Generalized dynamic analysis of structural single rocking walls (SRWs)     

Dimitrios Kalliontzis  Arturo E. Schultz  Sri Sritharan 《地震工程与结构动力学》2020,49(7):633-656

The investigation of structural single rocking walls (SRWs) continues to gain interest as they produce self-centering lateral load responses with reduced structural damage. The simple rocking model with modifications has been shown to capture these responses accurately if the SRW and its underlying base are infinitely rigid. This paper advances previous rocking models by accounting for (1) the inelastic actions at or near the base of the SRW and (2) the flexural responses within the wall. Included in the proposed advancements are hysteretic and inherent viscous damping associated with these two deformation components so that the total dynamic responses of SRWs can be captured with good accuracy. A system of nonlinear equations of motion is developed, in which the rocking base is discretized into fibers using a zero-length element to locate the associated compressive deformations and damage. The flexural deformations of the rocking body are captured using an elastic term, while the impact events are modeled using impulse-momentum equations. Comparisons with experiments of structural precast concrete and masonry SRWs show that the proposed approach accurately estimates the dynamic responses of different SRWs with and without unbonded posttensioning, for various dynamic excitations and degrees of hysteretic action. Using the proposed approach, a numerical investigation employs different configurations of structural SRWs to quantify the various sources of energy loss, including hysteretic action and impact damping, during various horizontal ground motions.  相似文献   

Reef fish structure assemblages in oceanic islands of the eastern tropical Pacific: Revillagigedo Archipelago and Clipperton atoll     

Manon Fourrire  Hctor Reyes‐Bonilla  Cristian Moiss Galvn‐Villa  Arturo Ayala Bocos  Fabin Alejandro Rodríguez‐Zaragoza 《Marine Ecology》2019,40(3)

Revillagigedo Archipelago and Clipperton atoll are oceanic islands located in the eastern tropical Pacific. The composition and trophic structure of their fish assemblages have never been characterized in detail, and the aim of this study was therefore to analyse the community structure and assess the similarity of fish assemblages between these two areas. Underwater visual fish censuses were conducted using band transects at two depth levels in three islands of the Revillagigedo Archipelago (Socorro, San Benedicto, and Roca Partida) and at Clipperton atoll. We calculated ecological indices (density, richness, Shannon diversity, Pielou evenness, and taxonomic distinctiveness) for each transect. These were compared in order to determine quantitative differences among the islands and bathymetric levels. Qualitative analyses (ANOSIM, nMDS, and SIMPER) were also performed. Finally, we analysed the trophic structure of the assemblages and the functional diversity of the four studied sites. The results showed significant differences for all indices, except diversity (H′). Roca Partida was the site with greatest abundance and richness due to the presence of pelagic species in large numbers. No significant differences were found in functional diversity, suggesting a high degree of ecological redundancy. Lower‐level carnivores with mean trophic level values of between 3.3 and 3.8 dominated both areas. The ordination analysis did not show a clear difference in fish composition among the islands, although Clipperton atoll has a particular fauna characterized by endemic species (Thalassoma robertsoni and Stegastes baldwini). In conclusion, the fish communities of the studied areas seem quite similar, but their assemblage structure differs. In particular, Clipperton is differentiated by the influence of endemic species.  相似文献   

Regional analysis of indirect factors affecting the recovery,degradation and deforestation in the tropical dry forests of Oaxaca,Mexico     

Francisco Guerra‐Martínez  Arturo García‐Romero  Andrea Cruz‐Mendoza  Laura Osorio‐Olvera 《Singapore journal of tropical geography》2019,40(3):387-409

