Polygons on a rotating fluid surface.

We report a novel and spectacular instability of a fluid surface in a rotating system. In a flow driven by rotating the bottom plate of a partially filled, stationary cylindrical container, the shape of the free surface can spontaneously break the axial symmetry and assume the form of a polygon rotating rigidly with a speed different from that of the plate. With water, we have observed polygons with up to 6 corners. It has been known for many years that such flows are prone to symmetry breaking, but apparently the polygonal surface shapes have never been observed. The creation of rotating internal waves in a similar setup was observed for much lower rotation rates, where the free surface remains essentially flat [J. M. Lopez, J. Fluid Mech. 502, 99 (2004). We speculate that the instability is caused by the strong azimuthal shear due to the stationary walls and that it is triggered by minute wobbling of the rotating plate.

Nanosphere-antibody conjugates with releasable fluorescent probes.

Surface-functionalized, probe-containing, polymeric nanospheres with diameters between 10 nm and 40 nm (depending on the probe) were used to provide a fluorescent endpoint for nonextractive immunoassay. The probes inside the nanospheres were lanthanoid ions. Methyl methacrylate was used as the monomer to reduce random adsorption of proteins onto the nanosphere surfaces. The acid-group surface functionalization allowed the nanospheres to be conjugated to the amine groups on the antibodies (IgG). The surfaces were further functionalized with alcohol and ester groups to improve the suspension characteristics of the nanospheres. As many as four probe ions may be quantified simultaneously, although only three with a single ligand. Co-measurement of four probes required a combination of two ligands. The intensity of the fluorescence produced by these complexes allows detection with a sensitivity equivalent to enzyme-linked immunoassay.

Functionalized, probe-containing, latex nanospheres.

Synthesis of surface-functionalized, probe-containing latex nanospheres is described. Approximately 40,000 probe ions may be encapsulated in a nanosphere of 50 nm diameter. The probe may be a radionuclide or a lanthanide with long-lived fluorescence. Alternatively, a "cargo" of pharmaceutical interest may be used. The surface of each nanosphere contains thousands of acid groups which may be functionalized for subsequent attachment to biomolecules such as antibodies. Functionalized nanospheres have been successfully coupled to a tobacco virus.

Longitudinal analysis of internal migration to La Paz, Bolivia.

"This study examines the migration patterns of Bolivians who have moved from other provinces to La Paz. In order to better understand these patterns, the capital city was divided into eight similar socio-economic regions and the migration patterns analyzed for selected regions. In addition, the study compares the migrant flows for two time periods: location at the time of birth, and the migrant's residence in 1971. The research analyzes statistically the differences between migration fields for a representative area."

Migrant flows to La Paz, Bolivia, as related to the internal structure of the city: a methodological treatment.

PIP: A methodology for studying Bolivian migration flows to the capital city, La Paz, is presented. It initially involves the identification of out-migration rates by region of origin of migrant in order to examine links between the city and migration-sending centers. La Paz is then divided into eight regions, and migration flows to each region are mapped and analyzed separately. (summary in SPA)^ieng