155 research outputs found
Mass Suppression in Octet Baryon Production
There is a striking suppression of the cross section for production of octet
baryons in annihilation, as the mass of the produced hadron
increases. We present a simple parametrization for the fragmentation functions
into octet baryons guided by two input models: the SU(3) flavor symmetry part
is given by a quark-diquark model, and the baryon mass suppression part is
inspired by the string model. We need only eight free parameters to describe
the fragmentation functions for all octet baryons. These free parameters are
determined by a fit to the experimental data of octet baryon production in annihilation. Then we apply the obtained fragmentation functions to
predict the cross section of the octet baryon production in charged lepton DIS
and find consistency with the available experimental data. Furthermore, baryon
production in collisions is suggested to be an ideal domain to check the
predicted mass suppression.Comment: 20 pages, 5 figure
Hyperon polarization in semi-inclusive deeply inelastic lepton-nucleon scattering at high energy
We calculate the polarizations for different octet hyperons produced in the
current fragmentation regions of the deeply inelastic lepton-nucleon
scatterings and at high energy
using different models for spin transfer in fragmentation processes. The
results show that measurements of those hyperon polarizations should provide
useful information to distinguish between different models in particular the
SU(6) and the DIS pictures used frequently in the literature. We found, in
particular, that measuring the polarization of produced in these
processes can give a better test to the validity of the different spin transfer
models.Comment: 30 pages, 13 figure
Neutron rich nuclei in density dependent relativistic Hartree-Fock theory with isovector mesons
Density dependent relativistic Hartree-Fock theory has been extended to
describe properties of exotic nuclei. The effects of Fock exchange terms and of
pi - and rho - meson contributions are discussed. These effects are found to be
more important for neutron rich nuclei than for nuclei near the valley of
stability.Comment: 10 pages, 5 figures, LaTeX, macro packages graphicx and time
Short Fatigue Crack Growth at Different Maintenance Times for LZ50 Steel
Based on the average fatigue life of LZ50 axle steel specimens without surface rolling, five maintenance times were determined. Accordingly, five groups of specimens were turned and rolled at above maintenance times and were fatigued using a replica technique. The results show that the crack growth rate is much lower than that before rolling at a given dominant short crack size. The effective short crack density of all specimens decreases significantly after maintenance. However, with the postponement of surface maintenance, the highest effective short crack density for the five studied groups of specimens increases continuously, while the average fatigue life decreases gradually. A maintenance time effect function is presented to refine a short crack growth model described previously. The revifined model can include a significant effect of the maintenance time on short crack growth and predict its patterns at different maintenance times with exiting test results for LZ50 axle steel.На основании средней усталостной долговечности образцов осевой стали LZ50, не подвергавшихся поверхностной обкатке роликами, были определены пять модельных межремонтных циклов. Соответственно пять групп образцов были обточены и обкатаны роликами при вышеуказанных межремонтных циклах и подвергнуты испытанию на усталость по методу реплик. Результаты показывают, что скорость роста трещин гораздо ниже таковой до обкатки роликами при заданном преобладающем размере коротких трещин. Эффективная плотность коротких трещин для всех образцов значительно уменьшается после обработки. Однако если поверхностную обработку вовремя не выполняют, наибольшая эффективная плотность коротких трещин для пяти исследуемых групп образцов непрерывно возрастает, тогда как средняя усталостная долговечность постепенно снижается. Приведена функция, описывающая эффект межремонтных циклов, для уточнения предложенной ранее модели роста коротких трещин. Уточненная модель может учитывать существенное влияние межремонтного цикла на рост коротких трещин и прогнозировать характер их роста при различных межремонтных циклах на основании полученных результатов испытаний осевой стали LZ50
A Probabilistic Model for Describing Short Fatigue Crack Growth Behavior of LZ50 Steel
Fatigue damage process of metal components and structures with smooth surface belongs primarily to stage of short fatigue crack. To characterize the random growth behavior of short fatigue crack and to apply the crack growth rate model for engineering safety assessment, a probabilistic model is proposed with consideration of the test data scattering regularity. This probabilistic model is based on the multi-microstructural barriers model and can describe the deceleration behavior of growth rate during the whole short fatigue crack propagation process. To take the statistical characteristics of whole test data into account, the idea from the general maximum likelihood method which is widely used in parameters estimation of fatigue S-N curves and ε-N curves is inherited. While estimating the parameters of the probabilistic model, conventional correlation coefficient optimization method is extended for calculating the parameters of both the mean curve and the standard deviation curve. Analysis on the test data of LZ50 steel indicates the reasonability and availability of present model
Probing gluon helicity distribution and quark transversity through hyperon polarization in singly polarized pp collisions
We study the polarization of hyperon in different processes in singly
polarized collisions, in particular its relation to the polarized parton
distributions. We show that by measuring hyperon polarization in particularly
chosen processes, one can extract useful information on these parton
distributions. We show in particular that, by measuring the
polarization in high direct photon production process, one can extract
information on the gluon helicity distribution; and by measuring the transverse
polarization of hyeprons with high in singly polarized reactions, one can
obtain useful information on the transversity distribution. We present the
numerical results obtained for those hyperon polarizations using different
models for parton distribution function and those for the spin transfer in
fragmentation processes.Comment: 25 pages, 8 figures, to appear in Phys. Rev.
