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Holistic consideration of grain growth behavior of tempering steel 34CrNiMo6 during heating processes

JOURNAL OF MATERIALS PROCESSING TECHNOLOGY 2016年 229卷 61-71页

作者： Herbst, Sebastian Besserer, Hans-Bernward Grydin, Olexandr Milenin, Andrzej Maier, Hans Juergen Nuernberger, Florian Univ Hannover Inst Werkstoffkunde Mat Sci Garbsen Germany Univ Paderborn Lehrstuhl Werkstekunde Mat Sci D-33098 Paderborn Germany Univ Sci & Technol Krakow PL-30059 Krakow Poland Leibniz Univ Hannover Zentrum Festkorperchem & Neue Mat D-30167 Hannover Germany

An easily applicable method to determine simplified heat transfer coefficients (HTCs), based on numerical modelling and heating experiments by means of response surface optimization (RSO) is introduced. The HTCs determined account for convective and radiative heat transfer. The approach leads to a phenomenological model that neglects phase transformation during heating. Consequently, the HTCs incorporate effects caused by the transformation enthalpy. For the steel 34CrNiMo6 an austenite grain growth model is parameterized and enhanced with a temperature-dependent activation energy to fit experimentally determined grain growth data. The grain growth model and the HTCs determined by RSO are combined into a numerical grain growth simulation for heating processes of large forging parts. Temperature trends of simulated heating processes using HTCs determined by RSO showed good agreement with experimental data and transferability of the HTCs to larger and more complex parts. The parameterized enhanced grain growth model was found to more accurately represent the measured data in the temperature range around 1100 degrees C than models from literature. Comparison of measured and calculated grain size evolution for temperatures in the range between 950 degrees C and 1100 degrees C revealed a very good agreement considering the uncertainties in grain size measurements and also a huge improvement compared to a conservative model. The grain growth simulation of the heating process of a large semi-finished crankshaft showed a significant difference in austenite grain size after the heating and before the forging process between core and near surface areas of above 100%. Consequently, either the optimization of the heating process or the consideration of the inhomogeneous grain size distribution for such parts are relevant for the subsequent thermomechanical treatment, as austenite grain size has an impact on both flow behavior and recrystallization kinetics. (C) 2015 Elsevier B.

关键词： Heating process Tempering steel 34CrNiMo6 Grain growth model parameterization Numerical simulation Heat transfer coefficient

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parameterization of G-93 isoprene emission formula for tropical trees Casuarina equisetifolia and Ficus septica

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ATMOSPHERIC ENVIRONMENT 2016年第Sep.期141卷 287-296页

作者： Mutanda, Ishmael Inafuku, Masashi Iwasaki, Hironori Saitoh, Seikoh Fukuta, Masakazu Watanabe, Keiichi Oku, Hirosuke Kagoshima Univ United Grad Sch Agr Sci Korimoto 1-21-24 Kagoshima 8900065 Japan Univ Ryukyus Mol Biotechnol Grp Trop Biosphere Res Ctr Senbaru 1 Nishihara Okinawa 9030213 Japan Univ Ryukyus Fac Agr Senbaru 1 Nishihara Okinawa 9030213 Japan Saga Univ Fac Agr 1 Honjo Machi Saga 8408502 Japan

Tropical trees account for most emissions of isoprene, a reactive biogenic volatile organic compound into the atmosphere. The Guenther 1993 (G-93) model is the most widely used algorithm for predicting isoprene emissions by leaves of terrestrial plants. Several studies have reported on the poor performance of the G-93 model in predicting emissions from tropical tree species. To improve the performance of the G-93 model in tropical regions, we carried out diurnal leaf-scale observations of tropical trees Casuarina equisetifolia and Ficus septica outdoors. We developed an iterative method that uses mutual and repetitive step-by-step optimization of the G-93 parameters for temperature (CT) and light (CL) variables using best fit practices, named "Ping-Pong" optimization. Using temperate tree species (Poplar) for comparison, we show that emissions from C. equisetifolia and F. septica had a diversion from predictions of the G-93 formula, especially at high temperatures and high light intensities during mid-day, whilst emissions from temperate tree species were fairly captured by G-93. Results demonstrate that our optimized formulas greatly improved capturing of high light and temperature responses of emission profiles from tropical trees whilst it also performed well for poplar species. parameterization of the G-93 formula greatly improved its performance on predicting diurnal isoprene emission from tropical trees C. equisetifolia and F. septica;explaining 81-96% of variation up from 73 to 77% explained by default G-93. We propose that there is a need to optimize the G-93 model to more accurately predict regional emissions from tropical ecosystems. (C) 2016 Elsevier Ltd. All rights reserved.

