Does arctic vegetation change when grazed by barnacle geese?:A pilot study

The effects of grazing by barnacle geese Branta leucopsis on arctic vegetation was studied. Two plots where grazers had been excluded five and six years previously were compared with grazed vegetation nearby. The exclosed plots contained more live biomass than the area with grazed vegetation. However, there was no significant difference in density of shoots and number of leaves per shoot in the heavily grazed Poa arctica. Within the exclosed plots, there was a slow build-up of dead material and the moss carpet had grown thicker than in the grazed plots. The number of inflorescences was the most prominent feature, which differentiated the exclosed vegetation from the sated surrounding. There is no evidence for habitat deterioration caused by increased grazing pressure from the expanding barnacle goose population as has been reported for the snow goose on the Hudson Bay lowlands in Canada. The increased activity of nitrogen fixation by cyanobacteria in grazed vegetation might be a mechanism which compensates for the nitrogen deficit caused by the migratory geese.</p

Host range, symbiotic effectiveness and nodulation competitiveness of some indigenous cowpea bradyrhizobia isolates from the transitional savanna zone of Ghana

To identify indigenous rhizobia with potential as inoculants for increasing cowpea (Vigna unguiculata) yields, we have assessed the host range, symbiotic effectiveness and competitiveness for noduleoccupancy among five (AII-2-1, AII-5-2, AI-4-3, AII-3-4 and BIII-2-2) indigenous cowpea bradyrhizobia isolates from the transitional savanna zone of Ghana. ERIC-PCR DNA fingerprinting patterns were used to identify the isolates occupying nodules. All the isolates nodulated cowpea, groundnut (Arachis hypogeae) and mungbean (Vigna radiata), but only AII-2-1, AII-3-4 and BIII-2-2 nodulated soybean (Glycine max). Apart from cowpea where all the isolates were effective, there were significant differences in the symbiotic effectiveness of the isolates on the other host legumes. Out of a total of about 250 cowpea nodules that were screened for each inoculum-mix, isolate AII-5-2 was the most competitive for nodule occupancy whilst AII-3-4 was the least. Isolate AII-5-2 occupied 71% of the nodules in an inoculum-mix consisting of equal proportions of AII-2-1, AII-5-2 and AI-4-3 (a 3-isolatemix) and 60% of nodules in an inoculum-mix consisting of equal proportions of all the five isolates (a 5- isolate-mix). Therefore, among the isolates tested, AII-5-2 has the best potential for use as inoculant formaximizing cowpea yield in N2- deficient agro-ecological zones of Ghana

WSO/UV: World Space Observatory/Ultraviolet

We summarize the capabilities of the World Space Observatory (UV) Project (WSO/UV). An example of the importance of this project (with a planned launch date of 2007/8) for the study of Classical Novae is given.Comment: 4 pages, To appear in the proceeedings of the "Classical Nova Explosions" conference, eds. M. Hernanz and J. Jose, AI

Doppler temperatures from O(¹D) airglow in the daytime thermosphere as observed by the Wind Imaging Interferometer (WINDII) on the UARS satellite

International audienceFrom 1992 to 1997, the WINDII interferometer on board the UARS satellite acquired a large set of thermospheric data from the O(1D) and O(1S) airglows. We report here for the first time on daytime O(1D) Doppler temperatures obtained with version 5.11 of the WINDII data processing software. Using a statistical analysis of the temperatures independently measured by the two WINDII fields of view, we estimate that the temperature variations larger than 40 K can be considered as geophysical. Comparisons of WINDII temperatures measured during magnetically quiet days with temperatures obtained by the MSIS-90 and DTM-94 thermospheric models show a 100 K bias. We demonstrate, however, that the modeled temperature variations represent very well the mean temperature variation observed by WINDII over 4 years. We also show that the observed latitudinal/local time variation is in very good agreement with the two empirical models. Finally, the temperature variations during a magnetically disturbed day are found to be qualitatively well represented in form by the models, but largely underestimated. The presence of non-thermal atoms and instrument related issues are discussed as possible explanations for the 100 K bias between the WINDII Doppler temperatures and the empirical models

Absence of "Ghost Images" Excludes Large Values of the Cosmological Constant

We used the 1.4 GHz NRAO NVSS survey to search for ghost images of radio sources, expected in cosmologies with a positive cosmological constant and positive space curvature. No statistically significant evidence for ghost images was found, placing constraints on the values of L, the space curvature or the duration of the radio-luminous phase of extragalactic radio sources.Comment: 11 pages 2 figure

First Attempt at Spectroscopic Detection of Gravity Modes in a Long-Period Pulsating Subdwarf B Star -- PG 1627+017

In the first spectroscopic campaign for a PG 1716 variable (or long-period pulsating subdwarf B star), we succeeded in detecting velocity variations due to g-mode pulsations at a level of 1.0-1.5 km/s.The observations were obtained during 40 nights on 2-m class telescopes in Arizona, South Africa,and Australia. The target,PG1627+017, is one of the brightest and largest amplitude stars in its class.It is also the visible component of a post-common envelope binary.Our final radial velocity data set includes 84 hours of time-series spectroscopy over a time baseline of 53 days. Our derived radial velocity amplitude spectrum, after subtracting the orbital motion, shows three potential pulsational modes 3-4 sigma above the mean noise level, at 7201.0s,7014.6s and 7037.3s.Only one of the features is statistically likely to be real,but all three are tantalizingly close to, or a one day alias of, the three strongest periodicities found in the concurrent photometric campaign. We further attempted to detect pulsational variations in the Balmer line amplitudes. The single detected periodicity of 7209 s, although weak, is consistent with theoretical expectations as a function of wavelength.Furthermore, it allows us to rule out a degree index of l= 3 or l= 5 for that mode. Given the extreme weakness of g-mode pulsations in these stars,we conclude that anything beyond simply detecting their presence will require larger telescopes,higher efficiency spectral monitoring over longer time baselines,improved longitude coverage, and increased radial velocity precision.Comment: 39 pages, 9 figures, 4 tables, ApJ accepted. See postscript for full abtrac