488 research outputs found
Measuring the productivity of national R&D systems: challenges in cross-national comparisons of R&D input and publication output indicators
Article / Letter to editorCWT
Measuring the productivity of national R&D systems: challenges in cross-national comparisons of R&D input and publication output indicators
Article / Letter to editorCWT
Observational detection of eclipses of J5 Amalthea by the Galilean satellites
We carried out observations of the small jovian satellite Amalthea (J5) as it
was being eclipsed by the Galilean satellites near the 2009 equinox of Jupiter
in order to apply the technique of mutual event photometry to the astrometric
determination of this satellite's position. The observations were carried out
during the period 06/2009-09/2009 from the island of Maui, Hawaii and Siding
Spring, Australia with the 2m Faulkes Telescopes North and South respectively.
We observed in the near-infrared part of the spectrum using a PanStarrs-Z
filter with Jupiter near the edge of the field in order to mitigate against the
glare from the planet. Frames were acquired at rates >1/min during eclipse
times predicted using recent JPL ephemerides for the satellites. Following
subtraction of the sky background from these frames, differential aperture
photometry was carried out on Amalthea and a nearby field star. We have
obtained three lightcurves which show a clear drop in the flux from Amalthea,
indicating that an eclipse took place as predicted. These were model-fitted to
yield best estimates of the time of maximum flux drop and the impact parameter.
These are consistent with Amalthea's ephemeris but indicate that Amalthea is
slightly ahead of, and closer to Jupiter than, its predicted position by
approximately half the ephemeris uncertainty in these directions. We argue that
a ground-based campaign of higher-cadence photometry accurate at the 5% level
or better during the next season of eclipses in 2014-15 should yield positions
to within 0".5 and affect a corresponding improvement in Amalthea's ephemeris.Comment: Published in A&A in 2010; 6 pages, 2 figures, 3 table
Assessment of ionospheric Joule heating by GUMICS-4 MHD simulation, AMIE, and satellite-based statistics: towards a synthesis
We investigate the Northern Hemisphere Joule heating from several observational and computational sources with the purpose of calibrating a previously identified functional dependence between solar wind parameters and ionospheric total energy consumption computed from a global magnetohydrodynamic (MHD) simulation (Grand Unified Magnetosphere Ionosphere Coupling Simulation, GUMICS-4). In this paper, the calibration focuses on determining the amount and temporal characteristics of Northern Hemisphere Joule heating. Joule heating during a substorm is estimated from global observations, including electric fields provided by Super Dual Auroral Network (SuperDARN) and Pedersen conductances given by the ultraviolet (UV) and X-ray imagers on board the Polar satellite. Furthermore, Joule heating is assessed from several activity index proxies, large statistical surveys, assimilative data methods (AMIE), and the global MHD simulation GUMICS-4. We show that the temporal and spatial variation of the Joule heating computed from the GUMICS-4 simulation is consistent with observational and statistical methods. However, the different observational methods do not give a consistent estimate for the magnitude of the global Joule heating. We suggest that multiplying the GUMICS-4 total Joule heating by a factor of 10 approximates the observed Joule heating reasonably well. The lesser amount of Joule heating in GUMICS-4 is essentially caused by weaker Region 2 currents and polar cap potentials. We also show by theoretical arguments that multiplying independent measurements of averaged electric fields and Pedersen conductances yields an overestimation of Joule heating.<br><br> <b>Keywords.</b> Ionosphere (Auroral ionosphere; Modeling and forecasting; Electric fields and currents
Ionospheric conductances derived from satellite measurements of auroral UV and X-ray emissions, and ground-based electromagnetic data: a comparison
International audienceGlobal instantaneous conductance maps can be derived from remote sensing of UV and X-ray emissions by the UVI and PIXIE cameras on board the Polar satellite. Another technique called the 1-D method of characteristics provides mesoscale instantaneous conductance profiles from the MIRACLE ground-based network in Northern Scandinavia, using electric field measurements from the STARE coherent scatter radar and ground magnetometer data from the IMAGE network. The method based on UVI and PIXIE data gives conductance maps with a resolution of ~800km in space and ~4.5min in time, while the 1-D method of characteristics establishes conductances every 20s and with a spatial resolution of ~50km. In this study, we examine three periods with substorm activity in 1998 to investigate whether the two techniques converge when the results from the 1-D method of characteristics are averaged over the spatial and temporal resolution of the UVI/PIXIE data. In general, we find that the calculated conductance sets do not correlate. However, a fairly good agreement may be reached when the ionosphere is in a state that does not exhibit strong local turbulence. By defining a certain tolerance level of turbulence, we show that 14 of the 15 calculated conductance pairs during relatively uniform ionospheric conditions differ less than ±30%. The same is true for only 4 of the 9 data points derived when the ionosphere is in a highly turbulent state. A correlation coefficient between the two conductance sets of 0.27 is derived when all the measurements are included. By removing the data points from time periods when too much ionospheric turbulence occurs, the correlation coefficient raises to 0.57. Considering the two very different techniques used in this study to derive the conductances, with different assumptions, limitations and scale sizes, our results indicate that simple averaging of mesoscale results allows a continuous transition to large-scale results. Therefore, it is possible to use a combined approach to study ionospheric events with satellite optical and ground-based electrodynamic data of different spatial and temporal resolutions. We must be careful, though, when using these two techniques during disturbed conditions. The two methods will only give results that systematically converge when relatively uniform conditions exist