Spin structure and longitudinal polarization of hyperon in e+e- annihilation at high energies
Longitudinal polarizations of different kinds of hyperons produced in e+e-
annihilation at LEP I and LEP II energies in different event samples are
calculated using two different pictures for the spin structure of hyperon: that
drawn from polarized deep inelastic lepton-nucleon scattering data or that
using SU(6) symmetric wave functions. The result shows that measurements of
such polarizations should provide useful information to the question of which
picture is more suitable in describing the spin effects in the fragmentation
processes.Comment: 26 pages with 10 figures. Submitted to Phys. Rev.
Bulk properties of light deformed nuclei derived from a medium-modified meson-exchange interaction
Deformed Hartree-Fock-Bogoliubov calculations for finite nuclei are carried
out. As residual interaction, a Brueckner G-matrix derived from a
meson-exchange potential is taken. Phenomenological medium modifications of the
meson masses are introduced. The binding energies, radii, and deformation
parameters of the Carbon, Oxygen, Neon, and Magnesium isotope chains are found
to be in good agreement with the experimental data.Comment: 10 pages, LaTeX2e, elsart, 4 eps-figures includes with graphic
Hyperon polarization in \nu_\mu charged current interaction at the NOMAD energies
We show that, in at the NOMAD energies, it is
impossible to separate the products of the fragmentation of the struck quark
from those of the nucleon remnant. The latter has a large contribution even in
the current fragmentation region and has to be taken into account in
calculating polarization using different pictures. Based on this, we
make a rough estimation for the longitudinal polarization in
at the NOMAD energies. A comparison with the
data is given and predictions for are presented.Comment: 11 pages, 3 figure
An Improved Projection Method for Determination of Fatigue Parameters of Metal Structures Based on Spherical Direction Cosine Group Construction
The key components of railway rolling stock are almost constantly in the multiaxial stress state in service. To evaluate the fatigue strength of the structure, stress parameters should be obtained beforehand. The traditional projection method assumes that the maximum principal stress is the maximum tensile stress, and then the projection process is performed without taking the tension/ compression states of principal stresses into account. To address these inadequacies, a method for fatigue parameter determination was proposed based on principal stress projection toward a spherical direction cosine group. This method can determine the direction of maximum tensile stress and preserve the tension/compression attribute of stress during calculating the maximum stress and the minimum stress. Therefore, the physical meaning of present improved method is more apparent than the traditional projection method, and its algorithm is simple and effective. The fatigue strength assessments of a welded bogie frame were performed utilizing the traditional projection method and present method respectively. Results show that some maximum stresses calculated by the improved method could be 19.4% higher than those obtained by the traditional one at some nodes, while the minimum stresses and the stress ratio deduced from these two methods could even be of opposite sign. The present method, which takes the tension/compression properties of principal stresses into consideration, is more reasonable, as compared with the traditional projection method, and thus the fatigue strength assessment results are more credible
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