人口流动对区域老龄化进程的影响——一个方法论探讨     

刘涛  张家瑞  曹广忠 《地理研究》2022,41(10):2680-2696

持续活跃的迁移流动不仅深刻改变着中国的人口分布格局,也已成为影响区域人口结构的关键因素。为量化估计人口流动对老龄化进程的影响,本研究构建了一个方法论框架,将人口流动的作用分解为规模效应和年龄结构效应,并从地级尺度分析中国人口流动对区域老龄化进程的作用,解读其空间规律和内在机制。总体而言,人口流动导致多数地区老龄化加深,仅有少数地区的老龄化得到缓解;人口流入对老龄化的降低作用和流出的提升作用并非绝对。人口流动的老龄化效应具有显著的空间分异和聚散特征：“胡焕庸线”是重要分界,人口大量流入的东部沿海城市群、内陆省会等区域性中心城市、西部多数地区降低作用突出,人口大量流出的长江中上游和淮河流域提升作用明显。规模效应在人口流动对老龄化及其空间格局的影响中发挥主导作用;按流入、流出分解后,结构效应的解释力得以体现。规模和结构效应在不同地区存在差异化的作用模式。最后开展了类型分析,并探讨了各类型区人口流动影响老龄化的特征和未来趋势。  相似文献   

固体火箭发动机粘接界面湿热老化实验     

张晓军  常新龙 《贵州气象》2013,(4):557-561

对固体火箭发动机粘接界面试验件进行了不同湿热条件下的加速老化试验,并测量了不同老化时间粘接界面的扯离强度,描述了湿热老化试验和性能测试中的试验现象,结合复合材料微粘接结构吸湿规律对试验现象和撤离强度随老化时间变化曲线进行了分析。研究结果表明:衬层-推进剂粘接界面是固体火箭发动机粘接结构中最薄弱环节,应予以重点考虑;湿热老化促进了环境水分从衬层–推进剂界面向推进剂内部的扩散和渗透,致使弱边界层向推进剂内部扩展,导致了衬层-推进剂界面粘接强度的降低。试验件平均扯离强度随老化时间呈下降趋势,中间有一个强度趋于稳定的平台期。   相似文献   

广东省医疗与养老设施空间格局、适老化与均等性——基于空间可达性的评价     

刘婷  胡伟平 《热带地理》2022,42(12):1993-2006

以广东省为例,采用改进两步移动搜索法测算医疗与养老设施可达性,然后采用自相关分析法、基尼系数分析医疗与养老设施的适老化及均等性,最后运用Spearman相关系数对医疗与养老设施可达性及均等性的影响因素进行分析。结果表明：1）改进两步移动搜索法更能准确反映医疗与养老设施可达性,珠三角地区老年人医疗、养老设施可达性相对较好,东、西部沿海经济区相对较差;但珠三角地区养老设施医疗可达性在四大区域中最差。2）广佛都市区、梅州市北部等地区的医疗与养老设施适老化不足,广东省医疗与养老设施可达性存在较大的不均等。3）路网密度、人口密度、人均GDP、公共财政支出与广东省医疗、养老设施可达性显著相关,平均海拔、生态环境状况指数、面积、路网密度、人口密度、人均GDP、公共财政支出与广东省老年人医疗、养老设施可达性的均等性显著相关。  相似文献   

Techniques for assessing spatial heterogeneity of carbonate δ13C values: Implications for craton‐wide isotope gradients     

