Extensional and torsional pipe flow

We study the dynamics of a viscous fluid confined within an elastic pipe that is being stretched and twisted in the axial and azimuthal directions, respectively. A comprehensive numerical exploration of self-similar flows has been conducted for a wide range of stretching and twisting acceleration rates. Up to eight different families of steady flows have been identified and tracked. For purely axial stretching, the presented computations recover the results obtained by former authors in the past. However, the twisting mechanism, seen as a homotopy parameter, has been crucial in this study to explain how different families of equilibria interact and azimuthal swirl is induced. The explorations conclude that stable time-periodic flows may also take over the dynamics when the pipe is contracting in the axial direction, with mild or absent azimuthal twist. These time-periodic flows may destabilize through different codimension-two bifurcation scenarios, sometimes leading to unstable tori that have been genuinely identified by means of edge-tracking techniques.Postprint (published version

High-Temperature Mineral Formation after Firing Clay Materials Associated with Mined Coal in Teruel (Spain)

The production of porcelain stoneware has experienced a considerable increase. Therefore, it was necessary to undertake an investigation that would allow knowing the mineralogical evolution that porcelain stoneware undergoes during the firing process, as well as establishing the influence of the formation of mullite and other mineral or vitreous phases and their quantification. The firing transformations of mine spoils associated with mined coal in the Utrillas-Escucha-Estercuel and Ariño-Andorra areas are studied in this paper. The mineralogical composition of the bulk mine spoils is kaolinite, illite, chlorite, and smectites (in traces), with quartz and feldspar, and minor hematite, calcite, and dolomite. The main objective is to understand the generation of high-temperature mineral phases after firing, and their quantification. The formation of mullite and other high-temperature phases are studied from samples that include variable proportions of illite. Samples with a high content of illite generate mullite at 995 °C. Cristobalite was not detected as a high-temperature phase. Mullite is the most abundant mineral. The hercynite content is higher at low temperatures (995 °C), and hematite content is higher at 1150 °C. The vitreous phase represents about 50% of fired bodies. Despite observing a porous microstructure, the non-porous areas are well sintered

Collective Remittances and the State: The 3x1 Program in Mexican Municipalities

The Mexican 3x1 Program for Migrants is a matching fund scheme that seeks to direct the money sent by hometown associations abroad (collective remittances) to productive uses. The federal, state and municipal governments contribute to the program multiplying by three the contributions sent by migrants abroad. Using municipal level data on program participation for the period 2002-2006, we evaluate the program’s capacity to target the poorest municipalities. Since migration has a nonlinear relationship with poverty and marginality, a program that unconditionally responds to project initiatives from migrant organizations is bound to be regressive due to self-selection bias. Indeed, poorer municipalities are less likely to participate and they also receive lower amounts and fewer projects than relatively richer localities. Moreover, we find evidence of a partisan bias: states and municipalities ruled by the PAN are significantly more likely to participate in the program, and electoral support for the PAN is associated with more funds or projects awarded. We argue that substantial changes should be implemented for the program to be a truly progressive poverty reduction tool.Latin American Studie

Methods for Proving Termination of Rewriting-based Programming Languages by Transformation

AbstractDespite the remarkable development of the theory of termination of rewriting, its application to high-level (rewriting-based) programming languages is far from being optimal. This is due to the need for features such as conditional equations and rules, types and subtypes, (possibly programmable) strategies for controlling the execution, matching modulo axioms, and so on, that are used in many programs and tend to place such programs outside the scope of current termination tools. The operational meaning of such features is often formalized in a proof theoretic manner by means of an inference system rather than just by a rewriting relation. The corresponding termination notions can also differ from the standard ones. During the last years we have introduced and implemented different notions and transformation techniques which have been proved useful for proving and disproving termination of such programs by using existing tools for proving termination of (variants of) rewriting. In this paper we provide an overview of our main contributions

Theoretical and Experimental Analysis of Stability Limits of Non-Axisymmetric Liquid Bridges under Microgravity Conditions

The stability of nonaxisymmetric liquid bridges under microgravity conditions is investigated. The influence on the stability of an almost cylindrical liquid bridge of axisymmetric effects like its volume, a small axial acceleration acting on it, and unequal-diameter supporting disks, as well as that of nonaxisymmetric perturbations like small lateral acceleration and noncoaxial supporting disks, has been analyzed by using standard bifurcation techniques. An expression for the maximum length of a liquid bridge, including all the above-mentioned effects, has been obtained. In addition, the effect on the stability of liquid bridges having noncoaxial supporting disks has been experimentally studied within the constraints of an Earth laboratory by using millimetric liquid bridges. Analytical and experimental results show that each one of the nonaxisymmetric perturbations like the ones here considered (lateral acceleration and eccentricity) can be, from the point of view of stability, as critical as axisymmetric perturbations. In addition, it is demonstrated that when both nonaxisymmetric perturbations are not negligible, the coupling of both perturbations can be a stabilizing effect on the liquid bridg

El Don Quixote de ahora con Sancho Panza el de antaño

Sign.: [a]-b8, c