Exhumation and incision history of the Torngat Mountains, northern Labrador and Quebec, Canada, using apatite (U-Th)/He thermochronology

M.S. University of Kansas, Geology 2005Apatite (U-Th)/He thermochronological data provide new insights into the exhumation history of the Torngat Mountains, which are located in Ungava Peninsula, northern Labrador and Quebec, Canada. Latest Jurassic to earliest Cretaceous rifting resulted in crustal extension and opening of the Labrador Sea, causing westward tilting and exhumation of the Labrador continental margin. Post-rift erosion and incision led to the formation of significant topographic relief in the Torngat Mountains. Thermal modeling of apatite (U-Th)/He thermochronological data from a vertical sample transect indicates that rapid cooling starting at ~140-150 Ma, which closely coincides in age with independent geological evidence for initial rifting in the area. Apatite (U-Th)/He ages along an E-W transect, which was collected perpendicular to the Torngat Mountains and the Labrador coast, record differential extensional and erosional exhumation diminishing westwards towards the interior of Ungava Peninsula. Ages near the Labrador coastline are as young as ~ 78 Ma and are significantly younger than the timing of onset of initial rifting (~140-150 Ma); this suggests significant amounts (~1-2 km) of post-rift erosion and incision along the eastern continental margin of the Labrador Sea. West of the Torngat Mountains, along the E-W transect, apatite (U-Th)/He ages also show evidence of substantial post-rift erosion likely related to Mesozoic and Tertiary fluvial erosion or to Pleistocene continental glaciation. Two constant-elevation N-S transects collected parallel to the Labrador coast show apatite (U-Th)/He ages that mimic the larger scale topographic features of the area, such as major rivers and fiords, indicating a deflection of shallow crustal isotherms due to post-rift development of highamplitude topography. Additional numerical modeling is required to refine the timing and spatial magnitude of post-rift erosion in more detail

Small and strong formulations for unions of convex sets from the Cayley embedding

There is often a significant trade-off between formulation strength and size in mixed integer programming (MIP). When modelling convex disjunctive constraints (e.g. unions of convex sets) this trade-off can be resolved by adding auxiliary continuous variables. However, adding these variables can result in a deterioration of the computational effectiveness of the formulation. For this reason, there has been considerable interest in constructing strong formulations that do not use continuous auxiliary variables. We introduce a technique to construct formulations without these detrimental continuous auxiliary variables. To develop this technique we introduce a natural nonpolyhedral generalization of the Cayley embedding of a family of polytopes and show it inherits many geometric properties of the original embedding. We then show how the associated formulation technique can be used to construct small and strong formulation for a wide range of disjunctive constraints. In particular, we show it can recover and generalize all known strong formulations without continuous auxiliary variables.National Science Foundation (U.S.) (grant CMMI-1351619

Embedding Formulations and Complexity for Unions of Polyhedra

It is well known that selecting a good Mixed Integer Programming (MIP) formulation is crucial for an effective solution with state-of-the art solvers. While best practices and guidelines for constructing good formulations abound, there is rarely a systematic construction leading to the best possible formulation. We introduce embedding formulations and complexity as a new MIP formulation paradigm for systematically constructing formulations for disjunctive constraints that are optimal with respect to size. More specifically, they yield the smallest possible ideal formulation (i.e. one whose LP relaxation has integral extreme points) among all formulations that only use 0-1 auxiliary variables. We use the paradigm to characterize optimal formulations for SOS2 constraints and certain piecewise linear functions of two variables. We also show that the resulting formulations can provide a significant computational advantage over all known formulations for piecewise linear functions.United States. National Science Foundation. (Grant CMMI-13516

Incremental and encoding formulations for Mixed Integer Programming

The standard way to represent a choice between n alternatives in Mixed Integer Programming is through n binary variables that add up to one. Unfortunately, this approach commonly leads to unbalanced branch-and-bound trees and diminished solver performance. In this paper, we present an encoding formulation framework that encompasses and expands existing approaches to mitigate this behavior. Through this framework, we generalize the incremental formulation for piecewise linear functions to any finite union of polyhedra with identical recession cones

El cambio en las políticas públicas de ciencia, tecnología e innovación: apuntes para el caso colombiano

Public policy change has been a frequent object of study in policy analysis literature. Particularly, science, technology and innovation (STI) policies incorporate technological change and innovation as drivers to transform different spheres of society. This article is interested in highlighting how some examples of the innovation studies literature address STI policy change, with some annotations for the Colombian case. This literature discusses the issue from three perspectives related to STI policy institutions, agendas and frames. The article outlines these three as relevant aspects for a better understanding of STI policy change in Colombia.El fenómeno del cambio en las políticas públicas (policy change) ha sido un objeto de estudio recurrente en la literatura del campo de análisis de políticas públicas. Particularmente, las políticas públicas de ciencia, tecnología e innovación (CTeI) incorporan el asunto del cambio tecnológico y la innovación como vehículos para transformar distintas esferas de la sociedad. Este artículo de revisión se interesa en destacar cómo algunos ejemplos de la literatura sobre estudios de innovación abordan el cambio en las políticas públicas de CTeI, con algunos apuntes sobre el caso colombiano. Se identifca que la literatura discute este asunto desde tres perspectivas relacionadas con las instituciones, las agendas y los modelos en las políticas de CTeI. Se pretende con esto resaltar algunos aspectos relevantes para una mejor comprensión de las transformaciones en las políticas públicas de CTeI en Colombia