J. Garrecht Metzger  David A. Fike 《Sedimentology》2013,60(6):1405-1431

The sedimentary record of carbonate carbon isotopes (δ¹³C_carb) provides one of the best methods for correlating marine strata and understanding the long‐term evolution of the global carbon cycle. This work focuses on the Late Ordovician Guttenberg isotopic carbon excursion, a ca 2·5‰ positive δ¹³C_carb excursion that is found in strata globally. Substantial variability in the apparent magnitude and stratigraphic morphology of the Guttenberg excursion at different localities has hampered high‐resolution correlations and led to divergent reconstructions of ocean chemistry and the biogeochemical carbon cycle. This work investigates the magnitude, spatial scale and sources of isotopic variability of the Guttenberg excursion in two sections from Missouri, USA. Centimetre‐scale isotope transects revealed variations in δ¹³C_carb and δ¹⁸O_carb greater than 2‰ across individual beds. Linear δ¹³C_carb to δ¹⁸O_carb mixing lines, together with petrographic and elemental abundance data, demonstrate that much of the isotopic scatter in single beds is due to mixing of isotopically distinct components. These patterns facilitated objective sample screening to determine the ‘least‐altered’ data. A δ¹⁸O_carb filter based on empirical δ¹⁸O_carb values of well‐preserved carbonate mudstones allowed further sample discrimination. The resulting ‘least‐altered’ δ¹³C_carb profile improves the understanding of regional as well as continental‐scale stratigraphic relations in this interval. Correlations with other Laurentian sections strongly suggest that: (i) small‐scale variability in Guttenberg excursion δ¹³C_carb values may result in part from local diagenetic overprinting; (ii) peak‐Guttenberg excursion δ¹³C_carb values of the Midcontinent are not distinct from their Taconic equivalents; and (iii) no primary continental‐scale spatial gradient in δ¹³C_carb (for example, arising from chemically distinct ‘aquafacies’) is required during Guttenberg excursion‐time. This study demonstrates the importance of detailed petrographic and geochemical screening of samples to be used for δ¹³C_carb chemostratigraphy and for enhancing understanding of epeiric ocean chemistry.  相似文献   

An Analysis of the Commuting and Jobs–Housing Patterns of Older Adult Workers     

Mark W. Horner  Daniel K. Schleith  Michael J. Widener 《The Professional geographer》2013,65(4):575-585

Many researchers have explored the relationships between land use and transportation via the jobs–housing balance concept. This type of research involves the disaggregation of commuter groups to understand variances in the relationship between land use and transportation outcomes. Disaggregation by commuter age has not been considered, however. To address this gap, we analyze spatially and temporally disaggregate census data for five areas in Florida. Using several jobs–housing balance metrics we compare and contrast the outcomes of different commuter age groups, across different geographies, and over time (2002–2011). Generally, commutes vary more by region than they do by any age category of commuter. Most of the differences in the commute metrics among the older age group tend to depend on where those commuters live. The results also suggest that there are more efficient and less sprawling commuting landscapes for older workers located near other older workers.  相似文献   

Modulation of longevity in Daphnia magna by food quality and simultaneous exposure to dissolved humic substances     

Rihab Bouchnak  Christian E.W. Steinberg 《Limnologica》2010,40(2):86-91

Various abiotic and biotic factors determine the natural fluctuations of Daphnia spec. populations; food quality and dissolved humic substances (HSs) being among these factors. In this contribution, we try to disentangle the relative impact of food quality and simultaneous HSs exposure on the fertility and longevity of D. magna. It is understood that HS-mediated stress leads to reduced fecundity in well-fed D. magna females; hence, it was expected that poor food, as a second stressor, would aggravate the HS-mediated effects. Three diets were tested: the green algae Pseudokirchneriella subcapitata, baker’s yeast alone, and baker’s yeast plus dissolved ascorbic acid, and exposed D. magna to a HS preparation which has been shown effective in previous bioassays. It was hypothesized that the lifespan and fertility of D. magna would be best when fed green algae, and worst when fed only baker’s yeast. However, contrary to these expectations, any addition of HSs reduced the stress caused by poor food quality and increased lifespan and fecundity. In the yeast series, asexually produced diapausing eggs occurred via a so far unknown pathway. With yeast diet, the expanded lifespans were slightly above, whereas the increased offspring numbers lay below, the corresponding data of the algae-fed individuals. The potential of HSs as an additional food source and as a means to extend the lifespan is discussed. These findings open the innovative perspective that under low quality food conditions, additional stressors at certain intensities may even be beneficial to individuals and populations.  相似文献   

Clay slides in the Målselv valley, northern Norway: Characteristics, occurrence, and triggering mechanisms     

Raymond S. Eilertsen  Louise Hansen  Terje H. Bargel  Inger-Lise Solberg 《Geomorphology》2008,93(3-4):548-562

