1,243 research outputs found

    First-principles thermodynamic modeling of atomic ordering in yttria-stabilized zirconia

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    Yttria-stabilized zirconia YSZ is modeled using a cluster expansion statistical thermodynamics method built upon a density-functional theory database. The reliability of cluster expansions in predicting atomic ordering is explored by comparing with the extensive experimental database. The cluster expansion of YSZ is utilized in lattice Monte Carlo simulations to compute the ordering of dopant and oxygen vacancies as a function of concentration. Cation dopants show a strong tendency to aggregate and vacate significantly sized domains below 9 mol % Y_2O_3, which is likely important for YSZ aging processes in ionic conductivity. Evolution of vibrational and underlying electronic properties as a function of Y doping is explored

    First-principles thermodynamic modeling of lanthanum chromate perovskites

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    Tendencies toward local atomic ordering in (A,A′)(B,B′)O_(3−δ) mixed composition perovskites are modeled to explore their influence on thermodynamic, transport, and electronic properties. In particular, dopants and defects within lanthanum chromate perovskites are studied under various simulated redox environments. (La_(1−x),Sr_x)(Cr_(1−y),Fe_y)O_(3−δ) (LSCF) and (La_(1−x),Sr_x)(Cr_(1−y),Ru_y)O_(3−δ) (LSCR) are modeled using a cluster expansion statistical thermodynamics method built upon a density functional theory database of structural energies. The cluster expansions are utilized in lattice Monte Carlo simulations to compute the ordering of Sr and Fe(Ru) dopant and oxygen vacancies (Vac). Reduction processes are modeled via the introduction of oxygen vacancies, effectively forcing excess electronic charge onto remaining atoms. LSCR shows increasingly extended Ru-Vac associates and short-range Ru-Ru and Ru-Vac interactions upon reduction; LSCF shows long-range Fe-Fe and Fe-Vac interaction ordering, inhibiting mobility. First principles density functional calculations suggest that Ru-Vac associates significantly decrease the activation energy of Ru-Cr swaps in reduced LSCR. These results are discussed in view of experimentally observed extrusion of metallic Ru from LSCR nanoparticles under reducing conditions at elevated temperature

    The Analysis of Real Estate Cycles, Regime Segmentation and Structural Change Using Multiple Indices (or A Multiple Index Analysis of Real Estate Cycles and Structural Change)

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    This article explores real estate cycles and structural change at an overall industry level, focusing on three key questions. First, are real estate cycle stages distinct and observable? Second, can the cycle stages be modeled using variables and relationships that hold for extended periods? Third, can the impact of exogenous shocks that cause structural changes in the market be monitored and modeled? The results of the research are generally positive, suggesting that indeed the variables and relationships that distinguish various real estate cycle stages can be isolated, and are sufficiently stable to help model cyclical changes. Furthermore, the research suggests it is possible to track key exogenous shocks that trigger structural changes that affect cycle models.

    Advances in Green Infrastructure Planning

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    The expansion of urban areas has facilitated the conversion of undeveloped lands, which has led to environmental degradation, such as loss of habitats, hydro-modification, and the collapse of existing ecosystems. Recent climate change has exacerbated these damages by causing more frequent and serious hazards. To attenuate the impacts of urbanization and the negative effects of climate change, green infrastructure (GI) planning (e.g., nature-based strategies, technologies, policies, and solutions) has arisen as an important approach for balancing urban development and nature. GI offers a variety of benefits to our cities by reducing stormwater runoff, heat waves, and air pollution; expanding wildlife habitats; and increasing recreational opportunities and even nearby property values

    Atomistic Models to Study Thermodynamics and Kinetics of Solid-Liquid and Solid-Solid Transitions in Binary Metals

