Enhanced domain wall velocity near a ferromagnetic instability

Assuming a Fermi liquid behavior for $s$-conduction electrons, we rewrite the extended Landau-Lifshitz-Gilbert (LLG) equation renormalized by interactions through the Landau parameters $F^{a}_{l}$ ($l=0,1,2 \cdots$) in an explicit form to describe the dynamic of a domain wall (DW) due to spin transfer torque phenomenon. The interaction between spins of the \textit{s}-conduction electrons explains qualitatively the DW velocity experimental observations in $\mathrm{Ni_{81}}\mathrm{Fe_{19}}$ (Permalloy) recalculated by us without defects or impurity hypothesis. Close to Stoner ferromagnetic instability point where $F^{a}_{0} \approx -0.99$, the DW velocity becomes high ($v^{*}_{DW}\approx 600$ $ms^{-1}$) and critical spin current density becomes reduced ($j^{*}_{c}\approx1\times10^{12}$ $Am^{-2}$) when compared to that calculated by nonadiabatic approach. At the critical point, the DW velocity diverges while critical spin current density at the same point goes to zero. Our theory also provides a prediction to looking for materials in which is possible applies a smallest critical spin current density and observes higher DW velocity.Comment: 7 pages, 5 figure

Multi-criteria analysis applied to multi-objective optimal pump scheduling in water systems

This work presents a multi-criteria-based approach to automatically select specific non-dominated solutions from a Pareto front previously obtained using multi-objective optimization to find optimal solutions for pump control in a water supply system. Optimal operation of pumps in these utilities is paramount to enable water companies to achieve energy efficiency in their systems. The Fuzzy Technique for Order of Preference by Similarity to Ideal Solution (FTOPSIS) is used to rank the Pareto solutions found by the Non-Dominated Sorting Genetic Algorithm (NSGA-II) employed to solve the multi-objective problem. Various scenarios are evaluated under leakage uncertainty conditions, resulting in fuzzy solutions for the Pareto front. This paper shows the suitability of the approach for quasi real-world problems. In our case-study, the obtained solutions for scenarios including leakage represent the best trade-off among the optimal solutions, under some considered criteria, namely, operational cost, operational lack of service, pressure uniformity and network resilience. Potential future developments could include the use of clustering alternatives to evaluate the goodness of each solution under the considered evaluation criteria

Design of a microbreather for two-phase microchannel devices

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2008.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Includes bibliographical references (p. 50-52).Multiphase flows in microchannels are encountered in a variety of microfluidic applications. Two-phase microchannel heat sinks leverage the latent heat of vaporization to offer an efficient method of dissipating large heat fluxes in a compact device. In microscale methanol-based fuel cells, the chemical reactions produce a two-phase flow of methanol solution and carbon dioxide gas. Differences in the underlying physics between microscale and macroscale systems, however, provide a new set of challenges for multiphase microscale devices. In thermal management devices, large pressure fluctuations caused by the rapid expansion of vapor are prevalent in the flow channels. In fuel cells, the gaseous carbon dioxide blocks reaction sites. In both of these cases, dry-out is a problem that limits device performance. We propose a design for a microscale breather that uses surface chemistry and microstructures to separate gas from a liquid flow to improve two-phase microchannel performance. To better understand the physics and governing parameters of the proposed breather, we have designed and fabricated test devices that allow cross-sectional visualization of the breathing events. We have conducted various experiments to examine the effects of device channel hydraulic diameters ranging from 72 [mu]m to 340 [mu]m and liquid inlet flow rates ranging from 0.5 cm/s to 4 cm/s on the maximum gas removal rate. We demonstrated a maximum breather removal rate of 48.1 [mu]l/min through breather ports with a hydraulic diameter of 4.6 [mu]m connected to a microchannel with a hydraulic diameter of 72 [mu]m, and a liquid inlet flow velocity of 0.5 cm/s. A model was developed that accurately predicts the exponential dependence of the maximum gas removal rate on a non-dimensional ratio of the pressure across the breather ports compared to the pressure drop in the main channel caused by the venting bubble.(cont.) These results serve as design guidelines to aid in the development of more efficient and sophisticated breathing devices. The successful implementation of a microchannel with an efficient breather will allow for new technologies with higher heat removal capacities or chemical reaction rates that can be effectively used by industry.by Brentan R. Alexander.S.M

