大地主题解算方法综述   总被引：3，自引：1，他引：3  

周振宇  郭广礼  贾新果 《测绘科学》2007,32(4):190-191,174

大地主题解算是大地测量中的重要问题,由于椭球的复杂性,随之产生的解算方法也是多种多样。本文分析了大地主题解算的一般方法及其公式的适用范围,指出了它们的特点和不足,讨论了现今常用解算方法存在的问题和进一步的研究方向。  相似文献   

Setting minimum head capsule abundance and taxa deletion criteria in chironomid-based inference models   总被引：6，自引：0，他引：6  

Roberto Quinlan  John P. Smol 《Journal of Paleolimnology》2001,26(3):327-342

Criteria for removing training set lakes and taxa in chironomidbased inference models, due to low abundances, have largely been ad hoc. We used an anoxia inference model and a hypolimnetic oxygen model from southcentral Ontario to determine what effect subfossil head capsule abundance and taxa deletion criteria have on fossil inference statistics. Results from six training set lakes suggest that a minimum abundance of 40–50 head capsules is sufficient for use in inference models, however more diverse samples likely require more than 50 head capsules. Taxa deletion criteria substantially improved the predictive ability of inference models (lowered the root mean squared error of prediction (RMSEP)). The common practice of including taxa with only 2% abundance in at least two lakes was one of the deletion criteria that much improved inference models. Similar deletion criteria, such as 2% in at least 3 lakes and 3% in at least 1 lake, produced comparable improvements (up to 18% reduction in RMSEP).  相似文献   

An algorithm to aid varve counting and measurement from thin-sections     

Pierre Francus  Frank Keimig  Mark Besonen 《Journal of Paleolimnology》2002,28(2):283-286

An algorithm has been implemented to count and measure laminations from digital images of petrographic thin-sections. Boundaries and limits of laminations are first marked manually using imaging software. These marks are then exported to a workable format output file. Using the output file, the algorithm extracts the relevant information for lamination counts and thickness measurements along one or more parallel vertical lines. Compared to manual counts, the use of the algorithm improves the accuracy of measurements and speeds up the process. The method requires tools commonly available in most laboratories, i.e., a digital camera or a flat bed scanner with transparency capability and a desktop computer with 64 MB of RAM. From the algorithm, two utilities are implemented in Visual Basic for Applications and Fortran to be used on both Apple Macintosh and a PC-compatible, with Adobe^® Photoshop^®.  相似文献   

土粒度分维的确定方法探讨   总被引：5，自引：1，他引：4  

张凌 《水文地质工程地质》1999,26(5):43-45

本文通过对目前国内外研究土的粒度分维的三种方法的理论进行分析并一实际土样进行了比较,得到利用质量法求得土的粒度是三维方法中最方便实用的方法。  相似文献   

Investigation of the fractal dimension of rainfall occurrence in a semi-arid Mediterranean climate     

H. Ghanmi  Z. Bargaoui 《水文科学杂志》2013,58(3):483-497

Abstract

The scale invariance of rainfall series in the Tunis area, Tunisia (semi-arid Mediterranean climate) is studied in a mono-fractal framework by applying the box counting method to four series of observations, each about 2.5 years in length, based on a time resolution of 5 min. In addition, a single series of daily rainfall records for the period 1873–2009 was analysed. Three self-similar structures were identified: micro-scale (5 min to 2 d) with fractal dimension 0.44, meso-scale (2 d to one week) and synoptic-scale (one week to eight months) with fractal dimension 0.9. Interpretation of these findings suggests that only the micro-scale and transition to saturation are consistent, while the high fractal dimension relating to the synoptic scale might be affected by the tendency to saturation. A sensitivity analysis of the estimated fractal dimension was performed using daily rainfall data by varying the series length, as well as the intensity threshold for the detection of rain.

Editor Z.W. Kundzewicz; Associate editor S. Grimaldi

Citation Ghanmi, H., Bargaoui, Z., and Mallet, C., 2013. Investigation of the fractal dimension of rainfall occurrence in a semi-arid Mediterranean climate. Hydrological Sciences Journal, 58 (3), 483–497.  相似文献   

Silicon-32 as a tool for dating the recent past   总被引：2，自引：2，他引：0  

L. Keith Fifield  Uwe Morgenstern 《Quaternary Geochronology》2009,4(5):400-405

Silicon-32, with a half-life of approximately 140 years, has the potential to fill the dating gap that lies between those chronologies based on the shorter-lived isotopes of ³H and ²¹⁰Pb, and those based on the longer-lived ¹⁴C. Silicon-32 is produced in the atmosphere by cosmic ray bombardment of argon, and falls out on the Earth's surface in precipitation. Silicon-32 methods may be used to date siliceous sediments and sponges, groundwater and glacier ice. Measurement of ³²Si concentrations in these archives is, however, not straightforward. Two methods are available: radioactive-decay counting of the activity of the daughter nucleus, ³²P, and accelerator mass spectrometry, but in both cases the detection of ³²Si pushes the boundaries of the technique. Even the half-life of ³²Si is not known to a precision of better than ±10%. In this paper, we review efforts to determine the isotope's half-life, survey the detection methods and discuss the applications of ³²Si chronology. We show that at least some of the chronometric potential of this radioisotope is close to being realised as a result of recent improvements in methods of measurement.  相似文献   

