2,796 research outputs found
Open Gromov-Witten Invariants of Toric Calabi-Yau 3-Folds
We present a proof of the mirror conjecture of Aganagic-Vafa
[arXiv:hep-th/0012041] and Aganagic-Klemm-Vafa [arXiv:hep-th/0105045] on disk
enumeration in toric Calabi-Yau 3-folds for all smooth semi-projective toric
Calabi-Yau 3-folds. We consider both inner and outer branes, at arbitrary
framing. In particular, we recover previous results on the conjecture for (i)
an inner brane at zero framing in the total space of the canonical line bundle
of the projective plane (Graber-Zaslow [arXiv:hep-th/0109075]), (ii) an outer
brane at arbitrary framing in the resolved conifold (Zhou [arXiv:1001.0447]),
and (iii) an outer brane at zero framing in the total space of the canonical
line bundle of the projective plane (Brini [arXiv:1102.0281, Section 5.3]).Comment: 39 pages, 11 figure
Plant community structure mediates potential methane production and potential iron reduction in wetland mesocosms.
Abstract
Wetlands are the largest natural source of methane to the atmosphere, but factors controlling methane emissions from wetlands are a major source of uncertainty in greenhouse gas budgets and projections of future climate change. We conducted a controlled outdoor mesocosm experiment to assess the effects of plant community structure (functional group richness and composition) on potential methane production and potential iron reduction in freshwater emergent marshes. Four plant functional groups (facultative annuals, obligate annuals, reeds, and tussocks) were arranged in a full-factorial design and additional mesocosms were assigned as no-plant controls. Soil samples from the top 10 cm were collected three times during the growing season to determine potential methane production and potential iron reduction (in unamended soils and in soils amended with 200 mM formate). These data were compared to soil organic matter, soil pH, and previously published data on above and belowground plant biomass. We found that functional group richness was less important than the presence of specific functional groups (reeds or tussocks) in mediating potential iron reduction. In our mesocosms, where oxidized iron was abundant and electron donors were limiting, iron reducing bacteria outcompeted methanogens, keeping methane production barely detectable in unamended lab incubations. When the possibility of re-oxidizing iron was eliminated via anaerobic incubations and the electron donor limitation was removed by adding formate, potential methane production increased and followed the same patterns as potential iron reduction. Our findings suggest that in the absence of abundant oxidized iron and/or the presence of abundant electron donors, wetlands dominated by either reeds or tussocks may have increased methane production compared to wetlands dominated by annuals. Depending on functional traits such as plant transport and rhizospheric oxygenation capacities, this could potentially lead to increased methane emissions in some wetlands. Additional research examining the role these plant functional groups play in other aspects of methane dynamics will be useful given the importance of methane as a greenhouse gas
Temperature dependence of the nitrogen-vacancy magnetic resonance in diamond
The temperature dependence of the magnetic resonance spectra of
nitrogen-vacancy (NV-) ensembles in the range of 280-330 K was studied. Four
samples prepared under different conditions were studied with NV-
concentrations ranging from 10 ppb to 15 ppm. For all of these samples, the
axial zero-field splitting (ZFS) parameter, D, was found to vary significantly
with temperature, T, as dD/dT = -74.2(7) kHz/K. The transverse ZFS parameter,
E, was non-zero (between 4 and 11 MHz) in all samples, and exhibited a
temperature dependence of dE/(EdT) = -1.4(3) x 10^(-4) K^(-1). The results
might be accounted for by considering local thermal expansion. The observation
of the temperature dependence of the ZFS parameters presents a significant
challenge for room-temperature diamond magnetometers and may ultimately limit
their bandwidth and sensitivity.Comment: 5 pages, 2 figures, 1 tabl
Bidding process in online auctions and winning strategy:rate equation approach
Online auctions have expanded rapidly over the last decade and have become a
fascinating new type of business or commercial transaction in this digital era.
Here we introduce a master equation for the bidding process that takes place in
online auctions. We find that the number of distinct bidders who bid times,
called the -frequent bidder, up to the -th bidding progresses as
. The successfully transmitted bidding rate by the
-frequent bidder is obtained as , independent of
for large . This theoretical prediction is in agreement with empirical data.
