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Articles 1 - 19 of 19
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Constraints On The Origin Of The Remarkable Lithium Abundance In The Halo Star Bd+23 3912, Jeremy R. King, Constantine P. Deliyannis, Ann Merchant Boesgaard
Constraints On The Origin Of The Remarkable Lithium Abundance In The Halo Star Bd+23 3912, Jeremy R. King, Constantine P. Deliyannis, Ann Merchant Boesgaard
Publications
The Li abundance of the halo star BD+23 3912 ([Fe/H]=-1.5) lies a factor of 2 - 3 above the Spite plateau. This remarkable difference could reflect either less-than-average stellar Li depletion from a higher primordial Li abundance (as predicted by the Yale rotational stellar evolutionary models), which may have interesting implications for Big Bang nucleosynthesis, or the extraordinary action of Galactic Li production mechanisms. It is also possible that both processes have acted. We use our high resolution, high S/N Keck HIRES spectrum of BD+23 3912 to determine the s-process element abundances and 6Li/7Li ratio in this star. These values …
Stellar Oxygen Abundances.V.Abundances Of Two Hyades Dwarfs Derived From The 6300 Angstroms [Oi] Line, Jeremy R. King, Daniel D. Hiltgen
Stellar Oxygen Abundances.V.Abundances Of Two Hyades Dwarfs Derived From The 6300 Angstroms [Oi] Line, Jeremy R. King, Daniel D. Hiltgen
Publications
We present observations of the 6300 Å [O I] spectral region in two cool Hyades dwarfs, vB 79 and vB 25. We derive a mean iron abundance, [Fe/H]˜+0.11, in good agreement with recent analyses of F and G Hyades dwarfs. The O abundance derived from spectrum synthesis, [O/H]˜+0.15, is between the values deduced by Garcia Lopez et al. (1993, ApJ, 412, 173; [O/H]=-0.05 to -0.10) and King (1993, Ph. D. Dissertation, University of Hawaii; [O/H]=+0.26), who employed the 7774 Å O I triplet in hotter Hyades dwarfs. An accounting of differences between these two 7774 Å analyses is given. Our …
Galactic Evolution Of Silicon Isotopes: Applications To Presolar Sic Grains From Meteorites, F X. Timmes, Donald D. Clayton
Galactic Evolution Of Silicon Isotopes: Applications To Presolar Sic Grains From Meteorites, F X. Timmes, Donald D. Clayton
Publications
We calculate and discuss the chemical evolution of the isotopic silicon abundances in the interstellar medium (ISM) at distances and times appropriate to the birth of the solar system. This has several objectives, some of which are related to anomalous silicon isotope ratios within presolar grains extracted from meteorites; namely: (1) What is the relative importance for silicon isotopic compositions in the bulk ISM of Type II supernovae, Type Ia supernovae, and AGB stars? (2) Are 29Si and 30Si primary or secondary nucleosynthesis products? (3) In what isotopic direction in a three-isotope plot do core-collapse supernovae of different mass move …
A Role For A Rab4-Like Gtpase In Endocytosis And In Regulation Of Contractile Vacuole Structure And Function In Dictyostelium Discoideum, John Bush, Lesly A. Temesvari, Juan Rodriguez-Paris, Greg Buczynski, James Cardelli
A Role For A Rab4-Like Gtpase In Endocytosis And In Regulation Of Contractile Vacuole Structure And Function In Dictyostelium Discoideum, John Bush, Lesly A. Temesvari, Juan Rodriguez-Paris, Greg Buczynski, James Cardelli
Publications
The small Mr Rab4-like GTPase, RabD, localizes to the endosomal pathway and the contractile vacuole membrane system in Dictyostelium discoideum. Stably transformed cell lines overexpressing a dominant negative functioning RabD internalized fluid phase marker at 50% of the rate of wild-type cells. Mutant cells were also slower at recycling internalized fluid. Microscopic and biochemical approaches indicated that the transport of fluid to large postlysosome vacuoles was delayed in mutant cells, resulting in an accumulation in acidic smaller vesicles, probably lysosomes. Also, RabD N121I-expressing cell lines missorted a small but significant percentage of newly synthesized lysosomal alpha-mannosidase precursor polypeptides. However, the …
