Theory of disk accretion onto supermassive black holes

Accretion onto supermassive black holes produces both the dramatic phenomena associated with active galactic nuclei and the underwhelming displays seen in the Galactic Center and most other nearby galaxies. I review selected aspects of the current theoretical understanding of black hole accretion, emphasizing the role of magnetohydrodynamic turbulence and gravitational instabilities in driving the actual accretion and the importance of the efficacy of cooling in determining the structure and observational appearance of the accretion flow. Ongoing investigations into the dynamics of the plunging region, the origin of variability in the accretion process, and the evolution of warped, twisted, or eccentric disks are summarized.Comment: Mostly introductory review, to appear in "Supermassive black holes in the distant Universe", ed. A.J. Barger, Kluwer Academic Publishers, in pres

Processamento auditivo em gagos: análise do desempenho das orelhas direita e esquerda Auditory processing in stutterers: performance of right and left ears

OBJETIVO: Comparar a diferença entre as orelhas nos testes comportamentais do processamento auditivo e os resultados de sujeitos com diferentes graus de gravidade de gagueira em cada teste do processamento auditivo. MÉTODOS: Cinqüenta e seis indivíduos, com idades entre quatro e 34 anos, foram encaminhados pelo Ambulatório de Avaliação Fonoaudiológica da UNIFESP para avaliação comportamental do processamento auditivo. Todos os pacientes foram submetidos à avaliação de audição, fala e linguagem. A disfluência foi classificada segundo o protocolo de Riley (1994), o qual prevê os seguintes graus de gravidade da gagueira: muito leve, leve, moderado, severo e muito severo. Os testes para avaliação do processamento auditivo foram selecionados e analisados de acordo com a idade do paciente e a proposta de Pereira & Schochat (1997). RESULTADOS: Observamos prevalência da gagueira de grau leve nas faixas etárias de quatro a sete anos e de 12 a 34 anos de idade, e de grau moderado nos indivíduos de oito a 11 anos de idade. Dos 56 indivíduos avaliados 92,85% apresentaram alteração do processamento auditivo. Houve diferença estatisticamente significante entre as orelhas direita e esquerda na etapa de atenção direcionada do teste dicótico não verbal, em todas as faixas etárias estudadas. Não foram encontradas diferenças significativas entre os graus de gravidade da gagueira em nenhum dos testes de processamento auditivo. CONCLUSÕES: A orelha direita apresentou melhor desempenho do que a esquerda nos diferentes testes comportamentais. O grau de gravidade da gagueira não interferiu no resultado de cada teste.<br>PURPOSE: To compare the difference between the performances of right and left ears in behavioral tests of auditory processing and to compare the results obtained by subjects with different stuttering severity classifications in each auditory processing test. METHODS: Fifty six subjects (49 male, 7 female), with ages ranging from four to 34 years, were referred to auditory processing evaluation as a complement to speech and language evaluation. All subjects were submitted to auditory, speech and language evaluation. Disfluency severity was classified according to the Riley Stuttering Severity Index as: very mild, mild, moderate, severe and very severe. Behavioral auditory processing tests were selected and analyzed regarding the patients' age and following the proposal of Pereira & Schochat (1997). RESULTS: Mild stuttering was prevalent among subjects with ages ranging from four to seven years and from 12 to 34 years. Moderate stuttering was the most prevalent degree among subjects with eight to 11 years old. Auditory processing disorders were observed in 92,85% of the subjects tested. Significant statistical differences between left and right ears were found in directed attention conditions for the nonverbal dichotic test, in all age ranges. No differences were found among subjects with different stuttering severity classifications in any of the auditory processing tests carried out. CONCLUSIONS: Right ear showed better results than left ear in both monotic and dichotic tests. Stuttering severity didn't interfere with the results of each test