Neu- und Wiederfunde von Gefäßpflanzen in der Grafschaft Bentheim

Bei der Kartierung der Gefäßpflanzen im Landkreis Grafschaft Bentheim in den Jahren 1990-1996 wurden eine Reihevon Sippen neu entdeckt und einige verschollene wiedergefunden; davon werden 36 Sippen mit Fundortangaben vorgestellt.Whilst investigating phanerogam plants in the district of the "Grafschaft Bentheim", Lower Saxony, Northwest Germany between 1990 and 1996, a number of new taxa were discovered and some absent taxa were found again, 36 of which will be dealt with in further detail

Advanced Rotorcraft Transmission (ART) program-Boeing helicopters status report

The Advanced Rotorcraft Transmission (ART) program is structured to incorporate key emerging material and component technologies into an advanced rotorcraft transmission with the intention of making significant improvements in the state of the art (SOA). Specific objectives of ART are: (1) Reduce transmission weight by 25 pct.; (2) Reduce transmission noise by 10 dB; and (3) Improve transmission life and reliability, while extending Mean Time Between Removal to 5000 hr. Boeing selected a transmission sized for the Tactical Tilt Rotor (TTR) aircraft which meets the Future Air Attack Vehicle (FAVV) requirements. Component development testing will be conducted to evaluate the high risk concepts prior to finalizing the advanced transmission configuration. The results of tradeoff studies and development test which were completed are summarized

Bacterial evolution and the cost of antibiotic resistance

Bacteria clearly benefit from the possession of an antibiotic resistance gene when the corresponding antibiotic is present. But do resistant bacteria suffer a cost of resistance (i.e., a reduction in fitness) when the antibiotic is absent? If so, then one strategy to control the spread of resistance would be to suspend the use of a particular antibiotic until resistant genotypes declined to low frequency. Numerous studies have indeed shown that resistant genotypes are less fit than their sensitive counterparts in the absence of antibiotic, indicating a cost of resistance. But there is an important caveat: these studies have put resistance genes into naive bacteria, which have no evolutionary history of association with the resistance genes. An important question, therefore, is whether bacteria can overcome the cost of resistance by evolving adaptations that counteract the harmful side-effects of resistance genes. In fact, several experiments (in vitro and in vivo) show that the cost of antibiotic resistance can be substantially diminished, even eliminated, by evolutionary changes in bacteria over rather short periods of time. As a consequence, it becomes increasingly difficult to eliminate resistant genotypes simply by suspending the use of antibiotics

Punctuated equilibrium in an evolving bacterial population

Recently, Lenski et al have carried out an experiment on bacterial evolution. Their findings support the theory of punctuated equilibrium in biological evolution. We show that the M=2 Bak-Sneppen model can explain some of the experimental results in a qualitative manner.Comment: LaTeX, Five PS figures, Accepted for publication in Physica A, 1st August, 199