6,104 research outputs found
Twisting commutative algebraic groups
If is a commutative algebraic group over a field , is a
commutative ring that acts on , and is a finitely generated free
-module with a right action of the absolute Galois group of , then there
is a commutative algebraic group over , which is a twist of
a power of . These group varieties have applications to cryptography (in the
cases of abelian varieties and algebraic tori over finite fields) and to the
arithmetic of abelian varieties over number fields. For purposes of such
applications we devote this article to making explicit this tensor product
construction and its basic properties.Comment: To appear in Journal of Algebra. Minor changes from original versio
Numerical Studies of Weakly Stochastic Magnetic Reconnection
We study the effects of turbulence on magnetic reconnection using
three-dimensional numerical simulations. This is the first attempt to test a
model of fast magnetic reconnection proposed by Lazarian & Vishniac (1999),
which assumes the presence of weak, small-scale magnetic field structure near
the current sheet. This affects the rate of reconnection by reducing the
transverse scale for reconnection flows and by allowing many independent flux
reconnection events to occur simultaneously. We performed a number of
simulations to test the dependencies of the reconnection speed, defined as the
ratio of the inflow velocity to the Alfven speed, on the turbulence power, the
injection scale and resistivity. Our results show that turbulence significantly
affects the topology of magnetic field near the diffusion region and increases
the thickness of the outflow region. We confirm the predictions of the Lazarian
& Vishniac model. In particular, we report the growth of the reconnection speed
proportional to ~ V^2, where V is the amplitude of velocity at the injection
scale. It depends on the injection scale l as ~ (l/L)^(2/3), where L is the
size of the system, which is somewhat faster but still roughly consistent with
the theoretical expectations. We also show that for 3D reconnection the Ohmic
resistivity is important in the local reconnection events only, and the global
reconnection rate in the presence of turbulence does not depend on it.Comment: 8 pages, 8 figure
The gravitational path integral and trace of the diffeomorphisms
I give a resolution of the conformal mode divergence in the Euclidean
gravitational path-integral by isolating the trace of the diffeomorphisms and
its contribution to the Faddeev-Popov measure.Comment: 20 pgs
Large-scale radio continuum properties of 19 Virgo cluster galaxies The influence of tidal interactions, ram pressure stripping, and accreting gas envelopes
Deep scaled array VLA 20 and 6cm observations including polarization of 19
Virgo spirals are presented. This sample contains 6 galaxies with a global
minimum of 20cm polarized emission at the receding side of the galactic disk
and quadrupolar type large-scale magnetic fields. In the new sample no
additional case of a ram-pressure stripped spiral galaxy with an asymmetric
ridge of polarized radio continuum emission was found. In the absence of a
close companion, a truncated HI disk, together with a ridge of polarized radio
continuum emission at the outer edge of the HI disk, is a signpost of ram
pressure stripping. 6 out of the 19 observed galaxies display asymmetric 6cm
polarized emission distributions. Three galaxies belong to tidally interacting
pairs, two galaxies host huge accreting HI envelopes, and one galaxy had a
recent minor merger. Tidal interactions and accreting gas envelopes can lead to
compression and shear motions which enhance the polarized radio continuum
emission. In addition, galaxies with low average star formation rate per unit
area have a low average degree of polarization. Shear or compression motions
can enhance the degree of polarization. The average degree of polarization of
tidally interacting galaxies is generally lower than expected for a given
rotation velocity and star formation activity. This low average degree of
polarization is at least partly due to the absence of polarized emission from
the thin disk. Ram pressure stripping can decrease whereas tidal interactions
most frequently decreases the average degree of polarization of Virgo spiral
galaxies. We found that moderate active ram pressure stripping has no influence
on the spectral index, but enhances the global radio continuum emission with
respect to the FIR emission, while an accreting gas envelope can but not
necessarily enhances the radio continuum emission with respect to the FIR
emission.Comment: 37 pages, 26 figures, accepted for publication in A&
Using a well-being approach to develop a framework for an integrated socio-economic evaluation of professional fishing
© 2017 John Wiley & Sons Ltd The principles of Ecologically Sustainable Development and Ecosystem Based Fisheries Management require that fisheries be managed for social as well as environmental and economic objectives. Comprehensive assessments of the success of fisheries in achieving all three objectives are, however, rare. There are three main barriers to achieving integrated assessments of fisheries. Firstly, disciplinary divides can be considered “too hard” to bridge with inherent conflicts between the predominately empirical and deductive traditions of economics and biophysical sciences and the inductive and interpretative approach of much of the social sciences. Secondly, understanding of the social pillar of sustainability is less well developed. And finally, in-depth analysis of the social aspects of sustainability often involves qualitative analysis and there are practical difficulties in integrating this with largely quantitative economic and ecological assessments. This article explores the social well-being approach as a framework for an integrated evaluation of the social and economic benefits that communities in New South Wales, Australia, receive from professional fish harvesting. Using a review of existing literature and qualitative interviews with more than 160 people associated with the fishing industry the project was able to identify seven key domains of community well-being to which the industry contributes. Identification of these domains provided a framework through which industry contributions could be further explored, through quantitative surveys and economic analysis. This framework enabled successful integration of social and economic, and both qualitative and quantitative information in a manner that enabled a comprehensive assessment of the value of the fishery
Characteristic Energy of the Coulomb Interactions and the Pileup of States
Tunneling data on crystals confirm
Coulomb interaction effects through the dependence of the
density of states. Importantly, the data and analysis at high energy, E, show a
pileup of states: most of the states removed from near the Fermi level are
found between ~40 and 130 meV, from which we infer the possibility of universal
behavior. The agreement of our tunneling data with recent photoemission results
further confirms our analysis.Comment: 4 pages, 4 figures, submitted to PR
Quantum Diffeomorphisms and Conformal Symmetry
We analyze the constraints of general coordinate invariance for quantum
theories possessing conformal symmetry in four dimensions. The character of
these constraints simplifies enormously on the Einstein universe . The global conformal symmetry algebra of this space determines
uniquely a finite shift in the Hamiltonian constraint from its classical value.
In other words, the global Wheeler-De Witt equation is {\it modified} at the
quantum level in a well-defined way in this case. We argue that the higher
moments of should not be imposed on the physical states {\it a priori}
either, but only the weaker condition . We
present an explicit example of the quantization and diffeomorphism constraints
on for a free conformal scalar field.Comment: PlainTeX File, 37 page
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