30,636 research outputs found
Coauthorship and Thematic Networks in AAEP Annual Meetings
We analyze the coauthorship production of the AAEP Annual Meeting since 1964.
We use social network analysis for creating coauthorship networks and given
that any paper must be tagged with two JEL codes, we use this information for
also structuring a thematic network. Then we calculate network metrics and find
main actors and clusters for coauthors and topics. We distinguish a gender gap
in the sample. Thematic networks show a cluster of codes and the analysis of
the cluster shows the preeminence of the tags related to trade, econometric,
distribution/poverty and health and education topics.Comment: 30 pages, 12 Figures, 16 Table
Using Column Generation to Solve Extensions to the Markowitz Model
We introduce a solution scheme for portfolio optimization problems with
cardinality constraints. Typical portfolio optimization problems are extensions
of the classical Markowitz mean-variance portfolio optimization model. We solve
such type of problems using a method similar to column generation. In this
scheme, the original problem is restricted to a subset of the assets resulting
in a master convex quadratic problem. Then the dual information of the master
problem is used in a sub-problem to propose more assets to consider. We also
consider other extensions to the Markowitz model to diversify the portfolio
selection within the given intervals for active weights.Comment: 16 pages, 3 figures, 2 tables, 1 pseudocod
A free boundary model for oxygen diffusion in a spherical medium
The goal of this article is to find a correct approximated solution using a
polynomial of sixth degree for the free boundary problem corresponding to the
diffusion of oxygen in a spherical medium with simultaneous absorption at a
constant rate, and to show some mistakes in previously published solutions.Comment: 10 pages, 6 figures and 2 tables. Paper accepted, in press in Journal
of Biological Systems (2015
Reaction Dynamics for the Systems 7Be,8B + 208Pb at Coulomb Barrier Energies
In this contribution we describe the first results obtained for the investigation of
the elastic scattering process in the reactions induced by the Radioactive Ion Beams 7Be and
8B on a 208Pb target at Coulomb barrier energies. The experimental data were analyzed within
the framework of the optical model in order to extract the total reaction cross section. The
comparison with data available in literature for reactions induced on 208Pb by light ions in the
mass range A = 6-8 shows that the loosely-bound 8B has the largest reactivity
Effects of ion magnetization on the Farley-Buneman instability in the solar chromosphere
Intense heating in the quiet-Sun chromosphere raises the temperature from 4000 to 6500 K but, despite decades of study, the underlying mechanism remains a mystery. This study continues to explore the possibility that the Farley–Buneman instability contributes to chromospheric heating. This instability occurs in weakly ionized collisional plasmas in which electrons are magnetized, but ions are not. A mixture of metal ions generate the plasma density in the coolest parts of the chromosphere; while some ions are weakly magnetized, others are demagnetized by neutral collisions. This paper incorporates the effects of multiple, arbitrarily magnetized species of ions to the theory of the Farley–Buneman instability and examines the ramifications on instability in the chromosphere. The inclusion of magnetized ions introduces new restrictions on the regions in which the instability can occur in the chromosphere—in fact, it confines the instability to the regions in which heating is observed. For a magnetic field of 30 G, the minimum ambient electric field capable of driving the instability is 13.5 V/m at the temperature minimum.This work was supported by NSF-AGS Postdoctoral Research Fellowship Award No. 1433536 and NSF/DOE grant No. PHY-1500439. The authors also acknowledge a recent contribution from William Longley. (1433536 - NSF-AGS Postdoctoral Research Fellowship Award; PHY-1500439 - NSF/DOE grant)First author draftPublished versio
Dual composition of odd-dimensional models
A general way of interpreting odd dimensional models as a doublet of chiral
models is discussed. Based on the equations of motion this dual composition is
illustrated. Examples from quantum mechanics, field theory and gravity are
considered. Specially the recently advocated topologically massive gravity is
analysed in some details.Comment: minor modification
Mass Exchange Dynamics of Surface and Subsurface Oil in Shallow-Water Transport
We formulate a model for the mass exchange between oil at and below the sea
surface. This is a particularly important aspect of modeling oil spills.
Surface and subsurface oil have different chemical and transport
characteristics and lumping them together would compromise the accuracy of the
resulting model. Without observational or computational constraints, it is thus
not possible to quantitatively predict oil spills based upon partial field
observations of surface and/or sub-surface oil. The primary challenge in
capturing the mass exchange is that the principal mechanisms are on the
microscale. This is a serious barrier to developing practical models for oil
spills that are capable of addressing questions regarding the fate of oil at
the large spatio-temporal scales, as demanded by environmental questions. We
use upscaling to propose an environmental-scale model which incorporates the
mass exchange between surface and subsurface oil due to oil droplet dynamics,
buoyancy effects, and sea surface and subsurface mechanics. While the mass
exchange mechanism detailed here is generally applicable to oil transport
models, it addresses the modeling needs of a particular to an oil spill model
[1]. This transport model is designed to capture oil spills at very large
spatio-temporal scales. It accomplishes this goal by specializing to
shallow-water environments, in which depth averaging is a perfectly good
approximation for the flow, while at the same time retaining mass conservation
of oil over the whole oceanic domain.Comment: 18 pages, 6 figure
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