A method to assess the application of additive manufacturing to inventory replenishment : a thesis presented in partial fulfilment of the requirements for the Master of Supply Chain Management at Massey University, Albany, New Zealand

Companies have historically struggled to deal with their stock, especially the long inventory tail. As most of the inventory management techniques that deal with slow-moving stock have proved to be rather inefficient, this research investigates the use of additive manufacturing to 3D print items on demand and therefore mitigate the inventory carrying and associated costs. This research has been applied to a Hydraulic Equipment Business in New Zealand, which was tested through an inequation that models the traditional manufacturing and 3D printing costs, yielding the ‘tipping point’ for the use of the 3D printing technology. Even though the results obtained herein were negative for this particular case regarding the use of additive manufacturing, this research has developed a methodology to assess the trade-off between traditional manufacturing and 3D printing and also provides insights into the characteristics of the inventory of the businesses that are most likely to benefit from the use of the technology

Micro-meteoroid seismic uplift and regolith concentration on kilometric scale asteroids

Seismic shaking is an attractive mechanism to explain the destabilisation of regolith slopes and the regolith migration found on the surfaces of asteroids (Richardson et al. 2004; Miyamoto et al. 2007). Here, we use a continuum mechanics method to simulate the seismic wave propagation in an asteroid. Assuming that asteroids can be described by a cohesive core surrounded by a thin non-cohesive regolith layer, our numerical simulations of vibrations induced by micro-meteoroids suggest that the surface peak ground accelerations induced by micro-meteoroid impacts may have been previously under-estimated. Our lower bound estimate of vertical accelerations induced by seismic waves is about 50 times larger than previous estimates. It suggests that impact events triggering seismic activity are more frequent than previously assumed for asteroids in the kilometric and sub-kilometric size range. The regolith lofting is also estimated by a first order ballistic approximation. Vertical displacements are small, but lofting times are long compared to the duration of the seismic signals. The regolith movement has a non-linear dependence on the distance to the impact source which is induced by the type of seismic wave generating the first movement. The implications of regolith concentration in lows of surface acceleration potential are also discussed. We suggest that the resulting surface thermal inertia variations of small fast rotators may induce an increased sensitivity of these objects to the Yarkovsky effect.Comment: Accepted for publication in Icaru

The Basque Diaspora in Latin America: Euskal Etxeak, Integration, and Tensions. EDAP 1/2016

The establishment of the Basque diaspora in Latin America can be divided in several different periods. First, from the 16th to 18th century, the so-called original diaspora of Basques who were part of the Spanish colonial regime. The second can be traced to the 19th century, consisting of a mixture of impoverished Basque migrants seeking jobs, especially in Uruguay and Argentina, and of refugees fleeing from the Spanish War of Independence and the Carlist wars. The third wave is identified by, but not only through, the considerable amount of refugees from the Spanish Civil War on the 1930's. The fourth wave came during the 1970s, with refugees from the Franco Dictatorship, ETA members and sympathisers. In this paper I will argue that each new wave of migrants brought tension to the diaspora, with the Euskal Etxeak, or ‘Basque houses’, as a focus point. The main idea is to analyse the different tensions and political discussions of this set of diasporic waves in Latin America

Esquemas esencialmente no oscilatorios aplicados a la ecuación de Buckley-Leverett con término difusivo

The purpose of this work was to investigate the flow of two-phase fluids via the Buckley-Leverett equation, corresponding to three types of scenarios applied in oil extraction, including a diffusive term. For this, a weighted essentially non-oscillatory scheme, a Runge-Kutta method and a central finite difference were computationally implemented. In addition, a numerical study related to the precision order and stability was performed. The use of these methods made it possible to obtain numerical solutions without oscillations and without excessive numerical dissipation, sufficient to assist in the understanding of the mixing profiles of saturated water and petroleum fluids, inside pipelines filled with porous material, in addition to allowing the investigation of the impact of adding the diffusive term in the original equation.El propósito de este trabajo fue investigar el flujo de fluidos bifásicos a través de la ecuación de Buckley-Leverett, correspondiente a tres tipos de escenarios aplicados en la extracción de petróleo, incluyendo un término difusivo. Para ello se implementaron computacionalmente un esquema esencialmente no oscilatorio ponderado , un método de Runge-Kutta y un esquema de diferencias finitas centrado. Además, se realizó un estudio numérico relacionado con el orden de precisión y estabilidad. El uso de estos métodos permitió obtener soluciones numéricas sin oscilaciones y sin disipación numérica excesiva, suficientes para auxiliar en la comprensión de los perfiles de mezcla de agua saturada y fluidos derivados del petróleo, en el interior de tuberías llenas de material poroso, además de permitir la investigación del impacto de sumar el término difusivo en la ecuación original

Atmospheric gravity waves due to the Tohoku-Oki tsunami observed in the thermosphere by GOCE

