Context. Stellar feedback is one of the fundamental factors regulating the evolution of galaxies. However, we still do not have access to strong observational constraints on the relative importance of the di fferent feedback mechanisms (e.g. radiation, ionised gas pressure, stellar winds) in driving H II region evolution and molecular cloud disruption. To quantify and compare the di fferent feedback mechanisms, the size of an H II region is crucial, whereas samples of well-resolved H II regions are scarce.

The chlorophyll a antenna of photosystems I and II were each isolated after detergent treatment by gel electrophoresis or sucrose gradient centrifugation from a b-less mutant of barley grown in daylight and from wildtype barley developed in intermittent light. We identified each fraction by both its electrophoretic position and PS I activity (P700 content) in the case of the mutant, and by both PS I and PS II activity (DCIP reduction from DPC) in the light-limited plants. The proportion of Chl a in each photosystem was estimated from the amount in each gel or sucrose gradient band, and from addition of the areas under the absorption spectra (650-710 nm) of each fraction to match the spectrum of the solubilized thylakoids. The latter method was possible because the spectrum (77 K) of each fraction was unique; in the mutant about 70% of chlorophyll is associated with PS I and 30% with PS II. In the light-limited plants, the reverse is true with nearly 70% associated with PS II. RESOL analyses of both absorption and fluorescence emission spectra of all isolated fractions indicated an abnormal arrangement of antenna chlorophyll molecules in the light-limited, developing membranes even though their reaction centers are fully functional.

We present photometric and spectroscopic observations of 15 high-redshift quasars (z > 3.6) discovered from similar to 140 deg(2) of five-color (u', g', r', i', and z') imaging data taken by the Sloan Digital Sky Survey (SDSS) during its commissioning phase. The quasars are selected by their distinctive colors in SDSS multicolor space. Four of the quasars have redshifts higher than 4.6 (z = 4.63, 4.75, 4.90, and 5.00, the latter being the highest redshift quasar yet known). In addition, two previously known z > 4 objects were recovered from the data. The quasars all have i* < 20 and have luminosities comparable to that of 3C 273. The spectra of the quasars have similar features (strong, broad emission lines and substantial absorption blueward of the Ly alpha emission line) seen in previously known high-redshift quasars. Although the photometric accuracy and image quality fail to meet the final survey requirements, our success rate for identifying high-redshift quasars (17 quasars from 27 candidates) is much higher than that of previous multicolor surveys. However, the numbers of high-redshift quasars found is in close accord with the number density inferred from previous surveys.

The Sloan Digital Sky Survey (SDSS) will provide the data to support detailed investigations of the distribution of luminous and nonluminous matter in the universe: a photometrically and astrometrically calibrated digital imaging survey of pi sr above about Galactic latitude 30 degrees in five broad optical bands to a depth of g' similar to 23 mag, and a spectroscopic survey of the approximately 10(6) brightest galaxies and 10(5) brightest quasars found in the photometric object catalog produced by the imaging survey. This paper summarizes the observational parameters and data products of the SDSS and serves as an introduction to extensive technical on-line documentation.