957 research outputs found
Risks of Large Portfolios
Estimating and assessing the risk of a large portfolio is an important topic
in financial econometrics and risk management. The risk is often estimated by a
substitution of a good estimator of the volatility matrix. However, the
accuracy of such a risk estimator for large portfolios is largely unknown, and
a simple inequality in the previous literature gives an infeasible upper bound
for the estimation error. In addition, numerical studies illustrate that this
upper bound is very crude. In this paper, we propose factor-based risk
estimators under a large amount of assets, and introduce a high-confidence
level upper bound (H-CLUB) to assess the accuracy of the risk estimation. The
H-CLUB is constructed based on three different estimates of the volatility
matrix: sample covariance, approximate factor model with known factors, and
unknown factors (POET, Fan, Liao and Mincheva, 2013). For the first time in the
literature, we derive the limiting distribution of the estimated risks in high
dimensionality. Our numerical results demonstrate that the proposed upper
bounds significantly outperform the traditional crude bounds, and provide
insightful assessment of the estimation of the portfolio risks. In addition,
our simulated results quantify the relative error in the risk estimation, which
is usually negligible using 3-month daily data. Finally, the proposed methods
are applied to an empirical study
Subset measurement selection for globally self-optimizing control of Tennessee Eastman process
The concept of globally optimal controlled variable selection has recently been proposed to improve self-optimizing control performance of traditional local approaches. However, the associated measurement subset selection problem has not be studied. In this paper, we consider the measurement subset selection problem for globally self-optimizing control (gSOC) of Tennessee Eastman (TE) process. The TE process contains substantial measurements and had been studied for SOC with controlled variables selected from individual measurements through exhaustive search. This process has been revisited with improved performance recently through a retrofit approach of gSOC. To extend the improvement further, the measurement subset selection problem for gSOC is considered in this work and solved through a modification of an existing partially bidirectional branch and bound (PB3) algorithm originally developed for local SOC. The modified PB3 algorithm efficiently identifies the best measurement candidates among the full set which obtains the globally minimal economic loss. Dynamic simulations are conducted to demonstrate the optimality of proposed results
Retrofit self-optimizing control of Tennessee Eastman process
This paper considers near-optimal operation of the Tennessee Eastman (TE) process by using a retrofit self-optimizing control (SOC) approach. Motivated by the factor that most chemical plants in operation have already been equipped with a workable control system for regulatory control, we propose to improve the economic performance by controlling some self-optimizing controlled variables (CVs). Different from traditional SOC methods, the proposed retrofit SOC approach improves economic optimality of operation through newly added cascaded SOC loops, where carefully selected SOC CVs are maintained at constant by adjusting set-points of the existing regulatory control loops. To demonstrate the effectiveness of the retrofit SOC proposed, we adopted measurement combinations as the CVs for the TE process, so that the economic cost is further reduced comparing to existing studies where single measurements are controlled. The optimality of the designed control architecture is validated through both steady state analysis and dynamic simulations
Asymptotic distributions of the average clustering coefficient and its variant
In network data analysis, summary statistics of a network can provide us with
meaningful insight into the structure of the network. The average clustering
coefficient is one of the most popular and widely used network statistics. In
this paper, we investigate the asymptotic distributions of the average
clustering coefficient and its variant of a heterogeneous Erd\"{o}s-R\'{e}nyi
random graph. We show that the standardized average clustering coefficient
converges in distribution to the standard normal distribution. Interestingly,
the variance of the average clustering coefficient exhibits a phase transition
phenomenon. The sum of weighted triangles is a variant of the average
clustering coefficient. It is recently introduced to detect geometry in a
network. We also derive the asymptotic distribution of the sum weighted
triangles, which does not exhibit a phase transition phenomenon as the average
