981 research outputs found
Charge-Dependence of the Nucleon-Nucleon Interaction
Based upon the Bonn meson-exchange-model for the nucleon-nucleon ()
interaction, we calculate the charge-independence breaking (CIB) of the
interaction due to pion-mass splitting. Besides the one-pion-exchange (OPE), we
take into account the -exchange model and contributions from three and
four irreducible pion exchanges. We calculate the CIB differences in the
effective range parameters as well as phase shift differences for
partial waves up to total angular momentum J=4 and laboratory energies below
300 MeV. We find that the CIB effect from OPE dominates in all partial waves.
However, the CIB effects from the model are noticable up to D-waves and
amount to about 40% of the OPE CIB-contribution in some partial waves, at 300
MeV. The effects from 3 and 4 contributions are negligible except in
and .Comment: 12 pages, RevTex, 14 figure
Generalized h-index for Disclosing Latent Facts in Citation Networks
What is the value of a scientist and its impact upon the scientific thinking?
How can we measure the prestige of a journal or of a conference? The evaluation
of the scientific work of a scientist and the estimation of the quality of a
journal or conference has long attracted significant interest, due to the
benefits from obtaining an unbiased and fair criterion. Although it appears to
be simple, defining a quality metric is not an easy task. To overcome the
disadvantages of the present metrics used for ranking scientists and journals,
J.E. Hirsch proposed a pioneering metric, the now famous h-index. In this
article, we demonstrate several inefficiencies of this index and develop a pair
of generalizations and effective variants of it to deal with scientist ranking
and with publication forum ranking. The new citation indices are able to
disclose trendsetters in scientific research, as well as researchers that
constantly shape their field with their influential work, no matter how old
they are. We exhibit the effectiveness and the benefits of the new indices to
unfold the full potential of the h-index, with extensive experimental results
obtained from DBLP, a widely known on-line digital library.Comment: 19 pages, 17 tables, 27 figure
FunMap: Efficient Execution of Functional Mappings for Knowledge Graph Creation
Data has exponentially grown in the last years, and knowledge graphs
constitute powerful formalisms to integrate a myriad of existing data sources.
Transformation functions -- specified with function-based mapping languages
like FunUL and RML+FnO -- can be applied to overcome interoperability issues
across heterogeneous data sources. However, the absence of engines to
efficiently execute these mapping languages hinders their global adoption. We
propose FunMap, an interpreter of function-based mapping languages; it relies
on a set of lossless rewriting rules to push down and materialize the execution
of functions in initial steps of knowledge graph creation. Although applicable
to any function-based mapping language that supports joins between mapping
rules, FunMap feasibility is shown on RML+FnO. FunMap reduces data redundancy,
e.g., duplicates and unused attributes, and converts RML+FnO mappings into a
set of equivalent rules executable on RML-compliant engines. We evaluate FunMap
performance over real-world testbeds from the biomedical domain. The results
indicate that FunMap reduces the execution time of RML-compliant engines by up
to a factor of 18, furnishing, thus, a scalable solution for knowledge graph
creation
Charge-Asymmetry of the Nucleon-Nucleon Interaction
Based upon the Bonn meson-exchange model for the nucleon-nucleon ()
interaction, we study systematically the charge-symmetry-breaking (CSB) of the
interaction due to nucleon mass splitting. Particular attention is payed
to CSB generated by the -exchange contribution to the interaction,
diagrams, and other multi-meson-exchanges. We calculate the CSB
differences in the effective range parameters as well as phase shift
differences in , and higher partial waves up to 300 MeV lab. energy. We
find a total CSB difference in the singlet scattering length of 1.6 fm which
explains the empirical value accurately. The corresponding CSB phase-shift
differences are appreciable at low energy in the state. In the other
partial waves, the CSB splitting of the phase shifts is small and increases
with energy, with typical values in the order of 0.1 deg at 300 MeV in and
waves.Comment: 11 pages, RevTex, 14 figure
Theorem on the Distribution of Short-Time Particle Displacements with Physical Applications
The distribution of the initial short-time displacements of particles is
considered for a class of classical systems under rather general conditions on
the dynamics and with Gaussian initial velocity distributions, while the
positions could have an arbitrary distribution. This class of systems contains
canonical equilibrium of a Hamiltonian system as a special case. We prove that
for this class of systems the nth order cumulants of the initial short-time
displacements behave as the 2n-th power of time for all n>2, rather than
exhibiting an nth power scaling. This has direct applications to the initial
short-time behavior of the Van Hove self-correlation function, to its
non-equilibrium generalizations the Green's functions for mass transport, and
to the non-Gaussian parameters used in supercooled liquids and glasses.Comment: A less ambiguous mathematical notation for cumulants was adopted and
several passages were reformulated and clarified. 40 pages, 1 figure.
