178,377 research outputs found
Toward Understanding the Quark Parton Model of Feynmant
No full textThe quark parton model of Feynman, which has been used for analyses of high energy
physics experiments, invokes a set of parton distributions in the description of the nucleon
structure (the probability concept), contrary to the traditional use of wave functions in nuclear
and medium ener,7 physics for structural studies (the amplitude concept). In this paper, I first
review briefly how the various parton distributions of a nucleon may be extracted from high energy
physics experiments. I then proceed to consider how the sea distributions of a free nucleon at low
and moderate Q2 (e.g., up to 20 Ge?) may be obtained in the meson-baryon picture, a proposal
made by Hwang, Speth, and Brown. Using the form factors associated with the couplings of
mesons to baryons such as nNN, xNA, and KNA couplings which are constrained by the CCFR
neutrino data, we find that the model yields predictions consistent with the CDHS and Fermilab
E61S data on the sea-to-valence ratio. We also find that the recent finding by the New Muon
Collaboration (NMC) on the violation of the Gottfried sum rule can be understood quantitatively.
Finally, we consider, using the pion as the example, how valence quark distributions of a hadron
may be linked to the hadron wave function written in the light-cone language. Specifically, we
use the leading pion wave function that is constrained by the QCD sum rules, and find that, at Q*
= (0.5 Gev2, the leading Fock component accounts for about 40 % of the observed valence quark
distributions in the pion. The question of how to generate the entire valence quark distributions
from the valence quark distribution calculated from the leading Fock component is briefly
considered again using the specific proposal of Hwang, Speth, and Brown
Pion Excess for the Observed Nuclear Effects in Deep Inelastic Scattering and Drell-Yan Production
No full text
Effect of debonding on natural frequencies and frequency response functions of honeycomb sandwich beams
No full textThe natural frequencies of honeycomb sandwich beams having debonding or delamination embedded between the face-layer laminates and the honeycomb core are studied herein. A theoretical analysis of the effect of the extent of debonding on the flexural stiffness and on the natural frequency is compared with experimental observations. In this analysis the free vibration of the delaminated sandwich beams is studied using the split sandwich beam model, and the equations of motion are set up for the undelaminated region of the sandwich beam and the delaminated region of the laminated beams. Finally, changes in the peaks and valleys of the frequency response functions (FRFs) due to delamination are examined. By using the modal parameter identification method [H.Y. Kim, W. Hwang, Compos. Struct., 2001 (in press)], the extent of delamination of the sandwich beams can be identified in terms of the natural frequencies and damping ratios of the debonded beams. Vibration testing was conducted on honeycomb sandwich beams with carbon/epoxy laminated composite faces and Nomex-aramid honeycomb core. Agreement between the predictions of the model and experimental results is good. (C) 2001 Elsevier Science Ltd. All rights reserved.X1155sciescopu
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