Enhancing ecosystem services in vineyards: using cover crops to decrease botrytis bunch rot severity

Botrytis bunch rot is a disease that causes loss of yield and quality in many fruit and vegetable crops in temperate climates worldwide. The rot is caused by the fungus Botrytis cinerea, a saprophytic necrotroph. In grapes, the presence of the fungus can reduce yield, taint wine and increase its sensitivity to oxidation. In the current work, inter-row phacelia and ryegrass were mulched in situ in winter 2005 and compared with a bare ground control. The mulches were applied under 10-year-old Chardonnay vines in a 10-replicate randomized block design in New Zealand. Functional soil biological activity increased by 1.5–4.5 times in the two cover crop treatments compared with the control, an effect related to elevated soil moisture in these treatments. This increase in soil moisture and a higher rate of soil biological activity increased vine debris degradation, reduced B. cinerea primary inoculum on the debris and decreased B. cinerea severity at flowering (December 2005) and harvest (April 2006). These results show the potential of mulched cover crops to enhance soil ecosystem services, reduce variable costs and improve the sustainability of viticulture and potentially other agricultural systems, in temperate climates worldwide.     

A mixed C-vine copula model for hedging price and volumetric risk in wind power trading

When energy trading companies enter into long-term agreements with wind power producers, where a fixed price is paid for the fluctuating production, they are facing a joint price and volumetric risk. Since the pay-off of such agreements is non-linear, a hedging portfolio would ideally consist of not only forwards, but also a basket of e.g. call and put options. Illiquidity and an almost non-existent market for options challenge however the optimal hedging of joint price and volumetric risk in many market places. Here, we consider the case of the Danish power market, and exploit its strong positive correlation with the much more liquid German market to construct a proxy hedge. We propose a three-dimensional mixed vine copula to model the evolution of the Danish and German spot electricity prices and the Danish wind power production. We construct a realistic hedging portfolio by identifying various instruments available in the market, such as real options in the form of the right to transfer electricity across the border and the right to convert electricity to heat. Using the proposed vine copula to determine optimal hedging decisions, we show that significant benefits are to be drawn by extending the hedging portfolio with the proposed instruments.     

The asymptotic distribution of the determinant of a random correlation matrix

Our main result gives the asymptotic distribution of the determinant of a random correlation matrix sampled in a particular way from the space of d ×d correlation matrices. Several spin‐off results are proven along the way, and an interesting connection with the law of the determinant of general random matrices is investigated. As different methods for generating random correlation matrices are proposed in the literature, one application of our result is that in can be employed to differentiate between those methods.     

基于藤结构pair—copula分解法的分布估计算法

借鉴copula研究中藤结构在高维相关关系上的构建能力,提出了基于藤结构pair—copula分解法的分布估计算法,给出了新算法的模型框架,研究了相应的概率模型的采样算法,并对C藤、D藤两种特殊的藤进行了仿真实验,结果表明,该算法不仅可行,寻优能力也大大提高．