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Jara J. Joaquín Moreno Francisco Jara Raúl Dubournais Francisco Mata Rodrigo Peters David Marquardt Carlos Lagos Gustavo 《Natural Resources Research》2019,28(3):813-832
Chile has a rich, but poorly known history of placer gold mining. At present, this sector is almost nonexistent and there are some restrictions for its revival: disperse and partial information on existing resources and limited technical expertise to assess the potential of placer gold mine sites. This paper presents the background, methodology and results of the prioritization process of known prospects of this kind in Chile. This research was part of a publicly funded project aimed to incentivize the development of this industry. The ranking was carried out using the analytic hierarchy process, which allowed to include different quantitative and qualitative variables related to the economic potential, technical aspects, contextual viability and socioeconomic factors in the analysis. The results show that, despite the increasing relevance of environmental and community issues in mining development, the business potential and the economic/technical aspects are the main factors in the early selection of a site to advance in exploration and development activities. Both variables represented around 40% and 37% of weights in the final selection, respectively. In contrast, contextual viability and local socioeconomic impacts only accounted for the remaining 23%. This study also shows that the inclusion of experts with different backgrounds in the process enriches the analysis and does not significantly distort the final outcome of the prioritization. Finally, the relevance of using MCDM tools when assessing the attractiveness of mine sites for their development is highlighted, particularly when public funds for subsequent exploration activities are committed.
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Valentina Jara Francisco J. Meza Tania Zaviezo Rodrigo Chorbadjian 《Climatic change》2013,117(1-2):305-317
Maconellicoccus hirsutus (Green) (Hemiptera:Pseudoccidae) is an important pest in many countries being responsible for considerable economic loses. Although it is not currently present in Chile, the chance that it could be accidentally introduced rises with the list of infested countries increasing over the last years. In addition, climate change projections indicate that a larger region would fit as potential habitat for this pest, allowing it to persist over time and colonize a larger proportion of the Chilean territory. In this study the geographic distribution and the number of generations this mealybug would develop in Chile were determined, under current temperatures and under two projected climatic scenarios. Cumulative degree days were calculated for current and future scenarios using a lower temperature threshold of 14.5 °C, with 624.5 degree-days as the thermal requirement for the species to complete one generation. The results show that under current climate conditions M. hirsutus could develop up to three generations in the north of the country (i.e. 18° South) and one generation in the region near 37° South. Under future scenarios’ conditions the pest could develop up to five generations in the north, and one generation around the 42° South. Present climate conditions in Chile would allow the establishment of the pink hibiscus mealybug, if the pest enters the country. Climate change conditions would allow the potentially invaded area to expand south, and would promote the development of more generations per year of the mealybug in the studied territory. 相似文献
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J. M. Jara B. A. Olmos M. Jara W. M. Conejo 《Bulletin of Earthquake Engineering》2016,14(10):2859-2880
Highway bridges are essential structures in the transportation system of any country in the world. Many highway bridges are reinforced concrete (RC) bridges that were constructed before the 1980s, prior to current seismic regulation codes. The continuous modification of regulation codes makes it necessary to evaluate structures, and in many cases, existing bridges require interventions to increase their seismic capacity. Among the different techniques used to improve bridge capacity, encasing the columns with RC jackets increases the strength and stiffness of the substructure. RC jacketing increases the column cross sections, improves the seismic capacity and reduces the seismic vulnerability of the bridge substructures. This work presents a parametric study to assess the expected demands of seismically deficient medium length highway bridges retrofitted with RC jacketing aimed at determining the best jacket parameters. A suite of twenty strong ground motions, recorded from a subduction seismic source close to the Pacific Coast in Mexico, was selected to characterize the seismic demand. The bridge superstructures are simply supported with five 30 m long spans for a total length of 150 m. The bridge models have five possible pier heights of 5, 10, 15 20 and 25 m and three different jacket thicknesses and steel ratios. Pushover analyses and capacity spectra of the family of accelerograms allow for the determination of the pier demands by obtaining the performance point as the intersection of the capacity and demand curves. The results allow for the determination of the influence of each parameter on the expected seismic behavior of the bridge models, with the aim of selecting the most suitable jacket characteristics to improve the seismic bridge performance. 相似文献
4.
