Bleaching of High Yield Mutual Sulphite Semichemical Pulp

The objective of this research project was to investigate the effect of various bleaching agents and procedures on brightness, degree of yellowness and retention of the original high yield of the unbleached neutral sulphite semichemical pulp. In order to avoid excessive losses in bleaching of the high yield pulp, it was decided to limit the selection of bleaching chemicals to hypochlorites, peroxides and hydrosulphites. Furthermore, caustic extraction was to be employed only under relatively mild conditions as to temperature and concentration. Based on the experimental conditions and results described in this report and on the use of an unbleached pulp with relatively low brightness of 32 percent, the following conclusions were drawn: Bleaching of neutral sulphite semichemical pulp by means of one stage calcium hypochlorite treatment brought about only limited brightness development with concurrent relatively high yellowness. Two stage bleaching with calcium hypochlorite was found to be more effective than one stage bleaching for a given amount of chemical. Best results were obtained when about 25 percent of the total hypochlorite were used in the first stage and the remaining 75 percent in the second stage. Caustic extraction between two stages of hypochlorite bleaching improved brightness and reduced the yellow cast of the bleached pulp. With this procedure, best results were obtained by using 50 to 75 percent of the total hypochlorite in the first stage. Pulp bleached with hypochlorite followed by acidification and hydrogen peroxide treatment produced encouraging results as to brightness and decrease yellow cast. Zinc hydrosulphite, although it did not improve brightness was effective in reducing the yellow cast of the bleached pulp. All experiments caused only modest shrinkage of the pulp used

Effective theory of the D = 3 center vortex ensemble

By means of lattice calculations, center vortices have been established as the infrared dominant gauge field configurations of Yang-Mills theory. In this work, we investigate an ensemble of center vortices in D = 3 Euclidean space-time dimension where they form closed flux loops. To account for the properties of center vortices detected on the lattice, they are equipped with tension, stiffness and a repulsive contact interaction. The ensemble of oriented center vortices is then mapped onto an effective theory of a complex scalar field with a U(1) symmetry. For a positive tension, small vortex loops are favoured and the Wilson loop displays a perimeter law while for a negative tension, large loops dominate the ensemble. In this case the U(1) symmetry of the effective scalar field theory is spontaneously broken and the Wilson loop shows an area law. To account for the large quantum fluctuations of the corresponding Goldstone modes, we use a lattice representation, which results in an XY model with frustration, for which we also study the Villain approximation.Comment: 23 page

The DaVinci Center For Community Progress: Making The Community More Liveable

There are many innovations, projects, and programs which can make a community more liveable. The elements that they have in common are 1) the vision of the founder (or co-founders), 2) a dedicated connection to the community and populations in which the innovation or project is located, 3) the necessary social skills and contacts of the founder(s) and other key people involved in the innovation, 4) hard work, and 5) funding sources that continue over time to keep the services (or project) going, as well as to add services as needs change. The DaVinci Center for Community Progress, in Providence, RI, is an excellent example of how to make a community more liveable for diverse populations for whom it has provided services since it opened its doors in 1972. The DaVinci Center is a multi-purpose facility based on the settlement house model in regard to many of the services it offers. It differs from the settlement house model in that the DaVinci Center staff does not live at the Center. The Center was co-founded by John DeLuca who has also served as its longtime Executive Director. The content for this article was gathered, in part, through a lengthy, structured interview both authors conducted with John at the Center, a review of written materials produced by the Center, and information provided on the Center’s website

Handlung und Wissenschaft. Die Epistemologie der praktischen Wissenschaften im 13. und 14. Jahrhundert. Action and Science. The Epistemology of the Practical Sciences in the 13th and 14th Centuries. [Reseña]

Reseña de: Matthias Lutz-Bachma nn – Alexander Fidora (Hgg.), Handlung und Wissenschaft. Die Epistemologie der praktischen Wissenschaften im 13. und 14. Jahrhundert. Action and Science. The Epistemology of the Practical Sciences in the 13th and 14th Centuries, Akademie-Verlag («Wissenskultur und gesellschaftlicher Wandel», 29), Berlin 2008, 176 pp

Die Not-Wendigkeit der Gerechtigkeit. Eine Interpretation zu «Cur Deus homo » von Anselm von Canterbury (Reseña)

Reseña del libro de Georg PLASGER, Die Not-Wendigkeit der Gerechtigkeit. Eine Interpretation zu «Cur Deus homo » von Anselm von Canterbury, Aschendorff («Beiträge zur Geschichte und Philosophie des Mittelalters. Neue Folge», Band 38), Münster 1993, XX + 178 pp

El deseo de entender la verdad en la Summa contra Gentiles de Santo Tomás de Aquino. [Reseña]

Reseña de: Guillermo José Cambiasso, El deseo de entender la verdad en la Summa contra Gentiles de Santo Tomás de Aquino, Educa, Buenos Aires 2007, 447 pp