These results imply that bidding at the last moment is a rational and effective
strategy to win in an eBay auction.Comment: 4 pages, 6 figure
Universality of Cluster Dynamics
We have studied the kinetics of cluster formation for dynamical systems of
dimensions up to interacting through elastic collisions or coalescence.
These systems could serve as possible models for gas kinetics, polymerization
and self-assembly. In the case of elastic collisions, we found that the cluster
size probability distribution undergoes a phase transition at a critical time
which can be predicted from the average time between collisions. This enables
forecasting of rare events based on limited statistical sampling of the
collision dynamics over short time windows. The analysis was extended to
L-normed spaces () to allow for some amount of
interpenetration or volume exclusion. The results for the elastic collisions
are consistent with previously published low-dimensional results in that a
power law is observed for the empirical cluster size distribution at the
critical time. We found that the same power law also exists for all dimensions
, 2D L norms, and even for coalescing collisions in 2D. This
broad universality in behavior may be indicative of a more fundamental process
governing the growth of clusters
Unusual statistics of interference effects in neutron scattering from compound nuclei
We consider interference effects between p-wave resonance scattering
amplitude and background s-wave amplitude in low-energy neutron scattering from
a heavy nucleus which goes through the compound nucleus stage. The first effect
is in the difference between the forward and backward scattering cross
sections. Because of the chaotic nature of the compound states, this effect is
a random variable with zero mean. However, a statistical consideration shows
that the probability distribution of this effect does not obey the standard
central limit theorem. That is, the probability density for the effect averaged
over n resonances does not become a Gaussian distribution with the variance
decreasing as 1/sqrt(n) (``violation'' of the theorem!). We derive the
probability distribution of the effect and the limit distribution of the
average. It is found that the width of this distribution does not decrease with
the increase of n, i.e., fluctuations are not suppressed by averaging.
Furthermore, we consider the correlation between the neutron spin and the
scattering plane and find that this effect, although much smaller, shows
fluctuations which actually increase upon averaging over many measurements.
Limits of the effects due to finite resonance widths are also considered. In
the appendix we present a simple derivation of the limit theorem for the
average of random variables with infinite variances.Comment: 15 pages, RevTeX, submitted to Phys. Rev.
Open orbifold Gromov-Witten invariants of [C^3/Z_n]: localization and mirror symmetry
We develop a mathematical framework for the computation of open orbifold
Gromov-Witten invariants of [C^3/Z_n], and provide extensive checks with
predictions from open string mirror symmetry. To this aim we set up a
computation of open string invariants in the spirit of Katz-Liu, defining them
by localization. The orbifold is viewed as an open chart of a global quotient
of the resolved conifold, and the Lagrangian as the fixed locus of an
appropriate anti-holomorphic involution. We consider two main applications of
the formalism. After warming up with the simpler example of [C^3/Z_3], where we
verify physical predictions of Bouchard, Klemm, Marino and Pasquetti, the main
object of our study is the richer case of [C^3/Z_4], where two different
choices are allowed for the Lagrangian. For one choice, we make numerical
checks to confirm the B-model predictions; for the other, we prove a mirror
theorem for orbifold disc invariants, match a large number of annulus
invariants, and give mirror symmetry predictions for open string invariants of
genus \leq 2.Comment: 44 pages + appendices; v2: exposition improved, misprints corrected,
version to appear on Selecta Mathematica; v3: last minute mistake found and
fixed for the symmetric brane setup of [C^3/Z_4]; in pres
Swing Options Valuation: a BSDE with Constrained Jumps Approach
We introduce a new probabilistic method for solving a class of impulse
control problems based on their representations as Backward Stochastic
Differential Equations (BSDEs for short) with constrained jumps. As an example,
our method is used for pricing Swing options. We deal with the jump constraint
by a penalization procedure and apply a discrete-time backward scheme to the
resulting penalized BSDE with jumps. We study the convergence of this numerical
method, with respect to the main approximation parameters: the jump intensity
, the penalization parameter and the time step. In particular,
we obtain a convergence rate of the error due to penalization of order
. Combining this approach with Monte Carlo techniques, we
then work out the valuation problem of (normalized) Swing options in the Black
and Scholes framework. We present numerical tests and compare our results with
a classical iteration method.Comment: 6 figure
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