Formation of spatially periodic fronts of high-energy electrons in a radio-frequency driven surface microdischarge

The generation of spatially periodic fronts of high-energy electrons (>13.48 eV) has been investigated in a radio-frequency surface microdischarge in atmospheric-pressure argon. Optical emission spectroscopy is used to study the Ar I 2p1−1s2 transition surrounding a filamentary microdischarge, both spatially and with respect to the phase of the applied voltage. The formation of excitation fronts, which remain at a constant propagation distance throughout the RF cycle and for the duration of the pulse, may be explained by a localized increase in the electric field at the tip of surface-charge layers that are deposited during the extension phase

Nanosecond optical imaging spectroscopy of an electrothermal radiofrequency plasma thruster plume

Nanosecond optical imaging spectroscopy is employed to investigate the spatio-temporal dynamics of the plasma plume expanding from a 4.2 mm-diameter, 20 mm-long cylindrical capacitively coupled electrothermal radiofrequency (rf) driven thruster using 10 W of power at 12.50 MHz and an argon pressure of 1.5 Torr. On-axis, the plume exhibits four distinct peaks of optical emission intensity within the rf period. The plume has a spherical shape with a transient radial extension (during half of the rf cycle) at the thruster exit plane due to an rf current to ground when the grounded electrode acts as an anode

Hot Populations in M87 Globular Clusters

We have obtained HST/STIS far- and near-UV photometry of globular clusters in four fields in the gE galaxy M87. To a limit of m(FUV) = 25 we detect a total of 66 globular clusters (GCs) in common with the deep HST optical-band study of Kundu et al. (1999). Despite strong overlap in V- and I-band properties, the M87 GCs have UV/optical properties that are distinct from clusters in the Milky Way and in M31. M87 clusters, especially metal-poor ones, produce larger hot HB populations than do Milky Way analogues. Cluster mass is probably not a factor in these distinctions. The most metal-rich M87 GCs in our sample are near Z_sun and overlap the local E galaxy sample in estimated Mg_2 line indices. Nonetheless, the clusters produce much more UV light at a given Mg_2, being up to 1 mag bluer than any gE galaxy in (FUV-V) color. The M87 GCs do not appear to represent a transition between Milky Way-type clusters and E galaxies. The differences are in the correct sense if the clusters are significantly older than the E galaxies. Comparisons with Galactic open clusters indicate that the hot stars lie on the extreme horizontal branch, rather than being blue stragglers, and that the EHB becomes well populated for ages > 5 Gyr. We find that 43 of our UV detections have no optical-band counterparts. Most appear to be UV-bright background galaxies, seen through M87. Eleven NUV variable sources detected at only one epoch in the central field are probably classical novae. [Abridged]Comment: 70 pages, 25 figures (including 4 jpgs), 7 tables. To appear in AJ. Full resolution version available at http://www.astro.virginia.edu/~rwo/m87/m87-hotpops.pd

Genome-Wide Characterization of the Phosphate Starvation Response in Schizosaccharomyces pombe

Background: Inorganic phosphate is an essential nutrient required by organisms for growth. During phosphate starvation, Saccharomyces cerevisiae activates the phosphate signal transduction (PHO) pathway, leading to expression of the secreted acid phosphatase, PHO5. The fission yeast, Schizosaccharomyces pombe, regulates expression of the ScPHO5 homolog (pho1+) via a non-orthologous PHO pathway involving genetically identified positive (pho7+) and negative (csk1+) regulators. The genes induced by phosphate limitation and the molecular mechanism by which pho7+ and csk1+ function are unknown. Here we use a combination of molecular biology, expression microarrays, and chromatin immunoprecipitation coupled with high-throughput sequencing (ChIP-Seq) to characterize the role of pho7+ and csk1+ in the PHO response. Results: We define the set of genes that comprise the initial response to phosphate starvation in S. pombe. We identify a conserved PHO response that contains the ScPHO5 (pho1+), ScPHO84 (SPBC8E4.01c), and ScGIT1 (SPBC1271.09) orthologs. We identify members of the Pho7 regulon and characterize Pho7 binding in response to phosphate-limitation and Csk1 activity. We demonstrate that activation of pho1+ requires Pho7 binding to a UAS in the pho1+ promoter and that Csk1 repression does not regulate Pho7 enrichment. Further, we find that Pho7-dependent activation is not limited to phosphate-starvation, as additional environmental stress response pathways require pho7+ for maximal induction. Conclusions: We provide a global analysis of the transcriptional response to phosphate limitation in S. pombe. Our results elucidate the conserved core regulon induced in response to phosphate starvation in this ascomycete distantly related to S. cerevisiae and provide a better understanding of flexibility in environmental stress response networks.Chemistry and Chemical BiologyMolecular and Cellular Biolog

