Temporally overlapped linear frequency-chirped pulse programming for true-time-delay applications.

A novel technique for programming broadband true-time delays that uses two frequency-offset temporally overlapped linear frequency-chirped pulses to produce periodic spectral gratings in an inhomogeneously broadened absorber is presented. Advantages of this technique include its ability to use chirped pulses that are longer than the coherence time of the crystal, less stringent laser frequency-stability requirements for grating accumulation, lower power requirements, a simplified system design, and the ability to tune broadband (multigigahertz) delays over a wide dynamic range (picoseconds to microseconds).

Demonstration of optical coherent transient true-time delay at 4 Gbits/s.

Multigigabit-per-second true time delay (TTD) was experimentally demonstrated by use of optical coherent transient techniques in a Tm(3+):YAG crystal. A delay accuracy of 1 ps and a delay resolution of 7 ps (both measurement limited) were achieved. The retrieved data retained good fidelity.

Cowdria ruminantium antibodies in acaricide-treated and untreated cattle exposed to Amblyomma variegatum ticks in The Gambia.

An indirect enzyme-linked immunosorbent assay (ELISA), based on the major antigenic protein I fragment B (MAPI-B) of Cowdria ruminantium, was used to assess seroprevalence in cattle in The Gambia. Two groups of 20 N'Dama and 20 Gobra zebu cattle were monitored for 12 months with flumethrin treatment and for another 10 months without acaricidal treatment. Two groups of 20 N'Dama and 20 Gobra cattle served as untreated controls. During the period of acaricidal treatment, the cumulative proportions of positive serum samples were 25.6 +/- 5.6% (+/- confidence interval) and 34.7 +/- 6.8% in treated N'Dama and Gobra cattle respectively; the proportion of positive sera in untreated cattle was 52.2 +/- 6.9% in N'Damas and 61.4 +/- 7.3% in Gobras. Within breed, difference in antibody prevalence between treated and untreated cattle was significant (P < 0.001) but between breed differences were not significant. In the 10 months following suspension of acaricide application, there was an increase of proportion of positive serum samples in previously treated N'Dama and Gobra cattle. In both previously treated and untreated animals the peak of positive seroreactions occurred during and subsequent to the period of activity of Amblyomma variegatum adults. Cumulative seroprevalences in previously treated N'Dama and Gobra cattle were 32.6 +/- 6.9% and 44.7 +/- 8.5%, respectively; in untreated animals seroprevalence was 38.6 +/- 7.2% in N'Dama and 65.3 +/- 8.4% in Gobra cattle. Throughout the study period, within the N'Dama breed, the seropositive rate in previously treated cattle did not differ from that in untreated animals. Conversely, within the Gobra breed, the number of positive seroreactions was higher (P < 0.002) in untreated animals than in previously treated cattle. These results provide a support for designing A. variegatum and heartwater control strategies, if necessary, in The Gambia in relation to cattle breeds.