关键词： G-93 model Isoprene emission Tropical tree model parameterization Temperature response Light response

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Using a dynamic forest model to predict tree species distributions

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GLOBAL ECOLOGY AND BIOGEOGRAPHY 2016年第3期25卷 347-358页

作者： Gutierrez, Alvaro G. Snell, Rebecca S. Bugmann, Harald ETH Inst Terr Ecosyst Dept Environm Sci Forest Ecol CH-8092 Zurich Switzerland Univ Chile Dept Ciencias Ambientales & Recursos Nat Renovabl Fac Ciencias Agron Santiago Chile

AimIt has been suggested that predicting species distributions requires a process-based and preferably dynamic approach. If dynamic models are to contribute towards understanding species distributions, uncertainties related to their spatial extrapolation and bioclimatic parameters need to be addressed. Here, we analyse the potential of a forest gap model for predicting species distributions. LocationPacific Northwest of North America (PNW). MethodsWe used the dynamic forest gap model ForClim, which includes climate, competition and demographic processes, to simulate the distribution of 18 tree species outside the domain of the data used for fitting. We explored model accuracy for species distributions at the regional scale by: (1) estimating species climatic tolerances so as to maximize agreement with regional distribution maps versus (2) employing a bioclimatic parameter set that produces high accuracy at the local scale. We then performed the opposite tests and simulated local forest composition in a small area in the PNW, using (3) the local bioclimatic parameters and (4) the bioclimatic parameters that produced the highest accuracy at the regional scale. We also compared the ForClim results with predictions from a standard correlative species distribution model (SDM). ResultsForClim produced regional species distributions with fair to very good agreement for 12 tree species. The optimized bioclimatic parameters consistently improved the accuracy of regional predictions compared with simulations run with the local parameters, and were consistent with SDM results. At the local scale, predictions using the local parameters conformed to descriptions of forest composition, but accuracy decreased strongly when using the regionally calibrated parameters. Main conclusionsForest gap models can predict regional species distributions, but at the cost of reduced accuracy at the local scale. Future applications of gap models to understand regional species distributions shoul

关键词： Dynamic biogeography dynamic vegetation models forest gap models inverse modelling model parameterization prediction accuracy sensitivity analysis temperate rainforests

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On the equivalence of the edge/isolate and edge/concurrent tie ERGM families, and their extensions

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JOURNAL OF MATHEMATICAL SOCIOLOGY 2016年第1期40卷 1-6页

作者： Butts, Carter T. Univ Calif Irvine Dept Sociol SSPA 2145 Irvine CA 92697 USA Univ Calif Irvine Dept Stat SSPA 2145 Irvine CA 92697 USA Univ Calif Irvine Dept EECS SSPA 2145 Irvine CA 92697 USA Univ Calif Irvine Inst Math Behav Sci SSPA 2145 Irvine CA 92697 USA

Partnership concurrency is a major driver of permeability of social networks to diffusion, and an important modeling target in the context of sexually transmitted infections. A seemingly unrelated phenomenon of concern in modeling social networks is isolation avoidancethe tendency of individuals to maintain at least one tie. Although concurrency bias and bias in isolate formation would naively seem to be distinct, we here show that their respective ERGM expressions (edge/concurrent tie and edge/isolate families, and their regular extensions) are equivalent, and that both are equivalent to a special case of the geometrically weighted degree families. In addition to being statistically useful, this equivalence provides insight into the essential connection between these apparently different structural phenomena.

关键词： Concurrency ERGMs geometrically weighted degree k-stars Markov graphs model parameterization social isolation

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Online parameterization for WOFOST for United States Using Open Geospatial Standards 5

Online Parameterization for WOFOST for United States Using O...

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5th International Conference on Agro-Geoinformatics (Agro-Geoinformatics)

作者： Yu, Eugene G. Di, Liping Kang, Lingjun Shrestha, Ranjay Rahman, Md Shahinoor Lin, Li Deng, Meixia Yang, Zhengwei George Mason Univ Ctr Spatial Informat Sci & Syst Fairfax VA 22030 USA Natl Agr Stat Serv USDA Washington DC USA

