Detecting 6 MV X-rays using an organic photovoltaic device

An organic photovoltaic (OPV) device has been used in conjunction with a flexible inorganic phosphor to produce a radiation tolerant, efficient and linear detector for 6 MV Xrays. The OPVs were based on a blend of poly(3-hexylthiophene-2,5-diyl) (P3HT) and phenyl-C61-butyric acid methyl ester (PCBM). We show that the devices have a sensitivity an order of magnitude higher than a commercial silicon detector used as a reference. Exposure to 360 Grays of radiation resulted in a small (2%) degradation in performance demonstrating that these detectors have the potential to be used as flexible, real-time, in vivo dosimeters for oncology treatments. (C) 2009 Elsevier B.V. All rights reserved

Evidence for suboxic nitrification in recent marine sediments

The classical scheme of biogeochemical zones (BGZ) is known to be an oversimplification of the microbial processes that occur in organic-rich marine sediments. Results from a coupled deployment of pore-water gel probes in Loch Duich, Scotland, provide direct evidence for rapid recycling within the iron reduction (FeR) and sulphate reduction (SR) zones. High resolution porewater profiles obtained using diffusive equilibrium in thin films (DET) gel probes found a nitrate peak at the boundary between the FeR and SR zones. This non-steady state feature is consistent with recycling of reduced N occurring throughout the FeR zone. Both conventional pore-water iron profiles and results from diffusive gradient in thin films (DGT) probes indicate that iron is solubilised and precipitated in rapid Fe/S recycling reactions throughout the SR zone. The presence of such complex recycling reactions confirms the oversimplification of the classical BGZ scheme

Anoxic nitrification in marine sediments

Nitrate peaks are found in pore-water profiles in marine sediments at depths considerably below the conventional zone of oxic nitrification. These have been interpreted to represent nonsteady- state effects produced by the activity of nitrifying bacteria, and suggest that nitrification occurs throughout the anoxic sediment region. In this study, ΣNO3 peaks and molecular analysis of DNA and RNA extracted from anoxic sediments of Loch Duich, an organic-rich marine fjord, are consistent with nitrification occurring in the anoxic zone. Analysis of ammonia oxidiser 16S rRNA gene fragments amplified from sediment DNA indicated the abundance of autotrophic ammonia-oxidising bacteria throughout the sediment depth sampled (40 cm), while RT-PCR analysis indicated their potential activity throughout this region. A large non-steady-state pore-water ΣNO3 peak at ~21 cm correlated with discontinuities in this ammonia-oxidiser community. In addition, a subsurface nitrate peak at ~8 cm below the oxygen penetration depth, correlated with the depth of a peak in nitrification rate, assessed by transformation of 15N-labelled ammonia. The source of the oxidant required to support nitrification within the anoxic region is uncertain. It is suggested that rapid recycling of N is occurring, based on a coupled reaction involving Mn oxides (or possibly highly labile Fe oxides) buried during small-scale slumping events. However, to fully investigate this coupling, advances in the capability of high-resolution pore-water techniques are required

Dbl3 drives Cdc42 signaling at the apical margin to regulate junction position and apical differentiation

Epithelial cells develop morphologically characteristic apical domains that are bordered by tight junctions, the apical–lateral border. Cdc42 and its effector complex Par6–atypical protein kinase c (aPKC) regulate multiple steps during epithelial differentiation, but the mechanisms that mediate process-specific activation of Cdc42 to drive apical morphogenesis and activate the transition from junction formation to apical differentiation are poorly understood. Using a small interfering RNA screen, we identify Dbl3 as a guanine nucleotide exchange factor that is recruited by ezrin to the apical membrane, that is enriched at a marginal zone apical to tight junctions, and that drives spatially restricted Cdc42 activation, promoting apical differentiation. Dbl3 depletion did not affect junction formation but did affect epithelial morphogenesis and brush border formation. Conversely, expression of active Dbl3 drove process-specific activation of the Par6–aPKC pathway, stimulating the transition from junction formation to apical differentiation and domain expansion, as well as the positioning of tight junctions. Thus, Dbl3 drives Cdc42 signaling at the apical margin to regulate morphogenesis, apical–lateral border positioning, and apical differentiation

