The VLT-FLAMES survey of massive stars: observations centered on the Magellanic Cloud clusters NGC 330, NGC 346, NGC 2004, and the N11 region

We present new observations of 470 stars using the Fibre Large Array Multi-Element Spectrograph ( FLAMES) instrument in fields centered on the clusters NGC330 and NGC346 in the Small Magellanic Cloud (SMC), and NGC2004 and the N11 region in the Large Magellanic Cloud (LMC). A further 14 stars were observed in the N11 and NGC330 fields using the Ultraviolet and Visual Echelle Spectrograph (UVES) for a separate programme. Spectral classifications and stellar radial velocities are given for each target, with careful attention to checks for binarity. In particular, we have investigated previously unexplored regions around the central LH9/LH10 complex of N11, finding similar to 25 new O-type stars from our spectroscopy. We have observed a relatively large number of Be-type stars that display permitted Fe II emission lines. These are primarily not in the cluster cores and appear to be associated with classical Be-type stars, rather than pre main-sequence objects. The presence of the Fe II emission, as compared to the equivalent width of Ha, is not obviously dependent on metallicity. We have also explored the relative fraction of Be- to normal B-type stars in the field-regions near to NGC330 and NGC2004, finding no strong evidence of a trend with metallicity when compared to Galactic results. A consequence of service observations is that we have reasonable time-sampling in three of our FLAMES fields. We find lower limits to the binary fraction of O- and early B-type stars of 23 to 36%. One of our targets (NGC346-013) is especially interesting with a massive, apparently hotter, less luminous secondary component.

Standoff detection of weapons and contraband in the 100 GHz to 1 THz region

The techniques and technologies currently being investigated to detect weapons and contraband concealed on persons under clothing are reviewed. The basic phenomenology of the atmosphere and materials that must be understood in order to realize such a system are discussed. The component issues and architectural designs needed to realize systems are outlined. Some conclusions with respect to further technology developments are presented.

The N-terminal region of the Escherichia coli WecA (Rfe) protein, containing three predicted transmembrane helices, is required for function but not for membrane insertion

The correct site for translation initiation for Escherichia coli WecA (Rfe), presumably involved in catalyzing the transfer of N-acetylglucosamine 1-phosphate to undecaprenylphosphate, was determined by using its FLAG-tagged derivatives. The N-terminal region containing three predicted transmembrane helices was found to be necessary for function but not for membrane localization of this protein.

Promoter region of the Escherichia coli O7-specific lipopolysaccharide gene cluster:structural and functional characterization of an upstream untranslated mRNA sequence

We report the identification of the promoter region of the Escherichia coli O7-specific lipopolysaccharide (LPS) gene cluster (wbEcO7). Typical -10 and -35 sequences were found to be located in the intervening region between galF and rlmB, the first gene of the wbEcO7 cluster. Data from RNase protection experiments revealed the existence of an untranslated leader mRNA segment of 173 bp, including the JUMPStart and two ops sequences. We characterized the structure of this leader mRNA by using the program Mfold and a combination of nested and internal deletions transcriptionally fused to a promoterless lac operon. Our results indicated that the leader mRNA may fold into a series of complex stem-loop structures, one of which includes the JUMPStart element. We have also found that one of the ops sequences resides on the predicted stem and the other resides on the loop region, and we confirmed that these sequences are essential for the RfaH-mediated regulation of the O polysaccharide cluster. A very similar stem-loop structure could be predicted in the promoter region of the LPS core operon encoding the waaQGPSBIJYZK genes. We observed another predicted stem-loop, located immediately downstream from the wbEcO7 transcription initiation site, which appeared to be involved in premature termination of transcription. This putative stem-loop is common to many other O polysaccharide gene clusters but is not present in core oligosaccharide genes. wbEcO7-lac transcriptional fusions in single copy numbers were also used to determine the effects of various environmental cues in the transcriptional regulation of O polysaccharide synthesis. No effects were detected with temperature, osmolarity, Mg2+ concentration, and drugs inducing changes in DNA supercoiling. We therefore conclude that the wbEcO7 promoter activity may be constitutive and that regulation takes place at the level of elongation of the mRNA in a RfaH-mediated manner.

