6,977 research outputs found
The influence of self-citation corrections on Egghe's g index
The g index was introduced by Leo Egghe as an improvement of Hirsch's index h
for measuring the overall citation record of a set of articles. It better takes
into account the highly skewed frequency distribution of citations than the h
index. I propose to sharpen this g index by excluding the self-citations. I
have worked out nine practical cases in physics and compare the h and g values
with and without self-citations. As expected, the g index characterizes the
data set better than the h index. The influence of the self-citations appears
to be more significant for the g index than for the h index.Comment: 9 pages, 2 figures, submitted to Scientometric
Ultrasensitive 3He magnetometer for measurements of high magnetic fields
We describe a 3He magnetometer capable to measure high magnetic fields (B >
0.1 Tesla) with a relative accuracy of better than 10^-12. Our approach is
based on the measurement of the free induction decay of gaseous, nuclear spin
polarized 3He following a resonant radio frequency pulse excitation. The
measurement sensitivity can be attributed to the long coherent spin precession
time T2* being of order minutes which is achieved for spherical sample cells in
the regime of motional narrowing where the disturbing influence of field
inhomogeneities is strongly suppressed. The 3He gas is spin polarized in-situ
using a new, non-standard variant of the metastability exchange optical
pumping. We show that miniaturization helps to increase T2* further and that
the measurement sensitivity is not significantly affected by temporal field
fluctuations of order 10^-4.Comment: 27 pages, 7 figure
Introducing the Fission-Fusion Reaction Process: Using a Laser-Accelerated Th Beam to produce Neutron-Rich Nuclei towards the N=126 Waiting Point of the r Process
We propose to produce neutron-rich nuclei in the range of the astrophysical
r-process around the waiting point N=126 by fissioning a dense
laser-accelerated thorium ion bunch in a thorium target (covered by a CH2
layer), where the light fission fragments of the beam fuse with the light
fission fragments of the target. Via the 'hole-boring' mode of laser Radiation
Pressure Acceleration using a high-intensity, short pulse laser, very
efficiently bunches of 232Th with solid-state density can be generated from a
Th layer, placed beneath a deuterated polyethylene foil, both forming the
production target. Th ions laser-accelerated to about 7 MeV/u will pass through
a thin CH2 layer placed in front of a thicker second Th foil closely behind the
production target and disintegrate into light and heavy fission fragments. In
addition, light ions (d,C) from the CD2 production target will be accelerated
as well to about 7 MeV/u, inducing the fission process of 232Th also in the
second Th layer. The laser-accelerated ion bunches with solid-state density,
which are about 10^14 times more dense than classically accelerated ion
bunches, allow for a high probability that generated fission products can fuse
again. In contrast to classical radioactive beam facilities, where intense but
low-density radioactive beams are merged with stable targets, the novel
fission-fusion process draws on the fusion between neutron-rich, short-lived,
light fission fragments both from beam and target. The high ion beam density
may lead to a strong collective modification of the stopping power in the
target, leading to significant range enhancement. Using a high-intensity laser
as envisaged for the ELI-Nuclear Physics project in Bucharest (ELI-NP),
estimates promise a fusion yield of about 10^3 ions per laser pulse in the mass
range of A=180-190, thus enabling to approach the r-process waiting point at
N=126.Comment: 13 pages, 6 figure
Electronic properties of disordered corner-sharing tetrahedral lattices
We have examined the behaviour of noninteracting electrons moving on a
corner-sharing tetrahedral lattice into which we introduce a uniform (box)
distribution, of width W, of random on-site energies. We have used both the
relative localization length and the spectral rigidity to analyze the nature of
the eigenstates, and have determined both the mobility edge trajectories as a
function of W, and the critical disorder, Wc, beyond which all states are
localized. We find (i) that the mobility edge trajectories (energies Ec vs.
disorder W) are qualitatively different from those found for a simple cubic
lattice, and (ii) that the spectral rigidity is scale invariant at Wc and thus
provides a reliable method of estimating this quantity -- we find Wc/t=14.5. We
discuss our results in the context of the metal-to-insulator transition
undergone by LiAlyTi{2-y}O4 in a quantum site percolation model that also
includes the above-mentioned Anderson disorder, and show that the effects
produced by Anderson disorder are far less important than those produced by
quantum site percolation, at least in the determination of the doping
concentration at which the metal-to-insulator transition is predicted to occur
The concept of correlated density and its application
The correlated density appears in many physical systems ranging from dense
interacting gases up to Fermi liquids which develop a coherent state at low
temperatures, the superconductivity. One consequence of the correlated density
is the Bernoulli potential in superconductors which compensates forces from
dielectric currents. This Bernoulli potential allows to access material
parameters. Though within the surface potential these contributions are largely
canceled, the bulk measurements with NMR can access this potential. Recent
experiments are explained and new ones suggested. The underlying quantum
statistical theory in nonequilibrium is the nonlocal kinetic theory developed
earlier.Comment: 14 pages, CMT30 proceeding
Parton Distributions for the Octet and Decuplet Baryons
We calculate the parton distributions for both polarized and unpolarized
octet and decuplet baryons, using the MIT bag, dressed by mesons. We show that
the hyperfine interaction responsible for the and splittings leads to large deviations from SU(3) and SU(6) predictions.
For the we find significant polarized, non-strange parton
distributions which lead to a sizable polarization in polarized,
semi-inclusive scattering. We also discuss the flavour symmetry violation
arising from the meson-cloud associated with the chiral structure of baryons.Comment: 29 pages, 15 figure
Non-Perturbative Mass Renormalization in Quenched QED from the Worldline Variational Approach
Following Feynman's successful treatment of the polaron problem we apply the
same variational principle to quenched QED in the worldline formulation. New
features arise from the description of fermions by Grassmann trajectories, the
supersymmetry between bosonic and fermionic variables and the much more
singular structure of a renormalizable gauge theory like QED in 3+1 dimensions.
We take as trial action a general retarded quadratic action both for the
bosonic and fermionic degrees of freedom and derive the variational equations
for the corresponding retardation functions. We find a simple analytic,
non-perturbative, solution for the anomalous mass dimension gamma_m(alpha) in
the MS scheme. For small couplings we compare our result with recent four-loop
perturbative calculations while at large couplings we find that gamma_m(alpha)
becomes proportional to (alpha)^(1/2). The anomalous mass dimension shows no
obvious sign of the chiral symmetry breaking observed in calculations based on
the use of Dyson-Schwinger equations, however we find that a perturbative
expansion of gamma_m(alpha) diverges for alpha > 0.7934. Finally, we
investigate the behaviour of gamma_m(alpha) at large orders in perturbation
theory.Comment: 18 pages, 1 Figure, RevTeX; the manuscript has been substantially
revised and enlarged in order to make it selfcontained; accepted for
publication in Phys. Rev.
- âŠ