462 research outputs found
Descartes, corpuscles and reductionism : mechanism and systems in Descartes' physiology
I argue that Descartes explains physiology in terms of whole systems, and not in terms of the size, shape and motion of tiny corpuscles (corpuscular mechanics). It is a standard, entrenched view that Descartes’s proper means of explanation in the natural world is through strict reduction to corpuscular mechanics. This view is bolstered by a handful of corpuscular-mechanical explanations in Descartes’s physics, which have been taken to be representative of his treatment of all natural phenomena. However, Descartes’s explanations of the ‘principal parts’ of physiology do not follow the corpuscular–mechanical pattern. Des Chene (2001) has identified systems in Descartes’s account of physiology, but takes them ultimately to reduce down to the corpuscle level. I argue that they do not. Rather, Descartes maintains entire systems, with components selected from multiple levels of organisation, in order to construct more complete explanations than corpuscular mechanics alone would allow
Open cluster candidates in the VVVX area: VVVX CL 076 and CL 077
We are reporting some basic parameters of two newly discovered clusters, VVVX CL 076 and CL 077, recently discovered in the galactic disk area covered by the VISTA Variables in the Via Lactea eXtended (VVVX) ESO Public Survey. The preliminary analysis shows that both clusters are young and relatively close to the Sun.Peer reviewedFinal Published versio
Involvement of Plasmodium falciparum protein kinase CK2 in the chromatin assembly pathway
<p>Abstract</p> <p>Background</p> <p>Protein kinase CK2 is a pleiotropic serine/threonine protein kinase with hundreds of reported substrates, and plays an important role in a number of cellular processes. The cellular functions of <it>Plasmodium falciparum </it>CK2 (PfCK2) are unknown. The parasite's genome encodes one catalytic subunit, PfCK2α, which we have previously shown to be essential for completion of the asexual erythrocytic cycle, and two putative regulatory subunits, PfCK2β1 and PfCK2β2.</p> <p>Results</p> <p>We now show that the genes encoding both regulatory PfCK2 subunits (PfCK2β1 and PfCK2β2) cannot be disrupted. Using immunofluorescence and electron microscopy, we examined the intra-erythrocytic stages of transgenic parasite lines expressing hemagglutinin (HA)-tagged catalytic and regulatory subunits (HA-CK2α, HA-PfCK2β1 or HA-PfCK2β2), and localized all three subunits to both cytoplasmic and nuclear compartments of the parasite. The same transgenic parasite lines were used to purify PfCK2β1- and PfCK2β2-containing complexes, which were analyzed by mass spectrometry. The recovered proteins were unevenly distributed between various pathways, with a large proportion of components of the chromatin assembly pathway being present in both PfCK2β1 and PfCK2β2 precipitates, implicating PfCK2 in chromatin dynamics. We also found that chromatin-related substrates such as nucleosome assembly proteins (Naps), histones, and two members of the Alba family are phosphorylated by PfCK2α <it>in vitro</it>.</p> <p>Conclusions</p> <p>Our reverse-genetics data show that each of the two regulatory PfCK2 subunits is required for completion of the asexual erythrocytic cycle. Our interactome study points to an implication of PfCK2 in many cellular pathways, with chromatin dynamics being identified as a major process regulated by PfCK2. This study paves the way for a kinome-wide interactomics-based approach to elucidate protein kinase function in malaria parasites.</p
Modeling Variable Linear Polarization Produced by Co-Rotating Interaction Regions (CIRs) Across Optical Recombination Lines of Wolf-Rayet Stars
Massive star winds are structured both stochastically ("clumps") and often
coherently (Co-rotation Interaction Regions, or CIRs). Evidence for CIRs
threading the winds of Wolf-Rayet (WR) stars arises from multiple diagnostics
including linear polarimetry. Some observations indicate changes in
polarization position angle across optical recombination emission lines from a
WR star wind but limited to blueshifted Doppler velocities. We explore a model
involving a spherical wind with a single conical CIR stemming from a rotating
star as qualitative proof-of-concept. To obtain a realistic distribution of
limb polarization and limb darkening across the pseudo-photosphere formed in
the optically thick wind of a WR star, we used Monte Carlo radiative transfer
(MCRT). Results are shown for a parameter study. For line properties similar to
WR 6 (EZ CMa; HD 50896), the combination of the MCRT results, a simple model
for the CIR, and the Sobolev approximation for the line formation, we were able
to reproduce variations in both polarization amplitude and position angle
commensurate with observations. Characterizing CIRs in WR~winds has added
importance for providing stellar rotation periods since the v sin i values are
unobtainable because the pseudo-photosphere forms in the wind itself.Comment: This is a pre-copyedited, author-produced PDF of an article accepted
for publication in MNRAS following peer revie
Premenopausal endogenous oestrogen levels and breast cancer risk: a meta-analysis.
