Trace metal composition of and accumulation rates of sediments in the Upper Gulf of Thailand     

Herbert L. Windom  Suchada Silpipat  Aurapin Chanpongsang  Ralph G. Smith  Manuwadi Hungspreugs 《Estuarine, Coastal and Shelf Science》1984,19(2):133-142

Sediment cores and grab samples were collected in the Upper Gulf of Thailand to determine sedimentation rates and to determine if metal concentrations reflect anthropogenic inputs.Accumulation rates of sediments in the Upper Gulf measured using the ²¹⁰Pb method, appear to vary from ca. 4 to 11 mm yr^?1. Sediment budgets suggest that little of the sediment delivered to the Upper Gulf by the major rivers is ultimately transported to the Lower Gulf. Metal concentrations in Upper Gulf sediments appear to be dominantly controlled by natural inputs.  相似文献   

A summer and winter apportionment of particulate matter at urban and rural areas in northern France     

F. Ledoux  L. Courcot  D. Courcot  A. Aboukaïs  E. Puskaric   《Atmospheric Research》2006,82(3-4):633

The apportionment of atmospheric aerosols undertaken in Northern France during two sampling campaigns allowed to determine the influence of the atmospheric contribution of a heavy industrialized urban center on the particulate matter composition at a nearby rural site. The concentrations of major components and trace elements sampled by bulk filtration have been determined on June–July 2000 and January–February 2001, and the comparison of these two campaigns shows very well the importance of wind directions. The sources of 10 trace elements (Al, Ba, Cu, Fe, K, Mn, Pb, Sr, Ti and Zn) and 7 major components (Cl⁻, NO₃⁻, SO₄²⁻, NH₄⁺, Na, Mg and Ca) are better identified by studying their elemental contribution at each sampling site according to wind sectors. This kind of study shows that the concentrations recorded at the urban sampling site are always higher than those observed at the rural site as well during the summer campaign (about + 35%) as during the winter campaign (+ 90%), because of the predominance of the W–NW wind sector, corresponding to the influence of the urban and industrialized areas.  相似文献   

以海原断裂甘肃老虎山段为例浅析走滑断裂古地震记录的完整性——兼论古地震研究中的若干问题     

刘静徐锡伟  李岩峰冉勇康 《地质通报》2007,26(6):50-660

在简单介绍海原断裂老虎山段松山探槽点古地震工作的基础上,分析了制约走滑断裂上古地震记录完整性的因素。松山探槽点跨断裂开挖的2个探槽揭示颜色和粒度不同的地层互层的沉积序列呈近水平面状展布。在断裂带内地层发生错断、旋转和拖曳等变形现象。多个层位上的这种变形表明该点揭示了6次古地震事件。炭屑的~(14)C年龄限定了6次事件均发生在距今3500～3900年以来,其中最新的4次事件从老到新分别为0～410aAD、890～1000年之后不久、1440～1640 aAD和1990年景泰-天祝Mw5.8级历史地震。该序列及其他例子表明连续的、高沉积速率的微构造环境是走滑断裂上探槽选取的重要原则。  相似文献   

Late Miocene–Pliocene eclogite facies metamorphism, D'Entrecasteaux Islands, SE Papua New Guinea     

B. D. MONTELEONE  S. L. BALDWIN  L. E. WEBB  P. G. FITZGERALD  M. GROVE  A. K. SCHMITT 《Journal of Metamorphic Geology》2007,25(2):245-265

The D'Entrecasteaux Islands of south‐eastern Papua New Guinea are active metamorphic core complexes that formed within a region where the plate tectonic regime has transitioned from subduction to rifting. While rapid, post 4 Myr exhumation and cooling of amphibolite and greenschist facies rocks that constitute the footwall of the crustal scale detachment fault system have been previously documented on Fergusson and Goodenough Islands of the D'Entrecasteaux chain, the timing of eclogite facies metamorphism in rocks of the footwall was unknown. Recent work revealed that at least one of the eclogite bodies formed during the Pliocene. We present combined in situ ion microprobe U–Pb age analyses of zircon from five variably retrogressed eclogite samples from Fergusson and Goodenough Islands that document Late Miocene–Pliocene (8–2 Ma) eclogite formation on these islands. Textural relationships and zircon–garnet rare earth element partition coefficients indicate that U–Pb ages constrain zircon crystallization under eclogite facies conditions in all samples. Results suggest westward younging of eclogite facies metamorphism from Fergusson to Goodenough Island. Present‐day exposure of Late Miocene–Pliocene eclogites requires exhumation rates > 2.5 cm yr^?1.  相似文献   

基于局部条纹频率估计的二维高斯滤波方法   总被引：1，自引：0，他引：1  

汪沛  王岩飞  张冰尘  麻丽香 《武汉大学学报(信息科学版)》2007,32(10):868-871

提出一种基于局部条纹频率估计的干涉相位图二维高斯滤波方法。该方法采用最大似然法估计局部条纹频率,并用相位噪声的局部标准差评价噪声强度,从而控制滤波器参数实现自适应滤波,并采用仿真数据和SIR-C/XSAR在意大利Etna火山的干涉数据进行试验,将本算法与均值滤波方法和中值滤波方法以及Goldstein滤波方法进行了比较。试验结果表明,该方法不仅能够有效抑制干涉相位噪声,还能够很好地保持干涉条纹的细节信息。  相似文献   

