Temporal dynamics of airborne lead-210 in Missouri (USA): implications for geochronological methods     

R. W. Sheets  A. E. Lawrence 《Environmental Geology》1999,38(4):343-348

 Lead-210 (²¹⁰Pb) deposited from the atmosphere is used in the dating of certain geological materials such as glacial ice and lacustrine sediments, but its long-term atmospheric behavior has been little studied. The present investigation reports measurements of airborne ²¹⁰Pb at 21 monitoring stations in Springfield, Missouri, during 1975–1995. Seasonal and diurnal patterns of atmospheric concentrations are established, and the mean annual concentrations of ²¹⁰Pb in ground level air during the 20-year period are examined. Although airborne ²¹⁰Pb concentrations are found to vary diurnally and seasonally, mean annual concentrations in southwest Missouri have remained relatively constant during this time period. This finding is important for geochronological methods that assume a constant ²¹⁰Pb flux from the atmosphere. Received: 8 September 1998 · Accepted: 12 October 1998  相似文献   

A Morphological Classification Scheme for ULIRGs     

K.D. Borne  H. Bushouse  L. Colina  R.A. Lucas  A. Baker  D. Clements  A. Lawrence  S. Oliver  M. Rowan-Robinson 《Astrophysics and Space Science》1999,266(1-2):137-142

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Island-enhanced cooling mechanism in typhoon events revealed by field observations and numerical simulations for a coral reef area,Sekisei Lagoon,Japan     

Lawrence Patrick C. Bernardo  Kazuo Nadaoka  Takashi Nakamura  Atsushi Watanabe 《Ocean Dynamics》2017,67(11):1369-1384

While widely known for their destructive power, typhoon events can also bring benefit to coral reef ecosystems through typhoon-induced cooling which can mitigate against thermally stressful conditions causing coral bleaching. Sensor deployments in Sekisei Lagoon, Japan’s largest coral reef area, during the summer months of 2013, 2014, and 2015 were able to capture local hydrodynamic features of numerous typhoon passages. In particular, typhoons 2015-13 and 2015-15 featured steep drops in near-bottom temperature of 5 °C or more in the north and south sides of Sekisei Lagoon, respectively, indicating local cooling patterns which appeared to depend on the track and intensity of the passing typhoon. This was further investigated using Regional Ocean Modeling System (ROMS) numerical simulations conducted for the summer of 2015. The modeling results showed a cooling trend to the north of the Yaeyama Islands during the passage of typhoon 2015-13, and a cooling trend that moved clockwise from north to south of the islands during the passage of typhoon 2015-15. These local cooling events may have been initiated by the Yaeyama Islands acting as an obstacle to a strong typhoon-generated flow which was modulated and led to prominent cooling of waters on the leeward sides. These lower temperature waters from offshore may then be transported to the shallower inner parts of the lagoon area, which may partly be due to density-driven currents generated by the offshore-inner area temperature difference.  相似文献   

Grain-size Analysis of Surface Material Under Wind Erosion Using the Effective Surface Concept     

Lawrence W. Martz  Long Li 《地球表面变化过程与地形》1997,22(1):19-29

The grain mobility and roughness of a surface exposed to wind are dependent on the grain size of the surface particles. This paper deals with the temporal variation in the grain size of surface material using an analytical method based on the effective surface concept. The analysis of grain size data obtained from a wind tunnel experiment indicated that, above the threshold wind friction velocity for all surface particles, the grain-size distribution of surface particles was very similar to that of the parent material over a time period of 10 to 15 minutes. However, the mean grain size of surface particles apparently decreased over the initial time period of 2 to 3 minutes. We therefore confirm earlier studies that on a non-uniform grain bed a larger particle could be more mobile than a smaller particle if the wind friction velocity was higher than the threshold for the larger particle. However, this does not imply that the largest particle is most mobile due to the non-linear dynamics of aeolian sediment transport processes. © 1997 by John Wiley & Sons, Ltd.  相似文献   

