Measurement of Walnut Properties and Analysis on the Compressive Stiffness of the Critical Value of Shell-cracking

Based on the measurement of walnut properties, a computational analysis was conducted on the compressive stiffness of the critical val-ue of shell-cracking. As indicated by the results, to crack the walnuts shell from its longitudinal or edge directions could save lots of efforts. The study provided theoretical basis for the design and improvement of walnut shell-cracking machine as well as theoretical references for the design, mak ng and use of some spec a crack ng-a d ng too s such as nutcracker.

改进选择实验法在居民浒苔治理意愿评估中的应用

选择实验法是通过问卷调查获取大量个体对资源环境属性状态选择集的偏好信息,评估资源环境非市场价值的前沿方法。受访者面对多种选择集的高信息负荷,由于认知水平受限,经常通过为物品属性设定可接受的最低/最高水平,即属性临界值,以简化决策过程,易造成模型估计结果的偏差。本文针对黄海胶州湾海域浒苔治理支付意愿,考虑属性临界值的存在及违反情况,设计引出属性临界值的选择实验问卷,建立修正选择模型,以青岛市实地调研的397个有效样本为数据来源,对居民浒苔治理意愿进行评估。研究结果表明:(1)属性临界值的存在及违反具有普遍性,忽略其存在及违反情况将导致估计结果的偏差;(2)将属性临界值存在及违反情况纳入效用方程,对传统选择实验分析框架进行修正,结果表明,经修正的选择模型的拟合度更优,能更好地解释受访者选择行为。在参数估计方面,浒苔治理恢复属性对居民效用水平显著正向影响,滨海景观、近海水质属性临界值的违反对居民效用水平显著负向影响;(3)青岛市居民对治理浒苔恢复滨海景观、改善近海水质、增加生物多样性和修复海洋生物资源的年支付意愿分别为90.68元、84.92元、49.34元、43.17元,2017年青岛市胶州湾海域浒苔治理总支付意愿为33.006亿元。与传统模型的对比表明,考虑属性临界值存在及违反情况的选择模型能更有效地反映受访者的实际边际效用,并在此基础上提高支付意愿估计结果的效度。