Genetic analysis of the dTDP-rhamnose biosynthesis region of the Escherichia coli VW187 (O7:K1) rfb gene cluster:identification of functional homologs of rfbB and rfbA in the rff cluster and correct location of the rffE gene

The O-repeating unit of the Escherichia coli O7-specific lipopolysaccharide is made of galactose, mannose, rhamnose, 4-acetamido-4,6-dideoxyglucose, and N-acetyglucosamine. We have recently characterized the genes involved in the biosynthesis of the sugar precursor GDP-mannose occurring in the E. coli O7:K1 strain VW187 (C. L. Marolda and M. A. Valvano, J. Bacteriol. 175:148-158, 1993). In the present study, we identified and sequenced the rfbBDAC genes encoding the enzymes for the biosynthesis of another precursor, dTDP-rhamnose. These genes are localized on the upstream end of the rfbEcO7 region, and they are strongly conserved compared with similar genes found in various enteric and nonenteric bacteria. Upstream of rfbB we identified a DNA segment containing the rfb promoter and a highly conserved untranslated leader sequence also present in the promoter regions of other surface polysaccharide gene clusters. Also, we have determined that rfbB and rfbA have homologs, rffG (o355) and rffH (o292), respectively, located on the rff cluster, which is involved in the synthesis of enterobacterial common antigen. We provide biochemical evidence that rffG and rffH encode dTDP-glucose dehydratase and glucose-1-phosphate thymidylyltransferase activities, respectively, and we also show that rffG complemented the rfbB defect in the O7+ cosmid pJHCV32. We also demonstrate that rffG is distinct from rffE and map the rffE gene to the second gene of the rff cluster.

Genetic analysis of the O-specific lipopolysaccharide biosynthesis region (rfb) of Escherichia coli K-12 W3110:identification of genes that confer group 6 specificity to Shigella flexneri serotypes Y and 4a

We recently reported a novel genetic locus located in the sbcB-his region of the chromosomal map of Escherichia coli K-12 which directs the expression of group 6-positive phenotype in Shigella flexneri lipopolysaccharide, presumably due to the transfer of O-acetyl groups onto rhamnose residues of the S. flexneri O-specific polysaccharide (Z. Yao, H. Liu, and M. A. Valvano, J. Bacteriol. 174:7500-7508, 1992). In this study, we identified the genetic region encoding group 6 specificity as part of the rfb gene cluster of E. coli K-12 strain W3110 and established the DNA sequence of most of this cluster. The rfbBDACX block of genes, located in the upstream region of the rfb cluster, was found to be strongly conserved in comparison with the corresponding region in Shigella dysenteriae type 1 and Salmonella enterica. Six other genes, four of which were shown to be essential for the expression of group 6 reactivity in S. flexneri serotypes Y and 4a, were identified downstream of rfbX. One of the remaining two genes showed similarities with rfc (O-antigen polymerase) of S. enterica serovar typhimurium, whereas the other, located in the downstream end of the cluster next to gnd (gluconate-6-phosphate dehydrogenase), had an IS5 insertion. Recently, it has been reported that the IS5 insertion mutation (rfb-50) can be complemented, resulting in the formation of O16-specific polysaccharide by E. coli K-12 (D. Liu and P. R. Reeves, Microbiology 140:49-57, 1994). We present immunochemical evidence suggesting that S. flexneri rfb genes also complement the rfb-50 mutation; in the presence of rfb genes of E. coli K-12, S. flexneri isolates express O16-specific polysaccharide which is also acetylated in its rhamnose residues, thereby eliciting group 6 specificity.

