ondine

    2010-01-01

    The mammalian pancreas is a highly branched gland, essential for both digestion and glucose homeostasis. Pancreatic branching, however, is poorly understood, both at the ultrastructural and cellular levels. In this article, we characterize the morphogenesis of pancreatic branches, from gross anatomy to the dynamics of their epithelial organization. We identify trends in pancreatic branch morphology and introduce a novel mechanism for branch formation, which involves transient epithelial stratification and partial loss of cell polarity, changes in cell shape and cell rearrangements, de novo tubulogenesis and epithelial tubule remodeling. In contrast to the classical epithelial budding and tube extension observed in other organs, a pancreatic branch takes shape as a multi-lumen tubular plexus coordinately extends and remodels into a ramifying, single-lumen ductal system. Moreover, our studies identify a role for EphB signaling in epithelial remodeling during pancreatic branching. Overall, these results illustrate distinct, step-wise cellular mechanisms by which pancreatic epithelium shapes itself to create a functional branching organ. PMID:21098570

  14. Horizontal well planning

    SciTech Connect

    Schuh, F.J. )

    1991-03-01

    Interest in horizontal drilling has exploded at a rate well above even the most optimistic projections. Certainly, this technique will not end with the Bakken and Austin Chalk plays. However, future reservoirs will undoubtedly require much more complicated well designs and multi-disciplined technical interaction than has been used so far. The horizontal drilling costs are too high to permit resolving of all the technical issues by trial and error. A multi-disciplinary team approach will be required in order for horizontal drilling to achieve its economic potential.

  15. 10. VIEW EAST, RECESS AREA WITH BOTTOM HORIZONTAL BEAM FOR ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    10. VIEW EAST, RECESS AREA WITH BOTTOM HORIZONTAL BEAM FOR EAST GATE - Bald Eagle Cross-Cut Canal Lock, North of Water Street along West Branch of Susquehanna River South bank, 500 feet East of Jay Street Bridge, Lock Haven, Clinton County, PA

  16. The rms-flux relations in different branches in Cyg X-2

    NASA Astrophysics Data System (ADS)

    Li, Z. B.; Song, L. M.; Qu, J. L.; Lei, Y. J.; Nie, J. Y.; Zhang, C. M.

    2012-10-01

    In this paper, the rms-flux (root mean square-flux) relation along the Z-track of the bright Z-Source Cyg X-2 is analyzed using the observational data of Rossi X-ray Timing Explorer (RXTE). Three types of rms-flux relations, i.e. positive, negative, and `arch'-like correlations are found in different branches. The rms is positively correlated with flux in normal branch (NB), but anti-correlated in the vertical horizontal branch (VHB). The rms-flux relation shows an `arch'-like shape in the horizontal branch (HB). We also try to explain this phenomenon using existing models.

  17. Horizontal drilling spurs optimism

    SciTech Connect

    Crouse, P.C. )

    1991-02-01

    1990 proved to be an exciting year for horizontal wells. This budding procedure appears to be heading for the mainstream oil and gas market, because it can more efficiently recover hydrocarbons from many reservoirs throughout the world. This paper reports on an estimated 1,000 wells that were drilled horizontally (all laterals) in 1990, with the Austin Chalk formation of Texas accounting for about 65% of all world activity. The Bakken Shale play in Montana and North Dakota proved to be the second most active area, with an estimated 90 wells drilled. Many operators in this play have indicated the bloom may be off the Bakken because of poor results outside the nose of the formation, further complicated by some of the harshest rock, reservoir and completion problems posed to horizontal technology.

  18. Horizontal carbon nanotube alignment.

    PubMed

    Cole, Matthew T; Cientanni, Vito; Milne, William I

    2016-09-21

    The production of horizontally aligned carbon nanotubes offers a rapid means of realizing a myriad of self-assembled near-atom-scale technologies - from novel photonic crystals to nanoscale transistors. The ability to reproducibly align anisotropic nanostructures has huge technological value. Here we review the present state-of-the-art in horizontal carbon nanotube alignment. For both in and ex situ approaches, we quantitatively assess the reported linear packing densities alongside the degree of alignment possible for each of these core methodologies. PMID:27546174

  19. Horizontal Advanced Tensiometer

    SciTech Connect

    Hubbell, Joel M.; Sisson, James B.

    2004-06-22

    An horizontal advanced tensiometer is described that allows the monitoring of the water pressure of soil positions, particularly beneath objects or materials that inhibit the use of previous monitoring wells. The tensiometer includes a porous cup, a pressure transducer (with an attached gasket device), an adaptive chamber, at least one outer guide tube which allows access to the desired horizontal position, a transducer wire, a data logger and preferably an inner guide tube and a specialized joint which provides pressure on the inner guide tube to maintain the seal between the gasket of the transducer and the adaptive chamber.

  20. Melons are Branched Polymers

    NASA Astrophysics Data System (ADS)

    Gurau, Razvan; Ryan, James P.

    2014-11-01

    Melonic graphs constitute the family of graphs arising at leading order in the 1/N expansion of tensor models. They were shown to lead to a continuum phase, reminiscent of branched polymers. We show here that they are in fact precisely branched polymers, that is, they possess Hausdorff dimension 2 and spectral dimension 4/3.

  1. Effect of a forced Couette flow on coupled convective and morphological instabilities during unidirectional solidification

    NASA Technical Reports Server (NTRS)

    Coriell, S. R.; Mcfadden, G. B.; Boisvert, R. F.; Sekerka, R. F.

    1984-01-01

    The effect of a forced Couette flow, parallel to a horizontal crystal-melt interface during directional solidification of an alloy of lead containing tin, on the onset of convective and morphological instabilities, is calculated numerically via a linear stability analysis. Such a flow does not affect perturbations with wave vectors perpendicular to the flow. For perturbations with wave vectors parallel to the flow, the onset of morphological instability is somewhat suppressed and thermosolutal convection is greatly suppressed. When instabilities occur, they are oscillatory and correspond to travelling waves. For values of the crystal growth velocity for which mixed morphological and convective modes occur, the presence of a forced flow produces sufficient decoupling to allow otherwise degenerate branches to be identified.

  2. Materials Test Branch

    NASA Technical Reports Server (NTRS)

    Gordon, Gail

    2012-01-01

    The Materials Test Branch resides at Marshall Space Flight Center's Materials and Processing laboratory and has a long history of supporting NASA programs from Mercury to the recently retired Space Shuttle. The Materials Test Branch supports its customers by supplying materials testing expertise in a wide range of applications. The Materials Test Branch is divided into three Teams, The Chemistry Team, The Tribology Team and the Mechanical Test Team. Our mission and goal is to provide world-class engineering excellence in materials testing with a special emphasis on customer service.

  3. The Olive Branch Awards.

    ERIC Educational Resources Information Center

    Harnack, William

    1984-01-01

    The first annual Olive Branch Awards, sponsored by the Writers' and Publishers Alliance and the Editors' Organizing Committee, were given to ten magazines, out of 60 that submitted entries. Winning entries are described briefly. (IM)

  4. Horizontal Cross Bracing Detail, Vertical Cross Bracing Detail, Horizontal Cross ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    Horizontal Cross Bracing Detail, Vertical Cross Bracing Detail, Horizontal Cross Bracing Joint, Vertical Cross Bracing End Detail - Ceylon Covered Bridge, Limberlost Park, spanning Wabash River at County Road 900 South, Geneva, Adams County, IN

  5. Horizontal geophone transducer assembly

    SciTech Connect

    Hefer, F.W.

    1985-06-25

    The geophone transducer comprises in combination: a geophone capable of detecting horizontal seismic waves, and a rigid casing having a gimbal chamber. A gimbal is provided inside the chamber on which the geophone is mounted for limited free angular movement in one direction only. The gimbal includes in one preferred embodiment a viscous liquid in which the geophone is only partially submerged while it is supported by a U-shaped bracket which is mounted for rotation about a fixed axis.

  6. Branch retinal vein occlusion.

    PubMed

    Hamid, Sadaf; Mirza, Sajid Ali; Shokh, Ishrat

    2008-01-01

    Retinal vein occlusions (RVO) are the second commonest sight threatening vascular disorder. Branch retinal vein occlusion (BRVO) and central retinal vein occlusion (CRVO) are the two basic types of vein occlusion. Branch retinal vein occlusion is three times more common than central retinal vein occlusion and- second only to diabetic retinopathy as the most common retinal vascular cause of visual loss. The origin of branch retinal vein occlusion undoubtedly includes both systemic factors such as hypertension and local anatomic factors such as arteriovenous crossings. Branch retinal vein occlusion causes a painless decrease in vision, resulting in misty or distorted vision. Current treatment options don't address the underlying aetiology of branch retinal vein occlusion. Instead they focus on treating sequelae of the occluded venous branch, such as macular oedema, vitreous haemorrhage and traction retinal detachment from neovascularization. Evidences suggest that the pathogenesis of various types of retinal vein occlusion, like many other ocular vascular occlusive disorders, is a multifactorial process and there is no single magic bullet that causes retinal vein occlusion. A comprehensive management of patients with retinal vascular occlusions is necessary to correct associated diseases or predisposing abnormalities that could lead to local recurrences or systemic event. Along with a review of the literature, a practical approach for the management of retinal vascular occlusions is required, which requires collaboration between the ophthalmologist and other physicians: general practitioner, cardiologist, internist etc. as appropriate according to each case. PMID:19385476

  7. Formation of chiral branched nanowires by the Eshelby Twist.

    PubMed

    Zhu, Jia; Peng, Hailin; Marshall, A F; Barnett, D M; Nix, W D; Cui, Yi

    2008-08-01

    Manipulating the morphology of inorganic nanostructures, such as their chirality and branching structure, has been actively pursued as a means of controlling their electrical, optical and mechanical properties. Notable examples of chiral inorganic nanostructures include carbon nanotubes, gold multishell nanowires, mesoporous nanowires and helical nanowires. Branched nanostructures have also been studied and been shown to have interesting properties for energy harvesting and nanoelectronics. Combining both chiral and branching motifs into nanostructures might provide new materials properties. Here we show a chiral branched PbSe nanowire structure, which is formed by a vapour-liquid-solid branching from a central nanowire with an axial screw dislocation. The chirality is caused by the elastic strain of the axial screw dislocation, which produces a corresponding Eshelby Twist in the nanowires. In addition to opening up new opportunities for tailoring the properties of nanomaterials, these chiral branched nanowires also provide a direct visualization of the Eshelby Twist. PMID:18685634

  8. Horizontal drilling in shallow reservoirs

    SciTech Connect

    Murray, W.F. Jr.; Schrider, L.A.; Haynes, C.D.; Mazza, R.L.

    1992-06-01

    The objectives of this joint horizontal drilling effort by the US DOE and Belden & Blake in the complex, low permeability Clinton Sandstone will focus on the following objectives: (1) apply horizontal drilling technology in hard, abrasive, and tight Clinton Sandstone; (2) evaluate effects of multiple hydraulic fracturing in a low permeability horizontal wellbore; (3) assess economic viability of horizontal drilling in the Clinton and similar tight gas sands.

