Localization, interactions, and the metal-insulator transition

Recent advances in our understanding of electronic conduction have pointed up deficiencies in traditional thinking. For a metal at a sufficiently low temperature, it is known both theoretically and experimentally that the conventional picture in terms of the Boltzmann theory breaks down. Improved understanding of both electron localization and the effects of electron-electron interactions in a disordered medium has led to experimentally verifiable predictions. These effects have an important influence on the nature of the metal-insulator transition.     

城乡转型背景下林区劳动力非农就业影响因素分析——以福建省三明市为例

农民就业是我国面临的重大经济与社会问题。在人多地少等多种因素下,农业自身无法吸纳我国庞大的农村剩余劳动力,只有实现向非农产业的转移,才能逐步解决农村剩余劳动力的就业问题。利用福建省三明市的12个村84户农民的样本数据,通过Logistic回归模型对影响林区劳动力非农就业的因素进行了分析。结果表明,有劳动力外出务工的农户占76.2%。随着林农受教育程度的提高,林农对身份转变的认识显著提高,非农就业意愿明显增强。家庭人数越多,小孩越少,劳动力流动率就越高。人均林地面积越丰富,林业对劳动力的粘性就越强,林农外出务工的意愿下降。务农收入和农村非农产业收入是农户决定其成员是否流动所参考的重要依据。重视微观层次的户主禀赋、家庭特征、林地禀赋和收入差异,对于促进林区劳动力外出务工具有重要意义。     

A surface-tailored, purely electronic, mott metal-to-insulator transition

Mott transitions, which are metal-insulator transitions (MITs) driven by electron-electron interactions, are usually accompanied in bulk by structural phase transitions. In the layered perovskite Ca(1.9)Sr(0.1)RuO4, such a first-order Mott MIT occurs in the bulk at a temperature of 154 kelvin on cooling. In contrast, at the surface, an unusual inherent Mott MIT is observed at 130 kelvin, also on cooling but without a simultaneous lattice distortion. The broken translational symmetry at the surface causes a compressional stress that results in a 150% increase in the buckling of the Ca/Sr-O surface plane as compared to the bulk. The Ca/Sr ions are pulled toward the bulk, which stabilizes a phase more amenable to a Mott insulator ground state than does the bulk structure and also energetically prohibits the structural transition that accompanies the bulk MIT.     

制度的形成、产权与农地流转

运用制度形成原理及产权理论解释了我国农地流转制度形成的困境,地方集体组织与政府、农户之间相悖的利益关系以及农户残缺的农地产权是农地流转发展缓慢的主要原因。地方集体组织利用职权通过对农户农地产权的侵蚀以达到自身利益最大化的行为已经严重阻碍了农业的发展,依靠政府的力量变革农村中的部分生产关系、削弱地方集体组织的权利是农地新制度形成的关键所在。     

Strategies for increasing the capture,storage, and utilization of precipitation in semiarid regions

Crop production in semiarid regions is always challenging because of the high variability of amount and distribution of precipitation.These regions become more important each year, however, because the rapidly increasing and more prosperous world population seeks greater consumption of animal products(meat, milk and eggs) that requires additional grain to that consumed directly.The dry areas of the developing world where approximately 40% of the world population lives comprise about 40% of the earth's land area.Crop production, particularly cereal grains, must increase in these areas to meet these growing demands.Grain yield of cereal crops is a function of the amount of water used for evapotranspiration(ET), the portion of ET used for transpiration(T), the units of water as T to produce 1 unit of biomass, and the harvest index(HI).The most important factor is the amount of evapotranspiration not only because it is closely proportional to grain yield, but because it tends to also make the other factors more favorable.Therefore, even small increases in ET can be significant.Strategies for manipulating soil and plant conditions for increasing ET, and how additional ET affects the other factors, are discussed for water deficient areas.The use of crop residues as mulch is highly beneficial but often insufficient in dryland regions or is required for animal feed and fuel.Plastic mulch, mainly restricted to China, has significantly increased grain yields in dryland areas by decreasing evaporation from the soil surface.     