Energy decay and frequency shift of a superconducting qubit from non-equilibrium quasiparticles

Quasiparticles are an important decoherence mechanism in superconducting qubits, and can be described with a complex admittance that is a generalization of the Mattis-Bardeen theory. By injecting non-equilibrium quasiparticles with a tunnel junction, we verify qualitatively the expected change of the decay rate and frequency in a phase qubit. With their relative change in agreement to within 4% of prediction, the theory can be reliably used to infer quasiparticle density. We describe how settling of the decay rate may allow determination of whether qubit energy relaxation is limited by non-equilibrium quasiparticles.Comment: Main paper: 4 pages, 3 figures, 1 table. Supplementary material: 8 pages, 3 figure

T-infinity: The Dependency Inversion Principle for Rapid and Sustainable Multidisciplinary Software Development

The CFD Vision 2030 Study recommends that, NASA should develop and maintain an integrated simulation and software development infrastructure to enable rapid CFD technology maturation.... [S]oftware standards and interfaces must be emphasized and supported whenever possible, and open source models for noncritical technology components should be adopted. The current paper presents an approach to an open source development architecture, named T-infinity, for accelerated research in CFD leveraging the Dependency Inversion Principle to realize plugins that communicate through collections of functions without exposing internal data structures. Steady state flow visualization, mesh adaptation, fluid-structure interaction, and overset domain capabilities are demonstrated through compositions of plugins via standardized abstract interfaces without the need for source code dependencies between disciplines. Plugins interact through abstract interfaces thereby avoiding N 2 direct code-to-code data structure coupling where N is the number of codes. This plugin architecture enhances sustainable development by controlling the interaction between components to limit software complexity growth. The use of T-infinity abstract interfaces enables multidisciplinary application developers to leverage legacy applications alongside newly-developed capabilities. While rein, a description of interface details is deferred until the are more thoroughly tested and can be closed to modification

Superscaling in inclusive electron-nucleus scattering

We investigate the degree to which the scaling functions $F(\psi')$ derived from cross sections for inclusive electron-nucleus quasi-elastic scattering define the same function for different nuclei. In the region where the scaling variable $\psi'< 0$, we find that this superscaling is experimentally realized to a high degree.Comment: Corrected previously mislabeled figures and cross references; 9 pages, 4 color figures, using BoxedEPS and REVTeX; email correspondence to [email protected]

Functional central limit theorems for vicious walkers

We consider the diffusion scaling limit of the vicious walker model that is a system of nonintersecting random walks. We prove a functional central limit theorem for the model and derive two types of nonintersecting Brownian motions, in which the nonintersecting condition is imposed in a finite time interval $(0,T]$ for the first type and in an infinite time interval $(0,\infty)$ for the second type, respectively. The limit process of the first type is a temporally inhomogeneous diffusion, and that of the second type is a temporally homogeneous diffusion that is identified with a Dyson's model of Brownian motions studied in the random matrix theory. We show that these two types of processes are related to each other by a multi-dimensional generalization of Imhof's relation, whose original form relates the Brownian meander and the three-dimensional Bessel process. We also study the vicious walkers with wall restriction and prove a functional central limit theorem in the diffusion scaling limit.Comment: AMS-LaTeX, 20 pages, 2 figures, v6: minor corrections made for publicatio