Modelling a complex supply chain: understanding the effect of simplified assumptions

The benefits of coordinating activities and consolidating distribution points in supply chains are well highlighted and intuitively logical. However, the impact of these decisions on the overall performance of a complex supply chain may not be as obvious as usually perceived. This study models a relatively complex supply chain and evaluates the impact of simplifying demand and lead time assumptions under various supply chain configurations. Of particular interest is the investigation of the effect of risk pooling and the synchronization of production cycles in a multi-level multi-retailer supply chain under the influence of various parameters such as batch size, delivery frequency and ordering cycle. This study highlights the extent of complicated interaction effects among various factors exist in a complex supply chain and shows that that the intricacy of these effects can be better understood with a simulation model.     

Measurement and analysis of temperature and pressure in high altitude air shipments

This study was performed (at the request of the FAA) to measure temperature and pressure conditions observed by standard packages in the FedEx ‘Next Day Air’ network and the environmental conditions of passenger aircrafts. To measure the single parcel environment, two destinations known to be served by non‐pressurized feeder and pressurized aircrafts in the USA, San Luis Obispo, California, and Twin Falls, Idaho, were used to represent higher altitude paths. Test packages (0.30 × 0.30 × 0.30 m) containing one MadgeTech PRTemp110 recorder were shipped Priority Overnight by FedEx from East Lansing, Michigan. For 6 weeks, two test packages were shipped to each destination. To measure the passenger aircraft environment, test packages (0.14 × 0.11 × 0.06 m) were both carried in the passenger cabin and checked with luggage. Results show temperature ranges, pressure drop rates, and maximum altitudes observed from 52 flights (17 feeder aircrafts) in the FedEx environment and from eight commercial passenger flights. This study compares these results with the ASTM D6653‐01 test procedure with respect to suggested test pressure, pressure change rate, temperature, and test duration. Copyright © 2009 John Wiley & Sons, Ltd.     

Energy Storage Likely to Increase in Utility Resource Planning

Today energy storage is a diverse asset class, and technological advances and rapid cost declines have now resulted in a wide array of energy storage technologies increasingly being deployed on utility systems across the country. Utilities from Hawaii to New York have been finding energy storage an extremely attractive and cost-effective way to solve grid needs.     

Direct synthesis of carbon nanofibers from South African coal fly ash

Carbon nanofibers (CNFs), cylindrical nanostructures containing graphene, were synthesized directly from South African fly ash (a waste product formed during the combustion of coal). The CNFs (as well as other carbonaceous materials like carbon nanotubes (CNTs)) were produced by the catalytic chemical vapour deposition method (CCVD) in the presence of acetylene gas at temperatures ranging from 400°C to 700°C. The fly ash and its carbonaceous products were characterized by transmission electron microscopy (TEM), thermogravimetric analysis (TGA), laser Raman spectroscopy and Brunauer-Emmett-Teller (BET) surface area measurements. It was observed that as-received fly ash was capable of producing CNFs in high yield by CCVD, starting at a relatively low temperature of 400°C. Laser Raman spectra and TGA thermograms showed that the carbonaceous products which formed were mostly disordered. Small bundles of CNTs and CNFs observed by TEM and energy-dispersive spectroscopy (EDS) showed that the catalyst most likely responsible for CNF formation was iron in the form of cementite; X-ray diffraction (XRD) and Mössbauer spectroscopy confirmed these findings.     

Structural characterization of the oligomeric constituents of petroleum pitches

The separation of petroleum pitch into its oligomeric fractions via dense-gas extraction (DGE), followed by the application of both new and conventional analytical techniques to those fractions, has given us unique capabilities for identifying both the specific molecular structures that exist in petroleum pitches and their concentration. Specifically, pitch fractions containing 98% monomer or 97% dimer were isolated by DGE and characterized using MALDI, MALDI-PSD, and FD mass spectrometry (MS); and ¹H NMR, UV-Vis, and FT-IR spectroscopy. Results indicate that the molecular weight distribution (MWD) of the 98% monomer pitch fraction is approximately Gaussian, with the dominant species being methylated derivatives of the polycyclic aromatic hydrocarbons (PAH) benzofluorene (216.4 m/z), chrysene, (228.3 m/z), benzofluoranthene (252.3 m/z), and their isomers. The distribution of methyl substituents per molecule is also approximately Gaussian, with a maximum at 2. The MWD of the 97% dimer pitch fraction is also approximately Gaussian, and the most prevalent species (m/z = 454.6, 468.7, and 482.8) are consistent with condensation reactions of the most common monomer species with an accompanying loss of 4-6 hydrogens. As mesophase pitches that contain up to 25% dimer were previously identified, herein are proposed specific molecular structures that are significant constituents in mesophase pitch.     

