Analysis of equivalent-dose distributions for single grains of quartz from modern deposits   总被引：1，自引：0，他引：1  

M. Ballarini  J. Wallinga  A.G. Wintle  A.J.J. Bos 《Quaternary Geochronology》2007,2(1-4):77-82

Two modern coastal sands are studied through single-grain optical dating techniques. The first sample is estimated to be less than 10 y old by means of independent age control and is known to be well-bleached on the basis of preliminary single-aliquot studies. The second sample is less than 1 y old, but an age of 73±24 years had been determined through single-aliquot analysis. For both samples we compare equivalent doses obtained from single-grain analysis to those obtained by means of similar single-aliquot methods. We found that results are comparable although equivalent doses determined through single-aliquot methods are more precise. The reason for this may be ascribed to the limited number of grains on which single-grain measurements were carried out. The presence of poorly bleached grains within a sample could be identified by dose distribution analysis of individual grains.  相似文献   

单井同位素稀释技术测定西台吉乃尔盐湖水文地质参数   总被引：1，自引：0，他引：1       下载免费PDF全文

孙亚联  马海州  高东林  李继成  张西营  张明刚 《盐湖研究》2007,15(4):1-5

我国含水层的水文地质参数测定,主要依靠传统的抽水试验方法,然而此方法却需要花费大量的试验和钻井费用。同位素示踪方法比传统的抽水试验方法获得含水层参数的周期短、费用低,有效地提高了水文地质参数的测试精度、缩短了工期、节省了投资。为了测定柴达木盆地西台吉乃尔盐湖地下水流速、流向、渗透系数等水文地质参数,采用单井同位素稀释法测试水文地质参数,正确确定其水文地质参数,无论对科学研究还是对生产开采,均有着重要的理论和现实意义。  相似文献   

基于参考站的GPS单点观测在城市及工程测量中的应用探讨   总被引：1，自引：0，他引：1  

熊远社  陈现春 《四川测绘》2003,26(4):173-175

本文对基于连续运行参考站(跟踪站)的高精度GPS单点观测模式及其特点进行了简要的介绍，并对该方法用于城市及工程测量的可行性进行了分析和探讨。最后通过生产实例，展示了该方法在城市及工程GPS测量应用中所具有的一些优点。  相似文献   

乌鲁木齐国际机场2001年5月11日强沙暴天气分析     

张利平  王春红  胡建军 《气象》2003,29(6):46-49

从天气形势、天气特点、卫星云图、雷达回波等方面对乌鲁木齐国际机场2001年5月11日发生的强沙尘暴天气进行了分析。结果表明，这是一次由冷锋尾部前方产生的对流云团触发的强沙尘暴天气，该对流云团具有超级雷暴单体的性质。  相似文献   

波动方程法共成像点道集偏移速度建模   总被引：15，自引：1，他引：15       下载免费PDF全文

李振春  姚云霞  马在田  王华忠 《地球物理学报》2003,46(1):86-93

叠前深度偏移的成像效果对偏移速度场相当敏感，建立正确的偏移速度场是实现高质量叠前深度偏移成像的关键。首先应用成像精度高的波动方程法叠前深度偏移抽取共成像点道集；然后基于摄动法通过参数化速度函数和改进的剩余曲率分析建立偏移速度误差和成像深度误差的定量关系；最后采用单参数／多参数联合迭代反演实现偏移速度建模。对Marmousi模型的试算结果表明：该方法对复杂地质体具有较强的适应性和较好的建模和成像效果，一般只需分析和控制主要反射层，通过3－4次近代就可以满足精度要求。  相似文献   

Polyatomic Interferences Produced by Macroelements During Direct Multi-Elemental ICP-MS Hydrochemical Analysis     

Vladimir N. Epov  Dominic Lariviere  Ekaterina N. Epova  R. Douglas Evans 《Geostandards and Geoanalytical Research》2004,28(2):213-224

An experimental study of the interferences produced by macroelements (Na, K, Ca, Mg, Sr, S, Cl, Si, N and C) contained in natural waters during inductively coupled plasma-mass spectrometry (ICP-MS) is presented. The most significant interferences created by these elements were found to be SO, CO, CAr, SiH, SiO, NaH, NaAr, MgAr, CaO, KO and KAr, the magnitude of which was dependant on the concentration of each macroelement. To reduce these interferences, different approaches, for example, desolvating nebulisation, high resolution and dynamic reaction cell ICP-MS were applied and compared. All three approaches were found to be useful tools for significantly reducing various polyatomic interferences. Advantages and disadvantages for each approach are discussed.  相似文献   

