1,971 research outputs found
Do we expect light flavor sea-quark asymmetry also for the spin-dependent distribution functions of the nucleon?
After taking account of the scale dependence by means of the standard DGLAP
evolution equation, the theoretical predictions of the chiral quark soliton
model for the unpolarized and longitudinally polarized structure functions of
the nucleon are compared with the recent high energy data. The theory is shown
to explain all the qualitative features of the experiments, including the NMC
data for , , the Hermes and NuSea
data for , the EMC and SMC data for ,
and . Among others, flavor asymmetry of the longitudinally
polarized sea-quark distributions is a remarkable prediction of this model,
i.e., it predicts that with a sizable negative coefficient
(and ) in qualitative consistency with the recent
semi-phenomenological analysis by Morii and Yamanishi.Comment: 14pages, including 5 eps_figures with epsbox.sty, late
Human eosinophil-airway smooth muscle cell interactions.
Eosinophils are present throughout the airway wall of asthmatics. The nature of the interaction between human airway smooth muscle cells (ASMC) and eosinophils was investigated in this study. We demonstrated, using light microscopy, that freshly isolated eosinophils from healthy donors rapidly attach to ASMC in vitro. Numbers of attached eosinophils were highest at 2 h, falling to 50% of maximum by 20 h. Eosinophil attachment at 2 h was reduced to 72% of control by anti-VCAM-1, and to 74% at 20 h by anti-ICAM-1. Pre-treatment of ASMC for 24h with TNF-alpha, 10 nM, significantly increased eosinophil adhesion to 149 and 157% of control after 2 and 20 h. These results provide evidence that eosinophil interactions with ASMC involve VCAM-1 and ICAM-1 and are modulated by TNF-alpha
Gluon distributions in nucleons and pions at a low resolution scale
In this paper we study the gluon distribution functions in nucleons and pions
at a low resolution scale. This is an important issue since parton
densities at low have always been taken as an external input which is
adjusted through DGLAP evolution to fit the experimental data at higher scales.
Here, in the framework of a model recently developed, it is shown that the
hypothetical cloud of {\it neutral} pions surrounding nucleons and pions
appears to be responsible for the characteristic valence-like gluon
distributions needed at the inital low scale. As an additional result, we get
the remarkable prediction that neutral and charged pions have different
intrinsic sea flavor contents.Comment: final version to appear in Phys. Rev. D. Discussion on several points
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High-density information storage in an absolutely defined aperiodic sequence of monodisperse copolyester
Synthesis of a polymer composed of a large discrete number of chemically distinct monomers in an absolutely defined aperiodic sequence remains a challenge in polymer chemistry. The synthesis has largely been limited to oligomers having a limited number of repeating units due to the difficulties associated with the step-by-step addition of individual monomers to achieve high molecular weights. Here we report the copolymers of ??-hydroxy acids, poly(phenyllactic-co-lactic acid) (PcL) built via the cross-convergent method from four dyads of monomers as constituent units. Our proposed method allows scalable synthesis of sequence-defined PcL in a minimal number of coupling steps from reagents in stoichiometric amounts. Digital information can be stored in an aperiodic sequence of PcL, which can be fully retrieved as binary code by mass spectrometry sequencing. The information storage density (bit/Da) of PcL is 50% higher than DNA, and the storage capacity of PcL can also be increased by adjusting the molecular weight (~38???kDa)
Isovector unpolarized quark distribution in the nucleon in the large-N_c limit
We calculate the isovector (flavor-nonsinglet) unpolarized quark- and
antiquark distributions in the nucleon at a low normalization point in the
large-N_c limit. The nucleon is described as a soliton of the effective chiral
theory. The isovector distribution appears in the next-to-leading order of the
1/N_c-expansion. Numerical results for the quark- and antiquark distributions
compare well with the parametrizations of the data at a low normalization
point. This large-N_c approach gives a flavor asymmetry of the antiquark
distribution (violation of the Gottfried sum rule) in good agreement with the
measurements.Comment: 31 pages, LaTeX, 1 table, 4 figures included using eps
Next-to-Leading Order Constituent Quark Structure and Hadronic Structure Functions
We calculate the partonic structure of a constituent quark in the
Next-to-Leading Order framework. The structure of any hadron can be obtained
thereafter using a convolution method. Such a procedure is used to generate the
structure function of proton and pion in NLO, neglecting certain corrections to
. It is shown that while the constituent quark structure is
generated purely perturbatively and accounts for the most part of the hadronic
structure, there is a few percent contributions coming from the nonperturbative
sector in the hadronic structure. This contribution plays the key role in
explaining the SU(2) symmetry breaking of the nucleon sea and the observed
violation of Gottfried sum rule. These effects are calculated. We obtained an
Excellent agreement with the experimental data in a wide range of and for the proton structure function. We
have also calculated Pion structure and compared it with the existing data.
