Interactions of river discharge and tidal modulation in a tropical estuary, NE Brazil     

Luiz Bruner de Miranda  Alessandro Luvizon Bérgamo  Belmiro Mendes de Castro 《Ocean Dynamics》2005,55(5-6):430-440

Observations of thermohaline properties and currents were undertaken in the Curimataú River estuary (6°18′S), Rio Grande do Norte state (RN), Brazil, during consecutive neap–spring tidal cycles in the austral autumn rainy season. Highly asymmetric neap tide along channel velocities (−0.4 to 0.9 m s⁻¹) and highly stratified conditions were generated by an increase of the buoyancy energy from the freshwater input (R _iE≈5.6). During the spring-tidal cycle the river discharge decreased and the longitudinal velocity components were higher, less asymmetrical (−0.8 to 1.1 m s⁻¹) and semidiurnal, associated with moderately stratified conditions (R _iE≈0.1) due to the increase of the kinetic tidal energy forcing mechanism. The overall salinity variation from surface to bottom during two tidal cycles was from 20.5 to 36.3 and 29 to 36.7 in the neap and spring tide experiments, respectively; in the last experiment, the tropical water (TW) mass intrusion was enhanced. The net salt transport reversed from down to up estuary during the neap and spring tide experiments, respectively, varied from 6.0 to –2.0 kg m⁻¹ s⁻¹, an indication of changes in the main forcing of the estuary dynamics. Evaluation of a classical steady analytical model, in comparison with nearly steady experimental vertical profiles of velocity, shows an agreement classifiable as reasonably fair.  相似文献   

On tuned mass dampers for reducing the seismic response of structures     

Julio C. Miranda 《地震工程与结构动力学》2005,34(7):847-865

This paper presents an energy‐based theoretical model for a two degree‐of‐freedom mechanical system. After a general formulation in Appendix A, the model is specialized to study tuned mass dampers as a means to substantially increase modal damping in order to induce a consequential decrease of the seismic response of the structures thus provided. Although approximate since it neglects coupling due to damping, it is shown that the model yields a first‐order approximation to the exact frequencies, providing values of optimum damping that closely match exact results proposed by others. In view of this, it is proposed that the model be applied through an iterative numerical procedure that identifies the pertinent optimum parameters. It is also shown that for certain particular benchmark cases the model provides closed‐form equations for the parameters defining the dynamic states related to these special conditions. Despite its approximate nature the model presented in this paper is rational, and due to its explicit consideration of energy balance and overall simplicity, it provides a convenient platform for the study of tuned mass dampers, as well as for other methods of structural passive control. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

Reply on the comment by J.P. Lefort and H.G. Miller     

E. A. Silva  J. M Miranda  J. F. Luis  A. Galdeano 《Tectonophysics》2001,340(3-4):261-263

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Climate variability and planktonic communities: The effect of an extreme event (severe drought) in a southern European estuary   总被引：1，自引：2，他引：1  

Snia Cotrim Marques  Ulisses Miranda Azeiteiro  Filipe Martinho  Miguel ngelo Pardal 《Estuarine, Coastal and Shelf Science》2007,73(3-4):725-734

As a consequence of climate change, flood and drought events are increasing in frequency throughout the world. Nevertheless, knowledge of the effects on zooplankton estuarine communities is still scarce. The present study aimed to examine zooplankton ecology over two contrasting environmental conditions: regular years and extreme dry years, in a shallow temperate southern European estuary, the Mondego Estuary (Portugal). Monthly samples were carried out during three consecutive years: 2003 characterized as a regular temperate year concerning precipitation and river flow, and an extremely dry period during 2004–2005. The spatial and temporal structure of the biological data was evaluated by a three-mode principal component analysis (PCA), which allowed us to distinguish three distinct ecological areas based on their biological composition and their relationship with hydrologic parameters. The severe drought in 2004–2005 was responsible for spatial shifts in the estuary regarding zooplankton community and interannual variability, with an increase in abundance and diversity during the period of low freshwater flow. This freshwater flow regime influenced the composition of the zooplankton community at the most upstream section of Mondego estuary (zone 3), with a replacement of the freshwater community by one predominantly dominated by estuarine organisms. The occurrence of such estuarine community contributed to the increase in zooplankton abundance which is ascribed to the estuarine species Acartia tonsa. The comparison with previous data obtained for this estuarine ecosystem, demonstrated the occurrence of a different scenario at times of high freshwater flow, being defined the existence of two sub-estuarine systems, the north and south arm, presenting the south one the highest values of abundance.  相似文献   

On the Discrepancy in Simultaneous Observations of the Structure Parameter of Temperature Using Scintillometers and Unmanned Aircraft     

Miranda Braam  Frank Beyrich  Jens Bange  Andreas Platis  Sabrina Martin  Björn Maronga  Arnold F. Moene 《Boundary-Layer Meteorology》2016,158(2):257-283

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Transpiration and evaporation from heather Moorland     