ISBN: (纸本)9781509023509

WOFOST (WOrld FOod STudies) is a well-known, widely applied simulation model to analyze quantitatively the growth and production annual field crops that was originally developed for crops in European countries. It is the base model for Monitoring Agricultural ResourceS (MARS) Crop Growth Monitoring System (CGMS) in operational use for yield estimation in European Union. The model is of great potential in providing effective modeling of crops in the United States. The first step to adopt the model to be fit for applications to crop modeling in the US is to provide required parameters at any region and any time in the United States. In this study, several data sources have been identified and enabled to be readily fed into the models through standard, open, automatic, Web-based, online geospatial Web services. These Web services have the flexibility of accessing, re-processing, and customization to the models at different levels from regional (i.e. counties, agricultural statistic districts) modeling to point (i.e. pixel) modeling because of their spatiotemporal capabilities. Three major data sources and parameters for WOFOST model are meteorological data, crop data, and soil data. Soil data are accessed and customized through standard Web Feature Service (WFS) request to the online services of Soil Survey Geographic Database (SSURGO). Crop data are retrieved from Web Coverage Service (WCS) from CropScape that serves Cropland Data Layer (CDL). Assimilated data from ground observations provide meteorological observations. Meteorological observations are retrieved online through public service application programming interface (API) of DayMet that provide gridded estimates of daily weather parameters for North America, including daily continuous surfaces of minimum and maximum temperature, precipitation occurrence and amount, humidity, shortwave radiation, snow water equivalent, and day length. Workflow is enabled to support the on-demand customization and live feeding

关键词： WOFOST model parameterization crop growth model open geospatial Web services CropScape CDL SSURGO Daymet WCS WFS

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Novel Parametric Circuit modeling for Li-Ion Batteries

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ENERGIES 2016年第7期9卷 539页

作者： Cheng, Ximing Yao, Liguang Xing, Yinjiao Pecht, Michael Beijing Inst Technol Sch Mech Engn Collaborat Innovat Ctr Elect Vehicles Beijing Natl Engn Lab Elect Vehicles Beijing 100081 Peoples R China Univ Maryland CALCE College Pk MD 20742 USA

Because of their simplicity and dynamic response, current pulse series are often used to extract parameters for equivalent electrical circuit modeling of Li-ion batteries. These models are then applied for performance simulation, state estimation, and thermal analysis in electric vehicles. However, these methods have two problems: The assumption of linear dependence of the matrix columns and negative parameters estimated from discrete-time equations and least-squares methods. In this paper, continuous-time equations are exploited to construct a linearly independent data matrix and parameterize the circuit model by the combination of non-negative least squares and genetic algorithm, which constrains the model parameters to be positive. Trigonometric functions are then developed to fit the parameter curves. The developed model parameterization methodology was applied and assessed by a standard driving cycle.

关键词： Li-ion battery model parameterization equivalent electrical circuit non-negative least squares

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Perennial rhizomatous grasses as bioenergy feedstock in SWAT: parameter development and model improvement

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GLOBAL CHANGE BIOLOGY BIOENERGY 2015年第6期7卷 1185-1202页

作者： Trybula, Elizabeth M. Cibin, Raj Burks, Jennifer L. Chaubey, Indrajeet Brouder, Sylvie M. Volenec, Jeffrey J. Purdue Univ Dept Agr & Biol Engn W Lafayette IN 47907 USA Purdue Univ Dept Agron W Lafayette IN 47907 USA Purdue Univ Dept Earth Atmospher & Planetary Sci W Lafayette IN 47907 USA

The Soil and Water Assessment Tool (SWAT) is increasingly used to quantify hydrologic and water quality impacts of bioenergy production, but crop-growth parameters for candidate perennial rhizomatous grasses (PRG) Miscanthusxgiganteus and upland ecotypes of Panicum virgatum (switchgrass) are limited by the availability of field data. Crop-growth parameter ranges and suggested values were developed in this study using agronomic and weather data collected at the Purdue University Water Quality Field Station in northwestern Indiana. During the process of parameterization, the comparison of measured data with conceptual representation of PRG growth in the model led to three changes in the SWAT 2009 code: the harvest algorithm was modified to maintain belowground biomass over winter, plant respiration was extended via modified-DLAI to better reflect maturity and leaf senescence, and nutrient uptake algorithms were revised to respond to temperature, water, and nutrient stress. Parameter values and changes to the model resulted in simulated biomass yield and leaf area index consistent with reported values for the region. Code changes in the SWAT model improved nutrient storage during dormancy period and nitrogen and phosphorus uptake by both switchgrass and Miscanthus.

