5,932 research outputs found
Domains of invasion organelle proteins from apicomplexan parasites are homologous with the Apple domains of blood coagulation factor XI and plasma pre-kallikrein and are members of the PAN module superfamily
AbstractMicronemes are specialised organelles, found in all apicomplexan parasites, which secrete molecules that are essential for parasite attachment to and invasion of host cells. Regions of several microneme proteins have sequence similarity to the Apple domains (A-domains) of blood coagulation factor XI (FXI) and plasma pre-kallikrein (PK). We have used mass spectrometry on a recombinant-expressed, putative A-domain from the microneme protein EtMIC5 from Eimeria tenella, to demonstrate that three intramolecular disulphide bridges are formed. These bridges are analogous to those that stabilise A-domains in FXI and PK. The data confirm that the apicomplexan domains are structural homologues of A-domains and are therefore novel members of the PAN module superfamily, which also includes the N-terminal domains of members of the plasminogen/hepatocyte growth factor family. The role of A-domains/PAN modules in apicomplexan parasites is not known, but their presence in the microneme suggests that they may be important for mediating proteinâprotein or proteinâcarbohydrate interactions during parasite attachment and host cell invasion
The bumpy light curve of supernova iPTF13z
A Type IIn supernova (SN) is dominated by the interaction of SN ejecta with
the circumstellar medium (CSM). Some SNe IIn (e.g., SN 2006jd) have episodes of
re-brightening ("bumps") in their light curves. We present iPTF13z, a SN IIn
discovered by the intermediate Palomar Transient Factory (iPTF) and
characterised by several bumps in its light curve. We analyse this peculiar
behaviour trying to infer the properties of the CSM and of the SN explosion, as
well as the nature of its progenitor star. We obtained multi-band optical
photometry for over 1000 days after discovery with the P48 and P60 telescopes
at Palomar Observatory. We obtained low-resolution optical spectra in the same
period. We did an archival search for progenitor outbursts. We analyse our
photometry and spectra, and compare iPTF13z to other SNe IIn. A simple
analytical model is used to estimate properties of the CSM. iPTF13z was a SN
IIn showing a light curve with five bumps during its decline phase. The bumps
had amplitudes between 0.4 and 0.9 mag and durations between 20 and 120 days.
The most prominent bumps appeared in all our different optical bands. The
spectra showed typical SN IIn characteristics, with emission lines of H
(with broad component FWHM ~ and narrow
component FWHM ~) and He I, but also with Fe II, Ca II,
Na I D and H P-Cygni profiles (with velocities of ~ ). A pre-explosion outburst was identified lasting days,
with mag around 210 days before discovery. Large, variable
progenitor mass-loss rates (~> 0.01 ) and CSM densities
(~> 10 g cm) are derived. We suggest that the light curve bumps
of iPTF13z arose from SN ejecta interacting with denser regions in the CSM,
possibly produced by the eruptions of a luminous blue variable star.Comment: Version 2: Update to match published paper. 21 pages, 14 figures,
abstract abridged to comply with arXiv length limit. In version 1 of the
paper on arXiv, Table 3 had some erroneous entries. Table 3 is now corrected
and available via VizieR. Version 1 comment: Accepted for publication in
Astronomy & Astrophysics (24 pages, 14 figures, abstract abridged by 20 % not
to exceed the arXiv length limit
Discovery of the heavily obscured supernova 2002cv
On the 13th of May 2002, supernova 2002cv was discovered using a
near-infrared camera working at the AZT-24 1.1m telescope at Campo Imperatore
(AQ-Italy). After the infrared detection a simultaneous photometric follow-up
was started at optical wavelengths. The preliminary results confirm a heavily
obscured object with a V-K color not lower than 6 magnitudes, making SN 2002cv
the most reddened supernova ever observed. This finding, along with the recent
discovery of another obscured supernova, suggests a critical revision of the
rates known to date. The estimate of the visual extinction and the light curves
are provided here. These latter indicate that our SN 2002cv observations are
the earliest available for a type-Ia supernova at IR wavelengths.Comment: 4 page
Free radical reactions in atherosclerosis; An EPR spectrometry study
