Ytterbium-doped silica fibers exhibit very broad absorption and emission bands, from -800 nm to -1064 nm for absorption and -970 nm to -1200 nm for emission. The simplicity of the level structure provides freedom from unwanted processes such as excited state absorption, multiphonon nonradiative decay, and concentration quenching. These fiber lasers therefore offer a very efficient and convenient means of wavelength conversion from a wide variety of pump lasers, including AlGaAs and InCaAs diodes and Nd:YAG lasers. Efficient operation with narrow linewidth at any wavelength in the emission range can be conveniently achieved using fiber gratings. A wide range of application for these sources can be anticipated. In this paper, the capabilities of this versatile source are reviewed. Analytical procedures and numerical data are presented to enable design choices to be made for the wide range of operating conditions.

This paper describes how a unique type of virtual team, deploying a computer-mediated collaborative technology, developed a radically new product. The uniqueness of the team-what we call VC 3 teams, for Virtual Cross-value-chain, Creative Collaborative Teams-stemmed from the fact that it was inter-organizational and virtual, and had to compete for the attention of team members who also belong to collocated teams within their own organizations. Existing research on virtual teams does not fully address the challenges of such VC 3 teams. Using the case of Boeing-Rocketdyne, we describe the behavior of members of a VC 3 team to derive implications for research on virtual teaming, especially for studying teams within emerging contexts such as the one we observed. The data we collected also allowed us to identify successful managerial practices and develop recommendations for managers responsible for such teams.

SummaryPrevious epidemiological studies have implicated Clostridium perfringens enterotoxin (CPE) as a virulence factor in the pathogenesis of several gastrointestinal (GI) illnesses caused by C. perfringens type A isolates, including C. perfringens type A food poisoning and non-food-borne GI illnesses, such as antibiotic-associated diarrhoea and sporadic diarrhoea. To further evaluate the importance of CPE in the pathogenesis of these GI diseases, allelic exchange was used to construct cpe knock-out mutants in both SM101 (a derivative of a C. perfringens type A food poisoning isolate carrying a chromosomal cpe gene) and F4969 (a C. perfringens type A non-food-borne GI disease isolate carrying a plasmid-borne cpe gene). Western blot analyses con®rmed that neither cpe knock-out mutant could express CPE during either sporulation or vegetative growth, and that this lack of CPE expression could be complemented by transforming these mutants with a recombinant plasmid carrying the wild-type cpe gene. When the virulence of the wild-type, mutant and complementing strains were compared in a rabbit ileal loop model, sporulating (but not vegetative) culture lysates of the wild-type isolates induced signi®cant ileal loop¯uid accumulation and intestinal histopathological damage, but neither sporulating nor vegetative culture lysates of the cpe knock-out mutants induced these intestinal effects. However, full sporulation-associated virulence could be restored by complementing these cpe knock-out mutants with a recombinant plasmid carrying the wildtype cpe gene, which con®rms that the observed loss of virulence for the cpe knock-out mutants results from the speci®c inactivation of the cpe gene and the resultant loss of CPE expression. Therefore, in vivo analysis of our isogenic cpe mutants indicates that CPE expression is necessary for these two cpe-positive C. perfringens type A human disease isolates to cause GI effects in the culture lysate:ileal loop model system, a ®nding that supports CPE as an important virulence factor in GI diseases involving cpe-positive C. perfringens type A isolates.

Binary toxin CDT or its genes have been identified in some strains of Clostridium difficile that also produce the large clostridial toxins, toxins A and B (A+B+CDT+), including a newly recognized epidemic strain in the United States and Canada. To study the effects of binary toxin alone, we characterized 4 binary toxin CDT-positive only (A-B-CDT+) C. difficile strains. Unlike other clostridial binary toxins, binary toxin CDT required exogenous trypsin for activation. Supernatants from all A-B-CDT+ strains caused marked fluid accumulation in the rabbit ileal loop assay after concentration and trypsinization. In addition, the ileal loop response was neutralized by antisera raised against other binary toxin-producing clostridia. Challenge of clindamycin-treated hamsters with these strains resulted in colonization but not diarrhea or death. Binary toxin CDT may play an adjunctive role to toxins A and B in the pathogenesis of C. difficile-associated disease but by itself may not be sufficient to cause disease.

Segmented filamentous bacteria (SFB) are nonpathogenic bacteria that are commonly found attached to the intestinal walls of many animals. Until now, these bacteria have not been cultured in vitro. Recently, a 16s rRNA sequence analysis revealed that SFB isolated from mice represent a distinct subline within the Cfostridium subphylum of the gram-positive bacteria. Since SFB isolated from mice, rats, and chickens are known to be host specific, we investigated the phylogenetic relationships among SFB obtained from these three hosts.Total DNAs from the intestinal floras of chickens and rats were used as templates for PCR amplification of 16s rRNA genes. PCR products were cloned and screened by a dot blot hybridization procedure to identify homologous sequences that cross-reacted with mouse SFB-specific oligonucleotide probes. A phylogenetic analysis of these 16s ribosomal DNA sequences revealed that SFB isolated from these three hosts form a natural group, which is peripherally related to the genus Cfostridiurn sensu strict0 (group I Cfostridiurn). The SFB obtained from chickens, rats, and mice had closely related, albeit different, 16s rRNA gene sequences. The observed levels of 16s rRNA sequence divergence, ca. 1.5 to 3%, together with host specificity, suggest that SFB isolated from mice, rats, and chickens represent different species and that coevolution of the SFB and their hosts occurred. "Candidatus Arthromitus" is proposed as the provisional generic name for this group of organisms.The small intestines of many animals (e.g., mice, rats, pigs, and other mammals, as well as chickens, amphibians, and insects) are inhabited by segmented filamentous bacteria (SFB), which are also referred to as long segmented filamentous organisms (reviewed in reference 10). These bacteria cannot be cultured in vitro and do not have official taxonomic names. Until recently, SFB could be recognized only on the basis of their morphology and their ecological niches. In intestines, these gram-positive, endospore-forming organisms are attached via holdfasts to the epithelial walls. In rodents, colonization by SFB is restricted to the ileum (4). In birds, SFB are also found in the ceca (9). No pathologic effects of SFB have been found, even in immunodeficient animals. SFB found in different animal species are morphologically very similar. However, attempts to transfer bacteria from one host species to another have revealed that SFB found in mice, rats, and chickens exhibit host specificity (1, 13, 21). It is not known if SFB that inhabit different hosts are taxonomically closely related or whether they belong to different species.In a recent study, the 16s rRNA-encoding gene sequence of SFB obtained from mice was determined (19). This study was greatly facilitated by the use of a monoculture of these organisms in formerly germfree mice (12). A comparative 16s rRNA * Corresponding author. Mailing address: Central Animal Laboratory, University of Nijmegen, P.O. Box 9101, NL-6500 HB Nijmegen, 'The Netherlands. analysis revealed that th...