Value of coordination and flexibility in aluminum recycling operations

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2013.Cataloged from PDF version of thesis.Includes bibliographical references (p. 212-219).The growing motivation for aluminum recycling has prompted interest in recycling alternative and more challenging secondary materials. The nature of these alternative secondary materials necessitates the development of an intermediate recycling facility that can reprocess the secondary materials into a liquid product. Two downstream aluminum remelters will incorporate the liquid products into their aluminum alloy production schedules. Energy and environmental benefits result from delivering the products as liquid but coordination challenges persist because of the energy cost to maintain the liquid. Further coordination challenges result from the necessity to establish a long term recycling production plan in the presence of long term downstream aluminum remelter production uncertainty and inherent variation in the daily order schedule of the downstream aluminum remelters. In this context a fundamental question arises, considering the metallurgical complexities of dross reprocessing, what is the value of operating a coordinated set of by-product reprocessing plants and remelting cast houses? A methodology is presented to calculate the optimal recycling center production parameters including 1) the number of recycled products, 2) the volume of recycled products, 3) allocation of recycled materials across recycled products, 4) allocation of recycled products across finished alloys, 4) the level of flexibility for the recycling center to operate. The methods implemented include, 1) an optimization model to describe the long term operations of the recycling center, 2) an uncertainty simulation tool, 3) a simulation optimization method, 4) a dynamic simulation tool with four embedded daily production optimization models of varying degrees of flexibility. This methodology is used to quantify the performance of several recycling center production designs of varying levels of coordination and flexibility. This analysis allowed the identification of the optimal recycling center production design based on maximizing liquid recycled product incorporation and minimizing cast sows. The long term production optimization model was used to evaluate the theoretical viability of the proposed two stage scrap and aluminum dross reprocessing operation including the impact of reducing coordination on model performance. Reducing the coordination between the recycling center and downstream remelters by reducing the number of recycled products from ten to five resulted in only 1.3% less secondary material incorporated into downstream production. The dynamic simulation tool was used to evaluate the performance of the calculated recycling center production plan when resolved on a daily timeframe for varying levels of operational flexibility. The dynamic simulation revealed the optimal performance corresponded to the fixed recipe with flexible production daily optimization model formulation. Calculating recycled product characteristics using the proposed simulation optimization method increased profitability in cases of uncertain downstream remelter production and expensive aluminum dross and post-consumed secondary materials.by Tracey H. Brommer.Ph.D

Magnetic properties of Gd_xY_{1-x}Fe_2Zn_{20}: dilute, large, S\textbf {S} moments in a nearly ferromagnetic Fermi liquid

Single crystals of the dilute, rare earth bearing, pseudo-ternary series, Gd_xY_{1-x}Fe_2Zn_{20} were grown out of Zn-rich solution. Measurements of magnetization, resistivity and heat capacity on Gd_xY_{1-x}Fe_2Zn_{20} samples reveal ferromagnetic order of Gd^{3+} local moments across virtually the whole series ($x \geq 0.02$). The magnetic properties of this series, including the ferromagnetic ordering, the reduced saturated moments at base temperature, the deviation of the susceptibilities from Curie-Weiss law and the anomalies in the resistivity, are understood within the frame work of dilute, $\textbf {S}$ moments (Gd^{3+}) embedded in a nearly ferromagnetic Fermi liquid (YFe_2Zn_{20}). The s-d model is employed to further explain the variation of $T_{\mathrm{C}}$ with x as well as the temperature dependences of of the susceptibilities

Fracture of complex metallic alloys: An atomistic study of model systems

Molecular dynamics simulations of crack propagation are performed for two extreme cases of complex metallic alloys (CMAs): In a model quasicrystal the structure is determined by clusters of atoms, whereas the model C15 Laves phase is a simple periodic stacking of a unit cell. The simulations reveal that the basic building units of the structures also govern their fracture behaviour. Atoms in the Laves phase play a comparable role to the clusters in the quasicrystal. Although the latter are not rigid units, they have to be regarded as significant physical entities.Comment: 6 pages, 4 figures, for associated avi file, see http://www.itap.physik.uni-stuttgart.de/~frohmut/MOVIES/C15.LJ.011.100.av

Costs and Benefits of Experimentally Induced Changes in the Allocation of Growth versus Immune Function under Differential Exposure to Ectoparasites

Conclusions: We found no strong benefits of an increased investment in immunocompetence in a parasite-rich environment. Any deviation from the growth trajectory (due to changes in allocation induced by methionine) is largely detrimental for survival. Hence, while costs are apparent identifying the benefits of investment in immunocompetence during ontogeny is challenging

Effects of 3D-printed horseshoes on kinematic hoof-parameters at trot on hard surface

