Upwelling-enhanced seasonal stratification in a semiarid bay

The role of wind-driven upwelling in stratifying a semiarid bay in the Gulf of California is demonstrated with observations in Bahía Concepción, Baja California Sur, Mexico. The stratification in Bahía Concepción is related to the seasonal heat transfer from the atmosphere as well as to cold water intrusions forced by wind-driven upwelling. During winter, the water column is relatively well-mixed by atmospheric cooling and by northwesterly, downwelling-favorable, winds that typically exceed 10 m/s. During summer, the water column is gradually heated and becomes stratified because of the heat flux from the atmosphere. The wind field shifts from downwelling-favorable to upwelling-favorable at the beginning of summer, i.e., the winds become predominantly southeasterly. The reversal of wind direction triggers a major cold water intrusion at the beginning of the summer season that drops the temperature of the entire water column by 3–5 °C. The persistent upwelling-favorable winds during the summer provide a continuous cold water supply that helps maintain the stratification of the bay.     

Seismic stability analysis of piled embankments: A multiphase approach

The seismic stability analysis of an embankment lying over a soft foundation soil reinforced by a group of vertical piles is performed within the framework of the upper bound kinematic approach of yield design. The analysis is based on a previously developed ‘multiphase’ model of the reinforced ground, which explicitly accounts for the shear and bending resistances of the piles. Making use of appropriate failure mechanisms involving shear zones across which the reinforcements are continuously deforming, along with ‘plastic hinge’ surfaces, upper bound estimates to the critical seismic coefficient of the structure are derived. The results, which are confirmed by the simulations obtained from a finite element elastoplastic code, give clear evidence of the key role played by the bending strength capacities of the piles in ensuring the stability of the pile reinforced embankment. Copyright © 2009 John Wiley & Sons, Ltd.     

Estimating impacts of warming temperatures on California's electricity system

Despite a clear need, little research has been carried out at the regional-level to quantify potential climate-related impacts to electricity production and delivery systems. This paper introduces a bottom-up study of climate change impacts on California's energy infrastructure, including high temperature effects on power plant capacity, transmission lines, substation capacity, and peak electricity demand. End-of-century impacts were projected using the A2 and B1 Intergovernmental Panel on Climate Change emission scenarios. The study quantifies the effect of high ambient temperatures on electricity generation, the capacity of substations and transmission lines, and the demand for peak power for a set of climate scenarios. Based on these scenarios, atmospheric warming and associated peak demand increases would necessitate up to 38% of additional peak generation capacity and up to 31% additional transmission capacity, assuming current infrastructure. These findings, although based on a limited number of scenarios, suggest that additional funding could be put to good use by supporting R&D into next generation cooling equipment technologies, diversifying the power generation mix without compromising the system's operational flexibility, and designing effective demand side management programs.     

The Barny Sentinel trawl-resistant ADCP bottom mount: design,testing, and application

A trawl-resistant bottom mount (TRBM) has been developed to meet the needs of long-term deployment of Acoustic Doppler Current Profilers (ADCPs) and Wave-Tide Gauges in water depths up to 300 m. This paper describes the unit's construction and operation together with practical lessons learned during development, testing, and use that can be applied to comparable platforms. The Barny Sentinel is derived from a larger version developed several years ago at SACLANT Center, now extensively redesigned to incorporate an RDI Sentinel ADCP and a Sea-Bird Wave-Tide Gauge. A concrete ring surrounding the fiberglass instrument housing serves as ballast and impact protection. Two independent recovery modes may be activated by acoustic commands, one of which can operate whether or not the platform is upright. Features have also been included to facilitate recovery by remotely operated underwater vehicle. A sending unit, temporarily attached during launch, provides real time information on platform depth and tilt, and confirms that the platform is properly positioned on the bottom before a launch commitment is made. A series of tests and applications have validated all basic functions and trawl resistance. Platform cost has been kept below that of the on-board instruments, while still maintaining the required high level of recoverability     

Water flux measurement and prediction in young cashew trees using sap flow data

Measurements of sap flow, meteorological parameters, soil water content and tension were made for 4 months in a young cashew (Anacardium occidentale L.) plantation during the 2002 rainy season in Ejura, Ghana. This experiment was part of a sustainable water management project in West Africa. The Granier system was used to measure half‐hourly whole‐tree sap flow. Weather variables were observed with an automatic weather station, whereas soil moisture and tension were measured with a Delta‐T profile probe and tensiometers respectively. Clearness index (CI), a measure of the sky condition, was significantly correlated with tree transpiration (r² = 0·73) and potential evaporation (r² = 0·86). Both diurnal and daily stomata conductance were poorly correlated with the climatic variables. Estimated daily canopy conductance g_c ranged from 4·0 to 21·2 mm s⁻¹, with a mean value of 8·0 ± 3·3 mm s⁻¹. Water flux variation was related to a range of environmental variables: soil water content, air temperature, solar radiation, relative humidity and vapour pressure deficit. Linear and non‐linear regression models, as well as a modified Priestley–Taylor formula, were fitted with transpiration, and the well‐correlated variables, using half‐hourly measurements. Measured and predicted transpiration using these regression models were in good agreement, with r² ranging from 0·71 to 0·84. The computed measure of accuracy δ indicated that a non‐linear model is better than its corresponding linear one. Furthermore, solar radiation, CI, clouds and rain were found to influence tree water flux. Copyright © 2005 John Wiley & Sons, Ltd.     

