Jorge L. Pousa

Changes in the Regime of Storm Surges at Buenos Aires, Argentina

Abstract Located on the west margin of the Rio de la Plata estuary, the capital city of Buenos Aires is often affected by positive and negative storm surges due to strong southeasterly and northwesterly winds, respectively, which sweep the estuary. While positive surges cause severe flooding, negative surges affect navigation and drinking water supply. Since Buenos Aires is densely populated, a quantitative assessment of the variations in the regime of storm surges will help to develop policies for reducing their impacts. Changes in frequency, duration, and height of storm surges over the period 1905–2003 were determined from statistical analyses of hourly water levels. Calculations of the tidal constants used harmonic analyses of 19 y periods to account for any variation in the astronomical tide. Positive and negative surges were chosen from the residuals between observed levels and the predicted tide. The results show that the decadal averages of frequency and duration for positive surges have increased in the last three decades, but they have decreased for negative surges. The average decadal trends of the maximum positive and negative surges in each year, +1.46 ± 0.08 mm/y and +1.02 ± 0.09 mm/y, respectively, compare well with the relative mean water-level rise for Buenos Aires: +1.68 ± 0.05 mm/y. However, the height of positive surges has decreased in the last decade, and negative surges have become more intense in the last two decades.

Environmental impacts and simultaneity of positive and negative storm surges on the coast of the Province of Buenos Aires, Argentina

The Argentine shore of the Rio de la Plata estuary and its southwards adjacent maritime front are normally affected by extratropical positive and negative storm surges that affect human activities seriously. Positive surges can raise the water level in the estuary by more than 3xa0m over the predicted tide; thus, flooding the coastal plain where over 13 million people live and causing extensive property damage. Sometimes, there has been loss of life too. Although less populated than the coastal plain, the maritime front has many important tourist resorts and also undergoes severe beach erosion processes and loss of property owing to positive surges. Negative surges are particularly troublesome in the Rio de la Plata because they critically affect navigation safety and drinking water supply by lowering the predicted water level in an amount that sometimes reached more than 4xa0m. A remarkable point is that the same storm event can simultaneously give rise to a positive surge on the maritime front and a negative one in the Rio de la Plata. The environmental impacts of positive storm surges are strongly aggravated by human intervention. At the same time, sea level rise due to global climatic change has also its influence.

Numerical and experimental study of a thermal probe for measuring groundwater velocity

A thermal method for a rapid measurement of groundwater velocity, particularly in aquifers with preferential flow where groundwater velocities over tenths of (m/d) are expected, was studied. Some instruments for measuring groundwater velocity are based on the application of heat. Those consisting of a central heater surrounded by several thermistors seem adequate for the above purpose, but their measuring range lies below 30 md (meters per day) and there are few works about their theory. Based on the diffusion-convection-dispersion equation, an electrical model is proposed for representing this type of instruments and a theoretical study is presented in an attempt to extend their measuring range. The model can be excited with any shape of power or temperature signals, allows the signals to be feedbacked for controlling the heaters excitation, and includes the thermal features of the heater and thermistors. The model was validated through laboratory tests with velocities of up to 100 md and extrapolated up to 1000 md. Numerical results suggest that exciting the heater with constant temperature allows the measuring range of these probes to be extended.

The ring puckering potential function of trimethylene sulfide and trimethylene selenide

Abstract The rotational constants A , B and C are functions of the vibrational quantum numbers for the out-of-plane bending modes of trimethylene sulfide and trimethylene selenide. Infrared and microwave spectroscopy have been used to determine the dependence between these parameters. The height and shape of the barrier arising from combination of the ring bending modes is also determined. CNDO/2 calculations are used to predict the position of the hydrogen atoms of the methylene groups in trimethylene sulfide and trimethylene selenide. The four-membered rings are non-planar for several vibrational states of the ring bending modes.

A Method to Improve Flow-Velocity Measurements From an Array of Partially Cosine Response Sensors

A groundwater flowmeter whose working principle is based on an array of thermal sensor axes was studied to analyze the errors introduced when the angular response of the sensor axes is partially cosine and varies with flow velocity. It is shown that, although errors due to the partially cosine response can be reduced by increasing the number of sensor axes, the increment in the number of axes introduces some additional errors. A method is proposed to keep the advantages of increasing the number of axes and to minimize the observed additional errors. This method could be extended to other type of arrays whose sensors have a partial cosine response varying with the physical quantity of interest.

Application of absorbent markov chains for a selling model of two independent logi

We have considered self-fertilization with selection for a pair of independent diallelic loci. The average, variance and third order moment about the mean have been calculated for the distribution representing the number of generations needed to reach an absorption beginning in any one of the transient states. n nWe have analysed four cases: no selection and those arising from the combination of advantage selective values for the heterozygous and homozygous genotypes for both genes. n nAll cases have been compared. For the calculations we have used the theory of absorbent Markov chains. The formalism employed, which arises from a transition matrix P, was previously developed by Kemeny & Snell (1960) and Bosso, Sorarrain & Favret (1969).

Some remarks about the ring puckering potential function of 3-methyleneoxetane

Abstract The rotational constants A, B, C are functions from the vibrational quantum numbers for the out-of-plane ring bending vibration of 3-methyleneoxetane. Gibson and Harris [1] using microwave spectroscopy had given the dependence between quantum vibrational numbers for the out-of-plane bending mode and rotational constants. In this paper, the agreement between experimental results from the microwave measurements and theoretical ones from the CNDO/2 is analysed. The planarity for the strained four-member ring is confirmed from the information available. The position corresponding to the methylene groups is also predicted from CNDO/2 calculations.