clustering coefficient. This result signifies the difference between the two
summary statistics
Proper Scaling of the Anomalous Hall Effect
Working with epitaxial films of Fe, we succeeded in independent control of
different scattering processes in the anomalous Hall effect. The result
appropriately accounted for the role of phonons, thereby clearly exposing the
fundamental flaws of the standard plot of the anomalous Hall resistivity versus
longitudinal resistivity. A new scaling has been thus established that allows
an unambiguous identification of the intrinsic Berry curvature mechanism as
well as the extrinsic skew scattering and side-jump mechanisms of the anomalous
Hall effect.Comment: 5 pages, 4 figure
Multivariable Scaling for the Anomalous Hall Effect
We derive a general scaling relation for the anomalous Hall effect in
ferromagnetic metals involving multiple competing scattering mechanisms,
described by a quadratic hypersurface in the space spanned by the partial
resistivities. We also present experimental findings, which show strong
deviation from previously found scaling forms when different scattering
mechanism compete in strength but can be nicely explained by our theory
Dual Branch Neural Network for Sea Fog Detection in Geostationary Ocean Color Imager
Sea fog significantly threatens the safety of maritime activities. This paper
develops a sea fog dataset (SFDD) and a dual branch sea fog detection network
(DB-SFNet). We investigate all the observed sea fog events in the Yellow Sea
and the Bohai Sea (118.1{\deg}E-128.1{\deg}E, 29.5{\deg}N-43.8{\deg}N) from
2010 to 2020, and collect the sea fog images for each event from the
Geostationary Ocean Color Imager (GOCI) to comprise the dataset SFDD. The
location of the sea fog in each image in SFDD is accurately marked. The
proposed dataset is characterized by a long-time span, large number of samples,
and accurate labeling, that can substantially improve the robustness of various
sea fog detection models. Furthermore, this paper proposes a dual branch sea
fog detection network to achieve accurate and holistic sea fog detection. The
poporsed DB-SFNet is composed of a knowledge extraction module and a dual
branch optional encoding decoding module. The two modules jointly extracts
discriminative features from both visual and statistical domain. Experiments
show promising sea fog detection results with an F1-score of 0.77 and a
critical success index of 0.63. Compared with existing advanced deep learning
networks, DB-SFNet is superior in detection performance and stability,
particularly in the mixed cloud and fog areas
Evidence of the side jump mechanism in the anomalous Hall effect in paramagnets
Persistent confusion has existed between the intrinsic (Berry curvature) and
the side jump mechanisms of anomalous Hall effect (AHE) in ferromagnets. We
provide unambiguous identification of the side jump mechanism, in addition to
the skew scattering contribution in epitaxial paramagnetic NiCu
thin films, in which the intrinsic contribution is by definition excluded.
Furthermore, the temperature dependence of the AHE further reveals that the
side jump mechanism is dominated by the elastic scattering
Estimating Properties of Solid Particles Inside Container Using Touch Sensing
Solid particles, such as rice and coffee beans, are commonly stored in
containers and are ubiquitous in our daily lives. Understanding those
particles' properties could help us make later decisions or perform later
manipulation tasks such as pouring. Humans typically interact with the
containers to get an understanding of the particles inside them, but it is
still a challenge for robots to achieve that. This work utilizes tactile
sensing to estimate multiple properties of solid particles enclosed in the
container, specifically, content mass, content volume, particle size, and
particle shape. We design a sequence of robot actions to interact with the
container. Based on physical understanding, we extract static force/torque
value from the F/T sensor, vibration-related features and topple-related
features from the newly designed high-speed GelSight tactile sensor to estimate
those four particle properties. We test our method on very different daily
particles, including powder, rice, beans, tablets, etc. Experiments show that
our approach is able to estimate content mass with an error of g, content
volume with an error of ml, particle size with an error of mm, and
achieves an accuracy of % for particle shape estimation. In addition, our
method can generalize to unseen particles with unknown volumes. By estimating
these particle properties, our method can help robots to better perceive the
granular media and help with different manipulation tasks in daily life and
industry.Comment: 8 pages, 14 figure
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