A. C. Miranda  P. G. Jarvis  J. Grace 《Boundary-Layer Meteorology》1984,28(3-4):227-243

The energy balance of an upland heath dominated by heather (Calluna vulgaris) was measured in dry and wet weather. Median values of both transpiration and evaporation rates were ca. 2 mm hr^-1. The median Bowen ratio for the dry canopy was 2.0 and for the wet canopy 0.6. On dry days the median value of the saturation deficit was only 3.8 mb and that of the climatological resistance was 30 s m^-1. The bulk stomatal resistance increased from ca. 50 s m ^-2 in the morning to over 290 s m^-1 in the afternoon with an overall median value of 110 s m^-1. Transpiration from the dry canopy was controlled by a combination of small saturation deficits and large stomatal resistances. The median value of the boundary-layer resistance of the canopy was 22 s m^-1 and was low partly because of a large low-level drag coefficient. Saturation deficits on wet days were close to zero and evaporation of intercepted water proceeded at close to the equilibrium rate, being largely limited by the low fluxes of available energy. The water loss from heather was compared with simulated losses from coniferous forest, herbaceous crops and grassland in the same conditions to evaluate the effects of vegetation on water loss from catchments.Laboratorio de Ecologia, Dept. de Biologia Vegetal, Universidade de Brasilia, 70 910 — Brasila — DF, Brazil.  相似文献   

Comparison of Different Gold Recovery Methods with Regard to Pollution Control and Efficiency     

Lars D. Hylander  David Plath  Conrado R. Miranda  Sofie Lücke  Jenny Öhlander  Ana T. F. Rivera 《洁净——土壤、空气、水》2007,35(1):52-61

This case study performed at the largest gold mining village in the Philippines compares four methods for gold recovery: amalgamation, cyanide leaching, a shaking sluice, and Cleangold® sluices. The results show that a combination of manual panning or Cleangold® sluices followed by cyanidation is the best solution under present conditions, followed by cyanidation alone. Based on the knowledge obtained, remarks on suitable policy actions, which may be applied also in other gold fields, are made.  相似文献   

Probabilistic estimation of maximum inelastic displacement demands for performance‐based design     

Jorge Ruiz‐García  Eduardo Miranda 《地震工程与结构动力学》2007,36(9):1235-1254

A probabilistic approach to estimate maximum inelastic displacement demands of single‐degree‐of‐freedom (SDOF) systems is presented. By making use of the probability of exceedance of maximum inelastic displacement demands for given maximum elastic spectral displacement and the mean annual frequency of exceedance of elastic spectral ordinates, a simplified procedure is proposed to estimate mean annual frequencies of exceedance of maximum inelastic displacement demands. Simplifying assumptions are thoroughly examined and discussed. Using readily available elastic seismic hazard curves the procedure can be used to compute maximum inelastic displacement seismic hazard curves and uniform hazard spectra of maximum inelastic displacement demands. The resulting maximum inelastic displacement demand spectra provide a more rational way of establishing seismic demands for new and existing structures when performance‐based approaches are used. The proposed procedure is illustrated for elastoplastic SDOF systems having known‐lateral strength located in a region of high seismicity in California. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

Missing women: Reflections on the experiences of Swazi migrant women on the Rand, 1920–1970     

Miranda Miles 《GeoJournal》1993,30(1):85-91

The migration of Swazi women to the Witwatersrand in the period 1920–1970 marked an era of change in the lives of many Swazi women. Under the constraints of rural impoverishment, many women were forced onto the Swazi labour market, one which had little room for women. By the 1930s the exodus of Swazi women to the Rand had gathered so much momentum, that women quickly became objects of national concern to the British colonial government, Swazi traditional authorities and South African authorities. Their experiences as migrant workers in South Africa have largely gone unnoticed. As African women, they suffered the triple oppression of class, race and gender, and as foreign women were subject to a battery of laws designed to keep foreign Africans out of South Africa. The personal experiences of Swazi women as migrants and workers in South Africa are examined here, using life-history or personal narrative techniques which have considerable potential as a way of recovering hidden histories and reinstating the marginalised as makers of their own past.  相似文献   

Average spectral acceleration as an intensity measure for collapse risk assessment          下载免费PDF全文

Laura Eads  Eduardo Miranda  Dimitrios G. Lignos 《地震工程与结构动力学》2015,44(12):2057-2073

This paper investigates the performance of spectral acceleration averaged over a period range (Sa_avg) as an intensity measure (IM) for estimating the collapse risk of structures subjected to earthquake loading. The performance of Sa_avg is evaluated using the following criteria: efficiency, sufficiency, the availability or ease of developing probabilistic seismic hazard information in terms of the IM and the variability of collapse risk estimates produced by the IM. Comparisons are also made between Sa_avg and the more traditional IM: spectral acceleration at the first‐mode period of the structure (Sa(T₁)). Though most previous studies have evaluated IMs using a relatively limited set of structures, this paper considers nearly 700 moment‐resisting frame and shear wall structures of various heights to compare the efficiency and sufficiency of the IMs. The collapse risk estimates produced by Sa_avg and Sa(T₁) are also compared, and the variability of the risk estimates is evaluated when different ground motion sets are used to assess the structural response. The results of this paper suggest that Sa_avg, when computed using an appropriate period range, is generally more efficient, more likely to be sufficient and provides more stable collapse risk estimates than Sa(T₁). Copyright © 2015 John Wiley & Sons, Ltd.  相似文献