717 research outputs found
Anomalous microwave emission from spinning nanodiamonds around stars
Several interstellar environments produce 'anomalous microwave emission'
(AME), with brightness peaks at tens-of-gigahertz frequencies. The
emission's origins are uncertain -- rapidly spinning nanoparticles could
emit electric-dipole radiation, but the polycyclic aromatic hydrocarbons
that have been proposed as the carrier are now found not to correlate
with Galactic AME signals. The difficulty is in identifying co-spatial
sources over long lines of sight. Here we identify AME in three
proto-planetary discs. These are the only known systems that host
hydrogenated nanodiamonds, in contrast to the very common detection of
polycyclic aromatic hydrocarbons. Using spectroscopy, the nanodiamonds
are located close to the host stars, at physically well-constrained
temperatures. Developing disc models, we reproduce the emission with
diamonds 0.75--1.1 nm in radius, holding <= 1-2% of the carbon budget.
Ratios of microwave emission to stellar luminosity are approximately
constant, allowing nanodiamonds to be ubiquitous but emitting below
detection thresholds in many star systems. This result is compatible
with the findings with similar-sized diamonds found within Solar System
meteorites. As nanodiamond spectral absorption is seen in interstellar
sightlines, these particles are also a candidate for generating
galaxy-scale AME
A meta-analysis of the association between day-care attendance and childhood acute lymphoblastic leukaemia
Background Childhood acute lymphoblastic leukaemia (ALL) may be the result of a rare response to common infection(s) acquired by personal contact with infected individuals. A meta-analysis was conducted to examine the relationship between day-care attendance and risk of childhood ALL, specifically to address whether early-life exposure to infection is protective against ALL
Dusty Planetary Systems
Extensive photometric stellar surveys show that many main sequence stars show
emission at infrared and longer wavelengths that is in excess of the stellar
photosphere; this emission is thought to arise from circumstellar dust. The
presence of dust disks is confirmed by spatially resolved imaging at infrared
to millimeter wavelengths (tracing the dust thermal emission), and at optical
to near infrared wavelengths (tracing the dust scattered light). Because the
expected lifetime of these dust particles is much shorter than the age of the
stars (>10 Myr), it is inferred that this solid material not primordial, i.e.
the remaining from the placental cloud of gas and dust where the star was born,
but instead is replenished by dust-producing planetesimals. These planetesimals
are analogous to the asteroids, comets and Kuiper Belt objects (KBOs) in our
Solar system that produce the interplanetary dust that gives rise to the
zodiacal light (tracing the inner component of the Solar system debris disk).
The presence of these "debris disks" around stars with a wide range of masses,
luminosities, and metallicities, with and without binary companions, is
evidence that planetesimal formation is a robust process that can take place
under a wide range of conditions. This chapter is divided in two parts. Part I
discusses how the study of the Solar system debris disk and the study of debris
disks around other stars can help us learn about the formation, evolution and
diversity of planetary systems by shedding light on the frequency and timing of
planetesimal formation, the location and physical properties of the
planetesimals, the presence of long-period planets, and the dynamical and
collisional evolution of the system. Part II reviews the physical processes
that affect dust particles in the gas-free environment of a debris disk and
their effect on the dust particle size and spatial distribution.Comment: 68 pages, 25 figures. To be published in "Solar and Planetary
Systems" (P. Kalas and L. French, Eds.), Volume 3 of the series "Planets,
Stars and Stellar Systems" (T.D. Oswalt, Editor-in-chief), Springer 201
The debris disk host star HD 61005: a member of the Argus Association?
HD 61005 is a nearby young solar type star that shows a large infrared excess
due to a debris disk. The disk has been recently imaged from ground and space,
with indications of several components. Some characteristics of the disk
suggest the presence of planetary companions around the star, that remain
undetected in deep adaptive optics imaging. For a better understanding of the
system we aim to refine the determination of the stellar parameters, with
emphasis on the stellar age and system orientation. We used ASAS and Hipparcos
photometry and FEROS spectra to determine the rotation period, radial and
rotational velocity, chromospheric emission, effective temperature, and
chemical composition. We find no indication of any misalignment between the
star rotation axis and the disk. The standard age calibrations applied to
several indicators yield an age close to that of the Pleiades (120 Myr);
however the kinematic properties strongly support its membership in the younger
(40 Myr) Argus association, which also includes the IC 2391 open cluster.