  9. Horizontal drilling in shallow reservoirs

    SciTech Connect

    Murray, W.F. Jr.; Schrider, L.A.; Haynes, C.D.; Mazza, R.L.

    1992-01-01

    The objectives of this joint horizontal drilling effort by the US DOE and Belden Blake in the complex, low permeability Clinton Sandstone will focus on the following objectives: (1) apply horizontal drilling technology in hard, abrasive, and tight Clinton Sandstone; (2) evaluate effects of multiple hydraulic fracturing in a low permeability horizontal wellbore; (3) assess economic viability of horizontal drilling in the Clinton and similar tight gas sands.

  10. Damage Tolerance Assessment Branch

    NASA Technical Reports Server (NTRS)

    Walker, James L.

    2013-01-01

    The Damage Tolerance Assessment Branch evaluates the ability of a structure to perform reliably throughout its service life in the presence of a defect, crack, or other form of damage. Such assessment is fundamental to the use of structural materials and requires an integral blend of materials engineering, fracture testing and analysis, and nondestructive evaluation. The vision of the Branch is to increase the safety of manned space flight by improving the fracture control and the associated nondestructive evaluation processes through development and application of standards, guidelines, advanced test and analytical methods. The Branch also strives to assist and solve non-aerospace related NDE and damage tolerance problems, providing consultation, prototyping and inspection services.

  11. Pen Branch delta expansion

    SciTech Connect

    Nelson, E.A.; Christensen, E.J.; Mackey, H.E.; Sharitz, R.R.; Jensen, J.R.; Hodgson, M.E.

    1984-02-01

    Since 1954, cooling water discharges from K Reactor ({anti X} = 370 cfs {at} 59 C) to Pen Branch have altered vegetation and deposited sediment in the Savannah River Swamp forming the Pen Branch delta. Currently, the delta covers over 300 acres and continues to expand at a rate of about 16 acres/yr. Examination of delta expansion can provide important information on environmental impacts to wetlands exposed to elevated temperature and flow conditions. To assess the current status and predict future expansion of the Pen Branch delta, historic aerial photographs were analyzed using both basic photo interpretation and computer techniques to provide the following information: (1) past and current expansion rates; (2) location and changes of impacted areas; (3) total acreage presently affected. Delta acreage changes were then compared to historic reactor discharge temperature and flow data to see if expansion rate variations could be related to reactor operations.

  12. Horizontal baffle for nuclear reactors

    DOEpatents

    Rylatt, John A.

    1978-01-01

    A horizontal baffle disposed in the annulus defined between the core barrel and the thermal liner of a nuclear reactor thereby physically separating the outlet region of the core from the annular area below the horizontal baffle. The horizontal baffle prevents hot coolant that has passed through the reactor core from thermally damaging apparatus located in the annulus below the horizontal baffle by utilizing the thermally induced bowing of the horizontal baffle to enhance sealing while accommodating lateral motion of the baffle base plate.

  13. Branch classification: A new mechanism for improving branch predictor performance

    SciTech Connect

    Chang, P.Y.; Hao, E.; Patt, Y.; Yeh, T.Y.

    1996-04-01

    There is wide agreement that one of the most significant impediments to the performance of current and future pipelined superscalar processors is the presence of conditional branches in the instruction stream. Speculative execution is one solution to the branch problem, but speculative work is discarded if a branch is mispredicted. For it to be effective, speculative work is discarded if a branch is mispredicted. For it to be effective, speculative execution requires a very accurate branch predictor; 95% accuracy is not good enough. This paper proposes branch classification, a methodology for building more accurate branch predictors. Branch classification allows an individual branch instruction to be associated with the branch predictor best suited to predict its direction. Using this approach, a hybrid branch predictor can be constructed such that each component branch predictor predicts those branches for which it is best suited. To demonstrate the usefulness of branch classification, an example classification scheme is given and a new hybrid predictor is built based on this scheme which achieves a higher prediction accuracy than any branch predictor previously reported in the literature.

  14. Radioiodinated branched carbohydrates

    DOEpatents

    Goodman, Mark M.; Knapp, Jr., Furn F.

    1989-01-01

    A radioiodinated branched carbohydrate for tissue imaging. Iodine-123 is stabilized in the compound by attaching it to a vinyl functional group that is on the carbohydrate. The compound exhibits good uptake and retention and is promising in the development of radiopharmaceuticals for brain, heart and tumor imaging.

  15. Front Range Branch Officers

    NASA Astrophysics Data System (ADS)

    The Front Range Branch of AGU has installed officers for 1990: Ray Noble, National Center for Atmospheric Research, chair; Sherry Oaks, U.S. Geological Survey, chair-elect; Howard Garcia, NOAA, treasurer; Catharine Skokan, Colorado School of Mines, secretary. JoAnn Joselyn of NOAA is past chair. Members at large are Wallace Campbell, NOAA; William Neff, USGS; and Stephen Schneider, NCAR.

  16. HORIZONTAL BOILING REACTOR SYSTEM

    DOEpatents

    Treshow, M.

    1958-11-18

    Reactors of the boiling water type are described wherein water serves both as the moderator and coolant. The reactor system consists essentially of a horizontal pressure vessel divided into two compartments by a weir, a thermal neutronic reactor core having vertical coolant passages and designed to use water as a moderator-coolant posltioned in one compartment, means for removing live steam from the other compartment and means for conveying feed-water and water from the steam compartment to the reactor compartment. The system further includes auxiliary apparatus to utilize the steam for driving a turbine and returning the condensate to the feed-water inlet of the reactor. The entire system is designed so that the reactor is self-regulating and has self-limiting power and self-limiting pressure features.

  17. Horizontally shaken impact pendulums

    NASA Astrophysics Data System (ADS)

    Alexander, T. J.; Xu, Y.; Sidhu, H.

    2016-03-01

    We consider two pendulum masses attached to the same pivot point and which interact with each other through Hertzian impacts. We show that this splitting of the mass leads to an instability in the conservative case, in which initially synchronized large amplitude motion may evolve into out-of-phase (impacting) motion. We then study in detail the response of the impacting masses in the presence of damping and driving through horizontal shaking of the pivot point. We find that synchronized modes are usually accompanied by small amplitude quasi-periodic, or even chaotic, impacts and a number of multi-period solutions may appear in the bifurcation diagram. We reveal the existence and stability of a number of impact modes and scan the frequency response of the system to a series of initial conditions to identify which modes may be more easily generated in experiment.

  18. Horizontal drilling in shallow reservoirs

    SciTech Connect

    Murray, W.F. Jr.; Schrider, L.A.; McCallister, J.V.; Mazza, R.L.

    1993-12-31

    Belden & Blake and the US DOE will cofund a horizontal well to be drilled in the Clinton Sandstone as part of the DOE`s multi well program titled ``Horizontal Drilling in Shallow Geologic Complex Reservoirs.`` This well will be located in Mahoning County, Ohio in an area which has demonstrated above average Clinton gas production. To the best of our knowledge, this will be the first horizontal well drilled to the Clinton Sand formation in Ohio. Since many of the remaining Clinton Sand drilling sites are of poorer reservoir quality, they may not be developed unless technology such as horizontal drilling can be successfully demonstrated.

  19. Atomic branching in molecules

    NASA Astrophysics Data System (ADS)

    Estrada, Ernesto; Rodríguez-Velázquez, Juan A.; Randić, Milan

    A graph theoretic measure of extended atomic branching is defined that accounts for the effects of all atoms in the molecule, giving higher weight to the nearest neighbors. It is based on the counting of all substructures in which an atom takes part in a molecule. We prove a theorem that permits the exact calculation of this measure based on the eigenvalues and eigenvectors of the adjacency matrix of the graph representing a molecule. The definition of this measure within the context of the Hückel molecular orbital (HMO) and its calculation for benzenoid hydrocarbons are also studied. We show that the extended atomic branching can be defined using any real symmetric matrix, as well as any Hermitian (self-adjoint) matrix, which permits its calculation in topological, geometrical, and quantum chemical contexts.

  20. Study on the Optimization of Staged Fracturing for Horizontal Wells

    NASA Astrophysics Data System (ADS)

    Qin, J.; Wang, S.; Hu, J. H.

    In order to connect natural fracture with hydraulic fracture formed in staged fracturing for horizontal wells, forming a complex fracture network to improve the production of single well. Geometric model of hydraulic fracture induced stress field has been established, we studied the induced stress distribution of staged fracturing for horizontal well, compared the different effect of induced stress under the condition of different fracturing technology showed that: Induced stress along the minimum horizontal principal stress direction is the largest, with the increase of crack distance, induced stress decreased. Different fracturing technology can lead to different induced stress, the third crack fractured between two former cracks; induced stress of the third crack is obviously bigger than induced stress of crack by sequential fracturing. By comparing induced stress in the condition of fracturing three cracks, five cracks, seven cracks, found that induced stress increased with the increase of quantity of cracks. The larger induced stress made the branch crack shifted, enhancing connectivity among branch crack, main crack and natural fracture to improve channel structure for oil and gas flowing to the main crack, and finally achieve the purpose of improving productivity for oil and gas well. The study results had important guiding significance for efficient development of reservoir and optimization of parameters for horizontal wells.

  1. Underwater branch connection study

    SciTech Connect

    Not Available

    1992-06-01

    This report was prepared with the object of developing guidelines for designing underwater connections of branch pipelines to main lines at existing tap valves and with hot taps in diver accessible water depths. The report considers ANSI Classes 600 and 900 branch pipelines of up to twelve inches in diameter that conform to API Specification 5L minimum. Loads due to gravity, buoyancy, intemal and external pressure, thermal expansion, hydrodynamics and random events are considered. External corrosion, temperature, cover, bottom conditions, stability, testing, commissioning, trenching, and pigging are also addressed. A general discussion of these issues is included in the body of the report. Methods of analysis are included in the appendices and in various references. Lotus 123'' spreadsheets that compute the expansion stresses resulting from pressure and temperature at points on a generic piping geometry are presented. A program diskette is included with the report. The report summarizes, and draws from, the results of a survey of the relevant practice and experience of fifteen gas pipeline operating companies. The survey indicates that most existing branch connections do not provide for pigging of the lateral lines, but that there is a growing consensus that cleaning and inspection pigging of lateral lines is desirable or necessary.

