364 research outputs found
An observation of a mutual event between two satellites of Uranus
We present observations of the occultation of Umbriel by Oberon on 4 May,
2007. We believe this is the first observed mutual event between satellites of
Uranus. Fitting a simple geometric model to the lightcurve, we measure the
mid-event time with a precision of 4 seconds. We assume previously measured
values for the albedos of the two satellites (Karkoschka 2001), and measure the
impact parameter to be 500 +/- 80 km. These measurements are more precise than
estimates based on current ephemerides for these satellites. Therefore
observations of additional mutual events during the 2007-2008 Uranian equinox
will provide improved estimates of their orbital and physical parameters.Comment: 4 pages, 3 figures, accepted for publication in MNRAS Letter
Cassini ISS mutual event astrometry of the mid-sized Saturnian satellites 2005-2012
Reproduced with permission from Astronomy & Astrophysics, © ES
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
Astrometric positions for 18 irregular satellites of giant planets from 23 years of observations
The irregular satellites of the giant planets are believed to have been
captured during the evolution of the solar system. Knowing their physical
parameters, such as size, density, and albedo is important for constraining
where they came from and how they were captured. The best way to obtain these
parameters are observations in situ by spacecrafts or from stellar occultations
by the objects. Both techniques demand that the orbits are well known. We aimed
to obtain good astrometric positions of irregular satellites to improve their
orbits and ephemeris. We identified and reduced observations of several
irregular satellites from three databases containing more than 8000 images
obtained between 1992 and 2014 at three sites (Observat\'orio do Pico dos Dias,
Observatoire de Haute-Provence, and European Southern Observatory - La Silla).
We used the software PRAIA (Platform for Reduction of Astronomical Images
Automatically) to make the astrometric reduction of the CCD frames. The UCAC4
catalog represented the International Celestial Reference System in the
reductions. Identification of the satellites in the frames was done through
their ephemerides as determined from the SPICE/NAIF kernels. Some procedures
were followed to overcome missing or incomplete information (coordinates,
date), mostly for the older images. We managed to obtain more than 6000
positions for 18 irregular satellites: 12 of Jupiter, 4 of Saturn, 1 of Uranus
(Sycorax), and 1 of Neptune (Nereid). For some satellites the number of
obtained positions is more than 50\% of what was used in earlier orbital
numerical integrations. Comparison of our positions with recent JPL ephemeris
suggests there are systematic errors in the orbits for some of the irregular
satellites. The most evident case was an error in the inclination of Carme.Comment: 9 pages, with 3 being online materia
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
Astrophysics Uses aa style packag
The Five Factor Model of personality and evaluation of drug consumption risk
The problem of evaluating an individual's risk of drug consumption and misuse
is highly important. An online survey methodology was employed to collect data
including Big Five personality traits (NEO-FFI-R), impulsivity (BIS-11),
sensation seeking (ImpSS), and demographic information. The data set contained
information on the consumption of 18 central nervous system psychoactive drugs.
Correlation analysis demonstrated the existence of groups of drugs with
strongly correlated consumption patterns. Three correlation pleiades were
identified, named by the central drug in the pleiade: ecstasy, heroin, and
benzodiazepines pleiades. An exhaustive search was performed to select the most
effective subset of input features and data mining methods to classify users
and non-users for each drug and pleiad. A number of classification methods were
employed (decision tree, random forest, -nearest neighbors, linear
discriminant analysis, Gaussian mixture, probability density function
estimation, logistic regression and na{\"i}ve Bayes) and the most effective
classifier was selected for each drug. The quality of classification was
surprisingly high with sensitivity and specificity (evaluated by leave-one-out
cross-validation) being greater than 70\% for almost all classification tasks.
