一种推广的Bernstein定理

本文引进了一种新型的Ｂｅｒｎｓｔｅｉｎ多项式，在此基础上推广了经典的Ｂｅｒｎｓｔｅｉｎ定理。     

Designing cropping systems for efficient use of limited water in southern Australia

There has been continuous change in the systems of cereal production in southern Australia where the climate is semi-arid with moderately wet winters and hot dry summers. At the outset wheat (c. 1840) was grown in continuous culture as the land was gradually cleared for cropping, but yields declined to uneconomic levels by 1900. That system was then replaced with fallow-wheat rotations, and using phosphorus fertilizer, yields recovered, but not to the original level. From 1945, the high profitability of sheep production encouraged improvement of legume-based pastures and the introduction of pasture-crop sequences – ley-farming. Productivity was greatly increased and the yield of wheat crops regained the original level. But such were the rates of acidification and salinization of soil that reduced productivity and, in the case of salinity, reduced stream quality and threatened adjacent natural ecosystems. This ley-farming system was used until the late 1980s when prices for wool fell dramatically, and farmers reduced sheep numbers and intensified cropping. The thrust since then has been to design cropping systems that are economically as well as environmentally acceptable with salinity control as the major objective. There is now a search for systems that use more water to reduce drainage through the soil and lower saline water tables. A major contribution is the much restricted use of fallow but summer active plants are also required to provide a soil water storage buffer to retain autumn–winter rainfall. New systems under evaluation include herbaceous perennials such as lucerne that are readily integrated into a crop-livestock system and agroforestry combinations with various trees. The design and appropriate distribution of the new systems is aided by remote sensing techniques to locate areas of saline discharge and linkages to zones of groundwater recharge, geographical information systems to arrange the data for land system analysis, and computer models of crops and cropping systems. There is a substantial challenge for farmers, agronomists and others to identify and assess suitable new systems and to bring the public into the debate and into the solution.     

Land-use legacy of historical tree harvesting for charcoal production in a semi-arid woodland

Historical processes may have longer lasting effects in arid forest and woodlands because of slow rates of succession. We investigated the influence of historical tree harvesting upon contemporary spatial dynamics of pinyon-juniper woodland in the western United States. Despite intensive and widespread harvesting of woodland by the charcoal industry during the late 19th century, the role of afforestation has seldom been addressed as a potential mechanism for the dramatic expansion of pinyon-juniper woodlands over the past century. Spatial models of disturbance processes are one way to ascertain effects of such historical influences. We developed a process-based spatial model to estimate the historical tree harvest pressure according to a parsimonious set of rules and constraints. The model used a convection-diffusion approach that incorporated the influences of topography, transportation, and mining production. We used a combination of field-surveyed, archaeological, historical, and GIS data sets to calibrate, validate, and compare the alternative mathematical models. Model results were consistent with the historical harvest evidence (AUC > 0.66), with high harvest intensity closer to the mining districts, quickly decreasing at the maximum distance of influence. Performance was improved by including the local terrain. Harvesting initially showed radial patterns emanating from the significant mining districts, and then gradually expanded northward with development of the railway system. Our spatial modeling approach provides a means to assess the pattern and magnitude of historical tree harvesting in semi-arid woodlands. The general approach can be applied to explore the importance of other historical disturbance and cultural processes, whose effects may no longer be evident, in forests and woodlands worldwide.     

History matters: Impact of historical land use on butterfly diversity in clear-cuts in a boreal landscape

In Swedish boreal landscapes, the loss of species-rich semi-natural grasslands is largely due to a long history of agricultural abandonment. Large areas historically managed as meadows have become mature coniferous forest. This study focused on the potential biological legacy following a long period of grassland abandonment. The butterfly fauna in clear-cuts which was historically meadows and abandoned long enough to allow a generation of conifers to mature (70-90 years) was compared with clear-cuts which were historically coniferous forest. The results showed that clear-cuts historically managed as meadows were: (i) much richer in individuals, (ii) more species-rich, and (iii) contained many more grassland specialists than clear-cuts with a history as forest, with many of these species threatened in other parts of Europe.The results from our study demonstrate for the first time, to our knowledge, that the legacy of historical land-use in remnant plant communities can affect butterfly diversity in clear-cuts and hence the large-scale dynamics over a timescale of a full tree rotation. The results of this study have implications for forest management practices. Replanting clear-cuts on land that was previously meadows with deciduous trees or allowing the forest to regenerate naturally instead of planting conifers would make it possible to preserve a greater diversity of habitats for butterflies and other organisms.     

