On the intrinsic charm and the recombination mechanisms in charm hadron production

We study $\Lambda_c^\pm$ production in $pN$ and $\pi^-N$ interactions. Recent experimental data from the SELEX and E791 Collaborations at FNAL provide important information on the production mechanism of charm hadrons. In particular, the production of the $\Lambda_c$ baryon provides a good test of the intrinsic charm and the recombination mechanisms, which have been proposed to explain the so called leading particle effects.Comment: 11 pages, two figures (postscript), late

Stellar Populations, Bars and Secular Evolution in Late-Type Galaxies

We have done a robust statistical analysis of UBV color profiles of 257 Sbc barred and unbarred galaxies. We found that there is an excess of barred galaxies among the objects with null or positive (bluish inward) color gradients, which seems to indicate that bars act as a mechanism of homogenization of the stellar population along galaxies. Moreover, the relationship found between total and bulge colors shows that, in the process of homogenization, the stellar population of bulges are getting bluer, whereas the total color of galaxies remains the same. These characteristics are expected in a secular evolutionary scenario, and seem incompatible with both the monolithic and the hierarchical scenarios for spiral galaxy formation.Comment: 2 pages, 1 table, no figures. To appear in ASP Conference Series, "Galaxy Disks and Disk Galaxies", J. G. Funes S. J. and E. M. Corsini, ed

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

We propose a two component model for charmed baryon production in $pp$ collisions consisting of the conventional parton fusion mechanism and fragmentation plus quarks recombination in which a $ud$ valence diquark from the proton recombines with a $c$-sea quark to produce a $\Lambda_c^+$. 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

Influence of wood storage time in the paper properties of Eucalyptus globulus

In this work we studied the effect of moisture and chip pile storage time of Eucalyptus globulus wood, regarding the impact in kraft cooking and papermaking. Experimentally, chip samples were collected with different storage times (0, 15, 30, 60 and 90 days) from two distinct piles (wet and dry). The cooked chips after disintegration, screening and washing were submitted to a bleaching stage, in ECF sequence following five stages (D0E1D1E2D2). The pulps were beaten in a PFI mill at 1000, 2000 and 3000 revolutions. For the cooking results we observed higher yield and lower alkali consumption for the wet pile chips and lower storage time (15 days). The results showed that storage time is a significant factor (ANOVA results) for almost paper properties studied and influenced mainly the internal fibre links. For what paper properties are concerned, the difference between piles isn’t so evident, the major differences are observed for the lower storage time (15 days)

Radiative Heavy Meson Transitions

We evaluate the radiative and hadronic decay rates of the $D^*$ mesons using the Heavy Quark Effective Theory and the Vector Meson Dominance hypothesis. We also estimate the width of the $B^*$ electromagnetic transitions and the radiative decays of positive parity $J^P=0^+, 1^+$ charmed mesons.Comment: 12 pages, LaTex, BARI-TH/93-14

Heavy Quark Symmetry Violation in Semileptonic Decays of D Mesons

The decays of $D$ mesons to $K l \nu$ and $K^* l \nu$ final states exhibit significant deviations from the predictions of heavy-quark symmetry, as one might expect since the strange quark's mass is of the same order as the QCD scale. Nonetheless, in order to understand where the most significant effects might lie for heavier systems (such as $B \to D l\nu$ and $B \to D^* l\nu$), the pattern of these deviations is analyzed from the standpoint of perturbative QCD and ${\cal O}(1/m_s)$ corrections. Two main effects are noted. First, the perturbative QCD corrections lead to an overall decrease of predicted rates, which can be understood in terms of production of excited kaonic states. Second, ${\cal O}(1/m_s)$ effects tend to cancel the perturbative QCD corrections in the case of $Kl\nu$ decay, while they have minimal effect in $K^*l\nu$ decay.Comment: 25 pages (LaTeX) + 7 pages of Postscript figures (included at end), EFI-92-3

Evaluation of kraft cooking behaviour for different hardwood species

In this study six wood species (birch, chestnut, oak, beech, poplar and eucalyptus) were analysed separately. Lignin content, Polysaccharides content (cellulose and hemicelluloses), Yield, Hexenuronic acids were evaluated for three cooking temperatures (140ºC, 150ºC and 160ºC) and different cooking times. Common cooking conditions were applied and temperature program included cold impregnation, a plateau at 110°C (2.5 hours) to perform initial delignification separately followed by a second plateau at cooking temperature. The results of PCA show that the almost all parameters (excluding hexenuronic acids) are well correlated between them (total variance: 62%). For Eucalyptus and poplar species the hemicelluloses content aren’t well correlated with the previously parameter, caused by the difference observed for the higher temperatures. In some samples was observed that xylans are partially resistant and their elimination is only partial (30 to 40%) in the early stage of cooking. For the highest cooking time there were observed a significant difference between the three temperatures studied. Chestnut and oak wood species present a different behaviour compared with the other species, caused by their similar anatomical and chemical structure. For the 160º of cooking temperature in the second plateau was the poplar, beech and birch that present a different performance