Probing for the Charm Content of BB and Υ\Upsilon Mesons

A slow $J/\psi$ bump exists in the inclusive $B\to J/\psi + X$ spectrum, while the softness of $J/\psi$ spectrum in $\Upsilon(1S) \to J/\psi + X$ decay is in strong contrast with expectations from color octet mechanism. We propose {\it intrinsic} charm as the explanation:the former is due to $\bar B\to J/\psi D \pi$,with three charm quarks in the final state; the latter is just a small fraction of $\Upsilon(1S) \to (c\bar c)_{\rm slow} + 2$"jet" events, where the slow moving $c\bar c$ system evolves into $D^{(*)}$ pairs. Experimental search for these phenomena at B Factories and the Tevatron is strongly urged, as the implications go beyond QCD.Comment: 4 pages, REVTEX, 10 eps figures included. Major revision with more discussions on the rescattering background, and a reappraisal of the Upsilon(1S) decay in the presence of intrinsic charm, leading to a change in Titl

The intrinsic charm contribution to the proton spin

The charm quark contribution to the first moment of $g_1(x,Q^2)$ is calculated using a heavy mass expansion of the divergence of the singlet axial current. It is shown to be small.Comment: LATEX, 6 page

Photoproduction of charm near threshold

Charm and bottom production near threshold is sensitive to the multi-quark, gluonic, and hidden-color correlations of hadronic and nuclear wavefunctions in QCD since all of the target's constituents must act coherently within the small interaction volume of the heavy quark production subprocess. Although such multi-parton subprocess cross sections are suppressed by powers of $1/m^2_Q$, they have less phase-space suppression and can dominate the contributions of the leading-twist single-gluon subprocesses in the threshold regime. The small rates for open and hidden charm photoproduction at threshold call for a dedicated facility.Comment: 5 pages 5 figures Changes: 1- Added refs 24,25; 2- Added two sentences, top of column 2 of page 3, on the definition of x, its range and the domain of validity of the mode

Dissipative collisions in 16^{16}O + 27^{27}Al at Elab_{lab}=116 MeV

The inclusive energy distributions of fragments (3$\leq$Z$\leq$7) emitted in the reaction $^{16}$O + $^{27}$Al at $E_{lab} =$116 MeV have been measured in the angular range $\theta_{lab}$= 15$^\circ$ - 115$^\circ$. A non-linear optimisation procedure using multiple Gaussian distribution functions has been proposed to extract the fusion-fission and deep inelastic components of the fragment emission from the experimental data. The angular distributions of the fragments, thus obtained, from the deep inelastic component are found to fall off faster than those from the fusion-fission component, indicating shorter life times of the emitting di-nuclear systems. The life times of the intermediate di-nuclear configurations have been estimated using a diffractive Regge-pole model. The life times thus extracted ($\sim 1 - 5\times 10^{-22}$ Sec.) are found to decrease with the increase in the fragment charge. Optimum Q-values are also found to increase with increasing charge transfer i.e. with the decrease in fragment charge.Comment: 9 pages, 4 figures, 1 tabl

Continent stabilisation by lateral accretion of subduction zone-processed depleted mantle residues; insights from Zealandia

To examine how the mantle lithosphere stabilises continents, we present a synthesis of the mantle beneath Zealandia in the SW Pacific Ocean. Zealandia, Earth's “8th continent”, occurs over 4.9 M km2 and comprises a fore-arc, arc and back-arc fragment rifted from the Australia–Antarctica Gondwana margin 85 Myr ago. The oldest extant crust is ∼500 Ma and the majority is Permian–Jurassic. Peridotitic rocks from most known locations reveal the underpinning mantle to comprise regional domains varying from refractory (Al2O3 < 1 wt%, olivine Mg# > 92, spinel Cr# up to 80, Pt/Ir < 1) to moderately depleted (Al2O3 = 2–4 wt%, olivine Mg# ∼90.5, spinel Cr# < ∼60). There is no systematic distribution of these domains relative to the former arc configuration and some refractory domains underlie crust that is largely devoid of magmatic rocks. Re-depletion Os model ages have no correlation with depletion indices but do have a distribution that is very similar to global convecting mantle. Whole rock, mineral and isotopic data are interpreted to show that the Zealandia mantle lithosphere was constructed from isotopically heterogeneous convecting mantle fragments swept into the sub-arc environment, amalgamated, and variably re-melted under low-P hydrous conditions. The paucity of mafic melt volumes in most of the overlying crust that could relate to the depleted domains requires melting to have been followed by lateral accretion either during subduction or slab rollback. Recent Australia–Pacific convergence has thickened portions of the Zealandia mantle to >160 km. Zealandia shows that the generation of refractory and/or thick continental lithosphere is not restricted to the Archean. Since Archean cratons also commonly display crust–mantle age decoupling, contain spinel peridotites with extreme Cr# numbers that require low-P hydrous melting, and often have a paucity of mafic melts relative to the extreme depletion indicated by their peridotitic roots, they too may – in part – be compilations of peridotite shallowly melted and then laterally accreted at subduction margins