5,702 research outputs found

    The Charm of the Proton and the Λc+\Lambda _c^{+} Production

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    We propose a two component model for charmed baryon production in pppp collisions consisting of the conventional parton fusion mechanism and fragmentation plus quarks recombination in which a udud valence diquark from the proton recombines with a cc-sea quark to produce a Λc+\Lambda_c^+. Our two-component model is compared with the intrinsic charm two-component model and experimental data.Comment: 6 pages, LaTex, 2 figures included, aipproc.sty included. Talk presented at Simposio Latino Americano de Fisica de Altas Energias, Merida, Mexico, November 199

    Asymmetry studies in Lambda 0/Lambda 0-bar, Xi-/Xi+ and Omega-/Omega+ production

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    We present a study on hyperon/anti-hyperon production asymmetries in the framework of the recombination model. The production asymmetries for Lambda 0/Lambda 0-bar, Xi-/Xi+ and Omega-/Omega+ are studied as a function of x_F. Predictions of the model are compared to preliminary data on hyperon/anti-hyperon production asymmetries in 500 GeV/c pi- p interactions from the Fermilab E791 experiment. The model predicts a growing asymmetry with the number of valence quarks shared by the target and the produced hyperons in the x_F < 0 region. In the positive x_F region, the model predicts constant asymmetries for Lambda 0/Lambda 0-bar and Omega-/Omega+ production and a growing asymmetry with x_F for Xi-/Xi+. We found a qualitatively good agreement between the model predictions and data, showing that recombination is a competitive mechanism in the hadronization process.Comment: One reference correcte

    Paper making potential of Acacia dealbata and Acacia melanoxylon

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    The pulping and papermaking potential of Acacia dealbata and Acacia melanoxylon were studied using Eucalyptus globulus as a reference. Pulp yield, alkali consumption and delignification in the kraft process, of both species, compare very well with the reference. Pulp yield can be higher than that of E. globulus and the residual lignin content lower after cooking, which is in good agreement with the lower lignin and extractives content of the wood samples used. Pulps produced from Acacia have slightly lower fibre length and coarseness and higher fibre width and wet fibre flexibility than E. globulus pulps. As a consequence of fibre characteristics, the paper produced from Acacia is denser and exhibits higher tensile and burst strength, and lower tear resistance than that from E. globulus, at a given PFI revolution.info:eu-repo/semantics/publishedVersio

    Populational fluctuation and spatial distribution of Alphitobius diaperinus (Panzer) (Coleoptera; Tenebrionidae) in a poultry house, Cascavel, Parana state, Brazil.

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    Abstract Knowledge of the population fluctuation and spatial distribution of pests is fundamental for establishing an appropriate control method. The population fluctuation and spatial distribution of the Alphitobius diaperinus in a poultry house in Cascavel, in the state of Parana, Brazil, was studied between October, 2001 and October 2002. Larvae and adults of the lesser mealworm were sampled weekly using Arends tube traps (n = 22) for six consecutive flock grow-outs. The temperature of the litter and of the poultry house was measured at the same locations of the tube traps. Beetle numbers increased continuously throughout all the sampling dates (average 5,137 in the first week and 18,494 insects on the sixth week). Significantly greater numbers of larvae were collected than adults (1 to 20 times in 95% of the sampling points). There was no correlation between temperature and the number of larvae and adults collected, therefore no fluctuation was observed during the sampling period. The population growth was correlated to litter re-use. The highest temperatures were observed in deep litter. The spatial distribution of larvae and adults in the poultry house was heterogeneous during the whole period of evaluation. Results suggest that monitoring in poultry houses is necessary prior to adopting and evaluating control measures due to the great variability of the insect distribution in the poultry house. Keywords: lesser mealworm, poultry house, temperature, population dynamicbitstream/item/78871/1/ID-27879.pd

    Influence of wood basic density on acacia melanoxylon kraft process

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    Wood density is a complex physical property related to the anatomical structure and the chemical composition of wood and one of the most important wood quality factors. Sampling was based on a total of 20 trees from four sites in Portugal that were harvested at a sawmill diameter class of 40 cm and wood discs taken at different height levels from the base to the top of the tree. The mean basic density of the Acacia melanoxylon trees measured at 5% height level (near breast height level) was 516 kg/m3 with a 34 kg/m3 standard deviation. The within-tree axial variation of density was of small magnitude, but showing higher values at the stem base and top. Site had no influence on the basic density of the wood. Overall the between tree variation of density was small possibly linked to the narrow genetic diversity of this introduced exotic species. In the Kraft process we can observe variability between stands and an increase of the pulp yield, and fiber width and length with the higher level in the tree. The wood basic density is well correlated with the ISO brightness and well correlated in inverse order with the pulp Yield and fiber width and length. The kappa number don’t present a great variation with the wood basic density

    Relation between wood density and paper properties of some hardwood species

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    Relation between wood density and paper properties of some hardwood species

    Direct effects of refining pilot-scale (Andritz Sprout-Bauer) on suspension and hand sheet properties of Eucalyptus globulus

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    Só está disponível o resumo do poster.Direct effects of refining pilot-scale (Andritz Sprout-Bauer) on suspension and hand sheet properties of Eucalyptus globulu

    Efeito do teor de hemiceluloses na qualidade de papel produzido com fibra de eucalipto

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    Este estudo analisa o efeito do teor de hemiceluloses das pastas de eucalipto nas características do papel produzido. Para o efeito, utilizaram-se aparas industriais de Eucalyptus globulus, com massa volúmica básica de 536 ± 4 kg/m3. As aparas crivadas foram sujeitas ao processo kraft, convencional e modificado, para a produção das respectivas pastas cruas com teores de hemiceluloses diferentes. Os cozimentos realizaram-se num digestor descontínuo de circulação forçada, com 1000g de madeira. A pasta crua foi submetida a um branqueamento ECF com dióxido de cloro, segundo uma sequência de cinco estágios (D0E1D1E2D2). As duas pastas, convencional e modificada, apresentaram teores de hemiceluloses da ordem dos 19% e 14%, respectivamente. Posteriormente, a pasta branca foi caracterizada em termos biométricos e papeleiro. Para este fim, a pasta foi refinada em PFI (ISO 5264/2-79) a diversas revoluções e com uma carga específica de bordo de 2 Nmm-1, tendo-se contabilizado o consumo de energia. Caracterizou-se a suspensão fibrosa e o potencial papeleiro. Para um dado número de revoluções em PFI, a resistência à drenagem, a densidade e a resistência à tracção das folhas aumentam com o incremento do teor de hemiceluloses. Assim, para produzir papéis com a mesma densidade, as pastas com menor teor de hemiceluloses requerem mais energia de refinação
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