迁移者的居留、返乡与再迁移决策——基于事件史的分析

作为一个多阶段的空间行为决策过程,人口迁移是城镇化和区域发展研究的核心议题;但现有研究普遍存在重意愿轻行为、重状态轻过程以及较少关注再迁移行为等不足。本文构建了迁移者居留、返乡和再迁移三元选择行为的分析框架,并利用具有全国代表性的调查数据,采用事件史分析法开展了实证研究。结果发现：迁移者普遍会经历三年左右的不稳定期,而后进入稳定居留状态。迁移者的居留、返乡与再迁移行为存在空间分异：省际迁移者较省内迁移者更倾向于再迁移;迁入地规模等级越高,迁移者居留的比例越低。重要生命事件会显著影响人们的迁移行为：婚姻会让迁移者更偏好在特定迁入地稳定居留;毕业就职是人们重新选择居住地的重要时机,而失业这一负面冲击则很可能促使迁移者返回家乡。迁入地经济增长放缓、迁出地经济发展水平提高、两地间文化环境差异较大等因素都会导致更多迁移者选择返乡;但区域发展和地域联系对高学历、低学历迁移者和省际、省内迁移者的影响存在明显异质性。研究结果证实了在人口迁移决策研究中关注实际迁移行为、引入动态过程视角并统筹考虑居留返乡和再迁移三元选择的重要意义。     

Consistent long-term Holocene warming trend at different elevations in the Altai Mountains in arid central Asia

Recent results indicate contrasting Holocene moisture histories at different elevations in arid central Asia (ACA). However, relatively little is known about Holocene temperature changes at different elevations. Here we report an independently dated peat brGDGTs-based MBT'_5ME record from the Narenxia peatland (NRX) in the southern Altai Mountains. The record suggests a long-term warming trend since ~7.7 cal. kyr bp , with a warmer stage during ~7–5.5 cal. kyr bp , a cold stage during ~5.5–4 cal. kyr bp , and a warming trend over the last ~4 kyr. The long-term warming trend indicated by the NRX MBT'_5ME record is largely consistent with Holocene temperature records from nearby sites covering an altitudinal range of ~1700–4100 m above sea level. This consistent long-term warming trend at different elevations differs from the long-term Holocene drying/wetting trends at high/low elevations of the Altai Mountains. We propose that the warming trend and consequent permafrost thawing at high elevations could have resulted in increased meltwater runoff, which would have contributed to the long-term wetting trend at low elevations. Our findings potentially provide an improved understanding of regional climate change and associated water resource availability, with implications for their possible future status.     

银行业结构与经济增长——基于京津冀经济圈和长三角经济圈的比较研究

银行业结构与经济增长之间的关系是经济学界较为关注的问题,尤其是中国的银行业结构与快速发展的中国经济之间的微妙关系更为国内经济学家所关注。选取中国经济较为发达的京津冀经济圈和长三角经济圈作为研究样本,把银行业结构变量引入通常的经济增长模型,采用1987—2007年的面板数据对我国京津冀经济圈和长三角经济圈的银行业结构与经济增长的关系进行了对比分析。结果表明,与长三角经济圈相比,京津冀经济圈银行业集中度的降低将对经济增长更为有利,降低京津冀经济圈银行集中度将会给该地区的经济增长带来新的动力。最后,提出优化京津冀经济圈银行业结构的建议。     

基于农业地质调查成果的开封市土壤质量综合评价

从土壤质量的内涵出发,选取农业地质调查中土壤环境质量、肥力与健康质量的土壤地球化学指标,采用内梅罗指数、加权指数和模型及综合比较分析等方法对开封市的土壤质量进行评价。开封市土壤质量由高至低划分为5个等级,其中土壤环境质量1级到5级的面积比例分别为99.13%,0.39%,0.37%,0.05%,0.05%,仅极少量的城市郊区土壤表现出一定程度的污染;土壤肥力与健康质量1级到5级面积比例分别为0.35%,26.65%,46.27%,17.20%,9.53%;土壤综合质量1级到5级的面积比例依次为0.04%,26.50%,46.47%,17.34%,9.65%。本研究拓展了农业地质调查成果的应用范围,所采用的研究方法减少了单项指标评价的单一性,提高了评价结果的科学性。应用叠加法直观地显示出单项质量评价结果与综合评价结果存在的差异,为评价成果的应用奠定了基础。综合评价结果对农业生产布局、粮食安全和绿色产能评价等具有实践意义。     

西安市城镇化进程中人口与土地协调发展研究

选取西安市为研究区域,建立人口与土地协调发展综合评价指标体系,运用因子分析法和协调发展度模型定量分析西安市2002—2012年城镇化进程中人口与土地的协调发展状况。2002—2012年西安市人口城镇化指数和土地城镇化指数均呈逐年上升态势,2006年之前为土地城镇化滞后型,之后为人口城镇化滞后型;人口与土地协调发展度呈逐年波动上升趋势,协调发展度由2002年的0.154 0上升为2012年的0.976 8;人口城镇化系统中人口构成与人民生活水平发展不均衡,人口构成增长较快,人民生活水平基本稳定于较低水平。在新型城镇化进程中,西安市政府应在保持人口与土地优度协调发展态势的同时,着力提高城镇居民的生活水平。     

Where are the prompt emitting regions of long GRBs?