  2. Branching instability in expanding bacterial colonies

    PubMed Central

    Giverso, Chiara; Verani, Marco; Ciarletta, Pasquale

    2015-01-01

    Self-organization in developing living organisms relies on the capability of cells to duplicate and perform a collective motion inside the surrounding environment. Chemical and mechanical interactions coordinate such a cooperative behaviour, driving the dynamical evolution of the macroscopic system. In this work, we perform an analytical and computational analysis to study pattern formation during the spreading of an initially circular bacterial colony on a Petri dish. The continuous mathematical model addresses the growth and the chemotactic migration of the living monolayer, together with the diffusion and consumption of nutrients in the agar. The governing equations contain four dimensionless parameters, accounting for the interplay among the chemotactic response, the bacteria–substrate interaction and the experimental geometry. The spreading colony is found to be always linearly unstable to perturbations of the interface, whereas branching instability arises in finite-element numerical simulations. The typical length scales of such fingers, which align in the radial direction and later undergo further branching, are controlled by the size parameters of the problem, whereas the emergence of branching is favoured if the diffusion is dominant on the chemotaxis. The model is able to predict the experimental morphologies, confirming that compact (resp. branched) patterns arise for fast (resp. slow) expanding colonies. Such results, while providing new insights into pattern selection in bacterial colonies, may finally have important applications for designing controlled patterns. PMID:25652464

  3. DNS of Horizontal Convection

    NASA Astrophysics Data System (ADS)

    White, Brian; Scotti, Alberto

    2014-11-01

    We perform three-dimensional DNS of Horizontal Convection in a rectangular tank with idealized boundary conditions. The flow is driven by imposing the profile for the buoyancy b at the surface, where it ranges from b0 to b0 + Δb and the transition region is confined to a very small area. The Rayleigh based on the domain depth ranges from 105 to 1012. The scaling observed for the Nusselt number and the strength of the circulation is consistent with Rossby's scaling across the range of Rayleigh numbers considered, indicating that the dynamics in the boundary layer under the ``warming'' side throttles the flow. Energetically, we find that Available Potential Energy (APE) is generated along the surface, and converted to Kinetic Energy (KE). Along the descending plume energy goes from APE to KE up to Ra ~1011 . For higher Rayleigh numbers the plume becomes a net sink of APE. When the switch occurs, a stagnant layer develops near the bottom, and the overall circulation becomes characterized by a narrow plume which retroflects rapidly towards the surface, with a shallow recirculation to close the flow. This may indicate the beginning of a Sandström regime characterized by a stagnant abyssal region and a shallow circulation. Work supported by the National Science Foundation.

  4. Calibration of a Horizontal Sundial

    ERIC Educational Resources Information Center

    Rovsek, Barbara

    2010-01-01

    This paper describes how a horizontal sundial can be calibrated in a classroom without using the nontrivial equations of projective geometry. If one understands how a simple equatorial sundial works, one will also understand the procedure of calibrating a horizontal (or "garden," as it is also called) sundial.

  5. Understanding Horizontal Governance. Research Brief

    ERIC Educational Resources Information Center

    Ferguson, Daniel

    2009-01-01

    Horizontal governance is an umbrella term that covers a range of approaches to policy development, service delivery issues, and management practices. A horizontal initiative may take place across levels of government, across boundaries between units of a single department or agency or among multiple departments or agencies, or across public,…

  6. A tree canopy height delineation method based on Morphological Reconstruction—Open Crown Decomposition

    NASA Astrophysics Data System (ADS)

    Liu, Q.; Jing, L.; Li, Y.; Tang, Y.; Li, H.; Lin, Q.

    2016-04-01

    For the purpose of forest management, high resolution LIDAR and optical remote sensing imageries are used for treetop detection, tree crown delineation, and classification. The purpose of this study is to develop a self-adjusted dominant scales calculation method and a new crown horizontal cutting method of tree canopy height model (CHM) to detect and delineate tree crowns from LIDAR, under the hypothesis that a treetop is radiometric or altitudinal maximum and tree crowns consist of multi-scale branches. The major concept of the method is to develop an automatic selecting strategy of feature scale on CHM, and a multi-scale morphological reconstruction–open crown decomposition (MRCD) to get morphological multi-scale features of CHM by: cutting CHM from treetop to the ground; analysing and refining the dominant multiple scales with differential horizontal profiles to get treetops; segmenting LiDAR CHM using watershed a segmentation approach marked with MRCD treetops. This method has solved the problems of false detection of CHM side-surface extracted by the traditional morphological opening canopy segment (MOCS) method. The novel MRCD delineates more accurate and quantitative multi-scale features of CHM, and enables more accurate detection and segmentation of treetops and crown. Besides, the MRCD method can also be extended to high optical remote sensing tree crown extraction. In an experiment on aerial LiDAR CHM of a forest of multi-scale tree crowns, the proposed method yielded high-quality tree crown maps.

  7. Combustion Branch Website Development

    NASA Technical Reports Server (NTRS)

    Bishop, Eric

    2004-01-01

    The NASA combustion branch is a leader in developing and applying combustion science to focused aerospace propulsion systems concepts. It is widely recognized for unique facilities, analytical tools, and personnel. In order to better communicate the outstanding research being done in this Branch to the public and other research organization, a more substantial website was desired. The objective of this project was to build an up-to-date site that reflects current research in a usable and attractive manner. In order to accomplish this, information was requested from all researchers in the Combustion branch, on their professional skills and on the current projects. This information was used to fill in the Personnel and Research sections of the website. A digital camera was used to photograph all personnel and these photographs were included in the personnel section as well. The design of the site was implemented using the latest web standards: xhtml and external css stylesheets. This implementation conforms to the guidelines recommended by the w3c. It also helps to ensure that the web site is accessible by disabled users, and complies with Section 508 Federal legislation (which mandates that all Federal websites be accessible). Graphics for the new site were generated using the gimp (www.gimp.org) an open-source graphics program similar to Adobe Photoshop. Also, all graphics on the site were of a reasonable size (less than 20k, most less than 2k) so that the page would load quickly. Technologies such as Macromedia Flash and Javascript were avoided, as these only function on some clients which have the proper software installed or enabled. The website was tested on different platforms with many different browsers to ensure there were no compatibility issues. The website was tested on windows with MS IE 6, MSIE 5 , Netscape 7, Mozilla and Opera. On a Mac, the site was tested with MS IE 5 , Netscape 7 and Safari.

  8. [Masquerading bundle branch block].

    PubMed

    Kukla, Piotr; Baranchuk, Adrian; Jastrzębski, Marek; Bryniarski, Leszek

    2014-01-01

    We here describe a surface 12-lead electrocardiogram (ECG) of a 72-year-old female with a prior history of breast cancer and chemotherapy-induced cardiomyopathy. An echocardiogram revealed left ventricular dysfunction, ejection fraction of 23%, with mild enlarged left ventricle. The 12-lead ECG showed atrial fibrillation with a mean heart rate of about 100 bpm, QRS duration 160 ms, QT interval 400 ms, right bundle branch block (RBBB) and left anterior fascicular block (LAFB). The combination of RBBB features in the precordial leads and LAFB features in the limb leads is known as ''masquerading bundle branch block''. In most cases of RBBB and LAFB, the QRS axis deviation is located between - 80 to -120 degrees. Rarely, when predominant left ventricular forces are present, the QRS axis deviation is near about -90 degrees, turning the pattern into an atypical form. In a situation of RBBB associated with LAFB, the S wave can be absent or very small in lead I. Such a situation is the result of not only purely LAFB but also with left ventricular hypertrophy and/or focal block due to scar (extensive anterior myocardial infarction) or fibrosis (cardiomyopathy). Sometimes, this specific ECG pattern is mistaken for LBBB. RBBB with LAFB may imitate LBBB either in the limb leads (known as 'standard masquerading' - absence of S wave in lead I), or in the precordial leads (called 'precordial masquerading' - absence of S wave in leads V₅ and V₆). Our ECG showed both these types of masquerading bundle branch block - absence of S wave in lead I and in leads V₅ and V₆. PMID:24469750

  9. Thermal Energy Conversion Branch

    NASA Technical Reports Server (NTRS)

    Bielozer, Matthew C.; Schreiber, Jeffrey, G.; Wilson, Scott D.

    2004-01-01

    The Thermal Energy Conversion Branch (5490) leads the way in designing, conducting, and implementing research for the newest thermal systems used in space applications at the NASA Glenn Research Center. Specifically some of the most advanced technologies developed in this branch can be broken down into four main areas: Dynamic Power Systems, Primary Solar Concentrators, Secondary Solar Concentrators, and Thermal Management. Work was performed in the Dynamic Power Systems area, specifically the Stirling Engine subdivision. Today, the main focus of the 5490 branch is free-piston Stirling cycle converters, Brayton cycle nuclear reactors, and heat rejection systems for long duration mission spacecraft. All space exploring devices need electricity to operate. In most space applications, heat energy from radioisotopes is converted to electrical power. The Radioisotope Thermoelectric Generator (RTG) already supplies electricity for missions such as the Cassini Spacecraft. The focus of today's Stirling research at GRC is aimed at creating an engine that can replace the RTG. The primary appeal of the Stirling engine is its high system efficiency. Because it is so efficient, the Stirling engine will significantly reduce the plutonium fuel mission requirements compared to the RTG. Stirling is also being considered for missions such as the lunar/Mars bases and rovers. This project has focused largely on Stirling Engines of all types, particularly the fluidyne liquid piston engine. The fluidyne was developed by Colin D. West. This engine uses the same concepts found in any type of Stirling engine, with the exception of missing mechanical components. All the working components are fluid. One goal was to develop and demonstrate a working Stirling Fluidyne Engine at the 2nd Annual International Energy Conversion Engineering Conference in Providence, Rhode Island.

  10. Flight Dynamics Analysis Branch

    NASA Technical Reports Server (NTRS)

    Stengle, Tom; Flores-Amaya, Felipe

    2000-01-01

    This report summarizes the major activities and accomplishments carried out by the Flight Dynamics Analysis Branch (FDAB), Code 572, in support of flight projects and technology development initiatives in fiscal year 2000. The report is intended to serve as a summary of the type of support carried out by the FDAB, as well as a concise reference of key accomplishments and mission experience derived from the various mission support roles. The primary focus of the FDAB is to provide expertise in the disciplines of flight dynamics, spacecraft trajectory, attitude analysis, and attitude determination and control. The FDAB currently provides support for missions and technology development projects involving NASA, government, university, and private industry.

  11. Clear Evidence for the Presence of Second-generation Asymptotic Giant Branch Stars in Metal-poor Galactic Globular Clusters

    NASA Astrophysics Data System (ADS)

    García-Hernández, D. A.; Mészáros, Sz.; Monelli, M.; Cassisi, S.; Stetson, P. B.; Zamora, O.; Shetrone, M.; Lucatello, S.

    2015-12-01

    Galactic globular clusters (GCs) are known to host multiple stellar populations: a first generation (FG) with a chemical pattern typical of halo field stars and a second generation (SG) enriched in Na and Al and depleted in O and Mg. Both stellar generations are found at different evolutionary stages (e.g., the main-sequence turnoff, the subgiant branch, and the red giant branch (RGB)). The non detection of SG asymptotic giant branch (AGB) stars in several metal-poor ([Fe/H] < -1) GCs suggests that not all SG stars ascend the AGB phase, and that failed AGB stars may be very common in metal-poor GCs. This observation represents a serious problem for stellar evolution and GC formation/evolution theories. We report fourteen SG-AGB stars in four metal-poor GCs (M13, M5, M3, and M2) with different observational properties: horizontal branch (HB) morphology, metallicity, and age. By combining the H-band Al abundances obtained by the Apache Point Observatory Galactic Evolution Experiment survey with ground-based optical photometry, we identify SG Al-rich AGB stars in these four GCs and show that Al-rich RGB/AGB GC stars should be Na-rich. Our observations provide strong support for present, standard stellar models, i.e., without including a strong mass-loss efficiency, for low-mass HB stars. In fact, current empirical evidence is in agreement with the predicted distribution of FG and SG stars during the He-burning stages based on these standard stellar models.

