环境库兹涅茨曲线在文山县城的应用     

丁贤法 《云南地理环境研究》2007,19(3):50-54

环境库兹涅茨曲线认为随着经济发展，环境质量先下降后改善，环境质量与收入之间表现为倒U形曲线，这意味着经济发展最终会解决环境问题。应用这一思想，根据1991～2000年文山县城区大气污染指数及1998～2002年盘龙河水污染物浓度与同期人均居民收入进行了回归分析，发现对多数污染物而言，表现为N形的高次曲线能很好的拟合两者之间的关系，据此提出一种简单但普遍的机理来解释EKC曲线，即经济发展对环境质量的正负反馈作用决定其在涨落中演变。  相似文献   

Origin and stratigraphy of phreatomagmatic deposits at the Pleistocene Sinker Butte Volcano, Western Snake River Plain, Idaho   总被引：1，自引：3，他引：1  

Brittany D. Brand  Craig M. White   《Journal of Volcanology and Geothermal Research》2007,160(3-4):319-339

Sinker Butte is the erosional remnant of a very large basaltic tuff cone of middle Pleistocene age located at the southern edge of the western Snake River Plain. Phreatomagmatic tephras are exposed in complete sections up to 100 m thick in the walls of the Snake River Canyon, creating an unusual opportunity to study the deposits produced by this volcano through its entire sequence of explosive eruptions. The main objectives of the study were to determine the overall evolution of the Sinker Butte volcano while focusing particularly on the tephras produced by its phreatomagmatic eruptions. Toward this end, twenty-three detailed stratigraphic sections ranging from 20 to 100 m thick were examined and measured in canyon walls exposing tephras deposited around 180° of the circumference of the volcano.Three main rock units are recognized in canyon walls at Sinker Butte: a lower sequence composed of numerous thin basaltic lava flows, an intermediate sequence of phreatomagmatic tephras, and a capping sequence of welded basaltic spatter and more lava flows. We subdivide the phreatomagmatic deposits into two main parts, a series of reworked, mostly subaqueously deposited tephras and a more voluminous sequence of overlying subaerial surge and fall deposits. Most of the reworked deposits are gray in color and exhibit features such as channel scour and fill, planar-stratification, high and low angle cross-stratification, trough cross-stratification, and Bouma-turbidite sequences consistent with their being deposited in shallow standing water or in braided streams. The overlying subaerial deposits are commonly brown or orange in color due to palagonitization. They display a wide variety of bedding types and sedimentary structures consistent with deposition by base surges, wet to dry pyroclastic fall events, and water saturated debris flows.Proximal sections through the subaerial tephras exhibit large regressive cross-strata, planar bedding, and bomb sags suggesting deposition by wet base surges and tephra fallout. Medial and distal deposits consist of a thick sequence of well-bedded tephras; however, the cross-stratified base-surge deposits are thinner and interbedded within the fallout deposits. The average wavelength and amplitude of the cross strata continue to decrease with distance from the vent. These bedded surge and fall deposits grade upward into dominantly fall deposits containing 75–95% juvenile vesiculated clasts and localized layers of welded spatter, indicating a greatly reduced water-melt ratio. Overlying these “dryer” deposits are massive tuff breccias that were probably deposited as water saturated debris flows (lahars). The first appearance of rounded river gravels in these massive tuff breccias indicates downward coring of the diatreme and entrainment of country rock from lower in the stratigraphic section. The “wetter” nature of these deposits suggests a renewed source of external water. The massive deposits grade upward into wet fallout tephras and the phreatomagmatic sequence ends with a dry scoria fall deposit overlain by welded spatter and lava flows.Field observations and two new ⁴⁰Ar–³⁹Ar incremental heating dates suggest the succession of lavas and tephra deposits exposed in this part of the Snake River canyon may all have been erupted from a closely related complex of vents at Sinker Butte. We propose that initial eruptions of lava flows built a small shield edifice that dammed or disrupted the flow of the ancestral Snake River. The shift from effusive to explosive eruptions occurred when the surface water or rising ground water gained access to the vent. As the river cut a new channel around the lava dam, water levels dropped and the volcano returned to an effusive style of eruption.  相似文献   