Hybrid regression model for near real-time urban water demand forecasting

[EN] The most important factor in planning and operating water distribution systems is satisfying consumer demand. This means continuously providing users with quality water in adequate volumes at reasonable pressure, thus ensuring reliable water distribution. In recent years, the application of statistical, machine learning, and artificial intelligence methodologies has been fostered for water demand forecasting. However, there is still room for improvement; and new challenges regarding on-line predictive models for water demand have appeared. This work proposes applying support vector regression, as one of the currently better machine learning options for short-term water demand forecasting, to build a base prediction. On this model, a Fourier time series process is built to improve the base prediction. This addition produces a tool able to eliminate many of the errors and much of the bias inherent in a fixed regression structure when responding to new incoming time series data. The final hybrid process is validated using demand data from a water utility in Franca, Brazil. Our model, being a near real-time model for water demand, may be directly exploited in water management decision-making processes. (C) 2016 Elsevier B.V. All rights reserved.This work has been partially supported by CAPES Foundation of Brazil’s Ministry of Education. The data were provided by SABESP, São Paulo state water management company.Brentan, BM.; Luvizotto, E.; Herrera Fernández, AM.; Izquierdo Sebastián, J.; Pérez García, R. (2017). Hybrid regression model for near real-time urban water demand forecasting. Journal of Computational and Applied Mathematics. 309:532-541. doi:10.1016/j.cam.2016.02.009S53254130

Coal fired power generation scheme with near-zero carbon dioxide emissions

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2007.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Includes bibliographical references (leaves 91-93).Humans are releasing record amounts of carbon dioxide into the atmosphere through the combustion of fossil fuels in power generation plants. With mounting evidence that this carbon dioxide is a leading cause of global warming and with energy demand exploding, it is time to seek out realistic power production methods that do not pollute the environment with CO2 waste. The relative abundance and low cost of fossil fuels remains attractive and clean coal technologies are examined as a viable solution. This paper helps identify the many options currently available, including post-combustion capture, pre-combustion capture, and a number of oxy-fuel combustion schemes. One cycle design in particular, the Graz cycle, holds some promise as a future power generation cycle. A model of the Graz cycle developed in this paper predicts a cycle efficiency value of 56.72%, a value that does not account for efficiency losses in the liquefaction and sequestration of carbon dioxide, or the efficiency penalty associated with the gasification of coal. This high efficiency number, coupled with the low technological barriers of this cycle compared to similar schemes, is used as a justification for investigating this cycle further.(cont.) A sensitivity analysis is performed in order to identify key system parameters. Using this information, a computational optimization algorithm based on a simulated annealing scheme is devised and used to alter the parameters until an overall efficiency of 60.11% is achieved. Another optimization scheme which accounts for hardware limitations and plant capital costs is also discussed. This optimization yields a total efficiency of 58.76% while limiting the system high pressure to 110 bar. With such high efficiency values for this cycle, it is suggested that further study with more advanced models be conducted to better assess the viability of the Graz cycle as a clean technology.by Brentan R. Alexander.S.B

