A distance and shape-based methodology for the unequal area facility layout problem

Significant improvements in production effectiveness have resulted from implementing cellular manufacturing systems (CMS). Following the cell formation, an important issue that needs to be addressed is the unequal cell (or department/facility) layout problem, which is the sub-issue in the CF problem. The work reported in this thesis illustrates the assignment of unequal cell locations in dealing with the known traffic movements on a shop floor. In addition, this research addresses the impact of the geometry or shape of the department as an important design factor in the unequal area facility layout problem, an issue that has not been addressed by the previous researchers. The problem is formulated as a mixed-binary non-linear programming model and is proven to be NP-hard in the strong sense. Due to its computational complexity, a higher-level heuristic, based on a concept known as tabu-search, is proposed to efficiently solve the problem. Six different versions of the tabu search-based heuristic algorithm are tested on three different problem structures. The results obtained from performing the experiment concluded that the tabu search-based heuristic using short-term memory and variable tabu-list sizes is preferred over other heuristics as the problem size increases. The performance comparison between the current and the previous research shows that the solution obtained for the well-known problems in this research are better than that obtained in the past

Protein diagenesis in "Patella" shells: Implications for amino acid racemisation dating

Abstract: The inter- and intra-crystalline fractions of Patella vulgata limpets recovered from archaeological sites in Northern Spain (covering Neolithic, Mesolithic, Magdalenian, Solutrean, and Aurignacian periods) were examined for amino acid composition and racemisation over time. The calcitic apex and rim areas of the shells were found to probably be composed of similar proteins, as the D/L values and amino acids were comparable and varied in the same way with increasing age; however, the mineral structures present in these areas differed. The aragonitic intermediate part of the shell showed a distinctly different amino acid composition and mineral structure. The main protein leaching from the inter-crystalline fraction occurred within the first 6000 yr after the death of the organism. In contrast, the intra-crystalline fraction d comprised of a different protein composition than the inter-crystalline fraction d appeared to behave as a closed system for at least 34 ka, as reflected by the lack of a significant decrease in the amino acid content; however, changes in the amino acid percentages occurred during this period. The concentration of aspartic acid remained almost constant with age both in inter- and intra-crystalline proteins, and its contribution to the total amino acid content increased with age at the expense of other amino acids such as glutamic acid, serine, glycine and alanine. Temperature is thought to play a key role in the amino acid racemisation of P. vulgata and could explain why in the localities belonging to the Gravettian and Solutrean period, which formed during relatively cold conditions, D/L values were similar to those detected in shells from sites formed during the Magdalenian.This paper was made possible by funding from the Spanish Ministry of Science and Innovation projects: HAR2010-22115-C02-01 “La respuesta humana al cambio climático global en una zona litoral: el caso del tránsito al Holoceno en la costa cantábrica (10000-5000 cal BC)”, and HAR2010-22115-C02-02 “Aplicación del análisis de sustancias orgánicas e inorgánicas a la reconstrucción paleoambiental, cronológica y tafonómica de yacimientos arqueológicos del Norte de España”

U-Series and Amino-acde Racemization Geochronology of Bermuda - Implications for Eustatic Sea-Llevel Fluctuation Over the Past 250,000 Years

Bermuda is a stable, mid-oceanic carbonate platform for which a particularly complete record of Late Pleistocene eustatic sea-level fluctuation has been reconstructed from a detailed study of geological field relationships combined with an extensive programme of U-series and amino-acid racemization geochronology. Only twice in the past 250,000 yr. has sea level in Bermuda been above its present level, once at approximately 200 k.y. when it stood at about + 2 m and most recently at 125 ± 4 k.y. when it stood at 5 ± 1 m. These times of interglacial high sea level are characterized by the development of patch reefs and marine calcarenites at elevations above present sea level. Episodes of lower sea stand onto the Bermuda platform at elevations higher than −20 m are observed within the two interglacial periods and are characterized by the deposition of eolianites. By contrast glacial periods are times of residual soil formation and deposition of speleothems in caves at elevations below present sea level. Excellent correlation is observed between the Bermuda glacio-eustatic sea-level record and other marine and terrestrial paleoclimate records

Closed-system behaviour of the intra-crystalline fraction of amino acids in mollusc shells

When mollusc shells are analysed conventionally for amino acid geochronology, the entire population of amino acids is included, both inter- and intra-crystalline. This study investigates the utility of removing the amino acids that are most susceptible to environmental effects by isolating the fraction of amino acids encapsulated within mineral crystals of mollusc shells (intra-crystalline fraction). Bleaching, heating and leaching (diffusive loss) experiments were undertaken on modern and fossil Corbicula fluminalis, Margaritifera falcata, Bithynia tentaculata and Valvata piscinalis shells. Exposure of powdered mollusc shells to concentrated NaOCl for 48 h effectively reduced the amino acid content of the four taxa to a residual level, assumed to represent the intra-crystalline fraction. When heated in water at 140 °C for 24 h, only 1% of amino acids were leached from the intra-crystalline fraction of modern shells compared with 40% from whole shell. Free amino acids were more effectively retained in the intra-crystalline fraction, comprising 55% (compared with 18%) of the whole shell after 24 h at 140 °C. For fossil gastropods, the inter-shell variability in D/L values for the intra-crystalline fraction of a single-age population was reduced by 50% compared with conventionally analysed shells. In contrast, analysis of the intra-crystalline fraction of C. fluminalis does not appear to improve the results for this taxon, possibly due to variability in shell ultrastructure. Nonetheless, the intra-crystalline fraction in gastropods approximates a closed system of amino acids and appears to provide a superior subset of amino acids for geochronological applications

Intra-crystalline protein diagenesis (IcPD) in Patella vulgata. Part II: Breakdown and temperature sensitivity

Artificial diagenesis of the intra-crystalline proteins isolated from Patella vulgata was induced by isothermal heating at 140 °C, 110 °C and 80 °C. Protein breakdown was quantified for multiple amino acids, measuring the extent of peptide bond hydrolysis, amino acid racemisation and decomposition. The patterns of diagenesis are complex; therefore the kinetic parameters of the main reactions were estimated by two different methods: 1) a well-established approach based on fitting mathematical expressions to the experimental data, e.g. first-order rate equations for hydrolysis and power-transformed first-order rate equations for racemisation; and 2) an alternative model-free approach, which was developed by estimating a “scaling” factor for the independent variable (time) which produces the best alignment of the experimental data. This method allows the calculation of the relative reaction rates for the different temperatures of isothermal heating. High-temperature data were compared with the extent of degradation detected in sub-fossil Patella specimens of known age, and we evaluated the ability of kinetic experiments to mimic diagenesis at burial temperature. The results highlighted a difference between patterns of degradation at low and high temperature and therefore we recommend caution for the extrapolation of protein breakdown rates to low burial temperatures for geochronological purposes when relying solely on kinetic data