The Science of Sungrazers, Sunskirters, and Other Near-Sun Comets

This review addresses our current understanding of comets that venture close to the Sun, and are hence exposed to much more extreme conditions than comets that are typically studied from Earth. The extreme solar heating and plasma environments that these objects encounter change many aspects of their behaviour, thus yielding valuable information on both the comets themselves that complements other data we have on primitive solar system bodies, as well as on the near-solar environment which they traverse. We propose clear definitions for these comets: We use the term near-Sun comets to encompass all objects that pass sunward of the perihelion distance of planet Mercury (0.307 AU). Sunskirters are defined as objects that pass within 33 solar radii of the Sun’s centre, equal to half of Mercury’s perihelion distance, and the commonly-used phrase sungrazers to be objects that reach perihelion within 3.45 solar radii, i.e. the fluid Roche limit. Finally, comets with orbits that intersect the solar photosphere are termed sundivers. We summarize past studies of these objects, as well as the instruments and facilities used to study them, including space-based platforms that have led to a recent revolution in the quantity and quality of relevant observations. Relevant comet populations are described, including the Kreutz, Marsden, Kracht, and Meyer groups, near-Sun asteroids, and a brief discussion of their origins. The importance of light curves and the clues they provide on cometary composition are emphasized, together with what information has been gleaned about nucleus parameters, including the sizes and masses of objects and their families, and their tensile strengths. The physical processes occurring at these objects are considered in some detail, including the disruption of nuclei, sublimation, and ionisation, and we consider the mass, momentum, and energy loss of comets in the corona and those that venture to lower altitudes. The different components of comae and tails are described, including dust, neutral and ionised gases, their chemical reactions, and their contributions to the near-Sun environment. Comet-solar wind interactions are discussed, including the use of comets as probes of solar wind and coronal conditions in their vicinities. We address the relevance of work on comets near the Sun to similar objects orbiting other stars, and conclude with a discussion of future directions for the field and the planned ground- and space-based facilities that will allow us to address those science topics

Late Winter Biogeochemical Conditions Under Sea Ice in the Canadian High Arctic

With the Arctic summer sea-ice extent in decline, questions are arising as to how changes in sea-ice dynamics might affect biogeochemical cycling and phenomena such as carbon dioxide (CO2) uptake and ocean acidification. Recent field research in these areas has concentrated on biogeochemical and CO2 measurements during spring, summer or autumn, but there are few data for the winter or winter–spring transition, particularly in the High Arctic. Here, we present carbon and nutrient data within and under sea ice measured during the Catlin Arctic Survey, over 40 days in March and April 2010, off Ellef Ringnes Island (78° 43.11′ N, 104° 47.44′ W) in the Canadian High Arctic. Results show relatively low surface water (1–10 m) nitrate (<1.3 µM) and total inorganic carbon concentrations (mean±SD=2015±5.83 µmol kg−1), total alkalinity (mean±SD=2134±11.09 µmol kg−1) and under-ice pCO2sw (mean±SD=286±17 µatm). These surprisingly low wintertime carbon and nutrient conditions suggest that the outer Canadian Arctic Archipelago region is nitrate-limited on account of sluggish mixing among the multi-year ice regions of the High Arctic, which could temper the potential of widespread under-ice and open-water phytoplankton blooms later in the season