Genetic analysis of the O7-polysaccharide biosynthesis region from the Escherichia coli O7:K1 strain VW187

We recently cloned biosynthesis genes for the O7-lipopolysaccharide (O7-LPS) side chain from the Escherichia coli K-1 strain VW187 (M. A. Valvano, and J. H. Crosa, Infect. Immun. 57:937-943, 1989). To characterize the O7-LPS region, the recombinant cosmids pJHCV31 and pJHCV32 were mutagenized by transposon mutagenesis with Tn3HoHo1, which carries a promoterless lac operon and can therefore generate lacZ transcriptional fusions with target DNA sequences. Cells containing mutated plasmids were examined for their ability to react by coagglutination with O7 antiserum. The LPS pattern profiles of the insertion mutants were also investigated by electrophoresis of cell envelope fractions, followed by silver staining and immunoblotting analysis. These experiments identified three phenotypic classes of mutants and defined a region in the cloned DNA of about 14 kilobase pairs that is essential for O7-LPS expression. Analysis of beta-galactosidase production by cells carrying plasmids with transposon insertions indicated that transcription occurs in only one direction along the O7-LPS region. In vitro transcription-translation experiments revealed that the O7-LPS region encodes at least 16 polypeptides with molecular masses ranging from 20 to 48 kilodaltons. Also, the O7-LPS region in VW187 was mutagenized by homologous recombination with subsets of the cloned O7-LPS genes subcloned into a suicide plasmid vector. O7-LPS-deficient mutants of VW187 were complemented with pJHCV31 and pJHCV32, confirming that these cosmids contain genetic information that is essential for the expression of the O7 polysaccharide.

Corruption and subsidiary profitability: US MNC subsidiaries in the Asia Pacific region

Would multinational corporation (MNC) subsidiaries be more profitable in host countries where corruption is less severe? Would MNC subsidiaries be more profitable in less corrupt countries if they focus on local sales? This paper examines the impact of the level of corruption on the profitability of US MNCs in the Asia Pacific region. Using foreign direct investment (FDI) data archived by the US Bureau of Economic Analysis and corruption data reported by the World Bank, we find that MNC subsidiaries located in countries with a lower level of corruption are more profitable. In addition, MNC subsidiaries with a greater focus on local sales are more profitable when the corruption level is low. This study contributes to the literature by showing that when local sales are important to MNC subsidiaries, a lower level of corruption by host countries positively affects the profitability of the MNC subsidiaries.

Assessment of bioavailable arsenic and copper in soils and sediments from the Antofagasta region of northern Chile

Copper levels of nearly 500 mg l(-1) were measured in aqueous extracts of soil and sediment samples from the lowlands of Antofagasta. Arsenic levels of up to 183 mg l(-1) were found in river sediments, and 27.5 mg l(-1) arsenic was found at the location of a dam where potable water is extracted. This indicates that the arsenic contamination of water supplies reported recently for the pre-Andes may be a widespread problem throughout the region. Copper contamination from smelting activities also provides cause for concern as elevated levels were found in aqueous extracts of soil up to 20 km away from a smelter. This study went beyond traditional chemical analysis by assessing the potential benefits of using microbial biosensors as an alternative to determination of chemical speciation, to provide an environmentally relevant interpretation of soil/sediment residue levels. This approach is simple to use and enables a rapid, low cost assessment of pollutant bioavailability. It may, therefore, be of use for further investigations in the region and beyond.

Shape corrections to exchange-correlation potentials by gradient-regulated seamless connection of model potentials for inner and outer region

Shape corrections to the standard approximate Kohn-Sham exchange-correlation (xc) potentials are considered with the aim to improve the excitation energies (especially for higher excitations) calculated with time-dependent density functional perturbation theory. A scheme of gradient-regulated connection (GRAC) of inner to outer parts of a model potential is developed. Asymptotic corrections based either on the potential of Fermi and Amaldi or van Leeuwen and Baerends (LB) are seamlessly connected to the (shifted) xc potential of Becke and Perdew (BP) with the GRAC procedure, and are employed to calculate the vertical excitation energies of the prototype molecules N-2, CO, CH2O, C2H4, C5NH5, C6H6, Li-2, Na-2, K-2. The results are compared with those of the alternative interpolation scheme of Tozer and Handy as well as with the results of the potential obtained with the statistical averaging of (model) orbital potentials. Various asymptotically corrected potentials produce high quality excitation energies, which in quite a few cases approach the benchmark accuracy of 0.1 eV for the electronic spectra. Based on these results, the potential BP-GRAC-LB is proposed for molecular response calculations, which is a smooth potential and a genuine "local" density functional with an analytical representation. (C) 2001 American Institute of Physics.