We have used a simple method to estimate the prompt emission radii of 27 Swift and 37 pre-Swift long gamma-ray bursts with known redshift and jet break time. The prompt γ-rays are found to emit mainly from a beamed jet with dynamic open angle narrower than its geometric open angle, suggesting an obviously dynamic evolution from prompt to follow-up phases for the jetted outflow. Under condition of the external shock scenario, we confirm that long gamma-ray bursts are produced at a larger radius of ∼10¹⁶ cm, which puts a strict constraint on the currently theoretical models.     

Compensatory growth in hybrid tilapia (<Emphasis Type="Italic">Oreochromis mossambicus ×O. niloticus</Emphasis>) reared in seawater,following restricted feeding

Hybrid tilapia weighing 7.71 g were reared in seawater at 24.0–29.0°C for 8 weeks. The controls were fed to satiation twice a day throughout the experiment, whereas treatment groups were fed at 0.5%, 1.5% or 3.0% body weight per day for 4 weeks, and then to satiation for the remainder of the experiment. During the first 4-week period, there was a curvilinear relationship between growth rate and ration size. Fish fed 0.5% and 1.5% rations displayed compensatory growth response of 2 weeks duration during realimentation. The weight-adjusted growth rate of fish fed at 3% ration was not significantly different from that of the controls by the end of the experiment, when none of the treatment groups had caught up in body weight with the controls. Hyperphagia was observed for the first 2 weeks of realimenatation in fish previously fed at 3% ration, but persisted for the whole realimentation period in groups previously fed at 0.5% and 1.5% rations. None of the feed restricted groups showed improved digestibility, feed efficiency, or protein and energy retention efficiency. Supported by the State Key Laboratory of Freshwater Ecology and Biotechnology of China and Shanghai Fisheries University (Grant No. 200015).     

近55年来云南区域性干旱事件的分布特征和变化趋势研究

本文利用一种简化的区域性干旱事件识别方法,对近55年来云南区域性干旱事件进行了识别,在此基础上,选取区域性干旱事件的持续天数、影响站点数、平均强度、累积强度和极端最大强度这5个单一事件评价指标,构建了云南区域性干旱的综合评估模型,确定干旱等级划分标准。进一步分析表明,云南区域性干旱的发生频次、累积强度和累积影响站次均呈现上升趋势;云南在12、1和3月干旱发生最多,7、8月干旱发生最少;干旱持续天数集中在15～45 d,最长的可达222d;云南多发全省性的干旱且旱情偏重。云南中部区域干旱偏多、偏重发生;在严重的干旱事件中,中部型发生频次最多。     

旅游小企业成长路径及其驱动机制——以世界文化遗产地宏村为例

以世界文化遗产地宏村为例,借助企业成长理论,采用深度访谈和非参与观察等研究方法,探求遗产地旅游小企业成长路径及其驱动机制。宏村旅游小企业的创立、发展、退出是一个动态的过程。在企业家精神和市场需求双重因素作用下,社区居民利用民居开展经营,实现了身份转化和场所转变,创立了旅游小企业。发展过程中,受遗产保护限制和市场竞争压力,旅游小企业主群体分化,成长意愿不足的小企业主通过租售退出市场,推动新的小企业创立;具有成长意愿的旅游小企业通过模仿创新、代际传承、连锁扩张、抱团经营和品牌加盟等路径实现企业成长。研究发现,一体化、多元化、跟随、抱团等企业成长战略,以及家族企业的内部传承等共同构成了旅游小企业成长路径;同时,遗产保护、市场消费升级等旅游发展因素驱动了旅游小企业成长的循环更新。     

东亚和南亚夏季风对中国季风区径流深影响

为揭示中国东部季风区径流深对东亚和南亚夏季风变化的响应规律,建立了八大流域VIC(Variable Infiltration Capacity)水文模型以及应用了Mann-Kendall和局部加权回归分析(Locally Weighted Scatter Plot Smoothing, LOWESS)相关性检验方法,并分析了径流深系数空间变化情况。结果表明:东亚夏季风与径流深显著性相关范围要明显大于南亚夏季风,主要位于长江流域以北和松花江流域以南的广大地区以及华南部分地区,并分别成正相关和负相关;而南亚夏季风与径流深显著性正负相关的区域则分别位于华南地区及长江流域上游部分地区。此外,季风区径流深系数空间差异明显,易产流区主要位于长江流域及东南沿海地区,而黄河及海河流域则产流较难。因此,对东亚及南亚夏季风的研究可为预测中国东部不同地区的水文过程及水资源变化提供重要的科学参考。