563 research outputs found
Hadron formation in high energy photonuclear reactions
We present a new method to account for coherence length effects in a
semi-classical transport model. This allows us to describe photo- and
electroproduction at large nuclei (A>12) and high energies using a realistic
coupled channel description of the final state interactions that goes beyond
simple Glauber theory. We show that the purely absorptive treatment of the
final state interactions can lead to wrong estimates of color transparency and
formation time effects in particle production. As an example, we discuss
exclusive rho^0 photoproduction on Pb at a photon energy of 7 GeV as well as
K^+ production in the photon energy range 1-7 GeV.Comment: 14 pages, 6 figures, version published in Phys. Rev.
Photoproduction of mesons in nuclei at GeV energies
In a transport model that combines initial state interactions of the photon
with final state interactions of the produced particles we present a
calculation of inclusive photoproduction of mesons in nuclei in the energy
range from 1 to 7 GeV. We give predictions for the photoproduction cross
sections of pions, etas, kaons, antikaons, and invariant mass
spectra in ^{12}C and ^{208}Pb. The effects of nuclear shadowing and final
state interaction of the produced particles are discussed in detail.Comment: Text added in summary in general reliability of the method,
references updated. Phys. Rev. C (2000) in pres
Magnetic properties of Fe3O4 nanoparticles coated with oleic and dodecanoic acids
Magnetic nanoparticles (NP) of magnetite (Fe3O4) coated with oleic acid (OA)
and dodecanoic acid (DA) were synthesized and investigated through Transmission
Electron Microscopy (TEM),magnetization M, and ac magnetic susceptibility
measurements. The OA coated samples were produced with different magnetic
concentrations (78, 76, and 65%) and the DA sample with 63% of Fe3O4. Images
from TEM indicate that the NP have a nearly spherical geometry and mean
diameter ~ 5.5 nm. Magnetization measurements, performed in zero field cooled
(ZFC) and field cooled (FC) processes under different external magnetic fields
H, exhibited a maximum at a given temperature TB in the ZFC curves, which
depends on the NP coating (OA or DA), magnetite concentration, and H. The
temperature TB decreases monotonically with increasing H and, for a given H,
the increase in the magnetite concentration results in an increase of TB. The
observed behavior is related to the dipolar interaction (DI) between NP which
seems to be an important mechanism in all samples studied. This is supported by
the results of the ac magnetic susceptibility Xac measurements, where the
temperature in which X' peaks for different frequencies follows the
Vogel-Fulcher model, a feature commonly found in systems with dipolar
interactions. Curves of H vs. TB/TB(H=0) for samples with different coatings
and magnetite concentrations collapse into a universal curve, indicating that
the qualitative magnetic behavior of the samples may be described by the NP
themselves, instead of the coating or the strength of the dipolar interaction.
Below TB, M vs. H curves show a coercive field (HC) that increases
monotonically with decreasing temperature. The saturation magnetization (MS)
follows the Bloch's law and values of MS at room temperature as high as 78
emu/g were estimated, a result corresponding to ~80% of the bulk value. The
overlap of M/MS vs. H/T curves for a given sample and the low HC at high
temperatures suggest superparamagnetic behavior in all samples studied. The
overlap of M/MS vs. H curves at constant temperature for different samples
indicates that the NP magnetization behavior is preserved, independently of the
coating and magnetite concentration.Comment: 8 pages and 9 figure
Hadron formation and attenuation in deep inelastic lepton scattering off nuclei
We investigate hadron formation in deep inelastic lepton scattering on N, Kr
and Xe nuclei in the kinematic regime of the HERMES experiment. The elementary
electron-nucleon interaction is described within the event generator PYTHIA
while a full coupled-channel treatment of the final state interactions is
included by means of a BUU transport model. We find a good agreement with the
measured charged hadron multiplicity ratio for N and Kr targets by
accounting for the deceleration and absorption of the primarily produced
particles as well as for the creation of secondary hadrons in the final state
interactions.Comment: 13 pages, 5 figures; revised and extended version, accepted for
publication in Phys. Lett.
