The structure of the upper layer of a comet is a product of its surface activity. The Rosetta Lander Imaging System (ROLIS) on board Philae acquired close-range images of the Agilkia site during its ...descent onto comet 67P/Churyumov-Gerasimenko. These images reveal a photometrically uniform surface covered by regolith composed of debris and blocks ranging in size from centimeters to 5 meters. At the highest resolution of 1 centimeter per pixel, the surface appears granular, with no apparent deposits of unresolved sand-sized particles. The thickness of the regolith varies across the imaged field from 0 to 1 to 2 meters. The presence of aeolian-like features resembling wind tails hints at regolith mobilization and erosion processes. Modeling suggests that abrasion driven by airfall-induced particle "splashing" is responsible for the observed formations.
•Philae’s ROLIS camera acquired 6 images of the surface of 67P after the final landing.•Illumination of the comet surface was provided by LEDs of four colors.•A local horizon is visible in one image ...corner, beyond which we can see the coma.•Seen at low phase angle, the comet surface displays a bimodal brightness distribution.•The surface seems to consist of plates with a consolidated crust, separated by cracks.
After coming to rest on the night side of comet 67P/Churyumov-Gerasimenko, the ROLIS camera on-board Rosetta’s Philae lander acquired five images of the surface below the lander, four of which were with the aid of LED illumination of different colors. The images confirm that Philae was perched on a sloped surface. A local horizon is visible in one corner of the image, beyond which we can see the coma. Having spent a full day on the surface Philae was commanded to lift and rotate, after which a final, sixth, LED image was acquired. The change in perspective allowed us to construct a shape model of the surface. The distance to the foreground was about 80 cm, much larger than the nominal 30 cm. This caused stray light, rather than directly reflected LED light, to dominate the image signal, complicating the analysis. The images show a lumpy surface with a roughness of apparently fractal nature. Its appearance is completely different from that of the first landing site, which was characterized by centimeter to meter-sized debris (Mottola et al., 2015). We recognize neither particles nor pores at the image resolution of 0.8 mm per pixel and large color variations are absent. The surface has a bi-modal brightness distribution that can be interpreted in terms of the degree of consolidation, a hypothesis that we support with experimental evidence. We propose the surface below the lander to consist of smooth, cracked plates with unconsolidated edges, similar to terrain seen in CIVA images.
By using the images acquired by the OSIRIS and ROLIS cameras, we derive the size-frequency distribution (SFD) of cometary pebbles and boulders covering the size range 0.05 - 30.0 m on the Agilkia ...landing site. The global SFD measured on OSIRIS images, reflects the different properties of the multiple morphological units present on Agilkia, combined with selection effects related to lifting, transport and redeposition. Contrarily, the different ROLIS SFD derived on the smooth and rough units may be related to their different regolith thickness present on Agilkia. In the thicker, smoother layer, ROLIS mainly measures the SFD of the airfall population that almost completely obliterate the signature of underlying boulders up to a size of the order of 1 m. This is well matched by the power-law index derived analysing coma particles identified by the grain analyser GIADA. This result confirms the important blanketing dynamism of Agilkia. The steeper SFD observed in rough terrains from 0.4 to 2 m could point out intrinsic differences between northern and southern dust size distributions, or it may suggest that the underlying boulders ”peek through” the thinner airfall layer in the rough terrain, thereby producing the observed excess in the decimeter size range. Eventually, the OSIRIS SFD performed on Philae landing unit may be due to water sublimation from a static population of boulders, affecting smaller boulders before the bigger ones, thus shallowing the original SFD.
To examine the association between prevalent cerebral abnormalities identified on MRI and cognitive functioning in a predominantly middle-aged, population-based study cohort.
Cerebral MRI was ...performed on 1,538 individuals (aged 55 to 72) from the Atherosclerosis Risk in Communities (ARIC) cohort, with no history of stroke or TIA, at study sites in Forsyth County, NC, and Jackson, MS. White matter hyperintensities (WMHs), ventricular size, and sulcal size were graded by trained neuroradiologists on a semiquantitative, 10-point scale. Cognitive functioning was assessed using the Delayed Word Recall Test (DWRT), Digit Symbol Substitution Test (DSST), and Word Fluency Test (WFT).
High ventricular grade was independently associated with significantly lower scores on the DWRT and DSST and greater risk (odds ratio OR 2.32, 95% confidence interval CI 1.51 to 3.56) of impaired scores (i.e., < or =10th percentile) on the DWRT. High sulcal grade was associated with a modest decrement in scores on the DWRT. The presence of coexisting high grade WMHs and silent infarcts was independently associated with lower scores on all cognitive tests and greater risk of impaired functioning on the DSST (OR 2.91, 95% CI: 1.23 to 6.89) and WFT (OR 2.28, 95% CI 1.03 to 5.08). The presence of two or more high-grade abnormalities was associated with increased risk of impaired functioning on all cognitive tests (DWRT: OR 2.23, 95% CI 1.40 to 3.55; DSST: OR 2.06, 95% CI 1.13 to 3.76; WFT: OR 2.07, 95% CI 1.23 to 3.49) independent of multiple covariates and silent infarcts.
Common changes in brain morphology are associated with diminished cognitive functioning in middle-aged and young-elderly individuals.
New UBV photometry for 878 luminous member stars of the Large Magellanic Cloud (LMC) and 13 stars of uncertain membership is presented. The data will be available at Centre de Données astronomiques ...de Strasbourg. Including former observations now UBV data are available for altogether 2470 luminous LMC stars and 2106 foreground stars plus 65 stars of uncertain membership. The observations have been used already for several investigations dealing e.g. with interstellar reddening lines and intrinsic colours, the dust distribution and the calibration of charge-coupled device exposures.