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    Design of novel materials and novel manufacturing process requires understandingthermophysical properties of materials during their process and working conditions.Microstructure of materials, which is usually, consists of grains, phases, and defectsdetermines the overall physical and mechanical properties of materials. Specifically inmetals, the formation of solid crystal from liquid is considered as one of the most importantfactors during the solidification, which can elucidate the final formation of microstructureof materials. The experimental study of the phenomena related to the coexistence of solidliquid phases is generally arduous, because the experiments are needed to be carried out atthe melting points of the materials. Thanks to recent improvements in computational powerand supercomputing capabilities, many research and industrial institutions have started toemploy computational materials modeling as a suitable alternative to costly and/orimpractical experiments. Molecular dynamic (MD) is a powerful computational approachthat can be used for tracking individual atoms with great accuracy in length scales of tensto hundreds nanometers and timescales of picoseconds to nanoseconds. However, thereliability of MD simulations for each alloy system is based on the reliability of how theatoms talk or interact with each other, through the interatomic potential energy.Interatomic potentials, which are mathematical functions of the coordinates of all atoms inthe system, are essential for determining both equilibrium and non-equilibrium propertiesof materials. The objective of this work is to develop advanced interatomic potentials inthe concept of modified embedded-atom method (MEAM) for alloy system that are capableof predictive modeling of alloys in solid-liquid transitions. Interatomic potentials includingMEAM contain parameters that are determined by fitting model predictions to specificexperimental or first principle data, which are mostly to the 0-K properties. In order tostudy the liquid and solid properties at high and the near melting point, the potential has tobe fitted to the not only 0-K properties but also to the high temperature properties such asmelting point and elastic constants at high temperatures. Therefore, our goal in this thesis,is calculating the thermodynamics and kinetics properties of solid and liquid in metallicsystem at high temperatures by MD simulation through developing reliable interatomicpotential for studying pure Fe, Cu, Ni, Ti, Pb, and Sn and binary system (Pb-Sn)

    Asymmetric cryorolling for fabrication of nanostructural aluminum sheets

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    Nanostructural Al 1050 sheets were produced using a novel method of asymmetric cryorolling under ratios of upper and down rolling velocities (RUDV) of 1.1, 1.2, 1.3, and 1.4. Sheets were rolled to about 0.17 mm from 1.5 mm. Both the strength and ductility of Al 1050 sheets increase with RUDVs. Tensile strength of Al sheets with the RUDV 1.4 is larger 22.3% of that for RUDV 1.1, which is 196 MPa. The TEM observations show the grain size is 360 nm when the RUDV is 1.1, and 211 nm for RUDV 1.4

    Aggregate Shocks vs Reallocation Shocks: an Appraisal of the Applied Literature

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    This paper critically appraises the di erent approaches that have characterized the literature on the macroeconomic e ects of job reallocations from Lilien's seminal work to recent developments rooted in structural general equilibrium models, nonlinear econometric techniques and the concepts of job creation and destruction. Despite a ourishing of empirical analysis no unifying theoretical framework has obtained consensus in the scienti c debate. We face a corpus of research which is heterogeneous in variables' selection and experimental design. This widespread heterogeneity makes the evaluation of results a daunting task. Reliability of outcomes becomes almost impossible to assess when, even within models of the same generation, the lack of a rigorous theoretical background hinders well de ned experimental design and makes comparisons di cult. The strong pace at which the empirical literature on the macroeconomic e ects of job reallocations has been growing in recent years suggests that a general assessment of the state of the art is valuable and maybe indispensable. As a guiding principle for our excursion we track down the methodological development of the proposed solutions to the crucial problem of observational equivalence. We do not linger on speci c econometric methods nor on strictly theoretical issues not relevant to our main purpose. We draw the conclusion that the asymmetric and non-directional nature of allocative shocks, which holds the key to the solution of the problem, is better captured by multivariate, non-linear, dynamic econometric models and numerical simulation techniques. Davis and Haltiwanger's perspective on job creation and destruction seems to us of paramount importance for future research because of its potential to encompass a wealth of micro-level data sets within a rigorous analytical framework.Sectoral shifts, methodology, measurement, assessment

    Multifamily Housing: A Review of Theory and Evidence

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    The growing importance of multifamily housing as a viable choice of residence is evidenced by the number of empirical and theoretical studies in real estate literature. Researchers have investigated the role of this sector of the real estate market for decades. This survey article examines more than one hundred studies and categorizes them into five groups: economic and market efficiency issues; property valuation and appraisal issues; regulatory, zoning, and clustering of multifamily complexes; costs, returns, and rental income issues; and demand, vacancy, and occupancy issues. This study seeks to provide a concise, categorical presentation of findings on issues related to the environment and performance of multifamily housing.
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