Aplicação da borra da tinta automotiva na produção de cerâmica branca refratária

Orientador: Prof. Dr. Haroldo de Araujo PonteCo-orientador: Prof. Dr. Vsévolod MymrineDissertação (mestrado) - Universidade Federal do Paraná, Setor de Tecnologia, Programa de Pós-Graduação em Engenharia e Ciência dos Materiais - PIPE. Defesa: Curitiba, 27/06/2013Inclui referênciasÁrea de concentração: Engenharia e ciência de materiaisResumo: Este trabalho foi desenvolvido com intuito de apresentar uma alternativa a destinação da borra residual do processo de pintura automotiva, utilizando este material rico em metais pesados como uma matéria-prima de reforço a cerâmica branca refratária. Para verificar a possibilidade de utilização destes materiais foi feito uma caracterização física, química, morfológica e mineralógica do caulim e da borra residual da tinta. Foram gerados corpos de prova com incorporações em massa seca de borra de tinta com 0%, 1%, 2%, 4% e 8% na matriz composta por caulim. Os corpos de prova manufaturados foram moldados, prensados uniaxialmente a 10 MPa e queimados em forno elétrico à 1000 °C, 1200 °C, 1250 °C e 1300 °C. Após a queima foram determinadas as novas propriedades físicas e mecânicas do material manufaturado e pode-se observar que, com o aumento da temperatura de queima e da inserção da borra de tinta houve uma diminuição da retração linear e da absorção de água. Houve também um aumento da densidade aparente e da resistência à flexão que chegou a 12,77 MPa. As análises mineralógicas por XRD demonstraram que houve a formação de novas estruturas cristalográfica, tais como: a cristobalita, e a mulita e manteve-se a rutila na estrutura cerâmica. Morfologicamente através do MEV pode-se constatar a formação destas novas conformações cristalinas pelo aparecimento de regiões vítreas e formas cristalográficas dentro dos poros.Abstract: Paint wastes of an automotive industry were evaluated in terms of their chemical, morphological and mineralogical characteristics in order to analyse its potential use as a reinforcing agent in white ceramic. Both kaolin and sludge paint were analysed using the techniques of XRF, XRD, SEM, EDS. In order to understand the behaviour of the sludge during firing, thermogravimetric analysis and differential thermal analysis were done. Samples containing kaolin and 0, 1, 2, 4 and 8 (wt.%) sludge paint were prepared. The ceramics were compacted at 10MPa and sintered in an electric furnace at 1000 ?C, 1200 ?C, 1250 ?C and 1300 ?C. Water absorption, linear shrinkage and flexural strength were the mechanical properties evaluated in manufactured samples. The experimental results showed that the samples with lagers amounts of sludge performed better or similar to the samples that only contained kaolin. Flexural strength increased 63% in the ceramic bodies with 8 (wt.%) of sludge and as shown by SEM, an increased number of vitrified regions

Comissioning and evaluation of methodologies for determining tbp curves for blended fuels

Orientadores: Maria Regina Wolf Maciel, Leonardo Vasconcelos FregolenteDissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia QuímicaResumo: Por conta do aumento constante da demanda de combustíveis fósseis, a indústria brasileira de petróleo vem, durante os últimos anos, buscando alternativas de aperfeiçoar os processos já existentes. Pesquisadores de todo o mundo vêm estudando fatores, que vão desde a qualidade do óleo a ser refinado até o destino do resíduo orgânico pesado, para assegurar a qualidade oferecida e, ao mesmo tempo, diminuir ao máximo o impacto ambiental gerado. Um dos problemas encontrados é a eventual mistura (blends) de variados tipos de petróleos diferentes nos tanques de carga das refinarias, o que altera a composição e as propriedades antes mesmo de se iniciar o refino, cujas condições operacionais dependem destas propriedades. O preço e qualidade do petróleo estão diretamente ligados com sua densidade relativa, propriedades e porcentagem de cada uma das espécies orgânicas que o compõem. Por este motivo, este trabalho tem como objetivo desenvolver um procedimento confiável e aplicável à indústria de forma a confirmar as propriedades destes blends. Utilizando equipamentos de destilação atmosférica e a vácuo, baseados nas normas ASTM D2892 e ASTM D5236, respectivamente, além de um cromatógrafo gasoso para destilação simulada (SimDis-HT), será possível obter curvas de ponto de ebulição verdadeiro, densidade, valores de °API e outras propriedades de diesel, querosene e seus blendsAbstract: Considering the increase on demand of fossil fuels for the oil industry in the last years, the search for new methods to upgrade the current process is essential. All around the world, researchers have studied topics from the quality of oils before the refinery up to how to properly dispose the heavy residue created during the distillation process. In this way, it is possible to maximize the oil¿s worth and reduce the environmental problems that could be caused. One problem currently found in oil refineries is the unavoidable mixture (or blends) of several different brands of oil during the storage process on tanks, varying their composition and properties, which can alter the accuracy of the operational inputs that control the refining process. Additionally, the price of oil is directly related to its properties such as specific gravity and the percentage of each organic compound in its composition. Therefore, this dissertation offers a reliable methodology to determine the properties of fuels and its blends. Utilizing distillation equipment with and without reduced pressure, based on the standards ASTM D2892 and ASTM D5236, respectively, as well as a gas chromatographer that simulate distillations at high temperatures (SimDis-HT), we will be capable of obtaining true boiling point curves, density, API grade values, and other properties of diesel, kerosene and their blendsMestradoEngenharia QuímicaMestre em Engenharia Química88887.372049/2019-00170393/2018-6CAPESCNP

