The Spatiotemporal Pattern of Fires in Northern Taiga Larch Forests of Central Siberia

The periodicity of fires in larch forests of Evenkia and their relationship with landscape elements have been studied. Cross-sections with “burns” in them caused by past fires have been analyzed in 72 test plots; the fire chronology encompassed the period from the 15th to the 20th century. The between-fire intervals (BFIs) have been calculated by two methods: (I) on the basis of burns alone and (II) on the basis of burns and the start of growth of the new generation of larch after the earliest fire. The BFI depends on local orographic features; it is 86 ± 11 (105 ± 12), 61 ± 8 (73 ± 8), 139 ± 17 (138 ± 18), and 68 ± 14 (70 ± 13) years for northeastern slopes, southwestern slopes, bogs, and flatlands, respectively. The mean BFIs calculated by methods I and II are 82 ± 7 and 95 ± 7 years, respectively. The permafrost horizon rises at a mean rate of 0.3 cm per year after a forest fire. It has been shown that the number of fires regularly peaks at periods of 36 and 82 years. There is also a temporal trend in fire frequency: the mean BFI was approximately 100 years in the 19th century and 65 years in the 20th century.     

Food aid and food crisis in Sub-Saharan Africa: Statistical trends and implications*

This paper documents the rapid expansion and changes in food aid flows to Sub-Saharan Africa up to mid-1985. Trends for Sub-Saharan Africa as a whole and for the more seriously affected countries are examined, as are the comparative experiences of food aid of individual countries in the region. Table 11 lists the Sub-Saharan African countries and indicates the most seriously affected food-short countries, as defined by the WFP/FAO task force. It should be borne in mind that some practical problems exist in compiling data on food aid. These include lack of availability of reliable data, especially of most recent data; lack of common terminology and definitions; and different accounting systems. These data problems are sometimes a source of confusion. However, the basic facts are clear: food aid gradually emerged during the early 1980s as a resource too often of considerable significance to many countries of Sub-Saharan Africa. These trends were only accelerated with the crisis of 1984-1985. These facts provide a point of reference for further analysis of the sources of the crisis, its actual dimensions and consequences.     

板材成形新技术及其发展趋势(Ⅱ)

介绍了多点成形技术、激光成形技术、冲压智能化技术、成形过程的计算机仿真技术等几种柔性化程度高的板材成形新技术及其发展趋势     

从第31届国际地质大会命题看：地球科学研究的热点和趋势

本文论述了第 31届国际地质大会学科和专题命题情况 ,统计了大会收到的论文和摘要数并将各命题重新排序。将位于前 12位的学科和前 5位的专题命题进一步列出重点讨论题目和摘要数。通过与第 30届国际地质大会命题的比较 ,试图大致了解国际地球科学研究的热点和趋势 ;通过上述分析和了解 ,就地球科学与可持续发展阐述了笔者的认识 ,提出了地球科学基础性研究和应用基础研究的重点领域     

遂宁市城区大气中二氧化硫、二氧化氮和总悬浮颗粒物的污染现状及其成因分析

依据近5年的环境空气监测基础数据，分析评价了遂宁市城区大气中周报监测项目(二氧化硫、二氧化氮、总悬浮颗粒物)的污染现状，并对其变化趋势及其成因进行了系统分析。     

SUMMER LOW FLOWS IN NEW ENGLAND DURING THE 20TH CENTURY1

ABSTRACT: High springtime river flows came earlier by one to two weeks in large parts of northern New England during the 20th Century. In this study it was hypothesized that late spring/early summer recessional flows and late summer/early fall low flows could also be occurring earlier. This could result in a longer period of low flow recession and a decrease in the magnitude of low flows. To test this hypothesis, variations over time in the magnitude and timing of low flows were analyzed. To help understand the relation between low flows and climatic variables in New England, low flows were correlated with air temperatures and precipitation. Analysis of data from 23 rural, unregulated rivers across New England indicated little evidence of consistent changes in the timing or magnitude of late summer/early fall low flows during the 20th Century. The interannual variability in the timing and magnitude of the low flows in northern New England was explained much more by the interannual variability in precipitation than by the interannual variability of air temperatures. The highest correlation between the magnitude of the low flows and air temperatures was with May through November temperatures (r =?0.37, p= 0.0017), while the highest correlation with precipitation was with July through August precipitation (r = 0.67, p > 0.0001).     

2010—2019年台州市市区降水化学组成特征及变化趋势

为了解台州市市区大气降水化学成分组成特征及变化规律,对2010—2019年台州市市区降水监测数据进行了统计分析。结果表明:2010—2019年降水样品pH为4.20～4.84夏高冬低,强酸性降水频率下降显著,电导率平均值为3.16 mS/cm。SO₄^2-和NO₃^-是降水中最主要的阴离子,NH₄⁺和Ca²⁺是降水中最主要的阳离子。Ca²⁺浓度在2018年开始有所抬升,SO₄^2-和NO₃^-浓度整体呈波动下降趋势。SO₄^2-与NO₃^-浓度比均值为1.50,呈下降趋势,同大气中SO₂与NO₂的质量浓度比变化趋势基本一致。SO₄^2-和NO₃<...     

中亚热带次生林成林规律及经营技术研究——Ⅲ.次生林数量动态与经营的生态经济对策

本文通过种群自我调节的规律以及Leslie模型进行数量动态分析,从而提出了次生林数量动态与经营的生态经济对策。     

污水分析方法监测城市毒品滥用长期趋势

毒品滥用问题是全球广泛关注的社会问题,对城市毒品滥用情况进行长期监测具有重要意义.采用污水流行病学的方法,对大连市毒品的滥用情况进行连续长期调查.2020～2021年采集大连市22个污水处理厂的进口污水,通过气相色谱衍生化方法分析测定甲基苯丙胺、海洛因、氯胺酮、摇头丸和可卡因的生物标志物的浓度,即其尿液代谢产物甲基苯丙胺、吗啡、氯胺酮、摇头丸和苯甲酰芽子碱.结果表明,2020年p(甲基苯丙胺)、p(吗啡)和p(氯胺酮)均值分别为23.69、23.21和2.40 ng·L-1;2021年均值分别为20.64、20.92和0.47 ng·L-1,在所有的污水样品中均未检测出摇头丸和苯甲酰芽子碱,根据相关信息估算5种毒品的人均滥用量,并结合往年监测数据分析大连市这5种毒品的滥用趋势.甲基苯丙胺和海洛因滥用量均在2019年有上升趋势,2020大幅度下降,2021年基本保持不变;氯胺酮的滥用则一直处于较低水平.本研究为大连市实时监控毒品滥用情况提供科学依据,对防治毒品犯罪具有重要意义.     

五常流域拉林河水环境现状、变化趋势及防治对策

本文运用单因子指数细致分析了五常流域拉林河水环境质量现状,运用秩相关系数定量研究9a的水环境污染变化趋势,明确提出了防治水污染的主要对策。