1,762 research outputs found
Decuplet baryon magnetic moments in a QCD-based quark model beyond quenched approximation
We study the decuplet baryon magnetic moments in a QCD-based quark model
beyond quenched approximation. Our approach for unquenching the theory is based
on the heavy baryon perturbation theory in which the axial couplings for baryon
- meson and the meson-meson-photon couplings from the chiral perturbation
theory are used together with the QM moment couplings. It also involves the
introduction of a form factor characterizing the structure of baryons
considered as composite particles. Using the parameters obtained from fitting
the octet baryon magnetic moments, we predict the decuplet baryon magnetic
moments. The magnetic moment is found to be in good agreement with
experiment: is predicted to be compared to the
experimental result of (2.02 0.05) .Comment: 19 pages, 2 figure
Effective field theory and the quark model
We analyze the connections between the quark model (QM) and the description
of hadrons in the low-momentum limit of heavy-baryon effective field theory in
QCD. By using a three-flavor-index representation for the effective baryon
fields, we show that the ``nonrelativistic'' constituent QM for baryon masses
and moments is completely equivalent through O(m_s) to a parametrization of the
relativistic field theory in a general spin--flavor basis. The flavor and spin
variables can be identified with those of effective valence quarks. Conversely,
the spin-flavor description clarifies the structure and dynamical
interpretation of the chiral expansion in effective field theory, and provides
a direct connection between the field theory and the semirelativistic models
for hadrons used in successful dynamical calculations. This allows dynamical
information to be incorporated directly into the chiral expansion. We find, for
example, that the striking success of the additive QM for baryon magnetic
moments is a consequence of the relative smallness of the non-additive
spin-dependent corrections.Comment: 25 pages, revtex, no figure
Baryon Magnetic Moments in Relativistic Quark Models
It is shown that the phenomenological description of the baryon magnetic
moments in the quark model carries over to the Poincar\'e covariant extension
of the model. This applies to all the three common forms of relativistic
kinematics with structureless constituent currents, which are covariant under
the corresponding kinematic subgroups. In instant and front form kinematics the
calculated magnetic moments depend strongly on the constituent masses, while in
point form kinematics the magnetic moments are fairly insensitive to both the
quark masses and the wave function model. The baryon charge radii and magnetic
moments are determined in the different forms of kinematics for the
light-flavor, strange and charm hyperons. The wave function model is determined
by a fit to the electromagnetic form factor of the proton.Comment: Six references and one paragraph adde
Baryon masses in a loop expansion with form factor
We show that the average multiplet masses in the baryon octet and decuplet
can be fitted with an average error of only MeV in a meson loop
expansion with chiral SU(6) couplings, with the hadrons treated as composite
particles using a baryon-meson form factor. The form factor suppresses
unphysical short distance effects and leads to a controllable expansion. We
find, in contrast to the results of standard chiral perturbation theory, that
pion loops are as important as kaon or eta loops as would be expected when only
intermediate- and long-distance contributions are retained. We also find that
the contributions of decuplet intermediate states are important in the
calculation of the masses, and those states must be included explicitly in a
consistent theory. These results agree with those of our recent loop-expansion
analysis of the baryon magnetic moments. We show, finally, that the parts of
the loop contributions that change the tree-level structure of the baryon
masses are small, but largely account for the violations of the baryon mass sum
rules which hold at tree level.Comment: 20 pages, 2 figures, submitted to Phys. Rev. D. Title changed, the
introduction and discussion of the results rewritte
Developed graphene/Si Schottky junction solar cells based on the top-window structure
Chemical Vapor Deposition (CVD)-graphene has potentially been integrated with silicon (Si) substrates for developing graphene/n-Si Schottky junction solar cells prepared with the top window structure. However, there are drawbacks to prepared devices such as complex silicon dioxide (SiO2)-etching steps, low fill factors and stability of doped devices. In this work, SiO2 patterns are simply formed using a sputtering process rather than the previous complex method. Additionally, the fill factor for prepared devices is developed by using transferred residue-free multi-graphene layers. The usage of 3 graphene layers improves the power conversion efficiency (PCE) to 7.1%. A recorded PCE of around 17% with a fill factor of 74% is achieved by the HNO3 dopant. To overcome the issue of stability, Poly(methyl methacrylate) as an encapsulated layer is introduced. Hence, the doped devices show great stability for storage in air for 2 weeks, and devices recovered about 95% of their efficiency. This work shows that the developed fabrication process is suitable to develop simple, low cost, stable and efficient graphene/Si Schottky solar cells
