Intradaily dynamic portfolio selection

A portfolio selection model which allocates a portfolio of currencies by maximizing the expected return subject to Value-at-Risk (VaR) constraint is designed and implemented. Based on an econometric implementation using intradaily data, the optimal portfolio allocation is forecasted at regular time intervals. For the estimation of the conditional variance from which the VaR is computed, univariate and multivariate GARCH models are used. Model evaluation is done using two economic criteria and two statistical tests. The result for each model is given by the best forecasted intradaily investment recommendations in terms of the optimal weights of the currencies in the risky portfolio. The results show that estimating the VaR from multivariate GARCH models improves the results of the forecasted optimal portfolio allocation, compared to using a univariate model.     

Walking and steering control for a 3D biped robot considering ground contact and stability

This paper presents a stable walking control method for a 3D bipedal robot with 14 joint actuators. The overall control law consists of a ZMP (zero moment point) controller, a swing ankle rotation controller and a partial joint angles controller. The ZMP controller guarantees that the stance foot remains in flat contact with the ground. The swing ankle rotation controller ensures a flat foot impact at the end of the swinging phase. Each of these controllers creates 2 constraints on joint accelerations. As a consequence, the partial joint angles controller is implemented to track only 10 independent outputs. These outputs are defined as a linear combination of the 14 joint angles. The most important question addressed in this paper is how this linear combination can be defined in order to ensure walking stability. The stability of the walking gait under closed loop control is evaluated with the linearization of the restricted Poincare map of the hybrid zero dynamics. As a result, the robot can achieve an asymptotically stable and periodic walking along a straight line. Finally, another feedback controller is supplemented to adjust the walking direction of the robot and some examples of the robot steered to walk along different paths with mild curvature are given.     

pp60c-src activation in hepatocellular carcinoma of humans and LEC rats

For the related Src kinases, a close correlation exists between elevated tyrosine kinase activity and cell transformation. However, the involvement of pp60c-src in hepatocellular carcinoma (HCC) remains obscure. The aim of this study was to evaluate whether pp60c-src tyrosine kinase activity is elevated in HCC. We analyzed the kinase activity of pp60c-src in normal liver tissue, chronic hepatitis liver tissue, and tumorous and adjacent nontumorous portions of HCC tissue from patients and Long-Evans cinnamon (LEC) rats that are known to develop liver cancer spontaneously. The kinase activity of pp60c-src was rarely detected in the normal human liver tissue and chronic hepatitis liver tissue, but it was elevated in tumorous and nontumorous portions of HCC tissue. Furthermore, the kinase activity of pp60c-src was significantly elevated in tumorous tissues compared with nontumorous tissues. The kinase activity of pp60c-src was also higher in poorly differentiated HCC. In addition, the kinase activity of pp60c-src increased proportionately with the development of HCC of LEC rats. Our results suggest that activation of the protooncogene product pp60c-src may play an important role in the malignant transformation of hepatocytes in human and LEC rats, and that it may be closely related to the histopathological grading of human HCC.     

Is China ready for its nuclear expansion?

China’s rapid pace of nuclear energy growth is unique, and its impact on the global nuclear market as both a customer and potential future supplier is already tremendous and will continue to expand. It is crucial to understand this energy policy development and its impact on various global areas. Unfortunately, there is relatively limited English-language information available about China’s nuclear power industry and its current development. This paper aims to provide a comprehensive assessment of the Chinese nuclear energy program and policy, reviewing its past, present, likely future developments, as well as to consider potential challenges that deserve further attention. This paper will explore reasons that have caused the existing industry, describe China’s nuclear bureaucracy and decision making process to understand how different stakeholders play a role in China’s nuclear energy development. This study concludes that China’s existing nuclear program and industry, in combination with its current stable economic and political environment, provides a sound foundation for the planned nuclear expansion. However, challenges which are crucial to the success of the nuclear expansion will need to be addressed.     

Reduction of erosion rate by particle size distribution (PSD) modification of hematite as weighting agent for oil based drilling fluids

Natural hematite (Fe₂O₃) and barite (Ba₂SO₄) are usually employed as weighting agents for oil based drilling fluids in several venezuelan fields. Hematite has shown some physico-chemical advantages with respect to barite: a greater specific gravity and solubility in acid media and lower attrition rate. However, the most challenging issue related to hematite field applications has been to reduce its high erosive potential. Effects of particle size distribution (PSD) have been evaluated with four different samples of hematite (48, 38, 30 and 18 μm based on the statistical parameter D_(v,0.9)) respect to commercial barite. These samples were used to prepare fluids with a density of 1977 kg/m³. An erosion test loop was used to expose different samples of AISI 1020 flat steel to the erosive action of jet fluid. Wear of metallic samples was measured by weight lost and wear mechanisms were identified by laser profilometry, SEM and EDS. The investigation showed that the erosion rate (E) produced by hematite decreases potentially with size grain reduction (D_(v,0.9)) and depends on the morphology and angularity of the particle in comparison with barite. Laboratory results were validated on field tests with drilling fluids formulated with hematite of different PSD.     

Effect of 2D WS<Subscript>2</Subscript> Addition on Cold-Sprayed Aluminum Coating

Tungsten disulfide (WS₂) has excellent solid lubrication properties due to its 2D layered structure. This study focuses on depositing Al-2 wt.% WS₂ composite coating by cold spray technique. The effect of WS₂ addition on the microstructure, mechanical and tribological properties of the composite coatings is examined in the as-deposited and heat-treated conditions. After heat treatment, the coating density increased to 99% with improved intersplat bonding. The microhardness of the heat-treated Al-2 wt.% WS₂ coating increased by 56% as compared to the as-sprayed coating. The wear resistance of heat-treated Al-2 wt.% WS₂ coating improved by 75% with a synergistic reduction in the coefficient of friction (COF) by 51%. Transmission electron microscopy investigation reveals the presence of layered WS₂ within aluminum splats with a strong interface. This study shows that cold spraying can be effectively used to integrate 2D layered WS₂ as a solid lubricant in the metallic coatings.