Accepted by J. Stat. Phy
The high-precision, charge-dependent Bonn nucleon-nucleon potential (CD-Bonn)
We present a charge-dependent nucleon-nucleon (NN) potential that fits the
world proton-proton data below 350 MeV available in the year of 2000 with a
chi^2 per datum of 1.01 for 2932 data and the corresponding neutron-proton data
with chi^2/datum = 1.02 for 3058 data. This reproduction of the NN data is more
accurate than by any phase-shift analysis and any other NN potential. The
charge-dependence of the present potential (that has been dubbed `CD-Bonn') is
based upon the predictions by the Bonn Full Model for charge-symmetry and
charge-independence breaking in all partial waves with J <= 4. The potential is
represented in terms of the covariant Feynman amplitudes for one-boson exchange
which are nonlocal. Therefore, the off-shell behavior of the CD-Bonn potential
differs in a characteristic and well-founded way from commonly used local
potentials and leads to larger binding energies in nuclear few- and many-body
systems, where underbinding is a persistent problem.Comment: 69 pages (RevTex) including 20 tables and 9 figures (ps files
Magnetic vortex oscillator driven by dc spin-polarized current
Transfer of angular momentum from a spin-polarized current to a ferromagnet
provides an efficient means to control the dynamics of nanomagnets. A peculiar
consequence of this spin-torque, the ability to induce persistent oscillations
of a nanomagnet by applying a dc current, has previously been reported only for
spatially uniform nanomagnets. Here we demonstrate that a quintessentially
nonuniform magnetic structure, a magnetic vortex, isolated within a nanoscale
spin valve structure, can be excited into persistent microwave-frequency
oscillations by a spin-polarized dc current. Comparison to micromagnetic
simulations leads to identification of the oscillations with a precession of
the vortex core. The oscillations, which can be obtained in essentially zero
magnetic field, exhibit linewidths that can be narrower than 300 kHz, making
these highly compact spin-torque vortex oscillator devices potential candidates
for microwave signal-processing applications, and a powerful new tool for
fundamental studies of vortex dynamics in magnetic nanostructures.Comment: 14 pages, 4 figure
Determination of the pion-nucleon coupling constant and scattering lengths
We critically evaluate the isovector GMO sum rule for forward pion-nucleon
scattering using the recent precision measurements of negatively charged
pion-proton and pion-deuteron scattering lengths from pionic atoms. We deduce
the charged-pion-nucleon coupling constant, with careful attention to
systematic and statistical uncertainties. This determination gives, directly
from data a pseudoscalar coupling constant of
14.11+-0.05(statistical)+-0.19(systematic) or a pseudovector one of 0.0783(11).
This value is intermediate between that of indirect methods and the direct
determination from backward neutron-proton differential scattering cross
sections. We also use the pionic atom data to deduce the coherent symmetric and
antisymmetric sums of the negatively charged pion-proton and pion-neutron
scattering lengths with high precision. The symmetric sum gives
0.0012+-0.0002(statistical)+-0.0008 (systematic) and the antisymmetric one
0.0895+-0.0003(statistical)+-0.0013(systematic), both in units of inverse
charged pion-mass. For the need of the present analysis, we improve the
theoretical description of the pion-deuteron scattering length.Comment: 27 pages, 5 figures, submitted to Phys. Rev. C, few modifications and
clarifications, no change in substance of the pape
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