Assuring reliable performance of antibiotic assay media

The Microbiological Assay Branch of the National Center for Antibiotics Analysis assays over 100,000 samples of antibiotic products annually, using more than 1000 Ib dehydrated media. The media must be consistently dependable to produce accurate, reliable test results. To assure that the supply of media will meet the established requirements, each lot before purchase is subjected to a series of trials designed to examine growth support, sensitivity, and behavioral and physical factors. Actual antibiotic assays are conducted with the test medium, and performance is rated against a control medium. Controls on the system reduce the variables to allow appraisal of the medium itself.     

Polychlorinated Biphenyls and Organochlorine Pesticides in Great Lakes Precipitation

Snow samples from the winter of 1975-6 and rain samples (seven locations) from the period May-November, 1976, were collected from around the Canadian side of the Great Lakes. All were examined for polychlorinated biphenyls and a range of organochlorine pesticides. The snow samples were time-integrated, being collected in February 1976. The rain samples were collected on an event basis, using stainless steel samplers with several complete events and the intervening dry-fall frequently being included in one sample.PCBs, lindane, α-BHC, DDT residues, α- and β-endosulfan, dieldrin, and methoxychlor were frequently found with mean rain levels of 21, 5, 12, 3, 2, 5, 1 and 8 ng/L, respectively. Concentrations in snowmelt were generally reduced from the rain values, except for PCBs.     

Structure-function activity of azasterols and nitrogen-containing steroids

Thirty-nine nitrogen-containing steroids were tested against two gram-negative, five gram-positive, and two yeast organisms. Many of these steroids have been previously reported to inhibit various metabolic processes involving sterol metabolism. While low minimal inhibitory concentration (MIC) values were recorded for sterol producing yeast, growth of bacteria which contain no sterols was also inhibited. Structure-function studies provided no relationship between biological activity and hypocholesteremic effects of these azasteroids. A hypothesis put forward is that amino and azasteroids are effectors of membrane which, in the case of mitochondria, lead to changes in adenosine triphosphate levels and/or dehydrogenase activity. Their effects on sterol metabolism, therefore, may be of secondary consideration.     

Investigating dehydration from compacts using terahertz pulsed, Raman, and near-infrared spectroscopy

The purpose of this study was to investigate the dehydration of piroxicam monohydrate (PRXMH) in compacts using terahertz pulsed spectroscopy (TPS), Raman spectroscopy, and reflectance near-infrared (NIR) spectroscopy. Compacts were prepared by using PRXMH and poly(tetrafluoro)ethylene powders and combining them in three different manners before compression to produce compacts in which the PRXMH was dispersed throughout the compact, deposited on one face of the compact, or included as a layer within the compact. TPS was a suitable technique to assess the effect of sample preparation on dehydration, whereas Raman and NIR spectroscopy were limited by their sampling depth and the interference of the polymer matrix. TPS revealed that the dehydration behavior depended largely on the compact preparation method. Non-isothermal dehydration was investigated with all three spectroscopic techniques, combined with principal component analysis (PCA) on samples where the PRXMH was deposited on one face of the compact. In addition, variable temperature X-ray powder diffractometry (VT-XRPD) was used to verify the transformation from PRXMH to anhydrous PRX form I, while thermogravimetric analysis (TGA) was used to monitor the water loss. All three spectroscopic techniques allowed in situ monitoring of the dehydration from the surface layers of the compacts. TPS and Raman spectroscopy detected structural changes of the crystal, while NIR spectroscopy was more sensitive to water loss. PCA of the TPS, Raman spectroscopy, and XRPD data revealed similar dehydration profiles. In contrast, the NIR spectroscopy profile was more similar to the TGA results. The spectroscopic techniques were more suitable than slower techniques such as VT-XRPD for monitoring rapid structural changes that occurred during the dehydration.     

Parallel fabrication of nanogap electrodes

We have developed a technique for simultaneously fabricating large numbers of nanogaps in a single processing step using feedback-controlled electromigration. Parallel nanogap formation is achieved by a balanced simultaneous process that uses a novel arrangement of nanoscale shorts between narrow constrictions where the nanogaps form. Because of this balancing, the fabrication of multiple nanoelectrodes is similar to that of a single nanogap junction. The technique should be useful for constructing complex circuits of molecular-scale electronic devices.     