  12. Functional morphology of the hallucal metatarsal with implications for inferring grasping ability in extinct primates.

    PubMed

    Goodenberger, Katherine E; Boyer, Doug M; Orr, Caley M; Jacobs, Rachel L; Femiani, John C; Patel, Biren A

    2015-03-01

    Primate evolutionary morphologists have argued that selection for life in a fine branch niche resulted in grasping specializations that are reflected in the hallucal metatarsal (Mt1) morphology of extant "prosimians", while a transition to use of relatively larger, horizontal substrates explains the apparent loss of such characters in anthropoids. Accordingly, these morphological characters-Mt1 torsion, peroneal process length and thickness, and physiological abduction angle-have been used to reconstruct grasping ability and locomotor mode in the earliest fossil primates. Although these characters are prominently featured in debates on the origin and subsequent radiation of Primates, questions remain about their functional significance. This study examines the relationship between these morphological characters of the Mt1 and a novel metric of pedal grasping ability for a large number of extant taxa in a phylogenetic framework. Results indicate greater Mt1 torsion in taxa that engage in hallucal grasping and in those that utilize relatively small substrates more frequently. This study provides evidence that Carpolestes simpsoni has a torsion value more similar to grasping primates than to any scandentian. The results also show that taxa that habitually grasp vertical substrates are distinguished from other taxa in having relatively longer peroneal processes. Furthermore, a longer peroneal process is also correlated with calcaneal elongation, a metric previously found to reflect leaping proclivity. A more refined understanding of the functional associations between Mt1 morphology and behavior in extant primates enhances the potential for using these morphological characters to comprehend primate (locomotor) evolution. PMID:25378276

  13. URBAN MORPHOLOGY FOR HOUSTON TO DRIVE MODELS-3/CMAQ AT NEIGHBORHOOD SCALES

    EPA Science Inventory

    Air quality simulation models applied at various horizontal scales require different degrees of treatment in the specifications of the underlying surfaces. As we model neighborhood scales ( 1 km horizontal grid spacing), the representation of urban morphological structures (e....

  14. Horizontal and Vertical Line Designs.

    ERIC Educational Resources Information Center

    Johns, Pat

    2003-01-01

    Presents an art lesson in which students learn about the artist Piet Mondrian and create their own abstract artworks. Focuses on geometric shapes using horizontal and vertical lines. Includes background information about the artist. (CMK)

  15. Horizontal Cells, the Odd Ones Out in the Retina, Give Insights into Development and Disease.

    PubMed

    Boije, Henrik; Shirazi Fard, Shahrzad; Edqvist, Per-Henrik; Hallböök, Finn

    2016-01-01

    Thorough investigation of a neuronal population can help reveal key aspects regarding the nervous system and its development. The retinal horizontal cells have several extraordinary features making them particularly interesting for addressing questions regarding fate assignment and subtype specification. In this review we discuss and summarize data concerning the formation and diversity of horizontal cells, how morphology is correlated to molecular markers, and how fate assignment separates the horizontal lineage from the lineages of other retinal cell types. We discuss the novel and unique features of the final cell cycle of horizontal cell progenitors and how they may relate to retinoblastoma carcinogenesis. PMID:27486389

  16. Horizontal Cells, the Odd Ones Out in the Retina, Give Insights into Development and Disease

    PubMed Central

    Boije, Henrik; Shirazi Fard, Shahrzad; Edqvist, Per-Henrik; Hallböök, Finn

    2016-01-01

    Thorough investigation of a neuronal population can help reveal key aspects regarding the nervous system and its development. The retinal horizontal cells have several extraordinary features making them particularly interesting for addressing questions regarding fate assignment and subtype specification. In this review we discuss and summarize data concerning the formation and diversity of horizontal cells, how morphology is correlated to molecular markers, and how fate assignment separates the horizontal lineage from the lineages of other retinal cell types. We discuss the novel and unique features of the final cell cycle of horizontal cell progenitors and how they may relate to retinoblastoma carcinogenesis. PMID:27486389

  17. Branches in the Everett interpretation

    NASA Astrophysics Data System (ADS)

    Cunningham, Arthur J.

    2014-05-01

    Hugh Everett III describes a quantum measurement as resulting in the "branching" of the quantum state of observer and measured system, with all possible measurement outcomes represented by the ensuing branches of the total quantum state. But Everett does not specify a general rule for decomposing a quantum state into branches, and commentators have long puzzled over how, and even whether, to regard Everett's notion of branching states as physically meaningful. It is common today to appeal to decoherence considerations as a way of giving physical content to the Everettian notion of branches, but these appeals to decoherence are often regarded as considerations foreign to Everett's own approach. This paper contends that this assessment is only half right: though he does not invoke environmental decoherence, Everett does appeal to decoherence considerations, broadly understood, in his treatment of measurement. Careful consideration of his idealized models of measurement, and of the significance he ascribes to the branching of states corresponding to definite measurement outcomes, reveals that his notion of branching refers to a special physical characteristic of elements of a particular decomposition, namely the absence of interference between these component states as a result of the particular dynamics governing the evolution of the system. Characterizations of branching that appeal to the results of modern decoherence theory should therefore be regarded as a natural development of Everett's own physically meaningful conception of branching.

  18. Methods and Technologies Branch (MTB)

    Cancer.gov

    The Methods and Technologies Branch focuses on methods to address epidemiologic data collection, study design and analysis, and to modify technological approaches to better understand cancer susceptibility.

  19. The control of branching morphogenesis

    PubMed Central

    Iber, Dagmar; Menshykau, Denis

    2013-01-01

    Many organs of higher organisms are heavily branched structures and arise by an apparently similar process of branching morphogenesis. Yet the regulatory components and local interactions that have been identified differ greatly in these organs. It is an open question whether the regulatory processes work according to a common principle and how far physical and geometrical constraints determine the branching process. Here, we review the known regulatory factors and physical constraints in lung, kidney, pancreas, prostate, mammary gland and salivary gland branching morphogenesis, and describe the models that have been formulated to analyse their impacts. PMID:24004663

  20. Texaco sets horizontal well marks

    SciTech Connect

    Not Available

    1992-07-06

    This paper reports that Texaco Exploration and Production Inc. has completed the first dual lateral horizontal well in East Texas and claimed a horizontal oil well record in the Gulf of Mexico. The East Texas well, 1 Texaco Fee Brookeland, is the company's first dual lateral well. Site is in Newton County. The Brookeland well was drilled vertically to the top of Cretaceous Austin chalk at 9,138 ft. Texaco set casing, then drilled horizontally 3,242 ft to the southeast and 3,000 ft to the northwest for a total horizontal displacement of 6,242 ft. Texaco set an industry record offshore with its B19-ST well on its Teal prospect in Eugene Island Block 338, its first horizontal oil well in the gulf, by drilling a horizontal section of 1,414 ft. Measured depth (MD) is 7,500 ft and true vertical depth (TVD) 4,662 ft. Site is in 268 ft of water. Drilling horizontally through the Pleistocene prograding sand complex allowed Texaco to penetrate 50% more of the reservoir than would have been possible with a conventional well, Wallace the. In another industry first, Texaco isolated the Teal reservoir gas cap by setting intermediate casing 50 ft below the oil-gas contact with the 90{degrees} angle already established because of concern that the reservoir had an expanded gas cap. The dual lateral Brookeland well cost $500,000-700,000 less than two vertical wells capable of comparable production rates and recovery. Texaco expects the full cost of the well, production facilities, and gathering system to pay out in about 4 months. Texaco estimates the B19-ST well cost about 10% more than a Teal vertical well. A cross discipline team of Texaco geologists, geophysicists, engineers, and field technicians contributed to the success of both projects.

  1. Contrast between the vertical and horizontal mercury discharge lamps

    SciTech Connect

    Ben Hamida, M. B.; Helali, H.; Araoud, Z.; Charrada, K.

    2011-06-15

    This paper discusses the thermal behavior of a high pressure mercury lamp in a horizontal position, compared with that of a vertical lamp. The model adopted is three-dimensional, steady, and powered DC. After the model validation, we analyzed temperature fields and velocities for the case of the lamp in a horizontal position by comparing it with those of a lamp in vertical position. This setting initially fixed the wall temperature equal to 1000 K. However, the morphology of the temperature profile in the case of the horizontal lamp indicates that the temperature of the wall cannot be uniform. Thus, we have, in a second time, performed an energy balance at the wall to calculate its temperature. This aims to understand the influence of convection on the thermal properties of the source.

  2. Pressure analysis for horizontal wells

    SciTech Connect

    Davlau, F.; Mouronval, G.; Bourdarot, G.; Curutchet, P.

    1988-12-01

    This paper presents horizontal-well test design and interpretation methods. Analytical solutions are developed that can be handled easily by a desktop computer to carry out design as well as interpretation with semilog and log-log analysis. These analytical solutions point out the distinctive behavior of horizontal wells: (1) at early time, there is a circular radial flow in a vertical plane perpendicular to the well, and (2) at late time, there is a horizontal pseudoradial flow. Each type of flow is associated with a semilog straight line to which semilog analysis has to be adapted. The horizontal pseudoradial flow takes into account a pseudoskin depending on system geometry, which is a priori defined and estimated. Practical time criteria are proposed to determine the beginning and the end of each type of flow and to provide a guide to semilog analysis and well test design. The authors study the behavior of uniform-flux or infinite-conductivity horizontal wells, with wellbore storage and skin. The homogeneous reservoir is infinite or limited by impermeable or constant-pressure boundaries. A method is also outlined to transform all our solutions for homogeneous reservoirs into corresponding solutions for double-porosity reservoirs.

  3. Modeling branching in cereals

    PubMed Central

    Evers, Jochem B.; Vos, Jan

    2013-01-01

    Cereals and grasses adapt their structural development to environmental conditions and the resources available. The primary adaptive response is a variable degree of branching, called tillering in cereals. Especially for heterogeneous plant configurations the degree of tillering varies per plant. Functional–structural plant modeling (FSPM) is a modeling approach allowing simulation of the architectural development of individual plants, culminating in the emergent behavior at the canopy level. This paper introduces the principles of modeling tillering in FSPM, using (I) a probability approach, forcing the dynamics of tillering to correspond to measured probabilities. Such models are particularly suitable to evaluate the effect structural variables on system performance. (II) Dose–response curves, representing a measured or assumed response of tillering to an environmental cue. (III) Mechanistic approaches to tillering including control by carbohydrates, hormones, and nutrients. Tiller senescence is equally important for the structural development of cereals as tiller appearance. Little study has been made of tiller senescence, though similar concepts seem to apply as for tiller appearance. PMID:24133499

  4. A Branch Meeting in Avon

    ERIC Educational Resources Information Center

    Vaughan, Kathryn; Coles, Alf

    2011-01-01

    The Association of Teachers of Mathematics (ATM) exists for, and is run by, its members. Branch meetings are so much more than the "grass roots" of the association--it can be a powerhouse of inspiration and creativity. In this article, the authors provide commentaries on a recent branch meeting.

