Two independent and primitive envelopes of the bilobate nucleus of comet 67P

The factors shaping cometary nuclei are still largely unknown, but could be the result of concurrent effects of evolutionary(1,2) and primordial processes(3,4). The peculiar bilobed shape of comet 67P/Churyumov-Gerasimenko may be the result of the fusion of two objects that were once separate or the result of a localized excavation by outgassing at the interface between the two lobes(5). Here we report that the comet's major lobe is enveloped by a nearly continuous set of strata, up to 650 metres thick, which are independent of an analogous stratified envelope on the minor lobe. Gravity vectors computed for the two lobes separately are closer to perpendicular to the strata than those calculated for the entire nucleus and adjacent to the neck separating the two lobes. Therefore comet 67P/Churyumov-Gerasimenko is an accreted body of two distinct objects with 'onion-like' stratification, which formed before they merged. We conclude that gentle, low-velocity collisions occurred between two fully formed kilometre-sized cometesimals in the early stages of the Solar System. The notable structural similarities between the two lobes of comet 67P/Churyumov-Gerasimenko indicate that the early-forming cometesimals experienced similar primordial stratified accretion, even though they formed independently.

On the nucleus structure and activity of comet 67P/Churyumov-Gerasimenko

Images from the OSIRIS scientific imaging system onboard Rosetta show that the nucleus of 67P/Churyumov-Gerasimenko consists of two lobes connected by a short neck. The nucleus has a bulk density less than half that of water. Activity at a distance from the Sun of >3 astronomical units is predominantly from the neck, where jets have been seen consistently. The nucleus rotates about the principal axis of momentum. The surface morphology suggests that the removal of larger volumes of material, possibly via explosive release of subsurface pressure or via creation of overhangs by sublimation, may be a major mass loss process. The shape raises the question of whether the two lobes represent a contact binary formed 4.5 billion years ago, or a single body where a gap has evolved via mass loss.

Large heterogeneities in comet 67P as revealed by active pits from sinkhole collapse

Pits have been observed on many cometary nuclei mapped by spacecraft(1-4). It has been argued that cometary pits are a signature of endogenic activity, rather than impact craters such as those on planetary and asteroid surfaces. Impact experiments(5,6) andmodels(7,8) cannot reproduce the shapes of most of the observed cometary pits, and the predicted collision rates imply that few of the pits are related to impacts(8,9). Alternative mechanisms like explosive activity(10) have been suggested, but the driving process remains unknown. Here we report that pits on comet 67P/Churyumov-Gerasimenko are active, and probably created by a sinkhole process, possibly accompanied by outbursts. We argue that after formation, pits expand slowly in diameter, owing to sublimation-driven retreat of the walls. Therefore, pits characterize how eroded the surface is: a fresh cometary surface will have a ragged structure with many pits, while an evolved surface will look smoother. The size and spatial distribution of pits imply that large heterogeneities exist in the physical, structural or compositional properties of the first few hundred metres below the current nucleus surface.

Domain Globalization: Using Languages to Support Technical and Social Coordination

When a project is realized in a globalized environment, multiple stakeholders from different organizations work on the same system. Depending on the stakeholders and their organizations, various (possibly overlapping) concerns are raised in the development of the system. In this context a Domain Specific Language (DSL) supports the work of a group of stakeholders who are responsible for addressing a specific set of concerns. This chapter identifies the open challenges arising from the coordination of globalized domain-specific languages. We identify two types of coordination: technical coordination and social coordination. After presenting an overview of the current state of the art, we discuss first the open challenges arising from the composition of multiple DSLs, and then the open challenges associated to the collaboration in a globalized environment.

Cerebral Microembolization During Aortic Valve Replacement Using Minimally Invasive or Conventional Extracorporeal Circulation: A Randomized Trial.

To compare intraoperative cerebral microembolic load between minimally invasive extracorporeal circulation (MiECC) and conventional extracorporeal circulation (CECC) during isolated surgical aortic valve replacement (SAVR), we conducted a randomized trial in patients undergoing primary elective SAVR at a tertiary referral hospital. The primary outcome was the procedural phase-related rate of high-intensity transient signals (HITS) on transcranial Doppler ultrasound. HITS rate was used as a surrogate of cerebral microembolism in pre-defined procedural phases in SAVR using MiECC or CECC with (+F) or without (-F) an oxygenator with integrated arterial filter. Forty-eight patients were randomized in a 1:1 ratio to MiECC or CECC. Due to intraprocedural Doppler signal loss (n = 3), 45 patients were included in final analysis. MiECC perfusion regimen showed a significantly increased HITS rate compared to CECC (by a factor of 1.75; 95% confidence interval, 1.19-2.56). This was due to different HITS rates in procedural phases from aortic cross-clamping until declamping [phase 4] (P = 0.01), and from aortic declamping until stop of extracorporeal perfusion [phase 5] (P = 0.05). Post hoc analysis revealed that MiECC-F generated a higher HITS rate than CECC+F (P = 0.005), CECC-F (P = 0.05) in phase 4, and CECC-F (P = 0.03) in phase 5, respectively. In open-heart surgery, MiECC is not superior to CECC with regard to gaseous cerebral microembolism. When using MiECC for SAVR, the use of oxygenators with integrated arterial line filter appears highly advisable. Only with this precaution, MiECC confers a cerebral microembolic load comparable to CECC during this type of open heart surgery.

Bivalirudin for Alternative Anticoagulation in Extracorporeal Membrane Oxygenation: A Systematic Review.

BACKGROUND Extracorporeal membrane oxygenation (ECMO) offers therapeutic options in refractory respiratory and/or cardiac failure. Systemic anticoagulation with heparin is routinely administered. However, in patients with heparin-induced thrombocytopenia or heparin resistance, the direct thrombin inhibitor bivalirudin is a valid option and has been increasingly used for ECMO anticoagulation. We aimed at evaluating its safety and its optimal dosing for ECMO. METHODS Systematic web-based literature search of PubMed and EMBASE performed via National Health Service Library Evidence and manually, updated until January 30, 2016. RESULTS The search revealed 8 publications relevant to the topic (5 case reports). In total, 58 patients (24 pediatrics) were reported (18 received heparin as control groups). Bivalirudin was used with or without loading dose, followed by infusion at different ranges (lowest 0.1-0.2 mg/kg/h without loading dose; highest 0.5 mg/kg/h after loading dose). The strategies for monitoring anticoagulation and optimal targets were dissimilar (activated partial thromboplastin time 45-60 seconds to 42-88 seconds; activated clotting time 180-200 seconds to 200-220 seconds; thromboelastography in 1 study). CONCLUSION Bivalirudin loading dose was not always used; infusion range and anticoagulation targets were different. In this systematic review, we discuss the reasons for this variability. Larger studies are needed to establish the optimal approach with the use of bivalirudin for ECMO.