Peanut yield,nutrient uptake and nutrient requirements in different regions of China

Nutrient balance is essential for attaining high yield and improving profits in agricultural farming systems, and crop nutrient uptake ratio and stoichiometry can indicate crop nutrient limitations in the field. We collected a large amount of field data to study the variations in yield, nutrient uptake and nutrient stoichiometry of peanut(Arachis hypogaea L.) in Southeast China(SEC), North-central China(NCC), and Northeast China(NEC), during 1993 to 2018. Peanut pod yield gradually increased from 1993 to 2018, with average yields of 4 148, 5 138, and 4 635 kg ha–1 in SEC, NCC, and NEC, respectively. The nitrogen(N) internal efficiency(NIE, yield to N uptake ratio) was similar among the three regions, but phosphorus(P) IE(PIE, yield to P uptake ratio) changed from low to high among regions: NCCSECNEC, while potassium(K) IE(KIE, yield to K uptake ratio) portrayed a different pattern of SECNCCNEC. Based on the nutrient IE, to produce 1 Mg of pod yield, the average N, P, and K requirements of the above-ground parts of peanut were roughly 47.2, 5.1, and 25.5 kg in SEC, 44.8, 5.7, and 20.6 kg in NCC, and 44.6, 4.4, and 14.7 kg in NEC, respectively. The N/P ratio changed in the sequence NCCSECNEC, and the N/K ratio was similar in NEC and NCC, but lower in SEC. The N harvest index(HI) and KHI declined with increasing nutrient uptake across all regions under high nutrient uptake. The low PIE and N/P ratios in NCC could be explained by the high P accumulation in stover, and high KIE and N/K ratios in NEC may be attributed to the low soil K supply. The frontier analysis approach provides a practical framework and allows documentation of a decline in nutrient HI as nutrient uptake increases. Lastly, this study reveals the limitation and surplus of nutrients of peanut in different regions of China.     

江河源区的生态环境地位初探

为了客观评价江河源区生态环境的重要性,提出了“生态环境地位”的概念,并从区内、青藏高原、黄河与长江流域3方面进行了分析。结果表明,江河源区是青藏高原的重要组成部分,其独特的生态环境是当地生物和居民赖以生存的基础,同时参与青藏高原独特的水文循环及对全球气候和环境的影响;黄河与长江流域的水资源分布受青藏高原的影响,江河源区对黄河流域的贡献主要体现在水量上(48.3%),而对其泥沙及长江流域的水量(1.8%)和泥沙量的输出影响均较小。因此,应正确对待江河源区的生态环境地位,不应夸大局部作用,仍需关注其独特性与变化。     

河北省浅山丘陵区土地利用变化及人文驱动分析

基于地形梯度差异分析浅山丘陵区土地利用变化及驱动因素,有助于针对地形特征进行土地利用规划和调控。本文引入地形位和分布指数,采用叠加法和主成分分析法,基于不同地形梯度,探讨了研究区土地利用变化及人文驱动因素,并提出了相应的土地利用结构调整方向。结果表明:1)Ⅰ区(地形位1-10)海拔较低,地形平缓,为耕地、建设用地和水域的优势分布区,土地利用动态度和土地利用程度最高,土地利用处于发展阶段;主要人文驱动因子为年末总人口、人口密度、地区生产总值、常用耕地面积、化肥施用量、有效灌溉面积、第二产业比重;2)Ⅱ区(地形位11-25)有一定地形起伏,是林草地结合的优势分布区,土地利用动态度与土地利用程度均较低,土地利用处于调整阶段;主要驱动因子为公路里程、农民人均纯收入、第一产业比重;3)Ⅲ区(地形位26-50)海拔高,地形破碎度大,是林地的优势分布区,土地利用动态度和土地利用程度相对最低;主要驱动因子为第一产业比重、常用耕地面积、粮食产量。     

有关江河源区的科学问题

回顾了建国后青藏高原研究的历程,结合实地考察提出了"江河源区"的称谓、范围、经济生态区划、生态系统的主体、自然和人为因素、生物多样性问题、气候演变规律、生态环境的质量评判、重大工程和旅游活动、自然灾害、生态环境地位等11个方面的科学问题。     

江河源区地域界定研究

通过现有的各种文献资料、遥感资料,结合实地考察,确定江河源区主要包括江源地区和河源地区,江源地区主要指长江源区和澜沧江源区,其流域面积约为19.4578万km2;河源地区主要指黄河源区,其流域面积为12.3612万km2(不包括甘川大转弯);江河源区流域面积在青海省境内为31.8190万km2。     