  5. Branching mechanisms in surfactant micelles

    NASA Astrophysics Data System (ADS)

    Dhakal, Subas; Sureshkumar, Radhakrishna

    The mechanisms of branch formation in surfactant micelles of cetyltrimethylammonium chloride (CTAC) in presence of sodium salicylate (NaSal) counter ions in water are studied using molecular dynamics simulations. The curvature energy associated with the formation of micelle branches and the effect of branching on the solution viscosity are quantified. Highly curved surfaces are energetically stabilized by a higher density of binding counter ions near the branch points. Simulations show that micellar branches result in a significant reduction in the solution viscosity as observed in experiments [Dhakal & Sureshkumar, J. Chem. Phys. 143, 024905 (2015)]. This reduction in viscosity has long been attributed to the sliding motion of micelle branches across the main chain. However, to date, such dynamics of micelle branches have never been visualized in either experiments or simulations. Here, we explicitly illustrate and quantify, for the first time, how branches slide along the micelle contour to facilitate stress relaxation. We acknowledged the computational resources provided by XSEDE which is supported by NSF Grant Number OCI-1053575 and the financial support by National Science Foundation under Grants 1049489 and 1049454.

  6. SnapShot: Branching Morphogenesis.

    PubMed

    Chuong, Cheng-Ming; Bhat, Ramray; Widelitz, Randall B; Bissell, Mina J

    2014-08-28

    Ectodermal appendages such as feathers, hair, mammary glands, salivary glands, and sweat glands form branches, allowing much-increased surface for functional differentiation and secretion. Here, the principles of branching morphogenesis are exemplified by the mammary gland and feathers. PMID:25171418

  7. Nuclear component horizontal seismic restraint

    DOEpatents

    Snyder, Glenn J.

    1988-01-01

    A nuclear component horizontal seismic restraint. Small gaps limit horizontal displacement of components during a seismic occurrence and therefore reduce dynamic loadings on the free lower end. The reactor vessel and reactor guard vessel use thicker section roll-forged rings welded between the vessel straight shell sections and the bottom hemispherical head sections. The inside of the reactor guard vessel ring forging contains local vertical dovetail slots and upper ledge pockets to mount and retain field fitted and installed blocks. As an option, the horizontal displacement of the reactor vessel core support cone can be limited by including shop fitted/installed local blocks in opposing alignment with the reactor vessel forged ring. Beams embedded in the wall of the reactor building protrude into apertures in the thermal insulation shell adjacent the reactor guard vessel ring and have motion limit blocks attached thereto to provide to a predetermined clearance between the blocks and reactor guard vessel ring.

  8. Horizontal displacement profiles in N Reactor horizontal control rod channels

    SciTech Connect

    Woodruff, E.M.

    1988-12-01

    One of the potential results from N Reactor graphite moderator distortion is horizontal curvature of the horizontal control rod (HCR) channels. Mockup testing has identified two possible problem scenarios resulting from such curvature: slow scram times and rod abrasion due to rubbing of the rod on the side of the channel and subsequent displacement of T-blocks that form the sides of the channels. As a result of these potential events, surveillance tools (instrumentation) to measure HCR channel horizontal displacement was recently developed. Surveillance of HCR channel 65, performed on December 11, 1987, indicated a six inch rearward displacement near the center of the channel. This approximated the displacement which mockup testing has identified as a concern with regard to T-block movement. Closed Circuit Television (CCTV) observations indicate that T-block movement has not occurred in HCR channel 65, but that there has been some rubbing of the rod on the channel sides. Review of most recent rod hot scram times indicates normal performance for HCR 65. To further evaluate this concern, horizontal deflection and CCTV surveillance was scheduled in six HCR channels surrounding HCR channel 65. Inspection of the HCR rod tip was also performed. 13 refs., 6 figs.

  9. Success in horizontal barrier developments

    SciTech Connect

    Pettit, P.J.; Ridenour, D.E.; Jalovec, J.

    1996-06-01

    A successful proof of concept demonstration has been conducted of operational methods and tooling for the in situ construction of underground horizontal barriers for the control and containment of groundwater and contamination. The method involves jet grouting with specially adapted tools guided between twin, parallel wells for the placement of a grout beneath a waste site. The objective of the work is to develop reliable methods of constructing extensive, competent horizontal barriers underneath waste sites without excavating or penetrating the waste during the process.

  10. Speckle imaging over horizontal paths

    NASA Astrophysics Data System (ADS)

    Carrano, Carmen J.

    2002-09-01

    Atmospheric aberrations reduce the resolution and contrast in surveillance images recorded over horizontal or slant paths. This paper describes our recent horizontal and slant-path imaging experiments of extended scenes as well as the results obtained using speckle imaging. The experiments were performed with an 8-inch diameter telescope placed on either a rooftop or hillside and cover ranges of interest from 0.5 km up to 10 km. The scenery includes resolution targets, people, vehicles, and other structures. The improvement in image quality using speckle imaging is dramatic in many cases, and depends significantly upon the atmospheric conditions. We quantify resolution improvement through modulation transfer function measurement comparisons.

  11. Speckle Imaging Over Horizontal Paths

    SciTech Connect

    Carrano, C J

    2002-05-21

    Atmospheric aberrations reduce the resolution and contrast in surveillance images recorded over horizontal or slant paths. This paper describes our recent horizontal and slant path imaging experiments of extended scenes as well as the results obtained using speckle imaging. The experiments were performed with an 8-inch diameter telescope placed on either a rooftop or hillside and cover ranges of interest from 0.5 km up to 10 km. The scenery includes resolution targets, people, vehicles, and other structures. The improvement in image quality using speckle imaging is dramatic in many cases, and depends significantly upon the atmospheric conditions. We quantify resolution improvement through modulation transfer function measurement comparisons.

  12. Horizontal completions challenge for industry

    SciTech Connect

    Zaleski, T.E. Jr.; Spatz, E.

    1988-05-02

    As the technology to drill horizontal wells continues to evolve, the problem of efficiently and cost-effectively completing such wells grows. The economics of applying horizontal technology in high-productivity reservoirs demands both increased production and lower development costs. Such high productivity reservoirs are typical of the Gulf of Mexico, North Sea, South China basin, and other areas. Lowering development costs is achieved by drilling fewer wells and in the offshore environment by reducing the number of platforms and other well structures. Specifically addressed in this article are the problems of achieving high efficiency, long lasting completions while controlling costs in unconsolidated and poorly consolidated sandstone reservoirs.

  13. Genetic species delineation among branching Caribbean Porites corals

    NASA Astrophysics Data System (ADS)

    Prada, C.; DeBiasse, M. B.; Neigel, J. E.; Yednock, B.; Stake, J. L.; Forsman, Z. H.; Baums, I. B.; Hellberg, M. E.

    2014-12-01

    Coral species are difficult to discern because of their morphological plasticity, long generation times, and slow rates of mitochondrial DNA evolution. Among Caribbean representatives of the genus Porites are three named species ( P. divaricata, P. furcata, and P. porites) with branching colony morphologies whose validity as genetically isolated species has been debated. We present sequence data from the mitochondrial control region, nuclear ITS, and nine single-copy nuclear loci for the Caribbean Porites and a related eastern Pacific species. mtDNA sequences were nearly invariant among the three branching species and their crustose sister P. branneri, and ITS sequences from these four were intermingled. An information theoretic analysis provided no support for upholding the three named Caribbean branching species. Both a clustering analysis and an analysis of molecular variance showed that sequence variation from the three branching forms is partitioned more by geography than by taxonomy. Multi-locus coalescent phylogenetic analysis provided a calibrated estimate for the nuclear DNA substitution rate (0.14 % Ma-1) close to that for other corals. Because no generalities have emerged from genetic investigations of the validity of morphologically defined coral species, the use of single-copy nuclear data is likely to be important in testing problematic species designations.

  14. Factors affecting branch failures in open-grown trees during a snowstorm in Massachusetts, USA.

    PubMed

    Kane, Brian; Finn, John T

    2014-01-01

    In October 2011, a snowstorm in the northeastern USA caused many branch failures of many tree species commonly planted in urbanized settings. Immediately following the storm, we assessed 1,764 trees for possible snow-induced damage and factors affecting it on the campus of the University of Massachusetts in Amherst, MA, USA. Nearly all failures were of branches, most of which were not defective. We used logistic regression to assess whether the probability of branch failure differed among species, diameter at breast height (DBH) and the presence of a defect or leaves increased for different species. We also measured branch morphology of (i) branches that did and did not fail for one angiosperm species and (ii) all branches on a sub-sample (stratified by DBH) of three individuals of seven other angiosperm species. Probability of branch failure differed among species. It also increased with greater DBH in eight of ten species studied, decreased when defects were present in four of ten species, and increased in one species when leaves were present. The relationship between branch failure and DBH appeared to be due to the correlation between DBH and branch morphology, which was mostly similar among species. As DBH increased, so did the mean diameter and length of primary branches, and the cumulative diameter of secondary branches. In contrast, branch slenderness decreased with increasing DBH. Combined, these factors presumably expedited the accumulation of snow on branches due to greater surface area and less flexibility. This explained why most failed branches were not defective. Since the frequency of intense storms is predicted to increase with global climate change, urban foresters should consider the timing of leaf senescence when selecting deciduous trees, to reduce the likelihood of failure of open-grown, deciduous trees in urbanized areas. PMID:25674460

  15. Branch strategies - Modeling and optimization

    NASA Technical Reports Server (NTRS)

    Dubey, Pradeep K.; Flynn, Michael J.

    1991-01-01

    The authors provide a common platform for modeling different schemes for reducing the branch-delay penalty in pipelined processors as well as evaluating the associated increased instruction bandwidth. Their objective is twofold: to develop a model for different approaches to the branch problem and to help select an optimal strategy after taking into account additional i-traffic generated by branch strategies. The model presented provides a flexible tool for comparing different branch strategies in terms of the reduction it offers in average branch delay and also in terms of the associated cost of wasted instruction fetches. This additional criterion turns out to be a valuable consideration in choosing between two strategies that perform almost equally. More importantly, it provides a better insight into the expected overall system performance. Simple compiler-support-based low-implementation-cost strategies can be very effective under certain conditions. An active branch prediction scheme based on loop buffers can be as competitive as a branch-target-buffer based strategy.

