3,948 research outputs found
Dissecting the Functions of Conserved Prolines within Transmembrane Helices of the D2 Dopamine Receptor
G protein-coupled receptors (GPCRs) contain a number of conserved proline residues in their transmembrane helices, and it is generally assumed these play important functional and/or structural roles. Here we use unnatural amino acid mutagenesis, employing α-hydroxy acids and proline analogues, to examine the functional roles of five proline residues in the transmembrane helices of the D2 dopamine receptor. The well-known tendency of proline to disrupt helical structure is important at all sites, while we find no evidence for a functional role for backbone amide cis–trans isomerization, another feature associated with proline. At most proline sites, the loss of the backbone NH is sufficient to explain the role of the proline. However, at one site, P210^(5.50), a substituent on the backbone N appears to be essential for proper function. Interestingly, the pattern in functional consequences that we see is mirrored in the pattern of structural distortions seen in recent GPCR crystal structures
Reducing fuel consumption by using a new fuel-efficiency support tool
A fuel-efficiency support tool has been designed, which includes a normative model describing optimal driver behaviour for minimising fuel consumption. If actual behaviour deviates from optimal behaviour, the system presents advice on how to change behaviour. Evaluation revealed that drivers used ~16% less fuel compared with `normal driving
International Comparisons of R&D Expenditure: Does an R&D PPP Make a Difference?
Purchasing power parities (PPPs) for R&D expenditure in 19 manufacturing industries are developed for France, Germany, Japan, the Netherlands and the United Kingdom relative to the United States for the years 1997 and 1987. These PPPs are based on R&D input prices for specific cost categories and differ substantially from current practice of comparing R&D expenditure using GDP PPPs and deflators. After taking into account differences in the relative price of R&D labor and materials, separate PPPs for other R&D cost categories are less essential, and a simpler version using GDP PPPs for these other categories should suffice. Our preferred PPPs are used to compare international R&D costs and intensity. The results suggest that the efforts devoted to R&D in each country are more similar across countries than is apparent using the nominal R&D intensities that are currently the norm.
Non-thermal radio emission from O-type stars III. Is Cyg OB2 No. 9 a wind-colliding binary?
The star Cyg OB2 No. 9 is a well-known non-thermal radio emitter. Recent
theoretical work suggests that all such O-stars should be in a binary or a
multiple system. However, there is no spectroscopic evidence of a binary
component. Re-analysis of radio observations from the VLA of this system over
25 years has revealed that the non-thermal emission varies with a period of
2.35+-0.02 yr. This is interpreted as a strong suggestion of a binary system,
with the non-thermal emission arising in a wind-collision region. We derived
some preliminary orbital parameters for this putative binary and revised the
mass-loss rate of the primary star downward from previous estimates.Comment: 13 pages, 5 figures, includes online data, accepted by A&
Non-thermal radio emission from O-type stars. IV. Cyg OB2 No. 8A
We study the non-thermal radio emission of the binary Cyg OB2 No. 8A, to see
if it is variable and if that variability is locked to the orbital phase. We
investigate if the synchrotron emission generated in the colliding-wind region
of this binary can explain the observations and we verify that our proposed
model is compatible with the X-ray data. We use both new and archive radio data
from the Very Large Array (VLA) to construct a light curve as a function of
orbital phase. We also present new X-ray data that allow us to improve the
X-ray light curve. We develop a numerical model for the colliding-wind region
and the synchrotron emission it generates. The model also includes free-free
absorption and emission due to the stellar winds of both stars. In this way we
construct artificial radio light curves and compare them with the observed one.
