Tracking error minimization is commonly used by the traditional passive fund managers as well as alternative portfolio (for example, hedge fund) managers. We propose a graduated non-convexity method to minimize portfolio tracking error with the total number of assets no greater than a specified integer K. The solution of this tracking error minimization problem is a global minimizer of a minimization problem with a discontinuous counting function in a constraint. We attempt to track the globally minimal tracking error portfolio by approximating the discontinuous counting function with a sequence of continuously differentiable non-convex functions, a graduated non-convexity process. We discuss the advantages of this approach, present numerical results, and compare it with two methods from recent literature.
Vocational education is an important composition of educational system in China and also is a base of national economy and social development We must build modern vocational education system for speeding up vocational education development The article expounded concrete measures of building modern vocational education system
Reservoir/lake sediments are potential pollutant acceptors and sources of pollution. The Danjiangkou Reservoir, as the largest drinking water source in China, is the source water area for the Mid-route Project of the South-North Water Diversion. To illustrate the temporal and spatial changes in the environmental risks of both nutrients and heavy metals in the surface sediments of Danjiangkou Reservoir, the levels of pH, OM, TP, TN, and six kinds of metal elements during the period 2011-2016 were measured at five ecological sites. Canadian freshwater sediment quality guidelines for aquatic environments (from the CCME) were used to assess the potential ecological risks. The results showed that the contents of OM, TP, and TN in the surface sediments were 25.85, 0.57, and 1.34 g·kg-1, respectively, and those of Cr, Mn, Cu, Zn, Cd, and Pb were 57.96, 521.78, 13.91, 195.74, 0.37, and 12.92 mg·kg-1, respectively. The contents of both Zn and Cd were under the corresponding Ⅱ-level standards of soil environmental quality, but the contents of the other four heavy metals were lower than their corresponding I-level standards. After water diversion of the Mid-route Project, the OM, TN, Mn, and Zn contents increased, and the TP and other heavy metal contents displayed downward trends. Excluding the pH value, the distribution of measured nutrients and heavy metals in the surface sediments of the Danjiangkou Reservoir reached the extremely significant level (P<0.01). OM in the sediments was negatively correlated with TN and Pb, but had positive correlations with the other indicators measured. The results from the potential ecological risk assessment showed that:①Cd, Cu, and Pb had no harmful effects on organisms; ② OM had low ecological risk in most years; ③ the risk of TP was between zero and low ecological risk; and ④Cr, Zn, and TN had low ecological risk in most cases. The K and H sites had higher ecological risk for Cr, Zn, and TN, thus attention should be paid to those cases. These results illustrate the effects of human activities on nutrients and heavy metals in surface sediments.
Exploring the relationship between topography and forest multifunctionality enhances understanding of the mechanisms maintaining forest multifunctionality and proves beneficial for managing overall forest functions across different landscapes. Leveraging census data from a 20 ha subtropical forest plot, we investigated the topographic variations in individual functions, multifunctionality, and their interrelationships. Our results revealed that relative to lower elevations, higher elevations had higher woody productivity, sapling growth, and recruitment that drove higher average forest multifunctionality (FMA). However, forest multifunctionality at the 50% threshold level (FMt50) had no significant difference between high and low elevations. Compared with the valley and slope, higher woody productivity, higher sapling recruitment, and higher soil organic carbon stock drove higher forest multifunctionality (FMA and FMt50) in the ridge. These results indicate the ridge serves as a forest multifunctionality “hotspot” within the Tiantong 20 hm2 plot. Additionally, relative to the low elevation, the degree of synergy among functions at the high elevation was significantly lower, indicating difficulties in attaining high forest multifunctionality at the high elevation. Our work underscores the importance of topography in regulating subtropical forest multifunctionality and relationships between forest functions at a local scale, suggesting that future forest management strategies (such as regulating synergistic or trade-off relationships between functions) should give particular attention to topographic conditions.
The study compared the effect of different methods for pretreating waste activated sludge(WAS),including different combination of alkali treatment,alkali treatment and ultrasonic treatment(20 kHz,150 W).In the experiments testing dissolution effect with the alkali pretreatment,the ratio of soluble COD to the total COD could be increased to 30.1%;if ultrasonic treatment followed,the ratio could be increased to 79.3%;if alkali and ultrasound treatment were used simultaneously,the ratio reached 75.9%.In the subsequent BAP experiment,the ratio of volatile fatty acid to the total COD in the initial activated sludge was less than 10%;by adopting alkali pretreatment,the ratio could be increased to 30%;if ultrasonic treatment followed,the ratio could be increased to 59%;if alkaline and ultrasonic treatments were adopted simultaneously,the maximum ratio of 80% was reached.In addition,the simultaneous use of alkaline and ultrasonic treatments could significantly shorten the pre-processing time.Therefore,simultaneously using alkali and ultrasound treatments could effectively increase the production of volatile fatty acids in activated sludge and improve the follow-up digestive process.
Flotation agents can enter the soil and water environment around mining areas through beneficiation wastewater discharge and overflow from tailings ponds. The adsorption of Pb2+ and Cd2+ on soil around a lead-zinc dressing plant was investigated in the presence of potassium butyl xanthate (PBX). Batch experiments were conducted with different initial pH, PBX, Pb2+, and Cd2+solution concentrations. The fractions of lead and cadmium were altered after treatment with different concentrations of PBX. The results showed that adsorption of Pb2+and Cd2+ on soil was seriously inhibited by PBX. When PBX concentration was 40 mg·L-1, the adsorption capacity of Pb2+ and Cd2+ decreased from 3540 mg·kg-1 and 387 mg·kg-1 to 3085 mg·kg-1 and 100 mg·kg-1, respectively. The Pb2+ and Cd2+ adsorption kinetic process was best fitted by the quasi-second-order kinetic model, which indicated that the adsorption process of Pb2+ and Cd2+ on soil was mainly chemical adsorption. The formation of a hydrophobic and insoluble complex and competitive adsorption between PBX, Pb2+, and Cd2+ on the soil surface was the main reason for reducing the adsorption capacity. The results showed that PBX could increase the mobility of Pb2+ and Cd2+ on soil. The degree of impact improved with increasing initial concentration of PBX and pH but decreased with increasing initial concentration of Pb2+ and Cd2+, and the adsorption isotherms conformed to the Freundlich isotherm. Under low PBX content (100 mg·kg-1), exchangeable and reducible cadmium contents in the soil increased, which could lead to the activation of cadmium in soil. However, the addition of PBX to the treated soil could reduce the content of exchangeable and reducible lead. As the concentration of PBX increased, the reduction effect also increased, which was related to the stronger complex stability of Pb(C4H9OCS2)2 than that of Cd(C4H9OCS2)2. The results showed that residual flotation reagents in beneficiation wastewater may increase the potential ecological risk of heavy metals such as Pb and Cd in soil, and the prevention and control of the potential ecological risk should be strengthened.
Many complex options (for example, options embedded in insurance contracts) have an early exercising feature. It is important to evaluate the impact of the nonoptimal exercising in the pricing and risk management of these options. We consider the problem of discrete hedging under irrational exercising. We propose a framework under which irrational exercising is modeled explicitly and local risk-minimization hedging strategies can be computed. We evaluate quadratic and piecewise linear risk-minimization approaches in this framework and compare hedging performance between different hedging strategies. In addition, we compare hedging effectiveness under irrational exercising with that of European contracts and American contracts with optimal exercising.We find that irrational exercising may have a significant impact on discrete-hedging strategies and hedging costs.
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