4,245 research outputs found
Cross-linking of structural proteins in ageing skin: An in situ assay for the detection of amine oxidase activity
Transporter gene acquisition and innovation in the evolution of Microsporidia intracellular parasites.
The acquisition of genes by horizontal transfer can impart entirely new biological functions and provide an important route to major evolutionary innovation. Here we have used ancient gene reconstruction and functional assays to investigate the impact of a single horizontally transferred nucleotide transporter into the common ancestor of the Microsporidia, a major radiation of intracellular parasites of animals and humans. We show that this transporter provided early microsporidians with the ability to steal host ATP and to become energy parasites. Gene duplication enabled the diversification of nucleotide transporter function to transport new substrates, including GTP and NAD+, and to evolve the proton-energized net import of nucleotides for nucleic acid biosynthesis, growth and replication. These innovations have allowed the loss of pathways for mitochondrial and cytosolic energy generation and nucleotide biosynthesis that are otherwise essential for free-living eukaryotes, resulting in the highly unusual and reduced cells and genomes of contemporary Microsporidia
Properties of the Galactic population of cataclysmic variables in hard X-rays
We measure the spatial distribution and hard X-ray luminosity function of
cataclysmic variables (CVs) using the INTEGRAL all-sky survey in the 17-60 keV
energy band. The vast majority of the INTEGRAL detected CVs are intermediate
polars with luminosities in the range 10^{32}-10^{34} erg/sec. The scale height
of the Galactic disk population of CVs is found to be 130{+90}{-50} pc. The CV
luminosity function measured with INTEGRAL in hard X-rays is compatible with
that previously determined at lower energies (3--20 keV) using a largely
independent sample of sources detected by RXTE (located at |b|>10deg as opposed
to the INTEGRAL sample, strongly concentrated to the Galactic plane). The
cumulative 17-60 keV luminosity density of CVs per unit stellar mass is found
to be (1.3+/-0.3)x10^{27} erg/sec/Msun and is thus comparable to that of
low-mass X-ray binaries in this energy band. Therefore, faint but numerous CVs
are expected to provide an important contribution to the cumulative hard X-ray
emission of galaxies.Comment: 8 pages, 8 figures. Submitted to A&
The Galactic Plane at faint X-ray fluxes - I: Properties and characteristics of the X-ray source population
We investigate the serendipitous X-ray source population revealed in
XMM-Newton observations targeted in the Galactic Plane within the region
315<l<45 and |b|<2.5 deg. Our study focuses on a sample of 2204 X-ray sources
at intermediate to faint fluxes, which were detected in a total of 116 XMM
fields and are listed in the 2XMMi catalogue. We characterise each source as
spectrally soft or hard on the basis of whether the bulk of the recorded counts
have energies below or above 2 keV and find that the sample divides roughly
equally (56%:44%) into these soft and hard categories. The X-ray spectral form
underlying the soft sources may be represented as either a power-law continuum
with Gamma~2.5 or a thermal spectrum with kT~0.5 keV, with N_H ranging from
10^{20-22} cm^{-2}. For the hard sources, a significantly harder continuum form
is likely, i.e., Gamma~1 with N_H=10^{22-24} cm^{-2}. For ~50% of the hard
sources, the inferred column density is commensurate with the total Galactic
line-of-sight value; many of these sources will be located at significant
distances across the Galaxy implying a hard band luminosity L_X>10^{32} erg/s,
whereas some will be extragalactic interlopers. >90% of the soft sources have
potential NIR (2MASS and/or UKIDSS) counterparts inside their error circles,
consistent with the dominant soft X-ray source population being relatively
nearby coronally-active stars. These stellar counterparts are generally
brighter than J=16, a brightness cutoff which corresponds to the saturation of
the X-ray coronal emission at L_X=10^{-3} L_{bol}. In contrast, the success
rate in finding likely IR counterparts to the hard X-ray sample is no more than
~15% down to J=16 and ~25% down to J=20, set against a rapidly rising chance
coincidence rate. The make-up of the hard X-ray source population, in terms of
the known classes of accreting and non-accreting systems, remains uncertain.Comment: 17 pages, 17 figures, accepted for publication in MNRA
Is Context-aware Reasoning = Case-based Reasoning?
The purpose of this paper is to explore the similarities and differences and then argue for the potential synergies between two methodologies, namely Context-aware Reasoning and Case-based Reasoning, that are amongst the tools which can be used for intelligent environment (IE) system development. Through a case study supported by a review of the literature, we argue that context awareness and case based reasoning are not equal and are complementary methodologies to solve a domain specific problem, rather, the IE development paradigm must build a cooperation between these two approaches to overcome the individual drawbacks and to maximise the success of the IE systems
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