3,351 research outputs found
Efficient computation of the Shapley value for game-theoretic network centrality
The Shapley value—probably the most important normative payoff division scheme in coalitional games—has recently been advocated as a useful measure of centrality in networks. However, although this approach has a variety of real-world applications (including social and organisational networks, biological networks and communication networks), its computational properties have not been widely studied. To date, the only practicable approach to compute Shapley value-based centrality has been via Monte Carlo simulations which are computationally expensive and not guaranteed to give an exact answer. Against this background, this paper presents the first study of the computational aspects of the Shapley value for network centralities. Specifically, we develop exact analytical formulae for Shapley value-based centrality in both weighted and unweighted networks and develop efficient (polynomial time) and exact algorithms based on them. We empirically evaluate these algorithms on two real-life examples (an infrastructure network representing the topology of the Western States Power Grid and a collaboration network from the field of astrophysics) and demonstrate that they deliver significant speedups over the Monte Carlo approach. Fo
Finite formation time effects in quasi-elastic scattering on nuclear targets
The problem of the final state interaction in quasi-elastic
scattering at large , is investigated by exploiting the idea that the
ejected nucleon needs a finite amount of time to assume its asymptotic form. It
is shown that when the dependence of the scattering amplitude of the ejected
nucleon on its virtuality is taken into account, the final state interaction is
decreased. The developed approach is simpler to implement than the one based on
the color transparency description of the damping of the final state
interaction, and is essentially equivalent to the latter in the case of the
single rescattering term. The process on the deuteron is numerically
investigated and it is shown that, at , appreciable finite formation time
effects at of the order of 10 (GeV/c) are expected.Comment: 23 pages, 3 figure
Moving the Horse before the Cart: Aligning Fundraising with Academic Library Trends
Academic libraries undergo change at an almost constant rate, yet the effect of change can differ across various institutions. As technological and educational environments evolve, the impact to advancement activities can be overlooked if not kept in consideration as it relates to engaging donor investment. Strategically these opportunities for the organization may be hidden and not as visible to stakeholders as traditional or legacy options.
This panel will explore six of these broader academic library trends and lead discussion regarding impact to donors, potential modification to fundraising strategies and challenges to library administrators.
This panel of senior library and advancement leaders will provide strategies, examples and concepts for recognizing these trends as well as modifying and aligning your library’s institutional advancement efforts
Solar Magnetic Field Studies Using the 12-Micron Emission Lines. IV. Observations of a Delta-Region Solar Flare
We have recently developed the capability to make solar vector (Stokes IQUV)
magnetograms using the infrared line of MgI at 12.32 microns. On 24 April 2001,
we obtained a vector magnetic map of solar active region NOAA 9433,
fortuitously just prior to the occurrence of an M2 flare. Examination of a
sequence of SOHO/MDI magnetograms, and comparison with ground-based H-alpha
images, shows that the flare was produced by the cancellation of newly emergent
magnetic flux outside of the main sunspot. The very high Zeeman-sensitivity of
the 12-micron data allowed us to measure field strengths on a spatial scale
which was not directly resolvable. At the flare trigger site, opposite polarity
fields of 2700 and 1000 Gauss occurred within a single 2 arc-sec resolution
element, as revealed by two resolved Zeeman splittings in a single spectrum.
Our results imply an extremely high horizontal field strength gradient (5 G/km)
prior to the flare, significantly greater than seen in previous studies. We
also find that the magnetic energy of the cancelling fields was more than
sufficient to account for the flare's X-ray luminosity.Comment: 14 pages, 5 figures, accepted for Ap.