Entropy‐based equation to assess hillslope sediment production     

José Carlos de Araújo 《地球表面变化过程与地形》2007,32(13):2005-2018

A new equation to assess hillslope sediment production, based on physical and probabilistic approaches, is presented. The equation, which allows the computation of the delivery ratio for every event, considers the physical variables of travel distance, stream power, settling velocity and gross erosion. The probability density function that arises from the new formulation is solved using the principle of maximum entropy. Based on data from five watersheds in both tropical and temperate zones, the new delivery parameter K_v is calibrated and associated with vegetation cover and conservation practice. The proposed equation is rationally based in relation to parameter K_v. The entropy‐based equation was applied to assess sediment yield in two other experimental watersheds, showing good predictability for the set (mean absolute error of 20·8%). No systematic error was found in the analysed data. The entropy‐based equation showed good predictability for long‐term sets of data and for high‐erosivity events, but did not perform well for the low‐erosivity ones. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

对青藏高原末次冰盛期降温值、平衡线下降值与模拟结果的讨论   总被引：5，自引：2，他引：5       下载免费PDF全文

施雅风 《第四纪研究》2002,22(4):312-322

1999年 5期《第四纪研究》刊登的“青藏高原冰期环境与冰期全球降温”论文 ,内容丰富 ,提出了许多重大问题和新鲜讯息 ,发人深思。本文就部分内容进行讨论 ,认为根据新近若干冰期降温值较大的信息 ,就得出冰期降温幅度为过去认识的两倍的普遍性推断 ,还为时过早。青藏高原新近研究表明夏季降温值是较小的 ;冰川平衡线高度取决于以夏季温度为标志所提供的消融热量与全年降雪积累量的平衡 ,单纯就降温值 ,不能决定平衡线下降值 ;全球各地气候、地形差别很大 ,冰期变化也很悬殊 ,不存在全球均一的 1 0 0 0m左右平衡线下降值 ,干旱区的下降值多低于此数。青藏高原末次冰盛期 (LGM)冰川堆积 (终碛、侧碛 )和侵蚀形态(冰斗、槽谷 )一般保存良好、形态鲜明 ,较易识别 ,近年已获取测年资料 ,证明过去地貌法判别的LGM冰川规模 ,并以此决定的LGM平衡线位置基本恰当 ,当然也有误判者。从 2 0世纪 2 0年代起 ,研究者逐渐认识高原内部主要是中西部LGM平衡线下降值较小 ,经过多次改进的LGM平衡线高度分布图显示约有 1 /3左右地区 ,平衡线下降值不足 30 0m ,实为世所罕见。其原因可能主要在高原西北部是全球惟一高海拔寒旱核心区域 ,为极大陆型或极地型冰川分布区 ,以现代西昆仑山崇测冰川、古里雅冰帽为例 ,平衡线高度  相似文献   

基于MEM1谱分析的水文时间序列隐含周期特性研究   总被引：13，自引：1，他引：13  

王栋  朱元甡 《水文》2002,22(2):19-23

水文时间序列的隐含周期(本文将简单周期、复合周期及近似周期等统称为隐含周期)的识别、判定是一个重要而又较为困难的问题,相对成熟和有效的做法是对其进行频谱分析。建立在最大熵原理(POME)基础之上的MEM1谱分析,克服了传统谱分析方法的诸多不足,具有频谱光滑、分辨率高等独特优势。为此,以黄河花园口(秦厂)测站年径流系列、月径流系列和年最大洪峰流量序列隐含周期特性的研究为例,探讨了MEM1谱分析在水文时间序列隐含周期特性中的应用。  相似文献   

根据天气类型划分欧洲中期天气预报中心的集合预报产品   总被引：4，自引：0，他引：4  

杨学胜  JeanNicolau  NicoleGirardot 《气象学报》2001,59(2):173-182

该研究的主要目的是找出一种对集合预报产品进行释用的新方法。其基本假定是集合预报要素在一定程度上代表了未来可能发生的天气形势。为了解决天气尺度在中期预报的不可预报性问题 ,引入了天气类型的概念。对集合预报进行划分的方法是 Diday提出的动力模糊法 ,初始划分时的重心由天气类型定义 ,划分用到的距离是位移和最大相关方法。根据城市块 (City- Block)距离找出了影响中国的按冬夏两季划分的天气类型 ,初步划分结果表明 ,欧洲中期天气预报中心的集合预报系统可以预报出横槽转竖型天气类型的演变情况 ,在夏天的预报效果则没有冬天好。  相似文献   

Maximum likelihood environmental calibration and the compute program WACALIB a correction     