International audienceOceanic tsunami waves couple with atmospheric gravity waves, as previously observedthrough ionospheric and airglow perturbations. Aerodynamic velocities and density variations are computed from Gravity Field and Steady-State Ocean Circulation Explorer (GOCE) accelerometer and thruster data during Tohoku-Oki tsunami propagation. High-frequency perturbations of these parameters are observed during three expected crossings of the tsunami-generated gravity waves by the GOCE satellite. From theoretical relations between air density and vertical and horizontal velocities inside the gravity wave, we demonstrate that the measured perturbations are consistent with a gravity wave generated by the tsunami and provide a way to estimate the propagation azimuth of the gravity wave. Moreover, because GOCE measurements can constrain the wave polarization, a marker (noted C 3 ) of any gravity wave crossing by the GOCE satellite is constructed from correlation coefficients between the observed atmospheric state parameters. These observations validate a new observation tool of thermospheric gravity waves generated by tsunamis above the open ocean

A Multicut Approach to Compute Upper Bounds for Risk-Averse SDDP

Stochastic Dual Dynamic Programming (SDDP) is a widely used and fundamental algorithm for solving multistage stochastic optimization problems. Although SDDP has been frequently applied to solve risk-averse models with the Conditional Value-at-Risk (CVaR), it is known that the estimation of upper bounds is a methodological challenge, and many methods are computationally intensive. In practice, this leaves most SDDP implementations without a practical and clear stopping criterion. In this paper, we propose using the information already contained in a multicut formulation of SDDP to solve this problem with a simple and computationally efficient methodology. The multicut version of SDDP, in contrast with the typical average cut, preserves the information about which scenarios give rise to the worst costs, thus contributing to the CVaR value. We use this fact to modify the standard sampling method on the forward step so the average of multiple paths approximates the nested CVaR cost. We highlight that minimal changes are required in the SDDP algorithm and there is no additional computational burden for a fixed number of iterations. We present multiple case studies to empirically demonstrate the effectiveness of the method. First, we use a small hydrothermal dispatch test case, in which we can write the deterministic equivalent of the entire scenario tree to show that the method perfectly computes the correct objective values. Then, we present results using a standard approximation of the Brazilian operation problem and a real hydrothermal dispatch case based on data from Colombia. Our numerical experiments showed that this method consistently calculates upper bounds higher than lower bounds for those risk-averse problems and that lower bounds are improved thanks to the better exploration of the scenarios tree

Regularization and Optimization in Model-Based Clustering

Due to their conceptual simplicity, k-means algorithm variants have been extensively used for unsupervised cluster analysis. However, one main shortcoming of these algorithms is that they essentially fit a mixture of identical spherical Gaussians to data that vastly deviates from such a distribution. In comparison, general Gaussian Mixture Models (GMMs) can fit richer structures but require estimating a quadratic number of parameters per cluster to represent the covariance matrices. This poses two main issues: (i) the underlying optimization problems are challenging due to their larger number of local minima, and (ii) their solutions can overfit the data. In this work, we design search strategies that circumvent both issues. We develop more effective optimization algorithms for general GMMs, and we combine these algorithms with regularization strategies that avoid overfitting. Through extensive computational analyses, we observe that optimization or regularization in isolation does not substantially improve cluster recovery. However, combining these techniques permits a completely new level of performance previously unachieved by k-means algorithm variants, unraveling vastly different cluster structures. These results shed new light on the current status quo between GMM and k-means methods and suggest the more frequent use of general GMMs for data exploration. To facilitate such applications, we provide open-source code as well as Julia packages (UnsupervisedClustering.jl and RegularizedCovarianceMatrices.jl) implementing the proposed techniques

Destacamento de revestimentos cerâmicos de fachadas e áreas externas: estudo de caso em Cabo Frio – Rio de Janeiro

Considerando as condições climáticas no Brasil, tem-se um ambiente favorável para a grande utilização de revestimentos cerâmicos em fachadas, devido a maior durabilidade das características antitérmicas e do seu poder de conservação. Portanto, este trabalho buscou entender o surgimento de patologias que prejudicam diretamente as características de conservação do Sistema de Revestimento Cerâmico, diminuindo o seu desempenho. Para tal, realizou-se um estudo de diversas edificações, buscando identificar as ocorrências patológicas que culminam no destacamento de peças cerâmicas e quais etapas da edificação originaram tais defeitos. Além disso, também foram descritas possíveis medidas de intervenção para combater o avanço dos sintomas observados. Por fim, através da comparação das origens das patologias nas edificações estudadas, constatou-se o maior impacto das etapas construtivas e de projeto, revelando a grande necessidade do adequado conhecimento técnico da mão de obra empregada neste sistema. Foi verificado a redução do desempenho e durabilidade dos revestimentos, confirmando a importância de um projeto de revestimento de fachada que contemple medidas para inibir o surgimento de defeitos nas peças cerâmicas