Transverse momentum dependent parton distributions in a light-cone quark model

The leading twist transverse momentum dependent parton distributions (TMDs) are studied in a light-cone description of the nucleon where the Fock expansion is truncated to consider only valence quarks. General analytic expressions are derived in terms of the six amplitudes needed to describe the three-quark sector of the nucleon light-cone wave function. Numerical calculations for the T-even TMDs are presented in a light-cone constituent quark model, and the role of the so-called pretzelosity is investigated to produce a nonspherical shape of the nucleon.Comment: references added and typos corrected; version to appear in Phys. Rev.

Transverse momentum dependent distribution functions in a covariant parton model approach with quark orbital motion

Transverse parton momentum dependent distribution functions (TMDs) of the nucleon are studied in a covariant model, which describes the intrinsic motion of partons in terms of a covariant momentum distribution. The consistency of the approach is demonstrated, and model relations among TMDs are studied. As a byproduct it is shown how the approach allows to formulate the non-relativistic limit.Comment: 16 page

Many-body effects in 16O(e,e'p)

Effects of nucleon-nucleon correlations on exclusive $(e,e'p)$ reactions on closed-shell nuclei leading to single-hole states are studied using $^{16}O(e,e'p)^{15}N$ ($6.32$ MeV, $3/2^-$) as an example. The quasi-hole wave function, calculated from the overlap of translationally invariant many-body variational wave functions containing realistic spatial, spin and isospin correlations, seems to describe the initial state of the struck proton accurately inside the nucleus, however it is too large at the surface. The effect of short-range correlations on the final state is found to be largely cancelled by the increase in the transparency for the struck proton. It is estimated that the values of the spectroscopic factors obtained with the DWIA may increase by a few percent due to correlation effects in the final state.Comment: 21 Pages, PHY-7849-TH-9

Intra-datacenter links exploiting PCI express generation 4 interconnections

We demonstrate few-km reaches for PCIe-based optical fiber interconnections according to latency limitations, characterizing 16-Gb/s per lane Generation4 up to 10 km and confirming the Generation3 compliance of 2-km links employing suitable PCIe cards

Overlap functions in correlation methods and quasifree nucleon knockout from 16^{16}O

The cross sections of the ($e,e'N$) and ($\gamma,p$) reactions on $^{16}$O are calculated, for the transitions to the $1/2^{-}$ ground state and the first $3/2^{-}$ excited state of the residual nucleus, using single-particle overlap functions obtained on the basis of one-body density matrices within different correlation methods. The electron-induced one-nucleon knockout reaction is treated within a nonrelativistic DWIA framework. The theoretical treatment of the ($\gamma,p$) reaction includes both contributions of the direct knockout mechanism and of meson-exchange currents. The results are sensitive to details of the different overlap functions. The consistent analysis of the reaction cross sections and the comparison with the experimental data make it possible to study the nucleon--nucleon correlation effects.Comment: 26 pages, LaTeX, 5 Postscript figures, submitted to PR

Analysis of Meson Exchange and Isobar Currents in (e,e'p) Reactions from O-16

An analysis of the effects of meson exchange and isobar currents in exclusive (e,e'p) processes from O-16 under quasi-free kinematics is presented. A model that has probed its feasibility for inclusive quasi-elastic (e,e') processes is considered. Sensitivity to final state interactions between the outgoing proton and the residual nucleus is discussed by comparing the results obtained with phenomenological optical potentials and a continuum nuclear shell-model calculation. The contribution of the meson-exchange and isobar currents to the response functions is evaluated and compared to previous calculations, which differ notably from our results. These two-body contributions cannot solve the puzzle of the simultaneous description of the different responses experimentally separated. Copyright 1999 by The American Physical SocietyComment: 5 pages, plus 3 PS figures. To be published in Phys. Rev. C Updated figure

Meson exchange currents in electromagnetic one-nucleon emission

The role of meson exchange currents (MEC) in electron- and photon-induced one-nucleon emission processes is studied in a nonrelativistic model including correlations and final state interactions. The nuclear current is the sum of a one-body and of a two-body part. The two-body current includes pion seagull, pion-in-flight and the isobar current contributions. Numerical results are presented for the exclusive 16O(e,e'p)15N and 16O(\gamma,p)15N reactions. MEC effects are in general rather small in (e,e'p), while in (\gamma,p) they are always large and important to obtain a consistent description of (e,e'p) and (\gamma,p) data, with the same spectroscopic factors. The calculated (\gamma,p) cross sections are sensitive to short-range correlations at high values of the recoil momentum, where MEC effects are larger and overwhelm the contribution of correlations.Comment: 9 pages, 6 figure

Low-lying magnetic excitations of doubly-closed-shell nuclei and nucleon-nucleon effective interactions

We have studied the low lying magnetic spectra of 12C, 16O, 40Ca, 48Ca and 208Pb nuclei within the Random Phase Approximation (RPA) theory, finding that the description of low-lying magnetic states of doubly-closed-shell nuclei imposes severe constraints on the spin and tensor terms of the nucleon-nucleon effective interaction. We have first made an investigation by using four phenomenological effective interactions and we have obtained good agreement with the experimental magnetic spectra, and, to a lesser extent, with the electron scattering responses. Then we have made self-consistent RPA calculations to test the validity of the finite-range D1 Gogny interaction. For all the nuclei under study we have found that this interaction inverts the energies of all the magnetic states forming isospin doublets.Comment: 19 pages, 13 figures, 7 tables, accepted for publication in Phys. Rev.

