1,212 research outputs found
Erratum to "Azimuthal asymmetry in electro-production of neutral pions in semi-inclusive DIS" published in Phys. Lett. B522 (2001) 37
We correct our analysis of the HERMES experiment for the azimuthal
sin(phi)-spin asymmetry in semi-inclusive hadroproduction in DIS on
longitudinally (with respect to the lepton momentum) polarized target because
of discovered misprint in sign in the paper P.J.Mulders and R.D.Tangerman,
Nucl. Phys. B 461 (1996) 197.Comment: 3 pages, 4 figures. Sign of sin(2phi)-asymmetry correcte
Numerical investigation of the conditioning for plane wave discontinuous Galerkin methods
We present a numerical study to investigate the conditioning of the plane
wave discontinuous Galerkin discretization of the Helmholtz problem. We provide
empirical evidence that the spectral condition number of the plane wave basis
on a single element depends algebraically on the mesh size and the wave number,
and exponentially on the number of plane wave directions; we also test its
dependence on the element shape. We show that the conditioning of the global
system can be improved by orthogonalization of the local basis functions with
the modified Gram-Schmidt algorithm, which results in significantly fewer GMRES
iterations for solving the discrete problem iteratively.Comment: Submitted as a conference proceeding; minor revisio
Sivers vs. Collins effect in azimuthal single spin asymmetries in pion production in SIDIS
Recently it has been argued that the transverse momentum dependent twist-2
Sivers distribution function does not vanish in QCD. Therefore both, the
Collins and Sivers effects, should be considered in order to explain the
azimuthal single spin asymmetries A(UL) in pion production in semi-inclusive
deeply inelastic lepton scattering of a longitudinally polarized target. On the
basis of presently available phenomenological information on the Sivers
function we estimate that for those asymmetries A(UL) in the kinematic region
of the HERMES experiments the Sivers effect can be neglected with respect to
the Collins effect. It is argued that the same feature holds also for the
COMPASS and CLAS experiments. This justifies theoretical approaches to
understand the HERMES data on the basis of the Collins effect only.Comment: 8 pages, 4 figures. References added, small changes in text, Appendix
adde
New observables in longitudinal single-spin asymmetries in semi-inclusive DIS
We analyze longitudinal beam and target single-spin asymmetries in
semi-inclusive deep inelastic scattering and in jet deep inelastic scattering,
including all possible twist-3 contributions as well as quark mass corrections.
We take into account the path-ordered exponential in the soft correlators and
show that it leads to the introduction of a new distribution and a new
fragmentation function contributing to the asymmetries.Comment: 8 page
Azimuthal single spin asymmetries in SIDIS in the light of chiral symmetry breaking
An attempt is made to understand the z-dependence of the azimuthal single
spin asymmetries observed by the HERMES collaboration in terms of chiral models
based on effective quark and Goldstone boson degrees of freedom. The effects of
respectively neglecting and considering Gaussian intrinsic parton transverse
momenta and the Sivers effect are explored. Predictions for the transverse
target polarization experiment at HERMES are presented.Comment: 14 pages, 18 figure
Collins effect and single spin azimuthal asymmetries in the HERMES and COMPASS experiments
Predictions are made for single spin azimuthal asymmetries due to the Collins
effect in pion production from semi-inclusive deeply inelastic scattering off
transversely and longitudinally polarized targets for the HERMES and COMPASS
experiments. The x-dependence of the asymmetries is evaluated using the parton
distribution functions from the chiral quark-soliton model. The overall
normalization of the predicted asymmetries is determined by the information on
the Collins fragmentation function extracted from previous HERMES data on
azimuthal asymmetries from a longitudinally polarized target. The single spin
asymmetries from the transversely polarized proton target are found to be about
20% for positive and neutral pions both at HERMES and COMPASS. For a
longitudinally polarized target we obtain for COMPASS a sin(phi) asymmetry of
1% and a sin(2phi) asymmetry of about 3%.Comment: 10 pages, 9 figures, Ref.[29] adde
Lorentz invariance relations between parton distributions and the Wandzura-Wilczek approximation
The violation of the so-called Lorentz invariance relations between parton
distribution functions is considered in a model independent way. It is shown
that these relations are not violated in a generalized Wandzura-Wilczek
approximation, indicating that numerically their violation may be small.Comment: 13 pages, added references, minor changes, to appear in Phys. Lett.
Understanding the proton's spin structure
We discuss the tremendous progress that has been towards an understanding of
how the spin of the proton is distributed on its quark and gluon constituents.
This is a problem that began in earnest twenty years ago with the discovery of
the proton ``spin crisis'' by the European Muon Collaboration. The discoveries
prompted by that original work have given us unprecedented insight into the
amount of spin carried by polarized gluons and the orbital angular momentum of
the quarks.Comment: Review article for J. Phys. G, 1 figure, 22 page
Empirical Evaluation of Bone Extraction Protocols
The application of high-resolution analytical techniques to characterize ancient bone proteins requires clean, efficient extraction to obtain high quality data. Here, we evaluated many different protocols from the literature on ostrich cortical bone and moa cortical bone to evaluate their yield and relative purity using the identification of antibody-antigen complexes on enzyme-linked immunosorbent assay and gel electrophoresis. Moa bone provided an ancient comparison for the effectiveness of bone extraction protocols tested on ostrich bone. For the immunological part of this study, we focused on collagen I, osteocalcin, and hemoglobin because collagen and osteocalcin are the most abundant proteins in the mineralized extracellular matrix and hemoglobin is common in the vasculature. Most of these procedures demineralize the bone first, and then the remaining organics are chemically extracted. We found that the use of hydrochloric acid, rather than ethylenediaminetetraacetic acid, for demineralization resulted in the cleanest extractions because the acid was easily removed. In contrast, the use of ethylenediaminetetraacetic acid resulted in smearing upon electrophoretic separation, possibly indicating these samples were not as pure. The denaturing agents sodium dodecyl sulfate, urea, and guanidine HCl have been used extensively for the solubilization of proteins in non-biomineralized tissue, but only the latter has been used on bone. We show that all three denaturing agents are effective for extracting bone proteins. One additional method tested uses ammonium bicarbonate as a solubilizing buffer that is more appropriate for post-extraction analyses (e.g., proteomics) by removing the need for desalting. We found that both guanidine HCl and ammonium bicarbonate were effective for extracting many bone proteins, resulting in similar electrophoretic patterns. With the increasing use of proteomics, a new generation of scientists are now interested in the study of proteins from not only extant bone but also from ancient bone
Impact of UV Radiation from Giant Spirals on the Evolution of Dwarf Galaxies
We show that ultraviolet radiation, with wavelengths shorter than 2000 A,
escaping from the disks of giant spirals could be one of the principal factors
affecting the evolution of low mass satellite galaxies. We demonstrate, using a
semi-qualitative model, that the Lyman continuum part of the radiation field
can lead to ionization of the ISM of the dwarf galaxies through the process of
photoevaporation, making the ISM virtually unobservable. The FUV part (912 <
lambda < 2000 A) is shown to dominate over the internal sources of radiation
for most of the Galactic dwarf spheroidals. The proposed environmental factor
could be at least partially responsible for the bifurcation of the low mass
proto-galaxies into two sequences - dwarf irregulars and dwarf spheroidals. We
discuss many peculiarities of the Local Group early-type dwarfs which can be
accounted for by the impact of the UV radiation from the host spiral galaxy
(Milky Way or M31).Comment: 15 pages, 12 figures. Accepted for publication in MNRAS. More
consistent photoionization model is used in Sect. 2. All main results stay
unchange
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