1,484 research outputs found
A leitura crítica em língua estrangeira
The purpose of this study is to verify whether non-native speakers of English in an advanced level of linguistic competence are able to perform the kind of critical reading described by Norman Fairclough in Language and Power as specifically oriented towards the identification of ideological assumptions embedded in several types of discourse.The purpose of this study is to verify whether non-native speakers of English in an advanced level of linguistic competence are able to perform the kind of critical reading described by Norman Fairclough in Language and Power as specifically oriented towards the identification of ideological assumptions embedded in several types of discourse.The purpose of this study is to verify whether non-native speakers of English in an advanced level of linguistic competence are able to perform the kind of critical reading described by Norman Fairclough in Language and Power as specifically oriented towards the identification of ideological assumptions embedded in several types of discourse.The purpose of this study is to verify whether non-native speakers of English in an advanced level of linguistic competence are able to perform the kind of critical reading described by Norman Fairclough in Language and Power as specifically oriented towards the identification of ideological assumptions embedded in several types of discourse.The purpose of this study is to verify whether non-native speakers of English in an advanced level of linguistic competence are able to perform the kind of critical reading described by Norman Fairclough in Language and Power as specifically oriented towards the identification of ideological assumptions embedded in several types of discourse.The purpose of this study is to verify whether non-native speakers of English in an advanced level of linguistic competence are able to perform the kind of critical reading described by Norman Fairclough in Language and Power as specifically oriented towards the identification of ideological assumptions embedded in several types of discourse.The purpose of this study is to verify whether non-native speakers of English in an advanced level of linguistic competence are able to perform the kind of critical reading described by Norman Fairclough in Language and Power as specifically oriented towards the identification of ideological assumptions embedded in several types of discourse
dependence of the - and -induced production of the from nuclei
Using results of a recent calculation of the in the nuclear
medium, which show that the medium width is about five times the free width, we
study the A dependence of the production cross section in the
reactions and . We find a sizable A dependence in the ratio of the
nuclear cross sections for heavy nuclei with respect to a light one due to the
large value of the width in the medium, showing that devoted
experiments, easily within reach in present facilities, can provide good
information on that magnitude by measuring the cross sections studied here.Comment: 14 pages, 5 figure
Absorption of phi mesons in near-threshold proton-nucleus reactions
In the framework of the nuclear spectral function approach for incoherent
primary proton--nucleon and secondary pion--nucleon production processes we
study the inclusive meson production in the interaction of 2.83 GeV
protons with nuclei. In particular, the A-dependences of the absolute and
relative meson yields are investigated within the different scenarios
for its in-medium width as well as for the cross section ratio . Our model calculations take into account
the acceptance window of the ANKE facility used in a recent experiment
performed at COSY. They show that the pion--nucleon production channel
contributes distinctly to the creation in heavy nuclei in the chosen
kinematics and, hence, has to be taken into consideration on close examination
of the dependences of the phi meson yields on the target mass number with the
aim to get information on its width in the medium. They also demonstrate that
the experimentally unknown ratio has a weak effect on the A-dependence of the relative meson
production cross section at incident energy of present interest, whereas it is
found to be appreciably sensitive to the phi in-medium width, which means that
this relative observable can indeed be useful to help determine the above width
from the direct comparison the results of our calculations with the future data
from the respective ANKE-at-COSY experiment.Comment: 16 pages, 9 figure
Dilepton production by bremsstrahlung of meson fields in nuclear collisions
We study the bremsstrahlung of virtual omega mesons due to the collective
deceleration of nuclei at the initial stage of an ultrarelativistic heavy-ion
collision. It is shown that electromagnetic decays of these mesons may give an
important contribution to the observed yields of dileptons. Mass spectra of
positron-electron and muon pairs produced in central Au+Au collisions are
calculated under some simplifying assumptions on the space-time variation of
the baryonic current in a nuclear collision process. Comparison with the CERES
data for 160 AGev Pb+Au collisions shows that the proposed mechanism gives a
noticeable fraction of the observed lepton pairs in the intermediate region of
invariant masses. Sensitivity of the dilepton yield to the in-medium
modification of masses and widths of vector mesons is demonstrated.Comment: 14 page
Nuclear shadowing at low photon energies
We calculate the shadowing effect in nuclear photoabsorption at low photon
energies (1-3 GeV) within a multiple scattering approach. We avoid some of the
high energy approximations that are usually made in simple Glauber theory like
the narrow width and the eikonal approximation. We find that the main
contribution to nuclear shadowing at low energies stems from mesons
with masses well below their pole mass. We also show that the possibility of
scattering in non forward directions allows for a new contribution to shadowing
at low energies: the production of neutral pions as intermediate hadronic
states enhances the shadowing effect in the onset region. For light nuclei and
small photon energies they give rise to about 30% of the total shadowing
effect.Comment: RevTeX, 16 pages including 6 eps figures; new calculation of
effective pion propagator, negligible effect on results; version to be
published in Phys. Rev.