An empirical approach to estimating population parameters from censored fracture-length distributions

Most fracture data sets are length-censored because of incomplete exposure at the surface, so estimating values of parameters of the sampled populations is difficult. Unless the form of the distribution function of the population is known, or one which is analytically tractable is assumed, length-censoring presents formidable problems in determining population parameters. Tests conducted on experimental fracture patterns developed in clay samples subjected to simple shear loading are the basis of a distribution-free way to estimate population parameters. Comparison of random samples of censored and uncensored fracture lengths shows that a useful, homogeneous data set consists of those cracks which lie entirely within the sampling area (two-ended cracks). The properties of this data set can be used to estimate the mean and variance of uncensored data. Estimates of the maximum fracture length of uncensored data, using the variance and maximum length of these two-ended cracks, show good agreement with measured values. Knowledge of the mean, variance, and maximum value of fracture-length populations are of interest in engineering and hydraulic studies, as well as in remote sensing studies of the Earth and other planets. Application of these results to data on rock masses are subject to the caveat that different crack-growth mechanisms in clay and rock may affect the accuracy of the calculations.     

Interaction of glucose and cellulose with hydrogen sulphide and polysulphides

This paper describes simulation experiments in which glucose and cellulose were reacted with polysulphide and hydrogen sulphide at ambient temperatures in an aqueous environment. Organic sulphur containing compounds were formed that yield several thiophenes upon pyrolysis/evaporation. The experiments show that interaction of carbohydrates with hydrogen sulphide or polysulphides is a possible way for carbohydrates to react in very recent sediments. From the results of this study it can be concluded that carbohydrate carbon can be preserved in sediments in a form that is resistant to microbial attack and that will have a greater potential for survival during diagenesis than the carbohydrate precursor.     

Radon in soil anomaly observed at Los Azufres geothermal field,Michoacan: a possible precursor of the 1985 Mexico earthquake (Ms = 8.1)

A radon anomaly in a nuclear track detector placed on a fault was detected prior to the destructive (Ms = 8.1) Mexican earthquake of 19 September 1985. The fault is a structural feature of the geothermal field Los Azufres, 260 km NE of the epicentral area. Since no other phenomenon can be found as a possible cause for the radon anomaly, it is proposed that preseismic regional stress perturbations may produce changes in the fluid transport patterns at the fault, suggesting that radon measurements in similar conditions could provide a good precursor in high seismic risk areas.     

Seismic hazard computations for regions with low earthquake activity — A case study for the Belgium,The Netherlands and NW Germany area

The algorithms to evaluate seismic hazard, used and/or developed by five teams participating in the TERESA project, applied to the low seismicity area Belgium, The Netherlands and NW Germany are compared. The main differences in the results can be explained by the majority criterion of Egozcue et al. (1989), the differences in the upper bound and zonification and, in some cases, by a higher attenuation.     

Mechanisms of shear failure in artificial fractures of sandstone and their implication for models of hydromechanical coupling

Summary Direct shear tests, in which the behaviour of the rock surfaces during shear could be continuously observed, were used to study the shear failure of a profiled and clean discontinuity artificially prepared from natural sandstone. Displacement transducers were used to measure the normal and shear displacements. A series of strain gauges glued on the sides of the upper block provided information on the change of the stress field occurring close to the discontinuities whilst shear displacement increased, and these changes were then compared with the behaviour of the profiled surface. The results of the laboratory tests, the sequence of photographs taken for most of them, and the results conducted with a sample of similar shape made from the same rock material and tested in a rotary shear machine, allowed several stages and mechanisms of failure to be defined: static friction and mobilization of initial shear stiffness; mobilization of sliding; mobilization of brittle fracture; post-peak failure of the teeth; descent of the teeth; gliding and ploughing; commencement of second cycle of shearing. In many respects these stages are similar to those occurring between sliding surfaces of metal and suggest that the analyses developed in tribology may be relevant to the development of constitutive models for predicting the hydromechanical coupled behaviour of a discontinuity with shear displacement. Such models will have to consider these different stages of shear, because the original discontinuity changes its geometry with displacement and is filled with gouge which changes its grain size with displacement.