[Todos] Coloquios del Departamento de Física (martes 12/4 extra y jueves 14/4)

pdmitruk en df.uba.ar pdmitruk en df.uba.ar
Vie Abr 8 16:00:39 ART 2011



                                  Charla, café y galletitas
                        En el Aula Federman, 1er piso, Pabellón I,
                                      Ciudad Universitaria


                                    Martes 12 de abril, 14hs,

                 Caracterización y superresolución en pinzas ópticas
                               mediante cámaras rápidas

                                    Carlos Saavedra

                      Departamento de Física, Universidad de Concepción
                                 Centro de Óptica y Fotónica

Una pinza óptica (OT) es un técnica de microscopía para el
atrapamiento de sistemas microscópicos transparentes, inorgánicos y
biológicos. La caracterización usual de las OT es efectuada mediante
mediciones indirectas de movimiento, a menudo efectuadas por
detectores de cuatro cuadrantes. Sin embargo, las cámaras de alta
velocidad son alternativas confiables de caracterización directa de
fuerzas de atrapamiento óptico y movimiento de partículas en una OT.
Los datos de movimiento subpixel de las partículas atrapadas es
obtenido de una secuencia de video proveniente de una cámara de alta
velocidad y baja resolución. Debido a la diversidad del movimiento de
las partículas microscópicas atrapadas, se propuso el empleo de la
información del movimiento para superar la falta de resolución,
aplicando para ellos un método de super-resolución en secuencias de
video de baja resolución, aplicándose a partículas de calibración y
bacterias vivas. En estos momentos, estamos estudiando la
generación en tiempo real de imágenes de video de alta resolución.


                              Jueves 14 de abril, 14 hs

                                 José M. Carcione

                         Istituto Nazionale di Oceanografia e
                            di Geofisica Sperimentale
                                 Trieste, Italia.

The main anthropic cause of climate change is the release of carbon  
dioxide (CO2) into the atmosphere. Fossil-fuel combustion generates in  
excess 27 billion tons of CO2 per year. There is evidence that this  
concentration of CO2 has increased the atmosphere temperature by  
0.3-0.6 oC during the last 150 years. To solve this problem,  
geological sequestration is an immediate option. The possibilities are  
injection into hydrocarbon reservoirs, methane-bearing coal beds and  
saline aquifers. An example of the latter is the Sleipner field in the  
North Sea, where CO2 is stored in the Utsira formation, a highly  
permeable porous sandstone 800 m below the sea bottom. Carbon dioxide  
stored in
saline aquifers has some advantages, because it does not require  
structural and
stratigraphic trap geometries. The storage can be hydrodynamic as  
dissolved CO2 in the formation waters. However, the disposal should be  
made at supercritical pressures to avoid the presence of the gas  
phase, with the minimum aquifer depth of nearly 1 km (the critical  
pressure and temperature of CO2 are 7.4 MPa and 31 oC, respectively)  
(1 MPa = 10 bar = 145.04 psi = 9.87 atm.).
We present a new petro-elastical model and seismic monitoring  
methodology for reservoirs subject to CO2 sequestration. The  
petro-elastical equations model the seismic properties of reservoir  
rocks  saturated with CO2, methane, oil and brine. The gas properties  
are obtained from the van der Waals equations and we take into account  
the absorption of gas by oil and brine as a function of the in-situ  
pore pressure and temperature. The dry-rock bulk and shear moduli can  
be obtained either by calibration from real data or by using  
rock-physics models based on the Hertz-Mindlin and Hashin-Shtrikman  
theories. Mesoscopic
attenuation due to fluids effects is quantified by using White's model  
of patchy
saturation, and the wet-rock velocitiesare calculated with Gassmann  
equations by using an effective fluid modulus to describe the  
velocities predicted by White's model. Synthetic seismograms are  
computed with a poro-viscoelastic modeling code based on Biot's  
theory, where viscoelasticity is described by generalizing the  
solid/fluid coupling modulus to a relaxation function. Using the  
pseudospectral method, which allows general material variability, a  
complete and accurate characterization of the reservoir can be  
obtained. Two cases consider the Utsira sand of the North Sea and the  
Atzbach-Schwanenstadt gas field in Upper Austria. The monitoring  
approach involves traveltime reflection tomography
and rock physics; the synthetic seismograms can be used to test the  
sensitivity of the methodology.

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