利用三维CT扫描技术定量计算熔岩流气泡体积的研究与实现   总被引：1，自引：0，他引：1  

张茂亮  刘真  陈德峰  郭正府  郭文峰 《岩石学报》2014,30(12):3709-3716

气泡体积算法及其计算机实现是火山熔岩流气泡古高度计应用研究中的难点之一,直接制约着古高度计算结果的精确度。本文提出了一种新的基于计算机断层成像技术的熔岩流气泡众数统计方法,即通过计算机断层成像技术对气孔状玄武岩样品进行三维重构,利用不同物质对射线吸收衰减系数的不一致性,标记重构数据中的岩石、气泡与无效部分,进而提取气泡连通区域的骨架,确定独立气泡之间的分割面,最终统计出气泡的数量与体积。考虑到玄武岩中气泡截面轮廓不规则的特点,采用逐点法有效地计算了截面面积,排除了连通区域轮廓对面积计算结果的影响。采用基于区域划分的阈值计算方法统计玄武岩样品的气泡数量与体积,解决了传统的单一阈值计算方法导致的小连通区域过度分割的问题。在上述新方法的基础上,本文设计并构建了新的气泡数量与体积的统计软件,计算程序的初步运算结果证实了研究方法的有效性与可行性。该方法有望提高熔岩流气泡数量、体积以及火山熔岩流气泡古高度计的计算精度,成为重建高原隆升历史的快速分析工具。  相似文献   

Empirical models of rain-spells characteristics – A case study of a Mediterranean-arid climatic transect     

《Journal of Arid Environments》2013

Environmental (geomorphological, hydrological and ecological) processes are controlled by rainfall, particularly in the Mediterranean, semi-arid and arid regions. Rainfall was analyzed using the concept of rain-spells, i.e., a period of successive rain days preceded and followed by at least one day without rainfall. Daily data from 13 stations along a climatic transect extending from the Judean Mountains with a Mediterranean climate to the Dead Sea arid region in Israel were studied. Rain-spell characteristics (number, yield and duration), based on these data, are presented for different rainfall thresholds, which might be used for different environmental processes such as rock weathering, soil organic matter dynamics, landslides, overland flow and floods and soil erosion. Three estimation models have been developed in order to predict the mean annual Number of Rain-Spells (NRS), mean Rain-Spell Yield (RSY), and mean Rain-Spell Duration (RSD) for the mean annual rainfall and for any given rainfall threshold. These models can be used for current climatic conditions and for scenarios in which the rainfall total changes.  相似文献   

塔克拉玛干沙漠腹地一次风蚀起沙观测试验     

杨兴华 《沙漠与绿洲气象(新疆气象)》2012,6(5):67-72

风蚀起沙对生态环境、人类健康及社会经济等具有很大的负面效应。利用美国Sensit公司生产的H11-LIN型风蚀传感器及贴地层风速梯度探测仪,对塔克拉玛干沙漠腹地塔中地区一次风蚀起沙过程进行了监测。结果表明：（1）风蚀起沙与微气象是一个互相影响互相制约的变化过程;（2）在此次观测试验过程中,我们观测到的最小起沙风速为6.0 m/s左右,同时发现起沙风速是一个变化的值,随着时间的延续呈现逐步增大的趋势,最小的起沙风速出现在风蚀开始发生的时候;（3）近地表风速廓线受沙粒运动影响明显,随着起沙量的增加,风速随高度变化的幅度增大,此时的风速廓线已不再遵循对数分布规律;（4）利用风蚀传感器测得塔中地区沙粒的临界起动摩擦速度为0.25 m/s,该值与经验公式估算的0.24 m/s非常接近,表明风蚀传感器在塔中地区具有较好的适用性;夏季塔中地区地表土壤湿度对风蚀起沙的阻碍作用可以忽略不计。 ?  相似文献   