This study evaluates the dynamics and identifies the indirect biophysical and socio‐economic factors related to the recovery, degradation and deforestation of the tropical dry forest (TDF) cover in the municipality of Tehuantepec, Oaxaca, Mexico. Annual rates and transition matrices were determined to identify indirect factors; the cartographic information of 25 variables with shift points were overlaid and Generalized Linear Models (GLM) were applied. The change process with the greatest impact in TDF during the study period (1993–2011) was degradation, with 10468 ha degraded (12 per cent of the initial tropical cover); recovery of coverage was the second most important change process, with 4808 ha (5.5 per cent); and deforestation was the change process with the lowest impact, with a loss of 2800 ha (3.23 per cent). The net balance was negative, with a decrease (through land degradation and deforestation) of 8460 ha (9.75 per cent). The recovery of coverage was mainly associated with biophysical factors such as land suitability and accessibility to natural vegetation. On the other hand, deforestation and degradation of coverage were associated with both biophysical and socioeconomic factors such as land suitability, accessibility to natural vegetation, migration, marginalization, population pressure, economy, education and health. The findings of this study determined the spatial distribution of forest recovery, deforestation and degradation processes at a regional level, allowing for future researchers to focus their efforts at local and landscape levels. Also, the work allows for an approximation of the factors associated with the change processes studied, hence supporting the allocation of resources for the establishment of management, conservation, development and restoration strategies of tropical dry forests at the regional level.  相似文献   

Seasonal trend analysis (STA) of MODIS vegetation index time series for the mangrove canopy of the Teacapan-Agua Brava lagoon system,Mexico     

César Alejandro Berlanga-Robles  Arturo Ruiz-Luna  Marta Rocío Nepita Villanueva 《地理信息系统科学与遥感》2019,56(3):338-361

Monthly time series, from 2001 to 2016, of the Normalized Difference Vegetation Index (NDVI) and the Enhanced Vegetation Index (EVI) from MOD13Q1 products were analyzed with Seasonal Trend Analysis (STA), assessing seasonal and long-term changes in the mangrove canopy of the Teacapan-Agua Brava lagoon system, the largest mangrove ecosystem in the Mexican Pacific coast. Profiles from both vegetation indices described similar phenological trends, but the EVI was more sensitive in detecting intra-annual changes. We identified a seasonal cycle dominated by Laguncularia racemosa and Rhizophora mangle mixed patches, with the more closed canopy occurring in the early autumn, and the maximum opening in the dry season. Mangrove patches dominated by Avicennia germinans displayed seasonal peaks in the winter. Curves fitted for the seasonal vegetation indices were better correlated with accumulated precipitation and solar radiation among the assessed climate variables (Pearson’s correlation coefficients, estimated for most of the variables, were r ≥ 0.58 p < 0.0001), driving seasonality for tidal basins with mangroves dominated by L. racemosa and R. mangle. For tidal basins dominated by A. germinans, the maximum and minimum temperatures and monthly precipitation fit better seasonally with the vegetation indices (r ≥ 0.58, p < 0.0001). Significant mangrove canopy reductions were identified in all the analyzed tidal basins (z values for the Mann-Kendall test ≤ ?1.96), but positive change trends were recorded in four of the basins, while most of the mangrove canopy (approximately 87%) displayed only seasonal canopy changes or canopy recovery (z > ?1.96). The most resilient mangrove forests were distributed in tidal basins dominated by L. racemosa and R. mangle (Mann-Kendal Tau t ≥ 0.4, p ≤ 0.03), while basins dominated by A. germinans showed the most evidence of disturbance.  相似文献   

Dealing with locally-driven degradation: A quick start option under REDD+     

Skutsch MM  Torres AB  Mwampamba TH  Ghilardi A  Herold M 《Carbon balance and management》2011,6(1):16