Gerenciamento ótimo das pressões em redes de abastecimento de água através da criação de distritos de medição com base na aprendizagem de máquinas

Integrated management of water supply systems with efficient use of natural resources requires optimization of operational performances. Dividing the water supply networks into small units, so-called district metered areas (DMAs), is a strategy that allows the development of specific operational rules, responsible for improving the network performance. In this context, clustering methods congregate neighboring nodes in groups according to similar features, such as elevation or distance to the water source. Taking into account hydraulic, operational and mathematical criteria to determine the configuration of DMAs, this work presents the k-means model and a hybrid model, that combines a self-organizing map (SOM) with the k-means algorithm, as clustering methods, comparing four mathematical criteria to determine the number of DMAs, namely Silhouette, GAP, Calinski-Harabasz and Davies Bouldin. The influence of three clustering topological criteria is evaluated: the water demand, node elevation and pipe length, in order to determine the optimal number of clusters. Furthermore, to identify the best DMA configuration, the particle swarm optimization (PSO) method was applied to determine the number, cost, pressure setting of Pressure Reducing Valves and location of DMA entrances.24A gestão integrada dos sistemas de abastecimento de água com o uso eficiente dos recursos requer a otimização das operações. O agrupamento das redes de abastecimento de água em pequenas unidades, chamadas de distritos de medição (DMAs), é uma estratégia que permite o desenvolvimento de regras operacionais específicas, responsáveis por melhorar o desempenho da rede. Neste contexto, os métodos de classificação agrupam os nós vizinhos de acordo com características semelhantes, como elevação ou distância à fonte de água. Utilizando os critérios topológicos, operacionais e matemáticos para determinar a configuração dos DMAs, o trabalho apresenta um modelo k-means e um modelo híbrido, que combina um mapa auto-organizado (SOM) com o algoritmo k-means, como métodos de agrupamento. Comparou-se quatro critérios matemáticos, Silhouette, GAP, CalinskiHarabasz e Davies-Bouldin e analisou-se a influência de três critérios topológicos variáveis, a demanda de água, a elevação dos nós e o comprimento do tubo, para determinar o número ótimo de agrupamentos. Ademais, com o intuito de identificar a melhor configuração de DMAs, o método de otimização de enxame de partículas (PSO) foi aplicado para determinar o número, o custo, as pressões e a localização das entradas do DMA

Social Network Community Detection for DMA Creation: Criteria Analysis through Multilevel Optimization

[EN] Management of large water distribution systems can be improved by dividing their networks into so-called district metered areas (DMAs). However, such divisions must be based on appropriated technical criteria. Considering the importance of deeply understanding the relationship between DMA creation and these criteria, this work proposes a performance analysis of DMA generation that takes into account such indicators as resilience index, demand similarity, pressure uniformity, water age (and thus water quality), solution implantation costs, and electrical consumption. To cope with the complexity of the problem, suitable mathematical techniques are proposed in this paper. We use a social community detection technique to define the sectors, and then a multilevel particle swarm optimization approach is applied to find the optimal placement and operating point of the necessary devices. The results obtained by implementing themethodology in a real water supply network show its validity and the meaningful influence on the final result of, especially, elevation and pipe length.Brentan, BM.; Campbell-Gonzalez, E.; Meirelles, GL.; Luvizotto, EJ.; Izquierdo Sebastián, J. (2017). Social Network Community Detection for DMA Creation: Criteria Analysis through Multilevel Optimization. Mathematical Problems in Engineering. (9053238):1-12. doi:10.1155/2017/9053238S112905323

