1,869 research outputs found
Comparison of Relativistic Nucleon-Nucleon Interactions
We investigate the difference between those relativistic models based on
interpreting a realistic nucleon-nucleon interaction as a perturbation of the
square of a relativistic mass operator and those models that use the method of
Kamada and Gl\"ockle to construct an equivalent interaction to add to the
relativistic mass operator. Although both models reproduce the phase shifts and
binding energy of the corresponding non-relativistic model, they are not
scattering equivalent. The example of elastic electron-deuteron scattering in
the one-photon-exchange approximation is used to study the sensitivity of
three-body observables to these choices. Our conclusion is that the differences
in the predictions of the two models can be understood in terms of the
different ways in which the relativistic and non-relativistic -matrices are
related. We argue that the mass squared method is consistent with conventional
procedures used to fit the Lorentz-invariant cross section as a function of the
laboratory energy.Comment: Revtex 13 pages, 5 figures, corrected some typo
A Three-Year Study on Peer Evaluation in a Software Engineering Project Course
Background: Peer evaluation in software engineering
(SE) project courses enhances the learning experience of students.
It also helps instructors monitor and assess both teams and
individual students. Peer evaluations might influence the way
individual students and teams work therefore the quality of the
peer evaluations should be tracked through the project course.
Contribution: In this paper, we analyzed the quality and scoring
behavior of students in peer evaluation in an undergraduate SE
project course over three years.
Research Questions: RQ1: What is the quality of peer evaluation of undergraduate students in a SE project course? RQ2:
How do undergraduate students in a SE project course score
each other?
Methodology: The quality of peer evaluation (length, level of
detail, etc.) and scoring of peers based on various aspects of
peer evaluations of third-year students in a year-long SE project
course were studied. Taking into account the grade students
received at the end of the course (A, B, C and F-calibers), peer
evaluations were categorized, analyzed over time and compared
between students calibers.
Findings: After analyzing 6,854 peer evaluations from 193
students, it was found that the quality of peer evaluations
across students was mostly consistent throughout the course.
Also, it was observed that quantitative aspects of the peer
evaluation were scored similarly across student calibers. However,
the qualitative aspects of the peer evaluation were impacted
by the caliber of students. These findings suggest that weaker
students (i.e., C-caliber students) generally receive better quality
peer evaluations than stronger students (i.e., A-caliber students).
Lastly, a preliminary analysis showed a positive connotation of
emotions and sentiments found in textual feedback delivered by
students
Lattice Calculation of the Strangeness Magnetic Moment of the Nucleon
We report on a lattice QCD calculation of the strangeness magnetic moment of
the nucleon. Our result is . The sea contributions
from the u and d quarks are about 80% larger. However, they cancel to a large
extent due to their electric charges, resulting in a smaller net sea
contribution of to the nucleon magnetic moment. As
far as the neutron to proton magnetic moment ratio is concerned, this sea
contribution tends to cancel out the cloud-quark effect from the Z-graphs and
result in a ratio of which is close to the SU(6) relation and
the experiment. The strangeness Sachs electric mean-square radius
is found to be small and negative and the total sea contributes substantially
to the neutron electric form factor.Comment: 10 pages, 5 figures, LaTex, UK/97-23, ADP-97-55/T28
Point-Form Analysis of Elastic Deuteron Form Factors
Point-form relativistic quantum mechanics is applied to elastic
electron-deuteron scattering. The deuteron is modeled using relativistic
interactions that are scattering-equivalent to the nonrelativistic Argonne
and Reid '93 interactions. A point-form spectator approximation (PFSA)
is introduced to define a conserved covariant current in terms of
single-nucleon form factors. The PFSA is shown to provide an accurate
description of data up to momentum transfers of 0.5 , but falls
below the data at higher momentum transfers. Results are sensitive to the
nucleon form factor parameterization chosen, particularly to the neutron
electric form factor.Comment: RevTex, 31 pages, 1 table, 13 figure
Electro-Magnetic Nucleon Form Factors and their Spectral Functions in Soliton Models
It is demonstrated that in simple soliton models essential features of the
electro-magnetic nucleon form factors observed over three orders of magnitude
in momentum transfer are naturally reproduced. The analysis shows that
three basic ingredients are required: an extended object, partial coupling to
