21 research outputs found
Origins of the Ambient Solar Wind: Implications for Space Weather
The Sun's outer atmosphere is heated to temperatures of millions of degrees,
and solar plasma flows out into interplanetary space at supersonic speeds. This
paper reviews our current understanding of these interrelated problems: coronal
heating and the acceleration of the ambient solar wind. We also discuss where
the community stands in its ability to forecast how variations in the solar
wind (i.e., fast and slow wind streams) impact the Earth. Although the last few
decades have seen significant progress in observations and modeling, we still
do not have a complete understanding of the relevant physical processes, nor do
we have a quantitatively precise census of which coronal structures contribute
to specific types of solar wind. Fast streams are known to be connected to the
central regions of large coronal holes. Slow streams, however, appear to come
from a wide range of sources, including streamers, pseudostreamers, coronal
loops, active regions, and coronal hole boundaries. Complicating our
understanding even more is the fact that processes such as turbulence,
stream-stream interactions, and Coulomb collisions can make it difficult to
unambiguously map a parcel measured at 1 AU back down to its coronal source. We
also review recent progress -- in theoretical modeling, observational data
analysis, and forecasting techniques that sit at the interface between data and
theory -- that gives us hope that the above problems are indeed solvable.Comment: Accepted for publication in Space Science Reviews. Special issue
connected with a 2016 ISSI workshop on "The Scientific Foundations of Space
Weather." 44 pages, 9 figure
Infecção pelo HIV: descritores de mortalidade em pacientes hospitalizados Mortality descriptors in HIV inpatients
OBJETIVO: Estudar os descritores clínico-epidemiológicos da mortalidade em pacientes internados por condições clínicas associadas à infecção pelo HIV. MÉTODO: Estudo retrospectivo de todos os pacientes adultos hospitalizados em 1990, 1992 e 1994 em hospital universitário. Os resultados foram descritos como números absolutos, percentagens e médias, sendo a significância estatística entre as diferenças avaliada pelos testes do qui-quadrado, exato de Fisher ou t de Student, conforme o caso. Um modelo de regressão logística foi elaborado visando a identificar os principais fatores associados ao risco de evolução para o óbito. RESULTADOS: Foram incluídos no estudo 240 pacientes. Entre 1990 e 1994 a idade média dos pacientes aumentou de 35,0 para 36,9 anos, a razão entre os sexos masculino e feminino caiu de 9,8 para 2,0, a proporção de não brancos cresceu de 18,5 para 41,3 e registrou-se um aumento do tempo médio entre a descoberta da infecção pelo HIV e a hospitalização de 0,7 para 2,5 anos. Observou-se a redução do número médio de dias de hospitalização de 31,3 para 25,3 e aumento da proporção de pacientes em acompanhamento ambulatorial de 47,8 para 83,3%. As infecções respiratórias representaram a principal causa de hospitalização (58%) e as infecções oportunistas apresentadas com maior freqüência foram: candidíase oral (27,1%), tuberculose (18,3%), pneumonia por Pneumocystis carinii (15,4%) e neurotoxoplasmose (10,4%). Na análise multivariada, apenas o tempo de hospitalização menor ou igual a 7 dias (Odds Ratio [OR]=3,88; p=0,02) e a ausência de acompanhamento ambulatorial (OR=3,29; p=0,01) mostraram-se associados a um maior risco de evolução para óbito. CONCLUSÃO: O conhecimento dos fatores associados a um risco aumentado de morte pode ser útil na tomada de decisão frente a pacientes hospitalizados com infecção pelo HIV.<br>OBJECTIVE: To assess the clinical-epidemiological descriptors of inpatient mortality in persons infected with the human immunodeficiency virus (HIV). METHOD: All adult HIV/AIDS patients hospitalized at a university hospital in 1990, 1992 and 1994 were studied retrospectively. Descriptive statistics for all variables of interest were generated. Chi-square test and Fisher's exact test were performed to compare categorical variables. Means were compared using the Student t test. Stepwise logistic regression was used to identify the odds of dying associated with each risk factor. RESULTS: Two hundred and forty patients were included in the study. Between 1990 and 1994 the mean age rose from 35 to 36.9 years, the male/female ratio decreased from 9.8 to 2.0, the non-white proportion increased from 18.5 to 41.3% and the mean time between detection of HIV infection and hospitalization rose from 0.7 to 2.5 years. In addition, length of stay dropped from 31.3 to 25.3 days and the proportion of patients being followed up in the outpatient clinic of the Universitary Hospital increased from 47.8 to 83.3%. Respiratory infections were the main cause of hospitalization (58.0%). Oral candidiasis (27.1%), tuberculosis (18.3%), Pneumocystis carinii pneumonia (15.4%) and toxoplasmic encephalitis (10.4%) were the most frequent opportunistic infections. Multivariate analysis showed that the factors associated with a worse outcome included the length of stay less than or equal to 7 days (Odds Ratio [OR]=3.88; p=0.02) and no outpatient follow-up at the Hospital (OR=3.29; p=0.01). CONCLUSION: Identification of independent risk factors for death may help in the implementation of more efficient interventions directed towards inpatients with HIV/AIDS
The Dynamic Quasiperpendicular Shock: Cluster Discoveries
The physics of collisionless shocks is a very broad topic which has been
studied for more than five decades. However, there are a number of important
issues which remain unresolved. The energy repartition amongst particle
populations in quasiperpendicular shocks is a multi-scale process related to
the spatial and temporal structure of the electromagnetic fields within the
shock layer. The most important processes take place in the close vicinity of
the major magnetic transition or ramp region. The distribution of
electromagnetic fields in this region determines the characteristics of ion
reflection and thus defines the conditions for ion heating and energy
dissipation for supercritical shocks and also the region where an important
part of electron heating takes place. All of these processes are crucially
dependent upon the characteristic spatial scales of the ramp and foot region
provided that the shock is stationary. The earliest studies of collisionless
shocks identified nonlinearity, dissipation, and dispersion as the processes
that arrest the steepening of the shock transition. Their relative role
determines the scales of electric and magnetic fields, and so control the
characteristics of processes such as of ion reflection, electron heating and
particle acceleration. The purpose of this review is to address a subset of
unresolved problems in collisionless shock physics from experimental point of
view making use multi-point observations onboard Cluster satellites. The
problems we address are determination of scales of fields and of a scale of
electron heating, identification of energy source of precursor wave train, an
estimate of the role of anomalous resistivity in energy dissipation process by
means of measuring short scale wave fields, and direct observation of
reformation process during one single shock front crossing