The paper reviews a number of challenges associated with reducing degradation and its related emissions through national approaches to REDD+ under UNFCCC policy. It proposes that in many countries, it may in the short run be easier to deal with the kinds of degradation that result from locally driven community over-exploitation of forest for livelihoods, than from selective logging or fire control. Such degradation is low-level, but chronic, and is experienced over very large forest areas. Community forest management programmes tend to result not only in reduced degradation, but also in forest enhancement; moreover they are often popular, and do not require major political shifts. In principle these approaches therefore offer a quick start option for REDD+. Developing reference emissions levels for low-level locally driven degradation is difficult however given that stock losses and gains are too small to be identified and measured using remote sensing, and that in most countries there is little or no forest inventory data available. We therefore propose that forest management initiatives at the local level, such as those promoted by community forest management programmes, should monitor, and be credited for, only the net increase in carbon stock over the implementation period, as assessed by ground level surveys at the start and end of the period. This would also resolve the problem of nesting (ensuring that all credits are accounted for against the national reference emission level), since communities and others at the local level would be rewarded only for increased sequestration, while the national reference emission level would deal only with reductions in emissions from deforestation and degradation.  相似文献   

Impacts of irrigation on dry season precipitation in India     

Shouraseni Sen Roy  Rezaul Mahmood  Arturo I. Quintanar  Astrid Gonzalez 《Theoretical and Applied Climatology》2011,104(1-2):193-207

There is a lack of observed data-based studies examining the role of enhanced soil moisture conditions (due to irrigation) on the prevailing precipitation. Therefore, in the present study, we have examined the impacts of the Green Revolution (GR) related expansion of irrigation and changes in dry season (the rabi (November to May) and the zaid (March to June)) precipitation in India. The results for some regions indicated decreasing and increasing trend in precipitation during the pre- and post-GR periods, respectively. For example, in eastern Madhya Pradesh, the pre- and post-GR precipitation trends for the zaid season were ?0.45 and 2.40?mm?year^?1, respectively. On the other hand, some regions reported lower rate of decline in precipitation during the post-GR period. This paper suggests that both positive and lower declining trend during the post-GR period were linked to increased precipitation due to the introduction of irrigation. The study has found up to 69?mm (121%) increase in total amount of precipitation for growing seasons during the post-GR period. Moreover, a 175% increase in average precipitation was also recorded. All irrigated regions show a notable increase in precipitation during post-GR growing seasons. It was found that differences in growing season average precipitation between the pre- and post-GR periods were statistically significant for most of the regions. For further verification of results, the MM5 and Noah land surface model were applied. These applications show changes in precipitation and various precipitation controlling factors due to changes in soil moisture.  相似文献   

Paleomagnetic results from the Permian Rodez basin implications: the Late Variscan tectonics in the southern French Massif Central     

Arturo Diego-Orozco  Yan Chen  Bernard Henry  Jean-François Becq-Giraudon 《Geodinamica Acta》2013,26(4):249-260

Abstract

A paleomagnetic study has been carried out on three sedimentary formations of the Permian Rodez basin in the southern France. Two of them yield paleomagnetic poles of Saxonian and Thuringian age showing counterclockwise rotation of moderate amplitude, during or after the Thuringian deposition. For the French Massif Central, contrary to its stable southern (Lodève basin) and eastern (Largentière basin) borders, on its southwestern border, in a large area including the Rodez, Saint-Affrique and perhaps Brive basins suffered rotations due to the extensional tectonics during the Late Variscan period. © 2002 Editions scientifiques et médicales Elsevier SAS. All rights reserved.  相似文献   

Rock‐Magnetic and Archaeointensity Investigation of Pottery and a Burned Floor at the Tzintzuntzan Archaeological Site,Western Mexico     

Juan Morales  Avto Goguitchaichvili  Bertha A. Aguilar‐Reyes  Modesto Pineda  Claire Carvallo  Laura Beramendi‐Orosco  Galia Gonzlez‐Hernndez  Arturo Oliveros 《Geoarchaeology》2012,27(6):521-537

