1,759 research outputs found
Rare event sampling in applied stochastic dynamical systems
Predicting rare events is a challenging problem in many complex systems arising in physics, chemistry, biology, and materials science. Simulating rare events is often prohibitive in such systems due to their high dimensionality and the numerical cost of their simulation, yet analytical expressions for rare event probabilities are usually not available. This dissertation tackles the problem of approximation of the probability of rare catastrophic events in optical communication systems and spin-torque magnetic nanodevices. With the application of the geometric minimum action method, the probability of pulse position shifts or other parameter changes in a model of an actively mode-locked laser subject to noise from amplified spontaneous emission can be quantified. Similarly, by applying importance sampling with biasing functions motivated by optimal control, read and write soft error rates of macrospin and coupled-spin systems of spin-torque magnetic nanodevices can be efficiently estimated
Broadband Quantum Efficiency Enhancement in High Index Nanowires Resonators
Light trapping in sub-wavelength semiconductor nanowires (NWs) offers a
promising approach to simultaneously reducing material consumption and
enhancing photovoltaic performance. Nevertheless, the absorption efficiency of
a NW, defined by the ratio of optical absorption cross section to the NW
diameter, lingers around 1 in existing NW photonic devices, and the absorption
enhancement suffers from a narrow spectral width. Here, we show that the
absorption efficiency can be significantly improved in NWs with higher
refractive indices, by an experimental observation of up to 350% external
quantum efficiency (EQE) in lead sulfide (PbS) NW resonators, a 3-fold increase
compared to Si NWs. Furthermore, broadband absorption enhancement is achieved
in single tapered NWs, where light of various wavelengths is absorbed at
segments with different diameters analogous to a tandem solar cell. Overall,
the single NW Schottky junction solar cells benefit from optical resonance,
near bandgap open circuit voltage, and long minority carrier diffusion length,
demonstrating power conversion efficiency (PCE) comparable to single Si NW
coaxial p-n junction cells11, but with much simpler fabrication processes
Consumer Asset Pricing Model Based on Heterogeneous Consumers and the Mystery of Equity Premium
As one of the core models of finance, the consumer capital asset pricing model (CCAPM) has produced
the puzzle of equity premium. In order to explain this problem and get a more realistic pricing
formula, this paper uses constant absolute risk aversion coefficient (Cara) utility function and introduces
heterogeneous consumers to improve the original model, and finally gets a more effective form and there
is no original puzzle in this form. At the end of the article, the American data are used to verify the
results. The regression results support this model very well
OBMeshfree: An optimization-based meshfree solver for nonlocal diffusion and peridynamics models
We present OBMeshfree, an Optimization-Based Meshfree solver for compactly
supported nonlocal integro-differential equations (IDEs) that can describe
material heterogeneity and brittle fractures. OBMeshfree is developed based on
a quadrature rule calculated via an equality constrained least square problem
to reproduce exact integrals for polynomials. As such, a meshfree
discretization method is obtained, whose solution possesses the asymptotically
compatible convergence to the corresponding local solution. Moreover, when
fracture occurs, this meshfree formulation automatically provides a sharp
representation of the fracture surface by breaking bonds, avoiding the loss of
mass. As numerical examples, we consider the problem of modeling both
homogeneous and heterogeneous materials with nonlocal diffusion and
peridynamics models. Convergences to the analytical nonlocal solution and to
the local theory are demonstrated. Finally, we verify the applicability of the
approach to realistic problems by reproducing high-velocity impact results from
the Kalthoff-Winkler experiments. Discussions on possible immediate extensions
of the code to other nonlocal diffusion and peridynamics problems are provided.
OBMeshfree is freely available on GitHub.Comment: For associated code, see
https://github.com/youhq34/meshfree_quadrature_nonloca
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