植物矮化激素对茶条槭生长及观赏性作用的研究

利用不同植物矮化激素对茶条槭进行喷施试验。结果表明,不同激素对茶条槭的生长效果及观赏性有明显的作用;对茶条槭矮化效果最佳的是10ml/L的国光矮壮素和浓度为2g/L的国光多效唑。     

北京市观赏渔业养殖经营的现状分析及对策研究

观赏鱼已被列为北京市农业技术创新体系首批试点的三个(生猪、果类蔬菜、观赏鱼)品种之一,成为北京市农业发展扶持的重要品种,对北京市观赏鱼产业发展进行全面深入的研究具有十分现实的意义。本文依托北京市观赏鱼创新团队产业经济研究团队调研资料,比较全面系统地分析了北京市观赏渔业养殖、经营的现状及存在的问题,并提出政府应在资金支持、科技创新、推广及指导、渔病防治防疫、规范管理等方面对北京市观赏渔业的养殖与经营予以扶持,使北京市观赏鱼产业更好更快地发展。     

活力度分级法在天津空港经济区行道树健康评价中的应用

树木活力度分级评价方法被作为主要评价方法,对天津空港经济区10种主要行道树的生长态势进行了分级和统计,结果显示:空港经济区主要行道树的活力度以4级为主,3级和5级次之,1级和2级较少,反映出该区域行道树生长态势总体情况较差。在此基础上,提出行道树养护管理建议,并对活力度分级评价方法的应用进行了展望,为将来的行道树分级和绿化管理提供了有益的参考。     

Adaptation of Agroforestry Systems in South-Eastern Mexico through Integration of Farmer and Bioeconomic Evaluations

Agroforestry systems have been promoted as sustainable land-use systems for regions where shifting agriculture is the traditional predominant land-use. Although environmentally sustainable, agroforestry systems require investment to establish that may affect their economic sustainability. In the southern Yucatan Peninsula 47 agroforestry plots of two timber and 10 fruit tree species were established with 22 farmers in three communities covering two rainfall zones and five soil types. Some fruit trees had wide adaptability to different soil, rainfall and management conditions, e.g. Manilkara zapota; others were restricted to the best soil, rainfall management conditions, e.g. Persea americana. The Meliaceae timber trees responded little to rainfall and soil, but stem borer attack was markedly lower in less intensively managed systems. Level of system maintenance greatly affected costs, but also opportunities for intercropping and obtaining immediate income. All levels of managements had negative net present value (NPV) for the three-year establishment phase, but so does traditional maize production. Farmers preferred to inter-crop their agroforestry systems, but were often limited by site quality. Determining sustainable agroforestry options for farmers requires multiple decisions related to species adaptability to the site, farmer production objectives and farmer capacity to invest in different management strategies. One production technology did not fit all.     

Models for data transmission delay in cable networks

Cable networks have been upgraded in recent years to support bidirectional traffic rather than just unidirectional television signals. Thus, it has become possible to use cable networks for internet browsing and telephony. In this paper, we propose delay models to determine how this bidirectional traffic is best handled and to evaluate the resulting performance of the network, notably its delay properties. It is shown that these models, variations on the repairman problem and the bulk service queue, lead to actual improvements in the data transmission schedules for cable networks. Moreover, these models can be combined in order to arrive at approximations for the average packet delay. Our theoretical calculations are backed up by simulations.     

The GARCH Option Pricing Model: A Modification of Lattice Approach

Ritchken and Trevor (1999) proposed a lattice approach for pricing American options under discrete time-varying volatility GARCH frameworks. Even though the lattice approach worked well for the pricing of the GARCH options, it was inappropriate when the option price was computed on the lattice using standard backward recursive procedures, even if the concepts of Cakici and Topyan (2000) were incorporated. This paper shows how to correct the deficiency and that with our adjustment, the lattice method performs properly for option pricing under the GARCH process. JEL Classification: C10, C32, C51, F37, G12     

A data driven binning strategy for the construction of insurance tariff classes

We present a fully data driven strategy to incorporate continuous risk factors and geographical information in an insurance tariff. A framework is developed that aligns flexibility with the practical requirements of an insurance company, the policyholder and the regulator. Our strategy is illustrated with an example from property and casualty (P&C) insurance, namely a motor insurance case study. We start by fitting generalized additive models (GAMs) to the number of reported claims and their corresponding severity. These models allow for flexible statistical modeling in the presence of different types of risk factors: categorical, continuous, and spatial risk factors. The goal is to bin the continuous and spatial risk factors such that categorical risk factors result which captures the effect of the covariate on the response in an accurate way, while being easy to use in a generalized linear model (GLM). This is in line with the requirement of an insurance company to construct a practical and interpretable tariff that can be explained easily to stakeholders. We propose to bin the spatial risk factor using Fisher’s natural breaks algorithm and the continuous risk factors using evolutionary trees. GLMs are fitted to the claims data with the resulting categorical risk factors. We find that the resulting GLMs approximate the original GAMs closely, and lead to a very similar premium structure.     

Measuring the effects of advertising on green industry sales: a generalized propensity score approach

This article estimates the effects of advertising expenditures on annual gross sales of green industry firms using a quasi-experimental framework. In order to account for potential selection bias, a generalized propensity score and a dose-response function are used to estimate advertising treatment effects. The method used allows us to investigate the relationship between the dose (advertising expenditures) and the response (firm sales). We use data from the National Green Industry Surveys of 2009 and 2014 to conduct the analysis. To further investigate potential heterogeneous advertising effects of the size of the firms, we separate the sample into small firms and large firms, according to their annual gross sales. The results indicate that the magnitude and shape of the response function depend on the size of the firm. For small firms, increasing advertising spending yields to higher sales within a range of advertising spending. Beyond this range, advertising spending increases do not impact sales any more. Thus, small firms’ management should carefully monitor advertising input. For large firms, on the other hand, the current evidence does not support a positive relationship between advertising spending and sales since the marginal treatment effect is insignificant almost over the entire range of adverting spending.     

On extensive form implementation of contracts in differential information economies

Summary. In the context of differential information economies, with and without free disposal, we consider the concepts of Radner equilibrium, rational expectations equilibrium, private core, weak fine core and weak fine value. We look into the possible implementation of these concepts as perfect Bayesian or sequential equilibria of noncooperative dynamic formulations. We construct relevant game trees which indicate the sequence of decisions and the information sets, and explain the rules for calculating ex ante expected payoffs. The possibility of implementing an allocation is related to whether or not it is incentive compatible. Implementation through an exogenous third party or an endogenous intermediary is also considered. Received: November 19, 2001; revised version: April 17, 2002 RID="*" ID="*" This paper comes out of a visit by Nicholas Yannelis to City University, London, in December 2000. We are grateful to Dr A. Hadjiprocopis for his invaluable help with the implementation of Latex in a Unix environment. We also thank Leon Koutsougeras and a referee for several, helpful comments. Correspondence to: N.C. Yannelis     

大叶茶树无性系选育有关问题的分析探讨

本文从多年的研究实践中总结、概述高产优质大叶茶树无性系的选育和方法,从理论上探讨茶树选育的鉴定标准,并提出了今后茶树优良无性系选育工作的方向及展望。