Analysis of land-cover transitions based on 17th and 18th century cadastral maps and aerial photographs

This paper explores the possibility of using non-geometric cadastral maps from the 17th and 18th century together with aerial photographs from 1945 and 1981 to analyse land-cover change in south-east Sweden. Habitats rich in plant species in the European rural landscape seem to be correlated with a long continuity of management. Accurate spatial data from historical data sources are fundamental to understand patterns of vegetation and biodiversity in the present-day landscape. However, traditional methods for rectification of non-geometric maps using corresponding points from orthophotos or modern maps are not satisfying, as internal inaccuracies will remain in the maps. This study presents a method to rectify the maps by local warping, thereby eliminating geometrical irregularities. Further, the land-cover changes were calculated and presented as transition matrices. The extent of arable fields and grasslands were analysed in relation to soil characteristics and continuity of management. The results show a dynamic relation between grassland and arable field, albeit the overall proportions remained almost the same between 17th and 18th centuries: 60% grassland to 32% arable field. The most substantial changes in land-cover were prior to 1945. Today there is 18% grasslands left in the study area, while 56% of the land-cover is arable field. Approximately 8% of present-day land-cover is semi-natural grassland 300 years of age or more. Compared to 300 years ago there is only 1% grassland left on peat and 2% on clay. In contrast, grassland covers associated with bare bedrock have been fairly stable in size. All semi-natural grasslands with a long continuity of management were situated on shallow soils, less than 50 cm depth. The major conclusions from this study are that (i) correctly rectified, old maps are very useful to address questions of land-cover changes in historical time, (ii) general trends in land use over 300 years in this hemi-boreal landscape seem to underestimate the full dynamics of land use change, and (iii) only a small proportion of the semi-natural grassland area had a 300 year continuity of management.     

Burrow systems of endogeic earthworms: Effects of earthworm abundance and consequences for soil water infiltration

By creating burrows, earthworms influence the transfer properties of soils. The effects of endogeic species on soil transfer properties, however, are not yet well understood because these earthworms generally create burrows that are refilled by casts and have no preferential vertical orientation. Thirty soil cores were incubated for various periods (1–3 or 4 weeks) at different earthworm densities (70, 210, 345 or 480 individuals m⁻²). The cores were then scanned using X-ray tomography and the burrow systems were characterised by measuring the total burrow volume, bioturbation volume (refilled burrows and lateral compaction around the burrows), the number of branches, tortuosity and continuity (assessed by computing the number of burrows with a vertical extension greater than 15, 20 and 25% of the core). We also computed the mean geodesic distance, i.e. the mean distance from the bottom to the top of the core assuming that distances inside burrows are null. Rainfall simulations were carried out on 17 cores chosen to encompass the variations observed in the burrow systems. The water transfer efficiency of each core was estimated by measuring two parameters: breakthrough volume and the percentage of water transmitted after 1 h of rain. Burrow and bioturbation volume increased significantly and steadily with time and earthworm density. We estimated that on average Allolobophora chlorotica burrowed 22 cm per week. All other burrow system characteristics also increased with time and earthworm density except the mean geodesic distance, which decreased significantly. This suggests that intraspecific interactions had no significant effect on burrow system geometry. Univariate PLS regressions were used to understand which burrow system characteristics had the strongest influence on water transfer. These regressions showed that the mean geodesic distance was the most important parameter. This means that in addition to individual burrow characteristics, the spatial arrangement of the whole burrow system also had a major effect on transfer properties.     

试析晏式平民教育思想的历史意义及对现代农村教育的价值

晏阳初平民教育思想的目标与对象非常明确,教育内容与方式行之有效。在历史上平民教育思想丰富了乡村教育的内容,实现了教育对象的大众化,教育内容的实用化,教学方法的多样化;促进了教育者信仰的坚定与能力的提高;激发了受教育民众的思想与活力。晏式的平民教育思想对现代农村教育仍有积极的价值导向:现代代农村教育需要"平教专家"的指导,实现农业现代化;需要"四大教育"的推进,实现农民市民化;需要"三大方式"的连锁推进,实现农村城市化,从而更好促进城乡一体化的实现。     

Land use history and historical soil erosion at Albersdorf (northern Germany) — Ceased agricultural land use after the pre-historical period

The Holocene landscape history and historical soil erosion were reconstructed at Albersdorf (Schleswig-Holstein, Germany) from soils and colluvial layers. In contrast to many landscapes in central Europe, agricultural land use and soil erosion were more frequent during pre-historical times, whereas it has almost ceased after the advent of history. Pre-historical soil erosion rates from about 0.1 to 6.9 t ha^− 1 a^− 1 were reconstructed with no significant differences between the prehistoric cultural phases. The study of buried soils within the soil/soil-sediment-sequences provided evidence for an acceleration of soil formation processes probably as a consequence of excessive prehistoric woodland pasture on poor sandy soils.     

苏州环古城西段绿地景观规划

苏州环古城西段绿地景观规划以古城墙和护城河为轴线,利用丰富的历史遗存与原有的城市水系,形成了环古城绿地的西段景观带,完善了城市绿地系统的构建。     

生物资产计量模式选择的思考

概述了生物资产的含义和特征,介绍了我国生物资产计量模式的选择及我国选择历史成本计量模式的原因,并提出了相关建议。