Dilepton and Photon Emission Rates from a Hadronic Gas
We analyze the dilepton and photon emission rates from a hadronic gas using
chiral reduction formulas and a virial expansion. The emission rates are
reduced to pertinent vacuum correlation functions, most of which can be
assessed from experiment. Our results indicate that in the low mass region, the
dilepton and photon rates are enhanced compared to most of the calculations
using chiral Lagrangians. The enhancement is further increased through a finite
pion chemical potential. An estimate of the emission rates is also made using
Haag's expansion for the electromagnetic current. The relevance of these
results to dilepton and photon emission rates in heavy-ion collisions is
discussed.Comment: 7 pages, LaTeX using revTeX, 6 figures imbedded in text. Figures
slightly changed, text left unchange
Hadronic properties of the S_{11}(1535) studied by electroproduction off the deuteron
Properties of excited baryonic states are investigated in the context of
electroproduction of baryon resonances off the deuteron. In particular, the
hadronic radii and the compositeness of baryon resonances are studied for
kinematic situations in which their hadronic reinteraction is the dominant
contribution. Specifically, we study the reaction at for kinematics in which the produced hadronic state reinteracts
predominantly with the spectator nucleon. A comparison of constituent quark
model and effective chiral Lagrangian calculations of the shows
substantial sensitivity to the structure of the produced resonance.Comment: 24 pages, 5 figure
New study of the isotensor pi-pi interaction
With t-channel rho, f2(1270) exchange and the pi pi -> rho rho -> pi pi box
diagram contribution, we reproduce the pi pi isotensor S-wave and D-wave
scattering phase shifts and inelasticities up to 2.2 GeV quite well in a
K-matrix formalism. The t-channel rho exchange provides repulsive negative
phase shifts while the t-channel f2(1270) gives an attractive force to increase
the phase shifts for pi pi scattering above 1 GeV, and the coupled-channel box
diagram causes the inelasticities. The implication to the isoscalar pi pi
S-wave interaction is discussed.Comment: 17 pages, 5 figure
The meson width in the medium from proton induced production in nuclei
We perform calculations for the production of mesons in nuclei at
energies just above threshold and study the dependence of the cross
section. We use results for the selfenergy in the medium obtained within
a chiral unitary approach. We find a strong dependence which is tied to the
distortion of the incident proton and to the absorption of the in its
way out of the nucleus. The effect of this latter process reduces the cross
section in about a factor two in heavy nuclei proving that the dependence
of the cross section bears valuable information on the width in the
nuclear medium. Calculations are done for energies which are accessible in an
experimental facility like COSY.Comment: 26 pages, 13 figures. More detailed calculations have been performed.
Paper is accepted for publication in Phys. Rev.
Charmonium absorption by nucleons
dissociation in collisions with nucleons is studied within a boson
exchange model and the energy dependence of the dissociation cross section is
calculated from the threshold for production to high
energies. We illustrate the agreement of our results with calculations based on
short distance QCD and Regge theory. The compatibility between our calculations
and the data on photoproduction on a nucleon is discussed. We evaluate
the elastic cross section using a forward dispersion relation and
demonstrate the overall agreement with the predictions from QCD sum rules. Our
results are compatible with the phenomenological dissociation cross section
evaluated from the experimental data on production from ,
and collisions.Comment: 14 pages, revtex, including 13 figures, accepted for publication in
Phys. Rev.
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