Jos E Celis Winfred Espejo Ricardo Barra Daniel Gonzalez-Acua Francisca Gonzalez Solange Jara 《极地研究(英文版)》2015,(1)
In recent decades, polar regions of the planet have witnessed an increase in human presence. Antarctica is considered one of the most pristine regions of the world, but it could be affected by pollutio... 相似文献
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Pollen–climate reconstruction from northern South Island,New Zealand (41°S), reveals varying high‐ and low‐latitude teleconnections over the last 16 000 years 
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We present detailed pollen and charcoal records from Lago Pichilafquén (~ 41°S) to decipher the effects of climate change and varying disturbance regimes on the composition and structure of the vegetation on the Andean foothills of northwestern Patagonia during the last 2600 yr. Here, temperate rainforests have dominated the landscape since 2600 cal yr BP with variations ranging from cool-temperate and wet north Patagonian rainforests to relatively warm and summer-drought-resistant Valdivian rainforests. We interpret relatively warm/dry conditions between 1900–2600, 690–750 and 320–430 cal yr BP, alternating with cold/wet conditions between 1500–1900, 750–1100 and 430–690 cal yr BP. Rapid deforestation and spread of plants introduced by Europeans occurred at 320 and 140 cal yr BP. The record includes five tephras with ages of 2130, 1460, 1310, 1210, and 340 cal yr BP, all of which precede local fire events and increases in trees favored by disturbance by less than 100 yr. We conclude that centennial-scale changes in the southern westerlies were the primary driver of vegetation shifts in northwestern Patagonia over the last 2600 yr. Within this interval, local disturbance regimes altered the structure, composition, and dynamics of the lowland rainforest vegetation during several discrete, short-lived episodes. 相似文献
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The objective of this study was to investigate the effect of lead rubber isolators on the seismic response of bridges designed
according to current codes for two different soil conditions: hard and medium type soils, in order to assess their applicability
for the design of new bridges or retrofit of existing ones. The study was conducted for two levels of earthquake, one corresponding
to a return period of 50 years and a service limit state, the other with a return period of 1,000 years and a failure limit
state. Twenty one subduction earthquake records on the two types of soil were used to evaluate the linear and nonlinear dynamic
response of a set of bridges designed for this purpose with and without base isolation. The response parameters evaluated
are the maximum relative displacement on top of the piers, the maximum pier distortion, the maximum shear forces in the piers
and the ductility demands for the isolators. The results presented are the average of these maxima for the various earthquakes.
This study is an expansion of a previous one in which the seismic response of 36 bridges considering models with and without
base isolators, structures with linear base isolators and bridges with nonlinear isolators. The results of this study confirm
the conclusions previously obtained and show that the isolation can have beneficial effects even for bridges located in medium
soil types. 相似文献
9.
José M. Jara Dorian Villanueva Manuel Jara Bertha A. Olmos 《Bulletin of Earthquake Engineering》2013,11(2):663-686
Bridge structures are usually built on irregular topographical surfaces which create substructures with different pier heights and non uniform stiffness distribution. Three irregularity types of typical reinforced concrete (RC) medium length bridges located in a high seismicity zone of Mexico, were analyzed aimed at determining the best strength and stiffness parameters of an isolation system. The isolation system is composed by lead rubber bearings (LRB) located on each pile and abutment. The variation of the bridge characteristics and the isolation parameters produced 169 models that were subjected to ten seismic records representative of the subduction zone in the Pacific Coast of Mexico. A total of 1690 nonlinear time history analyses (NLTHA) were carried out in longitudinal and transverse directions of the structures. The maximum pier drifts, bending moments and shear forces demands were analyzed to identify the best isolation properties for reducing the concentration of damage in one or two elements and for improving the structural behavior of irregular bridges. Additionally, the analysis of the seismic response of the bridges supported on traditional neoprene bearings was carried out. 相似文献
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