江河源区生态地理区划

利用气候—地貌—植被模式,在充分考虑人类活动因素的基础上,将江河源区划分为黄河东部河谷高原暖温半干旱农牧交错水土流失生态大区、高原凉温带大区、高原冷温带大区、高原寒带大区4个大区;再分别以降水、植被和人类活动为主要因子,将其划分为7个二级区,11个三级区。     

平原河湖地区乡村空间的半网络活力结构模式研究

快速城镇化时期,人口收缩的乡村空间结构变得越发单一化、线型化,从而导致结构可承载的社会交往活力降低,难以满足乡村振兴背景下乡村空间社会、经济、文化可持续发展的需求。本研究借鉴空间活力结构的相关理论与方法,识别传统乡村空间的活力结构类型,发现传统乡村具有节点众多、层间交叠、中度关联的半网络特征,以此构建激发乡村活力的半网络结构模式,并利用该模式通过完善节点构造、巧设跨级交叠、实现中度关联等方式重塑三产融合示范村的结构活力。希冀半网络活力结构模式能推动平原河湖地区的乡村振兴建设。     

西藏东南部边缘地区昆虫多样性的特点

根据西藏东南部边缘地区:墨脱、察隅和米林三县的204科昆虫,分别统计了这三个地区昆虫属和种的数量,其中墨脱昆虫922属、1433种,大大超过西藏已知昆虫的1/3,察隅319属、446种,米林119属、152种;列出了每个地区的珍奇昆虫和特有物种;总结了这些地区物种多样性的种种特点。首先,这些地区昆虫区系的主要组成属于亚热带、热带的区系性质,它们的起源和演化与东洋区的昆虫区系密切相关;第二,这些地区的生态环境复杂,昆虫种类非常丰富,物种的分化十分活跃;第三,这三个地区的特有物种都十分富庶,作为县级行政单位,这种现象在其它地区是非常少见的;第四,这里还保存了众多的古老类群和珍稀物种。     

Temporal dynamics of nutrient balance,plasma biochemical and immune traits,and liver function in transition dairy cows

The objective of this study was to analyze the dynamics of nutrient balance, physiological biomarkers and comprehensive indexes associated with metabolism and function of organs in transition cows. Fourteen transition cows were used for this research. Dietary intake was recorded daily, and samples of the diet, venous blood and milk were collected for measurements. The balance values of net energy for lactation(NE_L), metabolizable protein(MP), and metabolizable glucose(MG) were calculated, and regression analysis and calculation of comprehensive indexes were performed. Accordingly, the prepartum cows presented positive balances of NE_L, MP, and MG, while severe negative balances were found during the postpartum period. Dynamic changes of energy metabolism, nutrient mobilization, liver function, anti-oxidative status and immune response, as indicated by blood biomarkers and modified comprehensive indexes, were out of sync with the calculated balance values, but they were closely related to the day relative to calving. Compared with the 21 d prepartum, the plasma concentrations of non-esterified fatty acids(NEFA) and β-hydroxybutyric acid(BHBA) were significantly increased around and after calving(P0.05), and similar variation tendency was observed for most of other parameters. The occurrence of parturition and the initiation of lactation were more responsible for the negative balances of nutrients in transition dairy cows. Although negative balances of NE_L, MP and MG were not observed using the assessment model, the nutritional strategies should be applied before calving, because metabolic adaptations had been validated during the prepartum period. In addition, it was plausible to conclude that the decline of hepatic metabolism, defense function and insulin sensitivity are critical causes of metabolic dysfunction.     

长三角地区乡村空间变迁特点、存在的问题及对策建议

改革开放特别是进入新世纪以来,长三角地区工业化和城市化互促推进,生产要素加快集聚,市场化水平不断提高,有力推动全地域资源要素的均衡化配置,形成了乡村地区空间高密度均质化转型的独特趋势,主要表现为乡村生产要素非农化、农居布局分散化、村落区位郊区化。但在较大程度上引发长三角地区乡村空间土地利用效率较低、生态环境保护压力较大、产业同质化竞争、城乡二元结构固化等深层次问题。针对这一状况,本文提出完善现有乡村规划建设法律法规,构建新型乡村空间的对策建议。重点是研究制定乡村空间布局、农居建设整治、农田水利及附属设施建设、乡土景观建设等方面的规范和标准,引导长三角地区乡村布局建设向更加规范有序、集聚集约的方向转型。