Theoretical study of electric field-dependent polaron-type mobility in conjugated polymers

We have used a self-consistent quantum molecular dynamics approach to calculate the mobility of both positive and negative polaron-type carriers on solated chains of poly(p-phenylene vinylene) (PPV) and some of its derivatives and the dependence of their mobility on the applied electric field. Our results suggest that polaron-type mobility along most of these polymer chains has a clear dependence on the electric field which is quite different from the result derived for bulk PPV-based materials.Fundação para a Ciência e a Tecnologia (FCT) Programa Operacional “Ciência , Tecnologia, Inovação” – POCTI/CTM/41574/2001, CONC-REEQ/443/EEI/2001 e SFRH/BD/11231/200

Substituent effects on the excited states of phenyl-capped phenylene vinylene tetramers

The singlet and triplet excited states of phenyl-capped tetramers of phenylene vinylene with different alkyl, alkoxy or cyano substituents, were investigated in benzene solution. The lowest singlet states were studied by laser flash-photolysis with time-resolved microwave conductivity and flourescence. The triplets were generated by pulse radiolysis, via energy transfer from the solvent excited singlet followed by inter-system crossing or by energy transfer from the naphthalene triplet. Their absorption spectra and rates of quenching by oxygen were determined

Prevalence of antibodies to the BK and JC papovaviruses in isolated populations Prevalência de anticorpos contra os papovavirus BK e JC em populações isoladas

A total of 173 sera from isolated Brazilian Indian populations, 39 from the Diauarun area, and 68 from the Alto Xingú area, respectively in the North and the South of the Xingú National Park and 66 Kren-Akorore Indians, were examined for hemagglutination - inhibiting (HI) antibodies against BK and JC viruses. The global percentages of positive sera (<FONT FACE=Symbol>></FONT> 1:40) were 5.2% for BK virus and 1.7% for JC virus. The distribution of positive sera according to the population groups showed one individual to be positive for BK virus in the Diauarun Indians and none of the sera contained HI antibody to JC virus; in the Alto Xingú Indians, 4 were positive for BK virus and 3 others were positive for JC virus; as regards Kren-Akorore Indians none of the sera contained antibody to JC virus, and only 4 were BK positive. Due to the limited number of observations it was neither possible to determine the time of occurrence of seroconversion nor correlate the positivity rates for both viruses in the different tribes with the respective "contact" with the white population.<br>Foram estudados 173 soros de índios brasileiros, sendo 39 da área Diauarum, 68 do Alto Xingú e 66 índios Kren-Akorore. A pesquisa de anticorpos inibidores da hemaglutinação para os papovavirus BK e JC mostrou uma percentagem global de positividade (<FONT FACE=Symbol>></FONT> 40) para os virus BK de 5,2% e para o virus JC de 1,7%. A distribuição dos soros positivos segundo sua origem foi a seguinte: dos 39 índios Diauarum somente um apresentou titulo significante para o virus BK e nenhum deles foi positivo para o virus JC; dos 68 índios do Alto Xingú, 4 apresentaram título significante para o virus BK e 3 para o virus JC, sendo estes últimos diferentes dos indivíduos positivos para o virus BK; dos 66 índios Kren-Akorore, 4 mostraram possuir título significante para o virus BK, sem positividade para o virus JC. O número reduzido de soros não permitiu estabelecer o momento da ser o conservação, em termos de idade, como não permitiu relacionar as taxas de positividade com o maior ou menor "contato" com a população branca