We report a detailed rock‐magnetic and archaeointensity analysis of four pottery fragments and a burned floor recovered from the Tzintzuntzan archaeological site in western Mexico. Results from rock‐magnetic experiments (x‐T curves and first‐order reversal curves [FORC] diagrams) indicate the suitability of most of these materials as faithful geomagnetic field recorders. Potsherds were archaeomagnetically dated by comparing their mean intensity values against the paleosecular variation curve CALS3k, suggesting A.D. 600–941 as the most probable age range. This is younger than ¹⁴C‐dated charcoal from the same burned floor (A.D. 1294–1426). More precise age estimates will require the use of the full geomagnetic vector (declination, inclination, and intensity). Multiple reheatings of the ceramic pieces, evidenced as secondary components in Zijderveld plots, could reflect multiple heating of these objects, perhaps from use as incense burners. Our study demonstrates the potential of archaeomagnetic analysis to both date burned ceramics recovered in situ and provide insight into their use‐history.  相似文献   

Paleoseismicity and seismic hazard in southern Patagonia (Argentina-Chile; 50°–55°S) and the role of the Magallanes-Fagnano transform fault     

Gustavo González Bonorino  Víctor Rinaldi  Liliana del Valle Abascal  Patricia Alvarado  Gustavo G. Bujalesky  Arturo Güell 《Natural Hazards》2012,61(2):337-349

Patagonia, including the island of Tierra del Fuego, lies in southernmost South America at the junction of the South American, Antarctic, and Scotia tectonic plates. Historical and instrumental records have documented several local earthquakes of damaging magnitude, posing a threat to the rapidly growing population of 300,000 and the expanding industrial and service infrastructure. Short and inaccurate instrumental records of local seismic events and a diffuse epicenter distribution not clearly related to the recognized seismogenic structures have hindered an adequate evaluation of the seismic hazard for this region. To improve this situation, a paleoseismological study was carried out on two gravelly strandplains on the Atlantic coast of Patagonia. Surveying combined ground-probing radar, vertical electric sounding, and seismic refraction. Coseismic normal faults buried beneath the strandplain bodies were revealed and related to the morphology of the strandplains. The faults have probable ages between 0.9 and 6.4 kyr BP and a recurrence rate of about 1 kyr. The more likely source for these structures is the Magallanes-Fagnano fault, a continental transform fault that crosses Tierra del Fuego. The distance of more than 300 km from the buried coseismic structures to the trace of the Magallanes-Fagnano fault argues for high-magnitude earthquake activity on this fault throughout the Holocene. Urban development on soft glacial and alluvial substrates increases the hazard.  相似文献   

Building global and diffuse solar radiation series and assessing decadal trends in Girona (NE Iberian Peninsula)     

Calbó  Josep  González  Josep-Abel  Sanchez-Lorenzo  Arturo 《Theoretical and Applied Climatology》2017,129(3-4):1003-1015

Measurement of solar radiation was initiated in Girona, northeast of the Iberian Peninsula, in the late 1980s. Initially, two pyranometers were installed, one of them equipped with a shadowband for measuring the diffuse component. Two other pyranometers currently exist, both ventilated and one of them shadowed, with a sphere, and a pyrheliometer for measuring direct radiation. Additional instruments for other shortwave and longwave components, clouds, and atmospheric aerosols have been installed in recent years. The station is subject to daily inspection, data are saved at high temporal resolution, and instruments are periodically calibrated, all in accordance with the directions of the Baseline Surface Radiation Network. The present paper describes how the entire series of global solar radiation (1987–2014) and diffuse radiation (1994–2014) were built, including the quality control process. Appropriate corrections to the diffuse component were made when a shadowband was employed to make measurements. Analysis of the series reveals that annual mean global irradiance presents a statistically significant increase of 2.5 W m⁻² (1.4 %) decade⁻¹ (1988–2014 period), mainly due to what occurs in summer (5.6 W m⁻² decade⁻¹). These results constitute the first assessment of solar radiation trends for the northeastern region of the Iberian Peninsula and are consistent with trends observed in the regional surroundings and also by satellite platforms, in agreement with the global brightening phenomenon. Diffuse radiation has decreased at −1.3 W m⁻² (−2 %) decade⁻¹ (1994–2014 period), which is a further indication of the reduced cloudiness and/or aerosol load causing the changes.

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