An ultraviolet-selected galaxy redshift survey: new estimates of the local star formation rate     

Marie A. Treyer  Richard S. Ellis  Bruno Milliard  José Donas  & Terry J. Bridges 《Monthly notices of the Royal Astronomical Society》1998,300(1):303-314

We present the first results of an ongoing spectroscopic survey of galaxies selected in the rest frame ultraviolet (UV). The source catalogue has been constructed from a flux-limited sample of stars, galaxies and QSOs imaged at 2000 Å in Selected Area 57 with the FOCA balloon-borne imaging camera. Accurate positions for the UV sources have been obtained by matching with optical counterparts using APM scans of the Palomar Sky Survey limited at B   20.5. Here we present results derived from optical spectroscopy conducted with the WIYN telescope and the WHT for 142 faint sources. The redshift distribution for this UV-selected sample extends over 0 <  z  < 0.5, and a high fraction of the sources show intense nebular emission lines and UV–optical colours bluer than normal Hubble sequence galaxies. Such UV-selected surveys are thus a very efficient way to locate and study intermediate-redshift galaxies undergoing intense star formation. Although our sample is currently small, we derive a rest frame UV luminosity function with a steep faint-end slope consistent with that found for late-type galaxies in optical samples. However, the integrated luminosity density derived implies a volume-averaged star formation rate higher than other recent estimates, assuming a normal initial mass function. If representative of other UV fields, as suggested by UV number count studies, our data imply that the local abundance of star-forming galaxies may have been underestimated, and consequently claims for strong evolution in the global star formation rate in the range 0 <  z  < 1 overstated. An intensive study of a large UV-selected sample is likely to reveal important information on the declining population of star-forming galaxies of all types.  相似文献   

Accuracy of cosmogenic ages for moraines   总被引：1，自引：0，他引：1  

Jaakko Putkonen  Terry Swanson 《Quaternary Research》2003,59(2):255-261

Analyses of all published cosmogenic exposure ages for moraine boulders show an average age range of 38% between the oldest and youngest boulders from each moraine. This range conflicts with the common assumption that ages of surface boulders are the same as the age of the landform. The wide spread in boulder ages is caused by erosion of the moraine surface and consequent exhumation of fresh boulders. A diffusion model of surface degradation explains the age range and shows that a randomly sampled small set of boulders (n = 3-7) will always yield a lower age limit for the moraine. The model indicates that for identical dating accuracy, six to seven boulders are needed from old and tall moraines (40,000-100,000 yr, 50-100 m initial height) but only one to four boulders from small moraines (20,000-100,000 yr, 10-20 m). By following these guidelines the oldest obtained boulder age will be ≥90% of the moraine age (95% probability). This result is only weakly sensitive to a broad range of soil erosion rates. Our analysis of published boulder ages indicates that <3% of all moraine boulders have prior exposure, and 85% of these boulders predate the dated moraine.  相似文献   

Doppler imaging and surface differential rotation of young open cluster stars – I. HD 307938 (R58) in IC 2602     

S. C. Marsden  I. A. Waite  B. D. Carter  J.-F. Donati 《Monthly notices of the Royal Astronomical Society》2005,359(2):711-724

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The 2dF Galaxy Redshift Survey: the luminosity function of cluster galaxies     

Roberto De Propris  Matthew Colless  Simon P. Driver  Warrick Couch  John A. Peacock  Ivan K. Baldry  Carlton M. Baugh  Joss Bland-Hawthorn  Terry Bridges  Russell Cannon  Shaun Cole  Chris Collins  Nicholas Cross  Gavin B. Dalton  George Efstathiou  Richard S. Ellis  Carlos S. Frenk  Karl Glazebrook  Edward Hawkins  Carole Jackson  Ofer Lahav  Ian Lewis  Stuart Lumsden  Steve Maddox  Darren S. Madgwick  Peder Norberg  Will Percival  Bruce Peterson  Will Sutherland  Keith Taylor 《Monthly notices of the Royal Astronomical Society》2003,342(3):725-737

