Complex free energy landscapes in biaxial nematics and role of repulsive interactions : A Wang - Landau study

General quadratic Hamiltonian models, describing interaction between crystal molecules (typically with $D_{2h}$ symmetry) take into account couplings between their uniaxial and biaxial tensors. While the attractive contributions arising from interactions between similar tensors of the participating molecules provide for eventual condensation of the respective orders at suitably low temperatures, the role of cross-coupling between unlike tensors is not fully appreciated. Our recent study with an advanced Monte Carlo technique (entropic sampling) showed clearly the increasing relevance of this cross term in determining the phase diagram, contravening in some regions of model parameter space, the predictions of mean field theory and standard Monte Carlo simulation results. In this context, we investigated the phase diagrams and the nature of the phases therein, on two trajectories in the parameter space: one is a line in the interior region of biaxial stability believed to be representative of the real systems, and the second is the extensively investigated parabolic path resulting from the London dispersion approximation. In both the cases, we find the destabilizing effect of increased cross-coupling interactions, which invariably result in the formation of local biaxial organizations inhomogeneously distributed. This manifests as a small, but unmistakable, contribution of biaxial order in the uniaxial phase.The free energy profiles computed in the present study as a function of the two dominant order parameters indicate complex landscapes, reflecting the difficulties in the ready realization of the biaxial phase in the laboratory.Comment: 23 pages, 12 figure

Knowledge, Attitudes and Practices on HIV Prevention\ud Among Secondary School Students in Bukoba Rural,\ud Kagera Region- Tanzania

It is estimated that about 42 million people are living with HIV/AIDS worldwide. Among them 90% are from developing countries and more than 70% of them are found in Sub-Saharan Africa including Tanzania. About 4.8 million people are infected annually, 70% being women and 3 million are in Sub-Saharan Africa. Approximately 3 million people died from AIDS in 2003 worldwide. Documented data show that the reproductive age group is more vulnerable and thus an intervention is necessary in this age group. To assess knowledge, attitudes and practices on HIV preventive measures among secondary school students. Bukoba district, Kagera region, Tanzania A cross sectional study was conducted in Bukoba rural district, Kagera region, in September 2005. Multi-stage sampling technique was used to determine the study population and 364 students were interviewed using structured questionnaire. Our study findings showed that 93.7% of students knew how HIV is transmitted and 86.6% knew at least one method of HIV prevention. Students mentioned abstinence and faithfulness to one partner as best methods for HIV prevention. Despite the knowledge they have, very few students reported to have used condoms in their last sexual contacts. Radio was reported to be the major source of information even though information given was not satisfactory to most of the students. In addition, 50% of students reported to have experienced sex, the peak age of first sexual intercourse being 15 years. Most of the students had an objective knowledge on HIV/AIDS transmission and prevention though their attitudes and practices were differen

Classifications of undernutrition-their limitations and fallacies

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