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

Acute hepatitis C infection after sexual exposure

A case is described of a woman with acute hepatitis C infection whose partner had chronic hepatitis C infection and where heterosexual contact was the only major risk factor. Infection of both partners was confirmed serologically and by the finding of virus RNA by reverse transcription and polymerase chain reaction amplification. Nucleotide sequence analysis of the NS5 region (RNA polymerase) was used to show that both partners were infected with virus of the same genotype (1a). The nucleotide sequence of virus RNA found in the female patient is closest to variants cocirculating in the male contact, consistent with transmission having occurred between the two

Geographical patterns of proportionate mortality for the most common causes of death in Brazil Variações geográficas no padrão de mortalidade proporcional por doenças crônico-degenerativas no Brasil

Mortality due to chronic diseases has been increasing in all regions of Brazil with corresponding decreases in mortality from infectious diseases. The geographical variation in proportionate mortality for chronic diseases for 17 Brazilian state capitals for the year 1985 and their association with socio-economic variables and infectious disease was studied. Calculations were made of correlation coefficients of proportionate mortality for adults of 30 years or above due to ischaemic heart disease, stroke and cancer of the lung, the breast and stomach with 3 socio-economic variables, race, and mortality due to infectious disease. Linear regression analysis included as independent variables the % of illiteracy, % of whites, % of houses with piped water, mean income, age group, sex, and % of deaths caused by infectious disease. The dependent variables were the % of deaths due to each one of the chronic diseases studied by age-sex group. Chronic diseases were an important cause of death in all regions of Brazil. Ischaemic heart diseases, stroke and malignant neoplasms accounted for more than 34% of the mortality in each of the 17 capitals studied. Proportionate cause-specific mortality varied markedly among state capitals. Ranges were 6.3-19.5% for ischaemic heart diseases, 8.3-25.4% for stroke, 2.3-10.4% for infections and 12.2-21.5% for malignant neoplasm. Infectious disease mortality had the highest (p < 0.001) correlation with all the four socio-economic variables studied and ischaemic heart disease showed the second highest correlation (p < 0.05). Higher socio-economic level was related to a lower % of infectious diseases and a higher % of ischaemic heart diseases. Mortality due to breast cancer and stroke was not associated with socio-economic variables. Multivariate linear regression models explained 59% of the variance among state capitals for mortality due to ischaemic heart disease, 50% for stroke, 28% for lung cancer, 24% for breast cancer and 40% for stomach cancer. There were major differences in the proportionate mortality due to chronic diseases among the capitals which could not be accounted for by the social and environmental factors and by the mortality due to infectious disease.<br>Em razão de a mortalidade por doenças crônico -degenerativas estar aumentando no Brasil, com correspondente redução das doenças infecciosas, foi realizado estudo comparativo entre 17 capitais brasileiras em relação à mortalidade proporcional para as principais causas de morte em 1985. Foram calculados coeficientes de correlação entre a mortalidade proporcional decorrente de doença isquêmica do coração, doença cerebrovascular, câncer de pulmão, mama e estômago e 3 variáveis socioeconômicas, raça e a mortalidade proporcional por doenças infecciosas. A análise multivariada através de regressão linear incluiu como variáveis independentes os percentuais de: analfabetismo, casas com instalação domiciliar de água, renda média, população da cor branca, faixa etária e sexo. As variáveis dependentes foram as percentagens de óbito devido a cada uma das doenças crônico-degenerativas em estudo, por grupo de idade e sexo. Os resultados mostraram que as doenças crônico-degenerativas são importantes causas de morte em todas as regiões do país. A doença isquêmica do coração, a doença cerebrovascular e as neoplasias malignas foram responsáveis por mais do que 34% da mortalidade em todas as capitais estudadas. A mortalidade proporcional variou de forma marcante entre as capitais estudadas, com amplitudes de variação de 6,3-19,5% para a doença isquêmica do coração, 8,3-25,4% para a doença cerebrovascular, 2,3-10,4% para infecções e 12,2-21,5% para as neoplasias malignas. A mortalidade proporcional por infecções apresentou a maior correlação com os indicadores socioeconômicos (p < 0,001), sendo acompanhada pela doença isquêmica do coração (p < 0,05). O alto nível socioeconômico relacionou-se com menor percentagem de mortalidade por infecções e mais alta percentagem de doença isquêmica do coração, enquanto que a mortalidade por doença cerebrovascular e câncer de mama não se associaram com os indicadores socioeconômicos. Os modelos de análise multivariada explicaram 59% da variação entre as capitais, para a doença isquêmica do coração, 50% para a doença cerebrovascular, 28% para o câncer de pulmão, 24% para o câncer de mama e 40% para o câncer de estômago. As importantes diferenças geográficas encontradas para a mortalidade proporcional devido às doenças crônico-degenerativas não podem ser totalmente explicadas pela variação na mortalidade por doenças infecciosas e pelos fatores socioeconômicos estudados, sugerindo a existência de fatores de risco específicos