San Francisco State University

About: San Francisco State University is a education organization based out in San Francisco, California, United States. It is known for research contribution in the topics: Population & Planet. The organization has 5669 authors who have published 11433 publications receiving 408075 citations. The organization is also known as: San Francisco State & San Francisco State Normal School.

Silicate regulation of new production in the equatorial Pacific upwelling

Abstract: Surface waters of the eastern equatorial Pacific Ocean present the enigma of apparently high plant-nutrient concentrations but low phytoplankton biomass and productivity1. One explanation for this ‘high-nitrate, low-chlorophyll’ (HNLC) phenomenon has been that growth is limited by iron availability2,3. Here we use field data and a simple silicon-cycle model4 to investigate the HNLC condition for the upwelling zone of this ocean region. Measured silicate concentrations in surface waters are low and largely invariant with time, and set the upper limit on the total possible biological utilization of dissolved inorganic carbon. Chemical and biological data from surface waters indicate that diatoms—silica-shelled phytoplankton—carry out all the ‘new production’ (nitrate uptake)5. Smaller phytoplankton (picoplankton) accomplish most of the total primary production, largely fuelled by nitrogen regenerated in reduced forms as a result of grazing by zooplankton. The model predicts values of new and export production (the production exported to below the euphotic zone) that compare well with measured values6. New and export production are in balance for biogenic silica, whereas new production exceeds export for nitrogen. The HNLC condition in the upwelling zone can therefore be understood to be due to a chemostat-like regulation of nitrate uptake by upwelled silicate supply to diatoms: ‘low-silicate HNLC’. These results are not inconsistent with observations of iron-fertilized diatom growth during in situ experiments in ‘low-iron HNLC’ waters outside this upwelling zone2,3, but reflect the role of different supply rates of iron and silicate in determining the nature of the HNLC condition.

A Planetary Companion to 70 Virginis

Abstract: An extremely low mass companion to the solar-type star 70 Virginis is inferred from the observed periodic Doppler reflex motion of the primary during 8 yr. The minimum mass (M2 sin i) of 70 Vir "B" is 6.6 Jovian masses (MJ), which falls in the mass range associated with "extrasolar giant planets" (0.3-15 MJ). An orbital fit to the velocities yields a period P = 116.6 days, an amplitude K = 318 m s-1, and an eccentricity e = 0.40. The residuals to the fit scatter by 8 m s-1, consistent with the errors. Thus 70 Vir B and 51 Peg B represent the first planets found outside our solar system. Alternatively, the probability that 70 Vir B is an orbiting brown dwarf of mass M > 40 MJ is ~1%, requiring an extreme (face-on) orbital inclination of i < 9°. With a likely mass of 6.6-9 MJ, 70 Vir B lies in the nebulously defined domain between solar system planets and brown dwarfs. Its effective temperature is computed to be ~90°C. The formation of such giant planets in eccentric orbits is not explained by current theory.

The sloan digital sky survey-II supernova survey: technical summary

Abstract: The Sloan Digital Sky Survey-II (SDSS-II) has embarked on a multi-year project to identify and measure light curves for intermediate-redshift (0.05 < z < 0.35) Type Ia supernovae (SNe Ia) using repeated five-band (ugriz) imaging over an area of 300 sq. deg. The survey region is a stripe 2.5° wide centered on the celestial equator in the Southern Galactic Cap that has been imaged numerous times in earlier years, enabling construction of a deep reference image for the discovery of new objects. Supernova imaging observations are being acquired between September 1 and November 30 of 2005-7. During the first two seasons, each region was imaged on average every five nights. Spectroscopic follow-up observations to determine supernova type and redshift are carried out on a large number of telescopes. In its first two three-month seasons, the survey has discovered and measured light curves for 327 spectroscopically confirmed SNe Ia, 30 probable SNe Ia, 14 confirmed SNe Ib/c, 32 confirmed SNe II, plus a large number of photometrically identified SNe Ia, 94 of which have host-galaxy spectra taken so far. This paper provides an overview of the project and briefly describes the observations completed during the first two seasons of operation.

The Social Network Ties of Group Leaders: Implications for Group Performance and Leader Reputation

Abstract: This paper uses data from the sales division of a financial services firm to investigate how a leader's centrality in external and internal social networks is related to the objective performance of the leader's group, and to the leader's personal reputation for leadership among subordinates, peers, and supervisors. External social network ties were based on the friendship ties among all 88 of the division's sales group leaders and the 10 high-ranking supervisors to whom they reported. Internal social network ties consisted of 28 separate networks, each representing the set of friendship relations among all members of a given sales group. Objective group performance data came directly from company records. Data on each group leader's personal reputation for leadership was based on the perceptions of three different constituencies: subordinates, peers, and supervisors. Results revealed that leaders' centrality in external and internal friendship networks was related both to objective measures of group performance and to their reputation for leadership among different organizational constituencies.

Three New “51 Pegasi-Type” Planets*

Abstract: We report Keplerian Doppler velocity variations, consistent with orbiting "51 Pegasi-type" planets, for the three stars HR 3522 (G8V), HR 5185 (F7V), and HR 458 (F8V). HR 3522 exhibits a velocity semiamplitude of 77 m s-1 and a period of 14.65 days, implying a semimajor axis of 0.11 AU and a minimum mass for the companion of M2 sin i = 0.84MJUP. For HR 5185, the semiamplitude is 469 m s-1, and the period is 3.3128 days, implying an orbital radius of 0.0462 AU and a minimum mass of 3.87MJUP. For HR 458, the semiamplitude is 74 m s-1, and the period is 4.61 days, implying an orbital radius of 0.057 AU and a minimum mass of 0.68MJUP. These three companions, along with 51 Peg b, may constitute a heretofore unrecognized class of planets, defined by circular orbits, Jupiter-like masses, and orbital radii less than ~0.2 AU. The relatively large orbital radius for HR 3522 (0.11 AU) precludes tidal circularization, suggesting that the circular orbits are primordial. During the past 9 years, the velocity residuals to the Keplerian fit of HR 3522 exhibit a long-term systematic trend, suggestive of an additional companion. HR 5185 exhibits velocity residuals that fluctuate erratically by ~70 m s-1, which are as yet unaccounted for. HR 5185 has a rotation period very close to the orbital period of the planet, suggesting that the companion may have tidally locked the primary.