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

An exploration of nutrition and eating disabilities in relation to quality of life at 6 months post-stroke

Quality of life (QoL) is increasingly recognised as an important healthcare outcome, especially for those living with enduring disability. Stroke is a major source of long-term disablement and many aspects of life after stroke have been explored. Little attention has been paid to nutritional issues despite the cultural and hedonistic importance of food and eating, and the deleterious effects of malnutrition. The present study employed an epidemiological survey to investigate the contribution of dietary and nutritional factors in relation to QoL after stroke. The participants were 206 survivors of a cohort of acute stroke patients consecutively admitted to a National Health Service trust hospital in South London, UK, between March 1998 and April 1999. They were interviewed in their homes at 6 months post-stroke. Cognitively or communication-impaired patients were precluded from interview except where a live-in carer participated as a proxy (n = 10). The participation rate for those who were eligible and could be contacted was 206 out of 218 (94%). Participants were assessed using standardised, validated tools for functional abilities in activities of daily living and eating, cognition and mood state, social support and economic indices, nutritional status, dietary intake, and QoL. Overall group scores demonstrated relatively minor degrees of physical disablement; exclusion of those with limited cognition and communication precluded assessment of a small subgroup with greater disablement at hospital discharge. Nonetheless, the overall assessment results were not dissimilar to other reported groups. Indices of poor nutritional status and substantial dietary inadequacy were revealed, linked with reduced appetite and depression. Multiple regression analyses revealed the dominant impact of mood state in relation to QoL scores; additional significant effects were identified for social support, eating-related disabilities and age. The effects of mood and social support are well-recognised, whilst nutrition-related effects have previously received little attention. Intervention in these areas might achieve improvements in survivors' perceived QoL