Dynamics of DNA damage in leukocytes of thoroughbred equines subjected to a standardized excercise test

Esta claramente establecido que durante el ejercicio se produce un aumento en la produccion de radicales libres que pueden romper el equilibrio oxido-reductor y causar dano en el ADN. El objetivo del presente trabajo fue establecer la existencia de dano en el ADN en leucocitos circulantes de equinos sometidos a ejercicio sub-maximo mediante el empleo del ensayo cometa. Se usaron cinco equinos sometidos a un test estandarizado de ejercicio, a los que se les extrajeron muestras antes de comenzar el ejercicio, a los 8,5 m/s, a los 15 m/s, y 1 y 30 min post-ejercicio. Simultaneamente se realizo una ergoespirometria continua para determinar el consumo de oxigeno durante el test de ejercicio. La frecuencia de celulas con dano en el ADN fue 0,448, 0,537, 0,617, 0,556 y 0,592 respectivamente, observandose diferencias significativas con respecto a los valores del tiempo basal (p<0,05). Luego las celulas se clasificaron por niveles de dano, observandose incrementos significativos (p<0,05) especialmente a los 15 m/s y 30 min post-ejercicio. Se observo una asociacion significativa entre la frecuencia de celulas con dano en el ADN y el consumo de oxigeno durante el test estandarizado de ejercicio. Estos resultados sugieren que los factores inductores de dano genotoxico se producen mayoritariamente durante el esfuerzo fisico.It is well established that during exercising, an increase in the production of free radicals occurs, which can break the oxide-reducing balance of the cell causing DNA damage. The aim of this study was to establish the existence of DNA damage in circulating leukocytes of horses undergoing sub-maximal exercise by using the comet assay. Five horses subjected to a standardized exercise test were used. Samples were extracted before starting the exercise and, then, at 8.5 m/s, at 15 m/s, and 1 and 30 min post-exercise. Simultaneously, oxygen consumption during the exercise test was measured. The frequency of cells with DNA damage was 0.448, 0.537, 0.617, 0.556 and 0.592 respectively, being significant the differences from the baseline values over time (p<0.05). Then, the cells were classified by levels of damage, with significant increases (p<0.05), especially at 15 m/s and 30 min after exercise. A significant association between the frequency of cells with DNA damage and oxygen consumption during standardized exercise test is observed. These results suggest that genotoxic damage inducing factors occur mainly during physical exertion.Fil: Muriel, M.. Universidad Nacional de La Plata. Facultad de Ciencias Veterinarias; ArgentinaFil: Seoane, Analia Isabel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico CONICET- La Plata. Instituto de Genética Veterinaria "Ing. Fernando Noel Dulout". Universidad Nacional de La Plata. Facultad de Ciencias Veterinarias. Instituto de Genética Veterinaria; ArgentinaFil: Savignone, C.. Universidad Nacional de La Plata. Facultad de Ciencias Veterinarias; ArgentinaFil: Palacios, A.. Universidad Nacional de La Plata. Facultad de Ciencias Veterinarias; ArgentinaFil: Ferreira, V.. Universidad Nacional de La Plata. Facultad de Ciencias Veterinarias; ArgentinaFil: Boffi, F. M.. Universidad Nacional de La Plata. Facultad de Ciencias Veterinarias; ArgentinaFil: Picco, Sebastian Julio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico CONICET- La Plata. Instituto de Genética Veterinaria "Ing. Fernando Noel Dulout". Universidad Nacional de La Plata. Facultad de Ciencias Veterinarias. Instituto de Genética Veterinaria; Argentin

Polynomiality of unpolarized off-forward distribution functions and the D-term in the chiral quark-soliton model

Mellin moments of off-forward distribution functions are even polynomials of the skewedness parameter. This constraint, called polynomiality property, follows from Lorentz- and time-reversal invariance. We prove that the unpolarized off-forward distribution functions in the chiral quark-soliton model satisfy the polynomiality property. The proof is an important contribution to the demonstration that the description of off-forward distribution functions in the model is consistent. As a byproduct of the proof we derive explicit model expressions for moments of the D-term and compute the first coefficient in the Gegenbauer expansion for this term.Comment: 18 pages, no figures. Corrections and improvements in section 6. To appear in Phys.Rev.