Textos tipo manual para la enseñanza de las políticas públicas en Colombia: un caso de estudio

Despite the increasing institutionalization of public policy as a field of study, there has been little reflection on the teaching in this field. The purpose of this paper is to contri­bute to the characterization of public policy teaching in Colombia based on the case of a handbook-type text on public policy. A citation analysis was carried out and surveys applied to students and graduates of a mas­ter program in public policy. A rationalistic oriented use of the book was identified, with a focus on the implementation phase at diffe­rent territorial levels. The popularization of the field and the operational definition of public policy are some of the main contributions of the book. The profile of the public policy ap­prentice was identified and some opportunities and challenges are outlined in the end.A pesar de la creciente institucionaliza­ción de las políticas públicas como campo de estudio, poco se ha reflexionado sobre su enseñanza. El propósito del artículo es con­tribuir a la caracterización de la enseñanza de las políticas públicas en Colombia a partir del caso de un libro de texto tipo manual sobre el tema. Se realizó un análisis de citas y de encuestas aplicadas a estudiantes y egresados de maestría en Políticas Públicas. Se identificó una orientación racionalista en el uso del libro, con énfasis en la fase de implementación en distintos niveles territoriales. La divulgación de este campo de estudio y la definición ope­racional de política pública que propone son los principales aportes del libro. Se identifica el perfil del aprendiz en políticas públicas y se esbozan al final algunos retos y oportunidades para la enseñanza en políticas públicas

I bet you don’t look good on the dance floor: Re-examining the innovation policy dance metaphor in the case of Colombia

Innovation heuristics offer guidance on how to navigate through the complex dynamics of innovation governance. However, further discussion is needed on the premises of such analytical tools to inquire on their implications on innovation policy and practice. This paper builds on the innovation policy dance metaphor to better grasp the ever-changing interplays (or dance) between innovation practice (I), policy (P) and theory (T). We critically assess the basic underlying assumptions of this metaphor, by examining the extent to which its heuristic pretensions are relevant in the Latin American context. To do so, we explore three illustrative cases in Colombia, shedding light on some crosscutting opportunities and gaps for the dancing metaphor across different innovation I-P-T situations. Some derived lessons suggest that dancing occurs within and/or between different governance levels, where variables such as politics shape the innovation I-P-T interplay and time defines first and second order learning pathways

On packing and covering polyhedra in infinite dimensions

We consider the natural generalizations of packing and covering polyhedra in infinite dimensions, and study issues related to duality and integrality of extreme points for these sets. Using appropriate finite truncations we give conditions under which complementary slackness holds for primal/dual pairs of the infinite linear programming problems associated with infinite packing and covering polyhedra. We also give conditions under which the extreme points are integral. We illustrate an application of our results on an infinite-horizon lot-sizing problem. Keywords: Covering polyhedron; Packing polyhedron; Infinite linear program; Complementary slackness; Integral extreme poin

Strong mixed-integer formulations for the floor layout problem

The floor layout problem (FLP) tasks a designer with positioning a collection of rectangular boxes on a fixed floor in such a way that minimizes total communication costs between the components. While several mixed integer programming (MIP) formulations for this problem have been developed, it remains extremely challenging from a computational perspective. This work takes a systematic approach to constructing MIP formulations and valid inequalities for the FLP that unifies and recovers all known formulations for it. In addition, the approach yields new formulations that can provide a significant computational advantage and can solve previously unsolved instances. While the construction approach focuses on the FLP, it also exemplifies generic formulation techniques that should prove useful for broader classes of problems.United States. National Science Foundation. Graduate Research Fellowship Program (Grant 1122374)United States. National Science Foundation. Graduate Research Fellowship Program (Grant CMMI-1351619

Solution strategies to the stochastic design of mineral flotation plants

The aim of this study is two-fold: first, to analyze the effect of stochastic uncertainty in the design of flotation circuits and second, to analyze different strategies for the solution of a two-stage stochastic problem applied to a copper flotation circuit. The paper begins by introducing a stochastic optimization problem whose aim is to find the best configuration of superstructure, equipment design and operational conditions, such as residence time and stream flows. Variability is considered in the copper price and ore grade. This variability is represented by scenarios with their respective probability of occurrence. The resulting optimization problem is a two-stage stochastic mixed integer nonlinear program (TS-MINLP), which can be extremely challenging to solve. For this reason, several solvers for this problem are compared and two stochastic programming methodologies are applied. The combination of these techniques allows the production of high quality solutions and an analysis of their sensitivity to epistemic uncertainty. The results show that the stochastic problem gives better designs because it allows operational parameters to adapt to the uncertainty of the parameters. The results also show that the flotation circuit structure can vary with the feed grade and copper price. The sensitivity analysis shows small to moderate variability with epistemically uncertain parameters