Cardiovascular magnetic resonance (CMR) has shown excellent results for interstudy reproducibility in the assessment of left ventricular (LV) parameters. However, interstudy reproducibility data for ...the more complex-shaped right ventricle in a large study group have not yet been reported. We sought to determine the interstudy reproducibility of measurements of right ventricular (RV) volumes, function, and mass with CMR and compare it with correspondent LV values.
Sixty subjects (47 men; 20 healthy volunteers, 20 patients with heart failure, 20 patients with ventricular hypertrophy) underwent 2 CMR studies for assessment of RV measurements with a minimum time interval between each study.
The overall interstudy reproducibility (range between groups) for the RV was 6.2% (4.2%–7.8%) for end-diastolic volume, 14.1% (8.1%–18.1%) for end-systolic volume, 8.3% (4.3%–10.4%) for ejection fraction (EF), and 8.7% (7.8%–9.4%) for RV mass. RV reproducibility was not as good as for the LV for all measures in all 3 groups, but this was only statistically significant for EF (
P <.01).
CMR showed good interstudy reproducibility for RV function parameters in healthy subjects, patients with heart failure, and patients with hypertrophy, which suggests that CMR is reliable for serial RV assessment. These data can be used to power sample sizes for longitudinal research studies of RV volume and function. The reproducibility values were similar to, but generally lower than, the reproducibility values for the LV in the same study population, which indicates that sample sizes for RV studies are in general larger than those for LV studies.
Fast breath-hold cardiovascular magnetic resonance (CMR) shows excellent results for interstudy reproducibility of left ventricular (LV) volumes, ejection fraction, and mass, which are thought to be ...superior to results of 2-dimensional echocardiography. However, there is no direct comparison of the interstudy reproducibility of both methods in the same subjects. A total of 60 subjects (normal volunteers n = 20, or patients with heart failure n = 20 or LV hypertrophy n = 20) underwent 2 CMRs and 2 echocardiographic studies for assessment of LV volumes, function, and mass. The interstudy reproducibility coefficient of variability was superior for CMR in all groups for all parameters. Statistical significance was reached for end-systolic volume (4.4% to 9.2% vs 13.7% to 20.3%, p <0.001), ejection fraction (2.4% to 7.3% vs 8.6% to 19.4%, p <0.001), and mass (2.8% to 4.8% vs 11.6% to 15.7% p <0.001), with a trend for end-diastolic volume (2.9% to 4.9% vs 5.5% to 10.5%, p = 0.17). The superior interstudy reproducibility resulted in considerably lower calculated sample sizes (reductions of 55% to 93%) required by CMR compared with echocardiography to show clinically relevant changes in LV dimensions and function. Thus, CMR has excellent interstudy reproducibility in normal, dilated, and hypertrophic hearts, and is superior to 2-dimensional echo- cardiography.
We systematically investigate the encounters between the Sun and neighbouring stars and their effects on cometary orbits in the Oort cloud, including the intrinsic one with the star Gl 710 (HIP 89 ...825), with some implications to stellar and cometary dynamics.
Our approach is principally based on the combination of a Keplerian‐rectilinear model of stellar passages and the Hipparcos Catalogue (ESA 1997). Beyond the parameters of encounter, we pay particular attention to the observational errors in parallaxes and stellar velocities, and their propagation in time. Moreover, as a special case of this problem, we consider the collision probability of a star passing very closely to the Sun, taking also into account the mutual gravitational attraction between the stars.
In the part dealing with the influence of stellar encounters on the orbital elements of Oort cloud comets, we derive new simple formulae calculating the changes in the cometary orbital elements, expressed as functions of the Jeans impulse formula. These expressions are then applied to calculate numerical values of the element changes caused by close encounters of neighbouring stars with some model comets in the Oort cloud. Moreover, the general condition for an ejection of comets from the cloud effected by a single encounter is derived and discussed.
The structure of the upper layer of a comet is a product of its surface activity. The Rosetta Lander Imaging System (ROLIS) on board Philae acquired close-range images of the Agilkia site during its ...descent onto comet 67P/Churyumov-Gerasimenko. These images reveal a photometrically uniform surface covered by regolith composed of debris and blocks ranging in size from centimeters to 5 meters. At the highest resolution of 1 centimeter per pixel, the surface appears granular, with no apparent deposits of unresolved sand-sized particles. The thickness of the regolith varies across the imaged field from 0 to 1 to 2 meters. The presence of aeolian-like features resembling wind tails hints at regolith mobilization and erosion processes. Modeling suggests that abrasion driven by airfall-induced particle "splashing" is responsible for the observed formations.
A concept is presented of a compact and very light-weight camera system for planetary exploration and terrestrial remote sensing with a (panchromatic) ground resolution of about 0.2 to 1.5 m per ...pixel from orbits of 100 km (Moon) to 800 km (Mars, Earth). The core of the camera system is a new 7k × 8k Philips CCD (12 μm pixels) which allows to realize a sufficiently large area on the ground at the given very high spatial resolution. In order to arrive at an adequate signal-to-noise ratio the detector has to be operated in TDI mode (Time Delay Integration). Using modern, properly tailored ceramic composite materials (C/C-SiC or C/SiC) for the primary and secondary mirrors, parts of the optical bench, and the mechanical structure, will — together with an extremely short optical design — limit the mass of the system (camera including CCD and detector electronics) to about 7 to 8 kg. Nevertheless, it may be an advantage to manufacture the whole opto-mechanical system (mirrors and optical bench) from Zerodur which will, however, increase the mass. The main fields of application of the camera will be detailed geologic surface studies and preparation of lander and rover missions in planetary exploration, and operational (terrestrial) remote sensing, e.g. for regional planning, disaster monitoring, and military verification tasks.
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