757 research outputs found
On the magnetic accretor GK Persei in outburst
RXTE made 5 X-ray observations of the magnetic accretor GK Per during its
1996 outburst, recording a count rate of ten times the quiescent level. The
351-s spin pulse shows a deep, nearly sinusoidal modulation, in contrast to the
weaker, double-humped profile of quiescence. The spectrum shows absorption
increased by two orders of magnitude over quiescence. We explain these
differences in terms of the changing accretion geometry as the outbursting disc
forces the magnetosphere inwards, and discuss the 5000-s X-ray QPOs seen during
GK Per's outbursts.Comment: To appear in MNRAS; 5 page
Lion Localizer: A Software tool for inferring the provenance of lions (Panthera leo) based on their mitochondrial DNA
On the nature of the X-ray source in GK Per
We report XMM-Newton observations of the intermediate polar (IP) GK Per on
the rise to the 2002 outburst and compare them to Chandra observations during
quiescence. We find an asymmetric spin light curve implying an asymmetric shape
of a semi-transparent accretion curtain. A low Fe xvii (15.01/15.26 A) line
flux ratio confirms the need for an asymmetric geometry and significant effects
of resonant line scattering. Medium resolution spectra in outburst and
quiescence are both fitted with a leaky absorber model for the post shock hard
X-ray emission, a black body (outburst) for the thermalized X-ray emission from
the white dwarf and an optically thin spectrum. The difference between high and
low spin as well as QPO/flares states can be explained by a variation in the
absorbing column density. The Fe fluorescence at 6.4 keV (equivalent width of
447 eV) is not significantly variable during spin cycle or on QPO periods.
High-resolution RGS spectra reveal a number of emission lines from H-like and
He-like elements. The lines are broader than the instrumental response with a
roughly constant velocity dispersion for different lines, indicating identical
origin. He-like emission lines are used to give values for the electron
densities of log n_e ~ 12. We do not detect any variation in the emission lines
during the spin cycle, implying that the lines are not noticeably obscured or
absorbed. We conclude that they originate in the accretion curtains and propose
a model for their shape.Comment: 14 pages, 22 figures, accepted by A&A; text re quiescent data changed
slightly, references adde
The unusual 2006 dwarf nova outburst of GK Perseii
The 2006 outburst of GK Perseii differed significantly at optical and
ultraviolet wavelengths from typical outbursts of this object. We present
multi-wavelength (X-ray, UV and optical) Swift and AAVSO data, giving
unprecedented broad-band coverage of the outburst, allowing us to follow the
evolution of the longer-than-normal 2006 outburst across these wavelengths. In
the optical and UV we see a triple-peaked morphology with maximum brightness
~1.5 magnitudes lower than in previous years. In contrast, the peak hard X-ray
flux is the same as in previous outbursts. We resolve this dichotomy by
demonstrating that the hard X-ray flux only accounts for a small fraction of
the total energy liberated during accretion, and interpret the optical/UV
outburst profile as arising from a series of heating and cooling waves
traversing the disc, caused by its variable density profile.Comment: 9 pages, 7 figures, accepted for publication in MNRA
Periplakin, a novel component of cornified envelopes and desmosomes that belongs to the plakin family and forms complexes with envoplakin
The cornified envelope is a layer of transglutaminase cross-linked protein that is assembled under the plasma membrane of keratinocytes in the outermost layers of the epidermis. We have determined the cDNA sequence of one of the proteins that becomes incorporated into the cornified envelope of cultured epidermal keratinocytes, a protein with an apparent molecular mass of 195 kD that is encoded by a mRNA with an estimated size of 6.3 kb. The protein is expressed in keratinizing and nonkeratinizing stratified squamous epithelia and in a number of other epithelia. Expression of the protein is upregulated during the terminal differentiation of epidermal keratinocytes in vivo and in culture. Immunogold electron microscopy was used to demonstrate an association of the 195-kD protein with the desmosomal plaque and with keratin filaments in the differentiated layers of the epidermis. Sequence analysis showed that the 195-kD protein is a member of the plakin family of proteins, to which envoplakin, desmoplakin, bullous pemphigoid antigen 1, and plectin belong. Envoplakin and the 195-kD protein coimmunoprecipitate. Analysis of their rod domain sequences suggests that the formation of both homodimers and heterodimers would be energetically favorable. Confocal immunofluorescent microscopy of cultured epidermal keratinocytes revealed that envoplakin and the 195-kD protein form a network radiating from desmosomes, and we speculate that the two proteins may provide a scaffolding onto which the cornified envelope is assembled. We propose to name the 195-kD protein periplakin
