All-Orders Singular Emission in Gauge Theories

I present a class of functions unifying all singular limits for the emission of soft or collinear gluons in gauge-theory amplitudes at any order in perturbation theory. Each function is a generalization of the antenna functions of ref. [1]. The helicity-summed interferences these functions are thereby also generalizations to higher orders of the Catani--Seymour dipole factorization function.Comment: 5 pages, 1 figur

Using deuterated PAH amendments to validate chemical extraction methods to predict PAH bioavailability in soils

Validating chemical methods to predict bioavailable fractions of polycyclic aromatic hydrocarbons (PAHs) by comparison with accumulation bioassays is problematic. Concentrations accumulated in soil organisms not only depend on the bioavailable fraction but also on contaminant properties. A historically contaminated soil was freshly spiked with deuterated PAHs (dPAHs). dPAHs have a similar fate to their respective undeuterated analogues, so chemical methods that give good indications of bioavailability should extract the fresh more readily available dPAHs and historic more recalcitrant PAHs in similar proportions to those in which they are accumulated in the tissues of test organisms. Cyclodextrin and butanol extractions predicted the bioavailable fraction for earthworms (Eisenia fetida) and plants (Lolium multiflorum) better than the exhaustive extraction. The PAHs accumulated by earthworms had a larger dPAH:PAH ratio than that predicted by chemical methods. The isotope ratio method described here provides an effective way of evaluating other chemical methods to predict bioavailability

Design and implementation of robust decentralized control laws for the ACES structure at Marshall Space Flight Center

Many large space system concepts will require active vibration control to satisfy critical performance requirements such as line-of-sight accuracy. In order for these concepts to become operational it is imperative that the benefits of active vibration control be practically demonstrated in ground based experiments. The results of the experiment successfully demonstrate active vibration control for a flexible structure. The testbed is the Active Control Technique Evaluation for Spacecraft (ACES) structure at NASA Marshall Space Flight Center. The ACES structure is dynamically traceable to future space systems and especially allows the study of line-of-sight control issues

X-ray observations of cataclysmic variables

Cataclysmic variables are close binary systems where mass is accreted onto a white dwarf through an accretion disc. Approximately half the gravitational energy in the disc is released in a boundary layer as X-rays. X-rays originate from matter under the extreme and energetic conditions and provide a unique view of high energy processes. X-ray luminosities are sensitive to the accretion rate through the disc and to the conditions in the inner accretion zone. Accretion discs are wide spread throughout astronomy. The extraction of potential energy from accreted material is known to be the principal source of power in several types of system; quasars, galactic nuclei, binary X-ray sources, cataclysmic variables (CVs) and proto-planetary discs. CVs provide probably the best opportunity to study the accretion process in isolation. Previous X-ray analysis of dwarf novae relied upon relatively short snap shot observations, which are unable to provide a full picture of the outburst cycle evolution. Multiple outbursts with far greater temporal accuracy and coverage than has ever been observed before are presented in this thesis. Pointed observations using the proportional counter array on the Rossi X-ray Timing Explorer of SS Cygni, U Gem and SU UMa are analysed. The behaviour in the optical band is similar for the three systems in this thesis, however, a large distinction is seen in the X-ray band. The hard X-ray outburst flux in SS Cygni and SU UMa are quenched below the quiescent flux, while in U Gem it is unusually faint in quiescence brightening in outburst. The hard quiescent X-ray spectrum is replaced by an intense soft X-ray component in outburst for all dwarf novae. Analysis of U Gem suggests that X-rays originate from the inner accretion disc with a scale height not much greater than the disc thickness. The start of the hard X-ray outburst is delayed behind the optical rise, this delay is roughly consistent for the three systems presented. This indicates that the origin of the heating wave in the accretion disc and the time it takes to propagate to the boundary layer are similar for these systems. The hard X-ray recovery also has a range of times, with the peak occurring as the optical flux reaches quiescence suggesting the cooling front reaches the boundary layer at the same time in relation to the end of the optical outburst. The spectra for all three systems presented in this thesis are well described by a thermal plasma model with sub-solar abundances and are consistent with higher reflection during the hard X-ray suppression. This indicates that the disc is likely to be truncated in quiescence. SS Cygni has a wide range of quiescent accretion rates. However, the X-ray flux in SS Cygni and U Gem always increases when the boundary layer transitions from both optically thick to thin, into outburst, and optically thin to thick, out of outburst. This is surprising, the flux is expected to decrease when the critical accretion rate is reached suggesting that the critical accretion rate when the boundary layer transitions is not fixed. The quiescent X-ray flux in SU UMa decreases and, with SS Cygni, is between 2 − 3 orders of magnitude higher than predictions by the disc instability model

Dynamical evidence for a strong tidal interaction between the Milky Way and its satellite, Leo V

We present a chemodynamical analysis of the Leo~V dwarf galaxy, based on Keck II DEIMOS spectra of 8 member stars. We find a systemic velocity for the system of $\langle v_r\rangle = 170.9^{+ 2.1}_{-1.9}$kms$^{-1}$, and barely resolve a velocity dispersion for the system, with $\sigma_{vr} = 2.3^{+3.2}_{-1.6}$kms$^{-1}$, consistent with previous studies of Leo~V. The poorly resolved dispersion means we are unable to adequately constrain the dark matter content of Leo~V. We find an average metallicity for the dwarf of [Fe/H]$= -2.48\pm0.21$, and measure a significant spread in the iron abundance of its member stars, with $-3.1\le$[Fe/H]$\le-1.9$ dex, which cleanly identifies Leo~V as a dwarf galaxy that has been able to self-enrich its stellar population through extended star formation. Owing to the tentative photometric evidence for tidal substructure around Leo~V, we also investigate whether there is any evidence for tidal stripping or shocking of the system within its dynamics. We measure a significant velocity gradient across the system, of $\frac{{\rm d}v}{{\rm d}\chi} = -4.1^{+2.8}_{-2.6}$kms$^{-1}$ per arcmin (or $\frac{{\rm d}v}{{\rm d}\chi} = -71.9^{+50.8}_{-45.6}$kms$^{-1}$~kpc$^{-1}$), which points almost directly toward the Galactic centre. We argue that Leo~V is likely a dwarf on the brink of dissolution, having just barely survived a past encounter with the centre of the Milky Way.Comment: 14 pages, 12 figures, accepted for publication in MNRAS. Updated to include minor revisions from referee proces

Statistical comparison of ensemble implementations of Grover's search algorithm to classical sequential searches

We compare pseudopure state ensemble implementations, quantified by their initial polarization and ensemble size, of Grover's search algorithm to probabilistic classical sequential search algorithms in terms of their success and failure probabilities. We propose a criterion for quantifying the resources used by the ensemble implementation via the aggregate number of oracle invocations across the entire ensemble and use this as a basis for comparison with classical search algorithms. We determine bounds for a critical polarization such that the ensemble algorithm succeeds with a greater probability than the probabilistic classical sequential search. Our results indicate that the critical polarization scales as N^(-1/4) where N is the database size and that for typical room temperature solution state NMR, the polarization is such that the ensemble implementation of Grover's algorithm would be advantageous for N > 10^2