1,793 research outputs found
Strong color fields and heavy flavor production
The clustering of color sources provides a natural framework for soft
partonic interactions producing strong color fields. We study the consequences
of these color fields in the production of heavy flavor and the behavior of the
nuclear modification factor.Comment: 11 pages, 7 figures, to appear in Physical Review
Rapidity long range correlations, parton percolation and color glass condensate
The similarities between string percolation and Glasma results are
emphasized, special attention being paid to rapidity long range correlations,
ridge structure and elliptic flow. As the string density of high multiplicity
pp collisions at LHC energies has similar value as the corresponding to Au-Au
semi-central collisions at RHIC we also expect in pp collisions long rapidity
correlations and ridge structure, extended more than 8 units in rapidity.Comment: 3 pages, 3 figures, conference Quark Confinement and the hadron
spectrum I
Elliptic flow at RHIC and LHC in the string percolation approach
The percolation of strings gives a good description of the RHIC experimental
data on the elliptic flow, v2 and predicted a rise on the integrated v2 of the
order of 25% at LHC such as it has been experimentally obtained. We show that
the dependence of v2 on pT for RHIC and LHC energies is approximately the same
as it has been observed, for all the centralities. We show the results for
different particles and the dependence of v2 on the centralities and rapidity.
Our results are compatible with an small value of the ratio eta/s in the whole
energy range such as it was expected in the percolation framework.Comment: 20 pages, 12 figure
Atomic Processes in Planetary Nebulae and H II Regions
Spectroscopic studies of Planetary Nebulae (PNe) and H {\sc ii} regions have
driven much development in atomic physics. In the last few years the
combination of a generation of powerful observatories, the development of ever
more sophisticated spectral modeling codes, and large efforts on mass
production of high quality atomic data have led to important progress in our
understanding of the atomic spectra of such astronomical objects. In this paper
I review such progress, including evaluations of atomic data by comparisons
with nebular spectra, detection of spectral lines from most iron-peak elements
and n-capture elements, observations of hyperfine emission lines and analysis
of isotopic abundances, fluorescent processes, and new techniques for
diagnosing physical conditions based on recombination spectra. The review is
directed toward atomic physicists and spectroscopists trying to establish the
current status of the atomic data and models and to know the main standing
issues.Comment: 9 pages, 1 figur
Chemical Abundances from the Continuum
The calculation of solar absolute fluxes in the near-UV is revisited,
discussing in some detail recent updates in theoretical calculations of
bound-free opacity from metals. Modest changes in the abundances of elements
such as Mg and the iron-peak elements have a significant impact on the
atmospheric structure, and therefore self-consistent calculations are
necessary. With small adjustments to the solar photospheric composition, we are
able to reproduce fairly well the observed solar fluxes between 200 and 270 nm,
and between 300 and 420 nm, but find too much absorption in the 270-290 nm
window. A comparison between our reference 1D model and a 3D time-dependent
hydrodynamical simulation indicates that the continuum flux is only weakly
sensitive to 3D effects, with corrections reaching <10% in the near-UV, and <2%
in the optical.Comment: 10 pages, 5 figures, to appear in the proceedings of the conference A
Stellar Journey, a symposium in celebration of Bengt Gustafsson's 65th
birthday, June 23-27, 2008, Uppsal
Removal of anionic surfactant from aqueous solutions by adsorption onto biochars:characterisation, kinetics, and mechanism
Biochar, a waste biomass-derived adsorbent, holds promise for decentralised wastewater treatment. However, limited research exists on its efficacy in adsorbing anionic surfactants in wastewater. To address this, the adsorption of sodium dodecyl sulphate (SDS), a common anionic surfactant, was studied using various biochar types: rice husk biochar (RH-550 and RH-700), wheat straw biochar (WS-550 and WS-700) produced at 550°C and 700°C, wood-based biochar (OB), and activated carbon (AC) as a control. The study investigated the impact of pH (3–9), adsorbent loading (1–10 g/L), adsorbent size (<0.5–2.5 mm), contact time (5–180 min), and initial concentration (50–200 mg/L) on SDS removal. Under optimised conditions (100 mg/L SDS, 4 g/L adsorbent, 1–2 mm particle size, pH 8.3, and 180 min contact time), maximum SDS removals were RH-550 (78%), RH-700 (82.4%), WS-550 (89.5%), WS-700 (90.4%), AC (97%), and OB (88.4%). Among the tested adsorbent materials, WS-550 exhibited the highest SDS adsorption capacity at 66.23 mg/g compared to AC (80.65 mg/g), followed by RH-550 (49.75 mg/g), OB (45.87 mg/g), RH-700 (43.67 mg/g), and WS-700 (42.74 mg/g). SDS adsorption followed a pseudo-second-order kinetic model, indicating chemisorption on the adsorbent surface. The Freundlich isotherm model exhibited a better fit for the experimental data on SDS adsorption using all tested adsorbents except for RH-550. This study showed that biochars produced from agricultural and forestry residues are effective adsorbents for SDS in aqueous solutions and can be a promising sustainable and low-cost material for the treatment of greywater containing anionic surfactants (e.g. handwashing, laundry, kitchen, and bathroom greywaters)
Formic Acid Ionization and Fragmentation by Multiphoton Absorption
Multiphoton absorption is an intensity dependent nonlinear effect related to the excitation of virtual intermediate states. In the present work, multiphoton ionization and dissociation of the formic acid molecule (HCOOH) by the interaction with photons from 532 Nd: YAG laser at different intensities are discussed, using different carrier gases. The induced fragmentation-ionization patterns show up to 17 fragments and dissociation channels are proposed. Some evidence of small clusters formation and conformational memory from the ratio of the detected products, CO+ and CO2+, on the light of the available results, it is possible to conclude that they arise from trans and cis formic acid. Our results are compared with those obtained in other laboratories under different experimental conditions, some of them show only partial agreement and differences are discussed. Following the Keldysh description it is possible, from our experimental parameters, characterize our results, in the multiphoton absorption regime
Elliptic flow: pseudorapidity and number of participants dependence
We discuss the elliptic flow dependence on pseudorapidity and number of
participating nucleons in the framework of string percolation, and argue that
the geometry of the initial overlap region of interaction, projected in the
impact parameter plane, determines the experimentally measured azimuthal
asymmetries. We found good agreement with data.Comment: 7 pages, 2 figure
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