The 9be Abundances Of Alpha Centauri A And B And The Sun: Implications For Stellar Evolution And Mixing, Jeremy R. King, Constantine P. Deliyannis, Ann Merchant Boesgaard
The 9be Abundances Of Alpha Centauri A And B And The Sun: Implications For Stellar Evolution And Mixing, Jeremy R. King, Constantine P. Deliyannis, Ann Merchant Boesgaard
Publications
We present high-resolution, high signal-to-noise ratio spectra, obtained at the Cerro Tololo Inter-American Observatory 4 m telescope, of the Be II 3131 Å region in the metal-rich solar analog α Centauri A and its companion α Centauri B. Be abundances are derived relative to the Sun in a consistent fashion via spectrum synthesis. For α Cen A, we find [Be/H] = +0.20 ± 0.15, where the error reflects random uncertainties at the 1 σ confidence level; systematic errors of ~0.1 dex are also possible. The analysis of α Cen B is more uncertain since inadequacies in the line list, which …
The Double Infared Source Toward The Soft Gamma-Ray Repeater Sgr 1900+14, F. J. Vrba, C. B. Luginbuhl, K. C. Hurley, P. Li, S. R. Kulkarni, M. H. Van Kerkwuk, Dieter H. Hartmann, L. E. Campusano, M. J. Graham, R. G. Clowes
The Double Infared Source Toward The Soft Gamma-Ray Repeater Sgr 1900+14, F. J. Vrba, C. B. Luginbuhl, K. C. Hurley, P. Li, S. R. Kulkarni, M. H. Van Kerkwuk, Dieter H. Hartmann, L. E. Campusano, M. J. Graham, R. G. Clowes
Publications
We report the results of an extensive set of optical and near-infrared photometry and spectroscopy of the double infrared source reported by Hartmann et al. (1995) as a potential counterpart for the Galatic soft gamma-ray repeater SGR 1900 + 14. These objects are found to be variable but otherwise normal M5 supergiant stars at a distance of ~ 12-15 kpc and extinguised by Av ~ 19.2 mag, primarily by the general interstellar medium. We argue that the supergiants are likely gravitationally bround. These stars are positionally coincident with both quiescent X-ray and IRAS sources, suggestive of a yet-undetected third component …
The Angular Power Spectrum Of Batse 3b Gamma-Ray Bursts, Max Tegmark, Dieter H. Hartmann, Michael S. Briggs, Charles A. Meegan
The Angular Power Spectrum Of Batse 3b Gamma-Ray Bursts, Max Tegmark, Dieter H. Hartmann, Michael S. Briggs, Charles A. Meegan
Publications
We compute the angular power spectrum C1 from the BATSE 3B catalog of 1122 gamma-ray burts and find no evidence of clustering on any scale. These constraints bridge the entire range from samall scales (which probe source clustering and burst repetition) to the largest scales (which constrain possible anisotropies from the Galactic hal or from nearby cosmological large-scale structures). We develop an analysis tecnique that takes the angular position errors into account. For specific clustering or repetition models, strong upper limits can be obtained down to scales l ~ 30, corresponding to abou couple of degrees on the sky. The …
The Gamma-Ray Burst Rate At High Photon Energies, Karl Mannheim, Dieter H. Hartmann, Burkhardt Funk
The Gamma-Ray Burst Rate At High Photon Energies, Karl Mannheim, Dieter H. Hartmann, Burkhardt Funk
Publications
Some gamma-ray burst (GRB) spectra exhibit high energy tails with the highest photon energy detected at 18 GeV. The spectral slope of the high-energy tails is suffieniently flat in vF, to consider the possibility of their dectection at still higher energies. We calculate how many bursts can resonably be expected above a given energy threshold for a cosmological distribution of bursts satisfying the observed apparent birghtness distribution. The crucial point is that the gamma-ray absorption by pair production in the intergalactic diffuse radiation field climinates burts from beyond the gamma-ray horizion, thus drastically reducing the number of bursts at high …
Overview Of Results From 1994 & 1995 School-Based Decision Making Surveys, Jane Clark Lindle, Bruce S. Gale, Brenda Curry-White
