Flash tube chambers for electron and photon detection

The construction and operation of a simple, inexpensive, electron-photon detector, of the sampled shower type, is described the sampling planes consisting of layers of high pressure, methane doped, neon flash tubes, with CAMAC compatible digitised outputs. The detector was tested in a positron beam at energies from 0.5 to 4,0 GeV, No adverse effects due to the high background radiation were experienced, and an energy resolution of 43% and spatial and angular resolutions of 5 mm and 4º (FWHM) were obtained. The maximum event rate at which the detector could operate was limited to ~1 sec(^-1), by the presence of internal fields which resulted in spuriousness or inefficiency. The use of modified H„T, pulsing systems has also been investigated as a means of reducing the internal field, A modified detector was constructed, utilising large diameter, low pressure flash tubes, in an attempt to improve the maximum event rate, yet maintain the same useful resolution. An energy resolution of 33% and spatial and angular resolutions of 11 mm and 2º (FWHM) were obtained, which compares favourably with more complex and expensive detectors. Unexpectedly, at event rates in excess of a few per second, the tubes behaved either spuriously or inefficiently, due to large internal fields. Investigations into the mechanisms of formation and decay of the internal fields have been made by observation of the digitisation output pulse. This novel approach may, with refinement, be of use in future studies of gas discharges since it is particularly sensitive to the gas breakdown mechanism. The significance of the outer surface resistance of the flash tube has also beer demonstrated to be of importance to the performance of the tube. A mechanism, which results in the flash tube igniting spuriously, is suggested and a threshold value of the internal field, at which spuriousness occurs, has been determined

First-principles study of iron oxyfluorides and lithiation of FeOF

First-principles studies of iron oxyfluorides in the FeF[subscript 2] rutile framework (FeO[subscript x]F[subscript 2−x], 0≤x≤1) are performed using density functional theory (DFT) in the general gradient approximation (GGA) with a Hubbard U correction. Studies of O/F orderings reveal FeOF to be particularly stable compared to other FeO[subscript x]F[subscript 2−x] (x≠1) structures, where FeF[subscript 2]-FeOF mixing is not energetically favored. The band gap of FeF[subscript 2] is found to decrease as oxygen is substituted into its structure. The GGA + U electronic structure evolves from that of a Mott-Hubbard insulator (x=0) to a charge transfer semiconductor (x=1). Lithiation studies reveal that lithiation sites offering mixed O/F environments are the most stable. An insertion voltage plateau up to Li[subscript 0.5]FeOF on lithiation is found, in agreement with recent Li-ion battery experiments. The energetics of further lithiation with respect to conversion scenarios are discussed.United States. Dept. of Energy. Office of Basic Energy Sciences (Northeastern Center for Chemical Energy Storage Award DE-SC0001294

Zfh1, a somatic motor neuron transcription factor, regulates axon exit from the CNS

AbstractMotor neurons are defined by their axon projections, which exit the CNS to innervate somatic or visceral musculature, yet remarkably little is known about how motor axons are programmed to exit the CNS. Here, we describe the role of the Drosophila Zfh1 transcription factor in promoting axon exit from the CNS. Zfh1 is detected in all embryonic somatic motor neurons, glia associated with the CNS surface and motor axons, and one identified interneuron. In zfh1 mutants, ventral projecting motor axons often stall at the edge of the CNS, failing to enter the muscle field, despite having normal motor neuron identity. Conversely, ectopic Zfh1 induces a subset of interneurons—all normally expressing two or more “ventral motor neuron transcription factors” (e.g. Islet, Hb9, Nkx6, Lim3)—to project laterally and exit the CNS. We conclude that Zfh1 is required for ventral motor axon exit from the CNS