Value-added centers have been established in many states. These centers vary greatly in objectives, operational structures, staffing, and funding. This paper uses examples of several centers and programs, with a specific emphasis on three centers, to provide a better understanding of value-added centers and their operations.

Heritage speakers who re-learn their childhood language in adulthood are an important group for the study of L3 acquisition. Such re-learners have selective advantages over other L2/L3 learners in phonetics/phonology, but lack a global advantage at re-learning the prestige variety of their L1. These learners show asymmetrical transfer effects in morphosyntax: transfer occurs only from the dominant language. Two tentative explanations for this asymmetry are suggested. First, re-learners may deploy the skills acquired in a classroom setting, where they have used only their dominant language. Second, re-learners may implicitly strive to increase the typological distance between their childhood language and the language of classroom instruction. These findings have implications for models of L3/Ln learning: the Cumulative Enhancement Model, the Typological Proximity Model, and the L2 Status Factor Model. The data discussed in this paper are most consistent with the latter model, but they also highlight the significance of the typological distance between languages under acquisition.

A cDNA library constructed from 3 day post-infective L3 of the filarial nematode Brugia pahangi was screened by differential hybridization with cDNA probes prepared from different life-cycle stages. Five cDNA clones hybridizing selectively to the mosquito-derived L3 probe were isolated and characterized. Northern blot analysis of 4 of the clones confirmed that each was most highly expressed in the mosquito-derived L3. The expression of each mRNAduring parasite development in the mosquito vector was investigated using RT–PCR, and all were shown to be abundant in the immature L3. Four of the 5 cDNAs cloned coded for structural proteins: 2 cuticular collagens, and the muscle proteins tropomyosin and troponin. Further studies on troponin using an antiserum raised to the recombinant protein demonstrated that the protein, unlike the mRNA, was present in all life-cycle stages examined, while immunogold labelling demonstrated that it was localized to the muscle blocks.

In order to assess the prevalence of the cattle filaria Onchocerca ochengi in onchocerciasis vectors (Simulium damnosum s.l.) in North Cameroon, we searched for a means to morphologically identify its developing larvae, which closely resemble those of O. volvulus. To this end microfilariae of the 2 Onchocerca species were isolated from slaughter cattle in Ngaoundéré and injected into neonate Simulium species. Whereas the early developmental stages (sausage stage, L2 and pre-infective larva) were indistinguishable, the infective larvae (L3) of O. ochengi were longer (median: 740 μm), more slender (diameter = 19·3 μm = 2·6% of body length) and had a relatively shorter tail (4·9% of body length) than those of O. volvulus (680 μm, 20·5 μm, 3·0% and 5·8% respectively). The tail of O. ochengi L3 was thick and rounded, whereas it was slightly tapering in O. volvulus L3. O. ochengi L3 produced by feeding flies on infected cattle in a different area in North Cameroon (Sora Mboum) showed the same features as intrathoracically produced O. ochengi L3 from Ngaoundéré, but were even longer (785 μm). On the basis of the differences in length, relative diameter, length of the tail and shape of the tail, a simple key for the separation of O. volvulus and O. ochengi L3 was elaborated, and 248 L3 found in wild S. damnosum s.l. were separated into ‘O. ochengi’ (160 L3) and ‘O. volvulus’ (88 L3) following this key. Sequential dot blot hybridization of each of the 248 larvae with a DNA probe which reacts with O. ochengi and O. volvulus but not with other Onchocerca species (pOo5/1) and with an O. volvulus-specific DNA probe (pOv12) revealed that the morphological identification had been correct in 86–91% of the cases. Only a small proportion (6–9%) of the dot blots did not react with either probe. Since this proportion was equal in experiments using experimentally produced L3 and in experiments using wild L3, the non-hybridization was certainly due to a loss of L3 during washing of the filters and not due to the presence of other unknown L3 species resembling O. volvulus and O. ochengi. Our study shows that in Cameroon it is possible to identify O. volvulus and O. ochengi infective larvae during routine fly dissections by morphology alone.

The various articles about standardisation decisions tend to overlook an important phenomenon, that of the competition between a private and a public company (mixed duopoly). Such a competition occurs essentially in international trade. It is the purpose of this paper to study standardisation decisions made in this context. In a model of vertical differentiation, we show that the competition system in which standardisation is the most likely to emerge depends on the degree of differentiation of the intrinsic qualities. If this degree is high and if the public firm sells the best product, then mixed duopoly is more favourable to standardisation; otherwise, when products are then relatively similar, it is public duopoly.