CALCIUM URANIUM(IV) FLUORIDE PRECIPITATION AND REDUCTION TO METAL

The double salt calcium uranium(IV) fluoride can be precipitated from uranyl nitrate solution. In the presence of fluoride and calcium ions, ferrous salts will reduce uranium(VI) nitrate to the four state precipitating calcium uranium(IV) fluoride. X-ray studies showed that the compound is a true double salt. The salt can be dehydrated under argon at 250 deg C and reduced to metal by the bomb technique. Reduction yields are high, but co-precipitated iron in the salt is concentrated in the uranium button, resulting in iron impurities of approximately 0.6%. The double salt is a suitable feed for fused salt electrolysis. Electrolyzing from a solution of 30% double salt dissolved in LiC1- KC1 eutectic dendritic uranium was recovered with a current efficiency of 35%. Iron impurity in the electrolyztically prepared uranium was reduced from an expected concentration of 5700 ppm to an actual concentration of 250 ppm. (auth

Automated production of high rep rate foam targets

Manufacturing low density targets in the numbers needed for high rep rate experiments is highly challenging. This report summarises advances from manual production to semiautomated and the improvements that follow both in terms of production time and target uniformity. The production process is described and shown to be improved by the integration of an xyz robot with dispensing capabilities. Results are obtained from manual and semiautomated production runs and compared. The variance in the foam thickness is reduced significantly which should decrease experimental variation due to target parameters and could allow for whole batches to be characterised by the measurement of a few samples. The work applies to both foil backed and free standing foam targets.Publisher PDFPeer reviewe

Molecular phylogenetics reveals a complex history underlying cryptic diversity in the Bush Squeaker Frog (Arthroleptis wahlbergii) in southern Africa

Throughout the Miocene, the African landscape underwent broad climatic shifts that profoundly influenced the distribution of fauna and flora. Since the late Miocene, these shifts have created a landscape in southern Africa that is strongly characterised by savanna and arid environments. Forests persist in small fragments, primarily in mountainous or heterogeneous landscapes. Arthroleptis wahlbergii is a small frog endemic to eastern South Africa that has presumed low dispersal ability. Because of its preference for forests, the dynamics of forests since the late Miocene in this region might have promoted diversification within A. wahlbergii. To investigate whether habitat fragmentation might have driven divergences among populations, we carried out species distribution modelling and population level and phylogenetic analyses using two genetic loci (16S, mitochondrial; RAG-1, nuclear) sequenced for 48 individuals from 14 forests across the c. 500 km range of this species. There is substantial population level structuring within A. wahlbergii, however the structure does not relate to forest types or catchments. We instead propose that the structure is a result of dynamic and idiosyncratic changes in forest connectivity over the Pleistocene. We identified two geographically circumscribed clades, the northern of which corresponds to true A. wahlbergii. The southern clade corresponds to populations from which Arthroleptis wageri FitzSimons, 1930 was described. This has long been considered a synonym of A. wahlbergii, but our molecular phylogenetic and distribution modelling supports recognising A. wageri as a distinct species

ArchEnemy: Removing scattered-light glitches from gravitational wave data

Data recorded by gravitational wave detectors includes many non-astrophysical transient noise bursts, the most common of which is caused by scattered-light within the detectors. These so-called ``glitches'' in the data impact the ability to both observe and characterize incoming gravitational wave signals. In this work we use a scattered-light glitch waveform model to identify and characterize scattered-light glitches in a representative stretch of gravitational wave data. We identify $2749$ scattered-light glitches in $5.96$ days of LIGO-Hanford data and $1306$ glitches in $5.93$ days of LIGO-Livingston data taken from the third LIGO-Virgo observing run. By subtracting identified scattered-light glitches we demonstrate an increase in the sensitive volume of the gravitational wave search for binary black hole signals by $\sim1\%$.Comment: 30 pages + acknowledgements and references, 13 figure

Scaling Solutions to 6D Gauged Chiral Supergravity

We construct explicitly time-dependent exact solutions to the field equations of 6D gauged chiral supergravity, compactified to 4D in the presence of up to two 3-branes situated within the extra dimensions. The solutions we find are scaling solutions, and are plausibly attractors which represent the late-time evolution of a broad class of initial conditions. By matching their near-brane boundary conditions to physical brane properties we argue that these solutions (together with the known maximally-symmetric solutions and a new class of non-Lorentz-invariant static solutions, which we also present here) describe the bulk geometry between a pair of 3-branes with non-trivial on-brane equations of state.Comment: Contribution to the New Journal of Physics focus issue on Dark Energy; 28 page

