Nuevas consideraciones sobre la sismicidad inducida en los diques de embalse

Si bien los resultados obtenidos en las investigaciones realizadas por el instituto Sismológico Zonda (ISZ), entre 1978 y 1981, sobre las variaciones de la actividad sísmica en la zona del embalse del dique de Ullum, fueron claros y convincentes en demostrar que el peso del agua del embalse no producía variaciones significativas en la actividad sísmica de la zona, nos ha dejado, sin embarco, con el deseo de conocer las causas mas profundas por las cuales los hechos sucedían de ese modo.Asociación Argentina de Geofísicos y Geodesta

Nanotribological characterization of industrial Polytetrafluorethylene-based coatings by atomic force microscopy

We present the result of a systematic study of the tribological properties of industrial Polytetrafluorethylene (PTFE)-based coatings carried out with an atomic force microscope. A new characterization protocol allowed the reliable and quantitative assessment of the friction coefficient and adhesion forces at the sub-micrometer scale even for highly corrugated industrial samples. We have studied and compared PTFE coatings charged with different additives in dry and humid environment. The influence of additives and humidity on the friction coefficient and on adhesion forces has been investigated using standard silicon nitride tips as sliders in the low-load regime.Comment: to be published in Thin Solid Films 18 pages, 2 tables, 3 figure

Nutrient function over form: Organic and inorganic nitrogen additions have similar effects on lake phytoplankton nutrient limitation

The concentration of dissolved organic nitrogen (DON) is increasing in many northern hemisphere lakes, yet its use by phytoplankton and fate in the environment seldom have been quantified. We conducted 1 week, insitu, microcosm incubations across 25 lakes in northeastern North America to understand how DON, dissolved norganic nitrogen (DIN), and dissolved inorganic phosphorus (P) affected phytoplankton biomass. In addition,we tested whether lakes were limited by single macronutrients (N or P) or colimited by both. Phytoplankton biomass in 80% of lakes responded similarly to DON and DIN additions. Of the lakes where N form produced differential responses, the majority of phytoplankton communities exhibited greater biomass accumulation with DON than DIN. Colimitation was the most common type of nutrient limitation among the study lakes,followed by P limitation. Limitation type shifted with N form in 40% of the study lakes, but without consistent patterns explaining how shifts occurred. Regardless of N form, lakes with watersheds more dominated by agriculture and higher total dissolved nitrogen (TDN) tended to show P‐limited phytoplankton responses, while lakes with less agricultural watersheds and lower TDN tended to show colimited phytoplankton responses.Finally, ambient TDN and total phosphorus (TP) nutrient concentrations were stronger predictors of limitation type than ambient TDN : TP ratios. The different contributions of DON and DIN to phytoplankton biomass insome of our study lakes suggest that DON loading from surrounding watersheds may be an overlooked compo-nent in predicting phytoplankton productivity and nutrient limitation dynamics in freshwater ecosystems

La actividad sísmica en la Sierra Chica de Zonda antes y después del Dique de Ullum

