Acousto-Electric Effects in Cadmium Sulphide at Microwave Frequencies

Acoustic amplifiers, operating at frequencies of 1GHz and above, have been constructed from hexagonal cadmium sulphide crystals. The main problem in making these devices was in obtaining efficient acousto-electric transducers for microwave frequencies. Evaporated thin films of CdS were used as transducers, and a close study was made of their properties, in order to obtain efficient generation of both shear and longitudinal acoustic waves, above 1 GHz. The transducers were deposited on heated substrates by direct vacuum evaporation of CdS crystals. X-ray analysis showed that under most deposition conditions, the films were polycrystalline, composed of hexagonal phase crystallites of CdS, preferentially oriented with their c-axes perpendicular to the substrate. The degree of structural order increased with film thickness, and. films under 0.5mu thick had a high degree of disorder. Acoustic waves were generated by applying an r.f. electric field perpendicular to the substrate, and parallel to the transducer thickness, so that normal films were thickness resonant longitudinal mode transducers. Evaporation at an oblique angle to the substrate, and at a deposition rate in excess of 0. 1u/min, caused the c-axes of the crystallites to tilt away from the normal, and grow towards the direction of evaporation. With the electric field normal to the substrate, and the c-axis at about 38.

Stability of a bi-layer free film: simultaneous or individual rupture events?

We consider the stability of a long free film of liquid composed of two immiscible layers of differing viscosities, where each layer experiences a van der Waals force between its interfaces. We analyse the different ways the system can exhibit interfacial instability when the liquid layers are sufficiently thin. For an excess of surfactant on one gas–liquid interface the coupling between the layers is relatively weak and the instability manifests as temporally separated rupture events in each layer. Conversely, in the absence of surfactant the coupling between the layers is much stronger and the instability manifests as rupture of both layers simultaneously. These features are consistent with recent experimental observations

High Angular Resolution Stellar Imaging with Occultations from the Cassini Spacecraft II: Kronocyclic Tomography

We present an advance in the use of Cassini observations of stellar occultations by the rings of Saturn for stellar studies. Stewart et al. (2013) demonstrated the potential use of such observations for measuring stellar angular diameters. Here, we use these same observations, and tomographic imaging reconstruction techniques, to produce two dimensional images of complex stellar systems. We detail the determination of the basic observational reference frame. A technique for recovering model-independent brightness profiles for data from each occulting edge is discussed, along with the tomographic combination of these profiles to build an image of the source star. Finally we demonstrate the technique with recovered images of the {\alpha} Centauri binary system and the circumstellar environment of the evolved late-type giant star, Mira.Comment: 8 pages, 8 figures, Accepted by MNRA

Parallel analysis of ribonucleotide-dependent deletions produced by yeast Top1 in vitro and in vivo

Ribonucleotides are the most abundant non-canonical component of yeast genomic DNA and their persistence is associated with a distinctive mutation signature characterized by deletion of a single repeat unit from a short tandem repeat. These deletion events are dependent on DNA topoisomerase I (Top1) and are initiated by Top1 incision at the relevant ribonucleotide 3′-phosphodiester. A requirement for the re-ligation activity of Top1 led us to propose a sequential cleavage model for Top1-dependent mutagenesis at ribonucleotides. Here, we test key features of this model via parallel in vitro and in vivo analyses. We find that the distance between two Top1 cleavage sites determines the deletion size and that this distance is inversely related to the deletion frequency. Following the creation of a gap by two Top1 cleavage events, the tandem repeat provides complementarity that promotes realignment to a nick and subsequent Top1-mediated ligation. Complementarity downstream of the gap promotes deletion formation more effectively than does complementarity upstream of the gap, consistent with constraints to realignment of the strand to which Top1 is covalently bound. Our data fortify sequential Top1 cleavage as the mechanism for ribonucleotide-dependent deletions and provide new insight into the component steps of this process

Patterns of recruitment and injury in a heterogeneous airway network model

In respiratory distress, lung airways become flooded with liquid and may collapse due to surface-tension forces acting on air-liquid interfaces, inhibiting gas exchange. This pa- per proposes a mathematical multiscale model for the mechanical ventilation of a network of occluded airways, where air is forced into the network at a fixed tidal volume, allowing investigation of optimal recruitment strategies. The temporal response is derived from mechanistic models of individual airway reopening, incorporating feedback on the airway pressure due to recruitment. The model accounts for stochastic variability in airway di- ameter and stiffness across and between generations. For weak heterogeneity, the network is completely ventilated via one or more avalanches of recruitment (with airways recruited in quick succession), each characterised by a transient decrease in the airway pressure; avalanches become more erratic for airways that are initially more flooded. However, the time taken for complete ventilation of the network increases significantly as the network becomes more heterogeneous, leading to increased stresses on airway walls. The model predicts that the most peripheral airways are most at risk of ventilation-induced damage. A positive-end-expiratory pressure (PEEP) reduces the total recruitment time but at the cost of larger stresses exerted on airway walls