H.J.B. Birks 《Journal of Paleolimnology》2001,25(1):111-115

A recently discovered error in the part of the computer program WACALIB that implements maximum likelihood (ML) calibration has been discovered and corrected. The new version of WACALIB has been re-run with all the data-sets from which results based on the earlier version of WACALIB had been published. The new results suggest that ML regression and calibration perform as well or even better than weighted averaging (WA), at least when judged by the apparent root mean squared error. Further work involving cross-validation is required to evaluate more fully the relative performance of WA and ML approaches.  相似文献   

可变电荷土壤和恒电荷土壤与氢离子相互作用机理   总被引：2，自引：4，他引：2  

朱茂旭  蒋新  杨杰文  季国亮  王芳 《地球化学》2001,30(2):194-199

研究了可变电荷土壤和恒电荷土壤与H相互作用的机理，并比较了它们之间的差别，研究结果表明，氢离子输入土壤后可以转化为表面正电荷，可溶性铝和可交换性酸，但是由于土壤的组成和性质不同，不同土壤中H＋三种去向的贡献不同。H＋转化为表面正电荷是由于土壤表面Fe-OH,Al-OH的质子化造成的，因此H＋转化为表面正电荷的能力与土壤中氧化铁的含量密切相关，从而可变电荷土壤中H＋转化为表面正电荷的贡献比恒电荷土壤中的大。H＋转化为可溶性铝的能力与土教育部 的矿物组成密切相关，随着H＋输入量的增加，土壤中可溶性铝的含量也增加。可变电荷土壤中可溶性铝增加的顺序为红壤＞赤红壤＞铁质砖红壤，在H＋的加入量小于15mmol/kg时，黄棕壤的可溶性铝介于红壤和赤红壤之间，当H＋的加入量大于约15mmol/kg时，黄棕壤的可溶性铝略小于赤红壤，棕壤的可溶性铝明显小于红壤和赤红壤，但比铁质砖红壤高，恒电荷土壤的可变性酸量明显大于可变电荷土壤，但从总的看来，H＋加入量的变化对可交换性酸量的影响不大。  相似文献   

一种气候预测综合决策的方法——递归正权综合决策法   总被引：2，自引：0，他引：2  

项静恬  陈国珍  刘海波  赵振国 《大气科学》1999,23(5):551-558

根据气候预测的特点，提供了以误差平方和为风险函数，以正权综合为模式的多途径气候预测决策方案。不仅从理论上论证了几种正权方法的优性，还提供了递归技巧，进一步提高了正权综合的预测精度。对1997年汛期降水预测所做的综合决策表明，该方法具有较好的综合决策能力。  相似文献   

Pyroclastic flows and surges over water: an example from the 1883 Krakatau eruption     

S. Carey  H. Sigurdsson  C. Mandeville  S. Bronto 《Bulletin of Volcanology》1996,57(7):493-511

Pyroclastic deposits from the 1883 eruption of Krakatau are described from areas northeast of the volcano on the islands of Sebesi, Sebuku, and Lagoendi, and the southeast coast of Sumatra. Massive and poorly stratified units formed predominantly from pyroclastic flows and surges that traveled over the sea for distances up to 80 km. Granulometric and lithologic characteristics of the deposits indicate that they represent the complement of proximal subaerial and submarine pyroclastic flow deposits laid down on and close to the Krakatau islands. The distal deposits exhibit a decrease in sorting coefficient, median grain size, and thickness with increasing distance from Krakatau. Crystal fractionation is consistent with the distal facies being derived from the upper part of gravitationally segregated pyroclastic flows in which the relative amount of crystal enrichment and abundance of dense lithic clasts diminished upwards. The deposits are correlated to a major pyroclastic flow phase that occurred on the morning of 27 August at approximately 10 a.m. Energetic flows spread out away from the volcano at speeds in excess of 100 km/h and traveled up to 80 km from source. The flows retained temperatures high enough to burn victims on the SW coast of Sumatra. Historical accounts from ships in the Sunda Straits constrain the area affected by the flows to a minimum of 4x10³ km². At the distal edge of this area the flows were relatively dilute and turbulent, yet carried enough material to deposit several tens of centimeters of tephra. The great mobility of the Krakatau flows from the 10 a.m. activity may be the result of enhanced runout over the sea. It is proposed that the generation of steam at the flow/seawater interface may have led to a reduction in the sedimentation of particles and consequently a delay in the time before the flows ceased lateral motion and became buoyantly convective. The buoyant distal edge of these ash-and steam-laden clouds lifted off into the atmosphere, leading to cooling, condensation, and mud rain.  相似文献