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Small scale and low cost hydrokinetic turbines can effectively contribute to solve energy deficits in developing countries, particularly in isolated communities, but some obstacles remain before they become a cost effective solution. This work reports on a methodology for designing and fabricating the main parts of small scale horizontal axis hydrokinetic turbines (HAHT) optimized for a specific site or operation conditions. A suitable software design tool, and low cost fabrication methods within reach and understanding of less developed communities are the basis of this methodology. A free and open source software package called Turbem developed by the authors allows a non-expert user to enter a minimum set of parameters and to obtain the complete optimal rotor geometry of the HAHT, with its estimated performance curves and maximum stresses. Turbem uses a combined approach of BEM theory and pseudo-gradient root finding for rotor optimal design, and classical solid mechanics for preliminary structural verification. The geometric information generated is sufficient for fabricating the rotor by a wide range of methods, ranging from hand carving up to CNC machining. In the latter case, Turbem generates CNC programs that are downloadable to any standard CNC machine, for direct fabrication of the blades and hub, or blade section templates as well. Hence, a technically sound rotor can be fabricated at a very low cost using wood as core and applying external layups of fiberglass with epoxy resin, as described herein. Using this methodology, small scale, cost effective HAHTs can be custom designed to take full advantage of specific site stream velocities and bathymetry. A 5kW (nominal) hydrokinetic turbine was successfully designed, fabricated and field tested in order to validate and improve this methodology. [ABSTRACT FROM AUTHOR]

We report x-ray reflectivity measurements on the free surface of \(4-n-heptylphenyl-4'-(4"-nitrobenzoyloxy)benzoate (DB7NO_2)\) at the nematic to smectic-A phase transition, \(T_{NA}=99.9^{\circ}C\). The free surface in the nematic phase exhibits smecticlike ordering at two q vectors, one which is commensurate with the smectic-A monolayer q vector \(q_2\). The other q vector is incommensurate corresponding to ordering at \(\sim 0.59q_2\). The commensurate peak constructively interferes with the air-liquid interface while the incommensurate peak destructively interferes. These results are compared with bulk-phase x-ray scattering measurements., Engineering and Applied Sciences