8,375 research outputs found
Different contributions to space weather and space climate from different big solar active regions
The purpose of this paper is to show that large active regions (ARs) with
different magnetic configurations have different contributions to short-term
and long-term variations of the Sun. As a case study, the complex -type
AR 12673 and the simple -type AR 12674 are investigated in detail. Since
the axial dipole moment at cycle minimum determines the amplitude of the
subsequent cycle and space climate, we have assimilated the individual observed
magnetic configurations of these two ARs into a surface flux transport model to
compare their contributions to the axial dipole moment . We find that AR
12673 has a significant effect on at the end of the cycle, making it weaker
because of the abnormal and complicated magnetic polarities. An initial
strongly positive ends up with a strongly negative value. The flare-poor AR
12674 has a greater contribution to the long-term axial dipole moment than the
flare-rich AR 12673. We then carry out a statistical analysis of ARs larger
than 800 Hem from 1976 to 2017. We use the flare index FI and define an
axial dipole moment index DI to quantify the effects of each AR on space
weather and space climate, respectively. Whereas the FI has a strong dependence
on the magnetic configuration, the DI shows no such dependence. The DI is
mainly determined by the latitudinal location and the latitudinal separation of
the positive and negative magnetic fluxes of the ARs. Simple ARs have the same
possibility as complex ARs to produce big DI values affecting space climate.Comment: 18 pages, 8 figures, Accepted for publication in the Astrophysical
Journa
One qubit and one photon -- the simplest polaritonic heat engine
Hybrid quantum systems can often be described in terms of polaritons. These
are quasiparticles formed of superpositions of their constituents, with
relative weights depending on some control parameter in their interaction. In
many cases, these constituents are coupled to reservoirs at different
temperatures. This suggests a general approach to the realization of
polaritonic heat engines where a thermodynamic cycle is realized by tuning this
control parameter. Here we discuss what is arguably the simplest such engine, a
single qubit coupled to a single photon. We show that this system can extract
work from feeble thermal microwave fields. We also propose a quantum
measurement scheme of the work and evaluate its back-action on the operation of
the engine.Comment: 8 pages, 4 figures, new contents adde
Implementing the Black-Litterman Model with Resampling: A Typical Investment Portfolio with Hedge Funds
Asset allocation decision is ranked as the most important investment decision an investor should make. Researchers have developed many optimization tools to find the best allocation for investors. Our paper will focus on implementing Black-Litterman model together with resampling techniques for portfolio allocations. In our paper, we are going to empirically test the usefulness of those techniques. The results from our research proved that Black-Litterman model and Resampling techniques are advanced methods, which help to generate better allocations than the traditional Markowitz method does. As focusing on typical Canadian investors, our reference portfolio is consisted of S&P TSX, S&P 500, DEX Universe Bond Index, T-Bills and various Canadian hedge funds indices. Using new data sets, we will test whether the results presented in Kooli and Selam’s 2010 paper will still hold. Lastly, further thoughts of our research will be discussed
Corporate Governance and Market Valuation in China
This paper studies the relationship between the governance mechanisms and the market valuation of publicly listed firms in China empirically. We construct measures for corporate governance mechanisms and measures of market valuation for all publicly listed firms on the two stock markets in China by using data from the firm’s annual reports. We then investigate how the market-valuation variables are affected by the corporate governance variables while controlling for a number of factors commonly considered in market valuation analysis. A corporate governance index is also constructed to summarize the information contained in the corporate governance variables. The index is found to have statistically and economically significant effect on market valuation. The analysis indicates that investors pay a significant premium for well-governed firms in China, benefiting firms that improve their governance mechanisms.http://deepblue.lib.umich.edu/bitstream/2027.42/39949/3/wp564.pd
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