The copper catalysed oxidation of homocysteine has been studied by electron paramagnetic resonance (EPR) spectroscopy and spin trapping techniques to determine the nature of free radical species formed under varying experimental conditions. Three radicals; thiyl, alkyl and hydroxyl were detected with hydroxyl being predominant. A reaction mechanism is proposed involving Fenton chemistry. Inclusion of catalase to test for intermediate generation of hydrogen peroxide showed a marked reduction in amount of hydroxyl radical generated. In contrast, the addition of superoxide dismutase showed no significant effect on the level of hydroxyl radical formed. Enhanced radical formation was observed at higher levels of oxygen, an effect which has consequences for differential oxygen levels in arterial and venous systems. Implications are drawn for a higher incidence of atherosclerotic plaque formation in arteries versus veins. © 2006 - IOS Press and the authors. All rights reserved
The Population of Tiny Near-Earth Objects Observed by NEOWISE
Only a very small fraction of the asteroid population at size scales
comparable to the object that exploded over Chelyabinsk, Russia has been
discovered to date, and physical properties are poorly characterized. We
present previously unreported detections of 106 close approaching near-Earth
objects (NEOs) by the Wide-field Infrared Survey Explorer mission's NEOWISE
project. These infrared observations constrain physical properties such as
diameter and albedo for these objects, many of which are found to be smaller
than 100 m. Because these objects are intrinsically faint, they were detected
by WISE during very close approaches to the Earth, often at large apparent
on-sky velocities. We observe a trend of increasing albedo with decreasing
size, but as this sample of NEOs was discovered by visible light surveys, it is
likely that selection biases against finding small, dark NEOs influence this
finding.Comment: Accepted to Ap
Reactivity of a dititanium bis(pentalene) complex toward heteroallenes and main-group elementâelement bonds
The reactivity of the TiâTi double bond in (ÎŒ,η5:η5-Pnâ )2Ti2 (1; Pnâ = 1,4-{SiiPr3}2C8H4) toward isocyanide and heteroallene substrates, and molecules featuring homonuclear bonds between main-group elements (EâE) has been explored. Reaction of 1 with methyl isocyanide or 1,3-N,NâČ-di-p-tolylcarbodiimide resulted in the formation of the 1:1 adducts (ÎŒ,η5:η5-Pnâ )2Ti2(ÎŒ,η2-CNMe) (2) and (ÎŒ,η5:η5-Pnâ )2Ti2(ÎŒ-C{N(4-C6H4CH3)}2) (3), respectively, which are thermally stable up to 100 °C in contrast to the analogous adducts formed with CO and CO2. Reaction of 1 with phenyl isocyanate afforded a paramagnetic complex, [(η8-Pnâ )Ti]2(ÎŒ,Îș2:Îș2-O2CNPh) (4), in which the âdouble-sandwichâ architecture of 1 has been broken and an unusual phenyl-carbonimidate ligand bridges two formally Ti(III) centers. Reaction of 1 with diphenyl dichalcogenides, Ph2E2 (E = S, Se, Te), led to the series of TiâTi single-bonded complexes (ÎŒ,η5:η5-Pnâ )2[Ti(EPh)]2 (E = S (5), Se (6), Te (7)), which can be considered the result of a 2eâ redox reaction or a 1,2-addition across the TiâTi bond. Treatment of 1 with azobenzene or phenyl azide afforded [(η8-Pnâ )Ti]2(ÎŒ-NPh)2 (8), a bridging imido complex in which the pentalene ligands bind in an η8 fashion to each formally Ti(IV) center, as the result of a 4eâ redox reaction driven by the oxidative cleavage of the TiâTi double bond. The new complexes 2â8 were extensively characterized by various techniques including multinuclear NMR spectroscopy and single-crystal X-ray diffraction, and the experimental work was complemented by density functional theory (DFT) studies
Ambiguity, multiple streams, and EU policy
The multiple streams framework draws insight from interactions between agency and institutions to explore the impact of context, time, and meaning on policy change and to assess the institutional and issue complexities permeating the European Union (EU) policy process. The authors specify the assumptions and structure of the framework and review studies that have adapted it to reflect more fully EU decision-making processes. The nature of policy entrepreneurship and policy windows are assessed to identify areas of improvement. Finally, the authors sketch out a research agenda that refines the logic of political manipulation which permeates the lens and the institutional complexity which frames the EU policy process
