Bayesian methods of astronomical source extraction

We present two new source extraction methods, based on Bayesian model selection and using the Bayesian Information Criterion (BIC). The first is a source detection filter, able to simultaneously detect point sources and estimate the image background. The second is an advanced photometry technique, which measures the flux, position (to sub-pixel accuracy), local background and point spread function. We apply the source detection filter to simulated Herschel-SPIRE data and show the filter's ability to both detect point sources and also simultaneously estimate the image background. We use the photometry method to analyse a simple simulated image containing a source of unknown flux, position and point spread function; we not only accurately measure these parameters, but also determine their uncertainties (using Markov-Chain Monte Carlo sampling). The method also characterises the nature of the source (distinguishing between a point source and extended source). We demonstrate the effect of including additional prior knowledge. Prior knowledge of the point spread function increase the precision of the flux measurement, while prior knowledge of the background has onlya small impact. In the presence of higher noise levels, we show that prior positional knowledge (such as might arise from a strong detection in another waveband) allows us to accurately measure the source flux even when the source is too faint to be detected directly. These methods are incorporated in SUSSEXtractor, the source extraction pipeline for the forthcoming Akari FIS far-infrared all-sky survey. They are also implemented in a stand-alone, beta-version public tool that can be obtained at http://astronomy.sussex.ac.uk/$\sim$rss23/sourceMiner\_v0.1.2.0.tar.gzComment: Accepted for publication by ApJ (this version compiled used emulateapj.cls

Strong decays of radially excited vector mesons

Motivated by the recent discovery at Orsay of ϕ′ (1680), we study the strong interaction decays of radially excited vector mesons within the framework of the3P0 quark pair creation model. We stress the relative importance of phase space, algebraic spinflavor couplings, and spatial overlaps. Quite a few features of the data can be will understood by the presence of a node in the spatial wave function, but the detailed structure of the modes ρ′→4π remains a serious challenge

Observations of neutral circulation at mid-latitudes during the Equinox Transition Study

Measurements of ion drift velocity made by the Millstone Hill incoherent scatter radar have been used to calculate the meridional neutral wind velocity during the Sept. 17 to 24, 1984 period. Strong daytime southward neutral surges were observed during the magnetically disturbed days of September 19 and 23, in contrast to the small daytime winds obtained as expected during the magnetically quiet days. The surge on September 19 was also seen at Arecibo. In addition, two approaches have been used to calculate the meridional wind component from the radar-derived height of the F-layer electron density peak. Results confirm the wind surge, particularly when the strong electric fields measured during the disturbed days are included in the calculations. The two approaches for the F-layer peak wind calculations are applied to the radar-derived electron density peak height as a function of latitude to study the variation of the southward daytime surges with latitude

Study on the neuronal circuits implicated in postural tremor and hypokinesia

The effect of various tegmentary lesions at the level of the pontomesenchphalon in monkeys on motor function was observed. The importance of the monoaminergic mechanisms of the brainstem is discussed. The results also show the importance of the descending tegmentary rubral system and the rubroolivocerebellar circuit in controlling peripheral motor activity. The destruction of the sensory motor cortex proves to be a more effective way of eliminating spontaneous or harmaline induced tremor than the complete interruption of the pyramidal system on the level of the cerebral peduncle

The structure of vitreous binary oxides : silicate, germanate and plumbite networks

Structural aspects of three related binary oxide glass systems have been studied in detail using a combination of neutron and x-ray diffraction, empirical modelling techniques, and information from bulk property and spectroscopic measurements. The local Pb2+ environment in PbO SiO2 glasses changes only subtly with composition, having, on average 3.33 short (2:70 Å) and 1.3 long (2.70 <rPbO <3:27 Å) Pb- O bonds at 35 mol% PbO, and 3.57 short and 1.3(2) long Pb-O bonds at 80 mol% PbO. Therefore, over the entire series, lead behaves as a glass network forming cation, with highly asymmetric ligand distribution and stereochemically active electron lone-pair (LP), with gradual transition toward more axially symmetric environments (cf. crystalline PbO) as the PbO content increases. Structural modelling of the highest lead content oxide glass (80 PbO < 20 SiO2) to date reveals organisation of LPs to form voids, analogous to interlayer spaces in crystalline PbO polymorphs, and channels found within other crystalline lead oxide compounds such as Pb11Si3O17. The plumbite glass network is characterised by a high degree of intermediate-range ordering, evidenced by a very narrow first sharp diffraction peak (FSDP), as well as significant edge-sharing of Pb polyhedra and high oxygen-cation coordination numbers, e.g. [OPb4], [OPb3Si]. PbOGeO2 glass formation was found as high as 75 mol% PbO using rapid twinroller quenching. Such high lead glasses are analogues of the silicates, but with a 10% enhancement in correlation length derived from the FSDP. In the low PbO region a broad maximum in Ge-O coordination number of nGeO = 4:14(3) at 26:5(5) mol% PbO was observed. This is much smaller, and at higher metal oxide content than in Na, K and Cs germanate glasses and contradicts published results [N. Umesaki et al., Physica B 213, (1995), 490]. The weakness of the effect is attributed to Pb2+ playing a predominantly network forming role, although Ge-O and Pb-O coordination numbers showed positive correlation, such that the presence of [GeO5] or [GeO6] is indicative of Pb having some ‘modifying’ character. It was argued, based on empirical models and the known crystal chemistry, that Pb may occupy sites of intermediate character, with mixed s-p LP character, rather than invoking a bimodal distribution of network forming and modifying Pb sites. Homogeneous calcium germanate glasses were obtained in the region 21 to 41 mol% CaO by rapid twin-roller quenching, with glass-in-glass phase separation occuring in the low CaO region, and crystallisation around the CaGeO3 composition. A very broad maximum of nGeO = 4:30(3) at 28:0(5) mol% CaO was observed, correlating approximately with maxima in atomic number densities and glass transition temperatures. Nonbridging oxygen (NBO) are present in all glasses, again in contrast to alkali germanates. The position of the maximum is attributed to stabilisation of vertex sharing [GeOm>4] and/or [GeO6] units by divalent Ca2+. The presence of NBOs is related to the Ca-O coordination number of 7, with higher nGeO and less NBO predicted in Sr and Ba germanate glasses, where M-O coordination is expected to be larger. In both Ca and Pb germanate systems, the equilibrium crystals have much larger nGeO than the glasses, and this implies a decrease of nGeO with liquid, supercooled liquid and glass fictive temperatures. This tentative conclusion is supported by measurements on two 40 PbO 60 GeO2 glasses with different thermal histories

