A homogeneous nucleus for comet 67P/Churyumov-Gerasimenko from its gravity field.

Cometary nuclei consist mostly of dust and water ice. Previous observations have found nuclei to be low-density and highly porous bodies, but have only moderately constrained the range of allowed densities because of the measurement uncertainties. Here we report the precise mass, bulk density, porosity and internal structure of the nucleus of comet 67P/Churyumov-Gerasimenko on the basis of its gravity field. The mass and gravity field are derived from measured spacecraft velocity perturbations at fly-by distances between 10 and 100 kilometres. The gravitational point mass is GM = 666.2 ± 0.2 cubic metres per second squared, giving a mass M = (9,982 ± 3) × 10(9) kilograms. Together with the current estimate of the volume of the nucleus, the average bulk density of the nucleus is 533 ± 6 kilograms per cubic metre. The nucleus appears to be a low-density, highly porous (72-74 per cent) dusty body, similar to that of comet 9P/Tempel 1. The most likely composition mix has approximately four times more dust than ice by mass and two times more dust than ice by volume. We conclude that the interior of the nucleus is homogeneous and constant in density on a global scale without large voids. The high porosity seems to be an inherent property of the nucleus material.

Mid-infrared emissivity of partially dehydrated asteroid (162173) Ryugu shows strong signs of aqueous alteration.

The near-Earth asteroid (162173) Ryugu, the target of Hayabusa2 space mission, was observed via both orbiter and the lander instruments. The infrared radiometer on the MASCOT lander (MARA) is the only instrument providing spectrally resolved mid-infrared (MIR) data, which is crucial for establishing a link between the asteroid material and meteorites found on Earth. Earlier studies revealed that the single boulder investigated by the lander belongs to the most common type found on Ryugu. Here we show the spectral variation of Ryugu's emissivity using the complete set of in-situ MIR data and compare it to those of various carbonaceous chondritic meteorites, revealing similarities to the most aqueously altered ones, as well as to asteroid (101955) Bennu. The results show that Ryugu experienced strong aqueous alteration prior to any dehydration.

Association of KIR2DL2 polymorphism rs2756923 with type 1 diabetes and preliminary evidence for lack of inhibition through HLA-C1 ligand binding.

Killer cell immunoglobulin-like receptors (KIRs) on chromosome 19q13.4 regulate the function of not only human natural killer (NK) cells but also T cells. An increase in activating KIR- human leucocyte antigen ligand pairs has been associated with an additional risk to develop type 1 diabetes (T1D). T1D families [n = 184 (552 individuals); n = 176 (528 subjects)], unrelated T1D patients (n = 380; n = 394) and healthy controls (n = 315; n = 401) from Germany and Belgium, respectively, were genotyped for the rs2756923 polymorphism within the KIR gene cluster haplotype B in exon 8 of the KIR2DL2 gene. We observed in both Germans and Belgians an overtransmission of the allele 'G' of the KIR2DL2-rs2756923 polymorphism (64.2% vs 35.8%, P = 3 x 10(-4) and 60.0% vs 40.0%, P = 0.02, respectively). In addition, this allele was more frequent in German patients than in healthy controls (78.4% vs 21.6%, P = 1 x 10(-3)). Preliminary results from a cytotoxicity assay suggest that inhibition of NK-cell cytotoxicity may be impaired in individuals carrying the rs2756923 G allele. These data suggest a potential role of the KIR2DL2-rs2756923 polymorphism in T1D in Germans and Belgians.

The study of bronze statuettes with the help of neutron-imaging techniques.

Until recently fabrication techniques of Renaissance bronzes have been studied only with the naked eye, microscopically, videoscopically and with X-radiography. These techniques provide information on production techniques, yet much important detail remains unclear. As part of an interdisciplinary study of Renaissance bronzes undertaken by the Rijksmuseum Amsterdam, neutron-imaging techniques have been applied with the aim of obtaining a better understanding of bronze workmanship during the Renaissance period. Therefore, an explanation of the fabrication techniques is given to better understand the data collected by these neutron-imaging techniques. The data was used for tomography studies, which reveal hidden aspects that could not at all or scarcely be seen using X-radiography. For this specific study, the representative bronze 'Hercules Pomarius' of Willem van Tetrode (ca 1520-1588) has been examined, along with 20 other Renaissance bronzes from the Rijksmuseum collection.

Images from the surface of asteroid Ryugu show rocks similar to carbonaceous chondrite meteorites.

The near-Earth asteroid (162173) Ryugu is a 900-m-diameter dark object expected to contain primordial material from the solar nebula. The Mobile Asteroid Surface Scout (MASCOT) landed on Ryugu's surface on 3 October 2018. We present images from the MASCOT camera (MASCam) taken during the descent and while on the surface. The surface is covered by decimeter- to meter-sized rocks, with no deposits of fine-grained material. Rocks appear either bright, with smooth faces and sharp edges, or dark, with a cauliflower-like, crumbly surface. Close-up images of a rock of the latter type reveal a dark matrix with small, bright, spectrally different inclusions, implying that it did not experience extensive aqueous alteration. The inclusions appear similar to those in carbonaceous chondrite meteorites.

Rosetta's comet 67P/Churyumov-Gerasimenko sheds its dusty mantle to reveal its icy nature.

