Diseño para operabilidad: Una revisión de enfoques y estrategias de solución

In the last decades the chemical engineering scientific research community has largely addressed the design-foroperability problem. Such an interest responds to the fact that the operability quality of a process is determined by design, becoming evident the convenience of considering operability issues in early design stages rather than later when the impact of modifications is less effective and more expensive. The necessity of integrating design and operability is dictated by the increasing complexity of the processes as result of progressively stringent economic, quality, safety and environmental constraints. Although the design-for-operability problem concerns to practically every technical discipline, it has achieved a particular identity within the chemical engineering field due to the economic magnitude of the involved processes. The work on design and analysis for operability in chemical engineering is really vast and a complete review in terms of papers is beyond the scope of this contribution. Instead, two major approaches will be addressed and those papers that in our belief had the most significance to the development of the field will be described in some detail.En las últimas décadas, la comunidad científica de ingeniería química ha abordado intensamente el problema de diseño-para-operabilidad. Tal interés responde al hecho de que la calidad operativa de un proceso esta determinada por diseño, resultando evidente la conveniencia de considerar aspectos operativos en las etapas tempranas del diseño y no luego, cuando el impacto de las modificaciones es menos efectivo y más costoso. La necesidad de integrar diseño y operabilidad esta dictada por la creciente complejidad de los procesos como resultado de las cada vez mayores restricciones económicas, de calidad de seguridad y medioambientales. Aunque el problema de diseño para operabilidad concierne a prácticamente toda disciplina, ha adquirido una identidad particular dentro de la ingeniería química debido a la magnitud económica de los procesos involucrados. El trabajo sobre diseño y análisis para operabilidad es realmente vasto y una revisión completa en términos de artículos supera los alcances de este trabajo. En su lugar, se discutirán los dos enfoques principales y aquellos artículos que en nuestra opinión han tenido mayor impacto para el desarrollo de la disciplina serán descriptos con cierto detalle.Fil: Blanco, Anibal Manuel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Planta Piloto de Ingeniería Química. Universidad Nacional del Sur. Planta Piloto de Ingeniería Química; ArgentinaFil: Bandoni, Jose Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Planta Piloto de Ingeniería Química. Universidad Nacional del Sur. Planta Piloto de Ingeniería Química; Argentin

A Note on Tubular Brane Dynamics

We present new time dependent solutions for the dynamics of tubular D2-branes. We comment on the connection to cosmic string dynamics and explicitly give a few simple examples of oscillating and rotating brane configurations.Comment: 1+6 pages, 2 Figure

Inflation in Random Landscapes with two energy scales

We investigate inflation in a multi-dimensional landscape with a hierarchy of energy scales, motivated by the string theory, where the energy scale of Kahler moduli is usually assumed to be much lower than that of complex structure moduli and dilaton field. We argue that in such a landscape, the dynamics of slow-roll inflation is governed by the low-energy potential, while the initial condition for inflation are determined by tunneling through high-energy barriers. We then use the scale factor cutoff measure to calculate the probability distribution for the number of inflationary e-folds and the amplitude of density fluctuations $Q$, assuming that the low-energy landscape is described by a random Gaussian potential with a correlation length much smaller than $M_{\rm pl}$. We find that the distribution for $Q$ has a unique shape and a preferred domain, which depends on the parameters of the low-energy landscape. We discuss some observational implications of this distribution and the constraints it imposes on the landscape parameters.Comment: 39 pages, 3 figures; (v2) minor change

Farmers' Use of Improved Seed Selection Practices in Mexican Maize: Evidence and Issues from the Sierra de Santa Marta

The principal advantage of in situ conservation is that it allows adaptive evolutionary processes to continue in the species that are being conserved. For a cultivated crop species, in situ conservation involves farmers' management of their own genetic resources even as the farmers themselves adapt to a changing environment. Improved seed selection practices and other on-farm breeding strategies have been proposed as a means of providing economic incentives for farmers to continue growing traditional varieties or landraces identified as important for conservation. This paper describes a pilot study among a group of indigenous farmers in the Sierra de Santa Marta, Veracruz, Mexico, who have collaborated in such efforts. The findings raise key issues about the potential impact of such an approach, as well as some useful methodological points for applied economists. In the study area, there is a high frequency of experimentation, exchange, loss, and replacement of seed over time -- seed of the same varieties, including both modern and traditional varieties. This poses a challenge for economists' models of varietal choice, which tend to be based on static perceptions of a 'variety' as well as simplistic distinctions between 'modern' and 'traditional' varieties. Seed selection in the study area is not a single event but an iterative, continuous process. Women may be more involved in seed selection than previously thought, which may have implications for the welfare impact of new seed selection practices. Other implications of the study are that (1) the impact of introducing practices to enhance farmers' varieties is likely to be diffuse and difficult to observe, predict, or measure, and (2) in developing analytical models of farmer decision-making as it affects the diversity of genetic resources on the farm, the most appropriate unit of analysis for predicting the effects of some policy interventions is not likely to be the individual farmer or the individual farm household. A better understanding of the 'social infrastructure' shaping seed and information flows is needed, since in the diffusion of innovations of this type, the seed system is based entirely on farmers and their interactions.Crop Production/Industries,

The Initial State of a Primordial Anisotropic Stage of Inflation

We investigate the possibility that the inflationary period in the early universe was preceded by a primordial stage of strong anisotropy. In particular we focus on the simplest model of this kind, where the spacetime is described by a non-singular Kasner solution that quickly evolves into an isotropic de Sitter space, the so-called Kasner-de Sitter solution. The initial Big Bang singularity is replaced, in this case, by a horizon. We show that the extension of this metric to the region behind the horizon contains a timelike singularity which will be visible by cosmological observers. This makes it impossible to have a reliable prediction of the quantum state of the cosmological perturbations in the region of interest. In this paper we consider the possibility that this Kasner-de Sitter universe is obtained as a result of a quantum tunneling process effectively substituting the region behind the horizon by an anisotropic parent vacuum state, namely a $1+1$ dimensional spacetime compactified over an internal flat torus, $T_2$, which we take it to be of the form ${de Sitter}_2 \times T_2$ or ${Minkowski}_2 \times T_2$. As a first approximation to understand the effects of this anisotropic initial state, we compute the power spectrum of a massless scalar field in these backgrounds. In both cases, the spectrum converges at small scales to the isotropic scale invariant form and only present important deviations from it at the largest possible scales. We find that the decompactification scenario from $M_2 \times T_2$ leads to a suppressed and slightly anisotropic power spectrum at large scales which could be related to some of the anomalies present in the current CMB data. On the other hand, the spectrum of the universe with a $dS_2 \times T_2$ parent vacuum presents an enhancement in power at large scales not consistent with observations.Comment: 36 pages, 7 figures, references adde