Hybridization Capture Using Short PCR Products Enriches Small Genomes by Capturing Flanking Sequences (CapFlank)
Solution hybridization capture methods utilize biotinylated oligonucleotides as baits to enrich homologous sequences from next generation sequencing (NGS) libraries. Coupled with NGS, the method generates kilo to gigabases of high confidence consensus targeted sequence. However, in many experiments, a non-negligible fraction of the resulting sequence reads are not homologous to the bait. We demonstrate that during capture, the bait-hybridized library molecules add additional flanking library sequences iteratively, such that baits limited to targeting relatively short regions (e.g. few hundred nucleotides) can result in enrichment across entire mitochondrial and bacterial genomes. Our findings suggest that some of the off-target sequences derived in capture experiments are non-randomly enriched, and that CapFlank will facilitate targeted enrichment of large contiguous sequences with minimal prior target sequence information. (Résumé d'auteur
Altered vascular smooth muscle function in the ApoE knockout mouse during the progression of atherosclerosis
Objectives:
Relaxation of vascular smooth muscle (VSM) requires re-uptake of cytosolic Ca2+ into the sarcoplasmic reticulum (SR) via the Sarco/Endoplasmic Reticulum Ca2+ ATPase (SERCA), or extrusion via the Plasma Membrane Ca2+ ATPase (PMCA) or sodium Ca2+ exchanger (NCX). Peroxynitrite, a reactive species formed in vascular inflammatory diseases, upregulates SERCA activity to induce relaxation but, chronically, can contribute to atherogenesis and altered vascular function by escalating endoplasmic reticulum stress. Our objectives were to determine if peroxynitrite-induced relaxation and Ca2+ handling processes within vascular smooth muscle cells were altered as atherosclerosis develops.<p></p>
Methods:
Aortae from control and ApoE−/− mice were studied histologically, functionally and for protein expression levels of SERCA and PMCA. Ca2+ responses were assessed in dissociated aortic smooth muscle cells in the presence and absence of extracellular Ca2+.<p></p>
Results:
Relaxation to peroxynitrite was concentration-dependent and endothelium-independent. The abilities of the SERCA blocker thapsigargin and the PMCA inhibitor carboxyeosin to block this relaxation were altered during fat feeding and plaque progression. SERCA levels were progressively reduced, while PMCA expression was upregulated. In ApoE−/− VSM cells, increases in cytosolic Ca2+ [Ca2+]c in response to SERCA blockade were reduced, while SERCA-independent Ca2+ clearance was faster compared to control.<p></p>
Conclusion:
As atherosclerosis develops in the ApoE−/− mouse, expression and function of Ca2+ handling proteins are altered. Up-regulation of Ca2+ removal via PMCA may offer a potential compensatory mechanism to help normalise the dysfunctional relaxation observed during disease progression
Biome-specific effects of nitrogen and phosphorus on the photosynthetic characteristics of trees at a forest-savanna boundary in Cameroon
Journal ArticleThe final publication is available at Springer via http://dx.doi.org/10.1007/s00442-015-3250-5Photosynthesis/nutrient relationships of proximally growing forest and savanna trees were determined in an ecotonal region of Cameroon (Africa). Although area-based foliar N concentrations were typically lower for savanna trees, there was no difference in photosynthetic rates between the two vegetation formation types. Opposite to N, area-based P concentrations were—on average—slightly lower for forest trees; a dependency of photosynthetic characteristics on foliar P was only evident for savanna trees. Thus savanna trees use N more efficiently than their forest counterparts, but only in the presence of relatively high foliar P. Along with some other recent studies, these results suggest that both N and P are important modulators of woody tropical plant photosynthetic capacities, influencing photosynthetic metabolism in different ways that are also biome specific. Attempts to find simple unifying equations to describe woody tropical vegetation photosynthesis-nutrient relationships are likely to meet with failure, with ecophysiological distinctions between forest and savanna requiring acknowledgement.Natural Environment Research Council (NERC) TROBIT consortiumRoyal Society - University Research Fellowshi
Numerical Renormalization Group Study of Kondo Effect in Unconventional Superconductors
Orbital degrees of freedom of a Cooper pair play an important role in the
unconventional superconductivity. To elucidate the orbital effect in the Kondo
problem, we investigated a single magnetic impurity coupled to Cooper pairs
with a () symmetry using the numerical
renormalization group method. It is found that the ground state is always a
spin doublet. The analytical solution for the strong coupling limit explicitly
shows that the orbital dynamics of the Cooper pair generates the spin 1/2 of
the ground state.Comment: 4 pages, 2 figures, JPSJ.sty, to be published in J. Phys. Soc. Jpn.
70 (2001) No. 1
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