Post world war II Cuba: survey of political, economic and social trends, 1944-1951.

Thesis (M.A.)--Boston UniversityFollowing four hundred years of Spanish rule, the political scene for the first twenty-five years of the Republic saw the Liberal and Conservative Parties battle for political power. But no matter which party was in power, the corruption and graft remained. Within these years, Cuba also witnessed her largest economic boom followed by her severest depression from which she did not recover until the 1940s. [TRUNCATED] The major social developments have been the granting of labor's wage and job security demands by the government to maintain their political support at the expense of higher production costs. Educationally, the country has retrogressed as evidenced by decreasing enrollments and lack of educational opportunities, especially in the rural areas and on the higher levels of education. It Cuba is to have a dynamic society, capable of meeting the complexities of economic development, her educational system and opportunities will have to be improved. In general, the instabilities that existed in Cuba before World War II have not been decreased by the prosperity of this period, but in some ways have become intensified, as evidenced by the increasing importance of the sugar industry in the economic welfare of the island. [TRUNCATED

Polyamide Nanocomposites for Selective Laser Sintering

Current polyamide 11 and 12 are lacking in fire retardancy and high strength/high heat resistance characteristics for a plethora of finished parts that are desired and required for performance driven applications. It is anticipated that nanomodification of polyamide 11 and 12 will result in enhanced polymer performance, i.e., fire retardancy, high strength and high heat resistance for polyamide 11 and 12. It is expected that these findings will expand the market opportunities for polyamide 11 and 12 resin manufacturers. The objective of this research is to develop improved polyamide 11 and 12 polymers with enhanced flame retardancy, thermal, and mechanical properties for selective laser sintering (SLS) rapid manufacturing (RM). A nanophase was introduced into the polyamide 11 and 12 via twin screw extrusion to provide improved material properties of the polymer blends. Arkema RILSAN® polyamide 11 molding polymer pellets and Degussa VESTAMID® L1670 polyamide 12 were examined with three types of nanoparticles: chemically modified montmorillonite (MMT) organoclays, surface modified nanosilica, and carbon nanofibers (CNFs) to create polyamide 11 and 12 nanocomposites. Wide angle X-ray diffraction (WAXD) and transmission electron microscopy (TEM) were used to determine the degree of dispersion. Injection molded test specimens were fabricated for physical, thermal, mechanical properties, and flammability tests. Thermal stability of these polyamide 11 and 12 nanocomposites was examined by TGA. Mechanical properties such as tensile, flexural, and elongation at break were measured. Flammability properties were also obtained using the Cone Calorimeter at an external heat flux of 50 kW/m2. TEM micrographs, physical, mechanical, and flammability properties are included in the paper. Polyamide 11 and 12 nanocomposites properties are compared with polyamide 11 and 12 baseline polymers. Based on flammability and mechanical material performance, selective polymers including polyamide 11 nanocomposites and control polyamide 11 were cryogenically ground into fine powders and fabricated into SLS parts.Mechanical Engineerin