天津地区用电量与气温的非线性响应关系研究     

兰辉  于佳卉  曹经福  刘玉坤  孙玫玲  黄鹤 《气象与环境学报》2021,37(4):139-144

利用门限回归模型和非线性滑动回归模型,分析天津市2014-2019年日用电量和气温之间的非线性关系,并计算得到不同响应关系下的阈值气温。结果表明：天津地区的阈值气温在不同响应关系下存在明显差异,在"V"型非线性响应关系下,阈值气温为18.8℃,在"U"型响应关系下,线性不对称模型的舒适区范围为12.3-23.4℃,非线性模型的舒适区范围为13.7-21.7℃;对比不同模型的预测效果,认为"U"型优于"V"型模型,非线性模型优于线性模型。对阈值气温的影响要素分析表明,相对湿度对舒适区与冷却区的阈值气温影响较大,阈值气温在相对湿度为30%-50%时较相对湿度为50%-70%时偏大2.2℃,相比之下,相对湿度对舒适区与加热区的阈值气温影响不大;天津地区阈值气温会随时间发生明显变化,2002-2005年的舒适区范围较2014-2019年偏大1.4℃。在实践应用中,应根据模型的需求,并充分考虑相对湿度和时间变化的影响选择阈值气温,从而提升用电量预测的准确率。  相似文献   

参数线性规划及应用讨论     

龚强 《测绘与空间地理信息》1999,(3)

本文介绍了测绘运筹学参数线性规划的实用意义,并就如何应用参数线性规划为测绘生产管理提供量化决策依据进行了讨论。  相似文献   

Field investigation of surface sand and dust movement over different sandy grasslands in the Otindag Sandy Land,China     

Shulin Liu  Tao Wang  Guangting Chen  Jian Guo  Xian Xue  Shaoxiu Ma 《Environmental Geology》2008,53(6):1225-1233

The characteristics of sand and dust movement over different sandy grasslands in China’s Otindag Sandy Land were explored based on field observations and laboratory analyses. Threshold wind speeds (the speed required to initiate sand movement) at a height of 2 m above the ground were estimated in the field for different surface types. Threshold wind speed above shifting dunes in the study area is about 4.6 m s⁻¹ at this height. This value was smaller than values observed above other surfaces, resulting in a greater risk of blowing sand above these dunes. Differences in sand transport rates (STR) as a function of the severity of desertification resulted primarily from differences in surface vegetation cover and secondarily from the soil’s grain-size distribution. STR increased exponentially with increasing near-bed wind velocity. Under the same wind conditions, STR increased with increasing severity of desertification: from 0.08 g cm⁻² min⁻¹ above semi-fixed dunes to 8 g cm⁻² min⁻¹ above semi-shifting dunes and 25 g cm⁻² min⁻¹ above shifting dunes. Vegetation’s affect on STR was clearly large. Different components of sand and dust were trapped over different lands: mostly sand grains but little dust were trapped above shifting dunes, but much dust was collected over semi-shifting and semi-fixed dunes. Human disturbance is likely to produce dust even from fixed dunes as a result of trampling by animals and vehicle travel. In addition, spring rainfall decreased the risk of sand and dust movement by accelerating germination of plants and the formation of a soil crust.  相似文献   

Groundwater protection in Mediterranean countries after the European water framework directive     

C. Martínez Navarrete  J. Grima Olmedo  J. J. Durán Valsero  J. D. Gómez Gómez  J. A. Luque Espinar  J. A. de la Orden Gómez 《Environmental Geology》2008,54(3):537-549

The European Water Framework Directive (WFD) has driven the protection of groundwater and characterization of water bodies. Development of appropriate and efficient approaches which consider the special features of the hydrologic regime is essential. The results of different projects that have been carried out to integrate characterization and protection of water bodies are summarized herein. In the Les eaux de la Mediterranée (AQUAMED) Project, applicability to the Mediterranean Region of guidelines provided by the European Commission to facilitate the WFD implementation has been verified. The Background criteria for the identification of groundwater thresholds (BRIDGE) Project developed a methodology to establish threshold values of pollutants contributing to the chemical status of groundwater bodies. This method has been applied to pollutants used to classify groundwater bodies as at risk of not achieving objectives of the WFD. Selected features of protection areas for drinking water and safeguard zones are analyzed, as well as the possibility of using wellhead protection areas.  相似文献   

