Reentrant isotropic-calamitic nematic phase transition in potassium laurate-decanol- D2O mixtures.

The phase diagram is an interesting field of research, particularly in lyotropic liquid crystals (LLC). In this way, one of the most important phase diagrams of this LLC system was reported by Yu and Saupe. Two uniaxial (calamitic--N(C) and discotic--N(D)) and one biaxial nematic (N(B)) phases were determined by these authors. Furthermore, in this phase diagram the classical isotropic phase (I was observed at high temperature as well as a reentrant isotropic phase (I(RE)) which takes place at lower temperature. Later, this phase diagram was also studied by several authors and in all cases the I(RE)-N(C)-I phase transitions were not observed. In this work, we present a study of this phase diagram through digital image processing and refractometry optical techniques. The occurrence of these phase transitions is investigated and characterized. In addition, the order parameter is obtained based on the Vuks hypothesis from a particular point, in the range of the N(C) phase, where the absolute value of the optical birefringence (Deltan is maximum.

Bend and splay elastic constants at a reentrant isotropic-calamitic-nematic phase transition.

By measuring the ratio between the major and minor axes of closed elliptical loops created by a magnetic field, the ratio between the bend (K33) and splay (K11) elastic constants of a lyotropic mixture of potassium laurate, decanol, and water in the calamitic nematic phase is measured as a function of temperature. Since these systems present two nematic-isotropic phase transitions--the usual one, at high temperatures, and a reentrant one, at low temperatures--such measurements are used to compare the behavior of these elastic constants at the neighborhoods of these two distinct regions, which have in common the vanishing of the order parameter. The experimental data have revealed the existence of two elastic constant branches, characterizing a distinct low- and high-temperature behavior. To explain such asymmetry we support that, because of the lyotropic nature of the compound, the micellar variation, which is mainly responsible for the reentrant phase, plays a distinct role at these two phase transitions.

[The occurrence of hepatitis B and delta virus infection within seven Amerindian ethnic groups in the Brazilian western Amazon]. / Ocorrência da infecção pelo vírus da hepatite B (VHB) e delta (VHD) em sete grupos indígenas do Estado do Amazonas.

HBV and HDV infections are a major health problem in the Amazon. This study evaluates the prevalence of these viruses within Indians groups, measuring the frequency of serological markers. The prevalence of past infection was 54.5% and HBsAg was found in 9.7%. An important variation of those markers was detected between villages, inclusively within the same ethnic group. None showed evidence of an acute infection. All HBeAg reactive were Apurinã, living in the same village and three of them from the same family. The prevalence of anti-HDT was 13.4% in HBsAg positive individuals. The authors observed high prevalence of HBV and HDV infection with the following pattern: low degree of infectivity, marked transmission in early ages, intra-familial dissemination, and lack of importance of vertical transmission. However, the results suggest that these viruses were not yet introduced effectively in some of the studied groups.

Ocorrência da infecção pelo vírus da hepatite B (VHB) e delta (VHD) em sete grupos indígenas do Estado do Amazonas / The occurrence of hepatitis B and delta virus infection within seven Amerindian ethnic groups in the Brazilian western Amazon

HBV and HDV infections are a major health problem in the Amazon. This study evaluates the prevalence of these viruses within Indians groups, measuring the frequency of serological markers. The prevalence of past infection was 54.5% and HBsAg was found in 9.7%. An important variation of those markers was detected between villages, inclusively within the same ethnic group. None showed evidence of an acute infection. All HBeAg reactive were Apurinã, living in the same village and three of them from the same family. The prevalence of anti-HDT was 13.4% in HBsAg positive individuals. The authors observed high prevalence of HBV and HDV infection with the following pattern: low degree of infectivity, marked transmission in early ages, intra-familial dissemination, and lack of importance of vertical transmission. However, the results suggest that these viruses were not yet introduced effectively in some of the studied groups.

A infecção pelo VHB e VHD são importantes problemas de saúde na Amazônia. Este estudo avalia a prevalência da infecção por esses agentes em sete grupos indígenas do Estado do Amazonas. A taxa de infecção passada pelo VHB encontrada foi de 54,5% e a de portadores do AgHBs de 9,7%. Observa-se variação importante destes marcadores entre as aldeias, inclusive da mesma etnia. Não evidenciamos marcador de infecção aguda, os quatro AgHBe reativos eram todos Apurinã, da mesma aldeia, e três da mesma família. O VHD foi encontrado em 13,4% dos AgHBs reativos. O padrão de infecção pelo VHB e VHD encontrado possui as seguintes características: endemicidade elevada, baixo potencial de infectividade, transmissão marcada em idade precoce, provável transmissão familiar, e pouca importância da transmissão vertical. Entretanto, também sugere que esses vírus não tenham sido ainda introduzidos efetivamente em algumas das etnias estudadas