Turmalinitos do Grupo Brusque na região entre São João Batista e Tijucas, Santa Catarina, Brasil

The Dom Feliciano Belt, in the State of Santa Catarina, is represented by the Itajaí and Brusque groups and the Florianópolis Batholith. The basal Rio do Oliveira Formation of the Brusque Group consists of metabasic/calc-silicate, metavolcanic-exhalative, metapelitic and metapsammitic units. A discontinuous tourmalinite sequence integrating the metavolcanic-exhalative unit stretches out from São João Batista to Tijucas. Two types of tourmalinites were distinguished and named Rio do Oliveira and Morro do Carneiro. The first is very fine-grained, banded, and composed of greenish-yellow or brown tourmaline. The second is coarser-grained, massive to slightly foliated, and composed of color-zoned tourmaline. Microprobe and laser ablation-ICPMS analyses showed that the Rio do Oliveira tourmaline is richer in Al, alkalis, and poorer in Ti, Mg, Fe and Ca when compared to the Morro do Carneiro tourmaline. Rio do Oliveira tourmalinites were formed by selective substitution of pelitic and psammitic sediments by percolation of B-rich fluids through the volcanic-sedimentary unit during diagenesis and metamorphism. Morro do Carneiro tourmaline has detrital cores and rims enriched in Mg, Fe, Ti, Mn, Sr, Co and Ca, when compared to the Rio do Oliveira tourmaline. An intermediate dark zone is Ti- and Fe-rich. The abrupt increase in Ca from core to rim may have resulted from the equilibrium with the surrounding Ca-rich environment (underlying calc-silicate rocks). Even if the REE patterns obtained for Rio do Oliveira and Morro do Carneiro tourmalines are practically identical, it is proposed that the fluids that generated the Morro do Carneiro tourmalinites have also been metasomatic/igneous.O Cinturão Dom Feliciano no Estado de Santa Catarina é representado pelos grupos Itajaí e Brusque e o Batólito Florianópolis. A Formação Rio do Oliveira, basal do Grupo Brusque, constitui-se de unidades metabásicas/cálcio-silicáticas, metavulcânicas-exalativas, metapelíticas e metapsamíticas. Uma sequência descontínua de turmalinitos integrante da unidade metavulcânica-exalativa estende-se desde São João Batista até Tijucas. Dois tipos de turmalinitos foram distintos e denominados Rio do Oliveira e Morro do Carneiro. O primeiro é muito fino, bandado e composto por turmalina amarela-esverdeada ou castanha. O segundo é mais grosso, de textura maciça a levemente foliada, e formado por turmalina zonada. Análises por microssonda eletrônica e laser ablation-ICPMS mostraram que a turmalina do Rio do Oliveira é mais rica em Al, álcalis e mais pobre em Ti, Mg, Fe and Ca quando comparada com a do Morro do Carneiro. Os turmalinitos do Rio do Oliveira formaram-se por substituição seletiva de sedimentos pelíticos e psammíticos resultante da percolação de fluidos ricos em boro pela unidade vulcano-sedimentar durante a diagênese e metamorfismo. A turmalina do Morro do Carneiro possui núcleos detríticos e bordas mais ricas em Mg, Fe, Ti, Mn, Sr, Co e Ca que a turmalina do Rio do Oliveira. Uma zona intermediária escura é mais rica em Ti e Fe. O aumento brusco em Ca do núcleo para a borda pode ter resultado do equilíbrio com o ambiente circunvizinho rico em Ca (rochas cálcio-silicáticas subjacentes). Mesmo que os padrões definidos pelos ETR para as turmalinas do Rio do Oliveira e do Morro do Carneiro sejam praticamente idênticos, propõe-se que os fluidos formadores do turmalinito do Morro do Carneiro possam também ter tido origem metassomática/ígnea