An integrated magnetic,geochemical and archeointensity investigation of casting debris from ancient metallurgical sites of Michoacán,Western Mesoamerica     

Juan Morales  María del Sol Hernández-Bernal  Avto Goguitchaichvili  José Luis Punzo-Díaz 《Studia Geophysica et Geodaetica》2017,61(2):290-309

The ability of baked clay-elaborated objects to record the temporal variations of both direction and intensity of the geomagnetic field at the time of their elaboration or last use has been widely used during the last decades to fill the gaps left by available time-discrete volcanic-rock logs for a better knowledge of the evolution of the geomagnetic field. Further refinement of the secular variation curves has motivated the search for alternative non-conventional materials as attractive targets for archeomagnetic studies. Both clay and copper have been used since pre-Hispanic times for the elaboration of a wide variety of ornamental and utilitarian objects in Mesoamerica. Previous studies carried out in Europe and Israel have shown the usefulness of copper slags as one of these non-conventional materials. We present the results of an integrated study carried out on ten copper slags from seven ancient metallurgical sites of Michoacán. The analysis included a series of rock magnetism experiments, scanning electron microscope analysis, archeointensity determinations following the Thellier-Coe method and their corresponding dating. Based on the results obtained the slag-set analyzed can be divided in two main groups: low Fe concentrations (associated with high Cu concentrations) for slags comprising the first group, and high Fe concentrations (associated with low Cu concentrations) for slags from second group. Slags from the first group are characterized by almost reversible thermomagnetic curves, while those corresponding to the second group show a quite irreversible behavior. A crystalline (vitreous) structure within the massive surface of the slags is observed for those coming from the second (first) group. These striking features could reflect significant differences in the metallurgical process followed at these sites, which according to archeological and historical evidences correspond to Colonial and pre-Hispanic usage metallurgical sites; first and second group, respectively. The good experimental behavior exhibited by these materials demonstrates the suitability of copper slag to obtaining absolute archeointensity data which can be used to improve the existing Mesoamerican archeomagnetic record. This in turn, can be used both for geomagnetic field modelling purposes and archeomagnetic dating.  相似文献   

Interannual variability of wave climate in the Caribbean Sea     

Vega  Marco J.  Alvarez-Silva  Oscar  Restrepo  Juan C.  Ortiz  Juan C.  Otero  Luis J. 《Ocean Dynamics》2020,70(7):965-976

Ocean Dynamics - Low-frequency interannual climatic oscillations have been reported to influence the precipitation regimes, river discharges, winds, and sea level in the Caribbean Sea. Here, we...  相似文献   

Hidden in plain sight: How finding a lake in the Brazilian Pantanal improves understanding of wetland hydrogeomorphology     

Eder Renato Merino  Mario Luis Assine 《地球表面变化过程与地形》2020,45(2):440-458

Wetlands are permanently or seasonally flooded areas which support countless species of plants and animals. The Pantanal, in central-west Brazil is one of the largest freshwater wetlands in the world covering an area of ~150 000 km². The relationships between geomorphology, hydrology, sedimentation, and vegetation cover are critical for understanding how the landscape constrains the dynamics of wetlands. We provide a detailed study of the geomorphology and surface hydrology of the Negro River Interfan System (NRIS), in the southern Pantanal, by applying multiple approaches (i.e. remote sensing analysis, geomorphological zonation and hydrosedimentological surveys). A multitemporal analysis of Landsat imagery produced an inundation frequency map (2000–2011 period) that revealed a permanently flooded area in the central portion of the NRIS. A hidden fluvial lake was previously undetected due to the accumulation of floating mats and floating meadows of macrophytes. The Negro and Aquidauana feeder rivers exhibit remarkable differences in channel planform, water discharge, and sediment load. The Negro River presents a distributary pattern with marginal levees with decreasing elevation as it progrades into the lake and remains as a subaqueous landform conditioning the water flow downstream. The lake outflow to the Paraguay River occurs mainly by sheet flow during flood seasons and through small tributary channels during dry months. The lake's geometry is outlined by east–northeast and west–northwest straight borders, suggesting that the area is tectonically controlled. A cloud-based worldwide water surface database (1984–2015) revealed frequent channel changes within the NRIS. Recent channel avulsions in the lower course of the Negro River are noteworthy mainly because the former river channel at the confluence with the Paraguay River is no longer connected with the Negro River channel. © 2019 John Wiley & Sons, Ltd.  相似文献   

Tropical Cyclone Impacts on Coastal Regions: the Case of the Yucatán and the Baja California Peninsulas,Mexico     

Luis M. Farfán  Eurico J. D’Sa  Kam-biu Liu  Victor H. Rivera-Monroy 《Estuaries and Coasts》2014,37(6):1388-1402

Tropical cyclones (TCs) are large-scale natural disturbances that generate strong winds and heavy rainfall, impacting coastal and inland environments. TCs also influence biogeochemical and hydrological cycles controlling aquatic primary productivity in tropical and subtropical coastal ecosystems. We assessed TC landfall activity and identified sites along the Mexican east and west coasts with high frequency in the period 1970–2010 and evaluated TCs with significant precipitation. Changes in chlorophyll-a (Chl-a) concentrations before and after storm impacts were estimated using remotely sensed ocean color. There were 1,065 named TCs with a wide diversity in tracks. Three states with the highest number of landfalls were identified: Baja California Sur and Sinaloa on the west coast and Quintana Roo on the east coast. While a relative increase in Chl-a values following TC landfalls in the Baja California and Yucatán Peninsula regions appeared to be strongly linked to TC strength, the intensity of precipitation, the spatial scales of the two peninsulas, and the relative movement of TCs appeared to have contributed to Chl-a variability. Satellite estimates of Chl-a in the nearshore coastal waters following TC passage were likely enhanced by coastal morphology and water discharge along with constituents such as suspended particulate, colored dissolved organic matter and nutrients from rivers, tributaries, and groundwater.  相似文献   

Stochastic seismic performance evaluation of tuned liquid column dampers     

Luis Esteva  Sonia E. Ruiz 《地震工程与结构动力学》1997,26(8):875-876

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Improving the descendant relationship of cluster galaxies at z < 1     

Cleivison Souza de Jesus  Andre Luis Batista Ribeiro  Christine Cordula Dantas 《Astronomische Nachrichten》2024,345(1):e220081

In this work, we study how to improve well-known techniques for detecting progenitors/descendants of galaxies, such as the NDpredict program, when applied to galaxies in clusters. The improvement of this particular method is based on the use of the red sequence of galaxies in those environments. Objects close to the red sequence in the color and magnitude diagram are more likely to belong to the cluster. This defines a probability scale which is then combined with the one generated by NDpredict. This procedure is optimized for the study of galaxies in clusters over different epochs. Our main result is that, for a sample composed of $120$ clusters, with masses greater than ${10}^{13.25}{M}_{\odot }$, selected from the IllustrisTNG simulations (namely, the TNG100 runs). In $99\%$ of the cases (i.e., $119$ systems), we obtain better performance with the red sequence method in comparison to the original NDpredict, and the average gain obtained is $28\%$ in the identification of descendants for this sample of cluster galaxies.  相似文献