Resonant nonlinear quantum transport for a periodically kicked Bose condensate

Our realistic numerical results show that the fundamental and higher-order quantum resonances of the delta-kicked rotor are observable in state-of-the-art experiments with a Bose condensate in a shallow harmonic trap, kicked by a spatially periodic optical lattice. For stronger confinement, interaction-induced destruction of the resonant motion of the kicked harmonic oscillator is predicted.Comment: amended version, new Fig.

Crystal structure of the catalytic fragment of murine poly(ADP-ribose) polymerase-2.

Poly(ADP-ribose) polymerase-1 (PARP-1) has become an important pharmacological target in the treatment of cancer due to its cellular role as a 'DNA-strand break sensor', which leads in part to resistance to some existing chemo- and radiological treatments. Inhibitors have now been developed which prevent PARP-1 from synthesizing poly(ADP-ribose) in response to DNA-breaks and potentiate the cytotoxicity of DNA damaging agents. However, with the recent discoveries of PARP-2, which has a similar DNA-damage dependent catalytic activity, and additional members containing the 'PARP catalytic' signature, the isoform selectivity and resultant pharmacological effects of existing inhibitors are brought into question. We present here the crystal structure of the catalytic fragment of murine PARP-2, at 2.8 A resolution, and compare this to the catalytic fragment of PARP-1, with an emphasis on providing a possible framework for rational drug design in order to develop future isoform-specific inhibitors

Long-term variation in the Sun's activity caused by magnetic Rossby waves in the tachocline

Long-term records of sunspot number and concentrations of cosmogenic radionuclides (10Be and 14C) on the Earth reveal the variation of the Sun's magnetic activity over hundreds and thousands of years. We identify several clear periods in sunspot, 10Be, and 14C data as 1000, 500, 350, 200 and 100 years. We found that the periods of the first five spherical harmonics of the slow magnetic Rossby mode in the presence of a steady toroidal magnetic field of 1200-1300 G in the lower tachocline are in perfect agreement with the time scales of observed variations. The steady toroidal magnetic field can be generated in the lower tachocline either due to the steady dynamo magnetic field for low magnetic diffusivity or due to the action of the latitudinal differential rotation on the weak poloidal primordial magnetic field, which penetrates from the radiative interior. The slow magnetic Rossby waves lead to variations of the steady toroidal magnetic field in the lower tachocline, which modulate the dynamo magnetic field and consequently the solar cycle strength. This result constitutes a key point for long-term prediction of the cycle strength. According to our model, the next deep minimum in solar activity is expected during the first half of this century.Comment: 4 pages, 4 figures, accepted in ApJ

The IRAS 1-Jy Survey of Ultraluminous Infrared Galaxies: I. The sample and Luminosity Function

A complete flux-limited sample of 118 ultraluminous infrared galaxies (ULIGs) has been identified from the IRAS Faint Source Catalog (FSC). The selection criteria were a 60 micron flux density greater than 1 Jy in a region of the sky delta > -40 deg, |b| > 30 deg. All sources were subsequently reprocessed using coadded IRAS maps in order to obtain the best available flux estimates in all four IRAS wavelength bands. The maximum observed infrared luminosity is L_ir = 10^{12.90} L_{sun}, and the maximum redshift is z = 0.268. The luminosity function for ULIGs over the decade luminosity range L_ir = 10^{12} - 10^{13} L_{sun} can be approximated by a power law Phi (L) ~= L^{-2.35} Mpc^{-3} mag^{-1}. In the local Universe z < 0.1, the space density of ULIGs appears to be comparable to or slightly larger than that of optically selected QSOs at comparable bolometric luminosities. A maximum likelihood test suggests strong evolution for our sample; assuming density evolution proportional to (1+z)^{alpha} we find alpha = 7.6+/-3.2. Examination of the two-point correlation function shows a barely significant level of clustering, xi (r) = 1.6 +/- 1.2, on size scales r ~= 22 h^{-1} Mpc.Comment: 18 pages of text, 10 pages of figures 1 to 6, 6 pages of tables 1 to 3, ApJS accepte