319 research outputs found
Confidence Levels for CVaR Risk Measures and Minimax Limits*
Conditional value at risk (CVaR) has been widely used as a risk measure in finance. When the confidence level of CVaR is set close to 1, the CVaR risk measure approximates the extreme (worst scenario) risk measure. In this paper, we present a quantitative analysis of the relationship between the two risk measures and it’s impact on optimal decision making when we wish to minimize the respective risk measures. We also investigate the difference between the optimal solutions to the two optimization problems with identical objective function but under constraints on the two risk measures. We discuss the benefits of a sample average approximation scheme for the CVaR constraints and investigate the convergence of the optimal solution obtained from this scheme as the sample size increases. We use some portfolio optimization problems to investigate teh performance of the CVaR approximation approach. Our numerical results demonstrate how reducing the confidence level can lead to a better overall performance
Comprehensive Demonstration of Spin-Hall Hanle Effects in Epitaxial Pt Thin Films
We demonstrate a nonlinear Hall effect due to the boundary spin accumulation
in Pt films grown on Al2O3 substrates. This Hall effect and the previously
demonstrated Hanle magnetoresistance provide a complete picture of the
spin-precession control of the spin and charge transport at the boundary of a
spin-orbit coupled material, which we refer to as spin-Hall Hanle effects
(SHHE). We also show that the SHHE can be employed to measure the spin
diffusion length, the spin-Hall angle, and the spin relaxation time of heavy
metal without the need of magnetic interface or the input from other
measurements. The comprehensive demonstration of SHHE in such a simple system
suggests they may be ubiquitous and needs to be considered for unravelling the
spin and charge transport in more complex thin film structures of spin-orbit
coupled materials
Giant interfacial spin-Hall angle from Rashba-Edelstein effect revealed by the spin-Hall Hanle processes
The Rashba-Edelstein effect (REE), which generates interfacial spin
polarization and subsequent spin current, is a compelling spin-charge
conversion mechanism for spintronics applications, since it is not limited by
the elemental spin-orbit coupling. In this work, we demonstrate REE at
Pt/ferroelectric interfaces using the recently elucidated spin-Hall Hanle
effects (SHHE), in which a Larmor precession of spin polarization in a
diffusion process from the interface manifest as magnetoresistance and Hall
effect. We show that REE leads to a three-fold enhancement of the effective
spin Hall angle in ferroelectric interface Pt/h-LuFeO3 compared to that of Pt
/Al2O3, although the difference in the spin relaxation time is negligible.
Modeling using SHHEs involving REE as an additional source of interfacial
polarization suggests that REE can lead to an interfacial spin Hall angle
(~0.3) that is one order of magnitude larger than the bulk value of Pt. Our
results demonstrate that a ferroelectric interface can produce large
spin-charge conversion and that SHHEs are a sensitive tool for characterizing
interfacial spin transport properties
Modelling Ice and Wax Formation in a Pipeline in the Arctic Environment
PresentationIn the Arctic environment, fluid temperature in pipeline can drop below the freezing point of water, which causes wax and ice to form on pipeline surface. Solid formation on pipeline surface can lead to flow assurance and process safety issues, such as blockage of pipeline, pipeline component failure, and the release of hazardous liquid. The blockage of pipeline can cause additional burden or failure to pumping system. Remediating the plugging requires shutdown of pipeline operation, which cause tremendous cost and delay to the entire production system. Ice and wax deposition in pipeline is a slow process. Pigging operation can be used to remove the deposits on pipeline surface. However, if deposition is too thick, pipeline blockage can still occur. In order to prevent pipeline blockage, ice and wax deposition rates are required to be estimated. This paper investigates ice and wax deposition rates in a 90 km pipeline. A fundamental model for both ice and wax deposition is proposed using first principles of heat and mass transfer. The interaction between water and wax is analysed
Growth diagram of La0.7Sr0.3MnO3 thin films using pulsed laser deposition
An experimental study was conducted on controlling the growth mode of
La0.7Sr0.3MnO3 thin films on SrTiO3 substrates using pulsed laser deposition
(PLD) by tuning growth temperature, pressure and laser fluence. Different thin
film morphology, crystallinity and stoichiometry have been observed depending
on growth parameters. To understand the microscopic origin, the adatom
nucleation, step advance processes and their relationship to film growth were
theoretically analyzed and a growth diagram was constructed. Three boundaries
between highly and poorly crystallized growth, 2D and 3D growth, stoichiometric
and non-stoichiometric growth were identified in the growth diagram. A good fit
of our experimental observation with the growth diagram was found. This case
study demonstrates that a more comprehensive understanding of the growth mode
in PLD is possible
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