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The 2dF Galaxy Redshift Survey: the local E+A galaxy population     

Chris Blake  Michael B. Pracy  Warrick J. Couch  Kenji Bekki  Ian Lewis  Karl Glazebrook  Ivan K. Baldry  Carlton M. Baugh  Joss Bland-Hawthorn  Terry Bridges  Russell Cannon  Shaun Cole  Matthew Colless  Chris Collins  Gavin Dalton  Roberto De Propris  Simon P. Driver  George Efstathiou  Richard S. Ellis  Carlos S. Frenk  Carole Jackson  Ofer Lahav  Stuart Lumsden  Steve Maddox  Darren Madgwick  Peder Norberg  John A. Peacock  Bruce A. Peterson  Will Sutherland  Keith Taylor 《Monthly notices of the Royal Astronomical Society》2004,355(3):713-727

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The hydrothermal reaction kinetics of aspartic acid   总被引：1，自引：0，他引：1  

Jenny S. Cox  Terry M. Seward 《Geochimica et cosmochimica acta》2007,71(4):797-820

Experimental data on the hydrothermal reaction kinetics of aspartic acid were acquired using a custom-built spectrophotometric reaction cell which permits in situ observation under hydrothermal conditions. The results of this study indicate that the reaction kinetics of dilute aspartic acid solutions are significantly different depending on the presence or absence of catalytic surfaces such as standard metal alloys. The spectroscopic data presented here represent the first direct observations, in situ and in real time, of an amino acid reacting in a hydrothermal solution. Quantitative kinetic information, including rate constants, concentration versus time profiles, and calculations of the individual component spectra, was obtained from the data using a chemometric approach based on factor analysis/principle component analysis which treats the rate expressions simultaneously as a system of differential algebraic equations (DAE) of index 1. Identification of the products was confirmed where possible by high pressure anion exchange chromatography with pulsed amperometric detection (HPAEC-PAD). The reaction kinetics of aspartic acid under hydrothermal conditions was observed to be highly complex, in contrast to previous studies which indicated almost exclusively deamination. At lower temperatures (120-170 °C), several different reaction pathways were observed, including decarboxylation and polymerization, and the catalytic effects of reactor surfaces on the aspartic acid system were clearly demonstrated. At higher temperatures (above 170 °C), aspartic acid exhibited highly complex behaviour, with evidence indicating that it can simultaneously dimerize and cyclize, deaminate (by up to two pathways), and decarboxylate (by up to two pathways). These higher temperature kinetics were not fully resolvable in a quantitative manner due to the complexity of the system and the constraints of UV spectroscopy. The results of this study provide strong evidence that the reaction kinetics of aspartic acid are very sensitive to parameters such as temperature, reactor materials (i.e., reactive surfaces), and additives, and that previous observations on aspartic acid were specific to the choice of experimental conditions.  相似文献   

Development of a coral cDNA array to examine gene expression profiles in Montastraea faveolata exposed to environmental stress     

Edge SE  Morgan MB  Gleason DF  Snell TW 《Marine pollution bulletin》2005,51(5-7):507-523

The development of a cDNA array of coral genes and its application to investigate changes in coral gene expression associated with stressful conditions is described. The array includes both well-characterized and previously unidentified coral genes from Acropora cervicornis and Montastraea faveolata. Corals were exposed to either natural or anthropogenic stressors to elicit the expression of stress genes for isolation and incorporation onto the array. A total of 32 genes involved in protein synthesis, apoptosis, cell signaling, metabolism, cellular defense and inflammation were included on the array. Labeled cDNA from coral (Montastraea faveolata) exposed to elevated seawater temperature, salinity and ultraviolet light was tested against the microarray to determine patterns of gene expression associated with each stressor. Carbonic anhydrase, thioredoxin, a urokinase plasminogen activator receptor (uPAR) and three ribosomal genes demonstrated differential expression across all replicates on the array and between replicate colonies. Specific gene expression patterns produced in response to different stressors demonstrate the potential for gene expression profiling in characterizing the coral stress response.  相似文献   

