3,094 research outputs found
Universality of citation distributions: towards an objective measure of scientific impact
We study the distributions of citations received by a single publication
within several disciplines, spanning broad areas of science. We show that the
probability that an article is cited times has large variations between
different disciplines, but all distributions are rescaled on a universal curve
when the relative indicator is considered, where is the
average number of citations per article for the discipline. In addition we show
that the same universal behavior occurs when citation distributions of articles
published in the same field, but in different years, are compared. These
findings provide a strong validation of as an unbiased indicator for
citation performance across disciplines and years. Based on this indicator, we
introduce a generalization of the h-index suitable for comparing scientists
working in different fields.Comment: 7 pages, 5 figures. accepted for publication in Proc. Natl Acad. Sci.
US
NORSTAR Project: Norfolk public schools student team for acoustical research
Development of the NORSTAR (Norfolk Public Student Team for Acoustical Research) Project includes the definition, design, fabrication, testing, analysis, and publishing the results of an acoustical experiment. The student-run program is based on a space flight organization similar to the Viking Project. The experiment will measure the scattering transfer of momentum from a sound field to spheres in a liquid medium. It is hoped that the experimental results will shed light on a difficult physics problem - the difference in scattering cross section (the overall effect of the sound wave scattering) for solid spheres and hollow spheres of differing wall thicknesses
The NORSTAR Program: Space shuttle to space station
The development of G-325, the first high school student-run space flight project, is updated. An overview is presented of a new international program, which involves students from space station countries who will be utilizing Get Away Special technology to cooperatively develop a prototype experiment for controlling a space station research module environment
Center clusters in the Yang-Mills vacuum
Properties of local Polyakov loops for SU(2) and SU(3) lattice gauge theory
at finite temperature are analyzed. We show that spatial clusters can be
identified where the local Polyakov loops have values close to the same center
element. For a suitable definition of these clusters the deconfinement
transition can be characterized by the onset of percolation in one of the
center sectors. The analysis is repeated for different resolution scales of the
lattice and we argue that the center clusters have a continuum limit.Comment: Table added. Final version to appear in JHE
From bridewealth to dowry? A Bayesian estimation of ancestral states of marriage transfers in Indo-European groups
Significant amounts of wealth have been exchanged as part of marriage settlements throughout history. Although various models have been proposed for interpreting these practices, their development over time has not been investigated systematically. In this paper we use a Bayesian MCMC phylogenetic comparative approach to reconstruct the evolution of two forms of wealth transfers at marriage, dowry and bridewealth, for 51 Indo-European cultural groups. Results indicate that dowry is more likely to have been the ancestral practice, and that a minimum of four changes to bridewealth is necessary to explain the observed distribution of the two states across the cultural groups
The electron screening puzzle and nuclear clustering
Accurate measurements of nuclear reactions of astrophysical interest within,
or close to, the Gamow peak, show evidence of an unexpected effect attributed
to the presence of atomic electrons in the target. The experiments need to
include an effective "screening" potential to explain the enhancement of the
cross sections at the lowest measurable energies. Despite various theoretical
studies conducted over the past 20 years and numerous experimental
measurements, a theory has not yet been found that can explain the cause of the
exceedingly high values of the screening potential needed to explain the data.
In this letter we show that instead of an atomic physics solution of the
"electron screening puzzle", the reason for the large screening potential
values is in fact due to clusterization effects in nuclear reactions, in
particular for reaction involving light nuclei.Comment: 6 pages, 2 figures, accepted for publication in Physics Letters
Critical Droplets and Phase Transitions in Two Dimensions
In two space dimensions, the percolation point of the pure-site clusters of
the Ising model coincides with the critical point T_c of the thermal transition
and the percolation exponents belong to a special universality class. By
introducing a bond probability p_B<1, the corresponding site-bond clusters keep
on percolating at T_c and the exponents do not change, until
p_B=p_CK=1-exp(-2J/kT): for this special expression of the bond weight the
critical percolation exponents switch to the 2D Ising universality class. We
show here that the result is valid for a wide class of bidimensional models
with a continuous magnetization transition: there is a critical bond
probability p_c such that, for any p_B>=p_c, the onset of percolation of the
site-bond clusters coincides with the critical point of the thermal transition.
The percolation exponents are the same for p_c<p_B<=1 but, for p_B=p_c, they
suddenly change to the thermal exponents, so that the corresponding clusters
are critical droplets of the phase transition. Our result is based on Monte
Carlo simulations of various systems near criticality.Comment: Final version for publication, minor changes, figures adde
Continuum discretized BCS approach for weakly bound nuclei
The Bardeen-Cooper-Schrieffer (BCS) formalism is extended by including the
single-particle continuum in order to analyse the evolution of pairing in an
isotopic chain from stability up to the drip line. We propose a continuum
discretized generalized BCS based on single-particle pseudostates (PS). These
PS are generated from the diagonalization of the single-particle Hamiltonian
within a Transformed Harmonic Oscillator (THO) basis. The consistency of the
results versus the size of the basis is studied. The method is applied to
neutron rich Oxygen and Carbon isotopes and compared with similar previous
works and available experimental data. We make use of the flexibility of the
proposed model in order to study the evolution of the occupation of the
low-energy continuum when the system becomes weakly bound. We find a larger
influence of the non-resonant continuum as long as the Fermi level approaches
zero.Comment: 20 pages, 16 figures, to be submitte
Study of Giant Pairing Vibrations with neutron-rich nuclei
We investigate the possible signature of the presence of giant pairing states
at excitation energy of about 10 MeV via two-particle transfer reactions
induced by neutron-rich weakly-bound projectiles. Performing particle-particle
RPA calculations on Pb and BCS+RPA calculations on Sn, we
obtain the pairing strength distribution for two particles addition and removal
modes. Estimates of two-particle transfer cross sections can be obtained in the
framework of the 'macroscopic model'. The weak-binding nature of the projectile
kinematically favours transitions to high-lying states. In the case of (~^6He,
\~^4He) reaction we predict a population of the Giant Pairing Vibration with
cross sections of the order of a millibarn, dominating over the mismatched
transition to the ground state.Comment: Talk presented in occasion of the VII School-Semina r on Heavy Ion
Physics hosted by the Flerov Laboratory (FLNR/JINR) Dubna, Russia from May 27
to June 2, 200
Distributed Graph Clustering using Modularity and Map Equation
We study large-scale, distributed graph clustering. Given an undirected
graph, our objective is to partition the nodes into disjoint sets called
clusters. A cluster should contain many internal edges while being sparsely
connected to other clusters. In the context of a social network, a cluster
could be a group of friends. Modularity and map equation are established
formalizations of this internally-dense-externally-sparse principle. We present
two versions of a simple distributed algorithm to optimize both measures. They
are based on Thrill, a distributed big data processing framework that
implements an extended MapReduce model. The algorithms for the two measures,
DSLM-Mod and DSLM-Map, differ only slightly. Adapting them for similar quality
measures is straight-forward. We conduct an extensive experimental study on
real-world graphs and on synthetic benchmark graphs with up to 68 billion
edges. Our algorithms are fast while detecting clusterings similar to those
detected by other sequential, parallel and distributed clustering algorithms.
Compared to the distributed GossipMap algorithm, DSLM-Map needs less memory, is
up to an order of magnitude faster and achieves better quality.Comment: 14 pages, 3 figures; v3: Camera ready for Euro-Par 2018, more
details, more results; v2: extended experiments to include comparison with
competing algorithms, shortened for submission to Euro-Par 201
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