An Improved Clustering Method Based on Data Field

By analyzing the problem of k-means, we find the traditional k-means algorithm suffers from some shortcomings, such as requiring the user to give out the number of clusters k in advance, being sensitive to the initial cluster centers, being sensitive to the noise and isolated data, only being applied to the type found in globular clusters, and being easily trapped into a local solution et cetera. This improved algorithm uses the potential of data to find the center data and eliminate the noise data. It decomposes big or extended cluster into several small clusters, then merges adjacent small clusters into a big cluster using the information provided by the Safety Area. Experimental results demonstrate that the improved k-means algorithm can determine the number of clusters, distinguish irregular cluster to a certain extent, decrease the dependence on the initial cluster centers, eliminate the effects of the noise data and get a better clustering accuracy.

Characterization and Survival of Rhizoctonia solani AG2-2 LP Associated with Large Patch Disease of Zoysia Grass

Prevalence and sites of survival of Rhizoctonia solani AG2-2 LP were studied in zoysia grass for 6 years. AG2-2 LP isolates commonly were recovered over all seasons at sites with a history of large patch disease. In patch margins, AG2-2 LP isolates were recovered from crowns of zoysia grass regardless of whether the disease occurred, but were most frequently isolated from the sheath tissues during disease occurrence. In healthy sites approximately 30 cm from the patch, isolates were obtained before but not during disease occurrence. Once disease occurred, patch symptoms rapidly expanded to the edge of tissue colonized by the pathogen during autumn to early spring. To verify that the pathogen spread to healthy areas, the clonal relationship among isolates was examined using their anastomosis reaction. Isolates recovered from the patch and healthy area outside the patch were of the same clone, but isolates from different patches differed. Cultural characteristics and pathogenicity of the AG2-2 LP isolates were compared with R. solani AG2-2 IIIB and R. solani AG2-2 IV. The AG2-2 LP isolates showed an irregular cluster of mycelia (not sclerotia), an irregular zonation, dark brown main hyphae, and sparse aerial hyphae on potato dextrose agar after 4 weeks of incubation. Optimum temperature for growth was 23°C. Cultural characteristics of AG2-2 subgroups IIIB and IV differed from LP isolates. All isolates of AG2-2 LP caused moderate to high levels of disease on zoysia grass, but were nonpathogenic or caused little disease on bent grass and sugar beet. These results indicate that cultural characteristics and host range of AG2-2 LP are different than those of AG2-2 IIIB and AG2-2 IV.

The fate of the centrosome-microtubule network in monocyte-derived giant cells

Avian monocyte-derived giant cells in vitro, which are in many respects similar to osteoclasts, display a complex microtubule array that plays a prominent role in cell spreading. It is organized by a polygonal row of regularly spaced centrosomes surrounding an irregular cluster of nuclei. The immediate progenitor cells are binucleate cells with a single microtubule-organising center (MTOC), the result of the congregation of the two individual centrosomes. The one-to-one correspondence between numbers of centrosomes and nuclei in giant cells suggests that the centrosome of each precursor cell has been conserved through the fusion process. This is in marked contrast to the absence of centrosomes in myotubes, another example of a differentiated cell derived from the fusion of progenitor cells.