La construcción del Dique de Ullum en la Provincia de San Juan ofrece a los sismólogos una nueva oportunidad para investigar el problema de la Sismicidad Inducida. La suerte quiso que el embalse cayera dentro del área de una red de siete estaciones sismológicas de alta sensibilidad. La ubicación de la presa está en una quebrada de la Sierra Chica de Zonda, a unos 12 km al oeste de la ciudad de San Juan. La Sierra es reconocida como zona sísmicamente muy activa. El primero de abril de 1978 se empezó a estudiar los sismos que se producían dentro de un radio no mayor de 60 km a partir del dique. El llenado del embalse empezó el 28 de diciembre de 1979 y el 12 de diciembre de 1980 el agua alcanzó el umbral del vertedero. El embalse se mantuvo lleno hasta el 20 de marzo de 1981. Durante 21 meses, con el dique vacío, se registraron 119 sismos; mientras que durante los 15 meses del período del llenado y con el dique lleno se registraron 140 sismos. Pero ha sucedido que el 24 de enero de 1980 y el 18 de abril del mismo año, cuando todavía había muy poca agua en el embalse, se produjeron dos fuertes sismos en la Sierra Chica de Zonda, a unos 20 kilómetros al sud del embalse. Ambos fueron seguidos de réplicas que aumentaron notablemente la frecuencia de los sismos. En opinión de los autores, el embalse no ha intervenido en la generación de los dos fuertes sismos y se habrían producido igualmente sin el embalse. Como resultado final no se observa que, aún con el embalse lleno, se modifique la sismicidad natural de la zona.The construction of the Ullum Dam in the Province of San Juan provides, seismologists with a new opportunity to conduct research on the problem of Induced Seismicity. Fortunately, the dam was located within the area covered by seven high sensibility seismologic stations network. The dam is located in the Sierra Chica de Zonda valley, about 12 km, to the West of San Juan City. The Sierra is considered to be a very active seismical area. On April 1st, 1978 a study on the seisms that took place within 60 km from the dam, was started. The filling of the dam started on December 28th, 1979, and the water reached the spillway threshold on December 12th,1980. The dam remained full until March 20th, 1981. During 21 months, period in which the dam remained empty, 119 seisms were recorded, while during the 15 months, corresponding to the period when it was full, 140 seisms were recorded. But, on January 24th, and April 18th, 1980,when there was still very little water in the dam, two strong seisms took place at the Sierra Chica de Zonda at about 20 km South of the dam. Both seisms were followed by aftershocks that increased significantly their frecuency. In the authors opinion, the dam has had no influence in the generation of the two strong earthquakes wich could have taken place, even if the dam had no been built. We can conclude that there is no clear evidence indicating that, even with the dam filled up, the seismic nature of the area has been modified.Asociación Argentina de Geofísicos y Geodesta

Las variaciones de cotas del terremoto de Caucete (San Juan, 23 de noviembre de 1977) y su relación con las anomalías gravimétricas

Gracias a la oportuna coincidencia de que se realizaran, al este de la ciudad de.San Juan, nivelaciones de alta precisión y un relevamiento gravimétrico, en la misma zona que fue luego la zona epicentral del fuerte terremoto de Caucete (23 de noviembre de 1977), ha permitido verificar varios resultados de importancia geodinámica. Los más notables son los siguientes: (a) El fuerte levantamiento del cerro Pie de Palo (1,20 m aprox.) que produjo el terremoto, ya se venía manifestando anteriormente. En efecto, entre 1938 y 1967 el levantamiento del cerro con respecto a su base occidental era de unos 4 cm; este levantamiento llega a 6 cm en 1976, o sea un año antes del terremoto. Finalmente se verificó que después del sismo, entre mayo 1978 y abril 1980, el levantamiento continúa y crece unos 9 cm más. (b) El relevamiento gravimétrico realizado a lo largo de la misma línea sobre la cual se efectuaron las nivelaciones, mostró que en correspondencia con el cerro Pie de Palo existía una Anomalía de Aire Libre positiva de varios miligales respecto de los valores existentes a ambos lados del cerro. El hecho de que el cerro se encuentre en su proceso de levantamiento demostraría que el valor de la anomalía de Aire Libre también seguiría creciendo.High precisión levellings and a gravimetric survey perfomed, to the East of San Juan City in the same area that was later the epicentral area of the strong Caucete earthquake (November 23rd, 1977),made it possible to verify several results of geodynamic importance. The most remarkable are the following: (a) The strong uplift of the Pie de Palo Mount (1.20 m approximately), which caused the earthquake, had been previously shown. In fact, between 1938 and 1967, that uplift with respect to its western base was of about 4 cm, and it reached 6 cm in 1976, i.e. a year before the earthquake. Finally, it was verified that after the earthquake, between May 1978 and April 1980, the uplift continued and grew about 9 cm more, (b) The gravimetric survey carried out along the same line on which the levellings were performed, showed that in correspondence with the Pie de Palo Mount there was a positive Free Air Anomaly of several miligals with relation to the existing values at both sides of the mount. The fact that the mount is undergoing an uplifting process would show that the value of the Free Air Anomaly would also keep on growing.Asociación Argentina de Geofísicos y Geodesta

Using cloud radar to investigate the effect of rainfall on migratory insect flight

