College of Science

Theses and dissertations submitted to the College of Science

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We investigated the spectral and temporal characteristics of a 635 nm laser diode (LD) in an external cavity consisting of an etalon. The system utilized optical feedback (OF) from the etalon which transforms the effective reflectivity of the LD cavity. The experiments were carried out at two different temperatures, T=25°C and 20°C. The characteristics of a free-running LD were obtained initially. The LD was operated at three different operating currents, Iop=60, 65 and 70 mA. The free-running spectrum for each current consists of a broad profile. It was observed that the relative intensity of the free-running LD output increases with the operating current. This behavior holds for both temperature settings. For T=25°C, the average power measured were P=456.66, 965.00 and 1635.66 μW; the FWHM were Dl=9.2, 8.2 and 8.1 Å; and the associated coherence lengths are zc=70.84,79.58 and 80.69 μm for Iop=60,65 and 70 mA, respectively. For T=20°C, the average power measured were P= 667.00, 1026.66 and 1410.00 μW; the FWHM were Dl=8.5, 8.2 and 8.4Å; and the associated coherence lengths are zc= 76.59, 79.50 and 77.70 μm for Iop=60,65 and 70 mA, respectively. The behavior of temporal coherence length was also investigated at varying reflectivity. For T=25°C, the maximum associated coherence lengths obtained at R = 0.311, 0.300 and 0.303 are zc= 673.62, 1080.62 and 785.61 μm for Iop=60, 65 and 70 mA respectively. These maximum values of temporal coherence lengths obtained all fall within the reflectivity range 0.3

Plasmodium falciparum is a parasite responsible for the most common and deadly form of malaria in human beings. The factors affecting disease outcome in individuals however are currently unknown, but are believed to involve the host’s immune response against the parasite. In this experiment, the effect of sex on the antibody responses of Balb/c mice to the three allelic variants of P. falciparum merozoite surface protein-1 (PfMSP-1) block 2, namely RO33, K1, and Mad20, was investigated. The three proteins were expressed as thioredoxin-fusion proteins in BL21(DE3) E. coli cells. These proteins were purified using affinity chromatography. Ten (10) μg of each protein were injected into groups of 4-5 Balb/c mice along with an equal volume of complete Freund’s adjuvant for the initial immunization or incomplete Freund’s adjuvant for the two boosters at one week intervals. The same was done for mice immunized with thioredoxin alone which served as a negative control. Blood was collected from each mouse the day before immunization via tail bleeding and finally via cardiac puncture after a 3 week period. The relative levels of the antibody isotypes produced by each mouse in response to the different proteins was measured using ELISA. Analysis showed that there are significant differences in the antibody response between male and female Balb/c mice. Overall K1 elicited a significantly greater IgG2a response in males, Mad20 elicited a greater IgG3 response in females, and RO33 elicited a greater IgG1 response in females and a greater IgG2a response in males. Interestingly, RO33 which was non-immunogenic in females produced a response in males, while MAD20 was non-immunogenic in males but immunogenic in females. All in all, these results indicate that the two sexes respond to these antigens differently which may have implications on vaccine design. However, further studies are required to determine the implications of these differences on the battle against malaria.