715 research outputs found
Miniaturized atmospheric ionization detector
A small scintillator-based detector for atmospheric ionization measurements
has been developed, partly in response to a need for better ionization data in
the weather-forming regions of the atmosphere and partly with the intention of
producing a commercially available device. The device can measure both the
count rate and energy of atmospheric ionizing radiation. Here we report results
of a test flight over the UK in December 2017 where the detector was flown with
two Geiger counters on a meteorological radiosonde. The count rate profile with
height was consistent both with the Geigers and with previous work. The energy
of incoming ionizing radiation increased substantially with altitude.Comment: Proc 18th Conference on Atmospheric Electricity, Nara, Japan, June
201
How did ocean warming affect Australian rainfall extremes during the 2010/2011 La Niña event?
Author Posting. © American Geophysical Union, 2015. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 42 (2015): 9942â9951, doi:10.1002/2015GL065948.Extreme rainfall conditions in Australia during the 2010/2011 La Niña resulted in devastating floods claiming 35 lives, causing billions of dollars in damages, and far-reaching impacts on global climate, including a significant drop in global sea level and record terrestrial carbon uptake. Northeast Australian 2010/2011 rainfall was 84% above average, unusual even for a strong La Niña, and soil moisture conditions were unprecedented since 1950. Here we demonstrate that the warmer background state increased the likelihood of the extreme rainfall response. Using atmospheric general circulation model experiments with 2010/2011 ocean conditions with and without long-term warming, we identify the mechanisms that increase the likelihood of extreme rainfall: additional ocean warming enhanced onshore moisture transport onto Australia and ascent and precipitation over the northeast. Our results highlight the role of long-term ocean warming for modifying rain-producing atmospheric circulation conditions, increasing the likelihood of extreme precipitation for Australia during future La Niña events.Australian Research Council (ARC); ARC Centre of Excellence for Climate System Science; ARC Laureate Fellowship program; Penzance and John P. Chase Memorial Endowed Funds; Ocean Climate Change Institute at WHOI2016-05-1
Discovery of a New Soft Gamma Repeater, SGR 1627-41
We report the discovery of a new soft gamma repeater (SGR), SGR 1627-41, and
present BATSE observations of the burst emission and BeppoSAX NFI observations
of the probable persistent X-ray counterpart to this SGR. All but one burst
spectrum are well fit by an optically thin thermal bremsstrahlung (OTTB) model
with kT values between 25 and 35 keV. The spectrum of the X-ray counterpart,
SAX J1635.8-4736, is similar to that of other persistent SGR X-ray
counterparts. We find weak evidence for a periodic signal at 6.41 s in the
light curve for this source. Like other SGRs, this source appears to be
associated with a young supernova remnant G337.0-0.1. Based upon the peak
luminosities of bursts observed from this SGR, we find a lower limit on the
dipole magnetic field of the neutron star B_dipole > 5 * 10^14 Gauss.Comment: 5 pages, 4 figures, submitted to ApJ Letter
Use of methods for specifying the target difference in randomised controlled trial sample size calculations : Two surveys of trialists' practice
© The Author(s), 2014.Peer reviewedPublisher PD
21-cm synthesis observations of VIRGOHI 21 - a possible dark galaxy in the Virgo Cluster
Many observations indicate that dark matter dominates the extra-galactic
Universe, yet no totally dark structure of galactic proportions has ever been
convincingly identified. Previously we have suggested that VIRGOHI 21, a 21-cm
source we found in the Virgo Cluster using Jodrell Bank, was a possible dark
galaxy because of its broad line-width (~200 km/s) unaccompanied by any visible
gravitational source to account for it. We have now imaged VIRGOHI 21 in the
neutral-hydrogen line and find what could be a dark, edge-on, spinning disk
with the mass and diameter of a typical spiral galaxy. Moreover, VIRGOHI 21 has
unquestionably been involved in an interaction with NGC 4254, a luminous spiral
with an odd one-armed morphology, but lacking the massive interactor normally
linked with such a feature. Numerical models of NGC 4254 call for a close
interaction ~10^8 years ago with a perturber of ~10^11 solar masses. This we
take as additional evidence for the massive nature of VIRGOHI 21 as there does
not appear to be any other viable candidate. We have also used the Hubble Space
Telescope to search for stars associated with the HI and find none down to an I
band surface brightness limit of 31.1 +/- 0.2 mag/sq. arcsec.Comment: 8 pages, accepted to ApJ, uses emulateapj.cls. Mpeg animation (Fig.
2) available at ftp://ftp.naic.edu/pub/publications/minchin/video2.mp
How do people with asthma use Internet sites containing patient experiences?
Objective: To understand how people engage with websites containing patient authored accounts of health and illness. To examine how people with asthma navigate their way through this information and make use of the patient experiences they find.
Methods: Twenty-nine patients with diagnoses ranging from mild to severe asthma were shown a range of websites, some containing patient experiences, and selected two sites to explore further. They discussed their choices in a series of focus groups and interviews.
Results: Participants were influenced initially by the design quality of the sites and were subsequently drawn to websites containing patient experiences but only when contributions were from similar people offering ârelevant storiesâ. The experiences reminded participants of the serious nature of the disease, provided new insights into the condition and an opportunity to reflect upon the role of the disease in their lives.
