The distance to NGC 6397 by M-subdwarf main-sequence fitting

Recent years have seen a substantial improvement both in photometry of low luminosity stars in globular clusters and in modelling the stellar atmospheres of late-type dwarfs. We build on these observational and theoretical advances in undertaking the first determination of the distance to a globular cluster by main-sequence fitting using stars on the lower main sequence. The calibrating stars are extreme M subdwarfs, as classified by Gizis (1997), with parallaxes measured to a precision of better than 10%. Matching against King et al's (1998) deep (V, (V-I)) photometry of NGC 6397, and adopting E_{B-V}=0.18 mag, we derive a true distance modulus of 12.13 +- 0.15 mag for the cluster. This compares with (m-M)_0=12.24 +- 0.1 derived through conventional main-sequence fitting in the (V, (B-V)) plane. Allowing for intrinsic differences due to chemical composition, we derive a relative distance modulus of delta (m-M)_0=2.58 mag between NGC 6397 and the fiducial metal-poor cluster M92. We extend this calibration to other metal-poor clusters, and examine the resulting RR Lyrae (M_V, [Fe/H]) relation.Comment: 19 pages, AASTeX, to appear in the December 1998 A

The use of radiosonde data to examine lee waves and other small-scale motions in the atmosphere

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Modulation of HU-DNA interactions by salt concentration and applied force.

HU is one of the most abundant proteins in bacterial chromosomes and participates in nucleoid compaction and gene regulation. We report experiments using DNA stretching that study the dependence of DNA condensation by HU on force, salt and HU concentration. Previous experiments at sub-physiological salt levels revealed that low concentrations of HU could compact DNA, whereas larger HU concentrations formed a DNA-stiffening complex. Here we report that this bimodal binding behavior depends sensitively on salt concentration. Only the compaction mode was observed for 150 mM and higher NaCl levels, i.e. for physiological salt concentrations. Similar results were obtained for the more physiological salt K-glutamate. Real-time studies of dissociation kinetics revealed that HU unbound slowly (minutes to hours under the conditions studied) but completely for salt concentrations at or above 100 mM NaCl; the lifetime of HU complexes was observed to increase with the HU concentration at which the complexes were formed, and to decrease with salt concentration. Higher salt levels of 300 mM NaCl completely eliminated observable HU binding to DNA. Finally, we observed that the dissociation kinetics depend on force applied to the DNA: increased applied force in the sub-piconewton range accelerates dissociation, suggesting a mechanism for DNA tension to regulate chromosome structure and gene expression

Warrior aristocrats in crisis: the political effects of the transition from the slave trade to palm oil commerce in the nineteenth century Kingdom of Dahomey

Few exploratory ventures would ever be undertaken if the explorer appreciated his own limitations at the outset. Although his ultimate destination is unclear, the route uncertain, the terrain unfamiliar and the tools inadequate he is spurred initially by a self-assurance born of his own limited knowledge. Unfortunately, that same self-assurance ill-equips him for the difficulties which he inevitably has to face en route. This thesis has been no exception to this pattern. It has involved more than its fair share of blind alleys, false trails, disorientation, retracing of footsteps and re-establishment of bearings. It has occasionally been marked by that feeling of despairing bewilderment which confronts the uncertain traveller lost in unfamiliar territory or overwhelmed by the novelty and complexity of his surroundings. Like most exploratory journeys, it has been difficult to decide when the ultimate destination has been reached and almost impossible in restrospect to recall the exact route by which that particular point was achieved. However, the historian of Dahomey is fortunate in comparison with the explorer venturing into virgin territory. For he is well served by the pioneers who have blazed the trail before him and by the signposts which are available to him. The Kingdom of Dahomey has been well covered by primary source material and contemporary documentation and publications