The distribution of a large number of clay slides in the Målselv valley, northern Norway, is analysed and put into context with the stratigraphic organization of the valley-fill sediments. About 32% of the landslides larger than 10⁴ m³ occur close to the valley margins, where mud is either exposed or at shallow depth. About 57% of the landslides occur mid-valley, where relatively thin (< 15 m) coarse-grained deltaic sediments overlay fine-grained marine and glaciomarine sediments, and about 11% of the landslides occur in front of ice-contact deposits. The slide-prone areas are all characterized by the occurrence of heterogeneous sediments (interbedded clay, silt and sand), in addition to the presence of steep slopes eroded by rivers. The heterogeneous nature of the sediments probably enhanced groundwater drainage and leaching of salts from the clay, increasing sensitivity. Thus, the distribution and organization of the valley-fill sediments and groundwater drainage probably controlled the position of the slide scars and sliding planes. Since deglaciation of the valley (11,500 BP–present), isostatic rebound has enhanced fluvial incision and the creation of steep slopes due to a fall in relative sea level of up to 80 m.Arcuate-shaped, ‘bottleneck’ landslide scars ranging from c. 10⁴ to 10⁷ m³ in size is the dominant morphological signature of the slides, typical for quick clay slides or earth flows involving fluid mud. Their most common triggering mechanism is probably erosion at the toe slopes by the river Målselv or its tributaries. River erosion close to the valley margin, where glaciomarine and marine sediments are present, seems to give the most severe slides. The overall valley-fill organization controls the distribution of clay slides, which may apply to other fjord valleys having similar sediment distribution.  相似文献   

城市养老设施配置的微观模拟与规划政策分析——以北京市为例     

颜秉秋  高晓路  季珏 《地理科学进展》2015,34(12):1586-1597

养老设施规划配置的关键应着眼于老年群体对养老服务的差异化需求及其动态变化特征。本文提出了基于多主体模拟的理论框架,并通过对前期研究的梳理,归纳出养老机构配置问题中需要考虑的老年人、养老机构等主体的时间变异和空间差异特征、其行为规则以及他们与环境之间的相互作用规律。在此基础上,以北京市为例构建了多主体微观模拟模型,对2010-2030年间养老机构需求与供给态势进行了预测,并讨论了养老设施布局的评估指标,通过设施利用率、百人床位数和空间匹配度等指标,对北京市养老服务设施的规划政策进行了评估。研究表明,多智能体模拟技术对把握人口动向及养老服务需求的不确定性和动态变化特征而言是一个十分有效的研究工具,能够很好地体现各种要素的空间属性。对于北京市的“9064”养老服务规划和养老设施专项规划的分析表明,如果仅仅对养老模式的分担比例和百人床位数进行控制,而忽视对空间布局的管控,养老机构床位空置率有可能出现继续上升的趋势,为此,必须制定城市中心区养老机构的比例,同时对养老机构的定价、选址和服务质量采取必要的管控措施。  相似文献   

Using fluidized bed and flume experiments to quantify cohesion development from aging and drainage          下载免费PDF全文

Sayjro Kossi Nouwakpo  Chi‐hua Huang  Mark A. Weltz  Flavia Pimenta  Isis Chagas  Luiz Lima 《地球表面变化过程与地形》2014,39(6):749-757

Temporal variations in soil erosion resistance are often the result of decreased soil cohesion due to physical disruption followed by a regain of soil strength through a process called aging, stabilization or consolidation. The goal of this study was to quantify changes in soil cohesion due to aging and subsurface hydrologic condition using a fluidized bed method. A flume experiment was also used to verify that findings from the fluidized bed experiment translated into measurable changes in soil erodibility. Tests were performed on three different soils (a Miami soil, a Cecil soil and Crosby–Miami soil complex). Changes in soil cohesion due to aging and drainage state were successfully detected by the fluidized bed technique. For all soils tested, cohesion developed in a two‐stage process where an increase in cohesion with aging duration immediately after the soil was rewetted, was followed by a decrease in cohesion which often started after 24 h of aging. When soils were aged at field capacity, the resulting cohesion measured by the fluidized bed method was on average 3.13 times higher than that measured when aging was performed at saturation. Trends in soil rill erodibility K_r with aging duration measured in the flume experiment were consistent with the two‐stage pattern observed in soil cohesion estimates but the legacy effect of suction applied at field capacity faded after 72 h of aging. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

高地应力区大型洞室锚索时效受力特征及长期承载风险分析     

董志宏  丁秀丽  黄书岭  邬爱清  陈胜宏  周钟 《岩土力学》2019,(1):351-362

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