40,218 research outputs found
Continuum Theory for Piezoelectricity in Nanotubes and Nanowires
We develop and solve a continuum theory for the piezoelectric response of one
dimensional nanotubes and nanowires, and apply the theory to study
electromechanical effects in BN nanotubes. We find that the polarization of a
nanotube depends on its aspect ratio, and a dimensionless constant specifying
the ratio of the strengths of the elastic and electrostatic interactions. The
solutions of the model as these two parameters are varied are discussed. The
theory is applied to estimate the electric potential induced along the length
of a BN nanotube in response to a uniaxial stress.Comment: 4 pages in RevTex4, 2 epsf figure
Option Pricing on Renewable Commodity Markets
Options markets on agricultural commodities with maturities that exceed 13 months seldom trade. Our hypothesis is that this market failure is due to the absence of an accurate option pricing model for commodities where mean reversion can be expected. Standard option pricing models assume proportionality between price variance and time to maturity. This proportionality is not a valid assumption for commodities where supply response works to bring prices back to production costs. The model suggests that traditional option pricing models will overprice long-term options on these markets.commodity futures and option, price mean reverting, seasonality, Agricultural Finance, Financial Economics,
Update: Precision D_s decay constant from full lattice QCD using very fine lattices
We update our previous determination of both the decay constant and the mass
of the meson using the Highly Improved Staggered Quark formalism. We
include additional results at two finer values of the lattice spacing along
with improved determinations of the lattice spacing and improved tuning of the
charm and strange quark masses. We obtain = 1.9691(32) GeV, in good
agreement with experiment, and = 0.2480(25) GeV. Our result for
is 1.6 lower than the most recent experimental average
determined from the leptonic decay rate and using from CKM
unitarity. Combining our with the experimental rate we obtain a
direct determination of , or alternatively using a probability distribution for statistical errors for this
quantity which vanishes above 1. We also include an accurate prediction of the
decay constant of the , = 0.3947(24) GeV, as a calibration
point for other lattice calculations.Comment: 24 pages, 20 figures. Updated to include new experimental results
from BaBar, new experimental averages from HFAG and consequent discussion of
theory/experiment comparison. Other minor typographical changes. Version
accepted by Phys. Rev.
A Prediction of the B*_c mass in full lattice QCD
By using the Highly Improved Staggered Quark formalism to handle charm,
strange and light valence quarks in full lattice QCD, and NRQCD to handle
bottom valence quarks we are able to determine accurately ratios of the B meson
vector-pseudoscalar mass splittings, in particular,
(m(B*_c)-m(B_c))/(m(B*_s)-m(B_s)). We find this ratio to be 1.15(15), showing
the `light' quark mass dependence of this splitting to be very small. Hence we
predict m(B_c*) = 6.330(7)(2)(6) GeV where the first two errors are from the
lattice calculation and the third from existing experiment. This is the most
accurate prediction of a gold-plated hadron mass from lattice QCD to date.Comment: 4 pages, 2 figure
Operations on integral lifts of K(n)
This very rough sketch is a sequel to arXiv:1808.08587; it presents evidence
that operations on lifts of the functors K(n) to cohomology theories with
values in modules over valuation rings of local number fields, indexed by
Lubin-Tate groups of such fields, are extensions of the groups of automorphisms
of the indexing group laws, by the exterior algebras on the normal bundle to
the orbits of the group laws in the space of lifts.Comment: \S 2.0 hopefully less cryptic. To appear in the proceedings of the
2015 Nagoya conference honoring T Ohkawa. Comments very welcome
Prelude to the Anthropocene: Two new North American Land Mammal Ages (NALMAs)
Human impacts have left and are leaving distinctive imprints in the geological record. Here we show that in North America, the human-caused changes evident in the mammalian fossil record since c. 14,000 years ago are as pronounced as earlier faunal changes that subdivide Cenozoic epochs into the North American Land Mammal Ages (NALMAs). Accordingly, we define two new North American Land Mammal Ages, the Santarosean and the Saintagustinean, which subdivide Holocene time and complete a biochronologic system that has proven extremely useful in dating terrestrial deposits and in revealing major features of faunal change through the past 66 million years. The new NALMAs highlight human-induced changes to the Earth system, and inform the debate on whether or not defining an Anthropocene epoch is justified, and if so, when it began
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