Metabolomics: a valuable tool for stem cell monitoring in regenerative medicine

Metabolomics is a method for investigation of changes in the global metabolite profile of cells. This paper discusses the technical application of the approach, considering metabolite extraction, separation, mass spectrometry and data interpretation. A particular focus is on the application of metabolomics to the study of stem cell physiology in the context of biomaterials and regenerative medicine. Case studies are used to illustrate key points, focusing on the use of metabolomics in the examination of mesenchymal stem cell responses to titania-nanopillared substrata designed for orthopaedic applications.     

Thermophilic bacilli and their importance in dairy processing

The thermophilic bacilli, such as Anoxybacillus flavithermus and Geobacillus spp., are an important group of contaminants in the dairy industry. Although these bacilli are generally not pathogenic, their presence in dairy products is an indicator of poor hygiene and high numbers are unacceptable to customers. In addition, their growth may result in milk product defects caused by the production of acids or enzymes, potentially leading to off-flavours. Dairy thermophiles are usually selected for by the conditions during dairy manufacture. These bacteria are able to grow in sections of dairy manufacturing plants where temperatures reach 40-65 °C. Furthermore, because they are spore formers, they are difficult to eliminate. In addition, they exhibit a wide temperature growth range, exhibit a fast growth rate (generation time of approximately 15-20 min) and tend to readily form biofilms. Many strategies have been tested to remove, prevent and/or delay the formation of thermophilic bacilli biofilms in dairy manufacture, but with limited success. This is, in part, because little is known about the structure and composition of thermophilic bacilli biofilms in general and, more specifically, in milk processing environments. Therefore, new cleaning regimes often do not target the problem optimally. A greater understanding of the structure of thermophilic biofilms within the context of the milk processing environment and their link with spore formation is needed to develop better control measures. This review discusses the characteristics and food spoilage potential, enumeration and identification methods for the thermophilic bacilli, as well as their importance to dairy manufacture, with an emphasis on biofilm development and spore formation.     

Designing amino acid residues with single-conformations

Drug design can benefit from the use of non-coded amino acids, such as alpha-amino isobutyric acids (Aib) or sarcosine (N-methyl-glycine). Non-coded amino acids can confer resistance to enzymatic degradation and increase the conformational stability of the peptides. We have simulated the conformational effects of combining N-methylation, bulky groups on the Calpha atom and/or thioamides using the class II CFF91 force field and our thioamide force field parameters. Although single amino acid substitutions (e.g. Aib) can restrict the available conformations, they do not necessarily lead to unique conformers, however, we predict that some of the amino acids described in this report will fold to a single phi, psi conformation (e.g. N-methylated and thioamide penicillamine). Several other amino acid/thiopeptide combinations were designed, which are predicted to prefer only two conformations. Novel amino acids of this type should prove useful for designing peptides with defined conformations.     

Stirred reactor calculations to understand unwanted combustion enhancement by potential halon replacements

Several agents are under consideration to replace CF₃Br for use in suppressing fires in aircraft cargo bays. In a Federal Aviation Administration performance test simulating the explosion of an aerosol can, however, the replacements, when added at sub-inerting concentrations, have all been found to create higher pressure rise than with no agent, hence failing the test. Thermodynamic equilibrium calculations as well as perfectly-stirred reactor simulations with detailed reaction kinetics, are performed to understand the reasons for the unexpected enhanced combustion rather than suppression. The high pressure rise with added C₂HF₅ or C₃H₂F₃Br is shown to be dependent upon the amount of added agent, and can only occur if a large fraction of the available oxidizer in the chamber is consumed, corresponding to stoichiometric proportions of fuel, oxygen, and agent. Conversely, due to the unique stoichiometry of CF₃Br, this agent is predicted to cause no increase in pressure, even in the absence of chemical inhibition. The stirred-reactor simulations predict that the inhibition effectiveness of CF₃Br is highly dependent upon the mixing conditions of the reactants (which affects the local stoichiometry and hence the overall reaction rate). For C₂HF₅, however, the overall reaction rate was only weakly dependent upon stoichiometry, so the fuel–oxidizer mixing state has less effect on the suppression effectiveness.