Comet P/Holmes, 1892III: A case of duplicity?

The observations of comet P/Holmes 1892III, exhibiting two 8- to 10-mag bursts, have been carefully analyzed. The phenomena are consistent with the grazing encounter of a small satellite with the nucleus on November 4.6, 1892, and the final encounter on January 16.3, 1893. The grazing encounter produced, besides the first great burst, an active area on the nucleus, which was rotating retrograde with a period of 16.3 hr and inclination of nearly 180°. After the final encounter, the spin period was essentially unchanged, but two areas became active, separated some 164° in longitude on the nucleus. After the first burst the total magnitude fell less than 2 mag from November 7 to 30 (barely naked eye) while the nuclear region remained diffuse or complex, rarely of ever showing a stellar appearance. The fading was much more rapid after the second burst (barely naked eye at maximum) while the nucleus frequently appeared stellar after the first day. It seems reasonable to conclude that the grazing encounter distributed a volume of large chunks in the neighborhood of the nucleus, maintaining activity for weeks. The final encounter activated a new area on the nucleus, the shock and fall back disturbing the area already exposed by the grazing encounter. Several details of this scenario are fitted rather well.     

Identity building and social transformation: the cases of Namibia and Botswana compared

Namibia and Botswana differ from other sub-Saharan nations in their record of stable political performance. However, both countries have to face increasing social problems. In the case of Namibia these are still mainly related to the process of post-apartheid national reconciliation and identity building, in the case of Botswana they refer to issues of growing tribal tensions and of a gradual interior restructuring of society. This paper analyzes the various patterns of social transformation in the two countries and examines in what ways state-society relations are different from other African nations. This revised version was published online in July 2006 with corrections to the Cover Date.     

Simulated impacts of the South Atlantic Ocean Dipole on summer precipitation at the Guinea Coast

An intermediate complexity atmospheric general circulation model has been used to investigate the influence of the South Atlantic Ocean (SAO) dipole (SAOD) on summer precipitation over the Guinea Coast of West Africa. Two ensemble integrations in which idealized but realistic SAOD-type sea surface temperature (SST) anomaly is prescribed only in the SAO, and then globally are performed and inter-compared. Consistently, above (below) the average precipitation is simulated over the Guinea Coast during the positive (negative) phase of the SAOD. Comparison of the two set of experiments reveal that in its active years, the SAOD is a dominant mechanism that shapes the spatial character of summer precipitation at the Guinea coast, the global SST variability merely slightly moderate its effects. During the SAOD, cool SST anomaly in the extra-tropical SAO off the Brazil–Uruguay–Argentina coast gives rise to suppressed convection and mass divergence. In turn, the subsidence tends to amplify the sub-tropical arm of anomalous Hadley-type circulation and consequently large scale convection and mass flux convergence in the equatorial Atlantic Ocean/Gulf of Guinea region bordering on the coastal fringes of West Africa. Precipitation is therefore increased at the Guinea Coast.     

Upwelling signals in radiocarbon from early 20th-century Peruvian bay scallop (Argopecten purpuratus) shells

We quantified Δ¹⁴C, δ¹⁸O, and δ¹³C cycles along ontogeny within four bay scallop (Argopecten purpuratus) shells collected from Callao Bay, Salaverry, and Sechura Bay, Peru following the 1907–1908 non-El Niño years and the 1925–1926 El Niño. Δ¹⁴C and δ¹³C generally covary; Δ¹⁴C and δ¹⁸O vary inversely. Simultaneous decreases in Δ¹⁴C and increases in δ¹⁸O in non-El Niño shells are followed by constant Δ¹⁴C and gradually decreasing δ¹⁸O, which we interpret as evidence for discrete marine upwelling events followed by warming of the initially cold upwelled water. Upwelling changes from El Niño events are detectable with difficulty in mollusk shell Δ¹⁴C.     

Detection of silicate emission features in the 8- to 13-μm spectra of main belt asteroids

We present 8.0–13.0 micron spectra $\text{(}\text{Δλ}\text{λ}\text{= 0.02?0.03)}$ for six main belt asteroids, which range from 58 to 220 km in diameter and sample the five principal taxonomic classes (C, S, M, R and E). Narrow, well-defined silicate emission features are present on two of the asteroids, the C-type 19 Fortuna and the M-type 21 Lutetia. No comparable emission features are observed on the S-types 11 Parthenope and 14 Irene, the R-type 349 Dembowska or the E-type 64 Angelina.