乡村收缩的内涵界定与测度研究

乡村收缩是我国城乡结构转化进程中呈现的新现象。文章首先从概念层面阐释了乡村收缩的内涵,梳理了我国乡村收缩需要重点把握的逻辑线索,进而通过文献调查和实地调研,以甘肃省为例从县域尺度对乡村收缩程度进行测度,从乡村人口、经济和社会三个维度揭示其形成机理。研究发现:(1)乡村收缩在不同语境其内涵可能存在差异,但其本质均是青壮年劳动力的过度流失;(2)2000年、2010年、2020年甘肃省乡村收缩指数均值呈现动态大幅度上升趋势,分别为26.11%、38.97%、49.98%,且上升趋势具有比较显著的空间差异性;(3)城乡二元结构下,资源禀赋和地理区位、经济发展与要素流动、历史基础与社会文化、政策安排与治理能力都对乡村收缩有影响。新时代我国应从振兴县域经济出发,依靠产业聚集、人才引进、资金筹措、城乡融合的政策组合来回应乡村收缩现象。

热缩型力缆终端头材料的研制

利用辐射技术对高分子材料进行处理而制成的高聚物形状记忆材料 (也称热收缩材料 )是材料技术与核能技术结合的一种新技术产品 ,近年来发展迅速。其在电缆附件上的应用最受世人瞩目并产生了很好的经济效益和社会效益。本文论述了应用在户外的35

Establishment and verification of a shrinking core model for dilute acid hydrolysis of lignocellulose

The kinetics oflignocellulose hydrolysis under the conditions of high temperature and dilute acid （mass fraction 0.05%） was investigated in this paper. By studying the reducing sugar concentration versus reaction tempera ture （170℃-220℃） and reaction time （150-1800 s） during the hydrolysis process of five kinds of crop straw （rice, wheat, cotton, rape and corn）, the shrinking core model was established, and the differential equation of the model and its analytical solution were obtained. With a numerical calculation method, the kinetic equation was estimated, and the degradation of reducing sugar obeyed firstorder kinetics was obtained. The calculated results from the equations agreed well with the original experimental data. The calculation by the model showed that the reducing sugar concentration increases as the size of the particles decrease, and the uniform particles increase.