关键词： bioenergy feedstock hydrologic model Miscanthus model parameterization perennial rhizomatous grass soil and water assessment tool switchgrass

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A Flexible parameterization for Baseline Mean Degree in Multiple-Network ERGMs

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JOURNAL OF MATHEMATICAL SOCIOLOGY 2015年第3期39卷 163-167页

作者： Butts, Carter T. Almquist, Zack W. Univ Calif Irvine Dept Sociol Irvine CA 92697 USA Univ Calif Irvine Dept Stat Irvine CA 92697 USA Univ Calif Irvine Dept EECS Irvine CA 92697 USA Univ Calif Irvine Inst Math Behav Sci Irvine CA 92697 USA Univ Minnesota Sch Stat Dept Sociol Minneapolis MN 55455 USA Univ Minnesota Minnesota Populat Ctr Minneapolis MN USA

The conventional exponential family random graph model (ERGM) parameterization leads to a baseline density that is constant in graph order (i.e., number of nodes);this is potentially problematic when modeling multiple networks of varying order. Prior work has suggested a simple alternative that results in constant expected mean degree. Here, we extend this approach by suggesting another alternative parameterization that allows for flexible modeling of scenarios in which baseline expected degree scales as an arbitrary power of order. This parameterization is easily implemented by the inclusion of an edge count/log order statistic along with the traditional edge count statistic in the model specification.

关键词： model parameterization baseline models exponential family random graph models (ERGMs) mean degree

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Succinate overproduction: a case study of computational strain design using a comprehensive Escherichia coli kinetic model

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FRONTIERS IN BIOENGINEERING AND BIOTECHNOLOGY 2015年第0期2卷 76-76页

作者： Khodayari, Ali Chowdhury, Anupam Maranas, Costas D. Penn State Univ Dept Chem Engn 112 Fenske Lab University Pk PA 16802 USA

Computational strain-design prediction accuracy has been the focus for many recent efforts through the selective integration of kinetic information into metabolic models. In general, kinetic model prediction quality is determined by the range and scope of genetic and/or environmental perturbations used during parameterization. In this effort, we apply the k-OptForce procedure on a kinetic model of E. coli core metabolism constructed using the Ensemble modeling (EM) method and parameterized using multiple mutant strains data under aerobic respiration with glucose as the carbon source. Minimal interventions are identified that improve succinate yield under both aerobic and anaerobic conditions to test the fidelity of model predictions under both genetic and environmental perturbations. Under aerobic condition, k-OptForce identifies interventions that match existing experimental strategies while pointing at a number of unexplored flux re-directions such as routing glyoxylate flux through the glycerate metabolism to improve succinate yield. Many of the identified interventions rely on the kinetic descriptions that would not be discoverable by a purely stoichiometric description. In contrast, under fermentative (anaerobic) condition, k-OptForce fails to identify key interventions including up-regulation of anaplerotic reactions and elimination of competitive fermentative products. This is due to the fact that the pathways activated under anaerobic condition were not properly parameterized as only aerobic flux data were used in the model construction. This study shed light on the importance of condition-specific model parameterization and provides insight on how to augment kinetic models so as to correctly respond to multiple environmental perturbations.

关键词： computational strain design kinetic model bilevel optimization succinate overproduction model parameterization

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Large conversion rates of NO₂ to HNO₂ observed in air masses from the South China Sea: Evidence of strong production at sea surface?

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GEOPHYSICAL RESEARCH LETTERS 2014年第21期41卷 7710-7715页

作者： Zha, Qiaozhi Xue, Likun Wang, Tao Xu, Zheng Yeung, Chungpong Louie, Peter K. K. Luk, Connie W. Y. Hong Kong Polytech Univ Dept Civil & Environm Engn Hong Kong Hong Kong Peoples R China Shandong Univ Environm Res Inst Jinan 250100 Peoples R China Govt Hong Kong Special Adm Reg Environm Protect Dept Hong Kong Hong Kong Peoples R China

Nitrous acid (HONO) plays important roles in tropospheric chemistry, but its source(s) are not completely understood. Here we analyze measurements of HONO, nitrogen dioxide (NO2), and related parameters at a coastal site in Hong Kong during September-December 2012. The nocturnal NO2-to-HONO conversion rates were estimated in air masses passing over land and sea surfaces. The conversion rates in the "sea cases" (3.17-3.36 x 10(-2) h(-1)) were significantly higher than those in the "land cases" in our study (1.20-1.30 x 10(-2) h(-1)) and in previous studies by others. These results suggest that air-sea interactions may be a significant source of atmospheric HONO and need to be considered in chemical transport models.

关键词： HONO conversion rate air-sea interactions marine boundary layer model parameterization nitrous acid

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