19,369 research outputs found
Hadronic form factors and the secondary production cross section: an update
Improving previous calculations, we compute the cross section using the most complete effective lagrangians available. The
new crucial ingredients are the form factors on the charm meson vertices, which
are determined from QCD sum rules calculations. Some of them became available
only very recently and the last one, needed for our present purpose, is
calculated in this work.Comment: 12 pages, 9 eps figure
Does the production asymmetry decrease at large ?
We have applied the meson cloud model (MCM) to calculate the asymmetries in
and meson production in high energy -nucleus and
-nucleus collisions. We find a good agreement with recent data. Our
results suggest that the asymmetries may decrease at large .Comment: revised version with new figures and added references to appear in
Phys. Rev. Let
Meson Cloud and SU(3) Symmetry Breaking in Parton Distributions
We apply the Meson Cloud Model to the calculation of nonsinglet parton
distributions in the nucleon sea, including the octet and the decuplet cloud
baryon contributions. We give special attention to the differences between
nonstrange and strange sea quarks, trying to identify possible sources of SU(3)
flavor breaking. A analysis in terms of the parameter is presented,
and we find that the existing SU(3) flavor asymmetry in the nucleon sea can be
quantitatively explained by the meson cloud. We also consider the
baryon, finding similar conclusions.Comment: 17 pages, LaTeX, 8 figures in .ps file
Charm and longitudinal structure functions with the Kharzeev-Levin-Nardi model
We use the Kharzeev-Levin-Nardi model of the low gluon distributions to
fit recent HERA data on charm and longitudinal structure functions. Having
checked that this model gives a good description of the data, we use it to
predict and to be measured in a future electron-ion collider. The
results interpolate between those obtained with the de Florian-Sassot and
Eskola-Paukkunen-Salgado nuclear gluon distributions. The conclusion of this
exercise is that the KLN model, simple as it is, may still be used as an
auxiliary tool to make estimates both for heavy ion and electron-ion
collisions.Comment: 6 pages, 7 figure
Gluon saturation and the Froissart bound: a simple approach
At very high energies we expect that the hadronic cross sections satisfy the
Froissart bound, which is a well-established property of the strong
interactions. In this energy regime we also expect the formation of the Color
Glass Condensate, characterized by gluon saturation and a typical momentum
scale: the saturation scale . In this paper we show that if a saturation
window exists between the nonperturbative and perturbative regimes of Quantum
Chromodynamics (QCD), the total cross sections satisfy the Froissart bound.
Furthermore, we show that our approach allows us to describe the high energy
experimental data on total cross sections.Comment: 6 pages, 5 figures. Includes additional figures, discussion and
reference
Adsorption of landfill leachates onto activated carbon: Equilibrium and kinetics
The adsorption of stabilized leachates generated in a municipal landfill onto three commercial activated carbons has been investigated. Norit
0.8, Chemviron AQ40 and Picacarb 1240 have been used as adsorbents. Equilibrium experiments have been conducted to obtain the experimental isotherm profiles. Isotherms have been plotted based on the adsorption of general parameters, for instance chemical oxygen demand, total carbon, absorption at 410 nm and absorption at 254 nm. Different literature models and error functions have been used to adequately fit the experimental data. As a rule of thumb, three-parameter models do adjust experimental results better than two-parameter models. Norit 0.8 shows better adsorption characteristics than the rest of activated carbons, both in terms of contaminant level reduction of per unit mass of absorbent and in terms of the process kinetics
Fenton-like oxidation of landfill leachate
The treatment of stabilized leachates by means of Fenton's like reagent [Fe(III)-H2O2] has been studied. It has been demonstrated that the oxidation state of the catalyst does not influence the efficacy of the process in terms of chemical oxygen demand depletion profiles. The abrupt increase in temperature experienced in oxidation experiments involves a wastage of hydrogen peroxide diminishing the fraction of this reagent addressed at removing COD. If temperature is kept constant, the hydrogen peroxide uptake is 10 mg of H2O2 consumed per mg of COD abated (from 15 to 30°C). Working temperatures above 30°C does not lead to additional COD conversion, contrarily, the percentage of wasted H2O2 is increased. A rough economic analysis of the process indicates that this treatment can be a suitable alternative to deal with this type of effluents
Stabilized leachates: sequential coagulation–flocculation + chemical oxidation process
The combined sedimentation-chemical oxidation treatment of medium-stabilized landfill leachates has been investigated. The sequence of stages implemented was: (a) coagulation–flocculation by pH decrease (pH 2) to acidic conditions (COD removal ≈ 25% related to COD0 ≈ 7500 ppm); (b) coagulation–flocculation by Fe(III) addition (0.01 M) at pH 3.5 (COD removal ≈ 40% related to COD of supernatant after step (a); (c) Fenton (Fe(III) = 0.01 M; H2O2 = 1.0 M) oxidation (COD removal ≈ 80% related to COD of supernatant after step (a); and (d) coagulation–flocculation of Fenton’s effluent at pH 3.5 (COD removal ≈ 90% related to COD of supernatant after step (a). The use of Kynch theory allows for the design of clarifiers based on the amount of solids fed. For a general example of 1000 m3 day−1 of a feeding stream, clarifier area values of 286, 111 and 231 m2 were calculated for compacting indices of 3.7, 2.67 and 2.83 corresponding to the first, second and third consecutive sedimentation processes, respectively, (steps (a), (b) and (d))
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