Promotive effect of se on the growth and antioxidation of a blue-green algaSpirulina maxima     

Zhou Zhi-gang  Liu Zhi-li 《中国海洋湖沼学报》1998,16(4):346-358

Cultures of a blue-green algaSpirulina maxima (Setch. et Gard.) Geitler with various concentrations of Se in Zarrouk's medium showed that not higher than 40 mg/L Se could promote its growth. The present experiments showed thatS. maxima grown under normal conditions, has an oxidant stress defence system for hydrogen peroxide (H₂O₂) removal, which is the Halliwell-Asada pathway. When 4 to 20 mg/L Se was added to the algal medium, this pathway was replaced by a so-called Sestressed pathway containing GSH peroxidase (GSH-POD). As a result of the occurrence of both higher activity of GSH-POD and lower levels of hydroxyl radical (OH·), the Se-stressed pathway scavenged H₂O₂ so effectively that the growth ofS. maxima was promoted by 4 to 20 mg/L Se. While GSH-POD activity of the alga disappeared at 40 mg/L Se, the recovery of ascorbate peroxidase was observed. The lower levels of ascorbic acid and GSH made the Halliwell-Asada pathway for scavenging H₂O₂ less effective, while the highest activity of catalase might be responsible in part for the H₂O₂ removal, causing the level of OH· inS. maxima grown at 40 mg/L Se to be much higher than the OH· level in this alga grown at 4 to 20 mg/L Se, but lower than that in the control. The OH· level changes caused the growth ofS. maxima cultured at 40 mg/L Se to increase slightly to close to that of the control.  相似文献   

Improvement in the interpretation of stress measurements by use of the overcoring method: development of a new approach     

K. Fouial  M. Alheib  H. Baroudi  C. Trentsaux 《Engineering Geology》1998,49(3-4):239-252

Determination of the state of the initial stresses in a rock formation is still one of the most important and complex problems in geotechnics. The over-coring method of measuring the stresses is one of the measurement methods most frequently used in geotechnics. It has been shown to be highly suitable for measuring the stresses in “hard and sound” rocks. However, applied to rocks which have a partialy elastic behaviour the method comes up against many problems the biggest of which are: (1) the non-elastic behaviour of the rock; and (2) the presence of natural fractures or those caused by the overcoring operation. These problems make it impossible to obtain correct deformation measurements which can be interpreted in terms of stresses. To overcome these problems, a new method has been developed based on the use of the deformations recorded at the start of the overcoring tests this method is the subject of the present article.  相似文献   

一种单片机可编程温度控制装置     

陈雪云  郑玉城 《福建地震》1998,(4)

本文介绍了一种单片机可编程温度控制装置的组成工作原理和它如何实现生产工艺所要求的温度曲线控制。  相似文献   

Optical dating of aeolian dynamism on the West African Sahelian margin   总被引：1，自引：0，他引：1  

S. Stokes  R. M. Bailey  N. Fedoroff  K. E. O'Marah 《Geomorphology》2004,59(1-4):281

The Sahelian Margin of West Africa is widely recognised as an area of recent environmental catastrophe and human suffering arising from food shortage and land degradation associated with prolonged drought. The propensity of this region to suffer drought has been related, using environmental data collected during the period of instrumental records, to a combination of low mean annual rainfall levels and a high degree of rainfall variability which relates to sea surface temperature anomalies in the adjacent tropical Atlantic Ocean. Despite the significant environmental and human consequences of such droughts, there is a paucity of long-term environmental data for the West African Sahel. Aeolian dune reactivations in this area are a potentially highly useful environmental archive of past periods of extended drought conditions, which may have resulted in localised or widespread dune reactivation. Here we describe the initial results from an ongoing programme of research, which seeks to develop a detailed record of past dune reactivations in Mali. We find evidence for repeated Holocene dune reactivation events and a significant number of reactivations, which commenced at the time of onset of the last major drought cycle in the early 1970s. We obtain ages as young as 20–30 years for some significant dune units (thickness up to 1 m) and describe the results of experiments which test the performance of our dating exercise. We specifically test for the significance of preheat temperature on single aliquot regeneration (SAR) equivalent dose determinations and recycling ratios; neither are found vary significantly as a function of preheating. Optical dating of sand sized quartz could provide a useful tool for palaeogeographical mapping of ancient and historical dune reactivations in this region and elsewhere.  相似文献