BACKGROUND: Many of the established risk factors for breast cancer implicate circulating hormone levels in the aetiology of the disease. Increased levels of postmenopausal endogenous oestradiol (E2) have been found to increase the risk of breast cancer, but no such association has been confirmed in premenopausal women. We carried out a meta-analysis to summarise the available evidence in women before the menopause. METHODS: We identified seven prospective studies of premenopausal endogenous E2 and breast cancer risk, including 693 breast cancer cases. From each study we extracted odds ratios of breast cancer between quantiles of endogenous E2, or for unit or s.d. increases in (log transformed) E2, or (where odds ratios were unavailable) summary statistics for the distributions of E2 in breast cancer cases and unaffected controls. Estimates for a doubling of endogenous E2 were obtained from these extracted estimates, and random-effect meta-analysis was used to obtain a pooled estimate across the studies. RESULTS: Overall, we found weak evidence of a positive association between circulating E2 levels and the risk of breast cancer, with a doubling of E2 associated with an odds ratio of 1.10 (95% CI: 0.96, 1.27). CONCLUSION: Our findings are consistent with the hypothesis of a positive association between premenopausal endogenous E2 and breast cancer risk
Metallicity variations in the Type II globular cluster NGC6934
The Hubble Space Telescope photometric survey of Galactic globular clusters
(GCs) has revealed a peculiar "chromosome map" for NGC6934. Besides a typical
sequence, similar to that observed in Type I GCs, NGC 6934 displays additional
stars on the red side, analogous to the anomalous, Type II GCs, as defined in
our previous work. We present a chemical abundance analysis of four red giants
in this GC. Two stars are located on the chromosome map sequence common to all
GCs, and another two on the additional sequence. We find: (i) star-to-star Fe
variations, with the two anomalous stars being enriched by ~0.2 dex. Due to our
small-size sample, this difference is at the ~2.5 sigma level; (ii) no evidence
for variations in the slow neutron-capture abundances over Fe, at odds with
what is often observed in anomalous Type II GCs, e.g. M 22 and Omega Centauri;
(iii) no large variations in light elements C, O and Na, compatible with the
targets location on the lower part of the chromosome map where such variations
are not expected. Since the analyzed stars are homogeneous in light elements,
the only way to reproduce the photometric splits on the sub-giant (SGB) and the
red-giant (RGB) branches is to assume that red-RGB/faint-SGB stars are enhanced
in [Fe/H] by ~0.2. This fact corroborates the spectroscopic evidence of a
metallicity variation in NGC6934. The observed chemical pattern resembles only
partially the other Type II GCs, suggesting that NGC6934 might belong either to
a third class of GCs, or be a link between normal Type I and anomalous Type II
GCs.Comment: 26 pages, 9 figures, accepted for publication in Ap
Infrared photometry and CaT spectroscopy of globular cluster M 28 (NGC 6626)
Recent studies show that the inner Galactic regions host genuine bulge
globular clusters, but also halo intruders, complex remnants of primordial
building blocks, and objects likely accreted during major merging events. In
this study we focus on the properties of M 28, a very old and massive cluster
currently located in the Galactic bulge. We analysed wide-field infrared
photometry collected by the VVV survey, VVV proper motions, and
intermediate-resolution spectra in the calcium triplet range for 113 targets in
the cluster area. Our results in general confirm previous estimates of the
cluster properties available in the literature. We find no evidence of
differences in metallicity between cluster stars, setting an upper limit of
Delta[Fe/H]<0.08 dex to any internal inhomogeneity. We confirm that M 28 is one
of the oldest objects in the Galactic bulge (13-14 Gyr). From this result and
the literature data, we find evidence of a weak age-metallicity relation among
bulge globular clusters that suggests formation and chemical enrichment. In
addition, wide-field density maps show that M 28 is tidally stressed and that
it is losing mass into the general bulge field. Our study indicates that M 28
is a genuine bulge globular cluster, but its very old age and its mass loss
suggest that this cluster could be the remnant of a larger structure, possibly
a primeval bulge building block.Comment: Accepted for publication in Astronomy & Astrophysic
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