Early Observations of the Type Ia Supernova iPTF 16abc: A Case of Interaction with Nearby, Unbound Material and/or Strong Ejecta Mixing
Early observations of Type Ia supernovae (SNe Ia) provide a unique probe of
their progenitor systems and explosion physics. Here we report the intermediate
Palomar Transient Factory (iPTF) discovery of an extraordinarily young SN Ia,
iPTF 16abc. By fitting a power law to our early light curve, we infer that
first light for the SN, that is when the SN could have first been detected by
our survey, occurred only days before our first
detection. In the 24 hr after discovery, iPTF 16abc rose by 2 mag,
featuring a near-linear rise in flux for 3 days. Early spectra show
strong C II absorption, which disappears after 7 days. Unlike the
extensivelyobserved SN Ia SN 2011fe, the colors of iPTF 16abc are
blue and nearly constant in the days after explosion. We show that our early
observations of iPTF 16abc cannot be explained by either SN shock breakout and
the associated, subsequent cooling or the SN ejecta colliding with a stellar
companion. Instead, we argue that the early characteristics of iPTF 16abc,
including (i) the rapid, near-linear rise, (ii) the nonevolving blue colors,
and (iii) the strong C II absorption, are the result of either ejecta
interaction with nearby, unbound material or vigorous mixing of radioactive
Ni in the SN ejecta, or a combination of the two. In the next few years,
dozens of very young \textit{normal} SNe Ia will be discovered, and
observations similar to those presented here will constrain the white dwarf
explosion mechanism.Comment: 18 pages, 12 figures, accepted by Ap
A two-stage mechanism of viral RNA compaction revealed by single molecule fluorescence
Long RNAs often exist as multiple conformers in equilibrium. For the genomes of single-stranded RNA viruses, one of these conformers must include a compacted state allowing the RNA to be confined within the virion. We have used single molecule fluorescence correlation spectroscopy to monitor the conformations of viral genomes and sub-fragments in the absence and presence of coat proteins. Cognate RNA-coat protein interactions in two model viruses cause a rapid collapse in the hydrodynamic radii of their respective RNAs. This is caused by protein binding at multiple sites on the RNA that facilitate additional protein-protein contacts. The collapsed species recruit further coat proteins to complete capsid assembly with great efficiency and fidelity. The specificity in RNA-coat protein interactions seen at single-molecule concentrations reflects the packaging selectivity seen for such viruses in vivo. This contrasts with many in vitro reassembly measurements performed at much higher concentrations. RNA compaction by coat protein or polycation binding are distinct processes, implying that defined RNA-coat protein contacts are required for assembly
Whole grain intakes in the diets of Irish children and teenagers
A growing body of evidence supports the inclusion of whole grain foods in the diet to help prevent certain chronic diseases. Although much of the research has been conducted in adult cohorts, it is thought that younger populations may also benefit from whole-grain-rich diets. The aim of the present study was to quantify the intake of whole grain in Irish children and teenagers, and assess the major sources of intake. Data used in the present study were from the National Children's Food Survey and the National Teens' Food Survey, which used 7d food diaries to collect data on habitual food and beverage consumption in representative samples of Irish children and teenagers. Results showed that over 90% of children (5-12 years) and over 86% of teenagers (13-17 years) are consumers of whole grain, with mean daily intakes of 18·5 and 23·2g/d, respectively. Ready-to-eat breakfast cereals made the greatest contribution to whole grain intakes for both children and teenagers (59·3 and 44·3%), followed by bread (14·4 and 26·5%), with wheat being the major source of intake, accounting for over 65% of all whole grains consumed. Whole grain consumers had significantly higher intakes of fibre, P and Mg in comparison with non-consumers of whole grain, even though whole grain intakes in this sample were well below the recommendation of three servings or 48g/d. The present study characterises, for the first time, the patterns of whole grain consumption in Irish children and teenagers and shows whole grain intake to be lo
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