Conclusion: For people with asthma websites containing other patientsâ personal experiences can serve as a useful information resource, refresh their knowledge and ensure their health behaviours are appropriate and up-to-date.
Practice Implications: Health professionals should consider referring asthma patients to appropriate websites whilst being aware that online experiences are most engaging when they resonate with the participants own situation
Coupling carbon allocation with leaf and root phenology predicts tree-grass partitioning along a savanna rainfall gradient
The relative complexity of the mechanisms underlying savanna ecosystem dynamics, in comparison to other biomes such as temperate and tropical forests, challenges the representation of such dynamics in ecosystem and Earth system models. A realistic representation of processes governing carbon allocation and phenology for the two defining elements of savanna vegetation (namely trees and grasses) may be a key to understanding variations in treeâgrass partitioning in time and space across the savanna biome worldwide. Here we present a new approach for modelling coupled phenology and carbon allocation, applied to competing tree and grass plant functional types. The approach accounts for a temporal shift between assimilation and growth, mediated by a labile carbohydrate store. This is combined with a method to maximize long-term net primary production (NPP) by optimally partitioning plant growth between fine roots and (leaves + stem). The computational efficiency of the analytic method used here allows it to be uniquely and readily applied at regional scale, as required, for example, within the framework of a global biogeochemical model.
We demonstrate the approach by encoding it in a new simple carbonâwater cycle model that we call HAVANA (Hydrology and Vegetation-dynamics Algorithm for Northern Australia), coupled to the existing POP (Population Orders Physiology) model for tree demography and disturbance-mediated heterogeneity. HAVANA-POP is calibrated using monthly remotely sensed fraction of absorbed photosynthetically active radiation (fPAR) and eddy-covariance-based estimates of carbon and water fluxes at five tower sites along the North Australian Tropical Transect (NATT), which is characterized by large gradients in rainfall and wildfire disturbance. The calibrated model replicates observed gradients of fPAR, tree leaf area index, basal area, and foliage projective cover along the NATT. The model behaviour emerges from complex feedbacks between the plant physiology and vegetation dynamics, mediated by shifting above- versus below-ground resources, and not from imposed hypotheses about the controls on treeâgrass co-existence. Results support the hypothesis that resource limitation is a stronger determinant of tree cover than disturbance in Australian savannas.The contributions of V. Haverd and P. Briggs were made possible by the support of the Australian Climate
Change Science Program. B. Smith acknowledges funding as an OCE Distinguished Visiting Scientist to the CSIRO Oceans & Atmosphere Flagship, Canberr
Covariate-adjusted analysis of the Phase 3 REFLECT study of lenvatinib versus sorafenib in the treatment of unresectable hepatocellular carcinoma.
BACKGROUND: In the Phase 3 REFLECT trial in patients with unresectable hepatocellular carcinoma (uHCC), the multitargeted tyrosine kinase inhibitor, lenvatinib, was noninferior to sorafenib in the primary outcome of overall survival. Post-hoc review revealed imbalances in prognostic variables between treatment arms. Here, we re-analyse overall survival data from REFLECT to adjust for the imbalance in covariates. METHODS: Univariable and multivariable adjustments were undertaken for a candidate set of covariate values that a physician panel indicated could be prognostically associated with overall survival in uHCC. The values included baseline variables observed pre- and post-randomisation. Univariable analyses were based on a stratified Cox model. The multivariable analysis used a "forwards stepwise" Cox model. RESULTS: Univariable analysis identified alpha-fetoprotein (AFP) as the most influential variable. The chosen multivariable Cox model analysis resulted in an estimated adjusted hazard ratio for lenvatinib of 0.814 (95% CI: 0.699-0.948) when only baseline variables were included. Adjusting for post-randomisation treatment variables further increased the estimated superiority of lenvatinib. CONCLUSIONS: Covariate adjustment of REFLECT suggests that the original noninferiority trial likely underestimated the true effect of lenvatinib on overall survival due to an imbalance in baseline prognostic covariates and the greater use of post-treatment therapies in the sorafenib arm. TRIAL REGISTRATION: Trial number: NCT01761266 (Submitted January 2, 2013)
Statistical properties of SGR 1900+14 bursts
We study the statistics of soft gamma repeater (SGR) bursts, using a data
base of 187 events detected with BATSE and 837 events detected with RXTE PCA,
all from SGR 1900+14 during its 1998-1999 active phase. We find that the
fluence or energy distribution of bursts is consistent with a power law of
index 1.66, over 4 orders of magnitude. This scale-free distribution resembles
the Gutenberg-Richter Law for earthquakes, and gives evidence for
self-organized criticality in SGRs. The distribution of time intervals between
successive bursts from SGR 1900+14 is consistent with a log-normal
distribution. There is no correlation between burst intensity and the waiting
times till the next burst, but there is some evidence for a correlation between
burst intensity and the time elapsed since the previous burst. We also find a
correlation between the duration and the energy of the bursts, but with
significant scatter. In all these statistical properties, SGR bursts resemble
earthquakes and solar flares more closely than they resemble any known
accretion-powered or nuclear-powered phenomena. Thus our analysis lends support
to the hypothesis that the energy source for SGR bursts is internal to the
neutron star, and plausibly magnetic.Comment: 11 pages, 4 figures, accepted for publication in ApJ
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