The observed radio fluxes show phase-locked variability. Our model can explain
this variability because the synchrotron emitting region is not completely
hidden by the free-free absorption. In order to obtain a better agreement for
the phases of minimum and maximum flux we need to use stellar wind parameters
for the binary components which are somewhat different from typical values for
single stars. We verify that the change in stellar parameters does not
influence the interpretation of the X-ray light curve. Our model has trouble
explaining the observed radio spectral index. This could indicate the presence
of clumping or porosity in the stellar wind, which - through its influence on
both the Razin effect and the free-free absorption - can considerably influence
the spectral index. Non-thermal radio emitters could therefore open a valuable
pathway to investigate the difficult issue of clumping in stellar winds.Comment: 19 pages, 10 figures, accepted by A&
On disjoint Borel uniformizations
Larman showed that any closed subset of the plane with uncountable vertical
cross-sections has aleph_1 disjoint Borel uniformizing sets. Here we show that
Larman's result is best possible: there exist closed sets with uncountable
cross-sections which do not have more than aleph_1 disjoint Borel
uniformizations, even if the continuum is much larger than aleph_1. This
negatively answers some questions of Mauldin. The proof is based on a result of
Stern, stating that certain Borel sets cannot be written as a small union of
low-level Borel sets. The proof of the latter result uses Steel's method of
forcing with tagged trees; a full presentation of this method, written in terms
of Baire category rather than forcing, is given here
ISO spectroscopy of circumstellar dust in the Herbig Ae systems AB Aur and HD 163296
Using both the Short- and Long-wavelength Spectrometers on board the Infrared
Space Observatory (ISO), we have obtained infrared spectra of the Herbig Ae
systems AB Aur and HD 163296. In addition, we obtained ground-based N band
images of HD 163296. Our results can be summarized as follows: (1) The main
dust components in AB Aur are amorphous silicates, iron oxide and PAHs; (2) The
circumstellar dust in HD 163296 consists of amorphous silicates, iron oxide,
water ice and a small fraction of crystalline silicates; (3) The infrared
fluxes of HD 163296 are dominated by solid state features; (4) The colour
temperature of the underlying continuum is much cooler in HD 163296 than in AB
Aur, pointing to the existence of a population of very large (mm sized) dust
grains in HD 163296; (5) The composition and degree of crystallization of
circumstellar dust are poorly correlated with the age of the central star. The
processes of crystallization and grain growth are also not necessarily coupled.
This means that either the evolution of circumstellar dust in protoplanetary
disks happens very rapidly (within a few Myr), or that this evolution is
governed by factors other than stellar mass and age.Comment: 6 pages, 2 figures, accepted for publication in Astronomy &
Astrophysic
High resolution radio observations of the colliding-wind binary WR140
Milli-arcsecond resolution Very Long Baseline Array (VLBA) observations of
the archetype WR+O star colliding-wind binary (CWB) system WR140 are presented
for 23 epochs between orbital phases 0.74 and 0.97. At 8.4 GHz, the emission in
the wind-collision region (WCR) is clearly resolved as a bow-shaped arc that
rotates as the orbit progresses. We interpret this rotation as due to the O
star moving from SE to approximately E of the WR star, which leads to solutions
for the orbit inclination of 122+/-5 deg, the longitude of the ascending node
of 353+/-3 deg, and an orbit semi-major axis of 9.0+/-0.5 mas. The distance to
WR140 is determined to be 1.85+/-0.16 kpc, which requires the O star to be a
supergiant. The inclination implies the mass of the WR and O star to be 20+/-4
and 54+/-10 solar masses respectively. We determine a wind-momentum ratio of
0.22, with an expected half-opening angle for the WCR of 63 deg, consistent
with 65+/-10 deg derived from the VLBA observations. Total flux measurements
from Very Large Array (VLA) observations show the radio emission from WR140 is
very closely the same from one orbit to the next, pointing strongly toward
emission, absorption and cooling mechanism(s) that are controlled largely by
the orbital motion. The synchrotron spectra evolve dramatically through the
orbital phases observed, exhibiting both optically thin and optically thick
emission. We discuss a number of absorption and cooling mechanisms that may
determine the evolution of the synchrotron spectrum with orbital phase.Comment: Accepted by ApJ, to appear in v623, April 20, 2005. 14 pages, 13
figs, requires emulateapj.cls. A version with full resolution figs can be
obtained from http://www.drao.nrc.ca/~smd/preprint/wr140_data.pd
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