改进三峰谷雨流计数法在爆破震动损伤评价中的应用   总被引：1，自引：0，他引：1  

肖建清  丁德馨  张萍  蒋复量 《岩土力学》2009,30(Z1):244-249

构筑物在爆破地震载荷作用下发生破坏是一个非常复杂的损伤累积过程。在进行爆破地震效应研究时,不仅要考虑几何距离、爆破条件以及地质条件对爆破振动强度的影响,也要关注结构本身的劣化过程。据此提出应用疲劳理论进行爆破地震效应分析的思路。首先,阐述了爆破震动应力谱测量的基本方法。其次,针对于三峰谷雨流计数模型的不足,提出了改进方案。改进后的计数模型融等值点压缩、峰谷值检测以及循环计数为一体,简化了计数过程,运用改进的计数模型分析了震动应力谱,得出了各种循环的频数分布规律。统计结果表明,单次爆破中绝大部分为小幅疲劳循环,而且拉压循环所占的比例比较大。  相似文献   

Dating long thrust systems on Mercury:New clues on the thermal evolution of the planet     

《地学前缘(英文版)》2020,11(3):855-870

The global tectonics of Mercury is dominated by contractional features mainly represented by lobate scarps,high relief ridges,and wrinkle ridges.These structures are the expression of thrust faults and are linear or arcuate features widely distributed on Mercury.Locally,these structures are arranged in long systems characterized by a preferential orientation and non-random spatial distribution.In this work we identified five thrust systems,generally longer than 1000 km.They were named after the main structure or crater encompassed by the system as:Thakur,Victoria,Villa Lobos,Al-Hamadhani,and Enterprise.In order to gain clues about their formation,we dated them using the buffered crater counting technique,which can be applied to derive the ages of linear landforms such as faults,ridges and channels.To estimate the absolute age for the end of the thrust system's activity,we applied both Le Feuvre and Wieczorek Production Function and Neukum Production Functions.Moreover,to further confirm the results obtained with the buffered crater counting method,the classic stratigraphic approach has been adopted,in which a faulted and an unfaulted craters were dated for each system.The results gave consistent ages and suggested that the most movements along major structures all over Mercury most likely ended at about 3.6-3.8 Ga.This gives new clues to better understand the tectonics of the planet and,therefore,its thermal evolution.Indeed,the early occurrence of tectonic activity in the planet's history,well before than predicted by the thermophysical models,coupled with the orientation and spatial distribution of the thrust systems,suggests that other processes beside global contraction,like mantle downwelling or tidal despinning,could have contributed to the first stage of the planet's history.  相似文献   

Design Research on Drive System of Underwater Tapping Machine     

喻开安 《中国海洋工程》2009,23(1)

The underwater tapping machine is composed of a center bit,a tapping cutter,a sesl box,a main drive box,aboring bar assembly,a envelop,a gear case,a counter and so on.The drive system in underwater tapping machine consists of a worm drive,a gear drive system and a screw drive.The worm drive is in the main drive box.The worm is connected with a hydraulic motor and driven by the hydraulic motor.The gear drive system is a combined gear train which is the combinations of the fixed axes and differential gear train in the gear case.On the one hand,by means of the fixed axes gear trains the turn and power of transmission shaft are transferred to the boring bar and the screw rod,causing differential tam between the boring bar and the screw rod.On the other hand,the turns of the boring bar and the screw rod are transferred to the differential gear train.The differential gear train is used to drive a special counter to count axial travel of the boring bar.The screw drive is composed of a feed screw and a nut on the boring bar.There is the differential turn between the boring bar and the feed screw.By means of the nut,the boring bar can feed automatically.With the movement of the sliding gear 7 in the gear case,the designed drive system can also be provided with the ability of fast forward and fast backward movement of the boring bar in its idle motion,restdting in the increase of the tapping efficiency.  相似文献   

Daybreak厚源α-计数仪的标定及测量影响因素的初步研究   总被引：2，自引：0，他引：2       下载免费PDF全文

王同利  陈杰  杨传成 《地震地质》2005,27(4):633-644

年剂量测量是释光和电子自旋共振测年的关键之一。厚源α-计数仪(简称TSAC)是年剂量测量中的常用仪器。通过不同标准源的标定对比实验,对美国Daybreak公司582,583型低本底厚源α-计数仪的高压值(HV)和积分甄别器阈值(DISC)进行了标定。同时,对测量过程中的诸多影响因素如被测样品的氡逃逸、粒度、含水量、颜色以及ZnS闪烁屏的密度、测量时间等开展了初步的实验研究,并根据实验结果提出了针对本型号仪器在实际测量时的改进措施,以提高厚源α-计数仪的测量精度  相似文献