A phase IIa, nonrandomized study of radium-223 dichloride in advanced breast cancer patients with bone-dominant disease
Radium-223 dichloride (radium-223) mimics calcium and emits high-energy, short-range alpha-particles resulting in an antitumor effect on bone metastases. This open-label, phase IIa nonrandomized study investigated safety and short-term efficacy of radium-223 in breast cancer patients with bone-dominant disease. Twenty-three advanced breast cancer patients with progressive bone-dominant disease, and no longer candidates for further endocrine therapy, were to receive radium-223 (50 kBq/kg IV) every 4 weeks for 4 cycles. The coprimary end points were change in urinary N-telopeptide of type 1 (uNTX-1) and serum bone alkaline phosphatase (bALP) after 16 weeks of treatment. Exploratory end points included sequential 18F-fluorodeoxyglucose positron emission tomography and computed tomography (FDG PET/CT) to assess metabolic changes in osteoblastic bone metastases. Safety data were collected for all patients. Radium-223 significantly reduced uNTX-1 and bALP from baseline to end of treatment. Median uNTX-1 change was −10.1 nmol bone collagen equivalents/mmol creatinine (−32.8 %; P = 0.0124); median bALP change was −16.7 ng/mL (−42.0 %; P = 0.0045). Twenty of twenty-three patients had FDG PET/CT identifying 155 hypermetabolic osteoblastic bone lesions at baseline: 50 lesions showed metabolic decrease (≥25 % reduction of maximum standardized uptake value from baseline) after 2 radium-223 injections [32.3 % metabolic response rate (mRR) at week 9], persisting after the treatment period (41.5 % mRR at week 17). Radium-223 was safe and well tolerated. Radium-223 targets areas of increased bone metabolism and shows biological activity in advanced breast cancer patients with bone-dominant disease
Instantaneous ionospheric global conductance maps during an isolated substorm
International audienceData from the Polar Ionospheric X-ray Imager (PIXIE) and the Ultraviolet Imager (UVI) on board the Polar satellite have been used to provide instantaneous global conductance maps. In this study, we focus on an isolated substorm event occurring on 31 July 1997. From the PIXIE and the UVI measurements, the energy spectrum of the precipitating electrons can be derived. By using a model of the upper atmosphere, the resulting conductivity values are generated. We present global maps of how the 5 min time-averaged height-integrated Hall and Pedersen conductivities vary every 15 min during this isolated substorm. The method presented here enables us to study the time development of the conductivities, with a spatial resolution of ~ 700 km. During the substorm, a single region of enhanced Hall conductance is observed. The Hall conductance maximum remains situated between latitudes 64 and 70 corrected geomagnetic (CGM) degrees and moves eastward. The strongest conductances are observed in the pre-midnight sector at the start of the substorm expansion. Toward the end of the substorm expansion and into the recovery phase, we find the Hall conductance maximum in the dawn region. We also observe that the Hall to Pedersen conductance ratio for the regions of maximum Hall conductance is increasing throughout the event, indicating a hardening of the electron spectrum. By combining PIXIE and UVI measurements with an assumed energy distribution, we can cover the whole electron energy range responsible for the conductances. Electrons with energies contributing most to the Pedersen conductance are well covered by UVI while PIXIE captures the high energetic component of the precipitating electrons affecting the Hall conductance. Most statistical conductance models have derived conductivities from electron precipitation data below approximately 30 keV. Since the intensity of the shortest UVI-wavelengths (LBHS) decreases significantly at higher electron energies, the UVI electron energy range is more or less comparable with the energy ranges of the statistical models. By calculating the conductivities from combined PIXIE and UVI measurements to compare with the conductivities from using UVI data only, we observe significant differences in the Hall conductance. The greatest differences are observed in the early evening and the late morning sector. We therefore suggest that the existing statistical models underestimate the Hall conductance
Observational detection of eight mutual eclipses and occultations between the satellites of Uranus
We carried out observations, with five different instruments ranging in
aperture from 0.4m to 10m, of the satellites of Uranus during that planet's
2007 Equinox. Our observations covered specific intervals of time when mutual
eclipses and occultations were predicted.
The observations were carried out in the near-infrared part of the spectrum
to mitigate the glare from the planet. Frames were acquired at rates > 1/min.
Following modelling and subtraction of the planetary source from these frames,
differential aperture photometry was carried out on the satellite pairs
involved in the predicted events. In all cases but one, nearby bright
satellites were used as reference sources.
We have obtained fifteen individual lightcurves, eight of which show a clear
drop in the flux from the satellite pair, indicating that a mutual event took
place. Three of these involve the faint satellite Miranda. All eight
lightcurves were model-fitted to yield best estimates of the time of maximum
flux drop and the impact parameter. In three cases best-fit albedo ratios were
also derived. We used these estimates to generate intersatellite astrometric
positions with typical formal uncertainties of <0.01 arcsec, several times
better than conventional astrometry of these satellites. The statistics of our
estimated event midtimes show a systematic lag, with the observations later
than predictions. In addition, lightcurves of two partial eclipses of Miranda
show no statistically significant evidence of a light drop, at variance with
the predictions. These indicate that new information about the Uranian
satellite system is contained in observations of mutual events acquired here
and by other groups.Comment: 8 pages, 3 figures, accepted for publication in Astronomy and
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