101 research outputs found
On the structure of the directions not determined by a large affine point set
Given a point set in an -dimensional affine space of size
, we obtain information on the structure of the set of
directions that are not determined by , and we describe an application in
the theory of partial ovoids of certain partial geometries
Native Desorption Electrospray Ionization Liberates Soluble and Membrane Protein Complexes from Surfaces
Mass spectrometry (MS) applications for intact protein complexes typically require electrospray (ES) ionization and have not been achieved via direct desorption from surfaces. Desorption ES ionization (DESI) MS has however transformed the study of tissue surfaces through release and characterisation of small molecules. Motivated by the desire to screen for ligand binding to intact protein complexes we report the development of a native DESI platform. By establishing conditions that preserve non‐covalent interactions we exploit the surface to capture a rapid turnover enzyme–substrate complex and to optimise detergents for membrane protein study. We demonstrate binding of lipids and drugs to membrane proteins deposited on surfaces and selectivity from a mix of related agonists for specific binding to a GPCR. Overall therefore we introduce this native DESI platform with the potential for high‐throughput ligand screening of some of the most challenging drug targets including GPCRs
The death of massive stars - I. Observational constraints on the progenitors of type II-P supernovae
We present the results of a 10.5 yr, volume limited (28 Mpc) search for
supernova (SN) progenitor stars. We compile all SNe discovered within this
volume (132, of which 27% are type Ia) and determine the relative rates of each
sub-type from literature studies : II-P (59%), Ib/c (29%), IIb (5%), IIn (4%)
and II-L (3%). Twenty II-P SNe have high quality optical or near-IR
pre-explosion images that allow a meaningful search for the progenitor stars.
In five cases they are clearly red supergiants, one case is unconstrained, two
fall on compact coeval star clusters and the other twelve have no progenitor
detected. We review and update all the available data for the host galaxies
(distance, metallicity and extinction) and determine masses and upper mass
estimates using the STARS stellar evolutionary code and a single consistent
homogeneous method. A maximum likelihood calculation suggests that the minimum
stellar mass for a type II-P to form is m(min)=8.5 +1/-1.5 Msol and the maximum
mass for II-P progenitors is m(max)=16.5 +/- 1.5 Msol, assuming a Salpeter
initial mass function (in the range Gamma = -1.35 +0.3/-0.7). The minimum mass
is consistent with current estimates for white dwarf progenitor masses, but the
maximum mass does not appear consistent with massive star populations. Red
supergiants in the Local Group have masses up to 25Msol and the minimum mass to
produce a Wolf-Rayet star in single star evolution (between solar and LMC
metallicity) is similarly 25-30 Msol. We term this discrepancy the "red
supergiant problem" and speculate that these stars could have core masses high
enough to form black holes and SNe which are too faint to have been detected.
Low luminosity SNe with low 56Ni production seem to arise from explosions of
low mass progenitors near the mass threshold for core-collapse. (abridged).Comment: 37 pages, 9 figs, accepted for publication in MNRA
A conserved myotubularin-related phosphatase regulates autophagy by maintaining autophagic flux
Macroautophagy (autophagy) targets cytoplasmic cargoes to the lysosome for degradation. Like all vesicle trafficking, autophagy relies on phosphoinositide identity, concentration, and localization to execute multiple steps in this catabolic process. Here, we screen for phosphoinositide phosphatases that influence autophagy in Drosophila and identify CG3530. CG3530 is homologous to the human MTMR6 subfamily of myotubularin-related 3-phosphatases, and therefore, we named it dMtmr6. dMtmr6, which is required for development and viability in Drosophila, functions as a regulator of autophagic flux in multiple Drosophila cell types. The MTMR6 family member MTMR8 has a similar function in autophagy of higher animal cells. Decreased dMtmr6 and MTMR8 function results in autophagic vesicle accumulation and influences endolysosomal homeostasis
SN 2005cs in M51 II. Complete Evolution in the Optical and the Near-Infrared
We present the results of the one year long observational campaign of the
type II-plateau SN 2005cs, which exploded in the nearby spiral galaxy M51 (the
Whirlpool Galaxy). This extensive dataset makes SN 2005cs the best observed
low-luminosity, 56Ni-poor type II-plateau event so far and one of the best
core-collapse supernovae ever. The optical and near-infrared spectra show
narrow P-Cygni lines characteristic of this SN family, which are indicative of
a very low expansion velocity (about 1000 km/s) of the ejected material. The
optical light curves cover both the plateau phase and the late-time radioactive
tail, until about 380 days after core-collapse. Numerous unfiltered
observations obtained by amateur astronomers give us the rare opportunity to
monitor the fast rise to maximum light, lasting about 2 days. In addition to
optical observations, we also present near-infrared light curves that (together
with already published UV observations) allow us to construct for the first
time a reliable bolometric light curve for an object of this class. Finally,
comparing the observed data with those derived from a semi-analytic model, we
infer for SN 2005cs a 56Ni mass of about 0.003 solar masses, a total ejected
mass of 8-13 solar masses and an explosion energy of about 3 x 10^50 erg.Comment: 18 pages, 18 figures, accepted for publication in MNRA
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