盐湖氯化镁制备炼钢用镁钙造渣剂的实验研究          下载免费PDF全文

祁米香  段东平  崔杰  郭效瑛  郑红  杨占寿  王舒娅  李波  邹兴武 《盐湖研究》2020,28(2):95-100

本文探讨了盐湖副产氯化镁应用于炼钢冶金造渣的可行性。以盐湖水氯镁石和石灰为原料,通过化学合成制备了氧化镁,再将氧化镁与石灰、粘结剂混配成型制备炼钢用镁钙造渣剂,考察了粘结剂硼酸的不同用量时造渣剂形成的球团强度和抗压强度及微观结构变化;同时研究了不同煅烧温度、煅烧时间、氧化镁掺杂量的情况下,造渣剂的活性及杂质脱除率。实验结果表明,利用该方法制备的镁钙造渣剂应用于钢铁冶金造渣过程,可有效地脱除碳、磷、硫、硅等杂质成分,提高转炉冶炼的冶金效果的同时实现了盐湖资源再利用,具有较好的推广应用前景。  相似文献   

Long-term evolution of Baltic Sea wave climate near a coastal segment in Poland; its drivers and impacts     

Grzegorz Różyński 《Ocean Engineering》2010,37(2-3):186-199

The paper analyses long-term variability of wave climate near Poland for the 1958–2002 period. With spectral and cross-spectral analysis, linear regression and singular spectrum analysis the modes of long-term variability were quantified for the most energetic months (November–February). For monthly indices of North Atlantic Oscillation from 1950 until 2006, it was established that the long-term trends of NAO and significant wave height demonstrate a gentle coupling. For Januaries this relationship is strongest and dates back to 1960, for Februaries a certain consistency appears since 1975. For Novembers and Decembers no statistically discernible coupling was found. Thus, the Baltic Sea appears to be the easternmost NAO-affected region, despite its separation from the Atlantic. The hydrodynamic variability also includes a non-trivial oscillation in the January wave energy records with T=8 years. The same periodicity was identified with the multi-channel SSA technique in the long-term shoreline data of a neighboring beach. The study shows that even almost entirely isolated water bodies are becoming exposed to global climatic phenomena and accelerated erosion of sandy beaches, typical for the South Baltic region. On the other hand, the 8-year hydrodynamic cycle can be viewed as the driver of long-term shoreline evolution.  相似文献   

Reply to discussion of ‘Gisbornian (Caradoc) graptolites from New South Wales,Australia: systematics,biostratigraphy and evolution’ by B. Rickards,L. Sherwin and P. Williamson     

Barrie Rickards  Lawrence Sherwin  Penelope L. Williamson 《Geological Journal》2003,38(2):181-183

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Gisbornian (Caradoc) graptolites from New South Wales,Australia: systematics,biostratigraphy and evolution     

Barrie Rickards  Lawrence Sherwin  Penelope Williamson 《Geological Journal》2001,36(1):59-86

The biodiversity record of graptolites from the Cheeseman's Creek Formation, considered herein as late Gisbornian (Caradoc) in age, has been substantially increased to fifteen taxa, including the new species Dicellograptus praemorrisi sp. nov. and Climacograptus vandenbergi sp. nov. Some of the records have global correlative significance enabling us to identify the wilsoni Biozone ( = calcaratus Biozone of eastern Australia). Several evolutionary lineages have been recognized:

• 1 Dicellograptus moffatensis (Carruthers, 1858) → D. praemorrisi sp. nov → D. morrisi Hopkinson, 1871
• 2 Glossograptus hincksi Hopkinson, 1872 → Glossograptus? sp.
• 3 Climacograptus bicornis (J. Hall, 1847) → C. vandenbergi sp. nov. → C. lanceolatus VandenBerg, 1990.

Copyright © 2001 John Wiley & Sons, Ltd.  相似文献