23,568 research outputs found
Transition from Icosahedral to Decahedral Structure in a Coexisting Solid-Liquid Nickel Cluster
We have used molecular dynamics simulations to construct a microcanonical
caloric curve for a 1415-atom Ni icosahedron. Prior to melting the Ni cluster
exhibits static solid-liquid phase coexistence. Initially a partial icosahedral
structure coexists with a non-wetting melt. However at energies very close to
the melting point the icosahedral structure is replaced by a truncated
decahedral structure which is almost fully wet by the melt. This structure
remains until the cluster fully melts. The transition appears to be driven by a
preference for the melt to wet the decahedral structure.Comment: 7 pages, 6 figure
Hadronic form factors and the secondary production cross section: an update
Improving previous calculations, we compute the cross section using the most complete effective lagrangians available. The
new crucial ingredients are the form factors on the charm meson vertices, which
are determined from QCD sum rules calculations. Some of them became available
only very recently and the last one, needed for our present purpose, is
calculated in this work.Comment: 12 pages, 9 eps figure
Does the production asymmetry decrease at large ?
We have applied the meson cloud model (MCM) to calculate the asymmetries in
and meson production in high energy -nucleus and
-nucleus collisions. We find a good agreement with recent data. Our
results suggest that the asymmetries may decrease at large .Comment: revised version with new figures and added references to appear in
Phys. Rev. Let
Option Pricing in Multivariate Stochastic Volatility Models of OU Type
We present a multivariate stochastic volatility model with leverage, which is
flexible enough to recapture the individual dynamics as well as the
interdependencies between several assets while still being highly analytically
tractable.
First we derive the characteristic function and give conditions that ensure
its analyticity and absolute integrability in some open complex strip around
zero. Therefore we can use Fourier methods to compute the prices of multi-asset
options efficiently. To show the applicability of our results, we propose a
concrete specification, the OU-Wishart model, where the dynamics of each
individual asset coincide with the popular Gamma-OU BNS model. This model can
be well calibrated to market prices, which we illustrate with an example using
options on the exchange rates of some major currencies. Finally, we show that
covariance swaps can also be priced in closed form.Comment: 28 pages, 5 figures, to appear in SIAM Journal on Financial
Mathematic
Cavity-mediated long-range interaction for fast multiqubit quantum logic operations
Interactions among qubits are essential for performing two-qubit quantum
logic operations. However, nature gives us only nearest neighbor interactions
in simple and controllable settings. Here we propose a strategy to induce
interactions among two atomic entities that are not necessarily neighbors of
each other through their common coupling with a cavity field. This facilitates
fast multiqubit quantum logic operations through a set of two-qubit operations.
The ideas presented here are applicable to various quantum computing proposals
for atom based qubits such as, trapped ions, atoms trapped in optical cavities
and optical lattices.Comment: 10 pages, 3 figure
Meson Cloud and SU(3) Symmetry Breaking in Parton Distributions
We apply the Meson Cloud Model to the calculation of nonsinglet parton
distributions in the nucleon sea, including the octet and the decuplet cloud
baryon contributions. We give special attention to the differences between
nonstrange and strange sea quarks, trying to identify possible sources of SU(3)
flavor breaking. A analysis in terms of the parameter is presented,
and we find that the existing SU(3) flavor asymmetry in the nucleon sea can be
quantitatively explained by the meson cloud. We also consider the
baryon, finding similar conclusions.Comment: 17 pages, LaTeX, 8 figures in .ps file
Application of asymptotic expansions of maximum likelihood estimators errors to gravitational waves from binary mergers: the single interferometer case
In this paper we describe a new methodology to calculate analytically the
error for a maximum likelihood estimate (MLE) for physical parameters from
Gravitational wave signals. All the existing litterature focuses on the usage
of the Cramer Rao Lower bounds (CRLB) as a mean to approximate the errors for
large signal to noise ratios. We show here how the variance and the bias of a
MLE estimate can be expressed instead in inverse powers of the signal to noise
ratios where the first order in the variance expansion is the CRLB. As an
application we compute the second order of the variance and bias for MLE of
physical parameters from the inspiral phase of binary mergers and for noises of
gravitational wave interferometers . We also compare the improved error
estimate with existing numerical estimates. The value of the second order of
the variance expansions allows to get error predictions closer to what is
observed in numerical simulations. It also predicts correctly the necessary SNR
to approximate the error with the CRLB and provides new insight on the
relationship between waveform properties SNR and estimation errors. For example
the timing match filtering becomes optimal only if the SNR is larger than the
kurtosis of the gravitational wave spectrum
Chromoelectric fields and quarkonium-hadron interactions at high energies
We develop a simple model to study the heavy quarkonium-hadron cross section
in the high energy limit. The hadron is represented by an external electric
color field (capacitor) and the heavy quarkonium is represented by a small
color dipole. Using high energy approximations we compute the relevant cross
sections, which are then compared with results obtained with other methods. Our
calculations are presented in a pedagogical way accessible to undergraduate
students.Comment: To appear in Physical Review C, 24 pages, 10 eps figure
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