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We present results of a search for anomalous low-energy upscattering of ultracold neutrons from a beryllium surface. This upscattering is considered one for the possible reasons for UCN “disappearance” from very cold beryllium bottles, as observed in experiments. The indium foil activation method was used to measure a very low intensity flux of upscattered UCN. The (15–300) m/s velocity range of upscattered UCN is ruled out by these measurements at a confidence level of 90%. © 1999 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Results are presented on the search for anomalous transmission of ultracold neutrons (UCNs) through beryllium (thickness ∼0.14 mm), stainless steel (0.05 and 0.015 mm), and copper (0.01 and 0.018 mm) foils. This anomalous transmission is considered to be a possible reason for the disappearance of UCNs from beryllium bottles, an effect which was discovered in experiments at the St. Petersburg Nuclear Physics Institute and which was recently observed in the experiment of V. E. Varlamov et al., JETP Lett. 66, 336 (1997). No transmission was found in our measurements at the 10[sup -7] level except in the case of copper foils, which we attribute to the presence in the UCN flux of an admixture of neutrons with energies higher than the boundary energy for copper. [ABSTRACT FROM AUTHOR]

The activity of Escherichia coli pyruvate oxidase (PoxB) was shown to be growth-phase dependent; the enzyme activity reaches a maximum at early stationary phase. We report that PoxB activity is dependent on a functional rpoS(katF) gene which encodes a δ factor required to transcribe a number of stationary-phase-induced genes. PoxB activity as well as the β-galactosidase encoded by a poxB::lacZ protein fusion was completely abolished in a strain containing a defective rpoS gene. Northern and primer extension analyses showed that poxB expression was regulated at the transcriptional level and was transcribed from a single promoter; the 5' end of the mRNA being located 27 bp upstream of the translational initiation codon of poxB. The poxB gene was expressed at decreased levels under anaerobiosis; however, the anaerobic regulatory genes arcA, arcB or fnr were not involved in anaerobic poxB gene expression. Expression of the rpoS(katF) gene has been reported to be affected by acetate, the product of PoxB reaction. However, we found that poxB null mutations had no effect on rpoS(katF) expression, inactivation of two genes involved in acetate metabolism, ackA and pta, had no effect on either poxB or rpoS(katF) expression. [ABSTRACT FROM AUTHOR]