2,290 research outputs found

    Parameterized Complexity of Equitable Coloring

    Full text link
    A graph on nn vertices is equitably kk-colorable if it is kk-colorable and every color is used either n/k\left\lfloor n/k \right\rfloor or n/k\left\lceil n/k \right\rceil times. Such a problem appears to be considerably harder than vertex coloring, being NP-Complete\mathsf{NP\text{-}Complete} even for cographs and interval graphs. In this work, we prove that it is W[1]-Hard\mathsf{W[1]\text{-}Hard} for block graphs and for disjoint union of split graphs when parameterized by the number of colors; and W[1]-Hard\mathsf{W[1]\text{-}Hard} for K1,4K_{1,4}-free interval graphs when parameterized by treewidth, number of colors and maximum degree, generalizing a result by Fellows et al. (2014) through a much simpler reduction. Using a previous result due to Dominique de Werra (1985), we establish a dichotomy for the complexity of equitable coloring of chordal graphs based on the size of the largest induced star. Finally, we show that \textsc{equitable coloring} is FPT\mathsf{FPT} when parameterized by the treewidth of the complement graph

    Performance Measurements Utilizations Among Iranian and Portuguese Manufacturing Organizations: Similarities and Differences

    Get PDF
    This study compares the extent of utilization of five performance dimensions in the manufacturing organizations in Iran and Portugal. These dimensions include Financial, Product Quality and Customer Satisfaction, Quality and Independence of Management, Human Resource Management, and Social Responsibility. Results show that while there are some similarities among the two groups of participants in the two countries, there are major differences. These differences are particularly evident in the ranking of the performance measures, which could be attributed to the differences in the business culture. The similarities, however, might be linked to the global nature of doing business, which is competition-drive

    New heterogeneous catalysts for trans-esterification of triglycerides

    Get PDF
    This paper describes preliminary work done towards the development of new metallic heterogeneous catalysts to be used in the transesterification reaction of triglycerides, which is of considerable interest in the production of biodiesel. Biodiesel, is a mixture of mono-alkyl esters of fatty acids, and is currently manufactured by transesterification of triglycerides with methanol using NaOH or KOH as liquid base catalyst. Catalysts as such are corrosive to the equipment, and as these catalysts are in liquid phase must be neutralized after the completion of the reaction, typically using HCl, thus producing salt streams. Moreover, due to the presence of free fatty acids it reacts to form soaps as unwanted by-products, hence requiring more expensive separation processes. Therefore, there is a great need on the development of industrial processes for biodiesel production using solid acid catalysts. The key benefit of using solid acid catalysts is that no polluting by-products are formed and the catalysts do not have to be removed since they do not mix with the biodiesel product

    Escherichia coli expression, refolding and characterization of human laforin

    Get PDF
    Laforin is a unique human dual-specificity phosphatase as it contains an amino terminal carbohydrate binding module (CBM). Laforin gene mutations lead to Lafora disease, a progressive myoclonus epilepsy with an early fatal issue. Previous attempts to produce recombinant laforin faced various difficulties, namely the appearance of protein inclusion bodies, the contamination with bacterial proteins and a high tendency of the protein to aggregate, despite the use of fusion tags to improve solubility and ease the purification process. In this work, we have expressed human laforin in Escherichia coli in the form of inclusion bodies devoid of any fusion tags. After a rapid dilution refolding step, the protein was purified by two chromatographic steps, yielding 5–7 mg of purified protein per liter of bacterial culture. The purified protein was shown to have the kinetic characteristics of a dual-specificity phosphatase, and a functional carbohydrate binding module. With this protocol, we were able for the first time, to produce and purify laforin without fusion tags in the amounts traditionally needed for the crystallographic structural studies paving the way to the understanding of the molecular mechanisms of laforin activity and to the development of novel therapies for Lafora disease.Fundação para a Ciência e a Tecnologia (FCT) – Programa Operacional “Ciência, Tecnologia, Inovação” (POCTI

    Expression of the functional carbohydrate-binding module (CBM) of human laforin

    Get PDF
    Laforin is a human protein associated with the glycogen metabolism, composed of two structurally and functionally independent domains: a phosphatase catalytic domain and a substrate-binding module with glycogen and starch affinity. The main goal of this work is the development of a methodology for the expression of the so far poorly characterized carbohydrate-binding module (CBM) of laforin, allowing its study and development of biomedical applications. The laforin’s CBM sequence was originally cloned by PCR from a human muscle cDNA library. The recombinant protein, containing laforin’s CBM fused to an Arg-Gly-Asp sequence (RGD), was cloned and expressed using vector pET29a and recovered as inclusion bodies (IBs). Refolding of the IBs allowed the purification of soluble, dimeric and functional protein, according to adsorption assays using starch and glycogen. Several other experimental approaches, using both bacteria and yeast, were unsuccessfully tested, pointing towards the difficulties in producing the heterologous protein. Indeed, this is the first work reporting the production of the functional CBM from human laforin.Fundação para a Ciência e a Tecnologia (FCT, Portugal)

    Plasma turbulence in the scrape-off layer of the ISTTOK tokamak

    Get PDF
    The properties of plasma turbulence in a poloidally limited scrape-off layer (SOL) are addressed, with focus on ISTTOK, a large aspect ratio tokamak with a circular cross section. Theoretical investigations based on the drift-reduced Braginskii equations are carried out through linear calculations and non-linear simulations, in two-and three-dimensional geometries. The linear instabilities driving turbulence and the mechanisms that set the amplitude of turbulence as well as the SOL width are identified. A clear asymmetry is shown to exist between the low-field and the high-field sides of the machine. While the comparison between experimental measurements and simulation results shows good agreement in the far SOL, large intermittent events in the near SOL, detected in the experiments, are not captured by the simulations.United States. Department of Energy (Grant DE-FG02-91ER54109

    Determination of phytoextraction potential of plant speciesfor toxic elements in soils of abandoned sulphide-mining areas

    Get PDF
    This study has determined contamination levels in soils and plants from the Sa˜o Domingos mining area, Portugal, by k0-INAA. Total concentrations of As, Sb, Cr, Hg, Cu, Zn and Fe in soils were very high, exceeding the maximum limits in Portuguese legislation. Concentrations of toxic elements like As, Sb and Zn were highest in roots of Erica andevalensis, Juncus acutus, Agrostis castellana and Nicotiana glauca. Additionally, As, Br, Cr, Fe, Sb and Zn in all organs of most plants were above toxicity levels. Those species that accumulated relatively high concentrations of toxic elements in roots (and tops) may be cultivated for phytostabilisation of similar areas
    corecore