Kicking the Rugby Ball: Perturbations of 6D Gauged Chiral Supergravity

We analyze the axially-symmetric scalar perturbations of 6D chiral gauged supergravity compactified on the general warped geometries in the presence of two source branes. We find all of the conical geometries are marginally stable for normalizable perturbations (in disagreement with some recent calculations) and the nonconical for regular perturbations, even though none of them are supersymmetric (apart from the trivial Salam-Sezgin solution, for which there are no source branes). The marginal direction is the one whose presence is required by the classical scaling property of the field equations, and all other modes have positive squared mass. In the special case of the conical solutions, including (but not restricted to) the unwarped `rugby-ball' solutions, we find closed-form expressions for the mode functions in terms of Legendre and Hypergeometric functions. In so doing we show how to match the asymptotic near-brane form for the solution to the physics of the source branes, and thereby how to physically interpret perturbations which can be singular at the brane positions.Comment: 21 pages + appendices, references adde

Stochastic Inflation Revisited: Non-Slow Roll Statistics and DBI Inflation

Stochastic inflation describes the global structure of the inflationary universe by modeling the super-Hubble dynamics as a system of matter fields coupled to gravity where the sub-Hubble field fluctuations induce a stochastic force into the equations of motion. The super-Hubble dynamics are ultralocal, allowing us to neglect spatial derivatives and treat each Hubble patch as a separate universe. This provides a natural framework in which to discuss probabilities on the space of solutions and initial conditions. In this article we derive an evolution equation for this probability for an arbitrary class of matter systems, including DBI and k-inflationary models, and discover equilibrium solutions that satisfy detailed balance. Our results are more general than those derived assuming slow roll or a quasi-de Sitter geometry, and so are directly applicable to models that do not satisfy the usual slow roll conditions. We discuss in general terms the conditions for eternal inflation to set in, and we give explicit numerical solutions of highly stochastic, quasi-stationary trajectories in the relativistic DBI regime. Finally, we show that the probability for stochastic/thermal tunneling can be significantly enhanced relative to the Hawking-Moss instanton result due to relativistic DBI effects.Comment: 38 pages, 2 figures. v3: minor revisions; version accepted into JCA

Flux compactifications and supersymmetry breaking in 6D gauged supergravity

We review on a recent construction of the on-shell supersymmetric brane action for the codimension-two branes with nonzero tension in the flux compactification of a 6D chiral gauged supergravity. On dimesionally reducing on 4D gauged supergravity for a new supersymmetric unwarped background with conical branes, we consider the modulus stabilization for determining the soft masses of the scalars localized on the branes and show that the bulk U(1)_R provides a new mechanism for mediating the SUSY breaking.Comment: 12 pages, no figures, Invited review for Modern Physics Letters A, Published versio

The vacuum bubbles in de Sitter background and black hole pair creation

We study the possible types of the nucleation of vacuum bubbles. We classify vacuum bubbles in de Sitter background and present some numerical solutions. The thin-wall approximation is employed to obtain the nucleation rate and the radius of vacuum bubbles. With careful analysis we confirm that Parke's formula is also applicable to the large true vacuum bubbles. The nucleation of the false vacuum bubble in de Sitter background is also evaluated. The tunneling process in the potential with degenerate vacua is analyzed as the limiting cases of the large true vacuum bubble and false vacuum bubble. Next, we consider the pair creation of black holes in the background of bubble solutions. We obtain static bubble wall solutions of junction equation with black hole pair. The masses of created black holes are uniquely determined by the cosmological constant and surface tension on the wall. Finally, we obtain the rate of pair creation of black holes.Comment: 3 figures, minor including errors and typos corrected, and refs. adde

Fake supersymmetry versus Hamilton-Jacobi

We explain when the first-order Hamilton-Jacobi equations for black holes (and domain walls) in (gauged) supergravity, reduce to the usual first-order equations derived from a fake superpotential. This turns out to be equivalent to the vanishing of a newly found constant of motion and we illustrate this with various examples. We show that fake supersymmetry is a necessary condition for having physically sensible extremal black hole solutions. We furthermore observe that small black holes become scaling solutions near the horizon. When combined with fake supersymmetry, this leads to a precise extension of the attractor mechanism to small black holes: The attractor solution is such that the scalars move on specific curves, determined by the black hole charges, that are purely geodesic, although there is a non-zero potential.Comment: 20 pages, v2: Typos corrected, references adde