A study of temperature-related non-linearity at the metal-silicon interface
In this paper, we investigate the temperature dependencies of metal-semiconductor interfaces in an effort to better reproduce the current-voltage-temperature (IVT) characteristics of any Schottky diode, regardless of homogeneity. Four silicon Schottky diodes were fabricated for this work, each displaying different degrees of inhomogeneity; a relatively homogeneous NiV/Si diode, a Ti/Si and Cr/Si diode with double bumps at only the lowest temperatures, and a Nb/Si diode displaying extensive non-linearity. The 77–300 K IVT responses are modelled using a semi-automated implementation of Tung's electron transport model, and each of the diodes are well reproduced. However, in achieving this, it is revealed that each of the three key fitting parameters within the model display a significant temperature dependency. In analysing these dependencies, we reveal how a rise in thermal energy “activates” exponentially more interfacial patches, the activation rate being dependent on the carrier concentration at the patch saddle point (the patch's maximum barrier height), which in turn is linked to the relative homogeneity of each diode. Finally, in a review of Tung's model, problems in the divergence of the current paths at low temperature are explained to be inherent due to the simplification of an interface that will contain competing defects and inhomogeneities
Simple model for scanning tunneling spectroscopy of noble metal surfaces with adsorbed Kondo impurities
A simple model is introduced to describe conductance measurements between a
scanning tunneling microscope (STM) tip and a noble metal surface with adsorbed
transition metal atoms which display the Kondo effect. The model assumes a
realistic parameterization of the potential created by the surface and a
d3z2-r2 orbital for the description of the adsorbate. Fano lineshapes
associated with the Kondo resonance are found to be sensitive to details of the
adsorbate-substrate interaction. For instance, bringing the adsorbate closer to
the surface leads to more asymmetric lineshapes while their dependence on the
tip distance is weak. We find that it is important to use a realistic surface
potential, to properly include the tunnelling matrix elements to the tip and to
use substrate states which are orthogonal to the adsorbate and tip states. An
application of our model to Co adsorbed on Cu explains the difference in the
lineshapes observed between Cu(100) and Cu(111) surfaces.Comment: 11 pages, 8 eps figure
Extrasolar Planet Transits Observed at Kitt Peak National Observatory
We obtained J-, H- and JH-band photometry of known extrasolar planet
transiting systems at the 2.1-m Kitt Peak National Observatory Telescope using
the FLAMINGOS infrared camera between October 2008 and October 2011. From the
derived lightcurves we have extracted the mid-transit times, transit depths and
transit durations for these events. The precise mid-transit times obtained help
improve the orbital periods and also constrain transit-time variations of the
systems. For most cases the published system parameters successfully accounted
for our observed lightcurves, but in some instances we derive improved
planetary radii and orbital periods. We complemented our 2.1-m infrared
observations using CCD z'-band and B-band photometry (plus two Hydrogen Alpha
filter observations) obtained with the Kitt Peak Visitor's Center telescope,
and with four H-band transits observed in October 2007 with the NSO's 1.6-m
McMath-Pierce Solar Telescope. The principal highlights of our results are: 1)
our ensemble of J-band planetary radii agree with optical radii, with the
best-fit relation being: (Rp/R*)J = 0.0017 + 0.979 (Rp/R*)optical, 2) We
observe star spot crossings during the transit of WASP-11/HAT-P-10, 3) we
detect star spot crossings by HAT-P-11b (Kepler-3b), thus confirming that the
magnetic evolution of the stellar active regions can be monitored even after
the Kepler mission has ended, and 4) we confirm a grazing transit for
HAT-P-27/WASP-40. In total we present 57 individual transits of 32 known
exoplanet systems.Comment: 33 pages, 6 figures, accepted in Publications of the Astronomical
Society of the Pacifi
Delivering services by building and running virtual organisations
Non peer reviewedPostprin
Chiral Transparency
Color transparency is the vanishing of initial and final state interactions,
predicted by QCD to occur in high momentum transfer quasielastic nuclear
reactions. For specific reactions involving nucleons, the initial and final
state interactions are expected to be dominated by exchanges of pions. We argue
that these interactions are also suppressed in high momentum transfer nuclear
quasielastic reactions; this is ``chiral transparency". We show that studies of
the reaction could reveal the influence of chiral
transparency.Comment: 20 pages, three figures available by fax from
[email protected]; submitted to Phys. Rev.
Symmetry Decomposition of Potentials with Channels
We discuss the symmetry decomposition of the average density of states for
the two dimensional potential and its three dimensional
generalisation . In both problems, the energetically
accessible phase space is non-compact due to the existence of infinite channels
along the axes. It is known that in two dimensions the phase space volume is
infinite in these channels thus yielding non-standard forms for the average
density of states. Here we show that the channels also result in the symmetry
decomposition having a much stronger effect than in potentials without
channels, leading to terms which are essentially leading order. We verify these
results numerically and also observe a peculiar numerical effect which we
associate with the channels. In three dimensions, the volume of phase space is
finite and the symmetry decomposition follows more closely that for generic
potentials --- however there are still non-generic effects related to some of
the group elements
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