José Luis Zambrana García

Steady-state axial profiles of dissolved oxygen in tall bubble column bioreactors

A model is developed for prediction and interpretation of the observed steady-state axial dissolved oxygen concentration profiles in tall bubble columns. The observed concentration profiles are non-linear, unlike what would be expected if the hydrostatic pressure alone influenced the profiles. The non-linear profiles result from the axial mixing of liquid in the column. Several other factors influence the profiles, including the overall gas holdup, the volumetric overall gas—liquid mass transfer coeƒcient, and the static height of liquid in the column. The e⁄ect of mixing can be adequately accounted for using an axial dispersion coeƒcient. Because the axial dispersion coeƒcient is sensitive to the diameter of the column and to gas flow rate, the overall behavior of the profile is a⁄ected by the aspect ratio of the column and the superficial gas velocity in it. The mass transfer coeƒcient and the axial dispersion coeƒcient have mutually opposing e⁄ects on the shape of the profile. Because both those variables increase with increasing gas flow rate, the shape of the profile is a⁄ected less than would be the case if only mixing influenced the profile. The non-linearity of concentration profiles increases with increasing overall height of the column especially when the height exceeds about 2 m in a 0.24 m diameter column. The model-predicted axial concentration profiles agree closely — within

Axial inhomogeneities in steady-state dissolved oxygen in airlift bioreactors: predictive models

3% — with the measured data. Using the measured profile, the model allows for calculation of the liquid-phase axial dispersion coeƒcients. This method does not require the use of tracers. Being a steady-state method, the operation of the bioreactor does not need to the interrupted in any way for the determination of the axial dispersion coeƒcient or the state of mixing. Consequently, the proposed method is particularly suited to characterizing the axial dispersion coeƒcient in an operating bioreactor without disturbing the operation. If the axial dispersion coeƒcient is known, the model allows for quantifying the spatial inhomogeneities in oxygen concentration in a bioreactor vessel. ( 1999 Elsevier Science Ltd. All rights reserved.

Mortalidad poblacional por infarto agudo de miocardio. Estudio IBERICA

Models were developed for prediction and interpretation of the observed steady-state axial dissolved oxygen concentration profiles in tall airlift bioreactors. The observed concentration profiles were non-linear because of a combination of hydrodynamic and mass transport factors. The profiles were influenced mainly by the liquid-phase axial dispersion coefficient, the volumetric overall gas–liquid mass transfer coefficient, the gas velocity, the induced liquid circulation velocity. The model-predicted concentration profiles agreed within ±2% with the measured data in a tall (working aspect ratio ∼ 15) airlift vessel operated under aeration regimens that are typically used during wastewater treatment. Axial inhomogeneities in dissolved oxygen increased with increasing aeration rate. This phenomenon may influence activated sludge processes in airlift and deep-shaft reactors. The maximum attainable concentration of dissolved oxygen at the bottom of a typically aerated airlift reactor, ≥ 3.5 m deep, always remained at 10% axially up the reactor.

The Effect of the Underlying Distribution in Hurst Exponent Estimation

Fundamento y objetivo El estudio de la mortalidad poblacional del infarto agudo de miocardio (IAM), que incluye las muertes ocurridas antes de llegar al hospital, ofrece una vision mas completa sobre la magnitud del problema que la obtenida estudiando unicamente la mortalidad de los casos que reciben atencion hospitalaria. Pacientes y metodo Los datos provienen del estudio IBERICA (Investigacion, Busqueda Especifica y Regis-tro de Isquemia Coronaria Aguda). Se describe la mortalidad en los primeros 28 dias desde el inicio de los sintomas de los episodios de IAM registrados, durante 1997 y 1998, en la poblacion de 25 a 74 anos residente en 7 comunidades autonomas espanolas: Castilla-La Mancha (Toledo y Albacete), Cataluna (Girona), Comunidad Valenciana (Valencia), Islas Baleares (Mallorca), Murcia, Navarra y Pais Vasco. Ademas, se estudia la relacion entre mortalidad y otras variables como el sexo, la edad y el area geografica. Resultados Se registraron 10.654 casos de IAM de los que 4.105 fallecieron durante los 28 primeros dias (38,5%; intervalo de confianza [IC] del 95%, 37,6–39,4%). La mortalidad fue del 37,0% (IC del 95%, 35,9–38,0%) en los varones y del 44,3% (IC del 95%, 42,3–46,4%) en las mujeres. La muerte se produjo fuera del hospital en 2.869 (69,9%) casos. La mayor mortalidad en mujeres estuvo relacionada fundamentalmente con una mayor mortalidad hospitalaria (45% superior a la registrada en los varones), siendo menor la diferencia en la proporcion de casos que fallecieron fuera del hospital. La sintomatologia tipica de presentacion del episodio fue mas frecuente en varones (el 82,7 frente al 77,6%) (p Conclusiones La mortalidad poblacional por IAM en estas 7 areas espanolas es muy elevada aunque inferior a la de otros paises industrializados. Aproximadamente dos de cada tres muertes ocurren antes de llegar al hospital. Estos datos refuerzan el papel prioritario de la prevencion primaria y secundaria, ya que los cuidados hospitalarios tienen un impacto limitado en el control de la mortalidad poblacional por IAM. Tambien indican que una forma de reducir la mortalidad deberia incluir el acceso rapido a la desfibrilacion y a las maniobras de resucitacion de los pacientes que presenten una muerte subita.

Characterization of a flat plate photobioreactor for the production of microalgae

In this paper, a heavy-tailed distribution approach is considered in order to explore the behavior of actual financial time series. We show that this kind of distribution allows to properly fit the empirical distribution of the stocks from S&P500 index. In addition to that, we explain in detail why the underlying distribution of the random process under study should be taken into account before using its self-similarity exponent as a reliable tool to state whether that financial series displays long-range dependence or not. Finally, we show that, under this model, no stocks from S&P500 index show persistent memory, whereas some of them do present anti-persistent memory and most of them present no memory at all.