e^+e^- Pair Production from A Reactions
We present a calculation of e^+e^- production in reactions at MAMI
and TJNAF energies within a semi-classical BUU transport model. Dilepton
invariant mass spectra for C, Ca and Pb are calculated
at 0.8, 1.5 and 2.2 GeV. We focus on observable effects of medium modifications
of the and mesons. The in-medium widths of these mesons are
taken into account in a dynamical, consistent way. We discuss the transport
theoretical treatment of broad resonances.Comment: 42 pages including 16 figure
Purification and Characterization of a Novel (R)-Mandelonitrile Lyase from the Fern Phlebodium aureum
Transport study of charged current interactions in neutrino-nucleus reactions
Within a dynamical transport approach we investigate charged current
interactions in neutrino-nucleus reactions for neutrino energies of 0.3 - 1.5
GeV with particular emphasis on resonant pion production channels via the
resonance. The final-state-interactions of the resonance as
well as of the emitted pions are calculated explicitly for and
nuclei and show a dominance of pion suppression at moderate momenta
0.2 GeV/c. A comparison to integrated spectra for reactions with the available (preliminary) data demonstrates a
reasonable agreement.Comment: 13 pages incl. 6 eps-figures; computational error in final state
interactions corrected; to be published in Phys. Lett.
A Generalized Diffusion Tensor for Fully Anisotropic Diffusion of Energetic Particles in the Heliospheric Magnetic Field
The spatial diffusion of cosmic rays in turbulent magnetic fields can, in the
most general case, be fully anisotropic, i.e. one has to distinguish three
diffusion axes in a local, field-aligned frame. We reexamine the transformation
for the diffusion tensor from this local to a global frame, in which the Parker
transport equation for energetic particles is usually formulated and solved.
Particularly, we generalize the transformation formulas to allow for an
explicit choice of two principal local perpendicular diffusion axes. This
generalization includes the 'traditional' diffusion tensor in the special case
of isotropic perpendicular diffusion. For the local frame, we motivate the
choice of the Frenet-Serret trihedron which is related to the intrinsic
magnetic field geometry. We directly compare the old and the new tensor
elements for two heliospheric magnetic field configurations, namely the hybrid
Fisk and the Parker field. Subsequently, we examine the significance of the
different formulations for the diffusion tensor in a standard 3D model for the
modulation of galactic protons. For this we utilize a numerical code to
evaluate a system of stochastic differential equations equivalent to the Parker
transport equation and present the resulting modulated spectra. The computed
differential fluxes based on the new tensor formulation deviate from those
obtained with the 'traditional' one (only valid for isotropic perpendicular
diffusion) by up to 60% for energies below a few hundred MeV depending on
heliocentric distance.Comment: 8 pages, 6 figures, accepted in Ap
Pathogenesis of eosinophilic esophagitis: A comprehensive review of the genetic and molecular aspects
Eosinophilic esophagitis (EoE) is a relatively new condition described as an allergicmediated disease of the esophagus. Clinically, it is characterized by dysphagia, food impaction, and reflux-like symptoms. Multiple genome-wide association studies (GWAS) have been conducted to identify genetic loci associated with EoE. The integration of numerous studies investigating the genetic polymorphisms in EoE and the Mendelian diseases associated with EoE are discussed to provide insights into the genetic risk of EoE, notably focusing on CCL26 and CAPN14. We focus on the genetic loci investigated thus far, and their classification according to whether the function near the loci is known. The pathophysiology of EoE is described by separately presenting the known function of each cell and molecule, with the major contributors being eosinophils, Th2 cells, thymic stromal lymphopoietin (TSLP), transforming growth factor (TGF)-β1, and interleukin (IL)-13. This review aims to provide detailed descriptions of the genetics and the comprehensive pathophysiology of EoE
Proton polarizability contribution to the hydrogen hyperfine splitting
The contribution of the proton polarizability to the hydrogen hyperfine
splitting is evaluated on the basis of modern experimental and theoretical
results on the proton polarized structure functions. The value of this
correction is equal to 1.4 ppm.Comment: 11 pages, LaTeX2.09, 7 figures, uses linedraw.sty, psfig.sty,
epsf.st
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