舟山海雾特征及其对数值模式的初步订正     

陈梅汀  王连喜  徐哲永  陈淑琴  张蔺廉 《气象科学》2018,38(1):130-138

采用舟山海域1962—2015年的4个气象观测站资料、2014—2015年2 a的逐时自动气象数据和浮标站数据,统计分析了舟山海雾特征,结果表明:海雾总是在大尺度背景条件和一定的气象水文条件下发生;海雾春季最多,秋季最少,一天中多发生在夜间和早晨,又以下半夜到早晨最多,雾散一般在11∶00以后;海雾按天气形势可分4型,不同类型其季节变化和日变化存在差异;浓雾发生的要素特征为,气温5~27℃,海温9~27℃,气温露点差0~4℃,90%的浓雾发生在2 m相对湿度≥95%、气海温差-3.7~3.2℃时,浓雾风向主要落在东南风和偏南风之间,平均风力一般在1~5级;利用要素阈值对WRF能见度模式进行订正检验,发现对提高浓雾的定性预报准确率有较明显的作用。  相似文献   

Do 2-amino-3,8-dimethylimidazo[4,5-f] quinoxaline data support the conclusion of threshold carcinogenic effects?     

Chao Chen  Kate Z. Guyton 《Stochastic Environmental Research and Risk Assessment (SERRA)》2008,22(4):487-494

The objectives of this paper are to (1) reexamine the data that were used to support the conclusion of a threshold effect for 2-amino-3,8-dimethylimidazo[4,5-f] quinoxaline (MeIQx)-induced initiation and carcinogenicity at low doses in the rat liver, and (2) discuss issues and uncertainties about assessing cancer risk at low doses. Our analysis is part of an effort to understand proper interpretation and modeling of data related to cancer mechanisms and is not an effort to develop a risk assessment for this compound. The data reanalysis presented herein shows that the low-dose initiation activity of MeIQx, which can be found in cooked meat, cannot be dismissed. It is argued that the threshold effect for carcinogenic agents cannot be determined by statistical non-significance alone; more relevant biological information is required. A biologically motivated procedure is proposed for data analyses. The concept and procedure that are appropriate for analyzing MeIQx data are equally applicable to other compounds with comparable data. The ideas and approaches in this presentation are those of the authors and do not necessarily represent the positions or policies of the USEPA.  相似文献   

Critical phenomena in thermal conductivity: Implications for lower mantle dynamics     

Anne M. Hofmeister  David A. Yuen 《Journal of Geodynamics》2007,44(3-5):186-199

Microscopic mechanisms for heat transport in dense minerals (phonon scattering and photon attenuation) exhibit aspects of threshold behavior, discussed qualitatively here. For all minerals examined so-far using laser-flash analysis, the lattice component of the thermal conductivity of the mantle asymptotes to a constant above a critical temperature of 1500 K. Radiative transfer calculated from absorption spectra has thresholds in both grain-size and Fe content, and a rather complex dependence on temperature. These critical phenomena impact convection of the lower mantle, because the lattice contribution tends to destabilize the cold boundary layers, whereas radiative transfer mostly promotes stability in the lower mantle, unless the grains are large and Fe-rich, which makes convection chaotic and time-dependent. The specific behavior suggests that flow in the lower mantle is sluggish, whereas flow in the upper mantle-transition zone is time-dependent. The decrease in k_rad as Fe/(Fe + Mg) increases beyond 0.1 may be connected with formation of lower mantle, thermo-chemical plumes through positive feedback.  相似文献