CONSERVING WATER VOLES: BRITAIN'S FASTEST DECLINING MAMMAL

In Britain, the water vole is a declining species because of habitat loss and land-use change associated with the intensification of agriculture and urban encroachment. During recent years, this decline has accelerated due to predation by feral American Mink (escapees from fur farms) and population fragmentation. Legal protection and planning policy has allowed for conservation action to be incorporated into waterside developments. This paper examines the various options to maintain and enhance water-vole populations through planning design, sensitive mitigation procedures and strategic habitat restoration.     

Offshore wind farm with centralised power conversion and DC interconnection

The study of a hypothetical large offshore wind farm based on centralised power conversion and interconnected to the grid using a multiterminal parallel high voltage direct current (HVDC) link is presented. The 300 MW wind farm consists of 60 squirrel-cage based 5 MW generators connected to a common DC bus using ten voltage source converters (VSCs). The transmission system converters provide variable speed generator control, and therefore individual converters are not required for each wind generator, implying savings in wind farm costs. The paper studies the technical and economical benefits of the proposed topology, as well as the selection of the main components. A detailed analysis of the control circuits for both generator and grid facing converters, with respect to primary control functions, is also given. PSCAD/EMTDC simulation of the proposed concept is presented for realistic wind signals. The results confirm operation at an average optimum coefficient of performance at each respective generator group, as well as satisfactory stability even for severe wind speed changes. The proposed concept reduces the costs associated with DC interconnection and may simplify integration of large offshore wind farms at substantial distances.     

An essential saccharide binding domain for the mAb 2C7 established for Neisseria gonorrhoeae LOS by ES-MS and MSn

A study of bacterial surface oligosaccharides were investigated among different strains of Neisseria gonorrhoeae to correlate structural features essential for binding to the MAb 2C7. This epitope is widely expressed and conserved in gonococcal isolates, characteristics essential to an effective candidate vaccine antigen. Sample lipooligosaccharides (LOS), was prepared by a modification of the hot phenol-water method from which de-O-acetylated LOS and oligosaccharide (OS) components were analyzed by ES-MS-CID-MS and ES-MSnin a triple quadrupole and an ion trap mass spectrometer, respectively. Previously documented natural heterogeneity was apparent from both LOS and OS preparations which was admixed with fragments induced by hydrazine and mild acid treatment. Natural heterogeneity was limited to phosphorylation and antenni extensions to the alpha-chain. Mild acid hydrolysis to release OS also hydrolyzed the beta(1-->6) glycosidic linkage of lipid A. OS structures were determined by collisional and resonance excitation combined with MS and multistep MSn which provided sequence information from both neutral loss, and nonreducing terminal fragments. A comparison of OS structures, with earlier knowledge of MAb binding, enzyme treatment, and partial acid hydrolysis indicates a generic overlapping domain for 2C7 binding. Reoccurring structural features include a Hepalpha(1-->3)Hepbeta(1-->5)KDO trisaccharide core branched on the nonreducing terminus (Hep-2) with an alpha(1-->2) linked GlcNAc (gamma-chain), and an alpha-linked lactose (beta-chain) residue. From the central heptose (Hep-1), a beta(1-->4) linked lactose (alpha-chain), moiety is required although extensions to this residue appear unnecessary.     

The difficult breast

Generalized relative and absolute risk models, in which various functions of time and age modify the excess relative or absolute risk of radiation-induced cancer, are fitted to the Japanese atomic bomb survivor cancer incidence data set. Among generalized relative risk models, those in which a product of powers of time since exposure and attained age modify the relative risk provide the best fit. There are indications that the Armitage-Doll model (in its formulation as a generalized relative risk model) provides a poor fit to the data, possibly in part because of increasing age-adjusted cancer incidence rates in the Japanese cohort. Generalized absolute risk models, and in particular models in which either powers of time since exposure and attained age, or powers of time since exposure and age at exposure modify the excess absolute risk, provide a superior fit to any of the generalized relative risk models for all solid cancer sites analysed together. When six cancer subtypes are examined separately, only for respiratory cancers does this finding remain true, and for two other sites (female breast cancer and thyroid cancer) the generalized relative risk model yields a better fit than the generalized absolute risk model.