  16. Tension in Highly Branched Polymers

    NASA Astrophysics Data System (ADS)

    Rubinstein, Michael

    2012-02-01

    We propose a systematic method of designing branched macromolecules capable of building up high tension in their covalent bonds, which can be controlled by changing solvent quality. This tension is achieved exclusively due to intramolecular interactions by focusing lower tensions from its numerous branches to a particular section of the designed molecule. The simplest molecular architecture, which allows this tension amplification, is a so-called pom-pom macromolecule consisting of a relatively short linear spacer and two z-arm stars at its ends. Tension developed in the stars due to crowding of their branches is amplified by a factor of z and focused to the spacer. There are other highly branched macromolecules, such as molecular brushes - comb polymers with high density of side branches, that have similar focusing and amplification properties. In addition molecular brushes transmit tension along their backbone. Adsorption or grafting of these branched molecules on a substrate results in further increase in tension as compared to molecules in solution. Molecular architectures similar to pom-pom and molecular brushes with a high tension amplification parts can be used in numerous sensor applications. Unique conformations of molecular brushes in a pre-wetting layer allow direct visualization by atomic force microscope. Detailed images of individual molecules spreading along the surface enable critical evaluation of theories of chain dynamics in polymer monolayer. Strong spreading of densely branched macromolecules on a planar substrate can lead to high tension in the molecular backbone sufficient to break covalent bonds.

  17. Horizontal electric fields from lightning return strokes

    NASA Technical Reports Server (NTRS)

    Thomson, E. M.; Medelius, P. J.; Rubinstein, M.; Uman, M. A.; Johnson, J.

    1988-01-01

    An experiment to measure simultaneously the wideband horizontal and vertical electric fields from lightning return strokes is described. Typical wave shapes of the measured horizontal and vertical fields are presented, and the horizontal fields are characterized. The measured horizontal fields are compared with calculated horizontal fields obtained by applying the wavetilt formula to the vertical fields. The limitations and sources of error in the measurement technique are discussed.

  18. The making of a fusion branch in the Drosophila trachea.

    PubMed

    Gervais, Louis; Lebreton, Gaelle; Casanova, Jordi

    2012-02-15

    Connection of epithelial tubes to generate a common network is a key step in the formation of tubular organs such as the tracheal respiratory and the vascular systems. However, it is not clear how these connecting tubes arise. Here we address this issue by studying the dorsal fusion branches in the Drosophila trachea, taking into account the morphology and contribution of each cell type on the basis of their individual labeling. Our results explain how a fusion branch forms and also illustrate the different nature of the two seamless tubes in the Drosophila trachea, generated by fusion and terminal cells respectively. PMID:22178247

  19. Horizontal drilling installs dutch waterline

    SciTech Connect

    Not Available

    1986-08-01

    A 32-in. potable water line system, installed by Van Eijk Leidingen B.V. in Holland, was laid through an intensively cultivated vegetable gardening area, and designed to furnish additional irrigation water. Using a horizontally drilled 42-in. hole under the Maasdijk, though a difficult job, reduced the length by more than 3 miles.

  20. Dragging a floating horizontal cylinder

    NASA Astrophysics Data System (ADS)

    Lee, Duck-Gyu; Kim, Ho-Young

    2010-11-01

    A cylinder immersed in a fluid stream experiences a drag, and it is well known that the drag coefficient is a function of the Reynolds number only. Here we study the force exerted on a long horizontal cylinder that is dragged perpendicular to its axis while floating on an air-water interface with a high Reynolds number. In addition to the flow-induced drag, the floating body is subjected to capillary forces along the contact line where the three phases of liquid/solid/gas meet. We first theoretically predict the meniscus profile around the horizontally moving cylinder assuming the potential flow, and show that the profile is in good agreement with that obtained experimentally. Then we compare our theoretical predictions and experimental measurement results for the drag coefficient of a floating horizontal cylinder that is given by a function of the Weber number and the Bond number. This study can help us to understand the horizontal motion of partially submerged objects at air-liquid interface, such as semi-aquatic insects and marine plants.

  1. [Variations of the celiac trunk branches in the fetus].

    PubMed

    Bordei, P; Antohe, D S

    2002-09-01

    The study was performed on 60 human foetuses, aged between 4 to 9 months, using as methods dissection and plastic and contrast substances injection. We studied the celiac trunk in what concerns the division into its terminal branches, insisting on the possible morphological variations, some rare collateral branches starting from the common arterial trunk, the dimensional relations between the branches at their origin and the level of the celiac trunk origin from the aorta, in relation with the vertebral column, the diaphragmatic passage of the aorta and with the superior mesenteric artery. We also assessed the dimensional relations (calibers at origin) between the branches of the celiac trunk. Ass possible variations of the division of the celiac trunk, we assessed: gastro-hepatic trunk, with the splenic artery directly from the aorta or from the hepatic artery; gastro-splenic trunk, with the hepatic artery originating from the aorta; hepato-splenic trunk, with origin of the left gastric artery either directly from the aorta or from the hepatic artery. Rare variations: celiaco-mesenteric trunk; two arterial trunks, hepato-splenic and hepato-gastric; separate aortic origin for all three "classic" branches of the celiac trunk; two hepatic arteries, one from the celiac trunk and the other from the aorta or superior mesenteric artery; celiac trunk that divides into several terminal branches; one or two suprarenal arteries originating from the celiac trunk. PMID:12572348

  2. Multigraft Copolymer Superelastomers: Synthesis Morphology, and Properties

    SciTech Connect

    Uhrig, David; Schlegel, Ralf; Weidisch, Roland; Mays, Jimmy

    2011-01-01

    The synthesis of well-defined multigraft copolymers having a polydiene backbone with polystyrene side chains is briefly reviewed, with particular focus on controlling branch point spacing and branch point functionality. Use of living anionic polymerization and chlorosilane linking chemistry has led to the synthesis of series of materials having regularly spaced trifunctional (comb), tetrafunctional (centipede), and hexafunctional (barbwire) branch points. The morphologies of these materials were characterized by transmission electron microscopy and small-angle X-ray scattering, and it was found that the morphologies were controlled by the local architectural asymmetry associated with each branch point. Mechanical properties studies revealed that such multigraft copolymers represent a new class of thermoplastic elastomers (TPEs) with superior elongation at break and low residual strains as compared to conventional TPEs.

  3. Application of morphologic burrow architects: lungfish or crayfish?

    USGS Publications Warehouse

    Hasiotis, Stephen T.; Mitchell, Charles E.; Dubiel, Russell R.

    1993-01-01

    A methodology for trace fossil identification using burrowing signatures is tested by evaluating ancient and modern lungfish and crayfish burrows and comparing them to previously undescribed burrows in a stratigraphic interval thought to contain both lungfish and crayfish burrows. Permian burrows that bear skeletal remains of the lungfish Gnathorhiza, from museum collections, were evaluated to identify unique burrow morphologies that could be used to distinguish lungfish from crayfish burrows when fossil remains are absent. The lungfish burrows were evaluated for details of the burrowing mechanism preserved in the burrow morphologies together forming burrowing signatures and were compared to new burrows in the Chinle Formation of western Colorado to test the methodology of using burrow signatures to identify unknown burrows. Permian lungfish aestivation burrows show simple, nearly vertical, unbranched architectures and relatively smooth surficial morphologies with characteristic quasi‐horizontal striae on the burrow walls and vertical striae on the bulbous terminus. Burrow lengths do not exceed 0.5 m. In contrast, modern and ancient crayfish burrows exhibit simple to highly complex architectures with highly textured surficial morphologies. Burrow lengths may reach 4 to 5 m. Burrow morphologies unlike those identified in Gnathorhiza aestivation burrows were found in four burrow groups from museum collections. Two of these groups exhibit simple architectures and horizontal striae that were greater in sinuosity and magnitude, respectively. One of these burrows contains the remains of Lysorophus, but the burrow surface reveals no reliable surficial characteristics. It is not clear whether Lysorophus truly burrowed or merely occupied a pre‐existing structure. The other two groups exhibit surficial morphologies similar to those found on modern and ancient crayfish burrows and may provide evidence of freshwater crayfish in the Permian. Burrows from the Upper Triassic

  4. Soils of Walker Branch Watershed

    SciTech Connect

    Lietzke, D.A.

    1994-01-01

    The soil survey of Walker Branch Watershed (WBW) utilized the most up-to-date knowledge of soils, geology, and geohydrology in building the soils data base needed to reinterpret past research and to begin new research in the watershed. The soils of WBW were also compared with soils mapped elsewhere along Chestnut Ridge on the Oak Ridge Reservation to (1) establish whether knowledge obtained elsewhere could be used within the watershed, (2) determine whether there were any soils restricted to the watershed, and (3) evaluate geologic formation lateral variability. Soils, surficial geology, and geomorphology were mapped at a scale of 1:1200 using a paper base map having 2-ft contour intervals. Most of the contours seemed to reasonably represent actual landform configurations, except for dense wooded areas. For example, the very large dolines or sinkholes were shown on the contour base map, but numerous smaller ones were not. In addition, small drainageways and gullies were often not shown. These often small but important features were located approximately as soil mapping progressed. WBW is underlain by dolostones of the Knox Group, but only a very small part of the surface area contains outcroppings of rock and most outcrops were located in the lower part. Soil mapping revealed the presence of both ancient alluvium and ancient colluvium deposits, not recognized in previous soil surveys, that have been preserved in high-elevation stable portions of present-day landforms. An erosional geomorphic process of topographic inversion requiring several millions of years within the Pleistocene is necessary to bring about the degree of inversion that is expressed in the watershed. Indeed, some of these ancient alluvial and colluvial remnants may date back into the Tertiary. Also evident in the watershed, and preserved in the broad, nearly level bottoms of dolines, are multiple deposits of silty material either devoid or nearly devoid of coarse fragments. Recent research

  5. Some Considerations on Horizontal Displacement and Horizontal Displacement Coefficient B

    NASA Astrophysics Data System (ADS)

    Tajduś, Krzysztof; Tajduś, Antoni

    2015-12-01

    Mining-induced deformations of the ground surface and within the rock mass may pose danger not only for surface constructions but also for underground objects (e.g., tunnels, underground storages, garages), diverse types of pipelines, electric cables, etc. For a proper evaluation of hazard for surface and underground objects, such parameters as horizontal displacement and horizontal deformations, especially their maximum values, are of crucial importance. The paper is an attempt at a critical review of hitherto accomplished studies and state of the art of predicting horizontal displacement u, in particular the coefficient B, whose value allows determination of the value of maximum displacement if the value of maximum slope is known, or the value of maximum deformation if the value of maximum trough slope is recognized. Since the geodesic observations of fully developed subsidence troughs suggest that the value of the coefficient depends on the depth H, radius of main influences range r and properties of overburden rock, in particular the occurrence of sub-eras Paleogene and Neogene layers (old name: Quaternary and Tertiary) with low strength parameters, therefore a formula is provided in the present paper allowing for the estimation of the influence of those factors on the value of coefficient B.

