429 research outputs found
Weak and Semi-Strong Form Stock Return Predictability Revisited
This paper makes indirect inference about the time-variation in expected stock returns by comparing unconditional sample variances to estimates of expected conditional variances. The evidence reveals more predictability as more information is used, and no evidence that predictability has diminished in recent years. Semi-strong form evidence suggests that time-variation in expected returns remains economically important.
Weak and Semi-Strong Form Stock Return Predictability, Revisited
This paper makes indirect inference about the time-variation in expected stock returns by comparing unconditional sample variances to estimates of expected conditional variances. The evidence reveals more predictability as more information is used, and no evidence that predictability has diminished in recent years. Semi-strong form evidence suggests that time-variation in expected returns remains economically important.
Can Electromagnetic Information Theory Improve Wireless Systems? A Channel Estimation Example
Electromagnetic information theory (EIT) is an emerging interdisciplinary
subject that integrates classical Maxwell electromagnetics and Shannon
information theory. The goal of EIT is to uncover the information transmission
mechanisms from an electromagnetic (EM) perspective in wireless systems.
Existing works on EIT are mainly focused on the analysis of degrees-of-freedom
(DoF), system capacity, and characteristics of the electromagnetic channel.
However, these works do not clarify how EIT can improve wireless communication
systems. To answer this question, in this paper, we provide a novel
demonstration of the application of EIT. By integrating EM knowledge into the
classical MMSE channel estimator, we observe for the first time that EIT is
capable of improving the channel estimation performace. Specifically, the EM
knowledge is first encoded into a spatio-temporal correlation function (STCF),
which we term as the EM kernel. This EM kernel plays the role of side
information to the channel estimator. Since the EM kernel takes the form of
Gaussian processes (GP), we propose the EIT-based Gaussian process regression
(EIT-GPR) to derive the channel estimations. In addition, since the EM kernel
allows parameter tuning, we propose EM kernel learning to fit the EM kernel to
channel observations. Simulation results show that the application of EIT to
the channel estimator enables it to outperform traditional isotropic MMSE
algorithm, thus proving the practical values of EIT.Comment: Electromagnetic information theory (EIT) is an emerging
interdisciplinary subject, aiming at providing a unified analytical framework
for wireless systems as well as guiding practical system design. This paper
answers the question: "How can we improve wireless communication systems via
EIT"
Does the Law of One Price hold? A cross-regional study of China
This study considers the price convergence in different regions of
China, which is the largest developing country in the world and a
country in which the regional difference is much larger between
provinces. Whether there is price convergence between regions in one
country is an important economic issue according to the Law of One
Price (LOP) theory. Compared to previous studies, this article operates
with the Sequential Panel Selection Method (SPSM) to explore the
non-stationary properties of the LOP in China’s regions. We provide
robust evidence to specify that the LOP holds true for two-thirds of
the provinces in China, mainly in the Western and Central regions. This
means that the Eastern region’s price fluctuation is non-stationary
and that the consumer price index (CPI) levels of the Western, Central
and Northeastern regions are relatively convergent in China. The
conduction path of the CPI level is from the Eastern region to the other
regions. It shows that prices can converge with each other by LOP and
the values of the same goods in the Western and Central regions are
equal and if there is a price difference, then it can be eliminated by
interregional trade
Data-constrained MHD simulation for the eruption of a filament-sigmoid system in solar active region 11520
The separation of a filament and sigmoid is observed during an X1.4 flare on
July 12, 2012 in solar active region 11520, but the corresponding magnetic
field change is not clear. We construct a data-constrained magnetohydrodynamic
simulation of the filament-sigmoid system with the flux rope insertion method
and magnetic flux eruption code, which produces the magnetic field evolution
that may explain the separation of the low-lying filament and high-lying hot
channel (sigmoid). The initial state of the magnetic model contains a magnetic
flux rope with a hyperbolic flux tube, a null point structure and overlying
confining magnetic fields. We find that the magnetic reconnections at the null
point make the right footpoint of the sigmoid move from one positive magnetic
polarity (P1) to another (P3). The tether-cutting reconnection at the
hyperbolic flux tube occurs and quickly cuts off the connection of the
low-lying filament and high-lying sigmoid. In the end, the high-lying sigmoid
erupts and grows into a coronal mass ejection, while the low-lying filament
stays stable. The observed double J-shaped flare ribbons, semi-circular ribbon,
and brightenings of several loops are reproduced in the simulation, where the
eruption of the magnetic flux rope includes the impulsive acceleration and
propagation phases.Comment: This paper has been accepted for publication in the Ap
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