Towards a History of Mass Violence in the Etat Indépendant du Congo, 1885-1908

The present article provides an up-to-date scholarly introduction to mass violence in the Etat Indépendant du Congo (Congo Free State, EIC). Its aims are twofold: to offer a point of access to the extensive literature and historical debates on the subject, and to make the case for exchanging the currently prevalent top-down narrative, with its excessive focus on King Leopold's character and motives, for one which considers the EIC's culture of violence as a multicausal, broadly based and deeply engrained social phenomenon. The argument is divided into five sections. Following a general outline of the EIC's violent system of administration, I discuss its social and demographic impact (and the controversy which surrounds it) to bring out the need for more regionally focused and context sensitive studies. The dispute surrounding demographics demonstrates that what is fundamentally at stake is the place the EIC's extreme violence should occupy in the history of European ‘modernity’. Since approaches which hinge on Leopoldian exceptionalism are particularly unhelpful in clarifying this issue, I pause to reflect on how such approaches came to dominate the distinct historiographical traditions which emerged in Belgium and abroad before moving on to a more detailed exploration of a selection of causes underlying the EIC's violent nature. While state actors remain in the limelight, I shift the focus from the state as a singular, normative agent, towards the existence of an extremely violent society in which various individuals and social groups within and outside of the state apparatus committed violent acts for multiple reasons. As this argument is pitched at a high level of abstraction, I conclude with a discussion of available source material with which it can be further refined and updated

Integrated (epi)-Genomic Analyses Identify Subgroup-Specific Therapeutic Targets in CNS Rhabdoid Tumors

We recently reported that atypical teratoid rhabdoid tumors (ATRTs) comprise at least two transcriptional subtypes with different clinical outcomes; however, the mechanisms underlying therapeutic heterogeneity remained unclear. In this study, we analyzed 191 primary ATRTs and 10 ATRT cell lines to define the genomic and epigenomic landscape of ATRTs and identify subgroup-specific therapeutic targets. We found ATRTs segregated into three epigenetic subgroups with distinct genomic profiles, SMARCB1 genotypes, and chromatin landscape that correlated with differential cellular responses to a panel of signaling and epigenetic inhibitors. Significantly, we discovered that differential methylation of a PDGFRB-associated enhancer confers specific sensitivity of group 2 ATRT cells to dasatinib and nilotinib, and suggest that these are promising therapies for this highly lethal ATRT subtype.Jonathon Torchia ... Jordan R Hansford ... et al

Estudo do escápulo-coracóide e da cartilagem sinarcual cérvico-torácica de Rhinoptera brasiliensis Müller & Henle e Rhinoptera bonasus (Mitchill) Elasmobranchii, Rhinopteridae) Study of the scapulocoracoid and cervico-thoracic synarcual cartilage of Rhinoptera brasiliensis Müller & Henle and Rhinoptera bonasus (Mitchill) (Elasmobranchii, Rhinopteridae)

<abstract language="eng">A comparative analysis of the scapulocoracoid and cervico-thoracic synarcual cartilage of juvenile specimens of Rhinoptera brasiliensis Müller & Henle, 1841 and R. bonasus (Mitchill, 1815) was accomplished, in order to identify specific, individual and ontogenetic differences. In the scapulocoracoid, the scapular foramen and the posterodorsal fenestra is larger in R. brasiliensis. The anterior fenestra bridge is thicker and the metacondyle is thinner and longer in R. bonasus. This species also possesses a larger re-entrance between the mesocondyle and the metacondyle, as well as in the fitting region of'the synarcual cartilage, placed close to the scapular process. The individual differences are: posteroventral fenestra with variable diameter independent of the size of the specimens; scapulocoracoids, in some specimens, are more fragile even if they have been kept in the same conservation conditions. In the cervico-thoracic synarcual cartilage, the lateral stay in R. brasiliensis encloses completely the superior portion of the anteroscapular bridge. There are three more prominent condyles beside the suprascapula in R. brasiliensis, R. bonasus, however, shows a protuberance close to the suprascapula, inconspicuous and more distant from the scapular lamina. Several specimens of different size of R. bonasus show a synarcual cartilage wider in ventral view and higher in lateral view. In the majority of specimens, the number of ventral spinal foramina is higher than the dorsal ones in both species. R. bonasus has only one pair of asymmetric basal foramina, whereas R. brasiliensis possesses three or four foramina. Regarding individual differences, at least one specimen of R. bonasus exhibits a single basal foramen