  6. Structural Mechanics and Dynamics Branch

    NASA Technical Reports Server (NTRS)

    Stefko, George

    2003-01-01

    The 2002 annual report of the Structural Mechanics and Dynamics Branch reflects the majority of the work performed by the branch staff during the 2002 calendar year. Its purpose is to give a brief review of the branch s technical accomplishments. The Structural Mechanics and Dynamics Branch develops innovative computational tools, benchmark experimental data, and solutions to long-term barrier problems in the areas of propulsion aeroelasticity, active and passive damping, engine vibration control, rotor dynamics, magnetic suspension, structural mechanics, probabilistics, smart structures, engine system dynamics, and engine containment. Furthermore, the branch is developing a compact, nonpolluting, bearingless electric machine with electric power supplied by fuel cells for future "more electric" aircraft. An ultra-high-power-density machine that can generate projected power densities of 50 hp/lb or more, in comparison to conventional electric machines, which generate usually 0.2 hp/lb, is under development for application to electric drives for propulsive fans or propellers. In the future, propulsion and power systems will need to be lighter, to operate at higher temperatures, and to be more reliable in order to achieve higher performance and economic viability. The Structural Mechanics and Dynamics Branch is working to achieve these complex, challenging goals.

  7. Chalk play tops Gulf Coast horizontal scene

    SciTech Connect

    Not Available

    1991-11-18

    This paper reports on horizontal drilling in the Cretaceous Austin chalk of Texas which dominates news of U.S. Gulf Coast horizontal action. In spite of a significant decline in horizontal drilling in Texas-the Texas Railroad Commission reported a 15 unit decline in the number of permits to drill horizontal wells during the third quarter-operators in East and South Texas continue to expand plays and develop new ones. The Cretaceous Bruda may be gaining some respect as a horizontal target in Texas. Elsewhere on the Gulf Coast, Mississippi soon will see more action on the horizontal drilling front.

  8. Horizontal gene transfer in plants.

    PubMed

    Gao, Caihua; Ren, Xiaodong; Mason, Annaliese S; Liu, Honglei; Xiao, Meili; Li, Jiana; Fu, Donghui

    2014-03-01

    Horizontal gene transfer (HGT) describes the transmission of genetic material across species boundaries. HGT often occurs in microbic and eukaryotic genomes. However, the pathways by which HGTs occur in multicellular eukaryotes, especially in plants, are not well understood. We systematically summarized more than ten possible pathways for HGT. The intimate contact which frequently occurs in parasitism, symbiosis, pathogen, epiphyte, entophyte, and grafting interactions could promote HGTs between two species. Besides these direct transfer methods, genes can be exchanged with a vector as a bridge: possible vectors include pollen, fungi, bacteria, viruses, viroids, plasmids, transposons, and insects. HGT, especially when involving horizontal transfer of transposable elements, is recognized as a significant force propelling genomic variation and biological innovation, playing an important functional and evolutionary role in both eukaryotic and prokaryotic genomes. We proposed possible mechanisms by which HGTs can occur, which is useful in understanding the genetic information exchange among distant species or distant cellular components. PMID:24132513

  9. Horizontal Velocity Structure in Waterspouts.

    NASA Astrophysics Data System (ADS)

    Schwiesow, R. L.

    1981-04-01

    We have measured the spatial variation of a single horizontal component of the velocity in a number of waterspouts using an airborne infrared Doppler lidar. In 21 data sets, maximum velocities range from 4.2 to 33.6 m s1 and visible funnel diameters from 6.6 to 90 m. Data were taken at altitudes between 675 m, near cloud base, and 95 m above the surface. The sequences show time development of the velocity as a function of radius at a fixed altitude and the velocity structure at different altitudes and sequential times with a horizontal resolution of 0.75 m between data points. The variation in velocity structure between waterspouts is large, with some showing marked azimuthal asymmetry and mixing with the ambient flow, and others showing multiple concentric vortex shells.

  10. Horizontal drilling opportunities in Ohio

    SciTech Connect

    Noel, J.A. )

    1991-08-01

    Horizontal drilling has become commonplace in certain parts of Texas. The Austin Chalk is the favorite target, especially where fracture systems are present. The activity has become so intense that leases are now costly or nearly impossible to find. This type of activity was prevalent during the late oil boom, but with vertical wells. So, the same areas that were drilled then are being redone with horizontal drilling. In the past few months, carbonates with little or no evidence of fracture systems are being drilled with some success. Because of the difficulty in lease acquisition, operators are turning their attention elsewhere. Even though horizontal drilling has been conducted limitedly in the Devonian black shales, the Appalachian basin is an area that calls for attention. In Ohio, there have been instances of discoveries of one-well fields in both the Trenton and Trempealeau formations. The initial production from these wells ranges from a few to hundreds of barrels of oil per day. The lack of success in offset wells has been attributed to the interpretation that the producing wells were serendipitously drilled into a limited fractured reservoir. In most cases, the producer is surrounded by clusters of dry holes. These Ohio wells and wells in one other area are studied using well data, spectral and sonic logs, aerial photographs, side-looking radar surveys, and other data. The results are presented on structure contour and lineament maps, and quantitative log interpretations. The maps show the interpretations of those areas of fracture systems that might be viable targets for horizontal drilling.

  11. Musical morphology.

    PubMed

    Chakravarty, M Mallar; Vuust, Peter

    2009-07-01

    Morphologic measures have long been used to determine the patho-anatomical signature of different neurologic disorders. However, these measures can also be used to determine effects of specific learning tasks and quantifiable human abilities on cerebral structure. Musicians provide interesting opportunities for this type of analysis as their various skills, such as rhythmic ability and pitch and harmony discrimination (acquired through years of practicing and playing) can be quantified and compared using distinct morphologic analyses. Here, we review magnetic resonance imaging-based morphologic analyses in the music and neuroscience literature and provide some results from our own analysis of rhythmic ability in a cohort of musicians. PMID:19673757

  12. Stress Induced Branching of Growing Crystals on Curved Surfaces.

    PubMed

    Köhler, Christian; Backofen, Rainer; Voigt, Axel

    2016-04-01

    If two-dimensional crystals grow on a curved surface, the Gaussian curvature of the surface induces elastic stress and affects the growth pathway. The elastic stress can be alleviated by incorporating defects or, if this is energetically unfavorable, via an elastic instability which leads to anisotropic growth with branched ribbonlike structures. This instability provides a generic route to grow defect-free crystals on curved surfaces. Depending on the elastic properties of the crystal and the geometric properties of the surface, different growth morphologies with two-, four-, and sixfold symmetry develop. Using a phase field crystal type modeling approach, we provide a microscopic understanding of the morphology selection. PMID:27081988

  13. Stress Induced Branching of Growing Crystals on Curved Surfaces

    NASA Astrophysics Data System (ADS)

    Köhler, Christian; Backofen, Rainer; Voigt, Axel

    2016-04-01

    If two-dimensional crystals grow on a curved surface, the Gaussian curvature of the surface induces elastic stress and affects the growth pathway. The elastic stress can be alleviated by incorporating defects or, if this is energetically unfavorable, via an elastic instability which leads to anisotropic growth with branched ribbonlike structures. This instability provides a generic route to grow defect-free crystals on curved surfaces. Depending on the elastic properties of the crystal and the geometric properties of the surface, different growth morphologies with two-, four-, and sixfold symmetry develop. Using a phase field crystal type modeling approach, we provide a microscopic understanding of the morphology selection.

  14. Integrated UV fluxes and the HB morphology of Globular Clusters

    NASA Astrophysics Data System (ADS)

    Landsman, W. B.; Catelan, M.; O'Connell, R. W.; Pereira, D.; Stecher, T. P.

    2001-12-01

    The UV ( ~ 1500 Å) flux of a globular cluster will be dominated by its blue horizontal branch (HB) population, provided that such a population is present. Thus, the integrated UV - V color of a globular cluster can provide an indication of its HB morphology, without the need to resolve the cluster into a color-magnitude diagram. To date, UV photometry of extragalactic clusters are available for only a few globulars in M31 (e.g. Bohlin et al. 1993, ApJ, 417, 127), but additional UV photometry of extragalactic globulars is soon expected from GALEX (Yi et al. 2001, AAS, 198, 5501), and from STIS FUV-MAMA observations of M87 (HST program 8643). Here we calibrate the relation between UV flux and HB morphology for Galactic globular clusters. The OAO-2 and ANS data tabulated by deBoer (1985, A&A, 142, 321) are supplemented with photometry of 14 globular clusters observed with the Ultraviolet Imaging Telescope (UIT), and a few cluster cores observed with the STIS FUV-MAMA. The UIT data is especially useful since its 40' diameter FOV was sufficient to completely encompass most of the observed clusters, while allowing isolation of hot field and UV-bright stars. We compare the observed Galactic UV color - HB morphology relation with synthetic HB models as a function of age and metallicity. We also estimate the effect of radiative levitation of heavy metals in hot HB stars (e.g. Moehler et al. 2000, , A&A, 360, 120) on the integrated UV flux. This work is funded by STScI grant GO-8358.01.

  15. U. S. horizontal drilling continues to spread

    SciTech Connect

    Petzet, G.A.

    1990-12-10

    This paper reports that horizontal drilling is still spreading in onshore U.S. oil fields. One company completed a shallow well producing oil by gravity drainage through three horizontal legs about 120{sup {degrees}} apart on the La Barge platform in Wyoming. The author reports successful Austin chalk horizontal drilling in Sabine County, East Texas. Another horizontal completion of Cretaceous Niobrara was reported and several other wells were drilling or staked in Silo field, Laramie County, Wyoming.

  16. VizieR Online Data Catalog: Horizontal branch stars in NGC 6723 (Gratton+, 2015)

    NASA Astrophysics Data System (ADS)

    Gratton, R. G.; Lucatello, S.; Sollima, A.; Carretta, E.; Bragaglia, A.; Momany, Y.; D'Orazi, V.; Salaris, M.; Cassisi, S.; Stetson, P. B.

    2015-02-01

    We observed a total of 58 candidate HB stars of NGC 6723 with FLAMES + GIRAFFE at the VLT. The instrument was used in MEDUSA mode, with fibres pointing to each star and several (~20) fibres used for determining the local sky background. Observations were made between 2011-07-11 and 2011-08-27. (5 data files).

  17. VizieR Online Data Catalog: Extreme Horizontal Branch stars in ω Cen (Randall+, 2016)

    NASA Astrophysics Data System (ADS)

    Randall, S. K.; Calamida, A.; Fontaine, G.; Monelli, M.; Bono, G.; Alonso, M. L.; Van Grootel, V.; Brassard, P.; Chayer, P.; Catelan, M.; Littlefair, S.; Dhillon, V. S.; Marsh, T. R.

    2016-02-01

    We make available the reduced spectra for the 47 EHB stars in omega Cen that we derived atmospheric parameters for in Table 5. Each star is associated with two files (the flux-calibrated and the non-flux-calibrated spectrum), where the filename takes the format sxxxxxxx or fcxxxxxxx, where xxxxxxx is the star's ID as listed in Table 5. Filenames with s_ refer to non-flux calibrated spectra, while the fc_ files are flux calibrated. The format of all the files is the same, the first column being the wavelength in Angstroms, and the second the relative flux for the s_ files and the absolute flux for the fc_ files. (3 data files).

  18. VizieR Online Data Catalog: Horizontal branch stars in NGC 1851 (Gratton+, 2012)

    NASA Astrophysics Data System (ADS)

    Gratton, R. G.; Lucatello, S.; Carretta, E.; Bragaglia, A.; D'Orazi, V.; Al Momany, Y.; Sollima, A.; Salaris, M.; Cassisi, S.

