Disproof of solar influence on the decay rates of 90Sr/90Y     

《Astroparticle Physics》2015

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地下水32Si年龄测试技术——液体闪烁计数法   总被引：1，自引：0，他引：1  

刘存富  王佩仪  周炼  晁念英  万军伟 《地球学报》1997,18(Z1):224-226

本文介绍了应用Fe(OH)3共沉淀法从天然水中提取SiO2，然后提取32P的方法。将H3PO4溶液和TritonX-100混合制备计数溶液，用液体闪烁计数器测量32P的放射性。最后用公式计算32Si的放射性浓度和地下水的32Si年龄。  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   

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   

An avalanche photodiode photon counting camera for high-resolution astronomy     

Oliver Ryan  Mike Redfern  Andrew Shearer 《Experimental Astronomy》2006,21(1):23-30

A system is described which makes best use of the high quantum efficiency and high count rate capability of avalanche photodiodes for high time resolution observations of optical pulsars. The use of three APDs allows simultaneous photometry of the target and a reference star, and the monitoring of the sky background. By minimising the optical components in the light path the optical efficiency of the system is maximised. The TRIFFID (Shearer, A., Stappers, B., O'Connor, P., Golden, A., Strom, R., Redfern, M., Ryan, O.: Science 301, 493–495 (2003)) and OPTIMA (Straubmeier, C., Kanbach, G., Schrey, F.: Exp. Astron. 11, 157–170 (2001)) have shown that fibre-fed APD arrays can produce excellent results. This, new, system was used on the 6m BTA in November 2003 – results on the Crab pulsar are presented.  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   

Long-term measurements of 36Cl to investigate potential solar influence on the decay rate     

《Astroparticle Physics》2014

Recently, Jenkins et al. [6] reported on fluctuations in the detected decay events of ³⁶Cl which were measured with a Geiger–Müller counter. Experimental data of ³²Si measured by means of an end-window gas-flow proportional counter at the Brookhaven National Laboratory show similar periodicity, albeit a different amplitude. Jenkins et al. interpret the fluctuations as evidence of solar influence on the decay rates of beta-decaying radionuclides.In this work, liquid scintillation counting was used to check for potential variations in the ³⁶Cl decay rates. A custom-built counter with three photomultiplier tubes was used. In contrast to commercial counters, the relevant parameters of our system are well controlled and the discrimination threshold and HV setting can be adjusted and checked. The experimental data were analyzed by means of the triple-to-double coincidence ratio (TDCR) method which is a primary method for activity determination. Thus, our results do not depend on any other standard or reference source.Our data show fluctuations which are by more than one order of magnitude lower than those seen in the experiment using a Geiger–Müller counter. More importantly, no oscillation could be identified. Interestingly, our data overlap in time with those from Jenkins et al. [6]. We do not observe the phase and amplitude as seen by Jenkins and conclude that the fluctuations are not due to solar influence. This also implies that the interpretation by Jenkins et al. is false.  相似文献   

顾及视频地理映射的人群密度估计方法     

孙银萍  张兴国  石新雨  李奇泽 《地球信息科学学报》2022,24(6):1130-1138

针对复杂场景下人群计数及地图可视化问题,提出了一种顾及视频地理映射的人群密度估计方法。首先,通过迁移学习的方式,构建了适合于复杂场景的人群语义分割模型;将视频与GIS相结合,求解摄像机和人群场景的单应矩阵;基于人群语义分割结果及单应矩阵,可将人群多边形映射至二维地图。然后,设计等距分区和格网分区2种分区方案;根据人群语义分割结果,统计不同分区方案下各子区人群密度。最后,基于训练的各子区人群密度值,计算视域内人口总数;通过人群目标点符号均匀填充人群多边形,进行地图可视化。实验结果表明：① 本文构建的人群语义分割模型,可实现大场景下人群的高精度分割,精度为94.11%;② 将视频与GIS相结合,实现了人群的地图映射和地图可视化表达,达到了人群可定位、可量测和可空间分析的目标;③ 实现了监控视频人群的精准计数,将视域划分更多子区有利于提高计数精度。与基于密度图的人群密度估计方法相比,本文方法在高空、高密集度的大场景中具有优势,能有效解决人群难以精准计数及地图可视化的问题,可用于大型活动、车站、商场、运动场馆的人群监管。  相似文献   

Sedimentary processes controlling ultralong cells of littoral transport: Placer formation and termination of the Orange sand highway in southern Angola     

《Sedimentology》2018,65(2):431-460

This study focuses on the causes, modalities and obstacles of sediment transfer in the longest cell of littoral sand drift documented on Earth so far. Sand derived from the Orange River is dragged by swell waves and persistent southerly winds to accumulate in four successive dunefields in coastal Namibia to Angola. All four dunefields are terminated by river valleys, where aeolian sand is flushed back to the ocean; and yet sediment transport continues at sea, tracing an 1800 km long submarine sand highway. Sand drift would extend northward to beyond the Congo if the shelf did not become progressively narrower in southern Angola, where drifting sand is funnelled towards oceanic depths via canyon heads connected to river mouths. Garnet–magnetite placers are widespread along this coastal stretch, indicating systematic loss of the low‐density feldspatho‐quartzose fraction to the deep ocean. More than half of Moçamedes Desert sand is derived from the Orange River, and the rest in similar proportions from the Cunene River and from the Swakop and other rivers draining the Damara Orogen in Namibia. The Orange fingerprint, characterized by basaltic rock fragments, clinopyroxene grains and bimodal zircon‐age spectra with peaks at ca 0·5 Ga and ca 1·0 Ga, is lost abruptly at Namibe, and beach sands further north have abundant feldspar, amphibole‐epidote suites and unimodal zircon‐age spectra with a peak at ca 2·0 Ga, documenting local provenance from Palaeoproterozoic basement. Along with this oblique‐rifted continental margin, beach placers are dominated by Fe–Ti–Cr oxides with more monazite than garnet and thus have a geochemical signature sharply different from beach placers found all the way along the Orange littoral cell. High‐resolution mineralogical studies allow us to trace sediment dispersal over distances of thousands of kilometres, providing essential information for the correct reconstruction of ‘source to sink’ relationships in hydrocarbon exploration and to predict the long‐term impact of man‐made infrastructures on coastal sediment budgets.  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