Researchers recently introduced a tailormade three-dimensional (3D) printed shoe that fits the conformation of the individual horse. The aim of this study was to investigate the effects of this novel 3D-printed shoes on kinetic parameters compared to traditional steel shoes. The 3D-printed shoes, with frog- and heel-support, were designed based on a 3D scan of the hoof, printed in plastic materials, and then glued onto the hooves. Six rider-sound horses underwent a 3D-printed shoeing cycle and a steel shoeing cycle of seven weeks in a randomised order in which measurements were performed in week 1 (T0) and week 7 (T1). The horses were trotted with a pre-set speed range over a pressure- and force plate covered by a rubber mat. Kinetic parameters (n=10) were collected at a frequency of 250 Hz. Data were analysed using a linear mixed effect model with shoeing conditions and timepoints as fixed effects and horse and limbs as random effects. The results showed a significantly larger vertical impulse (VI) and peak vertical force (PVF) at T0 in the 3D-printed shoes (+179.0 N.s/kg,

Continuous versus discrete data analysis for gait evaluation of horses with induced bilateral hindlimb lameness

Background Gait kinematics measured during equine gait analysis are typically evaluated by analysing (asymmetry-based) discrete variables (eg, peak values) obtained from continuous kinematic signals (eg, timeseries of datapoints). However, when used for the assessment of complex cases of lameness, such as bilateral lameness, discrete variable analysis might overlook relevant functional adaptations. Objectives The overall aim of this paper is to compare continuous and discrete data analysis techniques to evaluate kinematic gait adaptations to lameness. Study design Method comparison. Methods Sixteen healthy Shetland ponies, enrolled in a research programme in which osteochondral defects were created on the medial trochlear ridges of both femurs, were used in this study. Kinematic data were collected at trot on a treadmill before and at 3 and 6 months after surgical intervention. Statistical parametric mapping and linear mixed models were used to compare kinematic variables between and within timepoints. Results Both continuous and discrete data analyses identified changes in pelvis and forelimb kinematics. Discrete data analyses showed significant changes in hindlimb and back kinematics, where such differences were not found to be significant by continuous data analysis. In contrast, continuous data analysis provided additional information on the timing and duration of the differences found. Main limitations A limited number of ponies were included. Conclusions The use of continuous data provides additional information regarding gait adaptations to bilateral lameness that is complementary to the analysis of discrete variables. The main advantage lies in the additional information regarding time dependence and duration of adaptations, which offers the opportunity to identify functional adaptations during all phases of the stride cycle, not just the events related to peak values

Регіональні й глобальні наслідки незалежності Косово

У статті розглянуто регіональні й міжнародні аспекти проголошення незалежності Косово. Проаналізовано конфліктні аспекти косовської проблеми у регіональному й глобальному контекстах.В статье рассматриваются региональные и международные аспекты провозглашения независимости Косово. Проанализировано конфликтные аспекты косовской проблемы в региональном и глобальном контекстах.The article presents the regional and international aspects of Kosovo Independents. Special attention is to the conflict of Kosovo in the regional and global context

Estimation of articular cartilage properties using multivariate analysis of optical coherence tomography signal

SummaryObjectiveThe aim was to investigate the applicability of multivariate analysis of optical coherence tomography (OCT) information for determining structural integrity, composition and mechanical properties of articular cartilage.DesignEquine osteochondral samples (N = 65) were imaged with OCT, and their total attenuation and backscattering coefficients (μt and μb) were measured. Subsequently, the Mankin score, optical density (OD) describing the fixed charge density, light absorbance in amide I region (Aamide), collagen orientation, permeability, fibril network modulus (Ef) and non-fibrillar matrix modulus (Em) of the samples were determined. Partial least squares (PLS) regression model was calculated to predict tissue properties from the OCT signals of the samples.ResultsSignificant correlations between the measured and predicted mean collagen orientation (R2 = 0.75, P < 0.0001), permeability (R2 = 0.74, P < 0.0001), mean OD (R2 = 0.73, P < 0.0001), Mankin scores (R2 = 0.70, P < 0.0001), Em (R2 = 0.50, P < 0.0001), Ef (R2 = 0.42, P < 0.0001), and Aamide (R2 = 0.43, P < 0.0001) were obtained. Significant correlation was also found between μb and Ef (ρ = 0.280, P = 0.03), but not between μt and any of the determined properties of articular cartilage (P > 0.05).ConclusionMultivariate analysis of OCT signal provided good estimates for tissue structure, composition and mechanical properties. This technique may significantly enhance OCT evaluation of articular cartilage integrity, and could be applied, for example, in delineation of degenerated areas around cartilage injuries during arthroscopic repair surgery

Local Isoelectronic Reactivity of Solid Surfaces

The quantity w^N(r) = ( 1/ k^2 T_el)[partial n(r, T_el) / partial T_el]_(v(r),N) is introduced as a convenient measure of the local isoelectronic reactivity of surfaces. It characterizes the local polarizability of the surface and it can be calculated easily. The quantity w^N(r) supplements the charge transfer reactivity measured e.g. by the local softness to which it is closely related. We demonstrate the applicability and virtues of the function w^N(r) for the example of hydrogen dissociation and adsorption on Pd(100).Comment: RevTeX, 13 pages, 3 figures, to appear in Phys. Rev. Let