Community forests and regeneration in post-industrial landscapes     

Lawrence Kitchen  Terry Marsden 《Geoforum》2006,37(5):831-843

Through a critique of existing regeneration literatures the paper points to the close relationship between regeneration and sustainable development. It suggests that the economic aspects of sustainable development have tended to dominate: leading to the neglect of nature in both regeneration and sustainable development, with regeneration having a principal focus on socio-economic issues in urban settings. To address these lacunae we suggest the need for a more environmentally sensitive regeneration theory. Using this approach the paper draws on recent in-depth research in three post-industrial coalfield areas where regeneration processes operate in the form of community forest projects. It provides a critical perspective on these regeneration processes, integrating theory with empirical data and highlighting how nature is drawn into broader economic and social processes of regeneration. In conclusion, using forestry initiatives as examples, we reflect on the conceptual dissonance apparent in regeneration theory and practice, and point to theoretical insights that could enable a more critical regeneration theory; more beneficial outcomes to regeneration processes; and an improved understanding of the relations between nature, capital and community in regeneration processes and sustainable development.  相似文献   

The 2dF Galaxy Redshift Survey: the power spectrum and the matter content of the Universe     

Will J. Percival  Carlton M. Baugh  Joss Bland-Hawthorn  Terry Bridges  Russell Cannon  Shaun Cole  Matthew Colless  Chris Collins  Warrick Couch  Gavin Dalton  Roberto De Propris  Simon P. Driver  George Efstathiou  Richard S. Ellis  Carlos S. Frenk  Karl Glazebrook  Carole Jackson  Ofer Lahav  Ian Lewis  Stuart Lumsden  Steve Maddox  Stephen Moody  Peder Norberg  John A. Peacock  Bruce A. Peterson  Will Sutherland  Keith Taylor 《Monthly notices of the Royal Astronomical Society》2001,327(4):1297-1306

The 2dF Galaxy Redshift Survey has now measured in excess of 160 000 galaxy redshifts. This paper presents the power spectrum of the galaxy distribution, calculated using a direct Fourier transform based technique. We argue that, within the k -space region     , the shape of this spectrum should be close to that of the linear density perturbations convolved with the window function of the survey. This window function and its convolving effect on the power spectrum estimate are analysed in detail. By convolving model spectra, we are able to fit the power-spectrum data and provide a measure of the matter content of the Universe. Our results show that models containing baryon oscillations are mildly preferred over featureless power spectra. Analysis of the data yields 68 per cent confidence limits on the total matter density times the Hubble parameter     , and the baryon fraction     , assuming scale-invariant primordial fluctuations.  相似文献   

The heliosphere after Ulysses     

R.G. Marsden 《Astrophysics and Space Science》2001,277(1-2):337-347

Launched in October 1990, the ESA-NASA Ulysses mission has conducted the very first survey of the heliosphere within 5 AU of the Sun over the full range of heliolatitudes. With polar passes taking place in 1994 and 1995, the timing of the mission has enabled Ulysses to characterise the global structure of the heliosphere at solar minimum, when the corona adopts its simplest configuration. The most important findings to date include a confirmation of the uniform nature of the high-speed (∼ 750 km/s)solar wind flow from the polar coronal holes, filling two-thirds of the volume of the inner heliosphere; the sharp boundary, existing from the chromosphere through the corona, between fast and slow solar wind streams; the latitude independence of theradial component of the heliospheric magnetic field; the lower-than-expected latitude gradient of galactic and anomalous cosmic rays; the continued existence of recurrent increases in the flux of low-energy ions and electrons up to the highest latitudes. Without doubt, the Ulysses mission has provided a unique set of observations of the heliosphere at solar minimum, resulting in a good understanding of many aspects of its behaviour. In this review, we will highlight some of the key findings to date, and also look ahead to the challenges that await as Ulysses returns to high latitudes to explore the heliosphere at solar maximum and beyond. Finally, a brief summary is given of the prospects for heliospheric research in the post-Ulysses era. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献