The Rosetta spacecraft has investigated comet 67P/Churyumov-Gerasimenko from large heliocentric distances to its perihelion passage and beyond. We trace the seasonal and diurnal evolution of the colors of the 67P nucleus, finding changes driven by sublimation and recondensation of water ice. The whole nucleus became relatively bluer near perihelion, as increasing activity removed the surface dust, implying that water ice is widespread underneath the surface. We identified large (1500 square meters) ice-rich patches appearing and then vanishing in about 10 days, indicating small-scale heterogeneities on the nucleus. Thin frosts sublimating in a few minutes are observed close to receding shadows, and rapid variations in color are seen on extended areas close to the terminator. These cyclic processes are widespread and lead to continuously, slightly varying surface properties.

COMETARY SCIENCE. The structure of the regolith on 67P/Churyumov-Gerasimenko from ROLIS descent imaging.

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.

Vesta's shape and morphology.

Vesta's surface is characterized by abundant impact craters, some with preserved ejecta blankets, large troughs extending around the equatorial region, enigmatic dark material, and widespread mass wasting, but as yet an absence of volcanic features. Abundant steep slopes indicate that impact-generated surface regolith is underlain by bedrock. Dawn observations confirm the large impact basin (Rheasilvia) at Vesta's south pole and reveal evidence for an earlier, underlying large basin (Veneneia). Vesta's geology displays morphological features characteristic of the Moon and terrestrial planets as well as those of other asteroids, underscoring Vesta's unique role as a transitional solar system body.

Images of asteroid 21 Lutetia: a remnant planetesimal from the early Solar System.

Images obtained by the Optical, Spectroscopic, and Infrared Remote Imaging System (OSIRIS) cameras onboard the Rosetta spacecraft reveal that asteroid 21 Lutetia has a complex geology and one of the highest asteroid densities measured so far, 3.4 ± 0.3 grams per cubic centimeter. The north pole region is covered by a thick layer of regolith, which is seen to flow in major landslides associated with albedo variation. Its geologically complex surface, ancient surface age, and high density suggest that Lutetia is most likely a primordial planetesimal. This contrasts with smaller asteroids visited by previous spacecraft, which are probably shattered bodies, fragments of larger parents, or reaccumulated rubble piles.

Femoropopliteal occlusions and the adductor canal hiatus, Duplex study.

The majority of lower limb arterial occlusions are located in the distal third of the thigh. However, the exact location of occlusions in relation to the surrounding anatomy has never been examined. Duplex ultrasound was used to determine the location of femoropopliteal occlusions in 50 patients by comparing the level of occlusions to the level of the adductor canal hiatus. We found that although the level of the adductor canal hiatus may vary, 72% of occlusions are related to the site of the adductor canal hiatus. Short occlusions were located in the hiatus region, longer occlusions extended mainly in the proximal direction.

US location of the adductor canal hiatus: morphologic study.

In the lower extremities, the adductor canal hiatus is a site of predilection for arterial stenoses and occlusions. The high incidence of vascular disease in this region is thought to be due to a local factor. To gain more insight into the mechanisms leading to such disease, the authors used ultrasound to locate the adductor canal hiatus in dissecting room preparations and in healthy volunteers.

Antegrade puncture of the femoral artery: morphologic study.

To determine the optimal site for antegrade puncture of the femoral artery, the authors evaluated three cadaver specimens and computed tomographic (CT) scans of 50 patients. The relationships among the common femoral artery, the femoral artery bifurcation, the center of the femoral head, and the inguinal ligament were evaluated. CT showed that the center of the femoral head was always located caudal to the level of the inguinal ligament but cranial to the bifurcation of the common femoral artery. Therefore, the femoral head seems to provide a reliable landmark for entering the common femoral artery.

Arterial tortuosity in the femoropopliteal region during knee flexion: a magnetic resonance angiographic study.

Dynamic changes in curvature are expected in the femoropopliteal region during knee flexion. The location of the artery dorsal to the axis of movement implicates a relative length excess that may influence local morphology. To study arterial morphology in vivo, magnetic resonance angiography was performed in 22 healthy volunteers (aged 23-68 y). The curvature of the femoral vessels was studied and quantified in stretched and flexed positions. During knee flexion the vessel followed the movement of the leg and in the sagittal plane one curve was visible distal to the adductor hiatus. Three or more small curves were seen proximal to the knee joint in all volunteers. In the group aged under 30 y these minor curves were located proximal to the adductor hiatus as if the artery curls up in Hunter's canal. In the group aged over 45 y one or more curves were located distal to the adductor hiatus in the popliteal fossa. In volunteers aged 60 y and older some of these curves did not disappear during knee extension. In older individuals, natural elongation and loss of arterial elasticity will contribute to the formation of these curves. Impairment of the free gliding mechanism of the femoral vessels in the adductor canal could explain the differences in location of these minor curves between younger and older subjects. It is concluded that morphological changes in the femoral artery occur during knee flexion and that this tortuosity is age dependent. This may influence local haemodynamics and therefore possibly contribute to atherogenesis.

Bone growth and remodeling after distraction epiphysiolysis of the proximal tibia of the rabbit. Effect of electromagnetic stimulation.

The effect of pulsed electromagnetic stimulation on bone formation was tested in a lower-limb-lengthening model in the rabbit. Limb lengthening was performed by distraction epiphysiolysis. A specially designed external distraction device allowed 10 mm of lengthening of the tibia. Coils to generate a pulsed electromagnetic field were clipped onto the distractor. Stimulation started after a distraction period of three weeks and was continuous for 18 weeks. A control group received the same treatment without stimulation. Bone formation in the elongated zone was evaluated by computed tomography, scintigraphy, and histology. Bone healing involved accretion of callus followed by a process of remodeling, resulting in the formation of a solid cortex. The formation of a diaphysislike structure at the original site of the metaphysis progressed from the distal end of the elongated zone upward. Electromagnetic stimulation had no effect on the rate or extent of bone formation and remodeling.