Detailed comparison of the properties of HD 61005 and IC 2391 members shows
that the characteristics of HD 61005 are compatible with membership to the
Argus association, once its rather slow rotation is taken into account, because
lithium and other age indicators are somewhat correlated with stellar rotation
at a fixed age. We also identify systematic differences between the field and
cluster population of the Argus association, which are probably selection
effects, so we suggest that additional members with slower rotation and lower
activity level are waiting to be identified.Comment: A&A, in press, 13 pages, 11 figure
Radon and childhood cancer
British Journal of Cancer (2002) 87, 1336–1337. doi:10.1038/sj.bjc.6600671 www.bjcancer.co
Altered phobic reactions in frontotemporal dementia: a behavioural and neuroanatomical analysis
Introduction:
Abnormal behavioural and physiological reactivity to emotional stimuli is a hallmark of frontotemporal dementia (FTD), particularly the behavioural variant (bvFTD). As part of this repertoire, altered phobic responses have been reported in some patients with FTD but are poorly characterised.
Methods:
We collected data (based on caregiver reports) concerning the prevalence and nature of any behavioural changes related to specific phobias in a cohort of patients representing canonical syndromes of FTD and Alzheimer’s disease (AD), relative to healthy older controls. Neuroanatomical correlates of altered phobic reactivity were assessed using voxel-based morphometry.
Results:
46 patients with bvFTD, 20 with semantic variant primary progressive aphasia, 25 with non-fluent variant primary progressive aphasia, 29 with AD and 55 healthy age-matched individuals participated. Changes in specific phobia were significantly more prevalent in the combined FTD cohort (15.4% of cases) and in the bvFTD group (17.4%) compared both to healthy controls (3.6%) and patients with AD (3.5%). Attenuation of phobic reactivity was reported for individuals in all participant groups, however new phobias developed only in the FTD cohort. Altered phobic reactivity was significantly associated with relative preservation of grey matter in left posterior middle temporal gyrus, right temporo-occipital junction and right anterior cingulate gyrus, brain regions previously implicated in contextual decoding, salience processing and reward valuation.
Conclusion:
Altered phobic reactivity is a relatively common issue in patients with FTD, particularly bvFTD. This novel paradigm of strong fear experience has broad implications: clinically, for diagnosis and patient well-being; and neurobiologically, for our understanding of the pathophysiology of aversive sensory signal processing in FTD and the neural mechanisms of fear more generally
Lime stabilisation for earthworks: a UK perspective
Lime stabilisation is a versatile technique applied during earthworks operations. Modern soil recycling units are much more efficient at pulverising fill material and intermixing the added binder/water than machinery available 20 years ago. While supplier innovation adds flexibility to the site working method, specifications have not been sufficiently updated to permit optimal application. This review paper details the physico-chemical changes instigated through the lime-clay soil reaction, updating previous reviews. It aims to assist scientific debate, current practitioners and future specification changes. For example, the application of the minimum 24 h mellowing periods (mandatory to UK specifications) with high reactivity, quicklime powders is concluded to cause increased air voids in the compacted fill. Increased air voids are associated with reduced long-term strength and potential volume change from water ingress, which is of particular concern for sulfate swelling. Shorter mellowing periods and/or use of hydrated lime may lesson this issue; however, a 'one size fits all' approach is discouraged in preference to site-specific methodologies refined to suit the fill material and project requirements. The discussion also summarises working methods which may lower the risk of sulfate swell and defines areas requiring further practical research
Genetic Variation in the Chemical Components of Eucalyptus globulus Wood
Despite the ecological and economic importance of lignin and other wood chemical components, there are few studies of the natural genetic variation that exists within plant species and its adaptive significance. We used models developed from near infra-red spectroscopy to study natural genetic variation in lignin content and monomer composition (syringyl-to-guaiacyl ratio [S/G]) as well as cellulose and extractives content, using a 16-year-old field trial of an Australian tree species, Eucalyptus globulus. We sampled 2163 progenies of 467 native trees from throughout the native geographic range of the species. The narrow-sense heritability of wood chemical traits (0.25–0.44) was higher than that of growth (0.15), but less than wood density (0.51). All wood chemical traits exhibited significant broad-scale genetic differentiation (QST = 0.34–0.43) across the species range. This differentiation exceeded that detected with putatively neutral microsatellite markers (FST = 0.09), arguing that diversifying selection has shaped population differentiation in wood chemistry. There were significant genetic correlations among these wood chemical traits at the population and additive genetic levels. However, population differentiation in the S/G ratio of lignin in particular was positively correlated with latitude (R2 = 76%), which may be driven by either adaptation to climate or associated biotic factors
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