Emergence of biaxial nematic phases in solutions of semiflexible dimers.

We investigate the isotropic, uniaxial nematic and biaxial nematic phases, and the transitions between them, for a model lyotropic mixture of flexible molecules consisting of two rigid rods connected by a spacer with variable bending stiffness. We apply density-functional theory within the Onsager approximation to describe strictly excluded-volume interactions in this athermal model and to self-consistently find the orientational order parameters dictated by its complex symmetry, as functions of the density. Earlier work on lyotropic ordering of rigid bent-rod molecules is reproduced and extended to show explicitly the continuous phase transition at the Landau point, at a critical bend angle of 36^{∘}. For flexible dimers with no intrinsic biaxiality, we find that a biaxial nematic phase can nevertheless form at a sufficiently high density and low bending stiffness. For bending stiffness κ>0.86k_{B}T, this biaxial phase manifests as dimer bending fluctuations occurring preferentially in one plane. When the dimers are more flexible, κ<0.86k_{B}T, the modal shape of the fluctuating dimer is a V with an acute opening angle, and one of the biaxial order parameters changes sign, indicating a rotation of the directors. These two regions are separated by a narrow strip of uniaxial nematic in the phase diagram, which we generate in terms of the spacer stiffness and particle density

Assessment of chemiluminescence and PCR effectiveness in relation to conventional serological tests for the diagnosis of Chagas' disease Avaliação da eficiência da quimiluminescência e PCR em relação aos testes sorológicos convencionais para o diagnóstico da doença de Chagas

While testing 414 sera for the diagnosis of Chagas' disease, the conventional reactions of indirect hemagglutination, indirect immunofluorescence and the immunosorbent assay showed a sensitivity of 95.7%, 100% and 98.2% and a specificity of 98%, 98% and 96.4%, respectively, and an excellent association using Fisher's exact test. Chemiluminescence presented 100% sensitivity and 89.6% specificity, while PCR showed 100% specificity and 1.2% sensitivity. It is believed that the three conventional serological reactions are still adequate for diagnosing Chagas' disease.<br>No exame de 414 soros, para o diagnóstico da doença de Chagas, as reações convencionais de hemaglutinação indireta, imunofluorescência indireta e o ensaio imunoenzimático mostraram, respectivamente, uma sensibilidade de 95,7%, 100% e 98,2% e uma especificidade de 98%, 98% e 96,4% e excelente associação usando teste exato de Fisher. A quimioluminescência apresentou 100% de sensibilidade, 89,6% de especificidade e a PCR 100% de especificidade e 1,2% de sensibilidade. Acredita-se que as três reações sorológicas convencionais ainda são suficientes para o diagnóstico da doença de Chagas