Overview Of Results From 1994 & 1995 School-Based Decision Making Surveys, Jane Clark Lindle, Bruce S. Gale, Brenda Curry-White
Publications
The 1994 and 1995 School-Based Decision Making (SBDM) Surveys were conducted in the fall of each of those years for the Study of Education Policy. This report compares the 1994 and 1995 responses to three questions: (1) What do people think of the effectiveness of SBDM? (2) Who is involved in the SBDM decisions? and (3) What are councils doing? The discussion focuses on school and district effectiveness, the barriers to SBDM, SBDM trainers' network, parent involvement, efforts to involve minorities and women, council productivity, improvement strategies, and the budget process. Findings show that most people rate SBDM as good …
The Production Of 44ti And 60co In Supernovae, F. X. Timmes, S. E. Woosley, Dieter H. Hartmann, R. D. Hoffman
The Production Of 44ti And 60co In Supernovae, F. X. Timmes, S. E. Woosley, Dieter H. Hartmann, R. D. Hoffman
Publications
The production of the radioactive isotopes 44Ti and 60Co in all types of supernovae is examined and compared to observational constraints inculding Galactic gamma-ray surveys, measurements of the diffuse 511 keV radiation, gamma-ray observations of Cas A, the late-time light curve of SN 1987A, and isotopic anomalies found in silicon carbide grains in meteorities. The (revished) line flux from 44Ti decay in the Cas A supernova remnant reported by COMPTEL on the Compton Gamma Ray Observatory is near the upper bound expected from our models. The necessary concurrent ejection of 56Ni would also imply that Cas A was a brighter …
Involvement Of The Vacuolar Proton-Translocating Atpase In Multiple Steps Of The Endo-Lysosomal System And In The Contractile Vacuole System Of Dictyostelium Discoideum, Lesly A. Temesvari, Juan M. Rodriguez-Paris, John M. Bush, Linyi Zhang, James A. Cardelli
Involvement Of The Vacuolar Proton-Translocating Atpase In Multiple Steps Of The Endo-Lysosomal System And In The Contractile Vacuole System Of Dictyostelium Discoideum, Lesly A. Temesvari, Juan M. Rodriguez-Paris, John M. Bush, Linyi Zhang, James A. Cardelli
Publications
We have investigated the effects of Concanamycin A (CMA), a specific inhibitor of vacuolar type H(+)-ATPases, on acidification and function of the endo-lysosomal and contractile vacuole (CV) systems of D. discoideum. This drug inhibited acidification and increased the pH of endo-lysosomal vesicles both in vivo and in vitro in a dose dependent manner. Treatment also inhibited endocytosis and exocytosis of fluid phase, and phagocytosis of latex beads. This report also confirms our previous conclusions (Cardelli et al. (1989) J. Biol. Chem. 264, 3454–3463) that maintenance of acidic pH in lumenal compartments is required for efficient processing and targeting of a …
A Possible X-Ray Counterpart To Sgr 1900+14, K. Hurley, P. Li, F. Vrba, C. Luginbuhl, Dieter H. Hartmann, C. Kouvelioutou, C. Meegan, G. Fishman, S. Kulkarni, D. Frail
A Possible X-Ray Counterpart To Sgr 1900+14, K. Hurley, P. Li, F. Vrba, C. Luginbuhl, Dieter H. Hartmann, C. Kouvelioutou, C. Meegan, G. Fishman, S. Kulkarni, D. Frail
Publications
The location of the soft gamma repeater SGR 1900ϩ14 was recently reduced to two 15 arcmin2 alternate error boxes by the network synthesis method. We have used the ROSAT High Resolution Imager to observe the error box that is closest to the supernova remnant G42.8ϩ0.6. A quiescent, steady, point X-ray source was found at ␣(2000) ϭ 19h07m14!15, ␦(2000) ϭ 9Њ19Ј19"06, whose unabsorbed flux is 3 ϫ 10Ϫ12 ergs cmϪ2 sϪ1. Its position is also consistent with a peculiar double infrared source described in a companion paper. We have also examined this region using the VLA,1 and have obtained upper limits …
48ca Production In Matter Expanding From High Temperature And Density, B S. Meyer, Tracy D. Krishnan, Donald D. Clayton
