Comparative Analysis of Ledoit\u27s Covariance Matrix and Comparative Adjustment Liability Management (CALM) Model Within the Markowitz Framework

Estimation of the covariance matrix of asset returns is a key component of portfolio optimization. Inherent in any estimation technique is the capacity to inaccurately reflect current market conditions. Typical of Markowitz portfolio optimization theory, which we use as the basis for our analysis, is to assume that asset returns are stationary. This assumption inevitably causes an optimized portfolio to fail during a market crash since estimates of covariance matrices of asset returns no longer re ect current conditions. We use the market crash of 2008 to exemplify this fact. A current industry standard benchmark for estimation is the Ledoit covariance matrix, which attempts to adjust a portfolio\u27s aggressiveness during varying market conditions. We test this technique against the CALM (Covariance Adjustment for Liability Management Method), which incorporates forward-looking signals for market volatility to reduce portfolio variance, and assess under certain criteria how well each model performs during recent market crash. We show that CALM should be preferred against the sample convariance matrix and Ledoit covariance matrix under some reasonable weight constraints

Effect of Investment in Environmental Protection on Green Development of Industrial Enterprises: Evidence from Central China

China\u27s industrialization and urbanization process is advancing rapidly. While using natural resources, the country also generates a large amount of waste, causing serious environmental pollution and affecting further development of human society. Expanding the scale of investment in environmental protection has gradually become an effective means to address the problem. China is continuously increasing investment in environmental protection, actively improving environmental conditions, and achieving the dual goals of promoting high-quality development and environmental protection. Six provinces in central China were taken as research objects and the regional differences in their investments in environmental protection were analyzed. A panel entropy weight model was used to calculate the green development level of industrial enterprises, and a panel regression model was employed to calculate the impact of investment in environmental protection on the degree of influence of the green development of industrial enterprises. Results show that the six provinces in central China have significant differences in their investment in industrial environmental pollution control. The unreasonable allocation of environmental protection investment funds has led to the insignificant improvement of environmental pollution caused by industrial enterprises in the six central provinces of investment in environmental protection. R&D expenditure of industrial enterprises, the total import, and export volume of foreign-invested enterprises, and the fixed asset investment of the entire society have a positive role in promoting the green development of industrial enterprises. The added value of the secondary industry has a significant negative effect on the green development of industrial enterprises. Conclusions can be used as a reference for encouraging industrial enterprises to increase investment in environmental protection and promote green development

The Production-oriented Approach to Teaching English Writing in Chinese Junior High Schools

With the acceleration of globalization, English communicative competence has become a necessary ability in modern society. The teaching of English writing in junior high schools not only improves students’ comprehensive language ability, but also lays a favorable foundation for their future English learning. Writing classes should highlight the importance of writing. But in fact, students’ actual output is neglected. The writing classes exist in name only. Based on the above questions, this research attempts to apply the Production-Oriented Approach (POA) in junior high school English writing teaching which is proposed by Chinese scholar Wen Qiufang. This research aims to find the effectiveness of POA in English writing teaching of Chinese junior high schools. We adopt the experimental research approaches, using classroom observation, interviews and tests to collect research data. Taking a class of 50 students in Grade 8 of junior high school as the research subjects, the researcher carries out the production-oriented English teaching experiment for one semester. It has been found: (1) Compared with traditional English instructions, POA can improve the English writing quality and comprehensive language using ability of junior high school students. (2) Both teachers and students believe that POA can stimulate students’ positive emotional experience, and students have more opportunities to use language in class. Through “enabling”, the quality of students’ language output has been significantly improved

Flower heads in Asteraceae—recruitment of conserved developmental regulators to control the flower-like inflorescence architecture

Inflorescences in the Asteraceae plant family, flower heads, or capitula, mimic single flowers but are highly compressed structures composed of multiple flowers. This transference of a flower-like appearance into an inflorescence level is considered as the key innovation for the rapid tribal radiation of Asteraceae. Recent molecular data indicate that Asteraceae flower heads resemble single flowers not only morphologically but also at molecular level. We summarize this data giving examples of how rewiring of conserved floral regulators have led to evolution of morphological innovations in Asteraceae. Functional diversification of the highly conserved flower meristem identity regulator LEAFY has shown a major role in the evolution of the capitulum architecture. Furthermore, gene duplication and subsequent sub-and neofunctionalization of SEPALLATA and CYCLOIDEA-like genes in Asteraceae have been shown to contribute to meristem determinacy, as well as flower type differentiation-key traits that specify this large family. Future challenge is to integrate genomic, as well as evolutionary developmental studies in a wider selection of Asteraceae species to understand the detailed gene regulatory networks behind the elaborate inflorescence architecture, and to promote our understanding of how changes in regulatory mechanisms shape development.Peer reviewe

Control of biodegradation of a Mg alloy in simulated body fluid

Mg alloy AZ31 is an attractive candidate for coronary artery stents, as it possesses excellent biocompatibility in human body and good mechanical properties. However, AZ31 magnesium alloys generally have poor corrosion resistance in the body environment. This paper reports on the early stages of an investigation into the corrosion mechanism and the morphology of corrosion of AZ31 in simulated body fluid (SBF). The investigation will also consider ways of improving corrosion resistance of this alloy in SBF through the use of ionic liquids. The results to date have shown that AZ31 suffers severe localized pitting corrosion in SBF. The pits mainly develop adjacent to the Al-Mn intermetallic second phase in the α matrix. Energy Dispersive X-Ray Spectroscopy results revealed the presence of Mg, O, Ca, and P in the layer of corrosion product. Treatment of the AZ31 alloy prior to corrosion testing in SBF with the ionic liquid trimethyl (butyl) phosphonium diphenyl phosphate (P1444DPP) produced some increase in the corrosion resistance of the alloy

Improving the seismic performance of staircases in building structures with a novel isolator

A staircase provides the main escape way from a building in an emergency. Unfortunately, it may suffer severe damages or even collapse during an earthquake. For improving the seismic performance of staircases, this paper proposes an innovative staircase isolator with the features of lightweight, cost-effective and ease of construction and replacement, which is formed by suitable engineering plastic shims between rubber layers. A connection construction scheme is also proposed for the isolated staircase. Systematic performance tests have been carried out to characterize the isolator in terms of mechanic behavior and ultimate states. The test results show that mechanical properties of the proposed staircase isolator are excellent and suitable for staircase in building structure. In order to investigate the influence of staircase on building structural responses, time history analyses of a typical building structure without staircase (WS), with fixed staircase (FS) and with isolated staircase (IS) are conducted and compared within the environment of SAP2000. Results show that staircase isolation can effectively eliminate the diagonal bracing effect of staircase slab and make structural components uniformly stressed. When the novel isolator is employed for staircase in a building structure, there is no vulnerable position in staircase and the performance of staircase in building structure can be greatly enhanced