Optimized Design of a Furnace Cooling System

This paper presents a case study of manufacturing furnace optimized re-design. The bottleneck in the production process is the cooling of heat treatment furnaces. These ovens are on an approximate 24-hour cycle, heating for 12 hours and cooling for 12 hours. Pressurized argon and process water are used to expedite cooling. The proposed modifications aim to minimize cycling by reducing cooling time; they are grouped into three fundamental mechanisms. The first is a recommendation to modify current operating procedures. This entails opening the furnace doors at higher than normal temperatures. A furnace temperature model based on current parameters is used to show the reduction in cooling time in response to opening the furnace doors at higher temperatures. The second mechanism considers the introduction of forced argon convection. Argon is used in the process to mitigate part oxidation. Cycling argon through the furnace during cooling increases convection over the parts and removes heat from the furnace envelope. Heat transfer models based on convective Nusselt correlations are used to determine the increase in heat transfer rate. The last mechanism considers a modification to the current heat exchanger. By decreasing the temperature of the water jacket and increasing heat exchanger efficiency, heat transfer from the furnace is increased and cooling time is shortened. This analysis is done using the Effectiveness-NTU method

Genetics of Serum Resistance in Neisseria gonorrhoeae: The sac-1 Genetic Locus

A genetic locus affecting susceptibility to the bactericidal activity of normal human serum has been designated sac-1. This locus was shown to be closely linked to, but not identical with, a second locus (designated nmp-2) that affects protein 1 of the outer membrane. The sac-1 locus could be linked to known antibiotic resistance markers on the gonococcal chromosome by genetic transformation

Post-transcriptional modifications in the small subunit ribosomal RNA from Thermotoga maritima, including presence of a novel modified cytidine

Post-transcriptional modifications of RNA are nearly ubiquitous in the principal RNAs involved in translation. However, in the case of rRNA the functional roles of modification are far less established than for tRNA, and are subject to less knowledge in terms of specific nucleoside identities and their sequence locations. Post-transcriptional modifications have been studied in the SSU rRNA from Thermotoga maritima (optimal growth 80°C), one of the most deeply branched organisms in the Eubacterial phylogenetic tree. A total of 10 different modified nucleosides were found, the greatest number reported for bacterial SSU rRNA, occupying a net of ∼14 sequence sites, compared with a similar number of sites recently reported for Thermus thermophilus and 11 for Escherichia coli. The relatively large number of modifications in Thermotoga offers modest support for the notion that thermophile rRNAs are more extensively modified than those from mesophiles. Seven of the Thermotoga modified sites are identical (location and identity) to those in E. coli. An unusual derivative of cytidine was found, designated N-330 (M (r) 330.117), and was sequenced to position 1404 in the decoding region of the rRNA. It was unexpectedly found to be identical to an earlier reported nucleoside of unknown structure at the same location in the SSU RNA of the archaeal mesophile Haloferax volcanii

Polymer Molecular Weight and Chain Transfer During the Photopolymerization of an Aliphatic Monoacrylate in a Smectic Liquid Crystal

Polymer/liquid crystal (LC) composites offer a unique opportunity to study polymerizations in ordered media, specifically the potential effect mesophase order can have on polymer properties including molecular weight. To develop successful polymer/LC composites for display applications, it is important to understand the effect of mesophase order on polymer molecular weight in order to optimize the electrooptic (EO) properties of the polymerALC composite. Polymer molecular weight may be influenced in a LC by changes in polymerization rate as LC order is modulated and by chain transfer. This work focuses on the photopolymerization of an aliphatic monoacrylate monomer, decyl acrylate (DA), both in the ordered LC phases of 8CB as well as in isotropic solutions with LC and co-solvent. When DA is polymerized using the LC as the solvent, enhanced polymerization rates and polymer molecular weights are observed in the highly ordered smectic phase compared to the less ordered nentatic and isotropic phases. When conducted strictly in an isotropic environment using a co-solvent with increasing 8CB percentages, a dramatic decrease in the polymerization rate and a significant reduction of the polymer molecular weight is observed, implying degradative chain transfer to the LC. NMR results show that this chain transfer is a result of hydrogen abstraction from the liquid crystals, which leads to the reduction in the polymerization rate with increasing 8CB concentration. The most likely site of hydrogen abstraction is from the benzyl hydrogens of the alkyl chain of 8CB. This chain transfer also plays a role for polymerizations performed in the ordered phases of the LC. Chain transfer appears to be less significant when polymerizations are conducted in the smectic phase due to the anti-parallel association of the LC molecules. When polymerizations occur in the less ordered phases, chain transfer dominates leading to a large reduction in polymer molecular weight and polymerization rate. (C) 2003 Elsevier Science Ltd. All rights reserved