The best results with sensitivity and specificity being greater than 75\% were
achieved for cannabis, crack, ecstasy, legal highs, LSD, and volatile substance
abuse (VSA).Comment: Significantly extended report with 67 pages, 27 tables, 21 figure
Strontium ranelate and alendronate have differing effects on distal tibia bone microstructure in women with osteoporosis
The structural basis of the antifracture efficacy of strontium ranelate and alendronate is incompletely understood. We compared the effects of strontium ranelate and alendronate on distal tibia microstructure over 2 years using HR-pQCT. In this pre-planned, interim, intention-to-treat analysis at 12 months, 88 osteoporotic postmenopausal women (mean age 63.7 ± 7.4) were randomized to strontium ranelate 2 g/day or alendronate 70 mg/week in a double-placebo design. Primary endpoints were changes in microstructure. Secondary endpoints included lumbar and hip areal bone mineral density (aBMD), and bone turnover markers. This trial is registered with http://www.controlled-trials.com, number ISRCTN82719233. Baseline characteristics of the two groups were similar. Treatment with strontium ranelate was associated with increases in mean cortical thickness (CTh, 5.3%), cortical area (4.9%) and trabecular density (2.1%) (all P < 0.001, except cortical area P = 0.013). No significant changes were observed with alendronate. Between-group differences in favor of strontium ranelate were observed for CTh, cortical area, BV/TV and trabecular density (P = 0.045, 0.041, 0.048 and 0.035, respectively). aBMD increased to a similar extent with strontium ranelate and alendronate at the spine (5.7% versus 5.1%, respectively) and total hip (3.3% versus 2.2%, respectively). No significant changes were observed in remodeling markers with strontium ranelate, while suppression was observed with alendronate. Within the methodological constraints of HR-pQCT through its possible sensitivity to X-ray attenuation of different minerals, strontium ranelate had greater effects than alendronate on distal tibia cortical thickness and trabecular volumetric density
The astrometric Gaia-FUN-SSO observation campaign of 99 942 Apophis
Astrometric observations performed by the Gaia Follow-Up Network for Solar
System Objects (Gaia-FUN-SSO) play a key role in ensuring that moving objects
first detected by ESA's Gaia mission remain recoverable after their discovery.
An observation campaign on the potentially hazardous asteroid (99 942) Apophis
was conducted during the asteroid's latest period of visibility, from
12/21/2012 to 5/2/2013, to test the coordination and evaluate the overall
performance of the Gaia-FUN-SSO . The 2732 high quality astrometric
observations acquired during the Gaia-FUN-SSO campaign were reduced with the
Platform for Reduction of Astronomical Images Automatically (PRAIA), using the
USNO CCD Astrograph Catalogue 4 (UCAC4) as a reference. The astrometric
reduction process and the precision of the newly obtained measurements are
discussed. We compare the residuals of astrometric observations that we
obtained using this reduction process to data sets that were individually
reduced by observers and accepted by the Minor Planet Center. We obtained 2103
previously unpublished astrometric positions and provide these to the
scientific community. Using these data we show that our reduction of this
astrometric campaign with a reliable stellar catalog substantially improves the
quality of the astrometric results. We present evidence that the new data will
help to reduce the orbit uncertainty of Apophis during its close approach in
2029. We show that uncertainties due to geolocations of observing stations, as
well as rounding of astrometric data can introduce an unnecessary degradation
in the quality of the resulting astrometric positions. Finally, we discuss the
impact of our campaign reduction on the recovery process of newly discovered
asteroids.Comment: Accepted for publication in A&
A Method for Analyzing the Ubiquitination and Degradation of Aurora-A
The cell cycle machinery consists of regulatory proteins that control the progression through the cell cycle ensuring that DNA replication alternates with DNA segregation in mitosis to maintain cell integrity. Some of these key regulators have to be degraded at each cell cycle to prevent cellular dysfunction. Mitotic exit requires the inactivation of cyclin dependent kinase1 (cdk1) and it is the degradation of the cyclin subunit that inactivates the kinase. Cyclin degradation has been well characterized and it was shown that it is ubiquitin proteasome pathway that leads to the elimination of cyclins. By now, many other regulatory proteins were shown to be degraded by the same pathway, among them members of the aurora kinase family, degraded many other regulatory proteins. Aurora kinases are involved in mitotic spindle formation as well as in cytokinesis. The abundance and activity of the kinase is precisely regulated during the cell cycle. To understand how proteolysis regulates transitions through the cell cycle we describe two assays for ubiquitination and degradation of xenopus aurora kinase A using extracts from xenopus eggs or somatic cell lines
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