Again, the model calculations agree rather well with the data from experiment.Comment: 32 pages,10 figures, Accepted to publish in Phys. Rev.
Light-flavor sea-quark distributions in the nucleon in the SU(3) chiral quark soliton model (I) -- phenomenological predictions --
Theoretical predictions are given for the light-flavor sea-quark
distributions including the strange quark ones on the basis of the flavor SU(3)
version of the chiral quark soliton model. Careful account is taken here of the
SU(3) symmetry breaking effects due to the mass difference between the strange
and nonstrange quarks. This effective mass difference between the
strange and nonstrange quarks is the only one parameter necessary for the
flavor SU(3) generalization of the model. A particular emphasis of study is put
on the {\it light-flavor sea-quark asymmetry} as exemplified by the observables
as well as on the {\it particle-antiparticle asymmetry} of
the strange quark distributions represented by etc. As for the unpolarized
sea-quark distributions, the predictions of the model seem qualitatively
consistent with the available phenomenological information provided by the NMC
data for , the E866 data for , the CCFR data and Barone et al.'s fit for etc. The
model is shown to give several unique predictions also for the spin-dependent
sea-quark distribution, such that and , although the verification
of these predictions must await more elaborate experimental investigations in
the near future.Comment: 36 pages, 20 EPS figures. The revised version accepted for
publication in Phys. Rev. D. The title has been changed, and the body of the
paper has been divided into two pieces, i.e.. the present one which discusses
the main phenomenological predictions of the model and the other one which
describes the detailed formulation of the flavor SU(3) chiral quark soliton
model to predict light-flavor quark and antiquark distribution functions in
the nucleo
Non-perturbative structure of the polarized nucleon sea
We investigate the flavour and quark-antiquark structure of the polarized
nucleon by calculating the parton distribution functions of the nucleon sea
using the meson cloud model. We find that the SU(2) flavor symmetry in the
light antiquark sea and quark-antiquark symmetry in the strange quark sea are
broken, {\it i.e.} \Delta\ubar < \Delta \dbar and \Delta s < \Delta \sbar.
The polarization of the strange sea is found to be positive, which is in
contradiction to previous analyses. We predict a much larger quark-antiquark
asymmetry in the polarized strange quark sea than that in the unpolarized
strange quark sea. Our results for both polarized light quark sea and polarized
strange quark sea are consistent with the recent HERMES data.Comment: RevTex, 17 pages plus 8 PS figure
Polarized light-flavor antiquarks from Drell-Yan processes of h+\vec{N}\to\vec{l^{+-}} + l^{-+} + X
We propose a formula to determine the first moment of difference between the
polarized - and -quarks in the nucleon, {\it i.e.} from the Drell-Yan processes in collisions of unpolarized
hadrons with longitudinally polarized nucleons by measuring outgoing lepton
helicities. As coefficients in the differential cross section depend on the
- and -quark numbers in the unpolarized hadron beam, the difference
can be independently tested by changing the hadron
beam. Moreover, a formula for estimating the -factor in Drell-Yan processes
is also suggested.Comment: 10 pages, 1 figur
dbar/ubar Asymmetry and the Origin of the Nucleon Sea
The Drell-Yan cross section ratios, , measured in
Fermilab E866, have led to the first determination of ,
, and the integral of for the
proton over the range . The E866 results are compared
with predictions based on parton distribution functions and various theoretical
models. The relationship between the E866 results and the NMC measurement of
the Gottfried integral is discussed. The agreement between the E866 results and
models employing virtual mesons indicates these non-perturbative processes play
an important role in the origin of the , asymmetry in the
nucleon sea.Comment: 5 pages, 3 figures, ReVTe
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