1,290 research outputs found
Changes in erythropoietin levels during space flight or space flight simulation
Two hundred and seventy samples from 24 subjects involved in 3 bedrest studies and from 3 subjects involved in Spacelab Mission Development Test 3 were assayed for erythropoietin (Ep), in an in vitro fetal mouse liver cell assay, and for ferritin using a commercially available immunoradiometric assay kit. No trends or significant changes in serum Ep were observed. Serum ferritin concentrations tended to increases slightly during the 'missions', reflecting a redirection of iron from the suppressed erythron into iron stores
The nuclear contacts and short range correlations in nuclei
Atomic nuclei are complex strongly interacting systems and their exact
theoretical description is a long-standing challenge. An approximate
description of nuclei can be achieved by separating its short and long range
structure. This separation of scales stands at the heart of the nuclear shell
model and effective field theories that describe the long-range structure of
the nucleus using a mean- field approximation. We present here an effective
description of the complementary short-range structure using contact terms and
stylized two-body asymptotic wave functions. The possibility to extract the
nuclear contacts from experimental data is presented. Regions in the two-body
momentum distribution dominated by high-momentum, close-proximity, nucleon
pairs are identified and compared to experimental data. The amount of
short-range correlated (SRC) nucleon pairs is determined and compared to
measurements. Non-combinatorial isospin symmetry for SRC pairs is identified.
The obtained one-body momentum distributions indicate dominance of SRC pairs
above the nuclear Fermi-momentum.Comment: Accepted for publication in Physics Letters. 6 pages, 2 figure
Spontaneous Breaking of Rotational Symmetry in Rotating Solitons - a Toy Model of Excited Nucleons with High Angular Momentum
We study the phenomenon of spontaneous breaking of rotational symmetry (SBRS)
in the rotating solutions of two types of baby Skyrme models. In the first the
domain is a two-sphere and in the other, the Skyrmions are confined to the
interior of a unit disk. Numerical full-field results show that when the
angular momentum of the Skyrmions increases above a certain critical value, the
rotational symmetry of the solutions is broken and the minimal energy
configurations become less symmetric. We propose a possible mechanism as to why
SBRS is present in the rotating solutions of these models, while it is not
observed in the `usual' baby Skyrme model. Our results might be relevant for a
qualitative understanding of the non-spherical deformation of excited nucleons
with high orbital angular momentum.Comment: RevTex, 9 pages, 9 figures. Added conten
Measurement of transparency ratios for protons from short-range correlated pairs
Nuclear transparency, Tp(A), is a measure of the average probability for a
struck proton to escape the nucleus without significant re-interaction.
Previously, nuclear transparencies were extructed for quasi-elastic A(e,e'p)
knockout of protons with momentum below the Fermi momentum, where the spectral
functions are well known. In this paper we extract a novel observable, the
transparency ratio, Tp(A)/T_p(12C), for knockout of high-missing-momentum
protons from the breakup of short range correlated pairs (2N-SRC) in Al, Fe and
Pb nuclei relative to C. The ratios were measured at momentum transfer Q^2 >
1.5 (GeV/c)^2 and x_B > 1.2 where the reaction is expected to be dominated by
electron scattering from 2N-SRC. The transparency ratios of the knocked-out
protons coming from 2N-SRC breakup are 20 - 30% lower than those of previous
results for low missing momentum. They agree with Glauber calculations and
agree with renormalization of the previously published transparencies as
proposed by recent theoretical investigations. The new transparencies scale as
A^-1/3, which is consistent with dominance of scattering from nucleons at the
nuclear surface.Comment: 6 pages, 4 figure
Constraints on the large-x d/u ratio from electron-nucleus scattering at x>1
Recently the ratio of neutron to proton structure functions F_2n/F_2p was
extracted from a phenomenological correlation between the strength of the
nuclear EMC effect and inclusive electron-nucleus cross section ratios at x>1.
Within conventional models of nuclear smearing, this "in-medium correction"
(IMC) extraction constrains the size of nuclear effects in the deuteron
structure functions, from which the neutron structure function F_2n is usually
extracted. The IMC data determine the resulting proton d/u quark distribution
ratio, extrapolated to x=1, to be 0.23 +- 0.09 with a 90% confidence level.
This is well below the SU(6) symmetry limit of 1/2 and significantly above the
scalar diquark dominance limit of 0.Comment: 4 pages, 3 figure
Short Range Correlations and the EMC Effect
This paper shows quantitatively that the magnitude of the EMC effect measured
in electron deep inelastic scattering (DIS) at intermediate , , is linearly related to the Short Range Correlation (SRC) scaling
factor obtained from electron inclusive scattering at . The observed
phenomenological relationship is used to extract the ratio of the deuteron to
the free pair cross sections, the DIS cross section for a free neutron,
and , the ratio of the free neutron to free proton structure
functions. We speculate that the observed correlation is because both the EMC
effect and SRC are dominated by the high virtuality (high momentum) nucleons in
the nucleus.Comment: 5 pages, 2 figures, minor changes for PRL acceptance, reference 12
correcte
Hexagonal Structure of Baby Skyrmion Lattices
We study the zero-temperature crystalline structure of baby Skyrmions by
applying a full-field numerical minimization algorithm to baby Skyrmions placed
inside different parallelogramic unit-cells and imposing periodic boundary
conditions. We find that within this setup, the minimal energy is obtained for
the hexagonal lattice, and that in the resulting configuration the Skyrmion
splits into quarter-Skyrmions. In particular, we find that the energy in the
hexagonal case is lower than the one obtained on the well-studied rectangular
lattice, in which splitting into half-Skyrmions is observed.Comment: RevTeX, 7 pages, 6 figure
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