1,546 research outputs found
Geometric and homological finiteness in free abelian covers
We describe some of the connections between the Bieri-Neumann-Strebel-Renz
invariants, the Dwyer-Fried invariants, and the cohomology support loci of a
space X. Under suitable hypotheses, the geometric and homological finiteness
properties of regular, free abelian covers of X can be expressed in terms of
the resonance varieties, extracted from the cohomology ring of X. In general,
though, translated components in the characteristic varieties affect the
answer. We illustrate this theory in the setting of toric complexes, as well as
smooth, complex projective and quasi-projective varieties, with special
emphasis on configuration spaces of Riemann surfaces and complements of
hyperplane arrangements.Comment: 30 pages; to appear in Configuration Spaces: Geometry, Combinatorics
and Topology (Centro De Giorgi, 2010), Edizioni della Normale, Pisa, 201
Riding the Yield Curve: Diversification of Strategies
Riding the yield curve, the fixed-income strategy of purchasing a longer-dated security and selling before maturity, has long been a popular means to achieve excess returns compared to buying-and-holding, despite its implicit violations of market efficiency and the pure expectations hypothesis of the term structure. This paper looks at the historic excess returns of different strategies across three countries and proposes several statistical and macro-based trading rules which seem to enhance returns even more. While riding based on the Taylor Rule works well even for longer investment horizons, our empirical results indicate that, using expectations implied by Fed funds futures, excess returns can only be increased over short horizons. Furthermore, we demonstrate that duration-neutral strategies are superior to standard riding on a risk- adjusted basis. Overall, our evidence stands in contrast to the pure expectations hypothesis and points to the existence of risk premia which may be exploited consistently.Term Structure, Interest Rates, Market Efficiency, Taylor Rule
AGN Feedback Compared: Jets versus Radiation
Feedback by Active Galactic Nuclei is often divided into quasar and radio
mode, powered by radiation or radio jets, respectively. Both are fundamental in
galaxy evolution, especially in late-type galaxies, as shown by cosmological
simulations and observations of jet-ISM interactions in these systems. We
compare AGN feedback by radiation and by collimated jets through a suite of
simulations, in which a central AGN interacts with a clumpy, fractal galactic
disc. We test AGN of and erg/s, considering jets
perpendicular or parallel to the disc. Mechanical jets drive the more powerful
outflows, exhibiting stronger mass and momentum coupling with the dense gas,
while radiation heats and rarifies the gas more. Radiation and perpendicular
jets evolve to be quite similar in outflow properties and effect on the cold
ISM, while inclined jets interact more efficiently with all the disc gas,
removing the densest in Myr, and thereby reducing the amount of
cold gas available for star formation. All simulations show small-scale inflows
of M/yr, which can easily reach down to the Bondi radius of
the central supermassive black hole (especially for radiation and perpendicular
jets), implying that AGN modulate their own duty cycle in a feedback/feeding
cycle.Comment: 21 pages, 15 figures, 2 table
The Basel Process and Financial Stability
The Basel Process is a key element of the global financial system and as such plays an important role in co-ordinating the multilateral efforts of various committees, uniquely geared towards fostering and maintaining financial stability.Basel Process, Monetary Stability, Financial Stability
Haydeeite: a spin-1/2 kagome ferromagnet
The mineral haydeeite, alpha-MgCu3(OD)6Cl2, is a S=1/2 kagome ferromagnet
that displays long-range magnetic order below TC=4.2 K with a strongly reduced
moment. Our inelastic neutron scattering data show clear spin-wave excitations
that are well described by a Heisenberg Hamiltonian with ferromagnetic
nearest-neighbor exchange J1=-38 K and antiferromagnetic exchange Jd=+11 K
across the hexagons of the kagome lattice. These values place haydeeite very
close to the quantum phase transition between ferromagnetic order and
non-coplanar twelve-sublattice cuboc2 antiferromagnetic order. Diffuse dynamic
short-range ferromagnetic correlations observed above TC persist well into the
ferromagnetically ordered phase with a behavior distinct from critical
scattering
On the Indeterministic Nature of Star Formation on the Cloud Scale
Molecular clouds are turbulent structures whose star formation efficiency
(SFE) is strongly affected by internal stellar feedback processes. In this
paper we determine how sensitive the SFE of molecular clouds is to randomised
inputs in the star formation feedback loop, and to what extent relationships
between emergent cloud properties and the SFE can be recovered. We introduce
the yule suite of 26 radiative magnetohydrodynamic (RMHD) simulations of a
10,000 solar mass cloud similar to those in the solar neighbourhood. We use the
same initial global properties in every simulation but vary the initial mass
function (IMF) sampling and initial cloud velocity structure. The final SFE
lies between 6 and 23 percent when either of these parameters are changed. We
use Bayesian mixed-effects models to uncover trends in the SFE. The number of
photons emitted early in the cluster's life and the length of the cloud provide
are the strongest predictors of the SFE. The HII regions evolve following an
analytic model of expansion into a roughly isothermal density field. The more
efficient feedback is at evaporating the cloud, the less the star cluster is
dispersed. We argue that this is because if the gas is evaporated slowly, the
stars are dragged outwards towards surviving gas clumps due to the
gravitational attraction between the stars and gas. While star formation and
feedback efficiencies are dependent on nonlinear processes, statistical models
describing cloud-scale processes can be constructed.Comment: 24 pages, 16 figures, 6 tables. Accepted to MNRAS, version updated
with published titl
Carotenoids and Antioxidant Nutrients following Burn Injury a
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/72213/1/j.1749-6632.1993.tb26193.x.pd
Positive Cross Correlations in a Normal-Conducting Fermionic Beam Splitter
We investigate a beam splitter experiment implemented in a normal conducting
fermionic electron gas in the quantum Hall regime. The cross-correlations
between the current fluctuations in the two exit leads of the three terminal
device are found to be negative, zero or even positive depending on the
scattering mechanism within the device. Reversal of the cross-correlations sign
occurs due to interaction between different edge-states and does not reflect
the statistics of the fermionic particles which `antibunch'.Comment: 4 pages, 4 figure
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