Socioeconomic Correlates of Increasing Crime Rates in Smaller Communities     

William V. Ackerman 《The Professional geographer》1998,50(3):372-387

This research analyzes changes in crime rates by city size and determines the extent to which these changes can be explained by socioeconomic variables. More particularly it addresses rates of change in mean crime rates for violent and property crime between 1976–1984 and 1985–1994 for all U. S. cities, then compares results to Ohio cities. It provides a detailed analysis of changing crime rates in 111 Ohio cities with populations between 10,000 and 99,999 inhabitants and attempts to account for crime differentials between these cities employing linear regression and factor analysis. Results indicate that crime is significantly related to poverty and its associated conditions and processes.  相似文献   

Sex expression and growth rates in natural populations of the desert soil crustal mossSyntrichia caninervis     

Lloyd R. Stark  Brent D. Mishler  D.Nicholas McLetchie 《Journal of Arid Environments》1998,40(4):401-416

The low elevation Mojave Desert cryptobiotic crust is dominated by the mossSyntrichia caninervis. In 16 populations of this moss, stem height and population were significantly associated with sex expression, with longer stems expressing sex more frequently and producing more perichaetia. The above-ground age of stems ranged up to 10 years, with a mean growth rate across populations of 0.36 mm year⁻¹. The overall stem sex ratio, as a proportion of the total number of stems, was 0.30♀: 0♂: 0.70 non-expressing. The probability of expressing sex in a given season was 0.09. The absence of sexual reproduction (no sporophytes) and likely absence of the male sex from the area indicate that the non-expressing plants are female individuals. The slow growth rates, low rates of sex expression, absence of male plants, and absence of sexual reproduction in this crustal species may help explain why re-establishment of mosses on desert soils can take decades.  相似文献   

Interpretation of cosmogenic nuclides in meteorites on the basis of accelerator experiments and physical model calculations     

R. Michel  S. Neumann 《Journal of Earth System Science》1998,107(4):441-457

Cosmogenic nuclides in extraterrestrial matter provide a wealth of information on the exposure and collision histories of small objects in space and on the history of the solar and galactic cosmic radiation. The interpretation of the observed abundances of cosmogenic nuclides requires detailed and accurate knowledge of their production rates. Accelerator experiments provide a quantitative basis and the ground truth for modeling cosmogenic nuclide production by measurements of the relevant cross sections and by realistic simulations of the interaction of galactic protons with meteoroids under completely controlled conditions, respectively. We review the establishment of physical model calculations of cosmogenic nuclide production in extraterrestrial matter on the basis of such accelerator experiments and exemplify this approach by presenting new experimental and theoretical results for the cosmogenic nuclide⁴⁴Ti. The model calculations describe all aspects of cosmogenic nuclide production and allow the determination of long-term solar and galactic cosmic ray spectra and a consistent interpretation of cosmogenic nuclides in extraterrestrial matter.  相似文献   

Runoff and erosion processes and rates in the Zin valley badlands,northern Negev,Israel     

A. Yair  H. Lavee  R. B. Bryan  E. Adar 《地球表面变化过程与地形》1980,5(3):205-225

Badland areas are usually regarded as impermeable zones which generate high runoff and are very vulnerable to sheetwash and rainsplash. To test those considerations sprinkling experiments using two rainfall simulators were carried out on slopes of varying aspect in the northern Negev (Israel). For one unit 1·5 m² plots were used with rainfall of natural characteristics at 36 mm/hr intensity and 43–48 minute duration, runoff being recorded and water/sediment samples taken every 5 minutes. The second unit was used on 30–50 m² plots but rainfall energy production was below that of natural rainfall. Results show that due to the high stability and strong flocculation of clay-rich aggregates rainsplash is ineffective in surface sealing so that infiltration capacities remain high despite intense, prolonged rainfall. Aspect differences are reflected in variation of surface properties despite homogenous bed-rock, which cause marked differences in hydrological response. North-facing slopes respond more quickly, more frequently and produce more runoff than south-facing slopes. Non-uniform runoff generation is also seen within plots of one aspect reflecting subtle variations in surface properties. Comparison of rainfall intensity and duration used during the experiments with those prevailing under natural conditions shows that under present day conditions surface flow in the Zin valley badlands must be extremely infrequent and denudation rates very low.  相似文献   

Determination of predevelopment denudation rates of an agricultural watershed (Cayaguás River, Puerto Rico) using in-situ-produced Be in river-borne quartz     

Erik Thorson Brown  Robert F. Stallard  Matthew C. Larsen  Didier L. Bourls  Grant M. Raisbeck  Franoise Yiou 《Earth and Planetary Science Letters》1998,160(3-4):723-728

Accurate estimates of watershed denudation absent anthropogenic effects are required to develop strategies for mitigating accelerated physical erosion resulting from human activities, to model global geochemical cycles, and to examine interactions among climate, weathering, and uplift. We present a simple approach to estimate predevelopment denudation rates using in-situ-produced cosmogenic ¹⁰Be in fluvial sediments. Denudation processes in an agricultural watershed (Cayaguás River Basin, Puerto Rico) and a matched undisturbed watershed (Icacos River Basin) were compared using ¹⁰Be concentrations in quartz for various size fractions of bed material. The coarse fractions in both watersheds bear the imprint of long subsurface residence times. Fine material from old shallow soils contributes little, however, to the present-day sediment output of the Cayaguás. This confirms the recent and presumably anthropogenic origin of the modern high denudation rate in the Cayaguás Basin and suggests that pre-agricultural erosional conditions were comparable to those of the present-day Icacos.  相似文献