Baryon Magnetic Moments in a QCD-based Quark Model with loop corrections
We study meson loop corrections to the baryon magnetic moments starting from
a QCD-based quark model derived earlier in a quenched approximation to QCD. The
model reproduces the standard quark model with extra corrections for the
binding of the quarks. The loop corrections are necessary to remove the
quenching. Our calculations use heavy baryon perturbation theory with chiral
baryon-meson couplings and a form factor characterizing the structure of
baryons as composite particles. The form factor reflects soft wave function
effects with characteristic momenta MeV, well below the usual
chiral cutoff of GeV. The resulting model involves only three
parameters, the quark moments and and a parameter
that sets the momentum scale in the wavefunctions. We find that this approach
substantially improves the agreement between the theoretical and experimental
values of the octet baryon magnetic moments, with an average difference between
the theoretical and experimental moments of 0.05. An extension to the
decuplet states using the same input predicts a moment of 1.97 for the
hyperon, in excellent agreement with the measured moment of
.Comment: 23 pages, 3 figure
Using baryon octet magnetic moments and masses to fix the pion cloud contribution
Using SU(3) symmetry to constrain the pion BB' couplings, assuming SU(3)
breaking comes only from one-loop pion cloud contributions, and using the the
covariant spectator theory to describe the photon coupling to the quark core,
we show how the experimental masses and magnetic moments of the baryon octet
can be used to set a model independent constraint on the strength of the pion
cloud contributions to the octet, and hence the nucleon, form factors at Q2=0.Comment: 7 pages, 1 figur
Analysis of dynamical corrections to baryon magnetic moments
We present and analyze QCD corrections to the baryon magnetic moments in
terms of the one-, two-, and three-body operators which appear in the effective
field theory developed in our recent papers. The main corrections are extended
Thomas-type corrections associated with the confining interactions in the
baryon. We investigate the contributions of low-lying angular excitations to
the moments quantitatively and show that they are completely negligible. When
the QCD corrections are combined with the non-quark model contributions of the
meson loops, we obtain a model which describes the moments within a mean
deviation of 0.04 . The nontrivial interplay of the two types of
corrections to the quark-model moments is analyzed in detail, and explains why
the quark model is so successful. In the course of these calculations, we
parametrize the general spin structure of the baryon wave functions
in a form which clearly displays the symmetry properties and the internal
angular momentum content of the wave functions, and allows us to use spin-trace
methods to calculate the many spin matrix elements which appear in the
expressions for the moments. This representation may be useful elsewhere.Comment: 32 pages, 3 figures, submitted to Phys. Rev.
Contribution of the cyclic nucleotide gated channel subunit, CNG-3, to olfactory plasticity in Caenorhabditis elegans.
In Caenorhabditis elegans, the AWC neurons are thought to deploy a cGMP signaling cascade in the detection of and response to AWC sensed odors. Prolonged exposure to an AWC sensed odor in the absence of food leads to reversible decreases in the animal's attraction to that odor. This adaptation exhibits two stages referred to as short-term and long-term adaptation. Previously, the protein kinase G (PKG), EGL-4/PKG-1, was shown necessary for both stages of adaptation and phosphorylation of its target, the beta-type cyclic nucleotide gated (CNG) channel subunit, TAX-2, was implicated in the short term stage. Here we uncover a novel role for the CNG channel subunit, CNG-3, in short term adaptation. We demonstrate that CNG-3 is required in the AWC for adaptation to short (thirty minute) exposures of odor, and contains a candidate PKG phosphorylation site required to tune odor sensitivity. We also provide in vivo data suggesting that CNG-3 forms a complex with both TAX-2 and TAX-4 CNG channel subunits in AWC. Finally, we examine the physiology of different CNG channel subunit combinations
Going to the exclusive show : exhibition strategies and moviegoing memories of Disneys animated feature films in Ghent (1937-1982)
This is a case study of the exploitation and experience of Disney's animated feature films from the 1930s to the 1980s in Ghent (Belgium). It is a historical study of programming practices and financial strategies which constructed childhood memories on watching Disney. The study is a contribution to a historical understanding of the implications of global distribution of film as cultural products and the counter pull of localism. Using a multi-method approach, the argument is made that the scarce screenings were strategically programmed to uplift the moviegoing experience into something out of the ordinary in everyday life. Programming and revenue data characterize the screenings as exclusive and generating high intakes. Consequently, the remembered screenings did not exhale an easy accessible social status nor an image of pervasiveness of popular childhood film, contradictory to conventional accounts of Disney's ubiquity in popular culture
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