48ca Production In Matter Expanding From High Temperature And Density, B S. Meyer, Tracy D. Krishnan, Donald D. Clayton
Publications
We calculate with a large nuclear reaction network the nuclear dynamics associated with the expansions and cooling of initially hot and dense matter. We study matter with neutron excess near that of 48Ca, because one objective is to clarify the nucleosynthesis of that abundant neutron-rich nucleus, whose origin has been enigmatic. Expecting that supernovae provide the site of its origin, we take initial temperatures near T9 = 10 but survey a wide range of initial densities, corresponding to a wide range in initial entropies. The highest entropies are probably associated with winds from newborn neutron stars in Type II collapse …
The Wisdom Of Teacher Involvement In School-Linked Social Services, Jane Clark Lindle
The Wisdom Of Teacher Involvement In School-Linked Social Services, Jane Clark Lindle
Publications
Recently, school-linked services phenomena have been examined through various implementation strategies. Most discussions are divided over issues such as points of deliver, institutional or agency territoriality, as well as financing and payment schemes. This debate focuses on the less well examined concern over the role of classroom teachers in school-linked service delivery.
Examination Of The Endosomal And Lysosomal Pathways In Dictyostelium Discoideum Myosin I Mutants, Lesly A. Temesvari, John M. Bush, Michelle D. Peterson, Kristine D. Novak, Margaret A. Titus, James A. Cardelli
Examination Of The Endosomal And Lysosomal Pathways In Dictyostelium Discoideum Myosin I Mutants, Lesly A. Temesvari, John M. Bush, Michelle D. Peterson, Kristine D. Novak, Margaret A. Titus, James A. Cardelli
Publications
The role of myosin Is in endosomal trafficking and the lysosomal system was investigated in a Dictyostelium discoideum myosin I double mutant myoB-/C-, that has been previously shown to exhibit defects in fluid-phase endocytosis during growth in suspension culture (Novak et al., 1995). Various properties of the endosomal pathway in the myoB-/C- double mutant as well as in the myoB- and myoC- single mutants, including intravesicular pH, and intracellular retention time and exocytosis of a fluid phase marker, were found to be indistinguishable from wild-type parental cells. The intimate connection between the contractile vacuole complex and the endocytic pathway in …
Book Review - The Adult Limnephilus Leach (Trichoptera:Limnephilidae) Of The New World, John C. Morse
Book Review - The Adult Limnephilus Leach (Trichoptera:Limnephilidae) Of The New World, John C. Morse
Publications
No abstract provided.
Book Review - Caddisflies (Trichoptera) Of The Interior Highlands Of North America, John C. Morse
Book Review - Caddisflies (Trichoptera) Of The Interior Highlands Of North America, John C. Morse
Publications
No abstract provided.
Computer Conferencing And The Classroom Writing Context, 1996, Chris Benson
Computer Conferencing And The Classroom Writing Context, 1996, Chris Benson
Publications
Published as the final chapter in "The Nearness of You: Students and Teachers Writing On-Line." Eds. Chris Edgar and Susan Nelson Wood, NY: Teachers and Writers, 1996.
Improved Limits On Gammy-Ray Burst Repetition From Batse, Max Tagmark, Dieter H. Hartmann, Michael S. Briggs, Jon Hakkila, Charles A. Meegan
Improved Limits On Gammy-Ray Burst Repetition From Batse, Max Tagmark, Dieter H. Hartmann, Michael S. Briggs, Jon Hakkila, Charles A. Meegan
Publications
We tighten previous upper limits on gamma-ray burst repetition by analyzing the angular power spectrum of the BATSE 3B catalog of 1122 bursts. At 95% confidence, we find that no more that 2% of all observed bursts can be labeled as repeaters, even if no sources are observed to repeat more than once. If a fraction f of all observed bursts can be labeled as repeaters that are observed to bursts v times each, then all models ( v - 1) f >~ 0.05 are rules out as 99% confidence, as compares to the best previous 99% limit (v - …