vector mesons, and relativistic recoil corrections. We use for the extended
object the standard skyrmion, one vector meson propagator for both isospin
channels, and the relativistic boost to the Breit frame. Continuation to
timelike leads to quite stable results for the spectral functions in the
regime from the 2- or 3-pion threshold to about two rho masses. Especially the
onset of the continuous part of the spectral functions at threshold can be
reliably determined and there are strong analogies to the results imposed on
dispersion theoretic approaches by the unitarity constraint.Comment: 24 pages, (RevTeX), 5 PS-figures; Data points in fig.2 and
corresponding references added. Final version, to be published in Z.Physik
Elastic electron deuteron scattering with consistent meson exchange and relativistic contributions of leading order
The influence of relativistic contributions to elastic electron deuteron
scattering is studied systematically at low and intermediate momentum transfers
( fm). In a -expansion, all leading order
relativistic -exchange contributions consistent with the Bonn OBEPQ models
are included. In addition, static heavy meson exchange currents including boost
terms and lowest order -currents are considered. Sizeable
effects from the various relativistic two-body contributions, mainly from
-exchange, have been found in form factors, structure functions and the
tensor polarization . Furthermore, static properties, viz. magnetic
dipole and charge quadrupole moments and the mean square charge radius are
evaluated.Comment: 15 pages Latex including 5 figures, final version accepted for
publication in Phys.Rev.C Details of changes: (i) The notation of the curves
in Figs. 1 and 2 have been clarified with respect to left and right panels.
(ii) In Figs. 3 and 4 an experimental point for T_20 has been added and a
corresponding reference [48] (iii) At the end of the text we have added a
paragraph concerning the quality of the Bonn OBEPQ potential
Nucleon electromagnetic form factors and polarization observables in space-like and time-like regions
We perform a global analysis of the experimental data of the electromagnetic
nucleon form factors, in space-like and time-like regions. We give the
expressions of the observables in annihilation processes, such as , or , in terms of form factors. We discuss some
of the phenomenological models proposed in the literature for the space-like
region, and consider their analytical continuation to the time-like region.
After determining the parameters through a fit on the available data, we give
predictions for the observables which will be experimentally accessible with
large statistics, polarized annihilation reactions.Comment: 25 pages, 5 figures 7 table
Effect of recent R_p and R_n measurements on extended Gari-Krumpelmann model fits to nucleon electromagnetic form factors
The Gari-Krumpelmann (GK) models of nucleon electromagnetic form factors, in
which the rho, omega, and phi vector meson pole contributions evolve at high
momentum transfer to conform to the predictions of perturbative QCD (pQCD), was
recently extended to include the width of the rho meson by substituting the
result of dispersion relations for the pole and the addition of rho' (1450)
isovector vector meson pole. This extended model was shown to produce a good
overall fit to all the available nucleon electromagnetic form factor (emff)
data. Since then new polarization data shows that the electric to magnetic
ratios R_p and R_n obtained are not consistent with the older G_{Ep} and G_{En}
data in their range of momentum transfer. The model is further extended to
include the omega' (1419) isoscalar vector meson pole. It is found that while
this GKex cannot simultaneously fit the new R_p and the old G_{En} data, it can
fit the new R_p and R_n well simultaneously. An excellent fit to all the
remaining data is obtained when the inconsistent G_{Ep} and G_{En} is omitted.
The model predictions are shown up to momentum transfer squared, Q^2, of 8
GeV^2/c^2.Comment: 14 pages, 8 figures, using RevTeX4; email correspondence to
[email protected] ; minor typos corrected, figures added, conclusions
extende
Poincare' Covariant Current Operator and Elastic Electron-Deuteron Scattering in the Front-form Hamiltonian Dynamics
The deuteron electromagnetic form factors, and , and the
tensor polarization , are unambiguously calculated within the
front-form relativistic Hamiltonian dynamics, by using a novel current, built
up from one-body terms, which fulfills Poincar\'e, parity and time reversal
covariance, together with Hermiticity and the continuity equation. A
simultaneous description of the experimental data for the three deuteron form
factors is achieved up to . At higher momentum transfer,
different nucleon-nucleon interactions strongly affect , , and
and the effects of the interactions can be related to -state
kinetic energy in the deuteron. Different nucleon form factor models have huge
effects on , smaller effects on and essentially none on
.Comment: 31 pages + 16 figures. Submitted to Phys. Rev.
- …