The fate of migrating insects that encounter rainfall in flight is a critical consideration when modelling insect movement, but few field observations of this common phenomenon have ever been collected due to the logistical challenges of witnessing these encounters. Operational cloud radars have been deployed around the world by meteorological agencies to study precipitation physics, and as a byproduct, provide a rich database of insect observations that is freely available to researchers. Although considered unwanted ‘clutter’ by the meteorologists who collect the data, the analysis method presented here enables ecologists to delineate co-occurring signals from insects and raindrops. We present a method that uses image processing techniques on cloud radar velocity spectra to examine the fate of migrating insects when they encounter precipitation. By analysing velocity spectra, we can distinguish flying insects from falling rain and compare the relative density of insects in flight before, during and after the rainfall. We demonstrate the method on a case of insect migration in Oklahoma, USA. Using this method, we show the first reconstructed images of migrating insect layers in flight during rainfall. Our analysis shows that mild to moderate rainfall diminishes the number of insects aloft but does not cause full termination of migratory flight, as has previously been suggested. We hope this technique will spur further investigations of how changing weather conditions impact insect migration, and enable some of the first of such studies in regions of the world that are underrepresented in the literature

Propulsion Health Management System Development for Affordable and Reliable Operation of Space Exploration Systems

The constraints of future Exploration Missions will require unique integrated system health management capabilities throughout the mission. An ambitious launch schedule, human-rating requirements, long quiescent periods, limited human access for repair or replacement, and long communication delays, all require an integrated approach to health management that can span distinct, yet interdependent vehicle subsystems, anticipate failure states, provide autonomous remediation and support the Exploration Mission from beginning to end. Propulsion is a critical part of any space exploration mission, and monitoring the health of the propulsion system is an integral part of assuring mission safety and success. Health management is a somewhat ubiquitous technology that encompasses a large spectrum of physical components and logical processes. For this reason, it is essential to develop a systematic plan for propulsion health management system development. This paper provides a high-level perspective of propulsion health management systems, and describes a logical approach for the future planning and early development that are crucial to planned space exploration programs. It also presents an overall approach, or roadmap, for propulsion health management system development and a discussion of the associated roadblocks and challenges

Swirling astrophysical flows - efficient amplifiers of Alfven waves

We show that a helical shear flow of a magnetized plasma may serve as an efficient amplifier of Alfven waves. We find that even when the flow is purely ejectional (i.e., when no rotation is present) Alfven waves are amplified through the transient, shear-induced, algebraic amplification process. Series of transient amplifications, taking place sequentially along the flow, may result in a cascade amplification of these waves. However, when a flow is swirling or helical (i.e., some rotation is imposed on the plasma motion), Alfven waves become subject to new, much more powerful shear instabilities. In this case, depending on the type of differential rotation, both usual and parametric instabilities may appear. We claim that these phenomena may lead to the generation of large amplitude Alfven waves and the mechanism may account for the appearance of such waves in the solar atmosphere, in accretion-ejecion flows and in accretion columns. These processes may also serve as an important initial (linear and nonmodal) phase in the ultimate subcritical transition to MHD Alfvenic turbulence in various kinds of astrophysical shear flows.Comment: 12 pages, 11 figures, accepted for publication (25-11-02) in Astronomy and Astrophysic

Immobilization, stabilization and patterning techniques for enzyme based sensor systems.

Sandia National Laboratories has recently opened the Chemical and Radiation Detection Laboratory (CRDL) in Livermore CA to address the detection needs of a variety of government agencies (e.g., Department of Energy, Environmental Protection Agency, Department of Agriculture) as well as provide a fertile environment for the cooperative development of new industrial technologies. This laboratory consolidates a variety of existing chemical and radiation detection efforts and enables Sandia to expand into the novel area of biochemically based sensors. One aspect of this biosensor effort is further development and optimization of enzyme modified field effect transistors (EnFETs). Recent work has focused upon covalent attachment of enzymes to silicon dioxide and silicon nitride surfaces for EnFET fabrication. They are also investigating methods to pattern immobilized proteins; a critical component for development of array-based sensor systems. Novel enzyme stabilization procedures are key to patterning immobilized enzyme layers while maintaining enzyme activity. Results related to maximized enzyme loading, optimized enzyme activity and fluorescent imaging of patterned surfaces will be presented