EPR of a novel high-spin component in activated hydrogenase from Desulfovibrio vulgaris (Hildenborough)

The EPR of reoxidized hydrogenase from Desulfovibrio vulgaris (H.) has been reinvestigated. In contrast to other workers [(1984) Proc. Natl. Acad. Sci. USA 81, 3728-3732] we find the axial signal with g = 2.06; 2.01 to be only a minor component of concentration 0.03 spin/mol. In the spectrum of fully active reoxidized enzyme this signal is overshadowed by a rhombic signal (0.1 spin/mol) with g = 2.11; 2.05; 2.00 reminiscent of the only signal found for other oxidized bidirectional hydrogenases. In addition, a novel signal has been detected with geff = 5.0 which, under the assumptions that S = 2 and |[Delta]ms|= 2, quantitates to roughly one spin/mol. Ethylene glycol affects the relative intensity of the different signals. It is suggested that O2 sensitization parallels a spin-state transition of an iron-sulfur cluster.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/26169/1/0000246.pd

Deep incision in an Aptian carbonate succession indicates major sea-level fall in the Cretaceous

Long-term relative sea-level cycles (0 5 to 6 Myr) have yet to be fully understood for the Cretaceous. During the Aptian, in the northern Maestrat Basin (Eastern Iberian Peninsula), fault-controlled subsidence created depositional space, but eustasy governed changes in depositional trends. Relative sea-level history was reconstructed by sequence stratigraphic analysis. Two forced regressive stages of relative sea-level were recognized within three depositional sequences. The first stage is late Early Aptian age (intra Dufrenoyia furcata Zone) and is characterized by foreshore to upper shoreface sedimentary wedges, which occur detached from a highstand carbonate platform, and were deposited above basin marls. The amplitude of relative sea-level drop was in the order of tens of metres, with a duration of 2 km wide and cut 115 m down into the underlying Aptian succession. With the subsequent transgression, the incision was back-filled with peritidal to shallow subtidal deposits. The changes in depositional trends, lithofacies evolution and geometric relation of the stratigraphic units characterized are similar to those observed in coeval rocks within the Maestrat Basin, as well as in other correlative basins elsewhere. The pace and magnitude of the two relative sea-level drops identified fall within the glacio-eustatic domain. In the Maestrat Basin, terrestrial palynological studies provide evidence that the late Early and Late Aptian climate was cooler than the earliest part of the Early Aptian and the Albian Stage, which were characterized by warmer environmental conditions. The outcrops documented here are significant because they preserve the results of Aptian long-term sea-level trends that are often only recognizable on larger scales (i.e. seismic) such as for the Arabian Plate

The Physics of Star Cluster Formation and Evolution

© 2020 Springer-Verlag. The final publication is available at Springer via https://doi.org/10.1007/s11214-020-00689-4.Star clusters form in dense, hierarchically collapsing gas clouds. Bulk kinetic energy is transformed to turbulence with stars forming from cores fed by filaments. In the most compact regions, stellar feedback is least effective in removing the gas and stars may form very efficiently. These are also the regions where, in high-mass clusters, ejecta from some kind of high-mass stars are effectively captured during the formation phase of some of the low mass stars and effectively channeled into the latter to form multiple populations. Star formation epochs in star clusters are generally set by gas flows that determine the abundance of gas in the cluster. We argue that there is likely only one star formation epoch after which clusters remain essentially clear of gas by cluster winds. Collisional dynamics is important in this phase leading to core collapse, expansion and eventual dispersion of every cluster. We review recent developments in the field with a focus on theoretical work.Peer reviewe

Influence of drought on predation of elephant (Loxodonta africana) calves by lions (Panthera leo) in an African wooded savannah

Data were collected on species killed by lions Panthera leo in Hwange National Park, Zimbabwe between 1998 and 2004. Lions killed predominantly large to medium-sized herbivores, concentrating on buffalo Syncerus caffer, elephant Loxodonta africana, giraffe Giraffa camelopardalis, wildebeest Connochaetes taurinus and zebra Equus burchelli. These species made up 83% of all lion kills found and 94% of the biomass of kills actually observed. Elephant calves made up an unusually large proportion of lion prey during the study period (23% of kills recorded). All elephants killed were dependent juveniles. Elephant calves appear more vulnerable during the dry months of the year, particularly in years of below average rainfall. Elephant calves are usually well protected. However, high-density aggregations of elephants around limited water sources during the dry season may deplete local food resources, forcing elephant herds to travel large distances between water and forage. Under these circumstances, elephant calves may become lost or separated from family groups, accounting for their high incidence in lion diet. © 2006 The Authors