2,638 research outputs found
The Collapse of the Soviet Union and the Productivity of American Mathematicians
It has been difficult to open up the black box of knowledge production. We use unique international data on the publications, citations, and affiliations of mathematicians to examine the impact of a large post-1992 influx of Soviet mathematicians on the productivity of their American counterparts. We find a negative productivity effect on those mathematicians whose research overlapped with that of the Soviets. We also document an increased mobility rate (to lower-quality institutions and out of active publishing) and a reduced likelihood of producing “home run” papers. Although the total product of the pre-existing American mathematicians shrank, the Soviet contribution to American mathematics filled in the gap. However, there is no evidence that the Soviets greatly increased the size of the “mathematics pie.” Finally, we find that there are significant international differences in the productivity effects of the collapse of the Soviet Union, and that these international differences can be explained by both differences in the size of the émigré flow into the various countries and in how connected each country is to the global market for mathematical publications.
Traction drive system design considerations for a lunar roving vehicle
Optimum design considerations of traction drive for lunar roving vehicl
US Metropolitan Area Resilience: Insights from dynamic spatial panel estimation
In this paper, we show that the economic crisis commencing in 2007 had different impacts across US Metropolitan Statistical Areas, and seek to understand why differences occurred. The hypothesis of interest is that differences in industrial structure are a cause of variations in response to the crisis. Our approach uses a state-of-the art dynamic spatial panel model to obtain counterfactual predictions of Metropolitan Statistical Area employment levels from 2008 to 2014. The counterfactual employment series are compared with actual employment paths in order to obtain Metropolitan Statistical Area-specific measures of crisis impact, which then are analysed with a view to testing the hypothesis that resilience to the crisis was dependent on Metropolitan Statistical Area industrial structure. </jats:p
New Techniques for Analysing Axisymmetric Gravitational Systems. 1. Vacuum Fields
A new framework for analysing the gravitational fields in a stationary,
axisymmetric configuration is introduced. The method is used to construct a
complete set of field equations for the vacuum region outside a rotating
source. These equations are under-determined. Restricting the Weyl tensor to
type D produces a set of equations which can be solved, and a range of new
techniques are introduced to simplify the problem. Imposing the further
condition that the solution is asymptotically flat yields the Kerr solution
uniquely. The implications of this result for the no-hair theorem are
discussed. The techniques developed here have many other applications, which
are described in the conclusions.Comment: 30 pages, no figure
Early Dark Energy Cosmologies
We propose a novel parameterization of the dark energy density. It is
particularly well suited to describe a non-negligible contribution of dark
energy at early times and contains only three parameters, which are all
physically meaningful: the fractional dark energy density today, the equation
of state today and the fractional dark energy density at early times. As we
parameterize Omega_d(a) directly instead of the equation of state, we can give
analytic expressions for the Hubble parameter, the conformal horizon today and
at last scattering, the sound horizon at last scattering, the acoustic scale as
well as the luminosity distance. For an equation of state today w_0 < -1, our
model crosses the cosmological constant boundary. We perform numerical studies
to constrain the parameters of our model by using Cosmic Microwave Background,
Large Scale Structure and Supernovae Ia data. At 95% confidence, we find that
the fractional dark energy density at early times Omega_early < 0.06. This
bound tightens considerably to Omega_early < 0.04 when the latest Boomerang
data is included. We find that both the gold sample of Riess et. al. and the
SNLS data by Astier et. al. when combined with CMB and LSS data mildly prefer
w_0 < -1, but are well compatible with a cosmological constant.Comment: 6 pages, 3 figures; references added, matches published versio
Gaming machine accessibility and use in suburban Canberra: a detailed analysis of the Tuggeranong Valley
This report outlines research which focuses on club use and gambling activity in a specific region of suburban Canberra, namely the Tuggeranong Valley. The study builds on the 2001 ACT gambling survey by focussing in detail on the local level patterns of club use and gambling activity
Painleve-Gullstrand Coordinates for the Kerr Solution
We construct a coordinate system for the Kerr solution, based on the zero
angular momentum observers dropped from infinity, which generalizes the
Painleve-Gullstrand coordinate system for the Schwarzschild solution. The Kerr
metric can then be interpreted as describing space flowing on a (curved)
Riemannian 3-manifold. The stationary limit arises as the set of points on this
manifold where the speed of the flow equals the speed of light, and the
horizons as the set of points where the radial speed equals the speed of light.
A deeper analysis of what is meant by the flow of space reveals that the
acceleration of free-falling objects is generally not in the direction of this
flow. Finally, we compare the new coordinate system with the closely related
Doran coordinate system.Comment: 6 pages; v2: new section, matches final published version; v3: sign
error in the expression of the function delta correcte
On the Construction and the Structure of Off-Shell Supermultiplet Quotients
Recent efforts to classify representations of supersymmetry with no central
charge have focused on supermultiplets that are aptly depicted by Adinkras,
wherein every supersymmetry generator transforms each component field into
precisely one other component field or its derivative. Herein, we study
gauge-quotients of direct sums of Adinkras by a supersymmetric image of another
Adinkra and thus solve a puzzle from Ref.[2]: The so-defined supermultiplets do
not produce Adinkras but more general types of supermultiplets, each depicted
as a connected network of Adinkras. Iterating this gauge-quotient construction
then yields an indefinite sequence of ever larger supermultiplets, reminiscent
of Weyl's construction that is known to produce all finite-dimensional unitary
representations in Lie algebras.Comment: 20 pages, revised to clarify the problem addressed and solve
Effective Symmetries of the Minimal Supermultiplet of N = 8 Extended Worldline Supersymmetry
A minimal representation of the N = 8 extended worldline supersymmetry, known
as the `ultra-multiplet', is closely related to a family of supermultiplets
with the same, E(8) chromotopology. We catalogue their effective symmetries and
find a Spin(4) x Z(2) subgroup common to them all, which explains the
particular basis used in the original construction. We specify a constrained
superfield representation of the supermultiplets in the ultra-multiplet family,
and show that such a superfield representation in fact exists for all adinkraic
supermultiplets. We also exhibit the correspondences between these
supermultiplets, their Adinkras and the E(8) root lattice bases. Finally, we
construct quadratic Lagrangians that provide the standard kinetic terms and
afford a mixing of an even number of such supermultiplets controlled by a
coupling to an external 2-form of fluxes.Comment: 13 Figure
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