    2012-10-01

    We acquired spectra for 35 stars on the BHB, 1 RR Lyrae variable, 57 stars on the RHB, and 13 on the lower RGB (luminosity below the bump) of NGC 1851 using the GIRAFFE fibre-fed spectrograph at VLT . (3 data files).

  19. VizieR Online Data Catalog: Spectra of 2 halo red horizontal branch stars (Pereira+, 2013)

    NASA Astrophysics Data System (ADS)

    Pereira, C. B.; Jilinski, N. A.; Drake, E. G.; Ortega, V. G.; Roig, F.

    2013-08-01

    The high-resolution spectra of CD-41 15048 and HD 214362 analyzed in this work the were obtained with FEROS, the Fiber-fed extended range optical spectrograph, at the 2.2m ESO telescope at La Silla (Chile) on the night of September 6, 2007 and August 26, 2007. (2 data files).

  20. REVEALING PROBABLE UNIVERSAL FEATURES IN THE LOWER RED GIANT BRANCH LUMINOSITY FUNCTIONS OF GALACTIC GLOBULAR CLUSTERS

    SciTech Connect

    Kravtsov, V. V.

    2009-06-15

    This paper aims at demonstrating, for the first time, very probable universal peculiarities of the evolution of stars in the lower red giant branch (RGB) of Galactic globular clusters (GCs), reflected in two corresponding dips in the luminosity functions (LFs). By relying on the database of Hubble Space Telescope photometry of GCs, we analyze the lower RGB LFs of a sample of 18 GCs in a wide metallicity range, {delta}[Fe/H] {approx} 1.9 dex. We first show that in the F555W-(F439W-F555W) color-magnitude diagrams (CMDs), the lower RGB of GCs, except for the most metal-poor of them, frequently shows an apparent 'knee'. It reveals itself as a fairly abrupt change of the RGB slope. At the same luminosity level, the RGB LFs show a feature in the form of a more or less pronounced dip. We find that the magnitude difference between the RGB base and the given feature is, on average, around {delta} F555W{sup dip} {sub base}{approx} 1.4 mag. It shows a marginal variation with metallicity, if any, comparable to the error. At the same time, the magnitude difference between the dip and the RGB bump, {delta} F555W{sup bump} {sub dip}, decreases with increasing metallicity and falls within the range 0.8 {approx}< {delta} F555W{sup bump} {sub dip} {approx}< 1.7 mag. Generalized LFs (GLFs) have been obtained for three subsamples of GCs within limited metallicity ranges and with different horizontal branch (HB) morphology. They reproduce the 'knee-related' dip that is statistically significant in two of the GLFs. This feature turns out to be more pronounced in the GLFs of GCs with either the blue or red HB morphology than with the intermediate one. The same GLFs also reveal an additional probable universal dip. It shows up below the RGB bump at {delta} F555W slightly increasing from {approx}0.3 to {approx}0.5 mag with increasing metallicity. Also, the statistical significance of this 'prebump' dip increases, on average, toward higher metallicity. Except for the well known RGB bump, no

  1. 17 CFR 166.4 - Branch offices.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... 17 Commodity and Securities Exchanges 1 2010-04-01 2010-04-01 false Branch offices. 166.4 Section 166.4 Commodity and Securities Exchanges COMMODITY FUTURES TRADING COMMISSION CUSTOMER PROTECTION RULES § 166.4 Branch offices. Each branch office of each Commission registrant must use the name of the firm of which it is a branch for all...

  2. First evidence of root morphological and architectural variations in young Posidonia oceanica plants colonizing different substrate typologies

    NASA Astrophysics Data System (ADS)

    Balestri, Elena; de Battisti, Davide; Vallerini, Flavia; Lardicci, Claudio

    2015-03-01

    Root morphology and root system architecture of young Posidonia oceanica plants established on two contrasting substrate types, sand and rock, were examined to provide insights into the strategy of adaptation of seagrasses to their environment. After germination, seedlings were planted on sandy patches and on rock within the same area, and survived plants were collected five years later for measurements of the size of the entire root complex and analysis of individual morphological and architectural root traits. Collected plants exhibited up to nine highly intermingled root systems and approx. 2.5 m of total root length. Maximum horizontal extension, total biomass and total length of roots were not significantly affected by substrate. However, on sand roots grew vertically reaching up to 13 cm, while on rock they extended more horizontally and did not penetrate deeper than 5-7 cm leading to the formation of a shallow, densely packed root complex. On rock, the number and the length of second-order laterals on an individual root system were reduced and the topological index higher than on sand (0.8 vs. 0.7) reflecting a more simple (herringbone) branching pattern. Again, root diameter was greater than on sand. The results suggest that P. oceanica can adjust root traits early during plant development according to substrate typology to maximize anchorage and substrate exploration efficiency. This plasticity enables the species to establish and persist also on rocky bottoms which generally prevent establishment of the majority of seagrasses.

  3. Horizontal drilling comes full circle

    SciTech Connect

    Fritz, M.

    1991-06-01

    This paper discusses the new discoveries of oil and gas in Utah's Paradox Fold and Fault Belt resulting from horizontal drilling techniques. The Kane Spring Federal {number sign}27-1 is the first successful horizontal wildcat drilled in Utah. The discovery well recorded an initial potential test rate of 914 barrels of oil and 290 thousand cubic feet of gas per day through a 10/64-inch choke, with a flowing tubing pressure of 3,460 psi. A one-hour test on a 14/64-inch choke produced a rate of 2,302 barrels of oil and 627 thousand cubic feet of gas per day. The paper describes the engineering aspects of the well construct which was needed to direct the drill stem in salt beds and relatively incompetent beds. The pay zone is located in the Cane Creek Shale of the Pennsylvanian Paradox Formation. The oil and gas are located in geologic fractures and sealed by two layers of salt. The future of the prospect area is described.

  4. Orphan penumbrae: Submerging horizontal fields

    NASA Astrophysics Data System (ADS)

    Jurčák, J.; Bellot Rubio, L. R.; Sobotka, M.

    2014-04-01

    Aims: We investigate the properties of orphan penumbrae, which are photospheric filamentary structures observed in active regions near polarity inversion lines that resemble the penumbra of regular sunspots but are not connected to any umbra. Methods: We use Hinode data from the Solar Optical Telescope to determine the properties of orphan penumbrae. Spectropolarimetric data are employed to obtain the vector magnetic field and line-of-sight velocities in the photosphere. Magnetograms are used to study the overall evolution of these structures, and G-band and Ca ii H filtergrams are to investigate their brightness and apparent horizontal motions. Results: Orphan penumbrae form between regions of opposite polarity in places with horizontal magnetic fields. Their magnetic configuration is that of Ω-shaped flux ropes. In the two cases studied here, the opposite-polarity regions approach each other with time and the whole structure submerges as the penumbral filaments disappear. Orphan penumbrae are very similar to regular penumbrae, including the existence of strong gas flows. Therefore, they could have a similar origin. The main difference between them is the absence of a "background" magnetic field in orphan penumbrae. This could explain most of the observed differences. Conclusions: The fast flows we detect in orphan penumbrae may be caused by the siphon flow mechanism. Based on the similarities between orphan and regular penumbrae, we propose that the Evershed flow is also a manifestation of siphon flows. A movie attached to Fig. 11 is available in electronic form at http://www.aanda.org

  5. NCI: DCTD: Biometric Research Branch

    Cancer.gov

    The Biometric Research Branch (BRP) is the statistical and biomathematical component of the Division of Cancer Treatment, Diagnosis and Centers (DCTDC). Its members provide statistical leadership for the national and international research programs of the division in developmental therapeutics, developmental diagnostics, diagnostic imaging and clinical trials.

  6. Branching of keratin intermediate filaments.

    PubMed

    Nafeey, Soufi; Martin, Ines; Felder, Tatiana; Walther, Paul; Felder, Edward

    2016-06-01

    Keratin intermediate filaments (IFs) are crucial to maintain mechanical stability in epithelial cells. Since little is known about the network architecture that provides this stiffness and especially about branching properties of filaments, we addressed this question with different electron microscopic (EM) methods. Using EM tomography of high pressure frozen keratinocytes, we investigated the course of several filaments in a branching of a filament bundle. Moreover we found several putative bifurcations in individual filaments. To verify our observation we also visualized the keratin network in detergent extracted keratinocytes with scanning EM. Here bifurcations of individual filaments could unambiguously be identified additionally to bundle branchings. Interestingly, identical filament bifurcations were also found in purified keratin 8/18 filaments expressed in Escherichia coli which were reassembled in vitro. This excludes that an accessory protein contributes to the branch formation. Measurements of the filament cross sectional areas showed various ratios between the three bifurcation arms. This demonstrates that intermediate filament furcation is very different from actin furcation where an entire new filament is attached to an existing filament. Instead, the architecture of intermediate filament bifurcations is less predetermined and hence consistent with the general concept of IF formation. PMID:27039023

  7. Cash efficiency for bank branches.

    PubMed

    Cabello, Julia García

    2013-01-01

    Bank liquidity management has become a major issue during the financial crisis as liquidity shortages have intensified and have put pressure on banks to diversity and improve their liquidity sources. While a significant strand of the literature concentrates on wholesale liquidity generation and on the alternative to deposit funding, the management of an inventory of cash holdings within the banks' branches is also a relevant issue as any significant improvement in cash management at the bank distribution channels may have a positive effect in reducing liquidity tensions. In this paper, we propose a simple programme of cash efficiency for the banks' branches, very easy to implement, which conform to a set of instructions to be imposed from the bank to their branches. This model proves to significantly reduce cash holdings at branches thereby providing efficiency improvements in liquidity management. The methodology we propose is based on the definition of some stochastic processes combined with renewal processes, which capture the random elements of the cash flow, before applying suitable optimization programmes to all the costs involved in cash movements. The classical issue of the Transaction Demand for the Cash and some aspects of Inventory Theory are also present. Mathematics Subject Classification (2000) C02, C60, E50. PMID:24010026

  8. National Zoological Park Branch Library.

    ERIC Educational Resources Information Center

    Kenyon, Kay A.

    1988-01-01

    Describes the functions of the National Zoological Park Branch of the Smithsonian Institution Libraries, which is dedicated to supporting the special information needs of the zoo. Topics covered include the library's history, collection, programs, services, future plans, and relations with other zoo libraries. (two references) (Author/CLB)

  9. 76 FR 13272 - Branch Offices

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-03-10

    ... Office of Thrift Supervision Branch Offices AGENCY: Office of Thrift Supervision (OTS), Treasury. ACTION... 1995, 44 U.S.C. 3507. The Office of Thrift Supervision within the Department of the Treasury will... approval number, to Information Collection Comments, Chief Counsel's Office, Office of Thrift...

  10. Risk Factor Assessment Branch (RFAB)

    Cancer.gov

    The Risk Factor Assessment Branch (RFAB) focuses on the development, evaluation, and dissemination of high-quality risk factor metrics, methods, tools, technologies, and resources for use across the cancer research continuum, and the assessment of cancer-related risk factors in the population.